J. Fluid Mech. 526, 277 (2005)] and others have suggested that sweeping effects make Lagrangian properties in Kinematic Simulations (KS), Fung et al , unreliable. However, such a conclusion can only be drawn under the assumption of locality. The major aim here is to quantify the sweeping errors in KS without assuming locality. Through a novel analysis based upon analysing pairs of particle trajectories in a frame of reference moving with the large energy containing scales of motion it is shown that the normalized integrated error K) due to the sweeping effect decreases with increasing pair separation (σl), such that σl/η → ∞; and σl/η → 0. η is the Kolmogorov turbulence microscale. There is an intermediate range of separations 1 < σl/η < ∞ in which the error σl/η < 105, implying that the deviation from locality observed in KS cannot be atributed to sweeping errors. This is important for pair diffusion theory and modeling. PACS numbers: 47.27.E?, 47.27.Gs, 47.27.jv, 47.27.Ak, 47.27.tb, 47.27.eb, 47.11.-j.Thomson, D. J. & Devenish, B. J. [ Turbulent particle pair diffusion has attained somewhat of an iconic status in the turbulence community, many researchers having addressed this topic over the decades. Nevertheless, most if not all theories of turbulent particle pair diffusion in homogeneous turbulence with extended inertial ranges have been based upon the hypothesis of locality since Richardson in 1926 –5 for rel(t) is the pair displacement vector at time t, l = |l|, v(l) is the pair relative velocity, and 〈⋅〉 is the ensemble average over all particle pairs.Richardson pioneered this field and introduced the idea of a scale dependent pair diffusivity as the fundamental quantity of interest in turbulent pair diffusion studies. The turbulent pair diffusivity is defined as,l in homogeneous isotropic and statistically stationary turbulence is determined only by the energies contained in the eddies of a similar size to l. This, leads to the scaling E(l) ∼ l5/3, then K(l) ∼ l4/3 is readily obtained, showing the equivalence of locality and the 4/3 law.Locality states that the further increase in separation of particle pairs which are separated at a distance of K have been proposed in the past. Hentchel and Procaccia [K ∼ εalbtc, for 2a + c = 2 and 3a − b = 1, and c ≠ 0 in their work on a fractal based model for cloud dispersion; see also Klafter [K = K(t) could be made dependent on the time alone—here the time is the time from release of the particle pair. However, such a time-dependent pair diffusivity would give unrealistically high values for K(t) at large times (tending to infinity). For short times, however, when the relative velocity is highly correlated with its initial value, such a scaling can recover the well known short-time ballistic motion although it lasts only for a very short time. As our interest here is in the pair diffusion scalings inside the inertial subrange when the times after release are much greater than the short ballistic time scale, we will not consider a time-dependent pair diffusivity here.In passing, we note that alternative scalings for rocaccia  proposed Klafter . In fact Klafter  had earlE(k) ∼ kp−, for 1 < p ≤ 3; the pair diffusivity then scales like p = 5/3, this gives the well known Richardson scaling l2〉 ∼ t3 [The locality hypothesis can readily be applied to generalized power law spectra of the type, (1+p)/2, , where σp = 5/3, yielding instead Kinematic Simulations (KS) , 11 has S(l) is the structure function of the turbulence velocity field and τs(l) is an effective time scale of velocity increments. In real turbulence, assuming locality scaling for S(l) ∼ l2/3 and for τs(l) ∼ l2/3 leads to Richardson’s classical scaling K at typical values of l, namely σl = 〈l2〉1/2 which is commonly assumed in these studies.Thomson & Devenish , for exaτs ∼ l/Us which is a time scale for the large scales flow to cut through smaller local eddies, Us being the sweeping velocity scale. This leads to, u′ is taken instead of Us, they obtained Thomson & Devenish argue that in KS because of the lack of true dynamical sweeping, the time scale must be a sweeping time scale, namely They concluded that whereas locality is true in real turbulence, it is not true in KS. In turbulence the large energy containing eddies carry the smaller eddies, but in KS as there is an absence of true dynamics the large scales force the fluid particles to cut through the smaller eddies in an unphysical manner, a view supported by Nicolleau & Nowakowski , and EyiK, but do not quantified the errors in K in KS—is it large or small? This is important because although it is accepted that KS lacks true physical sweeping effects, if these errors are quantitatively small under given circumstances, then KS could still yield accurate and meaningful results under these conditions.However, Thomson & Devenish address only the scaling laws in the diffusivity Furthermore, it is important to observe that the locality hypothesis itself, for the pair diffusion, has never been confirmed unequivocally as noted by Salazar & Collins , “… therAs such, in the absence of definitive proof of Richardson’s pair diffusion hypothesis, there is room for new thinking in this field, and it is reasonable to explore alternative, more analytic, approaches to address this problem, which is the main concern of this work.Ks compared to the physical pair diffusivity K. For this purpose, we focus upon the differences in the relative velocities along pairs of particle paths in the sweeping frame of reference. This frame of reference accounts for the physical sweeping effect of the largest energy containing scales; but a residual sweeping effect still remains due to the largest inertial range eddies sweeping the smaller inertial range eddies.Here we re-examine the sweeping effect in KS with a view of quantitfying the error in the KS pair diffusivity l in the inertial subrange being swept by a large scale flow. A real fluid particle pair will be swept by the physical velocity field u and will follow certain particle paths; but a KS flow will transport the pair along neighbouring particle paths due to an additional KS sweeping motion, us, and thereby force the particles to cut through local flow structures.Consider The large scale physical sweeping velocity is assumed not to affect the relative motion of particles in a pair in the inertial subrange. The critical question is, are the deviations from the physical trajectories induced by KS in the pair diffusion process large or small?Ks − K|, will be calculated assuming zero mean flow. We will consider generalised power law energy spectra, E(k) ∼ kp−, because the analysis is valid for all such power spectra and this will add weight to the conclusions that can be drawn from this work if validated over the whole range of p considered.A mean flow will also sweep the smaller scales; but in a KS flow it will force a fluid particle through smaller flow structures very quickly. Thus KS clearly is not suitable for particle diffusion in the presence a non-zero mean flow. Therefore, in the ensuing analysis the error between the KS and the physical pair diffusivities, |In this paper we address only the scalings and the quantitative estimates for the sweeping errors in KS. The main questions of interest are, is the KS sweeping error large or small, and in what range of separations? These questions are addressed first through a novel mathematical analysis focussing upon pairs of neighbouring particle trajectories. This is then verified against simulations using KS with very large inertial subranges.In Section 2, we derive an expression for the error in the pair diffusivity in KS flows by analysing neighbouring trajectories in the swept frame of reference. In Section 3, the KS method is discussed and simulation results presented. In the final Section 4, we discuss the results and its implications for theory and modeling.The idea of sweeping scales of motion implies a clear separation of scales between the sweeping and the swept scales. In reality, although there is a broad division between large and small scales, there is no well-defined cut-off between them because the spectrum of turbulence is continuous.k < k1. Thus, in the swept frame of reference the sweeping action itself can be approximatedd in KS by setting E(k) = 0 for k < k1. However, there still remains a residual sweeping caused by the largest of the inertial scales sweeping the scales local to the pair separation.However, the situation in KS is easier because all scales are already separated by construction as a Fourier series, un}, n = 1, 2, 3, … in which each flow field un is a Fourier series with given coefficients and is therefore smooth and differentiable. The randomness in KS comes from choosing each Fourier mode and each coefficient in the Fourier expansion in each flow field un randomly from specified probability distributions, the square of the magnitudes of the coefficients being proportional to a given energy spectrum, see Section 3.2.In the ensuing analysis we will make use of Taylor expansions applied to KS flow fields. It is important to note that this is possible because although KS is a Lagrangian method, it is not in the genre of stochastic models such as Random Walk models. In KS, we generate an ensemble of flow fields, {t = 0 with some small initial separation l0. At some time t later, the ensemble average of the separation is assumed to be well inside the inertial subrange and the relative motions are independent of l0 [Consider an ensemble of particle pairs released in a field of homogeneous turbulence at time nt of l0 .x1(t) and x2(t) respectively at time t; and the pair displacement is l(t) = x2 − x1, and l(t) = |x2 − x1|. u is the flow due to inertial range of turbulent motions that are effective in increasing the pair separation. We will refer to u as the ‘physical’ flow. All quantities are assumed at time t unless otherwise stated.Consider the particles in one of these pairs, labeled 1 and 2, as shown in t the additional  KS sweeping flow us is ‘switched on’—this is not to be confused with the total KS velocity field which is us = 0. In KS, the larger scales force a particle to cut through the smaller scales, hence us ≠ 0; but the spatial gradients of us are much smaller than the spatial gradients of u.At time u transports the particles to x1(t*) and x2(t*) respectively at the next time step t* = t + dt; while the KS flow (u + us) transports the particles to The flow t*, e.g. l* = l(t + dt). The superscript s will refer to quantities related to the KS residual sweeping, e.g. ls(t*) = ls(t + dt).The superscript * will refer to quantities at time The following quantities are defined:u = u is the ‘physical’ fluid velocity fieldus = us is the additional  sweeping velocity fieldv(l) = u(x2) − u(x1) is the ‘physical’ relative velocityvs(l) = us(x2) − us(x1) is the additional  relative velocityu2 = u, and We will simplifying the notation as much as possible, e.g. t later, the pair separation l = |l| is still small compared to some characteristic large length scale L and inside the inertial subrange, i.e. η ≪ l ≪ L; where η is the Kolmogorov scale. we will assume that inertial subrange is large enough, L/η ≫ 1, such that inertial range scaling will apply.In the following analysis, we consider the situation where particle pairs have been released at some earlier time, and now at time dt, where the increment, dt, is small compared to all other timescales in the system, governed only by the need for numerical accuracy.Furthermore, the following Taylor expansions in the KS velocity fields will be assumed,t* is, K* = 〈l* · v(l*)〉—we ignore constants of proportionality, like 2, because we are interested only in the power scalings in this work. The KS equivalent is dt2 and higher,The pair diffusivity at time sing Eqs  and 6)  t* is, Kdt is, EK = |Ks* − K*|. Using the expansion The incremental timestep error between the KS and physical diffusivities for a given timestep Ts is much larger than the local time scale of the pair separation. Hence, in the last four terms l(t) is replaced by l(t*) without affecting their magnitudes or scalings (the associated errors are ∼O(dt2) which is neglected).The time scale of the sweeping t*, so without loss of generality t* is replaced by t and the superscript ‘*’ is dropped. The subscript ‘1’ is also dropped because of homogeneity. All the terms in us, which is caused by the largest of the inertial range eddies, is close to uniform across small distances, and therefore the relative velocities across the local separation scales l that it induces is small, i.e. gradients like |(l · ∇)us| ≈ 0. However, gradients of the relative velocity v(l) itself can be large. The magnitude of us = |us| is assumed large compared to v(l) = |v(l)|, and also as compared to vs(l) = |vs(l)|. us scales differently to v(l).It is reasonable to assume that the  sweeping flow field v(l) also scales differently to vs(l), the former being governed by inertial range turbulence scaling, and the latter by differences in the residual sweeping velocity across a small distance l. This can be seen clearly in the limit of uniform  sweeping flow, where the v(l) is unaffected, but vs(l) = 0 and all the terms on the right hand side in E(k) = ε2/3Lp5/3−kp−, for k1 ≤ k ≤ kη and for 1 < p ≤ 3, and with kη/k1 ≫ 1 [E(k) = 0 for k < k1. The rate of energy dissipation is ε ∼ U3/L, where U is the velocity scale in the energy containing scales.Consider generalized energy spectra of the form η/k1 ≫ 1 , 15. In The previous discussion implies that l is, v2(l) ∼ E(1/l)/l, and therefore,The energy in turbulent inertial scales local to l ∼ σl as previously mentioned. Then, the second term in It is usual to assume the scaling E1, E3, …, E7, scale proportional to us or are much smaller, and this leads to the following estimates,All the other terms in σl/L < 1 and 1 < p ≤ 3. This is true even in the expression for E1/E2 because the factor L/Udt is subdued by the very small factor in the brackets. It is reasonable to conclude that the 2nd term in EK ≈ E2.All of these ratios are small for E2 itself, an estimate for us(l) is needed. The inertial subrange contains only a small part of the total turbulence energy across the entire wavenumber range, 0 < k < ∞; a typical turbulence spectrum is the von Karman spectrum Evk(k). The von Karman spectrum is essentially a fit between the low wavenumber energy spectrum (E(k) ∼ k4), and the high wavenumber inertial subrange spectrum (E(k) ∼ k−5/3); the exact form is not important for our purposes; but see [To estimate  but see .I2 = EIN/ETOT, where EIN is the energy in the inertial range, and ETOT is the total turbulence energy. Then if, ETOT ∼ U2, then we obtain, uks ≈ IU. The choice of wavenumber which separates the inertial range from the large scales is somewhat arbitrary.Let, the fraction of the turbulence energy in the inertial part of the spectrum be, σl are in the range k1 ≤ k < kl, where kl ∼ 1/σl. In the KS sweeping frame of reference, the larger inertial scales are the sweeping scales, and the energy in these scales is approximately,ε ∼ (uks)3/L ∼ (IU)3/L, this givesThe wavenumbers that contribute to the sweeping of particle pairs at separation EK to represent this quantity), isCk is the constant of proportionality, which can depend upon p.Using this in p = 5/3, the residual error per unit timestep is,For p → 1, EK → EK(1) ≈ CkU2/L ≈ Constant for σl/L < 1, but is nearly zero close to σl/L = 1. In this limit, p → 1, the pair diffusion is strongly local and is not affected by long range sweeping.As p = 3, the residual error per unit timestep is negligibly small for σl/L < 1,For In this limit, nearly all the energy is contained in the largest scales and inertial subrange scaling is no longer applicable.EK only tells us the error in KS due to the lack of dynamic sweeping per numerical time step. As the particle pair separations increase (on average), these errors will not only increase, but they will also accumulate over a period of time. The important question is, does this integrated error remain small?The incremental timestep error in the diffusivity σl ∼ L, implies that σl/η ≫ 1. In the limit of infinite inertial subrange this corresponds to σl/η → ∞.We therefore need to calculate the integrated error, relative to the actual diffusivity, over the period while the pair separation remains within the inertial subrange. The limit that the pair separation approaches the upper end of the inertial subrange, p ≤ 3. The range over which x = 1; but over the rest of the range f(x) < xp−1)/2 is an exact relation.If the pair diffusivity scales like, χp, and replacing the scaling with L by scaling with η, leads toThe most important quantity is the relative integrated residual error with respect to the pair diffusivity, γp = (1 + p)/2, and this becomesFor strict locality scaling γp − 1 > 0, p > 1. For p = 5/3, we have γp = 4/3 and we obtain,Since σl/η → ∞ then σl/η → 0 then Thus, as γp does not deviate too far from the local scaling, the above order of magnitude for γp is slightly greater than locality so the errors will be slightly smaller than in Even for non-local scaling, assuming that σl/η < ∞, where the errors remain negligible. In reality, all turbulence spectra are finite in range. So what size of the inertial subrange do we need to approximate an ‘infinite’ subrange?However, between these two asymptotic limits there must exist an intermediate range of separations, between 1 < Even then, the crucial question is: is the intermediate range of scales where the KS sweeping errors are negligible wide enough for inertial range scaling to be actually observable in KS?To determine the extent of this intermediate range of scales, if it exists at all, simulations with KS must be performed with very large inertial subranges.The errors in Eqs  and 25)25) cannoHowever, the effects of the error analysis can be observed in several important ways that will be described in the next section where we carry out KS calculations for the pair diffusivity.σl/η → ∞. It is expected that if there is an appreciable intermediate range where the errors are negligible, then the power scaling in Ks must be constant and asymptotic to the limiting case where σl/η → ∞. The extent of this intermediate range is determined by the range over which the power scaling in Ks is constant.The normalised integrated error, Furthermore, significant levels of the sweeping error means that the fluid particles cut through KS eddies, and therefore must be accompied by high levels of noise—the larger the relative sweeping error the larger the noise level.Ks ≈ K, will be observed in that part of the of the inertial subrange.Thus, where the errors are negligible it is expected that the correct power law scaling, Ks will deviate from the true power law scaling for K and also be accompanied with significant statistical noise due to fluid particles being swept through local eddies in that part of the inertial subrange. Even in this case, however, it is expected that the errors and the associated noise diminish as the pair separation increases.On the other hand, where the errors are significant it is expected that Ks is obtained from KS in the physically correct sweeping frame of reference; and second, the case where large scale random sweeping velocities are explicitly added to the flow.Comparison will be made between two cases: first, where Case 1Swept frame. Set the spectrum to be E(k) ∼ kp− in the inertial subrange, and set E(k) = 0 for k < k1.Case 2Non-swept frame. Set the spectrum to be E(k) ∼ kp− in the inertial subrange as in Case 1, and add E(k) = E0δ(k − k0) at some low wavenumber k0 < k1, and such that E0 is the energy in the von Karman spectrum in the range 0 < k < k1.dt ≪ τη, is used in all the simulations reported here. τη is the Kolmogorov time scale.A very small fixed timestep, smaller than any timescale in the system U, L, and I are different. From I2 ∼ EIN/U2, we obtain L in the two cases, and assuming Ak = CkUI ≈ constant we obtain,The analysis for Case 2 is similar to that which leads to ressions  and 25)U, L, andL is about 10 times bigger than in Case 1. We may thereore expect the errors to be about 10 times bigger in Case2 than in Case 1.In Case 2, when large random scales are included in the simulations then U, L, I, and the actual level of error can only be determined by simulations.The exact level of the error in E(k). Although KS cannot capture the full dynamics of particle motion, it has the advantage that it can generate extremely large energy spectra that is far beyond current experimental or DNS capabilities, and therefore it can be used to examine some aspects of very high Reynolds number scaling laws. KS continues to be used in turbulent diffusion studies for both passive and inertial particle motion, including cases with generalized power-law energy spectra of the form E(k) ∼ kp− for p > 1, Maxey [Kinematic Simulation , 5 is a 1, Maxey , Turfus 1, Maxey , Fung & 1, Maxey , Malik &1, Maxey , Farhan 1, Maxey . Meneguz1, Maxey  carried 1, Maxey  investigN is a suitable number of representative wavemodes, typically hundreds for very long spectral ranges, kη/k1 ≫ 1. kn = |kn|). The coefficients An and Bn are chosen such that their orientations are randomly distributed and uncorrelated with any other Fourier coefficient or wavenumber, and their amplitudes are determined by E(k), k1 ≤ k ≤ kη, is the turbulent energy specturm. The angled brackets 〈⋅〉 denotes the ensemble average over many flow fields. This construction ensures incompressibility in each flow realization, ∇ · u = 0. The flow field ensemble generated in this manner is statistically homogeneous, isotropic, and stationary.KS generates turbulent-like non-Markovian particle trajectories by releasing particles in flow fields that are incompressible by construction and which satisfy Eulerian statistics up to second order. A turbulent flow field realization is produced as a truncated Fourier series,An important feature of KS is that unlike some other Lagrangian methods, by generating entire kinematic flow fields in which particles are tracked it does not suffer from the crossing-trajectories error which is caused when two fluid particles occupy the same location at the same time in violation of incompressibility; but because KS flow fields are incompressible by construction this error is completely eliminated.E(k) can be chosen freely within a finite range of scales. In turbulent particle pair studies the interest is in Kolmogorov-like power law spectra,CE is a constant. The largest represented scale of turbulence is 2π/k1, and the smallest is the Kolmogorov scale η = 2π/kη. The constant is normalized such that the total energy contained in the range k1 ≤ k ≤ kη is 3(u′)2/2, where u′ is the rms turbulent velocity fluctuations in each direction. ε(p) is determined by integrating the spectrum, p = 1 is a singular limit which is not consider here.) vη = (εη)1/3 is the velocity micrcoscale, and τη = ε−1/3η2/3 is the Kolmogorov time micrcoscale.The energy spectrum The frequencies are chosen according to usual practice to be proportional to the eddy-turnover frequencies, i.e.  scaling . λ = 0.5kn = k1rn−1, with r = (kη/k1)N−1)1/,A particle trajectory is obtained by integrating the Lagrangian velocity t should be smaller than any other time scale in the system—in this case the Kolmogorov time scale τk = 2π/kη; thus we require Δt ≪ τk. In our simulations, particle trajectories are produced by integrating t ≈ 0.01τk in a fourth order Adams-Bashforth predictor-corrector method.The method of computing trajectories in KS is well established in the literature, see previous references above. Briefly, since an individual KS flow field realization is smooth and differentiable, l0/η = 0.5. To obtain a true ensemble, this process is repeated in many thousands of KS flow realizations. (Releasing thousands of particle pairs in the same KS flow field will not produce the required independence which may produce biased statistics.) Pairs of trajectories are thus harvested over a large ensemble of flow realizations and pair statistics are then obtained from it for analysis.It is important to produce a very large ensemble of independent particle pair trajectories. Only eight independent particle pairs are released in any one given KS flow realization, each pair set part by more than an integral length scale. Each pair is initially released with a pair separation distance of K(l) ∼ 〈l · v(l)〉, i.e. the ensemble average of the scalar producted of v and l. But it has been found that using the equivalent formula, K(l) ∼ d〈l2〉/dt, i.e. the derivative of the 〈l2〉, converges faster statistically needing a much smaller ensemble of trajectories, although the two methods give identical results for large enesmbles of particle trajectories. The latter method has been adopted here.The turbulent diffusivity itself can be computed in two ways. Directly from the forumla not correct to compare the kinematically generated flow fields directly with DNS flow fields. As such, KS is like Lagrangian methods such as Random Walk models where an individual particle trajectory has no physical meaning, but the ensemble average over many such random trajectories produces physically meaningful Lagrangian statistics.Lagrangian statistics are the physically meaningful output from KS. It is L = 1, k1 = 1/L = 1, and kη = 106, CE = 1.5 (Kolmogorov constant) and u′ = 1. There were 200 wavemodes per realization.KS simulations were performed with E(k) = 0 for k < 1.In Case 1 (swept frame of reference), k0 = 1/10, with E(k) = E0δ(k − k0). The energy in these sweeping scales, E0, was equal to the energy contained in the von Karman turbulence spectrum for k < 1. k0 corresponds approximately to the location of the peak in the von Karman spectrum.In Case 2, large scale random sweeping were added at the low wavenumber p = 1.01, 5/3, and 3. With 8 pairs released in 5000 flow realizations, the Lagrangian statistics were obtained from 40,000 particle pair trajectories.In both cases, three different power spectra were considered with, respectively, K/(ηvη) against σl/η, for Case 1 (red lines) and Case 2 (green lines). The energies in the two cases are different, so Case 2 plots have been shifted vertically in order to compare the two cases directly. This does not affect the scalings (the slopes) which is the main interest here. Hence the ordinate is shown without scale.p = 1.01, the two cases align with a constant power-law scaling, γ1.01 ≈ 1.07, over most of the inertial subrange of scales and there is very little statistical noise, indicating that For p = 5/3 (Kolmogorov turbulence), in Case 1 (red) a clear power-law scaling is observed, γKol ≈ 1.53 > 4/3, and very little statistical noise in the range 1 < σl/η < 105, indicating that σl/η > 102 is good.For p = 3, the two cases overlap with a power-law scaling, γ3 = 2, with almost no statistical noise. In this limit nearly all the energy is in the large scales and inertial range scaling is no longer applicable; rather uniform strained motion with the characteristic slope of 2 is obtained.For σl/η < 105, and the very low level of statistical noise in the swept frame of reference are especially important.  show pair diffusion which appear to display locality scaling, see  for examssilicos ; here noσl/η < 105.The main contribution of this work is that it has been shown that the departure from locality scaling observed in KS cannot be attributed to the sweeping effect; in a reference frame moving with the large energy containing scales in zero mean flow turbulence the sweeping errors in the turbulent pair diffusion process in KS is negligible in the inertial subrange where, 1 < p = 5/3 where KS yields γKol ≈ 1.53 > 4/3—could the locality hypothesis itself be in error? This cannot be concluded for certain from the present results alone—only detailed experiments or DNS can provide a definitive answer to that, and both are decades away at the present time. But the results presented here, do excite an important new line of thinking that has been neglected in the turbulence community, but one which has as much validity per se as the locality hypothesis itself. A non-local theory of pair diffusion that could explain the observed results and available data is currently the subject of active research by the author.But if the sweeping errors in KS are negligible, why is locality scaling not observed for


Hollow nanofibers are largely gaining interest from the scientific community for diverse applications in the fields of sensing, energy, health, and environment. The main reasons are: their extensive surface area that increases the possibilities of engineering, their larger accessible active area, their porosity, and their sensitivity. In particular, semiconductor ceramic hollow nanofibers show greater space charge modulation depth, higher electronic transport properties, and shorter ion or electron diffusion length . In this review, we discuss and introduce the latest developments of ceramic hollow nanofiber materials in terms of synthesis approaches. Particularly, electrospinning derivatives will be highlighted. The electrospun ceramic hollow nanofibers will be reviewed with respect to their most widely studied components, i.e., metal oxides. These nanostructures have been mainly suggested for energy and environmental remediation. Despite the various advantages of such one dimensional (1D) nanostructures, their fabrication strategies need to be improved to increase their practical use. The domain of nanofabrication is still advancing, and its predictable shortcomings and bottlenecks must be identified and addressed. Inconsistency of the hollow nanostructure with regard to their composition and dimensions could be one of such challenges. Moreover, their poor scalability hinders their wide applicability for commercialization and industrial use. Nowadays, one-dimensional 1D) nanostructures, including nanofibers, nanotubes, nanorods, nanowires, and nanobelts have drawn immense attention from various scientific communities. This attraction stems from their unique properties, such as size effects, surface effects, and superparamagnetism, leading to their intriguing applications in many advanced areas including sensors, solar cells, nanoresonators, etc. [D nanostrUp to now, techniques such as drawing, template synthesis, phase separation, self-assembly, and electrospinning have been employed for the fabrication of nanofibers made of polymers, metals, ceramics, glass, etc. These methods not only produce nanofibers, but also further assemble them into two-dimensional (2D) and three-dimensional (3D) nanostructures for practical applications .2/g), high porosity, and small pore sizes. Thus, they could be excellent candidates for a wide range of applications, including tissue engineering, drug delivery, textiles, filtration, composite reinforcements, etc. [For the last two decades, an almost old technique, called electrospinning, has been underlined mainly because of its extraordinary capabilities in the production of polymer nanofibers ,3,4. In ts, etc. ,17.The main advantages of electrospinnig are: its relatively easiness (easy to set up), high speed, low cost, high versatility allowing control over the fibers’ diameters, microstructures and arrangements, and the possibility of a vast selection of materials ,18,19. THollow nanofibers are able to offer a very extensive surface area that could be highly beneficial for surface-related applications, e.g., chemical sensors, photocatalysis, electromagnetic wave absorbing materials, etc. ,25. It iIn this review, we aim to present a comprehensive overview of the latest development of ceramic hollow nanofiber materials in terms of synthesis approaches, material types, and applications. The emphasis will be on electrospinning for the production of hollow nanofibers, while, with respect to nanofiber materials, we will consider the most common ceramic  materials that have been particularly studied in relevance with energy and environmental remediation applications.The most widely applied process for the fabrication of hollow nanofibers is electrospinning. Unlike the template synthesis and self-assembly methods relying on complex manipulations of molecules to form the desired structure, electrospinning is an efficient and straightforward method to produce hollow nanofibers from either inorganic or organic components .Electrospinning is an effective, adaptable method to form nanofibers with various structures such as, for example, beads on a string, ribbon, cylindrical, grooved, porous, multichannel, core-shell, side by side, helical, hierarchical, and hollow ,39,40. EA simple electrospinning apparatus comprises a Direct Current (DC) high voltage source with positive and negative electrodes connected to a spinning solution container with a nozzle (or spinneret) and a collector, respectively. During the process, an electric field is formed between the spinneret and the collector as a result of their opposite charges. Induced by this electric field, a conical shaped droplet, called “Taylor cone”, is pulled out from the nozzle. Once the electric force dominates the surface tension of the spinning solution, a charged jet is expelled, the solvent gradually evaporates, and the nanofibers are deposited on the collector . Since 2The single-spinneret, or single-nozzle, electrospinning is the simplest electrospinning procedure to form hollow nanofibers from either one component or multiple components ,53,54,552 nanofibers using a coaxial electrospinning set-up [2 nanofibers are made. Scanning Electron Microscopy (SEM) images of the produced core-sheath, then TiO2 hollow nanofibers are shown in Among the derivative techniques of electrospinning, coaxial electrospinning is indeed the most widely employed for the production of hollow nanofibers of polymers ,63,64, cg set-up . By remoThe sheath layer must be strong enough to retain the hollow structure, otherwise the produced hollow nanofibers will collapse.Despite the easiness of this method, continuous and perfect hollow nanofibers are hardly made because of the post-treatment processes applied to remove the core.Complete elimination of the core is challenging.The hollow nanofibers prepared by this method can consist of only one layer wall.Since the sheath and core solutions meet at the end of the nozzle, two physical phenomena take place simultaneously: the wrapping of the sheath solution around the core solution and the formation of the Taylor cone by the sheath solution to equilibrate the charge effect and the fluid surface tension . Hence, Additionally, the limited number of suitable inner solvents and the lack of control over the electrospinning parameters are other problems that can hinder the applicability of the coaxial electrospinning for some systems .If the inner needle of the coaxial electrospinning possesses two or more channels, multichannel hollow nanofibers can be made ,77,78. ITriaxial electrospinning employs a spinneret with three concentric needles a. As seeTo successfully perform the triaxial electrospinning, a compound Taylor cone must be formed, and the three involved fluids should be held concentrically together during the procedure . MoreoveTriaxial electrospinning has been applied to fabricate hollow nanofibers from a wide variety of materials ,88. For The main advantage of this technique is the possibility of formation of nanofibers with a higher surface area enabling the sustained release of important agents . For insEmulsion electrospinning, which is the electrospinning of a blend of two immiscible liquid phases, is principally similar to solution electrospinning, but different in chemistry ,92. ThroThere are two types of emulsion for the electrospinning process: water in oil (W/O) and oil in water (O/W) ,96. In aEmulsion electrospinning does not require complex spinnerets compared to the coaxial electrospinning, and it could simply provide good concentric core-sheath nanofibers ,98. Anot2 nanotubes via emulsion electrospinning of a W/O system. As shown in 2 precursor (tetrabutyl titanate), wherein a mechanical pump oil was dispersed. During the electrospinning, as shown in 2 nanotubes are created  . More sp2 is a semiconducting material with promising characteristics, such as a long-standing stability against chemical and photo corrosion. It is environmentally friendly and shows great photo-reactivity, robust oxidizing activity, and good optical transparency. Moreover, optimum dielectric properties and electrical conductivity, a large refractive index of about 2.52 for anatase and 2.49 for rutile, as well as a large band gap of 3–3.5 eV are other interesting features of TiO2 [TiO of TiO2 . Thanks  of TiO2 ,133,134.2 absorbs Ultraviolet (UV) light and shows optimum photocatalytic activity. This ability is enhanced on large surface areas, e.g., hollow nanostructures, and brings about an efficient degradation of inorganic and organic molecules [2 microfibers. The multichannel structured fibers were synthesized by a multifluidic compound-jet electrospinning method (2 fibers (2 is done via a reaction with first-order kinetics. This fact is confirmed by the linear plot of ln(C0/Ct) versus the photocatalytic reaction time t. While C0 is the initial concentration of acetaldehyde, Ct is the concentration of acetaldehyde after the photocatalytic reaction for t in hours. This Figure implies that the initial rate constant (k) for acetaldehyde degradation increases proportionally to the channel number from solid fibers (k0CF ≈ 0.37 h−1), one-channel fibers (k1CF ≈ 0.40 h−1), two-channel fibers (k2CF ≈ 0.47 h−1), to three-channel fibers (k3CF ≈ 0.83 h−1). Hollow TiO2 nanofibers with a promising photocatalytic effect for the decomposition of the methylene blue (MB) dye have also been synthesized by Chang et al. [2 nanofibers. The core fluid was solely a PVP/ethanol/deionized water solution. Both types of nanofibers showed a similar tubular structure. Yet, they were different in terms of surface morphology and shell thickness. When titanium sol was used, a small amount of water in the core hampered the diffusion of the core and shell solutions. Since the titanium precursor is not spinnable, PVP nanofibers were used as core and shell templates during the coaxial electrospinning process. Both hollow TiO2 nanofibers were superior to their solid counterparts in terms of MB dye degradation efficiency. In this context, Jung et al. [2 hollow nanofibers that could efficiently photodegrade MB. They stated that the improved degradation efficiency is due to electrons transfer between TiO2 and MWCNT and to the MWCNT adsorption ability. The maximum MB decomposition rate of 62% was obtained after 70 min. Regarding another composite hollow nanofiber system, Peng et al. [2/TiO2 nanofibers prepared by coaxial electrospinning is greater than that of the commercial TiO2 photocatalysts. This could be due to their one-dimensional hollow structure and to a continuous hetero-junction between TiO2 and SnO2. The SnO2/TiO2 hollow nanofibers could decompose Rhodamine-B (RhB) dye faster than solid TiO2 nanofibers and TiO2 nanoparticles did. As a result of the wide band gap, TiOolecules . In factolecules . In thisolecules  introducg method a. The op2 fibers b causes k2CF ≈ 0. h−1, to g et al.  also prog et al.  reported2 hollow nanofibers whose composition consisted of rutile (5.4%) and anatase (94.6%). To confer mesoporosity to the nanofibers, a foaming agent was added to the mixed-phase composition. Accordingly, the hollow structure and the mesoporous walls of the nanofibers could cooperatively bring about an excellent photocatalytic efficiency and stability. The as-synthesized nanofibers, whose inner diameter and wall thickness were 215 and 100 nm, respectively, were able to decompose RhB efficiently (99.5%) in 60 min.In another research, Hou et al.  produced2 in order to extend its photocatalytic applicability to visible light, Yang et al. [2 nanofibers with Pt nanoparticles. The schematic of the entire process, including electrospinning, calcination, and Pt loading of the nanofibers, is demonstrated in 2 hollow nanofiber is depicted in −1, which was 11.5 and 3.63 times larger than that for the unloaded hollow nanofibers and Pt/P25 (TiO2 nanoparticles), respectively. The factors affecting this performance included the Pt loading amount, the calcination temperature of the TiO2 hollow nanofibers, the pH of the primary solution, and the light source. The results demonstrated that by addition of 2 wt. % Pt, calcination of the nanofibers at 350 °C, and application of the nanofibers in acidic condition and under solar light, the best photocatalytic activity can be achieved. The main decomposition mechanism of Orange II was attributed to the oxidation by H+ and O2− radicals, as shown in To shorten the band gap of TiOg et al.  loaded h2O4, in which M stands for Fe, Co, Ni, or Mn. They show interesting magneto-optical, magnetic, electrical, and magnetoresistive characteristics [Ferrites are natural, abundant, inexpensive, and sustainably permanent magnets. They are known for their spinel shape and the common formula of MFeeristics ,138. Suceristics , batterieristics . 2O4 hollow nanofibers via electrospinning of a PVP/nitrate salts solution and subsequent calcination. The as-synthesized nanofibers were characterized in terms of crystalline structure, morphology, magnetic properties, etc. The results of X-ray diffraction analysis (XRD), SEM and TEM confirmed the cubic spinel structure, one-dimensional texture, and the existence of many nanoparticles in the wall of the hollow fibers, respectively.Among various ferrites, the one based on cobalt (Co) has received considerable attention especially for magnetic recording applications because of its anisotropy, optimum chemical stability, mechanical hardness, saturation magnetization, and high coercivity ,142. The3+ and Co2+, thereby forming a metal–organic framework structure. During the electrospinning process, by evaporation of the solvent (here ethanol/water) the composite fibers are created and can then act as a self-sacrificial template for the CoFe2O4 hollow nanofibers. Subsequently, the composite fibers are converted to the hollow nanofibers. The mechanism of formation of the hollow nanofibers could be related to the diffusion of the gas product of the PVP decomposition, driving the nanoparticles constituting the fibers from the inside to the outside of the composite fibers. In solution, the carbonyl and tertiary amine groups of PVP can coordinate with Fe2O4 hollow fibers show a typical ferromagnetic (FM) behavior. As a definition, saturation magnetization (Ms) is the highest induced magnetic moment that a material can get in a magnetic field. As the authors report, the Ms value of the CoFe2O4 hollow fibers increases with increasing annealing temperatures. The hollow fibers synthesized in this study are made of many nanoparticles, whose interactions and properties determine the magnetic behavior of the CoFe2O4 hollow fibers. For small CoFe2O4 nanoparticles, the inner sides of the nanoparticles are in the usual spin arrangement, whereas the arrangement of their surface atomic moments is disordered. This discrepancy could break their surface exchange bond and change their surface cations coordination, thus decreasing the Ms of the CoFe2O4 nanoparticles. As a fact, the higher the calcination temperature is, the larger the particle size will be. Thus, the surface shell contribution to the Ms would decline when the nanoparticles' size increases. This means that the Ms would increase at higher annealing temperatures. As shown in this study, at the higher calcination temperature of 700 °C, Ms for the CoFe2O4 hollow fibers is 34.71 emu·g−1 at 300 K, and 36.82 emu·g−1 at 2 K, respectively. This difference can be attributed to the surface spin-canting effect and to the existence of a magnetic dead layer on the surface. When the temperature is low, the surface spins will be frozen along, and thus the local surface anisotropy will be higher. However, at high applied fields, the surface anisotropy once again decreases, and the surface spins are arranged along the field direction, leading to a higher Ms magnitude. In general, the magnetic measurements verified that the CoFe2O4 hollow nanofibers are able to offer novel magnetic properties that are promising for electromagnetic and spintronic devices.As shown in this study, the CoFe2O4 hollow nanofibers could also be employed in connection with photocatalytic applications. In this regard, Kim et al. [2O4 internal sheath and a PANI external sheath through electrospinning, annealing, and in situ chemical oxidative polymerization. The mechanism of formation of such nanofibers is demonstrated in 2O4 and PANI enhanced visible light photocatalysis. The authors concluded that the hollow CoFe2O4-PANI nanofibers harvest visible light, make the quantum confinement impact, assist the electron and mass transfer, and support the charge separation. Thanks to the unique core-shell mesoporous structure of the CoFe2O4-PANI nanofibers, the pseudo-first-order kinetic constant of the photocatalytic degradation of the methyl orange (MO) dye under visible light was 80 times larger than that for the CoFe2O4 nanofibers. This finding, along with the photodegradation efficiency of the mentioned nanofibers, is presented in 2O4-PANI nanofibers is because of the interaction and synergistic effects of CoFe2O4 and PANI, optimally inducing the separation of electron–hole in the CoFe2O4 and PANI coupling system.Other than their electromagnetic properties, CoFem et al.  produced3O4), hematite (α-Fe2O3), and maghemite (γ-Fe2O3) are widely applied because of their catalytic, biomedical, and magnetic properties. Moreover, their abundance, low-cost processing, lack of toxicity, great theoretical capacity (≈1000 mA·h·g−1), and corrosion resistance are promising for a diverse range of applications [Among the eight known types of iron oxides and different transition metal oxides, magnetite 3 nanofibers at 500 °C for 4 h, with the heating rate of 1–7 °C·min−1. By changing the production conditions, the morphology of Fe2O3 changes from solid belt to hollow belts and hollow fibers. They found that the key parameter for the hollow nanostructure formation is the PVP decomposition rate, which can be controlled by tuning the heating rate and the rigidity of the surface gel layer. The latter can be changed by the solvent composition as well as by the PVP and Fe(NO3)3·9H2O content. The authors also investigated the magnetic properties of hollow fibers at room temperature, with the field sweeping from −15 to +15 kOe. The hollow fibers remnant magnetization (Mr) and coercivity (Hc) are 0.13 emu·g−1 and 177.4 Oe, respectively. These values imply that the hollow fibers show ferromagnetic behaviors at room temperature. Compared to the urchin-like, rod-like, and rhombohedral Fe2O3 counterparts, the reported values of Mr and Hc of the hollow fibers are higher . The reason should be sought in the sensitivity of the magnetization of the ferromagnetic materials to the morphology and structure of the samples made thereof. Here, the assembly of the nanoparticles into the hollow fibers can convert a single domain to a multidomain, thus increasing the Mr and Hc values.In comparison with other iron oxide polymorphs, α-Fepacitors . To indupacitors  synthesi3O4 shows the strongest magnetism among the transition metal oxides. Also, it offers optimum biocompatibility and low level of cytotoxicity in living cells [3O4 component via one-pot coaxial electrospinning without a core solution (using air only), as shown in 3O4/Eu(BA)3phen/PVP hollow nanofibers. In another work, Liu et al. [3phen/PANI/Fe3O4/PVP hollow nanofibers (−3 S·cm−1 was reported for these hollow nanofibers. The fluorescence emission peaks of Eu3+ were detected in the hollow nanofibers and attributed to the 5D0 → 7F0 (580 nm), 5D0 → 7F1 (592 nm), and 5D0 → 7F2 (616 nm) energy level transitions of Eu3+ ions. The latter hypersensitive transition induces the strongest emission peak. Interestingly, the luminescent intensity, electrical conductivity, and magnetic properties of the hollow nanofibers were proportional to the amount of Eu(BA)3phen, PANI and Fe3O4 nanoparticles, respectively, and could be adjusted. The photoluminescent–electrical–magnetic trifunctional flexible hollow nanofibers can be proposed for diverse applications, such as electromagnetic interference shielding, microwave absorption, molecular electronics, and biomedicine. Feng cells . The preu et al.  construcnofibers b,c. The 2, H2, CO, C2H5OH, H2S, and NH3) [S) of the sensor follows the equation S = Ra/Rg, where Ra and Rg are the sensor resistance in atmospheric air and in ethanol–air mixed gas, respectively. The response and recovery time are the times spent by the sensor to achieve 90% of the total resistance change in the case of adsorption and desorption, respectively.Zinc oxide (ZnO) is a semiconductor with the band gap energy of 3.37 eV, a large exciton binding energy of 60 meV, excellent chemical and thermal stabilities, and high transparency. Such features enable its use for a wide variety of applications, such as solar cells, sensors, photodetectors, transistors, etc. ,150,151.and NH3) . A much and NH3)  develope2−, O2−, and O−) are adsorbed on the inner and outer surfaces of the hollow nanofibers at high temperatures. While at low temperatures, O2− is commonly chemisorbed, at high temperatures, O− and O2− are mainly chemisorbed, and O2− vanishes immediately. Thus, the reaction kinematics could be represented as: O2 (gas) ↔ O2 (absorbed) + e− ↔ O2− + e− ↔ 2O−.In the ethanol sensing process by the ZnO hollow nanofibers, oxygen sorption adversely contributes to the electrical transport properties of the nanofibers. When oxygen is adsorbed by the nanofibers, the ZnO conduction electrons are stolen, and thus conductance declines. In the case of the ZnO hollow nanofibers, reactive oxygen species (O3CH2OH (absorbed) + 6O− (absorbed) → 2CO2 + 3H2O + 6e−. The optimum ethanol sensing ability of the ZnO hollow nanofibers could be attributed to their 1D hollow nanofiber structure . This interesting nanostructure facilitates fast mass transfer of ethanol molecules to and from the interaction region. In addition, it rises the rate for charge carriers to traverse the barriers induced by molecular recognition along the nanofibers.By exposure of the ZnO hollow nanofibers to ethanol, and thus its reaction with ionic oxygen species, the concentration of the oxygen species decreases, and the electron concentration, and thereby the conductance of the ZnO hollow nanofibers, increases. This fact can be demonstrated by the following reaction: CHRa/Rg = 51) was measured at the temperature of 270 °C. As shown in the inset image, the rapid response and recovery time of the the ZnO hollow nanofiber sensors were around 3 and 5 s, respectively. Ra/Rg respectively. The response and recovery time were also around 3 and 5 s, respectively. In addition, as shown in 2-ZnO nanofibers via single-spinneret electrospinning. These hollow nanofibers showed optimum stability and remarkable sensitivity against toluene at 190 °C, thanks to their hollow structure and the SnO2–ZnO hetero-junction. By themselves, SnO2 hollow nanofibers have also been considered for magneto-optoelectronic devices, as will be introduced in the next section.In addition to ethanol, the gas sensing ability of the hollow ZnO nanofibers for formaldehyde  and acet2 has shown an amazing potential as a host lattice for the dilute magnetic semiconductors (DMSs), thanks to its wide band gap, native oxygen vacancies, and high carrier density [2 is one of the most widely studied materials for magneto-opto-electronic devices, as well. By reducing the size of SnO2 to nanoscale, the surface area of the ensuing materials increases, which, for instance, is important to improve their magnetic properties [2 in 1D nanostructures is electrospinning [2 nanofibers by single-spinneret electrospinning. In this study, the Kirkendall effect, as a result of the concentration gradient between Sn precursors and SnO2, was responsible for the formation of hollow SnO2 nanofibers. Moreover, the lattice and surface diffusion were found to be the driving forces for the growth of nanograins on the surface of the SnO2 nanofibers.Among the metal oxides, SnO density . DMSs aroperties . Moreoveoperties . One of spinning ,158,159.spinning  develope2 confers new properties to the ensuing hollow nanofibers. For instance, Mohanapriya et al. [2 hollow electrospun nanofibers. The authors observed a reasonable FM transition at 10 K that was attributed to the precipitated impurity phases. In another relevant work, Mohanapriya et al. [2, the optical band gap of SnO2 hollow nanofibers declined. This confirms the direct energy transfer between f-electrons of Ce ions and the SnO2 conduction or valence band. Doping of SnOa et al.  prepareda et al.  reported2 valence or the conduction band and the 4f electrons of the Ce ions. The Ce concentration-dependent red shift of the absorption edge witnesses the applicability of the Ce-doped SnO2 hollow nanofibers for narrow band-gap optoelectronic devices. The Tauc plots shown in Eg) for undoped and Ce-doped SnO2 hollow nanofibers through the following equation:hv is photon energy, A is constant, n = 1/2 for a direct band-gap semiconductor. The Eg values are obtained via extrapolation at the linear portion of the Tauc plot at α = 0. These values for the undoped and doped SnO2 nanofibers are 3.65 and 3.4 eV, respectively. 2 (3.6 eV). This discrepancy could be correlated to the direct electronic transition between the donor level and the valence band. As shown in the inset Figure, the Ce-doped SnO2 hollow fibers also exhibit an evident blue emission with an additional peak around 420 nm that is induced by presence of the Ce ions. The peaks at 467 nm are attributed to the electron transition between the new unoccupied states of Ce3+ 5d, the excited states near the conduction band of SnO2, and the 4f states. As demonstrated in 2 and Ce ions, respectively. When the doping level reaches 6 mol. %, a room temperature FM property with 19 × 10−5 emu·g−1 saturation magnetization could be obtained. In general, this study implies the applicability of the Ce-doped SnO2 hollow nanofibers for magneto-optoelectronic devices.As shown in 2O3) is a bio-inert ceramic that possesses unique properties, such as high abrasion resistance, biocompatibility, and chemical inertness [2O3 hollow nanofibers, as schematically shown in 2 adsorption–desorption isotherm was employed to extract the specific surface area of 67.17 m2·g−1 and the mean pore size of 17.3 nm. The authors proposed that the diameter and pore size of the hollow nanofibers can be controlled through altering the ratio of Al(NO3)3·9H2O to PAN. The hollow nanofibers showed excellent dye adsorption efficiency for three different dyes , methylene blue (MB), and acid fuchsine (AF)).Alumina  was the basis to characterize the adsorption performance. As reported by the authors, with respect to CR, the adsorption process proceeds in two stages. First, the adsorption mainly occurred within a short time, so that about 75.28% of CR in the solution was adsorbed in only 5 min. Subsequently, between 5 and 60 min, the adsorption rate decreased. After 60 min, the CR removal efficiency was about 96.52%. The adsorption process for MB proceeded in the same manner. The MB removal efficiency was 72.68% and 92.38% after 5 and 60 min, respectively. On the contrary, for AF, the primary removal after 5 min was not so notable, being only about 32.44%. However, after 60 min, about 91.70% of AF was removed. Thus, in the case of AF, the adsorption was done gradually.2O3 nanofibers, various interactions between γ-Al2O3 and CR (or MB) could be imagined: (1) likely hydrogen bonding between –OH on the surface of γ-Al2O3 and the N atom in the dye molecules, (2) electrostatic interactions resulting from excess Al3+ ions available on the surface of γ-Al2O3 nanofibers that can adsorb the dye molecules electrostatically, (3) with a lesser significance, Van Der Waals force that can play a role in the adsorption of the dye onto the surface of the porous adsorbent.Considering the hydroxylated surface of the γ-Al2O5) is a functional ceramic currently stimulating immense research interest for its employment in optical switching devices, catalysis, solar cell, sensors, etc. [2O5. For instance, Zeng et al. [2O5 and Au/V2O5 nanofibers. Both the hollow nanofibers indicated a quick response–recovery and an outstanding sensitivity against ethanol. As shown in 2O5 show an enhanced performance due to the catalytic effect of Au nanoparticles that improve surface reactions. The response/recovery time of V2O5 is 5 s/5 s, and the sensing response is ~2.6 s, while such parameters for Au/V2O5 are 7 and 5 s, and ~2.7, respectively, as shown in 2O5 sensor is exposed to air, electrons on the V2O5 surface move towards the Au nanoparticles mainly because of the Schottky contacts between the Au and the V2O5 nanoparticles. Concurrently, the embedded Au nanoparticles induce a spill-over effect that contributes to the catalytic activation of oxygen dissociation, enhancing the molecule–ion conversion level, and dissociating oxygen into oxygen species Ox− . These species are then transported and distributed onto both the outer and inner surfaces of the nanotubes. As soon as ethanol is released, thanks to the catalytic effect, the sensing reaction between the surface Ox− and the ethanol molecules is facilitated by the Au nanoparticles. This process leads to the transfer of the trapped electrons back to V2O5, through the following reactions:Au (Svo) is an adsorption site on the Au (V2O5), and evo− is an electron from V2O5.Vanadium pentoxide . Among the derivative techniques of electrospinning, coaxial electrospinning is indeed the most widely employed method for the production of ceramic hollow nanofibers. With respect to the ceramic hollow nanofiber material, metal oxides have been extensively investigated for the production of hollow nanofibers for electrodes, photocatalytic adsorbents, sensors etc. For this reason, they were precisely introduced in this review, and their promising features were thoroughly discussed according to the literature. As we mentioned, metal oxide hollow nanofibers are able to develop an extensive surface area that, depending on the employed metal oxide, offers various amazing functionalities. For instance, ZnO and VDespite highly remarkable properties and potentials for future cutting-edge applications, there are several challenges with regard to the production of ceramic hollow nanofibers. Such difficulties must be addressed and circumvented for the sake of industrialization and upscaling. One of the greatest challenges in this regard is the lack of consistency of the core-shell morphology throughout the length of the fiber. Although what is presented in the literature about the core-shell and hollow fibers often implies a homogenous structure, this is not convincing when a much wider scope, rather than a selected TEM image, is considered. It is noteworthy that a continuous and consistent core-shell morphology necessitates a stable and steady injection of the core and the shell solution during electrospinning. However, this is not possible without any disruption to the core solution feed during the entire spinning process. Also, due to the post-treatment processes applied to remove the core, continuous and perfect hollow nanofibers are hardly made. In fact, the complete elimination of the core is challenging. The sheath layer should be strong enough to retain the hollow structure, otherwise the produced hollow nanofibers will collapse. Additionally, the limited number of suitable inner solvents and the lack of control over electrospinning parameters are other problems that can hinder the applicability of the coaxial electrospinning for some systems. Despite such challenges, the need of a uniform hollow (or core-shell) structure at a large scale depends on the envisaged application. For instance, for the sake of drug delivery, a non-continuous core-shell structure does not affect adversely the drug delivery capability. However, for other applications wherein such a structure is of utmost importance, this requirement should be investigated. As Na et al.  suggesteThe other significant challenge is related to the scalability of the technique. In general, along with the rapid progress of nanotechnology, nanofibers and their products are more demanded now than ever, but the throughput of the conventional electrospinning is not high enough to satisfy such needs. Therefore, methods able to increase the yields of the electrospun nanofibers are necessary and should be developed.


Bedtime routines has shown important associations with areas associated with child wellbeing and development. Research into bedtime routines is limited with studies mainly focusing on quality of sleep. The objectives of the present study were to examine the relationship between bedtime routines and a variety of factors associated with child wellbeing and to examine possible determinants of bedtime routines.A total of 50 families with children between 3 and 5 years old took part in the study. Data on bedtime routines, parenting styles, school readiness, children’s dental health, and executive function were collected.p ≤ .001), inhibition and attention (t (48)= − 9.70, p ≤ .001) and cognitive flexibility (t (48)= − 13.1, p ≤ .001). Also, children in households with optimal bedtime routines scored higher in their readiness for school (t (48)= 6.92, p ≤ .001) and had better dental health . Parents in households with suboptimal bedtime routines showed worse performance on all measures of executive function including working memory (t (48)= − 10.47, p ≤ .001), inhibition-attention (t (48)= − 10.50, p ≤ .001) and cognitive flexibility (t (48)= − 13.6, p ≤ .001). Finally, parents with optimal bedtime routines for their children deployed a more positive parenting style in general (i.e. authoritative parenting) compared to those with suboptimal bedtime routines (t (48)= − 6.45, p ≤ .001).Children in families with optimal bedtime routines showed better performance in terms of executive function, specifically working memory (t (44)= − 8.51, The results of the present study highlight the potentially important role of bedtime routines in a variety of areas associated with child wellbeing and the need for further research.The online version of this article (10.1186/s12889-018-5290-3) contains supplementary material, which is available to authorized users. A limitof life” –6. Qualiof life” , 2, 4–7.Overall, bedtime routines and quality of sleep has attracted the most research interest with studies consistently showing that better quality bedtime routines are associated with better sleep quality and duration for both adults and children –8. OtherAnother area closely associated with bedtime routines is dental health. Oral hygiene behaviours  as part of bedtime routines have shown significant correlations with improved oral health with lower prevalence of caries (decay) in both children and adults , 11, 12.Finally, bedtime routines have been associated with emotional and psychological wellbeing in parents and children. Children with non-regular bedtime routines experience more frequent behavioural difficulties than others  and pareDespite the reported likely importance of bedtime routines, no clear statement or policy on what constitutes an optimal bedtime routine exists. Based on available studies and limited guidelines from different organisation and professional bodies, an optimal bedtime routine for infants and preschool children is likely to; be consistent throughout the week and weekend, follow the recommended sleep times for each age group , include tooth brushing and avoidance of drinks (such as bottle feeding) and snacks before bed, minimise the use of electronic devices and television around and during bedtimes, consider a bath or shower before bed and finally, include book reading and book sharing activities before sleep , 21–23.As optimal bedtime routines have multiple potentially beneficial components the cumulative effect of all of them can result in multiple positive outcomes and wider benefits for wellbeing and development. However, the majority of research in this area focuses on just one beneficial outcome of routines – sleep quality. That focus is creating a gap in our understanding that needs to be addressed by more inclusive studies that move away from quality of sleep and examine other areas associated with wellbeing and development as highlighted by a review from Mindell & Williamson .The principle objective of this study was to investigate if bedtime routines are associated with a diverse range of key indicators of child wellbeing and development. More specifically, the study investigated whether optimal bedtime routines are associated with (a) greater readiness for school, (b) better dental health and (c) higher executive function in preschool age children. These three areas of child health and wellbeing were selected due to their important associations with further child development, overall wellbeing, achievement and impact on quality of life. Moreover, prior research into bedtime routines heavily focused on quality of sleep as its primary objective with only a limited number of studies incorporating additional measurements of health, wellbeing and development. Additionally, an examination of possible determinants of bedtime routines formed the secondary objective of the study by exploring whether optimal routines are more likely in families where parents have (a) higher executive function and (b) positive parenting styles.One parent and one child from each of fifty (50) families took part in the study. Parents had a mean age of 35 years (SD = 5) and were, as expected in research involving families, predominantly female (78%). Most (70%) had no university-level education and were either part-time employed 19%) or stay at home parents (21%). Children had a mean age of 4 years (SD = 0.8 months) and were relatively evenly split by gender . Socio-demographic characteristics of the sample represented the overall demographic composition of the area where the study was conducted with 66% White, 18% Asian and 16% Black in terms of ethnicity. Finally regarding their socio-economic background, based on the Index of Multiple Deprivation (IMD) where higher quintiles represent higher deprivation, 10% of the sample came from the 2nd quintile, 22% from the 3rd, 26% from the 4th and 42% from the 5th quintile respectively. There were no refusals to participate in the study and no withdrawals throughout the duration of data collection. Additional file 9% or staDuring February to May 2017, participants were recruited in the study: (a) through an active study on General Dental Anaesthetic teeth extraction who had expressed interest in participating in future studies and (b) through General Dental Practices (GDPs). Two selection criteria were present during recruitment: (a) having children between the ages of 3 and 5 and (b) sufficient English literacy to provide informed consent and complete questionnaires and assessments. During recruitment, information leaflets for both adults and children were provided; parents completed consent forms while child assent was sought throughout the process in order to ensure the willingness of each child to participate in the study. Parents were the ones initially approached at GDPs resulting in researchers not being aware of each child’s attendance to regular dental appointments.Data collection took place between March and June 2017, while recruitment was underway, either in house visit, in the dental practices where the families were recruited or in a neutral venue. Two visits/meetings were necessary in order to complete the data collection with the first visit/meeting comprising of the parent-related assessment and the second meeting including the child-related assessments. In between the two visits/meetings, parents were sent a 5 nightlong interactive text questionnaire to assess the quality of each night’s bedtime routines. Each participating family received a total of £50 in shopping vouchers as compensation for their time.All available measures of bedtime routines utilise a retrospective design with many of them containing a long-list of questions with increase risk of recall bias. The present study, following Patient Public Involvement (PPI) work, opted for the development of an interactive text based survey for the assessment of bedtime routines.Focusing on the areas previously identified from the literature as being components of optimal bedtime routines, the interactive assessment focused on 5 target areas: a. consistency (determined as child going to bed within the space of an hour every night), b. tooth brushing, c. avoidance of snack/drinks before bed, d. avoidance of electronic devices before bed and e. book reading  . BSRA-3 Child dental health was objectively assessed through dmft  scores assigned either through examination of dental charts, history of extraction of carious teeth under general anaesthetic or by a registered dentist. Dmft scores are amongst the most commonly used methods in oral epidemiology for assessing dental caries prevalence and overall dental health. Higher dmft scores indicate poorer dental health.Executive function was assessed by two separate assessments. First, executive function for both adults and children was assessed using the National Institute of Health (NIH) Toolbox for the assessment of neurological and behavioural function (NIH-Toolbox) . All assPerceived executive functioning in day to day life was assessed using the Behavioural Rating Inventory of Executive Function (BRIEF) with versions focusing on adults (18+) (BRIEF-A) and preschool –5 (BRIEF) [The short-version of the Parenting Style and Dimensions Questionnaire (PSDQ)  was admiAll paper-based measurements  were scored following the official professional manuals of the developers. BRIEF-A/P uses T scores  that are transformations of the raw scale scores. BSRA-3 uses standard scores based on the age of the child and his/her raw score. Age-corrected scores  from the neuropsychological assessment (NIH-Toolbox) were automatically calculated. Based on the 0–5 scales used to score bedtime routines, families with scores between 0 and 2 were coded as having “suboptimal bedtime routines” while families with scores between 3 and 5 were coded as having “optimal bedtime routines”. All data were entered into SPSS version 22 .Bivariate correlations (Pearson’s r) were conducted between standardised metrics collected for the study  to ensure that, as with previous studies, these measurements present strong inter-correlations that will allow for subsequent analyses. Between groups comparisons (independent sample t-test) were conducted for optimal and sub-optimal bedtime routines while a Mann-Whitney U test was conducted to examine differences in dental health between children with optimal and suboptimal bedtime routines.p ≤ .001. Negative parenting including both authoritarian and permissive parenting styles was more common in households with suboptimal  (authoritarian) /  (permissive) than optimal  (authoritarian) / M = 1.9, SD = 0.54) (permissive) bedtime routines, t (48)= 6.50, p ≤ .001 for authoritarian and t (48)= 5.82, p = .003 for permissive parenting. Children presented as less ready for school with lower scores of school readiness in households with suboptimal  rather than optimal  bedtime routines, t (48)= − 12.15, p ≤ .001.Table p ≤ .001. Also, parents with suboptimal bedtime routines scored lower in the working memory task  than those with optimal routines , t (48)= − 10.47, p ≤ .001. Finally, lower scores of cognitive flexibility were observed in parents reporting suboptimal  than optimal  bedtime routines, t (48)= − 13.6, p ≤ .001. In the case of children, lower scores in the attention and inhibition task were present in suboptimal  than optimal  bedtime routines, t (48)= − 9.70, p ≤ .001. Also, children from households with suboptimal bedtime routines showed poorer performance in working memory  compared to those from households with optimal  bedtime routines, t (44)= − 8.51, p ≤ .001. Finally, children with suboptimal bedtime routines showed less cognitive flexibility  than those with optimal  bedtime routines, t (48)= − 13.1, p ≤ .001. Regarding self-reported executive functioning (BRIEF-A & BRIEF-P), both parents and children in households with suboptimal bedtime routines scored higher  (adults) /  (children) – indicating poorer executive function- compared with those in households with optimal bedtime routines  (adults) /  (children), t (48)= 8.42, p ≤ .001 for adults and t (48)= 6.92, p ≤ .001 for children.As for executive function, in the case of adults and regarding the assessments performed using the neuropsychological assessment, poorer performance on the inhibition and attention task was found in parents of households with suboptimal  than optimal  bedtime routines, t (48)= − 10.50, p = .011.The Mann-Whitney test indicated that children in families with optimal bedtime routines presented with better dental health, i.e. less decay and fewer missing or filled teeth (dmft = 0) (Mdn = 4) compared to children in families with suboptimal bedtime routines (dmft > 0) (Grand Mdn = 2), U = 85.5, p ≤ .001, the Global Executive Composite of BRIEF-P and working memory of the neuropsychological assessment, r (46)= − .575, p ≤ .001 and Global Executive Composite of BRIEF-P and cognitive flexibility of the neuropsychological assessment, r(50) = −.639, p ≤ .001. Also, in the case of adults, there was a strong negative significant correlation between the Global Executive Composite of BRIEF-A and inhibition and attention of the neuropsychological assessment, r(50) = −.654, p ≤ .001, the Global Executive Composite of BRIEF-A and working memory of the neuropsychological assessment, r(50) = − 636, p ≤ .001 and the Global Executive Composite of BRIEF-A and cognitive flexibility of the neuropsychological assessment, r(50) = −.656, p ≤ .001.Table p ≤ .001 for inhibition and attention, r (46)=.755, p ≤ .001 for working memory and r(50) = .795, p ≤ .001 for cognitive flexibility indicating that better executive function was related to greater readiness for school. Adults with better EF exhibited more positive parenting with authoritative parenting highly positively correlated with all executive function metrics for adults with r(50) = .664, p ≤ .001 for inhibition and attention, r(50) = .649, p ≤ .001 for working memory and r(50) = .705, p ≤ .001 for cognitive flexibility. Conversely, poor performance on executive function measurements was associated with more negative parenting practices (i.e. authoritarian and permissive parenting) with r(50) = −.608, p ≤ .001 for attention/inhibition, r(50) = −.593, p ≤ .001 for working memory and r(50) = −.627, p ≤ .001 for cognitive flexibility and r(50) = −.462, p ≤ .001 for attention/inhibition, r(50) = −.469, p ≤ .001 for working memory and r(50) = −.552, p ≤ .001 for cognitive flexibility for authoritarian and permissive parenting respectively. Finally, higher parent executive function scores were associated with higher child executive function scores across all metrics of executive function with r(50) = .783, p ≤ .001 for attention/inhibition, r(50) = .686, p = .001 for working memory and r(50) = .590, p ≤ .001 for cognitive flexibility.School readiness was significantly correlated with better executive function in children with r(50) = .819, The present study attempted to explore the effects of bedtime routines on child wellbeing and development and their association with parenting and executive function. Overall, results indicated the optimal routines were associated with better dental health, cognitive function and school readiness in children and that optimal routines were more likely to be present in households where parents were authoritative in style and had good executive function. Many of the findings from this study are unique while others follow existing observations from previous studies in the field.The between group comparisons based on the quality of bedtime routines  resulted in highly significant differences across all metrics associated with child wellbeing and child development. For school readiness the results of the present study echoed recommendations and findings from previous studies where children with suboptimal routines, including absence of activities like book sharing and book reading, presented with lower school readiness a metric closely associated with subsequent school performance and academic achievement , 9, 33. Finally, with regards to the observed differences in executive function between children with optimal and suboptimal bedtime routines, with the former presenting better scores across all metrics of executive function, this finding is new. Previous studies on the development and manifestation of executive function focused primarily on brain development and cortical changes with factors such as deprivation, environmental factors, parenting and sleep , 35–38. Between group comparisons based on the quality of bedtime routines showed significant differences in parenting styles and parent executive function between parents with suboptimal bedtime routines as compared to those with optimal bedtime routines. Parents with optimal bedtime routines systematically scored better on executive function tasks including inhibition/attention, working memory and cognitive flexibility and their parenting style was also consistently more authoritative as compared to parents with suboptimal bedtime routines. The differences in executive function between parents with optimal and suboptimal routines can be the result of the previously known relationship between executive functioning and parenting styles , 43 wherSince this is the first time that different parenting styles and parent executive function are examined in relation to their effect on the quality of bedtime routines and that the present data are cross sectional, no firm conclusions can be made. It is important to further examine the stability of the observed, significant, differences in parenting styles and executive function with regards to optimal and suboptimal routines with the inclusion of other important parameters. A series of questions arise from the findings of this study and future studies will need to better understand the very nature of bedtime routines and how they are shaped. Are bedtime routines a direct product of parenting styles and practices with parent executive function serving as a possible mediator of that relationship or vice versa? If bedtime routines change, given that bedtime routines are behaviours repeated over a period of time, will the changes affect parenting and parent executive function? Finally, with changes in parenting styles and practices and even improvements in executive function, despite its inherit decline over time due to aging, will changes in bedtime routines occur?Consistently with existing literature in the field, school readiness scores were strongly positively associated with better executive function scores in the cognitive assessment and strongly negatively associated with the parent-completed inventory. The three aspects of executive function  assessed during the study are considered fundamental for school readiness . GreaterAt the moment, mixed and relatively limited results exist with regards to early childhood executive functioning and its association with parental executive function with some studies reporting strong associations that faded over time as the child grew . In our Finally, and in full accordance with previous studies in the field, positive parenting (i.e. an authoritative parenting style) was strongly positively associated with higher executive function. Moreover, negative parenting styles (i.e. authoritarian and permissive) were significantly negatively correlated with executive functioning showing that the parents with worse executive function were more inclined to manifest authoritarian and/or permissive parenting styles and vice versa. The importance of executive function on parenting styles and practices is not difficult to understand when taking into consideration different aspects associated with both elements.Despite the significant, and in areas unique, findings of the present study some limitations exist. The main limitation of the study is its cross-sectional design that did not account for all possible confounders resulting in constrains regarding our understanding of the potentially causal relationships between the variables measured. Another limitation is the lack of information on potentially important metrics such as: child’s psychosocial development, parental psychological wellbeing and child’s quality of sleep that can have direct and/or indirect effects on observed associations. With regards to the latter, quality of sleep is associated with a number of social-emotional, cognitive, physical health and family functioning domains therefore future studies will need to account for it in order to be able to present an inclusive and holistic picture of all possible associations.The main objective of the present study was to explore if bedtime routines affect child wellbeing as measured by dental health, school readiness and executive function. Additionally, the role of parenting and parental executive function as possible determinants of the quality of bedtime routines was examined. Following the analyses, all available findings point to the importance of routines with regards to child wellbeing with significant differences in key metrics between children who have optimal and suboptimal bedtime routines. Moreover, positive parenting and better executive function were both significantly associated with optimal routines allowing for a better understanding in the complex nature of mechanisms involved in the establishment and manifestation of bedtime routines. The present study showed important associations of bedtime routines with a variety of health-related metrics involved in child wellbeing and their relationship with parent-related factors. Despite limitations, the results of this study are unique in the literature, showing the need for more in-depth exploration of bedtime routines given their potentially crucial role in child wellbeing and their association with parent-related factors.Additional file 1:Descriptive statistics of sample. Sample characteristics including gender, age, educational level, Index of Multiple Deprivation scores, ethnicity and employment status for all participants. (DOCX 20 kb)


Charge transport in organic semiconductors is strongly dependent on the molecular orientation and packing, such that manipulation of this molecular packing is a proven technique for enhancing the charge mobility in organic transistors. However, quantitative measurements of molecular orientation in micrometre-scale structures are experimentally challenging. Several research groups have suggested polarised Raman spectroscopy as a suitable technique for these measurements and have been able to partially characterise molecular orientations using one or two orientation parameters. Here we demonstrate a new approach that allows quantitative measurements of molecular orientations in terms of three parameters, offering the complete characterisation of a three-dimensional orientation. We apply this new method to organic semiconductor molecules in a single crystal field-effect transistor in order to correlate the measured orientation with charge carrier mobility measurements. This approach offers the opportunity for micrometre resolution (diffraction limited) spatial mapping of molecular orientation using bench-top apparatus, enabling a rational approach towards controlling this orientation to achieve optimum device performance. Organic semiconductors have attracted interest as a promising alternative to traditional inorganic semiconductors for low cost, light-weight, flexible electronic devices. Their use in various applications has been demonstrated, including light-emitting diodes, photovoltaics, biosensors, and field-effect transistors123in situ studies6912In this study, we consider specifically the measurement of molecular orientation, which has a profound impact on charge transport within an organic molecular crystal and determines the charge carrier mobility in an electronic device678910et al.14161718192021et al. were able to use polarised Raman spectroscopy to characterise the orientation of pentacene molecules in terms of two orientation angles, whereas James et al. made a qualitative comparison based on a single orientation angle17The theoretical basis of polarised Raman spectroscopy and its relationship with molecular orientation are well-known, and helpfully reviewed by Tanaka j, is given by:In the general case, the intensity of polarised Raman scattering from a molecule for a particular vibrational mode, Is is the intensity of Raman scattering, Rj is the Raman tensor of mode j for the molecule, ei is the electric field vector of the light incident on the molecule (controlled by a polariser), such that the product Rjei represents the electric field vector of the Raman scattered light, and es is the electric field vector sampled by the instrument . −1 and 1576 cm−1, corresponding to collective stretching modes of the acene core of the pentacene molecule, and the relative intensities of these modes show a strong dependence on the molecular orientation arising from the different forms of the Raman tensors for these modes142h point group and the corresponding peaks at 1371 cm−1 and 1596 cm−1 are assigned to Ag and B3g modes, respectivelywhere a, b, c, and d are unknown values. Note that the Raman tensor for the B3g mode differs from the usual form for a B3g tensor due to the non-standard molecular orientation used here to facilitate comparison with TIPS pentacene. The addition of TIPS-groups breaks the symmetry of the pentacene molecule such that we expect the Raman tensors to adopt more complex forms. We therefore use density functional theory (DFT) calculations on the TIPS pentacene molecule to optimise the molecular geometry and simulate the Raman scattering . The calculated spectrum is compared with the measured case in −1 and 1576 cm−1 peaks and strong simulated modes enables us to match the measured modes with calculated Raman tensors, whose normalised values are:where In fact, several elements in these normalised Raman tensors for TIPS pentacene are much less than unity, such that the overall form is similar to the theoretical tensors for pentacene. This is in line with the expectation that the Raman activity of TIPS pentacene is dominated by the conjugated pentacene core, and that the solubilising TIPS groups have little impact on the molecular optoelectronic properties. It is important to recognise that these Raman tensors are valid only in the non-resonant regime and so 785 nm excitation is used for experimental measurements since the sample does not absorb light at this wavelength.x, y, z axes). The Raman tensors (R′) are also calculated in this molecular frame. The laboratory frame  resulting in a difference between the linear polarisation direction of the laser beam after the half-wave plate and when it reaches the sample. The polarisation of the scattered light is similarly affected. These effects can be adequately accommodated by introducing the correction factors, k and m, into ei and es, which makes the reasonable assumptions that these instrumental factors are symmetric with respect to the The objective of the measurement is to elucidate the rotation that must be applied to the molecular frame in order to bring the simulated molecule into the same orientation as the real molecules in the laboratory frame. This is achieved by measuring the polarisation dependence of the Raman scattering intensity. To do this, we vary the polarisation direction of the excitation laser, k and m, we use a silicon wafer reference sample and measure the integrated intensity of the 520 cm−1 peak as a function of θA and θP, the results of which are plotted in In order to obtain values for −1 peak comprises three degenerate modes with the tensors:For the silicon reference sample, the 520 cmx = [100], y = [010], z = [001], and where f is some unknown valuez-axis is required to bring the tensors in k = m = 1, the least squares difference between the measured and simulated values for a full matrix of θA and θP values over the measured range is minimised using a MATLAB script to find that the best fit is achieved when k = 0.829 and m = 0.747. The resulting simulated data are shown in in the system with crystal coordinates: θA and θP values. However, we note that there are some minor discrepancies, particularly in the relative intensities, which are illustrated by the comparison of profiles in θA. Considering silicon to be a good reference material, we attribute the imperfect fitting to the incomplete representation of instrument properties in the model, specifically, the depolarisation effects mentioned above. The impact of these factors on the reliability of the fitting is minimised by collecting data over an extended range of θA and θP values .The fitting of the experimental data with the simulated results for the silicon reference sample demonstrates that the model is able to reproduce the main features of the experiment, with the maxima and minima close to the measured k and m evaluated from the silicon reference sample, we apply the technique to a single crystal of TIPS pentacene, where the molecular orientation is unknown. An image of the sample is given in Using the values for −1 and 1576 cm−1 modes. The measurement is also performed with the sample in two different orientations by applying tilt angles to the sample of 0° and 30° around the −1 and 1576 cm−1 peaks for both tilt angles are shown in In this work we assume an idealised single crystal of TIPS pentacene where all the molecules share a single orientation: in reality we expect some degree of disorder resulting in a distribution of molecular orientations within the sample. In order to obtain sufficient polarised Raman data to assign the measured results to a single molecular orientation, we extract the integrated intensities of both the 1374 cmRj from ψ, θ and φ, which rotate the Raman tensors to give the best fit of the simulation to the experimental data. ψ = 68.3°, θ = 118.5°, φ = −124.6° are found to describe the rotation of the TIPS pentacene molecule from the molecular frame into the same orientation as the sample molecules in the laboratory frame. r′,  into the laboratory frame, r, using As before, a simulation of the polarised Raman scattering measurement is carried out, this time using the calculated Raman tensors given in Comparing the molecular orientation derived from this method with other published reports reveals a broad agreement. In particular, we note that our solution shows the TIPS groups tilted closest to the substrate, and the shape of the crystal as a whole, shown in 261328622The charge transport in TIPS pentacene crystals is anisotropic since the charge transfer is mediated through overlapping π-orbitals of the acene core and the molecules adopt a ‘brick-wall’ packing motif10This study has demonstrated the use of polarised Raman spectroscopy as a probe for molecular orientation, taking the example of a TIPS pentacene single crystal transistor as a model system. Importantly, we have been able to express the solution quantitatively using Euler coordinates to fully describe the orientation of the molecule with respect to the substrate. This work opens the way for meaningful and unambiguous measurements of molecular orientation using a non-destructive, non-invasive, bench-top technique capable of offering diffraction-limited lateral resolution. Further refinement of this method might be achieved by incorporating additional factors into the simulation to account for instrumental depolarisation effects more explicitly, or with additional parameters to describe the orientational disorder present in the sample. In the example considered here, the molecular orientation of TIPS pentacene in the small single crystal is found to differ slightly from that reported for larger crystals. Subtle modifications to the bulk molecular packing motif in thin films have been found to have dramatic impacts on the charge transport properties of organic semiconductors, and so polarised Raman spectroscopy offers a particularly appropriate tool for probing molecular orientations in thin film or microstructured devices. Combining this technique with methods to control the molecular orientation provides a way to intelligently tune the fabrication conditions for optimised performance of organic molecular electronics.2/Si substrate using conventional photolithography2 (purchased from Si-Mat). S1813 positive photoresist was spin-coated at 4000 rpm, followed by baking at 100 °C for 1 min. The photoresist was patterned with a laser writer (Durham magneto-optics) at 405 nm with a dose of 150 mJ/cm2. The sample was developed with MF319 developer for 1 min and rinsed with deionised H2O. Subsequently the metal layers were evaporated; 5 nm of Cr (rate 0.3 Å/s) followed by 35 nm of Au (rate 0.5 Å/s). Lift-off was performed by sonicating in acetone and further cleaning by sonicating in HPLC grade acetone and isopropanol. For the single crystals, 2 mg of TIPS-pentacene, synthesised with previously described techniquesA circular array of Au electrodes was patterned on top of a SiOThe lateral dimensions of the crystal were measured using optical microscopy, and the vertical thickness measured by atomic force microscopy using an MFP-3D (Asylum Research) instrument in tapping mode. Line profiles across the crystal edge were measured in three places giving values of 221, 220, and 210 nm as approximations for the crystal thickness.P, is related to θP and the resulting orientation of the incident polarisation vector, ei, using: A, relates to θA and the orientation of the sampled polarisation vector, es, using: P < 190 in 1.5° steps, and 0 < A < 200 in 3° steps with a 1 s acquisition time at each point. The laser power at the sample was ~10 mW for TIPS pentacene samples and ~100 mW for the silicon reference. No change in the Raman spectrum of pentacene was observed after multiple excitations indicating that no significant sample degradation occurred during the measurement. A 50× long working distance objective was used throughout to accommodate the tilting of the sample up to 30° out of plane, the numerical aperture of this objective (0.45) is sufficiently low enough that the depolarisation effect introduced by focusing the laser beam is not expected to be problematicRaman spectra were measured using a Horiba HR800 Evolution Labram Spectrometer. A 785 nm excitation laser was used with a half-wave plate polariser and an analyser for polarised measurements. The angular position of the polariser, DFT calculations were carried out using the GAUSSIAN09 software package to optimise the geometry of the TIPS pentacene molecule and then perform frequency analysis34363738For the electrical characterisation, a Keithley 4200 semiconductor characterisation system was used. Each transistor channel was defined by the fixed distance between the electrodes (L = 20 μm) and the width, W, of the crystal that was crossing it (W(60° device) = 70 μm, W(30° device) = 40 μm, W(0° device) = 60 μm) - see How to cite this article: Wood, S. et al. Precise Characterisation of Molecular Orientation in a Single Crystal Field-Effect Transistor Using Polarised Raman Spectroscopy. Sci. Rep. 6, 33057; doi: 10.1038/srep33057 (2016).


The dopamine hypothesis of psychosis suggests that dopamine abnormalities are present in psychotic illness, irrespective of diagnostic class. Meta-analyses of Positron Emission Tomography (PET) studies of the dopamine system have shown elevated dopamine synthesis capacity in schizophrenia, though there is a dearth of studies examining this in other psychotic disorders.We therefore sought to answer the question of whether abnormalities of the presynaptic dopamine system are seen in bipolar psychosis, how this compared to schizophrenia, and whether positive psychotic symptoms were associated with dopamine synthesis capacity, irrespective of diagnostic class.Cross-sectional, case-control 18F-DOPA Positron Emission Tomography (PET) study in people with first episode bipolar psychosis, schizophrenia and control subjects. Clinical measures included the Positive and Negative Syndrome Scale (PANSS), Young Mania Rating Scale and Global Assessment of Functioning (GAF).Mean (SD) ages were 23.6 (3.6) years in 22 people with bipolar psychosis , 26.3 (4.4) years in 16 people with schizophrenia , and 24.5 (4.5) years in controls . There was a significant group difference in striatal dopamine synthesis capacity (Kicer) , post-hoc tests indicating Kicer was significantly elevated in both the bipolar group  and the schizophrenia group  compared with controls . Kicer was positively correlated with positive psychotic symptom severity in the combined bipolar and schizophrenia sample currently experiencing psychosis, explaining 27% of the variance in symptom severity .This is the first study to examine the presynaptic dopamine system in bipolar psychosis, finding an elevation compared to controls, equivalent to schizophrenia, from first onset of illness. A relationship was found between dopamine synthesis capacity and positive psychotic symptoms, across diagnostic classes, indicating a transdiagnostic role for dopamine synthesis capacity and positive psychotic symptoms.