Atomically sharp heterojunctions in lateral two-dimensional heterostructures can provide the narrowest one-dimensional functionalities driven by unusual interfacial electronic states. For instance, the highly controlled growth of patchworks of graphene and hexagonal boron nitride (h-BN) would be a potential platform to explore unknown electronic, thermal, spin or optoelectronic property. However, to date, the possible emergence of physical properties and functionalities monitored by the interfaces between metallic graphene and insulating h-BN remains largely unexplored. Here, we demonstrate a blue emitting atomic-resolved heterojunction between graphene and h-BN. Such emission is tentatively attributed to localized energy states formed at the disordered boundaries of h-BN and graphene. The weak blue emission at the heterojunctions in simple in-plane heterostructures of h-BN and graphene can be enhanced by increasing the density of the interface in graphene quantum dots array embedded in the h-BN monolayer. This work suggests that the narrowest, atomically resolved heterojunctions of in-plane two-dimensional heterostructures provides a future playground for optoelectronics. Here, the authors explore the blue photoluminescence signal arising from the interface between graphene and h-BN arranged in in-plane heterostructures, and fabricate a blue light emitting device utilizing the heterojunction as the emitting layer. These examples illustrate the emergence of quantum phenomena arising from differences in the properties of two types of 2D materials divided by a heterojunction. However, it has been rarely reported that 1D heterojunctions themselves show unknown properties and functionality.In-plane two-dimensional (2D) heterostructures serve as a perfect platform to explore one-dimensional (1D) functionalities because of their atomically sharp (resolved) heterojunctions. Because the edge contacts offer easier band offset tuning, lateral heterostructures-based heterojunctions have led to improved performance for P-N rectifying diode6. Thus far, most of the theoretical calculations predicted that the zigzag and armchair interfaces between graphene and h-BN have half‐metallic and semiconducting properties9. In addition, some experimental attempts using scanning tunneling microscopy have identified a clear sharp peak close to zero bias, which was ascribed to the localized interfacial states at the zigzag edges connecting graphene with h-BN11. Park et al. observed an enhanced local density of states at zigzag interfaces composed of several segments forming 120° angles and found distinct states with energy levels of −0.6 eV (or +0.6 eV) at C–B (or −N) terminated boundaries12. Finally, disordered interfaces between h-BN and graphene, which would be common in lateral heterostructures fabricated by patterned regrowth14, have been observed experimentally, but the presence and role of localized energy states occurring at these interfaces are unknown.Interestingly, a recent theoretical paper reported the formation of localized density of states (LDOS) at the random, disordered interface of hexagonal boron nitride (h-BN) and grapheneHere, we demonstrate luminescent, atomic-resolved heterojunctions connecting graphene and h-BN domains in 2D in-plane heterostructures. Blue-emitting photoluminescence (PL) at 410 nm wavelength from 1D heterojunctions of h-BN and graphene was observed, which supposedly originates from the localized energy states at the disordered heterojunction between h-BN and graphene (G/h-BN junction). The weak blue emission at the 1D heterojunctions in a simple in-plane heterostructure of h-BN and graphene can be enhanced by increasing the amount of interface through embedding a graphene quantum dot array in a h-BN monolayer (GQD/h-BN in-plane heterostructures). Finally, we stacked four GQD/h-BN films by placing h-BN intercalation layer between each film to improve the emission.15. Figure 2/Si substrate. The red and blue lines in Fig. 2g peak), respectively. Notably, the Raman mapping image  clearly differentiates the graphene from the h-BN regions of the heterostructures. Figure 12. Since the grown in-plane heterostructures were fabricated in sequential growth, they resulted in epitaxial hetero-junctions between graphene and h-BN with well-defined zigzag edges. However, in our work, we fabricate heterostructures by using conversion reactions of h-BN to graphene and hence expect that a different atomic arrangement of the heterojunctions emerges at boundaries.First, we examine simple in-plane graphene/h-BN heterostructures to confirm that the desired heterostructures has formedage Fig.  in the 216  is ~6.3 times longer than that for the G/h-BN sample (0.0013 nm−1), which is comparable to the ratio of PL intensities of the two samples.In order to increase the amount of interface per unit area for improved PL intensity, we prepare in-plane heterostructures of graphene quantum dots in a h-BN monolayer by a spatially controlled conversion on Pt nanoparticles (Pt NPs) prepared with the aid of self-patterning diblock copolymer micelles2/Si substrate. However, carbon doping in the h-BN monolayer during the conversion reaction might be the origin. To check, we achieved the conversion of h-BN on a SiO2/Si substrate without the Pt NP array under the same conditions . The PL emission was not observed in the sample . Supplementary Fig. 2 substrate. No PL emission was observed for this sample  hydrogenated edges24 in large nanoholes, (iii) atomic defects like NBVN (nitrogen substitution at boron site + nitrogen vacancy)26 and carbon substitution at nitrogen sites27 in h-BN, and (iv) point defects in WSe232. Also, note that a slight difference of emission wavelength between theoretical and experimental results is due to limitations of a tight-binding Hamiltonian (TBH) calculation that cannot cover all experimental parameters such as electron-electron interaction effects or Coulomb screening caused by the generated excitons. To support above localized energy states at G/h-BN junctions, we need to show atomic structures at the disordered G/h-BN junctions. Thus, we measured annular dark-field scanning tunneling electron microcopy (ADF-STEM) images and electron energy loss spectroscopy (EELS) maps at the boundary of h-BN and graphene as shown in Fig. We confirmed that the PL emission is not due to the intrinsic properties in the GQDs and nano-sized holes of h-BN by the absence of PL in control experiments. Actually, it would be difficult to attribute the PL definitely to the 1D graphene/h-BN heterojunction because of the large area probed with a confocal Raman system. PL from surrounding areas is also measured. Focusing the laser only on the atomic-resolved interface is very challenging in the current PL technique. Based on this, it is difficult to conclusively attribute the observed PL emission to the 1D interface. Alternatively, to elucidate the origin of PL, we theoretically characterized the local energy states due to the disordered G/h-BN junction. First, we set-up an in-plane graphene/h-BN heterostructures lattice using molecular dynamics, in which there is an orientation mismatch between the graphene and h-BN like in a polycrystalline sample. Due to the mismatch, the G/h-BN junction  is disordered; i.e., it is formed by a variety of non-hexagonal rings. Second, we set-up a tight-binding Hamiltonian to describe the electronic properties (see details in the Supplementary Information). We calculate the local density of states projected over all the sites at the interface by using the Kernel Polynomial Method eV Fig. . The ene34. However, utilizing h-BN intercalation layers substantially improved the PL intensity since the charges generated on the GQD/h-BN film were not transported to GQDs in adjacent layers, blocked by the h-BN charge barrier  single crystal using ammonia borane as a precursor by CVD method35. The resulting complex, h-BN/Pt(111), was then loaded into the center of a vacuum quartz tube placed in a furnace. The tube was pumped down to 0.21 torr with pure argon gas (50 sccm), and then heated to 1000 °C at a steady rate for over 40 min. The reaction was initiated with a flow of methane (5 sccm) and argon (50 sccm) gases to produce the in-plane heterostructures with a shorter 10 min reaction time.The in-plane heterostructure of graphene and h-BN was prepared by a catalytic conversion reaction of h-BN to graphene on a Pt metal substrate2 substrate was prepared using self-patterning diblock copolymer micelles36. A single-layer of polystyrene-block-poly(4-vinylpyridine) (PS-P4VP) micelles with H2PtCl6, a precursor of Pt NPs, in their cores was spin-coated on the SiO2 substrate. To fabricate the Pt NP array, the micellar film on the SiO2 was annealed at 400 °C for 30 min in air. The h-BN grown on Pt substrate were transferred onto the Pt NPs/SiO2 substrate using a wet-transfer method . Then, the sample was loaded into the center of a vacuum quartz tube in a furnace for the conversion reaction. The tube was pumped down to 0.21 Torr with pure Argon gas (50 sccm). Then the furnace was heated to 950 °C in 40 min. When the reaction started, methane gas (5 sccm) with Argon (50 sccm) was flown as the source for graphene growth. During the reaction, the h-BN region on the Pt NPs was converted to graphene, and after 10 min of growth a uniform GQD array embedded in the h-BN film was obtained15.A Pt nanoparticle (NP) array on a SiO2 was transferred onto other substrates via a wet-transfer method using HF and an aqua regia solution. First, polystyrene (PS) was spin-coated on the sample, and it was immersed in a HF solution (5% in DI water) to remove the SiO2 layer. Then, the floating PS film was transferred to the aqua regia solution (3:1 mixture of hydrochloric acid and nitric acid) to remove the Pt NPs. Finally, the film was transferred onto the desired substrate and the PS film was removed with toluene to obtain a GQD/h-BN film on the substrate.The GQD/h-BN film on Pt NPs/SiOScanning electron microscopy  and atomic force microscopy  were used to determine the surface morphology of the samples. PL and Raman spectra were measured using a micro Raman spectroscope  with 266-nm and 532-nm lasers, respectively. The h-BN/graphene heterostructure sample was transferred to a microporous silicon nitride membrane TEM grid  for scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). JEOL JEM-2100F electron microscope equipped with JEOL Delta spherical aberration correctors and Gatan Quantum electron spectrometer was operated at an electron accelerating voltage of 60 kV. EELS chemical maps of boron, carbon and nitrogen were obtained by measuring their K edge signals at each point of a scanned area.n: 25,000–50,000) was deposited onto the PEDOT:PSS layer by spin-coating (1500 rpm for 40 s) using a PVK solution (15 mg/mL in chlorobenzene) and annealed at 120 °C for 20 min. The fabricated GQD/h-BN was transferred onto the top of the PVK by using the wet-transfer method. The samples with PVK or GQD/h-BN were loaded into a thermal evaporator  for deposition of the TPBI and LiF/Al under high vacuum (~10−6 Torr). The current density-luminance-voltage characteristics of the fabricated LED devices were evaluated using a Keithley 2400 source meter and a calibrated photodiode . The EL spectra were measured by a fiber-optic spectrometer . All measurement processes were performed in an inert environment.A GQD-based LED device consists of the following layers (of corresponding thickness): indium tin oxide (ITO) (150 nm), poly:poly(styrene sulfonate) (PEDOT:PSS) (40 nm), poly(N-vinylcarbazole) (PVK) (20 nm), an emitting layer, 2,2′,2″--tris(1-phenyl-1-H-benzimidazole) (TPBI) (60 nm), lithium fluoride (LiF) (1 nm), and Al (100 nm). A glass substrate pre-deposited with a 150 nm thick ITO electrode  was cleaned in an ultrasonic bath using de-ionized (DI) water, acetone, and isopropyl alcohol, and then it was treated with air plasma using a plasma cleaner . The PEDOT:PSS (CLEVIOS P VP AI 4083) was deposited by spin-coating (3000 rpm for 40 s) and annealed at 150 °C for 30 min. Then, the PVK (MSupplementary InformationPeer Review File


Among them, we use concentrical circle structure to achieve broadband absorption, and adjust graphene’s Fermi level to achieve tunable absorption. In addition, we propose an encoding method that can achieve flexible control of the absorption response at the terahertz frequency based on the external voltage applied on the graphene membrane, thereby having a programmable function. We also use COMSOL to simulate the electric field distribution diagram to explain the underlying physical mechanism. The programmable broadband adjustable absorber proposed in this paper has potential application prospects in the fields of optical equipment, information transmission, digital coding and artificial intelligence (AI).A method of coding patterns is proposed to achieve flexible control of absorption response at terahertz frequencies. The designed absorber consists of an Au-graphene pattern layer, a SiO Over the past two decades, due to their designability and feasibility, metamaterials have attracted wide attention from experts in various fields, such as stealth ,2, radia2  and grap2 ,19. NowaIn 2014, Professor Cui Tiejun’s research team proposed a digitally encoded metasurface , low-scaGraphene, the thinnest two-dimensional material found, exhibits metallic properties when it meets particular conditions. Due to its strong interaction with terahertz waves, graphene can be a prospective candidate for perfect absorption at terahertz waves. More importantly, a significant feature of graphene is that the Fermi level can be adjusted by applying a gate voltage. The change of Fermi level will cause the dielectric properties of graphene to be changed, and then achieve the purpose of tuning absorption. Therefore, graphene is a good candidate for tunable absorbers.2 layer and a metal reflective layer. Based on this structure, we mainly design two absorbers. One is that the pattern layer is an Au-ring with two symmetrical graphene-notches. When the bias voltage external to the graphene is 0 V, the absorption is an ultra-wideband absorption with 3.8 THz whose value is greater than 80% from 1.9 THz to 5.7 THz. When the bias voltage changes, we can achieve adjustable absorption. In addition, we code according to voltage conversion, and realize a programmable 22-element absorber. The other is that the pattern layer is two Au-rings with four graphene-notches. Similar to the first work, when the bias voltage external to the graphene is 0 V, the absorption is an ultra-wideband absorption with 3.74 THz whose value is greater than 89% from 1.95 THz to 5.69 THz. Furthermore, we encode according to voltage changes, and realize a programmable 24-element absorber. Different from phase encoding, our work is to use grapheme’s good controllability to realize the regulation of spectral characteristics, and use this as a method of information encoding.In 2018, Meng reported a double-notch metal ring absorber, which achieved a broadband absorption of 3.7 THz . In this2 having a dielectric constant of The metamaterial absorbers we proposed are composed of an Au-graphene pattern layer, a dielectric layer and a metal reflective layer, as shown in The conductivity of graphene is provided by Kubo’s equation, which is determined by both intra-band and inter-band transition :(1)σg=σiIn the terahertz band, the conductivity of graphene is mainly provided by the intra-band transport of carriers, while the inter-band transport is restrained. At this time, the calculation equation of the conductivity of graphene is simplified:The dielectric constant of graphene is expressed as:Here, The Fermi level of graphene is determined by the carrier concentration and is given by the Equation (6):Here, Here, It can also be seen from x and y directions are set as the Floquet periodic boundary, and the z direction is set as the perfect matching layer (PML). With normal incidence, the reflectance Performance simulations of the metamaterial absorbers are demonstrated using the full-wave electromagnetic simulation software COMSOL Multiphysics 5.4 which based on finite element method. In the simulation, a unit cell in the periodic structure is used as the calculation object, and the We first calculate the absorption performance of the double notch single ring absorber. When the Fermi level of graphene is 0 eV, the simulated absorption curves of metamaterial absorbers with different parameters are shown in In the case of 2 patterns can be obtained by this coding method. Because the unit cells are symmetrical about the diagonal line, the patterns corresponding to the two coding sequences “01” and “10” have the same geometric information.We introduce two coding numbers “0” and “1”, which correspond to the two states of graphene controlled by zero voltage and non-zero voltage, respectively, and independently control the switching states at the two gaps in the unit cell. According to the definition above, the patterns are sequenced with a set of binary coding, where the first number corresponds to the gap in the lower left corner and the second number corresponds to the gap in the upper right corner, encoding in the order indicated by the red clips in the After coding the patterns, we calculate the relationship between the absorption spectrum and Fermi level under different patterns, as shown in Afterwards, we set the Fermi level of graphene to which non-zero voltage is applied to 0.3 eV uniformly, and compare the four coding patterns’ absorption curves in Each code has its own maximum absorption efficiency. Therefore, we can distinguish coding patterns based on the maximum absorption. Adjusting the Fermi level of graphene not only affects the absorption rate, but also changes the absorption bandwidth. Compared with the narrowband absorber, the bandwidth of the broadband absorber has a larger fluctuation range. This helps us to distinguish tuning codes based on the difference in absorption bandwidth. In order to reflect the relationship between the absorption bandwidth and the encoding, we calculate the absorption bandwidth of the encoded absorption spectrum appearing in In addition, we calculate the absorption performance of the four-notch double ring absorber. Similarly, we introduce two coding numbers “0” and “1”, which correspond to the two states of graphene controlled by zero voltage and non-zero voltage, respectively, and control the switching states at four gaps in unit cells. According to the definition above, the pattern is sequenced by a set of four digits. The first digit to the last digit of the array, respectively, correspond to the voltage application of the four gaps in the order from bottom left to top right, as shown by the red arrow in 4 patterns can be obtained by this encoding method. Because the unit cell is symmetrical about the diagonal, there are six sets of coding patterns with the same geometric information, in fact there are only 10 different patterns. After coding the modes, we calculate the absorption spectra of these 16 codes, as shown in Since there are two options of “0” and “1” at each gap, 2In order to explain the absorption mechanism of the device, the electric field diagrams of the four absorption peaks under the “0000” structure were simulated, as shown in Following, the graphenes labeled “0” are controlled by zero voltage and the Fermi level of graphenes labeled “1” are uniformly adjusted to 0.5 eV, drawing the absorption spectrum in the In addition to the method of distinguishing codes introduced above, we can also distinguish codes based on absorption bandwidth. We calculate the absorption bandwidth of the coded absorption spectrum appearing in It can be seen that each tuning code corresponds to a different absorption spectrum (different absorption and different bandwidth). Therefore, the transmission and exchange of information can be realized by using electromagnetic waves as the carrier and digital coding and spectrum as the conversion interface.2-element absorber. After that, we add a gap ring. When the Fermi energy level of graphene is all 0 eV, ultra-wideband absorption of 3.74 THz is achieved, and the absorption rate exceeds 89%. The Fermi level of graphene is then adjusted from 0.1 eV to 0.7 eV to achieve adjustable absorption. The voltage applied to graphene is then used to encode at four locations in the structure, and a 24-element programmable absorber is implemented, which expand the encoding range. Our design is not only useful for broadband transmission and tuning signals, but also has programming capabilities. It is a combination of electromagnetic artificial materials and information science, which has important reference value for promoting intelligent devices and intelligent operations.In conclusion, we propose an encoding method to achieve flexible control of the absorption response at terahertz frequencies. For the terahertz band, an Au-graphene double notch single ring absorber is designed. Utilizing the principle of overlapping absorption peaks, ultra-wideband absorption of 3.8 THz can be achieved when the Fermi energy level of graphene is all 0 eV, and the absorption rate exceeds 80%. The Fermi level of graphene is then adjusted from 0.1 eV to 0.5 eV to achieve adjustable absorption. More importantly, we use the voltage of the two graphenes in the structure to encode, thus achieving a programmable 2


Questions about a text or an image that cannot be answered raise distinctive issues for an AI. This note discusses the problem of unanswerable questions in VQA , in QA , and in AI generally. The paper under discussion -based AI systems. In particular, Kafle, Shrestha, and Kanan write:Human beings can provide explanations, point to evidence, and convey confidence in their predictions. They also have the ability to say “I do not know” when the information provided is insufficient. However, almost none of the existing V&L algorithms are equipped with these abilities, making their models highly uninterpretable and unreliable.In VQA [visual question answering], algorithms provide high-confidence answers even when the question is non-sensical for a given image, e.g., “What color is the horse?” for an image that does not contain a horse can yield “brown” with a very high confidence.There has been a flurry of recent papers addressing the issue of unanswerable questions, both in visual question answering (VQA) and in text-based question answering (QA). As far as can be judged from citations, these two directions of research have been largely independent; that is, the VQA papers rarely cite QA research and vice versa. This note discusses the problem of unanswerable questions in VQA (section 1) and in QA (section 2) and compares them (section 3); they have some commonalities and many important differences. Section 4 briefly discusses some related work from knowledge-based AI. Section 5 discusses the problem of unsolvable problems and unanswerable questions in AI generally. Section 6 discusses why it is important for AI systems to deal with unanswerable questions.always output an answer, even if the question is unanswerable, because in every example in its training set, the proper response was to output an answer. Researchers interested in detecting irrelevant and unanswerable questions have therefore had to add these deliberately to their datasets.In the last few years many VQA datasets have been created in the computer vision research community  is visually similar to I+; (b) violates one aspect of the premise; e.g., an image showing dry ground. The two pairs 〈I+, Q〉 and 〈I−, Q〉 are then added to the database; the discrimination that the first is answerable and the second is unanswerable is generally quite challenging for VQA systems . For instance, looking at the picture of the picnic in Unanswerable questions in VQA can be categorized in terms of the reason that they are unanswerable  indicated in the photo, to a viewer with the appropriate general knowledge:What is the material of the white rug with the black stripes? In what decade was the photo taken?V.6. Information of a kind that is indicated in some photos but doesn't happen to be in this photo:What are the people eating for lunch? Who is the youngest person at the picnic?V.7. Information that can rarely be indicated in any photo:Does the woman in the center have perfect pitch? What is the conversation about?V.8. Questions with a false premise:What color is the horse? Which woman is punching the man? What colors are the boots?V.9. Low-quality image: As mentioned, these are common in VizWiz, though essentially non-existent in datasets such as VQA.V.10. Completely irrelevant:What is the capital of Alaska?V.11. Not a question:Hello, this is another try. These exist in some number in VizWiz.V.12. Nonsense : What did the rug eat for lunch? Will the shadows set fire to the tree?V.13. Gibberish:What color are the margialigoelntest farbitlangefs?Some of the questions that I have put in categories V.1-V.4 and V.6 may well be in category V.5; that is, a sufficiently knowledgeable or perceptive viewer could answer them from the photo, though I cannot. There may well be people who can tell whether the woman in the center is wearing lipstick, who can identify the tree at the top just from the trunk, or who can judge accurately the distance from the tree to the pole, or who can tell whether the woman in brown is barefoot from the way she is sitting. But some of the questions are unquestionably impossible to answer; there is simply no way to tell whether the woman has perfect pitch or what the conversation is about .For categories V.1-V.7, the best answer would be “I don't think it's possible to tell” when that is the case, or “I can't judge” when I think that perhaps someone else could answer the question. In category V.8, it would be better to deny the premise—“There's no horse in the picture,” “No one is punching the man”—and better yet, when possible, to clear up the questioner's inferred confusion “Those aren't boots, they're black sandals.” As discussed above, the system developed by Mahendru et al.  generateA number of recent papers, stemming from the seminal paper .QA datasets prior to SQuAD 2.0 had contained a fraction of questions that were unanswerable, due mostly to noise. These were mostly easy to detect as they did not have plausible answers. Jia and Liang  had propA number of papers since have taken up the challenge posed by SQuAD 2.0. The U-Net system  This particular example no longer works; Google Translate output now just echoes the input. But similar, if less entertaining, errors persist. For example, as of 1/17/2020, when asked to translate “margialigoelntest farbitlangefs” from English into Hebrew, Google Translate outputs “shodedei m'raglim rabim,” which means “many spy bandits.” If you ask Google Translate to translate it into Turkish, you get “margialigoelntest Instagram Hesabındaki Resim ve Videoları farbitlangefs” which means (I think) “margialigoelntest the Instagram account photos and videos farbitlangefs”64 arrangements of the twelve pieces and “empty” on the chess board as a legitimate input, and for any of these, it will output a move, because its output space is the class of moves. But the rules of chess are only defined for boards in which both players have exactly one king . Therefore, in a situation like There are even unanswerable questions in chess. A chess program, such as the chess version of AlphaZero  meaning “y is a good output  on the task for input x.” We assume that for every x ∈ X there is at least one y ∈ Y such that Q. Define Y to be the set of all good outputs for reasonable inputs: Y = {y | ∃x∈XQ}.Generally speaking AI systems, and for that matter computer programs of any kind for a particular task, the actual ultimate objective can be formulated as follows. There is a class C. Ideally C should be a representative sample of X, but often because of the way it is constructed, it is biased and omits large swaths of X. You randomly divide C into the training set T and the test set S. You then construct an architecture that takes arguments of form I and produces outputs of form O. I is often much larger than C; O can be equal to Y, or it can be much larger, or much smaller. You then apply the machine learning function to the training set T and learn a function ΦT which is the system's judgment of how good y is as an output for x. Now, at inference time, given any x ∈ I, the machine will output argmaxy∈OΦT, the most suitable output . You test the machine over S; of course, this test can detect overfitting to T but not biases in C.We now consider an ML-based AI system for this task. The construction of the system begins by the assembling a corpus X is the set of all things that someone might plausibly say. Y is the set of meaningful natural language expression. I is the set of all waveforms. C is the corpus of speech samples that have been collected.In a speech recognition system, X is the set of all game states that plausibly might come up in an actual game. Y = O is the set of all moves. I is the set of all placements of chess pieces on a chess board, including T is the set of games that the program has looked at in training.In a chess-playing program X is the set of all reasonable images. Y is the set of all categories of objects that appear in images. I is the set of all pixel arrays. O is the set of ImageNet categories. In this case, O is considerably smaller than Y; that is, there are images of objects where a good answer is a category not in ImageNet.For an image categorization system based on ImageNet, X is the set of all pairs of a high-quality image together with an answerable question about the image. I is the set of all pairs of a pixel array and a character string. Y is the class of all reasonable answers to questions about images. O is the space of the possible outputs of the system—some subset of the space of all character strings.For high-quality VQA, X is the set of pairs of a text together with an answerable question about the text. Y is the set of plausible answers to such questions. I is the set of pairs of character stringsO is the space of character strings.For textual QA, A few examples:x with either “It's impossible to tell” or “the question is meaningless” if the question is unanswerable; that is, if x ∈ I but x ∉ X (Our framework here is not rich enough to distinguish between these two answers). The system should respond, “I don't know” in either of the following cases:T is small for all y ∈ O .The system has no confidence in any possible answer: ϕx is so dissimilar to any part of the training set that the there is no reason for confidence that ϕT approximates Q at x. That is, you have no confidence that the learning method will do out-of-domain generalization with any quality. As an example, one can consider inputting a line drawing to a vision system that has been trained exclusively on photographs, or an audio of French speech to a voice-recognition system trained on English.The input Ideally, a system should respond to an input possible, of course, that the second case reduces to the first—that whenever the input is too far from the training set, that will be properly registered in the function ϕT—but one certainly cannot assume that will hold in any particular case.It is X and Y vary to an extreme degree from I and O is the system for symbolic integration developed by Lample and Charton  as input and is supposed to produce as output the indefinite integral of f, likewise expressed as a symbolic elementary functions. It was trained and tested over a corpus of elementary functions whose integral is also elementary and, over this corpus, achieved a higher success rate than state-of-the-art systems for symbolic mathematics such as Mathematica and Matlab.A case where  Charton  . Y is the class of elementary functions union the output “The integral of the input is non-elementary.” C is a corpus of elementary functions whose integral is elementary. LC achieved an almost perfect success rate over a test set drawn from C, but would almost never succeed over a test set drawn from complex expressions in X.So in terms of our framework: The unanswerability of a question like, “What is the integral of sin(sin(x))?” is in a different category from those we have discussed for QA and VQA. The question is meaningful—the function has an indefinite integral—but the answer is not expressible in the language of elementary functions.Why is it important to deal with unanswerable questions or invalid inputs at all? Why not just say, “Garbage in, garbage out” and leave it at that?Sometimes, in fact, that's fine. There is no reason that the AlphaZero team at DeepMind should spend any time getting the program to respond correctly to the situation in But often it is important to respond properly to unanswerable questions and invalid inputs, for a number of reasons. First, once a program is deployed to the real world, invalid inputs do often occur, and they have to be flagged. Serious conventional programs for general use are always built to address the problem of invalid inputs; it's a basic principle of software engineering. If a program bombs out without explanation when it gets invalid input, that's not great, but it is much worse if the program returns a plausible-looking answer, because then the user has no warning that there is a problem. A compiler which, analogously to LC, produced correct executable code when the source was syntactically correct, but also produced random executable code when the source is syntactically incorrect would be a disaster.The same applies for AI applications. It's a ridiculously far-fetched example, of course, but suppose that a public figure were to tweet something like, “Despite the constant negative press covfefe,” and you were tasked with translating that into a foreign language. There are various options you might consider, and it's not clear what would be best, but simply rationalizing it to a phrase that makes some sense would not be a good option.X, and asks “What is Obama doing with X”? The AI system answers “Obama is shaking hands with X.” The mis- or disinformation now gets posted on social media, with the imprimatur of the AI system.Similar considerations apply to answering unanswerable questions in QA and VQA. As we have seen, invalid inputs, both in image and in question, are fairly common in VizWiz. More generally, suppose that you had a powerful VQA system that could reliably answer legitimate questions, but also answered unanswerable question. Now, someone maliciously or not, gives the system a photo of a tall, thin African-American man shaking hands with some terrorist Second, when AI outputs are being used as guides to action, then it becomes extremely important to know how reliable they are. You want to avoid deciding on an expensive or risky action on the base of unreliable information. This is all the more important, because it is often completely impossible to anticipate how an output will be used. A passage is mistranslated, a person in an image is misidentified, speech is mistranscribed; OCR misreads a text; the mistaken information is uploaded to Web, or posted on social media; and then there is no telling what anyone will do with it.Third, unanswerable questions can be used as adversarial examples that give a means of probing the depths of an AI system's understanding. If a VQA system confidently answers “brown” to the question “What color in the horse in This is probably useful, but a couple of cautions should be noted, in both directions. On the one hand, if a system has been trained to respond correctly to unanswerable questions, that may indeed reflect a deeper understanding, or it may just mean that the system has learned “Clever Hans” tricks for that category as well. Conversely, even if a system answers “brown” to the question, “What color is the horse?” or “Yes” to the question, “Is the woman in the brown shirt barefoot?”, that may not reflect any gap in the system's understanding of horses, brown, or bare feet. The gap may simply be in its understanding of what is best to do when confronted with an unanswerable question .Fourth, under some circumstances, including unanswerable questions in training may improve performance even on other tasks. Mahendru et al.  report tFifth, it is important to keep unanswerable questions as a category in mind when comparing human beings or conventional computer systems against AI systems. Human beings generally deal with unanswerable questions flexibly and effectively; conventional software is often written to give useful output for invalid inputs; AI systems mostly avoid the issue altogether. The claim that “Chess programs are always better at analyzing a chess board than humans” is inarguably mostly true but comes with a very small asterisk for the reasons discussed above; the claim that “Watson can answer Jeopardy-style questions better than human competitors” comes with a significant asterisk; the claim that “Lample and Charton's symbolic integrator outperforms Mathematica at symbolic integration” comes with a very large asterisk, and indeed is more false than true Davis, .Finally, identifying what information is missing and why it missing is the first step toward taking action to obtain the information. If the image in The ability to recognize input as ill-formed or nonsensical is one aspect of understanding what the input means when it is well-formed and meaningful. The ability to realize that a picture or text does not provide a particular kind of information is part of understanding what kind of information it does provide. The ability to realize that you do not have the experience, knowledge, information, or cognitive capacity to be sure of any answer is an aspect of self-knowledge critical in reasoning, acting, and learning.The original contributions presented in the study are included in the article/supplementary materials, further inquiries can be directed to the corresponding author.The author confirms being the sole contributor of this work and has approved it for publication.The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Owing to the tremendous demands for high-resolution pixel-scale thin lenses in displays, we developed a graphene-based ultrathin square subpixel lens (USSL) capable of electrically tuneable focusing (ETF) with a performance competitive with that of a typical mechanical refractive lens. The fringe field due to a voltage bias in the graphene proves that our ETF-USSL can focus light onto a single point regardless of the wavelength of the visible light—by controlling the carriers at the Dirac point using radially patterned graphene layers, the focal length of the planar structure can be adjusted without changing the curvature or position of the lens. A high focusing efficiency of over 60% at a visible wavelength of 405 nm was achieved with a lens thickness of <13 nm, and a change of 19.42% in the focal length with a 9% increase in transmission was exhibited under a driving voltage. This design is first presented as an ETF-USSL that can be controlled in pixel units of flat panel displays for visible light. It can be easily applied as an add-on to high resolution, slim displays and provides a new direction for the application of multifunctional autostereoscopic displays. Graphene-based ultrathin lenses with an electrically tuneable focal length could prove useful for providing displays with autostereoscopic 3D functionality, multiview or privacy protection. Developed by scientists in South Korea, the UK and the US, the lenses are just 13 nm thick and are based on a Fresnel Zone Plate (FZP) design made from a series of concentric rings of graphene on a glass substrate. Consisting of up to 5 layers of graphene that is patterned by focused ion-beam milling, the lenses offer a 60% transmission in the visible region and a focal length of 200–300 µm that can be tuned within ~20% range by applying a DC bias voltage. The applied voltage changes the charge carrier density in the graphene, modifying the topology of the FZP and thus its focusing behaviour. Ultrathin flat lenses, which are different from conventional lenses, have been extensively investigated owing to the growing interest in ultrasmall devices, with various applications in telescopes2, aerospace technology3, holograms4, and displays5. Realisation of ultrathin flat lenses has been achieved using diffractive optical elements7 or metasurfaces9. In particular, Fresnel zone plates10 (FZPs) comprise a planar ring pattern and can be designed as thin, low-volume, and high-numerical-aperture lenses for applications in various fields, such as ultrathin nanolithography13, near/far-field optical microscopy15, optical antennas, and X-ray optics19. For highly efficient Fresnel lenses, a 200-nm thick graphene-oxide-based FZP with an absolute focusing efficiency of 32% has been developed7. In the case of ultrathin films, an FZP with a radius of 40 µm and 24 zones employing multilayer graphene was reported to have a thickness of 3.47 nm for ten layers, and a focusing efficiency of 6.6% with transmittance in the range of 75–78% (ref. 6). Additionally, an FZP with nanoribbons can achieve high intensity and efficiency owing to the optical plasmon coupling phenomenon, depending on the width of the nanoribbons and the carrier concentration of the graphene21. Hence, a material that significantly enhances the current ultrathin lenses through higher transmittance, higher focusing efficiency. and lower thickness is essential.Traditional tuneable lensesN, as the absorption A(ω) = 1−T(ω) = παN, with fine-structure constant α (refs. 23). This property facilitates control of visible light transmittance by varying the number of graphene layers. In addition, the transmittance of graphene is determined by the optical conductivity  G(ω), which is correlated with the Fermi energy EF and the carrier density n induced by an external electric field, as the integrated absorption 24). These properties represent potential tuneability in the optical response regime25. In fact, owing to the tuneable characteristics of graphene, graphene-based devices, such as optical waveguides26, polarisers28, optical modulators29, and photodetectors30, have been developed because the charge density of graphene can be easily varied by chemical doping, gate biasing25, and changing the magnitude and direction of an externally applied electric field31. Therefore, if the graphene can be patterned into nanoribbons32, then a graphene-based FZP lens can be an ideal combination of near and far optical fields because the optical conductivity of graphene can be tuned by adjusting the Fermi level or by varying the geometry. In the past, the lenticular lens33 and parallax barrier34 used in multiview autostereoscopic displays were considered infeasible in displays owing to their thickness, low transmittance, high aberration, and low resolution. However, the Fresnel lens made of graphene enables electrically tuneable focusing (ETF) based on the difference in the absorption characteristics of the Fermi level; thus, a multifunctional display using an ultrathin square subpixel lens (USSL) of high transmittance and high resolution can be realised. In this study, we developed an ETF-USSL with a transmittance of over 80% for displays with a thickness of 13 nm, using the focused ion beam (FIB) method35 to create a nanoscale pattern on a thin graphene structure. The results indicate that the graphene can be used to change the viewing angle of the display via dynamic control of the focal length with a DC voltage bias. When an ultrathin lens with an ETF is used in a display, it is possible to achieve an autostereoscopic display with multiple functions36, such as glassless three-dimensional (3D) viewing, privacy protection, and multiview, depending on the variation of the focal length.Graphene and graphene composites have dynamic optical properties and unique electrical properties. Because the interlayer interaction is negligible for monolayer graphene, it is transparent in the visible light regime. Meanwhile, few-layer graphene with <10 layers exhibits light absorption characteristics linearly proportional to the number of graphene layers A graphene ultrathin pixel lens was designed considering the field of view (FOV) of a multifunctional autostereoscopic display. The FZP-based USSL with tuneable focusing capability was developed to realise multifunctional lenses. The structure of the ETF-USSL was determined based on the desired optical path of a multifunctional system, based on the same frame as that of the subpixels. It is thus possible to realise glassless 3D and privacy images, when the ETF-USSL changes the optical paths of view 1 and view 2 from the near field to the far field within a single display. Therefore, the optical path of our lens was designed according to the FOVs of view 1 and view 2 for the conventional Fresnel lens by considering the subpixel size in the display panel. For two red–green–blue/red–green–blue (RGB/RGB) pixels, the RGB subpixel for view 1 on the right side (or the right eye) and the neighbouring pixel for view 2 on the left side (or the left eye) are designed such that they can be fitted into the pixel structure of a Fresnel lens pattern . In the Kubo model, the Fermi level depends on the change in the carrier density due to an electric field. Because the optical conductivity in the intraband is proportional to the Drude weight vF, the carrier density n increases as the optical conductivity increases. However, as the carrier density related to the Fermi level increases, the optical conductivity in the interband decreases due to interband Pauli blocking24. To clarify the relation between the optical conductivity and carrier density, the integrated absorption in the Kubo model is 31. The transparency of graphene decreases when the Fermi level moves near the Dirac point because the photons from the incident light are absorbed and excite the electrons , the transparency of graphene is increased; as shown in Fig. ħω2 < 2EF), then no absorption occurs29. Therefore, the electric field normal to the plane due to the DC bias concentrates the carrier density at the edges of the arc ribbon. The arc ribbon then absorbs light in the central area (C), but the Fermi level moves away from the Dirac point, owing to the increase in the carriers on the left (L) and right (S) sides, as shown in Fig. We therefore prepared a graphene-based USSL with an arc ribbon pattern for the application of an electromagnetic field, supported by the beneficial optical properties of graphene. The external electrical variationons Fig. . On the hp) of the subpixel was set to 26 μm, and the FOV was set in the range of 2°–12°. Under these conditions, the calculated value of the focal length of a single USSL is 140 μm. This result determines the radius of the mth ring of the USSL. The radius is designed considering the light wavelength of a single USSL, and it must satisfy the following condition7  and the focal length (f), assuming that Δφ is insignificant in the calculation.The phase difference is Δrm can be obtained from the subpixel size of the display; thus, a single USSL was designed by matching the subpixel size (hp × vp) to the area of the FOV for the developed symmetrical FZP ring lens  for the red USSL.The maximum value of ens Fig. . Here, θ41, we built a simulation model for our diffraction pattern to analyse the focusing performance of a single USSL. We simulated three different types of designs: a conventional ring, an arc ribbon, and a cylinder. This simulation allows the study of the paraxial intensity distributions in the focal region throughout the subpixel. According to the simulation, the focus was formed on the designed focal plane at 140 μm, where the subpixel lens of the arc ribbon type showed the same results as the conventional ring type. On the other hand, the subpixel lens of the cylindrical type showed multifocal spots in the designed focal plane  measurements, as shown in the SEM images in Fig. r1 (ref. 7); however, the FWHM of the USSL was as low as 2.0 μm even for an r1 value of 12.97 μm. This difference in the FZP lens and the USSL indicates that the focusing efficiency of the USSL is remarkably high. In addition, the focusing efficiency is defined as the ratio of the intensity at the focal spot plane (IF) to the incident intensity transmitted through the focal objective plane , as shown in Fig. hp = 26 μm, vp = 78 μm; Supplementary Fig. r1, r2, r3,…, rm and with λ = 630 nm (m = 13) for the red pixel lens, λ = 550 nm (m = 15) for the green pixel lens, and λ = 445 nm (m = 19) for the blue pixel lens  to demonstrate the multifunctional capability of the USSL. The subpixels, which represent the minimum number of pixels (six subpixels) required to display an image in different directions from the display, were designed based on the pixel size  between pixels. The maximum intensity is the highest ~0 V, and decreases in the positive and negative voltage directions in Fig. 43. In these circumstances, the focal spot area is the largest at ~0 V and decreases at other voltages, as shown in Fig. df) decreases when the external potential reaches 0 V in Fig. f) can be obtained by calculations based on the measured focal spot distances (df) and focal spot positions  of the two peaks moved outward with increasing voltage, and the focal position shift in a fixed focal plane showed an increase in the focal length; the red focal spot was shifted by 25.6 μm, the green focal spot was shifted by 36.9 μm, and the blue focal spot was shifted by 16.4 μm at a potential of 50 V. The largest change, observed for the green focal spot, is due to the largest voltage effect. Because the green USSL is between the red and blue USSLs, the first red USSL is open on the left, and the last blue USSL is open on the right. This explains why the ETF-USSL focal length of 190 μm can vary up to 19.42% (36.9 μm) after applying a voltage. This indicates that the FOV of the observer can also be controlled by the electromagnetic field in the ETF-USSL in multifocusing.As a result Table , the foc5 or device. The ETF parameters are shown in Table 44, acoustic applications45, and optical devices comprising metasurfaces47.The graphene-based ETF-USSL with five graphene layers had a transmittance of 82% and a focusing efficiency of >60%. In our lenses with the arc ribbon design, the effective spacing of the arc ribbons varies due to the difference in the carrier distribution depending on the position of the electric field. This results in a variation of the diffraction characteristics of the slit such that the focal length can be adjusted in the visible regime without any change in the design. The ETF-USSL can be customised according to the wavelength of each subpixel in the display device without any additional light source4 gas partial pressure of 290 mTorr and a corresponding flow rate of 20 ccm) and hydrogen . The growth procedure was performed using a commercially available 100-μm-thick Goodfellow Cu foil (item #CU000565) with a diameter of 50 mm as the growth substrate in a quartz chamber. The graphene grown on the Cu foil was spin-coated with a poly(methyl methacrylate) (PMMA) layer  for 32 s at 4200 rpm to form a supporting layer, which was baked at 180 °C for 2 min to improve the adhesion to the substrate.For single-layer graphene, a Cu substrate was first annealed at 1010 °C for 30 min, and single-layer graphene was grown in a chamber at 1010 °C with methane (with a CH4)2S2O8, Sigma-Aldrich). Finally, after air-drying, this process was repeated five times to produce five graphene layers . Oxygen plasma was used to remove titanium from the regions where it was milled by the FIB. The titanium on the remaining graphene was removed, using a titanium etchant Fig. .An ultraviolet/visible spectrometer  was used to measure the transmittance in the wavelength range of 200–900 nm  illuminated the lens, and its focal response was measured with a charge-coupled device (CCD) camera. The DC voltage bias of the ETF-USSL was measured using a source measure unit  at 1 min intervals, from −50 V to +50 V in steps of 5 V (Figs. Supplementary information for Electrically focus-tuneable ultrathin lens for high-resolution square subpixelsSupplementary Video 1Supplementary Video 2


Sicca symptoms and Raynaud’s disease are amongst the common presentation of Sjögren’s syndrome (SS) which has an estimated prevalence of 1%. We are reporting a case that was initially considered as SS, but subsequent lip biopsy confirmed histological evidence of sarcoidosis in the presence of abnormal nailfold capillaroscopy and negative autoimmune profile. Sarcoidosis can be associated with various autoimmune diseases including systemic sclerosis, Hashimoto's thyroiditis, systemic lupus erythematosus, rheumatoid arthritis, Sjögren’s syndrome and spondyloarthropathy.A 29-year-old Caucasian man was referred to rheumatology clinic, suffering with ongoing sicca symptoms including dry itchy gritty eyes, sore red eyelids, persistent mouth dryness and cracking ulcers. He has history of Raynaud’s disease, dysphagia for solid, dry cough and photosensitive rash on his chest and arms. His other symptoms were polyarthralgia, myalgia, headache, persistent fatigue, poor memory, dry skin over the hands and tingling sensation at the feet. There was no history of joint swelling, uveitis, chest pain or shortness of breath. He has hypothyroidism secondary to radioiodine treatment and is currently on levothyroxine. He works in a factory, drinks alcohol occasionally and is non-smoker. There was no family history of autoimmune conditions.General and systemic examination was unremarkable, and there were no stigmata of connective tissue disease except for tenderness and crepitus at the right knee joint. His saliva flow rate was 0.4ml/5 mins and Schirmer’s test was 20mm/5 mins .Autoimmune profile was negative; ANA: 0.2 units, RF factor: <10, CCP antibodies (IgG): 1.1U/mL.   Apart from mild lymphopenia, the other laboratory tests were at normal range including CK, CRP, adjusted calcium, ACE, immunoglobulins, serum protein electrophoresis and urine test for protein. Chest X-ray and lung function test were both normal.Nailfold capillaroscopy shows grade1 enlarged capillaries, prominent capillary ramifications in the form of bushy capillaries and some microhaemorrhages, a pattern suggestive of mixed connective tissue disease.Lip biopsy showed small non-caseating epithelioid granuloma within the parenchyma.The initial working diagnosis was a possible serology-negative SS, but the later results of lip biopsy confirmed sarcoidosis.He was commenced on Hydroxychloroquine and advised about cognitive-behavioural therapy for generalised ache and fatigue. As he was not responding to pilocarpine, a referral for ophthalmology review was requested.Sarcoidosis is a multisystem disease of unknown aetiology, known to exist worldwide with a variable prevalence of around 20 per 100,000 in the UK. It is characterized by the presence of multiple non-caseating granulomas, inflammation which may occur in any tissue in the body manifested as local symptoms with or without systemic features. Involvement of the salivary and lacrimal glands can result in xerostomia and xerophthalmia, respectively.Chronic sarcoid has an often subtle, insidious, progressive, and highly variable clinical course; it can be asymptomatic in a significant percentage of the cases.In addition to the clinical and radiological findings, the diagnosis of sarcoidosis should be based on the histological proof of non-caseating granulomas and ruling out other diseases that shares similar features.SS has many features in common with sarcoidosis; these may include sicca symptoms, arthralgia, myalgia, arthritis, erythematous rash, lymphadenopathy, peripheral neuropathy, fatigue and raised inflammatory markers. Moreover, positive rheumatoid factor, defective T suppressor cell regulation and HLA-DR3 are linked to both diseases. Pulmonary involvement in either of them may have similar clinical and radiographic manifestations, making it difficult for the clinician to distinguish between these diseases.In terms of management, hydroxychloroquine may help the skin and joint manifestations in both diseases whereas more severe diseases may require treatment with glucocorticoids, methotrexate, and azathioprine.Nevertheless, prompt confirmation of the diagnosis is crucial provided the difference in response to medication, complications, outcome, and prognosis.Based on the clinical and lip biopsy findings, the above case was diagnosed with sarcoidosis. The case did not meet the criteria for the diagnosis of SS provided the negative results of Schirmer’s test, saliva flow test and autoimmune profile.Raynaud’s phenomenon (secondary Raynaud’s) with positive capillaroscopy findings was an unusual early presenting feature of sarcoidosis in the above case. There was one case report of similar presentation published in 2011. However, literature did not reveal specific information about abnormal nailfold capillaroscopy results in sarcoidosis.Dry eyes and dry mouth may occur in sarcoidosis mimicking the presentation of primary SS. In addition, true coexistence of sarcoidosis and SS has also been defined based on the histopathologic examination of the exocrine glands. Diagnostic criteria need to be applied for patients with suspected overlap of the two diseases.Clinicians will need to be vigilant and perform appropriate investigations for overlapping rheumatic conditions with sarcoidosis. Lip biopsy remains a crucial investigation for cases referred with sicca features, not only to establish the diagnosis of SS but also to exclude   associated lymphoma or sarcoidosis.


Heterocephalus glaber) are the longest-living rodent species. A reason for their long lifespan is pronounced cancer resistance. Therefore, researchers believe that NMRs have unknown secrets of cancer resistance and seek to find them. Here, to reveal the secrets, we noticed a retrotransposon, long interspersed nuclear element 1 (L1). L1s can amplify themselves and are considered endogenous oncogenic mutagens. Since the NMR genome contains fewer L1-derived sequences than other mammalian genomes, we reasoned that the retrotransposition activity of L1s in the NMR genome is lower than those in other mammalian genomes. In this study, we successfully cloned an intact L1 from the NMR genome and named it NMR-L1. An L1 retrotransposition assay using the NMR-L1 reporter revealed that NMR-L1 was active retrotransposon, but its activity was lower than that of human and mouse L1s. Despite lower retrotrasposition activity, NMR-L1 was still capable of inducing cell senescence, a tumor-protective system. NMR-L1 required the 3′ untranslated region (UTR) for retrotransposition, suggesting that NMR-L1 is a stringent-type of L1. We also confirmed the 5′ UTR promoter activity of NMR-L1. Finally, we identified the G-quadruplex structure of the 3′ UTR, which modulated the retrotransposition activity of NMR-L1. Taken together, the data indicate that NMR-L1 retrotranspose less efficiently, which may contribute to the cancer resistance of NMRs.Naked mole-rats (NMRs,  Heterocephalus glaber) are mouse-sized and the longest-living rodents discovered1. A unique feature of NMRs that contributes to their long lifespan is their pronounced cancer resistance, as there are only a few reports of spontaneous neoplasia in NMRs4. Several studies have sought to reveal the underlying mechanisms of NMR cancer resistance. For example, NMR cells transformed by oncogenic genes rapidly enter crisis or permanent cell cycle arrest, which may contribute to cancer resistance5. Activation of the tumor suppressor ARF and the disruption of oncogenic ERAS can also exhibit tumor resistance in NMR-induced pluripotent stem cells6. Another feature of NMRs that may be related to cancer resistance is fewer transposon-derived sequences than found in other mammals 7. Transposons, such as endogenous retroviruses (ERVs) and long interspersed elements (LINEs), can autonomously amplify themselves in the genome8, which may produce oncogenic mutations and/or induce genomic instability, thereby promoting cancer development13. Thus, fewer transposon-derived sequences may indicate lower transposition activity of the NMR transposons, which may contribute to NMR cancer resistance.Naked mole-rats , two open reading frames (ORFs) that encode two proteins, ORF1p and ORF2p, and a 3′ UTR with a polyadenylation signal. ORF1p is an RNA-binding protein with nucleic acid chaperone activity that is required for L1 retrotransposition. ORF2p is a protein required for endonuclease (EN) and reverse transcriptase (RT) activity for a “copy-and-paste” retrotransposition of L1s to new genomic loci15. L1 retrotransposition occurs by target-site primed reverse transcription (TPRT), during which ORF2p makes a nick in genomic DNA and synthesizes L1 cDNA using the 3′ hydroxyl group at the nick16. The active retrotransposition of L1 is considered a major source of endogenous mutagenesis that can promote cancer development13. Consistently, we have found that Kaposi’s sarcoma-associated herpesvirus, an oncogenic virus, stimulates L1 retrotransposition, thereby enhancing transformation17. Together with the extraordinary resistance of NMR to cancer and the fewer transposon-derived sequences in the NMR genome, as described above, we reasoned that the retrotransposition of L1s in the NMR genome is less efficient than those in other genomes, which might contribute to cancer resistance. In this study, we cloned an active L1 from the NMR genome and characterized it to evaluate our hypothesis.LINE-1 (L1) is a transposon that is abundant in many eukaryotic genomesRP (accession no.: AAD39215) and mouse L1spa (accession no.: AAC53542) using tblastn. The search using human L1RP led to the identification of many potential ORF2p sequences (~ 3 kB) with a potential ORF1p (~ 1 kB) in the upstream region, while the search using mouse L1spa found only short ORFs in the top 30 candidate sequences. Among these candidates identified by the search using human L1RP, we chose an intact L1 sequence and named it NMR-L1  was 63%. A comparison of the amino acid sequences of each gene showed 33% sequence identity and 79% similarity in the ORF1 gene and 63% identity and 92% similarity in the ORF2 gene. Phylogenetic analysis of the nucleotides coding ORF1p and ORF2p showed that NMR-L1 and human L1 Hs constituted a clade that was different from that of mouse L1s . We compared the amino acid residues of NMR-L1 to those important for retrotransposition of human L1RP. All the residues we compared were conserved in the NMR-L1 ORF1p and ORF2p  downstream of the 5′ UTR of L1RP  reporter cassette in the antisense orientation, in which the FLuc gene was interrupted by an antisense intron, downstream of the 3′ UTR  gene in the plasmid was used to normalize the transfection efficiency. We also constructed FLuc-tagged NMR-L1 reporters with an D714A mutation in ORF2p 20, pMY11 . Mouse L1 showed more robust retrotransposition activity than a human L1 . These results suggest that retrotransposition activity of NMR-L1 is still low even if compared to a mouse L1. Then, to evaluate the contribution of EN activity to NMR-L1 retrotransposition, we constructed another reporter with an D217A mutation in ORF2p, which was expected to be defective in EN activity since an Asp in position 217 of the NMR-L1 ORF2p, which corresponds to an Asp in position 205 of the human L1 ORF2p21, a critical residue for EN activity, was substituted with an Ala residue . Using this reporter, we found that NMR-L1 defective for the EN activity showed lower retrotransposition activity than the wild-type , suggesting a critical role of EN activity in NMR-L1 retrotransposition. Furthermore, to test whether the cognate 3′ UTR was required for retrotransposition activity, we conducted an L1 retrotransposition assay using a FLuc-tagged NMR-L1 reporter lacking the cognate 3′ UTR , we reasoned that NMR-L1 may contain guanine-rich sequences that can fold into G4 structures in the 3′ UTR, similar to human L1s. Consistent with our assumption, we found several guanine-rich sequences capable of forming G4 structures in the 3′ UTR of NMR-L1 , a stabilizer of G4 structures, on NMR-L1 retrotransposition. NMR-L1 retrotransposition was enhanced by PDS treatment when NMR-L1 with the cognate 3′ UTR (pMY07) was used for the assay  structures in the 3′ UTR structur24. Although L1 retrotransposition drives oncogenic insertions, it can also induce cell senescence at least through stimulation of IFN responses25. To evaluate whether NMR-L1 induces cell senescence, we measured senescence-associated Cell senescence is one of tumor-protective mechanisms and also a hallmark of aging1. Previous studies have proposed several possible reasons for this resistance, including a highly efficient surveillance system of cell cycles and resistance to multiple stressors26. In addition, we reasoned that such secrets likely include low retrotransposition activity since the NMR genome contains fewer retrotransposons than other mammalian genomes7. L1 is a retrotransposon that is considered to be an endogenous mutagen, which can cause oncogenic mutations and contribute to cancer development13. In this study, we, for the first time, cloned an intact L1 from the NMR genome and determined its retrotransposition activity. The amino acids important for L1 retrotransposition in a human L1 appeared to be conserved in NMR-L1  predicted the secondary structure of the 3′ UTR of NMR-L1 . Since the 3′ UTRs of primate L1s are devoid of canonical secondary structures23, the 3′ UTR secondary structures likely play a role in NMR-L1 retrotransposition, and thus, the 3′ UTR was required for it. Although the 3′ UTRs of primate L1s are thought to lack a secondary structure, they reportedly contain conserved guanine-rich sequences that can form G4 structures23. Similarly, we found that the 3′ UTR of NMR-L1 contained G4 structures , and 3T3 cells (a mouse fibroblast cell line from ATCC) were cultured in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 5%, 5%, and 10% fetal bovine serum (FBS), respectively. NMR SV40ER cells  were cultured in DMEM supplemented with 15% FBS, non-essential amino acids (Gibco) and L-glutamine .293T cells (a human embryonic kidney cell line from ATCC), OL cells (a human oligodendroglioma cell line2 and 5% O2. NMR fibroblasts expressing simian virus 40 early region (SV40ER) were generated by lentiviral infection with the pCSII-EF-SV40ER-TK-hyg vector [The backbone vector (pCSII-EF-RfA-TK-Hyg) was kindly provided by Dr. Hayato Naka-Kaneda ] and selection of hygromycin-resistant cells for 4 days. Subsequently, cloning by limiting dilution was performed, and stable clones (NMR SV40ER cells) were established. Animal experiments were done in accordance with protocols approved by the Institutional Animal Care and Use Committee in Kumamoto University (A2020-042) and in compliance with the ARRIVE guidelines.Primary NMR fibroblasts were isolated from back skin of 1-year-old adult NMR. Fibroblasts were cultured at 32 °C in a humidified atmosphere containing 5% CO18. pYX015 is a mutant L1 construct defective for L1 retrotransposition18. The reporter plasmids for a mouse L1 retrotransposition were prepared by substituting a human L1 sequence of pYX14 with ORFeus-Mm or ORFeus-Mm-D212G/D709Y, which was kindly provided by Dr. Jef D Boeke 20. The reporter plasmids for NMR-L1 retrotransposition were prepared by substituting human L1 sequences with partially codon-optimized NMR-L1 ORF1 and ORF2 sequences with or without the 3′ UTR of NMR-L1. The reporter plasmids with a putative retrotransposition-defective mutation were prepared by site-directed mutagenesis using PrimeSTAR Max DNA polymerase . Summary descriptions of the constructed plasmids are shown in Figs. 32.pYX014 and pYX015, reporter plasmids for a human L1 retrotransposition, were kindly provided by Dr. Wenfeng An Firefly and Renilla luciferase activity levels were measured using a Dual-Luciferase Reporter Assay System  according to the manufacturer’s instructions in a single-well luminometer . The Firefly luciferase activity level was normalized to the corresponding Renilla luciferase activity level. Then, the activity was further normalized to that of pYX14. PDS  was added to the cells at 200 nM at 2 days after transfection.293T cells were transfected with retrotransposition reporter plasmids using Lipofectamine 2000 or 3000 reagent (Invitrogen). At 4 days after transfection, Gaussia and Cypridina luciferase activity levels were measured using Gaussia and Cypridina Luciferase Assay Kits (New England Biolabs) according to the manufacturer’s instructions. Gaussia luciferase activity level was normalized to the corresponding Cypridina luciferase activity level. Then, the activity was further normalized to that of pGLuc-Basic (Mock).293T cells were cotransfected with pGLuc-5′-UTR (human) or pGLuc-NMR-L1-5′-UTR, together with pCMV-CLuc (New England Biolabs) using Lipofectamine 2000 reagent. At 3 days after transfection, the Renilla luciferase activity level. Then, the activity was further normalized to that of pYX14 or pMY07.293T cells were transfected with pYX14, pYX15, pMY07, or pMY07′ using Lipofectamine 2000 reagent. At 3 days after transfection, SA-t-test with a threshold of P < 0.05.Statistical significance was assessed using a two-tailed Student’s Supplementary Information


Moreover, a wireless temperature sensing platform was obtained by integrating the printed sensor to a printed flexible hybrid circuit, which performed a stable real-time healthcare monitoring.Facile fabrication and high ambient stability are strongly desired for the practical application of temperautre sensor in real-time wearable healthcare. Herein, a fully printed flexible temperature sensor based on cross-linked poly:poly(styrenesulfonate) (PEDOT:PSS) was developed. By introducing the crosslinker of (3-glycidyloxypropyl)trimethoxysilane (GOPS) and the fluorinated polymer passivation (CYTOP), significant enhancements in humidity stability and temperature sensitivity of PEDOT:PSS based film were achieved. The prepared sensor exhibited excellent stability in environmental humidity ranged from 30% RH to 80% RH, and high sensitivity of −0.77% °C Therefore, the flexible temperature sensor is highly desired to realize personal healthcare devices, which enable real-time monitoring of an individual’s health state6.Body temperature is an essential vital parameter reflecting the physiological activities. Monitoring of body temperature provides insight into human health conditions, such as cardiovascular condition, wound healing, pulmonological diagnostics, and syndromes prediction8, resistive temperature detectors (RTDs)10, and thermistors11. Among them, the thermistor which relies on the thermo-resistive effect of sensing material is widely used, due to its simple device structure, fast response, and wide sensing range13. Various thermistor materials have been developed and investigated, including composites of conductive filler with polymer, and temperature sensing conductive materials such as silver nanowire (AgNW)15, carbon nanotubes (CNTs)16, reduced graphene oxide (rGO)18, and poly: poly(styrenesulfonate) (PEDOT:PSS)20. However, most of these studies focused on improving the sensitivity and mechanical performance of temperature sensors, while their ambient stability, especially humidity stability, has rarely been considered. Additionally, the development of wearable temperature sensors via simple fabrication still a big challenge. Since the use of wearable devices inevitably exposed to ambient humidity, it is of great interest to develop a facile fabricated humidity-resistant temperature sensor.Many efforts have been made to develop flexible temperature sensors, which mainly contain three types: pyroelectric detectors22. However, as a water-soluble polymer, the resistance of PEDOT:PSS also be easily affected by the environmental humidity, which would cause cross-talk with temperature24. Despite various demonstrations of PEDOT:PSS based temperature sensors, the humidity effect have rarely been clarified, and humidity stability has so far not been developed.In contrast to its counterparts, PEDOT:PSS has been proven as a promising candidate for the wearable temperature sensor, not only owing to its outstanding mechanical properties and turntable electrical characteristics, but also the superior in simple, patternable, and high reproducible fabrication, such as printing−1 at a wide sensing range form 25 °C to 50 °C. Additionally, a wireless temperature sensing platform with the functions of on-site signal acquisition, condition, and data transmission was achieved by integrating the printed sensor to a printed flexible hybrid circuit, which performed a stable real-time body temperature monitoring.In this work, we developed a fully printed PEDOT:PSS-based temperature sensor which possessed excellent humidity stability. A high-performance sensing layer was achieved by crosslinking of PEDOT:PSS by (3-glycidyloxypropyl)trimethoxysilane (GOPS). Combined with fluorinated polymer passivation (CYTOP), the developed temperature sensor exhibits excellent stability in environmental humidity varied from 30% RH to 80% RH, and high temperature coefficient of resistance (TCR) of −0.77% °C31. The structure of the temperature sensor was shown in Fig. The proposed temperature sensor was developed by a fully printing process. As a facile fabrication technique, printing not only possesses advantages in low cost and easy patterning, but also offers good uniformity and reproducibility in devices performance22. Thus the temperature-sensitive property of the PEDOT:PSS-based temperature sensor can be explained primarily based on the enhancement of charge carrier transport and the generation of charge carriers under thermal stimulus35. As thermal energy (given temperature) increases, the limited carrier hopping and tunneling both inside the individual grain and between the neighbored nanosheets is enhanced. Therefore, the resistance of sensing film decreases with increasing the temperature, behaves a negative temperature coefficient (NTC). The sensitivity of the temperature sensor is defined by its temperature coefficient of resistance (TCR), can be calculated from Eq. (R and R0 are the resistance at measured temperature and room temperature (25 °C) of the sensor, ∆T is the change in applied temperature.As a well-known conductive polymer, PEDOT:PSS has a core-shell grain structure in which conducting PEDOT enriched cores are surrounded by the insulating PSS enriched shellsfrom Eq. :1\docume36. On the contrary, the humidity desorption would cause the decrease in resistance. Such effects would induce inaccuracy for temperature measurement37. At a fixed humidity condition, the sensor was equilibrium with the environment. When the sensor was heated up by thermal source (hot plate), the water molecule will be desorbed from the film  was chosen as the passivation layer, due to its low water vapor permeability and good adhesion on the substrateure Fig. .44, but have yet to be studied for the temperature sensor. Since the GOPS mainly reacts with the excess PSS unit, i.e. the shell part of PEDOT:PSS grain, it will also increase the barrier at grain boundary for charge carrier hopping45. Therefore, the enhancements in both humidity stability and temperature sensitivity of the sensor can be expected.To further enhance the humidity stability and temperature sensitivity of the sensor. The crosslinker of GOPS was introduced to crosslink the hydrophilic part of PSS unit. This method was used to obtain water-stable PEDOT:PSS films for organic electrochemical transistors (OECTs)Temperature sensors based on PEDOT:PSS films with different ratios of GOPS were investigated. To enable good printing performance, the surfactant TX-100 was also added. As we expected, the humidity stability of the sensors was largely improved by the adding of GOPS. Only 5% resistance increase was observed under the humidity changes for 30% RH to 80% RH when the weight ratio of GOPS to PEDOT:PSS was over 5 Fig. . After d−1, further increasing the amount of GOPS resulted in a nonhomogeneous ink solution. The optimized thickness of CYTOP passivation deposited on the sensor is 10μm, and the effect of CYTOP thickness on TCR and humidity stability of the sensor was also investigated and showed in supporting information trimethoxysilane (GOPS) and the fluorinated polymer passivation (CYTOP), the prepared sensor exhibited excellent stability in environmental humidity ranged from 30% RH to 80% RH, and high sensitivity of −0.77% °CPEDOT:PSS (1.3 wt% in water), Triton X-100, and (3-glycidyloxypropyl)trimethoxysilane were purchased from Sigma Aldrich, silver nanoparticle (AgNP) ink in hydrocarbon-based solution (NPS-JL) was purchased form Harima Chemicals, Fluorinated polymer CYTOP (CTX-809A) were purchased from AGC Inc. 50-μm thick poly (PEN) film substrate (Q65HA) was purchased from Dupont. All materials were used as received without further purification.−1 and with a discharge pressure of 2 kPa. During the dispensing process, the plates and nozzle temperatures were kept at 30 °C. Followed by an anneal at 140 °C in an air ambient for 30 min to remove the solvent and enable the cross-linking process. Finally, the encapsulation layer of CYTOP was printed by the dispenser system at 30 °C, with a pattering speed of 5 mm s−1 and a discharge pressure of 5 kPa, and then cured at 140 °C for 30 min. The geometry of the printed sensor was shown in supporting information Figure AgNP ink was printed as electrodes using an inkjet printer  with 10 pl nozzles. During the inkjet printing process, the substrates and cartridge were kept at 50 and 35 °C, respectively. The substrates were then heated at 120 °C for 30 min in an air ambient to sinter the silver nanoparticles. To print the sensing layer, 100 mg PEDOT:PSS solution and 50 mg TX-100 solution (1.3 wt% in DI water) was mixed with different amount of GOPS  by a planetary centrifugal mixer (THINKY MIXER AR-100) for 15 min (10 min mixing and 5 min degassing). The developed inks were then printed using a dispenser system  at a pattering speed of 5 mm sAg paste was screen printed on 50 μm  PEN film as interconnections of the flexible hybrid circuit, an operational amplifier , 7 chip resistors (2 mm × 1.2 mm), and 3 chip capacitors (2 mm × 1.2 mm) and a wireless BLE module  were assembled on the substrate by surface mount soldering. Further, the printed temperature sensor and a sheet-type cell battery of 25 mAh  were connected to the substrate of the circuit using conductive epoxy . Detailed experiments of design, fabrication, and optimization of the circuit will be reported elsewhere. The achieved sensor platform was attached to the skin of a volunteer using a skin-compatible adhesive.The resistance change of the sensor response to the temperature was monitored by a digital multimeter  by 4 W measurement, and recorded by a personal computer (PC) with corresponding data acquisition system. A hotplate was offered to control the measurement temperature of sensors and the temperature calibration was performed by a commercial thermocouple. A temperature and humidity chamber  was used to control the temperature and humidity of the measurement environment. For the demonstration of skin temperature monitoring, the developed wireless temperature sensing platform was attached on the arm of a volunteer . An adhesive sheet used for tattoo paper was used here to ensure proper adhesion between the sensor patch and skin, as illustrated in supporting information Figure Informed consent to participation in the study and publication of identified information/images in an online open-access publication was obtained from all subjects prior to their enrollment in the study. The experiments of monitoring body temperature and breath rate of a volunteer by developed sensing device were approved by the institutional review board of the Yamagata University (No. 2019–152). All the experiments that were conducted on human body in this study were performed in accordance with relevant guidelines and regulations.Supplementary information.Supplementary information.


In-situ characterization and theoretical calculations reveal a reversible intercalation mechanism of cations in the 2D multilayered heterostructure with a negligible volume change. When applied as cathodes in K+-ion batteries, we achieve a high specific capacity of 160 mA h g−1 and a large energy density of ~570 W h kg−1, presenting the best reported performance to date. Moreover, the as-prepared 2D multilayered heterostructure can also be extended as cathodes for high-performance Na+, Zn2+, and Al3+-ion batteries. This work heralds a promising strategy to utilize strain engineering of 2D materials for advanced energy storage applications.Beyond-lithium-ion batteries are promising candidates for high-energy-density, low-cost and large-scale energy storage applications. However, the main challenge lies in the development of suitable electrode materials. Here, we demonstrate a new type of zero-strain cathode for reversible intercalation of beyond-Li +-ion batteries are promising energy storage systems but suffer from lack of suitable electrode materials. Here the authors report a new type of zero-strain cathodes for Na+, K+, Zn2+, and Al3+ ion batteries through strain engineering of a 2D multilayered VOPO4-graphene heterostructure.Beyond-Li In this regards, beyond-lithium-ion batteries (LIBs) are recently extensively investigated, including sodium-ion batteries (SIBs), potassium-ion batteries (PIBs), zinc-ion batteries (ZIBs), and aluminum-ion batteries (AIBs)5. Na, K, Zn, and Al are abundant metallic elements in the earth crust, far exceeding Li  during guest ion insertion and extraction. This merit is crucial to meet the long-term cycling requirement of beyond-LIBs, however, has rarely been achieved thus far, to the best of our knowledge14. Compared with Li+ (0.76 Å), Na+ (1.02 Å) and K+ (1.38 Å) have much larger ionic radii  molecular nanosheets produced from exfoliation of their layered precursors have been well recognized in electrochemical energy storage. Through the recently developed exfoliation and assembly strategy, vertical assembly of different nanosheets on top of each other generates 2D multilayered heterostructures as promising layered materials for energy storage+ ions such as Na+, K+, Zn2+, Al3+. A reversible intercalation mechanism with a negligible volume change during charge and discharge processes has been demonstrated. Consequently, high-performance SIBs, PIBs, ZIBs, and AIBs are obtained in terms of high specific capacity, large energy density, and long-term cycling stability.Here, we report that interface strain engineering of 2D multilayered heterostructure produces a zero-strain cathode for reversible intercalation of beyond-Li4-graphene multilayered heterostructure was utilized as a proof-of-concept layered material for our design .A 2D VOPOign Fig. . VOPO4 n4·2H2O crystals are platelet chunks composed of tightly stacked layers , suggests the intercalation of acrylamide  observation revealed an ultrathin sheet-like morphology of the obtained VOPO4 nanosheets  (PDDA), resulting in a positively charged nature31. Due to electrostatic attraction, these two oppositely charged nanosheets self-assembled into a face-to-face stacked 2D multilayered heterostructure. An optimized mass ratio between the VOPO4 nanosheets and modified graphene could be theoretically estimated as ~11.4 based on a hypothesized area-matching model  image and the corresponding elemental mapping indicate the uniform distribution of VOPO4 and graphene nanosheets . After exfoliation, red shifts of Raman bands of these two stretching modes were observed for the VOPO4 nanosheets. However, clear blue shifts of ~15 cm−1 for O–P–O and ~3 cm−1 for V=O were observed when the VOPO4 nanosheets were stacked with graphene, supporting the presence of interface-induced compressive strain on the VOPO4 sheets. Furthermore, the strain (δ) can be approximatively calculated byω is the Raman shift and Δω is the change of Raman peak34. Taking the O–P–O model as an example, a strain of ~4.0% was determined in the 2D VOPO4-graphene multilayered heterostructures. Density functional theory (DFT) calculations based on VOPO4–VOPO4 and VOPO4-graphene bilayers were performed to investigate the lattice strains induced by the interface in the heterostructures. As shown in Supplementary Fig. 4–VOPO4 bilayers to 1.594 and 1.548 Å in VOPO4-graphene bilayers. The lattices (a × b) of VOPO4 were optimized to be 6.212 × 6.212 Å. The lattice strain (δ) for VOPO4-graphene is defined asδ) of 3.2% can be estimated in VOPO4-graphene, which is consistent with the result based on the Raman analysis.Due to the mismatch of the in-plane lattice spacing between VOPOsis Fig.  of the 2ing Fig.  comprisi4·2H2O, VOPO4 nanoflakes and 2D VOPO4-graphene multilayered heterostructure are shown in Fig. 4 structures with dominant 00l peaks. The bulk VOPO4·2H2O showed an interlayer distance of ~0.74 nm. The shifted 001 peaks resulted in a decreased interlayer separation of ~0.66 nm for the VOPO4 nanoflakes and the 2D VOPO4-graphene multilayered heterostructure. The significantly different intensities of 001 peaks imply the stacking density of VOPO4 in these layered structures, which can be roughly estimated based on the Scherrer formula. Consequently, the 2D VOPO4-graphene multilayered heterostructures exhibited an average restacking thickness of ~15 nm  and VOPO4 nanoflakes (~50 nm). These results strongly confirm that limited number of VOPO4 sheets were confined and stabilized between the graphene nanosheets, resulting in a 2D VOPO4-graphene multilayered heterostructure with interface strain.The XRD patterns of the VOPO nm Fig. , which i4-graphene multilayered heterostructure was first investigated. In situ XRD measurements of the 2D VOPO4-graphene multilayered heterostructure cathodes were conducted during charge/discharge cycles  and reversed back to the original value after charge , which can be attributed to the continuous lattice volume variations during cycling  and (010) facets of VOPO4, as well as K intercalated into the (001) interlayer of the layered VOPO4 structures  of the three models for the restacked bilayer and four-layer structures were shown in Fig. 4 bilayers  and restacked VOPO4 nanoflakes (~160 mA h g−1). In a control experiment, practically no capacity was exhibited for the modified graphene under the same condition  and scan rate (v) was investigated, according to i = avb45. The value of b = 0.5 indicates a diffusion-controlled process, whereas b = 1 means a capacitive-dominated process. The b-value can be obtained by plotting log(i) versus log(v)  and diffusion-controlled (k2ν1/2) process according to i(V) = k1v + k2v1/245. At the scan rate of 0.3 mVs−1, a capacitive contribution was calculated to be ~81% 6 are promising cathode materials due to their high voltage and theoretical capacity54. Unfortunately, their residual crystal water may block the insertion of K+ ions, and even cause safety issues in ‘high’ voltage operation. Impressively, the 2D VOPO4-graphene multilayered heterostructure cathode can deliver a high potassiation/depotassiation potential of ~3.5 V, which results in the highest energy density of ~570 W h kg−1 among recently reported cathode materials for PIBs , zinc-ion batteries (ZIBS) and aluminum-ion batteries (AIBs). As shown in Fig. + ions was observed for 2D VOPO4-graphene multilayered heterostructure. A continuous lattice volume variation during charge/discharge cycling , H3PO4 (85% 26.6 mL), and H2O (115.4 mL) was refluxed at 110 °C for 16 h. The resulting yellow precipitate was collected by centrifugation, washed several times with water and acetone, and then dried in oven at 60 °C.Bulk layered VOPO4 nanosheets were synthesized by an intercalation-exfoliation process60. For the synthesis of intercalated VOPO4, the bulk VOPO4·2H2O (1 g), acrylamide (10 g) and ethanol (50 mL) were mixed and stirred at 30 °C for 72 h. The product was washed with acetone, and then dried under ambient conditions. The VOPO4–acrylamide intercalation compound was dispersed in isopropanol with a concentration of 2 mg mL−1 and then followed by stirring at room temperature for 24 h. The obtained suspensions were allowed to stand for more than 7 days, after which the supernatant was separated and collected for use. In a direct exfoliation process61, bulk VOPO4·2H2O was dispersed in isopropanol with a concentration of 2 mg mL−1 and then ultra-sonicated for 30 min. The suspension was separated and collected for use.The VOPO22. The VOPO4-graphene multilayered heterostructures were prepared by a solution-phase self-assembly strategy. Specifically, the suspensions of VOPO4 and modified graphene nanosheets were mixed dropwise under continuous stirring. The flocculated VOPO4-graphene was collected and washed by centrifugation and then freeze-dried.The modified graphene nanosheets with a positively charged nature were synthesized according to our previous studies−1. XPS measurements were performed using an ESCALAB250Xi  equipped with mono-chromated Al K alpha (energy: 1486.68 eV). Raman spectra were obtained from a Renishaw inVia spectrometer system  equipped with a Leica DMLB microscope  and a Renishaw He–Ne laser source.Powder XRD data were recorded using a Bruker D8 Discover diffractometer equipped with monochromatic Cu Kα radiation (λ = 0.15405 nm). A field-emission scanning electron microscope  and a JEOL JEM-ARM200F TEM instrument were employed to observe the microstructures and morphologies of the samples. A Dimension 3100 SPM instrument was used to examine the topography of the nanosheets deposited onto Si wafer substrates. The zeta potentials of nanosheet suspensions were determined using an ELS-Z zeta-potential analyzer. The thermogravimetric (TG) analysis were carried out using an SDT 2960 thermoanalyzer under an air atmosphere from 25 to 800 °C with a heating rate of 5 °C min4 active materials. The cathodes were prepared by making a slurry of active material, carbon black, and poly(tetrafluoroethylene) (PTFE) in a weight ratio of 80:15:5. For the PIBs, the slurry was casted onto Al foils with a mass loading of the active material of approximately 1.5 mg cm−2. Potassium foils were used as the counter and reference electrodes. Whatman glassy fibers were used as the separators. The electrolyte was 0.8 M KPF6 in ethylene carbonate (EC)/propylene carbonate (PC) (1/1 V/V) with a 5 wt% fluoroethylene carbonate (FEC) additive. For the SIBs, the slurry was casted onto Al foils with a mass loading of the active material of approximately 1.5 mg cm−2. Sodium foils were used as the counter and reference electrodes. Whatman glassy fibers were used as the separators. The electrolyte was 1 M NaClO4 in PC with 2% FEC additive. For the ZIBs, the slurry was coated on a stainless steel foil with an active-material mass loading of 1.5 mg cm−2. 1 M Zn(CF3SO3)2 in acetonitrile was used as an electrolyte. A zinc foil and a filter paper were used as anode and separator, respectively. For the AIBs, the slurry was pasted on a Mo foil with an average mass loading of the active material of 1.0 mg cm−2. The electrolyte was a room temperature ionic liquid (RTIL) consisting of aluminum chloride and 1-ethyl-3-methylimidazolium chloride (molar ratio AlCl3: [EMIm]Cl = 1.5). Aluminum disk was used as the anode electrode. A glass fiber filter paper was employed as the separator.All the battery measurements were carried out using a half-cell system in CR2032-type coin cells. The specific capacity was calculated based on the mass ratio of the VOPO63. The exchange-correlation potentials were treated by the generalized gradient approximation (GGA) parameterized by Perdew, Burke and Ernzerholf (PBE)64. The interaction between valence electrons and ion cores was described by the projected augmented wave (PAW) method65 and the DFT-D2 method68 was adopted for the multilayered systems taking into account of van der Waals (vdW) interaction. The electronic wave functions were expanded in a plane-wave basis with a cutoff energy of 400 eV. For two-dimensional bilayer or four layered VOPO4, the lattice parameters along two periodic directions were set as a = b = 6.02 Å, and for the nonperiodic direction, the lattice character was set as c = 35 Å. As for the consideration of the bilayer or multilayer systems with edges, one-dimensional models were constructed with the lattices parameter of b = 6.02 Å. Besides, the lattice characters along the other directions were set as a = 22 Å and c = 35 Å, respectively. The reciprocal space was sampled by 5 × 5 × 1 and 1 × 5 × 1 grid meshes for the geometry optimization of 2D and 1D systems, by using the Monkhorst–Pack scheme69. All the atoms were fully relaxed until the Hellmann–Feynman force on each atom was less than 0.01 eV Å−1.All the calculations were performed by the framework of spin polarized DFT as implemented in the Vienna ab-initio Simulation Package (VASP)Supplementary InformationPeer Review File