124213992
High performance computation on beam dynamics problems in high intensity compact cyclotrons
This paper presents the research progress in the beam dynamics problems for future high intensity compact cyclotrons by utilizing the state-of-the-art high performance computation technology. A “Start-to-Stop” model, which includes both the interaction of the internal particles of a single bunch and the mutual interaction of neighboring multiple bunches in the radial direction, is established for compact cyclotrons with multi-turn extraction. This model is then implemented in OPAL-CYCL, which is a 3D object-oriented parallel code for large scale particle simulations in cyclotrons. In addition, to meet the running requirement of parallel computation, we have constructed a small scale HPC cluster system and tested its performance. Finally, the high intensity beam dynamics problems in the 100 MeV compact cyclotron, which is being constructed at CIAE, are studied using this code and some conclusions are drawn.
111221941
ASTROD and ASTROD I: Progress Report
Over the next decade the gravitational physics community will benefit from dramatic improvements in many technologies critical to the tests of gravity and gravitational-wave detection. The highly accurate deep space navigation, interplanetary laser ranging and communication, interferometry and metrology, high precision frequency standards, precise pointing and attitude control, together with the drag-free technologies will revolutionize the field of the experimental gravitational physics. Deep-space laser ranging will be ideal for gravitational-wave detection, and testing relativity and measuring solar-system parameter to an unprecedented accuracy. ASTROD I is such a mission with single spacecraft; it is the first step of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) with 3 spacecraft. In this paper, we will present the progress of ASTROD and ASTROD I with emphases on the acceleration noises, mission requirement, charging simulation, drag-free control and low-frequency gravitational-wave sensitivity.
206352395
The attachment of amino fragment to purine: inner-shell structures and spectra.
The impact of the amino fragment (-NH(2)) attachment on the inner-shell structures and spectra of unsubstituted purine and the purine ring of adenine are studied. Density functional theory calculations, using the LB94/TZ2P//B3LYP/TZVP model, reveal significant site-dependent electronic structural changes in the inner shell of the species. A condensed Fukui function indicates that all of the N and C sites, except for N((1)) and C((5)), demonstrate significant electrophilic reactivity (f(-) > 0.5 in |e|) in the unsubstituted purine. Once the amino fragment binds to the C((6)) position of purine to form adenine, the electrophilic reactivity of these N and C sites is greatly reduced. As expected, the C((6)) position experiences substantial changes in energy and charge transfer, owing to the formation of the C-NH(2) bond in adenine. The present study reveals that the N1s spectra of adenine inherit the N1s spectra of the unsubstituted purine, whereas the C1s spectra experience significant changes although purine and adenine have geometrically similar carbon frames. The findings also indicate that the attachment of the NH(2) fragment to purine exhibits deeply rooted influences to the inner-shell structures of DNA/RNA bases. The present study suggests that some fragment-based methods may not be applicable to spectral analyses in the inner shell.
93891215
Gamma-ray spectra of methane in the positron–electron annihilationprocess
Abstract Bound electron contribution to the Doppler-shift of gamma-ray spectra in the positron–electron annihilation process of molecular methane has been studied in gas phase. Two accurate ab initio quantum mechanical schemes, i.e. the delocalised molecular orbital (MO) and the localised natural bond orbital (NBO) schemes, are applied to study the multi-centred methane molecule. The present ab initio calculations of methane indicate that the C–H bonds are polarised with the partial negative charge of −0.36 a.u on the carbon atom and the partial positive charge of +0.09 a.u. on each of the hydrogen atoms. The positively charged hydrogen atoms produce repulsive Coulomb potentials to a positron. Both the MO and NBO schemes further reveal that the 2a 1 electrons of methane, that is, the 2a 1 electron component of the CH bonds rather than the whole CH bonds of methane, predominates the positron–electron annihilation gamma-ray spectra of the molecule. Electrons of a molecule which are dominant the positron–electron annihilation processes are called “positrophilic” electrons in the present study. It is further shown that the negative electrostatic potential (ESP) of methane facilitates with the density of the “positrophilic” 2a 1 electrons of methane. Other valence electrons (e.g. 1t 2 ) in the CH bonds play a minor “spectator” role in the annihilation process of methane.
119293060
Gamma-ray spectra of hexane in gas phase and liquid phase
Theoretical gamma-ray spectra of molecule hexane have been calculated and compared with the experimental results in both gas (Surko et al, 1997) and liquid (Kerr et al, 1965) phases. The present study reveals that in gas phase not all valence electrons of hexane exhibit the same probability to annihilate a positron. Only the positrophilic electrons in the valence space dominate the gamma-ray spectra, which are in good agreement with the gas phase measurement. When hexane is confined in liquid phase, however, the intermolecular interactions ultimately eliminate the free molecular orientation and selectivity for the positrophilic electrons in the gas phase. As a result, the gamma-ray spectra of hexane become an averaged contribution from all valence electrons, which is again in agreement with liquid phase measurement. The roles of the positrophilic electrons in annihilation process for gas and liquid phases of hexane have been recognized for the first time in the present study.
118676242
Gravitational effects of condensate dark matter on compact stellar objects
We study the gravitational effect of non-self-annihilating dark matter on compact stellar objects. The self-interaction of condensate dark matter can give high accretion rate of dark matter onto stars. Phase transition to condensation state takes place when the dark matter density exceeds the critical value. A compact degenerate dark matter core is developed and alter the structure and stability of the stellar objects. Condensate dark matter admixed neutron stars is studied through the two-fluid TOV equation. The existence of condensate dark matter deforms the mass-radius relation of neutron stars and lower their maximum baryonic masses and radii. The possible effects on the Gamma-ray Burst rate in high redshift are discussed.
55717747
The drive laser system for dc-sc injector
PKU-SCAF has developed a photoinjector which adopt a 1+1/2 cell super conducting cavity and DC electron gun. We also developed a low cost drive laser system for the photocathode DC gun to provide high average beam current. This laser system include a commercial high repetition rate, ps, all solid-state laser, the home made SHG and FHG, Fourier relay optics and the uniform illumination optics. The test results shows the output power at 266 nm of the laser system is more than 1.2W and got more than 500 µA beam current from CsTe cathode from the DC gun.
119308692
The updated luminosity correlations of gamma-ray bursts and cosmological implications
Several interesting luminosity correlations among gamma-ray burst (GRB) variables have been recently discussed extensively. In this paper, we derive the six luminosity correlations ($\tlag-L$, $V-L$, $\epkk-L$, $\epkk-E_\gamma$, $\trt-L$, $\epkk-E_{\gamma, \mathrm{iso}}$) from the light curves and spectra of the latest 116 long GRBs, including the time lag ($\tlag$) between low and high photon energy light curves, the variability ($V$) of the light curve, the peak energy of the spectrum ($\epkk$), and the minimum rise time ($\trt$) of the peaks. We find that the intrinsic scatter of the $V-L$ correlation is too large and there seems no inherent correlation between the two parameters using the latest GRB data. The other five correlations indeed exist when the sample is enlarged. The $\epkk-E_\gamma$ correlation has a significantly lower intrinsic scatter compared to the other correlations. We divide the full data into four redshift bins when testing possible evolution of the correlations with redshift. We find no statistically significant evidence for the redshift evolution of the luminosity correlations. To avoid the circularity problem when constraining the cosmological parameters, we simultaneously minimize $\chi^2$ with respect to both correlation parameters $a$, $b$ and the cosmological parameters using the maximum likelihood method. For the flat $\Lambda$CDM, the best fit is $\omm=0.31^{+0.13}_{-0.10}$. We also constrain the possible evolution of the equation of state (EOS) of the dark energy using the GRBs together with the Union2 compilation of SNe Ia and the $H(z)$ data. The result is consistent with the cosmological constant at $2 \sigma$ confidence level and mainly due to the GRB data, the dark energy EOS shows slight deviation from -1 at $z \geq0.5$ as was persistently presented with many previous data sets.
17589853
AMiBA Observations, Data Analysis and Results for Sunyaev-Zel'dovich Effects
We present observations, analysis and results for the first-year operation of AMiBA, an interferometric experiment designed to study cosmology via the measurement of Cosmic Microwave Background (CMB). AMiBA is the first CMB interferometer operating at 3 mm to have reported successful results, currently with seven close-packed antennas of 60-cm diameter giving a synthesized resolution of around 6'. During 2007 AMiBA detected the Sunyaev-Zel'dovich effects (SZE) of six galaxy clusters at redshift 0.091 <= z <= 0.322. An observing strategy with on-off-source switching is used to minimize the effects from electronic offset and ground pickup. Planets were used to test the observational capability of AMiBA and to calibrate the conversion from correlator time-lag data to visibilities. The detailed formalism for data analysis is given. We summarize our early tests including observations of planets and quasars, and present images, visibility profiles, the estimated central coordinates, sizes, and SZE amplitudes of the galaxy clusters. Science results are summarized. We also discuss possible systematic effects in the results.
18621135
Localization of RF Breakdowns in a Standing Wave Cavity
At SLAC, a 5-cell, normal-conducting, L-band (1.3 GHz), standing-wave (SW) cavity was built as a prototype positron capture accelerator for the ILC. The structure met the ILC gradient goal but required extensive rf processing. When rf breakdowns occurred, a large variation was observed in the decay rate of the stored energy in the cavity after the input power was shut off. It appeared that the breakdowns were isolating sections of the cavity, and that the trapped energy in those sections was then partitioned among its natural modes, producing a distinct beating pattern during the decay. To explore this phenomenon further, an equivalent circuit model of cavity was created that reproduces well its normal operating characteristics. The model was then used to compute the spectra of trapped energy for different numbers of isolated cells. The resulting modal patterns agree well with those of the breakdown data, and thus such a comparison appears to provide a means of identifying the irises on which the breakdowns occurred.