R1234yf/RE170混合工质用于汽车空调的可行性

目前汽车空调常用的制冷剂四氟乙烷(R134a)存在较高的温室效应指数(GWP =1 300),会对环境造成不利的影响.将R1234yf和RE170以质量配比为70∶30组成新型混合制冷剂(代号NCUR04)应用于汽车空调中,通过热力学性质、环境特性、循环性能、安全特性、润滑特性方面综合考虑替代R134a的可行性,并与潜...     

Nanostructure identification using interference microscope with database

Interference microscopy with complex-amplitude pattern matching between an observed image and images stored in a database can observe nanostructures beyond the diffraction limit of light. The fundamental performance was investigated from size measurement of a single rectangular convex element with a height and width less than 100 nm under illumination light with a wavelength of 400 nm, using an objective lens with a numerical aperture of 0.85. A 50 nm rectangular convex element was reconstructed with an identification error rate of less than 1% and a root-mean square error lower than 1 nm in the presence of random noise. The element height could be detected with a lower error than its width when the element size was larger than ~?50 nm. However, this tendency reversed when the size was smaller than ~?50 nm, that is, the detection of the width had a slightly lower error than that of the height. In addition to these findings, position detection showed a small dependency on the element size when the position was in the laser beam.     

Interface corrugation effect on the polarization anisotropy of photoluminescence from (311)A GaAs/AlAs short-period superlattices

Studying GaAs/AlAs superlattices containing a quantum-well-wire array revealed photoluminescence polarization anisotropy for samples with GaAs layers less than 21 Å thick. It was found that polarization for a thickness of more than 40 Å was mainly due to valence band anisotropy, whereas polarization for a thickness of less than 21 Å was equally attributable to both valence band anisotropy and anisotropy associated with interface corrugation. For a GaAs layer thickness of less than 21 Å, a blueshift of the Γ electron-Γ heavy hole transition was observed. In this transition, the position of the peak of photoluminescence from the GaAs/AlAs (311)A superlattices containing a quantum-well-wire array is shifted toward higher energies compared to the (311)B and (100) superlattices containing no quantum-well wire with the same GaAs layer thickness. The conclusion was made that a blueshift is observed in GaAs/AlAs superlattices with GaAs layers less than 21 Å thick and a red-shift is observed when the thickness is larger than 43 Å.     

An angle-resolved laser incident beam detector based on a pair ofFabry-Perot etalons

An angle-resolved laser detector based on a pair of a non-mechanical scanning Fabry-Perot cavities is described. The differential signal from the two cavities is approximately independent from the polarization of the incident laser beam and it is used to determine the angle of incidence of the beam on the Fabry-Perot cavities. The F-P etalon is made of interferometric filter combination. A laser incident angle sensor experimental platform is built up, and the experiment is carried out with a given laser range finder. When the incident angle is less than 5°, the transmission difference measured by the laser angle sensor is significantly lower than theoretical value, and deviation is more than 10%. When the incident angle is greater than 10°, the deviation is much lower than that of the situation of the incident angle is lower than 10°.     

用于快点火研究的超短脉冲的相干合成

 利用傅里叶光学方法，建立了一个基于远场的多束超短脉冲相干合成的理论模型。研究了一个口径为50 cm，脉宽为1 ps的超短脉冲相干合成系统的各种误差对脉冲远场时域和空域特性的影响。结果表明：若要求远场的一倍衍射极限区域的积分能量分布达到理想情况下的90％，该系统的相位延迟误差小于0.63，沿x方向角度误差小于0.37 μrad，沿y方向角度误差小于0.34 μrad；若要求远场叠加脉冲的时域展宽小于25％，系统的剩余啁啾因子应小于1.32(不考虑相位延迟)或1.52(考虑0.63的相位延迟)。     

Time and frequency parameters of bottlenose dolphin whistles as predictors of surface behavior in the Mississippi Sound

In this study, an algorithm previously developed for estimating the total ultrasonic attenuation along the propagation path from the surface of the transducer to a region of interest (ROI) in tissue, was modified to make it more practical for use in clinical settings. Specifically, the algorithm was re-derived for when a tissue mimicking phantom rather than a planar reflector is used to obtain the reference power spectrum. The reference power spectrum is needed to compensate for the transfer function of the transmitted pulse, the transfer function of transducer, and the diffraction effects that result from focusing/beam forming. The modified algorithm was tested on simulated radio frequency (RF) echo lines obtained from two samples that have different scatterer sizes and different attenuation coefficient slopes, one of which was used as a reference. The mean and standard deviation of the percent errors in the attenuation coefficient estimates (ACEs) were less than 5% and 10%, respectively, for ROIs that contain more than 10 pulse lengths and more than 25 independent echo lines. The proposed algorithm was also tested on two tissue mimicking phantoms that have attenuation coefficient slopes of 0.7 dB/cm-MHz and 0.5 dB/cm-MHz respectively, the latter being the reference phantom. When a single element spherically focused source was used, the mean and standard deviation of the percent errors in the ACEs were less than 5% and 10% respectively for windows that contain more than 10 pulse lengths and more than 17 independent echo lines. When a clinical array transducer was used, the mean and standard deviation of the percent errors in the ACEs were less than 5% and 25%, respectively, for windows that contain more than 12 pulse lengths and more than 45 independent echo lines.     

New source of dense, cryogenic positron plasmas

We have developed a new method, based on the ballistic transfer of preaccumulated plasmas, to obtain large and dense positron plasmas in a cryogenic environment. The method involves transferring plasmas emanating from a region with a low magnetic field (0.14 T) and relatively high pressure (10(-9) mbar) into a 15 K Penning-Malmberg trap immersed in a 3 T magnetic field with a base pressure better than 10(-13) mbar. The achieved positron accumulation rate in the high field cryogenic trap is more than one and a half orders of magnitude higher than the previous most efficient UHV compatible scheme. Subsequent stacking resulted in a plasma containing more than 1.2 x 10(9) positrons, which is a factor 4 higher than previously reported. Using a rotating wall electric field, plasmas containing about 20 x 10(6) positrons were compressed to a density of 2.6 x 10(10) cm(-3). This is a factor of 6 improvement over earlier measurements.     

200kV/100kA低抖动环轨式多通道场畸变开关

 研制了一种200kV/100kA环轨式场畸变开关。对该开关以Ar，N₂，SF₆及SF₆/N₂，SF₆/Ar 混合气为工作介质的耐压及触发性能研究结果表明：该开关耐压最大偏差小于自击穿电击的4%；欠压比大于等于自击穿电击80%时，抖动极差小于2ns，标准方差抖动小于等于1ns；实现了多通道导通，通道数大于等于3；开关工作范围极大，在欠压比大于等于自击穿电击20%时抖动极差小于2.85ns。     

C波段50 MW行波输出速调管设计

设计了导流系数1.53 P的电子枪,枪内场强低于22.1 kV/mm,阴极平均负载小于6.3 A/cm2;采用部分屏蔽流均匀场电磁聚焦系统,实现了对电子注的良好聚焦;设计了C波段/2模盘荷波导行波输出结构,采用CST软件对其色散特性、耦合阻抗进行了计算分析。首先以单间隙输出腔代替行波输出结构对5腔注-波互作用系统进行计算,确定了前4腔的设计参数,然后采用PIC模拟软件对具有盘荷波导结构的输出系统进行了三维模拟,获得了大于50 MW的输出功率,效率大于45%,饱和增益大于50 dB,盘荷波导结构间隙电压比单间隙输出腔下降30%,效率提高4%。     

Analysis of the efficiency and multifractality of gold markets based on multifractal detrended fluctuation analysis

In this paper, we investigate the efficiency and multifractality of a gold market based on multifractal detrended fluctuation analysis. Our evidence shows that the gold return series are multifractal both for time scales smaller than a month and for time scales larger than a month. For time scales smaller than a month, the main contribution of multifractality is fat-tail distribution. For time scales larger than a month, both long-range correlations and fat-tail distribution play important roles in the contribution of multifractality. Using the method of rolling windows, we find that the gold market became more and more efficient over time, especially after 2001. The abnormal points of scaling exponents can also be related to some occasional events. By defining a new inefficiency measure related to the multifractality, we find that the gold market is more efficient during the upward periods than during the downward periods.     

Resolution enhancement in a light-sheet-based microscope (SPIM)

Light-sheet-based microscopy [single-plane illumination microscope (SPIM)] performs very well at low numerical apertures. It complements conventional (FM), confocal (CFM), and two-photon fluorescence microscopy (2hnu-FM) currently used in modern life sciences. Lateral and axial SPIM point spread function (PSF) extents are measured by using fluorescent beads to determine the 3D resolution. The results are compared with values derived from an analytical theory and numerical simulations. The discrepancies are found to be less than 5%. The axial extent of a SPIM-PSF (10x/0.3 W) is approximately 5.7 microm. This value is almost a factor of 2 smaller than in CFM, more than 2.5 times smaller than in FM, and more than three times smaller than in 2hnu-FM. SPIM outperforms 2hnu-FM and FM, while CFM has a better axial resolution at NAs above 0.8.     

Differential thickness measurement using a polarization interferometer

A method for measuring the differential thickness of a thin film using a polarization interferometer is described. Theoretical estimation shows that the measurement error is less than 0.1%. Experiments performed on a PZT sample indicate high sensitivity and excellent linearity of the system. PZT expansions ranging from 300 nm to less than 1 nm could be measured with a precision better than 0.1 nm.     

0.22THz宽带折叠波导行波管设计与实验

为了获得0.22THz宽带折叠波导行波管,对行波管的慢波结构和输入输出窗结构进行了宽带设计。通过理论分析和电磁仿真计算出合适的参数,使慢波结构在0.22THz工作点附近的色散曲线平坦,耦合阻抗变化小,模拟计算得到的慢波结构3dB带宽大于16GHz;通过对盒型窗结构及匹配段的优化计算,得到的输入输出结构在大于30GHz范围内S11参数小于-25dB。根据该设计进行了两轮制管和实验研究,得到了一支3dB瞬时带宽约8.8GHz,另一支3dB瞬时带宽大于12GHz的0.22THz折叠波导行波管,中心频率的峰值功率大于400mW。     

Structure and thermophysical properties of single-wall Si nanotubes

In this work, molecular dynamics (MD) simulation based on the environment-dependent interatomic potential is carried out to explore the structure, atomic energy distribution, and thermophysical properties of single-wall Si nanotubes (SWSNTs). The unique structure of SWSNTs leads to a wider range energy distribution than crystal Si (c-Si), and results in a bond order in the range of 4.8–5. The thermal conductivity of SWSNTs is much smaller than that of bulk Si, and shows significantly slower change with their characteristic size than that of Si films. Out of the three types of SWSNTs studied in this work, pentagonal SWSNTs have the highest thermal conductivity while hexagonal SWSNTs have the lowest one. The specific heat of SWSNTs is a little larger than that of bulk c-Si. Pentagonal and hexagonal SWSNTs have close specific heats, which are a little larger than that of rectangular SWSNTs.     

On the possibility of the emission of attosecond pulses owing to the interaction of counterpropagating relativistically intense laser pulses with a thin layer of a diluted plasma

A numerical experiment in which two relativistically intense laser pulses are normally incident on a layer of a diluted plasma from two opposite sides is described. The period of Langmuir plasma oscillations is much larger than the pulse duration and the product of this period by the speed of light is much larger than the thickness of the layer. A pulse propagating to the right is incident on the layer earlier than the counter pulse and carries a significant fraction of electrons or all of the electrons from the plasma. Under certain conditions, electrons form a bunch, which contains most of the electrons and has a thickness much smaller than the wavelength of light. The counter pulse perturbs the motion of the bunch and initiates the emission of a short few-cycle pulse, which propagates in the positive direction (to the right), significantly differs in structure from the counter pulse, and has a duration much smaller than the field period in laser pulses.     

Courtship and agonistic sounds by the cichlid fish Pseudotropheus zebra

Courtship and agonistic interactions in an African cichlid species present a richer diversity of acoustic stimuli than previously reported. Male cichlids, including those from the genus Pseudotropheus (P.), produce low frequency short pulsed sounds during courtship. Sounds emitted by P. zebra males in the early stages of courtship (during quiver) were found to be significantly longer and with a higher number of pulses than sounds produced in later stages. During agonistic intrasexual quiver displays, males produced significantly longer sounds with more pulses than females. Also, male sounds had a shorter duration and pulse period in courtship than in male-male interactions. Taken together, these results show that the acoustic repertoire of this species is larger than what was previously known and emphasize the importance of further research exploiting the role of acoustic stimuli in intra- and interspecific communication in African cichlids.     

北洋2#制冷剂循环性能试验研究

研究了一种双元混合物——北洋2#,它具有优于R22的环保性能和良好的循环性能。在同机型标准空调工况下检测,其性能(COP)较R22低1.7%,但其制冷量较R22高14.6%;其COP较R410A和R32均高8%。在低温区的检测试验证明:其COP稍低于R22,但是其能达到比R22更低的温度。并且北洋2#的制冷速度比R22快35.9%。所以,北洋2#可以作为R22有潜力的替代制冷剂。     

Characteristics of Au/n-Si surface barrier nuclear radiation detectors with a nanometer native oxide layer

The effect of a surface charge on the characteristics of silicon surface barrier detectors with a nanometer oxide layer is studied. Interaction between the surface charge and a metal or a semiconductor at an oxide layer thickness of less than 1 or more than 2 nm, respectively, is taken into account. The application of silicon detectors with an oxide layer having a thickness of more than 2 nm in detecting nuclear resonance reactions is considered.     

Effect of minute’s-scale aging on refractive index of chopped and non-chopped optical films

The refractive indices of non-chopped and chopped films of cryolite, MgF₂ and mixed cryolite-MgF₂, which is higher than the bulk value, measured using spectro-photometer, ellipsometer and Abeles method are observed to be higher than corres-ponding bulk values. Chopped films show a higher refractive index than non-chopped films. The electron diffraction study shows a more amorphous structure for the chopped films. The major part played by chop-time seems to be in increasing the initial minute’s-scale aging rather than settling of ad-atoms during chop-time. The observed dispersion curve shows that some unknown material other than water gives an important aging effect.     

Quasi-phase-matched DC-induced three wave mixing versus four wave mixing: a simulated comparison

A comparison is made between DC-induced three-wave mixing under an on-off quasi-phase-matching scheme and a perfectly phase-matched four wave mixing process. It is shown that the DC-induced process is capable of producing a significantly larger conversion efficiency than the four wave mixing process. Despite the fact that it suffers greater effects of dispersion, the enhanced growth rate of the DC-induced process provides a conversion efficiency roughly 300× larger than that of four wave mixing. Over a sample length of 20 cm the DC-induced process is able to generate idler power more than 270 times greater than that produced by the equivalent four wave mixing process.