The competition of neutrino energy loss due to the pair, photo-, plasma process at the late stages of stellar evolution

Based on the Weinberg-Salam theory, the competition of the Neutrino Energy Loss （NEL） rates due to the pair, photo-and plasma process are canvassed. The ratio factor C1, C2 and C3 which correspond the different contributions of the pair, photo-and plasma neutrino process to those of the total NEL rates are accurately taken into account. The ratio factors are very sensitive to the temperature and density. The ratio factor C2 always is lower than the ratio factor C1 and C3. The pair NEL process is the dominant contribution before the crossed point 0（C1 = C3 = 0.45） and the plasma NEL process will be the main dominant contribution after the crossed point O. With increasing temperature, the crossed point O will move to the direction of higher density.     

重复频率脉冲大气放电中氮气的振动温度

氮气分子的振动自由度在大气放电低温等离子体中会被高度激发。从振动能级的简谐振子模型和Boltzmann分布近似出发,研究重复频率脉冲放电中振动温度的变化行为。结果表明,决定重频条件下振动温度的主要过程是电子碰撞振动激发和振动-平动弛豫,而在振动能级高度激发的情形下其与氧原子的化学反应也会产生影响。对于振动激发过程,通过跃迁反比相似率推导出的特征弛豫时间与动理学模型符合较好。在振动-平动弛豫中占主导贡献的为干燥大气中的氧原子或潮湿大气中的水分子。当氧原子数密度为1014 cm-3时,若初始振动温度在5000 K,在化学反应过程中振动能量的特征弛豫时间在0.1~1 s量级。     

Monte Carlo Simulation of Helium Transport in the Vicinity of Divertor Plate

A Monte Carlo code “1DHET” has been utilized for simulating the transport of neutral helium near divertor flat pumping target plate. The dominant atomic processes of electron impact ionization and elastic scattering by plasma ions are included. The thermal and streaming motion of the ions along the magnetic field is taken into consideration. Calculations show that the probability of neutral helium turning back to the target plate will increase by 45% if the divertor edge plasma density is smoothly raised up to 4.7 times higher at the divertor plate than that at 7cm apart inward as compared with the ordinary outward decreasing density profile while keeping temperature profile fixed. The temperature decreases smoothly from 40 eV at z = 7 cm to 3 eV at the plate. The effects of angle between the magnetic field and the target plate, the temperature of plate, edge plasma sheath potential and different target materials on the probability of helium particles scattered back to the plate are studied.     

One-step preparation of N-doped strontium titanate films by pulsed laser deposition

Perovskite-type oxynitrides exhibit promising electrical and optical properties and can possibly be used in the future as functional materials for electrical, photo-, and electrochemical applications. Continuous heterovalent substitution of oxygen ions by nitrogen ions allows tuning of the desired optical and/or electronic properties to the application specifications. In the present work deposition of SrTiO₃:N films by pulsed reactive crossed beam laser ablation was studied in order to examine the influence of different deposition parameters on the film crystallinity and composition. The deposited films exhibit a perovskite-type crystal structure and reveals epitaxial growth on MgO(100) substrates. The unit cell parameters of the deposited SrTiO₃:N films range within , which is slightly larger than for polycrystalline SrTiO₃ (a=3.905). The studied films reveal an oxygen content in the range of (2.70-2.98)±0.15. The relative N content (vs. O) can be tuned within the range of 1.0–3.0% by adjusting the deposition parameters. The N:O concentration ratio increases with increasing laser fluence and target-to-substrate distances, while the substrate temperature has a more complex influence on the nitrogen concentration. In the range of 580–650 °C the [N]/[O] ratio increases while further heating results in a gradual decrease of the N content. PACS  81.15.Fg; 68.55.-a; 81.05.Zx     

Plasma neutrino energy loss due to the axial-vector current at the late stages of stellar evolution

Based on the Weinberg-Salam theory, the plasma neutrino energy loss rates of vector and axialvector contributions are studied.A ratable factor of the rates from the axial-vector current relative to those of the total neutrino energy loss rates is accurately calculated.The results show that the ratable factor will reach a maximum of 0.95 or even more at relatively higher temperature and lower density (such as P/μe＜ 10~7 g/cm~3).Thus the rates of the axial-vector contribution cannot be neglected.On the other hand, the rates of the axialvector contribution are on the order of～0.01% of the total vector contribution, which is in good agreement with Itoh's at relatively high density (such as p/μe＞10~7 g/cm~3) and a temperature of T≤10~(11) K.     

Molecular dynamics simulation studies of cryoprotective agent solutions: the relation between melting temperature and the ratio of hydrogen bonding acceptor to donor number

Molecular dynamics simulations have been carried out for glycerol–water–sodium chloride ternary solution due to its important role in cryopreservation engineering. The radial distribution functions for atom pairs potentially related to C–H ··· O and O–H ··· O hydrogen bonds were calculated. The radial distribution functions for the H (connected to C)–O atom pair do not exhibit peaks between 2 and 3 Å, whereas the radial distribution functions for the C–O atom pair exhibit distinct peaks between 3 and 4 Å. The reason for this is because most C–H ··· O geometries are bent and deviate from linearity. The ratios of acceptor to donor numbers for water and glycerol molecules decrease as the solute concentration increases. A characteristic concentration has been found that divides solutions with different mechanisms. Below the characteristic concentration, the melting temperature is linearly related to the ratio of acceptor to donor number for water molecules, whereas above the characteristic concentration, the melting temperature is linearly related to the ratio of acceptor to donor number for glycerol molecules. Further studies indicate that the relations are independent of hydrogen bonding criteria and temperature.     

Gaussian modification of neutrino energy loss on strongly screening nuclides 55Co and 56Ni by electron capture in stellar interior

Gaussian modifications of the neutrino energy loss (NEL) by electron capture on the strongly screening nuclides 55Co and 56Ni are investigated. The results show that in strong electron screening (SES),the NEL rates decrease without modifying the Gamow-Teller (G-T) resonance transition. For instance, the NEL rates of 55Co and 56Ni decrease more than two and three orders of magnitude for ρ7 = 5.86, T9≤ 5,Ye = 0.47, △ = 6.3, respectively. In contrast, due to Gaussian modification, the NEL rates increase about two orders of magnitude in SES. Due to SES, the maximum values of the C-factor (in %) on NEL of 55Co, 56Ni are of the order of 99.80%, 99.56% at ρ7 = 5.86 Ye = 0.47 and 99.60%, 99.65% at ρ7 = 106 Ye = 0.43, respectively.     

Effect of parameters on Si plasma emission in collinear double-pulse laser-induced breakdown spectroscopy

Collinear dual-pulse laser-induced breakdown spectroscopy was carried out on Si crystal by using a pair of nanosecond Nd:YAG laser sources emitting at 1064 nm. The spectral intensities and signalto-noise ratios of selected Si atomic and ionic lines were used to evaluate the optical emission. The optical emission intensity was recorded while varying the interpulse delay time and energy ratio of the two pulsed lasers. The effects of the data acquisition delay time on the line intensity and signal-to-noise ratio have been investigated as well. Based on the results, the optimal interpulse delay time, energy ratio of the two pulsed lasers, and data acquisition delay time for achieving the maximum atomic and ionic line intensities were found for generation of Si plasma with the collinear dual-pulse laser approach. The dominant mechanism for the observed line intensity variation was also discussed. In addition, the plasma temperature and electron number density at different gate delay times and different interpulse delay times were derived. A significant influence of plasma shielding on the electron temperature and electron number density at shorter interpulse delay times was observed.     

高温原位拉曼光谱研究BiFeO3陶瓷反应烧结相变过程

多铁性材料BiFeO3(BFO)由于具有潜在的磁电耦合效应而备受关注,但纯相陶瓷的制备始终是一个难点,部分原因在于对其反应烧结相变规律的认识尚不充分。高温原位拉曼光谱技术(HT-Raman)是表征复杂的固体相变及反应的有力手段。首次利用HT-Raman,研究了不同配比(1∶1, 1.03∶1和1.05∶1)的Bi2O3-Fe2O3在不同升降温速率(10和100℃·min-1)下的反应烧结相变过程,以及降温时反应产物的收缩效应。结果表明:Bi2O3-Fe2O3反应烧结生成BiFeO3的过程中,会产生中间过渡相Bi2Fe4O9和Bi25FeO39∶Bi2O3-Fe2O3配比为1.03∶1、升降温速率较快时,产物中杂相含量最少,可见Bi过量及较快的升降温速率能有效抑制杂相的生成。降温过程中,发现BFO的A1-1峰位随着温度降低发生蓝移,且二者呈良好的线性关系,这说明降温过程中BFO仅因温度变化产生晶格收缩,并没有结构相变。此外,还利用二维X射线衍射(2D-XRD)及背散射电子衍射(EBSD),表征了烧结产物的相组成及形貌。XRD结果也显示Bi过量时杂相含量较少,与拉曼结果一致。结合2D-XRD和EBSD的结果可知, Bi过量时烧结产物晶粒尺寸较大且均一,可见快速升降温有利于晶粒的成核与生长。研究结果可帮助进一步认清反应烧结规律,并指导纯相BiFeO3基陶瓷的制备。     

Quantum melting of the hole crystal in the spin ladder of Sr(14-x)CaxCu24O41

We have used resonant soft x-ray scattering to study the effects of discommensuration on the hole Wigner crystal (HC) in the spin ladder Sr(14-x)CaxCu24O41 (SCCO). As the hole density is varied the HC forms only with the commensurate wave vectors L(L) = 1/5 and L(L) = 1/3; for incommensurate values it "melts." A simple scaling between L(L) and temperature is observed, tau1/3/tau1/5 = 5/3, indicating an inverse relationship between the interaction strength and wavelength. Our results suggest that SCCO contains hole pairs that are crystallized through an interplay between lattice commensuration and Coulomb repulsion, reminiscent of the "pair density wave" scenario.     

Influence of Temperature on the Luminescence Properties of MgAl2O4:Dy3+ Ceramics Synthesized by Spark Plasma Sintering

Physics of the Solid State - Transparent MgAl2O4:Dy3+ ceramic samples were synthesized by spark plasma sintering. Their optical properties, photo- and cathodoluminescence, the luminescence decay...     

真空弧Ti-H等离子体热力学参数的原子发射光谱双温度研究北大核心CSCD

金属氢化物作阴极的真空弧离子源,假设其放电产生双温度的非平衡态Ti-H等离子体,其内部的气体解离过程和粒子电离过程分别由Culdberg-Waage解离方程和Saha电离方程进行描述,结合原子发射光谱以及电荷准中性条件,求出Ti-H等离子体的电子温度Te、重粒子温度Th和粒子数密度之后,可更进一步对等离子体的质量密度、焓、比热容等热力学参数进行描述。在不同的电子数密度下,研究各参数随变量θ(电子温度Te与重粒子温度Th的比值)变化的情况。计算结果显示:电子数密度已知,随θ值升高,除氢气分子数密度外,等离子体温度和单原子粒子数密度的计算结果均变化甚微。高电子数密度时,等离子体中单原子粒子占绝对优势,热力学参数由其控制;低电子数密度下,随θ值的升高,等离子体逐步由单原子粒子占优势转为氢气分子占绝对优势,热力学参数的变化情况表现出相同的规律。     

AlK壳层等离子体辐射谱模型的比对

碰撞辐射模型的比对研究对校验发展等离子体辐射谱模型、提高等离子体参数的诊断精度具有重要意义. 基于Al等离子体, 对常用的辐射模型代码FAC和FLYCHK K壳层辐射谱模型开展了比对研究, 详细比较了它们的离子丰度、特征线强度、谱发射率曲线和吸收系数曲线等特征, 并根据各能态的速率方程, 从FAC和FLYCHK模型的结构特点出发, 分析了造成这些差异的原因. FAC 和FLYCHK计算得到的类H、类He离子n=2, n=3激发态数密度有显著差异, 进而引起特征线发射率及其比值(He-IC/He-αup, He-βup/H-βup)的差异, 从而对等离子体参数的诊断结果产生影响. 除了模型中采用的能级结构和碰撞辐射过程速率外, 计算结果显著地受到FAC 和FLYCHK 模型结构的影响. n=2激发态数密度的差异是由FAC和FLYCHK分别采用能级和超组态(组态)的方式构建n=2激发态的速率方程而引起的, 而FAC代码忽略了n=3与更高激发态之间的碰撞耦合过程, 是引起n=3激发态数密度差异的原因. 主要特征线的吸收系数与基态能级的数密度相关, 受到激发态数密度的影响较小, 因此与谱发射率曲线相比, FAC和FLYCHK计算结果的差异更小.     

常压等离子体作用下CO2氧化CH4转化反应的光谱分析

采用光谱原位诊断技术在200～900nm范围内采集并标识了不同CO2添加量时CH4等离子体光谱。确定了常压下不同CO2添加量时CH4等离子体的活性物种。CO2添加量不同活性物种谱峰相对强度变化趋势不同,O活性物种谱峰相对强度随CO2添加量增加迅速增加。C2活性物种谱峰相对强度随CO2添加量增加逐渐降低。反应体系产生的活性O对CH4转化反应产物具有明显影响,CO2添加量不同,CH4转化反应机理不同。当CO2添加量小于30%时,CH4转化以偶联反应为主。CO2添加量大于30%时,CH4转化以重整反应为主。     

The strange border of the QCD phases

We address the flavour composition along the border between the hadronic and the quark–gluon plasma phases of QCD. The ratio of strange to up and down antiquarks () produced in particle and nuclear collisions is found to increase in collisions with an initially reached energy density () up to GeV/fm. Above this value it decreases approximately linearly and reaches its asymptotic value at zero baryon chemical potential (). We demonstrate that in nuclear collisions approaches its asymptotic value at –9 GeV/fm, corresponding to –8 TeV per pair, which will be reached at the LHC. After correcting for the difference in the chemical potentials of various colliding systems, universally saturates across the QCD phase boundary, following the temperature. Recent experimental puzzles as the increase in the ratio in collisions at 40 GeV per nucleon, its different behaviour at midrapidity, the decrease of the double ratio of in nucleus–nucleus over collisions with increasing , and the increase of in over collisions at the same , are naturally explained. We study the approach of thermodynamic observables at to the transition point and extract an estimate of the critical temperature. Received: 17 April 2001 / Published online: 24 August 2001     

Shot noise in ballistic graphene

We have investigated shot noise in graphene field effect devices in the temperature range of 4.2-30 K at low frequency (f=600-850 MHz). We find that for our graphene samples with a large width over length ratio W/L, the Fano factor F reaches a maximum F ~ 1/3 at the Dirac point and that it decreases strongly with increasing charge density. For smaller W/L, the Fano factor at Dirac point is significantly lower. Our results are in good agreement with the theory describing that transport at the Dirac point in clean graphene arises from evanescent electronic states.     

Effect of operating temperatures on the coefficient of performance of active carbon-methanol systems

Experimental and predicted results of an active carbon (AC35)-methanol pair as a function of operating temperatures are discussed.Experimental COP's higher than 0.5 are obtained when the evaporating temperature lift is less than 25°C. The COP is seen to be very sensitive to the evaporating and adsorbing temperatures. The regenerating temperature is of the order of 100°C which makes that pair a good candidate for solar cooling applications.A comparison between the results obtained with that pair and predicted performances of three other pairs (NH₃H₂O, ZeoliteH₂O and another active carbon-methanol pair) shows that:

• 1.(1) two adsorber cycles give higher COP's than the NH₃H₂H₂O continuous cycle;
• 2.(2) intermittent adsorptive cycles give higher COP's than the NH₃H₂O continuous cycle as long as the evaporating temperature lift is less than 50°C;
• 3.(3) among the solid adsorbents, the active carbon-methanol pairs seem to be the most promising for cooling applications. The choice of the active carbon depends on the evaporating temperature lift: AC35 is very well adapted for temperature lifts larger than 30°C; ACLH could be better adapted to smaller evaporating temperature lifts, as suggested by Passos et al.

     

Plasma Blow-Off from Electrode Surfaces in the Presence of Vacuum-Ultraviolet Radiation

Experiments have been performed using a low-energy pulser (100 J electrical) to simulate the PITHON wire initiation process by exploding two stainless steel wires and thus providing a UV radiation source. The plasma boundary and density profie near the surface of a sample (electrode material) placed near the radiating wires was observed by taking both a shodowgraph and a hologram. The total energy radiated per wire ranged from 2.0 to 9.5 J/wire for peak currents of 13.5 and 25 kA/wire, respectively. The plasma density profile shows ne = 1.0 × 1018/cm3 near the surface of the sample and ne = 2 × 1016/cm3 near the plasma vacuum interface (plasma front). The final plasma front position has a linear dependence on the total incident energy density with the constant being 1.43 mm/(J/cm2), thus the average expansion velocity dependence on energy density is 1.02 cm/?s/ -J/cm2. Upon varying the sample material, the sample temperature, magnetic field, and the surface roughness, only the magnetic field and the rough electrode surface reduced the plasma front position by approximately a factor of two.     

Pair neutrino energy loss for nuclei 56Fe at the late stages of stellar evolution

Based on the Weinberg-Salam theory,the pair neutrino energy loss rates for nuclei 56Fe are canvassed for the wide range of density and temperature.The results of ours (QLJ) are compared with those of Beaudet G,Petrosian V and Salpeter E.E's (QBPS),and it shows that the pair neutrino energy loss rates of QBPS are always larger than QLJ .The QBPS is 12.57%,12.86%,14.99%,19.80% times higher than QLJ corresponding to the temperature T9=0.385,1.0,5.0,10,respectively.     

用密度泛函方法研究质子化苯基丙酮-水团簇

应用密度泛函B3LYP/631+G(d,p)计算方法,对质子化苯基丙酮水团簇这个弱相互作用体系进行了全自由度能量梯度优化,得到该系列团簇的稳定结构.结果表明,H+C8H8OH2O团簇的形成过程为一无能垒的反应过程,在质子与C8H8O分子中O原子的距离为1.015时达到平衡几何.对H+C8H8O(H2O)n(n=1,2,3)团簇,质子位于C8H8O分子和水分子之间,且随着团簇尺寸的增加,质子与C8H8O分子中O原子之间的距离也增加;C8H8OH+H2O可以视为溶剂壳.而对H+C8H8O(H2O)n(n=4,5,6,7,8)团簇,质子位于两个水分子之间,形成H5O2+结构,即C8H8OH5O2+为该系列团簇的中心结构,新增加的水分子以从不同方向进攻这个中心的方式形成更大尺寸的团簇.