Anomalous behavior of proton zero point motion in water confined in carbon nanotubes

The momentum distribution of the protons in ice Ih, ice VI, high density amorphous ice, and water in carbon nanotubes has been measured using deep inelastic neutron scattering. We find that at 5 K the kinetic energy of the protons is 35 meV less than that in ice Ih at the same temperature, and the high momentum tail of the distribution, characteristic of the molecular covalent bond, is not present. We observe a phase transition between 230 and 268 K to a phase that does resemble ice Ih. Although there is yet no model for water that explains the low temperature momentum distribution, our data reveal that the protons in the hydrogen bonds are coherently delocalized and that the low temperature phase is a qualitatively new phase of ice.     

(1)H and (87)Rb nuclear magnetic resonance study of the order-disorder phase transition of RbHSeO(4) single crystals

The ferroelectric phase transition at T(C2) (=370K) in RbHSeO(4) has been studied by (1)H and (87)Rb solid-state NMR. Although not large, the spin-lattice relaxation time, T(1), and the spin-spin relaxation time, T(2), of rubidium and of the alpha- and beta-type protons show distinct change near the phase transition. The intensity of the signal due to the alpha-type protons decreases with increasing temperature, and the intensity of alpha-type protons is quite weak above 330K: at a temperature which is about 40K lower than the phase transition temperature, the ordering of the alpha-type protons occurs. The alpha-type protons in the ferroelectric phase lead to a noticeable change in the proton magnetic resonance spectra. Our study of the (1)H spectra shows that the ferroelectric phase transition in RbHSeO(4) is of order-disorder type and is due to the ordering of protons in hydrogen bonds.     

One-dimensional beam ordering of protons in a storage ring

The ordering of protons has been observed at a new storage ring, S-LSR, at Kyoto University. Abrupt jumps in the momentum spread and the Schottky noise power were observed for protons for the first time at a particle number of approximately 2000, upon applying electron cooling with electron currents of 25, 50, and 100 mA. The transition temperature was 0.17 and 1 meV in the longitudinal and transverse directions, respectively. The transverse temperature of the proton beam was much below that of electrons at the transition, which played an essential role in the ordering of protons.     

Effect of tetrasodium tripolyphosphate on the freeze-concentrated glass-like transition temperature of sugar aqueous solutions

The freeze-concentrated glass-like transition temperatures (Tg2), so-called ante-melting temperature or ice-melting temperature of tripolyphosphate-sugar aqueous solutions prepared with various sugars (ribose, sorbitol, glucose, maltose, sucrose, and trehalose) were investigated by using differential scanning calorimetry to evaluate the effect of tetrasodium tripolyphosphate on the Tg2 of sugar aqueous solutions. The Tg2 of tripolyphosphate-sugar aqueous solutions were higher than those of tripolyphosphate or sugar aqueous solutions and converged in a narrow temperature range of 238 to 243 K. Furthermore, a study of the Tg2 of tripolyphosphate-glucose aqueous solutions adjusted to various ratios indicated that the Tg2 increment depended on the ratio and that another glass-like transition appeared at a temperature below the Tg2 by increasing the ratio of tripolyphosphate. The drastic increase in the Tg2 of sugars with the addition of tripolyphosphate will be useful for improving the cryostabilization of biomaterials.     

Molecular dynamics study of a two-dimensional model of squaric acid

The vibrational properties of the two-dimensional model of squaric acid are studied. Intermolecular and intramolecular interactions are taken to be either harmonic or of Lippincot-Schroeder type. Special attention is paid to the influence of the anharmonicity on the infrared active vibrations of the protons in the hydrogen bonds. The potential for the proton is chosen in such a way that in the room temperature phase the protons are found in an asymmetric position between two neighbouring oxygens. In the high temperature phase a symmetric distribution of protons is accessible indicating that a structural phase transition can occur.     

High-energy photons as a thermometer for ultra-relativistic nuclear collisions

I calculate the transverse momentum distribution for high-energy (p _T =1–3 GeV) photons produced in ultra-relativistic nuclear collisions. I assume a strong first-order deconfinement phase transition, and consider transition temperatures in the range 150–200 MeV. For simplicity, I also assume thermal and chemical equilibrium throughout the collision. I then fit the transverse momentum distribution in the range 1–2 GeV to a thermal distribution. The fitting temperature depends only on the transition temperature, so this provides an accurate (although theory-dependent) measure of the QCD transition temperature.     

Rapidity dependence of hadron PT spectra in central Au+Au collisions at = 200 GeV

The transverse momentum spectra for identified hadrons at different rapidities in central Au+Au collisions at = 200 GeV are studied in a quark combination model. The results for PT spectra of π±,K±, p(p-) and for the p/π ratios in a broader PT range at midrapidity agree well with the data. The transverse momentum spectra of pions, protons and antiprotons at various rapidities y 1, η= 2.2 and y≈3.2 are calculated and compared with the data.     

THE CRITICAL TEMPERATURE OF SUPERFLUID HELIUM AND THE FRACTION OF NONZERO MOMENTUM COPJDENSATION

Using the method of momentum nonconserved Green function,we derive a critical temperature value T^(l)=2.71°K for ⁴He system below which the system undergoes a phase transition and has a nonuniform condensate.The temperature dependepce of the speed of the first sound near T=0°K is also discussqd.     

Molecular dynamics of poly(L-lactide) biopolymer studied by wide-line solid-state 1H and 2H NMR spectroscopy

The molecular dynamics of poly(L-lactide) (PLLA) biopolymer was characterized through analyses of 1H and 2H NMR line-shapes and spin-lattice relaxation times at different temperatures. At low temperatures (e.g. 90 K), the methyl group rotation is dominant leading to a significant reduction in the proton second moment. Fast methyl group reorientation occurs at ca. 130 K. In additional to the fast methyl group rotation, hydroxyl groups start to reorient as the temperature increases further, eventually leading to the breakdown of the segments of the biopolymer chains above its glass transition temperature Tg of 323 K. The analyses of the 2H NMR line-shapes indicate that both the methyl and hydroxyl reorientations can be described by the so-called cone model, in which the former has three equilibrium positions with theta(C-D) = 70.5 degrees and phi = 120 degrees while the latter one exhibits two equilibrium positions with theta(O-D) = 78 degrees and phi = 180 degrees .     

磁阱中超冷玻色气体临界行为的观测

超冷玻色气体为研究量子临界现象提供了一个非常干净的实验系统. 弱相互作用下的三维玻色气体的临界行为与⁴He发生超流相变时的临界行为类似, 都属于三维XY型普适类. 从正常流体到超流的量子相变过程中, 系统会经历一个从无序相到长程有序相的转变; 而在相变点附近, 系统参量会表现出一些奇点的特征. 本文从实验上观测到了静磁阱中超冷⁸⁷Rb玻色气体在凝聚体相变温度T_c附近的临界行为. 原子气体从静磁阱中释放, 经过30 ms的自由飞行后, 通过吸收成像得到原子气体的动量分布; 然后从中扣除热原子气体的动量分布, 提取出空间上处于临界区域内的原子气体动量分布, 并对不同温度下的动量分布半高宽进行统计. 统计结果显示: 在非常接近相变温度T_c时, 动量分布的半高宽突然减小, 表现出十分明显的奇点行为.     

Production of mesons and baryons at high rapidity and high p(T) in proton-proton collisions at square root[s] = 200 GeV

We present particle spectra for charged hadrons pi(+/-), K(+/-), p, and p[over] from pp collisions at square root[s] = 200 GeV measured for the first time at forward rapidities (2.95 and 3.3). The kinematics of these measurements are skewed in a way that probes the small momentum fraction in one of the protons and large fractions in the other. Large proton to pion ratios are observed at values of transverse momentum that extend up to 4 GeV/c, where protons have momenta up to 35 GeV. Next-to-leading order perturbative QCD calculations describe the production of pions and kaons well at these rapidities, but fail to account for the large proton yields and small p[over]/p ratios.     

Local heating and quenching effects on amorphous selenium configurational disorder,during reactor neutron irradiations

A new observation about the influence of reactor neutron bombardment on the configurational disorder of glasses has been drawn from enthalpy change diagrams (DSC) performed near Tg on amorphous selenium.

The irradiation was done at low temperature (30 K) and fission and capture effects were shielded by enclosing samples in NB cells.

Near Tg (320 K) a progressive change is observed from a stabilized relaxation state (initial state) to a highly quenched state in the bulk, as a function of the neutron dose.

A local heating and quenching effect induced by deposited energy spikes, is assumed and calculated to explain the apparent 300 K temperature incursion in the material, followed by fast cooling of configurational state through the liquid-glass transition.     

Quantum momentum distribution and kinetic energy in solid 4He

We present measurements of neutron scattering from solid 4He at high momentum transfer. The solid is held close to the melting line at molar volume 20.87 cm3/mol and temperature T=1.6 K. From the data, we determine the shape of the momentum distribution, n(k), of atoms in the solid and the leading final state contribution to the scattering. We show that n(k) in this highly anharmonic, quantum solid differs significantly from a Gaussian. The n(k) is more sharply peaked with larger occupation of low momentum states than in a Maxwell-Boltzmann distribution, as found in liquid 4He and predicted qualitatively by path integral Monte Carlo calculations. The atomic kinetic energy is =(24.25+/-0.30) K. If n(k) is assumed to be Gaussian, as is usually the practice, a 10% smaller is obtained.     

Heat capacity and phase transition of tetrahydrofuran clathrate hydrate

Heat capacity of tetrahydrofuran clathrate hydrate THF·16.81H₂O doped with KOH (x = 1.8 × 10⁻⁴ in the mole fraction of KOH in KOH and water) was measured in the temperature range 13–280 K. A sharp first-order phase transition having a large tail on the high temperature side was observed at 62 K and excess entropy due to the transition was determined to be 2.56JK⁻¹ (H₂O-mol)⁻¹. From a comparison with thermal behavior of hexagonal ice, it was indicated that this transition was related to ordering of protons in the host lattice.     

Delocalized positronium in alkali-halide crystals: analysis of possible lattice-scattering processes

A theoretical analysis of possible lattice-scattering processes for delocalized positronium atoms (Ps) in alkali-halide crystals is presented. Optic deformation-potential scattering, unless forbidden by selection rules, is shown to renormalize the acoustic deformation-potential constant of Ps thereby dramatically broadening its momentum distribution with increasing temperature. This explains the anomalous temperature broadening of the momentum distribution of Ps in crystalline MgF₂ and its absence in α-SiO₂ as recently observed. An effect analogous to that in MgF₂ is predicted for β-SiO₂ above the α–β phase transition at 846 K.     

喷射器临界背压对喷射制冷系统性能的影响

为了确保喷射器在良好的工况条件下运行,文中针对太阳能喷射制冷系统的工况范围,以R134 a为工质建立了喷射器运行特性计算模型,计算分析了临界背压随喷射器运行工况的变化关系,以及对制冷系统性能的影响。结果表明:喷射器的临界背压随发生温度和蒸发温度的增大而增大,极限喷射系数随发生温度的升高而降低,随蒸发温度的升高而升高;喷射制冷系统COP随喷射器背压(冷凝压力)的升高先保持不变后减小,当Tg=353K,Te=281K和Te=283K时,喷射器分别在Tc=307K左右和Tc=308K左右时,达到临界状态,临界背压分别为0.85MPa、0.88MPa,COP分别为0.2和0.227。     

液态合金NiAl凝固过程中微观结构转变的分子动力学模拟

采用分子动力学模拟方法对液态NiAl凝固过程进行了研究 ,考察了不同冷却速度下液态NiAl结构变化特点 ,原子间相互作用势采用F S多体势 ,结构分析采用键取向序和对分析技术 .计算结果表明 ,冷却速度对液态NiAl结构转变有重要影响 ,在不同的冷却速度下 ,NiAl凝固过程出现了明显不同 ,冷速为 4× 10 13 和4× 10 12 K/s时 ,NiAl快速凝固为无序的非晶体结构 ;而在较慢的 8× 10 11K/s冷速下 ,NiAl凝固为晶态结构 .给出了不同冷却速度下液态NiAl结构转变的微观信息 .     

Neutron spin-echo investigation of slow spin dynamics in kagomé-bilayer frustrated magnets as evidence for phonon assisted relaxation in SrCr9xGa12-9xO19

A neutron spin-echo investigation of the low temperature spin dynamics in two well-characterized kagomé bilayer compounds SrCr9xGa12-9xO19 (x=0.95, SCGO) and Ba2Sn2ZnCr7xGa10-7xO22 (x=0.97, BSZCGO) reveals two novel features. One is the slowing down of the relaxation rate without critical behavior at Tg, where a macroscopic spin-glass-like freezing occurs. The second is, in SCGO at 4 K (approximately Tg)相似文献   

Dynamics of supercooled confined water measured by deep inelastic neutron scattering

In this paper, we present the results of deep inelastic neutron scattering (DINS) measurements on supercooled water confined within the pores (average pore diameter ~ 20 Å) of a disordered hydrophilic silica matrix obtained through hydrolysis and polycondensation of the alkoxide precursor Tetra-Methyl-Ortho-Silicate via the sol-gel method. Experiments were performed at two temperatures (250 K and 210 K, i.e., before and after the putative liquid–liquid transition of supercooled confined water) on a “wet” sample with hydration h ~ 40% w/w, which is high enough to have water-filled pores but low enough to avoid water crystallization. A virtually “dry” sample at h ~ 7% was also investigated to measure the contribution of the silica matrix to the neutron scattering signal. As is well known, DINS measurements allow the determination of the mean kinetic energy and the momentum distribution of the hydrogen atoms in the system and therefore, allow researchers to probe the local structure of supercooled confined water. The main result obtained is that at 210 K the hydrogen mean kinetic energy is equal or even slightly higher than at 250 K. This is at odds with the predictions of a semiempirical harmonic model recently proposed to describe the temperature dependence of the kinetic energy of hydrogen in water. This is a new and very interesting result, which suggests that at 210 K, the water hydrogens experience a stiffer intermolecular potential than at 250 K. This is in agreement with the liquid–liquid transition hypothesis.     

利用深度学习方法研究核物质状态方程

对核物质状态方程的研究将有助于人们更好地了解原子核的性质以及宇宙和星体的演化过程等基本问题。重离子碰撞能产生高温高密核物质,利用输运模型的模拟结合相关实验数据的比较是研究核物质状态方程最常用方法之一。本文利用深度学习中的卷积神经元网络(CNN)方法对不同核物质状态方程给出的末态质子横动量和快度分布进行学习,使神经元网络具有从末态粒子信息来判断核物质状态方程软硬的能力。利用预测差异分析方法(Prediction Different Analysis),可以找到横动量和快度分布中对状态方程最敏感的区域。此外,还测试了一种基于决策树的梯度提升算法(LightGBM),发现得到的准确度和CNN方法类似。