Network topology of deeply supercooled water

Empirical potential structure refinements have been made to recent high-energy x-ray diffraction data, providing molecular models of deeply supercooled water. The average O-O coordination number is found to drop from 5.13 at 293?K to 4.85 at 244?K, within 3.5?Å. Triplet O-O-O bond angle distributions reveal a broad peak centred at 96.4° at 293?K which shifts to 100.0° at 244?K, indicative of the local geometry becoming increasingly tetrahedral with decreasing temperature. However, although the number of non-bonded interstitial molecules between the first and second shells is depleted upon cooling, the number of interstitial molecules forming triplets that are embedded within the hydrogen bonded tetrahedral network at θ_OOO?=?53°, remains constant. This is consistent with previous observations of an invariant O-O coordination number with temperature (4.24 out to 3.3?Å) and corresponds to non-bonded molecules positioned at close to half the ideal tetrahedral angle. Both -O-O-O- and hydrogen-bonded -O-H-O- ring length distributions show increases in 6 and 7-membered rings upon supercooling. This is concomitant with a shift and increase in intensity of peaks at r₄ ～8.7?Å and r₅ ～10.8?Å in the oxygen-oxygen pair distribution function, which in the models correspond to correlations between adjacent and next-nearest-neighbour hydrogen-bonded rings.     

A Practical Method for the Analysis of Overlapped Peaks in Energy Dispersive X-Ray Spectra

ABSTRACT

In this study a practical method for the spectral analysis of some overlapped characteristic X-ray peaks is presented. The overlapped characteristic K, and K, peaks and the artificially overlapped two K, peaks (peak doublet) of arsenic obtained by the radioisotope-excited, energy dispersive X-ray fluorescence (EDXRF) technique, are resolved. A total of 34 overlapped peak systems were investigated: the proposed method provided 18 reliable results, whereas the first and the second methods gave 15 and 1, respectively. The intensity ratios of K_β/K_α, obtained by the novel method are also in good agreement with the theoretical relativistic Hartree-Slater values.     

A structural comparison of supercooled water and intermediate density amorphous ices

New data are presented on neutron diffraction in ultrapure bulk supercooled heavy water measured down to 262?K. The data are analysed in terms of the trends observed in the first sharp diffraction peak (FSDP) parameters, the feature which dominates the measured neutron spectra. The neutron FSDP position, height and width are compared to literature data for supercooled water, water under pressure and to the same parameters obtained for recently discovered intermediate density amorphous ices. It is found that the FSDP parameters in supercooled water and the amorphous ices generally exhibit a similar behaviour, suggesting a new structural regime may occur in deeply supercooled water below Q ₀?～?1.83?Å^?1 (T?～?251?K) associated with increased intermediate range ordering. It is argued that this structural regime may be linked to a similar trend in the density which appears when the density is plotted as a function of FSDP position. A detailed comparison of the neutron and X-ray structure factors for supercooled water and intermediate density amorphous ices with the same FSDP positions is also made. The diffraction data show that although the overall general structures are qualitatively very similar, the amorphous ice correlations are considerably sharper and extend to much higher radial distances.     

Effects of Uniaxial Stress on X-ray Diffraction Spectra

Uniaxial stress is a typical drawback of solid pressure transmitting medium, at low temperature, which affects experimental spectra by shifting and broadening the diffraction peaks. Corrections to this effects have been proposed in the past only for the systematic shifts. We presented a simple model based on elasticity theory which rationalizes both peak shifts and broadening observed in X-ray diffraction. Our results are compared to the popular Singh model.     

Effect of Polarization Temperature on the Chain Segment Motion and Space Charge Detrapping in Polyamide 610 Film Electrets

The effect of polarization temperature on the chain segment motion and charge trapping and detrapping in polyamide 610 films has been investigated by means of thermally stimulated depolarization current (TSDC) and wide-angle X-ray diffraction (WAXD). A small part of the amorphous phase of quenched polyamide 610 changes into the crystalline state with increasing polarization temperature. There are three current peaks (named α, ρ₁, and ρ₂ peak, respectively) in the TSDC spectra. The α peak corresponds to the glass transition, the ρ ₁ peak is attributed to space charge trapped in the amorphous phase, and interphase between crystalline and amorphous phases, and the ρ ₂ peak originates from space charge trapped in the crystalline phase. By analyzing the characteristic parameters of these peaks, it was found that the increase of polarization temperature induced a decrease of the chain segment mobility and promoted the creation of structural traps in polyamide 610. The decrease of the chain segment mobility in the amorphous phase made the intensity of the α peak weak and the activation energy increased. The higher the polarization temperature, the higher the degree of crystallinity and the more charge carriers trapped in the crystalline phase. So, the increase of polarization temperature made the intensity of the ρ ₂ peak strong and increased the stability of trapped charge in the crystalline phase. The increase of polarization temperature also made the intensity of the ρ ₁ peak strong and decreased the stability of trapped charge in the amorphous phase and interphase.     

Diffraction theory applied to X‐ray imaging with clessidra prism array lenses

Clessidra (hourglass) lenses, i.e. two large prisms each composed of smaller identical prisms or prism‐like objects, can focus X‐rays. As these lenses have a periodic structure perpendicular to the incident radiation, they will diffract the beam like a diffraction grating. Refraction in the prisms is responsible for blazing, i.e. for the concentration of the diffracted intensity into only a few diffraction peaks. It is found that the diffraction of coherent radiation in clessidra lenses needs to be treated in the Fresnel, or near‐field, regime. Here, diffraction theory is applied appropriately to the clessidra structure in order to show that blazing in a perfect structure with partly curved prisms can indeed concentrate the diffracted intensity into only one peak. When the lens is entirely composed of identical perfect prisms, small secondary peaks are found. Nevertheless, the loss in intensity in the central peak will not lead to any significant widening of this peak. Clessidras with perfect prisms illuminated by full coherent X‐ray radiation can then provide spatial resolutions, which are consistent with the increased aperture, and which are far below the height of the single small prisms.     

Pressure-induced structure change of molten KCl

Abstract

Energy-dispersive X-ray diffraction experiments of molten KCl under high pressure have been carried out by using synchrotron radiation. The diffraction profiles of molten KCl were acquired just above the melting temperature of KCl up to 4 GPa. The reduced structure factor S(Q)'s for molten KCl do not show any change in their primary features, except for a gradual increase in the first peak intensity with increasing pressure. This implies that molten KCl does not show a first-order phase transition, such as the B1-B2 transition, found in solid KCl, but that the local structure in molten KCl must be changed by compression. According to a molecular-dynamics simulation, this change of S(Q) can be explained by a continuous increase in the coordination number of the nearest-neighbor ions in molten KCl with pressure.     

Anomalous second harmonic generation in iron-doped barium titanate

The temperature evolution of the angular dependence of the second harmonic intensity in iron-doped barium titanate is measured in the region of the transition from the cubic to the tetragonal phase. An unusual asymmetry of the angular distribution of this intensity is found in the temperature range corresponding to the peak in the temperature dependence of the integral intensity. The possible physical mechanisms of these anomalies are discussed. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 4, 247–249 (25 August 1996)     

纯铌酸锂晶体红外光谱的低温研究

测量了同成分纯铌酸锂的低温红外光谱,发现低温下铌酸锂晶体将会出现位于3200 cm^-1左右的新红外吸收峰.研究发现该峰与晶体中的氢离子无关,并且其峰强和峰形都随温度的升高发生复杂的变化.基于上述实验结果,认为该峰应该起源于电子在相邻的小极化子（Nb⁴⁺_Li）和自由极化子（Nb⁴⁺_Nb）之间的跃迁.另外,通过拟合发现新红外吸收峰可分解成三个高斯峰,这三峰应归因于能量有细微差别的三种跃迁. 关键词： 铌酸锂 红外吸收光谱 杂质缺陷     

Dislocation emission in A1 during recrystallization

Summary The dislocation structure evolution during isothermal recrystallization of Al has been followed by means of internal friction, modulus defect and X-ray diffraction analyses accompanying the microscopical observations. Many peaks ofQ ⁻¹ and of modulus defect and X-ray diffraction line width have been found, both in nucleation and grain growth, all referable to dislocations. The first of these peaks, at the beginning of recrystallization, presents recovery characteristics, different from those shown by the subsequent, secondary peaks. Secondary peaks are interpreted in terms of dislocation emission from grain boundaries, whereas the first peak appears connected with subboundaries, walls present in the initial stages of recrystallization. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

High-resolution X-ray diffraction study of the cubic-to-tetragonal transition in BaTiO3

A drastic change is found in the diffraction pattern of a single-crystal specimen of BaTiO₃. At and just below the transition temperature, the original single peak of 004 of the tetragonal phase splits or collapses into a group of small peaks. They appear around the positions of 004 and 400, and probably correspond to different orientations of grains and domains. The positions and relative intensities of the peaks randomly vary with time and temperature. These features are observed for both heating and cooling processes.     

非掺杂ZnO薄膜中紫外与绿色发光中心

用直流反应溅射方法在硅衬底上淀积了ZnO薄膜,测量它们的光致发光(PL)光谱,观察到两个发光峰,峰值能量分别为3.18(紫外峰,UV)和2.38eV(绿峰).样品用不同温度分别在氧气、氮气和空气中热处理后,测量了PL光谱中绿峰和紫外峰强度随热处理温度和气氛的变化,同时比较了用FP-LMT方法计算的ZnO中几种本征缺陷的能级位置.根据实验和能级计算的结果,推测出ZnO薄膜中的紫外峰与ZnO带边激子跃迁有关,而绿色发光主要来源于导带底到氧错位缺陷(O_Zn)能级的跃迁,而不是通常认为的氧空 关键词： ZnO薄膜 热处理 光致发光光谱 缺陷能级     

基于CIE色度图的博尔塔拉河与精河水体荧光峰发光性初探

以艾比湖主要入湖河流博尔塔拉河及精河水体为研究对象,使用寻峰法找出水体荧光峰,采用色坐标分析法对博尔塔拉河与精河水体荧光发射光谱特性及荧光峰的发光性进行分析。首先,博尔塔拉河与精河水体的荧光发射光谱均含有3个荧光峰,各荧光峰的出现位置与峰强度大小均不同。博尔塔拉河第二荧光峰远大于第一荧光峰或第一荧光峰与第二荧光峰基本持平;精河前5个样点的3个荧光峰强度随波长增大呈依次递减分布,6号采样点第一荧光峰与第二荧光峰基本持平。其次,博尔塔拉河与精河3个荧光峰在色坐标中分布位置大致相同,且各点的荧光峰分布较为聚集,均在蓝光区域,属蓝光发射。最后,各荧光峰在CIE坐标中聚集分布,第一荧光峰在色坐标最底端;第二荧光峰分布在第一荧光峰上端,x坐标与第一荧光峰接近;第三荧光峰整体聚集分布在蓝光区域的右上角。     

Crystallization kinetics in phosphate sodium-based glass studied by DSC technique

In this work, differential scanning calorimetry (DSC) was used to study the mechanism of crystallization of 50P₂O₅-27.8Na₂O-16ZnO-6.2Al₂O₃ glass. DSC measurements were performed on bulk and powdered glasses with different particle size. The curve for bulk glass shows one crystallization peak while powdered glasses presented two distinct crystallization peaks. Based on DSC studies, the activation energies obtained were 336±6 and 213±3 kJ mol⁻¹, associated with first and second crystallization peaks, respectively. Analyzing the DSC parameters as a function of particle size, the Avrami n parameter suggests that the peak at low temperature may be associated with surface crystallization while the peak at high temperature is associated with bulk crystallization.     

Spatial correlation of an electron and hole in quasi-two-dimensional electronic system in a strong magnetic field and its relationship to the light-scattering tensor

The spatial correlation of light-generated electrons and holes in a quasi-two-dimensional electron gas in a strong magnetic field is investigated in an approximation linear in the intensity of the exciting light. The correlation is due to the interaction of the electrons and holes with longitudinal optical (LO) phonons. The theory permits calculating, on the basis of a special diagrammatic technique, two distribution functions of an electron-hole pair with respect to the distance between the electron and the hole after the emission of N phonons: first, the function determining the total number of pairs which have emitted N phonons and, second, the function related to the rank-4 light-scattering tensor in interband resonance Raman scattering of light. A special feature of the system is that the electron and hole energy levels are discrete. The calculation is performed for a square quantum well with infinitely high barriers. The distribution function and the total number of electron-hole pairs before the emission of phonons as well as the distribution function corresponding to two-phonon resonance Raman scattering are calculated. The theory predicts the appearance of several close-lying peaks in the excitation spectrum under resonance conditions. The number of peaks is related to the number of the Landau level participating in the optical transition. The distance between peaks is determined by the electron-phonon coupling constant. Far from resonance there is one peak, which is much weaker than the peaks obtained under resonance conditions. Zh. éksp. Teor. Fiz. 111, 2194–2214 (June 1997)     

A liquid film or droplet of miscible binary fuel burning on a heated surface at elevated pressures

An experimental study has been made of the combustion and evaporation of miscible binary fuels on a heated surface at elevated pressures. Photographic observation was made for elucidating how the binary fuel droplets or films behaved on the heated surface and for obtaining the characteristic lifetime as a function of the surface temperature, the ambient pressure and the initial concentration of highly volatile component of the fuels. The binary fuels tested were mixtures of n-hexane and n-decane. The results showed that the lifetime curve both for the combustion and for the evaporation of n-hexane/n-decane on the heated surface had two peaks at lower pressures, the first peak in the film-type evaporation region and the second peak in the spheroid-type evaporation region. The preferential evaporation of the highly volatile component was responsible for the appearance of the first peak in the film-type evaporation region. The second peak corresponded to Leidenfrost point. The increase in the ambient pressure caused a shift of the lifetime curve toward higher surface temperature and a decrease in the lifetime at two peaks. The lifetime curve decreased monotonically with increasing the surface temperature and the spheroid-type evaporation was not observed at higher pressures. The increase in the initial concentration of highly volatile component caused a shift of the first peak toward higher surface temperature, a decrease in its lifetime and a slight shift of the second peak toward lower surface temperature. The combustion caused a remarkable decrease in the lifetimes around the first peak and in the spheroid-type evaporation region and a slight increase in the surface temperature at the first peak, while the surface temperature at the second peak remained almost unchanged.     

The analysis of thermoluminescent glow peaks of copper doped ZnS thin films after β-irradiation

In the given study, the thermoluminescence (TL) properties of copper (Cu)-doped ZnS thin films were investigated after β-irradiation at room temperature (RT). It was observed that the glow curve of this material has two broad TL peaks, in which one of them was centered at about 110 °C and the other at about 170 °C for a heating rate of 1 °C s⁻¹ in the temperature range from RT to 350 °C. The additive dose (AD), T_m(E_a)−T_stop, repeated initial rise (RIR), variable heating rate (VHR) and computerized glow curve deconvolution (CGCD) methods were used to analyze its glow curves. These methods indicated that the glow curve of this material is the superposition of a number of first- and general-order glow peaks, or at least due to the distribution of traps. The dose responses and fading process of both peaks were also examined, and it was observed that the dose responses of both peaks have similar pattern. First they follow a good linearity with different slopes and then saturate at approximately same dose level (2 kGy). The low-temperature broad peak nearly disappeared after 1 week storage in the dark at RT. On the other hand, the intensity of the high-temperature broad peak was approximately reduced to 50% of its original value. The TL emission spectrum of this material has two main emission bands, namely, the blue and green bands. The first glow peak emits predominantly in blue region, whereas the second glow peak in the green region.     

Mechanistic model for the dielectric spectrum of a simple dielectric material

ABSTRACT

In this paper, we perform molecular dynamics simulations of a dielectric fluidic material composed of permanent molecular dipoles. The dielectric spectrum features two peaks at lower frequencies than the system phonon frequency. The primary peak is observed at all temperatures studied and shifts toward lower frequencies as the temperature decreases. During this shift, the secondary peak emerges with a higher peak frequency than the primary peak. The secondary peak amplitude increases as the temperature decreases. Both peaks are dependent on the wavevector; in the small wavevector regime, the primary peak is shifted to higher frequencies as the wavevector squared and the secondary peak amplitude increases as the wavevector increases, but shows no shift in frequency. From the polarisation balance equation, we propose a model for the dielectric spectrum. This captures the spectrum features, and we conjecture that the primary peak is due to dipole moment correlations (Debye-type) and the secondary peak is due to the correlation between the dipole moment and a microscopic local field.     

Composites Based on Polyethylene and Keratin Hydrolysates

Novel composites based on polyethylene ELITE? 5230GC and keratin hydrolysates (amino acid composition, dipeptide, tetrapeptide) have been first developed and studied. It has been shown that the introduction of keratin hydrolysates leads to an increase in the elastic modulus E₀ of the composites compared with the E₀ value of the matrix and a decrease in their tensile strength and elongation at break. It has been found that the water content in keratin hydrolysates is 3–4%. The differential scanning calorimetry curves of keratin hydrolysates exhibit a broad peak during the first heating and no peaks during the second heating of keratin hydrolysates. The temperature corresponding to the minimum of the broad peak observed during the first heating is shifted to low temperatures: from 99.1 to 82.5°C. In this case, the peak area varies from 109.3 J/g for the amino acid composition and 104.0 J/g for dipeptide to 140.8 J/g for tetrapeptide. During the second heating, the peak temperatures for the composites decrease compared with the peak temperature for polyethylene. The enthalpy of the composites also decreases compared with the enthalpy of the matrix.     

张应变In1-xGaxAsyP1-y/InP材料光致荧光谱温度特性的测试与分析

报道了具有2，3个量子阱的In_1-x1Ga_x1As_y1P_1-y1/In_1-x2Ga_x2As_y2P_1-y2/InP张应变量子阱材料的光致荧光谱和X射线双晶衍射摇 关键词：