Raman-brillouin light scattering determination of the structural correlation range in ges2 glass

Polarized Brillouin and low frequency (3 cm^?1 ? ω ? 40 cm^?1) Raman spectra of GeS₂ glass have been measured. Parameters determined from the Brillouin spectra have been used in the theory of Martin and Brenig to obtain from a fit of the Raman spectrum the structural correlation range, 2σ. We find 2σ = 8 ± 1 Å.     

Magneto-Brillouin scattering of polaritons in CdS

Resonant Brillouin scattering of excitonic polaritons is investigated for the first time in high magnetic fields. For the A-exciton of CdS the observed number of scattering lines and their Brillouin shifts in fields up to 10.0 Tesla can be explained assuming two excitonic oscillators which result from the field induced mixing and splitting of allowed Γ₅- and forbidden Γ₆-states. The determined parameters are : Δ₅₆ = (0.2±0.03) meV, g_e⊥ = 1.75±0.05 and δ_dia = (0.2±0.02) · 10^-2 meV/Tesla².     

Brillouin spectrum of Ca(OH)2

Brillouin spectrum of several directions, such as [0,0,1], [0,1,1]/?2, [0,1,0] and [1,/?2,1/2,1/2] of Ca(OH)₂ crystals were measured. The elastic stiffness coefficients c₁₁, c₃₃, c₄₄, c₆₆ and c₁₃ are estimated to be (in N/m² × 10¹⁰): 9.928±0.15, 3.260±0.2, 0.985±0.2, 3.155±0.15 and 2.965±1.5, respectively. Large dispersion of ultrasonic and hypersonic longitudinal velocities is noted.     

Quadrupole interaction at Ta and lattice location of Hf in Be

The time-differential perturbed angular correlation technique (TDPAC) has been applied to the 482 keV excited state of¹⁸¹Ta, to determine the nuclear electric quadrupole interaction (QI) at Ta in Be. Sources were prepared by ion-implantation of¹⁸¹Hf in Be. Particle channeling measurements have revealed that. Hf impurities implanted in Be reside primarily at the tetrahedral interstitial site. The fundamental QI frequency obtained for Ta at this interstitial site in Be is |v _Q| =e ² qQ/h = 227.0 ± 2.2 MHz which corresponds to an electric field gradient |eq|=(3.71±0.15)×10¹⁷ V/cm². This result is discussed in terms of results for Cd impurities in the same system and the systematics of the impurity QI in metals.     

含12mol%铈的四方氧化锆多晶的变温喇曼散射研究

对含12mol％铈的四方氧化锆多晶耐高温材料从17—505K温度范围进行了50—800cm^-1的喇曼散射研究,同时还实测了线膨胀系数随温度的变化。降温时,在165±1K观察到了类四方相向类单斜相的转变,而升温时,在450土2K发生了与之相反的转变。为了探讨该转变的原因,对布里渊区声子凝聚和可能引起的相转变做了较仔细的说明。 关键词：     

Low-frequency spectroscopy of four-photon scattering of laser radiation in aqueous solutions of biopolymers

Four-photon scattering (FPS) spectroscopy is used to record rotational resonances of H₂O and H₂O₂ molecules in aqueous solutions of DNA and denatured DNA within a range of ±10 cm^-1 with a spectral resolution of 3 GHz. The resonance contribution of rotational transitions of these molecules in solutions was found to be considerably larger than that in distilled water. This fact is interpreted as a manifestation of the specific properties of a hydrate layer at the interface between water and DNA or denatured DNA molecules. An analysis of the FPS spectra shows that the concentration of H₂O₂ molecules in the hydrate layer of the DNA molecule increases threefold after denaturation. In addition, the FPS spectra of aqueous solutions of α-chymotrypsin protein with concentrations of 0-20 mg cm^-3 were measured in the spectral range of ±7 cm^-1. It is found that the velocity of hypersound in the protein aqueous solution, which is measured by the shift of the Mandelstam—Brillouin scattering spectrum components, is a cubic function of the concentration and reaches 3000 m/s at 20 mg/cm³.     

不同临界保留因子下天然有机物亲疏水组分光谱特性

吸附树脂层析法是表征环境水样有机物亲疏水组分分布的常用方法。作为柱层析的基本参数,临界保留因子对亲疏水物质的吸附及分离效果具有潜在影响。以河北某水库的水样为例,将有机物分为亲水物(HIS)、疏水酸(HOB)、疏水碱(HOA)和疏水中性物(HON),考察了在不同临界保留因子分离条件下(k′_cr=5, 10, 25, 50, 100)亲疏水组分有机物含量分布,并着重考察了其光谱学特性。研究发现,亲疏水组分的浓度分布取决于k′_cr值的设置,疏水组分的比例和疏水程度随k′_cr的增大而增大。在250~280 nm波长范围内,亲水组分HIS的紫外吸光度随k′_cr的增高而增高,而疏水组分HOA和HOB则呈现相反趋势,亲水与疏水组分之间的紫外光谱差异性随k′_cr增大而增大。此外,疏水组分单位质量浓度的吸光度对k′_cr的取值敏感,推测k′_cr可能影响所得组分的芳香族官能团性质。进一步考察了各组分的三维荧光光谱,并采用荧光区域积分和荧光指数对图谱进行解析。结果表明,亲疏水组分的荧光峰形态、荧光区域分布和荧光团密度与k′_cr值有关,荧光指数BIX,HIX_em和Peak T/C对k′_cr的取值敏感,说明k′_cr可能对所得组分的具体化学组成乃至迁移转化行为产生影响。因此在分离并表征环境水样的亲疏水组分分布时,应特别注意临界保留因子的设置并明确标明其取值。     

Structure of water in mesoporous organosilica by calorimetry and inelastic neutron scattering

In this paper, we describe the preparation of mesoporous organosilica samples with hydrophilic or hydrophobic organic functionality inside the silica channel. We synthesized mesoporous organosilica of identical pore sizes based on two different organic surface functionality namely hydrophobic (based on octyltriethoxysilane OTES) and hydrophilic (3-aminopropyltriethoxysilane ATES) and MCM-41 was used as a reference system. The structure of water/ice in those porous silica samples have been investigated over a range temperatures by differential scanning calorimetry (DSC) and inelastic neutron scattering (INS). INS study revealed that water confined in hydrophobic mesoporous organosilica shows vibrational behavior strongly different than bulk water. It consists of two states: water with strong and weak hydrogen bonds (with ratio 1:2.65, respectively), compared to ice-Ih. The corresponding O-O distances in these water states are 2.67 and 2.87 ?, which strongly differ compared to ice-Ih (2.76 ?). INS spectra for water in hydrophilic mesoporous organosilica ATES show behavior similar to bulk water, but with greater degree of disorder.     

Low temperature thermal properties of PbI2

The heat capacity and thermal conductivity of a large (56.5 g) crystal of PbI₂ have been measured in the temperature region 0.5 < T < 3.9°K. Analysis of the heat capacity data yields a value of the limiting apparent Debye characteristic temperature θ₀^c = 99.4 (±0.3)°K, which corresponds to an average lattice wave velocity of 1.151 (±0.005) × 10⁵ cm sec^?1. It is consistent with a wave velocity estimated from neutron scattering experiments, but not with one determined from Brillouin spectra. The heat capacity data also show that dispersion of the low frequency waves is not unusual, as might have been expected for a layer-type crystal. The apparent thermal conduction is found to be surprisingly small in the crystal.     

Spin waves in Fe3−xMnxSi ordered alloys

Spin wave dispersion relations in Fe_3?xMn_xSi ordered alloys have been measured by neutron scattering for alloys with x = 0.04 and x = 0.18. The dispersion relations have been found to be quadratic in the magnon wavevector q? up to about half of the Brillouin zone along [111] direction. The measured values of the spin wave stiffness constant are 169±7 meV Å⁰² and 207±7 meV Å⁰² for samples with x = 0.18 and x = 0.04, respectively. The energy gap found from the rough data turned out to be almost totally due to the triple-axis spectrometer resolution properties. The nearest neighbour exchange integral for FeFe interaction, calculated from the above data, equals to 22.5±1.0 meV.     

The initial oxidation of molybdenum: III. Oxide nucleation rates on (100) and (110) molybdenum surfaces

The induction periods for the nucleation of epitaxial oxide on (100) and (110) surfaces of molybdenum have been determined. The role of impurities has been investigated by AES. It is found that only gross amounts of impurity are likely to be significant. Under isobaric conditions the activation energy associated with nucleation is 0.11 ± 0.2 MJ mole^?1 on both faces between 700 and 1050 K. At 850 K the induction rate is proportional to the pressure. Under isoposal conditions on the (110) surface an activation energy of 0.22 ± 0.03 MJ mole^?1 is found.     

Binding of Phenols with Amphipathic Cationic Polyelectrolytes

The association of phenols, such as p-cresol, tribromophenol, and trichlorophenol, with several amphipathic poly (n-alkylmethyldiallylammonium) chlorides in aqueous solution was studied by ultrafiltration. The n-alkyl residues were octyl, decyl, and dodecyl and the binding degrees were significantly higher than those found with the hydrophilic poly (diallyldimethylammonium) chloride. The results agreed well with the Satake and Yang's treatment and Hill's empirical equation for the association process, thereby revealing, in both cases, an increasing cooperative effect as the polyelectrolyte side chain increased in length for the same phenol, and when the hydrophobic nature of the phenol increased for the same kind of polyelectrolyte. From the phenomenological association constants, the estimated molar standard free energies of association ranged from ?19 kJmol^?1, for the more hydrophilic phenoxide–polyelectrolyte pair, to ?28 kJmol^?1 for the more hydrophobic pairs. The main result is that the amphipathic nature of these polyelectrolytes makes them efficient systems to trap anionic contaminants, better than hydrophilic flocculants.     

Phonon lifetimes in fused quartz at low temperatures

Thermal Brillouin scattering from fused quartz has been observed with high resolution at low temperatures. At 2.4 K the longitudinal phonons of ν = 33 GHz are very well-defined excitations, with a lifetime of (2.0±.2)×10^-7 sec. This value is in substantial disagrement with those reported by Pelous and Vacher¹.     

Anisotropic polariton dispersion in red HgI2

We have measured resonant Brillouin Scattering near the A-exciton region of a layer-semiconductor, red-HgI₂. The Brillouin shift is interpreted in terms of a scattering process between the two polariton states by an acoustic phonon. The estimated exciton masses for the translational motion are (0.68 ± 0.1)m₀ and (1.2 ± 0.1)m₀ for the (100 and (001) directions, respectively.     

Les systèmes hétérogènes « eau–zéolithe hydrophobe »: de nouveaux ressorts moléculaires

Pressure–volume isotherms have been determined for three heterogeneous ‘water–zeolite’ systems. The first two concern hydrophobic purely siliceous zeolites: silicalite-1 (F⁻) and zeolite β (F⁻); the third comprises a more hydrophilic commercial zeolite of the type ZSM-5. The P–V diagram for the water–silicalite-1 (F⁻) system is characterized by a plateau corresponding to the intrusion of water inside the pores of the solid. During the release the phenomenon is reversible. This system, which is able to accumulate and restore superficial energy, constitutes a molecular spring. For zeolite β, the P–V curve displays a plateau during the compression, but during the release, the phenomenon is not reversible. In that case, the system absorbs mechanical energy and acts as a bumper. The third system, based on the more hydrophilic ZSM-5 zeolite shows a linear isotherm without any plateau. These results open new applications perspectives in the field of the energetics for hydrophobic zeolites in contact with water. To cite this article: V. Eroshenko et al., C. R. Physique 3 (2002) 111–119     

Hyperfine interaction of Ce and La in 3-d ferromagnets

NMR/ON measurements on¹⁴¹CeFe show the sign of the hyperfine field of CeFe to be negative. For the¹⁴¹Ce nucleus a g-factor of ¦g_N¦=0.311±0.011 is found. With this g-value a hyperfine field of H_hf=?41±2 T for CeFe is derived. Low temperature nuclear orientation experiments on¹⁴¹CeCo and¹⁴⁰LaFe yield ¦H_hf¦=30±3 T and ¦H_hf¦=46±5 T respectively. The valence of cerium impurities in Fe, Co and Ni is discussed.     

Low frequency four-wave mixing spectroscopy of biopolymer hydration layers in aqueous solutions

Four-wave mixing (FWM) spectroscopy has been applied to detection of H₂O₂ molecules rotational resonances in both DNA and denatured DNA aqueous solutions in the range ±100 cm⁻¹. A considerable growth of rotational lines intensity of H₂O and H₂O₂ has been observed in comparison with distilled water. This fact was interpreted as an exhibition of specific property of a hydration layer formation at DNA/water and denatured DNA/water interfaces. The fitting of four-wave mixing spectra shows the increasing of the H₂O₂ rotational line’s amplitude by a factor of ∼3 in DNA solutions due to denaturizing. The shifting of FWM Brillouin resonances in opposite way in protein solution and SWNT (single wall carbon nanotube) suspension to comparison with water was observed and discussed.     

Spin-dependent scattering of slow neutrons on polarized 17O

The method of pseudomagnetism has been applied to measure the spin-dependent scattering length b_N of slow neutrons on ¹⁷O nuclei. A powder sample of CaO, enriched with ¹⁷O, has been used. In this sample, dynamic nuclear polarizations of ± 10 % have been achieved at 2.5 T and 0.2 K using paramagnetic impurities created by fast neutron irradiation (F-centers). b_N = 0.12 ± 0.04 fm has been found. This value is close to an earlier shell model calculation.     

Hydrophobic/hydrophilic solvation: inferences from Monte Carlo simulations and experiments

In this study Monte Carlo simulations are used to determine the solvation properties of model hydrophobic (xenon and hard sphere) and hydrophilic (dimethyl ether) solutes in SPC/E water. Various contributions to the experimental solvation entropy, including the solvent reorganization entropy, have been determined. The main conclusion drawn, which is in accord with solubility data, is that poor solubility correlates with poor solute-water interaction. At room temperature, energy dominates the aqueous solubility of both hydrophobic and hydrophilic solutes, rather than entropy. However, at higher temperatures the solubility can pass through a minimum, and then entropy becomes dominant. Another interesting finding is the presence of larger than expected cavities in water. Two different simulation results support this finding. This unexpected hollow structure in water explains why a hard sphere solute is more soluble in water than in a comparable hard sphere or Lennard-Jones solvent. Hydrogen bonding causes water to aggregate into clusters that produce a few large cavities rather than many smaller cavities. The propensity for clustering also explains why water gives the illusion of being a low density liquid. Sufficient theoretical apparatus is developed to connect theoretical solvation properties to those measured by simulation and experiment. Finally, based on gas solubility, an intuitive hydrophobic/hydrophilic scale is developed.     

Molecular mobility in biodegradable poly( $ \varepsilon$ -caprolactone)/poly(hydroxyethyl acrylate) networks

Poly( e \varepsilon -caprolactone)/poly(hydroxyethyl acrylate) networks have been investigated by thermally stimulated depolarization currents (TSDC) and differential scanning calorimetry (DSC). The introduction of hydrophilic units (HEA) in the system aiming at tailoring the hydrophilicity of the system results in a series of copolymer networks with microphase separation into hydrophobic/hydrophilic domains. Polycaprolactone (PCL) crystallization is prevented by the topological constraints HEA units imposed in such heterogeneous domains. Moreover, the mobility of the amorphous PCL chains is enhanced as revealed by the main relaxation process which becomes faster. The glass transition of PHEA-rich domains shifts to lower temperatures, as the total amount of PCL in the copolymer increases, due to the presence of PCL units within the same region. The behaviour of the copolymer networks swollen with different content of water has been investigated to analyze the interaction between water molecules and hydrophobic/hydrophilic domains and provide further insights into the molecular structure of the system.