Giant viscosity enhancement in a spin-polarized fermi liquid

The viscosity is measured for a Fermi liquid, a dilute 3He-4He mixture, under extremely high magnetic field/temperature conditions (Bor=1.5 mK). The spin-splitting energy microB is substantially greater than the Fermi energy kBTF; as a consequence the polarization tends to unity and s-wave quasiparticle scattering is suppressed for T相似文献   

Effects of ZnS:Mn concentrated vinyl ester matrices under flexural loading on the triboluminescent yield

This paper investigates the feasibility of using zinc sulfide manganese (ZnS:Mn) concentrated vinyl ester resin as a photon emitter for damage monitoring of polymer composites under flexural loading. Unreinforced vinyl ester resins doped with optical emitting materials (ZnS:Mn phosphors) in ratios of 5–50% by weight were cast, and subjected to flexural loading using standard 3-point bend tests. The intent of this work was to observe the transient response of triboluminescence (TL) throughout the failure cycle. Results indicate TL crystals emit light at various intensities corresponding to crystal concentration and imminent matrix fracture. Consequently, concentrated samples showed nearly 50% reductions of mechanical moduli. Scanning electron microscopy (SEM) revealed particulate inclusions with shearing bands and semblance of particle to resin adhesion. Despite significant parasitic effect to mechanical properties, the triboluminescent properties occur at yielding and point of matrix fracture.     

Diffusion-controlled synthesis of gold nanoparticles: nano-liposomes as mass transfer barrier

Lipid vesicles and other types of amphiphilic materials are of great interest in the size-controlled synthesis of metal nanoparticles. In this study, we prepared nano-sized liposomes encapsulating tetrachloroauric acid for the facile synthesis of gold nanoparticles with controlled size over a range of 2–5 nm at room temperature. The semi-permeable character of the lipid membrane to the varying concentrations of reducing agent—sodium borohydride-regulated the particle formation kinetics. Diffusion of the reducing agent through the liposomal membrane in a controlled manner resulted in ultrasmall nanoparticles of a narrow size distribution with less aggregation as compared to the solution-based preparation method.     

Spectra and structure of silicon containing compounds

The Raman (50 to 3200 cm^–1) and infrared (50 to 3500 cm^–1) spectra of chlorodimethylmethoxysilane, Cl(CH₃)₂SiOCH₃, in the vapor and solid phases have been recorded. Raman spectra of the liquid including depolarization ratios have also been recorded. Optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing the RHF/3–21G* and RHF/6–31G* basis sets. The calculations from both of these basis sets indicated the gauche conformer to be significantly more stable than the trans conformer. Since the gauche has twice the multiplicity of the trans form it is unlikely that the trans conformer will be detected in the fluid phases at room temperature. This is supported by the fact that no infrared or Raman bands were found to vanish in the spectra of the crystalline solid. The vibrational frequencies have been calculated using appropriate scaling factors, and the vibrational spectra are interpreted in detail. The results have been compared with those obtained for some related molecules.Dedicated to Professor Dr. H. Kriegsmann on the occasion of his 70th birthdayFor part XX, see J Raman Spectrosc 26:in press (1995)Analytical R/D Department, Organic Products Division, Miles Inc., Bushy Park Plant. Charleston, SC 9411, USAChemistry Department, Mu'tah University, P.O.Box 7, Mu'tah-Karak, JordanDepartment of Chemistry, Moscow State University, Moscow, B-234, RussiaDepartment of Ceramic Engineering, Inha University, Nam-Ku, Incheon 160, KoreaDepartment of Chemistry, University of Oslo, P.O.Box 1033, 0315 Oslo, Norway     

Thermoelasticity of networks in swelling equilibrium with single component diluents: Specific polymer-diluent interactions

Using thermoelastic measurements, specific polymer-diluent interactions have been demonstrated for atactic poly(vinyl alcohol) networks swollen in water. This was done by following a thermodynamic parameter as a function of network swelling, which was controlled by varying the extent of network crosslinking. At low crosslinking (high swelling) the ratio of the energy component f_e of the force to the total force f was found to be perhaps a little less than ?0.38 for poly(vinyl alcohol) swollen in water to less than 0.36 volume fraction of polymer. The method of evaluation is new and should be applicable to other polymer single component diluent systems.     

In situ ultraviolet Raman spectroscopy of the reduction of chromia on alumina catalysts

A fluidized bed in situ cell is used to examine the chromia on alumina catalyst surface. The loading is varied from 1 to 20% chromium oxide on alumina. The structure of the surface is monitored as a function of temperature, reduction, and hydration. This is the first study to use ultraviolet excitation to study a reduced chromium catalyst surface. Reduction of the sample in hydrogen gas leads to the formation of noncrystalline Cr(3+) species. Addition of potassium to the surface reduces the size of the chromia clusters.     

Role of recording geometry in the performance of spectral diversity filters with spherical beam volume holograms

We present experimental demonstrations of spectral diversity filters with spherical beam volume holograms for multimodal multiplex spectroscopy. Major properties of filters under diffuse-light illumination are discussed. The comparisons of spectral diversity between the transmission geometry holograms and the reflection geometry holograms are also studied. The results show that there is a trade-off between the degree of the spatial coherence of the source and the spectral diversity of the filter. We also conclude that the reflection geometry holograms have better spectral diversity and less sensitivity to the spatial coherence of the source.     

Electron correlation in the second Landau level: a competition between many nearly degenerate quantum phases

At a very low-temperature of 9 mK, electrons in the second Landau level of an extremely high-mobility two-dimensional electron system exhibit a very complex electronic behavior. With a varying filling factor, quantum liquids of different origins compete with several insulating phases leading to an irregular pattern in the transport parameters. We observe a fully developed nu=2+2/5 state separated from the even-denominator nu=2+1/2 state by an insulating phase and a nu=2+2/7 and nu=2+1/5 state surrounded by such phases. A developing plateau at nu=2+3/8 points to the existence of other even-denominator states.     

Do superconductors have zero resistance in a magnetic field?

We show that dc voltage versus current measurements of a YBa(2)Cu(3)O(7-delta) film in a magnetic field can be collapsed onto scaling functions proposed by Fisher et al. [Phys. Rev. B 43, 130 (1991)] as is widely reported in the literature. We find, however, that good data collapse is achieved for a wide range of critical exponents and temperatures. These results strongly suggest that agreement with scaling alone does not prove the existence of a phase transition. We propose a criterion to determine if the data collapse is valid, and thus if a phase transition occurs. To our knowledge, none of the data reported in the literature meet our criterion.     

Excitation of molecular vibrations by positron impact

Absolute cross sections for the vibrational excitation of CO, CO2, and H2 by positron impact are presented for incident positron energies from 0.5 eV to several electron volts. The measurements use a novel technique that exploits the adiabatic motion of a positron beam in a strong magnetic field. This work is the first systematic experimental study of vibrational excitation by positron impact, and extends to energies where positron measurements have traditionally been difficult. The measured cross sections are compared with available theoretical calculations.