The frozen state in the liquid phase of side-chain liquid-crystal polymers

Quenched isotropic melts of side-chain liquid-crystal polymers reveal surprisingly an anisotropic polymer conformation. This small-angle neutron-scattering (SANS) result is consistent with the identification of a macroscopic, solidlike response in the isotropic phase. Both experiments (rheology and SANS) indicate that the polymer system appears frozen on millimeter length scales and at the time scales of the observation. This result implies that the flow behavior is not the terminal behavior and that cross-links or entanglements are not a necessary condition to provide elasticity in melts.     

Half life measurement of the first excited O+ state in102Pd

Electron-gamma coincidences have been performed on mass separated sources of¹⁰²Ag. The 1592-keV EO transition is placed in the decay scheme of 8-min¹⁰²Ag^m. The measured half life, (17±2) nsec, reveals the anomalous nature of the first excited O⁺ state in¹⁰²Pd.     

Degradative encryption: An efficient way to protect SPIHT compressed images

Degradative encryption, a new selective image encryption paradigm, is proposed to encrypt only a small part of image data to make the detail blurred but keep the skeleton discernible. The efficiency is further optimized by combining compression and encryption. A format-compliant degradative encryption algorithm based on set partitioning in hierarchical trees (SPIHT) is then proposed, and the scheme is designed to work in progressive mode for gaining a tradeoff between efficiency and security. Extensive experiments are conducted to evaluate the strength and efficiency of the scheme, and it is found that less than 10% data need to be encrypted for a secure degradation. In security analysis, the scheme is verified to be immune to cryptographic attacks as well as those adversaries utilizing image processing techniques. The scheme can find its wide applications in online try-and-buy service on mobile devices, searchable multimedia encryption in cloud computing, etc.     

Active-to-absorbing phase transition subjected to the velocity fluctuations in the frozen limit case

The directed bond percolation process is studied in the presence of compressible velocity fluctuations with long-range correlations. We discuss a construction of a field theoretic action and a way of obtaining its large scale properties using the perturbative renormalization group. The most interesting results for the frozen velocity limit are given.     

Thermal diffusion and the approach to the steady state in gases: II

The theory of the rate of approach to the steady state in themal diffusion is tested experimentally on the systems He-Ar, He-CO₂, H₂-CO₂, and D₂-CO₂ over a temperature range of about -78°c to 325°c. The course of the diffusion has been followed by means of the radioactive tracers ³⁷Ar and ¹⁴CO₂. The theory appears to be verified, and the results are used to calculate ordinary diffusion coefficients, which are in reasonable accord with previous measurements by other techniques. The thermal diffusion factors, which are obtained from the same measurements, also appear to have reasonable accuracy. The experimental method therefore appears to have promise as a sensitive method for the determination of forces between unlike molecules.     

The new EC Noise Directive to protect employees at the workplace

The planned provisions of the new Noise Directive to protect employees drawn up in 2001 are analysed and evaluated on the basis of the existing Directive. Although the new Noise Directive provides for a number of major changes, the basic problems of noise control at the workplace are not dealt with.     

Superconductivity close to the Mott state: From condensed-matter systems to superfluidity in optical lattices

Since the discovery of high-temperature superconductivity in 1986 by Bednorz and Müller, great efforts have been devoted to finding out how and why it works. From the d-wave symmetry of the order parameter, the importance of antiferromagnetic fluctuations, and the presence of a mysterious pseudogap phase close to the Mott state, one can conclude that high-T_c superconductors are clearly distinguishable from the well-understood BCS superconductors. The d-wave superconducting state can be understood through a Gutzwiller-type projected BCS wavefunction. In this review article, we revisit the Hubbard model at half-filling and focus on the emergence of exotic superconductivity with d-wave symmetry in the vicinity of the Mott state, starting from ladder systems and then studying the dimensional crossovers to higher dimensions. This allows to confirm that short-range antiferromagnetic fluctuations can mediate superconductivity with d-wave symmetry. Ladders are also nice prototype systems allowing to demonstrate the truncation of the Fermi surface and the emergence of a Resonating Valence Bond (RVB) state with preformed pairs in the vicinity of the Mott state. In two dimensions, a similar scenario emerges from renormalization group arguments. We also discuss theoretical predictions for the d-wave superconducting phase as well as the pseudogap phase, and address the crossover to the overdoped regime. Finally, cold atomic systems with tunable parameters also provide a complementary insight into this outstanding problem.     

Spin frozen in the Kondo-lattice compound: CeCuSi2

In this paper, we present the experimental results of X-ray powder diffraction, electrical resistivity, magnetic susceptibility, and specific-heat measurements as well as Ce-L_III-edge X-ray absorption spectrum of the Ce-based intermetallic compound CeCuSi₂. The results revealed that CeCuSi₂ is a Kondo-lattice compound with no superconducting or magnetic-phase transition above 0.4 K. In addition, we found spin-glass behavior in the DC susceptibility measurements. The AC susceptibility measurements and the magnetic entropy calculation also confirm the presence of the spin-glass phase. The possible formation mechanism for the spin-frozen state is also discussed in this paper.     

Electron excitation from ground state to first excited state:Bohmian mechanics method

The excitation process of electrons from the ground state to the first excited state via the resonant laser pulse is investigated by the Bohmian mechanics method. It is found that the Bohmian particles far away from the nucleus are easier to be excited and are excited firstly, while the Bohmian particles in the ground state is subject to a strong quantum force at a certain moment, being excited to the first excited state instantaneously. A detailed analysis for one of the trajectories is made, and finally we present the space and energy distribution of 2000 Bohmian particles at several typical instants and analyze their dynamical process at these moments.     

Transport in Nb-InAs structures: from phase coherence to the edge state regime

We investigated transport in Nb-InAs hybrid structures in perpendicular magnetic fields up to the quantum Hall regime. Due to the high contact quality of our samples, Andreev reflection dominates the transport properties in a range of experimental parameters. Our experiments were performed on periodic arrays of Nb filled stripes or antidots in an InAs-based 2DEG. According to geometry and field strength we observe the following effects: At low fields, up to a few flux quanta per unit cell, we find phase-coherent behavior, such as flux-periodic oscillations. At slightly higher fields, the Andreev reflection probability is determined by induced superconductivity in the 2DEG, which is gradually suppressed by an increasing magnetic field. In the arrays of Nb filled antidots we find that the commensurability peaks are suppressed since Andreev reflection restores regular motion in velocity space. Due to the high critical field of the Nb nanostructures, we can also enter the edge state regime, where we observe a pronounced increase of the amplitude of 1/B-periodic magnetoresistance oscillations. The latter can be traced to an enhanced backscattering of Andreev-reflected edge channels, which contain both electrons and holes. PACS 74.45.+c; 73.43.Qt; 73.63.-b     

Sensitivity to disorder of the metallic state in the ruthenates

We report the results of transport measurements on SrRuO3, Sr3Ru2O7, and CaRuO3. In SrRuO3 and Sr3Ru2O7, our findings are consistent with the predictions of Fermi liquid theory, in contrast to previous reports based on samples with much shorter mean free paths. In CaRuO3, however, a T1.5 power law is seen in the resistivity in the high purity samples studied here. Our work gives concrete evidence that even the metallic state of the ruthenates is highly sensitive to disorder.     

Transition to the nonmetallic state in liquid cesium-gold alloys

The electrical conductivity of the liquid Cs-Au alloy system was measured as a function of temperature and composition to 710°C and 57 at 0% Au, respectively. A change to non-metallic behavior is observed near the equi-atomic composition.     

Transition to the quasi-two-dimensional magnetic state in Pd-Fe films

The Mössbauer spectra of Pd-Fe films with different thicknesses and iron concentrations are measured. In these films, the spin fluctuations associated with the transition to a quasi-two-dimensional magnetic state are observed over a wide range of temperatures. The dependences of the magnetic field strength and the Curie temperature on the film thickness are quite consistent with the scaling theory. Owing to the long-range exchange coupling, the films containing 14.4 and 7.8 at. % Fe undergo a transition to the quasi-two-dimensional state at a film thickness of several thousand angströms.     

Nematic ordering in anisotropic elastomers: Effect of frozen anisotropy

Nematic ordering in anisotropic non-Gaussian elastomers is considered theoretically using mean field approximation. We focus on the effect of anisotropy during network cross-linking on the system elasticity and, in particular, on the so-called soft deformation mode. As the main result, we calculate the dependence of the elastomer free energy on the angle between the axis of “frozen” anisotropy and the nematic director. The dependence of the isotropic-nematic transition point on the orientational field acting on the monomers during the cross-linking process is also calculated. Received: 5 November 1997 / Revised and Accepted: 29 June 1998     

Cassie-Baxter to Wenzel state wetting transition: Scaling of the front velocity

We experimentally study the dynamics of water in the Cassie-Baxter state to Wenzel state transition on surfaces decorated with assemblies of micrometer-size square pillars arranged on a square lattice. The transition on the micro-patterned superhydrophobic polymer surfaces is followed with a high-speed camera. Detailed analysis of the movement of the liquid during this transition reveals the wetting front velocity dependence on the geometry and material properties. We show that a decrease in gap size as well as an increase in pillar height and intrinsic material hydrophobicity result in a lower front velocity. Scaling arguments based on balancing surface forces and viscous dissipation allow us to derive a relation with which we can rescale all experimentally measured front velocities, obtained for various pattern geometries and materials, on one single curve.