Rolling friction of a hard cylinder on a viscous plane

The resistance against rolling of a rigid cylinder on a flat viscous surface is investigated. We found that the rolling-friction coefficient reveals strongly non-linear dependence on the cylinder's velocity. For low velocity the rolling-friction coefficient rises with velocity due to increasing deformation rate of the surface. For larger velocity, however, it decreases with velocity according to decreasing contact area and deformation of the surface. Received 24 December 1998 and Received in final form 14 January 1999     

Recognition determinants in a T4 ← G4 mutant derived from a 5′-GCGTGGGCGT-3′ oligomer in a zinc finger 268–DNA complex.

The 5′-GCGTGGGCGT-3′ (T4) oligomer found in the zinc finger 268–DNA complex was mutated into the sequence 5′-GCGGGGGCGT-3′ (G4). A 3D model was constructed from the T4 sequence using an X-ray structure as a template. Molecular dynamics simulations were used to test the thermal stability of the model. A 500-ps trajectory was obtained for the fully charged complex in water using GROMOS87. The complex and the G4 sequence are found to have dynamically stationary behavior. Comparisons made with a previous T4 sequence molecular dynamics simulation show both systems have similar thermal stability. The structure of DNA appears to be maintained by its global interactions with the protein although the mutated site does not contribute with its full potential for binding. The protein structure shows some small differences compared to the T4 simulation. The simulation provided evidence for the role of a chloride ion interacting with the protein and helping in the recognition process. Received: 21 June 1999 / Accepted: 19 October 1999 / Published online: 14 March 2000     

Reprint of : Quantum point contacts as heat engines

The efficiency of macroscopic heat engines is restricted by the second law of thermodynamics. They can reach at most the efficiency of a Carnot engine. In contrast, heat currents in mesoscopic heat engines show fluctuations. Thus, there is a small probability that a mesoscopic heat engine exceeds Carnot's maximum value during a short measurement time. We illustrate this effect using a quantum point contact as a heat engine. When a temperature difference is applied to a quantum point contact, the system may be utilized as a source of electrical power under steady state conditions. We first discuss the optimal working point of such a heat engine that maximizes the generated electrical power and subsequently calculate the statistics for deviations of the efficiency from its most likely value. We find that deviations surpassing the Carnot limit are possible, but unlikely.     

Interface polarons in a heterojunction with triangular bending-band

The interface polaron states in a heterojunction are discussed by considering an energy-band bending near the interface and the influence of an image potential. The ground state energy and the effective mass of a polaron are variationally calculated. The numerical results for the GaAs/ heterojunction are given. It is shown that even though the influences from bulk longitudinal optical (LO) phonons are more important for the heterojunctions with lower Al composition, the contributions from two branches of interface optical (IO) phonons are not negligible. For the heterojunctions with higher Al composition, both the influences from LO phonons and two branches of IO phonons are important. The band-bending plays an important role for the interface localization of polarons, but the influence of the image potential is not essential. Received: 4 November 1997 / Revised and Accepted: 9 March 1998     

Nonlinear optical effects for plasma diagnostics

Experimental investigations show that the 1/f noise intensityC and the contact resistanceR can be used to analyse contacts. The simply prepared contacts are fritted by discharging a capacitor, resulting in a multi-spot contact. A model relatesC andR to a number of contact spotsk with radiusa. More impulse-frittings at increasing energies decreaseC andR, thus enhancing the values ofk anda. From experimentalC vsR plots two regions are determined for GaAs: A fritting (a=constant) and A+B fritting (a∝k). Calculated values ofk are in good agreement with the number of peaks or pits formed by etching the semiconductor surface. From experimentalC vsW orR vsW curves, withW the cumulative impulse-fritting energy, the conclusion can be made thatka ³ is proportional toW.     

Shielded distribution approximation for a wall-bounded classical fluid

We investigate lower order distribution functions in classical fluids in the presence of large-scale inhomogeneities, in particular those imposed by wall contacts. The consequences of the effective shielding of a wall by the nearest particle of the set being considered are determined in the context of two distribution function hierarchies, kinematic and dynamic in origin. The effects of both flat and spherical, hard and soft walls are considered, as well as those of curved and double walls. A few correction sequences to the basic shielding approximation are discussed.Supported in part by the Department of Energy under contract DE-AC02-76 ERO 3077.     

The contribution of frictional contacts to the shear strength of coarse glass bead powders and slurries

This paper investigates the use of the shear vane technique as a means of determining frictional and cohesive interparticle force contributions to the shear strength of coarse glass bead powders and slurries. To this end, the shear strength of 203-μm glass beads in air and slurried in water and kaolinite suspensions was determined as a function of vane immersion depth, vane geometry, and container size. Both vane immersion depth and container diameter are found to significantly impact the shear strength measured using the vane technique. An equation describing interparticle frictional and cohesive contributions to shear vane measurements was derived in an effort to describe the experimental results. A Janssen stress distribution model for granular materials forms the basis for this equation and appears to explain the behavior of shear strength measurements at varying immersion depths. The presence of the Janssen stress distribution can affect the interpretation of shear vane results. Rather than shear strength being a material property, as is the case with flocculated colloid slurries and polymer solutions, shear strength becomes a process property where vane depth, container size, and container material can result in significant measurement variations. Such parameters should be considered before using the shear vane results on applications involving granular material components.US Department of Energy Environmental Management Science Program project no. 90162.     

Chemical vapour etching for double-sided buried metallic contacts in polycrystalline silicon solar cells processing

In this paper, we investigate the effect of double-sided buried metallicontacts (BMCs) on the photovoltaic performances of polycrystalline-silicon (pc-Si) solar cells. Prior to junction formation, groove patterns were achieved on both surface sides of the pc-Si wafers using a chemical vapour etching-based technique. The BMCs were realized onto the grooved areas using the screen printing technique. Once the BMCs were formed, we point out a significant increase of the spectral response in the 400-1100 nm wavelength range, particularly at short and long wavelengths. These results were attributed to an enlargement of the contact areas in both emitter and base regions of the cells, leading to a reduction of their effective thickness and to an enhancement of the minority carrier collection. The dark I-V characteristics of BMCs-based pc-Si cells show a significant reduction of the reverse current together with an improvement of the rectifying behaviour. The I-V characteristic under AM1.5 illumination shows that the introduction of BMCs in polycrystalline silicon solar cells processing improves the conversion efficiency by about 2.5-3.5%.     

Effects of cap layer on ohmic Ti/Al contacts to Si implanted GaN

A low resistivity ohmic contact to Si-implanted GaN was achieved using a metal combination of Ti/Al. The effect of a protection cap during post-implantation annealing is investigated, and how it affects the specific contact resistivity (ρ_c). Relevant differences between the protected (PR) sample with SiO₂ and unprotected (UP) sample during the post-implantation annealing were observed after metal alloying at 700 °C. The lower values of ρ_c have been obtained for UP sample, but with very low reproducibility. In contrast, SiO₂ cap layer has demonstrated its relevance in yielding a much more uniformity of a relatively low ρ_c around 10⁻⁵ Ω cm². Related mechanism for the uniformity in ρ_c was discussed based on the results obtained from electrical measurements, XRD (X-ray diffraction) analysis, AFM (atomic force microscopy) and SEM (scanning electron microscopy) observations.     

Particle–hole symmetric Luttinger liquids in a quantum Hall circuit

We report finite-bias differential conductance measurements through a split-gate constriction in the integer quantum Hall regime at ν=1. Both enhanced and suppressed zero-bias inter-edge backscattering can be obtained in a controllable way by changing the split-gate voltage. This behavior is interpreted in terms of local charge depletion and particle–hole symmetry. We discuss the relevance of particle–hole symmetry in connection with the chiral Luttinger model of edge states.