Non-Contact Friction for Ion-Surface Interactions

Non-contact friction forces are exerted on physical systems through dissipative processes, when the two systems are not in physical contact with each other, or, in quantum mechanical terms, when the overlap of their wave functions is negligible. Non-contact friction is mediated by the exchange of virtual quanta, with the additional requirement that the scattering process needs to have an inelastic component. For finite-temperature ion-surface interactions, the friction is essentially caused by Ohmic resistance due to the motion of the image charge moving in a dielectric material. A conceivable experiment is difficult because the friction force needs to be isolated from the interaction with the image charge, which significantly distorts the ion's flight path. We propose an experimental setup which is designed to minimize the influence of the image charge interaction though a compensation mechanism, and evaluate the energy loss due to non-contact friction for helium ions (He+) interacting with gold, vanadium, titanium and graphite surfaces. Interactions with the infinite series of mirror charges in the plates are summed in terms of the logarithmic derivatives of the Gamma function, and of the Hurwitz zeta function.Comment: 9 pages; ReVTeX; accepted for publication in Eur.Phys.J.

Ciba Protek vs. Vistakon One-Day Acuvue: A comparison of antibiotic reservoir and delivery effects

Since the Food and Drug Administration approved the use of hydrophilic lenses as ocular bandages in 1973, they have become the treatment of choice for many corneal problems, not the least being superficial corneal abrasions. Practitioners are opting for the more readily available disposable soft contact lenses because of the limited number of expensive therapeutically approved bandage soft contact lenses. In this study we set out to determine if there is a significant difference in the antibiotic reservoir and delivery effect of these two groups of soft contact lenses. The eyes in this study were divided into three groups: Protek® group, Acuvue® group and control group. Two drops of Tobramycin 0.3% solution were instilled into each eye followed by subsequent isolation of tear samples using diffusion disks. The relative amount of antibiotic in the tears at certain time intervals was inferred using kill zone ring width (KZRW) measures around the diffusion disks. The data were then analyzed using an ANOVA statistical test. From this analysis we found that while there was a significant difference in KZRW between both Protek® versus control and Acuvue® versus control, there was no significant difference between Protek® versus Acuvue®. This study shows that, when used as an antibiotic reservoir and delivery system, the Ciba Protek® therapeutic contact lens and One-day Acuvue® disposable contact lens behave very similarly

Role of interfaces on severe plastic deformation and He-irradiation tolerance in Cu-Nb nanocomposites

Interface structure in immiscible metal nanocomposites plays a key role in deformation tolerance and radiation damage tolerance. Interface structure, just like microstructure, can vary within the same material system depending on the processing route; the properties of a material can also vary depending on the interface structure. The role of interface structure on the tolerance to severe plastic deformation in Cu-Nb nanocomposites was investigated by comparing the microstructural evolution after high pressure torsion (HPT) of multilayer nanocomposites grown by physical vapor deposition (PVD) with low shear strength interfaces and fabricated by accumulative roll bonding (ARB) with high shear strength interfaces. And the role of interface structure on the trapping of He was studied by comparing He-bubble formation in nano-multilayers grown by PVD, nanolaminates fabricated by ARB, and three-dimensional nanocomposites obtained by high pressure torsion (HPT); each of these has a different preferred orientation relationship. The stability of PVD-grown multilayers when subjected to HPT is significantly better to high shear strain than the ARB-fabricated multilayers. The PVD-grown multilayers remain largely stable up to a strain of ~81 and still have regions of multilayers at a strain of ~357 before transforming to a 3D nanocomposite by a strain of ~685; the ARB multilayer composites meanwhile become unstable at shear strain of ~10 and completely transform to a 3D interconnected composite at a strain of ~278. The mechanisms for deformation depend on the interface character; the PVD-grown material with low shear strength interfaces deform by interfacial sliding while the ARB-fabricated material deforms by dislocation glide across the interface. In both layered systems, there is kink and shear banding of layers at higher shear strain that changes the local orientation of layers relative to the shear direction resulting in a route to transition to a 3D nanocomposite structure. Likewise under He-ion irradiation, the critical He dose per unit interfacial area for bubble formation was largest for the PVD multilayers, lower by a factor of ~1.4 in the HPT nanocomposites annealed at 500 ˚C, and lower by a factor of ~4.6 in the ARB nanolaminates relative to the PVD multilayers. The high concentration of free volume at interfaces in PVD-grown multilayers is excellent for trapping He atoms and point defects, and the amount of trapped He at the interface scales with interface area density. A combination of efficient interfaces and high density of interfaces is ideal for trapping He atoms and point defects. The results of both high shear strain using HPT and He implantation indicate that the (111)FCC||(110)BCC Kurdjumov-Sachs (KS), or {111}KS, interfaces predominant in PVD provide more effective traps for both point and line defects than the {112}KS interfaces predominant in ARB nanolaminates. The steady-state microstructural stability, good trapping efficiency, and high interface area of 3D structures processed by severe plastic deformation make them most attractive for structural applications such as nuclear energy

One-Loop Dominance in the Imaginary Part of the Polarizability: Application to Blackbody and Non-Contact van der Waals Friction

Phenomenologically important quantum dissipative processes include black-body friction (an atom absorbs counterpropagating blue-shifted photons and spontaneously emits them in all directions, losing kinetic energy) and non-contact van der Waals friction (in the vicinity of a dielectric surface, the mirror charges of the constituent particles inside the surface experience drag, slowing the atom). The theoretical predictions for these processes are modified upon a rigorous quantum electrodynamic (QED) treatment, which shows that the one-loop "correction" yields the dominant contribution to the off-resonant, gauge-invariant, imaginary part of the atom's polarizability at room temperature, for typical atom-surface interactions. The tree-level contribution to the polarizability dominates at high temperature.Comment: 5 pages; RevTe

Collection efficiency and design of microbial air samplers

The variables affecting the physical collection efficiency of air samplers of the type that impact microbe-carrying particles onto agar were investigated using a simplified analytical method and computational fluid dynamics. The results from these two techniques were compared, as were the effect of jet velocity, nozzle size, and nozzle distance from the agar surface; also considered was the optimisation of these variables to obtain an efficient design of sampler. A technique is described that calculates the proportion of microbe-carrying particles that a sampler will collect from a typical size distribution of microbe-carrying particles found in an occupied room; the three air samplers studied were found to collect from about 22% to over 99% of the micro-organisms in the room air

No self-similar aggregates with sedimentation

Two-dimensional cluster-cluster aggregation is studied when clusters move both diffusively and sediment with a size dependent velocity. Sedimentation breaks the rotational symmetry and the ensuing clusters are not self-similar fractals: the mean cluster width perpendicular to the field direction grows faster than the height. The mean width exhibits power-law scaling with respect to the cluster size, ~ s^{l_x}, l_x = 0.61 +- 0.01, but the mean height does not. The clusters tend to become elongated in the sedimentation direction and the ratio of the single particle sedimentation velocity to single particle diffusivity controls the degree of orientation. These results are obtained using a simulation method, which becomes the more efficient the larger the moving clusters are.Comment: 10 pages, 10 figure

GDR Feeding of the Highly-Deformed Band in 42Ca

The gamma-ray spectra from the decay of the GDR in the compound nucleus reaction 18O+28Si at bombarding energy of 105 MeV have been measured in an experiment using the EUROBALL IV and HECTOR arrays. The obtained experimental GDR strength function is highly fragmented, with a low energy (10 MeV) component, indicating a presence of a large deformation and Coriolis effects. In addition, the preferential feeding of the highly-deformed band in 42Ca by this GDR low energy component is observed.Comment: 6 pages, 2 figures, Proceedings of the Zakopane2004 Symposium, to be published in Acta Phys. Pol. B36 (2005

Direct observation of a highly spin-polarized organic spinterface at room temperature

The design of large-scale electronic circuits that are entirely spintronics-driven requires a current source that is highly spin-polarised at and beyond room temperature, cheap to build, efficient at the nanoscale and straightforward to integrate with semiconductors. Yet despite research within several subfields spanning nearly two decades, this key building block is still lacking. We experimentally and theoretically show how the interface between Co and phthalocyanine molecules constitutes a promising candidate. Spin-polarised direct and inverse photoemission experiments reveal a high degree of spin polarisation at room temperature at this interface. We measured a magnetic moment on the molecules's nitrogen pi orbitals, which substantiates an ab-initio theoretical description of highly spin-polarised charge conduction across the interface due to differing spinterface formation mechanims in each spin channel. We propose, through this example, a recipe to engineer simple organic-inorganic interfaces with remarkable spintronic properties that can endure well above room temperature

Long Distance Contribution to s→dγs \to d\gamma and Implications for Ω−→Ξ−γ,Bs→Bd∗γ\Omega^-\to \Xi ^-\gamma, B_s \to B_d^*\gamma and b→sγb \to s\gamma

We estimate the long distance (LD) contribution to the magnetic part of the $s \to d\gamma$ transition using the Vector Meson Dominance approximation $(V=\rho,\omega,\psi_i)$. We find that this contribution may be significantly larger than the short distance (SD) contribution to $s \to d\gamma$ and could possibly saturate the present experimental upper bound on the $\Omega^-\to \Xi^-\gamma$ decay rate, $\Gamma^{\rm MAX}_{\Omega^-\to \Xi^-\gamma} \simeq 3.7\times10^{-9}$eV. For the decay $B_s \to B^*_d\gamma$, which is driven by $s \to d\gamma$ as well, we obtain an upper bound on the branching ratio $BR(B_s \to B_d^*\gamma)<3\times10^{-8}$ from $\Gamma^{\rm MAX}_{\Omega^-\to \Xi^-\gamma}$. Barring the possibility that the Quantum Chromodynamics coefficient $a_2(m_s)$ be much smaller than 1, $\Gamma^{\rm MAX}_{\Omega^-\to \Xi^-\gamma}$ also implies the approximate relation $\frac{2}{3} \sum_i \frac{g^2_{\psi_i}(0)}{m^2_{\psi_i}} \simeq \frac{1}{2} \frac{g^2_\rho(0)}{m^2_\rho} + \frac{1}{6}\frac{g^2_\omega(0)}{m^2_\omega}$. This relation agrees quantitatively with a recent independent estimate of the l.h.s. by Deshpande et al., confirming that the LD contributions to $b \to s\gamma$ are small. We find that these amount to an increase of $(4\pm2)\%$ in the magnitude of the $b \to s \gamma$ transition amplitude, relative to the SD contribution alone.Comment: 16 pages, LaTeX fil