Investigation of a hopping transporter concept for lunar exploration

Performance and dynamic characteristics determined for hopping transporter for lunar exploratio

Complex Line Bundles over Simplicial Complexes and their Applications

Discrete vector bundles are important in Physics and recently found remarkable applications in Computer Graphics. This article approaches discrete bundles from the viewpoint of Discrete Differential Geometry, including a complete classification of discrete vector bundles over finite simplicial complexes. In particular, we obtain a discrete analogue of a theorem of Andr\'e Weil on the classification of hermitian line bundles. Moreover, we associate to each discrete hermitian line bundle with curvature a unique piecewise-smooth hermitian line bundle of piecewise constant curvature. This is then used to define a discrete Dirichlet energy which generalizes the well-known cotangent Laplace operator to discrete hermitian line bundles over Euclidean simplicial manifolds of arbitrary dimension

Bilayer Membrane in Confined Geometry: Interlayer Slide and Steric Repulsion

We derived free energy functional of a bilayer lipid membrane from the first principles of elasticity theory. The model explicitly includes position-dependent mutual slide of monolayers and bending deformation. Our free energy functional of liquid-crystalline membrane allows for incompressibility of the membrane and vanishing of the in-plane shear modulus and obeys reflectional and rotational symmetries of the flat bilayer. Interlayer slide at the mid-plane of the membrane results in local difference of surface densities of the monolayers. The slide amplitude directly enters free energy via the strain tensor. For small bending deformations the ratio between bending modulus and area compression coefficient, Kb/KA, is proportional to the square of monolayer thickness, h. Using the functional we performed self-consistent calculation of steric potential acting on bilayer between parallel confining walls separated by distance 2d. We found that temperature-dependent curvature at the minimum of confining potential is enhanced four times for a bilayer with slide as compared with a unit bilayer. We also calculate viscous modes of bilayer membrane between confining walls. Pure bending of the membrane is investigated, which is decoupled from area dilation at small amplitudes. Three sources of viscous dissipation are considered: water and membrane viscosities and interlayer drag. Dispersion has two branches. Confinement between the walls modifies the bending mode with respect to membrane in bulk solution. Simultaneously, inter-layer slipping mode, damped by viscous drag, remains unchanged by confinement.Comment: 23 pages,3 figures, pd

Water and Carbon Dioxide Adsorption on CaO(001) Studied via Single Crystal Adsorption Calorimetry

A new method to analyze microcalorimetry data was employed to study the adsorption energies and sticking probabilities of D2O and CO2 on CaO(001) at several temperatures. This method deconvolutes the line shapes of the heat detector response into an instrument response function and exponential decay functions, which correspond to the desorption of distinct surface species. This allows for a thorough analysis of the adsorption, dissociation, and desorption processes that occur during our microcalorimetry experiments. Our microcalorimetry results, show that D2O adsorbs initially with an adsorption energy of 85–90 kJ/mol at temperatures ranging from 120 to 300 K, consistent with prior spectroscopic studies that indicate dissociation. This adsorption energy decreases with increasing coverage until either D2O multilayers are formed at low temperatures (120 K) or the surface is saturated (150 K). Artificially producing defects on the surface by sputtering prior to dosing D2O sharply increases this adsorption energy, but these defects may be healed after annealing the surface to 1300 K. CO2 adsorbs on CaO(001) with an initial adsorption energy of ~ 125 kJ/mol, and decreases until the saturation coverage is reached, which is a function of surface temperature. The results showed that pre-adsorbed water blocks adsorption sites, lowers the saturation coverage, and lowers the measured adsorption energy of CO2. The calorimetry data further adds to our understanding of D2O and CO2 adsorption on oxide surfaces

Improved Thermoelectric Cooling Based on the Thomson Effect

Traditional thermoelectric Peltier coolers exhibit a cooling limit which is primarily determined by the figure of merit, zT. Rather than a fundamental thermodynamic limit, this bound can be traced to the difficulty of maintaining thermoelectric compatibility. Self-compatibility locally maximizes the cooler's coefficient of performance for a given zT and can be achieved by adjusting the relative ratio of the thermoelectric transport properties that make up zT. In this study, we investigate the theoretical performance of thermoelectric coolers that maintain self-compatibility across the device. We find such a device behaves very differently from a Peltier cooler, and term self-compatible coolers "Thomson coolers" when the Fourier heat divergence is dominated by the Thomson, as opposed to the Joule, term. A Thomson cooler requires an exponentially rising Seebeck coefficient with increasing temperature, while traditional Peltier coolers, such as those used commercially, have comparatively minimal change in Seebeck coefficient with temperature. When reasonable material property bounds are placed on the thermoelectric leg, the Thomson cooler is predicted to achieve approximately twice the maximum temperature drop of a traditional Peltier cooler with equivalent figure of merit (zT). We anticipate the development of Thomson coolers will ultimately lead to solid state cooling to cryogenic temperatures.Comment: The Manuscript has been revised for publication in PR

Plant Disease Resistance Inducing Activity of 7-Oxo- and 7-Hydroxysterols

The 7-oxosterols 1–2 and the 7-hydroxysterols 3–6 induce resistance toward the fungal pathogens Puccinia striiformis West, and Puccinia hordei Otth in barley and wheat. Primary leaves of the plants were sprayed with solutions of the compounds (10-4 mol/l in 1% aqu. ethanol) followed, 2 days later, by challenge inoculation with the fungal pathogens. The results indicate that 7a- and 7β-hydroxylated epimers of β-sitosterol and cholesterol show the highest value of induced resistance (39-49% reduction of infection sites). No enhanced resistance toward the fungi Erysiphe graminis DC f. sp. tritici and hordei and Cochliobolus sativus Ito & Kuribayashi was observed. © 1995 Verlag der Zeitschrift für Naturforschung. All rights reserved

Coexistence of dilute and densely packed domains of ligand-receptor bonds in membrane adhesion

We analyze the stability of micro-domains of ligand-receptor bonds that mediate the adhesion of biological model membranes. After evaluating the effects of membrane fluctuations on the binding affinity of a single bond, we characterize the organization of bonds within the domains by theoretical means. In a large range of parameters, we find the commonly suggested dense packing to be separated by a free energy barrier from a regime in which bonds are sparsely distributed. If bonds are mobile, a coexistence of the two regimes should emerge, which agrees with recent experimental observations.Comment: 6 pages, 6 figures, accepted by EP

Shell Crossing Singularities in Quasi-Spherical Szekeres Models

We investigate the occurrence of shell crossing singularities in quasi-spherical Szekeres dust models with or without a cosmological constant. We study the conditions for shell crossing singularity both from physical and geometrical point of view and they are in agreement.Comment: 10 latex pages, RevTex style, no figure

Arbitrarily slow, non-quasistatic, isothermal transformations

For an overdamped colloidal particle diffusing in a fluid in a controllable, virtual potential, we show that arbitrarily slow transformations, produced by smooth deformations of a double-well potential, need not be reversible. The arbitrarily slow transformations do need to be fast compared to the barrier crossing time, but that time can be extremely long. We consider two types of cyclic, isothermal transformations of a double-well potential. Both start and end in the same equilibrium state, and both use the same basic operations---but in different order. By measuring the work for finite cycle times and extrapolating to infinite times, we found that one transformation required no work, while the other required a finite amount of work, no matter how slowly it was carried out. The difference traces back to the observation that when time is reversed, the two protocols have different outcomes, when carried out arbitrarily slowly. A recently derived formula relating work production to the relative entropy of forward and backward path probabilities predicts the observed work average.Comment: 6 pages, 6 figure

Efficiency of a Brownian information machine

A Brownian information machine extracts work from a heat bath through a feedback process that exploits the information acquired in a measurement. For the paradigmatic case of a particle trapped in a harmonic potential, we determine how power and efficiency for two variants of such a machine operating cyclically depend on the cycle time and the precision of the positional measurements. Controlling only the center of the trap leads to a machine that has zero efficiency at maximum power whereas additional optimal control of the stiffness of the trap leads to an efficiency bounded between 1/2, which holds for maximum power, and 1 reached even for finite cycle time in the limit of perfect measurements.Comment: 9 pages, 2 figure