Counterion-mediated Electrostatic Interactions between Helical Molecules

We study the interaction of two cylinders with helical charge distribution mediated by neutralizing counterions, by analyzing the separation as well as the azimuthal angle dependence of the interaction force in the weak and strong coupling limit. While the azimuthal dependence of the interaction in the weak coupling limit is overall small and mostly negligible, the strong coupling limit leads to qualitatively new features of the interaction, among others also to an orientationally dependent optimal configuration that is driven by angular dependence of the correlation attraction. We investigate the properties of this azimuthal ordering in detail and compare it to existing results.Comment: 11 pages, 12 figure

Change of the yield stress in roll formed ERW pipes considering the Bauschinger effect

ERW pipes formed with the roll forming process show a yield stress distribution along the circumferential direction and their quality is strongly influenced by the magnitude and by the distributions of the yield stress. In addition to that, strips are subjected to cyclic loading during roll forming process. Since ERW pipes are firstly roll formed, welded and then sized, in order to develop an enhanced predicting method for the calculation of the ERW pipe yield stress, the same process flow has been also applied to authors\u2019 numerical simulations. The Yoshida-Uemori kinematic hardening model has been applied considering several subdivision of the strain range, and different parameters, aiming to find the best correlation between the estimated Bauschinger effect and the one measured in the relevant cyclic loading experiment. The comparisons between estimated and experimentally-measured values of the thickness distribution, and of the locally-measured yield stress, prove both reliability and accuracy of the adopted process chain analysis. The growth of the sizing effect ratio has shown to cause the increase of the yield stress, which becomes more uniform along the circumferential direction

Microstructural and morphological properties of homoepitaxial (001)ZnTe layers investigated by x-ray diffuse scattering

The microstructural and morphological properties of homoepitaxial (001)ZnTe layers are investigated by x-ray diffuse scattering. High resolution reciprocal space maps recorded close to the ZnTe (004) Bragg peak show different diffuse scattering features. One kind of cross-shaped diffuse scattering streaks along directions can be attributed to stacking faults within the epilayers. Another kind of cross-shaped streaks inclined at an angle of about 80deg with respect to the in-plane direction arises from the morphology of the epilayers. (abridged version

Eskers in a complete, wet-based glacial system in the Phlegra Montes region, Mars

Although glacial landsystems produced under warm/wet based conditions are very common on Earth, even here, observations of subglacial landforms such as eskers emerging from extant glaciers are rare. This paper describes a system of sinuous ridges emerging from the in situ but now degraded piedmont terminus of a Late Amazonian-aged (∼150 Ma) glacier-like form in the southern Phlegra Montes region of Mars. We believe this to be the first identification of martian eskers that can be directly linked to their parent glacier. Together with their contextual landform assemblage, the eskers are indicative of significant glacial meltwater production and subglacial routing. However, although the eskers are evidence of a wet-based regime, the confinement of the glacial system to a well-defined, regionally significant graben, and the absence of eskers elsewhere in the region, is interpreted as evidence of sub-glacial melting as a response to locally enhanced geothermal heat flux rather than climate-induced warming. These observations offer important new insights to the forcing of glacial dynamic and melting behaviour on Mars by factors other than climate

Electric field and tip geometry effects on dielectrophoretic growth of carbon nanotube nanofibrils on scanning probes

Single-wall carbon nanotube (SWNT) nanofibrils were assembled onto a variety of conductive scanning probes including atomic force microscope (AFM) tips and scanning tunnelling microscope (STM) needles using positive dielectrophoresis (DEP). The magnitude of the applied electric field was varied in the range of 1-20 V to investigate its effect on the dimensions of the assembled SWNT nanofibrils. Both length and diameter grew asymptotically as voltage increased from 5 to 18 V. Below 4 V, stable attachment of SWNT nanofibrils could not be achieved due to the relatively weak DEP force versus Brownian motion. At voltages of 20 V and higher, low quality nanofibrils resulted from incorporating large amounts of impurities. For intermediate voltages, optimal nanofibrils were achieved, though pivotal to this assembly is the wetting behaviour upon tip immersion in the SWNT suspension drop. This process was monitored in situ to correlate wetting angle and probe geometry (cone angles and tip height), revealing that probes with narrow cone angles and long shanks are optimal. It is proposed that this results from less wetting of the probe apex, and therefore reduces capillary forces and especially force transients during the nanofibril drawing process. Relatively rigid probes (force constant >= 2 N/m) exhibited no perceivable cantilever bending upon wetting and de-wetting, resulting in the most stable process control

Three-dimensional MHD flow and heat transfer in a channel with internal obstacle

The magnetohydrodynamic flow and heat transfer of a liquid metal in a channel past a circular cylinder with walls of non-uniform conductivity were investigated. The applied magnetic field was transversal to the forced flow (x-direction) and coplanar with the obstacle, featuring non-null components in both the z- and y-directions. Moreover, the cylinder was displaced by the duct centreline toward the bottom wall and its surface was at uniform temperature, so that a ΔT was present between the obstacle and the fluid at the inlet. Non-uniform thickness for the duct-bounding walls is considered which leads to the promotion of jets close to the less-conductive surfaces. The flow features and heat transfer for this case were numerically investigated for different values of the Reynolds number (20 ≤ Re ≤ 80) and Hartmann number (0 ≤ Ha ≤ 100). Their effects on the flow features, pressure drop and heat transfer are analysed and discussed in detail in the present paper. The additional pressure drop introduced by the cylinder presence is found to be independent by Re and decreasing with Ha. Enhanced heat transfer is observed for an increasing Ha with NuMHD/Nu = 1.25. at Ha = 100 due to the augmented mass flow rate in the bottom sub-channel

Proving Safety with Trace Automata and Bounded Model Checking

Loop under-approximation is a technique that enriches C programs with additional branches that represent the effect of a (limited) range of loop iterations. While this technique can speed up the detection of bugs significantly, it introduces redundant execution traces which may complicate the verification of the program. This holds particularly true for verification tools based on Bounded Model Checking, which incorporate simplistic heuristics to determine whether all feasible iterations of a loop have been considered. We present a technique that uses \emph{trace automata} to eliminate redundant executions after performing loop acceleration. The method reduces the diameter of the program under analysis, which is in certain cases sufficient to allow a safety proof using Bounded Model Checking. Our transformation is precise---it does not introduce false positives, nor does it mask any errors. We have implemented the analysis as a source-to-source transformation, and present experimental results showing the applicability of the technique

Emergent behavior in active colloids

Active colloids are microscopic particles, which self-propel through viscous fluids by converting energy extracted from their environment into directed motion. We first explain how articial microswimmers move forward by generating near-surface flow fields via self-phoresis or the self-induced Marangoni effect. We then discuss generic features of the dynamics of single active colloids in bulk and in confinement, as well as in the presence of gravity, field gradients, and fluid flow. In the third part, we review the emergent collective behavior of active colloidal suspensions focussing on their structural and dynamic properties. After summarizing experimental observations, we give an overview on the progress in modeling collectively moving active colloids. While active Brownian particles are heavily used to study collective dynamics on large scales, more advanced methods are necessary to explore the importance of hydrodynamic and phoretic particle interactions. Finally, the relevant physical approaches to quantify the emergent collective behavior are presented.Comment: 31 pages, 14 figure