Conformational Mechanics of Polymer Adsorption Transitions at Attractive Substrates

Conformational phases of a semiflexible off-lattice homopolymer model near an attractive substrate are investigated by means of multicanonical computer simulations. In our polymer-substrate model, nonbonded pairs of monomers as well as monomers and the substrate interact via attractive van der Waals forces. To characterize conformational phases of this hybrid system, we analyze thermal fluctuations of energetic and structural quantities, as well as adequate docking parameters. Introducing a solvent parameter related to the strength of the surface attraction, we construct and discuss the solubility-temperature phase diagram. Apart from the main phases of adsorbed and desorbed conformations, we identify several other phase transitions such as the freezing transition between energy-dominated crystalline low-temperature structures and globular entropy-dominated conformations.Comment: 13 pages, 15 figure

A simple quantum cosmology

A simple and surprisingly realistic model of the origin of the universe can be developed using the Friedmann equation from general relativity, elementary quantum mechanics, and the experimental values of h, c, G and the proton mass. The model assumes there are N space dimensions (with N > 6) and the potential constraining the radius r of the invisible N -3 compact dimensions varies as r^4. In this model, the universe has zero total energy and is created from nothing. There is no initial singularity. If space-time is eleven dimensional, as required by M theory, the scalar field corresponding to the size of the compact dimensions inflates the universe by about 26 orders of magnitude (60 e-folds). If the Hubble constant is 65 km/sec Mpc, the energy density of the scalar field after inflation results in Omega-sub-Lambda = 0.68, in agreement with recent astrophysical observations.Comment: To be published in General Relativity and Gravitation, August 200

Microcanonical entropy inflection points: Key to systematic understanding of transitions in finite systems

We introduce a systematic classification method for the analogs of phase transitions in finite systems. This completely general analysis, which is applicable to any physical system and extends towards the thermodynamic limit, is based on the microcanonical entropy and its energetic derivative, the inverse caloric temperature. Inflection points of this quantity signal cooperative activity and thus serve as distinct indicators of transitions. We demonstrate the power of this method through application to the long-standing problem of liquid-solid transitions in elastic, flexible homopolymers.Comment: 4 pages, 3 figure

Thickness-dependent secondary structure formation of tubelike polymers

By means of sophisticated Monte Carlo methods, we investigate the conformational phase diagram of a simple model for flexible polymers with explicit thickness. The thickness constraint, which is introduced geometrically via the global radius of curvature of a polymer conformation, accounts for the excluded volume of the polymer and induces cooperative effects supporting the formation of secondary structures. In our detailed analysis of the temperature and thickness dependence of the conformational behavior for classes of short tubelike polymers, we find that known secondary-structure segments like helices and turns, but also ringlike conformations and stiff rods are dominant intrinsic topologies governing the phase behavior of such cooperative tubelike objects. This shows that the thickness constraint is indeed a fundamental physical parameter that allows for a classification of generic polymer structures

Retroperitoneoskopische Nierenchirurgie: Indikationen, Technik und eigene Erfahrungen nach 360 Eingriffen

Zusammenfassung: Die retroperitoneoskopische Operationstechnik überzeugt durch den schnellen, direkten und einfachen Zugang ins Retroperitoneum und zu den Nierengefäßen unter Umgehung des Peritonealraums. Wir beschreiben unsere Operationstechnik und diskutieren Vor- und Nachteile der Retroperitoneoskopie. Unsere Erfahrungen mit dieser Operationstechnik bei insgesamt 360 retroperitoneoskopischen Eingriffen werden vorgestellt: Nephrektomie, Nierenteilresektion, Lebendnierenspende, Kryotherapie von Nierentumoren, Pyelonplastik sowie Adrenalektomie und weitere Indikationen werden dargestellt. Wir zeigen, welche Eingriffe sich zum Einstieg in die Technik eignen und auf was geachtet werden mus

Structural assessment of the gripper interlock of the DEMO breeding blanket transporter

The maintenance of the DEMO Breeding Blanket (BB) remotely is a crucial aspect in development of the DEMO power plant. It is a challenge due to the huge mass of the BB segment of about 180 tons. A new concept for the BB transporter has recently been developed. To properly grip and manipulate each BB segment, the BB transporter has been equipped with a gripper interlock. Due to the geometry of the BB and the vacuum vessel, the attachment point on the BB segment is not aligned with its center of gravity. Hence in addition to the vertical lifting load, large moments about the horizontal axes need to be reacted.The work discussed here concerns the structural analysis conducted on the gripper interlock; its structural integrity has been checked against the most severe load conditions that include also seismic loads according to the EN13001. Elastic analyses were performed using a finite element model in accordance with EN 13001-3-1:2012 + A2:2018, Cranes - General Design - Part 3-1: Limit States and proof competence of steel structure. The effect of the gap sizes at the contact surfaces between gripper interlock and BB after engagement as well as the effect of different friction coefficients on the sliding areas were assessed. The improvements of the design based on the structural analysis are presented, too

N-body Gravity and the Schroedinger Equation

We consider the problem of the motion of $N$ bodies in a self-gravitating system in two spacetime dimensions. We point out that this system can be mapped onto the quantum-mechanical problem of an N-body generalization of the problem of the H$_{2}^{+}$ molecular ion in one dimension. The canonical gravitational N-body formalism can be extended to include electromagnetic charges. We derive a general algorithm for solving this problem, and show how it reduces to known results for the 2-body and 3-body systems.Comment: 15 pages, Latex, references added, typos corrected, final version that appears in CQ

Compatibility of Einstein minimally coupled self interacting scalar field theory with the solar system tests of gravity

We examine the compatibility of the Einstein minimally coupled self-interacting scalar field theory with the local tests of gravity. We find that apart from the trivial case of the Schwarzschild-de Sitter solution with constant scalar field the theory does not admit any other static solution, which is consistent with the solar system tests of gravity.Comment: 6 pages, a part of the earlier version removed, final version accepeted by CQ

Photovoltaic -Battery System to Power Fan-Controlled Rice Husk Gasifier Cooking Stove

More than three billion people use wood, dung, coal and other traditional fuels for cooking inside their homes. Inefficient wood stoves are responsible for indoor air pollution, respiratory related diseases and deaths but also accelerated deforestation due to excessive fuel consumption. A promising stove is the open-source, fan-controlled, top-lit updraft, autothermal Belonio gasifier. The need of electricity to power the fan proves to be an obstacle for low-income families without access to electricity. The aim of this study therefore was to develop an economical, environmentally friendly, emission-free solution to power the Belonio stove fan. Consequently, a PV-battery system was designed inclusive of charge controller and inverter. The overall efficiency of the PV-battery, battery-inverter, and inverter-fan in the system was found to be 43.8 %. Fan speed had a great effect on inverter efficiency requiring either additional electricity consumers such as lighting or mobile phone charger or the use of a DC fan in which case the inverter can be omitted. However, economically viable fan speed controllers for DC fans must be developed. The daily cost of cooking for an average 5 family household was estimated to be RM 0.40 which can be further reduced with mass production of the stand-alone PV powered Belonio gasifier system