Dynamics of magnetization coupled to a thermal bath of elastic modes

We study the dynamics of magnetization coupled to a thermal bath of elastic modes using a system plus reservoir approach with realistic magnetoelastic coupling. After integrating out the elastic modes we obtain a self-contained equation for the dynamics of the magnetization. We find explicit expressions for the memory friction kernel and hence, {\em via} the Fluctuation-Dissipation Theorem, for the spectral density of the magnetization thermal fluctuations. For magnetic samples in which the single domain approximation is valid, we derive an equation for the dynamics of the uniform mode. Finally we apply this equation to study the dynamics of the uniform magnetization mode in insulating ferromagnetic thin films. As experimental consequences we find that the fluctuation correlation time is of the order of the ratio between the film thickness, $h$, and the speed of sound in the magnet and that the line-width of the ferromagnetic resonance peak should scale as $B_1^2h$ where $B_1$ is the magnetoelastic coupling constant.Comment: Revised version as appeared in print. 12 pages 9 figure

Non-minimality of corners in subriemannian geometry

We give a short solution to one of the main open problems in subriemannian geometry. Namely, we prove that length minimizers do not have corner-type singularities. With this result we solve Problem II of Agrachev's list, and provide the first general result toward the 30-year-old open problem of regularity of subriemannian geodesics.Comment: 11 pages, final versio

Biology as Destiny? Short and Long-Run Determinants of Intergenerational Transmission of Birth Weight

Abstract Little is known about the mechanisms underlying the transfer of economic status between generations. This paper addresses the question of whether inter-generational correlations in health contribute to the perpetuation of economic status. We examine inter-generational correlations in birth weight, a key indicator of the health of newborns that we link to future educational attainment and earnings using a unique data set based on California births from 1960s to the present. We use names and birth dates to link the records of mothers and children. We also identify mothers who are siblings. We show that there is a strong intergenerational correlation in the birth weight of mothers and children, but that a measure of household income at the time of the mother's birth is also predictive of low birth weight and that there is an interaction between maternal low birth weight and poverty in the production of low birth weight. Together these findings suggest that intergenerational correlations in health could play a role in the intergenerational transmission of income. Parent's income affects child health, and health at birth affects future income

When Models Interact with their Subjects: The Dynamics of Model Aware Systems

A scientific model need not be a passive and static descriptor of its subject. If the subject is affected by the model, the model must be updated to explain its affected subject. In this study, two models regarding the dynamics of model aware systems are presented. The first explores the behavior of "prediction seeking" (PSP) and "prediction avoiding" (PAP) populations under the influence of a model that describes them. The second explores the publishing behavior of a group of experimentalists coupled to a model by means of confirmation bias. It is found that model aware systems can exhibit convergent random or oscillatory behavior and display universal 1/f noise. A numerical simulation of the physical experimentalists is compared with actual publications of neutron life time and {\Lambda} mass measurements and is in good quantitative agreement.Comment: Accepted for publication in PLoS-ON

Fully Modular Robotic Arm Architecture Utilizing Novel Multifunctional Space Interface

The current paradigm in space robotics is the design of specialized robotic manipulators to meet the requirements for a specific mission profile. This research aims to develop a novel concept of a modular robotic arm for multi-purpose and multi-mission use. The overall approach is based on a manipulator formed by serial connection of identical modules. Each module contains one rotational joint. The joints, rotation axis is tilted under an angle of 45° to the normal axis, which requires less stowage space compared to a traditional joint configuration. A manipulator can be reconfigured in orbit by adding or removing modules and end effectors, therefore modifying the degrees of freedom (DoF) as well as the workspace. Redundancies are introduced, since defect modules may be removed or replaced. This paper outlines the overall concept of modularization of a robotic arm. The development and mechanical design of a terrestrial demonstrator based on the multifunctional interface iSSI (intelligent Space System Interface) is presented, which is intended for OOS and OOA activities. Furthermore, a variant of the modular robotic system with 24 DoF is presented, which can be stowed in a Cubesat-sized environment. It can operate in spaces with limited accessibility and is dedicated for tasks like inspection and delicate repairs. Finally, an outlook to further research potential and future use cases for the modular robotic system is given.BMWi, 50RP1960A, Verbundvorhaben HOMER: Hoch-redundante modulare Robotersysteme zum flexiblen Einsatz in der Raumfahrt und der Automotive-Serienfertigung; Teilvorhaben Kinematik und RedundanzBMWi, 50RP1960B, Verbundvorhaben: HOMER - Hoch-redundante modulare Robotersysteme zum flexiblen Einsatz in der Raumfahrt und der Automotive-Serienfertigung; Teilvorhaben: modulare Robotikstrukture

Z', new fermions and flavor changing processes, constraints on E6_6 models from μ\mu --> eee

We study a new class of flavor changing interactions, which can arise in models based on extended gauge groups (rank $>$4) when new charged fermions are present together with a new neutral gauge boson. We discuss the cases in which the flavor changing couplings in the new neutral current coupled to the $Z^\prime$ are theoretically expected to be large, implying that the observed suppression of neutral flavor changing transitions must be provided by heavy $Z^\prime$ masses together with small $Z$-$Z^\prime$ mixing angles. Concentrating on E$_6$ models, we show how the tight experimental limit on $\mu \rightarrow eee$ implies serious constraints on the $Z^\prime$ mass and mixing angle. We conclude that if the value of the flavor changing parameters is assumed to lie in a theoretically natural range, in most cases the presence of a $Z^\prime$ much lighter than 1 TeV is unlikely.Comment: plain tex, 22 pages + 2 pages figures in PostScript (appended after `\bye'), UM-TH 92-1

Detecting the Higgs boson(s) in LambdaSUSY

We reconsider the Higgs bosons discovery potential in the LambdaSUSY framework, in which the masses of the scalar particles are increased already at tree level via a largish supersymmetric coupling between the usual Higgs doublets and a Singlet. We analyze in particular the interplay between the discovery potential of the lightest and of the next-to-lightest scalar, finding that the decay modes of the latter should be more easily detected at the LHC.Comment: 9 pages, 2 figure

Scaling in DNA unzipping models: denaturated loops and end-segments as branches of a block copolymer network

For a model of DNA denaturation, exponents describing the distributions of denaturated loops and unzipped end-segments are determined by exact enumeration and by Monte Carlo simulations in two and three dimensions. The loop distributions are consistent with first order thermal denaturation in both cases. Results for end-segments show a coexistence of two distinct power laws in the relative distributions, which is not foreseen by a recent approach in which DNA is treated as a homogeneous network of linear polymer segments. This unexpected feature, and the discrepancies with such an approach, are explained in terms of a refined scaling picture in which a precise distinction is made between network branches representing single stranded and effective double stranded segments.Comment: 8 pages, 8 figure

Evolution of Robustness to Noise and Mutation in Gene Expression Dynamics

Phenotype of biological systems needs to be robust against mutation in order to sustain themselves between generations. On the other hand, phenotype of an individual also needs to be robust against fluctuations of both internal and external origins that are encountered during growth and development. Is there a relationship between these two types of robustness, one during a single generation and the other during evolution? Could stochasticity in gene expression have any relevance to the evolution of these robustness? Robustness can be defined by the sharpness of the distribution of phenotype; the variance of phenotype distribution due to genetic variation gives a measure of `genetic robustness' while that of isogenic individuals gives a measure of `developmental robustness'. Through simulations of a simple stochastic gene expression network that undergoes mutation and selection, we show that in order for the network to acquire both types of robustness, the phenotypic variance induced by mutations must be smaller than that observed in an isogenic population. As the latter originates from noise in gene expression, this signifies that the genetic robustness evolves only when the noise strength in gene expression is larger than some threshold. In such a case, the two variances decrease throughout the evolutionary time course, indicating increase in robustness. The results reveal how noise that cells encounter during growth and development shapes networks' robustness to stochasticity in gene expression, which in turn shapes networks' robustness to mutation. The condition for evolution of robustness as well as relationship between genetic and developmental robustness is derived through the variance of phenotypic fluctuations, which are measurable experimentally.Comment: 25 page