Force-Velocity Relations of a Two-State Crossbridge Model for Molecular Motors

We discuss the force-velocity relations obtained in a two-state crossbridge model for molecular motors. They can be calculated analytically in two limiting cases: for a large number and for one pair of motors. The effect of the strain-dependent detachment rate on the motor characteristics is studied. It can lead to linear, myosin-like, kinesin-like and anomalous curves. In particular, we specify the conditions under which oscillatory behavior may be found.Comment: 5 pages, 4 figures, REVTeX; thoroughly revised version; also available at http://www.physik.tu-muenchen.de/~frey

Cooperative Transport of Brownian Particles

We consider the collective motion of finite-sized, overdamped Brownian particles (e.g., motor proteins) in a periodic potential. Simulations of our model have revealed a number of novel cooperative transport phenomena, including (i) the reversal of direction of the net current as the particle density is increased and (ii) a very strong and complex dependence of the average velocity on both the size and the average distance of the particles.Comment: 4 pages, 5 figure

Fluctuating-friction molecular motors

We show that the correlated stochastic fluctuation of the friction coefficient can give rise to long-range directional motion of a particle undergoing Brownian random walk in a constant periodic energy potential landscape. The occurrence of this motion requires the presence of two additional independent bodies interacting with the particle via friction and via the energy potential, respectively, which can move relative to each other. Such three-body system generalizes the classical Brownian ratchet mechanism, which requires only two interacting bodies. In particular, we describe a simple two-level model of fluctuating-friction molecular motor that can be solved analytically. In our previous work [M.K., L.M and D.P. 2000 J. Nonlinear Opt. Phys. Mater. vol. 9, 157] this model has been first applied to understanding the fundamental mechanism of the photoinduced reorientation of dye-doped liquid crystals. Applications of the same idea to other fields such as molecular biology and nanotechnology can however be envisioned. As an example, in this paper we work out a model of the actomyosin system based on the fluctuating-friction mechanism.Comment: to be published in J. Physics Condensed Matter (http://www.iop.org/Journals/JPhysCM

'This is what democracy looks like' : New Labour's blind spot and peripheral vision

New Labour in government since 1997 has been roundly criticized for not possessing a clear, coherent and consistent democratic vision. The absence of such a grand vision has resulted, from this critical perspective, in an absence of 'joined-up' thinking about democracy in an evolving multi-level state. Tensions have been all too apparent between the government's desire to exert central direction - manifested in its most pathological form as 'control freakery' - and its democratising initiatives derived from 'third-way' obsessions with 'decentralising', 'empowering' and 'enabling'. The purpose of this article is to examine why New Labour displayed such apparently impaired democratic vision and why it appeared incapable of conceiving of democratic reform 'in the round'. This article seeks to explain these apparent paradoxes, however, through utilising the notion of 'macular degeneration'. In this analysis, the perceived democratic blind spot of New Labour at Westminster is connected to a democratic peripheral vision, which has envisaged innovative participatory and decentred initiatives in governance beyond Westminster

Steps in the bacterial flagellar motor

The bacterial flagellar motor is a highly efficient rotary machine used by many bacteria to propel themselves. It has recently been shown that at low speeds its rotation proceeds in steps [Sowa et al. (2005) Nature 437, 916--919]. Here we propose a simple physical model that accounts for this stepping behavior as a random walk in a tilted corrugated potential that combines torque and contact forces. We argue that the absolute angular position of the rotor is crucial for understanding step properties, and show this hypothesis to be consistent with the available data, in particular the observation that backward steps are smaller on average than forward steps. Our model also predicts a sublinear torque-speed relationship at low torque, and a peak in rotor diffusion as a function of torque

Evaluation of the London Measure of Unplanned Pregnancy in a United States population of women

Copyright @ 2012 Morof et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Objective: To evaluate the reliability and validity of the London Measure of Unplanned Pregnancy (a U.K.-developed measure of pregnancy intention), in English and Spanish translation, in a U.S. population of women. Methods: A psychometric evaluation study of the London Measure of Unplanned Pregnancy (LMUP), a six-item, self-completion paper measure was conducted with 346 women aged 15–45 who presented to San Francisco General Hospital for termination of pregnancy or antenatal care. Analyses of the two language versions were carried out separately. Reliability (internal consistency) was assessed using Cronbach’s alpha and item-total correlations. Test-retest reliability (stability) was assessed using weighted Kappa. Construct validity was assessed using principal components analysis and hypothesis testing. Results: Psychometric testing demonstrated that the LMUP was reliable and valid in both U.S. English (alpha = 0.78, all item-total correlations .0.20, weighted Kappa = 0.72, unidimensionality confirmed, hypotheses met) and Spanish translation (alpha = 0.84, all item-total correlations .0.20, weighted Kappa = 0.77, unidimensionality confirmed, hypotheses met). Conclusion: The LMUP was reliable and valid in U.S. English and Spanish translation and therefore may now be used with U.S. women.The study was funded by an anonymous donation

Ethnic differences in early onset multimorbidity and associations with health service use, long-term prescribing, years of life lost, and mortality: A cross-sectional study using clustering in the UK Clinical Practice Research Datalink

BACKGROUND: The population prevalence of multimorbidity (the existence of at least 2 or more long-term conditions [LTCs] in an individual) is increasing among young adults, particularly in minority ethnic groups and individuals living in socioeconomically deprived areas. In this study, we applied a data-driven approach to identify clusters of individuals who had an early onset multimorbidity in an ethnically and socioeconomically diverse population. We identified associations between clusters and a range of health outcomes. METHODS AND FINDINGS: Using linked primary and secondary care data from the Clinical Practice Research Datalink GOLD (CPRD GOLD), we conducted a cross-sectional study of 837,869 individuals with early onset multimorbidity (aged between 16 and 39 years old when the second LTC was recorded) registered with an English general practice between 2010 and 2020. The study population included 777,906 people of White ethnicity (93%), 33,915 people of South Asian ethnicity (4%), and 26,048 people of Black African/Caribbean ethnicity (3%). A total of 204 LTCs were considered. Latent class analysis stratified by ethnicity identified 4 clusters of multimorbidity in White groups and 3 clusters in South Asian and Black groups. We found that early onset multimorbidity was more common among South Asian (59%, 33,915) and Black (56% 26,048) groups compared to the White population (42%, 777,906). Latent class analysis revealed physical and mental health conditions that were common across all ethnic groups (i.e., hypertension, depression, and painful conditions). However, each ethnic group also presented exclusive LTCs and different sociodemographic profiles: In White groups, the cluster with the highest rates/odds of the outcomes was predominantly male (54%, 44,150) and more socioeconomically deprived than the cluster with the lowest rates/odds of the outcomes. On the other hand, South Asian and Black groups were more socioeconomically deprived than White groups, with a consistent deprivation gradient across all multimorbidity clusters. At the end of the study, 4% (34,922) of the White early onset multimorbidity population had died compared to 2% of the South Asian and Black early onset multimorbidity populations (535 and 570, respectively); however, the latter groups died younger and lost more years of life. The 3 ethnic groups each displayed a cluster of individuals with increased rates of primary care consultations, hospitalisations, long-term prescribing, and odds of mortality. Study limitations include the exclusion of individuals with missing ethnicity information, the age of diagnosis not reflecting the actual age of onset, and the exclusion of people from Mixed, Chinese, and other ethnic groups due to insufficient power to investigate associations between multimorbidity and health-related outcomes in these groups. CONCLUSIONS: These findings emphasise the need to identify, prevent, and manage multimorbidity early in the life course. Our work provides additional insights into the excess burden of early onset multimorbidity in those from socioeconomically deprived and diverse groups who are disproportionately and more severely affected by multimorbidity and highlights the need to ensure healthcare improvements are equitable

Biological measurement beyond the quantum limit

Quantum noise places a fundamental limit on the per photon sensitivity attainable in optical measurements. This limit is of particular importance in biological measurements, where the optical power must be constrained to avoid damage to the specimen. By using non-classically correlated light, we demonstrated that the quantum limit can be surpassed in biological measurements. Quantum enhanced microrheology was performed within yeast cells by tracking naturally occurring lipid granules with sensitivity 2.4 dB beyond the quantum noise limit. The viscoelastic properties of the cytoplasm could thereby be determined with a 64% improved measurement rate. This demonstration paves the way to apply quantum resources broadly in a biological context

The supply chain of violence

Every year, more people are killed defending the environment than are soldiers from the United Kingdom and Australia on overseas deployments in war zones combined. During the last 15 years, the number of both deaths of environmental defenders, and the countries where they occur, have increased. Recorded deaths have increased from two per week to four per week over this period. These deaths are primarily related to conflict over natural resources, across a range of sectors. Of 683 total deaths, >230 were related to mining and agribusiness between 2014 and 2017. We find that rule of law and corruption indices are closely linked to patterns of killings. Using spatial data, we investigate the drivers of these conflicts and violence and seek to identify who may be most at risk and why. We argue that businesses, investors and national governments at both ends of the chain of violence need to be more accountable

Force and Motion Generation of Molecular Motors: A Generic Description

We review the properties of biological motor proteins which move along linear filaments that are polar and periodic. The physics of the operation of such motors can be described by simple stochastic models which are coupled to a chemical reaction. We analyze the essential features of force and motion generation and discuss the general properties of single motors in the framework of two-state models. Systems which contain large numbers of motors such as muscles and flagella motivate the study of many interacting motors within the framework of simple models. In this case, collective effects can lead to new types of behaviors such as dynamic instabilities of the steady states and oscillatory motion.Comment: 29 pages, 9 figure