Force Dependence of the Michaelis Constant in a Two-State Ratchet Model for Molecular Motors

We present a quantitative analysis of recent data on the kinetics of ATP hydrolysis, which has presented a puzzle regarding the load dependence of the Michaelis constant. Within the framework of coarse grained two-state ratchet models, our analysis not only explains the puzzling data, but provides a modified Michaelis law, which could be useful as a guide for future experiments.Comment: 4 pages, 3 eps figures, accepted for publication on Physical Review Letter

A Microscopic Mechanism for Muscle's Motion

The SIRM (Stochastic Inclined Rods Model) proposed by H. Matsuura and M. Nakano can explain the muscle's motion perfectly, but the intermolecular potential between myosin head and G-actin is too simple and only repulsive potential is considered. In this paper we study the SIRM with different complex potential and discuss the effect of the spring on the system. The calculation results show that the spring, the effective radius of the G-actin and the intermolecular potential play key roles in the motion. The sliding speed is about $4.7\times10^{-6}m/s$ calculated from the model which well agrees with the experimental data.Comment: 9 pages, 6 figure

Motor-driven Dynamics of Cytoskeletal FIlaments in Motility Assays

We model analytically the dynamics of a cytoskeletal filament in a motility assay. The filament is described as rigid rod free to slide in two dimensions. The motor proteins consist of polymeric tails tethered to the plane and modeled as linear springs and motor heads that bind to the filament. As in related models of rigid and soft two-state motors, the binding/unbinding dynamics of the motor heads and the dependence of the transition rates on the load exerted by the motor tails play a crucial role in controlling the filament's dynamics. Our work shows that the filament effectively behaves as a self-propelled rod at long times, but with non-Markovian noise sources arising from the coupling to the motor binding/unbinding dynamics. The effective propulsion force of the filament and the active renormalization of the various friction and diffusion constants are calculated in terms of microscopic motor and filament parameters. These quantities could be probed by optical force microscopy.Comment: 13 pages, 8 figures, 1 Tabl

Prevalence of somatisation as a determinant of burnout amongst staff working in drug and alcohol services

Purpose: This study explored the prevalence of somatisation as a determinant of burnout amongst drug and alcohol staff in the UK. Design/methodology/approach: The study employed a cross-sectional design utilising a self-completion online questionnaire. Data was collected from substance misuse workers across England and Wales. 165 responses were eligible for analysis, yielding a response rate of 5%. Burnout and somatization were measured with Maslach’s Burnout Inventory and the Physical Symptoms Inventory. Findings: The prevalence of somatic symptoms was relatively low in the sample studied. The reported levels of burnout were moderate. Personal accomplishment remained high in the sample. There was a strong association between burnout and incidence of stress related somatic symptoms, with higher levels of burnout correlating with multiple symptoms. Research limitations/implications: It was not possible to determine the extent of non-response bias, as at the time of the study there was no information available relating to the characteristics of drug and alcohol staff in the selected services. Therefore, as the response rate was very low (5%) it was recognised that non-response bias might have affected the findings, in such way that non-respondents may have differed in their experiences of work stress, satisfaction, burnout and health outcomes. Practical implications: Despite the limitations, the study provided practical information relating to burnout vulnerability and associated physical symptoms in this specific occupational group. These findings can support employers to address staff wellbeing with a view to prevent burnout and reduce existing levels of burnout and related somatic symptoms, and improve job performance, job satisfaction, and staff retention through making appropriate adjustments, such as developing staff-wellbeing programmes. These adjustments could potentially contribute to improvement in substance misuse practice, through maintenance of healthy and satisfied workforce. Social implications: Originality/value: There is very few studies looking at burnout in drug and alcohol staff. This study is also novel in a way that it reveals correlations between a variety of specific stress related physical symptoms and the three components of burnout

Pressure-temperature phase diagram of ferromagnetic superconductors

The symmetry approach to the description of the (P,T) phase diagram of ferromagnet superconductors with triplet pairing is developed. Taking into account the recent experimental observations made on UCoGe it is considered the case of a crystal with orthorhombic structure and strong spin-orbital coupling. It is shown that formation of ferromagnet superconducting state from a superconducting state is inevitably accompanied by the first order type transition.Comment: 4 pages, 1 figur

Brownian molecular motors driven by rotation-translation coupling

We investigated three models of Brownian motors which convert rotational diffusion into directed translational motion by switching on and off a potential. In the first model a spatially asymmetric potential generates directed translational motion by rectifying rotational diffusion. It behaves much like a conventional flashing ratchet. The second model utilizes both rotational diffusion and drift to generate translational motion without spatial asymmetry in the potential. This second model can be driven by a combination of a Brownian motor mechanism (diffusion driven) or by powerstroke (drift driven) depending on the chosen parameters. In the third model, elements of both the Brownian motor and powerstroke mechanisms are combined by switching between three distinct states. Relevance of the model to biological motor proteins is discussed.Comment: 11 pages, 8 figure

One dimensional chain of quantum molecule motors as a mathematical physics model for muscle fibre

A quantum chain model of many molecule motors is proposed as a mathematical physics theory on the microscopic modeling of classical force-velocity relation and tension transients of muscle fibre. We proposed quantum many-particle Hamiltonian to predict the force-velocity relation for the slow release of muscle fibre which has no empirical relation yet, it is much more complicate than hyperbolic relation. Using the same Hamiltonian, we predicted the mathematical force-velocity relation when the muscle is stimulated by alternative electric current. The discrepancy between input electric frequency and the muscle oscillation frequency has a physical understanding by Doppler effect in this quantum chain model. Further more, we apply quantum physics phenomena to explore the tension time course of cardiac muscle and insect flight muscle. Most of the experimental tension transients curves found their correspondence in the theoretical output of quantum two-level and three-level model. Mathematically modeling electric stimulus as photons exciting a quantum three-level particle reproduced most tension transient curves of water bug Lethocerus Maximus.Comment: 16 pages, 12 figures, Arguments are adde

Microscopic theories for cubic and tetrahedral superconductors: application to PrOs_4Sb_{12}

We examine weak-coupling theory for unconventional superconducting states of cubic or tetrahedral symmetry for arbitrary order parameters and Fermi surfaces and identify the stable states in zero applied field. We further examine the possibility of having multiple superconducting transitions arising from the weak breaking of a higher symmetry group to cubic or tetrahedral symmetry. Specifically, we consider two higher symmetry groups. The first is a weak crystal field theory in which the spin-singlet Cooper pairs have an approximate spherical symmetry. The second is a weak spin orbit coupling theory for which spin-triplet Cooper pairs have a cubic orbital symmetry and an approximate spherical spin rotational symmetry. In hexagonal UPt_3, these theories easily give rise to multiple transitions. However, we find that for cubic materials, there is only one case in which two superconducting transitions occur within weak coupling theory. This sequence of transitions does not agree with the observed properties of PrOs_4Sb_{12}. Consequently, we find that to explain two transitions in PrOs_4Sb_{12} using approximate higher symmetry groups requires a strong coupling theory. In view of this, we finally consider a weak coupling theory for which two singlet representations have accidentally nearly degenerate transition temperatures (not due to any approximate symmetries). We provide an example of such a theory that agrees with the observed properties of PrOs_4Sb_{12}.Comment: 11 pages,1 figur

The thermodynamics of urban population flows

Orderliness, reflected via mathematical laws, is encountered in different frameworks involving social groups. Here we show that a thermodynamics can be constructed that macroscopically describes urban population flows. Microscopic dynamic equations and simulations with random walkers underlie the macroscopic approach. Our results might be regarded, via suitable analogies, as a step towards building an explicit social thermodynamics