Structural Reorganization of Parallel Actin Bundles by Crosslinking Proteins: Incommensurate States of Twist

We construct a coarse-grained model of parallel actin bundles crosslinked by compact, globular bundling proteins, such as fascin and espin, necessary components of filapodial and mechanosensory bundles. Consistent with structural observations of bundles, we find that the optimal geometry for crosslinking is overtwisted, requiring a coherent structural change of the helical geometry of the filaments. We study the linker-dependent thermodynamic transition of bundled actin filaments from their native state to the overtwisted state and map out the "twist-state'' phase diagram in terms of the availability as well as the flexibility of crosslinker proteins. We predict that the transition from the uncrosslinked to fully-crosslinked state is highly sensitive to linker flexibility: flexible crosslinking smoothly distorts the twist-state of bundled filaments, while rigidly crosslinked bundles undergo a phase transition, rapidly overtwisting filaments over a narrow range of free crosslinker concentrations. Additionally, we predict a rich spectrum of intermediate structures, composed of alternating domains of sparsely-bound (untwisted) and strongly-bound (overtwisted) filaments. This model reveals that subtle differences in crosslinking agents themselves modify not only the detailed structure of parallel actin bundles, but also the thermodynamic pathway by which they form.Comment: Main Text (25 pages, 7 figures) with supporting material (12 pages, 9 figures, 2 tables

Prospects of In-Flight Hyperfine Spectroscopy of (Anti)Hydrogen for Tests of CPT Symmetry

The ground-state hyperfine splitting of antihydrogen promises one of the most sensitive tests of CPT symmetry. The ASACUSA collaboration is pursuing a measurement of this splitting in a Rabi-type experiment using a polarized beam from a CUSP magnet at the Antiproton Decelerator of CERN. With the initial intention of characterizing the Rabi apparatus, a polarized source of cold hydrogen was built and the $\sigma_1$ transition of hydrogen was measured to a few ppb precision. A measurement of the $\pi_1$ transition is being prepared. The availability of this beam opens the possibility to perform first measurements of some coefficients within the nonminimal Standard-Model Extension.Comment: Presented at the Seventh Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 20-24, 201

Bistability and regular spatial patterns in arid ecosystems.

A variety of patterns observed in ecosystems can be explained by resource–concentration mechanisms. A resource–concentration mechanism occurs when organisms increase the lateral flow of a resource toward them, leading to a local concentration of this resource and to its depletion from areas farther away. In resource–concentration systems, it has been proposed that certain spatial patterns could indicate proximity to discontinuous transitions where an ecosystem abruptly shifts from one stable state to another. Here, we test this hypothesis using a model of vegetation dynamics in arid ecosystems. In this model, a resource– concentration mechanism drives a positive feedback between vegetation and soil water availability. We derived the conditions leading to bistability and pattern formation. Our analysis revealed that bistability and regular pattern formation are linked in our model. This means that, when regular vegetation patterns occur, they indicate that the system is along a discontinuous transition to desertification. Yet, in real systems, only observing regular vegetation patterns without identifying the pattern-driving mechanism might not be enough to conclude that an ecosystem is along a discontinuous transition because similar patterns can emerge from different ecological mechanisms

Availability analysis of thermal power plant boiler air circulation system using Markov approach

The long term operation and planning of power plant depend upon an effective availability analysis and assessment of various systems in the plant concerned. The plant is expected to remain operational in a continual manner to achieve the desired production targets. Hence, the availability analysis of the boiler air circulation system plays an important role in this direction. For this purpose, the concerned system mathematical model based on Markov Birth-Death process has been developed. The system consists of four subsystems. The transition diagram represents reduced capacity, full working and failed state of the system. The differential equations associated with the transition diagram based on probabilistic approach have been solved recursively in order to develop the system steady state availability. Availability matrices represented measures the performance of the system concerned. In addition, different combinations of failures and repair rates provide various availability levels of the system. Maintenance decisions are taken based upon these values for improving availability of the power plant as well as the power supply. The result shows that the failure of the primary air fan affects the system availability at most, while failure of air heater affect it at least for different failures and repair rate combination of subsystems under study

Direct probing of the Mott crossover in the SU(NN) Fermi-Hubbard model

The Fermi-Hubbard model (FHM) is a cornerstone of modern condensed matter theory. Developed for interacting electrons in solids, which typically exhibit SU($2$) symmetry, it describes a wide range of phenomena, such as metal to insulator transitions and magnetic order. Its generalized SU($N$)-symmetric form, originally applied to multi-orbital materials such as transition-metal oxides, has recently attracted much interest owing to the availability of ultracold SU($N$)-symmetric atomic gases. Here we report on a detailed experimental investigation of the SU($N$)-symmetric FHM using local probing of an atomic gas of ytterbium in an optical lattice to determine the equation of state through different interaction regimes. We prepare a low-temperature SU($N$)-symmetric Mott insulator and characterize the Mott crossover, representing important steps towards probing predicted novel SU($N$)-magnetic phases

Effective Scheduling of Road and Bridge Closures: Phase 2

This research provides a study on work zone impact analysis. In case of multiple road closures, the network approach is used to find an effective scheduling such that the total user delay is reduced. A dynamic model for analyzing the work zone impact during the period when network is in transition state is also developed. A salient feature of the dynamic model is drives’ perception updating model, which incorporates availability and the quality of information as perceived by drivers

Statistical Mechanics of Double sinh-Gordon Kinks

We study the classical thermodynamics of the double sinh-Gordon (DSHG) theory in 1+1 dimensions. This model theory has a double well potential, thus allowing for the existence of kinks and antikinks. Though it is nonintegrable, the DSHG model is remarkably amenable to analysis. Below we obtain exact single kink and kink lattice solutions as well as the asymptotic kink-antikink interaction. In the continuum limit, finding the classical partition function is equivalent to solving for the ground state of a Schrodinger-like equation obtained via the transfer integral method. For the DSHG model, this equation turns out to be quasi-exactly solvable. We exploit this property to obtain exact energy eigenvalues and wavefunctions for several temperatures both above and below the symmetry breaking transition temperature. The availability of exact results provides an excellent testing ground for large scale Langevin simulations. The probability distribution function (PDF) calculated from Langevin dynamics is found to be in striking agreement with the exact PDF obtained from the ground state wavefunction. This validation points to the utility of a PDF-based computation of thermodynamics utilizing Langevin methods. In addition to the PDF, field-field and field fluctuation correlation functions were computed and also found to be in excellent agreement with the exact results.Comment: 10 pages, 5 figures (embedded using epsfig), uses RevTeX plus macro (included). To appear in Physica

A mobility analysis of the occupational status of the graduates of the University of Palermo in an economic crisis context

In such a global economic crisis context, our aims are describing the mobility of the Palermitan graduates in the labour market, identifying the variables that influence most their occupational status and finally outlining a transition probability structure among the states: Work, Search for a Job, Study, Other. The availability of a large amount of longitudinal data provided by the surveys carried out by STELLA (Statistics about Graduates and Labour Market) allowed us to analyze the mobility of the graduates of the University of Palermo among the different occupational states in three different times. We analyze data coming from a disproportionate stratified sample of graduates in 2009, interviewed three different times: one year (2010), three years (2012), five years (2014) after the graduation. To achieve our aim, first we provide a brief descriptive analysis of the main characteristics of the graduates gathered by the three different surveys; secondly we fit a time inhomogeneous multi-state Markov model with piecewise constant intensities; eventually implications from the main results are discussed

Optimal Exploitation of Groundwater and the Potential for a Tradable Permit System in Irrigated Agriculture

A great challenge facing future agricultural water policy is to explore the potential for transition from the current myopic competitive (common) exploitation of groundwater resources to a long-term efficient and sustainable allocation. A number of economic and/or command and control instruments can be used by the relevant water authority in order to deal with the economic and environmental problems generated by competitive exploitation. However, according to previous experience in both developed and developing countries, tradable permits seem as one of the most effective and efficient instruments, especially under conditions of limited water availability. On this account, the aim of the current study is to explore the feasibility and implementation of a tradable permit system in irrigated agriculture. To this end, two distinct optimization models are applied and compared: (a) an individual farmer’s model (representing the myopic non-cooperative exploitation of groundwater) and (b) a social planner’s model (representing the cooperative and sustainable allocation). The deviation of their results shows the rationale for using a tradable permit system, while the final allocation of the social planner’s model, solved as an optimal control problem that maximizes the social welfare under specific water policy objectives, denotes the equilibrium state of this system. The two models are then applied in a typical rural area of Greece where groundwater is the only source of irrigated agriculture. The derived time paths for water consumption and water availability illustrate the significant environmental benefits from the future implementation of a tradable permit system.Tradable Water Permits, Sustainable Water Use, Irrigated Agriculture