64,831 research outputs found
Adaptive Ising Model and Bacterial Chemotactic Receptor Network
We present a so-called adaptive Ising model (AIM) to provide a unifying
explanation for sensitivity and perfect adaptation in bacterial chemotactic
signalling, based on coupling among receptor dimers. In an AIM, an external
field, representing ligand binding, is randomly applied to a fraction of spins,
representing the states of the receptor dimers, and there is a delayed negative
feedback from the spin value on the local field. This model is solved in an
adiabatic approach. If the feedback is slow and weak enough, as indeed in
chemotactic signalling, the system evolves through quasi-equilibrium states and
the ``magnetization'', representing the signal, always attenuates towards zero
and is always sensitive to a subsequent stimulus.Comment: revtex, final version to appear in Europhysics Letter
Geometries and energetics of methanol–ethanol clusters: a VUV laser/time-of-flight mass spectrometry and density functional theory study
Hydrogen-bonded clusters, formed above liquid methanol (Me) and ethanol (Et) mixtures of various compositions, were entrained in a supersonic jet and probed using 118 nm vacuum ultraviolet (VUV) laser single-photon ionization/time-of-flight mass spectrometry. The spectra are dominated by protonated cluster ions, formed by ionizing hydrogen-bonded MemEtn neutrals, m = 0–4, n = 0–3, and m + n = 2–5. The structures and energetics of the neutral and ionic species were investigated using both the all-atom optimized potential for liquid state, OPLS-AA, and the density functional (DFT) calculations. The energetic factors affecting the observed cluster distributions were examined. Calculations indicate that the large change in binding energy going from trimer to tetramer can be attributed more to pair-wise interactions than to cooperativity effects
A Two-Dimensional CA Traffic Model with Dynamic Route Choices Between Residence and Workplace
The Biham, Middleton and Levine (BML) model is extended to describe dynamic
route choices between the residence and workplace in cities. The traffic
dynamic in the city with a single workplace is studied from the velocity
diagram, arrival time probability distribution, destination arrival rate and
convergence time. The city with double workplaces is also investigated to
compared with a single workplace within the framework of four modes of urban
growth. The transitional region is found in the velocity diagrams where the
system undergoes a continuous transition from a moving phase to a completely
jamming phase. We perform a finite-size scaling analysis of the critical
density from a statistical point of view and the order parameter of this
jamming transition is estimated. It is also found that statistical properties
of urban traffic are greatly influenced by the urban area, workplace area and
urban layout.Comment: 18 pages, 13 figure
Exotic Topological States with Raman-Induced Spin-Orbit Coupling
We propose a simple experimental scheme to realize simultaneously the
one-dimensional spin-orbit coupling and the staggered spin-flip in ultracold
pseudospin- atomic Fermi gases trapped in square optical lattices. In the
absence of interspecies interactions, the system supports gapped Chern
insulators and gapless topological semimetal states. By turning on the -wave
interactions, a rich variety of gapped and gapless inhomogeneous topological
superfluids can emerge. In particular, a gapped topological Fulde-Ferrell
superfluid, in which the chiral edge states at opposite boundaries possess the
same chirality, is predicted.Comment: 11 pages, 6 figure
Geochemistry of reduced inorganic sulfur, reactive iron, and organic carbon in fluvial and marine surface sediment in the Laizhou Bay region, China
Understanding the geochemical cycling of sulfur in sediments is important because it can have implications for both modern environments (e.g., deterioration of water quality) and interpretation of the ancient past (e.g., sediment C/S ratios can be used as indicators of palaeodepositional environment). This study investigates the geochemical characteristics of sulfur, iron, and organic carbon in fluvial and coastal surface sediments of the Laizhou Bay region, China. A total of 63 sediment samples were taken across the whole Laizhou Bay marine region and the 14 major tidal rivers draining into it. Acid volatile sulfur, chromium (II)-reducible sulfur and elemental sulfur, total organic carbon, and total nitrogen were present in higher concentrations in the fluvial sediment than in the marine sediment of Laizhou Bay. The composition of reduced inorganic sulfur in surface sediments was dominated by acid volatile sulfur and chromium (II)-reducible sulfur. In fluvial sediments, sulfate reduction and formation of reduced inorganic sulfur were controlled by TOC and reactive iron synchronously. High C/S ratios in the marine sediments indicate that the diagenetic processes in Laizhou Bay have been affected by rapid deposition of sediment from the Yellow River in recent decades
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