242 research outputs found
Attractive instability of oppositely charged membranes induced by charge density fluctuations
We predict the conditions under which two oppositely charged membranes show a
dynamic, attractive instability. Two layers with unequal charges of opposite
sign can repel or be stable when in close proximity. However, dynamic charge
density fluctuations can induce an attractive instability and thus facilitate
fusion. We predict the dominant instability modes and timescales and show how
these are controlled by the relative charge and membrane viscosities. These
dynamic instabilities may be the precursors of membrane fusion in systems where
artificial vesicles are engulfed by biological cells of opposite charge
Discrete energy landscapes and replica symmetry breaking at zero temperature
The order parameter P(q) for disordered systems with degenerate ground-states
is reconsidered. We propose that entropy fluctuations lead to a trivial P(q) at
zero temperature as in the non-degenerate case, even if there are zero-energy
large-scale excitations (complex energy landscape). Such a situation should
arise in the 3-dimensional +-J Ising spin glass and in MAX-SAT. Also, we argue
that if the energy landscape is complex with a finite number of ground-state
families, then replica symmetry breaking reappears at positive temperature.Comment: 7 pages; clarifications on valley definition
Pores in Bilayer Membranes of Amphiphilic Molecules: Coarse-Grained Molecular Dynamics Simulations Compared with Simple Mesoscopic Models
We investigate pores in fluid membranes by molecular dynamics simulations of
an amphiphile-solvent mixture, using a molecular coarse-grained model. The
amphiphilic membranes self-assemble into a lamellar stack of amphiphilic
bilayers separated by solvent layers. We focus on the particular case of
tension less membranes, in which pores spontaneously appear because of thermal
fluctuations. Their spatial distribution is similar to that of a random set of
repulsive hard discs. The size and shape distribution of individual pores can
be described satisfactorily by a simple mesoscopic model, which accounts only
for a pore independent core energy and a line tension penalty at the pore
edges. In particular, the pores are not circular: their shapes are fractal and
have the same characteristics as those of two dimensional ring polymers.
Finally, we study the size-fluctuation dynamics of the pores, and compare the
time evolution of their contour length to a random walk in a linear potential
State Hierarchy Induced by Correlated Spin Domains in short range spin glasses
We generate equilibrium configurations for the three and four dimensional
Ising spin glass with Gaussian distributed couplings at temperatures well below
the transition temperature T_c. These states are analyzed by a recently
proposed method using clustering. The analysis reveals a hierarchical state
space structure. At each level of the hierarchy states are labeled by the
orientations of a set of correlated macroscopic spin domains. Our picture of
the low temperature phase of short range spin glasses is that of a State
Hierarchy Induced by Correlated Spin domains (SHICS). The complexity of the low
temperature phase is manifest in the fact that the composition of such a spin
domain (i.e. its constituent spins), as well as its identifying label, are
defined and determined by the ``location'' in the state hierarchy at which it
appears. Mapping out the phase space structure by means of the orientations
assumed by these domains enhances our ability to investigate the overlap
distribution, which we find to be non-trivial. Evidence is also presented that
these states may have a non-ultrametric structure.Comment: 30 pages, 17 figure
Fundamental limitations for quantum and nano thermodynamics
The relationship between thermodynamics and statistical physics is valid in
the thermodynamic limit - when the number of particles becomes very large.
Here, we study thermodynamics in the opposite regime - at both the nano scale,
and when quantum effects become important. Applying results from quantum
information theory we construct a theory of thermodynamics in these limits. We
derive general criteria for thermodynamical state transformations, and as
special cases, find two free energies: one that quantifies the
deterministically extractable work from a small system in contact with a heat
bath, and the other that quantifies the reverse process. We find that there are
fundamental limitations on work extraction from nonequilibrium states, owing to
finite size effects and quantum coherences. This implies that thermodynamical
transitions are generically irreversible at this scale. As one application of
these methods, we analyse the efficiency of small heat engines and find that
they are irreversible during the adiabatic stages of the cycle.Comment: Final, published versio
酸化物ガラスの塩基度と XPS による O1s 化学シフトの相関に関する考察
O1s binding energy measured by X-ray photoelectron spectroscopy (XPS) is candidate as a new tool to determine a new scale of Lewis basicity of oxide ions in glass. Some mathematical expressions for the basicity or XPS chemical shift, such as charge parameter and optical basicity, were compared with the experimental O1s binding energy in binary alkali oxide glasses. The expressions so far in use needed some modification in parameters. A new empirical expression introduced in this paper gives a new concept and universal scale of basicity
Evidence for the double degeneracy of the ground-state in the 3D spin glass
A bivariate version of the multicanonical Monte Carlo method and its
application to the simulation of the three-dimensional Ising spin glass
are described. We found the autocorrelation time associated with this
particular multicanonical method was approximately proportional to the system
volume, which is a great improvement over previous methods applied to
spin-glass simulations. The principal advantage of this version of the
multicanonical method, however, was its ability to access information
predictive of low-temperature behavior. At low temperatures we found results on
the three-dimensional Ising spin glass consistent with a double
degeneracy of the ground-state: the order-parameter distribution function
converged to two delta-function peaks and the Binder parameter
approached unity as the system size was increased. With the same density of
states used to compute these properties at low temperature, we found their
behavior changing as the temperature is increased towards the spin glass
transition temperature. Just below this temperature, the behavior is consistent
with the standard mean-field picture that has an infinitely degenerate ground
state. Using the concept of zero-energy droplets, we also discuss the structure
of the ground-state degeneracy. The size distribution of the zero-energy
droplets was found to produce the two delta-function peaks of .Comment: 33 pages with 31 eps figures include
Effect of splenectomy on type-1/type-2 cytokine gene expression in a patient with adult idiopathic thrombocytopenic purpura (ITP)
BACKGROUND: In view of clinical observations and laboratory results that support a central role of the spleen in idiopathic thrombocytopenic purpura (ITP) pathophysiology, we studied the effect of splenectomy on type-1 and type-2 cytokine gene expression in an adult ITP case, refractory to conservative treatment. CASE PRESENTATION: The patient was subjected to splenectomy 9 months after the diagnosis with complete response, attaining platelet counts over 150 × 10(6)/L within 10 days after the operation. Two consecutive blood samples were obtained from the patient, 3 and 7 months after the splenectomy for the purposes of this study. A control group consisted of 11 healthy adults. Peripheral blood mononuclear cells were prepared from each blood sample and cultured in vitro for 8 h with the addition of the mitogens phorbol myristate acetate and ionomycin. Total cellular RNA extracted from 10(6 )cells was submitted to semiquantitave reverse transcriptase-polymerase chain reaction (RT-PCR) for the amplification of IL-2, IFN-γ, IL-4, IL-5, and IL-10 metagraphs. The PCR products were run on ethidium-stained agarose gels, photographed and quantified by densitometry. A steep decrease of type-1 cytokine expression (IL-2, IFN-γ) and their calculated sum expressing Th1 activity was observed at 7 months post-splenectomy compared to 3 months post-splenectomy, in parallel with a rise of platelet count from 190 × 10(6)/L to 265 × 10(6)/L. The change of type-2 cytokine expression (IL-4, IL-5, IL-10) was slight and the Th2 activity (IL-4+IL-5) remained largely unchanged. The Th1/Th2 ratio, that reflects the pathogenic disease-specific T-cell immune deviation, was accordingly reduced 7 months post-splenectomy (Th1/Th2 = 1.3) compared to 3 months (Th1/Th2 = 3.5). CONCLUSIONS: The reduction of the Th1/Th2 cytokine ratio that was observed over time after splenectomy was accompanied by full clinical remission. Nevertheless, the persistence of a type-1 polarization, even after several months following spleen removal, is suggestive of a more basic abnormality of the immune function in these patients
Partially Annealed Disorder and Collapse of Like-Charged Macroions
Charged systems with partially annealed charge disorder are investigated
using field-theoretic and replica methods. Charge disorder is assumed to be
confined to macroion surfaces surrounded by a cloud of mobile neutralizing
counterions in an aqueous solvent. A general formalism is developed by assuming
that the disorder is partially annealed (with purely annealed and purely
quenched disorder included as special cases), i.e., we assume in general that
the disorder undergoes a slow dynamics relative to fast-relaxing counterions
making it possible thus to study the stationary-state properties of the system
using methods similar to those available in equilibrium statistical mechanics.
By focusing on the specific case of two planar surfaces of equal mean surface
charge and disorder variance, it is shown that partial annealing of the
quenched disorder leads to renormalization of the mean surface charge density
and thus a reduction of the inter-plate repulsion on the mean-field or
weak-coupling level. In the strong-coupling limit, charge disorder induces a
long-range attraction resulting in a continuous disorder-driven collapse
transition for the two surfaces as the disorder variance exceeds a threshold
value. Disorder annealing further enhances the attraction and, in the limit of
low screening, leads to a global attractive instability in the system.Comment: 21 pages, 2 figure
- …