Macroscopic Clusters Research Articles

貯蔵に伴う蒸留酒のマクロなクラスターサイズの変化

We defined the macroscopic cluster size of liquor in order to discuss quantitative changes in solution structure with storage. We determined the size of three kinds of clusters in malt whiskies. First, NMR spectra were measured for aqueous ethanol solutions, and the population fractions defied by eq.(3)were calculated from the changes in the proton chemical shifts with increases in ethanol concentrations. Next, IR spectra were taken for the gases evaporated from the whiskies and aqueous ethanol solutions. Comparisons between the band areas from the whisky and those from the aqueous ethanol solution made it possible to obtain the ratios of the water and of the ethanol molecules evaporated from the two solutions. Finally, the population fractions for aqueous ethanol solutions were converted into those for the whiskies by these ratios according to eq.(12), and the sizes of the three clusters were calculated for each whisky. The results differ from previous ones: specifically, as the period of storage becomes longer, the size of the water clusters increases while that of the ethanol clusters decreases and that of the water-ethanol clusters is almost constant.

Novel spin dynamics in a Josephson junction.

We address the dynamics of a single spin embedded in the tunneling barrier between two superconductors. As a consequence of pair correlations in the superconducting state, the spin displays a rich and unusual dynamics. To properly describe the time evolution of the spin we find the generalized Wess-Zumino-Witten-Novikov term in the effective action for the spin on the Keldysh contour. The superconducting correlations lead to an effective spin action which is nonlocal in time leading to unconventional precessions. Our predictions might be directly tested for macroscopic spin clusters.

Bound states of an electron and a macroscopic cluster at a liquid helium surface

In a strong electric field, there are bound states of an electron at the surface of liquid helium, interacting with a large cluster of atoms in the bulk of liquid. This phenomenon is related to long-range interaction between the electron and the dipole moment of the cluster. The electron, holding the cluster under the liquid surface, is localized at this surface. One electron is capable of binding a cluster of up to 106 atoms. The value of the binding energy may reach up to several kelvins.

Thermal conductivity by two-level systems in glasses

We study the possibility of heat conductivity by two-level systems in amorphous solids. Transport requires a macroscopic cluster of weakly interacting, almost degenerate two-level systems. We find that such a cluster exists for a sufficiently large spectral diffusion kernel. The resulting heat conductivity of TLS is, however, by several orders of magnitude smaller than that of thermal phonons. As a consequence, transport through TLS can be ruled out as an explanation for possible anomalies in the measured heat conductivity in the milliKelvin range.

Calculating the Electrochemical Activity of Porous Electrodes of a Filled-up Type with an Immobilized Enzyme

The electrochemical activity of porous electrodes of a filled-up type with an immobilized enzyme is calculated with the aid of computer-aided modeling. The percolation properties of two-component (a mixture of dispersed particles of the substrate and the enzyme) and three-component (a carrier of a gas reactant is added) models of a porous electrode are investigated. Taking into account specific features inherent in the forming macroscopic clusters (collections of particles of one sort or another connected with one another), i.e. an “electron” cluster and a “gas” cluster, makes it possible to determine the concentration of an active catalyst which is capable of taking part in the electrochemical process. The calculation of the electrochemical activity is performed in two-component structures, where the process of the current generation is limited by diffusion limitations, and in three-component structures, where the process of the current generation is limited by ohmic limitations. Estimates of the current are performed using an oxygen porous electrode with Nafion and an enzyme as an example. The electrochemical characteristics of this model electrode are close to those obtained on laccase. Introducing a hydrophobizing agent into the active layer of the porous electrode (passing from two-component structures to three-component structures) produces a positive effect. Although the number of active molecules of the enzyme drops in this case by an order of magnitude, the liquidation of diffusion limitations eventually raises the magnitude of the current by approximately threefold. Calculations show that it is quite feasible to obtain currents of ∼0.2 A cm–2 on a porous electrode 16 μm thick at an overvoltage of ∼30 mV.

Computer Simulation of Porous Electrodes with Immobilized Enzymes: The Percolation Properties of Multicomponent Structures

The percolation characteristics of porous electrodes with immobilized enzymes are calculated. It is presumed that active centers of the enzymes undergo direct oxidation or reduction on the electrode. Two versions of a three-dimensional electrode structure consisting of particles of identical size are studied. In one, the frame of the porous electrode (PE) comprises only those parts of the support that conduct electrons. In the other, the electrode is a two-component structure capable of ensuring the supply of two participants of the electrochemical process to the enzymes. Calculated are: the fraction of the support parts that conduct electrons (taken as a whole, they form an “electron cluster”); the electron cluster's transparency; and the number of exits the electron cluster has onto the rear surface of PE. The character of distribution of enzymes that are in contact with one or two macroscopic clusters, which comprise “conductive” particles, over the PE thickness is established. In doing so, it is assumed that the two clusters can be supplied either from one side (“parallel” clusters) or from two opposite sides (“collision” clusters) of PE. The electron cluster surface accessible to contact with enzymes and the number of enzymes in contact with such an electron cluster are determined. Two possibilities of the PE functioning are examined. In one, the electrochemical process proceeds at any contact of the enzyme with the support particles. In the other, a certain type of enzyme immobilization on the support is required. The region of optimum concentrations of components that make PE is established. Within this region the electrochemical activity may reach a maximum.

Phase coexistence in Ising, Potts and percolation models

We study phase coexistence (separation) phenomena in Ising, Potts and random cluster models in dimensions d⩾3 below the critical temperature. The simultaneous occurrence of several phases is typical for systems with appropriately arranged (mixed) boundary conditions or for systems satisfying certain physically natural constraints (canonical ensembles). The various phases emerging in these models define a partition, called the empirical phase partition, of the space. Our main results are large deviations principles for (the shape of) the empirical phase partition. More specifically, we establish a general large deviation principle for the partition induced by large (macroscopic) clusters in the Fortuin–Kasteleyn model and transfer it to the Ising–Potts model where we obtain a large deviation principle for the empirical phase partition induced by the various phases. The rate function turns out to be the total surface free energy (associated with the surface tension of the model and with boundary conditions) which can be naturally assigned to each reasonable partition. These LDP-s imply a weak law of large numbers: asymptotically, the law of the phase partition is determined by an appropriate variational problem. More precisely, the empirical phase partition will be close to some partition which is compatible with the constraints imposed on the system and which minimizes the total surface free energy. A general compactness argument guarantees the existence of at least one such minimizing partition. Our results are valid for temperatures T below a limit of slab-thresholds T ̂ c conjectured to agree with the critical point T c . Moreover, T should be such that there exists only one translation invariant infinite volume state in the corresponding Fortuin–Kasteleyn model; a property which can fail for at most countably many values and which is conjectured to be true for every T≠ T c .

Scaling limits of loop-erased random walks and uniform spanning trees

The uniform spanning tree (UST) and the loop-erased random walk (LERW) are strongly related probabilistic processes. We consider the limits of these models on a fine grid in the plane, as the mesh goes to zero. Although the existence of scaling limits is still unproven, subsequential scaling limits can be defined in various ways, and do exist. We establish some basic a.s. properties of these subsequential scaling limits in the plane. It is proved that any LERW subsequential scaling limit is a simple path, and that the trunk of any UST subsequential scaling limit is a topological tree, which is dense in the plane.The scaling limits of these processes are conjectured to be conformally invariant in dimension 2. We make a precise statement of the conformal invariance conjecture for the LERW, and show that this conjecture implies an explicit construction of the scaling limit, as follows. Consider the Löwner differential equation $$\frac{{\partial f}}{{\partial t}} = z\frac{{\zeta (t) + z}}{{\zeta (t) - z}}\frac{{\partial f}}{{\partial z}}$$ (1) , with boundary valuesf(z,0)=z, in the rangez ∈U= {w ∈ ℂ : •w• < 1},t≤0. We choose ζ(t):=B(−2t), where B(t) is Brownian motion on ∂\( \mathbb{U} \) starting at a random-uniform point in ∂\( \mathbb{U} \). Assuming the conformal invariance of the LERW scaling limit in the plane, we prove that the scaling limit of LERW from 0 to ∂\( \mathbb{U} \) has the same law as that of the pathf(ζ(t),t) (wheref(z,t) is extended continuously to ∂\( \mathbb{U} \)) ×(−∞,0]). We believe that a variation of this process gives the scaling limit of the boundary of macroscopic critical percolation clusters.

Mesoscopic and macroscopic dipole clusters: Structure and phase transitions

A two dimensional (2D) classical system of dipole particles confined by a quadratic potential is studied. This system can be used as a model for rare electrons in semiconductor structures near a metal electrode, indirect excitons in coupled quantum dots etc. For clusters of N ≤ 80 particles ground state configurations and appropriate eigenfrequencies and eigenvectors for the normal modes are found. Monte-Carlo and molecular dynamic methods are used to study the order-disorder transition (the “melting” of clusters). In mesoscopic clusters (N 37) an orientational “melting” of only the outer shell is possible. The most stable clusters (having both maximal lowest nonzero eigenfrequencies and maximal temperatures of total melting) are those of completed crystal shells which are concentric groups of nodes of 2D hexagonal lattice with a number of nodes placed in the center of them. The picture of disordering in clusters is compared with that in an infinite 2D dipole system. The study of the radial diffusion constant, the structure factor, the local minima distribution and other quantities shows that the melting temperature is a nonmonotonic function of the number of particles in the system. The dynamical equilibrium between “solid-like” and “orientationally disordered” forms of clusters is considered.

In situ observation of coalescence growth of small gold clusters by X-ray diffraction technique

An in situ observation of coalescence growth among small Au clusters (1–2 nm) have been performed by means of a grazing-incidence X-ray diffraction method. The Au clusters, having predominantly the decahedral multiple-twinned structures, were piled up on a cold Si substrate at 92 K so that the coalescence growth could be avoided. By annealing the sample from 82 K up to 325 K, the broad diffraction pattern was found to be gradually sharpened as the annealing temperature increased. The morphology was observed by scanning electron microscopy, after annealing at 325 K showed lumpy-type networks having a typical lump size of 100 nm, indicating coagulation growth of clusters. However, the corresponding diffraction pattern could not be explained without the multiple-twinning relation of small grains; this suggests that the initial cluster structure strongly influences the growth of macroscopic cluster aggregates.

Mesoscopic and macroscopic dipole clusters: structure and phase transitions

Two dimensional (2D) classical system of dipole particles confined by a quadratic potential is studied. For clusters of N < 81 particles ground state configurations and appropriate eigenfrequencies and eigenvectors for the normal modes are found. Monte Carlo and molecular dynamic methods are used to study in detail the order - disorder transition (the "melting" of clusters). In mesoscopic clusters (N < 37) there is a hierarchy of transitions: at lower temperatures an intershell orientational disordering of pairs of shells takes place; at higher temperatures the intershell diffusion sets in and the shell structure disappears. In "macroscopic" clusters (N > 37) an orientational "melting" of only the outer shell is possible. The most stable clusters (having both maximal lowest nonzero eigenfrequencies and maximal temperatures of total melting) are that of completed crystal shells which are concentric groups of nodes of 2D hexagonal lattice with a number of nodes placed in the center of them. The study of different quantities shows that the melting temperature is a nonmonotonic function of the number of particles in the system. The dynamical equilibrium between "solidlike" and "orientationally disordered" forms of clusters is considered.

Intrinsic stress upon Stranski–Krastanov growth of Ge on Si(001)

It is well established that the growth of Ge on Si(001) proceeds by Stranski–Krastanov mode, i.e. 3D islands (“hut” and macroscopic clusters) nucleate on top of a 3–4 ML thick pseudomorphic layer. Here, we present in-situ intrinsic stress measurements of Ge/Si(001) up to the film thicknesses at which the 3D islands percolate. From the film stress – and supported by AFM investigations – three stages of film growth characterised by different reliefs of the misfit strain can be discriminated: (1) the pseudomorphic layer-by-layer stage, (2) nucleation and growth and (3) coalescence of 3D islands.

Competing growth mechanisms of Ge/Si(001) coherent clusters

The growth of Ge three-dimensional coherent clusters on Si(001) during gas source molecular-beam epitaxy and post-deposition anneals has been investigated using in situ elevated-temperature scanning tunneling microscopy. By monitoring the growth of individual so-called ``hut'' clusters, this technique allowed us to separate various factors that may affect the final size distribution of entire cluster ensembles. It has been found that during the course of epitaxy the hut clusters grow by nucleation and growth of deposited material on the cluster facets; however, the low growth rate ($r\ensuremath{\propto}{t}^{1/n},$ where $4&lt;n&lt;5$), and the large scatter in absolute rate constants indicate diffusion-limited, rather than interface-limited mass transport, although both the facet-nucleation step and the wetting-layer defects inhibit the cluster growth. The strain-induced energy barriers at the cluster bases prevent material addition, and thus growth of large clusters, facilitating the domination of growth mechanisms other than Ostwald ripening at temperatures below 700 K, leading to symmetric or positively skewed cluster-size distribution functions. The tendency towards negatively skewed and bimodal distributions at higher temperatures signaled the contribution of the ripening in accord with the Lifshitz-Slyozov-Wagner theory. Raising the temperature above 770 K leads to a gradual replacement of the huts by the 〈110〉-based macroscopic clusters.

Synaptic Clustering of the Cell Adhesion Molecule Fasciclin II by Discs-Large and its Role in the Regulation of Presynaptic Structure

The cell adhesion molecule Fasciclin II (FASII) is involved in synapse development and plasticity. Here we provide genetic and biochemical evidence that proper localization of FASII at type I glutamatergic synapses of the Drosophila neuromuscular junction is mediated by binding between the intracellular tSXV bearing C-terminal tail of FASII and the PDZ1–2 domains of Discs-Large (DLG). Moreover, mutations in fasII and/or dlg have similar effects on presynaptic ultrastructure, suggesting their functional involvement in a common developmental pathway. DLG can directly mediate a biochemical complex and a macroscopic cluster of FASII and Shaker K + channels in heterologous cells. These results indicate a central role for DLG in the structural organization and downstream signaling mechanisms of cell adhesion molecules and ion channels at synapses.

Clustering Instability in Granular Gases: A Mesoscopic Investigation

We present a numerical study of the density fluctuations in granular flows in the hydrodynamic limit. By simulating the continuum equations posed for granular flows,1,2 we study the onset of the density-cluster formation. Clusters are observed when the restitution coefficient of granular collision is sufficiently small. However, unlike the clusters seen in molecular dynamics simulations,3,4 these macroscopic clusters appear to be transient. In the long time limit, they are damped by the viscous dissipation.

Single-channel kinetics, inactivation, and spatial distribution of inositol trisphosphate (IP3) receptors in Xenopus oocyte nucleus.

Single-channel properties of the Xenopus inositol trisphosphate receptor (IP3R) ion channel were examined by patch clamp electrophysiology of the outer nuclear membrane of isolated oocyte nuclei. With 140 mM K+ as the charge carrier (cytoplasmic [IP3] = 10 microM, free [Ca2+] = 200 nM), the IP3R exhibited four and possibly five conductance states. The conductance of the most-frequently observed state M was 113 pS around 0 mV and approximately 300 pS at 60 mV. The channel was frequently observed with high open probability (mean P(o) = 0.4 at 20 mV). Dwell time distribution analysis revealed at least two kinetic states of M with time constants tau < 5 ms and approximately 20 ms; and at least three closed states with tau approximately 1 ms, approximately 10 ms, and >1 s. Higher cytoplasmic potential increased the relative frequency and tau of the longest closed state. A novel "flicker" kinetic mode was observed, in which the channel alternated rapidly between two new conductance states: F1 and F2. The relative occupation probability of the flicker states exhibited voltage dependence described by a Boltzmann distribution corresponding to 1.33 electron charges moving across the entire electric field during F1 to F2 transitions. Channel run-down or inactivation (tau approximately 30 s) was consistently observed in the continuous presence of IP3 and the absence of change in [Ca2+]. Some (approximately 10%) channel disappearances could be reversed by an increase in voltage before irreversible inactivation. A model for voltage-dependent channel gating is proposed in which one mechanism controls channel opening in both the normal and flicker modes, whereas a separate independent mechanism generates flicker activity and voltage-reversible inactivation. Mapping of functional channels indicates that the IP3R tends to aggregate into microscopic (<1 microm) as well as macroscopic (approximately 10 microm) clusters. Ca2+-independent inactivation of IP3R and channel clustering may contribute to complex [Ca2+] signals in cells.

The mechanism of electroreduction of silver cyanide complexes in aqueous electrolytes—II. Interpretation of SERS data

Time dependencies of the intensities and FWHM of the adsorbed cyanide Raman stretching band correlate with the features of the time dependencies of electron numbers obtained from EQCM measurements. Quantum-chemical ab initio calculations show that the excitation wavelength of about 765 nm excites electron transitions between the [Ag 4 3CN −] states, whose quadrupole moments differ greatly. The earlier measured maxima in Raman excitation profiles for different adsorbates on roughened silver surface are in the following order (nm): ruthenium red ([ Ru 3 O 2( NH 3) 14] 6+) ~ 590 < triphenylphosphine ~ 620 nm < pyridine ~ 720 < cyanide which coincides with the decrease in size of these molecules. The contribution due to the excitation in the Ag 4 + cluster is larger when the adsorbate is smaller because of the more closely localized vibrational modes whereas contribution to the Raman scattering enhancement due to the excitation of surface plasma oscillations in the macroscopic silver clusters is constant.

Values of δ 34 S in iron disulphides of the North Bohemian Lignite Basin, Czech Republic

Abstract Three main, genetically different, types of iron disulphides occur in lignite of the North Bohemian Basin — synsedimentary, diagenetic and epigenetic. Among them the synsedimentary disulphide appears to be the most abundant. It forms fine dispersed microscopic framboids or veinlets mostly parallel with the coal bedding. This disulphide is mostly represented by pyrite. The other types are much less abundant. The epigenetic variety consists of large macroscopic clusters of crystals of marcasite twins or crystalline filling of fractures. The shift in sulphur isotopic composition between the original sulphate and the derived sulphides, which originated through bacterial reduction, may vary considerably depending on conditions, particularly on the open or closed nature of the system with respect to sulphate. The largest shifts in the isotopic composition between sulphate and sulphide sulphur are typical for an open system. Dissolved sulphate which supplied the North Bohemian Basin during the Miocene is likely to have been derived from weathered sulphides of the Krušné hory crystalline complex. This unit has isotopic compositions of sulphide sulphur varying between −1 and +5‰ and assuming no significant shifts in sulphur isotope compositions, the sulphate supplying the basin should exhibit a slightly positive δ 34 S value. Organic sulphur is thought to have played a much less important role. Synsedimentary pyrites, which form microframboids or veinlets in coal, show δ 34 S values close to 0‰. These values when compared with those of sulphur dioxide in gases exhaled by power stations burning lignite of the North Bohemian Basin indicate that they correspond to mean values for synsedimentary pyrite. This also implies that no considerable shifts in isotopic composition take place during thermal oxidation in power plants.

Normal human peripheral blood mononuclear cells mobilized with granulocyte colony-stimulating factor have increased osteoclastogenic potential compared to nonmobilized blood

Single-cell suspensions of granulocyte colony-stimulating factor (G- CSF)-mobilized peripheral blood mononuclear cells (G-PBMC) cultured in alpha minimal essential medium (alphaMEM) containing 10% fetal bovine serum formed multicellular aggregates within 24 hours. In six separate experiments, formation of aggregates appeared to be dependent on cell density per surface area, so that 5.8 +/- 1.3 aggregates formed per 1 x 10(5) cells when G-PBMC were cultured at densities greater than or equal to 1 x 10(5) cells/cm2. The frequency of aggregate formation was less than 1 per 10(5) cells when G-PBMC were cultured at densities less than 1 x 10(5) cells/cm2. Once formed, aggregates became adherent within 72 hours, and then, over the course of 21 days, released CD3/CD4/CD25-positive cells into the supernatant. This T-cell production peaked between days 7 and 14, reaching a total of 1,269 +/- 125.9 cells released per aggregate by day 21. Between days 14 and 21, the aggregates also generated macroscopic clusters of adherent mononuclear and giant multinucleated cells that stained positive for tartrate-resistant acid phosphatase (TRAP). At 4 weeks, the macroscopic foci coalesced into monolayers. Multinucleated TRAP-positive cells were distinguished from macrophage polykaryons by the absence of CD14 expression and the presence of osteoclast-specific membrane receptors for calcitonin and alphavbeta3-vitronectin. The osteoclast nature of these cells was further demonstrated by their ability to form resorption lacunae on dentine slices. Comparable osteoclast formation was not detected in cultures of normal marrow or normal nonmobilized peripheral blood.

Normal Human Peripheral Blood Mononuclear Cells Mobilized With Granulocyte Colony-Stimulating Factor Have Increased Osteoclastogenic Potential Compared To Nonmobilized Blood

Single-cell suspensions of granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood mononuclear cells (G-PBMC) cultured in alpha minimal essential medium (alphaMEM) containing 10% fetal bovine serum formed multicellular aggregates within 24 hours. In six separate experiments, formation of aggregates appeared to be dependent on cell density per surface area, so that 5.8 +/- 1.3 aggregates formed per 1 x 10(5) cells when G-PBMC were cultured at densities greater than or equal to 1 x 10(5) cells/cm2. The frequency of aggregate formation was less than 1 per 10(5) cells when G-PBMC were cultured at densities less than 1 x 10(5) cells/cm2. Once formed, aggregates became adherent within 72 hours, and then, over the course of 21 days, released CD3/CD4/CD25-positive cells into the supernatant. This T-cell production peaked between days 7 and 14, reaching a total of 1,269 +/- 125.9 cells released per aggregate by day 21. Between days 14 and 21, the aggregates also generated macroscopic clusters of adherent mononuclear and giant multinucleated cells that stained positive for tartrate-resistant acid phosphatase (TRAP). At 4 weeks, the macroscopic foci coalesced into monolayers. Multinucleated TRAP-positive cells were distinguished from macrophage polykaryons by the absence of CD14 expression and the presence of osteoclast-specific membrane receptors for calcitonin and alphavbeta3-vitronectin. The osteoclast nature of these cells was further demonstrated by their ability to form resorption lacunae on dentine slices. Comparable osteoclast formation was not detected in cultures of normal marrow or normal nonmobilized peripheral blood.