Communication: Unusual dynamics of hybrid nanoparticles and their binary mixtures

We present the results on the evolution of microscopic dynamics of hybrid nanoparticles and their binary mixtures as a function of temperature and wave vector. We find unexpectedly a nonmonotonic dependence of the structural relaxation time of the nanoparticles as a function of the morphology. In binary mixtures of two of the largest nanoparticles studied, we observe re-entrant vitrification as a function of the volume fraction of the smaller nanoparticle, which is unusual for such high diameter ratio. Possible explanation for the observed behavior is provided. (C) 2010 American Institute of Physics. doi:10.1063/1.3495480]

Inertial effects in solvation dynamics

The dynamics of solvation of newly created charged species in dense dipolar liquids can proceed at a high speed with time constants often in the subpicosecond domain. The motion of the solvent molecules can be in the inertial limit at such short times. In this paper we present a microscopic study of the effects of inertial motion of solvent molecules on the solvation dynamics of a newly created ion in a model dipolar liquid. Interesting dynamical behavior emerges when the relative contribution of the translational modes in the wave-vector-dependent longitudinal relaxation time is significant. Especially, the theory predicts that the time correlation function of the solvation energy can become oscillatory in some limiting situations. In general, the dynamics becomes faster in the presence of the inertial contribution. We discuss the experimental situations where the inertial effects can be noticeable.

Regulation and Function of GATA Transcription Factors in Adrenocortical Tumors and Granulosa Cells

Transcription factors play a key role in tumor development, in which dysfunction of genes regulating tissue growth and differentiation is a central phenomenon. The GATA family of transcription factors consists of six members that bind to a consensus DNA sequence (A/T)GATA(A/G) in gene promoters and enhancers. The two GATA factors expressed in the adrenal cortex are GATA-4 and GATA-6. In both mice and humans, GATA-4 can be detected only during the fetal period, whereas GATA-6 expression is abundant both throughout development and in the adult. It is already established that GATA factors are important in both normal development and tumorigenesis of several endocrine organs, and expression of GATA-4 and GATA-6 is detected in adrenocortical tumors. The aim of this study was to elucidate the function of these factors in adrenocortical tumor growth. In embryonal development, the adrenocortical cells arise and differentiate from a common pool with gonadal steroidogenic cells, the urogenital ridge. As the adult adrenal cortex undergoes constant renewal, it is hypothesized that undifferentiated adrenocortical progenitor cells reside adjacent to the adrenal capsule and give rise to daughter cells that differentiate and migrate centripetally. A diverse array of hormones controls the differentiation, growth and survival of steroidogenic cells in the adrenal gland and the gonads. Factors such as luteinizing hormone and inhibins, traditionally associated with gonadal steroidogenic cells, can also influence the function of adrenocortical cells in physiological and pathophysiological states. Certain inbred strains of mice develop subcapsular adrenocortical tumors in response to gonadectomy. In this study, we found that these tumors express GATA-4, normally absent from the adult adrenal cortex, while GATA-6 expression is downregulated. Gonadal markers such as luteinizing hormone receptor, anti-Müllerian hormone and P450c17 are also expressed in the neoplastic cells, and the tumors produce gonadal hormones. The tumor cells have lost the expression of melanocortin-2 receptor and the CYP enzymes necessary for the synthesis of corticosterone and aldosterone. By way of xenograft studies utilizing NU/J nude mice, we confirmed that chronic gonadotropin elevation is sufficient to induce adrenocortical tumorigenesis in susceptible inbred strains. Collectively, these studies suggest that subcapsular adrenocortical progenitor cells can, under certain conditions, adopt a gonadal fate. We studied the molecular mechanisms involved in gene regulation in endocrine cells in order to elucidate the role of GATA factors in endocrine tissues. Ovarian granulosa cells express both GATA-4 and GATA-6, and the TGF-β signaling pathway is active in these cells. Inhibin-α is both a target gene for, and an atypical or antagonistic member of the TGF-β growth factor superfamily. In this study, we show that GATA-4 is required for TGF-β-mediated inhibin-α promoter activation in granulosa cells, and that GATA-4 physically interacts with Smad3, a TGF-β downstream protein. Apart from the regulation of steroidogenesis and other events in normal tissues, TGF-β signaling is implicated in tumors of multiple organs, including the adrenal cortex. Another signaling pathway found often to be aberrantly active in adrenocortical tumors is the Wnt pathway. As both of these pathways regulate the expression of inhibin-α, a transcriptional target for GATA-4 and GATA-6, we wanted to investigate whether GATA factors are associated with the components of these signaling cascades in human adrenocortical tumors. We found that the expression of Wnt co-receptors LRP5 and LRP6, Smad3, GATA-6 and SF-1 was diminished in adrenocortical carcinomas with poor outcome. All of these factors drive inhibin-α expression, and their expression in adrenocortical tumors correlated with that of inhibin-α. The results support a tumor suppressor role previously suggested for inhibin-α in the mouse adrenal cortex, and offer putative pathways associated with adrenocortical tumor aggressiveness. Unraveling the role of GATA factors and associated molecules in human and mouse adrenocortical tumors could ultimately contribute to the development of diagnostic tools and future therapies for these diseases.

Exact path-integral evaluation of the heat distribution function of a trapped Brownian oscillator

Using path integrals, we derive an exact expression-valid at all times t-for the distribution P(Q,t) of the heat fluctuations Q of a Brownian particle trapped in a stationary harmonic well. We find that P(Q, t) can be expressed in terms of a modified Bessel function of zeroth order that in the limit t > infinity exactly recovers the heat distribution function obtained recently by Imparato et al. Phys. Rev. E 76, 050101(R) (2007)] from the approximate solution to a Fokker-Planck equation. This long-time result is in very good agreement with experimental measurements carried out by the same group on the heat effects produced by single micron-sized polystyrene beads in a stationary optical trap. An earlier exact calculation of the heat distribution function of a trapped particle moving at a constant speed v was carried out by van Zon and Cohen Phys. Rev. E 69, 056121 (2004)]; however, this calculation does not provide an expression for P(Q, t) itself, but only its Fourier transform (which cannot be analytically inverted), nor can it be used to obtain P(Q, t) for the case v=0.

Molecular hydrodynamic theory of non‐Markovian collective orientational relaxation in dense dipolar liquids

A microscopic study of the non‐Markovian (or memory) effects on the collective orientational relaxation in a dense dipolar liquid is carried out by using an extended hydrodynamic approach which provides a reliable description of the dynamical processes occuring at the molecular length scales. Detailed calculations of the wave‐vector dependent orientational correlation functions are presented. The memory effects are found to play an important role; the non‐Markovian results differ considerably from that of the Markovian theory. In particular, a slow long‐time decay of the longitudinal orientational correlation function is observed for dense liquids which becomes weaker in the presence of a sizeable translational contribution to the collective orientational relaxation. This slow decay can be attributed to the intermolecular correlations at the molecular length scales. The longitudinal component of the orientational correlation function becomes oscillatory in the underdamped limit of momenta relaxations and the frequency dependence of the friction reduce the frictional resistance on the collective excitations (commonly known as dipolarons) to make them long lived. The theory predicts that these dipolarons can, therefore, be important in chemical relaxation processes, in contradiction to the claims of some earlier theoretical studies.

Molecular theory of dielectric relaxation in a dense binary dipolar liquid

A molecular theory of dielectric relaxation in a dense binary dipolar liquid is presented. The theory takes into account the effects of intra- and interspecies intermolecular interactions. It is shown that the relaxation is, in general, nonexponential. In certain limits, we recover the biexponential form traditionally used to analyze the experimental data of dielectric relaxation in a binary mixture. However, the relaxation times are widely different from the prediction of the noninteracting rotational diffusion model of Debye for a binary system. Detailed numerical evaluation of the frequency-dependent dielectric function epsilon-(omega) is carried out by using the known analytic solution of the mean spherical approximation (MSA) model for the two-particle direct correlation function for a polar mixture. A microscopic expression for both wave vector (k) and frequency (omega) dependent dielectric function, epsilon-(k,omega), of a binary mixture is also presented. The theoretical predictions on epsilon-(omega) (= epsilon-(k = 0, omega)) have been compared with the available experimental results. In particular, the present theory offers a molecular explanation of the phenomenon of fusing of the two relaxation channels of the neat liquids, observed by Schallamach many years ago.

Propagation Of Vlf Electromagnetic-Waves In An Idealized Earth-Crust Wave-Guide With Overburden

Theoretical study of propagation characteristics of VLF electromagnetic waves through an idealised parallel-plane earth-crust waveguide with overburden, experimental verification of some of these characteristics with the aid of a model tank and use of range equation reveal the superiority of radio communication between land and a deeply submerged terminal inside a ocean via the earth-crust over direct link communication through the ocean.

Solution of a Boundary-Value Problem associated with Diffraction of Water Waves by a Nearly Vertical Barrier

An exact solution is derived for a boundary-value problem for Laplace's equation which is a generalization of the one occurring in the course of solution of the problem of diffraction of surface water waves by a nearly vertical submerged barrier. The method of solution involves the use of complex function theory, the Schwarz reflection principle, and reduction to a system of two uncoupled Riemann-Hilbert problems. Known results, representing the reflection and transmission coefficients of the water wave problem involving a nearly vertical barrier, are derived in terms of the shape function.

Spiral states in the square-lattice Hubbard model

We present a variety of physical implications of a mean-field theory for spiral spin-density-wave states in the square-lattice Hubbard model for small deviations from half filling. The phase diagram with the paramagnetic metal, two spiral (semimetallic) states, and ferromagnet is calculated. The momentum distribution function and the (quasiparticle) density of states are discussed. There is a significant broadening of the quasiparticle bands when the antiferromagnetic insulator is doped. The evolution of the Fermi surface and the variation of the plasma frequency and a charge-stiffness constant with U/t and δ are calculated. The connection to results based on the Schwinger-boson-slave-fermion formalism is made.

Structure-function relationships of icosahedral plant viruses

X-ray diffraction studies on single crystals of a few viruses have led to the elucidation of their three dimensional structure at near atomic resolution. Both the tertiary structure of the coat protein subunit and the quaternary morganization of the icosahedral capsid in these viruses are remarkably similar. These studies have led to a critical re-examination of the structural principles in the architecture of isometric viruses and suggestions of alternative mechanisms of assembly. Apart from their role in the assembly of the virus particle, the coat proteins of certian viruses have been shown to inhibit the replication of the cognate RNA leading to cross-protection. The coat protein amino acid sequence and the genomic sequence of several spherical plant RNA viruses have been determined in the last decade. Experimental data on the mechanisms of uncoating, gene expression and replication of several classes of viruses have also become available. The function of the non-structural proteins of some viruses have been determined. This rapid progress has provided a wealth of information on several key steps in the life cycle of RNA viruses. The function of the viral coat protein, capsid architecture, assembly and disassembly and replication of isometric RNA plant viruses are discussed in the light of this accumulated knowledge.

Tonically Active Kainate Receptors (tKARs) : A Novel Mechanism Regulating Neuronal Function in the Brain

Fast excitatory transmission between neurons in the central nervous system is mainly mediated by L-glutamate acting on ligand gated (ionotropic) receptors. These are further categorized according to their pharmacological properties to AMPA (2-amino-3-(5-methyl-3-oxo-1,2- oxazol-4-yl)propanoic acid), NMDA (N-Methyl-D-aspartic acid) and kainate (KAR) subclasses. In the rat and the mouse hippocampus, development of glutamatergic transmission is most dynamic during the first postnatal weeks. This coincides with the declining developmental expression of the GluK1 subunit-containing KARs. However, the function of KARs during early development of the brain is poorly understood. The present study reveals novel types of tonically active KARs (hereafter referred to as tKARs) which play a central role in functional development of the hippocampal CA3-CA1 network. The study shows for the first time how concomitant pre- and postsynaptic KAR function contributes to development of CA3-CA1 circuitry by regulating transmitter release and interneuron excitability. Moreover, the tKAR-dependent regulation of transmitter release provides a novel mechanism for silencing and unsilencing early synapses and thus shaping the early synaptic connectivity. The role of GluK1-containing KARs was studied in area CA3 of the neonatal hippocampus. The data demonstrate that presynaptic KARs in excitatory synapses to both pyramidal cells and interneurons are tonically activated by ambient glutamate and that they regulate glutamate release differentially, depending on target cell type. At synapses to pyramidal cells these tKARs inhibit glutamate release in a G-protein dependent manner but in contrast, at synapses to interneurons, tKARs facilitate glutamate release. On the network level these mechanisms act together upregulating activity of GABAergic microcircuits and promoting endogenous hippocampal network oscillations. By virtue of this, tKARs are likely to have an instrumental role in the functional development of the hippocampal circuitry. The next step was to investigate the role of GluK1 -containing receptors in the regulation of interneuron excitability. The spontaneous firing of interneurons in the CA3 stratum lucidum is markedly decreased during development. The shift involves tKARs that inhibit medium-duration afterhyperpolarization (mAHP) in these neurons during the first postnatal week. This promotes burst spiking of interneurons and thereby increases GABAergic activity in the network synergistically with the tKAR-mediated facilitation of their excitatory drive. During development the amplitude of evoked medium afterhyperpolarizing current (ImAHP) is dramatically increased due to decoupling tKAR activation and ImAHP modulation. These changes take place at the same time when the endogeneous network oscillations disappear. These tKAR-driven mechanisms in the CA3 area regulate both GABAergic and glutamatergic transmission and thus gate the feedforward excitatory drive to the area CA1. Here presynaptic tKARs to CA1 pyramidal cells suppress glutamate release and enable strong facilitation in response to high-frequency input. Therefore, CA1 synapses are finely tuned to high-frequency transmission; an activity pattern that is common in neonatal CA3-CA1 circuitry both in vivo and in vitro. The tKAR-regulated release probability acts as a novel presynaptic silencing mechanism that can be unsilenced in response to Hebbian activity. The present results shed new light on the mechanisms modulating the early network activity that paves the way for oscillations lying behind cognitive tasks such as learning and memory. Kainate receptor antagonists are already being developed for therapeutic use for instance against pain and migraine. Because of these modulatory actions, tKARs also represent an attractive candidate for therapeutic treatment of developmentally related complications such as learning disabilities.

A new general method for the introduction of the aldehyde function in aromatic compounds

Side chain bromination of aromatic amidomethylated compounds yields aldehydes.

Spectral element approach to wave propagation in uncertain beam structures

This paper presents a study on the uncertainty in material parameters of wave propagation responses in metallic beam structures. Special effort is made to quantify the effect of uncertainty in the wave propagation responses at high frequencies. Both the modulus of elasticity and the density are considered uncertain. The analysis is performed using a Monte Carlo simulation (MCS) under the spectral finite element method (SEM). The randomness in the material properties is characterized by three different distributions, the normal, Weibull and extreme value distributions. Their effect on wave propagation in beams is investigated. The numerical study shows that the CPU time taken for MCS under SEM is about 48 times less than for MCS under a conventional one-dimensional finite element environment for 50 kHz loading. The numerical results presented investigate effects of material uncertainties on high frequency modes. A study is performed on the usage of different beam theories and their uncertain responses due to dynamic impulse load. These studies show that even for a small coefficient of variation, significant changes in the above parameters are noticed. A number of interesting results are presented, showing the true effects of uncertainty response due to dynamic impulse load.

Properties of Toeplitz operators on analytic function spaces : from function symbols to distributions

Toeplitz operators are among the most important classes of concrete operators with applications to several branches of pure and applied mathematics. This doctoral thesis deals with Toeplitz operators on analytic Bergman, Bloch and Fock spaces. Usually, a Toeplitz operator is a composition of multiplication by a function and a suitable projection. The present work deals with generalizing the notion to the case where the function is replaced by a distributional symbol. Fredholm theory for Toeplitz operators with matrix-valued symbols is also considered. The subject of this thesis belongs to the areas of complex analysis, functional analysis and operator theory. This work contains five research articles. The articles one, three and four deal with finding suitable distributional classes in Bergman, Fock and Bloch spaces, respectively. In each case the symbol class to be considered turns out to be a certain weighted Sobolev-type space of distributions. The Bergman space setting is the most straightforward. When dealing with Fock spaces, some difficulties arise due to unboundedness of the complex plane and the properties of the Gaussian measure in the definition. In the Bloch-type spaces an additional logarithmic weight must be introduced. Sufficient conditions for boundedness and compactness are derived. The article two contains a portion showing that under additional assumptions, the condition for Bergman spaces is also necessary. The fifth article deals with Fredholm theory for Toeplitz operators having matrix-valued symbols. The essential spectra and index theorems are obtained with the help of Hardy space factorization and the Berezin transform, for instance. The article two also has a part dealing with matrix-valued symbols in a non-reflexive Bergman space, in which case a condition on the oscillation of the symbol (a logarithmic VMO-condition) must be added.