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OBJECTIVE: This paper reports results from studies on modifications of histone marks in transcriptional regulatory regions of H19, Igf2 and Mest genes in vitrified-warmed and cultured mouse embryos.Non vitrified and vitrified-warmed 8-cell embryos were cultured in Ham's F10+10% BSA into blastocyst stage in two experimental groups. Gene expression level was assessed by quantitative PCR and histone modifications were evaluated by ChIP assay method.The expression levels of the selected genes in vitrified embryos were found to be markedly reduced compared to the control group. Significant increase in H3K9me2 as a gene silencer was seen in the regulatory regions of all genes in vitrified group. Furthermore, H3K4me3 and H3K9ac decreased in some regulatory regions but not in all of them. Additionally, H3K9me2 in regulatory regions of Igf2 and H19 significantly increased in group I, whereas, there was no change in Mest compared to the control group.Vitrification and culture condition affects gene down regulation of Igf2 and H19. Although changes in each histone mark are not always the same as gene expression, the total pattern and sum of their changes are in line with gene down regulation upon vitrification and culture.

An unusual negative differential resistance (NDR) has been observed in I – V response in p -toluensulfonate-doped polypyrrole films, leading to a conductivity switching effect of almost four orders of magnitude. The effect appears at temperatures below 20 K for highly conducting samples while it is displaced to temperatures close to the room temperature for more resistive samples. The observed correlation between conductivity and switching phenomenon provides a fingerprint of the influence played by the sample nanostructure. The relation between the chemical structure of the material and the observed physical phenomenon is discussed.

Electrochemical impedance spectroscopy has been applied to the analysis of the behavior of monolayers of dioleoyl phosphatidylcholine (DOPC) on a mercury electrode. Experiments were carried out in electrolytes KCl and NaCl (0.1 mol dm(-3)) and Mg(NO3)2 (0.05 mol dm(-3)), and the frequency dependence of the complex impedance was estimated between 65 000 and 0.1 Hz at potentials -0.4 to -1.5 V versus Ag/AgCl 3.5 mol dm(-3) KCl at uncoated and coated electrode surfaces. Experiments were also carried out in the presence of gramicidin A (gA). Between the potentials of -0.4 and -0.7 V, the DOPC monolayer behaves as an almost ideal capacitor with little frequency dispersion. At more negative potentials, the impedance data show the formation of defects (-0.7 to -0.85 V), ingression of electrolyte into the layer (capacitance peak approximately -0.935 V), reorientation of phospholipid-water structures (capacitance peak approximately -1.0 V), and initiation of phospholipid desorption (approximately -1.3 V). gA interaction with the phospholipid monolayer at -0.4 V is shown as an additional low-frequency element. A general "one capacitor model" in a RC series equivalent circuit is developed incorporating the frequency dispersion of the capacitance, distribution of the time constants of the dispersion, and a coefficient related to the interface between the solution and the coated electrode. This latter coefficient is the most robust and decreases at potentials approaching those coincident with the DOPC phase transitions.

The pyroelectric properties and the Curie temperature of a ferroelectric/ferroelectric superlattice with two alternative layers are studied for the transverse Ising model using the effective field theory with a probability distribution technique. The pyroelectric coefficient of bulk materials shows a sharp peak at the Curie temperature. For large-period superlattices two pyroelectric peaks are found. The pyroelectric peak at low temperatures disappears when the period is very small.

We evaluate the consequences of interactions between charge carriers on the transport dynamics or currents in normally insulating one-dimensional systems where excess charges have been injected electrically, chemically, or optically. The time-dependent currents and space charge distribution are calculated using a many body Monte Carlo method adapted to stochastic transport. The idea is to study collective interaction phenomena and to learn how to distinguish them from disorder effects. The latter can in principle be modeled to explain almost any experimental result, however, this is often done at the expense of having to use unphysical or inconsistent parameters. Interactions can we argue, give for example, rise to low frequency anomalies in ac conductivity, negative differential resistance, low field spin magnetoresistance, and critical nonlinear noise like oscillations in currents as a function of time.

The question has been investigated whether resonant tunnelling is responsible for observed bump-like irregularities in current-voltage characteristics of double-barrier structures based on hydrogenated amorphous Si (a-Si:H) and its alloys with C or N. In this paper, general physical considerations, as well as elementary calculations taking into account special features of amorphous barrier structures, are compared with the results of a systematic experimental study of a-Si: H/a-Sil _ XCX : H heterostructures. Different series of samples, each consisting of a double and a single barrier, and a sample without any heterostructure barrier, have been investigated. A wide variety of experimental features from complete smoothness of the I—V curves, to bumps, noise and even accidental step-like switching behaviour, were recorded at different temperatures. From an overall inconsistency of our experimental data with the calculations, and in agreement with basic physical considerations, resonant tunnelling ...

The new stretch-oriented trans -polyacetylene exhibits a degree of macroscopic order combined with novel transport properties. The modelling of the electronic structure is still a matter of controversy. This controversy is mainly among three models which emphasize (a) the electronic correlations, (b) the three dimensionality and band structure, and (c) the electron-phonon interaction. The experimental magnetoresistance and low temperature conduction properties are particularly well suited as a means of discriminating between the models presented by the various schools of thought. We focus on the highly metallic limit and conclude that the bulk properties are better described by a percolation-type model than Anderson localization. The strong negative magnetoresistance is linked to an energy renormalization and a positive contribution to the wave-function shrinkage.

Standard formulations of hopping transport use energy- and space-dependent rates which are not always adequate to deal with the variety of situations encountered. In this paper we deal with several additional effects which include: polaron and Coulomb selfenergies in the limit of weak to intermediate interactions. Electric-field-induced localisation and delocalisation and finally also with the very topical problem of field-dependent tunnelling in organic molecules. The new transport rates are derived and discussed.

We consider the problem of high field Photoconduction in undoped trans-Polyacetylene. The new highly orientated anisotropic materials make it possible we argue, to observe the existence of polarons and solitons by looking at the high field transport properties. We suggest that polarons can be field ionised into the continuum and that evidence for this effect already exists in the photoconductivity work of Tubino et al.. We think that under suitable conditions, one may even be able to see soliton assisted Zener-tunnelling in this material.

Time-resolved photoluminescence studies in films, powders and single crystals of C60 are reported. The observed spectra in all forms are consistent with those reported for steady state conditions and may be associated with an intramolecular process. The spectrum is largely temperature independent and, at low temperatures, the observed luminescence decays with a lifetime of 1.2 ns. No long-lived decay from the triplet is observed at these intensities.In the case of the films, both the emission spectrum and lifetime are independent of excitation intensity. In the powder and single crystallite, a dramatic increase in the lifetime as well as a red-shift and broadening of the spectrum is observed at higher intensities. The luminescence intensity is seen to increase with the cube of the input intensity. The behaviour is interpreted as an abrupt onset of emission from the highly populated triplet state resulting from a banding of the intramolecular triplet states, a process which is dependent on a critical excited state density.

The synthesis of macroscopic amounts of the fullerenes [1] has stimulated a variety of experimental and theoretical investigations of this new allotropic form of carbon. The photophysical properties in solution have been well characterised. The lowest energy optical transitions are strongly forbidden by symmetry selection rules and no luminescence is observable [2–7]. In the case of the solid state, there is still no conclusive experimental evidence for electronic banding [8], posing questions as to the degree of inter- versus intramolecular interactions. However, in thin films luminescence has been observed, indicating a departure from the behaviour of the isolated molecules [6]. Tn this study, time resolved luminescence of films, powders and crystals of C60 are carried out in an effort to characterise this departure. A strong dependance of the luminescence on excitation intensity is observed in powders and crystals, but not in films. The results are discussed in terms of a transition between intramolecular and banded intermolecular behaviour at high excited state densities, which is dependent on microcrystallite size.

We have recently demonstrated that the Meyer-Neldel (MN) rule (compensation law) may be understood as arising naturally when the activation energy for a process is significantly larger than both the typical excitations available and kT. This conclusion was supported by the results of two microscopic models, related to special cases. In the present paper we present arguments, based on general results from statistical physics, which lead to the same conclusion. We show that this simple explanation also leads to the solution of a number of puzzles which have been associated with Meyer-Neldel behavior. We show that phenomena in groups of similar materials yield similar MN slopes. Finally, we show that the values of the slope for semiconductors with gaps in the 1--2-eV range are consistent with the suggestion that optical phonons are the source of the excitation energy in such processes.

In most problems involving localization caused by disorder, the density of states is both conceptually and experimentally the basic starting point. This point has been emphasized in Mott's work for many years. Current descriptions of localization often do not explicitly involve this important quantity. We have therefore formulated a new scaling approach to localization which emphasizes the role of the density of states in generating localization below the mobility edge ec. The theory is also applied to magnetoresistance and magnetolocalization (shift of ec with magnetic field).

Conduction processes in polymers depend on the degree of order in the material. In crystalline materials such as polydiacetylene, polaron and bipolaron transport are indeed possible. The same is true for the partially ordered materials in the polyacetylene category. The disordered materials, however, are usually well described by hopping conductivity either in equilibrium or in non-equilibrium situations. Two interesting and controversial questions remain. One is related to the role of Coulomb interactions and the other is related to high-field transport characteristics. We shall examine these questions in this paper.

We investigate the influence of many body effects on banding in systems with low dimensionality. This includes organic solids, polymers and layered materials. It is argued in this paper, that many-body effects can become important in generating quasi-3-dimensinality. We suggest that this effect is particularly important in doped systems where there are locally regions of free charge like in doped polymers and in highTc superconductors. Various mechanisms for enhanced many-body induced banding in the weak direction are discussed. This includes polarisation effects and correlations of the Hubbard type.

Current bumps in the current-voltage characteristics of amorphous semiconductor double barrier structures have previously been associated with a resonant tunneling process through quantized levels in the well region of the structure. We investigate the perpendicular transport through a-Si:H/a-SiNx:H single (SB) and double (DB) barrier structures grown by glow discharge. Current bumps are observed in the I-V characteristics of both SB and DB structures at 77 K which suggests a different transport mechanism than previously proposed. We propose that the first current bump is simply a transition from a low-field (space-charge-limited) transport mechanism to a high-field (multiple hopping) transport mechanism. The additional bumps are associated with the energy-dependence of the density of localized states in the a-SiNx:H and a-Si:H.

Field and temperature dependence of transits in amorphous semiconductors are tackled using two different methods. We use analytical and Monte-Carlo simulation techniques. We compare with existing data on hopping systems. The model does seem to account reasonably well for the observed temperature and exp (−η Fα) field dependence of transit times in amorphous semiconductor multilayers. The anomaly in the low field temperature dependence observed by the Dundee group however cannot be produced by the simple hopping model. The reasons are discussed.

We consider transport in the insulating regime of GaMnAs. We calculate the resistance, magnetoresitance and Hall effect, assuming that the Fermi energy is in the region of localized states above the valence band mobility edge. Both hopping and activated band transport contributions are included. The anomalous Hall current from band states is very different from the hopping Hall current and has extrinsic (skew) and intrinsic (Luttinger) contributions. Comparison with experiment allows us to assess the degree to which band and hopping contribution determine each of the three transport coefficients in a particular temperature range. There are strong indications that the insulating state transport in GaMnAs is controlled primarily by extended state, band edge, transport rather than by variable range hopping, as reported in the literature., Comment: submitted to Phys. Rev. B, we changed the title, we corrected typos and we added few explanations

The standard model of Mn doping in GaAs is subjected to a coherent potential approximation (CPA) treatment. Transport coefficients are evaluated within the linear response Kubo formalism. Both normal (NHE) and anomalous contributions (AHE) to the Hall effect are examined. We use a simple model density of states to describe the undoped valence band. The CPA bandstructure evolves into a spin split band caused by the $p-d$ exchange scattering with Mn dopants. This gives rise to a strong magnetoresistance, which decreases sharply with temperature. The temperature ($T$) dependence of the resistance is due to spin disorder scattering (increasing with $T$), CPA bandstructure renormalization and charged impurity scattering (decreasing with $T$). The calculated transport coefficients are discussed in relation to experiment, with a view of assessing the overall trends and deciding whether the model describes the right physics. This does indeed appear to be case, bearing in mind that the hopping limit needs to be treated separately, as it cannot be described within the band CPA., Comment: submitted to Phys. Rev. B

Starting from the Kubo formula, we expand the Hall conductivity using a cumulant approach which converges quickly at high temperatures (k_BT > energy differences of initial and final scattering states) and can be extended to low temperatures. The theory can deal with the sign, the ordinary and the anomalous contributions to the Hall effect. When applied to include the spin-orbit interaction to first order, we recover what is essentially the Karplus-Luttinger result for the anomalous Hall effect. Contact is made to the Chazalviel and Nozieres-Lewiner formulae. A side-jump type formula is obtained by using an exact application of linear response. We show that there exists an exact rigid Hall current which is not a Fermi level property. We introduce a relationship between mass and diffusivity which allows us to generalize the theory to strong disorder and even introduce a mobility edge. The formalism provides a systematic and practical way of analyzing both ordinary and anomalous contributions to the Hall conduction including the changes of sign, and in the presence of serious disorder. As a byproduct of the method, we show that the anomalous Hall coefficient can vary with resistance to the power n, with 1, Accepted for publication in Physical Review B

Recent experiments on a variety of polymeric and other disordered organic semiconductors indicate an apparent anomaly in the field dependence of the carrier mobility, anomaly in the sense that conventional high field hopping theory does not appear to account for the apparently universally observed exp{γF 1 2 } law. Various explanations suggesting polaronic and Poole-Frenkel type effects have been put forward in the literature. Similar effects had been observed some years ago in low mobility dielectrics. We re-examine non-equilibrium hopping transport in the high field limit and conclude that the anomaly is due to a density of states effect. The latter may or may not include electronic correlation effects. This depends on the system and type of disorder.

A computational model of the frequency dependent conductivity in hybrid metal/organic multilayer nanostructures is presented. The structures under investigation are fabricated by evaporation of liquid crystal molecules onto an ultrathin MBE grown metal film. The disk-like liquid crystal molecules self-assemble in conducting columns which, in turn, self-organise on the metal surface to form an ordered 2-dimensional array. Electronic transport in the metal film is influenced by this molecular overlayer, and such systems may thus be used in a range of sensor applications, with the specific sensor functions being determined by customised chemical synthesis of the molecules.

Irregularities in the current-voltage-characteristics of a-Si:H based potential barriers have been investigated experimentally, and are discussed theoretically with respect to different transport mechanisms. The investigated samples were different series of double and single barrier a-Si:H - a-Si1-xCx:H - heterostructures, as well as homogeneous samples without heterostructure barrier. Current-voltage-(I-V)-characteristics showing a wide variety of features, from complete smoothness of the curves, to bumps and even accidental step-like switching behaviour, as well as different forms of noise, were recorded at different temperatures. Resonant tunnelling as an explaining transport mechanism for the anomalies was excluded because of inconsistency between experiment and calculations partially including special amorphous features. Instead it is argued that all observed irregularities, i. e. bumps in I-V-curves, switching-like behaviour, and appearance of noise, are related to current transport via trap-assisted tunnelling through locally strongly confined transport paths, leading to the meta-stable formation, change and break-down of conductory filaments.

development of vitrified bovine oocytes. Mechanisms of positive influence pre-treating bovine oocytes with the follicle fluid prior to vitrification on nuclear-cytoplasmic maturation of oocytes are under further investigation. The results propose that these markers (content of calcium in intracellular stores, level of mitochondrial activity and concentration of NADH) may be considered in further optimization of the conditions for vitrification of oocyte. This study was supported by grant No.10 04 00389-a from Russian Foundation of Basic Research.

Organic materials very frequently constitute systems of low dimensionality. Conjugated polymers and Langmuir-Blodgett multilayers are two examples. A survey will be given of novel phenomena associated with the electron transport along polymer chains and across LB films. An attempt will be made to compare and contrast organic and inorganic low dimensionality with emphasis on potential applications to the subject of Molecular Electronics.

The ground state and lowest-lying excited states of polydiacetylene chains are investigated using a tight-binding Hamiltonian which includes electron-phonon interactions but does not explicitly include electron-electron repulsion. The parameters of the model are obtained by comparison with experiment and the character and properties of the low-lying charge states are determined. This calculation shows that localised polaron states will dominate charge conduction in these systems. In contrast to the situation for polyacetylene, bipolaron states are stable in the polydiacetylenes. Moreover, they are so strongly bound that they may survive the inclusion of electron-electron repulsion.

There exist novel classes of materials ranging from conjugated polymers and anisotropic salts to Langmuir-Blodgett films which under certain experimental conditions exhibit one-dimensional excitation dynamics. In this paper we consider the Master equation approach to diffusion drift and trapping in such ‘quasi one-dimensional systems’. Using exact, scaling, and coherent potential approaches we consider a series of phenomena appropriate to the description of such systems. These include the following category of problems:1. the deep trapping problem (exact),2. the bond disorder problem (scaling and coherent medium),3. and finally the combination of1. with2. The relationship to present and planned experiments is discussed.

The tight binding approximation for d electrons in liquid metals first studied by Roth (1972) using multiple scattering theory is re-examined by a diagrammatic analysis and is rederived by a new method and also extended to liquid metal alloys. The diagrammatic analysis permits a simple physical interpretation of the multiple scattering theory discussed by Schwartz and Ehrenreich (1971). Using a selfconsistent approximation the authors derive expressions for the electronic density of states N(E) using various approximations for the atomic correlation functions. In particular, it is shown that for a correlated liquid treated within SCA the electronic self energy Sigma (E) can be decomposed quite generally into a local and a non local part and that only the local part of Sigma (E) contributes to N(E).

The resonant and non-resonant luminescence changes in a-silicon are considered. It is suggested, that the effect is closely related to the anomalous spin-dependent magnetoresistance and photoconductivity changes observed in evaporated and glow-discharge-deposited silicon. The novel feature here is the existence of stable quenching lines. This considerably reduces the choice of recombination models to either a geminate radiative process with singlet-spin memory or to the usual localized-localized recombination process with a spin-dependent, non-radiative transition. The steady-state and time-dependent features of the latter model are analysed. The results are in good agreement with experiment if the exchange interaction between the spins is assumed to be negligibly small. Some interesting and novel time-dependent effects are found and related to recent observations. In particular, it is found that microwave chopping can turn a quenching line into an enhancing one. The problems associated with exch...

The authors present a theoretical framework for the transport of charge carriers in semiconductor multiple-quantum-well structures for motion perpendicular to the layers. The formalism is derived on the basis of strong electric fields but they allow the possibility of describing the low-field ohmic region by using a simple scaling argument. Stark localisation in narrow energy bands implies that the transport phenomena are a superposition of phonon-assisted hopping and intra-band tunnelling. The transport equations and transition rates are derived and discussed in relation to experimental results. In addition they also consider the influence of an external magnetic field both parallel and perpendicular to the layers. The influence of disorder is considered and it is found that it can considerably modify the nature of the physical effects predicted on the basis of the 'pure' eigenstates. Recent experiments on magneto-transport perpendicular to the layers are discussed in the light of this theoretical formalism.

An exact solution is obtained for the survival fraction in the one-dimensional diffusion problem with randomly distributed deep traps. The time decay is studied both with and without a bias field. The small concentration (x) long time (t) decay behaves as exp[-(x 2 t/t 0)1/3]. The exact results are compared with the coherent potential approximation (CPA) and the first passage time approach (FPT). We find that in most cases of practical interest the FPT is superior to the CPA.

The master-equation approach to transport in disordered systems is considered. The diffusion of excitations is treated within a self-consistent scheme. This has been shown previously to lead to very satisfactory results when exponentially varying jump rates are used. The effective-medium idea is extended to treat diffusion., limiting trapping or relaxation in amorphous networks. The theory is compared with some of the predictions made using the 'continuous time random walk' model of trapping. The method is also applied to the problem of spin relaxation in amorphous semiconductors in the hopping regime.

The resonant and non-resonant photoconductivity changes due to a magnetic field and an additional microwave field are ocnsidered. The effect is shown to bear a close relationship to the anomalous spin-dependent magnetoresistance observed in amorphous semiconductors. It is suggested that a spin-dependent, non-radiative recombination process is responsible for the resonant and non-resonant photo-conductivity changes. Interesting time-dependent effects are found; in particular microwave chopping can turn a quenching line into an enhancing one. The problems associated with exchange-coupled spins are discussed. We compare our results with our recent luminescence results and conclude that the same model can account for both experiments.

The magnetic-field dependence of the E.S.R. linewidth in amorphous silicon has been measured in order to investigate the influence of the exchange interaction on the E.S.R. linewidth. A different field dependence was obtained for amorphous silicon prepared by the glow-discharge technique and by electron-beam evaporation. The experimental results are discussed in terms of exchange-coupled spins which are distributed either homogeneously or inhomogeneously. It is concluded that exchange interaction is necessary to account for a variety of experimental results obtained in these materials.

The authors present a systematic and exact evaluation of diffusivity, energy, photoluminescence (PL) decay and photoconduction for systems with energetic and positional disorder in the low-temperature limit. Whereas most quantities can be calculated analytically in the long-time limit (slowing down of relaxation), the PL requires explicit calculation of the total transition probability Gij(t). The problem can be solved by a step-by-step approximation for a simplified PL model, emphasising the diffusional aspect. Finite electric fields lead to drastic modifications of relaxation laws at low temperature. They derive a formalism which can be applied with great generality in particular to amorphous semiconductors, quantum-well superlattices and disordered organic materials.

Spin diffusion and relaxation is considered in the framework of the Master equation. The formalism is applied to the nuclear spin-lattice relaxation in a-Si:H. In the framework of the model proposed by Carlos and Taylor (1980), the experimental data require that at least 10% of the hydrogen participates in local mode relaxation centres.

Within the novel non-equilibrium theory of incoherent motion we study the current and energy relaxation of excited charge carriers as observed in transient photoconductivity experiments. The theory is applied to an exponential band tail model commonly used for a-As 2 Se 3 and a-Si:H. The typical temperature dependence of the decay parameter can be explained in the whole temperature regime and the mean energy loss as a function of initial energy is calculated.

The contributions to the spin resonance absorption lines observed in amorphous silicon and germanium are discussed in terms of the different relaxation processes. It is shown that besides a g-value distribution, hyperfine interaction contributes significantly. Dipolar and anisotropic exchange interactions are shown to be of minor importance except at the highest spin densities. The temperature-dependent increase in linewidth is explained by a modulation of the spin-orbit interaction owing to the motion of the carriers. A semiclassical model is used to show that the distribution of spin-flip times given by a sequence of consecutive hops in the framework of variable-range hopping can lead to the observed changes in linewidth and lineshape. Some exchange interaction is required to narrow the lines and to transfer the hopping-induced spin-flip rate to the spins far below the Fermi level. An anti-ferromagnetic exchange of the order of 1 K as reported recently, however does not seem likely in the light...

The theory of hopping transport in disordered systems is extended by introducing intrasite electron-electron interaction within the Hubbard model. We present numerical calculations for the conductivity σxx in the case of positive correlation energy. A more detailed report of this paper is given in ref. 1.

A theory is outlined for the temperature dependence of the ESR linewidth in amorphous germanium and silicon. By connecting the lifetime broadening with the motion of the spins, and assuming a distribution of spin relaxation times, the experimental results may be explained, in particular the observed relationship between temperature dependent linewidth and dc conductivity. Es wird eine Theorie fur die Temperaturabhangigkeit der ESR-Linienbreite in amorphem Germanium und Silizium entwickelt. Die experimentellen Ergebnisse lassen sich durch Verknupfung der Lebensdauerverbreiterung mit der Bewegung der Spins und unter Berucksichtigung einer Verteilung der Spin-Relaxationszeiten erklaren. Insbesondere kann die beobachtete Beziehung zwischen der temperaturabhangigen Linienbreite und der Gleichstromleitfahigkeit erklart werden.

The frequency-dependent Hall conductivity and Hall mobility are evaluated for the R-percolation network. The results based on a verified self-consistent theory are compared with simple pair and three-site approximations. The Hall conductivity has the characteristic omega s behaviour found for the AC conductivity with an exponent s which decreases with density. Previous discrepancies found between experiment and theories based on three-site approximations are resolved.

A new method has been developed to study non-equilibrium transport and energy relaxation phenomena in disordered organic and inorganic semiconductors. Given a distribution of localized states, the mean-square displacement and average energy of the excitation may be evaluated as functions of initial energy and time. The theory has a wide range of possible applications, for example to exciton and carrier transport in disordered organic and inorganic semiconductors. In disordered organic semiconductors, the density of excited states is usually well described by a Gaussian model. Current and energy relaxation and temperature-dependent mobilities have been studied for this Gaussian model using Monte-Carlo simulations. The theoretical results are found to be in excellent agreement with those of the simulations.