bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Differential Gene Expression in Human Cirrhosis Detected by Suppression Subtractive Hybridization
Authors: Shackel Nicholas A. , McGuinness Peter H. , Abbott Catherine A. , Gorrell Mark D. , McCaughan Geoffrey W.
Published: September 2003

Pathogenic molecular pathways in cirrhotic liver diseases such as hepatitis C virus (HCV), autoimmune hepatitis (AIH) and primary biliary cirrhosis (PBC) are poorly characterized. Differentially expressed genes are often important in disease pathogenesis. Suppression subtractive hybridization (SSH) is a genome–wide approach that enriches for differentially expressed mRNA transcripts. We aimed to make novel observations of differential gene expression in cirrhosis using SSH combined with quantitative real–time reverse transcriptase polymerase chain reaction (RT–PCR). Liver transcriptomes in HCV cirrhosis, AIH cirrhosis, PBC, and nondiseased liver tissue were examined by SSH. Resulting complementary DNA (cDNA) clones were rescreened for differential expression by dot–blot hybridization and then sequenced. Selected gene expression was quantified by real–time RT–PCR. Following SSH, 694 clones were rescreened for differential gene expression, of which 145 were sequenced and found to derive from 89 different genes. Seven clones were homologous only with expressed sequence tag (EST) sequences encoding genes having no known function. Up–regulated expression of four genes was confirmed by real–time RT–PCR: transmembrane 4 superfamily member 3 (tetraspanin CO–029) in all forms of cirrhosis, hedgehog interacting protein (HIP) in AIH cirrhosis and chitinase 3–like–1 (HC gp–39 or ykl–40) and arginine–glutamic acid repeat (RERE) in HCV cirrhosis. RERE gene polymorphisms and splice variants were observed in all tissues examined. Tetraspanin CO–029 up–regulation was primarily localized to bile ductular cells. In conclusion, novel observations of differential gene expression in human cirrhosis were made using SSH as the primary discovery tool. In particular, further studies of the RERE gene and its products in HCV associated liver disease are warranted.
Biliary Lipid Secretion, Bile Acid Metabolism, and Gallstone Formation Are Not Impaired in Hepatic Lipase–Deficient Mice
Authors: Amigo Ludwig , Mardones Pablo , Ferrada Carla , Zanlungo Silvana , Nervi Flavio , Miquel Juan Francisco , Rigotti Attilio
Published: September 2003

Whereas hepatic lipase (HL) has been implicated in lipoprotein metabolism and atherosclerosis, its role in controlling biliary lipid physiology has not been reported. This work characterizes plasma lipoprotein cholesterol, hepatic cholesterol content, bile acid metabolism, biliary cholesterol secretion, and gallstone formation in HL–deficient mice and C57BL/6 controls fed standard chow, a cholesterol–supplemented diet, or a lithogenic diet. Compared with C57BL/6 controls, HL knockout mice exhibited increased basal plasma high–density lipoprotein (HDL) cholesterol as well as reduced cholesterol levels transported in large lipoproteins in response to cholesterol–enriched diets. Hepatic cholesterol content and biliary cholesterol secretion of chow–fed HL knockout and wild–type mice were not different and increased similarly in both strains after feeding dietary cholesterol or a lithogenic diet. There were no differences in biliary bile acid secretion, bile acid pool size and composition, or fecal bile acid excretion between HL–deficient and control mice. HL knockout mice had a similar prevalence of gallstone formation as compared with control mice when both strains were fed with a lithogenic diet. In conclusion, the deficiency of HL has no major impact on the availability of lipoprotein–derived hepatic cholesterol for biliary secretion; HL expression is not essential for diet–induced gallstone formation in mice.
Late onset of tacrolimus-related posterior leukoencephalopathy after living donor liver transplantation
Authors: Frühauf Nils R. , Koeppen Susanne , Saner Fuat H. , Egelhof Thomas , Stavrou Gregor , Nadalin Silvio , Broelsch Christoph E.
Published: September 2003

Neurotoxicity is a well-known side effect of tacrolimus-based immunosuppression after liver transplantation. Until now, only 31 cases of immunosuppression-associated leukoencephalopathy in liver transplant recipients reported in the literature are related to tacrolimus therapy. We report a patient who developed a posterior leukoencephalopathy syndrome, secondary to tacrolimus-based immunosuppression, after living donor liver transplantation. The special features of this case are the sudden and late onset of neurologic symptoms, a persistent comatose state, and increased signal intensity in follow-up MRI.
Endothelin-A receptor antagonist reduces microcirculatory disturbances and transplant dysfunction after partial liver transplantation
Authors: Palmes Daniel , Budny Tymotheus B. , Stratmann Udo , Herbst Hermann , Spiegel Hans-Ullrich
Published: September 2003

Endothelin-1 can induce microcirculatory disorders by mediating sinusoidal vasoconstriction, lowering the perfusion rate and promoting leukocyte adhesion, all of which may play a role in the pathogenesis of the damage sustained by partial liver transplants. In this pilot study, we investigated a selective endothelin-A receptor antagonist (Darusentan; Knoll GmbH, Ludwigshafen, Germany) for its potential influence on the microcirculation in the setting of partial liver transplantation. One hundred and forty isogeneic Lewis rats were divided into four groups: 1. partial liver transplantation (30% of the initial liver volume); 2. partial liver transplantation treated with Darusentan (1 mg/kg bodyweight intravenously) immediately before reperfusion; 3. full-size liver transplantation; and 4. sham operation. Subsequently, the liver microcirculation was evaluated by intravital microscopy, and survival, liver function, and morphology were followed up to the fourteenth day. Compared with full-size transplanted animals, rats subjected to partial liver transplantation without Darusentan (group I) displayed severe microcirculatory lesions characterized by a significantly decreased perfusion rate, increased leukocyte velocity, and increased leukocyte adhesion. Disintegration of endothelium and increased recruitment of Kupffer cells were frequent morphologic findings. The Darusentan-treated group II showed improved parameters of microcirculatory function and morphology as well as improved liver function. Microcirculatory disturbances play a key role in the pathogenesis of partial liver transplant dysfunction. Treatment with selective endothelin-A receptor antagonists represent a new therapeutic approach to improve the function of partial liver transplants by reducing microcirculatory lesions and their sequelae affecting sinusoidal endothelium and hepatocytes.
Small-for-size liver syndrome after auxiliary and split liver transplantation: Donor selection
Authors: Heaton Nigel
Published: September 2003

Small-for-size liver grafts can be defined by a recognizable clinical syndrome that results from the transplantation of too small a functional mass of liver for a designated recipient. A graft to recipient body weight ratio less than 0.8, impaired venous inflow, and enhanced metabolic demands in patients with poor clinical conditions must be considered as main factors leading to the small-for-size syndrome (SFSS) when using living and cadaveric partial grafts such as split and auxiliary liver grafts. Increased risk of graft dysfunction is currently observed in fatty infiltration of more than 30%, abnormal liver test results (especially bilirubin and gamma glutaryl transferase), and other donor risk factors such as high inotrope administration and donor stay in the intensive care unit (>5 days). Older donors are especially vulnerable to prolonged cold ischemia and high inotrope levels, giving rise to early graft dysfunction and prolonged cholestasis. Increased metabolic need on a functionally small-for-size graft predisposes to surgical and septic complications and poorer survival. Splitting livers into right and left lobe grafts increases the potential risk of small-for-size grafts for both recipients. Several techniques of venous outflow reconstruction/implantation have been proposed to reduce the risk of obstruction postoperatively. Prevention and management of SFSS will improve in parallel with the increased experience, allowing us optimum usage of available organs and reducing overall morbidity and mortality. (Liver Transpl 2003;9:S26-S28.)
Small-for-size graft in living donor liver transplantation: How far should we go?
Authors: Kiuchi Tetsuya , Tanaka Koichi , Ito Takashi , Oike Fumitaka , Ogura Yasuhiro , Fujimoto Yasuhiro , Ogawa Kohei
Published: September 2003

With the extensive use of living donor liver grafts in adult patients, controversy over small-for-size syndrome has escalated in recent years. Although several symptoms have been suggested as manifestations of the syndrome, small-for-size syndrome remains difficult to diagnose because these symptoms are neither specific nor inevitable. The occurrence of small-for-size syndrome also seems to depend on a number of recipient and graft factors. Potential pathogenic mechanisms include persistent portal hypertension and portal overperfusion. At present, several techniques are being explored in an attempt to ameliorate the impact of small-for-size syndrome. Recent experience suggests that the occurrence of small-for-size syndrome is multifactorial and that complications relating to small-for-size grafts should be examined in relation to a variety of graft, recipient, and technical factors. (Liver Transpl 2003;9:S29-S35.)
Organizational and ethical aspects of living donor liver transplantation
Authors: Colardyn Francis
Published: September 2003

The well-known shortage of organs for transplantation can partly be managed with organs (or parts of them) from living donors. This form of organ donation is hampered by two important drawbacks: the harm to the donor and the lack of certainty that the donation is free of coercion. As often happens in medicine, both aspects have no clear solution. Therefore, all guarantees must be built into the processes leading to transplantation, under the control of peers. Also, the transplantation centers as the organ providers (in the large sense, the donor family and eventually an intermediate agency) must undergo this peer review. Eventually, a local ethical committee could perform an initial screening if there is a legal background for its competence in this matter. Alternatives for living donation are to be expected in the future, but this cannot circumvent the actual problems. (Liver Transpl 2003;9:S2-S5.)
Dendrogram Seriation Using Simulated Annealing
Authors: Morris Steven A. , Asnake Benyam , Yen Gary G.
Published: August 2003

Seriation is the ordering of the leaves of a dendrogram, such that leaves representing similar items are placed near each other according to some metric, within the constraints of the cluster tree. Such ordering greatly aids the interpretation of the relations represented by the dendrogram and reduces visual misinterpretation caused by unrelated items from different sub-trees being placed near each other during random ordering. The seriation method presented here uses simulated annealing to find an approximately optimal dendrogram ordering by minimizing a penalty function. The method employs a ‘similarity weighted distance’ penalty function that tends to avoid artifacts introduced by the traveling salesman problem algorithms commonly used for dendrogram seriation. Examples are given showing the effectiveness of the method in presenting dendrograms of the structure of a social network, and additional examples show an application for interpreting the structure of a network of journal papers covering the subject of anthrax research.
A Framework for Augmenting the Visualization of Dynamic Raster Surfaces
Authors: Rana Sanjay , Dykes Jason
Published: August 2003

Animated sequences of raster images that represent continuously varying surfaces, such as a temporal series of an evolving landform or an attribute series of socio-economic variation, are often used in an attempt to gain insight from ordered sequences of raster spatial data. Despite their aesthetic appeal and condensed nature, such representations are limited in terms of their suitability for prompting ideas and offering insight due to their poor information delivery and the lack of the levels of interactivity that are required to support visualization. Cartographic techniques aim to assist users of geographic information through processes of abstraction, by selecting, simplifying, smoothing and exaggerating when representing an underlying spatial data set graphically. Here we suggest a number of transformations and abstractions that take advantage of these techniques in a specific context–that of addressing the limitations associated with using animated raster surfaces for visualization, and propose them in the context of a framework that can be used to inform practice. The five techniques proposed are spatial and attribute smoothing, temporal interpolation, transformation of the surfaces into a network of morphometric features, the use of a graphic lag or fading and the employment of techniques for conditional interactivity that are appropriate for visualization. These efforts allow us to generate graphical environments that support visualization when using animated sequences of images representing continuous surfaces and are analogous to traditional cartographic techniques, namely, smoothing and exaggeration, simplification, enhancement and the various issues of design. By developing a framework for considering cartography in support of visualization from this particular type of data and phenomenon we aim to highlight the utility of a generically cartographic approach to information visualization. A number of particular techniques originating from computer science and conventional cartography are used in an application of the framework. A suitably interactive software tool is offered for evaluation–to establish the results of applying the framework and demonstrate ways in which we may augment the visualization of dynamic raster surfaces through animation and more generally aim to offer opportunity for insight through cartographic design.
Network Intrusion Visualization with NIVA, an Intrusion Detection Visual and Haptic Analyzer
Authors: Scott Craig , Nyarko Kofi , Capers Tanya , Ladeji-Osias Jumoke
Published: August 2003

The rapid growth of malicious activities on worldwide communication networks, such as the Internet, has highlighted the need for efficient intrusion detection systems. The efficiency of traditional intrusion detection systems is limited, in part, by their inability to relay effectively relevant information due to their lack of interactive/immersive technologies. In this paper, we explore several network visualization techniques geared toward intrusion detection on small- and large-scale networks. We also examine the use of haptics in network intrusion visualization. By incorporating concepts from electromagnetics, fluid dynamics, and gravitational theory, we show that haptic technologies can provide another dimension of information critical to the efficient visualization of network intrusion data. Furthermore, we explore the applicability of these visualization techniques in conjunction with commercial network intrusion detectors. Finally, we present a network intrusion visualization application with haptic integration, NIVA, which allows the analyst to interactively investigate as well as efficiently detect structured attacks across time and space using advanced interactive three-dimensional displays.
A Visualization Model of Interactive Knowledge Discovery Systems and Its Implementations
Authors: Han Jianchao , Hu Xiaohua , Cercone Nick
Published: August 2003

We briefly introduce an interactive visualization model, RuleViz, for knowledge discovery and data mining, which consists of five components: data preparation and visualization, interactive data reduction, data preprocessing, pattern discovery, and pattern visualization. With this model, the implementation issues are considered and three implementation paradigms, including image-based paradigm, algorithm-embedded paradigm, and interaction-driven paradigm, are discussed. We implement an interactive visualization system, AViz, which discovers 3D numerical association rules from large data sets based on the image-based paradigm. The framework of the AViz system is presented and each component is explored. To discretize numerical attributes, three approaches, including equal-sized, bin-packing-based equal-depth, and interaction-based approaches are proposed, and the algorithm for mining and visualizing numerical association rules is developed. Our experimental result on a census data set is illustrated, which shows that the AViz system is useful and helpful for discovering and visualizing numerical association rules.
Ab initio calculations of mode selective tunneling dynamics in CH312OH and CH313OH
Authors: Fehrensen Benjamin , Luckhaus David , Quack Martin , Willeke Martin , Rizzo Thomas R.
Published: August 2003

A simplified formulation of the harmonic reaction path Hamiltonian (RPH) approach is used to calculate mode specific tunneling splittings and stereomutation times in CH312OH and CH313OH. The experimental torsional spectrum is very well reproduced, as well as the few known isotope shifts. The mode specific changes in tunneling splitting are investigated for the excitation of fundamentals and OH stretching overtones. Good agreement between experiment and the RPH model is obtained, except for excitations of modes which are perturbed by anharmonic resonances. The inverted tunneling splittings (E level below A) experimentally observed for the fundamental transitions of the CH-stretching modes ν2 and ν9 and of the CH-rocking mode ν11 are shown to result from a pure symmetry effect and not from a breakdown of vibrational adiabaticity. Introducing a proper geometrical phase factor but retaining the adiabatic separation of the torsional dynamics yields calculated values of Δν̃2=−3.6 cm−1, Δν̃9=−3.2 cm−1, and Δν̃11=−8.2 cm−1 that are in satisfactory agreement with experimental data. Negative tunneling splittings are also predicted for the asymmetric CH-bending modes ν4 and ν10 and the CH3-rocking mode ν7. A smooth decrease of the tunneling splitting is calculated for increasing OH stretching excitation [Δν̃(ν1)=6.2 cm−1,…,Δν̃(6ν1)=1.5 cm−1] in quantitative agreement with experiment [Δν̃(ν1)=6.3 cm−1,…,Δν̃(6ν1)=1.6 cm−1]. The effect is shown to result in about equal parts from the increase of the effective torsional barrier and the effective lengthening of the OH bond.
Point-vortex cluster formation in the plane and on the sphere: An energy bifurcation condition
Authors: Boatto Stefanella , Laskar Jacques
Published: August 2003

The dynamics of a system of point vortices is considered in the plane and on the sphere. Particular attention is given to the formation of vortex clusters and to global vortex dynamics, especially in the spherical case. For integrable systems and systems with given symmetries, we show the existence of a critical energy above or below which (depending on the geometry of the surface) the system splits into clusters and vortex dynamics is confined to a particular region. The case of nonidentical vortices is of particular interest since we observe quite different global dynamics depending on the energy and the initial conditions. Furthermore we identify all the relative equilibria configurations as critical points of the reduced energy and we give an instability criterion to deduce instability for certain configurations.
Chaotic itinerancy based on attractors of one-dimensional maps
Authors: Sauer Timothy
Published: August 2003

A general methodology is described for constructing systems that have a slowly converging Lyapunov exponent near zero, based on one-dimensional maps with chaotic attractors. In certain parameter ranges, these relatively simple systems display the properties of intermittent dynamics known as chaotic itinerancy. We show that in addition to the local sensitivity characteristic of chaotic dynamics, these itinerant systems display a global sensitivity, in the sense that fine-scale additive noise may significantly change the natural measure on the large scale.
Phase resetting effects for robust cycles between chaotic sets
Authors: Ashwin Peter , Field Michael , Rucklidge Alastair M. , Sturman Rob
Published: August 2003

In the presence of symmetries or invariant subspaces, attractors in dynamical systems can become very complicated, owing to the interaction with the invariant subspaces. This gives rise to a number of new phenomena, including that of robust attractors showing chaotic itinerancy. At the simplest level this is an attracting heteroclinic cycle between equilibria, but cycles between more general invariant sets are also possible. In this paper we introduce and discuss an instructive example of an ordinary differential equation where one can observe and analyze robust cycling behavior. By design, we can show that there is a robust cycle between invariant sets that may be chaotic saddles (whose internal dynamics correspond to a Rössler system), and/or saddle equilibria. For this model, we distinguish between cycling that includes phase resetting connections (where there is only one connecting trajectory) and more general non(phase) resetting cases, where there may be an infinite number (even a continuum) of connections. In the nonresetting case there is a question of connection selection: which connections are observed for typical attracted trajectories? We discuss the instability of this cycling to resonances of Lyapunov exponents and relate this to a conjecture that phase resetting cycles typically lead to stable periodic orbits at instability, whereas more general cases may give rise to “stuck on” cycling. Finally, we discuss how the presence of positive Lyapunov exponents of the chaotic saddle mean that we need to be very careful in interpreting numerical simulations where the return times become long; this can critically influence the simulation of phase resetting and connection selection.
Chaotic cluster itinerancy and hierarchical cluster trees in electrochemical experiments
Authors: Kiss István Z. , Hudson John L.
Published: August 2003

Experiments on an array of 64 globally coupled chaotic electrochemical oscillators were carried out. The array is heterogeneous due to small variations in the properties of the electrodes and there is also a small amount of noise. Over some ranges of the coupling parameter, dynamical clustering was observed. The precision-dependent cluster configuration is analyzed using hierarchical cluster trees. The cluster configurations varied with time: spontaneous changes of number of clusters and their configurations were detected. Simple transitions occurred with the switch of a single element or groups of elements. During more complicated transitions subclusters were exchanged among clusters but original cluster configurations were revisited. At weaker coupling the system itinerated among lower-dimensional quasistationary chaotic two-cluster states and higher-dimensional states with many clusters. In this region the transitions showed characteristics of on–off intermittency.
Nasca lines: A mystery wrapped in an enigma
Authors: Castrejón-Pita J. R. , Castrejón-Pita A. A. , Sarmiento-Galán A. , Castrejón-Garcı́a R.
Published: August 2003

We analyze the geometrical structure of the astonishing Nasca geoglyphs in terms of their fractal dimension with the idea of dating these manifestations of human cultural engagements in relation to one another. Our findings suggest that the first delineated images consist of straight, parallel lines and that having sophisticated their abilities, the Nasca artists moved on to the design of more complex structures.
Extremely precise free energy calculations of amino acid side chain analogs: Comparison of common molecular mechanics force fields for proteins
Authors: Shirts Michael R. , Pitera Jed W. , Swope William C. , Pande Vijay S.
Published: August 2003

Quantitative free energy computation involves both using a model that is sufficiently faithful to the experimental system under study (accuracy) and establishing statistically meaningful measures of the uncertainties resulting from finite sampling (precision). We use large-scale distributed computing to access sufficient computational resources to extensively sample molecular systems and thus reduce statistical uncertainty of measured free energies. In order to examine the accuracy of a range of common models used for protein simulation, we calculate the free energy of hydration of 15 amino acid side chain analogs derived from recent versions of the OPLS-AA, CHARMM, and AMBER parameter sets in TIP3P water using thermodynamic integration. We achieve a high degree of statistical precision in our simulations, obtaining uncertainties for the free energy of hydration of 0.02–0.05 kcal/mol, which are in general an order of magnitude smaller than those found in other studies. Notably, this level of precision is comparable to that obtained in experimental hydration free energy measurements of the same molecules. Root mean square differences from experiment over the set of molecules examined using AMBER-, CHARMM-, and OPLS-AA-derived parameters were 1.35 kcal/mol, 1.31 kcal/mol, and 0.85 kcal/mol, respectively. Under the simulation conditions used, these force fields tend to uniformly underestimate solubility of all the side chain analogs. The relative free energies of hydration between amino acid side chain analogs were closer to experiment but still exhibited significant deviations. Although extensive computational resources may be needed for large numbers of molecules, sufficient computational resources to calculate precise free energy calculations for small molecules are accessible to most researchers.
Dynamic transitions through scattors in dissipative systems
Authors: Nishiura Yasumasa , Teramoto Takashi , Ueda Kei-Ichi
Published: August 2003

Scattering of particle-like patterns in dissipative systems is studied, especially we focus on the issue how the input–output relation is controlled at a head-on collision where traveling pulses or spots interact strongly. It remains an open problem due to the large deformation of patterns at a colliding point. We found that a special type of unstable steady or time-periodic solutions called scattors and their stable and unstable manifolds direct the traffic flow of orbits. Such scattors are in general highly unstable even in the one-dimensional case which causes a variety of input–output relations through the scattering process. We illustrate the ubiquity of scattors by using the complex Ginzburg–Landau equation, the Gray–Scott model, and a three-component reaction diffusion model arising in gas-discharge phenomena.
Clustering zones in the turbulent phase of a system of globally coupled chaotic maps
Authors: Maistrenko Yu. , Panchuk A.
Published: August 2003

The paper develops an approach to investigate the clustering phenomenon in the system of globally coupled chaotic maps first introduced by Kaneko in 1989. We obtain a relation between the transverse and longitudinal multipliers of the periodic clusters and prove the stability of these clusters for the case of symmetric, equally populated distributions between subclusters. Stable clusters emanate from the periodic windows of the logistic map and extend far into the turbulent phase. By numerical simulations we estimate a total basin volume of low-periodic clusters issued from the period-3 window and analyze the basin structure. The complement to the basin volume is ascribed to chaotic, very asymmetric high-dimensional clusters that are characterized by the presence of one or more leading clusters, accumulating about half of the oscillators while all the remaining oscillators do not cluster at all.
Energy conversion by autonomous regulation of chaos: Dynamical mechanism of loose coupling
Authors: Nakagawa Naoko , Kaneko Kunihiko , Komatsu Teruhisa S.
Published: August 2003

Inspired by recent experiments of molecular motors, a dynamical systems model for a flexible machine is proposed which converts injected energy to output directional motion. The output amount is distributed broadly, and thus the coupling between input energy and output motion is loose, as in the experiments. This energy conversion is shown to be robust against the change of surrounding environment. Stability analysis on the fixed point solutions of the model is presented, which suggests that transient chaotic motion, induced by temporal three-body motion, is relevant to the energy conversion.
Observation of a continuous interior crisis in the Hindmarsh–Rose neuron model
Authors: González-Miranda J. M.
Published: August 2003

Interior crises are understood as discontinuous changes of the size of a chaotic attractor that occur when an unstable periodic orbit collides with the chaotic attractor. We present here numerical evidence and theoretical reasoning which prove the existence of a chaos-chaos transition in which the change of the attractor size is sudden but continuous. This occurs in the Hindmarsh–Rose model of a neuron, at the transition point between the bursting and spiking dynamics, which are two different dynamic behaviors that this system is able to present. Moreover, besides the change in attractor size, other significant properties of the system undergoing the transitions do change in a relevant qualitative way. The mechanism for such transition is understood in terms of a simple one-dimensional map whose dynamics undergoes a crossover between two different universal behaviors.
Charge carrier mobility in quasi-one-dimensional systems: Application to a guanine stack
Authors: Beleznay F. B. , Bogár F. , Ladik J.
Published: August 2003

First the correct expression of charge mobilities in the one-dimensional (1-D) case in the deformation potential approximation are derived in detail. They differ substantially from the usual 3-D expressions. Starting from an ab initio HF band structure of a guanine stack, the effective masses, the deformation potentials, and the 1-D electron and hole mobilities, respectively, were calculated. The mobility values obtained seem to bee quite reasonable. No attempt was made to calculate from the mobilities the conductivities because of the lack of reliable experimental data (the activation energies of the electron and hole conductivities and dopant concentrations).
A challenge to chaotic itinerancy from brain dynamics
Authors: Kay Leslie M.
Published: August 2003

Brain hermeneutics and chaotic itinerancy proposed by Tsuda are attractive characterizations of perceptual dynamics in the mammalian olfactory system. This theory proposes that perception occurs at the interface between itinerant neural representation and interaction with the environment. Quantifiable application of these dynamics has been hampered by the lack of definable history and action processes which characterize the changes induced by behavioral state, attention, and learning. Local field potentials measured from several brain areas were used to characterize dynamic activity patterns for their use as representations of history and action processes. The signals were recorded from olfactory areas (olfactory bulb, OB, and pyriform cortex) and hippocampal areas (entorhinal cortex and dentate gyrus, DG) in the brains of rats. During odor-guided behavior the system shows dynamics at three temporal scales. Short time-scale changes are system-wide and can occur in the space of a single sniff. They are predictable, associated with learned shifts in behavioral state and occur periodically on the scale of the intertrial interval. These changes occupy the theta (2–12 Hz), beta (15–30 Hz), and gamma (40–100 Hz) frequency bands within and between all areas. Medium time-scale changes occur relatively unpredictably, manifesting in these data as alterations in connection strength between the OB and DG. These changes are strongly correlated with performance in associated trial blocks (5–10 min) and may be due to fluctuations in attention, mood, or amount of reward received. Long time-scale changes are likely related to learning or decline due to aging or disease. These may be modeled as slow monotonic processes that occur within or across days or even weeks or years. The folding of different time scales is proposed as a mechanism for chaotic itinerancy, represented by dynamic processes instead of static connection strengths. Thus, the individual maintains continuity of experience within the stability of fast periodic and slow monotonic processes, while medium scale events alter experience and performance dramatically but temporarily. These processes together with as yet to be determined action effects from motor system feedback are proposed as an instantiation of brain hermeneutics and chaotic itinerancy.
Evidence from human scalp electroencephalograms of global chaotic itinerancy
Authors: Freeman Walter J.
Published: August 2003

My objective of this study was to find evidence of chaotic itinerancy in human brains by means of noninvasive recording of the electroencephalogram (EEG) from the scalp of normal subjects. My premise was that chaotic itinerancy occurs in sequences of cortical states marked by state transitions that appear as temporal discontinuities in neural activity patterns. I based my study on unprecedented advances in spatial and temporal resolution of the phase of oscillations in scalp EEG. The spatial resolution was enhanced by use of a high-density curvilinear array of 64 electrodes, 189 mm in length, with 3 mm spacing. The temporal resolution was advanced to the limit provided by the digitizing step, here 5 ms, by use of the Hilbert transform. The numerical derivative of the analytic phase revealed plateaus in phase that lasted on the order of 0.1 s and repeated at rates in the theta (3–7 Hz) or alpha (7–12 Hz) ranges. The plateaus were bracketed by sudden jumps in phase that usually took place within 1 to 2 digitizing steps. The jumps were commonly synchronized in each cerebral hemisphere over distances of up to 189 mm, irrespective of the orientation of the array. The jumps were usually not synchronized across the midline separating the hemisphere or across the sulcus between the frontal and parietal lobes. I believe that the widespread synchrony of the jumps in analytic phase manifest a metastable cortical state in accord with the theory of self-organized criticality. The jumps appear to be subcritical bifurcations. They reflect the aperiodic evolution of brain states through sequences of attractors that on access support the experience of remembering.
Statistics of rare strong bursts in autocatalytic stochastic growth with diffusion
Authors: Nakao Hiroya , Mikhailov Alexander S.
Published: August 2003

A general model of autocatalytic stochastic growth with diffusion is analytically and numerically investigated. Exact analytical results for the intermittency exponents and the probability of rare strong bursts in an infinite system are presented. Finite-size saturation effects, leading to the stretched exponential growth of statistical moments, are further considered. These analytical predictions are checked in numerical simulations.
Simulation of a stochastic vortex tangle
Authors: Kondaurova L. P. , Nemirovskii S. K. , Nedoboiko M. V.
Published: August 2003

We present the results of a simulation of the chaotic dynamics of quantized vortices in the bulk of superfluid He II. The evolution of vortex lines is calculated on the basis of the Biot—Savart law. The dissipative effects arising from the interaction with the normal component or/and from relaxation of the order parameter are taken into account. Chaotic dynamics appears in the system via a random forcing, i.e., we use the Langevin approach to the problem. In the present paper we require the correlator of the random force to satisfy the fluctuation-dissipation relation, which implies that thermodynamic equilibrium should be reached. We describe numerical methods for integration of the stochastic differential equation (including a new algorithm for reconnection processes), and we present the results of a calculation of some characteristics of a vortex tangle such as the total length, the length distribution of the loops, and the energy spectrum.
Unstable states of a superfluid confined between rotating spheres
Authors: Gongadze A. , Kiknadze L. , Mamaladze Yu. , Tsakadze S.
Published: August 2003

The unstable states (including those related to self-accelerations of pulsars) in which the mutual friction causes an irreversible motion of vortices are considered.
Features of the angular dependence of the critical current in thin epitaxial films of HTSC YBa2Cu3O7−δ in a magnetic field
Authors: Fedotov Yu. V. , Pashitskiı̆ É. A. , Ryabchenko S. M. , Komashko V. A. , Pan V. M. , Flis V. S. , Cherpak Yu. V.
Published: August 2003

The dependence of the critical current density jc on the magnitude and direction of the magnetic field H is investigated in thin epitaxial films of YBa2Cu3O7−δ having a high value of jc in the absence of field (∼106 A/cm2 at 77 K) and a thickness d less than twice the magnetic field penetration depth λ. It is found that the jc(H) curves have a low-field plateau both for fields perpendicular and parallel to the film. In a magnetic field perpendicular to the film, the “effective pinning” plateau extends to a field corresponding to a density of Abrikosov vortices threading the film at which it is no longer favorable for them all to be pinned at edge dislocations in the interblock walls, and a fraction of them become unpinned. In contrast, in a field parallel to the film the end of the plateau is unrelated to depinning of threading vortices parallel to the film; instead, jc(H) decreases after the plateau region because the magnetic field parallel to the film weakens the pinning of vortices perpendicular to the film. The low-field plateau on jc(H) for an in-plane is wider than that for the case of normal magnetization. Therefore, the dependence of jc on the angle between H and the normal to the film has a single maximum at which the field is lying in the film plane. In films obtained by laser or electron-beam evaporation of YBa2Cu3O7−δ or its constituents, the measurements of jc on which were made by an inductive method, the decrease of jc with increasing field in the film plane begins at fields lower than the first critical field for penetration of the vortices into the film plane. For the magnetron-deposited film, where jc was measured by a transport method, this decrease of jc begins in a field much higher than that critical field. The possible relationships between the parameters of the jc(H) curves and the first critical field for penetration of the vortices into the film plane are discussed, including some which lead to different angular dependences of the critical current.
Electrical conductance of superconducting point contacts containing magnetic impurities
Authors: Beloborod’ko S. I.
Published: August 2003

The nonlinear electrical conductance of superconductor–constriction–normal-metal contacts containing magnetic impurities is investigated. The influence of the transparency of the potential barrier arising at the boundary of metals in contact on the behavior of the conductance and on the value of the excess current is analyzed. It is shown that in the case of a low transparency the differential conductance of such a contact is proportional to the electron density of states.
Magnetoelastic surface waves in a semi-infinite ferromagnet in an external magnetic field
Authors: Fridman Yu. A. , Spirin D. V.
Published: August 2003

The magnetoelastic wave spectra are found for a semi-infinite Heisenberg ferromagnet in an external magnetic field. Near the surface of the ferromagnet the interaction of Rayleigh waves with surface spin waves gives rise to an additional activation energy in the spin-wave spectrum and leads to a decrease in the sound velocity. The magnetoelastic coupling increases the difference between the velocity of surface acoustic waves and that of bulk sound waves.
Dynamics of domain walls with lines in rare-earth orthoferrites in magnetic and electric fields with exchange relaxation processes taken into account
Authors: Ekomasov E. G.
Published: August 2003

The influence of exchange relaxation on the dynamics of domain walls with a “fine structure” in rare-earth orthoferrites in the presence of external magnetic and electric fields is investigated. A system of differential equations is obtained which describe the dynamics of a domain wall with a solitary line. The dependence of the steady-state velocity of the domain wall and line on the values of the relaxation parameters and on the components of the magnetic and electric fields is found. The results are compared with the known experimental results.
Magnetic and transport properties of La0.8Sr0.2MnO3/La0.8Ca0.2MnO3 bilayer
Authors: Prokhorov V. G. , Kaminsky G. G. , Komashko V. A. , Lee Y. P. , Park J. S.
Published: August 2003

The effects of lattice strain on the magnetic and the transport properties of La0.8Sr0.2MnO3 films grown on an (001) LaAlO3 substrate and on a La0.8Ca0.2MnO3 layer were studied. It was observed that the metal-insulator and the ferromagnetic transitions occur at higher temperatures for the film deposited on La0.8Ca0.2MnO3 layer than on LaAlO3. The dependence of Curie temperature on the bulk and the Jahn—Teller strains were also determined.
Spectroscopy of bosonic excitations in manganite-based heterostructures
Authors: Belogolovskiı̆ M. A. , Revenko Yu. F. , Gerasimenko A. Yu. , Medvedev Yu. V. , Chernyak O. I. , Svistunov V. M. , Plitnik G.
Published: August 2003

The tunneling current transport is investigated in layered structures based on lanthanum manganite. The spectral function of the electron–boson interaction is reconstructed over a wide energy range. High-energy excitations localized in the barrier and near-barrier regions are revealed. The inelastic scattering of charge carriers on these states can lead to suppression of the magnetoresistance of tunnel junctions with increasing applied voltage.
Features of low-temperature exciton dynamics in J-aggregates with topological disorder
Authors: Malyukin Yu. V. , Katrich G. S. , Efimova S. L. , Sorokin A. V.
Published: August 2003

It is shown on the basis of an analysis of the J-band shape, luminescence spectra, and luminescence decay that self-trapping of excitons takes place in J-aggregates with strong topological disorder. A self-trapping barrier must be overcome for this to occur. A microscopic model of the self-trapped state is presented.
Low-frequency conductivity of a two-dimensional Wigner solid coupled to surface excitations of liquid helium
Authors: Monarkha Yu. P.
Published: August 2003

The line-shape and broadening of coupled phonon-ripplon resonances of Wigner-solid conductivity are studied using the memory function formalism. The analytic properties of the memory function permit coordinating the approximations of the secular equation for the coupled phonon-ripplon modes and the line-broadening of these resonances. Special attention is paid to the description of the strong-coupling regime realized for surface electrons on superfluid helium. For this case it is shown that the line-broadening is much smaller than and the line-shape is different from those found previously using the weak-coupling theory. Different theoretical approaches are compared with available experimental data.
Excitonic absorption spectra and phase transitions in thin films of the ferroelastics Cs2CdI4 and Rb2CdI4
Authors: Yunakova O. N. , Miloslavsky V. K. , Kovalenko E. N.
Published: August 2003

The absorption spectrum of thin films of the ferroelastics M2CdI4 (M=Cs, Rb) with a structure of the β-K2SO4 type is investigated in the energy range 3–6 eV and temperature range 90–420 K. It is found that both compounds are direct-gap insulators, and the low-frequency electronic and excitonic excitations are localized in the CdI42− structural elements of their crystal lattice. From the temperature dependence of the spectral absorption and the half-widths of the low-frequency excitonic bands in Rb2CdI4 it is found that there is a phase transition at 380 K (paraphase→incommensurate), a first-order phase transition at 320 K (incommensurate→first ferroelastic phase), and a second-order phase transition at 210 K (first→second ferroelastic phase). Similar, but less pronounced phase transitions are found in Cs2CdI4 at lower temperatures. In the ferroelastic phases of these compounds an additional broadening of the bands appears, apparently due to the scattering of excitons on strain fluctuations in the domain-wall regions.
Resonant scattering of solitons
Authors: Miroshnichenko A. E. , Flach S. , Malomed B.
Published: August 2003

We study the scattering of solitons in the nonlinear Schrödinger equation on local inhomogeneities which may give rise to resonant transmission and reflection. In both cases, we derive resonance conditions for the soliton’s velocity. The analytical predictions are tested numerically in regimes characterized by various time scales. Special attention is paid to intermode interactions and their effect on coherence, decoherence, and dephasing of plane-wave modes which build up the soliton.
Non-ergodicity induced by isotropic random perturbation
Authors: Matsumoto Kenji
Published: August 2003

We present a two-well Hamiltonian system in which isotropic random perturbation induces non-ergodic behavior where orbits tend to spend more time in one of two wells. It is numerically shown that this behavior is due to the difference in its orbital separation rates near the exits of wells.
Bifurcation cascade as chaotic itinerancy with multiple time scales
Authors: Fujimoto Koichi , Kaneko Kunihiko
Published: August 2003

A coupled chaotic system with a variety of time scales is studied. Under a certain condition, it is shown that a change in fast dynamics can influence slow dynamics with a huge time-scale difference, successively through propagation of correlation over elements. This propagation is given by bifurcation cascade, for which three conditions are found to be essential: strong correlation, bifurcation of fast element dynamics by the change of its parameter, and marginal stability. By using coupled Lorenz equation with multiple time scales, it is shown that chaotic itinerancy (CI) observed there leads for the system to satisfy the three conditions, and the bifurcation cascade occurs. Through the analysis of the CI, characteristic properties of the bifurcation cascade, asymmetry in propagation with regards to the time scale, and the universality of the results are discussed, with possible relevance to biological memory.
Theoretical study of ionization potentials and dissociation energies of Cnq+ fullerenes (n=50–60, q=0, 1 and 2)
Authors: Dı́az-Tendero Sergio , Alcamı́ Manuel , Martı́n Fernando
Published: August 2003

We have evaluated electronic energies of neutral, singly charged and doubly charged fullerenes with sizes n=50–60 using density functional (DFT) theory. For each value of the cluster charge, we have considered around 40 possible structures. We have found that, except for C522+, the most stable isomer always has the minimum possible number of C2 units between adjacent pentagons. We have evaluated adiabatic dissociation energies corresponding to the various dissociation channels leading to the emission of carbon dimers with different charges. Our findings for dissociation leading to C2 emission are in reasonable agreement with the latest experimental values. As a byproduct of our calculations, we have also evaluated the first and second adiabatic ionization potentials. Both dissociation energies and ionization potential are useful data to interpret fragmentation of fullerenes by impact of energetic photons, electrons and ions.