Nonlinear dynamics in sliding processes： the single-particle case

Dynamical behaviours of the motion of particles in a periodic potential under a constant driving velocity by a spring at one end are explored. In the stationary case, the stable equilibrium position of the particle experiences an elasticity instability transition. When the driving velocity is nonzero, depending on the elasticity coefficient and the pulling velocity, the system exhibits complicated and interesting dynamics, such as periodic and chaotic motions. The results obtained here may shed light on studies of dynamical processes in sliding friction.     

Increased Neural Efficiency in Visual Word Recognition: Evidence from Alterations in Event-Related Potentials and Multiscale Entropy

Visual word recognition is a relatively effortless process, but recent research suggests the system involved is malleable, with evidence of increases in behavioural efficiency after prolonged lexical decision task (LDT) performance. However, the extent of neural changes has yet to be characterized in this context. The neural changes that occur could be related to a shift from initially effortful performance that is supported by control-related processing, to efficient task performance that is supported by domain-specific processing. To investigate this, we replicated the British Lexicon Project, and had participants complete 16 h of LDT over several days. We recorded electroencephalography (EEG) at three intervals to track neural change during LDT performance and assessed event-related potentials and brain signal complexity. We found that response times decreased during LDT performance, and there was evidence of neural change through N170, P200, N400, and late positive component (LPC) amplitudes across the EEG sessions, which suggested a shift from control-related to domain-specific processing. We also found widespread complexity decreases alongside localized increases, suggesting that processing became more efficient with specific increases in processing flexibility. Together, these findings suggest that neural processing becomes more efficient and optimized to support prolonged LDT performance.     

Neural mechanisms underlying the facilitation of naming in aphasia using a semantic task: an fMRI study

Background

In the fruit fly, Drosophila melanogaster, serotonin functions both as a neurotransmitter to regulate larval feeding, and in the development of the stomatogastric feeding circuit. There is an inverse relationship between neuronal serotonin levels during late embryogenesis and the complexity of the serotonergic fibers projecting from the larval brain to the foregut, which correlate with perturbations in feeding, the functional output of the circuit. Dopamine does not modulate larval feeding, and dopaminergic fibers do not innervate the larval foregut. Since dopamine can function in central nervous system development, separate from its role as a neurotransmitter, the role of neuronal dopamine was assessed on the development, and mature function, of the 5-HT larval feeding circuit.

Results

Both decreased and increased neuronal dopamine levels in late embryogenesis during development of this circuit result in depressed levels of larval feeding. Perturbations in neuronal dopamine during this developmental period also result in greater branch complexity of the serotonergic fibers innervating the gut, as well as increased size and number of the serotonin-containing vesicles along the neurite length. This neurotrophic action for dopamine is modulated by the D₂ dopamine receptor expressed during late embryogenesis in central 5-HT neurons. Animals carrying transgenic RNAi constructs to knock down both dopamine and serotonin synthesis in the central nervous system display normal feeding and fiber architecture. However, disparate levels of neuronal dopamine and serotonin during development of the circuit result in abnormal gut fiber architecture and feeding behavior.

Conclusions

These results suggest that dopamine can exert a direct trophic influence on the development of a specific neural circuit, and that dopamine and serotonin may interact with each other to generate the neural architecture necessary for normal function of the circuit.     

Neural mechanisms underlying the facilitation of naming in aphasia using a semantic task: an fMRI study

ABSTRACT: BACKGROUND: Previous attempts to investigate the effects of semantic tasks on picture naming in both healthy controls and people with aphasia have typically been confounded by inclusion of the phonological word form of the target item. As a result, it is difficult to isolate any facilitatory effects of a semantically-focused task to either lexical-semantic or phonological processing. This functional magnetic resonance imaging (fMRI) study examined the neurological mechanisms underlying short-term (within minutes) and long-term (within days) facilitation of naming from a semantic task that did not include the phonological word form, in both participants with aphasia and age-matched controls. RESULTS: Behavioral results showed that a semantic task that did not include the phonological word form can successfully facilitate subsequent picture naming in both healthy controls and individuals with aphasia. The whole brain neuroimaging results for control participants identified a repetition enhancement effect in the short-term, with modulation of activity found in regions that have not traditionally been associated with semantic processing, such as the right lingual gyrus (extending to the precuneus) and the left inferior occipital gyrus (extending to the fusiform gyrus). In contrast, the participants with aphasia showed significant differences in activation over both the short- and the long-term for facilitated items, predominantly within either left hemisphere regions linked to semantic processing or their right hemisphere homologues. CONCLUSIONS: For control participants in this study, the short-lived facilitation effects of a prior semantic task that did not include the phonological word form were primarily driven by object priming and episodic memory mechanisms. However, facilitation effects appeared to engage a predominantly semantic network in participants with aphasia over both the short- and the long-term. The findings of the present study also suggest that right hemisphere involvement may be supportive rather than maladaptive, and that a large distributed perisylvian network in both cerebral hemispheres supports the facilitation of naming in individuals with aphasia.     

Evidence of marked glycogen variations in the characteristic Raman signatures of human embryonic stem cells

Human embryonic stem cells (hESCs) have typical Raman signatures, but specific factors that contribute to variations in these signatures have not been reported to date. Furthermore, variations due to the passaging that is necessary for hESC culture maintenance could potentially distort these signatures. It is therefore important to characterize the impact of these culture manipulations on the Raman spectra to gain a better understanding of the origins and nature of their variations. Here we report on the Raman microspectroscopy of hESCs samples from maintenance cultures, complemented with periodic acid Schiff (PAS, carbohydrates) and 4′‐6‐diamidino‐2‐phenlyindol (DAPI, nuclei) staining. The component predominantly responsible for variations between spectra was spectrally identified as glycogen. Variations in the Raman map of the 480 cm⁻¹ glycogen marker band corresponded with those of a PAS stain of the same sample area. The 785‐nm Raman microspectra of hESC cultures examined daily after passaging showed that the same nonrandom spectral variances occurred at all time points after passaging. The pattern of these variances was identified as being due to glycogen spectral components. Our results help validate the previously observed spectral signatures of hESCs and further delineate and characterize the variations that can be expected in these signatures under normal maintenance culture conditions, and aid distinguishing them from those corresponding to differentiation, thus providing a benchmark for future studies. Copyright © 2010 John Wiley & Sons, Ltd.     

Evidence for biogenic processes during formation of ferromanganese crusts from the Pacific Ocean: Implications of biologically induced mineralization

Ferromanganese [Fe/Mn] crusts formed on basaltic seamounts, gain considerable economic importance due to their high content of Co, Ni, Cu, Zn and Pt. The deposits are predominantly found in the Pacific Ocean in depths of over 1000 m. They are formed in the mixing layer between the upper oxygen-minimum zone and the lower oxygen-rich bottom zone. At present an almost exclusive abiogenic origin of crust formation is considered. We present evidence that the upper layers of the crusts from the Magellan Seamount cluster are very rich in coccoliths/coccolithophores (calcareous phytoplankton) belonging to different taxa. Rarely intact skeletons of these unicellular algae are found, while most of them are disintegrated into their composing prisms or crystals. Studies on the chemical composition of crust samples by high resolution SEM combined with an electron probe microanalyzer (EPMA) revealed that they are built of distinct stacked piles of individual compartments. In the center of such piles Mn is the dominant element, while the rims of the piles are rich in Fe (mineralization aspect). The compartments contain coccospheres usually at the basal part. Energy dispersive X-ray spectroscopy (EDX) analyses showed that those coccospheres contain, as expected, CaCO₃ but also Mn-oxide. Detailed analysis displayed on the surface of the coccolithophores a high level of CaCO₃ while the concentration of Mn-oxide is relatively small. With increasing distance from the coccolithophores the concentration of Mn-oxide increases on the expense of residual CaCO₃. We conclude that coccoliths/coccolithophores are crucial for the seed/nucleation phase of crust formation (biomineralization aspect). Subsequently, after the biologically induced mineralization phase Mn-oxide deposition proceeds “auto”catalytically.     

Evidence of two viscous relaxation processes in the collective dynamics of liquid lithium

New inelastic x-ray scattering experiments have been performed on liquid lithium in a wide wave vector range. With respect to the previous measurements, the instrumental resolution, improved up to 1. 5 meV, allows one to accurately investigate the dynamical processes determining the observed shape of the dynamic structure factor S(Q, omega). A detailed analysis of the line shapes shows the coexistence of relaxation processes with both slow and fast characteristic time scales, and therefore shows that pictures of the relaxation mechanisms based on a simple viscoelastic model must be abandoned.     

Primary nucleation processes in binary oxide growth: The case of MgO

The smallest forms of stoichiometric and non-stoichiometric MgO clusters appearing on the MgO(0 0 1) surface during the growth under atomic and/or molecular deposition are investigated from first-principles and empiric potentials. The basic entities (MgO molecule and (MgO)₂ cluster) result from a very exoenergetic and spontaneous redox reaction that involves directly the deposited species (Mg and O atoms, O₂ molecule). The stoichiometric clusters, resulting from the agglomeration of MgO molecules, are very stable under non-polar forms. Their formation energy is modelized, down to very small sizes, within an independent defect model. We point out the specificity of such clusters in the framework of the classical nucleation theory. The high-energy polar isomers are associated to destabilizing macroscopic electric fields and dipoles. These forms may nevertheless be strongly stabilized by incorporating extra Mg adatoms that give part of their valence shell to the cluster and decrease the total dipole in this way, illustrating the delicate coupling between chemistry and electrostatics in growth processes of oxides. Based on these considerations, we propose a scenario describing MgO growth both in the step-flow and in the nucleation regime.     

On nonlinear irreversible processes II: The case of even and odd variables

The nonlinear generalization of the theory of Onsager and Machlup presented in a previous paper is extended to the case in which both of even and odd variables exist simultaneously.The generalization of Onsager's principle of least dissipation for the general nonlinear process is presented based on the diffusion and the semi-classical approximations.     

Emission of electrons from mim systems: Discussion of processes in the cathode

Experimentally derived emission characteristics — the transfer ratio, angular distribution, energy distributionsN(E) andN(E _x ) and energy-angular distribution of emitted electrons — are discussed on the basis of our theoretical model of the sandwich cathode. It was found that electrons during their transfer through the cathode are scattered in the dielectric layer mostly by interactions with optical phonons and traps and in the top metal electrode by collisions with conduction electrons. Comparison of our model with experimental results gave us approximate values of mean free paths and further cathode parameters.     

Low energy activation processes in amorphous polymers - the case of selenium

We present an internal friction experiment in amorphous selenium at low frequency (30 kHz) and low temperature (4 K < T). Our results prove that, below the glass transition, there exists in amorphous selenium only one kind of thermal activated processes involving internal friction. We suggest that the underlying microscopic mechanisms are closely related to the polymeric amorphous structure and so should exist in any amorphous polymers.     

Polaron formation in superconducting cuprates: Evidence from the infrared reflectivity

Il Nuovo Cimento D - Evidence of polaron formation in superconducting cuprates is provided by infrared reflectivity spectra. In the Nd−Ce−Cu−O with T c≈20 K, polaron...     

Long memory properties in return and volatility: Evidence from the Korean stock market

In this paper, we study the dual long memory property of the Korean stock market. For this purpose, the ARFIMA-FIGARCH model is applied to two daily Korean stock price indices (KOSPI and KOSDAQ). Our empirical results indicate that long memory dynamics in the returns and volatility can be adequately estimated by the joint ARFIMA-FIGARCH model. We also found that the assumption of a skewed Student-t distribution is better for incorporating the tendency of asymmetric leptokurtosis in a return distribution.     

Complex tone processing in primary auditory cortex of the awake monkey. I. Neural ensemble correlates of roughness

Previous physiological studies [e.g., Bieser and Muller-Preuss, Exp. Brain Res. 108, 273-284 (1996); Schulze and Langner, J. Comp. Physiol. A 181, 651-663 (1997); Steinschneider et al., J. Acoust. Soc. Am. 104, 2935-2955 (1998)] have suggested that neural activity in primary auditory cortex (A1) phase-locked to the waveform envelope of complex sounds with low (<300 Hz) periodicities may represent a neural correlate of roughness perception. However, a correspondence between these temporal response patterns and human psychophysical boundaries of roughness has not yet been demonstrated. The present study examined whether the degree of synchronized phase-locked activity of neuronal ensembles in A1 of the awake monkey evoked by complex tones parallels human psychoacoustic data defining the existence region and frequency dependence of roughness. Stimuli consisted of three consecutive harmonics of fundamental frequencies (f(0)s) ranging from 25 to 4000 Hz. The center frequency of the complex tones was fixed at the best frequency (BF) of the cortical sites, which ranged from 0.3 to 10 kHz. Neural ensemble activity in the thalamorecipient zone (lower lamina III) and supragranular cortical laminae (upper lamina III and lamina II) was measured using multiunit activity and current source density techniques and the degree of phase-locking to the f0 was quantified by spectral analysis. In the thalamorecipient zone, the stimulus f0 at which phase-locking was maximal increased with BF and reached an upper limit between 75 and 150 Hz for BFs greater than about 3 kHz. Estimates of limiting phase-locking rates also increased with BF and approximated psychoacoustic values for the disappearance of roughness. These physiological relationships parallel human perceptual data and therefore support the relevance of phase-locked activity of neuronal ensembles in A1 for the physiological representation of roughness.