Rapid acquisition strategy for functional T1ρ mapping of the brain

Functional T1ρ mapping has been proposed as a method to assess pH and metabolism dynamics in the brain with high spatial and temporal resolution. The purpose of this work is to describe and evaluate a variant of the spin-locked echo-planar imaging sequence for functional T1ρ mapping at 3 T. The proposed sequence rapidly acquires a time series of T1ρ maps with 4.0 second temporal resolution and 10 slices of volumetric coverage. Simulation, phantom, and in vivo experiments are used to evaluate many aspects of the sequence and its implementation including fidelity of measured T1ρ dynamics, potential confounds to the T1ρ response, imaging parameter tradeoffs, time series analysis approaches, and differences compared to blood oxygen level dependent functional magnetic resonance imaging. It is shown that the high temporal resolution and volumetric coverage of the sequence are obtained with some expense including underestimation of the T1ρ response, sensitivity to T1 dynamics, and reduced signal-to-noise ratio. In vivo studies using a flashing checkerboard functional magnetic resonance imaging paradigm suggest differences between T1ρ and blood oxygen level dependent activation patterns. Possible sources of the functional T1ρ response and potential sequence improvements are discussed. The capability of T1ρ to map whole-brain pH and metabolism dynamics with high temporal and spatial resolution is potentially unique and warrants further investigation and development.     

Direct observation of signal evolution of slow and fast light in media with saturated and reverse saturated absorption

Recently, many researchers had reported their work about sub- and superluminal propagation. And several experiments had demonstrated the signal evolution of slow and fast light. In this letter, the authors described a simple experiment for the tracing of the light signal in saturated absorption (SA) and reverse saturated absorption (RSA) media, firstly. We had, directly, observed the evolution of slow and fast signals with different waveforms that traveled in a ruby crystal and C₆₀. Through tracking the signal when slow light (v _g ≪ c) and fast light (v _g<0) was observed in a ruby crystal and C₆₀, we concluded that asymmetrical absorption on the periodical signal could account for the generation of slow and fast light in SA and RSA media.     

Distribution of light alkanes in the reaction of graphite hydrogenation at pressure of 0.1–7.8 GPa and temperatures of 1000–1350°C

ABSTRACT

We studied the effect of pressure and temperature on the hydrocarbon (HC) chain length distribution and total amount of HCs in the reaction of direct graphite hydrogenation at pressures of 0.1–7.8?GPa and temperatures of 1000–1350°C. An increase in pressure was found to lead both to an increase in the absolute yield of HCs due to direct graphite hydrogenation and to chain elongation of HC products. Light alkanes predominate among HCs in the entire studied range of P–T parameters. However, their concentration in quenched fluids increases as pressure is elevated, from less than 10?rel.% at 0.1?GPa to more than 40–50?rel.% at P?≥?3.8?GPa. Methane is actually the only light alkane among reaction products at 0.1?GPa and 1000°C, while it is a minor component at 7.8?GPa and 1350°C. The most stable alkane at pressures above 3.8?GPa is ethane (C₂H₆).     

An observation of Relationship between the Fine Structure Constant and the Gibbs Phenomenon in Fourier Analysis

A value given by a simple mathematical expression is proposed,which is close to the fine structure constant given by 1998 CODATA recommended values of the fundamental physical constants up to relative accuracy 10^-7.This expression is related closely with the value of the overshoot of the Gibbs phenomenon in the Fourier analysis.     

Dependence of sonochemical parameters on the platinization of rutile titania – An observation of a pronounced increase in photocatalytic efficiencies

Using a standing wave sonochemical reactor (SWSR), the influences of parameters of ultrasonic power input, sonication time, sonication temperature and the amount of propanol (which generates the reducing radicals) were systemically investigated to ascertain and optimize the best conditions for the sonochemical reduction of Pt from its precursor hexachloroplatinic acid and then its deposition on rutile TiO₂ (platinization of rutile titania) catalysts. Catalytic activity of the prepared platinized catalysts was tested in the reaction of methyl orange degradation. The results of photocatalytic activity study in the degradation of methyl orange further demonstrate that sonochemically as-prepared Pt/TiO₂ catalysts show a pronounced increase (～2 times) in photodegradation, even with a deposition of small amounts of platinum (1.4 wt.%), as compared to the unsupported or naked rutile titania. Although there are various parameters that influence the sonochemical platinization of rutile titania, the present optimization results clearly indicate that the best photocatalytic degradation of methyl orange can be obtained when the experimental conditions of the preparation were with an input power of 50 W, an initial hexachloroplatinic acid volume of 70 ml (which results into 1.4 wt.% Pt on TiO₂), sonication time of 90 min, 0.18 g of propanol and a temperature of 10 °C were adopted. The method of ultrasound application to prepare metal supported semiconductors has many advantages such as convenience, safety and high efficiency. Furthermore, it is hopeful that this optimization study can also be extended to the generation of similar metal supported semiconductors.     

Mössbauer study of the microscopic surrounding of co atoms implanted in si and ge below the full amorphization limit

Mössbauer spectroscopy on ⁵⁷Co implanted into Si and Ge at doses between 10¹¹ and 10¹⁵ atoms/cm² supports the single track amorphization model. Calculations based on linear cascade theory do not give quantitative agreement with the experiment.     

Constraints on distribution amplitudes of the η and η′ mesons in the light of new experimental results

Constraints on the distribution amplitudes of the SU _f (3) singlet η ₁ and octet η ₈ states are obtained from a comparison of the theoretical predictions for the η γ and η′γ electromagnetic transition form factors with experimental data of the CLEO and BaBar Collaborations. In calculations of the form factors F _η(η′)γ (Q ²) the power-suppressed corrections arising from the end-point integration regions x→0,1 are taken into account by employing the infrared renormalon approach. It is demonstrated that the power-suppressed corrections allow one to describe the data on the η γ and η′γ transitions within a framework of the SU _f (3) octet–singlet basis using one mixing angle for both the physical states and decay constants.     

Evaluation of the brain pH using a phosphorus magnetic resonance spectroscopy technique – a comparison of women and men

The aim of this study was to determine the reference value of pH in healthy women and men using the phosphorus magnetic resonance spectroscopy technique. The brains of 65 young volunteers were examined. The intracellular pH was calculated in the group of women and the group of men. In both groups, the average pH was slightly alkaline (respectively 7.10?±?0.08 and 7.08?±?0.12). No statistically significant sex difference in brain pH was found. Thus, in case if this method is used to estimate possible brain pathology in the young population, it is not needed to take the gender factor into consideration.     

Distribution of nuclear quadrupole splittings in amorphous materials and the topology of the (Vzz, η)-parameter space

In structural investigations of amorphous materials by determination of nuclear quadrupole splittings, the connectivity of the region of non-zero probability density in the space of the splitting parameters V_zz and is important. The conventional presentation of the parameter plane conceals the continuous connection between regions of positive and negative V_zz via the common boundary defined by =1. A new conceptual view of the (V_zz, )-plane is proposed which clearly expresses its topological structure.     

Response characteristics of an ascending auditory neuron AN3 and its projections in the brain of the bushcricket Gampsocleis grationsa

The phonotaxis of bushcrickets demonstrates that they have goodcapability of recognizing conspecific songs and locating the sound source,which bases on complicated auditory mechanisms of the central nervoussystem(CNS).This article describes the response characteristics of AN3,an auditory ascending neuron in the prothoracic ganglion,and its projec-tions within the brain.The AN3,with a quasi-tonic discharge pattern,has high sensitivity,directionality and ability to encode sound intensity.Therefore,it plays an important role in auditory information processingof CNS.Its projections in the brain are mainly concentrated in the lateralzone of the deutencephalon,where synaptically connecting local auditoryinterneurons in the brain.     

On the observation of intrinsic defects in (Co1-xInx)1-δO by PAC

We report on the results of Perturbed Angular Correlation measurements in polycrystalline (Co_1-xIn_x)_1-δO samples (x = 0.04 and 0.8 at.%) using ion-implanted ¹¹¹In tracers. The temperature and the oxygen activity (adjusted via a CO/CO₂ mixture) were chosen in such a way as to be able to observe defect trapping and detrapping in thermal equilibrium. The results are compared with those obtained for (Co_1-xIn_x)_1-δO (x= 0.04 at.%) rapidly cooled to 350 K and for CoO. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparison of α-chloralose,medetomidine and isoflurane anesthesia for functional connectivity mapping in the rat

Functional connectivity measures based upon low-frequency blood-oxygenation-level-dependent functional magnetic resonance imaging (BOLD fMRI) signal fluctuations have become a widely used tool for investigating spontaneous brain activity in humans. Still unknown, however, is the precise relationship between neural activity, the hemodynamic response and fluctuations in the MRI signal. Recent work from several groups had shown that correlated low-frequency fluctuations in the BOLD signal can be detected in the anesthetized rat — a first step toward elucidating this relationship. Building on this preliminary work, through this study, we demonstrate that functional connectivity observed in the rat depends strongly on the type of anesthesia used. Power spectra of spontaneous fluctuations and the cross-correlation-based connectivity maps from rats anesthetized with α-chloralose, medetomidine or isoflurane are presented using a high-temporal-resolution imaging sequence that ensures minimal contamination from physiological noise. The results show less localized correlation in rats anesthetized with isoflurane as compared with rats anesthetized with α-chloralose or medetomidine. These experiments highlight the utility of using different types of anesthesia to explore the fundamental physiological relationships of the BOLD signal and suggest that the mechanisms contributing to functional connectivity involve a complicated relationship between changes in neural activity, neurovascular coupling and vascular reactivity.     

Plasma Dynamic Synthesis of Nanocrystalline WC1 – x and the Dependence of the Product Structure on the Ratio of Precursors

Technical Physics - The results of plasma dynamic synthesis of nanocrystalline cubic tungsten carbide using a system based on a coaxial magnetoplasma accelerator are presented. It is found that an...     

Phase Formation and Electronic Structure Peculiarities in the Al1 – xSi x Film Composites under the Conditions of Magnetron and Ion-Beam Sputtering

Physics of the Solid State - The peculiarities of the phase composition and electronic structure of aluminum–silicon composite films near the Al0.75Si0.25 composition obtained by the...     

Features of the Percolation Scheme of Vibrational Spectrum Reconstruction in the Ga1 – xAl x P Alloy

Specific features of the properties of Ga–P lattice vibrations have been investigated using the percolation model of a mixed Ga_{1 – x}Al _x P crystal (alloy) with zero lattice mismatch between binary components of the alloy. In contrast to other two-mode alloy systems, in Ga_{1 – x}Al _x P a percolation splitting of δ ~ 13 cm^–1 is observed for the low-frequency mode of GaP-like vibrations. An additional GaP mode (one of the percolation doublet components) split from the fundamental mode is observed for the GaP-rich alloy, which coincides in frequency with the gap corresponding to the zero density of one-phonon states of the GaP crystal. The vibrational spectrum of impurity Al in the GaP crystal has been calculated using the theory of crystal lattice dynamics. Upon substitution of lighter Al for the Ga atom, the calculated spectrum includes, along with the local mode, a singularity near the gap with the zero density of phonon states of the GaP crystal, which coincides with the mode observed experimentally at a frequency of 378 cm^–1 in the Ga_{1 – x}Al _x P (x < 0.4) alloy.

     

Harbingers and latecomers – the order of appearance of exact coherent structures in plane Poiseuille flow

The transition to turbulence in plane Poiseuille flow (PPF) is connected with the presence of exact coherent structures. We here discuss a variety of different structures that are relevant for the transition, compare the critical Reynolds numbers and optimal wavelengths for their appearance, and explore the differences between flows operating at constant mass flux or at constant pressure drop. The Reynolds numbers quoted here are based on the mean flow velocity and refer to constant mass flux. Reynolds numbers based on constant pressure drop are always higher. The Tollmien–Schlichting (TS) waves bifurcate subcritically from the laminar profile at Re = 5772 at wavelength 6.16 and reach down to Re = 2610 at a different optimal wave length of 4.65. Their streamwise localised counter part bifurcates at the even lower value Re = 2334. Three-dimensional exact solutions appear at much lower Reynolds numbers. We describe one exact solutions that has a critical Reynolds number of 316. Streamwise localised versions of this state require higher Reynolds numbers, with the lowest bifurcation occurring near Re = 1018. The analysis shows that the various branches of TS-waves cannot be connected with transition observed near Re ≈ 1000 and that the exact coherent structures related to downstream vortices come in at lower Reynolds numbers and prepare for the transition.