Near infrared spectroscopy to study the brain: an overview

This paper gives an overview of principles, technologies, and applications using near infrared spectrometry and imaging (NIRS and NIRI) to study brain function. The physical background is reviewed and technologies and their properties are discussed. Advantages and limitations of NIRI are described. The basic functional signals obtained by NIRI, the neuronal and the hemodynamic signal are described and in particular publications about the former are reviewed. Applications in adults and neonates are reviewed, too.     

Rotation does not enhance mixing in the mixmaster universe

We investigate closed rotating cosmologies to determine if rotation leads to an enhancement of causal mixing proposed by Misner to guarantee the homogeneity of such models. We conclude that rotation cannot lead to significantly more efficient mixing than occurs in non-rotating models. Since arguments presented by Doroshkevich and Novikov and calculations made by Chitre give very small probability of mixing in nonrotating models, we therefore conclude that a plausible explanation of the homogeneity of the universe cannot be found within the framework of classical General Relativity. Such an explanation may lie in quantum effects on mixing near the singularity.Supported in part by NSF Grant No. GP-20033, by NASA Grant No. NGR-21-002-010, and by the Center for Theoretical Physics, University of Maryland.     

The Tail does not Determine the Size of the Giant

The size of the giant component in the configuration model, measured by the asymptotic fraction of vertices in the component, is given by a well-known expression involving the generating function of the degree distribution. In this note, we argue that the distribution over small degrees is more important for the size of the giant component than the precise distribution over very large degrees. In particular, the tail behavior of the degree distribution does not play the same crucial role for the size of the giant as it does for many other properties of the graph. Upper and lower bounds for the component size are derived for an arbitrary given distribution over small degrees \(d\le L\) and given expected degree, and numerical implementations show that these bounds are close already for small values of L. On the other hand, examples illustrate that, for a fixed degree tail, the component size can vary substantially depending on the distribution over small degrees.     

Total reaction cross section for 12C + 16O below the Coulomb barrier

The energy dependence of the total reaction cross section, σ(E), for ¹²C + ¹⁶O has been measured over the range E_c.m. = 4–12 MeV, by detecting γ-rays from the various possible residual nuclei with two large NaI(Tl) detectors placed close to the target. This technique for measuring total reaction cross sections was explored in some detail and shown to yield reliable values for σ(E). Although the principal emphasis of this work was placed on obtaining reliable cross sections, a preliminary study has been made of the suitability of various methods for extrapolating the cross section to still lower energies. The statistical model provides a good fit with a reasonable value for the strength function, 〈γ²〉/〈D〉 = 6.8 × 10^?2, over the range E_c.m. = 6.5–12 MeV, but predicts cross sections which are much too large for E_c.m. < 6.5 MeV. Optical model fits at low energies are especially sensitive to the radius and diffuseness of the imaginary component of the potential and, since these are still poorly known at present, such extrapolations may be wrong by orders of magnitude. A simple barrier penetration model gives a moderately good fit to the data and seems to provide the safest extrapolation to lower energies at the present time. It is clear, however, that our knowledge of the heavy-ion reaction mechanism at low energies is incomplete, and that cross-section measurements at still lower energies are needed to establish the correct procedure for extrapolating heavy-ion reaction cross sections to low energies.     

Reduced blood brain barrier breakdown in P-selectin deficient mice following transient ischemic stroke: a future therapeutic target for treatment of stroke

Background  

The link between early blood- brain barrier (BBB) breakdown and endothelial cell activation in acute stroke remain poorly defined. We hypothesized that P-selectin, a mediator of the early phase of leukocyte recruitment in acute ischemia is also a major contributor to early BBB dysfunction following stroke. This was investigated by examining the relationship between BBB alterations following transient ischemic stroke and expression of cellular adhesion molecule P-selectin using a combination of magnetic resonance molecular imaging (MRMI), intravital microscopy and immunohistochemistry. MRMI was performed using the contrast, gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) conjugated to Sialyl Lewis X (Sle^x) where the latter is known to bind to activated endothelium via E- or P selectins. Middle cerebral artery occlusion was induced in male C57/BL 6 wild-type (WT) mice and P-selectin-knockout (KO) mice. At 24 hours following middle cerebral artery occlusion, T₁ maps were acquired prior to and following contrast injection. In addition to measuring P- and E-selectin expression in brain homogenates, alterations in BBB function were determined immunohistochemically by assessing the extravasation of immunoglobulin G (IgG) or staining for polymorphonuclear (PMN) leukocytes. In vivo assessment of BBB dysfunction was also investigated optically using intravital microscopy of the pial circulation following the injection of Fluorescein Isothiocyanate (FITC)-dextran (MW 2000 kDa).     

At least one Lyapunov exponent vanishes if the trajectory of an attractor does not contain a fixed point

We treat a set of coupled ordinary nonlinear differential equations and show that for each trajectory which belongs to an attractor (or to its basin) and which does not contain a fixed point, at least one Lyapunov exponent vanishes.     

Preventing transition to turbulence: a viscosity stratification does not always help

In channel flows a step on the route to turbulence is the formation of streaks, often due to algebraic growth of disturbances. While a variation of viscosity in the gradient direction often plays a large role in laminar-turbulent transition in shear flows, we show that it has, surprisingly, little effect on the algebraic growth. Nonuniform viscosity therefore may not always work as a flow-control strategy for maintaining the flow as laminar.     

High-frequency ultrasound backscattering by blood: analytical and semianalytical models of the erythrocyte cross section

This paper proposes analytical and semianalytical models of the ultrasonic backscattering cross section (BCS) of various geometrical shapes mimicking a red blood cell (RBC) for frequencies varying from 0 to 90 MHz. By assuming the first-order Born approximation and by modeling the shape of a RBC by a realistic biconcave volume, different scattering behaviors were identified for increasing frequencies. For frequencies below 18 MHz, a RBC can be considered a Rayleigh scatterer. For frequencies less than 39 MHz, the general concept of acoustic inertia tensor is introduced to describe the variation of the BCS with the frequency and the incidence direction. For frequencies below 90 MHz, ultrasound backscattering by a RBC is equivalent to backscattering by a cylinder of height 2 microm and diameter 7.8 microm. These results lay the basis of ultrasonic characterization of RBC aggregation by proposing a method that distinguishes the contribution of the individual RBC acoustical characteristics from collective effects, on the global blood backscattering coefficient. A new method of data reduction that models the frequency dependence of the ultrasonic BCS of micron-sized weak scatterers is also proposed. Applications of this method are in tissue characterization as well as in hematology.     

Why the high-lying glueball does not mix with the neighbouring f 0

Chiral symmetry restoration in high-lying hadron spectra implies that hadrons which belong to different irreducible representations of the parity-chiral group cannot mix. This explains why the , which was suggested to be a glueball, and hence must belong to the scalar (0,0) representation of the chiral group, cannot mix with the neighbouring , which was interpreted as a state, and that belongs to the (1/2,1/2) representation of the chiral group. If confirmed, then we have an access to a true glueball of QCD.Received: 18 July 2003, Published online: 5 January 2004PACS: 12.39.Mk Glueball and nonstandard multi-quark/gluon states - 11.30.Rd Chiral symmetries     

Detergency of stainless steel surface soiled with human brain homogenate: an XPS study

In the detergency field of re-usable medical devices, a special attention is focused on the non conventional transmissible agent called prions which is a proteinaceous infectious agent. Few cleaning procedures are effective against prions and few techniques are available to study cleaning effectiveness with respect to proteins in general. In our study, X-ray photoelectron spectroscopy (XPS) has been used to evaluate the effectiveness of detergent formulations to remove proteins from stainless steel surface soiled with a brain homogenate (BH) from human origin. Our results showed that XPS is a reliable surface analysis technique to study chemical species remaining on surface and substrate properties after cleaning procedures. A semi-quantitative evaluation of the detergency effectiveness could also be performed.     

Beryllium carbide as diffusion barrier against Cu:First-principles study

Beryllium carbide is used in inertial confinement fusion(ICF) capsule ablation material due to its low atomic number,low opacity, and high melting point properties. We used the method of climbing image nudged elastic band(CINEB) to calculate the diffusion barrier of copper atom in the crystal of beryllium and beryllium carbide. The diffusion barrier of copper atom in crystal beryllium is only 0.79 eV, and the barrier in beryllium carbide is larger than 2.85 eV. The three structures of beryllium carbide: anti-fluorite Be_2C, Be_2C-Ⅰ, and Be_2C-Ⅲ have a good blocking effect to the diffusion of copper atom. Among them, the Be_2C-Ⅲ structure has the highest diffusion barrier of 6.09 eV. Our research can provide useful help for studying Cu diffusion barrier materials.     

Higgs production at the LHC: an update on cross sections and branching ratios

New theoretical and experimental information motivates a re-examination of the Standard Model Higgs production rates at the LHC pp collider. We present calculations of the relevant cross sections and branching ratios, including recently calculated QCD next-to-leading order corrections, new parton distributions fitted to recent HERA structure function data, and new values for electroweak input parameters, in particular for the top quark mass. Cross sections are calculated at two collider energies, √s = 10 TeV and 14 TeV.     

Remarks on the fact that the uncertainty principle does not determine the quantum state

We discuss the relation between density matrices and the uncertainty principle; this allows us to justify and explain a recent statement by Man'ko et al. We thereafter use Hardy's uncertainty principle to prove a new result for Wigner distributions dominated by a Gaussian and we relate this result to the coarse-graining of phase-space by “quantum blobs”.     

Synchrotron radiation circular dichroism spectroscopy: vacuum ultraviolet irradiation does not damage protein integrity

Synchrotron radiation circular dichroism (SRCD) spectroscopy is an emerging technique for sensitive determination of protein secondary structures and for monitoring of conformational changes. An important issue for its adoption as a useful technique is whether the high-intensity low-wavelength vacuum ultraviolet radiation in the SRCD chemically damages proteins. In this paper, using horse myoglobin as a test sample, it is shown that extensive irradiation in the SRCD does not produce any change in the chemical nature of the protein as detected by either SDS gel electrophoresis or mass spectrometry. In addition, no changes in the protein secondary structure are detectable from the SRCD spectra after extensive exposure to the SRCD beam.     

Fragmentation of rods by cascading cracks: why spaghetti does not break in half

When thin brittle rods such as dry spaghetti pasta are bent beyond their limit curvature, they often break into more than two pieces, typically three or four. With the aim of understanding these multiple breakings, we study the dynamics of a bent rod that is suddenly released at one end. We find that the sudden relaxation of the curvature at this end leads to a burst of flexural waves, whose dynamics are described by a self-similar solution with no adjustable parameters. These flexural waves locally increase the curvature in the rod, and we argue that this counterintuitive mechanism is responsible for the fragmentation of brittle rods under bending. A simple experiment supporting the claim is presented.     

Squeezing the local oscillator does not improve signal-to-noise ratio in heterodyne laser radar

The signal-to-noise ratio for heterodyne laser radar with a coherent target-return beam and a squeezed local-oscillator beam is lower than that obtained using a coherent local oscillator, regardless of the method employed to combine the beams at the detector.