Effects of phase regression on high-resolution functional MRI of the primary visual cortex

High-resolution functional MRI studies have become a powerful tool to non-invasively probe the sub-millimeter functional organization of the human cortex. Advances in MR hardware, imaging techniques and sophisticated post-processing methods have allowed high resolution fMRI to be used in both the clinical and academic neurosciences. However, consensus within the community regarding the use of gradient echo (GE) or spin echo (SE) based acquisition remains largely divided. On one hand, GE provides a high temporal signal-to-noise ratio (tSNR) technique sensitive to both the macro- and micro-vascular signal while SE based methods are more specific to microvasculature but suffer from lower tSNR and specific absorption rate limitations, especially at high field and with short repetition times. Fortunately, the phase of the GE-EPI signal is sensitive to vessel size and this provides a potential avenue to reduce the macrovascular weighting of the signal (phase regression, Menon 2002). In order to determine the efficacy of this technique at high-resolution, phase regression was applied to GE-EPI timeseries and compared to SE-EPI to determine if GE-EPI\u27s specificity to the microvascular compartment improved. To do this, functional data was collected from seven subjects on a neuro-optimized 7 T system at 800 μm isotropic resolution with both GE-EPI and SE-EPI while observing an 8 Hz contrast reversing checkerboard. Phase data from the GE-EPI was used to create a microvasculature-weighted time series (GE-EPI-PR). Anatomical imaging (MP2RAGE) was also collected to allow for surface segmentation so that the functional results could be projected onto a surface. A multi-echo gradient echo sequence was collected and used to identify venous vasculature. The GE-EPI-PR surface activation maps showed a high qualitative similarity with SE-EPI and also produced laminar activity profiles similar to SE-EPI. When the GE-EPI and GE-EPI-PR distributions were compared to SE-EPI it was shown that GE-EPI-PR had similar distribution characteristics to SE-EPI (p \u3c 0.05) across the top 60% of cortex. Furthermore, it was shown that GE-EPI-PR has a higher contrast-to-noise ratio (0.5 ± 0.2, mean ± std. dev. across layers) than SE-EPI (0.27 ± 0.07) demonstrating the technique has higher sensitivity than SE-EPI. Taken together this evidence suggests phase regression is a useful method in low SNR studies such as high-resolution fMRI

Exact Conductance through Point Contacts in the ν=1/3\nu =1/3 Fractional Quantum Hall Effect

The conductance for tunneling through a point contact between two $\nu =1/3$ quantum Hall edges is described by a universal scaling function, which has recently been measured experimentally. We compute this universal function exactly, by using the thermodynamic Bethe ansatz and a Boltzmann equation.Comment: 10 pages, 1 figur

Halothane potentiates the alcohol-adduct induced TNF-alpha release in heart endothelial cells

BACKGROUND: The possibility exists for major complications to occur when individuals are intoxicated with alcohol prior to anesthetization. Halothane is an anesthetic that can be metabolized by the liver into a highly reactive product, trifluoroacetyl chloride, which reacts with endogenous proteins to form a trifluoroacetyl-adduct (TFA-adduct). The MAA-adduct which is formed by acetaldehyde (AA) and malondialdehyde reacting with endogenous proteins, has been found in both patients and animals chronically consuming alcohol. These TFA and MAA-adducts have been shown to cause the release of inflammatory products by various cell types. If both adducts share a similar mechanism of cell activation, receiving halothane anesthesia while intoxicated with alcohol could exacerbate the inflammatory response and lead to cardiovascular injury. METHODS: We have recently demonstrated that the MAA-adduct induces tumor necrosis factor-α (TNF-α) release by heart endothelial cells (HECs). In this study, pair and alcohol-fed rats were randomized to receive halothane pretreatments intra peritoneal. Following the pretreatments, the intact heart was removed, HECs were isolated and stimulated with unmodified bovine serum albumin (Alb), MAA-modified Alb (MAA-Alb), Hexyl-MAA, or lipopolysaccharide (LPS), and supernatant concentrations of TNF-α were measured by ELISA. RESULTS: Halothane pre-treated rat HECs released significantly greater TNF-α concentration following MAA-adduct and LPS stimulation than the non-halothane pre-treated in both pair and alcohol-fed rats, but was significantly greater in the alcohol-fed rats. CONCLUSION: These results demonstrate that halothane and MAA-adduct pre-treatment increases the inflammatory response (TNF-α release). Also, these results suggest that halothane exposure may increase the risk of alcohol-induced heart injury, since halothane pre-treatment potentiates the HEC TNF-α release measured following both MAA-Alb and LPS stimulation

Spin-SS generalization of fractional exclusion statistics

We study fractional exclusion statistics for quantum systems with SU(2) symmetry (arbitrary spin $S$), by generalizing the thermodynamic equations with squeezed strings proposed by Ha and Haldane. The bare hole distributions as well as the statistical interaction defined by an infinite-dimensional matrix specify the universality class. It is shown that the system is described by the level-$2S$ WZW model and has a close relationship to non-abelian fractional quantum Hall states. As a low-energy effective theory, the sector of {\it massless} Z$_{2S}$ parafermions is extracted, whose statistical interaction is given by a finite-dimensional matrix.Comment: 11pages, REVTE

Solving 1d plasmas and 2d boundary problems using Jack polynomials and functional relations

The general one-dimensional ``log-sine'' gas is defined by restricting the positive and negative charges of a two-dimensional Coulomb gas to live on a circle. Depending on charge constraints, this problem is equivalent to different boundary field theories. We study the electrically neutral case, which is equivalent to a two-dimensional free boson with an impurity cosine potential. We use two different methods: a perturbative one based on Jack symmetric functions, and a non-perturbative one based on the thermodynamic Bethe ansatz and functional relations. The first method allows us to compute explicitly all coefficients in the virial expansion of the free energy and the experimentally-measurable conductance. Some results for correlation functions are also presented. The second method provides in particular a surprising fluctuation-dissipation relation between the free energy and the conductance.Comment: 19 page

Scaling Limit of the Ising Model in a Field

The dilute A_3 model is a solvable IRF (interaction round a face) model with three local states and adjacency conditions encoded by the Dynkin diagram of the Lie algebra A_3. It can be regarded as a solvable version of an Ising model at the critical temperature in a magnetic field. One therefore expects the scaling limit to be governed by Zamolodchikov's integrable perturbation of the c=1/2 conformal field theory. Indeed, a recent thermodynamic Bethe Ansatz approach succeeded to unveil the corresponding E_8 structure under certain assumptions on the nature of the Bethe Ansatz solutions. In order to check these conjectures, we perform a detailed numerical investigation of the solutions of the Bethe Ansatz equations for the critical and off-critical model. Scaling functions for the ground-state corrections and for the lowest spectral gaps are obtained, which give very precise numerical results for the lowest mass ratios in the massive scaling limit. While these agree perfectly with the E_8 mass ratios, we observe one state which seems to violate the assumptions underlying the thermodynamic Bethe Ansatz calculation. We also analyze the critical spectrum of the dilute A_3 model, which exhibits massive excitations on top of the massless states of the Ising conformal field theory.Comment: 29 pages, RevTeX, 11 PostScript figures included by epsf, using amssymb.sty (v2.2

Metabolism of a hybrid algal galactan by members of the human gut microbiome

Native porphyran is a hybrid of porphryan and agarose. As a common element of edible seaweed, this algal galactan is a frequent component of the human diet. Bacterial members of the human gut microbiota have acquired polysaccharide utilization loci (PULs) that enable the metabolism of porphyran or agarose. However, the molecular mechanisms that underlie the deconstruction and use of native porphyran remains incompletely defined. Here, we have studied two human gut bacteria, porphyranolytic Bacteroides plebeius and agarolytic Bacteroidesuniformis, that target native porphyran. This reveals an exo-based cycle of porphyran depolymerization that incorporates a keystone sulfatase. In both PULs this cycle also works together with a PUL-encoded agarose depolymerizing machinery to synergistically reduce native porphyran to monosaccharides. This provides a framework for understanding the deconstruction of a hybrid algal galactan, and insight into the competitive and/or syntrophic relationship of gut microbiota members that target rare nutrients

Initiation and propagation of coronal mass ejections

This paper reviews recent progress in the research on the initiation and propagation of CMEs. In the initiation part, several trigger mechanisms are discussed; In the propagation part, the observations and modelings of EIT waves/dimmings, as the EUV counterparts of CMEs, are described.Comment: 8 pages, 1 figure, an invited review, to appear in J. Astrophys. Astro