Origins of choice-related activity in mouse somatosensory cortex.

During perceptual decisions about faint or ambiguous sensory stimuli, even identical stimuli can produce different choices. Spike trains from sensory cortex neurons can predict trial-to-trial variability in choice. Choice-related spiking is widely studied as a way to link cortical activity to perception, but its origins remain unclear. Using imaging and electrophysiology, we found that mouse primary somatosensory cortex neurons showed robust choice-related activity during a tactile detection task. Spike trains from primary mechanoreceptive neurons did not predict choices about identical stimuli. Spike trains from thalamic relay neurons showed highly transient, weak choice-related activity. Intracellular recordings in cortex revealed a prolonged choice-related depolarization in most neurons that was not accounted for by feed-forward thalamic input. Top-down axons projecting from secondary to primary somatosensory cortex signaled choice. An intracellular measure of stimulus sensitivity determined which neurons converted choice-related depolarization into spiking. Our results reveal how choice-related spiking emerges across neural circuits and within single neurons

Testing a new luminosity/redshift indicator for γ\gamma-ray bursts

We have tested a relative spectral lag (RSL) method suggested earlier as a luminosity/redshift (or distance) estimator, using the generalized method by Schaefer & Collazzi. We find the derivations from the luminosity/redshift-RSL (L/R-RSL) relation are comparable with the corresponding observations. Applying the luminosity-RSL relation to two different GRB samples, we find that there exist no violators from the generalized test, namely the Nakar & Piran test and Li test. We also find that about 36 per cent of Schaefer's sample are outliers for the L/R-RSL relation within 1$\sigma$ confidence level, but no violators at 3$\sigma$ level within the current precision of L/R-RSL relation. An analysis of several potential outliers for other luminosity relations shows they can match the L/R-RSL relation well within an acceptable uncertainty. All the coincident results seem to suggest that this relation could be a potential tool for cosmological study.Comment: 7 pages, 6 figures and 1 table; Comments are welcom

Ghrelin, motilin in health and disease

Ghrelin is a 28 amino-acid peptide produced predominantly by the stomach. Two main isoforms of ghrelin are currently known (octanoyl- and desoctanoyl ghrelin). It functions as a circulating orexigenic hormone In addition, it has an effect on the nervous, cardiovascular and immune system. Current data suggest that ghrelin may have beneficial anti-inflammatory effects. Chapter 3 in this thesis primarily examines the relationship between ghrelin and inflammation in Crohn’s disease (CD). Modulation of inflammation with infliximab, a powerful anti-TNFα antibody therapy, can increase total ghrelin concentration by 25%. In addition, a normal physiological post-prandial decrease in ghrelin following a meal is restored when infused with infliximab, suggesting a dysregulation of ghrelin in CD patients with active inflammation. At cellular level, there is evidence that ghrelin may have an immunosuppressive effect on activated T-lymphocytes. Chapter 4 of this thesis examines the effect of ghrelin, a manufactured agonist and des-octanoyl ghrelin on NFκB activation on a human Blymphocyte cell line. This study demonstrated that exposure to octanoyl ghrelin confers an initial increase of NFκB activation in inactivated cells of up to 50% which suggests a pro-inflammatory effect. However, NFκB activation appears to decrease at much higher concentrations of octanoyl ghrelin, which may indicate toxicity at supra-physiological levels. Ghrelin is also involved in the regulation of gastric motility and has structural similarities to motilin. Symptoms of delayed gastric emptying can occur long after cancer chemotherapy has ended. Chapter 5 of this thesis compares the contractility and pro-motility neurotransmitter expression in chemotherapy and non-chemotherapy exposed stomach tissues obtained from patients undergoing surgery for oesophagogastric cancers. Chemotherapy exposed tissues have reduced contractility to carbachol and apparent destruction of the cholinergic activity. The tendency for ghrelin receptors to increase suggests an attempt to upregulate compensating systems. In conclusion, ghrelin can be altered by inflammation and may have beneficial effects on gastric motility

Lanczos exact diagonalization study of field-induced phase transition for Ising and Heisenberg antiferromagnets

Using an exact diagonalization treatment of Ising and Heisenberg model Hamiltonians, we study field-induced phase transition for two-dimensional antiferromagnets. For the system of Ising antiferromagnet the predicted field-induced phase transition is of first order, while for the system of Heisenberg antiferromagnet it is the second-order transition. We find from the exact diagonalization calculations that the second-order phase transition (metamagnetism) occurs through a spin-flop process as an intermediate step.Comment: 4 pages, 4 figure

Non-monotonic temperature dependent transport in graphene grown by Chemical Vapor Deposition

Temperature-dependent resistivity of graphene grown by chemical vapor deposition (CVD) is investigated. We observe in low mobility CVD graphene device a strong insulating behavior at low temperatures and a metallic behavior at high temperatures manifesting a non-monotonic in the temperature dependent resistivity.This feature is strongly affected by carrier density modulation. To understand this anomalous temperature dependence, we introduce thermal activation of charge carriers in electron-hole puddles induced by randomly distributed charged impurities. Observed temperature evolution of resistivity is then understood from the competition among thermal activation of charge carriers, temperature-dependent screening and phonon scattering effects. Our results imply that the transport property of transferred CVD-grown graphene is strongly influenced by the details of the environmentComment: 7 pages, 3 figure

Improving Database Quality through Eliminating Duplicate Records

Redundant or duplicate data are the most troublesome problem in database management and applications. Approximate field matching is the key solution to resolve the problem by identifying semantically equivalent string values in syntactically different representations. This paper considers token-based solutions and proposes a general field matching framework to generalize the field matching problem in different domains. By introducing a concept of String Matching Points (SMP) in string comparison, string matching accuracy and efficiency are improved, compared with other commonly-applied field matching algorithms. The paper discusses the development of field matching algorithms from the developed general framework. The framework and corresponding algorithm are tested on a public data set of the NASA publication abstract database. The approach can be applied to address the similar problems in other databases

Carbon Uptake Rates of Sea Ice Algae and Phytoplankton under Different Light Intensities in a Landfast Sea Ice Zone, Barrow, Alaska

To determine whether nitrogen or light exerts the most control for the rates of carbon production of ice algae and phytoplankton under the ice, nitrogen addition (NO3 or NH4) and light increment experiments were executed on the landfast sea ice of Barrow, Alaska, during the 2003 growing season by using a 13C-15N dual isotope tracer technique. The productivity of the bottom sea ice algae and phytoplankton at Barrow in 2003 was limited mainly by low light levels (approximately 0.3% of the surface irradiance) at the bottom under the snow-covered sea ice. The carbon and nitrate uptake rates of ice algae and phytoplankton increased as the incubation depth in the ice hole decreased and light intensity increased. In addition, under higher light conditions, the relative production of proteins of the bottom ice algae decreased, whereas the lipid proportion increased. The higher level of lipid synthesis of the ice algae might be significant to the nutrition of zooplankton and benthos because lipids are the most energy-dense biomolecules.Afin de déterminer si c’est l’azote ou la lumière qui exerce le plus grand contrôle sur les taux de production de carbone émanant des algues de glace et du phytoplancton sous la glace, des expériences consistant en l’ajout différentiel d’azote (NO3 ou NH4) et de lumière ont été effectuées sur la glace de mer côtière de Barrow, en Alaska, pendant la saison de croissance de 2003 grâce à une technique de traceurs d’isotopes mixtes de 13C-15N. La productivité des algues de glace de mer et de phytoplancton de fond à Barrow en 2003 a été surtout restreinte par les faibles taux de lumière (environ 0,3 % de l’éclairement de la surface) au fond, sous la glace de mer couverte de neige. Les taux d’absorption de carbone et d’azote chez les algues de glace et le phytoplancton augmentaient au fur et à mesure que la profondeur d’incubation du trou de glace diminuait et que l’intensité lumineuse s’intensifiait. De plus, lorsque les conditions de luminosité étaient plus grandes, la production relative de protéines des algues de glace de fond diminuait, tandis que la proportion de lipides grimpait. Le taux plus élevé de synthèse des lipides des algues de glace pourrait revêtir de l’importance dans la nutrition du zooplancton et du benthos parce que les lipides sont les biomolécules les plus denses en énergie

An XMM-Newton view of the young open cluster NGC 6231 III. Optically faint X-ray sources

We discuss the properties of the X-ray sources with faint optical counterparts in the very young open cluster NGC 6231. From their positions in the H-R diagram, we find that the bulk of these objects probably consists of low-mass pre-main sequence stars with masses in the range 0.3 to 3.0 M$_{\odot}$. The age distribution of these objects indicates that low-mass star formation in NGC 6231 started more than 10 Myr ago and culminated in a starburst-like event about 1 to 4 Myr ago when the bulk of the low-mass PMS stars as well as the massive cluster members formed. We find no evidence for a spatial age gradient that could point towards a sequential star formation process. Only a few X-ray sources have counterparts with a reddening exceeding the average value of the cluster or with infrared colours indicating the presence of a moderate near-IR excess. The X-ray spectra of the brightest PMS sources are best fitted by rather hard thermal plasma models and a significant fraction of these sources display flares in their light curve. The X-ray brightest flaring sources have decay times between 2 and 16 ks. The X-ray selected PMS stars in NGC 6231 have $\log{L_{\rm X}/L_{\rm bol}}$ values that increase strongly with decreasing bolometric luminosity and can reach a saturation level ($\log{L_{\rm X}/L_{\rm bol}} \sim -2.4$) for non-flaring sources and even more extreme values during flares.Comment: Accepted by MNRAS, 14pages, 19 figure