High Pressure Effects on Thermal Properties of MgO

Using the non-empirical Variational Induced Breathing (VIB) model, the thermal properties of periclase (MgO) under high pressures and temperatures are investigated using molecular dynamics, which includes all anharmonic effects. Equations of state for temperatures up to 3000K and pressures up to 310 GPa were calculated. Bulk modulus, thermal expansivity, Anderson-Gruneisen parameter, thermal pressure, Gruneisen parameter and their pressure and temperature dependencies are studied in order to better understand high pressure effects on thermal properties. The results agree very well with experiments and show that the thermal expansivity decreases with pressure up to about 100 GPa ($\eta$=0.73), and is almost pressure and temperature independent above this compression. It is also effected by anharmonicity at zero pressure and temperatures above 2500K. The thermal pressure changes very little with increasing pressures and temperatures, and the Gruneisen parameter is temperature independent and decreases slightly with pressure.Comment: Geophys. Res. Lett., in press, 7 pages, 4 figures, uuencoded ps fil

Stage-specific vertical distribution of Alaska plaice (Pleuronectes quadrituberculatus) eggs in the eastern Bering Sea

The stage-specific distribution of Alaska plaice (Pleuronectes quadrituberculatus) eggs in the southeastern Bering Sea was examined with collections made in mid-May in 2002, 2003, 2005, and 2006. Eggs in the early stages of development were found primarily offshore of the 40-m isobath. Eggs in the middle and late stages of development were found inshore and offshore of the 40-m isobath. There was some evidence that early-stage eggs occur deeper in the water column than late-stage eggs, although year-to-year variability in that trend was observed. Most eggs were in the later stages of development; therefore the majority of spawning is estimated to have occurred a few weeks before collection—probably April—and may be highly synchronized among local spawning areas. Results indicate that sampling with continuous underway fish egg collectors(CUFES) should be supplemented with sampling of the entire water column to ensure adequate samples of all egg stages of Alaska plaice. Data presented offer new information on the stage-dependent horizontal and vertical distribution of Alaska plaice eggs in the Bering Sea and provide further evidence that the early life history stages of this species are vulnerable to near-surface variations in hydrographical conditions and climate forcing

Seismic Velocities in Mantle Minerals and the Mineralogy of the Upper Mantle

Comparison of seismic velocities in mantle minerals, under mantle conditions, with seismic data is a first step toward constraining mantle chemistry. The calculation, however, is uncertain due to lack of data on certain physical properties. “Global” systematics have not proved very useful in estimating these properties, particularly for the shear parameters. A new approach to elasticity estimation is used in this study to produce estimates of unknown quantities, primarily pressure and temperature derivatives of elastic moduli, from the structural and chemical trends evident in the large amount of elasticity data now available. These trends suggest that the derivatives of unmeasured high-pressure phases can be estimated from “analogous” low-pressure phases. Using these predictions and the best available measurements, seismic velocities are computed along high-temperature adiabats for a set of mantle minerals using third-order finite strain theory. The calculation of density and moduli at high temperature, to initiate the adiabat, must be done with care since parameters such as thermal expansion are not independent of temperature. Both compressional and shear seismic profiles are well-matched by a mineralogy dominated by clinopyroxene and garnet and with an olivine content of approximately 40% by volume. Between 670 and 1000 km, perovskite alone provides a good fit to the seismic velocities. Combining seismic velocities with recent phase equilibria data for a hypothetical pure olivine mantle suggests that a mineralogy with a maximum of 35% olivine (shear profile) or 40–53% olivine (compressional profile) by volume can satisfy the constraint imposed by the 400-km discontinuity. Other features of the upper mantle can then be matched by appropriate combinations of pyroxenes, garnets, and their high-pressure equivalents. While mantle models with a substantially larger fraction of olivine cannot be ruled out, they are acceptable only if the derivatives of the spinel phases are substantially different from olivine and deviate from trends in the larger data set

Fermion kinetics in the Falicov-Kimball limit of the three-band Emery model

The three-band Emery model is reduced to a single-particle quantum model of Falicov-Kimball type, by allowing only up-spins to hop, and forbidding double occupation by projection. It is used to study the effects of geometric obstruction on mobile fermions in thermodynamic equilibrium. For low hopping overlap, there appears a plateau in the entropy, due to charge correlations, and related to real-space disorder. For large overlap, the equilibrium thermopower susceptibility remains anomalous, with a sign opposite to the one predicted from the single-particle density of states. The heat capacity and non-Fermi liquid response are discussed in the context of similar results in the literature. All results are obtained by evaluation of an effective single-particle free-energy operator in closed form. The method to obtain this operator is described in detail.Comment: New calculations, method explained in detail, 16 pages, 9 figure

Charmonium Suppression - Interplay of Hadronic and Partonic Degrees of Freedom

Last year the E866-group of the Fermilab measured the $x_F$ dependence of $J/\Psi$ and $\Psi'$ suppression in $pA$ collisions. We discuss two of the effects found in that experiment with regard to color coherence effects: the different suppression of the $J/\Psi$ and the $\Psi'$ at $x_F<0$ and the significant suppression of both at large $x_F$. The small $x_F$ regions is dominated by fully formed charmonium states and thus enables us to discuss the formation time and the cross section of the different charmonium states. In the large $x_F$ region the interaction of the charmonium states with nuclear matter has to be described by partonic degrees of freedom, because in that kinematic domain the formation time is much larger than the nuclear radii. The understanding of this region will be crucial for the interpretation of the data of the future heavy ion colliders RHIC and LHC.Comment: 4 pages, 1 table, 1 figure, Contribution to the Proceedings of the 15th Particles and Nuclei International Conference (PANIC 99), Uppsala, Sweden, June 10-16, 199

Spatial assessment of intertidal seagrass meadows using optical imaging systems and a lightweight drone

Seagrass ecosystems are highly sensitive to environmental change. They are also in global decline and under threat from a variety of anthropogenic factors. There is now an urgency to establish robust monitoring methodologies so that changes in seagrass abundance and distribution in these sensitive coastal environments can be understood. Typical monitoring approaches have included remote sensing from satellites and airborne platforms, ground based ecological surveys and snorkel/scuba surveys. These techniques can suffer from temporal and spatial inconsistency, or are very localised making it hard to assess seagrass meadows in a structured manner. Here we present a novel technique using a lightweight (sub 7 kg) drone and consumer grade cameras to produce very high spatial resolution (∼4 mm pixel−1) mosaics of two intertidal sites in Wales, UK. We present a full data collection methodology followed by a selection of classification techniques to produce coverage estimates at each site. We trialled three classification approaches of varying complexity to investigate and illustrate the differing performance and capabilities of each. Our results show that unsupervised classifications perform better than object-based methods in classifying seagrass cover. We also found that the more sparsely vegetated of the two meadows studied was more accurately classified - it had lower root mean squared deviation (RMSD) between observed and classified coverage (9–9.5%) compared to a more densely vegetated meadow (RMSD 16–22%). Furthermore, we examine the potential to detect other biotic features, finding that lugworm mounds can be detected visually at coarser resolutions such as 43 mm pixel−1, whereas smaller features such as cockle shells within seagrass require finer grained data (<17 mm pixel−1)

Comentarios a la ponencia "Igualdades, desigualdades y derechos", presentada por Mirta Lobato

Teniendo en cuenta -como advierte Mirta Lobato a los comentaristas- que cuando habla de desigualdades en su ponencia se refiere a que "el trabajo es el eje articulador de estas reflexiones", y sin dejar de reconocer la importancia que cabe a los otros temas y sujetos sobre los que tan bien desarrolla su exposición, quiero centrarme en un grupo que estoy estudiando desde hace unos años, como es el de los inmigrantes limítrofes a la Argentina de fin de siglo XX e inicios del XXI. Para ello, voy a analizar brevemente -como así lo exigen las reglas del comentario- a estos sujetos sociales, a quienes, como también ella afirma, ya los habríamos de encontrar censalmente a inicios del siglo pasado, aunque su visibilidad fuera menor porque aún no habían arribado a Buenos Aires; es decir, al escenario donde "las cosas suceden".Fil: Benencia, Roberto Rodolfo. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Information choice in a social learning experiment

We document heterogeneity of rationality and bias in information acquisition in a social learning experiment, where subjects, prior to guessing an unknown binary state of the world, must choose between receiving a private signal or seeing social information containing the guesses made by previous subjects in the sequence - rather than observing both pieces of information as in the classic design of Anderson and Holt (1997). By requiring subjects to make this information choice at different points in the sequence, our within-subject design allows us to separate biased from optimal information choices. Overall, the majority of subjects exhibit a suboptimal bias in favor of choosing social rather than private information, consistent with underestimating both mistakes made by other subjects and the frequency of uninformative social information. Furthermore, a substantial minority behave according to a refined equilibrium prediction, while some subjects consistently choose social information and others consistently choose private information

Shock compression and isentropic release of granite

New equation of state data for a weathered granite shocked to about 125 GPa are reported and combined with the Westerly granite data of McQueen, Marsh & Fritz (1967). The shock velocity (U_s)-particle velocity (U_p) relations can be fitted with two linear regressions: U_s= 4.40 + 0.6U_p for a range of U_p up to about 2 km s^(-1) and U_s= 2.66 + 1.49U_p for a range of about 2 to 5 km s^(-1). The third-order Birch-Murnaghan equation of state parameters are K_(os) = 51-57 GPa and K'_(os) = 1.4-1.8 for the low-pressure regime and K_(os) = 251 ± 30 GPa and an assumed K'_(os) = 4 for the high-pressure regime. Compressive waveforms in dry and water-saturated granite were measured at 10-15 GPa using the VISAR technique. The measured wave profiles were successfully modelled using a Maxwellian stress-relaxation material model. Water-saturated granite is characterized by a ~25 per cent lower yield strength and a ~75 per cent longer material relaxation time than dry granite

Acute engagement of Gq-mediated signaling in the bed nucleus of the stria terminalis induces anxiety-like behavior

The bed nucleus of the stria terminalis (BNST) is a brain region important for regulating anxiety-related behavior in both humans and rodents. Here we used a chemogenetic strategy to investigate how engagement of G protein-coupled receptors (GPCR) signaling cascades in genetically defined GABAergic BNST neurons modulates anxiety-related behavior and downstream circuit function. We saw that stimulation of vesicular γ-Aminobutyric acid (GABA) transporter (VGAT)-expressing BNST neurons using hM3Dq, but neither hM4Di nor rM3Ds Designer Receptors Exclusively Activated by a Designer Drug (DREADDs), promotes anxiety-like behavior. Further, we identified that activation of hM3Dq receptors in BNST VGAT neurons can induce a long-term depression (LTD)-like state of glutamatergic synaptic transmission, indicating DREADD-induced changes in synaptic plasticity. Further, we used DREADD-assisted metabolic mapping (DREAMM) to profile brain-wide network activity following activation of Gq-mediated signaling in BNST VGAT neurons and saw increased activity within ventral midbrain structures, including the ventral tegmental area (VTA), and hindbrain structures such as the locus coeruleus (LC) and parabrachial nucleus (PB). These results highlight that Gq-mediated signaling in BNST VGAT neurons can drive downstream network activity that correlates with anxiety-like behavior, and points to the importance of identifying endogenous GPCRs within genetically defined cell populations. We next used a microfluidics approach to profile the receptorome of single BNST VGAT neurons. This approach yielded multiple Gq-coupled receptors that are associated with anxiety-like behavior and several potential novel candidates for regulation of anxiety-like behavior. From this, we identified that stimulation of the Gq-coupled receptor 5-HT2CR in the BNST is sufficient to elevate anxiety-like behavior in an acoustic startle task. Together, these results provide a novel profile of receptors within genetically defined BNST VGAT neurons that may serve as therapeutic targets for regulating anxiety states and provide a blueprint for examining how G-protein mediated signaling in a genetically defined cell type can be used to assess behavior and brain-wide circuit function