Which mechanism underlies the water-like anomalies in core-softened potentials?

Using molecular dynamics simulations we investigate the thermodynamic of particles interacting with a continuous and a discrete versions of a core-softened (CS) intermolecular potential composed by a repulsive shoulder. Dynamic and structural properties are also analyzed by the simulations. We show that in the continuous version of the CS potential the density at constant pressure has a maximum for a certain temperature. Similarly the diffusion constant, $D$, at a constant temperature has a maximum at a density $\rho_{\mathrm{max}}$ and a minimum at a density $\rho_{\mathrm{min}}<\rho_{\mathrm{max}}$, and structural properties are also anomalous. For the discrete CS potential none of these anomalies are observed. The absence of anomalies in the discrete case and its presence in the continuous CS potential are discussed in the framework of the excess entropy.Comment: 8 page

Extragalactic Foregrounds of the Cosmic Microwave Background: Prospects for the MAP Mission

(Abridged) While the major contribution to the Cosmic Microwave Background (CMB) anisotropies are the sought-after primordial fluctuations produced at the surface of last scattering, other effects produce secondary fluctuations at lower redshifts. Here, we study the extragalactic foregrounds of the CMB in the context of the upcoming MAP mission. We first survey the major extragalactic foregrounds and show that discrete sources, the Sunyaev-Zel'dovich (SZ) effect, and gravitational lensing are the most dominant ones for MAP. We then show that MAP will detect (>5 sigma) about 46 discrete sources and 10 SZ clusters directly with 94 GHz fluxes above 2 Jy. The mean SZ fluxes of fainter clusters can be probed by cross-correlating MAP with cluster positions extracted from existing catalogs. For instance, a MAP-XBACs cross-correlation will be sensitive to clusters with S(94GHz)>200mJy, and will thus provide a test of their virialization state and a measurement of their gas fraction. Finally, we consider probing the hot gas on supercluster scales by cross-correlating the CMB with galaxy catalogs. Assuming that galaxies trace the gas, we show that a cross-correlation between MAP and the APM catalog should yield a marginal detection, or at least a four-fold improvement on the COBE upper limits for the rms Compton y-parameter.Comment: 27 LaTeX pages, including 5 ps figures and 2 tables. To appear in ApJ. Minor revisions to match accepted version. Color figures and further links available at http://www.astro.princeton.edu/~refreg

Soil biochemistry and microbial activity in vineyards under conventional and organic management at Northeast Brazil.

The São Francisco Submedium Valley is located at the Brazilian semiarid region and is an important center for irrigated fruit growing. This region is responsible for 97% of the national exportation of table grapes, including seedless grapes. Based on the fact that orgThe São Francisco Submedium Valley is located at the Brazilian semiarid region and is an important center for irrigated fruit growing. This region is responsible for 97% of the national exportation of table grapes, including seedless grapes. Based on the fact that organic fertilization can improve soil quality, we compared the effects of conventional and organic soil management on microbial activity and mycorrhization of seedless grape crops. We measured glomerospores number, most probable number (MPN) of propagules, richness of arbuscular mycorrhizal fungi (AMF) species, AMF root colonization, EE-BRSP production, carbon microbial biomass (C-MB), microbial respiration, fluorescein diacetate hydrolytic activity (FDA) and metabolic coefficient (qCO2). The organic management led to an increase in all variables with the exception of EE-BRSP and qCO2. Mycorrhizal colonization increased from 4.7% in conventional crops to 15.9% in organic crops. Spore number ranged from 4.1 to 12.4 per 50 g-1 soil in both management systems. The most probable number of AMF propagules increased from 79 cm-3 soil in the conventional system to 110 cm-3 soil in the organic system. Microbial carbon, CO2 emission, and FDA activity were increased by 100 to 200% in the organic crop. Thirteen species of AMF were identified, the majority in the organic cultivation system. Acaulospora excavata, Entrophospora infrequens, Glomus sp.3 and Scutellospora sp. were found only in the organically managed crop. S. gregaria was found only in the conventional crop. Organically managed vineyards increased mycorrhization and general soil microbial activity

The thermodynamics, heat transer and fluid mechanics role of lubricant oil in hermetic reciprocating compressors

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The present paper reviews recent developments on the influence of oil on several thermophysical phenomena in reciprocating compressors. Besides the more essential role of lubrication, the oil is responsible for several tasks in the compressor, from cooling to keeping a low system pressure while the compressor is idle. Thermodynamics dictates the amount of dissolved refrigerant the oil can retain at a particular condition. Hence, the viscosity of the lubricant is directly affected by the refrigerant solubility in the oil. Heat transfer is crucial for keeping a low temperature in the compressor because thermodynamic losses increase with increasing gas temperature. Fluid mechanics is essential to guarantee that oil is delivered to the bearings and that lubrication is performed efficiently under any operating condition.cs201

Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory

Atmospheric parameters, such as pressure (P), temperature (T) and density, affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of pressure and density. The former affects the longitudinal development of air showers while the latter influences the Moliere radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle Physic

Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{$6\times 10^{19}$eV}. The anisotropy was measured by the fraction of arrival directions that are less than $3.1^\circ$ from the position of an active galactic nucleus within 75 Mpc (using the V\'eron-Cetty and V\'eron $12^{\rm th}$ catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating fraction is $(38^{+7}_{-6})$, compared with $21$ expected for isotropic cosmic rays. This is down from the early estimate of $(69^{+11}_{-13})$. The enlarged set of arrival directions is examined also in relation to other populations of nearby extragalactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-rays by the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has the largest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation function is shown for the enlarged set of arrival directions and compared to the isotropic expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201

Entangled-Photon Generation from Parametric Down-Conversion in Media with Inhomogeneous Nonlinearity

We develop and experimentally verify a theory of Type-II spontaneous parametric down-conversion (SPDC) in media with inhomogeneous distributions of second-order nonlinearity. As a special case, we explore interference effects from SPDC generated in a cascade of two bulk crystals separated by an air gap. The polarization quantum-interference pattern is found to vary strongly with the spacing between the two crystals. This is found to be a cooperative effect due to two mechanisms: the chromatic dispersion of the medium separating the crystals and spatiotemporal effects which arise from the inclusion of transverse wave vectors. These effects provide two concomitant avenues for controlling the quantum state generated in SPDC. We expect these results to be of interest for the development of quantum technologies and the generation of SPDC in periodically varying nonlinear materials.Comment: submitted to Physical Review

The Fluorescence Detector of the Pierre Auger Observatory

The Pierre Auger Observatory is a hybrid detector for ultra-high energy cosmic rays. It combines a surface array to measure secondary particles at ground level together with a fluorescence detector to measure the development of air showers in the atmosphere above the array. The fluorescence detector comprises 24 large telescopes specialized for measuring the nitrogen fluorescence caused by charged particles of cosmic ray air showers. In this paper we describe the components of the fluorescence detector including its optical system, the design of the camera, the electronics, and the systems for relative and absolute calibration. We also discuss the operation and the monitoring of the detector. Finally, we evaluate the detector performance and precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics Research Section

Effects of chronic caffeine on episodic-like mrmory tasks in rats

Objectives: Caffeine is a mild stimulant of the central nervous system and improves memory, particularly at low doses. Caffeine can improve cognitive function through antagonism of adenosine receptors, which induces the release of acetylcholine, or even the induction of synaptic changes, due to prolonged use (Nature 31-39; 361, 1993; Ann. Rev. Neurosci. 149; 21, 1998). Recently, caffeine administration has also been associated with changes in the rate of neurogenesis in adult rodents hippocampi (Neurophamacol. 1-7; 30, 2009), what could affect memory and learning (Science 325, 210-213, 2009). In this study, we investigated the effects of treatment with low and high doses of caffeine on two episodic-like memory tasks, which have been shown to be hippocampal- dependent (Behav. Brain Res. 1-8; 300, 2009; Hippocampus 955-964; 18, 2008). Methods and Results: Eighteen three-month-old male Wistar rats (200 - 350g) were treated i.p. with saline, 15 or 30 mg/kg caffeine once a day for 45 days, and episodic-like memory behavioral tasks were started on the 29th and 41th days of treatment, respectively. The first one recollects what-when and what-where aspects of memory. The rats were exposed to four copies of an object on the first trial and then to a second sample of four copies of a new object on the second trial (after 1 h interval). The objects were placed on different positions on two trials. In the test, after 24h, the animals were exposed to two objects from each sample trial, located on the same position as before, except for one copy of the first sample (displaced old object). The second task consists of three 5-min-trials with 3-min-intervals between them in which the animal is exposed to the same object located in different positions in each trial. In the test trial, after 30 min, two copies of the object are presented (one of them in the same position as the first sample and the other in the same position as the third sample trial. Test trial is performed upon two conditions: high and low interference, with the two copies of the object distant 42 or 84 cm apart, respectively.Our results showed that in the first task rats treated with saline failed to present increased exploration of old objects (mean ± SE: 0.43 ± 0.11) compared to recent ones (0.57 ± 0.11), while rats treated with caffeine (15 mg/kg) explored more the old (0.77 ± 0.09) compared to recent objects (0.24 ± 0.09, paired samples t-test, p = 0.033). However there were no differences between exploration rate of displaced and non-displaced objects, in any of the groups. In the second task, under high interference condition, there was no difference in the exploration time of the first object compared to the third object in both control (2.72 ± 1.79; 4.72 ± 3.76) and caffeine 15 mg/kg (4.23 ± 1.99; 2.63 ± 1.04) groups. However, the caffeine 30 mg/kg group explored more the first (11.08 ± 3.79) object than the third one (4.68 ± 1.95; ANOVA and Bonferroni post-hoc, p = 0.050) Conclusions: Our results suggest that chronic caffeine administration improves temporal aspects of episodic-like memory in object recognition tasks. It should be noted that caffeine, even at high doses could improve memory on conditions of greater difficulty