Excited-state quantum phase transitions in a two-fluid Lipkin model

Background: Composed systems have became of great interest in the framework of the ground state quantum phase transitions (QPTs) and many of their properties have been studied in detail. However, in these systems the study of the so called excited-state quantum phase transitions (ESQPTs) have not received so much attention. Purpose: A quantum analysis of the ESQPTs in the two-fluid Lipkin model is presented in this work. The study is performed through the Hamiltonian diagonalization for selected values of the control parameters in order to cover the most interesting regions of the system phase diagram. [Method:] A Hamiltonian that resembles the consistent-Q Hamiltonian of the interacting boson model (IBM) is diagonalized for selected values of the parameters and properties such as the density of states, the Peres lattices, the nearest-neighbor spacing distribution, and the participation ratio are analyzed. Results: An overview of the spectrum of the two-fluid Lipkin model for selected positions in the phase diagram has been obtained. The location of the excited-state quantum phase transition can be easily singled out with the Peres lattice, with the nearest-neighbor spacing distribution, with Poincar\'e sections or with the participation ratio. Conclusions: This study completes the analysis of QPTs for the two-fluid Lipkin model, extending the previous study to excited states. The ESQPT signatures in composed systems behave in the same way as in single ones, although the evidences of their presence can be sometimes blurred. The Peres lattice turns out to be a convenient tool to look into the position of the ESQPT and to define the concept of phase in the excited states realm

The Prediction of Training Proficiency in Firefighters: A Study of Predictive Validity in Spain

The present study provides results of criterion validity in the selection of firefighters in Spain. The predictors were cognitive skills, job knowledge, and physical aptitudes, and the criterion was training proficiency. The process involves 639 candidates, but only 44 complete successfully the selection process. Our results support previous evidence showing that general cognitive ability is the best predictor of training proficiency, with an operational validity of .57. With respect to the other predictors, job knowledge presented an operational validity of .55 and physical tests of .49. In addition, multiple regression analysis showed that cognitive aptitude explains 33% of the variance, but when physical aptitudes are included the explained variance increases to 50%. If we also add job knowledge, explained variance increases to 55%. Our study offers recent results of criterion validity in a barely investigated job, gathered in a country other than the one where prior research had been carried out. Este estudio ofrece resultados de la validez de criterio en la selección de bomberos en España. Los predictores fueron las aptitudes cognitivas, el conocimiento del puesto y las aptitudes físicas, siendo el criterio el aprovechamiento de la formación. El proceso comenzó con 639 candidatos, de los cuales solamente 44 superaron la selección. Nuestros resultados apoyan la evidencia previa, mostrando que la aptitud cognitiva general es el mejor predictor, con una validez operativa de .57, seguido del conocimiento del puesto con .55 y las pruebas físicas con .49. Además, el análisis de regresión múltiple mostró que la aptitud cognitiva explica un 33% de la varianza, que se incrementa hasta el 50% al incluir pruebas físicas y hasta el 55% si además se añade conocimiento del puesto. Estos resultados resultan especialmente interesantes al haber sido obtenidos en un país diferente al de las principales investigaciones de referencia (i.e., Estados Unidos de América)

eta-prime nucleus optical potential and possible eta-prime bound states

Starting from a recent model of the eta'N interaction, we evaluate the eta'-nucleus optical potential, including the contribution of lowest order in density, t rho/2m_eta', together with the second order terms accounting for eta' absorption by two nucleons. We also calculate the formation cross section of the eta' bound states from (pi+,p) reactions on nuclei. The eta'-nucleus potential suffers from uncertainties tied to the poorly known eta'N interaction, which can be partially constrained by the experimental modulus of the eta'N scattering length and/or the recently measured transparency ratios in eta' nuclear photoproduction. Assuming an attractive interaction and taking the claimed experimental value |a_eta'N| = 0.1 fm, we obtain a eta' optical potential in nuclear matter at saturation density of V_eta' = -(8.7 + 1.8i) MeV, not attractive enough to produce eta' bound states in light nuclei. Larger values of the scattering length give rise to deeper optical potentials, with moderate enough imaginary parts. For a value |a_eta'| = 0.3 fm, which can still be considered to lie within the uncertainties of the experimental constraints, the spectra of light and medium nuclei show clear structures associated to eta'-nuclear bound states and to threshold enhancements in the unbound region.Comment: 11 pages, 4 figures, 2 table

The origin of power-law distributions in deterministic walks: the influence of landscape geometry

We investigate the properties of a deterministic walk, whose locomotion rule is always to travel to the nearest site. Initially the sites are randomly distributed in a closed rectangular ($A/L \times L)$ landscape and, once reached, they become unavailable for future visits. As expected, the walker step lengths present characteristic scales in one ($L \to 0$) and two ($A/L \sim L$) dimensions. However, we find scale invariance for an intermediate geometry, when the landscape is a thin strip-like region. This result is induced geometrically by a dynamical trapping mechanism, leading to a power law distribution for the step lengths. The relevance of our findings in broader contexts -- of both deterministic and random walks -- is also briefly discussed.Comment: 7 pages, 11 figures. To appear in Phys. Rev.

EFFECT OF MESQUITE SEED GUM ON THE RHEOLOGICAL PROPERTIES OF MIXTURES WITH ARABIC AND GELLAN GUMS

ABSTRACT The mesquite seed gum (Prosopis sp.) represents an alternative application in the food industry, due to its structural likeness with other galactomannans used at the moment. The information about the properties of mesquite seed gum is scarce, for this is important to known the rheological properties of this biopolymer and its interactions with other polymers for seeing future applications. The aim of this work was study the rheological behavior of mesquite seed gum and their effects in arabic and gellan gum mixtures. They were prepared aqueous dispersions according to a Simplex-Centroid design, being obtained gum combinations of total concentration of 1% from mesquite-arabic, mesquite-gellan, arabic-gellan and mesquitearabic-gellan, the pH from the dispersions were adjusted to 4, 5 and 6. The mixtures as well as the individual biopolymers were dispersed to ambient temperature, and later heated during 20 minutes at 90 °C and cooling at 25 °C. The rheological studies were made using an Haake RV2 viscometer. The statistical analysis showed differences (a = 0.05) among the rheologic value for mixtures at different pH. The mixtures showed a nonNewtonian behavior, type pseudoplastic flow (shear thinning) and showed high viscosities to low shears rates (100 s l) in all the cases. The tendency of mixtures with two or three components showed an antagonistic effect in the viscosity. Particularly the mesquite seed gum suffers an antagonistic effect in the viscosity when it was mixed with the arabic and gellan gums, being observed decreases from a 8 until 45%, below the control

An Antimethanogenic Nutritional Intervention in Early Life of Ruminants Modifies Ruminal Colonization by Archaea

The aim of this work was to study whether feeding a methanogen inhibitor from birth of goat kids and their does has an impact on the archaeal population colonizing the rumen and to what extent the impact persists later in life. Sixteen goats giving birth to two kids were used. Eight does were treated (D+) with bromochloromethane after giving birth and over 2 months. The other 8 goats were not treated (D−). One kid per doe in both groups was treated with bromochloromethane (k+) for 3 months while the other was untreated (k−), resulting in four experimental groups: D+/k+, D+/k−, D−/k+, and D−/k−. Rumen samples were collected from kids at weaning and 1 and 4 months after (3 and 6 months after birth) and from does at the end of the treating period (2 months). Pyrosequencing analyses showed a modified archaeal community composition colonizing the rumen of kids, although such effect did not persist entirely 4 months after; however, some less abundant groups remained different in treated and control animals. The different response on the archaeal community composition observed between offspring and adult goats suggests that the competition occurring in the developing rumen to occupy different niches offer potential for intervention

A multispectral microscope for in vivo oximetry of rat dorsal spinal cord vasculature

Quantification of blood oxygen saturation (SO2) in vivo is essential for understanding the pathogenesis of diseases in which hypoxia is thought to play a role, including inflammatory disorders such as multiple sclerosis (MS) and rheumatoid arthritis (RA). We describe a low-cost multispectral microscope and oximetry technique for calibration-free absolute oximetry of surgically exposed blood vessels in vivo. We imaged the vasculature of the dorsal spinal cord in healthy rats, and varied inspired oxygen (FiO2) in order to evaluate the sensitivity of the imaging system to changes in SO2. The venous SO2 was calculated as 67.8  ±  10.4% (average  ±  standard deviation), increasing to 83.1  ±  11.6% under hyperoxic conditions (100% FiO2) and returning to 67.4  ±  10.9% for a second normoxic period; the venous SO2 was 50.9  ±  15.5% and 29.2  ±  24.6% during subsequent hypoxic states (18% and 15% FiO2 respectively). We discuss the design and performance of our multispectral imaging system, and the future scope for extending this oximetry technique to quantification of hypoxia in inflamed tissue

Comparison between xenogeneic and allogeneic adipose mesenchymal stem cells in the treatment of acute cerebral infarct: Proof of concept in rats

Background: Rat adipose tissue-derived-mesenchymal stem cells (rAD-MSCs) have proven to be safe in experimental animal models of stroke. However, in order to use human AD-MSCs (hAD-MSCs) as a treatment for stroke patients, a proof of concept is needed. We analyzed whether the xenogeneic hAD-MSCs were as safe and effective as allogeneic rAD-MSCs in permanent Middle Cerebral Artery Occlusion (pMCAO) in rats. Methods: Sprague–Dawley rats were randomly divided into three groups, which were intravenously injected with xenogeneic hAD-MSCs (2 × 106), allogeneic rAD-MSCs (2 × 106) or saline (control) at 30 min after pMCAO. Behavior, cell implantation, lesion size and cell death were evaluated. Brain markers such as GFAP (glial fibrillary acid protein), VEGF (vascular endothelial growth factor) and SYP (synaptophysin) and tumor formation were analyzed. Results: Compared to controls, recovery was significantly better at 24 h and continued to be so at 14 d after IV administration of either hAD-MSCs or rAD-MSCs. No reduction in lesion size or migration/implantation of cells in the damaged brain were observed in the treatment groups. Nevertheless, cell death was significantly reduced with respect to the control group in both treatment groups. VEGF and SYP levels were significantly higher, while those of GFAP were lower in the treated groups. At three months, there was no tumor formation. Conclusions: hAD-MSCs and rAD-MSCs were safe and without side effects or tumor formation. Both treatment groups showed equal efficacy in terms of functional recovery and decreased ischemic brain damage (cell death and glial scarring) and resulted in higher angiogenesis and synaptogenesis marker levelsThis research was supported by research grants FIS06/0575, FIS09/01606, FIS12/01754 and INVICTUS (RD12/0014/0006) (Spanish Neurovascular Network), Cellerix, and Research Institute Carlos III, Ministry of Science and Innovation of Spain

Hierarchical Assembly of a Micro- and Macroporous Hydrogen-Bonded Organic Framework with Tailored Single-Crystal Size

Porous organic molecular materials represent an emergent field of research in Chemistry and Materials Science due to their unique combination of properties. To enhance their performance and expand the number of applications, the incorporation of hierarchical porosity is required, as exclusive microporosity entails several limitations. However, the integration of macropores in porous organic molecular materials is still an outstanding challenge. Herein, we report the first example of a hydrogen-bonded organic framework (MM-TPY) with hierarchical skeletal morphology, containing stable micro- and macroporosity. The crystal size, from micro to centimetre scale, can be controlled in a single step without using additives or templates. The mechanism of assembly during the crystal formation is compatible with a skeletal crystal growth. As proof of concept, we employed the hierarchical porosity as a platform for the dual, sequential and selective co-recognition of molecular species and microparticles.J.F.-S. thanks “Ramón y Cajal“ program (RYC2019-02794-I), MINECO (Spain) (Projects PID2019−104778GB−I00 and Excellence Unit “Maria de Maeztu” CEX2019−000919−M) and Generalitat Valenciana (SEJI/2020/034). E.V.R.F. thanks Ministerio de Ciencia e innovación (PID2020-116998RB-I00) and Ministerio de Educación y Formación Profesional (PRX21/00407)

New VVV Survey Globular Cluster Candidates in the Milky Way Bulge

© 2017 The American Astronomical Society. All rights reserved.It is likely that a number of Galactic globular clusters remain to be discovered, especially toward the Galactic bulge. High stellar density combined with high and differential interstellar reddening are the two major problems for finding globular clusters located toward the bulge. We use the deep near-IR photometry of the VISTA Variables in the Vía Láctea (VVV) Survey to search for globular clusters projected toward the Galactic bulge, and hereby report the discovery of 22 new candidate globular clusters. These objects, detected as high density regions in our maps of bulge red giants, are confirmed as globular cluster candidates by their color-magnitude diagrams. We provide their coordinates as well as their near-IR color-magnitude diagrams, from which some basic parameters are derived, such as reddenings and heliocentric distances. The color-magnitude diagrams reveal well defined red giant branches in all cases, often including a prominent red clump. The new globular cluster candidates exhibit a variety of extinctions (0.06 < A Ks < 2.77) and distances (5.3 < D < 9.5 kpc). We also classify the globular cluster candidates into 10 metal-poor and 12 metal-rich clusters, based on the comparison of their color-magnitude diagrams with those of known globular clusters also observed by the VVV Survey. Finally, we argue that the census for Galactic globular clusters still remains incomplete, and that many more candidate globular clusters (particularly the low luminosity ones) await to be found and studied in detail in the central regions of the Milky Way.Peer reviewedFinal Accepted Versio