Atomic Fermi-Bose mixtures in inhomogeneous and random lattices: From Fermi glass to quantum spin glass and quantum percolation

We investigate atomic Fermi-Bose mixtures in inhomogeneous and random optical lattices in the limit of strong atom-atom interactions. We derive the effective Hamiltonian describing the dynamics of the system and discuss its low temperature physics. We demonstrate possibility of controlling the interactions at local level in inhomogeneous but regular lattices. Such a control leads to the achievement of Fermi glass, quantum Fermi spin glass, and quantum percolation regimes involving bare and/or composite fermions in random lattices.Comment: minor changes; Physical Review Letters 93, 040401 (2004

Convergence of the Generalized Volume Averaging Method on a Convection-Diffusion Problem: A Spectral Perspective

A mixed formulation is proposed and analyzed mathematically for coupled convection-diffusion in heterogeneous medias. Transfer in solid parts driven by pure diffusion is coupled with convection-diffusion transfer in fluid parts. This study is carried out for translation-invariant geometries (general infinite cylinders) and unidirectional flows. This formulation brings to the fore a new convection-diffusion operator, the properties of which are mathematically studied: its symmetry is first shown using a suitable scalar product. It is proved to be self-adjoint with compact resolvent on a simple Hilbert space. Its spectrum is characterized as being composed of a double set of eigenvalues: one converging towards −∞ and the other towards +∞, thus resulting in a nonsectorial operator. The decomposition of the convection-diffusion problem into a generalized eigenvalue problem permits the reduction of the original three-dimensional problem into a two-dimensional one. Despite the operator being nonsectorial, a complete solution on the infinite cylinder, associated to a step change of the wall temperature at the origin, is exhibited with the help of the operator’s two sets of eigenvalues/eigenfunctions. On the computational point of view, a mixed variational formulation is naturally associated to the eigenvalue problem. Numerical illustrations are provided for axisymmetrical situations, the convergence of which is found to be consistent with the numerical discretization

Coexisting ordinary elasticity and superfluidity in a model of defect-free supersolid

We present the mechanics of a model of supersolid in the frame of the Gross-Pitaevskii equation at $T=0K$ that do not require defects nor vacancies. A set of coupled nonlinear partial differential equations plus boundary conditions is derived. The mechanical equilibrium is studied under external constrains as steady rotation or external stress. Our model displays a paradoxical behavior: the existence of a non classical rotational inertia fraction in the limit of small rotation speed and no superflow under small (but finite) stress nor external force. The only matter flow for finite stress is due to plasticity.Comment: 6 pages, 2 figure

Origin and distribution of Rare Earth Elements (REEs) in the water and sediments of El Hito Lake (Cuenca, Central Spain)

Determination of Rare Earth Elements (REEs) in the waters and sediments of El Hito Lake and its drainage basin was carried out. Distribution maps for REEs concentrations show increasing values in the lake sediments from the center to the eastern edge reaching 166.5 mg/kg. In the drainage basin, higher values were observed with a maximum of 350.9 mg/kg in the southern part. Concentrations in the water were considerably lower with a maximum value of 1.3 µg/L. Ce, La and Nd were the most abundant elements. When normalized REE concentrations against NASC (North American Shale Composite), a positive anomaly of Eu in the water and of Nd in the sediments (lake and basin) was observed. The (La/Gd)NASC and (La/Yb)NASC ratios determined the predominance of light REE (LREE) over medium (MREE) and heavy REE (HREE)Se llevó a cabo el estudio de Tierras Raras (REEs) del agua y los sedimentos de la Laguna de El Hito así como de su cuenca de recepción. Los mapas de distribución de las concentraciones de REE en los sedimentos de la laguna mostraron valores crecientes desde el centro hacia el margen este alcanzando 166,5 mg/kg. En la cuenca se midieron valores más elevados llegando hasta 350,9 mg/kg en la mitad sur. Los valores en el agua fueron notablemente inferiores, con un máximo de 1,3 µg/L. El elemento más abundante fue el Ce seguido del Nd. Se normalizaron las concentraciones de REEs frente a las del NASC (North American Shale Composite), observándose una anomalía positiva de Eu en el agua, así como de Nd en los sedimentos (laguna y cuenca). Mediante los índices (La/Gd)NASC y (La/Yb)NASC se determinó el predominio de las REEs ligeras (LREEs) frente a las medias (MREE) y pesadas (HREE

Physical activity and bone health in schoolchildren: the mediating role of fitness and body fat

This is the final version of the article. Available from Public Library of Science via the DOI in this record.BACKGROUND: The relationship between physical activity (PA) and bone health is well known, although the role of percent body fat (%BF) and fitness as confounders or mediators in this relationship remains uncertain. OBJECTIVE: To examine whether the association between PA and bone mineral content (BMC) is mediated by %BF and cardiorespiratory fitness (CRF). METHODS: In this cross sectional study, BMC, total %BF (by DXA), vigorous PA (VPA), CRF, age and height were measured in 132 schoolchildren (62 boys, aged 8-11 years). ANCOVA was used to test differences in BMC by %BF, CRF and VPA, controlling for different sets of confounders. Simple mediation analyses and serial multiple mediation analyses were fitted to examine whether the relationship between PA and BMC is mediated by %BF and fitness. RESULTS: Children with high %BF had higher total body BMC than their peers after controlling for all sets of confounders. Children with good CRF or VPA had significantly less total body BMC after controlling for age and sex but in children with good CRF this inverse relation disappeared after adjusting by %BF. %BF and CRF both act as a full mediator in the association between VPA and BMC, after inclusion of the potential confounders in the models. CONCLUSION: Fitness and %BF seem to have a mediator role on the relationship between physical activity and bone mass.This study was funded by grant numbers PII1I09-0259-9898 and POII10-0208-5325 from the Ministry of Education and Science - Junta de Comunidades de Castilla-La Mancha, and Ministry of Health (FIS grant number PI081297). Additional funding was provided by the Research Network on Preventative Activities and Health Promotion (RD06/0018/0038)

Rayleigh Scattering and Atomic Dynamics in Dissipative Optical Lattices

We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals (S. Guibal {\it et al}, Phys. Rev. Lett. {\bf 78}, 4709 (1997); C. Jurczak {\it et al}, Phys. Rev. Lett. {\bf 77}, 1727 (1996)), we study whether the Rayleigh resonance originates from the diffraction on a density grating, and is therefore a probe of transport of atoms in optical lattices. It turns out that this is not the case: the Rayleigh line is instead a measure of the cooling rate, while spatial diffusion contributes to the scattering spectrum with a much broader resonance

Biomarkers and inorganic proxies in the paleoenvironmental reconstruction of mires: The importance of landscape in Las Conchas (Asturias, Northern Spain)

We determined the lipid distributions (n-alkanes, n-alkan-2-ones, n-alkanoic acids), total organic carbon (TOC), total nitrogen (TN), Ca/Mg and ash content in Las Conchas mire, a 3.2 m deep bryophyte-dominated mire in Northern Spain covering 8000 cal yr BP. Bog conditions developed in the bottom 20 cm of the profile, and good preservation of organic matter (OM) was inferred from n-alkanoic acid distribution, with the exception of the uppermost 20 cm (last ca. 200 yr). Microbial synthesis of long chain saturated fatty acids from primary OM likely produced a dominance of short chain n-alkanoic acids with a bimodal distribution, as well as the lack of correspondence between the n-alkane and n-alkanoic acid profiles in the upper 20 cm. This was accompanied by an increase in ash content, a decrease in TOC and variation in n-alkane ratios, thereby suggesting significant changes in the mire, namely drainage and transformation to a meadow, in the last ca. 200 yr. The distribution of n-alkan-2-ones indicated an increase in bacterial source from the bottom of the record to 94 cm, whereas their distribution in the upper part could be attributed mainly to plant input and/or the microbial oxidation of n-alkanes. The different n-alkane proxies showed variations, which we interpreted in terms of changes in vegetation (Sphagnum vs. non-Sphagnum dominated phases) during the last 8000 cal yr BP. C23 was the most abundant homolog throughout most of the record, thereby suggesting dominant humid conditions alternating with short drier phases. However, such humid conditions were not linked to paleoclimatic variation but rather to geomorphological characteristics: Las Conchas mire, at the base of the Cuera Range, receives continuous runoff—even during drier periods—which is not necessarily accompanied by additional mineral input to peat, producing the development of Sphagnum moss typical of waterlogged ecotopes and damp habitats. Thus, although geochemical proxies indicated an ombrotrophic regime in the mire, geomorphological characteristics may make a considerable contribution to environmental conditions

Análisis de la docencia universitaria por la influencia de la COVID-19: algunas lecciones aprendidas

La crisis sanitaria producida por el virus del SARS-COV-2 produjo un cambio drástico en la educación en marzo de 2020, cuando la enseñanza presencial se vio forzada a adaptarse a la telenseñanza. Esto produjo cambios en las metodologías docentes, los materiales didácticos y los métodos de evaluación. El objetivo de este estudio es determinar cuáles de estos cambios, implementados en la Universidad presencial, han sido positivos y deberían mantenerse en el tiempo. Para ello se ha realizado una encuesta a los alumnos de los distintos cursos de los grados impartidos en la E.T.S.I. Minas y Energía (E.T.S.I.M.E) de la Universidad Politécnica de Madrid que permite conocer cómo ha influido la pandemia en el uso de los nuevos materiales didácticos, qué tipo de modalidades de enseñanza prefieren los alumnos y qué recursos utilizan más durante el estudio. A pesar de que los apuntes y diapositivas de clase siguen siendo el recurso predilecto de los alumnos, se ha visto un gran interés por las grabaciones de clases. Otros materiales más tradicionales, como la bibliografía o las tutorías, son menos utilizados por los estudiantes. En cuanto a las modalidades de enseñanza, la opinión está polarizada. Por tanto, es necesario realizar un esfuerzo para combinar eficientemente las metodologías y recursos didácticos de telenseñanza a la docencia presencial, generando recursos asíncronos sin perjuicio de las actividades presenciales tradicionales