Thickness-dependent thermal properties of amorphous insulating thin films measured by photoreflectance microscopy

In this work, we report on the measurement of the thermal conductivity of thin insulating films of SiO2 obtained by thermal oxidation, and Al2O3 grown by atomic layer deposition (ALD), both on Si wafers. We used photoreflectance microscopy to determine the thermal properties of the films as a function of thickness in the 2 nm to 1000 nm range. The effective thermal conductivity of the Al2O3 layer is shown to decrease with thickness down to 70% for the thinnest layers. The data were analyzed upon considering that the change in the effective thermal conductivity corresponds to an intrinsic thermal conductivity associated to an additional interfacial thermal resistance. The intrinsic conductivity and interfacial thermal resistance of SiO2 were found to be equal to 0.95 W/m·K and 5.1 × 10− 9 m2K/W respectively; those of Al2O3 were found to be 1.56 W/m·K and 4.3 × 10− 9 m2K/W

Perfil logístico de Colombia

El presente documento ofrece un estudio del perfil logístico de Colombia con la finalidad de dar a conocer el estado de arte de las ciudades, puertos e infraestructura principal para facilitar la toma de decisiones de los empresarios. Para el desarrollo de este trabajo se determinaron a partir de un análisis competitivo del país; las principales ciudades y puertos; logrando establecer un inventario de maquinaria y equipo e infraestructura logística; enmarcados en retos ya establecidos en las políticas públicas.This document provides a profile study logistics Colombia in order to present the state of art of the cities, ports and infrastructure in facilitating the decision making of managers. For the development of this work were determined from a competitive analysis of the country's major cities and ports, making an inventory of machinery and equipment and logistics infrastructure; framed challenges established in public policy

The Distance to the Soft Gamma Repeater SGR 1627-41

We report millimeter observations of the line of sight to the recently discovered Soft Gamma Repeater, SGR 1627-41, which has been tentatively associated with the supernova remnant SNR G337.0-0.1 Among the eight molecular clouds along the line of sight to SGR 1627-41, we show that SNR G337.0-0.1 is probably interacting with one of the most massive giant molecular clouds (GMC) in the Galaxy, at a distance of 11 kpc from the sun. Based on the high extinction to the persistent X-ray counterpart of SGR 1627-41, we present evidence for an association of this new SGR with the SNR G337.0-0.1; they both appear to be located on the near side of the GMC. This is the second SGR located near an extraordinarily massive GMC. We suggest that SGR 1627-41 is a neutron star with a high transverse velocity (~ 1,000 \kms) escaping the young (~ 5,000 years) supernova remnant G337.0-0.1Comment: 17 pages, including 2 figures. Accepted for publication in the Astrophysical Journal Letter

The study of incommensurate structures as a probe to reveal atomic interactions in crystals

The structure of aperiodic crystals which includes incommensurate, quasi- and composite crystals is usually described in spaces of higher dimension, the so called superspace. The main advantage of the superspace formalism is that an aperiodic structure in three dimensions recovers its full periodicity in higher dimensions. The symmetry properties of aperiodic crystals are obviously more convenient to describe in superspace too. The origin of the incommensurate nature of structures can often be found in competing interatomic interactions. From molecular dynamics simulation of a simple three dimensional model with close-packed layers and a single degree of freedom for each particle, it is possible to find the existence conditions of commensurate and incommensurate phases. Incommensurate phases can already be predicted on the basis of nearest and next nearest neighbour particle interactions only. We illustrate this principle of interactions with two examples of structures, Na2CO3 and K3In(PO4)(2). These examples shows clearly the importance of non-oxygen interactions i.e. next nearest interactions for the formation of incommensurate structures

Atomic clusters and phase transitions in the metastable beta-Ta phase between 4.2 and 293 K

Atomic clusters were identified in the ground state of the non-equilibrium Ta phase (Frank-Kasper sigma-structure type) at 15, 120 and 293K. The evolution of the clusters with temperature leads to two phase transformations at 65 and 150K which are related to the electrical and magnetic properties. The magnetic phase transition at 65 K is associated with the magnetic symmetry group transformation P4'(2) /mn'm ( 65 K). It is shown that beta-U is also a two-component composite containing similar clusters. The nature of the stabilisation of beta-Ta at the cathode is discussed

A reinterpretation of the phase transitions in Na2CO3

Based on the structural data of phases alpha (hexagonal; 756-972 K), beta (monoclinic; 605-751 K), gamma (incommensurate, monoclinic; 295 K) and delta (lock-in, monoclinic; 110 K) of sodium carbonate, Na2CO3, we could draw a parallel between the phase transitions and the evolution of the second coordination sphere of the C atoms. The temperature-dependent structures observed in the beta phase are reproduced in the incommensurate gamma phase as a modulation wave, which relates to the content of the symmetrically equivalent {110} lattice planes in the alpha phase. By decreasing the temperature, the phase transitions are associated with a stepwise increase in the number of Na ions participating in the second coordination sphere of the C atoms. Over the full temperature range, this number increases from 3 to 7. The C-O distances and the mobility of the O atoms depends on the number of Na ions in the vicinity of the C atoms