Formation of a Metallic Contact: Jump to Contact Revisited

The transition from tunneling to metallic contact between two surfaces does not always involve a jump, but can be smooth. We have observed that the configuration and material composition of the electrodes before contact largely determines the presence or absence of a jump. Moreover, when jumps are found preferential values of conductance have been identified. Through combination of experiments, molecular dynamics, and first-principles transport calculations these conductance values are identified with atomic contacts of either monomers, dimers or double-bond contacts.Comment: 4 pages, 5 figure

Mechanical, Electrical, and Magnetic Properties of Ni Nanocontacts

The dynamic deformation upon stretching of Ni nanowires as those formed with mechanically controllable break junctions or with a scanning tunneling microscope is studied both experimentally and theoretically. Molecular dynamics simulations of the breaking process are performed. In addition, and in order to compare with experiments, we also compute the transport properties in the last stages before failure using the first-principles implementation of Landauer's formalism included in our transport package ALACANT.Comment: 5 pages, 6 figure

Surface abundances of ON stars

Massive stars burn hydrogen through the CNO cycle during most of their evolution. When mixing is efficient, or when mass transfer in binary systems happens, chemically processed material is observed at the surface of O and B stars. ON stars show stronger lines of nitrogen than morphologically normal counterparts. Whether this corresponds to the presence of material processed through the CNO cycle or not is not known. Our goal is to answer this question. We perform a spectroscopic analysis of a sample of ON stars with atmosphere models. We determine the fundamental parameters as well as the He, C, N, and O surface abundances. We also measure the projected rotational velocities. We compare the properties of the ON stars to those of normal O stars. We show that ON stars are usually helium-rich. Their CNO surface abundances are fully consistent with predictions of nucleosynthesis. ON stars are more chemically evolved and rotate - on average - faster than normal O stars. Evolutionary models including rotation cannot account for the extreme enrichment observed among ON main sequence stars. Some ON stars are members of binary systems, but others are single stars as indicated by stable radial velocities. Hence, mass transfer is not a simple explanation for the observed chemical properties. We conclude that ON stars show extreme chemical enrichment at their surface, consistent with nucleosynthesis through the CNO cycle. Its origin is not clear at present.Comment: 18 pages, 10 figures (+ appendix). A&A accepte

Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers

Quantum nanomagnets can show a field dependence of the relaxation time very different from their classical counterparts, due to resonant tunneling via excited states (near the anisotropy barrier top). The relaxation time then shows minima at the resonant fields H_{n}=n D at which the levels at both sides of the barrier become degenerate (D is the anisotropy constant). We showed that in Mn12, near zero field, this yields a contribution to the nonlinear susceptibility that makes it qualitatively different from the classical curves [Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to finite dc fields showing how the bias can trigger the system to display those quantum nonlinear responses, near the resonant fields, while recovering an classical-like behaviour for fields between them. The analysis of the experiments is done with heuristic expressions derived from simple balance equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report

A SENSITIVITY ANALYSIS OF ORGANIC VERSUS CONVENTIONAL SYSTEMS OF SHEEP-FARMING

In the Mediterranean Agriculture, the organic production constitutes a real possibility for sustainable development, it can keep a population in these areas and provide it with a decent work. This paper try to establish differences between conventional and organic systems of production, so that observation of these differences would lead to conclusions relating to the level of efficiency of one system as against the other. To achieve this objective, the research team analyzed the evolution of seventeen milk sheep farms in various places in the Castilla y León Region for a whole year. The study consisted in the modeling of the results of a Cobb-Douglas production function. The findings reveal that organic farms have higher production levels with the same combination of inputs. This result is a guarantee of future for this type of production and guarantee of feasibility for these areas

A comprehensive study of a versatile magnetic refrigeration demonstrator

A versatile room temperature reciprocating magnetic refrigeration demonstrator has been designed, built and tested in order to evaluate the influence of different running parameters and to check suitable magnetocaloric materials for cooling at room temperature. A comprehensive study has been done with Gd spheres of 0.2-0.4 mm diameter arranged as a double regenerator with 15 g each. A Halbach Nd2e14B permanent magnet with a slot of 10 mm width has been used to generate the magnetic field with a maximum value of 1.4 T. The heat transfer fluid is a mixture of water and ethylene glycol in a 75-25 percentage. The demonstrator achieves a maximum no-load temperature span close to 20 K, with a regeneration ratio of ¿ = 4.1, and a maximum cooling power Qc=6 W at zero temperature span. COP values have been shown and different thermodynamic AMR cycles have been studied looking for the best parameters

Enabling SmartWorkflows over heterogeneous ID-sensing technologies

Sensing technologies in mobile devices play a key role in reducing the gapbetween the physical and the digital world. The use of automatic identification capabilitiescan improve user participation in business processes where physical elements are involved(Smart Workflows). However, identifying all objects in the user surroundings does notautomatically translate into meaningful services to the user. This work introduces Parkour,an architecture that allows the development of services that match the goals of each ofthe participants in a smart workflow. Parkour is based on a pluggable architecture thatcan be extended to provide support for new tasks and technologies. In order to facilitatethe development of these plug-ins, tools that automate the development process are alsoprovided. Several Parkour-based systems have been developed in order to validate theapplicability of the proposal

Amount, preparation and type of formula consumed and its association with weight gain in infants participating in the WIC Program in Hawaii and Puerto Rico.

The aim of this study was to assess the association between amount (below or above recommendations), preparation (liquid vs. powder), and type (regular vs. hydrolysate) of infant formula consumed and weight in infants participating in the Women, Infant and Children (WIC) Program in Hawaii (HI) and Puerto Rico (PR). This was a secondary analysis of 162 caregivers with healthy term 0-2-month-old infants. Socio-demographics, infant food frequency questionnaires, and weight and length were assessed at baseline and after four months. Infant feeding practices were associated with weight-for-length z-scores using multivariable logistic regression. In total, 37.7% were exclusively breastfed and 27.2% were exclusively formula-fed. Among formula users, regular (63.6%) and powder (87.0%) formula were the most common; 43.2% consumed formula above recommendations. Most infants had rapid weight gain (61.1%). Infants fed regular formula had higher odds of overweight after four months (adjusted OR = 8.77, 95% CI: 1.81-42.6) and higher odds of rapid weight gain (adjusted OR = 3.10, 95% CI: 1.12, 8.61). Those exclusively formula fed had higher odds of slow weight gain (adjusted OR = 4.07, 95% CI: 1.17-14.2). Formula preparation and amount of formula were not associated with weight. These results could inform the WIC program's nutrition education messages on infant feeding. Studies with longer follow-up are needed to confirm these results

Acceptability of a text message-based intervention for obesity prevention in infants from Hawaii and Puerto Rico WIC.

Background: Low-income and minority children are at increased risk for obesity. Text messaging offers advantages for delivering education, but few studies have assessed the acceptability of text messaging in interventions aimed at preventing excessive weight gain in infants. This study investigated the acceptability of a text message-based intervention for prevention of excessive weight gain in infants from Hawai'i and Puerto Rico WIC clinics. Methods: The four-month text message based intervention designed to improve infant feeding practices and reduce excessive weight gain was a randomized controlled trial that included mothers with infants ages 0-2 months at baseline. Participants in the intervention arm received 18 text messages (1/week) promoting breastfeeding and appropriate complementary feeding. Acceptability of the intervention was assessed from participant retention, satisfaction, and evidence of behavior change in a sequential multimethod approach, quantitatively from questions sent via text and qualitatively during the in-person exit interview. The final analysis included 80 mother-infant pairs from the intervention arm. Results: When asked about messages liked and disliked the most, the majority of responses via text indicated that they liked all messages. From the qualitative analyses, most participants reported that all messages were useful and that the messages led them to make changes in the way they fed their infants. Participant retention was good at 78.4%. Conclusions: The intervention was acceptable to participants based upon participant retention, measures of satisfaction, and reports of behavior change. Results may inform development of mobile health programs for minority childhood obesity prevention