Singular Contractions of W-algebras

Many $W$-algebras (e.g. the $W_N$ algebras) are consistent for all values of the central charge except for a discrete set of exceptional values. We show that such algebras can be contracted to new consistent degenerate algebras at these exceptional values of the central charge.Comment: 10 pages, phyzzx.tex, QMW-92-7.(minor spelling and acknowledgement corrections

Modeling contact formation between atomic-sized gold tips via molecular dynamics

The formation and rupture of atomic-sized contacts is modelled by means of molecular dynamics simulations. Such nano-contacts are realized in scanning tunnelling microscope and mechanically controlled break junction experiments. These instruments routinely measure the conductance across the nano-sized electrodes as they are brought into contact and separated, permitting conductance traces to be recorded that are plots of conductance versus the distance between the electrodes. One interesting feature of the conductance traces is that for some metals and geometric configurations a jump in the value of the conductance is observed right before contact between the electrodes, a phenomenon known as jump-to-contact. This paper considers, from a computational point of view, the dynamics of contact between two gold nano-electrodes. Repeated indentation of the two surfaces on each other is performed in two crystallographic orientations of face-centred cubic gold, namely (001) and (111). Ultimately, the intention is to identify the structures at the atomic level at the moment of first contact between the surfaces, since the value of the conductance is related to the minimum cross-section in the contact region. Conductance values obtained in this way are determined using first principles electronic transport calculations, with atomic configurations taken from the molecular dynamics simulations serving as input structures.Comment: 6 pages, 4 figures, conference submissio

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

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

26Al yields from rotating Wolf--Rayet star models

We present new $^{26}$Al stellar yields from rotating Wolf--Rayet stellar models which, at solar metallicity, well reproduce the observed properties of the Wolf-Rayet populations. These new yields are enhanced with respect to non--rotating models, even with respect to non--rotating models computed with enhanced mass loss rates. We briefly discuss some implications of the use of these new yields for estimating the global contribution of Wolf-Rayet stars to the quantity of $^{26}$Al now present in the Milky Way.Comment: 6 pages, 2 figures, to appear in New Astronomy Review

The Lithium Flash - Thermal instabilities generated by lithium burning in RGB stars

We present a scenario to explain the lithium-rich phase which occurs on the red giant branch at the so-called bump in the luminosity function. The high transport coefficients required to enhance the surface lithium abundance are obtained in the framework of rotation-induced mixing thanks to the impulse of the important nuclear energy released in a lithium burning shell. Under certain conditions a lithium flash is triggered off. The enhanced mass loss rate due to the temporary increase of the stellar luminosity naturally accounts for a dust shell formation

Effect of a text intervention during pregnancy on birth weight in participants of the WIC program in Hawaii.

ObjectivesThere are limited studies testing the effect of a pregnancy educational intervention on infants’ birth weight. This study investigated the effect of a short message service (SMS), or text message, intervention for promoting adequate gestational weight gain on infants’ birth weight in a sample of pregnant women in Hawai‘i.MethodsA randomized clinical trial was conducted among women participating in the Special Supplemental Nutrition Program for Women, Infant, and Children (WIC) program in Hawai‘i (n = 83). The intervention group (n = 42) received weekly SMS about appropriate energy intake and physical activity and the control group (n = 41) received weekly SMS about general health issues for 4 months during pregnancy. Weight and length at birth were obtained from the participant's chart in WIC and compared between groups. Birthweight was categorized as small (SGA), appropriate (AGA) or large (LGA) for gestational age.ResultsWomen were age 27.7 ± 5.3y on average, 65.5% were Native Hawaiian, Pacific Islander or American Indian, 54.8% had some college or more and 37.8% were employed. Infant birth weight was similar in the intervention (3431 ± 682 g) and control groups (3232 ± 599 g; P > 0.05). Mothers in the control group had higher odds of having a SGA baby (OR: 2.21; 95% CI 0.40, 12.2) but similar risk of having a LGA baby (0.27; 95% CI 0.07, 1.05) compared to the intervention group. After adjusting for mothers’ age, education level and employment status, results were similar for SGA (OR: 2.34; 95% CI 0.43, 14.7) and LGA (OR: 0.35; 95% CI 0.08, 1.49).ConclusionsThere was no significant difference in birth weight between groups in mothers from the WIC program in Hawai‘i. More intensive educational interventions may be needed to observe an impact on birth weight

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

Effect of a multi-site trial using short message service (SMS) on infant feeding practices and weight gain in low-income minorities.

Objective: To test the effects of weekly SMS for improving infant feeding practices and infant weight. Methods: This was a multi-site randomized clinical trial in a convenience sample of 202 caregivers of healthy term infants 0–2 months participating in the WIC program in Puerto Rico and Hawaii. Participants were randomized to receive SMS about infant's general health issues (control) or SMS for improving feeding practices (intervention) for four months. Weight, length and infant feeding practices were assessed at baseline and four months later. Results: A total of 170 participants completed the study (n = 86 control and n = 84 intervention). Baseline characteristics were similar between groups. At the end, exclusive breastfeeding rates were similar between groups (67.4% control and 59.1% intervention). Introduction of other foods and beverages, addition of foods to the bottle, placing infants to sleep with milk bottles, caregiver's method and response to feeding infants and distractions while feeding infants were similar between groups. Also, weight status or rate of weight gain was similar between groups. Conclusion: There were no significant improvements in feeding practices or in weight with the intervention. The timeline of the messages in relation to the targeted behavior may have affected the effectiveness of the intervention. Earlier dissemination of messages, higher level of intensity, longer intervention, additional contacts and inclusion of other caregivers may be needed to achieve the desired effects