Metastable supersymmetry breaking in N=2 non-linear sigma-models

We perform a general study of the issue of metastability for supersymmetry-breaking vacua in theories with N=1 and N=2 global supersymmetry. This problem turns out to capture all the important qualitative features of the corresponding question in theories with local supersymmetry, where gravitational effects induce only quantitative modifications. Moreover, it allows to directly compare the conditions arising in the N=1 and N=2 cases, since the latter becomes particular case of the former in the rigid limit. Our strategy consists in a systematic investigation of the danger of instability coming from the sGoldstini scalars, whose masses are entirely due to supersymmetry breaking mass-splitting effects. We start by reviewing the metastability conditions arising in general N=1 non-linear sigma-models with chiral and vector multiplets. We then turn to the case of general N=2 non-linear sigma-models with hyper and vector multiplets. We first reproduce and clarify the known no-go theorems applying to theories with only Abelian vector multiplets and only hyper multiplets, and then derive new results applying to more general cases. To make the comparison with N=1 models as clear as possible, we rely on a formulation of N=2 models where one of the supersymmetries is manifestly realized in terms of ordinary superfields, whereas the other is realized through non-trivial transformations. We give a self-contained account of such a construction of N=2 theories in N=1 superspace, generalizing previous work on various aspects to reach a general and coordinate-covariant construction. We also present a direct computation of the supertrace of the mass matrix.Comment: 50 pages, no figures; v2 minor corrections and addition of comments and reference

High speed simulation of flexible multibody dynamics

A multiflexible body dynamics code intended for fast turnaround control design trades is described. Nonlinear rigid body dynamics and linearized flexible dynamics combine to provide efficient solution of the equations of motion. Comparison with results from the DISCOS code provide verification of accuracy

Laser Repair of Superalloy Single Crystals with Varying Substrate Orientations

The casting and repair of single-crystal gas turbine blades require specific solidification conditions that prevent the formation of new grains, equiaxed or columnar, ahead of the epitaxial columnar dendrites. These conditions are best determined by microstructure modeling. Present day analytical models of the columnar-to-equiaxed transition (CET) relate the microstructure to local solidification conditions (temperature gradient and interface velocity) without taking into account the effects of (1) a preferred growth direction of the columnar dendrites and (2) a growth competition between columnar grains of different orientations. In this article, the infiuence of these effects on the grain structure of nickel-base superalloy single crystals, which have been resolidified after laser treatment or directionally cast, is determined by experiment and by analytical and numerical modeling. It is shown that two effects arise for the case of a nonzero angle between the local heat flux direction and the preferred dendrite growth axis: (1) the regime of equiaxed growth is extended and (2) a loss of the crystal orientation of the substrate often occurs by growth competition of columnar grains leading to an "oriented-to-misoriented transition” (OMT). The results are essential for the definition of the single-crystal processing window and are important for the service life extension of expensive components in land-based or aircraft gas turbine

Significance of Legumes for the Distribution of Plant Species in Grassland Ecosystems at Different Altitudes in the Alps

The composition of plant species in grassland communities is determined in part by negative and positive interactions among neighbouring plants; such interactions could be dispersal or - in the case of legumes - symbiotic N2 fixation or resource acquisition. We hypothesised that small scale distribution of plant species may be in part affected by (i) the plant's narrow dispersal in the close neighbourhood, (ii) by the N input into the soil through symbiotic N2 fixation by legumes, and (iii) by small scale heterogeneity of N availability in the soil. To address these hypotheses, in four species-rich semi-natural and natural grasslands along an altitudinal gradient from 900 to 2100ma.s.l., the association of species that grew within a radius of 5cm of selected plant species (central plant, CP) was studied. The distribution of the plant species within the plant community was not random and the species composition that grew within a radius of 5cm of a CP varied with altitude. The strength of the association between a CP and its neighbouring species decreased with increasing altitude. The 5cm radius was most dominated by individuals of the same species as the CP, suggesting that narrow dispersal (either through seeds or through vegetative propagates) may be most important for the species composition within the sward. δ15N values of non leguminous species growing near legumes compared to non leguminous species that grew far from legumes indicate that N from symbiotic N2 fixation may be another factor influencing the association of plant species. Effects of small scale heterogeneity in apparent N availability in the soil were detected to be the least important for the species compositio

A numerical model for the description of the lamellar and massive phase transformations in TiAl alloys

A phenomenological modelling approach has been developed to describe the massive transformation and the formation of lamellar microstructures during cooling in binary gamma titanium aluminides. The modelling approach is based on a combination of nucleation and growth laws which take into account the specific mechanisms of each phase transformation. Nucleation of massive and lamellar gamma is described with classical nucleation theory, accounting for the fact that nuclei are formed predominantly at alpha/alpha grain boundaries. Growth of the massive gamma grains is based on theory for interface-controlled reactions. A modified Zener model is used to calculate the thickening rate of the gamma lamellar precipitates. The model incorporates the effect of particle impingement and coverage of the nucleation sites by the growing phase. The driving pressures of the phase transformations are obtained from Thermo-Calc based on the actual temperature and matrix composition. CCT diagrams and lamellar spacings calculated with the model are in good agreement with experimental data obtained from dedicated heat treatment experiments and from the literature. The model permitted investigating the influence of cooling rate, alloy chemistry and average alpha grain size upon the amount of massive gamma and the average thickness and spacing of the lamellae. In particular it indicates that the Al depletion of the alpha phase during lamellar precipitation seems to play an important role in the suppression of the massive transformation at moderate cooling rate and in the large lamellar spacings observed at low cooling rate. (C) 2008 Elsevier Ltd. All rights reserved

Adolescents' contraception continuation in Switzerland: a prospective observational study.

Securing the adherence over time to contraception by adolescent girls is a challenge. Until now little was known about this topic in Switzerland. The aim of our study was to determine contraceptive continuation rates among adolescents in this country and assess possible predictive factors for discontinuation. A prospective observational cohort study of 12- to 19-year-old girls starting contraception was performed. Patients were interviewed again after 1 year by phone, email or postal mail. A total of 204 patients were included, of whom 85.8% chose a combined oestrogen-progestogen pill. The answer rate 1 year later was 71%. Among these, continuation of the initially prescribed contraceptive method was observed in 73.1%. Factors statistically affecting the continuation rate were the initial contraceptive method, the place of residence and sexual activity after 1 year. Classification of contraceptive methods in decreasing order of continuation rate was the following: long acting reversible contraception (LARC) methods, oestrogen-progestogen pills, injections, progestogen pills, patches and rings. Major reasons reported for stopping the prescribed contraceptive method were ending sexual relations (54.3%), developing side effects (34.3%) or changing to another contraceptive method (22.9%). Neither age, nationality, smoking, occupation, nor the legal representative's knowledge of the contraception influenced adherence. Contraceptive continuation rate was high among the adolescent population studied. The only predictive factor of discontinuation was the contraceptive method. Our study also reveals that respecting teenagers' confidentiality is essential as it does not negatively impact the continuation rate. The significant impact of the type of contraception on continuation rates stresses the importance of individualised counselling

Bi-directional thruster development and test report

The design, calibration and testing of a cold gas, bi-directional throttlable thruster are discussed. The thruster consists of an electro-pneumatic servovalve exhausting through opposite nozzles with a high gain pressure feedback loop to optimize performance. The thruster force was measured to determine hysteresis and linearity. Integral gain was used to maximize performance for linearity, hysteresis, and minimum thrust requirements. Proportional gain provided high dynamic response (bandwidth and phase lag). Thruster performance is very important since the thrusters are intended to be used for active control

The tobacco industry's past role in weight control related to smoking

Background: Smoking is thought to produce an appetite-suppressing effect by many smokers. Thus, the fear of body weight gain often outweighs the perception of health benefits associated with smoking cessation, particularly in adolescents. We examined whether the tobacco industry played a role in appetite and body weight control related to smoking and smoking cessation. Methods: We performed a systematic search within the archives of six major US and UK tobacco companies (American Tobacco, Philip Morris, RJ Reynolds, Lorillard, Brown & Williamson and British American Tobacco) that were Defendants in tobacco litigation settled in 1998. Findings are dated from 1949 to 1999. Results: The documents revealed the strategies planned and used by the industry to enhance effects of smoking on weight and appetite, mostly by chemical modifications of cigarettes contents. Appetite-suppressant molecules, such as tartaric acid and 2-acetylpyridine were added to some cigarettes. Conclusion: These tobacco companies played an active and not disclaimed role in the anti-appetite effects of smoking, at least in the past, by adding appetite-suppressant molecules into their cigarette

Origin of intragranular crystallographic misorientations in hot-dip Al-Zn-Si coatings

The origin of intragranular variations of the crystallographic orientation in hot-dip Al-Zn-Si coatings is discussed based on new experimental results and modelling. The solidification microstructure in as-received 55Al-43.4Zn-l.6Si (in wt.%) coatings deposited on steel plates in an industrial production line was analyzed by electron backscattered diffraction, glow-discharge optical emission spectroscopy and atomic force microscopy (AFM). The results were compared with those obtained in coatings re-solidified under different cooling and mechanical loading conditions. Continuous variations of the crystallographic orientation as large as 35 degrees were observed within individual grains of Al-Zn-Si, consistent with previous Studies. However, the mechanisms previously proposed for the origin of intragranular crystallographic misorientations had to be revisited. The new experimental data acquired during this study indicate that the solidification shrinkage accumulating in the area of the grain envelope is the driving Force for the formation of intragranular misorientations. The solidification shrinkage leads to the development of tensile stresses in the oxide film covering the coating while it solidifies. Estimations based on AFM profiles and phase field Simulations of the dendritic structure indicate that the stresses applied on the dendrite network are sufficient to deform plastically the dendrite arms during solidification. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved