Array synthesis problems via convex relaxation

International audienceA general procedure, based on the SemiDefinite Re-laxation (SDR) technique, is presented to solve efficiently a wide range of difficult (because non-convex) array synthesis problems. This powerful approximation technique is easy to implement and the so-approximated problem can then be efficiently solved using off-the-shelf numerical routines. Examples of shaped beam and reconfigurable array synthesis are shown to illustrate the potentialities of the proposed approach

The Effect of Teenage Employment on Character Skills and Occupational Choice Strategies

A growing body of research suggests that, even after controlling for cognitive abilities, personality predicts economic success in later life. The learning environment at school focuses on knowledge and cognitive skills. The transmission of character skills, however, is not at the center of attention. Leisure activities as informal learning activities outside of school may affect the formation of personality. E.g. working while attending school is seen as a stepping stone toward independence and adulthood and can foster important character skills by providing opportunities to promote responsibility and further character skills. However, the channel of the positive influence has not been identified empirically. I suggest that employment during adolescence affects character skills that are known to have a positive effect on labor market outcomes and educational achievements. Employing a flexible strategy involving propensity score matching combined with regression adjustment, I find beneficial effects on character skills. Working while attending secondary school leads to a higher internal locus of control. In addition to promoting character skills, teenage employment improves knowledge on which skills and talents school students have and also the importance of parents' advices with respect to their future career. These results are robust to several model specifications and varying samples and robust to including family-fixed effects

Polarization Synthesis of Arbitrary Arrays with Shaped Beam Pattern

International audienceThe joint synthesis of the spatial power pattern and polarization of arbitrary arrays is addressed. Specifically, the element excitations are determined such that the array radiates a shaped power pattern while its polarization is optimized in an angular region. Any state of polarization (elliptical, circular and linear) can be synthesized and there is no restriction regarding the array geometry and element patterns. The synthesis problem is rewritten as a convex optimization problem, that is efficiently solved using readily available software. Various numerical results are presented to validate the proposed method and illustrate its potentialities

Application of Convex Relaxation to Array Synthesis Problems

International audienceA general procedure to solve efficiently non convex array synthesis problems is presented. It is based on the SemiDefinite Relaxation (SDR) technique. The way to properly relax the constraints in order to formulate the synthesis of shaped beams, phase-only arrays and reconfigurable arrays as semidefinite programming problems is detailed. These so-approximated array synthesis problems are then convex, easy to implement and can be efficiently solved using off-the-shelf numerical routines. The conditions under which the relaxed problems provide the optimal solution to the original non convex synthesis problems are specified. Various representative numerical comparisons with arrays designed by other approaches show the validity of the proposed method and illustrate its potentialities

Accurate array diagnosis from near-field measurements using ℓ1 reweighted minimization

International audienceIn this contribution the use of ℓ1 weighted minimization for the diagnosis of arrays from a reduced set of near-field data is investigated. Numerical results show that reweighed method gives a higher probability of an accurate estimation of the failures compared to the classic ℓ1 minimization proposed in the past literature

Tenancy Law Reform Act and Length of Tenancy Discount: Heterogenous Effects in a West German Household Sample

Compared to other European countries rental apartments dominate the German housing market. Policymakers and a large part of the population alike worry about the amount of affordable living space. Especially in metropolitan areas a high demand for living space exists and has been leading to a shortage and as a consequence to increasing rents. In 2001 the German government passed the Tenancy Law Reform Act to restrict the growth in rents (at least partially) and to strengthen the tenant's position. Up to now the efficacy of this reform has not been examined on national level. A further point of interest is the identification of a length of tenancy discount. The existing literature confirms such a discount where long-term tenants have to pay a lower real valued rent than short-term tenants. Our empirical analysis exploits data from the German Socio-Economic Panel (SOEP) that offers the unique advantage of a large and representative sample. We find that the Tenancy Law Reform Act in 2001 appears to have been successful in the restriction of exorbitant rents. Further, we identify a significant duration discount in the first years of a tenancy. This discount is significantly larger in the upper part of the conditional rent distribution

Neural Correlates of Social Behavior in Mushroom Body Extrinsic Neurons of the Honeybee Apis mellifera

The social behavior of honeybees (Apis mellifera) has been extensively investigated, but little is known about its neuronal correlates. We developed a method that allowed us to record extracellularly from mushroom body extrinsic neurons (MB ENs) in a freely moving bee within a small but functioning mini colony of approximately 1,000 bees. This study aimed to correlate the neuronal activity of multimodal high-order MB ENs with social behavior in a close to natural setting. The behavior of all bees in the colony was video recorded. The behavior of the recorded animal was compared with other hive mates and no significant differences were found. Changes in the spike rate appeared before, during or after social interactions. The time window of the strongest effect on spike rate changes ranged from 1 s to 2 s before and after the interaction, depending on the individual animal and recorded neuron. The highest spike rates occurred when the experimental animal was situated close to a hive mate. The variance of the spike rates was analyzed as a proxy for high order multi-unit processing. Comparing randomly selected time windows with those in which the recorded animal performed social interactions showed a significantly increased spike rate variance during social interactions. The experimental set-up employed for this study offers a powerful opportunity to correlate neuronal activity with intrinsically motivated behavior of socially interacting animals. We conclude that the recorded MB ENs are potentially involved in initiating and controlling social interactions in honeybees

Installing, Running and Maintaining Large Linux Clusters at CERN

Having built up Linux clusters to more than 1000 nodes over the past five years, we already have practical experience confronting some of the LHC scale computing challenges: scalability, automation, hardware diversity, security, and rolling OS upgrades. This paper describes the tools and processes we have implemented, working in close collaboration with the EDG project [1], especially with the WP4 subtask, to improve the manageability of our clusters, in particular in the areas of system installation, configuration, and monitoring. In addition to the purely technical issues, providing shared interactive and batch services which can adapt to meet the diverse and changing requirements of our users is a significant challenge. We describe the developments and tuning that we have introduced on our LSF based systems to maximise both responsiveness to users and overall system utilisation. Finally, this paper will describe the problems we are facing in enlarging our heterogeneous Linux clusters, the progress we have made in dealing with the current issues and the steps we are taking to gridify the clustersComment: 5 pages, Proceedings for the CHEP 2003 conference, La Jolla, California, March 24 - 28, 200

Level-rank duality of untwisted and twisted D-branes of the so(N)_K WZW model

We analyze the level-rank duality of untwisted and epsilon-twisted D-branes of the so(N)_K WZW model. Untwisted D-branes of so(N)_K are characterized by integrable tensor and spinor representations of so(N)_K. Level-rank duality maps untwisted so(N)_K D-branes corresponding to (equivalence classes of) tensor representations onto those of so(K)_N. The epsilon-twisted D-branes of so(2n)_2k are characterized by (a subset of) integrable tensor and spinor representations of so(2n-1)_2k+1. Level-rank duality maps spinor epsilon-twisted so(2n)_2k D-branes onto those of so(2k)_2n. For both untwisted and epsilon-twisted D-branes, we prove that the spectrum of an open string ending on these D-branes is isomorphic to the spectrum of an open string ending on the level-rank-dual D-branes.Comment: 18 page