Youth unemployment, labor market transitions, and scarring : evidence from Bosnia and Herzegovina, 2001-04

Relatively little is known about youth unemployment and its lasting consequences in transition economies, despite the difficult labor market adjustment experienced by these countries over the past decade. The authors examine early unemployment spells and their longer-term effects among the youth in Bosnia and Herzegovina (BiH), where the labor market transition is made more difficult by the challenges of a post-conflict environment. They use panel data covering up to 4,800 working-age individuals over the 2001 to 2004 period. There are three main findings from their analysis. First, youth unemployment is high-about twice the national average-consistent with recent findings from the BiH labor market study. Younger workers are more likely to go into inactivity or unemployment and are also less likely to transition out of inactivity, holding other things constant. Second, initial spells of unemployment or joblessness appear to have lasting adverse effects on earnings and employment ("scarring"). But there is no evidence that the youth are at a greater risk of scarring, or suffer disproportionately worse outcomes from initial joblessness, compared with other age groups. Third, higher educational attainment is generally associated with more favorable labor market outcomes. Skilled workers are less likely to be jobless and are less likely to transition from employment into joblessness. But there is evidence that the penalty from jobless spells may also be higher for more educated workers. The authors speculate that this may be due in part to signaling or stigma, consistent with previous findings in the literature.Labor Markets,Youth and Governance,Population Policies,Adolescent Health,Social Protections&Assistance

Asymptotically Optimal Approximation Algorithms for Coflow Scheduling

Many modern datacenter applications involve large-scale computations composed of multiple data flows that need to be completed over a shared set of distributed resources. Such a computation completes when all of its flows complete. A useful abstraction for modeling such scenarios is a {\em coflow}, which is a collection of flows (e.g., tasks, packets, data transmissions) that all share the same performance goal. In this paper, we present the first approximation algorithms for scheduling coflows over general network topologies with the objective of minimizing total weighted completion time. We consider two different models for coflows based on the nature of individual flows: circuits, and packets. We design constant-factor polynomial-time approximation algorithms for scheduling packet-based coflows with or without given flow paths, and circuit-based coflows with given flow paths. Furthermore, we give an $O(\log n/\log \log n)$-approximation polynomial time algorithm for scheduling circuit-based coflows where flow paths are not given (here $n$ is the number of network edges). We obtain our results by developing a general framework for coflow schedules, based on interval-indexed linear programs, which may extend to other coflow models and objective functions and may also yield improved approximation bounds for specific network scenarios. We also present an experimental evaluation of our approach for circuit-based coflows that show a performance improvement of at least 22% on average over competing heuristics.Comment: Fixed minor typo

Airframe Noise Simulations of a Full-Scale Aircraft

Computational results for a full-scale simulation of a Gulfstream G-III aircraft are presented. In support of a NASA airframe noise flight test campaign, Exa Corporations lattice Boltzmann PowerFLOW solver was used to perform time-accurate simulations of the flow around a highly detailed, full-scale aircraft model. Free-air boundary conditions were used at a Mach number of 0.23 and a Reynolds number of 10.5 10(exp 6) based on mean aerodynamic chord. This paper documents the simulation campaign for the baseline aircraft configuration at several flight conditions, including multiple flap deflections and main landing gear deployed or retracted. The high-fidelity, synthetic data were post-processed using a Ffowcs-Williams and Hawkings integral approach to estimate farfield acoustic behavior, with pressures on the model solid surface or a permeable surface enveloping the acoustic near field used as input. The numerical approach, simulation attributes, and the effects of grid resolution, gear deployment, and multiple flap deflections, are discussed as well

Time-scales of close-in exoplanet radio emission variability

We investigate the variability of exoplanetary radio emission using stellar magnetic maps and 3D field extrapolation techniques. We use a sample of hot Jupiter hosting stars, focusing on the HD 179949, HD 189733 and tau Boo systems. Our results indicate two time-scales over which radio emission variability may occur at magnetised hot Jupiters. The first is the synodic period of the star-planet system. The origin of variability on this time-scale is the relative motion between the planet and the interplanetary plasma that is co-rotating with the host star. The second time-scale is the length of the magnetic cycle. Variability on this time-scale is caused by evolution of the stellar field. At these systems, the magnitude of planetary radio emission is anticorrelated with the angular separation between the subplanetary point and the nearest magnetic pole. For the special case of tau Boo b, whose orbital period is tidally locked to the rotation period of its host star, variability only occurs on the time-scale of the magnetic cycle. The lack of radio variability on the synodic period at tau Boo b is not predicted by previous radio emission models, which do not account for the co-rotation of the interplanetary plasma at small distances from the star.Comment: 10 pages, 7 figures, 2 tables, accepted in MNRA

Analysis of Simulated and Experimental Noise Sources of Boeing 777 Main Gear Model via CLEAN in 3D

Previously obtained experimental and simulated phased microphone array data for the NASA 26%-scale model of a six-wheel main landing gear, with and without a toboggan-shaped noise reduction fairing, were analyzed using the CLEAN technique in three dimensions. The model is a high-fidelity representation of the Boeing 777-200 aircraft main landing gear. The reprocessing of the acoustic data was undertaken to address the deficiencies encountered in the source localization (beamform) maps and the integrated farfield spectra at mid to high frequencies in our previous study, where conventional array processing techniques were applied to the same data sets. Application of the CLEAN approach resulted in higher quality beamform maps with many of the previously observed side lobes either eliminated or suppressed significantly. As a result, integration of the experimentally and computationally based maps showed substantial improvement in the quality of the high-frequency spectral content relative to the corresponding spectra generated via conventional array processing, thus extending the good agreement achieved between the measured and predicted farfield spectra from 8 kHz to 14 kHz in model-scale frequencies. In addition, an examination of the simulated surface pressure fluctuations, off-surface flow field, and three-dimensionally constructed noise sources was conducted to determine the cause of the subtle discrepancies between measured and predicted sound pressure levels that occur in the 1,800 Hz to 4,000 Hz model-scale frequency range

Design and manufacture of engineered titanium-based materials for biomedical applications

Metallic materials have gained much attention recently from the areas of medical devices and orthopaedics. Artificial organs, dental implants, prostheses and implants that replace damaged or malfunctioning parts in the body are, or contain, metal components. Our ageing society poses an increased demand to provide devices and implants that can demonstrate better performance than those presented by traditional solutions. Matching the mechanical properties (i.e. stiffness and strength) of the device to those of the host tissue is a major challenge for the design and manufacture of engineered metal materials for biomedical applications. Failure in doing so provokes implant loosening, patient discomfort and repeated surgeries. Therefore, tailoring physical properties and biocompatibility of those materials is the main final aim of this research programme. This PhD study has focused on the tailoring of the mechanical properties of titanium-based materials and titanium-based alloys. Titanium inertness and the selection of biocompatible alloying elements were set as the baseline. Two approaches were employed to decrease stiffness (i.e. Young s modulus): one, by introducing porosity in a titanium matrix and therefore, reduce its Young s modulus, and two, by designing and manufacturing beta-titanium-based alloys with a reduced Young s modulus. Titanium scaffolds were manufactured using powder metallurgy with space holder technique and a sintering process. Different space holder sizes were used in four different categories to study the effect of pore size and porosity on the mechanical properties of the porosity engineered Ti scaffolds. Ti-based alloys were manufactured using manufacturing techniques such as sintering and arc-melting. The effect of different fabrication processes and the addition of beta-stabilising elements were studied and investigated. The obtained results of mechanical properties for pore size and porosity were within the values that match bone properties. This means these materials are suitable for biomedical application and the beta-Ti alloys results show that the mechanical properties can be decreased via tailoring the crystal structures. The characterisation of the Ti-based alloys helps to develop this material for its use in biomedical application

On the environment surrounding close-in exoplanets

Exoplanets in extremely close-in orbits are immersed in a local interplanetary medium (i.e., the stellar wind) much denser than the local conditions encountered around the solar system planets. The environment surrounding these exoplanets also differs in terms of dynamics (slower stellar winds, but higher Keplerian velocities) and ambient magnetic fields (likely higher for host stars more active than the Sun). Here, we quantitatively investigate the nature of the interplanetary media surrounding the hot Jupiters HD46375b, HD73256b, HD102195b, HD130322b, HD179949b. We simulate the three-dimensional winds of their host stars, in which we directly incorporate their observed surface magnetic fields. With that, we derive mass-loss rates (1.9 to 8.0 $\times 10^{-13} M_{\odot}$/yr) and the wind properties at the position of the hot-Jupiters' orbits (temperature, velocity, magnetic field intensity and pressure). We show that these exoplanets' orbits are super-magnetosonic, indicating that bow shocks are formed surrounding these planets. Assuming planetary magnetic fields similar to Jupiter's, we estimate planetary magnetospheric sizes of 4.1 to 5.6 planetary radii. We also derive the exoplanetary radio emission released in the dissipation of the stellar wind energy. We find radio fluxes ranging from 0.02 to 0.13 mJy, which are challenging to be observed with present-day technology, but could be detectable with future higher sensitivity arrays (e.g., SKA). Radio emission from systems having closer hot-Jupiters, such as from tau Boo b or HD189733b, or from nearby planetary systems orbiting young stars, are likely to have higher radio fluxes, presenting better prospects for detecting exoplanetary radio emission.Comment: 15 pages, 5 figures, accepted to MNRA

Exoplanet Transit Variability: Bow Shocks and Winds Around HD 189733b

By analogy with the solar system, it is believed that stellar winds will form bow shocks around exoplanets. For hot Jupiters the bow shock will not form directly between the planet and the star, causing an asymmetric distribution of mass around the exoplanet and hence an asymmetric transit. As the planet orbits thorough varying wind conditions, the strength and geometry of its bow shock will change, thus producing transits of varying shape. We model this process using magnetic maps of HD 189733 taken one year apart, coupled with a 3D stellar wind model, to determine the local stellar wind conditions throughout the orbital path of the planet. We predict the time-varying geometry and density of the bow shock that forms around the magnetosphere of the planet and simulate transit light curves. Depending on the nature of the stellar magnetic field, and hence its wind, we find that both the transit duration and ingress time can vary when compared to optical light curves. We conclude that consecutive near-UV transit light curves may vary significantly and can therefore provide an insight into the structure and evolution of the stellar wind.Comment: 9 Pages, 7 figures. Accepted for publication in Monthly Notices of The Royal Astronomical Societ