A systematic review of associations between environmental exposures and development of asthma in children aged up to 9 years

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First Simultaneous Optical and EUV Observations of the Quasi-Coherent Oscillations of SS Cygni

Using EUV photometry obtained with the Extreme Ultraviolet Explorer (EUVE) satellite and UBVR optical photometry obtained with the 2.7-m telescope at McDonald Observatory, we have detected quasi-coherent oscillations (so-called ``dwarf nova oscillations'') in the EUV and optical flux of the dwarf nova SS Cygni during its 1996 October outburst. There are two new results from these observations. First, we have for the first time observed ``frequency doubling:'' during the rising branch of the outburst, the period of the EUV oscillation was observed to jump from 6.59 s to 2.91 s. Second, we have for the first time observed quasi-coherent oscillations simultaneously in the optical and EUV. We find that the period and phase of the oscillations are the same in the two wavebands, finally confirming the long-held assumption that the periods of the optical and EUV/soft X-ray oscillations of dwarf novae are equal. The UBV oscillations can be simply the Rayleigh-Jeans tail of the EUV oscillations if the boundary layer temperature kT_bb <~ 15 eV and hence the luminosity L_bb >~ 1.2e34 (d/75 pc)^2 erg/s (comparable to that of the accretion disk). Otherwise, the lack of a phase delay between the EUV and optical oscillations requires that the optical reprocessing site lies within the inner third of the accretion disk. This is strikingly different from other cataclysmic variables, where much or all of the disk contributes to the optical oscillations.Comment: 16 pages including 3 tables and 4 encapsulated postscript figures; LaTeX format, uses aastex.cls; accepted on 2001 August 2 for publication in The Astrophysical Journa

A high-finesse Fabry-Perot cavity with a frequency-doubled green laser for precision Compton polarimetry at Jefferson Lab

A high-finesse Fabry-Perot cavity with a frequency-doubled continuous wave green laser (532~nm) has been built and installed in Hall A of Jefferson Lab for high precision Compton polarimetry. The infrared (1064~nm) beam from a ytterbium-doped fiber amplifier seeded by a Nd:YAG nonplanar ring oscillator laser is frequency doubled in a single-pass periodically poled MgO:LiNbO$_{3}$ crystal. The maximum achieved green power at 5 W IR pump power is 1.74 W with a total conversion efficiency of 34.8\%. The green beam is injected into the optical resonant cavity and enhanced up to 3.7~kW with a corresponding enhancement of 3800. The polarization transfer function has been measured in order to determine the intra-cavity circular laser polarization within a measurement uncertainty of 0.7\%. The PREx experiment at Jefferson Lab used this system for the first time and achieved 1.0\% precision in polarization measurements of an electron beam with energy and current of 1.0~GeV and 50~$\mu$A.Comment: 20 pages, 22 figures, revised version of arXiv:1601.00251v1, submitted to NIM

Run Generation Revisited: What Goes Up May or May Not Come Down

In this paper, we revisit the classic problem of run generation. Run generation is the first phase of external-memory sorting, where the objective is to scan through the data, reorder elements using a small buffer of size M , and output runs (contiguously sorted chunks of elements) that are as long as possible. We develop algorithms for minimizing the total number of runs (or equivalently, maximizing the average run length) when the runs are allowed to be sorted or reverse sorted. We study the problem in the online setting, both with and without resource augmentation, and in the offline setting. (1) We analyze alternating-up-down replacement selection (runs alternate between sorted and reverse sorted), which was studied by Knuth as far back as 1963. We show that this simple policy is asymptotically optimal. Specifically, we show that alternating-up-down replacement selection is 2-competitive and no deterministic online algorithm can perform better. (2) We give online algorithms having smaller competitive ratios with resource augmentation. Specifically, we exhibit a deterministic algorithm that, when given a buffer of size 4M , is able to match or beat any optimal algorithm having a buffer of size M . Furthermore, we present a randomized online algorithm which is 7/4-competitive when given a buffer twice that of the optimal. (3) We demonstrate that performance can also be improved with a small amount of foresight. We give an algorithm, which is 3/2-competitive, with foreknowledge of the next 3M elements of the input stream. For the extreme case where all future elements are known, we design a PTAS for computing the optimal strategy a run generation algorithm must follow. (4) Finally, we present algorithms tailored for nearly sorted inputs which are guaranteed to have optimal solutions with sufficiently long runs

On the Correlated X-ray and Optical Evolution of SS Cygni

We have analyzed the variability and spectral evolution of the prototype dwarf nova system SS Cygni using RXTE data and AAVSO observations. A series of pointed RXTE/PCA observations allow us to trace the evolution of the X-ray spectrum of SS Cygni in unprecedented detail, while 6 years of optical AAVSO and RXTE/ASM light curves show long-term patterns. Employing a technique in which we stack the X-ray flux over multiple outbursts, phased according to the optical light curve, we investigate the outburst morphology. We find that the 3-12 keV X-ray flux is suppressed during optical outbursts, a behavior seen previously, but only in a handful of cycles. The several outbursts of SS Cygni observed with the more sensitive RXTE/PCA also show a depression of the X-rays during optical outburst. We quantify the time lags between the optical and X-ray outbursts, and the timescales of the X-ray recovery from outburst. The optical light curve of SS Cygni exhibits brief anomalous outbursts. During these events the hard X-rays and optical flux increase together. The long-term data suggest that the X-rays decline between outburst. Our results are in general agreement with modified disk instability models (DIM), which invoke a two-component accretion flow consisting of a cool optically thick accretion disk truncated at an inner radius, and a quasi-spherical hot corona-like flow extending to the surface of the white dwarf. We discuss our results in the framework of one such model, involving the evaporation of the inner part of the optically thick accretion disk, proposed by Meyer & Meyer-Hofmeister (1994).Comment: 24 pages, 8 figures, 2 tables, accepted for publication in Ap

Behavior and Weight Loss of Feeder Calves in a Railcar Modified for Feeding and Watering in Transit

The behavior of 164kg Angus and Hereford calves was studied in a double deck 26m x 2.6m jumbo railcar equipped with feed and water. A 4,180 liter water tank positioned in the center of each deck divided the car into four compartments. Fifty head were loaded into the lower and upper forward compartment (252kg/m2floor space], each containing 675kg of hay in racks. The two rear compartments served as quarters for equipment and researchers. Two video cameras were mounted in the upper forward compartment containing calves. Behavior of the calves was monitored, with portions video taped during rail transport from Memphis, Tennessee to Amarillo, Texas (57 hr) in June, 1979. The calves commenced eating and drinking immediately after being loaded in the railcar. Up to 75% of the cattle could lie down while the car was not in motion (14.4 hr of trip]. Calves stood at high speeds (80km/h] on unimproved track but continued to eat, drink and move about. Self and mutual grooming commonly occurred while traveling up to 40km/hr. Railcar temperature and relative humidity ranged from 17.8 to 41.1°C and 54 to 99%, respectively, and was identical to outside. Weight loss for 50 similar calves shipped by truck was 10.6% while rail calves lost 4.5% during truck transport to the railcar (11.3 hr) and 2.1% during rail transport for a total of 6.6%. Average daily gain (ADG) from initial weight to 7 days postshipment was .45kg for rail and -.02kg for truck, but ADG became similar at 30 days indicating full recovery. One truck calf was dead on arrival and 8% of the truck and 5% of the rail calves were treated for shipping fever. Excluding feedcosts, rail transport at 252kg/m 2 floor space costs 30% less per calf than transport in fully loaded trucks

Behavior and Weight Loss of Feeder Calves in a Railcar Modified for Feeding and Watering in Transit

The behavior of Angus and Hereford calves was studied in a double deck 26m x 2.6m jumbo railcar equipped with feed and water. A 4,180-liter water tank positioned in the center of each deck divided the car into four compartments. Fifty heads were loaded into the lower and upper forward compartments (252kg/m2 floor space], each containing 675kg of hay in racks. The two rear compartments served as quarters for equipment and researchers. Two video cameras were mounted in the upper forward compartment containing calves. The behavior of the calves was monitored, with portions video-taped during rail transport from Memphis, Tennessee, to Amarillo, Texas (57 hours) in June 1979. The calves commenced eating and drinking immediately after being loaded in the railcar. Up to 75% of the calves could lie down while the car was not in motion (14.4 hours of the trip]. Calves stood at high speeds (80km/h] on an unimproved track but continued to eat, drink and move about. Self and mutual grooming commonly occur while traveling up to 40km/hr. Railcar temperature and relative humidity ranged from 17.8 to 41.1oC and 54 to 99%, respectively, and were identical to the outside. Weight loss for 50 similar calves shipped by truck was 10.6%, while rail calves lost 4.5% during truck transport to the railcar (11.3 hours] and 2.1% during rail transport for a total of 6.6%. Average daily gain (ADG) from initial weight to 7 days post shipment was .45kg for rail and -.02 kilograms for truck, but ADG became similar at 30 days indicating full recovery. One truck calf was dead on arrival, and 8% of the truck and 5% of the rail calves were treated for shipping fever. Excluding feed costs, rail transport at 252kglm 2-floor space costs 30% less per calf than transport in fully loaded trucks

Non-Oberbeck-Boussinesq effects in turbulent thermal convection in ethane close to the critical point

As shown in earlier work (Ahlers et al., J. Fluid Mech. 569, p.409 (2006)), non-Oberbeck Boussinesq (NOB) corrections to the center temperature in turbulent Rayleigh-Benard convection in water and also in glycerol are governed by the temperature dependences of the kinematic viscosity and the thermal diffusion coefficient. If the working fluid is ethane close to the critical point the origin of non-Oberbeck-Boussinesq corrections is very different, as will be shown in the present paper. Namely, the main origin of NOB corrections then lies in the strong temperature dependence of the isobaric thermal expansion coefficient \beta(T). More precisely, it is the nonlinear T-dependence of the density \rho(T) in the buoyancy force which causes another type of NOB effect. We demonstrate that through a combination of experimental, numerical, and theoretical work, the latter in the framework of the extended Prandtl-Blasius boundary layer theory developed in Ahlers et al., J. Fluid Mech. 569, p.409 (2006). The latter comes to its limits, if the temperature dependence of the thermal expension coefficient \beta(T) is significant.Comment: 18 pages, 15 figures, 3 table

Coexistence of opposite opinions in a network with communities

The Majority Rule is applied to a topology that consists of two coupled random networks, thereby mimicking the modular structure observed in social networks. We calculate analytically the asymptotic behaviour of the model and derive a phase diagram that depends on the frequency of random opinion flips and on the inter-connectivity between the two communities. It is shown that three regimes may take place: a disordered regime, where no collective phenomena takes place; a symmetric regime, where the nodes in both communities reach the same average opinion; an asymmetric regime, where the nodes in each community reach an opposite average opinion. The transition from the asymmetric regime to the symmetric regime is shown to be discontinuous.Comment: 14 pages, 4 figure

The chemical evolution of the solar neighbourhood

Recent models of galactic chemical evolution account for updated evolutionary models of massive stars (with special emphasis on stellar winds) and for the effects of intermediate mass and massive binaries. The results are summarised. We also present a critical discussion on possible effects of stellar rotation on overall galactic chemical evolutionary simulations.Comment: 12 pages, 3 figures, Pacific Rim Conference, Xi'an, China, 11-17 July 200