The Size and Nature of Lyman alpha Forest Clouds Probed by QSO Pairs and Groups

We describe a robust Bayesian statistical method for determining Lyman alpha forest cloud sizes in spherical and in thin disk geometries, using absorption in adjacent sightlines toward closely separated QSO pairs and groups, apply this method to the available data, and discuss implications of our results for models of Ly alpha clouds. Under the assumption of a population of uniform- size and unclustered clouds, the data from Q1343+2640A/B give a 99% confidence lower and upper bounds 61<R<533 kpc/h on the radius of spherical clouds at z about 1.8, with a median value of 149 kpc/h [$(\Omega_0, \Lambda_0) =(1,0)$]. The baryonic mass of such large clouds is comparable to that of dwarf irregular galaxies. Their cosmic overdensity is close to the turn-around density but generally below the virialization density, suggesting a population of gravi- tationally bound but unvirialized protogalactic objects at z about 2. Their comoving volume density is similar to that of the faint blue galaxies (FBGs) at the limiting magnitude B of 26-27. The dynamical collapsing timescale of over- densities like these clouds is also comparable with the cosmic time difference between z of 2 to 1. Both populations of objects show similar weak clustering in space. All this evidence suggests a possible identification of Ly alpha clouds as the collapsing progenitors of the FBGs at z about 1. We also investigate the other QSO pairs: Q0307-1931/1932, Q0107-0232/0235, and the triplet of Q1623+268. Imposing an uniform W_0 > 0.4 A threshold on all linelists, we find a trend of larger inferred cloud radius with larger proper separation of QSO pairs, significant at the 3.4 sigma level. This indicates that the idealization of unclustered, uniform-sized clouds does not accurately describe the Ly alpha cloud population.Comment: Astrophysical Journal accepted; 28 pages of uuencoded gzip compressed postscript file (including 8 figures). Also see the uncompressed postscript file at http://www.astro.columbia.edu/~fang

Electro-optic and Acousto-optic Laser Beam Scanners

Optical solid state deflectors rely on the electro-optical or acousto-optic effect. These Electro-Optical Deflectors (EODs) and Acousto-Optical Deflectors (AODs) do not contain moving parts and therefore exhibit high deflection velocities and are free of drawbacks associated with mechanical scanners. A description of the principles of operation of EODs and AODs is presented. In addition, characteristics, properties and the (dis)advantages of EODs and AODs, when compared to mirror based mechanical deflectors, is discussed. Deflection angles, speed and accuracy are discussed in terms of resolvable spots and related quantities. Also, response time, damage threshold, efficiency and the type and magnitude of beam distortions is addressed. Optical deflectors are characterized by high angular deflection velocities, but small deflection angles. Whereas mechanical mechanical scanners are characterized by relatively small deflection velocities, but large deflection angles. Arranging an optical deflector and a mechanical scanner in series allows to take advantage of the best of both world

A systematic review on biomonitoring of individuals living near or working at solid waste incinerator plants

Background: Solid waste incinerators (SWI) emit several pollutants among which polychlorodibenzodioxins and furans (PCDD/Fs), polychlorobiphenyls, metals, monocyclic and polycyclic aromatic hydrocarbons (PAHs). Aim of the study: To present a systematic review of peer-reviewed literature on human biological monitoring of exposure and effect following potential exposure to SWI pollutants to bring together evidences and to highlight strengths and deficiencies of the studies conducted so far. Methods: Relevant studies on biomonitoring of individuals living near or working at SWIs were selected through three steps: (1) a literature search in the Medline, CAplus, and Embase database; (2) the retrieved abstracts were screened by four independent reviewers; (3) the full text of the relevant papers was read, papers were pooled in studies, and then analyzed to highlight strengths and weaknesses. Studies with the strongest epidemiological design and/or the largest sample size were identified as reference studies. Results: One hundred and thirty-two papers, pooled in 82 studies, were included in the review: 67 on general population, 52 on SWI workers, and 14 on both groups. The most frequently investigated biomarkers were PCDD/Fs in plasma (87). Several studies presented limitations, such as a small samples size, scarce information on confounders, and a poor statistical analysis. Some earlier studies showed an increase of PCDD/Fs, lead, and PAHs in individuals (mainly workers) exposed to emissions from old SWIs; studies from the year 2000 showed no increase of biomarkers or biomarkers within the range of the general population; decreasing trends were observed in prospective studies. Conclusions: Most studies presented methodological pitfalls; reference studies showed no or a limited evidence of the impact of SWI on exposure and effect biomarkers

Uncertainties related to the representation of momentum transport in shallow convection

Convective momentum transport (CMT) has mostly been studied for deep convection, whereas little is known about its characteristics and importance in shallow convection. In this study, CMT by shallow convection is investigated by analyzing both data from large-eddy simulations (LESs) and reforecasts performed with the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). In addition, the central terms underlying the bulk mass-flux parametrization of CMT are evaluated offline. Further, the uncertainties related to the representation of CMT are explored by running the stochastically perturbed parametrizations (SPP) approach of the IFS. The analyzed cases exhibit shallow convective clouds developing within considerable low-level wind shear. Analysis of the momentum fluxes in the LES data reveals significant momentum transport by the convection in both cases, which is directed downgradient despite substantial organization of the cloud field. A detailed inspection of the convection parametrization reveals a very good representation of the entrainment and detrainment rates and an appropriate representation of the convective mass and momentum fluxes. To determine the correct values of mass-flux and in-cloud momentum at the cloud base in the parametrization yet remains challenging. The spread in convection-related quantities generated by the SPP is reasonable and addresses many of the identified uncertainties.ISSN:1942-246

The representation of the trade winds in ECMWF forecasts and reanalyses during EUREC4A

The characterization of systematic forecast errors in lower-tropospheric winds is an essential component of model improvement. This paper is motivated by a global, long-standing surface bias in the operational medium-range weather forecasts produced with the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). Over the tropical oceans, excessive easterly flow is found. A similar bias is found in the western North Atlantic trades, where the EUREC 4 A field campaign provides an unprecedented wealth of measurements. We analyze the wind bias in the IFS and ERA5 reanalysis throughout the entire lower troposphere during EUREC4 A. The wind bias varies greatly from day to day, resulting in root mean square errors (RMSEs) up to 2.5 m s(-1), with a mean wind speed bias up to -1 m s(-1) near and above the trade inversion in the forecasts and up to -0.5 m s(-1) in reanalyses. These biases are insensitive to the assimilation of sondes. The modeled zonal and meridional winds exhibit a diurnal cycle that is too strong, leading to a weak wind speed bias everywhere up to 5 km during daytime but a wind speed bias below 2 km at nighttime that is too strong. Removing momentum transport by shallow convection reduces the wind bias near the surface but leads to stronger easterly near cloud base. The update in moist physics in the newest IFS cycle (cycle 47r3) reduces the meridional wind bias, especially during daytime. Below 1 km, modeled friction due to unresolved physical processes appears to be too strong but is (partially) compensated for by the dynamics, making this a challenging coupled problem

Why is it so difficult to represent stably stratified conditions in numerical weather prediction (NWP) models?

In the 1990s, scientists at European Centre for Medium-Range Weather Forecasts (ECMWF) suggested that artificially enhancing turbulent diffusion in stable conditions improves the representation of two important aspects of weather forecasts, i.e., near-surface temperatures and synoptic cyclones. Since then, this practice has often been used for tuning the large-scale performance of operational numerical weather prediction (NWP) models, although it is widely recognized to be detrimental for an accurate representation of stable boundary layers. Here we investigate why, 20 years on, such a compromise is still needed in the ECMWF model. We find that reduced turbulent diffusion in stable conditions improves the representation of winds in stable boundary layers, but it deteriorates the large-scale flow and the near-surface temperatures. This suggests that enhanced diffusion is still needed to compensate for errors caused by other poorly represented processes. Among these, we identify the orographic drag, which influences the large-scale flow in a similar way to the turbulence closure for stable conditions, and the strength of the land-atmosphere coupling, which partially controls the near-surface temperatures. We also take a closer look at the relationship between the turbulence closure in stable conditions and the large-scale flow, which was not investigated in detail with a global NWP model. We demonstrate that the turbulent diffusion in stable conditions affects the large-scale flow by modulating not only the strength of synoptic cyclones and anticyclones, but also the amplitude of the planetary-scale standing waves

Implications of flexible spacer rotational processes on the liquid crystal behavior of 4,5-dihydroisoxazole benzoate dimers

The synthesis of some novel non-symmetric liquid crystal dimers, {3-[4-(octyloxyphenyl)]-4,5-dihydroisoxazol-5-yl}alkyl 4-(decyloxy)benzoates (5a–d) and 4-{3-[4-(octyloxyphenyl)]-4,5-dihydroisoxazol-5-yl}alkyl 4-{[6-(octyloxy)naphthalen-2-yl]ethynyl}benzoate (9a–d), are reported. The liquid-crystalline properties, theoretical calculations based on the conformational aspects of the flexible alkyl spacer and X-ray experiments are discussed. The syntheses of the key intermediates, 2-{3-[4-(octyloxy)phenyl]-4,5-dihydroisoxazol-5-yl}alkanol (3a–d), presenting the flexible alkyl spacer were achieved through [3+2] cycloaddition reactions between nitrile oxides, which were generated in situ by oxidation of the respective aromatic oximes, and dipolarophile alkenols (CH2[double bond, length as m-dash]CH(CH2)nOH, n = 1, 2, 3, and 4). The benzoates 5a–d were synthesized through esterification of 3a–d and p-n-decyloxybenzoic acid (4). The esters 9a–d were synthesized through derivatization of isoxazolines 3a–d into 4-{3-[4-(octyloxyphenyl)]-4,5-dihydroisoxazol-5-yl}alkyl 4-bromobenzoate (7a–d) followed by a Sonogashira reaction with 2-ethynyl-6-octyloxynaphthalene (8). 5a and 5b showed a monotropic smectic C phase. 9a/c displayed a enantiotropic nematic (N) mesophase, whereas 9b/d showed a monotropic nematic mesophase. No mesophase was observed for 7a–d. An odd–even effect was observed for 5a–d and 9a–d associated with the crystal to isotropic phase transition and crystal to nematic phase, respectively, as the length of the spacer was increased from 1 to 4 carbon atoms. The transitional properties were higher for odd-numbered members (n = 1 and 3) for all of the series studied. The X-ray data of compounds 5a and 5b are in agreement with polarizing optical microscopy observations with the assignment of an SmC mesophase. Density functional theory calculations using the B3LYP hybrid functional with the level 6-311G(d,p) basis set were performed for molecules 5a–d to correlate the conformation of the flexible spacer and the transitional properties. The conformational analysis showed that the most stable conformation for 5a–d is one where all of the carbon atoms of the flexible spacer are orientated at 180° (antiperiplanar orientation) except for 5a because the spacer is too short. The odd-numbered members have a more bent shape and are less elongated molecules than the even-numbered members. Thus, mesomorphic behavior is dictated by the conformational constraint imposed by the flexible spacer on the mesogenic groups

Model order reduction for nonlinear problems in circuit simulation

Electrical circuits usually contain nonlinear components. Hence we are interested in MOR methods that can be applied to a system of nonlinear Differential-Algebraic Equations (DAEs). In particular we consider the TPWL (Trajectory PieceWise Linear) and POD (Proper Orthogonal Decomposition) methods. While the first one fully exploits linearity, the last method needs modifications to become efficient in evaluation. We describe a particular technique based on Missing Point Estimatio