Aquaculture for the poor in Cambodia

This lesson learned reviewed the current status of aquaculture in Cambodia. It primarily covers inland fish farming development and coastal aquaculture projects targeted at poverty alleviation and food security. It focuses on approaches aimed at developing low cost systems, and less on high input aquaculture systems that are usually inaccessible to poor families.

Mixing height determination by ceilometer

International audienceA novel method for estimating the mixing height based on ceilometer measurements is described and tested against commonly used methods for determining mixing height. In this method an idealised backscatter profile is fitted to the observed backscatter profile. The mixing height is one of the idealised backscatter profile parameters. An extensive amount of ceilometer data and vertical soundings data from the Helsinki area in 2002 is utilized to test the applicability of the ceilometer for mixing height determination. The results, including 71 convective and 38 stable cases, show that in clear sky conditions the mixing heights determined from ceilometer based aerosol profiles and BL-height estimates based on sounding data are in a good agreement. Rejected outlier cases corresponded to very low aerosol concentrations in the mixed layer leading to a very weak aerosol backscatter signal in the lowest layer

Localized thinning for strain concentration in suspended germanium membranes and optical method for precise thickness measurement

We deposited Ge layers on (001) Si substrates by molecular beam epitaxy and used them to fabricate suspended membranes with high uniaxial tensile strain. We demonstrate a CMOS-compatible fabrication strategy to increase strain concentration and to eliminate the Ge buffer layer near the Ge/Si hetero-interface deposited at low temperature. This is achieved by a two-steps patterning and selective etching process. First, a bridge and neck shape is patterned in the Ge membrane, then the neck is thinned from both top and bottom sides. Uniaxial tensile strain values higher than 3% were measured by Raman scattering in a Ge membrane of 76 nm thickness. For the challenging thickness measurement on micrometer-size membranes suspended far away from the substrate a characterization method based on pump-and-probe reflectivity measurements was applied, using an asynchronous optical sampling technique.EC/FP7/628197/EU/Heat Propagation and Thermal Conductivity in Nanomaterials for Nanoscale Energy Management/HEATPRONAN

A Cold Front in A3667: Hydrodynamics and Magnetic Field in the Intracluster Medium

This conference presentation discusses a Chandra observation of the cold front in Abell 3667. We first review our earlier results which include a measurement of the front velocity, M~1, using the ratio of exterior and interior gas pressures; observations of the hydrodynamic effects expected for a transonic front motion (weak bow shock and gas compression near the leading edge of the front); direct observation of the suppressed diffusion across the front, and estimate of the magnetic field strength near the front from suppression of the Kelvin-Helmholtz instabilities. The new results include using the 2-dimensional brightness distribution inside the cold front (a) to show that the front is stable and (b) to map the mass distribution in the gas cloud. This analysis confirms the existence of a dark matter subcluster traveling with the front. We also fix an algebraic error in our published calculations for the growth rate of the KH instability and discuss an additional effect which could stabilize the front against the small-scale perturbations. These updates only strengthen our conclusions regarding the importance of the magnetic fields for the front dynamics.Comment: Shortened version of the paper published in Astronomy Letters; based on talk at conference "High Energy Astrophysics 2001", Moscow, Dec 200

Weak Lensing with SDSS Commissioning Data: The Galaxy-Mass Correlation Function To 1/h Mpc

(abridged) We present measurements of galaxy-galaxy lensing from early commissioning imaging data from the Sloan Digital Sky Survey (SDSS). We measure a mean tangential shear around a stacked sample of foreground galaxies in three bandpasses out to angular radii of 600'', detecting the shear signal at very high statistical significance. The shear profile is well described by a power-law. A variety of rigorous tests demonstrate the reality of the gravitational lensing signal and confirm the uncertainty estimates. We interpret our results by modeling the mass distributions of the foreground galaxies as approximately isothermal spheres characterized by a velocity dispersion and a truncation radius. The velocity dispersion is constrained to be 150-190 km/s at 95% confidence (145-195 km/s including systematic uncertainties), consistent with previous determinations but with smaller error bars. Our detection of shear at large angular radii sets a 95% confidence lower limit $s>140^{\prime\prime}$, corresponding to a physical radius of $260h^{-1}$ kpc, implying that galaxy halos extend to very large radii. However, it is likely that this is being biased high by diffuse matter in the halos of groups and clusters. We also present a preliminary determination of the galaxy-mass correlation function finding a correlation length similar to the galaxy autocorrelation function and consistency with a low matter density universe with modest bias. The full SDSS will cover an area 44 times larger and provide spectroscopic redshifts for the foreground galaxies, making it possible to greatly improve the precision of these constraints, measure additional parameters such as halo shape, and measure the properties of dark matter halos separately for many different classes of galaxies.Comment: 28 pages, 11 figures, submitted to A

Revealing high-z Fermi-LAT BL Lacs using Swift and SARA data with photometric analysis

BL Lacertae (BL Lac) objects are one type of blazar, distinguished by their featureless optical spectrum. This presents a challenge in measuring the redshift of the BL Lacs. This paper uses the photometric dropout technique to measure the redshifts of BL Lac objects. Space-based telescope \emph{Swift} and ground-based SARA telescopes are employed to provide magnitudes in the $uvw2,\ uvm2,\ uvw1,\ u,\ b,\ v,\ g',\ r',\ i',\ z'$filters. We observe 60 BL Lacs and report reliable redshift upper limits for 41 sources. We discover four high-$z$BL Lacs ($z>1.3$), bringing the number of high-$z BL Lacs found by this method up to 20. We also discuss the blazar sequence, the \emph{Fermi} blazar divide, and the gamma-ray horizon using the 4LAC catalog and all high-z$ BL Lacs discovered with the photo-z technique.Comment: 16pages, 7 figure

Cluster Lenses

Clusters of galaxies are the most recently assembled, massive, bound structures in the Universe. As predicted by General Relativity, given their masses, clusters strongly deform space-time in their vicinity. Clusters act as some of the most powerful gravitational lenses in the Universe. Light rays traversing through clusters from distant sources are hence deflected, and the resulting images of these distant objects therefore appear distorted and magnified. Lensing by clusters occurs in two regimes, each with unique observational signatures. The strong lensing regime is characterized by effects readily seen by eye, namely, the production of giant arcs, multiple-images, and arclets. The weak lensing regime is characterized by small deformations in the shapes of background galaxies only detectable statistically. Cluster lenses have been exploited successfully to address several important current questions in cosmology: (i) the study of the lens(es) - understanding cluster mass distributions and issues pertaining to cluster formation and evolution, as well as constraining the nature of dark matter; (ii) the study of the lensed objects - probing the properties of the background lensed galaxy population - which is statistically at higher redshifts and of lower intrinsic luminosity thus enabling the probing of galaxy formation at the earliest times right up to the Dark Ages; and (iii) the study of the geometry of the Universe - as the strength of lensing depends on the ratios of angular diameter distances between the lens, source and observer, lens deflections are sensitive to the value of cosmological parameters and offer a powerful geometric tool to probe Dark Energy. In this review, we present the basics of cluster lensing and provide a current status report of the field.Comment: About 120 pages - Published in Open Access at: http://www.springerlink.com/content/j183018170485723/ . arXiv admin note: text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author