A new stochastic differential equation approach for waves in a random medium

We present a mathematical approach that simplifies the theoretical treatment of electromagnetic localization in random media and leads to closed form analytical solutions. Starting with the assumption that the dielectric permittivity of the medium has delta-correlated spatial fluctuations, and using the Ito lemma, we derive a linear stochastic differential equation for a one dimensional random medium. The equation leads to localized wave solutions. The localized wave solutions have a localization length that scales inversely with the square of the frequency of the wave in the low frequency regime, whereas in the high frequency regime, this length varies inversely with the frequency to the power of two thirds

Galaxy Clustering at z ~ 2 and Halo Radii

The amplitude of the angular two-point galaxy correlation function w(\theta) for galaxies at z~2 is estimated for galaxies in the Hubble Deep Field by using a U < 27 complete sub-sample. (i) It is confirmed that the amplitude of the correlation can be corrected for the integral constraint without having to make assumptions about the shape of the correlation function and by avoiding the introduction of linear error terms. The estimate using this technique is w(5'') = 0.10 \pm 0.09. (ii) If the biases introduced in faint galaxy selection due to obscuration by large objects are not corrected for by masking areas around them, then the estimate would be w(5'') =0.16\pm 0.07. (iii) The effective (3-D) galaxy pair separation at 5'' and this redshift range is ~ 25-250 /h kpc, so the correction to the spatial correlation function \xi(r) due to exclusion of overlapping galaxy dark matter haloes should be considered. For clustering stable in proper units in an \Omega=1,\lambda=0 universe, our w(5\arcs) estimate (a) implies a present-day correlation length of r_0 ~ 2.6^{+1.1}_{-1.7}/h Mpc if halo overlapping is ignored, but (b) for a present-day correlation length of r_0=5.5/h Mpc implies that a typical halo exclusion radius is r_halo=70^{+420}_{-30}/h kpc. (iv) The decreasing correlation period (DCP) of a high initial bias in the spatial correlation function is not detected at this redshift. For an \Omega=1,\lambda=0 universe and (proper) stable clustering, possible detections of the DCP in other work would imply that \xi at redshifts greater than z_t = 1.7\pm0.9 would be [(1+z)/(1+z_t)]^{2.1\pm3.6} times higher than at z_t, which is consistent with our lack of a detection at z ~ 2.Comment: 17 pages, 13 figures, accepted for MNRAS, additional FITS files with HDF images available at http://www.iap.fr/users/roukema/xi2

Nonlocality of Accelerated Systems

The conceptual basis for the nonlocality of accelerated systems is presented. The nonlocal theory of accelerated observers and its consequences are briefly described. Nonlocal field equations are developed for the case of the electrodynamics of linearly accelerated systems.Comment: LaTeX file, no figures, 9 pages, to appear in: "Black Holes, Gravitational Waves and Cosmology" (World Scientific, Singapore, 2003

On Measuring Gravitomagnetism via Spaceborne Clocks: A Gravitomagnetic Clock Effect

DOI:10.1002/(SICI)1521-3889(199902)8:2<135The difference in the proper azimuthal periods of revolution of two standard clocks in direct and retrograde orbits about a central rotating mass is proportional to J/Mc^2, where J and M are, respectively, the proper angular momentum and mass of the source. In connection with this gravitomagnetic clock effect, we explore the possibility of using spaceborne standard clocks for detecting the gravitomagnetic field of the Earth. It is shown that this approach to the measurement of the gravitomagnetic field is, in a certain sense, theoretically equivalent to the Gravity Probe-B concept.This work has been supported in part by the Alexander von Humboldt Foundation

Beyond Gravitoelectromagnetism: Critical Speed in Gravitational Motion

A null ray approaching a distant astronomical source appears to slow down, while a massive particle speeds up in accordance with Newtonian gravitation. The integration of these apparently incompatible aspects of motion in general relativity is due to the existence of a critical speed. Dynamics of particles moving faster than the critical speed could then be contrary to Newtonian expectations. Working within the framework of gravitoelectromagnetism, the implications of the existence of a critical speed are explored. The results are expected to be significant for high energy astrophysics.Comment: 13 pages, to appear in the Special December 2005 Issue of Int. J. Mod. Phys.

The Dwarf Starburst Host Galaxy of a Type Ia SN at z = 1.55 from CANDELS

We present VLT/X-shooter observations of a high redshift, type Ia supernova host galaxy, discovered with HST/WFC3 as part of the CANDELS Supernova project. The galaxy exhibits strong emission lines of Ly{\alpha}, [O II], H{\beta}, [O III], and H{\alpha} at z = 1.54992(+0.00008-0.00004). From the emission-line fluxes and SED fitting of broad-band photometry we rule out AGN activity and characterize the host galaxy as a young, low mass, metal poor, starburst galaxy with low intrinsic extinction and high Ly{\alpha} escape fraction. The host galaxy stands out in terms of the star formation, stellar mass, and metallicity compared to its lower redshift counterparts, mainly because of its high specific star-formation rate. If valid for a larger sample of high-redshift SN Ia host galaxies, such changes in the host galaxy properties with redshift are of interest because of the potential impact on the use of SN Ia as standard candles in cosmology.Comment: 25 pages, 8 figures. Accepted for publication in Ap

Production modeling and forecasting of natural gas production from Barrow methane hydrate deposits

Thesis (M.S.) University of Alaska Fairbanks, 2011In this work, state-of-the-art existing simulation models of East Barrow and Walakpa natural gas fields with associated gas hydrates were rebuilt, tuned with additional data (some of the data used were from the Mt. Elbert Well, which significantly improved earlier models), and updated in terms of production data and history matching. Fluid contacts, saturations and hydrate dissociation/formation reactions were initialized for both models, actual production was matched and planned wells were placed accordingly. For each model, a gas hydrate saturation sensitivity study was performed. Simulation models were run and production forecasts for Walakpa field were made. There is a clear picture of East Barrow field behavior, but the Walakpa model still involves significant approximations. Additional log data from new wells planned in the Walakpa field will reduce reservoir properties uncertainty and make the model a more realistic reservoir management tool. A well choking study was performed on a hypothetical simplistic radial simulation grid with a vertical well. It was discovered that vertical gas wells drilled close to a hydrate zone tend to die due to hydrate blockage. Higher gas rates revealed improved production, but faster flow rate decline because of hydrate reformation. Horizontal wells could mitigate this problem due to their lower pressure drop per unit length of completed interval. They are also capable of higher production at lower drawdown. Since higher rate causes faster choking due to hydrate reformation, intermittent reduction of the flow rate is recommended for vertical wells in order to mitigate or at least delay the choking problem. Overall, both horizontal and vertical well designs are suitable for natural gas production from hydrate reservoirs.U.S. Department of Energy (DE-FC26-06NT42962), Petrotechnical Resources Alaska, Inc

Role of public sector in developing agricultural biotechnology in Iran

Agricultural experts in the field of biotechnology in Iran were surveyed in order to explore their perception  about factors influencing the participation of public sector in developing agricultural biotechnology in Iran.  Based on the results of the study, policy making, marketing, infrastructural, educational and research factors determined about 74% of variance of factors influencing the participation of public sector in developing agricultural biotechnology.Key words: Biotechnology, agriculture, Iran, public sector