Low Frequency VLA Observations of Abell 754: Evidence for a Cluster Radio Halo and Possible Radio Relics

We present 74 MHz and 330 MHz VLA observations of Abell 754. Diffuse, halo-like emission is detected from the center of the cluster at both frequencies. At 330 MHz the resolution of 90'' distinguishes this extended emission from previously known point sources. In addition to the halo and at a much lower level, outlying steep-spectrum emission regions straddle the cluster center and are seen only at 74 MHz. The location, morphology and spectrum of this emission are all highly suggestive of at least one, and possibly two cluster radio relics. Easily obtained higher resolution, higher sensitivity VLA observations at both frequencies are required to confirm the extended nature of the halo-like emission and the 74 MHz relic detections. However, since there is prior evidence that this cluster is or has recently been in the process of a major merger event, the possible discovery of relics in this system is of great interest in light of recent observational and theoretical evidence in favor of a merger-relic connection. We discuss the possible role the merger shock waves, which are seen in the X-ray emission, may have played in the formation of the halo and radio relics in A754.Comment: 15 pages including 4 figures. Accepted for publication by Ap

A New System of Parallel Isolated Nonthermal Filaments Near the Galactic Center: Evidence for a Local Magnetic Field Gradient

We report the discovery of a system of isolated nonthermal filaments approximately 0.5 deg. northwest (75 pc in projection) of Sgr A. Unlike other isolated nonthermal filaments which show subfilamentation, braiding of subfilaments, and flaring at their ends, these filaments are simple linear structures and more closely resemble the parallel bundled filaments in the Galactic center radio arc. However, the most unusual feature of these filaments is that the 20/90 cm spectral index uniformly decreases as a function of length, in contrast to all other nonthermal filaments in the Galactic center. This spectral gradient may not be due to simple particle aging but could be explained by a curved electron energy spectrum embedded in a diverging magnetic field. If so, the scale of the magnetic gradient is not consistent with a large scale magnetic field centered on Sgr A* suggesting that this filament system is tracing a local magnetic field.Comment: 10 pages, AASTeX 5.01 LaTeX2e; 7 figures in 9 PostScript files; scheduled for publication in the 2001 December 10, v. 563 issue of Ap

Holographic Screening Length in a Hot Plasma of Two Sphere

We study the screening length of a quark-antiquark pair moving in a hot plasma living in two sphere $S^2$ manifold using AdS/CFT correspondence where the background metric is four dimensional Schwarzschild-AdS black hole. The geodesic solution of the string ends at the boundary is given by a stationary motion in the equatorial plane as such the separation length $L$ of quark-antiquark pair is parallel to the angular velocity $\omega$. The screening length and the bound energy are computed numerically using Mathematica. We find that the plots are bounded from below by some functions related to the momentum transfer $P_c$ of the drag force configuration. We compare the result by computing the screening length in the quark-antiquark reference frame where the gravity dual are "Boost-AdS" and Kerr-AdS black holes. Finding relations of the parameters of both black holes, we argue that the relation between mass parameters $M_{Sch}$ of the Schwarzschild-AdS black hole and $M_{Kerr}$ of the Kerr-AdS black hole in high temperature is given by $M_{Kerr}=M_{Sch}(1-a^2l^2)^{3/2}$, where $a$ is the angular momentum parameter.Comment: Major revision: title changed, adding authors, 13 pages, 8 figures, etc. Accepted for publication in European Physical Journal

Temperature effects on the strengh properties of microbially stabilized residual soil

Microbially Induced Calcite Precipitation (MICP) is a rather new technology that has shown greater potential in geotechnical engineering applications. The technique utilizes the concept of microbial involvements in carbonate precipitation within the soil matrix that lead to the improvement in strength and stiffness of the soil. This paper evaluated the effects of temperature variations on the performance of microbial calcite precipitations in residual soil. The soil specimens were cured under different temperature conditions; that are atmospheric temperature, 40, 45 and 50° C. Shear strength, pH and amount of calcite precipitated were determined for each curing condition. A bacterial concentration of 1×105 cfu/ml and 0.5 M concentration of the cementation reagents were used for the study. The results indicated a general increase in strength with increase in curing temperature; which is an indication of temperature influence in bacterial activity. The results so far obtained also revealed that the higher the amount of calcite precipitated the more the strength improvement up to 48 hours treatment duration; after which increase in calcite content does not results in the increase in strength

Optimal rice/colocasia cropping systems in the Ashanti, Eastern and Central regions within the semi-deciduous forest zone of Ghana.

This study is a follow-up survey to investigate the economic viability of the Rice/Colocasia cropping systems introduced by the Root and Tuber Improvement Project (RTIP)/Ministry of Food and Agriculture in the year 2000. It explores the possibility of improving the net earnings of farm families through appropriate farm plans. A Linear Programming model was developed to optimize net income from the Rice and Colocasia enterprises subject to land and labour constraints. The model selected the inter-cropping system as the optimal enterprise in relation to the resources available and allocated 1.2 ha for this cropping system out of the 3 ha available to the typical farm household. The maximum net income obtained from the inter-cropping system for the model farm was ¢4,454,726 ($543.26). There was a binding labour constraint for the first weeding of the farming activities with a shadow price of ¢14.65. Due to labour bottlenecks in certain times of the year, farmers paid unrealistic labour wages of up to ¢8,000 which resulted in low labour productivity in the study area. About 56% of the farmers were females with the younger generation forming the majority (58.9%). Journal of Science and Technology (Ghana) Vol. 27 (2) 2007: pp. 51-6

Upper Limits on the Continuum Emission from Geminga at 74 and 326 MHz

We report a search for radio continuum emission from the gamma-ray pulsar Geminga. We have used the VLA to image the location of the optical counterpart of Geminga at 74 and 326 MHz. We detect no radio counterpart. We derive upper limits to the pulse-averaged flux density of Geminga, taking diffractive scintillation into account. We find that diffractive scintillation is probably quenched at 74 MHz and does not influence our upper limit, S < 56 mJy (2\sigma), but that a 95% confidence level at 326 MHz is S < 5 mJy. Owing to uncertainties on the other low-frequency detections and the possibility of intrinsic variability or extrinsic variability (refractive interstellar scintillation) or both, our non-detections are nominally consistent with these previous detections.Comment: 8 pages, LaTeX2e with AASTeX 4.0, 3 figures; to be published in Ap

Discovery of a Non-Thermal Galactic Center Filament (G358.85+0.47) Parallel to the Galactic Plane

We report the discovery of a new non-thermal filament, G358.85+0.47, the ``Pelican'', located ~225 pc in projection from SgrA, and oriented parallel to the Galactic plane. VLA continuum observations at 20 cm reveal that this 7' (17.5 pc) structure bends at its northern extension and is comprised of parallel strands, most apparent at its ends. Observations at 6 and 3.6 cm reveal that the Pelican is a synchrotron-emitting source and is strongly linearly polarized over much of its extent. The spectral index of the filament changes from alpha(20/6)=-0.8 to alpha(6/3.6)=-1.5. The rotation measures exhibit a smooth gradient, with values ranging from -1000 rad/m2 to +500 rad/m2. The intrinsic magnetic field is well-aligned along the length of the filament. Based on these properties, we classify the Pelican as one of the non-thermal filaments unique to the Galactic center. Since these filaments (most of which are oriented perpendicular to the Galactic plane) are believed to trace the overall magnetic field in the inner Galaxy, the Pelican is the first detection of a component of this field parallel to the plane. The Pelican may thus mark a transition region of the magnetic field orientation in the inner kiloparsec of the Galaxy.Comment: 6 pages, 4 figures, to appear in ApJ Letters; Figs. 2 & 3 are color .ps files and best viewed in colo