Lensed Arcs and Inner Structure of Abell 697

We present new optical observations of the z=0.282 cluster Abell 697 from the Keck II telescope. Images show an unusual disturbed structure in the cD halo and a previously unknown faint gravitational lens arc. A spectrum of the arc did not yield a redshift, but its spectrum and colors suggest it lies at z>1.3. We construct models to reproduce the arc that show the potential is likely to be highly elliptical. We suggest that this cluster may have undergone a recent merger and is in the process of forming its cD galaxy. Analysis of X-ray data from ROSAT and ASCA suggests that the merging process is sufficiently advanced that the gas in the cluster has relaxed, and A697 lies near the L_x-T_x relation for normal clusters.Comment: LaTeX; 12 pages, 3 figures, submitted to ApJ Letter

Constaints on the shape and scale of the galactic gravitational potential

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994.Includes bibliographical references (leaves 212-213).by Mark Robert Metzger.Ph.D

A Search for Distant Galactic Cepheids Toward l=60

We present results of a survey of a 6-square-degree region near l=60, b=0 to search for distant Milky Way Cepheids. Few MW Cepheids are known at distances >~ R_0, limiting large-scale MW disk models derived from Cepheid kinematics; this work was designed to find a sample of distant Cepheids for use in such models. The survey was conducted in the V and I bands over 8 epochs, to a limiting I~=18, with a total of ~ 5 million photometric observations of ~ 1 million stars. We present a catalog of 578 high-amplitude variables discovered in this field. Cepheid candidates were selected from this catalog on the basis of variability and color change, and observed again the following season. We confirm 10 of these candidates as Cepheids with periods from 4 to 8 days, most at distances > 3 kpc. Many of the Cepheids are heavily reddened by intervening dust, some with implied extinction A_V > 10 mag. With a future addition of infrared photometry and radial velocities, these stars alone can provide a constraint on R_0 to 8%, and in conjunction with other known Cepheids should provide good estimates of the global disk potential ellipticity.Comment: 18 pages, 4 tables, 13 figures (LaTeX / AASTeX

Generation of Transplantable Beta Cells for Patient-Specific Cell Therapy

Islet cell transplantation offers a potential cure for type 1 diabetes, but it is challenged by insufficient donor tissue and side effects of current immunosuppressive drugs. Therefore, alternative sources of insulin-producing cells and isletfriendly immunosuppression are required to increase the efficiency and safety of this procedure. Beta cells can be transdifferentiated from precursors or another heterologous (non-beta-cell) source. Recent advances in beta cell regeneration from somatic cells such as fibroblasts could circumvent the usage of immunosuppressive drugs. Therefore, generation of patient-specific beta cells provides the potential of an evolutionary treatment for patients with diabetes

Stable reduction of CCR5 by RNAi through hematopoietic stem cell transplant in non-human primates

RNAi is a powerful method for suppressing gene expression that has tremendous potential for therapeutic applications. However, because endogenous RNAi plays a role in normal cellular functions, delivery and expression of siRNAs must be balanced with safety. Here we report successful stable expression in primates of siRNAs directed to chemokine (c-c motif) receptor 5 (CCR5) introduced through CD34+ hematopoietic stem/progenitor cell transplant. After hematopoietic reconstitution, to date 14 months after transplant, we observe stably marked lymphocytes expressing siRNAs and consistent down-regulation of chemokine (c-c motif) receptor 5 expression. The marked cells are less susceptible to simian immunodeficiency virus infection ex vivo. These studies provide a successful demonstration that siRNAs can be used together with hematopoietic stem cell transplant to stably modulate gene expression in primates and potentially treat blood diseases such as HIV-1

HST and Palomar Imaging of GRB 990123: Implications for the Nature of Gamma-Ray Bursts and their Hosts

We report on HST and Palomar optical images of the field of GRB 990123, obtained on 8 and 9 February 1999. We find that the optical transient (OT) associated with GRB 990123 is located on an irregular galaxy, with magnitude V=24.20 +/- 0.15. The strong metal absorption lines seen in the spectrum of the OT, along with the low probability of a chance superposition, lead us to conclude that this galaxy is the host of the GRB. The OT is projected within the ~1'' visible stellar field of the host, nearer the edge than the center. We cannot, on this basis, rule out the galactic nucleus as the site of the GRB, since the unusual morphology of the host may be the result of an ongoing galactic merger, but our demonstration that this host galaxy has extremely blue optical to infrared colors more strongly supports an association between GRBs and star formation. We find that the OT magnitude on 1999 Feb 9.05, V = 25.45 +/- 0.15, is about 1.5 mag fainter than expected from extrapolation of the decay rate found in earlier observations. A detailed analysis of the OT light curve suggests that its fading has gone through three distinct phases: an early rapid decline (f_{nu} \propto t^{-1.6} for t < 0.1 days), a slower intermediate decline power-law decay (f_{nu} \propto t^{-1.1} for 0.1 < t < 2 days), and then a more rapid decay (at least as steep as (f_{\nu} \propto t^{-1.8} for t > 2 days). The break to steeper slope at late times may provide evidence that the optical emission from this GRB was highly beamed.Comment: Accepted for publication in Astrophysical Journal (Letters). Fourteen pages. Three encapsulated figure

Mid-infrared spectroscopy as an alternative to laboratory extraction for the determination of lime requirement in tillage soils

peer-reviewedLime is a crucial soil conditioner to bring agricultural soils to optimum pH values for nutrient availability. Lime recommendations are typically determined in laboratory extractions, the most common being the “Shoemaker- McLean and Pratt” (SMP) buffer method, that requires carcinogenic reagents soon to be abolished under the EU legislation. As an alternative to wet chemistry, mid-infrared (MIR) spectroscopy has shown to be a cost-and time effective method at predicting soil properties. The capability and feasibility of diffuse reflectance infrared spectroscopy (DRIFTS) to predict lime requirement (LR) in tillage fields is examined. Samples from 41 cereal tillage fields (n = 655) are used to build a calibration for DRIFTS using partial least squares regression (PLSR). The samples were split into calibration set (31 fields, n=495) and validation set (10 fields, n= 160). After preprocessing with trim, smoothing and standard normal variate, a calibration model using 6 latent variables, provided R2 of 0.89 and root mean square error of cross-validation (RMSECV) of 1.56 t/ha. Prediction of all fields from the validation set resulted in R2 of 0.76 and root mean square error of prediction (RMSEP) of 1.68 t/ ha. The predictions of the single fields ranged from R2 values of 0.41 to 0.72, RMSEP of 0.48 to 4.2 t/ha and ratios of performance to inter-quartile distance (RPIQ) of 0.45 to 3.56. It was shown that the signals of soil constituents having an influence on the LR were picked up in the spectra and were identified in the loading weights of the PLSR. While the error is too high to predict the variability of LR within the field, MIR prediction using field averages provided a viable alternative to current laboratory methods for blanket spreading of lime on tillage fields.Teagas