9 research outputs found
Toward Empirical Constraints on the Global Redshifted 21 cm Brightness Temperature During the Epoch of Reionization
Preliminary results are presented from a simple, single-antenna experiment
designed to measure the all-sky radio spectrum between 100 and 200 MHz. The
system used an internal comparison-switching scheme to reduce non-smooth
instrumental contaminants in the measured spectrum to 75 mK. From the
observations, we place an initial upper limit of 450 mK on the relative
brightness temperature of the redshifted 21 cm contribution to the spectrum due
to neutral hydrogen in the intergalactic medium (IGM) during the epoch of
reionization, assuming a rapid transition to a fully ionized IGM at a redshift
of 8. With refinement, this technique should be able to distinguish between
slow and fast reionization scenarios. To constrain the duration of reionization
to dz > 2, the systematic residuals in the measured spectrum must be reduced to
3 mK.Comment: Submitted to ApJ. 9 pages including 6 figure
Multiwavelength Observations of the Second Largest Known FR II Radio Galaxy, NVSS 2146+82
We present multi-frequency VLA, multicolor CCD imaging, optical spectroscopy,
and ROSAT HRI observations of the giant FR II radio galaxy NVSS 2146+82. This
galaxy, which was discovered by the NRAO VLA Sky Survey (NVSS), has an angular
extent of nearly 20' from lobe to lobe. The radio structure is normal for an FR
II source except for its large size and regions in the lobes with unusually
flat radio spectra. Our spectroscopy indicates that the optical counterpart of
the radio core is at a redshift of z=0.145, so the linear size of the radio
structure is ~4 h_50^-1 Mpc. This object is therefore the second largest FR II
known (3C 236 is ~6 h_50^-1 Mpc). Optical imaging of the field surrounding the
host galaxy reveals an excess number of candidate galaxy cluster members above
the number typically found in the field surrounding a giant radio galaxy. WIYN
HYDRA spectra of a sample of the candidate cluster members reveal that six
share the same redshift as NVSS 2146+82, indicating the presence of at least a
``rich group'' containing the FR II host galaxy. ROSAT HRI observations of NVSS
2146+82 place upper limits on the X-ray flux of 1.33 x 10^-13 ergs cm^-2 s^-1
for any hot IGM and 3.52 x 10^-14 ergs cm^-2 s^-1 for an X-ray AGN, thereby
limiting any X-ray emission at the distance of the radio galaxy to that typical
of a poor group or weak AGN. Several other giant radio galaxies have been found
in regions with overdensities of nearby galaxies, and a separate study has
shown that groups containing FR IIs are underluminous in X-rays compared to
groups without radio sources. We speculate that the presence of the host galaxy
in an optically rich group of galaxies that is underluminous in X-rays may be
related to the giant radio galaxy phenomenon.Comment: 46 pages, 15 figures, AASTeX aaspp4 style, accepted for publication
in A
The arrival directions of the most energetic cosmic rays
In this Letter we examine the arrival directions of the most energetic cosmic
rays (E > 2 * 10^19 eV) detected by several air shower experiments. We find
that data taken by different air shower arrays show positive correlations,
indicating a non--uniform arrival direction distribution. We also find that the
events with energy $ > 4 * 10^19 eV exhibit a correlation with the general
direction of the supergalactic plane, where a large number of potential sources
is located. If confirmed by data from other experiments our results would
support models for the extragalactic origin of the highest energy cosmic rays.Comment: 7 pages; 1 figure included; uuencoded, compressed PostScript file;
final version, corrected in some points, accepted for publication in
Phys.Rev.Let
Constructing an engineering model for moisture migration in bulk solids as a prelude to predicting moisture migration caking
The aim of this study was to examine one of the mechanisms behind moisture migration caking, where liquid solution bridges form between particles in a bulk solid system because of an increase in local relative humidity, and then solidify as the local relative humidity drops - the effect being increased as more cycles occur. The goal was to develop a one-dimensional model for the heat and mass transfer processes involved, based on established physics and the characteristic moisture sorption curve of the solid (in this case sugar). The model was verified using scaled-down equipment (a caking box) to simulate the caking in a big bag. The results of this study will assist in the prediction of caking produced in this way
Using virally expressed melanoma cDNA libraries to identify tumor-associated antigens that cure melanoma
Multiple intravenous injections of a cDNA library, derived from human melanoma cell lines and expressed using the highly immunogenic vector vesicular stomatitis virus (VSV), cured mice with established melanoma tumors. Successful tumor eradication was associated with the ability of mouse lymphoid cells to mount a tumor-specific CD4(+) interleukin (IL)-17 recall response in vitro. We used this characteristic IL-17 response to screen the VSV-cDNA library and identified three different VSV-cDNA virus clones that, when used in combination but not alone, achieved the same efficacy against tumors as the complete parental virus library. VSV-expressed cDNA libraries can therefore be used to identify tumor rejection antigens that can cooperate to induce anti-tumor responses. This technology should be applicable to antigen discovery for other cancers, as well as for other diseases in which immune reactivity against more than one target antigen contributes to disease pathology