Comparison of hot wire/laser velocimeter turbulence intensity measurements

The question of whether a random measure of particle velocities yields a good statistical estimate of the stationary condition of the turbulence flow field was investigated by comparing hot-wire and laser velocimeter turbulence intensity measurements. Great care was taken to insure that the instrument precision of both the laser velocimeter and hot wire was maximized. In this attempt to reduce the measurement uncertainties in the hot wire, direct digitization of the analog output signal was performed with point-by-point conversion to velocity through a spline fit calibration curve and the turbulence intensity function was calculated statistically. Frequent calibrations of the hot wire were performed using the laser velocimeter as the velocity standard to account for the presence of the small seed particles in the air flow and signal drift in the hot wire

Dark Radiation Emerging After Big Bang Nucleosynthesis?

We show how recent data from observations of the cosmic microwave background may suggest the presence of additional radiation density which appeared after big bang nucleosynthesis. We propose a general scheme by which this radiation could be produced from the decay of non-relativistic matter, we place constraints on the properties of such matter, and we give specific examples of scenarios in which this general scheme may be realized.Comment: v3: 5 pages, 1 figure. References added, typos corrected, notation changed throughout. v2: 5 pages, 1 figure. Reformatted, references added, acknowledgments updated, effect of radiation on CMB clarified. v1: 11 pages, 1 figur

Finite-size effects in lead scandium tantalate relaxor thin films

Large electromechanical effects in relaxor ferroelectrics are generally attributed to the collective response of an ensemble of correlated, nanometer-sized polar structures induced by chemical and charge disorder. Here, we study finite-size effects on such polar order (i.e., how it evolves when sample dimensions approach the polarization correlation length) in 7-70-nm-thick films of the relaxor ferroelectric PbSc0.5Ta0.5O3. Temperature-dependent polarization studies reveal a linear suppression of the polarization and nonlinearity associated with relaxor order as the film thickness decreases to ≈30 nm. Below this thickness, however, the suppression rapidly accelerates, and polarization is completely absent by film thicknesses of ≈7 nm, despite the continued observation of a broad peak in dielectric permittivity and frequency dispersion. Diffuse-scattering measurements reveal the diffuse-scattering symmetry, and analysis suggests the films have a polarization correlation length of ≈23 nm. Taken together, it is apparent that reduction of sample size and the resulting distribution of polar structures drive suppression and eventual quenching of the electrical response of relaxors, which may be attributed to increasing dipole-dipole and dipole-interface interactions

Glioblastoma multiforme tumor cells treated with Cisplatin and gamma irradiation

Includes bibliographical references.Glioblastoma multiforme (GBM) is the most prevalent and aggressive malignant primary brain tumor in humans. Once diagnosed, patient survival times range from three months if left untreated to a 12 percent survival rate at two years with palliative treatment. Death is usually a result of cerebral edema and increased intracranial pressure associated with a necrotic mass. Treatment of GBM is very difficult due to the vulnerability of healthy brain tissue to conventional treatments and the restricted ability of the brain to repair itself, as well as the difficulties associated with administering chemotherapeutic agents across the blood brain barrier. Treatment with gamma irradiation and chemotherapy concurrently has been shown to significantly improve patient survival rates when compared to tumor resection alone (Patwardhan et. al., 2004). The expression of apoptosis genes in response to treatment with cisplatin or a combination cisplatin and gamma irradiation in two GBM cell lines, U87 and U251, was investigated by quantitative real time polymerase chain reaction (qPCR). Ideally, up regulation of genes associated with pro-apoptotic pathways and down regulation of genes associated with anti-apoptotic pathways would increase levels of programmed cell death by apoptosis, as opposed to necrosis. This may result in decreased cerebral edema and pressure, thereby increasing patient survival rates.B.S. (Bachelor of Science