Neutron Detection Using Amorphous Boron-Carbide Hetero-Junction Diodes

The high energy products of the 10B(n,α)7Li neutron capture reaction were explored as a means of thermal neutron detection in thin film amorphous boron carbide (a--B5C:Hx) on n-type silicon hetero-junction diodes. Pulse height spectroscopy was conducted on the diodes while they were subjected to a moderated plutonium-beryllium (PuBe) source. Neutron capture could not be confirmed experimentally in any of the devices tested. Device modeling was performed to investigate the cause for the diode detector\u27s negative response. A 1.47 MeV α particle produced transient current of 10-7 A and the induced was 4.7 times less than intrinsic noise charge of the preamplifier. Further investigation of the model emphasized the transient current magnitude was most dependent on the electric field strength. The possibility of direct-conversion hetero-junction neutron detectors was not experimentally confirmed, but simulations using only 10μm of silicon however did generate transient currents 2 factors larger than steady-state reverse bias currents

Testing predictions of the oxidative stress hypothesis of aging using a novel invertebrate model of longevity: the giant clam (Tridacna derasa).

Bivalve species with exceptional longevity are newly introduced model systems in biogerontology to test evolutionarily conserved mechanisms of aging. Here, we tested predictions based on the oxidative stress hypothesis of aging using one of the tropical long-lived sessile giant clam species, the smooth giant clam (Tridacna derasa; predicted maximum life span: >100 years) and the short-lived Atlantic bay scallop (Argopecten irradians irradians; maximum life span: 2 years). The warm water-dwelling giant clams warrant attention because they challenge the commonly held view that the exceptional longevity of bivalves is a consequence of the cold water they reside in. No significant interspecific differences in production of H2O2 and O2- in the gills, heart, or adductor muscle were observed. Protein carbonyl content in gill and muscle tissues were similar in T derasa and A i irradians. In tissues of T derasa, neither basal antioxidant capacities nor superoxide dismutase and catalase activities were consistently greater than in A i irradians. We observed a positive association between longevity and resistance to mortality induced by exposure to tert-butyl hydroperoxide (TBHP). This finding is consistent with the prediction based on the oxidative stress hypothesis of aging. The findings that in tissues of T derasa, proteasome activities are significantly increased as compared with those in tissues of A i irradians warrant further studies to test the role of enhanced protein recycling activities in longevity of bivalves

Gene expression profiles of human breast cancer progression

Although distinct pathological stages of breast cancer have been described, the molecular differences among these stages are largely unknown. Here, through the combined use of laser capture microdissection and DNA microarrays, we have generated in situ gene expression profiles of the premalignant, preinvasive, and invasive stages of human breast cancer. Our data reveal extensive similarities at the transcriptome level among the distinct stages of progression and suggest that gene expression alterations conferring the potential for invasive growth are already present in the preinvasive stages. In contrast to tumor stage, different tumor grades are associated with distinct gene expression signatures. Furthermore, a subset of genes associated with high tumor grade is quantitatively correlated with the transition from preinvasive to invasive growth