Search Results - (Author, Cooperation:M. Gallagher)

2018-03-06

Rockefeller University Press

0022-1007

1540-9538

Medicine

2018-01-03

Rockefeller University Press

0022-1007

1540-9538

Medicine

2018-01-26

Wiley-Blackwell

0148-0227

Geosciences

Physics

2018-02-09

Genetics Society of America (GSA)

2160-1836

Biology

2011-09-13

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; B-Lymphocytes/cytology/metabolism ; Cell Lineage/genetics ; Chromosomes, Mammalian/genetics/metabolism ; DNA, Intergenic/*genetics ; Enhancer Elements, Genetic/genetics ; Feedback, Physiological ; Gene Rearrangement, B-Lymphocyte, Heavy Chain/*genetics ; Germ Cells/metabolism ; Immunoglobulin Heavy Chains/genetics ; Immunoglobulin Variable Region/genetics ; Mice ; Mutation/genetics ; Recombination, Genetic/*genetics ; Regulatory Sequences, Nucleic Acid/*genetics ; Repressor Proteins/*metabolism ; Thymus Gland/cytology ; Transcription, Genetic/genetics ; VDJ Exons/*genetics

1440-1797

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1440-1797

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We present a general theory that describes the operation of scanning force microscopy in the contact force regime. We find that force derivatives along the surface of a sample produce images that can be dramatically enhanced relative to those of surface topography. For scanning tunneling microscopy atomic force microscopy (STM/AFM) and AFM configurations, the spring constant of the cantilever and the force derivatives perpendicular to the surface of the sample determine the enhancement, respectively.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We have conducted a detailed study of the thermal stability of Bragg gratings written in hydrogen-loaded and unloaded germanium-doped optical fiber. Interference of either continuous-wave or pulsed ultraviolet light was used to induce the index modulation gratings. Some gratings were kept at room temperature and others were annealed at fixed temperatures for 10–20 h. For temperatures between room temperature and 350 °C, gratings in the hydrogen-loaded fiber showed significantly greater decay than those in the unloaded counterpart. The ultraviolet-induced index modulation in hydrogen-loaded fiber was reduced by 40% after 10 h at 176 °C, whereas it was reduced by only 5% in unloaded fiber under the same conditions. The annealing behavior of gratings written using the pulsed source was identical to that of gratings written with the continuous-wave source, and the thermal stability of gratings in hydrogen-loaded fiber did not depend on the magnitude of the index modulation. We also observed that the annealing of ultraviolet-induced OH absorption in the hydrogen-loaded fiber was not correlated with the grating decay. Our annealing results show that the species responsible for the index change in the hydrogen-loaded fiber are less stable than those in the unloaded fiber. © 1995 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) of quantum well structures can give an independent method of measuring superlattice spacing and uniformity without having to resort to more involved techniques requiring intricate sample preparation. We present the first AFM images of cleaved InGaAs/InP multiple quantum wells and compare them with STM images taken of the same heterostructure. The images were stable in air for over a day. Based on our results, we propose that the mechanism for contrast in our images is due to an oxide layer that grows primarily on the InGaAs wells and not on the InP barriers. Both STM and AFM clearly resolve the individual wells of the heterostructure, although STM measured a larger corrugation than an AFM. STM also exhibited superior lateral resolution of about 2 nm while AFM had a lateral resolution of approximately 6 nm.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Accurate ultraviolet absorption measurements are reported in telecommunication single-mode optical fibers in the range from 280 to 600 nm (4.4–2.1 eV) using a cutback method. An absorption peak at 325 nm (3.8 eV) and an absorption edge near 290 nm (4.3 eV) are attributed to features seen in preform spectra. We suggest that fiber and preform absorption spectra are generally the same and do not find that there is any dependence in the absorption on the fiber dimensions. The effects of preparation for second harmonic generation on fiber absorption are also discussed.

Electronic Resource

1365-3083

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The effect of neonatal thymectomy on the development of splenic and bone marrow natural cell-mediated cytotoxicity and on genetic resistance to bone marrow transplantation was examined in mice. Natural cytotoxicity was measured by a 51Cr release assay; the ability to engraft foreign bone marrow was assayed by the spleen colony method. The natural cytolytic response of spleen cells increased progressively from youth to early adulthood, whereas that of the bone marrow declined during the same age period. Neonatal thymectomy significantly elevated the natural killer cell response of young mice only (4 weeks, spleen; 6 weeks, bone marrow). In other experiments, neonatally thymectomized and sham-operated mice were lethally irradiated at 4 or 6 weeks of age and injected with 2.5, 5.0 or 10 million rat marrow cells. Six days later spleen colonies were markedly reduced in both 4- and 6-week-old neonatally thymectomized mice with all rat marrow cell doses tested. Neonatal thymectomy did not alter the percentage of erythroid versus other colonies at either 4 or 6 weeks. In both thymectomized and sham-operated mice the number of colonies increased with increases in marrow cell dose. The data are suggestive of a production and dissemination to the spleen of cells involved in the natural cytotoxic response from the bone marrow.

Electronic Resource

1467-8535

Blackwell Publishing Journal Backfiles 1879-2005

Education

Electronic Resource

1365-2427

Blackwell Publishing Journal Backfiles 1879-2005

Biology

1. Natural variation in environmental parameters, as well as practical constraints in study design and sampling methodology, often pose difficulties in treating impact assessments in river catchments as controlled field experiments. It is frequently impossible to develop robust relationships between reference and test stations prior to the onset of an impact and the range of statistical tools which can be adopted in data analysis to detect a change or disturbance is limited.2. In an attempt to overcome these problems we introduce a novel disturbance index to assess the impact of landuse activities on river systems. The index identifies differences in hydrochemical parameters and macroinvertebrate community metrics between reference and test stations (at a set level of significance). This approach allows for objective assessment of the occurrence and direction of change as well as the duration of an impact. The disturbance index can be applied at different scales – for a single stream, a catchment or a region.3. In this paper we describe the derivation of the index and illustrate its utility through worked examples. We use the index to assess impact of clearfelling on hydrochemical parameters such as hydrogen ion concentration, total hardness, suspended solids, conductivity and nitrate concentration as well as on macroinvertebrate parameters including abundance, richness, reciprocal of Simpson's diversity index, evenness, Ephemeroptera/Plecoptera/Trichoptera (EPT) richness and percentage of EPT taxa.4. The sensitivity of the disturbance index changes with scale of application however, and the clearfelling (CF) index has proven sensitive to the detection of even quite small changes, although in these cases ecological significance should be considered. We show that the CF index, particularly when derived from a regional scale, is a conservative index but is very robust to variation in the number of samples used in its derivation. The application of the index corresponded very well with the application of more standard statistical approaches. We believe that the index can thus be applied to other impact studies with similar project design.

Electronic Resource

1460-9568

Blackwell Publishing Journal Backfiles 1879-2005

Medicine

The identification of neurogenesis in the dentate gyrus of adult mammals has sparked much interest in a functional role for these new neurons in hippocampal-dependent cognition. The current investigation used a model of age-related cognitive decline in rodents to study the relationship between changes in markers of neurogenesis and hippocampal function. New cell production in the granule cell layer was progressively reduced across the lifespan of male Long Evans rats, with a 40% reduction at middle age (13 months) and a reduction in excess of 80% in advanced age (25 months), compared with young mature adults (7 months). These effects of aging were not, however, predictive of cognitive status. In particular, the pronounced decrease in new cell production during aging did not distinguish among rats that varied over a wide range of cognitive abilities.

Electronic Resource

1365-2109

Blackwell Publishing Journal Backfiles 1879-2005

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract. The influence of temperature on growth of European eels, Anguilla anguilla L., of various body sizes was studied. The mean weight of small eels (SE) (0·6g body weight) maintained at 23°C was significantly lower than that of SE maintained at 25°C or 27°C. No significant differences were found at the end of the experimental period between SE maintained at 25 and 27°C. Similar results were obtained among the moderate-size eels (ME) (l·5gbody weight). However, the average weight increase maintained at 25°C was significantly higher than that of large eels (LE) (3·25g body weight) maintained at 23 or 27°C. It seems that the optimum growth temperature for European eels is different at various stages in their growth and development.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

The oligopeptide permease of Salmonella typhimurium is a periplasmic binding protein-dependent transport system. Five gene products, OppABCDF, are required for the functioning of this transporter, two of which (OppB and OppC) are highly hydrophobic, integral membrane proteins and are responsible for mediating passage of peptides across the cytoplasmic membrane. OppB and OppC are each predicted, from their sequences, to span the membrane many times. In this paper we describe experimental evidence confirming these predictions using a combination of biochemical, immunological and genetic procedures. Each of these two proteins is shown to span the membrane six times, with the N- and C-termini both being located at the cytoplasmic face of the membrane. Opp is apparently a typical member of the ABC (ATP-binding cassette) superfamily of transporters. These findings, therefore, have general implications for the organization and function of other ABC transporters, including the human multidrug resistance protein and the product of the cystic fibrosis gene.

Electronic Resource

1365-2958

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

Bacillus subtilis spo0K mutants are blocked at the first step in sporulation. The spo0K strain was found to contain two mutations: one was linked to the trpS locus, and the other was elsewhere on the chromosome. The mutation linked to trpS was responsible for the sporulation defect (spo-). The unlinked mutation enhanced this sporulation deficiency but had no phenotype on its own. The spo- mutation was located in an operon of five genes highly homologous to the oligopeptide transport (Opp) system of Gram-negative species. Studies with toxic peptide analogues showed that this operon does indeed encode a peptide-transport system. However, unlike the Opp system of Salmonella typhimurium, one of the two ATP-binding proteins, OppF, was not required for peptide transport or for sporulation. The OppA peptide-binding protein, which is periplasmically located in Gram-negative species, has a signal sequence characteristic of lipo-proteins with an amino-terminal lipo-amino acid anchor. Cellular location studies revealed that OppA was associated with the cell during exponential growth, but was released into the medium in stationary phase. A major role of the Opp system in Gram-negative bacteria is the recycling of cell-wall peptides as they are released from the growing peptidoglycan. We postulate that the accumulation of such peptides may play a signaling role in the initiation of sporulation, and that the sporulation defect in opp mutants results from an inability to transport these peptides.

Electronic Resource

1095-8649

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Carnivorous juveniles (〈16 mm LS) of pinfish Lagodon rhomboides apparently lacked gastric glands in the stomach while larger fish, intermediates (30-33 mm LS) and herbivorous adults (〉80 mm LS) had numerous gastric glands. Two cell types were identified in the gastric glands of larger fish: mucous secreting cells and secretory cells which had ultrastructure features typical of digestive enzymes and acid secretion. Lipid absorption occurred throughout the caeca and intestine in all sizes of fish. Microvilli found on the rectal epithelial cells of the intermediate and adult pinfish occurred on stalks and were possibly associated with water reabsorption. Liver enzyme activities changed in small fish (26–39 mm LS) compared to the adult fish. Alanine amino transferase (ALT) and fructose diphosphotase (FDP) activities declined while pyruvate kinase (PK) activities increased significantly. These changes were consistent with a change in diet from a carnivorous (high protein) diet in juveniles to an omnivorous (lower protein) diet determined by stomach content analyses.

Electronic Resource

1095-8649

Blackwell Publishing Journal Backfiles 1879-2005

Biology

This study examined the influence of body size and temperature on oxygen consumption and food converstion in juvenile American eels (Anguilla rostrata). The weight-specific oxygen consumption rate for underdeveloped eels (18 months old) was significantly higher than the weight-specific oxygen consumption rate of developed eels of the same weight (6 months old). Oxygen consumption rates increased linearly with weight at each experimental temperature (15, 20, 25°C) when data were transformed logarithmically. No significant differences were found among slopes oflog transformed data at varying temperatures. Oxygen consumption was significantly higher at night (2300 h) as compared to morning (0900 h). The results indicate that underdeveloped eels use more energy and use less food less efficiently than developed eels.

Electronic Resource