Photoproduction of η\eta mesons off neutrons from a deuteron target

A formalism is developed for the partial wave analysis of data on meson photoproduction off deuterons and applied to photoproduction of $\eta$ and $\pi^0$ mesons. Different interpretations of a dip-bump structure of the $\eta$ photoproduction cross section in the 1670 MeV region are presented and discussed. Helicity amplitudes for two low-mass $S_{11}$ states are determined.Comment: 11 pages, 13 figure

Sources and budgets for CO and O-3 in the northeastern Pacific during the spring of 2001: Results from the PHOBEA-II Experiment

Abstract. Ground and airborne measurements of CO, ozone, and aerosols were obtained in th

Analytical solutions for a two-level system driven by a class of chirped pulses

We present analytical solutions for the problem of a two-level atom driven by a class of chirped pulses. The solutions are given in terms of Heun functions. Using appropriate chirping parameters an enhancement of four-orders of magnitudes in the population transfer is obtained.Comment: 5 pages, 5 figure

Neural crest stem cells undergo multilineage differentiation in developing peripheral nerves to generate endoneurial fibroblasts in addition to Schwann cells

Neural crest stem cells (NCSCs) persist in peripheral nerves throughout late gestation but their function is unknown. Current models of nerve development only consider the generation of Schwann cells from neural crest, but the presence of NCSCs raises the possibility of multilineage differentiation. We performed Cre-recombinase fate mapping to determine which nerve cells are neural crest derived. Endoneurial fibroblasts, in addition to myelinating and non-myelinating Schwann cells, were neural crest derived, whereas perineurial cells, pericytes and endothelial cells were not. This identified endoneurial fibroblasts as a novel neural crest derivative, and demonstrated that trunk neural crest does give rise to fibroblasts in vivo, consistent with previous studies of trunk NCSCs in culture. The multilineage differentiation of NCSCs into glial and non-glial derivatives in the developing nerve appears to be regulated by neuregulin, notch ligands, and bone morphogenic proteins, as these factors are expressed in the developing nerve, and cause nerve NCSCs to generate Schwann cells and fibroblasts, but not neurons, in culture. Nerve development is thus more complex than was previously thought, involving NCSC self-renewal, lineage commitment and multilineage differentiation

Coherent Excitation of a Two-Level Atom driven by a far off-resonant Classical Field: Analytical Solutions

We present an analytical treatment of coherent excitation of a Two-Level Atom driven by a far-off resonant classical field. A class of pulse envelope is obtained for which this problem is exactly solvable. The solutions are given in terms of Heun function which is a generalization of the Hypergeometric function. The degeneracy of Heun to Hypergeometric equation can give all the exactly solvable pulse shapes of Gauss Hypergeometric form, from the generalized pulse shape obtained here. We discuss the application of the results obtained to the generation of XUV.Comment: 9 Pages, 8 Figures. Accepted for Physical Review A as a regular articl

Reactive nitrogen budget during the NASA SONEX Mission

The SASS Ozone and Nitrogen Oxides Experiment (SONEX) over the North Atlantic during October/November 1997 offered an excellent opportunity to examine the budget of reactive nitrogen in the upper troposphere (8–12 km altitude). The median measured total reactive nitrogen (NOy) mixing ratio was 425 parts per trillion by volume (pptv). A data set merged to the HNO3 measurement time resolution was used to calculate NOy (NOy sum) by summing the reactive nitrogen species (a combination of measured plus modeled results) and comparing it to measured NOy (NOy meas.). Comparisons were done for tropospheric air (O3 \u3c100 parts per billion by volume (ppbv)) and stratospherically influenced air (O3 \u3e 100 ppbv) with both showing good agreement between NOy sum and NOy meas. (slope \u3e0.9 and r² ≈ 0.9). The total reactive nitrogen budget in the upper troposphere over the North Atlantic appears to be dominated by a mixture of NOx (NO + NO2), HNO3, and PAN. In tropospheric air median values of NOx/NOywere ≈ 0.25, HNO3/NOy ≈ 0.35 and PAN/NOy ≈ 0.17. Particulate NO3− and alkyl nitrates together composed \u3c10% of NOy, while model estimated HNO4 averaged 12%. For the air parcels sampled during SONEX, there does not appear to be a large reservoir of unidentified NOy compounds

Global simulations of monoterpene-derived peroxy radical fates and the distributions of highly oxygenated organic molecules (HOMs) and accretion products

We evaluate monoterpene-derived peroxy radical (MT-RO2) unimolecular autoxidation and self- and cross-reactions with other RO2 species in the GEOS-Chem global chemical transport model. The formation of associated highly oxygenated organic molecules (HOMs) and accretion products are tracked in competition with other bimolecular reactions. Autoxidation is the dominant fate up to 6-8 km for first-generation MT-RO2, which can undergo unimolecular H shifts. Reaction with NO can be a more common fate for H-shift rate constants < 0.1 s(-1) or at altitudes higher than 8 km due to the imposed Arrhenius temperature dependence of unimolecular H shifts. For MT-derived HOM-RO2, generated by multistep autoxidation of first-generation MT-RO2, reaction with other RO2 species is predicted to be the major fate throughout most of the boreal and tropical forest regions, whereas reaction with NO dominates in the temperate and subtropical forests of the Northern Hemisphere. The newly added reactions result in an approximate 4 % global average decrease in HO2 and RO2, mainly due to faster self-/cross-reactions of MT-RO2, but the impact upon HO2, OH, and NOx abundances is only important in the planetary boundary layer (PBL) over portions of tropical forests. Predicted HOM concentrations in MT-rich regions and seasons can exceed total organic aerosol predicted by the standard version of the GEOS-Chem model depending on the parameters used. Comparisons to observations reveal that large uncertainties remain for key reaction parameters and processes, especially with respect to the photochemical lifetime and volatility of HOMs as well as the rates and branching of associated RO2 accretion products. Further observations and laboratory studies related to MT-RO2-derived HOMs and gas-phase RO2 accretion product formation kinetics - especially their atmospheric fate, such as gas-particle partitioning, multiphase chemistry, and net secondary organic aerosol formation - are needed.Peer reviewe

A tissue-specific knockout reveals that Gata1 is not essential for Sertoli cell function in the mouse

The transcription factor Gata1 is essential for the development of erythroid cells. Consequently, Gata1 null mutants die in utero due to severe anaemia. Outside the haematopoietic system, Gata1 is only expressed in the Sertoli cells of the testis. To elucidate the function of Gata1 in the testis, we made a Sertoli cell-specific knockout of the Gata1 gene in the mouse. We deleted a normally functioning 'floxed' Gata1 gene in pre-Sertoli cells in vivo through the expression of Cre from a transgene driven by the Desert Hedgehog promoter. Surprisingly, Gata1 null testes developed to be morphologically normal, spermatogenesis was not obviously affected and expression levels of putative Gata1 target genes, and other Gata factors, were not altered. We conclude that expression of Gata1 in Sertoli cells is not essential for testis development or spermatogenesis in the mouse