Spring bloom dynamics and zooplankton biomass response on the US Northeast Continental Shelf

This paper is not subject to U.S. copyright. The definitive version was published in Continental Shelf Research 102 (2015): 47-61, doi:10.1016/j.csr.2015.04.005.The spring phytoplankton bloom on the US Northeast Continental Shelf is a feature of the ecosystem production cycle that varies annually in timing, spatial extent, and magnitude. To quantify this variability, we analyzed remotely-sensed ocean color data at two spatial scales, one based on ecologically defined sub-units of the ecosystem (production units) and the other on a regular grid (0.5°). Five units were defined: Gulf of Maine East and West, Georges Bank, and Middle Atlantic Bight North and South. The units averaged 47×103 km2 in size. The initiation and termination of the spring bloom were determined using change-point analysis with constraints on what was identified as a bloom based on climatological bloom patterns. A discrete spring bloom was detected in most years over much of the western Gulf of Maine production unit. However, bloom frequency declined in the eastern Gulf of Maine and transitioned to frequencies as low as 50% along the southern flank of the Georges Bank production unit. Detectable spring blooms were episodic in the Middle Atlantic Bight production units. In the western Gulf of Maine, bloom duration was inversely related to bloom start day; thus, early blooms tended to be longer lasting and larger magnitude blooms. We view this as a phenological mismatch between bloom timing and the “top-down” grazing pressure that terminates a bloom. Estimates of secondary production were available from plankton surveys that provided spring indices of zooplankton biovolume. Winter chlorophyll biomass had little effect on spring zooplankton biovolume, whereas spring chlorophyll biomass had mixed effects on biovolume. There was evidence of a “bottom up” response seen on Georges Bank where spring zooplankton biovolume was positively correlated with the concentration of chlorophyll. However, in the western Gulf of Maine, biovolume was uncorrelated with chlorophyll concentration, but was positively correlated with bloom start and negatively correlated with magnitude. This observation is consistent with both a “top-down” mechanism of control of the bloom and a “bottom-up” effect of bloom timing on zooplankton grazing. Our inability to form a consistent model of these relationships across adjacent systems underscores the need for further research

The Structure of the {\beta} Leonis Debris Disk

We combine nulling interferometry at 10 {\mu}m using the MMT and Keck Telescopes with spectroscopy, imaging, and photometry from 3 to 100 {\mu}m using Spitzer to study the debris disk around {\beta} Leo over a broad range of spatial scales, corresponding to radii of 0.1 to ~100 AU. We have also measured the close binary star o Leo with both Keck and MMT interferometers to verify our procedures with these instruments. The {\beta} Leo debris system has a complex structure: 1.) relatively little material within 1 AU; 2.) an inner component with a color temperature of ~600 K, fitted by a dusty ring from about 2 to 3 AU; and 3.) a second component with a color temperature of ~120 K fitted by a broad dusty emission zone extending from about ~5 AU to ~55 AU. Unlike many other A-type stars with debris disks, {\beta} Leo lacks a dominant outer belt near 100 AU.Comment: 14 page body, 3 page appendix, 15 figure

A Study of the Diverse T Dwarf Population Revealed by WISE

We report the discovery of 87 new T dwarfs uncovered with the Wide-field Infrared Survey Explorer (WISE) and three brown dwarfs with extremely red near-infrared colors that exhibit characteristics of both L and T dwarfs. Two of the new T dwarfs are likely binaries with L7+/-1 primaries and mid-type T secondaries. In addition, our follow-up program has confirmed 10 previously identified T dwarfs and four photometrically-selected L and T dwarf candidates in the literature. This sample, along with the previous WISE discoveries, triples the number of known brown dwarfs with spectral types later than T5. Using the WISE All-Sky Source Catalog we present updated color-color and color-type diagrams for all the WISE-discovered T and Y dwarfs. Near-infrared spectra of the new discoveries are presented, along with spectral classifications. To accommodate later T dwarfs we have modified the integrated flux method of determining spectral indices to instead use the median flux. Furthermore, a newly defined J-narrow index differentiates the early-type Y dwarfs from late-type T dwarfs based on the J-band continuum slope. The K/J indices for this expanded sample show that 32% of late-type T dwarfs have suppressed K-band flux and are blue relative to the spectral standards, while only 11% are redder than the standards. Comparison of the Y/J and K/J index to models suggests diverse atmospheric conditions and supports the possible re-emergence of clouds after the L/T transition. We also discuss peculiar brown dwarfs and candidates that were found not to be substellar, including two Young Stellar Objects and two Active Galactic Nuclei. The coolest WISE-discovered brown dwarfs are the closest of their type and will remain the only sample of their kind for many years to come.Comment: Accepted to ApJS on 15 January 2013; 99 pages in preprint format, 30 figures, 12 table

Microstructure of single-droplet granules formed from ultra-fine powders

A quantitative analysis of variations in granule microstructure based upon changes in primary particle size and bed preparation is presented. The granule microstructures are obtained using X-Ray Computed Tomography (XRCT). An algorithm is developed to measure the number and size of macro-voids (pore space with volume equivalent size greater than or equal to 30 μm or 3 times the primary particle size). Four size fractions of alumina, ranging in primary particle size from 0.5 μm to 108 μm, are sieved using three different sieve sizes to create static powder beds from which single-droplet granules are produced. The analysis shows that large macro-voids exist in ultra-fine powders (0.1–10 μm). The macro-voids take up to 7% of the granule volume and the largest macro-voids are 200–700 μm in volume equivalent size. Changing the sieve preparation changes the size and total volume of macro-voids. In contrast, there are very few macro-voids in granules formed from coarser powders. This study shows that micron sized powders have the opportunity to form complex structures during granulation and that the handling history of the materials should receive greater scrutiny than it currently gets

Measurement of Angular Distributions and R= sigma_L/sigma_T in Diffractive Electroproduction of rho^0 Mesons

Production and decay angular distributions were extracted from measurements of exclusive electroproduction of the rho^0(770) meson over a range in the virtual photon negative four-momentum squared 0.5< Q^2 <4 GeV^2 and the photon-nucleon invariant mass range 3.8< W <6.5 GeV. The experiment was performed with the HERMES spectrometer, using a longitudinally polarized positron beam and a ^3He gas target internal to the HERA e^{+-} storage ring. The event sample combines rho^0 mesons produced incoherently off individual nucleons and coherently off the nucleus as a whole. The distributions in one production angle and two angles describing the rho^0 -> pi+ pi- decay yielded measurements of eight elements of the spin-density matrix, including one that had not been measured before. The results are consistent with the dominance of helicity-conserving amplitudes and natural parity exchange. The improved precision achieved at 47 GeV, reveals evidence for an energy dependence in the ratio R of the longitudinal to transverse cross sections at constant Q^2.Comment: 15 pages, 15 embedded figures, LaTeX for SVJour(epj) document class Revision: Fig. 15 corrected, recent data added to Figs. 10,12,14,15; minor changes to tex

Beam-Induced Nuclear Depolarisation in a Gaseous Polarised Hydrogen Target

Spin-polarised atomic hydrogen is used as a gaseous polarised proton target in high energy and nuclear physics experiments operating with internal beams in storage rings. When such beams are intense and bunched, this type of target can be depolarised by a resonant interaction with the transient magnetic field generated by the beam bunches. This effect has been studied with the HERA positron beam in the HERMES experiment at DESY. Resonances have been observed and a simple analytic model has been used to explain their shape and position. Operating conditions for the experiment have been found where there is no significant target depolarisation due to this effect.Comment: REVTEX, 6 pages, 5 figure

Health and survival of young children in southern Tanzania

With a view to developing health systems strategies to improve reach to high-risk groups, we present information on health and survival from household and health facility perspectives in five districts of southern Tanzania. We documented availability of health workers, vaccines, drugs, supplies and services essential for child health through a survey of all health facilities in the area. We did a representative cluster sample survey of 21,600 households using a modular questionnaire including household assets, birth histories, and antenatal care in currently pregnant women. In a subsample of households we asked about health of all children under two years, including breastfeeding, mosquito net use, vaccination, vitamin A, and care-seeking for recent illness, and measured haemoglobin and malaria parasitaemia. In the health facility survey, a prescriber or nurse was present on the day of the survey in about 40% of 114 dispensaries. Less than half of health facilities had all seven 'essential oral treatments', and water was available in only 22%. In the household survey, antenatal attendance (88%) and DPT-HepB3 vaccine coverage in children (81%) were high. Neonatal and infant mortality were 43.2 and 76.4 per 1000 live births respectively. Infant mortality was 40% higher for teenage mothers than older women (RR 1.4, 95% confidence interval (CI) 1.1 - 1.7), and 20% higher for mothers with no formal education than those who had been to school (RR 1.2, CI 1.0 - 1.4). The benefits of education on survival were apparently restricted to post-neonatal infants. There was no evidence of inequality in infant mortality by socio-economic status. Vaccine coverage, net use, anaemia and parasitaemia were inequitable: the least poor had a consistent advantage over children from the poorest families. Infant mortality was higher in families living over 5 km from their nearest health facility compared to those living closer (RR 1.25, CI 1.0 - 1.5): 75% of households live within this distance. Relatively short distances to health facilities, high antenatal and vaccine coverage show that peripheral health facilities have huge potential to make a difference to health and survival at household level in rural Tanzania, even with current human resources

Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-inclusive Deep-inelastic Scattering

Spin asymmetries of semi-inclusive cross sections for the production of positively and negatively charged hadrons have been measured in deep-inelastic scattering of polarized positrons on polarized hydrogen and 3He targets, in the kinematic range 0.023<x<0.6 and 1 GeV^2<Q^2<10 GeV^2. Polarized quark distributions are extracted as a function of x for up $(u+u_bar) and down (d+d_bar) flavors. The up quark polarization is positive and the down quark polarization is negative in the measured range. The polarization of the sea is compatible with zero. The first moments of the polarized quark distributions are presented. The isospin non-singlet combination Delta_q_3 is consistent with the prediction based on the Bjorken sum rule. The moments of the polarized quark distributions are compared to predictions based on SU(3)_f flavor symmetry and to a prediction from lattice QCD.Comment: 14 pages, 6 figures (eps format), 10 tables in Latex New version contains tables of asymmetries and correlation matri

Measurement of the Neutron Spin Structure Function g1ng_1^n with a Polarized ^3He Target

Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function $g_1^n(x,Q^2)$ in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized $^3$He internal gas target. The data cover the kinematic range $0.023<x<0.6$ and $1 (GeV/c)^2 < Q^2 <15 (GeV/c)^2$. The integral $\int_{0.023}^{0.6} g_1^n(x) dx$ evaluated at a fixed $Q^2$ of $2.5 (GeV/c)^2$ is $-0.034\pm 0.013(stat.)\pm 0.005(syst.)$. Assuming Regge behavior at low $x$, the first moment $\Gamma_1^n=\int_0^1 g_1^n(x) dx$ is $-0.037\pm 0.013(stat.)\pm 0.005(syst.)\pm 0.006(extrapol.)$.Comment: 4 pages TEX, text available at http://www.krl.caltech.edu/preprints/OAP.htm

Observation of a Single-Spin Azimuthal Asymmetry in Semi-Inclusive Pion Electro-Production

Single-spin asymmetries for semi-inclusive pion production in deep-inelastic scattering have been measured for the first time. A significant target-spin asymmetry of the distribution in the azimuthal angle phi of the pion relative to the lepton scattering plane was observed for pi+ electro-production on a longitudinally polarized hydrogen target. The corresponding analyzing power in the sin(phi) moment of the cross section is 0.022 +/- 0.005 +/- 0.003. This result can be interpreted as the effect of terms in the cross section involving chiral-odd spin distribution functions in combination with a time-reversal-odd fragmentation function that is sensitive to the transverse polarization of the fragmenting quark.Comment: 5 pages of RevTex, 3 ps figures, 2 table