668 research outputs found
Feeding habitats of the Gulf sturgeon, Acipenser oxyrinchus desotoi, in the Suwannee and Yellow rivers, Florida, as identified by multiple stable isotope analyses
Stable 13C, 15N, and 34S isotopes were analyzed to define the feeding habitats of Acipenser oxyrinchus desotoi in the Suwannee and Yellow River populations. For the majority (93.9%) of Suwannee sub adults and adults, 13C and 34S signatures indicate use of nearshore marine waters as primary winter feeding habitat, probably due to the limiting size of the Suwannee Sound estuary. In the Yellow River population, 13C isotope signatures indicate that adults remain primarily within Pensacola Bay estuary to feed in winter, rather than immigrating to the open Gulf of Mexico. A minor Suwannee River subset (6% of samples), comprised of juveniles and sub adults, displayed 13C signatures indicating continued feeding in freshwater during the spring immigration and fall emigration periods. This cannot be interpreted as incidental feeding since it resulted in a 20.5% turnover in tissue δ13C signatures over a 1–3 month period. Cessation of feeding in the general population does not coincide with high river water temperatures. The hypothesis of reduced feeding in freshwater due to localized prey depletion as a result of spatial activity restriction is not supported by the present study. Instead, Suwannee River A. o. desotoi appear to follow two trophic alternatives; 1) complete cessation of feeding immediately upon immigration in spring, continuing through emigration 8–9 months later (the predominant alternative); 2) continued intensive feeding for 1– 3 months following immigration, switching to freshwater prey, selected primarily from high trophic levels (i.e., large prey). Stable δ34S data verifies that recently immigrated, fully-anadromous A. o. desotoi adults had fed in nearshore marine waters, not offshore waters
Feeding habitats of the Gulf sturgeon, Acipenser oxyrinchus desotoi, in the Suwannee and Yellow rivers, Florida, as identified by multiple stable isotope analyses
Stable 13C, 15N, and 34S isotopes were analyzed to define the feeding habitats of Acipenser oxyrinchus desotoi in the Suwannee and Yellow River populations. For the majority (93.9%) of Suwannee sub adults and adults, 13C and 34S signatures indicate use of nearshore marine waters as primary winter feeding habitat, probably due to the limiting size of the Suwannee Sound estuary. In the Yellow River population, 13C isotope signatures indicate that adults remain primarily within Pensacola Bay estuary to feed in winter, rather than immigrating to the open Gulf of Mexico. A minor Suwannee River subset (6% of samples), comprised of juveniles and sub adults, displayed 13C signatures indicating continued feeding in freshwater during the spring immigration and fall emigration periods. This cannot be interpreted as incidental feeding since it resulted in a 20.5% turnover in tissue δ13C signatures over a 1–3 month period. Cessation of feeding in the general population does not coincide with high river water temperatures. The hypothesis of reduced feeding in freshwater due to localized prey depletion as a result of spatial activity restriction is not supported by the present study. Instead, Suwannee River A. o. desotoi appear to follow two trophic alternatives; 1) complete cessation of feeding immediately upon immigration in spring, continuing through emigration 8–9 months later (the predominant alternative); 2) continued intensive feeding for 1– 3 months following immigration, switching to freshwater prey, selected primarily from high trophic levels (i.e., large prey). Stable δ34S data verifies that recently immigrated, fully-anadromous A. o. desotoi adults had fed in nearshore marine waters, not offshore waters
Asymptotics of the heat equation with `exotic' boundary conditions or with time dependent coefficients
The heat trace asymptotics are discussed for operators of Laplace type with
Dirichlet, Robin, spectral, D/N, and transmittal boundary conditions. The heat
content asymptotics are discussed for operators with time dependent
coefficients and Dirichlet or Robin boundary conditions.Comment: A talk of P.B. Gilkey at "Quantum Gravity and Spectral Geometry",
Naples, July 2001, to appear in the proceedings v2: a misprint in eq. (3)
correcte
Documentation of a Gulf Sturgeon Spawning Site on the Yellow River, Alabama, USA
The Gulf Sturgeon Recovery Plan (USFWS, GSMFC and NMFS 1995) stressed the need to provide maximum protection to Gulf sturgeon spawning habitat. The approach employed by various Gulf sturgeon researchers, including ourselves, to document spawning has been to identify potential spawning habitat on the basis of physical characteristics and/or tracking data, collect eggs, and then raise the eggs in the laboratory until the point where the larval fish can be identified (e.g., Marchant and Shutters 1996, Sulak and Clugston 1998, 1999). However, collecting eggs in any appreciable number is usually difficult, and these eggs may not always be viable upon return to the laboratory. Molecular methods provide an alternative means of identifying the species represented by an egg. Notable examples related to sturgeon conservation include cases where molecular markers were used to verify the sources of commercially available caviar (DeSalle and Birstein 1996, Birstein et al. 1999).
Parauka and Giorgianni (2002) reported that potential Gulf sturgeon spawning habitat is present in the Yellow River; however, efforts to document spawning by the collection of eggs or larvae have been unsuccessful in the past. Herein, we report on the first successful collection of eggs from a potential spawning site on the Yellow River and the verification of their identity as Gulf sturgeon by using molecular methods
Superpotential de-sequestering in string models
Non-perturbative superpotential cross-couplings between visible sector matter
and K\"ahler moduli can lead to significant flavour-changing neutral currents
in compactifications of type IIB string theory. Here, we compute corrections to
Yukawa couplings in orbifold models with chiral matter localised on D3-branes
and non-perturbative effects on distant D7-branes. By evaluating a threshold
correction to the D7-brane gauge coupling, we determine conditions under which
the non-perturbative corrections to the Yukawa couplings appear. The flavour
structure of the induced Yukawa coupling generically fails to be aligned with
the tree-flavour structure. We check our results by also evaluating a
correlation function of two D7-brane gauginos and a D3-brane Yukawa coupling.
Finally, by calculating a string amplitude between n hidden scalars and visible
matter we show how non-vanishing vacuum expectation values of distant D7-brane
scalars, if present, may correct visible Yukawa couplings with a flavour
structure that differs from the tree-level flavour structure.Comment: 37 pages + appendices, 8 figure
The Throat as a Randall-Sundrum Model with Goldberger-Wise Stabilization
An interesting feature of type IIB flux compactifications is the natural
presence of strongly warped regions or `throats'. These regions allow for a 5d
Randall-Sundrum model interpretation with a large hierarchy between the UV and
IR brane. We show that, in the 5d description, the flux stabilization of this
hierarchy (or, equivalently, of the brane-to-brane distance) can be understood
as an implementation of the Goldberger-Wise mechanism. This mechanism relies on
the non-trivial bulk profile of the so-called Goldberger-Wise scalar, which in
addition has fixed expectation values at the boundaries and thereby stabilizes
the size of the 5d interval. The Goldberger-Wise scalar is realized
microscopically by the continuously varying flux of the Neveu-Schwarz 2-form
potential B_2 on the S^2 cycle in the throat. Its back-reaction on the 5d
geometry leads to a significant departure from a pure AdS_5 background. We also
find that, for a wide range of parameters, the universal Kaehler modulus of the
10d compactification plays the role of a UV-brane field in the equivalent 5d
model. It governs the size of a large 4d curvature term localized at the UV
brane. We hope that our simple 5d description of the stabilized throat will be
useful in various phenomenological and cosmological applications and that
refined versions of this construction will be able to account for all relevant
details of the 10d model.Comment: 27 pages, 2 figures; references adde
Neutralino Dark Matter in BMSSM Effective Theory
We study thermal neutralino dark matter in an effective field theory
extension of the MSSM, called "Beyond the MSSM" (BMSSM) in Dine, Seiberg and
Thomas (2007). In this class of effective field theories, the field content of
the MSSM is unchanged, but the little hierarchy problem is alleviated by
allowing small corrections to the Higgs/higgsino part of the Lagrangian. We
perform parameter scans and compute the dark matter relic density. The light
Higgsino LSP scenario is modified the most; we find new regions of parameter
space compared to the standard MSSM. This involves interesting interplay
between the WMAP dark matter bounds and the LEP chargino bound. We also find
some changes for gaugino LSPs, partly due to annihilation through a Higgs
resonance, and partly due to coannihilation with light stops in models that are
ruled in by the new effective terms.Comment: 37 pages + appendi
Butyltin compounds in a sediment core from the old Tilbury basin, London, UK
Sections from a sediment core taken from the River Thames were analysed for butyltin species using gas chromatography with species-specific isotope dilution mass spectrometry. Results demonstrated that in most samples tributyltin concentrations of 20–60 ng/g accounted for <10% of the total butyltin species present, which is in agreement with data from other sediment samples which were historically contaminated with tributyltin. Vertical distribution of the organotin residues with depth throughout the core, with data on organochlorine compounds and heavy metals allowed for the construction of a consistent hypothesis on historical deposition of contaminated sediments. From this it was possible to infer that the concentrations of tributyltin in sediments deposited during the early 1960s were in the order of 400–600 lg/g by using degradation rate constants derived by other workers. Such values fall well within the range quoted for harbour sediments in the literature
Soft Supersymmetry Breaking in Calabi-Yau Orientifolds with D-branes and Fluxes
In this paper we compute the N=1 effective low energy action for a stack of N
space-time filling D3-branes in generic type IIB Calabi-Yau orientifolds with
non-trivial background fluxes by reducing the Dirac-Born-Infeld and
Chern-Simons actions. Specifically, we determine the Kahler potential for the
excitations of the D-brane including their couplings to all bulk moduli fields.
In the effective theory, N=1 supergravity is spontaneously broken by the
presence of fluxes and we compute the induced soft supersymmetry breaking
terms. We find an interesting structure in the resulting soft terms with
generically universal soft scalar masses.Comment: LaTeX, 41 pages, minor corrections and references adde
Hierarchically Split Supersymmetry with Fayet-Iliopoulos D-terms in String Theory
We show that in string theory or supergravity with supersymmetry breaking
through combined F-terms and Fayet-Iliopoulos D-terms, the masses for charged
scalars and fermions can be hierarchically split. The mass scale for the
gauginos and higgsinos of the MSSM is controlled by the gravitino mass m_{3/2},
as usual, while the scalars get extra contributions from the D-terms of extra
abelian U(1) factors, which can make them much heavier. The vanishing of the
vacuum energy requires that their masses lie below {m_{3/2} M_{Pl}}^{1/2},
which for m_{3/2}=O(TeV) sets a bound of 10^{10-13} GeV. Thus, scalars with
non-vanishing U(1) charges typically become heavy, while others remain light,
producing a spectrum of scalars with masses proportional to their charges, and
therefore non-universal. This is a modification of the split supersymmetry
scenario, but with a light gravitino. We discuss how Fayet-Iliopoulos terms of
this size can arise in orientifold string compactifications with D-branes.
Furthermore, within the frame work of D-term inflation, the same vacuum energy
that generates the heavy scalar masses can be responsible for driving
cosmological inflation.Comment: 25 pages, 1 figure; v2: references adde
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