493 research outputs found
Individual variability in Diel Vertical migration of a marine copepod : why some individuals remain at depth when others migrate
The diel vertical migration (DVM) of the copepod Metridia pacifica was examined in Dabob Bay (47°45.05′N, 122°49.71′W), a fjord in Washington state. Although the population showed deep daytime residence (75-175 m), a proportion of the population was found in the surface waters at night. For individuals that migrated to the surface, the mean size of the oil sac was much smaller than those that remained at depth (mean lengths of oil sac 0.25 mm for individuals collected between 0 and 25 m at night, compared with 0.43 mm for individuals from between 125 and 175 m). Similarly, the C : N ratio was lower for animals collected from near the surface, indicative of their lower lipid reserves. These results suggest that individual variability in DVM was influenced by body condition, with those animals with larger lipid stores not needing to risk coming to the surface to feed at night
The response to high magnetic fields of the vacuum phototriodes for the compact muon solenoid endcap electromagnetic calorimeter
The endcap electromagnetic calorimeter of the Compact Muon Solenoid (CMS) detects particles with the dense fast scintillator lead tungstate (PbWO4). Due to the low light yield of this scintillator photodetectors with internal gain are required. Silicon avalanche photodiodes cannot be used in the endcap region due to the intense neutron flux. Following an extensive R&D programme 26 mm diameter single-stage photomultipliers (vacuum phototriodes) have been chosen as the photodetector in the endcap region. The first 1400 production devices are currently being evaluated following recent tests of a pre-production batch of 500 tubes. Tubes passing our acceptance tests have responses, averaged over the angular acceptance of the endcap calorimeter, corresponding to the range 20 to 55 electrons per MeV deposited in PbWO4. These phototriodes operate, with a typical gain of 10, in magnetic fields up to 4T.PPARC, EC(INTAS-CERN scheme 99-424
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Chemical and isotopic characteristics of the coso east flankhydrothermal fluids: implications for the location and nature of the heatsource
Fluids have been sampled from 9 wells and 2 fumaroles fromthe East Flank of the Coso hydrothermal system with a view toidentifying, if possible, the location and characteristics of the heatsource inflows into this portion of the geothermal field. Preliminaryresults show that there has been extensive vapor loss in the system, mostprobably in response to production. Wells 38A-9, 51-16 and 83A-16 showthe highest CO2-CO-CH4-H2 chemical equilibration temperatures, rangingbetween 300-340oC, and apart from 38A-9, the values are generally inaccordance with the measured temperatures in the wells. Calculatedtemperatures for the fractionation of 13C between CO2 and CH4 are inexcess of 400oC in fluids from wells 38A-9, 64-16-RD2 and 51A-16,obviously pointing to equilibrium conditions from deeper portions of thereservoir. Given that the predominant reservoir rock lithologies in theCoso system are relatively silicic (granitic to dioritic), the isotopicsignatures appear to reflect convective circulation and equilibrationwithin rocks close to the plastic-brittle transition. 3He/4He signatures,in conjunction with relative volatile abundances in the Coso fluids,point to a possibly altered mantle source for the heat sourcefluids
Constraints on the SU(3) Electroweak Model
We consider a recent proposal by Dimopoulos and Kaplan to embed the
electroweak SU(2)_L X U(1)_Y into a larger group SU(3)_W X SU(2) X U(1) at a
scale above a TeV. This idea is motivated by the prediction for the weak mixing
angle sin^2 theta_W = 1/4, which naturally appears in these models so long as
the gauge couplings of the high energy SU(2) and U(1) groups are moderately
large. The extended gauge dynamics results in new effective operators that
contribute to four-fermion interactions and Z pole observables. We calculate
the corrections to these electroweak precision observables and carry out a
global fit of the new physics to the data. For SU(2) and U(1) gauge couplings
larger than 1, we find that the 95% C.L. lower bound on the matching (heavy
gauge boson mass) scale is 11 TeV. We comment on the fine-tuning of the high
energy gauge couplings needed to allow matching scales above our bounds. The
remnants of SU(3)_W breaking include multi-TeV SU(2)_L doublets with electric
charge (+-2,+-1). The lightest charged gauge boson is stable, leading to
cosmological difficulties.Comment: 17 pages, LaTeX, 4 figures embedded, uses JHEP.cl
On the energy-momentum tensor for a scalar field on manifolds with boundaries
We argue that already at classical level the energy-momentum tensor for a
scalar field on manifolds with boundaries in addition to the bulk part contains
a contribution located on the boundary. Using the standard variational
procedure for the action with the boundary term, the expression for the surface
energy-momentum tensor is derived for arbitrary bulk and boundary geometries.
Integral conservation laws are investigated. The corresponding conserved
charges are constructed and their relation to the proper densities is
discussed. Further we study the vacuum expectation value of the energy-momentum
tensor in the corresponding quantum field theory. It is shown that the surface
term in the energy-momentum tensor is essential to obtain the equality between
the vacuum energy, evaluated as the sum of the zero-point energies for each
normal mode of frequency, and the energy derived by the integration of the
corresponding vacuum energy density. As an application, by using the zeta
function technique, we evaluate the surface energy for a quantum scalar field
confined inside a spherical shell.Comment: 25 pages, 2 figures, section and appendix on the surface energy for a
spherical shell are added, references added, accepted for publication in
Phys. Rev.
Novel Approach to Confront Electroweak Data and Theory
A novel approach to study electroweak physics at one-loop level in generic
theories is introduced. It separates the 1-loop
corrections into two pieces: process specific ones from vertex and box
contributions, and universal ones from contributions to the gauge boson
propagators. The latter are parametrized in terms of four effective form
factors , , and corresponding to the , , and
propagators. Under the assumption that only the Standard Model contributes to
the process specific corrections, the magnitudes of the four form factors are
determined at and at q^2=\mmz by fitting to all available precision
experiments. These values are then compared systematically with predictions of
theories. In all fits \alpha_s(\mz) and
\bar{\alpha}(\mmz) are treated as external parameters in order to keep the
interpretation as flexible as possible. The treatment of the electroweak data
is presented in detail together with the relevant theoretical formulae used to
interpret the data. No deviation from the Standard Model has been identified.
Ranges of the top quark and Higgs boson masses are derived as functions of
\alpha_s(\mz) and \bar{\alpha}(\mmz). Also discussed are consequences of
the recent precision measurement of the left-right asymmetry at SLC as well as
the impact of a top quark mass and an improved mass measurement.Comment: 123 pages, LaTeX (33 figures available via anonymous ftp),
KEK-TH-375, KEK preprint 93-159, KANAZAWA-94-19, DESY 94-002, YUMS 94-22,
SNUTP 94-82, to be published in Z.Phys.
Avaliação de métodos de estimação de componentes de variância utilizando dados simulados
Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
The extreme ultraviolet portion of the solar spectrum contains a wealth of
diagnostic tools for probing the lower solar atmosphere in response to an
injection of energy, particularly during the impulsive phase of solar flares.
These include temperature and density sensitive line ratios, Doppler shifted
emission lines and nonthermal broadening, abundance measurements, differential
emission measure profiles, and continuum temperatures and energetics, among
others. In this paper I shall review some of the advances made in recent years
using these techniques, focusing primarily on studies that have utilized data
from Hinode/EIS and SDO/EVE, while also providing some historical background
and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the
Topical Issue on Solar and Stellar Flare
Measurement of the partial widths of the Z into up- and down-type quarks
Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma
decays were selected by tagging hadronic final states with isolated photon
candidates in the electromagnetic calorimeter. Combining the measured rates of
Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the
simultaneous determination of the widths of the Z into up- and down-type
quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18}
MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with
the Standard Model expectation.Comment: 22 pages, 5 figures, Submitted to Phys. Letts.
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