1,263 research outputs found
Plankton community composition, organic carbon and thorium-234 particle size distributions, and particle export in the Sargasso Sea
Measurements of plankton community composition (eight planktonic groups), particle size-fractionated (10, 20, 53, 70, and 100-μm Nitex screens) distributions of organic carbon (OC) and 234Th, and particle export of OC and 234Th are reported over a seasonal cycle (2006–2007) from the Bermuda Atlantic Time-Series (BATS) site. Results indicate a convergence of the particle size distributions of OC and 234Th during the winter-spring bloom period (January–March, 2007). The observed convergence of these particle size distributions is directly correlated to the depth-integrated abundance of autotrophic pico-eukaryotes (r = 0.97, P \u3c 0.05) and, to a lesser extent, Synechococcus (r = 0.85, P \u3c 0.14). In addition, there are positive correlations between the sediment trap flux of OC and 234Th at 150 m and the depth-integrated abundance of pico-eukaryotes (r = 0.94, P \u3c 0.06 for OC, and r = 0.98, P \u3c 0.05 for 234Th) and Synechococcus (r = 0.95, P \u3c 0.05 for OC, and r = 0.94, P \u3c 0.06 for 234Th). An implication of these observations and recent modeling studies (Richardson and Jackson, 2007) is that, although small in size, pico-plankton may influence large particle export from the surface waters of the subtropical Atlantic
On homothetic cosmological dynamics
We consider the homogeneous and isotropic cosmological fluid dynamics which
is compatible with a homothetic, timelike motion, equivalent to an equation of
state . By splitting the total pressure into the sum of an
equilibrium part and a non-equilibrium part , we find that on
thermodynamical grounds this split is necessarily given by and , corresponding to a dissipative stiff (Zel'dovich) fluid.Comment: 8 pages, to be published in Class. Quantum Gra
Dust-filled axially symmetric universes with a cosmological constant
Following the recent recognition of a positive value for the vacuum energy
density and the realization that a simple Kantowski-Sachs model might fit the
classical tests of cosmology, we study the qualitative behavior of three
anisotropic and homogeneous models: Kantowski-Sachs, Bianchi type-I and Bianchi
type-III universes, with dust and a cosmological constant, in order to find out
which are physically permitted. We find that these models undergo
isotropization up to the point that the observations will not be able to
distinguish between them and the standard model, except for the Kantowski-Sachs
model
with smaller than some critical value
. Even if one imposes that the Universe should be nearly
isotropic since the last scattering epoch (), meaning that the
Universe should have approximately the same Hubble parameter in all directions
(considering the COBE 4-Year data), there is still a large range for the matter
density parameter compatible with Kantowsky-Sachs and Bianchi type-III if
, for a very small . The
Bianchi type-I model becomes exactly isotropic owing to our restrictions and we
have in this case. Of course, all these models
approach locally an exponential expanding state provided the cosmological
constant .Comment: 12 pages, 9 figures, 1 table. Published in Physical Review D 1
Centrifugation and capillarity integrated into a multiple analyte whole blood analyser
A unique clinical chemistry analyser is described which processes
90 μl of whole blood (fingerstick or venous) into multiple aliquots of diluted plasma and reports the results of 12 tests in 14 min. To perform a panel of tests, the operator applies the unmetered sample directly into a single use, 8 cm diameter plastic rotor which contains the required liquid diluent and dry reagents. Using centrifugal and capillary forces, the rotor meters the required amount of blood, separates the red cells, meters the plasma, meters the diluent, mixes the fluids, distributes the fluid to the reaction cuvettes and mixes the reagents and the diluted plasma in the cuvettes. The instrument monitors the reagent reactions simultaneously using nine wavelengths, calculates the results from the absorbance data, and reports the results
Exponential potentials and cosmological scaling solutions
We present a phase-plane analysis of cosmologies containing a barotropic
fluid with equation of state , plus a scalar
field with an exponential potential where . In addition to the well-known inflationary
solutions for in which the scalar field energy density tracks that of the barotropic
fluid (which for example might be radiation or dust). We show that the scaling
solutions are the unique late-time attractors whenever they exist. The
fluid-dominated solutions, where at late times, are
always unstable (except for the cosmological constant case ). The
relative energy density of the fluid and scalar field depends on the steepness
of the exponential potential, which is constrained by nucleosynthesis to
. We show that standard inflation models are unable to solve
this `relic density' problem.Comment: 6 pages RevTeX file with four figures incorporated (uses RevTeX and
epsf). Matches published versio
Evolution of the Bianchi I, the Bianchi III and the Kantowski-Sachs Universe: Isotropization and Inflation
We study the Einstein-Klein-Gordon equations for a convex positive potential
in a Bianchi I, a Bianchi III and a Kantowski-Sachs universe. After analysing
the inherent properties of the system of differential equations, the study of
the asymptotic behaviors of the solutions and their stability is done for an
exponential potential. The results are compared with those of Burd and Barrow.
In contrast with their results, we show that for the BI case isotropy can be
reached without inflation and we find new critical points which lead to new
exact solutions. On the other hand we recover the result of Burd and Barrow
that if inflation occurs then isotropy is always reached. The numerical
integration is also done and all the asymptotical behaviors are confirmed.Comment: 22 pages, 12 figures, Self-consistent Latex2e File. To be published
in Phys. Rev.
Clinical investigation of an outbreak of alveolitis and asthma in a car engine manufacturing plant
Background Exposure to metal working fluid (MWF) has been associated with outbreaks of EAA in the US, with bacterial contamination of MWF being a possible cause, but was uncommon in the UK. Twelve workers developed extrinsic allergic alveolitis (EAA) in a car engine manufacturing plant in the UK, presenting clinically between December 2003 and May 2004. This paper reports the subsequent epidemiological investigation of the whole workforce. This had three aims:-
• To measure the extent of the outbreak by identifying other workers who may have developed EAA or other work-related respiratory diseases.
• To provide case-detection so that those affected can be treated.
• To provide epidemiological data to identify the cause of the outbreak.
Methods The outbreak was investigated in a three-phase cross-sectional survey of the workforce.
Phase I A respiratory screening questionnaire was completed by 808/836 workers (96.7%) in May 2004.
Phase II 481 employees with at least one respiratory symptom on screening and 50 asymptomatic controls were invited for investigation at the factory in June 2004. This included a questionnaire, spirometry and clinical opinion. 454/481(94.4%) responded along with 48/50(96%) controls. Workers were identified who needed further investigation and serial measurements of peak expiratory flow (PEF).
Phase III 162 employees were seen at the Birmingham Occupational Lung Disease clinic. 198 employees returned PEF records, including 141 of the 162 who attended for clinical investigation. Case definitions for diagnoses were agreed.
Results 87 workers (10.4% of workforce) met case definitions for occupational lung disease, comprising EAA(19), occupational asthma(74) and humidifier fever(7). 12 workers had more than one diagnosis. The peak onset of work-related breathlessness was Spring 2003. The proportion of workers affected was higher for those using metal working fluid (MWF) from a large sump(27.3%) compared with working all over the manufacturing area (7.9%) (OR=4.39,p<0.001). Two workers had positive specific provocation tests to the used but not the unused MWF solution.
Conclusions Extensive investigation of the outbreak of EAA detected a large number of affected workers, not only with EAA but also occupational asthma. This is the largest reported outbreak in Europe. Mist from used MWF is the likely cause. In workplaces using MWF, there is a need to carry out risk assessments, to monitor and maintain fluid quality, to control mist and to carry out respiratory health surveillance
The stability of cosmological scaling solutions
We study the stability of cosmological scaling solutions within the class of
spatially homogeneous cosmological models with a perfect fluid subject to the
equation of state p_gamma=(gamma-1) rho_gamma (where gamma is a constant
satisfying 0 < gamma < 2) and a scalar field with an exponential potential. The
scaling solutions, which are spatially flat isotropic models in which the
scalar field energy density tracks that of the perfect fluid, are of physical
interest. For example, in these models a significant fraction of the current
energy density of the Universe may be contained in the scalar field whose
dynamical effects mimic cold dark matter. It is known that the scaling
solutions are late-time attractors (i.e., stable) in the subclass of flat
isotropic models. We find that the scaling solutions are stable (to shear and
curvature perturbations) in generic anisotropic Bianchi models when gamma <
2/3. However, when gamma > 2/3, and particularly for realistic matter with
gamma >= 1, the scaling solutions are unstable; essentially they are unstable
to curvature perturbations, although they are stable to shear perturbations. We
briefly discuss the physical consequences of these results.Comment: AMSTeX, 7 pages, re-submitted to Phys Rev Let
Cluster formation and anomalous fundamental diagram in an ant trail model
A recently proposed stochastic cellular automaton model ({\it J. Phys. A 35,
L573 (2002)}), motivated by the motions of ants in a trail, is investigated in
detail in this paper. The flux of ants in this model is sensitive to the
probability of evaporation of pheromone, and the average speed of the ants
varies non-monotonically with their density. This remarkable property is
analyzed here using phenomenological and microscopic approximations thereby
elucidating the nature of the spatio-temporal organization of the ants. We find
that the observations can be understood by the formation of loose clusters,
i.e. space regions of enhanced, but not maximal, density.Comment: 11 pages, REVTEX, with 11 embedded EPS file
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