1,362 research outputs found
Artificial Reef Development Along the Atlantic Coast of Guatemala
A visual census of a four year old artificial reef in the Bahia de Amatique off Guatemala\u27s Atlantic coast indicates a substantial standing number of fishes. The fish fauna is comprised chiefly of juvenile grunts (Haemulon aurolineatum; 7.39/m2) accounting for the reef\u27s low species diversity (H\u27 = 0.68). A considerable portion of the assemblage is composed of commercially exploitable adults of Lutjanus griseus (0.38/m2) and Haemulon plumieri (0.03/m2). The proximate grassbeds have large populations of juveniles and small adults of all the commercially exploitable species. Further development of the reef is indicated providing the grassbed biotope remains healthy and fishing pressure does not become excessive
Effects of different ACE inhibitor combinations on albuminuria: results of the GUARD study
Clinical practice guidelines recommend blockers of the renin-angiotensin system alone or in combination with other agents to reduce blood pressure and albuminuria in patients with type 2 diabetes. Dihydropyridine calcium channel blockers, however, may lower blood pressure but not albuminuria in these patients. Here we tested the hypothesis that combining an ACE inhibitor with either a thiazide diuretic or a calcium channel blocker will cause similar reductions in blood pressure and albuminuria in hypertensive type 2 diabetics. We conducted a double blind randomized controlled trial on 332 hypertensive, albuminuric type 2 diabetic patients treated with benazepril with either amlodipine or hydrochlorothiazide for 1 year. The trial employed a non-inferiority design. Both combinations significantly reduced the urinary albumin to creatinine ratio and sitting blood pressure of the entire cohort. The percentage of patients progressing to overt proteinuria was similar for both groups. When we examined patients who had only microalbuminuria and hypertension we found that a larger percentage of the diuretic and ACE inhibitor normalized their albuminuria. We conclude that initial treatment using benzaepril with a diuretic resulted in a greater reduction in albuminuria compared to the group of ACE inhibitor and calcium channel blocker. In contrast, blood pressure reduction, particularly the diastolic component, favored the combination with amilodipine. The dissociation between reductions in blood pressure and albuminuria may be related to factors other than blood pressure
Estimated Costs and Returns for Catfish Farms with Recirculating Ponds Along the Upper Texas Coast.
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Effects of old landfills on groundwater quality. Phase 2, investigation of the Thriplow landfill 1996–1997
Disused sand and gravel excavations overlying the major Chalk aquifer at Thriplow in Cambridgeshire have
been filled with domestic waste in two phases. One area (Phase 1) was filled between 1957–77 with little compaction
of the refuse and was left uncapped, while Phase 2 was deposited between 1981–87 and capped with
clay. Aerial photography and surface resistivity surveys indicate that the site geometry is complex, with several
phases of landfilling into excavations of differing depths. Drilling through the waste indicates that leachate production
and waste stabilisation proceed at different rates in capped and uncapped landfills. Analysis of leachate
obtained by centrifugation or squeezing appears to give more insight into the pollution potential than do leach
tests with distilled water. The Biological Methane Potential (BMP) of the waste appears to be related to the
quantity of decomposable material but the chemical oxygen demand (COD) values are distorted by the presence
of reduced metals. Too few boreholes have been drilled to define the leachate source in terms of its spatial distribution
and little is known of how its composition has changed with time. However, hydraulic conductivity measurements
on the landfill caps suggest that it is sufficiently permeable for all rainfall to potentially infiltrate the
waste.
Boreholes outside the landfill penetrate the Upper and Lower Chalk, and identify the Melbourn Rock and underlying
Plenus Marls at the junction of the two formations about 20 m below ground level (bgl). Surface resistivity
surveys using the BGS RESCAN system, confirm aerial photographs of the extent of the landfill and also
suggest that leachate has migrated beyond the base of the landfill. Evidence of leachate migration in pre-existing
screened boreholes completed above and below the Plenus Marls suggests that leachate is flowing above the
Plenus Marls. Hydraulic head measurements whilst drilling a borehole to the base of the lower Chalk approx. 70
m bgl revealed the potential for upward groundwater flow through the Plenus Marls. Thus, previously-drilled
boreholes penetrating the Plenus Marls are expected to recharge upwards into the shallow aquifer above the
Plenus Marls diluting any leachate in the upper aquifer and distorting the flow regime. Several of these boreholes
have subsequently been modified to stem the flow across the Plenus Marls.
One borehole down-gradient to the west of the site revealed a large thickness of drift composed of both sand and
clay rich material. This suggests the existence of a buried channel, the hydrogeological significance of which has
yet to be assessed.
Groundwater chemistry appears to be influenced by three major factors. (a) the landfill leachate (b) the composition
of shallow groundwater in the top 10 m of the Chalk, and (c) the composition of water from the Lower
Chalk. Limited groundwater monitoring data appear to display a cyclic variation in chloride concentration. The
origin for this is not clear but it may correlate with cyclic variations in groundwater levels when the water table
rises into the waste. Cyclic flushing of the landfill may release leachate into the aquifer giving rise to pulses of
chloride. Alternatively changes in chloride may arise by the changing direction of groundwater flow which as yet
has not been assessed.
A conceptual hydrogeological model in which flow is limited to above the Plenus Marls has been used to
develop a more appropriate groundwater flow and solute transport model. However, the model lacks data on
aquifer properties, on contaminant inputs concentrations, fluxes and spatial variations, and there is a paucity of
monitoring data for calibration. Nonetheless preliminary transport modelling using an equivalent porous medium
approach shows that an effective porosity of about 5% best fits the regional data. Since this is much less than the
total porosity of about 40% for the Chalk, it would appear that only part of the Chalk is available for flow but
that matrix diffusion could play an important role in leachate attenuation. Discrete fracture modelling using the
FRACTRAN code has allowed some scoping to be made of the hydraulic properties of the aquifer by comparison
with chloride hydrographs, but these again need to be better conditioned by in-situ measurement of fracture
distributions and transmissivities.
A number of additional activities are required to improve the understanding of flow and contaminant transport at
the site. These include better spatial definition of the waste distribution, improved data on the hydraulic properties
of the Chalk aquifer, and the use of automatic monitoring to record temporal changes in groundwater chemistry
and groundwater levels
Cosmological parameter estimation using Very Small Array data out to ℓ= 1500
We estimate cosmological parameters using data obtained by the Very Small Array (VSA) in its extended configuration, in conjunction with a variety of other cosmic microwave background (CMB) data and external priors. Within the flat Λ cold dark matter (ΛCDM) model, we find that the inclusion of high-resolution data from the VSA modifies the limits on the cosmological parameters as compared to those suggested by the Wilkinson Microwave Anisotropy Probe (WMAP) alone, while still remaining compatible with their estimates. We find that Ωbh2= 0.0234+0.0012−0.0014, Ωdmh2= 0.111+0.014−0.016, h= 0.73+0.09−0.05, nS= 0.97+0.06−0.03, 1010AS= 23+7−3 and τ= 0.14+0.14−0.07 for WMAP and VSA when no external prior is included. On extending the model to include a running spectral index of density fluctuations, we find that the inclusion of VSA data leads to a negative running at a level of more than 95 per cent confidence ( nrun=−0.069 ± 0.032 ), something that is not significantly changed by the inclusion of a stringent prior on the Hubble constant. Inclusion of prior information from the 2dF galaxy redshift survey reduces the significance of the result by constraining the value of Ωm. We discuss the veracity of this result in the context of various systematic effects and also a broken spectral index model. We also constrain the fraction of neutrinos and find that fν < 0.087 at 95 per cent confidence, which corresponds to mν < 0.32 eV when all neutrino masses are equal. Finally, we consider the global best fit within a general cosmological model with 12 parameters and find consistency with other analyses available in the literature. The evidence for nrun < 0 is only marginal within this model
Dynamics with Infinitely Many Derivatives: The Initial Value Problem
Differential equations of infinite order are an increasingly important class
of equations in theoretical physics. Such equations are ubiquitous in string
field theory and have recently attracted considerable interest also from
cosmologists. Though these equations have been studied in the classical
mathematical literature, it appears that the physics community is largely
unaware of the relevant formalism. Of particular importance is the fate of the
initial value problem. Under what circumstances do infinite order differential
equations possess a well-defined initial value problem and how many initial
data are required? In this paper we study the initial value problem for
infinite order differential equations in the mathematical framework of the
formal operator calculus, with analytic initial data. This formalism allows us
to handle simultaneously a wide array of different nonlocal equations within a
single framework and also admits a transparent physical interpretation. We show
that differential equations of infinite order do not generically admit
infinitely many initial data. Rather, each pole of the propagator contributes
two initial data to the final solution. Though it is possible to find
differential equations of infinite order which admit well-defined initial value
problem with only two initial data, neither the dynamical equations of p-adic
string theory nor string field theory seem to belong to this class. However,
both theories can be rendered ghost-free by suitable definition of the action
of the formal pseudo-differential operator. This prescription restricts the
theory to frequencies within some contour in the complex plane and hence may be
thought of as a sort of ultra-violet cut-off.Comment: 40 pages, no figures. Added comments concerning fractional operators
and the implications of restricting the contour of integration. Typos
correcte
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