42,942 research outputs found
Nutrients in waters on the inner shelf between Cape Charles and Cape Hatteras
The distribution of nutrients in the shelf waters of the southern tip of the Middle Atlantic Bight was investigated. It is concluded that the outflow of freshwater from the Chesapeake Bay is a potential source of nutrients to the adjacent shelf waters. However, a quantitative estimation of its importance cannot yet be made because (1) there are other sources of nutrients to the study area and these sources cannot yet be quantified and (2) the concentrations of nutrients in the outflow from Chesapeake Bay exhibit significant short-term and long-term temporal variabilities
Toxicological approach to setting spacecraft maximum allowable concentrations for carbon monoxide
The Spacecraft Maximum Allowable Concentrations (SMACs) are exposure limits for airborne chemicals used by NASA in spacecraft. The aim of these SMACs is to protect the spacecrew against adverse health effects and performance decrements that would interfere with mission objectives. Because of the 1 and 24 hr SMACs are set for contingencies, minor reversible toxic effects that do not affect mission objectives are acceptable. The 7, 30, or 180 day SMACs are aimed at nominal operations, so they are established at levels that would not cause noncarcinogenic toxic effects and more than one case of tumor per 1000 exposed individuals over the background. The process used to set the SMACs for carbon monoxide (CO) is described to illustrate the approach used by NASA. After the toxicological literature on CO was reviewed, the data were summarized and separated into acute, subchronic, and chronic toxicity data. CO's toxicity depends on the formation of carboxyhemoglobin (COHb) in the blood, reducing the blood's oxygen carrying capacity. The initial task was to estimate the COHb levels that would not produce toxic effects in the brain and heart
Realizing quantum controlled phase-flip gate through quantum dot in silicon slow-light photonic crystal waveguide
We propose a scheme to realize controlled phase gate between two single
photons through a single quantum dot in slow-light silicon photonic crystal
waveguide. Enhanced Purcell factor and beta factor lead to high gate fidelity
over broadband frequencies compared to cavity-assisted system. The excellent
physical integration of this silicon photonic crystal waveguide system provides
tremendous potential for large-scale quantum information processing.Comment: 9 pages, 3 figure
Electroproduction of the d* dibaryon
The unpolarized cross section for the electroproduction of the isoscalar
di-delta dibaryon is calculated for deuteron target using a
simple picture of elastic electron-baryon scattering from the and the components of the deuteron. The calculated
differential cross section at the electron lab energy of 1 GeV has the value of
about 0.24 (0.05) nb/sr at the lab angle of 10 (30) for the
Bonn B potential when the dibaryon mass is taken to be 2.1 GeV. The cross
section decreases rapidly with increasing dibaryon mass. A large calculated
width of 40 MeV for combined with a small
experimental upper bound of 0.08 MeV for the decay width appears to have
excluded any low-mass model containing a significant admixture of the
configuration.Comment: 11 journal-style pages, 8 figure
Alkalinity and pH in the Southern Chesapeake Bay and the James River Estuary
The ranges of alkalinity and pH in the southern Chesapeake Bay and the James River estuary were 2.25 meq·liter−1 at 32‰ to \u3c0.85 at salinities below 6‰ and 7.5– 8.3 during the sampling period. Alkalinity is linearly related to salinity in southern Chesapeake Bay. In the James River estuary, the relationship is more complicated as a result of the mixing of various sources of water or the removal of alkalinity. pH values increase with salinity. The variations in pH may be caused by the salinity‐dependence of the apparent dissociation constants of carbonic acid. © 1979, by the Association for the Sciences of Limnology and Oceanography, Inc
Dissolved inorganic and particulate iodine in the oceans
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts institute of Technology and the Woods Hole Oceanographic Institution February 1976Analytical methods have been developed for the
determination of iodate, iodide and particulate iodine in
sea water. Iodate is converted to tri-iodide and the absorbance
of tri-iodide at 353 nm is measured. The precision of
this method is ca. ±3%. Iodide is first separated from most
other anions by an AG 1-x8 anion exchange column and then
precipitated as palladous iodide with elemental palladium
as the carrier. The precipitate is analyzed by neutron activation
analysis. The precision of the method is ±5% and the
reagent blank is 0.005 uM. Marine suspended matter is collected
by passing sea water under pressure through a 0.6 u
(37 mm diameter) Nuclepore filter. The iodine content of the
particles is determined by neutron activation analysis. The
method has excellent reproducibility and the filter blank is
ca. 3 ng.
Iodate is depleted in the surface waters of the
Equatorial Atlantic. The depletion is more pronounced than
in the Argentine Basin and possibly reflects the higher productivity in the equatorial area. Superimposed on this feature,
a thin lens of water, of a few tens of meters thick and
with high iodate concentrations, can be traced across the
Atlantic. Along the equator, this lens occurs at 80 m at 33˚W
and rises upwards to 55 m at 10˚W and it coincides with a
core of highly saline water which is characteristic of the
Equatorial Undercurrent. Longitudinal sections reflect the
complexity of the equatorial current system. At least three
cores of water with high iodate concentrations may be identified.
These waters may be transported to the equatorial
region from the highly productive areas along the north-western
and western African coasts and the Amazon plume.
In anoxic basins, the concentration of iodide increases
rapidly in the mixing zone from 0.02 uM to 0.44 uM in the Cariaco Trench and from 0.01 uM to 0.23 uM in the
Black Sea. The iodate concentration, meanwhile. decreases to
zero. A maximum in the total iodine to salinity ratio is observed
just above the oxygen-sulfide interface (15 to 17
nmoles/g); it is suggestive of particle dissolution in a
strong pycnocline. Below the interface, the total iodine to
salinity ratio is constant at 12.3 nmoles/g in the anoxic
zone of the Cariaco Trench, whereas, in the Black Sea, it
increases with depth from 10.0 to 19.4 nmoles/g and suggests
a possible flux of iodide from the sediments. By considering
the distribution of iodate and iodide in oxic and anoxic
basins and our present analytical capability, the lower limit
of the pE of the oceans is estimated to be 10.7. Thermodynamic
considerations further suggest that the iodide-iodate
couple is a poor indica tor for the pE of the oceans with a
limited usable range of 10.0 to 10.7.
In the Gulf of Maine during the winter of 1974 to
1975. the effect of winter mixing was conspicuous. Uniform
concentrations of iodide and iodate were observed in the
mixed layer above the sill. The absence of a depletion of
iodate and the low iodide concentration (0.04 uM) in the surface
waters reflect the low biological activity in this region during winters.
Profiles of particulate iodine are characterized
by high concentrations in the euphotic zone (>5 ng/kg), and
lower concentrations (< 2 ng/kg) at greater depths. Occasionally,
high concentrations have also been observed in the
nepheloid layer. The iodine-containing particles are probably
biogenic. A section in the Western Atlantic from 75°N to 55˚S
shows evidence of the transport of particles along isopycnals
and the re-suspension of surface sediments to considerable
distance from the bottom. The standing crops in the top 200
m may be qualitatively correlated with the primary productivity.
Thermodynamic considerations show that iodide is a
metastable form at the pH of sea water. Laboratory studies
fail to show the oxidation of iodide at measurable rates.
Elemental iodine is unstable in sea water and undergoes hydrolysis
to form hypoiodous acid in seconds. Hypoiodous acid is
also unstable and has a life time of minutes to hours. It may
react with organic compounds to form iodinated derivatives or
it may be reduced to iodide by a reducing agent. The disproportionation
of hypoiodite to form iodate seems to be a
slower process. A possible chemical cycle for iodine in the
marine environment is proposed.This work was supported at various phases by NSF
Grant GA-13574, NSF-IDOE Grant GX 33295, NSF Grant DES 74-
22292 and by a research fellowship from the Woods Hole
Oceanographic Institution
The Effect of Spectral Composition on the Photochemical Production of Hydrogen Peroxide in Lake Water
Hydrogen peroxide was produced when samples of lake water were exposed to direct or filtered sunlight in which UV or UV(B+C) light was selectively removed. In all cases, the concentration of hydrogen peroxide increased linearly with time-integrated irradiance. While both visible and UV light can induce the formation of hydrogen peroxide, the contribution from the latter was disproportionately large as it was responsible for about two-thirds of the formation of hydrogen peroxide. Among the UV lights, the contributions from UV-A and UV-(B+C) light were 70% and 30% respectively. The contribution from UV-A light was equivalent to about one half of the total production of hydrogen peroxide. Thus, relative to its contribution to the total irradiance in the solar spectrum, UV-A light is the most efficient type of light for the formation of hydrogen peroxide in lake waters
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