Measuring Estuarine Total Exchange Flow From Discrete Observations.

The exchange between estuaries and the coastal ocean is a key dynamical driver impacting nutrient and phytoplankton concentrations and regulating estuarine residence time, hypoxia, and acidification. Estuarine exchange flows can be particularly challenging to monitor because many systems have strong vertical and lateral velocity shear and sharp gradients in water properties that vary over space and time, requiring high-resolution measurements in order to accurately constrain the flux. The total exchange flow (TEF) method provides detailed information about the salinity structure of the exchange, but requires observations (or model resolution) that resolve the time and spatial co-variability of salinity and currents. The goal of this analysis is to provide recommendations for measuring TEF with the most efficient spatial sampling resolution. Results from three realistic hydrodynamic models were investigated. These model domains included three estuary types: a bay (San Diego Bay), a salt-wedge (Columbia River), and a fjord (Salish Sea). Model fields were sampled using three different mooring strategies, varying the number of mooring locations (lateral resolution) and sample depths (vertical resolution) with each method. The exchange volume transport was more sensitive than salinity to the sampling resolution. Most (>90%) of the exchange flow magnitude was captured by three to four moorings evenly distributed across the estuarine channel with a minimum threshold of 1-5 sample depths, which varied depending on the vertical stratification. These results can improve our ability to observe and monitor the exchange and transport of water masses efficiently with limited resources.

The Reaction between Sodium Hydroxide and Atomic Hydrogen in Atmospheric and Flame Chemistry.

We report the first direct kinetic study of the gas-phase reaction NaOH + H → Na + H2O, which is central to the chemistry of sodium in the upper atmosphere and in flames. The reaction was studied in a fast flow tube, where NaOH was observed by multiphoton ionization and time-of-flight mass spectrometry, yielding k(NaOH + H, 230-298 K) = (3.8 ± 0.8) × 10-11 cm3 molecule -1 s-1 (at 2σ confidence level), showing no significant temperature dependence over the indicated temperature range and essentially in agreement with previous estimates of the rate constant in hydrogen-rich flames. We show, using theoretical trajectory calculations, that the unexpectedly slow, yet T-independent, rate coefficient for NaOH + H is explained by severe constraints in the angle of attack that H can make on NaOH to produce H2O. This reaction is also central to explaining Na-catalyzed flame inhibition, which has been proposed to occur via the sequence Na + OH (+ M) → NaOH followed by NaOH + H → Na + H2O, thereby effectively recombinating H and OH to H2O. RRKM calculations for the recombination of Na and OH yield k(Na + OH + N2, 300-2400 K) = 2.7 × 10-29 (300/T)1.2 cm6 molecule-2 s-1, in agreement with a previous flash photolysis measurement at 653 K and Na-seeded flame studies in the 1800-2200 K range. These results therefore provide strong evidence to support the mechanism of flame inhibition by Na.

Sarcocystis cruzi infection in wood bison (Bison bison athabascae).

Endangered wood bison (Bison bison athabascae) is the largest terrestrial mammal in the American continent. Animal health is an important issue in their conservation, and Sarcocystis cruzi may be a cause of clinical disease in Bovidae. Hearts of eight wood bison from Alaska, USA were examined for sarcocysts by histology, transmission electron microscopy, pepsin digestion, and molecularly. Sarcocystis bradyzoites were found in pepsin digests of all eight and sarcocysts were found in histologic sections of myocardium of four bison. Sarcocysts were thin-walled and ultrastructurally consistent with S. cruzi. Characterization of DNA obtained from lysis of pepsin liberated bradyzoites by PCR-RFLP and subsequent phylogenetic analyses matched with that previously reported for S. cruzi infecting cattle in the USA. Collectively, data indicate that wood bison is a natural intermediate host for S. cruzi.

The effects of CaNa(2)EDTA on brain lead mobilization in rodents determined using a stable lead isotope tracer.

Studies have demonstrated the efficacy of CaNa(2)EDTA for reducing lead (Pb) levels in blood and soft tissues, including brain. However, a concern remains that a single dose of CaNa(2)EDTA may cause a significant increase in brain Pb levels due to a redistribution of endogenous Pb. Here we utilized a rodent model of Pb exposure in combination with a sensitive stable Pb isotope tracer methodology to assess the effects of CaNa(2)EDTA chelation treatment on the redistribution of Pb in brain, blood, kidney, and bone tissues. Thirty-two adult female albino rats (n = 6-7 animals/group) were exposed to 100 microg Pb/mL in drinking water for 4 weeks. Stable (204)Pb tracer was administered via i.p. injection over 2 days prior to chelation. CaNa(2)EDTA was administered i.p. at a dose of 150 mg/kg/day for 1 to 5 days. Statistical differences were evaluated with univariate ANOVA. Under the Pb exposure and chelation treatment regimens utilized here, there was no evidence of a measurable redistribution of endogenous Pb (as total Pb or labile (204)Pb tracer) into the brain after a single CaNa(2)EDTA dose. Further, CaNa(2)EDTA was not efficacious in measurably reducing brain or bone Pb levels, although brain levels of labile (204)Pb tracer were significantly reduced after 5 days of chelation. CaNa(2)EDTA treatment was effective in significantly reducing both blood and kidney Pb levels. Overall, these data substantiate the efficacy of CaNa(2)EDTA for reducing soft tissue Pb levels, but not total brain Pb, and they do not support concern for a transient increase in brain Pb levels with treatment.

Comparative disposition and biotransformation of naphthalene in fresh- and seawater-acclimated striped bass (Morone saxatilis).

1. The disposition and biotransformation of naphthalene in striped bass (Morone saxatilis) acclimated to either fresh- or seawater have been determined. 2. The 24-h total concentration factor did not significantly differ between the freshwater (283.7 +/- 61.5 [+/- SD]) and seawater (245.5 +/- 44.4)-acclimated bass. At both salinities, the viscera/gonad and liver accumulated large concentrations of residues, whereas the skin retained the largest total residue mass. 3. During the 24-h depuration period, the freshwater-acclimated bass depurated 45% of retained residue and the seawater-acclimated bass depurated 85% of retained residue. 4. Naphthalene was primarily excreted unchanged (> 99% in freshwater-acclimated bass and > 88% in seawater-acclimated bass), but small amounts of 1,2-dihydro-1,2-dihydroxynaphthalene and 1- and/or 2-naphthylsulphate were formed.

Transvaginal sonographic diagnosis of sigmoid diverticulitis.

The development of the transvaginal technique has allowed for high-resolution, detailed evaluation of the female pelvis. Although not previously emphasized, gut pathology can also be recognized with this technique. We report two cases of sigmoid diverticulitis which were prospectively diagnosed using endovaginal sonography. In both patients, pelvic sonogram was the first imaging study performed for evaluation of nonspecific abdominal pain.

Picosecond pump-probe interferometric measurement of optical nonlinearities in channel waveguides.

An interferometric technique for measuring with picosecond resolution the time evolution of the real and imaginary components of optical nonlinearities in channel waveguides is described. Characteristics of the technique are illustrated with measurements of band-filling optical nonlinearities in CdS(x)Se(1-x)-doped glass channel waveguides.

Optical fibers with negative group-velocity dispersion in the visible.

Dispersion measurements have been performed in optical fibers having a photoinduced refractive-index grating in the core. The results show that negative group-velocity dispersion can be obtained in these fibers over a frequency region of 500 MHz for wavelengths shorter than 550 nm.

Exact dispersion relations for transverse magnetic polarized guided waves at a nonlinear interface.

We derive exact dispersion relations for transverse magnetic polarized guided waves at an interface between either a linear dielectric or a metal and a nonlinear dielectric. The nonlinearity is taken to be a Kerr-type nonlinearity. Numerical results are presented for the dielectric-metal case.

Prism coupling into ZnS waveguides: a classic example of a nonlinear coupler.

Prism coupling of an argon laser into a nonlinear ZnS waveguide was investigated for power slew rates much less than the nonlinearity relaxation time. The angular variation in coupling efficiency becomes progressively more asymmetric with increasing power until switching occurs on one side of the curve. For large detunings on the switching side, increasing absorption bistability was observed.

Beam-propagation method analysis of a nonlinear directional coupler.

The beam-propagation method is employed to analyze nonlinear directional-coupler operation for various combinations nonlinear materials and initially mismatched guides. A mixed focusing-defocusing configuration is found optimal results.

Comparison of solutions for TM-polarized nonlinear guided waves.

We show that physically realistic solutions for nonlinear TM waves guided by thin dielectric films are obtained in the uniaxial approximation for a dielectric constant proportional to the square of the normal-field component and not of the parallel-field component as assumed previously.

Observation of intensity-dependent guided waves.

We have observed an intensity-dependent hysteresis in the transmission of guided waves through a thin-film waveguide with a cladding characterized by an intensity-dependent refractive index. Good agreement with theory was obtained.

Nonlinear surface plasmons guided by thin metal films.

We have derived and solved numerically the dispersion relations for waves guided by a thin metal film bounded on one or both sides by media with intensity-dependent refractive indices. Depending on the conditions, the usual two modes can be cut off and can undergo radical changes in their field distributions, and new modes can exist above certain power threshholds.