bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Spironolactone Treatment on Gentamicin‐Induced Nephrotoxicity in Rats
Authors: Ali Badreldin H. , Al‐Qarawi Ali A. , Mahmoud Osama M. , Hashad Mahmoud
Published: July 2004

Abstract: The effect of treatment of rats with gentamicin (80 mg/kg/day for 6 days), oral doses of spironolacatone (20 mg/kg/day for 6 days), and the combined treatment (spironolactone + gentamicin) on renal histology and reduced glutathione (GSH) concentration, and some serum constituents indicative of kidney function were studied. The serum concentrations of creatinine and urea were not significantly affected by spironolactone treatment, but were significantly elevated (P<0.05) by gentamicin administration. The antibiotic treatment also reduced GSH concentration and caused a moderate renal cortical necrosis. However, rats exposed to spironolactone + gentamicin revealed drastic increases in the serum urea and creatinine concentrations amounting to about 1.8 and 2.1 times those of rats treated with gentamicin alone, respectively. The histological examination of slides of the renal cortex of rats exposed to the combined drugs exhibited more extensive necrosis in the tubules when compared to those treated with gentamicin alone. The reduction in GSH induced by gentamicin was unaffected by the concomitant treatment of gentamicin and spironolactone. The concentration of gentamicin accumulated in the renal cortex was significantly larger (twofold) in rats treated concomitantly with spironolactone + gentamicin than in rats treated with gentamicin alone. The present results indicate that spironolactone aggravates gentamicin‐induced nephrotoxicity in the rat.
Up‐Regulation of Endothelin Receptor Function and mRNA Expression in Airway Smooth Muscle Cells Following Sephadex‐Induced Airway Inflammation
Authors: Granström Bengt W. , Xu Cang‐Bao , Nilsson Elisabet , Bengtsson Ursula Hultkvist , Edvinsson Lars
Published: July 2004

Abstract: The hypothesis that up‐regulation of bronchial constrictor endothelin receptors in airway smooth muscle cells may contribute to hyperreactivity during airway inflammation was tested in the present study by quantitative endothelin receptor mRNA analysis and functional responses in ring segments of rat trachea and bronchi. Real time reverse transcription polymerase chain reaction was used to quantify endothelin receptor expression in rat airway smooth muscle cells following Sephadex‐induced inflammation. Compared with controls, Sephadex‐induced airway inflammation caused a significant increase (3.9 times P<0.05) of endothelin receptor type B mRNA expression in bronchial smooth muscle cells, but not in tracheal smooth muscle cells. Functional myograph studies of bronchial and tracheal ring segments without epithelium (mechanically denuded) revealed an increase of the maximum contractile effects of endothelin‐1 (a dual agonist for both endothelin type A and B receptors) and sarafotoxin 6c (a selective agonist for endothelin B receptors) in bronchial smooth muscle cells in Sephadex‐induced inflammation, but not in tracheal smooth muscle cells. The enhanced maximal responses of bronchial smooth muscle cells to endothelin‐1 and sarafotoxin 6c in Sephadex‐induced inflammation support our molecular findings and hence imply a role for endothelin B receptors in airway hyperreactivity during airway inflammation.
Monte Carlo parametric study of stent impact on dose for catheter‐based intravascular brachytherapy with
Authors: Ortego Pedro M. , Prieto Carlos , Vano Eliseo
Published: July 2004

The radiation treatment of catheter‐based β‐emitter sources is being used to prevent restenosis following interventional coronary procedures. We present the results of a Monte Carlo calculation study to assess the dosimetric impact in the vessel tissue due to the presence of the stent. A catheter‐based β‐emitter system is modeled using the Monte‐Carlo code MCNP4B. Dose distributions are calculated in annular voxels section) along the axis of a 40 mm. source with and without the stent (at a distance of 1.5–3.0 mm from the longitudinal axis of the source). The main results include: (a) a clear difference between the local perturbation just behind the strut and a more general perturbation seen deeper into the vessel tissue; (b) the local perturbations disappears at a depth of 300–400 μm while the more general perturbation affects the tissue in its full thickness including the prescription point; (c) in the local perturbation the maximum impact is determined mainly by the material and the thickness of the strut while the spatial attenuation of this impact is defined mainly by the strut width; (d) in the general perturbation, the most important magnitude is the free‐area ratio for the path of the electrons, being the material characteristics and strut thickness of secondary importance; (e) analytical expressions are presented to estimate the magnitude of this perturbation according to the complete characteristics of the expanded strut, i.e., thickness, free‐area ratio, and material; and (f) a simple algorithm is presented for estimating the free‐area ratio when this information is not available.
Fiber‐optic, real‐time dosimeter based on optically stimulated luminescence of and KBr:Eu for potential use in the radiotherapy of cancer
Authors: Gaza Razvan
Published: July 2004

This thesis describes a single‐fiber dosimetry system based on optically stimulated luminescence (OSL) of artificially grown single crystals of and KBr:Eu, with potential application in the medical field, especially in radio oncology. Small fiber‐shaped dosimeters with dimensions (diameter/length) on the order of 500 μm/5 mm are attached to one end of an optical fiber, resulting in fiber probes with diameters of less than 1 mm and lengths of up to 15 m. The opposite end of the fiber is connected to an OSL reader that contains a stimulation light source (laser) and a photomultiplier tube that is used for luminescence detection. During irradiation, an optomechanical shutter periodically allows laser light to be transmitted down the optical fiber, to stimulate the luminescence response from the dosimeter being irradiated at a remote location. The luminescence measured during each interval of laser stimulation is indicative of the radiation dose absorbed in the dosimeter since the previous stimulation. The integral absorbed dose is obtained via a summation procedure from the measured dose fractions. Several operating procedures and data processing algorithms were developed in order to increase the speed and accuracy of the measurements, and integrated into the software that controls automated operation of the OSL readers. Periodic modulation of the stimulation also allows the OSL signal to be discriminated from background fluorescence, and thus yields measurements that are unaffected by Čerenkov light (the so‐called “stem effect”). Depending on the type of material used, the speed of the measurements, expressed as the time required to estimate an individual dose fraction, can be as short as 67 ms. Integral dose estimates from real‐time OSL of and KBr:Eu were obtained for water‐phantom irradiations performed with medical teletherapy sources, and were found to agree within 3.7% and 2.8%, respectively, with reference measurements from ionization chambers. We also investigated the possibility of using the fiber OSL readers for other purposes, such as two‐dimensional mapping of dose distributions on compacted layers of grains, and detection of low‐level doses, for possible application in Homeland Security projects.
Determination of the depth of 50% of maximum ionization, for electron beams by the divided difference method
Authors: Hoshina Masao , Shibuya Hitoshi , Kubo Hideo D. , Miura Masahiko , Ohashi Isamu , Yoshimura Ryoichi , Oota Sayako
Published: July 2004

A new characterization of depth‐ionization parameters for electron beams is empirically deduced from our data analysis based on the divided difference method (the DD method), which employs the numerical differential of an ionization curve. The important feature of the present method is that it does not necessarily require normalized percent depth‐ionization (NPDI) data. The depth of 50% of maximum ionization, which is an important parameter for electron beam dosimetry, can be deduced from the analysis of an unnormalized (or partial) depth‐ionization (UDI) curve obtained over a short interval of depth. The values of determined by the DD method are in agreement to within 0.1 mm for energies of 4, 6, and 9 MeV, compared with the ones determined by the TG‐51 protocol method (or the conventional method), and the difference was 0.9 mm for 12 and 15 MeV. The dose at the reference depth, calculated from by the DD method, is found to be in agreement with TG‐51 to within 0.1%. The field size dependence of the DD method using UDI data was studied for three field sizes: 6×6, 10×10, and 20×20 cm2. For all energies, the discrepancies of as determined by both methods were 0.9 mm on average for the 6×6 cm2 fields and 0.6 mm for the other two field sizes. This dependence was remarkable for 6×6 cm2 fields for 12 and 15 MeV, and the discrepancies shown by the DD method were 1.2 mm for 12 MeV and 1.8 mm for 15 MeV, respectively. Since the reference field size in clinical dosimetry is usually 10×10 cm2, this dependence will not affect clinical dosimetry. The DD method could be an alternative option for checking beam quality in dose calibration.
Monte Carlo simulation of the Compton scattering technique applied to characterize diagnostic x‐ray spectra
Authors: Gallardo S. , Ródenas J. , Verdú G.
Published: July 2004

The quality control of x‐ray tubes for medical radiodiagnostic services is very important for such devices. Therefore, the development of new procedures to characterize the x‐ray primary beam is highly interesting in order to obtain an accurate assessment of the actual photon spectrum. The Compton scattering technique is very useful to determine x‐ray spectra (in the 10–150 kVp range), avoiding a pile‐up effect in the detector since a large room is not usually available to apply other techniques. In this work, this process has been simulated using a Monte Carlo code, MCNP 4C. Some geometrical models have been developed and different techniques have been studied in order to improve statistics and accuracy in the acquisition of Pulse Height Distribution (PHD). The effect of both the collimation of the primary beam and the scattering angle of the spectrometer has been analyzed. Results obtained using simulation models have been compared with experimental measurements.
The cone‐beam algorithm of Feldkamp, Davis, and Kress preserves oblique line integrals
Authors: Rodet Thomas , Noo Frédéric , Defrise Michel
Published: July 2004

The algorithm of Feldkamp, Davis, and Kress [J. Opt. Soc. Am. A1, 612–619 (1984)] is a widely used filtered‐backprojection algorithm for three‐dimensional image reconstruction from cone‐beam (CB) projections measured with a circular orbit of the x‐ray source. A well‐known property of this approximate algorithm is that the integral of the reconstructed image along anyaxialline orthogonal to the plane of the orbit is exact when the cone‐beam projections are not truncated. We generalize this result to oblique line integrals, thus providing an efficient method to compute synthetic radiographs from cone‐beam projections. Our generalized result is obtained by showing that the FDK algorithm is invariant under transformations that map oblique lines onto axial lines.
Use of EPID for leaf position accuracy QA of dynamic multi‐leaf collimator (DMLC) treatment
Authors: Chang J. , Obcemea C. H. , Sillanpaa J. , Mechalakos J. , Burman C.
Published: July 2004

We describe in this paper an alternative method for routine dynamic multi‐leaf collimator (DMLC) quality assurance (QA) using an electronic portal imaging device (EPID). Currently, this QA is done at our institution by filming an intensity‐modulated radiotherapy (IMRT) test field producing a pattern of five 1‐mm bands 2 cm apart and performing a visual spot‐check for leaf alignment, motion lags, sticking and any other mechanical problems. In this study, we used an amorphous silicon aS500 EPID and films contemporaneously for the DMLC QA to test the practicality and efficacy of EPID vis‐à‐vis film. The EPID image was transformed to an integrated dose map by first converting the reading to dose using a calibration curve, and then multiplying by the number of averaged frames. The EPID dose map was then back‐projected to the central axis plane and was compared to the film measurements which were scanned and converted to dose using a film dosimetry system. We determined the full‐width half‐maximum (FWHM) of each band for both images, and evaluated the dose to the valley between two peaks. We also simulated mechanical problems by increasing the band gap to 1.5 mm for some leaf pairs. Our results show that EPID is as good as the film in resolving the band pattern of the IMRT test field. Although the resolution of the EPID is lower than that of the film (0.78 mm/pixel vs 0.36 mm/pixel for the film), it is high enough to faithfully reproduce the band pattern without significant distortion. The FWHM of the EPID is 2.84 mm, slightly higher than the 2.01 mm for the film. The lowest dose to the valley is significantly lower for the EPID (15.5% of the peak value) than for the film (28.6%), indicating that EPID is less energy independent. The simulated leaf problem can be spotted by visual inspection of both images; however, it is more difficult for the film without being scanned and contrast‐enhanced. EPID images have the advantage of being already digital and their analysis can easily be automated to flag leaf pairs outside tolerance limits of set parameters such as FWHM, peak dose values, peak location, and distance between peaks. This automation is a new feature that will help preempt MLC motion interlocks and decrease machine downtime during actual IMRT treatment. We conclude that since EPID images can be acquired, analyzed and stored much more conveniently than film, EPID is a good alternative to film for routine DMLC QA.
The cause of the artifact in 4‐slice helical computed tomography
Authors: Taguchi Katsuyuki , Aradate Hiroshi , Saito Yasuo , Zmora Ilan , Han Kyung S. , Silver Michael D.
Published: July 2004

The causes of the image artifacts in a 4‐slice helical computed tomography have been discussed as follows: (1) changeover in pairs of data used in z interpolation, (2) sampling interval in z, and (3) the cone angle. This study analyzes the first two causes of the artifact and describes how the current algorithm [K. Taguchi and H. Aradate, Radiology 205P, 390 (1997); 205P, 618 (1997); Med. Phys. 25, 550–561 (1998); H. Hu, ibid. 26, 5–18 (1999); S. Schaller et al., IEEE Trans. Med. Imaging 19, 822–834 (2000); K. Taguchi, Ph.D. thesis, University of Tsukuba, 2002] solves the problem. An interpolated sinogram for a slice at the edge of a ball phantom shows discontinuity caused by the changeover. If we extend the streak artifact in the reconstructed image, it crosses the focus orbit at the corresponding projection angle. Applying z filtering can reduce such causes by its feathering effect and mixing data obtained by different cone angles; the best results are provided when z filtering is applied to densely sampled helical data.
Technical Note: Output and energy fluctuations of the tomotherapy Hi‐Art helical tomotherapy system
Authors: Mahan Stephen L. , Chase Daniel J. , Ramsey Chester R.
Published: July 2004

The output and energy calibrations for the first clinical Hi‐Art 2.0 helical tomotherapy system have been reviewed. Fixed‐gantry/fixed‐couch and rotational‐gantry/fixed‐couch measurements were made on a daily basis over a period of 20 weeks to investigate system stability. Static gantry measurements were taken at 10 cm depth in a rectangular stack of Virtual Water at an SSD distance of 90 cm and a field size of Rotational gantry measurements were taken in a cylindrical phantom Virtual Water phantom for a field size of The Hi‐Art 2.0 system has maintained its calibration to within and energy to within over the initial 20 week period.
Noninvasive measurements of tissue hemodynamics with hybrid diffuse optical methods
Authors: Durduran Turgut
Published: July 2004

Diffuse optical techniques were used to measure hemodynamics of tissues noninvasively. Spectroscopy and tomography of the brain, muscle, and implanted tumors were carried out in animal models and humans. Two qualitatively different methods, diffuse optical tomography and diffuse correlation tomography, were hybridized permitting simultaneous measurement of total hemoglobin concentration, blood oxygen saturation, and blood flow. This combination of information was processed further to derive estimates of oxygen metabolism (e.g., in tissue. The diffuse correlation measurements of blood flow were demonstrated in human tissues, for the first time, demonstrating continous noninvasive imaging of oxygen metabolism in large tissue volumes several centimeters below the tissue surface. The bulk of these investigations focussed on cerebral hemodynamics. Extensive validation of this methodology was carried out in in vivo rat brain models. Three‐dimensional images of deep tissue hemodynamics in middle cerebral artery occlusion and cortical spreading depression (CSD) were obtained. CSD hemodynamics were found to depend strongly on partial pressure of carbon dioxide. The technique was then adapted for measurement of human brain. All optical spectroscopic measurements of during functional activation were obtained through intact human skull noninvasively. Finally, a high spatiotemporal resolution measurement of cerebral blood flow due to somatosensory cortex activation following electrical forepaw stimulation in rats was carried out with laser speckle flowmetry. New analysis methods were introduced for laser speckle flowmetry. In other organs, deep tissue hemodynamics were measured on human calf muscle during exercise and cuff‐ischemia and were shown to have some clinical utility for peripheral vascular disease. In mice tumor models, the measured hemodynamics were shown to be predictive of photodynamic therapy efficacy, again suggesting the promise of clinical utility. In total, the research has pioneered the development of diffuse optical measurements of blood flow, oxygenation, and oxygen metabolism in a large range of research and clinical applications.
Monte Carlo computation of dosimetric amorphous silicon electronic portal images
Authors: Siebers Jeffrey V. , Kim Jong Oh , Ko Lung , Keall Paul J. , Mohan Radhe
Published: July 2004

This study develops and tests a method to compute dosimetric images for an amorphous siliconflat‐panel detector so that an accurate quantitative comparison between measured and computed portal images may be made. An EGS4‐based Monte Carlo (MC) algorithm is developed to efficiently tally the energy deposition through the use of a virtual detector dose‐scoring methodology. The complete geometry of theimager is utilized in the MC calculation up to the imager rear housing, which is replaced with a uniform thickness material slab. The detector‐mounting hardware is modeled as a uniform backscattering material. The amount of backscatter material required to reproduce the measured backscatter is 0.98 g/cm2of water. A flood‐field irradiation, performed in the measurement imaging session, is used to cross‐calibrate the computed images with the measured images. Calibrated MC‐computed images reproduce measured field‐size dependencies of the electronic portal imaging device (EPID) response to within <1%, without the need for optical glare or other empirical corrections. A 10% dose difference between measured and computed images was observed outside the field edge for afield that was entirely blocked by the multileaf collimator (MLC). However, this error corresponded with less than 0.15% of the open‐field dose. Forfields produced by 5 and 20 mm dynamically sweeping MLC gaps, more than 98% of the points were found to have a gamma less than one with a 2%, 2 mm criteria. For an intensity modulated radiation therapy (IMRT) patient test field, over 99% of the points were found to have a gamma less than one with a 2%, 2 mm criteria. This study demonstrates that MC can be an effective tool for predicting measuredportal images and may be useful for IMRT EPID‐based dosimetry.
Optical characterization of a radiochromic film by total reflectance and transmittance measurements
Authors: Fusi Franco , Mercatelli Luca , Marconi Giacomo , Cuttone Giacomo , Romano Giovanni
Published: July 2004

The GafChromic™ film (GCF) MD‐55‐2, a radiochromic material, was examined for its optical properties through total reflectance and transmittance measurements in visible spectrum (400–700 nm). By using a multilayer model of the film and Kubelka–Munk's (KM) theory, absorption and scattering coefficients of the film sensitive layer (K and S, respectively) were obtained from measurements of irradiated and nonirradiated slides. This has allowed calculation of the absorbance of the sensitive layer of the GCF. The model easily splits scattering from absorption. Unlike absorption, scattering is essentially insensitive to irradiation dose and decreases slowly as the wavelength increases. The scattering effect is predominant over absorption in the 400–500 nm range, while beyond 600 nm absorption prevails. The absorbance of the sensitive layer was calculated using the K coefficient and compared with the optical densities (OD) measured considering only ballistic photons (as in a standard spectrophotometer) as well as the optical densities measured collecting all the transmitted photons (as in many densitometers). The values of found were always lower than OD measured by the other methods and they had the best linearity on the whole visible range. These data support the hypothesis that the sensitive layer reacts to irradiation more linearly than that shown by measurements using standard commercial devices. However, in the 600–680 nm range, correction is not very important because absorption is predominant over scattering. When GCF is used for imaging, scattering produces a loss of spatial information. Consequently, it is necessary to collect only ballistic photons and to correct absorbance by K and S coefficients.
Assessment of a global climatology of oceanic dimethylsulfide (DMS) concentrations based on SeaWiFS imagery (1998-2001)
Authors: Belviso S , Moulin C , Bopp L , Stefels J
Published: July 2004

A method is developed to estimate sea-surface particulate dimethylsulfoniopropionate (DMSPp) and dimethylsulfide (DMS) concentrations from sea-surface concentrations of chlorophyll a (Chl a). When compared with previous studies, the 1° × 1° global climatology of oceanic DMS concentrations computed from 4 years (19982001) of Chl a measurements derived from SeaWiFS (satellite-based, sea-viewing wide field of view sensor) exhibits lower seasonal variability in the southern hemisphere than in the northern hemisphere. A first evaluation of the method shows that it reasonably well represents DMSPp and DMS in the North Atlantic subtropical gyre, in large blooms of mixed populations of diatoms and Phaeocystis spp., and in massive blooms of Phaeocystis spp. but fails for large, almost pure blooms of diatoms. DMSPp and DMS concentrations derived from SeaWiFS were also compared with spatially and temporally coincident in situ measurements acquired independently in the Atlantic between 39°N and 45°N and in subtropical and subantarctic Indian Ocean surface waters. Moderate spring and summer phytoplankton blooms there exhibited similar trends in DMSPp and DMS levels vs. moderate blooms of mixed populations of prymnesiophytes and dinoflagellates investigated by others. Measured DMS largely exceeded simulated DMS concentrations, whereas measured and simulated DMSPp levels were in close agreement. DMS accumulation is tentatively attributed to dinoflagellate DMSP lyase activity.
Ecosystem modelling of the cycling of marine dimethylsulfide: a review of current approaches and of the potential for extrapolation to global scales
Authors: Vézina Alain F
Published: July 2004

There is rising interest from oceanic and atmospheric scientists in the potential role of dimethylsulphide (DMS) in regulating global climate. The increased availability of field observations of DMS and related compounds (DMS(P)) and of their transformation rates in the ocean has stimulated the development of ecosystem models of marine sulfur cycling. The models cover a wide range of complexity levels and spatial/temporal scales, from zero-dimensional local simulations spanning a few days to regional/global simulations driven by ocean general circulation models. The degree of complexity required to model DMS(P) dynamics, particularly the differentiation into phyto plankton species or groups, remains an important open question. First attempts to drive these models with vertically resolved turbulence models suggest interesting interactions between DMS(P) dynamics and fine-scale ocean mixing that can modify fluxes of DMS to the atmosphere. Recent models also bring into focus the strong affinities between the cycling of DMS(P) and that of dissolved organic carbon in the surface ocean. Formal parameter estimation techniques, which are increasingly used in ecosystem modelling of carbon and nitrogen dynamics, should play a stronger role in the development of DMS sulfur modelling. Extrapolation of DMS cycling and fluxes to the global scale presently relies largely on empirical approach. A semiempirical approach, based on a simple ecosystem model, is shown to reproduce gross features of the global distribution of DMS in the surface ocean. This shows promise for the continuing development of ecosystem models for global modelling of marine sulfur fluxes to the atmosphere.
Vertically resolved cycling of dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) in the Northwest Atlantic in spring
Authors: Levasseur M , Scarratt M , Roy S , Laroche D , Michaud S , Cantin G , Gosselin M , Vézina A
Published: July 2004

In May 1998, profiles of ambient concentration and net changes of particulate dimethylsulfoniopropionate (DMSPp), dissolved dimethylsulfoniopropionate (DMSPd), and dimethylsulfide (DMS) were measured in three bio geographic provinces of the Northwest Atlantic: Northwest Atlantic Continental Shelf (Grand Banks), North Atlantic Drift, and North Atlantic Subtropical Gyre (Sargasso Sea). All stations/depths exhibited large losses of DMSPp(up to 18.0 nmol·L1·day1). DMSP and DMS cycling varied in relation to the type and development stage of the plankton assemblages. The postdiatom bloom conditions on the Grand Banks were associated with an efficient utilization of DMSP by microzooplankton and bacteria. Bacterial DMS production balanced the DMS bacterial consumption, resulting in little net DMS production (0.3 nmol·L1·day1). This contrasted with the North Atlantic Drift and Sargasso Sea stations where flagellates were thriving and most of the DMSPploss was recovered in the dissolved pool, indicating a less active microbial DMSP metabolism. DMSPdcleavage was high in these latter cases and exceeded DMS bacterial consumption, allowing a net production of DMS (up to 1.8 nmol·L1·day1). These results indicate that maximum DMS net production occurs in growing algal systems where the production of DMSPdresulting from microzooplankton grazing exceeds the bacterial requirement in carbon and sulfur.
Behaviour of the ocean DMS(P) pools in the Sargasso Sea viewed in a coupled physical-biogeochemical ocean model
Authors: Clainche Yvonnick Le , Levasseur Maurice , Vézina Alain , Dacey John WH , Saucier François J
Published: July 2004

The dimethylsulfide (DMS) production model NODEM (Northern Oceans DMS Emission Model) was coupled with the water column ocean model GOTM (General Ocean Turbulence Model) that includes a two-equation kε turbulence scheme. This coupled physical-biogeochemical ocean model represents a significant improvement over the previous uncoupled version of NODEM that was driven by a diagnostic vertical mixing scheme. Using the same set of biogeochemical parameters, the coupled model is used to simulate the annual cycles of 1992 and 1993 at Hydrostation S in the Sargasso Sea. The better reproduction of the turbulent mixing environment corrects some deficiencies in nitrogen cycling, especially in the seasonal evolution of the nutrient concentrations. Hence, the coupled model captures the late-winter chlorophyll- and DMS(P)-rich blooms. It is also more adept at reproducing the vertical distribution of chlorophyll and DMS(P) in summer. Moreover, the DMS pool becomes less dependent on parameters controlling the nitrogen cycle and relatively more sensitive to parameters related to the sulfur cycle. Finally, the coupled model reproduces some of the observed differences in DMS(P) pools between 1992 and 1993, the latter being an independent data set not used in calibrating the initial version of NODEM.
Modelling of the seasonal patterns of dimethylsulphide production and fate during 1989 at a site in the North Sea
Authors: Archer Stephen D , Gilbert Francis J , Allen J Icarus , Blackford Jerry , Nightingale Philip D
Published: July 2004

This modelling study aimed to extend our understanding of the biogeochemistry of the climatically active gas dimethylsulphide (DMS) in marine surface waters to an annual cycle. Processes involved in the production and fate of DMS and its precursor β-dimethylsulphoniopropionate (DMSP), a product of phytoplankton synthesis, were incorporated into a complex, coupled one-dimensional physical ecosystem model (European Regional Seas Ecosystem Model (ERSEM) and the General Ocean Turbulence Model (GOTM)) to create a model of DMS biogeochemistry at a seasonally stratified site in the North Sea for 1989. The model was validated against nutrient concentrations, biological standing stocks, biological production, DMS and DMSP concentrations, and DMS sea to air flux determined throughout 1989 during the North Sea Project. The validation results demonstrated that complex ecosystem models, combined with a comprehensive network of processes that control the production and fate of DMSP and DMS, could accurately mimic DMS biogeochemistry. The model provides insights into the impact of seasonally changing physical forcing on the relative contribution of individual processes to DMS production and sea to air flux.
Dimethylsulfoniopropionate in six species of giant clams and the evolution of dimethylsulfide after death
Authors: Hill Richard W , Dacey John WH , Hill Susan D , Edward Ahser , Hicks Wayne A
Published: July 2004

Substantial accumulation of dimethylsulfoniopropionate (DMSP) is documented in tissues of all six of the common species of giant clams (Tridacnidae). Results include measures of DMSP concentrations in siphonal mantle, byssal mantle, adductor muscle, and gill tissues obtained by gas chromatography of alkalized extracts plus evidence of DMSP from mass spectrometry. Formation of dimethylsulfide (DMS) by tissues after death is documented. The tridacnid clams maintain symbiotic associations with populations of dinoflagellates, which live within the enlarged siphonal mantle. We postulated that because of their association with dinoflagellates, the clams would chronically accumulate DMSP to high concentrations. Our results show that DMSP occurs at over 30 mmol·kg1 in many tissues of tridacnid clams (sometimes 5060 mmol·kg1), meaning that these clams accumulate DMSP to the highest documented tissue concentrations in the animal kingdom. DMSP at such concentrations could affect multiple properties and functions. Our particular interest for this research was to assess whether postmortem breakdown of DMSP is responsible for the rapid development of potent off-odors and off-tastes that have blocked the commercial success of giant clam aquaculture. High concentrations of DMS produced in the day after death probably account for the peculiar perishability of giant clam tissues.
From cells to globe: approaching the dynamics of DMS(P) in the ocean at multiple scales
Authors: Simó Rafel
Published: July 2004

Major advances in dimethylated sulfur research are being made by approaching its dynamics at multiple scales. At the molecular to cellular level, single-cell techniques in molecular biology allow us to identify the microbes involved in cycling of dimethylated sulfur. Also, we find that dimethylsulfoxide (DMSO) is as ubiquitous as dimethyl sulfoniopropionate (DMSP) in marine plankton, which supports the recent suggestion that both compounds are involved in coping with oxidative stress. At the community level, there is recent evidence for the role of DMSP as a major carrier in organic sulfur transfer and cycling through trophic levels, from phytoplankton to bacteria and to zooplankton through herbivore protozoans. As a consequence, the food web dynamics drive the oceanic emission of atmospheric sulfur. At the ecosystem level, the diverse and intricate effects of the physicochemical setting (light, wind, nutrients) on the oceanic cycling of dimethylated sulfur are being uncovered. A proposed shortcut to detailed understanding of the individual processes presents the depth of the surface mixed layer as the variable that integrates most of the environmental effects and serves for predicting dimethylsulfide (DMS) concentrations, even at the global ocean level. This opens the door to assessing the strength of the DMS biogeophysical system as a climate regulator.
Will marine dimethylsulfide emissions amplify or alleviate global warming? A model study
Authors: Bopp Laurent , Boucher Olivier , Aumont Olivier , Belviso Sauveur , Dufresne Jean-Louis , Pham Mai , Monfray Patrick
Published: July 2004

Dimethylsulfide (DMS) is the most abundant volatile sulfur compound at the sea surface and has a strong marine phytoplanktonic origin. Once outgased into the atmosphere, it contributes to the formation of sulfate aerosol particles that affect the radiative budget as precursors of cloud condensation nuclei (CCN). It has been postulated that climate may be partly modulated by variations in DMS production. We test this hypothesis in the context of anthro pogenic climate change and present here, modelled for the first time, an estimate of the radiative impact resulting from changes in DMS airsea fluxes caused by global warming. At 2× CO2, our model estimates a small increase (3%) in the global DMS flux to the atmosphere but with large spatial heterogeneities (from 15% to 30%). The radiative perturbation resulting from the DMS-induced change in cloud albedo is estimated to be 0.05 W·m2, which represents only a small negative climate feedback on global warming. However, there are large regional changes, such as a perturbation of up to 1.5 W·m2 in summer between 40°S and 50°S, that can impact the regional climate. In the Southern Ocean, the radiative impact resulting from changes in the DMS cycle may partly alleviate the radiative forcing resulting from anthropogenic CO2.
Direct measurements of biogenic dimethylsulphide fluxes from the oceans: a synthesis
Authors: Zemmelink H J , Dacey J WH , Hintsa E J
Published: July 2004

This paper provides a brief overview of the state-of-the-art of techniques that are currently used for field measurements of trace gas fluxes and the subsequent derivation of gas transfer rates over the oceans. Special attention is given to the relaxed eddy accumulation (REA) and gradient flux (GF) techniques, which rely on empirical functions thus far mainly validated over land. The universality of these functions and their application at sea have not yet been fully evaluated. New experiments have shown that the emission of dimethylsulphide (DMS) can be measured by the REA and GF techniques. Moreover, these measurements have provided parameterizations of gas exchange rates that are within the range of relationships between wind speed and gas transfer that have recently been derived from eddy correlation (EC) and deliberate tracer measurements. Using DMS as a model, gas is potentially a powerful approach to intercalibrate the REA, GF, and EC techniques, test their applicability in the marine environment, and investigate processes that determine trace gas exchange across the ocean surface.
Particulate dimethylsulfoniopropionate and dimethylsulfoxide in relation to iron availability and algal community structure in the Peru Upwelling System
Authors: Riseman S F , DiTullio G R
Published: July 2004

The influence of iron on phytoplankton biogenic sulfur production, physiological status, and community structure in the Peruvian Upwelling System was investigated in September 2000. Vertical profiles of particulate dimethylsulfoniopropionate (DMSPp) and dimethylsulfoxide (DMSOp) were measured at stations along two transects passing from the high-iron waters of the continental shelf, across the Peru trench, to low-iron open-ocean waters. Although chlorophyll a (Chl a) biomass decreased significantly across the shelf, DMSPp and DMSOpconcentrations relative to Chl a were higher at the offshore stations (DMSPp:Chl a 2.36.4 times greater and DMSOp:Chl a 2.64 times greater). These changes were associated with lower iron concentrations, as well as a shift from diatom-dominated communities to ones dominated by cryptophytes and haptophytes (based on algal pigment concentrations). The results of a shipboard iron-addition incubation experiment were similar to patterns observed on the transects. DMSPp:Chl a ratios decreased with increasing iron and diatoms preferentially outgrew other taxa. The possible role of DMSPpand DMSOpas free radical scavengers (stimulated by iron limitation) was supported by the increased concentrations of these compounds measured under low-iron conditions, as well as by the positive correlations (r2= 0.69 and 0.82, respectively) observed between these compounds and the known antioxidant β-carotene.
Responses of coastal phytoplankton populations to nitrogen additions: dynamics of cell-associated dimethylsulfoniopropionate (DMSP), glycine betaine (GBT), and homarine
Authors: Keller Maureen D , Matrai Patricia A , Kiene Ronald P , Bellows Wendy K
Published: July 2004

Dimethylsulfoniopropionate (DMSP) and glycine betaine (GBT) are organic osmolytes abundant in many marine phytoplankton. Herein, we field tested for the first time the hypothesis that GBT production might be favored over DMSP in natural phytoplankton populations growing in high-N environments or when N is added to a system. Concentrations of particulate DMSP (DMSPp; 1545 nmol·L1) were equal to, or greater than, concentrations of particulate GBT (GBTp; 015 nmol·L1) in the upper water column. Homarine, another N-containing osmolyte, was detected at lower levels in all samples. These are the first reported values of GBTp, and homarine in seawater. During N enrichment experiments, no consistent pattern of response in the DMSP pool resulted. Under N stress, nitrate addition either caused DMSP to be released but without an equivalent increase in GBT or DMSP dynamics were not affected but GBT increased. In populations under less N stress, GBT levels were similar to those of DMSPpthroughout the experiments. Homarine levels remained low at all times. We conclude that no simple switch between DMSP and GBT occurs as a function of N availability in natural populations. Variable responses to N supply probably resulted from differences in species composition and physiological state of the populations present.
Influence of dinoflagellate diurnal vertical migrations on dimethylsulfoniopropionate and dimethylsulfide distribution and dynamics (St. Lawrence Estuary, Canada)
Authors: Merzouk Anissa , Levasseur Maurice , Scarratt Michael , Michaud Sonia , Gosselin Michel
Published: July 2004

The influence of the diurnal vertical migration of the dinoflagellates Alexandrium tamarense and Scrippsiella trochoidea on dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) dynamics was studied during a 34-h Lagrangian experiment in the St. Lawrence Estuary in July 2000. Particulate DMSP (DMSPp), dissolved DMSP (DMSPd), and DMS exhibited diel patterns with minimum concentrations during the night and maximum concentrations around noon. DMSPp concentrations were correlated with the abundance of the two vertically migrating DMSP-rich dinoflagellates. The DMSPp:Chl a ratio exhibited similar diel variations, suggesting a light-induced de novo DMSP synthesis during the day. Diel variations of the DMS:Chl a ratio suggest that the accumulation of DMS around noon resulted from physiological responses of the algae and (or) bacteria to light. Biological gross DMS production and bacterial DMS consumption were decoupled, leading to rapid fluctuations in DMS. These results show that in systems dominated by DMSP-rich dinoflagellates containing DMSP lyases, DMS concentrations may vary by as much as a factor of 10 over a 24-h period. Such diel variations must be considered when estimating the contribution of such systems to the DMS sea to air flux.
Tomographic retrieval of the oxygen infrared atmospheric band with the OSIRIS infrared imager
Authors: Degenstein D A , Llewellyn E J , Lloyd N D
Published: July 2004

The infrared imager (IRI) component of the optical spectrograph and infrared imager system (OSIRIS) onboard the Odin spacecraft provides a set of line-of-sight brightness measurements of the oxygen infrared atmospheric (OIRA) band. This set of measurements is unique in the fact that they are ideal inputs to a two-dimensional retrieval scheme that accurately recovers the volume emission rate of the OIRA band. The retrieval is done simultaneously in two dimensions, the angle along the satellite track and the distance from the centre of the Earth. The latter is easily converted to altitude above the surface of the Earth. In this work, we present the measurement set, the retrieval technique, and some preliminary results. We clearly demonstrate that the OSIRIS infrared imager provides maps of the OIRA band volume emission rate with unprecedented spatial resolution. PACS Nos.: 07.05.Pj, 07.60.Dq, 94.10.Fa, 94.10.Gb, 94.10.Rk
Theoretical study of energy levels of atomic Ga
Authors: Zheng N W , Li Z , Ma D , Zhou T , Fan J
Published: July 2004

There are few documented values of the energy levels of the gallium atom. The values in some series remain blank and some series have no values in high Rydberg states. In this paper, based on the weakest bound electron potential model theory we treat the many-valence electron system of the excited gallium atom as a single-electron system of the weakest bound electron and use Martin's expression to determine the parameters. Most of the results are satisfying with deviations less than 1 cm1 compared with the documented values in the National Institute of Standards and Technology. In addition, we fill many blanks in some high Rydberg energy levels of the gallium atom. PACS Nos.: 31.15.Ct, 32.10.Fn
MHD combined convection flow of a non-Newtonian power-law fluid due to a rotating cone or disk
Authors: Abo-Eldahab E M , Salem A M
Published: July 2004

The problem of laminar mixed convection flow of non-Newtonian power-law fluids from a constantly rotating isothermal cone or disk in the presence of a uniform magnetic field is investigated in this paper. The effect of Joule heating is also considered. The governing partial-differential equations are transformed into ordinary differential equations using similarity transformations. The transformed equations, on the assumption of a small magnetic Reynolds number, are solved numerically by employing the shooting method. Graphical results for the velocity and temperature profiles as well as tabulated results for the skin friction and the Nusselt number for various parametric conditions are presented and discussed. PACS No.: 47.50.td
A new way of finding locations of zeros of wave functions
Authors: Nanayakkara A
Published: July 2004

A new analytic method is presented for evaluating zeros of wave functions. In this method, locating the zeros of wave functions of the Schrodinger equation is converted to finding the roots of a polynomials. The coefficient of this polynomial can be evaluated analytically for a class of potentials. The speciality of this method is that the zeros are located without solving an equation of motion for the wave function. The method is valid for both real and complex systems and can be applied for locating both real and complex zeros. Examples are given to illustrate the method. PACS Nos.: 02.30.Mv, 03.65.Ge, 03.65.Sq, 03.65.w, 04.20.Jb, 04.20.Ha, 05.45.Mt
Antisymmetric tensor gauge fields on S4
Authors: McKeon D.G.C.
Published: July 2004

Antisymmetric tensor gauge fields ϕab(η) are formulated on the surface of a sphere S4(η2 = a2) embedded in five dimensions. Such compact manifolds occur in the dimensional reduction of higher dimensional spaces that naturally occur in string theories. The free field model is equivalent to a scalar model on this sphere. Interactions with gauge fields are discussed. It is feasable to formulate models for interactions with U(1) gauge fields Aa(η) that are akin to those of Freedman and Townsend in flat space. In addition, it proves possible to have a novel interaction of ϕab with Aa and a spinor field Ψ(η) on S4 with both Abelian and non-Abelian gauge invariance. In these models, Aa plays the role of a Stueckelberg field.PACS No.: 11.30.Ly
On diffraction of electromagnetic waves by an aperture in a conducting screen
Authors: Hirose A , Li H , Livingstone S , Lu X F
Published: July 2004

The Smythe formula for diffraction of electromagnetic waves by an aperture in a large conducting screen is revisited without resorting to a fictitious magnetic current.PACS Nos.: 42.25.Fx, 41.20.Jb
Shear strength of a compacted residual soil from consolidated drained and constant water content triaxial tests
Authors: Rahardjo Harianto , Heng Ong Boo , Choon Leong Eng
Published: July 2004

Rainfall-induced landslides in unsaturated residual soils can occur slowly under drained conditions or rapidly under undrained conditions. Consolidated drained (CD) and constant water content (CW) tests have been performed to simulate the stress paths followed by soil elements in a slope that fails under drained and undrained conditions. The study was carried out to investigate the shear strength characteristics of soils associated with rainfall-induced slope failures. The soil tested was residual soil from the Jurong sedimentary formation and was reconstituted using static compaction. The test results indicate that the shear strength of the compacted specimens obtained from the CW tests agrees well with the shear strength obtained from the CD tests for the specimens with initial matric suctions less than their air-entry values. The shear strength results from the CD and CW triaxial tests start to differ when the matric suction exceeds the air-entry value of the soil. The CD and CW triaxial tests also indicate that the compacted specimens behave as a normally consolidated soil at matric suctions below the air-entry value of the soil and as an overconsolidated soil at matric suctions above the air-entry value of the soil. Results of the CW triaxial tests show that the relationship between the response of pore-water pressure and the total volume change of the specimen is more complicated than that found in the saturated undrained triaxial tests. In other words, the change in pore-water pressure during shearing is not directly related to the overall volume change of the specimen.Key words: unsaturated soil, compacted soil, residual soil, consolidated drained triaxial test, constant water content triaxial test.