bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential modulation of cardiac and skeletal muscle ryanodine receptors by NADH
Authors: Zima Aleksey V , Copello Julio A , Blatter Lothar A
Published: June 2003

The effects of nicotinamide‐adenine dinucleotides (NADH, NAD+, NADPH) on ryanodine receptor channels (RyRs) from cardiac and skeletal muscle were compared in planar bilayers. NADH decreased cardiac RyR activity, which was counteracted by NAD+. In contrast, NADH and NAD+ both activated skeletal RyRs. NADPH/NADP+ were without effect on cardiac and skeletal RyRs. In the presence of ATP, NADH inhibition of cardiac RyRs remained. Differently, in the presence of ATP both NADH and NAD+ were ineffective as skeletal RyR agonists, suggesting interactions with the ATP binding site(s) of the channels. The results suggest that the direct effect of cytosolic NADH is physiologically important for the modulation of cardiac RyRs.
The variant ‘his‐box’ of the C18‐Δ9‐PUFA‐specific elongase IgASE1 from Isochrysis galbana is essential for optimum enzyme activity
Authors: Qi Baoxiu , Fraser Thomas C.M. , Bleakley Claire L. , Shaw Elisabeth M. , Stobart A.Keith , Lazarus Colin M.
Published: June 2003

IgASE1, a C18‐Δ9‐polyunsaturated fatty acid‐specific fatty acid elongase component from Isochrysis galbana, contains a variant histidine box (his‐box) with glutamine replacing the first histidine of the conserved histidine‐rich motif present in all other known equivalent proteins. The importance of glutamine and other variant amino acid residues in the his‐box of IgASE1 was determined by site‐directed mutagenesis. Results showed that all the variation in amino acid sequence between this motif in IgASE1 and the consensus sequences of other elongase components was required for optimum enzyme activity. The substrate specificity was shown to be unaffected by these changes suggesting that components of the his‐box are not directly responsible for substrate specificity.
Isolation and characterisation of 5′‐fluorodeoxyadenosine synthase, a fluorination enzyme from Streptomyces cattleya
Authors: Schaffrath Christoph , Deng Hai , O'Hagan David
Published: June 2003

5′‐Fluorodeoxyadenosine synthase, a C–F bond‐forming enzyme, has been purified from Streptomyces cattleya. The enzyme mediates a reaction between inorganic fluoride and S‐adenosyl‐L‐methionine (SAM) to generate 5′‐fluoro‐5′‐deoxyadenosine. The molecular weight of the monomeric protein is shown to be 32.2 kDa by electrospray mass spectrometry. The kinetic parameters for SAM (K
m 0.42 mM, V
max 1.28 U/mg) and fluoride ion (K
m 8.56 mM, V
max 1.59 U/mg) have been evaluated. Both S‐adenosyl‐L‐homocysteine (SAH) and sinefungin were explored as inhibitors of the enzyme. SAH emerged as a potent competitive inhibitor (K
i 29 μM) whereas sinefungin was only weakly inhibitory.
Proteolytic cleavage of the EMR2 receptor requires both the extracellular stalk and the GPS motif
Authors: Chang Gin-Wen , Stacey Martin , Kwakkenbos Mark J. , Hamann Jörg , Gordon Siamon , Lin Hsi-Hsien
Published: June 2003

EMR2 is a human myeloid‐restricted member of the EGF‐TM7 receptor family that contains a highly conserved protein‐coupled receptor roteolysis ite (GPS) in the membrane‐proximal region. Here the post‐translational proteolytic cleavage of EMR2 at GPS was investigated. We show the cleavage occurs at Leu517‐Ser518 and is independent of the transmembrane domains. The non‐covalent association of the resulting extracellular α‐subunit and transmembrane β‐subunit requires a minimum of eight amino acids in the β‐subunit. The GPS motif is necessary, but not sufficient for receptor cleavage, which requires the entire extracellular stalk. Thus, an alternatively spliced EMR2 isoform with a truncated stalk fails to undergo proteolytic cleavage. Alternative splicing therefore provides a means to regulate GPS cleavage, producing receptors with two distinct structures.
Real‐time evidence of surface modification at polystyrene lattices by poloxamine 908 in the presence of serum: in vivo conversion of macrophage‐prone nanoparticles to stealth entities by poloxamine 908
Authors: Moghimi S.M , Pavey K.D , Hunter A.C
Published: June 2003

Intravenously injected polystyrene nanoparticles, which are prone to rapid sequestration by professional phagocytes, are converted to stealth entities by prior bolus intravenous injection of poloxamine 908. This behaviour is not due to alteration in macrophage phagocytic activity. Laser Doppler anemometry and surface plasmon resonance were used to unravel the mechanisms fundamental to generation of such stealth entities in vivo by poloxamine 908. Electrophoretic mobility of poloxamine pre‐coated monodisperse polystyrene nanoparticles in serum, which behave as stealth entities in vivo, was similar to that of uncoated nanoparticles incubated in poloxamine pre‐treated serum. This observation supported the notion that poloxamine in serum can modify the surface of nanoparticles with similar topography to that of stealth poloxamine pre‐coated particles, i.e. with polyoxyethylene chains projected from the surface. Surface plasmon resonance optical phenomenon was used for real‐time monitoring of protein–poloxamine interactions and adsorption at the polystyrene interface. It was found that poloxamine can not only adsorb to a serum‐modified surface but in addition poloxamine in serum can form macromolecular complexes with high affinity for adsorption to a polystyrene lattice. A role for serum albumin in surface modification of nanoparticles by poloxamine 908 is also identified. Hence, our biophysical observations correlate precisely with the in vivo longevity of uncoated polystyrene nanoparticles in poloxamine pre‐treated rats. This rational and sensitive biophysical approach has unravelled the probable mechanism fundamental to generation of stealth entities in vivo and therefore has application in the design and nano‐engineering of stealth colloidal carriers for optimal biological performance.
Regulation of amyloid precursor protein (APP) phosphorylation and processing by p35/Cdk5 and p25/Cdk5
Authors: Liu Feng , Su Yuan , Li Baolin , Zhou Yan , Ryder John , Gonzalez-DeWhitt Patricia , May Patrick C , Ni Binhui
Published: June 2003

The phosphorylation status of amyloid precursor protein (APP) at Thr668 is suggested to play a critical role in the proteolytic cleavage of APP, which generates either soluble APPβ(sAPPβ) and β‐amyloid peptide (Aβ), the major component of senile plaques in patient brains inflicted with Alzheimer's disease (AD), or soluble APPα(sAPPα) and a peptide smaller than Aβ. One of the protein kinases known to phosphorylate APPThr668is cyclin‐dependent kinase 5 (Cdk5). Cdk5 is activated by the association with its regulatory partner p35 or its truncated form, p25, which is elevated in AD brains. The comparative effects of p35 and p25 on APPThr668phosphorylation and APP processing, however, have not been reported. In this study, we investigated APPThr668phosphorylation and APP processing mediated by p35/Cdk5 and p25/Cdk5 in the human neuroblastoma cell line SH‐SY5Y. Transient overexpression of p35 and p25 elicited distinct patterns of APPThr668phosphorylation, specifically, p35 increasing the phosphorylation of both mature and immature APP, whereas p25 primarily elevated the phosphorylation of immature APP. Despite these differential effects on APP phosphorylation, both p35 and p25 overexpression enhanced the secretion of Aβ, sAPPβ, as well as sAPPα. These results confirm the involvement of Cdk5 in APP processing, and suggest that p35‐ and p25‐mediated Cdk5 activities lead to discrete APP phosphorylation.
A training program on exclusive breastfeeding in maternity wards
Authors: Labarere J. , Castell M. , Fourny M. , Durand M. , Pons J.‐C.
Published: June 2003

Objectives: To estimate whether a 3‐day training program for health professionals was followed by changes in maternity ward practices and in the rate of exclusive breastfeeding. Methods: A retrospective study in the maternity ward of a French university hospital involved two cross‐sectional samples of 323 mother–infant pairs in 1997 and 324 in 2000. Results: The rate of exclusive breastfeeding at discharge increased from 15.8% (12.0–20.2) in the before sample to 35.2% (30.0–40.6) in the after sample (P<0.01). This result persisted in the multivariable analysis [adjusted odds ratio, 2.74 (1.72–4.37)]. Infants in the before sample were less likely to be breastfed within 1 h of birth (9.2% vs. 16.9%, P=0.01), to room‐in 24 h/day (56.6% vs. 72.6%, P<0.01), and were more likely to receive formula supplementation (77.6% vs. 54.0%, P<0.01). Conclusions: A training program for health professionals can be effective in improving maternity ward practices and increasing exclusive breastfeeding rate at discharge.
Ectopic pregnancy and emergency care: ethical and legal issues
Authors: Dickens B.M. , Faúndes A. , Cook R.J.
Published: June 2003

Ectopic or tubal pregnancy presents a medical emergency that requires prompt treatment in order to contain risks of maternal death and morbidity, including loss of future fertility. Medical circumstances involving individual patients and resources of the prevailing health care system will determine the options and means of treatment. Termination of ectopic pregnancy does not constitute or directly implicate abortion. Any practice of deliberately delaying treatment of reliably diagnosed ectopic pregnancy, on non‐clinical grounds, until rupture of the fallopian tube has occurred or is imminent, in order to justify termination of the ectopic pregnancy on grounds of saving the patient's life, is unethical and illegal. Those who undertake or counsel deliberate delay of medically‐indicated treatment can be charged with criminal offences and civil (non‐criminal) liability, and medical professional misconduct. On reliable diagnosis, prompt treatment to remove ectopic pregnancy is legally justified, and ethically and legally required.
New type of snRNP containing nuclear bodies in plant cells
Authors: Niedojadło Janusz , Górska‐Brylass Alicja
Published: June 2003

In larch (Larix decidua Mill.) microspores a new type of nuclear bodies has been found which are an element of the spatial organization of the splicing system in plant cell. These are bizonal bodies, ultrastructurally differentiated into a coiled part and a dense part. Using immunocytochemistry and in situ hybridization at the EM level, the coiled part of the bizonal body was found to contain snRNA including U2 snRNA, Sm proteins and nucleolar proteins of the agyrophilic type and fibrillarin. The dense part contains Sm proteins but lacks snRNA. Such a separation of macromolecules related to splicing occurring within the bizonal bodies microspore is striking by the similarity of these bodies to amphibian oocyte snurposomes. The occurrence in plant cells, beside widely known coiled bodies (CBs), also of other nuclear bodies related to splicing proves that in plants similarly as for animals the differentiation among domains containing elements of the splicing system occurs.
Weak solutions for a hyperbolic system with unilateral constraint and mass loss
Authors: Berthelin F , Bouchut F
Published: June 2003

We consider isentropic gas dynamics equations with unilateral constraint on the density and mass loss. The

γ

and pressureless pressure laws are considered. We propose an entropy weak formulation of the system that incorporates the constraint and Lagrange multiplier, for which we prove weak stability and existence of solutions. The nonzero pressure model is approximated by a kinetic BGK relaxation model, while the pressureless model is approximated by a sticky-blocks dynamics with mass loss.

Nous considérons les équations de la dynamique des gaz isentropique avec contrainte unilatérale sur la densité et perte de masse. Les lois de pression

γ

et sans pression sont considérées. Nous proposons une formulation faible entropique du système qui incorpore la contrainte et le multiplicateur de Lagrange, pour laquelle nous montrons la stabilité faible et l’existence de solutions. Le modèle avec pression non nulle est approché par un modèle de relaxation BGK cinétique, tandis que le modèle sans pression est approché par une dynamique de bouchons collants avec perte de masse.
Asymptotic behavior of ground states of quasilinear elliptic problems with two vanishing parameters, Part II
Authors: Gazzola Filippo , Peletier Bert , Pucci Patrizia , Serrin James
Published: June 2003

We study the pointwise asymptotic behavior of the radially symmetric ground state solution of a quasilinear elliptic equation involving the

m

-Laplacian in

ℝ^n

with two competing parameters. Roughly speaking, the first parameter

ε

measures the distance to a critical growth problem while the second parameter

δ

measures the weight of the “linear” term. We obtain the exact asymptotic behavior of the ground state, for any

1<m<n

, both at the origin and outside the origin, when the equation tends to critical growth (

ε→0

). We also obtain the “equilibrium relation” between

ε

and

δ

so that when they both vanish according to this relation, ground states neither blow up nor vanish. The results of this paper complete the description begun in [F. Gazzola, J. Serrin, Ann. Inst. H. Poincaré AN 19 (2002) 477–504].

Nous étudions le comportement asymptotique ponctuel de l’état fondamental à symétrie radiale d’une équation elliptique quasilinéaire contenant le

m

-Laplacien en

ℝ^n

avec deux paramètres en compétition. En gros, le premier paramètre

ε

mesure la distance d’un problème à croissance critique tandis que le second paramètre

δ

mesure le poids du terme “linéaire”. Nous obtenons le comportement asymptotique exact de l’état fondamental, pour tout

1<m<n

, aussi bien à l’origine que ailleurs, lorsque l’équation tend à la croissance critique (

ε→0

). Nous obtenons également la “relation d’équilibre” entre

ε

et

δ

de façon que lorsqu’ils convergent vers 0 en respectant cette relation, l’état fondamental n’explose ni ne converge vers la solution nulle. Les résultats de ce papier complètent la description commencée en [F. Gazzola, J. Serrin, Ann. Inst. H. Poincaré AN 19 (2002) 477–504].
A Bayesian maximum entropy reconstruction of stock distribution and inference of stock density from line-transect acoustic-survey data
Authors: Brierley Andrew S. , Gull Stephen F. , Wafy Maged H.
Published: June 2003

We present a maximum-entropy (MaxEnt) method for inferring stock density and mapping stock distribution from acoustic line-transect data. MaxEnt is founded on the bedrock of probability theory and allows the most efficient possible use of known data in the inference process. The method takes explicit account of spatial correlation in the observed data and seeks to reconstruct a distribution of density across the whole survey area that is both consistent with the observed data and for which the entropy is maximized. The method is iterative and uses the Bayesian approach of evaluating the posterior probability of a candidate solution under the constraint of the observed data to progress towards a converged solution. We apply the method to reconstruct maps of the distribution of Antarctic krill throughout areas 100 × 80 km2. Survey data were integrated at 0.5-km intervals along ten 80-km transects, giving approximately 1600 observed data points. We inferred the krill density for all 32 000 0.5 × 0.5 km2 cells in the area. The method is demanding computationally, but appears to work well even in cases when the distribution of density is highly skewed. The MaxEnt technique has proved to be powerful for reconstructing quantitative images from incomplete and noisy physical data (e.g. radio-telescope data): we suggest that it has utility in biological systems too and could be of benefit to the fisheries-acoustics community, increasing the accuracy of acoustic estimates of stock density and generating better maps of stock distribution.
Material properties of North Atlantic cod eggs and early-stage larvae and their influence on acoustic scattering
Authors: Chu Dezhang , Wiebe Peter H. , Copley Nancy J. , Lawson Gareth L. , Puvanendran Velmurugu
Published: June 2003

To study the acoustic signatures of Atlantic cod (Gadus morhua) at different biological stages from eggs to early-stage larvae (<37 days post-hatch), we conducted a series of experiments to estimate their sound-speed and density contrasts. A laboratory version of the “Acoustic Properties of Zooplankton” system was used. Sound speed was estimated by means of travel time between two transducers using a broadband acoustic signal (∼300–600 kHz). Density was estimated using a dual-density method in which two fluids of different densities were employed. It was found that the density contrasts of cod eggs and early-stage larvae were nearly all slightly less than unity (0.969–0.998), while the effective sound-speed contrasts were only slightly greater than unity (1.017–1.024) for eggs and yolk-sac stage larvae (<5 days post-hatch), and increased significantly (>1.130) for larvae older than 16 days. This change in sound-speed contrast reflected the transition of the swimbladder from an uninflated state to an inflated state. The regression relation between estimated target strength at 500 kHz and larval length in centimetres was found to be TS = 176.1 log10L − 82.4(dB). The inflation ratio of the swimbladder for early-stage larvae was an exponential function of time. The predicted period of time until full swimbladder inflation was 43.3 days.
Characterizing uncertainty in target-strength measurements of a deepwater fish: orange roughy (Hoplostethus atlanticus)
Authors: Kloser R.J , Horne J.K
Published: June 2003

The variability of ensemble 38 kHz, target-strength (TS38) estimates for orange roughy (Hoplostethus atlanticus) (4.9 dB, factor of 3.1) in deep water (>600 m) limits the use of echo integration for absolute-biomass estimates. Orange roughy are high in oil content, have a wax-ester swimbladder, and show an active-avoidance response to sampling gear. The interpretations of ensemble, in situ target strengths of orange roughy (range 〈TS38〉=−52.9 to −51.0 dB for standard fish length 〈SL〉 = 35 cm) are lower than previous model and surface-based measurements (〈TS38〉 = −48 dB, SL = 35 cm). In situ TS measurements from individuals on the periphery of dense schools were processed to minimize uncertainties from single-target selection criteria, species composition, and active avoidance. Video and acoustic-tracking data quantified the variability in TS measurements arising from the variability in fish orientation. Multi-frequency acoustics and fish tracking are used to quantify in situ TS variability due to species identification and fish density. The Kirchhoff-ray-mode backscatter model was used to illustrate the sensitivity of species-specific backscatter to assumptions of tilt-angle and material properties (density and sound-speed contrasts). We conclude that a remaining source of uncertainty for in situ TS measurements is the assumption that dispersed targets are representative of the survey population.
A method for evaluating the effects of biological factors on fish target strength
Authors: Hazen Elliott L , Horne John K
Published: June 2003

Understanding the relationship between fish biology and target strength potentially improves the accuracy of acoustic assessments. The effects of individual biological factors (e.g., length, tilt, and depth) on backscatter amplitude have been examined, but the relative contribution of each factor has not been quantified. Dimensionless ratios, which facilitate comparison of disparate quantities, were used to evaluate the effects of individual biological factors on echo intensities. Ratios from 25 adult walleye pollock (Theragra chalcogramma) were calculated using a Kirchhoff-ray-mode, backscatter model parameterized for each fish. This comparative approach can be used to identify the influence of biological factors on backscatter intensity and is potentially a tool for improving accuracy when converting acoustic size to fish length.
Time-based signal characteristics as predictors of fish size and species for a side-looking hydroacoustic application in a river
Authors: Burwen Debby L , Fleischman Steven J , Miller James D , Jensen Mark E
Published: June 2003

Side-looking, fixed-location sonar is used to estimate the abundance of migrating chinook salmon Oncorhynchus tshawytscha in the Kenai River, Alaska. For this application, echo-envelope length has previously been shown to predict fish size better than target strength. Using tethered-fish experiments we generalize these findings to other hydroacoustic descriptors based on time measurements, including range-measurement variability and fish lateral movement. These variables are all descriptors of the echo signal through time. Measurements of these attributes were correlated with daily indices of the species composition of unrestrained fish passing the sonar site. We hypothesize that time-based characteristics are superior predictors of fish size because they capitalize on, or are robust to, the factors which compromise amplitude-based measurements with side-looking sonar.
Improved techniques for studying the temporal and spatial behavior of fish in a fixed location
Authors: Ehrenberg John E , Steig Tracey W
Published: June 2003

There are many situations when it is important to know accurately the behavior of fish as a function of time and space in a fixed, three-dimensional volume. One example is the optimal design of techniques that minimize the mortality of fish approaching hydroelectric dams or the cooling intakes of a power plant. The behavior of fish in other fixed volumes, such as estuaries and open rivers, is also of interest in the case of many migrating fish stocks. Both active (echosounding) and passive systems based on acoustic-emitting tags implanted in fish have been used to collect behavioral data. Active acoustic systems, including those with electronically and mechanically steered beams, only insonify a small part of the total volume of interest at any given time. Tag systems, on the other hand, can be used to monitor the behavior of tagged fish over the entire volume. A number of advances in the implementation, deployment, and analysis of acoustic-tag systems have been made over the past few years. These improvements include techniques for positioning optimally the receiving hydrophones to minimize the location measurement errors, the development of acoustic-signal waveforms that provide both unique target identification and accurate location estimates, and the development of tracking algorithms that associate and track the multiple returns from an individual fish. These various techniques are described. Guidelines are presented for selecting the various parameters for the tag system, including the positions of the hydrophones. Specific examples that compare the predicted and actual performance of the tag systems are described.
Tyrosine phosphorylation is involved in Ca2+entry in human gingival fibroblasts
Authors: Ogata Yorimasa , Nakao Sumi , Shimizu Emi , Matsuda‐Honjyo Yuko , Yamazaki Muneyoshi , Furuyama Shunsuke , Sugiya Hiroshi
Published: June 2003

Bradykinin (1 μM) and histamine (100 μM) evoked an initial transient increase and a subsequent sustained increase in intracellular Ca2+concentration ([Ca2+]i) in fura‐2‐loaded human gingival fibroblasts, which may be attributed to Ca2+release from intracellular stores and Ca2+entry from extracellular sites, respectively. In fibroblasts pretreated with tyrosine kinase inhibitors such as herbimycin A (1 μM) and tyrphostin 47 (20 μM), the sustained level of [Ca2+]iinduced by bradykinin and histamine increased, but not the initial peak level. In the absence of external Ca2+, bradykinin and histamine induced only the transient increase in [Ca2+]i, but a subsequent addition of Ca2+to the medium resulted in a sustained increase in [Ca2+]icaused by Ca2+entry. Thapsigargin, an inhibitor of Ca2+‐ATPase in inositol 1,4,5‐trisphosphate‐sensitive Ca2+stores, mimicked the effect of bradykinin and histamine. In the fibroblasts pretreated with tyrosine kinase inhibitors, the bradykinin‐, histamine‐ and thapsigargin‐induced Ca2+entry was clearly enhanced, but not the transient [Ca2+]iincrease. Tyrosine phosphatase inhibitor benzylphosphonic acid (200 μM) had no effect on Ca2+entry or transient [Ca2+]iincrease. These results suggest that tyrosine phosphorylation is involved in Ca2+entry in human gingival fibroblasts.
Secondary hyperalgesia and presynaptic inhibition: an update
Authors: Cervero Fernando , Laird Jennifer M.A. , García‐Nicas Esther
Published: June 2003

One of the most prominent features of secondary hyperalgesia is touch‐evoked pain, i.e., pain evoked by dynamic tactile stimuli applied to areas adjacent or remote from the originating injury. It is generally accepted that the neurobiological mechanism of this sensory alteration involves the central nervous system (CNS) so that incoming impulses in low‐threshold mechanoreceptors from the area of secondary hyperalgesia can evoke painful sensations instead of touch. Some years ago we proposed a mechanistic model for this form of pain based on presynaptic interactions in the spinal dorsal horn between the terminals of low‐threshold mechanoreceptors and of nociceptors. Here we review the evidence gathered in support of this model in the intervening years with special reference to experimental studies of antidromic activity (Dorsal Root Reflexes – DRRs) in nociceptive afferents and on the acquisition of low‐threshold inputs by nociceptor‐specific neurons in the spinal dorsal horn. We also discuss and identify potential molecular mechanisms that may underlie the presynaptic interaction model and therefore that could be responsible for the development of secondary hyperalgesia.
A retrospective study of non-specific rhinitis in 22 cats and the value of nasal cytology and histopathology
Authors: Michiels L , Day M.J , Snaps F , Hansen P , Clercx C
Published: June 2003

Case records from 40 cats subjected to rhinoscopic examination for investigation of chronic nasal disease were reviewed. Cases in which no specific underlying cause (eg neoplasia) was detected were further selected for detailed retrospective study. In these 22 cats (55% of the initial population), a final diagnosis of non-specific chronic nasal disease was made. The radiographic, rhinoscopic, cytological and histopathological findings were reviewed.

Mucosal biopsy specimens were obtained in 20 cases. Despite clinical signs of more than 4 weeks duration, histopathology indicated acute inflammation in four cases. Two cases had chronic lymphoplasmacytic inflammation and 14 had mixed (lymphoplasmacytic and neutrophilic) inflammation. Specimens for cytology were obtained from 17 cases by brush sampling. Three of these samples were not diagnostic due to the poor quality of the slides; one showed normal cytology. Acute inflammation was diagnosed by cytology ( n=11) more commonly than chronic ( n=1) or mixed inflammation ( n=1). Concurrent samples, of quality suitable for both histopathological and cytological interpretation, were collected from 12 cases only. Cytological results were in agreement with the histological results in 25% of these cases, the main discrepancy being the nature of the dominant inflammatory cell type. Therefore cytology does not appear to be a reliable means for detection of chronic inflammation.

Further studies are needed in order to investigate the correlation between the nature of mucosal inflammation as defined by both histological and cytological evaluation, and the relationship of these test results to prognosis and therapy.
Identification of the magnetic cloud boundary layers
Authors: Wei Fengsi , Liu Rui , Fan Quanlin , Feng Xueshang
Published: June 2003

Based on a statistical analysis of the boundary physical states of 80 magnetic clouds reported in the literature from the years 1969 to 2001, we suggest a new identification of the magnetic cloud boundary by describing it as front and tail boundary layers (BLs) formed through the interaction between the magnetic cloud and the ambient medium. In our identification the outer boundary of the layer often displays the properties of magnetic reconnection, which could be characterized by a “three‐high state” (relatively high proton temperature, high proton density, and high plasma beta) and the corresponding magnetic signatures (the intensity drop and the abrupt azimuthal changes, Δϕ ∼ 180°, and latitudinal changes, Δθ ∼ 90°, in the magnetic field). The inner boundary of the layer exhibits a “three‐low state” (relatively low proton temperature, low proton density, and low plasma β) and separates the magnetic cloud body, which has not basically been affected by the interactions, from the boundary layers. The front boundary layer could be associated with the outer loops of CMEs and its average time scale is 1.7 hours; the tail boundary layer seems not be a filament and its average time scale is 3.1 hours. The distribution function of magnetic fluctuations in the boundary layer is significantly different from those in the ambient solar wind and the cloud body itself. The preliminary numerical simulation in principle confirms this new identification and could qualitatively explain most of the observations of the cloud boundary. This work could help partly overcome some inconsistencies in identifying the boundaries of magnetic clouds.
Viscous flow and deformation of regional metamorphic belts at convergent plate boundaries
Authors: Iwamori Hikaru
Published: June 2003

Viscous flow and deformation of a Newtonian fluid between rigid boundaries have been modeled for investigating deformation of a forearc wedge and a regional metamorphic belt as a weak deforming zone between the plates at convergent boundaries. Three types of analytic formulations together with numerical formulations for a Newtonian fluid with a constant viscosity are used for investigating various flows and deformation: (1) flows induced by squeezing between two parallel boundaries, (2) flows induced by squeezing and heterogeneous mass influx in the wedge between two oblique boundaries (e.g., accretionary wedge over the subducting plate with the continental plate as a backstop), and (3) flows induced by dragging along the boundaries and by homogeneous mass influx in the wedge as in type 2. All cases include strike‐slip movements of the boundaries, which allows us to investigate three‐dimensional (3‐D) deformation (e.g., 3‐D corner flow). The corresponding flow, deformation of infinitesimal and finite elements, and the timescale of flow are calculated for each configuration with various mechanical boundary conditions. The model results show that configuration and mechanism of the flow can be inferred from the spatial variation of finite deformation (e.g., deformed radiolarians as a strain marker and geometry of folding as finite deformation of a large block). In particular, prolate strain nearly parallel to the strike of subduction zone, together with a large‐scale folding, can be a good indicator for deformation in the forearc wedge associated with 3‐D corner flow induced by oblique subduction. Deformation observed in the Cretaceous regional metamorphic belts in southwest Japan can be explained by this mechanism.
Overview and conclusions of the International Photolysis Frequency Measurement and Modeling Intercomparison (IPMMI) study
Authors: Cantrell Christopher A. , Calvert Jack G. , Bais Alkiviadis , Shetter Richard E. , Lefer Barry L. , Edwards Gavin D.
Published: June 2003

An overview is given of the International Photolysis Frequency Measurement and Modeling Intercomparison (IPMMI) study which was held at the Marshall field site of the National Center for Atmospheric Research near Boulder, Colorado, for 4 days during the period 15–19 June 1998. The major objectives of the study were (1) to compare in blind experiments the results of different techniques of measuring j(NO2) and j(O1D) under identical and well‐defined experimental conditions, (2) to compare results of blind theoretical modeling of j(NO2) and j(O1D) expected at the experimental site using several current models, (3) to compare the experimental and model results for the j values, (4) to compare the measured and modeled downwelling actinic flux, and (5) on the basis of the results, make recommendations for the choices between alternative quantum yield and cross‐section data. The findings of the IPMMI experiment are described in a series of papers in this issue [e.g., Shetter et al., 2003; Bais et al., 2003], and the overall conclusions are summarized here. Actinic fluxes can be measured to accuracies of ∼5% and can be estimated with radiative transfer models to ∼10%. Photolysis rate coefficients can be measured and modeled with accuracies of ∼10% for high‐sun, clear‐sky, and low‐aerosol loadings. Comparisons between chemical actinometers and spectroradiometers favor more recent, larger cross‐section and quantum yield values for NO2 and O3.
Direct observations of daytime NO3: Implications for urban boundary layer chemistry
Authors: Geyer A. , Alicke B. , Ackermann R. , Martinez M. , Harder H. , Brune W. , di Carlo Piero , Williams E. , Jobson T. , Hall S. , Shetter R. , Stutz J.
Published: June 2003

The nitrate radical (NO3) is the dominant atmospheric oxidant during the night in most environments. During the day, however, NO3 has thus far been considered insignificant. Here we present daytime measurements of NO3 by Differential Optical Absorption Spectroscopy near Houston, Texas, during the Texas Air Quality Study 2000. On 3 consecutive days in August/September 2000, NO3 reached levels from ∼5 ppt 3 hours before sunset to 31 ppt around sunset. Daytime NO3 had a negligible effect on the photostationary state (PSS) between O3 and NOx, with the exception of the last hour before sunset, when it significantly accelerated NO‐to‐NO2 conversion. On August 31, chemical reactions involving NO3 destroyed 8 (±4) ppb Ox (= O3 + NO2) during the day and 27 (±6) ppb at night. NO3 chemistry contributed 10 (±7)% to the total Ox loss during the daytime, and 28% (±18%) integrated over a 24‐hour period. It therefore played an important role in the Ox budget. NO3 also contributed significantly to the daytime oxidation of hydrocarbons such as monoterpenes and phenol in Houston. The observed daytime NO3 mixing ratios can be described as a function of O3 and NOx. Above [NOx]/[O3] ratios of 3%, daytime NO3 becomes independent of NOx and proportional to the square of O3. Our calculations indicate that elevated (>1 ppt) NO3 levels can be present whenever ozone mixing ratios exceed typical urban smog levels of 100 ppb.
Large‐scale seabed dynamics in offshore morphology: Modeling human intervention
Authors: Roos Pieter C. , Hulscher Suzanne J. M. H.
Published: June 2003

We extend the class of simple offshore models that describe large‐scale bed evolution in shallow shelf seas. In such seas, shallow water flow interacts with the seabed through bed load and suspended load transport. For arbitrary topographies of small amplitude we derive general bed evolution equations. The initial topographic impulse response (initial sedimentation and erosion patterns around an isolated feature on a flat seabed) provides analytical expressions that provide insight into the inherent instability of the flat seabed, the Coriolis‐induced preference for cyclonically oriented features, and bed load transport being a limiting case of suspended load transport. The general evolution equation can be used to describe sandbank formation, known as the result of self‐organization. Examples of human intervention at the seabed include applications to a dredged channel and an offshore sandpit. An outlook toward future research is also presented.
Changes in the chemistry of lakes and precipitation in high‐elevation national parks in the western United States, 1985–1999
Authors: Clow David W. , Sickman James O. , Striegl Robert G. , Krabbenhoft David P. , Elliott John G. , Dornblaser Mark , Roth David A. , Campbell Donald H.
Published: June 2003

High‐elevation lakes in the western United States are sensitive to atmospheric deposition of sulfur and nitrogen due to fast hydrologic flushing rates, short growing seasons, an abundance of exposed bedrock, and a lack of well‐developed soils. This sensitivity is reflected in the dilute chemistry of the lakes, which was documented in the U.S. Environmental Protection Agency's Western Lake Survey of 1985. Sixty‐nine lakes in seven national parks sampled during the 1985 survey were resampled during fall 1999 to investigate possible decadal‐scale changes in lake chemistry. In most lakes, SO4 concentrations were slightly lower in 1999 than in 1985, consistent with a regional decrease in precipitation SO4 concentrations and in SO2 emissions in the western United States. Nitrate concentrations also tended to be slightly lower in 1999 than in 1985, in contrast with generally stable or increasing inorganic N deposition in the west. Differences in alkalinity were variable among parks but were relatively consistent within each park. Possible effects of annual and seasonal‐scale variations in precipitation amount on lake chemistry were evaluated based on climate data available for the parks and an analysis of climatic effects at two research watersheds with long‐term records. Results suggest that rain prior to sampling in 1985 may have caused elevated NO3 in some lakes due to direct runoff of precipitation and flushing of NO3 from alpine soils, which may explain some of the decrease in NO3 concentrations observed in survey lakes.
Watershed‐scale effects of urbanization on sediment export: Assessment and policy
Authors: Randhir Timothy
Published: June 2003

Built components of watersheds are associated with impervious surfaces that alter hydrology, disrupt ecosystems, and affect water quality. This study focuses on the impervious factor as a tool for assessment and policy design to address water quality impacts. The empirical model uses a combination of watershed simulation and statistical regression modeling to study sediment loading at various stages of urbanization. The policy design is based on private behavior in a watershed setting to develop appropriate economic approaches. The incentives through taxes, subsidies, and cost sharing are based on water quality impacts. It was observed that nonlinearity in response functions resulted in transition effects that are continuous. This is due to gradual shifts in landscape characteristics as a result of urbanization. On a regional basis, impervious factor had a varying effect on water quality and depend on the state of urbanization and spatial characteristics. Economic policies based on a metric like impervious cover can be used to mitigate the negative effects of urbanization in watersheds through use of appropriate BMPs, urban forestry methods, and spatial targeting. While linear rules in policy are easier to implement, nonlinear rules were more effective in representing the changes in marginal social cost of impervious factor, especially initial and late stages of urbanization. There exists excellent scope in using this targeted policy to address specific problems associated with complex urban systems.
Tropical mesopause climatology over the Arecibo Observatory
Authors: Friedman Jonathan S.
Published: June 2003

We report on the first annual cycle of mesopause‐region (82–105 km) temperature profiles at a tropical latitude site, the Arecibo Observatory (18.35°N, 66.75°W), measured by potassium resonance lidar. Based on 74 night‐time temperature profiles of observing periods greater than 5 hours we observe a mean temperature profile with a mesopause altitude of 98 km and temperature of 193 K. The annual mean nighttime temperature profile is similar to that seen at mid‐latitudes, but there are striking differences in seasonal structure. The mesopause region mean seasonal structure at Arecibo experiences a temperature minimum of 176 K at 100 km during mid‐summer. The winter period minimum of about 190 K is found mostly in a broad flat distribution between 90 and 95 km, and less frequently near 100 km.
Global SST/SLP waves during the 20th century
Authors: White Warren B. , Tourre Yves M.
Published: June 2003

A discrete number of global signals in covarying sea surface temperature (SST) and sea level pressure (SLP) dominated climate variability from 40°S to 60°N during the 20th Century. They are the quasi‐biennial (∼2.2‐year period), interannual (3‐ to 7‐year period band), quasi‐decadal (∼11‐year period), and interdecadal (∼17‐year period) signals. A joint frequency‐domain analysis of SST and SLP anomalies over the global ocean finds these signals composed of mixed global standing modes and traveling waves that are similar in pattern and evolution. On each period scale, the global traveling wave is composed of global zonal wavenumbers‐1 and ‐2, directed eastward with a phase speed that takes 1 to 2 cycles to traverse the global ocean between 40°S and 20°N. The existence of these global traveling waves may enhance the predictability of regional climate variability.
Gas‐chromatographic measurements of the atmospheric oxygen/nitrogen ratio at Hateruma Island and Cape Ochi‐ishi, Japan
Authors: Tohjima Y. , Mukai H. , Machida T. , Nojiri Y.
Published: June 2003

The O2/N2 ratios were determined of air samples collected at Hateruma Island (lat 24°3′N, long 123°49′E) from July 1997 to December 2001, and at Cape Ochi‐ishi (lat 43°10′N, long 145°30′E) from December 1998 to December 2001. The O2/N2 ratios, based on gas‐chromatographic analysis, clearly showed decreasing trends and seasonal variations, increasing in spring and summer, and decreasing in autumn and winter. The amplitudes of the seasonal O2/N2 cycles for Ochi‐ishi were twice as large as those for Hateruma. The average rates of decrease were 18.4 ± 1.4 per meg yr−1 over a 4‐year period (1998–2001) for Hateruma, and 19.2 ± 1.6 per meg yr−1 over a 3‐year period (1999–2001) for Ochi‐ishi.
Response to “Comment on ‘Ultrafast electron optics: Propagation dynamics of femtosecond electron packets’ ” [J. Appl. Phys. 94, 803 (2003)]
Authors: Siwick Bradley J. , Dwyer Jason R. , Jordan Robert E. , Miller R. J. Dwayne
Published: June 2003

In this reply, we address the main issues raised by Qian et al. regarding our recent article [J. Appl. Phys. 92, 1643 (2002)]. In particular, we reiterate the approximations used in the development of the mean-field model and demonstrate how the form used for the on-axis potential is applicable to the study of femtosecond electron packet propagation and is not in need of correction. We also repeat our assertion that the one-dimensional (1-D) fluid model developed by Qian et al. [J. Appl. Phys. 91, 462 (2002)] overestimates space-charge-induced pulse broadening and is in qualitative disagreement with femtosecond electron packet propagation dynamics. The key differences between the mean-field and 1-D fluid model are discussed and their range of applicability is clarified.
Facets, indium distribution, and lattice distortion of InGaAs/GaAs quantum dots observed by three-dimensional scanning transmission electron microscope
Authors: Ozasa Kazunari , Aoyagi Yoshinobu , Iwaki Masaya , Kurata Hiroki
Published: June 2003

Multiazimuth 360° observation of InGaAs/GaAs quantum dots (QDs) was performed with a 300 kV scanning transmission electron microscope, where both cross-sectional and plan-view images of the same specific QDs can be taken for a single specimen. The facet structure of truncated pyramids was reconstructed from facet-enhanced bright-field images newly observed with the incident axes slightly off from 〈−552〉 or 〈−332〉, resulting in high contrast for the lattice distortion on (110) facets of InGaAs QDs. Dark-field images for a large QD clearly indicate indium distribution inside the large QD, originating from the coalescence of two small QDs during growth. Localized relaxation of the lattices was observed, for the same large QD with indium content fluctuation, as disturbed/disappeared moire-fringes in the images taken with the incidence around 〈−552〉.
Comparison of acoustic properties between natural and synthetic α-quartz crystals
Authors: Kushibiki Jun-ichi , Ohtagawa Masanori , Takanaga Izumi
Published: June 2003

Accurate measurements of bulk and leaky surface acoustic wave (LSAW) velocities of natural α-quartz crystal were carried out using the line-focus-beam and plane-wave ultrasonic material characterization systems and then these measured velocities were compared with the velocities of synthetic α-quartz crystals. Longitudinal velocities of principal X-, Y-, and Z-cut specimens; shear velocities with X-axis polarized particle displacements of the Y- and Z-cut specimens; and LSAW velocities for these three specimens were precisely measured. We found all the velocities for the bulk waves and the LSAWs of natural quartz to be slightly smaller (within 1.00 m/s) than the velocities of synthetic quartz. Therefore, the acoustical physical constants of the natural quartz are very similar to those of synthetic quartz we reported recently.
Elastic properties of two-dimensional hard disks in the close-packing limit
Authors: Wojciechowski K. W. , Tretiakov K. V. , Brańka A. C. , Kowalik M.
Published: June 2003

Elastic constants and the Poisson ratio of defect-free hard-disk solid are determined by two independent methods: (1) analysis of the box side fluctuations in the N-p-T ensemble with variable box shape and (2) numerical differentiation (with respect to strain components) of the free energy computed in the N-V-T ensemble; N, p, V, and T denote the number of particles, the pressure, the volume, and the temperature, respectively. The efficiency of the applied methods is compared. It is shown that reasonable estimates of the elastic properties can be obtained by studying small systems in the N-p-T ensemble and that the singular behavior of the elastic constants near close packing is well described by the free volume approximation; the coefficients of the leading singularities are estimated.