bluuebunny/crossref_metadata_2025 huggingface dataset:
Echinoid limits R8 photoreceptor specification by inhibiting inappropriate EGF receptor signalling within R8 equivalence groups
Authors: Rawlins Emma L. , White Neil M. , Jarman Andrew P.
Published: June 2003

EGF receptor signalling plays diverse inductive roles during development. To achieve this, its activity must be carefully regulated in a variety of ways to control the time, pattern, intensity and duration of signalling. We show that the cell surface protein Echinoid is required to moderate Egfr signalling during R8 photoreceptor selection by the proneural gene atonal during Drosophila eye development. In echinoid mutants, Egfr signalling is increased during R8 formation, and this causes isolated R8 cells to be replaced by groups of two or three cells. This mutant phenotype resembles the normal inductive function of Egfr in other developmental contexts, particularly during atonal-controlled neural recruitment of chordotonal sense organ precursors. We suggest that echinoid acts to prevent a similar inductive outcome of Egfr signalling during R8 selection.
A 90° rotation of the mitotic spindle changes the orientation of mitoses of zebrafish neuroepithelial cells
Authors: Geldmacher-Voss Benedikt , Reugels Alexander M. , Pauls Stefan , Campos-Ortega José A.
Published: June 2003

In the neural plate and neural tube in the trunk region of the zebrafish embryo, dividing cells are oriented parallel to the plane of the neuroepithelium, while in neural keel/rod, cells divide perpendicular to it. This change in the orientation of mitosis is brought about by a 90°rotation of the mitotic spindle. As the two halves of the neural primordium in keel/rod stage are in apposition, the perpendicular orientation of mitoses in this stage determines that daughter cells become allocated to both sides of the neural tube. To assess the role played by cell junctions in controlling the orientation of dividing cells, we studied the expression of components of adherens and tight junctions in the neuroepithelial cells. We find that these proteins are distributed irregularly at the neural plate stage and become polarised apically in the cell membrane only during the keel/rod stage. The stereotypic orientation of mitoses is perturbed only weakly upon loss of function of the cell junction components ASIP and aPKCλ, suggesting that mitotic orientation depends in part on the integrity of cell junctions and the polarity of the epithelium as a whole. However, the 90° rotation of the spindle does not require perfectly polarised cell junctions between the neuroepithelial cells.
Lipase-catalyzed Enantioselective Acylation in a Halogen Free Ionic Liquid Solvent System
Authors: Itoh Toshiyuki , Ouchi Nozomi , Hayase Shuichi , Nishimura Yoshihito
Published: June 2003

Lipase-catalyzed enantioselective transesterification was demonstrated using several types of imidazolium alkyl sulfate as a reaction medium. The desired optically pure acetate was successfully obtained under the conditions used, although reaction rate was inferior to that in imidazolium tetrafluoroborate.
Synthesis and applied properties of carboxymethyl cornstarch
Authors: Xiaodong Zhang , Xin Liu , Wenying Li
Published: June 2003

In this article, carboxymethyl starch (CMS) with a high degree of substitution (0.91) and a high viscosity was synthesized by optimized reaction conditions, and its structure and surface morphology were analyzed by IR spectroscopy and scanning electron microscopy. The results of this application study show that CMS exhibited excellent printing behavior. CMS could substitute for 60% sodium alginate when it was used as a thickening agent in the printing paste of reactive dyes; therefore, the cost was greatly reduced. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3016–3020, 2003
Notch sensitivity of polycarbonate and toughened polycarbonate
Authors: Cho Kilwon , Yang JaeHo , Il Byung , Chan Kang , Park Eon
Published: June 2003

Notch sensitivity, the effect of a notch radius on the impact behavior of polycarbonate and rubber‐toughened polycarbonate, is investigated by using a model based on the slip‐lines field theory. Impact strength, determined by the Charpy impact test, was found to increase drastically with an increasing notch radius for pure polycarbonate, whereas the increase of impact strength with increased notch radius was not as extreme for rubber‐toughened polycarbonate. These results indicate that the inclusion of rubber particles reduces notch sensitivity. An examination of fracture surfaces reveals that cracks were initiated by internal crazing at some distance from the notch tip for specimens with blunt notches. For pure polycarbonate, the impact strength is found to have a linear relationship with the square of the notch radius, which is in good agreement with that predicted by the proposed model. However, for rubber‐toughened polycarbonate, the linear relationship broke down as the notch radius increased due to the enhanced toughening effect. The proposed model can be applied to clearly explain the notch sensitivity of ductile polymers which exhibit large plastic yielding around the notch tip. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3115–3121, 2003
Central regulation of thyroidal status in a teleost fish: Nutrient stimulation of T4 secretion and negative feedback of T3
Authors: Leiner Kevin A. , Mackenzie Duncan S.
Published: June 2003

Several experiments were conducted to investigate the dynamics of central regulation of thyroid function in the red drum, Sciaenops ocellatus, by manipulating a well‐characterized circadian rhythm of T4 secretion. In the first experiment, red drum were reared under either a long (16L:8D) or short (8L:16D) photoperiod and fed at the same time relative to dawn. The same feeding time under different photoperiods maintained the same phase relationship between T4 cycles under each photoperiod. This suggests that the circadian clock that determines when the hypothalamus‐pituitary‐thyroid (HPT) axis is activated is comprised of a feeding‐entrained oscillator and a light‐entrained oscillator that interact to determine the phase of the T4 rhythm. Additionally, the amplitude of the main T4 peak of the cycle was inversely related to the frequency of feeding, while the duration of the main T4 peak was directly related to feeding frequency under a long photoperiod. Feeding time appears to modify the diurnal profile of circulating T4 by stimulating post‐prandial T4 secretion that subsequently results in negative feedback on the HPT axis to regulate thyroidal status. In following experiments, red drum immersed in T3, in lieu of a meal at a specific time that would diminish the main T4 peak, exhibited a dose‐dependent decline in amplitude of the T4 cycle. This demonstrates that T3 can exert negative feedback on the HPT axis of red drum to maintain appropriate thyroid hormone concentrations. These data are consistent with a dynamic and physiologically important central component of the regulation of thyroid function in fish. J. Exp. Zool. 298A:32–43, 2003. © 2003 Wiley‐Liss, Inc.
Miniature microstrip patch antenna loaded with a space‐filling transmission line based on the fractal Hilbert curve
Authors: Gala D. , Soler J. , Puente C. , Borja C. , Anguera J.
Published: June 2003

A novel miniature antenna loaded with a space‐filling shaped transmission line is presented. Return loss and antenna gain results are compared with a traditional square patch. Experimental results show that the antenna presents an electrical area 18 times less than the square patch. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 311–312, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11046
Sry and Sox9 expression during canine gonadal sex determination assayed by quantitative reverse transcription‐polymerase chain reaction
Authors: Meyers‐Wallen V.N.
Published: June 2003

Testis induction is associated with gonadal Sry and Sox9 expression in mammals, and with Sox9 expression in vertebrates where Sry is absent. In mammals, Sry might initiate testis induction by upregulating Sox9 expression; however, direct evidence supporting this hypothesis is lacking. Models of Sry‐negative XX sex reversal (XXSR), in which testes develop in the absence of Sry, could provide the link between Sry and Sox9 in testis induction. To define the stages at which testis determination occurs in the canine model, Sry and Sox9 expression were measured in normal urogenital ridges (UGR) and gonads by quantitative reverse transcription‐polymerase chain reaction (qRT‐PCR). Testicular Sry expression rose continuously during canine developmental ages comparable to human carnegie stages (CS) 16–18, with maximal expression at CS 18. Sox9 was expressed in both male and female canine UGR up to CS 17, at which time testis expression became tenfold greater than in the ovary. Although Sox9 was detected by qRT‐PCR in ovaries and mesonephroi of both sexes, expression was detected only in canine testes by whole mount in situ hybridization (WMISH). The timing of Sry and Sox9 expression is consistent with a role in testis determination: Sry expression begins at CS 16 in testes, followed by upregulation of Sox9 expression at CS 17. The quantity and temporal and spatial patterns of Sry and Sox9 expression in normal canine gonads are similar to those in humans, sheep, and pigs. These studies should provide the basis for understanding the mechanism of testis induction in the canine model of Sry‐negative XXSR. Mol. Reprod. Dev. 65: 373–381, 2003. © 2003 Wiley‐Liss, Inc.
Three novel spermatogenesis‐specific zinc finger genes
Authors: Weissig Helge , Narisawa Sonoko , Sikström Carin , Olsson Per G , McCarrey John R , A. Tsonis Panagiotis , Del Rio-Tsonis Katia , Millán José Luis
Published: June 2003

We have cloned and characterized the expression, during spermatogenesis, of three novel zinc finger genes (Zfp94, Zfp95, Zfp96). Analysis of the deduced protein sequences reveals that all three molecules belong to the LeR family (leucine‐rich zinc fingers) and that ZFP95 contains a domain homologous to the Krüppel‐associated box. All three genes were found expressed at high levels in testis among other tissues, but testis‐specific transcripts were observed for Zfp95 and Zfp96. Northern blot analyses of the testis‐specific transcripts of Zfp95 and Zfp96 were performed using whole testis RNA as well as RNA isolated from enriched populations of specific spermatogenic cell types. The testis‐specific transcript of Zfp95 showed the highest expression in pachytene spermatocytes, while that of Zfp96 was highly expressed in pachytene spermatocytes, in round spermatids and residual bodies. Northern blot analysis of RNA from the testis of mice carrying the atrichosis mutation further validated these expression patterns. In particular, the testis‐specific transcripts of Zfp95 and Zfp96 were greatly reduced in heterozygous, and completely absent in homozygous testis RNA from atrichosis mutant mice, further defining the germ cell specificity of these transcripts.
Molecular stability of chemically modified collagen triple helices
Authors: Giudici Camilla , Viola Manuela , Tira M.Enrica , Forlino Antonella , Tenni Ruggero
Published: June 2003

Ionic residues influence the stability of collagen triple helices and play a relevant role in the spontaneous aggregation of fibrillar collagens. Collagen types I and II and some of their CNBr peptides were chemically modified in mild conditions with two different protocols. Primary amino groups of Lys and Hyl were N‐methylated by formaldehyde in reducing conditions or N‐acetylated by sulfosuccinimidyl acetate. The positive charge of amino groups at physiological pH was maintained after the former modification, whereas it was lost after the latter. These chemical derivatizations did not significantly alter the stability of the triple helical conformation of peptide trimeric species. Also the enthalpic change on denaturation was largely unaffected by derivatizations. This implies that no significant variation of weak bonds, either in number or overall strength, and of entropy occur on modification. These properties can probably be explained by the fact that chemically modified groups maintain the ability to form hydrogen bonds.
Anatomical analysis of the femoral condyle in normal and osteoarthritic knees
Authors: Matsuda Shuichi , Miura Hiromasa , Nagamine Ryuji , Mawatari Taro , Tokunaga Masami , Nabeyama Ryotaro , Iwamoto Yukihide
Published: June 2003

It is important to understand anatomical feature of the distal femoral condyle for treatment of osteoarthritic knees. Detailed measurement of the femoral condyle geometry, however, has not been available in osteoarthritic knees including valgus deformity. This study evaluated femoral condyle geometry in 30 normal knees, 30 osteoarthritic knees with varus deformity, and 30 osteoarthritic knees with valgus deformity using radiographs and magnetic resonance imaging (MRI). In radiographic analysis in the coronal plane, the femoral joint angle (lateral angle between the femoral anatomic axis and a tangent to femoral condyles) was 83.3° in the normal knees, 83.8° in the varus knees, and 80.7° in the valgus knees. In MRI analysis in the axial plane, the posterior condylar tangent showed 6.4° of internal rotation relative to the transepicondylar axis in the normal knees, 6.1° in the varus knees, and 11.5° in the valgus knees. These results suggested that there was no hypoplasia of the medial condyle in the varus knees, but the lateral condyle in the valgus knees was severely distorted. Surgeons should take this deformity of the lateral femoral condyle into account when total knee arthroplasty is performed for a valgus knee. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
The dexamethasone suppression test and CSF-5-HIAA in relation to suicidality and depression in suicide attempters
Authors: Westrin Åsa , Niméus Anders
Published: June 2003

This study tested suicidality in relation to cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA) and the dexamethasone suppression test. Patients with nonsuppression of cortisol had the highest scores of the Suicide Assessment Scale (SUAS) and the Montgomery Asberg Depression Rating Scale (MADRS), respectively (P< 0.05;P< 0.01). The results persisted when analysed for covariance with CSF-5-HIAA. We have previously noted an elevated suicide risk in suicide attempters with high SUAS-scores, why a large part of nonsuppressors may be at high risk for future suicide.
A psychopathological study of a group of schizophrenic patients after attempting suicide. Are there two different clinical subtypes?
Authors: Aguilar E.J. , Leal C. , Acosta F.J. , Cejas M.R. , Fernández L. , Gracia R.
Published: June 2003

Fifty-six schizophrenic patients at the moment of their suicidal attempt were compared to a control group of 60 patients. Schizophrenic suicidal attempters showed an identifiable clinical profile at the acute phase. Two main groups could be differentiated in regard to their reasons (depressive or psychotic) for attempting suicide.
Sampling variance of species identification in fisheries acoustic surveys based on automated procedures associating acoustic images and trawl hauls
Authors: Petitgas Pierre , Massé Jacques , Beillois Pierre , Lebarbier Emilie , Le Cann Arnaud
Published: June 2003

During the acoustic surveys of fish stocks, a small number of echo traces are identified to species by fishing. During data analysis, the process of echogram scrutiny leads to allocating echo-trace backscattered energies to species. While the precision of survey estimates is generally based on the spatial variation in the energy, no variance term accounts for species identification and energy allocation. In this paper, the sampling variance of species identification is developed and automated procedures are used allowing energy allocation to be carried out by a non-expert. The procedures are based on the fact that at the sampling stage trawl hauls are linked with particular acoustic images. The procedures have two steps: the classification step corresponds to species identification and the aggregation step to energy allocation. Classification is performed on the identified images and results in defining groups of images and estimating in each the sampling variability of the species identification. Aggregation is performed on non-identified images and results in post-stratifying the data. The estimation (map, abundance and variance per species) is then derived automatically and is conditioned by the post-stratification. Two approaches are followed, one based on the echo-trace characteristics making full use of the echogram (acoustic-image classification) and the other on the spatial continuity of the species composition between trawl hauls (trawl-haul classification). These methods are described and compared. The species-identification variance term is also compared to the spatial variance.
Evaluation of a Doppler sonar system for fisheries applications
Authors: Tollefsen Cristina D.S , Zedel Len
Published: June 2003

We report on tests of a general-purpose, coherent, Doppler sonar system undertaken to explore its capabilities when applied to detecting discrete fish targets. This 250-kHz, 30 kHz bandwidth instrument provides for phase coding of the transmit pulses and coherent sampling of successive acoustic returns. Towtank tests were used to determine the basic operating capabilities of the system. Under these ideal conditions a single-ping velocity accuracy of between 3 and 8 cm s−1 can be achieved approaching the theoretical limit for this instrument. Field trials were undertaken on the Fraser River in British Columbia near the Pacific Salmon Commission's field site, allowing comparisons with conventional fisheries sonar systems. While the long-term goal is to apply the Doppler sonar system in a larger-scale marine environment, the passage of migrating salmon provides an ideal test opportunity with fish of predictable and well defined swimming behaviour. Individual fish-swimming speed can be measured with an accuracy of between 5 and 10 cm s−1. By comparison, water velocity measurements made with the same instrument can only achieve a theoretical accuracy of 60 cm s−1.
Acoustic seabed classification of marine habitats: studies in the western coastal-shelf area of Portugal
Authors: Freitas Rosa , Silva Susana , Quintino Victor , Rodrigues Ana Maria , Rhynas Karl , Collins William T
Published: June 2003

Two single-beam, seabed-classification systems, QTC VIEW Series IV and QTC VIEW Series V, were used to identify and map biosedimentary gradients in a mid-shelf area off Western Portugal. The survey area has a moderate slope, a depth ranging from 30 to 90 m along a 3.5-km axis perpendicular to the shoreline, and is characterized by smooth sedimentary and biological gradients. Ground truth for sediment grain size and macrofaunal communities was based on grab sampling at 20 sites. The sedimentary and biological data were analysed using classification and ordination techniques. The acoustic data were analysed with qtc impact software and classified into acoustic classes. The affinity groups obtained in each data set were mapped using a Geographics Information System. All showed good agreement and identified prevailing gradients along a northwest–southeast direction. Three acoustic classes were identified, corresponding to the predominant sediment types, namely fine sand with low silt and clay content, silty, very fine sand, and mud. A close relationship with benthic communities was also verified, although less marked because benthic communities continuously change along the northwest–southeast gradient. Overall, the acoustic system coupled with ground-truthing data was able to discriminate and characterize the various benthic biotopes in the survey area.
Pain questionnaires in the analysis of long lasting (chronic) pain conditions
Authors: Wincent Anders , Lidén Ylva , Arnér Staffan
Published: June 2003

A study on mainly non‐cancer‐related pain patients was performed concerning clinical patient data used for pain history‐taking and diagnosis. More than 2100 consecutive patients referred to the anaesthetic branch of the Multidisciplinary Pain Centre (MPC) were evaluated at the first visit. The use of a paper questionnaire, including a pain‐drawing and pain intensity Visual Analogue Scale (VAS), was analysed. In a substudy of more than 290 consecutive patients, data from a computerised questionnaire and database was analysed. The European Organization for Research and Treatment of Cancer Quality of Life Questionnaires (EORTC QLQ‐C30) (version 2.0) was used for recording of the Global Health Status/Quality of Life (GHS/QoL) score. The substudy also included the summarized mechanism‐based evaluation of the patients at the first visit, judged by a specialist in pain medicine. The patients' GHS/QoL score was low. The most important pain mechanisms, were nociceptive and peripheral neurogenic. The clinical use of these tools for patient evaluation and for the choice of treatment is suggested. Information technology may be used for analysis of descriptive, evaluative, predictive and prognostic data in pain patients. It can also be used as a tool for clinical pain research towards a mechanism‐based evaluation. Evaluation of patient quality of life and function is suitable for outcome research.
Difficulties in stratifying neuropathic pain by mechanisms
Authors: Hansson Per
Published: June 2003

The paper addresses issues related to the clinical relevance of currently employed animal models of neuropathic pain and our inability to translate clinical symptoms and signs into pathophysiological mechanisms. A machanism‐based classification of pain is therefore currently not feasible. Suggestions on how to facilitate progress within this area are put forward.
Flow through porous media with multifractal hydraulic conductivity
Authors: Veneziano Daniele , Essiam Albert K.
Published: June 2003

We make a nonlinear analysis of flow through saturated porous media when the hydraulic conductivity K is an isotropic lognormal field with multifractal scale invariance. In this case, logK is isotropic Gaussian with spectral density , where D is the space dimension. Our main result is that the hydraulic gradient ∇H and specific flow q are also multifractal fields, whose renormalization under space contraction involves random rotation of the field and random scaling of its amplitude. The scaling properties and marginal distributions of ∇H and q are obtained analytically as functions of the space dimension D and a multifractal parameter of K (the codimension CK). The fields ∇H and q are anisotropic at large scales but approach isotropy at very small scales. Using scaling arguments, we obtain the effective conductivity of the medium Keff as an explicit function of D, CK, and the scaling range of K.
Periodic magnetospheric substorms and their relationship with solar wind variations
Authors: Huang Chao‐Song , Reeves G. D. , Borovsky J. E. , Skoug R. M. , Pu Z. Y. , Le G.
Published: June 2003

Outstanding problems in magnetospheric substorms include what causes substorm onsets and whether substorms have some specific periodicity. This paper provides observations and interpretations that relate to these problems. We study a specific type of geosynchronous particle injections during magnetic storms and the possible relationship between the solar wind and injections. Three storm events are analyzed: the March–April 2001, October 2000, and September 1998 storms. During the main phase or initial recovery phase of the storms, recurrent particle injections with a period of 2–3 hours were observed by geosynchronous satellites. The particle fluxes exhibited a well‐defined “sawtooth” profile with gradual decreases (flux dropouts) followed by rapid increases (injections). The sawtooth injections coincided well with AE increases and are interpreted as the signature of periodic substorms. In one case, sawtooth substorm injections were correlated with continuous solar wind pressure oscillations. In two other cases, sawtooth substorm injections occurred after a solar wind pressure impulse arrived at the magnetosphere. The observations show that substorms during storm times can be indeed periodic with a period of 2–3 hours and that solar wind variations may trigger the periodic substorms. We suggest that magnetospheric substorms have an intrinsic cycle time of 2–3 hours. If solar wind pressure oscillations with periods comparable to the substorm cycle time are imposed on the magnetosphere, some magnetospheric resonant state may be excited, and periodic substorms can be triggered. Otherwise, if the solar wind oscillates too fast, not enough energy is accumulated in the magnetotail for substorms to occur; if the period of solar wind pressure oscillations is too long, magnetospheric energy may be released through other processes including internally triggered substorms.
Optimal dip based on dissipation of back thrusts and hinges in fold‐and‐thrust belts
Authors: Maillot Bertrand , Leroy Yves M.
Published: June 2003

Back thrusts and hinges are two types of transition between rigid sections of hanging walls observed in fold‐and‐thrust belts. Back thrusts are typical of frictional and homogeneous solids and hinges of creeping and layered materials. Our objective is to study the orientation of these transitions for the special case of a lower flat‐ramp transition in a fault‐bend fold with the following general two‐step methodology. In the first step, the forces acting on the transition are determined using equilibrium of each rigid section. In the second step, the optimal dip of the transition is obtained by minimizing the total dissipation of the structure. The three sources of dissipation, of comparable magnitude, are at the transition, on the flat, and on the ramp. For frictional material flows, the back thrusts are velocity discontinuities with optimal dips always less than half the complementary ramp angle, leading to hanging wall thickening. The optimal dip agrees well with the results of physical analogue and numerical experiments. For creeping and layered materials, it is shown that a destabilizing deformation mechanism, selected to be flexural slip, is necessary for the strain to localize and the existence of hinges to be justified. Activation of flexural slip reduces dissipation at the transition and affects the optimal transition dip. The two‐step methodology proposed here could be seen as a first attempt in producing mechanically balanced cross sections accounting for material rheology. This approach should complement the now classical kinematic models of folding.
Annual and interannual variability of sea level in the northern North Atlantic Ocean
Authors: Volkov Denis L. , van Aken Hendrik M.
Published: June 2003

The combined TOPEX/Poseidon + ERS‐1/2 sea level anomaly (SLA) data from the northern North Atlantic Ocean for the time period 22 October 1992 to 29 December 2000 (300 cycles) were processed. The annual and interannual signals were examined, and their contribution to the total variance is estimated. Both signals appeared to be responsible for a greatest portion of variability outside the North Atlantic Current (NAC) and its branches. The annual signal manifested consistency with seasonal changes in the heat storage, possibly enhanced by seasonal variations of advection. A considerable interannual change was monitored in the vast areas of the northern North Atlantic Ocean as well as along the NAC. The interannual change in SLA was found to be consistent with the North Atlantic Oscillation (NAO) index when it changed from its positive to its negative phase in 1996. The significant negative correlation coefficient between the annually averaged SLA and NAO index time series was estimated in all dynamically calm areas outside the NAC. Hydrographic data obtained during several cruises for the time interval studied were also investigated and coupled with the variations of SLA and NAO index. The analysis showed a good agreement between the altimeter‐derived SLA and dynamic height anomalies suggesting that the sea level changes in the northern North Atlantic have a baroclinic nature.
Hydrostatic correction for sigma coordinate ocean models
Authors: Chu Peter C. , Fan Chenwu
Published: June 2003

How to reduce the horizontal pressure gradient error is a key issue in terrain‐following coastal models. The horizontal pressure gradient splits into two parts, and incomplete cancellation of the truncation errors of those parts cause the error. Use of the finite volume discretization leads to a conserved scheme for pressure gradient computation that has better truncation properties with high accuracy. The analytical coastal topography and seamount test cases are used to evaluate the new scheme. The accuracy of the new scheme is comparable to the sixth‐order combined compact scheme (with an error reduction by a factor of 70 comparing to the second‐order scheme) with mild topography and much better than the sixth‐order combined compact scheme with steep topography. The computational efficiency of the new scheme is comparable to the second‐order difference scheme. The two characteristics, high accuracy and computational efficiency, make this scheme useful for the sigma coordinate ocean models.
Intercontinental transport and its influence on the ozone concentrations over central Europe: Three case studies
Authors: Trickl Thomas , Cooper Owen R. , Eisele Holger , James Paul , Mücke Robert , Stohl Andreas
Published: June 2003

In this paper we report on a detailed analysis of the first clear observation of ozone import from North America in the free troposphere over central Europe in May 1996 and of two more recent cases of transatlantic transport. The analysis is based on calculations with the FLEXTRA trajectory model and the FLEXPART tracer model and data from Measurements of Ozone and Water Vapor by Airbus In‐Service Aircraft (MOZAIC) flights and North American surface sites. Lidar measurements carried out under conditions of developing anticyclonicity at Garmisch‐Partenkirchen, Germany, consistently yield peak ozone mixing ratios in the middle and upper troposphere between 80 and 110 ppb during the warm season. These layers are traced back to North America by FLEXTRA trajectories. The prevailing transport pathway involves a warm conveyor belt exporting high amounts of ozone, formed during a prefrontal high‐ozone episode, from the central part of the eastern United States to the upper troposphere. The polluted air may enter central Europe above an airstream descending from the stratosphere, thus inverting the normal atmospheric stratification, with stratospheric air at low levels and boundary layer air in the upper troposphere. However, the first two cases studied in this paper show that the export from the eastern United States may arrive over Europe at times prior to the onset of the anticyclonic conditions. Analysis of these cases reveals the complexity of the air export from North America. The ozone maxima occurring during the observational periods are traced back to the planetary boundary layer (PBL) in other source areas in the United States. Some of them are related to entrainments even from source areas beyond North America, either in the stratosphere or in Asia. The third case is quite different in its advection pathway, with almost straight and horizontal advection at 6 to 8 km above sea level starting from the Great Lakes area. A positive correlation between ozone and aerosol in that layer verifies the presence of PBL air. However, the very high ozone mixing ratio (up to 130 ppb) and an anticorrelation of ozone and humidity suggest the entrainment of another component from long‐range transport in the upper troposphere from beyond North America. In two of the case studies the export from the PBL was presumably influenced by large‐scale convection.
Distribution and height of methane bubble plumes on the Cascadia Margin characterized by acoustic imaging
Authors: Heeschen Katja U. , Tréhu Anne M. , Collier Robert W. , Suess Erwin , Rehder Gregor
Published: June 2003

Submersible investigations of the Cascadia accretionary complex have identified localized venting of methane gas bubbles in association with gas hydrate occurrence. Acoustic profiles of these bubble plumes in the water column in the vicinity of Hydrate Ridge offshore Oregon provide new constraints on the spatial distribution of these gas vents and the fate of the gas in the water column. The gas vent sites remained active over the span of two years, but varied dramatically on time scales of a few hours. All plumes emanated from local topographic highs near the summit of ridge structures. The acoustic images of the bubble plumes in the water column disappear at water depths between 500 to 460 m, independent of the seafloor depth. This coincides with the predicted depth of the gas hydrate stability boundary of 510 to 490 m, suggesting that the presence of a hydrate skin on the bubble surface prevents them from rapid dissolution. The upper limit of the acoustic bubble plumes at 460 m suggests that dissolution of the residual bubbles is relatively rapid above the hydrate stability zone.
Influence of an organic coating on the reactivity of aqueous aerosols probed by the heterogeneous hydrolysis of N2O5
Authors: Folkers M. , Mentel Th. F. , Wahner A.
Published: June 2003

Surface‐active organic compounds are common constituents of atmospheric aerosol particles. In this work, the effects of organic coatings on the heterogeneous hydrolysis of N2O5 was investigated. For this purpose aqueous NH4HSO4 particles were coated in situ in a large aerosol chamber. The experiments show that films composed of the ozonolysis products of α‐pinene can reduce the reaction probability by more than an order of magnitude. Model calculations indicate that the main cause for the retardation of the hydrolysis is a slower uptake possibly due to a lower solubility of N2O5 in the organic film.
Yet another caveat to using the Dessler‐Parker‐Sckopke relation
Authors: Liemohn M. W.
Published: June 2003

The analytical formulation of the Dessler‐Parker‐Sckopke (DPS) equation relating the energy content of the ring current to the magnetic field depression at the Earth's center is examined. To conduct this study, a method is presented for numerically integrating inner magnetospheric pressure distributions according to the Biot‐Savart law to obtain magnetic field perturbations at an arbitrary location. It is found that the implicit assumption of the DPS relation requiring that all of the particle pressure is included in the integration can generate large errors relative to the true perturbation. When there is a nonzero pressure just inside the outer boundary of the integration volume, the DPS relation implicitly includes large azimuthal currents at this pressure discontinuity. By including ghost cells of adiabatically decreasing pressure beyond the outer boundary, a “true” perturbation from the currents within the simulation is obtained. The ratio of this corrected value to the DPS value systematically varies according to a simple pressure ratio. Other aspects of the DPS relation are also confirmed with this code, including the validity criterion imposed by the plasma pressure anisotropy and the validity of the relation for any local time asymmetry. The inclusion of closure currents in the perturbation calculation, which were not part of the DPS derivation, changes the local time profile of the perturbation and can make either a negligible or a substantial contribution in either a positive or a negative sense to the globally averaged perturbation.
Computational method for calculating multidimensional Franck–Condon factors: Based on Sharp–Rosenstock’s method
Authors: Kikuchi Hiroto , Kubo Minoru , Watanabe Noboru , Suzuki Hideo
Published: June 2003

Normal mode coordinates of vibrational states associated with one electronic state are generally different from those of vibrational states associated with other electronic states in polyatomic molecules (normal coordinate mixing). This has prevented the multidimensional Franck–Condon integrals from being widely used in spite of their importance. We introduce a simple, noncumbersome numerical computer method for calculating those integrals despite including a mixing of the normal coordinates in the harmonic oscillator approximation on the basis of the expressions by Sharp and Rosenstock. We also introduce more simple expressions of Sharp–Rosenstock’s formulas.
Strain gradients along the growth direction in thin diamond film deposited on silicon wafer
Authors: Roy D. , Barber Z. H. , Clyne T. W.
Published: June 2003

A strain gradient has been observed along the growth direction of 5 μm thick diamond films, grown on silicon wafers. On detachment, films were found to adopt curvature such that the free surfaces became concave which indicates residual stresses which are compressive near the interface and tensile near the free surface. Raman peak positions were found to shift upward near the interface and downward near the growth surface. Raman spectra from the interface showed higher level of sp2 hybridized carbon. The quality of the diamond was found to improve as the film thickness increased. Luminescence spectra were also examined to study the variation in defect density across the film thickness and its possible contribution to the observed strain gradient.
Intracluster superelastic scattering via sequential photodissociation in small HI clusters
Authors: Chastaing D. , Underwood J. , Wittig C.
Published: June 2003

The photodissociation of expansion-cooled HI monomer by using 266 nm radiation yields H atoms having 12 830 and 5287 cm−1 of translational energy in the HI center-of-mass system for the I(2P3/2) and I(2P1/2) (i.e., I and I*, respectively) co-fragments. Irradiating HI clusters [i.e., (HI)n, with n=2 being the dominant cluster] with 266 nm radiation produces, among other things, some H atoms whose translational energies are peaked at 20 285 cm−1, which is 7455 cm−1 higher in energy than the more energetic of the monomer peaks. These very fast H atoms arise from sequential photodissociation within the clusters. Namely, a weakly bound I*⋅(HI)n−1 complex is first created by the photodissociation of an HI moiety within (HI)n, and then the photodissociation of a second HI moiety [within I*⋅(HI)n−1] produces a fast H atom that scatters from the nearby I*, in some cases deactivating it in the process. Thus, the latter superelastically scattered H atom acquires, as translational energy, nearly all of the I* energy (7603 cm−1). For example, for the dimer, the first dissociation event, (HI)2+hv→H+I(I*)⋅HI, is followed by I*⋅HI+hv→Hsuperelastic+I–I. High quality potentials for the relevant HI excited states have been calculated recently, and coupling between Π0+3 (which correlates with I*) and Π1 (which correlates with I) has been shown to be due to spin–rotation interaction. There is a high degree of separability between the photodissociation of the second HI moiety and the subsequent H+I* scattering (within a given cluster). This is due mainly to the shape of the Π0+3 potential; specifically, it has a shallow well that persists to small r. The shape of the Π0+3 potential is influenced by relativity; i.e., strong spin–orbit coupling maintains the I* spherical electron density to relatively small r. The Π0+3→1Π transition probabilities are calculated for H+I* collisions having different values of the collisional orbital angular momentum quantum number, l, by scaling the spin–rotation matrix elements by [l(l+1)]1/2 and using the Landau–Zener model to treat the electronically nonadiabatic dynamics. It is shown that large l values (lmax=52) play a dominant role in the quenching of I* by H. For example, the partial superelastic scattering cross section is six orders of magnitude larger for l=52 than for l=1, underscoring the dramatic role of angular momentum in this system. It is noted that HI photodissociation (which is dominated by low l) proceeds almost entirely along the diabats with little transfer of flux between them, whereas H+I* intracluster “collisions” take place with sufficiently large l to facilitate the electronically nonadiabatic process.
Dielectric properties of Ba(ZrxTi1−x)O3 thin films prepared using radio frequency magnetron sputtering
Authors: Hsi Chi-Shiung , Chen Chung-Yi , Wu Nan-Chung , Wang Moo-Chin
Published: June 2003

Pt/Ba ( Zr x Ti 1−x ) O 3 / Pt/Ti/SiO 2 / Si capacitors were fabricated using radio frequency (rf) magnetron sputtering. The deposition parameter effects on the dielectric constant, capacitance, and leakage current density of the capacitors were investigated. Amorphous Ba(ZrxTi1−x)O3 (BZxT1−x) thin films were sputtered onto a substrate with a temperature of 300 °C, rf power of 130 W, and in a no-oxygen atmosphere. BZxT1−x thin films deposited onto Pt-coated Si substrates show a preferred orientation in the (100) reflection. The dielectric constants of the BZxT1−x thin films increased with increasing Zr content and deposition temperature. The diffuse phase transition behavior of the BZxT1−x thin films became more pronounced at high Zr content films. The leakage current density of the Pt/Ba(ZrxTi1−x)O3/Pt/Ti/SiO2/Si capacitors at 1 kV/cm was about 1.0×10−7 A/cm2. This increased with increasing deposition temperature but decreased with increasing O2/(O2+Ar) ratio. From the films, P–E hysteresis loops, the BZ0.1T0.9 thin films had ferroelectric characteristics. The BZ0.3T0.7 thin films exhibited paraelectric characteristics at room temperature.
A model metal potential exhibiting polytetrahedral clusters
Authors: Doye Jonathan P. K.
Published: June 2003

Putative global minima have been located for clusters interacting with an aluminum glue potential for N⩽190. Virtually all the clusters have polytetrahedral structures, which for larger sizes involve an ordered array of disclinations that are similar to those in the Z, H, and σ Frank–Kasper phases. Comparisons of sequences of larger clusters suggest that the majority of the global minima will adopt the bulk face-centered-cubic structure beyond N≈500.
Nonlinear screening of pyroelectric films and grains in semiconductor matrix
Authors: Dmitriev A. P. , Kachorovskii V. Yu. , Shur M. S. , Gaska R.
Published: June 2003

Many semiconductor electronic and photonic devices use heterostructures, where strain induced and/or spontaneous polarization play a key role. The polarization charges are screened by accumulation and depletion regions, which determine the device properties. This article considers nonlinear screening of the polarization dipole for pyroelectric (or ferroelectric) films and grains in a semiconductor matrix. Our results show that, for a pyroelectric of a finite size in a semiconductor matrix, a nonlinear screening length involved in most relevant cases is different from the conventional depletion length and depends on the geometry of the problem. These results are important for AlN/GaN/InN and SiC based electronic and photonic devices, ferroelectric random access memories, and other pyroelectric and ferroelectric semiconductor materials and devices.
Experimental study of a chemical reaction between LiF and Al
Authors: Wang S. D. , Fung M. K. , Lai S. L. , Tong S. W. , Lee C. S. , Lee S. T. , Zhang H. J. , Bao S. N.
Published: June 2003

The interaction between LiF and Al has been studied by x-ray photoemission spectroscopy and high-resolution electron energy loss spectroscopy (HREELS). At room temperature, reaction between LiF and Al already occurred in the presence of Alq3, as revealed by the 0.25 eV shift of the Li 1s peak relative to the F 1s peak. Upon heating the LiF-coated Al substrate above 70 °C, reaction between LiF and Al also occurred in the absence of Alq3, suggested by the emergence of a peak 0.85 eV below the original Li 1s peak. The relatively large shift of 0.85 eV indicated that the emergent Li state possessed a metallic character. The reaction between LiF and Al upon heating was also corroborated by HREELS measurements. Heating of the Al/LiF/polymer device enhanced its electroluminescence, and may be associated with free Li atoms.
Scattering of electrons in silicon inversion layers by remote surface roughness
Authors: Gámiz F. , Roldán J. B.
Published: June 2003

A model to study the effect of the roughness at the poly-Si/SiO2 interface in silicon inversion layers on the electron mobility is obtained. Screening of the resulting perturbation potential by the channel carriers is taken into account, considering Green’s functions for metal–oxide–semiconductor geometry, i.e., taking into account the finite thickness of the gate oxide. Mobility of electrons is evaluated at room temperature by the Monte Carlo method, taking into account the simultaneous contribution of phonon scattering, SiO2/Si interface roughness scattering, Coulomb scattering, and remote surface roughness scattering. The contribution of excited subbands is considered. The resulting remote surface roughness scattering is shown to be strongly dependent on the oxide thickness, and degrades mobility curves at low inversion charge concentrations. The results obtained show that the effect of this scattering mechanism cannot be ignored when the oxide thickness is below 5 nm, (as in actual devices), even when (as is usual) very high doping concentrations are used.
Electron beam generation in a diode with a gaseous plasma electron source I: Plasma source based on a hollow anode ignited by a multi-arc system
Authors: Krokhmal A. , Gleizer J. Z. , Krasik Ya. E. , Felsteiner J. , Gushenets V. I.
Published: June 2003

We report on the operation of an electron diode with a cathode based on a hollow plasma anode (HPA) design. Six arc sources placed inside the anode cavity were used to produce a preliminary plasma. The latter was used to produce a high-current (up to 4 kA) gaseous discharge without formation of plasma spots at the anode wall and output grid. The plasma parameters inside the HPA were measured for different N2 and Xe gas pressures and discharge current amplitudes. It was found that the HPA operation is characterized by a negative anode potential fall and that the plasma density and temperature inside the anode are ≈6×1012 cm−3 and ≈9 eV, respectively. The characteristics of an electron diode and the generated electron beam were studied under an accelerating voltage amplitude ⩽250 kV and 400 ns pulse duration for different parameters of the HPA. It was found that in the beginning of the accelerating pulse the diode operates in a plasma prefilled mode while later the diode current is determined by the emission capability of the HPA plasma. It was shown that this source allows generation of an electron beam with a cross-sectional area of 100 cm2 and a current amplitude up to 1.2 kA, without the formation of explosive plasma at the surface of the HPA output grid.
Controlled p doping of the hole-transport molecular material N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine with tetrafluorotetracyanoquinodimethane
Authors: Gao Weiying , Kahn Antoine
Published: June 2003

We investigate p-type doping of the hole-transport organic molecular material N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) with tetrafluorotetracyanoquinodimethane (F4-TCNQ) using direct and inverse photoemission spectroscopy, contact potential difference measurements, and in situ current–voltage (I–V) measurements. The close match between the ionization energy of α-NPD and the electron affinity of F4-TCNQ leads to an efficient charge transfer between highest occupied molecular orbital of the host and lowest occupied molecular orbital of the dopant. The Fermi level moves down towards the valence states by 0.62 eV in the 0.5% doped film with respect to the undoped film, and a narrow space charge layer (∼60 Å) forms at the interface with Au. Hole injection in the doped devices increases by several orders of magnitude due to tunneling through the depletion region. The large relaxation energy of the ionized α-NPD molecule limits the movement of the Fermi level and, ultimately, the hole injection.