bluuebunny/crossref_metadata_2025 huggingface dataset:
Glycocinnasperimicin D Synthetic Studies: Synthesis of Cinnamoyl Glycosides via Iodination‐Heck Reaction Sequence Starting from Phenyl Glycosides.
Authors: Nishiyama Taihei , Ichikawa Yoshiyasu , Isobe Minoru
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Lambertellols A and B, Novel 3,4‐Dihydronaphthalen‐1(2H)‐ones with Spiro‐butenolide Produced by Lambertella sp. 1346.
Authors: Murakami Takanori , Morikawa Yoshifumi , Hashimoto Masaru , Okuno Toshikatsu , Harada Yukio
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Enantioselective Access to 2,7‐cis‐Disubstituted Oxepanes: Formal Synthesis of (+)‐Isolaurepan.
Authors: Carreno M. Carmen , Des Mazery Renaud , Urbano Antonio , Colobert Francoise , Solladie Guy
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Study on the Structure—Activity Relationships of NPTX‐594, a Spider Toxin Belonging to the Type‐B Acylpolyamine Structure.
Authors: Wakamiya Tateaki , Kinoshita Tomohiko , Hattori Yoshihide , Yamaguchi Yoshihiro , Naoki Hideo , Corzo Gerardo , Nakajima Terumi
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Fluorescent Nucleotides: Synthesis and Characterization
Authors: Cremo Christine R.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Late Transition Metal (Co, Rh, Ir)‐Siloxide Complexes: Synthesis, Structure and Application to Catalysis
Authors: Marciniec B. , Kownacki I. , Kubicki M. , Krzyzanowski P. , Walczuk E. , Blazejewska‐Chadyniak P.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Bryostatin and Their Analogues
Authors: Diederichsen Ulf
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Aryl Sulfur Pentafluorides: A New Building‐Block Generation for Life Sciences Applications
Authors: Carlini Filippo M.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Photooxygenation of 1,3‐Dienes
Authors: Adam Waldemar , Bosio Sara , Bartoschek Anna , Griesbeck Axel G.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Extreme Miniaturization: Molecular‐Level Devices and Machines
Authors: Balzani V. , Credi A. , Venturi M. , Di Fabio A.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Synthetic Models for Heme—Copper Oxidases
Authors: Kim Eunsuk , Chufan Eduardo E. , Kamaraj Kaliappan , Karlin Kenneth D.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Recent Advances in Selective Opioid Receptor Agonists and Antagonists
Authors: Eguchi Masakatsu
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
KATP Channel Openers: Structure—Activity Relationships and Therapeutic Potential
Authors: Mannhold Raimund
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Reflections on Routes to Enantioselective Solid Catalysts
Authors: Davis Mark E.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
The Clusters of Nitrogenase: Synthetic Methodology in the Construction of Weak‐Field Clusters
Authors: Lee Sonny C. , Holm R. H.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
The Structure—Function Relationship of Hemoglobin in Solution at Atomic Resolution
Authors: Lukin Jonathan A. , Ho Chien
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
The Partitioning Mechanism of Phenazine Ethosulfate into Polymer Film Electrodes
Authors: Coleman Brian D.
Published: April 2004

Phenazine ethosulfate (PES+) partitioning into the AQ55 cation‐exchange polymer has been demonstrated by immersion and continuous electrochemical cycling experiments. Cyclic voltammetric waveshapes indicate that both the reduction of PES+ and the oxidation of PESH are diffusion‐controlled when incorporated into the polymer film. This is in dramatic contrast to the behavior exhibited at bare glassy carbon where the reduction of PES+ is diffusion‐controlled but the oxidation of PESH is characteristic of a surface‐confined redox process. The straightforward determination of the partition coefficient is complicated by the uncertainty associated with accurately knowing the thickness of the swollen polymer. Therefore Randles‐Sevcik data for the reduction of PES+ at the bare and polymer‐modified electrode were compared to qualitatively assess the extent of possible partitioning, which was determined to be on the order of 101–102. The partition coefficient was determined to be 9.1±0.4, a value in agreement with qualitative assessment. Partitioning was found to be sensitive to the cations present in solution with the order of extractability of PES+ from solutions of Li+, Na+, and K+, increasing in the order: Li+>Na+>K+. Continuous cycling experiments suggest PES+ partitions into the film during the reductive cycle to restore the equilibrium concentration in the film caused by the electrochemical consumption of the species.
Cost‐effectiveness acceptability curves – facts, fallacies and frequently asked questions
Authors: Fenwick Elisabeth , O'Brien Bernie J. , Briggs Andrew
Published: April 2004

Cost‐effectiveness acceptability curves (CEACs) have been widely adopted as a method to quantify and graphically represent uncertainty in economic evaluation studies of health‐care technologies. However, there remain some common fallacies regarding the nature and shape of CEACs that largely result from the ‘textbook’ illustration of the CEAC. This ‘textbook’ CEAC shows a smooth curve starting at probability 0, with an asymptote to 1 for higher money values of the health outcome (λ). But this familiar ‘ogive’ shape which makes the ‘textbook’ CEAC look like a cumulative distribution function is just one special case of the CEAC. The reality is that the CEAC can take many shapes and turns because it is a graphic transformation from the cost‐effectiveness plane, where the joint density of incremental costs and effects may ‘straddle’ quadrants with attendant discontinuities and asymptotes. In fact CEACs: (i) do not have to cut the y‐axis at 0; (ii) do not have to asymptote to 1; (iii) are not always monotonically increasing in λ; and (iv) do not represent cumulative distribution functions (cdfs). Within this paper we present a ‘gallery’ of CEACs in order to identify the fallacies and illustrate the facts surrounding the CEAC. The aim of the paper is to serve as a reference tool to accompany the increased use of CEACs within major medical journals. Copyright © 2004 John Wiley & Sons, Ltd.
Habit formation and college students' demand for alcohol
Authors: Williams Jenny
Published: April 2004

This research investigates whether the positive association between college students' current and high‐school drinking is due to habit formation or whether it is solely due to the influence of unobserved individual characteristics that are correlated over time. The empirical investigation is based on individual level data from the 1997 and 1999 waves of the Harvard School of Public Health's College Alcohol Study (CAS). Amemyia's generalized least squares is used to address the heterogeneity issue in examining the relationship between past and current drinking. The results suggest that after controlling for correlation in unobserved characteristics that influence alcohol use, high‐school drinking has a significant and positive impact on college drinking, indicating the existence of habit formation. Both structural evidence of habit formation and reduced form results reveal that stricter drunk driving laws faced while in high‐school have a long lived effect, reducing drinking while in college. The results also highlight the importance of access to alcohol, both on campus and in the college neighborhood, as a determinant of college students' drinking behavior. Copyright © 2004 John Wiley & Sons, Ltd.
An inner product lemma
Authors: Gustafson Karl
Published: April 2004

Given the operator product BA in which both A and B are symmetric positive‐definite operators, for which symmetric positive‐definite operators C is BA symmetric positive‐definite in the C inner product 〈x, y〉C? This question arises naturally in preconditioned iterative solution methods, and will be answered completely here. Copyright © 2004 John Wiley & Sons, Ltd.
Normal degree
Authors: Gustafson Karl
Published: April 2004

The H‐normal degree n(A,H) associated with GCG‐LS algorithms is shown to be independent of H, thereby correcting an incompleteness in the literature. The normal degree n(A) for any normalizable matrix A when n(A)>1 is shown to sometimes occur sharply in the interval $\sqrt{m}$≦n(A)≦m−1, where m is the degree of A's minimum polynomial, thereby clarifying previous estimates in the literature. Copyright © 2004 John Wiley & Sons, Ltd.
Computing projections via Householder transformations and Gram–Schmidt orthogonalizations
Authors: Dax Achiya
Published: April 2004

Let x* denote the solution of a linear least‐squares problem of the form

where A is a full rank m × n matrix, m > n. Let r*=b ‐ Ax* denote the corresponding residual vector. In most problems one is satisfied with accurate computation of x*. Yet in some applications, such as affine scaling methods, one is also interested in accurate computation of the unit residual vector r*/∥r*∥2. The difficulties arise when ∥r*∥2 is much smaller than ∥b∥2. Let x̂ and r̂ denote the computed values of x* and r*, respectively. Let εdenote the machine precision in our computations, and assume that r̂ is computed from the equality r̂ =b‐Ax̂. Then, no matter how accurate x̂ is, the unit residual vector û =r̂/∥r̂∥2 contains an error vector whose size is likely to exceed ε∥b∥2/∥r*∥2. That is, the smaller ∥r*∥2 the larger the error. Thus although the computed unit residual should satisfy ATû=0, in practice the size of ∥ATû∥2 is about ε∥A∥2∥b∥2/∥r*∥2. The methods discussed in this paper compute a residual vector, r̂, for which ∥ATr̂∥2 is not much larger than ε∥A∥2∥r̂∥2. Numerical experiments illustrate the difficulties in computing small residuals and the usefulness of the proposed safeguards. Copyright © 2004 John Wiley & Sons, Ltd.
An expanded mixed covolume method for elliptic problems
Authors: Rui Hongxing , Lu Tongchao
Published: April 2004

We consider the mixed covolume method combining with the expanded mixed element for a system of first‐order partial differential equations resulting from the mixed formulation of a general self‐adjoint elliptic problem with a full diffusion tensor. The system can be used to model the transport of a contaminant carried by a flow in porous media. We use the lowest order Raviart‐Thomas mixed element space. We show the first‐order error estimate for the approximate solution in L2 norm. We show the superconvergence both for pressure and velocity in certain discrete norms. We also get a finite difference scheme by using proper approximate integration formulas. Finally we give some numerical examples. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005
A comparison between Nova T and Copper T 200 Ag in Hungary
Authors: Batar Istvan , Lampe Laszlo , Rakoczi Istvan , Gati Istvan , Allonen Hannu
Published: April 2004

In a comparative use‐effectiveness study, 855 Nova T and 883 TCu 200 Ag devices were inserted in a randomised sequence. By the end of the first year the gross rate of unplanned pregnancy was 1.1 per 100 users of Nova T and 2.1 per 100 users of TCu. After 2 years the pregnancy rates for Nova T and TCu were 3.1 and 4.8 per 100 users, respectively. Although there was no statistically significant difference between the rates for the two devices, they suggest a higher contraceptive efficacy for Nova T.
Urethral prolapse in the premenarcheal female
Authors: Carlson Nancy J. , Mercer Lane J. , Hajj Samir N.
Published: April 2004

Urethral prolapse in the premenarcheal female manifests as vaginal bleeding and a periurethral mass. In the past, the recommended management was surgical excision or cautery. However, conservative management has been shown to have excellent results. Five premenarcheal patients with urethral prolapse treated by conservative therapy are presented. Treatment regimen consisted of local hygiene with sitz baths, hexachlorophene soap, topical providone iodine and estrogen cream. There were no complications or recurrences. Surgery is not warranted in the treatment of urethral prolapse in the premenarcheal female. Medical management is equally effective and less traumatic in this age group.
Patent ductus arteriosus after prolonged treatment with indomethacin during pregnancy: Case report
Authors: Atad J. , Lissak A. , Rofe A. , Abramovici H.
Published: April 2004

Indomethacin was administered to suppress premature uterine contractions in a twin pregnancy from the 27th until the 32nd week of pregnancy. Patent ductus arteriosus was diagnosed after delivery in one twin and persisted patent for a period of 4 weeks. A hypothesis of the constrictive influence of prostaglandin synthetase inhibitors on the fetal ductus arteriosus during intrauterine and neonatal periods is suggested.
Progesterone challenge test and estrogen assays in menopausal women with endometrial adenomatous hyperplasia
Authors: Toppozada M.K. , Ismail A.A.A. , Hamed R.S.M. , Sid Ahmed K. , EL‐Faras A.
Published: April 2004

In an attempt to detect asymptomatic endometrial adenomatous hyperplasia in postmenopausal women, 40 cases were subjected to progesterone challenge test (PCT), measurement of serum estrogen and endometrial curettage. Group A (n = 30) included asymptomatic postmenopausal women, while group B (control group; n = 10) were cases with adenomatous hyperplasia (AH) diagnosed by biopsy. PCT showed a 100% sensitivity, 92% specificity, 71.4% predictive value of a positive test and 100% predictive value of a negative test in the detection of AH. Mean serum concentrations of E1 and E2 were significantly higher in patients with AH compared to cases with other endometrial histologies. Serum E1 and E2 and PCT can be used as screening tests to identify postmenopausal women with endometrial AH and thus at a greater risk of developing carcinoma.
The effect of mesterolone on sperm count, on serum follicle stimulating hormone, luteinizing hormone, plasma testosterone and outcome in idiopathic oligospermic men
Authors: Varma T.R. , Patel R.H.
Published: April 2004

Two hundred fifty subfertile men with idiopathic oligospermia (count less than 20 million/ml) were treated with mesterolone (100–150 mg/day) for 12 months. Seminal analysis were assayed 3 times and serum follicle stimulating hormone (FSH) luteinizing hormone (LH) and plasma testosterone were assayed once before treatment and repeated at 3, 6, 9 and 12 months after the initiation of treatment. One hundred ten patients (44%) had normal serum FSH, LH and plasma testosterone, 85 patients (34%) had low serum FSH, LH and low plasma testosterone. One hundred seventy‐five patients (70%) had moderate oligospermia (count 5 to <20 million/ml) and 75 patients (30%) had severe oligospermia (count <5 million/ml). Seventy‐five moderately oligospermic patients showed significant improvement in the sperm density, total sperm count and motility following mesterolone therapy whereas only 12% showed improvement in the severe oligospermic group. Mesterolone had no depressing effect on low or normal serum FSH and LH levels but had depressing effect on 25% if the levels were elevated. There was no significant adverse effect on testosterone levels or on liver function. One hundred fifteen (46%) pregnancies resulted following the treatment, 9 of 115 (7.8%) aborted and 2 (1.7%) had ectopic pregnancy. Mesterolone was found to be more useful in patients with a sperm count ranging between 5 and 20 million/ml. Those with severe oligospermia (count <5 million) do not seem to benefit from this therapy.
Single ectopic ureter opening into blind vagina, with renal dysplasia and associated utero‐vaginal duplication
Authors: Acien P. , Garcia‐Lopez F. , Ferrando J. , Chehab H.E.
Published: April 2004

A rare case of single ectopic ureter opening into a blind vagina with renal dysplasia and associated uterovaginal duplication is reported. The findings are interesting from the clinical diagnostic viewpoint and also contribute to our knowledge of the embryology of the female genitourinary system, especially concerning the origin of the vagina.
Assessment of fetal growth and serum hCG titers after in vitro fertilization and embryo transfer
Authors: Nisikori K. , Nagoshi K. , Shimizu K. , Yoshida N.
Published: April 2004

Fetal growth in early pregnancy was estimated by transvaginal ultrasonic measurement and serum hCG measurement in 13 women who became pregnant through in vitro fertilization and embryo transfer treatment. The first day of observation of a gestational sac (GS) or fetal heart movement (FHM) of over 120 beats/min confirmed the pregnancy. There were 6 or 7 days difference in GS or FHM confirmation within 20 or 30 days after insemination, although statistical deviations were very small (GS: 21.3 ± 1.8, FHM: 29.5 ± 1.8 days after insemination, mean ± S.D.). Increases in crown‐rump length (CRL) and serum hCG were used as indicators of fetal growth. There was a good correlation between CRL or serum hCG and days after insemination (CRL: r = 0.95, n = 55; hCG: r = 0.96, n = 77), and individual cases had almost the same velocity of CRL growth and serum hCG elevation as each regression line. This data suggests that each embryo has a different growth velocity from the fertilized oocyte until the first clinical confirmation of pregnancy.
Fixed laws, fluid lives: the citizenship status of post-retirement migrants in the European Union
Authors: ACKERS LOUISE , DWYER PETER
Published: April 2004

This paper presents key findings of a recently completed socio-legal study of international retirement migration in the European Union (EU). It highlights the diverse nature of retirement migration and the differential citizenship status that is formally granted to various groups of retired migrants. ‘Citizenship of the European Union’ (Articles 17–22 of the Treaty establishing the European Community) bestows important social and political rights on nationals of EU Member States (‘Community nationals’). These rights are not, however, universal or based on nationality as such. In practice, the residency and social rights that a mobile EU national can claim in another Member State depend on the type of social contribution they have made and their personal relationships. Contributions through paid employment and/or membership of the family of a mobile EU worker gives rise to maximum social benefit. Whilst the European Union citizenship provisions extend residency rights to all EU nationals (irrespective of work status), those whose mobility is not connected to employment derive significantly inferior social entitlements when resident in a host Member State. Put simply, the rights of people (and members of their family) who move following retirement in their home country differ substantially from those who retire following a period of working in another Member State (and achieve the status of ‘community migrant worker’ prior to retirement). This formal ‘discrimination’ is further compounded by the diversity of the social welfare systems of the member states that results in distinct social, economic and spatial inequalities across the EU. To that extent, the ‘choice’ of retirement location significantly impacts on citizenship status. However, retired migrants are not merely passive spectators of formal rights and policies. Many show considerable skill in actively managing their rights (at both national and EU levels) and other resources to optimise personal benefit. This ability to maximise wellbeing is unevenly distributed.
How to speed up to be in time: Action-judgment dissociations in children and adults
Authors: Wilkening Friedrich , Martin Claudia
Published: April 2004

Children 6 and 10 years of age and adults were asked how fast a toy car had to be to catch up with another car, the latter moving with a constant speed throughout. The speed change was required either after half of the time (linear condition) or half of the distance (nonlinear condition), and responses were given either on a rating scale (judgment condition) or by actually producing the motion (action condition). In the linear condition, the data patterns for both judgments and actions were in accordance with the normative rule at all ages. This was not true for the nonlinear condition, where children’s and adults’ judgment and also children’s action patterns were linear, and only adults’ action patterns were in line with the nonlinearity principle. Discussing the reasons for the misconceptions and for the action-judgment dissociations, a claim is made for a new view on the development of children’s concepts of time and speed.
A simplified interferometer design for use with meteor radars
Authors: Poole L. M. G.
Published: April 2004

A relatively simple design for a meteor radar interferometer with 4 receiving antennas is described. A basic 3 element interferometer provides a set of possible directions for each radio echo detected. The ambiguity is resolved using a 4th antenna, placed according to the results of a numerical simulation. Details of the procedure are provided. The resolution in echo direction is between ∼1° and ∼2° for altitudes (elevations) above ∼30° at all azimuths. A general purpose meteor radar based on this principle has been in use since 1986 at Grahamstown, South Africa.
Influence of time interval and filter bandwidth on measured rain fade slope
Authors: van de Kamp M. M. J. L. , Clérivet P.
Published: April 2004

The rate of change of rain attenuation, or ‘fade slope,’ observed on a microwave link, is dependant on system parameters of the receiver. This paper assesses its dependence on two data processing parameters: the time interval over which the fade slope is defined, and the low‐pass filter bandwidth used to remove tropospheric scintillation. A theoretical expression of this dependence is derived. The expression is compared with measured results, which show a good agreement. The results show that the time interval has a strong influence when it is larger than the inverse of the filter bandwidth, and the filter bandwidth has a strong influence when its inverse is larger than the time interval. In general, the fade slope always depends strongly on at least one of the two parameters.
A dynamic model to investigate coupling between erosion, deposition, and three‐dimensional (thin‐plate) deformation
Authors: Simpson Guy
Published: April 2004

This paper presents a mathematical model developed to investigate fully coupled interactions between erosion, deposition, and dynamic three‐dimensional deformation within fold belt settings. The mechanical part of the model is an elastic‐plastic (thin) plate overlying an inviscid substrate. This plate can be compressed from the side and responds by the development of buckle folds. The surface topography is advected along with the underlying deforming plate and can be modified through time by a combination of fluvial and hillslope sediment transport. The resulting mass redistribution creates loads on the plate which then feed back and influence subsequent deformation, erosion, and deposition. Preliminary results calculated with the model indicate that erosion and deposition have two main effects on deformation: The first is to decrease the amount of shortening required to initiate folding, while the second is to increase the fold wavelength. Both effects result from the ability of erosion and deposition to reduce the influence of gravity on deformation. In the extreme case of efficient erosion and deposition, deformation becomes localized on a single large‐scale mega‐anticline, as opposed to being distributed on a train of anticlines and synclines. This study indicates that erosion and deposition play a major role in governing the deformation and topography of fold belts and the sediment routing system acting within such a setting.
Observations of trapped humidity layer and Kelvin‐Helmholtz instability using UHF radar and GPS sonde
Authors: Das Siddarth Shankar , Kumar K. Kishore , Jain A. R. , Rao D. Narayana , Nakamura K.
Published: April 2004

UHF radar observations at Gadanki (13.47°N, 79.18°E) and Vaisala type GPS sonde measurements of atmospheric thermodynamic parameters (temperature, pressure, relative humidity, wind speed, and wind direction) from Tirupati (13.63°N, 79.40°E) have shown two distinct features of the lower troposphere over this region. One of the features is the observation of trapped humidity layer just above the boundary layer. These trapped humidity layers and associated gradients are observed to contribute significantly to the UHF radar backscattering, especially at the edges of the humidity layer. The second phenomenon is the observation of a long‐lasting Kelvin‐Helmholtz instability (KHI), at the height of ∼3 km, which lasted for about ∼210 min. The UHF radar vertical beam echo power has shown the characteristic power bursts pattern associated with KHI. The characteristic wavelength and time period of KHI waves are found to be 3.78 km and 18.4 min, respectively. Thus these results illustrate two important processes in the lower tropical troposphere, which are very important in UHF radar backscattering.
A viscoelastic model for groundwater level changes in the Cho‐Shui River alluvial fan after the Chi‐Chi earthquake in Taiwan
Authors: Lin Yun‐Bin , Tan Yih‐Chi , Yeh Tian‐Chyi Jim , Liu Chen‐Wuing , Chen Chu‐Hui
Published: April 2004

A viscoelastic model is developed to simulate the groundwater level changes in the Cho‐Shui River alluvial fan in Taiwan after the Chi‐Chi earthquake. An analytical solution is derived with the assumption that no leakage occurred in confined aquifers during the coseismic period. The solution is used to analyze the data collected from a high‐density network of hydrologic monitoring wells in the Cho‐Shui River alluvial fan. The simulated groundwater level changes agree with the observations. The viscosity coefficient of the model was found to correlate with the hydraulic conductivity of the aquifer. The field observations and the simulations reveal the influence of geological structures and heterogeneity on the groundwater changes and locations of sediment liquefactions in the alluvial fan during the Chi‐Chi earthquake. Possible applications to imaging subsurface hydraulic heterogeneity are discussed using information about groundwater level changes induced by earthquakes.
Experimental measurements of saturation overshoot on infiltration
Authors: DiCarlo David A.
Published: April 2004

Gravity‐driven fingers in uniform porous medium are known to have a distinctive nonmonotonic saturation profile, with saturated (or nearly so) tips and much less saturation in the tails. In this work, constant‐flux infiltrations into confined porous media (laterally smaller than the finger diameter, thus essentially one‐dimensional) are found to produce saturation overshoot identical to that found in gravity‐driven fingers. Light transmission is used to measure the saturation profiles as a function of infiltrating flux, porous media grain size, grain sphericity, and initial water saturation. Saturation overshoot is found to cease below a certain minimum infiltrating flux. This minimum flux depends greatly on the grain sphericity and initial water content of the media and slightly on the mean grain size. The observed saturation overshoot is inconsistent with a continuum description of porous media but qualitatively matches well observations and predictions from discrete pore‐filling mechanisms. This suggests that pore‐scale physics controls saturation overshoot and in turn gravity‐driven fingering.
Sulphur dioxide fluxes from Papua New Guinea's volcanoes
Authors: McGonigle A. J. S. , Oppenheimer C. , Tsanev V. I. , Saunders S. , Mulina K. , Tohui S. , Bosco J. , Nahou J. , Kuduon J. , Taranu F.
Published: April 2004

Papua New Guinea (PNG) hosts some of the most prolific degassing volcanoes in the world. Collectively, they are thought to be responsible for a significant contribution of sulfur dioxide to the regional and global atmosphere. Despite their importance, very few measurements of SO2 fluxes from PNG volcanoes have been made in the past, leading to uncertainty in estimates of total global volcanic sulfur budgets. We report here sulphur dioxide flux measurements obtained by ultraviolet spectroscopy during July and August 2003 for the following PNG volcanoes: Tavurvur, Ulawun, Pago, Langila, Bagana and Manam. We found fluxes of 1.3, 7.4, 1.4, 2.9, 23 and 2.1 kg s−1, respectively, for these sources. This amounts to a total of 38 kg s−1 of SO2, constituting some 6–9% and 7–12% of the estimated global time‐integrated volcanic emissions to the atmosphere, and troposphere, respectively.
Nonlocal closures for plasma fluid simulations
Authors: Held E. D. , Callen J. D. , Hegna C. C. , Sovinec C. R. , Gianakon T. A. , Kruger S. E.
Published: April 2004

The application of fluid models in studies of transport and macroscopic stability of magnetized, nearly collisionless plasmas requires closure relations that are inherently nonlocal. Such closures address the fact that particles are capable of carrying information over macroscopic parallel scale lengths. In this work, generalized closures that embody Landau, collisional and particle-trapping physics are derived and discussed. A gyro/bounce-averaged drift kinetic equation is solved via an expansion in eigenfunctions of the pitch-angle scattering operator and the resulting system of algebraic equations is solved by integrating along characteristics. The desired closure moments take the form of integral equations involving perturbations in the flow and temperature along magnetic field lines. Implementation of the closures in massively parallel plasma fluid simulation codes is also discussed. This implementation includes the use of a semi-implicit time advance of the fluid equations to stabilize the dominant closure terms which are introduced explicitly. Application of the nonlocal, parallel heat flow closure, q∥, in studies of temperature flattening across helical magnetic islands in toroidal geometry reveal a scaling of temperature versus critical island width for flattening of T∼wd−1.5. This result predicts more robust flattening at small island widths when compared to the diffusive scaling, T∼wd−1.7, which assumes a Braginskii-type parallel heat conductivity. Preliminary application of q∥ to tokamak disruption simulations shows qualitative agreement of wall heat loads with experimental observations, smooth distribution in toroidal angle, and striation in the poloidal direction along the wall.
Toroidal rotation and momentum transport in Alcator C-Mod plasmas with no momentum input
Authors: Rice J. E. , Lee W. D. , Marmar E. S. , Basse N. P. , Bonoli P. T. , Greenwald M. J. , Hubbard A. E. , Hughes J. W. , Hutchinson I. H. , Ince-Cushman A. , Irby J. H. , Lin Y. , Mossessian D. , Snipes J. A. , Wolfe S. M. , Wukitch S. J. , Zhurovich K.
Published: April 2004

The time evolution of toroidal rotation velocity profiles has been measured in Alcator C-Mod [Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] plasmas using a tangentially viewing x-ray spectrometer array. The strong co-current toroidal rotation in enhanced Dα (EDA) high confinement mode (H-mode) plasmas is observed to propagate in from the edge on a time scale similar to the energy confinement time. The ensuing steady state rotation velocity profiles in both Ohmic and ion cyclotron range of frequencies (ICRF) heated EDA H modes, which are generated in the absence of any external momentum input, are found to be relatively flat. These profiles may be simulated by a simple diffusion model with the boundary condition of an edge rotation, which appears during the H-mode period. The observed profiles are well matched by the simulations using a momentum diffusivity of ∼0.1 m2/s, which is much larger than the calculated neo-classical value, and the momentum transport may be regarded as anomalous. The Alcator C-Mod rotation observations have been compared in detail with the calculations of neo-classical and sub-neo-classical theory, to the predictions from modeling of ICRF wave induced energetic ion orbit shifts, and to estimates from turbulence driven mechanisms. The magnitude and scalings of the observed rotation results are in accord with neo-classical and sub-neo-classical calculations, but the measured momentum diffusivity is higher than the predictions by a large factor. The prediction of rotation reversal with a high magnetic field side resonance location for ICRF wave induced ion orbit shifts has not been observed in the experiments. While the turbulence driven rotation calculations are mostly qualitative, they represent some of the observed features.
Effects of electromagnetic turbulence in the neoclassical Ohm’s law
Authors: Hinton F. L. , Waltz R. E. , Candy J.
Published: April 2004

An Ohm’s law for tokamak plasmas has been derived, which includes the effect of electromagnetic turbulence as well as the neoclassical conductivity and bootstrap current. The most important current-driving effects of the turbulence have been identified, expressions for the driven (dynamo) current have been derived and these have been evaluated using the GYRO electromagnetic turbulence code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)]. The most important current drive mechanism, the divergence of the radial flux of parallel electron momentum induced by magnetic flutter, drives a current density which has positive peaks on low order rational surfaces, with compensating negative dips nearby, thus driving zero total current. Another current drive mechanism, the beating of the parallel electric field fluctuations with the electron density fluctuations, drives a current density which is much smaller than that driven by the magnetic flutter mechanism, but could drive a nonzero total current.
Tracer spectroscopy diagnostics of doped ablators in inertial confinement fusion experiments on OMEGA
Authors: Cohen David H. , MacFarlane Joseph J. , Jaanimagi Paul , Landen Otto L. , Haynes Donald A. , Conners David S. , Penrose Katherine L. , Shupe Nathan C.
Published: April 2004

A technique has been developed for studying the time-dependent, local physical conditions in ablator samples in an inertial confinement fusion (ICF) hohlraum environment. This technique involves backlit point-projection absorption spectroscopy of thin tracer layers buried in the interior of solid samples mounted on laser-driven hohlraums. It is shown how detailed view-factor, atomic, hydrodynamics, and radiation-transport modeling can be used to infer time-dependent physical conditions in the interiors of these samples from the observed absorption spectra. This modeling is applied to the results of an experimental campaign on the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] designed to compare radiation-wave velocities in doped and undoped ICF ablator materials.
Energy release by forced magnetic reconnection in a marginally stable plasma
Authors: Vekstein G.
Published: April 2004

Forced magnetic reconnection in a sheared force-free magnetic field brings about relaxation of the system to a state of lower magnetic energy. The resulting energy release becomes strongly amplified when the field is close to the tearing instability threshold, which makes the linear theory [Vekstein and Jain, Phys. Plasmas 5, 1506 (1998)] not applicable in this case. In the present Brief Communication the reconnective energy release in the marginally stable magnetic field is derived by exploring the quasilinear theory of tearing modes.
Enhancement of high-energy ion generation by preplasmas in the interaction of an intense laser pulse with overdense plasmas
Authors: Lee H. J. , Pae K. H. , Suk H. , Hahn S. J.
Published: April 2004

High-energy ion generation from the interaction of an ultraintense subpicosecond laser pulse with an overdense plasma slab combined with an underdense preplasma has been studied by using fully electromagnetic and relativistic particle-in-cell simulations. It was observed that the forward ion acceleration from the front and rear surfaces can be enhanced with a proper preplasma profile. The energy distribution functions of the accelerated ions, and Doppler shift of the reflected laser pulse are investigated with the variation of laser intensity, pulse duration, and preplasma profiles.
Experiments on laser driven beatwave acceleration in a ponderomotively formed plasma channel
Authors: Tochitsky S. Ya. , Narang R. , Filip C. V. , Musumeci P. , Clayton C. E. , Yoder R. B. , Marsh K. A. , Rosenzweig J. B. , Pellegrini C. , Joshi C.
Published: April 2004

A 10 ps long beam of 12 MeV electrons is externally injected into a ∼3-cm long plasma beatwave excited in a laser ionized hydrogen gas. The electrons have been accelerated to 50 MeV with a gradient of ∼1.3 GeV/m. It is shown that when the effective plasma wave amplitude-length product is limited by ionization-induced defocusing (IID), acceleration of electrons is significantly enhanced by using a laser pulse with a duration longer than the time required for ions to move across the laser spot size. Both experiments and two-dimensional simulations reveal that, in this case, self-guiding of the laser pulse in a ponderomotively formed plasma channel occurs. This compensates for IID and drives the beatwave over the longer length compared to when such a channel is not present.
Magnetohydrodynamic stability of centrifugally confined plasmas
Authors: Huang Yi-Min , Hassam A. B.
Published: April 2004

Four types of magnetohydrodynamic modes determine the overall stability of centrifugally confined plasmas: flute interchanges and the Kelvin–Helmholtz instability, in a low β system, and the magnetorotational instability (MRI) and the Parker instability, in a high β system. Analytic calculations and numerical simulations of velocity shear stabilization of flute interchanges are reviewed. The results showed strong evidence of stabilization. The Kelvin–Helmholtz instability is ideally stable if the generalized Rayleigh’s inflexion criterion is satisfied. The physical mechanisms of both the MRI and the Parker instability are examined and an explanation of why the MRI mechanism is insufficient to destabilize the system while the Parker instability could occur is given. Numerical simulations of the nonlinear behavior of the Parker instability are presented. It is shown that clumping from the Parker instability could reinforce centrifugal confinement.
Gases of exploding laser-heated cluster nanoplasmas as a nonlinear optical medium
Authors: Kim K. Y. , Alexeev I. , Kumarappan V. , Parra E. , Antonsen T. , Taguchi T. , Gupta A. , Milchberg H. M.
Published: April 2004

The manner in which strongly heated nanoclusters explode in the presence of intense laser fields influences all applications of this interaction. By measuring, with femtosecond time resolution, the ensemble average polarizability in a gas of intense laser-heated clusters, we have inferred the cluster explosion dynamics. The time evolution of the polarizability is characteristic of competition in the optical response between supercritical and subcritical density regions of the exploding cluster. These results are consistent with complementary time-resolved Rayleigh scattering measurements and with the predictions of a near-field plasma hydrodynamic model of the laser–cluster interaction. A significant implication of this cluster evolution appears in its macroscopic effect on a laser beam: a gas of exploding cluster plasmas causes nonlinear beam propagation owing to the space and time dependence of the ensemble polarizability. A strong self-focusing effect is observed experimentally that strongly contrasts with the ionization-induced refraction and beam spreading usually observed in the interaction of intense femtosecond laser pulses with nonclustered gases. These results illustrate how high energy density femtosecond plasma physics at the nanoscale determines what at first appears to be a gas-phase interaction.
Nonlinear paradigm for drift wave–zonal flow interplay: Coherence, chaos, and turbulence
Authors: Zonca Fulvio , White Roscoe B. , Chen Liu
Published: April 2004

Starting from the coherent four-wave drift wave–zonal flow modulation interaction model of Chen, Lin, and White [Phys. Plasmas 7, 3129 (2000)], nonlinear equations for drift wave–zonal flow interplay are systematically derived from first principles for nonuniform toroidal plasmas. The paradigm model, presented here, is based on a hierarchy in nonlinear wave–wave couplings, which assumes that different drift wave interactions on the shortest nonlinear time scale are mediated by zonal flows. The resulting coherent model demonstrates turbulence spreading to be the cause of transport scaling with system size. The nonlinear saturated state can be either coherent, with limit cycles, or chaotic, depending on the proximity to marginal stability.
Terahertz radiation from laser accelerated electron bunches
Authors: Leemans W. P. , van Tilborg J. , Faure J. , Geddes C. G. R. , Tóth Cs. , Schroeder C. B. , Esarey E. , Fubiani G. , Dugan G.
Published: April 2004

Coherent terahertz and millimeter wave radiation from laser accelerated electron bunches has been measured. The bunches were produced by tightly focusing (spot diameter ≈6 μm) a high peak power (up to 10 TW), ultra-short (⩾50 fs) laser pulse from a high repetition rate (10 Hz) laser system (0.8 μm), onto a high density (>1019 cm−3) pulsed gas jet of length ≈1.5 mm. As the electrons exit the plasma, coherent transition radiation is generated at the plasma-vacuum boundary for wavelengths long compared to the bunch length. Radiation in the 0.3–19 THz range and at 94 GHz has been measured and found to depend quadratically on the bunch charge. The measured radiated energy for two different collection angles is in good agreement with theory. Modeling indicates that optimization of this table-top source could provide more than 100 μJ/pulse. Together with intrinsic synchronization to the laser pulse, this will enable numerous applications requiring intense terahertz radiation. This radiation can also be used as a powerful tool for measuring the properties of laser accelerated bunches at the exit of the plasma accelerator. Preliminary spectral measurements indicates that bunches as short as 30–50 fs have been produced in these laser driven accelerators.
Strongly coupled plasma physics and high energy-density matter
Authors: Murillo M. S.
Published: April 2004

High energy–density matter—matter with pressures in excess of a megabar—covers a wide range of parameter space. Many laboratory experiments span a large portion of this parameter space as they evolve from a liquid or solid phase through the strongly coupled plasma phase to a hot plasma phase. This tutorial will introduce the basic physics of the intermediate, strongly coupled plasma phase from a very general point of view, including a discussion of experiments, such as laser-cooled ions, dusty plasmas, and white dwarfs. Basic definitions and results will be given for simple strongly coupled plasmas in the context of concepts familiar from weakly coupled plasma physics, to the extent possible. Definitions relevant to high energy–density physics are then introduced before focusing on dense plasmas, which form the overlap between the strongly coupled and high energy–density regions.
Large-scale high-resolution simulations of high gain direct-drive inertial confinement fusion targets
Authors: Schmitt Andrew J. , Colombant D. G. , Velikovich A. L. , Zalesak S. T. , Gardner J. H. , Fyfe D. E. , Metzler N.
Published: April 2004

Targets have been designed that produce moderate to high gain when directly driven by lasers. The intrinsic sensitivity of these targets to hydro instabilities is found using the FAST(2D) multidimensional radiation hydrocode [J. H. Gardner, A. J. Schmitt, J. P. Dahlburg et al., Phys. Plasmas 5, 1935 (1998)], which simulates the simultaneous behavior of a large bandwidth (e.g., l=2–256) of perturbations from compression to acceleration, and then to stagnation and burn. The development of the structure in these multimode simulations is benchmarked to theoretical analysis and single-mode calculations, which reveals the need to “renormalize” the simulation after compression. The simulations predict that a direct drive point design is expected to degrade significantly from its one-dimensional clean yield, yet still ignite and give appreciable gain. Simulations of high-gain pellets using a spike prepulse to inhibit Richtmyer–Meshkov growth show a considerable robustness, with high (>100) gains possible even with nominal surface finishes and laser imprint.
Generation of large-scale magnetic flows in turbulent plasma
Authors: Andrushchenko Zhanna N. , Pavlenko Vladimir P.
Published: April 2004

Nonlinear dynamics of the magnetic electron drift mode turbulence is outlined and generation of large-scale magnetic structures in a nonuniform unmagnetized plasma by turbulent Reynolds stress is demonstrated. A two-component turbulent system consisting of magnetic fluctuations and generated secondary flows is considered. The evolution equations for mean magnetic flow generation are obtained by averaging the two-field model equations over fast small scales. It is found, in turn, that the pattern of the flow modulates and regulates the turbulence dynamics. The main features of the flows are controlled by the structure of the nonlinear coupling to the small-scale magnetic fluctuations as well as by the spectral properties of the turbulence and its anisotropy. Thus, the parent waves and secondary magnetic flows form a self-regulating system. It is shown that the presence of large-scale structures leads to shearing of turbulence. The k-space diffusion coefficient for the magnetic zonal flows and streamers are calculated.
Landau damping and anomalous skin effect in low-pressure gas discharges: Self-consistent treatment of collisionless heating
Authors: Kaganovich Igor D. , Polomarov Oleg V. , Theodosiou Constantine E.
Published: April 2004

In low-pressure discharges, where the electron mean free path is larger or comparable with the discharge length, the electron dynamics is essentially nonlocal. Moreover, the electron energy distribution function (EEDF) deviates considerably from a Maxwellian. Therefore, an accurate kinetic description of the low-pressure discharges requires knowledge of the nonlocal conductivity operator and calculation of the non-Maxwellian EEDF. The previous treatments made use of simplifying assumptions: a uniform density profile and a Maxwellian EEDF. In the present study a self-consistent system of equations for the kinetic description of nonlocal, nonuniform, nearly collisionless plasmas of low-pressure discharges is reported. It consists of the nonlocal conductivity operator and the averaged kinetic equation for calculation of the non-Maxwellian EEDF. This system was applied to the calculation of collisionless heating in capacitively and inductively coupled plasmas. In particular, the importance of accounting for the nonuniform plasma density profile for computing the current density profile and the EEDF is demonstrated. The enhancement of collisionless heating due to the bounce resonance between the electron motion in the potential well and the external rf electric field is investigated. It is shown that a nonlinear and self-consistent treatment is necessary for the correct description of collisionless heating.