bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of structural analogs of putrescine on proliferation, morphology and karyotype of glioblastoma cells in culture
Authors: Quemener Véronique , Moulinoux Jacques‐Philippe , Lucas Josette , Khan Naim , Darcel Françoise , Martin Lucie‐Anne , Primault Roselyne , Seiler Nikolaus
Published: August 2005

Summary— In a previous study, we identified regions on the surface of tumor cells which act as acceptor sites for putrescine (Put) and studied the competition between structural analogs of Put (N,N′‐tetramethyl‐α,ω‐diaminoalkanes) and Put bound to latex microspheres. A chain of four to seven carbons was necessary for inhibition of Put‐latex binding to the cell surface of human glioblastoma (U251) cells. We show here that under the experimental conditions, N,N′‐tetramethyl‐1,4‐butanediamine and N,N′‐tetramethyl‐1,7‐heptanediamine exhibit an antitumor effect. In a first step (1–48 h after treatment), cells exposed to these compounds show large intracellular vacuoles. We failed to detect any acid phosphatase activity in these intracellular structures revealing that they were not lysosomes. Electron microscopy observations argue for the conclusion that these vacuoles are an hypertrophy of the endoplasmic reticulum (ER) and/or of the Golgi vesicles. Our hypothesis is that this typical effect of the analogs reveals that ER could be a physiological target of endogenous polyamines. At a later stage (6 days after treatment), the cells undergo morphological and biochemical changes: thin and long expansions characterize the cells and the GFA protein is overexpressed. Correlated to both these effects, karyotypic modifications are found in chromosomes 3 and 6. These changes evoke a differentiation of the treated cells. The work provides evidence that N‐methylated polyamine analogs taking the place of endogenous putrescine demonstrate a hopeful antitumor effect.
The onset of cell proliferation is stimulated by ascorbate free radical in onion root primordia
Authors: De Cabo Rafael C , Gonzalez‐Reyes José A , Navas Plácido
Published: August 2005

Summary— Ascorbate free radical (AFR) accelerates the quiescency‐proliferation shift in onion root primordia. The acceleration was detected by the increase of [3H]thymidine incorporation and by the anticipated kinetics of the increase in the labeling index. The shortening of the onset of cell proliferation is attributted to the role of AFR in the energization of the plasma membrane.
Enhancement of phorbol ester induced cell aggregation after alterations in asparagine‐linked oligosaccharides
Authors: Ahrens Patricia B
Published: August 2005

Summary— Human erythroleukemia (K‐562) cells grown in the presence of phorbol 12,13‐dibutyrate formed aggregates of cells not seen in untreated control cultures. Furthermore, the proportion of cells in aggregates and the size of the aggregates both increased dramatically in cultures treated with both phorbol ester and kifunensine, an inhibitor of asparagine‐linked oligosaccharide processing. Relative to control cells, phorbol ester treated cells exhibited a greater proportion of N‐linked oligosaccharides of the complex‐type. Kifunensine prevented this change and caused an accumulation of Man9GlcNAc2. The enhanced aggregation of cells treated with phorbol ester plus kifunensine depended on phorbol ester concentration and was blocked by inhibitors of protein kinase C (H7, sphinganine and sangivamycin). In flow cytometry analysis, phorbol ester treated K‐562 cells showed an increase in CD44, a glycoprotein involved in cell adhesion. Moreover, monoclonal antibody to CD44 augmented reaggregation of phorbol ester treated cells. The results implicate phorbol ester induction of CD44 in aggregation of K‐562 cells and demonstrate that the presence of high mannose‐type asparagine‐linked oligosaccharides on cell glycoproteins correlates with increased aggregation of phorbol ester treated cells.
Age group differences in psychological distress: the role of psychosocial risk factors that vary with age
Authors: JORM A. F. , WINDSOR T. D. , DEAR K. B. G. , ANSTEY K. J. , CHRISTENSEN H. , RODGERS B.
Published: August 2005

Background. There is continuing controversy about how age affects depression and anxiety, with a lack of consistent results across studies. Two reasons for this inconsistency are age bias in measures and different patterns of exposure to risk factors across age groups in various studies.

Method. Data on anxiety and depression symptoms were collected in a community survey of 7485 persons aged 20–24, 40–44 or 60–64 years. These measures were investigated for factorial invariance across age groups. Data were also collected on a wide range of potential risk factors, including social, physical health and personal factors, with the aim of determining whether these factors might partly or wholly account for age group differences.

Results. The invariance of correlated latent factors representing anxiety and depression was examined across age groups, and a generalized measure of psychological distress was computed. Depression, anxiety and psychological distress showed a decline across age groups for females and a decline from 40–44 to 60–64 years for males. Some of these age differences were accounted for by other risk factors, with the most important being recent crises at work and negative social relationships with family and friends.

Conclusion. Psychological distress generally declined across the age range 20–64 years and this was not attributable to measurement bias. Differential exposure to risk factors explained some, but not all, of the age group difference. Therefore other mechanisms that explain the lower level of distress in older age groups remain to be identified.
The epidemiology of chronic fatigue in the Swedish Twin Registry
Authors: EVENGÅRD BIRGITTA , JACKS ANDREAS , PEDERSEN NANCY L. , SULLIVAN PATRICK F.
Published: August 2005

Background. Chronic fatigue syndrome (CFS) remains an idiopathic and controversial entity.

Method. We screened 31405 individual members of the Swedish Twin Registry (aged 42–64 years) for the symptoms of fatiguing illness via a telephone questionnaire. We refined self-reported symptoms via data from several national registries and from physician review of all available medical records in order to approximate closely the dominant case definition of CFS.

Findings. The 6-month prevalence of CFS-like illness was 2·36% (95% CI 2·19–2·53) and was markedly higher in women than men, odds ratio 3.92 (95% CI 3·24–4·72) with no significant association with age or years of education. There was a highly significant association with occupation that disappeared after accounting for gender.

Interpretation. CFS-like illness may be more common that previously acknowledged. There is a marked increase in risk by gender. Previous reports that CFS is more prevalent in individuals in certain occupational categories were not confirmed and may have been due to confounding by gender.
Adult learning in traditional music
Authors: Cope Peter
Published: August 2005

This study is based on interviews carried out with 13 adult learners of traditional fiddle playing. The average age of the learners was 56 and they had been learning to play for between 2 and 20 years. All of the interviewees had taken music at school but none of them had been stimulated to participate further in any significant sense. The aspiration to learn to play the fiddle had various sources. Learning usually took place through traditional workshops and through the medium of the tune rather than through scales and exercises. Only one of the participants took regular conventional individualised lessons. They tended to take a pragmatic stance with regard to technique, looking for technical advice when they came up against barriers to progress. The music they played was within an aural culture and most of them learned by ear although they tended to regard notation as a useful supplement. All of them played in some sort of social context and all of them described an immense sense of pleasure and achievement from their playing. It is suggested that this kind of informal learning may have implications for learning to play instruments at school.
Peripatetic music teachers approaching mid-career: a cause for concern?
Authors: Baker David
Published: August 2005

This article discusses music service teachers' notions of pedagogical competence and occupational prospects as they approach mid-career. Respondents were drawn from a comprehensive life history study of 28 Local Education Authority employees. Of this larger cohort, 20 individuals contributed to findings discussed here. Data were collected and analysed between October 2002 and March 2004. Findings suggest a critical phase between 36 and 42 years of age. The episode entails reaching a professional apex, plateau or crisis in light of high pedagogical efficacy and career limitations. It culminates in a transformation of self-identity. Owing to respondents' unease about this period, the career structure of music service teachers is questioned.
Baseline assessment of pupil composing competencies on entry to secondary school: a pilot study
Authors: Fautley Martin
Published: August 2005

This study addresses the baseline assessment of pupil composing competencies at age 11+. It asks whether it might be possible for these to be evaluated by the use of a whole-class listening task. A rationale for this proposal is discussed. Results from a pilot study which administered an original audiated puzzle-task to a cohort of pupils, followed by a related composing assignment, are presented, analysed and discussed. This methodology is shown to reveal information about pupil composing competencies.
A PHILOSOPHICAL PERSPECTIVE ON ALHAZEN'S OPTICS
Authors: EL-BIZRI NADER
Published: August 2005

Although numerous studies have been conducted on the Optics (Kitāb al-Manāzir) of Alhazen (al-Hasan ibn al-Haytham, d. 1040 C.E.), and on its reception, assimilation and maturation within the course of development of the perspectivae traditions in the history of science and art, ambiguities do hitherto still surround the epistemological and ontological entailments of his theory of visual perception. In addressing this question, our inquiry herein is principally philosophical in scope and our textual reading combines exegesis with hermeneutics. While we observe the delicate procedures of historiography and philology, we do not unguardedly assume that they are exhaustive of all rigorous methods of thoughtful investigation. Moreover, in heeding the internal coherence of Alhazen's text, we do not simply lock his views within reductive contextual chronologies, or readily confine them to epochal matters of textual transmission. Our endeavour is therefore not exclusively set in view of serving the purposes of archival documentation, even if we preserve a thorough and sound sense of historicity. We ultimately recognize the philosophical pertinence of numerous subtle leitmotifs within Alhazen's thinking that speak to us in an effective timely manner, which is significantly relevant in its attuned bearings to the thrust of phenomenological theories of perception.
IN MEMORIAM
Authors: Thiele Rüdiger
Published: August 2005

Matthias Schramm, a well-known historian of science and professor at the University of Tübingen from 1966 to 1996, died in Dusslingen near Tübingen on 24 January 2005, shortly before his 77th birthday. He was born on 6 February 1928 in Paris as a child of painters. Due to wartime difficulties, most of his education was acquired at home. In spite of this, he passed the examination of a high-school prior to his matriculation (Abitur). Although Schramm's school had a pure classical orientation (humanistisches Gymnasium), he read on his own initiative Euclid in Greek.
Introduction: Wales, a new agenda for urban history
Authors: BORSAY PETER , MISKELL LOUISE , ROBERTS OWEN
Published: August 2005

The publication in 2000 of the three-volume Cambridge Urban History of Britain presented British urban historians with an ideal opportunity to take stock of the current state of research in their discipline. For Welsh urban historians it raised a number of particularly thorny issues. Whilst it contained some important chapters focused exclusively on the history of Welsh towns, it also identified Wales as one of the most under-researched areas of urban Britain. This special issue, dedicated specifically to Welsh urban history, has been conceived in part as a response to that finding. It also represents the collective efforts of scholars, new and established, whose research on urban Wales was presented at a conference on ‘Understanding Urban Wales’ at the University of Wales Swansea in September 2003. The event demonstrated the existence of a healthy ‘critical mass’ of scholarship, at both postgraduate and postdoctoral level, on Welsh towns and their development.
Wealth, status and ‘race’ in the Ruthin of Edward II
Authors: STEVENS MATTHEW
Published: August 2005

This article is a case study of the racially mixed, seigniorial borough of Ruthin (modern Denbighshire) in the early fourteenth century. It seeks to explore material inequalities and social aspects of the integration of English and Welsh burgesses in an urban setting. It concludes that whilst a disproportionate quantity of wealth did lie with the borough's English residents, Welsh burgesses enjoyed nearly comprehensive access to the community's wealth-generating and status-affirming activities. And, the behaviour of Ruthin's elites was more strongly dictated by their socioeconomic strata than racial background.
Reassessing the towns of southern Wales in the later middle ages
Authors: DIMMOCK SPENCER
Published: August 2005

On the basis of an emerging reassessment of the medieval urban experience in southern Wales, this article seeks to challenge the predominant view of Wales as being overwhelmingly rural before the nineteenth century. The study of Welsh towns has been limited by the survival of sources that in other regions have generated a renewed interest in the study of medieval urban society. Employing unusual sources that are available, generalizations are made here from the findings of case studies of two towns, Haverfordwest and Chepstow, in order to contribute to a regional synthesis of the urban experience in southern Wales. From this regional synthesis it will be possible to compare urban society in late medieval southern Wales with other regions in Britain and Europe in order to determine its particular characteristics, and with implications for later developments.
Do numbers count? Towns in early modern Wales
Authors: POWELL NIA
Published: August 2005

Although early modern Welsh towns were small by European standards, appearing to follow Clark's model for Europe's northern periphery of localized settlements not closely integrated within a wider urban hierarchy, Welsh towns showing greatest expansion were commercial outlets for specialist produce within the wider commercial matrix of southern Britain. Their smallness indicates a role within this wider, integrated network rather than constriction born of isolation.
‘A very thriving place’: the peopling of Swansea in the eighteenth century
Authors: ANTHONY ROBERT
Published: August 2005

In this article, the town of Swansea is suggested as an exemplar of pre-nineteenth-century Welsh industrial and urban development. Small in comparison with English towns, Swansea in 1801 had nevertheless risen up the Welsh urban rank-order to stand second only, in terms of population, to the industrial boomtown Merthyr Tydfil. Contemporary descriptions of Swansea as ‘Copperopolis’, ‘the Metropolis of Wales’, ‘the Mecca of Nonconformity’ and ‘the Brighton [or Naples] of Wales’ reflect the range of its functions at this time, and the high regard in which the town was held, both by its inhabitants and by visitors. Such a town inevitably attracted settlers and this article also examines eighteenth-century population change, the scale of immigration and the provenance of the settlers, and attempts to link the influx with the physical development of the town.
Inspecting the ‘extraordinary drain’: emigration and the urban experience in Merthyr Tydfil in the 1860s
Authors: JONES BILL
Published: August 2005

In the 1860s mass emigration from Merthyr Tydfil made a major impact on the town's fortunes and developing public sphere. The ‘extraordinary drain’ occasioned much concern and comment and reconfigured ongoing debates about Merthyr's contemporary condition and future survival. In turn, local power struggles, notions of the town's interests and emerging civic consciousness influenced interpretations of the nature, causes and meanings of the outflow. Emigration and the ‘urban’ thus interacted tellingly to help shape contemporary mentalities.
Rethinking urban Wales
Authors: EVANS NEIL
Published: August 2005

Five separate strands which have gone into the making of urban studies in Wales are identified and reviewed. The need for a broad, interdisciplinary approach, derived from H.J. Dyos, is suggested. The most comprehensive existing work is that of the geographer, Harold Carter, whose massive contribution is briefly outlined and evaluated. A more historical approach, centring on the idea of urbanization, is advocated, with the aim of drawing together the disparate fields of study.
Psychology and Design Processes
Authors: Wilpert Bernhard
Published: August 2005

Abstract. The most fundamental issue for any design is to pursue a strategy that guarantees that the final design product matches user expectations in terms of the product's usability, functionality, and requisite user competencies. This presentation illustrates this problem in reference to three separate but interrelated major themes: (1) the design of highly complex sociotechnical systems with high hazard potential; (2) the processes of everyday product design in teams; (3) the theoretical aspects of design and creative problem finding/solving. The first theme articulates the specific difficulties arising from the usual conflicts between purely technology-driven demands and the need to integrate the cognitive and action capacities, limitations, and needs of the human operator into the ultimate facility in order to guarantee system safety and reliability. What is called for here is more than a dialog between engineering sciences and psychology, but a genuine active cooperation of diverse disciplines in all design stages. The second theme addresses the social psychological processes of everyday product design under conditions of distributed decision making and the cooperative demands of diverse groups with heterogeneous professional socialization, divergent competencies, and diverse interests. The concluding section reflects on the theoretical dimensions of creativity and design. It discusses the research evidence concerning the social and organizational conditions under which innovative design solutions may be generated such as cognitive competencies and strategies, leadership, and organizational arrangements.
Earthquakes and strain in subhorizontal slabs
Authors: Brudzinski Michael R. , Chen Wang‐Ping
Published: August 2005

Using an extensive database of fault plane solutions and precise locations of hypocenters, we show that the classic patterns of downdip extension (DDE) or downdip compression (DDC) in subduction zones deteriorate when the dip of the slab is less than about 20°. This result is depth‐independent, demonstrated by both intermediate‐focus (depths from 70 to 300 km) and deep‐focus (depths greater than 300 km) earthquakes. The absence of pattern in seismic strain in subhorizontal slabs also occurs locally over scales of about 10 km, as evident from a detailed analysis of a large (Mw 7.1) earthquake sequence beneath Fiji. Following the paradigm that a uniform strain of DDE/DDC results from sinking of the cold, dense slab as it encounters resistance from the highly viscous mantle at depth, breakdown of DDE/DDC in subhorizontal slabs reflects waning negative buoyancy (“slab pull”) in the downdip direction. Our results place a constraint on the magnitude of slab pull that is required to dominate over localized sources of stress and to align seismic strain release in dipping slabs. Under the condition of a vanishing slab pull, eliminating the only obvious source of regional stress, the abundance of earthquakes in subhorizontal slabs indicates that a locally variable source of stress is both necessary and sufficient to sustain the accumulation of elastic strain required to generate intermediate‐ and deep‐focus seismicity. Evidence is growing that the process of seismogenesis under high pressures, including localized sources of stress, is tied to the presence of petrologic anomalies.
Global mass balance and the length‐of‐day variation
Authors: Chen Jianli
Published: August 2005

Variations of atmospheric angular momentum are dominated driving forces behind the length‐of‐day change, while mass redistribution in the oceans and hydrosphere is expected to cause the length‐of‐day to change as well. We estimate atmospheric, oceanic, and hydrological contributions to the length‐of‐day variations during 1993–2004 using the National Centers for Environmental Prediction reanalysis atmospheric model, the Estimating the Circulation and Climate of the Ocean consortium's data assimilating ocean general circulation model, and the U.S. Climate Prediction Center's land data assimilation system model. A coherent mass balance among the atmosphere, ocean, and continental water is implemented. At seasonal timescales the mass balance among the atmosphere, land, and oceans is very important and nearly cancels all the contributions to the length‐of‐day variation predicted by the oceanic and hydrological models, although at intraseasonal timescales, good correlations exist between observed length‐of‐day variations unaccounted for by the atmosphere and contributions from the ocean and continental water. This study indicates that in a fully mass balanced Earth system the combined seasonal oceanic and hydrological contributions to the length‐of‐day variation are too small to explain the residual length‐of‐day variations unaccounted for by the atmosphere. The discrepancies between observed length‐of‐day variations and atmospheric contributions appear more likely caused by the errors of the atmospheric models, in particular of the wind fields.
Characterization and sources of regional‐scale transported carbonaceous and dust aerosols from different pathways in coastal and sandy land areas of China
Authors: Zhang X. Y. , Wang Y. Q. , Wang D. , Gong S. L. , Arimoto R. , Mao L. J. , Li J.
Published: August 2005

Concentrations of 12‐hour averaged organic carbon (OC), elemental carbon (EC), and other trace elements were determined from bulk aerosol samples at a coastal city of Lian Yun Gang (LYG) in east China from June to December 2003 and a sandy land site of Tong Liao in northeast China from June to August 2003. Regional transports from four main source areas accounted for ∼35–49% of the Asian dust and 16–18% of the carbonaceous particles for both sites. The regional mean concentrations of various species, especially EC, were comparable to or lower than those in urban areas of inland China, Korea, and Japan but tended to be higher than those in Hong Kong or rural sites in east Asia. At LYG, OC showed a clear seasonal pattern with a peak loading in winter (24 μg m−3) and a low in summer (10 μg m−3). Seasonality of EC was more pronounced than that of OC with a difference of approximately threefold (3.8 to 11 μg m−3). Three types of air masses with high particulate loadings were found to be responsible for the peak EC and low OC/EC ratios in winter. Clean air masses with more than 50% secondary organic carbon contents were largely of marine origins. Elemental concentrations (Ca, Fe, K, Mn, and Ti) were mainly associated with Asian dust aerosols with a certain fraction of K from biomass burning in mainland China characterized with a ratio of 1.3 for OC/K.
Observational study of the 4‐day wave in the mesosphere preceding the sudden stratospheric warming events during 1995 and 2002
Authors: Azeem S. M. I. , Talaat E. R. , Sivjee G. G. , Liu H.‐L. , Roble R. G.
Published: August 2005

We have examined the Michelson Interferometer (MI) OH airglow measurements at the South Pole Station and the National Center for Environment Prediction (NCEP) temperatures to investigate the dynamical effects of sudden stratospheric warming (SSW) events on the Antarctic mesosphere and stratosphere. Comparisons of stratospheric and mesospheric temperatures at the South Pole during the 1995 and 2002 observing seasons show evidence of mesospheric cooling preceding the SSW events. Spectral analyses of South Pole OH air glow brightness measurements from the 1995 and 2002 observing season and NCEP stratospheric temperatures show amplification of the 4‐day wave planetary wave before the start of the mesospheric cooling trend, the latter preceding the onset of SSW event. A similar behavior of planetary wave is also seen in the stratosphere where the 4‐day wave is seen to grow in amplitude just before the peak of the sudden increase in temperatures.
The transcription factor GATA2 regulates differentiation of brown adipocytes
Authors: Tsai Judy , Tong Qiang , Tan Guo , Chang Aaron N , Orkin Stuart H , Hotamisligil Gökhan S
Published: August 2005

Brown adipose tissue (BAT) is a specialized mammalian tissue and a site of adaptive thermogenesis. Although the metabolic functions of brown and white adipocytes are distinct, terminal differentiation of both adipocyte lineages is regulated by well‐characterized common transcription factors. However, the early stages of adipocyte differentiation and regulation of precursor cells are not well understood. We report here that GATA2 is expressed in brown adipocyte precursors, and its expression is downregulated in a differentiation‐dependent manner. Constitutive expression of GATA2 suppressed expression of BAT‐specific genes in brown adipocytes, whereas disruption of a GATA2 allele in brown preadipocytes resulted in significantly elevated differentiation and expression of several markers of brown adipogenesis. Collectively, these results show that GATA2 functions to suppress brown adipocyte differentiation, whereas reduction of GATA2 promotes brown adipogenesis.
Disconnection of the Left Atrial Appendage for Elimination of Foci Maintaining Atrial Fibrillation
Authors: TAKAHASHI YOSHIHIDE , SANDERS PRASHANTHAN , ROTTER MARTIN , HAÏSSAGUERRE MICHEL
Published: August 2005

We report a case with paroxysmal atrial fibrillation, in whom multiple foci were identified in the left atrial appendage after pulmonary vein isolation. The patient was successfully treated by catheter ablation to disconnect this structure.
The all-Cartesian reaction plane Hamiltonian: Formulation and application to the H-atom transfer in tropolone
Authors: Giese Kai , Kühn Oliver
Published: August 2005

In this work we present an all-Cartesian reaction surface approach, where the large amplitude coordinates span the so-called reaction plane, that is, the unique plane defined by the two minima and the saddle-point structure of an isomerization reaction. Orthogonal modes are treated within harmonic approximation which gives the total Hamiltonian an almost separable form that is suitable for multidimensional quantum dynamics calculations. The reaction plane Hamiltonian is constructed for the H-atom transfer in tropolone as an example for a system with an intramolecular O⋯H–O hydrogen bond. We find ground-state tunneling splittings of 3.5 and 0.16cm−1 for the normal and deuterated species, respectively. We calculated infrared-absorption spectra for a four-dimensional model focusing on the low-frequency region. Here, we identify a reaction mode which is closely connected to the tautomerization that is reflected in the increase of tunneling splitting to 18cm−1 upon excitation.
The Kohn-Sham density of states and band gap of water: From small clusters to liquid water
Authors: Cabral do Couto P. , Estácio S. G. , Costa Cabral B. J.
Published: August 2005

Electronic properties of water clusters (H2O)n, with n=2, 4, 8, 10, 15, 20, and 30 molecules were investigated by sequential Monte Carlo/density-functional theory (DFT) calculations. DFT calculations were carried out over uncorrelated configurations generated by Monte Carlo simulations of liquid water with a reparametrized exchange-correlation functional that reproduces the experimental information on the electronic properties (first ionization energy and highest occupied molecular orbital-lowest unoccupied molecular orbital gap) of the water dimer. The dependence of electronic properties on the cluster size (n) shows that the density of states (DOS) of small water clusters (n>10) exhibits the same basic features that are typical of larger aggregates, such as the mixing of the 3a1 and 1b1 valence bands. When long-ranged polarization effects are taken into account by the introduction of embedding charges, the DOS associated with 3a1 orbitals is significantly enhanced. In agreement with valence-band photoelectron spectra of liquid water, the 1b1, 3a1, and 1b2 electron binding energies in water aggregates are redshifted by ∼1eV relative to the isolated molecule. By extrapolating the results for larger clusters the threshold energy for photoelectron emission is 9.6±0.15eV (free clusters) and 10.58±0.10eV (embedded clusters). Our results for the electron affinity (V0=−0.17±0.05eV) and adiabatic band gap (EG,Ad=6.83±0.05eV) of liquid water are in excellent agreement with recent information from theoretical and experimental works.
Direct evaluation of the lifetime matrix by the hyperquantization algorithm: Narrow resonances in the F+H2 reaction dynamics and their splitting for nonzero angular momentum
Authors: Aquilanti Vincenzo , Cavalli Simonetta , De Fazio Dario , Simoni Andrea , Tscherbul Timur V.
Published: August 2005

We propose a new method for the direct and efficient evaluation of the Felix Smith’s lifetime Q matrix for reactive scattering problems. Simultaneous propagation of the solution to a set of close-coupled equations together with its energy derivative allows one to avoid common problems pertinent to the finite-difference approach. The procedure is implemented on a reactive scattering code which employs the hyperquantization algorithm and the Johnson–Manolopoulos [J. Comput. Phys. 13, 455 (1973); J. Chem. Phys 85, 6425 (1986)] propagation to obtain the complete S matrix and scattering observables. As an application of the developed formalism, we focus on the total angular momentum dependence of narrow under-barrier resonances supported by van der Waals wells of the title reaction. Using our method, we fully characterize these metastable states obtaining their positions and lifetimes from Lorentzian fits to the largest eigenvalue of the lifetime matrix. Remarkable splittings of the resonances observed at J>0 are rationalized in terms of a hyperspherical model. In order to provide an insight on the decay mechanism, the Q-matrix eigenvectors are analyzed and the dominant channels populated during the decomposition of metastable states are determined. Possible relevance of the present results to reactive scattering experiments is discussed.
Three-photon near-threshold photoionization dynamics of isooctane
Authors: Healy Andrew T. , Underwood David F. , Lipsky Sanford , Blank David A.
Published: August 2005

The electron survival probability following three-photon (9.3eV total) near-threshold photoionization of neat isooctane is measured with sub-50fs time resolution. The measured dynamics are nonexponential in time and are well described by a diffusion-controlled electron-cation recombination model. Excitation-power-dependent studies indicate that the unperturbed three-photon threshold ionization is only observed for pump irradiance below 0.5TW∕cm2. At excitation fields above this level, the signal is no longer cubic in the excitation irradiance, and the observed electron survival probability dramatically changes, decaying as a single exponential in time.
Formation of porous silicon: Electron microscope investigation
Authors: Dimov Virgil I. , Vitanov Petko K.
Published: August 2005

Porous silicon structure was investigated by scanning electron microscope images of secondary electrons as well as by transmission electron microscope images of diffraction and phase contrasts. Different structure types in each one of the dissolution zones are found: crystalline structure of primary silicon, changed crystalline structure as a result of a partial dissolution process, and amorphous structure in the porous zone. A hypothesis about the type of the changed structure in the intermediate dissolution zone is put forward and an atomic model of this structure is presented. A theory of the mechanism of the dissolution process based on structure peculiarities, observed in the images, was formulated: the dissolution proceeds along the most favorable atomic planes of types (110) and (111). The dissolution front advances mainly in the direction [010]—it is zigzag shaped and parallel to the dissolution surface. Images of phase and diffraction contrasts have been simulated on the basis of models accounting for structure changes. A good correspondence between experimental and simulated high-resolution transmission electron microscopy images has been found.
Design of amino acid sequences to fold into Cα-model proteins
Authors: Amatori A. , Tiana G. , Sutto L. , Ferkinghoff-Borg J. , Trovato A. , Broglia R. A.
Published: August 2005

In order to extend the results obtained with minimal lattice models to more realistic systems, we study a model where proteins are described as a chain of 20 kinds of structureless amino acids moving in a continuum space and interacting through a contact potential controlled by a 20×20 quenched random matrix. The goal of the present work is to design and characterize amino acid sequences folding to the SH3 conformation, a 60-residue recognition domain common to many regulatory proteins. We show that a number of sequences can fold, starting from a random conformation, to within a distance root-mean-square deviation between 2.6 and 4.0 Å from the native state. Good folders are those sequences displaying in the native conformation an energy lower than a sequence-independent threshold energy.
Ionic correlations in highly charge-asymmetric colloidal liquids
Authors: Fernández-Nieves A. , Fernández-Barbero A. , de las Nieves F. J. , Vincent B.
Published: August 2005

We use electrophoretic mobility (μ) measurements of charged colloidal particles under the presence of multivalent counterions as a probe of the electrostatic correlations between them; they become important for sufficiently high surface charge densities of the colloid (σ) and result in a decreasing μ upon increasing σ. The physics of this decrease is the same as that giving rise to charge inversion. We account qualitatively for the observations by considering recent theoretical arguments that assume the counterions next to the colloid surface as a strongly correlated liquid of properties similar to that of a Wigner crystal.
Dissociation of energy-selected c-C2H4S+ in a region 10.6–11.8 eV: Threshold photoelectron—photoion coincidence experiments and quantum-chemical calculations
Authors: Fang Yung-Sheng , Lin I-Feng , Lee Yao-Chang , Chiang Su-Yu
Published: August 2005

Dissociation of energy-selected c-C2H4S+ was investigated in a region of 10.6–11.8 eV with a threshold photoelectron-photoion coincidence technique and a synchrotron as a source of vacuum ultraviolet radiation. Branching ratios and average releases of kinetic energy in channels of formation of c-C2H4S+, CH3CS+, and HCS+ were obtained from well-resolved time-of-flight peaks in coincidence mass spectra. Measured average releases of kinetic energy for channel CH3CS++H of least energy are substantial and much greater than calculated with quasiequilibrium theory; in contrast, small releases of kinetic energy near the appearance onset for channel HCS++CH3 agree satisfactorily with statistical calculations. Calculations of molecular electronic structures and energetics of c-C2H4S+ and C2H3S+ isomers and various fragments and transition states were also performed with Gaussian 3 method to establish dissociation mechanisms. A predicted dissociation energy of 11.05 eV for c-C2H4S→HCS++CH3 agrees with a linearly extrapolated threshold at 10.99±0.04eV and a predicted dissociation mechanism that c-C2H4S+ isomerizes to CH3CHS+ before dissociating to HCS++CH3 supports the experimental results. The large releases of kinetic energy for channel CH3CS++H might result from a dissociation mechanism according to which c-C2H4S+ isomerizes to a local minimum CH3CSH+ and then dissociates through a transition state to form CH3CS++H.
Structural defects in Sr2FeMoO6 double perovskite: Experimental versus theoretical approach
Authors: Colis S. , Stoeffler D. , Mény C. , Fix T. , Leuvrey C. , Pourroy G. , Dinia A. , Panissod P.
Published: August 2005

The lower than expected magnetization of imperfect Sr2FeMoO6 (SFMO) double perovskites is usually attributed to the presence of Fe at antisite positions that would be antiferromagnetically coupled to their regular neighbors. However, ab initio calculations suggest strongly that such defective Fe sites would be ferromagnetically coupled and, consequently, the magnetization reduction would originate from other kinds of defects. The magnetic, hyperfine, and structural properties of SFMO perovskites prepared by solid-state reaction under a variety of conditions are reported and correlated with ab initio calculations of the magnetic moments and hyperfine fields of Mo and Fe ions in different local environments (antisites, antisite neighbors, and neighbors of an oxygen vacancy). When plotted against the order parameter the experimental magnetization is found to decrease at a rate of about −7.6μB per Mo–Fe antisite pair as in other previous experiments, where the theoretical calculation predicts −6.56μB per antisite pair if the moments of Fe antisites are antiparallel to the regular Fe moments. Unfortunately, the energy of this configuration is found to be 0.7eV higher than that of the parallel configuration for which the magnetization reduction is only −0.19μB per antisite pair. Sources for the supplementary reduction of magnetization have then been considered. The presence of spurious phases cannot account for the observation. Oxygen vacancies do reduce significantly the magnetization (−2.00μB∕vacancy), but no significant sign of their effect is found in the Fe Mössbauer and Mo nuclear magnetic resonance spectra. Moreover, the position of the spectral lines of defects are compatible with the theoretical findings for Fe antisites in the antiparallel spin configuration.
Influence of the upper critical-field anisotropy on the transport properties of polycrystalline MgB2
Authors: Eisterer M. , Krutzler C. , Weber H. W.
Published: August 2005

The intrinsic properties of MgB2 form the basis for all applications of this superconductor. We wish to emphasize that the application range of polycrystalline MgB2 is limited by the upper critical field Hc2 and its anisotropy. In wires or tapes, the MgB2 grains are randomly oriented or only slightly textured and the anisotropy of the upper critical field leads to different transport properties in different grains, if a magnetic field is applied and the current transport becomes percolative. The irreversibility line is caused by the disappearance of a continuous superconducting current path and not by depinning as in high-temperature superconductors. Based on a percolation model, we demonstrate how the changes of the upper critical field and its anisotropy and how the changes of flux pinning will influence the critical currents of a wire or a tape. These predictions are compared to results of neutron irradiation experiments, where these parameters were changed systematically.
Geometry of the Schrödinger equation and stochastic mass transportation
Authors: Völlinger Stephan
Published: August 2005

The Schrödinger equation is deduced from a geometric principle. Lagrange, Hamilton-Jacobi, and Hamilton formalisms are defined almost analogously to the deterministic case, which can be identified as geometric optic. The form of these formalisms is identical to the deterministic formalisms. Furthermore, it will be shown how the deterministic case is “superficial” to the stochastic one if Planck’s constant is very small. An elementary proof of Heisenberg’s uncertainty relation finishes the paper.
Theory and experiment for one-dimensional directed self-assembly of nanoparticles
Authors: Mertens Keith , Putkaradze Vakhtang , Xia Deying , Brueck S. R. J.
Published: August 2005

A promising method of particle self-assembly using patterned surfaces is described. A set of long (order of millimeters), nanoscale-width grooves is etched into a substrate, and an aqueous solution containing particles of ∼50- or 80-nm diameter is deposited on the surface. Upon the evaporation of the solution, the particles are dragged into the grooves by the receding contact line. A partial differential equation, incorporating screening, is constructed to investigate the final distribution of particles in the grooves. A complete analysis of the stationary states for the density equation in one and two dimensions is performed. Additionally, the nonlinear evolution of the density is studied numerically and the results compare well with both the analytic results and the experiments.
Enthalpy and entropy of twin boundaries in superconducting YBa2Cu3O7−x
Authors: Mei Linfeng , Chan Siu-Wai
Published: August 2005

Twin boundary energy (γtw) and its temperature dependence are important factors to be evaluated for engineering twin morphology for strong flux pinning and high critical current density in superconducting YBa2Cu3O7−x. Here, it has been measured as a function of oxygenation temperature from 450 to 680 °C using both the twin spacing method and a twin tip method. By comparing the twin energies obtained by the two methods, the geometrical factor α used in twin spacing method is determined. This geometrical factor is directly related to the sharpness of the twin tips. From the temperature dependence of twin boundary energy per unit area, twin boundary entropy (Δs) and enthalpy (Δh) for twin boundaries are projected to be 0.24mJ∕Km2 and 246mJ∕m2, respectively.
Electromigration in Pb-free SnAg3.8Cu0.7 solder stripes
Authors: Hsu Ying-Chao , Chou Chung-Kwuang , Liu P. C. , Chen Chih , Yao D. J. , Chou T. , Tu K. N.
Published: August 2005

Electromigration behavior in the eutectic SnAg3.8Cu0.7 solder stripes was investigated in the vicinity of the device operation temperature of 100°C by using the edge displacement technique. Measurements were made for relevant parameters for electromigration of the solder, such as drift velocity, threshold current density, activation energy, as well as the product of diffusivity and effective charge number (DZ*). The threshold current densities were estimated to be 4.3×104A∕cm2 at 80°C, 3.2×104A∕cm2 at 100°C, and 1.4×104A∕cm2 at 120°C. These values represent the maximum current densities that the SnAg3.8Cu0.7 solder can carry without electromigration damage at the three stressing temperatures. The electromigration activation energy was determined to be 0.45eV in the temperature range of 80–120°C. The measured products of diffusivity and the effective charge number, DZ*, were −1.8×10−10cm2∕s at 80°C, −5.0×10−10cm2∕s at 100°C, and −7.2×10−10cm2∕s at 120°C.
Improved thermoelectric properties in double-filled Cey∕2Yby∕2Fe4−x(Co∕Ni)xSb12 skutterudites
Authors: Bérardan D. , Alleno E. , Godart C. , Puyet M. , Lenoir B. , Lackner R. , Bauer E. , Girard L. , Ravot D.
Published: August 2005

We have investigated the thermal and electrical properties of filled skutterudites belonging to the series Ce1−zYbzFe4Sb12 and Cey∕2Yby∕2Fe4−x(Co∕Ni)xSb12, as well as their potential for thermoelectric power generation. In the first series, increasing the Yb fraction decreases the resistivity and thermopower. These effects are related to the variations of valence of Yb with the Yb fraction (from 2.2 in Yb0.92Fe4Sb12 to 2.7 in Ce0.85Yb0.05Fe4Sb12). The power factor is increased in Ce0.40Yb0.53Fe4Sb12 while the thermal conductivity is reduced and this leads to an improved figure of merit in this compound when compared to Ce0.85Fe4Sb12. Co or Ni substitution was used to tune the carrier concentration and improve the power factor: we measure a ZT=0.5 at 500K in Ce0.44Yb0.32Fe3.02Co0.98Sb12 and an extrapolation leads to ZT=0.95 at 800K, which is close to state-of-the-art Ce0.28Fe1.52Co2.48Sb12 although the composition is far from being optimized. Double filling happens to be a promising path to provide good thermoelectric performances.
On the dynamics of the damage growth in 5 MeV oxygen-implanted lithium niobate
Authors: Bianconi M. , Argiolas N. , Bazzan M. , Bentini G. G. , Chiarini M. , Cerutti A. , Mazzoldi P. , Pennestrì G. , Sada C.
Published: August 2005

The damage induced by 5 MeV oxygen ion implantation in x-cut congruent LiNbO3 has been investigated by Rutherford backscattering spectrometry channeling technique. The dynamics of the damage growth has been described by an analytical formula considering the separate contributions of nuclear and electronic energy deposition. It has been hypothesized that the nuclear damage provides the localization of the energy released to the electronic subsystem necessary for the conversion into atomic displacements. The strong influence of the preexisting defects on the damage pileup, foreseen by the analytical formula, has been experimentally verified by pre-implanting the samples with 500 keV oxygen ions. It has been shown that a subsequent 5 MeV oxygen implantation step gives rise to an impressive damage accumulation, eventually leading to the total amorphization of the surface, even at moderate fluences.
Novelty filtering with a photorefractive lithium–niobate crystal
Authors: Krishnamachari Vishnu Vardhan , Grothe Oliver , Deitmar Hendrik , Denz Cornelia
Published: August 2005

In this letter we present a technique which employs a photorefractive lithium–niobate crystal for novelty filtering. Due to the minimal trail formation exhibited by this novelty filter, it can be used for reliable quantitative phase measurement for time intervals of the order of a few hours. We present a simplified theoretical description of this filter based on a coupled wave theory [N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, and V. L. Vinetskii, Ferroelectrics 22, 949 (1979); N. V. Kukhtarev, V. B. Markov, S. G. Odulov, M. S. Soskin, and V. L. Vinetskii, Ferroelectrics22, 961 (1979)]. We also demonstrate the first experimental results of employing this device in the field of microfluid dynamics for measuring the concentration changes produced due to the mixing of two transparent liquids in a microchannel.
Electron-optical-phonon interaction in the In0.73Ga0.27As–AlAs intersubband laser
Authors: Drachenko O. , Galibert J. , Léotin J. , Tomm J. W. , Semtsiv M. P. , Ziegler M. , Dressler S. , Müller U. , Masselink W. T.
Published: August 2005

The magnetic-field dependence of the operation of a quantum-cascade intersubband laser (QCL) is used to investigate the energetic relaxation of injected electrons through phonon emission. The QCL emits at 3.8μm and incorporates a strain-compensated active region with a large degree of internal strain. Energies of the relevant electron-phonon scattering responsible for the depopulation of the upper laser level are determined from the analysis of the Landau-level spectra. A comparison of those energies with the Raman spectrum of the active region is used to identify which phonon is primarily involved in the electron-phonon scattering. In spite of the low Ga-content in the (In,Ga)As quantum wells and high Al-content in the AlAs∕(In,Al)As composite barriers, the depopulation of the upper laser level appears to be dominated by the resonant electron-GaAs-like-longitudinal-phonon intersubband scattering. In particular, the contribution due to AlAs-like modes is negligible.