bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular epidemiology of African sleeping sickness
Authors: HIDE G. , TAIT A.
Published: June 2009

Human sleeping sickness in Africa, caused by Trypanosoma brucei spp. raises a number of questions. Despite the widespread distribution of the tsetse vectors and animal trypanosomiasis, human disease is only found in discrete foci which periodically give rise to epidemics followed by periods of endemicity A key to unravelling this puzzle is a detailed knowledge of the aetiological agents responsible for different patterns of disease – knowledge that is difficult to achieve using traditional microscopy. The science of molecular epidemiology has developed a range of tools which have enabled us to accurately identify taxonomic groups at all levels (species, subspecies, populations, strains and isolates). Using these tools, we can now investigate the genetic interactions within and between populations of Trypanosoma brucei and gain an understanding of the distinction between human- and nonhuman-infective subspecies. In this review, we discuss the development of these tools, their advantages and disadvantages and describe how they have been used to understand parasite genetic diversity, the origin of epidemics, the role of reservoir hosts and the population structure. Using the specific case of T.b. rhodesiense in Uganda, we illustrate how molecular epidemiology has enabled us to construct a more detailed understanding of the origins, generation and dynamics of sleeping sickness epidemics.
Algebraic Polymorphisms– ERRATUM
Authors: SCHMIDT KLAUS , VERSHIK ANATOLY
Published: June 2009

We give three corrections to the paper [K. Schmidt and A. M. Vershik, Algebraic polymorphisms, Ergod. Th. & Dynam. Sys.28 (2008), 633–642].
The Economy, Obama, and the 2008 Election
Authors: Lewis-Beck Michael S.
Published: June 2009

In late summer of 2008, there were clear objective signs of a weakening economy. Industrial production was negative (−1.5 in August), inflation was creeping up (+5.4 in August), the unemployment rate was rising (6.1% in September). Housing starts were at a near-record low, with mortgages getting hard to come by, and hard to pay for. Consumer sentiment, as measured in public opinion surveys, was dropping to levels not seen since the 1980s. But there was no talk of an “economic crisis,” and reported conditions still did not qualify officially as a “recession.” The disintegration of Wall Street financial giants, which began in September, quickly accelerated the scale of the perceived, and actual, decline. “At that point,” as Campbell (2009, 13–14) puts it, “the economy was in crisis, perhaps teetering on the brink [of] a deep recession or even a depression,” with the stock market experiencing about a 25% drop in value over one month. By October 3, a $700 billion Economic Stabilization Act had passed through Congress, and was signed by President Bush. Despite this unprecedented emergency measure, the stock market continued to tumble. During the 2008 presidential campaign, at least one voter saw the electoral relevance of these economic struggles. Francine Caruso wanted a president who would “fix the economy.” Francine, an administrative assistant who lost her job, couldn't sell her home, and watched her husband postpone retirement, declared that Obama and McCain “need to stop knocking each other and tell us what they can do for us” (Amon 2008). Our overarching question, in this collection of articles, is how other voters linked the economy to their 2008 candidate choice.
Internet Voting in Comparative Perspective: The Case of Estonia
Authors: Alvarez R. Michael , Hall Thad E. , Trechsel Alexander H.
Published: June 2009

Several countries have conducted Internet voting trials in binding public elections over the past decade, including Switzerland, the United Kingdom, and the United States. However, Estonia—a former Soviet republic and now a full member of the European Union—has advanced the farthest in deploying Internet voting. In this article, we focus on how the Estonians have systematically addressed the legal and technical considerations required to make Internet voting a functioning voting platform, as well as the political and cultural framework that promoted this innovation. Using data from our own qualitative and quantitative studies of the Estonian experience, we consider who voted over the Internet in these elections, and the political implications of the voting platform.
Are Two (or Three or Four … or Nine) Heads Better than One? Collaboration, Multidisciplinarity, and Publishability
Authors: Sigelman Lee
Published: June 2009

Although collaborative research has become much more common in the social sciences, including political science, little is known about the consequences of collaboration. This article uses papers submitted to the American Political Science Review to assess whether the widely acknowledged benefits of collaboration produced papers that were more likely to be accepted for publication. The results indicate that collaboration per se made little or no difference, but that the disciplinary configuration of the authors did result in differences in the success of these submissions.
Tenure Standards in Political Science Departments: Results from a Survey of Department Chairs
Authors: Rothgeb John M. , Burger Betsy
Published: June 2009

This article presents the results from a survey of political science department chairs regarding the tenure procedures and standards at their colleges or universities. The findings reveal that only a small fraction of the colleges and universities in the United States refuse to offer tenure or are attempting to limit tenure. We also find general agreement regarding the standards for evaluating teaching and service and that research expectations vary according to the highest degree offered by a department.
Representation and the Rules of the Game: An Electoral Simulation
Authors: Hoffman Donna R.
Published: June 2009

It is often a difficult proposition for introductory American government students to comprehend different electoral systems and how the rules of the game affect the representation that results. I have developed a simulation in which different proportional-based electoral systems are compared with a single-member plurality electoral system. In addition, the simulation can also serve to illustrate other concepts commonly introduced in introductory courses.
Learning Opportunities in a Department-Wide Crisis Simulation: Bridging the International/National Divide
Authors: Zaino Jeanne S. , Mulligan Tricia
Published: June 2009

When designed and executed properly, role-playing simulations go a long way to enhance student learning. Typically, however, simulations are divided along subfields. Most exercises, whether based on real or fictitious events, either place students in various roles within a country or have them represent the international interests of one country among others. In an effort to bridge this divide and answer recent calls to internationalize the curriculum, we have designed and implemented a department-wide crisis simulation. The article demonstrates that students engaged in a large-scale, department-wide simulation gain a greater appreciation and understanding of political processes and variables including negotiation, the opportunities and constraints of institutional design, identity, and strategic thinking.
Learning through Publishing The Pi Sigma Alpha Undergraduate Journal of Politics
Authors: Bauer Benjamin J. , Ogás Whitney C. , Shakir Omar R. , Oxley Zoe M. , Clawson Rosalee A.
Published: June 2009

Publishing a research journal can be a rewarding and useful learning experience for undergraduate students. Drawing upon our experiences with The Pi Sigma Alpha Undergraduate Journal of Politics, we describe the benefits of producing a peer-reviewed journal. Among the benefits we highlight are gains in political science knowledge, increased understanding of research methodologies, refinement of writing and debating skills, and development of interpersonal skills. We close with a call for professors to encourage their students to submit papers to the journal.
Getting the Most from Pi Sigma Alpha Chapters: Exploring the Chapter Activity Grant Program and its Multiplier Effects
Authors: Alexander Robert M.
Published: June 2009

The political science honor society, Pi Sigma Alpha, has chapters in nearly 700 institutions across the United States. The organization sponsors many programs that can contribute a great deal to students of political science; however, many students are unaware of these opportunities. This article encourages chapter advisors to make use of these programs. My chapter's experience suggests many benefits can occur to those who take advantage of the opportunities presented through Pi Sigma Alpha.
President George W. Bush and His War Cabinet
Authors: Pfiffner James P.
Published: June 2009

George W. Bush certainly did not expect to be a war president. In his private sector career and as Governor of Texas he had seldom traveled abroad, and he did not demonstrate much interest in international affairs. In his campaign for the presidency he expressed skepticism about foreign entanglements and a disdain for “nation building.” Yet events conspired to make war the central concern of his presidency; after the terrorist attack on the United States in September 2001, Bush saw the war on terrorism as the primary mission of his presidency. “I'm here for a reason, and this [the war on terrorism] is going to be how we're to be judged.”1 Soon thereafter he decided that the U.S. should conduct a campaign for regime change in Iraq, by military means, if necessary.
“WAVING AMOUCHOIR À LAWILKES”: HUME, RADICALISM AND THENORTH BRITON
Authors: DEW BEN
Published: June 2009

This article examines the use of David Hume's political writing by the extra-parliamentary opposition writers of the 1760s and early 1770s. The disturbances surrounding the publication ofNorth Briton45 and Wilkes's abortive attempts to become MP for Middlesex attracted a level of public support which was remarkable for its size, social diversity and ideological coherence. Hume, as is well known, reacted angrily to this growth in popular politics, condemning both the “mobs” that swept through London in the latter part of the decade and the Ministry's failure to deal with them. However, while Hume may have been highly critical of the Wilkites, the Wilkites frequently used ideas and quotations from the Scotsman's work in their anti-Ministerial polemics. My discussion traces the various ways in which Hume was employed in Wilkite political discourse, and aims to establish the significance of these appropriations for our understanding both of Hume's later life and of the radical politics of the period.
THE ASSUMPTION BY MAN OF HIS ORIGINAL FRACTURING: MARCEL GAUCHET, GLADYS SWAIN, AND THE HISTORY OF THE SELF
Authors: MOYN SAMUEL
Published: June 2009

This essay reconstructs conceptually and situates historically contemporary French philosopher Marcel Gauchet's theory of the origins and development of modern selfhood. It argues that his history of the self as the interiorization of constitutive alienation, and of the history of self-consciousness as the progressive recognition of this alienation, originated out of a unique combination of historical factors—the radical politics of May 1968, the rise of the antipsychiatry movement, and (perhaps most surprisingly) the new psychoanalysis of Jacques Lacan. The essay considers Gauchet's study, together with his partner Gladys Swain, of the foundations of psychiatry, and investigates the connections of their narrative of origins to Michel Foucault's work. The essay concludes by turning to Gauchet's more recent contributions and considering the implications of his history of the self for Anglo-American scholarship.
THE CULTURE OF VIENNESE SCIENCE AND THE RIDDLE OF AUSTRIAN LIBERALISM
Authors: HACOHEN MALACHI HAIM
Published: June 2009

Vienna's scientific culture has long attracted historians' attention. Impressive though the scientific accomplishments of Viennese scientists were, and recognized by numerous Nobel prizes, they alone do not account for the historians' interest. Rather, Vienna's culture of science was imbedded in broader humanistic visions and invested in political and educational projects of major historical significance. Viennese philosophy placed humanity's hopes in science and articulated its historical ramifications to the public, drawing out the political implications of competing scientific methodologies and tying them to dramatic historical events. This philosophy of science still reverberates nowadays in debates on liberty, markets, and government that quickly reveal their underpinning in the methodology of science. Vienna's scientific culture, it seems, has never ceased to capture the imagination, far beyond Austria.
TANGLED LOOPS: THEORY, HISTORY, AND THE HUMAN SCIENCES IN MODERN AMERICA
Authors: ISAAC JOEL
Published: June 2009

During the first two decades of the Cold War, a new kind of academic figure became prominent in American public life: the credentialed social scientist or expert in the sciences of administration who was also, to use the parlance of the time, a “man of affairs.” Some were academic high-fliers conscripted into government roles in which their intellectual and organizational talents could be exploited. McGeorge Bundy, Walt Rostow, and Robert McNamara are the archetypes of such persons. An overlapping group of scholars became policymakers and political advisers on issues ranging from social welfare provision to nation-building in emerging postcolonial states. Many of these men—and almost without exception they were men—were also consummate operators within the patronage system that grew up around American universities after World War II. Postwar leaders of the social and administrative sciences such as Talcott Parsons and Herbert Simon were skilled scientific brokers of just this sort: good “committee men,” grant-getters, proponents of interdisciplinary inquiry, and institution-builders. This hard-nosed, suit-wearing, business-like persona was connected to new, technologically refined forms of social science. No longer sage-like social philosophers or hardscrabble, number-crunching empiricists, academic human scientists portrayed themselves as possessors of tools and programs designed for precision social engineering. Antediluvian “social science” was eschewed in favour of mathematical, behavioural, and systems-based approaches to “human relations” such as operations research, behavioral science, game theory, systems theory, and cognitive science.
Inquiry Learning
Authors: Wichmann Astrid , Leutner Detlev
Published: June 2009

Seventy-nine students from three science classes conducted simulation-based scientific experiments. They received one of three kinds of instructional support in order to encourage scientific reasoning during inquiry learning: (1) basic inquiry support, (2) advanced inquiry support including explanation prompts, or (3) advanced inquiry support including explanation prompts and regulation prompts. Knowledge test as well as application test results show that students with regulation prompts significantly outperformed students with explanation prompts (knowledge: d = 0.65; application: d = 0.80) and students with basic inquiry support only (knowledge: d = 0.57; application: d = 0.83). The results are in line with a theoretical focus on inquiry learning according to which students need specific support with respect to the regulation of scientific reasoning when developing explanations during experimentation activities.
Complex Problem Solving and Worked Examples
Authors: Schmidt-Weigand Florian , Hänze Martin , Wodzinski Rita
Published: June 2009

How can worked examples be enhanced to promote complex problem solving? N = 92 students of the 8th grade attended in pairs to a physics problem. Problem solving was supported by (a) a worked example given as a whole, (b) a worked example presented incrementally (i.e. only one solution step at a time), or (c) a worked example presented incrementally and accompanied by strategic prompts. In groups (b) and (c) students self-regulated when to attend to the next solution step. In group (c) each solution step was preceded by a prompt that suggested strategic learning behavior (e.g. note taking, sketching, communicating with the learning partner, etc.). Prompts and solution steps were given on separate sheets. The study revealed that incremental presentation lead to a better learning experience (higher feeling of competence, lower cognitive load) compared to a conventional presentation of the worked example. However, only if additional strategic learning behavior was prompted, students remembered the solution more correctly and reproduced more solution steps.
Promoting Self-Regulated Learning Through Prompts
Authors: Wirth Joachim
Published: June 2009

Prompts are effective means for promoting self-regulated learning provided that learners show “only” a production deficiency. Prompts can be classified with respect to their content, the condition for their presentation, and their method. In sum, the studies presented in the special issue demonstrate that prompts are effective means if their content aims at activating cognitive strategies or both cognitive as well as metacognitive strategies. Additionally, all studies used the feed forward method to present prompts. However, the studies differ with respect to how the deal with the cyclic character of self-regulated learning and whether they use prompts as the only instructional method or as a supplement to other instructions.
A limits of acceptability approach to model evaluation and uncertainty estimation in flood frequency estimation by continuous simulation: Skalka catchment, Czech Republic
Authors: Blazkova Sarka , Beven Keith
Published: June 2009

In this study continuous simulation flood frequency predictions on the Skalka catchment in the Czech Republic (672 km2, range of altitudes from 460 to 1041 m above sea level), are compared against summary information of rainfall characteristics, the flow duration curve, and the frequency characteristics of flood discharges and snow water equivalent using the generalized likelihood uncertainty estimation limits of acceptability approach outlined by Beven (2006). Limits of acceptability have been defined, prior to running the Monte Carlo model realizations for subcatchment rainfalls, discharges (using rating data) at 5 sites within the catchment, and snow water equivalent in 13 snow zones, 4 of which have observed data. Flood frequency and flow duration data at the outlet of the whole catchment are not used in the evaluation but are used to test the predictions. In order to get sufficient behavioral models to assess adequately the prediction uncertainty it was necessary to refine the model structure, sample the model space more densely, and, in the end, relax the limits of acceptability to allow for a strong realization effect in predicted flood frequencies. We use a procedure of scoring deviations relative to the limits of acceptability to identify the minimum extension of the limits across all criteria to obtain a sample of 4192 parameter sets that were accepted as potentially useful in prediction. Results show that individual model realizations, with the same parameter values, of similar length to the observations can vary significantly in acceptability. Long‐term simulations of 10,000 years for retained models were used to obtain uncertain estimates of the 1000 year peak and associated flood hydrographs required for the assessment of dam safety at the catchment outlet.
Soil organic carbon pools in the northern circumpolar permafrost region
Authors: Tarnocai C. , Canadell J. G. , Schuur E. A. G. , Kuhry P. , Mazhitova G. , Zimov S.
Published: June 2009

The Northern Circumpolar Soil Carbon Database was developed in order to determine carbon pools in soils of the northern circumpolar permafrost region. The area of all soils in the northern permafrost region is approximately 18,782 × 103 km2, or approximately 16% of the global soil area. In the northern permafrost region, organic soils (peatlands) and cryoturbated permafrost‐affected mineral soils have the highest mean soil organic carbon contents (32.2–69.6 kg m−2). Here we report a new estimate of the carbon pools in soils of the northern permafrost region, including deeper layers and pools not accounted for in previous analyses. Carbon pools were estimated to be 191.29 Pg for the 0–30 cm depth, 495.80 Pg for the 0–100 cm depth, and 1024.00 Pg for the 0–300 cm depth. Our estimate for the first meter of soil alone is about double that reported for this region in previous analyses. Carbon pools in layers deeper than 300 cm were estimated to be 407 Pg in yedoma deposits and 241 Pg in deltaic deposits. In total, the northern permafrost region contains approximately 1672 Pg of organic carbon, of which approximately 1466 Pg, or 88%, occurs in perennially frozen soils and deposits. This 1672 Pg of organic carbon would account for approximately 50% of the estimated global belowground organic carbon pool.
Venus Express bistatic radar: High‐elevation anomalous reflectivity
Authors: Simpson Richard A. , Tyler G. Leonard , Häusler Bernd , Mattei Riccardo , Pätzold Martin
Published: June 2009

Magellan (MGN) bistatic radar observations in 1994 confirmed earlier Pioneer Venus reports of unusual Venus surface reflectivity and emissivity at elevations above 6054 km radius. They also revealed that the anomalous values of surface dielectric constant ɛ near Cleopatra Patera included a large imaginary component (ɛ ≈ −i 100) at 13 cm wavelength, consistent with a semiconducting surface material. The MGN observations were conducted using a linearly polarized wave, canted at 45° with respect to the plane of incidence and radiated by the MGN synthetic aperture radar antenna toward the specularly reflecting region of the mean planetary surface. In 2006 similar experiments were conducted using 13 cm circularly polarized transmissions from Venus Express (VEX). The VEX signal‐to‐noise ratio (SNR) was lower than that of MGN, but elevated ∣ɛ∣ has been inferred broadly over Maxwell Montes. A quasi‐specular echo was detected near Cleopatra but with insufficient SNR to address the question of conductivity. An early failure of the VEX 13 cm radio system precludes further measurements with VEX.
Impact of manipulated drought and heavy rainfall events on peat mineralization processes and source‐sink functions of an acidic fen
Authors: Reiche Marco , Hädrich Anke , Lischeid Gunnar , Küsel Kirsten
Published: June 2009

Climate change models predict changes in precipitation patterns over the next several decades for northern temperate regions. Resulting fluctuations of the water level may drastically affect the source‐sink functions of peatlands. Here, we manipulated the water table level in an acidic, minerotrophic fen using drying and rewetting experiments to simulate summer drought and heavy rainfalls to estimate changes in peat decomposition and source‐sink functions. We found that carbon dioxide (CO2) formation rates and exoenzymatic activities increased in the most active surface layer during the initial water table drawdown; however, extreme drying did not further increase these activities. Activity stimulated in deeper oxygenated peat layers did not substantially contribute to CO2 emissions. Additionally, no phenol oxidase activity was determined. Rewetting of peat after drying did not lead to a CO2 flush like in mineral soils. Water table manipulations yielded a higher availability of nitrate, ferric iron, and sulfate and prolonged the onset of methane formation. Sulfate was exported to a nearby stream. We concluded that the increasing frequency of extreme weather conditions like summer droughts and heavy rainfalls might not affect carbon storage but instead strengthen the sink function for nitrate and ferrous iron and the source function for sulfate in peatlands.
Stream‐aquifer interactions and hyporheic exchange in gaining and losing sinuous streams
Authors: Cardenas M. Bayani
Published: June 2009

The irregular planform morphology of rivers leads to formation of hyporheic zones along its banks. This study investigates how hyporheic exchange in stream banks, whose planform is idealized as sinusoidal, is affected by net gains from and net losses of water to the adjacent aquifer. These effects are studied via numerical modeling of groundwater flow adjacent to sinuous channels across a broad range of sinuosity and gain/loss magnitude. Hyporheic zone areas and fluxes both decrease exponentially with increasing magnitude of net gain or loss relative to the case where the stream has no net flux of water (neutral). Residence time through the hyporheic zone also decreases with gain/loss magnitude. The hyporheic zones become constrained near the apex of bends, indicating that these areas could be hot spots for mixing and biogeochemical processing. Hyporheic zones in channels with smaller sinuosity are more prone to hyporheic flux and area reduction while very sinuous channels are able to maintain a hyporheic zone even under largely losing or gaining conditions. Equations fitted to the suite of simulation results allow for prediction of hyporheic flux, area, and residence time on the basis of aquifer hydraulic conductivity, channel sinuosity, and the ratio of along‐valley and across‐valley mean head gradients.
Effect of anomalous warming in the central Pacific on the Australian monsoon
Authors: Taschetto A. S. , Ummenhofer C. C. , Sen Gupta A. , England M. H.
Published: June 2009

The influence of sea surface temperature (SST) anomalies in the central Pacific Ocean on rainfall variability over Australia is investigated using observations and idealized simulations from an atmospheric general circulation model. We show that the SST warming centered at 180°W is associated with increased monsoon precipitation over northern Australia from January to February and a decrease in December and March over the same region, leading to a shorter and more intense monsoon period. In recent years SST anomalies commonly associated with El Niño events have often exhibited a peak signature in the central, not eastern, Pacific. These so‐called El Niño Modoki events are shown here to result in a markedly shorter and more intense Australian monsoon season.
REDD1, an inhibitor of mTOR signalling, is regulated by the CUL4A–DDB1 ubiquitin ligase
Authors: Katiyar Samiksha , Liu Enbo , Knutzen Christine A , Lang Elizabeth S , Lombardo Christian R , Sankar Sabita , Toth Julia I , Petroski Matthew D , Ronai Ze'ev , Chiang Gary G
Published: June 2009

The cellular response to hypoxia involves several signalling pathways that mediate adaptation and survival. REDD1 (regulated in development and DNA damage responses 1), a hypoxia‐inducible factor‐1 target gene, has a crucial role in inhibiting mammalian target of rapamycin complex 1 (mTORC1) signalling during hypoxic stress. However, little is known about the signalling pathways and post‐translational modifications that regulate REDD1 function. Here, we show that REDD1 is subject to ubiquitin‐mediated degradation mediated by the CUL4A–DDB1–ROC1–β‐TRCP E3 ligase complex and through the activity of glycogen synthase kinase 3β. Furthermore, REDD1 degradation is crucially required for the restoration of mTOR signalling as cells recover from hypoxic stress. Our findings define a mechanism underlying REDD1 degradation and its importance for regulating mTOR signalling.
The mechanism of the interstellar isomerization reaction HOC+→HCO+ catalyzed by H2: New Insights from the reaction electronic flux
Authors: Vogt-Geisse Stefan , Toro-Labbé Alejandro
Published: June 2009

A theoretical study of the mechanism of the isomerization reaction HOC+→HCO+ is presented. The mechanism was studied in terms of reaction force, chemical potential, reaction electronic flux (REF), and bond orders. It has been found that the evolution of changes in REF along the intrinsic reaction coordinate can be explained in terms of bond orders. The energetic lowering of the hydrogen assisted (catalyzed) reaction has been identified as being due to the stabilization of the H3+ transition state complex and the stepwise bond dissociation and formation of the H–O and H–C bonds, respectively.
Optical transport of semiconductor nanowires on silicon nitride waveguides
Authors: Néel D. , Gétin S. , Ferret P. , Rosina M. , Fedeli J. M. , Hellesø O. G.
Published: June 2009

We investigate the behavior of silicon and ZnO nanowires in the evanescent field on the surface of a silicon nitride waveguide. The nanowires in aqueous solution are attracted to the waveguide by the gradient force and then propelled along the waveguide by the radiation pressure. Observed experimental velocities are higher for silicon nanowires than for ZnO nanowires, with relatively large variations for both kinds of nanowires. Simulations with the finite element method show that the forces on the nanowires are very dependent on their geometrical parameters and refractive index, which explains the observed variations.
Co layer fragmentation effect on magnetoresistive and structural properties of nanogranular Co/Cu multilayers
Authors: Spizzo F. , Ferrero C. , Mazuelas A. , Albertini F. , Casoli F. , Nasi L. , Ronconi F. , Metzger T. H.
Published: June 2009

We deposited nanogranular Co/Cu multilayers made of thin fragmented Co layers separated by thicker Cu layers to study how the structure and the microstructure of magnetic nanogranular samples change as the average particle size is reduced and how these changes affect the giant magnetoresistive response of the samples. Indeed, thanks to the vertical periodicity of the structure, namely, to the fact that Co/Cu interfaces display an ordered stacking and are not randomly distributed within the samples as in conventional granular materials, their self-correlation and cross correlation can be investigated. In this way, the characteristic length scale of the Co/Cu interfacial roughness that is strictly related to the giant magnetoresistive response of the samples and the universality class of the growth mechanism that affects the systems structure can be both accessed. The Co/Cu nanogranular multilayers were characterized using different x–ray techniques, from specular reflectivity, which allows to probe the multilayer development in the vertical direction, to grazing incidence small angle diffuse scattering, which provides information on the self-correlation and cross correlation of the Co/Cu interfaces. Furthermore, diffraction measurements indicate that the degree of structural disorder increases by decreasing the thickness of the Co layers. Magnetoresistive and magnetization measurements are as well presented and discussed with the results of the structural characterization.
Stripe domain structure in epitaxial (001) BiFeO3 thin films on orthorhombic TbScO3 substrate
Authors: Folkman C. M. , Baek S. H. , Jang H. W. , Eom C. B. , Nelson C. T. , Pan X. Q. , Li Y. L. , Chen L. Q. , Kumar A. , Gopalan V. , Streiffer S. K.
Published: June 2009

We have analyzed the ferroelastic and ferroelectric domain structure of high crystalline quality (001) BiFeO3 films on orthorhombic (110) TbScO3 substrates. Two domains were present in stripes separated by (010) vertical boundaries, with spontaneous polarizations in adjacent domains rotated by 109°. The striped morphology was caused by nucleation of only two ferroelastic domains on the low symmetry GdFeO3-type substrate. Domain engineering through substrate symmetry is an important finding for rhombohedral ferroelectric epitaxial thin films. The stripe pattern with vertical walls may be useful for extracting domain wall contributions to magnetism and electrical transport properties of BiFeO3 materials.
Structural and electrical properties of thin SrHfON films for high-k gate dielectric
Authors: Feng Li-ping , Liu Zheng-tang
Published: June 2009

Thin SrHfON films were prepared by reactive cosputtering of Hf–O and Sr–O targets in Ar/N2 ambient environment. Structural and electrical properties of the as-deposited and annealed SrHfON films used as gate dielectrics have been investigated. The SrHfON films have crystallization temperature higher than 900 °C. After annealing at 900 °C, high dielectric constant of 19.3 and effective work function of 4.13 eV was obtained for the SrHfON films. It is worth mentioning that the leakage current density of Au/SrHfON/IL SiOx gate stack is two orders of magnitude lower than that of polycrystalline silicon/HfO2 structure.
Morphology of the Cu2O surface oxide phase formed on Cu(100) at high temperature
Authors: Devlin C. L. H. , Sato Y. , Chiang S.
Published: June 2009

We have observed the nucleation and growth of the Cu2O surface oxide on a Cu(100) surface at 870 K using low energy electron microscopy. Nucleating on a surface exhibiting the (2×22)R45°-O overlayer, this phase caused the overall step morphology to change from long, mostly straight narrow-terraced step bunches to broad, deeply curved terraces with more highly bunched steps. Using x-ray photoelectron spectroscopy, we have measured an upper bound of 2.6 ML (monolayer) for the surface oxygen coverage at which we observed this oxide phase. The lattice constant of the observed oxide phase matches that of the (111) face of Cu2O. We postulate that the oxide does not form epitaxially on this surface at this temperature due to interactions with the centered rectangular phase of oxygen, which provides a nearly hexagonal template for the Cu2O(111) hexagonal structure.
Growth behavior of nanocrystalline diamond films on ultrananocrystalline diamond nuclei: The transmission electron microscopy studies
Authors: Wang Chuan-Sheng , Chen Huang-Chin , Cheng Hsiu-Fung , Lin I-Nan
Published: June 2009

Micron-crystalline diamond (MCD) films with a unique microstructure were synthesized using a modified nucleation and growth process, in which a thin layer of ultrananocrystalline diamond (UNCD) was used as nucleation layer for growing diamond films in H2-plasma. Thus obtained (MCD)UNCD diamond films consist of nanosized diamond clusters (∼10 nm in size) surrounding the large diamond grains (∼300 nm in size), exhibiting better electron field emission (EFE) properties than the conventional diamond materials with faceted grains. The EFE of these (MCD)UNCD films can be turned on at E0=11.1 V/μm, achieving EFE current density as large as (Je)=0.7 mA/cm2 at 25 V/μm applied field, which can be attributed to the presence of large proportion of UNCD grains lying in between the MCD grains, forming an electron conduction path and thus facilitating the EFE process. Transmission electron microscopy examinations reveal that such a unique microstructure was formed by agglomeration and coalescence of the nanosized UNCD grains.
Electric and magnetic responses in the multiple-split ring resonators by electric excitation
Authors: Chen Chia-Yun , Yen Ta-Jen
Published: June 2009

We experimentally demonstrate both the electric and magnetic responses from the multiple-split-ring resonators (MSRRs) via normal reflectance measurements. All the fabricated MSRRs exhibit electric resonances under electric couplings but the magnetic resonances are only excited in MSRRs with odd numbers of splits from the asymmetrically electric couplings. Furthermore, the dependence of split numbers on the resonant positions and strengths is also investigated. In addition, the coupling mechanism of correlated resonances in the MSRRs can be well elucidated by the concept of standing-wave plasmonic resonances. Such scalable MSRRs present the tailored electromagnetic responses at desired frequencies, paving ways toward integrated nanophotonic applications.
Estimation of the control parameter from symbolic sequences: Unimodal maps with variable critical point
Authors: Arroyo David , Alvarez Gonzalo , Amigó José María
Published: June 2009

The work described in this paper can be interpreted as an application of the order patterns of symbolic dynamics when dealing with unimodal maps. Specifically, it is shown how Gray codes can be used to estimate the probability distribution functions (PDFs) of the order patterns of unimodal maps whose dynamics is controlled by an external parameter. Furthermore, these PDFs depend on the value of the external parameter, which eventually provides a handle to estimate the parameter value from symbolic sequences (in form of Gray codes), even when the critical point depends on the parameter.
Electronic structure and molecular dynamics of breaking the RO–NO2 bond
Authors: Schweigert Igor V. , Dunlap Brett I.
Published: June 2009

Decomposition of energetic molecules such as pentaerythritol tetranitrate is accompanied by extensive changes in their electronic configuration and thus is challenging for ab initio Born–Oppenheimer molecular dynamics simulations. The performance of single-determinant methods (in particular, density-functional theory) is validated on electronic structure and molecular dynamics simulations of RO–NO2 bond dissociation in a smaller nitric ester, ethyl nitrate. Accurate description of dissociating molecule requires using unrestricted, spin-symmetry-broken orbitals. However, the iterative self-consistent field procedure is prone to convergence failures in the bond-breaking region even if robust convergence algorithms are employed. As a result, molecular dynamics simulations of unimolecular decomposition need to be closely monitored and manually restarted to ensure seamless transition from the closed-shell to open-shell configuration.
On the dynamical stability and metallic behavior of YH3 under pressure
Authors: de Almeida J. S. , Kim D. Y. , Ortiz C. , Klintenberg M. , Ahuja R.
Published: June 2009

We report on the behavior of structural and electronic properties of yttrium trihydride under pressure using first principles calculations. We show that YH3 undergoes a structural transformation and its high pressure phase is dynamically stable under pressure since the peak at the imaginary frequencies of the phonon density of states, which account for the structural instability disappears at high pressure. Additionally, our GW calculations indicate a metallization of the high pressure cubic phase of YH3.
Sensitivity of Ag/Al interface specific resistances to interfacial intermixing
Authors: Sharma A. , Theodoropoulou N. , Wang Shuai , Xia Ke , Pratt W. P. , Bass J.
Published: June 2009

We have measured a Ag/Al interface specific resistance, 2ARAg/Al(111)=1.4 fΩ m2, that is twice that predicted for a perfect interface, 50% larger than for a 2 ML 50%–50% alloy, and even larger than our newly predicted 1.3 fΩ m2 for a 4 ML 50%–50% alloy. Such a large value of 2ARAg/Al(111) confirms a predicted sensitivity to interfacial disorder and suggests an interface ≥4 ML thick. From our calculations, a predicted anisotropy ratio, 2ARAg/Al(001)/2ARAg/Al(111), of more than 4 for a perfect interface should be reduced to less than 2 for a 4 ML interface, making it harder to detect any such anisotropy.
X-ray diffraction, Raman, and photoacoustic studies of ZnTe nanocrystals
Authors: Ersching K. , Campos C. E. M. , de Lima J. C. , Grandi T. A. , Souza S. M. , da Silva D. L. , Pizani P. S.
Published: June 2009

Nanocrystalline ZnTe was prepared by mechanical alloying. X-ray diffraction (XRD), energy dispersive spectroscopy, Raman spectroscopy, and photoacoustic absorption spectroscopy techniques were used to study the structural, chemical, optical, and thermal properties of the as-milled powder. An annealing of the mechanical alloyed sample at 590 °C for 6 h was done to investigate the optical properties in a defect-free sample (close to bulk form). The main crystalline phase formed was the zinc-blende ZnTe, but residual trigonal tellurium and hexagonal ZnO phases were also observed for both as-milled and annealed samples. The structural parameters, phase fractions, average crystallite sizes, and microstrains of all crystalline phases were obtained from Rietveld analyses of the X-ray patterns. Raman results corroborate the XRD results, showing the longitudinal optical phonons of ZnTe (even at third order) and those modes of trigonal Te. Nonradiative surface recombination and thermal bending heat transfer mechanisms were proposed from photoacoustic analysis. An increase in effective thermal diffusivity coefficient was observed after annealing and the carrier diffusion coefficient, the surface recombination velocity, and the recombination time parameters remained the same.
Investigation of coupled air-water turbulent boundary layers using direct numerical simulations
Authors: Liu Song , Kermani Alireza , Shen Lian , Yue Dick K. P.
Published: June 2009

We perform direct numerical simulation of air and water turbulence in a Couette flow. The air-water interface is kept flat, and the coupling between the two fluids is through continuity of velocity and shear stress at the interface. True air-to-water ratios of density and viscosity are used in the simulation to illustrate features of air-water coupled boundary layers. Our analysis of statistics of the velocity, vorticity, and turbulent kinetic energy budget confirms known features, notably the similarity of the airside interface boundary layer to wall boundary layer. Our study obtains new insights on the characteristics of the waterside motions. Compared to the airside, waterside turbulence structures are more persistent and larger in scale, which dominate the interface signatures. The interface boundary layer on the waterside possesses unique features that are intermediate between but qualitatively different from wall boundary layer and free-slip surface layer. On the waterside, as the interface is approached, enstrophy and viscous dissipation first decrease together, with higher turbulence mixing and production than the airside, and then increase sharply in response to airside stress fluctuations. The waterside turbulence is characterized by interface-connected, hairpin, and quasistreamwise vortices that are closely related to each other in their evolutions. Conditional average using a variable-interval space averaging approach illustrates the strong air-water coupling in splat, hairpin vortex, and quasistreamwise vortex events. It is found that waterside velocity gradients are amplified significantly across the interface, with the presence of horizontal jets at splat and quasistreamwise vortex regions. We also study the transport of passive scalars near the air-water coupled boundary layers. As expected, vertical advection associated with coupling air-water coherent structures greatly enhances interfacial transfer of scalars. By considering scalars of different diffusivity and solubility values, we investigate the partition of interfacial transfer between the waterside and airside. We illustrate statistical characteristics of gaslike and heatlike scalars and perform detailed analysis of the scalar variance budget for these to reveal unique features that are substantially different from wall boundary layer or free-slip surface layer.
Slow photoelectron velocity-map imaging spectroscopy of the vinoxide anion
Authors: Yacovitch Tara I. , Garand Etienne , Neumark Daniel M.
Published: June 2009

High resolution photoelectron spectra of the vinoxide anion are obtained by slow electron velocity-map imaging. Transitions between the anion X̃ A1′ ground electronic state and the radical X̃ A2″ and Ã A2′ states are observed. This experiment yields a precise value of 1.8250±0.0012 eV for the adiabatic electron affinity and 0.996±0.003 eV for the Ã-X̃ term energy of the vinoxy radical. Franck–Condon simulations of the X̃ A2″←X̃ A1′ transition are performed at varying levels of approximation. Full treatment with Duschinsky rotation is necessary to reproduce experimental results. Comparison of the experimental and simulated spectra leads to the assignment of previously unresolved transitions, notably between levels of a″ symmetry.
Propagation of chirped laser pulses in a plasma channel
Authors: Jha Pallavi , Malviya Amita , Upadhyay Ajay K.
Published: June 2009

Propagation of an initially chirped, Gaussian laser pulse in a preformed parabolic plasma channel is analyzed. A variational technique is used to obtain equations describing the evolution of the phase shift and laser spot size. The effect of initial chirp on the laser pulse length and intensity of a matched laser beam propagating in a plasma channel has been analyzed. The effective pulse length and chirp parameter of the laser pulse due to its interaction with plasma have been obtained and graphically depicted. The resultant variation in laser frequency across the laser pulse is discussed.
The role of optical rectification in the generation of terahertz radiation from GaBiAs
Authors: Radhanpura K. , Hargreaves S. , Lewis R. A. , Henini M.
Published: June 2009

We report on a detailed study of the emission of terahertz-frequency electromagnetic radiation from layers of GaBiyAs1−y (0≤y<0.04) grown by molecular beam epitaxy on (311)B and (001) GaAs substrates. We measure two orthogonally polarized components of the terahertz radiation emitted under excitation by ultrashort near-infrared laser pulses in both transmission and reflection geometries as a function of the crystal rotation about its surface normal as well as the effect of in-plane magnetic field and pump fluence on the terahertz emission. We conclude that the principal mechanism for terahertz generation is via optical rectification rather than transient currents.
Predicted bound states and microwave spectrum of N2–He van der Waals complexes
Authors: Li Hui , Le Roy Robert J. , McCourt Frederick R. W.
Published: June 2009

Numerical calculations show that four modern potential energy surfaces for N2–He all support 18 bound intermolecular states for the homonuclear isotopologues N14,142–H4e and N15,152–H4e, and 12 (or 13, for one surface) truly bound states for N14,152–He. This contradicts a recent statement [Patel et al., J. Chem. Phys. 119, 909 (2003)] that one of these surfaces supports no bound states, and it yields predictions for 27 allowed pure rotational transitions among the truly bound states of the homonuclear isotopologues of this complex.
Temperature dependence of reactions involving electron transfer in K(np)/C2Cl4 collisions
Authors: Cannon M. , Wang C. H. , Liu Y. , Dunning F. B. , Steill J. D.
Published: June 2009

Electron transfer in K(np)–C2Cl4 collisions, which leads to formation of both Cl− and C2Cl4− anions, is investigated as a function of target temperature over the range of 300–650 K. Measurements at high n (n∼30) show that the likelihood of Cl− production increases rapidly with temperature indicating the presence of a dissociation barrier. The data yield an activation energy of ∼0.1 eV. A broad distribution of product C2Cl4− lifetimes is observed that extends from microseconds to milliseconds, this distribution moving toward shorter lifetimes as the target temperature is increased. The measured lifetimes are consistent with the predictions of quasiequilibrium theory. Studies at low n (n∼14) show a substantial fraction of the product K+–Cl− and K+–C2Cl4− ion pairs is electrostatically bound leading to creation of heavy-Rydberg ion-pair states. Variations in target temperature lead to changes in kinetic energy of relative motion of the reactants that can result in marked changes in the fraction of ion pairs that is bound, especially at low Rydberg atom velocities. In the case of bound K+–C2Cl4− ion pairs a few percent subsequently dissociate by the conversion of internal energy in the anion into translational energy of the ion pair. Analysis of the data points to a mean energy conversion of ∼60–90 meV, much less than the available excess energy of reaction, ∼0.7 eV.