bluuebunny/crossref_metadata_2025 huggingface dataset:
Innovative einseitige Verankerung von Sandwichelementen
Authors: Ungermann Dieter , Lübke Sebastian
Published: December 2012

Die Tragfähigkeit einseitiger Befestigungen von Sandwichelementen ist derzeit weder bauaufsichtlich geregelt noch existieren Berechnungsmodelle. Die Verankerung von Sandwichelementen oder die Einleitung äußerer Lasten an nur einem Deckblech wurde im Rahmen eines Forschungsvorhabens systematisch untersucht und weiterentwickelt. Im Ergebnis konnten die wesentlichen Phänomene bei einer einseitigen Lasteinleitung durch experimentelle und numerische Untersuchungen aufgedeckt werden und mögliche Verankerungssysteme auf experimenteller Basis entwickelt werden.

Innovative fastening of sandwich panels in one face sheet only. One sided fastenings of sandwich panels at one face sheet only are not yet covered by technical approvals. In the context of a research project possible fastening technologies for one face sheet only have been systematically examined und developed. As a result the main difficulties with such fastenings could be identified, based on experimental and numerical investigations, and possible fastening systems could be developed based on testing.
Bahn frei für die Architektur – Approximation von Freiform‐Flächen durch abwickelbare Streifen
Authors: Mehrtens Peter , Schmieder Markus
Published: December 2012

Blickfang der zeitgenössischen Architektur ist seit mehreren Jahren die so genannte Freiform‐Architektur. Diese überzeugend zu planen ist viel mehr als eine Frage der Form – erst mit einer sauberen Fügung der Bauteile und einer konstruktionsbewussten Ausarbeitung der Einzelteile wird diese auch im Detail zum Erfolg. Im Idealfall sind der materialgerechten Formbarkeit durch innovative Technik fast keine Grenzen gesetzt.

Rolling out of architectural design intent – Approximation of freeform surfaces by developable strips. For a number of years the eye catcher of contemporary architecture has been so called Freeform‐Architecture. To design such in a convincing manner, it takes far more than the mere shape – only when the composition of the whole and the parts takes place in a construction aware manner, the project will be successful. Ideally innovative technology can almost remove the geometric constraints when forming materials by appropriate processes.
Einfluss von Inhomogenitäten im Kernwerkstoff von Sandwichelementen auf die Tragfähigkeit
Authors: Hassinen Paavo , Misiek Thomas
Published: December 2012

Der Einfluss typischer struktureller Imperfektionen und Inhomogenitäten im Schaumkern auf die elastische Bettung der Deckschichten eines Sandwichelementes wird vorgestellt und diskutiert. Hierzu wurden sowohl theoretische als auch numerische Untersuchungen herangezogen bzw. durchgeführt. Darauf basierend werden Erweiterungen für ein Bemessungsmodell für die Tragfähigkeitsermittlung abgeleitet. Das Bemessungsmodell sowie ein abschließendes Fazit werden präsentiert.

Influence of structural imperfections and inhomogeneities of the core material of sandwich panels on load‐bearing capacity. The paper presents and discusses the effects of the typical structural imperfections and inhomogeneities of the core on the elastic foundation. Both theoretical and numerical investigations were done to study their effect on the elastic critical buckling stress and on the compressive strength of the plane cross‐section parts. Based on these investigations, extensions for the design model for the calculation of the load‐bearing capacity were derived. The model with conclusive remarks is given in the paper.
Photovoltaikelemente auf bestehenden Sandwichdachelementen – Einfaches Bemessungskonzept für Punktlasten
Authors: Naujoks Bernd , Zapfe Cedrik
Published: December 2012

Es werden zunehmend Photovoltaikelemente auf Sandwich‐Dachelementen installiert. Diese zusätzlichen Punktlasten sind durch die geltende Norm EN 14509 nicht abgedeckt. Deshalb besteht ein großer Bedarf nach einem einheitlichen Bemessungskonzept. Basierend auf Versuchsreihen wird ein Vorschlag für ein einfaches Verfahren zur Ermittlung der Lastverteilung und Spannungen im Sandwichelement mit profilierter äußerer Deckschicht vorgestellt und zu beachtende Konstruktionsdetails beschrieben.

Installation of photovoltaic‐elements on sandwich roof panels ‐ Construction details and design model. A large number of photovoltaic modules have been subsequently mounted on existing roofs and new structures for several years. Point loads are not covered by the existing standard EN 14509. For this reason, there is a great need for a basic design concept that is covered by a simple, documented model and test series. Construction details will be shown also.
Robust hard decision combination scheme based on Kullback–Leibler divergence for cooperative spectrum sensing in cognitive radio
Authors: Vu‐Van Hiep , Koo Insoo
Published: December 2012

Cognitive radio (CR) network is a new, emerging research area because it has the ability to improve spectrum utilization by detecting and using vacant channels that are unused by licensed users. Reliable detection of the licensed user signal is a prerequisite for CR network to avoid interference to the licensed user. Cooperative spectrum sensing (CSS) is able to offer better sensing performance in comparison with individual sensing. However, CSS is vulnerable to attack from malicious users who falsify sensing data. In this paper, we propose a robust hard decision combination rule based on the Kullback–Leibler divergence (KL divergence) for CSS. The proposed scheme can achieve sensing performance similar to that of the optimal hard decision combination rule, the Chair–Varshney rule, while not requiring information on the signal‐to‐noise ratio. Furthermore, the proposed scheme can provide secure CSS against some common types of malicious users without any user identification step. Our simulation results prove the effectiveness of the proposed scheme. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
Curriculum‐based learning communities centered within a discipline
Authors: Zrull Mark C. , Rocheleau Courtney A. , Smith M. Corinne , Bergman Shawn M.
Published: December 2012

Curriculum‐based learning communities centered within a discipline can take on many forms. Through the use of specific institutional examples, this chapter examines three models requiring minimal to more complex coordination.
Creating learning communities in the classroom
Authors: Saville Bryan K. , Lawrence Natalie Kerr , Jakobsen Krisztina V.
Published: December 2012

This chapter describes three approaches to creating classroom‐based learning communities: interteaching; team‐based learning; and cooperative learning in large, lecture‐based courses.
Using student‐based organizations within a discipline as a vehicle to create learning communities
Authors: Hall Michael D.
Published: December 2012

Student‐based organizations offer another approach to promote learning communities above and beyond particular curricular or classroom approaches. Not only can they create connections among students with shared disciplinary or professional interests on a single campus, but they also offer the possibility for creating connections to larger communities beyond an institution.
The evolution of learning communities: A retrospective
Authors: Matthews Roberta S. , Smith Barbara Leigh , MacGregor Jean
Published: December 2012

In 1990, the current authors with Faith Gabelnick authored their first book about learning community initiatives, which has gone on to become one of the most widely cited volumes in the New Directions for Teaching and Learning series. In this chapter, they reflect on the developments and evolution of learning communities since that time, including their reflections on each chapter from the present volume.
RNAs of the human chromosome 15q11‐q13 imprinted region
Authors: Chamberlain Stormy J.
Published: December 2012

The human chromosome 15q11‐q13 region hosts a wide variety of coding and noncoding RNAs, and is also the site of nearly every imaginable type of RNA processing. To deepen the intrigue, the transcripts in the human chromosome 15q11‐q13 region are subject to regulation by genomic imprinting, and some of these transcripts are imprinted in a tissue‐specific manner. As the region is critically important for three human neurogenetic disorders, Angelman syndrome, Prader‐Willi syndrome, and 15q duplication syndrome, there is intense interest in understanding the types of RNA and RNA processing that occurs among the imprinted genes. This review summarizes what is known about the various RNAs within the imprinted domain, including a novel type of RNA that was only very recently identified. WIREs RNA 2013, 4:155–166. doi: 10.1002/wrna.1150

This article is categorized under:

RNA in Disease and Development > RNA in Disease

RNA in Disease and Development > RNA in Development
One‐Stage Hepatectomy Following Portal Vein Embolization for Colorectal Liver Metastasis
Authors: Yamashita Suguru , Hasegawa Kiyoshi , Takahashi Michiro , Inoue Yosuke , Sakamoto Yoshihiro , Aoki Taku , Sugawara Yasuhiko , Kokudo Norihiro
Published: December 2012

Background

Although portal vein embolization (PVE) has been applied for surgical resection of colorectal liver metastases (CLM), the clinical usefulness of liver surgery following PVE for CLM remains unknown.

Methods

A total of 115 patients were evaluated retrospectively. Among them, 49 underwent one‐stage hepatectomy following PVE (PVE group). The remaining 66 patients underwent at least hemihepatectomy without PVE (non‐PVE group). This analysis compared the short‐ and long‐term outcomes between the PVE and non‐PVE groups.

Results

There were no deaths in either group. Using the Clavien–Dindo classification, the rates of postoperative morbidity ≥ grade 1 were 34.7 % in the PVE group and 25.0 % in the non‐PVE group (p = 0.26). The 3‐year overall survival rates were 54.6 and 64.5 % in the PVE and non‐PVE groups, respectively (p = 0.89). The multivariate analysis the variable performance/nonperformance of PVE was not detected as an independent predictor of poor survival.

Conclusions

Our one‐stage hepatectomy policy of using PVE provides acceptable morbidity and favorable long‐term outcomes.
Letters from the Soviet ‘Paradise’: The Image of Russia among the Western Armenian Diaspora
Authors: Shahnazarian Nona
Published: December 2012

The paper deals with the complicated relationships between the Western Armenian Diaspora and Russians. These relations are mediated by the ambiguous attitude of Diaspora to the Eastern Armenians. The study examines two social contexts, the Soviet and Post-Soviet eras. To elaborate the topic the author draws from letters, jokes, and anecdotes taken from different kinds of international interlocutors, ranging from scholars to ordinary people.

I argue that the image of Russia is constructed of intertwined discourses of negative and positive meanings. Positive discourses are based around the Russian-(Eastern) Armenians' cultural connections and Russian involvement to the political movement for recognition of the 1915–1923 Armenian Genocide, while negative ones are extracted from (1) the bitter experience of Armenian repatriates to Soviet Armenia (totalitarianism, political reprisals, and harsh social censorship), (2) the low standard of living in the USSR as well as (3) the idiosyncrasies of Russian/Eastern Armenian everyday life in post-Soviet times. So the stereotyped image of Russia is formed at least by three aspects of social life such as political, cultural, and routine. These types of exoticization/stereotyping engender some social distance between the Western Armenian Diaspora and Russians as well as between the Western Armenian Diaspora and post-Soviet Armenians. I conclude that nevertheless a litmus test for the Western Armenian Diaspora attitude to USSR/Russia is the latter's official position regarding the 1915–1923 Armenian Genocide in the Ottoman Empire.
Micromagnetics and magnetomineralogy of ultrafine magnetite inclusions in the Modipe Gabbro
Authors: Muxworthy A. R. , Evans M. E.
Published: December 2012

Iron oxide inclusions in pyroxene crystals from the Modipe Gabbro, Botswana, have been studied to determine their recording fidelity. Hysteresis parameters, first‐order reversal curves, isothermal remanent magnetization acquisition curves, and thermomagnetic data all indicate that the iron oxide occurs as stoichiometric magnetite in the form of single‐domain and/or small pseudo single‐domain particles. Using distributions for the grain shape and nearest‐neighbor spacings determined from optical micrographs as input, a first‐order reversal curve (FORC) diagram was simulated using a numerical micromagnetic model. The simulated FORC diagram was found to closely match the measured FORC distributions. Analysis of the interaction fields in the model found that the standard deviation of the interaction field distribution was 2.7 mT compared to a bulk coercivity of ~20 mT, suggesting that the majority of particles are unlikely to be affected by magnetostatic interactions. Thellier analysis of the samples induced with an initial laboratory thermoremanence yielded near‐perfect behavior. It is suggested that the Modipe Gabbro dated at 2784.0 ± 1.5 (2σ) Ma is potentially an ideal recorder of the geomagnetic field.
Delayed winter warming: A robust decadal response to strong tropical volcanic eruptions?
Authors: Zanchettin Davide , Timmreck Claudia , Bothe Oliver , Lorenz Stephan J. , Hegerl Gabriele , Graf Hans‐F. , Luterbacher Jürg , Jungclaus Johann H.
Published: December 2012

Climate simulations suggest that strong tropical volcanic eruptions (SVEs) induce decadal dynamical responses in the coupled ocean‐atmosphere system, which protract the climate recovery beyond the short‐lived radiative forcing. Here, for the first time, we diagnose the signature of such responses in European seasonal climate reconstructions over the past 500 years. The signature consists of a decadal‐scale positive phase of the winter North Atlantic Oscillation accompanied by winter warming over Europe peaking approximately one decade after a major eruption. The reconstructed delayed winter warming is compatible with formerly suggested mechanisms behind simulated SVE‐driven climate responses, thus corroborating the existence of SVE‐driven decadal climate variability. Historical climate‐state uncertainty may, however, hamper unambiguous statistical and dynamical assessments both for multiple and for individual SVEs.
A unique seasonal pattern in dissolved elemental mercury in the South China Sea, a tropical and monsoon‐dominated marginal sea
Authors: Tseng C. M. , Lamborg C. H. , Hsu S. C.
Published: December 2012

A unique seasonal pattern in dissolved elemental mercury (DEM) was observed in the tropical monsoon‐dominated South China Sea (SCS). The DEM concentration varied seasonally, with a high in summer of 160 ± 40 fM (net evasion 580 ± 120 pmol m−2 d−1, n = 4) and a low in winter of 60 ± 30 fM (net invasion −180 ± 110, n = 4) and showed a positive correlation with sea surface temperature (SST). The elevated DEM concentration in summer appears mainly abiologically driven. In winter, the SCS acts as a sink of atmosphere Hg0 as a result of low SST and high wind of the year, enhanced vertical mixing, and elevated atmospheric gaseous elemental mercury. Annually, the SCS serves as a source of Hg0 to the atmosphere of 300 ± 50 pmol m−2 d−1 (385 ± 64 kmol Hg yr−1, ~2.6% of global emission in ~1% of global ocean area), suggesting high regional Hg pollution impacts from the surrounding Mainland (mostly China).
The influence of subglacial hydrology on the flow of Kamb Ice Stream, West Antarctica
Authors: van der Wel Narelle , Christoffersen Poul , Bougamont Marion
Published: December 2012

Ice streams on the Siple Coast, West Antarctica, have a complex history of flow because their basal motion is governed by time‐varying basal conditions. Although the mechanical interaction between ice and till is well established, very little is known about the potential effect of regionally scaled water transport in a basal water system, which has only recently become apparent. To investigate the combined effect of hydrological and mechanical processes, we developed the Hydrology, Ice and Till model, in which ice flow is coupled to a Coulomb‐plastic till layer and a basal water system consisting of discrete conduits. When the model is applied to Kamb Ice Stream (KIS), results confirm that it is capable of oscillating between fast and stagnant modes of flow. We show that when subglacial conduits are disregarded or do not extend to the grounding line, the oscillatory behavior of the ice stream is governed by the basal thermal regime. When conduits extend to the grounding line, the modelled ice stream oscillation period is increased, peak speeds are reduced, and oscillations may ultimately cease if the volume of water supplied is sufficiently high. Three different hydrological states characterize the behavioral patterns of ice flow and these states are distinguished by conditions at the grounding line. Modelled ice stream velocities were found to oscillate with fast and slow periods typically lasting a few hundred years, although varying according to hydrological activity. Our results indicate that KIS could reactivate this century, given its hydrological setting and ~170 years of stagnation.
Measurement Validity is Fundamentally a Matter of Definition, Not Correlation
Authors: Krause Merton S.
Published: December 2012

Correlations between sets of measurements produced by several measures can be determinative of the validity of these measures only insofar as theories about how these measurements relate in correlation and regression terms are already known to be true. However, scientific theories can only be known to be true insofar as they have already been demonstrated to be true by valid measurements. Therefore, only the nature of a measure that produces the measurements for representing a dimension can justify claims that these measurements are valid for that dimension, and this is ultimately exclusively a matter of the normative definition of that dimension in the science that involves that dimension. Thus, contrary to the presently prevailing theory of construct validity, a measure's measurements themselves logically cannot at all indicate their own validity or invalidity by how they relate to other measures' measurements unless these latter are already known to be valid and the theories represented by all these several measures' measurements are already known to be true. It is only the conformity of a measure to the normative conceptual analysis and so definition of a dimension that can make the measurements it produces valid measurements on that dimension. This makes it essential for each basic science to achieve normative conceptual analyses and definitions for each of the dimensions in terms of which it describes and causally explains its phenomena.
A Model for Ethical Reasoning
Authors: Sternberg Robert J.
Published: December 2012

This article presents a model of ethical reasoning. The article reviews lapses in ethical reasoning and the great costs they have had for society. It presents an eight-step model of ethical reasoning that can be applied to ethical challenges and illustrates its application. It proposes that ethical reasoning can be taught across the curriculum. It further points to a source of frustration in the teaching and application of ethics: ethical drift. Finally it draws conclusions.
TNFRp55 controls regulatory T cell responses in Yersinia‐induced reactive arthritis
Authors: Cargnelutti Ethelina , Arias José L , Valdez Susana R , Rabinovich Gabriel A , Di Genaro María S
Published: December 2012

In addition to its well‐known pro‐inflammatory effects, tumor necrosis factor (TNF) displays anti‐inflammatory activities through mechanisms poorly understood. Previously, we reported the development of severe chronic Yersinia enterocolitica‐induced reactive arthritis (ReA) in mice lacking the TNF receptor (TNFR)p55. As regulatory T (Treg) cells limit chronic inflammation, here we aim to investigate the expansion and function of CD4+CD25+FoxP3+ Treg cells in the ReA animal model. The number of Treg cells as well as the FoxP3 mRNA expression and interleukin (IL)‐10 levels were significantly decreased in joint regional lymph nodes (RLNs) of TNFRp55−/− mice vs wild‐type (WT) mice at the arthritis onset. However, at chronic phase of arthritis, the number of Treg cell in TNFRp55−/− was similar to WT mice. To explore the in vivo function of Treg cells at this chronic phase in WT and TNFRp55‐deficient mice, we adoptively transferred CD4+ T cells from TNFRp55‐deficient mice of day 21, into naïve WT or TNFRp55−/− mice. When knockout mice were used as recipients we observed higher delayed‐type hypersensitivity (DTH) responses and joint inflammation after heat‐killed Yersinia (HKY) stimulation. Accordingly, we found higher levels of IL‐17, interferon (IFN)‐γ, IL‐6, transforming growth factor (TGF)‐β1 and IL‐12/23p40 and lower IL‐10 levels in RLN of paws challenged with HKY in TNFRp55−/− recipient mice. In addition, we found that CD4+ T cells from TNFRp55−/− mice controlled antigen‐specific IL‐12/23(p40) production in recipient WT mice. Our results show that TNFRp55 controls the induction and function of Treg cells through differential regulation of cytokine production, suggesting a novel molecular target for immune intervention in ReA.
Imaging macrophage development and fate in atherosclerosis and myocardial infarction
Authors: Swirski Filip K , Nahrendorf Matthias
Published: December 2012

Macrophages are central regulators of disease progression in both atherosclerosis and myocardial infarction (MI). In atherosclerosis, macrophages are the dominant leukocyte population that influences lesional development. In MI, which is caused by atherosclerosis, macrophages accumulate readily and have important roles in inflammation and healing. Molecular imaging has grown considerably as a field and can reveal biological process at the molecular, cellular and tissue levels. Here, we explore how various imaging modalities, from intravital microscopy in mice to organ‐level imaging in patients, are contributing to our understanding of macrophages and their progenitors in cardiovascular disease.
Towards An Understanding of Identity and Technology in the Workplace
Authors: Stein Mari-Klara , Galliers Robert D , Markus M Lynne
Published: December 2012

Despite the ubiquitous presence of information technology (IT) in the workplace and the continued computerization of all kinds of work practices, investigations into how IT artifacts play a role in professional identity construction remain rare. Existing studies tend to emphasize sense-making and discourses around IT. This study attempts to fill some of this gap by offering an empirical investigation of how IT artifacts play a role in professional identity enactment at a back office of a Big 4 accounting firm. Building on the socio-technical school of thought and the concept of self as storied, the paper offers a complementary perspective to existing views on the role of IT in identity formation. Our findings reveal that IT artifacts become part of professional identity performances by acting as landmarks in individuals’ self-narratives around which the self and others are positioned and a preferred professional identity is enacted. The findings also indicate that different types of preferred selves may be expressed in specific patterns of technology use. As such, our study contributes to a better understanding of professional identity construction, workplace behavior and ongoing use or non-use of IT at work.
Electrical and optical properties of Ta-Si-N thin films deposited by reactive magnetron sputtering
Authors: Oezer D. , Ramírez G. , Rodil S. E. , Sanjinés R.
Published: December 2012

The electrical and optical properties of TaxSiyNz thin films deposited by reactive magnetron sputtering from individual Ta and Si targets were studied in order to investigate the effects of nitrogen and silicon contents on both properties and their correlation to the film microstructure. Three sets of fcc-TaxSiyNz thin films were prepared: sub-stoichiometric TaxSiyN0.44, nearly stoichiometric TaxSiyN0.5, and over-stoichiometric TaxSiyN0.56. The optical properties were investigated by near-normal-incidence reflectivity and ellipsometric measurements in the optical energy range from 0.375 eV to 6.8 eV, while the d.c. electrical resistivity was measured in the van der Pauw configuration from 20 K to 300 K. The optical and electrical measurements were interpreted using the standard Drude-Lorentz model and the so-called grain boundary scattering model, respectively. The electronic properties were closely correlated with the compositional and structural modifications of the TaxSiyNz films due to variations in the stoichiometry of the fcc-TaNz system and the addition of Si atoms. According to the nitrogen and silicon contents, fcc-TaxSiyNz films can exhibit room temperature resistivity values ranging from 102 μΩ cm to about 6 × 104 μΩ cm. The interpretation of the experimental temperature-dependent resistivity data within the Grain Boundary Scattering model, combined with the results from optical investigations, showed that the mean electron transmission probability G and the free carriers concentration, N, are the main parameters that control the transport properties of these films. The results indicated that the correlation between electrical and optical measurements with the chemical composition and the nanostructure of the TaxSiyNz thin films provides a pertinent and consistent description of the evolution of the Ta-Si-N system from a solid solution to a nanocomposite material due to the addition of Si atoms.
Negative Poisson's ratio and piezoelectric anisotropy of tetragonal ferroelectric single crystals
Authors: Aleshin V. I. , Raevski I. P.
Published: December 2012

Orientational dependences of the Poisson's ratio have been calculated for several perovskite tetragonal ferroelectric singe crystals: 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3, PbTiO3, and BaTiO3. All these crystals are shown to have negative values of Poisson's ratio in some crystallographic directions thus being so-called partial auxetics. The largest negative Poisson's ratio values possess 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 single crystals. The thermodynamic restrictions for the d33 and d31 piezoelectric moduli of the tetragonal crystals have been revealed. The relation between Poisson's ratio and piezoelectric properties of perovskite tetragonal ferroelectric singe crystals is discussed.
First-principles investigations of crystallographic, magnetic, and electronic structures in Ni2XIn (X = Mn, Fe, and Co)
Authors: Bai J. , Xu N. , Raulot J.-M. , Zhang Y. D. , Esling C. , Zhao X. , Zuo L.
Published: December 2012

Ni-Mn-In is a novel type of magnetic shape memory alloy. It shows that the martensitic transition from the ferromagnetic austenite to the antiferro- or paramagnetic martensite, which is different from the well-known Ni-Mn-Ga alloy, can be reversed by a magnetic field. We present the results of the crystallographic, magnetic, and electronic structures of Ni2MnIn alloy by means of the ab initio calculations within the framework of density functional theory using Vienna ab initio software package. Furthermore, the effects of substitution of Mn by Fe or Co have been systematically investigated in this paper.
Effect of heterostructure design on current-voltage characteristics in AlxGa1−xN/GaN double-barriers resonant tunneling diode
Authors: Boucherit M. , Soltani A. , Rousseau M. , Farvacque J.-L. , DeJaeger J.-C.
Published: December 2012

Ballistic transport in double-barriers resonant tunneling diodes based on GaN is investigated in this work using the non-equilibrium Green's functions formalism. The electron density of states, the electrons concentration, and the current-voltage characteristics are calculated taking into account the internal electric field induced in the AlxGa1−xN/GaN heterostructures. The effect of the geometrical parameters on the evolution of the current resonances characteristics was analyzed qualitatively by varying GaN quantum well width, thicknesses and height of the AlxGa1−xN barriers.
Effect of oxygen vacancy distribution on the thermoelectric properties of La-doped SrTiO3 epitaxial thin films
Authors: Sarath Kumar S. R. , Abutaha A. I. , Hedhili M. N. , Alshareef H. N.
Published: December 2012

A detailed study of the role of oxygen vacancies in determining the effective mass and high temperature (300–1000 K) thermoelectric properties of La-doped epitaxial SrTiO3 thin films is presented. It is observed that at intermediate temperatures, a transition from degenerate to non-degenerate behavior is observed in the Seebeck coefficient, but not electrical conductivity, which is attributed to heterogeneous oxygen non-stoichiometry. Heikes formula is found to be invalid for the films with oxygen vacancies. By fitting the spectroscopic ellipsometry (SE) data, obtained in the range 300–2100 nm, using a Drude-Lorentz dispersion relation with two Lorentz oscillators, the electrical and optical properties of the films are extracted. Using the excellent agreement between the transport properties extracted from SE modeling and direct electrical measurements, we demonstrate that an increase in concentration of oxygen vacancies results in a simultaneous increase of both carrier concentration and electron effective mass, resulting in a higher power factor.
Concurrent presence of unipolar and bipolar resistive switching phenomena in pnictogen oxide Sb2O5 films
Authors: Ahn Youngbae , Ho Lee Jong , Hwan Kim Gun , Woon Park Ji , Heo Jaeyeong , Wook Ryu Seung , Seok Kim Young , Seong Hwang Cheol , Joon Kim Hyeong
Published: December 2012

The concurrent presence of unipolar resistive switching (URS) and bipolar resistive switching (BRS) characteristics of the Sb/Sb2O5/Pt structure were examined. It was discovered that the BRS phenomenon was driven by the abnormal reset process during URS cycles which was induced by the rupture and recovery of the conducting filament (CF) in the localized region near the anode. The electrical conduction behavior in the high resistance state of URS and BRS was explained by the Schottky emission and space-charge-limited current mechanism, meaning that the URS and BRS phenomena are induced by the extent of reoxidaton and reduction regarding the local CF-ruptured region.
Coalescence kinetics in surfactant stabilized emulsions: Evolution equations from direct numerical simulations
Authors: Skartlien R. , Grimes B. , Meakin P. , Sjöblom J. , Sollum E.
Published: December 2012

Lattice Boltzmann simulations were used to study the coalescence kinetics in emulsions with amphiphilic surfactant, under neutrally buoyant conditions, and with a significant kinematic viscosity contrast between the phases (emulating water in oil emulsions). The 3D simulation domain was large enough (2563 ∼ 107 grid points) to obtain good statistics with droplet numbers ranging from a few thousand at early times to a few hundred near equilibrium. Increased surfactant contents slowed down the coalescence rate between droplets due to the Gibbs-Marangoni effect, and the coalescence was driven by a quasi-turbulent velocity field. The kinetic energy decayed at a relatively slow rate at early times, due to conversion of interfacial energy to kinetic energy in the flow during coalescence. Phenomenological, coupled differential equations for the mean droplet diameter D(t) and the number density nd(t) were obtained from the simulation data and from film draining theories. Local (in time) power law exponents for the growth of the mean diameter (and for the concomitant decrease of nd) were established in terms of the instantaneous values of the kinetic energy, coalescence probability, Gibbs elasticity, and interfacial area. The model studies indicated that true power laws for the growth of the droplet size and decrease of the number of droplets with time may not be justified, since the exponents derived using the phenomenological model were time dependent. In contrast to earlier simulation results for symmetric blends with surfactant, we found no evidence for stretched logarithmic scaling of the form D ∼ [ln (ct)]α for the morphology length, or exponential scalings associated with arrested growth, on the basis of the phenomenological model.
Structural, vibrational, and rovibrational analysis of tetrafluoroethylene
Authors: Medcraft C. , Fuss W. , Appadoo D. R. T. , McNaughton D. , Thompson C. D. , Robertson E. G.
Published: December 2012

High resolution FTIR spectra of 13C enriched tetrafluoroethylene (C2F4) were measured at 150 K at the Australian Synchrotron. Rovibrational transitions were assigned in the a-type symmetric and b-type antisymmetric CF2 stretches of 12C13CF4 and 13C2F4 near 1170 cm−1 and 1300 cm−1, respectively. Ground vibrational state spectroscopic constants for both molecules were determined in addition to the upper state constants for ν11 and ν9 of 13C2F4 and ν11, ν2+ν6, and ν5 of 12C13CF4. The ground state constants, along with those determined for the 12C2F4 isotopologue from previously published data, were used to determine a semi-experimental re structure rCC = 132.36 ± 0.37 pm, rCF = 131.11 ± 0.23 pm, αFCC = 123.3 ± 0.3° in excellent agreement with ab initio structures. Lower resolution FTIR spectra were measured between 100 and 5000 cm−1 at room temperature and band centres obtained for all modes of the three isotopologues; although only 5 out of 12 modes in 12C2F4 and 13C2F4 are infrared (IR) active, the others were inferred from combination and hot-band positions. A number of modes are observed to be infrared active only in the 12C13CF4 isotopologue due to its lower symmetry. Most notably, decoupling of the antisymmetric CF2 motions in the two halves of 12C13CF4 results in 2 strongly IR active modes that involve motion at one carbon or the other.
Efficient copper vapor laser using metal (Cu, Ag) chlorides in thermal insulation and performance with new prism resonator configurations
Authors: Singh Bijendra
Published: December 2012

A copper vapor laser based on the use of copper chloride and silver chloride mixture embedded inside the laser head thermal insulation is successfully demonstrated. The use of external HCl generator cell containing zirconium chloride normally used for its kinetically enhanced mode of operation is completely eliminated. With this new configuration laser power of ∼70 W was achieved from a wide aperture ∼47–50 mm bore discharge tube with input power of ∼5 kW and overall high efficiency of ∼1.4% without external supply of HCl vapors to the laser head. In a typical operational cycle the laser initially operates as low temperature CuCl laser with startup time of few minutes and output power of ∼10 W during low tube temperature range of ∼300–500 °C. Thereafter, the laser transforms itself into efficient kinetically enhanced copper vapor laser (CVL) at high temperature range of ∼1200–1600 °C with maximum laser output power of ∼70 W. This dual mode of operation observed in a single CVL system is unique and has not been reported so far in any high temperature copper vapor laser. New resonator configurations, namely, the prism resonator in stable and unstable form are successfully demonstrated for the first time in a copper vapor laser to achieve low divergence beam with dramatic increase in misalignment tolerance to ∼25 mrad, which is an improvement of about ∼50 times compared to standard CVLs with conventional spherical or plane-plane resonators. With these new resonator configurations the CVL functions almost as an “alignment free laser” system with significantly reduced beam divergence of ∼0.2 mrad and high optical extraction efficiency of ∼70%–80%.
Atomic layer deposition of Al2O3 on GaSb using in situ hydrogen plasma exposure
Authors: Ruppalt Laura B. , Cleveland Erin R. , Champlain James G. , Prokes Sharka M. , Brad Boos J. , Park Doewon , Bennett Brian R.
Published: December 2012

In this report, we study the effectiveness of hydrogen plasma surface treatments for improving the electrical properties of GaSb/Al2O3 interfaces. Prior to atomic layer deposition of an Al2O3 dielectric, p-GaSb surfaces were exposed to hydrogen plasmas in situ, with varying plasma powers, exposure times, and substrate temperatures. Good electrical interfaces, as indicated by capacitance-voltage measurements, were obtained using higher plasma powers, longer exposure times, and increasing substrate temperatures up to 250 °C. X-ray photoelectron spectroscopy reveals that the most effective treatments result in decreased SbOx, decreased Sb, and increased GaOx content at the interface. This in situ hydrogen plasma surface preparation improves the semiconductor/insulator electrical interface without the use of wet chemical pretreatments and is a promising approach for enhancing the performance of Sb-based devices.
Exchange-biased magnetic tunnel junctions with antiferromagnetic ε-Mn3Ga
Authors: Kurt H. , Rode K. , Tokuc H. , Stamenov P. , Venkatesan M. , Coey J. M. D.
Published: December 2012

Oriented c-axis films of the hexagonal triangular antiferromagnetic ε-Mn3Ga have been used in bottom-pinned synthetic antiferromagnet magnetic tunnel junctions with MgO barriers, which show up to 150% tunneling magnetoresistance at room temperature. Exchange bias fields as high as 150 mT can be achieved for samples field-cooled from 100 °C. Thin films of the antiferromagnet have a Néel temperature in excess of 650 K and provide an interface exchange energy with CoFe of 0.09 mJ m−2. They show an isotropic uncompensated magnetization of Ms = 48 kA m−1, with a coercivity μ0Hc > 3 T.
Enhanced infrared photo-response from GaSb/GaAs quantum ring solar cells
Authors: Carrington P. J. , Wagener M. C. , Botha J. R. , Sanchez A. M. , Krier A.
Published: December 2012

GaAs-based solar cells containing stacked layers of nanostructured type II GaSb quantum ring solar cells are reported which show significantly enhanced infrared photo-response extending out to 1400 nm. The ring formation reduces the net strain energy associated with the large lattice mismatch making it possible to stack multi-layers without the need for strain balancing. The (1 sun) short-circuit current for a 10 layer sample is enhanced by ∼6% compared to a GaAs control cell. The corresponding open-circuit voltage of 0.6 V is close to the theoretical maximum expected from such structures.
Efficiency and droop improvement in green InGaN/GaN light-emitting diodes on GaN nanorods template with SiO2 nanomasks
Authors: Lin Da-Wei , Lee Chia-Yu , Liu Che-Yu , Han Hau-Vei , Lan Yu-Pin , Lin Chien-Chung , Chi Gou-Chung , Kuo Hao-Chung
Published: December 2012

This study presents the green InGaN/GaN multiple quantum wells light-emitting diodes (LEDs) grown on a GaN nanorods template with SiO2 nanomasks by metal–organic chemical vapor deposition. By nanoscale epitaxial lateral overgrowth, microscale air voids were formed between nanorods and the threading dislocations were efficiently suppressed. The electroluminescence measurement reveals that the LEDs on nanorods template with SiO2 nanomasks suffer less quantum-confined Stark effect and exhibit higher light output power and lower efficiency droop at a high injection current as compared with conventional LEDs.
Microwave frequency comb attributed to the formation of dipoles at the surface of a semiconductor by a mode-locked ultrafast laser
Authors: Hagmann M. J. , Pandey S. , Nahata A. , Taylor A. J. , Yarotski D. A.
Published: December 2012

The generation of terahertz radiation by focusing a mode-locked ultrafast laser on the surface of a semiconductor was demonstrated by Zhang in 1990, and others have made numerous measurements and analyses of this effect. We have measured the surge current which causes this radiation, showing that this current, and presumably the radiation, are frequency combs with harmonics at integer multiples of the pulse repetition rate of the laser. The harmonics in the current are enhanced by placing the semiconductor in a tunneling junction, where the fundamental is increased by 8 dB with a DC tunneling current of 100 pA.
Nanogap-based dielectric-specific colocalization for highly sensitive surface plasmon resonance detection of biotin-streptavidin interactions
Authors: Kim Yonghwi , Chung Kyungwha , Lee Wonju , Ha Kim Dong , Kim Donghyun
Published: December 2012

We have performed highly sensitive surface plasmon resonance (SPR) detection by colocalizing the evanescent near-fields and target molecular distribution. The colocalization is based on oblique metal evaporation to form nanogaps of a size under 100 nm without using electron-beam lithography. The concept was demonstrated by detecting siloxane-based biotin/streptavidin interactions. 50-nm nanogaps produced the largest amplification of optical signatures and two orders of magnitude enhancement of sensitivity over conventional thin film-based measurements. The enhancement is associated with efficient overlap of localized near-fields and target. Colocalized detection scheme is expected to provide clues to molecular sensitivity for SPR biosensing.
Depth-selective electronic and magnetic properties of a Co2MnSi tunnel magneto-resistance electrode at a MgO tunnel barrier
Authors: Krumme B. , Ebke D. , Weis C. , Makarov S. I. , Warland A. , Hütten A. , Wende H.
Published: December 2012

We investigated the electronic structure as well as the magnetic properties of a Co2MnSi film on MgO(100) element-specifically at the interface to a MgO tunnel barrier by means of X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The electronic structure of the Co atoms as a function of the capping layer thickness remained unchanged, whereas the XA spectra of Mn indicate an increase of the unoccupied d states. The experimental findings are consistent with the interfacial structure proposed in the work by B. Hülsen et al. [Phys. Rev. Lett. 103, 046802 (2009)], where a MnSi layer is present at the interface to the MgO with oxygen atoms at top positions in the first MgO layer.
Note: A transimpedance amplifier for remotely located quartz tuning forks
Authors: Kleinbaum Ethan , Csáthy Gábor A.
Published: December 2012

The cable capacitance in cryogenic and high vacuum applications of quartz tuning forks imposes severe constraints on the bandwidth and noise performance of the measurement. We present a single stage low noise transimpedance amplifier with a bandwidth exceeding 1 MHz and provide an in-depth analysis of the dependence of the amplifier parameters on the cable capacitance.
Beam model and three dimensional numerical simulations on suspended microchannel resonators
Authors: Huang Kuan-Rong , Chang Jeng-Shian , Chao Sheng D. , Wu Kuang-Chong
Published: December 2012

At the microscale level, the vibrational characteristics of microstructures have been widely applied on biochemical microchips, especially for bio-molecules detection. The vibrational mechanics and mechanism of microcantilever beams immersed in the fluids for detecting target bio-molecules carried in the fluids have been widely studied and realized in recent years. However, it is not the case for microcantilever beams containing fluids inside (called suspended microchannel resonators, SMR). In this paper, an 1-D beam model for SMR is proposed and the formula for prediction of resonant frequency and resonant frequency shift are derived. For verification of validity of the 1-D beam model, three dimensional finite element simulations using ANSYS are performed. The effects of relevant parameters, such as density and viscosity of the fluids, on the frequency response are investigated. A link between numerical simulations and mathematical modeling is established through an equivalence relation. Subsequently, a useful formula of the resonant frequency shift as a function of the mass variation and the viscosity of the contained fluid is derived. Good agreement between the numerical simulations and the experimental data is obtained and the physical mechanism is elucidated.
Molecular participants in regulation of the meiotic cell cycle in mammalian oocytes
Authors: Pomerantz Yael , Dekel Nava
Published: December 2012

Meiosis in oocytes consists of two consecutive asymmetric cell divisions, each completed by the extrusion of one set of chromosomes into a small polar body. First polar body (PBI) extrusion is triggered by the inactivation of cyclin-dependent kinase 1 (CDK1), following the degradation of its regulatory subunit cyclin B1 by the ubiquitin proteasome pathway. The present review covers the sequence of events leading to PBI extrusion, and compares them to the corresponding events in mitotic cell division. The latest findings regarding the contribution of ubiquitin chain topology, separase, securin, cyclin B1, CDK1, Polo-like kinase 1 and mitogen-activated protein kinase kinase 1/2 to the regulation of meiosis are discussed.
Scientific basis for safely shutting in the Macondo Well after the April 20, 2010Deepwater Horizonblowout
Authors: Hickman Stephen H. , Hsieh Paul A. , Mooney Walter D. , Enomoto Catherine B. , Nelson Philip H. , Mayer Larry A. , Weber Thomas C. , Moran Kathryn , Flemings Peter B. , McNutt Marcia K.
Published: December 2012

As part of the government response to theDeepwater Horizonblowout, a Well Integrity Team evaluated the geologic hazards of shutting in the Macondo Well at the seafloor and determined the conditions under which it could safely be undertaken. Of particular concern was the possibility that, under the anticipated high shut-in pressures, oil could leak out of the well casing below the seafloor. Such a leak could lead to new geologic pathways for hydrocarbon release to the Gulf of Mexico. Evaluating this hazard required analyses of 2D and 3D seismic surveys, seafloor bathymetry, sediment properties, geophysical well logs, and drilling data to assess the geological, hydrological, and geomechanical conditions around the Macondo Well. After the well was successfully capped and shut in on July 15, 2010, a variety of monitoring activities were used to assess subsurface well integrity. These activities included acquisition of wellhead pressure data, marine multichannel seismic profiles, seafloor and water-column sonar surveys, and wellhead visual/acoustic monitoring. These data showed that the Macondo Well was not leaking after shut in, and therefore, it could remain safely shut until reservoir pressures were suppressed (killed) with heavy drilling mud and the well was sealed with cement.
Control of the multimillennial wildfire size in boreal North America by spring climatic conditions
Authors: Ali Adam A. , Blarquez Olivier , Girardin Martin P. , Hély Christelle , Tinquaut Fabien , El Guellab Ahmed , Valsecchi Verushka , Terrier Aurélie , Bremond Laurent , Genries Aurélie , Gauthier Sylvie , Bergeron Yves
Published: December 2012

Wildfire activity in North American boreal forests increased during the last decades of the 20th century, partly owing to ongoing human-caused climatic changes. How these changes affect regional fire regimes (annual area burned, seasonality, and number, size, and severity of fires) remains uncertain as data available to explore fire–climate–vegetation interactions have limited temporal depth. Here we present a Holocene reconstruction of fire regime, combining lacustrine charcoal analyses with past drought and fire-season length simulations to elucidate the mechanisms linking long-term fire regime and climatic changes. We decomposed fire regime into fire frequency (
FF
) and biomass burned (
BB
) and recombined these into a new index to assess fire size (
FS
) fluctuations. Results indicated that an earlier termination of the fire season, due to decreasing summer radiative insolation and increasing precipitation over the last 7.0 ky, induced a sharp decrease in
FF
and
BB ca
. 3.0 kyBP toward the present. In contrast, a progressive increase of
FS
was recorded, which is most likely related to a gradual increase in temperatures during the spring fire season. Continuing climatic warming could lead to a change in the fire regime toward larger spring wildfires in eastern boreal North America.