bluuebunny/crossref_metadata_2025 huggingface dataset:
Multichannel interferometric SAR phase unwrapping using extended Kalman Smoother
Authors: Chirico Davide , Schirinzi Gilda
Published: April 2013

Phase unwrapping (PU) is one of the key processing steps in reconstructing the digital elevation model (DEM) of a scene from interferometric synthetic aperture radar (InSAR) data. The PU problem entails the estimation of an absolute phase from observation of its noisy principal (wrapped) values. Recently, PU approaches based on Kalman filtering have proved their efficacy in tackling the PU problem even when strong discontinuities of the height profile and noisy data are involved. This paper presents a novel multichannel InSAR PU algorithm using several interferometric SAR images based on the extended Kalman filter. The proposed technique exploits the capability of the Kalman algorithm to simultaneously perform noise filtering, PU, and multi-sensor data fusion. The proposed method, even being a Bayesian estimator, optimally fuses height information coming from an additional maximum likelihood estimator (MLE) combining the benefits of both the Bayesian and the non-Bayesian approaches. The performance of the proposed algorithm has been tested on simulated interferometric images proving the effectiveness of the proposed method.
0.7–1.8 GHz multiband digital polar transmitter using watt-class current-mode class-D CMOS power amplifier and digital envelope modulation technique for reduced spurious emissions
Authors: Nakatani Toshifumi , Kimball Donald F. , Larson Lawrence E. , Asbeck Peter M.
Published: April 2013

A polar transmitter driven by digital input signals for envelope and phase is demonstrated, using a band-switching output resonator to achieve multiband operation. A new digital pulse width modulation algorithm is also shown to partially suppress spurious signals associated with the digital input envelope signal. The transmitter consists of a current-mode class-D (CMCD) CMOS power amplifier (PA), together with a buck converter with a dead-time generator for improved efficiency. The CMCD PA is tuned by band-switching capacitors that can handle up to 9 V, and is measured to have approximately 30 dBm output power with 31–35% drain efficiency under single-tone testing. The proposed spurious signal reduction technique works to partially suppress quantization noise without increasing power consumption. Overall efficiencies of 27.1/25.6% are obtained at 30.2/28.9 dBm continuous wave (CW) output powers and 0.85/1.75 GHz carrier frequencies, respectively. Spur suppression of 9–10 dB peak is achieved when the proposed algorithm is applied with wideband code division multiple access (WCDMA) modulation.
Die juckende Haut – Differenzialdiagnose und Therapie
Authors: Möhrenschlager Matthias , Ring Johannes
Published: April 2013

Juckende Missempfindungen am Hautorgan können sowohl durch Dermatosen als auch nicht-dermatologische Erkrankungen hervorgerufen werden. Die folgende Arbeit geht auf mögliche Differentialdiagnosen und Therapiemöglichkeiten ein.
Einsatz in einer befremdlichen Welt?
Authors: Rohde Katrin S. , Knapp Sylvia , Baddack Mandy
Published: April 2013

„Was kann uns dort an verwirrenden Situationen, Aggression und Traurigkeit begegnen?“, fragen sich Auszubildende häufig vor ihrem Einsatz in einer psychiatrischen Institution. Wie können Lehrende der Unsicherheit und den Vorurteilen der Lernenden begegnen, damit der Einsatz zum positiven Lernerlebnis wird? Mit dieser Frage beschäftigt sich der Beitrag auf praktischer und wissenschaftlicher Ebene.
Phosphorylation of the guanine-nucleotide-exchange factor CalDAG-GEFI by protein kinase A regulates Ca2+-dependent activation of platelet Rap1b GTPase
Authors: Guidetti Gianni Francesco , Manganaro Daria , Consonni Alessandra , Canobbio Ilaria , Balduini Cesare , Torti Mauro
Published: April 2013

In blood platelets the small GTPase Rap1b is activated by cytosolic Ca2+ and promotes integrin αIIbβ3 inside-out activation and platelet aggregation. cAMP is the major inhibitor of platelet function and antagonizes Rap1b stimulation through a mechanism that remains unclear. In the present study we demonstrate that the Ca2+-dependent exchange factor for Rap1b, CalDAG-GEFI (calcium and diacylglycerol-regulated guanine-nucleotide-exchange factor I), is a novel substrate for the cAMP-activated PKA (protein kinase A). CalDAG-GEFI phosphorylation occurred in intact platelets treated with the cAMP-increasing agent forskolin and was inhibited by the PKA inhibitor H89. Purified recombinant CalDAG-GEFI was also phosphorylated in vitro by the PKA catalytic subunit. By screening a panel of specific serine to alanine residue mutants, we identified Ser116 and Ser586 as PKA phosphorylation sites in CalDAG-GEFI. In transfected HEK (human embryonic kidney)-293 cells, as well as in platelets, forskolin-induced phosphorylation of CalDAG-GEFI prevented the activation of Rap1b induced by the Ca2+ ionophore A23187. In platelets this effect was associated with the inhibition of aggregation. Moreover, cAMP-mediated inhibition of Rap1b was lost in HEK-293 cells transfected with a double mutant of CalDAG-GEFI unable to be phosphorylated by PKA. The results of the present study demonstrate that phosphorylation of CalDAG-GEFI by PKA affects its activity and represents a novel mechanism for cAMP-mediated inhibition of Rap1b in platelets.
Biogenesis and the regulation of the maturation of miRNAs
Authors: Tran Nham , Hutvagner Gyorgy
Published: April 2013

Regulation of gene expression is a fundamental process in both prokaryotic and eukaryotic organisms. Multiple regulatory mechanisms are in place to control gene expression at the level of transcription, post-transcription and post-translation to maintain optimal RNA and protein expressions in cells. miRNAs (microRNAs) are abundant short 21–23 nt non-coding RNAs that are key regulators of virtually all eukaryotic biological processes. The levels of miRNAs in an organism are crucial for proper development and sustaining optimal cell functions. Therefore the processing and regulation of the processing of these miRNAs are critical. In the present chapter we highlight the most important steps of miRNA processing, describe the functions of key proteins involved in the maturation of miRNAs, and discuss how the generation and the stability of miRNAs are regulated.
Piwi-interacting RNAs: biological functions and biogenesis
Authors: Sato Kaoru , Siomi Mikiko C.
Published: April 2013

The integrity of the germline genome must be maintained to achieve successive generations of a species, because germline cells are the only source for transmitting genetic information to the next generation. Accordingly, the germline has acquired a system dedicated to protecting the genome from ‘injuries’ caused by harmful selfish nucleic acid elements, such as TEs (transposable elements). Accumulating evidence shows that a germline-specific subclass of small non-coding RNAs, piRNAs (piwi-interacting RNAs), are necessary for silencing TEs to protect the genome in germline cells. To silence TEs post-transcriptionally and/or transcriptionally, mature piRNAs are loaded on to germline-specific Argonaute proteins, or PIWI proteins, to form the piRISC (piRNA-induced silencing complex). The present chapter will highlight insights into the molecular mechanisms underlying piRISC-mediated silencing and piRNA biogenesis, and discuss a possible link with tumorigenesis, particularly in Drosophila.
Small nucleolar RNAs and RNA-guided post-transcriptional modification
Authors: Lui Lauren , Lowe Todd
Published: April 2013

snoRNAs (small nucleolar RNAs) constitute one of the largest and best-studied classes of non-coding RNAs that confer enzymatic specificity. With associated proteins, these snoRNAs form ribonucleoprotein complexes that can direct 2′-O-methylation or pseudouridylation of target non-coding RNAs. Aided by computational methods and high-throughput sequencing, new studies have expanded the diversity of known snoRNA functions. Complexes incorporating snoRNAs have dynamic specificity, and include diverse roles in RNA silencing, telomerase maintenance and regulation of alternative splicing. Evidence that dysregulation of snoRNAs can cause human disease, including cancer, indicates that the full scope of snoRNA roles remains an unfinished story. The diversity in structure, genomic origin and function between snoRNAs found in different complexes and among different phyla illustrates the surprising plasticity of snoRNAs in evolution. The ability of snoRNAs to direct highly specific interactions with other RNAs is a consistent thread in their newly discovered functions. Because they are ubiquitous throughout Eukarya and Archaea, it is likely they were a feature of the last common ancestor of these two domains, placing their origin over two billion years ago. In the present chapter, we focus on recent advances in our understanding of these ancient, but functionally dynamic RNA-processing machines.
Identification and function of long non-coding RNAs
Authors: Young Robert S. , Ponting Chris P.
Published: April 2013

It is now clear that eukaryotic cells produce many thousands of non-coding RNAs. The least well-studied of these are longer than 200 nt and are known as lncRNAs (long non-coding RNAs). These loci are of particular interest as their biological relevance remains uncertain. Sequencing projects have identified thousands of these loci in a variety of species, from flies to humans. Genome-wide scans for functionality, such as evolutionary and expression analyses, suggest that many of these molecules have functional roles to play in the cell. Nevertheless, only a handful of lncRNAs have been experimentally investigated, and most of these appear to possess roles in regulating gene expression at a variety of different levels. Several lncRNAs have also been implicated in cancer. This evidence suggests that lncRNAs represent a new class of non-coding gene whose importance should become clearer upon further experimental investigation.
Therapeutic targeting of non-coding RNAs
Authors: Roberts Thomas C. , Wood Matthew J.A.
Published: April 2013

ncRNAs (non-coding RNAs) are implicated in a wide variety of cellular processes, including the regulation of gene expression. In the present chapter we consider two classes of ncRNA: miRNAs (microRNAs) which are post-transcriptional regulators of gene expression and lncRNAs (long ncRNAs) which mediate interactions between epigenetic remodelling complexes and chromatin. Mutation and misexpression of ncRNAs have been implicated in many disease conditions and, as such, pharmacological modulation of ncRNAs is a promising therapeutic approach. miRNA activity can be antagonized with antisense oligonucleotides which sequester or degrade mature miRNAs, and expressed miRNA sponges which compete with target transcripts for miRNA binding. Conversely, synthetic or expressed miRNA mimics can be used to treat a deficiency in miRNA expression. Similarly, conventional antisense technologies can be used to silence lncRNAs. Targeting promoter-associated RNAs with siRNAs (small interfering RNAs) results in recruitment of chromatin-modifying activities and induces transcriptional gene silencing. Alternatively, targeting natural antisense transcripts with siRNAs or antisense oligonucleotides can abrogate endogenous epigenetic silencing leading to transcriptional gene activation. The ability to modulate gene expression at the epigenetic level presents exciting new opportunities for the treatment of human disease.
The Ongoing Quest for the it Artifact: Looking Back, Moving Forward
Authors: Akhlaghpour Saeed , Wu Jing , Lapointe Liette , Pinsonneault Alain
Published: April 2013

More than 10 years ago, Orlikowski and Iacono (2001) examined the conceptualization of Information Technology (IT) in Information Systems Research (ISR) articles published in the 1990s. Their main conclusion was that the majority of these articles did not properly conceptualize the IT artifact. They recommended that IS researchers start to theorize about the IT artifact and employ rich conceptualizations of IT. The Orlikowski and Iacono paper provides a strong anchor point from which to analyze the evolution of the IS discipline. In order to obtain an up-to-date image of contemporary IS research, and to assess how the IS field has evolved since the 1990s, we carried out a similar analysis on a more recent and broader set of articles, that is, the full set (N = 644) of papers published between 2006 and 2009 by six top North American (ISR, MISQ, JAIS) and European (JIT, ISJ, EJIS) journals. The statistics in our results reveal no drastic advance in terms of deeper engagement with the IT artifact; more than 39% of the articles in our set are virtually mute about the artifact, and less than 16% employ an ensemble view of IT. Moreover, we note differences among the North American and European journals. Implications of the findings for two perspectives central to the IS research legitimacy debate are discussed.
Facile synthesis of single-phase spherical α″-Fe16N2/Al2O3 core-shell nanoparticles via a gas-phase method
Authors: Ogi Takashi , Dani Nandiyanto Asep Bayu , Kisakibaru Yutaka , Iwaki Toru , Nakamura Keitaro , Okuyama Kikuo
Published: April 2013

When nitrogen was inserted into the spherical α-Fe/Al2O3 core shell of 45 nm nanoparticles, the XRD pattern showed a clear change in the crystal modification from a body-centered cubic crystal to that of a single-phase α″-Fe16N2 structure. SEM, TEM, and energy-dispersive X-ray spectroscopy mapping analysis gave the particle size distributions, the shell thickness, and the Fe and Al elements. An examination of the total electron yield (surface sensitive) and fluorescence yield (bulk sensitive) of X-ray absorption fine structure on Fe and N atoms of these core shell nanoparticles confirmed the nitriding of the core iron and showed iron oxide formations on the core surface, indicating stability and resistivity performance. The nitriding process also changed the magnetic properties from paramagnetic to ferromagnetic with a coercivity above 3000 Oe, indicating a promising material for a “rear-earth-free” giant magnet.
Van Hove scenario and superconductivity in full Heusler alloy Pd2ZrGa
Authors: Ramesh Kumar K. , Chunchu Venkatrao , Thamizhavel A.
Published: April 2013

Ab-initio band structure calculation using the state-of-the-art density functional theory was carried out for the sample Pd2ZrGa. The equilibrium lattice parameter was found by fitting the energy vs volume data to Murnaghan equation of state and the value was observed to be 6.467 Å. Non analytical behavior of the energy functional was observed in band structure as well as in density of states diagram near the Fermi level. Polycrystalline sample synthesized using arc-furnace showed compositional variation in X-ray diffraction and energy dispersive analysis of X-ray spectrum studies. Magnetic measurements showed Meissner diamagnetic shielding in the as-cast sample below 2 K. From the Zero Field Cooled (ZFC) and Field Cooled (FC) measurements, we observed that the system is a type II BCS superconductor. The volume susceptibility at 2 K was observed to be 3.1 emu/Oe cm3.
Coalescence of armored interface under impact
Authors: Planchette C. , Biance A.-L. , Pitois O. , Lorenceau E.
Published: April 2013

Armored interfaces refer to fluid interfaces on which a compact monolayer of particles is adsorbed. In this paper, we probe their robustness under impact. For such an investigation, the impact of a drop (covered or not by particles) on a flat armored interface is considered. Two regimes are observed: small drops impacting at low velocities do not coalesce, while bigger drops falling at higher velocities lead to coalescence. The coalescence which occurs when the impacting drop has just reached its maximum extension directly results from the formation of bare regions within the armor. We therefore propose a geometric criterion to describe this transition. This simple modeling is able to capture the dependence of the measured velocity threshold with particle size and drop diameter. The additional robustness experienced by double armors (both drop and puddle covered) results in an increase of the measured velocity threshold, which is quantitatively predicted.
Conformation-resolved UV spectra of Pb(II) complexes: A gas phase study of the sandwich structures [Pb(toluene)2]2+ and [Pb(benzene)2]2+
Authors: Ma Lifu , Takashima Tsukiko , Koka Joseph , Kimber Helen J. , Cox Hazel , Stace Anthony J.
Published: April 2013

Toxic heavy metals, such as Pb2+, have become important targets for the development of efficient receptors that are capable of recognizing their presence as environmental and biological pollutants, and an important part of that receptor–metal characterization process is the provision of spectral evidence that identifies the presence of a metal ion. From results reported here on a combined experimental and theoretical study it is shown that, when complexed with aromatic ligands, Pb2+ is capable of yielding structured UV spectra, which: (i) exhibit discrete electronic transitions that include significant contributions from the metal ion; (ii) are very sensitive to the electronic properties of coordinating ligands; and (iii) are sensitive to subtle changes in coordination geometry. Two aromatic sandwich complexes, [Pb(benzene)2]2+ and [Pb(toluene)2]2+ have been prepared in the gas phase and their UV action spectra recorded from ions held and cooled in an ion trap. Whilst [Pb(benzene)2]2+ exhibits a spectrum with very little detail, that recorded for [Pb(toluene)2]2+ reveals a rich structure in the wavelength range 220–280 nm. Theory in the form of density functional theory (DFT) shows that both types of complex take the form of hemidirected structures, and that [Pb(toluene)2]2+ can adopt three distinct conformers depending upon the relative positions of the two methyl groups. Further calculations, using adiabatic time-dependent DFT to assign electronic transitions, provide evidence of individual [Pb(toluene)2]2+ conformers having been resolved in the experimental spectrum. Of particular significance for the development of methods for identifying Pb2+ as an environmental or biological pollutant, is the observation that there are distinct ligand-to-metal charge transfer transitions in the UV that are sensitive to both the geometry and the electronic characteristics of molecules that accommodate the metal ion.
Piezoresponse force microscopy at sub-room temperatures
Authors: Lilienblum M. , Hoffmann Á. , Soergel E. , Becker P. , Bohatý L. , Fiebig M.
Published: April 2013

Piezoresponse force microscopy is demonstrated at temperatures between −80 °C and +120 °C using a commercial room temperature atomic force microscope upgraded with a home-built cooling/heating-stage. We applied temperature-ramp-synchronized piezoresponse force microscope (PFM) for tracing the temperature dependence of the formation of ferroelectric domains. The potential of our sub-room temperature PFM is demonstrated by investigating the formation and evolution of ferroelectric domains in RbHSO4 as a function of temperature and time, respectively.
An improved first-order mean spherical approximation theory for the square-shoulder fluid
Authors: Hlushak S. P. , Hlushak P. A. , Trokhymchuk A.
Published: April 2013

The theory, which utilizes an exponential enhancement of the first-order mean spherical approximation (FMSA) for the radial distribution functions of the hard-core plus square-well fluid, is adopted to study the properties of the simplest model of the core-softened fluids, i.e., the hard spheres with a square-shoulder interaction. The results for structure and thermodynamic properties are reported and compared against both the Monte Carlo simulation data as well as with those obtained within the conventional FMSA theory. We found that in the region of low densities and low temperatures, where the conventional FMSA theory fails, the exponential-based FMSA theory besides being qualitatively correct also provides with a notable quantitative improvement of the theoretical description.
The Schrödinger operator on an infinite wedge with a tangent magnetic field
Authors: Popoff Nicolas
Published: April 2013

We study a model Schrödinger operator with constant magnetic field on an infinite wedge with Neumann boundary condition. The magnetic field is assumed to be tangent to a face. We compare the bottom of the spectrum to the model spectral quantities coming from the regular case. We are particularly motivated by the influence of the magnetic field and the opening angle of the wedge on the spectrum of the model operator and we exhibit cases where the bottom of the spectrum is smaller than in the regular case. Numerical computations enlighten the theoretical approach.
Structure and functionality of bromine doped graphite
Authors: Hamdan Rashid , Kemper A. F. , Cao Chao , Cheng H. P.
Published: April 2013

First-principles calculations are used to study the enhanced in-plane conductivity observed experimentally in Br-doped graphite, and to study the effect of external stress on the structure and functionality of such systems. The model used in the numerical calculations is that of stage two doped graphite. The band structure near the Fermi surface of the doped systems with different bromine concentrations is compared to that of pure graphite, and the charge transfer between carbon and bromine atoms is analyzed to understand the conductivity change along different high symmetry directions. Our calculations show that, for large interlayer separation between doped graphite layers, bromine is stable in the molecular form (Br2). However, with increased compression (decreased layer-layer separation) Br2 molecules tend to dissociate. While in both forms, bromine is an electron acceptor. The charge exchange between the graphite layers and Br atoms is higher than that with Br2 molecules. Electron transfer to the Br atoms increases the number of hole carriers in the graphite sheets, resulting in an increase of conductivity.
High-resolution electron spectroscopy of lanthanide (Ce, Pr, and Nd) complexes of cyclooctatetraene: The role of 4f electrons
Authors: Kumari Sudesh , Roudjane Mourad , Hewage Dilrukshi , Liu Yang , Yang Dong-Sheng
Published: April 2013

Cerium, praseodymium, and neodymium complexes of 1,3,5,7-cyclooctatetraene (COT) complexes were produced in a laser-vaporization metal cluster source and studied by pulsed-field ionization zero electron kinetic energy spectroscopy and quantum chemical calculations. The computations included the second-order Møller-Plesset perturbation theory, the coupled cluster method with single, double, and perturbative triple excitations, and the state-average complete active space self-consistent field method. The spectrum of each complex exhibits multiple band systems and is assigned to ionization of several low-energy electronic states of the neutral complex. This observation is different from previous studies of M(COT) (M = Sc, Y, La, and Gd), for which a single band system was observed. The presence of the multiple low-energy electronic states is caused by the splitting of the partially filled lanthanide 4f orbitals in the ligand field, and the number of the low-energy states increases rapidly with increasing number of the metal 4f electrons. On the other hand, the 4f electrons have a small effect on the geometries and vibrational frequencies of these lanthanide complexes.
A progressive correction to the circular hydraulic jump scaling
Authors: Rojas N. , Argentina M. , Tirapegui E.
Published: April 2013

This document presents theoretical and numerical results of the circular hydraulic jump derived from the inertial lubrication theory [N. O. Rojas, M. Argentina, E. Cerda, and E. Tirapegui, Phys. Rev. Lett. 104, 187801–1187801–4 (2010)]10.1103/PhysRevLett.104.187801. In particular, a correction for the hydraulic jump scaling is obtained. The results depend on subcritical depth, density, and surface tension, in agreement with experimental data at low Reynolds numbers [T. Bohr, C. Ellegaard, A. E. Hansen, and A. Haaning, Physica B 228, 1–10 (1996)10.1016/S0921-4526(96)00373-0; S. H. Hansen, S. Horluck, D. Zauner, P. Dimon, C. Ellegaard, and S. C. Creagh, Phys. Rev. E 55, 7048–7061 (1997)]10.1103/PhysRevE.55.7048.
Magneto-optical harmonic susceptometry of superparamagnetic materials
Authors: Vandendriessche Stefaan , Brullot Ward , Slavov Dimitar , Valev Ventsislav K. , Verbiest Thierry
Published: April 2013

We describe a technique to optically characterize superparamagnetism. Faraday rotation measurements are performed on a superparamagnetic nanocomposite using small alternating current magnetic fields. The superparamagnetism of the iron oxide nanoparticles causes signals at the uneven harmonics of the magnetic field frequency. These signals provide information on the magnetic moment of the superparamagnetic nanoparticles. Dia- and paramagnetism do not cause signals at higher harmonics, resulting in a high sensitivity to superparamagnetism, even in samples with large dia- or paramagnetic contributions. This technique provides a rapid, economical method to characterize superparamagnetism in composite samples not easily accessible by other techniques.
Electron correlation dynamics in atoms and molecules
Authors: Nest M. , Ludwig M. , Ulusoy I. , Klamroth T. , Saalfrank P.
Published: April 2013

In this paper, we present quantum dynamical calculations on electron correlation dynamics in atoms and molecules using explicitly time-dependent ab initio configuration interaction theory. The goals are (i) to show that in which cases it is possible to switch off the electronic correlation by ultrashort laser pulses, and (ii) to understand the temporal evolution and the time scale on which it reappears. We characterize the appearance of correlation through electron-electron scattering when starting from an uncorrelated state, and we identify pathways for the preparation of a Hartree-Fock state from the correlated, true ground state. Exemplary results for noble gases, alkaline earth elements, and selected molecules are provided. For Mg we show that the uncorrelated state can be prepared using a shaped ultrashort laser pulse.
A computational analysis of graphene adhesion on amorphous silica
Authors: Paek Eunsu , Hwang Gyeong S.
Published: April 2013

We present a computational analysis of the morphology and adhesion energy of graphene on the surface of amorphous silica (a-SiO2). The a-SiO2 model surfaces obtained from the continuous random network model-based Metropolis Monte Carlo approach show Gaussian-like height distributions with an average standard deviation of 2.91 ± 0.56 Å, in good agreement with existing experimental measurements (1.68–3.7 Å). Our calculations clearly demonstrate that the optimal adhesion between graphene and a-SiO2 occurs when the graphene sheet is slightly less corrugated than the underlying a-SiO2 surface. From morphology analysis based on fast Fourier transform, we find that graphene may not conform well to the relatively small jagged features of the a-SiO2 surface with wave lengths of smaller than 2 nm, although it generally exhibits high-fidelity conformation to a-SiO2 topographic features. For 18 independent samples, on average the van der Waals interaction at the graphene/a-SiO2 interface is predicted to vary from EvdW = 0.93 eV to 1.56 eV per unit cross-sectional area (nm2) of the a-SiO2 slab, depending on the choice of 12-6 Lennard-Jones potential parameters, while the predicted strain energy of corrugated graphene on a-SiO2 is Est = 0.25–0.36 eV/nm2. The calculation results yield the graphene/a-SiO2 adhesion energy of about Ead = 0.7–1.2 eV/nm, given Ead = EvdW–Est. We also discuss how the adhesive strength is affected by the morphological conformity between the graphene sheet and the a-SiO2 surface.
Axial temperature gradient and stress measurements in the deformation-DIA cell using alumina pistons
Authors: Raterron Paul , Merkel Sébastien , Holyoke Caleb W.
Published: April 2013

The deformation-DIA apparatus (D-DIA) coupled with synchrotron X-rays allows investigating materials elastic and plastic properties at high pressure. Most D-DIA deformation cells use alumina pistons that can also be used for measurement of the differential stress in the compression column by in situ X-ray diffraction. Here, we quantify the axial temperature (T) gradient in the D-DIA deformation cell and better constrain stress measurements in its compression column by studying an alumina specimen compressed and deformed at pressure P in the range 3.9–5.5 GPa and nominal temperature To = 1673 K. The axial T gradient, obtained from alumina equation of state, is ∼155 K/mm at the centre of the cell and does not vary significantly during deformation to 20% specimen strain. This T gradient, if not taken into account when measuring the experimental pressure in the alumina pistons, leads to significantly overestimating pressure. Unlike pressure, stress measurements in alumina are weakly sensitive to temperature. During deformation, the “true” differential stress in the compression column is evaluated at 596 ± 20 MPa using an elastoplastic self-consistent model, while raw uncertainties on experimental differential stresses reach 84 MPa. A comparison between the simulated and experimental data allows to conclude that, although dislocation glide in the basal plane is the primary slip system at run condition, with an estimated critical resolved shear stress (CRSS) of 120 MPa, prism plane slips and pyramidal plane slips also contribute significantly to the aggregate homogenous deformation and texture development, with CRSS on the order of 280 MPa.
From Kelvin problem to Kelvin carbons
Authors: Zhao Hui-Yan , Wang Jing , Ma Qing-Min , Liu Ying
Published: April 2013

As children's toys, soap bubbles also underpin many important scientific questions. What is the most efficient structure for foam? – the “Kelvin problem,” has been one of the most intriguing science and widely discussed over the past hundred years. Soap bubbles' frameworks have similar topology with sp3-bonded carbon or silicon allotropes, e.g., Weaire-Phelan foam and superconducting clathrate Na8Si46. By looking at the most efficient structure for foams, we construct a series of new carbon allotropes, named “Kelvin carbons.” Unexpectedly, all 11 Kelvin carbons are structurally stable wide-bandgap semiconductors, and their densities and their intrinsic hardnesses are both about 81%–87% that of diamond. The seventh state of Kelvin carbons, KVII, is a very low energy carbon structure after graphite, diamond, lonsdaleite, and type-II carbon clathrate. Kelvin carbons, which constitute a “bridge” between macro-foams and micro-carbons, together with recently proposed novel carbon phases can enrich the study of carbon allotropes.
Electronic spectroscopy of the HCCN radical
Authors: Nakajima Masakazu , Toyoshima Hitomi , Sato Shigenori , Tanaka Kazunori , Hoshina Kennosuke , Kohguchi Hiroshi , Sumiyoshi Yoshihiro , Ohshima Yasuhiro , Endo Yasuki
Published: April 2013

The $\tilde A\,{}^3 A^{\prime \prime} - \tilde X\, {}^3\Sigma ^ - $ÃA″3−X̃Σ−3 electronic transition of the HCCN/DCCN radical was observed by laser-induced fluorescence spectroscopy. Rotationally resolved excitation spectra were observed for HCCN and DCCN, and effective molecular constants of the upper state were determined. The observed intensities of the rotational lines were anomalous, probably due to a level-dependent non-radiative decay process in the excited state. Fluorescence depletion spectroscopy was applied in order to observe non-fluorescent vibronic levels. A dispersed fluorescence spectrum was also observed to determine the vibrational level structure in the ground electronic state. The observed vibrational structures in the fluorescence depletion and dispersed fluorescence spectra were tentatively assigned based on the results of ab initio calculations.
Degradation of AlGaN/GaN Schottky diodes on silicon: Role of defects at the AlGaN/GaN interface
Authors: Meneghini Matteo , Bertin Marco , Stocco Antonio , dal Santo Gabriele , Marcon Denis , Malinowski Pawel E. , Chini Alessandro , Meneghesso Gaudenzio , Zanoni Enrico
Published: April 2013

We report on a detailed investigation of the degradation of AlGaN/GaN Schottky diodes grown on silicon, submitted to high reverse-bias. The analyzed devices have a vertical structure; thanks to this feature, it was possible (i) to characterize the effects of stress by means of capacitance-voltage (C-V) measurements, therefore, identifying and localizing the trap states generated as a consequence of the stress tests; (ii) to accurately control the intensity and distribution of the electric field over stress time. Results indicate that stress induces an increase in the leakage current, which is well correlated to the increase of a new capacitance peak in the C-V characteristics. Based on experimental data and bidimensional simulations, degradation is ascribed to the generation of donor traps in the GaN buffer, close to the AlGaN/GaN interface.
Centrifugally driven thermal convection in a rotating porous cylindrical annulus
Authors: Kang Jianhong , Chen Xi , Fu Ceji , Tan Wenchang
Published: April 2013

Thermal convection driven by centrifugal buoyancy in a rotating porous cylindrical annulus with conical end boundaries is investigated. The Darcy-Brinkman model with the addition of the time-derivative and Coriolis terms in a rotating frame of reference is applied to characterize the flow in porous media. The effects of the Darcy number and the Coriolis parameter on the thermal convective instability are analyzed by conducting linear stability analysis. Based on weakly nonlinear analysis, the Nusselt number is analytically determined in the neighborhood of onset points. The time evolution of convection patterns and the Nusselt number at high Rayleigh numbers are numerically simulated with the Galerkin method. Especially, the Nusselt number in the stage of stationary, time-periodic, and chaotic convection is obtained in our numerical simulation.
Particle control and plasma performance in the Lithium Tokamak eXperiment
Authors: Majeski R. , Abrams T. , Boyle D. , Granstedt E. , Hare J. , Jacobson C. M. , Kaita R. , Kozub T. , LeBlanc B. , Lundberg D. P. , Lucia M. , Merino E. , Schmitt J. , Stotler D. , Biewer T. M. , Canik J. M. , Gray T. K. , Maingi R. , McLean A. G. , Kubota S. , Peebles W. A. , Beiersdorfer P. , Clementson J. H. T. , Tritz K.
Published: April 2013

The Lithium Tokamak eXperiment is a small, low aspect ratio tokamak [Majeski et al., Nucl. Fusion 49, 055014 (2009)], which is fitted with a stainless steel-clad copper liner, conformal to the last closed flux surface. The liner can be heated to 350 °C. Several gas fueling systems, including supersonic gas injection and molecular cluster injection, have been studied and produce fueling efficiencies up to 35%. Discharges are strongly affected by wall conditioning. Discharges without lithium wall coatings are limited to plasma currents of order 10 kA, and discharge durations of order 5 ms. With solid lithium coatings discharge currents exceed 70 kA, and discharge durations exceed 30 ms. Heating the lithium wall coating, however, results in a prompt degradation of the discharge, at the melting point of lithium. These results suggest that the simplest approach to implementing liquid lithium walls in a tokamak—thin, evaporated, liquefied coatings of lithium—does not produce an adequately clean surface.
Resistance thermometry-based picowatt-resolution heat-flow calorimeter
Authors: Sadat S. , Meyhofer E. , Reddy P.
Published: April 2013

We demonstrate a microfabricated heat-flow calorimeter capable of measuring modulated heat currents with ∼5 pW resolution. This is achieved by combining the excellent thermal isolation of a microdevice suspended by thin and long beams (conductance ∼150 nW/K) with a high-resolution resistance thermometer that enables temperature measurements with 10–50 μK resolution [Sadat et al., Rev. Sci. Instrum. 83(8), 084902 (2012)). The calorimeter described here has a resolution comparable to state-of-the-art bimaterial cantilever-based calorimeters but surpasses previous designs by dissipating an order of magnitude lower power in the measurement process.
Separate-type scanner and wideband high-voltage amplifier for atomic-resolution and high-speed atomic force microscopy
Authors: Miyata Kazuki , Usho Satoshi , Yamada Satoshi , Furuya Shoji , Yoshida Kiyonori , Asakawa Hitoshi , Fukuma Takeshi
Published: April 2013

We have developed a liquid-environment atomic force microscope with a wideband and low-noise scanning system for atomic-scale imaging of dynamic processes at solid/liquid interfaces. The developed scanning system consists of a separate-type scanner and a wideband high-voltage amplifier (HVA). By separating an XY-sample scanner from a Z-tip scanner, we have enabled to use a relatively large sample without compromising the high resonance frequency. We compared various cantilever- and sample-holding mechanisms by experiments and finite element analyses for optimizing the balance between the usability and frequency response characteristics. We specifically designed the HVA to drive the developed scanners, which enabled to achieve the positioning accuracy of 5.7 and 0.53 pm in the XY and Z axes, respectively. Such an excellent noise performance allowed us to perform atomic-resolution imaging of mica and calcite in liquid. Furthermore, we demonstrate in situ and atomic-resolution imaging of the calcite crystal growth process in water.
Multiferroicity in manganite/titanate superlattices determined by oxygen pressure-mediated cation defects
Authors: Li Z. , You L. , Yang Z. , Tan H. R. , Ren P. , Chen X. F. , Pan J. S. , Wang J. L. , Wang L. , Bosman M. , Zhu W. G. , Dong Z. L.
Published: April 2013

Increasing demand for spintronic devices, such as high-density memory elements, has generated interest in magnetoelectric coupling and multiferroic materials. In heteroepitaxial structures, magnetoelectric coupling occurs only near the strained interfaces, which is why the interface-rich multiferroic multilayer/superlattice is viewed as one of the most efficient ways to enhance the magnetoelectric coupling coefficient. However, both ferroelectric and ferromagnetic properties are difficult to be maintained when materials are shrunk to ultrathin layers, forming interfacial dead layers and limiting the application of these materials in atomic-scale devices. In this work, we demonstrate that the largely suppressed multiferroic properties of the La0.8Sr0.2MnO3 (16 unit cells)/BaTiO3 (12 unit cells) superlattice correlate with cation defects including both pure edge dislocations and planar defects. This conclusion is reached by combining atomic-resolution electron microscopy, piezoelectric force microscopy, and low-temperature magnetism measurements. Furthermore, it is shown that the density of the observed cation defects can be largely reduced by improving the oxygen off-stoichiometry through increasing oxygen pressure during growth, resulting in robust multiferroic properties. Only by eliminating oxygen vacancies during growth can the ferroic dead layers be further reduced. This work therefore opens the pathway for the integration of ferromagnetic and ferroelectric materials into magnetoelectric devices at diminished length scales.
High speed photodetectors based on a two-dimensional electron/hole gas heterostructure
Authors: Gallo Eric M. , Cola Adriano , Quaranta Fabio , Spanier Jonathan E.
Published: April 2013

We report on high-speed metal-semiconductor-metal (MSM) resonant cavity enhanced photodetectors based on Schottky-contacted (Al,In)GaAs heterostructures containing both electron and hole quantum wells. Interdigitated detectors were fabricated and characterized with and without an underlying Distributed Bragg Reflector (DBR). All detectors had very low dark currents and high linear responsivities. The fastest measured temporal response with a 16 ps full-width at half-maximum and a 29 ps fall time was demonstrated on a device with 1 μm gap between electrodes and an underlying DBR. Single quantum well detectors have previously demonstrated increased responsivity and speed but were limited by a slow decaying tail in the high speed photoresponse, attributed to the long collection path of minority carriers. The use of an electron and hole well, separated by a 110 nm absorption region as well as an underlying DBR, eliminates the slow tail by providing an enhanced collection path for both optically generated electrons and holes. Here, we present the fabricated device structure along with the DC and high speed photoresponse under varying incident powers. We briefly compare these results to those of the previous single well devices and attribute improvements in the time response tail to enhanced diffusion created by the presence of the separated dual well structure.
Cracks measurement using fiber-phased array laser ultrasound generation
Authors: Pei Cuixiang , Demachi Kazuyuki , Fukuchi Tetsuo , Koyama Kazuyoshi , Uesaka Mitsuru
Published: April 2013

A phased array laser ultrasound generation system by using fiber optic delivery and a custom-designed focusing objective lens has been developed for crack inspection. The enhancement of crack tip diffraction by using phased array laser ultrasound is simulated with finite element method and validated by experiment. A non-contact and non-destructive measurement of inner-surface cracks by time-of-flight diffraction method using fiber-phased array laser ultrasound generation and electromagnetic acoustic transducer detection has been studied.
Influence of Cu crystallographic orientation on electron transport in graphene
Authors: Shin Hyeon-Jin , Yoon Seon-Mi , Mook Choi Won , Park Seongjun , Lee Dongwook , Yong Song In , Sung Woo Yun , Choi Jae-Young
Published: April 2013

The mobilities of graphene grown on single-orientation Cu (111), (220), and (200) substrates with sizes of 4-in. were measured, and the graphene nucleation shapes were characterized in the early growth stage so that their relationship with the electrical properties of the fully grown graphene could be determined. The graphene grown on Cu (111) substrates, where the structures match well with a lattice mismatch of only 3.8%, has a relatively high mobility. The rectangular shape on Cu (111) in the initial stage has the potential to minimize the number of defects, paving the way for the development of high-performance graphene devices.
Description of low temperature bandtail states in two-dimensional semiconductors using path integral approach
Authors: Pinsook Udomsilp , Thongnum Anusit , Sa-yakanit Virulh
Published: April 2013

We used the solutions from the variational path integral to suggest a function form of the bandtail states of a two-dimensional system. The analytic solutions provide two regimes, i.e., the ground state (low temperature) and the semiclassical (high temperature) limits. We used the theoretical results to describe the results of the bandtail states in Si/SiO2 heterostructure reported recently (Jock et al., Appl. Phys. Lett. 100, 023503 (2012)). The low-temperature bandtail provided good agreement to the experimental results (sample B) with the parameters of Δ = 0.225 nm, L = 3.55 nm, and a = 5 nm.
Kinetics of Ga droplet decay on thin carbon films
Authors: Kodambaka S. , Ngo C. , Palisaitis J. , Mayrhofer P. H. , Hultman L. , Persson P. O. Å.
Published: April 2013

Using in situ transmission electron microscopy, we investigated the kinetics of liquid Ga droplet decay on thin amorphous carbon films during annealing at 773 K. The transmission electron microscopy images reveal that liquid Ga forms spherical droplets and undergo coarsening/decay with increasing time. We find that the droplet volumes change non-linearly with time and the volume decay rates depend on their local environment. By comparing the late-stage decay behavior of the droplets with the classical mean-field theory model for Ostwald ripening, we determine that the decay of Ga droplets occurs in the surface diffusion limited regime.
Graphene transparent electrodes grown by rapid chemical vapor deposition with ultrathin indium tin oxide contact layers for GaN light emitting diodes
Authors: Kun Xu , Chen Xu , Jun Deng , Yanxu Zhu , Weiling Guo , Mingming Mao , Lei Zheng , Jie Sun
Published: April 2013

By virtue of the small active volume around Cu catalyst, graphene is synthesized by fast chemical vapor deposition (CVD) in a cold wall vertical system. Despite being highly polycrystalline, it is as conductive and transparent as standard graphene and can be used in light emitting diodes as transparent electrodes. 7–10 nm indium tin oxide (ITO) contact layer is inserted between the graphene and p-GaN to enhance hole injection. Devices with forward voltage and transparency comparable to those using traditional 240 nm ITO are achieved with better ultraviolet performances, hinting the promising future for application-oriented graphene by rapid CVD.
Enhanced and polarization dependence of surface-enhanced Raman scattering in silver nanoparticle array-nanowire systems
Authors: Dai Z. G. , Xiao X. H. , Liao L. , Ying J. J. , Mei F. , Wu W. , Ren F. , Li W. Q. , Jiang C. Z.
Published: April 2013

We report a surface-enhanced Raman scattering (SERS) platform composed of a single Ag nanowire (NW) and nanoparticle array (NW-array). There are three different fundamental combination patterns of NW-array systems. Optical excitation of sandwich nanostructure provides a stronger SERS hot array at the gap between the NW and array. We also have studied the polarization dependence of SERS in the coupled NW-array system for three kinds of pattern. We find SERS are strongly enhanced when the incident light is polarized across the junction between the particle of array and NW, the enhancement is amazingly insensitive to the detailed geometrical structure of coupled pattern.
Vertical conducting ultraviolet light-emitting diodes based on p-ZnO:As/n-GaN/n-SiC heterostructure
Authors: Shi Zhifeng , Zhang Yuantao , Wu Bin , Cai Xupu , Zhang Jinxiang , Xia Xiaochuan , Wang Hui , Dong Xin , Liang Hongwei , Zhang Baolin , Du Guotong
Published: April 2013

Vertical conducting light-emitting diodes based on p-ZnO/n-GaN structure were fabricated on conductive n-SiC(6H) substrates. The p-ZnO:As films were prepared by arsenic out-diffusion from a sandwiched GaAs interlayer on a GaN/SiC template, and the AsZn-2VZn complex was considered to be the most probable defect contributing to the p-type conductivity of the ZnO:As films. Under forward bias, an intense ultraviolet emission at ∼384 nm from the ZnO side was observed. The electroluminescence performance of the diode was remarkable in terms of its low emission onset and high-purity ultraviolet emission. Additionally, the unencapsulated diode showed good stability over a duration of 2 months.
Tunable giant magnetic anisotropy in amorphous SmCo thin films
Authors: Magnus F. , Moubah R. , Roos A. H. , Kruk A. , Kapaklis V. , Hase T. , Hjörvarsson B. , Andersson G.
Published: April 2013

SmCo thin films have been grown by magnetron sputtering at room temperature with a composition of 2–35 at. % Sm. Films with 5 at. % or higher Sm are amorphous and smooth. A giant tunable uniaxial in-plane magnetic anisotropy is induced in the films which peaks in the composition range 11–22 at. % Sm. This cross-over behavior is not due to changes in the atomic moments but rather the local configuration changes. The excellent layer perfection combined with highly tunable magnetic properties make these films important for spintronics applications.