bluuebunny/crossref_metadata_2025 huggingface dataset:
Interpretation of the cross‐correlation function of ACE and STEREO solar wind velocities using a global MHD Model
Authors: Riley Pete , Luhmann J. , Opitz A. , Linker J. A. , Mikic Z.
Published: November 2010

Measurements from the ACE and STEREO A and B spacecraft are allowing an unprecedented view of the structure of the three‐dimensional heliosphere. One aspect of this is the degree to which the measurements at one spacecraft correlate with those at the other. We have computed the cross‐correlation functions (CCFs) for all three combinations of ACE and STEREO A and B in situ observations of the bulk solar wind velocity as the spacecraft moved progressively farther away from one another. Our results confirm previous studies that the phase lag between the signals becomes linearly larger with time. However, we have identified two intervals where this appears to break down. During these “lulls,” the CCF reveals a phase lag considerably less than that which would be predicted based only on the angular separation of the spacecraft. We modeled the entire STEREO time period using a global MHD model to investigate the cause for these “lulls.” We find that a combination of time‐dependent evolution of the streams as well as spatial inhomogeneities, due to the latitudinal separation of the spacecraft, are sufficient to explain them.
Formation and decay of a tributary‐dammed lake, Laonong River, Taiwan
Authors: Capart Hervé , Hsu Jammie P. C. , Lai Steven Y. J. , Hsieh Meng‐Long
Published: November 2010

We use field observations, laboratory experiments, and mathematical theory to characterize the full life cycle of a tributary‐dammed lake. The natural lake formed in August 2007 at the confluence of the Laonong River, southern Taiwan, with a steep tributary. Due to heavy rains from typhoons Wutip and Sepat, the tributary delivered massive amounts of sediment to the confluence. This caused damming of the trunk river, the growth of a lake, and the demise of a bridge upstream of the confluence. The lake lasted until October 2007, gradually decaying due to incision and infill by subsequent stream flow. We reconstruct the episode using hydrological records, ground observations, and surveyed profiles. We then use the event to verify a mathematical theory of river and lake bed evolution. The theory is based on a diffusion description of river morphodynamics, constrained by backwater effects due to lake formation. After validation using laboratory experiments, the theory is applied to the Laonong field event. Good agreement is obtained between calculated and surveyed long profiles. The theory can also reproduce the complex stage hydrograph recorded upstream of the confluence. This suggests a role for simplified, but laboratory‐tested mathematical theory in quantitative investigations of fluvial processes in the field.
Floating particle trapping and diffusion in vegetated open channel flow
Authors: Defina Andrea , Peruzzo Paolo
Published: November 2010

In this paper we present early results of laboratory experiments to investigate the transport and diffusion of floating particles (e.g., buoyant seeds) in open channel flow with emergent vegetation. The experiments are aimed at providing a better understanding of the relevant particle‐vegetation interaction mechanisms responsible for the observed diffusion processes. Qualitative observational data are then used to set up a stochastic model for floating particle transport and diffusion. Quantitative observations, such as the distribution of distances travelled by a particle before it is permanently captured by a plant and the arrival‐time distributions at prescribed cross sections along the vegetated test section, are instead used to calibrate and validate the model. The comparison between theoretical predictions and experimental results is quite satisfactory and suggests that the observed relevant aspects of the particle‐vegetation interaction processes are properly described in the model.
The structure of the antimicrobial peptide Ac‐RRWWRF‐NH2 bound to micelles and its interactions with phospholipid bilayers
Authors: Jing W. , Hunter H.N. , Hagel J. , Vogel H.J.
Published: November 2010

Abstract: The hexapeptide Ac‐RRWWRF‐NH2 has earlier been identified as a potent antimicrobial peptide by screening synthetic combinatorial hexapeptide libraries. In this study, it was found that this peptide had a large influence on the thermotropic phase behavior of model membranes containing the negatively charged headgroup phosphatidylglycerol, a major component of bacterial membranes. In contrast, differential scanning calorimetry showed that it had little effect on model membranes containing the zwitterionic phosphatidylcholine headgroup, the main component of erythrocyte membranes. This behavior is consistent with its biological activity and with its affinity to these membranes as determined by titration calorimetry, implying that peptide–lipid interactions play an important role in this process. The structure of this peptide bound to membrane‐mimetic sodium dodecyl sulfate (SDS) and dodecylphosphocholine micelles has been determined using conventional two‐dimensional nuclear magnetic resonance methods. It forms a marked amphipathic structure in SDS with its hydrophobic residues on one side of the structure and with the positively charged residues on the other side. This amphipathic structure may allow this peptide to penetrate deeper into the interfacial region of negatively charged membranes, leading to local membrane destabilization. Knowledge about the importance of electrostatic interactions of Arg and the role of Trp residues as a membrane interface anchor will provide insight into the future design of potent antimicrobial peptidomimetics.
Identification and characterization of peptide probes directed against PKCα conformations
Authors: Ashraf S. S. , Anderson E. , Duke K. , Hamilton P.T. , Fredericks Z.
Published: November 2010

Abstract:  Phage display is a powerful technology that allows identification of high affinity peptides that bind specifically to a given molecular target. Using a highly complex peptide display library, we have identified separate classes of peptides that bind to protein kinase C alpha (PKCα) only under activation conditions. Furthermore, peptide binding was specific to PKCα and not to any of the other closely related PKC isoforms. The conformational and isoform specificity of the peptide binding was demonstrated using surface plasmon resonance as well as time‐resolved fluorescence assays. Kinase assays showed that these peptides were not direct substrates for PKC nor did they inhibit phosphorylation of PKC substrates. These peptides are most likely directed against protein–protein interaction sites on PKC. The data presented here offers another example of application of phage display technology to identify conformation‐dependent peptide probes against therapeutically important drug targets. These peptides are ideally suited to be used as surrogate ligands to identify compounds that bind specifically to PKCα, as well as conformational probes to detect activated forms of PKCα.
Commonness and rarity of species: Does species' rank influence contribution to ecosystem function?
Authors: Jain Meha , Prager Case , Flynn Dan , Devan Caroline , Hart Georgia , Ahrestani Farshid , Bunker Dan , Palmer Matt , Smukler Sean , Sircely Jason , Naeem Shahid
Published: November 2010

Across the globe, biodiversity loss is occurring at an unprecedented rate. Rare species are especially susceptible to extinction, given that they typically have small population sizes and restricted geographic ranges, are less adaptable to disturbances, and are greater habitat specialists. However, while rare species may be prone to extinction, it remains unclear whether the loss of rare species is important to ecosystem function. In addition, it is important to consider the way in which rarity is defined, given that there are multiple definitions of rarity based on a species' geographic range, habitat specificity, and abundance in a community. Therefore, to better understand the contribution of rare species to community function, our study has two goals: 1) to determine whether rare species contribute to community trait space, which serves as a proxy for ecosystem function, more than common species; 2) to determine if the effect of rare species differs based on the definition of rarity employed. Using grassland data from Cedar Creek Minnesota, we assessed the importance of rare species on community trait space. We found that rare species have an equal effect on trait space as common species, except in the case of rarity defined as mean abundance. This suggests that when defining rarity by geographic range and habitat specificity, rare species may play an important role in ecosystem functioning due to their unique contribution to trait space. When considering local abundance of species, however, rare species contribute less than common species to trait space, possibly due to habitat filtering. These results suggest that the importance of rare species to trait space, and possible ecosystem function, depend on the definition of rarity employed.
Wikis in the classroom: Properties and potential uses of this collaborative learning tool
Authors: DeVore Jayna , Cecala Kristen , Maerz John
Published: November 2010

Background/Question/Methods

Student engagement is tied to course performance and information retention. Shifting the focus of the classroom from a lecture-based approach to a student-centered learning environment is one way to achieve this goal. One tool that can be used to allow student contribution to the content and direction of a course is a wiki. Wikis are highly flexible collaborative websites that can be structured to meet course needs and allow multiple users to contribute to site content. They provide a platform where real-time editing can be performed in a flexible 'topical' format. They are intended to promote group learning through collaboration rather than isolated reflection, and can provide another avenue through which instructors can connect with various types of learners through multimedia learning.

Results/Conclusions

We will present multiple ways in which wikis can be used in the classroom, such as collaborative projects, peer review, debates, competitions, and student comments and reflections on course material. Within these contexts faculty can promote the use of multimedia and creativity within student work and enable peer learning through public project viewing. They also track each student’s edits and additions to site content, allowing for instructor assessment of an individual’s contributions to group progress. We have found that the use of the wiki format promoted class participation, a sense of community within the course in question, and a feeling of project ownership and accomplishment.
Structure characterization of human serum proteins in solution and dry state
Authors: Gorinstein S. , Weisz M. , Caspi A. , Libman I. , Lerner H.T. , Trakhtenberg S. , Rosen A. , Goshev I. , Zemser M. , An˜on M.C.
Published: November 2010

Abstract: The present report describes application of advanced analytical methods to establish correlation between changes in human serum proteins of patients with coronary atherosclerosis (protein metabolism) before and after moderate beer consumption. Intrinsic fluorescence, circular dichroism (CD), differential scanning calorimetry and hydrophobicity (So) were used to study human serum proteins. Globulin and albumin from human serum (HSG and HSA, respectively) were denatured with 8 m urea as the maximal concentration. The results obtained provided evidence of differences in their secondary and tertiary structures. The thermal denaturation of HSA and HSG expressed in temperature of denaturation (Td, °C), enthalpy (ΔH, kcal/mol) and entropy (ΔS kcal/mol K) showed qualitative changes in these protein fractions, which were characterized and compared with fluorescence and CD. Number of hydrogen bonds (n) ruptured during this process was calculated from these thermodynamic parameters and then used for determination of the degree of denaturation (%D). Unfolding of HSA and HSG fractions is a result of promoted interactions between exposed functional groups, which involve conformational changes of α‐helix, β‐sheet and aperiodic structure. Here evidence is provided that the loosening of the human serum protein structure takes place primarily in various concentrations of urea before and after beer consumption (BC). Differences in the fluorescence behavior of the proteins are attributed to disruption of the structure of proteins by denaturants as well as by the change in their compactability as a result of ethanol consumption. In summary, thermal denaturation parameters, fluorescence, So and the content of secondary structure have shown that HSG is more stable fraction than HSA.
Piezoelectric properties of high Curie temperature barium titanate–bismuth perovskite-type oxide system ceramics
Authors: Wada Satoshi , Yamato Keisuke , Pulpan Petr , Kumada Nobuhiro , Lee Bong-Yeon , Iijima Takashi , Moriyoshi Chikako , Kuroiwa Yoshihiro
Published: November 2010

Barium titanate (BaTiO3, BT)—bismuth magnesium titanium oxide [Bi(Mg0.5Ti0.5)O3, BMT] system ceramics were prepared in an ambient atmosphere in order to increase the Curie temperature (Tc) of BT above 132 °C. A single perovskite phase was observed for BT–BMT ceramics with BMT compositions less than 50 mol %, and their relative densities were greater than 94%. Synchrotron measured x-ray diffraction patterns revealed that all the cations in the ceramics were homogeneously distributed. The temperature dependence of the dielectric properties revealed that the BT–BMT system ceramics exhibited relaxorlike characteristics with a dielectric maximum temperature as high as 360 °C for the 0.5BT–0.5BMT ceramic. The apparent piezoelectric constant (d∗) was 60 pC/N for the 0.4BT–0.6BMT ceramic. Based upon these results, the BT–BMT system shows potential as a new type of lead-free material for high Tc piezoelectric applications.
Theoretical simulations of the effects of the indium content, thickness, and defect density of the i-layer on the performance of p-i-n InGaN single homojunction solar cells
Authors: Feng Shih-Wei , Lai Chih-Ming , Chen Chien-Hsun , Sun Wen-Ching , Tu Li-Wei
Published: November 2010

In this study, we conducted numerical simulations with the consideration of microelectronic and photonic structures to determine the feasibility of and to design the device structure for the optimized performance of InGaN p-i-n single homojunction solar cells. Operation mechanisms of InGaN p-i-n single homojunction solar cells were explored through the calculation of the characteristic parameters such as the absorption, collection efficiency (χ), open circuit voltage (Voc), short circuit current density (Jsc), and fill factor (FF). Simulation results show that the characteristic parameters of InGaN solar cells strongly depend on the indium content, thickness, and defect density of the i-layer. As the indium content in the cell increases, Jsc and absorption increase while χ, Voc, and FF decrease. The combined effects of the absorption, χ, Voc, Jsc, and FF lead to a higher conversion efficiency in the high-indium-content solar cell. A high-quality In0.75Ga0.25N solar cell with a 4 μm i-layer thickness can exhibit as high a conversion efficiency as ∼23%. In addition, the similar trend of conversion efficiency to that of Jsc shows that Jsc is a dominant factor to determine the performance of p-i-n InGaN solar cells. Furthermore, compared with the previous simulation results without the consideration of defect density, the lower calculated conversion efficiency verifies that the sample quality has a great effect on the performance of a solar cell and a high-quality InGaN alloy is necessary for the device fabrication. Simulation results help us to better understand the electro-optical characteristics of InGaN solar cells and can be utilized for efficiency enhancement through optimization of the device structure.
A microwave study of hydrogen-transfer-triggered methyl-group rotation in 5-methyltropolone
Authors: Ilyushin Vadim V. , Cloessner Emily A. , Chou Yung-Ching , Picraux Laura B. , Hougen Jon T. , Lavrich Richard
Published: November 2010

We present here the first experimental and theoretical study of the microwave spectrum of 5-methyltropolone, which can be visualized as a seven-membered “aromatic” carbon ring with a five-membered hydrogen-bonded cyclic structure at the top and a methyl group at the bottom. The molecule is known from earlier studies in the literature to exhibit two large-amplitude motions, an intramolecular hydrogen transfer and a methyl torsion. The former motion is particularly interesting because transfer of the hydrogen atom from the hydroxyl to the carbonyl group induces a tautomerization in the molecule, which then triggers a 60° internal rotation of the methyl group. Measurements were carried out by Fourier-transform microwave spectroscopy in the 8–24 GHz frequency range. Theoretical analysis was carried out using a tunneling-rotational Hamiltonian based on a G12m extended-group-theory formalism. Our global fit of 1015 transitions to 20 molecular parameters gave a root-mean-square deviation of 1.5 kHz. The tunneling splitting of the two J=0 levels arising from a hypothetical pure hydrogen-transfer motion is calculated to be 1310 MHz. The tunneling splitting of the two J=0 levels arising from a hypothetical pure methyl top internal-rotation motion is calculated to be 885 MHz. We have also carried out ab initio calculations, which support the structural parameters determined from our spectroscopic analysis and give estimates of the barriers to the two large-amplitude motions.
pCCSD: Parameterized coupled-cluster theory with single and double excitations
Authors: Huntington Lee M. J. , Nooijen Marcel
Published: November 2010

The primary characteristics of single reference coupled-cluster (CC) theory are size-extensivity and size-consistency, invariance under orbital rotations of the occupied or virtual space, the exactness of CC theory for N electron systems when the cluster operator is truncated to N-tuple excitations, and the relative insensitivity of CC theory to the choice of the reference determinant. In this work, we propose a continuous class of methods which display the desirable features of the coupled-cluster approach with single and double excitations (CCSD). These methods are closely related to the CCSD method itself and are inspired by the coupled electron pair approximation (CEPA). It is demonstrated that one can systematically improve upon CCSD and obtain geometries, harmonic vibrational frequencies, and total energies from a parameterized version of CCSD or pCCSD(α,β) by selecting a specific member from this continuous family of approaches. In particular, one finds that one such approach, the pCCSD(−1,1) method, is a significant improvement over CCSD for the calculation of equilibrium structures and harmonic frequencies. Moreover, this method behaves surprisingly well in the calculation of potential energy surfaces for single bond dissociation. It appears that this methodology has significant promise for chemical applications and may be particularly useful in applications to larger molecules within the framework of a high accuracy local correlation approach.
Resistive magnetohydrodynamic simulations of X-line retreat during magnetic reconnection
Authors: Murphy N. A.
Published: November 2010

To investigate the impact of current sheet motion on the reconnection process, we perform resistive magnetohydrodynamic simulations of two closely located reconnection sites that move apart from each other as reconnection develops. This simulation develops less quickly than an otherwise equivalent single perturbation simulation but eventually exhibits a higher reconnection rate. The unobstructed outflow jets are faster and longer than the outflow jets directed toward the magnetic island that forms between the two current sheets. The X-line and flow stagnation point are located near the trailing end of each current sheet very close to the obstructed exit. The speed of X-line retreat ranges from ∼0.02–0.06, while the speed of stagnation point retreat ranges from ∼0.03–0.07 in units of the initial upstream Alfvén velocity. Early in time, the flow stagnation point is located closer to the center of the current sheet than the X-line, but later on the relative positions of these two points switch. Consequently, late in time, there is significant plasma flow across the X-line in the opposite direction of X-line retreat. Throughout the simulation, the velocity at the X-line does not equal the velocity of the X-line. Motivated by these results, an expression for the rate of X-line retreat is derived in terms of local parameters evaluated at the X-line. This expression shows that X-line retreat is due to both advection by the bulk plasma flow and diffusion of the normal component of the magnetic field.
A simple backscattering microscope for fast tracking of biological molecules
Authors: Sowa Yoshiyuki , Steel Bradley C. , Berry Richard M.
Published: November 2010

Recent developments in techniques for observing single molecules under light microscopes have helped reveal the mechanisms by which molecular machines work. A wide range of markers can be used to detect molecules, from single fluorophores to micron sized markers, depending on the research interest. Here, we present a new and simple objective-type backscattering microscope to track gold nanoparticles with nanometer and microsecond resolution. The total noise of our system in a 55 kHz bandwidth is ∼0.6 nm per axis, sufficient to measure molecular movement. We found our backscattering microscopy to be useful not only for in vitro but also for in vivo experiments because of lower background scattering from cells than in conventional dark-field microscopy. We demonstrate the application of this technique to measuring the motion of a biological rotary molecular motor, the bacterial flagellar motor, in live Escherichia coli cells.
Tunability of magnetization in lateral few electron double quantum dots
Authors: Qu Fanyao , Santos D. R. , Morais P. C. , López-Richard V. , Marques G. E.
Published: November 2010

We demonstrate theoretically a pathway for electrical control of magnetic properties of tunable lateral double InAs quantum dots containing two-electrons, subjected to spin-orbit interaction (SOI), vertical electrical and magnetic fields. In the regime of low temperature and weak magnetic field, interplay of interdot tunnel coupling and hybridized magnetoelectric effect induces “s”-like behavior of magnetization and a peak of susceptibility which are very sensitive to interdot barrier voltage (VB) and interdot distance (d). Sweeping VB and adjusting d not only impact magnetic phase transition, but also switch electronic and magnetic properties from atomic to molecular in nature. Furthermore, SOI broadens the magnetic field interval of paramagnetic phase and changes magnitude of magnetization and susceptibility.
Shape anisotropy of polymers in disordered environment
Authors: Blavatska Viktoria , Janke Wolfhard
Published: November 2010

We study the influence of structural obstacles in a disordered environment on the size and shape characteristics of long flexible polymer macromolecules. We use the model of self-avoiding random walks on diluted regular lattices at the percolation threshold in space dimensions d=2 and d=3. Applying the pruned-enriched Rosenbluth method, we numerically estimate rotationally invariant universal quantities such as the averaged asphericity ⟨Ad⟩ and prolateness ⟨S⟩ of polymer chain configurations. Our results quantitatively reveal the extent of anisotropy of macromolecules due to the presence of structural defects.
Hydrodynamic performance of a fishlike undulating foil in the wake of a cylinder
Authors: Shao Xueming , Pan Dingyi , Deng Jian , Yu Zhaosheng
Published: November 2010

The hydrodynamic performances of a fishlike undulating foil in the wake of a D-section cylinder are numerically investigated by using a modified immersed boundary method. The results regarding the effects of various controlling parameters, including the distance between the foil and the D-cylinder, the frequency and the phase angle of foil’s undulation, and the phase angle of heaving motion on the thrust and the input power, are reported. It is observed that the foil without undulation in the vortex street can gain a thrust, as a result of the fact that the passing vortices produce reverse flows with respect to the mainstream in vicinity of the foil surface. When an undulating foil is placed at different distances behind the D-section cylinder, different wake structures form behind the cylinder. The wake area can be divided into three domains: suction domain, thrust enhancing domain, and weak influence domain. The undulation of the foil can inhibit the roll-up instability of the shear layers and vortex shedding from the cylinder and consequently significantly enlarge the suction domain, compared to the foil-free case or the stationary foil case. The thrust on the foil first increases and then decreases, as the distance between the foil and the cylinder increases. The undulation plays a negative role in the foil propulsion when the foil is located near the cylinder (largely in the suction domain) and a positive role when the distance between the foil and the cylinder is beyond a critical value. The mean thrusts do not vary significantly with the undulation phase angle when the heaving motion is not considered and the undulation amplitude studied is relatively small, instead, they are significantly affected by the phase angle of the heaving motion. The foil bypassing the vortices undergoes both minimum thrust and input power, whereas the one passing through vortices experiences a larger thrust. The phase angle difference between the heave and the undulation is important.
The statistical evolution of a stratified mixing layer with horizontal shear invoking feature extraction
Authors: Arobone Eric , Sarkar Sutanu
Published: November 2010

Direct numerical simulations of a horizontally oriented shear layer are performed with various values of uniform vertical stratification. The effects of stratification on statistics such as turbulent Reynolds stress, turbulent kinetic energy, and viscous dissipation are examined. Comparisons between turbulent kinetic energy and scalar variance budgets among the unstratified and stratified cases are presented. In the stratified cases, spatially sparse coherent structures emerge, affecting transport of momentum and density. Additional physical insight gained from quantification of the influence of the coherent structures on the flow statistics such as turbulent scalar transport is summarized. Vortex eduction revealed vortical structure similar to that observed in prior investigations of the zigzag instability.
Growth of polyaromatic molecules via ion-molecule reactions: An experimental and theoretical mechanistic study
Authors: Ascenzi Daniela , Aysina Julia , Tosi Paolo , Maranzana Andrea , Tonachini Glauco
Published: November 2010

The reactivity of naphthyl cations with benzene is investigated in a joint experimental and theoretical approach. Experiments are performed by using guided ion beam tandem mass spectrometers equipped with electron impact or atmospheric pressure chemical ion sources to generate C10H7+ with different amounts of internal excitation. Under single collision conditions, C–C coupling reactions leading to hydrocarbon growth are observed. The most abundant ionic products are C16H13+, C16Hn+ (with n=10–12), and C15H10+. From pressure-dependent measurements, absolute cross sections of 1.0±0.3 and 2±0.6 Å2 (at a collision energy of about 0.2 eV in the center of mass frame) are derived for channels leading to the formation of C16H12+ and C15H10+ ions, respectively. From cross section values a phenomenological total rate constant k=(5.8±1.9)×10−11 cm3 s−1 at an average collision energy of about 0.27 eV can be estimated for the process C10H7++C6H6→all products. The energy behavior of the reactive cross sections, as well as further experiments performed using partial isotopic labeling of reagents, support the idea that the reaction proceeds via a long lived association product, presumably the covalently bound protonated phenylnaphthalene, from which lighter species are generated by elimination of neutral fragments (H, H2, CH3). A major signal relevant to the fragmentation of the initial adduct C16H13+ belongs to C15H10+. Since it is not obvious how CH3 loss from C16H13+ can take place to form the C15H10+ radical cation, a theoretical investigation focuses on possible unimolecular transformations apt to produce it. Naphthylium can act as an electrophile and add to the π system of benzene, leading to a barrierless formation of the ionic adduct with an exothermicity of about 53 kcal mol−1. From this structure, an intramolecular electrophilic addition followed by H shifts and ring opening steps leads to an overall exothermic loss (−7.1 kcal mol−1 with respect to reagents) of the methyl radical from that part of the system which comes from benzene. Methyl loss can take place also from the “naphthyl” part, though via an endoergic route. Experimental and theoretical results show that an ionic route is viable for the growth of polycyclic aromatic species by association of smaller building blocks (naphthyl and phenyl rings) and this may be of particular relevance for understanding the formation of large molecules in ionized gases.
Simulation of hole-mobility in doped relaxed and strained Ge layers
Authors: Watling Jeremy R. , Riddet Craig , Chan Morgan Kah H. , Asenov Asen
Published: November 2010

As silicon based metal-oxide-semiconductor field-effect transistors (MOSFETs) are reaching the limits of their performance with scaling, alternative channel materials are being considered to maintain performance in future complementary metal-oxide semiconductor technology generations. Thus there is renewed interest in employing Ge as a channel material in p-MOSFETs, due to the significant improvement in hole mobility as compared to Si. Here we employ full-band Monte Carlo to study hole transport properties in Ge. We present mobility and velocity-field characteristics for different transport directions in p-doped relaxed and strained Ge layers. The simulations are based on a method for over-coming the potentially large dynamic range of scattering rates, which results from the long-range nature of the unscreened Coulombic interaction. Our model for ionized impurity scattering includes the affects of dynamic Lindhard screening, coupled with phase-shift, and multi-ion corrections along with plasmon scattering. We show that all these effects play a role in determining the hole carrier transport in doped Ge layers and cannot be neglected.
Straight macroscopic magnetic guide for cold atom interferometer
Authors: Tonyushkin Alexey , Prentiss Mara
Published: November 2010

We demonstrate a macroscopic magnetic guide for cold atom interferometry, where the magnetic guiding field is generated by a symmetrical array of racetrack coils of copper tape. This system represents a conceptual advance over previous guided atom interferometers based on nonsymmetrical geometries because the symmetry provides a much lower magnetic field curvature per fixed length than equivalent nonsymmetrical geometries, permitting a decrease in system length without increasing the decoherence rate associated with field curvature. We realized a magnetic guide a few cm away from each coil, where smooth translation of the guided atoms is achieved by changing the currents in second array of the multiple-conductor tape.
Shock wave loading and spallation of copper bicrystals with asymmetric Σ3⟨110⟩ tilt grain boundaries
Authors: Luo Sheng-Nian , Germann Timothy C. , Tonks Davis L. , An Qi
Published: November 2010

We investigate the effect of asymmetric grain boundaries (GBs) on the shock response of Cu bicrystals with molecular dynamics simulations. We choose a representative Σ3⟨110⟩ tilt GB type, (110)1/(114)2, and a grain size of about 15 nm. The shock loading directions lie on the GB plane and are along [001¯] and [221¯] for the two constituent crystals. The bicrystal is characterized in terms of local structure, shear strain, displacement, stress and temperature during shock compression, and subsequent release and tension. The shock response of the bicrystal manifests pronounced deviation from planar loading as well as strong stress and strain concentrations, due to GBs and the strong anisotropy in elasticity and plasticity. We explore incipient to full spallation. Voids nucleate either at GBs or on GB-initiated shear planes, and the spall damage also depends on grain orientation.
Continuous control of spatial mode rotation using second harmonic generation
Authors: Park Jun-Hee , Kim Woo-Kyung , Jeong Woo-Jin , Song Myung-Gun , Kim Hun-Hwa , Koo Kyung-Hwan , Lee Yeung-Lak , Kim Yena , Lee Ju-Han , Yang Woo-Seok , Lee Han-Young
Published: November 2010

This paper reports a continuously rotating spatial mode contributed from the interference between two second harmonic (SH) high-order modes, TM10 and TM01, which were generated in z-cut MgO:LN ridge waveguides with a periodically poled structure. The TM10 and TM01 SH modes were generated from the mixed first harmonic (FH) modes, the phase-matching conditions of the two modes were controlled to be close and to overlap so that the two modes can interference each other. The experiment results showed the interference of the two modes created an odd mode distribution with a specific angle and the distribution was continuously rotating according to the operation temperature.
Electronic properties of nanoscale silver crystals at the interface of silver thick film contacts on n-type silicon
Authors: Kontermann Stefan , Willeke Gerhard , Bauer Jan
Published: November 2010

Silver crystals at the interface of silver thick film contacts play a major role for the current transport across such contacts. As only few crystals are in direct contact with the contact bulk, the specific contact resistance needs to be orders of magnitude smaller compared to the specific contact resistance of the entire contact, if no other current transport mechanism is present. To clarify the current transport mechanism, we present microscopic IV-measurements on a single silver crystal to determine its specific contact resistance to the silicon. We find satisfactory agreement with theoretical values and can explain the macroscopic contact resistance.
On-chip superconductivity via gallium overdoping of silicon
Authors: Skrotzki R. , Fiedler J. , Herrmannsdörfer T. , Heera V. , Voelskow M. , Mücklich A. , Schmidt B. , Skorupa W. , Gobsch G. , Helm M. , Wosnitza J.
Published: November 2010

We report on superconducting properties of gallium-enriched silicon layers in commercial (100) oriented silicon wafers. Ion implantation and subsequent rapid thermal annealing have been applied for realizing gallium precipitation beneath a silicon-dioxide cover layer. Depending on the preparation parameters, we observe a sharp drop to zero resistance at 7 K. The critical-field anisotropy proofs the thin-film character of superconductivity. In addition, out-of-plane critical fields of above 9 T and critical current densities exceeding 2 kA/cm2 promote these structures to be possible playgrounds for future microelectronic technology.
Ultrasharp edge filtering in nanotethered photonic wires
Authors: Talneau A. , Sagnes I. , Gabet R. , Jaouen Y. , Benisty H.
Published: November 2010

Within a suspended photonic wire, the periodically-spaced nanotethers sustaining the wire can behave as damped transverse resonators that interact with the partially reflecting effect of the wire-tether intersection, and thus modify the Bragg reflection mechanism. This specific resonant mechanism is explored using a transfer matrix model, and is shown to result in an ultrasharp filter edge. This sharp behavior is evidenced experimentally on 300–400-nm-wide InP suspended wires through transmission data and further consolidated by optical low coherence reflectometry time-frequency analysis.
Influence of Ga/N ratio on morphology, vacancies, and electrical transport in GaN grown by molecular beam epitaxy at high temperature
Authors: Koblmüller G. , Reurings F. , Tuomisto F. , Speck J. S.
Published: November 2010

The effect of Ga/N flux ratio on surface morphology, incorporation of point defects and electrical transport properties of GaN films grown by plasma-assisted molecular beam epitaxy in a recently developed high-temperature growth regime was investigated. The homoepitaxial (0001) GaN films grown at ∼780–790 °C showed smoothest morphologies near the cross-over between N-rich and Ga-rich growth (0.75<Ga/N<1.1) contrasting previous observations for low-temperature growth. The higher-quality growth near Ga/N∼1 resulted from lower thermal decomposition rates and was corroborated by slightly lower Ga vacancy concentrations [VGa], lower unintentional oxygen incorporation, and improved electron mobilities. The consistently low [VGa], i.e., ∼1016 cm−3 for all films attribute further to the significant benefits of the high-temperature growth regime.
Control of gigahertz permeability and permittivity dispersion by means of nanocrystallization in FeCo based nanocrystalline alloy
Authors: Han Mangui , Lu Haipeng , Deng Longjiang
Published: November 2010

An amorphous (FeCo) based alloy has been prepared by a rapid quench method. Subsequent annealing on the amorphous samples gives rise to the coexistence of two magnetic phases: amorphous matrix and nanocrystalline grains (α′-FeCo) with an average size of 9.8 nm. Permeability dispersion behaviors have been studied by Kittel theory [C. Kittel, J. Phys. Radium 12, 332 (1951)]. The results show that these two magnetic phases contribute to the permeability dispersion. The Cole-Cole dispersion law [K. S. Cole and R. H. Cole, J. Chem. Phys. 9, 341 (1941)] has been employed to explain the permittivity dispersion within microwave region based on the assumption that multiple dielectric relaxation processes existing. Our results indicate the possibility of tuning the high frequency permeability and permittivity values of (FeCo) based alloy by controlling the magnetic microstructure, which suggests an alternative method to develop smart electromagnetic materials.
Fabrication of surface textures by ion implantation for antireflection of silicon crystals
Authors: Kadakia Nirag , Naczas Sebastian , Bakhru Hassaram , Huang Mengbing
Published: November 2010

We report on a method based on ion implantation and thermal annealing to fabricate silicon surface textures for antireflection purposes. Modification to crystalline Si surfaces by hydrogen ion implantation is a well known phenomenon, but the surface structures generated by H implantation alone, typically of a low packing density and small aspect ratio, are not effective in suppressing light reflection from Si. We show that coimplantation of hydrogen and argon, combined with thermal annealing and oxidation, can result in an interesting surface morphology in Si crystals, yielding the lowest light reflectance of ∼1% over a broad spectral range at various light incident angles. In addition, lattice damage to crystalline Si generated by ion implantation is reduced or completely removed by the annealing processes. Possible mechanisms for the formation of such observed surface textures are discussed.
The origin of oxygen in oxide thin films: Role of the substrate
Authors: Schneider C. W. , Esposito M. , Marozau I. , Conder K. , Doebeli M. , Hu Yi , Mallepell M. , Wokaun A. , Lippert T.
Published: November 2010

During the growth of oxide thin films by pulsed laser deposition, a strong oxygen substrate-to-film transfer has been experimentally observed for SrTiO3 and LaAlO3 thin films epitaxially grown on O18 exchanged SrTiO3 and LaAlO3 substrates by secondary ion mass spectrometry depth profiling. This oxygen transfer effect can seriously change the respective thin film properties. Taking the oxygen substrate contribution to the overall oxygen balance into account, original ways to design material properties of oxide thin films can be envisioned like a controlled charge carrier doping of SrTiO3 thin films.
Hydrogenated amorphous silicon solar cell on glass substrate patterned by hexagonal nanocylinder array
Authors: Tu Wei-Chen , Chang Yi-Tsung , Yang Chieh-Hung , Yeh Dan-Ju , Ho Chung-I , Hsueh Chun-Yuan , Lee Si-Chen
Published: November 2010

The hydrogenated amorphous silicon thin film solar cell fabricated on the glass substrate patterned by hexagonal nanocylinder array prepared by self-assembled SiO2 nanoparticles and nanosphere lithography was investigated. It is demonstrated that the short-circuit current of the patterned solar cell with 65 nm depth nanocylinder increases from 12.3 to 14.4 mA/cm2, and the efficiency increases from 5.18% to 6.59% as compared to the flat solar cell. These phenomena suggest that both effective light trapping and localized surface plasmon lead to significant improvement of light absorption in amorphous silicon solar cells.
Time evolution of the Ga droplet size distribution during Langmuir evaporation of GaAs(001)
Authors: Zhou Z. Y. , Tang W. X. , Jesson D. E. , Tersoff J.
Published: November 2010

The time evolution of the Ga droplet size distribution is measured by in situ surface electron microscopy during Langmuir evaporation of GaAs. With a minimum of complexity, we are able to reproduce and explain the major features of the droplet size distribution by a simple Monte Carlo model. Guided by the experiment, the model includes droplet formation in response to coalescence events.
Sequential coupling transport for the dark current of quantum dots-in-well infrared photodetectors
Authors: Lin L. , Zhen H. L. , Li N. , Lu W. , Weng Q. C. , Xiong D. Y. , Liu F. Q.
Published: November 2010

The dark current characteristics and temperature dependence for quantum dot infrared photodetectors have been investigated by comparing the dark current activation energies between two samples with identical structure of the dots-in-well in nanoscale but different microscale n-i-n environments. A sequential coupling transport mechanism for the dark current between the nanoscale and the microscale processes is proposed. The dark current is determined by the additive mode of two activation energies: Ea,micro from the built-in potential in the microscale and Ea,nano related to the thermally assisted tunneling in nanoscale. The activation energies Ea,micro and Ea,nano decrease exponentially and linearly with increasing applied electric field, respectively.
Shear-force atomic force microscope by using the second resonance regime of tuning fork probe
Authors: Liu Zhuang , Zhang Ying , Kok Shaw Wei , Ng Boon Ping , Soh Yeng Chai
Published: November 2010

An imaging scheme of shear-force atomic force microscope is proposed by exploiting the second resonance regime of the tuning fork probe. Theoretical analysis and experimental results demonstrate that the imaging scheme can deliver better sensitivity and higher resolution of topographic imaging.
Intrinsic and extrinsic causes of electron accumulation layers on InAs surfaces
Authors: Weber J. R. , Janotti A. , Van de Walle C. G.
Published: November 2010

Using first-principles calculations we investigate the origins of electron accumulation on InAs surfaces. Among the possible intrinsic causes (i.e., involving only In and/or As), In adatoms are the only native defects that can induce a surface electron accumulation layer. As an extrinsic mechanism, we find that adsorption of hydrogen on the surface also leads to charge accumulation. Hydrogen is an ubiquitous impurity, present in all growth and processing environments and therefore likely to be present on InAs surfaces. Both indium and hydrogen adatoms create donor states above the InAs conduction-band minimum and can explain the observed electron accumulation.
Effects of finite size on spin glass dynamics
Authors: Sato Tetsuya , Komatsu Katsuyoshi
Published: November 2010

In spite of comprehensive studies to clarify a variety of interesting phenomena of spin glasses, their understanding has been insufficiently established. To overcome such a problem, fabrication of a mesoscopic spin glass system, whose dynamics can be observed over the entire range to the equilibrium, is useful. In this review the challenges of research that has been performed up to now in this direction and our recent related studies are introduced. We have established to study the spin glass behaviour in terms of droplet picture using nanofabricated mesoscopic samples to some extent, but some problems that should be clarified have been left. Finally, the direction of some new studies is proposed to solve the problems.
Temperature dependence of the effective anisotropies in magnetic nanoparticles with Néel surface anisotropy
Authors: Yanes R , Chubykalo-Fesenko O , Evans R F L , Chantrell R W
Published: November 2010

We discuss the physical concept of the effective anisotropy in magnetic nanoparticles with surface anisotropy. A recently developed constrained Monte Carlo method allows evaluation of the temperature dependence of the energy surface in the whole temperature range, from which the effective anisotropy is determined. We consider nanoparticles of different shapes with cubic or uniaxial core anisotropy and Néel surface anisotropy. We demonstrate that at low temperatures surface effects can be dominant, leading to an overall cubic effective anisotropy even in spherical nanoparticles with uniaxial core anisotropy. This cubic anisotropy contribution decreases more rapidly with increasing temperature than the uniaxial core anisotropy, leading to a temperature-induced reorientation transition. We discuss the scaling behaviour of the effective anisotropy with magnetization in nanoparticles with surface anisotropy contribution. The scaling exponent deviates from that expected from Callen–Callen theory due to increased fluctuations of the surface spins.
Energy losses in interacting fine-particle magnetic composites
Authors: Burrows F , Parker C , Evans R F L , Hancock Y , Hovorka O , Chantrell R W
Published: November 2010

The coercivity and energy losses in superparamagnetic (SPM) magnetite and FePt nanoparticle composites subjected to an external, alternating magnetic field have been calculated as a function of the mean particle size and packing density. The effect of interactions has been investigated by fitting the Sharrock law to the coercivity results as a function of the field cycle frequency of the magnetic field. This fitting leads to effective parameters for the anisotropy field
and βeff = KV/k
B
T, which are themselves dependent on the interaction strength. The increase or decrease in the coercivity with interactions depends upon the relative change of
and βeff, thus demonstrating the complex effect that interactions have in these nanoparticle composites. The interparticle interactions have a non-trivial effect on the energy loss per cycle. The energy loss is reduced for systems with larger particles since the reduction in coercivity together with a corresponding reduction in the remanence dominates. For small particle sizes, the energy loss is increased. The primary mechanism here seems to be an enhancement of the energy barrier due to interactions, which changes the nature of the particles from SPM to being thermally stable.