bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving student learning by addressing misconceptions
Authors: Engelmann Carol A. , Huntoon Jacqueline E.
Published: December 2011

Students—and often those who teach them—come to class with preconceptions and misconceptions that hinder their learning. For instance, many K–12 students and teachers believe groundwater exists in the ground in actual rivers or lakes, but in fact, groundwater is found in permeable rock layers called aquifers. Such misconceptions need to be addressed before students can learn scientific concepts correctly. While other science disciplines have been addressing preconceptions and misconceptions for many years, the geoscience community has only recently begun to concentrate on the impact these have on students' learning. Valuable research is being done that illuminates how geologic thinking evolves from the “novice” to “expert” level. The expert is defined as an individual with deep understanding of Earth science concepts. As research progresses, geoscientists are realizing that correcting preconceptions and misconceptions can move teachers and students closer to the “expert” level [Libarkin, 2005].
Changes in the magnetotail configuration before near‐Earth reconnection
Authors: Snekvik K. , Tanskanen E. , Østgaard N. , Laundal K. , Gordeev E. I. , Borg A. L.
Published: December 2011

We have examined three typical substorm growth phase signatures in the magnetotail two hours before near Earth reconnection; namely current sheet thinning, field line stretching and increase in the lobe magnetic pressure. The reconnection events were identified from in situ measurements in the plasma sheet by the Cluster spacecraft. The events were signified by high speed plasma flows, often lasting more than one hour. The list of events contains time intervals with high solar wind driving and strong intensification in the auroral westward electrojet, and other intervals with weak driving and no intensification in the electrojet. Irrespective of the amount of driving, there was usually a significant thinning of the current sheet prior to the reconnection onsets. Multispacecraft measurements of the magnetic field revealed that the average thinning was from 24000 to 12000 km, lasting about an hour. In those events without thinning, the current sheet was thin for an extended period before reconnection. Furthermore, the thinning happens even when there is no increase in the lobe magnetic pressure in the same time interval. The magnetotail is often stretched for a long time before reconnection onset, and reconnection seems to commence only when the current sheet is thin enough. In those events with large increase in the lobe magnetic pressure before onset, there is also significant field line stretching.
An asymptotic model of the F layer
Authors: Oliver W. L.
Published: December 2011

A model of the F layer of the ionosphere is presented that consists of a bottomside asymptote that ignores transport and a topside asymptote that ignores chemistry. The asymptotes connect at the balance height dividing the chemistry and transport regimes. A combination of these two asymptotes produces a good approximation to the true F layer. Analogously, a model of F layer response to an applied vertical drift is presented that consists of two asymptotic responses, one that ignores transport and one that ignores chemistry. The combination of these asymptotic responses produces a good approximation to the response of the true F layer. This latter response is identical to the “servo” response of Rishbeth et al. (1978), derived from the continuity equation. The asymptotic approach bypasses the continuity equation in favor of “force balance” arguments and so replaces a differential equation with simpler algebraic equations. This new approach provides a convenient and intuitive mean for first‐order estimates of the change in F layer peak height and density in terms of changes in neutral density, composition, temperature, winds, and electric fields. It is applicable at midlatitudes and at magnetically quiet times at high latitudes. Forensic inverse relations are possible but are not unique. The validity of the asymptotic relations is shown through numerical simulation.
Observations of the vertical structure of turbulent oscillatory boundary layers above fixed roughness using a prototype wideband coherent Doppler profiler: 2. Turbulence and stress
Authors: Hay Alex E. , Zedel Len , Cheel Richard , Dillon Jeremy
Published: December 2011

Measurements of turbulence and shear stress in oscillatory boundary layers are reported from experiments carried out with a prototype wideband coherent Doppler profiler above fixed roughness beds of 0.37 mm diameter sand and 3.9 mm diameter gravel. The 10 s oscillation period and 0.75 m to 1.5 m oscillation excursions correspond to roughness Reynolds numbers for the gravel bed in the 290 to 490 range, assuring fully rough turbulent conditions. Bottom stress was estimated via the law‐of‐the‐wall, the vertical integral of the defect acceleration, and the Reynolds stress. The Reynolds stress was obtained from the second moment of the beam‐coordinate velocities. Bed friction factors, fw, from the defect stresses are in reasonable agreement with predictions based on Swart's empirical relation as modified by Nielsen (1992) and with values determined using Laser Doppler Anemometry (LDA) by Sleath (1987) via the defect method and by Jensen (1988) via the law‐of‐the‐wall. The fw values determined here from the law‐of‐the‐wall are higher than predicted (ca. 50% higher for the gravel bed), likely due to background vertical shear associated with residual motions in the tank. The Reynolds stresses are lower than the predictions by a factor of 3 to 4, compared to the factor of 5 to 10 obtained by Sleath (1987). Beam coordinate turbulent kinetic energy spectra indicate that the vertical momentum flux is mostly associated with fluctuations between the forcing frequency and the inertial subrange, the latter contributing typically less than 10% of the total observed Reynolds stress.
Numerical study on the pattern and origins of Kuroshio branches in the bottom water of southern East China Sea in summer
Authors: Yang Dezhou , Yin Baoshu , Liu Zhiliang , Bai Tao , Qi Jifeng , Chen Haiying
Published: December 2011

Pattern and origins of Kuroshio branches in the bottom water of southern East China Sea (ECS), were carefully examined by numerical simulations based on the Regional Ocean Modeling System (ROMS) together with observations. Model results show that in the bottom water of ECS, the intrusion pattern of Kuroshio is mainly composed of an Offshore Kuroshio Branch Current (OKBC) which, bifurcated from the Kuroshio northeast of Taiwan, flows nearly along the isobath of ∼100 m, and a Nearshore Kuroshio Branch Current (NKBC) which, originated from the Kuroshio northeast of Taiwan, upwells northwestward gradually from ∼250 m to ∼60 m, then turns to northeast around 27.5°N, 122°E, thereafter flows northeastward along the isobath of ∼60 m, and finally reaches at 30.5°N where it turns to east. Furthermore, we found that the NKBC mostly originated in the Kuroshio subsurface water (120–250 m) east of Taiwan, whereas the OKBC mainly stemmed from the Kuroshio water (60–120 m) east of Taiwan. This pattern and origins of OKBC and NKBC well addressed the observational phenomena that off the coast of Zhejiang province, China, there were colder, less saline, and more phosphate‐rich bottom water near the isobath of ∼60 m rather than near the isobath of ∼100 m in August 2009. Finally, it is proposed that on southern ECS continental shelf, Kuroshio exhibits its intrusion branches by an anticyclonical stair structure: bottom stair NKBC, middle stair OKBC, and top stair Kuroshio surface branch (KBC).
Synoptic variability in the Ross Sea region, Antarctica, as seen from back‐trajectory modeling and ice core analysis
Authors: Markle B. R. , Bertler N. A. N. , Sinclair K. E. , Sneed S. B.
Published: December 2011

Synoptic variability in the Ross Sea region, Antarctica over the last thirty years is investigated using back‐trajectory modeling and cluster analysis. We identify two dominant air‐mass trajectory clusters: oceanic/West Antarctic and continental/East Antarctic. Our analysis shows that the oceanic/West Antarctic trajectories have an annual cycle similar to the Semiannual Oscillation and on average peak in frequency during April, while continental/East Antarctic trajectories reach their annual maximum during December. We demonstrate a causal association between the El Niño Southern Oscillation (ENSO) and the frequency of oceanic/West Antarctic trajectories originating from the Ross Sea and Amundsen Sea regions. In contrast, we find that the Southern Annular Mode (SAM) has little influence on the trajectory cluster frequencies. We then develop proxy records for synoptic variability using a shallow firn core from Gawn Ice Piedmont in Southern Victoria Land. Continental/East Antarctic trajectory frequency correlates with concentrations of nitrate (NO3), which is sourced from stratospheric air‐masses descending over the Antarctic interior. At seasonal to inter‐annual scales, the frequency of oceanic/West Antarctic trajectory clusters strongly correlate with deuterium excess, which is sensitive to changes in relative humidity and sea surface temperature in the Ross and Amundsen Seas. Inter‐annual variability in the frequency of oceanic/West Antarctic trajectories is discussed with respect to ENSO and changes in SST and sea ice extent.
Effects of forestry operations on dissolved organic carbon concentrations and export in boreal first‐order streams
Authors: Schelker J. , Eklöf K. , Bishop K. , Laudon H.
Published: December 2011

The purpose of this study was to quantify the effects of clear‐cutting and site preparation on dissolved organic carbon (DOC) concentrations and export in four boreal headwater streams in northern Sweden. The data set included intensive stream water monitoring from 2 years of pretreatment conditions (2004–2005), a 2 year post‐clear‐cut period (2006–2007), and a 2 year period after site preparation (2008–2009). To investigate differences in [DOC], an analysis of variance on ranks was performed on the data sets. Clear‐cutting increased the median DOC concentrations significantly from 15.9 to 20.4 mg L−1, which represents a net increase (treatment versus control) of 3.0 mg L−1 in the 2006–2007 period. Site preparation had an even more profound effect on DOC levels; an increase from 20.4 to 27.6 mg L−1was found in the site‐prepared catchments, whereas the control sites increased slightly from 17.4 to 21.4 mg L−1during the wetter years of 2008–2009. Riverine C fluxes increased significantly by 100% after clear‐cutting and by 79% after site preparation (92% and 195%, respectively, if compared to pretreatment conditions). When comparing these yearly C fluxes (183 kg C ha−1 yr−1after clear‐cutting; 280 kg C ha−1 yr−1after site preparation) to the net ecosystem exchange (NEE) of a forest in the region, the DOC flux represented 10% of NEE before harvest, increased to 18% after the clear‐cut, and increased to 28% after site preparation. These results underline the large impact of forestry operations on stream water quality as well as DOC exports leaving managed boreal forests.
Where do you come from; where do you go? Pluripotency, differentiation and malfunction of stem cells
Authors: Spagnoli Francesca M , Besser Daniel , Benitah Salvador Aznar
Published: December 2011

The conference ‘Stem Cells in Development and Disease’ took place in September 2011 in Berlin. It covered the latest findings in stem cell biology, including the genetic and epigenetic mechanisms of reprogramming, maintenance of pluripotency and differentiation.
Stroke Survivors' Perceptions of Social Participation After Stroke
Authors: Hutton-Johnson Iona
Published: December 2011

Social participation is a key component of healthy aging, and stroke survivors often face challenges in this area. In this article, I will provide insight into stroke survivors' perceptions of social participation and strategies for speech-language pathologists to use to address this issue in clinical practice.
Tunable coherent infrared techniques show progress
Authors: Lubkin Gloria B.
Published: December 2011

Recently several groups have produced tunable coherent infrared sources; some of these sources are tunable over a broad range of wavelengths. They vary in their ability to be continuously tuned. The most novel of these sources was reported by James J. Wynne in an invited paper at the Washington meeting of the American Physical Society on 23 April. Wynne, Peter Sorokin and John Lankard, all of IBM Research Center, reported that they had produced a continuously tunable source over the range 2–24 microns with no apparent fundamental limitation to achieving longer-wavelength generation. Groups at MIT National Magnet Laboratory, Bell Laboratories, Rice University and the University of California at Berkeley have all recently reported on tunable coherent infrared sources.
Metadynamics in the conformational space nonlinearly dimensionally reduced by Isomap
Authors: Spiwok Vojtěch , Králová Blanka
Published: December 2011

Atomic motions in molecules are not linear. This infers that nonlinear dimensionality reduction methods can outperform linear ones in analysis of collective atomic motions. In addition, nonlinear collective motions can be used as potentially efficient guides for biased simulation techniques. Here we present a simulation with a bias potential acting in the directions of collective motions determined by a nonlinear dimensionality reduction method. Ad hoc generated conformations of trans,trans-1,2,4-trifluorocyclooctane were analyzed by Isomap method to map these 72-dimensional coordinates to three dimensions, as described by Brown and co-workers [J. Chem. Phys. 129, 064118 (2008)]. Metadynamics employing the three-dimensional embeddings as collective variables was applied to explore all relevant conformations of the studied system and to calculate its conformational free energy surface. The method sampled all relevant conformations (boat, boat-chair, and crown) and corresponding transition structures inaccessible by an unbiased simulation. This scheme allows to use essentially any parameter of the system as a collective variable in biased simulations. Moreover, the scheme we used for mapping out-of-sample conformations from the 72D to 3D space can be used as a general purpose mapping for dimensionality reduction, beyond the context of molecular modeling.
Direct comparison of phase-sensitive vibrational sum frequency generation with maximum entropy method: Case study of water
Authors: de Beer Alex G. F. , Samson Jean-Sebastièn , Hua Wei , Huang Zishuai , Chen Xiangke , Allen Heather C. , Roke Sylvie
Published: December 2011

We present a direct comparison of phase sensitive sum-frequency generation experiments with phase reconstruction obtained by the maximum entropy method. We show that both methods lead to the same complex spectrum. Furthermore, we discuss the strengths and weaknesses of each of these methods, analyzing possible sources of experimental and analytical errors. A simulation program for maximum entropy phase reconstruction is available at: http://lbp.epfl.ch/.
Efficiency of a parabolic trough collector as a water heater system in Yucatán, Mexico
Authors: Rosado Hau N. , Escalante Soberanis M. A.
Published: December 2011

The performance of a parabolic trough collector (PTC) manufactured in Merida, Yucatán, was evaluated under the ANSI/ASHRAE 93-1986 standard. The water heating system for testing with a constant flow limited to a maximum temperature of 55 °C was built; thus the tests were at low temperatures. Using water as working fluid, it was found that the maximum efficiency of the collector was 5.43%, with a flow rate of 0.022 kg/s at a direct solar irradiance with incidence angle 0°. The evaluation methodology and design of the system for testing the collector is reported in this paper.
Schottky barriers in carbon nanotube-metal contacts
Authors: Svensson Johannes , Campbell Eleanor E. B.
Published: December 2011

Semiconducting carbon nanotubes (CNTs) have several properties that are advantageous for field effect transistors such as high mobility, good electrostatics due to their small diameter allowing for aggressive gate length scaling and capability to withstand high current densities. However, in spite of the exceptional performance of single transistors only a few simple circuits and logic gates using CNTs have been demonstrated so far. One of the major obstacles for large scale integration of CNTs is to reliably fabricate p-type and n-type ohmic contacts. To achieve this, the nature of Schottky barriers that often form between metals and small diameter CNTs has to be fully understood. However, since experimental techniques commonly used to study contacts to bulk materials cannot be exploited and studies often have been performed on only single or a few devices there is a large discrepancy in the Schottky barrier heights reported and also several contradicting conclusions. This paper presents a comprehensive review of both theoretical and experimental results on CNT-metal contacts. The main focus is on comparisons between theoretical predictions and experimental results and identifying what needs to be done to gain further understanding of Schottky barriers in CNT-metal contacts.
Density-scaling and the Prigogine–Defay ratio in liquids
Authors: Casalini R. , Gamache R. F. , Roland C. M.
Published: December 2011

The term “strongly correlating liquids” refers to materials exhibiting near proportionality of fluctuations in the potential energy and the virial pressure, as seen in molecular dynamics simulations of liquids whose interactions are comprised primarily of van der Waals forces. Recently it was proposed that the Prigogine–Defay ratio, Π, of strongly correlating liquids should fall close to unity. We verify this prediction herein by showing that the degree to which relaxation times are a function T/ργ, the ratio of temperature to density with the latter raised to a material constant (a property inherent to strongly correlating liquids) is reflected in values of Π closer to unity. We also show that the dynamics of strongly correlating liquids are governed more by density than by temperature. Thus, while Π may never strictly equal 1 for the glass transition, it is approximately unity for many materials, and thus can serve as a predictor of other dynamic behavior. For example, Π ≫ 1 is indicative of additional control parameters besides T/ργ.
Assessing computationally efficient isomerization dynamics: ΔSCF density-functional theory study of azobenzene molecular switching
Authors: Maurer Reinhard J. , Reuter Karsten
Published: December 2011

We present a detailed comparison of the S0, S1 (n → π*) and S2 (π → π*) potential energy surfaces (PESs) of the prototypical molecular switch azobenzene as obtained by Δ-self-consistent-field (ΔSCF) density-functional theory (DFT), time-dependent DFT (TD-DFT) and approximate coupled cluster singles and doubles (RI-CC2). All three methods unanimously agree in terms of the PES topologies, which are furthermore fully consistent with existing experimental data concerning the photo-isomerization mechanism. In particular, sum-method corrected ΔSCF and TD-DFT yield very similar results for S1 and S2, when based on the same ground-state exchange-correlation (xc) functional. While these techniques yield the correct PES topology already on the level of semi-local xc functionals, reliable absolute excitation energies as compared to RI-CC2 or experiment require an xc treatment on the level of long-range corrected hybrids. Nevertheless, particularly the robustness of ΔSCF with respect to state crossings as well as its numerical efficiency suggest this approach as a promising route to dynamical studies of larger azobenzene-containing systems.
A high-sensitive static vector magnetometer based on two vibrating coils
Authors: Yin Jing , Pan Cheng Liang , Wang Hong Bo , Feng Zhi Hua
Published: December 2011

A static vector magnetometer based on two-dimensional (2D) vibrating coils actuated by a piezoelectric cantilever is presented. Two individual sensing coils are orthogonally fastened at the tip of cantilever and piezoelectric sheets are used to excite the cantilever bending. Due to off-axis coupler on the tip, the cantilever generates bending and twisting vibrations simultaneously on their corresponding resonant frequencies, realizing the 2D rotating vibrations of the coils. According to Faraday-Lenz Law, output voltages are induced from the coils. They are amplified by a pre-amplifier circuit, decoupled by a phase-sensitive detector, and finally used to calculate the vector of magnetic field at the coil location. The coil head of a prototype magnetometer possesses a dc sensitivity of around 10 μV/Gs with a good linearity in the measuring range from 0 to 16 μT. The corresponding noise level is about 13.1 nT in the bandwidth from 0.01 Hz to 1 Hz.
Rapid, substrate-independent thickness determination of large area graphene layers
Authors: Venkatachalam Dinesh K. , Parkinson Patrick , Ruffell Simon , Elliman Robert G.
Published: December 2011

Phase-shifting interferometric imaging is shown to be a powerful analytical tool for studying graphene films, providing quantitative analysis of large area samples with an optical thickness resolution of ≤0.05 nm. The technique is readily able to identify single sheets of graphene and to quantitatively distinguish between layers composed of multiple graphene sheets. The thickness resolution of the technique is shown to result from the phase shift produced by a graphene film as incident and reflected light pass through it, rather than from path-length differences produced by surface height variations. This is enhanced by the high refractive index of graphene, estimated in this work to be nG = 2.99 ± 0.18.
Interaction energies of large clusters from many-body expansion
Authors: Góra Urszula , Podeszwa Rafał , Cencek Wojciech , Szalewicz Krzysztof
Published: December 2011

In the canonical supermolecular approach, calculations of interaction energies for molecular clusters involve a calculation of the whole cluster, which becomes expensive as the cluster size increases. We propose a novel approach to this task by demonstrating that interaction energies of such clusters can be constructed from those of small subclusters with a much lower computational cost by applying progressively lower-level methods for subsequent terms in the many-body expansion. The efficiency of such “stratified approximation” many-body approach (SAMBA) is due to the rapid convergence of the many-body expansion for typical molecular clusters. The method has been applied to water clusters (H2O)n, n = 6, 16, 24. For the hexamer, the best results that can be obtained with current computational resources in the canonical supermolecular method were reproduced to within about one tenth of the uncertainty of the canonical approach while using 24 times less computer time in the many-body expansion calculations. For \documentclass[12pt]{minimal}\begin{document}$\rm (H_2 O)_{24}$\end{document}(H2O)24, SAMBA is particularly beneficial and we report interaction energies with accuracy that is currently impossible to obtain with the canonical supermolecular approach. Moreover, our results were computed using two orders of magnitude smaller computer resources than used in the previous best calculations for this system. We also show that the basis-set superposition errors should be removed in calculations for large clusters.
Alignment dependent chemisorption of vibrationally excited CH4(ν3) on Ni(100), Ni(110), and Ni(111)
Authors: Yoder Bruce L. , Bisson Régis , Morten Hundt P. , Beck Rainer D.
Published: December 2011

We present a stereodynamics study of the dissociative chemisorption of vibrationally excited methane on the (100), (110), and (111) planes of a nickel single crystal surface. Using linearly polarized infrared excitation of the antisymmetric C–H stretch normal mode vibration (ν3), we aligned the angular momentum and C–H stretch amplitude of CH4(ν3) in the laboratory frame and measured the alignment dependence of state-resolved reactivity of CH4 for the ν3 = 1, J = 0–3 quantum states over a range of incident translational energies. For all three surfaces studied, in-plane alignment of the C–H stretch results in the highest dissociation probability and alignment along the surface normal in the lowest reactivity. The largest alignment contrast between the maximum and minimum reactivity is observed for Ni(110), which has its surface atoms arranged in close-packed rows separated by one layer deep troughs. For Ni(110), we also probed for alignment effects relative to the direction of the Ni rows. In-plane C–H stretch alignment perpendicular to the surface rows results in higher reactivity than parallel to the surface rows. The alignment effects on Ni(110) and Ni(100) are independent of incident translational energy between 10 and 50 kJ/mol. Quantum state-resolved reaction probabilities are reported for CH4(ν3) on Ni(110) for translational energies between 10 and 50 kJ/mol.
Phonon behavior of CaSnO3 perovskite under pressure
Authors: Kung Jennifer , Lin Yi-Ji , Lin Chih-Ming
Published: December 2011

Raman scattering and x-ray diffraction studies of CaSnO3 perovskite were performed under high-pressure conditions. This high-pressure study was motivated by a recent theoretical study predicting a phase transition in CaSnO3 from GdFeO3-type perovskite to CaIrO3-type structure occurred at 12 GPa. Despite no obvious structure change up to a pressure of 26 GPa based on the x-ray diffraction data, high pressure Raman measurements revealed that some Raman modes disappeared upon compression; either merging into neighboring bands or vanishing. The signals for these Raman peaks were recovered during decompression. The measured pressure derivative of Raman shift (∂ν/∂P) of CaSnO3 ranged from ∼1.29 to ∼4.35, up to 20 GPa. Due to the lack of lattice dynamic study for CaSnO3 perovskite, the mode symmetry for CaSnO3 was tentatively assigned based on the empirical relation among Ca-bearing perovskites. The pressure derivative of the Raman shifts was found to be related to their mode vibrations: modes related to Ca and O shifts had a strong pressure dependence compared with those associated with oxygen octahedral rotation.
Dielectrophoretic assembly and atomic force microscopy modification of reduced graphene oxide
Authors: Zhang Yu , Liu Lianqing , Xi Ning , Wang Yuechao , Dong Zaili , Wejinya Uchechukwu C.
Published: December 2011

A simple and controllable method is developed to experimentally study the effects of defects on reduced graphene oxide (RGO) sheets for nanoelectronics application. First, a deterministic technique is developed to assemble a single layer graphene oxide sheet onto the gaps of microelectrodes by optimizing the dielectrophoretic parameters (10 Vpp at 1 MHz for 5 s). This is followed by the utilization of atomic force microscopy–based mechanical cutting method to form line defects on RGO sheets. Based on these two procedures, the experimental studies of the effects of line defects on RGO are investigated, which provides an alternative approach to study the influence of defects on graphene. The electric transport measurement results show that the electrical performance of the defected RGO devices generally decrease due to Anderson localization, which supports the theoretical studies of the influence of defects on the electrical properties of RGO.
Exciton dissociation and charge carrier recombination processes in organic semiconductors
Authors: Ribeiro Luiz A. , Oliveira Neto Pedro H. , da Cunha Wiliam F. , Roncaratti Luiz F. , Gargano Ricardo , da Silva Filho Demétrio A. , e Silva Geraldo M.
Published: December 2011

Exciton dissociation and charge recombination processes in organic semiconductors, with thermal effects taken into account, are described in this paper. Here, we analyzed the mechanisms of polaron-excitons dissociation into free charge carriers and the consequent recombination of those carriers under thermal effects on two parallel π-conjugated polymers chains electronically coupled. Our results suggest that exciton dissociation in a single molecule give rise to localized, polaron-like charge carrier. Besides, we concluded that in the case of interchain processes, the bimolecular polaron recombination does not lead to an usual exciton state. Rather, this type of recombination leads to an oscillating dipole between the two chains. The recombination time obtained here for these processes are in agreement with the experimental results. Finally, our results show that temperature effects are essential to the relaxation process leading to polaron formation in a single chain, as in the absence of temperature, this process was not observed. In the case of two chains, we conclude that temperature effects also help the bimolecular recombination process, as observed experimentally.
Microwave Debye relaxation analysis of dissolved proteins: Towards free-solution biosensing
Authors: Basey-Fisher T. H. , Hanham S. M. , Andresen H. , Maier S. A. , Stevens M. M. , Alford N. M. , Klein N.
Published: December 2011

Aqueous solutions of a variety of proteins at different concentrations are examined through microwave spectroscopy and compared to sodium chloride and polystyrene nanospheres. The complex permittivity is analysed in terms of the Debye model and the Stokes-Einstein-Debye relation in conjunction with the Maxwell-Garnett equation. According to Einstein’s classical theory of viscosity with Brenner’s adaptation [H. Brenner, Chem. Eng. Sci. 27, 1069 (1972)] for arbitrary solute shapes, the ratio of the alterations of static permittivity and relaxation time of low concentration solutions is found to be independent of concentration and determined by the molecular shape. Our results represent a route towards free-solution identification through molecular finger-printing.
Thickness effect on laser-induced-damage threshold of indium-tin oxide films at 1064 nm
Authors: Wang Haifeng , Huang Zhimeng , Zhang Dayong , Luo Fei , Huang Lixian , Li Yanglong , Luo Yongquan , Wang Weiping , Zhao Xiangjie
Published: December 2011

Laser-induced-damage characteristics of commercial indium-tin oxide (ITO) films deposited by DC magnetron sputtering deposition on K9 glass substrates as a function of the film thickness have been studied at 1064 nm with a 10 ns laser pulse in the 1-on-1 mode, and the various mechanisms for thickness effect on laser-induced-damage threshold (LIDT) of the film have been discussed in detail. It is observed that laser-damage-resistance of ITO film shows dramatic thickness effect with the LIDT of the 50-nm ITO film 7.6 times as large as the value of 300 nm film, and the effect of depressed carrier density by decreasing the film thickness is demonstrated to be the primary reason. Our experiment findings indicate that searching transparent conductive oxide (TCO) film with low carrier density and high carrier mobility is an efficient technique to improve the laser-damage-resistance of TCO films based on maintaining their well electric conductivity.
Broadening of metal-oxide-semiconductor admittance characteristics: Measurement, sources, and its effects on interface state density analyses
Authors: Paterson G. W. , Holland M. C. , Thayne I. G. , Long A. R.
Published: December 2011

The admittance characteristics of a well understood oxide system of Gd0.25Ga0.15O0.60/Ga2O3 on In0.53Ga0.47As are studied at low temperature where the majority of the defect states are frozen. The capacitance-voltage (C-V) characteristics are broadened beyond those expected for an ideal sample. The broadening is ascribed to the presence of a non-uniform surface potential. We report a simple method for measuring the surface potential distribution width using the ac signal amplitude dependence of the C-V profile. A distribution of surface potentials can explain the observed behavior, but only if it includes the admittance of the semiconductor. This is in contrast to the usual approximation that the effect of a distribution of surface potentials on the admittance of the semiconductor is ignored. It is found that the charge state of defect states in the oxide and variation in the doping density of the substrate contribute to the broadening. The implications for inclusion of the semiconductor admittance for the interpretation of ideal characteristics and for the analysisof characteristics with interface states are explored. Both the conductance method and the quasi-equilibrium C-V methods are affected to some extent. An alternative method that can more accurately extract information from the admittance characteristics of the MOS samples is proposed.
Note: Integration of trapped ion mobility spectrometry with mass spectrometry
Authors: Fernandez-Lima F. A. , Kaplan D. A. , Park M. A.
Published: December 2011

The integration of a trapped ion mobility spectrometer (TIMS) with a mass spectrometer (MS) for complementary fast, gas-phase mobility separation prior to mass analysis (TIMS-MS) is described. The ion transmission and mobility separation are discussed as a function of the ion source condition, bath gas velocity, analysis scan speed, RF ion confinement, and downstream ion optical conditions. TIMS mobility resolution depends on the analysis scan speed and the bath gas velocity, with the unique advantage that the IMS separation can be easily tuned from high speed (∼25 ms) for rapid analysis to slower scans for higher mobility resolution (R > 80).
Josephson Hall current in a noncentrosymmetric superconductor/ferromagnet/superconductor junction
Authors: Wang Jun , Hao Lei , Yang Y. H. , Chan K. S.
Published: December 2011

We theoretically study the transverse spin and charge transport in a 2D noncentrosymmetric superconductor (NCS)/ferromagnet (FM)/superconductor Josephson junction, in which the NCS has a dominant triplet order parameter and helical edge states. It is predicted that both equilibrium spin and charge Hall currents can flow transversely in the junction and are driven by the superconducting phase gradient. The physical origin of the Josephson Hall current is the broken time-reversal symmetry due to the FM and the mixing of the helical edge states. The Hall currents are sensitive to the FM magnetization direction, and the planar magnetization component is vitally important because it can lead to a spin flip effect that makes the Cooper pairs tunnel between unequal chiral edge states of the two NCSs.
Phase diagram and spin-glass phenomena in electron-doped La1−xHfxMnO3 (0.05 ≤ x ≤ 0.3) manganite oxides
Authors: Guo E. J. , Wang L. , Wu Z. P. , Wang L. , Lu H. B. , Jin K. J. , Gao J.
Published: December 2011

The effects of tetravalent hafnium doping on the structural, transport, and magnetic properties of polycrystalline La1−xHfxMnO3 (LHMO) (0.05 ≤ x ≤ 0.3) were investigated systematically. LHMO exhibited a typical colossal magnetoresistance effect via the double-exchange between Mn2+ and Mn3+ ions, instead of that between Mn3+ and Mn4+ ions in hole-doped manganites. A phase diagram was obtained for the first time through magnetization and resistance measurements in a broad temperature range. As the Hf concentration varied from x = 0.05 to 0.3, the Curie point and metal-to-insulator transition temperature increased significantly, whereas the magnetization and resistivity decreased remarkably. An abnormal enhancement of the magnetization was observed at about 42 K. It was further confirmed that a second magnetic phase MnO2 in LHMO gives rise to such a phenomenon. The possible causes are discussed in detail. The dynamic magnetic properties of LHMO, including relaxation and aging processes, were studied, demonstrating a spin-glass state at low temperature accompanied by a ferromagnetic phase.
Mismatched alloy nanowires for electronic structure tuning
Authors: Yim Joanne W. L. , Grigoropoulos Costas P. , Wu Junqiao
Published: December 2011

Electronic structure engineering is essential for producing materials suited for efficient solid-state devices. Mismatched semiconductors offer wide tunability of electronic structure with only a small change in composition. Here, we report a combined compound-elemental source vapor transport method for synthesis of mismatched alloy nanowires (NWs) of ZnSe1−xTex across the composition range. The alloy composition can be continuously tuned by varying the growth temperature from ZnSe (x = 0) at higher temperature to ZnTe (x = 1) at lower temperature. The nanowires have structure and bandgaps consistent with their compositions, with lattice parameters varying with Vegard’s law and emissions following predicted extreme bandgap bowing.
Critical behavior of megabase-size DNA toward the transition into a compact state
Authors: Yoshikawa Yuko , Suzuki Yuki , Yamada Kozo , Fukuda Wakao , Yoshikawa Kenichi , Takeyasu Kunio , Imanaka Tadayuki
Published: December 2011

We studied the changes in the higher-order structure of a megabase-size DNA (S120-1 DNA) under different spermidine (SPD) concentrations through single-molecule observations using fluorescence microscopy (FM) and atomic force microscopy (AFM). We examined the difference between the folding transitions in S120-1 DNA and sub-megabase-size DNA, T4 DNA (166 kbp). From FM observations, it is found that S120-1 DNA exhibits intra-chain segregation as the intermediate state of transition, in contrast to the all-or-none nature of the transition on T4 DNA. Large S120-1 DNA exhibits a folding transition at lower concentrations of SPD than T4 DNA. AFM observations showed that DNA segments become aligned in parallel on a two-dimensional surface as the SPD concentration increases and that highly intense parallel alignment is achieved just before the compaction. S120-1 DNA requires one-tenth the SPD concentration as that required by T4 DNA to achieve the same degree of parallel ordering. We theoretically discuss the cause of the parallel ordering near the transition into a fully compact state on a two-dimensional surface, and argue that such parallel ordering disappears in bulk solution.
Uniqueness of the solution to inverse scattering problem with scattering data at a fixed direction of the incident wave
Authors: Ramm A. G.
Published: December 2011

Let q(x) be real-valued compactly supported sufficiently smooth function. It is proved that the scattering data A(β, α0, k) ∀β ∈ S2, ∀k > 0, determine q uniquely. Here, α0 ∈ S2 is a fixed direction of the incident plane wave.
Band-gap-dependent emissions from conjugated polymers coupled silver nanocap array
Authors: Kong Fan , Zhang Xueqin , Lang Xianzhong , Lin Baoping , Yang Yimin , Qiu Teng
Published: December 2011

The optical properties of poly(2,5-dioctyloxy-p-phenylene) (PPP) and poly[3-(2,5,8-trioxanonyl) thiophene] (P3TT) coupled silver nanocap array have been investigated. The absorption spectrum of P3TT and the emission spectrum of PPP match the absorption of the silver nanocap array. Plasmon energy transfer occurs from the silver nanocap array to P3TT or from PPP to the silver nanocap array, resulting in the largely increased or decreased photoluminescence (PL), respectively. The PL enhancement of the P3TT coupled silver nanocap array is more than 9-fold; whereas the PL intensity of the PPP coupled silver nanocap array is less than one-tenth of the PPP film.
Direct and indirect excitation of Nd3+ ions sensitized by Si nanocrystals embedded in a SiO2 thin film
Authors: Steveler E. , Rinnert H. , Vergnat M.
Published: December 2011

The luminescence properties of Nd-doped SiOx layers containing silicon nanocrystals (Si-ncs) were investigated by steady state, time-dependent and power-dependent photoluminescence spectrometry and photoluminescence excitation experiments. Both direct and indirect excitation processes of Nd3+ ions have been evidenced. The energy transfer mechanism between Si-ncs and Nd3+ ions is favored by the overlap between the emission spectrum of confined excitons in Si-ncs and the Nd3+ absorption from the ground state to 4F5/2 electronic level. The more intense Nd-related emission was obtained in samples containing 0.5 at. % of Nd and characterized by an indirect excitation cross section equal to 8 × 10−15 cm2.
Model for nanosecond laser induced damage in potassium titanyl phosphate crystals
Authors: Wagner Frank R , Duchateau Guillaume , Hildenbrand Anne , Natoli Jean-Yves , Commandré Mireille
Published: December 2011

A model for nanosecond laser induced damage in the bulk of potassium titanyl phosphate nonlinear optical crystals is presented. In a first step, laser-induced damage precursors are produced by multiphoton absorption. In a second step, the damage precursors are activated. Damage occurs if the precursor activation rate exceeds a critical value. Basic considerations allow evaluating the parameters of the model. The validity of the model is discussed by comparing it to several experimental observations, in particular, the decrease of the laser damage threshold during second harmonic generation of 1064 nm pulses.
p-type doping effect on the performance of organic-inorganic hybrid solar cells
Authors: Lei Xiaofei , Zhang Fute , Song Tao , Sun Baoquan
Published: December 2011

The doping effects in poly(3-hexylthiophene) (P3HT) on the hybrid n-Si/P3HT solar cells were investigated. Oxygen and tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) doping in P3HT could dramatically improve the device performance. The improvements were related to the Fermi level shift in P3HT towards its highest occupied molecular orbital, leading to a larger built-in voltage generated at the n-Si/P3HT interface for favorable charge transfer. This Fermi level shift was ascribed to the electron transfer from P3HT to the dopant, which was characterized by the absorption spectra and the photoluminescence lifetime. Solution-based F4-TCNQ displayed as a potential candidate to p-doped conjugated polymer to improve charge transfer/transport properties for the hybrid solar cells.
Electrostatic carrier doping of GdTiO3/SrTiO3 interfaces
Authors: Moetakef Pouya , Cain Tyler A. , Ouellette Daniel G. , Zhang Jack Y. , Klenov Dmitri O. , Janotti Anderson , Van de Walle Chris G. , Rajan Siddharth , Allen S. James , Stemmer Susanne
Published: December 2011

Heterostructures and superlattices consisting of a prototype Mott insulator, GdTiO3, and the band insulator SrTiO3 are grown by molecular beam epitaxy and show intrinsic electronic reconstruction, approximately ½ electron per surface unit cell at each GdTiO3/SrTiO3 interface. The sheet carrier densities in all structures containing more than one unit cell of SrTiO3 are independent of layer thicknesses and growth sequences, indicating that the mobile carriers are in a high concentration, two-dimensional electron gas bound to the interface. These carrier densities closely meet the electrostatic requirements for compensating the fixed charge at these polar interfaces. Based on the experimental results, insights into interfacial band alignments, charge distribution, and the influence of different electrostatic boundary conditions are obtained.
Carrier dynamics and activation energy of CdTe quantum dots in a CdxZn1−xTe quantum well
Authors: Han W. I. , Lee J. H. , Yu J. S. , Choi J. C. , Lee H. S.
Published: December 2011

We investigate the optical properties of CdTe quantum dots (QDs) in a Cd0.3Zn0.7Te quantum well (QW) grown on GaAs (100) substrates. Carrier dynamics of CdTe/ZnTe QDs and quantum dots-in-a-well (DWELL) structure is studied using time-resolved photoluminescence (PL) measurements, which show the longer exciton lifetime of the DWELL structure. The activation energy of the electrons confined in the DWELL structure, as obtained from the temperature-dependent PL spectra, was also higher than that of electrons confined in the CdTe/ZnTe QDs. This behavior is attributed to the better capture of carriers into QDs within the surrounding QW.
Mg-induced terahertz transparency of indium nitride films
Authors: Ahn H. , Chia J.-W. , Lee H.-M. , Hong Y.-L. , Gwo S.
Published: December 2011

Terahertz time-domain spectroscopy (THz-TDS) has been used to investigate electrical properties of Mg-doped indium nitride (InN). Mg-doping in InN was found to significantly increase terahertz transmittance. THz-TDS analysis based on the Drude model shows that this high transmittance from Mg-doped InN is mainly due to the reduction in mobility associated with ionized dopants. The Hall-effect-measured mobility is typically lower than the THz-TDS-measured mobility for the same samples. However, the results of both measurements have the same slope in the linear relation between mobility and density. By introducing a compensation ratio of ∼0.2, an excellent agreement in mobilities of two methods is obtained.
Electrical detection of nonlinear ferromagnetic resonance in single elliptical permalloy thin film using a magnetic tunnel junction
Authors: Bi Chong , Fan Xin , Pan Liqing , Kou Xiaoming , Wu Jun , Yang Qinghui , Zhang Huaiwu , Xiao John Q.
Published: December 2011

A quantitative method to detect ferromagnetic resonance using magnetic tunnel junction structure has been developed. Experimental results reveal three distinct regions for single elliptical permalloy film of micrometer lateral size. Above the spin wave instability threshold, the experimental results show a linear response of the longitudinal magnetization component to the microwave field amplitude over a large range rather than a lock-up phenomenon appeared in macroscopic permalloy films and then a phase limiting behavior. The linear behavior can be described by the theoretical model describing subsidiary resonance.
Fabrication of horizontal silicon nanowire arrays on insulator by ion irradiation
Authors: Ou Xin , Kögler Reinhard , Wei Xing , Mücklich Arndt , Wang Xi , Skorupa Wolfgang , Facsko Stefan
Published: December 2011

We report a simple and potentially mass productive technique to fabricate horizontal single crystalline Si nanowire arrays on insulating substrate based on a self-organized pattern formation mechanism during Xe+ ion beam irradiation of Si-on-insulator material. A periodic ripple surface pattern is created by ion irradiation at 67o incidence angle to the surface normal. The transfer of this pattern to the oxide interface results in an array of electrically disconnected parallel ordered Si nanowires on the insulating oxide. Doping of the nanowires was demonstrated by boron ion implantation and annealing. The morphology and resistivity of the narrow nanowires with large aspect ratio were analysed by cross sectional transmission electron microscopy and scanning spreading resistance microscopy, respectively. Physical reasons of the observed low carrier activation are discussed.
Field-controlled electron transfer and reaction kinetics of the biological catalytic system of microperoxidase-11 and hydrogen peroxide
Authors: Choi Yongki , Yau Siu-Tung
Published: December 2011

Controlled reaction kinetics of the bio-catalytic system of microperoxidase-11 and hydrogen peroxide has been achieved using an electrostatic technique. The technique allowed independent control of 1) the thermodynamics of the system using electrochemical setup and 2) the quantum mechanical tunneling at the interface between microperoxidase-11 and the working electrode by applying a gating voltage to the electrode. The cathodic currents of electrodes immobilized with microperoxidase-11 showed a dependence on the gating voltage in the presence of hydrogen peroxide, indicating a controllable reduction reaction. The measured kinetic parameters of the bio-catalytic reduction showed nonlinear dependences on the gating voltage as the result of modified interfacial electron tunnel due to the field induced at the microperoxidase-11-electrode interface. Our results indicate that the kinetics of the reduction of hydrogen peroxide can be controlled by a gating voltage and illustrate the operation of a field-effect bio-catalytic transistor, whose current-generating mechanism is the conversion of hydrogen peroxide to water with the current being controlled by the gating voltage.