bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport of black carbon to polar regions: Sensitivity and forcing by black carbon
Authors: Zhou Cheng , Penner Joyce E. , Flanner Mark G. , Bisiaux Marion M. , Edwards Ross , McConnell Joseph R.
Published: November 2012

The transport of black carbon (BC) to polar regions is studied using the University of Michigan IMPACT aerosol model driven by two sets of meteorological fields from the NCAR CAM5 and GFDL AM3 models. The sensitivity of the transport of BC to wet deposition processes is tested by varying the wet deposition in large‐scale precipitation. BC concentrations and deposition in polar regions are shown to be sensitive to both the meteorological fields and the wet deposition treatment. Using the default wet deposition, both IMPACT‐CAM5 and IMPACT‐AM3 simulate an appropriate amount of BC deposition in polar regions as compared to ice core observations. Although the seasonal cycle of BC surface air concentrations is reasonable, the concentrations are about 1∼2 orders of magnitude smaller than observations. With reduced wet deposition efficiency, the total deposition of BC increases by a factor of ∼2 to ∼3 due to more transport to the poles. The near surface BC concentrations increase even more (by a factor of ∼3 to ∼10) but are still largely underestimated especially in the north polar region. The radiative forcing from the BC deposited on snow and sea ice is also sensitive to the wet deposition treatment and the different meteorological fields. The global (Arctic) annual mean forcing is about +0.020 W m−2 (+0.11 W m−2) for IMPACT‐CAM5 and +0.022 W m−2 (+0.13W m−2) for IMPACT‐AM3.
Evidence of ENSO mega‐drought triggered collapse of prehistory Aboriginal society in northwest Australia
Authors: McGowan Hamish , Marx Samuel , Moss Patrick , Hammond Andrew
Published: November 2012

The Kimberley region of northwest Australia contains one of the World's largest collections of rock art characterised by two distinct art forms; the fine featured anthropomorphic figures of the Gwion Gwion or Bradshaw paintings, and broad stroke Wandjina figures. Luminescence dating of mud wasp nests overlying Gwion Gwion paintings has confirmed an age of at least 17,000 yrs B.P. with the most recent dates for these paintings from around the mid‐Holocene (5000 to 7000 yrs B.P.). Radiocarbon dating indicates that the Wandjina rock art then emerged around 3800 to 4000 yrs B.P. following a hiatus of at least 1200 yrs. Here we show that a mid‐Holocene ENSO forced collapse of the Australian summer monsoon and ensuing mega‐drought spanning approximately 1500 yrs was the likely catalyst of this change in rock art. The severity of the drought we believe was enhanced through positive feedbacks triggered by change in land surface condition and increased aerosol loading of the atmosphere leading to a weakening or failure of monsoon rains. This confirms that pre‐historic aboriginal cultures experienced catastrophic upheaval due to rapid natural climate variability and that current abundant seasonal water supplies may fail again if significant change in ENSO occurs.
CMIP5 multimodel ensemble projection of storm track change under global warming
Authors: Chang Edmund K. M. , Guo Yanjuan , Xia Xiaoming
Published: November 2012

CMIP5 multimodel ensemble projection of midlatitude storm track changes has been examined. Storm track activity is quantified by temporal variance of meridional wind and sea level pressure (psl), as well as cyclone track statistics. For the Southern Hemisphere (SH), CMIP5 models project clear poleward migration, upward expansion, and intensification of the storm track. For the Northern Hemisphere (NH), the models also project some poleward shift and upward expansion of the storm track in the upper troposphere/lower stratosphere, but mainly weakening of the storm track toward its equatorward flank in the troposphere. Consistent with these, CMIP5 models project significant increase in the frequency of extreme cyclones during the SH cool season, but significant decrease in such events in the NH. Comparisons with CMIP3 projections indicate high degrees of consistency for SH projections, but significant differences are found in the NH. Overall, CMIP5 models project larger decrease in storm track activity in the NH troposphere, especially over North America in winter, where psl variance as well as cyclone frequency and amplitude are all projected to decrease significantly. In terms of climatology, similar to CMIP3, most CMIP5 models simulate storm tracks that are too weak and display equatorward biases in their latitude. These biases have also been related to future projections. In the NH, the strength of a model's climatological storm track is negatively correlated with its projected amplitude change under global warming, while in the SH, models with large equatorward biases in storm track latitude tend to project larger poleward shifts.
Interaction between injection points during hydraulic fracturing
Authors: Hals Kjetil M. D. , Berre Inga
Published: November 2012

We study the geomechanical stress interaction between two injection points during hydraulic fracturing (hydrofracking) and how this interaction in combination with disorder influences the fracturing process. To this end, we develop an effective continuum model of the hydrofracking of heterogeneous poroelastic media that captures the coupled dynamics of the fluid pressure and the fractured rock matrix and models both the tensile and shear failure of the rock. For injection points that are separated by less than a critical correlation length, our numerical simulations show that the fracturing process around each point is strongly correlated with the position of the neighboring point. The magnitude of the correlation length depends on the degree of heterogeneity of the rock and is on the order of 30–45 m for rocks with low permeabilities. In the strongly correlated regime, we predict a novel effective fracture force that attracts the fractures toward the neighboring injection point.
Glucose induces autophagy under starvation conditions by a p38 MAPK-dependent pathway
Authors: Moruno-Manchón Jose Félix , Pérez-Jiménez Eva , Knecht Erwin
Published: November 2012

Autophagy is a natural process of ‘self-eating’ that occurs within cells and can be either pro-survival or can cause cell death. As a pro-survival mechanism, autophagy obtains energy by recycling cellular components such as macromolecules or organelles. In response to nutrient deprivation, e.g. depletion of amino acids or serum, autophagy is induced and most of these signals converge on the kinase mTOR (mammalian target of rapamycin). It is commonly accepted that glucose inhibits autophagy, since its deprivation from cells cultured in full medium induces autophagy by a mechanism involving AMPK (AMP-activated protein kinase), mTOR and Ulk1. However, we show in the present study that under starvation conditions addition of glucose produces the opposite effect. Specifically, the results of the present study demonstrate that the presence of glucose induces an increase in the levels of LC3 (microtubule-associated protein 1 light chain)-II, in the number and volume density of autophagic vacuoles and in protein degradation by autophagy. Addition of glucose also increases intracellular ATP, which is in turn necessary for the induction of autophagy because the glycolysis inhibitor oxamate inhibits it, and there is also a good correlation between LC3-II and ATP levels. Moreover, we also show that, surprisingly, the induction of autophagy by glucose is independent of AMPK and mTOR and mainly relies on p38 MAPK (mitogen-activated protein kinase).
Post-translational modification in the archaea: structural characterization of multi-enzyme complex lipoylation
Authors: Posner Mareike G. , Upadhyay Abhishek , Crennell Susan J. , Watson Andrew J. A. , Dorus Steve , Danson Michael J. , Bagby Stefan
Published: November 2012

Lipoylation, the covalent attachment of lipoic acid to 2-oxoacid dehydrogenase multi-enzyme complexes, is essential for metabolism in aerobic bacteria and eukarya. In Escherichia coli, lipoylation is catalysed by LplA (lipoate protein ligase) or by LipA (lipoic acid synthetase) and LipB [lipoyl(octanoyl) transferase] combined. Whereas bacterial and eukaryotic LplAs comprise a single two-domain protein, archaeal LplA function typically involves two proteins, LplA-N and LplA-C. In the thermophilic archaeon Thermoplasma acidophilum, LplA-N and LplA-C are encoded by overlapping genes in inverted orientation (lpla-c is upstream of lpla-n). The T. acidophilum LplA-N structure is known, but the LplA-C structure is unknown and LplA-C's role in lipoylation is unclear. In the present study, we have determined the structures of the substrate-free LplA-N–LplA-C complex and E2lipD (dihydrolipoyl acyltransferase lipoyl domain) that is lipoylated by LplA-N–LplA-C, and carried out biochemical analyses of this archaeal lipoylation system. Our data reveal the following: (i) LplA-C is disordered but folds upon association with LplA-N; (ii) LplA-C induces a conformational change in LplA-N involving substantial shortening of a loop that could repress catalytic activity of isolated LplA-N; (iii) the adenylate-binding region of LplA-N–LplA-C includes two helices rather than the purely loop structure of varying order observed in other LplA structures; (iv) LplAN–LplA-C and E2lipD do not interact in the absence of substrate; (v) LplA-N–LplA-C undergoes a conformational change (the details of which are currently undetermined) during lipoylation; and (vi) LplA-N–LplA-C can utilize octanoic acid as well as lipoic acid as substrate. The elucidated functional inter-dependence of LplA-N and LplA-C is consistent with their evolutionary co-retention in archaeal genomes.
Transport properties of surface electrons in helium on a structured substrate
Authors: Smorodin A. V. , Nikolaenko V. A. , Sokolov S. S. , Karachevtseva L. A. , Lytvynenko O. A.
Published: November 2012

A zero-dimensional electron system is proposed and realized on superfluid helium in cylindrical macropores of a structured substrate made of silicon which undergoes a transition to an insulating state at liquid helium temperatures. It is shown that in the presence of holding electric field the depth of the potential well for an electron over a spherically concave surface of helium depends strongly on the radius of the liquid surface, which makes it possible to vary widely the system parameters. The conductivity of surface electrons on a structured substrate was measured. The experiments were carried out in the temperature range T = 0.5–1.6 K for the electron density from 2.6·106 to 8·108 cm−2 for the holding electric fields up to 10 V/cm. It is established that the character of the charge transfer on helium is highly dependent on both the carrier concentration and the curvature radius of liquid filling the substrate macropores. For a large curvature radius and thus a relatively large thickness of the helium film on the substrate the conductivity of electrons at low temperatures is of thermally activated character. With reducing the curvature radius of liquid the temperature dependence of conductivity weakens, and for some values of the radius the dependence of conductivity on the holding potential has a local "dip" ("dip"-effect). For a small curvature radius of the helium surface the conductivity of electron system depends weakly on the temperature, and the "dip"-effect is not observed. The observed dependences were interpreted assuming the formation of localized electron states in the vicinity of macropores.
Stationary property of the thermodynamic potential of the Hubbard model in strong coupling diagrammatic approach for superconducting state
Authors: Moskalenko V. A. , Dohotaru L. A. , Digor D. F. , Cebotari I. D.
Published: November 2012

Diagrammatic analysis for normal state of Hubbard model proposed in our previous paper is generalized and used to investigate superconducting state of this model. We use the notion of charge quantum number to describe the irreducible Green's function of the superconducting state. As in the previous paper we introduce the notion of tunneling Green's function and of its mass operator. This last quantity turns out to be equal to correlation function of the system. We proved the existence of exact relation between renormalized one-particle propagator and thermodynamic potential which includes integration over auxiliary interaction constant. The notion of skeleton diagrams of propagator and vacuum kinds were introduced. These diagrams are constructed from irreducible Green's functions and tunneling lines. Identity of this functional to the thermodynamic potential has been proved and the stationarity with respect to variation of the mass operator has been demonstrated.
The fluctuations of the spin state of 3d-ions near the “triple point”
Authors: Zhitlukhina E. S. , Lamonova K. V. , Orel S. M. , Pashkevich Yu. G.
Published: November 2012

The spin states of 3d ions placed in an arbitrarily distorted coordination complex are investigated within the semiempirical modified crystal-field theory. A scheme for constructing spin-state diagrams is presented. Spin-state diagrams are obtained for transition metal ions with electron configurations 3d4, 3d5, and 3d6 placed in a pyramidal environment. The spin-state diagrams for all configurations studied display so-called “triple points”, i.e., regions where the spin states are mixed in equal proportions. The spin-state evolution of a five-coordinated Co3+ ion in the layered rare-earth cobaltite GdBaCo2O5.5 is studied. It is found that the intermediate spin state of the Co3+ ion is stabilized by the apex oxygen displacement along the pyramidal axis.
Influence of magnetic anisotropy on hysteresis behavior in the two-spin model of a ferro/antiferromagnet bilayer with exchange bias
Authors: Grechnev A. G. , Kovalev A. S. , Pankratova M. L.
Published: November 2012

The influence of magnetic anisotropy of a ferromagnetic film on the phenomenon of exchange bias is studied here. Hysteresis behavior in the two-spin model of a ferro/antiferromagnetic (FM/AFM) bilayer with exchange bias has been investigated in detail. In this model a half-space of an AFM with fixed magnetic configuration comes in contact with a two-layer FM film. Twelve different types of magnetization curves M(H) (both with and without hysteresis) have been found. Some of the M(H) curves demonstrate unusual features, such as plateaus and inclined segments. The hysteresis loop becomes asymmetric if surface anisotropy is taken into account.
Saturation of fullerite C60 with hydrogen: Adsorption crossover studies
Authors: Yagotintsev K. A. , Legchenkova I. V. , Stetsenko Yu. E. , Zinoviev P. V. , Zoryansky V. N. , Prokhvatilov A. I. , Strzhemechny M. A.
Published: November 2012

The influence of hydrogen sorption in fullerite C60 at pressure of 30 atm and saturation temperature 150–380 °C on its structural and thermodynamic properties was studied using x-ray powder diffraction and photoluminescence methods. The kinetics of hydrogen sorption at different temperatures was studied by monitoring the time dependence of the fullerite lattice parameter. It was found that the sorption mechanism undergoes change upon the temperature increase. Diffusion-controlled filling of the cavities in fullerite lattice with hydrogen molecules at temperatures T ≤ 250 °C is replaced by chemical interaction between hydrogen and fullerene molecules at higher temperatures, resulting in the formation of a new molecular material: hydrofullerite C60Hx. It was established that the transition from physisorption to chemisorption of hydrogen by fullerite (adsorption crossover) occurs in the temperature range 300 °C > T > 250 °C. The hydrogenation of C60 was shown to dramatically increase the volume of the C60 cubic cell, decrease the thermal expansion of the crystals, and suppress the orientational transition and formation of a glass state. The maximum deformation levels of fcc lattice as well as the characteristic times of voids filling and hydrogenation were determined for the cases of diffusion-controlled voids filling and chemisorption, respectively.
Spin waves on the surface of a semiconductor nanotube with a superlattice
Authors: Ermolaev A. M. , Rashba G. I. , Solyanik M. A.
Published: November 2012

Landau-Silin spin waves spectra on the surface of a cylindrical semiconductor nanotube with a superlattice were studied. The energy spectrum of the tube was derived within the framework of short-range electron interaction model in Hartree-Fock approximation. The components of the tensor of electron gas dynamic spin susceptibility were calculated using the random phase approximation. Spin waves spectra in the cases of low and high electron density were obtained. It was shown that the wave frequencies exhibit oscillations similar to de Haas-van Alphen oscillations upon variation of nanotube parameters and Aharonov-Bohm oscillations upon variation of the magnetic flux through its cross-section. The beating pattern in the spectrum of magnons was found.
Diffusion of H2 and Ne impurities in fullerite C60. Quantum effects
Authors: Dolbin A. V. , Esel'son V. B. , Gavrilko V. G. , Manzhelii V. G. , Vinnikov N. A. , Popov S. N.
Published: November 2012

The kinetics of sorption and subsequent desorption of normal H2 and Ne gases in C60 powder has been investigated in the temperature range 12–292 K using the method of direct pressure measurement. The measured characteristic times for filling the octahedral interstitial sites of fullerite with gas molecules were used to obtain the temperature dependences of the diffusion coefficients in fullerite for H2 and Ne. Upon cooling down below room temperature the diffusion coefficients of the impurities were found to initially decrease in both solid state solutions and then rise steeply below 90 K (H2) or 100 K (Ne). At the lowest temperatures reached in the experiments, the temperature dependence of the diffusion leveled. The features revealed are attributed to the competition between the thermally activated diffusion, which is dominant at comparatively high temperatures, and the quantum diffusion, which prevails at low temperatures.
Structural homogeneity of nanocrystalline VT1-0 titanium. Low-temperature micromechanical properties
Authors: Rusakova A. V. , Lubenets S. V. , Fomenko L. S. , Moskalenko V. A.
Published: November 2012

The microhardness of samples of VT1-0 titanium with grain sizes ranging from 35 nm to 10 μm is measured at temperatures of 77-300 K. Nanocrystalline samples produced by rolling at low temperatures are found to be quite homogeneous, and their structure is stable with respect to thermal and mechanical interactions. The interrelationship between microhardness and grain size is well described by the Hall-Petch relationship, the parameters of which depend on temperature. Data on the temperature dependence of the microhardness and the Hall-Petch coefficient indicate that the microplastic deformation is of a thermally activated, dislocation character, regardless of grain size.
Atomic-resolution study of polarity reversal in GaSb grown on Si by scanning transmission electron microscopy
Authors: Hosseini Vajargah S. , Woo S. Y. , Ghanad-Tavakoli S. , Kleiman R. N. , Preston J. S. , Botton G. A.
Published: November 2012

The atomic-resolved reversal of the polarity across an antiphase boundary (APB) was observed in GaSb films grown on Si by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The investigation of the interface structure at the origin of the APB reveals that coalescence of two domains with Ga-prelayer and Sb-prelayer causes the sublattice reversal. The local strain and lattice rotation distributions of the APB, attributed to the discordant bonding length at the APB with the surrounding GaSb lattice, were further studied using the geometric phase analysis technique. The crystallographic characteristics of the APBs and their interaction with other planar defects were observed with HAADF-STEM. The quantitative agreement between experimental and simulated images confirms the observed polarities in the acquired HAADF-STEM data. The self-annihilation mechanism of the APBs is addressed based on the rotation induced by anti-site bonds and APBs' faceting.
Comparison of tunneling current assisted by neutral and positive traps with finite ranged core-potential
Authors: Sun Zhong , Zhang Manhong , Huo Zongliang , Wang Yong , Liu Ming
Published: November 2012

Trap assisted tunneling current (JTAT) has been computed for neutral and positive traps with finite ranged core-potential in a metal-oxide-semiconductor structure. The calculation is based on Bardeen transfer Hamiltonian approach and the elastic tunneling approximation and includes both direct tunneling at low voltage and tunneling ionization at high voltage. In both regimes, two different forms of transition matrix elements have been presented and their numerical values have been compared. For both kinds of traps, JTAT shows a similar shape for its dependence on the oxide voltage and increases slightly with increasing the radius of the core-potential. However, compared to the neutral traps, JTAT induced by positive traps is enhanced by about half order due to the existence of the long-ranged Coulomb potential tail. The usual δ-function approximation for the core potential of neutral traps underestimates JTAT by a half order.
Magnetic field driven transition from an antiferromagnetic ground state to a ferrimagnetic state in Rb0.19Ba0.3Mn1.1[Fe(CN)6]·0.48H2O Prussian blue analogue
Authors: Yusuf S. M. , Thakur N. , Medarde M. , Keller L.
Published: November 2012

We report a magnetic field dependent (H) antiferromagnetic (AFM) to ferrimagnetic (FIM) transition in Rb0.19Ba0.3Mn1.1[Fe(CN)6]·0.48H2O Prussian blue analogue. A microscopic understanding of the nature of this field induced AFM to FIM transition is achieved by carrying out a low temperature neutron diffraction study under an external magnetic field. A decrease in Néel temperature and an evolution of a ferrimagnetic phase with an increase in dc magnetic field are evident in dc magnetic field dependent ac susceptibility measurements. With an increase in H, the FIM phase grows at the expense of the AFM phase, and for H > 4 T, the system fully transforms to the FIM phase. A magnetic structure consisting of an antiparallel stacking of ferrimagnetic sheets along crystallographic c-direction is proposed for the FIM phase. Based on the results obtained, a phase diagram describing the evolution of both magnetic phases under external magnetic field is presented.
Comprehensive characterization of thermophysical properties in solids using thermal impedance
Authors: Martínez-Flores J. J. , Licea-Jiménez L. , Pérez García S. A. , Rodríguez-Viejo J. , Alvarez-Quintana J.
Published: November 2012

Thermal impedance Zth(iω) is a way of defining the thermophysical characteristics and behavior of thermal systems. Existing photoacoustic and photothermal approaches based on thermal impedance formalism merely allows a partial thermal characterization of the materials (generally, either thermal diffusivity or thermal effusivity). In this work, a new approach based on the thermal impedance concept in terms of its characteristic thermal time constant is developed from thermal quadrupoles formalism. The approach outlined in this contribution presents a set of analytical equations in which through a single measurement of thermal impedance is sufficient to obtain a comprehensive characterization of the thermophysical properties of solid materials in a simple way.
Phase constitution and interface structure of nano-sized Ag-Cu/AlN multilayers: Experiment and ab initio modeling
Authors: Pigozzi Giancarlo , Antušek Andrej , Janczak-Rusch Jolanta , Parlinska-Wojtan Magdalena , Passerone Daniele , Antonio Pignedoli Carlo , Bissig Vinzenz , Patscheider Jörg , Jeurgens Lars P. H.
Published: November 2012

Nano-sized Ag-Cu8nm/AlN10nm multilayers were deposited by reactive DC sputtering on α-Al2O3(0001) substrates. Investigation of the phase constitution and interface structure of the multilayers evidences a phase separation of the alloy sublayers into nanosized grains of Ag and Cu. The interfaces between the Ag grains and the quasi-single-crystalline AlN sublayers are semi-coherent, whereas the corresponding Cu/AlN interfaces are incoherent. The orientation relationship between Ag and AlN is constant throughout the entire multilayer stack. These observations are consistent with atomistic models of the interfaces as obtained by ab initio calculations.
Cyclic powder formation during pulsed injection of hexamethyldisiloxane in an axially asymmetric radiofrequency argon discharge
Authors: Despax B. , Makasheva K. , Caquineau H.
Published: November 2012

A new approach of periodic production of dusty plasma consisting of pulsed injection of hexamethyldisiloxane (HMDSO) in argon axially asymmetric radiofrequency (RF) discharge was investigated in this work. The range of plasma operating conditions in which this dusty plasma can exist was closely examined. The obtained results clearly show that a net periodicity in the formation/disappearance of dust particles in the plasma can be maintained on a very large scale of discharge duration. The significance of discharge axial asymmetry to the dust particles behaviour in the plasma is revealed by the development of an asymmetric in shape void shifted towards the powered RF electrode. The key role of the reactive gas and its pulsed injection on each stage of the oscillating process of formation/disappearance of dust particles is disclosed by optical and electrical measurements. It is shown that the period of dusty plasma formation/disappearance is inversely related to the HMDSO injection time. Moreover, the impact of time injection over short period (5 s) is examined. It indicates the conflicting role played by the HMDSO on the reduction of dusty plasma during the reactive gas injection and the reappearance of particles in the plasma during the time off. The electronegative behavior of the plasma in the presence of negatively charged particles seems to explain the energetic modifications in the discharge. A frequency analysis of the floating potential reveals all these cyclic processes. Particularly, in the 10–200 Hz frequency range, the presence and the evolution of dust particles in the plasma over one generation can be observed.
Nonlinear stress-strain relations for crystalline solids in initially deformed state
Authors: Wang Hao , Li Mo
Published: November 2012

We show a general nonlinear stress-strain response for crystalline materials subject to an initial deformation. The scheme is implemented using 3rd, 4th, and higher order elastic constants. We apply the formulation to a face-centered cubic crystalline Au under shear while in an initially hydrostatically deformed state. We then compare the nonlinear shear stress-strain relations from our derived formulation with Hellmann-Feynman shear stress-strain curves obtained directly from ab initio calculations. The results show that the general analytical expression for the nonlinear stress-strain relation is satisfactory and thus expected to have many applications where ab initio calculations are limited, including cases at finite temperature.
A transfer Hamiltonian approach for an arbitrary quantum dot array in the self-consistent field regime
Authors: Illera S. , Garcia-Castello N. , Prades J. D. , Cirera A.
Published: November 2012

A transport methodology to study electron transport between quantum dot arrays based on the transfer Hamiltonian approach is presented. The interactions between the quantum dots and between the quantum dots and the electrodes are introduced via transition rates and capacitive couplings. The effects of the local potential are computed within the self-consistent field regime. The model has been developed and expressed in a matrix form in order to make it extendable to larger systems. Transport through several quantum dot configurations has been studied in order to validate the model. Despite the simplicity of the model, well-known effects are satisfactorily reproduced and explained. The results qualitatively agree with other results obtained using more complex theoretical approaches.
Transmission of microwaves through exchange-coupled bi-layer magnetic films in ferromagnetic and standing spin wave resonances
Authors: Kostylev M.
Published: November 2012

In this work, we have studied theoretically the transmission and reflection of electromagnetic waves in the microwave frequency range through the in-plane magnetized exchange-coupled bi-layer ferromagnetic metallic films. It was found that responses of the films in transmission and reflection are very different. In transmission, the response of the fundamental mode dominates, but in reflection, the first exchange mode demonstrates the largest variation in amplitude with respect to the off-resonance regime. The theory also predicts an interesting regime of low-loss transmission associated with the resonance excitation of the first (anti-symmetric) exchange standing spin wave mode. In this regime, the transmission through the sample increases instead of decreasing for this mode.
Influence of the uniform electric field on viscosity of magnetic nanofluid (Fe3O4-EG)
Authors: Monajjemi Rarani E. , Etesami N. , Nasr Esfahany M.
Published: November 2012

Viscosity of Fe3O4/ethylene glycol nanofluids under electric field (ac and dc) was investigated experimentally. Magnetic nanofluids were prepared by dispersing Fe3O4 nanoparticles in ethylene glycol using a sonicator. Experiments showed that dilute magnetic nanofluids (<0.05 vol. %) as well as base fluid exhibit Newtonian behavior. Viscosity of Fe3O4 / ethylene glycol nanofluids in electric field was measured using capillary tube viscometer. Electric field decreased the viscosity of magnetic nanofluids and base fluid. The viscosity reduction was more profound in higher volume concentrations of nanoparticles. dc electric field caused greater viscosity reduction in magnetic nanofluids relative to ac electric field while ac electric field showed greater reduction effect for base liquid.
Increasing the switching speed of liquid crystal devices with magnetic nanorods
Authors: Garbovskiy Yu. , Baptist J. R. , Thompson J. , Hunter T. , Lim J. H. , Gi Min Seong , Wiley J. B. , Malkinski L. M. , Glushchenko A. , Celinski Z.
Published: November 2012

Liquid crystal (LC)/magnetic nanorods colloids were fabricated and tested using a magneto-optical setup. These thermotropic ferronematics do not show any signs of macroscopic aggregation, exhibit enhanced magnetic sensitivity, and faster time response in the simultaneous presence of crossed electric and magnetic fields. Magnetic nanorods increase an effective magnetic anisotropy of the colloid and decrease magnetic Freedericksz threshold. Applying a magnetic field along the direction perpendicular to the applied electric field leads to a decrease of the time OFF by a factor of 6 for pure liquid crystals, and by a factor of 9—for ferronematics.
Gate stack dielectric degradation of rare-earth oxides grown on high mobility Ge substrates
Authors: Shahinur Rahman Md. , Evangelou E. K. , Konofaos N. , Dimoulas A.
Published: November 2012

We report on the reliability characteristics and their analysis, of rare-earth oxides (REOs) dielectric degradation, when used as interfacial buffer layers together with HfO2 high-k films (REOs/HfO2) on high mobility Ge substrates. Metal-oxide-semiconductor (MOS) devices with these stacks, show dissimilar charge trapping phenomena under varying levels of constant-voltage-stress (CVS) conditions, influencing the measured densities of the interface (Nit) and border (NBT) traps. In the present study, we report on C-Vg hysteresis curves related to both Nit and NBT. We propose a new model based on the Maxwell-Wagner mechanism, and this model explains the current decay transient observed under CVS bias from low to higher fields of MOS gate stack devices grown on Ge substrates. The proposed model is unlike to those used for other MOS devices. Finally, CVS measurements for very long times at moderate fields reveal an initial current decay due to relaxation, followed by charge trapping and generation of stress-induced leakage which eventually lead to hard breakdown.
Limited thermal conductance of metal-carbon interfaces
Authors: Gengler Jamie J. , Shenogin Sergei V. , Bultman John E. , Roy Ajit K. , Voevodin Andrey A. , Muratore Chris
Published: November 2012

The thermal conductance for a series of metal-graphite interfaces has been experimentally measured with time-domain thermoreflectance (TDTR). For metals with Debye temperatures up to ∼400 K, a linear relationship exists with the thermal conductance values. For metals with Debye temperatures in excess of ∼400 K, the measured metal-graphite thermal conductance values remain constant near 60 MW m−2 K−1. Titanium showed slightly higher conductance than aluminum, despite the closeness of atomic mass and Debye temperature for the two metals. Surface analysis was used to identify the presence of titanium carbide at the interface in contrast to the aluminum and gold-carbon interfaces (with no detectable carbide phases). It was also observed that air-cleaved graphite surfaces in contact with metals yielded slightly higher thermal conductance than graphite surfaces cleaved in vacuo. Examination of samples with scanning electron microscopy revealed that the lack of absorbed molecules on the graphite surface resulted in differences in transducer film morphology, thereby altering the interface conductance. Classical molecular dynamic simulations of metal-carbon nanotube thermal conductance values were calculated and compared to the TDTR results. The upper limit of metal-graphite thermal conductance is attributed to the decreased coupling at higher frequencies of the lighter metals studied, and to the decreased heat capacity for higher vibrational frequency modes.
Pairing of 1-hexyl-3-methylimidazolium and tetrafluoroborate ions in n-pentanol
Authors: Zhu P. , Pratt L. R. , Papadopoulos K. D.
Published: November 2012

Molecular dynamics simulations are obtained and analyzed to study pairing of 1-hexyl-3-methylimidazolium and tetrafluoroborate ions in n-pentanol, in particular by evaluating the potential-of-mean-force between counter ions. The present molecular model and simulation accurately predicts the dissociation constant Kd in comparison to experiment, and thus the behavior and magnitudes for the ion-pair potential-of-mean-force at molecular distances, even though the dielectric constant of the simulated solvent differs from the experimental value by about 30%. A naive dielectric model does not capture molecule structural effects such as multiple conformations and binding geometries of the Hmim+ and BF4− ion-pairs. Mobilities identify multiple time-scale effects in the autocorrelation of the random forces on the ions, and specifically a slow, exponential time-decay of those long-ranged forces associated here with dielectric friction effects.
A van der Waals density functional study of chloroform and other trihalomethanes on graphene
Authors: Åkesson Joel , Sundborg Oskar , Wahlström Olof , Schröder Elsebeth
Published: November 2012

A computational study of chloroform (CHCl3) and other trihalomethanes (THMs) adsorbed on graphene is presented. The study uses the van der Waals density functional method to obtain adsorption energies and adsorption structures for these molecules of environmental concern. In this study, chloroform is found to adsorb with the H atom pointing away from graphene, with adsorption energy 357 meV (34.4 kJ/mol). For the other THMs studied the calculated adsorption energy values vary from 206 meV (19.9 kJ/mol) for fluoroform (CHF3) to 404 meV (39.0 kJ/mol) for bromoform (CHBr3). The corrugation of graphene as seen by the THMs is small, the difference in adsorption energy along the graphene plane is less than 6 meV for chloroform.
Interferometric background reduction for femtosecond stimulated Raman scattering loss spectroscopy
Authors: Dobner Sven , Cleff Carsten , Fallnich Carsten , Groß Petra
Published: November 2012

We present a purely optical method for background suppression in nonlinear spectroscopy based on linear interferometry. Employing an unbalanced Sagnac interferometer, an unprecedented background reduction of 17  dB over a broad bandwidth of 60  THz (2000  cm−1) is achieved and its application to femtosecond stimulated Raman scattering loss spectroscopy is demonstrated. Apart from raising the signal-to-background ratio in the measurement of the Raman intensity spectrum, this interferometric method grants access to the spectral phase of the resonant χ(3) contribution. The spectral phase becomes apparent as a dispersive lineshape and is reproduced numerically with a simple oscillator model.
Multiplexed dispersive readout of superconducting phase qubits
Authors: Chen Yu , Sank D. , O'Malley P. , White T. , Barends R. , Chiaro B. , Kelly J. , Lucero E. , Mariantoni M. , Megrant A. , Neill C. , Vainsencher A. , Wenner J. , Yin Y. , Cleland A. N. , Martinis John M.
Published: November 2012

We introduce a frequency-multiplexed readout scheme for superconducting phase qubits. Using a quantum circuit with four phase qubits, we couple each qubit to a separate lumped-element superconducting readout resonator, with the readout resonators connected in parallel to a single measurement line. The readout resonators and control electronics are designed so that all four qubits can be read out simultaneously using frequency multiplexing on the one measurement line. This technology provides a highly efficient and compact means for reading out multiple qubits, a significant advantage for scaling up to larger numbers of qubits.
Spectral patterns underlying polarization-enhanced diffractive interference are distinguishable by complex trigonometry
Authors: DeJarnette Drew , Norman Justin , Roper D. Keith
Published: November 2012

Superpositioned modes from scatterers in periodic arrays that prescribe spectral interference patterns are distinguishable using an analytic description. Interference arising from irradiation of ordered lattices with polarizable components yields far-field spectral patterns in which extraordinary features appear at resonant frequencies associated with lattice geometry. Organization of nanostructures utilizing these features has been limited by complexity of electrodynamic descriptions for coupling between these plasmon resonance energies and diffracted spectral modes. The trigonometric description shows how changing lattice constant and incident wavelength to adjust coupling between phase-dependent constructive interference and isometric values of plasmonic gold nanostructure polarizability results in extraordinary spectral features.
Ultra-sensitive magnetoelectric microcantilever at a low frequency
Authors: Gun Lee Dong , Man Kim Sung , Kyung Yoo Yong , Hyun Han Jun , Won Chun Dong , Kim Yu-Chan , Kim Jinseok , Seon Hwang Kyo , Song Kim Tae , Woo Jo Won , Kim Hyungsuk , Song Seung-Ho , Hoon Lee Jeong
Published: November 2012

Here, we propose the device platform of energy domain transfer using a magnetoelectric microcantilever. By incorporating Tb0.3Dy0.7Fe1.9 (Terfenol-D) magnetostrictive materials onto a Pb(Zr0.52Ti0.48)O3 (PZT) piezoelectric microcantilever, we demonstrated energy conversion from the magnetic to the electric domain. By measuring the charge signal from a PZT layer under variable dc magnetic field at constant 60 Hz AC magnetic field, we acquired the magnetoelectric coefficient of 24.4 V/cm·Oe. The proposed magnetoelectric microcantilever enables the generation of a minimum detectable DC magnetic field up to 1 × 10−12 T at off-resonance.
Making a continuous metal film transparent via scattering cancellations
Authors: Song Zhengyong , He Qiong , Xiao Shiyi , Zhou Lei
Published: November 2012

Based on theoretical analyses and full-wave simulations, we propose a scheme to make a continuous metal film transparent in optical regime, with light scattered from the metal film cancelled by those from two composite layers consisting of metallic and dielectric stripes. Such a transparency fully retains the conductance of the targeted metal and is robust against incidence angle as well as structural disorders. As a proof of concept, we performed microwave experiments to verify all theoretical predictions.
Indicators of mobility extraction error in bottom gate CdS metal-oxide-semiconductor field-effect transistors
Authors: Jung Ukjin , Gon Lee Young , Ju Kim Jin , Kyung Lee Sang , Mejia I. , Salas-Villasenor A. , Quevedo-Lopez Manuel , Hun Lee Byoung
Published: November 2012

Widely varying mobility values of CdS metal-oxide-semiconductor field-effect transistors have been reported in the literature (μ = 1–48 cm2/Vs). Sulfide vacancies in CdS channel generated by an incomplete post deposition anneal are found to be the origin of scattered mobility values. The presence of sulfide vacancies can be easily diagnosed by simple electrical measurements checking a strong channel length dependence of mobility and an abrupt drain current increase due to the carrier ionization at sulfur vacancies.
A two-dimensional nanopatterned thin metallic transparent conductor with high transparency from the ultraviolet to the infrared
Authors: Guo Du Qing , Sathiyamoorthy Krishnan , Ping Zhang Li , Volkan Demir Hilmi , Hin Kam Chan , Wei Sun Xiao
Published: November 2012

The optical properties of a two-dimensional nanohole patterned aluminum thin film in hexagonal lattice are studied. The transmission dip can be moved out from the visible range by manipulating the lattice constant. The resulting nanopatterned thin film is demonstrated to exhibit a high transparency in a wide wavelength range. The origins of the transmission dip and the transmission drop are explained. For constant resistance, thicker films with a larger filling ratio lead to better transmittance in the visible range. Angular response of the nanopatterned metallic film is also analyzed, and transmittances using several other metals are compared.
THz emission control by tuning density profiles of neutral gas targets during intense laser-gas interaction
Authors: Du Hai-Wei , Chen Min , Sheng Zheng-Ming , Zhang Jie , Wu Hui-Chun , Wang Wei-Min
Published: November 2012

Ionization currents generated from two-color or few-cycle intense femtosecond laser pulses interaction with neutral gas targets can emit strong THz waves. Here it is found that the initial non-uniformity of the gas density can significantly affect the ionization currents and subsequent THz emission both in amplitude and in spectrum. Density profile effects on the forward and backward emissions have been studied in details by particle-in-cell simulations, in which the field ionization module is included. Increasing the gas density gradient length, the emitted forward THz spectrum shifts from high to low frequency, and the spectrum width reduces, which offers a way to obtain a tunable THz emission source by laser-gas interaction.
Ion implantation induced modification of optical properties in single-crystal diamond studied by coherent acoustic phonon spectroscopy
Authors: Gregory Justin , Steigerwald Andrew , Takahashi Hiroaki , Hmelo Anthony , Tolk Norman
Published: November 2012

Single-crystal CVD diamond specimens were implanted with 1-MeV He+ ions at fluences ranging from 1014 to 1016 cm−2 and analyzed using coherent acoustic phonon spectroscopy. The coherent acoustic phonon response varies greatly with implantation fluence and provides depth-dependent information about the implantation defect-induced modification of diamond's optical characteristics. The results indicate an increase in the real and imaginary refractive index, as well as a sign reversal of the photoelastic coefficients at higher levels of implantation damage. These studies provide insight into the application of ion implantation to the fabrication of diamond-based photonic devices.
Positive colossal magnetoresistance observed in Co doped amorphous carbon/silicon heterostructures
Authors: Jiang Y. C. , Gao J.
Published: November 2012

Heterostructures of Co-doped amorphous carbon (Co-C)/silicon were fabricated by growing Co-C films on n-type Si substrates using pulsed laser deposition. The heterostructures exhibited a positive colossal magnetoresistance (CMR) effect over a temperature range of 55-240 K. The magnetoresistance (MR) for the reverse bias voltage reached around 270% at 5 T, whereas the MR under a forward bias was 7% only. Besides, the transmission electron microscopy results demonstrate that Co atoms tended to be aggregated at Co-C/Si interface. The Co aggregation in the interface may be a possible origin of the positive CMR effect.
Structural incommensurate modulation rule in hexagonal Ba(Ti1-xMx)O3-δ (M = Mn, Fe) multiferroics
Authors: Wei X. K. , Zhang Q. H. , Jin C. Q. , Yu R. C.
Published: November 2012

The structural incommensurate modulation (SIM) rule in hexagonal Ba(Ti1-xMx)O3-δ (1/18 ≤ x ≤ 1/3, M = Mn, Fe) multiferroic ceramics is investigated using transmission electron microscope (TEM). Our systematic analysis on the modulation characteristics in the electron diffraction patterns, especially along [001] direction, reveals that three types of anti-phase domain boundaries (APBs) dominate the SIMs. According to the derived APB models, the calculated oxygen vacancies at both O1 (face sharing) and O2 (corner sharing) sites qualitatively agree quite well with our previous results. Analysis on the high-resolution TEM images reveals that complex dislocation structures also play important roles in the formation of the SIMs.
Modeling of downconverter based on Pr3+-Yb3+ codoped fluoride glasses to improve sc-Si solar cells efficiency
Authors: Song P. , Jiang C.
Published: November 2012

Quantum cutting via a two-step resonant energy transfer in a spectral downconverter of Pr3+-Yb3+ codoped fluoride glass is investigated numerically by proposing up and solving the theoretical model of rate equations and power propagation equations. Based on the optimal Pr3+-Yb3+ concentration and the thickness of the spectral downconverter, the total power conversion efficiency of 175% and total quantum conversion efficiency of 186% are obtained. The performance of a sc-Si solar cell covered with a spectral downconverter is evaluated with the photovoltaic simulation programme PC1D. For sc-Si solar cells, the energy conversion efficiency of 14.90% for the modified AM1.5G compared to a 12.25% energy conversion efficiency for the standard AM1.5G has been obtained, and the simulated relative energy conversion efficiency for the sc-Si solar cell approaches up to 1.21. Our results show that the use of a spectral downconverter yields better sc-Si solar cell performance compared to the standard AM1.5G irradiation. The paper also provides a framework for investigating and optimizing the rare-earth doped spectral downconverter, potentially enabling a sc-Si solar cell with an efficiency improvement.
Atomic force microscopy probes fractional differences in chemical bond order
Authors: Miller Johanna L.
Published: November 2012

High-resolution images can map out subtle variations in a molecule’s electronic and geometric structure.
Manipulating the color and shape of single photons
Authors: Raymer Michael G. , Srinivasan Kartik
Published: November 2012

In a future quantum internet, individual photons might well be the agents that carry information between different kinds of devices. But physicists must first learn to tailor some of their essential features.
What separates a liquid from a gas?
Authors: Brazhkin Vadim V. , Trachenko Kostya
Published: November 2012

Standard ways to distinguish between the two phases don’t apply at high pressure and high temperature. But a look at a medium’s microscopic behavior makes it possible to discriminate between liquid and gas everywhere on a phase diagram.