bluuebunny/crossref_metadata_2025 huggingface dataset:
Neil Armstrong (1930–2012)
Authors: Showstack Randy
Published: September 2012

News of the death of Neil Armstrong on 25 August elicited tributes from around the world to the commander of NASA's Apollo 11 mission and the first person to walk on the Moon. A statement released by his family noted, in part, “While we mourn the loss of a very good man, we also celebrate his remarkable life and hope that it serves as an example to young people around the world to work hard to make their dreams come true, to be willing to explore and push the limits, and to selflessly serve a cause greater than themselves. “For those who may ask what they can do to honor Neil, we have a simple request. Honor his example of service, accomplishment, and modesty, and the next time you walk outside on a clear night and see the moon smiling down at you, think of Neil Armstrong and give him a wink.”
Progress in understanding the inner magnetosphere
Authors: Goldstein Jerry , Spasojevic Maria , Shprits Yuri
Published: September 2012

Inner Magnetosphere Coupling 2; Los Angeles, California, 19–22 March 2012 Solar activity can energize Earth's magnetosphere. Coupled plasma interactions—involving multiscale electromagnetic fields, currents, and waves—either dissipate this energy into the ionosphere (to influence upper atmospheric chemistry and possibly climate) or store it in belts of highly energetic particles in the inner magnetosphere. Decades of effort have advanced knowledge of this system, but understanding of the coupling processes is still very incomplete.
Bridging onshore and offshore present‐day kinematics of central and eastern Mediterranean: Implications for crustal dynamics and mantle flow
Authors: Pérouse Eugénie , Chamot‐Rooke Nicolas , Rabaute Alain , Briole Pierre , Jouanne François , Georgiev Ivan , Dimitrov Dimitar
Published: September 2012

We present a new kinematic and strain model of an area encompassing the Calabrian and Hellenic subduction zones, western Anatolia and the Balkans. Using Haines and Holt's (1993) method, we derive continuous velocity and strain rate fields by interpolating geodetic velocities, including recent GPS data in the Balkans. Relative motion between stable Eurasia and the western Aegean Sea is gradually accommodated by distributed N‐S extension from Southern Balkans to the Eastern Corinth Gulf, so that the westward propagation of the North Anatolian Fault (NAF) throughout continental Greece or Peloponnesus is not required. We thus propose that the NAF terminates in north Aegean and that N‐S extension localized in the Corinth Gulf and distributed in Southern Balkans is due to the retreat of the Hellenic slab. The motion of the Hyblean plateau, Apulia Peninsula, south Adriatic Sea, Ionian Basin and Sirte plain can be minimized by a single rigid rotation around a pole located in the Sirte plain, compatible with the opening the Pelagian rifts (2–2.5 mm/yr) and seismotectonics in Libya. We interpret the trenchward ultraslow motion of the Calabrian arc (2–2.5 mm/yr) as pure collapse, the Calabrian subduction being now inactive. In the absolute plate motion reference frame, our modeled velocity field depicts two toroïdal crustal patterns located at both ends of the Hellenic subduction zone, clockwise in NW Greece and counter‐clockwise in western Anatolia. We suggest the NW Greece toroïdal pattern is the surface expression of a slab tear and consequent toroïdal asthenospheric flow.
Cassini capturing of freshly‐produced water‐group ions in the Enceladus torus
Authors: Yaroshenko V. V. , Miloch W. J. , Thomas H. M. , Morfill G. E.
Published: September 2012

The water vapor plume on the geological‐active south‐polar region of the moon Enceladus is recognized as the main source of Saturn's neutral torus centered on the Enceladus orbit. The composition of the torus is dominated by water group species. Recent in situ Cassini plasma spectrometer measurements indicate the existence of freshly produced, slow and non‐thermalized water group ions throughout the Enceladus torus including regions far from the moon. We report the results of modeling spacecraft‐plasma interactions in the environment relevant for the Enceladus torus to show that new‐born non‐thermalized ions will inevitably be captured by the electric fields arising around the charged spacecraft. The associated plasma configuration can directly impact the plasma measurements and thus is important for reliable interpretation of data obtained by Cassini instruments in the Enceladus torus. The simulation results appear to be partially supported by Cassini observations and can provide new insights into intricate process of Enceladus‐plasma interactions.
A damage mechanics assessment of the Larsen B ice shelf prior to collapse: Toward a physically‐based calving law
Authors: Borstad C. P. , Khazendar A. , Larour E. , Morlighem M. , Rignot E. , Schodlok M. P. , Seroussi H.
Published: September 2012

Calving is a primary process of mass ablation for glaciers and ice sheets, though it still eludes a general physical law. Here, we propose a calving framework based on continuum damage mechanics coupled with the equations of viscous deformation of glacier ice. We introduce a scalar damage variable that quantifies the loss of load‐bearing surface area due to fractures and that feeds back with ice viscosity to represent fracture‐induced softening. The calving law is a standard failure criterion for viscous damaging materials and represents a macroscopic brittle instability quantified by a critical or threshold damage. We constrain this threshold using the Ice Sheet System Model (ISSM) by inverting for damage on the Larsen B ice shelf prior to its 2002 collapse. By analyzing the damage distribution in areas that subsequently calved, we conclude that calving occurs after fractures have reduced the load‐bearing capacity of the ice by 60 ± 10%.
Changes in the variability of global land precipitation
Authors: Sun Fubao , Roderick Michael L. , Farquhar Graham D.
Published: September 2012

In our warming climate there is a general expectation that the variability of precipitation (P) will increase at daily, monthly and inter‐annual timescales. Here we analyse observations of monthlyP (1940–2009) over the global land surface using a new theoretical framework that can distinguish changes in global Pvariance between space and time. We report a near‐zero temporal trend in global meanP. Unexpectedly we found a reduction in global land P variance over space and time that was due to a redistribution, where, on average, the dry became wetter while wet became drier. Changes in the P variance were not related to variations in temperature. Instead, the largest changes in P variance were generally found in regions having the largest aerosol emissions. Our results combined with recent modelling studies lead us to speculate that aerosol loading has played a key role in changing the variability of P.
Solar cycle dependence of the cusp O+access to the near‐Earth magnetotail
Authors: Liao J. , Kistler L. M. , Mouikis C. G. , Klecker B. , Dandouras I.
Published: September 2012

Ionospheric origin O+ accelerated in the cusp/cleft region is one source for the O+ observed in the plasma sheet. This O+ is convected over the polar cap, flowing along open field lines to the tail lobes, and finally entering the plasma sheet. In this paper we use Cluster/CODIF data to study how the occurrence of cusp origin O+ in the polar cap and tail lobe changes over the solar cycle. Our study shows that the probability to observe cusp origin O+ decreases steeply during the declining phase of solar cycle 23 and starts to increase again at the start of the solar cycle 24. The decrease is much greater in the tail lobes than in the polar cap. A detailed analysis reveals that the O+ on the dominant transport path moves to higher latitudes in the Northern Hemisphere and more sunward in the Southern Hemisphere during the declining phase of the solar cycle (from the solar maximum to the solar minimum), so that the O+no longer reaches the near‐Earth (<20RE) tail lobes. This change in transport is consistent with a significantly reduced convection velocity and a northward shift of the cusp region as the solar activity decreases, so that the O+ moves much further along the field line before it is convected into the tail. It will therefore enter the plasma sheet much further down the tail.
Magnetospheric responses to the passage of the interplanetary shock on 24 November 2008
Authors: Kim K.‐H. , Lee D.‐H. , Shiokawa K. , Lee E. , Park J.‐S. , Kwon H.‐J. , Angelopoulos V. , Park Y.‐D. , Hwang J. , Nishitani N. , Hori T. , Koga K. , Obara T. , Yumoto K. , Baishev D. G.
Published: September 2012

The passage of an interplanetary (IP) shock was detected by Wind, ACE, Geotail, and THEMIS‐B in the solar wind on 24 November 2008. From the propagation time of the IP shock at the spacecraft, it is expected that the IP shock front is aligned with the Parker spiral and strikes the postnoon dayside magnetopause first. Using multipoint observations of the sudden commencement (SC) at THEMIS probes, GOES 11, and ETS in the dayside magnetosphere, we confirmed that the magnetospheric response to the IP shock starts earlier in the postnoon sector than in the prenoon sector. We found that the estimated normal direction of the SC front is nearly aligned with the estimated IP shock normal. We also found that the SC front normal speed is much slower than the fast mode speed and is about 22–56% of the IP shock speed traveling in the solar wind. Thus, we suggest that the major field changes of the SC in the dayside magnetosphere are not due to the magnetic flux carried by hydromagnetic waves but to the increased solar wind dynamic pressure behind the shock front sweeping the magnetopause. The SC event appears as a step‐like increase in theHcomponent at the low‐latitude Bohyun station and a negative‐then‐positive variation in theHcomponent at the high‐latitude Chokurdakh (CHD) station in the morning sector. During the negative perturbation at CHD, the SuperDARN Hokkaido radar detected a downward motion in the ionosphere, implying westward electric field enhancement. Using the THEMIS electric field data, it is confirmed that the westward electric field corresponds to the inward plasma motion in the dayside magnetosphere due to the magnetospheric compression.
Effects of sudden stratospheric warming (SSW) on the lunitidal modulation of the F‐region dynamo
Authors: Park Jaeheung , Lühr Hermann
Published: September 2012

The E‐region dynamo in the equatorial ionosphere changes significantly during Sudden Stratospheric Warming (SSW) events. However, little is known about the modulation of the F‐region dynamo by SSW events. During the SSW event of December 2001 the vertical current density in the daytime equatorial F‐region, as observed by the CHAMP satellite, exhibited oscillations with a 13‐day period. This period reflects the lunar tide in the CHAMP satellite data. Two independent drivers are known to contribute to the F‐region vertical current: thermospheric zonal wind (F‐region dynamo) and vertical electric field (E‐region dynamo). The thermospheric zonal wind as observed by CHAMP was modulated in a similar way as the F‐region vertical current. Vertical electric field in the equatorial F‐region can be estimated from the magnetic and plasma/neutral observations of the CHAMP satellite. The obtained values also show quasi 13‐day modulations. The thermospheric wind and vertical electric field drove the F‐region vertical currents in opposite directions, and the polarity of the net current generally followed the former (F‐region dynamo). From the observed phase delays of the 13‐day oscillations we conclude that the F‐region vertical current during the SSW event was not only modulated by the variation of the thermospheric wind but also by the variations of the E‐region electric field and the F‐region plasma density distribution.
Diagnostic tools for evaluating quasi‐horizontal transport in global‐scale chemistry models
Authors: Lee Huikyo , Youn Daeok , Patten Kenneth O. , Olsen Seth C. , Wuebbles Donald J.
Published: September 2012

The upper troposphere and lower stratosphere (UTLS) plays an important role in climate and atmospheric chemistry. Despite its importance on the point of causing deep intrusions of tropics originated air into the midlatitudes, the quasi‐horizontal transport process in the UTLS, represented by global chemistry‐transport models (CTMs) or chemistry‐climate models (CCMs), cannot easily be diagnosed with conventional analyses on isobaric surfaces. We use improved diagnostic tools to better evaluate CTMs and CCMs relative to satellite observations in the region of UTLS. Using the Hellinger distance, vertical profiles of probability density functions (PDFs) of chemical tracers simulated by the Model for OZone And Related chemical Tracers 3.1 (MOZART‐3.1) are quantitatively compared with satellite data from the Microwave Limb Sounder (MLS) instrument in the tropopause relative altitude coordinate to characterize features of tracer distributions near the tropopause. Overall, the comparison of PDFs between MLS and MOZART‐3.1 did not satisfy the same population assumption. Conditional PDFs are used to understand the meteorological differences between global climate models and the real atmosphere and the conditional PDFs between MOZART‐3.1 and MLS showed better agreement compared to the original PDFs. The low static stability during high tropopause heights at midlatitudes suggests that the variation of tropopause height is related to transport processes from the tropics to midlatitudes. MOZART‐3.1 with the GEOS4 GCM winds reproduces episodes of the tropical air intrusions. However, our diagnostic analyses show that the GEOS4 GCM did not properly reproduce the high tropopause cases at midlatitudes especially in spring.
Nonlinear impact of the Arctic Oscillation on extratropical surface air temperature
Authors: Son Hye‐Young , Park Wonsun , Jeong Jee‐Hoon , Yeh Sang‐Wook , Kim Baek‐Min , Kwon Minho , Kug Jong‐Seong
Published: September 2012

The Arctic Oscillation (AO) is the leading climate mode of sea level pressure (SLP) anomalies during cold season in the Northern Hemisphere. To a large extent, the atmospheric climate anomalies associated with positive and negative phases of the AO are opposite to each other, indicating linear impact. However, there is also significant nonlinear relationship between the AO and other winter climate variability. We investigate nonlinear impacts of the AO on surface air temperature (SAT) using reanalysis data and a multimillennial long climate simulation. It is found that SAT response to the AO, in terms of both spatial pattern and magnitude, is almost linear when the amplitude of the AO is moderate. However, the response becomes quite nonlinear as the amplitude of the AO becomes stronger. First, the pattern shift in SAT depends on AO phase and magnitude, and second, the SAT magnitude depends on AO phase. In particular, these nonlinearities are distinct over the North America and Eurasian Continent. Based on the analyses of model output, we suggest that the nonlinear zonal advection term is one of the critical components in generating nonlinear SAT response, particularly over the North America.
Impact of melt ponds on Arctic sea ice in past and future climates as simulated by MPI‐ESM
Authors: Roeckner Erich , Mauritsen Thorsten , Esch Monika , Brokopf Renate
Published: September 2012

The impact of melt ponds on Arctic sea ice is estimated from model simulations of the historical and future climate. The simulations were performed with and without the effect of melt ponds on sea ice melt, respectively. In the last thirty years of the historical simulations, melt ponds develop predominantly in the continental shelf regions and in the Canadian archipelago. Accordingly, the ice albedo in these regions is systematically smaller than in the no‐pond simulations, the sea ice melt is enhanced, and both the ice concentration and ice thickness during the September minimum are reduced. Open ponds decrease the ice albedo, resulting in enhanced ice melt, less sea ice and further pond growth. This positive feedback entails a more realistic representation of the seasonal cycle of Northern Hemisphere sea ice area. Under the premise that the observed decline of Arctic sea ice over the period of modern satellite observations is mainly externally driven and, therefore, potentially predictable, both model versions underestimate the decline in Arctic sea ice. This presupposition, however, is challenged by our model simulations which show a distinct modulation of the downward Arctic sea ice trends by multidecadal variability. At longer time scales, an impact of pond activation on Arctic sea ice trends is more evident: In the Representative Concentration Pathway scenario RCP45, the September sea ice is projected to vanish by the end of the 21st century. In the active‐pond simulation, this happens up to two decades earlier than in the no‐pond simulations.
Molecular Design and Applications of Photofunctional Polymers and Materials
Authors:   Royal Society of Chemistry
Published: September 2012

Functional organic and organometallic polymers and materials have gained much attention as versatile materials for energy interconversions and optoelectronic/photonic applications, including electrical energy generation in photovoltaic cells and light generation in organic light-emitting diodes, as they offer a low cost, light weight and simple option for device fabrication. Molecular Design and Applications of Photofunctional Polymers and Materials, presents a critical perspective of the current field, with emphasis on fundamental concepts and current applications in optoelectronics, electronics and nanotechnology. The book also covers photochemically degradable polymers, electrochromic and photochromic materials, biosensing and bioimaging materials, and low- and high-refractive index materials. With contributions from leading experts in the field, this timely book will provide a valuable contribution to the community enabling new synthetic methods to be developed to produce new materials with specific functional roles.
Comparison of photo detectors and operating conditions for decay time determination in phosphor thermometry
Authors: Knappe C. , Nada F. Abou , Richter M. , Aldén M.
Published: September 2012

This work compares the extent of linear response regions from standard time-resolving optical detectors for phosphor thermometry. Different types of photomultipliers (ordinary and time-gated) as well as an avalanche photodiode were tested and compared using the phosphorescence decay time of cadmium tungstate (CdWO4). Effects originating from incipient detector saturation are revealed as a change in evaluated phosphorescence decay time, which was found to be a more sensitive measure for saturation than the conventional signal strength comparison between in- and output. Since the decay time of thermographic phosphors is used for temperature determination systematic temperature errors in the order of several tens of Kelvins may be introduced. Saturation from the initial intensity is isolated from temporally developed saturation by varying the CdWO4 decay time over the microsecond to nanosecond range, resultant of varying the temperature from 290 to 580 K. A detector mapping procedure is developed in order to identify linear response regions where the decay-to-temperature evaluations are unbiased. In addition, this mapping procedure generates a library of the degree of distortion for operating points outside of linear response regions. Signals collected in the partly saturated regime can thus be corrected to their unbiased value using this library, extending the usable detector operating range significantly.
Free-energy based pair-additive potentials for bulk Ni-Al systems: Application to study Ni-Al reactive alloying
Authors: Izvekov Sergei , Rice Betsy M.
Published: September 2012

We present new numerical pair-additive Al, Ni, and Al-Ni potentials by force-matching (FM) ionic force and virial data from single (bulk liquid) phase ab initio molecular dynamics (MD) simulations using the Born-Oppenheimer method. The potentials are represented by piece-wise functions (splines) and, therefore, are not constrained to a particular choice of analytical functional form. The FM method with virial constraint naturally yields a potential which maps out the ionic free-energy surface of the reference ensemble. To further improve the free energetics of the FM ensemble, the FM procedure is modified to bias the potentials to reproduce the experimental melting temperatures of the reference (FCC-Al, FCC-Ni, B2-NiAl) phases, the only macroscopic data included in the fitting set. The performance of the resultant potentials in simulating bulk metallic phases is then evaluated. The new model is applied to perform MD simulations of self-propagating exothermic reaction in Ni-Al bilayers at P = 0–5 GPa initiated at T = 1300 K. Consistent with experimental observations, the new model describes realistically a sequence of peritectic phase transformations throughout the reaction and at a realistic rate. The reaction proceeds through interlayer diffusion of Al and Ni atoms at the interface with formation of B2-NiAl in the Al melt. Such material responses have, in the past, been proven to be difficult to observe with then-existing potentials.
Dynamically biased statistical model for the ortho/para conversion in the ${\rm H}_2 + {\rm H}_3^+$H2+H3+ → ${\rm H}_3^{+} +$H3++ H2 reaction
Authors: Gómez-Carrasco Susana , González-Sánchez Lola , Aguado Alfredo , Sanz-Sanz Cristina , Zanchet Alexandre , Roncero Octavio
Published: September 2012

In this work we present a dynamically biased statistical model to describe the evolution of the title reaction from statistical to a more direct mechanism, using quasi-classical trajectories (QCT). The method is based on the one previously proposed by Park and Light [J. Chem. Phys. 126, 044305 (2007)10.1063/1.2430711]. A recent global potential energy surface is used here to calculate the capture probabilities, instead of the long-range ion-induced dipole interactions. The dynamical constraints are introduced by considering a scrambling matrix which depends on energy and determine the probability of the identity/hop/exchange mechanisms. These probabilities are calculated using QCT. It is found that the high zero-point energy of the fragments is transferred to the rest of the degrees of freedom, what shortens the lifetime of \documentclass[12pt]{minimal}\begin{document}${\rm H}_5^+$\end{document}H5+ complexes and, as a consequence, the exchange mechanism is produced with lower proportion. The zero-point energy (ZPE) is not properly described in quasi-classical trajectory calculations and an approximation is done in which the initial ZPE of the reactants is reduced in QCT calculations to obtain a new ZPE-biased scrambling matrix. This reduction of the ZPE is explained by the need of correcting the pure classical level number of the \documentclass[12pt]{minimal}\begin{document}${\rm H}_5^+$\end{document}H5+ complex, as done in classical simulations of unimolecular processes and to get equivalent quantum and classical rate constants using Rice–Ramsperger–Kassel–Marcus theory. This matrix allows to obtain a ratio of hop/exchange mechanisms, α(T), in rather good agreement with recent experimental results by Crabtree et al. [J. Chem. Phys. 134, 194311 (2011)10.1063/1.3587246] at room temperature. At lower temperatures, however, the present simulations predict too high ratios because the biased scrambling matrix is not statistical enough. This demonstrates the importance of applying quantum methods to simulate this reaction at the low temperatures of astrophysical interest.
Ultrafast vibrational dynamics of water at a charged interface revealed by two-dimensional heterodyne-detected vibrational sum frequency generation
Authors: Singh Prashant Chandra , Nihonyanagi Satoshi , Yamaguchi Shoichi , Tahara Tahei
Published: September 2012

Two-dimensional heterodyne-detected vibrational sum frequency generation (2D HD-VSFG) spectroscopy is performed for an aqueous interface for the first time. The 2D HD-VSFG spectra in the OH stretch region are obtained from a positively charged surfactant/water interface with isotopically diluted water (HOD/D2O) to reveal the femtosecond vibrational dynamics of water at the charged interface. The 2D HD-VSFG spectrum is diagonally elongated immediately after photoexcitation, clearly demonstrating inhomogeneity in the interfacial water. This elongation almost disappears at 300 fs owing to the spectral diffusion. Interestingly, the 2D HD-VSFG spectrum at the 0 fs shows an oppositely asymmetric shape to the corresponding 2D IR spectrum in bulk water: The bandwidth of the bleach signal gets narrower when the pump wavenumber becomes higher. This suggests that the dynamics and mechanism of the hydrogen bond rearrangement at the charged interface are significantly different from those in bulk water.
Comment on “Elastic wave propagation in a solid layer with laser-induced point defects” [J. Appl. Phys. 110, 064906 (2011)]
Authors: Martin P. A.
Published: September 2012

Mirzade [J. Appl. Phys. 110, 064906 (2011)] developed a linear theory for the propagation of waves in an elastic solid with atomic point defects, and then sought time-harmonic solutions. It is shown that Mirzade’s analysis is incomplete: substantial corrections are required.
Magnetostriction and ΔE effect of melt-spun (Fe81−xCoxGa19)80B20 ribbons
Authors: Jen S. U. , Wang S. P. , Chang W. C. , Chang H. W.
Published: September 2012

(Fe81−xCoxGa19)80B20 ribbons, with x = 0, 7, 11, 19, and 23, were made by the single-roller quenching method. The x-ray diffraction patterns showed the A2, D019, and L12 diffraction peaks coexisting with the amorphous matrix background. When Fe was replaced by Co, i.e., when x was increased, the first crystallization temperature (TX1) and Curie temperature (TC1) rose greatly. With a sufficiently heavy load (or weight) stretching the ribbon downward, the magnetization MS was pulled along the vertical direction (i.e., the tension-axis). Then, by applying a horizontal field (HE) up to 6 KOe, we determined the sign and magnitude of the saturation magnetostriction (λS). The Young’s modulus (ES) at magnetization saturation and ΔE effect was estimated from the stress-strain curve. We discovered that the stress-strain curve of (Fe81Ga19)80B20 exhibits the auxetic (or abnormal) characteristic with ΔE < 0. For the rest of the (Fe81−xCoxGa19)80B20 with x ≠ 0, their stress-strain curves are normal with ΔE > 0. Because the sign of λS of the A2 phase is opposite to that of the D019 and L12 phases, λS of (Fe81−xCoxGa19)80B20 is much reduced. However, ΔE/E0 ≒ 36% is quite large for (Fe58Co23Ga19)80B20.
Microstructure and dielectric property relationships in spherical inclusion ferroelectric composite ceramics
Authors: Zhang Qiwei , Zhai Jiwei , Zhang Haijun , Yao Xi
Published: September 2012

Dense Ba0.4Sr0.6TiO3-Mg2TiO4 composite ceramics with different grain sizes were prepared by three different sintering methods: spark plasma sintering, two-step sintering, and conventional sintering, respectively. The dielectric response, tunability, and loss properties of composite ceramics as a function of volume fraction of Mg2TiO4 were systematically investigated. The results showed that the dielectric constant and tunability are strongly dependent on the concentration of Mg2TiO4, grain sizes, and composite modes. In particular, near the percolation threshold for Mg2TiO4 volume fraction (∼60 vol. %), a remarkable variation of the tunability was observed. Nevertheless, the dielectric loss exhibited a relatively weak dependence on inclusion concentrations. The results are also in agreement with the theoretical predictions of the modified effective medium approximation approaches in the spherical inclusion model of composites.
Effects of the edge states on conductance and thermopower for the bilayer graphene nanoribbons
Authors: Lv Shu-Hui , Li Yu-Xian
Published: September 2012

By using the nonequilibrium Green’s function combined with the tight-binding Hamiltonian, we have studied the effects of the edge states on the conductance and the thermopower for zigzag bilayer graphene nanoribbons (ZBGNs). It is shows that the band structure, conductance, and thermopower can be modulated by the boundary potentials and the bias voltages to the layers of the ZBGNs. When the boundary potentials are adjusted to the nearest neighbor hopping energy, two gapless edge modes with opposite velocities appear in the vicinity of the two Dirac points, and the quantized conductance has a transition from 2(n+1)G0 to 2(n+1/2)G0 with G0=2e2/h being the conductance unit and n an integer. Particularly, under the strong bias voltage, compare to the gapless perfect ZBGN, the thermopower can be enhanced more than twice for the gapless edge modes with opposite velocities. Combining the reduced thermal conductivity in few-layer graphene, our results show that the modulated ZBGNs are more reliable in thermoelectric application.
Focusing and subwavelength imaging of surface acoustic waves in a solid-air phononic crystal
Authors: Veres Istvan A. , Berer Thomas , Matsuda Osamu , Burgholzer Peter
Published: September 2012

Focusing and subwavelength imaging of surface acoustic waves (SAWs) through a phononic crystal flat lens are discussed in the presented work. Experimental and numerical wave fields are obtained in the time-domain by an optical technique and by numerical simulations. Spatial distributions of the acoustic field are accessed using a temporal Fourier transform. The revealed focusing of the elastic waves in the first band of the crystal is governed by the concave equifrequency contour of the leaky-Rayleigh wave. The spatial distributions of the experimental and numerical acoustic fields also unfold subwavelength imaging of SAWs. Numerical simulations show that the imaging quality can be improved by embedding the flat lens into a medium with higher wave velocity.
Analysis of nonharmonic oscillations in Schottky diodes
Authors: Pardo D. , Grajal J. , Pérez S. , González T. , Mateos J.
Published: September 2012

We investigate damped nonharmonic oscillations at terahertz frequencies observed in the current response of Schottky diodes simulated with the Monte Carlo method under applied signals of a few hundred GHz. From Monte Carlo simulations of different diode structures, two kinds of nonharmonic oscillations have been identified. The first kind of oscillations is due to the coupling of the nonlinear performance of the Schottky junction with the inertial motion of the carriers in the non-depleted region of the epilayer. The second kind of oscillations is due to the modulation of the n+–n junction when high electric fields are induced in the non-depleted region of the epilayer. These oscillations constitute a promising mechanism for THz signal generation.
Praseodymium valence determination in Lu2SiO5, Y2SiO5, and Lu3Al5O12 scintillators by x-ray absorption spectroscopy
Authors: Zhuravleva Mariya , Friedrich Stephan , Melcher Charles L.
Published: September 2012

Until now, determination of both Pr3+ and Pr4+ at the low concentration levels commonly used in single crystal scintillators has proven to be difficult. We have found that it is possible to use synchrotron radiation and superconducting tunnel junction detectors to measure the X-ray absorption on the M4 and M5 edges of Pr to directly determine Pr3+ and Pr4+ in Lu2SiO5, Y2SiO5, and Lu3Al5O12. The spectra were measured at room temperature and compared to model samples of trivalent and tetravalent praseodymium, which provided clear signatures of the two charge states. The results show predominant Pr(III) in most samples.
Quantum optical switches and beam splitters with surface plasmons
Authors: Yan Cong-Hua , Wei Lian-Fu
Published: September 2012

We propose a nano-device, produced by a two-level quantum dot coupling with two different surface plasmons, to control the transport of the resonant photons along the waveguides. Our numerical results clearly show that the transporting probabilities of the incident photons are controlled by adjusting the coupling strength between the quantum dot and the surface plasmons. Therefore, the proposed nano-device can be served as either a quantum optical switcher or a beam splitter of the resonant photons. The feasibility with the experimental quantum dots and nanowires is also discussed.
Homonuclear decoupling for liquid-state NMR
Authors: Koroleva Van D. M. , Khaneja Navin
Published: September 2012

We present a solution to the problem of decoupling of a homonuclear two-spin system having weak isotropic scalar coupling. We describe non-selective pulse sequences that create an effective field perpendicular to the coupling interaction over a broad range of chemical shifts, with a magnitude proportional to the chemical shifts. Effective decoupling is achieved when the difference in chemical shifts imprinted on the perpendicular field is sufficiently larger than the coupling between the spins. The proposed methods scale down the chemical shifts. The pulse sequences may be useful in various applications in nuclear magnetic resonance spectroscopy.
Relativistically modulational instability by strong Langmuir waves
Authors: Liu X. L. , Liu S. Q. , Li X. Q.
Published: September 2012

Based on the set of nonlinear coupling equations, which has considered the relativistic effects of electrons, modulational instability by strong Langmuir waves has been investigated in this paper. Both the characteristic scale and maximum growth rate of the Langmuir field will enhance with the increase in the electron relativistic effect. The numerical results indicate that longitudinal perturbations induce greater instability than transverse perturbations do, which will lead to collapse and formation of the pancake-like structure.
Permeability and magnetic properties of Al3+ substituted Ni0.7Zn0.3Fe2O4 nanoparticles
Authors: Birajdar A. A. , Shirsath Sagar E. , Kadam R. H. , Mane M. L. , Mane D. R. , Shitre A. R.
Published: September 2012

In this work, the structural and magnetic properties of Al3+ substituted Ni-Zn ferrite powders were investigated. Ni0.7Zn0.3AlxFe2−xO4 (where x = 0.0–0.5) powders were obtained by sol-gel auto combustion method. X-ray diffractometer, vibrating sample magnetometer, scanning electron microscopy, infrared spectroscopy, and permeability were used to study the effects of Al3+ ions on the structural and magnetic properties. X-ray patterns reveal that all the samples have single-phase cubic spinel structure. Infrared spectroscopy was used to locate the absorption bands and to study the influence of Al3+ substitution on the spinel structure of the presently investigated system. The lattice constant and x-ray density were calculated from the XRD data. The density of the samples was measured and consequently the porosity was calculated too. Magnetic properties were carried out by means of magnetization measurement to study the magnetic interaction between the ions. This paper is also focused its discussion on the dependence of the permeability spectra with the frequency variation. The permeability and Curie temperature were determined using the temperature dependent permeability measurements.
Defect microstructural evolution in ion irradiated metallic nanofoils: Kinetic Monte Carlo simulation versus cluster dynamics modeling and in situ transmission electron microscopy experiments
Authors: Xu Donghua , Wirth Brian D. , Li Meimei , Kirk Marquis A.
Published: September 2012

Understanding materials degradation under intense irradiation is important for the development of next generation nuclear power plants. Here we demonstrate that defect microstructural evolution in molybdenum nanofoils in situ irradiated and observed on a transmission electron microscope can be reproduced with high fidelity using an object kinetic Monte Carlo (OKMC) simulation technique. Main characteristics of defect evolution predicted by OKMC, namely, defect density and size distribution as functions of foil thickness, ion fluence and flux, are in excellent agreement with those obtained from the in situ experiments and from previous continuum-based cluster dynamics modeling. The combination of advanced in situ experiments and high performance computer simulation/modeling is a unique tool to validate physical assumptions/mechanisms regarding materials response to irradiation, and to achieve the predictive power for materials stability and safety in nuclear facilities.
Plasmon resonances and electron transport in linear sodium atomic chains
Authors: Liu Dan-Dan , Zhang Hong , Cheng Xin-Lu
Published: September 2012

The plasmon resonances and electron transport in linear sodium atomic chains are investigated using time-dependent density functional theory. The dipole response and dynamic conductance are obtained as a function of inter-atomic distance d and the chain length, under an impulse excitation polarized along the chains axis. We found that the current enhancement associated with the plasmon-induced field enhancement is mainly due to plasmon excitation of the hybridized bonding dipolar plasmons (BDP) mode. And the high energy plasmon modes are relatively weaker and are more delocalized in space than the BDP mode. The intensity of the dipole response and the current show an opposite tendency as the d is decreased while a same tendency is found as the number of atom increased. This can be understood from the competition between global quantization and local atomic confinement.
Universal behavior of photoluminescence in GaN-based quantum wells under hydrostatic pressure governed by built-in electric field
Authors: Suski T. , Łepkowski S. P. , Staszczak G. , Czernecki R. , Perlin P. , Bardyszewski W.
Published: September 2012

Correlation between the photoluminescence (PL) energy at ambient pressure and the pressure coefficient of photoluminescence is studied in quantum wells (QWs) based on nitride alloys, such as InGaN/GaN, GaN/AlGaN, and GaN/InAlN, grown along the polar direction [0001] of the wurtzite structure. Analyzing previously published and new experimental data, we have found that for InGaN/GaN QWs independent of In content (in the range between 6% and 25%) and also QW number and QW width, a linear relationship between these two parameters occurs. The presented experimental results are in agreement with numerical calculations carried out in the framework of the k→⋅p→ method with excitonic effects, provided that nonlinear piezoelectricity and nonlinear elasticity are taken into account. The performed analytical analysis indicates that the slope of the linear relationship between the pressure coefficient of photoluminescence and the photoluminescence energy at ambient pressure is determined by the logarithmic derivative of the built-in electric field with respect to pressure. Then, we show that the pressure coefficient of photoluminescence depends linearly on the photoluminescence energy at ambient pressure also in GaN/AlGaN and GaN/InAlN QWs. In GaN/AlGaN QWs, the slope of this dependence slightly decreases with Al content in the barriers. For GaN/InAlN QWs, we predict an unusual dependence of this slope on In content, which is associated with the vanishing built-in electric field in structures with 30% of In. For all studied nitride systems, a reasonable agreement between the experimental and theoretical results is achieved when the effects of nonlinear piezoelectricity and nonlinear elasticity are taken into account.
Acoustic levitator for contactless motion and merging of large droplets in air
Authors: Bjelobrk Nada , Nabavi Majid , Poulikakos Dimos
Published: September 2012

Large droplet transport in a line-focussed acoustic manipulator in terms of maximum droplet size is achieved by employing a driving voltage control mechanism. The maximum volume of the transported droplets in the order of few microliters is thereby increased by three orders of magnitude compared to the constant voltage case, widening the application field of this method significantly. A drop-on-demand droplet generator is used to supply the liquid droplets into the system. The ejected sequence of picoliter-size droplets is guided along trajectories by the acoustic field and accumulates at the selected pressure node, merging into a single large droplet. Droplet movement is achieved by varying the reflector height. This also changes the intensity of the radiation pressure during droplet movement, which in turn could atomise the droplet. The acoustic force is adjusted by regulating the driving voltage of the actuator to keep the liquid droplet suspended in air and to prevent atomisation. In the herein presented levitation concept, liquids with a wide range of surface tension (water and tetradecane were tested) can be transported over distances of several mm. The aspect ratio of the droplet in the acoustic field is shown to be a good indicator for radiation pressure intensity and is kept between 1.1 and 1.4 during droplet transport. Despite certain limitations with volatile liquids, the presented acoustic levitator concept has the potential to expand the range of analytical characterisation and manipulation methods in applications ranging from chemistry and biology.
Enhancement of Kα emission through efficient hot electron generation in carbon nanotubes on intense laser pulse irradiation
Authors: Chakravarty U. , Arora V. , Naik P. A. , Chakera J. A. , Srivastava H. , Srivastava A. , Varma G. D. , Kumbhare S. R. , Gupta P. D.
Published: September 2012

Near complete absorption of the energy of intense ultra-short laser pulses (45 fs, intensity ∼1.6 × 1016 to 2.5 × 1017 W/cm2) is observed in carbon nanotubes deposited on a planar molybdenum substrate. The hollow structure of the nanotube plasma facilitates resonant electric field enhancement during its ionization phase. This resonantly enhanced localized field at a density much larger than the critical density nc leads to efficient hot electron generation, which results in enhanced Kα emission of Mo at 17.5 keV. It is observed that for nanotubes, depending on the degree of hollowness, there is an optimum laser intensity for maximum x-ray enhancement compared to a planar uncoated target.
Flexible, transparent dielectric capacitors with nanostructured electrodes
Authors: Sorel Sophie , Khan Umar , Coleman Jonathan N.
Published: September 2012

We have prepared flexible, transparent, dielectric capacitors by spraycasting very thin networks of single walled nanotubes (SWNTs) or silver nanowires (AgNWs) onto either side of free-standing polymer films. Impedance spectroscopy showed these structures to behave as a capacitor in combination with a series resistance. Those capacitors with SWNT electrodes displayed optical transmittance between 57% and 74%, capacitances ranging from 0.4 to 1.1 μF/cm2 and series resistances ranging 400 Ω/◻-10 kΩ/◻. However, using AgNW electrodes gave similar transmittance and capacitance but series resistance as low as 60 Ω/◻. Finally, the properties of these capacitors were invariant under flexing.
Selectively probing vibrations in a plasmonic supracrystal
Authors: Mante Pierre-Adrien , Chen Hung-Ying , Lin Meng-Hsien , Wen Yu-Chieh , Gwo Shangjr , Sun Chi-Kuang
Published: September 2012

The coupling of plasmonic resonances with the multiple phonon modes of a plasmonic supracrystal is studied. Ultrafast optical pump-probe spectroscopy with variable wavelength allows the selective detection of the breathing mode, the interparticle vibrations, and the vibration of the whole structure. Thanks to this selectivity, the characterization of the bonding strength between nanoparticles in different directions of the supracrystal is possible. The observation of these vibrations could be useful for the realization of future phonon modulated photonic and plasmonic devices.
A digital optical phase-locked loop for diode lasers based on field programmable gate array
Authors: Xu Zhouxiang , Zhang Xian , Huang Kaikai , Lu Xuanhui
Published: September 2012

We have designed and implemented a highly digital optical phase-locked loop (OPLL) for diode lasers in atom interferometry. The three parts of controlling circuit in this OPLL, including phase and frequency detector (PFD), loop filter and proportional integral derivative (PID) controller, are implemented in a single field programmable gate array chip. A structure type compatible with the model MAX9382/MCH12140 is chosen for PFD and pipeline and parallelism technology have been adapted in PID controller. Especially, high speed clock and twisted ring counter have been integrated in the most crucial part, the loop filter. This OPLL has the narrow beat note line width below 1 Hz, residual mean-square phase error of 0.14 rad2 and transition time of 100 μs under 10 MHz frequency step. A main innovation of this design is the completely digitalization of the whole controlling circuit in OPLL for diode lasers.
Magnetism in MoS2 induced by proton irradiation
Authors: Mathew S. , Gopinadhan K. , Chan T. K. , Yu X. J. , Zhan D. , Cao L. , Rusydi A. , Breese M. B. H. , Dhar S. , Shen Z. X. , Venkatesan T. , Thong John T. L.
Published: September 2012

Molybdenum disulphide, a diamagnetic layered dichalcogenide solid, is found to show magnetic ordering at room temperature when exposed to a 2 MeV proton beam. The temperature dependence of magnetization displays ferrimagnetic behavior with a Curie temperature of 895 K. A disorder mode corresponding to a zone-edge phonon and a Mo valence higher than +4 has been detected in the irradiated samples using Raman and x-ray photoelectron spectroscopy, respectively. The possible origins of long-range magnetic ordering in irradiated MoS2 samples are discussed.
Pulse voltage-induced dynamic magnetization switching in magnetic tunneling junctions with high resistance-area product
Authors: Shiota Yoichi , Miwa Shinji , Nozaki Takayuki , Bonell Frédéric , Mizuochi Norikazu , Shinjo Teruya , Kubota Hitoshi , Yuasa Shinji , Suzuki Yoshishige
Published: September 2012

We investigated pulse voltage-induced dynamic magnetization switchings in magnetic tunneling junctions with a high resistance-area product of 2 kΩ μm2. We found that bistable switching and the oscillatory behavior of switching probability as a function of voltage pulse duration are realized at a lower current density (−1.1 × 105 A/cm2) than in conventional spin-transfer-torque-induced magnetization switching. In addition, the switching probability at different voltage pulse strengths confirmed the existence of a voltage torque induced by a change in perpendicular magnetic anisotropy. This voltage-induced magnetization switching can be a useful technique in future spintronics devices with fast and highly reliable writing processes.
High-Q AlN photonic crystal nanobeam cavities fabricated by layer transfer
Authors: Sergent S. , Arita M. , Kako S. , Tanabe K. , Iwamoto S. , Arakawa Y.
Published: September 2012

High-quality-factor one-dimensional photonic crystal nanobeam cavities embedding GaN/AlN quantum dots are fabricated by an epilayer transfer method. The GaN/AlN quantum dots are first grown on SiC before being transferred to a Si substrate using a hydrogen silsesquioxane bonding layer and highly selective back-etching of the SiC. Nanobeam cavities are then fabricated by electron-beam lithography, dry etching, and HF underetching of the bonding layer. The resulting nanocavity exhibits quality factors larger than 6.3 × 103, the highest quality factor reported to date for an optically active group-III nitride photonic crystal nanocavity.