bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced organic mass fraction and decreased hygroscopicity of cloud condensation nuclei (CCN) during new particle formation events
Authors: Dusek U. , Frank G. P. , Curtius J. , Drewnick F. , Schneider J. , Kürten A. , Rose D. , Andreae M. O. , Borrmann S. , Pöschl U.
Published: February 2010

In a forested near‐urban location in central Germany, the CCN efficiency of particles smaller than 100 nm decreases significantly during periods of new particle formation. This results in an increase of average activation diameters, ranging from 5 to 8% at supersaturations of 0.33% and 0.74%, respectively. At the same time, the organic mass fraction in the sub‐100‐nm size range increases from approximately 2/3 to 3/4. This provides evidence that secondary organic aerosol (SOA) components are involved in the growth of new particles to larger sizes, and that the reduced CCN efficiency of small particles is caused by the low hygroscopicity of the condensing material. The observed dependence of particle hygroscopicity (κ) on chemical composition can be parameterized as a function of organic and inorganic mass fractions (forg, finorg) determined by aerosol mass spectrometry: κ = κorg forg + κinorg finorg. The obtained value of κorg ≈ 0.1 is characteristic for SOA, and κinorg ≈ 0.7 is consistent with the observed mix of ammonium, sulfate and nitrate ions.
Derivation of aurora scaling parameters from ground‐based imaging observations: Numerical tests
Authors: Kozelov B. V. , Golovchanskaya I. V.
Published: February 2010

In the study of scaling properties of auroral luminosity variations by ground‐based imaging observations, a problem arises that the actual scaling characteristics are distorted because of contributions to images from extension of auroral structures along the geomagnetic field. The field‐aligned trends come into play for whatever small deviations from the magnetic zenith, making questionable the appropriateness of ground imaging data for investigation of turbulence signatures in aurora. In order to clear up how to correct for this effect, we have modeled the distortions, stemming from aspect angle broadening, for synthesized self‐similar fluctuations with known scaling characteristics in the plane perpendicular to the magnetic field. Both narrow and wide field‐aligned profiles of luminosity were considered. Three estimators for deriving scaling parameters were applied, including the wavelet estimator, dyadic filter estimator, and standard deviation statistical estimator, of which the wavelet estimator is shown to be most robust. The formulas are presented that relate the observed scaling characteristics with the true ones for the case of aurora being observed near magnetic zenith.
New method for the characterization of three‐dimensional preferential flow paths in the field
Authors: Abou Najm Majdi R. , Jabro Jalal D. , Iversen William M. , Mohtar Rabi H. , Evans Robert G.
Published: February 2010

Preferential flow path development in the field is the result of the complex interaction of multiple processes relating to the soil's structure, moisture condition, stress level, and biological activity. Visualizing and characterizing the cracking behavior and preferential paths evolution with soil depth has always been a key challenge and a major barrier against scaling up existing hydrologic concepts and models to account for preferential flows. This paper presents a new methodology to quantify soil preferential paths in the field using liquid latex. The evolution of the preferential flow paths at different soil depths and moisture conditions is assessed. Results from different soil series (Savage clay loam soil versus Chalmers clay loam) and different vegetation covers and soil managements (corn/tilled field versus soybean no‐till field in the Chalmers soil series) are presented.
Ocean Gravity Models From Future Satellite Missions
Authors: Louis Gilles , Lequentrec‐Lalancette Marie‐Françoise , Royer Jean‐Yves , Rouxel Didier , Géli Louis , Maïa Marcia , Faillot Mathilde
Published: February 2010

Over the past 3 decades, satellite altimetry has been a key tool for dynamic ocean studies and for accurately estimating sea surface heights. The geodetic reference surface—the “geoid”—can be approximated as the mean sea surface height of an ocean corrected for dynamic terms such as tides and currents. It is an equipotential surface of the gravity field; and variations of this field are quantified as free‐air anomalies, from which density heterogeneities of the oceanic basement can be inferred.

Using such data in combination with other geophysical data, scientists have improved their knowledge of the nature of submarine relief and underlying structures. In solid Earth geophysics, major breakthroughs came from the development of high‐resolution marine gravity models based on closely spaced altimetry profiles collected during the U.S. Navy's Geosat satellite geodetic mission (launched in 1985) and the first version of the European Remote Sensing satellite geodetic mission (ERS 1, launched in 1991). These were combined with other repetitive profiles from the international TOPEX/ POSEIDON satellite (launched in 1992); ERS 1; TOPEX/POSEIDON's successor, Jason (launched in 2001); and the European Space Agency's (ESA) Envisat missions (ERS's successors [see, e.g., Sandwell and Smith, 1997; Andersen and Knudsen, 1998]).
AGU Unveils Redesigned Web Site
Authors: Cairns Ann
Published: February 2010

AGU's redesigned Web site made its debut in December during the Fall Meeting in San Francisco. Those who haven't yet visited the revamped site are in for some pleasant surprises, including easier navigation requiring fewer click‐throughs; increased visibility for AGU sections and focus groups; more Earth and space science content; and more AGU news.

The site's unveiling marked the completion of the first phase of a two‐phase overhaul. More improvements are on the way in the months ahead.
Supergrains produced by lateral growth using Joule-heating induced crystallization without artificial control
Authors: Hong Won-Eui , Chung Jangkyun , Kim Donghyun , Park Seungho , Ro Jae-Sang
Published: February 2010

In Joule-heating induced crystallization, phase transformation can occur through solid-to-solid or liquid-to-solid phases, according to the input conditions of the pulsed power. It was observed that during a Joule-heating period of several tens of microseconds, randomly nucleated liquid seeds followed by rapid solidification in an amorphous matrix play an important role, especially for liquid-to-solid transformation. Meanwhile, under high-power input processing conditions, supergrains of greater than 5 μm in size were produced by lateral growth from the initial seeds without artificial control.
General design of the International Fusion Materials Irradiation Facility deuteron injector: Source and beam line
Authors: Gobin R. , Blideanu V. , Bogard D. , Bourdelle G. , Chauvin N. , Delferrière O. , Girardot P. , Jannin J. L. , Langlois S. , Loiseau D. , Pottin B. , Rousse J.-Y. , Senée F.
Published: February 2010

In the framework of the International Fusion Materials Irradiation Facility-Engineering Validation and Engineering Design Activities (IFMIF-EVEDA) project, CEA/IRFU is in charge of the design and realization of the 140 mA cw deuteron Injector. The electron cyclotron resonance ion source operates at 2.45 GHz and a 4 electrode extraction system has been chosen. A 2 solenoid beam line, together with a high space charge compensation have been optimized for a proper beam injection in the 175 MHz radio frequency quadrupole. The injector will be tested with proton and deuteron beam production either in pulsed mode or in cw mode on the CEA-Saclay site before to be shipped to Japan. Special attention was paid to neutron emission due to (d,D) reaction. In this paper, the general IFMIF Injector design is reported, pointing out beam dynamics, radioprotection, diagnostics, and mechanical aspects.
Automated coregistered imaging using a hand-held probe-based optical imager
Authors: Regalado Steven , Erickson Sarah J. , Zhu Banghe , Ge Jiajia , Godavarty Anuradha
Published: February 2010

Near-infrared optical imaging holds a promise as a noninvasive technology toward cancer diagnostics and other tissue imaging applications. In recent years, hand-held based imagers are of great interest toward the clinical translation of the technology. However hand-held imagers developed to date are typically designed to obtain surface images and not tomography information due to lack of coregistration facilities. Herein, a recently developed hand-held probe-based optical imager in our Optical Imaging Laboratory has been implemented with novel coregistration facilities toward real-time and tomographic imaging of tissue phantoms. Continuous-wave fluorescence-enhanced optical imaging studies were performed using an intensified charge coupled device camera based imaging system in order to demonstrate the feasibility of automated coregistered imaging of flat phantom surfaces, using a flexible probe that can also contour to curvatures. Three-dimensional fluorescence tomographic reconstructions were also demonstrated using coregistered frequency-domain measurements obtained using the hand-held based optical imager. It was also observed from preliminary studies on cubical phantoms that multiple coregistered scans differentiated deeper targets (∼3 cm) from artifacts that were not feasible from a single coregistered scan, demonstrating the possibility of improved target depth detectability in the future.
Discrete Fourier transform and Jacobi θ function identities
Authors: Malekar R. A. , Bhate H.
Published: February 2010

Classical theta function identities are derived using properties of eigenvectors corresponding to the discrete Fourier transform Φ(2). In particular, an extended Watson addition formula is obtained corresponding to Φ(2), and the corresponding result for the discrete Fourier transform Φ(3) is obtained.
On a novel integrable generalization of the sine-Gordon equation
Authors: Lenells J. , Fokas A. S.
Published: February 2010

We consider an integrable generalization of the sine-Gordon (sG) equation that was earlier derived by one of the authors using bi-Hamiltonian methods. This equation is related to the sG equation in the same way that the Camassa–Holm equation is related to the Korteweg–de Vries equation. In this paper we (a) derive a Lax pair, (b) use the Lax pair to solve the initial-value problem on the line, (c) analyze solitons, (d) show that the generalized sG and sG equations are related by a Liouville transformation, (e) derive conservation laws, and (f) analyze traveling-wave solutions.
Long pulse H− ion beam acceleration in MeV accelerator
Authors: Taniguchi M. , Mizuno T. , Umeda N. , Kashiwagi M. , Watanabe K. , Tobari H. , Kojima A. , Tanaka Y. , Dairaku M. , Hanada M. , Sakamoto K. , Inoue T.
Published: February 2010

A multiaperture multigrid accelerator called “MeV accelerator” has been developed for neutral beam injection system of international thermonuclear experimental reactor. In the present work, long pulse H− ion beam acceleration was performed by the MeV accelerator equipped with new water-cooled grids. At present, the pulse length was extended to 5 s for the beams of 750 keV, 221 mA, and 10 s for the beams of 600 keV, 158 mA. Energy density, defined as products of beam energy (keV), current (mA), and pulse (s) divided by aperture area (m2), increased more than one order of magnitude higher compared with original MeV accelerator without water cooling in its grids. At higher energy and current, the grid was melted by beam deflection. Due to this grid melting, breakdowns occurred between the grids, and hence, the pulse length was limited. Beam deflection will be compensated by aperture displacement in next experiment.
Multiplication of distributions and Dirac formalism of quantum mechanics
Authors: Kim Namhoon
Published: February 2010

We define multiplication and convolution of distributions and ultradistributions by introducing the notions of evaluation of distributions and integration of ultradistributions. An application is made to an interpretation of the Dirac formalism of quantum mechanics. The role of the Hilbert space of states is played by what is termed a Hermitian orthonormal system, and operators are replaced by the generalized matrices. We describe a simple example of one dimensional free particle and construct explicitly a representation of the Weyl algebra as the generalized matrices.
Self-adjoint Lyapunov variables, temporal ordering, and irreversible representations of Schrödinger evolution
Authors: Strauss Y.
Published: February 2010

In nonrelativistic quantum mechanics time enters as a parameter in the Schrödinger equation. However, there are various situations where the need arises to view time as a dynamical variable. In this paper we consider the dynamical role of time through the construction of a Lyapunov variable—i.e., a self-adjoint quantum observable whose expectation value varies monotonically as time increases. It is shown, in a constructive way, that a certain class of models admits a Lyapunov variable and that the existence of a Lyapunov variable implies the existence of a transformation mapping the original quantum mechanical problem to an equivalent irreversible representation. In addition, it is proven that in the irreversible representation there exists a natural time ordering observable splitting the Hilbert space at each t>0 into past and future subspaces.
An application of decomposable maps in proving multiplicativity of low dimensional maps
Authors: Fukuda Motohisa
Published: February 2010

In this paper, we present a class of maps for which the multiplicativity of the maximal output p-norm holds for p=2 and p≥4. The class includes all positive trace-preserving maps from B(C3) to B(C2). In this sense, the result is a generalization of the corresponding result in the work of King and Koldan [“New multiplicativity results for qubit maps,” J. Math. Phys. 47, 042106 (2006)], where the multiplicativity was proved for all positive trace-preserving maps from B(C2) to B(C2) with p=2 and p≥4. Interestingly, by contrast, the multiplicativity of p-norm was investigated in the context of quantum information theory and shown not to hold, in general, for high dimensional quantum channels [Hayden, P. and Winter, A., “Counterexamples to the maximal p-norm multiplicativity conjecture for all p>1,” Commun. Math. Phys. 284, 263 (2008)]. Moreover, the Werner–Holevo channel, which is a map from B(C3) to B(C3), is a counterexample for p>4.79 [Werner and Holevo, J. Math. Phys. 43, 4353 (2002).].
Exact moduli space metrics for hyperbolic vortex polygons
Authors: Krusch S. , Speight J. M.
Published: February 2010

Exact metrics on some totally geodesic submanifolds of the moduli space of static hyperbolic N-vortices are derived. These submanifolds, denoted as Σn,m, are spaces of Cn-invariant vortex configurations with n single vortices at the vertices of a regular polygon and m=N−n coincident vortices at the polygon’s center. The geometric properties of Σn,m are investigated, and it is found that Σn,n−1 is isometric to the hyperbolic plane of curvature −(3πn)−1. The geodesic flow on Σn,m and a geometrically natural variant of geodesic flow recently proposed by Collie and Tong [“The dynamics of Chern-Simons vortices,” Phys. Rev. D Part. Fields Gravit. Cosmol. 78, 065013 (2008);e-print arXiv:hep-th/0805.0602] are analyzed in detail.
Note: Large rotation measurement using half shaded square patterns
Authors: Lee SangHeon , Jung KwangSuk
Published: February 2010

As the manufacturing technology ranging from micrometer to nanometer scale requires more planar motion devices, the demand for sensor measuring the planar motion is increasing. However, the previous sensors measuring the planar motion had a drawback in the measurement of rotation, especially regarding yaw angle. In this article, we present a novel method to measure large yaw angle with the planar position sensor based on the half shaded square patterns. The measuring range of the yaw angle is restricted to 45° in this article, but it can be expanded to as much as 360° with an improvement of the algorithm.
Microfluidic refractometer with integrated optical fibers and end-facet transmission gratings
Authors: Lei Lei , Li Hao , Shi Jian , Chen Yong
Published: February 2010

We demonstrated a microfluidic refractometer with an integrated high resolution transmission grating. This grating was fabricated by UV nanoimprinting on the end facet of a multimode optical fiber which was then placed in the plan of the microfluidic device and perpendicular to a microchannel. On the opposite side of the channel, three cleaved optical fibers were added for the light collection of the zeroth and the ± first diffraction orders. A white light source was used for illumination and the diffraction beams were analyzed with a minispectrometer. The transmission grating was merged in the sample solution of the channel, providing a refractive index-dependent diffraction efficiency. As expected, the diffraction efficiency of the zeroth and the ± first diffraction orders are different, both being reliable for the refractive index monitoring. Such a white source and multibeam diffraction analysis also allows monitoring the sample absorption or fluorescence, thereby providing a more accurate determination of the sample refraction index.
Substrate doping effects on Raman spectrum of epitaxial graphene on SiC
Authors: Yang R. , Huang Q. S. , Chen X. L. , Zhang G. Y. , Gao H.-J.
Published: February 2010

In this paper, we reported a Raman scattering study of epitaxial graphene on different doped 6H-SiC (0001) substrates and investigated the substrate induced charge-transfer doping to the epitaxial graphene. We found that the charge carrier type and concentration of epitaxial graphene can be altered by SiC substrates with different doping level and doping type. This effect is comparable to that obtained by electrochemical doping. As Raman scattering is very sensitive to the doping level, the charge carrier concentration of epitaxial graphene can be estimated by the Raman G-peak shift. Our results are fundamental and may have implications for future epitaxial-graphene-based micro/nanoelectronic devices.
Compositional effects on the growth of Mg(M)O films
Authors: Saraiva M. , Georgieva V. , Mahieu S. , Van Aeken K. , Bogaerts A. , Depla D.
Published: February 2010

The influence of the composition on the crystallographic properties of deposited Mg(M)O (with M=Al, Cr, Ti, Y, and Zr) films is studied. For a flexible control of the composition, dual reactive magnetron sputtering was used as deposition technique. Two different approaches to predict the composition are discussed. The first is an experimental way based on the simple relationship between the deposition rate and the target-substrate distance. The second is a route using a Monte Carlo based particle trajectory code. Both methods require a minimal experimental input and enable the user to quickly predict the composition of complex thin films. Good control and flexibility allow us to study the compositional effects on the growth of Mg(M)O films. Pure MgO thin films were grown with a (111) preferential out-of-plane orientation. When adding M to MgO, two trends were noticed. The first trend is a change in the MgO lattice parameters compared to pure MgO. The second tendency is a decrease in the crystallinity of the MgO phase. The experimentally determined crystallographic properties are shown to be in correspondence with the predicted properties from molecular dynamics simulations.
Drain current model for thin-film transistors with interface trap states
Authors: Tsuji Hiroshi , Kamakura Yoshinari , Taniguchi Kenji
Published: February 2010

A surface-potential-based drain current model for thin-film transistors (TFTs) is presented. In this model, the influence of traps located at the gate-oxide/silicon interface is accounted for to reproduce the gradual increase in the subthreshold current. The model uses a single equation that includes both drift and diffusion current components to describe the drain current in all operation regions. Calculations using the model produce results that are in good agreement with the measured current-voltage characteristics of polycrystalline silicon TFTs with large grains.
Long-ranged and high temperature ferromagnetism in (Mn,C)-codoped ZnO studied by first-principles calculations
Authors: Lin Xue-ling , Yan Shi-shen , Zhao Ming-wen , Hu Shu-jun , Yao Xin-xin , Han Chong , Chen Yan-xue , Liu Guo-lei , Dai You-yong , Mei Liang-mo
Published: February 2010

We theoretically investigated the electronic structures and magnetic properties of (Mn,C)-codoped ZnO system based on the first-principles calculations within a GGA+Up,d approach. We found that codoping C is a promising approach to enhance the ferromagnetic coupling between the nearest-neighboring Mn ions due to the strong hybridization between the C:2p and the Mn:3d states. Moreover, the spin-polarized states induced by C are so extended that they can mediate long-ranged ferromagnetic exchange interactions beyond the nearest-neighboring case. Therefore, (Mn,C)-codoped ZnO is expected to be a ferromagnetic semiconductor with long-ranged ferromagnetism and high Curie temperature.
Any ℓ-state solutions of the Hulthén potential in arbitrary dimensions
Authors: Gu Xiao-Yan , Sun Jian-Qiang
Published: February 2010

The energy spectra of the Hulthén effective potential in D dimensions are obtained within the new quantization rule approach for any ℓ states. The interdimensional degeneracies among states are also presented. In the case of D=3, the agreement between our results and those obtained by other methods is excellent.
Soft-core Coulomb potentials and Heun’s differential equation
Authors: Hall Richard L. , Saad Nasser , Sen K. D.
Published: February 2010

Schrödinger’s equation with the attractive potential V(r)=−Z/(rq+βq)1/q, Z>0, β>0, q≥1, is shown, for general values of the parameters Z and β, to be reducible to the confluent Heun equation in the case q=1 and to the generalized Heun equation in the case q=2. In a formulation with correct asymptotics, the eigenstates are specified a priori up to an unknown factor. In certain special cases, this factor becomes a polynomial. The asymptotic iteration method is used either to find the polynomial factor and the associated eigenvalue explicitly, or to construct accurate approximations for them. Detailed solutions for both cases are provided.
Enhanced high temperature thermoelectric characteristics of transition metals doped Ca3Co4O9+δ by cold high-pressure fabrication
Authors: Wang Yang , Sui Yu , Wang Xianjie , Su Wenhui , Liu Xiaoyang
Published: February 2010

A series of Fe, Mn, and Cu doped Ca3Co4O9+δ samples, Ca3(Co,M)4O9+δ (M=Fe, Mn, and Cu), were fabricated by cold high-pressure compacting technique. Their thermoelectric properties were investigated from room temperature up to 1000 K. The cold high-pressure compacting method is advantageous to increasing density and texture, in favor of the improvement of thermoelectric performance. The electrical transport measurements indicate that Fe/Mn substitutes for Co mainly in [CoO2] layers whereas the substitution of Cu for Co takes place in [Ca2CoO3] layers. The thermoelectric properties as well as electronic correlations depend not only on the substitution ion but also the Co site that is replaced. Thermopower can be well calculated by the carrier effective mass according to Boltzmann transport model, indicating that the electronic correlation plays a crucial role in the unusual thermoelectric characteristics of this system. From the changes in thermopower, resistivity, and thermal conductivity, thermoelectric performance of Ca3Co4O9+δ is efficiently improved by these transition metals doping. Fe doped samples possess the highest ZT values. Combining cold high-pressure technique, ZT of Ca3Co3.9Fe0.1O9+δ can reach ∼0.4 at 1000 K, which is quite large among ceramic oxides, suggesting that Fe doped Ca3Co4O9+δ could be a promising candidate for thermoelectric applications at elevated temperatures.
Note: Sensitivity enhancement in continuous-wave electron paramagnetic resonance: Adaptive signal averaging versus a moving average
Authors: Brinton Christopher G. , Hirsh Donald J.
Published: February 2010

We compare improvements in signal-to-noise in continuous-wave electron paramagnetic resonance (CW EPR) spectra resulting from adaptive signal averaging and a simple moving average. An adaptive filter module that uses a recursive least-squares (RLS) algorithm was incorporated into a CW EPR data acquisition program. After optimization, the RLS filter produces a significant improvement in the signal-to-noise ratio over conventional digital signal (spectral) averaging alone. However, conventional averaging of spectra combined with a central moving average of the data points provided equal or greater signal-to-noise improvement in the CW EPR spectra.
Properties of index transforms in modeling of nanostructures and plasmonic systems
Authors: Passian A. , Koucheckian S. , Yakubovich S. B. , Thundat T.
Published: February 2010

In material structures with nanometer scale curvature or dimensions, electrons may be excited to oscillate in confined spaces. The consequence of such geometric confinement is of great importance in nano-optics and plasmonics. Furthermore, the geometric complexity of the probe-substrate/sample assemblies of many scanning probe microscopy experiments often poses a challenging modeling problem due to the high curvature of the probe apex or sample surface protrusions and indentations. Index transforms such as Mehler–Fock and Kontorovich–Lebedev, where integration occurs over the index of the function rather than over the argument, prove useful in solving the resulting differential equations when modeling optical or electronic response of such problems. By considering the scalar potential distribution of a charged probe in the presence of a dielectric substrate, we discuss certain implications and criteria of the index transform and prove the existence and the inversion theorems for the Mehler–Fock transform of the order m∊N0. The probe charged to a potential V0, measured at the apex, is modeled, in the noncontact case, as a one-sheeted hyperboloid of revolution, and in the contact case or in the limit of a very sharp probe, as a cone. Using the Mehler–Fock integral transform in the first case, and the Fourier integral transform in the second, we discuss the necessary conditions imposed on the potential distribution on the probe surface.
Phase transitions in Co thin film induced by low energy and high energy ion beam irradiation
Authors: Gupta Ratnesh , Khandelwal A. , Avasthi D. K. , Nair K. G. M. , Gupta A.
Published: February 2010

Ion irradiation plays an important role to tailor the microcrystalline structure and the corresponding magnetic anisotropy by high local energy deposition and defect accumulation. In the present work, we have investigated the effects of nuclear energy loss and electronic energy loss on the phase transformation and magnetic anisotropy of thin polycrystalline Co films. As-deposited film shows polycrystalline behavior with twofold uniaxial magnetic anisotropy, characteristic to hcp-Co film. 320 keV Au ions induce phase transformation from hcp to fcc. Similar phase transformation have been observed in the case of film irradiated by 120 MeV Au ions. Rate of phase transformation is discussed in terms of electronic and nuclear energy losses and the corresponding changes in the magnetic anisotropic behavior are discussed in the light of uniaxial and fourfold magnetic anisotropy.
Microscopic simulation of nonequilibrium features in quantum-well pumped semiconductor disk lasers
Authors: Kühn Eckhard , Koch Stephan W. , Thränhardt Angela , Hader Jörg , Moloney Jerome V.
Published: February 2010

A microscopically motivated nonequilibrium theory is applied to study the power characteristics of an in-well pumped vertical external cavity surface emitting Laser for varying pump energies. Dynamic simulations yield steady state nonequilibrium carrier distributions resulting in gain reduction due to kinetic hole burning. Pauli blocking effects become prominent for more resonant pumping and increased pump powers. The reduced pump absorption results in a sublinear input-output power characteristics even for the optimized case where heating of the active mirror plays no role.
Atomic structure of a Ni diffused Si (001) surface layer: Precursor to formation of NiSi2 at low temperature
Authors: Ikarashi Nobuyuki
Published: February 2010

The atomic structure in a Ni-diffused Si (001) surface layer was determined by using aberration-corrected scanning-transmission electron microscopy (STEM). The STEM investigation revealed three key findings. First, Ni atoms occupy the tetrahedral interstitial voids of a Si crystal at an occupancy factor of about 0.5. Second, the Si atoms in the surface layer can dissociate from their lattice site at a low substrate temperature (300 °C). Third, CaF2-type NiSi2 is formed at that substrate temperature and is lattice matched to the surface layer.
Electronic and ionic contributions to the constant-volume specific heat of carbon tetrachloride shocked at pressures up to 23 GPa
Authors: Sano Yukio , Sano Tomokazu , Nagata Shinichi
Published: February 2010

For carbon tetrachloride, a temperature Hugoniot at 7–23 GPa and a distribution of the constant-volume specific heat on the Hugoniot CV(T) at 1057–3275 K are simultaneously estimated from the Walsh–Christian (WC) equation such that the Hugoniot fits well to the existing measured data. The estimated CV(T) distribution reveals the significance of the contribution of electrons and ions to the specific heat. That is, in contrast to the almost uniform distribution of the specific heat predicted from the Debye equation, the CV(T) distribution increases significantly with an increase in the Hugoniot temperature due to thermal excitation of electrons at 1057–1500 K (7–10.1 GPa), additional activation of the dimerization reaction at 1500–2350 K (10.1–16 GPa), and also additional activation of the polymerization reaction at 2350–3275 K (16–23 GPa). As an example, evidence is presented that carbon tetrachloride is a semiconductor at 1500 K. The CV(T) distribution in each temperature range is formulated and a temperature Hugoniot is reevaluated from the WC equation using the specific heat equations formulated. It is confirmed by a good fit of the reevaluated Hugoniot to the existing measured data that the specific heat equations express the CV(T) distribution appropriately.
Room temperature operation of photonic-crystal distributed-feedback quantum cascade lasers with single longitudinal and lateral mode performance
Authors: Lu Quan-Yong , Guo Wan-Hong , Zhang Wei , Wang Li-Jun , Liu Jun-Qi , Li Lu , Liu Feng-Qi , Wang Zhan-Guo
Published: February 2010

We demonstrate room temperature operation of photonic-crystal distributed-feedback quantum cascade lasers emitting at 4.7 μm. A rectangular photonic crystal lattice perpendicular to the cleaved facet was defined using holographic lithography. The anticrossing of the index- and Bragg-guided dispersions of rectangular lattice forms the band-edge mode with extended mode volume and reduced group velocity. Utilizing this coupling mechanism, single mode operation with a near-diffractive-limited divergence angle of 12° is obtained for 33 μm wide devices in a temperature range of 85–300 K. The reduced threshold current densities and improved heat dissipation management contribute to the realization of devices’ room temperature operation.
Improved ferroelectric behavior in (110) oriented BiFeO3 thin films
Authors: Wu Jiagang , Wang John
Published: February 2010

Multiferroic BiFeO3 thin films were grown on LaNiO3-buffered Pt/TiO2/SiO2/Si substrates by off-axis radio frequency magnetic sputtering, where (110) oriented texture was obtained. The LaNiO3 buffer layer promoted the growth of BiFeO3 film, resulting in a dense texture and columnar growth of BiFeO3 thin films. The BiFeO3 thin film exhibits 2Pr∼145.8 μC/cm2 and 2Ec∼573.5 kV/cm, together with a very low dielectric loss (0.80% at 10 kHz) and an almost fatigue-free behavior at 500 kHz up to 1010 switching cycles. The 2Pr value is comparable to the reported value of the BiFeO3 deposited on the SrTiO3(110) substrate. While a weak ferromagnetism is demonstrated for the multiferroic thin film at room temperature, the low leakage current and high (110) orientation contribute toward the improved ferroelectric behavior. The BFO thin film with a giant remanent polarization and a fatigue-free behavior promises a candidate material for high-temperature ferroelectric random access memory.
Tadpole shaped Ge0.96Mn0.04 magnetic semiconductors grown on Si
Authors: Wang Yong , Xiu Faxian , Zou Jin , Wang Kang L. , Jacob Ajey P.
Published: February 2010

Magnetic and structural properties of a Ge0.96Mn0.04 thin film grown on Si has been investigated by transmission electron microscopy and superconducting quantum interference device. Tadpole shaped coherent GeMn clusters induced by spinodal decomposition were revealed in the film. Although these coherent clusters are dominant, Mn5Ge3 precipitates can be still detectable, contributing to a complex ferromagnetism. The Ge buffer layer, by relieving the misfit strain between Si and Ge, can significantly reduce the density of lattice defects in the subsequent GeMn layer. Our findings unveil a particular morphology of GeMn clusters, which would contribute to better understand the GeMn system.
Theoretical study of the bonding in Mn+-RG complexes and the transport of Mn+ through rare gas (M=Ca, Sr, and Ra; n=1 and 2; and RG=He–Rn)
Authors: Gardner Adrian M. , Withers Carolyn D. , Wright Timothy G. , Kaplan Kimberly I. , Chapman Chivone Y. N. , Viehland Larry A. , Lee Edmond P. F. , Breckenridge W. H.
Published: February 2010

We present high level ab initio potential energy curves for the Mn+-RG complexes, where n=1 and 2; RG=He–Rn; and M=Ca, Sr, and Ra. Spectroscopic constants have been derived from these potentials and are compared with a wide range of experimental and previous theoretical data, and good agreement is generally seen. Large changes in binding energy, De, and bond length, Re, between M+–He, M+–Ne, and M+–Ar, also found previously in the analogous Ba+-RG complexes [M. F. McGuirk et al., J. Chem. Phys. 130, 194305 (2009)], are identified and the cause investigated; the results shed light on the previous Ba+-RG results. These unusual trends are not observed for the dicationic complexes, which behave in a fashion similar to the isoelectronic alkali metal ion complexes. The potentials have also been employed to calculate transport coefficients for Mn+ moving through a bath of rare gas (RG) atoms.
Variable-wavelength frequency-domain terahertz ellipsometry
Authors: Hofmann T. , Herzinger C. M. , Boosalis A. , Tiwald T. E. , Woollam J. A. , Schubert M.
Published: February 2010

We report an experimental setup for wavelength-tunable frequency-domain ellipsometric measurements in the terahertz spectral range from 0.2 to 1.5 THz employing a desktop-based backward wave oscillator source. The instrument allows for variable angles of incidence between 30° and 90° and operates in a polarizer-sample-rotating analyzer scheme. The backward wave oscillator source has a tunable base frequency of 107–177 GHz and is augmented with a set of Schottky diode frequency multipliers in order to extend the spectral range to 1.5 THz. We use an odd-bounce image rotation system in combination with a wire grid polarizer to prepare the input polarization state. A highly phosphorous-doped Si substrate serves as a first sample model system. We show that the ellipsometric data obtained with our novel terahertz ellipsometer can be well described within the classical Drude model, which at the same time is in perfect agreement with midinfrared ellipsometry data obtained from the same sample for comparison. The analysis of the terahertz ellipsometric data of a low phosphorous-doped n-type Si substrate demonstrates that ellipsometry in the terahertz spectral range allows the determination of free charge-carrier properties for electron concentrations as low as 8×1014 cm−3.
X-ray absorption fine structure studies of Mn coordination in doped perovskite SrTiO3
Authors: Levin I. , Krayzman V. , Woicik J. C. , Tkach A. , Vilarinho P. M.
Published: February 2010

The coordination of Mn in doped SrTiO3 ceramics having nominal compositions SrTi0.98Mn0.02O3 and Sr0.98Mn0.02TiO3 was analyzed using x-ray absorption fine structure (XAFS) measurements. As expected, Mn4+ substitution for Ti4+ leads to Mn occupancy of the octahedral B-sites of ABO3 perovskite lattice with a Mn–O bond distance of 1.902 Å (compared to 1.953 Å for Ti–O) and no significant local distortions around the Mn atoms. In contrast, for the composition Sr0.98Mn0.02TiO3, Mn segregates to both the A-sites (as Mn2+) and the B-sites (predominantly as Mn4+). Extended XAFS confirms strong (≈0.77 Å) displacements of Mn2+ cations off the ideal A-site positions along ⟨001⟩ directions with a significant distortion of several coordination shells around the dopant atoms.
Lateral propagation of MeV electrons generated by femtosecond laser irradiation
Authors: Seely J. F. , Szabo C. I. , Audebert P. , Brambrink E. , Tabakhoff E. , Hudson L. T.
Published: February 2010

The propagation of MeV electrons generated by intense (≈1020 W/cm2) femtosecond laser irradiation, in the lateral direction perpendicular to the incident laser beam, was studied using targets consisting of irradiated metal wires and neighboring spectator wires embedded in electrically conductive (aluminum) or resistive (Teflon) substrates. The K shell spectra in the energy range 40–60 keV from wires of Gd, Dy, Hf, and W were recorded by a transmission crystal spectrometer. The spectra were produced by 1s electron ionization in the irradiated wire and by energetic electron propagation through the substrate material to the spectator wire of a different metal. The electron range and energy were determined from the relative K shell emissions from the irradiated and spectator wires separated by varying substrate lateral distances of up to 1 mm. It was found that electron propagation through Teflon was inhibited, compared to aluminum, implying a relatively weak return current and incomplete space-charge neutralization. The energetic electron propagation in the direction parallel to the electric field of the laser beam was larger than perpendicular to the electric field. Energetic electron production was lower when directly irradiating aluminum or Teflon compared to irradiating the heavy metal wires. These experiments are important for the determination of the energetic electron production mechanism and for understanding lateral electron propagation that can be detrimental to fast-ignition fusion and hard x-ray backlighter radiography.
Density functional calculations of hole induced long ranged ferromagnetic ordering in Mn doped Cd28Se28 nanocluster
Authors: Ghosh S. , Sanyal B. , Das G. P.
Published: February 2010

We have investigated the possibility of long ranged ferromagnetic ordering in Mn doped Cd28Se28 nanocluster using density functional approach. Following the band repulsion theory we have explained that magnetic coupling between Mn atoms substituted in Cd sites is antiferromagnetic and short ranged. However, long ranged ferromagnetic coupling is possible via additional hole doping which leads to the spin splitting of the valence band. In this class of magnetic nanoclusters, additional hole doping induces spin polarization of host states at large distance. This property can lead to molecular magnets with tunable magnetic properties.
Nonthermal effects on existence domains for dust-acoustic solitary structures in plasmas with two-temperature ions
Authors: Verheest Frank , Hellberg Manfred A.
Published: February 2010

Large dust-acoustic waves are investigated in a multispecies plasma model consisting of adiabatic, negatively charged dust, in the presence of two ion species, a cooler one with a Boltzmann distribution and a hotter one with a nonthermal Cairns distribution. This is treated through a Sagdeev pseudopotential analysis, in a way which is physically transparent and puts great emphasis on the existence domains in compositional parameter space. The occurrence and properties of positive double layers have been studied, and this automatically also includes the existence domains for positive solitons with velocities and amplitudes smaller than the double layer values. A brief discussion is given of negative solitons and of conditions affecting the coexistence of negative and positive solitary structures for the same plasma properties. Subject to simple adjustments, these results apply equally to the conjugate plasma model of positive dust and two electron species, and in the limit without nonthermal effects, to the case of ion-acoustic solitary structures in a plasma with double Boltzmann electrons, and extensions of earlier results of that problem are presented.
Coaxial discharge with axial magnetic field: Demonstration that the Boltzmann relation for electrons generally does not hold in magnetized plasmas
Authors: Zimmermann T. M. G. , Coppins M. , Allen J. E.
Published: February 2010

A one-dimensional two-fluid model is used to describe the quasineutral plasma of a discharge formed between coaxial cylinders under the influence of an axial magnetic field. The geometry treated in this paper is symmetric about the z-axis and is radially varying. The nested cylinders are necessarily different in size, leading to a potential difference between the sheath edges of the discharge plasma. This can be removed by applying a strong enough magnetic field, which also has the effect of flattening the potential profile, i.e., reducing the electric field in the plasma volume. In a previous publication [T. M. G. Zimmermann et al., Phys. Plasmas 16, 043501 (2009)], the authors examined the validity of the Boltzmann relation for electrons when applied to a similar geometry. When the magnetic field becomes strong enough to affect the electron flow in the radial direction, this expression breaks down. It was further discovered that certain situations require a self-consistent treatment of magnetic fields, since significant azimuthal currents can arise in such geometries. This work is applied and extended to offer a complete description of the electron density.
Monolayer rigid arrays of cavity-controllable metallic mesoparticles: Electrochemical preparation and light transmission resonances
Authors: Chen Zhuo , Dong Han , Pan Jian , Zhan Peng , Tang Chaojun , Wang Zhen-Lin
Published: February 2010

We report an efficient and robust electrochemical deposition method to fabricate large-scale two-dimensional rigid arrays of metal colloids with a precise control of the particle morphology by monitoring metal growth that is confined within a templated organic porous mold. Light transmission resonances through the metallic periodic microstructures are observed and the resonance wavelengths are found to depend on the morphology of the scattering elements. Further numerical simulations confirm these transmission resonances and reveal that they are attributed to the excitations of localized or propagating surface plasmon modes supported by the specific structures. The present method of tailoring metallic microstructures could find applications in plasmonics.
Effect of boron on interstitial-related luminescence centers in silicon
Authors: Charnvanichborikarn S. , Villis B. J. , Johnson B. C. , Wong-Leung J. , McCallum J. C. , Williams J. S. , Jagadish C.
Published: February 2010

Photoluminescence measurements have been used to investigate the optically active defect centers formed by silicon implantation and a subsequent anneal at 275, 400, or 525 °C. The presence of boron in p-type silicon is found to produce deleterious effects on the luminescence of the interstitial-related W- and X-centers as well as a lower energy broad luminescence band. This effect has not been previously reported but it is consistent with the suppression of interstitial-related {311} extended defect formation in the presence of high boron concentrations at higher annealing temperatures. The results presented in this letter provide insight into the role of boron in the initial stages of interstitial cluster formation.
A microtip self-written on a vertical-cavity surface-emitting laser by photopolymerization
Authors: Bardinal V. , Reig B. , Camps T. , Daran E. , Doucet J. B. , Turck C. , Malval J. P. , Lougnot D. J. , Soppera O.
Published: February 2010

We present the integration of a self-aligned microtip on a vertical-cavity surface-emitting laser (VCSEL) by near infrared photopolymerization. This one-step fabrication process is triggered by the laser source itself. It is based on the use of photopolymers sensitive at the lasing wavelength and can be applied to VCSEL devices after their process fabrication. We have characterized the fabricated microtips and shown that they focus laser light at few micrometers from the device. The applications of this simple method may concern VCSEL beam shaping as well as the fabrication of microprobes for near-field optical microscopy.
Second-harmonic generation from a single wurtzite GaAs nanoneedle
Authors: Chen Roger , Crankshaw Shanna , Tran Thai , Chuang Linus C. , Moewe Michael , Chang-Hasnain Connie
Published: February 2010

We report and characterize second-harmonic generation from a single wurtzite GaAs nanoneedle. The wurtzite crystal structure of the nanoneedle relaxes the strict nonlinear selection rules of normal zincblende GaAs while maintaining its strong nonlinear optical coefficients. The ability to grow GaAs nanoneedles without catalysts on (111) Si makes them particularly attractive as nonlinear optoelectronic media compatible with complementary metal-oxide-semiconductor technology.
Resistance-dependent amplitude of random telegraph-signal noise in resistive switching memories
Authors: Ielmini Daniele , Nardi Federico , Cagli Carlo
Published: February 2010

Resistive-switching memory (RRAM) is attracting a considerable interest for the development of high-density nonvolatile memories. However, several scaling and reliability issues still affect the development path of RRAM. This work addresses random telegraph-signal noise (RTN) of the RRAM current, potentially affecting the memory stability. We show a clear resistance dependence of the RTN amplitude, and we propose a physical model describing the interaction of the localized current with a fluctuating defect. By estimating the diameter of the conductive filament, the model quantitatively accounts for the observed RTN amplitude, thus allowing for an analytical prediction of state stability in RRAMs.
Control of vortical structures on a flapping wing via a sinusoidal leading-edge
Authors: Ozen C. A. , Rockwell D.
Published: February 2010

The flow structure generated by a flapping wing in the form of a plate is fundamentally altered if the leading-edge has a sinusoidal shape. It is possible to attenuate both the positive and negative spanwise flows along the plate surface, as well as the onset and development of large-scale concentrations of positive and negative streamwise vorticities at inboard locations. These alterations of the inboard flow structure have an insignificant influence on the structure of the tip vortex.
Retardation effects breaking long-range orientational ordering in dipolar fluids
Authors: Karlström Gunnar , Linse Per
Published: February 2010

A strongly coupled dipolar fluid confined in a sphere has been examined by Monte Carlo simulations using a modified distance-dependent pair interaction to emulate retardation effects. The effective dipole-dipole interaction and a property closely related to Kirkwood’s g-factor have been analyzed for potentials with different distances at which the retardation effects became effective. The retardation effects were found to break the otherwise long-range structural ordering occurring in strongly coupled dipolar fluids.