bluuebunny/crossref_metadata_2025 huggingface dataset:
Sphingosine kinase type 1 inhibition reveals rapid turnover of circulating sphingosine 1-phosphate
Authors: Kharel Yugesh , Mathews Thomas P. , Gellett Amanda M. , Tomsig Jose L. , Kennedy Perry C. , Moyer Morgan L. , Macdonald Timothy L. , Lynch Kevin R.
Published: August 2011

S1P (sphingosine 1-phosphate) is a signalling molecule involved in a host of cellular and physiological functions, most notably cell survival and migration. S1P, which signals via a set of five G-protein-coupled receptors (S1P1–S1P5), is formed by the action of two SphKs (sphingosine kinases) from Sph (sphingosine). Interfering RNA strategies and SphK1 (sphingosine kinase type 1)-null (Sphk1−/−) mouse studies implicate SphK1 in multiple signalling cascades, yet there is a paucity of potent and selective SphK1 inhibitors necessary to evaluate the effects of rapid onset inhibition of this enzyme. We have identified a set of submicromolar amidine-based SphK1 inhibitors and report using a pair of these compounds to probe the cellular and physiological functions of SphK1. In so doing, we demonstrate that our inhibitors effectively lower S1P levels in cell-based assays, but we have been unable to correlate SphK1 inhibition with changes in cell survival. However, SphK1 inhibition did diminish EGF (epidermal growth factor)-driven increases in S1P levels and Akt (also known as protein kinase B)/ERK (extracellular-signal-regulated kinase) phosphorylation. Finally, administration of the SphK1 inhibitor to wild-type, but not Sphk1−/−, mice resulted in a rapid decrease in blood S1P levels indicating that circulating S1P is rapidly turned over.
Failed Fixation in Atrophic Mandibular Fractures: The Case against Miniplates
Authors: Madsen Matthew J. , Kushner George M. , Alpert Brian
Published: August 2011

Despite advances in the treatment of the fractured atrophic edentulous mandible, treatment continues to be difficult. Patient management is more complicated due to patients often being elderly with more complex medical problems. Rigid internal fixation has greatly improved outcomes with shorter treatment times, yet a consensus has yet to be reached regarding which method yields the most predictable results. Options include using small miniplates to larger reconstruction plates. Although each method has advantages, we present our experience with retreatment of failed miniplate fixation using load-bearing reconstruction plates of fractured atrophic edentulous mandibles.
Degloving Injuries of the Oral Cavity Change the Operative Approach to Fractures of the Anterior Segment of the Mandible
Authors: Pollock Richard A. , Huber Katherine M. , Van Sickels Joseph E.
Published: August 2011

No report to date describes the added risk traumatic, degloving injuries of the oral cavity may pose when treating fractures of the mandible. The authors describe the oral degloving injury, characterized by separation of periosteum and soft tissue of the anterior floor of the mouth from the inner cortex of the anterior segment. Vascular anatomy of the floor of the mouth is reviewed as a prelude to a description of pathomechanics of the injury and a case report. The higher incidence of oral degloving in youth and in young adulthood and parallels in elective, orthognathic surgery are identified. When this unusual clinical presentation occurs, and when open reduction of fractures of the anterior segment is chosen, a vestibular incision is best avoided. Instead, a submental or upper neck incision is chosen for sufficient exposure to allow reduction and the application of appliances. Meticulous closure of the intraoral void is achieved using one of two techniques, depending on the level of degloving.
Size distributions of chemically synthesized Ag nanocrystals
Authors: Thøgersen Annett , Bonsak Jack , Fosli Carl Huseby , Muntingh Georg
Published: August 2011

Silver nanocrystals made by a chemical reduction of silver salts (AgNO3) by sodium borohydride (NaBH4) were studied using transmission electron microscopy and light scattering simulations. For various AgNO3/NaBH4 molar ratios, the size distributions of the nanocrystals were found to be approximately log-normal. In addition, a linear relation was found between the mean nanocrystal size and the molar ratio. In order to relate the size distribution of Ag nanocrystals of the various molar ratios to the scattering properties of Ag nanocrystals in solar cell devices, light scattering simulations of Ag nanocrystals in Si, SiO2, SiN, and Al2O3 matrices were carried out using MiePlot. These light scattering spectra for the individual nanocrystal sizes were combined into light scattering spectra for the fitted size distributions. The evolution of these scattering spectra with respect to an increasing mean nanocrystal size was then studied. From these findings, it is possible to find the molar ratio for which the corresponding nanocrystal size distribution has maximum scattering at a particular wavelength in the desired matrix.
Robustness of the filamentation instability as shock mediator in arbitrarily oriented magnetic field
Authors: Bret A. , Alvaro E. Perez
Published: August 2011

The filamentation instability (sometimes also referred to as “Weibel”) is a key process in many astrophysical scenario. In the Fireball model for gamma ray bursts, this instability is believed to mediate collisionless shock formation from the collision of two plasma shells. It has been known for long that a flow aligned magnetic field can completely cancel this instability. We show here that in the general case where there is an angle between the field and the flow, the filamentation instability can never be stabilized, regardless of the field strength. The presented model analyzes the stability of two symmetric counter-streaming cold electron/proton plasma shells. Relativistic effects are accounted for, and various exact analytical results are derived. This result guarantees the occurrence of the instability in realistic settings fulfilling the cold approximation.
Presence of excited electronic state in CaWO4 crystals provoked by a tetrahedral distortion: An experimental and theoretical investigation
Authors: Gracia Lourdes , Longo Valéria M. , Cavalcante Laécio S. , Beltrán Armando , Avansi Waldir , Li Máximo S. , Mastelaro Valmor R. , Varela José A. , Longo Elson , Andrés Juan
Published: August 2011

By combining experimental techniques such as x-ray diffraction, Fourier transform Raman, ultraviolet-visible, x-ray absorption near edge structure, extended x-ray absorption fine structure spectroscopy, and theoretical models, a general approach to understand the relationship among photoluminescence (PL) emissions and excited electronic states in CaWO4 crystals is presented. First-principles calculations of model systems point out that the presence of stable electronic excited states (singlet) allow us to propose one specific way in which PL behavior can be achieved. In light of this result, we reexamine prior experiments on PL emissions of CaWO4.
Analytical modeling and numerical simulation of P+-Hg0.69 Cd0.31Te/n-Hg0.78Cd0.22Te/CdZnTe heterojunction photodetector for a long-wavelength infrared free space optical communication system
Authors: Dwivedi A. D. D.
Published: August 2011

In this paper an analytical modeling and 2D numerical simulation of P+-Hg0.69Cd0.31Te/ n-Hg0.78Cd0.22Te/CdZnTe single heterojunction photodetector using the commercially available atlasTM package from SILVACO® International for long-wavelength free space optical communication has been reported. The photodetector has been studied with respect to energy band diagram, electric field profile, doping profile, dark current, resistance area product, quantum efficiency, spectral response, responsivity, and detectivity by an analytical method using closed form equations. The results obtained on the basis of the analytical model have been compared and contrasted with the simulated results using atlasTM. The photodetector exhibits high values of quantum efficiency ∼80%, responsivity ∼6.75 A/W, specific detectivity ∼2.25 × 1011 mHz1/2W−1 at wavelength10.6 μm, and dark current of the order of 10−11 A. The estimated noise equivalent power (NEP) is of the order of 1 × 10−17 W.
Reflection of femtosecond laser light in multipulse ablation of metals
Authors: Vorobyev A. Y. , Guo Chunlei
Published: August 2011

The shot-to-shot reflectance of high-intensity laser light is studied as a function of both the number of laser shots and laser fluence in multipulse ablation of a metal when the irradiated surface undergoes structural changes from an initially smooth surface to a deep crater. Our study shows that the reflectance of the irradiated surface significantly decreases due to the high intensity of laser pulses and the laser-induced surface structures in ablation regimes typically used for femtosecond laser processing of materials. The high-intensity effect dominates in the reflection reduction at low numbers of laser shots when laser-induced surface structures do not cause the reflectance to decrease noticeably. With increasing the number of laser shots, the structural effect comes into play, and both high-intensity and structural effects quickly reduce the reflectance of the sample to a low value.
Patterned electrode vertical field effect transistor: Theory and experiment
Authors: Ben-Sasson Ariel J. , Tessler Nir
Published: August 2011

We present a theoretical and experimental investigation of the recently reported new architecture of a patterned electrode vertical field effect transistor (PE-VFET). The investigation focuses on the role of the embedded source electrode architecture in the device behavior. Current-voltage characteristics was unraveled through the use of a self-consistent numerical simulation resulting in guidelines for the PE-VFET architecture regarding the On/Off current ratio, output current density, and apparent threshold voltage. Current modulation characteristics are obtained through the formation of virtual contacts at the PE nano-features (i.e., perforations) under gate bias, which lead to the formation of vertical channels under drain bias. As the vertical channel is formed the device characteristics change from contact-limited to space-charge-limited. The analytical model strength is shown with the parameter extraction procedure applied to a measured PE-VFET device fabricated using block copolymer lithography and with the appropriate simulation results.
In-fiber shock propagation in Dyneema®
Authors: Hazell P. J. , Appleby-Thomas G. J. , Trinquant X. , Chapman D. J.
Published: August 2011

In this work, the in-fiber shock propagation in Dyneema® has been studied such that the shock propagated along the axis of one of the fiber directions. A fast moving precursor wave was detected that corresponded to the elastic wave velocity of the fibers suggesting that the fibers themselves were acting as wave guides. Further, it was noticed that above a threshold shock stress of ca. 3.5 GPa, this wave was not discernable. This shock stress corresponded with the stress at which shock-induced melt would be expected to occur suggesting that melting inhibited the fibers’ ability to act as wave guides.
Response to “Comment on ‘Interaction of two solitary waves in quantum electron-positron-ion plasma’” [Phys. Plasmas 18, 084701 (2011)]
Authors: Xu Yan-Xia , Liu Zong-Ming , Lin Mai-Mai , Shi Yu-Ren , Duan Wen-Shan
Published: August 2011

According to the comments of Akbari-Moghanjoughi that the electron-positron-ion(e-p-i) plasmas parameters σ representing the ratio of the positron to electron Fermi-temperature and p standing for the positron to electron number-density ratio are related by the equation of p = σ 3/2. Based on this conclusion, we have replaced the Figs. 1–6 (Ref. 1) in the present paper.
Out-of-plane anisotropy and low field induced magnetic domain reorientation in Al/Metglas-2605S2/Al trilayer sensors
Authors: Passamani E. C. , Larica C. , Moscon P. S. , Mendoza Zélis P. , Sánchez F. H.
Published: August 2011

Local magnetism of Al/Metglas-2605S2/Al trilayer-like sensors prepared by dc sputtering has been studied at room temperature by both in-field and zero-field Mössbauer spectroscopy for a maximum field of 60 mT. Ferromagnetic domain reorientation from out-of-ribbon plane to in-plane, induced by low applied fields, was measured by monitoring the intensities of lines 2 and 5 in the Mössbauer sextet spectra obtained for different magnitudes of applied magnetic field. Coating the Metglas-2605S2 with Al layers of 20 μm thickness, a stress-field is induced, allowing to distinguish different in-plane magnetic anisotropy distributions along the ribbon length (∼4 mT) as well along its width (∼10 mT). Using a phenomenological model for the magnetization reversal, out-of-plane anisotropies ranging up to 3 kJ/m3 were estimated for the Metglas-2605S2 alloy ribbons. This anisotropy range is similar to that observed for the in-plane case previously reported. The methodology applied in this work can be used to determine native out-of-plane anisotropy distributions for different melt-spun ribbons. It also allows understanding magnetization reversal associated with the ferromagnetic domains reorientation caused either by induced stress or by applied magnetic field.
Modeling the effect of mobile ion contamination on the stability of a microelectromechanical resonator
Authors: Haarahiltunen A. , Varpula A. , Savin H.
Published: August 2011

We present a theoretical model for mobile ion contamination in a silicon microelectromechanical resonator. In the model both drift and diffusion of the mobile charge in dielectric films are taken into account. The model is verified through a comparison to existing experimental data. We show that the model can describe the frequency drift of resonators in a wide temperature range.
A repetitive S-band long-pulse relativistic backward-wave oscillator
Authors: Jin Zhenxing , Zhang Jun , Yang Jianhua , Zhong Huihuang , Qian Baoliang , Shu Ting , Zhang Jiande , Zhou Shengyue , Xu Liurong
Published: August 2011

This paper presents both numerical and experimental studies of a repetitive S-band long-pulse relativistic backward-wave oscillator. The dispersion relation curve of the main slow-wave structure is given by the numerical calculation. Experimental results show that a 1 GW microwaves with pulse duration of about 100 ns (full width of half magnitude) under 10 Hz repetitive operation mode are obtained. The microwave frequency is 3.6 GHz with the dominant mode of TM01, and power conversion efficiency is about 20%. The single pulse energy is about 100 J. The experimental results are in good agreement with the simulation ones. By analyzing the experimental phenomenon, we obtain the conclusion that the explosive emission on the surface of the electrodynamics structure in intense radio frequency field mainly leads to the earlier unexpected termination of microwave output.
Donor−acceptor pair luminescence in compensated Si for solar cells
Authors: Tajima Michio , Iwai Takaaki , Toyota Hiroyuki , Binetti Simona , Macdonald Daniel
Published: August 2011

A broad band with a fine structure on the higher energy side has been commonly observed in photoluminescence at 4.2 K from compensated Si for solar cells involving P donors and B acceptors on the order of 1016 cm−3. We calculated the theoretical spectrum of donor−acceptor (DA) pair luminescence from the density distribution of pairs as a function of the transition energy of respective pairs with separations ranging from 1.9 to 3.3 nm. A close agreement was obtained between the observed spectral structure and the theoretical curve using the generally accepted P donor and B acceptor ionization energies, where a systematic deviation was explained by the Van der Waals interaction between shallow P donors and B acceptors. This allows us to conclude that the band with the fine structure is due to the P-donor−B-acceptor pair recombination. This identification was confirmed by the observation of As-donor−B-acceptor pair luminescence in an As-doped sample. The present findings indicate that P and B impurities with concentrations on the order of 1016 cm−3 are unlikely to form complexes and that their ionization energies are not changed from those in the low concentration range.
Magnetoresistivity in CoFe2O4-BaTiO3 composites produced by spark plasma sintering
Authors: Stingaciu Marian , Kremer Reinhard K. , Lemmens Peter , Johnsson Mats
Published: August 2011

Ceramic composites of (CoFe2O4)x−(BaTiO3)(1−x) with x = 0.20, 0.25, and 0.30 have been synthesized by spark plasma sintering at 1000 °C under a uniaxial pressure of 75 MPa using commercially available nanopowders as starting materials. The composites reveal a negative magnetoresistivity effect of about − 1% at room temperature. An enhancement was observed at lower temperatures, and an effect of − 4.1% was found in the composite with x = 0.30 at 150 K by applying an external magnetic field of 25 kOe. The temperature dependence of the resistivity indicates variable range hopping involved in charge transport.
Quantum restricted effects on ballistic thermal conductance associated with six types of vibration modes in nanowire superlattice
Authors: Peng Xiao-Fang , Wang Xin-Jun
Published: August 2011

We study ballistic phonon transport and thermal conductance associated with six low-lying vibrational modes in a quadrate nanowire superlattice at low temperatures. The results show that the transmission rates of the six vibrational modes display periodic forbidden regions of frequencies and have different relations with geometrical details of the nanowire superlattice. The thermal conductances contributed from different vibrational modes show different characteristics. On the basis of the theoretical analysis and calculated simulation, quantum restricted effects on ballistic thermal conductance in the quadrate nanowire superlattice are revealed.
Efficiency limit and example of a photonic solar cell
Authors: Peters Marius , Christoph Goldschmidt Jan , Bläsi Benedikt
Published: August 2011

Restricting the angular emission characteristics of a solar cell results in a reduction of entropy generation and allows for higher solar cell efficiencies. In this paper, we present the concept of a photonic solar cell which exhibits the combination of a solar cell and a photonic crystal. The basic idea is to structure a solar cell in such a way that the applied structure is a photonic crystal consisting of the solar cell material. The aim of having a solar cell in the form of a photonic crystal is to restrict the emission of the solar cell into certain angles This reduction reduces the radiative losses and results in a higher VOC and, consequently, a higher efficiency of the cell. To calculate the efficiency of a photonic solar cell we introduce an adaptation of the detailed balance approach. This adaptation takes into account the reduced radiative losses due to the presence of a photonic band structure. In the second part of the paper we use this approach to calculate the efficiency for an exemplary system. The exemplary system is an idealized edge filter, similar to a Bragg stack. The idealization concerns the reflection characteristic of this filter and its dependence on the polarization. For this idealized system we calculate an efficiency that exceeds that of a conventional solar cell by up to 2.5% absolute.
Dielectric response functions of the (0001¯), (101¯3) GaN single crystalline and disordered surfaces studied by reflection electron energy loss spectroscopy
Authors: Romanyuk O. , Jiricek P. , Zemek J. , Tougaard S. , Paskova T.
Published: August 2011

Polar GaN(0001¯) (1×1), semipolar GaN(101¯3) surfaces prepared in NH3 vapor, and their disordered counterparts are investigated by reflection electron energy loss spectroscopy (REELS) and low-energy electron diffraction. The REELS spectra are measured in a range of polar angles at electron kinetic energies of 200 and 1000 eV. The electron energy loss function is determined from the REELS within the framework of the semiclassical approach. Good agreement between experimental and theoretical functions is achieved at all angles for the disordered GaN surfaces and for the ordered surfaces measured at a kinetic energy of 1000 eV. The agreement is worse for the crystals measured at 200 eV, which is explained by the coherent scattering contributions at low energies. The optical constants of the GaN surfaces are derived from the computed dielectric functions: the optical properties of the (0001¯) and (101¯3) surfaces are similar, except for differences in bandgap values, which may be due to observed steps on the (101¯3) surface. The surface optical properties of a disordered GaN surface are found to be different from the GaN crystals. There are pronounced changes in the electronic band structure for disordered GaN due to the preferential sputtering of nitrogen.
Direct numerical simulation of an isothermal reacting turbulent wall-jet
Authors: Pouransari Zeinab , Brethouwer Geert , Johansson Arne V.
Published: August 2011

In the present investigation, Direct Numerical Simulation (DNS) is used to study a binary irreversible and isothermal reaction in a plane turbulent wall-jet. The flow is compressible and a single-step global reaction between an oxidizer and a fuel species is solved. The inlet based Reynolds, Schmidt, and Mach numbers of the wall-jet are Re = 2000, Sc = 0.72, and M = 0.5, respectively, and a constant coflow velocity is applied above the jet. At the inlet, fuel and oxidizer enter the domain separately in a non-premixed manner. The turbulent structures of the velocity field show the common streaky patterns near the wall, while a somewhat patchy or spotty pattern is observed for the scalars and the reaction rate fluctuations in the near-wall region. The reaction mainly occurs in the upper shear layer in thin highly convoluted reaction zones, but it also takes place close to the wall. Analysis of turbulence and reaction statistics confirms the observations in the instantaneous snapshots, regarding the intermittent character of the reaction rate near the wall. A detailed study of the probability density functions of the reacting scalars and comparison to that of the passive scalar throughout the domain reveals the significance of the reaction influence as well as the wall effects on the scalar distributions. The higher order moments of both the velocities and the scalar concentrations are analyzed and show a satisfactory agreement with experiments. The simulations show that the reaction can both enhance and reduce the dissipation of fuel scalar, since there are two competing effects; on the one hand, the reaction causes sharper scalar gradients and thus a higher dissipation rate, on the other hand, the reaction consumes the fuel scalar thereby reducing the scalar dissipation.
Role of streamwise dynamics in spreading and mixing of flows through a rectangular sudden expansion
Authors: Sau Amalendu
Published: August 2011

Direct numerical simulations are performed to examine roles of streamwise dynamics in the spreading and mixing of flows in a two-step rectangular sudden expansion channel. The configuration is observed to facilitate higher entrainment by virtue of developed inflow type streamwise dynamics, and the system-generated passive forcing provided the necessary impetus for sustainable growth/evolution of the vortices. In addition, with the introduction and proper placement of two tiny rectangular “tabs” over the inlet walls, the downstream growth/dynamics of the vortices could be effectively modified. Through their inflow/outflow type dynamics, the streamwise vortices are found to decisively dictate the transverse jet spreading. The physical process thereby either led to a quick axis switching of the jet, or stopped axis switching altogether. However, the stretching of the azimuthal vortices is found to remain directly linked to the streamwise continuation of jet’s azimuthal curvature variation. A pressure analysis as presented herein, and the simulated nature of dynamics of two azimuthal components of vortices further reveal that the transverse pressure gradient skewing is a dominant source of streamwise vorticity in such flows. With the knowledge of simulated transverse pressure distribution, we formulate here a mechanism which efficiently predicts the inception/dynamics of all the streamwise vortices. Moreover, a novel mathematical foundation in support of the pressure analysis has been outlined here, which ensures further broader universal scope of applicability of our proposed pressure analysis.
Electrical dipole-dipole interaction effects on magnetocurrent in organic phosphorescent materials
Authors: Shao Ming , Dai Yanfeng , Ma Dongge , Hu Bin
Published: August 2011

This letter reports the experimental studies on electrical dipole-dipole interaction effects on magnetocurrent (MC) and magneto-electroluminescence (MFEEL) based on two phosphorescent dyes: heavy-metal complex Ir(ppy)3 and Ir(ppy)2(acac) with strong spin-orbital coupling but different electrical dipole moments. We find that the Ir(ppy)3 with strong electrical dipole moment shows negligible MC and MFEEL. However, the Ir(ppy)2(acac) with weak dipole moment exhibits appreciable MC and MFEEL. The experimental results suggest that the electrical dipole-dipole interaction can change the MC and MFEEL from capture-based regime, where charge carriers are captured through spin-dependent process at short distance, to intersystem crossing-based regime, where charge carriers are captured through spin random process at long distance. As a result, changing electrical dipole-dipole interaction presents a new pathway to tune magnetic field effects in organic semiconductors.
Ultra-intense single attosecond pulse generated from circularly polarized laser interacting with overdense plasma
Authors: Ji Liangliang , Shen Baifei , Zhang Xiaomei , Wen Meng , Xia Changquan , Wang Wenpeng , Xu Jiancai , Yu Yahong , Yu Mingyang , Xu Zhizhan
Published: August 2011

Few-cycle relativistic circularly polarized (CP) laser pulse reflected from overdense plasma is investigated by analysis and particle-in-cell simulations. It is found that through the laser-induced one-time drastic oscillation of the plasma boundary, an ultra-intense single attosecond light pulse can be generated naturally. An analytical model is proposed to describe the interaction and it agrees well with simulation results. They both indicate that peak intensity of the generated attosecond pulse is higher when the plasma density is closer to the relativistic transparency threshold and/or the pulse duration is closer to plasma oscillating period. Two dimensional simulation shows that a two-cycle 1021 W/cm2 CP laser can generate a single 230 attosecond 2 × 1021 W/cm2 pulse of light at a conversion efficiency greater than 10-2.
Acoustic cloak for airborne sound by inverse design
Authors: García-Chocano V. M. , Sanchis L. , Díaz-Rubio A. , Martínez-Pastor J. , Cervera F. , Llopis-Pontiveros R. , Sánchez-Dehesa J.
Published: August 2011

This Letter presents practical realization of a two-dimensional low loss acoustic cloak for airborne sound obtained by inverse design. The cloak consists of 120 aluminum cylinders of 15 mm diameter surrounding the cloaked object—a cylinder of diameter 22.5 cm. The position of each cylinder in the cloak is optimized using the data from two different techniques: genetic algorithm and simulated annealing. The operation frequency of this cloak is 3061 Hz with the bandwidth of about 100 Hz. Being a multi-step approach to the desired cloaking, the inverse design is also valid, in principle, for non-symmetric cylinders and even for three-dimensional objects.
One real function instead of the Dirac spinor function
Authors: Akhmeteli Andrey
Published: August 2011

Three out of four complex components of the Dirac spinor can be algebraically eliminated from the Dirac equation (if some linear combination of electromagnetic fields does not vanish), yielding a partial differential equation of the fourth order for the remaining complex component. This equation is generally equivalent to the Dirac equation. Furthermore, following Schrödinger [Nature (London), 169, 538 (1952)], the remaining component can be made real by a gauge transform, thus extending to the Dirac field the Schrödinger conclusion that charged fields do not necessarily require complex representation. One of the two resulting real equations for the real function describes current conservation and can be obtained from the Maxwell equations in spinor electrodynamics (the Dirac-Maxwell electrodynamics). As the Dirac equation is one of the most fundamental equations, these results both belong in textbooks and can be used for development of new efficient methods and algorithms of quantum chemistry.
Local explicitly correlated second-order Møller–Plesset perturbation theory with pair natural orbitals
Authors: Tew David P. , Helmich Benjamin , Hättig Christof
Published: August 2011

We explore using a pair natural orbital analysis of approximate first-order pair functions as means to truncate the space of both virtual and complementary auxiliary orbitals in the context of explicitly correlated F12 methods using localised occupied orbitals. We demonstrate that this offers an attractive procedure and that only 10–40 virtual orbitals per significant pair are required to obtain second-order valence correlation energies to within 1–2% of the basis set limit. Moreover, for this level of virtual truncation, only 10–40 complementary auxiliary orbitals per pair are required for an accurate resolution of the identity in the computation of the three- and four-electron integrals that arise in explicitly correlated methods.
High voltage pulse shaping of e-beam diode using perveance variation
Authors: Mitra S. , Sharma V. , Senthil K. , Roy A. , Kumar D. D. P. , Menon Rakhee , Singh S. K. , Sharma Archana , Nagesh K. V. , Chakravarthy D. P.
Published: August 2011

This paper presents a new high voltage pulse shaping methodology for pulsed power applications. The aim is to generate high voltage square pulse across anode cathode gap of e-beam diodes. The non-linear time varying perveance characteristics of e-beam diodes are used for shaping of output voltage pulse across it, generated directly from Marx generator. Analytically, it has been shown in the paper that under certain conditions, if achieved, Marx generator feeding an e-beam diode can produce a square-like pulse at the output, without any extra pulse shaping arrangements. Experimental results to support the analysis are also presented in the paper.
Optical second harmonic generation from Pt nanowires with boomerang-like cross-sectional shapes
Authors: Ogata Yoichi , Anh Tuan Nguyen , Miyauchi Yoshihiro , Mizutani Goro
Published: August 2011

We have fabricated Pt nanowires with boomerang-like cross-sectional shapes on the MgO(110) faceted template and observed their optical second-harmonic generation (SHG) response. In the TEM images the Pt nanowires on the MgO substrate had macroscopic C2v symmetry, however, their structure had microscopic imperfections. In the SHG response, as a function of the sample rotation angle around the substrate normal, we found contributions from the nonlinear susceptibility elements χ113, χ223, χ311, χ322, and χ333 originating from the broken symmetry in the 3; [110] direction of the MgO substrate. The indices 1 and 2 denote the [001] and [11¯0] directions, respectively. Under C2v symmetry no SHG is expected in the s-in/s-out polarization configuration, however, a finite SHG was observed in this polarization configuration. We suggest that the SHG in the forbidden configuration might originate from the imperfections in the nanowire structure.
Tunable infrared plasmonic absorption by metallic nanoparticles
Authors: Das Naresh C.
Published: August 2011

We exploit unique infrared plasmonic absorption properties of gold (Au) nanoparticles in the range of 2.5 to 20 μm. Fabrication of Au nanoplasmon particles with variable nanometer (nm) scale size and thickness gave us full control of tuning the absorption wavelength in the above infrared (IR) spectral regions. We did not observe polarization dependence for square size plasmon particles. However, by using plateau crescent (metal crescent structure with flat instead of rounded side on the top) metal particles we observed significant polarization effects in IR absorption spectra. We observed that the position of the absorption peak has linear dependence on the size of nanoparticles, and the absorption quantity depends on the density of the nanoparticles per unit area. The proposed nanoplasmon structure can be used to improve the performance of detector and light emitting diode (LED) devices operating in the IR region.
An integral perturbation model of flow and momentum transport in rotating microchannels with smooth or microstructured wall surfaces
Authors: Romanin Vince D. , Carey Van P.
Published: August 2011

This paper summarizes the development of an integral perturbation solution of the equations governing flow momentum transport and energy conversion in microchannels between disks of multiple-disk drag turbines such as Tesla turbines. Analysis of this type of flow problem is a key element in optimal design of Tesla drag-type turbines for geothermal or solar alternative energy technologies. In multiple-disk turbines, high speed flow enters tangentially at the outer radius of cylindrical microchannels formed by closely spaced parallel disks, spiraling through the channel to an exhaust at a small radius, or at the center of the disk. Previous investigations have generally developed models based on simplifying idealizations of the flow in these circumstances. Here, beginning with the momentum and continuity equations for incompressible and steady flow in cylindrical coordinates, an integral solution scheme is developed that leads to a dimensionless perturbation series solution that retains the full complement of momentum and viscous effects to consistent levels of approximation in the series solution. This more rigorous approach indicates all dimensionless parameters that affect flow and transport and allows a direct assessment of the relative importance of viscous, pressure, and momentum effects in different directions in the flow. The resulting lowest-order equations are solved explicitly and higher order terms in the series solutions are determined numerically. Enhancement of rotor drag in this type of turbine enhances energy conversion efficiency. We also developed a modified version of the integral perturbation analysis that incorporates the effects of enhanced drag due to surface microstructuring. Results of the model analysis for smooth disk walls are shown to agree well with experimental performance data for a prototype Tesla turbine and predictions of performance models developed in earlier investigations. Model predictions indicate that enhancement of disk drag by strategic microstructuring of the disk surfaces can significantly increase turbine efficiency. Exploratory calculations with the model indicate that turbine efficiencies exceeding 75% can be achieved by designing for optimal ranges of the governing dimensionless parameters.
Growth mechanism of highly uniform InAs/GaAs quantum dot with periodic arsine interruption by metalorganic chemical vapor deposition
Authors: Kim Jungsub , Yang Changjae , Sim Uk , Lee Gun-Do , Park Jinsub , Lee Youngsoo , Yoon Euijoon
Published: August 2011

The mechanism for suppressing the formation of abnormally large islands during the conventional quantum dot (QD) growth was investigated. In comparison of the periodic arsine interruption method to the conventional method, InAs QDs grown on GaAs substrate by metal organic chemical vapor deposition has a higher density and aspect ratio without large islands. The formation of large islands was related to the inhomogeneity in the nucleation and growth process of QDs. The surface modification from As-stabilized to In-stabilized surfaces during arsine interruption modulated the surface energy and resulted in more homogeneous and simultaneous nucleation of QDs. The arsine interruption time was found to be a critical parameter for the homogeneous QD growth without abnormally large islands.
Interface for time-resolved electrochemical infrared microspectroscopy using synchrotron infrared radiation
Authors: Rosendahl Scott M. , Borondics Ferenc , May Tim E. , Pedersen Tor M. , Burgess Ian J.
Published: August 2011

A description of a coupled electrochemical and spectrometer interface using synchrotron infrared radiation is provided. The interface described allows for the precise and accurate timing needed for time-resolved IR spectroscopic studies of electrochemical systems. The overall interface uses a series of transistor-transistor logic trigger signals generated from the commercial FTIR spectrometer to regulate the recording of control, electrochemical, and IR signals with reproducible and adjustable timing. The instrument has been tested using a thin-layer electrochemical cell with synchrotron light focused through microscope optics. The time-resolved response of the benzoquinone/dihydroxybenzoquinone redox couple is illustrated as an example of the instrument's capability.
A novel smooth impact drive mechanism actuation method with dual-slider for a compact zoom lens system
Authors: Lee Jonghyun , Kwon Won Sik , Kim Kyung-Soo , Kim Soohyun
Published: August 2011

In this paper, a novel actuation method for a smooth impact drive mechanism that positions dual-slider by a single piezo-element is introduced and applied to a compact zoom lens system. A mode chart that determines the state of the slider at the expansion or shrinkage periods of the piezo-element is presented, and the design guide of a driving input profile is proposed. The motion of dual-slider holding lenses is analyzed at each mode, and proper modes for zoom functions are selected for the purpose of positioning two lenses. Because the proposed actuation method allows independent movement of two lenses by a single piezo-element, the zoom lens system can be designed to be compact. For a feasibility test, a lens system composed of an afocal zoom system and a focusing lens was developed, and the passive auto-focus method was implemented.
Observation and interpretation of adjacent Moire patterns of different shapes in bilayer graphene
Authors: Jasinski J. B. , Dumpala S. , Sumanasekera G. U. , Sunkara M. K. , Ouseph P. J.
Published: August 2011

In transmission electron micrography of few-layer thick graphene samples, two distinct regions, a region of superlattice and an adjacent region of parallel straight bands, are seen. These two features are explained as Moire patterns produced by (1) rotation of top part of one of the graphene layers and (2) a small change in the shape of the bottom part of the same layer. It is interesting to note that for the first time, Moire pattern of parallel straight bands is observed and satisfactorily explained.
Quantitative analysis of terahertz spectra for illicit drugs using adaptive-range micro-genetic algorithm
Authors: Chen Yi , Ma Yong , Lu Zheng , Peng Bei , Chen Qin
Published: August 2011

In the field of anti-illicit drug applications, many suspicious mixture samples might consist of various drug components—for example, a mixture of methamphetamine, heroin, and amoxicillin—which makes spectral identification very difficult. A terahertz spectroscopic quantitative analysis method using an adaptive range micro-genetic algorithm with a variable internal population (ARVIPɛμGA) has been proposed. Five mixture cases are discussed using ARVIPɛμGA driven quantitative terahertz spectroscopic analysis in this paper. The devised simulation results show agreement with the previous experimental results, which suggested that the proposed technique has potential applications for terahertz spectral identifications of drug mixture components. The results show agreement with the results obtained using other experimental and numerical techniques.
Applying an optical space-time coding method to enhance light scattering signals in microfluidic devices
Authors: Mei Zhe , Wu Tsung-Feng , Pion-Tonachini Luca , Qiao Wen , Zhao Chao , Liu Zhiwen , Lo Yu-Hwa
Published: August 2011

An “optical space-time coding method” was applied to microfluidic devices to detect the forward and large angle light scattering signals for unlabelled bead and cell detection. Because of the enhanced sensitivity by this method, silicon pin photoreceivers can be used to detect both forward scattering (FS) and large angle (45–60°) scattering (LAS) signals, the latter of which has been traditionally detected by a photomultiplier tube. This method yields significant improvements in coefficients of variation (CV), producing CVs of 3.95% to 10.05% for FS and 7.97% to 26.12% for LAS with 15 μm, 10 μm, and 5 μm beads. These are among the best values ever demonstrated with microfluidic devices. The optical space-time coding method also enables us to measure the speed and position of each particle, producing valuable information for the design and assessment of microfluidic lab-on-a-chip devices such as flow cytometers and complete blood count devices.
Direct simulation of electron transfer using ring polymer molecular dynamics: Comparison with semiclassical instanton theory and exact quantum methods
Authors: Menzeleev Artur R. , Ananth Nandini , Miller Thomas F.
Published: August 2011

The use of ring polymer molecular dynamics (RPMD) for the direct simulation of electron transfer (ET) reaction dynamics is analyzed in the context of Marcus theory, semiclassical instanton theory, and exact quantum dynamics approaches. For both fully atomistic and system-bath representations of condensed-phase ET, we demonstrate that RPMD accurately predicts both ET reaction rates and mechanisms throughout the normal and activationless regimes of the thermodynamic driving force. Analysis of the ensemble of reactive RPMD trajectories reveals the solvent reorganization mechanism for ET that is anticipated in the Marcus rate theory, and the accuracy of the RPMD rate calculation is understood in terms of its exact description of statistical fluctuations and its formal connection to semiclassical instanton theory for deep-tunneling processes. In the inverted regime of the thermodynamic driving force, neither RPMD nor a related formulation of semiclassical instanton theory capture the characteristic turnover in the reaction rate; comparison with exact quantum dynamics simulations reveals that these methods provide inadequate quantization of the real-time electronic-state dynamics in the inverted regime.
Exchange interaction of electrons with Mn in hybrid AlSb/InAs/ZnMnTe structures
Authors: Terent’ev Ya. V. , Zoth C. , Bel’kov V. V. , Olbrich P. , Drexler C. , Lechner V. , Lutz P. , Mukhin M. S. , Tarasenko S. A. , Semenov A. N. , Solov’ev V. A. , Sedova I. V. , Klimko G. V. , Komissarova T. A. , Ivanov S. V. , Ganichev S. D.
Published: August 2011

Diluted magnetic semiconductor heterovalent AlSb/InAs/ZnMnTe quantum well (QW) structures with an electron channel have been designed and grown applying molecular-beam epitaxy. The enhanced magnetic properties of QWs as a result of the exchange interaction with Mn2+ ions, are proved by measuring the microwave radiation induced spin polarized electric currents.
Polarization-sensitive Schottky photodiodes based on a-plane ZnO/ZnMgO multiple quantum-wells
Authors: Tabares G. , Hierro A. , Vinter B. , Chauveau J.-M.
Published: August 2011

Light polarization-sensitive UV photodetectors (PSPDs) using non-polar a-plane ZnMgO/ZnO multiple quantum wells grown both on sapphire and ZnO substrates have been demonstrated. For the PSPDs grown on sapphire with anisotropic biaxial in-plain strain, the responsivity absorption edge shifts by ΔE ∼ 21 meV between light polarized perpendicular (⊥) and parallel (||) to the c-axis, and the maximum responsivity (R) contrast is (R⊥/R||)max ∼ 6. For the PSPDs grown on ZnO, with strain-free quantum wells, ΔE ∼ 40 meV and (R⊥/R||)max ∼ 5. These light polarization sensitivities have been explained in terms of the excitonic transitions between the conduction and the three valence bands.
Nanobeam photonic crystal cavity light-emitting diodes
Authors: Shambat Gary , Ellis Bryan , Petykiewicz Jan , Mayer Marie A. , Sarmiento Tomas , Harris James , Haller Eugene E. , Vučković Jelena
Published: August 2011

We present results on electrically driven nanobeam photonic crystal cavities formed out of a lateral p-i-n junction in gallium arsenide. Despite their small conducting dimensions, nanobeams have robust electrical properties with high current densities possible at low drive powers. Much like their two-dimensional counterparts, the nanobeam cavities exhibit bright electroluminescence at room temperature from embedded 1250 nm InAs quantum dots. A small room temperature differential gain is observed in the cavities with minor beam self-heating suggesting that lasing is possible. These results open the door for efficient electrical control of active nanobeam cavities for diverse nanophotonic applications.
Microbridge structures for uniform interval control of flowing droplets in microfluidic networks
Authors: Lee Do-Hyun , Lee Wonhye , Um Eujin , Park Je-Kyun
Published: August 2011

Precise temporal control of microfluidic droplets such as synchronization and combinatorial pairing of droplets is required to achieve a variety range of chemical and biochemical reactions inside microfluidic networks. Here, we present a facile and robust microfluidic platform enabling uniform interval control of flowing droplets for the precise temporal synchronization and pairing of picoliter droplets with a reagent. By incorporating microbridge structures interconnecting the droplet-carrying channel and the flow control channel, a fluidic pressure drop was derived between the two fluidic channels via the microbridge structures, reordering flowing droplets with a defined uniform interval. Through the adjustment of the control oil flow rate, the droplet intervals were flexibly and precisely adjustable. With this mechanism of droplet spacing, the gelation of the alginate droplets as well as control of the droplet interval was simultaneously achieved by additional control oil flow including calcified oleic acid. In addition, by parallel linking identical microfluidic modules with distinct sample inlet, controlled synchronization and pairing of two distinct droplets were demonstrated. This method is applicable to facilitate and develop many droplet-based microfluidic applications, including biological assay, combinatorial synthesis, and high-throughput screening.
On form factors of the conjugated field in the nonlinear Schrödinger model
Authors: Kozlowski K. K.
Published: August 2011

Izergin-Korepin's lattice discretization of the nonlinear Schrödinger model along with Oota's inverse problem provides one with determinant representations for the form factors of the lattice discretized conjugated field operator. We prove that these form factors converge, in the zero lattice spacing limit, to those of the conjugated field operator in the continuous model. We also compute the large-volume asymptotic behavior of such form factors in the continuous model. These are, in particular, characterized by Fredholm determinants of operators acting on closed contours. We provide a way of defining these Fredholm determinants in the case of generic parameters.
Effect of free-carrier concentration on the phase transition and vibrational properties of VO2
Authors: Nazari M. , Chen Changhong , Bernussi A. A. , Fan Z. Y. , Holtz M.
Published: August 2011

The effects of native defect doping concentration on the phase transition properties of vanadium dioxide thin films are investigated. The onset temperature of the metal-insulator transition is found to depend on the free-carrier concentration and to correlate with an abrupt change in the temperature dependence of the vibrational energies of the V-O related Raman band. A phase diagram is proposed identifying insulating, intermediate, and conducting regimes. The intermediate region is attributed to a mixed phase.