bluuebunny/crossref_metadata_2025 huggingface dataset:
Outcomes following Laminoplasty or Laminectomy and Fusion in Patients with Myelopathy Caused by Ossification of the Posterior Longitudinal Ligament: A Systematic Review
Authors: Singhatanadgige Weerasak , Limthongkul Worawat , Valone Frank , Yingsakmongkol Wicharn , Riew K. Daniel
Published: February 2016

Study Design

Systematic review.

Objective

To compare laminoplasty versus laminectomy and fusion in patients with cervical myelopathy caused by OPLL.

Methods

A systematic review was conducted using PubMed/Medline, Cochrane database, and Google scholar of articles. Only comparative studies in humans were included. Studies involving cervical trauma/fracture, infection, and tumor were excluded.

Results

Of 157 citations initially analyzed, 4 studies ultimately met our inclusion criteria: one class of evidence (CoE) II prospective cohort study and three CoE III retrospective cohort studies. The prospective cohort study found no significant difference between laminoplasty and laminectomy and fusion in the recovery rate from myelopathy. One CoE III retrospective cohort study reported a significantly higher recovery rate following laminoplasty. Another CoE III retrospective cohort study reported a significantly higher recovery rate in the laminectomy and fusion group. One CoE II prospective cohort study and one CoE III retrospective cohort study found no significant difference in pain improvement between patients treated with laminoplasty versus patients treated with laminectomy and fusion. All four studies reported a higher incidence of C5 palsy following laminectomy and fusion than laminoplasty. One CoE II prospective cohort and one CoE III retrospective cohort reported that there was no significant difference in axial neck pain between the two procedures. One CoE III retrospective cohort study suggested that there was no significant difference between groups in OPLL progression.

Conclusion

Data from four comparative studies was not sufficient to support the superiority of laminoplasty or laminectomy and fusion in treating cervical myelopathy caused by OPLL.
Clinical Outcomes of Posterior Lumbar Interbody Fusion for Patients 80 Years of Age and Older with Lumbar Degenerative Disease: Minimum 2 Years’ Follow-Up
Authors: Hayashi Kazunori , Matsumura Akira , Konishi Sadahiko , Kato Minori , Namikawa Takashi , Nakamura Hiroaki
Published: February 2016

Study Design

Retrospective study.

Objective

To compare clinical outcomes, radiographic evaluations including bony union rate and incidence of osteoporotic vertebral fractures (OVFxs), and perioperative complications following posterior lumbar interbody fusion (PLIF) between patients ≥80 years of age and those <80 years.

Methods

Ninety-six patients ≥70 years old who underwent PLIF were reviewed. We divided the patients into the two age groups, ≥80 group ( n = 19) and <80 group ( n = 77), and compared the clinical outcomes using Japanese Orthopaedics Association (JOA) scores and the Short-Form Health Survey (SF-36). We also evaluated bony union and the incidence of OVFxs in the both groups.

Results

The JOA score improved 47.6% in the ≥80 group and 49.1% in the <80 group. There were no significant differences between the two groups. Only the bodily pain component of the SF-36 improved significantly in the ≥80 group, and seven of eight components (exception was general health) improved significantly in the <80 group. Bony union rate was significantly superior in the <80 group (94.8%) compared with that of the ≥80 group (73.7%, p = 0.013). OVFx prevalence and incidence were not significantly different between the two groups, although postoperative OVFx worsened the JOA score improvement in the ≥80 group (38.8%, p = 0.02).

Conclusions

The present study indicated that surgical outcomes of PLIF in patients ≥80 years were comparable to those < 80 years. However, bony union rate was significantly lower and postoperative OVFx worsened the clinical outcomes in patients ≥80 years.
Displacement sensor based on plasmonic slot metamaterials
Authors: Wu Wei , Ren Mengxin , Pi Biao , Cai Wei , Xu Jingjun
Published: February 2016

In this paper, we demonstrate a plasmonic type displacement sensor based on slot metamaterials. The sensors are formed by arranging metamaterial arrays with different dimension parameters adjacently. Hence, the measured spectra would be modified as a result of moving the sensors across the detecting area of the spectrometer. From the spectral changes, the displacement amount could be retrieved. The sensor is demonstrated to be capable of recognizing a displacement of 200 nm, which is equal to the period of the metamaterial lattice, and the sensitivity is largely dependent on the shape and size of the acquisition area of the spectrometer used for spectra analysis.
Obliquely propagating electromagnetic waves in magnetized kappa plasmas
Authors: Gaelzer R. , Ziebell L. F.
Published: February 2016

Velocity distribution functions (VDFs) that exhibit a power-law dependence on the high-energy tail have been the subject of intense research by the plasma physics community. Such functions, known as kappa or superthermal distributions, have been found to provide a better fitting to the VDFs measured by spacecraft in the solar wind. One of the problems that is being addressed on this new light is the temperature anisotropy of solar wind protons and electrons. In the literature, the general treatment for waves excited by (bi-)Maxwellian plasmas is well-established. However, for kappa distributions, the wave characteristics have been studied mostly for the limiting cases of purely parallel or perpendicular propagation, relative to the ambient magnetic field. Contributions to the general case of obliquely propagating electromagnetic waves have been scarcely reported so far. The absence of a general treatment prevents a complete analysis of the wave-particle interaction in kappa plasmas, since some instabilities can operate simultaneously both in the parallel and oblique directions. In a recent work, Gaelzer and Ziebell [J. Geophys. Res. 119, 9334 (2014)] obtained expressions for the dielectric tensor and dispersion relations for the low-frequency, quasi-perpendicular dispersive Alfvén waves resulting from a kappa VDF. In the present work, the formalism is generalized for the general case of electrostatic and/or electromagnetic waves propagating in a kappa plasma in any frequency range and for arbitrary angles. An isotropic distribution is considered, but the methods used here can be easily applied to more general anisotropic distributions such as the bi-kappa or product-bi-kappa.
Modelling the flow of a second order fluid through and over a porous medium using the volume averages. I. The generalized Brinkman’s equation
Authors: Minale Mario
Published: February 2016

In this paper, the generalized Brinkman’s equation for a viscoelastic fluid is derived using the volume averages. Darcy’s generalised equation is consequently obtained neglecting the first and the second Brinkman’s correction with respect to the drag term. The latter differs from the Newtonian drag because of an additional term quadratic in the velocity and inversely proportional to a “viscoelastic” permeability defined in the paper. The viscoelastic permeability tensor can be calculated by solving a boundary value problem, but it must be in fact experimentally measured. To isolate the elastic contribution, the constitutive equation of the second order fluid of Coleman and Noll is chosen because, in simple shear at steady state, second order fluids show a constant viscosity and first and second normal stress differences quadratic in the shear rate. The model predictions are compared with data of the literature obtained in a Darcy’s experiment and the agreement is good.
Equilibrium structures of anisometric, quadrupolar particles confined to a monolayer
Authors: Heinemann Thomas , Antlanger Moritz , Mazars Martial , Klapp Sabine H. L. , Kahl Gerhard
Published: February 2016

We investigate the structural properties of a two-dimensional system of ellipsoidal particles carrying a linear quadrupole moment in their center. These particles represent a simple model for a variety of uncharged, non-polar conjugated organic molecules. Using optimization tools based on ideas of evolutionary algorithms, we first examine the ground state structures as we vary the aspect ratio of the particles and the pressure. Interestingly, we find, besides the intuitively expected T-like configurations, a variety of complex structures, characterized with up to three different particle orientations. In an effort to explore the impact of thermal fluctuations, we perform constant-pressure molecular dynamics simulations within a range of rather low temperatures. We observe that ground state structures formed by particles with a large aspect ratio are in particular suited to withstand fluctuations up to rather high temperatures. Our comprehensive investigations allow for a deeper understanding of molecular or colloidal monolayer arrangements under the influence of a typical electrostatic interaction on a coarse-grained level.
Commissioning of the PRIOR proton microscope
Authors: Varentsov D. , Antonov O. , Bakhmutova A. , Barnes C. W. , Bogdanov A. , Danly C. R. , Efimov S. , Endres M. , Fertman A. , Golubev A. A. , Hoffmann D. H. H. , Ionita B. , Kantsyrev A. , Krasik Ya. E. , Lang P. M. , Lomonosov I. , Mariam F. G. , Markov N. , Merrill F. E. , Mintsev V. B. , Nikolaev D. , Panyushkin V. , Rodionova M. , Schanz M. , Schoenberg K. , Semennikov A. , Shestov L. , Skachkov V. S. , Turtikov V. , Udrea S. , Vasylyev O. , Weyrich K. , Wilde C. , Zubareva A.
Published: February 2016

Recently, a new high energy proton microscopy facility PRIOR (Proton Microscope for FAIR Facility for Anti-proton and Ion Research) has been designed, constructed, and successfully commissioned at GSI Helmholtzzentrum für Schwerionenforschung (Darmstadt, Germany). As a result of the experiments with 3.5–4.5 GeV proton beams delivered by the heavy ion synchrotron SIS-18 of GSI, 30 μm spatial and 10 ns temporal resolutions of the proton microscope have been demonstrated. A new pulsed power setup for studying properties of matter under extremes has been developed for the dynamic commissioning of the PRIOR facility. This paper describes the PRIOR setup as well as the results of the first static and dynamic proton radiography experiments performed at GSI.
Spontaneous emission of electromagnetic and electrostatic fluctuations in magnetized plasmas: Quasi-parallel modes
Authors: Kim Sunjung , Yoon Peter H. , Choe G. S.
Published: February 2016

The present paper is devoted to the theoretical and numerical analysis of the spontaneously emitted electromagnetic fluctuations characterized by quasi-parallel wave vectors relative to the ambient magnetic field. The formulation is based upon the Klimontovich plasma kinetic theory. The comparative study is carried out between the spontaneously emitted field fluctuation spectrum constructed on the basis of a single Maxellian velocity distribution function (VDF) and the spectrum that arises from multi-component electron VDFs similar to those found in the solar wind. Typical solar wind electron VDF is composed of a Gaussian core and kappa distributions of halo and super-halo components. Of these, the halo and super-halo populations represent tenuous but energetic components. It is found that the energetic electrons make important contributions to the total emission spectrum. It is also found that the halo electrons are largely responsible for the emission spectrum in the whistler frequency range, whereas the more energetic super-halo electrons emit quasi-longitudinal fluctuations in the Langmuir frequency range, thus validating the recent quasi-steady state model of the solar wind electrons put forth by the present authors [Kim et al., Astrophys. J. 806, 32 (2015); Yoon et al., Astrophys. J. 812, 169 (2015)].
Perspectives for spintronics in 2D materials
Authors: Han Wei
Published: February 2016

The past decade has been especially creative for spintronics since the (re)discovery of various two dimensional (2D) materials. Due to the unusual physical characteristics, 2D materials have provided new platforms to probe the spin interaction with other degrees of freedom for electrons, as well as to be used for novel spintronics applications. This review briefly presents the most important recent and ongoing research for spintronics in 2D materials.
Spatial chaos of Wang tiles with two symbols
Authors: Chen Jin-Yu , Chen Yu-Jie , Hu Wen-Guei , Lin Song-Sun
Published: February 2016

This investigation completely classifies the spatial chaos problem in plane edge coloring (Wang tiles) with two symbols. For a set of Wang tiles B, spatial chaos occurs when the spatial entropy h(B) is positive. B is called a minimal cycle generator if P(B)≠0̸ and P(B′)=0̸ whenever B′⫋B, where P(B) is the set of all periodic patterns on ℤ2 generated by B. Given a set of Wang tiles B, write B=C1∪C2∪⋯∪Ck∪N, where Cj, 1 ≤ j ≤ k, are minimal cycle generators and B contains no minimal cycle generator except those contained in C1∪C2∪⋯∪Ck. Then, the positivity of spatial entropy h(B) is completely determined by C1∪C2∪⋯∪Ck. Furthermore, there are 39 equivalence classes of marginal positive-entropy sets of Wang tiles and 18 equivalence classes of saturated zero-entropy sets of Wang tiles. For a set of Wang tiles B, h(B) is positive if and only if B contains a MPE set, and h(B) is zero if and only if B is a subset of a SZE set.
Solar cell parameters identification using hybrid Nelder-Mead and modified particle swarm optimization
Authors: Hamid Nurul Farhana Abdul , Rahim Nasrudin Abd , Selvaraj Jeyraj
Published: February 2016

Solar cell modelling primarily involves the formulation of the non-linear current versus voltage (I-V) curve. Determination of parameters plays an important role in solar cell accurate modelling. This paper presents an application of the hybrid Nelder-Mead simplex search method and modified Particle Swarm Optimization technique for identifying the parameters of solar cell and photovoltaic module models. The proposed technique is used to identify the unknown model parameters, namely, the generated photocurrent, saturation current, series resistance, shunt resistance, and ideality factor that govern the current-voltage relationship of a solar cell. A measurement data of 57 mm diameter commercial (R.T.C. France) silicon solar cell and a module consisting of 36 polycrystalline silicon cells (Photowatt-PWP 201) are used to test and verify the consistency of accurately estimating various parameters. Comparative study among different parameter estimation techniques is presented to demonstrate the effectiveness of the proposed approach. Furthermore, to verify the accurateness of the proposed technique, an experimental test bench unit is built using 72 mono-crystalline silicon cells (HIP-210NKHB5-2 module) on different environment conditions.
Thermally driven transverse transports and magnetic dynamics on a topological surface capped with a ferromagnet strip
Authors: Deng Ming-Xun , Zhong Ming , Zheng Shi-Han , Qiu Jian-Ming , Yang Mou , Wang Rui-Qiang
Published: February 2016

We theoretically study thermally driven transport of the Dirac fermions on the surface of a topological insulator capped with a ferromagnet strip. The generation and manipulation of anomalous Hall and Nernst effects are analyzed, in which the in-plane magnetization of the ferromagnet film is found to take a decisive role. This scenario is distinct from that modulated by Berry phase where the in-plane magnetization is independent. We further discuss the thermal spin-transfer torque as a backaction of the thermoelectric transports on the magnetization and calculate the dynamics of the anomalous Hall and Nernst effects self-consistently. It is found that the magnitude of the long-time steady Hall and Nernst conductance is determined by competition between the magnetic anisotropy and current-induced effective anisotropy. These results open up a possibility of magnetically controlling the transverse thermoelectric transports or thermally manipulating the magnet switching.
Towards microfluidic reactors for in situ synchrotron infrared studies
Authors: Silverwood I. P. , Al-Rifai N. , Cao E. , Nelson D. J. , Chutia A. , Wells P. P. , Nolan S. P. , Frogley M. D. , Cinque G. , Gavriilidis A. , Catlow C. R. A.
Published: February 2016

Anodically bonded etched silicon microfluidic devices that allow infrared spectroscopic measurement of solutions are reported. These extend spatially well-resolved in situ infrared measurement to higher temperatures and pressures than previously reported, making them useful for effectively time-resolved measurement of realistic catalytic processes. A data processing technique necessary for the mitigation of interference fringes caused by multiple reflections of the probe beam is also described.
A two force-constant model for complexes B⋯M–X (B is a Lewis base and MX is any diatomic molecule): Intermolecular stretching force constants from centrifugal distortion constants DJ or ΔJ
Authors: Bittner Dror M. , Walker Nicholas R. , Legon Anthony C.
Published: February 2016

A two force-constant model is proposed for complexes of the type B⋯MX, in which B is a simple Lewis base of at least C2v symmetry and MX is any diatomic molecule lying along a Cn axis (n ≥ 2) of B. The model assumes a rigid subunit B and that force constants beyond quadratic are negligible. It leads to expressions that allow, in principle, the determination of three quadratic force constants F11, F12, and F22 associated with the r(B⋯M) = r2 and r(M–X) = r1 internal coordinates from the equilibrium centrifugal distortion constants DJe or ΔJe, the equilibrium principal axis coordinates a1 and a2, and equilibrium principal moments of inertia. The model can be applied generally to complexes containing different types of intermolecular bond. For example, the intermolecular bond of B⋯MX can be a hydrogen bond if MX is a hydrogen halide, a halogen-bond if MX is a dihalogen molecule, or a stronger, coinage-metal bond if MX is a coinage metal halide. The equations were tested for BrCN, for which accurate equilibrium spectroscopic constants and a complete force field are available. In practice, equilibrium values of DJe or ΔJe for B⋯MX are not available and zero-point quantities must be used instead. The effect of doing so has been tested for BrCN. The zero-point centrifugal distortion constants DJ0 or ΔJ0 for all B⋯MX investigated so far are of insufficient accuracy to allow F11 and F22 to be determined simultaneously, even under the assumption F12 = 0 which is shown to be reasonable for BrCN. The calculation of F22 at a series of fixed values of F11 reveals, however, that in cases for which F11 is sufficiently larger than F22, a good approximation to F22 is obtained. Plots of F22 versus F11 have been provided for Kr⋯CuCl, Xe⋯CuCl, OC⋯CuCl, and C2H2⋯AgCl as examples. Even in cases where F22 ∼ F11 (e.g., OC⋯CuCl), such plots will yield either F22 or F11 if the other becomes available.
Hybrid acoustic energy harvesting using combined electromagnetic and piezoelectric conversion
Authors: Khan Farid Ullah , Izhar
Published: February 2016

This paper reports a novel hybrid acoustic energy harvester. The harvester utilizes both the electromagnetic and piezoelectric conversion mechanisms simultaneously to convert the ambient acoustical noise into electrical power for self-powered wireless sensor nodes. The proposed harvester is comprised of a Helmholtz resonator, two magnets mounted on a piezoelectric plate, and a wound coil located under the magnets. The harvester is characterized both under harmonic and real random acoustical excitations. In-lab, under harmonic acoustical excitation at a sound pressure level of 130 dB and frequency of 2.1 kHz, an optimum power of 2.86 μW (at 114 Ω optimum load) is obtained from electromagnetic conversion and 50 μW (at 1000 Ω optimum load) is generated by the piezoelectric harvester’s part. Moreover, in real acoustical environment of a domestic electric generator the peak voltages of 40 and 123 mV are produced by the electromagnetic and piezoelectric portions of the acoustic energy harvester.
Molecular electronic states near metal surfaces at equilibrium using potential of mean force and numerical renormalization group methods: Hysteresis revisited
Authors: Dou Wenjie , Nitzan Abraham , Subotnik Joseph E.
Published: February 2016

We investigate equilibrium observables for molecules near metals by employing a potential of mean force (PMF) that takes level broadening into account. Through comparison with exact data, we demonstrate that this PMF approach performs quite well, even for cases where molecule-electrode couplings depend on nuclear position. As an application, we reexamine the possibility of hysteresis effects within the Anderson-Holstein model (i.e., an impurity coupled both to a metal surface and a nuclear oscillator). As compared against the standard mean field approach by Galperin et al. [Nano Lett. 5, 125 (2005)], our PMF approach agrees much better with exact results for average electronic populations both at zero and finite temperature; we find, however, that mean field theory can be very useful for predicting the onset of dynamical instabilities, metastable states, and hysteresis.
Chaotifying delayed recurrent neural networks via impulsive effects
Authors: Şaylı Mustafa , Yılmaz Enes
Published: February 2016

In this paper, chaotification of delayed recurrent neural networks via chaotically changing moments of impulsive actions is considered. Sufficient conditions for the presence of Li-Yorke chaos with its ingredients proximality, frequent separation, and existence of infinitely many periodic solutions are theoretically proved. Finally, effectiveness of our theoretical results is illustrated by an example with numerical simulations.
Validation of local hybrid functionals for TDDFT calculations of electronic excitation energies
Authors: Maier Toni M. , Bahmann Hilke , Arbuznikov Alexei V. , Kaupp Martin
Published: February 2016

The first systematic evaluation of local hybrid functionals for the calculation of electronic excitation energies within linear-response time-dependent density functional theory (TDDFT) is reported. Using our recent efficient semi-numerical TDDFT implementation [T. M. Maier et al., J. Chem. Theory Comput. 11, 4226 (2015)], four simple, thermochemically optimized one-parameter local hybrid functionals based on local spin-density exchange are evaluated against a database of singlet and triplet valence excitations of organic molecules, and against a mixed database including also Rydberg, intramolecular charge-transfer (CT) and core excitations. The four local hybrids exhibit comparable performance to standard global or range-separated hybrid functionals for common singlet valence excitations, but several local hybrids outperform all other functionals tested for the triplet excitations of the first test set, as well as for relative energies of excited states. Evaluation for the combined second test set shows that local hybrids can also provide excellent Rydberg and core excitations, in the latter case rivaling specialized functionals optimized specifically for such excitations. This good performance of local hybrids for different excitation types could be traced to relatively large exact-exchange (EXX) admixtures in a spatial region intermediate between valence and asymptotics, as well as close to the nucleus, and lower EXX admixtures in the valence region. In contrast, the tested local hybrids cannot compete with the best range-separated hybrids for intra- and intermolecular CT excitation energies. Possible directions for improvement in the latter category are discussed. As the used efficient TDDFT implementation requires essentially the same computational effort for global and local hybrids, applications of local hybrid functionals to excited-state problems appear promising in a wide range of fields. Influences of current-density dependence of local kinetic-energy dependent local hybrids, differences between spin-resolved and “common” local mixing functions in local hybrids, and the effects of the Tamm-Dancoff approximation on the excitation energies are also discussed.
Electronic band structure and material gain of III-V-Bi quantum wells grown on GaSb substrate and dedicated for mid-infrared spectral range
Authors: Gladysiewicz M. , Kudrawiec R. , Wartak M. S.
Published: February 2016

The 8-band kp Hamiltonian is applied to calculate electronic band structure and material gain in III-V-Bi quantum wells (QWs) grown on GaSb substrates. We analyzed three Bi-containing QWs (GaSbBi, GaInSbBi, and GaInAsSbBi) and different Bi-free barriers (GaSb and AlGaInAsSb), lattice matched to GaSb. Bi-related changes in the electronic band structure of III-V host incorporated into our formalism are based on recent ab-initio calculations for ternary alloys (III-Ga-Bi and III-In-Bi) [Polak et al., Semicond. Sci. Technol. 30, 094001 (2015)]. When compared to Bi-free QWs, the analyzed Bi-containing structures show much better quantum confinement in the valence band and also larger redshift of material gain peak per percent of compressive strain. For 8 nm thick GaInSb/GaSb QWs, material gain of the transverse electric (TE) mode is predicted at 2.1 μm for the compressive strain of ε = 2% (32% In). The gain peak of the TE mode in 8 nm thick GaSbBi/GaSb QW reaches this wavelength for compressive strain of 0.15% that corresponds to about 5% Bi. It has also been shown that replacing In atoms by Bi atoms in GaInSbBi/GaSb QWs while keeping the same compressive strain (ε = 2%) in QW region enhances and shifts gain peak significantly to the longer wavelengths. For 8 nm wide GaInSbBi/GaSb QW with 5% Bi, the gain peak is predicted at around 2.6 μm, i.e., is redshifted by about 400 nm compared to Bi-free QW. For 8 nm wide GaInAsSbSb QWs (80% In, 5% Bi, and ε = 2%) with proper AlGaInAsSb barriers, it is possible to achieve large material gain even at 4.0 μm.
A condition for a perfect-fluid space-time to be a generalized Robertson-Walker space-time
Authors: Mantica Carlo Alberto , Molinari Luca Guido , De Uday Chand
Published: February 2016

A perfect-fluid space-time of dimension n ≥ 4, with (1) irrotational velocity vector field and (2) null divergence of the Weyl tensor, is a generalised Robertson-Walker space-time with an Einstein fiber. Condition (1) is verified whenever pressure and energy density are related by an equation of state. The contraction of the Weyl tensor with the velocity vector field is zero. Conversely, a generalized Robertson-Walker space-time with null divergence of the Weyl tensor is a perfect-fluid space-time.
Mode coupling theory and fragile to strong transition in supercooled TIP4P/2005 water
Authors: De Marzio M. , Camisasca G. , Rovere M. , Gallo P.
Published: February 2016

We study by molecular dynamics simulations supercooled water with the TIP4P/2005 potential. This model is able to predict many properties of water in a large range of the thermodynamic space in agreement with experiments. We explore the dynamical behavior and, in particular, the self intermediate scattering function of the oxygen atoms. We find that the structural relaxation in the range of mild supercooling is in agreement with the Mode Coupling Theory (MCT). The ideal MCT crossover takes place at decreasing temperature with increasing density. Deviations from the MCT behavior are found upon further supercooling. A crossover from the MCT, fragile, regime to a strong, Arrhenius, regime is found and it is connected to the presence of a liquid-liquid phase transition and the Widom line emanating from the liquid-liquid critical point.
Constructing two-dimensional optimal system of the group invariant solutions
Authors: Hu Xiaorui , Li Yuqi , Chen Yong
Published: February 2016

To search for inequivalent group invariant solutions of two-dimensional optimal system, a direct and systematic approach is established, which is based on commutator relations, adjoint matrix, and the invariants. The details of computing all the invariants for two-dimensional algebra are presented, which is shown more complex than that of one-dimensional algebra. The optimality of two-dimensional optimal systems is shown clearly for each step of the algorithm, with no further proof. To leave the algorithm clear, each stage is illustrated with a couple of examples: the heat equation and the Novikov equation. Finally, two-dimensional optimal system of the (2+1)-dimensional Navier-Stokes (NS) equation is found and used to generate intrinsically different reduced ordinary differential equations. Some interesting explicit solutions of the NS equation are provided.
Magnetic fluctuations sorted by magnetic field in MnSb clusters embedded in GaMnSb thin films
Authors: Dmitriev A. I. , Talantsev A. D. , Koplak O. V. , Morgunov R. B.
Published: February 2016

Dynamics of magnetization relaxation of the MnSb clusters under applied magnetic field has been studied in the 8–300 K temperature range. The lognormal distribution of ferromagnetic MnSb cluster sizes f(D) has been extracted from the field and temperature dependences of magnetic viscosity S(T, H) in GaMnSb thin films. An average cluster diameter D = 55 nm is in agreement with the magnetic force microscopy data. Magnetic anisotropy constant ∼3.2 × 104 erg/cm3 has been determined. The fluctuation field HF = 7 Oe and the activation volume VA = 1.7 × 10−16 cm3 have been calculated from the magnetic viscosity data. Stepped sweeping of the magnetic field expands the windows of experimentally detectable fluctuations. The change in the reversal magnetic field provides the scanning of the MnSb clusters sorting them by fluctuation time (or frequency).
Optical response of a two dimensional quantum ring in presence of Rashba spin orbit coupling
Authors: Gumber Sukirti , Gambhir Monica , Jha Pradip Kumar , Mohan Man
Published: February 2016

The influence of Rashba spin orbit interaction on the optical properties of two dimensional mesoscopic ring has been investigated in the presence of uniform perpendicular magnetic field. The Schrodinger equation for the Rashba coupled system is solved by effective mass approximation and diagonalization technique. Using the calculated energies and eigenfunctions, the laser field induced change in refractive index and optical absorption have been studied under the density matrix formalism. It has been found that Rashba spin orbit interaction removes the intersection of energy levels; however, avoided crossings are observed at finite magnetic field. At sufficient high values of Rashba coupling or laser intensity, the optical response of quantum ring is found to be dominated by third order nonlinear term. Also, Rashba interaction shifts the value of magnetic field that is needed to suppress the absorption drastically and to pass the incident light unattenuated. The results reveal that the geometry of the ring plays an important role in determining the magnitude of nonlinear absorption coefficient and change in refractive index which enable us to design the device with optimum efficiency.
Preconcentration of diluted mixed-species samples following separation and collection in a micro–nanofluidic device
Authors: Chen Yi-Ying , Chiu Ping-Hsien , Weng Chen-Hsun , Yang Ruey-Jen
Published: February 2016

A microfluidic device consisting of a nanoscale Nafion membrane and a polydimethylsiloxane microchannel is proposed for the preconcentration of diluted multi-mixed species samples then following separation and collection. When an electric field is applied across the microchip, an accumulation of the mixed-species sample occurs at the junction between the microchannel and the membrane by means of ion concentration polarization effect. A separation of the sample then takes place due to the difference in the electrophoretic mobilities of the sample components. Finally, the component of interest is guided to a collection reservoir by manipulating the external potential configuration and is trapped in place by means of a magnetically actuated valve. The preconcentration performance of the proposed device is evaluated in both straight and convergent microchannels using a fluorescein isothiocyanate labeled bovine serum albumin (FITC-BSA) sample. It is shown that a preconcentration factor of 40 times can be achieved using a straight microchannel. By contrast, the preconcentration factor increases to 50 times when using a convergent channel. The practical feasibility of the proposed device is demonstrated by performing the preconcentration, separation, and collection of a mixed FITC-BSA and Tetramethylrhodamine sample.
The hollow cathode effect in a radio-frequency driven microhollow cathode discharge in nitrogen
Authors: Zhang Lianzhu , Zhao Guoming , Wang Jing , Han Qing
Published: February 2016

A two-dimensional particle-in-cell Monte-Carlo code has been developed to study the physical mechanism of the hollow cathode effect (HCE) in an rf microhollow cathode discharge (rf-MHCD). Under the simulated conditions, the HCE in the rf-MHCD is the result of sheath-superposition, and both α ionization and γ ionization play a role. However, α ionization mode is predominant. Electrons undergo a pendular motion during the negative portion of the rf cycle. When the rf hollow electrode has a positive voltage, the majority of the electrons move toward the rf electrode, and the mean electron energy near the rf electrode is higher than that in a dc hollow cathode discharge, resulting in a large number of energetic electrons bombarding the hollow cathode wall, an important characteristic of the rf-MHCD. When the hollow cathode aperture is sufficiently small, many electrons strike the hollow electrode and are removed from the discharge space, so that the plasma density decreases. The average energy of the ions in the quasi-neutral plasma region near the axis is greater than the thermal energy in a molecular gas. Therefore, high density, high energy, and high chemical activity are characteristic advantages of rf-MHCD plasma sources.
Note: Brownian motion of colloidal particles of arbitrary shape
Authors: Cichocki Bogdan , Ekiel-Jeżewska Maria L. , Wajnryb Eligiusz
Published: February 2016

The analytical expressions for the time-dependent cross correlations of the translational and rotational Brownian displacements of a particle with arbitrary shape are derived. The reference center is arbitrary, and the reference frame is such that the rotational-rotational diffusion tensor is diagonal.
Performance and retention characteristics of nanocrystalline Si floating gate memory with an Al2O3 tunnel layer fabricated by plasma-enhanced atomic layer deposition
Authors: Ma Zhongyuan , Wang Wen , Yang Huafeng , Jiang Xiaofan , Yu Jie , Qin Hua , Xu Ling , Chen Kunji , Huang Xinfan , Li Wei , Xu Jun , Feng Duan
Published: February 2016

The down-scaling of nanocrystal Si (nc-Si) floating gate memory must overcome the challenge of leakage current induced by the conventional ultra-thin tunnel layer. We demonstrate that an improved memory performance based on the Al/SiNx/nc-Si/Al2O3/Si structure can be achieved by adopting the Al2O3 tunnel layer fabricated by plasma-enhanced atomic layer deposition. A larger memory window of 7.9 V and better retention characteristics of 4.7 V after 105 s can be obtained compared with the devices containing a conventional SiO2 tunnel layer of equivalent thickness. The capacitance-voltage characteristic reveals that the Al2O3 tunnel layer has a smaller electron barrier height, which ensures that more electrons are injected into the nc-Si dots through the Al2O3/Si interface. The analysis of the conductance-voltage and high-resolution cross-section transmission microscopy reveals that the smaller nc-Si dots dominate in the charge injection in the nc-Si floating gate MOS device with an Al2O3 tunnel layer. With an increase of the nc-Si size, both nc-Si and the interface contribute to the charge storage capacity and retention. The introduction of the Al2O3 tunnel layer in nc-Si floating gate memory provides a method to achieve an improved performance of nc-Si floating gate memory.
Study of CoFeB thickness and composition dependence in a modified CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction
Authors: Zhu M. , Chong H. , Vu Q. B. , Brooks R. , Stamper H. , Bennett S.
Published: February 2016

We studied the CoFeB thickness and composition dependence of tunneling magnetoresistance (TMR) and resistance-area product (RA) in a modified CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction (MTJ), in which the bottom CoFeB is coupled to an in-plane exchange biased magnetic layer. This stack structure allows us to measure TMR and RA of the MTJs in sheet film format without patterning them, using current-in-plane-tunneling (CIPT) technique. The thickness ranges for both top and bottom CoFeB to exhibit perpendicular magnetic anisotropy are similar to what are seen in each single magnetic film stack. However, CIPT measurement revealed that there exists an optimal thickness for both top and bottom CoFeB to achieve the highest TMR value. Magnetic hysteresis loops also suggest the thickness-dependent coupling between the top and bottom CoFeB layers. We studied MTJs with two CoFeB compositions (Co40Fe40B20 and Co20Fe60B20) and found that Co20Fe60B20 MTJs give higher TMR and also wider perpendicular thickness range when used at the top layer.
Eco-friendly exfoliation of graphite into pristine graphene with little defect by a facile physical treatment
Authors: Chen Jianping , Shi Weili , Chen Yongmei , Yang Quanling , Wang Mengkui , Liu Bin , Tang Zhen , Jiang Ming , Fang De , Xiong Chuanxi
Published: February 2016

The superior properties of graphene in applications ranging from electronic devices to composites have been extensively reported. So far, no mass production of defect-free few-layer graphene has been attained. The authors of this study have demonstrated a high-yield method to produce defect-free few-layer graphene by exfoliation of graphite in a degradable water-soluble polymer (I) with cholamine modification, and the obtained intercalated (D-I) chemical structure was confirmed by Fourier transform infrared spectroscopy. The electron donor forms π–π stacking interactions with the graphene sheets during sonication, which prevents the exfoliated graphene from restacking. The method is environment-friendly compared with other liquid exfoliation methods, and the aqueous and ethanolic solutions of graphene are stable for long durations. The authors also confirmed the presence of gossamer graphene sheets, which have typical wrinkled and folded structures, by using high resolution transmission electron microscopy. Atomic force microscopy images revealed that graphene sheets with a thickness of approximately 1 nm were uniformly distributed.
Tuning conductivity and magnetism in isopolar oxide superlattices via compressive and tensile strain: A case study of SrVO3/SrMnO3 and SrCrO3/SrMnO3 heterostructure
Authors: Tseng Allen , Pham Anh , Smith Sean C. , Li Sean
Published: February 2016

We demonstrate the role of compressive and tensile strain to effectively control the conductivity and magnetism in isopolar materials utilizing density functional theory. Using the examples of superlattices containing transition metals with electronegativity differences such as SrVO3/SrMnO3 and SrCrO3/SrMnO3, our results show that the lattice strain can alter the apical oxygen shift at the interface of the transition metal layers, thus affecting the internal charge transfer process between d electrons. In addition, lattice compression and tensile strain can also modify the orbital occupancies of the manganite layers. As a result, various exotic effects can be realized in the SrMnO3 layer such as Mott insulator, quasi-two-dimensional conductivity, and long-range magnetism.
Structure and dielectric properties of Na0.5Bi0.5TiO3-CaTiO3 solid solutions
Authors: Birks E. , Dunce M. , Ignatans R. , Kuzmin A. , Plaude A. , Antonova M. , Kundzins K. , Sternberg A.
Published: February 2016

Despite wide studies of Na0.5Bi0.5TiO3, structure of this material and its connection with the observed physical properties still raise numerous questions due to mutually contradicting results obtained. Here, structure and dielectric properties of poled and unpoled Na0.5Bi0.5TiO3-CaTiO3 solid solutions are studied, projecting the obtained concentration dependence of structure and dielectric properties on pure Na0.5Bi0.5TiO3 as the end member of this material group. X-ray diffraction patterns for Na0.5Bi0.5TiO3-CaTiO3 solid solutions reveal dominating of an orthorhombic Pnma phase, even for the compositions approaching the end composition (Na0.5Bi0.5TiO3), whereas structure of pure Na0.5Bi0.5TiO3 can be considered, assuming coexistence of rhombohedral and orthorhombic phases. This allows one to avoid appearance of a large difference of rhombohedral distortions between the unpoled and poled Na0.5Bi0.5TiO3, if the rhombohedral distortion is calculated as for single R3c phase. Features of dielectric permittivity, corresponding to the observed structural phase transition, are identified. It is discussed that the rhombohedral R3c phase is responsible for appearance of the frequency-dependent shoulder of dielectric permittivity temperature dependence, characteristic for unpoled Na0.5Bi0.5TiO3.
Theoretical efficiency limit for a two-terminal multi-junction “step-cell” using detailed balance method
Authors: Abdul Hadi Sabina , Fitzgerald Eugene A. , Nayfeh Ammar
Published: February 2016

Here we present detailed balance efficiency limit for a novel two-terminal dual and triple junction “step-cell” under AM 1.5G and AM 0 incident spectrums. The step-cell is a multi-junction (MJ) solar cell in which part of the top cell is removed, exposing some of the bottom cell area to unfiltered incident light, thus increasing bottom cell's photogenerated current. Optical generation of the bottom cell is modeled in two parts: step part, limited by the bottom cell bandgap, and conventional part, additionally limited by the top cell absorption. Our results show that conventionally designed MJ cell with optimized bandgap combination of 1.64 eV/0.96 eV for dual junction and 1.91 eV/1.37 eV/0.93 eV for triple junction has the highest theoretical efficiency limit. However, the step-cell design provides significant efficiency improvement for cells with non-optimum bandgap values. For example, for 1.41 eV ( ∼GaAs)/Si dual junction under AM 1.5G, efficiency limit increases from ∼21% in a conventional design to 38.7% for optimized step-cell. Similar benefits are observed for three-junction step-cell and for AM 0 spectrum studied here. Step-cell relaxes bandgap requirements for efficient MJ solar cells, providing an opportunity for a wider selection of materials and cost reduction.
Nonideal detonation regimes in low density explosives
Authors: Ershov A. P. , Kashkarov A. O. , Pruuel E. R. , Satonkina N. P. , Sil'vestrov V. V. , Yunoshev A. S. , Plastinin A. V.
Published: February 2016

Measurements using Velocity Interferometer System for Any Reflector (VISAR) were performed for three high explosives at densities slightly above the natural loose-packed densities. The velocity histories at the explosive/window interface demonstrate that the grain size of the explosives plays an important role. Fine-grained materials produced rather smooth records with reduced von Neumann spike amplitudes. For commercial coarse-grained specimens, the chemical spike (if detectable) was more pronounced. This difference can be explained as a manifestation of partial burn up. In fine-grained explosives, which are more sensitive, the reaction can proceed partly within the compression front, which leads to a lower initial shock amplitude. The reaction zone was shorter in fine-grained materials because of higher density of hot spots. The noise level was generally higher for the coarse-grained explosives, which is a natural stochastic effect of the highly non-uniform flow of the heterogeneous medium. These results correlate with our previous data of electrical conductivity diagnostics. Instead of the classical Zel'dovich–von Neumann–Döring profiles, violent oscillations around the Chapman–Jouguet level were observed in about half of the shots using coarse-grained materials. We suggest that these unusual records may point to a different detonation wave propagation mechanism.
Backward diodes using heavily Mg-doped GaN growth by ammonia molecular-beam epitaxy
Authors: Okumura Hironori , Martin Denis , Malinverni Marco , Grandjean Nicolas
Published: February 2016

We grew heavily Mg-doped GaN using ammonia molecular-beam epitaxy. The use of low growth temperature (740 °C) allows decreasing the incorporation of donor-like defects (<3 × 1017 cm−3) responsible for p-type doping compensation. As a result, a net acceptor concentration of 7 × 1019 cm−3 was achieved, and the hole concentration measured by Hall effect was as high as 2 × 1019 cm−3 at room temperature. Using such a high Mg doping level, we fabricated GaN backward diodes without polarization-assisted tunneling. The backward diodes exhibited a tunneling-current density of 225 A/cm2 at a reverse bias of −1 V at room temperature.
Ge-on-Si PIN-photodetectors with Al nanoantennas: The effect of nanoantenna size on light scattering into waveguide modes
Authors: Fischer Inga A. , Augel Lion , Kropp Timo , Jitpakdeebodin Songchai , Franz Nuno , Oliveira Filipe , Rolseth Erlend , Maß Tobias , Taubner Thomas , Schulze Jörg
Published: February 2016

Metallic nanoantennas can be used to enhance the efficiency of optical device operation by re-distributing electromagnetic energy. Here, we investigate the effect of a random distribution of disc-shaped Al nanoantennas of different diameters deposited on Ge-on-Si PIN-photodetectors on the wavelength-dependent responsivity. We compare our experimental results to simulations and find that the largest responsivity enhancement is obtained for wavelengths that correspond to energies at or below the bandgap energy of Ge. We argue that this is the result of antenna-mediated scattering of light into waveguide modes within the Ge-on-Si PIN-photodetectors, which is effectively influenced by nanoantenna size, and we discuss a possible application of the concept for integrated biosensing.
Improved hole mobility and suppressed trap density in polymer-polymer dual donor based highly efficient organic solar cells
Authors: Bharti Vishal , Sharma Abhishek , Gupta Vinay , Sharma Gauri D. , Chand Suresh
Published: February 2016

Here we report, the charge transport properties of polymer-polymer dual donor blended film, viz., polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) and poly [N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole) (PCDTBT) in the optimized concentration. Trap density and hole mobility in polymer-polymer (PTB7-PCDTBT) dual donor system have been studied by means of current density–voltage (J-V) characteristics at various temperatures, i.e., 280 K–120 K in hole only device configuration, i.e., indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) (PEDOT:PSS)/Polymer film/gold (Au). The J-V curves exhibit the space charge limited conduction behavior. The corresponding hole mobility for PTB7 and PCDTBT are 3.9 × 10−4 cm2 V−1 s−1 and 2.1 × 10−4 cm2 V−1 s−1, respectively, whereas it is 9.1 × 10−4 cm2 V−1 s−1 in the polymer-polymer blend of PTB7:PCDTBT (0.7:0.3). This enhancement in mobility can be attributed to the suppressed trap density in PTB7:PCDTBT (0.7:0.3) of 7.4 × 1016 cm−3, as compared to the trap density of 1.1 × 1017 cm−3 for PTB7 and 1.6 × 1017 cm−3 for PCDTBT. Atomic force microscopy shows an improvement in the morphology of the blend. The J–V characteristic at various light intensities in the bulk heterojunction (BHJ) solar cell reveals that the blending of PCDTBT in PTB7 suppressed the trap-assisted recombination. The corresponding power conversion efficiencies for PTB7:PC71BM, PCDTBT:PC71BM and PTB7:PCDTBT:PC71BM BHJ solar cells are 6.9%, 6.1% and 9.0%, respectively. This work unravels that the enhanced mobility and suppressed trap density play a significant role in the improvement of efficiency in dual donor based organic solar cells.