bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray studies of the black widow pulsar PSR B1957+20
Authors: Huang R. H. H. , Kong A. K. H. , Takata J. , Hui C. Y. , Lin L. C. C. , Cheng K. S.
Published: March 2013

We report on Chandra observations of the black widow pulsar, PSR B1957+20. Evidence for a binary-phase dependence of the X-ray emission from the pulsar is found with a deep observation. The binary-phase resolved spectral analysis reveals non-thermal X-ray emission of PSR B1957+20, confirming the results of previous studies. This suggests that the X-rays are mostly due to intra-binary shock emission which is strongest when the pulsar wind interacts with the ablated material from the companion star. The geometry of the peak emission is determined in our study. The marginal softening of the spectrum of the non-thermal X-ray tail may indicate that particles injected at the termination shock is dominated by synchrotron cooling.
Recoil velocity of pulsar/magnetar induced by magnetic dipole and quadrupole radiation
Authors: Kojima Yasufumi
Published: March 2013

Recoil velocity is examined as a back reaction to the magnetic dipole and quadrupole radiations from a pulsar/magnetar born with rapid rotation. The model is extended from notable Harrison-Tademaru one by including arbitrary field-strength of the magnetic quadrupole moment. The process is slow one operating on a spindown timescale. Resultant velocity depends on not the magnitude, but rather the ratio of the two moments and their geometrical configuration. The model does not necessarily lead to high spatial velocity for a magnetar with a strong magnetic field. This fact is consistent with the recent observational upper bound. The maximum velocity predicted with this model is slightly smaller than that of observed fast-moving pulsars.
Modelling X-ray Pulse Profiles of Millisecond Pulsars
Authors: Leahy D. A. , Morsink S. , Tian W.
Published: March 2013

The modelling of X-ray pulse profiles from accreting millisecond pulsars is a way to infer masses and radii of neutron stars. We briefly describe how a pulse shape encodes information on the mass and radius, but also depends on other parameters such as hot spot location and observer viewing angle. A numerical model that we have developed is then described. The model includes light bending, time-delay effects, and Doppler effects for photons. The model accounts for oblateness of the neutron star, caused by the rapid rotation, and for scattered light from the surface of the accretion disk. The millisecond pulsar SAX J1808-3658 has multiple observations taken during different outbursts. The observed pulse shapes vary greatly, and it is a challenging test to fit the different observations. Some of the latest results are given.
Revisiting quark stars under the influence of strong magnetic fields
Authors: Menezes Debora
Published: March 2013

Quark matter at finite temperature and subject to strong magnetic fields is possibly present in the early stages of heavy ion collisions and in the interior of protoneutron stars. We use the mean field approximation to investigate this type of quark matter described by the Nambu–Jona-Lasinio model. The energy per baryon of magnetized quark matter becomes more bound than nuclear matter made of iron nuclei, for magnetic fields around 1019 G. When the su(3) NJL model is applied to stellar matter, the maximum mass configurations are always above 1.45 solar masses and may be as high as 1.9 solar masses for a central magnetic field of 1018 G. These numbers are within the masses of observed neutron stars but exclude the recently measured star with 1.97 solar mass.

The effect of the magnetic field on the effective quark masses and chemical potentials is only felt for quite strong magnetic fields, above 5 × 1018 G, with larger effects for the lower densities. Spin polarizations are more sensitive to weaker magnetic fields and are larger for lower temperatures and lower densities.
The slow X-ray pulsar SXP 1062 and associated supernova remnant in the Wing of the Small Magellanic Cloud
Authors: Oskinova L. M. , Guerrero M. A. , Hénault-Brunet V. , Sun W. , Chu Y.-H. , Evans C. , Gallagher J. S. , Gruendl R. A. , Reyes-Iturbide J.
Published: March 2013

SXP 1062 is an exceptional case of a young neutron star in a wind-fed high-mass X-ray binary associated with a supernova remnant. A unique combination of measured spin period, its derivative, luminosity and young age makes this source a key probe for the physics of accretion and neutron star evolution. Theoretical models proposed to explain the properties of SXP 1062 shall be tested with new data.
AXPs & SGRs: Magnetar or Quarctar?
Authors: Qiao Guojun , Liu Xionwei , Xu Renxin , Du Yuanjie , Han Jinlin , Tong Hao , Wang Hongguang
Published: March 2013

The concept of a “magnetar” was proposed mainly because of two factors. First, the X-ray luminosity of Anomalous X-ray Pulsars (AXPs) and Soft Gamma-Ray Repeaters (SGRs) is larger than the rotational energy loss rate (Lx > Ėrot), and second, the magnetic field strength calculated from “normal method” is super strong. It is proposed that the radiation energy of magnetar comes from its magnetic fields. Here it is argued that the magnetic field strength calculated through the normal method is incorrect at the situation Lx > Ėrot, because the wind braking is not taken into account. Besides, the “anti-magnetar” and some other X-ray and radio observations are difficult to understand with a magnetar model.

Instead of the magnetar, we propose a “quarctar”, which is a crusted quark star in an accretion disk, to explain the observations. In this model, the persistent X-ray emission, burst luminosity, spectrum of AXPs and SGRs can be understood naturally. The radio-emitting AXPs, which are challenging the magnetar, can also be explained by the quarctar model.
Evidence for nonlinear and chaotic behaviour in pulsar spin-down rates
Authors: Seymour Andrew , Lorimer Duncan
Published: March 2013

We present evidence for chaotic dynamics in pulsar spin-down rates originally measured by Lyne et al. (2010). Using techniques that allow us to re-sample the original measurements without losing structural information, we have searched for evidence for a strange attractor in the time series of frequency derivative for each pulsar. Our measurements of correlation dimension and Lyapunov exponent show, particularly in the case of PSR B1828-11, that the underlying behavior appears to be driven by a strange attractor with approximately three governing nonlinear equations.
Electric current diagnostics in the magnetosphere of neutron stars
Authors: Stepanov Alexander V. , Zaitsev Valery V.
Published: March 2013

Active neutron stars – SGRs, reveal the high-quality QPOs at the ‘pulsating tail’ phase. We suggest diagnostics of the trapped fireball plasma, the source of high-frequency pulsations, using coronal seismology. The trapped fireball is represented as a set of current-carrying loops - equivalent of electric circuits. Our approach gives the following magnetosphere parameters in SGRs: an electric current of (2−8) × 1019 A, magnetic field of (0.6−2.7) × 1013 G, and electrons density of (1.3−6.0) × 1016 cm−3. We show high-frequency QPOs can be self-excited for a smaller electric current than the maximum current and/or due to the parametric resonance.
Discovery of an intermittent pulsar: PSR J1839+15
Authors: Surnis M. P. , Joshi B. C. , McLaughlin M. A. , Gajjar V.
Published: March 2013

We report the discovery of a new pulsar PSR J1839+15, having a period of 549 ms and a DM of 68 pc cm−3. We also present its timing solution and report the intermittent behaviour of its radio emission.
Is magnetar a fact or fiction to us?
Authors: Tong H. , Xu R. X.
Published: March 2013

The key point of studying AXPs/SGRs (anomalous X-ray pulsars/soft gamma-ray repeaters) is relevant to the energy budget. Historically, rotation was thought to be the only free energy of pulsar until the discovery of accretion power in X-ray binaries. AXPs/SGRs could be magnetars if they are magnetism-powered, but would alternatively be quark-star/fallback-disk systems if more and more observations would hardly be understood in the magnetar scenario.
What can Fermi tell us about magnetars?
Authors: Tong H. , Xu R. X.
Published: March 2013

We have analyzed the physical implications of Fermi observations of magnetars. Observationally, no significant detection is reported in Fermi observations of all magnetars. Then there are conflicts between outer gap model in the case of magnetars and Fermi observations. One possible explanation is that magnetars are wind braking instead of magnetic dipole braking. In the wind braking scenario, magnetars are neutron stars with strong multipole field. A strong dipole field is no longer required. A magnetism-powered pulsar wind nebula and a braking index smaller than three are the two predictions of wind braking of magnetars. Future deeper Fermi observations will help us make clear whether they are wind braking or magnetic dipole braking. It will also help us to distinguish between the magnetar model and the accretion model for AXPs and SGRs.
Search for the gravitational wave memory effect with the Parkes Pulsar Timing Array
Authors: Wang Jingbo , Hobbs G. , Wang Na
Published: March 2013

Gravitational wave bursts produced by supermassive binary black hole mergers will leave a persistent imprint on the space-time metric. Such gravitational wave memory signals are detectable by pulsar timing arrays as a glitch event that would seem to occur simultaneously for all pulsars. In this paper, we describe an initial algorithm which can be used to search for gravitational wave memory signals. We apply this algorithm to the Parkes Pulsar Timing Array data set. No significant gravitational wave memory signal is founded in the data set.
Curvature radiation in rotating pulsar magnetosphere
Authors: Wang P. F. , Wang C. , Han J. L.
Published: March 2013

We investigate the curvature radiation from relativistic particles streaming along magnetic field lines and co-rotating with a pulsar. The co-rotation affects the trajectories of the particles and hence the emission properties, especially the polarization. For three density models in the form of core, cone and patches, we calculate the polarized emission at a given height and also the integrated emission for the whole open field line region, and try to explain the generation of circular polarization.
Constraints on the standard model extension with binary pulsars
Authors: Xie Yi
Published: March 2013

Under the standard model extension (SME) framework, Lorentz invariance is tested in five binary pulsars: PSR J0737-3039, PSR B1534+12, PSR J1756-2251, PSR B1913+16 and PSR B2127+11C. By analyzing the advance of periastron, we obtain the constraints on a dimensionless combination of SME parameters that is sensitive to timing observations. The results imply no evidence for the break of Lorentz invariance at 10−10 level, one order of magnitude larger than previous estimation.
FAST low frequency pulsar survey
Authors: Yue Youling , Li Di , Nan Rendong
Published: March 2013

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is under construction and will be commissioned in September 2016. A low frequency 7-beam receiver working around 400 MHz is proposed for FAST early science. It will be optimized for a whole FAST sky drift-scan pulsar survey. Simulations show that about 1500 new normal pulsars will be discovered, as while as about 200 millisecond pulsars.
The effects of biochar on the physical properties of bare soil
Authors: Ventura Francesca , Salvatorelli Fiorenzo , Piana Stefano , Pieri Linda , Pisa Paola Rossi
Published: March 2013

The pyrolysis conversion of vegetable residues into energy and biochar, and its incorporation in agricultural soil, reduces CO2emission and provides a longterm soil carbon sequestration. Moreover, biochar application in soil seems to increase nutrient stocks in the rooting layer, improving crop yield. Compared with the numerous studies assessing the positive effect of biochar on yield, however, little research has been published elucidating the mechanisms responsible for the reported benefits. Few studies cited soil moisture as the key factor, attributing the increased yield to the higher soil water availability.

The aim of this study was to investigate the effect of biochar on the physical and hydraulic properties of a bare Padana Plain (Cadriano, Bologna) agricultural soil. A preliminary plot experiment in 2009 explored the influence of 10 and 30 kg ha–1of biochar on soil moisture, without effects from plants. Results of the first experiment suggested using higher biochar rates in a similar experimental scheme. During the second experiment, 30 and 60 t ha–1doses were investigated. Soil water content, bulk density, electrical conductivity and soil water retention were measured. The comparison between treated soils and the control indicates that the biochar rate is directly correlated to electrical conductibility and inversely correlated with bulk density. The effect on the density of soil can be very positive in case of heavy soils. The dark colour of the char increased the surface temperature with respect to the control, while no differences were detected at 7·5 cm depth. No influences were found on other soil characteristics, including soil pH, moisture and water retention.
Gene Expression Profiling of Blood in Ruptured Intracranial Aneurysms: in Search of Biomarkers
Authors: Pera Joanna , Korostynski Michal , Golda Slawomir , Piechota Marcin , Dzbek Jaroslaw , Krzyszkowski Tadeusz , Dziedzic Tomasz , Moskala Marek , Przewlocki Ryszard , Szczudlik Andrzej , Slowik Agnieszka
Published: March 2013

The molecular mechanisms underlying the systemic response to subarachnoid hemorrhage (SAH) from ruptured intracranial aneurysms (RAs) are not fully understood. We investigated whether the analysis of gene expression in peripheral blood could provide clinically relevant information regarding the biologic consequences of SAH. Transcriptomics were performed using Illumina HumanHT-12v4 microarrays for 43 RA patients and 18 controls (C). Differentially expressed transcripts were analyzed for overrepresented functional groups and blood cell type-specific gene expression. The set of differentially expressed transcripts was validated using quantitative polymerase chain reaction in an independent group of subjects (15 RA patients and 14 C). There were 135 differentially expressed genes (false discovery rate ≤1%, absolute fold change ≤1.7): the abundant levels of 78 mRNAs increased and 57 mRNAs decreased. Among RA patients, transcripts specific to T lymphocyte subpopulations were downregulated, whereas those related to monocytes and neutrophils were upregulated. Expression profiles of a set of 16 genes and lymphocyte-to-monocyte-and-neutrophil gene expression ratios distinguished RA patients from C. These results indicate that SAH from RAs strongly influences the transcription profiles of blood cells. A specific pattern of these changes suggests suppression in lymphocyte response and enhancements in monocyte and neutrophil activities. This is probably related to the immunodepression observed in SAH.
Laser Speckle Imaging Allows Real-Time Intraoperative Blood Flow Assessment During Neurosurgical Procedures
Authors: Hecht Nils , Woitzik Johannes , König Susanne , Horn Peter , Vajkoczy Peter
Published: March 2013

Currently, there is no adequate technique for intraoperative monitoring of cerebral blood flow (CBF). To evaluate laser speckle imaging (LSI) for assessment of relative CBF, LSI was performed in 30 patients who underwent direct surgical revascularization for treatment of arteriosclerotic cerebrovascular disease (ACVD), Moyamoya disease (MMD), or giant aneurysms, and in 8 control patients who underwent intracranial surgery for reasons other than hemodynamic compromise. The applicability and sensitivity of LSI was investigated through baseline perfusion and CO2 reactivity testing. The dynamics of LSI were assessed during bypass test occlusion and flow initiation procedures. Laser speckle imaging permitted robust (pseudo-) quantitative assessment of relative microcirculatory flow and standard bypass grafting resulted in significantly higher postoperative baseline perfusion values in ACVD and MMD. The applicability and sensitivity of LSI was shown by a significantly reduced CO2 reactivity in ACVD (9.6 ± 9%) and MMD (8.5 ± 8%) compared with control (31.2 ± 5%; P < 0.0001). In high- and intermediate-flow bypass patients, LSI was characterized by a dynamic real-time response to acute perfusion changes and ultimately confirmed a sufficient flow substitution through the bypass graft. Thus, LSI can be used for sensitive and continuous, non-invasive real-time visualization and measurement of relative cortical CBF in excellent spatial-temporal resolution.
Voxelwise Quantification of [11C](R)-Rolipram PET Data: A Comparison Between Model-Based and Data-Driven Methods
Authors: Rizzo Gaia , Veronese Mattia , Zanotti-Fregonara Paolo , Bertoldo Alessandra
Published: March 2013

This study compared model-based and data-driven methods to assess the best methodology for generating precise and accurate parametric maps of the parameters of interest in [ 11 C]( R)-rolipram brain positron-emission tomography studies. Parametric images were generated using (1) a two-tissue compartmental model (2TCM) solved with the hierarchical basis function method (H-BFM) linear estimator;(2) data-driven spectral-based methods: standard spectral analysis (std SA) and rank-shaping SA (RS);and (3) the Logan graphical plot. Nonphysiologic VT estimates were eliminated and the remaining ones were compared with the reference values, i.e., those obtained with a voxelwise 2TCM solved with a nonlinear estimator. With regard to voxelwise VT estimates, H-BFM showed the best agreement with weighted nonlinear least square (WNLLS) values and the lowest percentage of mean relative difference (1 ± 1%). All methods showed comparable variability in the relative differences. H-BFM provided the best correlation with WNLLS (y = 1.034x − 0.013; R 2 = 0.973). Despite a slight bias, the other three methods also showed good agreement and high correlation ( R 2 > 0.96). H-BFM yielded the most reliable voxelwise quantification of [ 11 C]( R)-rolipram as well as the complete description of the tracer kinetic. The Logan plot represents a valid alternative if only VT estimation is required. Its marginally higher bias was outweighed by a low computational time, ease of implementation, and robustness.
Interfaces of propylene carbonate
Authors: You Xinli , Chaudhari Mangesh I. , Pratt Lawrence R. , Pesika Noshir , Aritakula Kalika M. , Rick Steven W.
Published: March 2013

Propylene carbonate (PC) wets graphite with a contact angle of 31° at ambient conditions. Molecular dynamics simulations agree with this contact angle after 40% reduction of the strength of graphite-C atom Lennard-Jones interactions with the solvent, relative to the models used initially. A simulated nano-scale PC droplet on graphite displays a pronounced layering tendency and an Aztex pyramid structure for the droplet. Extrapolation of the computed tensions of PC liquid-vapor interface estimates the critical temperature of PC accurately to about 3%. PC molecules lie flat on the PC liquid-vapor surface and tend to project the propyl carbon toward the vapor phase. For close PC neighbors in liquid PC, an important packing motif stacks carbonate planes with the outer oxygen of one molecule snuggled into the positively charged propyl end of another molecule so that neighboring molecule dipole moments are approximately antiparallel. The calculated thermal expansion coefficient and the dielectric constants for liquid PC agree well with experiment. The distribution of PC molecule binding energies is closely Gaussian. Evaluation of the density of the coexisting vapor then permits estimation of the packing contribution to the PC chemical potential and that contribution is about two thirds of the magnitude of the contributions due to attractive interactions, with opposite sign.
Frequency-stepped acquisition in nuclear magnetic resonance spectroscopy under magic angle spinning
Authors: Pell Andrew J. , Clément Raphaële J. , Grey Clare P. , Emsley Lyndon , Pintacuda Guido
Published: March 2013

The nuclear magnetic resonance of paramagnetic solids is usually characterized by the presence of large chemical shifts and shift anisotropies due to hyperfine interactions. Frequently the resulting spectra cover a frequency range of several megahertz, which is greater than the bandwidth of commercially available radio-frequency (RF) probes, making it impossible to acquire the whole spectrum in a single experiment. In these cases it common to record a series of spectra, in which the probe is tuned to a different frequency for each, and then sum the results to give the “true” spectrum. While this method is very widely used on static samples, the application of frequency stepping under magic-angle spinning (MAS) is less common, owing to the increased complexity of the spin dynamics when describing the interplay of the RF irradiation with the mechanical rotation of the shift tensor. In this paper, we present a theoretical description, based on the jolting frame formalism of Caravatti et al. [J. Magn. Reson. 55, 88 (1983)10.1016/0022-2364(83)90279-2], for describing the spin dynamics of a powder sample under MAS when subjected to a selective pulse of low RF-field amplitude. The formalism is used to describe the frequency stepping method under MAS, and under what circumstances the true spectrum is reproduced. We also present an experimental validation of the methodology under ultra-fast MAS with the paramagnetic materials LiMnPO4 and TbCsDPA.
Tuning the Curie temperature in γ-FeNi nanoparticles for magnetocaloric applications by controlling the oxidation kinetics
Authors: Ucar Huseyin , Ipus John J. , Laughlin D. E. , McHenry M. E.
Published: March 2013

Mechanically alloyed Fe70Ni30 and Fe72Ni28 alloys were characterized in terms of their structural and magnetic properties. Previous studies showed that single phase FCC γ-FeNi alloys with ∼26-30 at. % Ni have Curie temperatures, Tc, near room temperature. Having Tc near room temperatures along with large magnetization makes γ-FeNi alloys attractive for room temperature magnetocaloric cooling technologies. To obtain a single γ-phase, particles were solution annealed in the γ-phase field and water quenched. The preferential oxidation of Fe during ball milling was used as a means to tune the Curie temperature, Tc, of the alloy. Refrigeration capacities, RCFWHM, of the Fe70Ni30 and the Fe72Ni28 alloys were calculated to be ≈470 J/kg and 250 J/kg at 5 T, with peak temperatures ≈363 K and ≈333 K, respectively. The RCFWHM for the Fe70Ni30 is higher than the previously reported Nanoperm (Fe70Ni30)89Zr7B4 type alloy and on the same order of magnitude with other Fe-based alloys. The maximum magnetic entropy change values observed for the Fe70Ni30 and the Fe72Ni28 are 0.65 and 0.5 J kg−1 K−1, respectively, at a field of 5 T. These are smaller than those of rare earth magnetic refrigerants showing first order transformation behavior. The larger RCFWHM value results mainly from the width of the magnetic entropy curve in these types of materials. We discuss the economic advantage of these rare earth free refrigerants.
The conformal metric structure of Geometrothermodynamics
Authors: Bravetti Alessandro , Lopez-Monsalvo Cesar S. , Nettel Francisco , Quevedo Hernando
Published: March 2013

We present a thorough analysis on the invariance of the most widely used metrics in the Geometrothermodynamics programme. We centre our attention in the invariance of the curvature of the space of equilibrium states under a change of fundamental representation. Assuming that the systems under consideration can be described by a fundamental relation which is a homogeneous function of a definite order, we demonstrate that such invariance is only compatible with total Legendre transformations in the present form of the programme. We give the explicit form of a metric which is invariant under total Legendre transformations and whose induced metric produces a curvature which is independent of the fundamental representation. Finally, we study a generic system with two degrees of freedom and whose fundamental relation is homogeneous of order one.
Steady-state and transient electron transport within wurtzite and zinc-blende indium nitride
Authors: Hadi Walid A. , Guram Prabhjot K. , Shur Michael S. , O'Leary Stephen K.
Published: March 2013

We study the steady-state and transient electron transport that occurs within wurtzite and zinc-blende indium nitride using a three-valley Monte Carlo simulation approach. For our steady-state results, we find that, for both cases, initially the electron drift velocity monotonically increases with the applied electric field strength, reaching a peak value followed by a region of negative differential mobility, and then a region of saturation. The peak fields are found to be around 30 kV/cm for the case of wurtzite indium nitride and about 50 kV/cm for the case of zinc-blende indium nitride, the corresponding peak and saturation electron drift velocities being around 5.6×107 and 1.2×107 cm/s for the case of wurtzite indium nitride and about 3.3×107 and 1.0×107 cm/s for the case of zinc-blende indium nitride. For the purposes of our transient electron transport analysis, we follow the approach of O'Leary et al. [Appl. Phys. Lett. 87, 222103 (2005)], and examine how an ensemble of electrons responds to the sudden application of a constant electric field. We find that the electrons within wurtzite indium nitride exhibit higher electron drift velocities and longer relaxation times than those within zinc-blende indium nitride. The device implications of these results are then discussed.
Tunneling, decoherence, and entanglement of two spins interacting with a dissipative bath
Authors: Sahrapour Mohammad M. , Makri Nancy
Published: March 2013

We use numerically exact iterative path integral methods to investigate the decoherence and entanglement dynamics of a tunneling pair of two coupled qubits (spins) system interacting with a dissipative bath. We find that decoherence is generally accompanied by the destruction of entanglement, although the specifics of this destruction depend sensitively on the parameters of the Hamiltonian (qubit-qubit coupling and/or energy bias), the strength of dissipation, the temperature, and the choice of initial condition. We also observe that dissipation can in some cases generate a substantial amount of entanglement. Finally, if an entangled eigenstate exists which does not couple to the environment, the long-time entanglement can significantly exceed the value corresponding to the Boltzmann equilibrium state.
Reconstructing equilibrium entropy and enthalpy profiles from non-equilibrium pulling
Authors: Jeong Daun , Andricioaei Ioan
Published: March 2013

The Jarzynski identity can be applied to instances when a microscopic system is pulled repeatedly but quickly along some coordinate, allowing the calculation of an equilibrium free energy profile along the pulling coordinate from a set of independent non-equilibrium trajectories. Using the formalism of Wiener stochastic path integrals in which we assign temperature-dependent weights to Langevin trajectories, we derive exact formulae for the temperature derivatives of the free energy profile. This leads naturally to analytical expressions for decomposing a free energy profile into equilibrium entropy and internal energy profiles from non-equilibrium pulling. This decomposition can be done from trajectories evolved at a unique temperature without repeating the measurement as done in finite-difference decompositions. Three distinct analytical expressions for the entropy-energy decomposition are derived: using a time-dependent generalization of the weighted histogram analysis method, a quasi-harmonic spring limit, and a Feynman-Kac formula. The three novel formulae of reconstructing the pair of entropy-energy profiles are exemplified by Langevin simulations of a two-dimensional model system prototypical for force-induced biomolecular conformational changes. Connections to single-molecule experimental means to probe the functionals needed in the decomposition are suggested.
Representations of some quantum tori Lie subalgebras
Authors: Jiang Jingjing , Wang Song
Published: March 2013

In this paper, we define the q-analog Virasoro-like Lie subalgebras in x∞ = a∞(b∞, c∞, d∞). The embedding formulas into x∞ are introduced. Irreducible highest weight representations of \documentclass[12pt]{minimal}\begin{document}$\tilde{\mathcal {A}}_{q}$\end{document}Ãq, \documentclass[12pt]{minimal}\begin{document}$\tilde{\mathcal {B}}_{q}$\end{document}B̃q, and \documentclass[12pt]{minimal}\begin{document}$\tilde{\mathcal {C}}_{q}$\end{document}C̃q-series of the q-analog Virasoro-like Lie algebras in terms of vertex operators are constructed. We also construct the polynomial representations of the \documentclass[12pt]{minimal}\begin{document}$\tilde{\mathcal {A}}_{q}$\end{document}Ãq, \documentclass[12pt]{minimal}\begin{document}$\tilde{\mathcal {B}}_{q}$\end{document}B̃q, \documentclass[12pt]{minimal}\begin{document}$\tilde{\mathcal {C}}_{q}$\end{document}C̃q, and \documentclass[12pt]{minimal}\begin{document}$\tilde{\mathcal {D}}_{q}$\end{document}D̃q-series of the q-analog Virasoro-like Lie algebras.
Quantum graph as a quantum spectral filter
Authors: Turek Ondřej , Cheon Taksu
Published: March 2013

We study the transmission of a quantum particle along a straight input–output line to which a graph Γ is attached at a point. In the point of contact we impose a singularity represented by a certain properly chosen scale-invariant coupling with a coupling parameter α. We show that the probability of transmission along the line as a function of the particle energy tends to the indicator function of the energy spectrum of Γ as α → ∞. This effect can be used for a spectral analysis of the given graph Γ. Its applications include a control of a transmission along the line and spectral filtering. The result is illustrated with an example where Γ is a loop exposed to a magnetic field. Two more quantum devices are designed using other special scale-invariant vertex couplings. They can serve as a band-stop filter and as a spectral separator, respectively.
Strategies for reducing dye aggregation in luminescent host-guest systems: Rhodamine 6G incorporated in new mesoporous sol-gel hosts
Authors: de Queiroz Thiago B. , Botelho Moema B. S. , De Boni Leonardo , Eckert Hellmut , de Camargo Andrea S. S.
Published: March 2013

Aiming at the design of new luminescent host-guest materials with minimized aggregation effects, two classes of sol-gel derived mesoporous materials were explored as hosts for Rhodamine 6G (Rh6G) dye: The first consists of pure (SiO2) and phenyl-modified silica (Ph0.17SiO1.915) xerogels, prepared via sol-gel reaction using an ionic liquid as catalytic agent. The second consists of mesoporous sodium aluminosilicate glasses with Si to Al ratio in the range of 6 ≤ Si/Al ≤ 9. Characterization through high resolution solid state NMR proved the successful obtention of the designed host matrices. Following Rh6G-loading in various concentrations, the resulting materials were characterized by their luminescence and excitation spectra, excited state lifetimes, and quantum yields. The dye doped silica xerogels presented high quantum yield values (up to 87%), with no substantial decrease in efficiency with increasing dye concentration. At suitable Rh6G contents, all the final materials presented laser action under 532 nm excitation from a Q-switched frequency doubled Nd:YAG laser. The phenyl silicate sample presents the highest laser photostability with a half-life of 6560 pulses, under 2 mJ/pulse pump power, and 10 Hz repetition rate. The laser experiments provided further insights on the photodegradation mechanisms of such organic species.
Effect of ZnO nanoparticles on nasopharyngeal cancer cells viability and respiration
Authors: Prasanth R. , Gopinath D.
Published: March 2013

Development of a therapeutic drugs based on nanoparticles requires a better understanding of the mechanism of selective cyto-toxic effects of nanopaticles over cancer cells. Scanning electrochemical microscopy provides opportunity to measure the real time chemical process at cell proximity in the presence of nanoparticle. Herein, the respiration process in nasopharyngeal cancer cells is investigated with the help of scanning electrochemical microscopy. The cell viability has been tested with MTT assay. The results show that ZnO nanoparticles have time and dose dependent effect in nasopharyngeal cancer cells and the cell respiration rate decreases with time.
Molecular and electronic structure of electroactive self-assembled monolayers
Authors: Méndez De Leo Lucila P. , de la Llave Ezequiel , Scherlis Damián , Williams Federico J.
Published: March 2013

Self-assembled monolayers (SAMs) containing electroactive functional groups are excellent model systems for the formation of electronic devices by self-assembly. In particular ferrocene-terminated alkanethiol SAMs have been extensively studied in the past. However, there are still open questions related with their electronic structure including the influence of the ferrocene group in the SAM-induced work function changes of the underlying metal. We have thus carried out a thorough experimental and theoretical investigation in order to determine the molecular and electronic structure of ferrocene-terminated alkanethiol SAMs on Au surfaces. In agreement with previous studies we found that the Fc-containing alkanethiol molecules adsorb forming a thiolate bond with the Au surface with a molecular geometry 30° tilted with respect to the surface normal. Measured surface coverages indicate the formation of a compact monolayer. We found for the first time that the ferrocene group has little influence on the observed work function decrease which is largely determined by the alkanethiol. Furthermore, the ferrocene moiety lies 14 Å above the metal surface covalently bonded to the alkanethiol SAM and its HOMO is located at −1.6 eV below the Fermi level. Our results provide new valuable insight into the molecular and electronic structure of electroactive SAMs which are of fundamental importance in the field of molecular electronics.
Self-assembled morphologies of ABA triblock copolymer brushes in selective solvents
Authors: Xu Jihua , Yin Yuhua , Wang Zheng , Jiang Run , Li Baohui , Shi An-Chang
Published: March 2013

A simulated annealing method is used to investigate the self-assembled morphologies of symmetric ABA triblock copolymer brushes, formed by one end of the A-blocks tethered onto a planar surface, immersed in a solvent selective for the middle B-blocks. The morphological dependences of the brushes on polymer grafting density and block lengths are investigated systematically. Phase diagrams for systems with different grafting densities are constructed. The simulation results show that the grafted amphiphilic triblock copolymers can self-assemble to form a variety of complicated morphologies which can be classified in terms of the number of A-rich layers in the morphology. In particular, the formation of the structures with one A-rich layer or called “folded” brush structures is consistent with the speculation from the experimental studies of ABA triblock copolymer brushes. More detailed structures depend on the grafting density and the lengths of the blocks. Furthermore, at a high grafting density, the effects of the lengths of blocks and the interaction energies between different species in the system on the conformation of chains are investigated to illustrate the formation mechanisms of self-assembled morphologies of the amphiphilic triblock copolymer brushes.
Tailoring of structure, surface, and luminescence properties of nanodiamonds using rapid oxidative treatment
Authors: Mona J. , Perevedentseva E. , Karmenyan A. , Liou H.-M. , Kang T.-Y. , Cheng C.-L.
Published: March 2013

Precise surface functional groups, low sp2 content, and controlled size of agglomerates are the major concerns for using nanodiamonds (NDs) successfully in many biological applications. In this context, we report on the surface modifications of NDs carried out in the temperature range from 450 °C to 750 °C via rapid thermal annealing (RTA). Advantage of RTA is that one can obtain sufficient quantity of final sample. Effects on the ND's surfaces have been scrutinized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, photoluminescence, and time-resolved photoluminescence spectroscopy. FTIR shows red-shift in C=O stretching frequency at 450 °C while at 550 °C and above the surface functional groups are either reduced or completely removed. Raman spectrum shows red-shift and peak broadening of diamond peak with increasing temperature from R.T. to 550 °C. The band characteristic to the graphite at 1585 cm−1 is not observed for oxidative temperatures at 550 °C and 650 °C. Raman measurements indicate that the size and surface of NDs are modified. Intriguingly, sharp increase in the PL intensity has been observed at 450 °C, while PL intensity decreases gradually at 550 °C and 650 °C. Comparison of the lifetime decay profile approximated with two exponential components, for the NDs, before and after oxidative treatments at 450 °C indicates that the photoluminescence decay is highly sensitive to the surface modifications due to oxidation. Substantial changes in the luminescence and its decay provide useful insights into the role of the graphite and disordered carbon shell.
High-throughput particle manipulation by hydrodynamic, electrokinetic, and dielectrophoretic effects in an integrated microfluidic chip
Authors: Li Shunbo , Li Ming , Bougot-Robin Kristelle , Cao Wenbin , Yeung Yeung Chau Irene , Li Weihua , Wen Weijia
Published: March 2013

Integrating different steps on a chip for cell manipulations and sample preparation is of foremost importance to fully take advantage of microfluidic possibilities, and therefore make tests faster, cheaper and more accurate. We demonstrated particle manipulation in an integrated microfluidic device by applying hydrodynamic, electroosmotic (EO), electrophoretic (EP), and dielectrophoretic (DEP) forces. The process involves generation of fluid flow by pressure difference, particle trapping by DEP force, and particle redirect by EO and EP forces. Both DC and AC signals were applied, taking advantages of DC EP, EO and AC DEP for on-chip particle manipulation. Since different types of particles respond differently to these signals, variations of DC and AC signals are capable to handle complex and highly variable colloidal and biological samples. The proposed technique can operate in a high-throughput manner with thirteen independent channels in radial directions for enrichment and separation in microfluidic chip. We evaluated our approach by collecting Polystyrene particles, yeast cells, and E. coli bacteria, which respond differently to electric field gradient. Live and dead yeast cells were separated successfully, validating the capability of our device to separate highly similar cells. Our results showed that this technique could achieve fast pre-concentration of colloidal particles and cells and separation of cells depending on their vitality. Hydrodynamic, DC electrophoretic and DC electroosmotic forces were used together instead of syringe pump to achieve sufficient fluid flow and particle mobility for particle trapping and sorting. By eliminating bulky mechanical pumps, this new technique has wide applications for in situ detection and analysis.
Relaxor- and phase-transition-like behaviors in ZnO single crystals at high temperatures
Authors: Liu L. N. , Wang C. C. , Lei C. M. , Li T. , Wang G. J. , Sun X. H. , Wang J. , Huang S. G. , Li Y. D. , Wang H.
Published: March 2013

We herein reported the dielectric properties of ZnO single crystals, and three dielectric anomalies were found. The first anomaly shows a relaxor-like behavior. It is composed of two oxygen-vacancy-related relaxation processes: a dipolar relaxation related to the hopping motions of single-ionized oxygen vacancies and a Maxwell-Wagner relaxation as the defects were blocked by the interfaces of sample/electrode contacts. The second anomaly behaves as a phase-transition-like behavior. It is ascribed to the distribution state transition for oxygen vacancies from static disorder to dynamic disorder. The third anomaly exhibits a relaxor-like behavior. It is an artificial effect caused by negative capacitance.
Ultra-flat BaTiO3 epitaxial films on Si(001) with large out-of-plane polarization
Authors: Scigaj M. , Dix N. , Fina I. , Bachelet R. , Warot-Fonrose B. , Fontcuberta J. , Sánchez F.
Published: March 2013

Ferroelectric BaTiO3 is rarely used in monolithic Si devices due to the low quality of BaTiO3 films on Si, as polycrystallinity, degradation of bottom Pt electrodes, low polarization, and high roughness. Here, we overcome these limitations by using a buffer structure that combines yttria-stabilized zirconia, CeO2, and conducting LaNiO3. BaTiO3 films on the multilayered buffer, with total thickness of the buffer below 100 nm, are epitaxial, display remnant polarization of 6–10 μC/cm2, and have roughness of a few Å. These unprecedented properties pave the way to integrate ferroelectric BaTiO3 into Si platforms.
Atom probe analysis of AlN interlayers in AlGaN/AlN/GaN heterostructures
Authors: Mazumder Baishakhi , Kaun Stephen W. , Lu Jing , Keller Stacia , Mishra Umesh K. , Speck James S.
Published: March 2013

Atom probe tomography was used to characterize AlN interlayers in AlGaN/AlN/GaN heterostructures grown by plasma-assisted molecular beam epitaxy (PAMBE), NH3-based molecular beam epitaxy (NH3-MBE), and metal-organic chemical vapor deposition (MOCVD). The PAMBE-grown AlN interlayer had the highest purity, with nearly 100% of group-III sites occupied by Al. The group-III site concentrations of Al for interlayers grown by NH3-MBE and MOCVD were ∼85% and ∼47%, respectively. Hall measurements were performed to determine the two-dimensional electron gas mobility and sheet concentration. Sheet concentrations were ∼25%–45% higher with molecular beam epitaxy than with MOCVD, and these results matched well with atom probe data.
Spin polarized carrier injection from full Heusler alloy Co2MnSi into superconducting NbN
Authors: Kumar Dushyant , Joshi P. C. , Hossain Z. , Budhani R. C.
Published: March 2013

The spin-polarized current injection (SPCI) experiments, where the spin-polarized current (IS) is injected into a 25 μm wide superconducting NbN bridge from a ferromagnetic Co2MnSi layer by tunneling through MgO barrier, show a large (≈67%) suppression of superconducting critical current (IC) due to IS injection at T/TC ≈ 0.4. This corresponds to a large dynamic gain of ≈36 at 3 K, which is 40 times higher than the gain at 6.5 K. Such a rapid rise of gain at lower temperatures strongly suggests a dominant role of SPCI in IC suppression as compared to the effect of Joule-heating.
Threshold current for switching of a perpendicular magnetic layer induced by spin Hall effect
Authors: Lee Ki-Seung , Lee Seo-Won , Min Byoung-Chul , Lee Kyung-Jin
Published: March 2013

We theoretically investigate the switching of a perpendicular magnetic layer by in-plane charge current due to the spin Hall effect. We find that in the high damping regime, the threshold switching current is independent of the damping constant and is almost linearly proportional to both effective perpendicular magnetic anisotropy field and external in-plane field applied along the current direction. We obtain an analytic expression of the threshold current, in excellent agreement with numerical results. Based on the expression, we find that magnetization switching induced by the spin Hall effect can be practically useful when it is combined with voltage-controlled anisotropy change.
Growth and electrical properties of AlOx grown by mist chemical vapor deposition
Authors: Kawaharamura Toshiyuki , Uchida Takayuki , Sanada Masaru , Furuta Mamoru
Published: March 2013

Aluminum oxide (AlOx) thin films were grown using aluminum acetylacetonate (Al(acac)3) as a source solute by mist chemical vapor deposition (mist CVD). The AlOx thin films grown at temperatures above 400°C exhibited a breakdown field (EBD) over 6 MV/cm and a dielectric constant (κ) over 6. It is suggested that residual OH bonding in the AlOx thin films grown at temperatures below 375°C caused degradation of the breakdown field (EBD). With FC type mist CVD, the reaction proceeded efficiently (Ea = 22–24 kJ/mol) because the solvent, especially H2O, worked as a stronger oxygen source. The AlOx film could be grown at 450°C with a high deposition rate (23 nm/min) and smooth surface (RMS = 1.5 nm). Moreover, the AlOx thin films grown by mist CVD had excellent practicality as insulators because the gate leakage current (IG) of the oxide thin film transistor (TFT) with an IGZO/AlOx stack was suppressed below 1 pA at a gate voltage (VG) of 20 V.
AlN/single crystalline diamond piezoelectric structure as a high overtone bulk acoustic resonator
Authors: Sorokin B. P. , Kvashnin G. M. , Volkov A. P. , Bormashov V. S. , Aksenenkov V. V. , Kuznetsov M. S. , Gordeev G. I. , Telichko A. V.
Published: March 2013

First, the Al/AlN/Al/Cr/diamond single crystal piezoelectric layered structure has been developed, and its properties have been investigated up to 8 GHz. The peculiarities associated with the influence of piezoelectric film on the Q factor of high overtones of substrate have been pointed out. High Q ∼ 104 has been found at 6–7 GHz band.
Self-Organizing Maps and the US Urban Spatial Structure
Authors: Arribas-Bel Daniel , Schmidt Charles R
Published: March 2013

In this paper we consider urban spatial structure in US cities using a multidimensional approach. We select six key variables (commuting costs, density, employment dispersion and concentration, land-use mix, polycentricity, and size) from the urban literature and define measures to quantify them. We then apply these measures to 359 metropolitan areas from the 2000 US Census. The adopted methodological strategy combines two novel techniques for the social sciences to explore the existence of relevant patterns in such multidimensional datasets. Geodesic self-organizing maps (SOM) are used to visualize the whole set of information in a meaningful way, while the recently developed clustering algorithm of the max- p is applied to draw boundaries within the SOM and analyze which cities fall into each of them.
Bargaining for Value Capturing: A Game-Theoretical Analysis and Experimental Approach
Authors: Samsura D Ary A , van Deemen A M A , van der Krabben Erwin , van der Heijden R E C M
Published: March 2013

Value capturing is considered a promising additional way of funding public infrastructure development. However, its implementation is often problematic because the instruments that can be used for it (ie, taxes, fees, and other types of fiscal regulation) generally face a lack of support. An alternative approach to value capturing might be to stimulate the stakeholders to bargain over the distribution of the increment values. This paper presents an analysis of bargaining processes with respect to the implementation of value capturing based on concepts drawn from cooperative game theory in partition function form. The institutional setting of location development related to infrastructure development in the Netherlands is used to provide an empirical context to the analysis. As a validation, the game is played with experts in Dutch planning and infrastructure development practice. Our study shows that a game-theoretical approach offers a useful method to conceptualise relationships between different stakeholders and analyse the bargaining and negotiation processes to reach an agreement about an efficient and fair allocation of the increment land values.