bluuebunny/crossref_metadata_2025 huggingface dataset:
Imagining and Living the Revolution: An Arendtian Reading of Rosa Luxemburg's Letters and Writings
Authors: Tamboukou Maria
Published: February 2014

In this paper, I look into personal and political entanglements in Rosa Luxemburg's letters and essays revolving around questions and problems of the revolution. The analysis is informed by Hannah Arendt's theorisation of revolutions in modernity, as well as her reading of narratives within the political. What is intriguing about the Luxemburg/ Arendt encounter is the fact that although both theorists consciously refused to connect themselves with feminist ideas and movements of their times and geographies, their writings have inspired a rich body of feminist theorisations of the political. What I argue is that Luxemburg's ideas and lived experiences of the revolution largely inspired Arendt's theorisation of the revolution as a political phenomenon in the pursuit of freedom, and are opening up new vistas in our understanding of gendered dynamics in historical and contemporary revolutionary events.
Red Girls’ Revolutionary Tales: Antifascist Women's Autobiographies in Italy
Authors: Bonfiglioli Chiara
Published: February 2014

This essay focuses on recent autobiographies written by Italian women born in the 1920s who engaged in revolutionary politics during and after the Second World War: Luciana Castellina ( La scoperta del mondo, 2011), Bianca Guidetti Serra ( Bianca la rossa, 2009), Marisa Ombra (La bella politico, 2010), Marisa Rodano ( Del mutare dei tempi, 2008) and Rossana Rossanda (La ragazza del secolo scorso, 2005). In these autobiographies, personal narratives of passionate engagement are entangled with the urgency of antifascist resistance, and with the social and political conflicts that traversed Cold War Italy. Women's multiple forms of political engagement within the Italian Communist Party are analysed, as well as the contradictory, ambivalent connection between Western European communist activists and Eastern European socialist regimes. The intersections between antifascist, communist and women's rights politics are also explored, since some of the authors were leaders of the nation-wide left-wing Union of Italian Women. The autobiographies tell the story of an antifascist, left-wing ‘middle wave’ that fought pioneering battles for women's political and social rights, and narrate its complex, conflictual encounter with second-wave feminism in the 1970s. These writings, therefore, allow us to reflect on changes in gendered subjectivities and revolutionary politics across time and generations.
Silent Voices: Mothers who Kill their Children and the Women's Liberation Movement in 1970s Japan
Authors: Castellini Alessandro
Published: February 2014

In the early 1970s Japan witnessed the emergence of a new women's liberation movement that put forward an unprecedented gendered critique of Japanese post-war society. Known as ūman ribu (woman lib) or simply ribu (lib), this movement appeared at a historical time when the numerical increase in cases of mothers who killed their own children prompted the news media to describe maternal filicide as a dramatic social phenomenon. This article explores ribu's engagement with the increased public visibility of mothers who kill. It contends that the solidarity and support the movement demonstrated for these criminalised mothers radically challenged idealised notions of motherhood, maternal love and the sanctity of the mother—child bond, and deeply questioned the post-war nuclear family as the cornerstone of society. The article investigates the revolutionary potential of ribu's preoccupation with murderous mothers by framing it in the context of the movement's call for consciousness transformation and for the pursuance of a more genuine relationality, and it gestures towards an understanding of what might be at stake in reading maternal filicide through the interpretative grid of a revolutionary agenda.
Mean-field RVB ground states of lattice models of CuNCN
Authors: Tchougréeff A. L. , Dronskowski R.
Published: February 2014

Recently we proposed to describe the fascinating physics of copper carbodiimide, CuNCN, with help of the anisotropic triangular antiferromagnetic Heisenberg model with the parameters Ja and Jab extending along the a, and a ± b lattice directions and a new frustrated Heisenberg antiferromagnetic model with exchange parameters Jc, Ja, and Jac, extending along the c, a, and a ± c (c-a-ca model) directions assuming the resonating valence bond (RVB) type of the corresponding phases. Here we discuss possible RVB ground states of these models in the mean-field approximation and show that in either case it is a two-dimensional RVB state. The difference between the models is that in the ground state of the triangular model the quasiparticle spectrum features a finite (although exponentially small) energy gap for arbitrary weak Jab whereas that of the c-a-ca model shows two pseudogaps and a linear dependence of the quasiparticle density of states in the low-energy range.
Optical analysis of TlInS2xSe2(1−x) mixed crystals
Authors: Guler I.
Published: February 2014

The ellipsometry measurements were carried out on TlInS2xSe2(1−x) mixed crystals in the spectral range of 1.5–6.0 eV at room temperature. The refractive index, extinction coefficient, real and imaginary parts of dielectric function were found as a result of ellipsometric measurements. The energies of interband transitions (critical point energies) of the TlInS2xSe2(1−x) mixed crystals were obtained by means of the second derivative of the real and imaginary parts of dielectric function. The variation of the critical point energies with the isomorphic anion substitution that is sulfur for selenium atoms was established.
Clustering versus non-clustering phase synchronizations
Authors: Liu Shuai , Zhan Meng
Published: February 2014

Clustering phase synchronization (CPS) is a common scenario to the global phase synchronization of coupled dynamical systems. In this work, a novel scenario, the non-clustering phase synchronization (NPS), is reported. It is found that coupled systems do not transit to the global synchronization until a certain sufficiently large coupling is attained, and there is no clustering prior to the global synchronization. To reveal the relationship between CPS and NPS, we further analyze the noise effect on coupled phase oscillators and find that the coupled oscillator system can change from CPS to NPS with the increase of noise intensity or system disorder. These findings are expected to shed light on the mechanism of various intriguing self-organized behaviors in coupled systems.
Photodissociation of CH3CHO at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Verification of roaming and triple fragmentation
Authors: Hung Kai-Chan , Tsai Po-Yu , Li Hou-Kuan , Lin King-Chuen
Published: February 2014

By using time-resolved Fourier-transform infrared emission spectroscopy, the HCO fragment dissociated from acetaldehyde (CH3CHO) at 248 nm is found to partially decompose to H and CO. The fragment yields are enhanced by the Ar addition that facilitates the collision-induced internal conversion. The channels to CH2CO + H2 and CH3CO + H are not detected significantly. The rotational population distribution of CO, after removing the Ar collision effect, shows a bimodal feature comprising both low- and high-rotational (J) components, sharing a fraction of 19% and 81%, respectively, for the vibrational state v = 1. The low-J component is ascribed to both roaming pathway and triple fragmentation. They are determined to have a branching ratio of <0.13 and >0.06, respectively, relative to the whole v = 1 population. The CO roaming is accompanied by a highly vibrational population of CH4 that yields a vibrational bimodality.
Characteristics and applications of micro-pixelated GaN-based light emitting diodes on Si substrates
Authors: Tian Pengfei , McKendry Jonathan J. D. , Gong Zheng , Zhang Shuailong , Watson Scott , Zhu Dandan , Watson Ian M. , Gu Erdan , Kelly Anthony E. , Humphreys Colin J. , Dawson Martin D.
Published: February 2014

Using a GaN-based light emitting diode (LED) epitaxial structure grown on Si, individually addressable 10 × 10 micro-pixelated LED (μLED) arrays with pixel diameters of 45 μm and peak emission at ∼470 nm have been demonstrated. The electrical and optical properties of these μLEDs were compared with those of broad-area LEDs fabricated from the same epistructure. The μLEDs can sustain a much higher current density, up to 6.6 kA/cm2, before thermal rollover. Also, the fabricated μLEDs show good pixel-to-pixel uniformity, which demonstrates potential for low-cost micro-displays. Furthermore, these μLEDs demonstrate a high electrical-to-optical modulation bandwidth of up to ∼270 MHz and are suitable for visible light communication at data transmission rate up to 400 Mbit/s. The electrical-to-optical modulation bandwidth of the μLEDs increases rapidly with injection currents less than ∼6 mA, temporarily saturates at injection currents of ∼6 to ∼35 mA, and gradually increases again with injection currents up to 110 mA. Carrier density dependent recombination processes are responsible for the bandwidth increase at low current, the resistance-capacitance product determines the modulation bandwidth in the saturation region, and self-heating, which changes series resistance of μLEDs, may cause a further bandwidth increase at high current.
Nonadiabatic calculations of ultraviolet absorption cross section of sulfur monoxide: Isotopic effects on the photodissociation reaction
Authors: Danielache Sebastian O. , Tomoya Suzuki , Kondorsky Alexey , Tokue Ikuo , Nanbu Shinkoh
Published: February 2014

Ultraviolet absorption cross sections of the main and substituted sulfur monoxide (SO) isotopologues were calculated using R-Matrix expansion technique. Energies, transition dipole moments, and nonadiabatic coupling matrix elements were calculated at MRCI/AV6Z level. The calculated absorption cross section of 32S16O was compared with experimental spectrum; the spectral feature and the absolute value of photoabsorption cross sections are in good agreement. Our calculation predicts a long lived photoexcited SO* species which causes large non-mass dependent isotopic effects depending on the excitation energy in the ultraviolet region.
Magnetization dynamics of a two-sublattice ferrimagnet near the angular momentum compensation point
Authors: Krivoruchko V. N.
Published: February 2014

The high-frequency properties of two-sublattice ferrimagnets are examined near the temperature TL at which the angular momentum of the sublattices is compensated. A diagram technique for spin operators is used, along with analytic expressions that are valid over the entire temperature range of the magnetically ordered state of the system. It is shown that near TL longitudinal fluctuations in the magnetization have a significant influence on the resonance properties of the magnet, with different temperature behaviors of the in-phase and out-of-phase precessions of the sublattice magnetization. As TL is approached the frequency of the in-phase precession increases simultaneously with a rise in the line width, while the frequency of the out-of-phase oscillations falls off significantly, so the two modes become equivalent. These results may be important for understanding the microscopic mechanisms of magnetic reversal by ultrashort laser pulses in rare earth ferrimagnets.
Spin waves in easy-axis antiferromagnets with precessing domain walls
Authors: Bogdan M. M. , Charkina O. V.
Published: February 2014

Equations for the antiferromagnetism vector are used to study the spectrum and scattering of spin waves on a domain wall with precessing spins in an easy-axis antiferromagnet with a constant magnetic field directed along the easy axis. It is shown that this kind of magnetic field can be completely eliminated from the equations of motion, so that they can be reduced to a Lorentz invariant form. The spectral problem for weak excitation of a precessing domain wall is solved and exact solutions are found for the linearized equations describing the propagation of spin waves in antiferromagnets with this kind of domain wall. An explicit expression is found for the reflection coefficient of spin waves from a domain wall as a function of the wave vectors of the incident and transmitted waves, along with its dependence on the spin wave frequency. The range of frequencies within which the spin waves are fully reflected is found and it is shown that the reflection coefficient falls off sharply above the upper limit of this range. These results can be generalized to the case of a moving domain wall in a three-dimensional crystal.
Spintronics of antiferromagnetic systems (Review Article)
Authors: Gomonay E. V. , Loktev V. M.
Published: February 2014

Spintronics of antiferromagnets is a new and rapidly developing field of the physics of magnetism. Even without macroscopic magnetization, antiferromagnets, similar to ferromagnetic materials are affected by spin-polarized current, and as in ferromagnets this phenomenon is based on a spin-dependent interaction between localized and free electrons. However, due to the nature of antiferromagnetic materials (complex magnetic structure, essential role of exchange interactions, absence of macroscopic magnetization) the study of possible spintronic effects requires new theoretical and experimental approaches. The purpose of this review is to systemize and describe recent developments in this area. After presenting the main features of structure and behavior of antiferromagnets various microscopic and phenomenological models for description of the current-induced phenomena in heterostructures containing ferro- and antiferromagnetic layers are considered. The questions related to an effect of antiferromagnetic ordering on an electric current, as well as the questions of possible creation of fully antiferromagnetic spin valves are discussed. In addition, we briefly discuss available experimental results and try to interpret them.
Investigation of temperature dependent dielectric constant of a sputtered TiN thin film by spectroscopic ellipsometry
Authors: Tripura Sundari S. , Ramaseshan R. , Jose Feby , Dash S. , Tyagi A. K.
Published: February 2014

The temperature dependence of optical constants of titanium nitride thin film is investigated using Spectroscopic Ellipsometry (SE) between 1.4 and 5 eV in the temperature range of 300 K to 650 K in steps of 50 K. The real and imaginary parts of the dielectric functions ε1(E) and ε2(E) marginally increase with increase in temperature. A Drude Lorentz dielectric analysis based on free electron and oscillator model are carried out to describe the temperature behavior. With increase in temperature, the unscreened plasma frequency and broadening marginally decreased and increased, respectively. The parameters of the Lorentz oscillator model also showed that the relaxation time decreased with temperature while the oscillator energies increased. This study shows that owing to the marginal change in the refractive index with temperature, titanium nitride can be employed for surface plasmon sensor applications even in environments where rise in temperature is imminent.
Quantitative study of fluctuation effects by fast lattice Monte Carlo simulations: Compression of grafted homopolymers
Authors: Zhang Pengfei , Wang Qiang
Published: February 2014

Using fast lattice Monte Carlo (FLMC) simulations [Q. Wang, Soft Matter 5, 4564 (2009)] and the corresponding lattice self-consistent field (LSCF) calculations, we studied a model system of grafted homopolymers, in both the brush and mushroom regimes, in an explicit solvent compressed by an impenetrable surface. Direct comparisons between FLMC and LSCF results, both of which are based on the same Hamiltonian (thus without any parameter-fitting between them), unambiguously and quantitatively reveal the fluctuations/correlations neglected by the latter. We studied both the structure (including the canonical-ensemble averages of the height and the mean-square end-to-end distances of grafted polymers) and thermodynamics (including the ensemble-averaged reduced energy density and the related internal energy per chain, the differences in the Helmholtz free energy and entropy per chain from the uncompressed state, and the pressure due to compression) of the system. In particular, we generalized the method for calculating pressure in lattice Monte Carlo simulations proposed by Dickman [J. Chem. Phys. 87, 2246 (1987)], and combined it with the Wang-Landau–Optimized Ensemble sampling [S. Trebst, D. A. Huse, and M. Troyer, Phys. Rev. E 70, 046701 (2004)] to efficiently and accurately calculate the free energy difference and the pressure due to compression. While we mainly examined the effects of the degree of compression, the distance between the nearest-neighbor grafting points, the reduced number of chains grafted at each grafting point, and the system fluctuations/correlations in an athermal solvent, the θ-solvent is also considered in some cases.
Relaxed active space: Fixing tailored-CC with high order coupled cluster. II
Authors: Melnichuk Ann , Bartlett Rodney J.
Published: February 2014

Due to the steep increase in computational cost with the inclusion of higher-connected cluster operators in coupled-cluster applications, it is usually not practical to use such methods for larger systems or basis sets without an active space partitioning. This study generates an active space subject to unambiguous statistical criteria to define a space whose size permits treatment at the CCSDT level. The automated scheme makes it unnecessary for the user to judge whether a chosen active space is sufficient to correctly solve the problem. Two demanding applications are presented: twisted ethylene and the transition states for the bicyclo[1,1,0]butane isomerization. As bi-radicals both systems require at least a CCSDT level of theory for quantitative results, for the geometries and energies.
Vibrational optical activity of chiral carbon nanoclusters treated by a generalized π-electron method
Authors: Nagy Péter R. , Surján Péter R. , Szabados Ágnes
Published: February 2014

Cross sections of inelastic light scattering accompanied by vibronic excitation in large conjugated carbon structures is assessed at the π-electron level. Intensities of Raman and vibrational Raman optical activity (VROA) spectra of fullerenes are computed, relying on a single electron per atom. When considering only first neighbor terms in the Hamiltonian (a tight-binding (TB) type or Hückel-model), Raman intensities are captured remarkably well, based on comparison with frequency-dependent linear response of the self-consistent field (SCF) method. Resorting to π-electron levels when computing spectral intensities brings a beneficial reduction in computational cost as compared to linear response SCF. At difference with total intensities, the first neighbor TB model is found inadequate for giving the left and right circularly polarized components of the scattered light, especially when the molecular surface is highly curved. To step beyond first neighbor approximation, an effective π-electron Hamiltonian, including interaction of all sites is derived from the all-electron Fockian, in the spirit of the Bloch-equation. Chiroptical cross-sections computed by this novel π-electron method improve upon first-neighbor TB considerably, with no increase in computational cost. Computed VROA spectra of chiral fullerenes, such as C76 and C28, are reported for the first time, both by conventional linear response SCF and effective π-electron models.
Positron interactions with water–total elastic, total inelastic, and elastic differential cross section measurements
Authors: Tattersall Wade , Chiari Luca , Machacek J. R. , Anderson Emma , White Ron D. , Brunger M. J. , Buckman Stephen J. , Garcia Gustavo , Blanco Francisco , Sullivan James P.
Published: February 2014

Utilising a high-resolution, trap-based positron beam, we have measured both elastic and inelastic scattering of positrons from water vapour. The measurements comprise differential elastic, total elastic, and total inelastic (not including positronium formation) absolute cross sections. The energy range investigated is from 1 eV to 60 eV. Comparison with theory is made with both R-Matrix and distorted wave calculations, and with our own application of the Independent Atom Model for positron interactions.
Interplay of radiative and nonradiative transitions in surface hopping with radiation-molecule interactions
Authors: Bajo Juan José , Granucci Giovanni , Persico Maurizio
Published: February 2014

We implemented a method for the treatment of field induced transitions in trajectory surface hopping simulations, in the framework of the local diabatization scheme, especially suited for on-the-fly dynamics. The method is applied to a simple one-dimensional model with an avoided crossing and compared with quantum wavepacket dynamics. The results show the importance of introducing a proper decoherence correction to surface hopping, in order to obtain meaningful results. Also the energy conservation policy of standard surface hopping must be revised: in fact, the quantum wavepacket energetics is well reproduced if energy absorption/emission is allowed for in the hops determined by radiation-molecule coupling. To our knowledge, this is the first time the issues of decoherence and energy conservation have been analyzed in depth to devise a mixed quantum-classical method for dynamics with molecule-field interactions.
Hydrogen bonding induced proton exchange reactions in dense D2-NH3 and D2-CH4 mixtures
Authors: Borstad Gustav M. , Yoo Choong-Shik
Published: February 2014

We have investigated high-pressure behaviors of simple binary mixtures of NH3 and D2 to 50 GPa and CH4 and D2 to 30 GPa using confocal micro-Raman spectroscopy. The spectral data indicate strong proton exchange reactions occur in dense D2-NH3 mixture, producing different isotopes of ammonia such as NH3, NH2D, NHD2, and ND3. In contrast, the proton exchange process in dense D2-CH4 mixture is highly limited, and no vibration feature is apparent for deuterated methane. The vibrational modes of H2 isotopes in D2-NH3 are blue shifted from those of pure H2 isotopes, whereas the modes of D2-CH4 show overall agreement with those in pure D2 and CH4. In turn, this result advocates the presence of strong repulsion and thereby internal pressure in D2-NH3 mixture, which are absent in D2-CH4. In fact, the bond length of hydrogen molecules in D2-NH3, calculated from the present spectral data, is shorter than that observed in pure hydrogen – supporting the enhanced intermolecular interaction in the mixture. Comparing the present spectral results with those previously observed in D2-H2O mixtures further suggests that the strength of repulsive interaction or the magnitude of internal pressure in the mixtures is proportional to the strength of hydrogen bonding in H2O, NH3, and CH4 in decreasing order. Hence, we suggest that the proton exchange is assisted by hydrogen bonding in these molecules.
Thermodynamic ground state of MgB6 predicted from first principles structure search methods
Authors: Wang Hui , LeBlanc K. A. , Gao Bo , Yao Yansun
Published: February 2014

Crystalline structures of magnesium hexaboride, MgB6, were investigated using unbiased structure searching methods combined with first principles density functional calculations. An orthorhombic Cmcm structure was predicted as the thermodynamic ground state of MgB6. The energy of the Cmcm structure is significantly lower than the theoretical MgB6 models previously considered based on a primitive cubic arrangement of boron octahedra. The Cmcm structure is stable against the decomposition to elemental magnesium and boron solids at atmospheric pressure and high pressures up to 18.3 GPa. A unique feature of the predicted Cmcm structure is that the boron atoms are clustered into two forms: localized B6 octahedra and extended B∞ ribbons. Within the boron ribbons, the electrons are delocalized and this leads to a metallic ground state with vanished electric dipoles. The present prediction is in contrast to the previous proposal that the crystalline MgB6 maintains a semiconducting state with permanent dipole moments. MgB6 is estimated to have much weaker electron-phonon coupling compared with that of MgB2, and therefore it is not expected to be able to sustain superconductivity at high temperatures.
Morphology and Curie temperature engineering in crystalline La0.7Sr0.3MnO3 films on Si by pulsed laser deposition
Authors: Nori Rajashree , Kale S. N. , Ganguly U. , Ravi Chandra Raju N. , Sutar D. S. , Pinto R. , Ramgopal Rao V.
Published: February 2014

Of all the colossal magnetoresistant manganites, La0.7Sr0.3MnO3 (LSMO) exhibits magnetic and electronic state transitions above room temperature, and therefore holds immense technological potential in spintronic devices and hybrid heterojunctions. As the first step towards this goal, it needs to be integrated with silicon via a well-defined process that provides morphology and phase control, along with reproducibility. This work demonstrates the development of pulsed laser deposition (PLD) process parameter regimes for dense and columnar morphology LSMO films directly on Si. These regimes are postulated on the foundations of a pressure-distance scaling law and their limits are defined post experimental validation. The laser spot size is seen to play an important role in tandem with the pressure-distance scaling law to provide morphology control during LSMO deposition on lattice-mismatched Si substrate. Additionally, phase stability of the deposited films in these regimes is evaluated through magnetometry measurements and the Curie temperatures obtained are 349 K (for dense morphology) and 355 K (for columnar morphology)—the highest reported for LSMO films on Si so far. X-ray diffraction studies on phase evolution with variation in laser energy density and substrate temperature reveals the emergence of texture. Quantitative limits for all the key PLD process parameters are demonstrated in order enable morphological and structural engineering of LSMO films deposited directly on Si. These results are expected to boost the realization of top-down and bottom-up LSMO device architectures on the Si platform for a variety of applications.
Critical point anomalies include expansion shock waves
Authors: Nannan N. R. , Guardone A. , Colonna P.
Published: February 2014

From first-principle fluid dynamics, complemented by a rigorous state equation accounting for critical anomalies, we discovered that expansion shock waves may occur in the vicinity of the liquid-vapor critical point in the two-phase region. Due to universality of near-critical thermodynamics, the result is valid for any common pure fluid in which molecular interactions are only short-range, namely, for so-called 3-dimensional Ising-like systems, and under the assumption of thermodynamic equilibrium. In addition to rarefaction shock waves, diverse non-classical effects are admissible, including composite compressive shock-fan-shock waves, due to the change of sign of the fundamental derivative of gasdynamics.
Electrodynamics of a ring-shaped spiral resonator
Authors: Maleeva N. , Fistul M. V. , Karpov A. , Zhuravel A. P. , Averkin A. , Jung P. , Ustinov A. V.
Published: February 2014

We present analytical, numerical, and experimental investigations of electromagnetic resonant modes of a compact monofilar Archimedean spiral resonator shaped in a ring, with no central part. Planar spiral resonators are interesting as components of metamaterials for their compact deep-subwavelength size. Such resonators couple primarily to the magnetic field component of the incident electromagnetic wave, offering properties suitable for magnetic meta-atoms. Surprisingly, the relative frequencies of the resonant modes follow the sequence of the odd numbers as f1:f2:f3:f4… = 1:3:5:7…, despite the nearly identical boundary conditions for electromagnetic fields at the extremities of the resonator. In order to explain the observed spectrum of resonant modes, we show that the current distribution inside the spiral satisfies a particular Carleman type singular integral equation. By solving this equation, we obtain a set of resonant frequencies. The analytically calculated resonance frequencies and the current distributions are in good agreement with experimental data and the results of numerical simulations. By using low-temperature laser scanning microscopy of a superconducting spiral resonator, we compare the experimentally visualized ac current distributions over the spiral with the calculated ones. Theory and experiment agree well with each other. Our analytical model allows for calculation of a detailed three-dimensional magnetic field structure of the resonators.
Optical properties of fluorescent zigzag graphene quantum dots derived from multi-walled carbon nanotubes
Authors: Chen Wei , Li Fushan , Wu Chaoxing , Guo Tailiang
Published: February 2014

Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating electronic and optical properties due to their quantum confinement and edge effect. In this paper, GQDs were synthesized by using acid treatment and chemical exfoliation of multi-walled carbon nanotubes (MWCNTs). The structure of the GQDs was investigated by transmission electron microscope. The GQDs have a uniform size distribution, zigzag edge structure and two-dimensional morphology. The results indicated that the GQDs have bright blue emission upon UV excitation. The highly fluorescent GQDs exhibited high water solubility and good stability. It is shown that the acid treatment of MWCNTs leads to the formation of the functional group in zigzag sites, which results in the pH-dependent fluorescence of the GQDs.
Static and dynamic magnetic properties of cubic Mn-Co-Ga Heusler films
Authors: Demiray A. S. , Kubota T. , Iihama S. , Mizukami S. , Miyazaki T. , Naganuma H. , Oogane M. , Ando Y.
Published: February 2014

We investigated the static and dynamic magnetic properties of thin films of Mn-Co-Ga Heusler compound. Gilbert damping and exchange stiffness constants of the films were evaluated by using the ferromagnetic resonance technique in the X-band regime (f = 9.4 GHz). By analyzing the experimental spectra, magnetic parameters of the films such as the line width and the Gilbert damping were deduced, and the exchange stiffness constant was estimated from the perpendicular standing spin-wave resonance. The Gilbert damping constant was estimated to be 0.017 in a specific film composition. The exchange stiffness constant showed a linear dependence on the film composition.
Effect of adverse pressure gradient on high speed boundary layer transition
Authors: Franko Kenneth J. , Lele Sanjiva
Published: February 2014

The effect of adverse pressure gradients (APG) on boundary layer stability, breakdown, and heat-transfer overshoot is investigated. Flat plate isothermal boundary layers initially at Mach 6 with APG imposed through the freestream boundary condition are simulated using suction and blowing to produce boundary layer instabilities. The three different transition mechanisms compared are first mode oblique breakdown, second mode oblique breakdown, and second mode fundamental resonance. For all of the transition mechanisms, an adverse pressure gradient increases the linear growth rates and quickens the transition to turbulence. However, the nonlinear breakdown for all three transition mechanisms is qualitatively the same as for a zero pressure gradient boundary layer. First mode oblique breakdown leads to the earliest transition location and an overshoot in heat transfer in the transitional region. Both types of Mack second mode forcing lead to a transitional boundary layer but even with the increased growth rates and N factors produced by the adverse pressure gradient, the breakdown process is still more gradual than first mode oblique breakdown because the primary Mack second mode instabilities saturate and produce streaks that breakdown further downstream.
Technique for measurement of magnetostriction in an individual nanowire using atomic force microscopy
Authors: Jin Park Jung , Estrine Eliot C. , Madhukar Reddy Sai , Stadler Bethanie J. H. , Flatau Alison B.
Published: February 2014

We have investigated a method for measuring the dimensions of an individual multilayered Fe-Ga/Cu nanowire (NW) as it changes with induced magnetization. In this study, we demonstrate the proposed approach and establish this as a viable method for measuring the magnetostrictive behavior of an individual Fe-Ga/Cu NW using atomic force microscopy (AFM). When an external magnetic field (∼300 Oe) was applied perpendicular to the NW axis, the NW length appeared minimized. When a field (∼1000 Oe) was applied parallel to the NW axis, the height profile of the NW was found to be higher than in the case with no parallel external field. Since both ends of the NW were welded to the substrate, the magnetic field induced dimensional change of the NW caused deflection of the NW in the upward direction, which was significant enough to be detected by AFM. An average height difference of 15 nm was measured with and without an applied field which was then used to calculate the magnetostriction of the multilayered NW.
A numerical investigation of impulsively generated vortical structures in deep and shallow fluid layers
Authors: Rojanaratanangkule Watchapon , Thomas T. Glyn , Coleman Gary N.
Published: February 2014

The evolution and formation of large-scale turbulent coherent structures induced by an impulsive jet between non-deformable stress-free layers are investigated via direct numerical simulation at a jet Reynolds number of 1250. The ratio of the initial size of the vortex to the domain depth is varied to study the influence of the bounding surface confinement. A non-conservative body force is applied to the governing equations to represent the momentum source. During the forcing period, the coherent structure appears in the form of a leading vortex ring together with a trailing jet, and breaks down to turbulence due to an instability very similar to the Widnall instability before interacting with the free surface. The input parameters (the momentum flux J, the forcing period Δtf, and the domain depth h) can be grouped together as the confinement number C = J1/2Δtf/h2 to parameterise the intensity and strength of the eddy signature at the free surface. Increasing the confinement number corresponds to reducing the ratio of the domain depth to the initial size of the vortex, which leads to a linear increase in the maximum amplitude of the surface signature in terms of the surface eddy strength. A dipole forms for values of C greater than about unity, even though the eddy signature appears at the free surface for all the confinement numbers considered.
Strong anisotropy in quasi-static magnetohydrodynamic turbulence for high interaction parameters
Authors: Reddy K. Sandeep , Verma Mahendra K.
Published: February 2014

We simulate forced quasi-static magnetohydrodynamic turbulence and investigate the anisotropy, energy spectrum, and energy flux of the flow, specially for large interaction parameters (N). We show that the angular dependence of the energy spectrum is well quantified using Legendre polynomials. For large N, the energy spectrum is exponential. Our direct computation of energy flux reveals an inverse cascade of energy at low wavenumbers, similar to that in two-dimensional turbulence. We observe the flow be two-dimensional (2D) for moderate N (N ∼ 20), and two-dimensional three-component (2D-3C) type for N ⩾ 27. In our forced simulation, the transition from 2D to 2D-3C occurs at higher value of N than that in Favier et al. [“On the two-dimensionalization of quasistatic magnetohydrodynamic turbulence,” Phys. Fluids 22, 075104 (2010)] who employ decaying simulations.
Semi-exact concentric atomic density fitting: Reduced cost and increased accuracy compared to standard density fitting
Authors: Hollman David S. , Schaefer Henry F. , Valeev Edward F.
Published: February 2014

A local density fitting scheme is considered in which atomic orbital (AO) products are approximated using only auxiliary AOs located on one of the nuclei in that product. The possibility of variational collapse to an unphysical “attractive electron” state that can affect such density fitting [P. Merlot, T. Kjærgaard, T. Helgaker, R. Lindh, F. Aquilante, S. Reine, and T. B. Pedersen, J. Comput. Chem. 34, 1486 (2013)] is alleviated by including atom-wise semidiagonal integrals exactly. Our approach leads to a significant decrease in the computational cost of density fitting for Hartree–Fock theory while still producing results with errors 2–5 times smaller than standard, nonlocal density fitting. Our method allows for large Hartree–Fock and density functional theory computations with exact exchange to be carried out efficiently on large molecules, which we demonstrate by benchmarking our method on 200 of the most widely used prescription drug molecules. Our new fitting scheme leads to smooth and artifact-free potential energy surfaces and the possibility of relatively simple analytic gradients.
Multi-reference vibration correlation methods
Authors: Pfeiffer Florian , Rauhut Guntram
Published: February 2014

State-specific vibration correlation methods beyond the vibrational multi-configuration self-consistent field (VMCSCF) approximation have been developed, which allow for the accurate calculation of state energies for systems suffering from strong anharmonic resonances. Both variational multi-reference configuration interaction approaches and an implementation of approximate 2nd order vibrational multi-reference perturbation theory are presented. The variational approach can be significantly accelerated by a configuration selection scheme, which leads to negligible deviations in the final results. Relaxation effects due to the partitioning of the correlation space and the performance of a VMCSCF modal basis in contrast to a standard modal basis obtained from vibrational self-consistent field theory have been investigated in detail. Benchmark calculations based on high-level potentials are provided for the propargyl cation and cis-diazene.
Ionization and dissociation dynamics of vinyl bromide probed by femtosecond extreme ultraviolet transient absorption spectroscopy
Authors: Lin Ming-Fu , Neumark Daniel M. , Gessner Oliver , Leone Stephen R.
Published: February 2014

Strong-field induced ionization and dissociation dynamics of vinyl bromide, CH2=CHBr, are probed using femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy. Strong-field ionization is initiated with an intense femtosecond, near infrared (NIR, 775 nm) laser field. Femtosecond XUV pulses covering the photon energy range of 50-72 eV probe the subsequent dynamics by measuring the time-dependent spectroscopic features associated with transitions of the Br (3d) inner-shell electrons to vacancies in molecular and atomic valence orbitals. Spectral signatures are observed for the depletion of neutral C2H3Br, the formation of C2H3Br+ ions in their ground (${\rm \tilde X}$X̃) and first excited ($\tilde {\rm A}$Ã) states, the production of C2H3Br++ ions, and the appearance of neutral Br (2P3/2) atoms by dissociative ionization. The formation of free Br (2P3/2) atoms occurs on a timescale of 330 ± 150 fs. The ionic $\tilde {\rm A}$Ã state exhibits a time-dependent XUV absorption energy shift of ∼0.4 eV within the time window of the atomic Br formation. The yield of Br atoms correlates with the yield of parent ions in the $\tilde {\rm A}$Ã state as a function of NIR peak intensity. The observations suggest that a fraction of vibrationally excited C2H3Br+ ($\tilde {\rm A}$Ã) ions undergoes intramolecular vibrational energy redistribution followed by the C–Br bond dissociation. The C2H3Br+ (${\rm \tilde X}$X̃) products and the majority of the C2H3Br++ ions are relatively stable due to a deeper potential well and a high dissociation barrier, respectively. The results offer powerful new insights about orbital-specific electronic processes in high field ionization, coupled vibrational relaxation and dissociation dynamics, and the correlation of valence hole-state location and dissociation in polyatomic molecules, all probed simultaneously by ultrafast table-top XUV spectroscopy.
The OH stretching spectrum of warm water clusters
Authors: Zischang Julia , Suhm Martin A.
Published: February 2014

The O–H stretching fundamental spectra of water clusters are well known from cold jet expansions, but their detection in the atmosphere remains elusive. Mild supersonic jet expansions of neat water vapor are used to detect trimers and tetramers with intermediate thermal excitation. Spectra close to the evaporative limit are obtained by interfering neighboring expansion fans in a multi slit nozzle experiment. They are interpreted in terms of ring opening in the water trimer, whereas the tetramer spectra can also be interpreted by conventional hot band contributions and thermal excitation of librational modes.
Theoretical investigation of conductivity sensitivities of SiC-based bio-chemical acoustic wave sensors
Authors: Fan Li , Chen Zhe , Zhang Shu-yi , Zhang Hui
Published: February 2014

The phase velocities, electromechanical coupling coefficients, conductivity sensitivities, insert losses, and minimum detectable masses of Rayleigh and Lamb waves sensors based on silicon carbide (SiC) substrates are theoretically studied. The results are compared with the performances of the sensors based on conventional silicon substrates. It is found that the sensors using SiC substrates have higher electromechanical coupling coefficients and conductivity sensitivities than the conventional silicon-based sensors in virtue of piezoelectricity of the SiC. Moreover, higher phase velocities in SiC substrates can reduce the insert losses and minimum detectable masses of the sensors. In this case, in the detection of the gas with the tiny mass as the hydrogen, in which the conductivity sensitivity is more important than the mass sensitivity, the sensor based on the SiC substrate has a higher sensitivity and exhibits the potential to detect the gas with the concentration below the ppm level. According to the results, the performances of the sensors based on the Rayleigh and Lamb waves using the SiC substrates can be optimized by properly selecting piezoelectric films, structural parameters, and operating wavelengths.
Resistive switching in doped BiFeO3 films
Authors: Wu Lei , Jiang Changjun , Xue Desheng
Published: February 2014

Polycrystalline Bi0.9Sr0.1FeO3 and Bi0.9Ca0.1Fe0.9Co0.1O3 films (BXFO) were synthesized by sol-gel spin coating method. Local resistive switching behavior was investigated. Bipolar resistive switching characteristics were clearly observed in both two samples. However, for the Bi0.9Sr0.1FeO3 film, the switching from the low resistance (LRS) to the high resistance (HRS) occurred at positive bias and the switching from the HRS to the LRS at negative bias. On the contrary, the resistance of Bi0.9Ca0.1Fe0.9Co0.1O3 film was switched from the LRS to the HRS when a negative bias was applied. Possible mechanisms for both resistive switching forms were discussed on the basis of the Schottky-like barrier.
Interactions of collinear acoustic waves propagating along pure mode directions of crystals
Authors: Liu Xiaozhou , Jiang Wenhua , Cao Wenwu , Jiang Zheng
Published: February 2014

Previous studies on the interaction of collinear acoustic waves have been devoted to waves propagating along pure modes directions of cubic crystals. In this paper, we show that the calculations can be readily extended to all crystal point groups. Nonlinearity parameters characterizing the nonlinear interactions are defined here. The effective third order elastic constants involved in the parameters can be calculated by using the method presented in this paper. Our results are very useful for the study of elastic nonlinearity of crystals with any given symmetry.
Fano interference and a slight fluctuation of the Majorana hallmark
Authors: Seridonio A. C. , Siqueira E. C. , Dessotti F. A. , Machado R. S. , Yoshida M.
Published: February 2014

According to the Liu and Baranger [Phys. Rev. B 84, 201308(R) (2011)], an isolated Majorana state bound to one edge of a long enough Kitaev chain in the topological phase and connected to a quantum dot, results in a robust transmittance of 1/2 at zero-bias. In this work, we show that the removal of such a hallmark can be achieved by using a metallic surface hosting two adatoms in a scenario where there is a lack of symmetry in the Fano effect, which is feasible by coupling the Kitaev chain to one of these adatoms. Thus in order to detect this feature experimentally, one should apply the following two-stage procedure: (i) first, attached to the adatoms, one has to lock AFM tips in opposite gate voltages (symmetric detuning of the levels Δε) and measure by an STM tip, the zero-bias conductance; (ii) thereafter, the measurement of the conductance is repeated with the gates swapped. For |Δε| away from the Fermi energy and in the case of strong coupling tip-host, this approach reveals in the transmittance, a persistent dip placed at zero-bias and immune to the aforementioned permutation, but characterized by an amplitude that fluctuates slightly around 1/2. However, in the case of a tip acting as a probe, the adatom decoupled from the Kitaev chain becomes completely inert and no fluctuation is observed. Therefore, the STM tip must be considered in the same footing as the “host+adatoms” system. As a result, we have found that despite the small difference between these two Majorana dips, the zero-bias transmittance as a function of the symmetric detuning yields two distinct behaviors, in which one of them is unpredictable by the standard Fano's theory. Therefore, to access such a non trivial pattern of Fano interference, the hypothesis of the STM tip acting as a probe should be discarded.
Twin boundary spacing effects on shock response and spall behaviors of hierarchically nanotwinned fcc metals
Authors: Yuan Fuping , Chen Liu , Jiang Ping , Wu Xiaolei
Published: February 2014

Atomistic deformation mechanisms of hierarchically nano-twinned (NT) Ag under shock conditions have been investigated using a series of large-scale molecular dynamics simulations. For the same grain size d and the same spacing of primary twins λ1, the average flow stress behind the shock front in hierarchically NT Ag first increases with decreasing spacing of secondary twins λ2, achieving a maximum at a critical λ2, and then drops as λ2 decreases further. Above the critical λ2, the deformation mechanisms are dominated by three type strengthening mechanisms: (a) partial dislocations emitted from grain boundaries (GBs) travel across other boundaries; (b) partial dislocations emitted from twin boundaries (TBs) travel across other TBs; (c) formation of tertiary twins. Below the critical λ2, the deformation mechanism are dominated by two softening mechanisms: (a) detwinning of secondary twins; (b) formation of new grains by cross slip of partial dislocations. Moreover, the twin-free nanocrystalline (NC) Ag is found to have lower average flow stress behind the shock front than those of all hierarchically NT Ag samples except the one with the smallest λ2 of 0.71 nm. No apparent correlation between the spall strength and λ2 is observed in hierarchically NT Ag, since voids always nucleate at both GBs and boundaries of the primary twins. However, twin-free NC Ag is found to have higher spall strength than hierarchically NT Ag. Voids can only nucleate from GBs for twin-free NC Ag, therefore, twin-free NC Ag has less nucleation sources along the shock direction when compared to hierarchically NT Ag, which requiring higher tensile stress to create spallation. These findings should contribute to the understandings of deformation mechanisms of hierarchically NT fcc metals under extreme deformation conditions.