bluuebunny/crossref_metadata_2025 huggingface dataset:
Dehydration of xylose and glucose to furan derivatives using bifunctional partially hydroxylated MgF2 catalysts and N2-stripping
Authors: Agirrezabal-Telleria I. , Guo Y. , Hemmann F. , Arias P. L. , Kemnitz E.
Published: February 2014

The current furfural production yield is low due to the use of non-selective homogeneous catalysts and expensive separation.
Electron induced chemistry: a new frontier in astrochemistry
Authors: Mason Nigel J. , Nair Binukumar , Jheeta Sohan , Szymańska Ewelina
Published: February 2014

The commissioning of the ALMA array and the next generation of space telescopes heralds the dawn of a new age of Astronomy, in which the role of chemistry in the interstellar medium and in star and planet formation may be quantified. A vital part of these studies will be to determine the molecular complexity in these seemingly hostile regions and explore how molecules are synthesised and survive. The current hypothesis is that many of these species are formed within the ice mantles on interstellar dust grains with irradiation by UV light or cosmic rays stimulating chemical reactions. However, such irradiation releases many secondary electrons which may themselves induce chemistry. In this article we discuss the potential role of such electron induced chemistry and demonstrate, through some simple experiments, the rich molecular synthesis that this may lead to.
Lithium storage improvement from hierarchical double-shelled SnO2 hollow spheres
Authors: Jing Shilong , Gu Feng , Kong Junhua , Ma Chunrong , Lee Pooi See , Li Chunzhong
Published: February 2014

We have developed hierarchical double-shelled SnO2 hollow spheres by a sequential template-engaged method, in which the loosened SnO2 floccules are well-grown on the inside wall of the hollow spheres.
In situ growth of ultrafine tin oxide nanocrystals embedded in graphitized carbon nanosheets for use in high-performance lithium-ion batteries
Authors: Fu Wei , Du Fei-Hu , Wang Kai-Xue , Ye Tian-Nan , Wei Xiao , Chen Jie-Sheng
Published: February 2014

A SnO2–CNS composite of ultrafine SnO2 nanocrystals grown in situ and graphitized carbon nanosheets has been prepared using a crystal-facet-induced formation method. It exhibits superior electrochemical performance for use in LIBs.
New Fe2TiO5-based nanoheterostructured mesoporous photoanodes with improved visible light photoresponses
Authors: Courtin E. , Baldinozzi G. , Sougrati M. T. , Stievano L. , Sanchez C. , Laberty-Robert C.
Published: February 2014

Triphasic nanocrystalline porous material based Fex–TiO2 anatase, pseudo-brookite and hematite are generated via a simple templated growth based strategy followed by carefully controlled temperature/atmosphere treatments.
High-performance all solid-state micro-supercapacitor based on patterned photoresist-derived porous carbon electrodes and an ionogel electrolyte
Authors: Wang Shuang , Hsia Ben , Carraro Carlo , Maboudian Roya
Published: February 2014

An all solid-state micro-supercapacitor is fabricated using patterned photoresist-derived porous carbon electrodes and an ionogel electrolyte. Excellent long-term stability and high specific energy are obtained.
Effects of a domain-selective ACE inhibitor in a mouse model of chronic angiotensin II-dependent hypertension
Authors: Burger Dylan , Reudelhuber Timothy L. , Mahajan Aman , Chibale Kelly , Sturrock Edward D. , Touyz Rhian M.
Published: February 2014

The somatic isozyme of ACE (angiotensin I-converting enzyme) comprises two distinct zinc-dependent catalytic domains with different substrate specificities for angiotensin I (cleaved selectively by the C-domain) and bradykinin (cleaved equally efficiently by both the N- and C-domains). Classical ACEIs (ACE inhibitors) target both domains, with side effects such as cough and angio-oedema being attributed, in part, to N-domain inhibition, probably through bradykinin accumulation. We questioned whether a novel C-domain-selective ACEI (lisW-S) has anti-hypertensive effects without influencing bradykinin status. AngII (angiotensin II)-dependent hypertension was studied in mice that express active human renin in the liver (TtRhRen). Compared with wild-type littermates, TtRhRen mice displayed cardiac hypertrophy and had significantly elevated SBP [systolic BP (blood pressure)] as determined by tail cuff sphygmomanometry (150±3 compared with 112±5 mmHg; P<0.05) and telemetry (163±3 compared with 112±2 mmHg; P<0.01). Treatment with the non-selective ACEI lisinopril (1 mg/kg of body weight per day via an osmotic mini-pump for 2 weeks) reduced SBP (127±3 compared with. 154±6; P<0.05). Similarly, treatment with the C-domain selective ACEI lisW-S (lisinopril-tryptophan; 3.6 mg/kg of body weight per day via an osmotic mini-pump for 2 weeks) reduced BP. Treatment with lisinopril or lisW-S significantly reduced levels of AngII in kidneys (~4-fold; P<0.001). Ang-(2–8) [angiotensin-2–8)] was significantly reduced by lisinopril, but not by lisW-S. Plasma bradykinin levels were significantly increased only in the lisinopril group. These data suggest that C-domain-selective ACEIs reduce BP and AngII levels similarly to classical ACEIs. C-domain-selective ACEIs have the potential to avoid undesirable effects on the bradykinin system common to classic ACEIs and may represent a novel approach to the treatment of hypertension.
Greedy framework for optical flow tracking of myocardium contours
Authors: Al‐Agamy Ahmed O. , Khalifa Ayman , Fahmy Ahmed S.
Published: February 2014

Optical flow (OF) tracking of the myocardium contours has a potential in segmenting the myocardium in time sequences of cardiac medical images. Nevertheless, to estimate the displacement field of the contour points, a number of assumptions are required to solve an under‐determined set of optical flow equations. In this work, a new framework is proposed to solve the OF tracking problem using greedy optimisation algorithm. The new framework allows different types of constraints such as motion invariance, shape and topology to be applied in a unified way. The developed methods are applied to a publicly‐available cardiac magnetic resonance imaging dataset containing image sequences for 33 patients. Quantitative evaluation of the results shows high potential of the methods to accurately track and segment the myocardium contours.
Range‐spread target detector using the frequency rate function
Authors: Zuo Lei , Li Ming , Zhang Xiaowei , Lu Yunlong , Wu Yan
Published: February 2014

In high‐resolution radar systems, stretch processing technique is generally used to process the returned signals of a range‐spread target. Consequently, this results in mixer outputs that consist of several linear frequency modulation components with a small frequency rate (FR). The authors define an FR function to transform a signal from the time domain into the FR domain and discuss the FR range of a discrete signal. Then an interesting phenomenon is found in the FR domain, that is, the mixer output is concentrated in a low FR region, while the Gaussian noise spreads over the entire FR region. Therefore, a range‐spread target detector has been proposed that regards the integration of the values in a vicinity of zero FR as the test statistic. This detector uses a single mixer output and thus has the ability to detect the target with a high velocity. Finally, the proposed detector is evaluated by recorded radar data. Experimental results show that the proposed detector outperforms the detectors using the high‐resolution range profile.
Spin injection and diffusion in silicon based devices from a space charge layer
Authors: Ghosh Joydeep , Sverdlov Viktor , Windbacher Thomas , Selberherr Siegfried
Published: February 2014

We have performed simulations on electron spin transport in an n-doped silicon bar with spin-dependent conductivity with or without the presence of an external electric field. We further consider three cases like charge neutrality, charge accumulation, and charge depletion at one boundary and found substantial differences in the spin transport behavior. The criteria determining the maximum spin current are investigated. The physical reason behind the transport behavior is explained.
Exact solution of the thermodynamics and size parameters of a polymer confined to a lattice of finite size: Large chain limit
Authors: Snyder Chad R. , Guttman Charles M. , Di Marzio Edmund A.
Published: February 2014

We extend the exact solutions of the Di Marzio-Rubin matrix method for the thermodynamic properties, including chain density, of a linear polymer molecule confined to walk on a lattice of finite size. Our extensions enable (a) the use of higher dimensions (explicit 2D and 3D lattices), (b) lattice boundaries of arbitrary shape, and (c) the flexibility to allow each monomer to have its own energy of attraction for each lattice site. In the case of the large chain limit, we demonstrate how periodic boundary conditions can also be employed to reduce computation time. Advantages to this method include easy definition of chemical and physical structure (or surface roughness) of the lattice and site-specific monomer-specific energetics, and straightforward relatively fast computations. We show the usefulness and ease of implementation of this extension by examining the effect of energy variation along the lattice walls of an infinite rectangular cylinder with the idea of studying the changes in properties caused by chemical inhomogeneities on the surface of the box. Herein, we look particularly at the polymer density profile as a function of temperature in the confined region for very long polymers. One particularly striking result is the shift in the critical condition for adsorption due to surface energy inhomogeneities and the length scale of the inhomogeneities; an observation that could have important implications for polymer chromatography. Our method should have applications to both copolymers and biopolymers of arbitrary molar mass.
Quantum gates controlled by spin chain soliton excitations
Authors: Cuccoli Alessandro , Nuzzi Davide , Vaia Ruggero , Verrucchi Paola
Published: February 2014

Propagation of soliton-like excitations along spin chains has been proposed as a possible way for transmitting both classical and quantum information between two distant parties with negligible dispersion and dissipation. In this work, a somewhat different use of solitons is considered. Solitons propagating along a spin chain realize an effective magnetic field, well localized in space and time, which can be exploited as a means to manipulate the state of an external spin (i.e., a qubit) that is weakly coupled to the chain. We have investigated different couplings between the qubit and the chain, as well as different soliton shapes, according to a Heisenberg chain model. It is found that symmetry properties strongly affect the effectiveness of the proposed scheme, and the most suitable setups for implementing single qubit quantum gates are singled out.
Design and transient behavior of magnetic gears
Authors: Zheng Ping , Bai Jingang , Lin Jia , Fu Zhenxing , Song Zhiyi , Lin Fei
Published: February 2014

The torque density is a key factor for magnetic gears. To obtain maximum torque density, the design principle of magnetic gears is proposed and the maximum transmitting torque is investigated under different combinations of the inner and outer permanent magnets (PM) rotor pole pairs. The research proves that the maximum transmitting torque and the minimum torque ripple can be obtained only when the ratio of the outer and inner PM pole pair numbers is fractional. Then, the optimal selection of the span ratio and thickness of magnetic blocks in the stationary modulating ring is investigated to obtain the maximum torque. Meanwhile, analyses of the losses of various parts in the magnetic gear show that the loss of the PMs is about 70% of the total losses. Therefore, the method of dividing the PM into several pieces along the circumferential direction is employed to reduce the PM loss, which makes the PM loss reduced by 73%. Additionally, the transient behavior of the magnetic gear is analyzed, indicating that the lower torsional stiffness is the main reason for oscillations during transient changes in speed and load. To suppress oscillations due to transients, damper windings are employed and the transient time and the maximum oscillation amplitude are reduced by 25% and 20%, respectively.
Percolation theory and quantum critical systems: A new description of the critical behavior in Ce(Ru0.24Fe0.76)2Ge2
Authors: Gaddy John , Heitmann Tom , Montfrooij Wouter
Published: February 2014

The onset of ordering in quantum critical systems is characterized by a competition between the Kondo shielding of magnetic moments and the ordering of these moments. We show how a distribution of Kondo shielding temperatures—resulting from chemical doping—leads to critical behavior whose main characteristics are given by percolation physics. With the aid of Monte Carlo computer simulations, we are able to infer the low temperature part of the distribution of shielding temperatures in heavily doped quantum critical Ce(Ru0.24Fe0.76)2Ge2. Based on this distribution, we show that the ordering dynamics—such as the growth of the correlation length upon cooling—can be understood by the spawning of magnetic clusters. Our findings explain why the search for universal exponents in quantum critical systems has been unsuccessful: the underlying percolation network associated with the chemical doping of quantum critical systems has to be incorporated in the modeling of these quantum critical systems.
Structural and magnetic properties of irradiated SiC
Authors: Wang Yutian , Chen Xuliang , Li Lin , Shalimov Artem , Tong Wei , Prucnal Slawomir , Munnik Frans , Yang Zhaorong , Skorupa Wolfgang , Helm Manfred , Zhou Shengqiang
Published: February 2014

We present a comprehensive structural characterization of ferromagnetic SiC single crystals induced by Ne ion irradiation. The ferromagnetism has been confirmed by electron spin resonance, and possible transition metal impurities can be excluded to be the origin of the observed ferromagnetism. Using X-ray diffraction and Rutherford backscattering/channeling spectroscopy, we estimate the damage to the crystallinity of SiC, which mutually influences the ferromagnetism in SiC.
Investigating rare events with nonequilibrium work measurements. I. Nonequilibrium transition path probabilities
Authors: Moradi Mahmoud , Sagui Celeste , Roland Christopher
Published: February 2014

We have developed a formalism for investigating transition pathways and transition probabilities for rare events in biomolecular systems. In this paper, we set the theoretical framework for employing nonequilibrium work relations to estimate the relative reaction rates associated with different classes of transition pathways. Particularly, we derive an extension of Crook's transient fluctuation theorem, which relates the relative transition rates of driven systems in the forward and reverse directions, and allows for the calculation of these relative rates using work measurements (e.g., in Steered Molecular Dynamics). The formalism presented here can be combined with Transition Path Theory to relate the equilibrium and driven transition rates. The usefulness of this framework is illustrated by means of a Gaussian model and a driven proline dimer.
Sm2Fe17Nx nanoflakes prepared by surfactant assisted cryomilling
Authors: Zhang Songlin , Liu Lidong , Du Juan , Xia Weixing , Zhang Jian , Guo Zhaohui , Yan Aru , Li Wei , Ping Liu J.
Published: February 2014

Hard magnetic Sm2Fe17Nx nanoflakes were prepared by surfactant assisted ball milling (SABM) at low temperature using liquid nitrogen cooling (surfactant assisted cryomilling). 2-methyl pentane was used as a milling medium and oleylamine as a surfactant. The morphology, structure, and magnetic properties of Sm2Fe17Nx were investigated using scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer, respectively. By comparing Sm2Fe17Nx nanoflakes produced by SABM at low temperature and at room temperature, we found that the former has many interesting features: more homogeneous morphology, smaller size, especially markedly increased remanent magnetization (Mr), saturation magnetization (Ms), and remanent magnetization ratio (Mr/Ms). These Sm2Fe17Nx nanoflakes have great potential to be used for preparing high performance bonded permanent magnets.
Microstructure and properties of the composite magnets fabricated with Nd-Fe-B powders coated with CaF2
Authors: Zheng Liyun , Xin Honghui , Bi Wenchao , Zhu Minggang , Li Wei , Zhou Dong
Published: February 2014

Nd-Fe-B powders were coated with CaF2 by three different chemical synthesis methods, named as A: One-step direct precipitation, B: One-step slow dropping, and C: Two-step process. The CaF2-coated Nd-Fe-B powders were hot-pressed and then hot-deformed to fabricate composite magnets. The microstructures, electrical resistivities, and magnetic properties of the Nd-Fe-B composite magnets obtained with different coating methods and parameters were investigated. The results showed that the thickness and continuity of CaF2 coating depended on the coating methods with different Ca(NO3)2 concentrations and coating time. When the Ca(NO3)2 concentration was 2 mol/l, the CaF2 coating synthesized by one-step direct precipitation was a loose and discontinuous film, while the CaF2 coating synthesized by one-step dropping for 30 min was a continuous and dense film, and its thickness reached to 410–450 nm. If the Ca(NO3)2 concentration was further increased to 5.5 mol/l, the thickness of CaF2 reached to 710–900 nm. The electrical resistivities of the composite magnets prepared by one-step slow dropping for 30 min with the Ca(NO3)2 concentrations of 2 and 5.5 mol/l were approximately 680 and 890 μΩ cm, which was a 195% and 287% increase, respectively, compared to that of the corresponding magnet prepared with uncoated Nd-Fe-B powders. The coercivities of the composite magnets decreased with increasing thickness of CaF2, while the remanence had only a slight reduction. The composite magnet fabricated by a two-step process achieved both higher maximum energy product ((BH)m = 47.2 MG Oe) and electrical resistivity (847 μΩ cm).
Crossover from first-order to second-order phase transitions and magnetocaloric effect in La0.7Ca0.3Mn0.91Ni0.09O3
Authors: Phan The-Long , Zhang P. , Thanh T. D. , Yu S. C.
Published: February 2014

We have prepared La0.7Ca0.3Mn0.91Ni0.09O3 and then studied its critical behavior and magnetocaloric effect. Analyzing temperature and field dependences of magnetization around the ferromagnetic-paramagnetic transition reveals the sample undergoing the second-order magnetic phase transition with the critical parameters TC ≈ 199.4 K, β = 0.171 ± 0.006, and γ = 0.976 ± 0.012. A considerable difference of these critical exponents compared with those expected for the standard models is due to the sample exhibiting the crossover property (tricriticality); its exponent values are more close to those expected for the tricritical mean-field theory with β = 0.25 and γ = 1. Under the field 40 kOe, the maximum magnetic entropy change (−ΔSmax) around TC is about 7.1 J·kg−1·K−1, corresponding to a refrigerant capacity RC ≈ 170 J/kg. Particularly, its magnetic-field dependence obeys a power law |ΔSmax| ∝ Hn, where n = 0.55 is quite far from the value calculated from the relation n = 1 + (β − 1)/(β + γ).
3d-4f spin interaction and field-induced metamagnetism in RCrO4 (R = Ho, Gd, Lu) compounds
Authors: Midya A. , Khan N. , Bhoi D. , Mandal P.
Published: February 2014

We observe that the zircon-type RCrO4 (R = Ho, Gd, Lu) compounds exhibit complicated magnetic properties and large magnetic entropy change due to the strong competition between ferromagnetic and antiferromagnetic interactions. For a field change of 7 T, the maximum values of entropy change and refrigerant capacity reach 28 J kg−1 K−1 and 740 J kg−1, respectively, for GdCrO4 whereas the corresponding values for HoCrO4 are 29 J kg−1 K−1 and 550 J kg−1. For GdCrO4 compound, the magnetic entropy change is quite large even at low temperatures well below the ferromagnetic transition.
A simplified model of ferromagnetic sheets considering the magnetization dynamics utilizing the saturation wave model
Authors: Steentjes S. , Zirka S. E. , Moroz Y. I. , Moroz E. Y. , Hameyer K.
Published: February 2014

The usual skin effect observed in magnetically linear medium (μ = const.) is absent in a magnetically non-linear medium, leading to wrong predictions of the eddy current field using the classical approach. For this reason, this paper proposes a thin sheet model, improving the eddy current field description on the basis of physical ideas in the framework of the saturation wave model, which describes the dynamic magnetization of the material with rectangular hysteresis loop. Therewith, the layer-to-layer nature of the magnetization reversal is taken into account. The hysteresis is modeled by means of a static history-dependent hysteresis model. This leads to a simplified model of conducting ferromagnetic sheet, which describes magnetization of isotropic electrical steels.
Enhanced sensitivity in magnetoelectric current-sensing devices with frequency up-conversion mechanism by modulating the magnetostrictive strain
Authors: Zhang Jitao , Li Ping , Wen Yumei , He Wei , Yang Jin , Yang Aichao , Lu Caijiang , Li Wenli
Published: February 2014

A frequency-tunable current sensor consisting of Terfenol-D/PZT/Terfenol-D magnetoelectric (ME) laminate and Fe73.5Cu1Nb3Si13.5B9 nanocrystalline alloy has been developed. Almost all ME current-sensing devices have higher outputs at resonance conditions, but this advantage is useful only for narrow bandwidth. For the purpose of broadband current sensing, a frequency up-conversion mechanism is introduced by means of nonlinearity of the field-dependence magnetostriction λ(H). Current sensitivity enhancement is realized by modulating the low-frequency dynamic magnetostrictive strain to its resonance conditions. This solution provides the possibility to achieve resonance-enhanced sensitivity at the power-line frequency of 50 Hz, and the capability to immune the noise floor. Experimental results show that the modulated sensitivity is increased from 48.6 mV/A to 178.4 mV/A at 50 Hz, and a small current step change of 3 mA can be clearly distinguished by amplitude or phase of the output signals. These results provide possibilities to accurately detect weak currents in the noise ambient at low frequencies.
Control of domain wall pinning by switchable nanomagnet state
Authors: van Mourik R. A. , Rettner C. T. , Koopmans B. , Parkin S. S. P.
Published: February 2014

We report on a novel approach to establish switchable pinning of magnetic domain walls in a nanowire with perpendicular magnetic anisotropy by a single in-plane magnetized single-domain nanomagnet positioned on top of the wire. Devices were prepared by depositing a permalloy nanomagnet on top of a nanowire formed from a Co/Ni multilayer with their long axes parallel, separated by a nonmagnetic layer. We show by electrical measurements that the domain wall pinning strength depends critically on the state of the bistable nanomagnet and can differ by more than 10 mT. We also performed micromagnetic calculations that show that the difference in pinning strength is caused by the interaction of the forced Néel wall with the nanomagnet's magnetostatic field.
Analysis of unswitched grains in thermally assisted magnetic recording
Authors: Greaves Simon John , Muraoka Hiroaki , Kanai Yasushi
Published: February 2014

A simplified model of thermally assisted magnetic recording was used to study the influence of thermal gradients and the average grain size in recording media. The signal to noise ratio (SNR) peaked for thermal gradients between 10 and 20 K/nm and increased as the average grain size was reduced. However, the number of unswitched grains in written bits increased for smaller grains, limiting the increase in SNR. Exchange coupling decreased the probability of a grain remaining unswitched, but increased the magnetic cluster size, although the transition noise remained unaffected until the exchange coupling strength exceeded 0.8 erg/cm2.
Coexistence of considerable inter-particle interactions and spin-glass behavior in La0.7Ca0.3MnO3 nanoparticles
Authors: Thanh T. D. , Manh D. H. , Phan T. L. , Phong P. T. , Hung L. T. , Phuc N. X. , Yu S. C.
Published: February 2014

We have studied the magnetic and spin-glass (SG) properties of La0.7Ca0.3MnO3 single-crystalline nanoparticles, which were prepared by the mechanical milling method with different milling times (tm). Analyzing the susceptibility data in the paramagnetic region indicates both ferromagnetic (FM) and anti-FM interactions coexisting in nanoparticles. Additionally, there is a peak associated with the freezing temperature (Tf) appearing on the real part curve of the ac susceptibility, χ′(T). The Tf value increases with increasing frequency as expected for SG systems. The SG behavior was also checked by using the criterion parameter c = ΔTf/TfΔ(log10f), and the power law τ = τ0(T/Tg − 1)−zν. The obtained values of c ≈ 5 × 10−2, τ0 ≈ 10−5 s and zν ≈ 2–3 are consistent with those expected for SG-like systems, suggesting an existence of a SG phase transition at Tg below Tf, which decreases with decreasing ⟨D⟩. Basing on ln(f) versus Tf data, and the Néel-Arrhenius model [ln(f) = ln(f0) - Ea/kBT] and Vogel–Fulcher law [ln(f) = ln(f0) - Ea/kB(T - T0)], the Larmor frequency (f0), activation energy (Ea) and effective temperature (T0) for the samples with different ⟨D⟩ were determined. Obtained results indicate the existence a strong interaction between nanoparticles.
Torque analysis and measurements of a permanent magnet type Eddy current brake with a Halbach magnet array based on analytical magnetic field calculations
Authors: Park Min-Gyu , Choi Jang-Young , Shin Hyeon-Jae , Jang Seok-Myeong
Published: February 2014

This paper presents the torque analysis and measurements of a permanent magnet (PM) type eddy current brake (ECB) with a Halbach magnet array based on analytical magnetic field calculations. On the basis of a magnetic vector potential and using a two-dimensional (2D) polar coordinate system, the analytical solution for magnetic flux density, including the eddy current reaction is evaluated. Based on these solutions, the magnetic torque is also determined analytically. A 2D finite element analysis is employed to validate the method used. Practical issues in the analytical study of the PM type ECBs, such as the maximum braking torque, the required rotor speed, and the segment-dependent, are fully discussed. Finally, the braking torque as a function of the rotor speed is measured to verify the results of the analytical study.
Ferromagnetic resonance: Electrical detection vs conventional absorption measurements
Authors: Seinige H. , Wang C. , Tsoi M.
Published: February 2014

Ferromagnetic resonance (FMR) in point contacts to a soft CoSiBFeNb magnet is examined by three different techniques: electrical detection via rectification, power-absorption measurements, and time-resolved measurements of magnetization dynamics. The electrical detection is realized by taking advantage of the point contact as a nano-scale bolometer which monitors the microwave current absorbed by the sample. The power-absorption measurements exploit an external sensor to monitor the microwave absorption as a function of applied magnetic field. Finally, a high-bandwidth sampling oscilloscope allows for the time-resolved measurement of magnetization dynamics during FMR and provides the phase- and amplitude-characterization of FMR at 4-8 GHz. Simultaneous detection of the rectification signal, microwave absorption, and time-resolved microwaves allows for a direct comparison of the electrical detection and conventional FMR schemes. A good agreement between different FMR methods was found and the expected phase shift and amplitude variation for a driven resonance were confirmed.
Fine structure of the red luminescence band in undoped GaN
Authors: Reshchikov M. A. , Usikov A. , Helava H. , Makarov Yu.
Published: February 2014

Many point defects in GaN responsible for broad photoluminescence (PL) bands remain unidentified. Their presence in thick GaN layers grown by hydride vapor phase epitaxy (HVPE) detrimentally affects the material quality and may hinder the use of GaN in high-power electronic devices. One of the main PL bands in HVPE-grown GaN is the red luminescence (RL) band with a maximum at 1.8 eV. We observed the fine structure of this band with a zero-phonon line (ZPL) at 2.36 eV, which may help to identify the related defect. The shift of the ZPL with excitation intensity and the temperature-related transformation of the RL band fine structure indicate that the RL band is caused by transitions from a shallow donor (at low temperature) or from the conduction band (above 50 K) to an unknown deep acceptor having an energy level 1.130 eV above the valence band.
Enhanced magnetism and ferroelectricity in epitaxial Pb(Zr0.52Ti0.48)O3/CoFe2O4/La0.7Sr0.3MnO3 multiferroic heterostructures grown using dual-laser ablation technique
Authors: Mukherjee Devajyoti , Hordagoda Mahesh , Lampen Paula , Phan Manh-Huong , Srikanth Hariharan , Witanachchi Sarath , Mukherjee Pritish
Published: February 2014

PbZr0.52Ti0.48O3/CoFe2O4/La0.7Sr0.3MnO3 (PZT/CFO/LSMO) and PZT/LSMO heterostructures were grown on single-crystal MgO (100) substrates using the dual-laser ablation technique. X-ray diffraction confirmed the epitaxial relationship between the layers in the heterostructures. Magnetization measurements showed in-plane uniaxial magnetic anisotropy in PZT/CFO/LSMO with enhanced saturation magnetization of 288 emu/cm3 as compared to 244 emu/cm3 for PZT/LSMO. With the introduction of the hard magnetic CFO, the low coercivity of PZT/LSMO increased from 0.1 kOe to 1.4 kOe. Polarization measurements showed well-saturated square hysteresis loops for PZT/CFO/LSMO with enhanced remanent polarization (Pr) values of 69 μC/cm2 at a coercive field (Ec) of 88 kV/cm as compared to Pr = 51 μC/cm2 at Ec = 39 kV/cm for PZT/LSMO. The improved hard ferromagnetic and ferroelectric properties in PZT/CFO/LSMO as compared to PZT/LSMO make it desirable for multiferroic device applications.
Inkjet printing of magnetic materials with aligned anisotropy
Authors: Song Han , Spencer Jeremy , Jander Albrecht , Nielsen Jeffrey , Stasiak James , Kasperchik Vladek , Dhagat Pallavi
Published: February 2014

3-D printing processes, which use drop-on-demand inkjet printheads, have great potential in designing and prototyping magnetic materials. Unlike conventional deposition and lithography, magnetic particles in the printing ink can be aligned by an external magnetic field to achieve both high permeability and low hysteresis losses, enabling prototyping and development of novel magnetic composite materials and components, e.g., for inductor and antennae applications. In this work, we report an inkjet printing technique with magnetic alignment capability. Magnetic films with and without particle alignment are printed, and their magnetic properties are compared. In the alignment-induced hard axis direction, an increase in high frequency permeability and a decrease in hysteresis losses are observed. Our results suggest that unique magnetic structures with arbitrary controllable anisotropy, not feasible otherwise, may be fabricated via inkjet printing.
Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis
Authors: Zhang C. , Yamanouchi M. , Sato H. , Fukami S. , Ikeda S. , Matsukura F. , Ohno H.
Published: February 2014

We investigate in-plane current-induced magnetization reversal under an in-plane magnetic field in Hall bar shaped devices composed of Ta/CoFeB/MgO structures with perpendicular magnetic easy axis. The observed relationship between the directions of current and magnetization switching and Ta thickness dependence of magnetization switching current are accordance with those for magnetization reversal by spin transfer torque originated from the spin Hall effect in the Ta layer.
Poisson property of the occurrence of flip-flops in a model membrane
Authors: Arai Noriyoshi , Akimoto Takuma , Yamamoto Eiji , Yasui Masato , Yasuoka Kenji
Published: February 2014

How do lipid molecules in membranes perform a flip-flop? The flip-flops of lipid molecules play a crucial role in the formation and flexibility of membranes. However, little has been determined about the behavior of flip-flops, either experimentally, or in molecular dynamics simulations. Here, we provide numerical results of the flip-flops of model lipid molecules in a model membrane and investigate the statistical properties, using millisecond-order coarse-grained molecular simulations (dissipative particle dynamics). We find that there are three different ways of flip-flops, which can be clearly characterized by their paths on the free energy surface. Furthermore, we found that the probability of the number of the flip-flops is well fitted by the Poisson distribution, and the probability density function for the inter-occurrence times of flip-flops coincides with that of the forward recurrence times. These results indicate that the occurrence of flip-flops is a Poisson process, which will play an important role in the flexibilities of membranes.
Observation of spin-wave dispersion in Nd-Fe-B magnets using neutron Brillouin scattering
Authors: Ono K. , Inami N. , Saito K. , Takeichi Y. , Yano M. , Shoji T. , Manabe A. , Kato A. , Kaneko Y. , Kawana D. , Yokoo T. , Itoh S.
Published: February 2014

The low-energy spin-wave dispersion in polycrystalline Nd-Fe-B magnets was observed using neutron Brillouin scattering (NBS). Low-energy spin-wave excitations for the lowest acoustic spin-wave mode were clearly observed. From the spin-wave dispersion, we were able to determine the spin-wave stiffness constant Dsw (100.0 ± 4.9 meV.Å2) and the exchange stiffness constant A (6.6 ± 0.3 pJ/m).
Influence of lattice strain on charge/orbital ordering and phase separation in Pr0.7(Ca0.6Sr0.4)0.3MnO3 thin films
Authors: Zhao Y. Y. , Wang J. , Hu F. X. , Kuang H. , Wu R. R. , Zheng X. Q. , Sun J. R. , Shen B. G.
Published: February 2014

The static and dynamic lattice strain effects on the competition between ferromagnetic and charge/orbital ordering (COO) phase, phase separation (PS) and transport properties were studied in Pr0.7(Ca0.6Sr0.4)0.3MnO3 (PCSMO) films. It is found that the tensile strained films show pronounced percolative transport behaviors with increased hysteresis, indicating that the stability of the long-range COO is enhanced by the tensile strain. On the other hand, a nearly reversible insulator-metal transition was observed in the compressive strained films, suggesting a strong suppression of the long-range COO. The experiment of dynamic strain effect induced by the bias electric field further verifies the conclusion. Moreover, coactions of the ferroelectric polarization of the substrate and the dynamic strain effect on the PS were found in present PCSMO/PMN-PT film.
Magnetoelectric response of AlN/[(Fe90Co10)78Si12B10 + Terfenol-D] composite films
Authors: Tong Bei , Yang Xiaofei , Ouyang Jun , Lin Gengqi , Zhang Yue , Chen Shi
Published: February 2014

The magnetoelectric (ME) composite films composed of piezoelectric layer AlN film and new magnetostrictive layer [(Fe90Co10)78Si12B10 + Terfenol-D] films were successfully prepared by RF magnetron sputtering. The influence of bias magnetic field Hdc on ME response, as well as, the ac magnetic field sensitivity were investigated in detail. The results demonstrated that the respective magnetic properties of (Fe90Co10)78Si12B10 and Terfenol-D films are coupled in this new magnetostrictive layer, resulting in the fact that ME voltage coefficient αME reaches the maximum of 78.1 V/cm Oe and 77.5 V/cm Oe at the bias field of 11 Oe and 96 Oe, respectively. Meanwhile, the composite films display ac magnetic field sensitivity of 0.45 nT/√Hz and 0.47 nT/√Hz at Hdc of 11 Oe and 96 Oe, respectively. The results above indicate that the AlN/[(Fe90Co10)78Si12B10 + Terfenol-D] composite films exhibit a promising potential application in diverse range of magnetic field detection.
Phonon-magnon interactions in body centered cubic iron: A combined molecular and spin dynamics study
Authors: Perera Dilina , Landau David P. , Nicholson Don M. , Malcolm Stocks G. , Eisenbach Markus , Yin Junqi , Brown Gregory
Published: February 2014

Combining an atomistic many-body potential with a classical spin Hamiltonian parameterized by first principles calculations, molecular-spin dynamics computer simulations were performed to investigate phonon-magnon interactions in body centered cubic iron. Results obtained for spin-spin and density-density dynamic structure factors show that noticeable softening and damping of magnon modes occur due to the presence of lattice vibrations. Furthermore, as a result of the phonon-magnon coupling, additional longitudinal spin wave excitations are observed, with the same frequencies as the longitudinal phonon modes.
Negative remanent magnetization
Authors: Torre Edward Della , Bennett Lawrence H.
Published: February 2014

A new model to explore negative remanent magnetization is presented. Recently, a model for magnetic materials that have wasp-waist hysteresis loops was applied to a homogeneous thin film. This model postulated two interacting antiferromagnetically coupled media: one medium with low moment and relatively high coercivity, and one medium with a relatively high moment and low coercivity. This model is applicable to the situation where the "width" of the loop near zero is "negative." The major loop of such a material crosses itself, leading to negative remanent magnetization. The present paper introduces a new concept of a need for a third dimension to add to the usual magnetization versus applied field graph, demonstrates that there is no crossing, and discusses the nature of the losses in these materials.
$GL(3,\mathbb {C})$
G
L
(
3
,
C
)
invariance of type B 3-fold supersymmetric systems
Authors: Tanaka Toshiaki
Published: February 2014

Type B 3-fold supersymmetry is a necessary and sufficient condition for a quantum Hamiltonian to admit three linearly independent local solutions in closed form. We show that any such a system is invariant under \documentclass[12pt]{minimal}\begin{document}$GL(3,\mathbb {C})$\end{document}GL(3,C) homogeneous linear transformations. In particular, we prove explicitly that the parameter space is transformed as an adjoint representation of it and that every coefficient of the characteristic polynomial appeared in 3-fold superalgebra is algebraic invariants. In the type A case, it includes as a subgroup the \documentclass[12pt]{minimal}\begin{document}$GL(2,\mathbb {C})$\end{document}GL(2,C) projective transformation studied in the literature. We argue that any \documentclass[12pt]{minimal}\begin{document}$\mathcal {N}$\end{document}N-fold supersymmetric system has a \documentclass[12pt]{minimal}\begin{document}$GL(\mathcal {N},\mathbb {C})$\end{document}GL(N,C) invariance for an arbitrary integral \documentclass[12pt]{minimal}\begin{document}$\mathcal {N}$\end{document}N.
Microtransformer with closed Fe-Co magnetic core for high frequency power applications
Authors: Dinulovic Dragan , Kaiser Matthias , Gerfer Alexander , Opitz Oliver , Wurz Marc C. , Rissing Lutz
Published: February 2014

This paper presents a development of a microtransformer device fabricated using MEMS technology. The device is designed for higher switching frequencies beyond to 50 MHz power applications. The microtransformer features a closed magnetic core and six identity coils (three coils on primary and three coils on secondary side). Depending on connecting technique, this design allows a wide flexibility to set different values of inductance and of transformer winding ratio. As a magnetic core material Fe-Co alloy is applied, this device shows a significant improvement compared to the first fabricated prototypes with Ni-Fe magnetic core.
Optically promoted bipartite atomic entanglement in hybrid metallic carbon nanotube systems
Authors: Gelin M. F. , Bondarev I. V. , Meliksetyan A. V.
Published: February 2014

We study theoretically a pair of spatially separated extrinsic atomic type species (extrinsic atoms, ions, molecules, or semiconductor quantum dots) near a metallic carbon nanotube, that are coupled both directly via the inter-atomic dipole-dipole interactions and indirectly by means of the virtual exchange by resonance plasmon excitations on the nanotube surface. We analyze how the optical preparation of the system by using strong laser pulses affects the formation and evolution of the bipartite atomic entanglement. Despite a large number of possible excitation regimes and evolution pathways, we find a few generic scenarios for the bipartite entanglement evolution and formulate practical recommendations on how to optimize and control the robust bipartite atomic entanglement in hybrid carbon nanotube systems.
Erosion threshold of a liquid immersed granular bed by an impinging plane liquid jet
Authors: Badr Sarah , Gauthier Georges , Gondret Philippe
Published: February 2014

Erosion threshold of a model granular bed by a jet in a quasi bidimensional configuration has been studied experimentally in both laminar and turbulent regimes. The jet is a liquid sheet which impinges normally a packing of immersed beads monodisperse in size and density. The erosion threshold has been characterized at different impact distances of the jet on the sediment and for different grain size and fluid viscosity. In the explored range of parameters, we show that the erosion threshold is well described by a critical inertial Shields number based on the local flow velocity at the impinging point. This has been done by a careful analysis of the different jet flow regimes taking into account the position of the virtual origin of the jet.
Unveiling the hidden structure of complex stochastic biochemical networks
Authors: Valleriani Angelo , Li Xin , Kolomeisky Anatoly B.
Published: February 2014

Complex Markov models are widely used and powerful predictive tools to analyze stochastic biochemical processes. However, when the network of states is unknown, it is necessary to extract information from the data to partially build the network and estimate the values of the rates. The short-time behavior of the first-passage time distributions between two states in linear chains has been shown recently to behave as a power of time with an exponent equal to the number of intermediate states. For a general Markov model we derive the complete Taylor expansion of the first-passage time distribution between two arbitrary states. By combining algebraic methods and graph theory approaches it is shown that the first term of the Taylor expansion is determined by the shortest path from the initial state to the final state. When this path is unique, we prove that the coefficient of the first term can be written in terms of the product of the transition rates along the path. It is argued that the application of our results to first-return times may be used to estimate the dependence of rates on external parameters in experimentally measured time distributions.
Accurate and systematically improvable density functional theory embedding for correlated wavefunctions
Authors: Goodpaster Jason D. , Barnes Taylor A. , Manby Frederick R. , Miller Thomas F.
Published: February 2014

We analyze the sources of error in quantum embedding calculations in which an active subsystem is treated using wavefunction methods, and the remainder using density functional theory. We show that the embedding potential felt by the electrons in the active subsystem makes only a small contribution to the error of the method, whereas the error in the nonadditive exchange-correlation energy dominates. We test an MP2 correction for this term and demonstrate that the corrected embedding scheme accurately reproduces wavefunction calculations for a series of chemical reactions. Our projector-based embedding method uses localized occupied orbitals to partition the system; as with other local correlation methods, abrupt changes in the character of the localized orbitals along a reaction coordinate can lead to discontinuities in the embedded energy, but we show that these discontinuities are small and can be systematically reduced by increasing the size of the active region. Convergence of reaction energies with respect to the size of the active subsystem is shown to be rapid for all cases where the density functional treatment is able to capture the polarization of the environment, even in conjugated systems, and even when the partition cuts across a double bond.
Scale by scale anisotropy in freely decaying rotating turbulence
Authors: Delache Alexandre , Cambon Claude , Godeferd Fabien
Published: February 2014

We analyse the anisotropy present at different scales in rotating homogeneous turbulence. The Zeman wavenumber \documentclass[12pt]{minimal}\begin{document}$k_\Omega$\end{document}kΩ [O. Zeman, “A note on the spectra and decay of rotating homogeneous turbulence,” Phys. Fluids 6, 3221 (1994)] was introduced to quantify the effect of nonlinearity compared to the Coriolis force, and was proposed as a threshold to separate the anisotropic subrange, at scales \documentclass[12pt]{minimal}\begin{document}$k \ll k_\Omega$\end{document}k≪kΩ (largest scales), from the isotropic subrange at \documentclass[12pt]{minimal}\begin{document}$k \gg k_\Omega$\end{document}k≫kΩ. We study the nature of anisotropy and the role of the Zeman wavenumber using high resolution direct numerical simulations of freely decaying rotating turbulence, for various initial Rossby numbers. The anisotropy is analysed scale-by-scale by considering the angle-dependent energy spectrum, which characterizes directional anisotropy as a tendency to selectively accumulate energy towards the transverse waveplane k∥ = 0. This ring-to-ring anisotropy is shown to develop in a non-monotonic way from small to large wavenumbers, first increasing, then decreasing. The Zeman wavenumber appears to be a suitable scale for estimating the separation between anisotropic and isotropic ranges. Consistently, when \documentclass[12pt]{minimal}\begin{document}$k_\Omega$\end{document}kΩ is larger than the dissipative wavenumber cut-off, even the smallest scales are significantly anisotropic. This situation occurs eventually in our simulations of freely decaying turbulence, and is also observed in recent experimental results. Our investigation of anisotropy is completed by analyzing the angle-dependent nonlinear energy transfer and separate poloidal and toroidal energy spectra. The excess of poloidal energy in the equatorial plane k∥ = 0 is linked with more energetic vertical motion.
Effect of an external electric field on the diffusion-influenced geminate reversible reaction of a neutral particle and a charged particle in three dimensions. IV. Excited-state ABCD reaction
Authors: Reigh Shang Yik
Published: February 2014

In the presence of an external electric field, an excited-state \documentclass[12pt]{minimal}\begin{document}$A+B^{*q} \rightleftharpoons C^{*q}+D$\end{document}A+B*q⇌C*q+D diffusion-influenced geminate reversible reaction of a neutral particle and a charged particle, with two unimolecular decay rates and contact quenching processes, is investigated in three dimensions. The probability density functions to find individual particles, rates of reactions, and survival probabilities are analytically derived in the Laplace domain and the long-time kinetics is resolved. The probability density functions to find the particles and the rates of reactions in a scaled form exhibit a kinetic transition behavior from a t−3/2 power law to t−3/2et increase with the increase of external fields. The scaled survival probabilities present a kinetic transition behavior of t−3/2 → constant → exponential with the increase of field strengths. The critical fields are found to determine the kinetic transition behaviors.