Investigation of the photothermally modulated ferromagnetic resonance signal from magnetostatic modes in yttrium iron garnet films

The conventional and photothermally modulated (PM) ferromagnetic resonance (FMR) of magnetostatic modes (MSM) in yttrium iron garnet (YIG) films have been investigated as a function of temperature. Approaching the ferrimagnetic transition at T _c=560 K a strong enhancement of the PM-FMR signal amplitude is observed which is accompanied by a change of the signal shape. The observations are discussed in the framework of a model that takes into account the temperature derivatives of those quantities that contribute to the high-frequency susceptibility. At temperatures still below T _c a paramagnetic line emerges. The MSM disappear in a state of finite magnetization which is explained on the basis of damping of the MSM being important in the vicinity of the magnetic phase transition. Additionally, frequency and power dependent measurements are presented and the imaging ability of PM-FMR is demonstrated.     

SEWDarkM

A number of observed phenomena in high energy physics and cosmology lack their resolution within the Standard Model of particle physics. These puzzles include neutrino oscillations, baryon asymmetry of the Universe, existence of Dark Matter and inflation. We discuss the suggestion, based on the νMSM (an extension of the Standard Model by three light singlet fermions) that all these problems can be solved by new physics which exists only below the electroweak scale. We describe the formalism which allows to compute from first principles of quantum field theory and statistical physics the abundance of dark matter in this theory. Predictions of the νMSM are compared with results of different cosmological and astrophysical observations.     

Analytical representations for the radial distribution functions of mixtures of adhesive spheres

A study has been made of the pole topology of the Laplace transforms of the pair distribution functions (PDFs) of a binary mixture of adhesive hard spheres (AHS) both for the Percus-Yevick equation and the mean spherical model (MSM). Expressions are given that describe how the distribution of the poles in the left half of the complex plane varies with the system parameters for the special case of the MSM for symmetric binary AHS mixtures. The locations of the poles closest to the imaginary axis are known to determine the asymptotic form of the PDFs, i.e. either exponentially monotonic or exponentially oscillatory decaying. As a byproduct of this inquiry analytical r space representations of the PDFs are derived that allow their accurate and efficient determination over the entire r range.     

Fraction‐Dimensional Accessible Solitons in a Parity‐Time Symmetric Potential

By using the modified Snyder‐Mitchell (MSM) model, which can describe the propagation of a paraxial beam in fractional dimensions (FDs), we find the exact "accessible soliton” solutions in the strongly nonlocal nonlinear media with a self‐consistent parity‐time (PT) symmetric complex potential. The exact solutions are constructed with the help of two special functions: the complex Gegenbauer and the generalized Laguerre polynomials in polar coordinates, parametrized by two nonnegative integer indices ‐ the radial and azimuthal mode numbers (n,m), and the beam modulation depth. By the choice of different soliton parameters, the intensity and angular profiles display symmetric and asymmetric structures. We believe that it is important to explore the MSM model in FDs and PT‐symmetric potentials, for a better understanding of nonlinear FD physical phenomena. Different physical systems in which the model might be of relevance are briefly discussed.     

Tensile properties of microtubules: A study by nonlinear molecular structural mechanics modelling

A nonlinear molecular structural mechanics (MSM) model is proposed in this paper for studying the tensile properties of microtubules (MTs). In the nonlinear MSM models, the interactions between tubulin monomers in MTs are treated as nonlinear axial and torsional springs, whose stiffness coefficients are extracted from all-atom molecular dynamics simulations. The Young's modulus and fracture properties of MTs under tension extracted from the present nonlinear MSM models are found to agree well with the existing simulation and experiment results, which shows the efficiency and accuracy of the proposed nonlinear MSM models. In addition, the nonlinear MSM models are also extended to investigate the tensile properties including Young's modulus and fracture strain of MTs possessing lattice defects. The results obtained from nonlinear MSM models are utilized to develop a predictive equation for quickly predicting the tensile properties of MTs with different lattice defect levels.     

High‐gain Zn1–xMgx O‐based ultraviolet photodetectors on Al2O3 and LiGaO2 substrates

We report the fabrication and characterization of highly responsive ZnMgO‐based ultraviolet (UV) photodetectors in the metal–semiconductor–metal (MSM) configuration for solar‐blind/visible‐blind optoelectronic application. MSM devices were fabricated from wurtzite Zn_1–xMg_x O/ZnO (x ～ 0.44) thin‐film heterostructures grown on sapphire (α‐Al₂O₃) substrates and w‐Zn_1–xMg_x O (x ～ 0.08), grown on nearly lattice‐matched lithium gallate (LiGaO₂) substrates, both by radio‐frequency plasma‐assisted molecular beam epitaxy (PAMBE). Thin film properties were studied by AFM, XRD, and optical transmission spectra, while MSM device performance was analyzed by spectral photoresponse and current–voltage techniques. Under biased conditions, α‐Al₂O₃ grown devices exhibit peak responsivity of ～7.6 A/W at 280 nm while LiGaO₂ grown samples demonstrate peak performance of ～119.3 A/W, albeit in the UV‐A regime (～324 nm). High photoconductive gains (76, 525) and spectral rejection ratios (～10³, ～10⁴) were obtained for devices grown on α‐Al₂O₃ and LiGaO₂, respectively. Exemplary device performance was ascribed to high material quality and in the case of lattice‐matched LiGaO₂ films, decreased photocarrier trapping probability, presumably due to low‐density of dislocation defects. To the best of our knowledge, these results represent the highest performing ZnO‐based photodetectors on LiGaO₂ yet fabricated, and demonstrate both the feasibility and substantial enhancement of photodetector device performance via growth on lattice‐matched substrates. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Insight into 3D micro‐CT data: exploring segmentation algorithms through performance metrics

Three‐dimensional (3D) micro‐tomography (µ‐CT) has proven to be an important imaging modality in industry and scientific domains. Understanding the properties of material structure and behavior has produced many scientific advances. An important component of the 3D µ‐CT pipeline is image partitioning (or image segmentation), a step that is used to separate various phases or components in an image. Image partitioning schemes require specific rules for different scientific fields, but a common strategy consists of devising metrics to quantify performance and accuracy. The present article proposes a set of protocols to systematically analyze and compare the results of unsupervised classification methods used for segmentation of synchrotron‐based data. The proposed dataflow for Materials Segmentation and Metrics (MSM) provides 3D micro‐tomography image segmentation algorithms, such as statistical region merging (SRM), k‐means algorithm and parallel Markov random field (PMRF), while offering different metrics to evaluate segmentation quality, confidence and conformity with standards. Both experimental and synthetic data are assessed, illustrating quantitative results through the MSM dashboard, which can return sample information such as media porosity and permeability. The main contributions of this work are: (i) to deliver tools to improve material design and quality control; (ii) to provide datasets for benchmarking and reproducibility; (iii) to yield good practices in the absence of standards or ground‐truth for ceramic composite analysis.     

Cantor–Bernstein Theorem for Pseudo-BCK-Algebras

We prove that if A and B are orthogonally σ-complete commutative pseudo-BCK-algebras such that A is isomorphic to a direct factor in B, and also B is isomorphic to a direct factor in A, then A and B are isomorphic. As a consequence we obtain previously known results for MV-algebras (by De Simone, Mundici and Navara), pseudo-MV-algebras (by Jakubík) and lattice-ordered groups (again by Jakubík). Supported by the Research and Development Council of the Czech Government, the research project MSM 6198959214.     

Optimization of reversible LPFG for sensing application

We report here for the first time to our knowledge the characterization of mechanically induced long period fiber gratings in novel MSM fiber structure. Reversible grating of same period and length was induced in single mode fiber, multimode fiber and novel multimode-singlemode-multimode (MSM) fiber structure. The spectral response of reversible LPFG in SMF is verified experimentally as well as from simulation results and then compared with the experimental spectral response of reversible LPFG in multimode fiber and MSM fiber structure. Reversible LPFG in novel MSM fiber structure is the most optimized and suitable grating for sensing application. For this grating we have obtained single resonant wavelength over a wide wavelength range and maximum transmission loss peak of around 20 dB.     

AlGaN-based high-performance metal–semiconductor–metal photodetectors

Design, structure growth, fabrication, and characterization of high performance AlGaN-based metal–semiconductor–metal (MSM) photodetectors (PD) are reported. By incorporating AlN nucleation and buffer layers, the leakage current density of GaN MSM PD was reduced to 1.96 × 10⁻¹⁰ A/cm² at a 50 V bias, which is four orders of magnitude lower compared to control devices. A 229 nm cut-off wavelength, a peak responsivity of 0.53 A/W at 222 nm, and seven orders of magnitude visible rejection was obtained from Al_0.75Ga_0.25N MSM PD. Two-color monolithic AlGaN MSM PD with excellent dark current characteristics were demonstrated, where both detectors reject the other detector spectral band with more than three orders of magnitude. High-speed measurements of Al_0.38Ga_0.62N MSM PD resulted in fast responses with greater than gigahertz bandwidths, where the fastest devices had a 3-dB bandwidth of 5.4 GHz.     

Searches for heavy neutrinos in the decays of positively charged kaons

According to predictions of the νMSM model, a heavy neutrino may exist in the mass range below 1 GeV. Searches for rare kaon decays make it possible to study the heavy-neutrino-mass range M _π < m _{ν H} < M _K . A preliminary analysis of data from the E949 experiment performed at the Brookhaven National Laboratory (BNL, USA) is performed in the present study. Basic background processes are studied, and it is shown that a sensitivity at a level of 4 × 10⁻⁸ to the K ⁺ → μ⁺ ν _H branching ratio can be reached for the mass value of m _{ν H} = 250 MeV.     

Giant magnetostrain based on strong single ion anisotropy of rare earth materials

The volume, shape and microstructure of solids can be influenced by magnetic fields. Much effort is focused on magnetic shape memory (MSM) materials. Recently, the MSM effect has been discovered to occur also in the paramagnetic state, e.g. in RCu₂ compounds (R = rare earth). RMSM materials distinguish themselves from conventional MSM materials by the new origin of the magnetoic anisotropy: the strong rare-earth single ion anisotropy. Due to the pseudo-hexagonal symmetry of RCu₂, three orientational variants exists, each of them rotated by about 60 deg with respect to the others. Switching these variants by an external field results in a change of the macroscopic shape. The strain is in the order of one percent (= Giant MagnetoStrain). The variant's fraction remains unchanged when ramping down the field. The virgin state can be recovered by heating or by a perpendicularly directed field. We present temperature and field dependent measurements of magnetostrain and magentization at the model substance Tb_0.5Dy_0.5Cu₂. The macroscopic characterization of the sample is complemented by a detailed microscopic analysis done by elastic neutron scattering. Although the GMS effect of RCu₂ was worked out at single crystals, the principle of this magneto-mechanical coupling phenomenon is also useful for polycrystalline or microscaled applications. The existence of this structural irreversibility shows the potential to construct field controlled actuators or switches.     

Mean spherical model for the square-well potential

The mean spherical model (MSM) equation has been solved for the aquare-well potential. Comparison of the MSM results with the simulation results shows the MSM radial distribution function and energy to be satisfactory in the liquid states.     

Synthesis and electrical characterization of tungsten oxide nanowires

Tungsten oxide nanowires of diameters ranging from 7 to 200~nm are prepared on a tungsten rod substrate by using the chemical vapour deposition (CVD) method with vapour--solid (VS) mechanism. Tin powders are used to control oxygen concentration in the furnace, thereby assisting the growth of the tungsten oxide nanowires. The grown tungsten oxide nanowires are determined to be of crystalline W₁₈O₄₉. I--V curves are measured by an \textit{in situ} transmission electron microscope (TEM) to investigate the electrical properties of the nanowires. All of the I--V curves observed are symmetric, which reveals that the tungsten oxide nanowires are semiconducting. Quantitative analyses of the experimental I--V curves by using a metal--semiconductor--metal (MSM) model give some intrinsic parameters of the tungsten oxide nanowires, such as the carrier concentration, the carrier mobility and the conductivity.     

Hybrid Integration of 1 × 12 Metal-Semiconductor-Metal Photodetector and Polyimide Waveguide Array

We report here a demonstration of hybrid integration of a 1 × 12 metal-semiconductor-metal (MSM) photodetector array and polyimide channel waveguides via 45° total-internal-reflection (TIR) micro-couplers. The two-layer polyimide waveguide array was constructed using Ultradel 9120D for the core and Ultradel 9020 for the lower cladding layer. The coupling loss and propagation loss of the waveguide are 0.2dB and 0.21 dB/cm, respectively. The cross talk of the adjacent channels is -32 dB. The MSM photodetector array was fabricated on a semi-insulated GaAs wafer. The photodetectors are integrated to operate in the conventional vertical illumination mode. We measured the external quantum-efficiency and 3 dB bandwidth of the integrated MSM photodetectors at 0.4 A/W and 2.648 GHz, respectively. The aggregate 3 dB bandwidth of the 12-channel integrated system is 32 GHz.     

Technology and characterisation of GaAsN/GaAs heterostructures for photodetector applications

The nitrogen-containing conventional A^IIIB^V semiconductor alloys, so-called diluted nitrides (A^IIIB^V-N), have been extensively studied recently. Unusual properties of these materials make them very promising for applications in lasers and very efficient multijunction solar cells. This work presents the technology and properties of undoped GaAs_1-xN_x/GaAs heterostructures used as active regions in the construction of metal-semiconductor-metal (MSM) photodetectors. The atmospheric pressure metal organic vapour phase epitaxy (APMOVPE) was applied for growing MSM test structures. Their structural and optical properties were examined using high resolution X-ray diffraction (HRXRD), photoluminescence (PL), and photoreflectance spectroscopy (PR). Chemical wet etching was applied for forming an active region and a multifinger Schottky metallization was used as MSM contacts. Dark and illuminated current-voltage characteristics were measured. Based on the obtained results, the main detector parameters as responsivity and spectral response were estimated     

Plasmonic modulator based on gain-assisted metal–semiconductor–metal waveguide

We investigate plasmonic modulators with gain material to be implemented as ultra-compact and ultra-fast active nanodevices in photonic integrated circuits. We analyze metal–semiconductor–metal (MSM) waveguides with InGaAsP-based active material layers as ultra-compact plasmonic modulators. The modulation is performed by changing the gain of the core, that results in different transmittance through the waveguides. A MSM waveguide enables high field localization and therefore high modulation speed. Bulk semiconductor, quantum wells and quantum dots, arranged in either horizontal or vertical layout, are considered as the core of the MSM waveguide. Dependences on the waveguide core size and gain values of various active materials are studied. The designs consider also practical aspects like n- and p-doped layers and barriers in order to obtain close to reality results. The effective propagation constants in the MSM waveguides are calculated numerically. Their changes in the switching process are considered as a figure of merit. We show that a MSM waveguide with electrical current control of the gain incorporates compactness and deep modulation along with having a reasonable level of transmittance.     

Manufacturing technology for the fabrication a discrete actuator using a magnetic shape memory alloy

To demonstrate the feasibility of combining thin-film fabrication techniques and discrete MSM stripes, a hybrid actuator system was designed. The actuator system consists of four thin-film stators and two discrete MSM stripes mounted in a row. For creating an actuator motion, one of the MSM stripes has to be excited by a pair of stators to cause variant switching. This results in an elongation plus a compression of the second stripe and vice versa. The technologies required for fabricating the thin-film stator are sputter deposition, PECVD, electroplating, etching, and photolithography. This paper describes the fabrication process for a thin-film stator used for the MSM micro actuator system. It also presents technology study results indicating the feasibility of the planned fabrication sequence.     

All-fiber optic acoustic sensor based on multimode-single mode-multimode structure

A simple and low cost optical fiber acoustic sensor based on multimode-single mode-multimode (MSM) fiber structure is presented. The optical coupling efficiency between hetero-core fibers spliced structure is modulated by acoustic pressure through a thin metal foil. Acoustic wave is detected by measuring the intensity change of transmission light. Experiments are carried on to testify the performance of MSM fiber acoustic sensor and the experimental results show that the acoustic wave can be sensitively detected within 11 kHz frequency range.