bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear interaction and wave breaking with a submerged porous structure
Authors: Hsieh Chih-Min , Sau Amalendu , Hwang Robert R. , Yang W. C.
Published: December 2016

Numerical simulations are performed to investigate interactive velocity, streamline, turbulent kinetic energy, and vorticity perturbations in the near-field of a submerged offshore porous triangular structure, as Stokes waves of different heights pass through. The wave-structure interaction and free-surface breaking for the investigated flow situations are established based on solutions of 2D Reynolds Averaged Navier-Stokes equations in a Cartesian grid in combination with K-ε turbulent closure and the volume of fluid methodology. The accuracy and stability of the adopted model are ascertained by extensive comparisons of computed data with the existing experimental and theoretical findings and through efficient predictions of the internal physical kinetics. Simulations unfold “clockwise” and “anticlockwise” rotation of fluid below the trough and the crest of the viscous waves, and the penetrated wave energy creates systematic flow perturbation in the porous body. The interfacial growths of the turbulent kinetic energy and the vorticity appear phenomenal, around the apex of the immersed structure, and enhanced significantly following wave breaking. Different values of porosity parameter and two non-porous cases have been examined in combination with varied incident wave height to reveal/analyze the nonlinear flow behavior in regard to local spectral amplification and phase-plane signatures. The evolution of leading harmonics of the undulating free-surface and the vertical velocity exhibits dominating roles of the first and the second modes in inducing the nonlinearity in the post-breaking near-field that penetrates well below the surface layer. The study further suggests the existence of a critical porosity that can substantially enhance the wave-shoaling and interface breaking.
Advanced methodology for measuring the extensive elastic compliance and mechanical loss directly in k31 mode piezoelectric ceramic plates
Authors: Majzoubi Maryam , Shekhani Husain N. , Bansal Anushka , Hennig Eberhard , Scholehwar Timo , Uchino Kenji
Published: December 2016

Dielectric, elastic, and piezoelectric constants, and their corresponding losses are defined under constant conditions of two categories; namely, intensive (i.e., E, electric field or T, stress), and extensive (i.e., D, dielectric displacement or x, strain) ones. So far, only the intensive parameters and losses could be measured directly in a k31 mode sample. Their corresponding extensive parameters could be calculated indirectly using the coupling factor and “K” matrix. However, the extensive loss parameters, calculated through this indirect method, could have large uncertainty, due to the error propagation in calculation. In order to overcome this issue, extensive losses should be measured separately from the measurable intensive ones in lead-zirconate-titanate (PZT) k31 mode rectangular plate ceramics. We propose a new mechanical-excitation methodology, using a non-destructive testing approach by means of a partial electrode configuration, instead of the conventional full electrode configuration. For this purpose, a non-electrode sample was prepared, where the electrode covered only 10% of the top and bottom surfaces at the center to actuate the whole sample, and also monitor the responding vibration. The admittance spectrum of this sample, corresponds to PZT properties under dielectric displacement D constant condition. Furthermore, ceramics with partial-electrodes were also prepared to create short and open circuit boundary conditions, attributing to resonance and anti-resonance modes. In the proposed way, we were able to measure both intensive and extensive elastic compliances and mechanical losses directly for the first time. The accuracy of this new method is compared with the conventional measurements by use of indirect calculations. The preliminary results (by neglecting the 10% actuator part difference at this point) were obtained, which were in good agreements (less than 3% difference) with the previous indirect method.
Experimental and density functional study of Mn doped Bi2Te3 topological insulator
Authors: Ghasemi A. , Kepaptsoglou D. , Figueroa A. I. , Naydenov G. A. , Hasnip P. J. , Probert M. I. J. , Ramasse Q. , van der Laan G. , Hesjedal T. , Lazarov V. K.
Published: December 2016

We present a nanoscale structural and density functional study of the Mn doped 3D topological insulator Bi2Te3. X-ray absorption near edge structure shows that Mn has valency of nominally 2+. Extended x-ray absorption fine structure spectroscopy in combination with electron energy loss spectroscopy (EELS) shows that Mn is a substitutional dopant of Bi and Te and also resides in the van der Waals gap between the quintuple layers of Bi2Te3. Combination of aberration-corrected scanning transmission electron microscopy and EELS shows that Mn substitution of Te occurs in film regions with increased Mn concentration. First-principles calculations show that the Mn dopants favor octahedral sites and are ferromagnetically coupled.
Optimized tomography methods for plasma emissivity reconstruction at the ASDEX Upgrade tokamak
Authors: Odstrčil T. , Pütterich T. , Odstrčil M. , Gude A. , Igochine V. , Stroth U. ,   ASDEX Upgrade Team
Published: December 2016

The soft X-ray (SXR) emission provides valuable insight into processes happening inside of high-temperature plasmas. A standard method for deriving the local emissivity profiles of the plasma from the line-of-sight integrals measured by pinhole cameras is the tomographic inversion. Such an inversion is challenging due to its ill-conditioned nature and because the reconstructed profiles depend not only on the quality of the measurements but also on the inversion algorithm used. This paper provides a detailed description of several tomography algorithms, which solve the inversion problem of Tikhonov regularization with linear computational complexity in the number of basis functions. The feasibility of combining these methods with the minimum Fisher information regularization is demonstrated, and various statistical methods for the optimal choice of the regularization parameter are investigated with emphasis on their reliability and robustness. Finally, the accuracy and the capability of the methods are demonstrated by reconstructions of experimental SXR profiles, featuring poloidal asymmetric impurity distributions as measured at the ASDEX Upgrade tokamak.
S2DS: Physics-based compact model for circuit simulation of two-dimensional semiconductor devices including non-idealities
Authors: Suryavanshi Saurabh V. , Pop Eric
Published: December 2016

We present a physics-based compact model for two-dimensional (2D) field-effect transistors (FETs) based on monolayer semiconductors such as MoS2. A semi-classical transport approach is appropriate for the 2D channel, enabling simplified analytical expressions for the drain current. In addition to intrinsic FET behavior, the model includes contact resistance, traps and impurities, quantum capacitance, fringing fields, high-field velocity saturation, and self-heating, the latter being found to play an important role. The model is calibrated with state-of-the-art experimental data for n- and p-type 2D-FETs, and it can be used to analyze device properties for sub-100 nm gate lengths. Using the experimental fit, we demonstrate the feasibility of circuit simulations using properly scaled devices. The complete model is implemented in SPICE-compatible Verilog-A, and a downloadable version is freely available at the nanoHUB.org.
Optical properties of azobenzene-functionalized self-assembled monolayers: Intermolecular coupling and many-body interactions
Authors: Cocchi Caterina , Moldt Thomas , Gahl Cornelius , Weinelt Martin , Draxl Claudia
Published: December 2016

In a joint theoretical and experimental work, the optical properties of azobenzene-functionalized self-assembled monolayers (SAMs) are studied at different molecular packing densities. Our results, based on density-functional and many-body perturbation theory, as well as on differential reflectance (DR) spectroscopy, shed light on the microscopic mechanisms ruling photo-absorption in these systems. While the optical excitations are intrinsically excitonic in nature, regardless of the molecular concentration, in densely packed SAMs intermolecular coupling and local-field effects are responsible for a sizable weakening of the exciton binding strength. Through a detailed analysis of the character of the electron-hole pairs, we show that distinct excitations involved in the photo-isomerization at low molecular concentrations are dramatically broadened by intermolecular interactions. Spectral shifts in the calculated DR spectra are in good agreement with the experimental results. Our findings represent an important step forward to rationalize the excited-state properties of these complex materials.
Optical emission spectroscopy of deuterium and helium plasma jets emitted from plasma focus discharges at the PF-1000U facility
Authors: Skladnik-Sadowska E. , Dan'ko S. A. , Kwiatkowski R. , Sadowski M. J. , Zaloga D. R. , Paduch M. , Zielinska E. , Kharrasov A. M. , Krauz V. I.
Published: December 2016

Optical emission spectroscopy techniques were used to investigate the spectra of dense deuterium-plasma jets generated by high-current pulse discharges within the large PF-1000U facility and to estimate parameters of plasma inside the jets and their surroundings. Time-resolved optical spectra were recorded by means of a Mechelle®900 spectrometer. From an analysis of the deuterium line broadening, it was estimated that the electron concentration at a distance 57 cm from the electrode outlets amounted to (0.4–3.7) × 1017 cm−3 depending on the initial gas distribution and the time interval of the spectrum registration after the instant of the plasma jet generation. From the re-absorption dip in the Dβ profile, it was assessed that the electron concentration in the surrounding gas was equal to about 1.5 × 1015 cm−3. On the basis of the measured ratio of He II 468.6 nm and He I 587.6 nm line intensities, it was estimated that the electron temperature amounted to about 5.3 eV. Also estimated were some dimensionless parameters of the investigated plasma jets.
Outstanding performance of configuration interaction singles and doubles using exact exchange Kohn-Sham orbitals in real-space numerical grid method
Authors: Lim Jaechang , Choi Sunghwan , Kim Jaewook , Kim Woo Youn
Published: December 2016

To assess the performance of multi-configuration methods using exact exchange Kohn-Sham (KS) orbitals, we implemented configuration interaction singles and doubles (CISD) in a real-space numerical grid code. We obtained KS orbitals with the exchange-only optimized effective potential under the Krieger-Li-Iafrate (KLI) approximation. Thanks to the distinctive features of KLI orbitals against Hartree-Fock (HF), such as bound virtual orbitals with compact shapes and orbital energy gaps similar to excitation energies; KLI-CISD for small molecules shows much faster convergence as a function of simulation box size and active space (i.e., the number of virtual orbitals) than HF-CISD. The former also gives more accurate excitation energies with a few dominant configurations than the latter, even with many more configurations. The systematic control of basis set errors is straightforward in grid bases. Therefore, grid-based multi-configuration methods using exact exchange KS orbitals provide a promising new way to make accurate electronic structure calculations.
High ionic conductivity in confined bismuth oxide-based heterostructures
Authors: Sanna Simone , Esposito Vincenzo , Christensen Mogens , Pryds Nini
Published: December 2016

Bismuth trioxide in the cubic fluorite phase (δ-Bi2O3) exhibits the highest oxygen ionic conductivity. In this study, we were able to stabilize the pure δ-Bi2O3 at low temperature with no addition of stabilizer but only by engineering the interface, using highly coherent heterostructures made of alternative layers of δ-Bi2O3 and Yttria Stabilized Zirconia (YSZ), deposited by pulsed laser deposition. The resulting [δ-Bi2O3/YSZ] heterostructures are found to be stable over a wide temperature range (500-750 °C) and exhibits stable high ionic conductivity over a long time comparable to the value of the pure δ-Bi2O3, which is approximately two orders of magnitude higher than the conductivity of YSZ bulk.
Synthesis of low-moment CrVTiAl: A potential room temperature spin filter
Authors: Stephen G. M. , McDonald I. , Lejeune B. , Lewis L. H. , Heiman D.
Published: December 2016

The efficient production of spin-polarized currents at room temperature is fundamental to the advancement of spintronics. Spin-filter materials—semiconductors with unequal band gaps for each spin channel—can generate spin-polarized current without the need for spin-polarized contacts. In addition, a spin-filter material with zero magnetic moment would have the advantage of not producing strong fringing fields that would interfere with neighboring electronic components and limit the volume density of devices. The quaternary Heusler compound CrVTiAl has been predicted to be a zero-moment spin-filter material with a Curie temperature in excess of 1000 K. In this work, CrVTiAl has been synthesized with a lattice constant of a = 6.15 Å. Magnetization measurements reveal an exceptionally low moment of μ = 2.3 × 10−3 μB/f.u. at a field of μ0H = 2 T that is independent of temperature between T = 10 K and 400 K, consistent with the predicted zero-moment ferrimagnetism. Transport measurements reveal a combination of metallic and semiconducting components to the resistivity. Combining a zero-moment spin-filter material with nonmagnetic electrodes would lead to an essentially nonmagnetic spin injector. These results suggest that CrVTiAl is a promising candidate for further research in the field of spintronics.
Note: Stability control of intermediate frequencies of a three laser far-infrared polarimeter-interferometer system
Authors: Yu Jiang-Tao , Li He-Ping , Nie Qiu-Yue , Zou Zhi-Yong , Liu Hai-Qing , Bao Cheng-Yu , Jie Yin-Xian , Li Zhan-Xian
Published: December 2016

Stability of the intermediate frequency (IF) in the far-infrared polarimeter-interferometer diagnostic system is critically important for the long pulse discharge experiments on the EAST tokamak. In this note, a real-time remote/local IF stability control system is described. The measured plasma parameters, including the Faraday rotation angle, electron density, lower hybrid wave, and plasma current, are obtained with the aid of this newly developed IF stability control system.
Coupled jump rotational dynamics in aqueous nitrate solutions
Authors: Banerjee Puja , Yashonath Subramanian , Bagchi Biman
Published: December 2016

A nitrate ion (NO3−) with its trigonal planar geometry and charges distributed among nitrogen and oxygen atoms can couple to the extensive hydrogen bond network of water to give rise to unique dynamical characteristics. We carry out detailed atomistic simulations and theoretical analyses to investigate these aspects and report certain interesting findings. We find that the nitrate ions in aqueous potassium nitrate solution exhibit large amplitude rotational jump motions that are coupled to the hydrogen bond rearrangement dynamics of the surrounding water molecules. The jump motion of nitrate ions bears certain similarities to the Laage-Hynes mechanism of rotational jump motions of tagged water molecules in neat liquid water. We perform a detailed atomic-level investigation of hydrogen bond rearrangement dynamics of water in aqueous KNO3 solution to unearth two distinct mechanisms of hydrogen bond exchange that are instrumental to promote these jump motions of nitrate ions. As observed in an earlier study by Xie et al., in the first mechanism, after breaking a hydrogen bond with nitrate ion, water forms a new hydrogen bond with a water molecule, whereas the second mechanism involves just a switching of hydrogen bond between the two oxygen atoms of the same nitrate ion (W. J. Xie et al., J. Chem. Phys. 143, 224504 (2015)). The magnitude as well as nature of the reorientational jump of nitrate ion for the two mechanisms is different. In the first mechanism, nitrate ion predominantly undergoes out-of-plane rotation, while in the second mechanism, in-plane reorientation of NO3− is favourable. These have been deduced by computing the torque on the nitrate ion during the hydrogen bond switching event. We have defined and computed the time correlation function for coupled reorientational jump of nitrate and water and obtained the associated relaxation time which is also different for the two mechanisms. These results provide insight into the relation between the coupled reorientational jump dynamics of solute and solvent molecules.
Revealing the connection between the slow β relaxation and sub-Tg enthalpy relaxation in metallic glasses
Authors: Zhou Chao , Yue Yuanzheng , Hu Lina
Published: December 2016

We report a new approach, i.e., the hyperquenching-calorimetric approach, by which the activation energy of slow β relaxation (Eβ) in metallic glasses can be determined. This method is based on the correlations among the kinetic liquid fragility index (m), the glass transition temperature (Tg), the characteristic fictive temperature (Tf,c), and the activation energy for sub-Tg enthalpy relaxation. Tf,c is the temperature at which Eβ is equal to the activation energy of the onset of the sub-Tg enthalpy relaxation of metallic glasses. The linear Tf,c/Tg ∼ m relation is attributed to the link between the contribution of the slow β relaxation to the entire relaxation process and the liquid fragility for metallic glasses. This relation is explained in terms of the potential energy landscape. The new approach reveals the inherent relation between the slow β relaxation and sub-Tg enthalpy relaxation in metallic glasses.
Fabrication of thermal-resistant gratings for high-temperature measurements using geometric phase analysis
Authors: Zhang Q. , Liu Z. , Xie H. , Ma K. , Wu L.
Published: December 2016

Grating fabrication techniques are crucial to the success of grating-based deformation measurement methods because the quality of the grating will directly affect the measurement results. Deformation measurements at high temperatures entail heating and, perhaps, oxidize the grating. The contrast of the grating lines may change during the heating process. Thus, the thermal-resistant capability of the grating becomes a point of great concern before taking measurements. This study proposes a method that combines a laser-engraving technique with the processes of particle spraying and sintering for fabricating thermal-resistant gratings. The grating fabrication technique is introduced and discussed in detail. A numerical simulation with a geometric phase analysis (GPA) is performed for a homogeneous deformation case. Then, the selection scheme of the grating pitch is suggested. The validity of the proposed technique is verified by fabricating a thermal-resistant grating on a ZrO2 specimen and measuring its thermal strain at high temperatures (up to 1300 °C). Images of the grating before and after deformation are used to obtain the thermal-strain field by GPA and to compare the results with well-established reference data. The experimental results indicate that this proposed technique is feasible and will offer good prospects for further applications.
Evolution of planar defects during homoepitaxial growth of β-Ga2O3 layers on (100) substrates—A quantitative model
Authors: Schewski R. , Baldini M. , Irmscher K. , Fiedler A. , Markurt T. , Neuschulz B. , Remmele T. , Schulz T. , Wagner G. , Galazka Z. , Albrecht M.
Published: December 2016

We study the homoepitaxial growth of β-Ga2O3 (100) grown by metal-organic vapour phase as dependent on miscut-angle vs. the c direction. Atomic force microscopy of layers grown on substrates with miscut-angles smaller than 2° reveals the growth proceeding through nucleation and growth of two-dimensional islands. With increasing miscut-angle, step meandering and finally step flow growth take place. While step-flow growth results in layers with high crystalline perfection, independent nucleation of two-dimensional islands causes double positioning on the (100) plane, resulting in twin lamellae and stacking mismatch boundaries. Applying nucleation theory in the mean field approach for vicinal surfaces, we can fit experimentally found values for the density of twin lamellae in epitaxial layers as dependent on the miscut-angle. The model yields a diffusion coefficient for Ga adatoms of D = 7 × 10−9 cm2 s−1 at a growth temperature of 850 °C, two orders of magnitude lower than the values published for GaAs.
Defect-induced magnon scattering mechanisms in exchange-coupled bilayers
Authors: Gallardo R. A. , Rodríguez-Suárez R. L. , Landeros P.
Published: December 2016

The influence of two-magnon scattering mechanisms, which may be activated by different sorts of defects, is theoretically studied in ferromagnetic/antiferromagnetic exchange-biased bilayers. The spin-wave based model considers the influence of geometrical defects in the ferromagnetic (FM) layer as well as small domains in the antiferromagnetic (AFM) sub-lattice of the FM/AFM interface in such a way that both kinds of defects are randomly distributed over their respective surfaces. The in-plane angular dependence of the ferromagnetic resonance (FMR) linewidth allows detection of the relevant influence of such defects in the relaxation mechanisms, where the role of the exchange-bias field is clearly identified. Typical experimental findings, such as quadratic dependence of the linewidth with the exchange-bias field and the in-plane angular dependence, are well explained within the proposed model. This lends confidence in the model's utility and leads to a better understanding of the role of the magnon-magnon scattering in the magnetization dynamics of exchange-coupled antiferromagnetic/ferromagnetic bilayers.
Functional metal-insulator-metal top contacts for Si-based color photodetectors
Authors: Butun Serkan , Aydin Koray
Published: December 2016

Here, we report on Si-based color photodetectors using monolithically integrated metal-insulator-metal Fabry-Perot cavity top contacts. Contacts were formed by depositing Ag/SiO2/Ag layers with different oxide thicknesses for each color. This allowed controlling the transmission band position and width while maintaining the high conductivity. We have obtained over 55% external quantum efficiency for different colors both numerically and experimentally. The FWHM was less than 50 nm and the rejection ratio was an order of magnitude for each color. The total transmission through these top contacts exceeded that of dye filters used in conventional color CCDs and CMOS imaging arrays. In addition, these contacts performed similarly to recently proposed plasmonic hole array filters without the necessity of complicated fabrication steps like FIB milling and e-beam lithography. This type of top contacts can serve as a cheap alternative to dye filters used in contemporary devices without making the fabrication complicated.
Trapping and rotating of a metallic particle trimer with optical vortex
Authors: Shen Z. , Su L. , Yuan X.-C. , Shen Y.-C.
Published: December 2016

We have experimentally observed the steady rotation of a mesoscopic size metallic particle trimer that is optically trapped by tightly focused circularly polarized optical vortex. Our theoretical analysis suggests that a large proportion of the radial scattering force pushes the metallic particles together, whilst the remaining portion provides the centripetal force necessary for the rotation. Furthermore, we have achieved the optical trapping and rotation of four dielectric particles with optical vortex. We found that, different from the metallic particles, instead of being pushed together by the radial scattering force, the dielectric particles are trapped just outside the maximum intensity ring of the focused field. The radial gradient force attracting the dielectric particles towards the maximum intensity ring provides the centripetal force for the rotation. The achieved steady rotation of the metallic particle trimer reported here may open up applications such as the micro-rotor.
Boiling crisis controlled by capillary pumping and viscous friction: Liquid penetration length and dry spot diameter
Authors: Kim Hyungdae , Ahn Ho Seon , Kwak Ho Jae , Kim Moo Hwan , Kim Dong Eok
Published: December 2016

A boiling crisis, or critical heat flux (CHF), is a condition that determines the upper bound on removable thermal energy at a boiling surface. In such situations, the liquid cannot wet the surface because a vapor film completely covers it. CHF is enhanced on micro-structured surfaces when under boiling conditions. CHF values were measured for surfaces with rectangular microchannel geometries of various channel widths, (10–30 μm) and generally increased in value as channel widths decreased. However, the CHF value for the 5-μm channel-width surface was found to be lower than the wider channel-width surfaces. This observation contradicts models based on vapor recoil and classical instability mechanisms. Hence, we present a fluid-dynamics model that considers capillary pumping and viscous friction. With a focus on the spatial distribution of the liquid penetration region and the local dry spot under a large vapor bubble, this model can accurately predict the CHF variation associated with different channel widths.
Time-resolved spectroscopy of light emission from plasma generated by a converging strong shock wave in water
Authors: Yanuka D. , Rososhek A. , Efimov S. , Nitishinskiy M. , Krasik Ya. E.
Published: December 2016

The results of time-resolved spectroscopic measurements of light emission from plasma formed in the vicinity of a converging spherical strong shock wave (SSW) are reported. This approach, together with hydrodynamic (HD) and radiative-transfer simulations, can be used for the characterization of the SSW convergence symmetry and the parameters of water at that location. It was shown that the obtained time-of-flight of the SSW and emission spectra agree well with the results of the simulation, showing that the water density, temperature, and pressure should be larger than ∼3 g/cm−3, ∼1.4 eV, and ∼2 × 1011 Pa, respectively, at radii <25 μm with respect to the origin of the SSW implosion.
Influence of the reduced dimensionality on the thermodynamical and electrical properties of photosensitive BiOX (X = Cl, Br, and I) semiconductors
Authors: Lotnyk D. , Komanický V. , Feher A. , Bunda V.
Published: December 2016

The influence of the layered structure on the temperature dependencies of the specific heat, thermal conductivity, and electric resistivity of photosensitive bismuth oxyhalides BiOX (X = Cl, Br and I) single crystals were investigated in the temperature range 2 K ≤ T ≤ 300 K. The low temperature specific heat data for BiOX demonstrated the presence of two-dimensional behavior with increased anisotropy for the BiOI sample. Moreover, the thermal conductivity values for BiOI are three times higher than for BiOCl and BiOBr, and this observation is consistent with increased anisotropy arising from the contribution of optical out-of-plane phonons. The influence of green (λ = 532 nm) and red (λ = 640 nm) laser excitations on the electrical conductivity properties has been investigated. Each photoconductivity curve reveals transitions from low to high sensitivity. The depletion temperature region for BiOX single crystals corresponds to the peak in temperature dependence of the charge carrier mobility.
The study of diffusion mechanism in network-forming liquid: Silica liquid
Authors: Hung P. K. , Vinh L. T. , Ba Van To , Thu Ha N. T.
Published: December 2016

Molecular dynamics simulation is employed to investigate the diffusion mechanism in silica melt, a typical network-forming liquid. From the analysis of SiOx→SiOx±1 and OSiy→OSiy±1 reactions we reveal two moving modes: fast hopping and slow collective moving. Accordingly the atoms diffuse in the melt by simple hopping or through displacing of super-molecule (SM). A cluster analysis is performed for several of atom sets. It is shown that the melt exhibits non-uniform spatial distribution of reaction which causes the dynamics heterogeneity (DH). Further, the network structure of the melt consists of main subnet and large defective subnets. These subnets differ strongly in local environment, chemical composition and atomic density. This result evidences two distinct phases, the structure heterogeneity in silica melt and supports the polymorphism of network-forming liquid. We also find out that the node transformation spreads non-uniformly through the network structure. It takes place mainly in large defective subnet. The strong localization of node transformation is responsible for dynamical slowdown.
Recommending teams promotes prosocial lending in online microfinance
Authors: Ai Wei , Chen Roy , Chen Yan , Mei Qiaozhu , Phillips Webb
Published: December 2016

Significance

With three billion people subsisting on the equivalent of $2.50 per day, alleviating poverty is one of the most urgent challenges facing the world today. One solution to this problem has been to encourage the growth of small enterprises through microlending. A successful innovation is represented by
Kiva.org
, which matches citizen lenders with low-income entrepreneurs in developing countries. To increase prosocial lending, we use a large-scale field experiment and machine-learning methods to recommend lending teams to lenders. We find that lenders who join a team contribute significantly more compared with those who do not. Our results suggest team recommendation can be an effective and low-cost behavioral mechanism to increase charitable contributions.
Rapid synthesis of cyclic oligomeric depsipeptides with positional, stereochemical, and macrocycle size distribution control
Authors: Batiste Suzanne M. , Johnston Jeffrey N.
Published: December 2016

Significance

This work resonates with the intense, rapidly broadening interest in macrocycle synthesis, enabling the preparation of collections of size-congener macrocycles in a single reaction. More specifically, we have outlined the use of the Mitsunobu reaction to forge ester linkages between hydroxy acid monomers for depsipeptides in an oligomerization/macrocyclization mode. Additionally, we disclose that salt additives, which are normally contraindicated in a Mitsunobu reaction, are able to either enhance ring-size diversity (collections) or optimize the production of one macrocycle (selection) in an ion-templated fashion. Combination of this strategy and contemporary chemical methods allows rapid access to cyclodepsipeptide natural products and their unnatural isomers.
Mechanism of membrane fusion induced by vesicular stomatitis virus G protein
Authors: Kim Irene S. , Jenni Simon , Stanifer Megan L. , Roth Eatai , Whelan Sean P. J. , van Oijen Antoine M. , Harrison Stephen C.
Published: December 2016

Significance

Enveloped viruses—those with a lipid-bilayer membrane such as influenza, dengue, and human immunodeficiency viruses—enter cells by fusion of the viral membrane with a membrane of the cell. A viral surface glycoprotein, known as its “fusion protein,” facilitates this step. Previous work studying the kinetics of single virus particles fusing with a target membrane has outlined a mechanism by which conformational changes in the fusion protein accelerate merger of the two bilayers. In this paper, we extend that mechanism to a structurally distinct class of viral fusion proteins, providing strong evidence for its general applicability to all viral membrane fusion processes.
Bounding theorem in finite plasticity with hardening effect
Authors: Gao Yang , Wierzbicki Tomasz
Published: December 2016

The complementary variational problems for finite plasticity with strain-hardening effect are developed in this paper based on the theory of convex analysis. A new lower bound theorem for the load intensity factor, in which the plastic yield condition is relaxed by a complementary plastic superpotential, is proved. A simple illustrative example is worked out.
A note on the thermistor problem in two space dimensions
Authors: Howison Sam
Published: December 2016

We consider two coupled nonlinear p.d.e’s describing heat and current flow in a thermistor. For certain boundary conditions these equations may be reduced to one nonlinear o.d.e. and Laplace’s equation, as noted in [1]. We give a geometrical interpretation of this reduction in two space dimensions in terms of a conformal map from the thermistor onto a rectangle.
The Jeffcott equations in nonlinear rotordynamics
Authors: Zalik R. A.
Published: December 2016

The Jeffcott equations are a system of coupled differential equations that represent the behavior of a rotating shaft. This is a simple model that allows investigation of the basic dynamic behavior of rotating machinery. Nonlinearities can be introduced by taking into consideration deadband, side force, and rubbing, among others.
Fluid dynamics of an expanding ideal fluid
Authors: Rongved Leif
Published: December 2016

One studies in this paper the spreading of disturbances superimposed on an infinite ideal fluid region that is everywhere expanding homogeneously and isotropically. All fluid motion studied satisfies Euler’s full nonlinear fluid dynamic equations for the ideal adiabatic monatomic gas.
Dynamic solutions of linear matrix differential equations
Authors: Ruiz-Claeyssen Julio Cesar , Tsukazan Teresa
Published: December 2016

We discuss the

m
m

th-order linear differential equation with matrix coefficients in terms of a particular matrix solution that enjoys properties similar to the exponential of first-order equations. A new formula for the exponential matrix is established with dynamical solutions related to the generalized Lucas polynomials.
An inverse problem for a general convex domain with impedance boundary conditions
Authors: Zayed E. M. E. , Younis A. I.
Published: December 2016

The spectral function

θ

(
t
)

=

∑

n
=
1

∞

exp
⁡

(

−
t

λ
n

)

\theta \left ( t \right ) = \sum \nolimits _{n = 1}^\infty {\exp \left ( { - t{\lambda _n}} \right )}

, where

{

λ
n

}

n
=
1

∞

\left \{ {{\lambda _n}} \right \}_{n = 1}^\infty

are the eigenvalues of the Laplace operator

Δ
=

∑

i
=
1

2

(

∂

/

∂

x
i

)

2

\Delta = \sum \nolimits _{i = 1}^2 {{{\left ( {\partial /\partial {x^i}} \right )}^2}}

in the

x
1

x
2

{x^1}{x^2}

-plane, is studied for a general convex domain

Ω
⊆

R
2

\Omega \subseteq {R^2}

with a smooth boundary

∂
Ω

\partial \Omega

together with a finite number of piecewise smooth impedance boundary conditions on the parts

Γ

1
,
.
.
.
,

Γ
m

{\Gamma _{1,...,}}{\Gamma _m}

of

∂
Ω

\partial \Omega

such that

∂
Ω
=

U

j
=
1

m

Γ
j

\partial \Omega = U_{j = 1}^m{\Gamma _j}

.
Nonexistence of monotonic solutions in a model of dendritic growth
Authors: Troy William C.
Published: December 2016

A simple model for dendritic growth is given by

δ
2

θ
′

+

θ
′

=
cos
⁡

(
θ
)

{\delta ^2}\theta ’ + \theta ’ = \cos \left ( \theta \right )

. For

δ
≈
1

\delta \approx 1

we prove that there is no bounded, monotonic solution which satisfies

θ

(

−
∞

)

=
−
π

/

2

\theta \left ( { - \infty } \right ) = - \pi /2

and

θ

(
∞
)

=
π

/

2

\theta \left ( \infty \right ) = \pi /2

. We also investigate the existence of bounded, monotonic solutions of an equation derived from the Kuramoto-Sivashinsky equation, namely

y
′

+

y
′

=
1
−

y
2

/

2

y’ + y’ = 1 - {y^2}/2

. We prove that there is no monotonic solution which satisfies

y

(

−
∞

)

=
−

2

y\left ( { - \infty } \right ) = - \sqrt 2

and

y

(
∞
)

=

2

y\left ( \infty \right ) = \sqrt 2

.
On the oscillation and asymptotic behavior of 𝑁̇(𝑡)=𝑁(𝑡)[𝑎+𝑏𝑁(𝑡-𝜏)-𝑐𝑁²(𝑡-𝜏)]
Authors: Gopalsamy K. , Ladas G.
Published: December 2016

We obtained sufficient conditions for all positive solutions of the equation in the title to oscillate about the positive equilibrium

N
∗

{N^ * }

. We also found sufficient conditions for the global attractivity of

N
∗

{N^ * }

.
Conservation laws in viscoelasticity
Authors: Caviglia Giacomo , Morro Angelo
Published: December 2016

The evolution equations of a linear viscoelastic solid are written in terms of the Laplace transform of the displacement field. A corresponding reformulation of the condition of vanishing divergence for vector fields is then proposed and, through a systematic procedure, an explicit representation for a very large family of such conserved vectors is derived. As an application it is shown how a suitable choice of the admissible parameters leads to specific conservation laws which involve spatial means of linear momentum, angular momentum, stress, and displacement, in terms of the known body force, and initial and boundary data. As a further application a Betti-type reciprocity relation is derived. The connection with Noether’s approach to conservation laws is also discussed.
Burner-stabilized cellular flames
Authors: Olagunju David O. , Matkowsky Bernard J.
Published: December 2016

We consider a model that governs the behavior of a premixed flame anchored on a flat burner. We show that a steady planar flame is stable for Lewis numbers

L
L

in the interval

L
l

>
L
>

L
u

{L_l} > L > {L_u}

where

L
l

>
1

{L_l} > 1

and

L
u

>
1

{L_u} > 1

and unstable otherwise.
Dynamically loaded rigid-plastic analysis under large deformation
Authors: Gao Yang
Published: December 2016

Extended bounding theorems on maximum deformation and minimum response time are developed for dynamically loaded rigid-plastic structures in the range of large deformations. It is proved that the existence of bounds is directly related to a so-called complementary gap function and its directional-derivative.
Singular perturbation solution of a class of singular integral equations
Authors: Willis J. R. , Nemat-Nasser S.
Published: December 2016

A formal method is developed for finding asymptotic solutions to a class of strongly singular integral equations containing a small parameter,

ε
\varepsilon

. The class has relevance to the analysis of microcrack growth in reinforced ceramics. The method makes use of the asymptotic matching principle of Van Dyke. Its application is mechanical and it appears to allow, in principle, the construction of asymptotic solutions to any order. Consistency to order

ε
\varepsilon

is demonstrated for the general case and a solution correct to order

ε
2

{\varepsilon ^2}

is constructed for a particular example, previously studied only to leading order.
Optimal distribution of knots for tensor-product spline approximation
Authors: Dyn Nira , Yad-Shalom Itai
Published: December 2016

This paper deals with optimal asymptotic distribution of knots for various types of spline approximations.
On the large time behaviour of a thermoviscous flow with dissipation
Authors: King A. C.
Published: December 2016

The large time behaviour of a dissipative, thermoviscous, Couette-Pousielle flow is examined by asymptotic methods. Previous results on the adiabatic case are confirmed. In the case of a weakly conductive fluid the approach to a bounded, hot, steady state is shown to be caused by a forced linear diffusion mechanism.
Traveling wave solutions for interfaces arising from phase boundaries based on a phase field model
Authors: Wilder J. W.
Published: December 2016

This work presents an analysis of the traveling wave solutions resulting from the phase field model which has been proposed for solidification. It is shown that solutions only exist for very restricted values of the parameters involved and these values are investigated. The basic nature of the traveling wave solutions resulting from this model are also discussed.
Wave propagation in a qualitative model of combustion under equilibrium conditions
Authors: Logan J. David
Published: December 2016

We study various aspects of wave motion within the context of the Fickett-Majda qualitative model of combustion, under the assumption that the waves are propagating into an equilibrium state of a material governed by a two-way, model chemical reaction. In particular, we examine the hydrodynamic stability of an equilibrium state and the properties of a wavefront propagating into the state. We also investigate the signalling problem and use asymptotic methods and steepest descent to determine the long time behavior of the solution. Comparisons are made to the real physical model.
Heat transfer for the flow through a pipe
Authors: Kasture D. Y.
Published: December 2016

The heat flux per unit length through the wall of a straight pipe of arbitrary but uniform cross section is shown to be the product of the constant pressure gradient and the volume flux, when a steady Poiseuille flow of a viscous incompressible fluid is maintained through it, and its wall is kept at a constant temperature. Bounds on the heat flux are obtained using the methods of isoperimetric inequalities.
On shakedown of elastoplastic shells
Authors: Stumpf Helmut , Le Khanh Chau
Published: December 2016

An asymptotic theory of adaptation for elastoplastic shells under a variable loading is proposed. The hypothesis of membrane state of an elastic response is used to reduce the three-dimensional variational problems for shakedown factor to two-dimensional ones. The duality and the possibility of algebraization allow the membrane shell shakedown theory to be analytically solvable in many interesting cases. The asymptotic accuracy of the constructed membrane approximation is proved.
Nonorthogonal stagnation flow on the surface of a quiescent fluid—an exact solution of the Navier-Stokes equation
Authors: Liu Tianshu
Published: December 2016

An exact solution of the Navier-Stokes equation that describes the two-dimensional impingement of a light fluid on the surface of a heavier fluid at an arbitrary angle of incidence, assuming no surface distortion is obtained.
Separation of variables on a triangular geometry
Authors: Look D. C.
Published: December 2016

The usual separation of variables technique is used to obtain solutions on a triangular region of interest. The resulting error is noted and a forced orthogonality procedure is used to investigate the error. The forced method allows a means to indicate the onset of error based on the magnitude of two parameters.
Relaxation of Euler equations and hydrodynamic instabilities
Authors: Duchon Jean , Robert Raoul
Published: December 2016

We present a relaxed version of incompressible Euler equations that permits foliated flows involving two velocities. These relaxed equations allow a two-phase evolution of some vortex sheets as an alternative to discontinuous solutions of Euler equations. In the case of two perfect fluids of different densities superposed one over the other, we show that this relaxation process yields a linearly well-posed two-phase solution.
Axisymmetric finite anti-plane shear of compressible nonlinearly elastic circular tubes
Authors: Polignone Debra A. , Horgan Cornelius O.
Published: December 2016

The axial shear problem for a hollow circular cylinder, composed of homogeneous isotropic compressible nonlinearly elastic material, is described. The inner surface of the tube is bonded to a rigid cylinder while the outer surface is subjected to a uniformly distributed axial shear traction and the radial traction is zero. For an arbitrary compressible material, the cylinder will undergo both a radial and axial deformation. These axisymmetric fields are governed by a coupled pair of nonlinear ordinary differential equations, one of which is second-order and the other first-order. The class of materials for which axisymmetric anti-plane shear (i.e., a deformation with zero radial displacement) is possible is described. The corresponding axial displacement and stresses are determined explicitly. Specific material models are used to illustrate the results.
Bending energy of highly elastic membranes
Authors: Hilgers M. G. , Pipkin A. C.
Published: December 2016

For a membrane composed of elastic material with strain energy

W
W

per unit initial volume, approximations to the energy per unit initial area are obtained by integrating

W
W

through the thickness. The usual stretching energy

M

(

r

,
a

)

M\left ( {{r_{,a}}} \right )

is modified by including a bending energy term

α
B

(

r

,
a

,

r

,
a
b

)

\alpha B\left ( {{r_{,a}}, {r_{,ab}}} \right )

that is quadratic in the second derivatives

r

,
a
b

{r_{,ab}}

. If

W
W

is the strain energy function for a stable material,

M
M

need not satisfy the Legendre-Hadamard material stability conditions, but the modified energy

M
+
α
B

M + \alpha B

does satisfy these conditions. The special form that

B
B

takes when the membrane is isotropic is given.
Stability results for a model of repression with external control
Authors: Mahaffy Joseph M. , Jorgensen David A. , Vanderheyden Robert L.
Published: December 2016

A stability analysis is performed for a mathematical model with negative feedback, diffusion, and time delays. The model of a cell includes three biochemical species that interact to control the transport of an extracellular nutrient. This study examines the effects of diffusion, cell size, and extracellular nutrient concentration on the model. With certain assumptions the symmetry, a linearized version of the model is studied in detail. The characteristic equation is shown to have no solutions with positive real part when extracellular nutrient concentration or the diffusivities are sufficiently small or the radius of the cell is sufficiently large. These results are compared to an earlier study that showed that biochemical oscillations could occur for certain parameter values. A discussion is provided for how the bifurcations from regions of stability to regions of instability could affect the biological response of the cell.
Interaction of gas fronts
Authors: Lacey A. A. , Vázquez J. L.
Published: December 2016

During rock blasting separate charges initiate movement of gas at high pressure through fractured rock. This gas occupies regions of compact support enclosed by moving boundaries, the gas fronts, at which the pressure is effectively zero. Here we consider the local behaviour of such gas fronts, albeit taking the system to be rather simpler so that the gas flow can be modelled by the porous medium equation, when two identically pressurized regions interact and when a gas front impinges upon a fixed boundary where the pressure is zero.
Exact analytic solutions describing unsteady plane gas flows with shocks of arbitrary strength
Authors: Sachdev P. L. , Gupta Neelam , Ahluwalia D. S.
Published: December 2016

Several classes of exact analytic solutions for one-dimensional plane gas-dynamic equations describing piston-driven shocks propagating into inhomogeneous media are presented. These solutions are obtained by writing the conservation forms of the basic equations, and hence using their equivalent differential forms. These forms enable introduction of special coordinate systems which make it possible to exactly satisfy boundary conditions at the shock and at the piston. Previous results of Sachdev and Reddy [1] and Ustinov [2, 3] are recovered as special cases. Several representative solutions are shown graphically. Strong shocks as well as shocks of arbitrary strength and characteristic fronts are considered.
The steady states of one-dimensional Sivashinsky equations
Authors: Novick-Cohen A. , Peletier L. A.
Published: December 2016

Phase plane analysis is used to calculate the number of steady states for two equations which arise in the context of directional solidification: the Sivashinsky equation and the modified Sivashinsky equation.
The effect on finite time breakdown due to modified Fourier laws
Authors: Kosiński W. , Saxton K.
Published: December 2016

This paper discusses the finite time blow-up of the amplitude of acceleration waves in the case of heat propagation in one-dimensional rigid and elastic bodies. In both cases dissipation is not strong enough to preserve the smoothness of the solutions whose initial data is far from equilibrium.