Miracle-dz/UniFAR-FTUs huggingface dataset:
Polytetrafluoroethylene Fibril Structure

The fine‐scale structure that exists in polytetrafluoroethylene fibers produced by different methods was investigated by electron microscopy and electron diffraction. These fibers were formed by mechanically abrading the surface and by fracture of compacted granular grade PTFE, and by stripping the fibers from the surface of Teflon‐coated aluminum foil. Bright‐field electron microscope observations indicate that the fibers are composed of microfibers or fibrils with a nearly uniform diameter of 450 A. These fibrils are composed of platelet‐like units 60 A thick, oriented normal to the fiber axis, and are organized into blocks on the order of 475 A in length. Electron diffraction from unshadowed individual fibers indicates that the crystal size must be fairly large, with few defects. These observations are well supported by the dark‐field micrographs of the fibers. The dark‐field photographs show crystalline regions along these fibrisl, which appear to be multiples of the fundamental 450‐A fibrill diameter.
Arrays of distributed-Bragg-reflector waveguide lasers at 1536 nm in Yb/Er codoped phosphate glass

We have demonstrated an array of monolithic, single-frequency-distributed-Bragg-reflector (DBR), waveguide lasers operating near 1536 nm wavelengths. The lasers were fabricated by forming waveguides in Yb/Er-codoped phosphate glass by ion exchange. The slope efficiency for each laser as a function of launched pump power is 26% and the thresholds occur at 50 mW of launched pump power. An output power of 80 mW was achieved with 350 mW of coupled pump power. Each laser exhibits stable operation on a single longitudinal mode and all have linewidths less than 500 kHz. A comb of waveguides with varying effective indices allows the selection of wavelength using a single-period grating.
The method of reduction of order and linearization of the two‐dimensional Ermakov system

We present the general form of the system of second‐order ordinary differential equations invariant under a representation of the Lie algebra sl(2, R) and show that a considerable simplification is achieved using a well‐known Kummer–Liouville transformation. We show that the system can be reduced to a combination of linear second‐order ordinary differential equations and a conservation law. The reduction makes the determination of the complete symmetry group of the standard Ermakov system an easier task than earlier reported (J. Nonlinear Math. Phys. 2005; 12:305–320). The reduced system is equivalent to the reduction of the Kepler problem under a further constraint. Copyright © 2007 John Wiley & Sons, Ltd.
Magnetic ordering effects in a Mn-modulation-doped high mobility two-dimensional hole system

We have studied the magnetotransport properties of a manganese (Mn)-modulation-doped high mobility two-dimensional hole system in a strained InAs quantum well (QW) structure. At precisely T=600 mK a phase transition from paramagnetism to ferromagnetism can be observed by a change of the low-field magnetotransport behavior and hysteresis. In the magnetically ordered phase a superposition of positive magnetoresistance and weak antilocalization was detected in the longitudinal resistance Rxx and in the Hall resistance Rxy a superposition of normal, anomalous, and planar Hall effects demonstrating spontaneous magnetization in the QW plane was detected. From extensive analysis of the temperature and magnetic field dependence of the Shubnikov–de Haas oscillations we deduce the effective mass, transport, and quantum-scattering times. The latter indicates presence of small-range scattering potential. From corrections to the Drude conductivity we determine the impurity interaction time, which is significantly reduced in the ferromagnetic phase indicating interaction of the two-dimensional free holes' spin with the localized magnetic moments of 5/2 from Mn ions.
Damage inspection and health monitoring of dynamical systems by advanced time-frequency analysis

This paper presents a conjugate-pair decomposition (CPD) method for offline damage inspection and online health monitoring of dynamical systems. Responses of damaged dynamical systems are often nonlinear and nonstationary. For a nonlinear non-stationary signal, empirical mode decomposition (EMD) uses the apparent time scales revealed by the signal's local maxima and minima to sequentially sift intrinsic mode functions (IMFs) of different time-varying scales, starting from high- to low-frequency ones. For offline detailed damage inspection, CPD uses one or more pairs of windowed adaptive harmonics and function orthogonality to track time-varying frequency and amplitude of each IMF. Because CPD processes only time-domain data, it is free from the edge effect caused by Gibbs' phenomenon and other mathematical and numerical problems caused by the use of Hilbert transform. Hence, results from CPD are valuable for accurate identification of dynamical systems. For parametric identification, one can compare the time-varying frequency and amplitude from CPD with those from perturbation analysis to determine the type and order of nonlinearity and system parameters. For online health monitoring, CPD tracks the instantaneous frequency of an arbitrary signal without signal decomposition by processing three or more most recent data to estimate its instantaneous frequency and amplitude. Numerical results show that CPD is versatile for system identification, damage inspection, and health monitoring of different linear/nonlinear dynamical systems.
A comparative study of the photoluminescence and conduction mechanisms of low temperature pulsed laser deposited and atomic layer deposited zinc oxide thin films

Zinc oxide (ZnO) thin films were synthesized by pulsed laser deposition (PLD) and atomic layer deposition (ALD) at 100 °C on glass, and their structural, electrical, and optical properties were compared before and after 300 °C post‐deposition annealing in argon, vacuum, and air. The room temperature photoluminescence (PL) of the ALD films grown at 100 °C was characterized by a broad, defect emission band peaking at 605 nm, which decreased in intensity after annealing. In contrast, the PL of the PLD films was dominated by 385 nm emission, and luminescence at 425 nm was also observed. The PL intensity of these films increased after annealing. The data suggest that overall electrical and photoluminescent characteristics of the ALD films are determined by the relative zinc interstitial and oxygen vacancy concentrations which vary with annealing treatment. The electro‐optical properties of the PLD films are determined by Zn interstitials. The potential impact of the observed absorption and emission bands on optoelectronic applications is discussed.
Numerical investigation of the oscillatory flow around a circular cylinder close to a wall at moderate Keulegan–Carpenter and low Reynolds numbers

The oscillatory flow around a circular cylinder close to a plane wall is investigated numerically, by direct numerical simulation of the Navier–Stokes equations. The main aim of the research is to gain insight into the effect of the wall on the vorticity dynamics and the forces induced by the flow over the cylinder. First, two-dimensional simulations are performed for nine values of the gap-to-diameter ratio e. Successively, three-dimensional simulations are carried out for selected cases to analyse the influence of the gap on the three-dimensional organization of the flow. An attempt to explain the pressure distribution around the cylinder in terms of vorticity time development is presented. Generally, the time development of the hydrodynamic forces is aperiodic (i.e. changes from cycle to cycle). In one case (Re = 200), when the distance of the cylinder from the wall is reduced, the behaviour of the flow changes from aperiodic to periodic. When the cylinder approaches the wall the drag coefficient of the in-line force increases in a qualitative agreement with the results reported in literature. The transverse force is not monotonic with the reduction of the gap: it first decreases down to a minimum, and then increases with a further reduction of the gap. For intermediate values of the gap the decrease of the transverse force is due to the reduction of the angle of ejection of the shedding vortices caused by the closeness of the wall; for small gaps the increase of the transverse force is due to the strong interaction between the vortex system ejected from the cylinder and the shear layer generated on the wall. Three-dimensional simulations show that the flow is unstable with respect to spanwise perturbations which cause the development of three-dimensional vortices and the distortion of the two-dimensional ones generated by flow separation. In all the analysed cases, the three-dimensional effects on the hydrodynamic forces are clearly attenuated when the cylinder is placed close to the wall. The spanwise modulation of the vortex structures induces oscillations of the sectional forces along the axis of the cylinder which in general are larger for the transverse sectional force. In the high-Reynolds-number case (Re = 500), the reduction of the gap produces a large number of three-dimensional vortex structures developing over a wide range of spatial scales. This produces homogenization of the flow field along the spanwise direction and a consequent reduction of the amplitudes of oscillation of the sectional forces.
Group delay control of picosecond optical pulses in superstructured fiber Bragg gratings

A theoretical and experimental analysis of group velocity reduction in periodic super-structured Bragg gratings is presented. Experimental demonstration of group velocity reduction of sub-nanosecond pulses at the 1.5 μm wavelength of optical communications is reported using either a 20-cm-long Moire and a periodically-spaced πphase shift fiber gratings. Time delays up to approximately 690 ps for 250-ps-duration optical pulses have been achieved leading to the realization of an optical buffer.
The occultation of HIP 107302 by Jupiter

Aims. Occultations of bright stars by planets provide information on the state of their atmospheres. An occultation of the bright star 45 Capricornii (HIP 107302) by Jupiter occurred on the night of 3/4 August 2009. Methods. The event was observed at multiple sites in Europe, Africa and South America and with instruments ranging in aperture from 0.4 m to 2.2 m. All observations, except one, were carried out in methane absorption bands centred at 0.89 μm and 2.2 μm to minimise the planetary contribution to the measured stellar flux. Following the application of special post-processing techniques, differential photometry was performed. Nearby bright satellites were used as reference sources. Results. Fifteen lightcurves were obtained. The photometric time series for fourteen of these were fitted to a model atmosphere of constant scale height (H). Estimates of H for most lightcurves lie within the range 20−30 km with an inverse-variance weighted mean of 23.6 ± 0.4 km, in good agreement with previous works. A comparison between half-light times at ingress and at egress implies an astrometric offset of 10−15 mas in Jupiter’s position relative to the star. Five lightcurves – two for ingress and three for egress – were numerically inverted into profiles of pressure versus temperature. Isothermal, mutually consistent behaviour is observed within the pressure range 3−10 μbar. The inferred temperature of 165 ± 5 K is consistent with, but slightly higher than, that measured by the Galileo Probe at 5 ◦ S latitude in 1995 at the same pressure level. Subtraction of isothermal models for nine cases show the presence of at least one, and possibly two, non-isothermal layers a few tens of km below the half-light datum. Their altitudes are similar to those of features previously reported during the occultation of HIP 9369 in 1999. Our temperature estimates are consistent with the expected small magnitude of the perturbation of the atmosphere following the impact event on Jupiter in July 2009.
Photochemical and thermal effects in laser irradiated fullerite: From periodic exfoliation to cone formation

We report a characterization of fullerite surface modification by cumulative laser irradiation. We show that the nano- and mesostructure of the transformed material are related and that they depend on the laser wavelength and fluence. Irradiating the sample at 1064 nm we observe periodic exfoliation of the transformed surface which is composed, on a nanometer scale, of a network of graphitic elongated nanoparticles. Under UV irradiation, the nanostructure is characterized by tangled graphene layers and cone formation is observed on a mesoscopic scale. Our observations show that different destabilization mechanisms of C60 produce coalescence pathways towards different nanostructures and mesoscopic morphologies.
Perturbation dynamics in viscous channel flows

Plane viscous channel flows are perturbed and the ensuing initial-value problems are investigated in detail. Unlike traditional methods where travelling wave normal modes are assumed as solutions, this work offers a means whereby arbitrary initial input can be specified without having to resort to eigenfunction expansions. The full temporal behaviour, including both early-time transients and the long-time asymptotics, can be determined for any initial small-amplitude three-dimensional disturbance. The bases for the theoretical analysis are: (a) linearization of the governing equations; (b) Fourier decomposition in the spanwise and streamwise directions of the flow; and (c) direct numerical integration of the resulting partial differential equations. All of the stability criteria that are known for such flows can be reproduced. Also, optimal initial conditions measured in terms of the normalized energy growth can be determined in a straightforward manner and such optimal conditions clearly reflect transient growth data that are easily determined by a rational choice of a basis for the initial conditions. Although there can be significant transient growth for subcritical values of the Reynolds number, it does not appear possible that arbitrary initial conditions will lead to the exceptionally large transient amplitudes that have been determined by optimization of normal modes when used without regard to a particular initial-value problem. The approach is general and can be applied to other classes of problems where only a finite discrete spectrum exists (e.g. the Blasius boundary layer). Finally, results from the temporal theory are compared with the equivalent transient test case in the spatially evolving problem with the spatial results having been obtained using both a temporally and spatially accurate direct numerical simulation code.
Optimal Design for Plate Buckling

This paper extends Keller’s classic solution for the optimal design of columns to the case of plates. After the introduction of nondimensional variables, a calculus of variations technique is used to derive an optimality condition, which states that “the strain-energy density is proportional to the thickness in an optimal plate design. ” The case of a simply supported plate is then discussed, using a truncated Fourier series solution. For a square, isotropic plate, the buckling load of the optimal design is larger than that of the uniform plate by a factor of 1.71 + 1.37 υ\N (υ\N is Poisson’s ratio). An appendix is included which discusses Keller’s original solution and shows how it can be applied when a fourth-order differential equation is used rather than the second-order one used by Keller. This appendix also discusses the use of a truncated Fourier series and Rayleigh’s method as an approximation of Keller’s result, thus laying the groundwork for the use of Fourier series in the plate problem.
Mechanism of the flexural resonance frequency shift of a piezoelectric microcantilever sensor in a dc bias electric field

The flexural resonance frequency of a lead magnesium niobate–lead titanate (PMN-PT)/tin piezoelectric microcantilever sensor (PEMS) was shown to vary in a dc bias electric field, similar to the behavior of width-mode resonance frequency of the PEMS. Both the flexural and the width-mode resonance frequency shifts were attributed to Young’s modulus change in the PMN-PT layer as confirmed by Young’s modulus measurements on a separate PMN-PT strip. Young’s modulus change of the PMN-PT layer in an electric field was a result of the non-180° polarization domain switching as evidenced by the dielectric constant change with the field.
Model Representation of Local Air Quality Characteristics

Abstract Daily (24 h) and hourly air quality data at several sites are used to examine the performance of the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5)–Community Multiscale Air Quality Model (CMAQ) system over a 3-month period in 2003. A coarse (36 km) model grid was expected to provide relatively poor performance for ozone and comparatively better performance for fine particles, especially the more regional sulfate and carbonaceous aerosols. However, results were different from this expectation. Modeling showed significant skill for ozone at several locations but very little skill for particulate species. Modeling did poorly identifying surface wind directions associated with the highest and lowest pollutant exposures at most sites, although results varied widely by location. Model skill appeared to be better for ozone when spatial–temporal (S–T) patterns were examined, due in part to the ability of the model to reproduce much of the temporal variance associated with the d.
Validation of a mixed‐layer closure. I: theoretical tests

A flux closure formula introduced earlier for predicting entrainment into a mixed layer is tested through analytic solution of the kinetic energy equation and through large‐eddy simulation. For this purpose, the closure formulation and the simulation model are applied to the ‘smoke cloud’ mixed layer, that includes both radiative cooling at the cloud top and surface heating or cooling at the surface, but without the effects of latent heat. The unique aspect of the closure, height weighting of the integral of buoyancy flux, is found to be directly related to the ratio of coefficients of the dissipation and diffusion terms of the energy equation.
Global existence of classical solutions for a hyperbolic chemotaxis model and its parabolic limit by

We consider a one dimensional hyperbolic system for chemosensitive movement, especially for chemotactic behavior. The model consists of two hyperbolic differential equations for the chemotactic species and is coupled with either a parabolic or an elliptic equation for the dynamics of the external chemical signal. The speed of the chemotactic species is allowed to depend on the external signal and the turning rates may depend on the signal and its gradients in space and time, as observed in experiments. Global classical solutions are established for regular initial data and a parabolic limit is proved.
Spatial geometric constraints histogram descriptors based on curvature mesh graph for 3D pollen particles recognition

This paper presents one novel spatial geometric constraints histogram descriptors (SGCHD) based on curvature mesh graph for automatic three-dimensional (3D) pollen particles recognition. In order to reduce high dimensionality and noise disturbance arising from the abnormal record approach under microscopy, the separated surface curvature voxels are extracted as primitive features to represent the original 3D pollen particles, which can also greatly reduce the computation time for later feature extraction process. Due to the good invariance to pollen rotation and scaling transformation, the spatial geometric constraints vectors are calculated to describe the spatial position correlations of the curvature voxels on the 3D curvature mesh graph. For exact similarity evaluation purpose, the bidirectional histogram algorithm is applied to the spatial geometric constraints vectors to obtain the statistical histogram descriptors with fixed dimensionality, which is invariant to the number and the starting position of the curvature voxels. Our experimental results compared with the traditional methods validate the argument that the presented descriptors are invariant to different pollen particles geometric transformations (such as posing change and spatial rotation), and high recognition precision and speed can be obtained simultaneously.
Inertial instability of intense stratified anticyclones. Part 2. Laboratory experiments

Abstract Large-scale laboratory experiments were performed on the Coriolis rotating platform to study the stability of intense vortices in a thin stratified layer. A linear salt stratification was set in the upper layer on top of a thick barotropic layer, and a cylinder was towed in the upper layer to produce shallow cyclones and anticyclones of similar size and intensity. We focus our investigations on submesoscale eddies, where the radius is smaller than the baroclinic deformation radius. Towing speed, cylinder size and stratification were changed in order to cover a large range of the parameter space, staying in a relatively high horizontal Reynolds number ( $Re= 2000{{\unicode{x2013}}}7000$ ). The Rayleigh criterion states that inertial instabilities should strongly destabilize intense anticyclonic eddies if the vorticity in the vortex core is negative enough ${\zeta }_{0} / f\lt - 1$ , where ${\zeta }_{0} $ is the relative vorticity in the core of the vortex, and $f$ is the Coriolis parameter. However, we found that some anticyclones remain stable even for very intense negative vorticity values, up to ${\zeta }_{0} / f= - 3. 5$ , when the Burger number is large enough. This is in agreement with the linear stability analysis performed in part 1 (J. Fluid Mech., vol. 732, 2013, pp. 457–484), which shows that the combined effect of a strong stratification and a moderate vertical dissipation may stabilize even very intense anticyclones, and the unstable eddies we found were located close to the marginal stability limit. Hence, these experimental results agree well with the simple stability diagram proposed in the Rossby, Burger and Ekman parameter space for inertial destabilization of viscous anticyclones within a shallow and stratified layer.
A first detailed study of the colliding wind WR+O binary WR 30a

We present a detailed, extensive investigation of the photometric and spectroscopic behaviour of WR 30a. This star is definitely a binary system with a period around 4.6 d. We propose the value . The identification of the components as WO4+O5((f)) indicates a massive evolved binary system; the O5 component is a main-sequence or, more likely, a giant star. The radial velocities of the O star yield a circular orbit with an amplitude and a mass function of 0.013 . The spectrum of WR 30a exhibits strong profile variations of the broad emission lines that are phase-locked with the orbital period. We report the detection of the orbital motion of the WO component with , but this should be confirmed by further observations. If correct, it implies a mass ratio . The star exhibits sinusoidal light variations of amplitude 0.024 mag peak-to-peak with the minimum of light occurring slightly after the conjunction with the O star in front. On the basis of the phase-locked profile variations of the C ivλ4658 blend in the spectrum of the WO, we conclude that a wind–wind collision phenomenon is present in the system. We discuss some possibilities for the geometry of the interaction region.
The Contribution of Methanol to the 3.4 Micron Emission Feature in Comets

In this paper a fluorescence model for cometary emission in the ν 2 , ν 3 , and ν 9 bands of methanol is described. This model is used in conjunction with observed spectra of several comets to determine the possible contribution of CH 3 OH to the frequently seen 3.4 μm «cometary organic» feature. For comets P/Halley and Wilson, methanol production rates are retrieved from the flux in the ν 3 band centered at ∼3.52 μm