Miracle-dz/UniFAR-FTUs huggingface dataset:
Linear processes in stably and unstably stratified rotating turbulence

Unsteady turbulence in stably and unstably stratified flow with system rotation around the vertical axis is analysed using the rapid distortion theory (RDT). Complete linear solutions for the spectra, variances and covariances are obtained analytically, and their characteristics, including the short- and long-time asymptotics and the effect of initial conditions, are examined in detail. It has been found that the rotation modifies the energy partition among the three kinetic energy components and the potential energy, and the ratio of the Coriolis parameter f to the Brunt–Väisälä frequency N, i.e. f/N, determines the final steady values of these components. The ratio also determines the phase of the energy/flux oscillation. Depending on whether f/N > 1 or f/N < 1, there is a phase shift of ±π/4. However, unsteady aspects are largely dominated by stratification. This occurs because the effects of the Coriolis parameter f appear only in the form of fk3, which vanishes for the horizontal wavenumber components (k3 = 0), which contribute most to the energies and the fluxes. For example, the oscillation frequency of the energies and the fluxes asymptotes to 2N over a long time, in agreement with the stratified non-rotating turbulence. The initial time development is also dominanted by the stratification, and the short-time asymptotics (Nt, ft [Lt ] 1) agree with those for non-rotating stratified fluids in the lowest-order approximation. In the special case of f = N, all the wavenumber components oscillate in phase, leading to no inviscid decay of oscillation. This is in contrast to the general case of f ≠ N, in which inviscid decay has been observed. For pure rotation (f ≠ 0, N = 0), analytical solutions showed that any turbulence that is initially axisymmetric around the rotation axis recovers exact three-dimensional isotropy in the kinetic energy components. Comparison with previous DNS and experiments shows that many of the unsteady aspects of the kinetic and potential energies and the vertical density flux can be explained by the linear processes described by RDT. Even the time development of the vertical vorticity, which would represent the small-scale characteristics of turbulence, agrees well with DNS. For unstably stratified turbulence, the initial processes observed in DNS and experiments, such as the initial decay of the kinetic energy due to viscosity and the subsequent rapid growth of the vertical kinetic energy compared to the horizontal kinetic energy, could be explained by RDT.
STRESSES IN A CIRCULAR DISC CONTAINING A RADIAL CRACK

An analytic solution to a particular boundary value problem in linear elasticity is presented. The problem considered is that of a circular disc, in plane strain or generalized plane stress, which is loaded quite generally at the perimeter by a set of self equilibrating forces. The disc has a radial crack extending completely from the centre to the perimeter. Three particular load cases are considered: the disc is loaded by uniform radial tension; the disc is pulled by two diametrical concentrated loads with line of action perpendicular to the crack; the disc is pulled by two concentrated forces acting at the mouth of the crack. In each case the stress intensity factor is evaluated and contours of the isochromatics are presented in dimensionless form. The results agree with those derived by other workers but the method presented here is more general, more efficient, and extends the previous results for finite bodies containing cracks. The three load cases have also been applied to the disc when the tip of the crack has been removed by the presence of a concentric hole. New results are presented for the stress concentration factors for a full range of geometric parameters. Finally it is shown how the second and third of the load cases may be used for controlled laboratory tests in the study of fracture and fracture toughness of brittle materials.
Slosh dynamics of inviscid fluids in two‐dimensional tanks of various geometry using finite element method

This paper brings into focus some of the interesting effects arising from the motion of the liquid free surface due to sloshing in partially filled containers of several geometrical shapes in two dimensions. The slosh characteristics that include frequencies, free surface profiles and the hydrodynamic pressure over the container walls have been reported in this study. The equations of motion of the fluid, considered inviscid, are expressed in terms of the pressure variable alone. It is assumed that the frequency of the exciting oscillation is not in the immediate neighborhood of the natural slosh frequency, so that the slope of the free surface is small. Simple harmonic oscillation and earthquake excitations are used as the prescribed boundary conditions. A finite difference‐based iterative time‐stepping technique is employed to advance the solution in the time domain. The paper presents numerical solutions for rectangular, vertically mounted annular cylindrical, trapezoidal and horizontal circular cylindrical containers. Numerical results obtained are compared with the available existing solutions to validate the code developed. The parametric study of the slosh dynamic systems shows the importance of the nature of excitation, fluid height and the geometry of the container. Copyright © 2007 John Wiley & Sons, Ltd.
Simultaneous tomography and topography of silicon integrated circuits using full-field swept-source optical coherence tomography

We demonstrate simultaneous tomography and topography of micro-electro-mechanical systems based on silicon integrated circuits using full-field swept-source optical coherence tomography. The optical set-up consists of a swept-source system, a compact Michelson interferometer, and an area detector. The swept-source system comprises a superluminescent diode as a broadband light source in conjunction with an acousto-optic tunable filter as a fast frequency tuning device. By means of sweeping the frequency of the light source, multiple interferograms were recorded and both the amplitude and the phase map of the interference fringe signal were reconstructed. Optically sectioned images of the silicon integrated circuits were obtained by selective Fourier filtering and the topography was retrieved from the phase map. The main advantages of the proposed system are completely non-mechanical scanning, ease of alignment, high stability because of its nearly common-path geometry, and compactness.
Arithmetic Properties of Moduli Spaces and Topological String Partition Functions of Some Calabi-Yau Threefolds

This thesis studies certain aspects of the global properties, including geometric and arithmetic, of the moduli spaces of complex structures of some special Calabi-Yau threefolds (B-model), and of the corresponding topological string partition functions defined from them which are closely related to the generating functions of Gromov-Witten invariants of their mirror Calabi-Yau threefolds (A-model) by the mirror symmetry conjecture. For the mirror families (B-model) of the one-parameter families (A-model) of KP2 , KdPn , n = 5, 6, 7, 8 with varying Kahler structures, the bases are the moduli spaces of complex structures of the corresponding mirror Calabi-Yaus. We identify them with certain modular curves by studying the Picard-Fuchs systems and periods of the corresponding mirror families. In particular, the singular points on the moduli spaces correspond to the cusps and elliptic points on the modular curves. We take the BCOV holomorphic anomaly equations with boundary conditions as the defining equations for the topological string partition functions. Using polynomial recursion and the above identification, we interpret the boundary conditions as regularity conditions for modular forms and express the equations purely in terms of the language of modular form theory. This turns the problem of solving the equations into a combinatorial problem. We also solve for the first few topological string partition functions genus by genus recursively in terms of almost-holomorphic modular forms. Assuming the validity of mirror symmetry conjecture, we prove a version of integrality for the Gromov-Witten
Development of Novel Ultrasonic Bone Densitometry Using Acoustic Parameters of Cancellous Bone for Fast and Slow Waves

A novel ultrasonic bone densitometer, prototype LD-100, has been developed to overcome problems inherent in an ultrasonic method and to obtain bone mass density in the unit of mg/cm3 and bone elasticity in the unit of GPa with a spatial resolution comparable to that of the peripheral quantitative computed tomography (pQCT) system. Bone mass density and bone elasticity are evaluated using ultrasonic parameters based on fast and slow waves in cancellous bone using a modeling of ultrasonic wave propagation path. A good reproducibility of measured values and two-dimensional (2D) imaging of bone density and bone quality are realized by two scannings with an automatic measurement algorithm.
Convergence properties of minimal vectors for normal operators and weighted shifts

We study the behaviour of the sequence of minimal vectors corresponding to certain classes of operators on reflexive L p spaces, including multiplication operators and bilateral weighted shifts. The results proved are based on explicit formulae for the minimal vectors, and provide extensions of results due to Ansari and Enflo, and also Wiesner. In many cases the convergence of sequences associated with the minimal vectors leads to the construction of hyperinvariant subspaces for cyclic operators.
Laser with a transmitting window.

The effect of transmission of radiation through one mirror of a laser is investigated. For a laser oscillator the result is to change the effective resonance frequency and $Q$ of the cavity. Using the same model for the cavity, a signal is injected into the active medium through the transmitting window, and its effect on the system studied. When the external signal is strong enough and sufficiently close to the natural frequency of the laser oscillator, the laser locks its frequency to the input signal. The equations describing the system are solved over the range of input frequencies where the laser is locked, and the resulting gain found. In the high-intensity limit the medium saturates, and the gain tends to that of a lossy cavity. As the input intensity vanishes, the gain approaches infinity and the system tends to a laser oscillator.
Some properties of dynamic feedback neural nets

The authors present models of feedback neural nets which are described by nonlinear differential equations. They show that their earlier proofs for convergence to bounded regions and for the existence of a finite number of equilibria are independent of the symmetry of the interconnection matrix and thus are also applicable to more general nongradient dynamic neural nets. However, when the interconnect matrix is asymmetric, the network is not guaranteed to have only (finite) equilibria as its limit set. The authors present computer simulations of a three-neuron network which demonstrate the coexistence of two stable equilibria within the same quadrant. The three-neuron example hence contradicts a recent theorem in the literature. <<ETX>>
Assimilating Altimetry Data into a HYCOM Model of the Pacific: Ensemble Optimal Interpolation versus Ensemble Kalman Filter

Abstract The ensemble Kalman filter (EnKF) has proven its efficiency in strongly nonlinear dynamical systems but is demanding in its computing power requirements, which are typically about the same as those of the four-dimensional variational data assimilation (4DVAR) systems presently used in several weather forecasting centers. A simplified version of EnKF, the so-called ensemble optimal interpolation (EnOI), requires only a small fraction of the computing cost of the EnKF, but makes the crude assumption of no dynamical evolution of the errors. How do both these two methods compare in realistic settings of a Pacific Ocean forecasting system where the computational cost is a primary concern? In this paper the two methods are used to assimilate real altimetry data via a Hybrid Coordinate Ocean Model of the Pacific. The results are validated against the independent Argo temperature and salinity profiles and show that the EnKF has the advantage in terms of both temperature and salinity and in all parts of t.
Stabilisation of reduced order models via restarting

This paper describes the development, implementation and validation of an explicit restarting scheme to stabilise reduced order models produced using the Eigensystem Realisation Algorithm. Here, the method is applied to a continuous time fluid dynamics model that is actually solved in discrete time space using a CFD approach. However, the methods described are generic and could be applied to any other similar dynamically linear system. The basic restarting approach successfully stabilises ROMs in the majority of cases. However, there are cases where this approach breaks down. The reasons for this breakdown in the basic restarting scheme are discussed, and the strategies for overcoming this problem are described. These include creating ROMs restricted to a range of time step sizes for a specific finite difference scheme and a more general approach using inexact shifts that overcome the problems associated with closely located eigenvalues. Copyright © 2013 John Wiley & Sons, Ltd.
Photoluminescence mechanism model for oxidized porous silicon and nanoscale-silicon-particle-embedded silicon oxide

There is much debate about the photoluminescence (PL) mechanisms of the nanoscale Si/Si oxide systems containing oxidized porous silicon and a nanoscale-Si-particle (NSP)-embedded Si oxide deposited by chemical vapor deposition, sputtering, or Si-ion implanting into Si oxide. In this paper, we suggest that two competitive processes, namely, the quantum confinement (QC) process and the quantum confinement-luminescence center (QCLC) process, take place in the PL. The photoexcitation occurs in the NSPs for both of the processes, while the photoemission occurs either in the NSPs for the QC process or in the luminescence centers (LCs) in Si oxide adjacent to the NSPs for the QCLC process. The rates of the two processes are compared quantitatively. Which process plays the major role in PL is determined by the capture cross section, the luminescence efficiency, and the density of the LCs, and the sizes of the NSPs. For a nanoscale Si/Si oxide system with the LCs having certain capture cross-section and luminescence efficiency, the higher the LC density and the larger the sizes of NSPs, the more beneficial for the QCLC process to surpass the QC process, and vice versa. For certain LC parameters, there is a critical most probable size for the NSPs. When the most probable size of the NSPs is larger than the critical one, the QCLC process dominates the PL, and when the most probable size of the NSPs is smaller than the critical one, the QC process dominates the PL. When the most probable size of the NSPs is close to the critical one, both the QC and QCLC processes should be taken into account. We have used this model to discuss PL experimental results reported for some nanoscale Si/Si oxide systems.
Effects of frequency compression on the intelligibility and quality of speech in noise.

Frequency‐lowering technologies such as frequency compression have become common in high‐end digital hearing aids. However, there are few data on the consequences of adjusting frequency compression ratio (FCR) and frequency compression cutoff (FCC). In this study, sentences at signal‐to‐noise ratios (SNRs) ranging from −10 to +10 dB were frequency compressed at a variety of FCRs (1.5–3) and FCCs (1–2 kHz). Frequency compression was implemented using sinusoidal modeling: the incoming signal was segmented, the spectral peaks found for each segment, and an output sinusoid at a shifted frequency was generated for each peak. Subjects were adult listeners with normal hearing or mild‐moderate sensorineural loss. Intelligibility results illustrate a complex interaction between SNR and frequency compression parameters. At favorable SNRs, frequency compression had minimal effects. At less favorable SNRs, reducing FCC degraded intelligibility more than reducing FCR. At the poorest SNRs any amount of frequency compre.
Water Footprint Assessment for Irrigated Paddy Cultivation in Walawe Irrigation Scheme, Sri Lanka

Water footprint (WF) is a comprehensive summation of the volume of freshwater consumed directly and indirectly in all the steps of the production chain of a product. The water footprint concept has been widely used in agricultural water resources management. Water for irrigation is supplied in Sri Lanka to farmers at no cost, and thus the question is arising, whether the current management strategies the authorities and the farmers follow are appropriate to achieve productive water utilization. Therefore, this study aims at evaluating the water footprint of rice production in an irrigation scheme in the dry zone of Sri Lanka, the Walawe irrigation scheme. Due to the unreliability of the rainfall in the study area paddy cultivation depends entirely on irrigation, thus, the WFblue, in other terms the volume of water evaporated from the irrigation water supply is considered as the total WF (WFtot) in this study. Actual crop evapotranspiration (equivalent to ETblue) was estimated based on the Penman-Monteith (P-M) model integrating effective rainfall, and crop coefficient published in Sri Lankan Irrigation Design Guidelines. The study spanned for three irrigation years from 2018–2021. Actual irrigation water issued to the field was estimated based on the data recorded by the government body responsible for irrigation water management of the area—Mahaweli Authority of Sri Lanka. The total volume of percolated water was computed employing the water balance method while assuming runoff is negligible. Results show that the average annual WFblue found to be 2.27 m3/kg, which is higher than global and national WFtot. As the crop yield in the study area (6.5 ton/ha) is also higher than the global (4.49 ton/ha) and national (3.5 ton/ha) yields, a conclusion was drawn that the irrigation water usage (CWUTblue) in the area may be significantly higher. It was then noted the higher CWUTblue was due to relatively higher evapotranspiration in the area. Thus, it is vital to reduce excess water usage by shifting irrigation practices from flooded irrigation to the System of Rice Intensification (SRI).
Quantum mysteries refined

A gedanken experiment discovered by Lucien Hardy is translated into a very direct black‐box gedanken demonstration of quantum nonlocality with red and green lights, using only two far apart detectors each of which operates in only two modes. The quantum mechanical underpinnings of the gedanken demonstration are quite simple. (This paper provides a text for the Klopsteg Memorial Lecture to the American Association of Physics Teachers at Notre Dame University, August 11, 1994.)
A parametrization of the ice water content observed in frontal and convective clouds

The properties of the ice phase in a number of cloud types are investigated to improve the ice phase parametrization in atmospheric global-climate models. Frontal clouds over southern England and the sea areas around the British Isles, maritime convective clouds over the North Atlantic, and continental convective clouds over New Mexico and Montana in the USA are studied. Ice concentrations are seen to be several orders of magnitude higher than those which could be attributed to primary nucleation of ice nuclei at cloud-top temperatures. Thus secondary ice multiplication processes must be operating in each cloud type. Evidence suggests that the process of ice splinter production during riming, the Hallett-Mossop process which operates at temperatures around -6 degrees C, is the dominant mechanism operating. The data analysed are parametrized as phase ratios, the fraction of cloud condensed water found in the liquid phase, and the variation of this phase ratio with temperature is examined. The greatest differences are observed between frontal and convective clouds, although smaller differences between continental and maritime clouds of the same type are also seen. In general, frontal clouds possess very high fractions of ice across a wide range of temperature. In contrast, convective clouds exhibit a wide range of phase ratio across the whole temperature range observed. These differences are attributed to the greater vertical wind velocities present in convective clouds. These parametrizations have been used in the UK Meteorological Office Global Climate Model. They are valid for clouds which span the Hallett-Mossop splinter-production temperature range.
Finite differences of the partition function

From the Hardy-Ramanujan-Rademacher formula for p(n)-the number of unrestricted partitions of n, it is not difficult to deduce that there exists a least positive integer n0(r) such that V p(n) > 0 for each n > nQ(r), where Vp(n) = p(n) — p(n — 1) and V p(n) = v{ V p(n)}. In this note, we give values"of iIq(/.) for each r < 10 and conjecture that nn(r)lr ~ 1. 1. Notation. In the following, small letters denote positive integers unless stated otherwise; pin) denotes the number of unrestricted partitions of n ; pin, m) is the number of partitions of n into exactly m summands, when m < n; and we take as usual p(0)=l, pi-n) = 0;
Vapor-liquid-solid nucleation of GaAs on Si(111): Growth evolution from traces to nanowires

GaAs nanowires were grown on Si 111 substrates by molecular-beam epitaxy employing Au droplets for the vapor-liquid-solid mechanism. The nucleation happens in three stages, which coincide with the abundance of one of three different GaAs manifestations: first Au-induced lateral traces, then three-dimensional islands, and finally Au-induced vertical nanowires. During deposition of the first 7 ML of GaAs no nanowires grew. By reflection high-energy electron diffraction and transmission electron microscopy, the crystal structure of the GaAs manifestations was examined. Traces and islands adopted the zinc-blende crystal structure and include twins, while nanowires grew in the hexagonal wurtzite structure. The delay in nanowire formation was observed to increase for higher growth temperatures. The gradual covering of the Si by GaAs was comparable to the case of Au-free growth and appears to be linked with the evolution from trace to nanowire growth. During trace formation, Au droplets kept in contact with the Si substrate and were pushed sideways by precipitating GaAs. The nucleation stages could thus be explained by considering that any Au droplet created a trace while in contact with the Si surface and a nanowire after having been pushed onto GaAs. This mechanism of trace growth was explained by the lower interface energy of liquid Au droplets on Si when compared with that on GaAs, as supported by numerical estimates.