Miracle-dz/UniFAR-FTUs huggingface dataset:
Fully developed intermittent flow in a curved tube

Fully developed intermittent flow in a strongly curved tube was numerically simulated using a numerical scheme based on the simpler method. Physiological pulsatile flow in the aorta was simulated as intermittent flow, with a waveform consisting of a pulse-like systolic flow period followed by a stationary diastolic period. Numerical simulations were carried out for the following conditions: Dean number κ=393, frequency parameter α=4–27, curvature ratio δ=1/2, 1/3 and 1/7, and intermittency parameter η=0–1/2, where η is the ratio of a systolic time to the cycle period. For α=18 and 27 the axial-flow profile in a systolic period becomes close to that of a sinusoidally oscillatory flow. At the end of the systole, a region of reversed axial velocity appears in the vicinity of the tube wall, which is caused by the blocking of the flow, similar to blocked flow in a straight tube. This area is enlarged near the inner wall of the bend by the curvature effect. Circumferential flow accelerated in a systole streams into the inner corner and collides at the symmetry line, which creates a jet-like secondary flow towards the outer wall. The region of reversed axial velocity is extended to the tube centre by the secondary flow. The development of the flow continues during the diastolic period for α higher than 8, and the flow does not completely dissipate, so that a residual secondary vortex persists until the next systole. Accordingly, the development of secondary flow in the following systolic phase is strongly affected by the residual vortex at the end of the previous diastolic phase, especially by stationary diastolic periods. Therefore, intermittent flow in a curved tube is strongly affected by the stationary diastolic period. For η=0 and 1/5, the induced secondary flow in a systole forms additional vortices near the inner wall, whereas for η=1/3 and 1/2 additional vortices do not appear. The characteristics of intermittent flow in a curved tube are also strongly affected by the length of the diastolic period, which represents a period of zero flow.
Three-dimensional convection in a horizontal fluid layer subjected to a constant shear

Rayleigh-Bénard convection in the presence of a plane Couette flow is investigated by numerical computations. From earlier work it is well known that longitudinal rolls are preferred at the onset of convection and that at Prandtl numbers of the order unity or less these rolls become unstable with respect to the wavy instability which introduces wavy distortions perpendicular to the axis of the rolls. In the present analysis the three-dimensional flows arising from these distortions are studied and their stability is considered. A main result is the subcritical existence of three-dimensional flows at Rayleigh numbers far below the critical value for onset of convection.
Vortex events in Euler and Navier–Stokes simulations with smooth initial conditions

Abstract We present high-resolution numerical simulations of the Euler and Navier–Stokes equations for a pair of colliding dipoles. We study the possible approach to a finite-time singularity for the Euler equations, and contrast it with the formation of developed turbulence for the Navier–Stokes equations. We present numerical evidence that seems to suggest the existence of a blow-up of the inviscid velocity field at a finite time (${t}_{s} $) with scaling $\vert u\vert _{\infty } \ensuremath{\sim} \mathop{ ({t}_{s} \ensuremath{-} t)}\nolimits ^{\ensuremath{-} 1/ 2} $, $\vert \omega \vert _{\infty } \ensuremath{\sim} \mathop{ ({t}_{s} \ensuremath{-} t)}\nolimits ^{\ensuremath{-} 1} $. This blow-up is associated with the formation of a ${k}^{\ensuremath{-} 3} $ spectral range, at least for the finite range of wavenumbers that are resolved by our computation. In the evolution toward ${t}_{s} $, the total enstrophy is observed to increase at a slower rate, $\Omega \ensuremath{\sim} \mathop{ ({t}_{s} \ensuremath{-} t)}\nolimits ^{\ensuremath{-} 3/ 4} $, than would naively be expected given the behaviour of the maximum vorticity, ${\omega }_{\infty } \ensuremath{\sim} \mathop{ ({t}_{s} \ensuremath{-} t)}\nolimits ^{\ensuremath{-} 1} $. This indicates that the blow-up would be concentrated in narrow regions of the flow field. We show that these regions have sheet-like structure. Viscous simulations, performed at various $\mathit{Re}$, support the conclusion that any non-zero viscosity prevents blow-up in finite time and results in the formation of a dissipative exponential range in a time interval around the estimated inviscid ${t}_{s} $. In this case the total enstrophy saturates, and the energy spectrum becomes less steep, approaching ${k}^{\ensuremath{-} 5/ 3} $. The simulations show that the peak value of the enstrophy scales as ${\mathit{Re}}^{3/ 2} $, which is in accord with Kolmogorov phenomenology. During the short time interval leading to the formation of an inertial range, the total energy dissipation rate shows a clear tendency to become independent of $\mathit{Re}$, supporting the validity of Kolmogorov’s law of finite energy dissipation. At later times the kinetic energy shows a ${t}^{\ensuremath{-} 1. 2} $ decay for all $\mathit{Re}$, in agreement with experimental results for grid turbulence. Visualization of the vortical structures associated with the stages of vorticity amplification and saturation show that, prior to ${t}_{s} $, large-scale and the small-scale vortical structures are well separated. This suggests that, during this stage, the energy transfer mechanism is non-local both in wavenumber and in physical space. On the other hand, as the spectrum becomes shallower and a ${k}^{\ensuremath{-} 5/ 3} $ range appears, the energy-containing eddies and the small-scale vortices tend to be concentrated in the same regions, and structures with a wide range of sizes are observed, suggesting that the formation of an inertial range is accompanied by transfer of energy that is local in both physical and spectral space.
Response of a Flexible Printed Circuit Board to Periodic Shock Loads Applied to its Support Contour

Treating a printed circuit board (PCB) as a thin flexible rectangular plate, we evaluate its dynamic response to periodic shock loads applied to the support contour. The effect of the load periodicity on the amplitudes, accelerations, and stresses is analyzed for transient and steady-state damped linear vibrations, as well as for steady-state undamped nonlinear vibrations. It is shown that the transient nonresonant linear response can exceed the steady-state response by up to two times, and that the linear approach can be misleading in the case of a nondeformable support contour and intense loading. The obtained results can be of help when evaluating the accelerations, experienced by surface mounted electronic components and devices, and the dynamic stresses in a PCB of the given type, dimensions, and support conditions.
Media noise improvement through head-disk spacing reduction

Experimental and theoretical results show that media noise decreases with reduced head-media separation. Media with the same magnetic layer but with Cr overlayers of varying thickness were fabricated as a means to adjust head-media separation. Noise power vs. recording density curves exhibit an initial linear region followed by a supralinear region indicative of appreciable bit interaction. The noise maximum for the lower flying cases occurs at a higher density. The slope of the noise curve is also lower for lower fly heights, indicating a lower noise level per transition. Simulations of transition pairs show a clearly defined zig-zag structure for large head-media separations. When flying near contact, the zig-zag amplitude is greatly diminished. >
REAL SPECTRUM OF NON-HERMITIAN HAMILTONIANS FOR HULTHÉN POTENTIAL

The non-Hermitian Hamiltonians of the type $H_\alpha=\frac{[p+i\alpha g(x)]^2}{2m}+V(x)$ is solved for the generalized Hulthen potential in terms of Jacobi polynomials by using Nikiforov–Uvarov method. The exact bound-state energy eigenvalues and eigenfunctions are presented.
A semiparametric Bayesian model for randomised block designs

SUMMARY A model is proposed for a Bayesian semiparametric analysis of randomised block experiments. The model is a hierarchical model in which a Dirichlet process is inserted at the middle stage for the distribution of the block effects. This model allows an arbitrary distribution of block effects, and it results in effective estimates of treatment contrasts, block effects and the distribution of block effects. An effective computational strategy is presented for describing the posterior distribution.
Reflections on the hysteretic damping model

This paper presents a reflection on a recently proposed solution to the problem of the free vibration response with the constant hysteretic damping model, that has been presented in some conferences in recent years, by the author himself and some of his colleagues. On the one hand, as expected, the subject has been received with natural criticism, mainly due to the well-known non-causal behaviour of the model in free vibration. On the other hand, it was not easy to understand what could be wrong in that proposal, as apparently everything was perfect from a mathematical point of view. The author decided that this subject deserved a more careful and detailed analysis and - in this kind of tutorial paper - the issue seems to have been clarified. It is concluded that the proposed solution involving the constant hysteretic damping corresponds in fact to an equivalent viscously damped model; it is therefore concluded that the application of the constant hysteretic damping to model the free vibration of practical engineering problems should be considered only in the perspective of an equivalent viscously damped model.
Some windows with very good sidelobe behavior

Some of the windows presented by Harris [1] are not correct in terms of their reported peak sidelobes and optimal behavior. We present corrected plots of Harris' windows and also derive additional windows with very good sidelobes and optimal behavior under several different constraints. The temporal weightings are characterized as a sum of weighted cosines over a finite duration. The plots enable the reader to select a window to suit his requirements, in terms of bias due to nearby sidelobes and bias due to distant sidelobes.
THE NONCOMMUTATIVE GEOMETRY OF APERIODIC SOLIDS

This mini-course, which will delivered at the INDAM Meeting Noncommutative Geometry, Index Theory and Applications, will offer a review of the achievements on a program of research that started in the Fall of 1979. The four lectures will concern the (i) The Gap Labeling Theorem, (ii) The Hull of aperiodic, repetitive, FLC tiling and the Anderson-Putnam Complex, (iii) The transverse Geometry of tiling spaces, (iv) Non FLC atomic distributions: a new approach to the Mechanics of real solids. 1. Plan of the Mini-Course The four lectures will provide a summary of the following topics 1.1. The Gap Labeling Theorem. This part will give a description of the Hamiltonians associated with the electron dynamic in an aperiodic solid. Various examples will be provided, showing the existence of a Cantor spectrum. The integrated density if state (IDS) will be defined and his properties summarized. The C∗-algebra A generated by the Hamiltonian and its translated will be introduced, leading to the first notion of Hull. The Shubin formula is a crucial step in connecting the IDS to the K0-group of A. The gap labeling theorem will be established. Some general consequences will be discussed. A series of results for various examples of systems will conclude this part. 1.2. The Hull and the Anderson-Putnam Complex. Various examples of tilings will illustrate this part. Two constructions will be offered: the cut-and-project and the substitutions. Illustration by quasicrystal materials will be shown. The Hull will be redefined starting from the atomic configurations. Through the Voronoi construction it will be described by tilings. The Anderson-Putnam complex will be defined for substitution tilings, and the Hull can be identified as an inverse limit of such complexes. Examples in one and two dimension will be provided. Results concerning the calculation of the Čech cohomology of the Hull will be presented, using the longitudinal cohomology, the pattern equivariant cohomology or the PV -cohomology. A spectral sequence permits to compute the K-group starting from the Čech cohomology of the Hull. A description of the transversal and of its groupoid will be provided using the notion of Michon tree and of Bratteli diagrams, as a conclusion. Work supported in part by NSF grants DMS 06009565, DMS 0901514 and by the CRC701, Spectral Structures and Topological Methods in Mathematics, Mathematik, Universität Bielefeld, Germany.
CLASSIFICATION OF SPACES OF THE SAME n-TYPE FOR ALL n

The set of homotopy equivalence classes of CW-spaces Y for which the Postnikov approximations are homotopy equivalent to those of a given space X is shown to be in one-to-one correspondence with liml of a tower of homotopy automorphism groups. Recall that two CW-spaces X and Y are said to have the same n-type if the nth Postnikov approximations X(n) and y(n) are homotopy equivalent. The homotopy classification problem for infinite dimensional complexes can be studied in two steps. First, classify all finite dimensional complexes (! ) and then classify for a given X all complexes of the same n-type for all n as X. The purpose of this note is to codify this second step. THEOREM I. Let X be a connected CW-space. Denote by SNT(X) the set of homotopy equivalence classes of CW-spaces Y such that Y has the same n-type for all n as X. Then SNT(X) is in one-to-one correspondence with the pointed set lim1(Aut(X (n))), where Aut(X (n)) is the group of homotopy classes of homotopy equivalences of X(n).
Design of a two‐level controller for an active suspension system

The paper focuses on a control design for a vehicle suspension system in which a balance between different performance demands is achieved. The starting point of the control design is a full–car model which contains nonlinear components, i.e. the dynamics of the dampers and springs and nonlinear actuator dynamics. In order to handle the high complexity of the problem this paper proposes the design of a two‐level controller of an active suspension system. The required control force is computed by applying a high‐level controller, which is designed using a linear parameter varying (LPV) method. For the control design the model is augmented with weighting functions specified by the performance demands and the uncertainty assumptions. The actuator generating the necessary control force is modelled as a nonlinear system for which a low‐level force‐tracking controller is designed. To obtain the low‐level controller a backstepping method is proposed. As an alternative solution a feedback linearization method is also presented. The operation of the controller is illustrated through simulation examples.
A new approach to the degree-constrained minimum spanning tree problem using genetic algorithm

The degree-constrained minimum spanning tree problem is of high practical importance. Up to now there have been few effective algorithms to solve this problem because of its NP-hard complexity. In this paper we present an approach to solving this problem by using genetic algorithms (GAs), and provide numerical example to demonstrate the efficiency of the proposed approach.
Small-scale structure in colliding off-axis vortex rings

Off-axis collisions of equal-strength vortex rings were experimentally examined. Two equal-strength vortices were generated which moved toward each other along parallel, but offset, trajectories. Two colour laser-induced fluorescence visualization techniques were used to observe these phenomena and gain insight into their importance in vortex interactions. The most prominent features of this interaction were rapid growth and rotation of the rings and formation of evenly spaced ringlets around the cores of the original rings. Large-scale motions are described using simple vortex induction arguments. The small scales are caused by nonlinear amplification of instabilities during the asymmetric interaction.
Adaptive Exponential Stabilization for a Class of Stochastic Nonholonomic Systems

This paper investigates the adaptive stabilization problem for a class of stochastic nonholonomic systems with strong drifts. By using input-state-scaling technique, backstepping recursive approach, and a parameter separation technique, we design an adaptive state feedback controller. Based on the switching strategy to eliminate the phenomenon of uncontrollability, the proposed controller can guarantee that the states of closed-loop system are global bounded in probability.
More than 160 near Earth asteroids observed in the EURONEAR network

Astrometry is mandatory in order to acquire the positional information necessary to define and improve orbits of NEAs and PHAs and to study their trajectories through the solar system, especially in the vicinity of Earth. Photometry is required to derive some physical information about NEAs and PHAs. In order to achieve these objectives, the main method of research of the EURONEAR is the follow-up programme of objects selected by a few criteria, carried out mostly at 1m-class telescopes endowed with medium and large field cameras. 162 NEAs summing more than 1,500 individual positions were observed for a total time of 55 nights in both visiting mode and regular runs using nine telescopes located in four countries. The observations were reduced promptly and reported to the Minor Planet Centre (MPC) which validated and included them in the MPC and NEODyS databases following the improvement of their orbital elements. For one binary NEA we acquired photometry and were able to determine its orbital and rotational periods. Complementary to the follow-up work, as many as 500 unknown moving objects consistent with new Main Belt asteroids and one possible NEA were discovered in the analyzed fields. Our positions present 1′′ precision with an accuracy of 0.2-0.4′′ , sufficient for achieving our immediate main goals. The observations and data reduction were conducted by our network members, which included some students and amateurs supervised by professional astronomers. In most cases, we increased the observational arcs decreasing the uncertainties in the orbits, while in some cases the new positions allowed us to recover some bodies endangered to be lost, defining their orbits.
Fabrication of Nb/Al-N/sub x//NbTiN junctions for SIS mixer applications

We discuss fabrication and characteristics of superconductor-insulator-superconductor (SIS) junctions which typically exhibit a 3.5 mV sum-gap voltage. Junctions have a sub-gap to normal state resistance ratio of R/sub SG//R/sub N/=27 for resistance-area products down to R/sub N/A=8 /spl Omega/ /spl mu/m/sup 2/ and high quality junctions have been produced with RNA products as low as 4 /spl Omega/ /spl mu/m/sup 2/. The device structure incorporates a Nb base electrode, a tunnel barrier formed by plasma nitridation of a thin Al proximity layer, and a NbTiN counter-electrode. Results for all Nb junctions with high current density aluminum-nitride barriers are also shown. Nitridation of the aluminum layer is investigated by control of the dc floating potential on a separate rf driven electrode in the vacuum process chamber. Devices are integrated to a mixer antenna structure incorporating NbTiN as a ground plane. The wire circuit layer can be either normal metal or NbTiN. Annealing results show improved I-V characteristics with increased RNA products. Recent receiver measurements employing these junctions exhibit low noise performance up to 900 GHz.
On Some Properties of Convex Matrix Sets Characterized by P -Matrices and Block P -Matrices

In this paper, we consider convex sets of real matrices and establish criteria characterizing these sets with respect to certain matrix properties of their elements. In particular, we deal with convex sets of P-matrices, block P-matrices and M-matrices, nonsingular and full rank matrices, as well as stable and Schur stable matrices. Our results are essentially based on the notion of a block P-matrix and extend and generalize some recently published results on this topic.
Study of wavelength shift in InGaAs/InAlGaAs QW DFB lasers based on laser parameters from a comparison of experiment and theory

Experimental data of InGaAs/InAlGaAs quantum well distributed feedback (DFB) lasers such as spectra, under continuous and pulsed biasing, relative intensity noise and linewidth, are compared with the results of model calculations based on a transfer matrix method. Using experimental data of different lasers, a set of physical DFB laser parameters was determined. We succeeded in describing all the experimental data of different lasers by the same set. The determined parameter set was further applied to study the influence of facet properties on the wavelength shift of DFB lasers. We found a very strong dependence of the wavelength tunability on the end facet phases. The wavelength shift varies by a factor up to three between different end facet phases and coatings. This is crucial for the yield of, for example, tunable multisection DFB lasers with an envisaged large tuning range. >
Efficient Pricing and Reliable Calibration in the Heston Model

We suggest a general scheme for improvement of FT-pricing formulas for European options and give efficient recommendations for the choice of the parameters of the numerical scheme, which allow for very accurate and fast calculations. The efficiency of the method stems from the properties of functions analytical in a strip, which were introduced to finance by Feng and Linetsky (2008). We demonstrate that an indiscriminate choice of parameters of a numerical scheme leads to an inaccurate pricing and calibration. As applications, we consider the Heston model and its generalization. For many parameter sets documented in empirical studies of financial markets, relative accuracy better than 0.01% can be achieved by summation of less than 10-20 terms even in the situations in which the standard approach requires more than 200. In some cases, the one-term formula produces an error of several percent, and the summation of two terms — less than 0.5%. Typically, 10 terms and fewer suffice to achieve the error tolerance of several percent and smaller.
Estimators for type-II censored (log)normal samples

Three common estimators for the parameters of the log-normal distribution are evaluated for censored samples. Correction factors which eliminate essentially all the bias, and formulas for the standard deviations of the estimators, are presented. It is reported that the Persson-Rootzen estimators are about as good as the maximum-likelihood estimators, without the penalty of requiring iterative (computer) optimization. Also, the estimators resulting from (least squares) fitting a line to the plot of log lifetimes on normal (Gaussian) probability paper are reasonably good. Formulas are given for obtaining these latter estimators without actually plotting the points. The author simulated 5 k to 30 k samples (more samples for smaller N for each case) and calculated the following: the means, standard deviations, and third moments of each estimator; correlations between the two members of each pair; comparisons between the estimators; and simple corrections to improve the performance of the estimators. >
Tunable silicon microring resonator with wide free spectral range

The authors present a silicon-on-insulator single ring resonator with a free spectral range equal to 47nm, which is the widest known value for this type of resonators. The ring radius is 2μm and is the smallest ring resonator ever reported, achieving experimentally such a wide spectral range. For this ring resonator, the authors demonstrate the quality factor to be equal to 6730±60. They thermally tune the resonant wavelength with 0.11nm∕°C, thus showing the ring resonator as an attractive component for on-chip ultracompact photonic add/drop filters and switches.