Miracle-dz/UniFAR-FTUs huggingface dataset:
Feedback and optimal sensitivity: Model reference transformations, multiplicative seminorms, and approximate inverses

In this paper, the problem of sensitivity, reduction by feedback is formulated as an optimization problem and separated from the problem of stabilization. Stable feedback schemes obtainable from a given plant are parameterized. Salient properties of sensitivity reducing schemes are derived, and it is shown that plant uncertainty reduces the ability, of feedback to reduce sensitivity. The theory is developed for input-output systems in a general setting of Banach algebras, and then specialized to a class of multivariable, time-invariant systems characterized by n \times n matrices of H^{\infty} frequency response functions, either with or without zeros in the right half-plane. The approach is based on the use of a weighted seminorm on the algebra of operators to measure sensitivity, and on the concept of an approximate inverse. Approximate invertibility, of the plant is shown to be a necessary and sufficient condition for sensitivity reduction. An indicator of approximate invertibility, called a measure of singularity, is introduced. The measure of singularity of a linear time-invariant plant is shown to be determined by the location of its right half-plane zeros. In the absence of plant uncertainty, the sensitivity, to output disturbances can be reduced to an optimal value approaching the singularity, measure. In particular, if there are no right half-plane zeros, sensitivity can be made arbitrarily small. The feedback schemes used in the optimization of sensitivity resemble the lead-lag networks of classical control design. Some of their properties, and methods of constructing them in special cases are presented.
A Note on Gaps between Zeros of the Zeta Function

Recently Montgomery and Odlyzko [1] showed, assuming the Riemann Hypothesis, that infinitely often consecutive zeros of the zeta function differ by at least 1.9799 times the average spacing and infinitely often they differ by at most 0.5179 times the average spacing. We improve their result by a better choice of a certain weight function which occurs in their proof and we give explicit bounds for what is possible by this method. In addition, we indicate a method of proof which is considerably simpler than that of Montgomery and Odlyzko. Let logy k = l imsup(/ — y)
Observed solar radio burst effects on GPS/Wide Area Augmentation System carrier‐to‐noise ratio

The first direct observations of Global Positioning System (GPS) L1 (1.57542 GHz) carrier‐to‐noise ratio degradation due to a solar radio burst are presented for an event that occurred on 7 September 2005. Concurrent carrier‐to‐noise ratio data from GPS satellites are available from receivers at Arecibo Observatory, Puerto Rico; San Juan, Puerto Rico; and also from Anderson, South Carolina, United States. The right‐hand circularly polarized (RHCP) signals from this solar radio burst caused a corresponding decrease in the carrier‐to‐noise ratio of about 2.3 dB across all visible satellites. The maximum solar radio burst power associated with this event was 8700 solar flux units (1 SFU = 10−22 W/m2/Hz) RHCP at 1600 MHz. Direct observations of GPS semicodeless L2 carrier‐to‐noise ratio degradation from receivers in Brazil are also presented for a solar radio burst that occurred on 28 October 2003. The maximum degradation at GPS L1 was about 3.0 dB, and a degradation of 10.0 dB was observed on the semicodeless L2 signal. Scaling to historic solar radio burst records suggests that GPS L1 receivers could fail to produce a navigation solution and that semicodeless L1/L2 receivers will fail.
Propagation of surface magnetoelastic waves in TmFeO3 at the spin reorientation

Experimental and theoretical studies of the propagation of surface magnetoelastic waves at the spin reorientation of TmFeO3 are presented. It was found that surface waves propagating on the (a‐b) surface and along the a axis of the orthorhombic crystal, exhibit velocity dips ΔV/V02.5% at the transition temperatures of the spin reorientation. A magnetic field applied in the reorientation plane suppresses and/or shifts the velocity dips. Similar effects were previously observed for shear bulk waves. The observed results are accounted for by using phenomenological magnetic and magnetoelastic expressions in the coupled equations of motion. It is concluded that the surface acoustic wave interacts with the antiferromagnetic modes of the bulk.
The Application of Neumann Type Systems for Solving Integrable Nonlinear Evolution Equations

An algorithm to obtain finite‐gap solutions of integrable nonlinear evolution equations (INLEEs) is provided by using the Neumann type systems in the framework of algebraic geometry. From the nonlinearization of Lax pairs, some INLEEs in 1+1 and 2+1 dimensions are reduced into a class of new Neumann type systems separating the spatial and temporal variables of INLEEs over a symplectic submanifold (M, ω2). Based on the Lax representations of INLEEs, we deduce the Lax–Moser matrix for those Neumann type systems that yield the integrals of motion, elliptic variables, and a hyperelliptic curve of Riemann surface. Then, we attain the Liouville integrability for a hierarchy of Neumann type systems in view of a Lax equation on (M, ω2) and a set of quasi‐Abel–Jacobi variables. We also specify the relationship between Neumann type systems and INLEEs, where the involutive solutions of Neumann type systems give rise to the finite parametric solutions of INLEEs and the Neumann map cuts out a finite dimensional invariant subspace for INLEEs. Under the Abel–Jacobi variables, the Neumann type flows, the 1+1, and 2+1 dimensional flows are integrated with Abel–Jacobi solutions; as a result, the finite‐gap solutions expressed by Riemann theta functions for some 1+1 and 2+1 dimensional INLEEs are achieved through the Jacobi inversion with the aid of the Riemann theorem.
Redeveloping Turbulent Boundary Layer in the Backward-Facing Step Flow

An experimental study has been performed to investigate the redeveloping turbulent boundary layer beyond separation-reattachment for a transitional separated flow. By considering the distribution of the intermittency, it has been confirmed that the turbulent structure changes gradually from a mixing layer to a turbulent boundary layer downstream of reattachment. The balances of the respective terms in the turbulent kinetic energy transport equation are evaluated from the energy dissipation rate obtained through numerical integration of the second moment of the energy spectrum. These terms together with those in the shear stress transport equation indicate the recovery process of the redeveloping boundary layer from nonequilibrium to equilibrium.
Control of antagonistic swarm dynamics via Lyapunov's method

We consider hostile conflicts between two multi‐agent swarms. First, we investigate the complex nature of a single pursuer attempting to intercept a single evader (1P‐1E), and establish some rudimentary rules of engagement. We elaborate on the stability repercussions of these rules. Second, we extend the modelling and stability analysis to multi‐agent swarms with conflicting interests. The present document considers only swarms with equal membership strengths for simplicity. This effort is based on a set of suggested momenta deployed on individual agents. Because pursuers and evaders differ in the influences that they exert on one another, we emphasize asymmetry in momenta between the two types of swarm members. The proposed centralized control law evolves from a Lyapunov concept. Swarm interactions are modelled in two phases: the approach phase during which the two swarms act like individuals in the 1P‐1E interaction; and the individual pursuit phase where each pursuer is assigned to an evader.
Alternative implementations of the semi‐Lagrangian semi‐implicit schemes in the ECMWF model

An important issue for the future development of global models is the degree of implicit solution required for optimum performance, and whether this will change the relative cost‐effectiveness of spectral and finite‐difference models. This is explored by using a predictor‐corrector integration scheme in the European Centre for Medium‐Range Weather Forecasts model, where both steps are integrated using the current semi‐implicit procedure. This is equivalent to taking a first iteration towards a fully implicit scheme, using the existing semi‐implicit method as a preconditioner. The results show that benefit can be obtained provided that both the nonlinear part of the gravity‐wave terms and the semi‐Lagrangian trajectory are recalculated. This suggests that more fully implicit schemes will be beneficial in numerical models. However, the cost of elliptic solvers will not dominate as significant recalculation of tendencies will be required at each iteration.
A mean field prediction of the asymptotic state of decaying 2D turbulence

We compare the quasi-stationary state obtained from a numerical integration of the two-dimensional Navier-Stokes equation, performed by Matthaeus et al. [Phys. Rev. Lett. 66, 2731 (1991)] with predictions of a mean field theory based on inviscid dynamics. We find that over a relatively short initial period, the theory does not apply, whereas at later stages its prediction for the quasi-stationary state is very good. We relate the failure and success of the inviscid theory to the relevance of viscous effects in the dynamics.
Thermal stress anomaly in rare-earth-doped fiber materials for high-power fiber lasers codoped with aluminum and phosphorus

It is well known that thermal stress can significantly influence the properties of optical fibers. These stresses are caused by variations in the coefficient of thermal expansion (CTE) of the differently doped areas in the fiber, like the core and the cladding. On the one hand, the stress has a strong effect on the mechanical stability of fibers. On the other hand, the stress also modifies the most essential property of a fiber, the refractive index distribution, and therefore also the propagation properties. Similar to the effect of generation of birefringence in polarisation maintaining fibers, thermal stress also generates changes in the refractive index of the differently doped regions in the fiber. We report on results of non-destructive polarimetric stress measurements in ytterbium doped fiber preforms, that are codoped with aluminum as well as with phosphorus. Simple models of changes in the CTE for samples doped with multiple elements assume an additive superposition of the changes caused by each dopant. In contrast to such simple models, our investigations have shown that the induced stress cannot be explained by an additive change in the CTE of the glass material. The occurring stresses turn out to be smaller than the simple sum of the effects generated by the respective dopants. This result is also in agreement with measurements of the refractive index profile of these samples. The changes in the index are again not additive for doping with both aluminum and phosphorus.
Dynamic response analysis of generally damped linear system with repeated eigenvalues

For generally damped linear systems with repeated eigenvalues and defective eigenvectors, this study provides a decomposition method based on residue matrix, which is suitable for engineering applications. Based on this method, a hybrid approach is presented, incorporating the merits of the modal superposition method and the residue matrix decomposition method, which does not need to consider the defective characteristics of the eigenvectors corresponding to repeated eigenvalues. The method derived in this study has clear physical concepts and is easily to be understood and mastered by engineering designers. Furthermore, this study analyzes the applicability of step-by-step methods, including the Newmark beta and Runge-Kutta methods for dynamic response calculation of defective systems. Finally, the implementation procedure of the proposed hybrid approach is illustrated by analyzing numerical examples, and the correctness and the effectiveness of the formula are judged by comparing the results obtained from the different methods.
The Ownership Structure, and the Environmental, Social, and Governance (ESG) Disclosure, Firm Value and Firm Performance: The Audit Committee as Moderating Variable

This study investigated the effect of ownership structure on environmental, social, and governance (ESG) disclosure, firm value, firm performance, and audit committees as moderating variables in the Indonesian context. The ownership structures in this study are foreign, public, state, and family ownership. This research is quantitative and uses secondary data. The sample consisted of 140 companies on the Indonesia Stock Exchange for the 2018–2020 period. This study used legitimacy, stakeholder, and agency theory. The analytical method used was partial least squares structural equation modeling. The results show that foreign and public ownership positively and significantly affect environmental, social, and governance disclosure. However, state and family ownership did not affect environmental, social, and governance disclosure. In addition, environmental, social, and governance disclosure positively impacts firm value. However, environmental, social, and governance disclosure do not affect a company’s performance. Audit committees moderate the influence of environmental, social, and governance disclosure and firm value. However, the audit committees do not moderate the effect of environmental, social, and governance disclosure and firm performance. The government should make stronger environmental, social, and government regulations that must be implemented by companies listed on the Indonesia Stock Exchange even though they are now voluntary.
Phonon Dispersion Relations in NaCl

Phonon dispersion relations in NaCl at 80\ifmmode^\circ\else\textdegree\fi{}K have been determined in the crystallographic [100], [101], and [111] symmetry directions using inelastic neutron scattering. Some measurements have also been made at 300\ifmmode^\circ\else\textdegree\fi{}K, and at (1.0, 0.5, 0) in reciprocal space. The results are compared with theoretical calculations: those of Karo and Hardy for their "deformed-dipole" model, those of Schr\"oder and N\"usslein for a "breathing-shell" model, and those of Caldwell and Klein for a shell model. Satisfactory agreement is obtained in many places, but significant discrepancies still remain, particularly close to the zone boundaries. Comparison is also made with earlier x-ray work on NaCl. The work was performed on a new crystal spectrometer at the R2 reactor at Studsvik, which is equipped with a two-crystal monochromator.
Analysis of the drop weight method

The drop weight method is an accurate yet simple technique for determining surface tension σ. It relies on dripping a liquid of density ρ at a low flow rate Q from a capillary of radius R into air and measuring the combined volumes of the primary and satellite drops that are formed. The method’s origin can be traced to Tate, who postulated that the volume Videal of the drop that falls from the capillary should be given by ρgVideal=2πRσ, where g is the gravitational acceleration. Since Tate’s law is only an approximation and the actual drop volume Vf<Videal, in practice the surface tension of the liquid-air interface is determined from the experimental master curve due to Harkins and Brown (HB). The master curve is a plot of the fraction of the ideal drop volume, Ψ≡Vf∕Videal, as a function of the dimensionless tube radius, Φ≡R∕Vf1∕3. Thus, once the actual drop volume Vf, and hence Φ, is known, σ is readily calculated upon determining the value of Ψ from the master curve and that Ψ=ρgVf∕2πRσ. Alth.
SIMULATION OF VISCOUS FINGERING IN MISCIBLE DISPLACEMENTS WITH NONMONOTONIC VISCOSITY PROFILES

The nonlinear evolution of viscous fingering instabilities in miscible displacement flows in porous media with nonmonotonic viscosity profiles is investigated. The flow is accurately simulated using a Hartley transform based spectral method. A flow with nonmonotonic viscosity profile has an unstable region followed downstream by a stable region. Instabilities first begin in the unstable region and then grow and penetrate the stable region. The striking contrast between viscous fingering in flows with monotonic and nonmonotonic viscosity profiles is the direction of fluid penetration. The nonmonotonicity in the viscosity profile gives rise to a new phenomena of ‘‘reverse’’ fingering in which the displaced fluid fingers through the displacing fluid more readily than vice versa. A forward and a reverse mixing lengths are defined to characterize the growth of the mixing zone in the two directions. At large times, both the forward and reverse mixing lengths grow linearly in time. A model nonmonotonic viscosity.
On a Bivariate Distribution with Exponential Marginals

A new bivariate distribution with exponential marginals has been introduced by Singpurwalla & Youngren (1993). This distribution is absolutely continuous and has a single parameter. It was originally motivated as the failure model for a two‐component system experiencing damage described by a shot–noise process. The purpose of this paper is two‐fold. The first is to articulate on several aspects of this distribution, in particular, its genesis, the nature of its dependence, its correlation structure, and its generalized version as a two‐parameter bivariate distribution with exponential marginals. The second purpose of this paper is more general. Prompted by the need to explain certain features of the bivariate distribution, it is found useful to introduce a new notion in reliability and survival analysis. This notion is called the “hazard potential”, of an item susceptible to failure. The hazard potential is viewed as a kind of hidden parameter of failure models that delineates a cause and effect relationship in reliability.
DIFFUSION CHARGING OF ATMOSPHERIC DROPLETS BY IONS, AND THE RESULTING COMBINATION COEFFICIENTS

Abstract The role of ionic diffusion in electrically charging drops in the atmosphere is investigated. Space charge and chemical adsorption being neglected, exact expressions are obtained for the charging rate and the average equilibrium charge acquired by a drop in an ionized atmosphere. The augmentation of the charge by appreciable relative motion is determined. The combination coefficients for neutral and charged droplets are calculated and found to agree with direct measurements. It is concluded that ionic diffusion plays a vital role in determining the electrical equilibrium in the atmosphere.
Atlas of Galactic Neutral Hydrogen

1. Introduction 2. Project motivation 3. Background 4. The Dwingeloo telescope 5. Observing strategy and parameters 6. Initial data reduction 7. Radio interference 8. Stray-radiation correction 9. Accuracy of the survey spectra 10. Preparation of the complete H1 data cube 11. Contamination by external galaxies 12. Atlas of moment maps of the H1 sky 13. CD-ROM 14. Epilogue Acknowledgements References.
A Serially Complete Simulated Observation Time Metadata File for U.S. Daily Historical Climatology Network Stations

Abstract A procedure to infer time of observation based on day—to—day temperature variations is refined and applied to the 1060—station daily Historical Climatology Network (HCN), creating a set of ersatz observation time metadata. Testing of the observation time inference procedure on the HCN data, as well as a set of U.S. normals stations at which no reported observation time changes occur from 1951 to 1991, indicates that, on average, the correct observation time category is identified in nearly 90% of the station years. Classification success decreases, however, at stations at which average annual interdiurnal temperature range falls below 1.9°C. At these stations, which represent only 4% of the HCN daily station years, the percentage of correctly classified years falls to 78%. Application of the observation time inference procedure yields a set of annual observation times for stations in the HCN. Primarily, this surrogate dataset provides a means of identifying observation time during years when docu.
Harvesting Wisdom on Social Media for Business Decision Making

The proliferation of social media provides significant opportunities for organizations to obtain wisdom of the crowds (WOC)-type data for decision making. However, critical challenges associated with collecting such data exist. For example, the openness of social media tends to increase the possibility of social influence, which may diminish group diversity, one of the conditions of WOC. In this research-in-progress paper, a new social media data analytics framework is proposed. It is equipped with well-designed mechanisms (e.g., using different discussion processes to overcome social influence issues and boost social learning) to generate data and employs state-of-the-art big data technologies, e.g., Amazon EMR, for data processing and storage. Design science research methodology is used to develop the framework. This paper contributes to the WOC and social media adoption literature by providing a practical approach for organizations to effectively generate WOC-type data from social media to support their decision making.
AOn WAF-Type Schemes for Multidimensional Hyperbolic Conservation Laws

We explore how the weighted average flux approach can be used to generate first- and second-order accurate finite volume schemes for the linear advection equatons in one, two, and three space dimensions. The derived schemes have multidimensional upwinding aspects and good stability properties. From the two-dimensional methods, we construct a scheme for nonlinear systems of hyperbolic conservation laws that is second-order accurate in smooth flow. Spurious oscillations are controlled by making use of one-dimensional TVD limiter functions. Numerical results are presented for the shallow water equations in two space dimensions. The equivalent schemes are derived for nonlinear systems in three space dimensions.
A general purpose sampling algorithm for continuous distributions (the t-walk)

We develop a new general purpose MCMC sampler for arbitrary continuous distributions that requires no tuning. We call this MCMC the t-walk . The t-walk maintains two independent points in the sample space, and all moves are based on proposals that are then accepted with a standard Metropolis-Hastings acceptance probability on the product space. Hence the t-walk is provably convergent under the usual mild requirements. We restrict proposal distributions, or ‘moves’, to those that produce an algorithm that is invariant to scale, and approximately invariant to aﬃne transformations of the state space. Hence scaling of proposals, and eﬀectively also coordinate transformations, that might be used to increase eﬃciency of the sampler, are not needed since the t-walk’s operation is identical on any scaled version of the target distribution. Four moves are given that result in an eﬀective sampling algorithm. We use the simple device of updating only a random subset of coordinates at each step to allow application of the t-walk to high-dimensional problems. In a series of test problems across dimensions we ﬁnd that the t-walk is only a small factor less eﬃcient than optimally tuned algorithms, but signiﬁcantly outperforms general random-walk M-H samplers that are not tuned for speciﬁc problems. Further, the t-walk remains eﬀective for target distributions for which no optimal aﬃne transformation exists such as those where correlation structure is very diﬀerent in diﬀering regions of state space. Several examples are presented showing good mixing and convergence characteristics, varying in dimensions from 1 to 200 and with radically diﬀerent scale and correlation structure, using exactly the same sampler. The t-walk is available for R, Python, MatLab and C++ at http://www.cimat. mx/~jac/twalk/ .