Miracle-dz/UniFAR-FTUs huggingface dataset:
Improvements in statistical forecasts of monthly and two‐monthly surface air temperatures using a stratospheric predictor

Anomalies in the extratropical stratospheric circulation are known to affect climate at the surface for up to 2 months during winter. Previously, several studies have proposed simple statistical models based on a stratospheric predictor to forecast surface climate; however, none of these studies considered a possibility, nor evaluated the skill, of categorical weather forecasts at individual sites. Here we evaluate the skill of the three‐category (below‐normal, near‐normal and above‐normal) monthly and two‐monthly mean surface air temperature statistical forecasts, both deterministic and probabilistic, which use, as predictors, normalized mean polar cap geopotential height at 150 hPa and mean surface air temperature over the preceding 30‐day period (persistence). We show that, during the period 1957–2013, at several sites influenced by the Northern Annular Mode variability, the monthly and two‐monthly forecasts based on the stratospheric predictor possess a moderate skill in December–March at lead times of several days, but in many cases they only marginally improve forecasts based on persistence only. Nevertheless at some sites in northeastern Europe and northwestern Russia the improvements indicate that statistical climate forecasting at these sites can benefit from addition of stratospheric information. The results of this study further demonstrate usefulness of simple statistical models based on stratospheric predictors, both as a complementary source of forecasts, and as providing benchmarks for evaluating the skill of more complex dynamical systems.
A behavioral approach to linear exact modeling

The behavioral approach to system theory provides a parameter-free framework for the study of the general problem of linear exact modeling and recursive modeling. The authors present the solution of the (continuous-time) polynomial-exponential time series modeling problem. Both recursive and nonrecursive solutions are provided and classified according to properties like complexity and controllability. It is shown, in particular, that recursive modeling corresponds to updating by means of a cascade inter-connection of systems. As a special case, the solution of several other problems, such as rational interpolation, realization, and modeling of arbitrary discrete-time time series, is obtained. >
Source-Sink Reconstruction Through Regularized Multicomponent Regression Analysis—With Application to Assessing Whether North Sea Cod Larvae Contributed to Local Fjord Cod in Skagerrak

The problem of reconstructing the source-sink dynamics arises in many biological systems. Our research is motivated by marine applications where newborns are passively dispersed by ocean currents from several potential spawning sources to settle in various nursery regions that collectively constitute the sink. The reconstruction of the sparse source-sink linkage pattern, that is, to identify which sources contribute to which regions in the sink, is a challenging task in marine ecology. We derive a constrained nonlinear multicomponent regression model for source-sink reconstruction, which is capable of simultaneously selecting important linkages from the sources to the sink regions and making inference about the unobserved spawning activities at the sources. A sparsity-inducing and nonnegativity-constrained regularization approach is developed for model estimation, and theoretically we show that our estimator enjoys the oracle properties. The empirical performance of the method is investigated via simulation studies mimicking real ecological applications. We examine the transport hypothesis that Atlantic cod larvae were transported by sea currents from the North Sea to a few exposed coastal fjords along the Norwegian Skagerrak. Our findings of the spawning date distribution is consistent with results from previous studies, and the proposed approach for the first time provides valid statistical support for the larval drift conjecture. Supplementary materials for this article are available online.
An excitation mechanism for the free ‘core nutation’

Summary. The Earth is believed to possess a free nutational mode due to its rotating, elliptical, fluid core, with an eigenfrequency of approximately (1 t 1/460) cycle sidereal day-’ as seen from the sidereally rotating Earth. This free ‘core nutation’ has not yet been undisputably observed. Furthermore, there has been considerable doubt that any known mechanism could excite this mode to an observable level. We show here that diurnal atmospheric and oceanic loading of the Earth’s surface provide an efficient excitation mechanism which depends critically on the physical damping of the mode. Possible effects of the mode on geodetic measurements are discussed. We also consider the effects of ‘wobble’ and ‘nutation’ on astrometric observations.
Using a partial least squares (PLS) method for estimating cyanobacterial pigments in eutrophic inland waters

Midwestern lakes and reservoirs are commonly exposed to anthropogenic eutrophication. Cyanobacteria thrive in these nutrient rich-waters and some species pose three threats: 1) taste & odor (drinking), 2) toxins (drinking + recreational) and 3) water treatment process disturbance. Managers for drinking water production are interested in the rapid identification of cyanobacterial blooms to minimize effects caused by harmful cyanobacteria. There is potential to monitor cyanobacteria through the remote sensing of two algal pigments: chlorophyll a (CHL) and phycocyanin (PC). Several empirical methods that develop spectral parameters (e.g., simple band ratio) sensitive to these two pigments and map reflectance to the pigment concentration have been used in a number of investigations using field-based spectroradiometers. This study tests a multivariate analysis approach, partial least squares (PLS) regression, for the estimation of CHL and PC. PLS models were trained with 35 spectra collected from three central Indiana reservoirs during a 2007 field campaign with dual-headed Ocean Optics USB4000 field spectroradiometers (355 - 802 nm, nominal 1.0 nm intervals), and CHL and PC concentrations of the corresponding water samples analyzed at Indiana University-Purdue University at Indianapolis. Validation of these models with 19 remaining spectra show that PLS (CHL R2=0.90, slope=0.91, RMSE=20.61 μg/L; PC R2=0.65, slope=1.15, RMSE=23.04. μg/L) performed equally well to the band tuning model based on Gitelson et al. 2005 (CHL: R2=0.75, slope=0.84, RMSE=40.16 μg/L; PC: R2=0.59, slope=1.14, RMSE=20.24 μg/L).
Formation and Detachment of Leading EdgeVortices on Unsteady Airfoils

The unsteady velocity field around a pitching and plunging airfoil has been investigated whereby two different mechanisms leading to the detachment of leading edge vortices, which form at the suction side of the airfoil during a motion cycle, were of central interest. One of these mechanisms is analogous to the classical vortex shedding mechanisms behind bluff bodies. The second mechanism is independent of any geometrical length and occurs as a result of the viscous/inviscid interaction between the leading edge vortex and the boundary layer on the airfoil. The mass transferred from the shear layer at the leading edge for one motion period was hypothesized to determine, which detachment mechanism limits LEV growth. A non-dimensional parameter kappa, describing the covering ratio of the LEV and the airfoil chord, has been introduced to predict for which flow parameters a detachment between both mechanism occurs. A decomposition of kappa yields a dependency on the Reynolds number, the reduced frequency and the shear layer parameters. Time-resolved particle image velocimetry was used to obtain two-dimensional velocity fields and direct force measurements were performed. The flow fields were analyzed be means of vortex identification methods, topological arguments and the finite time Lyapunov-exponent. The results show, that the commonly used set of non-dimensional parameters is not sufficient to completely describe the vortex detachment behavior, since it neglects the shear layer properties. Instead, the conducted experiments reveal, that the leading edge shape determining the shear layer curvature has a recognizable impact an the lift and the circulation created by an unsteady profile. It was found, that a critical chord length exists, above which the bluff body detachment mechanism is replaced by a mechanisms related to viscous/inviscid interactions between secondary flow structures and the shear layer. The formation these secondary structures is found to be limited to a low Reynolds-number regime. While at low reduced frequencies,the airfoil chord length is characteristic for LEV detachment, the airfoil kinematics determine the instant of LEV detachment at higher reduced frequencies. The results show, that the LEV detachment behavior is much more complex than previously assumed. Its dependency might be reduced to the chord as a characteristic parameter in the typical flight regime with moderate reduced frequencies and sufficiently high Reynolds numbers, but involves many more parameters if the airfoil kinematics leave this typical flight regime.
Nonlinear Response Surface and Mixture Experiment Methodologies Applied to the Study of Synergism

A new paradigm for the study of the joint action (synergism, additivity and antagonism) of different agents that combines nonlinear response surface modeling with mixture experiment methodologies is described. We achieve a global nonlinear response surface model using raw data modeling and hierarchical parameter modeling along with numerical and graphical evaluations. The method is applied to a very large previously‐published (Faessel et al., 1998) in vitro study of the combined effect of Trimetrexate (TMQ) and AG2034 on inhibition of cancer cell growth. The modulator Folic acid (Folate) concentration is also included as a continuous process variable. The mixture portion of the analysis is best identified as an “NLMAZ‐PV” experiment, incorporating a nonlinear mixture‐amount model with zero amounts (control observations) and the process variable. The underlying nonlinear structural model, describing the relationship between the mixture amount and the observed effect, is the four parameter Hill (1910) equation. This model for studying synergism was developed as an improvement over the flagship synergy/antagonism model of Greco et al. (1995) and other response surface synergy models. This new modeling approach allows for irregularly‐shaped isobols, complex patterns of local synergism and antagonism, a modulating agent with no effect of its own, and extensions to three or more drugs (White et al., 2003). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of infilled frames using A coupled finite element and boundary element solution scheme

The behaviour of infilled frames subjected to horizontal loads is analysed by an iterative numerical procedure. The stiffness of the structural system is determined with variations in geometrical and mechanical characteristics. The analysis is carried out utilizing the boundary element method (BEM) for the infill and opportunely dividing the frame into finite elements, so as to transform the mutual interactions of the two subsystems into stresses distributed along the boundary for the infill and into nodal actions for the frame. This makes it possible to take into account the separation arising between the two substructures when mutual tensile stresses are involved. At first, infills without openings are considered, using BEM with constant elements for two-dimensional problems in elasticity. The results are compared with those obtained using the simplified equivalent pin-jointed strut model, which is very common in the literature. Subsequently, using an analogous procedure, panels with openings are considered. For these systems, for which no satisfactory simplified models exist, the loss of stiffness in relation to the size of the opening is evaluated.
Exponential asymptotics of homoclinic snaking

We study homoclinic snaking in the cubic-quintic Swift–Hohenberg equation (SHE) close to the onset of a subcritical pattern-forming instability. Application of the usual multiple-scales method produces a leading-order stationary front solution, connecting the trivial solution to the patterned state. A localized pattern may therefore be constructed by matching between two distant fronts placed back-to-back. However, the asymptotic expansion of the front is divergent, and hence should be truncated. By truncating optimally, such that the resultant remainder is exponentially small, an exponentially small parameter range is derived within which stationary fronts exist. This is shown to be a direct result of the ‘locking’ between the phase of the underlying pattern and its slowly varying envelope. The locking mechanism remains unobservable at any algebraic order, and can only be derived by explicitly considering beyond-all-orders effects in the tail of the asymptotic expansion, following the method of Kozyreff and Chapman as applied to the quadratic-cubic SHE (Chapman and Kozyreff 2009 Physica D 238 319–54, Kozyreff and Chapman 2006 Phys. Rev. Lett. 97 44502). Exponentially small, but exponentially growing, contributions appear in the tail of the expansion, which must be included when constructing localized patterns in order to reproduce the full snaking diagram. Implicit within the bifurcation equations is an analytical formula for the width of the snaking region. Due to the linear nature of the beyond-all-orders calculation, the bifurcation equations contain an analytically indeterminable constant, estimated in the previous work by Chapman and Kozyreff using a best fit approximation. A more accurate estimate of the equivalent constant in the cubic-quintic case is calculated from the iteration of a recurrence relation, and the subsequent analytical bifurcation diagram compared with numerical simulations, with good agreement.
Generation of zonal flows through symmetry breaking of statistical homogeneity

In geophysical and plasma contexts, zonal flows (ZFs) are well known to arise out of turbulence. We elucidate the transition from homogeneous turbulence without ZFs to inhomogeneous turbulence with steady ZFs. Starting from the equation for barotropic flow on a β plane, we employ both the quasilinear approximation and a statistical average, which retains a great deal of the qualitative behavior of the full system. Within the resulting framework known as CE2, we extend recent understanding of the symmetry-breaking zonostrophic instability and show that it is an example of a Type Is? > instability within the pattern formation literature. The broken symmetry is statistical homogeneity. Near the bifurcation point, the slow dynamics of CE2 are governed by a well-known amplitude equation. The important features of this amplitude equation, and therefore of the CE2 system, are multiple. First, the ZF wavelength is not unique. In an idealized, infinite system, there is a continuous band of ZF wavelengths that allow a nonlinear equilibrium. Second, of these wavelengths, only those within a smaller subband are stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets. These behaviors are shown numerically to hold in the CE2 system. We also conclude that the stability of the equilibria near the bifurcation point, which is governed by the Eckhaus instability, is independent of the Rayleigh–Kuo criterion.
Statistical properties of low‐frequency magnetic field fluctuations in the solar wind from 0.29 to 1.0 AU during solar minimum conditions: HELIOS 1 and HELIOS 2

To obtain information on the temporal and spatial evolution of MHD waves and discontinuities in the solar wind, we studied by means of statistical methods magnetic field fluctuations measured by the two HELIOS spacecraft in the frequency range between 2.4×10−5 Hz and 1.3×10−2 Hz at distances from the sun between 0.29 AU and 1.0 AU. Some statistical properties as magnetic field variances show the fluctuations remaining very similar on their way out from the sun. A different picture of the fluctuations emerges from analyzing the spectral properties of the magnetic field: The slope of the power spectral densities (both the vector components and the magnitude of the magnetic field) as a function of frequency becomes steeper with increasing heliographic distance—the solar wind seems to act as a low-pass filter. The major changes occur within a heliographic distance up to about 0.4 AU. Field magnitude fluctuations fall off less rapidly with increasing radius than do fluctuations in the vector components. Cross spectral analysis between magnetic field components reveal the fluctuations as generally being field magnitude conserving.
Comparison of implicit and explicit hybridizable discontinuous Galerkin methods for the acoustic wave equation

We describe implicit and explicit formulations of the hybridizable discontinuous Galerkin method for the acoustic wave equation based on state‐of‐the‐art numerical software and quantify their efficiency for realistic application settings. In the explicit scheme, the trace of the acoustic pressure is computed from the solution on the two elements adjacent to the face at the old time step. Tensor product shape functions for quadrilaterals and hexahedra evaluated with sum factorization are used to ensure low operation counts. For applying the inverse mass matrix of Lagrangian shape functions with full Gaussian quadrature, a new tensorial technique is proposed. As time propagators, diagonally implicit and explicit Runge–Kutta methods are used, respectively. We find that the computing time per time step is 25 to 200 times lower for the explicit scheme, with an increasing gap in three spatial dimensions and for higher element degrees. Our experiments on realistic 3D wave propagation with variable material parameters in a photoacoustic imaging setting show an improvement of two orders of magnitude in terms of time to solution, despite stability restrictions on the time step of the explicit scheme. Operation counts and a performance model to predict performance on other computer systems accompany our results. Copyright © 2015 John Wiley & Sons, Ltd.
On the one-dimensional nonlinear elastohydrodynamic lubrication

In this paper the authors prove an abstract theorem for solutions of a variational inequality on a cone and use it to study the free boundary problem of elastohydrodynamic lubrication from mechanical engineering. The mathematical model is set in a one-dimensional geometry. The existence of a solution for every non-negative lubricant viscosity is proved, and some properties useful for the numerical analysis are obtained.
A time‐implicit high‐order compact differencing and filtering scheme for large‐eddy simulation

This work investigates a high‐order numerical method which is suitable for performing large‐eddy simulations, particularly those containing wall‐bounded regions which are considered on stretched curvilinear meshes. Spatial derivatives are represented by a sixth‐order compact approximation that is used in conjunction with a tenth‐order non‐dispersive filter. The scheme employs a time‐implicit approximately factored finite‐difference algorithm, and applies Newton‐like subiterations to achieve second‐order temporal and sixth‐order spatial accuracy. Both the Smagorinsky and dynamic subgrid‐scale stress models are incorporated in the computations, and are used for comparison along with simulations where no model is employed. Details of the method are summarized, and a series of classic validating computations are performed. These include the decay of compressible isotropic turbulence, turbulent channel flow, and the subsonic flow past a circular cylinder. For each of these cases, it was found that the method was robust and provided an accurate means of describing the flowfield, based upon comparisons with previous existing numerical results and experimental data. Published in 2003 by John Wiley & Sons, Ltd.
A possible association of a young pulsar (PSR J0855−4644) with the young Vela supernova remnant RX J0852.0−4622

The recently discovered young supernova remnant (SNR) RX J0852.0-4622 has attracted much interest since its discovery because of the possibility that it may have been generated by the nearest supernova in recent history. We note the presence of two Parkes Multibeam Survey pulsars within the boundary of the remnant. We discuss the properties of the two pulsars and the likelihood of either of them being physically linked to the SNR. We tentatively suggest that, given the current uncertainties in the distance to RX J0852.0-4622, one of these pulsars, the 65-ms period PSR J0855-4644 could indeed be the compact remnant of this supernova explosion. If the pulsar birth site is at the geometrical centre of the nebula, then, for the transverse pulsar velocity to be reasonable, the SNR must be nearby (around 250 pc) and no younger than about 3000 yr old.
The Gini Coefficient Reveals More

We revisit the well-known decomposition of the Gini coefficient into between-groups, within-groups and overlap terms in the context of two groups in which the incomes in one group may be scaled and that groupÂ’s population weight modified. In this more general setting than usual, we focus on the properties of the overlap term, proving inter alia that overlap unambiguously reduces as a result of a within-group progressive transfer, and is increased by scaling up the incomes in the group with the lower mean, reaching a maximum when the two means become the same. In the case of a socially heterogeneous population and equivalized incomes, the effect on the Gini overlap of changing the income unit is determined, along with that of adjusting the equivalence scale deflator in case the income unit is the equivalent adult (such adjustment simultaneously changing the weighting of income units). Relationships of the findings to existing literature are thoroughly explored.
Constrained General Regression in Pseudo- Sobolev Spaces with Application to Option Pricing

State price density (SPD) contains important information concerning market expectations. In existing literature, a constrained estimator of the SPD is found by nonlinear least squares in a suitable Sobolev space. We improve the behavior of this estimator by implementing a covariance structure taking into account the time of the trade and by considering simultaneously both the observed Put and Call option prices.