Miracle-dz/UniFAR-FTUs huggingface dataset:
Critical Level Reflection and the Resonant Growth of Nonlinear Mountain Waves.

Abstract We examine the evolution of a field of internal waves launched by stratified flow over symmetric topography in mean flows which reverse direction at some height above the surface. With the gradient Richardson number at this “critical level” in the undisturbed flow restricted to values greater than 0.25, the nonlinear interaction in the region is such that the surface strongly reflects large amplitude internal waves incident upon it. When the critical level is located near certain discrete heights above the ground the incident and reflected waves interfere constructively and the wave amplitude in the low levels is resonantly enhanced by a large factor. These results are related to our previous analyses of the process by which breaking internal waves are able to induce intense downslope windstorms.
Decaying Kolmogorov turbulence in a model of superflow

Superfluid turbulence is studied using numerical simulations of the nonlinear Schrodinger equation (NLSE), which is the correct equation of motion for superflows at low temperatures. This equation depends on two parameters: the sound velocity and the coherence length. It naturally contains nonsingular quantized vortex lines. The NLSE mass, momentum, and energy conservation relations are derived in hydrodynamic form. The total energy is decomposed into an incompressible kinetic part, and other parts that correspond to acoustic excitations. The corresponding energy spectra are defined and computed numerically in the case of the two-dimensional vortex solution. A preparation method, generating initial data reproducing the vorticity dynamics of any three-dimensional flow with Clebsch representation is given and is applied to the Taylor–Green (TG) vortex. The NLSE TG vortex is studied with resolutions up to 5123. The energetics of the flow is found to be remarkably similar to that of the viscous TG vortex. The.
Multidimensional Joint Recurrence Quantification Analysis: detecting coupling between time series of different dimensionalities

One issue with the analysis of complex systems and the interaction between such systems is that they are composed of different number of components, or simply the fact that a different number of observables is available for each system. The challenge is how to analyze the interaction of two systems which are not described by the same number of variables. The approach is to combine different types and number of time series so that they yield a matched set of data points from which coupling or correlation properties can be estimated. Here, we present multidimensional joint recurrence quantification analysis (MdJRQA), a recurrence-based technique that allows to analyze coupling properties between multivariate data sets that differ in dimensionality (i.e., number of observables) and type of data (such as nominal or interval-scaled, for example). First, we introduce the methods, and then test it on simulated data from linear and nonlinear systems. Finally, we discuss practical issue regarding the application of the method.
Well-Rounded ideal lattices of cyclic cubic and quartic fields

In this paper, we find criteria for when cyclic cubic and cyclic quartic fields have well-rounded ideal lattices. We show that every cyclic cubic field has at least one well-rounded ideal. We also prove that there exist families of cyclic quartic fields which have well-rounded ideals and explicitly construct their minimal bases. In addition, for a given prime number $p$, if a cyclic quartic field has a unique prime ideal above $p$, then we provide the necessary and sufficient conditions for that ideal to be well-rounded. Moreover, in cyclic quartic fields, we provide the prime decomposition of all odd prime numbers and construct an explicit integral basis for every prime ideal.
Stability and Bifurcation for a Delayed Predator–Prey Model and the Effect of Diffusion☆

Abstract We consider a predator–prey system with one or two delays and a unique positive equilibrium E∗. Its dynamics are studied in terms of the local stability of E∗ and of the description of the Hopf bifurcation that is proven to exist as one of the delays (taken as a parameter) crosses some critical values. We also consider a reaction–diffusion system with Neumann conditions, resulting from adding one spatial variable and diffusion terms in the previous model. The spectral and bifurcation analysis in the neighborhood of E∗, now as a stationary point of this latter system, is addressed and the results obtained for the case without diffusion are applied.
Capacity-Preserving Subgraphs of Directed Flow Networks

We introduce and discuss the Minimum Capacity-Preserving Subgraph (MCPS) problem: given a directed graph and a retention ratio $\alpha \in (0,1)$, find the smallest subgraph that, for each pair of vertices $(u,v)$, preserves at least a fraction $\alpha$ of a maximum $u$-$v$-flow's value. This problem originates from the practical setting of reducing the power consumption in a computer network: it models turning off as many links as possible while retaining the ability to transmit at least $\alpha$ times the traffic compared to the original network. First we prove that MCPS is NP-hard already on directed acyclic graphs (DAGs). Our reduction also shows that a closely related problem (which only considers the arguably most complicated core of the problem in the objective function) is NP-hard to approximate within a sublogarithmic factor already on DAGs. In terms of positive results, we present a simple linear time algorithm that solves MCPS optimally on directed series-parallel graphs (DSPs). Further, we introduce the family of laminar series-parallel graphs (LSPs), a generalization of DSPs that also includes cyclic and very dense graphs. Not only are we able to solve MCPS on LSPs in quadratic time, but our approach also yields straightforward quadratic time algorithms for several related problems such as Minimum Equivalent Digraph and Directed Hamiltonian Cycle on LSPs.
Teaching contact-rich tasks from visual demonstrations by constraint extraction

Contact-rich manipulation involves kinematic constraints on the task motion, typically with discrete transitions between these constraints during the task. Allowing the robot to detect and reason about these contact constraints can support robust and dynamic manipulation, but how can these contact models be efficiently learned? Purely visual observations are an attractive data source, allowing passive task demonstrations with unmodified objects. Existing approaches for vision-only learning from demonstration are effective in pick-and-place applications and planar tasks. Nevertheless, accuracy/occlusions and unobserved task dynamics can limit their robustness in contact-rich manipulation. To use visual demonstrations for contact-rich robotic tasks, we consider the demonstration of pose trajectories with transitions between holonomic kinematic constraints, first clustering the trajectories into discrete contact modes, then fitting kinematic constraints per each mode. The fit constraints are then used to (i) detect contact online with force/torque measurements and (ii) plan the robot policy with respect to the active constraint. We demonstrate the approach with real experiments, on cabling and rake tasks, showing the approach gives robust manipulation through contact transitions.
Heuristic Search For Physics-Based Problems: Angry Birds in PDDL+

Angry Birds is a very popular game that requires reasoning about sequential actions in a continuous world with discrete exogenous events. Different versions of the game are hard computationally, and the reigning world champion is still a human despite a long-running yearly competition in IJCAI conferences. In this work, we present the Hydra, the first successful game-playing agent for Angry Birds that uses a domain-independent planner and combinatorial search techniques. Hydra models the game using PDDL+, a rich planning language designed for mixed discrete/continuous domains. To reason about continuous aspects of the domain, Hydra employs time discretization techniques that raise a combinatorial search challenge. To meet this challenge, we propose domain-specific heuristics and a novel "preferred states" mechanism similar to the preferred operators mechanism from classical planning. We compared Hydra with state-of-the-art Angry Birds agents. The results show Hydra can solve a greater diversity of Angry Birds levels compared to other agents and highlight its current limitations.
Measurement-free fault-tolerant logical-zero-state encoding of the distance-three nine-qubit surface code in a one-dimensional qubit array

Generation of logical zero states encoded with a quantum error-correcting code is the first step for fault-tolerant quantum computation, but requires considerably large resource overheads in general. To reduce such overheads, we propose an efficient encoding method for the distance-three, nine-qubit surface code and show its fault tolerance. This method needs no measurement, unlike other fault-tolerant encoding methods. Moreover, this is applicable to a one-dimensional qubit array. Observing these facts, we experimentally demonstrate the logical zero-state encoding of the surface code using a superconducting quantum computer on the cloud. We also experimentally demonstrate the suppression of fast dephasing due to intrinsic residual interactions in this machine by a dynamical decoupling technique dedicated for the qubit array. To extend this method to larger codes, we also investigate the concatenation of the surface code with itself, resulting in a distance-nine, 81-qubit code. We numerically show that fault-tolerant encoding of this large code can be achieved by appropriate error detection. Thus, the proposed encoding method will provide a new way to low-overhead fault-tolerant quantum computation.
Efficient Multi-Cycle Folded Integer Multipliers

Fast combinational multipliers with large bit widths can occupy significant silicon area. Provided the application allows for a multiplication to last two or more clock cycles, the area can be reduced through resource sharing (i.e., folding). This work introduces multiple architectures and parameterized Verilog circuit generators for Multi-Cycle folded Integer Multiplier (MCIM) designs, which are based on Schoolbook and Karatsuba approaches. When implementing an application in hardware, it is possible that a fractional number of multiplications is performed per cycle on average, such as 3.5. In such a case, we can use 3 single-cycle multipliers plus an additional smaller multiplier with a ThroughPut (TP) of 0.5. Our MCIM designs offer customization in terms of TP, latency, and clock frequency. The MCIM idea is for a TP of $1/n$, where $n$ is an integer and $n \geq 2$. All proposed designs were synthesized and verified for various bit widths using scripts. ASIC synthesis results show that MCIM designs with a TP of 1/2 offer area savings of 21% to 48% for bit widths of 8 to 128, with respect to synthesizing the * operator. Additionally, MCIM designs can offer up to 33% energy savings and 84% average peak power reduction.
Seasonality and growth in tropical freshwater ectotherm vertebrates: Results from 1‐year experimentation in the African gray bichir, giraffe catfish, and the West African mud turtle

Abstract Growth in ectotherm vertebrates is strongly rhythmed by seasonal variation in environmental parameters. To track the seasonal variation in ancient times in a continental and tropical context, we aim to develop a method based on the use of the growth rate of fossil ectotherm vertebrates (actinopterygians and chelonians) influenced by seasonal environmental fluctuations they experienced in their lifetime. However, the impact of environmental parameters on growth, positive or negative, and its intensity, depends on the taxa considered, and data are scarce for tropical species. For 1 year, an experiment was conducted to better understand the effect of seasonal variation in environmental parameters (food abundance, temperature, and photoperiod) on the somatic growth rate of three species of tropical freshwater ectotherm vertebrates: the fishes Polypterus senegalus and Auchenoglanis occidentalis and the turtle Pelusios castaneus. Mimicking seasonal shifts expected to be experienced by the animals in the wild, the experiment highlighted the preponderant effect of food abundance on the growth rate of those three species. Water temperature variation had a significant effect on the growth rate of Po. senegalus and Pe. castaneus. Moreover, the photoperiod demonstrated no significant effect on the growth of the three species. The duration of application of starvation or cool water conditions, ranging from 1 to 3 months, did not affect the growth rate of the animals. However, Pelusios castaneus showed a temporary sensitivity to the return of ad libitum feeding or of warm water, after a period of starvation or cool water, by a period of compensatory growth. Finally, this experiment revealed, in the three species, fluctuations in the growth rate under controlled and constant conditions. This variation, similar to the variation in precipitation and temperature observed in their native environment, could be linked to a strong effect of an internal rhythm controlling somatic growth rate.
Accelerated mafic weathering in Southeast Asia linked to late Neogene cooling

Arc-continent collision in Southeast Asia during the Neogene may have driven global cooling through chemical weathering of freshly exposed ophiolites resulting in atmospheric CO2 removal. Yet, little is known about the cause-and-effect relationships between erosion and the long-term evolution of tectonics and climate in this region. Here, we present an 8-million-year record of seawater chemistry and sediment provenance from the eastern Indian Ocean, near the outflow of Indonesian Throughflow waters. Using geochemical analyses of foraminiferal shells and grain size–specific detrital fractions, we show that erosion and chemical weathering of ophiolitic rocks markedly increased after 4 million years (Ma), coincident with widespread island emergence and gradual strengthening of Pacific zonal sea-surface temperature gradients. Together with supportive evidence for enhanced mafic weathering at that time from re-analysis of the seawater 87Sr/86Sr curve, this finding suggests that island uplift and hydroclimate change in the western Pacific contributed to maintaining high atmospheric CO2 consumption throughout the late Neogene.
Variable selection in partially linear wavelet models

Variable selection is fundamental in high-dimensional statistical modelling, including non-and semiparametric regression. However, little work has been done for variable selection in a partially linear model (PLM). We propose and study a unified approach via double penalized least squares, retaining good features of both variable selection and model estimation in the framework of PLM. The proposed method is distinguished from others in that the penalty functions combine the l 1 penalty coming from wavelet thresholding in the non-parametric component with the l 1 penalty from the lasso in the parametric component. Simulations are used to investigate the performances of the proposed estimator in various settings, illustrating its effectiveness for simultaneous variable selection as well as estimation.
Dense sampling of ethnic groups within African countries reveals fine-scale genetic structure and extensive historical admixture

Previous studies have highlighted how African genomes have been shaped by a complex series of historical events. Despite this, genome-wide data have only been obtained from a small proportion of present-day ethnolinguistic groups. By analyzing new autosomal genetic variation data of 1333 individuals from over 150 ethnic groups from Cameroon, Republic of the Congo, Ghana, Nigeria, and Sudan, we demonstrate a previously underappreciated fine-scale level of genetic structure within these countries, for example, correlating with historical polities in western Cameroon. By comparing genetic variation patterns among populations, we infer that many northern Cameroonian and Sudanese groups share genetic links with multiple geographically disparate populations, likely resulting from long-distance migrations. In Ghana and Nigeria, we infer signatures of intermixing dated to over 2000 years ago, corresponding to reports of environmental transformations possibly related to climate change. We also infer recent intermixing signals in multiple African populations, including Congolese, that likely relate to the expansions of Bantu language–speaking peoples.
Optimal Singular Stochastic Problem On Harvesting System

This paper presents an optimal singular stochastic problem on harvesting sys- tem. For the first time we introduce the running function into the total expected discounted harvested value. By relying on both stochastic calculus and the classi- cal theory of singular control, we give a set of sufficient conditions for its solution in terms of optimal return function. Moreover, we also derive its optimal harvest- ing strategies and explicit form of optimal return function.
Sensitive photodetection below silicon bandgap using quinoid-capped organic semiconductors

High-sensitivity organic photodetectors (OPDs) with strong near-infrared (NIR) photoresponse have attracted enormous attention due to potential applications in emerging technologies. However, few organic semiconductors have been reported with photoelectric response beyond ~1.1 μm, the detection limit of silicon detectors. Here, we extend the absorption of organic small-molecule semiconductors to below silicon bandgap, and even to 0.77 eV, through introducing the newly designed quinoid-terminals with high Mulliken-electronegativity (5.62 eV). The fabricated photodiode-type NIR OPDs exhibit detectivity (D*) over 1012 Jones in 0.41 to 1.2 μm under zero bias with a maximum of 2.9 × 1012 Jones at 1.02 μm, which is the highest D* for reported OPDs in photovoltaic-mode with response spectra beyond 1.1 μm. The high D* in 0.9 to 1.2 μm is comparable to those of commercial InGaAs photodetectors, despite the detection limit of our OPDs is shorter than InGaAs (~1.7 μm). A spectrometer prototype with a wide measurable region (0.4 to 1.25 μm) and NIR imaging under 1.2-μm illumination are demonstrated successfully in OPDs.
Sunspot activity and the long‐term variation of the Sun's open magnetic flux

[1] The interplanetary magnetic field (IMF) originates in open magnetic regions of the Sun (coronal holes), which in turn form mainly through the emergence and dispersal of active region fields. The radial IMF strength is proportional to the total open flux Φopen, which can be estimated from source surface extrapolations of the measured photospheric field, after correction for magnetograph saturation effects. We derive the long-term variation of Φopen during 1971–2000 and discuss its relation to sunspot activity. The average value of Φopen was ∼20–30% higher during 1976–1996 than during 1971–1976 and 1996–2000, with major peaks occurring in 1982 and 1991. Near sunspot minimum, most of the open flux resides in the large polar coronal holes, whereas at sunspot maximum it is rooted in relatively small, low-latitude holes located near active regions and characterized by strong footpoint fields; since the decrease in the total area occupied by holes is offset by the increase in their average field strengths, Φopen remains roughly constant between activity minimum and maximum, unlike the total photospheric flux Φtot. The long-term variation of Φopen approximately follows that of the Sun's total dipole strength, with a contribution from the magnetic quadrupole around sunspot maximum. Global fluctuations in sunspot activity lead to increases in the equatorial dipole strength and hence to enhancements in Φopen and the IMF strength lasting typically ∼1 year. We employ simulations to clarify the role of active region emergence and photospheric transport processes in the evolution of the open flux. Representing the initial field configuration by one or more bipolar magnetic regions (BMRs), we calculate its subsequent evolution under the influence of differential rotation, supergranular convection, and a poleward bulk flow. The initial value of Φopen is determined largely by the equatorial dipole strength, which in turn depends on the longitudinal phase relations between the BMRs. As the surface flow carries the BMR flux to higher latitudes, the equatorial dipole is annihilated on a timescale of ∼1 year by the combined effect of rotational shearing and turbulent diffusion. The remaining flux becomes concentrated around the poles, and Φopen approaches a limiting value that depends on the axisymmetric dipole strengths of the original BMRs. The polar coronal holes thus represent the long-lived, axisymmetric remnant of the active regions that emerged earlier in the cycle.
ADAPTIVE ESTIMATION IN A NONPARAMETRIC REGRESSION MODEL WITH ERRORS-IN-VARIABLES

We consider a regression model with errors-in-variables. Let (Yi, Zi), i = 1, . , n be n i.i. d. copies of (Y, Z) satisfying Y = f(X) + ξ, Z = X + σe, involving independent and unobserved random variables X, ξ, e. The density of e and the constant noise level σ are known while the densities of X and ξ are unknown. Using the observations (Yi, Zi), i = 1,··· , n, we propose an estimator ˜ f of the regression function f which is defined as the ratio of two adaptive estimators an estimator of l = fg divided by an estimator of g, the density of X. Both estimators are obtained by minimization of penalized contrast functions. We prove that the MISE of ˜ f on a compact set is bounded by the sum of the two MISEs of the estimators of l and g. Rates of convergence are given when l and g belong to various smoothness classes and when the error e is either ordinary smooth or super smooth. The rate of ˜ f is optimal in a minimax sense in all cases where lower
Fault detection for singular networked control systems with randomly occurring delays and partially known distribution transmission delays

In this paper, the fault detection problem is discussed for a class of discrete-time singular networked control systems with randomly occurring delays and network-induced delays. The considered randomly occurring delays include the multiple state delays and the infinite-distributed delay. Both of them are assumed to occur in random ways, which are governed by two independent stochastic variables satisfying the Bernoulli binary distribution. Network-induced delays are modeled as a discrete-time homogeneous Markov chain, and the transition probabilities of the Markov chain are partially known. A stochastic Lyapunov functional is constructed to design a full-order fault detection filter guaranteeing that the fault detection dynamics is stochastically admissible with a prescribed H ∞ performance index. Hence, the fault detection filter design problem is converted into a convex optimization problem in terms of a set of linear matrix inequalities. If these linear matrix inequalities are feasible, the corresponding parameters of the designed fault detection filter are determined. Finally, a numerical example is addressed to demonstrate the effectiveness of the developed method.