Sharp Jumps Research Articles

Methods to Evaluate Subcolumn Profiles Based on Two‐Point Diagnostics

AbstractIn atmospheric models, stochastic generation of subgrid‐scale profiles or “subcolumns” has been used for a variety of purposes. Such subcolumns can be generated from subgrid probability density functions (PDFs) at different vertical levels, when such PDFs are available. To do so, the generator needs to decide how strongly points should be correlated in the vertical, that is, how much the values should be overlapped. This is sometimes called “PDF overlap.” To assess vertical correlation in a simplified, observable setting, here the vertical correlation of vertical velocity in subcloud layers is examined. Doppler lidar is used to evaluate the vertical profiles of vertical velocity produced by a large‐eddy simulation (LES) model and the Subgrid Importance Latin Hypercube Sampler (SILHS) subcolumn generator. In order to diagnose unrealistic features in subcolumn profiles, various statistical diagnostics are examined here, including the bivariate PDF of vertical velocity at two separated points (i.e., altitudes), the two‐point velocity correlation, the integral correlation length, the PDF of two‐point velocity differences, and the skewness and kurtosis of two‐point velocity differences. The profiles produced by LES match lidar well, except that they are too smooth at small scales. The profiles produced by SILHS exhibit sharp jumps from updraft to downdraft that are not observed in the lidar data. To reduce the generation of these unrealistically sharp jumps, the SILHS sampling method is revised. The diagnostics confirm that the revised sampling method reduces the overprediction of sharp jumps.

Phase jumps in coupled magnonic waveguides

In this work we present an experimental study of the phase characteristics of magnetostatic quasi-surface waves (MQSW) in a tangentially magnetized yttrium iron garnet (YIG) thin film bilayer. The phase of MQSWs was measured as a function of air gap (g) between two magnonic waveguides. It is shown that the energy exchange between two YIG layers is accompanied by relatively sharp π-radian phase jumps of MQSWs, at specific values of g. The effect was studied at large wavelengths of the MQSWs, and at a propagation distance of 1 cm. The theory predicts that the slope of the phase shift (∂φ/∂g) at submicrometric values of g can be of the order of a few degrees per nm.

Sloshing cold fronts in galaxy cluster Abell 2566

This paper presents properties of the intracluster medium (ICM) in the environment of a cool core cluster Abell 2566 (redshift z= 0.08247) based on the analysis of 20 ks Chandra X-ray data. 2D imaging analysis of the Chandra data from this cluster revealed spiral structures in the morphology of X-ray emission from within the central 109 kpc formed due to gas sloshing. This analysis also witness sharp edges in the surface brightness distribution along the south-east and north-west of the X-ray peaks at 41.6 kpc and 77.4 kpc, respectively. Spectral analysis of 0.5 – 7 keV X-ray photons along these discontinuities exhibited sharp temperature jumps from 2.3 to 3.1 keV and 1.8 to 2.8 keV, respectively, with consistency in the pressure profiles, implying their association with cold fronts due to gas sloshing of the gas. Further confirmation for such an association was provided by the deprojected broken power-law density function fit to the surface brightness distribution along these wedge shaped sectorial regions. This study also witness an offset of 4.6′′(6.8 kpc) between the BCG and the X-ray peak, and interaction of the BCG with a sub-system in the central region, pointing towards the origin of the spiral structure due to a minor merger.

A vortex damping outflow forcing for multiphase flows with sharp interfacial jumps

Outflow boundaries play an important role in multiphase fluid dynamics simulations that involve transition between liquid and vapor phases. These flows are dominated by low Weber numbers and a sharp jump in pressure, velocity and temperature. Inadequate treatment of these jumps at the outlet generates undesirable fluid disturbances that propagate upstream and lead to instabilities within the computational domain. To mitigate these disturbances, we introduce a forcing term that can be applied to incompressible Navier-Stokes equations to enforce stability in the numerical solution. The forcing term acts as a damping mechanism to control vortices that are generated by droplet/bubbles in multiphase flows, and is designed to be a general formulation that can be coupled with a fixed pressure outflow boundary condition to simulate a variety of multiphase flow problems. We demonstrate its applicability to simulate pool and flow boiling problems, where bubble-induced vortices during evaporation and condensation present a challenge at the outflow. Validation and verification cases are chosen to quantify accuracy and stability of the proposed method in comparison to established benchmarks and reference solutions, along with detailed performance analysis for three-dimensional simulations on leadership supercomputing platforms. Computational experiments are performed using Flash-X, which is a composable open-source software instrument designed for multiscale fluid dynamics simulations on heterogeneous architectures.

Methylene glycol-sulfite pH-clocks for the time-programming of soft materials: advantages, limitations, and yet unexplored opportunities.

Coupling nonlinear reaction networks with soft matter building blocks holds great potential for the design of life-mimicking, time-programmable dissipative self-assembly systems. In this regard, clock reactions are especially useful triggers since they allow to autonomously generate in situ chemical stimuli such as pH changes. The methylene glycol-sulfite (MGS) is a well-known acid-to-base pH-clock reaction which is able to produce sharp and intense pH jumps (up to 5 pH units) after a reliable, yet relatively short (tens of seconds rather than minutes), induction time. Here, after an introductory discussion on the main chemical aspects of MGS and MGS-based systems, their applications for the time-programming of soft matter will be showcased - from micelles, vesicles, and droplets to supramolecular aggregates, polymers and gels. Hopefully, this will help attracting more attention and foster research on the broader field of materials programming with chemical reaction networks.

Origin of discrete resistive switching in chemically heterogeneous vanadium oxide crystals.

Phase changes in oxide materials such as VO2 offer a foundational platform for designing novel solid-state devices. Tuning the V : O stoichiometry offers a vast electronic phase space with non-trivial collective properties. Here, we report the observation of discrete threshold switching voltages (Vth) with constant ΔVth between cycles in vanadium oxide crystals. The observed threshold fields over 10 000 cycles are ∼100× lower than that noted for stoichiometric VO2 and show unique discrete behaviour with constant ΔVth. We correlate the observed discrete memristor behaviour with the valence change mechanism and fluctuations in the chemical composition of spatially distributed VO2-VnO2n-1 complex oxide phases that can synergistically co-operate with the insulator-metal transition resulting in sharp current jumps. The design of chemical heterogeneity in oxide crystals, therefore, offers an intriguing path to realizing low-energy neuromorphic devices.

Volatility spillovers across Russian oil and gas sector. Evidence of the impact of global markets and extraordinary events

This paper provides empirical evidence on the evolution of the impact of external shocks on the volatility connectedness of Russian oil and gas companies’ stock prices. We examine how the spillover structure has changed following the outbreak of COVID-19, as well as under the impact of the 2022–2023 events.We have extended the Diebold–Yilmaz approach to calculate conditional connectivity measures adjusted for the influence of global factors and unexpected shocks caused by extraordinary events.We use an augmented vector autoregressive model (VARX) to evaluate the adjusted conditional connectivity measures. The dynamics of connectivity indices are analyzed using the moving window method for VAR and VARX models, as well as using a dynamic model with time-varying coefficients (TVP-VAR). The comparison of adjusted and unadjusted connectivity measures allows us to draw conclusions about the impact of changes in foreign financial markets as well as shocks caused by extraordinary events on connectedness structure.We found that measures of conditional connectivity change much more slowly than unconditional ones. Our results support the hypothesis that essential part of the fluctuation of Russian oil and gas connectedness indices can be explained by exposure to unexpected shocks and global economic and political factors. Accordingly, the transformation of the network structure of risk transfer occurs quite smoothly, without sharp jumps and takes a considerable amount of time.

Numerical simulation of thermo-throttle for iodine flow rate control in multidirectional plasma thruster

Background: Recently, a new direction in the field of electric propulsion has emerged – the multidirectional plasma thrusters. These thrusters are capable of producing propulsive forces in multiple directions. The thrusters are proposed to be used for orbit maintenance and alterations, formation flights, and interplanetary flights of space artificial objects ranging in size from CubeSats to fusion-powered interplanetary spacecraft. In this paper, the results of numerical simulation of the iodine propellant supply system for the multidirectional plasma thruster are presented. Methods: The geometry and temperature parameters of propellant supply system various elements are varied to determine the stable modes of iodine propellant ejection into the gas discharge chamber of the thruster. The temperatures of the thermo throttle and filter are found to ensure iodine mass flow rate in the range of 0.1 to 1.5 mg/s. The thermo throttle and filter temperatures are altered in the range of 65 to 200 °C and 65 to 100 °C, correspondingly. Results: The mass flow rate is critically dependent on the filter temperature and iodine saturated vapor pressure, as well as the filter and throttle geometries. The required values of iodine flow rate have been achieved by using the throttle with a diameter of 0.5 mm and a length of 60 mm and a filter with 56 holes, each hole diameter is 0.2 mm, and temperature from 90 C to 200 C. Conclusions: According to the data obtained, the iodine storage and supply system is preferably equipped with a thermos throttle, which provides precise control of the flow rate, as well as reduces sharp jumps of the flow rate when the temperature of the filter changes. Preferred filter geometry: 56 holes, each hole 0.2 mm in diameter.

Magnetization Process in Bilayer Honeycomb Spin Lattice

The magnetization process of the AA-stacked bilayer honeycomb spin lattice in the out-of-plane applied field is examined in the framework of the Ising model and mean field approximation. Competition between different kinds (antiferromagnetic: AF, or ferromagnetic: FM) of intra-layer and inter-layer spin exchange couplings could lead to the first order magnetization process, characterized by sharp jumps in magnetization curves occurring in critical external fields (spin-flop and spin- flip fields). There is only the spin-flip field at very low temperature and its magnitude depends not only on the intra-layer frustration level but also exchange coupling between spin layers. During the magnetization process, the initial AF bilayer honeycomb spin lattice may undergo ferrimagnetic or week-ferromagnetic states before reaching full ferromagnetic saturation state by the spin-flip field. The results of this work can be applied for an explanation of the spin-flip phenomenon registered in the AF bilayer CrI3.

Self-Association of the Anion of 7-Oxodeoxycholic Acid (Bile Salt): How Secondary Micelles Are Formed.

Bile acid anions are steroidal biosurfactants that form primary micelles due to the hydrophobic effect. At higher concentrations of some bile acid anions, secondary micelles are formed; hydrogen bonds connect primary micelles. Monoketo derivatives of cholic acid, which have reduced membrane toxicity, are important for biopharmaceutical examinations. The main goal is to explain why the processes of formation of primary and secondary micelles are separated from each other, i.e., why secondary micelles do not form parallel to primary micelles. The association of the anion of 7-oxodeoxycholic acid (a monoketo derivative of cholic acid) is observed through the dependence of the spin-lattice relaxation time on total surfactant concentration T1 = f(CT). On the function T1 = f(CT), two sharp jumps of the spin-lattice relaxation time are obtained, i.e., two critical micellar concentrations (CMC). The aggregation number of the micelle at 50 mM total concentration of 7-oxodeoxycholic acid anions in the aqueous solution is 4.2 ± 0.3, while at the total concentration of 100 mM the aggregation number is 9.0 ± 0.9. The aggregation number of the micelle changes abruptly in the concentration interval of 80-90 mM (the aggregation number determined using fluorescence measurements). By applying Le Chatelier's principle, the new mechanism of formation of secondary micelles is given, and the decoupling of the process of formation of primary and secondary micelles at lower concentrations of monomers (around the first critical micellar concentration) and the coupling of the same processes at higher equilibrium concentrations of monomers (around the second critical micellar concentration) is explained. Stereochemically and thermodynamically, a direct mutual association of primary micelles is less likely, but monomeric units are more likely to be attached to primary micelles, i.e., 7-oxodeoxycholic acid anions.

The Effect of Glycemic Status on the X-ray Image of Pulmonary Tuberculosis in Patients with Type 2 Diabetes Mellitus

The study is devoted to determining the effect of the level of glycemic status, on the X-ray picture in patients with type 2 diabetes mellitus. The X-ray archive of 82 patients with pulmonary tuberculosis and type 2 diabetes mellitus was analyzed. The evaluation of the radiological picture was carried out with the correlation of the level of glucose in the blood. In patients with fasting glucose values of 10 mmol/l and above, the X-ray picture of tuberculosis was characterized by extensive areas of lung tissue consolidation, with a 50 % frequency of localization in the lower sections, with the rapid formation of decay cavities. The course of tuberculosis with severe tuberculous intoxication was observed in patients with sharp jumps in the daily blood glucose index of more than 5 mmol/l, even in patients with an average glucose index of no more than 8 mmol/l. The X-ray picture was characterized by the presence of areas of consolidation in the lungs on both sides with many air cavities and dropout foci; the appearance of new areas of consolidation against the background of anti-tuberculosis therapy.

CoolPINNs: A physics-informed neural network modeling of active cooling in vascular systems

Emerging technologies like hypersonic aircraft, space exploration vehicles, and batteries avail fluid circulation in embedded microvasculatures for efficient thermal regulation. Modeling is vital during the design and operational phases of these engineered systems. However, many challenges exist in developing a modeling framework. What is lacking is an accurate framework that (i) captures sharp jumps in the thermal flux across complex vasculature layouts, (ii) deals with oblique derivatives (involving tangential and normal components), (iii) handles nonlinearity because of radiative heat transfer, (iv) provides a high-speed forecast for real-time monitoring, and (v) facilitates robust inverse modeling. This paper addresses these challenges by availing the power of physics-informed neural networks (PINNs). We develop a fast, reliable, and accurate Scientific Machine Learning (SciML) framework for vascular-based thermal regulation—called CoolPINNs: a PINNs-based modeling framework for active cooling. The proposed mesh-less framework elegantly overcomes all the mentioned challenges. The significance of the reported research is multi-fold. First, the framework is valuable for real-time monitoring of thermal regulatory systems because of rapid forecasting. Second, researchers can address complex thermoregulation designs since the approach is meshless. Finally, the framework facilitates systematic parameter identification and inverse modeling studies, perhaps the most significant utility of the current framework.

Endogenous thresholds in energy prices: Modeling and empirical estimation

Spot prices or front-month futures prices for energy commodities can exhibit occasional sharp peaks and drops (even to negative values), accompanied by large backwardations or contangos and unusually low or high levels of working stocks. We present a model of storage arbitrage that rationalizes such episodes, relevant for markets for energy commodities such as petroleum, natural gas, or storable electricity, where free disposal is not available. Based on price data only, we offer an empirical approach to estimate key parameters that determine the dynamics of prices, including endogenous price thresholds that indicate lower and upper bounds on discretionary stocks. Price movements in the regime within these bounds are moderated by responses of speculative storage. In the two regimes where price is respectively above or below threshold prices, sharp price jumps are more likely. We are the first to prove consistency and asymptotic normality of a method of estimating this model on prices with endogenous jumps. We explore the behavior of our estimator for small samples, and illustrate its application using petroleum prices. Although the model structure and the distributions of the disturbances in the Euler equation are quite complex, a nice feature of our estimator is its simplicity; it is straightforward non-linear least squares. Moreover, our estimation approach is robust to the demand functional form and the distribution of the shocks.

Tuning Logical Phi-Bit State Vectors in an Externally Driven Nonlinear Array of Acoustic Waveguides via Drivers’ Phase

We experimentally navigate the Hilbert space of two logical phi-bits supported by an externally driven nonlinear array of coupled acoustic waveguides by parametrically changing the relative phase of the drivers. We observe sharp phase jumps of approximately 180° in the individual phi-bit states as a result of the phase tuning of the drivers. The occurrence of these sharp phase jumps varies from phi-bit to phi-bit. All phi-bit phases also possess a common background dependency on the drivers’ phase. Within the context of multiple time scale perturbation theory, we develop a simple model of the nonlinear array of externally driven coupled acoustic waveguides to shed light on the possible mechanisms for the experimentally observed behavior of the logical phi-bit phase. Finally, we illustrate the ability to experimentally initialize the state of single- and multiple- phi-bit systems by exploiting the drivers’ phase as a tuning parameter. We also show that the nonlinear correlation between phi-bits enables parallelism in the manipulation of two- and multi-phi-bit superpositions of states.

The Winner’s Curse in Dynamic Forecasting of Auction Data: Empirical Evidence from eBay

Problem definition: Dynamic forecasting models in auctions have fallen short on two dimensions: (i) the lack of an equilibrium model for final bids and (ii) the lack of a winner’s curse (i.e., a tendency to overpay conditional on winning the auction) adjustment to allow bidders to account for a common value component in the auction item. In this paper, we develop a methodology to accurately predict equilibrium stage bids from the initial bidding dynamics and quantify the impact of the winner’s curse. This methodology allows us to conduct policy simulations to optimize auction design parameters. Methodology/Results: Dynamic auctions typically have a stage of high exploratory activity, followed by an inactivity period, and then an equilibrium stage of last-minute bids with sharp jumps. With a Kalman filter approach, we use exploratory stage bids to predict an auction item’s valuation distribution. We feed this prediction into an equilibrium model and apply item-specific adjustments for winner’s curse, bidder heterogeneity, and inactivity period. We use the resulting equilibrium model to predict the equilibrium stage bids. Our methodology improves the forecast of equilibrium stage bids by 11.33%, on average, compared with a state-of-the-art benchmark. This improvement is even higher (18.99%) for common value auctions. We also find that (i) significantly more (respectively, fewer) bidders internalize the winner’s curse in common value (respectively, private value) auctions; (ii) bidders in common value auctions decrease their bids by 6.03% because of the winner’s curse; and (iii) the inactivity period has a lesser impact on the equilibrium stage bids in private value auctions. Managerial implications: Our proposed methodology is intended to facilitate the need in academia and practice for real-time bid predictions that encompass different levels of the common value component in auctions. Using our methodology, auction platforms can support their choice of minimum bid increment policies and decide how to allocate resources across different auctions to mitigate the adverse effects of the winner’s curse. Supplemental Material: The online appendix is available at https://doi.org/10.1287/msom.2022.1165 .

Solving linear Bayesian inverse problems using a fractional total variation-Gaussian (FTG) prior and transport map

The Bayesian inference is widely used in many scientific and engineering problems, especially in the linear inverse problems in infinite-dimensional setting where the unknowns are functions. In such problems, choosing an appropriate prior distribution is an important task. Especially when the function to infer has much detail information, such as many sharp jumps, corners, and the discontinuous and nonsmooth oscillation, the so-called total variation-Gaussian (TG) prior is proposed in function space to address it. However, the TG prior is easy to lead the blocky (staircase) effect in numerical results. In this work, we present a fractional order-TG (FTG) hybrid prior to deal with such problems, where the fractional order total variation (FTV) term is used to capture the detail information of the unknowns and simultaneously uses the Gaussian measure to ensure that it results in a well-defined posterior measure. For the numerical implementations of linear inverse problems in function spaces, we also propose an efficient independence sampler based on a transport map, which uses a proposal distribution derived from a diagonal map, and the acceptance probability associated to the proposal is independent of discretization dimensionality. And in order to take full advantage of the transport map, the hierarchical Bayesian framework is applied to flexibly determine the regularization parameter. Finally we provide some numerical examples to demonstrate the performance of the FTG prior and the efficiency and robustness of the proposed independence sampler method.

Realizing acoustic qubit analogues with nonlinearly tunable phi-bits in externally driven coupled acoustic waveguides

Using experiments and theory, we investigate the behavior of nonlinear acoustic modes in a physical system composed of an array of three coupled acoustic waveguides, two of which are externally driven with two different frequencies. Nonlinear modes with frequency given by linear combinations of the driving frequencies are realizations of so-called logical phi-bits. A phi-bit is a two-state degree of freedom of an acoustic wave, which can be in a coherent superposition of states with complex amplitude coefficients, i.e., a qubit analogue. We demonstrate experimentally that phi-bit modes are supported in the array of waveguides. Using perturbation theory, we show that phi-bits may result from the intrinsic nonlinearity of the material used to couple the waveguides. We have also isolated possible effects on phi-bit states associated with the systems’ electronics, transducers and ultrasonic coupling agents used to probe the array and that may introduce extrinsic nonlinearities. These extrinsic effects are shown to be easily separable from the intrinsic behavior. The intrinsic behavior includes sharp jumps in phi-bit phases occurring over very narrow ranges of driving frequency. These jumps may also exhibit hysteretic behavior dependent on the direction of driving frequency tuning. The intrinsic states of phi-bits and multiple nonlinearly correlated phi-bits may serve as foundation for robust and practical quantum-analogue information technologies.

АНАЛИЗ И МОДЕЛИРОВАНИЕ РАСПРЕДЕЛЕНИЯ ТЯЖЕЛЫХ МЕТАЛЛОВ ПО РУСЛУ ВОДНОГО ОБЪЕКТА ВБЛИЗИ ЗОНЫ МЕЛИОРАЦИИ

The paper considers the migration of heavy metals along the riverbed with one reclamation channel. The authors use a simple mathematical model to analyze a distribution of pollutants concentration, including heavy metals, along the river bed in the presence of water discharge from the reclamation zone into the river. A simple method is proposed for estimating the metals concentration reduction intensity along the river runoff. It is assumed that the main parameters affecting the distribution of metals are the speed of water flow and the intensity of metal deposition along the riverbed. The proposed model was used to calculate the concentration of metals along the Uldura River in the Jewish Autonomous region. It was made an assessment of the metal concentration decrease intensity along the river course when moving away from the reclamation zone. In particular, it was shown that concentration of iron (Fe) reaches its background value at a distance of about 20 km, due to metal deposition along the channel. The authors also made a research based on data processing of the autumn samples from three different sites along the Uldura River which showed strong deviations in the concentration of detected metals in different years of the observed period either to sharp jumps in values or to their falls. This process can be described by a fairly simple model presented in this paper.

HIGHLY-PRODUCTIVE ADC WITH COMBINED BALANCING

Today analog-to-digital converters are used in computing and control systems which have greatly expanded in the era of the digital revolution. Increasing the accuracy, speed, energy efficiency, and reliability of analog-to-digital converters is extremely important. One of the most classic types of analog-to-digital converters is the sequential approximation and tracking type ADCs. The conversion time of the tracking type ADC is variable and is determined by the difference between the two readings of the input voltage. Therefore, combining the tracking approach and the method of successive approximation in the case of sharp jumps in the input signal allows you to significantly improve the conversion characteristic. Also the use of redundant counting systems for the weights of the ADC digits has significant advantages, which makes it possible to significantly increase the linearity of the conversion characteristic. The methods of construction of ADCs working on the principle of successive approximation and analog-digital converters whose operation algorithm is tracking are considered. A method of constructing a combined type ADC is proposed, which combines a follow-up conversion algorithm and a sequential approximation algorithm, which allows to improve the characteristics of ADC conversion. The expediency of using a combined type of redundant positional counting systems in ADCs has been proven. The analyzed property of redundant positional counting systems, which is inherent in them when the real weights of the digits deviate from their theoretical values, ensures the absence of “gaps” in the conversion characteristic, as well as the ability to perform the procedure of self-calibration of the weights of the ADC digits, thereby significantly improving the linearity of the conversion characteristic. It is indicated that even with the lengthening of the bit grid for ADCs built on the basis of redundant positional counting systems, their performance does not decrease.

Langmuir Probes' Secondary Power Supply System for the "Obstanovka" Experiment and Plasma-wave Complex Aboard the Russian Segment of the International Space Station


 
 
 The Plasma-wave complex is scientific instrumentation for plasma and wave parameters measurements in the vicinity of the International Space Station, and is implemented in the “Obstanovka” experiment aboard the Russian segment.
 The Langmuir probes instruments, developed at the Space Research and Technology Institute of the Bulgarian Academy of Sciences, measured the following parameters: electron temperature, electron and ion concentration, plasma and the International Space Station’s surface potential. One of the results is that sharp jumps in the surface potential are detected when crossing the terminator and the Equatorial anomaly.
 The Langmuir probes operate outside the Russian “Zvezda” module. Families of voltage-ampere characteristics of the Langmuir probe are measured – when the voltage changes in a certain range, the value of the current flowing is recorded.
 There are block and functional diagrams of the instrument Langmuir probes and its secondary power supply system, designed to supply the measuring probe, the analogue and digital circuit boards.