bluuebunny/crossref_metadata_2025_split huggingface dataset:
Odd-frequency pair density wave correlations in underdoped cuprates
Authors: Chakraborty Debmalya , Black-Schaffer Annica M 
Published: January 2021

Abstract
Pair density waves, identified by Cooper pairs with finite center-of-mass momentum, have recently been observed in copper oxide based high T
c superconductors (cuprates). A charge density modulation or wave is also ubiquitously found in underdoped cuprates. Within a general mean-field one-band model we show that the coexistence of charge density waves (CDWs) and uniform superconductivity in d-wave superconductors like cuprates, generates an odd-frequency spin-singlet pair density wave, in addition to the even-frequency counterparts. The strength of the induced odd-frequency pair density wave depends on the modulation wave vector of the CDW, with the odd-frequency pair density waves even becoming comparable to the even-frequency ones in parts of the Brillouin zone. We show that a change in the modulation wave vector of the CDW from bi-axial to uni-axial, can enhance the odd-frequency component of the pair density waves. Such a coexistence of superconductivity and uni-axial CDW has already been experimentally verified at high magnetic fields in underdoped cuprates. We further discuss the possibility of an odd-frequency spin-triplet pair density wave generated in the coexistence regime of superconductivity and spin density waves, applicable to the iron-based superconductors. Our work thus presents a route to bulk odd-frequency superconductivity in high T
c superconductors.
Influence of normal metal-superconductor interface on the statistics of conductance and shot noise power in a non-ideal chaotic quantum dot
Authors: Duarte-Filho Gerson C , Almeida Francisco A G 
Published: January 2021

Abstract
In this paper, we apply Andreev’s reflection to study the sub-gap coherent transport properties for a quantum dot attached to normal metal and superconductor reservoirs via non-ideal leads. We use the random matrix theory to obtain numerically the conductance and shot noise power probability densities varying the transparencies and the number of open scattering channels in each lead for the three Wigner–Dyson ensembles. We obtain results from the extreme quantum limit (where the conductance is of the order of 2e
2/h, the quantum of conductance) to the semiclassical regime (conductance much larger than 2e
2/h). We observe the appearance of non-analyticities in these probability densities and an interesting invariance break under the operation of exchanging the lead labels when time-reversal symmetry is absent.
Radiative MHD unsteady Casson fluid flow with heat source/sink through a vertical channel suspended in porous medium subject to generalized boundary conditions
Authors: Asifa  , Kumam Poom , Shah Zahir , Watthayu Wiboonsak , Anwar Talha 
Published: January 2021

Abstract
Unsteady, incompressible flow of Casson fluid between two infinitely long upward heated walls nested in a porous medium is analyzed in this work. The mass diffusion and heat transfer phenomena are also studied in the presence of thermal radiation, magnetic field, and heat source/sink. The generalized boundary conditions in terms of continuous time-dependent functions are considered for mass, energy, and momentum fields. Fick’s law, Fourier’s law, and momentum conservation principle are adopted to formulate the mathematical equations. Analytic solution for the concentration equation is established first by adding certain unit-less quantities and then by using the Laplace method of transformation. Semi-analytic solutions are calculated by means of Stehfest’s numerical Laplace inversion algorithm for energy and velocity equations. To demonstrate the verification of those solutions, a tabular comparison is drawn. Graphical illustrations along with physical descriptions are provided to discuss the essential contribution of thermo-physical parameters in heat and mass transfer and flow of the Casson fluid. The numerical computations of Sherwood number, Nusselt number, and skin friction for various inputs of related parameters are organized in tables to investigate mass transfer rate, heat transfer rate, and shear stress respectively. It is observed that porosity of the medium and buoyancy force tend to accelerate the flow. The heat and mass transfer rates are appreciated by Prandtl and Schmidt numbers respectively. Furthermore, radiation parameter and Grashof number significantly minimize the shear stress.
Kalman filter based demodulation in a dual-pulse phase-OTDR
Authors: Alekseev A E , Gorshkov B G , Bashaev A V , Potapov V T , Taranov M A , Simikin D E 
Published: January 2021

Abstract
In the present paper, we propose an approach based on the Kalman filter for demodulation in a dual-pulse phase-OTDR. Although the Kalman filter is well-developed and widely used method for the state estimation of a dynamic system, its use for demodulation in a phase-OTDR is proposed for the first time, to our best knowledge. Two main algorithms are considered and described in detail: the extended Kalman filter (EKF) and the unscented Kalman filter (UKF), the first one is fast and simple, but the second one is more accurate. A qualitative comparison of these algorithms with the differentiate and cross-multiply (DCM) algorithm is performed. The efficiency of the EKF and the UKF algorithms is experimentally verified.
Dynamics of k-essence in loop quantum cosmology *
Authors: Shi Jiali , Wu Jian-Pin 
Published: January 2021

Abstract
In this paper, we study the dynamics of k-essence in loop quantum cosmology (LQC). The study indicates that the loop quantum gravity (LQG) effect plays a key role only in the early epoch of the universe and is diluted in the later stages. The fixed points in LQC are basically consistent with those in standard Friedmann-Robertson-Walker (FRW) cosmology. For most of the attractor solutions, the stability conditions in LQC are in agreement with those for the standard FRW universe. For some special fixed points, however, tighter constraints are imposed thanks to the LQG effect.
Study properties of Eigenvalues, Eigenvectors and Eigenspace of matrices by using MatLab
Authors: Abbas Muntaha Khudair 
Published: January 2021

Abstract
The aim of this paper is to study the properties of eigenvalues with types (real, Repeated, complex) of matrices (2x2), (3x3), (4x4), eigenvectors and eigenspace of matrices by using Matlab. It also investigates the left and right eigenvectors, characteristic equation, existence and multiplicity of eigenvalues, gives some examples about the computation of eigenvalues, eigenvectors, and solves the Dynamic Systems of First Order Linear Differential Equations of (2 dim and 3 dim) as well as the Numerical solution to Dynamic systems by using program Matlab.
Influence of the limited room space on inlet conditions and fan operation at the rotating test rig
Authors: Sieradzki A , Łukasik B 
Published: January 2021

AbstractThe limited space of the laboratory room allows maintaining the selected ambient air parameters in the required ranges. It can be, however, a source of many problems in the case of rotating test rigs that blow a large amount of air. The aim of the paper is to examine the influence of limited space and its shape on the working conditions of axial fans test stand. The focus was particularly on the conditions prevailing at the inlet to the test rig and their potential impact on the tested fan operation. The article presents the results of CFD simulations for two rooms of different volumes and the results of experimental measurements carried out for the smaller one. Good qualitative agreement between the simulations and the experiment was obtained. The limited space around the test rig causes the unsteadiness of the axial velocity profile and introduces an unsteady swirl at the inlet. This leads, in turn, to local changes in the angle of attack of the fan blades and the resulting consequences related to the off-design working conditions. The paper proves the need to minimise the effects of the induced airflow in the test room and proposes some methods to accomplish this task.
Hydrodynamic advantages of in-line schooling
Authors: Saadat Mehdi , Berlinger Florian , Sheshmani Artan , Nagpal Radhika , Lauder George V , Haj-Hariri Hossein 
Published: January 2021

Abstract
Fish benefit energetically when swimming in groups, which is reflected in lower tail-beat frequencies for maintaining a given speed. Recent studies further show that fish save the most energy when swimming behind their neighbor such that both the leader and the follower benefit. However, the mechanisms underlying such hydrodynamic advantages have thus far not been established conclusively. The long-standing drafting hypothesis—reduction of drag forces by judicious positioning in regions of reduced oncoming flow–fails to explain advantages of in-line schooling described in this work. We present an alternate hypothesis for the hydrodynamic benefits of in-line swimming based on enhancement of propulsive thrust. Specifically, we show that an idealized school consisting of in-line pitching foils gains hydrodynamic benefits via two mechanisms that are rooted in the undulatory jet leaving the leading foil and impinging on the trailing foil: (i) leading-edge suction on the trailer foil, and (ii) added-mass push on the leader foil. Our results demonstrate that the savings in power can reach as high as 70% for a school swimming in a compact arrangement. Informed by these findings, we designed a modification of the tail propulsor that yielded power savings of up to 56% in a self-propelled autonomous swimming robot. Our findings provide insights into hydrodynamic advantages of fish schooling, and also enable bioinspired designs for significantly more efficient propulsion systems that can harvest some of their energy left in the flow.
The land use legacy effect: looking back to see a path forward to improve management
Authors: Martin Sherry L , Hamlin Quercus F , Kendall Anthony D , Wan Luwen , Hyndman David W 
Published: January 2021

Abstract
Water quality has suffered as humans have increased nutrient inputs across the landscape. In many cases, management actions to reduce nutrient inputs have not been met with concomitant ecosystem responses. These missed expectations are partly due to the continued slow delivery of nutrient-enriched groundwater pre-dating input reductions resulting from management actions. Land use legacies as expressed through this time lag are important to quantify in order to adjust management expectations. We present a novel coupling of nitrogen source maps with groundwater transport times to create a high-resolution (120 m) fully distributed estimate of the timing and magnitude of groundwater nitrogen deliveries to surface water across Michigan’s Lower Peninsula. This new view of the landscape has been designed around common management timelines for: elected officials looking to make a difference for re-election (<5 years), career managers hoping to see the fruits of their labor (5–30 years), and advocacy groups whose work can span generations (>30 years). One striking result is that after 100 years, in our study area, approximately 50% of the nitrogen that enters the groundwater system remains in transit. This means that actions taken now may not show the expected lower nitrogen loads to receiving ecosystems for decades to centuries. We show that differences in groundwater travel times create a heterogeneous patchwork over which managers can prioritize actions to best match their targeted response times. Across the highest nitrogen inputs in our study region, less than 10% had short enough groundwater legacies to match the management timeline of most government and agency work. Agricultural practices (manure and chemical fertilizer) are the main nitrogen contributors across the top three management classes; however, human contributions through septic tank effluent and lawn fertilizers contribute 5%–8% of nitrogen.
‘Fair’ inequality, consumption and climate mitigation
Authors: Millward-Hopkins Joel , Oswald Yannick 
Published: January 2021

AbstractEconomic inequality and climate change are pressing issues that have climbed high up the political agenda, yet action to mitigate both remains slow. As income is a key determinant of ecological impacts, the Global North—and wealthier classes elsewhere—are the primary drivers of global carbon emissions, while the least well off have contributed the least yet are set to be hit hardest by climate impacts. These inequalities are clearly unjust, but the interrelations between economic inequality and ecological impacts are complex, leaving open the question of whether reducing the former would mitigate the latter, in the absence of reductions in total economic output. Here, we contribute to these debates by estimating the carbon-footprint implications of reducing income (and hence expenditure) inequalities within 32 countries of the Global North to the levels people consider to befair; levels that are substantially smaller than currently exist. We find that realising these levels of economic inequality brings comparable reductions in carbon-footprint inequalities. However, in isolation, implementingfairinequalities has a negligible impact upon total emissions. In contrast, recomposing consumption—by reducing inequalities in household expenditure and the overall levels, then reallocating the reductions to public services—reduces carbon footprint by up to 30% in individual countries and 16% overall and, crucially, still allows the consumption of those at the bottom to rise. Such reductions could be significant on a global level, and they would be additional to the full range of conventional technological and demand-side measures to reduce carbon emissions.
Simulation of heat transfer processes in a diesel engine equipped with pistons coated by using Galvanic-plasma Method
Authors: Al-Bdeiri M S , Krasilnikov V V , Sergeyev S V 
Published: January 2021

Abstract
The methodology for analyzing the thermodynamics and heat transfer of the combustion chambers of a diesel engine is presented. The work is devoted to the modified quasi-steady method (MQM) for the analysis of a diesel engine piston coated with an aluminum alloy. The oxide-coated piston using a galvanic-plasma modification (GPM) depending on the thickness of the coating, including comparison with the results for uncoated piston temperature, to achieve higher characteristics of the Cummins KTA-50 diesel engine. In thermodynamic modeling of a diesel engine, instantaneous gas temperatures and convective heat exchanges are first predicted. The time-dependent boundary conditions are then applied to the gas-blown surfaces of two-dimensional, transitional finite element models of the components of the combustion chamber. Further, the predictions on the finite elements of the instantaneous heat flux passing through each surface of the component are used to determine when the engine goes into quasi-stationary operation. The results show that our path in methodology can identify the complex transition paths of the heat process in the engine combustion chamber and significantly improve heat conduction and convection heat models when modeling a diesel engine.
A new combined SPD technique to improve mechanical properties and electrical conductivity of long-sized billets
Authors: Bobruk E V , Botkin A V , Murashkin M Yu , Raab G I 
Published: January 2021

Abstract
As a result of computer simulation carried out using the DEFORM 3D software package, the influence of the shape of the extrusion die-set, combined with equal-channel angular pressing with parallel channels (ECAP-PC), on the stress-strain state of cylindrical billets of an aluminum alloy was established. The obtained data made it possible to manufacture an experimental die-set for extrusion, combined with ECAP-PC, and to produce in it a cylindrical long-sized UFG billet from the 6063 alloy. It was established that one cycle of direct extrusion combined with ECAP-PC in the matrix with a non-axisymmetric deforming section for direct extrusion leads to a significant microstructure refinement and an improvement of mechanical properties of the alloy.
Portevin-Le Chatelier effect in austenitic steel Fe-18%Cr-8%Ni
Authors: Borisova Yu , Yuzbekova D , Mogucheva A 
Published: January 2021

Abstract
The study of the mechanical behavior of the austenitic Fe-18% Cr-8% Ni steel was carried out in the temperature range of 530°C - 680°C at a strain rate of 1×10−3 s−1, as well as at a temperature of 620°C and strain rates of 1×10−2 s−1 - 1×10−4 s−1. At these conditions, the PLC effect was observed. Type A serrations were observed in the temperature range 530 - 680°C. A decrease in the strain rate at a temperature of 620°C leads to a change in the type of serrations from type A to type B.
Influence of ECAP on the structure and properties of Ti18Zr15Nb and Ti10Mo8Nb6Zr alloys for medical application
Authors: Churakova A A , Gunderov D V , Raab G I , Prokoshkin S D , Sheremetyev V A , Filho Paulo N Lisboa , Pedro João , Claro Ana Paula Rosifini Alves 
Published: January 2021

Abstract
Studies of the influence of ECAP on the structure and properties of the metastable β-Ti alloys Ti18Zr15Nb and Ti10Mo8Nb6Zr have been carried out. The XRD data shows that the BCC β is the main phase in the initial alloys and alloys after ECAP. As a result of ECAP, the strength and yield stress of the alloys increases significantly due to the refinement of the structure. After ECAP, UTS and YS of the Ti10Mb8Nb8Zr alloy increase more noticeably than the Ti18Zr15Nb alloy, but after 7 ECAP cycles according to the regimes used (n = 6 T 250 °C + n = 1 350 °C), the Ti10Mb8Nb8Zr alloy becomes brittle. The increment in the yield point of the Ti18Zr15Nb alloy after ECAP processing together with the preservation of the β-state, allows one to expect an increase in the functional properties of the alloy.
Effect of thermomechanical treatment on the microstructure and mechanical properties of a low-carbon low-alloy steel
Authors: Dolzhenko A S , Belyakov A N , Kaibyshev R O 
Published: January 2021

Abstract
The effect of thermomechanical treatment on the microstructure, tensile strength and impact toughness of low-carbon low-alloy steel is considered. The developed microstructure is characterized by grain elongation along the rolling direction. Both the yield strength and the ultimate tensile strength increase with a decrease in test temperature. The ultimate strength at room temperature is 797 MPa, and at 77 K the ultimate strength increases to 1198 MPa. The steel samples subjected to tempforming exhibit impact toughness of KCV = 410 J/cm2 at room temperature. A decrease in the test temperature to 233 K leads to a slight decrease in the KCV value to 340 J/cm2. It should be noted that the impact specimens are not completely fractured even at a test temperature of 233 K, suggesting higher real values of impact toughness.
Evolution of strengthening factors during long-term aging at 650 °C in advanced 10% Cr heat-resistant steel
Authors: Dudova N , Mishnev R , Kaibyshev R 
Published: January 2021

Abstract
The effect of long-term aging for 1000…∼40,000 h at 650 °C on the tensile strength at ambient temperature was studied in a low-nitrogen and high-boron 10%Cr martensitic steel. In order to establish the reason for increasing the yield stress and ultimate tensile strength after 10,000 h of aging, the evolution of strengthening factors was analyzed. A decrease in the substructure and solid solution strengthening during long-term aging is compensated by an increase in the dispersion strengthening due to the precipitation of V-rich MX carbonitrides.
Evolution of the tempered lath structure of the 12%Cr steels with low N and high B contents during creep
Authors: Fedoseeva A E , Nikitin I S , Fedoseev A E , Kaibyshev R O 
Published: January 2021

Abstract
9-12%Cr martensitic steels are promising materials for elements of boilers, tubes, pipes, heaters and steam blades for fossil power plants, which are able to operate at ultra-supercritical parameters of steam. Creep tests were carried out for two 12%Cr and 9%Cr steels at 650°C. After tempering at 750-770°C, a tempered lath structure was revealed in all the steels studied. The 12%Cr-Ta steel had the smallest lath width among the steels studied that provided the longest creep rupture time after creep test at 650°C/120 MPa. During creep, the applied stress causes the lath growth and the formation of subgrains instead of martensitic laths. The experimental sizes of subgrains and equilibrium subgrains, calculated on balance of driving and retarding forces and using the dependence of the size of subgrains on the applied stress during creep, were compared to estimate the contributions of secondary particles and applied stress to the growth of subgrains during tempering and creep in the different steels.
B2 precipitates formation in Al-containing CoCrFeMnNi-type high entropy alloy
Authors: Klimova M , Shaysultanov D , Semenyuk A , Zherebtsov S , Salishchev G , Stepanov N 
Published: January 2021

Abstract
The non-equiatomic Al7.5Co21.75Cr5.5Fe21.75Mn21.75Ni21.75 high entropy alloy was studied. After cold rolling and annealing at 700-900 °C, a dual-phase ultrafine-grained structure composed of the partially recrystallized fcc matrix and B2 particles was produced; complete recrystallization of the fcc phase was observed after annealing at 1000 °C. The B2 precipitates formation provided a significant strengthening of the alloy in comparison with the single-phase state. The alloy demonstrated an attractive combination of mechanical properties, presenting yield and ultimate tensile strengths of 900 MPa and 1200 MPa, respectively, along with a ductility of 22%.
Development of n-body interatomic potentials for calculating the thermodynamic characteristics of V-Nb-Mo-W alloys
Authors: Maksimenko V N , Lipnitskii A G 
Published: January 2021

Abstract
New interatomic potentials for Mo and binary systems V-Nb, V-Mo, Nb-Mo, Nb-W and Mo-W are constructed taking into account the angular dependencies of interatomic interactions. Together with the potentials constructed earlier in the same approach, a complete set of potentials for modeling alloys of the V-Nb-Mo-W system at any component concentrations is obtained. A tendency to narrow the range of values of the calculated enthalpy of formation and the volume of formation in equiatomic alloys of the V-Nb-Mo-W system with an increase in the number of components was found. Deviations from the Vegard’s rule in the volume of formation of these alloys are shifted to the negative range of values when the number of components is more than two.
Modelling of the Rolling Process of Titanium Alloy Tube Billets in Laboratory Conditions on a RSP 14-40 Rolling Mill
Authors: Martynov K G , Negodin D A , Klimenko D N , Gladkov Yu A , Zherebtsov S V 
Published: January 2021

Abstract
The development of screw rolling technology for the production of hot-deformed tubes over Ø250 mm on a SVP-500 rolling mill faces a number of challenges that influence the quality of tubes, such as: the screw trace formed on the external surface of tubes and bending of tubes that makes impossible subsequent manufacturing operations. The following experimental and laboratory research was performed to solve these problems: a number of experimental tube billets with and without mandrels were rolled to various strains on a RSP 14-40 laboratory rolling mill to obtain the best ratio of wall thickness to the external diameter. The temperature field distribution and the strain intensity in the deformation area of tube billets rolling were analyzed. A quality assessment of the influence of the section of the calibrating rolls used in industrial technology on the external surface of hot-deformed tubes was also carried out at the modeling stage. The angle changing options of the calibrating rollers section of the screw rolling mill were analyzed for the subsequent tool improvement.