Properties Of Pairs Research Articles

Isotope Substitution Effects on the Magnetic Compass Properties of Cryptochrome-Based Radical Pairs: A Computational Study.

The biophysical mechanism of the magnetic compass sense of migratory songbirds is thought to rely on the photochemical reactions of flavin-containing radical pairs in cryptochrome proteins located in the birds' eyes. A consequence of this hypothesis is that the effect of the Earth's magnetic field on the quantum yields of reaction products should be sensitive to isotopic substitutions that modify the hyperfine interactions in the radicals. In this report, we use spin dynamics simulations to explore the effects of 1H → 2H, 12C → 13C, and 14N → 15N isotopic substitutions on the functioning of cryptochrome 4a as a magnetic direction sensor. Two main conclusions emerge. (1) Uniform deuteration of the flavin chromophore appears to be the best way to boost the anisotropy of the magnetic field effect and to change its symmetry. (2) 13C substitution of three of the 12 flavin carbons, in particular C4, C4a, and C8α, seems to be the best recipe for attenuating the anisotropy. These predictions should give insight into the factors that control the magnetic sensitivity once spectroscopic techniques are available for measuring magnetic field effects on oriented protein samples.

Second-Neighbor Hopping Effects in the Two-Dimensional Attractive Hubbard Model

The emergence of superconductivity (SC) in lattice models, such as the attractive Hubbard one, has renewed interest since the realization of cold-atom experiments. However, reducing the temperature in these experiments is a bottleneck; therefore, investigating how to increase the energy scale for SC is crucial to cold atoms. In view of this, we examine the effects of next-nearest-neighbor hoppings (t′) on the pairing properties of the attractive Hubbard model in a square lattice. To this end, we analyze the model through unbiased Quantum Monte Carlo simulations for fixed density n=0.87, and perform finite-size scaling analysis to the thermodynamic limit. As our main result, we notice that the existence of further hopping channels leads to an enhancement of the pairing correlations, which, in turn, increases the ground-state order parameter Δ. Finally, at finite temperatures, for t′/t≠0, this enhancement of pairing correlations leads to an increase in the critical temperature Tc. That is, the fine-tuning of second-neighbor hoppings increases the energy scales for SC, and may be a route by which cold-atom experiments can achieve such a phase and to help us further understand the nature of this phenomenon.

BDG inequalities and their applications for model-free continuous price paths with instant enforcement

Shafer and Vovk introduce in their book [8] the notion of instant enforcement and instantly blockable properties. However, they do not associate these notions with any outer measure, unlike what Vovk did in the case of sets of “typical” price paths. In this paper an outer measure on the space $[0,+\infty )\times \Omega $ is introduced, which assigns zero value exactly to those sets (properties) of pairs of time t and an elementary event ω which are instantly blockable. Next, for a slightly modified measure, Itô’s isometry and BDG inequalities are proved, and then they are used to define an Itô-type integral. Additionally, few properties are proved for the quadratic variation of model-free continuous martingales, which hold with instant enforcement.

Statistics of Galactic-scale Quasar Pairs at Cosmic Noon

The statistics of galactic-scale quasar pairs can elucidate our understanding of the dynamical evolution of supermassive black hole (SMBH) pairs, the duty cycles of quasar activity in mergers, or even the nature of dark matter, but they have been challenging to measure at cosmic noon, the prime epoch of massive galaxy and SMBH formation. Here we measure a double quasar fraction of ∼6.2 ± 0.5 × 10−4 integrated over ∼0.″3–3″ separations (projected physical separations of ∼3–30 kpc at z ∼ 2) in luminous (L bol > 1045.8 erg s−1) unobscured quasars at 1.5 < z < 3.5 using Gaia EDR3-resolved pairs around SDSS DR16 quasars. The measurement was based on a sample of 60 Gaia-resolved double quasars (out of 487 Gaia pairs dominated by quasar+star superpositions) at these separations, corrected for pair completeness in Gaia, which we quantify as functions of pair separation, magnitude of the primary, and magnitude contrast. The double quasar fraction increases toward smaller separations by a factor of ∼5 over these scales. The division between physical quasar pairs and lensed quasars in our sample is currently unknown, requiring dedicated follow-up observations (in particular, deep, subarcsecond-resolution IR imaging for the closest pairs). Intriguingly, at this point, the observed pair statistics are in rough agreement with theoretical predictions both for the lensed quasar population in mock catalogs and for dual quasars in cosmological hydrodynamic simulations. Upcoming wide-field imaging/spectroscopic space missions such as Euclid, CSST, and Roman, combined with targeted follow-up observations, will conclusively measure the abundances and host galaxy properties of galactic-scale quasar pairs, offset AGNs, and subarcsecond lensed quasars across cosmic time.

Technologies assuring the service properties of friction pairs with cellular microrelief surfaces

Article focuses on the improvement of the technologies used to improve the durability of friction pair components. The authors use the piston compressor to study cellular microrelief surfaces of cylindrical components. The cells are shaped as elliptic paraboloid with uneven positive parameters. The use of cellular microrelief surfaces is highly preferred as they reduce the attrition wear of the friction pairs through assuring the hydrodynamic load capacity of the lubrication layer with the shape of the microrelief. The research goals included the parametric analysis of the lubrication layer behavior in the gap between the microrelief cells. To do this, the authors developed an analytical model based on the theory of hydrodynamic lubrication and constructed a CFD model using the ANSYS Fluent software. To contain the transfer equations, the authors used the turbulence model SST k–ω. Both models showed that the maximum hydrodynamic load capacity coincided with the 75%-length of the major axis of the elliptic cell, which also corresponds to 0.128 mm in cell depth. The maximum lifting hydrodynamic pressure on one microrelief cell amounted to 3 kPa. Based on the results of the parametric analysis, the authors claim that the cellular microrelief can be efficiently used to assure the service properties of friction pairs in process units. Keywords: friction pair; cylinder sleeve; piston ring; cellular microrelief; hydrodynamic model; mathematical model; ANSYS Fluent; two-dimensional parametric analysis.

Spatial and spectral characterization of photon pairs at telecommunication wavelengths from type-0 spontaneous parametric downconversion

The thorough characterization of entangled-photon sources is vital for their optimal use in quantum communication. However, this task is not trivial at telecommunication wavelengths. While cameras and spectrometers are well developed for visible and near-infrared spectra, this does not apply in the mid-infrared range. Here, we present a spatial and spectral characterization of photon pairs emitted in a type-0 phase-matched spontaneous parametric downconverted source. We experimentally show how these photon properties are modified by the crystal temperature. This parameter allows easy modification of photon-pair properties to fit multiplexing schemes based on only one entanglement photon source. Our results pave the way for the optimal design and use of spatial and spectral properties of quantum-correlated photon pairs at telecommunication wavelengths.

Algebra of Data Reconciliation

With distributed computing and mobile applications becoming ever more prevalent, synchronizing diverging replicas of the same data is a common problem. Reconciliation – bringing two replicas of the same data structure as close as possible without overriding local changes – is investigated in an algebraic model. Our approach is to consider two sequences of simple commands that describe the changes in the replicas compared to the original structure, and then determine the maximal subsequences of each that can be propagated to the other. The proposed command set is shown to be functionally complete, and an update detection algorithm is presented which produces a command sequence transforming the original data structure into the replica while traversing both simultaneously. Syntactical characterization is provided in terms of a rewriting system for semantically equivalent command sequences. Algebraic properties of sequence pairs that are applicable to the same data structure are investigated. Based on these results the reconciliation problem is shown to have a unique maximal solution. In addition, syntactical properties of the maximal solution allow for an efficient algorithm that produces it.

Sliding bearings with lead-bismuth liquid metal lubrication

The article presents the results of tribological tests of a thrust bearing made of steel-bronze materials when lubricated with a lead-bismuth metal melt under conditions of heating up to 500°C. The influence of steel-bronze on the coefficient of friction in the ranges of load 0.17–1.0 MPa, velocity 0.05–0.23 m/s, and temperature 250–500°C was studied. It has been established that the tribological properties of friction pairs under experimental conditions mainly depend on temperature, which determines the wetting angle and the viscosity of the metal melt. With an increase in the temperature of the melt above 300°C, the viscosity of the melt decreases, and the liquid metal lubricant is squeezed out of the actual contact areas.

WALLABY Pilot Survey: H i gas kinematics of galaxy pairs in cluster environment

ABSTRACT We examine the H i gas kinematics of galaxy pairs in two clusters and a group using Australian Square Kilometre Array Pathfinder (ASKAP) WALLABY pilot survey observations. We compare the H i properties of galaxy pair candidates in the Hydra I and Norma clusters, and the NGC 4636 group, with those of non-paired control galaxies selected in the same fields. We perform H i profile decomposition of the sample galaxies using a tool, baygaud, which allows us to deblend a line-of-sight velocity profile with an optimal number of Gaussian components. We construct H i superprofiles of the sample galaxies via stacking of their line profiles after aligning the central velocities. We fit a double Gaussian model to the superprofiles and classify them as kinematically narrow and broad components with respect to their velocity dispersions. Additionally, we investigate the gravitational instability of H i gas discs of the sample galaxies using Toomre Q parameters and H i morphological disturbances. We investigate the effect of the cluster environment on the H i properties of galaxy pairs by dividing the cluster environment into three subcluster regions (i.e. outskirts, infalling, and central regions). We find that the denser cluster environment (i.e. infalling and central regions) is likely to impact the H i gas properties of galaxies in a way of decreasing the amplitude of the kinematically narrow H i gas ($M_{\rm {narrow}}^{\rm {H\, \small {\rm I}}}$/$M_{\rm {total}}^{\rm {H\, \small {\rm I}}}$), and increasing the Toomre Q values of the infalling and central galaxies. This tendency is likely to be more enhanced for galaxy pairs in the cluster environment.

THERMODYNAMICS OF ION PAIR CONVERSION IN ALCOHOL SOLUTIONS OF HYDROGEN CHLORIDE

The thermodynamic quantities of the dissociation stages of contact ion pairs (CIP) and solvent-separated ion pairs (SSIP) into ions, conversion of CIP into SSIP of the ionization process of HCl in n-alcohols from methyl to n-octyl at 278.15 – 328.15 K, i.e. in non-aqueous solvents that are most frequently used in chemical research and in chemical technology have been calculated. The proton and chloride ion forming HCl are modeled in a comparative study of the solvation process and the molecular mechanism of acid ionization in various solvents, which emphasizes the relevance of this study, in which the influence of the nature of the solvent, hydrogen chloride ions and temperature on the above thermodynamic quantities are considered. The calculation of the dissociation constants of CIP was carried out according to Ebeling’s equation, which takes into account the short-range repulsive forces between the ions in the ion pair and the dispersion interactions between the solvent molecules. The dissociation constants and thermodynamic quantities of SSIPs have been calculated by the Schwartz method, which evaluates the physical and chemical parameters of the solvent (besides the dielectric permittivity also the free volume of the solvent molecules, isothermal compressibility, etc.) that significantly affect the properties of ion pairs. The main conclusions drawn from our analysis of the array of thermodynamic data on the ionization stages of HCl in n-alcohols from methyl to n-octyl: (a) in methanol the predominant among the ion pairs are SSIPs, in ethanol the concentration of CIPs and SSIPs is approximately the same, and in other alcohols, the CIPs predominate; b) the concentration of CIPs increases with increasing alkyl radical of the alcohol when passing from methanol to n-octanol respectively from 30% to 95%; c) ratio of enthalpic (ΔconvH°) and entropic (–TΔconvS°) factors in methanol and ethanol ensures spontaneous conversion of CIP to SSIP; d) in alcohols from n-propyl to n-octyl values and sign ΔG° for the stages of dissociation of CIP and SSIP into ions and conversion of CIP to SSIP are determined by the entropic term (–ТΔS°), which leads to deconversion of ion pairs, i.e., the conversion of SSIPs into CIPs.

Pairing properties of the t−t′−t″−J model

We study the pairing properties of the two-dimensional $t$-$t'$-$t''$-$J$ model, where $t'$ and $t''$ are second and third neighbor hoppings, at a doping level $x\approx0.1$. Recent studies of the $t$-$t'$-$J$ model find strong pairing for $t'>0$, associated with electron doping, but an absence of pairing for $t'<0$ associated with hole doping. This is in contrast to the cuprates, where the highest transition temperatures appear for hole doping. Model parameterizations for the cuprates estimate a $t''$ comparable to $t'$, which, in principle, might fix this discrepancy. However, we find that it does not; we observe a suppression of pairing for the hole-doped system ($t'0$) while for the electron-doped system ($t'>0, t''<0$) $d$-wave pairing is robust. Extended hoppings appear to be insufficient to make the one-band $t$-$t'$-$J$ model capable of describing the pairing in the hole doped system.

Adiabatic quantum Zeno dynamics of bosonic atom pairs with large inelastic losses

We report on experiments exploring the non-Hermitian dynamics of pairs of two-level atoms tightly confined in an optical lattice and driven by a near-resonant laser. Although spontaneous emission is negligible for the long-lived excited state, two-body dissipation arises from strong inelastic collisions between two atoms in the excited state. We demonstrate quasi-adiabatic control of the internal state of the pairs in the quantum Zeno regime where inelastic losses dominate. Preparing each atom pair in the longest-lived eigenstate of the non-Hermitian Hamiltonian describing the dissipative dynamics, we measure a lifetime enhanced by more than two orders of magnitude in comparison to the bare two-body lifetime. The measured enhancement factor is in quantitative agreement with the expected lifetime of the prepared ``non-Hermitian dressed state''.

Molecular Dynamics Simulation of Thermomechanical Properties of Hollow Palladium Nanoparticle Pairs during Additive Manufacturing

Molecular Dynamics Simulation of Thermomechanical Properties of Hollow Palladium Nanoparticle Pairs during Additive Manufacturing

Synthesizing Ag2Ox(3 wt%)-loaded ZnFe2O4 photocatalysts for efficiently saving polluted aquatic ecosystems

Herein, we report an Ag2Ox (3 wt%)-loaded ZnFe2O4 photocatalysts synthesized by co-precipitation and incipient wet impregnation approach for acetamiprid degradation, antibacterial, antioxidant, and toxicity assay. Initially, bare ZnFe2O4 nanostructures were made through a simple co-precipitation method. In the second step, 3 wt% of various transition metal oxides (CuOx, ZrOx, and Ag2Ox) were embedded on the surface of ZnFe2O4 photocatalysts via a wet impregnation method. Further, the prepared photocatalysts were systematically characterized using XRD, FTIR, FE-SEM, BET, HRTEM, and XPS analysis. The optimum Ag2Ox (3 wt%)-loaded ZnFe2O4 photocatalysts revealed higher degradation efficiencies for acetamiprid under sunlight irradiation. Additionally, the Ag2Ox (3 wt%)-loaded ZnFe2O4 photocatalysts showed more effective antioxidant and antibacterial activity than blank and bare ZnFe2O4 nanomaterials. The enriched catalytic efficiency can be accredited to the 3 wt% of Ag2Ox NPs loaded on ZnFe2O4 nanomaterials, possibly due to the boosted transport properties of the electron-hole pairs. This study will provide a new avenue for the development of simple and effective photocatalysts for efficiently saving polluted aquatic ecosystems.

A Nucleic Acid Sequence That is Catalytically Active in Both RNA and TNA Backbones.

Threose nucleic acid (TNA) is considered a potential RNA progenitor due to its chemical simplicity, base pairing property, and capability of folding into a functional tertiary structure. However, it is unknown whether the functional property can be maintained during transition from TNA to RNA. Here, we use a toggle in vitro selection to identify nucleic acid catalyst sequences that are active in both TNA and RNA backbones. One such nucleic acid enzyme with exchangeable backbone (CAMELEON) catalyzes an RNA cleavage reaction when prepared as TNA (T) and RNA (R). Further biochemical characterization reveals that CAMELEON R and T exhibit different catalytic behaviors such as rate enhancement and magnesium dependence. Structural probing and mutagenesis experiments suggest that they likely fold into distinct tertiary structures. This work demonstrates that the catalytic activity can be preserved during backbone transition from TNA to RNA and provides further experimental support for TNA as an RNA precursor in evolution.

Effect of Laser Surface Texturing on the Tribological Properties and Scuffing Mechanism of CKS Piston Ring Against Cast Iron Cylinder Liner Under High Intensifying

The objective of this study is to characterize and understand the evolutionary processes that the effect of surface texture has on the tribology properties of the Chrom-Keramik-Schicht (CKS) piston ring/cast iron cylinder liner system under high intensifying. Surface dimple textures with an area density of 3–9% were prepared on the CKS piston ring by YAG laser, and the antifriction and antiscuffing properties were tested on a reciprocating test rig at 200 °C and 80 MPa. The minimum friction coefficient and wear loss were both obtained at the area density of 5%, compared with the untextured cylinder liner–piston ring (CLPR). The friction coefficient decreased by 0.013 to 0.086, and the wear loss for the piston ring and cylinder liner decreased by 41% and 46%, respectively. The sharp decrease of the friction force induced by surface polishing of the cylinder liner is taken as a sign to indicate the cylinder scuffing under starved lubrication. The scuffing time for the piston ring/cylinder liner system reached a maximum value of 18 min at an area density of 3%, which is extended about 41% compared with that of the untextured piston ring. The dimple surface texture on the piston ring could extend the scuffing time by delaying the occurrence of polishing behavior on the surface of cylinder liner. It is found that the retarded surface polishing played a major role for the modification of the antiscuffing property of the friction pairs according to the friction curves and wear morphologies.

Constructing Z-scheme g-C3N4/TiO2 heterostructure for promoting degradation of the hazardous dye pollutants

The use of dyes and segments has increased widely in recent years, but it poses a serious health risk to ecosystems. In this work, TiO2 and two-dimensional g-C3N4 nanosheets (g-CN) were fabricated through co-precipitation and thermal polymerization technique, respectively. The g–CN–TiO2 photocatalyst (1: 3, 2: 2, 3: 1) in various weight percentages was prepared using a simple impregnation process. The photocatalytic behaviour of the g-CN, TiO2 NPs, and different weight percentages of g–CN–TiO2 photocatalyst was evaluated against methylene blue (MB) dye under UV–visible light illumination. Compared to pristine and other weight percentages of the g–CN–TiO2 nanocomposite, the optimized g–CN–TiO2 nanocomposite (3:1) showed promoted performance against MB dye. The enriched catalytic efficiency can be accredited to the low amount of TiO2 nanoparticles deposited on gCN nanosheets, possibly due to the boosted transport properties of the electron-hole pairs. The enriched photocatalytic behaviour can be attributed to the development of the Z-scheme system between TiO2 and g-CN. The current study is an outstanding demonstration of the development of maximum catalytic efficiency for destroying hazardous chemical dyes.

Two strategies for modeling nonlinear optics in lossy integrated photonic structures

We present two complementary strategies for modeling nonlinear quantum optics in realistic integrated optical devices, where scattering loss is present. In the first strategy, we model scattering loss as an attenuation; in the second, we employ a Hamiltonian treatment that includes a mechanism for scattering loss, such as a `phantom waveguide.' These strategies can be applied to a broad range of structures and processes. As an example, we use these two approaches to model spontaneous four-wave mixing in (i) a ring-channel system and (ii) an add-drop system. Even for these well-understood systems, our strategies yield some novel results. We show the rates of photon pairs, broken pairs, and lost pairs and their dependence on system parameters. We show that the properties of lost and broken photon pairs in such structures can be related to those of the un-scattered photon pairs, which are relatively simple to measure.

Multivalley Superconductivity in Monolayer Transition Metal Dichalcogenides.

In transition metal dichalcogenides (TMDs), Ising superconductivity with an antisymmetric spin texture on the Fermi surface has attracted wide interest due to the exotic pairing and topological properties. However, it is not clear whether the Q valley with a giant spin splitting is involved in the superconductivity of heavily doped semiconducting 2H-TMDs. Here by taking advantage of a high-quality monolayer WS2 on hexagonal boron nitride flakes, we report an ionic-gating induced superconducting dome with a record high critical temperature of ∼6 K, accompanied by an emergent nonlinear Hall effect. The nonlinearity indicates the development of an additional high-mobility channel, which (corroborated by first principle calculations) can be ascribed to the population of Q valleys. Thus, multivalley population at K and Q is suggested to be a prerequisite for developing superconductivity. The involvement of Q valleys also provides insights to the spin textured Fermi surface of Ising superconductivity in the large family of transition metal dichalcogenides.

Screening adsorbent-working solution pairs for adsorption-driven osmotic heat engines based on experimental water adsorption isotherm database and machine learning

Osmotic heat engines have attracted increasing attention in harvesting ultra-low temperature waste heat. In order to fill the gap in the high-throughput computational screening of adsorbent-aqueous salt solution working pairs for adsorption-driven osmotic heat engines, an experimental water adsorption isotherm database is constructed and eight common salt-water solutions are selected to identify the high-performance work pairs with system energy efficiency as evaluation indicator. The relationship between adsorbent properties, adsorbent structure characteristics and system performance is systematically analyzed. Results revealed that high working capacity and moderate adsorption enthalpy of adsorbents and large osmotic coefficients of salts are beneficial to energy efficiency. Adsorbents with larger accessible surface area, moderate available pore volume and critical pore diameter are favorable. Furthermore, regression machine learning is employed for achieving fast and accurate prediction of the system energy efficiency to accelerate screening. Genetic algorithm is adopted to search for the best-performing working pair properties.