Strong Pairing Research Articles

A simulation on the graphyne and its inorganic BN-like nanosheets as anode materials for Ca-ion batteries

ABSTRACT Although the Li-ion batteries have some advantages, they have some disadvantages such as high cost, short life, and safety issues. Recently, Ca-ion batteries (CIB) have been suggested to replace Li-ion batteries due to calcium wide availability, multivalent character, and nontoxicity. Now, we evaluated the potential application of graphyne and its BN analogous (BN-yne) in the CIBs with the use of the B3LYP-gCP-D3 approach. The adsorption of Ca2+ and Ca on the graphyne is stronger and weaker than those on the BN-yne, respectively. The highest energy barrier for Ca2+ migration on the BN-yne (4.3 kcal/mol) is much lesser than that on the graphyne (5.9 kcal/mol) because of a strong cation-lone pair interaction in the BN-yne compared to the weak cation-π interaction of graphyne. Therefore, we realise the potential of the BN-yne in providing a greater Ca ion mobility and a more rapid charge/discharge rate compared to graphyne. Diffusion coefficient values calculated for the Ca2+ on the surface of graphyne and BN-yne are 3.27 × 10−11 and 5.14 × 10−9 cm2/s, and the predicted cell voltages are 3.38 and 3.66 eV, respectively. The results suggest that the BN-yne sheet may be a superior anode candidate for CIBs compared to the graphyne.

Effect of π···π Interactions of Donor Rings on Persistent Room-Temperature Phosphorescence in D4-A Conjugates and Data Security Application.

Organic room-temperature phosphorescence (RTP) materials with persistent RTP (PRTP) have attracted huge interest in inks, bioimaging, and photodynamic therapy. However, the design principle to increase the lifetime of organic molecules is underdeveloped. Herein, we show donor(D4)–acceptor(A) molecules (TOEPh, TOCPh, TOMPh, TOF and TOPh) with similar orientation of donor rings in aggregates that cause a large number of noncovalent interactions. We observed that TOEPh, TOCPh, TOMPh and TOF showed PRTP, whereas TOPh showed only phosphorescence emission (ΦP = ∼11%) with no PRTP property at ambient conditions. The spectroscopic and single-crystal X-ray analyses confirm the molecular assembly via J-aggregation with a face-to-face orientation of the donor rings. The crystal structure analysis (TOEPh, TOCPh, TOMPh, TOF) reveals that moderate π···π interactions (3.706 to 4.065 Å) between the donor rings cause the enhancement of the phosphorescence lifetime (26 to 245 ms), whereas the short phosphorescence lifetime (12 ms) of TOPh was observed because of the absence of π···π interactions. We found that TOEPh shows a long lifetime (245 ms) as compared to other derivatives because of the presence of ethoxy (−OEt) groups that enables spin–orbit coupling caused by strong lone pair (O)···π interactions present in the molecule. Utilizing the PRTP feature of TOEPh and the fluorescence emission of TOPh, we have shown data security applications in poly(methyl methacrylate).

Room-temperature fast zinc-ion conduction in molecule-flexible solids

Understanding solid-state zinc-ion conduction will not only be academically interesting but also benefit the development of energy-dense devices. However, zinc ions in conventional ceramic and polymer hosts are only mobile at high temperatures, and intriguing questions remain regarding the correlation between ionic local environment and conductivity performance. Here, we demonstrate a room-temperature fast zinc-ion conduction in solids with a high degree of molecular flexibility and elucidate the subtle trade-off between molecular-scale interactions and ion transport properties. Importantly, a determining role of the strong cation-anion pairing in suppressing zinc-ion mobility has been experimentally uncovered. When removed, the upper limit of ionic conductivity can be extended to the order of 10−4 S/cm, exceeding those of previous solid (solvent-free) zinc-ion conductors. Concomitant with the reversible plating/stripping of zinc (over 700 h), the successful creation of solid-state zinc-ion batteries confirms the practical applicability of the resultant conductors.

Effect of jet inflow angle on heat transportation in an impinging jet interfering with a Couette flow

The effect of the incoming angle of a jet that interferes with a Couette flow is studied using numerical simulations. When the jet flows against the direction of the Couette flow, the instantaneous vortex structure and heat transfer on the jet-impinging surface become complex and irregular. In contrast, when the jet flows in the same direction as the Couette flow, the instantaneous vortex structure has a strong and distinct periodicity about the main flow direction as a vortex street with a sine wave velocity fluctuation. This periodicity also affects the heat transfer on the jet-impinging surface. The Strouhal number calculated from these time periodicity increases with increasing jet angle. In the time-averaged flows and temperature fields, the Nusselt number exhibits a few characteristic distributions. The heat transfer concentrates around the jet impingement region at a negative jet angle whereas the area associated with significant heat transfer coefficient separates symmetrically about the flow in spanwise direction at a positive jet angle and the value of heat transfer coefficient on the center axis is low. Furthermore, a large and strong counter-rotating vortex pair is formed when the jet flows in the same direction as the Couette flow. As reported in our previous study, this pair vortex involves a main flow fluid and results in a characteristic Nusselt number distribution. Comparing the overall heat transfers on the jet-impinging surface, the lowest time-averaged heat transfer is obtained when the jet is orthogonal to the Couette main flow. Generally, the heat transfer over the surface is higher when the jet flows against the Couette flow than when the jet flows in the same direction as the Couette flow. However, since the pressure loss also increases drastically at the same time, it is found that the ratio of heat transfer over pressure loss increases with increase in jet angle. Considering the temperature and velocity vector distributions, and plots of turbulent heat flux, when the jet flows against the Couette main flow, the effect of jet impingement is dominant on heat transfer. However, when the jet flows in the same direction as the Couette main flow, most of the heat transfer is carried by the pair vortex. Although the contributing vortex type is different from similar previous studies conducted, the mechanism of generating this pair vortex is based on time-averaging the legs of the periodic vortex street.

Characteristic decomposition of polynomial sets

An ordered pair $(\pset{G},\,~\pset{C})$ is called the characteristic pair of a polynomial ideal if $\pset{G}$ is the reduced lexicographic grobner basis of the ideal and $\pset{C}$ is the minimal triangular set contained in $\pset{G}$. A characteristic pair $(\pset{G},\,~\pset{C})$ is said to be regular or normal if $\pset{C}$ is regular or normal; it is said to be strong if the ideal generated by $\pset{G}$ and the saturated ideal of $\pset{C}$ are the same. A strong regular or normal characteristic decomposition of a polynomial set means a decomposition of the polynomial set into finitely many (strong) regular or normal characteristic pairs with an associated zero or ideal decomposition. This paper presents two algorithms for characteristic decomposition of any given polynomial set, one producing strong normal characteristic pairs with ideal splitting according to pseudo-divisibility relations between polynomials in reduced lexicographic grobner bases and the other producing strong regular characteristic pairs by constructing nontrivial ideals that can be divided out of given ideals by using ideal quotient. Novel theorems are established for regularizing characteristic pairs and strengthening regular and normal characteristic pairs by using ideal saturation. Strong regular or normal characteristic pairs produced by the algorithms possess nice properties and furnish two representations, one in terms of lexicographic grobner bases and the other in terms of triangular sets, for the zeros of the input set of multivariate polynomials. The paper includes a brief review on triangular decompositions of various kinds and discussions about inherent connections among triangular sets, Ritt characteristic sets, and reduced lexicographic grobner bases. Examples and experimental results are also provided to illustrate the method of characteristic decomposition and its applicability and performance.

Tuning the topology of p -wave superconductivity in an analytically solvable two-band model

We introduce and solve a two-band model of spinless fermions with $p_x$-wave pairing on a square lattice. The model reduces to the well-known extended Harper-Hofstadter model with half-flux quanta per plaquette and weakly coupled Kitaev chains in two respective limits. We show that its phase diagram contains a topologically nontrivial weak pairing phase as well as a trivial strong pairing phase as the ratio of the pairing amplitude and hopping is tuned. Introducing periodic driving to the model, we observe a cascade of Floquet phases with well defined quasienergy gaps and featuring chiral Majorana edge modes at the zero- or $\pi$-gap, or both. Dynamical topological invariants are obtained to characterize each phase and to explain the emergence of edge modes in the anomalous phase where all the quasienergy bands have zero Chern number. Analytical solution is achieved by exploiting a generalized mirror symmetry of the model, so that the effective Hamiltonian is decomposed into that of spin-$1/2$ in magnetic field, and the loop unitary operator becomes spin rotations. We further show the dynamical invariants manifest as the Hopf linking numbers.

Local heat transfer enhancement induced by a piezoelectric fan in a channel with axial flow

The present work experimentally and numerically investigates the local heat transfer enhancement induced by a piezoelectric fan interacting with a cross flow in a local heated channel. The piezoelectric fan is placed along the flow direction and tested under different amplitudes and flow rates. In the simulations, a spring-based smoothing method and a local remeshing technique are used to handle the moving boundary problems. Hybrid mesh is used to reduce the size of dynamic mesh domain and to improve computational efficiency. The experimental and numerical values of the time-averaged mean Nusselt number are found to be in good agreement, with deviations of less than 10%. The experimental result shows that the heat transfer performance of the heated surfaces is substantially enhanced with a vibrating piezoelectric fan. The numerical result shows that the heat transfer enhancement comes from the strong longitudinal vortex pairs generated by the piezoelectric fan, which significantly promote heat exchange between the main flow and the near-wall flow. In the case of a=0.66 (a is the dimensionless amplitude) and Re=1820, the enhancement ratio of the time-averaged mean Nusselt number reaches 119.9%.

Growth inhibition and deposition prevention of sulfide scales using dispersants

Although sulfide scales of FeS, PbS, and ZnS do not occur as frequently as carbonate and sulfate scales, it is difficult to remove them once they are formed and deposited. Effective prevention and remediation of sulfide scales have not been fully developed. For sulfide scales, the conventional threshold inhibition approach is not as effective as for carbonate and sulfate scales, presumably, due to strong ion pairs formation of FeS0 and fast precipitation kinetics of FeSs. Polyacrylamide (PAM), polyvinyl pyrrolidone (PVP), and carboxymethyl cellulose (CMC) were examined as dispersants for sulfide scales to prevent and mitigate sulfide scale deposition through controlling the particle sizes of FeS, PbS and ZnS. PAM, PVP, and CMC dispersed FeS particles more effectively at pH 6.7 than 5.0 and temperature 70 °C than 90 °C. PAM and CMC successfully dispersed FeS particles even in extremely high ionic strength (I) of 4.6 M, while, PVP, slightly less effective, up to I = 2.6 M. At pH 5.0 and 90 °C, CMC was able to disperse FeS particles up to I = 1.3 M and PVP up to I = 0.6 M. In contrast, PAM could not disperse FeS particles at all. When FeS particles were dispersed in the presence of polymeric dispersants, FeS particle sizes remained in nanometer ranges, from 100 to 600 nm. Our results demonstrated that CMC was the best dispersant for FeS particles among the three polymers we tested. For CMC, the larger molecular weight and the lower degree of substitution of carboxylic groups on cellulose, the more effective dispersant CMC became. PbS and ZnS were also well dispersed in the presence of CMC. Almost all fraction of PbS particles was smaller than 200 nm, while about 60% of ZnS particles were smaller than 200 nm. Results demonstrated that the promising treatment selection of CMC as a universal dispersant for sulfide scales.

Superconductivity, pseudogap, and phase separation in topological flat bands

We study a two-dimensional model of an isolated narrow topological band at partial filling with local attractive interactions. Numerically exact quantum Monte Carlo calculations show that the ground state is a superconductor with a critical temperature that scales nearly linearly with the interaction strength. We also find a broad pseudogap regime at temperatures above the superconducting phase that exhibits strong pairing fluctuations and a tendency towards electronic phase separation; introducing a small nearest neighbor attraction suppresses superconductivity entirely and results in phase separation. We discuss the possible relevance of superconductivity in this unusual regime to the physics of flat band moir\'{e} materials, and as a route to designing higher temperature superconductors.

Correlating AGP on a quantum computer

For variational algorithms on the near term quantum computing hardware, it is highly desirable to use very accurate ansatze with low implementation cost. Recent studies have shown that the antisymmetrized geminal power (AGP) wavefunction can be an excellent starting point for ansatze describing systems with strong pairing correlations, as those occurring in superconductors. In this work, we show how AGP can be efficiently implemented on a quantum computer with circuit depth, number of CNOTs, and number of measurements being linear in system size. Using AGP as the initial reference, we propose and implement a unitary correlator on AGP and benchmark it on the ground state of the pairing Hamiltonian. The results show highly accurate ground state energies in all correlation regimes of this model Hamiltonian.

An elliptic foil rotating in uniform low-Reynolds-number flows

A computational study is conducted to systematically investigate the effect of rotating speed on vortex shedding characteristics and far-field wake patterns of an elliptic foil rotating in uniform cross flows at low Reynolds numbers. It is found that at low rotating speed, vortices shed at the advancing and retreating edges of the foil could form a strong vortex pair in the wake. At high rotating speed, adjacent vortices are closer to each other, thus may evolve into a single vortex. The far-field wake pattern also strongly depends on the rotating speed and demonstrates complex behaviors. It is observed that the wake can defect from downwards to upwards by increasing the rotating speed. The mean lift force increases monotonically with the rotating speed, while a significant drag reduction occurs at a small rotating speed, which is explained by the corresponding wake pattern. Furthermore, a rotating speed regime exists in which the mean aerodynamic torque is positive so that the rotation of the foil could be solely promoted by the flow, indicating a possibility of flow energy harvesting in this regime.

350 - Support group for depressed elderly in the outpatient – challenges in the Asian context

Introduction:With Singapore’s ageing population, it was anticipated that the increasing number depressed elderly would make recurrent and expensive demands on old age services. There were evidence-based studies that demonstrated the benefits of group therapy in older people with depression, anxiety, low self-esteem and maladaptive behaviour. Aside from being cost effective, group therapy can be more helpful than individual therapy when social support and learning about interpersonal difficulties are objectives of treatment. This paper described the process of setting up and running an outpatient support group for depressed elderly in the psychiatric setting and highlighted the challenges encountered.Methodology:English-speaking subjects > 65 years old with a diagnosis of depressive disorder (ICD-10) with no significant cognitive impairment were recruited. Participants attended a weekly closed group for 12 consecutive weeks with each session lasting 75 minutes. Participants continued with their treatments offered by their psychiatrists. The content of the discussion was determined by the group members. Discussion notes were taken by the facilitators after each session. Depression and well-being rating scales were used to assess depression severity at baseline and at the end of 12 weeks.Results:The response for the study was poor with reluctance to participate in group treatment despite attempts made by the department to encourage participation. 8 participants were eventually enrolled with 3 dropouts. Attendance was disrupted due to sickness, medical appointments, hospitalizations and grandparenting duties. There was a trend of improvement in the evaluation scores of the participants. The main themes identified were (1) ageing and health concerns; (2) reminiscence of the past; (3) regrets and burdens; (4) strategies to defeat depression. Group dynamics observed included universality of painful experiences, mirroring of common experiences during Japanese occupation and strong pairing of the same gender. There were no re-admissions or suicide attempts during the study period.Conclusions:The lack of response to group work amongst the elderly was consistently observed in this study. This contrasted with the popularity of such interventions in non-Asian settings. Further research would help to elucidate the cultural reluctance in sharing psychological problems amongst the elderly within a psychiatric setting.

Superconductivity mediated by polar modes in ferroelectric metals

The occurrence of superconductivity in doped SrTiO3 at low carrier densities points to the presence of an unusually strong pairing interaction that has eluded understanding for several decades. We report experimental results showing the pressure dependence of the superconducting transition temperature, Tc, near to optimal doping that sheds light on the nature of this interaction. We find that Tc increases dramatically when the energy gap of the ferroelectric critical modes is suppressed, i.e., as the ferroelectric quantum critical point is approached in a way reminiscent to behaviour observed in magnetic counterparts. However, in contrast to the latter, the coupling of the carriers to the critical modes in ferroelectrics is predicted to be small. We present a quantitative model involving the dynamical screening of the Coulomb interaction and show that an enhancement of Tc near to a ferroelectric quantum critical point can arise due to the virtual exchange of longitudinal hybrid-polar-modes, even in the absence of a strong coupling to the transverse critical modes.

Loss Mechanism of Low-Pressure Turbine Secondary Flows Due to Different Incoming Boundary Layers

Abstract In high bypass ratio engines, the flow exits the interturbine duct (ITD) and enters the low-pressure (LP) turbine. This paper aims to understand the effects of the boundary layer at the exit of ITD on the endwall secondary flows and loss of the first blade row in a low-pressure turbine. From the Navier–Stokes equations, the loss is decomposed into the parts generated by the mean vortex as well as turbulence theoretically. The result of computational fluid dynamics (CFD) shows that the incoming boundary layer from the ITD increases the total pressure loss coefficient by 14% compared to the case with uniform inlet condition. Although the distribution of the secondary vortices is strongly affected by the inlet boundary layer, the loss generated by the mean vortex within the blade passage is hardly affected. The analysis based on the turbulent dissipation shows that the dominant factor leading to the loss increase is the turbulent dissipation downstream of the blade trailing edge (TE) near the hub. The mixing process of the wake and the strong counter-rotating vortex pair (CVP) increases the turbulent dissipation significantly. It is also found that a simplified incoming boundary layer defined by the Prandtl's one-seventh power law can not reproduce the complex effects of the incoming boundary layer from the ITD.

Effects of Mating and Social Exposure on Cell Proliferation in the Adult Male Prairie Vole (Microtus ochrogaster).

Microtus ochrogaster is a rodent with a monogamous reproductive strategy characterized by strong pair bond formation after 6 h of mating. Here, we determine whether mating-induced pair bonding increases cell proliferation in the subventricular zone (SVZ), rostral migratory stream (RMS), and dentate gyrus (DG) of the hippocampus in male voles. Males were assigned to one of the four groups: (1) control: males were placed alone in a clean cage; (2) social exposure to a female (SE m/f): males that could see, hear, and smell a sexually receptive female but where physical contact was not possible, because the animals were separated by an acrylic screen with small holes; (3) social exposure to a male (SE m/m): same as group 2 but males were exposed to another male without physical contact; and (4) social cohabitation with mating (SCM): males that mated freely with a receptive female for 6 h. This procedure leads to pair bond formation. Groups 2 and 3 were controls for social interaction. Male prairie voles were injected with 5-bromo-2′-deoxyuridine (BrdU) during the behavioral tests and were sacrificed 48 h later. Brains were processed to identify the new cells (BrdU-positive) and neuron precursor cells (neuroblasts). Our principal findings are that in the dorsal region of the SVZ, SCM and SE m/f and m/m increase the percentage of neuron precursor cells. In the anterior region of the RMS, SE m/f decreases the percentage of neuron precursor cells, and in the medial region SE m/f and m/m decrease the number of new cells and neuron precursor cells. In the infrapyramidal blade of the subgranular zone of the DG, SE m/m and SCM increase the number of new neuron precursor cells and SE m/m increases the percentage of these neurons. Our data suggests that social interaction, as well as sexual stimulation, leads to pair bonding in male voles modulating cell proliferation and differentiation to neuronal precursor cells at the SVZ, RMS, and DG.

Observational study of azithromycin in hospitalized patients with COVID-19.

The rapid spread of the disease caused by the novel SARS-CoV-2 virus has led to the use of multiple therapeutic agents whose efficacy has not been previously demonstrated. The objective of this study was to analyze whether there is an association between the use of azithromycin and the evolution of the pulmonary disease or the time to discharge, in patients hospitalized with COVID-19. This was an observational study on a cohort of 418 patients admitted to three regional hospitals in Catalonia, Spain. As primary outcomes, we studied the evolution of SAFI ratio (oxygen saturation/fraction of inspired oxygen) in the first 48 hours of treatment and the time to discharge. The results were compared between patients treated and untreated with the study drug through subcohort analyses matched for multiple clinical and prognostic factors, as well as through analysis of non-matched subcohorts, using Cox multivariate models adjusted for prognostic factors. There were 239 patients treated with azithromycin. Of these, 29 patients treated with azithromycin could be matched with an equivalent number of control patients. In the analysis of these matched subcohorts, SAFI at 48h had no significant changes associated to the use of azithromycin, though azithromycin treatment was associated with a longer time to discharge (10.0 days vs 6.7 days; log rank: p = 0.039). However, in the unmatched cohorts, the increased hospital stay associated to azithromycin use, was no significant after adjustment using Multivariate Cox regression models: hazard ratio 1.45 (IC95%: 0.88-2.41; p = 0.150). This study is limited by its small sample size and its observational nature; despite the strong pairing of the matched subcohorts and the adjustment of the Cox regression for multiple factors, the results may be affected by residual confusion. We did not find a clinical benefit associated with the use of azithromycin, in terms of lung function 48 hours after treatment or length of hospital stay.

Pairing in SU(6) × SU(2) one-dimensional fermionic clusters

We present diffusion Monte Carlo calculations on the behavior of a mixture of $^{173}\mathrm{Yb}$ and $^{171}\mathrm{Yb}$ fermionic isotopes in a one-dimensional environment. The interaction parameters between species were modeled by $\ensuremath{\delta}$ potentials, whose strengths were taken from their experimental scattering lengths and varied by changing the transversal confinement. This implies a repulsive interaction for the $^{173}\mathrm{Yb}\ensuremath{-}^{173}\mathrm{Yb}$ pair, a strong attractive one for the $^{173}\mathrm{Yb}\ensuremath{-}^{171}\mathrm{Yb}$ set, and a weak attraction between $^{171}\mathrm{Yb}\ensuremath{-}^{171}\mathrm{Yb}$ atoms. Those arrangements were described by a corrected geminal multiplied by the appropriate set of Jastrow functions. We found that, for the same number of strong attractive pairs, the width of the cluster decreases when the number of fermionic species increases, the narrower cluster being the one that includes a mixture of six $^{173}\mathrm{Yb}$ species and two $^{171}\mathrm{Yb}$ spin types.

Three-dimensional electron-hole superfluidity in a superlattice close to room temperature

Although there is strong theoretical and experimental evidence for electron-hole superfluidity in separated sheets of electrons and holes at low $T$, extending superfluidity to high $T$ is limited by strong 2D fluctuations and Kosterlitz-Thouless effects. We show this limitation can be overcome using a superlattice of alternating electron- and hole-doped semiconductor monolayers. The superfluid transition in a 3D superlattice is not topological, and for strong electron-hole pair coupling, the transition temperature $T_c$ can be at room temperature. As a quantitative illustration, we show $T_c$ can reach $270$ K for a superfluid in a realistic superlattice of transition metal dichalcogenide monolayers.

Correlating the antisymmetrized geminal power wave function.

Strong pairing correlations are responsible for superconductivity and off-diagonal long-range order in the two-particle density matrix. The antisymmetrized geminal power wave function was championed many years ago as the simplest model that can provide a reasonable qualitative description for these correlations without breaking number symmetry. The fact remains, however, that the antisymmetrized geminal power is not generally quantitatively accurate in all correlation regimes. In this work, we discuss how we might use this wave function as a reference state for a more sophisticated correlation technique such as configuration interaction, coupled cluster theory, or the random phase approximation.

Age-related differences in reproductive success support the selection hypothesis in a Mute Swan population

In many bird species, we observe age-related differences in reproductive success, which usually increases early in life and later decreases due to senescence. At the individual level, an early-life improvement in breeding performance may be associated with experience acquired during early reproductive events (experience hypothesis). At the population level, higher average reproductive success of older age cohorts can result from a disappearance of low-quality individuals from the population (selection hypothesis). Here, we tested these hypotheses in a wild population of the Mute Swan Cygnus olor from central Poland. In 1996–2016, we collected information on breeding success of 150 marked individuals (70 females and 80 males; 590 breeding attempts). At the population level, there was an initial increase in reproductive success (1–5 years), followed by a plateau (5–8 years), and then by a decrease in older age classes. Both within- and between-individual age variation contributed to the linear increase in reproductive success at the population level, but the latter effect was much more apparent. Short-term breeders (≤ 2 breeding events) had significantly lower reproductive success than long-term breeders (≥ 3 breeding events) during their first two breeding attempts, providing support for selection hypothesis and disappearance of low-quality phenotypes. After exclusion of short-term breeders, a positive age-related increase in reproductive success lost significance, suggesting that under-specific condition (rapid population growth and strong human disturbance) experience may have a limited effect on reproductive success in long-lived species with strong pair bonds, such as the Mute Swan.