Nearest-neighbor Pairing Research Articles

Model Averaging for Estimating Treatment Effects With Binary Responses

ABSTRACTIn this article, we present a novel approach for estimating the conditional average treatment effect in models with binary responses. Our proposed method involves model averaging, and we establish a weight choice criterion based on jackknife model averaging. We analyze the theoretical properties of this approach, including its asymptotic optimality in achieving the lowest possible squared error and the convergence rate of the weights assigned to correctly specified models. Additionally, we introduce a new matching method that combines partition and nearest neighbor pairing, leveraging the strengths of both techniques. To evaluate the performance of our method, we conduct comparisons with existing approaches via a Monte Carlo study and a real data analysis. Overall, our results demonstrate the effectiveness and practicality of our proposed approach for estimating the conditional average treatment effect in binary response models.

Quantum simulation of the bosonic Kitaev chain

Superconducting quantum circuits are a natural platform for quantum simulations of a wide variety of important lattice models describing topological phenomena, spanning condensed matter and high-energy physics. One such model is the bosonic analog of the well-known fermionic Kitaev chain, a 1D tight-binding model with both nearest-neighbor hopping and pairing terms. Despite being fully Hermitian, the bosonic Kitaev chain exhibits a number of striking features associated with non-Hermitian systems, including chiral transport and a dramatic sensitivity to boundary conditions known as the non-Hermitian skin effect. Here, using a multimode superconducting parametric cavity, we implement the bosonic Kitaev chain in synthetic dimensions. The lattice sites are mapped to frequency modes of the cavity, and the in situ tunable complex hopping and pairing terms are created by parametric pumping at the mode-difference and mode-sum frequencies, respectively. We experimentally demonstrate important precursors of nontrivial topology and the non-Hermitian skin effect in the bosonic Kitaev chain, including chiral transport, quadrature wavefunction localization, and sensitivity to boundary conditions. Our experiment is an important first step towards exploring genuine many-body non-Hermitian quantum dynamics.

Signatures of the order parameter of a superconducting adatom layer in magnetic field dependent quasiparticle interference

Experiments have observed superconductivity in atomically-thin metallic layers deposited on semiconducting substrates. As in any superconductor, it is important to determine the structure of the superconducting pairing function in order to reveal the mechanism responsible for superconductivity. To that end, we study the possible superconducting states of two-dimensional triangular lattices. We calculate the quasiparticle interference (QPI) patterns which would result from various nearest-neighbor pairing order parameters, and show how the QPI can be used to distinguish between those order parameters. The QPI patterns are the momentum-space representations of real-space local density-of-states fluctuations: the QPI signal at momentum $q$ reveals the strength of scattering processes at that momentum transfer. We show how characteristic differences between scattering from charge disorder (i.e. impurities) and from order-parameter disorder (i.e. vortices) can be used to identify the angular momentum of the superconducting pairs.

Eight-vertex criticality in the interacting Kitaev chain

We show that including pairing and repulsion into the description of 1D spinless fermions, as in the domain wall theory of commensurate melting or the interacting Kitaev chain, leads, for strong enough repulsion, to a line of critical points in the eight vertex universality class terminating floating phases with emergent U(1) symmetry. For nearest-neighbor repulsion and pairing, the variation of the critical exponents along the line that can be extracted from Baxter's exact solution of the XYZ chain at $J_x=-J_z$ is fully confirmed by extensive DMRG simulations of the entire phase diagram, and the qualitative features of the phase diagram are shown to be independent of the precise form of the interactions.

Spectral form factor in a minimal bosonic model of many-body quantum chaos.

We study spectral form factor in periodically kicked bosonic chains. We consider a family of models where a Hamiltonian with the terms diagonal in the Fock space basis, including random chemical potentials and pairwise interactions, is kicked periodically by another Hamiltonian with nearest-neighbor hopping and pairing terms. We show that, for intermediate-range interactions, the random phase approximation can be used to rewrite the spectral form factor in terms of a bistochastic many-body process generated by an effective bosonic Hamiltonian. In the particle-number conserving case, i.e., when pairing terms are absent, the effective Hamiltonian has a non-Abelian SU(1,1) symmetry, resulting in universal quadratic scaling of the Thouless time with the system size, irrespective of the particle number. This is a consequence of degenerate symmetry multiplets of the subleading eigenvalue of the effective Hamiltonian and is broken by the pairing terms. In such a case, we numerically find a nontrivial systematic system-size dependence of the Thouless time, in contrast to a related recent study for kicked fermionic chains.

ResPAN: a powerful batch correction model for scRNA-seq data through residual adversarial networks.

With the advancement of technology, we can generate and access large-scale, high dimensional and diverse genomics data, especially through single-cell RNA sequencing (scRNA-seq). However, integrative downstream analysis from multiple scRNA-seq datasets remains challenging due to batch effects. In this article, we propose a light-structured deep learning framework called ResPAN for scRNA-seq data integration. ResPAN is based on Wasserstein Generative Adversarial Network (WGAN) combined with random walk mutual nearest neighbor pairing and fully skip-connected autoencoders to reduce the differences among batches. We also discuss the limitations of existing methods and demonstrate the advantages of our model over seven other methods through extensive benchmarking studies on both simulated data under various scenarios and real datasets across different scales. Our model achieves leading performance on both batch correction and biological information conservation and maintains scalable to datasets with over half a million cells. An open-source implementation of ResPAN and scripts to reproduce the results can be downloaded from: https://github.com/AprilYuge/ResPAN. Supplementary data are available at Bioinformatics online.

Dually Insured Medicare/Medicaid Patients Undergoing Primary TJA Have More Comorbidities, Higher Complication Rates, and Lower Reimbursements Compared to Privately Insured Patients

BackgroundDual eligibility status (DES: qualifying for both Medicare and a Medicaid supplement) was recently proposed by the Center for Medicare and Medicaid Services as a socioeconomic qualifier for risk adjustment in primary total joint arthroplasty. However, the profile and outcomes of DES patients have never been compared to privately insured patients. MethodsA retrospective case–control study of the Mariner database within the PearlDiver server between 2010 and 2017 was performed. Patients aged 60 to 80 undergoing primary total hip arthroplasty (THA) and total knee arthroplasty (TKA) (separately) were stratified based upon payer type: DES versus private payer. A propensity score-matched analysis with nearest neighbor pairing (1:1 ratio) was performed to compare 90-day outcomes and reimbursements. ResultsA total of 315,664 private and 3961 DES THA patients and 670,899 private and 2255 DES TKA patients were identified. DES patients were older and had a greater prevalence of comorbidities (31/36, P < .001). The THA DES matched cohort had greater transfusion rates (6.8% versus 3.9%, P < .001), higher 90-day emergency department visits (22.8% versus 16.3%, P < .001) and readmissions (16.8% versus 9.5%, P < .001), and lower reimbursements ($19,615 versus $13,036, P < .001). The TKA DES matched cohort had more cardiac events (0.4% versus 0.09%, P = .03), emergency department visits (25.2% versus 19.9%, P < .001), readmissions (14.4% versus 11.2%, P = .001), and reoperations (0.85% versus 0.35%, P = .03) ConclusionDES patients have different comorbidity profiles, and even after propensity score matching have a greater risk of complications and are reimbursed less compared to privately insured patients. In the setting of alternative payment models, these differences should be accounted for through risk adjustment.

Z2 phases and Majorana spectroscopy in paired Bose-Hubbard chains

We investigate the Bose-Hubbard chain in the presence of nearest-neighbor pairing. The pairing term gives rise to an unusual gapped $\mathbb{Z}_2$ Ising phase that has number fluctuation but no off-diagonal long range order. This phase has a strongly correlated many-body doubly degenerate ground state which is effectively a gap-protected macroscopic qubit. In the strongly interacting limit, the system can be mapped onto an anisotropic transverse spin chain, which in turn can be mapped to the better-known fermionic sister of the paired Bose-Hubbard chain: the Kitaev chain which hosts zero-energy Majorana bound states. While corresponding phases in the fermionic and bosonic systems have starkly different wavefunctions, they share identical energy spectra. We describe a possible cold-atom realization of the paired Bose-Hubbard model in a biased zig-zag optical lattice with reservoir-induced pairing, opening a possible route towards experimental Kitaev chain spectroscopy.

One-dimensional spin–orbit coupled Dirac system with extended s-wave superconductivity: Majorana modes and Josephson effects

Motivated by the spin–momentum locking of electrons at the boundaries of certain topological insulators, we study a one-dimensional system of spin–orbit coupled massless Dirac electrons with s-wave superconducting pairing. As a result of the spin–orbit coupling, our model has only two kinds of linearly dispersing modes, and we take these to be right-moving spin-up and left-moving spin-down. Both lattice and continuum models are studied. In the lattice model, we find that a single Majorana zero energy mode appears at each end of a finite system provided that the s-wave pairing has an extended form, with the nearest-neighbor pairing being larger than the on-site pairing. We confirm this both numerically and analytically by calculating the winding number. We find that the continuum model also has zero energy end modes. Next we study a lattice version of a model with both Schrödinger and Dirac-like terms and find that the model hosts a topological transition between topologically trivial and non-trivial phases depending on the relative strength of the Schrödinger and Dirac terms. We then study a continuum system consisting of two s-wave superconductors with different phases of the pairing, with a δ-function potential barrier lying at the junction of the two superconductors. Remarkably, we find that the system has a single Andreev bound state (ABS) which is localized at the junction. When the pairing phase difference crosses a multiple of 2π, an ABS touches the top of the superconducting gap and disappears, and a different state appears from the bottom of the gap. We also study the AC Josephson effect in such a junction with a voltage bias that has both a constant V 0 and a term which oscillates with a frequency ω. We find that, in contrast to standard Josephson junctions, Shapiro plateaus appear when the Josephson frequency ω J = 2eV 0/ℏ is a rational fraction of ω. We discuss experiments which can realize such junctions.

Integrability of spin-[formula omitted] fermions with charge pairing and Hubbard interaction

In this paper we study the exact solution of a one-dimensional model of spin-12 electrons composed by a nearest-neighbor triplet pairing term and the on-site Hubbard interaction. We argue that this model admits a Bethe ansatz solution through a mapping to a Hubbard chain with imaginary kinetic hopping terms. The Bethe equations are similar to that found by Lieb and Wu [3] but with additional twist phases which are dependent on the ring size. We have studied the spectrum of the model with repulsive interaction by exact diagonalization and through the Bethe equations for large lattice sizes. One feature of the model is that it is possible to define the charge gap for even and odd lattice sites and both converge to the same value in the infinite size limit. We analyze the finite-size corrections to the low-lying spin excitations and argue that they are equivalent to that of the spin-12 isotropic Heisenberg model with a boundary twist depending on the lattice parity. We present the classical statistical mechanics model whose transfer matrix commutes with the model Hamiltonian. To this end we have used the construction employed by Shastry [6,7] for the Hubbard model. In our case, however, the building block is a free-fermion eight-vertex model with a particular null weight.

Zero modes of the Kitaev chain with phase-gradients and longer range couplings

We present an analytical solution for the full spectrum of Kitaev's one-dimensional p-wave superconductor with arbitrary hopping, pairing amplitude and chemical potential in the case of an open chain. We also discuss the structure of the zero-modes in the presence of both phase gradients and next nearest neighbor hopping and pairing terms. As observed by Sticlet et al, one feature of such models is that in a part of the phase diagram, zero-modes are present at one end of the system, while there are none on the other side. We explain the presence of this feature analytically, and show that it requires some fine-tuning of the parameters in the model. Thus as expected, these ‘one-sided’ zero-modes are neither protected by topology, nor by symmetry.

Spectroscopic signatures of different symmetries of the superconducting order parameter in metal-decorated graphene

Motivated by the recent experiments indicating superconductivity in metal-decorated graphene sheets, we investigate their quasi-particle structure within the framework of an effective tight-binding Hamiltonian augmented by appropriate BCS-like pairing terms for p-type order parameter. The normal state band structure of graphene is modified not only through interaction with adsorbed metal atoms, but also due to the folding of bands at Brillouin zone boundaries resulting from a reconstruction. Several different types of pairing symmetries are analyzed utilizing Nambu–Gorkov Green’s function techniques to show that -symmetric nearest-neighbor pairing yields the most enhanced superconducting gap. The character of the order parameter depends on the nature of the atomic orbitals involved in the pairing process and exhibits interesting angular and radial asymmetries. Finally, we suggest a method to distinguish between singlet and triplet type superconductivity in the presence of magnetic substitutional impurities using scanning tunneling spectroscopy.

On the effect of stabilizing mean firing rate of a neuron due to STDP

We show by numerical simulations that a neuron with additive Spike-Timing-Dependent Plasticity with restricted symmetric nearest-neighbor spike pairing scheme, receiving Poisson input, establishes mean firing rate that does not depend on input rates, in a sufficiently high range of input rates. The established rate also does not depend on the number of inputs and the existence of inhibitory inputs, and depends only on the neuron and STDP parameters. A possible way to utilize this effect in learning is shown.

Probing the d-wave pairing symmetry in cobaltate superconductors by a local impurity

To provide clues for experimental clarification of the pairing mechanism in cobaltate superconductors, we investigate two possible pairing symmetries, chiral and dxy waves, by making use of impurity effects. We consider both nearest-neighbor and next-nearest-neighbor pairing cases in real space. As expected, the superconducting order parameter exhibits a four-fold symmetric pattern in the nodal dxy-wave state while displaying a six-fold symmetry in the case of chiral pairing. By calculating the local density of states for various doping levels, we show the existence of quasiparticle bound states inside the gap in all cases. Surprisingly, it is found that although the full-gap feature in the nearest-neighbor chiral pairing is robust, the next-nearest-neighbor state shows a doping-dependent gap anisotropy with a crossover from a U-shaped to a V-shaped gap profile. This gap anisotropy can naturally explain the close-to-nodal gap features observed by experiments if it is not in the nodal d-wave pairing channel.

The 1D Ising model and the topological phase of the Kitaev chain

It has been noted that the Kitaev chain, a p-wave superconductor with nearest-neighbor pairing amplitude equal to the hopping term Δ=t, and chemical potential μ=0, can be mapped into a nearest neighbor Ising model via a Jordan–Wigner transformation. Starting from the explicit eigenstates of the open Kitaev chain in terms of the original fermion operators, we elaborate that despite this formal equivalence the models are physically inequivalent, and show how the topological phase in the Kitaev chain maps into conventional order in the Ising model.

Correlated Dirac particles and superconductivity on the honeycomb lattice

We investigate the properties of the nearest-neighbor singlet pairing and the emergence of d-wave superconductivity in the doped honeycomb lattice considering the limit of large interactions and the $t-J_1-J_2$ model. First, by applying a renormalized mean-field procedure as well as slave-boson theories which account for the proximity to the Mott insulating state, we confirm the emergence of d-wave superconductivity in agreement with earlier works. We show that a small but finite $J_2$ spin coupling between next-nearest neighbors stabilizes d-wave symmetry compared to the extended s-wave scenario. At small hole doping, to minimize energy and to gap the whole Fermi surface or all the Dirac points, the superconducting ground state is characterized by a $d+id$ singlet pairing assigned to one valley and a $d-id$ singlet pairing to the other, which then preserves time-reversal symmetry. The slightly doped situation is distinct from the heavily doped case (around 3/8 and 5/8 filling) supporting a pure chiral $d+id$ symmetry and breaking time-reversal symmetry. Then, we apply the functional Renormalization Group and we study in more detail the competition between antiferromagnetism and superconductivity in the vicinity of half-filling. We discuss possible applications to strongly-correlated compounds with Copper hexagonal planes such as In$_3$Cu$_{2}$VO$_9$. Our findings are also relevant to the understanding of exotic superfluidity with cold atoms.

Measurement of microchannel flow with digital holographic microscopy by integrated nearest neighbor and cross-correlation particle pairing

A micro digital in-line holographic particle tracking velocimetry (micro-DHPTV) system has been developed and applied to investigate the three-dimensional flow field in straight and Y-junction microchannels. The micro-DHPTV system comprises a cooled frame-transfer CCD camera and a double-pulsed laser. The processing algorithm introduced to evaluate the three-dimensional velocity is based on the combination of integrated cross-correlation and nearest neighbor matching algorithms, taking advantage of information from both the reconstructed particle field and the original holograms fringes patterns. Tests on simulated pairs of holograms show that the particles can be detected, located, and paired with high probability and accuracy. Results obtained in the straight and Y-junction microchannels show that the superimposed vector field is physically reasonable.

An ant colony optimization based stereoscopic particle pairing algorithm for three-dimensional particle tracking velocimetry

An ant colony optimization (ACO) based stereoscopic particle matching algorithm has been developed for three-dimensional (3-D) particle tracking velocimetry (PTV). In a stereoscopic particle pairing process, each individual particle in the left camera frame should be uniquely paired with the most probable correct partner in the right camera frame or vice-versa for evaluating the exact 3-D coordinate of the particles. In the present work, a new algorithm based on an ant colony optimization has been proposed for this stereoscopic particle matching. The algorithm is tested with various standard 3-D particle image velocimetry (PIV) images of the Visualization Society of Japan (VSJ) and the matching results show that the performance of the stereoscopic particle pairing is improved by applying proposed ACO techniques in comparison to the conventional nearest-neighbor particle pairing method of 3-D stereoscopic PTV.

Phase Diagram for Mixed-Parity Superconductors

We analyze the response of a two-dimensional superconductor to a magnetic field. We assume that the system can be described by an extended Hubbard model with an attractive nearest-neighbor pairing potential effective both in the singlet and the triplet channels. Treating the model Hamiltonian within the mean-field approximation, we study the competition at zero temperature between superconducting states characterized by different spin and spatial symmetries, as induced by electron density variations and by the explicit time-reversal symmetry breaking due to the presence of a magnetic field. We focus in particular on the competition between unitary and nonunitary states.

Vortex core states in a minimal two-band model for iron-based superconductors

The pairing symmetry is one of the major issues in the study of iron-based superconductors. We adopt a minimal two-band tight-binding model with various channels of pairing interaction, and derive a set of two-band Bogoliubov--de Gennes (BdG) equations. The BdG equations are implemented in real space and then solved self-consistently via exact diagonalization. In the uniform case, we find that the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave pairing state is most favorable for a nearest-neighbor pairing interaction while the ${s}_{{x}^{2}{y}^{2}}$-wave pairing state is most favorable for a next-nearest-neighbor pairing interaction, which is consistent with that reported by Seo et al. [Phys. Rev. Lett. 101, 206404 (2008)]. We then proceed to study the local electronic structure around a magnetic vortex core for both ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave and ${s}_{{x}^{2}{y}^{2}}$-wave pairing symmetry in the mixed state. It is found from the local density of states spectra and its spatial variation that the resonance core states near the Fermi energy for the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave pairing symmetry are bound while those for the ${s}_{{x}^{2}{y}^{2}}$-wave pairing symmetry can evolve from the localized states into extended ones with varying electron filling factor. Furthermore, by including an effective exchange interaction, the emergent antiferromagnetic spin-density-wave order can suppress the resonance core states, which provides one possible avenue to understand the absence of resonance peak as revealed by recent scanning tunneling microscopy experiment by Yin et al. [Phys. Rev. Lett. 102, 097002 (2009)].