Static Analog Research Articles

Realizing Exceptional Points by Floquet Dissipative Couplings in Thermal Atoms.

Exceptional degeneracies and generically complex spectra of non-Hermitian systems are at the heart of numerous phenomena absent in the Hermitian realm. Recently, it was suggested that Floquet dissipative coupling in the space-time domain may provide a novel mechanism to drive intriguing spectral topology with no static analogs, though its experimental investigation in quantum systems remains elusive. We demonstrate such Floquet dissipative coupling in an ensemble of thermal atoms interacting with two spatially separated optical beams, and observe an anomalous anti-parity-time symmetry phase transition at an exception point far from the phase-transition threshold of the static counterpart. Our protocol sets the stage for Floquet engineering of non-Hermitian topological spectra, and for engineering new quantum phases that cannot exist in static systems.

The active role of co-evolving haloes in stellar bar formation

ABSTRACT We use idealized N-body simulations of equilibrium discs in live and static haloes to study how dark matter co-evolution impacts the assembly of stellar particles into a bar and the halo response. Initial conditions correspond to a marginally unstable disc according to commonly used disc stability criteria, and are evolved for the equivalent of about 150 disc dynamical times (10 Gyr). An extensive convergence study ensures accurate modelling of the bar formation process. Live haloes lead to the formation of a strong bar, but the same disc remains unbarred when evolved in a static halo. Neither seeded disc instabilities nor longer (60 Gyr) simulations result in the formation of a bar when the halo is static. When the live halo is replaced with a static analogue at later times, the previously robust bar slowly dissipates, suggesting that (1) the co-evolution of the disc and halo is critical for the assembly and long-term survival of bars in marginally unstable discs and (2) global disc stability criteria must be modified for discs in the presence of live haloes. In our live halo runs, a ‘dark bar’ grows synchronously with the stellar bar. Processes that inhibit the transfer of angular momentum between the halo and disc may stabilize a galaxy against bar formation, and can lead to the dissolution of the bar itself. This raises further questions about the puzzling stability of observed discs that are marginally unstable, but unbarred.

The analgesic effect of ultrasound-guided cervical erector spinae block in arthroscopic shoulder surgery: a randomized controlled clinical trial

BackgroundErector spinae plane block (ESPB) is a novel fascial plane block technique that can provide effective perioperative analgesia for thoracic, abdominal and lumbar surgeries. However, the effect of cervical ESPB on postoperative analgesia after arthroscopic shoulder surgery is unknown. The aim of this study is to investigate the analgesic effect and safety of ultrasound-guided cervical ESPB in arthroscopic shoulder surgery.MethodsSeventy patients undergoing arthroscopy shoulder surgery were randomly assigned to one of two groups: ESPB group (n = 35) or control group (n = 35). Patients in the ESPB group received an ultrasound-guided ESPB at the C7 level with 30 mL of 0.25% ropivacaine 30 min before induction of general anesthesia, whereas patients in the control group received no block. The primary outcome measures were the static visual analogue scale (VAS) pain scores at 4, 12, and 24 h after surgery. Secondary outcomes included heart rate (HR) and mean arterial pressure (MAP) before anesthesia (t1), 5 min after anesthesia (t2), 10 min after skin incision (t3), and 10 min after extubation (t4); intraoperative remifentanil consumption; the Bruggrmann comfort scale (BCS) score, quality of recovery-15 (QoR-15) scale score and the number of patients who required rescue analgesia 24 h after surgery; and adverse events.ResultsThe static VAS scores at 4, 12 and 24 h after surgery were significantly lower in the ESPB group than those in the control group (2.17 ± 0.71 vs. 3.14 ± 1.19, 1.77 ± 0.77 vs. 2.63 ± 0.84, 0.74 ± 0.66 vs. 1.14 ± 0.88, all P < 0.05). There were no significant differences in HR or MAP at any time point during the perioperative period between the two groups (all P > 0.05). The intraoperative consumption of remifentanil was significantly less in the ESPB group compared to the control group (P < 0.05). The scores of BCS and QoR-15 scale were higher in the ESPB group 24 h after surgery than those in the control group (P < 0.05). Compared to the control group, fewer patients in the ESPB group required rescue analgesia 24 h after surgery (P < 0.05). No serious complications occurred in either group.ConclusionsUltrasound-guided cervical ESPB can provide effective postoperative analgesia following arthroscopic shoulder surgery, resulting in a better postoperative recovery with fewer complications.Trial registrationChictr.org.cn identifier ChiCTR2300070731 (Date of registry: 21/04/2023, prospectively registered).

Solving basic problems of compliant tolerance analysis by static analogy

AbstractPredicting the geometric variation of sheet metal assemblies is a complex task, because deformation during joining operations influences the propagation of initial part deviations. To consider this effect, the paper proposes a method that formulates tolerance analysis as an equivalent problem of static analysis. Previously proposed for rigid parts, the static analogy is extended to compliant parts and applied to two-dimensional problems modeled with straight beams under the assumptions of small displacements and normal distributions of errors. For such simple cases, the method solves the problem by linearization, avoiding the use of Monte Carlo simulation and the related computational burden. Compared to existing linearization methods, the static analogy is less efficient in the integration with a finite element solver. However, it features an especially simple procedure that does not require the calculation of deflections, thus allowing a streamlined solution and even manual calculations. The comparison with alternative methods provides a first verification of the feasibility of the method, in view of further developments with the aim of dealing with cases of realistic complexity.

Floquet non-Abelian topological insulator and multifold bulk-edge correspondence

Topological phases characterized by non-Abelian charges are beyond the scope of the paradigmatic tenfold way and have gained increasing attention recently. Here we investigate topological insulators with multiple tangled gaps in Floquet settings and identify uncharted Floquet non-Abelian topological insulators without any static or Abelian analog. We demonstrate that the bulk-edge correspondence is multifold and follows the multiplication rule of the quaternion group Q8. The same quaternion charge corresponds to several distinct edge-state configurations that are fully determined by phase-band singularities of the time evolution. In the anomalous non-Abelian phase, edge states appear in all bandgaps despite trivial quaternion charge. Furthermore, we uncover an exotic swap effect—the emergence of interface modes with swapped driving, which is a signature of the non-Abelian dynamics and absent in Floquet Abelian systems. Our work, for the first time, presents Floquet topological insulators characterized by non-Abelian charges and opens up exciting possibilities for exploring the rich and uncharted territory of non-equilibrium topological phases.

Short-term forecasting of electricity prices using generative neural networks

This article studies the predictive abilities of the generative-adversarial neural network approach in relation to time series using the example of price forecasting for the nodes of the Russian free electricity market for the day ahead. As a result of a series of experiments, we came to the conclusion that a generative adversarial network, consisting of two models (generator and discriminator), allows one to achieve a minimum of the error function with a greater generalizing ability than, all other things being equal, is achieved as a result of optimizing the static analogue of the generative model – recurrent neural network. Our own empirical results show that with a near-zero mean square error on the training set, which is demonstrated simultaneously by the recurrent and generative models, the error of the latter on the test set is lower. The adversarial approach also outperformed alternative reference models in out-of-sample forecasting accuracy: a convolutional neural network adapted for time series forecasting and an autoregressive linear model. Application of the proposed approach has shown that a generative-adversarial model with a given universal architecture and a limited number of explanatory factors, subject to additional training on data specific to the target node of the power system, can be used to predict prices in market nodes for the day ahead without significant deviations.

Hybrid-order topological odd-parity superconductors via Floquet engineering

Having the potential for performing quantum computation, topological superconductors have been generalized to the second-order case. The hybridization of different orders of topological superconductors is attractive because it facilitates the simultaneous utilization of their respective advantages. However, previous studies found that they cannot coexist in one system due to the constraint of symmetry. We propose a Floquet engineering scheme to generate two-dimensional (2D) hybrid-order topological superconductors in an odd-parity superconductor system. Exotic hybrid-order phases exhibiting the coexisting gapless chiral edge states and gapped Majorana corner states not only in two different quasienergy gaps but also in one single quasienergy gap are created by periodic driving. The generalization of this scheme to the 3D system allows us to discover a second-order Dirac superconductor featuring coexisting surface and hinge Majorana Fermi arcs. Our results break a fundamental limitation on topological phases and open a feasible avenue to realize topological superconductor phases without static analogs.

Tolerance analysis by static analogy on 2D assemblies with fits and fasteners

In tolerance analysis, the effect of clearance fits is especially difficult to estimate because the mating parts are not necessarily in actual contact and can take an infinite number of relative positions. The treatment of these situations is allowed in most of the available methods, possibly introducing additional elements in the dimension chains with appropriate statistical assumptions. The paper provides a similar extension for the static analogy, a previously proposed method that converts the tolerance analysis problem into an equivalent problem of force analysis. The procedure represents each fit, possibly between patterns of features (e.g., fasteners and holes), with a proper constraint in the equivalent static model. The ability of the constraint to transmit forces and torques is determined according to the types and directions of misalignments allowed by the joint clearance. With simple rules, this avoids complications in the static model, which must include only the constraint between parts rather than the geometric details of the mating features. The extended method, currently limited to 2D dimension chains, is demonstrated on examples involving both dimensional and geometric tolerances. The comparison with existing methods shows the correctness of the proposed procedure. The simplicity of the workflow confirms the possibility, already demonstrated for the static analogy, of avoiding numerical simulations or even the use of computer-based tools.

Exact (1 + 3 + 6)-Dimensional Cosmological-Type Solutions in Gravitational Model with Yang–Mills Field, Gauss–Bonnet Term and Λ Term

We consider a 10-dimensional gravitational model with an SO(6)Yang–Mills field, Gauss–Bonnet term, and Λ term. We study so-called cosmological-type solutions defined on the product manifold M=R×R3×K, where K is 6d a Calabi–Yau manifold. By setting the gauge field 1-form to coincide with the 1-form spin connection on K, we obtain exact cosmological solutions with exponential dependence of scale factors (upon t-variable) governed by two non-coinciding Hubble-like parameters: H&gt;0 and h obeying H+2h≠0. We also present static analogs of these cosmological solutions (for H≠0, h≠H, and H+2h≠0). The islands of stability for both classes of solutions are outlined.

Thouless pumping and topology

Thouless pumping provides one of the simplest manifestations of topology in quantum systems, and has attracted a lot of recent interest, both theoretically and experimentally. Since the seminal works by Thouless and Niu in 1983 and 1984, it is argued that the quantization of the pumped charge is robust against weak disorder, but a clear characterization of the localization properties of the relevant states, and the breakdown of quantized transport in the presence of interaction or out of the adiabatic approximation, has been long debated. Thouless pumping is also the first example of a topological phase emerging in a periodically-driven system. Driven systems can exhibit exotic topological phases without any static analogue and have been the subject of many recent proposals both in fermionic and bosonic systems in diverse platforms ranging from cold atoms to photonics and condensed matter systems. In this respect, this review has a twofold purpose: On the one hand, it serves as a basis to understand the robustness of the topology of slowly-driven systems per se; On the other hand, it highlights the rich properties of topological pumps and their diverse range of applications, for instance, in systems with synthetic dimensions or for understanding higher-order topological phases. These examples underline the relevance of topological pumping for the fast growing field of topological quantum matter.

Observation of π/2 Modes in an Acoustic Floquet System.

Topological phases of matter have remained an active area of research in the last few decades. Periodic driving is a powerful tool for enriching such exotic phases, leading to various phenomena with no static analogs. One such phenomenon is the emergence of the elusive π/2 modes, i.e., a type of topological boundary state pinned at a quarter of the driving frequency. The latter may lead to the formation of Floquet parafermions in the presence of interaction, which is known to support more computational power than Majorana particles. In this Letter, we experimentally verify the signature of π/2 modes in an acoustic waveguide array, which is designed to simulate a square-root periodically driven Su-Schrieffer-Heeger model. This is accomplished by confirming the 4T-periodicity (T being the driving period) profile of an initial-boundary excitation, which we also show theoretically to be the smoking gun evidence of π/2 modes. Our findings are expected to motivate further studies of π/2 modes in quantum systems for potential technological applications.

Tolerance analysis by static analogy: numerical and experimental results

Industrial requirements to design high quality products in shorter and shorter times impose the use of numerical models to estimate the geometrical deviations of these products, which are assemblies, starting from the geometrical deviations of their components. Numerical models may support this estimation activity, thus reducing the time to market and the design costs. The free-body model is an interesting numerical method to translate the tolerance chain into a static problem solved by algebraic or graphical procedures by using the free-body diagrams of force analysis. This work presents a free-body model that is able to deal with dimensional and geometrical tolerances that involve translations of the features to which the tolerances are applied. Moreover, it validates the free-body model for tolerance analysis of rigid parts by defining and solving a case study through numerical and experimental activities. The present work uses a case study to demonstrate the effectiveness of the free-body model by underlining that the experimental results obtained are very close to those from the numerical model.

Fractional resonances and prethermal states in Floquet systems

In periodically driven quantum systems, resonances can induce exotic nonequilibrium behavior and new phases of matter without static analog. We report on the emergence of fractional and integer resonances in a broad class of many-body Hamiltonians with a modulated hopping with a frequency that is either a fraction or an integer of the on-site interaction. We contend that there is a fundamental difference between these resonances when interactions bring the system to a Floquet prethermal state. Second-order processes dominate the dynamics in the fractional resonance case, leading to less entanglement and more localized quantum states than in the integer resonance case dominated by first-order processes. We demonstrate the dominating emergence of fractional resonances using the Magnus expansion of the effective Hamiltonian and quantify their effects on the many-body dynamics via quantum states' von Neumann entropy and Loschmidt echo. Our findings reveal novel features of the nonequilibrium quantum many-body system, such as the coexistence of Floquet prethermalization and localization, that may allow to development of quantum memories for quantum technologies and quantum information processing.

Topological edge modes without symmetry in quasiperiodically driven spin chains

We construct an example of a 1d quasiperiodically driven spin chain whose edge states can coherently store quantum information, protected by a combination of localization, dynamics, and topology. In a sharp departure from topological phases in static and periodically driven (Floquet) spin chains, this model does not rely upon microscopic symmetry protection: Instead, the edge states are protected purely by emergent dynamical symmetries. We explore the dynamical signatures of this emergent dynamical symmetry-protected topological (EDSPT) order through exact numerics, time evolving block decimation, and analytic high-frequency expansion, finding evidence that the EDSPT is a stable dynamical phase protected by bulk many-body localization up to (at least) stretched-exponentially long timescales, and possibly beyond. We argue that EDSPTs are special to the quasiperiodically driven setting, and cannot arise in Floquet systems. Moreover, we find evidence of a type of boundary critical with no known static or Floquet analogue, in which the edge spin dynamics transition from quasiperiodic to chaotic, leading to bulk thermalization.

Quantum phase transitions and a disorder-based filter in a Floquet system

Two-dimensional periodically-driven topological insulators have been shown to exhibit numerous topological phases, including ones which have no static analog, such as anomalous Floquet topological phases. We study a two dimensional model of spinless fermions on a honeycomb lattice with periodic driving. We show that this model exhibits a rich mixture of weak and strong topological phases, which we identify by computing their scattering matrix invariants. Further, we do an in-depth analysis of these topological phases in the presence of spatial disorder and show the relative robustness of these phases against imperfections. Making use of this robustness against spatial disorder, we propose a filter which allows the passage of only edge states, and which can be realized using existing experimental techniques.

The effects of local infiltration anesthesia and femoral nerve block analgesia after total knee arthroplasty: a systematic review and meta-analysis.

BackgroundLocal infiltration anesthesia (LIA) and femoral nerve block (FNB) are commonly used analgesia methods after total knee arthroplasty (TKA). However, there is no definitive conclusion about which of these two analgesia modes is superior. Therefore, this study aimed to systematically evaluate the analgesic effects of LIA and FNB after TKA.MethodsWe used the terms “total knee replacement, knee replacement, total knee arthroplasty, knee arthroplasty, local infiltration analgesia, periarticular infiltration, periarticular injection, intra-articular infiltration, intra-articular injection, peripheral nerve block, femoral nerve block” to search the PubMed, Cochrane Central Register of Controlled Trials, Embase, Web of Science, China National Knowledge Infrastructure (CNKI), Wanfang, and Weipu databases. The search period was set from the date of establishment of the database to September 2021. The Cochrane risk of bias tool was used to evaluate the quality of the included studies, and network meta-analysis was performed using Stata14.0 and RevMan 5.30 software.ResultsNine articles were included for analysis. The results of meta-analysis showed that compared with LIA and FNB, the difference in opioid use [mean difference (MD) −4.35, 95% confidence interval (CI): −7.26 to −1.45] was statistically significant. However, there was no significant difference between the static visual analogue score at 24 hours postoperatively (MD 0.20, 95% CI: −0.91 to 1.31), the visual analogue score for exercise visual analogy at 24 hours after surgery (MD 0.10, 95% CI: −0.12 to 0.32), and the length of hospital stay (MD 0.05, 95% CI: −0.40 to 0.50).DiscussionLIA and FNB have similar effects on pain relief after TKA, but LIA can reduce the use of analgesic drugs and is easy to operate. Therefore, LIA can be used as the priority analgesic method for patients with TKA. However, multi-center, large-sample, high-quality, randomized controlled trials are still needed for further verification.

A comparison of adductor canal block before and after thigh tourniquet during knee arthroscopy: a randomized, blinded study.

BackgroundAdductor canal block (ACB) provides effective analgesia after arthroscopic knee surgery. However, there is insufficient data regarding whether ACB should be performed before or after inflation of a thigh tourniquet. We aimed to investigate the efficacy of ACB performed before and after placement of a thigh tourniquet and evaluate associated quadriceps motor weakness.MethodsACB was performed before tourniquet inflation in the PreT group, and it was performed after inflation in the PostT group. In the PO group, ACB was performed at the end of surgery after deflation of the tourniquet.ResultsThere were no statistically significant differences between the groups in terms of demographic data. There was no statistically significant difference among the three groups in terms of total postoperative opioid consumption (P = 0.513). Patient satisfaction and the amount of rescue analgesia administered were also not significantly different between the groups. There was no significant difference in terms of static and dynamic visual analog scale scores between the groups (for 24 h: P = 0.306 and P = 0.271, respectively). The incidence of motor block was higher in the PreT group (eight patients) than in the PostT group (no patients) and the PO group (one patient) (P = 0.005).ConclusionsUsing a tourniquet before or after ACB did not result in differences in terms of analgesia quality; however, applying a tourniquet immediately after ACB may lead to quadriceps weakness.

Transmuscular Quadratus Lumborum Block versus Suprainguinal Fascia Iliaca Block for Hip Arthroplasty: A Randomized, Controlled Pilot Study.

BackgroundThis study aimed to investigate the analgesic efficacy and motor block profile of single-shot transmuscular quadratus lumborum block (QLB) in comparison with those of suprainguinal fascia iliaca block (FIB) in patients undergoing hip arthroplasty.MethodsThis randomized, double-blinded, controlled trial included adult patients undergoing hip arthroplasty under spinal anesthesia. Patients were allocated to one of two groups according to the regional block received: FIB group (n=19) or QLB group (n=17). Both study groups were compared with regard to the duration of analgesia (primary outcome), block performance time, pain during positioning for spinal anesthesia, total morphine consumption in the first postoperative 24-h period, quadriceps muscle power, and static and dynamic visual analog scale.ResultsThirty-six patients were included in the final analysis. Both study groups had comparable durations of analgesia. Postoperative visual analog scale (static and dynamic) values were comparable between the two groups in most readings. The block performance time was shorter in the FIB group. The number of patients with pain during positioning for the subarachnoid block was lower in the QLB group. The total morphine requirement during the first 24 h was marginally lower in the FIB group, whereas the quadriceps motor grade was higher in the FIB group than in the QLB group at 4 h and 6 h after surgery.ConclusionBoth single-shot blocks, namely the suprainguinal FIB and transmuscular QLB, provide effective postoperative analgesia after hip arthroplasty. FIB showed slightly lower 24-h morphine consumption, while QLB showed better quadriceps motor power.Clinical Trial RegistrationThe study was registered at clinical trials registry system before enrollment of the first participant (NCT04005326; initial release date, 2 July 2019; https://clinicaltrials.gov/ct2/show/NCT04005326).

Nonadiabatic Topological Energy Pumps with Quasiperiodic Driving.

We derive a topological classification of the steady states of d-dimensional lattice models driven by D incommensurate tones. Mapping to a unifying (d+D)-dimensional localized model in frequency space reveals anomalous localized topological phases (ALTPs) with no static analog. While the formal classification is determined by d+D, the observable signatures of each ALTP depend on the spatial dimension d. For each d, with d+D=3, we identify a quantized circulating current and corresponding topological edge states. The edge states for a driven wire (d=1) function as a quantized, nonadiabatic energy pump between the drives. We design concrete models of quasiperiodically driven qubits and wires that achieve ALTPs of several topological classes. Our results provide a route to experimentally access higher dimensional ALTPs in driven low-dimensional systems.

Concurrent optimization of dimensions and tolerances on structures and mechanisms

The paper deals with a problem of robust optimization of mechanical assemblies, which combines the allocation of tolerances with the selection of dimensional parameters. The two tasks are carried out together with the aim of minimizing the manufacturing cost and the variation on an assembly-level functional characteristic. The problem is addressed in the specific context of planar linkages used in structures and mechanisms. The proposed solution is based on an optimality condition involving both tolerances and dimensions, which allows to define a joint optimization problem avoiding the need of two sequential optimization phases. The condition is developed with the method of Lagrange multipliers using an expanded formulation of the reciprocal power cost-tolerance function. The optimal tolerances depend on the stackup coefficients of the output characteristic, which are calculated with a tolerance analysis method based on a static analogy. The procedure is demonstrated on two examples to illustrate some application details and discuss potential advantages and limitations.