Unidirectional Bias Research Articles

Ultrahigh Oxygen Ion Mobility in Ferroelectric Hafnia.

Ferroelectrics and ionic conductors are important functional materials, each supporting a plethora of applications in information and energy technology. The underlying physics governing their functional properties is ionic motion, and yet studies of ferroelectrics and ionic conductors are often considered separate fields. Based on first-principles calculations and deep-learning-assisted large-scale molecular dynamics simulations, we report ferroelectric-switching-promoted oxygen ion transport in HfO_{2}, a wide-band-gap insulator with both ferroelectricity and ionic conductivity. Applying a unidirectional bias can activate multiple switching pathways in ferroelectric HfO_{2}, leading to polar-antipolar phase cycling that appears to contradict classical electrodynamics. This apparent conflict is resolved by the geometric-quantum-phase nature of electric polarization that carries no definite direction. Our molecular dynamics simulations demonstrate bias-driven successive ferroelectric transitions facilitate ultrahigh oxygen ion mobility at moderate temperatures, highlighting the potential of combining ferroelectricity and ionic conductivity for the development of advanced materials and technologies.

Interdigitated Photoconductive Antenna Pumped by Reconfigurable Structured Light for Terahertz Emission and Modulation

To improve the terahertz (THz) generation of the interdigitated photoconductive antenna (iPCA), we demonstrate, for the first time, a novel design to pump the emission arrays by reconfigurable structured light generated by a spatial light modulator. The pump light is modulated into shapes to match the antenna’s every other electrode gap which has unidirectional bias field. This design makes full used of the pump power and avoids THz pulses with opposite polarity which causes the unwanted destructive interference in the far-field. Coherent combining efficiencies of THz electric field of 92.23%, 74.94%, and 61.73% are achieved for two-, three-, and five-element pumping, respectively. In addition, real-time phase reversal of THz emission can be achieved by adjusting the pump light location. This system could inspire new and challenging applications in the phase and amplitude control of the THz field, and the enhancement of the THz signal output.

Diffsound: Discrete Diffusion Model for Text-to-Sound Generation

Generating sound effects that people want is an important topic. However, there are limited studies in this area for sound generation. In this study, we investigate generating sound conditioned on a text prompt and propose a novel text-to-sound generation framework that consists of a text encoder, a Vector Quantized Variational Autoencoder (VQ-VAE), a token-decoder, and a vocoder. The framework first uses the token-decoder to transfer the text features extracted from the text encoder to a mel-spectrogram with the help of VQ-VAE, and then the vocoder is used to transform the generated mel-spectrogram into a waveform. We found that the token-decoder significantly influences the generation performance. Thus, we focus on designing a good token-decoder in this study. We begin with th21e traditional autoregressive (AR) token-decoder, which has shown state-of-the-art performance in previous sound generation works. However, the AR token-decoder always predicts the mel-spectrogram tokens one by one in order, which may introduce the unidirectional bias and accumulation of errors problems. Moreover, with the AR token-decoder, the sound generation time increases linearly with the sound duration. To overcome the shortcomings introduced by AR token-decoders, we propose a non-autoregressive token-decoder based on the discrete diffusion model, named Diffsound. Specifically, the Diffsound model predicts all of the mel-spectrogram tokens in one step and then refines the predicted tokens in the next step, so the best-predicted results can be obtained by iteration. Our experiments show that our proposed Diffsound model not only produces better text-to-sound generation results when compared with the AR token-decoder but also has a faster generation speed, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e.</i> , MOS: 3.56 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">v.s</i> 2.786, and the generation speed is five times faster than the AR decoder. Furthermore, to automatically assess the quality of generated samples, we define three different objective evaluation metrics <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i.e.</i> , Fréchet Inception Distance (FID), Kullback-Leibler (KL), and audio caption loss, which can comprehensively assess the relevance and fidelity of the generated samples.

Unidirectional language bias: The Implicit Association Test with Spanish and English in Miami

Aims and objectives/purpose/research questions: Automatic preferences and implicit biases toward Spanish and English in the context of Miami are tested. We investigate whether implicit language bias is conditioned by social factors (i.e., ethnicity, gender, first language) as well as different linguistic stimuli (orthographic vs oral/aural). Design/methodology/approach: Three Implicit Association Test (IAT) experiments were designed and implemented. IAT 1 uses semantically neutral furniture terms in English and Spanish with visual attribute words. IAT 2 uses an oral/aural condition employing US Latinx city names produced with both Spanish and English phonology. In IAT 3, we use nonce words to represent the categories of English and Spanish as well as positive/negative visual imagery for the attributes. Data and analysis: d-scores were automatically calculated considering response latency and accuracy. Data were subjected to linear regression for between- and within-experiment analyses as well as a post hoc regression considering participants born outside of the United States. Findings/conclusions: The within-experiment analysis for IAT 1 showed an effect of country of birth. The between-experiment analysis showed country of birth and the experiments themselves to be significant. Length of residency for the non-US born group was also a significant factor. Across the three experiments, none of the 89 participants demonstrated a strong automatic preference for Spanish. Originality: This study is conducted in the largest situation of bilingualism in the Americas and is the first study to examine nonconscious bias toward bilingual participants’ own language varieties in the United States. Significance/implications: Despite the popular construction of Miami as “Spanish-speaking,” results of this study demonstrate strong nonconscious automated preferences for English among participants in Miami and raise questions about language, power, and the vitality of Spanish in South Florida.

Stress Analysis of Concrete Materials Based on Finite Element Analysis

China’s construction industry standard “technical code for concrete special-shaped column structure” has been implemented since 2006, and the use of special-shaped walls in the actual construction of buildings is more common. The cross-section wall can effectively reduce the protruding angle of the building, thereby expanding the effective building area of the room, reducing the proportion of the building components themselves, and making the structure layout of the building more beautiful. In order to analyze the dynamic characteristics of eccentrically compressed prestressed concrete beams, the finite element simulation of different reinforcement parameters, longitudinal reinforcement diameter, and reinforcement ratio was constructed. Through comparison, the load flexibility curve change law of concrete stress cloud and reinforcement stress cloud under various working conditions and the influence change law of test mold are studied, and the influence change law of dynamic characteristics under the above four conditions and unidirectional bias pressure is clarified.

Spontaneous polarization and cell guidance on asymmetric nanotopography

Asymmetric nanotopography with sub-cellular dimensions has recently demonstrated the ability to provide a unidirectional bias in cell migration. The details of this guidance depend on the type of cell studied and the design of the nanotopography. This behavior is not yet well understood, so there is a need for a predictive description of cell migration on such nanotopography that captures both the initiation of migration, and the way cell migration evolves. Here, we employ a three-dimensional, physics-based model to study cell guidance on asymmetric nanosawteeth. In agreement with experimental data, our model predicts that asymmetric sawteeth lead to spontaneous motion. Our model demonstrates that the nanosawteeth induce a unidirectional bias in guidance direction that is dependent upon actin polymerization rate and sawtooth dimensions. Motivated by this model, an analysis of previously reported experimental data indicates that the degree of guidance by asymmetric nanosawteeth increases with the cell velocity.

Actin Dynamics as a Multiscale Integrator of Cellular Guidance Cues.

Migrating cells must integrate multiple, competing external guidance cues. However, it is not well understood how cells prioritize among these cues. We investigate external cue integration by monitoring the response of wave-like, actin-polymerization dynamics, the driver of cell motility, to combinations of nanotopographies and electric fields in neutrophil-like cells. The electric fields provide a global guidance cue, and approximate conditions at wound sites in vivo. The nanotopographies have dimensions similar to those of collagen fibers, and act as a local esotactic guidance cue. We find that cells prioritize guidance cues, with electric fields dominating long-term motility by introducing a unidirectional bias in the locations at which actin waves nucleate. That bias competes successfully with the wave guidance provided by the bidirectional nanotopographies.

Evidence for canonical spin glass behaviour in polycrystalline Mn1.5Fe1.5Al Heusler alloy

Magnetic properties of magnetically frustrated polycrystalline Mn1.5Fe1.5Al Heusler type alloy with a β-Mn structure were systematically studied using dc magnetization, ac susceptibility, magnetic relaxation and magnetic memory effect measurements to understand its magnetic ground state. The Mn1.5Fe1.5Al alloy system exhibits a sharp peak at low temperature around 34.5 K with strong antiferromagnetic correlations (θCW ∼ −639 K) and a high degree of frustration (fp ∼ 18.7) which suggest the presence of competing magnetic interactions. Despite of strong antiferromagnetic correlations, this peak has spin-glass character as confirmed by the observations of bifurcation of the zero-field-cooled and field-cooled magnetization curves below the irreversibility temperature, field dependent shift of the irreversibility temperature, unidirectional exchange bias effect on the field-cooled M-H hysteresis loop, exponential decay of the temperature variation of remanence and coercivity, frequency dependent shift of the spin glass freezing temperature (Tf) as per the dynamic scaling laws given by the critical slowing down model and Vogel-Fulcher law, magnetic relaxation and magnetic memory effect below Tf. The observation of a clear asymmetric response with respect to the temperature cycling in the magnetic relaxation measurements validates the hierarchical model of the spin-glass magnetic relaxation in Mn1.5Fe1.5Al alloy. Since the behaviour exhibited by the Mn1.5Fe1.5Al alloy has perfect similarity with the well-known atomic spin glasses like CuMn, AuFe, therefore, it may be considered as canonical spin-glass system.

Oscillations Governed by the Incoherent Dynamics in Necroptotic Signaling

Emerging evidences have suggested that oscillation is important for the induction of cell death. However, whether and how oscillation behavior is involved and required for necroptosis remain elusive. To address this question, a minimal necroptotic circuit is proposed based on the CNS pathway. Stochastic parameter analysis demonstrates that the essential structure for oscillation of the CNS circuit is constituted by a paradoxical component embedded with positive feedback among the three protein nodes, i.e., RIP1, caspase-8, and RIP3. Distribution characteristics of all parameters in the CNS circuit with stable oscillation are investigated as well, and a unidirectional bias with fast and slow dynamics that are required for high occurrence probability of oscillation is identified. Four types of oscillation behaviors are classified and their robustness is further explored, implying that the fast oscillation behavior is more robust than the slow behavior. In addition, bifurcation analysis and landscape approach are employed to study stochastic dynamics and global stability of the circuit oscillations, revealing the possible switching strategies among different behaviors. Taken together, our study provides a natural and physical bases for understanding the occurrence of oscillations in the necroptotic network, advancing our knowledge of oscillations in regulating the various cell death signaling.

Patterns and predictors of personal responsibility attributions after major trauma

BackgroundExternal responsibility attributions after injury are associated with worse recovery. However, there remains limited understanding of who accepts personal responsibilityfor their injury and whether or how responsibility attributions change over time. MethodsThis prospective cohort study included patients who received care from recovery co-ordinators following serious injury and admission to a major trauma centre in Victoria, Australia (n=850). Self-reported personal responsibility attributions (totally, partially, not responsible, or did not know) were collected at three timepoints (admission, discharge, and six months post-injury) and linked to demographic, injury and clinical characteristics from the Victorian State Trauma Registry. ResultsMixed effects multinomial analyses revealed that female sex (adjusted relative risk ratio, aRRR=3.11-4.66) and compensable injury (aRRR=7.83-15.27) were associated with reporting lower personal responsibility relative to total responsibility. Falls and motorcyclists had decreased risk of reporting lower personal responsibility than non-drivers (motor vehicle/motorcycle passengers, cyclists and pedestrians) (aRRR=0.11-0.19). More than one-third of participants changed their personal responsibility attribution within six months post-injury. Kappa analyses revealed fair to moderate agreement between the three timepoints (kappa=0.38-0.59), and Stuart-Maxwell tests showed unidirectional bias towards reporting lower levels of personal responsibility between admission and discharge (p<0.001). No demographic, health or injury characteristics predicted a change in responsibility attributions in logistic regression analyses. ConclusionsPersonal responsibility attributions often change over time. Therefore, responsibility attributions should not be considered static, and attributions made at different times post-injury should not be used interchangeably in research or clinical settings. Given that external responsibility attributions are associated with worse post-injury outcomes, potential interventions to optimise recovery should be prioritised for patients who predominantly report lower levels of personal responsibility, especially women and people with compensable injuries. Meanwhile, factors associated with high levels of personal responsibility highlight opportunities to implement targeted injury prevention strategies.

Understanding the Switching Mechanisms of the Antiferromagnet/Ferromagnet Heterojunction

Electric-field-driven spintronic devices are considered promising candidates for beyond CMOS logic and memory applications thanks to their potential for ultralow energy switching and nonvolatility. In this work, we have developed a comprehensive modeling framework to understand the fundamental physics of the switching mechanisms of the antiferromagnet/ferromagnet heterojunction by taking BiFeO3/CoFe heterojunctions as an example. The models are calibrated with experimental results and demonstrate that the switching of the ferromagnet in the antiferromagnet/ferromagnet heterojunction is caused by the rotation of the Neel vector in the antiferromagnet and is not driven by the unidirectional exchange bias at the interface as was previously speculated. Additionally, we demonstrate that the fundamental limit of the switching time of the ferromagnet is in the subnanosecond regime. The geometric dependence and the thermal stability of the antiferromagnet/ferromagnet heterojunction are also explored. Our simulation results provide the critical metrics for designing magnetoelectric devices.

From the South to the North: The circulation of Latin American dependency theories in the Federal Republic of Germany

Sociological research into the transregional North–South circulation of knowledge in the social sciences and humanities has tended to have a unidirectional bias to date. The standard assumption is that as a result of globalization, theories and methods are spread from the global North to the global South. Based on this premise, many of the studies of circulation focus on the transfer of knowledge in terms of ideas, traditions, authors and concepts from the North to the South. Thus far, little attention has been paid to the transregional circulation of theoretical approaches from the South to the North and their impact on the transformation of the European social sciences and humanities. Analysing the circulation of the Latin American dependency theories in the Federal Republic of Germany, this article addresses precisely this gap. The focus is on processes of institutional consolidation of area studies, North–South mobility, the translation-process into German, application in empirical research, modification and rejection. Focusing on this little-explored orientation regarding the circulation of knowledge, this article is in keeping with the current attempt to analyse transregional entanglements within European social sciences.

Programmable bias field observed in graded ferromagnetic semiconductor films with broken symmetry

We report on the observation of a field-induced magnetic bias effect in a $\mathrm{G}{\mathrm{a}}_{0.94}\mathrm{M}{\mathrm{n}}_{0.06}\mathrm{A}{\mathrm{s}}_{1\ensuremath{-}y}{\mathrm{P}}_{y}$ thin film with digitally graded phosphorus content. Although phosphorus concentration in the sample is changed in steps from $y\ensuremath{\approx}0.03$ to $y\ensuremath{\approx}0.28$, the magnetometry and magnetotransport data display a coherent magnetic response typical for single-layer in-plane magnetized films with cubic and weak [110] uniaxial anisotropy. Unexpectedly, low-temperature planar Hall resistance loops exhibit remarkable asymmetry tunable by application of strong in-plane initial magnetic field ${H}_{\mathrm{Ini}}$. We discuss this unusual memory effect, resembling the magnetization asymmetry in the exchange biased magnetic bilayers, in terms of a unidirectional bias field ${H}_{b}$ induced by ${H}_{\mathrm{Ini}}$. We show that such bias field defines the delayed or accelerated nucleation of domains with chiral domain walls performing the magnetization reversal.

Back-to-back Interface diodes induced symmetrical negative differential resistance and reversible bipolar resistive switching in β-CuSCN trigonal pyramid micro/nanoarray

As a superior p-type wide bandgap semiconductor, β-CuSCN has a huge potential in optoelectronic device application, and however its conduction could intensively be affected by externally applied bias. Here, we demonstrate electrodeposited individual β-CuSCN trigonal micro/nanopyramids and their array films can show Cu+ trap-controlled bias dependence of electron transport. Before being subjected to a large reverse bias or a unidirectional bias, their cyclic IV curves are coincident resulted from bulk-trap related carrier hopping. At relatively large bidirectional operation bias, they can symmetrically present two large hysteresis loops with negative differential resistance (NDR), and meanwhile accompany with nonvolatile negative resistive switching (RS) feature. After being applied respectively a relatively large fixed bias in two opposite directions, more importantly, switchable classic asymmetrical bipolar RS can successfully be realized at a relatively low operation bias. The switchable formation of reversion and depletion layer, resulted from the minority carriers (electrons) injection into the traps of surface connected with negative electrode, plays a crucial role. Under relatively large bias, the synergistic effect of two surface trap-related back-to-back connected bipolar RS devices results in symmetrical negative RS with NDR. After being applied a relatively large fixed bias, the bipolar RS effect can be enhanced at the surface connected with negative electrode due to the presence of electron injection induced high and narrow barrier, and conversely it disappears at the surface connected with positive electrode due to hole injection-induced ohmic contact. Then, the devices can be set and reset by the filling and emptying of holes in the thin reversion and depletion layer at low reverse and forward voltages, respectively, showing switchable bipolar RS behavior. Due to superior stability, reversibility, nondestructive readout, and low operation bias as well as remarkable cycle performance, the bias-governed conduction with negative RS and switchable bipolar RS makes it a potential candidate in next-generation erasable nonvolatile RRAM devices.

Asymmetric confinement for defining outgrowth directionality.

Directional connectivity is required to develop accurate in vitro models of the nervous system. This research investigated the interaction of murine neuronal outgrowths with asymmetric microstructured geometries to provide insights into the mechanisms governing unidirectional outgrowth bias. The structures were designed using edge-guidance and critical turning angle principles to study different prohibitive to permissive edge-guidance ratios. The different structures enable outgrowth in the permissive direction, while reducing outgrowth in the prohibitive direction. Outgrowth bias was probabilistic in nature, requiring multiple structures for effective unidirectional bias in primary hippocampal cultures at 14 days in vitro. Arrowhead structures with acute posterior corners were optimal, enabling 100% unidirectional outgrowth bias by virtue of re-routing and delay effects.

Extending the paleontology-biogeography reciprocity with SDMs: Exploring models and data in reducing fossil taxonomic uncertainty.

Historically, studies aimed at prospecting and analyzing paleontological and neontological data to investigate species distribution have developed separately. Research at the interface between paleontology and biogeography has shown a unidirectional bias, mostly focusing on how paleontological information can aid biogeography to understand species distribution through time. However, the modern suit of techniques of ecological biogeography, particularly species distribution models (SDM), can be instrumental for paleontologists as well, improving the biogeography-paleontology interchange. In this study, we explore how to use paleoclimatic data and SDMs to support paleontological investigation regarding reduction of taxonomic uncertainty. Employing current data from two neotropical species (Lagostomus maximus and Myocastor coipus), we implemented SDMs and performed model validation comparing hindcasts with dated fossil occurrences (~14k and ~20k years back present, respectively). Finally, we employed the hindcasting process for two South American fossil records of a misidentified species of caiman (Caiman sp.) to show that C. latirostris is the most likely species identity of these fossils (among four candidate species: C. latirostris, C. yacare, C. crocodilus, and Melanosuchus niger). Possible limitations of the approach are discussed. With this strategy, we have shown that current developments in biogeography research can favour paleontology, extending the (biased) current interchange between these two scientific disciplines.

Controllable Interfacial Coupling Effects on the Magnetic Dynamic Properties of Perpendicular [Co/Ni]5/Cu/TbCo Composite Thin Films.

Dynamic magnetic properties in perpendicularly exchange-coupled [Co/Ni]5/Cu (tCu = 0-2 nm)/TbCo structures show strong dependences on the interfacial antiferromagnetic strength Jex, which is controlled by the Cu interlayer thickness. The precession frequency f and effective damping constant αeff of a [Co/Ni]5 multilayer differ distinctly for parallel (P)and antiparallel (AP) magnetization orientation states. For samples with a thin tCu, f of the AP state is apparently higher, whereas αeff is lower than that in the P state, owing to the unidirectional exchange bias effect (HEB) from the TbCo layer. The differences in f and αeff between the two states gradually decrease with increasing tCu. By using a uniform precession model including an additional HEB term, the field-dependent frequency curves can be well-fitted, and the fitted HEB value is in good agreement with the experimental data. Moreover, the saturation damping constant α0 displays a nearly linear correlation with Jex. It decreases significantly with Jex and eventually approaches a constant value of 0.027 at tCu = 2 nm where Jex vanishes. These results provide a better understanding and effective control of magnetization dynamics in exchange-coupled composite structures for spintronic applications.

Least Squares Monte Carlo Credit Value Adjustment with Small and Unidirectional Bias

Credit value adjustment (CVA) and related charges have emerged as important risk factors following the Global Financial Crisis. These charges depend on uncertain future values of underlying products, and are usually computed by Monte Carlo simulation. For products that cannot be valued analytically at each simulation step, the standard market practice is to use the regression functions from least squares Monte Carlo method to approximate their values. However, these functions do not necessarily provide accurate approximations to product values over all simulated paths and can result in biases that are difficult to control. Motivated by a novel characterization of the CVA as the value of an option with an early exercise opportunity at a stochastic time, we provide an approximation for CVA and other credit charges that rely only on the sign of the regression functions. The values are determined, instead, by pathwise deflated cash flows. A comparison of CVA for Bermudan swaptions and cancellable swaps show that the proposed approximation results in much smaller errors than the standard approach of using the regression function values.

Signal transfer within a cultured asymmetric cortical neuron circuit

Objective. Simplified neuronal circuits are required for investigating information representation in nervous systems and for validating theoretical neural network models. Here, we developed patterned neuronal circuits using micro fabricated devices, comprising a micro-well array bonded to a microelectrode-array substrate. Approach. The micro-well array consisted of micrometre-scale wells connected by tunnels, all contained within a silicone slab called a micro-chamber. The design of the micro-chamber confined somata to the wells and allowed axons to grow through the tunnels bidirectionally but with a designed, unidirectional bias. We guided axons into the point of the arrow structure where one of the two tunnel entrances is located, making that the preferred direction. Main results. When rat cortical neurons were cultured in the wells, their axons grew through the tunnels and connected to neurons in adjoining wells. Unidirectional burst transfers and other asymmetric signal-propagation phenomena were observed via the substrate-embedded electrodes. Seventy-nine percent of burst transfers were in the forward direction. We also observed rapid propagation of activity from sites of local electrical stimulation, and significant effects of inhibitory synapse blockade on bursting activity. Significance. These results suggest that this simple, substrate-controlled neuronal circuit can be applied to develop in vitro models of the function of cortical microcircuits or deep neural networks, better to elucidate the laws governing the dynamics of neuronal networks.

Effects of surface asymmetry on neuronal growth.

Detailed knowledge of how the surface physical properties, such as mechanics, topography and texture influence axonal outgrowth and guidance is essential for understanding the processes that control neuron development, the formation of functional neuronal connections and nerve regeneration. Here we synthesize asymmetric surfaces with well-controlled topography and texture and perform a systematic experimental and theoretical investigation of axonal outgrowth on these substrates. We demonstrate unidirectional axonal bias imparted by the surface ratchet-based topography and quantify the topographical guidance cues that control neuronal growth. We describe the growth cone dynamics using a general stochastic model (Fokker-Planck formalism) and use this model to extract two key dynamical parameters: diffusion (cell motility) coefficient and asymmetric drift coefficient. The drift coefficient is identified with the torque caused by the asymmetric ratchet topography. We relate the observed directional bias in axonal outgrowth to cellular contact guidance behavior, which results in an increase in the cell-surface coupling with increased surface anisotropy. We also demonstrate that the disruption of cytoskeletal dynamics through application of Taxol (stabilizer of microtubules) and Blebbistatin (inhibitor of myosin II activity) greatly reduces the directional bias imparted by these asymmetric surfaces. These results provide new insight into the role played by topographical cues in neuronal growth and could lead to new methods for stimulating neuronal regeneration and the engineering of artificial neuronal tissue.