Response Regime Research Articles

Faster spectral density calculation using energy moments

Accurate predictions of inclusive scattering cross sections in the linear response regime require efficient and controllable methods to calculate the spectral density in a strongly-correlated many-body system. In this work we reformulate the recently proposed Gaussian Integral Transform technique in terms of Fourier moments of the system Hamiltonian which can be computed efficiently on a quantum computer. One of the main advantages of this framework is that it allows for an important reduction of the computational cost by exploiting previous knowledge about the energy moments of the spectral density. For a simple model of medium mass nucleus like ^{40}Ca and target energy resolution of 1 MeV we find an expected speed-up of approx 125 times for the calculation of the giant dipole response and of approx 50 times for the simulation of quasi-elastic electron scattering at typical momentum transfers.

Closed Formula for Transport across Constrictions

In the last decade, the Fick-Jacobs approximation has been exploited to capture transport across constrictions. Here, we review the derivation of the Fick-Jacobs equation with particular emphasis on its linear response regime. We show that, for fore-aft symmetric channels, the flux of noninteracting systems is fully captured by its linear response regime. For this case, we derive a very simple formula that captures the correct trends and can be exploited as a simple tool to design experiments or simulations. Lastly, we show that higher-order corrections in the flux may appear for nonsymmetric channels.

Extension of Linear Response Regime in Weak-Value Amplification Technique

The achievable precision of parameter estimation plays a significant role in evaluating a strategy of metrology. In practice, one may employ approximations in a theoretical model development for simplicity, which, however, will cause systematic error and lead to a loss of precision. We derive the error of maximum likelihood estimation in the weak-value amplification technique where the linear approximation of the coupling parameter is used. We show that this error is positively related to the coupling strength and can be effectively suppressed by improving the Fisher information. Considering the roles played by weak values and initial meter states in the weak-value amplification, we also point out that the estimation error can be decreased by several orders of magnitude by averaging the estimations resulted from different initial meter states or weak values. These results are finally illustrated in a numerical example where an extended linear response regime to the parameter is observed.

Decolonising Global Solidarity: The WHO’s Broken Alarm and Epidemiological Nationalism

The COVID-19 pandemic has traumatised world leaders, leading people to question the capability and accountability of global health governance. Against this background, we have heard multiple calls to strengthen ‘solidarity’ within and between states – which, weirdly, is practised by keeping a distance from ‘Others’ through, for instance, social distancing, lockdowns, and border control. In this paper, I first introduce the post-World War II international pandemic response regime, especially the International Health Regulations 2005, using the multiple positions of the Republic of China and/or Taiwan to illustrate the prioritisation of national sovereignty over health justice. In and beyond this context, I conceptualise epidemiological nationalism, which contains three dimensions (territorial, affective, and epistemic) to critically examine the responses to COVID-19 from the WHO and different states. This concept enables us to analyse the solidarity-through-distancing practices from a decolonial perspective to deconstruct the contemporary global health regime. The regime is underpinned by the coloniality of modern epidemiology, which creates the hierarchies between nations and races imposed on the making and working of geographical, population, and disease categories by racialising diseases and response measures. Such racialisation practices vary in different contexts and are often tied to states’ securitisation practices, which justify the exclusion of minority communities.

Linear viscoelastic response of the vertex model with internal and external dissipation: Normal modes analysis

We use the normal mode formalism to study the shear rheology of the vertex model for epithelial tissue mechanics in the overdamped linear response regime. We consider systems with external (e.g., cell-substrate) and internal (e.g., cell-cell) dissipation mechanisms, and derive expressions for stresses on cells due to mechanical and dissipative forces. The semi-analytical method developed here is, however, general and can be directly applied to study the linear response of a broad class of soft matter systems with internal and external dissipation. It involves normal mode decomposition to calculate linear loss and storage moduli of the system. Specifically, displacements along each normal mode produce stresses due to elastic deformation and internal dissipation, which are in force balance with loads due to external dissipation. Each normal mode responds with a characteristic relaxation timescale, and its rheological behavior can be described as a combination of a standard linear solid element due to elastic stresses and a Jeffreys model element due to the internal dissipative stresses. The total response of the system is then fully determined by connecting in parallel all the viscoelastic elements corresponding to individual normal modes. This allows full characterization of the potentially complex linear rheological response of the system at all driving frequencies and identification of collective excitations. We show that internal and external dissipation mechanisms lead to qualitatively different rheological behaviors due to the presence or absence of Jeffreys elements, which is particularly pronounced at high driving frequencies. Our findings, therefore, underscore the importance of microscopic dissipation mechanisms in understanding the rheological behavior of soft materials and tissues, in particular.

Synergistic analysis of performance, functional genes, and microbial community assembly in SNDPR process under Zn(II) stress

One of the most prevalent heavy metals found in rural sewage is Zn(II), while its effect on simultaneous nitrification, denitrification and phosphorus removal (SNDPR) remains unclear. In this work, the responses of SNDPR performance to long-term Zn(II) stress were investigated in a cross-flow honeycomb bionic carrier biofilm system. The results indicated that Zn(II) stress at 1 and 5 mg L−1 could increase nitrogen removal. Maximum ammonia nitrogen, total nitrogen, and phosphorus removal efficiencies of up to 88.54%, 83.19%, and 83.65% were obtained at Zn(II) concentration of 5 mg L−1. The functional genes, such as archaeal amoA, bacterial amoA, NarG, NirS, NapA, and NirK, also reached the highest value at 5 mg L−1 Zn(II), with the absolute abundances of 7.73 × 105, 1.57 × 106, 6.68 × 108, 1.05 × 109, 1.79 × 108, and 2.09 × 108 copies·g−1 dry weight, respectively. The neutral community model demonstrated that deterministic selection was responsible for the system's microbial community assembly. Additionally, response regimes with extracellular polymeric substances and cooperation among microorganisms facilitated the stability of the reactor effluent. Overall, the findings of this paper contribute to improving the efficiency of wastewater treatment.

Quantum oscillations as a robust fingerprint of chiral anomaly in nonlinear response in Weyl semimetals

In view of searching the signature of the celebrated chiral anomaly (CA) in Weyl semimetals (WSMs) in ongoing experiments, quantum oscillation in linear response regime has been considered as an important signature in the magneto transports in WSMs, due to its unique relation to CA. Investigating the nonlinear planar effects (NPEs) starting from the semiclassical regime to the ultra-quantum limit within the framework of Boltzmann transport theory incorporating Landau quantization, we here propose the quantum oscillations in NPEs can serve as a robust signature of CA in WSMs. By obtaining analytical expressions, we show that the quantum oscillations of the nonlinear effects exhibit two different period scales in 1/B (B is the magnetic field) compared to the linear responses where only one period scale exists. We find that these quantum oscillations in NPEs are attributed to the deviation of chiral chemical potential (CCP), which is proportional to the finite band tilt as well as transverse electric field and therefore, directly linked to CA in WSMs. In addition, we also show that the CA-induced nonlinear magneto conductivity is linear and independent in the magnetic field in the semiclassical and ultraquantum regimes, respectively. We conclude that the proposed behaviors of NPEs in different regimes uniquely signify the existence of CA and therefore, can serve as a probe of identifying CA in WSMs in experiments.

Si9C15 monolayer: A silicon carbide allotrope with remarkable physical properties

Zero band gap in graphene and silicene is an important obstacle to their application in nanodevices. Combining carbon and silicon atoms to form a silicon carbide (${\mathrm{Si}}_{x}{\mathrm{C}}_{y}$) sheet is an applicable proposal to solve the band gap issue. Very recently, a large-scale monolayer $\mathrm{Si}{}_{9}\mathrm{C}{}_{15}$ was successfully synthesized and exhibited suitable band gap and environment stability [Gao et al., Adv. Mater. 34, 2204779 (2022)]. Motivated by this recent experiment, we explore the electronic, mechanical, optical, and thermoelectric properties of a $\mathrm{Si}{}_{9}\mathrm{C}{}_{15}$ monolayer using first-principles calculations. Our results reveal that the monolayer is an auxetic material with a negative Poisson ratio of 0.175. The monolayer is a semiconductor with a direct band gap of 2.54 eV calculated by the Heyd-Scuseria-Ernzerhof functional (HSE06) functional. The optical properties of the monolayer are investigated by solving the Bethe-Salpeter equation. It is revealed that the optical band gap of the monolayer is 2.73 eV, and the exciton binding energy is equal to 1.14 eV, indicating a strongly bound bright exciton. Thermoelectric properties of the monolayer are calculated by combining density functional theory and Green's function formalism in the linear response regime. The lattice thermal conductance of the monolayer is 0.85 nW/K at room temperature, and the maximum figure of merit is 1.2 at 800 K, higher than that of other silicon carbide allotropes. High flexibility, a suitable band gap, high mobility, high optical absorption in the UV-visible region, and high thermoelectric efficiency make the $\mathrm{Si}{}_{9}\mathrm{C}{}_{15}$ monolayer a promising candidate for applications in mechanics, optoelectronics, and energy converters.

Quantifying quantum coherence via Kirkwood-Dirac quasiprobability

Kirkwood-Dirac (KD) quasiprobability is a quantum analog of phase space probability of classical statistical mechanics, allowing negative or/and nonreal values. It gives an informationally complete representation of a quantum state. Recent works have revealed the important roles played by the KD quasiprobability in the broad fields of quantum science and quantum technology. In the present work, we use the KD quasiprobability to access the quantum coherence in a quantum state. We show that the ${l}_{1}$ norm of the imaginary part of the KD quasiprobability over an incoherent reference basis and a second basis, maximized over all possible choices of the latter, can be used to quantify quantum coherence, satisfying certain desirable properties. It is upper bounded by the quantum uncertainty, i.e., the quantum standard deviation, of the incoherent basis in the state. It gives a lower bound to the ${l}_{1}$ norm quantum coherence, and for a single qubit, they are identical. We discuss the measurement of the KD coherence based on the measurement of the KD quasiprobability and an optimization procedure in hybrid quantum-classical schemes, and suggest statistical interpretations. We also discuss its relevance in the physics of linear response regime.

Steady-state dc transport through an Anderson impurity coupled to leads with spin-orbit coupling

We study the steady-state dc transport characteristics of a system comprised of an interacting quantum dot, modelled as an Anderson impurity, coupled to two metallic non-interacting leads with Rashba SOC, using an interpolative perturbative approach (IPA). The single-particle spectra, current and differential conductance are obtained in weak and strong coupling regimes over a wide range of SOC and bias values. Extensive benchmarking of the IPA validates the method in the linear as well as non-linear response regime. The universal, zero bias ($V_{sd}=0$) peak with a width proportional to the Kondo scale ($T_K$) and two non-universal finite bias peaks around $V_{sd}=\pm U$ in the zero temperature differential conductance show a clear separation with increasing $U$ or increasing SOC. In the strong coupling regime, increasing temperature induces melting of the zero bias peak leading to a crossover from a three-peak conductance to a two-peak conductance. Recent experiments find the emergence of a two-peak structure by increasing SOC at a fixed temperature. Our results appear to provide a qualitative explanation of these observations as a SOC tuned crossover from weak/intermediate to strong coupling, and a simultaneous crossover from low $T/T_K$ to high $T/T_K$ ratio. We also reproduce the experimentally observed temperature dependence of the zero bias conductance.

Limited water stress modulates expression of circadian clock genes in Brachypodium distachyon roots

Organisms have evolved a circadian clock for the precise timing of their biological processes. Studies primarily on model dicots have shown the complexity of the inner timekeeper responsible for maintaining circadian oscillation in plants and have highlighted that circadian regulation is more than relevant to a wide range of biological processes, especially organ development and timing of flowering. Contribution of the circadian clock to overall plant fitness and yield has also long been known. Nevertheless, the organ- and species-specific functions of the circadian clock and its relation to stress adaptation have only recently been identified. Here we report transcriptional changes of core clock genes of the model monocot Brachypodium distachyon under three different light regimes (18:6 light:dark, 24:0 light and 0:24 dark) in response to mild drought stress in roots and green plant parts. Comparative monitoring of core clock gene expression in roots and green plant parts has shown that both phase and amplitude of expression in the roots of Brachypodium plants differ markedly from those in the green plant parts, even under well-watered conditions. Moreover, circadian clock genes responded to water depletion differently in root and shoot. These results suggest an organ-specific form and functions of the circadian clock in Brachypodium roots.

Mitigating the effects of climate change on the nests of sea turtles with artificial irrigation.

For sea turtles, like many oviparous species, increasing temperatures during development threaten to increase embryonic mortality, alter offspring quality, and potentially create suboptimal primary sex ratios. Various methods are being implemented to mitigate the effects of climate change on reproductive success, but these methods, such as breeding programs, translocations, and shading, are often invasive and expensive. Irrigation is an alternative strategy for cooling nests that, depending on location, can be implemented relatively quickly and cheaply. However, multiple factors, including ambient conditions, nest substrate, and species characteristics, can influence irrigation success. Additionally, irrigation can vary in duration, frequency, and the volume of water applied to nests, which influences the cooling achieved and embryonic survival. Thus, it is critical to understand how to maximize cooling and manage risks before implementing irrigation as a nest-cooling strategy. We reviewed the literature on nest irrigation to examine whether artificial irrigation is feasible as a population management tool. Key factors that affected cooling were the volume of water applied and the frequency of applications. Embryonic responses varied with species, ambient conditions, and the timing of irrigation during development. Nest inundation was the key risk to a successful irrigation regime. Future irrigation regimes must identify clear targets, either primary or adult sex ratios, that maximize population viability. Monitoring population responses and adjusting the irrigation regime in response to population characteristics will be critical. Most studies reported on the manipulation of only one or two variables, further research is required to understand how altering multiple factors in an irrigation regime influences the cooling achieved and embryonic responses.

Design and experimental analysis of a pneumatic Nonlinear Energy Sink

Nonlinear Energy Sinks (NESs) have been the object of several theoretical and experimental studies over the past decade, as a subcategory of nonlinear vibration absorbers. The present work illustrates the theoretical design and experimental realisation of a pneumatic Nonlinear Energy Sink (so-called AirNES). The nonlinear elastic force of the NES is provided by a circular membrane. This membrane is fully bonded and delimits two air chambers, linked together via a pipeline. The nonlinear damping of the NES is ensured by the flow of the air at high velocity inside the pipeline. Thanks to this design, the AirNES is embedded on a one degree of freedom linear dynamic system to evaluate its performances. The Target Energy Transfer (TET) from primary system to the NES, as well as different response regimes such as the Strongly Modulated Regime (SMR), are experimentally observed. Additional experiments demonstrate the role of the air in the damping of the prototype. A simple modeling of the AirNES is proposed to ensure a quasi-analytical design of the prototype, including the analytical calculation of the damping. Simulations are then compared to the experiments and show good qualitative correlations as well as some discrepancies between model and reality.

Multidimensional spectroscopy of heavy impurities in ultracold fermions

We investigate the system of a heavy impurity immersed in a degenerate Fermi gas, where the impurity's internal degree of freedom (pseudospin) is manipulated by a series of radio-frequency (RF) pulses at several different times. Applying the functional determinant approach, we carry out an essentially exact calculation of the Ramsey-interference-type responses to the RF pulses. These responses can be regarded as multidimensional (MD) spectroscopy of the system in the time domain. Similar to their one-dimensional counterpart studied by Knap et al. [M. Knap et al., Phys. Rev. X 2, 041020 (2012)], these responses are universal functions. A Fourier transformation of the time intervals gives the MD spectroscopy in the frequency domain, providing insightful information on the many-body correlation and relaxation via the cross peaks, e.g., the off-diagonal peaks in a two-dimensional spectrum. These features are inaccessible for the conventional, one-dimensional absorption spectrum. Our scheme provides a different method to investigate many-body nonequilibrium physics beyond the linear response regime with accessible tools in cold atoms.

Revisiting Canada’s Access to Medicines Regime in Response to COVID-19: A Review of the Legislation and its Underlying Objectives

Revisiting Canada’s Access to Medicines Regime in Response to COVID-19: A Review of the Legislation and its Underlying Objectives

Simultaneous quantitative detection of hematocrit and hemoglobin from whole blood using a multiplexed paper sensor with a smartphone interface.

We report a highly accurate single-step label-free testing technology for simultaneous and independent hematocrit (Hct) and hemoglobin (Hb) level detection from a drop of whole blood by employing a disposable paper strip sensor interfaced with a portable impedimetric device. The paper strip is fabricated by in situ automated printing of a customized electrode template on the non-glossy side of a commercially available photo paper substrate followed by graphite deposition. The integrated platform device technology additionally includes a compact detection cum readout unit comprising a high precision impedance converter system that combines an on-board frequency generator with an analog-to-digital converter evaluation board, collectively interfaced with a central processor, calibration circuit, and smartphone. Employing a dispensed blood sample volume of 25 μL, the device is shown to have a sensitivity of 92 Ω/Hct and 287 Ω/Hb at an optimal frequency of 57 kHz. The respective linear response regimes appear to be wide enough to cover physiologically relevant limits, with excellent stability and reproducibility. Validation with clinical samples reveals limits of detection of Hct and Hb levels as low as 4.66% and 1.89 g dL-1, respectively, which are beyond the quantitative capability of commonly used affordable point of care test kits. The envisaged paradigm of rapid, robust, highly accurate, energy-efficient, simple, user-friendly, multiplex portable detection, obviating any possible ambiguities in interpretation due to common artefacts of colorimetric detection technologies such as optical interference with the image analytical procedure due to the inherent redness of blood samples and background illumination, renders this ideal for deployment in resource-limited settings.

Laboratory validation of an integrative passive sampler for per- and polyfluoroalkyl substances in water

The integrative response of a PFAS-specific passive sampler was evaluated in water streams where the concentration varied with time. An integrative response regime over 90 days was observed for most PFAS analytes.

Transverse magnetoconductance in two-terminal chiral spin-selective devices.

The phenomenon of chirality induced spin selectivity (CISS) has triggered significant activity in recent years, although many aspects of it remain to be understood. For example, most investigations are focused on spin polarizations collinear to the charge current, and hence longitudinal magnetoconductance (MC) is commonly studied in two-terminal transport experiments. Very little is known about the transverse spin components and transverse MC - their existence, as well as any dependence of this component on chirality. Furthermore, the measurement of the CISS effect via two-terminal MC experiments remains a controversial topic. Detection of this effect in the linear response regime is debated, with contradicting reports in the literature. Finally, the potential influence of the well-known electric magnetochiral effect on CISS remains unclear. To shed light on these issues, in this work we have investigated the bias dependence of the CISS effect using planar carbon nanotube networks functionalized with chiral molecules. We find that (a) transverse MC exists and exhibits tell-tale signs of the CISS effect, (b) transverse CISS MC vanishes in the linear response regime establishing the validity of Onsager's relation in two-terminal CISS systems, and finally (c) the CISS signal remains present even in the absence of electric magneto chiral effects, suggesting the existence of an alternative physical origin of CISS MC.

Anisotropic linear and nonlinear charge-spin conversion in topological semimetal SrIrO3

Over the past decade, utilizing spin currents in the linear response of electric field to manipulate magnetization states via spin-orbit torques (SOTs) is one of the core concepts for realizing a multitude of spintronic devices. Besides the linear regime, recently, nonlinear charge-spin conversion under the square of electric field has been recognized in a wide variety of materials with nontrivial spin textures, opening an emerging field of nonlinear spintronics. Here, we report the investigation of both linear and nonlinear charge-spin conversion in one single topological semimetal ${\mathrm{SrIrO}}_{3}(110)$ thin film that hosts strong spin-orbit coupling and nontrivial spin textures in the momentum space. In the nonlinear regime, the observation of crystalline direction dependent response indicates the presence of anisotropic surface states induced spin-momentum locking near the Fermi level. Such anisotropic spin textures also give rise to spin currents in the linear response regime, which mainly contributes to the fieldlike SOT component. Our work demonstrates the power of combination of linear and nonlinear approaches in understanding and utilizing charge-spin conversion in topological materials.

In-situ assessment of soil shrinkage and swelling behavior and hydro-thermal regimes with a thermo-time domain reflectometry technique

The shrinkage and swelling behaviors of clayey soils could lead to cracks and erosions inducing severe damages to agricultural lands and engineering projects. Thus, improving the understanding of shrink-swell characteristics is crucial to nonrigid soils. However, it remains difficult for in-situ monitoring of soil shrink-swell processes continuously and nondestructively. The objective of this study was to present a thermo-time domain reflectometry (thermo-TDR) technique for determination of soil shrinkage and swelling dynamics and hydro-thermal regimes in-situ during wet-dry cycles. A field experiment on two clayey soils (a paddy soil and an alluvial soil) was conducted to evaluate the performance of the thermo-TDR method for in-situ determination of soil volume changes and associated hydraulic and thermal properties during wet-dry cycles. The results showed that both soils experienced considerable shrinking and swelling processes with maximum vertical deformations of 2.4 and 1.8 cm for the paddy soil and alluvial soil, respectively, and with maximum horizontal deformations of 370 and 280 cm2 for the paddy soil and alluvial soil, respectively, during a 36-day period. The thermo-TDR method provided volume change values (shown as the bulk density) agreed well with independent core-sampling measurements with an average RMSE of 0.15 Mg m−3 and a R2 of 0.46. A better agreement was observed between thermo-TDR measured bulk densities and values from the ruler-image processing method with an average RMSE of 0.07 Mg m−3 and a R2 of 0.77. Besides, the thermo-TDR method gave consistent in-situ soil shrinkage curve and water retention surface measurements by combining with soil matric potential sensors. Unlike rigid soils, the paddy and alluvial soils showed complicated hydro-thermal regimes in response to the shrink-swell processes. We conclude that the thermo-TDR technique is a reliable tool for continuous in-situ determination of soil shrink-swell processes. Future studies should focus on development of comprehensive soil heat and water transport models accounting for both moisture content and volume changes.