Collective Modes Research Articles

Rheology of Ring Copolymers in Dilute Solutions.

We investigate the rheology of ring copolymers theoretically within the framework of the optimized Rouse-Zimm theory in dilute solutions. The ring copolymer is composed of two type of monomers (A and B) of different sizes (A < B), which is represented by unequal-sized beads connected via harmonic springs with different spring constants. The hydrodynamic interactions (HI) between the monomers is modeled using the preaveraged HI tensor. These interactions accelerate the collective relaxation modes and impede the local relaxation modes. In the presence of HI, the storage modulus shows a quasi-plateau regime, demonstrating a viscoelastic solid-like response of the polymer, while the loss modulus exhibits a bimodal pattern due to the difference in the mobilities of the monomers. The inverse of the crossover frequency represents the overall characteristic relaxation time, which is higher for the ring copolymers than for the Rouse rings, suggesting a slower relaxation of the ring copolymers due to the presence of relatively large sized monomers. The quasi-plateau in the storage modulus and the bimodality in the loss modulus are enhanced with an increase in the size and number fraction of B-type monomers. An increase in the size of the B-type monomers increases both storage and loss moduli, resulting in an overall decrease in the dynamics of the ring copolymers.

Chiroptical response of an array of isotropic plasmonic particles having a chiral arrangement under coherent interaction.

The chirality and chiroptical response of materials have attracted significant attention for their potential to introduce the new science of light-matter interactions. We demonstrate that collective mode formation under modal coupling between localized surface plasmon resonances (LSPRs) with a chiral arrangement and Fabry-Pérot (FP) nanocavity modes can induce chiroptical responses. We fabricated a cluster of isotropic gold nanodisks with a chiral arrangement (gold nano-windmills, Au-NWs) on the FP nanocavities of TiO2 and Au film. The differential absorption of the Au-NWs coupled with the FP nanocavities under left- and right-handed circularly polarized light irradiations in the far field was significantly enhanced compared with the differential absorption without the FP nanocavities. Far- and near-field analyses by numerical simulation revealed that the Au-NWs coupled with the FP nanocavities formed a collective mode in the near field, and the collective mode represented the chiroptical response in the far field. The light field with the large helicity, can be used in chiral light-matter interactions. The concept of collective mode formation using isotropic metal nanodisks coupled with FP nanocavities provides a platform for controlling complex light fields.

Collective mode across the BCS-BEC crossover in Holstein model

We investigate the emergence of the collective mode in the phonon spectra of the superconducting state within the Holstein model by varying the electron-phonon coupling. Using dynamical mean field theory combined with the numerical renormalization group technique, we calculate the phonon spectra. In the superconducting state with a pairing gap (ΔP), the peak position of the collective mode (ωcol) evolves from the Bardeen-Cooper-Schrieffer (BCS) regime, manifesting near 2ΔP and increasing with coupling, to the Bose-Einstein condensation (BEC) regime, where ωcol decreases with increasing coupling. The decrease of ωcol matches well with the reduction of superfluid stiffness, which originates from the increasing phase fluctuations of local pairs with coupling strength. In the crossover regime with intermediate coupling, ωcol aligns with the soft phonon mode (ωs) of the normal state and decreases with increasing coupling when ωs&lt;2ΔP. Additionally, comparing the collective mode weight to ΔP suggests that the collective mode predominantly stems from U(1) gauge symmetry breaking across all coupling strengths. Published by the American Physical Society 2024

Concurrent validity of scores from phone-based caregiver reports on early childhood development: Evidence from the Early Childhood Development Index 2030 implementation in Nepal

The Early Childhood Development Index 2030 (ECDI2030) is a caregiver-reported tool designed to monitor progress toward Sustainable Development Goal target 4.2, which aims to ensure universal access to quality early childhood development (ECD), care, and pre-primary education to prepare children for primary education and inform national policies. Using the ECDI2030 through phone-based administration for remote data collection is expected to contribute to efficient evidence generation. However, the existing evidence for caregiver-reported ECD measures are exclusively drawn from studies on assessments through face-to-face interviews. We conducted a validation trial in Nepal, comparing randomly divided in-person and telephone interviews groups. The results support the concurrent validity of phone-based ECDI2030 scores for measuring ECD at a group level while highlighting administrative challenges specific to the phone-based method. This study contributes to the literature on ECD measurement and provides insights into the practical implications of different modes of data collection.

Improving prediction accuracy in agricultural markets through the CIMA-AttGRU model.

In the Chinese futures market, agricultural product futures play a crucial role. While previous studies have primarily relied on historical price data and fundamental financial indicators of agricultural product futures, there is a growing recognition of the value that lies within the vast amounts of textual data generated in the financial domain. Our study specifically focuses on the limitations of existing methods in capturing the complex relationships and rich semantic information embedded in these textual sources. This article designs a CIMA AttGRU (CIMA-AttGRU) model for soybean futures, which is a forecasting method for the agricultural product market. This model uniquely integrates Collective Intrinsic Mode Analysis (CIMA) with an Attention-Gated Recurrent Unit (AttGRU), leveraging the strengths of both techniques to enhance predictive accuracy and adaptability. The rationale behind employing the CIMA-AttGRU model lies in its ability to effectively tackle the inherent challenges of financial market analysis. By incorporating CIMA, the model adeptly filters out market noise, directly addressing the challenge of high volatility. Additionally, with its attention mechanism, the CIMA-AttGRU targets the issue of non-linear patterns by allowing dynamic adjustment to temporal dependencies, offering differential learning capabilities crucial for capturing the nuanced fluctuations in futures prices. Complementing the CIMA and AttGRU, the integration of Class-wise Adversarial Domain Adaptation (CADA) further refines the model's robustness, addressing the critical challenge of domain adaptivity. This aspect is particularly vital for edamame futures, where price determinants can vary significantly over time and across regions. Our empirical results demonstrate a significant improvement in forecasting precision, with the CIMA-AttGRU model achieving a Mean Absolute Error (MAE) reduction of 15% and a Mean Squared Error (MSE) reduction of 20% compared to conventional models. This superior performance, especially in terms of prediction accuracy and handling market fluctuations, highlights the improve of the model compared to existing methods and has made significant explorations in agricultural market forecasting.

Research on anomaly detection and correction of power metering data based on machine learning algorithm

Electric energy measurement is the basis of marketization of electric energy. If the power metering device is abnormal, it will directly affect the economic interests of both sides. At present, the electric energy measurement data of power grid enterprises has generally adopted the mode of remote centralized collection. The existing methods of abnormal detection and location of electric energy metering are mainly through the analysis of the abnormal data alarm issued by the electric energy acquisition system and the on-site inspection of the metering device. With the continuous expansion of the scale of electric power data, the existing methods highlight the shortcomings of low accuracy and low efficiency. In order to explore the optimal solution to the above problems, this paper constructs a multi-model fusion anomaly detection method of electric energy measurement data based on machine learning, and gives the anomaly correction scheme of electric energy measurement data. The results show that the fusion model has the best performance in the actual situation, with AUC reaching 0.9653 and TPR exceeding 0.64 under the condition of zero FPT. The comprehensive performance is better than that of other single models.

Linear spectroscopy of collective modes and the gap structure in two-dimensional superconductors

We consider optical response in multiband, multilayer two-dimensional superconductors. Within a simple model, we show that linear response to AC gating can detect collective modes of the condensate, such as Leggett and clapping modes. We show how trigonal warping of the superconducting order parameter can help facilitate detection of clapping modes. Taking rhombohedral trilayer graphene as an example, we consider several possible pairing mechanisms and show that all-electronic mechanisms may produce in-gap clapping modes. These modes, if present, should be detectable in the absorption of microwaves applied via the gate electrodes, which are necessary to enable superconductivity in this and many other settings; their detection would constitute strong evidence for unconventional pairing. Last, we show that absorption at frequencies above the superconducting gap 2|Δ| also contains a wealth of information about the gap structure. Our results suggest that linear spectroscopy can be a powerful tool for the characterization of unconventional two-dimensional superconductors. Published by the American Physical Society 2024

Is the mechanism of "fast sound" the same in liquids with long-range interactions and disparate mass metallic alloys?

We present abinitio simulations of a large system of 2400 particles of molten NaCl to investigate the behavior of collective mode dispersion beyond the hydrodynamic regime. In particular, we aim to explain the unusually strong increase in the apparent speed of sound with wave number, which significantly exceeds the typical positive sound dispersion of 10%-25% observed in simple liquids. We compare dispersions of "bare" acoustic and optic modes in NaCl with abinitio simulations of other ionic melts such as CuCl and LiBr, metallic liquid alloys such as Pb44Bi56 and Li4Tl, and the regular Lennard-Jones KrAr liquid simulated by classical molecular dynamics. Analytical expressions for the "bare" acoustic and optic branches of collective excitations help us to identify the impact of the high-frequency optic branch on the emergence of "fast sound" in binary melts. Our findings show that in ionic melts, the high-frequency speed of sound is much larger than in the simple Lennard-Jones liquids and metallic melts, leading to an observed strong viscoelastic increase in the apparent speed of sound-more than double its adiabatic value.

Inducing exceptional points, enhancing plasmon quality and creating correlated plasmon states with modulated Floquet parametric driving

The control of low frequency collective modes in solids by light presents important challenges and opportunities for condensed matter physics. We propose a method to parametrically drive low THz range collective modes in an interacting many body system using Floquet driving at optical frequencies with a modulated amplitude. We demonstrate that it can be used to design plasmonic time-varying media with singular dispersions. Plasmons near resonance with half the modulation frequency exhibit two lines of exceptional points connected by dispersionless states. Above a critical driving strength, resonant plasmon modes become unstable and undergo a continuous transition towards a crystal-like structure stabilized by interactions and nonlinearities. This new state breaks the discrete time translational symmetry of the drive as well as the translational and rotational spatial symmetries of the system and exhibits soft, Goldstone-like phononic excitations. Below the instability threshold, our method can be used to enhance the quality of plasmon resonances.

The interplay between liquid–liquid and ferroelectric phase transitions in supercooled water

The distinctive characteristics of water, evident in its thermodynamic anomalies, have implications across disciplines from biology to geophysics. Considered a valid hypothesis to rationalize its unique properties, a liquid-liquid phase transition in water below the freezing point, in the so-called supercooled regime, has nowadays been observed in several molecular dynamics simulations and is being actively researched experimentally. The hypothesis of ferroelectric phase transition in supercooled water can be traced back to 1977, due to Stillinger. In this work, we highlight intriguing and far-reaching implications of water: The ferroelectric and liquid-liquid phase transitions can be designed as two facets of the same underlying phenomenon. Our results are based on the analysis of extensive molecular dynamics simulations and are explained in the context of a classical density functional theory in mean-field approximation valid for a polar liquid, where dipolar interaction is treated perturbatively. The theory underpins the potential role of ferroelectricity in promoting the liquid-liquid phase transition, being the density-polarization coupling inherent in the dipolar interaction potential. The existence of ferroelectric order in supercooled low-density liquid water is confirmed by the observation in molecular dynamics simulations of collective modes in space-time polarization correlation functions, traceable to spontaneous breaking of continuous rotational symmetry. Our work sheds light on water's supercooled behavior and opens the door to experimental investigations of the static and dynamic behavior of water's polarization.

Corotation of two quantized vortices coupled with collective modes in self-gravitating Bose-Einstein condensates

Corotation of two quantized vortices coupled with collective modes in self-gravitating Bose-Einstein condensates

Longitudinal and transverse collective dynamics in water by simulation using the BK3 model.

Using a recent polarizable model for water (the BK3 model), we explore the collective dynamic modes in liquid water by molecular dynamics (MD) simulation. The dynamic structure factor and the longitudinal and transverse current correlation spectral densities are computed over the whole frequency range below intramolecular excitations. MD results of atom-atom partial correlation functions are fitted using the Generalized Collective Modes (GCMs) model, involving relaxing modes occurring in the longitudinal component and propagating modes occurring in both components. Three systems are studied as follows: (1) BK3 ambient water, (2) SPC/E ambient water, and (3) BK3 ambient heavy water. Comparison between the results of these systems reveals the influence of the polarizability, or the influence of the molecular mass, on the collective dynamics. Moreover, the GCM fitting allows a quantitative description of the excitation modes in terms of the frequencies, damping coefficients and possible coupling between longitudinal and transverse modes. The differences between the three situations are also clearly evidenced within this formalism.

Spectroscopic properties under vibrational strong coupling in disordered matter from path-integral Monte Carlo simulations.

Vibrational strong coupling (VSC), the strong coupling between a Fabry-Perrot cavity and molecular vibrations at mid-infrared frequencies, has received important attention in the last years due to its capacity of modifying both vibrational spectra and chemical reactivity. VSC is a collective effect, and in this work, we introduce Path Integral Monte Carlo (PIMC) simulations that not only take into account the quantum character of the molecular vibrations and of the optical resonance of the cavity but also reproduce this collective behavior by considering multiple replicas of the molecular system. Moreover, we show that it is possible to extract from the PIMC simulations the decomposition of the hybrid optical and molecular states in terms of the bare molecular modes. On a model system of an ensemble of disordered Morse oscillators coupled to a single cavity through the Pauli-Fierz Hamiltonian, PIMC can retrieve known features obtained from analytical modes such as the Tavis-Cummings model and obtain a very close agreement with exact diagonalization for a small number of Morse oscillators. We also find that notwithstanding the anhamonic character of the Morse oscillators, the collective mode coupled to the cavity behaves as a harmonic oscillator, following the quantum central limit theorem.

Designing and Validating a Survey for National-Level Data During the COVID-19 Pandemic in Sri Lanka: Cross-Sectional Mobile Phone Surveys.

The COVID-19 pandemic has generated a demand for timely data, resulting in a surge of mobile phone surveys for tracking the impacts of and responses to the pandemic. Mobile phone surveys have become a preferred mode of data collection across low- and middle-income countries. This study piloted 2 population-based, cross-sectional mobile phone surveys among Sri Lankan residents in 2020 and 2021 during the COVID-19 pandemic. The surveys aimed to gather data on knowledge, attitudes, and practices, vaccine acceptability, availability, and barriers to COVID-19 testing, and use of a medicine distribution service. The study used Surveda, an open-source survey tool developed by the NCD (noncommunicable disease) Mobile Phone Survey Data 4 Health Initiative, for data collection and management. The surveys were conducted through interactive voice response using automated, prerecorded messages in Sinhala, Tamil, and English. The sample design involved random sampling of mobile phone numbers, stratified by sex, proportional to the general population. Eligibility criteria varied between surveys, targeting adults aged 35 years and older with any noncommunicable disease for the first survey and all adults for the second survey. The data were adjusted to population estimates, and statistical analysis was conducted using SAS (SAS Institute) and R software (R Core Team). Descriptive statistics, Rao-Scott chi-square tests, and z tests were used to analyze the data. Response rates, cooperation rates, and productivity of the sampling approach were calculated. In the first survey, n=5001, the overall response rate was 7.5%, with a completion rate of 85.6%. In the second survey, n=1250, the overall response rate was 10.9%, with a completion rate of 61.9%. Approximately 3 out of 4 adults reported that they avoided public places (888/1175, 75.6%), more than two-thirds avoided public transportation (808/1173, 68.9%), and 9 out of 10 practiced physical distancing (1046/1167, 89.7%). Approximately 1 out of 10 Sri Lankan persons reported being tested for COVID-19, and the majority of those received a polymerase chain reaction test (112/161, 70%). Significantly more males than females reported being tested for COVID-19 (98/554, 17.8% vs 61/578, 10.6%, respectively; P<.001). Finally, the majority of adult Sri Lankan people reported that they definitely or probably would get the COVID-19 vaccination (781/1190, 65.7%). The surveys revealed that, overall, the adult Sri Lankan population adhered to COVID-19 mitigation strategies. These findings underscore the use of mobile phone surveys in swiftly and easily providing essential data to inform a country's response during the COVID-19 pandemic, obviating the need for face-to-face data collection.

UAV-Enabled Diverse Data Collection via Integrated Sensing and Communication Functions Based on Deep Reinforcement Learning

Unmanned aerial vehicles (UAVs) and drones are considered to represent a flexible mobile aerial platform to collect data in various applications. However, the existing data collection methods mainly consider uplink communication. The burgeoning development of integrated sensing and communication (ISAC) provides a new paradigm for data collection. A diverse data collection framework is established where the uplink communication and sensing functions are both considered, which can also be referred to as the uplink ISAC system. An optimization is formulated to minimize the data freshness indicator for communication and the detection freshness indicator for sensing by optimizing the UAV paths, the transmitted power of IoT devices and UAVs, and the transmission allocation indicators. Three state-of-the-art deep reinforcement learning (DRL) algorithms are utilized to solve this optimization. Experiments are conducted in both single-UAV and multi-UAV scenarios, and the results demonstrate the effectiveness of the proposed algorithms. In addition, the proposed algorithms outperform the benchmark in terms of accuracy and efficiency. Moreover, the effectiveness of the data collection mode with only communication or sensing functions is also verified. Also, the numerical Pareto front between communication and sensing performance is obtained by adjusting the importance parameter.

Urine Contamination Prevalence Using a Midstream Collection Device Compared with Clean Voided Collections in Dogs.

Collecting clean-caught voided urine samples is minimally invasive, but contamination occurs when urine passes through the nonsterile urethra and external genitalia. Discarding the initial urine stream may reduce these contaminants. This study hypothesized that using a midstream urine collection device would decrease bacterial and cellular contamination as compared with cleanly caught voided urine. This descriptive cross-sectional study collected urine from dogs using standard clean-caught (SCC), midstream collection device (MCD), and cystocentesis (CYS) techniques. Urinalysis and aerobic urine culture characteristics were recorded with each characteristic's prevalence described using percentages and 95% confidence intervals for each mode of collection. Positive urine culture prevalence did not differ between SCC and MCD (adjusted P value = .099); however, CYS had a lower prevalence compared with SCC and MCD (adjusted P values of <.001 [CYS versus SCC] and 0.009 [CYS versus MCD]). For other variables, there was no difference in prevalence when comparing SCC with MCD. There was no identified advantage to collecting urine using an MCD as compared with the SCC technique. Either option is a suitable alternative when CYS is not practical; however, clinicians need to interpret results cautiously because bacterial contamination is more common as compared with CYS.

Correlation Between Microscopic Current Fluctuations Observed at Ultra-Microelectrodes and Macroscopic Bulk Electrolysis Performance in Redox-Active Microemulsions

Microemulsions (μEs) have been proposed as redox flow battery (RFB) electrolytes that maximize ionic conductivity and charge capacity by synergizing two immiscible phases. However, charge transfer during electrolysis in μEs is poorly understood. Here, we show that ultramicroelectrode electrolysis of ferrocene-loaded μEs −20%, 60%, and 90% water - reveals stochastic current fluctuations. These are differentiated in the scanning electrochemical microscopy (SECM) geometry, where power spectral density analysis showed distinct changes in the frequency contributions. SECM in the substrate generation-tip collection mode showed that fluctuations arise under mass-transfer control. Significant differences in the diffusion coefficient of ferrocene species were deducted from SECM approach curves, suggesting phase transfer behavior. Using bulk electrolysis, we calculated the charge accessibility and cycling behavior in the μEs. A decrease in the stochastic behavior of the μEs seems to correlate to a higher accessibility and cycling performance, with the 90% water μE displaying the best reversibility and the 60% the lowest. Altogether, these results suggest that Marangoni-type convection driven by concentration gradients and/or μE restructuring during charge transfer play a role in the electrochemical performance of μEs. This presents opportunities for screening and diagnosing the performance of these emerging RFB electrolytes.

Characteristics of web-based and paper-based respondents in The Danish Capital Region Health Survey

Abstract Background and aim This study aims to investigate the potential impact of adopting web-only surveys on the representativeness of survey participants by examining the sociodemographic characteristics of participants in the Danish Capital Region Health Survey (DCRHS) who respond online versus those who respond using a paper-based questionnaire. Methods The study utilizes data from the DCRHS including participants invited by a mixed-mode approach and given the choice to respond to a web-based or paper-based questionnaire in 2021 (N = 53,874) and 2017 (N = 51,902). Information on age and sex was obtained from national registers. Results The proportion of paper respondents decreased significantly from 18% in 2017 to 16% in 2021. In both years, women had higher odds of responding on paper compared with men (OR = 1.20; 95% CI: 1.16-1.24). In 2017, the highest prevalence of paper respondents was observed among participants aged ≥80 (29%) and 16-24 years (21%). In 2021, the highest prevalence was likewise observed among participants aged ≥80 (28%) but with the second highest among the 65-79 years age group (17%). The decrease in paper responses from 2017 to 2021 varied across age groups, with a greater decrease among younger participants than among older participants. Conclusions This study highlights the potential risk of excluding a significant proportion of elderly citizens from large population surveys if the web-based response option is the only option provided. Elderly individuals are less likely than younger individuals to switch to digital responses, emphasizing the importance of considering alternative modes of data collection to ensure representativeness in survey samples. Key messages • The use of web-only surveys has increased; however, we risk excluding a significant proportion of elderly citizens from large population surveys if only the web-based response option is provided. • Elderly individuals are less likely to switch to digital responses, emphasizing the importance of considering alternative modes of data collection to ensure representativeness in survey samples.

Are answers affected by data collection on paper or online? The case of Belgian adolescents

Abstract Background In the early 2000s, the prevalence estimations were compared in relation with the mode of data collection, i.e. paper or online. Following the widely spread routine use of connected devices, especially in adolescents, such a monitoring is of interest. Within the 2022 “Health Behaviour in school-aged children” survey in French-speaking primary and secondary schools of Belgium, those participating could choose between paper and online collection. Our objective was to compare a large set of indicators between the two modes after adjusting for the students’ characteristics. Methods After a two-stage random selection of schools and classes, 11,751 10-to-20-year-old adolescents completed the questionnaire either on paper or online. Descriptive analysis and comparisons were conducted using chi2 and multiple logistic regressions adjusted for the students’ sociodemographic characteristics that may vary according to the questionnaire mode. Results Overall, 54.9% of the questionnaires were completed online. The choice of the collection mode provided to the schools’ headteachers was associated with the adolescents’ characteristics. Those who completed the questionnaire online were more likely to be in secondary schools, in Wallonia, and of a more favourable socioeconomic profile. After adjustments, no difference in the indicators regarding health, well-being, substance use, or sleep duration was observed. Conversely, a difference was observed for screen time (internet ≥2h/weekday: 70.4% on paper vs. 72.3% online; adjusted P-value: 0.02), some food groups (daily vegetables: 51.2% vs. 58.0%; P-value&amp;lt;0.001) and body weight status (overweight including obesity: 16.7% vs. 14.0%; P-value&amp;lt;0.001). Conclusions In some circumstances such as data collection in the school setting, mixed modes are still necessary due to operational issues. While most indicators did not show a difference between online and paper collection, potential implications for others need to be further understood. Key messages • Collecting data through online or paper questionnaires does not lead to major differences in prevalence estimates. • With the rise of online surveys, further assessment is required to understand the potential declaration biases.

Electronic interactions in Dirac fluids visualized by nano-terahertz spacetime interference of electron-photon quasiparticles.

Ultraclean graphene at charge neutrality hosts a quantum critical Dirac fluid of interacting electrons and holes. Interactions profoundly affect the charge dynamics of graphene, which is encoded in the properties of its electron-photon collective modes: surface plasmon polaritons (SPPs). Here, we show that polaritonic interference patterns are particularly well suited to unveil the interactions in Dirac fluids by tracking polaritonic interference in time at temporal scales commensurate with the electronic scattering. Spacetime SPP interference patterns recorded in terahertz (THz) frequency range provided unobstructed readouts of the group velocity and lifetime of polariton that can be directly mapped onto the electronic spectral weight and the relaxation rate. Our data uncovered prominent departures of the electron dynamics from the predictions of the conventional Fermi-liquid theory. The deviations are particularly strong when the densities of electrons and holes are approximately equal. The proposed spacetime imaging methodology can be broadly applied to probe the electrodynamics of quantum materials.