Direct Mode Research Articles

Machine-learning assisted molecular formula assignment to high-resolution mass spectrometry data of dissolved organic matter

High-resolution mass spectrometry (HRMS) provides molecular compositional information of dissolved organic matter (DOM) through isotopic assignment from the molecular mass. However, due to the inevitable deviation of molecular mass measurement and the limitation of resolving power, multiple possible solutions frequently occur for a given molecular mass. Lowering the mass deviation threshold and adding assignment restriction rules are often applied to exclude the incorrect solutions, which generally involves time-consuming manual post-processing of mass data. To improve the result accuracy in an automated manner, we developed a molecular formula assignment algorithm based on machine-learning technology. The method integrated a logistic regression model using manually corrected isotopic composition and the peak features of HRMS data (m/z, signal-to-noise ratio, isotope type, and number, etc.) as training data. The developed model can evaluate the correctness of a candidate formula for the given mass peak based on the peak features. The method was verified by various DOM samples FT-ICR MS data (direct infusion negative mode electrospray), achieving a ∼90% accuracy (compared to the traditional approach) for formula assignment. The method was applied to a series of NOM samples and showed a significant improvement in formula assignment compared with the mass matching method.

Drone-Based Emergent Distribution of Packages to an Island from a Land Base

An island logistics system is vulnerable in emergency conditions and even isolated from land logistics. Drone-based distribution is an emerging solution investigated in this study to transport packages from a land base to the islands. Considering the drone costs, drone landing platforms in islands, and incorporation into the island ground distribution system, this study categorizes the direct, point-to-point, and cyclic bi-stage distribution modes: in the direct mode, the packages are distributed from the drone base station to the customers directly by drones; in the point-to-point mode, the packages are transported to the drone landing platform and then distributed to the customers independently; in the cyclic mode, the packages are distributed from a drone landing platform by a closed route. The modes are formulated, and evaluation metrics and solution methods are developed. In the experiments based on an island case, the models and solution methods are demonstrated, compared, and analyzed. The cyclic bi-stage distribution mode can improve drone flying distance by 50%, and an iterative heuristic algorithm can further improve drone flying distance by 27.8%, and the ground costs by 3.16%, average for the settings of twenty to sixty customers and two to four drone landing platforms. Based on the modeling and experimental studies, managerial implications and possible extensions are discussed.

Real-time data processing for ultrafast X-ray computed tomography using modular CUDA based pipelines

In this article, a new version of the Real-time Image Stream Algorithms (RISA) data processing suite is introduced. It now features online detector data acquisition, high-throughput data dumping and enhanced real-time data processing capabilities. The achieved low-latency real-time data processing extends the application of ultrafast electron beam X-ray computed tomography (UFXCT) scanners to real-time scanner control and process control. We implemented high performance data packet reception based on data plane development kit (DPDK) and high-throughput data storing using both hierarchical data format version 5 (HDF5) as well as the adaptable input/output system version 2 (ADIOS2). Furthermore, we extended RISA's underlying pipelining framework to support the fork-join paradigm. This allows for more complex workflows as it is necessary, e.g. for online data processing. Also, the pipeline configuration is moved from compile-time to runtime, i.e. processing stages and their interconnections can now be configured using a configuration file. In several benchmarks, RISA is profiled regarding data acquisition performance, data storage throughput and overall processing latency. We found that using direct IO mode significantly improves data writing performance on the local data storage. We could further prove that RISA is now capable of concurrently receiving, processing and storing data from up to 768 detector channels (3072 MB/s) at 8000 fps on a single-GPU computer in real-time. Program summaryProgram Title: GLADOS/RISACPC Library link to program files:https://doi.org/10.17632/65sx747rvm.2Developer's repository link:https://codebase.helmholtz.cloud/risaLicensing provisions: Apache-2.0Programming language: C++Journal reference of previous version: Comput. Phys. Commun. 219 (2017) 353-360 [1]Does the new version supersede the previous version?: Yes.Reasons for the new version: Extended capabilities for real-time operation with latest UFXCT hardware.Summary of revisions: (i) Add forking and joining of processing pipeline branches(ii) Add runtime (re-)configuration of pipeline stages and connections(iii) Add UDP receiver stage to acquire detector data in real-time(iv) Add high-throughput data dumpingNature of problem: Ultrafast electron beam X-ray computed tomography scanners stream multiple Gigabytes of raw data per second via Ethernet to a control computer. Receiving the data with low latency, real-time image-based control would become possible. For this, data need to be captured from the network, stored on disk, reconstructed and post-processed concurrently. The current total data rate of up to 3072 MB/s requires high-throughput solutions for each of these tasks.Solution method: Using a pipeline scheme, RISA processes incoming raw data in distinct stages (sources, processors, sinks). These are implemented in GPU kernels and are executed concurrently to exploit data parallelism as well as task parallelism. To capture detector data, we implemented a UDP packet capturing stage based on DPDK [2] which acts as a source stage. By allowing the pipeline to fork up into multiple branches, we concurrently acquire, store and process the data. For storing these data, we use the HDF5 format [3]. We achieve the required data rates by writing in direct IO mode onto an SSD array in RAID 0 configuration.Additional comments including restrictions and unusual features: RISA provides a set of general-purpose processing stages which are suitable for generic image stream processing.

Analyzing animal escape data with circular nonparametric multimodal regression

Analyzing the escape direction of animals subject to covariates is a problem that requires statistical techniques beyond classical regression methods. Apart from the periodicity of the angle of direction, which demands the use of circular statistics, animal escape data usually call for the exploration of the preferred orientations rather than the expected orientation. In this paper we propose the use of a nonparametric method to estimate the conditional local modes of the escape directions of animals from a regression perspective. We present the estimation algorithms and study the asymptotic properties of the estimators as well as its finite sample performance through some simulation experiments. Our proposal is used to model the escape behavior of a group of larval zebrafish escaping from a robot predator. More broadly, the approach presented in this paper can be applied to many existing problems related to animal behavior or other fields.

Performance Analysis of the Cylinder Gas Film Seal between Dual-Rotor Reverse Shafts Considering Lubrication and Centrifugal Expansion Effects

The cylinder gas film seal between dual-rotor reverse shafts is a new method for sealing aircraft engines that has excellent developmental prospects. We propose a novel method for determining if the sealing ring is fully fluid-lubricated using the average Reynolds equation. Considering surface roughness and centrifugal expansion, we calculated the dynamic pressure, gas film force and friction power consumption with and without inlet pressure differences for each of the four rotation modes. The gas film’s dynamic pressure effects were weakest when the dual rotors rotated in a reverse direction (Mode 3), with or without differences in inlet pressure, since solid contact is most likely to occur under counter-rotation. When the dual rotors were in counter-rotation with an inlet differential pressure of 80 kPa and fixed inner and outer rotor speeds (e.g., 3000 rpm), we calculated the minimum sealing ring film thickness, leakage rate, friction power consumption and gas film force. Changes in outer rotor speed greatly influenced the minimum film thickness and the sealing ring’s performance. Meanwhile, changes in the inner rotor speed had little influence on the minimum film thickness and sealing ring’s lubrication performance. When the speed difference was fixed and the sealing ring was fully fluid-lubricated, lubrication performance changes were mainly affected by changes in centrifugal expansion caused by the outer rotor speed. Given a fixed rotor speed and under dual-rotor counter-rotation, we calculated the effects of inlet differential pressure changes on minimum gas film thickness, leakage rate, friction power consumption, gas film force and other sealing performance variables. Leakage rate and the friction power consumption increase as inlet differential pressure increases. Our results provide a theoretical reference for avoiding solid contact of the cylinder seal between dual-rotor reverse shafts.

Activated carbon supported nickel catalyst for selective CO2 hydrogenation to synthetic methane under contactless induction heating

The use of CO2 methanation in the power-to-gas (PtG) technology chains has received increasing attention in recent years for clean energy and sustainable development. In this work, macroscopic mesoporous nickel catalyst was prepared and evaluated for selective CO2 hydrogenation to CH4 using commercial activated carbon (AC) pellets. Catalyst samples were fully characterized by liquid N2 adsorption-desorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), scanning and transmission electron microscopy (SEM/TEM). Catalytic performances were investigated under various reaction conditions with both direct induction heating (IH) and conventional indirect Joule heating (JH) modes. Results indicated that by simple thermal treatment, the surface and textural properties of the macroscopic carbon support could be greatly modified by improving the dispersion of metal sites and thus the catalytic performance. The advantages of IH combined with the inherent high thermal and electrical conductivity of the prepared materials could effectively avoid the temperature runaway and enhance the CO2 activation at relatively low reaction temperature. By comparison to the classical indirect JH mode, the resulting macroscopic nickel catalysts showed improving catalytic performances for CO2 methanation under IH mode. The efficient heat management under direct IH mode also prevented coke formation on the catalyst surface which contributes to its high stability as a function of time-on-stream.

Bacillus vallismortis TU-Orga21 blocks rice blast through both direct effect and stimulation of plant defense.

Beneficial microorganisms are an important strategy for sustainable plant production processes such as stimulate root exudation, stress tolerance, and yield improvement. This study investigated various microorganisms isolated from the rhizosphere of Oryza sativa L. in order to inhibit Magnaporthe oryzae cause of rice blast, by direct and indirect mode of action. The results indicated that Bacillus vallismortis strain TU-Orga21 significantly reduced M. oryzae mycelium growth and deformed the hyphal structures. The effects of biosurfactant TU-Orga21 was studied against M. oryzae spore development. The dose of ≥5% v/v biosurfactant significantly inhibited the germ tubes and appressoria formation. The biosurfactants were evaluated as surfactin and iturin A by Matrix-assisted laser desorption ionization dual time-of-flight tandem mass spectrometry. Under greenhouse conditions, priming the biosurfactant three times before M. oryzae infection significantly accumulated endogenous salicylic acid, phenolic compounds, and hydrogen peroxide (H2O2) during the infection process of M. oryzae. The SR-FT-IR spectral changes from the mesophyll revealed higher integral area groups of lipids, pectins, and proteins amide I and amide II in the elicitation sample. Furthermore, scanning electron microscope revealed appressorium and hyphal enlargement in un-elicitation leaves whereas appressorium formation and hyphal invasion were not found in biosurfactant-elicitation at 24h post inoculation. The biosurfactant treatment significantly mitigated rice blast disease severity. Therefore, B. vallismortis can be a promising novel biocontrol agent which contains the preformed active metabolites for a rapid control of rice blast by a direct action against pathogen and by boosting plant immunity.

Analysis of large deformation of deep water drilling riser considering vortex-induced vibration

In this study, a dynamic model for large deformation of deepwater drilling riser considering vortex-induced vibration (VIV) and actual ocean load was established. Nonlinear Van der Pol equation was used to simulate the VIV. The model was discretized by finite element method and solved by Newmark-β method. The dynamic characteristics of the riser under different marine environments and working conditions were analyzed. Results show that the force on the flow direction of the riser adds the pulsating drag term, which increases the riser deformation, after VIV is considered. The riser deflection and bending moment increase with the rise in surface velocity, decrease with the increment in top tension, and slightly change with the increase in wind speed and drilling fluid displacement. The rise in surface wind speed will increase the vibration mode and frequency of riser flow direction, while the increment in top tension will decrease the vibration mode and keep the vibration frequency unchanged. Wind speed and drilling fluid displacement slightly influence the riser deflection.

Aflatoxin M1 degradation using high voltage atmospheric cold plasma (HVACP) technology

ABSTRACT Aflatoxins are one of the highly toxic secondary metabolites with high decomposition temperatures, ranging from 237 °C to 306 °C. Therefore, non-thermal treatments are preferred to ensure safe food while preserving food quality. High voltage atmospheric cold plasma (HVACP) is a novel non-thermal technology with the potential to reduce contaminants (e.g. mycotoxins) owing to reactive species such as ozone. Therefore, the aim of this study was to investigate the efficacy of HVACP to degrade Aflatoxin M1 (AFM1) in pure water. A dielectric barrier discharge HVACP was performed at 90 kV using modified air (MA65: 65% O2, 30% CO2, 5% N2) fill gas for 1, 3, and 5 min in a direct and indirect mode with no post-treatment or 4.0 h post-storage at room temperature. The chemical properties of water were evaluated. Ozone concentration in both gas and liquid phases was also measured. A 77% reduction of AFM1 was observed after 1 min of direct treatment with no post-treatment storage. The nitrate and peroxide contents after 1 min of direct treatment were 4.50 ± 0.70 and 9.5 ± 0.70 mg/L, respectively. Longer treatment time and direct mode of exposure resulted in a higher ozone concentration in either the gas or liquid phase. These results demonstrate the potential of HVACP as a non-thermal treatment for reducing AFM1 concentration. HVACP was capable of significantly degrading AFM1 using a very short treatment time and 4.0-h post-treatment storage.

Constant current-exponential attenuation mode: A non-traditional power supply mode for electrocatalytic oxidation

Low average current efficiency (ACE) and high energy consumption (EC) have seriously hindered the industrial development of electrocatalytic oxidation (ECO) technology. Timely adjustment of the current output according to the attenuation law of the organic pollutants concentration during the reaction process can help to solve the low electrical energy utilization problem at source. In this study, a non-traditional power supply mode with “constant current-exponential attenuation” (Mode CC-EA) was proposed and applied to intermittent ECO systems. The current is first output in a constant state and then attenuated exponentially according to the decreasing law of pollutants concentration, enabling efficient use of electrons at all stages of the reaction, resulting in increased degradation rates and ACE, and reduced EC. Acidic red G (ARG) was used as the target pollutant and the degradation effects of the traditional constant current mode (Mode CC), the direct exponential attenuation mode (Mode EA) and the Mode CC-EA were compared with different evaluation parameters. The results showed that the optimized Mode EA (n4) and Mode CC-EA (70-n11) degraded ARG with an ACE of 5.28 and 6.09%, respectively, which were 1.26 and 1.45 times higher than Mode CC (4.2%). At the same time, the EC were 0.36 and 0.27 kWh gCOD−1, respectively, which were 12.2 and 34.2% lower than Mode CC (0.41 kWh gCOD−1). The parameters of Mode CC-EA were further optimized and used for the degradation of three typical dye wastewaters, crystal violet (CV), methylene blue (MB) and methyl orange (MO), to investigate their general applicability. The results showed that the optimized Mode CC-EA achieved higher decolorization rates, chemical oxygen demand (COD) and total organic carbon (TOC) removal rates for the four wastewaters, including ARG, than Mode CC within 120 min for the same total input charge. The ACE of Mode CC-EA was on average 1.3 times higher than that of Mode CC, while the EC was on average 25.3% lower. Mode CC-EA achieves efficient use of electrical energy while ensuring the catalytic effect, which is of great application for the efficient treatment of dye wastewater and significance for the industrial development of ECO technology.

Numerical simulation on the shock wave focusing detonation process in the semicircle reflector

Shock wave focusing is considered a new type of initiation method that does not require external ignition devices. For this method, understanding the shock wave/flame interaction accurately is one of the critical issues for revealing the ignition and triggering mechanisms during shock wave focusing processes. In this study, numerical simulations were carried out to investigate the detailed flow field evolution of the focusing process with kerosene as fuel. Two detonation initiation modes were found during the shock wave focusing processes, which were the direct initiation mode and the reflected shock wave collision initiation mode, respectively. At the detonation wave propagation stage, the primary detonation wave decouples and fails to propagate out of the cavity. The multiple initiation phenomenon occurs in the cavity, and it dominated detonation waves to propagate outside of the cavity to accomplish one thermal cycle. There is no positive correlation between jet temperature and detonation wave propagation velocity. When the jet temperature is low, the detonation wave velocity dominated by the multiple initiation mode is the fastest. The analysis of the shock wave focusing process under different jet velocities showed that when the jet velocity was lower than 2 Ma, the decoupling of the primary detonation wave failed to induce multiple detonation waves. Driven by the vortex in the semicircular cavity, the flame is almost stationary, which means the failure of the detonation wave propagation process.

Autonomic self-regulating systems based on polyelectrolyte microcapsules and microgel particles

Biological systems possess unique non-equilibrium functions, maintaining tight manipulation of their surroundings through inter-communication of multiple components and self-regulatory capability organized over different length scales. However, most artificial materials are incapable of communicating and self-regulating behavior due to their limited number of component and direct responsive modes. Herein, a new integrated self-regulation system is developed utilizing stimuli-responsive polyelectrolyte capsules as building blocks. The combination of stimuli-responsive capsules and enzyme immobilized microgels is designed to mimic life systems and its programmable interactive communications and self-regulation behavior is demonstrated through communication-feedback mechanism. Polyelectrolyte capsules can sense changes of their surrounding, then start the internal communication by releasing energy-rich cargo mimicking the behavior of the cells. The microgel particles subsequently complete closed-loop communication through providing negative feedback on capsules by enzymatic reaction and actuating pH-regulation of the whole system. Different communication modes and pH-regulation behaviors could be achieved by adjusting spatial and kinetic conditions. Proposed intelligent system is highly customizable due to the wide selection of encapsulated cargos, stimuli-responsive blocks and reaction networks, and would have broad influences in areas ranging from medical implants that assist in stabilizing body functions to microreactor system that regulate catalytic reactions.

Antimicrobial Activity of Quercetin, Naringenin and Catechin: Flavonoids Inhibit Staphylococcus aureus-Induced Hemolysis and Modify Membranes of Bacteria and Erythrocytes.

Search for novel antimicrobial agents, including plant-derived flavonoids, and evaluation of the mechanisms of their antibacterial activities are pivotal objectives. The goal of this study was to compare the antihemolytic activity of flavonoids, quercetin, naringenin and catechin against sheep erythrocyte lysis induced by α-hemolysin (αHL) produced by the Staphylococcus aureus strain NCTC 5655. We also sought to investigate the membrane-modifying action of the flavonoids. Lipophilic quercetin, but not naringenin or catechin, effectively inhibited the hemolytic activity of αHL at concentrations (IC50 = 65 ± 5 µM) below minimal inhibitory concentration values for S. aureus growth. Quercetin increased the registered bacterial cell diameter, enhanced the fluidity of the inner and surface regions of bacterial cell membranes and raised the rigidity of the hydrophobic region and the fluidity of the surface region of erythrocyte membranes. Our findings provide evidence that the antibacterial activities of the flavonoids resulted from a disorder in the structural organization of bacterial cell membranes, and the antihemolytic effect of quercetin was related to the effect of the flavonoid on the organization of the erythrocyte membrane, which, in turn, increases the resistance of the target cells (erythrocytes) to αHL and inhibits αHL-induced osmotic hemolysis due to prevention of toxin incorporation into the target membrane. We confirmed that cell membrane disorder could be one of the direct modes of antibacterial action of the flavonoids.

Psychologically informed health care.

The term "psychologically informed health care" refers to the comprehensive integration of psychological principles into health care. Psychologically informed health care has the potential to lead to a transformation of care, resulting in truly transdisciplinary care. To facilitate its future development, we discuss key characteristics of this approach. These include the direct mode (psychologists assessing and treating patients themselves) and indirect mode (psychologists working through other health care providers) of integrating psychological principles into healthcare; the range of health domains targeted using this approach; transdisciplinary care, transcending traditional disciplinary boundaries; and the positioning of care. We describe a framework for transdisciplinary care, which we refer to as the Framework for Catalytic Collaboration. This framework comprises six dimensions: setting, disciplines, patients/clients, mode of psychological care, primary components of care, and primary targets of care. We also provide four brief illustrations of psychologically informed health care. Finally, we discuss future directions, including the need for professional recognition of the indirect mode, financing of the indirect mode, cross-disciplinary training and trans-disciplinary research.

Scenes of subjection: Extractive frontiers, symbolic violence, dispossession

This article discusses how, besides structural and direct modes of violence traditionally attributed to natural resource exploitation, extractive frontiers also unfold through material and affective registers of symbolic violence. This concerns the violence of capital that promises a “better life” whose actual realisation, directly implicated in circuits of “free” market economy, is constantly deferred to the future. Empirically grounded in experiences of dispossession and resettlement caused by coal extraction in Tete, Mozambique, the article employs symbolic violence as an analytic to understand subjectivation constituted by the failed promise of “development” of Tete’s extractive frontier. This, the article argues, results in specific scenes of subjection – exposure to the symbolic violence of extractivism, as well as potential contestations of it, through which those dispossessed by mining come into being as subjects of power. These scenes of subjection are temporal: they transform –expand, flutter, retreat – reflecting broader, inherently unstable economies of extraction. As such, subjection to violence is not final but remains susceptible to contestation, mediation, or escalation. Nevertheless, the article shows how, in spite of this potentiality of change, until recently, in Tete symbolic violence had justified, reproduced, and sustained the power of extractivism, as well as of capital more broadly, even within the lifeworlds dispossessed, or otherwise laid to waste, by extractive frontiers of capital.

Frequency-Based Adaptive Interpolation Filter in Intra Prediction

This paper proposes a method to improve the fractional interpolation of reference samples in the Versatile Video Coding (VVC) intra prediction. The proposed method uses additional interpolation filters which use more integer-positioned reference samples for prediction according to the frequency information of the reference samples. In VVC, a 4-tap Discrete Cosine Transform-based interpolation filter (DCT-IF) and 4-tap Smoothing interpolation filter (SIF) are alternatively performed on the block size and block directional prediction mode for reference sample interpolation. This paper uses four alternative interpolation filters such as 8-tap/4-tap DCT-IFs, and 4-tap/8-tap SIFs and an interpolation filter selection method using a high-frequency ratio calculated from one-dimensional (1D) transform of the reference samples are proposed. The proposed frequency-based Adaptive Filter allows to achieve the overall Bjøntegaard Delta (BD) rate gains of −0.16%, −0.13%, and −0.09% for Y, Cb, and Cr components, respectively, compared with VVC.

Improving throughput in SWIPT-based wireless multirelay networks with relay selection and rateless codes

This paper studies a dual-hop Simultaneous Wireless Information and Power Transfer (SWIPT)-based multi-relay network with a direct link. To achieve high throughput in the network, a novel protocol is first developed, in which the network can switch between a direct transmission mode and a Single-Relay-Selection-based Cooperative Transmission (SRS-CT) mode that employs dynamic decode-and-forward relaying accomplished with Rateless Codes (RCs). Then, under this protocol, an optimization problem is formulated to jointly optimize the network operation mode and the resource allocation in the SRS-CT mode. The formulated problem is difficult to solve because not only does the noncausal Channel State Information (CSI) cause the problem to be stochastic, but also the energy state evolution at each relay is complicated by network operation mode decision and resource allocation. Assuming that noncausal CSI is available, the stochastic optimization issue is first to be addressed by solving an involved deterministic optimization problem via dynamic programming, where the complicated energy state evolution issue is addressed by a layered optimization method. Then, based on a finite-state Markov channel model and assuming that CSI statistical properties are known, the stochastic optimization problem is solved by extending the result derived for the noncausal CSI case to the causal CSI case. Finally, a myopic strategy is proposed to achieve a tradeoff between complexity and performance without the knowledge of CSI statistical properties. The simulation results verify that our proposed SRS-and-RC-based design can achieve a maximum of approximately 40% throughput gain over a simple SRS-and-RC-based baseline scheme in SWIPT-based multi-relay networks.

Topologically protected plasmonic phases in randomized aperture gratings

We experimentally show the excitation of surface plasmons by topologically protected diffraction from gratings with randomized periodicity. The structures are designed such that the plasmonic excitation is conditioned by the proper combination of the geometric and the dynamic phases. Accordingly, it is possible to obtain a precise interaction of the incident light signal and a specific plasmonic directional mode in a polarization dependent manner.

Evaluation of the Performance of a Direct Mode Solar Dryer of Local Manufacture: Application to Plantain

This study focused on the evaluation of the performance of a direct solar dryer designed at the National Institute of Research in Engineering Sciences, Innovation and Technology. It aims to contribute to the reduction of post-harvest losses of agro-resources in Congo through the conservation and manufacture of new food products. Plantain (<i>Musa AAB x paradisiaca</i>) of the Agnrin variety was used as raw material. The method used was that of dimensioning the dryer, evaluating its performance to assess its capacity and also to characterize physically and chemically the banana flour obtained. The results obtained revealed that the dryer temperature was higher than the ambient temperature 86.18% on average throughout the day, at the end of the day, the temperature reached 96.88% in three hours of time shortly before noon. The drying rate and efficiency of the system were 0.1106 kg/h and 44.1% respectively. The rapid drying rate in the dryer revealed the ability to dry the food quickly to a moisture content of 34%. The analyses led to the rates of 2.23±0.39%; 0.51±0.059%; 0.5±0.0%; 9.81±0.37%; 14.4±0.11% and 82.36±0.0% in protein, ash, lipids, soluble sugars, moisture and total sugars respectively. The low water content guarantees a longer shelf life and the ash content allows the flour to be classified as type 55.

Hierarchical Mapping for Efficient Simulation of Strong System-Environment Interactions.

Quantum dynamics (QD) simulation is a powerful tool for interpreting ultrafast spectroscopy experiments and unraveling their microscopic mechanism in out-of-equilibrium excited state behaviors in various chemical, biological, and material systems. Although state-of-the-art numerical QD approaches such as the time-dependent density matrix renormalization group (TD-DMRG) already greatly extended the solvable system size of general linearly coupled exciton-phonon models with up to a few hundred phonon modes, the accurate simulation of larger system sizes or strong system-environment interactions is still computationally highly challenging. Based on quantum information theory (QIT), in this work, we realize that only a small number of effective phonon modes couple to the excitonic system directly regardless of a large or even infinite number of modes in the condensed phase environment. On top of the identified small number of direct effective modes, we propose a hierarchical mapping (HM) approach through performing block Lanczos transformations on the remaining indirect modes, which transforms the Hamiltonian matrix to a nearly block-tridiagonal form and eliminates the long-range interactions. Numerical tests on model spin-boson systems and realistic singlet fission models in a rubrene crystal environment with up to 7000 modes and strong system-environment interactions indicate HM can reduce the system size by 1-2 orders of magnitude and accelerate the calculation by ∼80% without losing accuracy.