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Corrêa, Raul, Marina F. B. Cenni y Pablo L. Saldanha. "Quantum Interference of Force". Quantum 2 (14 de diciembre de 2018): 112. http://dx.doi.org/10.22331/q-2018-12-14-112.
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We show that a quantum particle subjected to a positive force in one path of a Mach-Zehnder interferometer and a null force in the other path may receive a negative average momentum transfer when it leaves the interferometer by a particular exit. In this scenario, an ensemble of particles may receive an average momentum in the opposite direction of the applied force due to quantum interference, a behavior with no classical analogue. We discuss some experimental schemes that could verify the effect with current technology, with electrons or neutrons in Mach-Zehnder interferometers in free space and with atoms from a Bose-Einstein condensate.
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Chen, Yan, Rolf J. Lorentzen y Erlend H. Vefring. "Optimization of Well Trajectory Under Uncertainty for Proactive Geosteering". SPE Journal 20, n.º 02 (28 de agosto de 2014): 368–83. http://dx.doi.org/10.2118/172497-pa.
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Summary Various logging-while-drilling (LWD) and seismic-while-drilling (SWD) tools offer opportunities to obtain geological information near the bottomhole assembly during the drilling process. These real-time in-situ data provide relatively high-resolution information around and possibly ahead of the drilling path compared with the data from a surface seismic survey. The use of these in-situ data offers substantial potential for improved recovery through continuous optimization of the remaining well path while drilling. We show an automated workflow for proactive geosteering through continuous updating of the estimates of the Earth model and robust optimization of the remaining well path under uncertainty. A synthetic example is shown to illustrate the proposed workflow. The estimates of the depths of the reservoir surfaces and the depth of the oil/water contact and their associated uncertainty are obtained through the ensemble Kalman filter by use of directional-resistivity measurements. A robust optimization is used to compute the well position that minimizes the average cost function evaluated on the ensemble of geological models estimated from the ensemble Kalman filter (EnKF). The effect of modeling errors and the effect of joint estimation of the depths of the boundaries and gridblock resistivity are also investigated.
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Pinty, Jean-Pierre y Christelle Barthe. "Ensemble Simulation of the Lightning Flash Variability in a 3D Cloud Model with Parameterizations of Cloud Electrification and Lightning Flashes". Monthly Weather Review 136, n.º 1 (1 de enero de 2008): 380–87. http://dx.doi.org/10.1175/2007mwr2186.1.
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Abstract A series of ensemble simulations were performed to study the statistics of flash characteristics produced by an electrification and lightning scheme in the cloud-resolving model Méso-NH. Here, the electrical variability of two storms—one supercellular and one multicellular—results from a random triggering location of the flashes and from a branching algorithm that describes the flash path. The study shows that the electrical model is able to generate several estimates of the total flash number for an identical evolution of the dynamics and microphysics of each storm in the 120 ensemble members. The variability of the flash number spans over three standard deviations taken from the ensemble mean. The simulations produce regularly shaped distributions of flash internal parameters (i.e., number of segments and branching levels per flash). The ensemble simulation shows that the model is stable and self-regulatory as suggested by the limited overshoot on the maximum electric field time series. An application to the production of nitrogen oxides indicates that the two storms produce 200 ± 150 mol of NO per flash on average.
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Okuboyejo, Damilola A. y Oludayo O. Olugbara. "Classification of Skin Lesions Using Weighted Majority Voting Ensemble Deep Learning". Algorithms 15, n.º 12 (24 de noviembre de 2022): 443. http://dx.doi.org/10.3390/a15120443.
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The conventional dermatology practice of performing noninvasive screening tests to detect skin diseases is a source of escapable diagnostic inaccuracies. Literature suggests that automated diagnosis is essential for improving diagnostic accuracies in medical fields such as dermatology, mammography, and colonography. Classification is an essential component of an assisted automation process that is rapidly gaining attention in the discipline of artificial intelligence for successful diagnosis, treatment, and recovery of patients. However, classifying skin lesions into multiple classes is challenging for most machine learning algorithms, especially for extremely imbalanced training datasets. This study proposes a novel ensemble deep learning algorithm based on the residual network with the next dimension and the dual path network with confidence preservation to improve the classification performance of skin lesions. The distributed computing paradigm was applied in the proposed algorithm to speed up the inference process by a factor of 0.25 for a faster classification of skin lesions. The algorithm was experimentally compared with 16 deep learning and 12 ensemble deep learning algorithms to establish its discriminating prowess. The experimental comparison was based on dermoscopic images congregated from the publicly available international skin imaging collaboration databases. We propitiously recorded up to 82.52% average sensitivity, 99.00% average specificity, 98.54% average balanced accuracy, and 92.84% multiclass accuracy without prior segmentation of skin lesions to outstrip numerous state-of-the-art deep learning algorithms investigated.
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Susskind, Leonard. "De Sitter Holography: Fluctuations, Anomalous Symmetry, and Wormholes". Universe 7, n.º 12 (29 de noviembre de 2021): 464. http://dx.doi.org/10.3390/universe7120464.
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The Goheer–Kleban–Susskind no-go theorem says that the symmetry of de Sitter space is incompatible with finite entropy. The meaning and consequences of the theorem are discussed in light of recent developments in holography and gravitational path integrals. The relation between the GKS theorem, Boltzmann fluctuations, wormholes, and exponentially suppressed non-perturbative phenomena suggests that the classical symmetry between different static patches is broken and that eternal de Sitter space—if it exists at all—is an ensemble average.
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Shi, Min, Dong Dong Yang, Yuan Zhou, Huan Zhao y Yu Fang. "Analysis of Migraine Induced Monitoring Imaging Data by Multilayer Mixed Cluster Detection". Journal of Medical Imaging and Health Informatics 9, n.º 6 (1 de agosto de 2019): 1278–83. http://dx.doi.org/10.1166/jmihi.2019.2729.
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The complex network of resting brain function was constructed by graph theory to study the difference of network topology between migraine patients and normal people. The complex network of brain function of the two groups was constructed respectively, and the average clustering coefficient, characteristic path length, small cosmopolitan, homology, median centrality and other measurement parameters of the two groups of complex networks were calculated and compared. The multi-layer hybrid ensemble clustering detection is introduced for data analysis, and the edge connectivity of consensus is optimized by modular analysis combined with hill climbing algorithm to improve the performance of the multi-layer hybrid ensemble clustering detection process driven by modularity. Conclusion: The abnormal areas of resting brain function network in migraine patients are related to pain management, visual processing and sensory relay, the findings of this study are helpful to better explain the clinical symptoms of migraine.
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Mallick, Swapan. "Impact of Adaptively Thinned GOES-16 Cloud Water Path in an Ensemble Data Assimilation System". Meteorology 1, n.º 4 (5 de diciembre de 2022): 513–30. http://dx.doi.org/10.3390/meteorology1040032.
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Assimilation of cloud properties in the convective scale ensemble data assimilation system is one of the prime topics of research in recent years. Satellites can retrieve cloud properties that are important sources of information of the cloud and atmospheric state. The Advance Baseline Imager (ABI) aboard the GOES-16 geostationary satellite brings an opportunity for retrieving high spatiotemporal resolution cloud properties, including cloud water path over continental United States. This study investigates the potential impacts of assimilating adaptively thinned GOES-16 cloud water path (CWP) observations that are assimilated by the ensemble-based Warn-on-Forecast System and the impact on subsequent weather forecasts. In this study, for CWP assimilation, multiple algorithms have been developed and tested using the adaptive-based thinning method. Three severe weather events are considered that occurred on 19 July 2019, 7 May and 21 June 2020. The superobbing procedure used for CWP data smoothed from 5 to 15 km or more depending on thinning algorithm. The overall performance of adaptively thinned CWP assimilation in the Warn-on-Forecast system is assessed using an object-based verification method. On average, more than 60% of the data was reduced and therefore not used in the assimilation system. Results suggest that assimilating less than 40% of CWP superobbing data into the Warn-on-Forecast system is of similar forecast quality to those obtained from assimilating all available CWP observations. The results of this study can be used on the benefits of cloud assimilation to improve numerical simulation.
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Yang, Caipei, Yingqi Zhao, Xuan Cai, Wei Wei, Xingxing Feng y Kaibo Zhou. "Path Planning Algorithm for Unmanned Surface Vessel Based on Multiobjective Reinforcement Learning". Computational Intelligence and Neuroscience 2023 (15 de febrero de 2023): 1–14. http://dx.doi.org/10.1155/2023/2146314.
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It is challenging to perform path planning tasks in complex marine environments as the unmanned surface vessel approaches the goal while avoiding obstacles. However, the conflict between the two subtarget tasks of obstacle avoidance and goal approaching makes the path planning difficult. Thus, a path planning method for unmanned surface vessel based on multiobjective reinforcement learning is proposed under the complex environment with high randomness and multiple dynamic obstacles. Firstly, the path planning scene is set as the main scene, and the two subtarget scenes including obstacle avoidance and goal approaching are divided from it. The action selection strategy in each subtarget scene is trained through the double deep Q-network with prioritized experience replay. A multiobjective reinforcement learning framework based on ensemble learning is further designed for policy integration in the main scene. Finally, by selecting the strategy from subtarget scenes in the designed framework, an optimized action selection strategy is trained and used for the action decision of the agent in the main scene. Compared with traditional value-based reinforcement learning methods, the proposed method achieves a 93% success rate in path planning in simulation scenes. Furthermore, the average length of the paths planned by the proposed method is 3.28% and 1.97% shorter than that of PER-DDQN and dueling DQN, respectively.
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Qazvinian, Vahed y Dragomir Radev. "Exploiting Phase Transition in Latent Networks for Clustering". Proceedings of the AAAI Conference on Artificial Intelligence 25, n.º 1 (4 de agosto de 2011): 908–13. http://dx.doi.org/10.1609/aaai.v25i1.7972.
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In this paper, we model the pair-wise similarities of a setof documents as a weighted network with a single cutoffparameter. Such a network can be thought of an ensemble of unweighted graphs, each consisting of edges withweights greater than the cutoff value. We look at this network ensemble as a complex system with a temperature parameter, and refer to it as a Latent Network. Ourexperiments on a number of datasets from two different domains show that certain properties of latent networks like clustering coefficient, average shortest path,and connected components exhibit patterns that are significantly divergent from randomized networks. We explain that these patterns reflect the network phase transition as well as the existence of a community structure in document collections. Using numerical analysis,we show that we can use the aforementioned networkproperties to predicts the clustering Normalized MutualInformation (NMI) with high correlation (rho > 0.9). Finally we show that our clustering method significantlyoutperforms other baseline methods (NMI > 0.5)
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Nagao, Hidemi, Yasuteru Shigeta, Hiroyuki Kawabe, Takashi Kawakami, Kiyoshi Nishikawa y Kizashi Yamaguchi. "Path integral method by means of generalized coherent states and its numerical approach to molecular systems. I. Ensemble average of total energy". Journal of Chemical Physics 107, n.º 16 (22 de octubre de 1997): 6283–89. http://dx.doi.org/10.1063/1.474290.
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Ackerman, Andrew S., Margreet C. vanZanten, Bjorn Stevens, Verica Savic-Jovcic, Christopher S. Bretherton, Andreas Chlond, Jean-Christophe Golaz et al. "Large-Eddy Simulations of a Drizzling, Stratocumulus-Topped Marine Boundary Layer". Monthly Weather Review 137, n.º 3 (1 de marzo de 2009): 1083–110. http://dx.doi.org/10.1175/2008mwr2582.1.
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Abstract Cloud water sedimentation and drizzle in a stratocumulus-topped boundary layer are the focus of an intercomparison of large-eddy simulations. The context is an idealized case study of nocturnal stratocumulus under a dry inversion, with embedded pockets of heavily drizzling open cellular convection. Results from 11 groups are used. Two models resolve the size distributions of cloud particles, and the others parameterize cloud water sedimentation and drizzle. For the ensemble of simulations with drizzle and cloud water sedimentation, the mean liquid water path (LWP) is remarkably steady and consistent with the measurements, the mean entrainment rate is at the low end of the measured range, and the ensemble-average maximum vertical wind variance is roughly half that measured. On average, precipitation at the surface and at cloud base is smaller, and the rate of precipitation evaporation greater, than measured. Including drizzle in the simulations reduces convective intensity, increases boundary layer stratification, and decreases LWP for nearly all models. Including cloud water sedimentation substantially decreases entrainment, decreases convective intensity, and increases LWP for most models. In nearly all cases, LWP responds more strongly to cloud water sedimentation than to drizzle. The omission of cloud water sedimentation in simulations is strongly discouraged, regardless of whether or not precipitation is present below cloud base.
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Kuraptsev, A. S., I. M. Sokolov y Ya A. Fofanov. "Coherent specular reflection of resonant light from a dense ensemble of motionless point-like scatters in a slab geometry". International Journal of Modern Physics: Conference Series 41 (enero de 2016): 1660141. http://dx.doi.org/10.1142/s2010194516601411.
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We analyze resonant light scattering from a dense and disordered ensemble of motionless point-like scatters with uniform (on average) spatial distribution of the density. The average interatomic distance is considered comparable with the resonant wavelength and the mean free path of photon. The inhomogeneity of dipole-dipole interaction near the surface is discussed. Angular distribution of the light scattered from a medium in a slab geometry is calculated. The total reflected light power [Formula: see text] and the reflectivity [Formula: see text] depending on the optical thickness of a medium [Formula: see text] are analyzed. It is shown that in the case of small optical thickness ([Formula: see text]) [Formula: see text] and [Formula: see text]. With further increasing of the optical thickness we observe oscillations of the dependencies [Formula: see text] and [Formula: see text]. The attenuation coefficient of these oscillations is discussed.
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Zhao, Qingfeng y Yulin Zhang. "Ensemble Method of Feature Selection and Reverse Construction of Gene Logical Network Based on Information Entropy". International Journal of Pattern Recognition and Artificial Intelligence 34, n.º 02 (13 de junio de 2019): 2059004. http://dx.doi.org/10.1142/s0218001420590041.
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In this paper, we propose a novel ensemble gene selection method to obtain a gene subset. Then we provide a reverse construction method of gene network derived from expression profile data of the gene subset. The uncertainty coefficient based on information entropy are used to define the existence of logical relations among these genes. If the uncertainty coefficient between some genes exceeds predefined thresholds, the gene nodes will be connected by directed edges. Thus, a gene network is generated, which we define as gene logical network. This method is applied to the breast cancer data including control group and experimental group, with comparisons of the 2nd-order logic type distribution, average degree as well as average path length of the networks. It is found that these structures with different networks are quite distinct. By the comparison of the degree difference between control group and experimental group, the key genes are picked up. By defining the dynamics evolution rules of state transition based on the logical regulation among the key genes in the network, the dynamic behaviors for normal breast cells and cells with cancer of different stages are simulated numerically. Some of them are highly related to the development of breast cancer through literature inquiry. The study may provide a useful revelation to the biological mechanism in the formation and development of cancer.
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Smeets, C. J. P. P., R. Holzinger, I. Vigano, A. H. Goldstein y T. Röckmann. "Eddy covariance methane measurements at a Ponderosa pine plantation in California". Atmospheric Chemistry and Physics Discussions 9, n.º 1 (26 de febrero de 2009): 5201–29. http://dx.doi.org/10.5194/acpd-9-5201-2009.
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Abstract. Long term methane flux measurements have been mostly performed with plant or soil enclosure techniques on specific components of an ecosystem. New fast response methane analyzers make it possible to use the eddy covariance (EC) technique instead. The EC technique is advantageous because it allows continuous flux measurements integrating over a larger and more representative area including the complete ecosystem, and allows fluxes to be observed as environmental conditions change naturally without disturbance. We deployed the closed-path Fast Methane Analyser (FMA) from Los Gatos Research Ltd and demonstrate its performance for EC measurements at a Ponderosa pine plantation at the Blodgett Forest site in central California. CH4 concentrations measured at 10 Hz showed a relatively high noise level that was caused by a software related problem. Nevertheless, in the frequency range important for turbulent exchange, the cospectra of CH4 compare very well with all other scalar cospectra confirming the quality of the FMA measurements are good for the EC technique. The low-pass filtering characteristics of our closed-path system and the use of the Webb-Pearman-Leuning (WPL) corrections for a combination of open and closed-path sensors are discussed using a large ensemble of cospectra. The diurnal variation of the methane concentration was up to 60 ppbv with an average of 1843 ppbv. Concentrations increased from morning to late afternoon as upslope flow from the valley below carried polluted air to the site, and then decreased through the night as downslope flow carried cleaner air from aloft. The fluxes were consistently directed downward with a well defined diurnal pattern, averaging −35±40 ng m−2 s−1 during the daytime. The detection limit of the system was estimated at 22 ng m−2 s−1. The average CH4 deposition during the daytime was higher than the average value for warm temperate forests in a recent global inventory and the results from a process-based model study.
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Zimnyakov, Dmitry, Elena Isaeva, Anna Isaeva y Sergey Volchkov. "Band-Limited Reference-Free Speckle Spectroscopy: Probing the Fluorescent Media in the Vicinity of the Noise-Defined Threshold". Applied Sciences 10, n.º 5 (29 de febrero de 2020): 1629. http://dx.doi.org/10.3390/app10051629.
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A method of reference-free speckle spectroscopy based on the statistical analysis of intensity spatial fluctuations of the spectrally-selected multiple-scattered fluorescence radiation is examined in the case of the finite-band spectral selection of fluorescence light emitted by the laser-pumped random medium, and detection conditions far from the ideal case. Intensity fluctuations are recorded during point-to-point scanning of the surface of a random multiple-scattering medium, which is characterized by the dependences of the second- and third-order statistical moments of intensity on the wavelength of detected spectrally selected light. In turn, the statistical moments of intensity fluctuations are determined by the average propagation path of fluorescent radiation in the medium. This makes it possible to analyze the features of the light-medium interactions at a scale of the order of the transport mean free path of radiation propagation in the medium. Depending on the spectral selection conditions, the method is applicable for characterizing micro- or nano-structured fluorescent layers with thicknesses from tens of micrometers to several millimeters. In the examined case, the finite-band spectral selection results in the values of coherence length of the detected fluorescence radiation compared with the ensemble-averaged absolute value of the path-length difference between the stochastically interfering and spectrally selected partial contributions to the fluorescence field. In addition, non-ideal detection conditions (usage of a multimode optical fiber in the light-collecting unit) cause additional strong damping of the detected speckle intensity fluctuations. These factors lead to a remarkable suppression of spatial fluctuations of the fluorescence intensity in the course of spatially- and spectrally-resolved surface scanning of the laser-pumped probed random medium. Nevertheless, with appropriate procedures of the intrinsic noise reduction and data correction, the obtained spectral dependencies of the normalized third-order statistical moment of the band-limited fluorescence intensity clearly indicate the fluorescence propagation features in the probed multiple-scattering random media (such as a strong influence of the scattering strength and multiple self-absorption–re-emission events on the average propagation path of light in the medium).The possibilities of noise reduction and data correction in the case of applying the band-limited reference-free spectroscopic instrumentation with low spectral and spatial resolution are illustrated by the experimental results obtained using the Rhodamine-6G-doped and continuous wave (CW)-laser-pumped layers of the densely packed titania and silica particles.
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Wang, Jike, Dongsheng Cao, Cunchen Tang, Xi Chen, Huiyong Sun y Tingjun Hou. "Fast and accurate prediction of partial charges using Atom-Path-Descriptor-based machine learning". Bioinformatics 36, n.º 18 (2 de septiembre de 2020): 4721–28. http://dx.doi.org/10.1093/bioinformatics/btaa566.
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Abstract Motivation Partial atomic charges are usually used to calculate the electrostatic component of energy in many molecular modeling applications, such as molecular docking, molecular dynamics simulations, free energy calculations and so forth. High-level quantum mechanics calculations may provide the most accurate way to estimate the partial charges for small molecules, but they are too time-consuming to be used to process a large number of molecules for high throughput virtual screening. Results We proposed a new molecule descriptor named Atom-Path-Descriptor (APD) and developed a set of APD-based machine learning (ML) models to predict the partial charges for small molecules with high accuracy. In the APD algorithm, the 3D structures of molecules were assigned with atom centers and atom-pair path-based atom layers to characterize the local chemical environments of atoms. Then, based on the APDs, two representative ensemble ML algorithms, i.e. random forest (RF) and extreme gradient boosting (XGBoost), were employed to develop the regression models for partial charge assignment. The results illustrate that the RF models based on APDs give better predictions for all the atom types than those based on traditional molecular fingerprints reported in the previous study. More encouragingly, the models trained by XGBoost can improve the predictions of partial charges further, and they can achieve the average root-mean-square error 0.0116 e on the external test set, which is much lower than that (0.0195 e) reported in the previous study, suggesting that the proposed algorithm is quite promising to be used in partial charge assignment with high accuracy. Availability and implementation The software framework described in this paper is freely available at https://github.com/jkwang93/Atom-Path-Descriptor-based-machine-learning Supplementary information Supplementary data are available at Bioinformatics online.
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Acharya, Rajeev, Igor Aleiner, Richard Allen, Trond I. Andersen, Markus Ansmann, Frank Arute, Kunal Arya et al. "Suppressing quantum errors by scaling a surface code logical qubit". Nature 614, n.º 7949 (22 de febrero de 2023): 676–81. http://dx.doi.org/10.1038/s41586-022-05434-1.
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AbstractPractical quantum computing will require error rates well below those achievable with physical qubits. Quantum error correction1,2 offers a path to algorithmically relevant error rates by encoding logical qubits within many physical qubits, for which increasing the number of physical qubits enhances protection against physical errors. However, introducing more qubits also increases the number of error sources, so the density of errors must be sufficiently low for logical performance to improve with increasing code size. Here we report the measurement of logical qubit performance scaling across several code sizes, and demonstrate that our system of superconducting qubits has sufficient performance to overcome the additional errors from increasing qubit number. We find that our distance-5 surface code logical qubit modestly outperforms an ensemble of distance-3 logical qubits on average, in terms of both logical error probability over 25 cycles and logical error per cycle ((2.914 ± 0.016)% compared to (3.028 ± 0.023)%). To investigate damaging, low-probability error sources, we run a distance-25 repetition code and observe a 1.7 × 10−6 logical error per cycle floor set by a single high-energy event (1.6 × 10−7 excluding this event). We accurately model our experiment, extracting error budgets that highlight the biggest challenges for future systems. These results mark an experimental demonstration in which quantum error correction begins to improve performance with increasing qubit number, illuminating the path to reaching the logical error rates required for computation.
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Otsuka, F., Y. Omura y O. Verkhoglyadova. "Energetic particle parallel diffusion in a cascading wave turbulence in the foreshock region". Nonlinear Processes in Geophysics 14, n.º 5 (7 de septiembre de 2007): 587–601. http://dx.doi.org/10.5194/npg-14-587-2007.
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Abstract. We study parallel (field-aligned) diffusion of energetic particles in the upstream of the bow shock with test particle simulations. We assume parallel shock geometry of the bow shock, and that MHD wave turbulence convected by the solar wind toward the shock is purely transverse in one-dimensional system with a constant background magnetic field. We use three turbulence models: a homogeneous turbulence, a regular cascade from a large scale to smaller scales, and an inverse cascade from a small scale to larger scales. For the homogeneous model the particle motions along the average field are Brownian motions due to random and isotropic scattering across 90 degree pitch angle. On the other hand, for the two cascade models particle motion is non-Brownian due to coherent and anisotropic pitch angle scattering for finite time scale. The mean free path λ|| calculated by the ensemble average of these particle motions exhibits dependence on the distance from the shock. It also depends on the parameters such as the thermal velocity of the particles, solar wind flow velocity, and a wave turbulence model. For the inverse cascade model, the dependence of λ|| at the shock on the thermal energy is consistent with the hybrid simulation done by Giacalone (2004), but the spatial dependence of λ|| is inconsistent with it.
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Nguyen, Trung Hai, Van Ngo, João Paulo Castro Zerba, Sergei Noskov y David D. L. Minh. "Nonequilibrium path-ensemble averages for symmetric protocols". Journal of Chemical Physics 151, n.º 19 (21 de noviembre de 2019): 194103. http://dx.doi.org/10.1063/1.5121306.
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Modanese, Giovanni. "Quantum-Only Metrics in Spherically Symmetric Gravity". Quantum Reports 2, n.º 2 (18 de junio de 2020): 314–25. http://dx.doi.org/10.3390/quantum2020021.
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The Einstein action for the gravitational field has some properties which make of it, after quantization, a rare prototype of systems with quantum configurations that do not have a classical analogue. Assuming spherical symmetry in order to reduce the effective dimensionality, we have performed a Monte Carlo simulation of the path integral with transition probability e − β | S | . Although this choice does not allow to reproduce the full dynamics, it does lead us to find a large ensemble of metric configurations having action | S | ≪ ħ by several magnitude orders. These vacuum fluctuations are strong deformations of the flat space metric (for which S = 0 exactly). They exhibit a periodic polarization in the scalar curvature R. In the simulation we fix a length scale L and divide it into N sub-intervals. The continuum limit is investigated by increasing N up to ∼ 10 6 ; the average squared action ⟨ S 2 ⟩ is found to scale as 1 / N 2 and thermalization of the algorithm occurs at a very low temperature (classical limit). This is in qualitative agreement with analytical results previously obtained for theories with stabilized conformal factor in the asymptotic safety scenario.
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Oikonomou, Panagiotis y Stylianos Pappas. "Decentralized Bioinspired Non-Discrete Model for Autonomous Swarm Aggregation Dynamics". Applied Sciences 10, n.º 3 (5 de febrero de 2020): 1067. http://dx.doi.org/10.3390/app10031067.
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In this paper a microscopic, non-discrete, mathematical model based on stigmergy for predicting the nodal aggregation dynamics of decentralized, autonomous robotic swarms is proposed. The model departs from conventional applications of stigmergy in bioinspired path-finding optimization, serving as a dynamic aggregation algorithm for nodes with limited or no ability to perform discrete logical operations, aiding in agent miniaturization. Time-continuous simulations were developed and carried out where nodal aggregation efficiency was evaluated using the following metrics: time to aggregation equilibrium, agent spatial distribution within aggregate (including average inter-nodal distance, center of mass of aggregate deviation from target), and deviation from target agent number. The system was optimized using cost minimization of the above factors through generating a random set of cost datapoints with varying initial conditions (number of aggregates, agents, field dimensions, and other specific agent parameters) where the best-fit scalar field was obtained using a random forest ensemble learning strategy and polynomial regression. The scalar cost field global minimum was obtained through basin-hopping with L-BFGS-B local minimization on the scalar fields obtained through both methods. The proposed optimized model describes the physical properties that non-digital agents must possess so that the proposed aggregation behavior emerges, in order to avoid discrete state algorithms aiming towards developing agents independent of digital components aiding to their miniaturization.
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Crooks, Gavin E. "Path-ensemble averages in systems driven far from equilibrium". Physical Review E 61, n.º 3 (1 de marzo de 2000): 2361–66. http://dx.doi.org/10.1103/physreve.61.2361.
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Escribà, P., A. Callado, D. Santos, C. Santos, J. A. García-Moya y J. Simarro. "Probabilistic prediction of raw and BMA calibrated AEMET-SREPS: the 24 of January 2009 extreme wind event in Catalunya". Advances in Geosciences 26 (22 de noviembre de 2010): 119–24. http://dx.doi.org/10.5194/adgeo-26-119-2010.
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Abstract. At 00:00 UTC of 24 January 2009 (24Jan09) an explosive cyclogenesis placed at the Gulf of Vizcaya, reached its maximum intensity with observed surface pressures below 970 hPa on its center. During its path through the south of France there were strong westerly and north-westerly winds over Iberian Peninsula (above 150 km/h). These extreme winds leaved 8 casualties in Catalunya, the north-east region of Spain. The aim of this work is validating the skill of the Spanish Meteorological Agency (AEMET) Short Range Ensemble Prediction System (SREPS) in forecasting this event. Two probabilistic forecasts of wind are compared, a non-calibrated (or raw) and a calibrated one using the Bayesian Model Averaging (BMA). AEMET runs a daily experimental SREPS twice a day (00:00 and 12:00 UTC). This system consists on 25 members that are constructed by integrating five different Limited Area Models (LAMs) at 0.25 degrees of horizontal resolution. Each model uses five different initial and boundary conditions from five Global Models (GMs). Thus it is obtained a probabilistic forecast that takes into account initial, contour and model uncertainties. BMA is a statistical tool for combining predictive Probability Distribution Functions (PDFs) from different sources. BMA predictive PDF is a weighted average of PDFs centered on the individual bias-corrected forecasts. Each weight is a measure of the corresponding forecast skill. Here BMA is applied to calibrate probabilistic forecasts of wind speed. In this work two time forecast ranges (H+60 and H+36) of 10-m wind speed over Catalonia are verified subjectively at 12:00 UTC of 24Jan09 valid time. We focus on the location and intensity of 10-m wind speed maximum values. Observations at 29 automatic ground stations of AEMET are used for the verification. On one hand results indicate that raw AEMET-SREPS is able to forecast 60 h ahead mean winds higher than 36 and 54 km/h and that it correctly locates them in three different areas. On the other hand, predicted probability loses its skill after BMA calibration of the ensemble. This is due to the fact that BMA bias correction underestimates the intensity of wind.
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Minh, David D. L. y John D. Chodera. "Optimal estimators and asymptotic variances for nonequilibrium path-ensemble averages". Journal of Chemical Physics 131, n.º 13 (7 de octubre de 2009): 134110. http://dx.doi.org/10.1063/1.3242285.
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Rodwell, M. J., D. S. Richardson, D. B. Parsons y H. Wernli. "Flow-Dependent Reliability: A Path to More Skillful Ensemble Forecasts". Bulletin of the American Meteorological Society 99, n.º 5 (mayo de 2018): 1015–26. http://dx.doi.org/10.1175/bams-d-17-0027.1.
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AbstractWhile chaos ensures that probabilistic weather forecasts cannot always be “sharp,” it is important for users and developers that they are reliable. For example, they should not be overconfident or underconfident. The “spread–error” relationship is often used as a first-order assessment of the reliability of ensemble weather forecasts. This states that the ensemble standard deviation (a measure of forecast uncertainty) should match the root-mean-square error on the ensemble mean (when averaged over a sufficient number of forecast start dates). It is shown here that this relationship is now largely satisfied at the European Centre for Medium-Range Weather Forecasts (ECMWF) for ensemble forecasts of the midlatitude, midtropospheric flow out to lead times of at least 10 days when averaged over all flow situations throughout the year. This study proposes a practical framework for continued improvement in the reliability (and skill) of such forecasts. This involves the diagnosis of flow-dependent deficiencies in short-range (∼12 h) reliability for a range of synoptic-scale flow types and the prioritization of modeling research to address these deficiencies. The approach is demonstrated for a previously identified flow type, a trough over the Rockies with warm, moist air ahead. The mesoscale convective systems that can ensue are difficult to predict and, by perturbing the jet stream, are thought to lead to deterministic forecast “busts” for Europe several days later. The results here suggest that jet stream spread is insufficient during this flow type, and thus unreliable. This is likely to mean that the uncertain forecasts for Europe may, nevertheless, still be overconfident.
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Muthalif, Asan G. A., Azni N. Wahid y Khairul A. M. Nor. "Estimating ensemble average power delivered by a piezoelectric patch actuator to a non-deterministic subsystem". Journal of Sound and Vibration 333, n.º 4 (febrero de 2014): 1149–62. http://dx.doi.org/10.1016/j.jsv.2013.10.012.
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Vassilev, P. M., R. W. Hadley, K. S. Lee y J. R. Hume. "Voltage-dependent action of tetrodotoxin in mammalian cardiac myocytes". American Journal of Physiology-Heart and Circulatory Physiology 251, n.º 2 (1 de agosto de 1986): H475—H480. http://dx.doi.org/10.1152/ajpheart.1986.251.2.h475.
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Single Na+ channel currents have been examined in isolated guinea pig ventricular myocytes using the patch-clamp technique. The effects of lidocaine, extracellular calcium [(Ca)o], and tetrodotoxin on patch Na+ channel availability were assessed using ensemble averages of Na+-channel openings during depolarizing test potential steps from 7 to 10 different patch-holding potentials in each cell-attached patch. In six control patches, the potential for 50% channel availability (Vh) was -15 mV (relative to an average resting membrane potential of -80 mV). Exposure of patches to either lidocaine or elevated (Ca)o produced the expected shifts in Vh [average -22 mV for lidocaine and +10 mV for 6 mM (Ca)o]. Exposure of patches to tetrodotoxin (0.5 microM or 1.0 microM) produced a dose-dependent hyperpolarizing shift of Vh (average -10 and -17 mV) compared with control patches. The hyperpolarizing shift by tetrodotoxin was observed with pulses applied at frequencies of 1.0 or 0.067 Hz. In agreement with earlier maximal upstroke velocity studies in the same preparation, we conclude that block of ventricular Na+ channels by tetrodotoxin exhibits genuine steady-state voltage dependence.
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Mieck, B. "Ensemble averaged coherent state path integral for disordered bosons with a repulsive interaction (Derivation of mean field equations)". Fortschritte der Physik 55, n.º 9-10 (3 de septiembre de 2007): 951–88. http://dx.doi.org/10.1002/prop.200710391.
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Tiwari, Ambuj y Bernd Ensing. "Reactive trajectories of the Ru2+/3+ self-exchange reaction and the connection to Marcus' theory". Faraday Discussions 195 (2016): 291–310. http://dx.doi.org/10.1039/c6fd00132g.
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Outer sphere electron transfer between two ions in aqueous solution is a rare event on the time scale of first principles molecular dynamics simulations. We have used transition path sampling to generate an ensemble of reactive trajectories of the self-exchange reaction between a pair of Ru2+ and Ru3+ ions in water. To distinguish between the reactant and product states, we use as an order parameter the position of the maximally localised Wannier center associated with the transferring electron. This allows us to align the trajectories with respect to the moment of barrier crossing and compute statistical averages over the path ensemble. We compare our order parameter with two typical reaction coordinates used in applications of Marcus theory of electron transfer: the vertical gap energy and the solvent electrostatic potential at the ions.
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Chhabra, P. S., N. L. Ng, M. R. Canagaratna, A. L. Corrigan, L. M. Russell, D. R. Worsnop, R. C. Flagan y J. H. Seinfeld. "Elemental composition and oxidation of chamber organic aerosol". Atmospheric Chemistry and Physics 11, n.º 17 (1 de septiembre de 2011): 8827–45. http://dx.doi.org/10.5194/acp-11-8827-2011.
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Abstract. Recently, graphical representations of aerosol mass spectrometer (AMS) spectra and elemental composition have been developed to explain the oxidative and aging processes of secondary organic aerosol (SOA). It has been shown previously that oxygenated organic aerosol (OOA) components from ambient and laboratory data fall within a triangular region in the f44 vs. f43 space, where f44 and f43 are the ratios of the organic signal at m/z 44 and 43 to the total organic signal in AMS spectra, respectively; we refer to this graphical representation as the "triangle plot." Alternatively, the Van Krevelen diagram has been used to describe the evolution of functional groups in SOA. In this study we investigate the variability of SOA formed in chamber experiments from twelve different precursors in both "triangle plot" and Van Krevelen domains. Spectral and elemental data from the high-resolution Aerodyne aerosol mass spectrometer are compared to offline species identification analysis and FTIR filter analysis to better understand the changes in functional and elemental composition inherent in SOA formation and aging. We find that SOA formed under high- and low-NOx conditions occupy similar areas in the "triangle plot" and Van Krevelen diagram and that SOA generated from already oxidized precursors allows for the exploration of areas higher on the "triangle plot" not easily accessible with non-oxidized precursors. As SOA ages, it migrates toward the top of the triangle along a path largely dependent on the precursor identity, which suggests increasing organic acid content and decreasing mass spectral variability. The most oxidized SOA come from the photooxidation of methoxyphenol precursors which yielded SOA O/C ratios near unity. α-pinene ozonolysis and naphthalene photooxidation SOA systems have had the highest degree of mass closure in previous chemical characterization studies and also show the best agreement between AMS elemental composition measurements and elemental composition of identified species within the uncertainty of the AMS elemental analysis. In general, compared to their respective unsaturated SOA precursors, the elemental composition of chamber SOA follows a slope shallower than −1 on the Van Krevelen diagram, which is indicative of oxidation of the precursor without substantial losss of hydrogen, likely due to the unsaturated nature of the precursors. From the spectra of SOA studied here, we are able to reproduce the triangular region originally constructed with ambient OOA compents with chamber aerosol showing that SOA becomes more chemically similar as it ages. Ambient data in the middle of the triangle represent the ensemble average of many different SOA precursors, ages, and oxidative processes.
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Wang, X., S. N. Treistman y J. R. Lemos. "Single channel recordings of Nt- and L-type Ca2+ currents in rat neurohypophysial terminals". Journal of Neurophysiology 70, n.º 4 (1 de octubre de 1993): 1617–28. http://dx.doi.org/10.1152/jn.1993.70.4.1617.
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1. Ca2+ currents through single channels in acutely dissociated nerve terminals from rat neurohypophyses were recorded using cell-attached patch recordings with 110 mM Ba2+ as the charge carrier. 2. One type (Nt, where the t denotes terminal) of single Ca2+ channel current was evoked only by depolarizing steps from holding potentials less negative than -50 mV. Because this channel opened primarily at the beginning of a 180-ms-long voltage pulse, the averaged ensemble current decayed rapidly (approximately 30 ms). Infrequently, the channel opened throughout such a long pulse, resulting in a long-lasting averaged ensemble current. The averaged channel open time constant (tau) was 0.34 ms and the two averaged closed time constants were 1.78 (tau 1) and 86.57 (tau 2) ms. The mean unitary slope conductance for this channel was 11 pS and its threshold for activation was approximately -10 mV. 3. The other type (L) of single Ca2+ channel current could be evoked in isolation by depolarizations from holding potentials more positive than or equal to -50 mV. This channel opened throughout an entire 180-ms-long voltage pulse. The averaged ensemble current, therefore, showed little inactivation. The averaged channel open-time constant was 0.49 ms and the two average closed time constants were 2.02 (tau 1) and 79.91 (tau 2) ms. The mean unitary slope conductance for this channel was 25 pS. 4. Bay K 8644 (5 microM), a dihydropyridine (DHP) Ca2+ channel agonist, increased the open probability of the larger-conductance L-type Ca2+ channel by prolonging the average duration (to 2.79 ms) of channel openings, but did not alter the single channel slope conductance. In contrast, the same concentration of Bay K 8644 did not affect the smaller-conductance Nt-type Ca2+ channel. The DHP Ca2+ channel antagonist nicardipine (5 microM), but not nifedipine (5 microM), reduced the open probability of the large-conductance L-type Ca2+ channel by shortening the duration (to 0.36 ms) of channel openings. 5. The voltage- and time-dependent properties of these two types of single Ca2+ channel currents are in close agreement with those of the two components of macroscopic Ca2+ currents previously reported using the "whole-terminal" recording method. Therefore these two types of single channels appear to underlie the macroscopic current. 6. Our studies suggest that the terminal Nt-type Ca2+ channel differs from the conventional somatic N- and T-type Ca2+ channels in some respects, and that the terminal L-type Ca2+ channel is similar to the conventional somatic L-type Ca2+ channel.(ABSTRACT TRUNCATED AT 400 WORDS)
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Böhm, Michael C., Rafael Ramírez y Joachim Schulte. "New Aspects in the Calculation of Electronic Momentum Properties; an All-Quantum Study". Zeitschrift für Naturforschung A 53, n.º 1-2 (1 de febrero de 1998): 38–44. http://dx.doi.org/10.1515/zna-1998-1-207.
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Abstract The electronic properties of the C6H6 and C6D6 molecules have been studied by an all-quantum approach, where the classical and quantum degrees of freedom of the nuclei are taken into ac-count in the evaluation of electronic expectation values. In the all-quantum approach suggested a Feynman path integral Monte Carlo (PIMC) formalism has been linked to an electronic ab initio Hamiltonian. The electronic expectation values have been calculated as averages over the manifold of nuclear configurations populated in thermal equilibrium. This theoretical setup leads to electronic expectation values that depend on the temperature and on the mass of the nuclei. The ensemble averaged electronic properties differ sizeably from the results derived on the basis of a single nuclear configuration of minimum energy. This behaviour should have physical implications for the theoretical calculation of electronic momentum properties such as Compton profiles, reciprocal form factors, etc. We describe an error source in the theoretical determination of electronic momentum properties which has not been commented so far.
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Polonsky, Igor y D. M. O’Brien. "Rapid Estimation of Column-Averaged CO2 Concentration Using a Correlation Algorithm". Journal of Atmospheric and Oceanic Technology 27, n.º 12 (1 de diciembre de 2010): 2002–16. http://dx.doi.org/10.1175/2010jtecha1487.1.
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Abstract Measurement of XCO2, the column-averaged mole fraction of CO2, using reflected sunlight in the near-infrared bands of CO2, is strongly influenced by photons that are scattered in the atmosphere because scattering can either decrease or increase the mean pathlength compared with the direct path from the sun to the surface to the satellite. A very simple algorithm that can be used to compensate for the errors introduced by scattering is presented. The algorithm is based on the observation that the apparent optical path differences in selected pairs of channels in the weak CO2 band at 1.6 μm and the O2 A band at 0.76 μm are tightly correlated for large ensembles of scattering atmospheres. The number of tightly correlated pairs of channels is many hundreds for the bands measured by NASA’s Orbiting Carbon Observatory (OCO). The physical reasons for the correlation are that the mean photon pathlengths are comparable for the members of each pair of channels, and that the extinction profiles vary similarly with height. For atmospheres with modest scattering optical thickness (less than 0.3), the slope and the intercept of the linear correlation for any pair depends weakly on the surface reflectance, the surface pressure, and the viewing geometry. Through numerical simulations the slope and intercept may be parameterized simply in terms of these variables. Thereafter, the task of retrieving XCO2 from measured spectra may be reduced to linear interpolation in precomputed tables of slopes and intercepts. Results with simulated data for NASA’s OCO satellite are presented, and random errors and biases are investigated. Although OCO did not reach orbit, the method is applicable to any instrument that operates using similar principles [such as those on the Greenhouse Gases Observing Satellite (GOSAT) and the replacement satellite OCO-2].
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Tomchuk, P. M. y V. N. Starkov. "Influence of Shape Spread in an Ensemble of Metal Nanoparticles on Their Optical Properties". Ukrainian Journal of Physics 63, n.º 3 (12 de abril de 2018): 204. http://dx.doi.org/10.15407/ujpe63.3.204.
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The theoretical basis of the work consists in that the dissipative processes in non-spherical nanoparticles, whose sizes are smaller than the mean free path of electrons, are characterized by a tensor quantity, whose diagonal elements together with the depolarization coefficients determine the half-widths of plasma resonances. Accordingly, the averaged characteristics are obtained for an ensemble of metal nanoparticles with regard for the influence of the nanoparticle shape on the depolarization coefficients and the components of the optical conductivity tensor. Three original variants of the nanoparticle shape distribution function are proposed on the basis of the joint application of the Gauss and “cap” functions.
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Kulie, Mark S., Ralf Bennartz, Thomas J. Greenwald, Yong Chen y Fuzhong Weng. "Uncertainties in Microwave Properties of Frozen Precipitation: Implications for Remote Sensing and Data Assimilation". Journal of the Atmospheric Sciences 67, n.º 11 (1 de noviembre de 2010): 3471–87. http://dx.doi.org/10.1175/2010jas3520.1.
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Abstract A combined active/passive modeling system that converts CloudSat observations to simulated microwave brightness temperatures (TB) is used to assess different ice particle models under precipitating conditions. Simulation results indicate that certain ice models (e.g., low-density spheres) produce excessive scattering and implausibly low simulated TBs for stratiform precipitation events owing to excessive derived ice water paths (IWPs), while other ice models produce unphysical TB depressions due to the combined effects of elevated derived IWP and excessive particle size distribution–averaged extinction. An ensemble of nonspherical ice particle models, however, consistently produces realistic results under most circumstances and adequately captures the radiative properties of frozen hydrometeors associated with precipitation—with the possible exception of very high IWP events. Large derived IWP uncertainties exceeding 60% are also noted and may indicate IWP retrieval accuracy deficiencies using high-frequency passive microwave observations. Simulated TB uncertainties due to the ice particle model ensemble members approach 9 (5) K at 89 (157) GHz for high ice water path conditions associated with snowfall and ∼2–3 (∼1–2) K under typical stratiform rain conditions. These uncertainties, however, display considerable variability owing to ice water path, precipitation type, satellite zenith angle, and frequency. Comparisons between 157-GHz simulations and observations under precipitating conditions produce low biases (<1.5 K) and high correlations, but lower-frequency channels display consistent negative biases of 3–4 K in precipitating regions. Sample error correlations and covariance matrices for select microwave frequencies also show strong functional relationships with ice water path and variability depending on precipitation type.
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Mu, Linqin, Jin Zhang, Yijin Liu y Feng Lin. "Resolving Charge Distribution for Compositionally Heterogeneous Layered Cathode Materials". ECS Meeting Abstracts MA2022-02, n.º 3 (9 de octubre de 2022): 254. http://dx.doi.org/10.1149/ma2022-023254mtgabs.
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Rechargeable batteries are built on the foundation of redox-active compounds. Thus, understanding charge compensation mechanisms represents one of the most critical research directions in developing battery materials. Due to the compositional versatility of Li-containing layered cathode, i.e., LiNi1-x-yMnxCoyO2 (NMC), one can tune the TMs (transition metals) composition to satisfy various demands. As the Ni/Mn/Co stoichiometry moves across the compositional space, the charge compensation mechanism also gradually evolves due to the changing of TM 3d orbital energy levels. Thus, tailoring TMs stoichiometry has become effective to fine-tune battery performance. In a previous study, we found that NMCs with a highly heterogeneous TM distribution still exhibited a globally layered structure.1Another study on dopant distribution also suggests that the heterogeneous dopant can positively impact battery performance.2 Our previous studies show that the charge heterogeneity can result in local stress hotspots and exacerbate the chemomechanical breakdown of NMC particles.3 When the compositional heterogeneity prevails in individual NMC particles, charge distribution likely exhibits a heterogeneous pattern due to distinct redox reactions in domains with different TM stoichiometries. Thus, we believe that understanding the interplay between compositional heterogeneity and its impact on charge distribution may provide insights into engineering compositional heterogeneity to achieve desired charge distribution. Herein, in this work, we designed the compositionally heterogeneous NMC cathode with the ensemble-average layered structure as the platform to investigate the charge distribution with single-particle spectroscopic imaging measurements.4 We establish the relationship between charge distribution and local compositional heterogeneity at the single-particle level. The local Mn and Ni concentrations in individual NMC particles are positively and negatively correlated with the electrochemically induced Ni oxidation, respectively, whereas the Co concentration does not impose a clear effect on the Ni oxidation. The resulting material delivers excellent reversible capacity, rate capability, and cycle life at high operating voltages. Engineering Ni/Mn/Co distribution in NMC particles may provide a path toward controlling the charge distribution and thus chemomechanical properties of polycrystalline battery particles. Lin, F.; Nordlund, D.; Markus, I. M.; Weng, T.-C.; Xin, H. L.; Doeff, M. M., Profiling the nanoscale gradient in stoichiometric layered cathode particles for lithium-ion batteries. Energy & Environmental Science 2014, 7 (9), 3077-3085. Mu, L.; Zhang, R.; Kan, W. H.; Zhang, Y.; Li, L.; Kuai, C.; Zydlewski, B.; Rahman, M. M.; Sun, C.-J.; Sainio, S.; Avdeev, M.; Nordlund, D.; Xin, H. L.; Lin, F., Dopant Distribution in Co-Free High-Energy Layered Cathode Materials. Chemistry of Materials 2019, 31 (23), 9769-9776. Yang, Y.; Xu, R.; Zhang, K.; Lee, S.-J.; Mu, L.; Liu, P.; Waters, C. K.; Spence, S.; Xu, Z.; Wei, C.; Kautz, D. J.; Yuan, Q.; Dong, Y.; Yu, Y.-S.; Xiao, X.; Lee, H.-K.; Pianetta, P.; Cloetens, P.; Lee, J.-S.; Zhao, K.; Lin, F.; Liu, Y., Quantification of Heterogeneous Degradation in Li-Ion Batteries. Advanced Energy Materials 2019, 9 (25), 1900674. Mu, L.; Zhang, J.; Xu, Y.; Wei, C.; Rahman, M. M.; Nordlund, D.; Liu, Y.; Lin, F., Resolving Charge Distribution for Compositionally Heterogeneous Battery Cathode Materials. Nano Letters 2022, 22 (3), 1278-1286.
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Eliseev, A. V., D. Coumou, A. V. Chernokulsky, V. Petoukhov y S. Petri. "Scheme for calculation of multi-layer cloudiness and precipitation for climate models of intermediate complexity". Geoscientific Model Development 6, n.º 5 (23 de octubre de 2013): 1745–65. http://dx.doi.org/10.5194/gmd-6-1745-2013.
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Abstract. In this study we present a scheme for calculating the characteristics of multi-layer cloudiness and precipitation for Earth system models of intermediate complexity (EMICs). This scheme considers three-layer stratiform cloudiness and single-column convective clouds. It distinguishes between ice and droplet clouds as well. Precipitation is calculated by using cloud lifetime, which depends on cloud type and phase as well as on statistics of synoptic and convective disturbances. The scheme is tuned to observations by using an ensemble simulation forced by the ERA-40-derived climatology for 1979–2001. Upon calibration, the scheme realistically reproduces basic features of fields of cloud fractions, cloud water path, and precipitation. The simulated globally and annually averaged total cloud fraction is 0.59, and the simulated globally averaged annual precipitation is 100 cm yr−1. Both values agree with empirically derived values. The simulated cloud water path is too small, probably because the simulated vertical extent of stratiform clouds is too small. Geographical distribution and seasonal changes of calculated cloud fraction and precipitation are broadly realistic as well. However, some important regional biases still remain in the scheme, e.g. too little precipitation in the tropics. We discuss possibilities for future improvements in the scheme.
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Periyasamy, Sivaselvi y Tarun K. Chandrayadula. "The broadband transport theory approach to model internal wave induced scattering across deep water acoustic time-fronts". Journal of the Acoustical Society of America 153, n.º 2 (febrero de 2023): 895–908. http://dx.doi.org/10.1121/10.0017102.
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There are currently no models to fully predict the effects of internal wave induced scattering on acoustic pulses. Existing models, which predict time domain statistics, either use the ray-based path integral method or Monte Carlo type simulations. The path integral method fails to accurately predict all of the effects of scattering. The Monte Carlo methods base the statistics on ensemble averages and are not physics-based models. This paper overcomes these limitations by using the modes of the waveguide in a transport theory application. The transport theory equations have, thus far, been used only to explain diffusion of mode intensities and decorrelation due to internal waves at individual frequencies. This paper extends the current narrowband application predict mode correlations across different frequencies and, from that, the broadband time-front, time wander, travel time bias, and the amount of spread in intensity across time and depth. To validate these predictions, this paper uses separate parabolic equation simulations. The comparisons between the two are good, suggesting a success for the mode-based transport theory approach.
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Eliseev, A. V., D. Coumou, A. V. Chernokulsky, V. Petoukhov y S. Petri. "Scheme for calculation of multi-layer cloudiness and precipitation for climate models of intermediate complexity". Geoscientific Model Development Discussions 6, n.º 2 (17 de junio de 2013): 3241–87. http://dx.doi.org/10.5194/gmdd-6-3241-2013.
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Abstract. In this study we present a scheme for calculating the characteristics of multi-layer cloudiness and precipitation for climate models of intermediate complexity (EMICs). This scheme considers three-layer stratiform cloudiness and single column convective clouds. It distinguishes between ice and droplet clouds as well. Precipitation is calculated by using cloud life time, which depends on cloud type and phase as well as on statistics of synoptic and convective disturbances. The scheme is tuned to observations by using an ensemble simulation forced by the ERA-40-derived climatology for 1979–2001. Upon calibration, the scheme realistically reproduces basic features of fields of cloud amounts, cloud water path, and precipitation. The simulated globally and annually averaged total cloud amount is 0.59, and the simulated globally averaged annual precipitation is 109 cm yr-1. Both values agree with empirically-derived values. Geographical distribution and seasonal changes of calculated variables are broadly realistic as well. However, some important regional biases still remain in the scheme.
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Ito, H. y K. Ono. "A rapidly activating delayed rectifier K+ channel in rabbit sinoatrial node cells". American Journal of Physiology-Heart and Circulatory Physiology 269, n.º 2 (1 de agosto de 1995): H443—H452. http://dx.doi.org/10.1152/ajpheart.1995.269.2.h443.
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The single-channel current of the delayed rectifier K+ current (IK) was recorded in rabbit sinoatrial node cells. In the cell-attached patch, depolarization from -70 mV to potentials more positive than -50 mV activated the IK channel while repolarization deactivated it. The single-channel conductance was 7.8 pS for the outward current and 10.8 pS for the inward current (n = 6). The steady-state open probability (NPo) was maximum at around -30 mV and markedly decreased at more positive potentials. On repolarization from positive potentials, the channel was initially closed and then rapidly opened. The ensemble average showed an initial rise to a peak followed by the deactivation time course. Because the channel events were completely blocked by E-4031, the drug-sensitive component was examined in the whole cell current. The steady-state current-voltage relation of the drug-sensitive current showed a marked negative slope at potentials more positive than -10 mV. Upon repolarization, the drug-sensitive current initially increased (removal of inactivation) to the peak of the outward tail current, which was in agreement with the ensemble average of the single-channel current. We conclude that IK in the sinoatrial node cells is largely composed of the rapidly activating IK (IK,r) channels and that the inward rectification of IK,r, which is more marked than had been assumed in previous studies, is due to the decrease in NPo.
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Sarafan, Sadaf, Tai Le, Michael P. H. Lau, Afshan Hameed, Tadesse Ghirmai y Hung Cao. "Fetal Electrocardiogram Extraction from the Mother’s Abdominal Signal Using the Ensemble Kalman Filter". Sensors 22, n.º 7 (5 de abril de 2022): 2788. http://dx.doi.org/10.3390/s22072788.
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Fetal electrocardiogram (fECG) assessment is essential throughout pregnancy to monitor the wellbeing and development of the fetus, and to possibly diagnose potential congenital heart defects. Due to the high noise incorporated in the abdominal ECG (aECG) signals, the extraction of fECG has been challenging. And it is even a lot more difficult for fECG extraction if only one channel of aECG is provided, i.e., in a compact patch device. In this paper, we propose a novel algorithm based on the Ensemble Kalman filter (EnKF) for non-invasive fECG extraction from a single-channel aECG signal. To assess the performance of the proposed algorithm, we used our own clinical data, obtained from a pilot study with 10 subjects each of 20 min recording, and data from the PhysioNet 2013 Challenge bank with labeled QRS complex annotations. The proposed methodology shows the average positive predictive value (PPV) of 97.59%, sensitivity (SE) of 96.91%, and F1-score of 97.25% from the PhysioNet 2013 Challenge bank. Our results also indicate that the proposed algorithm is reliable and effective, and it outperforms the recently proposed extended Kalman filter (EKF) based algorithm.
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Medvedev, Ilia N. "On the efficiency of using correlative randomized algorithms for solving problems of gamma radiation transfer in stochastic medium". Russian Journal of Numerical Analysis and Mathematical Modelling 37, n.º 4 (1 de agosto de 2022): 231–40. http://dx.doi.org/10.1515/rnam-2022-0020.
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Abstract To solve problems of radiation balance, optical sounding, and tomography, it may be necessary to take into account multiple scattering of radiation in a stochastically inhomogeneous medium. In real radiation models, for this purpose, the numerical-statistical ‘majorant cross-section method’ (MCM, delta-Woodcock tracking) is used based on the alignment of the optical density field by adding an artificial ‘delta scattering’ event. However, the computation cost of the corresponding unbiased estimate of the averaged problem solution infinitely increases as the correlation scale (correlation radius L) of standard mosaic models for a random medium density decreases. Previously, we constructed the MCM randomization providing asymptotically (for L → 0) unbiased estimates of the required functionals, in which the value of the physical attenuation coefficient is randomly chosen at the end of the particle free path l under condition l > L. Otherwise the value of the physical attenuation coefficient is the same as at the starting point of the particle (CR algorithm). In a more accurate functional correlative randomized algorithm (FCR algorithm), the coefficient remains the same with a probability determined by the correlation function. These correlative randomized algorithms were implemented for a mixture of homogeneous substance (water) and a Poisson ensemble of ‘empty’ balls. In the present paper, we construct correlative randomized algorithms for problems related to transfer through a ‘thick’ layer containing a water and a Poisson ensemble of ‘empty’ layers. A detailed comparative analysis of the results obtained by exact direct simulation (MCM) and approximate algorithms (CR, FCR) for the problems of gamma radiation transfer through a ‘thick’ water layer containing a Poisson ensemble of ‘empty’ layers or balls is presented.
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Miltenberger, Annette K. y Paul R. Field. "Sensitivity of mixed-phase moderately deep convective clouds to parameterizations of ice formation – an ensemble perspective". Atmospheric Chemistry and Physics 21, n.º 5 (10 de marzo de 2021): 3627–42. http://dx.doi.org/10.5194/acp-21-3627-2021.
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Abstract. The formation of ice in clouds is an important processes in mixed-phase and ice-phase clouds. Yet, the representation of ice formation in numerical models is highly uncertain. In the last decade, several new parameterizations for heterogeneous freezing have been proposed. However, it is currently unclear what the effect of choosing one parameterization over another is in the context of numerical weather prediction. We conducted high-resolution simulations (Δx=250 m) of moderately deep convective clouds (cloud top ∼-18 ∘C) over the southwestern United Kingdom using several formulations of ice formation and compared the resulting changes in cloud field properties to the spread of an initial condition ensemble for the same case. The strongest impact of altering the ice formation representation is found in the hydrometeor number concentration and mass mixing ratio profiles. While changes in accumulated precipitation are around 10 %, high precipitation rates (95th percentile) vary by 20 %. Using different ice formation representations changes the outgoing short-wave radiation by about 2.9 W m−2 averaged over daylight hours. The choice of a particular representation for ice formation always has a smaller impact then omitting heterogeneous ice formation completely. Excluding the representation of the Hallett–Mossop process or altering the heterogeneous freezing parameterization has an impact of similar magnitude on most cloud macro- and microphysical variables with the exception of the frozen hydrometeor mass mixing ratios and number concentrations. A comparison to the spread of cloud properties in a 10-member high-resolution initial condition ensemble shows that the sensitivity of hydrometeor profiles to the formulation of ice formation processes is larger than sensitivity to initial conditions. In particular, excluding the Hallett–Mossop representation results in profiles clearly different from any in the ensemble. In contrast, the ensemble spread clearly exceeds the changes introduced by using different ice formation representations in accumulated precipitation, precipitation rates, condensed water path, cloud fraction, and outgoing radiation fluxes.
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Jian, Bida, Jiming Li, Guoyin Wang, Yuxin Zhao, Yarong Li, Jing Wang, Min Zhang y Jianping Huang. "Evaluation of the CMIP6 marine subtropical stratocumulus cloud albedo and its controlling factors". Atmospheric Chemistry and Physics 21, n.º 12 (30 de junio de 2021): 9809–28. http://dx.doi.org/10.5194/acp-21-9809-2021.
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Abstract. The cloud albedo in the marine subtropical stratocumulus regions plays a key role in regulating the regional energy budget. Based on 12 years of monthly data from multiple satellite datasets, the long-term, monthly and seasonal cycle of averaged cloud albedo in five stratocumulus regions were investigated to intercompare the atmosphere-only simulations between phases 5 and 6 of the Coupled Model Intercomparison Project (AMIP5 and AMIP6). Statistical results showed that the long-term regressed cloud albedos were underestimated in most AMIP6 models compared with the satellite-driven cloud albedos, and the AMIP6 models produced a similar spread as AMIP5 over all regions. The monthly averaged values and seasonal cycle of cloud albedo of AMIP6 ensemble mean showed a better correlation with the satellite-driven observations than that of the AMIP5 ensemble mean. However, the AMIP6 model still failed to reproduce the values and amplitude in some regions. By employing the Modern-Era Retrospective Analysis for Research and Applications Version 2 (MERRA-2) data, this study estimated the relative contributions of different aerosols and meteorological factors on the long-term variation of marine stratocumulus cloud albedo under different cloud liquid water path (LWP) conditions. The multiple regression models can explain ∼ 65 % of the changes in the cloud albedo. Under the monthly mean LWP ≤ 65 g m−2, dust and black carbon dominantly contributed to the changes in the cloud albedo, while dust and sulfur dioxide aerosol contributed the most under the condition of 65 g m−2 < LWP ≤ 120 g m−2. These results suggest that the parameterization of cloud–aerosol interactions is crucial for accurately simulating the cloud albedo in climate models.
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Ersin, Özlem H., Shencheng Ge y Christy L. Haynes. "Real time, single-cell characterization of basophilic exocytosis through carbon-fiber microelectrode amperometry (CFMA) (42.1)". Journal of Immunology 182, n.º 1_Supplement (1 de abril de 2009): 42.1. http://dx.doi.org/10.4049/jimmunol.182.supp.42.1.
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Abstract Histamine released by previously sensitized basophils plays a crucial role in inflammation and immediate hypersensitivity reactions. Whereas ensemble-based immunohistochemical assays characterize the average release profile of cell populations, differences among individual basophils or basophil sub-populations remain largely unexplored based on technological limitations. Previous work in our lab has used microelectrochemical techniques to measure real time quantal release from single cells isolated from separate platelet and mast cell populations. Herein we report the use of carbon-fiber microelectrodes to measure the concentration and time course of single-cell histamine secretion by primary culture basophils in response to varying physiological and electrical stimuli. Future work will utilize CFMA and the patch clamp technique to probe single-cell degranulation in a polydimethylsiloxane (PDMS) microfluidic chip model of graduated complexity.
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Meech, R. W. y G. O. Mackie. "Potassium channel family in giant motor axons of Aglantha digitale". Journal of Neurophysiology 69, n.º 3 (1 de marzo de 1993): 894–901. http://dx.doi.org/10.1152/jn.1993.69.3.894.
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1. The simplicity of the jellyfish nervous system makes it an ideal preparation to assess the contributions of different ion channels to behavior. In the giant motor axons of the jellyfish Aglantha digitale, low-threshold spikes elicit slow swimming, whereas escape swimming depends on a higher-threshold, overshooting sodium-dependent action potential. At least three kinetically distinct transient potassium channels (fast, intermediate, and slow) are concerned with spike management in this preparation. 2. In situ recording with patch-clamp micropipettes from clusters of potassium channels provides a means of studying their properties in isolation. The three classes of ion channel were identified in ensemble current averages by their kinetics, their response to a conditioning prepulse and their voltage dependence. All three were highly selective for potassium, and the reversal potential of their unitary currents depended on the level of potassium used to fill the patch pipette. 3. A single potassium permeability coefficient (PK) calculated from the Goldman, Hodgkin, Katz “constant field” equation was used to fit unitary current data from all three channels in concentrations of external potassium < or = 500 mM. 4. Data from ensemble tail currents in seawater indicated that the sodium permeability coefficient (PNa) of channels with either intermediate or slow kinetics was < or = 0.015 PK; preliminary data from channels with fast kinetics suggested that they too had a PNa/PK selectivity of approximately 0.01. 5. We propose that spike management in the giant motor axons of Aglantha depends on three members of a family of potassium-selective ion channels that seem likely to be structurally related.
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Döös, Kristofer, Bror Jönsson y Joakim Kjellsson. "Evaluation of oceanic and atmospheric trajectory schemes in the TRACMASS trajectory model v6.0". Geoscientific Model Development 10, n.º 4 (24 de abril de 2017): 1733–49. http://dx.doi.org/10.5194/gmd-10-1733-2017.
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Abstract. Three different trajectory schemes for oceanic and atmospheric general circulation models are compared in two different experiments. The theories of the trajectory schemes are presented showing the differential equations they solve and why they are mass conserving. One scheme assumes that the velocity fields are stationary for set intervals of time between saved model outputs and solves the trajectory path from a differential equation only as a function of space, i.e. stepwise stationary. The second scheme is a special case of the stepwise-stationary scheme, where velocities are assumed constant between general circulation model (GCM) outputs; it uses hence a fixed GCM time step. The third scheme uses a continuous linear interpolation of the fields in time and solves the trajectory path from a differential equation as a function of both space and time, i.e. a time-dependent scheme. The trajectory schemes are tested offline, i.e. using the already integrated and stored velocity fields from a GCM. The first comparison of the schemes uses trajectories calculated using the velocity fields from a high-resolution ocean general circulation model in the Agulhas region. The second comparison uses trajectories calculated using the wind fields from an atmospheric reanalysis. The study shows that using the time-dependent scheme over the stepwise-stationary scheme greatly improves accuracy with only a small increase in computational time. It is also found that with decreasing time steps the stepwise-stationary scheme becomes increasingly more accurate but at increased computational cost. The time-dependent scheme is therefore preferred over the stepwise-stationary scheme. However, when averaging over large ensembles of trajectories, the two schemes are comparable, as intrinsic variability dominates over numerical errors. The fixed GCM time step scheme is found to be less accurate than the stepwise-stationary scheme, even when considering averages over large ensembles.
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Han, Ki Bong y Yong Ho Choi. "Characterization of Contact Resistance between Carbon Nanotubes Film and Metal Electrodes". Advanced Materials Research 683 (abril de 2013): 238–41. http://dx.doi.org/10.4028/www.scientific.net/amr.683.238.
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Carbon nanotube has attracted great research attentions due to its outstanding electrical, physical, mechanical, chemical properties. Based on its excellent properties, the carbon nanotube is promising nanoscale material for novel electrical, mechanical, chemical, and biological devices and sensors. However, it is very difficult to control the structure of carbon nanotube during synthesis. A carbon nanotubes film has 3 dimensional structures of interwoven carbon nanotubes as well as unique properties such as transparency, flexibility and good electrical conductivity. More importantly, the properties of carbon nanotubes are ensemble averaged in this formation. In this research, we study the contact resistance between carbon nanotubes film and metal electrode. For most of electrical devices using carbon nanotubes film, it is necessary to have metal electrodes on the film for current path. A resistance at the contact lowers the electrical efficiencies of the devices. Therefore, it is important to measure and characterize the contact resistance and lower it for better efficiencies. The device demonstrated in this study using classical technique for metal contacts provides relatively reliable contact resistance measurements for carbon nanotubes film applications.
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Ikromjanov, Kobiljon, Subrata Bhattacharjee, Rashadul Islam Sumon, Yeong-Byn Hwang, Hafizur Rahman, Myung-Jae Lee, Hee-Cheol Kim, Eunhyang Park, Nam-Hoon Cho y Heung-Kook Choi. "Region Segmentation of Whole-Slide Images for Analyzing Histological Differentiation of Prostate Adenocarcinoma Using Ensemble EfficientNetB2 U-Net with Transfer Learning Mechanism". Cancers 15, n.º 3 (26 de enero de 2023): 762. http://dx.doi.org/10.3390/cancers15030762.
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Recent advances in computer-aided detection via deep learning (DL) now allow for prostate cancer to be detected automatically and recognized with extremely high accuracy, much like other medical diagnoses and prognoses. However, researchers are still limited by the Gleason scoring system. The histopathological analysis involved in assigning the appropriate score is a rigorous, time-consuming manual process that is constrained by the quality of the material and the pathologist’s level of expertise. In this research, we implemented a DL model using transfer learning on a set of histopathological images to segment cancerous and noncancerous areas in whole-slide images (WSIs). In this approach, the proposed Ensemble U-net model was applied for the segmentation of stroma, cancerous, and benign areas. The WSI dataset of prostate cancer was collected from the Kaggle repository, which is publicly available online. A total of 1,000 WSIs were used for region segmentation. From this, 8,100 patch images were used for training, and 900 for testing. The proposed model demonstrated an average dice coefficient (DC), intersection over union (IoU), and Hausdorff distance of 0.891, 0.811, and 15.9, respectively, on the test set, with corresponding masks of patch images. The manipulation of the proposed segmentation model improves the ability of the pathologist to predict disease outcomes, thus enhancing treatment efficacy by isolating the cancerous regions in WSIs.
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Minaei, Amin, Sara Todeschini, Robert Sitzenfrei y Enrico Creaco. "Ensemble Evaluation and Member Selection of Regional Climate Models for Impact Models Assessment". Water 14, n.º 23 (5 de diciembre de 2022): 3967. http://dx.doi.org/10.3390/w14233967.
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Climate change increasingly is affecting every aspect of human life on the earth. Many regional climate models (RCMs) have so far been developed to carefully assess this important phenomenon on specific regions. In this study, ten RCMs captured from the European Coordinated Downscaling Experiment (EURO CORDEX) platform are evaluated on the river Chiese catchment located in the northeast of Italy. The models’ ensembles are assessed in terms of the uncertainty and error calculated through different statistical and error indices. The uncertainties are investigated in terms of signal (increase, decrease, or neutral changes in the variables) and value uncertainties. Together with the spatial analysis of the data over the catchment, the weighted averaged values are used for the models’ evaluations and data projections. Using weighted catchment variables, climate change impacts are assessed on 10 different hydro-climatological variables showing the changes in the temperature, precipitation, rainfall events’ features, and the hydrological variables of the Chiese catchment between historical (1991–2000) and future (2071–2080) decades under RCP (Representative Concentration Path for increasing greenhouse gas emissions) scenario 4.5. The results show that, even though the multi-model ensemble mean (MMEM) could cover the outputs’ uncertainty of the models, it increases the error of the outputs. On the other hand, the RCM with the least error could cause high signal and value uncertainties for the results. Hence, different multi-model subsets of ensembles (MMEM-s) of 10 RCMs are obtained through a proposed algorithm for different impact models’ calculations and projections, making tradeoffs between two important shortcomings of model outputs, which are error and uncertainty. The single model (SM) and multi-model (MM) outputs imply that catchment warming is obvious in all cases and, therefore, evapotranspiration will be intensified in the future where there are about 1.28% and 6% value uncertainties for monthly temperature increase and the decadal relative balance of evapotranspiration, respectively. While rainfall events feature higher intensity and shorter duration in the SM, there are no significant differences for the mentioned features in the MM, showing high signal uncertainties in this regard. The unchanged catchment rainfall events’ depth can be observed in two SM and MM approaches, implying good signal certainty for the depth feature trend; there is still high uncertainty about the depth values. As a result of climate change, the percolation component change is negligible, with low signal and value uncertainties, while decadal evapotranspiration and discharge uncertainties show the same signal and value. While extreme events and their anomalous outcomes direct the uncertainties in rainfall events’ features’ values towards zero, they remain critical for yearly maximum catchment discharge in 2071–2080 as the highest value uncertainty is observed for this variable.