316 research outputs found
Nonequilibrium spin injection in monolayer black phosphorus
Monolayer black phosphorus (MBP) is an interesting emerging electronic
material with a direct band gap and relatively high carrier mobility. In this
work we report a theoretical investigation of nonequilibrium spin injection and
spin-polarized quantum transport in MBP from ferromagnetic Ni contacts, in
two-dimensional magnetic tunneling structures. We investigate physical
properties such as the spin injection efficiency, the tunnel magnetoresistance
ratio, spin-polarized currents, charge currents and transmission coefficients
as a function of external bias voltage, for two different device contact
structures where MBP is contacted by Ni(111) and by Ni(100). While both
structures are predicted to give respectable spin-polarized quantum transport,
the Ni(100)/MBP/Ni(100) trilayer has the superior properties where the spin
injection and magnetoresistance ratio maintains almost a constant value against
the bias voltage. The nonequilibrium quantum transport phenomenon is understood
by analyzing the transmission spectrum at nonequilibrium.Comment: 6 pages, 6 figure
Co-membership, Networks Ties, and OSS Success: An Investigation Controlling for Alternative Mechanisms for Knowledge Flow
Co-membership has been considered as a major mechanism for constructing social networks, but it has met many criticisms over time for failing to control for alternative mechanisms for knowledge flow. Although social networks constructed in online environment can reduce such possibilities, it is not without limitations. One possible mechanism for learning and knowledge flow is direct watching and observation. This study investigates the impact of co-membership taking into account the alternative mechanism of watching under the setting of OSS development at GitHub. It finds that both co-membership and watching contribute positively to OSS success, and thus shows the co-existence of both experiential learning and vicarious learning for OSS development. Moreover, it finds the impact of co-membership is much stronger than watching. While the impact of co-membership may be biased in prior literature, this study confirms that co-membership is indeed an effective mechanism for constructing online social networks for knowledge flow
Seismic Response Calculation of Saturated Soft Soil
In this paper, Shanghai saturated soft soil is modeled as a two-phase porous media system consisting of solid and fluid phases. On the basis of resonant column test and dynamic triaxial test data of Shanghai saturated soft soil, the dynamic calculation model including a set of relationships of stress, strain, and pore water pressure and earthquake subsidence is developed to compute the seismic response of soil. The procedure to identify soil constants for the dynamic calculation model is also reported in detail. Subsequently, a dynamic effective stress analysis with the finite element method has been recommended to predict the seismic response of soil. Finally, the developed dynamic calculation model together with the dynamic effective stress analysis is utilized to predict the seismic response of Shanghai soil strata through the finite element method and some valuable conclusions are obtained from the results
Transient changes in magnetosphericâionospheric currents caused by the passage of an interplanetary shock: Northward interplanetary magnetic field case
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94908/1/jgra20240.pd
Global Fault-Tolerant Control of Underactuated Aerial Vehicles with Redundant Actuators
In this paper, we consider the fault-tolerant control problem for aerial vehicles with redundant actuators. The redundant actuator brings difficulty in fault identification and isolation. Active fault-tolerant control is adopted in this paper as it can detect actuator fault. The entire proposed fault-tolerant control algorithm contains a baseline controller, the fault detection and isolation scheme, and the controller reconstruction module. A robust parameter identification method is designed to identify the torque and thrust generated by the actuators. The feasibility of isolating the fault for the redundant actuators is analyzed through mathematical proof. Through the analysis, the practical fault isolation algorithm is also proposed. Two typical aerial vehicles with redundant actuators, an eight-rotor aircraft and a hexa-rotor aircraft, are adopted in numerical simulations to verify the effectiveness of the proposed fault-tolerant control approach
ME-PCN: Point Completion Conditioned on Mask Emptiness
Point completion refers to completing the missing geometries of an object
from incomplete observations. Main-stream methods predict the missing shapes by
decoding a global feature learned from the input point cloud, which often leads
to deficient results in preserving topology consistency and surface details. In
this work, we present ME-PCN, a point completion network that leverages
`emptiness' in 3D shape space. Given a single depth scan, previous methods
often encode the occupied partial shapes while ignoring the empty regions (e.g.
holes) in depth maps. In contrast, we argue that these `emptiness' clues
indicate shape boundaries that can be used to improve topology representation
and detail granularity on surfaces. Specifically, our ME-PCN encodes both the
occupied point cloud and the neighboring `empty points'. It estimates
coarse-grained but complete and reasonable surface points in the first stage,
followed by a refinement stage to produce fine-grained surface details.
Comprehensive experiments verify that our ME-PCN presents better qualitative
and quantitative performance against the state-of-the-art. Besides, we further
prove that our `emptiness' design is lightweight and easy to embed in existing
methods, which shows consistent effectiveness in improving the CD and EMD
scores.Comment: Accepted to ICCV 2021; typos correcte
Modeling subauroral polarization streams during the 17 March 2013 storm
The subauroral polarization streams (SAPS) are one of the most important features in representing magnetosphereâionosphere coupling processes. In this study, we use a stateâofâtheâart modeling framework that couples an inner magnetospheric ring current model RAMâSCB with a global MHD model BlockâAdaptive Tree Solarâwind Roe Upwind Scheme (BATSâRâUS) and an ionospheric potential solver to study the SAPS that occurred during the 17 March 2013 storm event as well as to assess the modeling capability. Both ionospheric and magnetospheric signatures associated with SAPS are analyzed to understand the spatial and temporal evolution of the electrodynamics in the midlatitude regions. Results show that the model captures the SAPS at subauroral latitudes, where Region 2 fieldâaligned currents (FACs) flow down to the ionosphere and the conductance is lower than in the higherâlatitude auroral zone. Comparisons to observations such as FACs observed by Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE), crossâtrack ion drift from Defense Meteorological Satellite Program (DMSP), and in situ electric field observations from the Van Allen Probes indicate that the model generally reproduces the global dynamics of the Regionâ2 FACs, the position of SAPS along the DMSP, and the location of the SAPS electric field around L of 3.0 in the inner magnetosphere near the equator. The model also demonstrates double westward flow channels in the dusk sector (the higherâlatitude auroral convection and the subauroral SAPS) and captures the mechanism of the SAPS. However, the comparison with ion drifts along DMSP trajectories shows an underestimate of the magnitude of the SAPS and the sensitivity to the specific location and time. The comparison of the SAPS electric field with that measured from the Van Allen Probes shows that the simulated SAPS electric field penetrates deeper than in reality, implying that the shielding from the Region 2 FACs in the model is not well represented. Possible solutions in future studies to improve the modeling capability include implementing a selfâconsistent ionospheric conductivity module from inner magnetosphere particle precipitation, coupling with the thermosphereâionosphere chemical processes, and connecting the ionosphere with the inner magnetosphere by the stronger Region 2 FACs calculated in the inner magnetosphere model.Key PointsSAPS simulation using BATSâRâUS coupled with ring current model RAMâSCBComparisons done with AMPERE, DMSP, and Van Allen Probes observationsCaptured the basic physics and mechanism of SAPSPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/111134/1/jgra51638.pd
DeWave: Discrete EEG Waves Encoding for Brain Dynamics to Text Translation
The translation of brain dynamics into natural language is pivotal for
brain-computer interfaces (BCIs), a field that has seen substantial growth in
recent years. With the swift advancement of large language models, such as
ChatGPT, the need to bridge the gap between the brain and languages becomes
increasingly pressing. Current methods, however, require eye-tracking fixations
or event markers to segment brain dynamics into word-level features, which can
restrict the practical application of these systems. These event markers may
not be readily available or could be challenging to acquire during real-time
inference, and the sequence of eye fixations may not align with the order of
spoken words. To tackle these issues, we introduce a novel framework, DeWave,
that integrates discrete encoding sequences into open-vocabulary EEG-to-text
translation tasks. DeWave uses a quantized variational encoder to derive
discrete codex encoding and align it with pre-trained language models. This
discrete codex representation brings forth two advantages: 1) it alleviates the
order mismatch between eye fixations and spoken words by introducing text-EEG
contrastive alignment training, and 2) it minimizes the interference caused by
individual differences in EEG waves through an invariant discrete codex. Our
model surpasses the previous baseline (40.1 and 31.7) by 3.06% and 6.34%,
respectively, achieving 41.35 BLEU-1 and 33.71 Rouge-F on the ZuCo Dataset.
Furthermore, this work is the first to facilitate the translation of entire EEG
signal periods without needing word-level order markers (e.g., eye fixations),
scoring 20.5 BLEU-1 and 29.5 Rouge-1 on the ZuCo Dataset, respectively. Codes
and the final paper will be public soon
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