1,123 research outputs found
Polarization-controlled modulation doping of a ferroelectric from first principles
In a ferroelectric field effect transistor (FeFET), it is generally assumed
that the ferroelectric gate plays a purely electrostatic role. Recently it has
been shown that in some cases, which could be called 'active FeFETs',
electronic states in the ferroelectric contribute to the device conductance as
the result of a modulation doping effect in which carriers are transferred from
the channel into the ferroelectric layers near the interface. Here we report
first-principles calculations and model analysis to elucidate the various
aspects of this mechanism and to provide guidance in materials choices and
interface termination for optimizing the on-off ratio, using BaTiO3/n-SrTiO3
and PbTiO3/n-SrTiO3 as prototypical systems. It is shown that the modulation
doping is substantial in both cases, and that extension of an electrostatic
model developed in previous work provides a good description of the transferred
charge distribution. This model can be used to suggest additional materials
heterostructures for the design of active FeFETs.Comment: 9 pages, 8 figure
Cosmic Reionization On Computers. Properties of the Post-reionization IGM
We present a comparison between several observational tests of the
post-reionization IGM and the numerical simulations of reionization completed
under the Cosmic Reionization On Computers (CROC) project. The CROC simulations
match the gap distribution reasonably well, and also provide a good match for
the distribution of peak heights, but there is a notable lack of wide peaks in
the simulated spectra and the flux PDFs are poorly matched in the narrow
redshift interval 5.5<z<5.7, with the match at other redshifts being
significantly better, albeit not exact. Both discrepancies are related:
simulations show more opacity than the data.Comment: Accepted by Ap
Ontology-based specific and exhaustive user profiles for constraint information fusion for multi-agents
Intelligent agents are an advanced technology utilized in Web Intelligence. When searching information from a distributed Web environment, information is retrieved by multi-agents on the client site and fused on the broker site. The current information fusion techniques rely on cooperation of agents to provide statistics. Such techniques are computationally expensive and unrealistic in the real world. In this paper, we introduce a model that uses a world ontology constructed from the Dewey Decimal Classification to acquire user profiles. By search using specific and exhaustive user profiles, information fusion techniques no longer rely on the statistics provided by agents. The model has been successfully evaluated using the large INEX data set simulating the distributed Web environment
Cosmic Reionization Redux
We show that numerical simulations of reionization that resolve the Lyman
Limit systems (and, thus, correctly count absorptions of ionizing photons) have
converged to about 10% level for 5<z<6.2 and are in reasonable agreement
(within 10%) with the SDSS data in this redshift interval. The SDSS data thus
constraint the redshift of overlap of cosmic HII regions to z_{OVL} =
6.1+-0.15. At higher redshifts, the simulations are far from convergence on the
mean Gunn-Peterson optical depth, but achieve good convergence for the mean
neutral hydrogen fraction. The simulations that fit the SDSS data, however, do
not have nearly enough resolution to resolve the earliest episodes of star
formation, and are very far from converging on the precise value of the optical
depth to Thompson scattering - any value between 6 and 10% is possible,
depending on the convergence rate of the simulations and the fractional
contribution of PopIII stars. This is generally consistent with the third-year
WMAP results, but much higher resolution simulation are required to come up
with the sufficiently precise value for the Thompson optical depth that can be
statistically compared with the WMAP data.Comment: Submitted to ApJ. Comments welcom
Recommended from our members
Anaplastic Thyroid Carcinoma Histologically Mimicking a Plasmacytoma.
Anaplastic (undifferentiated) thyroid carcinoma (ATC) is a rare malignancy which may arise from transformation of a pre-existing differentiated carcinoma. We report the unique case where a lesion of thyroid origin presented with the histological features of mature plasma cells. Immunohistochemistry confirmed the lesion to be an anaplastic thyroid carcinoma arising from papillary thyroid carcinoma. A tumor mimicking a malignancy of a different cellular origin can lead clinicians to incorrect treatment approaches. Careful correlation with clinical details and knowledge of these unique presentations is important for reaching the correct diagnosis
Gene Co-expression Network and Copy Number Variation Analyses Identify Transcription Factors Associated With Multiple Myeloma Progression
Multiple myeloma (MM) has two clinical precursor stages of disease: monoclonal gammopathy of undetermined significance (MGUS) and smoldering multiple myeloma (SMM). However, the mechanism of progression is not well understood. Because gene co-expression network analysis is a well-known method for discovering new gene functions and regulatory relationships, we utilized this framework to conduct differential co-expression analysis to identify interesting transcription factors (TFs) in two publicly available datasets. We then used copy number variation (CNV) data from a third public dataset to validate these TFs. First, we identified co-expressed gene modules in two publicly available datasets each containing three conditions: normal, MGUS, and SMM. These modules were assessed for condition-specific gene expression, and then enrichment analysis was conducted on condition-specific modules to identify their biological function and upstream TFs. TFs were assessed for differential gene expression between normal and MM precursors, then validated with CNV analysis to identify candidate genes. Functional enrichment analysis reaffirmed known functional categories in MM pathology, the main one relating to immune function. Enrichment analysis revealed a handful of differentially expressed TFs between normal and either MGUS or SMM in gene expression and/or CNV. Overall, we identified four genes of interest (MAX, TCF4, ZNF148, and ZNF281) that aid in our understanding of MM initiation and progression
Statistically Optimal K-means Clustering via Nonnegative Low-rank Semidefinite Programming
-means clustering is a widely used machine learning method for identifying
patterns in large datasets. Semidefinite programming (SDP) relaxations have
recently been proposed for solving the -means optimization problem that
enjoy strong statistical optimality guarantees, but the prohibitive cost of
implementing an SDP solver renders these guarantees inaccessible to practical
datasets. By contrast, nonnegative matrix factorization (NMF) is a simple
clustering algorithm that is widely used by machine learning practitioners, but
without a solid statistical underpinning nor rigorous guarantees. In this
paper, we describe an NMF-like algorithm that works by solving a nonnegative
low-rank restriction of the SDP relaxed -means formulation using a nonconvex
Burer--Monteiro factorization approach. The resulting algorithm is just as
simple and scalable as state-of-the-art NMF algorithms, while also enjoying the
same strong statistical optimality guarantees as the SDP. In our experiments,
we observe that our algorithm achieves substantially smaller mis-clustering
errors compared to the existing state-of-the-art
Polarization-controlled Ohmic to Schottky transition at a metal/ferroelectric interface
Ferroelectric polar displacements have recently been observed in conducting electron-doped BaTiO3 (n-BTO). The coexistence of a ferroelectric phase and conductivity opens the door to new functionalities that may provide a unique route for novel device applications. Using first-principles methods and electrostatic modeling, we explore the effect that the switchable polarization of n-BTO has on the electronic properties of the SrRuO3/n-BTO (001) interface. Ferroelectric polarization controls the accumulation or depletion of electron charge at the interface, and the associated bending of the n-BTO conduction band determines the transport regime across the interface. The interface exhibits a Schottky tunnel barrier for one polarization orientation, whereas an Ohmic contact is present for the opposite polarization orientation, leading to a large change in interface resistance associated with polarization reversal. Our calculations reveal a five orders of magnitude change in the interface resistance because of polarization switching
Polarization-controlled Ohmic to Schottky transition at a metal/ferroelectric interface
Ferroelectric polar displacements have recently been observed in conducting electron-doped BaTiO3 (n-BTO). The coexistence of a ferroelectric phase and conductivity opens the door to new functionalities that may provide a unique route for novel device applications. Using first-principles methods and electrostatic modeling, we explore the effect that the switchable polarization of n-BTO has on the electronic properties of the SrRuO3/n-BTO (001) interface. Ferroelectric polarization controls the accumulation or depletion of electron charge at the interface, and the associated bending of the n-BTO conduction band determines the transport regime across the interface. The interface exhibits a Schottky tunnel barrier for one polarization orientation, whereas an Ohmic contact is present for the opposite polarization orientation, leading to a large change in interface resistance associated with polarization reversal. Our calculations reveal a five orders of magnitude change in the interface resistance because of polarization switching
- …