8,624 research outputs found
Compactifications of Complete Riemannian manifolds and Their Applications
To study a noncompact Riemannian manifold, it is often useful to find a
compactification. We discuss several common compactifications and survey some
recent results
Wormbase Curation Interfaces and Tools
Curating biological information from the published literature can be time- and labor-intensive especially without automated tools. WormBase1 has adopted several curation interfaces and tools, most of which were built in-house, to help curators recognize and extract data more efficiently from the literature. These tools range from simple computer interfaces for data entry to employing scripts that take advantage of complex text extraction algorithms, which automatically identify specific objects in a paper and presents them to the curator for curation. By using these in-house tools, we are also able to tailor the tool to the individual needs and preferences of the curator. For example, Gene Ontology Cellular Component and gene-gene interaction curators employ the text mining software Textpresso2 to indentify, retrieve, and extract relevant sentences from the full text of an article. The curators then use a web-based curation form to enter the data into our local database. For transgene and antibody curation, curators use the publicly available Phenote ontology annotation curation interface (developed by the Berkeley Bioinformatics Open-Source Projects (BBOP)), which we have adapted with datatype specific configurations. This tool has been used as a basis for developing our own Ontology Annotator tool, which is being used by our phenotype and gene ontology curators. For RNAi curation, we created web-based submission forms that allow the curator to efficiently capture all relevant information. In all cases, the data undergoes a final scripted data dump step to make sure all the information conforms into a readable file by our object oriented database
Coherent Optical DFT-Spread OFDM
We consider application of the discrete Fourier transform-spread orthogonal
frequency-division multiplexing (DFT-spread OFDM) technique to high-speed fiber
optic communications. The DFT-spread OFDM is a form of single-carrier technique
that possesses almost all advantages of the multicarrier OFDM technique (such
as high spectral efficiency, flexible bandwidth allocation, low sampling rate
and low-complexity equalization). In particular, we consider the optical
DFT-spread OFDM system with polarization division multiplexing (PDM) that
employs a tone-by-tone linear minimum mean square error (MMSE) equalizer. We
show that such a system offers a much lower peak-to-average power ratio (PAPR)
performance as well as better bit error rate (BER) performance compared with
the optical OFDM system that employs amplitude clipping.Comment: This idea was originally submitted at Nov. 28th, 2009. After many
times of rejection and resubmission, it was finally accepted by the journal
of Advances in Optical Technologie
Valley excitons in two-dimensional semiconductors
Monolayer group-VIB transition metal dichalcogenides have recently emerged as
a new class of semiconductors in the two-dimensional limit. The attractive
properties include: the visible range direct band gap ideal for exploring
optoelectronic applications; the intriguing physics associated with spin and
valley pseudospin of carriers which implies potentials for novel electronics
based on these internal degrees of freedom; the exceptionally strong Coulomb
interaction due to the two-dimensional geometry and the large effective masses.
The physics of excitons, the bound states of electrons and holes, has been one
of the most actively studied topics on these two-dimensional semiconductors,
where the excitons exhibit remarkably new features due to the strong Coulomb
binding, the valley degeneracy of the band edges, and the valley dependent
optical selection rules for interband transitions. Here we give a brief
overview of the experimental and theoretical findings on excitons in
two-dimensional transition metal dichalcogenides, with focus on the novel
properties associated with their valley degrees of freedom.Comment: Topical review, published online on National Science Review in Jan
201
Beacon-Assisted Spectrum Access with Cooperative Cognitive Transmitter and Receiver
Spectrum access is an important function of cognitive radios for detecting
and utilizing spectrum holes without interfering with the legacy systems. In
this paper we propose novel cooperative communication models and show how
deploying such cooperations between a pair of secondary transmitter and
receiver assists them in identifying spectrum opportunities more reliably.
These cooperations are facilitated by dynamically and opportunistically
assigning one of the secondary users as a relay to assist the other one which
results in more efficient spectrum hole detection. Also, we investigate the
impact of erroneous detection of spectrum holes and thereof missing
communication opportunities on the capacity of the secondary channel. The
capacity of the secondary users with interference-avoiding spectrum access is
affected by 1) how effectively the availability of vacant spectrum is sensed by
the secondary transmitter-receiver pair, and 2) how correlated are the
perceptions of the secondary transmitter-receiver pair about network spectral
activity. We show that both factors are improved by using the proposed
cooperative protocols. One of the proposed protocols requires explicit
information exchange in the network. Such information exchange in practice is
prone to wireless channel errors (i.e., is imperfect) and costs bandwidth loss.
We analyze the effects of such imperfect information exchange on the capacity
as well as the effect of bandwidth cost on the achievable throughput. The
protocols are also extended to multiuser secondary networks.Comment: 36 pages, 6 figures, To appear in IEEE Transaction on Mobile
Computin
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