1,874 research outputs found
Excitonic Dynamical Franz-Keldysh Effect
The Dynamical Franz-Keldysh Effect is exposed by exploring near-bandgap
absorption in the presence of intense THz electric fields. It bridges the gap
between the DC Franz- Keldysh effect and multi-photon absorption and competes
with the THz AC Stark Effect in shifting the energy of the excitonic resonance.
A theoretical model which includes the strong THz field non-perturbatively via
a non-equilibrium Green Functions technique is able to describe the Dynamical
Franz-Keldysh Effect in the presence of excitonic absorption.Comment: 4 pages in revtex with 5 figures included using epsf. Submitted to
Physical Review Letter
People-to-People Lending: The Emerging e-Commerce Transformation of a Financial Market
This paper provides an overview of the concept of people-to-people (P2P) lending, a relatively new e-commerce phenomenon that has the potential to radically change the structure of the loan segment of the financial industry. P2P lending creates a marketplace of individuals and a social fabric through which these individuals interact. It provides efficient information transfer, thus perhaps creating more perfect markets. P2P lending requires information systems support to make it function, and to provide a social network mechanism that may be crucial for its success. We discuss different P2P lending marketplace models, and how information systems support the creation and management of these new marketplaces, and how they support the individuals involved. We conclude by providing some important research questions and directions, and issues for which further investigation is called
Quasienergy Spectroscopy of Excitons
We theoretically study nonlinear optics of excitons under intense THz
irradiation. In particular, the linear near infrared absorption and resonantly
enhanced nonlinear sideband generation are described. We predict a rich
structure in the spectra which can be interpreted in terms of the quasienergy
spectrum of the exciton, via a remarkably transparent expression for the
susceptibility, and show that the effects of strongly avoided quasienergy
crossings manifest themselves directly, both in the absorption and transmitted
sidebands.Comment: 4 pages RevTex, 3 eps figs included, as publishe
Domain ontology for digital marketplaces
Recently the sharing economy has emerged as a viable alternative to fulfilling a variety of consumer needs. As there is no consensus on the definition of âsharing economyâ we use the term âmarketplaceâ to refer more specifically to Internet/software-based sharing economy platforms connecting two different market segments. In the field of sharing economy and marketplaces we found a research gap concerning the (socio)technological aspects and the development of marketplaces. A marketplace ontology can help to have a clear account of marketplace concepts which will facilitate communication, consensus and alignment. In this paper we design this marketplace ontology in four steps. First the selection of UFO as foundation and UFO-S as core ontology. Second the search for a set of minimal conditions and properties common for marketplaces and the derivation into competency questions. Third, use the competency questions to identify fragmented sub-ontology pieces called Domain-Related Ontology Patterns (DROPs) and apply them informally by extending UFO-S concepts to design a marketplace domain ontology. This marketplace domain ontology is represented in OntoUML. The last step is the validation of the OntoUML model using expert knowledge
Are Essay Mills committing fraud? An analysis of their behaviours vs the 2006 Fraud Act (UK)
Many strategies have been proposed to address the use of Essay Mills and other âcontract cheatingâ services by students. These services generally offer bespoke custom-written essays or other assignments to students in exchange for a fee. There have been calls for the use of legal approaches to tackle the problem. Here we determine whether the UK Fraud Act (2006) might be used to tackle some of the activities of companies providing these services in the UK, by comparing their common practises, and their Terms and Conditions, with the Act. We found that all the sites examined have disclaimers regarding the use of their products but there are some obvious contradictions in the activities of the sites which undermine these disclaimers, for example all sites offer plagiarism-free guarantees for the work and at least eight have advertising which appears to contradict their terms and conditions. We identify possible areas in which the Act could be used to pursue a legal case but overall conclude that such an approach is unlikely to be effective. We call for a new offence to be created in UK law which specifically targets the undesirable behaviours of these companies in the UK, although the principles could be applied elsewhere. We also highlight other UK legal approaches that may be more successful
The TAOS Project Stellar Variability II. Detection of 15 Variable Stars
The Taiwanese-American Occultation Survey (TAOS) project has collected more
than a billion photometric measurements since 2005 January. These sky survey
data-covering timescales from a fraction of a second to a few hundred days-are
a useful source to study stellar variability. A total of 167 star fields,
mostly along the ecliptic plane, have been selected for photometric monitoring
with the TAOS telescopes. This paper presents our initial analysis of a search
for periodic variable stars from the time-series TAOS data on one particular
TAOS field, No. 151 (RA = 17^{\rm h}30^{\rm m}6\fs67, Dec = 27\degr17\arcmin
30\arcsec, J2000), which had been observed over 47 epochs in 2005. A total of
81 candidate variables are identified in the 3 square degree field, with
magnitudes in the range 8 < R < 16. On the basis of the periodicity and shape
of the lightcurves, 29 variables, 15 of which were previously unknown, are
classified as RR Lyrae, Cepheid, delta Scuti, SX Phonencis, semi-regular and
eclipsing binaries.Comment: 20 pages, 6 figures, accepted in The Astronomical Journa
Discovery of the optical counterpart and early optical observations of GRB990712
We present the discovery observations of the optical counterpart of the
gamma-ray burster GRB990712 taken 4.16 hours after the outburst and discuss its
light curve observed in the V, R and I bands during the first ~35 days after
the outburst. The observed light curves were fitted with a power-law decay for
the optical transient (OT), plus an additional component which was treated in
two different ways. First, the additional component was assumed to be an
underlying galaxy of constant brightness. The resulting slope of the decay is
0.97+/-0.05 and the magnitudes of the underlying galaxy are: V = 22.3 +/- 0.05,
R = 21.75 +/- 0.05 and I = 21.35 +/- 0.05. Second, the additional component was
assumed to be a galaxy plus an underlying supernova with a time-variable
brightness identical to that of GRB980425, appropriately scaled to the redshift
of GRB990712. The resulting slope of the decay is similar, but the
goodness-of-fit is worse which would imply that either this GRB is not
associated with an underlying supernova or the underlying supernova is much
fainter than the supernova associated with GRB980425. The galaxy in this case
is fainter: V = 22.7 +/- 0.05, R = 22.25 +/- 0.05 and I = 22.15 +/- 0.05; and
the OT plus the underlying supernova at a given time is brighter. Measurements
of the brightnesses of the OT and the galaxy by late-time HST observation and
ground-based observations can thus assess the presence of an underlying
supernova.Comment: To appear in Ap
DHODH modulates transcriptional elongation in the neural crest and melanoma
Melanoma is a tumour of transformed melanocytes, which are originally derived from the embryonic neural crest. It is unknown to what extent the programs that regulate neural crest development interact with mutations in the BRAF oncogene, which is the most commonly mutated gene in human melanoma1. We have used zebrafish embryos to identify the initiating transcriptional events that occur on activation of human BRAF(V600E) (which encodes an amino acid substitution mutant of BRAF) in the neural crest lineage. Zebrafish embryos that are transgenic for mitfa:BRAF(V600E) and lack p53 (also known as tp53) have a gene signature that is enriched for markers of multipotent neural crest cells, and neural crest progenitors from these embryos fail to terminally differentiate. To determine whether these early transcriptional events are important for melanoma pathogenesis, we performed a chemical genetic screen to identify small-molecule suppressors of the neural crest lineage, which were then tested for their effects on melanoma. One class of compound, inhibitors of dihydroorotate dehydrogenase (DHODH), for example leflunomide, led to an almost complete abrogation of neural crest development in zebrafish and to a reduction in the self-renewal of mammalian neural crest stem cells. Leflunomide exerts these effects by inhibiting the transcriptional elongation of genes that are required for neural crest development and melanoma growth. When used alone or in combination with a specific inhibitor of the BRAF(V600E) oncogene, DHODH inhibition led to a marked decrease in melanoma growth both in vitro and in mouse xenograft studies. Taken together, these studies highlight developmental pathways in neural crest cells that have a direct bearing on melanoma formation
The 0.5MJ transiting exoplanet WASP-13b
We report the discovery of WASP-13b, a low-mass M_{\rm p} = 0.46 ^_~M_J transiting exoplanet with an orbital period of 4.35298 0.00004 days. The transit has a depth of 9 mmag, and although our follow-up photometry does not allow us to constrain the impact parameter well (0 < b < 0.46), with radius in the range ~ 1.06-1.21 RJ the location of WASP-13b in the mass-radius plane is nevertheless consistent with H/He-dominated, irradiated, low core mass and core-free theoretical models. The G1V host star is similar to the Sun in mass (M__ ~M_{\odot}) and metallicity ([M/H] = 0.00.2), but is possibly older ( 8.5^_{\rm -4.9} Gyr)
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