7,718 research outputs found
Numerical study of the optical nonlinearity of doped and gapped graphene: From weak to strong field excitation
Numerically solving the semiconductor Bloch equations within a
phenomenological relaxation time approximation, we extract both the linear and
nonlinear optical conductivities of doped graphene and gapped graphene under
excitation by a laser pulse. We discuss in detail the dependence of second
harmonic generation, third harmonic generation, and the Kerr effects on the
doping level, the gap, and the electric field amplitude. The numerical results
for weak electric fields agree with those calculated from available analytic
perturbation formulas. For strong electric fields when saturation effects are
important, all the effective third order nonlinear response coefficients show a
strong field dependence.Comment: 12 pages with 9 figure
Third order nonlinearity of graphene: effects of phenomenological relaxation and finite temperature
We investigate the effect of phenomenological relaxation parameters on the
third order optical nonlinearity of doped graphene by perturbatively solving
the semiconductor Bloch equation around the Dirac points. An analytic
expression for the nonlinear conductivity at zero temperature is obtained under
the linear dispersion approximation. With this analytic formula as starting
point, we construct the conductivity at finite temperature and study the
optical response to a laser pulse of finite duration. We illustrate the
dependence of several nonlinear optical effects, such as third harmonic
generation, Kerr effects and two photon absorption, parametric frequency
conversion, and two color coherent current injection, on the relaxation
parameters, temperature, and pulse duration. In the special case where one of
the electric fields is taken as a dc field, we investigate the dc-current and
dc-field induced second order nonlinearities, including dc-current induced
second harmonic generation and difference frequency generation.Comment: 23+ pages, 10 figures. In this version we correct a sign typo in Eq.
(25), for which we thank the discussion in the work
http://arxiv.org/abs/1506.00534v
Machine Body Language: Expressing a Smart Speaker’s Activity with Intelligible Physical Motion
People’s physical movement and body language implicitly convey what they think and feel, are doing or are about to do. In contrast, current smart speakers miss out on this richness of body language, primarily relying on voice commands only. We present QUBI, a dynamic smart speaker that leverages expressive physical motion – stretching, nodding, turning, shrugging, wiggling, pointing and leaning forwards/backwards – to convey cues about its underlying behaviour and activities. We conducted a qualitative Wizard of Oz lab study, in which 12 participants interacted with QUBI in four scripted scenarios. From our study, we distilled six themes: (1) mirroring and mimicking motions; (2) body language to supplement voice instructions; (3) anthropomorphism and personality; (4) audio can trump motion; (5) reaffirming uncertain interpretations to support mutual understanding; and (6) emotional reactions to QUBI’s behaviour. From this, we discuss design implications for future smart speakers
Conjugate 18cm OH Satellite Lines at a Cosmological Distance
We have detected the two 18cm OH satellite lines from the
source PKS1413+135, the 1720 MHz line in emission and the 1612 MHz line in
absorption. The 1720 MHz luminosity is , more than
an order of magnitude larger than that of any other known 1720 MHz maser. The
profiles of the two satellite lines are conjugate, implying that they arise in
the same gas. This allows us to test for any changes in the values of
fundamental constants, without being affected by systematic uncertainties
arising from relative motions between the gas clouds in which the different
lines arise. Our data constrain changes in ,
where ; we find ,
consistent with no changes in , and .Comment: 5 pages, 1 figure. Minor changes to match published versio
The Proper Motion of SgrA*: I. First VLBA Results
We observed Sgr A* and two extragalactic radio sources nearby in angle with
the VLBA over a period of two years and measured relative positions with an
accuracy approaching 0.1 mas. The apparent proper motion of Sgr A* relative to
J1745-283 is 5.90 +/- 0.4 mas/yr, almost entirely in the plane of the Galaxy.
The effects of the orbit of the Sun around the Galactic Center can account for
this motion, and any residual proper motion of Sgr A*, with respect to
extragalactic sources, is less than about 20 km/s. Assuming that Sgr A* is at
rest at the center of the Galaxy, we estimate that the circular rotation speed
in the Galaxy at the position of the Sun is 219 +/- 20 km/s, scaled by Ro/8.0
kpc.
Current observations are consistent with Sgr A* containing all of the nearly
2.6 x 10^6 solar masses, deduced from stellar proper motions, in the form of a
massive black hole. While the low luminosity of Sgr A*, for example, might
possibly have come from a contact binary containing of order 10 solar masses,
the lack of substantial motion rules out a "stellar" origin for Sgr A*. The
very slow speed of Sgr A* yields a lower limit to the mass of Sgr A* of about
1,000 solar masses. Even for this mass, Sgr A* appears to be radiating at less
than 0.1 percent of its Eddington limit
Hydrography, Surface Geology and Geomorphology of the Deep Water Sedimentary Basins to the West of Ireland
This desk study involved the assembly, review and analysis of public domain and available data from an extensive deep water area offshore to the west of Ireland. All major bathymetric and sedimentary basins, in addition to associated shallow plateau and bank areas, were considered. Particular emphasis was placed on the Porcupine Seabight and Rockall Trough as these were considered to be the main areas of interest for the proposed 1996 AIRS (Atlantic Irish Regional Survey) project. Only relatively brief summaries are given for the Hatton Basin, Hatton Bank and the area further west. Also, as the GLORIA side-scan sonar system used in the project is effective only in deeper waters (continental slope and abyssal depths), a considerable portion of the shallow shelf has been ignored.
The primary goal of this study was to assemble a large existing data base on the above areas and to present this in a concise format. An introduction for each area describes the geological location and bathymetric characteristics. This is followed in each case by a description of the hydrography, in particular the characteristics of the water column and bottom current dynamics. Finally, an overview of the main geological and geomorphological features is given. Little reference will be made to the pre-Pleistocene geology of the region, with the focus of the project being on the modern sediments.
The water column over much of the study area is seen to be highly stratified, with a number of distinct layers of various origin evident. Vigorous bottom currents are also clearly present in many areas, often at significant depth, and undoubtedly have an influence on seafloor sedimentation patterns.
Sediment influx related to the cessation of the last glacial cycle has had a profound influence on the sea bed geomorphology. In a number of areas, massive sediment drifts or accumulations are evident, in addition to large scale mass-wasting and slope failure features which determine slope and basin floor character. Vigorous early post-glacial sea bed currents probably determined the distribution of much of the glacial sediment, but currents capable of transporting fine sand to silt grade sediments have been recorded and are still active today.Funder: Marine Institut
Deterministic delivery of remote entanglement on a quantum network
Large-scale quantum networks promise to enable secure communication,
distributed quantum computing, enhanced sensing and fundamental tests of
quantum mechanics through the distribution of entanglement across nodes. Moving
beyond current two-node networks requires the rate of entanglement generation
between nodes to exceed their decoherence rates. Beyond this critical
threshold, intrinsically probabilistic entangling protocols can be subsumed
into a powerful building block that deterministically provides remote entangled
links at pre-specified times. Here we surpass this threshold using diamond spin
qubit nodes separated by 2 metres. We realise a fully heralded single-photon
entanglement protocol that achieves entangling rates up to 39 Hz, three orders
of magnitude higher than previously demonstrated two-photon protocols on this
platform. At the same time, we suppress the decoherence rate of remote
entangled states to 5 Hz by dynamical decoupling. By combining these results
with efficient charge-state control and mitigation of spectral diffusion, we
are able to deterministically deliver a fresh remote state with average
entanglement fidelity exceeding 0.5 at every clock cycle of 100 ms
without any pre- or post-selection. These results demonstrate a key building
block for extended quantum networks and open the door to entanglement
distribution across multiple remote nodes.Comment: v2 - updated to include relevant citatio
Xeroderma pigmentosum complementation group G associated with cockayne syndrome
Xeroderma pigmentosum (XP) and Cockayne syndrome (CS) are two rare inherited disorders with a clinical and cellular hypersensitivity to the UV component of the sunlight spectrum. Although the two traits are generally considered as clinically and genetically distinct entities, on the biochemical level a defect in the nucleotide excision-repair (NER) pathway is involved in both. Classical CS patients are primarily deficient in the preferential repair of DNA damage in actively transcribed genes, whereas in most XP patients the genetic defect affects both "preferential" and "overall" NER modalities. Here we report a genetic study of two unrelated, severely affected patients with the clinical characteristics of CS but with a biochemical defect typical of XP. By complementation analysis, using somatic cell fusion and nuclear microinjection of cloned repair genes, we assign these two patients to XP complementation group G, which previously was not associated with CS. This observation extends the earlier identification of two patients with a rare combined XP/CS phenotype within XP complementation groups B and D, respectively. It indicates that some mutations in at least three of the seven genes known to be involved in XP also can result in a picture of partial or even full-blown CS. We conclude that the syndromes XP and CS are biochemically closely related and may be part of a broader clinical disease spectrum. We suggest, as a possible molecular mechanism underlying this relation, that the XPGC repair gene has an additional vital function, as shown for some other NER genes.</p
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