8,748 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
The AMC Linear Disability Score in patients with newly diagnosed Parkinson disease
Objective: The aim of this study was to examine the clinimetric properties of the AMC Linear Disability Score (ALDS), a new generic disability measure based on Item Response Theory, in patients with newly diagnosed Parkinson disease (PD).\ud
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Methods: A sample of 132 patients with PD was evaluated using the Hoehn and Yahr (H&Y), the Unified PD Rating Scale motor examination, the Schwab and England scale (S&E), the Short Form–36, the PD Quality of Life Questionnaire, and the ALDS.\ud
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Results: The internal consistency reliability of the ALDS was good ([alpha] = 0.95) with 55 items extending the sufficient item-total correlation criterion (r > 0.20). The ALDS was correlated with other disability measures (r = 0.50 to 0.63) and decreasingly associated with measures reflecting impairments (r = 0.36 to 0.37) and mental health (r = 0.23 to -0.01). With regard to know-group validity, the ALDS indicated that patients with more severe PD (H&Y stage 3) were more disabled than patients with mild (H&Y stage 1) or moderate PD (H&Y stage 2) (p < 0.0001). The ALDS discriminated between more or less severe extrapyramidal symptoms (p = 0.001) and patients with postural instability showed lower ALDS scores compared to patients without postural instability (p = < 0.0001). Compared to the S&E (score 100% = 19%), the ALDS showed less of a ceiling effect (5%).\ud
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Conclusion: The AMC Linear Disability Score is a flexible, feasible, and clinimetrically promising instrument to assess the level of disability in patients with newly diagnosed Parkinson disease
Verkenning mogelijkheden om energie-efficiëntie in de rozenteelt te verbeteren. Een modelstudie
Energie is verreweg de grootste kostenpost in de rozenteelt (ca. 40%) en is de afgelopen jaren sterk toegenomen door de toename van de belichtingsintensiteit en van het aantal belichtingsuren. De rentabiliteit staat de laatste jaren onder druk. Met als doel energiebesparing met behoud van rendabiliteit en als uitgangspunt geen grote aanpassingen in kasuitrusting of technologie zijn op basis van divers onderzoek een viertal alternatieve teeltstrategieën beschreven met potentie de energie'input in MJ per tak te verlagen. Om inzicht te geven in de te bereiken energiebesparing en in de consequenties voor de productie, de kwaliteit, en het economisch rendement zijn de strategieën na bepaling van de uitgangspunten met energetische en economische berekeningen vergelegen met een referentieteelt (KWIN 2008). De gehanteerde prijzen voor gas en elektriciteit zijn gebaseerd op het prijsniveau van december 200
Understanding life together: A brief history of collaboration in biology
AbstractThe history of science shows a shift from single-investigator ‘little science’ to increasingly large, expensive, multinational, interdisciplinary and interdependent ‘big science’. In physics and allied fields this shift has been well documented, but the rise of collaboration in the life sciences and its effect on scientific work and knowledge has received little attention. Research in biology exhibits different historical trajectories and organisation of collaboration in field and laboratory – differences still visible in contemporary collaborations such as the Census of Marine Life and the Human Genome Project. We employ these case studies as strategic exemplars, supplemented with existing research on collaboration in biology, to expose the different motives, organisational forms and social dynamics underpinning contemporary large-scale collaborations in biology and their relations to historical patterns of collaboration in the life sciences. We find the interaction between research subject, research approach as well as research organisation influencing collaboration patterns and the work of scientists
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
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
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