936 research outputs found
Synthesis, structure and non-linear optical properties of L-argininium perrhenate crystal
A new hybrid organic–inorganic non-linear optical crystalline material, L-argininium perrhenate has
been synthesized. The crystal belongs to P212121 space group, has a good optical quality and high
transmission in the visible and near infra-red spectral regions. L-argininium perrhenate has high
birefringence and is more than four times as efficient as KDP in second harmonic generation, making it
a potentially attractive material for non-linear optical applicationsThis work was financially supported by the European Regional Development Fund (ERDF) through Programa Operacional Factores de Competitividade (COMPETE: FCOMP-01-0124-FEDER-014628) and the Portugal Fundacao para a Ciencia e Tecnologia (PTDC/CTM-NAN/114269/2009, PTDC/CTM/105597/2008 and Pest-C/FIS/UI0036/2011)
Theory for a Hanbury Brown Twiss experiment with a ballistically expanding cloud of cold atoms
We have studied one-body and two-body correlation functions in a
ballistically expanding, non-interacting atomic cloud in the presence of
gravity. We find that the correlation functions are equivalent to those at
thermal equilibrium in the trap with an appropriate rescaling of the
coordinates. We derive simple expressions for the correlation lengths and give
some physical interpretations. Finally a simple model to take into account
finite detector resolution is discussed
Estimation of Econometric Model Using Nonlinear Full Information Maximum Likelihood: Preliminary Computer Results
This working paper provides some preliminary results on the computational feasibility of nonlinear full information maximum likelihood (NECML) estimation. Severa1 of the test cases presented were also subjected to nonlinear three stage least square (NLBSLS) estimation in order to illustrate the relative performance of the two estimation techniques. In addition, certain other aspects central to practical implementation are highlighted. These include the effect of various computers on the efficiency of the code, as well as the relative merits of numerical and analytical generation of gradient information. Broadly speaking, NLFIML appears competitive in cost and superior in statistical properties to NL3SLS.
High nonlinear optical anisotropy of urea nanofibers
Nanofibers consisting of the optically nonlinear organic molecule urea embedded in both poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) polymers were produced by the electrospinning technique. The second-harmonic generation produced by aligned fiber mats of these materials displays a strong dependence on the polarization of the incident light. In PVA-urea nanofibers the effectiveness in generating of the second-harmonic light is as high as that of a pure urea powder with an average grain size of 110 μm. The results suggest that single crystalline urea nanofibers were achieved with a long-range crystalline order extending into the range of 2–4 μm with PVA as the host polymer.This work was carried out in the frame of CIENCIA-2007 program (reference UMINHO-CF06) and financially supported by Fundacao para a Ciencia e Tecnologia, PTDC/CTM/105597/2008
Quantitative investigations of quantum coherence for a light-harvesting protein at conditions simulating photosynthesis
Recent measurements using two-dimensional electronic spectroscopy (2D ES) have shown that the
initial dynamic response of photosynthetic proteins can involve quantum coherence. We show
how electronic coherence can be differentiated from vibrational coherence in 2D ES. On that basis
we conclude that both electronic and vibrational coherences are observed in the phycobiliprotein
light-harvesting complex PC645 from Chroomonas sp. CCMP270 at ambient temperature. These
light-harvesting antenna proteins of the cryptophyte algae are suspended in the lumen, where the
pH drops significantly under sustained illumination by sunlight. Here we measured 2D ES of
PC645 at increasing levels of acidity to determine if the change in pH affects the quantum
coherence; quantitative analysis reveals that the dynamics are insensitive to the pH change.We acknowledge financial support from DARPA under the QuBE program, the United States Air Force Office of Scientific Research under contract number FA9550-10-1-0260, and the Natural Sciences and Engineering Research Council of Canada. We thank Min-Duk Seo and Mitsuhiko Ikura for assistance with the CD measurements and Philip Johnson, Alexei Halpin, and Jurgen Hauer for helpful conversations regarding the 2D ES apparatus
On the Creation of Acceptable Conjoint Analysis Experimental Designs
Conjoint analysis studies typically utilize orthogonal fractional factorial experimental designs to construct a set of hypothetical stimuli. Occasionally, these designs include environmentally correlated attributes that can lead to stimulus profiles that are not representative of the subject's environment. To date, no one has proposed a remedy well-grounded in statistical theory. This note presents a new methodology utilizing combinatorial optimization procedures for creating modified fractional factorial designs that are as “orthogonal” as possible, which do not contain nonrepresentative stimulus profiles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72641/1/j.1540-5915.1991.tb00357.x.pd
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