Optimal flip angles for in vivo liver 3D T1 mapping and B1+ mapping at 3T.

Purpose The spoiled gradient recalled echo (SPGR) sequence with variable flip angles (FAs) enables whole liver T1 mapping at high spatial resolutions but is strongly affected by B1+ inhomogeneities. The aim of this work was to study how the precision of acquired T1 maps is affected by the T1 and B1+ ranges observed in the liver at 3T, as well as how noise propagates from the acquired signals into the resulting T1 map. Theory The T1 variance was estimated through the Fisher information matrix with a total noise variance including, for the first time, the B1+ map noise as well as contributions from the SPGR noise. Methods Simulations were used to find the optimal FAs for both the B1+ mapping and T1 mapping. The simulations results were validated in 10 volunteers. Results Four optimized SPGR FAs of 2°, 2°, 15°, and 15° (TR = 4.1 ms) and B1+ map FAs of 65° and 130° achieved a T1 coefficient of variation of 6.2 ± 1.7% across 10 volunteers and validated our theoretical model. Four optimal FAs outperformed five uniformly spaced FAs, saving the patient one breath-hold. For the liver B1+ and T1 parameter space at 3T, a higher return in T1 precision was obtained by investing FAs in the SPGR acquisition rather than in the B1+ map. Conclusion A novel framework was developed and validated to calculate the SPGR T1 variance. This framework efficiently identifies optimal FA values and determines the total number of SPGR and B1+ measurements needed to achieve a desired T1 precision

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