Wavelength-tunable ultrashort-pulse output of a photonic-crystal fiber designed to resolve ultrafast molecular dynamics

Wavelength-tunable 100 fs pulses generated through the soliton self-frequency shift in a photonic-crystal fiber are employed to visualize femtosecond coherence and population relaxation dynamics in molecular aggregates by means of time-resolved sum-frequency generation. This technique reveals an ultrafast dephasing of coherent molecular excitations with a phase relaxation time of about 120 fs and resolves an ultrafast switching of the nonlinear-optical response of molecular aggregates.     

BioCores: identification of a drug/natural product-based privileged structural motif for small-molecule lead discovery

The analysis of known drugs (Comprehensive Medicinal Chemistry database (2008 version): ) and natural products (Koch et al., Proc Natl Acad Sci USA 102:17272–17277, 2008) has led to the identification of privileged saturated and aromatic heterocyclic ring pairs that we have termed as “BioCores.” This article explains how the BioCores can be used for the design of novel lead-like scaffolds.     

Radiative decays of scalar mesons σ(600), f 0(980) and a 0(980) in the local Nambu-Jona-Lasinio model

The two-photon decay widths of scalar mesons σ(600), f ₀(980) and a ₀(980) as well a ₀ → ju(ω)γ and f ₀ → ju(ω)γ are calculated in the framework of the local Nambu-Jona-Lasinio model. The contributions of the quark loops (Hartree-Fock approximation) and the meson loops (next 1/N _c -approximation where N _c is the number of colors) are taken into account. The values of these contributions, as we show, are of the same order of magnitude. For the f ₀ decay the K-loop contribution plays the dominant role. The results for two-gamma decays are in satisfactory agreement with modern experimental data. The predictions for a ₀ → ju(ω)γ and f ₀ → ju(ω)γ widths are given.     

Mixed convection heat transfer of a nanofluid in a lid-driven enclosure with two adherent porous blocks

Journal of Thermal Analysis and Calorimetry - Convective flow and heat transfer in an alumina/water nanofluid enclosure having two centered adherent porous blocks under the effect of moving upper...     

Naphthalene derivatives of a conformationally locked GFP chromophore with large stokes shifts

The active development of fluorescence microscopy requires an increase in the variety of the dyes and their characteristics. Compounds with a large Stokes shift, i.e., a large difference between the positions of the absorption and emission maxima, have attracted the interest of researchers as a tool that can be used for multicolor labeling. One of the known approaches to increase the Stokes shift is the introduction of additional polycyclic fragments. Herein, we report novel derivatives of a conformationally locked GFP chromophore containing the naphthalene ring. The proposed modification leads not only to the enhancement of the Stokes shift up to 100 nm but also leads to the noticeable red-shift of the emission and absorption spectra in contrast with the corresponding derivatives with one benzene ring.     

Comment on Sensitivity Coefficients to Variation of Fundamental Constants

Atoms and molecules can serve as sensitive probes of a possible variation of the fine structure constant α and electron‐to‐proton mass ratio μ. Two types of sensitivity coefficients are often used to quantify and compare the sensitivity of different species to the variation of fundamental constants. The dimensionless coefficients K are related to the fractional sensitivity, while dimensional factors q are related to the absolute sensitivity. Here, several common errors and misconceptions regarding these coefficients that frequently appear in the literature are discussed.     

Optimal Data Acquisition Methods for Single-Pixel Imaging

Single-pixel imaging is an image reconstruction technique, which uses spatially modulated illumination of an object and a single-pixel detector collecting the light scattered by the object. This technique is complementary to the conventional imaging based on multipixel matrices and becomes especially interesting when one needs to go beyond the capabilities of the standard silicon-based sensors, e.g., to perform imaging in the infrared range. One of the factors that limit the resolution of the reconstructed images is the signal-to-noise ratio during the data acquisition. We propose several methods for processing the photodetector signal and develop a universal method to determine the optimal pixel number in light patterns with respect to illuminance of the object. We use these methods to capture the standard test images and discuss their advantages.     

Improving the resolution in quantum and classical temporal imaging

The point-spread function of an optical system determines its optical resolution for both spatial and temporal imaging. For spatial imaging, it is given by a Fourier transform of the pupil function of the system. For temporal imaging based on nonlinear optical processes, such as sum-frequency generation or four-wave mixing, the pointspread function is related to the waveform of the pump wave by a nonlinear transformation. We compare the point-spread functions of three temporal imaging schemes: sum-frequency generation, co-propagating four-wave mixing, and counter-propagating four-wave mixing, and demonstrate that the last scheme provides the best temporal resolution. Our results are valid for both quantum and classical temporal imaging.     

High-resolution solid-state NMR structure of Alanyl-Prolyl-Glycine

We present a de novo high-resolution structure of the peptide Alanyl-Prolyl-Glycine using a combination of sensitive solid-state NMR techniques that each yield precise structural constraints. High-quality ¹³C–¹³C distance constraints are extracted by fitting rotational resonance width (R²W) experiments using Multimode Multipole Floquet Theory and experimental chemical shift anisotropy (CSA) orientations. In this strategy, a structure is first calculated using DANTE-REDOR and torsion angle measurements and the resulting relative CSA orientations are used as an input parameter in the ¹³C–¹³C distance calculations. Finally, a refined structure is calculated using all the constraints. We investigate the effect of different structural constraints on structure quality, as determined by comparison to the crystal structure and also self-consistency of the calculated structures. Inclusion of all or subsets of these constraints into CNS calculations resulted in high-quality structures (0.02 Å backbone RMSD using all 11 constraints).     

Förster resonance energy transfer in hybrid associates of colloidal Ag<Subscript>2</Subscript>S quantum dots with thionine molecules

Nonradiative resonance energy transfer in hydrophilic hybrid associates of thionine molecules (TH⁺) with colloidal Ag₂S quantum dots (QDs) with average diameter of 3.5 nm was studied. Photoluminescence spectra and its decay shown that for these systems the supplemental photosensitization of recombination luminescence of Ag₂S QDs (1200 nm) from the region of TH⁺ fluorescence (618 nm) is possible. It was found that the average lifetime of TH⁺ molecules luminescence is shortened during their association with Ag₂S QDs. Approximation of luminescence decay by stretched exponent with value of parameter β =?0.5 indicates on the inductive-resonance dipole-dipole (Förster) mechanism of nonradiative energy transfer (FRET). The efficiency of FRET was 0.29–0.41.