Method for improving the resolution and accuracy against birefringence dispersion in distributed polarization cross-talk measurements

We present a novel method for improving the spatial resolution and amplitude accuracy of distributed polarization cross-talk measurements in a polarization maintaining (PM) fiber against its birefringence dispersion. We show that the broadening of measured polarization cross-talk peaks caused by birefringence dispersion can be restored by simply multiplying the measurement data with a compensation function. The birefringence dispersion variable in the function can be obtained by finding the widths of measured cross-talk envelopes at known distances along the fiber. We demonstrate that this method can effectively improve spatial resolution and amplitude accuracy of the space-resolved polarization cross-talk measurements of long PM fibers.     

Strain relaxation of CdTe films growing on lattice-mismatched substrates

We have deposited CdTe films by laser-assisted epitaxy approach and investigated the influence of substrate and film thickness on the film properties. Grown on Si(001), GaAs(001), and quartz substrates; the CdTe films exhibit preferential orientation along the cubic CdTe(111) direction. When the films are thin (<500 nm), a blueshift of the band gap and splitting of valence bands were observed. These results are attributed to the existence of residual strains induced by mismatch of the film lattice constant with that of the substrate, and by their difference in thermal expansion coefficients. The bulk band-gap energy of 1.5 eV was achieved on the surface of thick CdTe films grown on Si(001) substrate, indicating that strain was almost completely relaxed in this case. Our results demonstrate that by a proper selection of substrate and film thickness it is possible to grow film semiconductors with band gap approaching those of bulk crystals.     

Facile synthesis of mercaptosuccinic acid-capped CdTe/CdS/ZnS core/double shell quantum dots with improved cell viability on different cancer cells and normal cells

Water-soluble, mercaptosuccinic acid (MSA)-capped CdTe/CdS/ZnS core/double shell quantum dots (QDs) were prepared by successive growth of CdS and ZnS shells on the as-synthesized CdTe/CdS_thin core/shell quantum dots. The formation of core/double shell structured QDs was investigated by ultraviolet-visible (UV–Vis) absorption and photoluminescence (PL) spectroscopy, PL decay studies, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The core/double shell QDs exhibited good photoluminescence quantum yield (PLQY) which is 70% higher than that of the parent core/shell QDs, and they are stable for months. The average particle size of the core/double shell QDs was ～3 nm as calculated from the transmission electron microscope (TEM) images. The cytotoxicity of the QDs was evaluated on a variety of cancer cells such as HeLa, MCF-7, A549, and normal Vero cells by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) cell viability assay. The results showed that core/double shell QDs were less toxic to the cells when compared to the parent core/shell QDs. MCF-7 cells showed proliferation on incubation with QDs, and this is attributed to the metalloestrogenic activity of cadmium ions released from QDs. The core/double shell CdTe/CdS/ZnS (CSS) QDs were conjugated with transferrin and successfully employed for the biolabeling and fluorescent imaging of HeLa cells. These core/double shell QDs are highly promising fluorescent probe for cancer cell labeling and imaging applications.     

Fluorescence and Rotational Dynamics of Dityrosine

We have examined the lifetimes and rotational correlation times of dityrosine emission by time-correlated single-photon counting. We first noticed dityrosine fluorescence in samples of tyrosine and tyrosine dipeptides by its characteristic red-shifted emission at 400 to 430 nm. The longer rotational correlation time relative to tyrosine proved that this fluorescence emanated from a distinct species. Comparison with the fluorescence properties of synthesized dityrosine established the identity of the emitting species. Fluorescence intensity decays of dityrosine are generally characterized by two decay components, one with a lifetime in the range of 150 to 800 ps and another between 2.5 and 4.5 ns. We found no evidence for an excited-state reaction, since a rising phase (negative-amplitude component) was not observed. In the pH range from 4 to 10, two ground-state species exist in equilibrium with pK _a 7. Both species exhibit two fluorescence decays. The average fluorescence lifetime increases gradually with pH over the pH range from 4 to 10 and decreases at pH 2. Anisotropy decays were measured for dityrosine and the alanine–dityrosine–alanine and leucine–dityrosine–leucine dipeptides. The rotational correlation times of dityrosine and dityrosine dipeptides increase linearly with van der Waals volumes. The slope indicates a stronger solute–solvent interaction than predicted with stick boundary conditions. It is suggested that these interactions result from the presence of two zwitterionic pairs.     

Chaotic inflation in supergravity with Heisenberg symmetry

We propose the introduction of a Heisenberg symmetry of the Kähler potential to solve the problems with chaotic inflation in supergravity, as a viable alternative to the use of shift symmetry. The slope of the inflaton potential emerges from a small Heisenberg symmetry breaking term in the superpotential. The modulus field of the Heisenberg symmetry is stabilized and made heavy with the help of the large vacuum energy density during inflation. The observable predictions are indistinguishable from those of typical chaotic inflation models, however the form of the inflationary superpotential considered here may be interpreted in terms of sneutrino inflation arising from certain classes of string theory.     

CanSAS‐IV

A two-day workshop on beamline integration and data formatting (HDF5/NeXus) of the EIGER detector was held in Baden, Switzerland, January 24–25, 2013. Its aim was to discuss the technical challenges inherent with the next generation of high-frame-rate, high-resolution X-ray imaging detectors, and specifically with the EIGER detector. EIGER is a photon-counting hybrid pixel detector developed at the Paul Scherrer Institute (PSI) and DECTRIS Ltd. With even higher spatial resolution and frame rates than its predecessor, the PILATUS detector, it will be able to continuously produce up to 3000 images per second. The corresponding extreme data rates generated by this and future detectors present a significant challenge for beamline integration of the detectors, for data handling by the users, and for data processing software. Efficient data flow, storage, and processing must be achieved to handle the huge data sets that will be produced in seconds by these devices.     

Ultrahigh pressure equation of state of CaS to 1.5 Mbar

Abstract

Energy Dispersive X-ray Diffraction (EDXD) was performed at room temperature to gather structural data on CaS between approximately 1.7 GPa to nearly 150GPa. In these experiments, CaS retained the B1 structure up to approximately 40 GPa above which it began to transform to the B2 structure. The B2 structure remained stable to the highest pressure reached, 149 GPa, where the relative volume V/V₀ was 0.490. Previous studies on CaS extended only up to 52 GPa, which is barely 10 GPa after the B1 phase changes to the B2 structure. Thus it was not possible to accurately extrapolate the equation of state (EOS) for the B2 phase region to significantly higher pressures. In the present study EOS data for CaS was collected to 150 GPa and no other structural change was observed. EOS parameters for the B1 and B2 phase regions agree well with values reported in the literature.     

Surface characterizations of fluorescent-functionalized silica nanoparticles: from the macroscale to the nanoscale

Journal of Nanoparticle Research - Fluorescent silica nanoparticles are widely used for various applications from mechanical reinforcement to biology. In many cases, their surface has to be...