Fluorescence lifetime imaging of molecular rotors to map microviscosity in cells

Fluorescence liftime imaging （FLIM） of modified hydrophobic bodipy dyes that act as fluorescent molecular rotors shows that the fluorescence lifetime of these probes is a function of the microviscosity of their environment. Incubating cells with these dyes, we find a punctate and continuous distribution of the dye in cells. The viscosity value obtained in what appears to be endocytotic vesicles in living cells is around 100 times higher than that of water and of cellular cytoplasm.Time-resolved fluorescence anisotropy measurements also yield rotational correlation times consistent with large microviscosity values. In this way, we successfully develop a practical and versatile approach to map the microviscosity in cells based on imaging fluorescent molecular rotors.     

Branching fractions for psi(2S)-to-J/psi transitions

We describe new measurements of the inclusive and exclusive branching fractions for psi(2S) transitions to J/psi using e(+)e(-) collision data collected with the CLEO detector operating at CESR. All branching fractions and ratios of branching fractions reported here represent either the most precise measurements to date or the first direct measurements. Indirectly and in combination with other CLEO measurements, we determine B(chi(cJ) --> gamma(J/psi)) and B[psi(2S) --> light hadrons].     

Measurement of the parity-violating asymmetry in inclusive electroproduction of π- near the Δ0 resonance

The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Δ)- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated d(Δ)- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(γ)-=-5.2 to +5.2 ppm. The measurement performed in this work leads to A(γ)-=-0.36±1.06±0.37±0.03 ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V(ud)/V(us). The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering.     

High pressure: a tool to improve the enzymatic production of glycosides

Naringinase, an enzyme complex that expresses α -l-rhamnosidase and β -d-glucosidase activities in native state, can be used to deglycosylate natural glycosides. The selective inactivation of one of these activities will allow the biosynthesis of different bioactive compounds in a simple, effective and cheap way. In this work, pressure and temperature were the tools used to selectively inactivate the activities expressed by naringinase. The main goal was the identification of pressure–temperature conditions to acquire conditions for the maximization of enzymatic hydrolysis of substrates with different numbers of glycosidic residues. α -l-Rhamnosidase was 32-fold more resistant against inactivation at 250 MPa than at atmospheric pressure. The best pressure condition to reduce β -d-glucosidase inactivation at 75°C was 173 MPa, while in the case of α -l-rhamnosidase inactivation at 85°C, it was above 250 MPa. Moreover, a selective inactivation of β -d-glucosidase activity of naringinase was attained, allowing an easy and cheap method with which to produce prunin and other expensive glycosides. The present work highlights the effect of high pressure on enzyme protection against thermal inactivation, demonstrating its potential as a powerful tool in biosynthesis.     

Noise Stability of SIS Receivers

There is a strong interest in the submillimeter astronomy community to increase the IF bandwidth of SIS receivers in order to better facilitate broad spectral linewidth and continuum observations of extragalactic sources. However, with an increase in receiver IF bandwidth there is a decrease in the mixer stability. This in turn effects the integration efficiency and quality of the measurement. In order to better understand the noise mechanisms responsible for reducing the receiver stability, we employed a technique first described by D.W. Allan and later elaborated upon by Schieder et al. In this paper we address a variety of factors that degrade the noise stability of SIS receivers. The goal of this exercise is to make recommendations aimed at maximizing SIS receiver stability.