The Q2 evolution of flavour singlet wave functions in QCD

We calculate the Q² evolution of the quark-antiquark and gluon-gluon components of helicity-zero, flavour and colour singlet wave functions by summing diagrams to all orders in axial gauge QCD perturbation theory in the leading logarithm approximation. We find that Gegenbauer moments of these components have exactly the same scale-breaking behaviour as moments of singlet quark and gluon distribution functions in leptoproduction. The resulting singlet wave function is used to calculate the amplitudes for quark-antiquark and gluon-gluon jet production in off-shell photon-photon collisions.     

Direct observation of the two-photon generation of free excitonic molecules in CuCl

Two-photon absorption spectra due to excitonic molecule generation in thin CuCl samples at 4.2°K are directly measured using the intense light from a pulsed, frequency tunable dye laser. One narrow induced absorption peak is observed at 3893 Å. This peak exhibits a Fano interference line profile at low laser light intensities. High laser light flux densities result in a saturation, broadening, and blue shift of the induced absorption peak. The maximum value of the two-photon absorption cross section is directly measured to be 2 x 10^-43 cm⁴ sec, and the binding energy of the molecule is found to be 39 meV.     

The transverse momentum of partons in large pT processes

An approximate method is used to investigate the effects of parton transverse momentum in large p_T particle production within the framework of hard scattering models. We derive an approximate expression for the mean bias towards the trigger of each of the two participating partons and find that event one of the partons is biased more than the other, even with a 90° trigger. We treat the transverse momentum of partons and their closely related off-mass-shell behaviour as a perturbation in the equation for the single-particle inclusive cross section, and then expand in a Taylor series. We calculate the first non-zero correction term and find that to this order, the cross section is increased by parton transverse momentum effects by typically a factor of 1.7 for p_T = 3 GeV/c with 〈k_T〉 = 500 MeV/c, or 1.25 for p_T = 3 GeV/c with 〈k_T〉 = 300 MeV/c, and that the correction decreases rapidly with increasing p_T.     

Event horizons in static scalar-vacuum space-times

The following theorem is established. Every zero-mass scalar field which is gravitationally coupled, static and asymptotically flat, becomes singular at a simply-connected event horizon. In the special case where the gravitational coupling of the scalar energy density is neglected, the solutions are computed explicitly. Some properties of the singular event horizons are discussed, and a brief mention of related work with non-static scalar fields is given.     

Raman scattering studies of the effects of a symmetry-breaking impurity on the ferroelectric phase transition in K1−xLixTa1−yNbyO3

Raman scattering and optical depolarization measurements on K_1?xLi_xTa_1?yNB_yO₃ with y ? 0.028 and x ? 0.06 show that lithium impurities destabilize the niobium-induced rhombohedral ferroelectric phase. With increasing x the phase transition is altered from a soft-mode dominated transition to a disorder-order transition into a tetragonal phase. The dependence of T_c on x disagrees with the predictions of classical mean-field theory.     

Synthetic Exploration of Bis(phenolate) Aza-BODIPYs and Heavier Group 13 Chelates

A series of boron, aluminum, gallium, and indium chelates containing the underexplored bis(phenolate) aza-dipyrromethene (aza-DIPY) core were prepared. These compounds were found to possess near-infrared absorption and emission profiles in the 710 to 770 nm domain and exhibit quantum yield values up to 14%. X-ray diffraction analysis revealed that heavier group 13 bis(phenolate) aza-DIPY chelates possessed octahedral geometries with either THF or pyridine groups occupying the axial positions as opposed to the tetrahedral geometry of the boron chelate.     

An experimental study of electrorheological fluid flow through a packed bed of glass beads

This paper shows that pressure drop-flow rate performance of an electrorheological (ER) fluid flowing through a packed bed of glass beads is consistent with a modified Ergun equation for yield stress flow through a packed bed. ER fluids are of scientific and engineering interest due to the sensitivity of their rheological properties on the applied electric field. As far as we know ER fluids have not been studied for flows through porous media. In this work a silica particle–silicone oil suspension is pumped through a rectangular packed bed of glass beads with applied electric fields. The silica particles are observed to form fibrous structures parallel to the electric field that stretch between the beads and extend between the electrodes. The pressure drop-flow rate performance agrees well with the expected performance calculated from a modified Ergun equation for a yield stress fluid flow through the packed bed with the viscosity and yield stress as functions of the applied electric field.     

Adsorptive detagging of poly-histidine tagged protein using hexa-histidine tagged exopeptidase

The ubiquitous use of poly-histidine fusion tags has made the purification of the recombinant target proteins much simpler, although the presence of residual fusion tags can generate immunogenic products or products with changed biological activities. This work presents a generic method of removing poly-histidine fusion tags from recombinant proteins through the use of a hexa-histidine tagged exopeptidase (DAPase) when both tagged species are adsorbed to the immobilized metal affinity chromatography (IMAC) adsorbent. Adsorptive detagging was performed in the presence of 50mM imidazole in order to allow the cleavage reaction by the hexa-histidine tagged DAPase to occur. The progress of batch and adsorptive detagging by DAPase of maltose binding protein (MBP) tagged with two variants of hexa-histidine fusion tag was successfully monitored using cationic exchange chromatography. A single-step, column-based detagging strategy was then optimized to maximize the recovery of native MBP. The kinetics of batch and on-column digestion for both HT6 and HT15 fusion tags were investigated. The process involved the sequential removal of dipeptides during the digestion of full-length fusion protein down to its fully detagged native form. During the course of tag digestion, 4 and 7 different intermediates were detected for HT6 and HT15 tagged MBP respectively. The characteristics of on-column cleavage of poly-histidine fusion tags by DAPase as a function of incubation temperature and amount of protease activity used were examined. It was found that the influence of fusion tag design on the batch and column-based detagging yield and efficiency was substantial. In addition, the structural difference of fusion tags affects the binding strength of the fusion protein, which can influence the resulting product purity. Despite being a longer tag, HT15 fusion tag was the preferred sequence for shortening the time needed for on-column detagging. These results can be applied to the wider use of the proposed platform protocol for the on-column cleavage of poly-histidine tagged proteins using exopeptidases.     

In contrast to BOLD: signal enhancement by extravascular water protons as an alternative mechanism of endogenous fMRI signal change

Despite the popularity and widespread application of functional magnetic resonance imaging (fMRI) in recent years, the physiological bases of signal change are not yet fully understood. Blood oxygen level-dependant (BOLD) contrast — attributed to local changes in blood flow and oxygenation, and therefore magnetic susceptibility — has become the most prevalent means of functional neuroimaging. However, at short echo times, spin-echo sequences show considerable deviations from the BOLD model, implying a second, non-BOLD component of signal change. This has been dubbed “signal enhancement by extravascular water protons” (SEEP) and is proposed to result from proton-density changes associated with cellular swelling. Given that such changes are independent of magnetic susceptibility, SEEP may offer new and improved opportunities for carrying out fMRI in regions with close proximity to air–tissue and/or bone–tissue interfaces (e.g., the prefrontal cortex and spinal cord), as well as regions close to large blood vessels, which may not be ideally suited for BOLD imaging. However, because of the interdisciplinary nature of the literature, there has yet to be a thorough synthesis, tying together the various and sometimes disparate aspects of SEEP theory. As such, we aim to provide a concise yet comprehensive overview of SEEP, including recent and compelling evidence for its validity, its current applications and its future relevance to the rapidly expanding field of functional neuroimaging. Before presenting the evidence for a non-BOLD component of endogenous functional contrast, and to enable a more critical review for the nonexpert reader, we begin by reviewing the fundamental principles underlying BOLD theory.