Differential exposure of surface epitopes in the beta-strand region of LOOP1 of the yeast H+-ATPase during catalysis

The plasma membrane H+-ATPase of yeast assumes distinct conformational states during its catalytic cycle. To better understand structural changes in the LOOP1 domain, a catalytically important cytoplasmic loop segment linking transmembrane segments 2 and 3, surface epitopes were examined at different stages of catalysis. A polyclonal rabbit antibody was prepared to a fusion protein consisting of LOOP1 and the maltose binding protein. This antibody was affinity-purified to produce a LOOP1-specific fraction that could be used in competition enzyme-linked immunosorbent assays to assess surface exposure of the LOOP1 epitopes. It was found that in an E1 conformation stabilized with either adenosine 5'-(beta,gamma -imino)triphosphate (AMP-PNP) or ADP, less than 10% of the LOOP1 epitopes were accessible on native enzyme. However, when the enzyme was stabilized in an E2-state with ATP plus vanadate, approximately 40% of the surface epitopes on LOOP1 became accessible to antibody. The remaining 60% of the LOOP1 epitopes were fully occluded in the native enzyme and never showed surface exposure. Enzyme-linked immunosorbent assays utilizing fusion proteins consisting of LOOP1 subdomains demonstrated that all of the available epitopes were contained in the beta-strand region (Glu-195-- Val-267) of LOOP1. The epitopes that were differentially exposed during catalysis were included in regions upstream and downstream of the highly conserved TGES sequence. Our results suggest that during catalysis either the beta-strand region of LOOP1 or an interacting domain undergoes substantial structural rearrangement that facilitates epitope exposure.     

Some aspects of wedge impact on granular layers and attendant flows

We observed and measured impacts of steel wedges on layers of 200 μ m solid glass spheres and the subsequent response with the ultimate aim to establish the effectiveness of these materials for blast panels and energy absorption. The success of the layers to absorb and dissipate energy is quantified, especially as regards the unconfined free surface of the granular material and its ability to dissipate and redirect momentum laterally through wave-like motion. Experiments were conducted with two granular layer depths; two drop elevations; and three wedge angles. As expected, as the wedge included-angle increases the peak force increases significantly, whereas the period associated with the response is much-reduced. It was shown that with a reduction in layer thickness, the bed can be forced to vacate locally, and subsequently the wedge strikes the reservoir bottom causing a rapid rise to a very large peak force. It was seen that the included-angle 180° wedge caused predominantly solid-like response (i.e. compaction); the 102° wedge generated mostly viscous/fluid-like behavior (i.e. similar to a Newtonian fluid); and as might be expected the 141° wedge exhibited both fluid-like and solid-like behavior. High-speed imaging of the surface response for the viscous-like motion showed breaking wavelike characteristics. In addition granular material was forced upward in a thin free sheet with hexagonal structure. Lastly we quantified the peak force ratio, the impulse, and the energy dissipation in the underlying load cells for the 102° wedge impacting the 16.36 cm bed versus the same test with no bed in place. For this last comparison the peak force ratio exceeded 15; the impulse was about a third less for the granular bed; and the ratio of energy dissipation in the load cells was more than 200.     

Initial water impact of a wedge at vertical and oblique angles

This paper examines initial asymmetric wedge-impact flows with horizontal as well as vertical impact velocity. The method of two-dimensional vortex distributions is employed to model the initial-boundary-value problem. The numerical analysis involves discretization of the body surface and an iterative solution technique. Experimental drop tests of a prismatic wedge were performed to gain understanding and provide data for comparison of initial water impact when asymmetry and horizontal impact velocity are present. The experimental investigation of initial flow separation off the wedge vertex (i.e., keel) during impact is described. Initial separation-ventilation of the flow from the vertex due to asymmetric impact or horizontal-vertical impact velocity is examined in relation to the present theory. Agreement between the data and the numerical predictions was demonstrated for small degrees of asymmetry and small ratios of horizontal to vertical impact velocity. The initial flow detachment from the vertex also revealed interesting hydrodynamic characteristics.     

Thermal analysis of InGaN/GaN (GaN substrate) laser diodes using transient interferometric mapping

Transient thermal behaviour and current distribution is investigated in InGaN/GaN blue lasers grown on GaN substrate. Back side transient interferometric mapping (TIM) method was applied for probing the temperature-induced phase shift due to increase in refractive index in the GaN laser ridge. The laser operates in a pulsed mode with pulse duration in the time scale from 300 ns to 2 μs. By using 2D thermal modeling, the comparison of the experimental and simulated phase shift allows to estimate a maximal temperature in the active region. The thermal mapping along the ridge reveals the inhomogeneity in the current flow attributed to substrate dopant distribution.     

The conductivity and Hall effect in CdF<Subscript>2</Subscript>:In and CdF<Subscript>2</Subscript>:Y

Temperature dependences of the static conductivity σ and Hall coefficient R_H in CdF₂ crystals doped with bistable indium and donor yttrium impurities have been measured. It is shown that this material contains different types of free carriers, i.e., electrons and polarons. A comparison of the calculated temperature dependences of σ and R_H with the experimental data also shows that the impurity-band conductivity makes a significant contribution (due to hops of bound polarons or holes) to σ and R_H.