Energy dissipation via radiative recombination and vibronic relaxation in σ-delocalized silicon backbone network polymers

The nature of ultrafast energy dissipation in poly(n-hexylsilyne), a prototypical σ-delocalized alkysilicon network polymer, is explored. This disordered silicon backbone material exhibits strong near-UV to visible band-edge absorption and a high quantum yield of visible emission. The time evolution of the emission band is studied over four decades of time using time-resolved luminescence as a probe. The data indicate that while there is an ‘intrinsic’ Stokes shift after photoexcitation due to kinetic energy relaxation (<10ps), thermalization within a dense band of vibronic states via intramolecular phonon-assisted hopping on a nanosecond timescale is the dominant mechanism for excited-state decay. The data can be understood in terms of theoretical predictions for energy relaxation in disordered materials.     

International comparison of power measurements at 33 GHz(GT-RF/92-4)

A measurement comparison of effective efficiency has been carried out between eight national metrology laboratories at 33 GHz in rectangular waveguide IEC R320. Two waveguide thermistor mounts were measured. The following national laboratories participated: BNM-LCIE (France), NIST (U.S.), NRC (Canada), KRISS (Korea), CSIRO (Australia), PTB (Germany), NMi VSL (The Netherlands), and NPL (U.K.). The Bureau National de Metrologie-Laboratoire Central des Industries Electriques (France) acted as the pilot laboratory for the comparison. Excellent harmony is observed between results given by the participants, especially for the item LCIE-92021     

Stability of a fluid-saturated porous medium heated from below by forced convection

A linear stability analysis determining the onset of convection in a bounded rectangular cavity containing a fluid-saturated porous medium is performed for insulated sidewalls, isothermal top wall, and bottom wall heated by forced convection. The nature of the bottom wall heating necessarily involves the Biot number, Bi. Numerical calculations of the critical Rayleigh number, R_c made over the range of Biot numbers 10⁻⁴?Bi?10⁴ for cavity aspect ratios 0?(a,b)?5 cover all effective bottom heating conditions from the constant heat flux global limit, R_c=27.096 found as Bi→0 to the isothermal global limit, R_c=4π² found as Bi→∞. Marginal stability boundaries, preferred cellular modes and disturbance temperature contours are displayed graphically.     

A response to Bruce (1998) on the Lashley-Hull debate.

Responds to D. Bruce's comments (see record 1998-00831-005) on N. Weidman's original article (see record 1995-00025-001) about the Lashley-Hull debate. The current article addresses the disagreements the author has with Bruce regarding their interpretations of the Lashley-Hull debate. These differences include what actually constituted "the debate," the extent to which the nature-nurture dichotomy was a feature of the debate, and the role of Watson's behaviorism in shaping Lashley's views. The article ends by noting a point on which both authors agree. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cleavage of transcriptional activator Oct-1 by poliovirus encoded protease 3Cpro

To understand the regulation of receptor-mediated endocytosis in hepatocytes, we have used two specific inhibitors of serine-threonine protein phosphatases (PP), microcystin (MCYST) and okadaic acid (OKA) as probes to alter protein phosphorylation in hepatocytes. We have then examined the impact of these changes on the specific binding and uptake of transferrin (Tf) in hepatocytes. The measurement of PP activity in hepatocyte lysates showed that OKA and MCYST shared a common inhibition of protein phosphatase 2A (PP2A). Our results showed that both OKA (250 nmol/L) and MCYST (500 nmol/L) significantly reduced Tf uptake at steady state (P < or = .05). The measurement of Tf internalization after 15 minutes in protein phosphatase inhibitor-pretreated cells revealed that the initial uptake was also significantly reduced. Binding studies showed that pretreatment with either of the phosphatase inhibitors did not result in significant changes in the K(d) for Tf binding to transferrin receptor (TfR). Additionally, no significant changes in the number of TfR in the plasma membrane were observed in phosphatase inhibitor-pretreated cells. The treatment of hepatocytes with nocodazole (NOC), which results in microtubule disassembly and inhibition of microtubule-based vesicle transport, caused comparable reductions in initial and steady state levels of transferrin accumulation. The changes in transferrin accumulation by both phosphatase inhibitors and nocodazole were accompanied by redistribution of the microtubule-anchored Golgi apparatus and lysosomal network from the perinuclear region to the cell periphery. Our data show that the regulation of Tf uptake by receptor-mediated endocytosis is mediated by PP2A and additionally may occur through regulation of microtubule-based vesicle transport.     

On the drag of model dendrite

An experimental study of low Reynolds number drag on laboratory models of dendrite fragments has been conducted. The terminal velocities of the dendrites undergoing free fall along their axis of symmetry were measured in a large Stokes flow facility. Corrections for wall interference give nearly linear dragvs Reynolds number curves. Corrections for both wall interference and inertia effects show that the dendrite Stokes settling velocities are always less than that of a sphere of equal mass and volume. In the Stokes limit, the settling speed ratio is found to correlate well with the primary dendrite arm aspect ratio and a second dimensionless shape parameter which serves as a measure of the fractal-like nature of the dendrite models. These results can be used to estimate equiaxed grain velocities and distance of travel in metal castings. The drag measurements may be used in numerical codes to calculate the movement of grains in a convecting melt in an effort to determine macrosegregation patterns caused by the sink/float mechanism.     

Variations à l’échelle submicroseconde des champs électromagnétiques rayonnes par la foudre

Electric fields (E) and electric field derivative signals (dE/dt) radiated by lightning have been recorded using a system with 40 ns and 10 ns response times respectively. Propagation between the source and the measuring station was entirely over the ocean (high electrical conductivity) so signal distortion below 20 MHz was minimal. Large normalized (to 100 km) electric field derivative values, from 10 to 40 V/m/μs, have been observed during return strokes, leader and intracloud discharge processes. Corresponding mean values of the maximum current derivative, estimated using the transmission line model, range from 80 to 154 IcA/μs, depending on the type of discharge and assuming a wavefront velocity of 10 ⁸ m/s.