Chemical reactions at metal surfaces Annual progress report, May 1, 1967 - Apr. 30, 1968

Hydrogen and oxygen effects on nickel surface, ammonia catalysis on tungsten surface, and work function measurements on tungsten crystal plane

Hydrogen and oxygen on a /110/ nickel surface

Hydrogen-oxygen reaction on nickel surface, electron diffraction stud

Ammonia adsorption and decomposition on a tungsten /211/ surface

Ammonia adsorption and decomposition on tungsten 211 surface studied by mass spectrometry, electron diffraction, and changes in work functio

First steps in the oxidation of a /110/ nickel surface

Initial steps in oxidation of nickel surface studied using low energy back-reflection electron diffractio

Throughfall and temporal trends of rainfall redistribution in an open tropical rainforest, south-western Amazonia (Rondônia, Brazil)

International audienceThroughfall volumes and incident rainfall were measured between 23 August and 2 December 2004 as well as from 6 January to 15 April 2005 for individual rain events of differing intensities and magnitudes in an open tropical rainforest in Rondônia, Brazil. Temporal patterns of throughfall spatial variability were examined. Estimated interception was compared to modeled interception obtained by applying the revised Gash model in order to identify sources of throughfall variability in open tropical rainforests. Gross precipitation of 97 events amounted to 1309 mm, 89±5.6% (S.E.) of which reached the forest floor as throughfall. The redistribution of water within the canopy was highly variable in time, which we attribute to the high density of babassu palms (Orbignya phalerata), their seasonal leaf growth, and their conducive morphology. We identified a 10-min rainfall intensity threshold of 30 mmh-1 above which interception was highly variable. This variability is amplified by funneling and shading effects of palms. This interaction between a rainfall variable and vegetation characteristics is relevant for understanding the hydrology of all tropical rainforests with a high palm density

A Bulk Optically Controlled Semiconductor Switch

Turn‐on and turn‐off of bulk semiconductor switches, based on excitation and quenching of photoconductivity, respectively, have been demonstrated with copper‐doped II‐VI semiconductor crystals. The increase of the conductivity (turn‐on) was realized with a xenon flash‐lamp pulse of 15‐μs duration. A reduction of the conductivity (turn‐off) was obtained by irradiating the samples with IR light using an 8‐ns Nd:YAG laser pulse (YAG denotes yttrium aluminum garnet). For turn‐on in CdS:Cu the conductivity follows the xenon flash excitation. The turn‐off time constant was 250 ns. ZnS and ZnSe crystals showed a slower response. A memory effect for the IR light was observed

An Optically Controlled Closing and Opening Semiconductor Switch

A concept for a bulk semiconductor switch is presented, where the conductivity is increased and reduced, respectively, through illumination with light of different wavelengths. The increase in conductivity is accomplished by electron ionization from deep centers and generation of bound holes. The reduction of conductivity is obtained by hole ionization from the excited centers and subsequent recombination of free electrons and holes. The transient behavior of electron and hole density in a high power semiconductor (GaAs:Cu) switch is computed by means of a rate equation model. Changes in conductivity by five orders of magnitude can be obtained

Particle-in-cell simulations of rf breakdown

Breakdown voltages of a capacitively coupled radio frequency argon discharge at 27 MHz are studied. We use a one-dimensional electrostatic PIC code to investigate the effect of changing the secondary emission properties of the electrodes on the breakdown voltage, particularly at low pd values. Simulation results are compared with the available experimental results and a satisfactory agreement is found.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Concordance of KRAS/BRAF Mutation Status in Metastatic Colorectal Cancer before and after Anti-EGFR Therapy

Anti-EGFR targeted therapy is a potent strategy in the treatment of metastatic colorectal cancer (mCRC) but activating mutations in the KRAS gene are associated with poor response to this treatment. Therefore, KRAS mutation analysis is employed in the selection of patients for EGFR-targeted therapy and various studies have shown a high concordance between the mutation status in primary CRC and corresponding metastases. However, although development of therapy related resistance occurs also in the context of novel drugs such as tyrosine kinase-inhibitors the effect of the anti-EGFR treatment on the KRAS/BRAF mutation status itself in recurrent mCRC has not yet been clarified. Therefore, we analyzed 21 mCRCs before/after anti-EGFR therapy and found a pre-/posttherapeutic concordance of the KRAS/BRAF mutation status in 20 of the 21 cases examined. In the one discordant case, further analyses revealed that a tumor mosaicism or multiple primary tumors were present, indicating that anti-EGFR therapy has no influence on KRAS/BRAF mutation status in mCRC. Moreover, as the preselection of patients with a KRASwt genotype for anti-EGFR therapy has become a standard procedure, sample sets such ours might be the basis for future studies addressing the identification of potential anti-EGFR therapy induced genetic alterations apart from KRAS/BRAF mutations

GaAs Photoconductive Closing Switches with High Dark Resistance and Microsecond Conductivity Decay

Silicon-doped n-type gallium arsenide crystals, compensated with diffused copper, were studied with respect to their application as photoconductive, high-power closing switches. The attractive features of GaAs:Cu switches are their high dark resistivity, their efficient activation with Nd:YAG laser radiation, and their microsecond conductivity decay time constant. In the authors\u27 experiment, electric fields are high as 19 kV/cm were switched, and current densities of up to 10 kA/cm2 were conducted through a closely compensated crystal. At field strengths greater than approximately 10 kV/cm, a voltage `lock-on\u27 effect was observed