Coherent electron-phonon coupling and polaron-like transport in molecular wires

We present a technique to calculate the transport properties through one-dimensional models of molecular wires. The calculations include inelastic electron scattering due to electron-lattice interaction. The coupling between the electron and the lattice is crucial to determine the transport properties in one-dimensional systems subject to Peierls transition since it drives the transition itself. The electron-phonon coupling is treated as a quantum coherent process, in the sense that no random dephasing due to electron-phonon interactions is introduced in the scattering wave functions. We show that charge carrier injection, even in the tunneling regime, induces lattice distortions localized around the tunneling electron. The transport in the molecular wire is due to polaron-like propagation. We show typical examples of the lattice distortions induced by charge injection into the wire. In the tunneling regime, the electron transmission is strongly enhanced in comparison with the case of elastic scattering through the undistorted molecular wire. We also show that although lattice fluctuations modify the electron transmission through the wire, the modifications are qualitatively different from those obtained by the quantum electron-phonon inelastic scattering technique. Our results should hold in principle for other one-dimensional atomic-scale wires subject to Peierls transitions.Comment: 21 pages, 8 figures, accepted for publication in Phys. Rev. B (to appear march 2001

Acoustic startle stimuli inhibit pain but do not alter nociceptive flexion reflexes to sural nerve stimulation

Acoustic startle stimuli inhibit pain, but whether this is due to a cross‐modal inhibitory process or some other mechanism is uncertain. To investigate this, electrical stimulation of the sural nerve either preceded or followed an acoustic startle stimulus (by 200 ms) or was presented alone in 30 healthy participants. Five electrical stimuli, five acoustic startle stimuli, 10 startle + electrical stimuli, and 10 electrical + startle stimuli were presented in mixed order at intervals of 30–60 s. Effects of the startle stimulus on pain ratings, pupillary dilatation and nociceptive flexion reflexes to the electric shock were assessed. The acoustic startle stimulus inhibited electrically evoked pain to the ensuing electric shock (p < .001), and the electrical stimulus inhibited the perceived loudness of a subsequent acoustic startle stimulus (p < .05). However, the startle stimulus did not affect electrically evoked pain when presented 200 ms after the electric shock, and electrically evoked pain did not influence the perceived loudness of a prior startle stimulus. Furthermore, stimulus order did not influence the pupillary responses or nociceptive flexion reflexes. These findings suggest that acoustic startle stimuli transiently inhibit nociceptive processing and, conversely, that electrical stimuli inhibit subsequent auditory processing. These inhibitory effects do not seem to involve spinal gating as nociceptive flexion reflexes to the electric shock were unaffected by stimulus order. Thus, cross‐modal interactions at convergence points in the brainstem or higher centers may inhibit responses to the second stimulus in a two‐stimulus train

QUARTERLY REPORT OF THE SOLUTION CORROSION GROUP FOR THE PERIOD ENDING JANUARY 31, 1958

The corrosion rate was determined and tabulated for stainless steels, nickel alloys, carbon steels, Zircaloy-2, and niobium in boiler water containing various concentrations of oxygen. The corrosion resistance of stainless steels and nickel alloys was compared with the resistance of the austenitic stainless steels in uranyl sulfate at 200 to 295 deg C. Additional loop runs with UO/sub 3/ --Li/sub 2/CO/sub 3/ --CO/sub 2/ so lution have confirmed previous data with regard to its nonaggressive nature to carbon steel. The corrosion of 347 stainless steel was investigated in 0.04M uranyl sulfate containing 0.04M beryllium sulfate and 0.006M copper sulfate, in 0.075M beryllium sulfate, and in 0.75M beryllium sulfate containing 0.25M dissolved uranium trioxide. centration to 0.03M or decreasing the uranium concentration to 0.02M in simulated HRT fuel solution (0.04M uranyl sulfate, 0.02M sulfuric acid, and 0.005M copper sulfate) has no significant effect on the solution stability or corrosiveness of the solution. The effect of varying the oxygen concentration between 250 and 2800 ppm in 0.17M uranyl sulfate at 250 deg C on the corrosion rate of 347 stainless steel was found to be negligible in the absence of added Cr/sup 4+/. The corrosion rate of 347 stainless steel in dilute sulfuric acid solutions was determined at 250 deg C. Metallographic examinations have been made of stainless steels and titanium alloys stressed to 76% of their room temperature yield strengths and exposed 19,364 hr to the vapor phase above the HRT solution at 300 deg C. The effect of preformed films on the stress-corrosion cracking of 347 stainless steel in boiling and aerated HRT core solutions containing 50 ppm of chloride was studied as a function of the prefilming time. The effect of HRT core solution components either singly or in combination on the stress corrosion of 347 stalnless steel was examined. In order to determine the susceptibility of 347 stainless steel to cracking in chloride-containing distilled water in the absence of oxygen, tests were run at 300 deg C in solutions containing 100 ppm chloride at adjusted pH values of 2.8, 6.5, and 10.5. Other stainless steels and nickel alloys were subjected to stress corrosion cracking tests at 300 deg C in distilled water with 100 ppm chioride at various pH levels. In general, the higher the nickel content, the more resistant the alloy was to cracking. The corrosion behavior of electroless nickel plate on carbon steel was excellent in distilled water at 300 deg C at adjusted pH levels of 2.5, 7.5, and 10.5. The corrosion of Incoloy, AM-350 stainless steel, Stellites 1, 3, and 98M2, and Rexalloy 33 in HRT core solution was studied. (For preceding period see CF-57-10- 80.) (J.S.R.

SOLUTION CORROSION GROUP QUARTERLY REPORT FOR THE PERIOD ENDING JULY 31, 1957

The second All-Ti loop, 1OOA loop H, was placed in operation for more than 400 hr with UO/sub 2/SO/sub 4/ solution at 250 deg C and -- 1000 psi. A fourth test of the mockup of the Zircaloy-2--stainless steel transition joint used in the HRT reactor vessel was completed. The joint and bellows functioned properly and were leaktight. The series of long-term runs at 200, 250, and 300 deg C with solution proposed for use in the HRT was concluded. Stainless steel and Ti stress specimens exposed during the latter 13,000 hr of these tests gave no evidence of stress-corrosion cracking. Results of a study of the effect of heat treatment on corrosion of type 347 stainless steel are presented. Pretreatment of stainless steel for 100 hr at 250 deg C with oxygenated H/sub 2/O containing 100 or 200 ppm Cr/sup 6+/ as CrO/sub 3/ decreased initial weight losses on subsequent exposures to UO/sub 2/SO/sub 4/ solutions. Stress-corrosion cracking of stainless steel in UO/sub 2/SO/sub 4/ solutions is described. A number of alloys of Zr were corrosion tested in simulated HRT core solutions at 300 deg C. Type 347 stainless steel, surface hardened either by malcomizing or Thermospray 16-C, corroded excessively in UO/sub 2/SO/sub 4/ solutions. Hastelloy R-235, Multimet, and Timken 16-25-6 demonstrated a high degree of corrosion resistance to simulated core solution at 300 deg C. Under the sanne conditions types 431 and 414 stainless steel corroded excessively. Type 420 stainless steel hardened at 50 to 52 Rockwell C corroded badly in 90 deg C UO/sub 2/SO/sub 4/ solution of the composition used in in-pile loops. (W.L.H.

QUARTERLY REPORT OF THE SOLUTION MATERIALS SECTION FOR THE PERIOD ENDING APRIL 30, 1959

Studies concerned with the deposition of salts from simulated fuel solution under boiling conditions were continued. Additional deposition tests were carried out in loop L-2-23 in which the core section was heated. Several reagents were tested to determine their ability to dissolve stainless steel corrosion products. A simulated HRT fuel solution was stable with regard to U concentration when diluted to 23 ppm at 250 C; however, some Cu was lost from solution. Preliminary tests in a uranyl sulfate solution indicate that an 18-8 stainless steel alloyed with either small amounts of Pt or Cu is more corrosion resistant at low flow rates than a conventional 18-8 stainless steel; however, the addition of either Cu or Pt did not reduce the corrosion rate of 18stainless steel at high flow rates. A study was made to determine the susceptibility of off-specification type 347 stainless steel to intergranular attack by uranyl sulfate solutions. Continued testing with a single heat of cast type 347 stainless steel has confirmed previously reported data to the effect that the cast alloy is more resistant a stress-corrosion cracking than is the wrought alloy. Six commercial grades of Al/sub 2/O/sub 3/ suitable for use as check balls in valves in slurry service were corrosion tested in static slurry environments. Corrosion tests with Uniloy 19-9DL showed that the alloy in the annealed and in the annealed and aged condition has corrosion resistance similar a that of type 347 stainless steel in simulated reactor fuel solution and has less tendency to gall than the austenitic stainless steels. (For preceding period see CF-59-1-79.) (W.L.H.

QUARTERLY REPORT OF THE SOLUTION MATERIALS SECTION FOR THE PERIOD ENDING OCTOBER 31, 1958

A simulated HRT fuel solution was unstable when passed through a heated Zircaloy-2 bypass section installed on a Ti loop. Losses of uranyl, cupric, and nickel sulfates were observed when the temperature of the solution emerging from the bypass was as low as 290 deg C. The 0.04 m UO/sub 2/SO/sub 4/ solutions containing Please delete abstract number 773