Single Detachment Research Articles

Single- and double-electron loss of H- in collisions with SF6, CH4, and CO.

Measurement of absolute, total cross sections for single- and double-electron detachment of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ projectiles in sulfur hexafluoride, methane, and carbon oxide has been made. The relative energy range under investigation was from 1 to 5 keV. The resulting cross sections for the single-electron loss of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ in ${\mathrm{SF}}_{6}$ exhibit a flat behavior, whereas for methane and carbon monoxide the single detachment cross section increases with the energy. A free-collision model for electron loss was applied, and very good agreement was found for ${\mathrm{SF}}_{6}$, while for the other targets there is a departure of the trend of the experimental data. A comparison with the results from other research laboratories is given. The measured double-electron detachment cross sections are roughly one order of magnitude smaller than the single detachment cross sections. \textcopyright{} 1996 The American Physical Society.

Flow cell for real time observation of single particle adhesion and detachment

A flow cell was built for observing particle removal from test surfaces in real time. The removal force is the hydrodynamic force exerted on the particle by liquid flowing parallel to the test surface. Particle removal was detected visually either through a microscope or on a video monitor. All experimental results reported here are based on the removal of deposited 10 μm polystyrene (PSL) spheres from one of 3 surfaces: polished aluminum; polished bare silicon wafers (native oxide only); or thertnally oxidized silicon wafers. One of 3 cleaning liquids was used: dilute SC-1, dilute SC-2, or de-ionized water containing 0.01% Micro®. The hydrodynamic removal force was controlled primarily by controlling the liquid flow rate. In all experiments, as the flow rate increased, single polystyrene latex (PSL) spheres detached first, then doublets, then triplets and finally larger agglomerates; that is, the adhesion force increased more rapidly with agglomeration than the hydrodynamic removal force. By applying the...

Experimental Study of Processes and Particle‐Size Distributions of Eroded Soil

The study presented here consisted of rainfall-runoff events produced with a large rainfall simulator. Three test plots were 2.44 m wide, with lengths of 6.1 m, 13.72 m, and 24.38 m, and a slope of 2%. The soil on the plots was loamy sand. Rainfall intensities of 44 mm/h, 79 mm/h, and 160 mm/h were run for 1 h for each test. Samples of the runoff were analyzed for sediment particle-size distribution, which led to several conclusions about the processes governing the erosion rates. Transport capacity tended to limit the erosion rate of larger particles, and supply limited the erosion rate of smaller particles. The data demonstrate that evaluating a single detachment or transport rate and assuming that it is constant for a season, or even a storm, may not always produce accurate results. The variations of these rates, due to armoring, must be taken into consideration.

LASER TREATMENT OF ECCENTRIC LEAKS IN CENTRAL SEROUS CHORIORETINOPATHY RESULTING IN DISAPPEARANCE OF UNTREATED JUXTAFOVEAL LEAKS

In central serous chorioretinopathy (CSCR) laser treatment of leaking points close to the macular center should be avoided because of the possibility of producing juxtafoveal scotoma and stimulating choroidal neovascularization. Nine eyes of nine consecutive patients with CSCR had two or more leaking points within a macular detachment, one of which was foveal or near to the fovea. Photocoagulation with green argon laser was performed in all eyes, treating all the leaking points except for the central one. Visual symptoms regressed after treatment, and the serous detachment was resolved 10 days to 4 weeks after photocoagulation in all cases. Fluorescein angiography showed no leakage at either the central leakage point or the leakage point that had been treated. These results led us to believe that the central or dependent leak in our cases was not sufficient to maintain the serous detachment by itself. An alternative hypothesis is that the untreated leak did not represent real fluid movement but only diffusion of fluorescein molecules, or a false leak. In cases of CSCR with multiple leaks within a single macular detachment, we believe that a foveal leak may be a dependent or false leak and that direct treatment is not necessary.

Near‐vertical and intermediate offset seismic reflection data from west of the Whipple Mountains, SE California

During a seismic reflection survey conducted by the California Consortium for Crustal Studies in the Basin and Range Province west of the Whipple Mountains, SE California, a piggyback experiment was carried out to collect intermediate offset data (12–31 km). These data were obtained by recording the Vibroseis energy with a second, passive recording array, deployed twice at fixed positions at opposite ends of the reflection lines. The reflection midpoints fall into a 3‐km‐wide and 15‐km‐long region in Vidal Valley, roughly parallel to a segment of one of the near‐vertical reflection profiles. This data set makes three unique contributions to the geophysical study of this region. (1) From forward modeling of the observed travel times using ray‐tracing techniques, a shallow layer with velocities ranging from 6.0 to 6.5 km/s was found. This layer dips to the south from 2‐km depth near the Whipple Mountains to a depth of 5‐km in Rice Valley. These depths correspond closely to the westward projection of the Whipple detachment fault, which is exposed 1 km east of the near‐vertical profiles in the Whipple Mountains. (2) On the near‐vertical profile, the reflections from the mylonitically deformed lower plate at upper crustal and mid crustal depths are seen to cease underneath a sedimentary basin in Vidal Valley. However, the piggyback data, which undershoot this basin, show that these reflections are continuous beneath the basin. Thus near‐surface energy transmission problems were responsible for the apparent lateral termination of the reflections on the near‐vertical reflection profile. (3) The areal distribution of the midpoints allows us to construct a quasi‐three‐dimensional image on perpendicular profiles; at the cross points we determined the true strike and dip of reflecting horizons. This analysis shows that the reflections from the mylonitically deformed lower plate dip to the southwest westward of the Whipple Mountains and dip to the south southward of the Turtle Mountains. The results of this study support the interpretation of crustal reflectivity in the near‐vertical reflection profiles to be related to the mid‐Tertiary episode of extension which produced the Whipple metamorphic core complex. This association geometrically suggests a more regionally distributed mechanism for crustal thinning as compared with single detachment fault models.

Cross sections for phosphorous negative-ion detachment in collisions with rare gas atoms

Atomic cross sections for single and double electron detachment from P− in collisions with rare-gas atoms are reported at laboratory collision energies between 13 and 113 keV.

Seismotectonics of the Zagros continental collision zone and a comparison with the Himalayas

Accurate focal depths of 16 medium to large Zagros earthquakes were determined from identification of surface‐reflected phases by comparing observed, long‐period P waves with synthetic seismograms. All events are shallow (6–12 km) and show no tendency to deepen toward the Main Zagros Thrust. Geological and geophysical evidence suggests that most of these earthquakes probably occurred within the uppermost Precambrian basement. Because the focal mechanisms of these events indicate high‐angle, reverse faulting, the events do not occur on a single detachment surface but rather reflect horizontal shortening of the basement on numerous, short‐segmented (<100 km) and subparallel reverse faults. This geometry may explain the absence of great earthquakes (M ≅ 8) in Zagros. Synchronous widespread deformation of both the sedimentary cover and basement is a unique feature for the Zagros region unlike other fold and thrust belts. In contrast to Zagros, medium to large, thrust‐type Himalayan earthquakes define a shallow, north dipping detachment that separates the underthrusting Indian plate from the Lesser Himalayan crustal block; the great Himalayan events (M > 8) probably occurred along this detachment. A comparative study of the Zagros with the Himalayas suggests that the active tectonics of the Zagros continental collision zone and the Iranian blocks arc similar to those of the Himalayas and the Tibetan terranes in Oligocene time.

Semiclassical (γ, 2e): absolute cross-sections for H-at threshold

The uniform semiclassical approximation is employed to calculate the first cross-sections for two-electron photodetachment from H- near threshold. Theory predicts that the single-photon total cross-section is given by sigma ( gamma ,2e) approximately=(3.14*10-20)E1.127 cm2, where E is the excess photon energy in eV. This cross-section is less than 1.3% of the corresponding single detachment cross-section for E<or approximately=1eV.

Origin of features in the energy spectra of electrons detached from fast H-in collisions with He and Ar atoms

Using Born's approximation the authors have analysed the structure of the doubly differential cross section for electron loss from fast H- near the forward direction. They show that electrons ejected with velocities slightly smaller than the projectile, originate in collisions in which the 'diffuse' electron of H- scatters as a nearly-free electron and excites (ionises) the target. Electrons ejected with velocities close to that of the projectile come from three sources: (i) double-electron loss in which the final state is strongly influenced by the Coulomb interaction with the resulting fast proton; (ii) single electron loss in which the target is excited by the H core, while the ejected 'diffuse' electron acts as a separator; and (iii) single detachment with no excitation of the target which comprises a small fraction of the events for He targets, but becomes important for heavier targets such as Ar.

Displacement-distance methods in the analysis of fold-thrust structures and linked-fault systems

A new method for analysing the internal strain in thrust sheets is described. The displacement-distance diagram can be used to quantify the relative shortening (or relative stretch) between the hangingwall and footwall beds of a thrust and is a useful way of analysing commonly occurring fold-thrust structures. The stretch is a function of the relative rates of thrust propagation and thrust slip. The cumulative displacement-distance diagram described here can be used to calculate the absolute shortening or extension, when this is accommodated above a single décollement in a linked-fault system. This method offers a useful way of analysing duplex structures and large-scale, foreland thrust zones, as well as extensional fault systems and can be used as an alternative to, or in conjunction with, balanced cross-sections. Both methods can be used to quantify the variation in shortening above a single detachment zone; this variation may be mechanically significant, reflecting lithological control on thrust or normal fault growth.

The formation of H+from H-ions by electron impact

Cross sections of the reaction H-+e to H+ +3e have been measured for interaction energies between threshold (14.4 eV) and 850 eV. The cross section reaches a maximum value 5.0*10-17 cm2 at 70 eV. Comparison with previous measurements shows that, for energies greater than 100 eV, the ratio of cross sections for single and double detachment is almost constant and equal to 39+or-10%. The present measurements are compared with similar results for helium and Li+.

Structure observed during detailed measurements of detachment from H-by electron impact

Absolute cross sections for single detachment from H- by electron impact have been measured by an inclined beam technique. At interaction energies close to 14.5 eV the detachment function shows structure which is attributed to the formation of H2- with a lifetime of the order of 10-15s.