Residual Slope Research Articles

Effect of a Dispersion of Interfacial Electron Transfer Rates on Steady State Catalytic Electron Transport in [NiFe]-hydrogenase and Other Enzymes

Redox enzymes can be adsorbed onto electrode surfaces such that there is a rapid and efficient direct electron transfer (ET) between the electrode and the enzyme's active site, along with high catalytic activity. In an idealized way, this may be analogous to protein−protein ET or, more significantly, the nonrigid interface between different domains of membrane-bound enzymes. The catalytic current that is obtained when substrate is added to the solution is directly proportional to the enzyme's turnover rate and its dependence on the electrode potential reports on the energetics and kinetics of the entire catalytic cycle. Although the current is expected to reach a limiting value as the electrode potential is varied to increase the driving force, a residual slope in voltammograms is often observed. This slope is significant, as it is unexpected from all simple considerations of electrochemical kinetics. A particularly remarkable result is obtained in experiments carried out with the [NiFe]-hydrogenase from ...

Analysis of the Chiufengershan landslide triggered by the 1999 Chi-Chi earthquake in Taiwan

A disastrous earthquake rocked Taiwan on September 21, 1999, with magnitude M L=7.3 and an epicenter near the small town of Chi-Chi in central Taiwan. The Chi-Chi earthquake triggered landslide on the dip slope at the Chiufengershan. In this study, a review of the topography and geology of this area was followed by field investigations. Laboratory testing was applied to understand the geomaterial composing the slope. Then, based on a series of limit equilibrium analyses, the failure mechanism of this landslide and the risk of the residual slope were studied. According to the stability analyses, the pre-quake slope is quite stable, with factor of safety of 1.77 (dry) to 1.35 (full groundwater level); explaining why there is no written record of a landslide here for the past 100 years. In contrast, a back analysis shows that the Chi-Chi earthquake-induced dynamic loading is far more than the dip slope can sustain, due in part to the short distance to the epicenter. A Monte Carlo type probability analysis suggests that the residual slope is more dangerous than the pre-quake slope and needs more attention.

Explanation for the simultaneous occurrence of bipolar structures and waves near ion‐cyclotron harmonics in the auroral ionosphere

In the downward current region of the auroral ionosphere, the FAST spacecraft has observed bipolar electrostatic structures on Debye length scales and waves at frequencies between the H+ ion cyclotron harmonics. Such bipolar structures have been previously identified with the nonlinearly evolved state of a two‐stream electron instability. In this paper, we present the results of long‐duration and large‐scale particle‐in‐cell (PIC) simulations which produce, from one set of initial conditions, both bipolar electrostatic structures and, at later times, ion Bernstein waves with peak intensities between multiples of the ion cyclotron frequency. The ion Bernstein waves are driven by a weaker beam instability caused by a residual positive slope in the nonlinearly evolved (nonthermal) electron distribution. Although there are a variety of processes which can produce ion Bernstein modes, we show that a common source (an electron beam) can produce both of these observed phenomena in the downward current region.

An advanced KB mirror pair for microfocusing

A new range of micro-focusing mirrors based on KB pairs has been developed by SESO for Beamline Nanospectroscopy at the Elettra Storage Ring in Trieste, Italy. Both the focusing and the aspheric shape are adjustable with stepper motors. The goal of the beamline is to have a high photon density spot with a variable size in the experimental chamber over the whole soft X-ray range. The estimated dimension of the final spot should be smaller than 4 μm 2 FWHM, with a photon density of the order of 10 13 photons/s μm 2; this may be achieved only by accepting an angular divergence on these mirrors of between 5 and 10 mrad. This condition can be fulfilled only with elliptical (or plane elliptical) mirrors with very limited residual slope errors (below 1 μrad RMS) that are able to correct even small focal distance errors.

Complete dispersion compensation for 400-fs pulse transmission over 10-km fiber link using dispersion compensating fiber and spectral phase equalizer

We have demonstrated essentially complete dispersion compensation for 400-fs pulses over a 10-km fiber link using dispersion compensating fiber and a programmable femtosecond pulse shaper functioning as a spectral phase equalizer. The pulse shaper impresses adjustable quadratic and cubic phases onto the spectrum and removes all the residual dispersion and dispersion slope in the dispersion compensated fiber link. Our work shows that the pulse shaper technique provides a powerful and convenient tool for programmable fiber dispersion compensation over broad optical bandwidth. This allows distortion-free femtosecond pulse transmission over a fiber link in excess of 10 km without requiring the exact trimming of the dispersion-compensating fiber.

Demonstration of timing skew compensation for bit-parallel WDM data transmission with picosecond precision

We demonstrate transmission of seven wavelength-division-multiplexed (WDM) bit-parallel channels with a total of 15-nm spectral span over a 2.5-km standard single-mode fiber/dispersion-compensating fiber link with less than 3-ps timing skew. The synchronized WDM channels are generated by spectrally slicing pulses from a single femtosecond fiber laser using a femtosecond pulse shaper. The small residual timing skew arises from the residual dispersion slope of the link. We measure a dispersion slope of D'=0.017 ps/km/mn/sup 2/, which is roughly four times less than for an equivalent length of dispersion-shifted fiber. Our work shows that the dispersion-compensating fiber technique could significantly reduce the timing skew for WDM bit-parallel transmission over a several-kilometer fiber link.

The influence of subsurface moisture on rill system evolution

Rill development studies have focused almost exclusively on surface erosion processes and critical threshold hydraulic conditions. Characteristic rill features, such as arcuate headcuts and knickpoints, are morphologically similar to the ‘theatre-headed’ valleys which have been associated with ‘sapping’ processes at various scales. This paper reports on laboratory experiments designed to identify linkages between surface flow hydraulics, subsurface moisture conditions and rill development. Experiments were carried out in a 16·57 m2 flume under simulated rainfall with soil samples up to 0·15 m depth in which moisture conditions were monitored by miniature time-domain reflectometer probes. Tests showed complex responses in which some rill incision reflected surface flow conditions, but major rill system development with markedly enhanced sediment yield was closely associated with high soil moisture contents. It was not possible to measure seepage forces directly, but calculation and observation indicate that these were less important than reduction in soil strength with saturation, which resulted in increased effective runoff erosivity. This caused concentrated undercutting along the water table at rill walls, while slightly stronger surface layers above the water table formed microscarps. These retreated along the water table into interrill surfaces, producing residual pediment transport slopes. The microscarps eventually disappeared when the water table reached the surface, eliminating differential soil strength. The experiments showed complex relationships between surface and subsurface erosional processes in evolving rill systems, strongly influenced by soil moisture dynamics. The very small topographic and hydraulic head amplitudes indicate that seepage forces and ‘sapping’ were minimal. The dominant effect of soil moisture was reduction of soil strength with saturation, and increased runoff entrainment. Experimental conditions were not unusual, either for agricultural fields or natural hillslopes, and the intricate interrelationship of surface and subsurface erosion processes observed is probably not uncommon. Attempts to link specific morphologic features at rill scale to dominance of surface or subsurface processes alone are therefore unlikely to be successful or reliable. © 1998 John Wiley & Sons, Ltd.

The influence of subsurface moisture on rill system evolution

Rill development studies have focused almost exclusively on surface erosion processes and critical threshold hydraulic conditions. Characteristic rill features, such as arcuate headcuts and knickpoints, are morphologically similar to the ‘theatre-headed’ valleys which have been associated with ‘sapping’ processes at various scales. This paper reports on laboratory experiments designed to identify linkages between surface flow hydraulics, subsurface moisture conditions and rill development. Experiments were carried out in a 16·57 m2 flume under simulated rainfall with soil samples up to 0·15 m depth in which moisture conditions were monitored by miniature time-domain reflectometer probes. Tests showed complex responses in which some rill incision reflected surface flow conditions, but major rill system development with markedly enhanced sediment yield was closely associated with high soil moisture contents. It was not possible to measure seepage forces directly, but calculation and observation indicate that these were less important than reduction in soil strength with saturation, which resulted in increased effective runoff erosivity. This caused concentrated undercutting along the water table at rill walls, while slightly stronger surface layers above the water table formed microscarps. These retreated along the water table into interrill surfaces, producing residual pediment transport slopes. The microscarps eventually disappeared when the water table reached the surface, eliminating differential soil strength. The experiments showed complex relationships between surface and subsurface erosional processes in evolving rill systems, strongly influenced by soil moisture dynamics. The very small topographic and hydraulic head amplitudes indicate that seepage forces and ‘sapping’ were minimal. The dominant effect of soil moisture was reduction of soil strength with saturation, and increased runoff entrainment. Experimental conditions were not unusual, either for agricultural fields or natural hillslopes, and the intricate interrelationship of surface and subsurface erosion processes observed is probably not uncommon. Attempts to link specific morphologic features at rill scale to dominance of surface or subsurface processes alone are therefore unlikely to be successful or reliable. © 1998 John Wiley & Sons, Ltd.

Design optimization of a flexural hinge-based bender for X-ray optics.

This paper presents a parameter study and design optimization of a flexural hinge-based bender by use of finite-element modelling and analytical formulation. The relationship between the mirror shape and the driving forces, the so-called bender driving equation, is established. Various parameters are investigated: the material properties, the geometrical parameters, the stress and deformation of the mirror and flexural hinge, the residual slope error of the mirror, and the resolution required for the actuators. Analysis results have been compared with test results for a prototype bender and a silicon mirror (170 x 40 x 10 mm). Both analysis and test results confirm the microradian accuracy of the bent mirror. Finally, a bender design for short-bending-radius applications is also presented.

The ratio of initial/residual DNA damage predicts intrinsic radiosensitivity in seven cervix carcinoma cell lines.

The single-cell gel electrophoresis (comet) assay was used to measure radiation-produced DNA double-strand breaks (dsbs) in a series of seven cervical tumour cell lines (ME180, HT3, C33A, C41, SiHa, MS751 and CaSki). The proportion of DNA dsbs was measured immediately after radiation treatment (initial damage) and 16 h later after incubation at 37 degrees C (residual damage). Linear dose-response curves were seen for initial (slopes 0.23-0.66) and residual (slopes 0.16-0.87) DNA dsbs. Neither of the slopes of the linear regression analysis on the initial and on the residual DNA dsbs dose-response curves (range 0-80 Gy) correlated with SF2 (surviving fraction at 2 Gy) measured after high- (HDR) or low-dose-rate (LDR) irradiation. An association was evident between SF2 after HDR and LDR irradiation and the ratio of the absolute level of initial and residual damage after a single dose of 60 Gy. However, a significant correlation was found between HDR (r= -0.78, P = 0.04) and LDR (r = -0.86, P = 0.03) SF2 values and the ratio of the slopes of the initial and residual DNA dsbs dose-response curves (range 0.47-0.99), representing the fraction of DNA damage remaining. These results indicate that the neutral comet assay can be used to predict radiosensitivity of cervical tumour cell lines by assessing the ratio of initial and residual DNA dsbs.

A Comparison of Two Approaches to Ranking Algorithms Used to Compute Hill Slopes

The calculation of slope (downhill gradient) for a point in a digital elevation model (DEM) is a common procedure in the hydrological, environmental and remote sensing sciences. The most commonly used slope calculation algorithms employed on DEM topography data make use of a three-by-three search window or kernel centered on the grid point (grid cell) in question in order to calculate the slope at that point. A comparison of eight such slope calculation algorithms has been carried out using an artificial DEM, consisting of a smooth synthetic test surface with various amounts of added Gaussian noise. Morrison’s Surface III, a trigonometrically defined surface, was used as the synthetic test surface. Residual slope grids were calculated by subtracting the slope grids produced by the algorithms on test from true/reference slope grids derived by analytic partial differentiation of the synthetic surface. The resulting residual slope grids were used to calculate root-mean-square (RMS) residual error estimates that were used to rank the slope algorithms from “best” (lowest value of RMS residual error) to “worst” (largest value of RMS residual error). Fleming and Hoffer’s method gave the “best” results for slope estimation when values of added Gaussian noise were very small compared to the mean smooth elevation difference (MSED) measured within three-by-three elevation point windows on the synthetic surface. Horn’s method (used in ArcInfo GRID) performed better than Fleming and Hoffer’s as a slope estimator when the noise amplitude was very much larger than the MSED. For the large noise amplitude situation the “best” overall performing method was that of Sharpnack and Akin. The popular Maximum Downward Gradient Method (MDG) performed poorly coming close to last in the rankings, for both situations, as did the Simple Method. A nonogram was produced in terms of standard deviation of the Gaussian noise and MSED values that gave the locus of the trade-off point between Fleming and Hoffer’s and Horn’s methods.

A correlation between residual DNA double-strand breaks and clonogenic measurements of radiosensitivity in fibroblasts from preradiotherapy cervix cancer patients

To study the relationship between residual DNA damage and clonogenic measurements of radiosensitivity in fibroblasts from pretreatment cervix cancer patients. Early passage vaginal fibroblasts from nine preradiotherapy cervix cancer patients and two radiosensitive skin fibroblast cell strains were studied. Cell survival was measured by clonogenic assay following both high and low dose rate irradiation. Residual DNA damage was measured using pulsed-field gel electrophoresis (PFGE) after irradiating radiolabeled, plateau-phase cells at 37 degrees C and allowing 24 h for repair. DNA damage was expressed both in terms of the residual damage slope (fitted to data from 60 to 150 Gy) and the fraction of activity released (FAR) following 150 Gy. The surviving fraction at 2 Gy (SF2) values after high dose rate irradiation for the vaginal fibroblasts ranged from 0.15 to 0.32 (a 2.2-fold difference). When the two radiosensitive cell strains were included, residual damage, expressed as the residual damage slope, correlated with alpha (r = 0.82, p = 0.002), D bar (r = -0.91, p < 0.001) and SF2 (p = -0.79, p = 0.004), and when the vaginal fibroblasts alone were studied, the residual damage slope again correlated with clonogenic survival, although less strongly [alpha (r = 0.66, p = 0.053), D bar (r = -0.83, p = 0.006), and SF2 (r = -0.63, p = 0.07)]. Within the group of vaginal fibroblasts there was a 4.0-fold difference in residual DNA damage slope. When residual damage was expressed as FAR at 150 Gy, then for all cell strains the correlations were alpha: r = 0.78, p = 0.004, D bar: r = -0.86, p = 0.001, and SF2: r = -0.78, p = 0.004, and for the vaginal fibroblast strains alone the correlations were alpha: r = 0.60, p = 0.088, D bar: r = -0.75, p = 0.02, and SF2: r = 0.62, p = 0.077. This study confirms previous findings that residual DNA damage correlates with clonogenic survival in fibroblasts. In addition, it demonstrates a correlation for fibroblasts from pretreatment cervix cancer patients demonstrating a relatively small range of SF2 values.

Fiber transmission for sub-500-fs pulses using a dispersion-compensating fiber

We report transmission of /spl sim/60-fs and /spl sim/245-fs pulses, respectively, over 42-m and 2.5-km fiber links which consist of standard single-mode fibers (SMF) concatenated with dispersion-compensating fibers (DCF). The experiments using very short pulses (/spl sim/60 fs) over a short fiber length (/spl sim/42 m) demonstrate the ability to achieve simultaneous dispersion and dispersion slope compensation using this technique. Femtosecond spectral interferometry measurements of this 42-m link show that its residual dispersion slope is approximately six times lower than that of the dispersion-shifted fiber. Finally, to demonstrate that the dispersion-limited propagation distance is proportional to the cube of the pulsewidth, we transmit /spl sim/245-fs pulses over a 2.5-km SMF-DCF link and achieve comparable pulse restoration as with the shorter fiber experiments.

Third-generation synchrotron radiation X-ray optics

In addition to these main research and development activities, a number of other developments have been followed up that cannot be described here in detail. It is, however, important to mention the very precise and stable mechanical support structures, in particular the bending devices for mirrors, multilayers and single crystals that are used on many beamlines for meridional and sagittal focusing. As an example, the performance tests of a monolithic bender based on flexure hinges showed a residual slope error of 1.1 μrad when focusing an X-ray beam by a multilayer supermirror coated on a 10 mm thick silicon substrate. A novel bimorph bending system for dynamical focusing by mirrors, single crystals and multilayers, based on piezoelectric materials, yielded a focal spot size of 11 μm. Focusing methods for high-energy X-rays have been developed, for instance for the medical beamline, and here typical focal spot sizes are in the range 5–150 μm, depending on magnification and other parameters.If smaller focal sizes are needed, BFO (Bragg–Fresnel optics) is mainly used, and tapered glass capillaries are also being developed for this purpose. Both single-crystal and multilayer-based BFO have been studied extensively for many years. They consist of micrometer-scale Fresnel structures machined into Bragg reflectors. Micron spot sizes in one or two directions can currently be obtained with both techniques. So-called Kirkpatrick–Baez systems deliver almost identical spatial resolution.By analogy to what is known from visible-light optics, half-wave or quarter-wave plates can also be made for X-rays using diamond, silicon or beryllium crystals. They permit the production and analysis of the polarization state of X-rays. This has recently been applied to magnetic diffraction and circular magnetic X-ray dichroism. Polarization efficiencies in excess of 95% can be achieved and it is expected that many beamlines will be equipped with such phase-shifting optics.

Determination of Particle Collision Efficiencies for Flocculent Transport Models

The object of this study is to investigate the data needs for accurate estimation of particle collision efficiencies ({alpha}). Batch flocculation and vertical flocculent settling studies were conducted on aquatic sediment particles in the size range of 2--80 {mu}m in diameter. Dynamic particle-size distribution data sets were generated using a 256-category binary-collision-based flocculent settling model and subsequently compressed into 128, 64, 32, 16, 8, and 4 logarithmically varying particle-diameter categories. A previously developed parameter-estimation framework was used to estimate {alpha} values from the compressed data sets. Variability in the {alpha} estimates indicates that it is not an artifact of the experimental data. The residual function value after 20 estimation iterations increased with the discretization levels, indicating shallower residual function slopes. Parameter estimate accuracy was unaffected by the levels of data sparsity considered. Increased random noise resulted in consistently lower estimated collision efficiencies. Rate of convergence was unaffected by random noise but decreased with data sparsity levels. Particle water column residence times were significantly overestimated using four category distributions.

Shear-strength characteristics of a residual soil

Shallow landslides in natural residual soils slopes are common all over the world. The slip surfaces associated with these landslides are often situated above the groundwater table. Therefore, it is important to quantify the contribution of negative pore-water pressure to the shear strength of soil. The shear-strength characteristics of residual soil from the Jurong Formation in Singapore were assessed using multistage, consolidated drained triaxial tests. These tests involved shearing under either a constant net confining pressure and varying matric suctions or under a constant matric suction and varying net confining pressures. An extended form of the Mohr–Coulomb equation was used to interpret the test results. The test results show that for matric suctions up to 400 kPa, the angle of internal friction associated with the matric suction, [Formula: see text], is similar to the effective angle of internal friction, [Formula: see text], which averages 26° for the residual soil of the Jurong Formation. The residual soil can maintain a high degree of saturation for matric suctions as high as 400 kPa. Examples involving stability analyses of a residual soil slope with varying pore-water pressure profiles indicate that soil suction contributes significantly to the factor of safety, particularly for shallow slip surfaces. Key words : residual soil, unsaturated soil, matric suction, shear strength, multistage triaxial test, slope stability.

Thermal analyses of premirrors for a SPring-8 undulator beamline

Large heat power will be loaded on a premirror in a SPring-8 undulator beamline. It has to be handled without reducing the optical performance of the premirror using as simple devices as possible. Thermal analyses using the finite element method for directly and indirectly water-cooled mirrors were performed for a high-power undulator beam assumed with a total power of up to 660 W and a peak power density of 1.1 W/mm2. The peak temperature rise calculated at the mirror surface is lower than 25 K. The performance of a four point load bending system was simulated to compensate the thermal slope error on the mirror surface in the meridional direction while also taking into account the effects of gravity sag. It is found that the correction of the mirror surface shape can be theoretically expected to produce a cylindrically bent figure in the area of incidence of the first harmonic radiation with a residual slope error less than 0.5 μrad.

Development of a chronocoulometric method for the determination of uranium at trace levels by using the catalytic nitrate reduction

AbstractThe electroanalytical determination of uranium at trace levels was studied with the purpose of improving the sensitivity of the uranium‐catalyzed reduction in the presence of nitrate on mercury electrode. Examination of the current dependence on time (chronoamperometry) revealed the advantage of measuring the current later and for a longer time interval than usual in pulse polarography. The uranium/nitrate system is particularly favorable in this sense because an intensification of the catalytic current with time is observed. The best signal‐to‐noise ratio was achieved using the technique of chronocoulometry. In this chronocoulometric catalytic determination (CCCD), analytical information was gathered, calculating the slope of the charge versus time curve during the period of 10 to 20 seconds after the application of the potential pulse and correcting it for the residual slope before the pulse. To establish the new analytical procedure, the effects of electrolyte composition, potential program, integration time, and blank correction were examined. A detection limit of 3 × 10−10 M was attained, a power of ten lower than the sensitivity reported for the same catalytic determination by differential pulse polarography. An exploratory study of the combination of this procedure with preconcentration of uranium on the electrode allowed reduction of the detection limit by an additional order of magnitude.

Charge conservation in intact frog skeletal muscle fibres in gluconate-containing solutions.

1. The conservation of intramembrane charge was investigated in intact voltage-clamped frog skeletal muscle fibres under conditions that minimized time-dependent ionic currents and so facilitated precise determination of capacitative charge. 2. Prolonged (q gamma) transients were demonstrated in 3,4-diaminopyridine and tetraethyl-ammonium gluconate-containing low [Ca2+] solutions in response to 125 ms pulses that explored the voltage range -90 to -20 mV. The tetracaine-sensitive, q gamma, component then accounted for a significant proportion (over 50%) of available charge. 3. Both delayed 'on' q gamma currents and 'off' current tails decayed to steady direct current (DC) baselines without significant residual ionic current slopes in the chosen extracellular solutions. This suggested that the current transients represented capacitative decays. It was also compatible with the precise determination of effective charge by integration. 4. The advent of 'on' q gamma current was accompanied by increased 'off' charge. Thus, charge was conserved through all 'on' and 'off' steps and through test voltages that extended from the threshold appearance of q gamma as a slow transient to its full merger with the earlier q beta decay at stronger depolarizations. 5. Charge conservation persisted through a wide range of 'on' pulse durations between 60 and 370 ms and was therefore independent of the interval following the q gamma decay. 6. The quantity of q gamma charge remained a monotonic single-valued function of test voltage, whether this potential was reached directly from the -90 mV holding potential or following a prepulse to -10 mV. 7. These findings suggest that the q gamma charge movement represents the electrical signature of an intramembrane entity whose transitions are primarily driven by, and therefore conserved with, the steady-state potential.

Automatisation of the single-breath nitrogen washout test.

The paper presents a computer-based system for performance and analysis of the single-breath nitrogen washout test (Sb-N2 test). A pneumotachometer and a rapid gas analyser are used for volume flow rate and nitrogen fraction measurements. The data are acquired and analysed by a PDP-11/34 computer. Several sources of measurement errors are considered. An algorithm is proposed to reduce errors in flow measurements due to viscosity variation in respired air. The algorithm for closing volume (CV) detection and calculation of other Sb-N2 parameters is developed from 50 tracings of 18 subjects. The CV is obtained by an iterative linear fitting of the later half of the Sb-N2 curve. Comparisons between computer and hand measurements of three trained readers show good correlations (r = 0.87, 0.93, 0.91). The variability of computer CV measurements was comparable with that of the hand reader with the lowest variance. The coefficient of variation of residual volume and slope of alveolar plateau measurements are apparently reduced. The results demonstrate the adequacy and convenience of using the computer to analyse the Sb-N2 test and indicate that the automation allows for reduction of experimental errors and of test parameter variabilities.