Slope Reversals Research Articles

Channel slope reversal near the Martian dichotomy boundary: Testing tectonic hypotheses

Faults along the Martian dichotomy boundary are evidence of tectonic activity, which by analogy with terrestrial tectonism may cause changes in or even reversal of fluvial longitudinal profiles. In the eastern hemisphere between 30° E and 150° E, this tectonic activity has been hypothesized to result from lower crustal flow or from lithospheric flexure, for which loading (e.g., by material deposition) of the northern lowlands is a possible cause (Watters, 2003a; Nimmo, 2005). The topographic (slope) changes resulting from these two different mechanisms are distinct and can provide a means for distinguishing between them, although other processes may complicate interpretations of reversed longitudinal profiles. Two fan-shaped networks of inverted channels are located near 150° E in the Aeolis Dorsa region just north of the dichotomy boundary. Their original flow directions, inferred from planform morphology, suggest flow to the northeast in contrast to their current longitudinal profiles sloping down to the southwest. This contrast indicates slope reversal. We investigate the lower crustal flow and flexure mechanisms for slope reversal by testing three different hypotheses: 1) lower crustal flow, 2) flexure caused by material erosion from the highlands and deposition in the lowlands, and 3) flexure caused by highland erosion and deposition in the lowlands plus deposition of the Medusae Fossae Formation in the lowlands. We test these three hypotheses by comparing the inferred magnitudes of the slope reversals with predicted slope changes from geophysical models for these processes. Taking the possibility of non-tectonic (i.e., collapse) processes into account, our results suggest that, among these three models, the slope reversal is most consistent with the predicted tectonic response to erosion and deposition of highland material in conjunction with deposition of the Medusae Fossae Formation. Contrary to previous findings, our results do not support the mechanism of lateral crustal flow, although they do not rule it out because lower crustal flow and erosion may both have been operating, but on different time scales. The result of this hypothesis-testing provides insight into the evolution of the dichotomy boundary and Martian crust in this location.

ECG feature extraction using differentiation, Hilbert transform, variable threshold and slope reversal approach

An accurate and reliable ECG feature extraction algorithm is presented in this paper. ECG samples are de-noised and its first derivative and Hilbert transform are computed. Sample having maximum amplitude in the transformed domain is found out and those samples having amplitudes within a lead wise specified threshold of that maximum are marked. In the original signal, where these marked samples undergo slope reversals are spotted as R-peak. On the left and right side of the R-peak, slope reversals are identified as Q and S peak, respectively. QRS onset-offset points, T and P waves are also detected. ECG baseline modulation correction is done after detecting characteristics points. The algorithm offers a good level of Sensitivity, Positive Predictivity and accuracy of R peak detection. Each wave and segment duration and each peak height is measured. Measurement errors of extracted ECG features are calculated. The algorithm is implemented on MATLAB 7.1 environment.

QRS complex identification using Hilbert transform, variable threshold and slope reversal approach

The present paper proposes an accurate detection algorithm of QRS complex of ECG signal. Here, Hilbert Transform of the first derivative of the ECG signal is computed at first. In the transformed signal, samples having amplitudes within a certain threshold are marked. In the original ECG signal, locations, where those marked samples undergo slope reversals, are identified as the R-peaks. Q, S, QRS onset and offset points are also detected properly. A good degree of accuracy is achieved in Sensitivity (Se = 99.89%) and Positive Predictivity (PP = 99.93%) of R peak detection. R peak height and QRS duration measurement errors are also less.

Tunable rectification and slope reversals in the I– V characteristics of ballistic nanojunctions

We investigate nonlinear effects at low temperature in the I– V characteristics of four-terminal nanojunctions fabricated from InGaAs/InAlAs heterostructures. The rectified voltage can be tuned by applying biases on side gates, as well as by changing cooldown conditions, i.e., by controlling the conductances of the junctions’ channels. In addition, we observe reversals in the slope of the I– V curves as the probe current grows. These reversals coincide with abrupt changes in the channels’ conductances. We discuss possible interpretations of these observations, and provide a comparison with previous experimental results.

Conditions for the reversal of ice/air surface slope on ice streams and shelves: a model study

AbstractReversals in the ice/air surface slope are important in geomorphic and glaciological contexts, thus motivating consideration of the conditions under which they form. Surface slope reversals are seen in numerous places, such as ice rumples on ice shelves, as surficial lakes, and at the down-glacier end of Vostok lake, Antarctica. Such slope reversals can reduce or reverse the subglacial hydrological gradient, thereby rerouting subglacial water transport and possibly leading to the creation of subglacial lakes. Supraglacial lakes produced by slope reversals in ablation zones may aid in driving water-filled cracks that allow surface water access to the bed. Surface slope reversals, in the absence of a concomitant reversal in ice flow, indicate a local violation of the so-called ‘shallow-ice’ approximation, and in this circumstance the longitudinal deviatoric stress becomes critical in the stress equilibrium. Using a simple numerical model, we have explored the conditions under which surface slope reversals form for certain simple scenarios. The results indicate that ice which initially possesses a normal slope will tend toward a reversed slope if the ice is thinned, the bed is strengthened or the downstream buttressing is increased.

Stellar Kinematics of Boxy Bulges: Large-Scale Bars and Inner Disks

Major-axis long-slit stellar kinematics was obtained for 30 edge-on spiral galaxies, 24 with a boxy/peanut-shaped (B/PS) bulge. B/PS bulges are present in >45% of highly inclined systems and much work suggests that they are the edge-on projection of thick bars. Profiles of the mean stellar velocity V, the velocity dispersion sigma, and the asymmetric (h3) and symmetric (h4) deviations from a Gaussian are presented. Comparing those with N-body bar diagnostics, we find bar signatures in 80% of our sample. B/PS bulge galaxies typically show a double-hump rotation curve with an intermediate dip or plateau. They often show a flat central velocity dispersion profile accompanied by a secondary peak or plateau and >=40% have a local central sigma minimum. The h3 profiles display up to 3 slope reversals and h3 is normally correlated with V over the presumed bar length, contrary to expectations from axisymmetric disks. Those characteristic bar signatures strengthen the case for a close link between B/PS bulges and bars. h3 is anti-correlated with V in the very center of most galaxies, indicating that they additionally harbor cold and dense decoupled nearly axisymmetric central stellar disks. These coincide with previously identified star-forming ionized-gas disks in the gas-rich systems, and we argue that they formed out of gas inflow driven by the bar. As suggested by N-body models, h3 appears to be a reliable tracer of asymmetries in disks, allowing to discriminate between axisymmetric and barred disks seen in projection. B/PS bulges (and thus a large fraction of all bulges) appear to be made-up mostly of disk material which has acquired a large vertical extent through bar-driven vertical instabilities. Their formation is thus probably dominated by secular evolution processes rather than merging. [Abridged]

Mars Global Surveyor observations of Martian fretted terrain

The Martian fretted terrain between latitudes 30° and 50°N and between 315° and 360°W has been reexamined in light of new Mars Orbiter Camera (MOC) and Mars Orbiter Laser Altimeter (MOLA) data from Mars Global Surveyor. Much of the terrain in the 30°–50° latitude belt in both hemispheres has a characteristic stippled or pitted texture at MOC (1.5 m) scale. The texture appears to result from partial removal of a formerly smooth, thin deposit as a result of sublimation and deflation. A complex history of deposition and exhumation is indicated by remnants of a former, thicker cover of layered deposits. In some hollows and on some slopes, particularly those facing the pole, are smooth textured deposits outlined by an outward facing escarpment. Throughout the study area are numerous escarpments with debris flows at their base. The escarpments typically have slopes in the 20°–30° range. At the base of the escarpment is commonly a deposit with striae oriented at right angles to the escarpment. Outside this deposit is the main debris apron with a surface that typically slopes 2°–3° and complex surface textures suggestive of compression, sublimation, and deflation. The presence of undeformed impact craters indicates that the debris flows are no longer forming. Fretted valleys contain lineated fill and are poorly graded. They likely form from fluvial valleys that were initially like those elsewhere on the planet but were subsequently widened and filled by the same mass‐wasting processes that formed the debris aprons. Slope reversals indicate that downvalley flow of the lineated fill is minor. The ubiquitous presence of breaks in slope formed by mass wasting and the complex surface textures that result from mass wasting, deflation, and sublimation decreases the recognizability of the shorelines formerly proposed for this area.

The geometric signature: Quantifying landslide-terrain types from digital elevation models

Topography of various types and scales can be fingerprinted by computer analysis of altitude matrices (digital elevation models, or DEMs). The critical analytic tool is the geometric signature, a set of measures that describes topographic form well enough to distinguish among geomorphically disparate landscapes. Different surficial processes create topography with diagnostic forms that are recognizable in the field. The geometric signature abstracts those forms from contour maps or their DEMs and expresses them numerically. This multivariate characterization enables once-in-tractable problems to be addressed. The measures that constitute a geometric signature express different but complementary attributes of topographic form. Most parameters used here are statistical estimates of central tendency and dispersion for five major categories of terrain geometry; altitude, altitude variance spectrum, slope between slope reversals, and slope and its curvature at fixed slope lengths. As an experimental application of geometric signatures, two mapped terrain types associated with different processes of shallow landsliding in Marin County, California, were distinguished consistently by a 17-variable description of topography from 21×21 DEMs (30-m grid spacing). The small matrix is a statistical window that can be used to scan large DEMs by computer, thus potentially automating the mapping of contrasting terrain types. The two types in Marin County host either (1) slow slides: earth flows and slump-earth flows, or (2) rapid flows: debris avalanches and debris flows. The signature approach should adapt to terrain taxonomy and mapping in other areas, where conditions differ from those in Central California.

Long‐term variations of the external and internal components of the Earth's magnetic field

The present study applies classical techniques of time series analysis to the separation of the external and internal signals from the geomagnetic field. We first differentiate the data with respect to time in order to get rid of the large secular variation over the long time span considered (up to 100 years). Next we filter the resulting data to eliminate short‐period components of the magnetic signals. We then proceed to identify the external signal by comparing the long‐term variations of the processed components of the geomagnetic field, as measured at different European observatories, with the long‐term variations of geomagnetic indices devised to characterize the fields from external sources. Finally, we remove the identified external signal from the geomagnetic field series and get a satisfactory estimate of the internal signal. This procedure is facilitated by the different behaviors of the two signals over the considered time span. The external signal is inherently of recurrent nature linked to solar‐terrestrial interaction; it oscillates around zero with a maximum amplitude of about 5 nT/yr. The internal signal, on the other hand, displays the characteristics of a secular trend, combining sustained monotonous behavior over periods of several decades with sudden slope variations and reversals; the total range of this internal secular signal is of the order of 50 nT/yr, far larger than any external contribution. Using the 1883–1983 magnetic series at Chambon‐la‐Forêt, the 1890–1983 series at Niemegk, and shorter series at the United Kingdom observatories of Eskdalemuir and Hartland, we have been able to get a coherent overall picture of the secular variation as measured in Europe. For instance, the first‐order time derivative of the Y (east) component essentially displays an increase in two steps from 1900 to 1925, a monotonous decrease from 1925 to 1969 with a regular steplike substructure, and a rapid increase since 1969, followed by a marked reversal of slope in 1979. These results emphasize the internal origin of the 1969 jerk and single out, in Europe, a 1979 event of opposite sign, these two features being quite reminiscent of the behavior of the secular variation during the first quarter of the century.

Ancient, giant rockslides, Sinking Creek Mountain, southern Appalachians, Virginia

Giant rockslides and slumps are recognized over a large part of the east limb of the Sinking Creek anticline, a southern Appalachian fold. The slides are among the largest such features known in the Appalachians and are found within 15 km of the active Giles County, Virginia, seismic zone. The zone of rockslides, identified by anomalous topography and geologic structures, is about 25 km long and 1.0 km wide. Downslope transport, ranging from 0.5 to 1.0 km, of at least 100 million m 3 of Silurian sandstones and shales can be identified. During sliding, bedding within individual blocks, as much as 5.0 km long, has undergone 30° to 90° rotation about a horizontal axis. The displaced masses have undergone extensive erosion and dissection and may be only remnants of previously more extensive slides. Secondary features associated with the rockslides include breakaway scarps, slope reversals, sag ponds, and slide breccias. The recognition of these features, which might be mistaken for remnants of an Alleghanian thrust sheet, suggests that examination of similar settings throughout the southern and central Appalachian Valley and Ridge province might disclose additional examples of large ancient rockslides.

System and method for speech recognition

A system and method for speech recognition provides a means of printing phonemes in response to received speech signals utilizing inexpensive components. The speech signals are inputted into an amplifier which provides negative feedback to normalize the amplitude of the speech signals. The normalized speech signals are delta modulated at a first sampling rate to produce a corresponding first sequence of digital pulses. The negative feedback signal of the amplifier is delta modulated at a second sampling rate to produce a second sequence of digital pulses corresponding to amplitude information of the speech signals. The speech signals are filtered and utilized to produce a digital pulse corresponding to high frequency components of the speech signals having magnitudes in excess of a threshold voltage. A microprocessor contains an algorithm for detecting major slope transitions of the analog speech signals in response to the first sequence of digital signals by detecting information corresponding to presence and absence of predetermined numbers of successive slope reversals in the delta modulator producing the first sequence of digital pulses. The algorithm computes cues from the high frequency digital pulse and the second sequence of pulses. The algorithm computes a plurality of speech waveform characteristic ratios of time intervals between various slope transitions and compares the speech waveform characteristic ratios with a plurality of stored phoneme ratios representing a set of phonemes to detect matching therebetween. The order of comparing is determined on the basis of the cues and a configuration of a phoneme decision tree contained in the algorithm. When a matching occurs, a signal corresponding to the matched phoneme is produced and utilized to cause the phoneme to be printed. In one embodiment of the invention, the speech signals are produced by the earphone of a standard telephone headset.

Earthquake signal processing and logging with a battery-powered microcomputer

abstract A low power microprocessor controlled event-triggered seismic data logging system has been designed and implemented in the ocean bottom seismic capsule. Three channels of seismic data are digitized, formated, and stored under control of an Intersil IM6100 microprocessor chip. The processor also controls event triggering, acoustic diagnostics, battery voltage monitoring, and self-diagnostic functions. A watchdog system restarts it in the rare case of a failure of proper program sequencing. The entire system consumes less than 0.15 watts in the idle mode. The event triggering algorithm consists of first measuring the ratio of the short-term signal average to the long-term signal average, with amplifier offset removed (STA/LTA ratio). When an STA/LTA trigger occurs, the number of slope reversals in the signal begin to be counted. After a preset time following the first STA/LTA trigger, if the number of subsequent STA/LTA triggers meet preset criteria, a system trigger is declared and data is stored on a 4-track Braemar cassette tape deck with 15-M-bit capacity. Various system diagnostics, unit and experiment identification, and battery voltages are recorded at the beginning of each new event record. Digital filters for the long- and short-term averages, and antialiasing have been efficiently implemented by dividing or multiplying by factors of 2, exclusively. This amounts to a shift right or left of a binary number. The recording system has been tested in numerous field experiments. Circuit cards from the ocean bottom capsule implementation are being assembled and used for land stations and could be applied to a wide variety of data acquisition tasks.

The Folded Ramp: A New Technique for Computer-Controlled Time-Interval Measurement

This paper describes the folded-ramp circuit, a computer-controlled device for measurements of time intervals from a few nanoseconds to a few seconds. The features of this circuit are single-range operation, binary-output format, measurement-error detection, and an output-register capacity that is set by dynamic range rather than accuracy or resolution. The circuit generates a ramp-type waveform that reverses slope at approximately 0 V and at a predetermined peak voltage; control of the ramp slope makes each leg of the folded ramp 100 ns in duration. The measured time interval is described by the number of slope reversals plus the amplitude difference between the voltage at termination of the measurement and at the last reversal. The circuit allows measurements of time over a 109 to 1 range with accuracies better than 1 percent of reading ±0.5 ns.

Interpretation of Sound Velocity Profiles in Sea Water

Interpretation of the principle features of sound velocity in terms of the basic oceanographic parameters—temperature, salinity, and depth—is undertaken using the functional relationship between the velocity of sound and the temperature, salinity, and pressure of the sea water through which the sound is propagating as expressed by Wayne D. Wilson of the U. S. Naval Ordnance Laboratory. The effect of independent variation of these parameters on the sound-velocity profiles is treated mathematically for a uniform and a stratified ocean. The slope, slope reversals, kinks, and minimums in the sound-velocity profiles are related to environmental conditions. A comprehensive discussion of the causes of the long- and short-term changes in the features of the profiles is included. The use of sound-velocity data to infer primary oceanographic parameters is demonstrated using the temperature-salinity relationships.

Structural Trends off the California Coast: ABSTRACT

The sea bottom off the California coast shows a series of steep escarpments with a dominant trend in a north-northwesterly direction. The continental slope escarpment follows this direction and is not influenced by the large change in trend found on shore at Point Conception. Many of the submarine escarpments show offsets with the northerly portions set to the northeast. Also a number of the escarpments show slope reversals along their length. Directly outside the continental slope there are a series of oval mountains with trends in a north-northeasterly direction. These are probably volcanoes and from their trends suggest possible tensional phenomena. End_of_Article - Last_Page 1716------------