A Mars orbital laser altimeter for rover trafficability: Instrument concept and science potential

Limited information on the types of geologic hazards (boulders, troughs, craters etc.) that will affect rover trafficability on Mars are available for the two Viking Lander sites, and there are no prospects for increasing this knowledge base in the near future. None of the instrument payloads on the upcoming Mars Observer or Soviet PHOBOS missions can directly measure surface obstacles on the scales of concern for rover safety (a few meters). Candidate instruments for the Soviet Mars 92 orbiter/balloon/rover mission such as balloon-borne stereo imaging, rover panoramic imaging, and orbital synthetic aperature imaging (SAR) are under discussion, but data from this mission may not be available for target areas of interest for the U.S. Mars Rover Sample Return (MRSR) mission. In an effort to determine how to directly measure the topography of surface obstacles that could affect rover trafficability on Mars, we are studying how to design a laser altimeter with extremely high spatial and vertical resolution that would be suitable for a future Mars Orbiter spacecraft (MRSR precursor or MRSR orbiter). This report discusses some of the design issues associated with such an instrument, gives examples of laser altimeter data collected for Mars analog terrains on Earth, and outlines the scientific potential of data that could be obtained with the system

The effects of Venus' thermal structure on buoyant magma ascent

The recent Magellan images have revealed a broad spatial distribution of surface volcanism on Venus. Previous work in modeling the ascent of magma on both Venus and Earth has indicated that the planetary thermal structure significantly influences the magmatic cooling rates and thus the amount of magma that can be transported to the surface before solidification. In order to understand which aspects of the thermal structure have the greatest influence on the cooling of ascending magma, we have constructed magma cooling curves for both plutonic and crack buoyant ascent mechanisms, and evaluated the curves for variations in the planetary mantle temperature, thermal gradient curvature with depth, surface temperature gradient, and surface temperature. The planetary thermal structure is modeled as T/T(sub 0) = 1-tau(1-Z/Z(sub 0)(exp n), where T is the temperature, T(sub 0) is the source depth temperature, tau = 1-(T(sub s)/T(sub 0)) where T(sub s) is the planetary surface temperature, Z is the depth, Z(sub 0) is the source depth, and n is a constant that controls thermal gradient curvature with depth. The equation is used both for mathematical convenience and flexibility, as well as its fit to the thermal gradients predicted by the cooling half-space models. We assume a constant velocity buoyant ascent, body-averaged magma temperatures and properties, an initially crystal-free magma, and the same liquidus and solidus for both Venus and Earth

Rheology, tectonics, and the structure of the Venus lithosphere

Given the absence of ground truth information on seismic structure, heat flow, and rock strength, or short wavelength gravity or magnetic data for Venus, information on the thermal, mechanical and compositional nature of the shallow interior must be obtained by indirect methods. Using pre-Magellan data, theoretical models constrained by the depths of impact craters and the length scales of tectonic features yielded estimates on the thickness of Venus' brittle-elastic lithosphere and the allowable range of crustal thickness and surface thermal gradient. The purpose of this study is to revisit the question of the shallow structure of Venus based on Magellan observations of the surface and recent experiments that address Venus' crustal rheology

Pulse shape discrimination performance of Inverted Coaxial Ge detectors

We report on the characterization of two inverted coaxial Ge detectors in the context of being employed in future $^{76}$Ge neutrinoless double beta ($0\nu\beta\beta$) decay experiments. It is an advantage that such detectors can be produced with bigger Ge mass as compared to the planar Broad Energy Ge detectors (BEGe) that are currently used in the GERDA $0\nu\beta\beta$ decay experiment. This will result in lower background for the search of $0\nu\beta\beta$ decay due to a reduction of cables, electronics and holders. The measured resolution near the $^{76}$Ge Q-value at 2039 keV is 2.5 keV and their pulse-shape characteristics are similar to BEGe-detectors. It is concluded that this type of Ge-detector is suitable for usage in $^{76}$Ge $0\nu\beta\beta$ decay experiments

The topography of Mars: A re-evaluation of current data

Our present knowledge of the topography of Mars is completely inadequate for addressing a wide range of geophysical, geological, and atmospheric problems. The data acquired to date by several techniques has not provided us with reliable and consistent values for even the equatorial and polar radii, and large uncertainties exist in the altitudes of many of the major volcanic constructs. While much of this can be blamed on a lack of reliable data, we feel that much more could be done to improve the analysis of the present data in a consistent global system that would necessarily involve the re-analysis of early spacecraft and Earth-based data in conjunction with more recent models of Mars' gravity field

Patterns of brittle deformation under extension on Venus

The development of fractures at regular length scales is a widespread feature of Venusian tectonics. Models of lithospheric deformation under extension based on non-Newtonian viscous flow and brittle-plastic flow develop localized failure at preferred wavelengths that depend on lithospheric thickness and stratification. The characteristic wavelengths seen in rift zones and tessera can therefore provide constraints on crustal and thermal structure. Analytic solutions were obtained for growth rates in infinitesimal perturbations imposed on a one-dimensional, layered rheology. Brittle layers were approximated by perfectly-plastic, uniform strength, overlying ductile layers exhibiting thermally-activated power-law creep. This study investigates the formation of faults under finite amounts of extension, employing a finite-element approach. Our model incorporates non-linear viscous rheology and a Coulomb failure envelope. An initial perturbation in crustal thickness gives rise to necking instabilities. A small amount of velocity weakening serves to localize deformation into planar regions of high strain rate. Such planes are analogous to normal faults seen in terrestrial rift zones. These 'faults' evolve to low angle under finite extension. Fault spacing, orientation and location, and the depth to the brittle-ductile transition, depend in a complex way on lateral variations in crustal thickness. In general, we find that multiple wavelengths of deformation can arise from the interaction of crustal and mantle lithosphere

Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations

The main background above 3\,MeV for in-beam nuclear astrophysics studies with $\gamma$-ray detectors is caused by cosmic-ray induced secondaries. The two commonly used suppression methods, active and passive shielding, against this kind of background were formerly considered only as alternatives in nuclear astrophysics experiments. In this work the study of the effects of active shielding against cosmic-ray induced events at a medium deep location is performed. Background spectra were recorded with two actively shielded HPGe detectors. The experiment was located at 148\,m below the surface of the Earth in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data with the same detectors at the Earth's surface, and at depths of 45\,m and 1400\,m, respectively.Comment: Minor errors corrected; final versio

Stellenwert der endoskopischen Axilladissektion beim invasiven Mammakarzinom

Zusammenfassung: Grundlagen: Die Axilladissektion liefert zuverlässige prognostische Information, bestimmt mehrheitlich die adjuvante Therapie und reduziert die axillären Tumorrezidive. Die Morbidität nach Axilladissektion kann jedoch nicht vernachlässigt werden (sensible Störungen, Schmerzen, motorische Schwäche, Lymphödem). Patientinnen mit kleinen Tumoren (pT1a, b, c) könnten von neueren weniger invasiven Verfahren (endoskopische Axilladissektion) oder von selektiveren Methoden (Sentinel-lymph-node-Procedere) profitieren. In dieser prospektiven Studie wurde die axilloskopische Lymphadenektomie evaluiert. Methodik: 55 klinisch nodal negative Patientinnen (Durchschnittsalter: 60 Jahre [30 bis 86 Jahre]) wurden von einem Chirurgen endoskopisch operiert (Januar 1996 bis Juni 1998). Nach Liposuktion des axillären Fettkörpers wurden die Lymphknoten von Level I+II identifiziert und unter direkter endoskopischer Sicht reseziert (erfolgreiches Verfahren in 95 %: n=52). Die Patientinnen wurden entsprechend dem Nachsorgeschema alle 4 Monate kontrolliert. Nach einer mittleren Beobachtungszeit von 22 Monaten (7 bis 37 Monate; n=51 [eine Patientin verweigerte die Nachsorge]) wurden die Patientinnen mit einem Evaluationsfragebogen, einem Interview und einer klinischen Untersuchung (inklusiv Schultergelenksfunktion, Zirkumferenzmessungen der oberen Extremität) nachkontrolliert. Ergebnisse: Durchschnittlich wurden 13,3 (5 bis 25) Lymphknoten endoskopisch entfernt. Nodal positive Lymphknoten wurden in 31 % (n=16) beobachtet. Der Durchschnittswert der positiven Lymphknoten/Patientin betrug 3,1 (1 bis 10). Acht Serome (15 %) mußten in der frühpostoperativen Phase punktiert werden. Es traten keine Hämatome, jedoch ein Infekt in der Axilla nach Chemotherapie auf (2 %). Nach einer mittleren Beobachtungszeit von 22 Monaten (7 bis 37 Monate) konnten keine axillären Rezidive nachgewiesen werden. Eine subkutane Implantationsmetastase in der Narbe eines Trokarkanals (1/55, 2 %) wurde diagnostiziert und reseziert. Klinisch traten keine Lymphödeme auf. Die frühe Mobilisation des Schultergelenkes war subjektiv und objektiv gut. Schlußfolgerungen: Die durchschnittlich 13 axilloskopisch entfernten Lymphknoten entsprechen der Anzahl resezierter Lymphknoten bei offener Axilladissektion. Die Morbidität dieses in Evaluation begriffenen Verfahrens ist niedrig. Nach einer mittleren Beobachtungszeit von 22 Monaten wurde ein Implantationsrezidiv im subkutanen Kanal des anterioren Arbeitstrokar nachgewiesen. Eine längere Beobachtungszeit ist nötig, um die Technik empfehlen zu können. Es zeichnet sich ab, daß die endoskopische, axilläre Lymphknotendissektion durch das selektivere Sentinel-lymph-node-Verfahren abgelöst wir