Modal Analysis of the Orion Capsule Two Parachute System

As discussed in Ref [1], it is apparent from flight tests that the system made up of two main parachutes and a capsule can undergo several distinct dynamical behaviors. The most significant and problematic of these is the pendulum mode in which the system develops a pronounced swinging motion with an amplitude of up to 24 deg. Large excursions away from vertical by the capsule could cause it to strike the ground at a large horizontal or vertical speed and jeopardize the safety of the astronauts during a crewed mission. In reference [1], Ali et al. summarized a series of efforts taken by the Capsule Parachute Assembly System (CPAS) Program to understand and mitigate the pendulum issue. The period of oscillation and location of the system's pivot point are determined from post-flight analysis. Other noticeable but benign modes include: 1) flyout (scissors) mode, where the parachutes move back and forth symmetrically with respect to the vertical axis similar to the motion of a pair of scissors; 2) maypole mode, where the two parachutes circle around the vertical axis at a nearly constant radius and period; and 3) breathing mode, in which deformation of the non-rigid canopies affects the axial acceleration of the system in an oscillatory manner. Because these modes are relatively harm- less, little effort has been devoted to analyzing them in comparison with the pendulum motion. Motions of the actual system made up of two parachutes and a capsule are extremely complicated due to nonlinearities and flexibility effects. Often it is difficult to obtain insight into the fundamental dynamics of the system by examining results from a multi-body simulation based on nonlinear equations of motion (EOMs). As a part of this study, the dynamics of each mode observed during flight is derived from first principles on an individual basis by making numerous simplifications along the way. The intent is to gain a better understanding into the behavior of the complex multi-body system by studying the reduced set of differential equations associated with each mode. This approach is analogous to the traditional modal analysis technique used to study airplane flight dynamics, in which the full nonlinear behavior of the airframe is decomposed into the phugoid and short period modes for the longitudinal dynamics and the spiral, roll-subsidence, and dutch-roll modes for the lateral dynamics. It is important to note that the study does not address the mechanisms that cause the system to transition from one mode to another, nor does it discuss motions during which two or more modes occur simultaneously

Potential for La Crosse virus segment reassortment in nature

The evolutionary success of La Crosse virus (LACV, family Bunyaviridae) is due to its ability to adapt to changing conditions through intramolecular genetic changes and segment reassortment. Vertical transmission of LACV in mosquitoes increases the potential for segment reassortment. Studies were conducted to determine if segment reassortment was occurring in naturally infected Aedes triseriatus from Wisconsin and Minnesota in 2000, 2004, 2006 and 2007. Mosquito eggs were collected from various sites in Wisconsin and Minnesota. They were reared in the laboratory and adults were tested for LACV antigen by immunofluorescence assay. RNA was isolated from the abdomen of infected mosquitoes and portions of the small (S), medium (M) and large (L) viral genome segments were amplified by RT-PCR and sequenced. Overall, the viral sequences from 40 infected mosquitoes and 5 virus isolates were analyzed. Phylogenetic and linkage disequilibrium analyses revealed that approximately 25% of infected mosquitoes and viruses contained reassorted genome segments, suggesting that LACV segment reassortment is frequent in nature

Mars sample return – a proposed mission campaign whose time is now

The analysis in Earth laboratories of samples that could be returned from Mars is of extremely high interest to the international Mars exploration community. IMEWG (the International Mars Exploration Working Group) has been evaluating options, by means of a working group referred to as iMOST, to refine the scientific objectives of MSR. The Mars 2020 sample-caching rover mission is the first component of the Mars Sample Return campaign, so its existence constitutes a critical opportunity. Finally, on April 26, 2018, NASA and ESA signed a Statement of Intent to work together to formulate, by the end of 2019, a joint plan for the retrieval missions that are essential to the completion of the MSR Campaign. All of these converged April 25-27, 2018 in Berlin, Germany, at the 2nd International Mars Sample Return Conference

Biological Monitoring Program for East Fork Poplar Creek

In May 1985, a National Pollutant Discharge Elimination System (NPDES) permit was issued for the Oak Ridge Y-12 Plant. As a condition of the permit, a Biological Monitoring and Abatement Program (BMAP) was developed to demonstrate that the effluent limitations established for the Y-12 Plant protect the classified uses of the receiving stream (East Fork Poplar Creek; EFPC), in particular, the growth and propagation of aquatic life (Lear et al. 1989). A second objective of the BMAP is to document the ecological effects resulting from the implementation of a water pollution control program designed to eliminate direct discharges of wastewaters to EFPC and to minimize the inadvertent release of pollutants to the environment. Because of the complex nature of the discharges to EFPC and the temporal and spatial variability in the composition of the discharges, a comprehensive, integrated approach to biological monitoring was developed. A new permit was issued to the Y-12 Plant on April 28, 1995 and became effective on July 1, 1995. Biological monitoring continues to be required under the new permit. The BMAP consists of four major tasks that reflect different but complementary approaches to evaluating the effects of the Y-12 Plant discharges on the aquatic integrity of EFPC. These tasks are (1) toxicity monitoring, (2) biological indicator studies, (3) bioaccumulation studies, and (4) ecological surveys of the periphyton, benthic macroinvertebrate, and fish communities

Recommended Maximum Temperature For Mars Returned Samples

The Returned Sample Science Board (RSSB) was established in 2015 by NASA to provide expertise from the planetary sample community to the Mars 2020 Project. The RSSB's first task was to address the effect of heating during acquisition and storage of samples on scientific investigations that could be expected to be conducted if the samples are returned to Earth. Sample heating may cause changes that could ad-versely affect scientific investigations. Previous studies of temperature requirements for returned mar-tian samples fall within a wide range (-73 to 50 degrees Centigrade) and, for mission concepts that have a life detection component, the recommended threshold was less than or equal to -20 degrees Centigrade. The RSSB was asked by the Mars 2020 project to determine whether or not a temperature requirement was needed within the range of 30 to 70 degrees Centigrade. There are eight expected temperature regimes to which the samples could be exposed, from the moment that they are drilled until they are placed into a temperature-controlled environment on Earth. Two of those - heating during sample acquisition (drilling) and heating while cached on the Martian surface - potentially subject samples to the highest temperatures. The RSSB focused on the upper temperature limit that Mars samples should be allowed to reach. We considered 11 scientific investigations where thermal excursions may have an adverse effect on the science outcome. Those are: (T-1) organic geochemistry, (T-2) stable isotope geochemistry, (T-3) prevention of mineral hydration/dehydration and phase transformation, (T-4) retention of water, (T-5) characterization of amorphous materials, (T-6) putative Martian organisms, (T-7) oxidation/reduction reactions, (T-8) (sup 4) He thermochronometry, (T-9) radiometric dating using fission, cosmic-ray or solar-flare tracks, (T-10) analyses of trapped gasses, and (T-11) magnetic studies

Managing affect in learners' questions in undergraduate science

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2012 Society for Research into Higher Education.This article aims to position students' classroom questioning within the literature surrounding affect and its impact on learning. The article consists of two main sections. First, the act of questioning is discussed in order to highlight how affect shapes the process of questioning, and a four-part genesis to question-asking that we call CARE is described: the construction, asking, reception and evaluation of a learner's question. This work is contextualised through studies in science education and through our work with university students in undergraduate chemistry, although conducted in the firm belief that it has more general application. The second section focuses on teaching strategies to encourage and manage learners' questions, based here upon the conviction that university students in this case learn through questioning, and that an inquiry-based environment promotes better learning than a simple ‘transmission’ setting. Seven teaching strategies developed from the authors' work are described, where university teachers ‘scaffold’ learning through supporting learners' questions, and working with these to structure and organise the content and the shape of their teaching. The article concludes with a summary of the main issues, highlighting the impact of the affective dimension of learning through questioning, and a discussion of the implications for future research

Piezoresistive Stress Sensors for Structural Analysis of Electronic Packages

Structural reliability of electronic packages has become an increasing concern for a variety of reasons including the advent of higher integrated circuit densities, power density levels, and operating temperatures. A powerful method for experimental evaluation of die stress distributions is the use of test chips incorporating integral piezoresistive sensors. In this paper, the theory of conduction in piezoresistive materials is reviewed and the basic equations applicable to the design of stress sensors on test chips are presented. General expressions are obtained for the stress-induced resistance changes which occur in arbitrarily oriented one-dimensional filamentary conductors fabricated out of crystals with cubic symmetry and diamond lattice structure. These relations are then applied to obtain basic results for stressed inplane resistors fabricated into thesurface of (100) and (111) oriented silicon wafers. Sensor rosettes developed by previous researchers for each of these wafer orientations are reviewed and more powerful rosettes are presented along with the equations needed for their successful application. In particular, a new sensor rosette fabricated on (111) silicon is presented which can measure the complete three-dimensional stress state at points on the surface of a die Introduction Stresses due to thermal and mechanical loadings are often produced in chips which are incorporated into electronic packages. During fabrication steps such as encapsulation and dieattachment, thermally-induced stresses are created. These occur due to nonuniform thermal expansions resulting from mismatches between the coefficients of thermal expansion of the materials comprising the package and the semiconductor die. Additional thermally-induced stresses can be produced from heat dissipated by high power density devices during operation. Finally, mechanical loadings can be transmitted to the package through contact with the printed circuit board to which it is mounted. The combination of all of the above loadings can lead to two-dimensional (biaxial) and three-dimensional (triaxial) states of stress on the surface of the die. If high-power density devices within the package are switched on and off, these stress states can be cyclic in time causing fatigue. All of these factors can lead to premature failure of the package due to such causes as fracture of the die, severing of bond connections, die attach failure, and encapsulant cracking. These reliability problems are of ever increasing concern as larger scale chips and higher temperature applications are considered. Stress analyses of electronic packages and their components have been performed using analytical, numerical, and experimental methods. Analytical investigations have been primarily concerned with finding closed-form elasticity solutions for lay- structures, while numerical studies have typically considered finite element solutions for sophisticated package geometries. Experimental approaches have included the use of test chips incorporating piezoresistive stress sensors (semiconductor strain gages), and the use of optical techniques such as holographic interferometry, moire interferometry, and photoelasticity. In this paper, the theory and design of piezoresistive stress sensors are considered in detail. Piezoresistive stress sensors are a powerful tool for experimental structural analysis of electronic packages. They are conveniently fabricated into the surface of the die as part of the normal processing procedure. In addition, they are capable of providing nonintrusive measurements of surface stress states on a chip even within encapsulated packages. If the piezoresistive sensors are calibrated over a wide temperature range, thermally induced stresses can be measured. Finally, a fullfield mapping of the stress distribution over a die's surface can be obtained using specially designed test chips which incorporate an array of sensor rosettes and multiplexing circuitry. Prior published applications of stress sensing test chips have included sensor rosettes with two and four resistors. Two element rosettes fabricated on (100) silicon have been utilized by Mathematical Theory of Piezoresistivity Anisotropic Conduction. A basic axiom of the theory of conduction of electric charge is that the current density vector is a function of the electric field vector (1) where J, and E t are the cartesian components of the current density and electric field vectors, respectively. In most solid conductors, this functional relation has been observed to be linear over a wide range of electric field magnitudes. Such conductors are referred to as ohmic materials. In an anisotropic ohmic conductor, the most general linear relationship is where K,J are the components of the conductivity tensor, and the summation convention is implied for repeated indices. This relation can be inverted to give Ei = PijJj (4) where p u are the components of the resistivity tensor. Using the reciprocity theorem derived by Onsager [1931a, 19316], it is possible to show that the conductivity and resistivity tensors are symmetric The Piezoresistive Effect. The piezoresistive effect is a stress-induced change in the components of the resistivity tensor. It is exhibited in so-called piezoresistive materials. The first observations of this phenomenon were made by Bridgman [1922, 1925, 1932] who subjected metals to tension and hydrostatic pressure. Experimental observations of the piezoresistive effect in semiconductors (silicon and germanium) were first made by The piezoresistive effect can be modeled mathematically using the series expansion where p°j are the resistivity components for the stress free material and iry«, A,j W ",", etc. are components of fourth, sixth, and higher order tensors which characterize the stress-induced resistivity change.-For sufficiently small stress levels, this relation is typically truncated so that the resistivity components are linearly related to the stress components For fixed environmental conditions (i.e. temperature), the 81 components ir iJk i of the fourth order piezoresisitvity tensor are constants. From Eq. It is also possible to model the resistivity changes in terms of the strain components using an expression such as where M ijk i are the components of the fourth order elastoresistivity tensor. In this paper, the stress-based formulation given in Eqs. The above relations are the most concise form for the fully expanded equations of the theory of piezoresistivity. They are not convenient in a notational sense since they cannot be expressed compactly in indicial notation. Historically, it has become a convention to reduce the complexities of the index labels through a renumbering scheme where index pairs are replaced by single indices which assume values of 1, 2, ..., 6 instead of 1, 2, 3. The following index conversions are typically used: 204 / Vol. 113, SEPTEMBER 1991 Transactions of the ASME Pl=Pl2> Pi- ., n 2 6 = 27r2212 A further notational simplification can be obtained by introduction of the so-called piezoresistive coefficients. They are defined by where p is the mean (hydrostatic) unstressed resistivity -P11+P22 + P33 Substitution of Eq. (19) into Eq. (14) leads to Pa^Pa + PKctpOp 7) are valid in the unprimed system (x\, x 2 , x 3 ), the appropriate expressions for the primed system are The components of the electric field vector, current density vector, resistivity tensor, stress tensor, and piezoresistivity tensor all transform from one coordinate system to the other using the standard tensor transformation relations: Transformation Relations. The basic mathematical relations for conduction and piezoresistivity found in Eqs. Crystal Symmetry. For general anisotropic materials, the equations of conduction and piezoresistivity are very complex and contain numerous terms. However, when considering crystalline materials exhibiting lattice symmetry, several simplifications can be made. These simplifications result because relationships can be established between the components of the unstressed resistivity tensor and between the components of the piezoresistivity tensor. Detailed general expositions on the ramifications of crystal symmetry on physical properties have been presented by A crystal is a solid whose local properties and structure are periodic in three dimensions. A rotation or a combination rotation/reflection of a crystal which brings its lattice structure into superposition with itself is called a symmetry operation for the crystal. The set of all symmetry operations for a given crystal defines the crystallographic point group symmetry for the crystal. All crystals with the same point group symmetry are said to be members of the same crystal class. There are 32 unique crystal classes. Silicon is a cubic crystal with diamond structure, and belongs to the crystal class denoted 32 in the international numbering system. This class has been notated several other ways including m3m and O h . The symmetry exhibited by a crystal determines the extent of anisotropy exhibited by the physical properties of the crystal. It is assumed that the physical properties of the crystalline material must possess at least the symmetry of the point group of the crystal. This is expressed mathematically by requiring the components of a physical property tensor for the crystal to be invariant under coordinate system transformations equivalent to the symmetry operations in the point group of the crystal. These relations hold when the initial coordinate system is aligned with the symmetry axes of the crystal. Therefore, using Eqs. (28, 29), the components of the unstressed resistivity tensor and the piezoresistivity tensor of a crystal must satisfy Pu = PV = a ikCjif>ii (38) *ijki = Tyki = a im aj n a ko ai p -K mnop (3 9) when the direction cosines between the two coordinate systems are chosen to be equivalent to one of the crystal's symmetry operations, and the initial coordinate system is aligned with the crystal's symmetry axes. In terms of reduced index notation, these conditions take the form The unique symmetry operations or so-called generating elements for each crystal point group have been listed by and the piezoresistivity coefficients of silicon required by its crystal symmetry are obtained by substituting each set of direction cosines in 41). If all of these calculations are considered, the following relations are found: The simplifications in the reduced index resistivity components General Conduction Equations for Stressed Materials. The governing tensor equation of conduction in a stressed anisotropic ohmic conductor is obtained by substituting Eq. The conduction equations for a stressed cubic crystal with diamond structure are more complex in an off-axis coordinate system (x\, x' 2 , x'i) rotated from the principal symmetry axes (x it x 2 , Xi) as shown in The primed piezoresistive coefficients in Eq. (53) are to be evaluated for the chosen primed coordinate system by substituting the unprimed values in Eq. (46) into the transformation relations given in Eq. (37). The expressions in Eq. (53) were first presented in the literature by Pfann and Thurston [1961]. Stress-Induced Resistance Changes in One-Dimensional Filamentary Conductors Introduction. Early applications of semiconductor strain (stress) gages which utilized the piezoresistive effect exhibited by silicon were made b

Analysis of the low-energy electron-recoil spectrum of the CDMS experiment

We report on the analysis of the low-energy electron-recoil spectrum from the CDMS II experiment using data with an exposure of 443.2 kg-days. The analysis provides details on the observed counting rate and possible background sources in the energy range of 2 - 8.5 keV. We find no significant excess in the counting rate above background, and compare this observation to the recent DAMA results. In the framework of a conversion of a dark matter particle into electromagnetic energy, our 90% confidence level upper limit of 0.246 events/kg/day at 3.15 keV is lower than the total rate above background observed by DAMA by 8.9$\sigma$. In absence of any specific particle physics model to provide the scaling in cross section between NaI and Ge, we assume a Z^2 scaling. With this assumption the observed rate in DAMA differs from the upper limit in CDMS by 6.8$\sigma$. Under the conservative assumption that the modulation amplitude is 6% of the total rate we obtain upper limits on the modulation amplitude a factor of ~2 less than observed by DAMA, constraining some possible interpretations of this modulation.Comment: 4 pages, 3 figure

Characterization of SuperCDMS 1-inch Ge Detectors

The newly commissioned SuperCDMS Soudan experiment aims to search for WIMP dark matter with a sensitivity to cross sections of 5×10^(−45)cm^2 and larger (90% CL upper limit). This goal is facilitated by a new set of germanium detectors, 2.5 times more massive than the ones used in the CDMS-II experiment, and with a different athermal phonon sensor layout that eliminates radial degeneracy in position reconstruction of high radius events. We present characterization data on these detectors, as well as improved techniques for correcting position-dependent variations in pulse shape across the detector. These improvements provide surface-event discrimination sufficient for a reach of 5×10^(−45)cm^2