Dual captures of Colorado rodents: implications for transmission of hantaviruses.

We analyzed dual-capture data collected during longitudinal studies monitoring transmission and persistence of Sin Nombre virus in rodents in Colorado. Our data indicate that multiple captures (two or more rodents captured in a single trap) may not be random, as indicated by previous studies, but rather the result of underlying, species-specific social behavior or cohesiveness. In the pairs we captured, most often, rodents were of the same species, were male, and could be recaptured as pairs. Therefore, dual captures of rodents, which are unusual but not rare, tend to occur among certain species, and appear to be nonrandom, group-foraging encounters. These demographic and ecologic characteristics may have implications for the study of the transmission of hantaviruses

idic(7)(q11.2)

Review on idic(7)(q11.2), with data on clinics, and the genes involved

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

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

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

A Search for WIMPs with the First Five-Tower Data from CDMS

We report first results from the Cryogenic Dark Matter Search (CDMS II) experiment running with its full complement of 30 cryogenic particle detectors at the Soudan Underground Laboratory. This report is based on the analysis of data acquired between October 2006 and July 2007 from 15 Ge detectors (3.75 kg), giving an effective exposure of 121.3 kg-d (averaged over recoil energies 10--100 keV, weighted for a weakly interacting massive particle (WIMP) mass of 60 \gev). A blind analysis, incorporating improved techniques for event reconstruction and data quality monitoring, resulted in zero observed events. This analysis sets an upper limit on the WIMP-nucleon spin-independent cross section of 6.6$\times10^{-44}$ cm$^2$ (4.6$\times10^{-44}$ cm$^2$ when combined with previous CDMS Soudan data) at the 90% confidence level for a WIMP mass of 60 \gev. By providing the best sensitivity for dark matter WIMPs with masses above 42 GeV/c$^2$, this work significantly restricts the parameter space for some of the favored supersymmetric models.Comment: 5 pages, 4 figures, submitted to PRL 28 March 200

Strategies for Investigating Early Mars Using Returned Samples

The 2011 Visions & Voyages Planeary Science Decadal Survey identified making significant progress toward the return of samples from Mars as the highest priority goal for flagship missions in next decade. Numerous scientific objectives have been identified that could be advanced through the potential return and analysis of martian rock, regolith, and atmospheric samples. The analysis of returned martian samples would be particularly valuable in in-creasing our understanding of Early Mars. There are many outstanding gaps in our knowledge about Early Mars in areas such as potential astrobiology, geochronology, planetary evolution (including the age, context, and processes of accretion, differentiation, magmatic, and magnetic history), the history of water at the martian surface, and the origin and evolution of the martian atmosphere. Here we will discuss scientific objectives that could be significantly advanced by Mars sample return

Scientific Goals and Objectives for the Human Exploration of Mars: 1. Biology and Atmosphere/Climate

To prepare for the exploration of Mars by humans, as outlined in the new national vision for Space Exploration (VSE), the Mars Exploration Program Analysis Group (MEPAG), chartered by NASA's Mars Exploration Program (MEP), formed a Human Exploration of Mars Science Analysis Group (HEM-SAG), in March 2007. HEM-SAG was chartered to develop the scientific goals and objectives for the human exploration of Mars based on the Mars Scientific Goals, Objectives, Investigations, and Priorities.1 The HEM-SAG is one of several humans to Mars scientific, engineering and mission architecture studies chartered in 2007 to support NASA s plans for the human exploration of Mars. The HEM-SAG is composed of about 30 Mars scientists representing the disciplines of Mars biology, climate/atmosphere, geology and geophysics from the U.S., Canada, England, France, Italy and Spain. MEPAG selected Drs. James B. Garvin (NASA Goddard Space Flight Center) and Joel S. Levine (NASA Langley Research Center) to serve as HEMSAG co-chairs. The HEM-SAG team conducted 20 telecons and convened three face-to-face meetings from March through October 2007. The management of MEP and MEPAG were briefed on the HEM-SAG interim findings in May. The HEM-SAG final report was presented on-line to the full MEPAG membership and was presented at the MEPAG meeting on February 20-21, 2008. This presentation will outline the HEM-SAG biology and climate/atmosphere goals and objectives. A companion paper will outline the HEM-SAG geology and geophysics goals and objectives