A 200 km suspected impact crater Kotuykanskaya near Popigai, Siberia, in the light of new gravity aspects from EIGEN 6C4, and other data

We provide arguments in favour of impact origin of a 200 km suspected impact crater Kotuykanskaya near Popigai, Siberia, Russia. We use the gravity aspects (gravity disturbances, the Marussi tensor of the second derivatives of the disturbing geopotential, the gravity invariants and their specific ratio, the strike angles and the virtual deformations), all derived from the combined static gravity field model EIGEN 6C4, with the ground resolution of about 10 km and a precision of about 10 milliGals. We also use the magnetic anomalies from the model EMAG2 and emphasize the evidence of much deeper sources in the suspected area, constraining the impact origin of this structure.Web of Science101art. no. 609

Magnetic record associated with tree ring density: Possible climate proxy

A magnetic signature of tree rings was tested as a potential paleo-climatic indicator. We examined wood from sequoia tree, located in Mountain Home State Forest, California, whose tree ring record spans over the period 600 – 1700 A.D. We measured low and high-field magnetic susceptibility, the natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM), and stability against thermal and alternating field (AF) demagnetization. Magnetic investigation of the 200 mm long sequoia material suggests that magnetic efficiency of natural remanence may be a sensitive paleoclimate indicator because it is substantially higher (in average >1%) during the Medieval Warm Epoch (700–1300 A.D.) than during the Little Ice Age (1300–1850 A.D.) where it is <1%. Diamagnetic behavior has been noted to be prevalent in regions with higher tree ring density. The mineralogical nature of the remanence carrier was not directly detected but maghemite is suggested due to low coercivity and absence of Verwey transition. Tree ring density, along with the wood's magnetic remanence efficiency, records the Little Ice Age (LIA) well documented in Europe. Such a record suggests that the European LIA was a global phenomenon. Magnetic analysis of the thermal stability reveals the blocking temperatures near 200 degree C. This phenomenon suggests that the remanent component in this tree may be thermal in origin and was controlled by local thermal condition

Programmable Aperture with MEMS Microshutter Arrays

A microshutter array (MSA) has been developed for use as an aperture array for multi-object selections in James Webb Space Telescope (JWST) technology. Light shields, molybdenum nitride (MoN) coating on shutters, and aluminum/aluminum oxide coatings on interior walls are put on each shutter for light leak prevention, and to enhance optical contrast. Individual shutters are patterned with a torsion flexure that permits shutters to open 90 deg. with a minimized mechanical stress concentration. The shutters are actuated magnetically, latched, and addressed electrostatically. Also, micromechanical features are tailored onto individual shutters to prevent stiction. An individual shutter consists of a torsion hinge, a shutter blade, a front electrode that is coated on the shutter blade, a backside electrode that is coated on the interior walls, and a magnetic cobalt-iron coating. The magnetic coating is patterned into stripes on microshutters so that shutters can respond to an external magnetic field for the magnetic actuation. A set of column electrodes is placed on top of shutters, and a set of row electrodes on sidewalls is underneath the shutters so that they can be electrostatically latched open. A linear permanent magnet is aligned with the shutter rows and is positioned above a flipped upside-down array, and sweeps across the array in a direction parallel to shutter columns. As the magnet sweeps across the array, sequential rows of shutters are rotated from their natural horizontal orientation to a vertical open position, where they approach vertical electrodes on the sidewalls. When the electrodes are biased with a sufficient electrostatic force to overcome the mechanical restoring force of torsion bars, shutters remain latched to vertical electrodes in their open state. When the bias is removed, or is insufficient, the shutters return to their horizontal, closed positions. To release a shutter, both the electrode on the shutter and the one on the back wall where the shutter sits are grounded. The shutters with one or both ungrounded electrodes are held open. Sub-micron bumps underneath light shields and silicon ribs on back walls are the two features to prevent stiction. These features ensure that the microshutter array functions properly in mechanical motions. The MSA technology can be used primarily in multi-object imaging and spectroscopy, photomask generation, light switches, and in the stepper equipment used to make integrated circuits and MEMS (microelectromechanical systems) devices

An Investigation of the Longitudinal Proximity Effect in Superconducting and Normal Metal TES

As the TES volume and (effective) Tc become very small - for volume > the TES Tc, connected at opposite ends of TES approaches zero, superconductivity is induced parallel to the current flow, or longitudinally, and results in a much higher effective TES Te. Here we present effective Te measurements of Mo/Au TES bounded by Nb leads as a function of L which ranges between 4 and 36 micrometer. We observe that the effective Te is suppressed for current density of order 10(exp -6) A/sq micrometers. We also explore the possibility of using a normal metal TES

Development and Operation of the Microshutter Array System

The microshutter array (MSA) is a key component in the James Webb Space Telescope Near Infrared Spectrometer (NIRSpec) instrument. The James Webb Space Telescope is the next generation of a space-borne astronomy platform that is scheduled to be launched in 2013. However, in order to effectively operate the array and meet the severe operational requirements associated with a space flight mission has placed enormous constraints on the microshutter array subsystem. This paper will present an overview and description of the entire microshutter subsystem including the microshutter array, the hybridized array assembly, the integrated CMOS electronics, mechanical mounting module and the test methodology and performance of the fully assembled microshutter subsystem. The NIRSpec is a European Space Agency (ESA) instrument requiring four fully assembled microshutter arrays, or quads, which are independently addressed to allow for the imaging of selected celestial objects onto the two 4 mega pixel IR detectors. Each microshutter array must have no more than approx.8 shutters which are failed in the open mode (depending on how many are failed closed) out of the 62,415 (365x171) total number of shutters per array. The driving science requirement is to be able to select up to 100 objects at a time to be spectrally imaged at the focal plane. The spectrum is dispersed in the direction of the 171 shutters so if there is an unwanted open shutter in that row the light from an object passing through that failed open shutter will corrupt the spectrum from the intended object

Development of Superconducting Transition Edge Sensors Based on Electron-Phonon Decoupling

We have successfully fabricated a superconducting transition edge sensor (TES), bolometer that centers on the use of electron-phonon decoupling (EPD) for thermal isolation. We have selected a design approach that separates the two functions of far-infrared and THz radiative power absorption and temperature measurement, allowing separate optimization of the performance of each element. We have integrated molybdenum/gold (Mo/Au) bilayer TES and ion assisted thermally evaporated (IAE) bismuth (Bi) films as radiation absorber coupled to a low-loss microstripline from niobium (Nb) ground plane to a twin-slot antenna structure. The thermal conductance (G) and the time constant for the different geometry device have been measured. For one such device, the measured G is 1.16 x 10(exp -10) W/K (plus or minus 0.61 x 10(exp- 10) W/K) at 60 mK, which corresponds to noise equivalent power (NEP) = 1.65 X 10(exp -18)W/vHz and time constant of approximately 5 microseconds

Ultrasensitive Superconducting Transition Edge Sensors Based On Electron-Phonon Decoupling

We have successfully fabricated the superconducting transition edge sensor (TES), bolometer technology that centers on the use of electron-phonon decoupling (EPD) to thermally isolate the bolometer. Along with material characterization for large format antenna coupled bolometer arrays, we present the initial test results of bolometer based on EPD designed for THz detection. We have selected a design approach that separates the two functions of photon absorption and temperature measurement, allowing separate optimization of the performance of each element. We have integrated Molybdenum/Gold (Mo/Au) bilayer TES and ion assisted thermally evaporated (IAE) Bismuth (Bi) films as radiation absorber coupled to a low-loss microstripline from Niobium (Nb) ground plane to a twin-slot antenna structure. The thermal conductance and the time constant of these devices have been measured, and are consistent with our calculations. The device exhibits a single time constant at 0.1 K of approx.160 IlS, which is compatible with readout by a high-bandwidth single SQUID or a time domain SQUID multiplexer. The effects of thermal conductance and electrothermal feedback are major determinants of the time constant, but the electronic heat capacity also plays a major role. The NEP achieved in the device described above is 2.5x10(exp -17)W(gamma)Hz. Our plan is to demonstrate a reduction of the volume in the superconducting element to 5 microns x 5 microns in films of half the thickness at Tc = 60mK. By calculation, this new geometry corresponds to an NEP reduction of two orders of magnitude to 2.5x10(exp -19)W/(gamma)Hz, with a time constant of ~130/ls

Could magnetic properties be used to image a grouted rock volume?

In this study, the feasibility to develop a detectable permeation grouting system is tested, based on the addition of magnetic materials to the grout, specifically, magnetite. A magnetic-based detection system is selected for development because unlike other previously trialled detection methods, magnetic fields are detectable over large distances within the subsurface, and importantly, attenuation of the magnetic field is not strongly dependent on the material properties of the surrounding rock. To test the conceptual feasibility of such a system, a finite element based numerical model is developed to simulate the magnetic field anomaly that can be achieved by the addition of magnetic materials to a cement grout. The model is verified against an analytical solution and then used to predict the magnetic field generated by a grouted cylinder of rock, assuming a fixed percentage of uniformly distributed magnetic minerals, and a central injection borehole. Two field trials are conducted to verify the detectable grouting concept, the first using a walkover survey that allowed mapping of the magnetic signal in 2D. The second is designed to mimic magnetic field measurements from a borehole monitoring array, with a single central magnetic grout block (representing the grout close to the injection point). Results of the two field trials show that the magnetic cement is detectable, even when the background magnetic noise within the surrounding soils/rocks is significant. A good agreement is obtained between the measured and the modelled magnetic anomaly. This research opens the door to the development of a ‘detectable’ magnetic grouting system, that can increase confidence in the integrity of grouted rock volumes and reduce the inefficiencies currently present in the grouting industry, enabling in-situ real-time optimisation of grouting campaigns

The Effects of Small Metal Additions (Co,Cu,Ga,Mn,Al,Bi,Sn) on the Magnetocaloric Properties of the Gd5Ge2Si2 Alloy

The structural and magnetic properties of arc-melted and homogenized (1300 °C, 1 h) alloys of Gd5Ge1.9Si2X0.1 (X = Cu, Co, Ga, Mn, Al, Bi, or Sn) were investigated by powder x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and magnetometry. The addition of Cu, Ga, Mn, and Al completely eliminated the large hysteresis losses present in the undoped Gd5Ge2Si2 alloy between 270 and 330 K, broadened the magnetic entropy change ΔSm peak, and shifted its peak value from 275 to 305 K similar to that observed earlier for Gd5Ge1.9Si2Fe0.1. The addition of Bi or Sn had a negligible effect on either the alloy hysteresis losses or the characteristics of the ΔSm vs T peak. The microstructure of the alloy doped with Cu, Co, Ga, Mn, or Al consisted of a majority phase (depleted of silicon) and a minor intergranular phase (rich in silicon and of the corresponding metal additive). For Bi or Sn doping, the microstructure consisted of only the Gd5Ge2Si2 phase. Low temperature x-ray diffraction data on an Fe-doped sample showed the same spectra at 245 and 300 K, consistent with the majority phase possessing an orthorhombic structure. Refrigeration capacity calculations show that Gd5Ge1.9Si2X0.1 (X = Fe,Cu,Co,Ga,Mn, or Al) alloys are superior magnetic refrigerants compared to the undoped Gd5Ge2Si2 alloy

Iron Abundances in Lunar Impact Basin Melt Sheets From Orbital Magnetic Field Data

International audienceMagnetic field data acquired from orbit shows that the Moon possesses many magnetic anomalies. Though most of these are not associated with known geologic structures, some are found within large impact basins within the interior peak ring. The primary magnetic carrier in lunar rocks is metallic iron, but indigenous lunar rocks are metal poor and cannot account easily for the observed field strengths. The projectiles that formed the largest impact basins must have contained a significant quantity of metallic iron, and a portion of this iron would have been retained on the Moon's surface within the impact melt sheet. Here we use orbital magnetic field data to invert for the magnetization within large impact basins using the assumption that the crust is unidirectionally magnetized. We develop a technique based on laboratory thermoremanent magnetization acquisition to quantify the relationship between the strength of the magnetic field at the time the rock cooled and the abundance of metal in the rock. If we assume that the magnetized portion of the impact melt sheet is 1 km thick, we find average abundances of metallic iron ranging from 0.11% to 0.45 wt %, with an uncertainty of a factor of about 3. This abundance is consistent with the metallic iron abundances in sampled lunar impact melts and the abundance of projectile contamination in terrestrial impact melts. These results help constrain the composition of the projectile, the impact process, and the time evolution of the lunar dynamo