1,450 research outputs found
Water in Comet 2/2003 K4 (LINEAR) with Spitzer
We present sensitive 5.5 to 7.6 micron spectra of comet C/2003 K4 (LINEAR)
obtained on 16 July 2004 (r_{h} = 1.760 AU, Delta_{Spitzer} = 1.409 AU, phase
angle 35.4 degrees) with the Spitzer Space Telescope. The nu_{2} vibrational
band of water is detected with a high signal-to-noise ratio (> 50). Model
fitting to the best spectrum yields a water ortho-to-para ratio of 2.47 +/-
0.27, which corresponds to a spin temperature of 28.5^{+6.5}_{-3.5} K. Spectra
acquired at different offset positions show that the rotational temperature
decreases with increasing distance from the nucleus, which is consistent with
evolution from thermal to fluorescence equilibrium. The inferred water
production rate is (2.43 +/- 0.25) \times 10^{29} molec. s^{-1}. The spectra do
not show any evidence for emission from PAHs and carbonate minerals, in
contrast to results reported for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp).
However, residual emission is observed near 7.3 micron the origin of which
remains unidentified.Comment: 33 pages, including 11 figures, 2 tables, ApJ 2007 accepte
Improving wafer-scale Josephson junction resistance variation in superconducting quantum coherent circuits
Quantum bits, or qubits, are an example of coherent circuits envisioned for
next-generation computers and detectors. A robust superconducting qubit with a
coherent lifetime of (100 s) is the transmon: a Josephson junction
functioning as a non-linear inductor shunted with a capacitor to form an
anharmonic oscillator. In a complex device with many such transmons, precise
control over each qubit frequency is often required, and thus variations of the
junction area and tunnel barrier thickness must be sufficiently minimized to
achieve optimal performance while avoiding spectral overlap between neighboring
circuits. Simply transplanting our recipe optimized for single, stand-alone
devices to wafer-scale (producing 64, 1x1 cm dies from a 150 mm wafer)
initially resulted in global drifts in room-temperature tunneling resistance of
30%. Inferring a critical current variation from this
resistance distribution, we present an optimized process developed from a
systematic 38 wafer study that results in 3.5% relative standard deviation
(RSD) in critical current () for 3000 Josephson junctions (both single-junctions and
asymmetric SQUIDs) across an area of 49 cm. Looking within a 1x1 cm moving
window across the substrate gives an estimate of the variation characteristic
of a given qubit chip. Our best process, utilizing ultrasonically assisted
development, uniform ashing, and dynamic oxidation has shown = 1.8% within 1x1 cm, on average,
with a few 1x1 cm areas having 1.0% (equivalent to 0.5%). Such stability would drastically improve the yield of
multi-junction chips with strict critical current requirements.Comment: 10 pages, 4 figures. Revision includes supplementary materia
Piezoelectric Phononic Plates: Retrieving the Frequency Band Structure via All-electric Experiments
We propose an experimental technique based on all-electric measurements to
retrieve the frequency response of a one-dimensional piezoelectric phononic
crystal plate, structured periodically with millimeter-scaled metallic strips
on its two surfaces. The metallic electrodes, used for the excitation of
Lamb-like guided modes in the plate, ensure at the same time control of their
dispersion by means of externally loaded electric circuits that offer
non-destructive tunability in the frequency response of these structures. Our
results, in very good agreement with finite-element numerical predictions,
reveal interesting symmetry aspects that are employed to analyze the frequency
band structure of such crystals. More importantly, Lamb-like guided modes
interact with electric-resonant bands induced by inductance loads on the plate,
whose form and symmetry are discussed and analyzed in depth, showing
unprecedented dispersion characteristics.Comment: This is the version of the article before peer review or editing, as
submitted by an author to Smart Materials and Structures. IOP Publishing Ltd
is not responsible for any errors or omissions in this version of the
manuscript or any version derived from it. The Version of Record is available
online at https://doi.org/10.1088/1361-665X/ab4aa
Observations of cometary parent molecules with the IRAM radio telescope
Several rotational transitions of HCN, H2S, H2CO, and CH3OH were detected in comets P/Brorsen-Metcalf 1989 X, Austin (1989c1) and Levy (1990c) with the Institute for Millimeter Radioastronomy (IRAM) 30-m radio telescope. This allows us to determine the production rates of these molecules and to probe the physical conditions of the coma
Observations of OH in comet Levy with the Nancay radio telescope
Due to extremely favorable excitation conditions, comet Levy (1990c) exhibited in August-September 1990 the strongest OH 18-cm signal ever recorded in a comet at the Nancay radio telescope. This unique opportunity was used to measure the OH satellite lines at 1612 and 1721 MHz, to perform extensive mapping of the OH radio emission and to make a sensitive evaluation of the cometary magnetic field, of the H2O outflow velocity and of the OH production rate
Millimetre continuum observations of comet C/2009 P1 (Garradd)
Little is known about the physical properties of the nuclei of Oort cloud
comets. Measuring the thermal emission of a nucleus is one of the few means for
deriving its size and constraining some of its thermal properties. We attempted
to measure the nucleus size of the Oort cloud comet C/2009 P1 (Garradd). We
used the Plateau de Bure Interferometer to measure the millimetric thermal
emission of this comet at 157 GHz (1.9 mm) and 266 GHz (1.1 mm). Whereas the
observations at 266 GHz were not usable due to bad atmospheric conditions, we
derived a 3-sigma upper limit on the comet continuum emission of 0.41 mJy at
157 GHz. Using a thermal model for a spherical nucleus with standard thermal
parameters, we found an upper limit of 5.6 km for the radius. The dust
contribution to our signal is estimated to be negligible. Given the water
production rates measured for this comet and our upper limit, we estimated that
Garradd was very active, with an active fraction of its nucleus larger than
50%.Comment: Accepted for publication in Astronomy & Astrophysics. 5 pages, 2
figure
Skyrmion-skyrmion and skyrmion-edge repulsions in skyrmion-based racetrack memory
Magnetic skyrmions are promising for building next-generation magnetic
memories and spintronic devices due to their stability, small size and the
extremely low currents needed to move them. In particular, skyrmion-based
racetrack memory is attractive for information technology, where skyrmions are
used to store information as data bits instead of traditional domain walls.
Here we numerically demonstrate the impacts of skyrmion-skyrmion and
skyrmion-edge repulsions on the feasibility of skyrmion-based racetrack memory.
The reliable and practicable spacing between consecutive skyrmionic bits on the
racetrack as well as the ability to adjust it are investigated. Clogging of
skyrmionic bits is found at the end of the racetrack, leading to the reduction
of skyrmion size. Further, we demonstrate an effective and simple method to
avoid the clogging of skyrmionic bits, which ensures the elimination of
skyrmionic bits beyond the reading element. Our results give guidance for the
design and development of future skyrmion-based racetrack memory.Comment: 15 pages, 6 figure
Interferometric imaging of carbon monoxide in comet C/1995 O1 (Hale-Bopp): evidence for a strong rotating jet
Observations of the CO J(1-0) 115 GHz and J(2-1) 230 GHz lines in comet
C/1995 O1 (Hale-Bopp) were performed with the IRAM Plateau de Bure
interferometer on 11 March, 1997. The observations were conducted in both
single-dish (ON-OFF) and interferometric modes with 0.13 km s-1 spectral
resolution. Images of CO emission with 1.7 to 3" angular resolution were
obtained. The ON-OFF and interferometric spectra show a velocity shift with
sinusoidal time variations related to the Hale-Bopp nucleus rotation of 11.35
h. The peak position of the CO images moves perpendicularly to the spin axis
direction in the plane of the sky. This suggests the presence of a CO jet,
which is active night and day at about the same extent, and is spiralling with
nucleus rotation. The high quality of the data allows us to constrain the
characteristics of this CO jet. We have developed a 3-D model to interpret the
temporal evolution of CO spectra and maps. The CO coma is represented as the
combination of an isotropic distribution and a spiralling gas jet, both of
nucleus origin. Spectra and visibilities (the direct output of interferometric
data) analysis shows that the CO jet comprises ~40% the total CO production and
is located at a latitude ~20 degrees North on the nucleus surface. Our
inability to reproduce all observational characteristics shows that the real
structure of the CO coma is more complex than assumed, especially in the first
thousand kilometres from the nucleus. The presence of another moving CO
structure, faint but compact and possibly created by an outburst, is
identified.Comment: 20 pages, 26 figures. Accepted for publication in Astronomy &
Astrophysic
A Coupled Euler-Lagrange CFD Modelling of Droplets-To-Film
In this paper, a droplet to film interaction model technique is presented. In the proposed approach, the liquid and gas continua are modelled using an enhanced Volume of Fluid (VoF) technique while the droplets are tracked using a Lagrangian framework and are coupled to the Eulerian phases using source terms. The eventual target application is an aeroengine bearing chamber in which oil is found as droplets, shed from the bearings, splashing on impact, separated from wall surfaces at obstacles or simply re-entrained, and as a continuum oil film coating the bearing chamber outer walls which it also cools. In finite volume CFD techniques, a prohibitively large number of cells would be required to describe the details of the droplet impact phenomenon. Based on published correlations, the splashing droplets are created and tracked as Lagrangian particles. The flowing film and the gas continua are handled with an enhanced Volume of Fluid technique
- …