共查询到20条相似文献,搜索用时 31 毫秒
1.
Johannes Staguhn Christine Allen Dominic Benford Elmer Sharp Troy Ames Rick Arendt David Chuss Eli Dwek Attila Kovacs Stephen Maher Catherine Marx Tim Miller S. Harvey Moseley Santiago Navarro Albrecht Sievers George Voellmer Edward Wollack 《Journal of Low Temperature Physics》2008,151(3-4):709-714
The 2 mm spectral range provides a unique terrestrial window enabling ground based observations of the earliest active dusty
galaxies in the universe and thereby allowing a better constraint on the star formation rate in these objects. We have built
GISMO (the Goddard-IRAM Superconducting 2-Millimeter Observer), a 2 mm, 128 element superconducting Transition Edge Sensor
(TES) based bolometer camera for the IRAM 30 m telescope in Spain. The camera uses an 8×16 planar array of multiplexed TES
bolometers, which incorporates our recently designed Backshort Under Grid (BUG) architecture, described elsewhere. The optical
design incorporates a 100 mm (4 inches) diameter silicon lens cooled to 4 K, which provides the required fast beam of 0.9
λ/D. With this spatial sampling, GISMO will be very efficient at detecting sources serendipitously in large sky surveys, while
the capability for diffraction-limited observations is preserved. With the background limited performance of the detectors,
the camera provides significantly greater imaging sensitivity and mapping speed at this wavelength than has previously been
possible. The major scientific driver for the instrument is to provide the IRAM 30 m telescope with the capability to rapidly
observe galactic and extragalactic dust emission, in particular from high-z Ultra Luminous Infrared Galaxies (ULIRGs) and
quasars, even in the summer season. The instrument will fill in the SEDs of high redshift galaxies at the Rayleigh-Jeans part
of the dust emission spectrum, even at the highest redshifts. Our source count models predict that GISMO will serendipitously
detect one galaxy every four hours on the blank sky, and that one quarter of these galaxies will be at a redshift of z 6.5.
We expect to install GISMO at the 30 m telescope in the second half of 2007.
相似文献
2.
In this paper, instrumented tension-impact (dynamic tensile) and instrumented Charpy impact test results for AISI 308 stainless steel welds at room temperature are reported. A few Charpy specimens precracked to a/W (crack length to width ratio) ratios of 0.42 to 0.59 were also tested. Dynamic yield strength obtained from tension-impact test agrees well with that from Charpy V-notch specimens. The strain rates obtained during the tension-impact test are compared with the various estimates of strain rates for V-notch and precracked Charpy specimens. A variation of the compliance changing rate method was necessary for determining the crack initiation point while crack growth was determined by power law key-curve procedure. J-R curves thus obtained from Charpy (precracked and V-notch) specimens are compared with those computed using handbook procedures using dynamic tensile results.
Key words: Tension-impact testing, 308 stainless steel weld, Charpy V-notch, dynamic fracture toughness, dynamic yield strength, J-R curve, strain rate, key-curve. 相似文献
3.
We implement the rotationally-invariant formulation of the two-dimensional Hubbard model, with nearest-neighbors hopping t, which allows for the analytic study of the system in the low-energy limit. Both U(1) and SU(2) gauge transformations are
used to factorize the charge and spin contribution to the original electron operator in terms of the corresponding gauge fields.
The Hubbard Coulomb energy U-term is then expressed in terms of quantum phase variables conjugate to the local charge and variable spin quantization axis,
providing a useful representation of strongly correlated systems. It is shown that these gauge fields play a similar role
as phonons in the BCS theory: they act as the “glue” for fermion pairing. By tracing out gauge degrees of freedom the form
of paired states is established and the strength of the pairing potential is determined. It is found that the attractive pairing
potential in the effective low-energy fermionic action is non-zero in a rather narrow range of U/t. 相似文献
4.
The problem of a uniform ship-hull girder vibrating vertically close to water bottom is studied. A simple formula for the added mass is found by use of the method of matched asymptotic expansions. Results obtained from the present method and BEM are compared. They are in good agreement in the range considered here. The obtained added mass is used to predict the natural vibrations of a uniform beam vibrating close to water bottom. Numerical values show that the effects of shallow water are significant. The first- and second-order frequencies of the ship hull studied in this paper in deep water are about 1·4–3 times higher than those in shallow water. 相似文献
5.
The cytotoxicity of single-walled carbon nanotubes (SWCNTs) suspended in various surfactants was investigated by phase contrast light microscopy characterization in combination with an absorbance spectroscopy cytotoxicity analysis. Our data indicate that individual SWCNTs suspended in the surfactants, sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS), were toxic to 1321N1 human astrocytoma cells due to the toxicity of SDS and SDBS on the nanotube surfaces. This toxicity was observed when cells were exposed to an SDS or SDBS solution having a concentration as low as 0.05?mg?ml(-1) for 30?min. The proliferation and viability of the cells were not affected by SWCNTs alone or by conjugates of SWCNTs with various concentrations of sodium cholate (SC) or single-stranded DNA. The cells proliferated similarly to untreated cells when surrounded by SWCNTs as they grow, which indicated that the nanotubes did not affect cells adversely. The cytotoxicity of the nanotube-surfactant conjugates was controlled in these experiments by the toxicity of the surfactants. Consequently, when evaluating a surfactant to be used for the dispersion of nanoscale materials in applications such as nanoscale electronics or non-viral biomolecular transporters, the cytotoxicity needs to be evaluated. The methodology proposed in this study can be used to investigate the cytotoxicity of other nanoscale materials suspended in a variety?of?surfactants. 相似文献
6.
W. Westphal C. Ciemniak C. Coppi F. von Feilitzsch A. Gütlein C. Isaila J.-C. Lanfranchi S. Pfister W. Potzel W. Rau S. Roth M. Stark 《Journal of Low Temperature Physics》2008,151(3-4):824-829
A potentially harmful background for experiments attempting direct dark matter detection like the CRESST (= Cryogenic Rare
Event Search with Superconducting Thermometers) experiment is caused by recoiling nuclei from 210Po alpha decays on surfaces close to the detector. In order to characterize this kind of background in CRESST, calibration
measurements have been performed at the TU München. A for this purpose an optimized version of the CRESST detector has been
developed consisting of a 38 g CaWO4 crystal and a separate cryogenic light detector, both equipped with Ir/Au transition edge sensors (TESs). The simultaneous
measurement of the phonon signal and the scintillation light from the CaWO4 crystal allows to discriminate between electron and nuclear recoils using their different light outputs. The unexpected results
of a first measurement with a 210Po source can be understood with the help of a Monte Carlo simulation performed for a similar system.
相似文献
7.
S. Roth C. Ciemniak C. Coppi F. v. Feilitzsch A. Gütlein C. Isaila J.-C. Lanfranchi S. Pfister W. Potzel W. Westphal 《Journal of Low Temperature Physics》2008,151(1-2):216-222
For the purpose of building very sensitive light and phonon detectors, as e.g. applied in the Dark Matter (DM) experiment
CRESST (Cryogenic Rare Event Search with Superconducting Thermometers), transition edge sensors (TESs) in combination with
a massive absorber crystal are used. To ensure high sensitivity of the detectors, low heat capacities, i.e. low working temperatures
of about 10 mK are aimed at. Therefore, TESs made of tungsten thin films exhibiting the alpha-tungsten (α-W) phase with transition temperatures of T
c
=10–15 mK are required. We have produced tungsten thin films with T
c
in the range of 25–55 mK by rf-sputtering. To decouple the thermometer production from the choice of the target material
and to avoid heating cycles of the absorber crystal, a composite design for detector production is applied. The composite
design includes fabrication of the TES on a separate substrate and then attaching of this separate TES to a massive absorber
crystal by gluing. For this purpose small sapphire substrates are used for the deposition of the TES. Properties of tungsten
thin films grown with the rf-sputtering technique as well as first results of composite detectors built with these films acting
as TESs will be presented.
相似文献
8.
A. Yamaguchi K. Takeda T. Matsumoto G. Motoyama H. Kashiwaya S. Kuriki S. Kashiwaya S. Ohkoshi A. Sumiyama 《Journal of Low Temperature Physics》2010,158(3-4):704-709
We report development of micro superconducting quantum interference device (μ-SQUID) magnetometers for investigation of quantum tunneling of magnetization in μm- and nm-size magnetic materials. Both high- and low-temperature superconductor (HTS and LTS) based μ-SQUID magnetometers were fabricated and a three dimensional magnetic coil system was constructed for this purpose. The HTS-μ-SQUIDs with a hole of 4×9 μm2 work at temperatures between 4.2 and 70 K and in magnetic fields up to 120 mT. A magnetization measurement of a ferrimagnetic micro-crystal was carried out at 35 K with an accuracy of 10?9 emu. The development of LTS-μ-SQUIDs has been started in order to study much smaller magnetic materials in a mK temperature range. We present a preliminary result on the LTS-μ-SQUID with a hole of 1×1 μm2. The critical current as a function of applied magnetic field shows the SQUID modulation at 4.2 K and up to 30 mT. The heat release associated with the present measurement method is estimated to be on the order of several microwatts. 相似文献
9.
V. A. Beloshenko T. E. Konstantinova N. I. Matrosov V. Z. Spuskanyuk V. V. Chishko D. Gajda A. J. Zaleski V. P. Dyakonov R. Puźniak H. Szymczak 《Journal of Superconductivity and Novel Magnetism》2009,22(5):505-510
An improvement of NbTi alloy functional properties by equal-channel multi-angle pressing (ECMAP) combined with hydrostatic
extrusion, drawing and thermal treatment is revealed. The ECMAP method allows to increase the billet accumulated deformation
with preserving its initial dimensions. The formed highly dispersed and homogeneous nanocrystalline structure with a more
uniform distribution of α-phase precipitations as a result of ECMAP treatment improves the functional properties of the alloy. In the field of 5 T,
the critical current density in wire samples produced with application of the ECMAP method is enhanced approximately by a
factor of 2 in comparison with the values obtained for the samples produced without the ECMAP treatment. 相似文献
10.
The whole collective mode spectrum in axial and planar phases of superfluid 3He with dispersion corrections is calculated for the first time. In axial A-phase the degeneracy of clapping modes depends on the direction of the collective mode momentum k with respect to the vector l (mutual orbital moment of Cooper pairs), namely: the mode degeneracy remains the same as in case of zero momentum k for k‖l only. For any other directions there is a threefold splitting of these modes, which reaches maximum for k ⊥ l. In planar 2D-phase, which exists in the magnetic field (at H>H C ) we find that for clapping modes the degeneracy depends on the direction of the collective mode momentum k with respect to the external magnetic field H, namely: the mode degeneracy remains the same as in case of zero momentum k for k‖H only. For any other directions different from this one (for example, for k ⊥ H) there is twofold splitting of these modes. The obtained results imply that new interesting features can be observed in ultrasound experiments in axial and planar phases: the change of the number of peaks in ultrasound absorption into clapping mode. One peak, observed for these modes by Ling et al. (J. Low Temp. Phys. 78:187, 1990), will split into two peaks in a planar phase and into three peaks in an axial phase under the change of ultrasound direction with respect to the external magnetic field H in a planar phase and with respect to the vector l in an axial phase. In planar phase, some Goldstone modes in the magnetic field become massive (quasi-Goldstone) and have a similar twofold splitting under the change of ultrasound direction with respect to the external magnetic field H. The obtained results as well will be useful under interpretation of the ultrasound experiments in axial and planar phases of superfluid 3He. 相似文献
11.
V. B. Efimov Deepak Garg O. Kolosov P. V. E. McClintock 《Journal of Low Temperature Physics》2010,158(3-4):456-461
The dynamics of an electrically-driven 8 kHz quartz tuning fork has been studied experimentally in liquid helium-4 in the temperature range 1.3<T<4.2 K under the saturated vapour pressure. The fork has relatively large dimensions compared to standard 32 kHz fork used in recent investigations. The velocity of the tip of the fork prong is measured by the indirect electromechanical equivalent method and is compared with the velocity of another 8 kHz fork (from the same batch) determined by direct optical measurement of the oscillation amplitude through Michelson interferometry. A comparison of these results has provided absolute values for the critical velocity of the transition to the turbulent state. 相似文献
12.
M. J. Myers K. Arnold P. Ade G. Engargiola W. Holzapfel A. T. Lee X. Meng R. O’Brient P. L. Richards H. Spieler H. T. Tran 《Journal of Low Temperature Physics》2008,151(1-2):464-470
We are building antenna-coupled Transition Edge Sensor bolometer arrays to measure the polarization of the cosmic microwave
background. 217 GHz prototype pixels have previously been characterized and showed promising performance (Myers et al. in
Appl. Phys. Lett. 86:114103, [2005]). Our design uses a double slot dipole antenna and an integrated microstrip band defining filter. New devices have been
tested which include on-chip test structures to improve our understanding of detector performance and guide future development.
In parallel with this, large arrays of bolometers based on the prototype pixel design have also been constructed. The array
pixels are a heterogeneous mixture of single band pixels at 90 GHz, 150 GHz, and 220 GHz and now incorporate dual-polarization
antennas (Chattopadhyay and Zmuidzinas in IEEE Trans. Antennas Propag. 46:736, [1998]). Preliminary results from optical testing of array pixels are presented. These bolometer arrays will be used in the upcoming
CMB polarization experiment Polarbear.
相似文献
13.
Within finite-range density-functional theory, we have addressed the infrared absorption and emission spectrum of electron bubbles attached to linear vortices in liquid 4He as a function of pressure. We have found that the presence of vortices affects very little the absorption spectrum, only causing a small shift in the 1s→2p peak. The energy of the lowest emission transition is also shown as a function of pressure for a vortex-free bubble and for a trapped bubble. In the emission energy the shift induced by the vortex line is proportionally bigger, especially when the waist around the electron probability density of the 1p state collapses, which happens at a pressure of ~8 bar. 相似文献
14.
The reconfigurable manufacturing system (RMS) is a recent manufacturing paradigm driven by the high responsiveness and performance efficiencies. In such system, machines, material handling units or machines components can be added, modified, removed or interchanged as needed. Hence, the design of RMS is based on reconfigurable machines capabilities and product specification. This paper addresses the problem of machines selections for RMS design under unavailability constraints and aims to develop an approach to ensure the best process plan according to the customised flexibility required to produce all parts of a given product. More specifically, we develop a flexibility-based multi-objective approach using an adapted version of the well-known non-dominated sorting genetic algorithm to select adequate machines from a set of candidate (potential) ones, in order to ensure the best responsiveness of the designed system in case of unavailability of one of the selected machines. The responsiveness is based on the flexibility of the designed system and a generated process plan, which guarantees the management of machines unavailability. It is defined as the ability and the capacity to adapt the process plan in response to machines unavailability. Two objectives are considered, respectively, the maximisation of the flexibility index of the system and the minimisation of the total completion time. To choose the best solution in the Pareto front, a multi-objective decision-making method called technique for order of preference by similarity to ideal solution is used. To demonstrate the applicability of the proposed approach, a simple example is presented and the numerical results are analysed. 相似文献
15.
We study theoretically the magnetic bipolar transistor and the spin-metal oxide semiconductor field-effect transistor (spin-MOSFET),
focusing our attention in comparing the performance of these spintronic devices with their counterparts, from engineering
point of view. We simulate the characteristic curves of both spintronic transistors and their corresponding conventional transistors,
and evaluate some merit parameters: current amplification factor (β), open-loop gain (G), hybrid parameters (HP) and cutoff frequency (f
T
), for the magnetic bipolar transistor, and the input capacitance (C), response time (t), cutoff frequency, and hybrid parameters, for the spin-MOSFET. With our results, we summarize spintronic transistors as
promising and challenging. 相似文献
16.
The interaction between individual Ga atoms and the inner walls of both (8, 8) and (12, 0) carbon nanotubes (CNTs) is investigated using first principles calculations based on the density functional theory. We find that a single Ga atom favorably adsorbs at the center site (H) of a hexagonal ring and diffuses on the inner wall of a perfect CNT with very low energy barriers. In the case of CNTs containing monovacancies, a single Ga?atom can heal the topological structure of a monovacancy in a (8, 8) CNT but not in a (12, 0) CNT. Our calculations show that the Ga atom adsorbed at the monovacancy in the CNT can alter the electronic structure of the tube significantly. 相似文献
17.
A. Mahé F. D. Parmentier G. Fève J.-M. Berroir T. Kontos A. Cavanna B. Etienne Y. Jin D. C. Glattli B. Plaçais 《Journal of Low Temperature Physics》2008,153(5-6):339-349
We describe here the realization of a single electron source similar to single photon sources in optics. On-demand single electron injection is obtained using a quantum dot connected to the conductor via a tunnel barrier of variable transmission (quantum point contact). Electron emission is triggered by a sudden change of the dot potential which brings a single energy level above the Fermi energy in the conductor. A single charge is emitted on an average time ranging from 100 ps to 10 ns ultimately determined by the barrier transparency and the dot charging energy. The average single electron emission process is recorded with a 0.5 ns time resolution using a real-time fast acquisition card. Single electron signals are compared to simulation based on scattering theory approach adapted for finite excitation energies. 相似文献
18.
H. Nagata J. Kobayashi H. Matsuo M. Nakahashi K. Kobayashi H. Ikeda M. Fujiwara 《Journal of Low Temperature Physics》2008,151(3-4):1022-1027
We present the design and fabrication of cryogenic readout integrated circuits (ROICs) for Superconducting Tunneling Junctions
using the SONY n-type GaAs-JFETs, which have good current-voltage characteristics and low noise performance even at <1 K. In order to fabricate
the ROICs, we have designed simple GaAs-JFET amplifiers based on the measurement results of the GaAs-JFETs at <4.2 K: source
follower amplifier, common source amplifier, and two types of cascode amplifiers. The obtainable gain of the cascode active
load amplifiers is >100. These amplifiers were fabricated with the other circuit elements as an integrated circuit. We also
show initial test results of the cascode active load amplifier. 相似文献
19.
Ribonucleic acid (RNA) is an important genetic material whose lifetime is most often determined by the rate of its enzymatic degradation. Our studies showed that multi-walled carbon nanotubes and single-walled carbon nanotubes functionalized with carboxylic groups interacted with ribonuclease A (RNase A) and caused the reduction of its activity by changing its conformation, thus protecting RNA from enzymatic cleavage. The results showed that RNase A was less active on the carbon nanotube surface than in free solution, and the activity was decreased further on larger carbon nanotubes, suggesting that carbon nanotubes with various surface modifications may be useful in RNA extraction, purification, and manipulation. 相似文献
20.
The predominant role of collagen in the nucleation, growth, structure and orientation of bone apatite 总被引:1,自引:0,他引:1
Wang Y Azaïs T Robin M Vallée A Catania C Legriel P Pehau-Arnaudet G Babonneau F Giraud-Guille MM Nassif N 《Nature materials》2012,11(8):724-733
The involvement of collagen in bone biomineralization is commonly admitted, yet its role remains unclear. Here we show that type I collagen in?vitro can initiate and orientate the growth of carbonated apatite mineral in the absence of any other vertebrate extracellular matrix molecules of calcifying tissues. We also show that the collagen matrix influences the structural characteristics on the atomic scale, and controls the size and the three-dimensional distribution of apatite at larger length scales. These results call into question recent consensus in the literature on the need for Ca-rich non-collagenous proteins for collagen mineralization to occur in vivo. Our model is based on a collagen/apatite self-assembly process that combines the ability to mimic the in vivo extracellular fluid with three major features inherent to living bone tissue, that is, high fibrillar density, monodispersed fibrils and long-range hierarchical organization. 相似文献