150 research outputs found
Interaction of Lamb modes with two-level systems in amorphous nanoscopic membranes
Using a generalized model of interaction between a two-level system (TLS) and
an arbitrary deformation of the material, we calculate the interaction of Lamb
modes with TLSs in amorphous nanoscopic membranes. We compare the mean free
paths of the Lamb modes with different symmetries and calculate the heat
conductivity . In the limit of an infinitely wide membrane, the heat
conductivity is divergent. Nevertheless, the finite size of the membrane
imposes a lower cut-off for the phonons frequencies, which leads to the
temperature dependence . This temperature dependence
is a hallmark of the TLS-limited heat conductance at low temperature.Comment: 9 pages, 2 figure
The low-temperature energy calibration system for the CUORE bolometer array
The CUORE experiment will search for neutrinoless double beta decay (0nDBD)
of 130Te using an array of 988 TeO_2 bolometers operated at 10 mK in the
Laboratori Nazionali del Gran Sasso (Italy). The detector is housed in a large
cryogen-free cryostat cooled by pulse tubes and a high-power dilution
refrigerator. The TeO_2 bolometers measure the event energies, and a precise
and reliable energy calibration is critical for the successful identification
of candidate 0nDBD and background events. The detector calibration system under
development is based on the insertion of 12 gamma-sources that are able to move
under their own weight through a set of guide tubes that route them from
deployment boxes on the 300K flange down into position in the detector region
inside the cryostat. The CUORE experiment poses stringent requirements on the
maximum heat load on the cryostat, material radiopurity, contamination risk and
the ability to fully retract the sources during normal data taking. Together
with the integration into a unique cryostat, this requires careful design and
unconventional solutions. We present the design, challenges, and expected
performance of this low-temperature energy calibration system.Comment: To be published in the proceedings of the 13th International Workshop
on Low Temperature Detectors (LTD), Stanford, CA, July 20-24, 200
Heat transport in ultra-thin dielectric membranes and bridges
Phonon modes and their dispersion relations in ultrathin homogenous
dielectric membranes are calculated using elasticity theory. The approach
differs from the previous ones by a rigorous account of the effect of the film
surfaces on the modes with different polarizations. We compute the heat
capacity of membranes and the heat conductivity of narrow bridges cut out of
such membranes, in a temperature range where the dimensions have a strong
influence on the results. In the high temperature regime we recover the
three-dimensional bulk results. However, in the low temperature limit the heat
capacity, , is proportional with (temperature), while the heat
conductivity, , of narrow bridges is proportional to , leading
to a thermal cut-off frequency .Comment: 6 pages and 6 figure
A continuous dry 300 mK cooler for THz sensing applications
We describe and demonstrate the automated operation of a novel cryostat design that is capable of maintaining an unloaded base temperature of less than 300 mK continuously, without the need to recycle the gases within the final cold head, as is the case for conventional single shot sorption pumped 3He cooling systems. This closed dry system uses only 5 l of 3He gas, making this an economical alternative to traditional systems where a long hold time is required. During testing, a temperature of 365 mK was maintained with a constant 20 μW load, simulating the cooling requirement of a far infrared camera
Effect of heat treatment on mechanical dissipation in TaO coatings
Thermal noise arising from mechanical dissipation in dielectric reflective
coatings is expected to critically limit the sensitivity of precision
measurement systems such as high-resolution optical spectroscopy, optical
frequency standards and future generations of interferometric gravitational
wave detectors. We present measurements of the effect of post-deposition heat
treatment on the temperature dependence of the mechanical dissipation in
ion-beam sputtered tantalum pentoxide between 11\,K and 300\,K. We find the
temperature dependence of the dissipation is strongly dependent on the
temperature at which the heat treatment was carried out, and we have identified
three dissipation peaks occurring at different heat treatment temperatures. At
temperatures below 200\,K, the magnitude of the loss was found to increase with
higher heat treatment temperatures, indicating that heat treatment is a
significant factor in determining the level of coating thermal noise.Comment: accepted Classical and Quantum Gravity 201
Predicting the response of a submillimeter bolometer to cosmic rays
Bolometers designed to detect. submillimeter radiation also respond to cosmic, gamma, and x rays. Because detectors cannot be fully shielded from such energy sources, it is necessary to understand the effect of a photon or cosmic-ray particle being absorbed. The resulting signal (known as a glitch) can then be removed from raw data. We present measurements using an Americium-241 gamma radiation source to irradiate a prototype bolometer for the High Frequency Instrument in the Planck Surveyor satellite. Our measurements showed no variation in response depending on where the radiation was absorbed, demonstrating that the bolometer absorber and thermistor thermalize quickly. The bolometer has previously been fully characterized both electrically and optically. We find that using optically measured time constants underestimates the time taken for the detector to recover from a radiation absorption event. However, a full thermal model for the bolometer, with parameters taken from electrical and optical measurements, provides accurate time constants. Slight deviations from the model were seen at high energies; these can be accounted for by use of an extended model
Supersolid behavior in confined geometry
We have carried out torsional oscillator (TO) and heat capacity (HC)
measurements on solid 4He samples grown within a geometry which restricts the
helium to thin (150 um) cylindrical discs. In contrast to previously reported
values from Rittner and Reppy of 20% non-classical rotational inertia (NCRI)
for similar confining dimensions, 0.9% NCRI (consistent with that found in bulk
samples and samples imbedded in porous media) was observed in our TO cell. In
this confined geometry the heat capacity peak is consistent with that found in
bulk solid samples of high crystalline quality
The Aquila prestellar core population revealed by Herschel
The origin and possible universality of the stellar initial mass function
(IMF) is a major issue in astrophysics. One of the main objectives of the
Herschel Gould Belt Survey is to clarify the link between the prestellar core
mass function (CMF) and the IMF. We present and discuss the core mass function
derived from Herschel data for the large population of prestellar cores
discovered with SPIRE and PACS in the Aquila Rift cloud complex at d ~ 260 pc.
We detect a total of 541 starless cores in the entire ~11 deg^2 area of the
field imaged at 70-500 micron with SPIRE/PACS. Most of these cores appear to be
gravitationally bound, and thus prestellar in nature. Our Herschel results
confirm that the shape of the prestellar CMF resembles the stellar IMF, with
much higher quality statistics than earlier submillimeter continuum
ground-based surveys
A Herschel study of the properties of starless cores in the Polaris Flare dark cloud region using PACS and SPIRE
The Polaris Flare cloud region contains a great deal of extended emission. It
is at high declination and high Galactic latitude. It was previously seen
strongly in IRAS Cirrus emission at 100 microns. We have detected it with both
PACS and SPIRE on Herschel. We see filamentary and low-level structure. We
identify the five densest cores within this structure. We present the results
of a temperature, mass and density analysis of these cores. We compare their
observed masses to their virial masses, and see that in all cases the observed
masses lie close to the lower end of the range of estimated virial masses.
Therefore, we cannot say whether they are gravitationally bound prestellar
cores. Nevertheless, these are the best candidates to be potentialprestellar
cores in the Polaris cloud region.Comment: 5 pages, 2 figures, accepted by A&
Herschel observations of embedded protostellar clusters in the Rosette Molecular Cloud
The Herschel OB young stellar objects survey (HOBYS) has observed the Rosette
molecular cloud, providing an unprecedented view of its star formation
activity. These new far-infrared data reveal a population of compact young
stellar objects whose physical properties we aim to characterise. We compiled a
sample of protostars and their spectral energy distributions that covers the
near-infrared to submillimetre wavelength range. These were used to constrain
key properties in the protostellar evolution, bolometric luminosity, and
envelope mass and to build an evolutionary diagram. Several clusters are
distinguished including the cloud centre, the embedded clusters in the vicinity
of luminous infrared sources, and the interaction region. The analysed
protostellar population in Rosette ranges from 0.1 to about 15 Msun with
luminosities between 1 and 150 Lsun, which extends the evolutionary diagram
from low-mass protostars into the high-mass regime. Some sources lack
counterparts at near- to mid-infrared wavelengths, indicating extreme youth.
The central cluster and the Phelps & Lada 7 cluster appear less evolved than
the remainder of the analysed protostellar population. For the central cluster,
we find indications that about 25% of the protostars classified as Class I from
near- to mid-infrared data are actually candidate Class 0 objects. As a
showcase for protostellar evolution, we analysed four protostars of low- to
intermediate-mass in a single dense core, and they represent different
evolutionary stages from Class 0 to Class I. Their mid- to far-infrared
spectral slopes flatten towards the Class I stage, and the 160 to 70um flux
ratio is greatest for the presumed Class 0 source. This shows that the Herschel
observations characterise the earliest stages of protostellar evolution in
detail.Comment: Astronomy & Astrophysics letter, 6 pages, 4 figures, accepted for
publication in the Special Issue for Herschel first result
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