14,459 research outputs found
Planck pre-launch status: The HFI instrument, from specification to actual performance
Context. The High Frequency Instrument (HFI) is one of the two focal instruments of the Planck mission. It will observe the whole sky in six
bands in the 100 GHz−1 THz range.
Aims. The HFI instrument is designed to measure the cosmic microwave background (CMB) with a sensitivity limited only by fundamental
sources: the photon noise of the CMB itself and the residuals left after the removal of foregrounds. The two high frequency bands will provide
full maps of the submillimetre sky, featuring mainly extended and point source foregrounds. Systematic effects must be kept at negligible levels
or accurately monitored so that the signal can be corrected. This paper describes the HFI design and its characteristics deduced from ground tests
and calibration.
Methods. The HFI instrumental concept and architecture are feasible only by pushing new techniques to their extreme capabilities, mainly:
(i) bolometers working at 100 mK and absorbing the radiation in grids; (ii) a dilution cooler providing 100 mK in microgravity conditions;
(iii) a new type of AC biased readout electronics and (iv) optical channels using devices inspired from radio and infrared techniques.
Results. The Planck-HFI instrument performance exceeds requirements for sensitivity and control of systematic effects. During ground-based
calibration and tests, it was measured at instrument and system levels to be close to or better than the goal specification
Remark on lattice BRST invariance
A recently claimed resolution to the lattice Gribov problem in the context of
chiral lattice gauge theories is examined. Unfortunately, I find that the old
problem remains.Comment: 4 pages, plain TeX, presentation improved (see acknowledgments
On central tendency and dispersion measures for intervals and hypercubes
The uncertainty or the variability of the data may be treated by considering,
rather than a single value for each data, the interval of values in which it
may fall. This paper studies the derivation of basic description statistics for
interval-valued datasets. We propose a geometrical approach in the
determination of summary statistics (central tendency and dispersion measures)
for interval-valued variables
Mapping the interstellar medium in galaxies with Herschel/SPIRE
The standard method of mapping the interstellar medium in a galaxy, by observing the molecular gas in the CO 1-0 line and the atomic gas in the 21-cm line, is largely limited with current telescopes to galaxies in the nearby universe. In this letter, we use SPIRE observations of the galaxies
M99 and M100 to explore the alternative approach of mapping the interstellar medium using the continuum emission from the dust. We have compared the methods by measuring the relationship between the star-formation rate and the surface density of gas in the galaxies using both
methods. We find the two methods give relationships with a similar dispersion, confirming that observing the continuum emission from the dust is a promising method of mapping the interstellar medium in galaxies
Parameter Estimation from Improved Measurements of the Cosmic Microwave Background from QUaD
We evaluate the contribution of cosmic microwave background (CMB) polarization spectra to cosmological parameter constraints. We produce cosmological parameters using high-quality CMB polarization data from the ground-based QUaD experiment and demonstrate for the majority of parameters that there is significant improvement on the constraints obtained from satellite CMB polarization data. We split a multi-experiment CMB data set into temperature and polarization subsets and show that the best-fit confidence regions for the ΛCDM six-parameter cosmological model are consistent with each other, and that polarization data reduces the confidence regions on all parameters. We provide the best limits on parameters from QUaD EE/BB polarization data and we find best-fit parameters from the multi-experiment CMB data set using the optimal pivot scale of k_p = 0.013 Mpc^(–1) to be {h^2Ω_c, h^2Ω_b, H_0, A_s, n_s, τ} = {0.113, 0.0224, 70.6, 2.29 × 10^(–9), 0.960, 0.086}
Engineered bamboo for structural applications
Bamboo is a rapidly renewable material that has many applications in construction. Engineered bamboo products result from processing the raw bamboo culm into a laminated composite, similar to glue-laminated timber products. These products allow the material to be used in standardised sections and have less inherent variability than the natural material. The present work investigates the mechanical properties of two types of commercially available products – bamboo scrimber and laminated bamboo sheets – and compares these to timber and engineered timber products. It is shown that engineered bamboo products have properties that are comparable to or surpass that of timber and timber-based products. Potential limitations to use in structural design are also discussed. The study contributes to a growing body of research on engineered bamboo and presents areas in which further investigation is needed.The presented work is supported by EPRSC Grant EP/K023403/1 and the Newton Trust, and forms part of a collaboration between the University of Cambridge, Massachusetts Institute of Technology (MIT) and University of British Columbia (UBC).This is the published version. It was first published at http://www.sciencedirect.com/science/article/pii/S0950061815001117
Thermal Kinetic Inductance Detectors for Millimeter-Wave Astrophysics
Thermal Kinetic Inductance Detectors (TKIDs) combine the excellent noise performance of traditional bolometers with a radio frequency (RF) multiplexing architecture that enables the large detector counts needed for the next generation of millimeter-wave instruments. Here we present dark prototype TKID pixels that demonstrate a noise equivalent power NEP = 2×10⁻¹⁷√W/Hz with a 1/f knee at 0.1 Hz, suitable for background-limited noise performance at 150 GHz from a ground-based site. We discuss the optimizations in the device design and fabrication techniques to realize optimal electrical performance and high quality factors at a bath temperature of 250 mK
Interplay between field-induced and frustration-induced quantum criticalities in the frustrated two-leg Heisenberg ladder
The antiferromagnetic Heisenberg two-leg ladder in the presence of
frustration and an external magnetic field is a system that is characterized by
two sorts of quantum criticalities, not only one. One criticality is the
consequence of intrinsic frustration, and the other one is a result of the
external magnetic field. So the behaviour of each of them in the presence of
the other deserves to be studied. Using the Jordan-Wigner transformation in
dimensions higher than one and bond-mean-field theory we examine the interplay
between the field-induced and frustration-induced quantum criticalities in this
system. The present work could constitute a prototype for those systems showing
multiple, perhaps sometimes competing, quantum criticalities. We calculate
several physical quantities like the magnetization and spin susceptibility as
functions of field and temperature.Comment: 9 pages, 8 figures, submitted to the Canadian Journal of Physic
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