143 research outputs found
Magnetic properties and magnetostructural phase transitions in Ni2+xMn1-xGa shape memory alloys
A systematic study of magnetic properties of Ni2+xMn1-xGa (0 \le x \le 0.19)
Heusler alloys undergoing structural martensite-austenite transformations while
in ferromagnetic state has been performed. From measurements of spontaneous
magnetization, Ms(T), jumps \Delta M at structural phase transitions were
determined. Virtual Curie temperatures of the martensite were estimated from
the comparison of magnetization in martensitic and austenitic phases. Both
saturation magnetic moments in ferromagnetic state and effective magnetic
moments in paramagnetic state of Mn and Ni atoms were estimated and the
influence of delocalization effects on magnetism in these alloys was discussed.
The experimental results obtained show that the shift of martensitic transition
temperature depends weakly on composition. The values of this shift are in good
correspondence with Clapeyron-Clausius formalism taking into account the
experimental data on latent heat at martensite-austenite transformations.Comment: 7 pages, 8 figure
Low-loss Si-based Dielectrics for High Frequency Components of Superconducting Detectors
Silicon-based dielectric is crucial for many superconducting devices,
including high-frequency transmission lines, filters, and resonators. Defects
and contaminants in the amorphous dielectric and at the interfaces between the
dielectric and metal layers can cause microwave losses and degrade device
performance. Optimization of the dielectric fabrication, device structure, and
surface morphology can help mitigate this problem. We present the fabrication
of silicon oxide and nitride thin film dielectrics. We then characterized them
using Scanning Electron Microscopy, Atomic Force Microscopy, and
spectrophotometry techniques. The samples were synthesized using various
deposition methods, including Plasma-Enhanced Chemical Vapor Deposition and
magnetron sputtering. The films morphology and structure were modified by
adjusting the deposition pressure and gas flow. The resulting films were used
in superconducting resonant systems consisting of planar inductors and
capacitors. Measurements of the resonator properties, including their quality
factor, were performed.Comment: 4 pages, 5 figures, conferenc
CMB Polarization B-mode Delensing with SPTpol and Herschel
We present a demonstration of delensing the observed cosmic microwave
background (CMB) B-mode polarization anisotropy. This process of reducing the
gravitational-lensing generated B-mode component will become increasingly
important for improving searches for the B modes produced by primordial
gravitational waves. In this work, we delens B-mode maps constructed from
multi-frequency SPTpol observations of a 90 deg patch of sky by subtracting
a B-mode template constructed from two inputs: SPTpol E-mode maps and a lensing
potential map estimated from the map of the
CIB. We find that our delensing procedure reduces the measured B-mode power
spectrum by 28% in the multipole range ; this is shown to be
consistent with expectations from theory and simulations and to be robust
against systematics. The null hypothesis of no delensing is rejected at . Furthermore, we build and use a suite of realistic simulations to
study the general properties of the delensing process and find that the
delensing efficiency achieved in this work is limited primarily by the noise in
the lensing potential map. We demonstrate the importance of including realistic
experimental non-idealities in the delensing forecasts used to inform
instrument and survey-strategy planning of upcoming lower-noise experiments,
such as CMB-S4.Comment: 17 pages, 10 figures. Comments are welcome
Measurements of Sub-degree B-mode Polarization in the Cosmic Microwave Background from 100 Square Degrees of SPTpol Data
We present a measurement of the -mode polarization power spectrum (the
spectrum) from 100 of sky observed with SPTpol, a
polarization-sensitive receiver currently installed on the South Pole
Telescope. The observations used in this work were taken during 2012 and early
2013 and include data in spectral bands centered at 95 and 150 GHz. We report
the spectrum in five bins in multipole space, spanning the range , and for three spectral combinations: 95 GHz 95 GHz, 95
GHz 150 GHz, and 150 GHz 150 GHz. We subtract small ( in units of statistical uncertainty) biases from these spectra and
account for the uncertainty in those biases. The resulting power spectra are
inconsistent with zero power but consistent with predictions for the
spectrum arising from the gravitational lensing of -mode polarization. If we
assume no other source of power besides lensed modes, we determine a
preference for lensed modes of . After marginalizing over
tensor power and foregrounds, namely polarized emission from galactic dust and
extragalactic sources, this significance is . Fitting for a single
parameter, , that multiplies the predicted lensed -mode
spectrum, and marginalizing over tensor power and foregrounds, we find
, indicating that our measured spectra are
consistent with the signal expected from gravitational lensing. The data
presented here provide the best measurement to date of the -mode power
spectrum on these angular scales.Comment: 21 pages, 4 figure
A Measurement of the Cosmic Microwave Background Gravitational Lensing Potential from 100 Square Degrees of SPTpol Data
We present a measurement of the cosmic microwave background (CMB)
gravitational lensing potential using data from the first two seasons of
observations with SPTpol, the polarization-sensitive receiver currently
installed on the South Pole Telescope (SPT). The observations used in this work
cover 100 deg of sky with arcminute resolution at 150 GHz. Using a
quadratic estimator, we make maps of the CMB lensing potential from
combinations of CMB temperature and polarization maps. We combine these lensing
potential maps to form a minimum-variance (MV) map. The lensing potential is
measured with a signal-to-noise ratio of greater than one for angular
multipoles between . This is the highest signal-to-noise mass map
made from the CMB to date and will be powerful in cross-correlation with other
tracers of large-scale structure. We calculate the power spectrum of the
lensing potential for each estimator, and we report the value of the MV power
spectrum between as our primary result. We constrain the ratio
of the spectrum to a fiducial CDM model to be . Restricting ourselves to
polarized data only, we find . This measurement rejects the hypothesis of no lensing at
using polarization data alone, and at using both
temperature and polarization data.Comment: 16 pages, 8 figure
Measurements of the Temperature and E-Mode Polarization of the CMB from 500 Square Degrees of SPTpol Data
We present measurements of the -mode polarization angular auto-power
spectrum () and temperature--mode cross-power spectrum () of the
cosmic microwave background (CMB) using 150 GHz data from three seasons of
SPTpol observations. We report the power spectra over the spherical harmonic
multipole range , and detect nine acoustic peaks in the
spectrum with high signal-to-noise ratio. These measurements are the most
sensitive to date of the and power spectra at and , respectively. The observations cover 500 deg, a fivefold increase
in area compared to previous SPTpol analyses, which increases our sensitivity
to the photon diffusion damping tail of the CMB power spectra enabling tighter
constraints on \LCDM model extensions. After masking all sources with
unpolarized flux mJy we place a 95% confidence upper limit on residual
polarized point-source power of at , suggesting that the damping tail
dominates foregrounds to at least with modest source masking. We
find that the SPTpol dataset is in mild tension with the model
(), and different data splits prefer parameter values that differ
at the level. When fitting SPTpol data at we
find cosmological parameter constraints consistent with those for
temperature. Including SPTpol data at results in a preference for
a higher value of the expansion rate (H_0 = 71.3 \pm
2.1\,\mbox{km}\,s^{-1}\mbox{Mpc}^{-1} ) and a lower value for present-day
density fluctuations ().Comment: Updated to match version accepted to ApJ. 34 pages, 17 figures, 6
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