2,484 research outputs found
Metamorphic fluids and uplift-erosion history of a portion of the Kapuskasing structural zone, Ontario, as deduced from fluid inclusions
Fluid inclusions can be used to determine the compositional evolution of fluids present in high grade metamorphic rocks (Touret, 1979) along with the general P-T path followed by the rocks during uplift and erosion (Hollister et al., 1979). In this context, samples of high grade gneisses from the Kapuskasing structural zone (KSZ, Fig. 1) of eastern Ontario were studied in an attempt to define the composition of syn- and post-metamorphic fluids and help constrain the uplift and erosion history of the KSZ. Recent work by Percival (1980), Percival and Card (1983) and Percival and Krogh (1983) shows that the KSZ represents lower crustal granulites that form the lower portion of an oblique cross section through the Archean crust, which was up faulted along a northeast striking thrust fault. The present fluid inclusion study places constraints upon the P-T path which the KSZ followed during uplift and erosion
Is the Sunyaev-Zeldovich effect responsible for the observed steepening in the spectrum of the Coma radio halo ?
The spectrum of the radio halo in the Coma cluster is measured over almost
two decades in frequency. The current radio data show a steepening of the
spectrum at higher frequencies, which has implications for models of the radio
halo origin. There is an on-going debate on the possibility that the observed
steepening is not intrinsic to the emitted radiation, but is instead caused by
the SZ effect. Recently, the Planck satellite measured the SZ signal and its
spatial distribution in the Coma cluster allowing to test this hypothesis.
Using the Planck results, we calculated the modification of the radio halo
spectrum by the SZ effect in three different ways. With the first two methods
we measured the SZ-decrement within the aperture radii used for flux
measurements of the halo at the different frequencies. First we adopted the
global compilation of data from Thierbach et al. and a reference aperture
radius consistent with those used by the various authors. Second we used the
available brightness profiles of the halo at different frequencies to derive
the spectrum within two fixed apertures, and derived the SZ-decrement using
these apertures. As a third method we used the quasi-linear correlation between
the y and the radio-halo brightness at 330 MHz discovered by Planck to derive
the modification of the radio spectrum by the SZ-decrement in a way that is
almost independent of the adopted aperture radius. We found that the spectral
modification induced by the SZ-decrement is 4-5 times smaller than that
necessary to explain the observed steepening. Consequently a break or cut-off
in the spectrum of the emitting electrons is necessary to explain current data.
We also show that, if a steepening is absent from the emitted spectrum, future
deep observations at 5 GHz with single dishes are expected to measure a halo
flux in a 40 arcmin radius that would be 7-8 times higher than currently seen.Comment: 8 pages, 6 figures, accepted in Astronomy and Astrophysics (date of
acceptance 19/08/2013
High resolution Ge/Li/ spectrometer reduces rate-dependent distortions at high counting rates
Modified spectrometer system with a low-noise preamplifier reduces rate-dependent distortions at high counting rates, 25,000 counts per second. Pole-zero cancellation minimizes pulse undershoots due to multiple time constants, baseline restoration improves resolution and prevents spectral shifts
Anderson transition of the plasma oscillations of 1D disordered Wigner lattices
We report the existence of a localization-delocalization transition in the
classical plasma modes of a one dimensional Wigner Crystal with a white noise
potential environment at T=0. Finite size scaling analysis reveals a divergence
of the localization length at a critical eigenfrequency. Further scaling
analysis indicates power law behavior of the critical frequency in terms of the
relative interaction strength of the charges. A heuristic argument for this
scaling behavior is consistent with the numerical results. Additionally, we
explore a particular realization of random-bond disorder in a one dimensional
Wigner lattice in which all of the collective modes are observed to be
localized.Comment: 4 pages, 3 figures, Typo for the localization length corrected.
Should read 1 / \n
Extragalactic Radio Sources and the WMAP Cold Spot
We detect a dip of 20-45% in the surface brightness and number counts of NVSS
sources smoothed to a few degrees at the location of the WMAP cold spot. The
dip has structure on scales of approximately 1-10 degrees. Together with
independent all-sky wavelet analyses, our results suggest that the dip in
extragalactic brightness and number counts and the WMAP cold spot are
physically related, i.e., that the coincidence is neither a statistical anomaly
nor a WMAP foreground correction problem. If the cold spot does originate from
structures at modest redshifts, as we suggest, then there is no remaining need
for non-Gaussian processes at the last scattering surface of the CMB to explain
the cold spot. The late integrated Sachs-Wolfe effect, already seen
statistically for NVSS source counts, can now be seen to operate on a single
region. To create the magnitude and angular size of the WMAP cold spot requires
a ~140 Mpc radius completely empty void at z<=1 along this line of sight. This
is far outside the current expectations of the concordance cosmology, and adds
to the anomalies seen in the CMB.Comment: revised version, ApJ, in pres
Obtaining the Quantum Fourier Transform from the Classical FFT with QR Decomposition
We present the detailed process of converting the classical Fourier Transform
algorithm into the quantum one by using QR decomposition. This provides an
example of a technique for building quantum algorithms using classical ones.
The Quantum Fourier Transform is one of the most important quantum subroutines
known at present, used in most algorithms that have exponential speed up
compared to the classical ones. We briefly review Fast Fourier Transform and
then make explicit all the steps that led to the quantum formulation of the
algorithm, generalizing Coppersmith's work.Comment: 12 pages, 1 figure (generated within LaTeX). To appear in Journal of
Computational and Applied Mathematic
EarthN: A new Earth System Nitrogen Model
The amount of nitrogen in the atmosphere, oceans, crust, and mantle have
important ramifications for Earth's biologic and geologic history. Despite this
importance, the history and cycling of nitrogen in the Earth system is poorly
constrained over time. For example, various models and proxies contrastingly
support atmospheric mass stasis, net outgassing, or net ingassing over time. In
addition, the amount available to and processing of nitrogen by organisms is
intricately linked with and provides feedbacks on oxygen and nutrient cycles.
To investigate the Earth system nitrogen cycle over geologic history, we have
constructed a new nitrogen cycle model: EarthN. This model is driven by mantle
cooling, links biologic nitrogen cycling to phosphate and oxygen, and
incorporates geologic and biologic fluxes. Model output is consistent with
large (2-4x) changes in atmospheric mass over time, typically indicating
atmospheric drawdown and nitrogen sequestration into the mantle and continental
crust. Critical controls on nitrogen distribution include mantle cooling
history, weathering, and the total Bulk Silicate Earth+atmosphere nitrogen
budget. Linking the nitrogen cycle to phosphorous and oxygen levels, instead of
carbon as has been previously done, provides new and more dynamic insight into
the history of nitrogen on the planet.Comment: 36 pages, 12 figure
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