365 research outputs found
Baroque Optics and the Disappearance of the Observer: From Kepler’s Optics to Descartes’ Doubt
In the seventeenth century the human observer gradually disappeared from optical treatises. It was a paradoxical process: the naturalization of the eye estranged the mind from its objects. Turned into a material optical instrument, the eye no longer furnished the observer with genuine representations of visible objects. It became a mere screen, on which rested a blurry array of light stains, accidental effects of a purely causal process. It thus befell the intellect to decipher one natural object—a flat image of no inherent epistemic value—as the vague, reversed reflection of another, wholly independent object. In reflecting on and trespassing the boundaries between natural and artificial, orderly and disorderly, this optical paradox was a Baroque intellectual phenomenon; and it was the origin of Descartes’ celebrated doubt— whether we know anything at all
Testing minimal lepton flavor violation with extra vector-like leptons at the LHC
Models of minimal lepton flavor violation where the seesaw scale is higher
than the relevant flavor scale predict that all lepton flavor violation is
proportional to the charged lepton Yukawa matrix. If extra vector-like leptons
are within the reach of the LHC, it will be possible to test the resulting
predictions in ATLAS/CMS.Comment: 19 pages, 8 figure
Models for Monolayers Adsorbed on a Square Substrate
Motivated by recent experimental studies of Hg and Pb monolayers on Cu(001)
we introduce a zero temperature model of a monolayer adsorbed on a square
substrate. Lennard-Jones potentials are used to describe the interaction
between pairs of adlayer-adlayer and adlayer-substrate atoms. We study a
special case in which the monolayer atoms form a perfect square structure and
the lattice constant, position and orientation with respect to the substrate
can vary to minimize the energy. We introduce a rule based on the Farey tree
construction to generate systematically the most energetically favored phases
and use it to calculate the phase diagram in this model.Comment: 14 pages, Table (included), Two Figures (available upon request).
SU-92-150
Clustering of Very Red Galaxies in the Las Campanas IR Survey
We report results from the first 1000 square arc-minutes of the Las Campanas
IR survey. We have imaged 1 square degree of high latitude sky in six distinct
fields to a 5-sigma H-band depth of 20.5 (Vega). Optical imaging in the
V,R,I,and z' bands allow us to select color subsets and
photometric-redshift-defined shells. We show that the angular clustering of
faint red galaxies (18 3) is an order of magnitude stronger
than that of the complete H-selected field sample. We employ three approaches
to estimate in order to invert w(theta) to derive r_0. We find that our
n(z) is well described by a Gaussian with = 1.2, sigma(z) = 0.15. From this
we derive a value for r_0 of 7 (+2,-1) co-moving H^{-1} Mpc at = 1.2. This
is a factor of ~ 2 larger than the clustering length for Lyman break galaxies
and is similar to the expectation for early type galaxies at this epoch.Comment: 5 pages, 2 figures, 1 table. To appear in proceedings of the
ESO/ECF/STScI workshop "Deep Fields" held in Garching, Germany, 9-12 October
200
Spectroscopic detection of quasars in the 2dF Galaxy Redshift Survey
The 100,000 spectra from the 2 degree Field Galaxy Redshift Survey (2dFGRS)
in the 100k Public Data Release represent the largest single compilation of
galaxy spectra available. By virtue of its sheer size and the properties of the
photometric catalogue that defines the sample, the 2dFGRS is expected to
contain a number of potentially interesting objects other than galaxies. A
search of the spectra in the 100k Data Release results in a census of 55
candidate high-redshift (z > 0.3) quasars. One additional 2dFGRS spectrum of a
low-redshift galaxy shows an apparent anomalous broad emission feature perhaps
indicating the presence of a gravitationally lensed quasar. These objects have
been identified primarily using two automated routines that we have developed
specifically for this task, one of which uses a matched filter and the other a
wavelet transform. A number of the quasar images possess complicated
morphologies, suggesting the presence of either diffuse foreground objects
along the line-of-sight or very nearby point sources. The quasar catalogue will
form a target list for future absorption and lensing studies, as well as
providing an assessment of the loss of quasars with non-stellar images from the
companion 2dF QSO Redshift Survey.Comment: Latex 13 pages, 8 figures. Accepted for publication in MNRA
Numerical Simulation of an EUV Coronal Wave Based on the February 13, 2009 CME Event Observed by STEREO
On 13 February 2009, a coronal wave -- CME -- dimming event was observed in
quadrature by the STEREO spacecraft. We analyze this event using a
three-dimensional, global magnetohydrodynamic (MHD) model for the solar corona.
The numerical simulation is driven and constrained by the observations, and
indicates where magnetic reconnection occurs between the expanding CME core and
surrounding environment. We focus primarily on the lower corona, extending out
to ; this range allows simultaneous comparison with both EUVI and
COR1 data. Our simulation produces a diffuse coronal bright front remarkably
similar to that observed by STEREO/EUVI at 195 \AA. It is made up of \emph{two}
components, and is the result of a combination of both wave and non-wave
mechanisms.
The CME becomes large-scale quite low ( 200 Mm) in the corona. It is not,
however, an inherently large-scale event; rather, the expansion is facilitated
by magnetic reconnection between the expanding CME core and the surrounding
magnetic environment. In support of this, we also find numerous secondary
dimmings, many far from the initial CME source region. Relating such dimmings
to reconnecting field lines within the simulation provides further evidence
that CME expansion leads to the "opening" of coronal field lines on a global
scale. Throughout the CME expansion, the coronal wave maps directly to the CME
footprint.
Our results suggest that the ongoing debate over the "true" nature of diffuse
coronal waves may be mischaracterized. It appears that \emph{both} wave and
non-wave models are required to explain the observations and understand the
complex nature of these events
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