1,382 research outputs found
“A Lover’s Complaint”: Bad Shakespeare, or Not Even That?
In this essay, author Madeline Duvall argues in favor of attributing A Lover\u27s Complaint to William Shakespeare. She observes the publication history and historical context of A Lover\u27s Complaint, as well as its metaphorical, prosodic, and thematic similarities to other works of Shakespeare, most prominently his sonnets and The Rape of Lucrece. To make her argument, the author cites other statistical and historical studies of A Lover\u27s Complaint, and provides her own line-by-line analysis of the work in order to find matching words
Time-distance helioseismology: Sensitivity of f-mode travel times to flows
Time-distance helioseismology has shown that f-mode travel times contain
information about horizontal flows in the Sun. The purpose of this study is to
provide a simple interpretation of these travel times. We study the interaction
of surface-gravity waves with horizontal flows in an incompressible,
plane-parallel solar atmosphere. We show that for uniform flows less than
roughly 250 m s, the travel-time shifts are linear in the flow
amplitude. For stronger flows, perturbation theory up to third order is needed
to model waveforms. The case of small-amplitude spatially-varying flows is
treated using the first-order Born approximation. We derive two-dimensional
Fr\'{e}chet kernels that give the sensitivity of travel-time shifts to local
flows. We show that the effect of flows on travel times depends on wave damping
and on the direction from which the observations are made. The main physical
effect is the advection of the waves by the flow rather than the advection of
wave sources or the effect of flows on wave damping. We compare the
two-dimensional sensitivity kernels with simplified three-dimensional kernels
that only account for wave advection and assume a vertical line of sight. We
find that the three-dimensional f-mode kernels approximately separate in the
horizontal and vertical coordinates, with the horizontal variations given by
the simplified two-dimensional kernels. This consistency between quite
different models gives us confidence in the usefulness of these kernels for
interpreting quiet-Sun observations.Comment: 34 pages, accepted to Astrophysical Journa
Comparison of acoustic travel-time measurement of solar meridional circulation from SDO/HMI and SOHO/MDI
Time-distance helioseismology is one of the primary tools for studying the
solar meridional circulation. However, travel-time measurements of the
subsurface meridional flow suffer from a variety of systematic errors, such as
a center-to-limb variation and an offset due to the P-angle uncertainty of
solar images. Here we apply the time-distance technique to contemporaneous
medium-degree Dopplergrams produced by SOHO/MDI and SDO/HMI to obtain the
travel-time difference caused by meridional circulation throughout the solar
convection zone. The P-angle offset in MDI images is measured by
cross-correlating MDI and HMI images. The travel-time measurements in the
south-north and east-west directions are averaged over the same observation
period for the two data sets and then compared to examine the consistency of
MDI and HMI travel times after correcting the systematic errors.
The offsets in the south-north travel-time difference from MDI data induced
by the P-angle error gradually diminish with increasing travel distance.
However, these offsets become noisy for travel distances corresponding to waves
that reach the base of the convection zone. This suggests that a careful
treatment of the P-angle problem is required when studying a deep meridional
flow. After correcting the P-angle and the removal of the center-to-limb
effect, the travel-time measurements from MDI and HMI are consistent within the
error bars for meridional circulation covering the entire convection zone. The
fluctuations observed in both data sets are highly correlated and thus indicate
their solar origin rather than an instrumental origin. Although our results
demonstrate that the ad hoc correction is capable of reducing the wide
discrepancy in the travel-time measurements from MDI and HMI, we cannot exclude
the possibility that there exist other systematic effects acting on the two
data sets in the same way.Comment: accepted for publication in A&
Solar meridional circulation from twenty-one years of SOHO/MDI and SDO/HMI observations: Helioseismic travel times and forward modeling in the ray approximation
The south-north travel-time differences are measured by applying
time-distance helioseismology to the MDI and HMI medium-degree Dopplergrams
covering May 1996-April 2017. Our data analysis corrects for several sources of
systematic effects: P-angle error, surface magnetic field effects, and
center-to-limb variations. An interpretation of the travel-time measurements is
obtained using a forward-modeling approach in the ray approximation. The
travel-time differences are similar in the southern hemisphere for cycles 23
and 24. However, they differ in the northern hemisphere between cycles 23 and
24. Except for cycle 24's northern hemisphere, the measurements favor a
single-cell meridional circulation model where the poleward flows persist down
to 0.8 , accompanied by local inflows toward the activity belts
in the near-surface layers. Cycle 24's northern hemisphere is anomalous:
travel-time differences are significantly smaller when travel distances are
greater than 20. This asymmetry between northern and southern
hemispheres during cycle 24 was not present in previous measurements (e.g.,
Rajaguru & Antia 2015), which assumed a different P-angle error correction
where south-north travel-time differences are shifted to zero at the equator
for all travel distances. In our measurements, the travel-time differences at
the equator are zero for travel distances less than 30, but they
do not vanish for larger travel distances. This equatorial offset for large
travel distances need not be interpreted as a deep cross-equator flow; it could
be due to the presence of asymmetrical local flows at the surface near the end
points of the acoustic ray paths.Comment: accepted for publication in A&
Atmospheric Models for Mars Aerocapture
level Mars atmospheric model. Applications include systems design, performance analysis, and operations planning for aerobraking, entry descent and landing, and aerocapture. Typical Mars aerocapture periapsis altitudes (for systems with rigid- aeroshell heat shields) are about 50 km. This altitude is above the 0-40 km height range covered by Mars Global Surveyor Thermal Emission Spectrometer (TES) nadir observations. Recently, TES limb sounding data have been made available, spanning more than two Mars years (more than 200,000 data profiles) with altitude coverage up to about 60 km, well within the height range of interest for aerocapture. Results are presented comparing Mars-GRAM atmospheric density with densities from TES nadir and limb sounding observations. A new Mars-GRAM feature is described which allows individual TES nadir or limb profiles to be extracted from the large TES databases, and to be used as an optional replacement for standard Mars-GRAM background (climatology) conditions. For Monte-Carlo applications such as aerocapture guidance and control studies, Mars-GRAM perturbations are available using these TES profile background conditions
Impact of Locally Suppressed Wave sources on helioseismic travel times
Wave travel-time shifts in the vicinity of sunspots are typically interpreted
as arising predominantly from magnetic fields, flows, and local changes in
sound speed. We show here that the suppression of granulation related wave
sources in a sunspot can also contribute significantly to these travel-time
shifts, and in some cases, an asymmetry between in and outgoing wave travel
times. The tight connection between the physical interpretation of travel times
and source-distribution homogeneity is confirmed. Statistically significant
travel-time shifts are recovered upon numerically simulating wave propagation
in the presence of a localized decrease in source strength. We also demonstrate
that these time shifts are relatively sensitive to the modal damping rates;
thus we are only able to place bounds on the magnitude of this effect. We see a
systematic reduction of 10-15 seconds in -mode mean travel times at short
distances ( Mm) that could be misinterpreted as arising from a
shallow (thickness of 1.5 Mm) increase ( 4%) in the sound speed. At
larger travel distances ( Mm) a 6-13 s difference between the ingoing
and outgoing wave travel times is observed; this could mistakenly be
interpreted as being caused by flows.Comment: Revised version. Submitted to Ap
Parents' Sense of “Entitlement” in Adoptive and Nonadoptive Families
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72242/1/j.1545-5300.1996.00441.x.pd
Mars Aerocapture and Validation of Mars-GRAM with TES Data
Mars Global Reference Atmospheric Model (Mars-GRAM) is a widely-used engineering- level Mars atmospheric model. Applications include systems design, performance analysis, and operations planning for aerobraking, entry descent and landing, and aerocapture. Typical Mars aerocapture periapsis altitudes (for systems with rigid-aeroshell heat shields) are about 50 km. This altitude is above the 0-40 km height range covered by Mars Global Surveyor Thermal Emission Spectrometer (TES) nadir observations. Recently, TES limb sounding data have been made available, spanning more than two Mars years (more than 200,000 data profiles) with altitude coverage up to about 60 km, well within the height range of interest for aerocapture. Results are presented comparing Mars-GRAM atmospheric density with densities from TES nadir and limb sounding observations. A new Mars-GRAM feature is described which allows individual TES nadir or limb profiles to be extracted from the large TES databases, and to be used as an optional replacement for standard Mars-GRAM background (climatology) conditions. For Monte-Carlo applications such as aerocapture guidance and control studies, Mars-GRAM perturbations are available using these TES profile background conditions
Global-scale equatorial Rossby waves as an essential component of solar internal dynamics
The Sun's complex dynamics is controlled by buoyancy and rotation in the
convection zone and by magnetic forces in the atmosphere and corona. While
small-scale solar convection is well understood, the dynamics of large-scale
flows in the solar convection zone is not explained by theory or simulations.
Waves of vorticity due to the Coriolis force, known as Rossby waves, are
expected to remove energy out of convection at the largest scales. Here we
unambiguously detect and characterize retrograde-propagating vorticity waves in
the shallow subsurface layers of the Sun at angular wavenumbers below fifteen,
with the dispersion relation of textbook sectoral Rossby waves. The waves have
lifetimes of several months, well-defined mode frequencies below 200 nHz in a
co-rotating frame, and eigenfunctions of vorticity that peak at the equator.
Rossby waves have nearly as much vorticity as the convection at the same
scales, thus they are an essential component of solar dynamics. We find a
transition from turbulence-like to wave-like dynamics around the Rhines scale
of angular wavenumber of twenty; this might provide an explanation for the
puzzling deficit of kinetic energy at the largest spatial scales.Comment: This is the submitted version of the paper published in Nature
Astronomy. 23 pages, 8 figures, 1 tabl
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A Computer Assisted Micro-Dye Uptake Interferon Assay System
A new rapid computer assisted micro-titer plate interferon assay system was developed and characterized for use in high capacity clinical and research applications. The biological aspect of the assay was a modification of the assay methods of Finter, Armstrong and McManus. It was an application of spectrophotometric quantification of the reduction of viral cytopathic effect (CPE) as reflected by neutral red dye uptake by viable cells. A computer program was developed for the extrapolation of raw data to reference interferon units
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