698 research outputs found
Report on estimating the size of dolphin schools, based on data obtained during a charter cruise of the M/V Gina Anne, October 11 -November 25, 1979
Estimates of dolphin school sizes made by observers and crew
members aboard tuna seiners or by observers on ship or aerial surveys are important components of population estimates of dolphins which are involved in the yellowfin tuna fishery in the eastern Pacific. Differences in past estimates made from tuna seiners and research ships and aircraft have been noted by Brazier (1978). To compare various methods of estimating dolphin school sizes a research cruise was undertaken with the following major objectives:
1) compare estimates made by observers aboard a tuna seiner and in the ship's helicopter, from aerial photographs, and from counts made at the backdown channel,
2) compare estimates of observers who are told the count of the school size after making their estimate to the observer who is not aware of the count to determine if observers can learn to estimate more accurately, and
3) obtain movie and still photographs of dolphin schools of known size at various stages of chase, capture and release to be used for observer training.
The secondary objectives of the cruise were to:
1) obtain life history specimens and data from any dolphins that were killed incidental to purse seining. These specimens and data were to be analyzed by the U.S. National Marine Fisheries Service ( NMFS ) ,
2) record evasion tactics of dolphin schools by observing them from the helicopter while the seiner approached the school,
3) examine alternative methods for estimating the distance and bearing of schools where they were first sighted,
4) collect the Commission's standard cetacean sighting, set log and daily activity data and expendable bathythermograph data.
(PDF contains 31 pages.
A first-principles study of oxygen vacancy pinning of domain walls in PbTiO3
We have investigated the interaction of oxygen vacancies and 180-degree
domain walls in tetragonal PbTiO3 using density-functional theory. Our
calculations indicate that the vacancies do have a lower formation energy in
the domain wall than in the bulk, thereby confirming the tendency of these
defects to migrate to, and pin, the domain walls. The pinning energies are
reported for each of the three possible orientations of the original Ti-O-Ti
bonds, and attempts to model the results with simple continuum models are
discussed.Comment: 8 pages, with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/lh_dw/index.htm
Separate and overlapping brain areas encode subjective value during delay and effort discounting
AbstractMaking decisions about rewards that involve delay or effort requires the integration of value and cost information. The brain areas recruited in this integration have been well characterized for delay discounting. However only a few studies have investigated how effort costs are integrated into value signals to eventually determine choice. In contrast to previous studies that have evaluated fMRI signals related to physical effort, we used a task that focused on cognitive effort. Participants discounted the value of delayed and effortful rewards. The value of cognitively effortful rewards was represented in the anterior portion of the inferior frontal gyrus and dorsolateral prefrontal cortex. Additionally, the value of the chosen option was encoded in the anterior cingulate cortex, caudate, and cerebellum. While most brain regions showed no significant dissociation between effort discounting and delay discounting, the ACC was significantly more activated in effort compared to delay discounting tasks. Finally, overlapping regions within the right orbitofrontal cortex and lateral temporal and parietal cortices encoded the value of the chosen option during both delay and effort discounting tasks. These results indicate that encoding of rewards discounted by cognitive effort and delay involves partially dissociable brain areas, but a common representation of chosen value is present in the orbitofrontal, temporal and parietal cortices
Effect of Axial Load on the Flexural Properties of an Elastomeric Total Disc Replacement
Study Design. Twelve Cadisc-L devices were subjected to flexion (0°–6°) and extension (0° to -3°) motions at compressive loads between 500 N and 2000 N at a flexural rate between 0.25°/s and 3.0°/s.\ud
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Objective. To quantify the change in flexural properties of the Cadisc-L (elastomeric device), when subjected to increasing magnitudes of axial load and at different flexural rates.\ud
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Summary of Background Data. The design of motion preservation devices, used to replace degenerated intervertebral discs, is commonly based on a low-friction, ball-and-socket-articulating joint. Recently, elastomeric implants have been developed that attempt to provide mechanical and motion properties that resemble those of the natural disc more closely.\ud
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Methods. Twelve Cadisc-L devices (MC-10 mm-9° and MC-10 mm-12° size) were supplied by Ranier Technology Ltd (Cambridge, United Kingdom). The devices were hydrated and tested using a Bose spinal disc-testing machine (Bose Corporation, ElectroForce Systems Group, Eden Prairie, MN) in Ringer's solution at 37°C. A static load of 500 N was applied to a device and it was then subjected to motions of 0° to 6° to 0° (flexion) and 0° to -3° to 0° (extension) at a flexural rate of 0.25°/s, 0.5°/s, 1.0°/s, 1.5°/s, 2.0°/s, and 3.0°/s. Tests were repeated at 1000 N, 1500 N, and 2000 N.\ud
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Results. Regression analyses showed a significant ( > 0.99, < 0.05) linear increase in bending moment and flexural stiffness with flexion and extension angles (at 1000 N and higher loads)—a significant (> 0.994, < 0.05) linear decrease in flexural stiffness in flexion and extension as flexural rate increased.\ud
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Conclusion. The bending moment of the Cadisc-L increased linearly with flexion and extension angles at 1000 N and higher loads. Flexural stiffness increased with compressive load but decreased with flexural rate.\ud
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Emergence of Skyrme crystal in Gross-Neveu and 't Hooft models at finite density
We study two-dimensional, large field theoretic models (Gross-Neveu
model, 't Hooft model) at finite baryon density near the chiral limit. The same
mechanism which leads to massless baryons in these models induces a breakdown
of translational invariance at any finite density. In the chiral limit baryonic
matter is characterized by a spatially varying chiral angle with a wave number
depending only on the density. For small bare quark masses a sine-Gordon kink
chain is obtained which may be regarded as simplest realization of the Skyrme
crystal for nuclear matter. Characteristic differences between confining and
non-confining models are pointed out.Comment: 27 pages, 11 figures, added reference, corrected sig
Short-term changes observed in multi-parametric liver MRI following therapy with direct acting antivirals in chronic hepatitis C virus patients
Methods: We applied multiparametric MRI to assess changes in liver composition, perfusion and blood flow in 17 patients before DAA therapy and after treatment completion (within 12 weeks of last DAA tablet swallowed).Results: We observed changes in hepatic composition indicated by a reduction in both liver longitudinal relaxation time (T1, 35±4 ms), transverse relaxation time (T2, 2.5±0.8 ms; T2* 3.0±0.7 ms) and liver perfusion (28.1±19.7ml/100g/min) which we suggest are linked to reduced pro-inflammatory milieu, including interstitial oedema, within the liver. No changes were observed in liver or spleen blood flow, splenic perfusion, or SMA blood flow.Conclusion: For the first time, our study has shown that treatment of HCV with DAAs in patients with cirrhosis leads to an acute reduction in liver T1, T2, T2* and an increase in liver perfusion measured using MR parameters. The ability of MRI to characterise changes in the angio-architecture of patients with cirrhosis after intervention in the short term will enhance our understanding of the natural history of regression of liver disease and potentially influence clinical decision algorithms
Is cosmology consistent?
We perform a detailed analysis of the latest CMB measurements (including
BOOMERaNG, DASI, Maxima and CBI), both alone and jointly with other
cosmological data sets involving, e.g., galaxy clustering and the Lyman Alpha
Forest. We first address the question of whether the CMB data are internally
consistent once calibration and beam uncertainties are taken into account,
performing a series of statistical tests. With a few minor caveats, our answer
is yes, and we compress all data into a single set of 24 bandpowers with
associated covariance matrix and window functions. We then compute joint
constraints on the 11 parameters of the ``standard'' adiabatic inflationary
cosmological model. Out best fit model passes a series of physical consistency
checks and agrees with essentially all currently available cosmological data.
In addition to sharp constraints on the cosmic matter budget in good agreement
with those of the BOOMERaNG, DASI and Maxima teams, we obtain a heaviest
neutrino mass range 0.04-4.2 eV and the sharpest constraints to date on gravity
waves which (together with preference for a slight red-tilt) favors
``small-field'' inflation models.Comment: Replaced to match accepted PRD version. 14 pages, 12 figs. Tiny
changes due to smaller DASI & Maxima calibration errors. Expanded neutrino
and tensor discussion, added refs, typos fixed. Combined CMB data, window and
covariance matrix at http://www.hep.upenn.edu/~max/consistent.html or from
[email protected]
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum
P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in
combination with WMAP and other data. Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt,
tensor modes or massive neutrinos. Adding SDSS information more than halves the
WMAP-only error bars on some parameters, tightening 1 sigma constraints on the
Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter
density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on
neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when
dropping prior assumptions about curvature, neutrinos, tensor modes and the
equation of state. Our results are in substantial agreement with the joint
analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive
consistency check with independent redshift survey data and analysis
techniques. In this paper, we place particular emphasis on clarifying the
physical origin of the constraints, i.e., what we do and do not know when using
different data sets and prior assumptions. For instance, dropping the
assumption that space is perfectly flat, the WMAP-only constraint on the
measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running
tilt, neutrino mass and equation of state in the list of free parameters, many
constraints are still quite weak, but future cosmological measurements from
SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt
figures available at http://www.hep.upenn.edu/~max/sdsspars.htm
Making Sense Through Participation
In this chapter we discuss the issue of social differences in relation to learning. In theories on co-operative learning or
collaborative learning social differences are treated as characteristics of individual learners. The focus on learning as
a social process is primarily elaborated in terms of interaction between pupils and the combined construction of knowledge. Sociocultural
theory (Vygotsky, Lave & Wenger), however, understands ‘social’ not only in terms of knowledge/meaning being constructed in
interaction with others, but also in terms of the cultural practices/activities informing these interaction processes. Learning
can be understood as increasing participating in communities of practice. As social differences are an intrinsic part of the
culture in which students are learning to participate, these are also an inherent aspect of learning processes in schools.
Students learn to participate in practices in different ways, depending on their social position, and thus develop distinguished
cultural identities. In this chapter we elaborate on this tenet, using examples from various empirical research projects on
learning in secondary education. We not only show how social differences in the cultural practices that underpin learning
influence what is learned by whom, but also explore the consequences of this perspective for the pedagogical space of the
school
The HASHTAG Project: The First Submillimeter Images of the Andromeda Galaxy from the Ground
Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome side effect of also removing the galaxy\u27s large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space telescope (Herschel or Planck) to determine the large-scale structure (the small Fourier components). Using this technique, we are carrying out the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international Large Program on the James Clerk Maxwell Telescope, with one aim being to produce the first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe the survey, the method we have developed for combining the space-based and ground-based data, and we present the first HASHTAG images of Andromeda at 450 and 850 μm. We also have created a method to predict the CO(J = 3-2) line flux across M31, which contaminates the 850 μm band. We find that while normally the contamination is below our sensitivity limit, it can be significant (up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with the predicted line emission removed
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