10,021 research outputs found
Mrs. Foot on the Sufficiency of Hypothetical Imperatives
The issue between Mrs. Foot and Immanuel Kant is this: does the reason why one ought to do something always lie in expected, desired consequences, so that the command to do it is hypothetical? Mrs. Foot argues that the answer is “yes,” and that any alternative use of “ought” is unintelligible. I think that her argument for this claim is stronger when it is directed at the intuitionists than when it is directed at Kant. An analogy with logic, which is full of categorical imperatives, supports Kant’s position against Mrs. Foot
Biases in the polarization position angles in the NVSS point source catalogue
We have examined the statistics of the polarization position angles
determined for point sources in the NRAO-VLA sky survey (NVSS) and find that
there is a statistically significant bias toward angles which are multiples of
45 degrees. The formal probability that the polarization angles are drawn from
a uniform distribution is exponentially small. When the sample of those NVSS
sources with polarizations detected with a signal to noise 3 is split
either around the median polarized flux density or the median fractional
polarization, the effect appears to be stronger for the more highly polarized
sources. Regions containing strong sources and regions at low galactic
latitudes are not responsible for the non-uniform distribution of position
angles. We identify CLEAN bias as the probable cause of the dominant effect,
coupled with small multiplicative and additive offsets on each of the Stokes
parameters. Our findings have implications for the extraction of science, such
as information concerning galactic magnetic fields, from large scale
polarization surveys
Testing of Candidate Rigid Heatshield Materials at LHMEL for the Entry, Descent, and Landing Technology Development Project
The material testing results described in this paper were part of a material development program of vendor-supplied, proposed heat shield materials. The goal of this program was to develop low density, rigid material systems with an appreciable weight savings over phenolic-impregnated carbon ablator (PICA) while improving material response performance. New technologies, such as PICA-like materials in honeycomb or materials with variable density through-the-thickness were tested. The material testing took place at the Wright-Patterson Air Force Base Laser Hardened Materials Laboratory (LHMEL) using a 10.6 micron CO2 laser operating with the test articles immersed in a nitrogen-gas environment at 1 atmosphere pressure. Test measurements included thermocouple readings of in-depth temperatures, pyrometer readings of surface temperatures, weight scale readings of mass loss, and sectioned-sample readings of char depth. Two laser exposures were applied. The first exposure was at an irradiance of 450 W/cm2 for 50 or 60 seconds to simulate an aerocapture maneuver. The second laser exposure was at an irradiance of 115 W/cm2 for 100 seconds to simulate a planetary entry. Results from Rounds 1 and 2 of these screening tests are summarized
Are rotation curves in NGC 6946 and the Milky Way magnetically supported?
Following the model of magnetically supported rotation of spiral galaxies,
the inner disk rotation is dominated by gravity but magnetism is not negligible
at radii where the rotation curve becomes flat, and indeed becomes dominant at
very large radii. Values of the order of 1 G, or even less, produce a
centripetal force when the absolute value of the slope of the curve [,
R] (azimuthal field strength versus radius) is less than . The
-profile is called the critical profile. From this hypothesis, the
following is to be expected: at large radii, a ``subcritical'' profile (slope
flatter than ); at still larger radii a -profile becoming
asymptotically critical as the density becomes asymptotically vanishing. Recent
observations of magnetic fields in NGC 6946 and the Milky Way are in very good
agreement with these predictions. This magnetic alternative requires neither
galactic dark matter (DM) nor modification of fundamental laws of physics, but
it is not in conflict with these hypotheses, especially with the existence of
cosmological cold dark matter (CDM).Comment: 11 pages, 2 figures, accepted for publication in Astron. Astrophy
Multi-epoch sub-arcsecond [Fe II] spectroimaging of the DG Tau outflows with NIFS-I. First data epoch
Investigating the outflows emanating from young stellar objects (YSOs) on sub-arcsecond scales provides important clues to the nature of the underlying accretion-ejection process occurring near the central protostar. We have investigated the structures and kinematics of the outflows driven by the YSO DG Tauri, using the Near-infrared Integral Field Spectrograph (NIFS) on Gemini North. The blueshifted outflow shows two distinct components in [Fe II] 1.644 μm emission, which are separated using multicomponent line fitting. Jet parameters are calculated for the high-velocity component. A stationary recollimation shock is observed, in agreement with previous X-ray and far-ultraviolet observations. The presence of this shock indicates that the innermost streamlines of the high-velocity component are launched at a very small radius, 0.01-0.15 au, from the central star. The jet accelerates and expands downstream of the recollimation shock; the 'acceleration' is likely a sign of velocity variations in the jet. No evidence of rotation is found, and we compare this non-detection to previous counterclaims. Moving jet knots, likely the result of the jet velocity variations, are observed. One of these knots moves more slowly than previously observed knots, and the knot ejection interval appears to be non-periodic. An intermediate-velocity component surrounds this central jet, and is interpreted as the result of a turbulent mixing layer along the jet boundaries generated by lateral entrainment of material by the high-velocity jet. Lateral entrainment requires the presence of a magnetic field of strength a few mG or less at hundreds of au above the disc surface, which is argued to be a reasonable proposition. In H2 1-0 S(1) 2.1218 μm emission, a wide-angle, intermediate-velocity blueshifted outflow is observed. Both outflows are consistent with being launched by a magnetocentrifugal disc wind, although an X-wind origin for the high-velocity jet cannot be ruled out. The redshifted outflow of DG Tau takes on a bubble-shaped morphology, which will be discussed in a future paper
The paths not (yet) taken: Ulrich Beck, the ‘cosmopolitized world’ and security studies
Variable accretion as a mechanism for brightness variations in T Tau S
(Note: this is a shortened version of the original A&A-style structured
abstract). The physical nature of the strong photometric variability of T Tau
Sa, the more massive member of the Southern "infrared companion" to T Tau, has
long been debated. Intrinsic luminosity variations due to variable accretion
were originally proposed but later challenged in favor of apparent fluctuations
due to time-variable foreground extinction. In this paper we use the timescale
of the variability as a diagnostic for the underlying physical mechanism.
Because the IR emission emerging from Sa is dominantly thermal emission from
circumstellar dust at <=1500K, we can derive a minimum size of the region
responsible for the time-variable emission. In the context of the variable
foreground extinction scenario, this region must be (un-) covered within the
variability timescale, which implies a minimum velocity for the obscuring
foreground material. If this velocity supercedes the local Kepler velocity we
can reject foreground extinction as a valid variability mechanism. The variable
accretion scenario allows for shorter variability timescales since the
variations in luminosity occur on much smaller scales, essentially at the
surface of the star, and the disk surface can react almost instantly on the
changing irradiation with a higher or lower dust temperature and according
brightness. We have detected substantial variations at long wavelengths in T
Tau S: +26% within four days at 12.8 micron. We show that this short-term
variability cannot be due to variable extinction and instead must be due to
variable accretion. Using a radiative transfer model of the Sa disk we show
that variable accretion can in principle also account for the much larger
(several magnitude) variations observed on timescales of several years. For the
long-term variability, however, also variable foreground extinction is a viable
mechanism.Comment: 15 pages, 8 figures, Accepted for publication in Astronomy and
Astrophysic
Longitudinal evaluation of cognitive functioning in young children with type 1 diabetes over 18 months
OBJECTIVE: Decrements in cognitive function may already be evident in young children with type 1 diabetes (T1D). Here we report prospectively acquired cognitive results over 18 months in a large cohort of young children with and without T1D. METHODS: 144 children with T1D (mean HbA1c: 7.9%) and 70 age-matched healthy controls (mean age both groups 8.5 years; median diabetes duration 3.9 yrs; mean age of onset 4.1 yrs) underwent neuropsychological testing at baseline and after 18-months of follow-up. We hypothesized that group differences observed at baseline would be more pronounced after 18 months, particularly in those T1D patients with greatest exposure to glycemic extremes. RESULTS: Cognitive domain scores did not differ between groups at the 18 month testing session and did not change differently between groups over the follow-up period. However, within the T1D group, a history of diabetic ketoacidosis (DKA) was correlated with lower Verbal IQ and greater hyperglycemia exposure (HbA1c area under the curve) was inversely correlated to executive functions test performance. In addition, those with a history of both types of exposure performed most poorly on measures of executive function. CONCLUSIONS: The subtle cognitive differences between T1D children and nondiabetic controls observed at baseline were not observed 18 months later. Within the T1D group, as at baseline, relationships between cognition (VIQ and executive functions) and glycemic variables (chronic hyperglycemia and DKA history) were evident. Continued longitudinal study of this T1D cohort and their carefully matched healthy comparison group is planned
Real-space grid representation of momentum and kinetic energy operators for electronic structure calculations
We show that the central finite difference formula for the first and the
second derivative of a function can be derived, in the context of quantum
mechanics, as matrix elements of the momentum and kinetic energy operators
using, as a basis set, the discrete coordinate eigenkets
defined on the uniform grid . Simple closed form expressions of the
matrix elements are obtained starting from integrals involving the canonical
commutation rule. A detailed analysis of the convergence toward the continuum
limit with respect to both the grid spacing and the approximation order is
presented. It is shown that the convergence from below of the eigenvalues in
electronic structure calculations is an intrinsic feature of the finite
difference method
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