1,271 research outputs found
Education and the Soviet aircraft industry
Cover title"#1123"--handwritten on cover"Project Education"--coverIncludes bibliographical referencesScience and technology in the Soviet schools / by Alexander Korol -- Education and the Soviet aircraft industry / Leon Trillin
Cloud-Chamber Study of the Production and Decay of Strange Particles
Out of 1242 decay events observed in a magnetic cloud chamber array triggered on penetrating showers, a total of 54 associated V-particle pairs has been obtained. All the associations observed are consistent with the "strangeness" selection rules. A statistical analysis of the numbers of double and single events has been used to obtain rough estimates of the fractions of neutral K particles and neutral hyperons which decay by "invisible" modes, and of the relative frequencies of occurrence of various production processes. The main uncertainties in the resulting values are discussed in detail
Cloud-Chamber Investigation of Charged V Particles
An analysis of 84 charged V events obtained during two years of operation of a vertical magnetic cloud-chamber array is presented. The particular features of interest which are studied in detail are the distribution of P*, the momentum of the charged secondary in the rest system of the primary, and the possible existence of a component of short lifetime (i.e., τ<5×10^-10 sec). The P* distribution from 19 slow, accurately measurable positive events is shown to imply that the large majority of these events arise from one or more two-body decays from primaries of mass approximately equal to that of the τ meson. One case turns out to be inconsistent with this interpretation, and is presumed to represent a three-body decay. The P* distribution from 6 slow, accurately measurable negative events is consistent with a single two-body decay having a P* value of about 200 Mev/c. This suggests the existence of a negative counterpart to the well-known θ0 particle, though the statistics are much too poor to permit any strong conclusion. The lifetime analysis provides strong evidence for the existence of a negative component of lifetime equal to or less than (1.3±0.6)×10^-10 sec. The transverse momentum distribution for these short-lived events is shown to suggest a two-body decay with a P* value of 201±12 Mev/c
Theoretical Transmission Spectra During Extrasolar Giant Planet Transits
The recent transit observation of HD 209458 b - an extrasolar planet orbiting
a sun-like star - confirmed that it is a gas giant and determined that its
orbital inclination is 85 degrees. This inclination makes possible
investigations of the planet atmosphere. In this paper we discuss the planet
transmission spectra during a transit. The basic tenet of the method is that
the planet atmosphere absorption features will be superimposed on the stellar
flux as the stellar flux passes through the planet atmosphere above the limb.
The ratio of the planet's transparent atmosphere area to the star area is
small, approximately 10^{-3} to 10^{-4}; for this method to work very strong
planet spectral features are necessary. We use our models of close-in
extrasolar giant planets to estimate promising absorption signatures: the
alkali metal lines, in particular the Na I and K I resonance doublets, and the
He I - triplet line at 1083.0 nm. If successful, observations
will constrain the line-of-sight temperature, pressure, and density. The most
important point is that observations will constrain the cloud depth, which in
turn will distinguish between different atmosphere models. We also discuss the
potential of this method for EGPs at different orbital distances and orbiting
non-solar-type stars.Comment: revised to agree with accepted paper, ApJ, in press. 12 page
Constraining the Physical Properties of Near-Earth Object 2009 BD
We report on Spitzer Space Telescope IRAC observations of near-Earth object
(NEO) 2009 BD that were carried out in support of the NASA Asteroid Robotic
Retrieval Mission (ARRM) concept. We did not detect 2009 BD in 25 hrs of
integration at 4.5 micron. Based on an upper-limit flux density determination
from our data, we present a probabilistic derivation of the physical properties
of this object. The analysis is based on the combination of a thermophysical
model with an orbital model accounting for the non-gravitational forces acting
upon the body. We find two physically possible solutions. The first solution
shows 2009 BD as a 2.9+/-0.3 m diameter rocky body (rho = 2.9+/-0.5 g cm-3)
with an extremely high albedo of 0.85(+0.20/-0.10) that is covered with
regolith-like material, causing it to exhibit a low thermal inertia (Gamma =
30(+20/-10) SI units). The second solution suggests 2009 BD to be a 4+/-1 m
diameter asteroid with pV = 0.45(+0.35/-0.15) that consists of a collection of
individual bare rock slabs (Gamma = 2000+/-1000 SI units, rho = 1.7(+0.7/-0.4)
g cm-3). We are unable to rule out either solution based on physical reasoning.
2009 BD is the smallest asteroid for which physical properties have been
constrained, in this case using an indirect method and based on a detection
limit, providing unique information on the physical properties of objects in
the size range smaller than 10 m.Comment: 28 pages, 8 figures, accepted for publication in Ap
The Size Distribution of Trans-Neptunian Bodies
[Condensed] We search 0.02 deg^2 for trans-Neptunian objects (TNOs) with
m<=29.2 (diameter ~15 km) using the ACS on HST. Three new objects are
discovered, roughly 25 times fewer than expected from extrapolation of the
differential sky density Sigma(m) of brighter objects. The ACS and other recent
TNO surveys show departures from a power law size distribution. Division of the
TNO sample into ``classical Kuiper belt'' (CKB) and ``Excited'' samples reveals
that Sigma(m) differs for the two populations at 96% confidence. A double power
law adequately fits all data. Implications include: The total mass of the CKB
is ~0.010 M_Earth, only a few times Pluto's mass, and is predominately in the
form of ~100 km bodies. The mass of Excited objects is perhaps a few times
larger. The Excited class has a shallower bright-end size distribution; the
largest objects, including Pluto, comprise tens of percent of the total mass
whereas the largest CKBOs are only ~2% of its mass. The predicted mass of the
largest Excited body is close to the Pluto mass; the largest CKBO is ~60 times
less massive. The deficit of small TNOs occurs for sizes subject to disruption
by present-day collisions, suggesting extensive depletion by collisions. Both
accretion and erosion appearing to have proceeded to more advanced stages in
the Excited class than the CKB. The absence of distant TNOs implies that any
distant (60 AU) population must have less than the CKB mass in the form of
objects 40 km or larger. The CKB population is sparser than theoretical
estimates of the required precursor population for short period comets, but the
Excited population could be a viable precursor population.Comment: Revised version accepted to the Astronomical Journal. Numerical
results are very slightly revised. Implications for the origins of
short-period comets are substantially revised, and tedious material on
statistical tests has been collected into a new Appendi
Spitzer/MIPS Limits on Asteroidal Dust in the Pulsar Planetary System PSR B1257+1
With the MIPS camera on Spitzer, we have searched for far-infrared emission
from dust in the planetary system orbiting pulsar PSR 1257+12. With accuracies
of 0.05 mJy at 24 um and 1.5 mJy at 70 um, photometric measurements find no
evidence for emission at these wavelengths. These observations place new upper
limits on the luminosity of dust with temperatures between 20 and 1000 K. They
are particularly sensitive to dust temperatures of 100-200 K, for which they
limit the dust luminosity to below of the pulsar's spin-down
luminosity, three orders of magnitude better than previous limits. Despite
these improved constraints on dust emission, an asteroid belt similar to the
Solar System's cannot be ruled out
Possible Observational Criteria for Distinguishing Brown Dwarfs from Planets
The difference in formation process between binary stars and planetary
systems is reflected in their composition as well as their orbital
architecture, particularly orbital eccentricity as a function of orbital
period. It is suggested here that this difference can be used as an
observational criterion to distinguish between brown dwarfs and planets.
Application of the orbital criterion suggests that with three possible
exceptions, all of the recently-discovered substellar companions discovered to
date may be brown dwarfs and not planets. These criterion may be used as a
guide for interpretation of the nature of sub-stellar mass companions to stars
in the future.Comment: LaTeX, 11 pages including 2 figures, accepted for publication in the
Astrophysical Journal Letter
Physical Properties of Near-Earth Asteroid 2011 MD
We report on observations of near-Earth asteroid 2011 MD with the Spitzer
Space Telescope. We have spent 19.9 h of observing time with channel 2 (4.5
{\mu}m) of the Infrared Array Camera and detected the target within the
2{\sigma} positional uncertainty ellipse. Using an asteroid thermophysical
model and a model of nongravitational forces acting upon the object we
constrain the physical properties of 2011 MD, based on the measured flux
density and available astrometry data. We estimate 2011 MD to be 6 (+4/-2) m in
diameter with a geometric albedo of 0.3 (+0.4/-0.2) (uncertainties are
1{\sigma}). We find the asteroid's most probable bulk density to be 1.1
(+0.7/-0.5) g cm^{-3}, which implies a total mass of (50-350) t and a
macroporosity of >=65%, assuming a material bulk density typical of
non-primitive meteorite materials. A high degree of macroporosity suggests 2011
MD to be a rubble-pile asteroid, the rotation of which is more likely to be
retrograde than prograde.Comment: 20 pages, 4 figure
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