46,458 research outputs found
The population of propellers in Saturn's A Ring
We present an extensive data set of ~150 localized features from Cassini
images of Saturn's Ring A, a third of which are demonstrated to be persistent
by their appearance in multiple images, and half of which are resolved well
enough to reveal a characteristic "propeller" shape. We interpret these
features as the signatures of small moonlets embedded within the ring, with
diameters between 40 and 500 meters. The lack of significant brightening at
high phase angle indicates that they are likely composed primarily of
macroscopic particles, rather than dust. With the exception of two features
found exterior to the Encke Gap, these objects are concentrated entirely within
three narrow (~1000 km) bands in the mid-A Ring that happen to be free from
local disturbances from strong density waves. However, other nearby regions are
similarly free of major disturbances but contain no propellers. It is unclear
whether these bands are due to specific events in which a parent body or bodies
broke up into the current moonlets, or whether a larger initial moonlet
population has been sculpted into bands by other ring processes.Comment: 31 pages, 10 figures; Accepted at A
Effective use of ERTS multisensor data in the Northern Great Plains
The author has identified the following significant results. ERTS imagery was used as a tool in the identification and refinement of soil association areas; to classify land use patterns between crop and fallow fields; to identify corn, soybeans, and oats; and to identify broad generalized range ecosystems. Various data handling techniques were developed and applied to accomplish these tasks. A map outlining soil associations and relative land values was completed on a base mosaic of ERTS imagery and is included as an appendix to the report
Observations on groundwater recharge in the Westdale catchment
A study of the role of groundwater carriers and barriers in controlling salinity was carried out in the Westdale Catchment by Lewis and McConnell (in preparation). Although that study was primarily concerned with groundwater flow and discharge processes, the data collected also provided rudimentary information on the timing of groundwater recharge events and their distribution across the landscape
Ectopic Maxillary Canines:Segregation Analysis and a Twin Study
The etiology of ectopic canines is controversial, with opinion divided as to a genetic or
environmental mechanism. This study addressed the hypothesis that genetic factors play a role in
the etiology of ectopic maxillary canines. Sixty-three probands were identified, and information
on the dental status of 395 relatives was determined. Pedigrees were constructed and the Relative
Risk calculated. Complex segregation analysis was carried out by means of the Pedigree Analysis
Package. The best mathematical model obtained was a single dominant gene with autosomal
transmission, incomplete penetrance, and highly variable expression. Only two of seven pairs of
monozygotic twins were concordant for ectopic canines. This is consistent with environmental or
epigenetic variables affecting the phenotype. The low concordance rate is consistent with the low
penetrance determined by the segregation analysis and further supports the existence of
environmental factors.peer-reviewe
A semiclassical model of light mesons
The dominantly orbital state description is applied to the study of light
mesons. The effective Hamiltonian is characterized by a relativistic kinematics
supplemented by the usual funnel potential with a mixed scalar and vector
confinement. The influence of two different finite quark masses and potential
parameters on Regge and vibrational trajectories is discussed.Comment: 1 figur
Carbon Deficiency in Externally-Polluted White Dwarfs: Evidence for Accretion of Asteroids
Existing determinations show that n(C)/n(Fe) is more than a factor of 10
below solar in the atmospheres of three white dwarfs that appear to be
externally-polluted. These results are not easily explained if the stars have
accreted interstellar matter, and we re-interpret these measurements as
evidence that these stars have accreted asteroids of a chrondritic composition.Comment: 23 pages, 6 figures, accepted for Ap
Recommended from our members
Rotational 3D Printing of Sensor Devices using Reactive Ink Chemistries
This paper charts progress in three key areas of a project supported by both UK
government and UK industry to manufacture novel sensor devices using rotary 3D printing
technology and innovative ink chemistries; (1) the development of an STL file slicing algorithm
that returns constant Z height 2D contour data at a resolution that matches the given print head
setup, allowing digital images to be generated of the correct size without the need for scaling;
(2) the development of image transformation algorithms which allow images to be printed at
higher resolutions using tilted print heads and; (3) the formulation of multi part reaction inks
which combine and react on the substrate to form solid material layers with a finite thickness. A
Direct Light Projection (DLP) technique demonstrated the robustness of the slice data by
constructing fine detailed three dimensional test pieces which were comparable to identical parts
built in an identical way from slice data obtained using commercial software. Material systems
currently under investigation include plaster, stiff polyamides and epoxy polymers and
conductive metallic’s. Early experimental results show conductivities of silver approaching
1.42x105 Siemens/m.Mechanical Engineerin
The perimeter of large planar Voronoi cells: a double-stranded random walk
Let be the probability for a planar Poisson-Voronoi cell to have
exactly sides. We construct the asymptotic expansion of up to
terms that vanish as . We show that {\it two independent biased
random walks} executed by the polar angle determine the trajectory of the cell
perimeter. We find the limit distribution of (i) the angle between two
successive vertex vectors, and (ii) the one between two successive perimeter
segments. We obtain the probability law for the perimeter's long wavelength
deviations from circularity. We prove Lewis' law and show that it has
coefficient 1/4.Comment: Slightly extended version; journal reference adde
- …