14,983 research outputs found
Method of statistical filtering
Minimal formula for bounding the cross correlation between a random forcing function and the state error when this correlation is unknown is used in optimal linear filter theory applications. Use of the bound results in overestimation of the estimation-error covariance
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MobGeoSen: facilitating personal geosensor data collection and visualization using mobile phones
Mobile sensing and mapping applications are becoming more prevalent because sensing hardware is becoming more portable and more affordable. However, most of the hardware uses small numbers of fixed sensors that report and share multiple sets of environmental data which raises privacy concerns. Instead, these systems can be decentralized and managed by individuals in their public and private spaces. This paper describes a robust system called MobGeoSens which enables individuals to monitor their local environment (e.g. pollution and temperature) and their private spaces (e.g. activities and health) by using mobile phones in their day to day life
The size, density, and formation of the Orcus-Vanth system in the Kuiper belt
The Kuiper belt object Orcus and its satellite Vanth form an unusual system
in the Kuiper belt. Orcus is amongst the largest objects known in the Kuiper
belt, but the relative size of Vanth is much larger than that of the tiny
satellites of the other large objects. From Hubble Space Telescope observations
we find that Orcus and Vanth have different visible colors and that Vanth does
not share the water ice absorption feature seen in the infrared spectrum of
Orcus. We also find that Vanth has a nearly face-on circular orbit with a
period of 9.5393 +-0.0001 days and semimajor axis of 8980+-20 km, implying a
system mass of 6.32+- 0.01 X 10^20 kg or 3.8% the mass of dwarf planet Eris.
From Spitzer Space Telescope observations we find that the thermal emission
is consistent with a single body with diameter 940+-70 km and a geometric
albedo of 0.28+-0.04. Assuming equal densities and albedos, this measurements
implies sizes of Orcus and Vanth of 900 and 280 km, respectively, and a mass
ratio of 33. Assuming a factor of 2 lower albedo for the non-icy Vanth,
however, implies sizes of 820 and 640 km and a mass ratio of 2. The measured
density depends on the assumed albedo ratio of the two objects but is
approximately 1.5+-0.3 g cm^-3$, midway between typical densities measured for
larger and for smaller objects. The orbit and mass ratio is consistent with
formation from a giant impact and subsequent outward tidal evolution and even
consistent with the system having now achieved a double synchronous state. The
system can equally well be explained, however, by initial eccentric capture,
Kozai cycling which increases the eccentricity and decreases the pericenter of
the orbit of Vanth, and subsequent tidal evolution inward.Comment: Submitted to A
Carrier dynamics in ion-implanted GaAs studied by simulation and observation of terahertz emission
We have studied terahertz (THz) emission from arsenic-ion implanted GaAs both
experimentally and using a three-dimensional carrier dynamics simulation. A
uniform density of vacancies was formed over the optical absorption depth of
bulk GaAs samples by performing multi-energy implantations of arsenic ions (1
and 2.4MeV) and subsequent thermal annealing. In a series of THz emission
experiments the frequency of peak THz power was found to increase significantly
from 1.4 to 2.2THz when the ion implantation dose was increased from 10^13 to
10^16 cm-3. We used a semi-classical Monte-Carlo simulation of ultra-fast
carrier dynamics to reproduce and explain these results. The effect of the
ion-induced damage was included in the simulation by considering carrier
scattering at neutral and charged impurities, as well as carrier trapping at
defect sites. Higher vacancy concentrations and shorter carrier trapping times
both contributed to shorter simulated THz pulses, the latter being more
important over experimentally realistic parameter ranges.Comment: 6 pages, 7 figure
Ground-based detection of a cloud of methanol from Enceladus: When is a biomarker not a biomarker?
Saturn's moon Enceladus has vents emerging from a sub-surface ocean, offering
unique probes into the liquid environment. These vents drain into the larger
neutral torus in orbit around Saturn. We present a methanol (CH3OH) detection
observed with IRAM 30-m from 2008 along the line-of-sight through Saturn's
E-ring. Additionally, we also present supporting observations from the Herschel
public archive of water (ortho-H2O; 1669.9 GHz) from 2012 at a similar
elongation and line-of-sight. The CH3OH 5(1,1)-4(1,1) transition was detected
at 5.9 sigma confidence. The line has 0.43 km/s width and is offset by +8.1
km/s in the moon's reference frame. Radiative transfer models allow for gas
cloud dimensions from 1750 km up to the telescope beam diameter ~73000 km.
Taking into account the CH3OH lifetime against solar photodissociation and the
redshifted line velocity, there are two possible explanations for the CH3OH
emission: methanol is primarily a secondary product of chemical interactions
within the neutral torus that (1) spreads outward throughout the E-ring or (2)
originates from a compact, confined gas cloud lagging Enceladus by several
km/s. We find either scenario to be consistent with significant redshifted H2O
emission (4 sigma) measured from the Herschel public archive. The measured
CH3OH:H2O abundance (> 0.5 per cent) significantly exceeds the observed
abundance in the direct vicinity of the vents (~0.01 per cent), suggesting
CH3OH is likely chemically processed within the gas cloud with methane (CH4) as
its parent species.Comment: 16 pages, 4 figures, accepted for publication in the International
Journal of Astrobiology (IJA
Equation modifying program, L219 (EQMOD). Volume 1: Engineering and usage
The analysis and use of the Equation Modifying Program (EQMOD) L219, digital computer program which modifies matrices according to specific instructions was described. The program modifies the theoretical equation of motion and load equations generated by the DYLOFLEX programs Equation of Motion L217 (EOM), and Load Equations, L218 (LOADS), respectively
Regulation of Contact with Offspring by Domestic Sows: Temporal Patterns and Individual Variation
We used a sow-controlled housing system to examine temporal and individual variation in the tendency of sows to associate with young. During a 5-week lactation, 22 sows and litters were housed in a pen where the sow could freely leave and re-enter the piglets\u27 area by stepping over a barrier that the piglets could not cross. Despite this option, the sows remained with the piglets almost constantly during the 1st day after birth. Nineteen sows (\u27leavers\u27) changed to spending most of their time away from the litter at some point in the lactation. The change was rapid, often within a single week, and occurred in week 2, 3, 4 or 5, depending on the individual. The time of rapid increase in time away was not related to characteristics of the sow or litter, including parity, litter size and sex ratio. Three sows (\u27stayers\u27) did not increase their time away as lactation advanced, and rarely spent more than 15% of their day in the piglet-free area. Nearly all sows showed a clear preference to defecate in the piglet-free area. This study shows 1. that sows voluntarily reduce their contact with the young; 2. that the timing of this reduction varies greatly amongst sows for reasons that may relate to differences in maternal motivation, and 3. that sows do not abandon the litter if the young cannot follow. The clear preference that most sows developed for the piglet-free area reinforces physiological evidence that constant confinement with older litters is aversive for many sows
Aquatic Feeding by Moose: Selection of Plant Species and Feeding Areas in Relation to Plant Chemical Composition and Characteristics of Lakes
Aquatic feeding by moose was studied with emphasis on (i) the chemical composition of aquatic plants compared with terrestrial browse, (ii) the chemical composition of preferred and unpreferred aquatic plant species and (iii) characteristics of preferred feeding areas. Compared with woody browse, aquatic plants had much higher levels of sodium and iron, and similar levels of other nutrients tested. In a cafeteria selection experiment, moose consistently ate seven species of aquatic plants (preferred plants), consistently rejected five species (unpreferred plants), and gave an intermediate response to seven species. Preferred species had significantly higher sodium content. Those in the intermediate class contained more crude protein and phosphorus than unpreferred species. Of 24 lakes and ponds, 6 were heavily used by moose. 16 were used relatively little, and 2 were difficult to classify. The six heavily used sites had shallower water, a higher mineral content in the lake sediment, and a greater abundance of preferred plant species. Plants growing in heavily used sites had higher levels of sodium, phosphorus, and manganese than the same species growing in lightly used sites. Results suggest that levels of sodium in aquatic plants have a major influence on the animals\u27 selection of aquatic plant species and feeding areas, while phosphorus and protein levels may also influence selection
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