1,960 research outputs found
All Sky Survey Mission Observing Scenario Strategy
This paper develops a general observing strategy for missions performing
all-sky surveys, where a single spacecraft maps the celestial sphere subject to
realistic constraints. The strategy is flexible such that targeted observations
and variable coverage requirements can be achieved. This paper focuses on
missions operating in Low Earth Orbit, where the thermal and stray-light
constraints due to the Sun, Earth, and Moon result in interacting and dynamic
constraints. The approach is applicable to broader mission classes, such as
those that operate in different orbits or that survey the Earth. First, the
instrument and spacecraft configuration is optimized to enable visibility of
the targeted observations throughout the year. Second, a constraint-based
high-level strategy is presented for scheduling throughout the year subject to
a simplified subset of the constraints. Third, a heuristic-based scheduling
algorithm is developed to assign the all-sky observations over short planning
horizons. The constraint-based approach guarantees solution feasibility. The
approach is applied to the proposed SPHEREx mission, which includes coverage of
the North and South Celestial Poles, Galactic plane, and a uniform coverage
all-sky survey, and the ability to achieve science requirements demonstrated
and visualized. Visualizations demonstrate the how the all-sky survey achieves
its objectives
The role of lighting in road traffic collisions
The paper reports a study that examines how to determine if a road traffic collision took place in daylight or in the dark. An innovative method was developed, based on solar altitude, to establish cut-off points of daylight and darkness determined from a study of daylight availability in England, Scotland and Wales. This approach provides a rigorous method to differentiate daytime and night-time collisions. The criteria were used in a study of the collisions reported in the STATS19 data set for the weeks either side of the clock changes that are necessary between Greenwich Mean Time and British Summer Time. By comparing periods with the same clock time either side of the time change, using the aforementioned method, it was possible to isolate collisions within the same time period that during one week occurred in darkness and in the other week in daylight. The initial finding was that there are 19.3% more collisions in the dark periods and there is an even greater increase (31.7%) in pedestrian injuries
New Approach to Achieving Stand Alone GPS Attitude Determination using Dual Short Baselines for Small-Satellite
This paper proposes a new approach to GPS (Global Positioning System) attitude determination for small satellite application in LEO (low Earth orbit). Prior knowledge of attitude and integer resolution is not required. The methodology of the new approach includes integer ambiguity search, initial estimation of attitude and line bias, attitude initialisation, path difference estimation and fine attitude determination. The observable is the carrier phase difference measurement between two GPS antennas. A dual short baseline (typical baseline length up to 30 cm) is assumed in this research. The key point to initialising attitude is to estimated the attitude of individual baseline vectors with respect to the reference frame. Elimination of integer ambiguity is a simple task. Two set of vectors are required to determine an initial attitude. Once attitude is initialised, an estimation algorithm based on the extended Kalman filter starts to determine the attitude. The integer ambiguities and cycle slips can be resolved properly. The filter now is converged and, fine attitude is estimated. The robustness of the filtering estimator is tested with simulated anomalous conditions
A Hydrophobic Gate in an Ion Channel: The Closed State of the Nicotinic Acetylcholine Receptor
The nicotinic acetylcholine receptor (nAChR) is the prototypic member of the
`Cys-loop' superfamily of ligand-gated ion channels which mediate synaptic
neurotransmission, and whose other members include receptors for glycine,
gamma-aminobutyric acid, and serotonin. Cryo-electron microscopy has yielded a
three dimensional structure of the nAChR in its closed state. However, the
exact nature and location of the channel gate remains uncertain. Although the
transmembrane pore is constricted close to its center, it is not completely
occluded. Rather, the pore has a central hydrophobic zone of radius about 3 A.
Model calculations suggest that such a constriction may form a hydrophobic
gate, preventing movement of ions through a channel. We present a detailed and
quantitative simulation study of the hydrophobic gating model of the nicotinic
receptor, in order to fully evaluate this hypothesis. We demonstrate that the
hydrophobic constriction of the nAChR pore indeed forms a closed gate.
Potential of mean force (PMF) calculations reveal that the constriction
presents a barrier of height ca. 10 kT to the permeation of sodium ions,
placing an upper bound on the closed channel conductance of 0.3 pS. Thus, a 3 A
radius hydrophobic pore can form a functional barrier to the permeation of a 1
A radius Na+ ion. Using a united atom force field for the protein instead of an
all atom one retains the qualitative features but results in differing
conductances, showing that the PMF is sensitive to the detailed molecular
interactions.Comment: Accepted by Physical Biology; includes a supplement and a
supplementary mpeg movie can be found at
http://sbcb.bioch.ox.ac.uk/oliver/download/Movies/watergate.mp
Albumin Uptake in OK Cells Exposed to Rotenone: A Model for Studying the Effects of Mitochondrial Dysfunction on Endocytosis in the Proximal Tubule?
Band 3 mutations, distal renal tubular acidosis, and Southeast Asian ovalocytosis
Band 3 mutations, distal renal tubular acidosis, and Southeast Asian ovalocytosis. Familial distal renal tubular acidosis (dRTA) and Southeast Asian ovalocytosis (SAO) may coexist in the same patient. Both can originate in mutations of the anion-exchanger 1 gene (AE1), which codes for band 3, the bicarbonate/chloride exchanger in both the red cell membrane and the basolateral membrane of the collecting tubule alpha-intercalated cell. Dominant dRTA is usually due to a mutation of the AE1 gene, which does not alter red cell morphology. SAO is caused by an AE1 mutation that leads to a nine amino acid deletion of red cell band 3, but by itself does not cause dRTA. Recent gene studies have shown that AE1 mutations are responsible for autosomal recessive dRTA in several countries in Southeast Asia; these patients may be homozygous for the mutation or be compound heterozygotes of two different AE1 mutations, one of which is usually the SAO mutation
Zero modes, entropy bounds and partition functions
Some recent finite temperature calculations arising in the investigation of
the Verlinde-Cardy relation are re-analysed. Some remarks are also made about
temperature inversion symmetry.Comment: 12 pages, JyTe
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