14,081 research outputs found
Evaluation of nickel-hydrogen battery for space application
Results of electrical space qualification tests of nickel-hydrogen battery type HR 23S are presented. The results obtained for the nickel-cadmium battery type VO 23S are similar except that the voltage level and the charge conservation characteristics vary significantly. The electrical and thermal characteristics permit predictions of the following optimal applications: charge coefficient in the order of 1.3 to 1.4 at 20C; charge current density higher than C/10 at 20C; discharge current density from C/10 to C/3 at 20C; maximum discharge temperature: OC; storage temperature: -20C
Optical control of solar sails using distributed reflectivity
The dynamics of solar sails with a variable surface reflectivity distribution are investigated. When changing the reflectivity across the sail film, which can be achieved using electro-chromic coatings, the solar radiation pressure forces and torques across the sail film can be controlled without changing the attitude of the spacecraft relative to the Sun and without using mechanical systems. The paper presents two approaches. First, a continuous reflectivity distribution is presented to control the sail attitude under the influence of, for example, gravity gradient torques in Earth orbit. The second approach assumes discrete on/o reflectivity regions across the surface. Both concepts of `optical reconfiguration' of solar sails enable a more flexible steering of the spacecraft and minimize actuation effort
Second-generation p-values: improved rigor, reproducibility, & transparency in statistical analyses
Verifying that a statistically significant result is scientifically
meaningful is not only good scientific practice, it is a natural way to control
the Type I error rate. Here we introduce a novel extension of the p-value - a
second-generation p-value - that formally accounts for scientific relevance and
leverages this natural Type I Error control. The approach relies on a
pre-specified interval null hypothesis that represents the collection of effect
sizes that are scientifically uninteresting or are practically null. The
second-generation p-value is the proportion of data-supported hypotheses that
are also null hypotheses. As such, second-generation p-values indicate when the
data are compatible with null hypotheses, or with alternative hypotheses, or
when the data are inconclusive. Moreover, second-generation p-values provide a
proper scientific adjustment for multiple comparisons and reduce false
discovery rates. This is an advance for environments rich in data, where
traditional p-value adjustments are needlessly punitive. Second-generation
p-values promote transparency, rigor and reproducibility of scientific results
by a priori specifying which candidate hypotheses are practically meaningful
and by providing a more reliable statistical summary of when the data are
compatible with alternative or null hypotheses.Comment: 29 pages, 29 page Supplemen
Density Distribution Sunflower Plots
Density distribution sunflower plots are used to display high-density bivariate data. They are useful for data where a conventional scatter plot is difficult to read due to overstriking of the plot symbol. The x-y plane is subdivided into a lattice of regular hexagonal bins of width w specified by the user. The user also specifies the values of l, d, and k that affect the plot as follows. Individual observations are plotted when there are less than l observations per bin as in a conventional scatter plot. Each bin with from l to d observations contains a light sunflower. Other bins contain a dark sunflower. In a light sunflower each petal represents one observation. In a dark sunflower, each petal represents k observations. (A dark sunflower with p petals represents between /2-pk k and /2+pk k observations.) The user can control the sizes and colors of the sunflowers. By selecting appropriate colors and sizes for the light and dark sunflowers, plots can be obtained that give both the overall sense of the data density distribution as well as the number of data points in any given region. The use of this graphic is illustrated with data from the Framingham Heart Study. A documented Stata program, called sunflower, is available to draw these graphs. It can be downloaded from the Statistical Software Components archive at http://ideas.repec.org/c/boc/bocode/s430201.html . (Journal of Statistical Software 2003; 8 (3): 1-5. Posted at http://www.jstatsoft.org/index.php?vol=8 .)
Nearly Blinking-Free, High-Purity Single-Photon Emission by Colloidal InP/ZnSe Quantum Dots
Colloidal core/shell InP/ZnSe quantum dots (QDs), recently produced using an
improved synthesis method, have a great potential in life-science applications
as well as in integrated quantum photonics and quantum information processing
as single-photon emitters. Single-particle spectroscopy of 10-nm QDs with
3.2-nm cores reveals strong photon antibunching attributed to fast (70-ps)
Auger recombination of multiple excitons. The QDs exhibit very good
photostability under strong optical excitation. We demonstrate that the
antibunching is preserved when the QDs are excited above the saturation
intensity of the fundamental-exciton transition. This result paves the way
towards their usage as high-purity on-demand single-photon emitters at room
temperature. Unconventionally, despite the strong Auger blockade mechanism,
InP/ZnSe QDs also display very little luminescence intermittency ("blinking"),
with a simple on/off blinking pattern. The analysis of single-particle
luminescence statistics places these InP/ZnSe QDs in the class of nearly
blinking-free QDs, with emission stability comparable to state-of-the-art
thick-shell and alloyed-interface CdSe/CdS, but with improved single-photon
purity.Comment: 15 pages, 5 figure
A homological interpretation of the transverse quiver Grassmannians
In recent articles, the investigation of atomic bases in cluster algebras
associated to affine quivers led the second-named author to introduce a variety
called transverse quiver Grassmannian and the first-named and third-named
authors to consider the smooth loci of quiver Grassmannians. In this paper, we
prove that, for any affine quiver Q, the transverse quiver Grassmannian of an
indecomposable representation M is the set of points N in the quiver
Grassmannian of M such that Ext^1(N,M/N)=0. As a corollary we prove that the
transverse quiver Grassmannian coincides with the smooth locus of the
irreducible components of minimal dimension in the quiver Grassmannian.Comment: final version, 7 pages, corollary 1.2 has been modifie
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Off-plane motion of an oblate capsule in a simple shear flow
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.We investigate the mechanical equilibrium state of an oblate capsule when its revolution axis is
initially off the shear plane. We consider an oblate capsule with an aspect ratio of 0.5 and a strain-hardening
membrane. The three-dimensional fluid-structure interaction problem is solved numerically by coupling a
finite element method with a boundary integral method. The capsule converges towards the same mechanical
equilibrium state whatever the initial orientation. This equilibrium depends on the capillary number Ca, which
compares the viscous to the elastic forces and on the viscosity ratio between the internal and external fluids.
For = 1, the tumbling and swinging motions, observed when the revolution axis is initially in the shear plane,
are mechanically stable until Ca 1; when Ca is further increased, the capsule assumes the rolling motion
that is observed when its revolution axis is initially aligned with the vorticity axis. When is increased, the tumbling-to-swinging transition appears for higher Ca and the swinging-to-rolling transition for lower Ca. For
5, the swinging regime completely disappears: depending on Ca, it is then either the tumbling or the rolling motion that is the mechanical equilibrium state
Orbit targeting specialist function: Level C formulation requirements
A definition of the level C requirements for onboard maneuver targeting software is provided. Included are revisions of the level C software requirements delineated in JSC IN 78-FM-27, Proximity Operations Software; Level C Requirements, dated May 1978. The software supports the terminal phase midcourse (TPM) maneuver, braking and close-in operations as well as supporting computation of the rendezvous corrective combination maneuver (NCC), and the terminal phase initiation (TPI). Specific formulation is contained here for the orbit targeting specialist function including the processing logic, linkage, and data base definitions for all modules. The crew interface with the software is through the keyboard and the ORBIT-TGT display
Density Distribution Sunflower Plots in Stata Version 8
Density distribution sunflower plots are used to display high-density bivariate data. They are useful for data where a conventional scatter plot is difficult to read due to overstriking of the plot symbol. The x-y plane is subdivided into a lattice of regular hexagonal bins of width w specified by the user. The user also specifies the values of l, d, and k that affect the plot as follows. Individual observations are plotted when there are less than l observations per bin as in a conventional scatter plot. Each bin with from l to d observations contains a light sunflower. Other bins contain a dark sunflower. In a light sunflower each petal represents one observation. In a dark sunflower, each petal represents k observations. The user can control the sizes and colors of the sunflowers. By selecting appropriate colors and sizes for the light and dark sunflowers, plots can be obtained that give both the overall sense of the data density distribution as well as the number of data points in any given region. The use of this graphic is illustrated with data from the Framingham Heart Study. Stata version 8.2 contains a program, called sunflower, that draws these graphs.
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