10,558 research outputs found
Spectroscopic Observations of New Oort Cloud Comet 2006 VZ13 and Four Other Comets
Spectral data are presented for comets 2006 VZ13 (LINEAR), 2006 K4 (NEAT),
2006 OF2 (Broughton), 2P/Encke, and 93P/Lovas I, obtained with the Cerro-Tololo
Inter-American Observatory 1.5-m telescope in August 2007. Comet 2006 VZ13 is a
new Oort cloud comet and shows strong lines of CN (3880 angstroms), the Swan
band sequence for C_2 (4740, 5160, and 5630 angstroms), C_3 (4056 angstroms),
and other faint species. Lines are also identified in the spectra of the other
comets. Flux measurements of the CN, C_2 (Delta v = +1,0), and C_3 lines are
recorded for each comet and production rates and ratios are derived. When
considering the comets as a group, there is a correlation of C_2 and C_3
production with CN, but there is no conclusive evidence that the production
rate ratios depend on heliocentric distance. The continuum is also measured,
and the dust production and dust-to-gas ratios are calculated. There is a
general trend, for the group of comets, between the dust-to-gas ratio and
heliocentric distance, but it does not depend on dynamical age or class. Comet
2006 VZ13 is determined to be in the carbon-depleted (or Tempel 1 type) class.Comment: 8 pages, 6 figures, 6 tables; Accepted by MNRA
Common drive unit
The Common Drive Unit (CDU) is a high reliability rotary actuator with many versatile applications in mechanism designs. The CDU incorporates a set of redundant motor-brake assemblies driving a single output shaft through differential. Tachometers provide speed information in the AC version. Operation of both motors, as compared to the operation of one motor, will yield the same output torque with twice the output speed
Optimal scales in weighted networks
The analysis of networks characterized by links with heterogeneous intensity
or weight suffers from two long-standing problems of arbitrariness. On one
hand, the definitions of topological properties introduced for binary graphs
can be generalized in non-unique ways to weighted networks. On the other hand,
even when a definition is given, there is no natural choice of the (optimal)
scale of link intensities (e.g. the money unit in economic networks). Here we
show that these two seemingly independent problems can be regarded as
intimately related, and propose a common solution to both. Using a formalism
that we recently proposed in order to map a weighted network to an ensemble of
binary graphs, we introduce an information-theoretic approach leading to the
least biased generalization of binary properties to weighted networks, and at
the same time fixing the optimal scale of link intensities. We illustrate our
method on various social and economic networks.Comment: Accepted for presentation at SocInfo 2013, Kyoto, 25-27 November 2013
(http://www.socinfo2013.org
Summary of booster propulsion/vehicle impact study results
Hydrogen, RP-1, propane, and methane were identified by propulsion technology studies as the most probable fuel candidates for the boost phase of future launch vehicles. The objective of this study was to determine the effects of booster engines using these fuels and coolant variations on representative future launch vehicles. An automated procedure for integrated launch vehicle, engine sizing, and design optimization was used to optimize two stage and single stage concepts for minimum dry weight. The two stage vehicles were unmanned and used a flyback booster and partially reusable orbiter. The single stage designs were fully reusable, manned flyback vehicles. Comparisons of these vehicle designs, showing the effects of using different fuels, as well as sensitivity and trending data, are presented. In addition, the automated design technique is described
Eluate derived by extracorporal antibody-based immunoadsorption elevates the cytosolic Ca2+ concentration in podocytes via B-2 kinin receptors
Background/Aim: Patients with idiopathic focal segmental glomerulosclerosis (FSGS) often develop a recurrence of the disease after kidney transplantation. In a number of FSGS patients, plasmapheresis and immunoadsorption procedures have been shown to transiently reduce proteinuria and are thought to do this by eliminating a circulating factor. Direct cellular effects of eluates from immunoadsorption procedures on podocytes, the primary target of injury in FSGS, have not yet been reported. Methods: Eluates were derived from antibody-based immunoadsorption of a patient suffering from primary FSGS, a patient with systemic lupus erythematosus, and a healthy volunteer. The cytosolic free Ca2+ concentration ({[}Ca2+](i)) of differentiated podocytes was measured by single-cell fura-2 microfluorescence measurements. Free and total immunoreactive kinin levels were measured by radioimmunoassay. Results: FSGS eluates increased the {[}Ca2+](i) levels concentration dependently (EC50 0.14 mg/ml; n = 3-19). 1 mg/ml eluate increased the {[}Ca2+](i) values reversibly from 82 +/- 12 to 1,462 +/- 370 nmol/l, and then they returned back to 100 16 nmol/l (n = 19). The eluate-induced increase of {[}Ca2+](i) consisted of an initial Ca2+ peak followed by a Ca2+ plateau which depended on the extracellular Ca2+ concentration. The eluate-induced increase of {[}Ca2+](i) was inhibited by the specific B-2 kinin receptor antagonist Hoe 140 in a concentration-dependent manner (IC50 2.47 nmol/l). In addition, prior repetitive application of bradykinin desensitized the effect of eluate on {[}Ca2+](i). A colonic epithelial cell line not reacting to bradykinin did not respond to eluate either (n = 6). Similar to FSGS eluates, the eluate preparations of both the systemic lupus patient and the healthy volunteer led to a biphasic, concentration-dependent {[}Ca2+](i) increase in poclocytes which again was inhibited by Hoe 140. Free kinins were detected in all eluate preparations. Conclusion: The procedure of antibody-based immunoadsorption leads to kinin in the eluate which elevates the {[}Ca2+](i) level of podocytes via B-2 kinin receptors. Copyright (C) 2002 S. Karger AG, Basel
Applying weighted network measures to microarray distance matrices
In recent work we presented a new approach to the analysis of weighted
networks, by providing a straightforward generalization of any network measure
defined on unweighted networks. This approach is based on the translation of a
weighted network into an ensemble of edges, and is particularly suited to the
analysis of fully connected weighted networks. Here we apply our method to
several such networks including distance matrices, and show that the clustering
coefficient, constructed by using the ensemble approach, provides meaningful
insights into the systems studied. In the particular case of two data sets from
microarray experiments the clustering coefficient identifies a number of
biologically significant genes, outperforming existing identification
approaches.Comment: Accepted for publication in J. Phys.
An ensemble approach to the analysis of weighted networks
We present a new approach to the calculation of measures in weighted
networks, based on the translation of a weighted network into an ensemble of
edges. This leads to a straightforward generalization of any measure defined on
unweighted networks, such as the average degree of the nearest neighbours, the
clustering coefficient, the `betweenness', the distance between two nodes and
the diameter of a network. All these measures are well established for
unweighted networks but have hitherto proven difficult to define for weighted
networks. Further to introducing this approach we demonstrate its advantages by
applying the clustering coefficient constructed in this way to two real-world
weighted networks.Comment: 4 pages 3 figure
Autowaves in a dc complex plasma confined behind a de Laval nozzle
Experiments to explore stability conditions and topology of a dense
microparticle cloud supported against gravity by a gas flow were carried out.
By using a nozzle shaped glass insert within the glass tube of a dc discharge
plasma chamber a weakly ionized gas flow through a de Laval nozzle was
produced. The experiments were performed using neon gas at a pressure of 100 Pa
and melamine-formaldehyde particles with a diameter of 3.43 {\mu}m. The
capturing and stable global confining of the particles behind the nozzle in the
plasma were demonstrated. The particles inside the cloud behaved as a single
convection cell inhomogeneously structured along the nozzle axis in a tube-like
manner. The pulsed acceleration localized in the very head of the cloud
mediated by collective plasma-particle interactions and the resulting wave
pattern were studied in detail.Comment: 6 pages, 4 figure
Linear plasmon dispersion in single-wall carbon nanotubes and the collective excitation spectrum of graphene
We have measured a strictly linear pi-plasmon dispersion along the axis of
individualized single wall carbon nanotubes, which is completely different from
plasmon dispersions of graphite or bundled single wall carbon nanotubes.
Comparative ab initio studies on graphene based systems allow us to reproduce
the different dispersions. This suggests that individualized nanotubes provide
viable experimental access to collective electronic excitations of graphene,
and it validates the use of graphene to understand electronic excitations of
carbon nanotubes. In particular, the calculations reveal that local field
effects (LFE) cause a mixing of electronic transitions, including the 'Dirac
cone', resulting in the observed linear dispersion
Information transfer through disordered media by diffuse waves
We consider the information content h of a scalar multiple-scattered, diffuse
wave field and the information capacity C of a communication
channel that employs diffuse waves to transfer the information through a
disordered medium. Both h and C are shown to be directly related to the
mesoscopic correlations between the values of at different
positions in space, arising due to the coherent nature of the wave.
For the particular case of a communication channel between two identical linear
arrays of equally-spaced transmitters/receivers (receiver spacing a),
we show that the average capacity and obtain explicit analytic
expressions for in the limit of and ,
where , is the wavelength, and is the mean
free path. Modification of the above results in the case of finite but large n
and is discussed as well.Comment: REVTeX 4, 12 pages, 7 figure
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