7,587 research outputs found
The effect of the relative orientation between the coronal field and new emerging flux: I Global Properties
The emergence of magnetic flux from the convection zone into the corona is an
important process for the dynamical evolution of the coronal magnetic field. In
this paper we extend our previous numerical investigations, by looking at the
process of flux interaction as an initially twisted flux tube emerges into a
plane parallel, coronal magnetic field. Significant differences are found in
the dynamical appearance and evolution of the emergence process depending on
the relative orientation between the rising flux system and any preexisting
coronal field. When the flux systems are nearly anti-parallel, the experiments
show substantial reconnection and demonstrate clear signatures of a high
temperature plasma located in the high velocity outflow regions extending from
the reconnection region. However, the cases that have a more parallel
orientation of the flux systems show very limited reconnection and none of the
associated features. Despite the very different amount of reconnection between
the two flux systems, it is found that the emerging flux that is still
connected to the original tube, reaches the same height as a function of time.
As a compensation for the loss of tube flux, a clear difference is found in the
extent of the emerging loop in the direction perpendicular to the main axis of
the initial flux tube. Increasing amounts of magnetic reconnection decrease the
volume, which confines the remaining tube flux.Comment: 21 pages, 16 figures Accepted for Ap
Adjustable mount for electro-optic transducers in an evacuated cryogenic system
The invention is an adjustable mount for positioning an electro-optic transducer in an evacuated cryogenic environment. Electro-optic transducers are used in this manner as high sensitivity detectors of gas emission lines of spectroscopic analysis. The mount is made up of an adjusting mechanism and a transducer mount. The adjusting mechanism provided five degrees of freedom, linear adjustments and angular adjustments. The mount allows the use of an internal lens to focus energy on the transducer element thereby improving the efficiency of the detection device. Further, the transducer mount, although attached to the adjusting mechanism, is isolated thermally such that a cryogenic environment can be maintained at the transducer while the adjusting mechanism remains at room temperature. Radiation shields also are incorporated to further reduce heat flow to the transducer location
Performance of alkaline battery cells used in emergency locator transmitters
The characteristics of battery power supplies for emergency locator transmitters (ELT's) were investigated by testing alkaline zinc/manganese dioxide cells of the type typically used in ELT's. Cells from four manufacturers were tested. The cells were subjected to simulated environmental and load conditions representative of those required for survival and operation. Battery cell characteristics that may contribute to ELT malfunctions and limitations were evaluated. Experimental results from the battery cell study are discussed, and an evaluation of ELT performance while operating under a representative worst-case environmental condition is presented
Paired-Domination Game Played in Graphs\u3csup\u3eā\u3c/sup\u3e
In this paper, we continue the study of the domination game in graphs introduced by BreÅ”ar, Klavžar, and Rall [SIAM J. Discrete Math. 24 (2010) 979-991]. We study the paired-domination version of the domination game which adds a matching dimension to the game. This game is played on a graph G by two players, named Dominator and Pairer. They alternately take turns choosing vertices of G such that each vertex chosen by Dominator dominates at least one vertex not dominated by the vertices previously chosen, while each vertex chosen by Pairer is a vertex not previously chosen that is a neighbor of the vertex played by Dominator on his previous move. This process eventually produces a paired-dominating set of vertices of G; that is, a dominating set in G that induces a subgraph that contains a perfect matching. Dominator wishes to minimize the number of vertices chosen, while Pairer wishes to maximize it. The game paired-domination number Ī³gpr(G) of G is the number of vertices chosen when Dominator starts the game and both players play optimally. Let G be a graph on n vertices with minimum degree at least 2. We show that Ī³gpr(G) ā¤ 45 n, and this bound is tight. Further we show that if G is (C4, C5)-free, then Ī³gpr(G) ā¤ 43 n, where a graph is (C4, C5)-free if it has no induced 4-cycle or 5-cycle. If G is 2-connected and bipartite or if G is 2-connected and the sum of every two adjacent vertices in G is at least 5, then we show that Ī³gpr(G) ā¤ 34 n
More Than Cows & Cooking: Newest Research Shows the Impact of 4-H
This article reports on a statewide survey of students\u27 use of out-of-school time conducted in 21 Montana counties. Only 17% of youth reported that they are not involved in out-of-school activities. Active students are more likely to lead healthier and happier lives than non-active youth. 4-H participants are less likely to shoplift or steal, smoke cigarettes, ride in a car with someone who has been drinking, or damage property for the fun of it. These participants are also more likely to develop self-confidence, social competence, and practical skills; to take on community leadership roles; and to feel more accepted and listened to by adults
Blow-up behavior of collocation solutions to Hammerstein-type volterra integral equations
We analyze the blow-up behavior of one-parameter collocation solutions for Hammerstein-type Volterra integral equations (VIEs) whose solutions may blow up in finite time. To approximate such solutions (and the corresponding blow-up time), we will introduce an adaptive stepsize strategy that guarantees the existence of collocation solutions whose blow-up behavior is the same as the one for the exact solution. Based on the local convergence of the collocation methods for VIEs, we present the convergence analysis for the numerical blow-up time. Numerical experiments illustrate the analysis
Algorithmic aspects of disjunctive domination in graphs
For a graph , a set is called a \emph{disjunctive
dominating set} of if for every vertex , is either
adjacent to a vertex of or has at least two vertices in at distance
from it. The cardinality of a minimum disjunctive dominating set of is
called the \emph{disjunctive domination number} of graph , and is denoted by
. The \textsc{Minimum Disjunctive Domination Problem} (MDDP)
is to find a disjunctive dominating set of cardinality .
Given a positive integer and a graph , the \textsc{Disjunctive
Domination Decision Problem} (DDDP) is to decide whether has a disjunctive
dominating set of cardinality at most . In this article, we first propose a
linear time algorithm for MDDP in proper interval graphs. Next we tighten the
NP-completeness of DDDP by showing that it remains NP-complete even in chordal
graphs. We also propose a -approximation
algorithm for MDDP in general graphs and prove that MDDP can not be
approximated within for any unless NP
DTIME. Finally, we show that MDDP is
APX-complete for bipartite graphs with maximum degree
No Hubble Bubble in the Local Universe
Zehavi et al. (1998) have suggested that the Hubble flow within 70/h Mpc may
be accelerated by the existence of a void centered on the Local Group. Its
underdensity would be ~20 %, which would result in a local Hubble distortion of
about 6.5 %. We have combined the peculiar velocity data of two samples of
clusters of galaxies, SCI and SCII, to investigate the amplitude of Hubble
distortions to 200/h Mpc. Our results are not supportive of that conclusion.
The amplitude of a possible distortion in the Hubble flow within 70/h Mpc in
the SCI+SCII merged data is 0.010\pm0.022. The largest, and still quite
marginal, geocentric deviation from smooth Hubble flow consistent with that
data set is a shell with (Delta H)/H =0.027\pm0.023, centered at hd = 101 Mpc
and extending over some 30/h Mpc. Our results are thus consistent with a Hubble
flow that, on distances in excess of about 50/h Mpc, is remarkably smooth.Comment: 11 pages, 1 tables, 1 figure; uses AAS LaTex; to appear in ApJ Nov 9
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