79,862 research outputs found
The formation of a T Tauri star: Observations of the infrared source in L 1551
The 5 to 25 micron observations show that an object previously discovered at 2.2 microns (IRS 5) within the densest part of the L1551 dark cloud is a strong source of radiation from grains as cool as 230 K. The energy distribution resembles that of infrared objects embedded within other molecular cloud cores, but implies a total solar luminosity of only 30. The luminosity of the source and its proximity to other T Tauri stars suggests that it is a 1 to 2 solar mass pre-main sequence star still swaddled within the L1551 cloud. The radio and optical evidence for mass motions around IRS 5 may mean that IRS 5 has been flaring in FU Ori-type eruptions within the last 1000 years
Computer routine adds plotting capabilities to existing programs
PLOTAN, a generalized plot analysis routine written for the IBM 7094 computer, minimizes the difficulties in adding plot capabilities to large existing programs. PLOTAN is used in conjunction with a binary tape writing routine and has the ability to plot any variable on the intermediate binary tape as a function of any other
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Radial basis function classifier construction using particle swarm optimisation aided orthogonal forward regression
We develop a particle swarm optimisation (PSO)
aided orthogonal forward regression (OFR) approach for constructing radial basis function (RBF) classifiers with tunable nodes. At each stage of the OFR construction process, the centre vector and diagonal covariance matrix of one RBF node is determined efficiently by minimising the leave-one-out (LOO) misclassification rate (MR) using a PSO algorithm. Compared with the state-of-the-art regularisation assisted orthogonal least square algorithm based on the LOO MR for selecting fixednode RBF classifiers, the proposed PSO aided OFR algorithm for constructing tunable-node RBF classifiers offers significant advantages in terms of better generalisation performance and smaller model size as well as imposes lower computational complexity in classifier construction process. Moreover, the proposed algorithm does not have any hyperparameter that requires costly tuning based on cross validation
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Sparse kernel density estimation technique based on zero-norm constraint
A sparse kernel density estimator is derived based on the zero-norm constraint, in which the zero-norm of the kernel weights is incorporated to enhance model sparsity. The classical Parzen window estimate is adopted as the desired response for density estimation, and an approximate function of the zero-norm is used for achieving mathemtical tractability and algorithmic efficiency. Under the mild condition of the positive definite design matrix, the kernel weights of the proposed density estimator based on the zero-norm approximation can be obtained using the multiplicative nonnegative quadratic programming algorithm. Using the -optimality based selection algorithm as the preprocessing to select a small significant subset design matrix, the proposed zero-norm based approach offers an effective means for constructing very sparse kernel density estimates with excellent generalisation performance
A conflict analysis of 4D descent strategies in a metered, multiple-arrival route environment
A conflict analysis was performed on multiple arrival traffic at a typical metered airport. The Flow Management Evaluation Model (FMEM) was used to simulate arrival operations using Denver Stapleton's arrival route structure. Sensitivities of conflict performance to three different 4-D descent strategies (clear-idle Mach/Constant AirSpeed (CAS), constant descent angle Mach/CAS and energy optimal) were examined for three traffic mixes represented by those found at Denver Stapleton, John F. Kennedy and typical en route metering (ERM) airports. The Monte Carlo technique was used to generate simulation entry point times. Analysis results indicate that the clean-idle descent strategy offers the best compromise in overall performance. Performance measures primarily include susceptibility to conflict and conflict severity. Fuel usage performance is extrapolated from previous descent strategy studies
Traveling waves and homogeneous fragmentation
We formulate the notion of the classical
Fisher-Kolmogorov-Petrovskii-Piscounov (FKPP) reaction diffusion equation
associated with a homogeneous conservative fragmentation process and study its
traveling waves. Specifically, we establish existence, uniqueness and
asymptotics. In the spirit of classical works such as McKean [Comm. Pure Appl.
Math. 28 (1975) 323-331] and [Comm. Pure Appl. Math. 29 (1976) 553-554], Neveu
[In Seminar on Stochastic Processes (1988) 223-242 Birkh\"{a}user] and Chauvin
[Ann. Probab. 19 (1991) 1195-1205], our analysis exposes the relation between
traveling waves and certain additive and multiplicative martingales via laws of
large numbers which have been previously studied in the context of
Crump-Mode-Jagers (CMJ) processes by Nerman [Z. Wahrsch. Verw. Gebiete 57
(1981) 365-395] and in the context of fragmentation processes by Bertoin and
Martinez [Adv. in Appl. Probab. 37 (2005) 553-570] and Harris, Knobloch and
Kyprianou [Ann. Inst. H. Poincar\'{e} Probab. Statist. 46 (2010) 119-134]. The
conclusions and methodology presented here appeal to a number of concepts
coming from the theory of branching random walks and branching Brownian motion
(cf. Harris [Proc. Roy. Soc. Edinburgh Sect. A 129 (1999) 503-517] and Biggins
and Kyprianou [Electr. J. Probab. 10 (2005) 609-631]) showing their
mathematical robustness even within the context of fragmentation theory.Comment: Published in at http://dx.doi.org/10.1214/10-AAP733 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Analysis of a Very Massive DA White Dwarf via the Trigonometric Parallax and Spectroscopic Methods
By two different methods, we show that LHS 4033 is an extremely massive white
dwarf near its likely upper mass limit for destruction by unstable electron
captures. From the accurate trigonometric parallax reported herein, the
effective temperature (T=10,900 K) and the stellar radius (R=0.00368 R_sun) are
directly determined from the broad-band spectral energy distribution -- the
parallax method. The effective temperature and surface gravity are also
estimated independently from the simultaneous fitting of the observed Balmer
line profiles with those predicted from pure-hydrogen model atmospheres -- the
spectroscopic method (T=10,760 K, log g=9.46). The mass of LHS 4033 is then
inferred from theoretical mass-radius relations appropriate for white dwarfs.
The parallax method yields a mass estimate of 1.310--1.330 M_sun, for interior
compositions ranging from pure magnesium to pure carbon, respectively, while
the spectroscopic method yields an estimate of 1.318--1.335 M_sun for the same
core compositions. This star is the most massive white dwarf for which a robust
comparison of the two techniques has been made.Comment: 17 pages, including 4 figures, Accepted for Ap.
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Layered Fabrication of Branched Networks Using Lindenmayer Systems
A current challenge impeding the growth of bone tissue engineering is the lack of
functional scaffolds of geometric sizes greater than 10mm due to the inability of cells to
survive deep within the scaffold. It is hypothesized that these scaffolds must have an
inbuilt nutrient distribution network to sustain the uniform growth of cells. In this
paper, we seek to enhance the design and layered fabrication of scaffold internal
architecture through the development of Lindenmayer systems, a graphical language
based theory to create nutrient delivery networks. The scaffolds are fabricated using the
Texas Instruments DLP™ system through UV‐photopolymerization to produce
polyethylene glycol hydrogels with internal branch structures. The paper will discuss
the Lindenmayer system, process planning algorithms, layered fabrication of samples,
challenges and future tasks.Mechanical Engineerin
Nomenclatural and systematic changes in the Neotropical caddisflies (Insecta: Trichoptera)
Recent work on a catalog of the Neotropical caddisflies has resulted in the recognition of the need to make numerous lectotype designations, new names for homonyms, specific and generic synonymies, transfers of species between genera and genera between families, and placement of many long ignored names of Muller and others
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