327 research outputs found
Star Formation in the Northern Cloud Complex of NGC 2264
We have made continuum and spectral line observations of several outflow
sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope
(HHT) and ARO 12m millimeter-wave telescope. This study explores the kinematics
and outflow energetics of the young stellar systems observed and assesses the
impact star formation is having on the surrounding cloud environment. Our data
set incorporates 12CO(3-2), 13CO(3-2), and 12CO(1-0) observations of outflows
associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS
25 and 27, respectively, in the northern cloud complex. Complementary 870
micron continuum maps were made with the HHT 19 channel bolometer array. Our
results indicate that there is a weak (approximately less than 0.5%) coupling
between outflow kinetic energy and turbulent energy of the cloud. An analysis
of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining
their dynamical integrity except where outflowing material directly interacts
with the core, such as along the outflow axes.Comment: 28 pages including 6 figures, to be published in ApJ 01 July 2006,
v645, 1 issu
Software systems for distributed computing
The computing power of present desktops is mostly unused under general office usage. These many computers can be unified into one grid, such that unused cycles can be scavenged to solve one computing task. Two software systems to build such grids are compared in this work: BOINC and Techila. These systems are critically compared through the computation of two different scientific tasks, making observations of each simultaneously.
BOINC is designed for volunteer computing where anyone can donate his or her computer to the joint computation via an Internet connection. The system has been designed to facilitate millions of client computers, from which the results can not be blindly trusted. In addition, the system holds volunteersâ interest in the computational work by giving credits for the processing donated. Also available is a screen saver that is related to the computational workload.
Techila is designed for the internal use of organizations that use scientific computing. In this case only the trusted, organization owned computers are used. The system makes it easy for many users to simultaneously add computation projects. Moreover, the user gets the results and error messages for his or her computations directly to their own computer. This makes it possible to run applications that are still under development in a grid.
This work concludes that BOINC is preferable for use in public projects where there is enough computation for thousands of client computers for months or even years. Techila is better suited for environments where many users want to use the grid for minor computation projects at the same time. Moreover, maintenance can be handled centrally with a web interface. BOINC does not provide such a tool
On Low Order Embedded Pairs of Implicit Runge-Kutta Formulas
Implicit Runge-Kutta methods are used for solving stiff ODEs such as those arising in mechanical or electrical system simulation and in semidiscretisation of partial differential equation evolution problems. Embedding one Runge-Kutta formula with another is a way of obtaining an estimate of the local error (for step size control) at a modest computation cost. Our interest is with the design of embedded pairs of low order. We consider both accuracy and basic stability properties of Runge-Kutta formulas with an eye to the performance of the pair as a whole. We present some negative results showing that embedded pairs with certain combinations of stability properties cannot exist. Finally we analyze and compare 7 pairs from the literature and 6 new pairs
A comparative survey of WLAN location fingerprinting methods
The term âlocation fingerprintingâ covers a wide variety of methods for determining receiver position using databases of radio signal strength measurements from different sources. In this work we present a survey of location fingerprinting methods, including deterministic and probabilistic methods for static estimation, as well as filtering methods based on Bayesian filter and Kalman filter. We present a unified mathematical formulation of radio map database and location estimation, point out the equivalence of some methods from the literature, and present some new variants. A set of tests in an indoor positioning scenario using WLAN signal strengths is performed to determine the influence of different calibration and location method parameters. In the tests, the probabilistic method with the kernel function approximation of signal strength histograms was the best static positioning method. Moreover, all filters improved the results significantly over the static methods.Peer reviewe
Star Formation in Massive Protoclusters in the Monoceros OB1 Dark Cloud
We present far-infrared, submillimetre, and millimetre observations of bright
IRAS sources and outflows that are associated with massive CS clumps in the
Monoceros OB1 Dark Cloud. Individual star-forming cores are identified within
each clump. We show that combining submillimetre maps, obtained with SCUBA on
the JCMT, with HIRES-processed and modelled IRAS data is a powerful technique
that can be used to place better limits on individual source contributions to
the far-infrared flux in clustered regions. Three previously categorized "Class
I objects" are shown to consist of multiple sources in different evolutionary
stages. In each case, the IRAS point source dominates the flux at 12 and 25
microns. In two cases, the IRAS point source is not evident at submillimetre
wavelengths. The submillimetre sources contribute significantly to the 60 and
100 micron fluxes, dominating the flux in the 100 micron waveband. Using fluxes
derived from our technique, we present the spectral energy distribution and
physical parameters for an intermediate-mass Class 0 object in one of the
regions. Our new CO J=2-1 outflow maps of the three regions studied indicate
complex morphology suggestive of multiple driving sources. We discuss the
possible implications of our results for published correlations between outflow
momentum deposition rates and "source" luminosities, and for using these
derived properties to estimate the ratio of mass ejection rates to mass
accretion rates onto protostars.Comment: 12 pages, 11 gzipped gif figures, LaTex file and MNRAS style files,
accepted by MNRAS, v2: reference typos and author affiliation have been
correcte
A pseudospectral approach to the McWhorter and Sunada equation for two-phase flow in porous media with capillary pressure
Liprin-α4 Is Required for Nickel Induced Receptor Protein Tyrosine Phosphatase-Leukocyte Antigen Related Receptor F (RPTP-LAR) Activity
Liprin-α4 was strongly induced following nickel (II) chloride exposure in a variety of cell types including BEAS-2B, A549, BEP2D and BL41 cells. Liprin-α4, a member of the Liprin alpha family, has seven isoforms but only three of these variants were detected in BEAS-2B cells (004, 201 and 202). The level of Liprin-α4 variants 201 and 004 were highly increased in BEAS-2B cells in response to nickel. We showed that Liprin-α4 bound directly to the cytoplasmic region of RPTP-LAR (receptor protein tyrosine phosphatase-leukocyte antigen-related receptor F). The cytoplasmic region of RPTP-LAR contains two phosphatase domains but only the first domain shows activity. The second domain interacts with other proteins. The phosphatase activity was increased both following nickel treatment and also in the presence of nickel ions in cell extracts. Liprin-α4 knock-down lines with decreased expression of Liprin-α4 variants 004 and 201 exhibited greater nickel toxicity compared to controls. The RPTP-LAR phosphatase activity was only slightly increased in a Liprin-α4 knock-down line. Liprin-α4 appeared necessary for the nickel induced tyrosine phosphatase activity. The presence of Liprin-α4 and nickel increased tyrosine phosphatase activity that reduced the global levels of tyrosine phosphorylation in the cell
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