2,636 research outputs found
Nicolaus Copernicus, 1473-1973
Nicolaus Copernicus, 1473-1973
His Revolutions and His Revolution
Catalogue of and Exhibition of Manuscripts and Books
With an Historical Essay by Seymour L. Chapin
Linderman Library, Lehigh University
Bethlehem, Pennsylvania : September-November 197
Trade Study Analysis for TNS Tokamaks.
A series of parametric trade studies was performed to consistently evaluate the relative.costs and performance parameters of D-T burning tokamaks over a range of plasma sizes and toroidal field (TF) coil technologies. Four different types of TF coil technologies were investigated: water-cooled copper coils, superconducting NbTi and Nb{sub 3}Sn coils, and a "hybrid" coil arrangement consisting of a· normal conducting Cu coil nested within a superconducting NbTi coil. Results of the analysis indicate for TNS operation, for example, that for a given plasma beta at ignition, the Cu TF coil devices are least expensive, followed by the Nb{sub 3}Sn, NbTi, and NbTi/Cu options. Other conclusions and trends resulting from the study are presented and analyzed
Simulating the Performance of Large-Format Submillimetre Focal-Plane Arrays
A robust measurement of the clustering amplitude of the sub-mm population of
starburst galaxies requires large-area surveys (>> 1 deg^2). The largest-format
arrays subtend only 10 arcmin^2 on the sky and hence scan-mapping is a
necessary observing mode. Providing realistic representations of the
extragalactic sky and atmosphere, as the input to a detailed simulator of the
telescope and instrument performance, allows important decisions to be made
about the design of large-area fully-sampled surveys and observing strategies.
In this paper we present preliminary simulations that include detector noise,
time-constants and array geometry, telescope pointing errors, scan speeds and
scanning angles, sky noise and sky rotation.Comment: 3 pages, 3 figures, Conference Contribution: 2K1BC Workshop
"Experimental Cosmology at millimetre wavelengths", July 9-13 2001, Ital
Breaking the Redshift Deadlock - I: Constraining the star formation history of galaxies with sub-millimetre photometric redshifts
Future extragalactic sub-millimetre and millimetre surveys have the potential
to provide a sensitive census of the level of obscured star formation in
galaxies at all redshifts. While in general there is good agreement between the
source counts from existing SCUBA (850um) and MAMBO (1.25mm) surveys of
different depths and areas, it remains difficult to determine the redshift
distribution and bolometric luminosities of the sub-millimetre and millimetre
galaxy population. This is principally due to the ambiguity in identifying an
individual sub-millimetre source with its optical, IR or radio counterpart
which, in turn, prevents a confident measurement of the spectroscopic redshift.
Additionally, the lack of data measuring the rest-frame FIR spectral peak of
the sub-millimetre galaxies gives rise to poor constraints on their rest-frame
FIR luminosities and star formation rates. In this paper we describe
Monte-Carlo simulations of ground-based, balloon-borne and satellite
sub-millimetre surveys that demonstrate how the rest-frame FIR-sub-millimetre
spectral energy distributions (250-850um) can be used to derive photometric
redshifts with an r.m.s accuracy of +/- 0.4 over the range 0 < z < 6. This
opportunity to break the redshift deadlock will provide an estimate of the
global star formation history for luminous optically-obscured galaxies [L(FIR)
> 3 x 10^12 Lsun] with an accuracy of 20 per cent.Comment: 14 pages, 22 figures, submitted to MNRAS, replaced with accepted
versio
High Angular Resolution Observations of Four Candidate BLAST High-Mass Starless Cores
We discuss high-angular resolution observations of ammonia toward four
candidate high-mass starless cores (HMSCs). The cores were identified by the
Balloon-borne Large Aperture Submillimeter Telescope (BLAST) during its 2005
survey of the Vulpecula region where 60 compact sources were detected
simultaneously at 250, 350, and 500 micron. Four of these cores, with no
IRAS-PSC or MSX counterparts, were observed with the NRAO Very Large Array
(VLA) in the NH3(1,1) and (2,2) spectral lines. Our observations indicate that
the four cores are cold (Tk <~ 14K) and show a filamentary and/or clumpy
structure. They also show a significant velocity substructure within ~1km/s.
The four BLAST cores appear to be colder and more quiescent than other
previously observed HMSC candidates, suggesting an earlier stage of evolution.Comment: Submitted to the Astrophysical Journal on January 22, 2010. Accepted
for publication on April 15, 2010. The paper has 21 pages and 17 figures
SANEPIC: A Map-Making Method for Timestream Data From Large Arrays
We describe a map-making method which we have developed for the Balloon-borne
Large Aperture Submillimeter Telescope (BLAST) experiment, but which should
have general application to data from other submillimeter arrays. Our method
uses a Maximum Likelihood based approach, with several approximations, which
allows images to be constructed using large amounts of data with fairly modest
computer memory and processing requirements. This new approach, Signal And
Noise Estimation Procedure Including Correlations (SANEPIC), builds upon
several previous methods, but focuses specifically on the regime where there is
a large number of detectors sampling the same map of the sky, and explicitly
allowing for the the possibility of strong correlations between the detector
timestreams. We provide real and simulated examples of how well this method
performs compared with more simplistic map-makers based on filtering. We
discuss two separate implementations of SANEPIC: a brute-force approach, in
which the inverse pixel-pixel covariance matrix is computed; and an iterative
approach, which is much more efficient for large maps. SANEPIC has been
successfully used to produce maps using data from the 2005 BLAST flight.Comment: 27 Pages, 15 figures; Submitted to the Astrophysical Journal; related
results available at http://blastexperiment.info/ [the BLAST Webpage
A broadband spectroscopic search for CO line emission in HDF850.1: the brightest submillimetre object in the Hubble Deep Field North
Using the 100-m Green Bank Telescope, we have conducted a cm-wavelength
search for CO J=1-0 line emission towards the high-redshift, far-infrared
luminous object, HDF850.1 over the redshift interval 3.3<z<5.4. Despite the
wealth of existing multi-wavelength observations, and the recent identification
of a galaxy counterpart in deep K' band (2.2 um) imaging, an unambiguous
spectroscopic redshift has not yet been obtained for this object. A
far-infrared-to-radio wavelength photometric redshift technique however,
predicts a ~90% probability that the redshift is in the range, 3.3<z<5.4
(equivalent to an observed redshifted CO J=1-0 emission line frequency,
26.5>nu(obs)>18.0 GHz), making HDF850.1 a potential occupent of the
`high-redshift tail' of submm selected galaxies. We have also conducted a
search for CO J=2-1 line emission over the narrower redshift range, 3.9<z<4.3.
although we do not detect any CO line emission in this object, our limits to
the CO line luminosity are in broad agreement with the median value measured in
the current sample of high-redshift, submm selected objects detected in high-J
CO line emission, but not sufficient to fully test the validity of the
photometric redshift technique.Comment: accepted for publication in MNRA
Analytical solution of a model for complex food webs
We investigate numerically and analytically a recently proposed model for
food webs [Nature {\bf 404}, 180 (2000)] in the limit of large web sizes and
sparse interaction matrices. We obtain analytical expressions for several
quantities with ecological interest, in particular the probability
distributions for the number of prey and the number of predators. We find that
these distributions have fast-decaying exponential and Gaussian tails,
respectively. We also find that our analytical expressions are robust to
changes in the details of the model.Comment: 4 pages (RevTeX). Final versio
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