1,645 research outputs found
The Competitive Crash in Large-Scale Commercial Computing
We examine the factors underlying buyer demand for large Information Technology solutions in order to understand the competitive crash in large scale commercial computing. We examine individual buyer data from two periods. The first is in the mid 1980's, late in the period of a mature and stable large-systems market. The other period is in the early 1990's, very early in the diffusion of a new, competitive technology, client/server, when many buyers chose to wait for the new technology to mature. We clarify the implications of different theories of the competitive crash and then test them. The most popular theories are far wrong, while the correct view emphasizes the 'internal' adjustment costs to organizations making IT investments. Understanding buyer behavior not only illuminates the competitive crash, but also the factors underlying the slow realization of the social gains to Information Technology in large complex applications more generally.
Identification of blue high proper motion objects in the Tycho-2 and 2MASS catalogues using Virtual Observatory tools
With available Virtual Observatory tools, we looked for new bright blue high
proper motion objects in the entire sky: white dwarfs, hot subdwarfs, runaway
OB stars, and early-type stars in nearby young moving groups. We performed an
all-sky cross-match between the optical Tycho-2 and near-infrared 2MASS
catalogues with Aladin, and selected objects with proper motions >50mas/yr and
colours Vt-Ks<-0.5mag with TOPCAT. We also collected multi-wavelength
photometry, constructed the spectral energy distributions and estimated
effective temperatures from fits to atmospheric models with VOSA for the most
interesting targets. We assembled a sample of 32 bright blue high proper motion
objects, including ten sdO/B subdwarfs, nine DA white dwarfs, five young
early-type stars (two of which are runaway stars), two blue horizontal branch
stars, one star with poor information, and five objects reported for the first
time in this work. These last five objects have magnitudes Bt~11.0-11.6mag,
effective temperatures ~24,000-30,000K, and are located in the region of known
white dwarfs and hot subdwarfs in a reduced proper motion-colour diagram. We
confirmed the hot subdwarf nature of one of the new objects, Albus 5, with
public far-ultraviolet spectroscopic data obtained with FUSE.Comment: Published in Astronomy & Astrophysic
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The Clemson Intelligent Design Environment For Stereolithography-Cides 2.0
There are a large number of commercial Rapid Prototyping (RP) devices available today. All
ofthese machines begin with a Computer-Aided Design (CAD) model, which is tessellated,
sliced and then built layer-by-Iayer on the RP device. All ofthese operations, except the actual
building ofthe part, are completed on a computer. Therefore, many improvements to the RP
processes can be achieved through software, without affecting the RP devices or the warranties
on them. This has led to the development of a front-end software product to support the task of
preparing the part to be built. The Clemson Intelligent Design Environment for
Stereolithography (CIDES) is a user-centered interface between the CAD system and RP
systems, primarily the Stereolithography Apparatus (SLA).
CIDES 2.0 is designed to provide a variety oftools which are valuable to the users ofRP
systems, including the ability to view and modify tessellated (STL) files, generate supports, and
slice STL files into layer (SLI) files for use on an SLA. It also provides the ability to view SLI
and merged (V) files. Furthermore, CIDES offers additional translation capabilities that make it
valuable for other RP processes. The package has proven useful in the Laboratory to Advance
Industrial Prototyping (LAIP) at Clemson University. CIDES 2.0 is a new X Windows-based
release based on the original version ofCIDES with many additional features. A new HumanComputer
Interface is the major improvement to this release.Mechanical Engineerin
Vitamins A & D Inhibit the Growth of Mycobacteria in Radiometric Culture
The role of vitamins in the combat of disease is usually conceptualized as acting by modulating the immune response of an infected, eukaryotic host. We hypothesized that some vitamins may directly influence the growth of prokaryotes, particularly mycobacteria. complex).Vitamins A and D cause dose-dependent inhibition of all three mycobacterial species studied. Vitamin A is consistently more inhibitory than vitamin D. The vitamin A precursor, ÎČ-carotene, is not inhibitory, whereas three vitamin A metabolites cause inhibition. Vitamin K has no effect. Vitamin E causes negligible inhibition in a single strain.We show that vitamin A, its metabolites Retinyl acetate, Retinoic acid and 13-cis Retinoic acid and vitamin D directly inhibit mycobacterial growth in culture. These data are compatible with the hypothesis that complementing the immune response of multicellular organisms, vitamins A and D may have heretofore unproven, unrecognized, independent and probable synergistic, direct antimycobacterial inhibitory activity
The proper motion and energy distribution of the isolated neutron star RX J0720.4-3125
ESO 4m class telescope and VLT deep imaging of the isolated neutron star RX
J0720.4-3125 reveals a proper motion of mu = 97 +/-12 mas/yr and a blue U-B
color index. We show that a neutron star atmosphere model modified to account
for a limited amount of hydrogen on the star's surface can well represent both
the optical and X-ray data without invoking any additional components. The
large proper motion almost completely excludes the possibility that accretion
from interstellar medium is the powering mechanism of the X-ray emission. It
also implies that the proposed spin down is entirely due to magnetic dipole
losses. RX J0720.4-3125 is thus a very likely middle aged cooling neutron star.
Its overall properties are quite similar to some of the long period radio
pulsars recently discovered, giving further support to the idea that RX
J0720.4-3125 may be a pulsar whose narrow radio beam does not cross the Earth.Comment: Submitted to Astronomy and Astrophysics, 8 pages 5 figure
An analysis of spectra in the Red Rectangle nebula
This paper presents an analysis of a series of spectra in the Red Rectangle
nebula. Only the reddest part of the spectra can safely be attributed to light
from the nebula, and indicates Rayleigh scattering by the gas, in conformity
with the large angles of scattering involved and the proximity of the star. In
the blue, light from HD44179, refracted or scattered in the atmosphere,
dominates the spectra. This paper questions the reliability of ground-based
observations of extended objects in the blue.Comment: 25 figure
CCD-based observations of PG 0856+121 and a theoretical analysis of its oscillation modes
BVRI CCD-based and near-IR (J) imaging, together with unfiltered photometry
of the hot subdwarf B star PG 0856+121 are reported. Two close, faint, red,
point-like sources are resolved. They account for the previously reported IR
excess observed in this hot subdwarf. In addition, the new unfiltered
differential photometry of PG 0856+121 confirms its previously reported
pulsational nature. A comparison with the oscillation modes of stellar models
suggests the possible presence of g modes.Comment: Accepted for publication in A&A. Seven pages, four figures include
Understanding light quanta: First quantization of the free electromagnetic field
The quantization of the electromagnetic field in vacuum is presented without
reference to lagrangean quantum field theory. The equal time commutators of the
fields are calculated from basic principles. A physical discussion of the
commutators suggest that the electromagnetic fields are macroscopic emergent
properties of more fundamental physical system: the photons
Effective area calibration of the reflection grating spectrometers of XMM-Newton. II. X-ray spectroscopy of DA white dwarfs
White dwarf spectra have been widely used as a calibration source for X-ray
and EUV instruments. The in-flight effective area calibration of the reflection
grating spectrometers (RGS) of XMM-Newton depend upon the availability of
reliable calibration sources. We investigate how well these white dwarf spectra
can be used as standard candles at the lowest X-ray energies in order to gauge
the absolute effective area scale of X-ray instruments. We calculate a grid of
model atmospheres for Sirius B and HZ 43A, and adjust the parameters using
several constraints until the ratio of the spectra of both stars agrees with
the ratio as observed by the low energy transmission grating spectrometer
(LETGS) of Chandra. This ratio is independent of any errors in the effective
area of the LETGS. We find that we can constrain the absolute X-ray spectrum of
both stars with better than 5 % accuracy. The best-fit model for both stars is
close to a pure hydrogen atmosphere, and we put tight limits to the amount of
helium or the thickness of a hydrogen layer in both stars. Our upper limit to
the helium abundance in Sirius B is 4 times below the previous detection based
on EUVE data. We also find that our results are sensitive to the adopted
cut-off in the Lyman pseudo-continuum opacity in Sirius B. We get best
agreement with a long wavelength cut-off. White dwarf model atmospheres can be
used to derive the effective area of X-ray spectrometers in the lowest energy
band. An accuracy of 3-4 % in the absolute effective area can be achieved.Comment: 15 pages, 7 figures, accepted for publication in Astronomy &
Astrophysics, main journa
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