2,062 research outputs found
Occurence of elliptical fractal patterns in multi-bit bandpass sigma delta modulators
It has been established that the class of bandpass sigma delta modulators (SDMs) with single
bit quantizers could exhibit state space dynamics represented by elliptic or fractal patterns
confined within trapezoidal regions. In this letter, we find that elliptical fractal patterns may
also occur in bandpass SDMs with multibit quantizers, even for the case when the saturation
regions of the multibit quantizers are not activated and a large number of bits are used for the
implementation of the quantizers. Moreover, the fractal pattern may occur for low bit quantizers,
and the visual appearance of the phase portraits between the infinite state machine and the finite
state machine with high bit quantizers is different. These phenomena are different from those
previously reported for the digital filter with twoâs complement arithmetic. Furthermore, some
interesting phenomena are found. A bit change of the quantizer can result in a dramatic change
in the fractal patterns. When the trajectories of the corresponding linear systems converge to a
fixed point, the regions of the elliptical fractal patterns diminish in size as the number of bits
of the quantizers increases
3D Printing - To print or not to print? Aspects to consider before adoption - A supply chain perspective
3D printing is believed by many to be the next industrial revolution. The technology is already deployed in production. However, supply chain literature is still in its infancy regarding this topic, despite 3D printings radical impact on supply chains. A framework has been developed to assess various aspects that need to be considered when deploying such technology as part of the production process. Literature has been drawn from cross-discipline (e.g. social sciences, engineering, and business). The challenge for businesses will be whether to incur the cost impact today or the opportunity cost of tomorrow if 3D printing is not adopted
An Ontology-Based Collaborative Interorganizational Knowledge Management Network
Web contents can be represented in a structural form by a finite list of vocabularies and their relationships using ontologies. The concept of ontology and its related mediation methods is capable of enhancing the collaboration among Knowledge Management (KM) approaches that only focus on managing organizational knowledge. Those KM approaches are developed in accordance with organizational KM strategies and business requirements without the concern of system interoperation. In this research, an ontology-based collaborative inter-organizational KM network is proposed to provide a platform for organizations to access and retrieve inter-organizational knowledge in a similar domain
A Collective Breaking of R-Parity
Supersymmetric theories with an R-parity generally yield a striking missing
energy signature, with cascade decays concluding in a neutralino that escapes
the detector. In theories where R-parity is broken the missing energy is
replaced with additional jets or leptons, often making traditional search
strategies ineffective. Such R-parity violation is very constrained, however,
by resulting B and L violating signals, requiring couplings so small that LSPs
will decay outside the detector in all but a few scenarios. In theories with
additional matter fields, R-parity can be broken collectively, such that
R-parity is not broken by any single coupling, but only by an ensemble of
couplings. Cascade decays can proceed normally, with each step only sensitive
to one or two couplings at a time, but B and L violation requires the full set,
yielding a highly suppressed constraint. s-channel production of new scalar
states, typically small for standard RPV, can be large when RPV is broken
collectively. While missing energy is absent, making these models difficult to
discover by traditional SUSY searches, they produce complicated many object
resonances (MORes), with many different possible numbers of jets and leptons.
We outline a simple model and discuss its discoverability at the LHC.Comment: 28 pages, 10 figure
A Stealth Supersymmetry Sampler
The LHC has strongly constrained models of supersymmetry with traditional
missing energy signatures. We present a variety of models that realize the
concept of Stealth Supersymmetry, i.e. models with R-parity in which one or
more nearly-supersymmetric particles (a "stealth sector") lead to collider
signatures with only a small amount of missing energy. The simplest realization
involves low-scale supersymmetry breaking, with an R-odd particle decaying to
its superpartner and a soft gravitino. We clarify the stealth mechanism and its
differences from compressed supersymmetry and explain the requirements for
stealth models with high-scale supersymmetry breaking, in which the soft
invisible particle is not a gravitino. We also discuss new and distinctive
classes of stealth models that couple through a baryon portal or Z' gauge
interactions. Finally, we present updated limits on stealth supersymmetry in
light of current LHC searches.Comment: 45 pages, 16 figure
Spectroscopic Target Selection in the Sloan Digital Sky Survey: The Quasar Sample
We describe the algorithm for selecting quasar candidates for optical
spectroscopy in the Sloan Digital Sky Survey. Quasar candidates are selected
via their non-stellar colors in "ugriz" broad-band photometry, and by matching
unresolved sources to the FIRST radio catalogs. The automated algorithm is
sensitive to quasars at all redshifts lower than z=5.8. Extended sources are
also targeted as low-redshift quasar candidates in order to investigate the
evolution of Active Galactic Nuclei (AGN) at the faint end of the luminosity
function. Nearly 95% of previously known quasars are recovered (based on 1540
quasars in 446 square degrees). The overall completeness, estimated from
simulated quasars, is expected to be over 90%, whereas the overall efficiency
(quasars:quasar candidates) is better than 65%. The selection algorithm targets
ultraviolet excess quasars to i^*=19.1 and higher-redshift (z>3) quasars to
i^*=20.2, yielding approximately 18 candidates per square degree. In addition
to selecting ``normal'' quasars, the design of the algorithm makes it sensitive
to atypical AGN such as Broad Absorption Line quasars and heavily reddened
quasars.Comment: 62 pages, 15 figures (8 color), 8 tables. Accepted by AJ. For a
version with higher quality color figures, see
http://archive.stsci.edu/sdss/quasartarget/RichardsGT_qsotarget.preprint.p
Photometric Redshifts of Quasars
We demonstrate that the design of the Sloan Digital Sky Survey (SDSS) filter
system and the quality of the SDSS imaging data are sufficient for determining
accurate and precise photometric redshifts (``photo-z''s) of quasars. Using a
sample of 2625 quasars, we show that photo-z determination is even possible for
z<=2.2 despite the lack of a strong continuum break that robust photo-z
techniques normally require. We find that, using our empirical method on our
sample of objects known to be quasars, approximately 70% of the photometric
redshifts are correct to within delta z = 0.2; the fraction of correct
photometric redshifts is even better for z>3. The accuracy of quasar
photometric redshifts does not appear to be dependent upon magnitude to nearly
21st magnitude in i'. Careful calibration of the color-redshift relation to
21st magnitude may allow for the discovery of on the order of 10^6 quasars
candidates in addition to the 10^5 quasars that the SDSS will confirm
spectroscopically. We discuss the efficient selection of quasar candidates from
imaging data for use with the photometric redshift technique and the potential
scientific uses of a large sample of quasar candidates with photometric
redshifts.Comment: 29 pages, 8 figures, submitted to A
Design and Performance of the Hotrod Melt-Tip Ice-Drilling System
We introduce the design and performance of a melt-tip ice-drilling system designed to insert a temperature sensor cable into ice. The melt tip is relatively simple and low cost, designed for a one-way trip to the ice-bed interface. The drilling system consists of a melt tip, umbilical cable, winch, interface, power supply, and support items. The melt tip and the winch are the most novel elements of the drilling system, and we make the hardware and electrical designs of these components available open access. Tests conducted in a laboratory ice well indicate that the melt tip has an electrical energy to forward melting heat transfer efficiency of ~35 % with a theoretical maximum penetration rate of ~12 m/hr at maximum 6.0 kW power. In contrast, ice-sheet testing suggests the melt tip has an analogous heat transfer efficiency of ~15 % with a theoretical maximum penetration rate of ~6 m/hr. We expect the efficiency gap between laboratory and field performance to decrease with increasing operator experience. Umbilical freeze-in due to borehole refreezing is the primary depth-limiting factor of the drilling system. Enthalpy-based borehole refreezing assessments predict refreezing below critical umbilical diameter in ~4 hours at -20 ËC ice temperatures and ~20 hours at -2 ËC. This corresponds to a theoretical depth limit of up to ~200 m, depending on firn thickness, ice temperature and operator experience.</p
The Sloan Digital Sky Survey Quasar Catalog V. Seventh Data Release
We present the fifth edition of the Sloan Digital Sky Survey (SDSS) Quasar
Catalog, which is based upon the SDSS Seventh Data Release. The catalog, which
contains 105,783 spectroscopically confirmed quasars, represents the conclusion
of the SDSS-I and SDSS-II quasar survey. The catalog consists of the SDSS
objects that have luminosities larger than M_i = -22.0 (in a cosmology with H_0
= 70 km/s/Mpc Omega_M = 0.3, and Omega_Lambda = 0.7) have at least one emission
line with FWHM larger than 1000 km/s or have interesting/complex absorption
features, are fainter than i > 15.0 and have highly reliable redshifts. The
catalog covers an area of 9380 deg^2. The quasar redshifts range from 0.065 to
5.46, with a median value of 1.49; the catalog includes 1248 quasars at
redshifts greater than four, of which 56 are at redshifts greater than five.
The catalog contains 9210 quasars with i < 18; slightly over half of the
entries have i< 19. For each object the catalog presents positions accurate to
better than 0.1" rms per coordinate, five-band (ugriz) CCD-based photometry
with typical accuracy of 0.03 mag, and information on the morphology and
selection method. The catalog also contains radio, near-infrared, and X-ray
emission properties of the quasars, when available, from other large-area
surveys. The calibrated digital spectra cover the wavelength region 3800-9200
Ang. at a spectral resolution R = 2000 the spectra can be retrieved from the
SDSS public database using the information provided in the catalog. Over 96% of
the objects in the catalog were discovered by the SDSS. We also include a
supplemental list of an additional 207 quasars with SDSS spectra whose archive
photometric information is incomplete.Comment: Accepted, to appear in AJ, 7 figures, electronic version of Table 2
is available, see
http://www.sdss.org/dr7/products/value_added/qsocat_dr7.htm
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