3,748 research outputs found
Properties of optically selected BL Lac candidates from the SDSS
\textbf{Context.} Deep optical surveys open the avenue for find large numbers
of BL Lac objects that are hard to identify because they lack the unique
properties classifying them as such. While radio or X-ray surveys typically
reveal dozens of sources, recent compilations based on optical criteria alone
have increased the number of BL Lac candidates considerably. However, these
compilations are subject to biases and may contain a substantial number of
contaminating sources. \textbf{Aims.} In this paper we extend our analysis of
182 optically selected BL Lac object candidates from the SDSS with respect to
an earlier study. The main goal is to determine the number of bona fide BL Lac
objects in this sample. \textbf{Methods.} We examine their variability
characteristics, determine their broad-band radio-UV SEDs, and search for the
presence of a host galaxy. In addition we present new optical spectra for 27
targets with improved S/N with respect to the SDSS spectra. \textbf{Results.}
At least 59% of our targets have shown variability between SDSS DR2 and our
observations by more than 0.1-0.27 mag de- pending on the telescope used. A
host galaxy was detected in 36% of our targets. The host galaxy type and
luminosities are consistent with earlier studies of BL Lac host galaxies.
Simple fits to broad-band SEDS for 104 targets of our sample derived
synchrotron peak frequencies between with a peak at
. Our new optical spectra do not reveal any new
redshift for any of our objects. Thus the sample contains a large number of
bona fide BL Lac objects and seems to contain a substantial fraction of
intermediate-frequency peaked BL Lacs.Comment: Accepted for publication in A\&
California GAMA Special Study: Stable Isotopic Composition of Boron in Groundwater - San Diego County Domestic Well Data
Resistance and resilience of social–ecological systems to recurrent typhoon disturbance on a subtropical island: Taiwan
Tropical cyclones (TCs) have major effects on ecological and social systems. However, studies integrating the effects of TCs on both social and ecological systems are rare, especially in the northwest Pacific, where the frequency of TCs (locally named typhoons) is the highest in the world. We synthesized studies of effects of recurrent typhoons on social and ecological systems in Taiwan over the last several decades. Many responses to TCs are comparable between social and ecological systems. High forest ecosystem resistance, evident from tree mortality below 2% even following multiple strong typhoons, is comparable with resistance of social systems, including the only 4% destruction of river embankments following a typhoon that brought nearly 3000 mm rainfall in three days. High resilience as reflected by quick returns of leaf area index, mostly in one year, and streamwater chemistry, one to several weeks to pre‐typhoon levels of ecosystems, are comparable to quick repair of the power grid within one to several days and returns of vegetable price within several weeks to pre‐typhoon levels of the social systems. Landslides associated with intense typhoons have buried mountain villages and transported large quantities of woody debris to the coast, affecting the coastal plains and reefs, illustrating a ridge‐to‐reef link between ecological and societal systems. Metrics of both social and ecological function showed large fluctuations in response to typhoons but quickly returned to pre‐disturbance levels, except when multiple intense typhoons occurred within a single season. Our synthesis illustrates that the social–ecological systems in Taiwan are highly dynamic and responsive to frequent typhoon disturbance, with extraordinarily high resistance and resilience. For ecosystems, the efficient responsiveness results from the selective force of TCs on ecosystem structure and processes. For social systems, it is the result of the effects of TCs on planning and decision making by individuals (e.g., farmers), management sectors, and ultimately the government. In regions with frequent TCs, the social–ecological systems are inevitably highly dynamic and rapid responses are fundamental to system resistance and resilience which in turn is key to maintaining structure and function of the social–ecological systems
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Iterated transportation simulations for Dallas and Portland
The goal of the TRansportation ANalysis and SIMulation System (TRANSIMS) is to combine the most important aspects of human decision-making related to transportation, from activities planning (sleep, work, eat, shop,...) via modal and route planning to driving, into a single, consistent methodological and software framework. This is meant to combine the functionalities of activities-based travel demand generation, modal choice and route assignment, and micro-simulation. TRANSIMS attempts to employ advanced methodologies in all these modules. Yet, it is probably the overall framework that is the most important part of this attempt. It is, for example, possible to replace the TRANSIMS microsimulation by another micro-simulation that uses the same input and generates the same output. TRANSIMS uses specific regions as examples in order to ensure that the technology is rooted in the real world. Until about the middle of 1997, an approximately five miles by five miles area in Dallas/Texas was used. Since then, TRANSIMS has moved to using data from Portland/Oregon; a case study for this region is planned to be completed by the end of the year 2000. In this paper the authors give short descriptions of these projects and give references to related publications
Fuzzy cellular model for on-line traffic simulation
This paper introduces a fuzzy cellular model of road traffic that was
intended for on-line applications in traffic control. The presented model uses
fuzzy sets theory to deal with uncertainty of both input data and simulation
results. Vehicles are modelled individually, thus various classes of them can
be taken into consideration. In the proposed approach, all parameters of
vehicles are described by means of fuzzy numbers. The model was implemented in
a simulation of vehicles queue discharge process. Changes of the queue length
were analysed in this experiment and compared to the results of NaSch cellular
automata model.Comment: The original publication is available at http://www.springerlink.co
Course of pattern-reversed visual evoked cortical potentials in 30 eyes after bony orbital decompression in dysthyroid optic neuropathy
Spin-Boson Hamiltonian and Optical Absorption of Molecular Dimers
An analysis of the eigenstates of a symmetry-broken spin-boson Hamiltonian is
performed by computing Bloch and Husimi projections. The eigenstate analysis is
combined with the calculation of absorption bands of asymmetric dimer
configurations constituted by monomers with nonidentical excitation energies
and optical transition matrix elements. Absorption bands with regular and
irregular fine structures are obtained and related to the transition from the
coexistence to a mixing of adiabatic branches in the spectrum. It is shown that
correlations between spin states allow for an interpolation between absorption
bands for different optical asymmetries.Comment: 15 pages, revTeX, 8 figures, accepted for publication in Phys. Rev.
Conservation Laws in Cellular Automata
If X is a discrete abelian group and B a finite set, then a cellular
automaton (CA) is a continuous map F:B^X-->B^X that commutes with all X-shifts.
If g is a real-valued function on B, then, for any b in B^X, we define G(b) to
be the sum over all x in X of g(b_x) (if finite). We say g is `conserved' by F
if G is constant under the action of F. We characterize such `conservation
laws' in several ways, deriving both theoretical consequences and practical
tests, and provide a method for constructing all one-dimensional CA exhibiting
a given conservation law.Comment: 19 pages, LaTeX 2E with one (1) Encapsulated PostScript figure. To
appear in Nonlinearity. (v2) minor changes/corrections; new references added
to bibliograph
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