969 research outputs found
CPN Tools 4: Multi-formalism and Extensibility
Abstract. CPN Tools is an advanced tool for editing, simulating, and analyzing colored Petri nets. This paper discusses the fourth major re-lease of the tool, which makes it simple to use the tool for ordinary Petri nets, including adding inhibitor and reset arcs, and PNML export. This version also supports declarative modeling using constraints, and adds an extension framework making it easy for third parties to extend CPN Tools using Java.
Ultrastable lasers based on vibration insensitive cavities
We present two ultra-stable lasers based on two vibration insensitive cavity
designs, one with vertical optical axis geometry, the other horizontal.
Ultra-stable cavities are constructed with fused silica mirror substrates,
shown to decrease the thermal noise limit, in order to improve the frequency
stability over previous designs. Vibration sensitivity components measured are
equal to or better than 1.5e-11 per m.s^-2 for each spatial direction, which
shows significant improvement over previous studies. We have tested the very
low dependence on the position of the cavity support points, in order to
establish that our designs eliminate the need for fine tuning to achieve
extremely low vibration sensitivity. Relative frequency measurements show that
at least one of the stabilized lasers has a stability better than 5.6e-16 at 1
second, which is the best result obtained for this length of cavity.Comment: 8 pages 12 figure
Ultraviolet Absorption Spectra at Reduced Temperatures. I. Principles and Methods
Low temperature absorption and fluorescence spectra of solids, liquids,
and solutions often reveal increased spectral detail of use in analytical
procedures and molecular structure studies. Nevertheless, while qualitative
observations of the influence of liquid air temperatures upon optical
properties were undertaken very early, investigations of the
absorption and fluorescence of organic compounds at the temperature
of liquid nitrogen (-195.6°; 77.4 °K.) and below have appeared only
sporadically. Because of the potential usefulness of the technique we have undertaken a systematic study of the low temperature spectra
of substances of biochemical interest. The present paper discusses the
methods employed; subsequent papers will deal with the experimental
results. In this work, we have emphasized the wave-length location of
absorption bands and the accurate determination of relative optical densities
rather than precision in the determination of absolute optical densities,
thus permitting the use of simpler methods than would otherwise be
necessary
Experimenting an optical second with strontium lattice clocks
Progress in realizing the SI second had multiple technological impacts and
enabled to further constraint theoretical models in fundamental physics.
Caesium microwave fountains, realizing best the second according to its current
definition with a relative uncertainty of 2-4x10^(-16), have already been
superseded by atomic clocks referenced to an optical transition, both more
stable and more accurate. Are we ready for a new definition of the second? Here
we present an important step in this direction: our system of five clocks
connects with an unprecedented consistency the optical and the microwave
worlds. For the first time, two state-of-the-art strontium optical lattice
clocks are proven to agree within their accuracy budget, with a total
uncertainty of 1.6x10^(-16). Their comparison with three independent caesium
fountains shows a degree of reproducibility henceforth solely limited at the
level of 3.1x10^(-16) by the best realizations of the microwave-defined second.Comment: 9 pages, 4 figures, 2 table
Cross-clade simultaneous HIV drug resistance genotyping for reverse transcriptase, protease, and integrase inhibitor mutations by Illumina MiSeq
The APEX framework: prototyping of ubiquitous environments based on Petri Nets
The user experience of ubiquitous environments is a determining factor in their success. The characteristics of such systems must be explored as early as possible to anticipate potential user problems, and to reduce the cost of redesign. However, the development of early prototypes to be evaluated in the target environment can be disruptive
to the ongoing system and therefore unacceptable. This paper reports on an ongoing effort to explore how model-based rapid prototyping of ubiquitous
environments might be used to avoid actual deployment while still enabling users to interact with a representation of the system. The paper describes APEX, a framework that brings together an existing 3D Application Server with CPN Tools. APEX-based prototypes enable users to navigate a virtual world simulation of the envisaged ubiquitous environment.
The APEX architecture and the proposed CPN-based modelling approach are described. An example illustrates their use.Fundação para a Ciência e a Tecnologia (FCT) - bolsa de doutoramento SFRH/BD/41179/200
INTEGRAL observations of the field of the BL Lacertae object S5~0716+714
We have performed observations of the blazar S5 0716+714 with INTEGRAL on 2-6
April 2004. In the first months of 2004, the source had increased steadily in
optical brightness and had undergone two outbursts. During the latter, occurred
in March, it reached the extreme level of R = 12.1 mag, which triggered our
INTEGRAL program. The target has been detected with IBIS/ISGRI up to 60 keV,
with a flux of ~3 x 10e-11 erg/s/cm2 in the 30-60 keV interval, a factor of ~2
higher than observed by the BeppoSAX PDS in October 2000. In the field of S5
0716+714 we have also detected the Flat Spectrum Radio Quasar S5 0836+710 and
the two Seyfert galaxies Mkn 3 and Mkn 6. Their IBIS/ISGRI spectra are rather
flat, albeit consistent with those measured by BeppoSAX. In the spectrum of Mkn
3 we find some evidence of a break between ~60 and ~100 keV, reminiscent of the
high energy cut-offs observed in other Seyfert galaxies. This is the first
report of INTEGRAL spectra of weak Active Galactic Nuclei.Comment: 5 pages, 5 figures, in press in A&
Detailed Radio to Soft Gamma-ray Studies of the 2005 Outburst of the New X-ray Transient XTE J1818-245
XTE J1818-245 is an X-ray nova that experienced an outburst in 2005, first
seen by the RXTE satellite. The source was observed simultaneously at various
wavelengths up to soft gamma-rays with the INTEGRAL satellite, from 2005
February to September. X-ray novae are extreme systems that often harbor a
black hole, and are known to emit throughout the electromagnetic spectrum when
in outburst. We analyzed radio, (N)IR, optical, X-ray and soft gamma-ray
observations and constructed simultaneous broad-band X-ray spectra. Analyzing
both the light curves in various energy ranges and the hardness-intensity
diagram enabled us to study the long-term behavior of the source. Spectral
parameters were typical of the Soft Intermediate States and the High Soft
States of a black hole candidate. The source showed relatively small spectral
variations in X-rays with considerable flux variation in radio. Spectral
studies showed that the accretion disc cooled down from 0.64 to 0.27 keV in 100
days and that the total flux decreased while the relative flux of the hot
medium increased. Radio emission was detected several times, and,
interestingly, five days after entering the HSS. Modeling the spectral energy
distribution from the radio to the soft gamma-rays reveals that the radio
flares arise from several ejection events. XTE J1818-245 is likely a black hole
candidate transient source that might be closer than the Galactic Bulge. The
results from the data analysis trace the physical changes that took place in
the system at a maximum bolometric luminosity of (0.4-0.9)e38 erg/s (assuming a
distance between 2.8-4.3 kpc) and they are discussed within the context of disc
and jet models.Comment: Accepted for publication in Astronomy and Astrophysics. 11 Figures, 3
Table
Serpens X-1 observed by INTEGRAL
Here we report results of an INTEGRAL-AO1 observation of the X-ray burst and
atoll source Ser X-1 performed in May 2003. The object was observed for a total
on-source time of 400 ks but nearly 8 degrees off-axis due to its amalgamation
with an observation of SS 433, the pointing target source. Ser X-1 has been
clearly detected up to 30 keV with unprecedented positional accuracy for
high-energy emission. The 20-30 keV light curve showed substantial variability
during the observation. Comparison with previous observations indicates that
the source was in its high (`banana') state and displayed a soft spectrum
during the INTEGRAL pointing. A (non simultaneous) radio-to-gamma-rays
broad-band spectral energy distribution is also presented for the first time
and discussed.Comment: 6 pages, 3 figures, 1 table; accepted for publication on Astronomy &
Astrophysics, main journal. Final version of the paper including the A&A
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