87 research outputs found
Towards a Formal Model of Privacy-Sensitive Dynamic Coalitions
The concept of dynamic coalitions (also virtual organizations) describes the
temporary interconnection of autonomous agents, who share information or
resources in order to achieve a common goal. Through modern technologies these
coalitions may form across company, organization and system borders. Therefor
questions of access control and security are of vital significance for the
architectures supporting these coalitions.
In this paper, we present our first steps to reach a formal framework for
modeling and verifying the design of privacy-sensitive dynamic coalition
infrastructures and their processes. In order to do so we extend existing
dynamic coalition modeling approaches with an access-control-concept, which
manages access to information through policies. Furthermore we regard the
processes underlying these coalitions and present first works in formalizing
these processes. As a result of the present paper we illustrate the usefulness
of the Abstract State Machine (ASM) method for this task. We demonstrate a
formal treatment of privacy-sensitive dynamic coalitions by two example ASMs
which model certain access control situations. A logical consideration of these
ASMs can lead to a better understanding and a verification of the ASMs
according to the aspired specification.Comment: In Proceedings FAVO 2011, arXiv:1204.579
Non-blackbody disks can help explain inferred AGN accretion disk sizes
If the atmospheric density ρatm in the accretion disk of an active galactic nucleus (AGN) is sufficiently low, scattering in the atmosphere can produce a non-blackbody emergent spectrum. For a given bolometric luminosity, at ultraviolet and optical wavelengths such disks have lower fluxes and apparently larger sizes as compared to disks that emit as blackbodies. We show that models in which ρatm is a sufficiently low fixed fraction of the interior density ρ can match the AGN STORM observations of NGC 5548 but produce disk spectral energy distributions that peak at shorter wavelengths than observed in luminous AGN in general. Thus, scattering atmospheres can contribute to the explanation for large inferred AGN accretion disk sizes but are unlikely to be the only contributor. In the appendix section, we present unified equations for the interior ρ and T in gas pressure-dominated regions of a thin accretion disk.PostprintPeer reviewe
Uso de glicerina residual e glicerol na preparação de biopolímero
A glicerina loira, um coproduto obtido na produção do biodiesel pela reação de transesterificação, tem sido gerado na última década, em grandes quantidades cada vez maiores, devido ao aumento na produção desse biocombustível. Dessa forma, tornam-se importantes pesquisas relacionadas ao desenvolvimento de materiais e produtos que agreguem valor e destino ecologicamente adequado à esse resíduo. Nesse contexto, o presente estudo trata do reaproveitamento da glicerina loira na síntese de um biopolímero biodegradável, o poli(citrato de glicerol). As polimerizações foram estudadas empregando-se ácido cítrico/glicerina loira e ZnCl2 como catalisador. Obtiveram-se conversões de 58,2 % em 120 min de reação, usando-se a glicerina loira, sem tratamento prévio. Tais dados indicam a viabilidade do reuso da glicerina loira, sem pré-tratamentos, na preparação do respectivo biopolímero, um material com valor agregado e vantajoso ambientalmente.A glicerina loira, um coproduto obtido na produção do biodiesel pela reação de transesterificação, tem sido gerado na última década, em grandes quantidades cada vez maiores, devido ao aumento na produção desse biocombustível. Dessa forma, tornam-se importantes pesquisas relacionadas ao desenvolvimento de materiais e produtos que agreguem valor e destino ecologicamente adequado à esse resíduo. Nesse contexto, o presente estudo trata do reaproveitamento da glicerina loira na síntese de um biopolímero biodegradável, o poli(citrato de glicerol). As polimerizações foram estudadas empregando-se ácido cítrico/glicerina loira e ZnCl2 como catalisador. Obtiveram-se conversões de 58,2% em 120 min de reação, usando-se a glicerina loira, sem tratamento prévio. Tais dados indicam a viabilidade do reuso da glicerina loira, sem pré-tratamentos, na preparação do respectivo biopolímero, um material com valor agregado e vantajoso ambientalmente
Revisão sobre a toxicidade e impactos ambientais relacionados à vinhaça, efluente da indústria sucroalcooleira
O Brasil é um dos maiores produtores mundiais de etanol proveniente de cana-de-açúcar. No processo de produção do biocombustível etanol vários resíduos são gerados, dentre eles destaca-se a vinhaça como o mais preocupante, devido as suas características físico-químicas e grande volume gerado. Este efluente é caracterizado altos teores de matéria orgânica, apresentando elevada demanda bioquímica de oxigênio (DBO), pH ácido e a presença de elementos como potássio e enxofre. Tais propriedades conferem a vinhaça um grande poder como poluidor ambiental. Estudos demonstram a contaminação de águas, solos, flora e fauna de mananciais. Considerando-se que o etanol é produzido empregando-se diferentes matérias primas, em inúmeros países, é possível concluir que estamos diante de um problema mundial bastante relevante, relacionado aos usos, armazenamento e descarte desse efluente. Essa revisão apresenta detalhadamente a origem, as propriedades e os impactos ambientais relacionados à vinhaça
A First Look at Spatially Resolved Balmer Decrements at from JWST NIRISS Slitless Spectroscopy
We present the first results on the spatial distribution of dust attenuation
at traced by the Balmer Decrement, H/H, in
emission-line galaxies using deep JWST NIRISS slitless spectroscopy from the
CAnadian NIRISS Unbiased Cluster Survey (CANUCS). H and H
emission line maps of emission-line galaxies are extracted and stacked in bins
of stellar mass for two grism redshift bins, and
. Surface brightness profiles for the Balmer Decrement are
measured and radial profiles of the dust attenuation towards H,
, are derived. In both redshift bins, the integrated
Balmer Decrement increases with stellar mass. Lower mass
(Log(/M)) galaxies have centrally
concentrated, negative dust attenuation profiles whereas higher mass galaxies
(Log(/M)) have flat dust attenuation
profiles. The total dust obscuration is mild, with on average and
mag in the low and high redshift bins respectively. We model the
typical light profiles of star-forming galaxies at these redshifts and stellar
masses with GALFIT and apply both uniform and radially varying dust attenuation
corrections based on our integrated Balmer Decrements and radial dust
attenuation profiles. If these galaxies were observed with typical JWST NIRSpec
slit spectroscopy ( shutters), on average,
H star formation rates (SFRs) measured after slit-loss corrections
assuming uniform dust attenuation will overestimate the total SFR by and at and
respectively.Comment: 7 pages, 5 figures, submitted to ApJ
CDM not dead yet: massive high-z Balmer break galaxies are less common than previously reported
Early JWST observations that targeted so-called double-break sources
(attributed to Lyman and Balmer breaks at ), reported a previously unknown
population of very massive, evolved high-redshift galaxies. This surprising
discovery led to a flurry of attempts to explain these objects' unexpected
existence including invoking alternatives to the standard CDM
cosmological paradigm. To test these early results, we adopted the same
double-break candidate galaxy selection criteria to search for such objects in
the JWST images of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS), and
found a sample of 19 sources over five independent CANUCS fields that cover a
total effective area of arcmin at . However, (1) our SED
fits do not yield exceptionally high stellar masses for our candidates, while
(2) spectroscopy of five of the candidates shows that while all five are at
high redshifts, their red colours are due to high-EW emission lines in
star-forming galaxies rather than Balmer breaks in massive, evolved systems.
Additionally, (3) field-to-field variance leads to differences of
dex in the maximum stellar masses measured in the different fields, suggesting
that the early single-field JWST observations may have suffered from cosmic
variance and/or sample bias. Finally, (4) we show that the presence of even a
single massive outlier can dominate conclusions from small samples such as
those in early JWST observations. In conclusion, we find that the double-break
sources in CANUCS are not sufficiently massive or numerous to warrant
questioning the standard CDM paradigm.Comment: V2: correction of display problem of Fig.1 in Chrome browser.
Submitted to MNRAS, 10 pages (+4 in Appendix), 5 figures (+4), 1 table (+1
The Sparkler: Evolved High-Redshift Globular Clusters Captured by JWST
Using data from JWST, we analyze the compact sources ("sparkles") located
around a remarkable galaxy (the "Sparkler") that is
strongly gravitationally lensed by the galaxy cluster SMACS
J0723.3-7327. Several of these compact sources can be cross-identified in
multiple images, making it clear that they are associated with the host galaxy.
Combining data from JWST's {\em Near-Infrared Camera} (NIRCam) with archival
data from the {\em Hubble Space Telescope} (HST), we perform 0.4-4.4m
photometry on these objects, finding several of them to be very red and
consistent with the colors of quenched, old stellar systems. Morphological fits
confirm that these red sources are spatially unresolved even in strongly
magnified JWST/NIRCam images, while JWST/NIRISS spectra show [OIII]5007
emission in the body of the Sparkler but no indication of star formation in the
red compact sparkles. The most natural interpretation of these compact red
companions to the Sparkler is that they are evolved globular clusters seen at
. Applying \textsc{Dense Basis} SED-fitting to the sample, we infer
formation redshifts of for these globular cluster
candidates, corresponding to ages of Gyr at the epoch of
observation and a formation time just 0.5~Gyr after the Big Bang. If
confirmed with additional spectroscopy, these red, compact "sparkles" represent
the first evolved globular clusters found at high redshift, could be amongst
the earliest observed objects to have quenched their star formation in the
Universe, and may open a new window into understanding globular cluster
formation. Data and code to reproduce our results will be made available at
\faGithub\href{https://niriss.github.io/sparkler.html}{http://canucs-jwst.com/sparkler.html}.Comment: Submitted to ApJL. Comments are welcome. Data and code to reproduce
our results will be made available at niriss.github.io/sparkler.htm
The first large catalogue of spectroscopic redshifts in Webb's First Deep Field, SMACS J0723.37327
We present a spectroscopic redshift catalogue of the SMACS J0723.37327
field ("Webb's First Deep Field") obtained from JWST/NIRISS grism spectroscopy
and supplemented with JWST/NIRSpec and VLT/MUSE redshifts. The catalogue
contains a total of 190 sources with secure spectroscopic redshifts, including
156 NIRISS grism redshifts, 123 of which are for sources whose redshifts were
previously unknown. These new grism redshifts are secured with two or more
spectroscopic features (64 sources), or with a single spectral feature whose
identity is secured from the object's nine-band photometric redshift (59
sources). These are complemented with 17 NIRSpec and 48 MUSE redshifts,
including six new NIRSpec redshifts identified in this work. In addition to the
cluster galaxy redshifts (for which we provide 40 new
NIRISS absorption-line redshifts), we also find three prominent galaxy
overdensities at higher redshifts - at , , and - that
were until now not seen in the JWST/NIRSpec and VLT/MUSE data. The paper
describes the characteristics of our spectroscopic redshift sample and the
methodology we have employed to obtain it. Our redshift catalogue is made
available to the community at https://niriss.github.io/smacs0723.Comment: 19 pages, 13 figures, 3 appendices. Accepted for publication in MNRA
The near-infrared imager and slitless spectrograph for the James Webb Space Telescope. II. Wide field slitless spectroscopy
We acknowledge support from the Natural Sciences and Engineering Research Council of Canada (NSERC) through a variety of its funding programs. This work is in part supported by Canadian Space Agency grant 18JWSTGTO1. C.P., S.R. and K.V. are supported by the Canadian Space Agency under a contract with NRC Herzberg Astronomy and Astrophysics. K.M. acknowledges funding by the Science and Technology Foundation of Portugal (FCT), grants No. IF/00194/2015, PTDC/FIS-AST/28731/2017, UIDB/00099/2020.We present the wide field slitless spectroscopy mode of the NIRISS instrument on the James Webb Space Telescope. This mode employs two orthogonal low-resolution (resolving power ≈150) grisms in combination with a set of six blocking filters in the wavelength range 0.8–2.3 μm to provide a spectrum of almost every source across the field-of-view. When combined with the low background, high sensitivity and high spatial resolution afforded by the telescope, this mode will enable unprecedented studies of the structure and evolution of distant galaxies. We describe the performance of the as-built hardware relevant to this mode and expected imaging and spectroscopic sensitivity. We discuss operational and calibration procedures to obtain the highest quality data. As examples of the observing mode usage, we present details of two planned Guaranteed Time Observations programs: The Canadian NIRISS Unbiased Cluster Survey and The NIRISS Survey for Young Brown Dwarfs and Rogue Planets.Publisher PDFPeer reviewe
Caracterização de acetato de celulose obtido a partir do bagaço de cana-de-açúcar por ¹H-RMN
- …