785 research outputs found
The Local Galaxy Density and the Arm Class of Spiral Galaxies
We have examined the effect of the environmental density on the arm
classification of an extensive sample of spiral galaxies included in the Nearby
Galaxy Catalog (Tully, 1988a). We have also explored the dependence of the arm
class of a galaxy on other factors, such as its blue absolute magnitude and its
disk-to-total mass ratio, inferred in the literature either from the gradient
of a good galaxy rotation curve or from a photometric mass decomposition
method. We have found that the arm class is strongly related to the absolute
magnitude in the mid-type spirals (in the sense that grand design galaxies are,
on average, more luminous than flocculent objects), whilst this relation is
considerably weaker in the early and late types. In general the influence of
the local density on the arm structure appears to be much weaker than that of
the absolute magnitude. The local density acts essentially in strengthening the
arm class--absolute magnitude relation for the mid types, whereas no
environmental density effects are observed in the early and late types. Using
the most recent estimates of the disk-to-total mass ratio, we do not confirm
this ratio to be a significant factor which affects the arm class;
nevertheless, owing to poor statistics and large uncertanties, the issue
remains open. Neither a local density effect nor an unambiguous bar effect on
the disk-to-total mass ratio is detectable; the latter finding may challenge
some theoretical viewpoints on the formation of bar structures.Comment: 15 pages, Latex, SISSA 102/93/A openbib.sty and 4 POSTSCRIPT figures
appende
Environmental Effects on Local Active Galactic Nuclei
Using an extensive sample of nearby galaxies (the Nearby Galaxies Catalog, by
Tully), we investigate the environment of the galaxies hosting low-luminosity
AGNs (Seyferts and LINERs). We define the local galaxy density, adopting a new
correction for the incompleteness of the galaxy sample at large distances. We
consider both a complete sample of bright and nearby AGNs, identified from the
nuclear spectra obtained in available wide optical spectroscopic surveys, and a
complete sample of nearby Seyferts. Basically, we compare the local galaxy
density distributions of the AGNs with those of non-AGN samples, chosen in
order to match the magnitude and morphological type distributions of the AGN
samples. We find, only for the early-type spirals more luminous than , that both LINERs and Seyferts tend to reside in denser environments on
all the scales tested, from tenths of Mpc to a few Mpc; moreover Seyferts show
an enhanced small-scale density segregation with respect to LINERs. This gives
support to the idea that AGNs can be stimulated by interactions. On larger
scales, tens of Mpc, we find that the AGNs hosted in luminous early-type
spirals show a tendency to stay near the center of the Local Supercluster.
Finally we discuss the interpretations of our findings and their consequences
for some possible scenarios of AGN formation and evolution and for the problem
of how AGNs trace the large-scale structures.Comment: 16 pages+3 figures, uuencoded postscript file, preprint SISSA 76/94/A
, ApJ November 20, 199
Lowering of the complexity of quantum chemistry methods by choice of representation
The complexity of the standard hierarchy of quantum chemistry methods is not
invariant to the choice of representation. This work explores how the scaling
of common quantum chemistry methods can be reduced using real-space,
momentum-space, and time-dependent intermediate representations without
introducing approximations. We find the scalings of exact Gaussian basis
Hartree--Fock theory, second-order M{\o}ller-Plesset perturbation theory, and
coupled cluster theory (specifically, linearized coupled cluster doubles and
the distinguishable cluster approximation with doubles) to be
, , and respectively,
where denotes system size. These scalings are not asymptotic and hold over
all ranges of
Effective Shareholder Engagement to Address the Food Sectorâs SDG-Related Impacts in Mexico
While investor engagement on environmental and social issues have grown in recent years, they remain limited in Mexico and other emerging markets.
Investors have an opportunity to do more to help address critical SDG-related issues in these contexts through their active ownership efforts. By doing so, they can be more responsible in ensuring respect for human rights, protecting shared systems, and supporting their long-term financial interests. Importantly, they can also ensure they comply with â and support their portfolio companies in complying with â emerging legal frameworks requiring reporting and due diligence on the impacts of their global value chains.
In our new report, Effective Shareholder Engagement to Address the Food Sectorâs SDG-Related Impacts in Mexico, CCSI summarizes key opportunities and barriers facing investors who wish to more actively drive positive SDG outcomes in Mexicoâs food sector through shareholder engagement.
The report explores the food sector-related SDG challenges in Mexico, the influential companies investors can engage with, relevant benchmarks of those companies, the status of sustainable investing in Mexico, and the extent and nature of investor influence over companies in Mexico. Based on this, the report provides recommendations on how active investors can best exercise their leverage in the particular context of Mexicoâs food sector
Galaxies in group and field environments: a comparison of optical-NIR luminosities and colors
We compare properties of galaxies in loose groups with those in field
environment by analyzing the Nearby Optical Galaxy (NOG) catalog of galaxy
systems. We consider as group galaxies, objects belonging to systems with at
least five members identified by means of the "friends of friends method", and,
as field galaxies, all galaxies with no companions. We analyze both a
magnitude--limited sample of 959 and 2035 galaxies (groups vs. field galaxies,
respectively, B<14 mag, and 2000<cz<6000 km/s) and a volume-limited sample (M_B
<-19.01 mag, 2000<cz<4000 km/s 369 group and 548 field galaxies). For all these
galaxies, blue corrected magnitudes and morphological types are available. The
cross-correlation of NOG with the 2MASS second release allow us to assign K
magnitudes and obtain B-K colors for about half of the galaxies in our samples.
We analyze luminosity and color segregation-effects in relation with the
morphological segregation. For both B and K bands, we find that group galaxies
are, on average, more luminous than field galaxies and this effect is not
entirely a consequence of the morphological segregation. After taking into
account the morphological segregation, the luminosity difference between group
and field galaxies is about 10%. When considering only very early-type galaxies
(T<-2) the difference is larger than 30%. We also find that group galaxies are
redder than field galaxies, Delta(B-K) about 0.4 mag. However, after taking
into account the morphological segregation, we find a smaller B-K difference,
poorly significant (only at the c.l. of about 80%).Comment: 11 pages, 10 eps figures, A&A in pres
The Mass Function of Nearby Galaxy Clusters
We present the distribution of virial masses for nearby galaxy clusters, as
obtained from a data-set of 75 clusters, each having at least 20 galaxy members
with measured redshifts within 1 Abell radius. After having accounted for
problems of incompleteness of the data-set, we fitted a power-law to the
cluster mass distribution.Comment: 10 pages (2 figures not included, available upon request), LATEX,
Ref.SISSA 54/93/
Commentary: Nature-Based Insetting: A Harmful Distraction from Corporate Decarbonization
Carbon offsetting is used worldwide on a massive scale, purportedly to mitigate climate change by capturing atmospheric carbon or by increasing or protecting carbon storage. Yet, in recent years, offsetting has been increasingly criticized as a strategy that can harm Indigenous peoples and local communities, exacerbate land inequality, and, paradoxically, worsen the global climate crisis. âCarbon insettingâ has emerged as an alternative approach to offsetting that localizes nature-based solutions projects and other greenhouse gas removal activities within company value chains and has been adopted by major global brands such as NestlĂ©, PepsiCo, and Burberry. This commentary takes a deep dive into insetting projects that employ nature-based solutions, finds that they are likely to suffer from many of the same shortcomings as nature-based offsetting, and argues that corporate reliance on insetting should be treated with extreme skepticism
Innovative Dodecacopter Design â Bulgarian Knight
The current article aims at introducing a novel dodecacopter multirotor design called Bulgarian Knight. The aircraft implements a number of innovations and characteristics that give it an advantage over other contemporary multi-copters. Some of its novel characteristics are the mounting of the rotors under the fuselage by use of pusher propellers. Further, the design implements twelve rotors positioned in an optimal geometric coverage
Structures in Galaxy Clusters
The analysis of the presence of substructures in 16 well-sampled clusters of
galaxies suggests a stimulating hypothesis: Clusters could be classified as
unimodal or bimodal, on the basis of to the sub-clump distribution in the {\em
3-D} space of positions and velocities. The dynamic study of these clusters
shows that their fundamental characteristics, in particular the virial masses,
are not severely biased by the presence of subclustering if the system
considered is bound.Comment: (16 pages in LATEX, 4 tables in LATEX are at the end of the file, the
figures not included are available upon request), REF SISSA 158/93/
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