112 research outputs found
T-duality and Generalized Complex Geometry
We find the explicit T-duality transformation in the phase space formulation
of the N=(1,1) sigma model. We also show that the T-duality transformation is a
symplectomorphism and it is an element of O(d,d). Further, we find the explicit
T-duality transformation of a generalized complex structure in this model. We
also show that the extended supersymmetry of the sigma model is preserved under
the T-duality.Comment: 18 pages; added references; published versio
Heat to Electricity Conversion by a Graphene Stripe with Heavy Chiral Fermions
A conversion of thermal energy into electricity is considered in the
electrically polarized graphene stripes with zigzag edges where the heavy
chiral fermion (HCF) states are formed. The stripes are characterized by a high
electric conductance Ge and by a significant Seebeck coefficient S. The
electric current in the stripes is induced due to a non-equilibrium thermal
injection of "hot" electrons. This thermoelectric generation process might be
utilized for building of thermoelectric generators with an exceptionally high
figure of merit Z{\delta}T \simeq 100 >> 1 and with an appreciable electric
power densities \sim 1 MW/cm2.Comment: 8 pages, 3 figure
Preliminary results for RR Lyrae stars and Classical Cepheids from the Vista Magellanic Cloud (VMC) Survey
The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting
-band time series photometry of the system formed by the two Magellanic
Clouds (MC) and the "bridge" that connects them. These data are used to build
-band light curves of the MC RR Lyrae stars and Classical Cepheids and
determine absolute distances and the 3D geometry of the whole system using the
-band period luminosity (), the period - luminosity - color ()
and the Wesenhiet relations applicable to these types of variables. As an
example of the survey potential we present results from the VMC observations of
two fields centered respectively on the South Ecliptic Pole and the 30 Doradus
star forming region of the Large Magellanic Cloud. The VMC -band light
curves of the RR Lyrae stars in these two regions have very good photometric
quality with typical errors for the individual data points in the range of
0.02 to 0.05 mag. The Cepheids have excellent light curves (typical
errors of 0.01 mag). The average magnitudes derived for both types
of variables were used to derive relations that are in general good
agreement within the errors with the literature data, and show a smaller
scatter than previous studies.Comment: 7 pages, 6 figure. Accepted for publication in Astrophysics and Space
Science. Following a presentation at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and the Gaia Perspective", Naples, May 201
Problems and possibilities in fine-tuning of the Cepheid P-L relationship
Factors contributing to the scatter around the ridge-line period-luminosity
relationship are listed, followed by a discussion how to eliminate the adverse
effects of these factors (mode of pulsation, crossing number, temperature
range, reddening, binarity, metallicity, non-linearity of the relationship,
blending), in order to reduce the dispersion of the P-L relationship.Comment: 7 pages, 8 figures; accepted for publication in Astrophysics & Space
Scienc
Realising local government visions for developing district heating: experiences from a learning country
District heating (DH) has an important role to play in enabling cities to transition to low-carbon heating. Although schemes are commonplace in some countries, in âlearning countriesâ where building-level technologies make up the majority of heating systems there are numerous barriers to introducing DH. Local governments are seen as key actors in helping to create a âshared visionâ for DH amongst stakeholders. This study uses interviews with stakeholders from a range of sectors in the UK (an example of a learning country) to examine the visions of local actors for developing DH and the types of national policy that would support local implementation of these visions. The analysis shows that in engaging with DH development local governments seek multiple types of value. Realising this value will most likely happen by taking a long-term, planned approach to development. In contrast, national government policy is geared towards techno-economic criteria and may lead to only a minority of potential sites being developed, without realisation of wider social or environmental benefits aligned to local visions. The work highlights the importance of local strategic planning, enabled by aligned national policy, in realising the full economic, environmental and social benefits of DH
The composition of the protosolar disk and the formation conditions for comets
Conditions in the protosolar nebula have left their mark in the composition
of cometary volatiles, thought to be some of the most pristine material in the
solar system. Cometary compositions represent the end point of processing that
began in the parent molecular cloud core and continued through the collapse of
that core to form the protosun and the solar nebula, and finally during the
evolution of the solar nebula itself as the cometary bodies were accreting.
Disentangling the effects of the various epochs on the final composition of a
comet is complicated. But comets are not the only source of information about
the solar nebula. Protostellar disks around young stars similar to the protosun
provide a way of investigating the evolution of disks similar to the solar
nebula while they are in the process of evolving to form their own solar
systems. In this way we can learn about the physical and chemical conditions
under which comets formed, and about the types of dynamical processing that
shaped the solar system we see today.
This paper summarizes some recent contributions to our understanding of both
cometary volatiles and the composition, structure and evolution of protostellar
disks.Comment: To appear in Space Science Reviews. The final publication is
available at Springer via http://dx.doi.org/10.1007/s11214-015-0167-
Young and Intermediate-age Distance Indicators
Distance measurements beyond geometrical and semi-geometrical methods, rely
mainly on standard candles. As the name suggests, these objects have known
luminosities by virtue of their intrinsic proprieties and play a major role in
our understanding of modern cosmology. The main caveats associated with
standard candles are their absolute calibration, contamination of the sample
from other sources and systematic uncertainties. The absolute calibration
mainly depends on their chemical composition and age. To understand the impact
of these effects on the distance scale, it is essential to develop methods
based on different sample of standard candles. Here we review the fundamental
properties of young and intermediate-age distance indicators such as Cepheids,
Mira variables and Red Clump stars and the recent developments in their
application as distance indicators.Comment: Review article, 63 pages (28 figures), Accepted for publication in
Space Science Reviews (Chapter 3 of a special collection resulting from the
May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space
Age
Erratum: The Carnegie Supernova Project. I. Third Photometry Data Release of Low-redshift Type Ia Supernovae and Other White Dwarf Explosions (2017, AJ, 154, 211)
GalaxiesStars and planetary system
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