3,180 research outputs found
Gas Turbines for Power Generation on Board of Cruise Ships: A Possible Solution to Meet the New IMO Regulations?
AbstractIn order to reduce the environmental impact caused by merchant ships, the International Maritimes Organization is imposing new and stricter regulations on NOx and SOx emissions. Therefore, ships propelled by Internal Combustion Engines (ICEs) burning HFO must adopt abatement devices or switch to a cleaner fuel such as MGO. If the use of MGO is considered, a further and more drastic modification of the power system can be analyzed, namely the use of Gas Turbines (GTs) in place of ICEs. GTs are an attractive solution thanks to a reduced weight, size and NOx emissions, but are penalized by a lower electric efficiency. The case of a real cruise ship is considered in the present paper and a detailed quantification of the above mentioned differences is provided by simulating the ship operation for a reference trip
Evaluation of gas turbines as alternative energy production systems for a large cruise ship to meet new maritime regulations
As a consequence of the new and up-coming regulations imposed by the International Maritime Organization (IMO), polluting emissions produced by large ships are now under strict control. Moreover, specific areas called \u201cEmission Controlled Area\u201d (ECA), which request even lower pollutant emissions, will be extended. To face up to this issue, ships propelled by Internal Combustion Engines (ICEs) burning Heavy Fuel Oil (HFO) can be equipped with abatement devices such as scrubbers and Selective Catalytic Reactor systems. Along with these solutions, which seem to be the route ship-owners will prefer, other methods can be considered, such as the use of Marine Gas Oil (MGO): a more expensive fuel, but with lower sulphur content. The use of MGO allows users to consider a further and more drastic modification of the power system, namely the use of Gas Turbines (GTs) in place of ICEs. GTs, despite being less efficient, are much lighter, more compact, and can more easily reach low NOx emissions than ICEs. Even if these aspects are theoretically well known, there are still difficulties in finding studies reporting quantitative analysis (weight, dimensions, fuel consumption) that compare GT and ICE power systems employed on board. The present paper aims to provide these data by analyzing different solutions applied to a real case. Unlike other studies, the work is focused on a cruise ship rather than on a cargo ship, because a cruise ship's operation profile is more variable during the trip
Distinguished quantum states in a class of cosmological spacetimes and their Hadamard property
In a recent paper, we proved that a large class of spacetimes, not
necessarily homogeneous or isotropous and relevant at a cosmological level,
possesses a preferred codimension one submanifold, i.e., the past cosmological
horizon, on which it is possible to encode the information of a scalar field
theory living in the bulk. Such bulk-to-boundary reconstruction procedure
entails the identification of a preferred quasifree algebraic state for the
bulk theory, enjoying remarkable properties concerning invariance under
isometries (if any) of the bulk and energy positivity, and reducing to
well-known vacua in standard situations. In this paper, specialising to open
FRW models, we extend previously obtained results and we prove that the
preferred state is of Hadamard form, hence the backreaction on the metric is
finite and the state can be used as a starting point for renormalisation
procedures. That state could play a distinguished role in the discussion of the
evolution of scalar fluctuations of the metric, an analysis often performed in
the development of any model describing the dynamic of an early Universe which
undergoes an inflationary phase of rapid expansion in the past.Comment: 41 page
Rigorous steps towards holography in asymptotically flat spacetimes
Scalar QFT on the boundary at null infinity of a general
asymptotically flat 4D spacetime is constructed using the algebraic approach
based on Weyl algebra associated to a BMS-invariant symplectic form. The
constructed theory is invariant under a suitable unitary representation of the
BMS group with manifest meaning when the fields are interpreted as suitable
extensions to of massless minimally coupled fields propagating in the
bulk. The analysis of the found unitary BMS representation proves that such a
field on coincides with the natural wave function constructed out of
the unitary BMS irreducible representation induced from the little group
, the semidirect product between SO(2) and the two dimensional
translational group. The result proposes a natural criterion to solve the long
standing problem of the topology of BMS group. Indeed the found natural
correspondence of quantum field theories holds only if the BMS group is
equipped with the nuclear topology rejecting instead the Hilbert one.
Eventually some theorems towards a holographic description on of QFT in
the bulk are established at level of algebras of fields for strongly
asymptotically predictable spacetimes. It is proved that preservation of a
certain symplectic form implies the existence of an injective -homomorphism
from the Weyl algebra of fields of the bulk into that associated with the
boundary . Those results are, in particular, applied to 4D Minkowski
spacetime where a nice interplay between Poincar\'e invariance in the bulk and
BMS invariance on the boundary at is established at level of QFT. It
arises that the -homomorphism admits unitary implementation and Minkowski
vacuum is mapped into the BMS invariant vacuum on .Comment: 62 pages, amslatex, xy package; revised section 2 and the
conclusions; corrected some typos; added some references; accepted for
pubblication on Rev. Math. Phy
Running a typical ROOT HEP analysis on Hadoop MapReduce
We evaluate how a typical ROOT High Energy Physics (HEP) analysis can be executed on Hadoop MapReduce. We take into account several aspects and we propose a method to perform the analysis in a completely transparent way to ROOT, the data and the user: the goal is to let ROOT run without any modifications and to store the data in its original format. The solutions which has been found to solve the encountered problems can be easily ported to any HEP code, and in general to any code working on binary data relying on independent sub-problems like HEP particle collision events. We tested the method by running an analysis code for the top quark pair production cross section measurement with the ATLAS experiment at the Large Hadron Collider in the CERN laboratory
Artificial intelligence evaluation of confocal microscope prostate images: our preliminary experience
The HADES RV Programme with HARPS-N at TNG XI. GJ 685 b: a warm super-Earth around an active M dwarf
Small rocky planets seem to be very abundant around low-mass M-type stars.
Their actual planetary population is however not yet precisely understood.
Currently several surveys aim to expand the statistics with intensive detection
campaigns, both photometric and spectroscopic. We analyse 106 spectroscopic
HARPS-N observations of the active M0-type star GJ 685 taken over the past five
years. We combine these data with photometric measurements from different
observatories to accurately model the stellar rotation and disentangle its
signals from genuine Doppler planetary signals in the RV data. We run an MCMC
analysis on the RV and activity indexes time series to model the planetary and
stellar signals present in the data, applying Gaussian Process regression
technique to deal with the stellar activity signals. We identify three periodic
signals in the RV time series, with periods of 9, 24, and 18 d. Combining the
analyses of the photometry of the star with the activity indexes derived from
the HARPS-N spectra, we identify the 18 d and 9 d signals as activity-related,
corresponding to the stellar rotation period and its first harmonic
respectively. The 24 d signals shows no relations with any activity proxy, so
we identify it as a genuine planetary signal. We find the best-fit model
describing the Doppler signal of the newly-found planet, GJ 685\,b,
corresponding to an orbital period d and a
minimum mass M. We also study a
sample of 70 RV-detected M-dwarf planets, and present new statistical evidence
of a difference in mass distribution between the populations of single- and
multi-planet systems, which can shed new light on the formation mechanisms of
low-mass planets around late-type stars.Comment: 18 pages, 13 figures, accepted for publication in A&
HADES RV Programme with HARPS-N at TNG. VII. Rotation and activity of M-Dwarfs from time-series high-resolution spectroscopy of chromospheric indicators
We aim to investigate the presence of signatures of magnetic cycles and
rotation on a sample of 71 early M-dwarfs from the HADES RV programme using
high-resolution time-series spectroscopy of the Ca II H & K and Halpha
chromospheric activity indicators, the radial velocity series, the parameters
of the cross correlation function and the V-band photometry. We used mainly
HARPS-N spectra, acquired over four years, and add HARPS spectra from the
public ESO database and ASAS photometry light-curves as support data, extending
the baseline of the observations of some stars up to 12 years. We provide
log(R'hk) measurements for all the stars in the sample, cycle length
measurements for 13 stars, rotation periods for 33 stars and we are able to
measure the semi-amplitude of the radial velocity signal induced by rotation in
16 stars. We complement our work with previous results and confirm and refine
the previously reported relationships between the mean level of chromospheric
emission, measured by the log(R'hk), with the rotation period, and with the
measured semi-amplitude of the activity induced radial velocity signal for
early M-dwarfs. We searched for a possible relation between the measured
rotation periods and the lengths of the magnetic cycle, finding a weak
correlation between both quantities. Using previous v sin i measurements we
estimated the inclinations of the star's poles to the line of sight for all the
stars in the sample, and estimate the range of masses of the planets GJ 3998 b
and c (2.5 - 4.9 Mearth and 6.3 - 12.5 Mearth), GJ 625 b (2.82 Mearth), GJ 3942
b (7.1 - 10.0 Mearth) and GJ 15A b (3.1 - 3.3 Mearth), assuming their orbits
are coplanar with the stellar rotation.Comment: 19 pages, 16 figures, 10 table
Horizons, Constraints, and Black Hole Entropy
Black hole entropy appears to be ``universal''--many independent
calculations, involving models with very different microscopic degrees of
freedom, all yield the same density of states. I discuss the proposal that this
universality comes from the behavior of the underlying symmetries of the
classical theory. To impose the condition that a black hole be present, we must
partially break the classical symmetries of general relativity, and the
resulting Goldstone boson-like degrees of freedom may account for the
Bekenstein-Hawking entropy. In particular, I demonstrate that the imposition of
a ``stretched horizon'' constraint modifies the algebra of symmetries at the
horizon, allowing the use of standard conformal field theory techniques to
determine the asymptotic density of states. The results reproduce the
Bekenstein-Hawking entropy without any need for detailed assumptions about the
microscopic theory.Comment: 16 pages, talk given at the "Peyresq Physics 10 Meeting on Micro and
Macro structures of spacetime
Poisson Algebra of Diffeomorphism Generators in a Spacetime Containing a Bifurcation
In this article we will analyze the possibility of a nontrivial central
extension of the Poisson algebra of the diffeomorphism generators, which
respect certain boundary conditions on the black hole bifurcation. The origin
of a possible central extension in the algebra is due to the existence of
boundary terms in the in the canonical generators. The existence of such
boundary terms depend on the exact boundary conditions one takes. We will check
two possible boundary conditions i.e. fixed bolt metric and fixed surface
gravity. In the case of fixed metric the the action acquires a boundary term
associated to the bifurcation but this is canceled in the Legendre
transformation and so absent in the canonical generator and so in this case the
possibility of a nontrivial central extension is ruled out. In the case of
fixed surface gravity the boundary term in the action is absent but present in
the Hamiltonian. Also in this case we will see that there is no nontrivial
central extension, also if there exist a boundary term in the generator.Comment: LaTex 20 pages, some misprints corrected, 2 references added.
Accepted for publication on Phys. Rev.
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