7,797 research outputs found
K3-fibered Calabi-Yau threefolds I, the twist map
A construction of Calabi-Yaus as quotients of products of lower-dimensional
spaces in the context of weighted hypersurfaces is discussed, including
desingularisation. The construction leads to Calabi-Yaus which have a fiber
structure, in particular one case has K3 surfaces as fibers. These Calabi-Yaus
are of some interest in connection with Type II -heterotic string dualities in
dimension 4. A section at the end of the paper summarises this for the
non-expert mathematician.Comment: 31 pages LaTeX, 11pt, 2 figures. To appear in International Journal
of Mathematics. On the web at
http://personal-homepages.mis.mpg.de/bhunt/preprints.html , #
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Implications of climate change for expanding cities worldwide
This paper analyses the trends of the changing environmental effects within growing megacities as their diameters
exceed 50–100 km and their populations rise beyond 30 million people. The authors consider how these effects are
influenced by climate change, to which urban areas themselves contribute, caused by their increasing greenhouse gas emissions associated with rapidly expanding energy use. Other environmental and social factors are assessed,
quantitatively and qualitatively, using detailed modelling of urban mesoscale meteorology, which shows how these
factors can lead to large conurbations becoming more vulnerable to climatic and environmental hazards. The paper
discusses the likely changes in meteorological and hydrological hazards in urban areas, both as the climate changes and the sizes of urban areas grow. Examples are given of how these risks are being reduced through innovations in warning and response systems, planning and infrastructure design, which should include refuges against extreme natural disasters. Policies are shown to be more effective when they are integrated and based on substantial
community involvement. Some conclusions are drawn regarding how policies for the natural and artificial environment and for reducing many kinds of climate and hazard risk are related to future designs and planning of infrastructure and open spaces
ALMA reveals the feeding of the Seyfert 1 nucleus in NGC 1566
We report ALMA observations of CO(3-2) emission in the Seyfert 1 galaxy NGC
1566, at a spatial resolution of 25 pc. Our aim is to investigate the
morphology and dynamics of the gas inside the central kpc, and to probe nuclear
fueling and feedback phenomena. NGC 1566 has a nuclear bar of 1.7 kpc radius
and a conspicuous grand design spiral starting from this radius. The ALMA field
of view, of diameter 0.9 kpc, lies well inside the nuclear bar and reveals a
molecular trailing spiral structure from 50 to 300~pc in size, which is
contributing to fuel the nucleus, according to its negative gravity torques.
The spiral starts with a large pitch angle from the center and then winds up
in a pseudo-ring at the inner Lindblad resonance (ILR) of the nuclear bar.
This is the first time that a trailing spiral structure is clearly seen
driving the gas inwards inside the ILR ring of the nuclear bar. This phenomenon
shows that the massive central black hole has a significant dynamical influence
on the gas, triggering its fueling.
The gaseous spiral is well correlated with the dusty spiral seen through
extinction in HST images, and also with a spiral feature emitting 0.87mm
continuum. This continuum emission must come essentially from cold dust heated
by the interstellar radiation field. The HCN(4-3) and HCO+(4-3) lines were
simultaneously mapped and detected in the nuclear spiral. The HCO+(4-3) line is
3 times stronger than the HCN(4-3), as expected when star formation excitation
dominates over active galactic nucleus (AGN) heating. The CO(3-2)/HCO+(4-3)
integrated intensity ratio is \sim 100.
The molecular gas is in remarkably regular rotation, with only slight
non-circular motions at the periphery of the nuclear spiral arms. These
perturbations are quite small, and no outflow nor AGN feedback is detected.Comment: 11 pages, 16 figures, accepted in Astronomy and Astrophysic
ALMA observations of feeding and feedback in nearby Seyfert galaxies: an AGN-driven outflow in NGC 1433
We report ALMA observations of CO(3-2) emission in the Seyfert 2
double-barred galaxy NGC1433, at the unprecedented spatial resolution of
0.5"=24 pc. Our aim is to probe AGN feeding and feedback phenomena through the
morphology and dynamics of the gas inside the central kpc. The CO map, which
covers the whole nuclear region (nuclear bar and ring), reveals a nuclear
gaseous spiral structure, inside the nuclear ring encircling the nuclear
stellar bar.
This gaseous spiral is well correlated with the dusty spiral seen in Hubble
Space Telescope images. The nuclear spiral winds up in a pseudo-ring at 200 pc
radius, which might correspond to the inner ILR. Continuum emission is detected
at 0.87 mm only at the very centre, and its origin is more likely thermal dust
emission than non-thermal emission from the AGN. It might correspond to the
molecular torus expected to exist in this Seyfert 2 galaxy. The HCN(4-3) and
HCO+(4-3) lines were observed simultaneously, but only upper limits are
derived, with a ratio to the CO(3-2) line lower than 1/60 at 3sigma, indicating
a relatively low abundance of very dense gas. The kinematics of the gas over
the nuclear disk reveal rather regular rotation only slightly perturbed by
streaming motions due to the spiral; the primary and secondary bars are too
closely aligned with the galaxy major or minor axis to leave a signature in the
projected velocities. Near the nucleus, there is an intense high-velocity CO
emission feature redshifted to 200 km/s (if located in the plane), with a
blue-shifted counterpart, at 2" (100 pc) from the centre. While the CO spectra
are quite narrow in the centre, this wide component is interpreted as an
outflow involving a molecular mass of 3.6 10^6 Mo and a flow rate 7 Mo/yr. The
flow could be in part driven by the central star formation, but is mainly
boosted by the AGN through its wind or radio jets.Comment: 11 pages, 9 figures, Accepted in Astronomy and Astrophysic
Probability of local bifurcation type from a fixed point: A random matrix perspective
Results regarding probable bifurcations from fixed points are presented in
the context of general dynamical systems (real, random matrices), time-delay
dynamical systems (companion matrices), and a set of mappings known for their
properties as universal approximators (neural networks). The eigenvalue spectra
is considered both numerically and analytically using previous work of Edelman
et. al. Based upon the numerical evidence, various conjectures are presented.
The conclusion is that in many circumstances, most bifurcations from fixed
points of large dynamical systems will be due to complex eigenvalues.
Nevertheless, surprising situations are presented for which the aforementioned
conclusion is not general, e.g. real random matrices with Gaussian elements
with a large positive mean and finite variance.Comment: 21 pages, 19 figure
Tailoring the specificity of the type C feruloyl esterase FoFaeC from Fusarium oxysporum towards methyl sinapate by rational redesign based on small molecule docking simulations
The type C feruloyl esterase FoFaeC from Fusarium oxysporum is a newly discovered enzyme with high potential for use in the hydrolysis of lignocellulosic biomass but it shows low activity towards sinapates. In this work, small molecule docking simulations were employed in order to identify important residues for the binding of the four model methyl esters of hydroxycinnamic acids, methyl ferulate/caffeate/sinapate/p-coumarate, to the predicted structure of FoFaeC. Subsequently rational redesign was applied to the enzyme’ active site in order to improve its specificity towards methyl sinapate. A double mutation (F230H/T202V) was considered to provide hydrophobic environment for stabilization of the methoxy substitution on sinapate and a larger binding pocket. Five mutant clones and the wild type were produced in Pichia pastoris and biochemically characterized. All clones showed improved activity, substrate affinity, catalytic efficiency and turnover rate compared to the wild type against methyl sinapate, with clone P13 showing a 5-fold improvement in catalytic efficiency. Although the affinity of all mutant clones was improved against the four model substrates, the catalytic efficiency and turnover rate decreased for the substrates containing a hydroxyl substitution
Italian Science Case for ALMA Band 2+3
The Premiale Project "Science and Technology in Italy for the upgraded ALMA
Observatory - iALMA" has the goal of strengthening the scientific,
technological and industrial Italian contribution to the Atacama Large
Millimeter/submillimeter Array (ALMA), the largest ground based international
infrastructure for the study of the Universe in the microwave. One of the main
objectives of the Science Working Group (SWG) inside iALMA, the Work Package 1,
is to develop the Italian contribution to the Science Case for the ALMA Band 2
or Band 2+3 receiver. ALMA Band 2 receiver spans from ~67 GHz (bounded by an
opaque line complex of ozone lines) up to 90 GHz which overlaps with the lower
frequency end of ALMA Band 3. Receiver technology has advanced since the
original definition of the ALMA frequency bands. It is now feasible to produce
a single receiver which could cover the whole frequency range from 67 GHz to
116 GHz, encompassing Band 2 and Band 3 in a single receiver cartridge, a so
called Band 2+3 system. In addition, upgrades of the ALMA system are now
foreseen that should double the bandwidth to 16 GHz. The science drivers
discussed below therefore also discuss the advantages of these two enhancements
over the originally foreseen Band 2 system.Comment: 43 pages, 21 figure
First time determination of the microscopic structure of a stripe phase: Low temperature NMR in La2NiO4.17
The experimental observations of stripes in superconducting cuprates and
insulating nickelates clearly show the modulation in charge and spin density.
However, these have proven to be rather insensitive to the harmonic structure
and (site or bond) ordering. Using 139La NMR in La2NiO4.17, we show that in the
1/3 hole doped nickelate below the freezing temperature the stripes are
strongly solitonic and site ordered with Ni3+ ions carrying S=1/2 in the domain
walls and Ni2+ ions with S=1 in the domains.Comment: 4 pages including 4 figure
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