4,521 research outputs found
Modelling the impact of liner shipping network perturbations on container cargo routing: Southeast Asia to Europe application
Understanding how container routing stands to be impacted by different scenarios of liner shipping network perturbations such as natural disasters or new major infrastructure developments is of key importance for decision-making in the liner shipping industry. The variety of actors and processes within modern supply chains and the complexity of their relationships have previously led to the development of simulation-based models, whose application has been largely compromised by their dependency on extensive and often confidential sets of data. This study proposes the application of optimisation techniques less dependent on complex data sets in order to develop a quantitative framework to assess the impacts of disruptive events on liner shipping networks. We provide a categorization of liner network perturbations, differentiating between systemic and external and formulate a container assignment model that minimises routing costs extending previous implementations to allow feasible solutions when routing capacity is reduced below transport demand. We develop a base case network for the Southeast Asia to Europe liner shipping trade and review of accidents related to port disruptions for two scenarios of seismic and political conflict hazards. Numerical results identify alternative routing paths and costs in the aftermath of port disruptions scenarios and suggest higher vulnerability of intra-regional connectivity
Modelling the impact of liner shipping network perturbations on container cargo routing: Southeast Asia to Europe application
Understanding how container routing stands to be impacted by different scenarios of liner shipping network perturbations such as natural disasters or new major infrastructure developments is of key importance for decision-making in the liner shipping industry. The variety of actors and processes within modern supply chains and the complexity of their relationships have previously led to the development of simulation-based models, whose application has been largely compromised by their dependency on extensive and often confidential sets of data. This study proposes the application of optimisation techniques less dependent on complex data sets in order to develop a quantitative framework to assess the impacts of disruptive events on liner shipping networks. We provide a categorization of liner network perturbations, differentiating between systemic and external and formulate a container assignment model that minimises routing costs extending previous implementations to allow feasible solutions when routing capacity is reduced below transport demand. We develop a base case network for the Southeast Asia to Europe liner shipping trade and review of accidents related to port disruptions for two scenarios of seismic and political conflict hazards. Numerical results identify alternative routing paths and costs in the aftermath of port disruptions scenarios and suggest higher vulnerability of intra-regional connectivity
The Tilt of the Fundamental Plane: Three-quarters Structural Nonhomology, One-quarter Stellar Population
The variation of the mass-to-light ratios M/L of early type galaxies as
function of their luminosities L is investigated. It is shown that the tilt
beta=0.27 (in the B--band) of the fundamental plane relation M/L ~ L^{beta} can
be understood as a combination of two effects: about one-quarter (i.e. dbeta
=0.07) is a result of systematic variations of the stellar population
properties with increasing luminosity. The remaining three-quarters (i.e. dbeta
=0.2) can be completely attributed to nonhomology effects that lead to a
systematic change of the surface brightness profiles with increasing
luminosity. Consequently, the observed tilt in the K-band (beta=0.17) where
stellar population effects are negligible, is explained by nonhomology effects
alone. After correcting for nonhomology, the mean value of the mass-to-light
ratio of elliptical galaxies (M/L_B) is 7.1+-2.8 (1 sigma scatter).Comment: 8 pages, 3 figures, ApJL, 600, 39, minor changes made to match the
published versio
Antiproton constraints on dark matter annihilations from internal electroweak bremsstrahlung
If the dark matter particle is a Majorana fermion, annihilations into two
fermions and one gauge boson could have, for some choices of the parameters of
the model, a non-negligible cross-section. Using a toy model of leptophilic
dark matter, we calculate the constraints on the annihilation cross-section
into two electrons and one weak gauge boson from the PAMELA measurements of the
cosmic antiproton-to-proton flux ratio. Furthermore, we calculate the maximal
astrophysical boost factor allowed in the Milky Way under the assumption that
the leptophilic dark matter particle is the dominant component of dark matter
in our Universe. These constraints constitute very conservative estimates on
the boost factor for more realistic models where the dark matter particle also
couples to quarks and weak gauge bosons, such as the lightest neutralino which
we also analyze for some concrete benchmark points. The limits on the
astrophysical boost factors presented here could be used to evaluate the
prospects to detect a gamma-ray signal from dark matter annihilations at
currently operating IACTs as well as in the projected CTA.Comment: 32 pages; 13 figure
The Spitzer/IRAC view of black hole - bulge scaling relations
We present a mid-IR investigation of the scaling relations between
supermassive black hole masses (MBH) and the structural parameters of the host
spheroids in local galaxies. The work is based on two-dimensional bulge-disk
decompositions of Spitzer/IRAC 3.6 um images of 57 galaxies with MBH estimates.
Our estimates of effective radii (Re) and surface brightnesses, combined with
velocity dispersions (sigma) from the literature, define a FP relation
consistent with previous determinations but doubling the observed range in Re.
None of our galaxies is an outlier of the FP, demonstrating the accuracy of our
bulge-disk decomposition which also allows us to independently identify
pseudobulges in our sample. We calibrate M/L at 3.6 um by using the tight
Mdyn-Lbul relation (~0.1 dex of rms) and find that no color corrections are
required to estimate the stellar mass. The 3.6 um luminosity is thus the best
tracer of Mstar yet studied. We then explore the connection between MBH and
bulge structural parameters (luminosity, mass, effective radius). We find tight
correlations of MBH with both 3.6 um bulge luminosity and dynamical mass
(MBH/Mdyn~1/1000), with rms of ~0.35 dex, similar to the MBH-sigma relation.
Our results are consistent with previous determinations at shorter wavelengths.
By using our calibrated M/L, we rescale MBH-Lbul to obtain the MBH-Mstar
relation, which can be used as the local reference for high-z studies which
probe the cosmic evolution of MBH-galaxy relations and where the stellar mass
is inferred directly from luminosity measurements. The analysis of pseudobulges
shows that 4 out of 9 lie on the scaling relations within the observed scatter,
while those with small MBH are significantly displaced. We explore the
different origins for such behavior, while considering the possibility of
nuclear morphological components not reproduced by our two-dimensional
decomposition.Comment: 30 pages, 8 figures, 5 tables. Accepted for pubblication in MNRAS.
Minor changes after proof correctio
Complete diagrammatics of the single ring theorem
Using diagrammatic techniques, we provide explicit functional relations
between the cumulant generating functions for the biunitarily invariant
ensembles in the limit of large size of matrices. The formalism allows to map
two distinct areas of free random variables: Hermitian positive definite
operators and non-normal R-diagonal operators. We also rederive the
Haagerup-Larsen theorem and show how its recent extension to the eigenvector
correlation function appears naturally within this approach.Comment: 18 pages, 6 figures, version accepted for publicatio
Increased risk of HPV-associated genital cancers in men and women as a consequence of pre-invasive disease
To assess the excess risk of HPVāassociated cancer (HPVaC) in two atārisk groups ā women with a previous diagnosis of high grade cervical intraepithelial neoplasia (CIN3) and both men and women treated for nonācervical preāinvasive anoāgenital disease. All CIN3 cases diagnosed in 1989ā2015 in Scotland were extracted from the Scottish cancer registry (SMR06). All cases of preāinvasive penile, anal, vulval, and vaginal disease diagnosed in 1990ā2015 were identified within the NHS pathology databases in the two largest NHS health boards in Scotland. Both were linked to SMR06 to extract subsequent incidence of HPVaC following the diagnosis of CIN3 or preāinvasive disease. Standardised incidence ratios were calculated for the risk of acquiring HPVaC for the two atārisk groups compared with the general Scottish population. Among 69714 females in Scotland diagnosed with CIN3 (890360.9 personāyears), 179 developed nonācervical HPVaC. CIN3 cases were at 3.2āfold (95% CI: 2.7 to 3.7) increased risk of developing nonācervical HPVaC, compared to the general female population. Among 1235 patients diagnosed with nonācervical preāinvasive disease (9667.4 personāyears), 47 developed HPVaC. Individuals with nonācervical preāinvasive disease had a substantially increased risk of developing HPVaC ā 15.5āfold (95% CI: 11.1 to 21.1) increased risk for females and 28āfold (11.3 to 57.7) increased risk for males. We report a significant additional risk of HPVāassociated cancer in those have been diagnosed with preāinvasive HPVāassociated lesions including but not confined to the cervix. Uncovering the natural history of preāinvasive disease has potential for determining screening, prevention and treatment
Local stability of self-gravitating fluid disks made of two components in relative motion
Context. We consider a simple self-gravitating disk, made of two fluid
components characterized by different effective thermal speeds and interacting
with one another only through gravity; two-component models of this type have
often been considered in order to estimate the impact of the cold interstellar
medium on gravitational instabilities in star-dominated galaxy disks.
Aims. This simple model allows us to produce a unified description of
instabilities in non-viscous self-gravitating disks, some originating from
Jeans collapse, and others from the relative motion between the two components.
In particular, the model suggests that the small streaming velocity between the
two components associated with the so-called asymmetric drift may be the origin
of instability for suitable non-axisymmetric perturbations.
Methods. The result is obtained by examining the properties of a local,
linear dispersion relation for tightly wound density waves in such
two-component model. The parameters characterizing the equilibrium model and
the related dispersion relation allow us to recover as natural limits the
cases, known in the literature, in which the relative drift between the two
components is ignored.
Results. Dynamically, the instability is similar to (although gentler than)
that known to affect counter-rotating disks. However, in contrast to the
instability induced by counter-rotation, which is a relatively rare phenomenon,
the mechanism discussed in this paper is likely to be rather common in nature.
Conclusions. We briefly indicate some consequences of the instability on the
evolution of galaxy disks and possible applications to other astrophysical
systems, in particular to protostellar disks and accretion disks.Comment: 9 pages, 5 figures, Astronomy & Astrophysics, in pres
Evidence for a Long-Standing Top-Heavy IMF in the Central Parsec of the Galaxy
We classify 329 late-type giants within 1 parsec of Sgr A*, using the
adaptive optics integral field spectrometer SINFONI on the VLT. These
observations represent the deepest spectroscopic data set so far obtained for
the Galactic Center, reaching a 50% completeness threshold at the approximate
magnitude of the helium-burning red clump (Ks ~ 15.5 mag.). Combining our
spectroscopic results with NaCo H and Ks photometry, we construct an observed
Hertzsprung-Russell diagram, which we quantitatively compare to theoretical
distributions of various star formation histories of the inner Galaxy, using a
chi-squared analysis. Our best-fit model corresponds to continuous star
formation over the last 12 Gyr with a top-heavy initial mass function (IMF).
The similarity of this IMF to the IMF observed for the most recent epoch of
star formation is intriguing and perhaps suggests a connection between recent
star formation and the stars formed throughout the history of the Galactic
Center.Comment: 18 pages, 10 figures, Accepted to ApJ: 15 July 200
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