1,555 research outputs found
Dense Molecular Filaments Feeding a Starburst: ALMA Maps of CO(3-2) in Henize 2-10
We present ALMA CO(3-2) observations at 0.3 arcsec resolution of He2-10, a
starburst dwarf galaxy and possible high-z galaxy analogue. The warm dense gas
traced by CO(3--2) is found in clumpy filaments that are kinematically and
spatially distinct. The filaments have no preferred orientation or direction;
this may indicate that the galaxy is not evolving into a disk galaxy. Filaments
appear to be feeding the active starburst; the velocity field in one filament
suggests acceleration onto an embedded star cluster. The relative strengths of
CO(3-2) and radio continuum vary strongly on decaparsec scales in the
starburst. There is no CO(3--2) clump coincident with the non-thermal radio
source that has been suggested to be an AGN, nor unusual kinematics.
The kinematics of the molecular gas show significant activity apparently
unrelated to the current starburst. The longest filament, east of the
starburst, has a pronounced shear of FWHM ~\kms\ across its 50~pc
width over its entire kpc length. The cause of the shear is not
clear. This filament is close in projection to a `dynamically distinct' CO
feature previously seen in CO(1--0). The most complex region and the most
highly disturbed gas velocities are in a region 200~pc south of the starburst.
The CO(3--2) emission there reveals a molecular outflow, of linewidth FWZI
120-140 \kms, requiring an energy . There is
at present {\it no} candidate for the driving source of this outflow.Comment: This was revised 31 October to correct some typos and to replace
Figure
Stochastic debt sustainability analysis for sovereigns and the scope for optimization modeling
We argue that sovereign debt sustainability analysis must be augmented
by stochastic correlated risk factors and a risk measure to capture tail effects. Crisis
situations can thus be adequately specified and analyzed with sufficient accuracy to
warrant the relevance of policy decisions. In this context there is significant scope
for optimization modeling for both strategic planning and operational management.
We discuss diverse aspects of the problem of debt sustainability and highlight
modeling approaches that can be brought to bear on the problem. Results with the
fictitious, but nor unrealistic, Kingdom of Atlantis, which is sinking under excessive
debt, illustrate the proposed models
ALMA CO(3-2) Observations of Star-Forming Filaments in a Gas-Poor Dwarf Spheroidal Galaxy
We report ALMA observations of CO(3-2) and CO(3-2) in the
gas-poor dwarf galaxy NGC 5253. These 0.3"(5.5 pc) resolution images reveal
small, dense molecular gas clouds that are located in kinematically distinct,
extended filaments. Some of the filaments appear to be falling into the galaxy
and may be fueling its current star formation. The most intense CO(3-2)
emission comes from the central 100 pc region centered on the luminous
radio-infrared HII region known as the supernebula. The CO(3-2) clumps within
the starburst region are anti-correlated with H on 5 pc scales,
but are well-correlated with radio free-free emission. Cloud D1, which
enshrouds the supernebula, has a high CO/CO ratio, as does
another cloud within the central 100 pc starburst region, possibly because the
clouds are hot. CO(3-2) emission alone does not allow determination of cloud
masses as molecular gas temperature and column density are degenerate at the
observed brightness, unless combined with other lines such as CO.Comment: 7 pages, 5 figures, Accepted to Ap
Designing and pricing guarantee options in defined contribution pension plans
The shift from defined benefit (DB) to defined contribution (DC) is pervasive among pension funds, due to demographic changes and macroeconomic pressures. In DB all risks are borne by the provider, while in plain vanilla DC all risks are borne by the beneficiary. However, for DC to provide income security some kind of guarantee is required. A minimum guarantee clause can be modeled as a put option written on some underlying reference portfolio and we develop a discrete model that selects the reference portfolio to minimise the cost of a guarantee. While the relation DB-DC is typically viewed as a binary one, the model shows how to price a wide range of guarantees creating a continuum between DB and DC. Integrating guarantee pricing with asset allocation decision is useful to both pension fund managers and regulators. The former are given a yardstick to assess if a given asset portfolio is fit-for-purpose; the latter can assess differences of specific reference funds with respect to the optimal one, signalling possible cases of moral hazard. We develop the model and report numerical results to illustrate its uses
A parsimonious model for generating arbitrage-free scenario trees
Simulation models of economic, financial and business risk factors are widely used to assess risks and support decision-making. Extensive literature on scenario generation methods aims at describing some underlying stochastic processes with the least number of scenarios to overcome the ‘curse of dimensionality’. There is, however, an important requirement that is usually overlooked when one departs from the application domain of security pricing: the no-arbitrage condition. We formulate a moment matching model to generate multi-factor scenario trees for stochastic optimization satisfying no-arbitrage restrictions with a minimal number of scenarios and without any distributional assumptions. The resulting global optimization problem is quite general. However, it is non-convex and can grow significantly with the number of risk factors, and we develop convex lower bounding techniques for its solution exploiting the special structure of the problem. Applications to some standard problems from the literature show that this is a robust approach for tree generation. We use it to price a European basket option in complete and incomplete markets
Ionized Gas Motions and the Structure of Feedback Near a Forming Globular Cluster in NGC 5253
We observed Brackett 4.05m emission towards the supernebula in
NGC 5253 with NIRSPEC on Keck II in adaptive optics mode, NIRSPAO, to probe
feedback from its exciting embedded super star cluster (SSC). NIRSPEC's
Slit-Viewing Camera was simultaneously used to image the K-band continuum at
resolution. We register the IR continuum with HST imaging, and
find that the visible clusters are offset from the K-band peak, which coincides
with the Br peak of the supernebula and its associated molecular
cloud. The spectra of the supernebula exhibit Br emission with a
strong, narrow core. The linewidths are 65-76 km s, FWHM, comparable to
those around individual ultra-compact HII regions within our Galaxy. A weak,
broad (FWHM150-175 km s) component is detected on the base of
the line, which could trace a population of sources with high-velocity winds.
The core velocity of Br emission shifts by +13 km s from NE to
SW across the supernebula, possibly indicating a bipolar outflow from an
embedded object, or linked to a foreground redshifted gas filament. The results
can be explained if the supernebula comprises thousands of ionized wind regions
around individual massive stars, stalled in their expansion due to critical
radiative cooling and unable to merge to drive a coherent cluster wind. Based
on the absence of an outflow with large mass loss, we conclude that feedback is
currently ineffective at dispersing gas, and the SSC retains enriched material
out of which it may continue to form stars.Comment: 24 pages, 9 figure
Asset and Liability Modelling for Participating Policies with Guarantee
We study the problem of asset and liability management of participating insurance policies with guarantees. We develop
a scenario optimization model for integrative asset and liability management, analyse the tradeoffs in structuring such policies,
and study alternative choices in funding them. The nonlinearly constrained optimization model can be linearised
through closed form solutions of the dynamic equations. Thus large-scale problems are solved with standard methods.
We report on an empirical analysis of policies offered by Italian insurers. The optimized model results are in general agreement
with current industry practices. However, some inefficiencies are identified and potential improvements are
highlighted
A coupled thermal-analytical and mechanical approach to investigate the behavior of bonded anchors cured at sub-zero temperatures
In post-installed connection in reinforced concrete structures, bonded anchors are commonly adopted when elevated mechanical performances are required. Such performances may be significantly impaired by adverse service conditions, above all temperature variations with respect to room ambient one. It is also generally acknowledged that the curing temperature may impact on the anchor performances, to the extent that all the main existing qualification procedures assess the anchor behavior when cured at different temperatures, in particular below zero Celsius degree. However, among the few investigations focusing on the impact of a low curing temperature on the long term behavior of an anchor, a low effort exists in addressing the relationship between the anchor mechanical behavior and the thermal properties of the bonding agent. The paper proposes a coupled thermal-analytical and mechanical approach to detect potential critical issues in the long term mechanical behavior of the anchor as a function of the adhesive behavior, as investigated by thermal or thermo-mechanical analyses. To the scope, a wide investigation on two adhesives is carried out comprising MDSC, DMA, pull-out and sustained load tests. On the basis of the obtained results, it is concluded that some thresholds in the variations of degree of conversion and phase transition temperatures may indicate a negligible impact of a low curing temperature on the anchor mechanical behavior, but also that existing qualification procedures are not able to capture the anchor behavior, when cured at low temperatures and subjected, during its service life, to temperatures higher than room ambient one
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