8,771 research outputs found
Cosmological constraints on the neutron lifetime
We derive new constraints on the neutron lifetime based on the recent Planck
2015 observations of temperature and polarization anisotropies of the CMB.
Under the assumption of standard Big Bang Nucleosynthesis, we show that Planck
data constrains the neutron lifetime to at
c.l.. Moreover, by including the direct measurements of primordial
Helium abundance of Aver et al. (2015) and Izotov et al. (2014), we show that
cosmological data provide the stringent constraints and respectively. The latter
appears to be in tension with neutron lifetime value quoted by the Particle
Data Group (). Future CMB surveys as
COrE+, in combination with a weak lensing survey as EUCLID, could constrain the
neutron lifetime up to a precision.Comment: 13 pages, 3 figures. Matching JCAP accepted versio
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
Scenario Modeling for the Management of International Bond Portfolios
We address the problem of portfolio management in the international bond markets. Interest rate risk in the local market, exchange rate volatility across markets, and decisions for hedging currency risk are integral parts of this problem. The paper develops a stochastic programming optimization model for integrating these decisions in a common framework. Monte Carlo simulation procedures, calibrated using historical observations of volatility and correlation data, generate jointly scenarios of interest and exchange rates. The decision maker's risk tolerance is incorporated through a utility function, and additional views on market outlook can also be incorporated in the form of user specified scenarios. The model prescribes optimal asset allocation among the different markets and determines bond-picking decisions and appropriate hedging ratios. Therefore several interrelated decisions are cast in a common framework, while in the past these issues were addressed separately. Empirical results illustrate the efficacy of the simulation models in capturing the uncertainties of the Salomon Brothers international bond market index.
The Value of Integrative Risk Management for Insurance Products with Guarantees
Insurers increasingly offer policies that converge with the products of the capital markets, and they face a need for integrative asset and liability management strategies. In this paper we show that an integrative approach -- based on scenario optimization modeling -- adds value to the risk management process, when compared to traditional methods. Empirical analysis with products offered by the Italian insurance industry are presented. The results have implications for the design of competitive insurance policies, and some examples are analyzed.
Distributed Consensus to Enable Merging and Spacing of UAS in an Urban Environment
This paper presents a novel approach to enable multiple Unmanned Aerial Systems approaching a common intersection to independently schedule their arrival time while maintaining a safe separation. Aircraft merging at a common intersection are grouped into a network and each aircraft broadcasts its arrival time interval to the network. A distributed consensus algorithm elects a leader among the aircraft approaching the intersection and helps synchronize the information received by each aircraft. The consensus algorithm ensures that each aircraft computes a schedule with the same input information. The elected leader also dictates when a schedule must be computed, which may be triggered when a new aircraft joins the network. Preliminary results illustrating the collaborative behavior of the vehicles are presented
Transformations of Logic Programs on Infinite Lists
We consider an extension of logic programs, called \omega-programs, that can
be used to define predicates over infinite lists. \omega-programs allow us to
specify properties of the infinite behavior of reactive systems and, in
general, properties of infinite sequences of events. The semantics of
\omega-programs is an extension of the perfect model semantics. We present
variants of the familiar unfold/fold rules which can be used for transforming
\omega-programs. We show that these new rules are correct, that is, their
application preserves the perfect model semantics. Then we outline a general
methodology based on program transformation for verifying properties of
\omega-programs. We demonstrate the power of our transformation-based
verification methodology by proving some properties of Buechi automata and
\omega-regular languages.Comment: 37 pages, including the appendix with proofs. This is an extended
version of a paper published in Theory and Practice of Logic Programming, see
belo
Asset and Liability Modeling for Participating Policies with Guarantees
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, analyze the tradeoffs in structuring such policies, and study alternative choices in funding them. The nonlinearly constrained optimization model can be linearized 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.
The Problem with Pacifism: How Pacifism Can Lead to Genocide and Why One Should Fight to Combat Evil
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