30,506 research outputs found
On the sustainability of currency boards : evidence from Argentina and Hong Kong : [Version: September 2008]
This paper examines the sustainability of the currency board arrangements in Argentina and Hong Kong. We employ a Markov switching model with two regimes to infer the exchange rate pressure due to economic fundamentals and market expectations. The empirical results suggest that economic fundamentals and expectations are key determinants of a currency board’s sustainability. We also show that the government’s credibility played a more important role in Argentina than in Hong Kong. The trade surplus, real exchange rate and inflation rate were more important drivers of the sustainability of the Hong Kong currency board
Altered Achilles Tendon Morphology in Individuals With Chronic Post-Stroke Hemiparesis: A Case Report
Background: Individuals post-stroke walk slowly and with more effort, which puts them at higher risks for falls. The slow walking speed results from insufficient propulsive forces generated by the paretic leg. Current rehabilitative efforts to improve walking function target increasing propulsive forces, but overlook the muscle-tendon unit. Case presentations: Two individuals with chronic post-stroke hemiparesis are presented. In both individuals post-stroke, paretic ankle plantarflexors presented with increased muscle tone. Gait kinetics revealed asymmetric propulsive forces, specifically, insufficient propulsive forces by the paretic legs, consistent with previous literature. Sonography revealed increased thickness of paretic Achilles tendon at the calcaneal insertion, in both stroke cases, in contrast to comparable Achilles tendon thickness between limbs in the non-neurologically impaired controls. Conclusion: Tendon unit integrity should be considered in individuals post-stroke who demonstrate abnormal muscle tone and insufficient propulsion during gait
On pattern classification algorithms - Introduction and survey
Pattern recognition algorithms, and mathematical techniques of estimation, decision making, and optimization theor
Scalar Dark Matter and Standard Model with Four Generations
We consider a scalar dark matter model, the SM4+D, consisting of the standard
model with four generations (SM4) and a real gauge-singlet scalar called
darkon, D, as the weakly interacting massive particle (WIMP) dark-matter (DM)
candidate. We explore constraints on the darkon sector of the SM4+D from WIMP
DM direct-search experiments, including CDMS II and CoGeNT, and from the decay
of a B meson into a kaon plus missing energy. We find that a sizable portion of
the darkon parameter space is still compatible with the experimental data.
Since the darkon-Higgs interaction may give rise to considerable enhancement of
the Higgs invisible decay mode, the existence of the darkon could lead to the
weakening or evasion of some of the restrictions on the Higgs mass in the
presence of fourth-generation quarks. In addition, it can affect the
flavor-changing decays of these new heavy quarks into a lighter quark and the
Higgs boson, as the Higgs may subsequently decay invisibly. Therefore we also
study these flavor-changing neutral transitions involving the darkon, as well
as the corresponding top-quark decay t -> cDD, some of which may be observable
at the Tevatron or LHC and thus provide additional tests for the SM4+D.Comment: 18 pages, 5 figure
Nonlocal Flow of Convex Plane Curves and Isoperimetric Inequalities
In the first part of the paper we survey some nonlocal flows of convex plane
curves ever studied so far and discuss properties of the flows related to
enclosed area and length, especially the isoperimetric ratio and the
isoperimetric difference. We also study a new nonlocal flow of convex plane
curves and discuss its evolution behavior. In the second part of the paper we
discuss necessary and sufficient conditions (in terms of the (mixed)
isoperimetric ratio or (mixed) isoperimetric difference) for two convex closed
curves to be homothetic or parallel.Comment: 23 page
A Radiative Neutrino Mass Model with SIMP Dark Matter
We propose the first viable radiative seesaw model, in which the neutrino
masses are induced radiatively via the two-loop Feynman diagram involving
Strongly Interacting Massive Particles (SIMP). The stability of SIMP dark
matter (DM) is ensured by a discrete symmetry, through which the
DM annihilation rate is dominated by the self-annihilating processes.
The right amount of thermal relic abundance can be obtained with perturbative
couplings in the resonant SIMP scenario, while the astrophysical bounds
inferred from the Bullet cluster and spherical halo shapes can be satisfied. We
show that SIMP DM is able to maintain kinetic equilibrium with thermal plasma
until the freeze-out temperature via the Yukawa interactions associated with
neutrino mass generation.Comment: 19 pages, 8 figures, 2 tables, expanded, new appendix added, new
references added, updated plots, fixed minor typos, matches journal versio
A Dynamic Oligopoly Game of the US Airline Industry: Estimation and Policy Experiments
This paper studies the contribution of demand, costs, and strategic factors to the adoption of hub-and-spoke networks in the US airline industry. Our results are based on the estimation of a dynamic oligopoly game of network competition that incorporates three groups of factors that may explain hub-and-spoke networks: (1) travelers may value the services associated with the scale of operation of an airline in the hub airport; (2) operating costs and entry costs in a route may decline with the airline's scale of operation in the origin and destination airports (e.g., economies of scale and scope); and (3) a hub-and-spoke network may be an effective strategy to deter the entry of other carriers. We estimate the model using data from the Airline Origin and Destination Survey with information on quantities, prices, and entry and exit decisions for every airline company in the routes between the 55 largest US cities. As methodological contributions, we propose and apply a method to reduce the dimension of the state space in dynamic games, and a procedure to deal with the problem of multiple equilibria when using a estimated model to make counterfactual experiments. We find that the most important factor to explain the adoption of hub-and-spoke networks is that the cost of entry in a route declines importantly with the scale of operation of the airline in the airports of the route. For some of the larger carriers, strategic entry deterrence is the second most important factor to explain hub-and-spoke networks.Airline industry; Hub-and-spoke networks; Entry costs; Industry dynamics; Estimation of dynamic games; Counterfactual experiments in models with multiple equilibria.
A Dynamic Oligopoly Game of the US Airline Industry: Estimation and Policy Experiments
This paper studies the contribution of demand, costs, and strategic factors to the adoption of hub-and-spoke networks in the US airline industry. Our results are based on the estimation of a dynamic oligopoly game of network competition that incorporates three groups of factors which may explain the adoption of hub-and-spoke networks: (1) travelers value the services associated with the scale of operation of an airline in the hub airport (e.g., more convenient check-in and landing facilities); (2) operating costs and entry costs in a route may decline with an airline's scale operation in origin and destination airports (e.g., economies of scale and scope); and (3) a hub-and-spoke network may be an effective strategy to deter the entry of other carriers. We estimate the model using data from the Airline Origin and Destination Survey with information on quantities, prices, and entry and exit decisions for every airline company in the routes between the 55 largest US cities. As a methodological contribution, we propose and apply a simple method to deal with the problem of multiple equilibria when using the estimated model to predict the effects of changes in structural parameters. We find that the most important factor to explain the adoption of hub-and-spoke networks is that the cost of entry in a route declines very importantly with the scale of operation of the airline in the airports of the route. For some of the larger carriers, strategic entry deterrence is the second most important factor to explain hub-and-spoke networks.Airline industry; Hub-and-spoke networks; Entry costs; Industry dynamics; Estimation of dynamic games; Counterfactuals with multiple equilibria
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