2,198,379 research outputs found
A Comparison of Simple Mass Estimators for Galaxy Clusters
High-resolution N-body simulations are used to investigate systematic trends
in the mass profiles and total masses of clusters as derived from 3 simple
estimators: (1) the weak gravitational lensing shear field under the assumption
of an isothermal cluster potential, (2) the dynamical mass obtained from the
measured velocity dispersion under the assumption of an isothermal cluster
potential, and (3) the classical virial estimator. The clusters consist of
order 2.5e+05 particles of mass m_p \simeq 10^{10} \Msun, have triaxial mass
distributions, and significant substructure exists within their virial radii.
Not surprisingly, the level of agreement between the mass profiles obtained
from the various estimators and the actual mass profiles is found to be
scale-dependent.
The virial estimator yields a good measurement of the total cluster mass,
though it is systematically underestimated by of order 10%. This result
suggests that, at least in the limit of ideal data, the virial estimator is
quite robust to deviations from pure spherical symmetry and the presence of
substructure. The dynamical mass estimate based upon a measurement of the
cluster velocity dispersion and an assumption of an isothermal potential yields
a poor measurement of the total mass. The weak lensing estimate yields a very
good measurement of the total mass, provided the mean shear used to determine
the equivalent cluster velocity dispersion is computed from an average of the
lensing signal over the entire cluster (i.e. the mean shear is computed
interior to the virial radius). [abridged]Comment: Accepted for publication in The Astrophysical Journal. Complete
paper, including 3 large colour figures can also be obtained from
http://bu-ast.bu.edu/~brainerd/preprints
Lagrangian Perturbation Theory : Exact One-Loop Power Spectrum in General Dark Energy Models
Recently, we find that the correction for the EdS assumption on the one-loop
matter power spectrum for general dark energy models using the standard
perturbation theory is not negligible \cite{LPB}. Thus, we investigate the same
problem by obtaining the exact displacement vector and kernels up to the third
order for the general dark energy models in the Lagrangian perturbation theory
(LPT). Using these exact solutions, we investigate the present one-loop matter
power spectrum in the CDM model with to
obtain about 0.2 (0.18) \% error correction compared to that obtained from the
EdS assumption for mode. If we consider the total
matter power spectrum, the correction is only 0.05 (0.03) \% for the same mode.
It means that EdS assumption is a good approximation for CDM model in
LPT theory. However, one can use this method for general models where EdS
assumption is improper.Comment: 7 pages, 3 figure
Theoretical correction to the neutral meson asymmetry
Certain types of asymmetries in neutral meson physics have not been treated
properly, ignoring the difference of normalization factors with an assumption
of the equality of total decay width. Since the corrected asymmetries in
meson are different from known asymmetries by a shift in the first order of CP-
and CPT-violation parameters, experimental data should be analyzed with the
consideration of this effect as in meson physics.Comment: 7 page
A single buyer-single supplier bargaining problem with asymmetric information : theoretical approach and software implementation
This paper is focused on the coordination of order and production policy between buyers and suppliers in supply chains. When a buyer and a supplier of an item work independently, the buyer will place orders based on his economic order quantity (EOQ). However, the buyer s EOQ may not lead to an optimal policy for the supplier. It can be shown that a cooperative batching policy can reduce total cost significantly. Should the buyer have the more powerful position to enforce his EOQ on the supplier, then no incentive exists for him to deviate from his EOQ in order to choose a cooperative batching policy. To provide an incentive to order in quantities suitable to the supplier, the supplier could offer a side payment. One critical assumption made throughout in the literature dealing with incentive schemes to influence buyer s ordering policy is that the supplier has complete information regarding buyer s cost structure. However, this assumption is far from realistic. As a consequence, the buyer has no incentive to report truthfully on his cost structure. Moreover there is an incentive to overstate the total relevant cost in order to obtain as high a side payment as possible. This paper provides a bargaining model with asymmetric information about the buyer s cost structure assuming that the buyer has the bargaining power to enforce his EOQ on the supplier in case of a break-down in negotiations. An algorithm for the determination of an optimal set of contracts which are specifically designed for different cost structures of the buyer, assumed by the supplier, will be presented. This algorithm was implemented in a software application, that supports the supplier in determining the optimal set of contracts
Fast and Robust Rank Aggregation against Model Misspecification
In rank aggregation, preferences from different users are summarized into a
total order under the homogeneous data assumption. Thus, model misspecification
arises and rank aggregation methods take some noise models into account.
However, they all rely on certain noise model assumptions and cannot handle
agnostic noises in the real world. In this paper, we propose CoarsenRank, which
rectifies the underlying data distribution directly and aligns it to the
homogeneous data assumption without involving any noise model. To this end, we
define a neighborhood of the data distribution over which Bayesian inference of
CoarsenRank is performed, and therefore the resultant posterior enjoys
robustness against model misspecification. Further, we derive a tractable
closed-form solution for CoarsenRank making it computationally efficient.
Experiments on real-world datasets show that CoarsenRank is fast and robust,
achieving consistent improvement over baseline methods
The cyclical volatility of labor markets under frictional financial markets
This paper shows in an economy with search on credit and labor markets that a financial multiplier raises the elasticity of labor market tightness to productivity shocks, and that this multiplier is an increasing function of total financial costs in the economy. Under a credit market Hosios-Pissarides rule, total search costs in the credit market are minimized, and so is the financial multiplier. Relaxing that condition leads to larger multipliers which can match or even overshoot the elasticity of market tightness in the data. The reason is similar to that of Hagedorn and Manovskii (2008) small labor surplus assumption: we identify the configurations of parameters leading to small "bank" surplus or a small "firm surplus" in the credit market, conducive of an amplification of productivity shocks. Furthermore, when wages are endogenous, it is possible to partially relax the small labor surplus assumption in order to match the data.
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