63,494 research outputs found
Setting per-field normalisation hyper-parameters for the named-page finding search task
Per-field normalisation has been shown to be effective for Web search tasks, e.g. named-page finding. However, per-field normalisation also suffers from having hyper-parameters to tune on a per-field basis. In this paper, we argue that the purpose of per-field normalisation is to adjust the linear relationship between field length and term frequency. We experiment with standard Web test collections, using three document fields, namely the body of the document, its title, and the anchor text of its incoming links. From our experiments, we find that across different collections, the linear correlation values, given by the optimised hyper-parameter settings, are proportional to the maximum negative linear correlation. Based on this observation, we devise an automatic method for setting the per-field normalisation hyper-parameter values without the use of relevance assessment for tuning. According to the evaluation results, this method is shown to be effective for the body and title fields. In addition, the difficulty in setting the per-field normalisation hyper-parameter for the anchor text field is explained
Model-independent Constraints on the Weak Phase (or ) and QCD Penguin Pollution in Decays
We present an {\it algebraic} isospin approach towards a more straightforward
and model-independent determination of the weak phase (or )
and QCD penguin pollution in decays. The world averages of
current experimental data allow us to impose some useful constraints on the
isospin parameters of transitions. We find that the magnitude of
(or ) extracted from the indirect CP violation in
mode is in agreement with the standard-model expectation from other indirect
measurements, but its four-fold discrete ambiguity has to be resolved in the
near future.Comment: 11 pages, 3 figures, 2 table
LOFF Pairing vs. Breached Pairing in Asymmetric Fermion Superfluids
A general analysis for the competition between breached pairing (BP) and LOFF
pairing mechanisms in asymmetric fermion superfluids is presented in the frame
of a four fermion interaction model. Two physical conditions which can induce
mismatched Fermi surfaces are considered: (1) fixed chemical potential
asymmetry and (2) fixed fermion number asymmetry . In case
(1), the BP state is ruled out because of Sarma instability and LOFF state is
thermodynamically stable in a narrow window of . In case (2), while
the Sarma instability can be avoided and both the BP and LOFF states can
survive provided is less than the corresponding critical value, the BP
state suffers magnetic instability and the LOFF state is always
thermodynamically stable. While the LOFF window in case (2) is much larger than
the one in the conventional case (1), for small the longitudinal
superfluid density of the LOFF state is negative and it suffers also magnetic
instability.Comment: 12 pages, 13 figures, published in Physical Review B. Notice: an
algebra error in Equation (39) correcte
Efficiency at maximum power output of an irreversible Carnot-like cycle with internally dissipative friction
We investigate the efficiency at maximum power of an irreversible Carnot
engine performing finite-time cycles between two reservoirs at temperatures
and , taking into account of internally dissipative
friction in two "adiabatic" processes. In the frictionless case, the
efficiencies at maximum power output are retrieved to be situated between
and , with being
the Carnot efficiency. The strong limits of the dissipations in the hot and
cold isothermal processes lead to the result that the efficiency at maximum
power output approaches the values of and
, respectively. When dissipations of two isothermal
and two adiabatic processes are symmetric, respectively, the efficiency at
maximum power output is founded to be bounded between 0 and the Curzon-Ahlborn
(CA) efficiency , and the the CA efficiency is achieved in
the absence of internally dissipative friction
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