2,649 research outputs found
Price Formation under Small Numbers Competition: Evidence from Land Auctions in Singapore
This paper examines the price formation process under small numbers competition using data from Singapore land auctions. The theory predicts that bid prices are less than the zero-profit asset value in these first-price sealed-bid auctions. The model also shows that expected sales price increases with the number of bidders both because each bidder has an incentive to offer a higher price and because of a greater likelihood that a high-value bidder is present. The empirical estimates are consistent with auction theory and show that the standard land attributes are reflected in auction prices as expected. Working Paper No. 04-0
XAX: a multi-ton, multi-target detection system for dark matter, double beta decay and pp solar neutrinos
A multi-target detection system XAX, comprising concentric 10 ton targets of
136Xe and 129/131Xe, together with a geometrically similar or larger target of
liquid Ar, is described. Each is configured as a two-phase
scintillation/ionization TPC detector, enhanced by a full 4pi array of
ultra-low radioactivity Quartz Photon Intensifying Detectors (QUPIDs) replacing
the conventional photomultipliers for detection of scintillation light. It is
shown that background levels in XAX can be reduced to the level required for
dark matter particle (WIMP) mass measurement at a 10^-10 pb WIMP-nucleon cross
section, with single-event sensitivity below 10^-11 pb. The use of multiple
target elements allows for confirmation of the A^2 dependence of a coherent
cross section, and the different Xe isotopes provide information on the
spin-dependence of the dark matter interaction. The event rates observed by Xe
and Ar would modulate annually with opposite phases from each other for WIMP
mass >~100 GeV/c^2. The large target mass of 136Xe and high degree of
background reduction allow neutrinoless double beta decay to be observed with
lifetimes of 10^27-10^28 years, corresponding to the Majorana neutrino mass
range 0.01-0.1 eV, the most likely range from observed neutrino mass
differences. The use of a 136Xe-depleted 129/131Xe target will also allow
measurement of the pp solar neutrino spectrum to a precision of 1-2%.Comment: 16 pages with 17 figure
Evidence for field-induced excitations in low-temperature thermal conductivity of Bi_2Sr_2CaCu_2O_8
The thermal conductivity ,, of Bi_2Sr_2CaCu_2O_8 was studied as a
function of magnetic field. Above 5 K, after an initial decrease,
presents a kink followed by a plateau, as recently reported by Krishana et al..
By contrast, below 1K, the thermal conductivity was found to \emph{increase}
with increasing field. This behavior is indicative of a finite density of
states and is not compatible with the existence of a field-induced fully gapped
state which was recently proposed to describe the
plateau regime. Our low-temperature results are in agreement with recent works
predicting a field-induced enhancement of thermal conductivity by Doppler shift
of quasi-particle spectrum.Comment: 4 pages including 4 eps figures, submitted to Phys. Rev. Let
Broadband strong optical dichroism in topological Dirac semimetals with Fermi velocity anisotropy
Prototypical three-dimensional (3D) topological Dirac semimetals (DSMs), such
as CdAs and NaBi, contain electrons that obey a linear
momentum-energy dispersion with different Fermi velocities along the three
orthogonal momentum dimensions. Despite being extensively studied in recent
years, the inherent \emph{Fermi velocity anisotropy} has often been neglected
in the theoretical and numerical studies of 3D DSMs. Although this omission
does not qualitatively alter the physics of light-driven massless
quasiparticles in 3D DSMs, it does \emph{quantitatively} change the optical
coefficients which can lead to nontrivial implications in terms of
nanophotonics and plasmonics applications. Here we study the linear optical
response of 3D DSMs for general Fermi velocity values along each direction.
Although the signature conductivity-frequency scaling, , of 3D Dirac fermion is well-protected from Fermi velocity anisotropy,
the linear optical response exhibits strong linear dichroism as captured by the
\emph{universal} extinction ratio scaling law,
(where denotes the three spatial coordinates , and is
the -direction Fermi velocity), which is independent of frequency,
temperature, doping, and carrier scattering lifetime. For CdAs and
NaBi, an exceptionally strong extinction ratio larger than 15 and
covering broad terahertz window is revealed. Our findings shed new light on the
role of Fermi velocity anisotropy in the optical response of Dirac semimetals
and open up novel polarization-sensitive functionalities, such as
photodetection and light modulation.Comment: 8 pages, 3 figure
Vortex Matter Transition in BiSrCaCuO under Tilted Fields
Vortex phase diagram under tilted fields from the axis in
BiSrCaCuO is studied by local magnetization
hysteresis measurements using Hall probes. When the field is applied at large
angles from the axis, an anomaly () other than the well-known
peak effect () are found at fields below . The angular dependence of
the field is nonmonotonic and clearly different from that of
and depends on the oxygen content of the crystal. The results suggest existence
of a vortex matter transition under tilted fields. Possible mechanisms of the
transition are discussed.Comment: Revtex, 4 pages, some corrections are adde
Melamin toxicity in pigs
Three farms in Penang, Malaysia, reported illness in grower-finisher pigs with discarded kidneys from abattoir. Affected animals were inappetant, anorexic, thin, dull, and depressed. The episode was closely related with the feed formulation changes, where soybean and fishmeal were replaced with yeast. No significant mycotoxin levels were detected in both the feed and yeasts. However, high levels of melamine were detected in yeast (30,064 ppm) and finished feed (750 to 1500 ppm), which exceeded the acceptance level set by WHO (<2.5 ppm). Nonetheless, prominent gross abnormalities were detected, except for the lesions in the kidneys during necropsy. The affected kidneys were enlarged and yellowish in colour, firm in consistency and the cortical surface was wrinkled and dimpled. Dilated cortical and medullary lesions with yellow gritty crystalline materials were also observed. A microscopic examination revealed the lesions of acute tubular nephrosis, interstitial nephritis with multiple cysts in the kidney cortex. After the removal of the yeast source in the feed, the illness and kidney lesions were in remission
Controlling laser spectra in a phaseonium photonic crystal using maser
We study the control of quantum resonances in photonic crystals with
electromagnetically induced transparency driven by microwave field. In addition
to the control laser, the intensity and phase of the maser can alter the
transmission and reflection spectra in interesting ways, producing hyperfine
resonances through the combined effects of multiple scattering in the
superstructure.Comment: 7 pages, 4 figure
An improved wrapper-based feature selection method for machinery fault diagnosis
A major issue of machinery fault diagnosis using vibration signals is that it is over-reliant on personnel knowledge and experience in interpreting the signal. Thus, machine learning has been adapted for machinery fault diagnosis. The quantity and quality of the input features, however, influence the fault classification performance. Feature selection plays a vital role in selecting the most representative feature subset for the machine learning algorithm. In contrast, the trade-off relationship between capability when selecting the best feature subset and computational effort is inevitable in the wrapper-based feature selection (WFS) method. This paper proposes an improved WFS technique before integration with a support vector machine (SVM) model classifier as a complete fault diagnosis system for a rolling element bearing case study. The bearing vibration dataset made available by the Case Western Reserve University Bearing Data Centre was executed using the proposed WFS and its performance has been analysed and discussed. The results reveal that the proposed WFS secures the best feature subset with a lower computational effort by eliminating the redundancy of re-evaluation. The proposed WFS has therefore been found to be capable and efficient to carry out feature selection tasks
Characteristics of predictor sets found using differential prioritization
<p>Abstract</p> <p>Background</p> <p>Feature selection plays an undeniably important role in classification problems involving high dimensional datasets such as microarray datasets. For filter-based feature selection, two well-known criteria used in forming predictor sets are relevance and redundancy. However, there is a third criterion which is at least as important as the other two in affecting the efficacy of the resulting predictor sets. This criterion is the degree of differential prioritization (DDP), which varies the emphases on relevance and redundancy depending on the value of the DDP. Previous empirical works on publicly available microarray datasets have confirmed the effectiveness of the DDP in molecular classification. We now propose to establish the fundamental strengths and merits of the DDP-based feature selection technique. This is to be done through a simulation study which involves vigorous analyses of the characteristics of predictor sets found using different values of the DDP from toy datasets designed to mimic real-life microarray datasets.</p> <p>Results</p> <p>A simulation study employing analytical measures such as the distance between classes before and after transformation using principal component analysis is implemented on toy datasets. From these analyses, the necessity of adjusting the differential prioritization based on the dataset of interest is established. This conclusion is supported by comparisons against both simplistic rank-based selection and state-of-the-art equal-priorities scoring methods, which demonstrates the superiority of the DDP-based feature selection technique. Reapplying similar analyses to real-life multiclass microarray datasets provides further confirmation of our findings and of the significance of the DDP for practical applications.</p> <p>Conclusion</p> <p>The findings have been achieved based on analytical evaluations, not empirical evaluation involving classifiers, thus providing further basis for the usefulness of the DDP and validating the need for unequal priorities on relevance and redundancy during feature selection for microarray datasets, especially highly multiclass datasets.</p
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