161 research outputs found
How good are your fits? Unbinned multivariate goodness-of-fit tests in high energy physics
Multivariate analyses play an important role in high energy physics. Such
analyses often involve performing an unbinned maximum likelihood fit of a
probability density function (p.d.f.) to the data. This paper explores a
variety of unbinned methods for determining the goodness of fit of the p.d.f.
to the data. The application and performance of each method is discussed in the
context of a real-life high energy physics analysis (a Dalitz-plot analysis).
Several of the methods presented in this paper can also be used for the
non-parametric determination of whether two samples originate from the same
parent p.d.f. This can be used, e.g., to determine the quality of a detector
Monte Carlo simulation without the need for a parametric expression of the
efficiency.Comment: 32 pages, 12 figure
Structural neural networks subserving oculomotor function in first-episode schizophrenia
BACKGROUND: Smooth pursuit and antisaccade abnormalities are well documented in schizophrenia, but their neuropathological correlates remain unclear.
METHODS: In this study, we used statistical parametric mapping to investigate the relationship between oculomotor abnormalities and brain structure in a sample of first-episode schizophrenia patients (n = 27). In addition to conventional volumetric magnetic resonance imaging, we also used magnetization transfer ratio, a technique that allows more precise tissue characterization.
RESULTS: We found that smooth pursuit abnormalities were associated with reduced magnetization transfer ratio in several regions, predominantly in the right prefrontal cortex. Antisaccade errors correlated with gray matter volume in the right medial superior frontal cortex as measured by conventional magnetic resonance imaging but not with magnetization transfer ratio.
CONCLUSIONS: These preliminary results demonstrate that specific structural abnormalities are associated with abnormal eye movements in schizophrenia
Nonperturbative Effects in Gluon Radiation and Photoproduction of Quark Pairs
We introduce a nonperturbative interaction for light-cone fluctuations
containing quarks and gluons. The interaction squeezes the transverse
size of these fluctuations in the photon and one does not need to simulate this
effect via effective quark masses. The strength of this interaction is fixed by
data. Data on diffractive dissociation of hadrons and photons show that the
nonperturbative interaction of gluons is much stronger. We fix the parameters
for the nonperturbative quark-gluon interaction by data for diffractive
dissociation to large masses (triple-Pomeron regime). This allows us to predict
nuclear shadowing for gluons which turns out to be not as strong as
perturbative QCD predicts. We expect a delayed onset of gluon shadowing at shadowing of quarks. Gluon shadowing turns out to be nearly scale
invariant up to virtualities due to presence of a semihard
scale characterizing the strong nonperturbative interaction of gluons. We use
the same concept to improve our description of gluon bremsstrahlung which is
related to the distribution function for a quark-gluon fluctuation and the
interaction cross section of a fluctuation with a nucleon. We expect
the nonperturbative interaction to suppress dramatically the gluon radiation at
small transverse momenta compared to perturbative calculations.Comment: 58 pages of Latex including 11 figures. Shadowing for soft gluons and
Fig. 6 are added as well as a few reference
The effect of autonomy, training opportunities, age and salaries on job satisfaction in the South East Asian retail petroleum industry
South East Asian petroleum retailers are under considerable pressure to improve service quality by reducing turnover. An empirical methodology from this industry determined the extent to which job characteristics, training opportunities, age and salary influenced the level of job satisfaction, an indicator of turnover. Responses are reported on a random sample of 165 site employees (a 68% response rate) of a Singaporean retail petroleum firm. A restricted multivariate regression model of autonomy and training opportunities explained the majority (35.4%) of the variability of job satisfaction. Age did not moderate these relationships, except for employees >21 years of age, who reported enhanced job satisfaction with additional salary. Human Capital theory, Life Cycle theory and Job Enrichment theory are invoked and explored in the context of these findings in the South East Asian retail petroleum industry. In the South East Asian retail petroleum industry, jobs providing employees with the opportunity to undertake a variety of tasks that enhanced the experienced meaningfulness of work are likely to promote job satisfaction, reduce turnover and increase the quality of service
- …