74,891 research outputs found
On image segmentation using information theoretic criteria
Image segmentation is a long-studied and important problem in image
processing. Different solutions have been proposed, many of which follow the
information theoretic paradigm. While these information theoretic segmentation
methods often produce excellent empirical results, their theoretical properties
are still largely unknown. The main goal of this paper is to conduct a rigorous
theoretical study into the statistical consistency properties of such methods.
To be more specific, this paper investigates if these methods can accurately
recover the true number of segments together with their true boundaries in the
image as the number of pixels tends to infinity. Our theoretical results show
that both the Bayesian information criterion (BIC) and the minimum description
length (MDL) principle can be applied to derive statistically consistent
segmentation methods, while the same is not true for the Akaike information
criterion (AIC). Numerical experiments were conducted to illustrate and support
our theoretical findings.Comment: Published in at http://dx.doi.org/10.1214/11-AOS925 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
The denitridation of nitrides of iron, cobalt and rhenium under hydrogen
The denitridation behaviour of binary iron, cobalt and rehnium nitrides under H2 /Ar has been investigated. The iron nitride was found to lose over 70 % of its as prepared nitrogen content at 400 °C. The cobalt nitride was completely denitrided at 250 °C. Rhenium nitride lost close to 90 % of its nitrogen at 350 °C. In addition, Co-Re4 prepared by ammonolyis was investigated, whilst only traces of NH<sub>3</sub> were lost from this material under H<sub>2</sub>/Ar at 400 °C, with H<sub>2</sub>/N2 it proved to be an active ambient pressure ammonia synthesis catalyst in accordance with previous literature
Magnitude and frequency of wind speed shears and associated downdrafts
Data are presented indicating the frequency of occurrence of wind shear and downdrafts together with information on the simultaneous occurrence of these two phenomena. High resolution wind profile measurements recorded at a 150 meter ground winds tower facility were used for the analysis. From instantaneous measurements during horizontal wind speeds of gale-force and below intensity, vertical motion at the 10, 60, and 150 m levels was approximately 60 percent downward and 40 percent upward. At the 18 level the percentages were reversed. Updraft maxima were an order of magnitude or two greater than downdrafts at all levels. Frequency of vertical motion or = 9.7 kts for a year at four levels was 338 occurrences upward and 274 downward. Approximately 90 percent of these updrafts occurred at the 18 m level almost equally during summer and winter, and 65 percent of the downdrafts were at the 150 m level during summer
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