2,634 research outputs found
A different perspective on canonicity
One of the most interesting aspects of Conceptual Structures Theory is the notion of canonicity. It is also one of the most neglected: Sowa seems to have abandoned it in the new version of the theory, and most of what has been written on canonicity focuses on the generalization hierarchy of conceptual graphs induced by the canonical formation rules. Although there is a common intuition that a graph is canonical if it is "meaningful'', the original theory is somewhat unclear about what that actually means, in particular how canonicity is related to logic. This paper argues that canonicity should be kept a first-class notion of Conceptual Structures Theory, provides a detailed analysis of work done so far, and proposes new definitions of the conformity relation and the canonical formation rules that allow a clear separation between canonicity and truth
Combining Information from and Decays
We consider the and decays
alongside each other, taking into account the contributions from all individual
penguin amplitudes generated by the internal , , and quarks. We argue
that three ratios of penguin amplitudes, each for a different internal quark,
formed by dividing the individual penguin amplitude in by the
corresponding amplitude in , should be equal. We
study the implications of the assumed existence of this connection between
and .
First, accepting that in the decays the ratio of the
colour-suppressed factorization amplitude to the tree factorization
amplitude is negligible, we determine the ratio of individual penguin
amplitudes. Then, from the data, we extract the
effective (i.e. possibly containing some penguin terms) tree and the effective
colour-suppressed amplitudes relevant for these processes, and the
corresponding solutions for the factorization amplitudes. Finally, we argue
that the ratio in should be identical to its counterpart
in (relevant for pion emission from the decaying
quark). This constraint permits the determination of and of other
amplitude ratios directly from the data. Although the ratio extracted
from the available data still carries a substantial error, it is consistent
with the expected value of 0.25 - 0.5.Comment: 24 pages, revise
Time Consumption of Skidding in Mature Stands Performed by Winches Powered by Farm Tractor
The aim of the present research was to determine the characteristics of time consumption in skidding by winch. The research was conducted in pine, fir, spruce and beech mature stands. It covered the operation of skidding from the stand to the skid trail at the distance of up to 50 m. A time study was performed for skidding operations, timber volume and thinning intensity. The average time consumption of skidding in the operational time, assessed in the examined mature stands, amounted to approximately 18 min/m3. Significant differences were observed in frequency levels between early thinnings (24 min/m3) and late ones (13 min/m3). The operational time structure for skidding by winch was characterized by a large share of auxiliary time: 71%. Out of that time, 30% was used for attaching and detaching the load and 36% for the transfer. Approximation was also done of the multiple regression equations. The equations described changes in skidding time consumption, i.e. the Empirical Efficiency Index (EST). The changes depended on environmental factors (stand, cutting category), elements of the working day structure (the share of a given time category in a shift) and task intensity (ratio of the number of harvested trees per area unit). The strongest correlations between the EST and the analyzed variables were observed for the factors related to the percentage of time required for attaching and detaching the load and factors related to operation intensity
Plenoptic x-ray microscopy
Plenoptic cameras use arrays of micro-lenses to capture multiple views of the
same scene in a single compound image. They enable refocusing on different
planes and depth estimation. However, until now, all types of plenoptic
computational imaging have been limited to visible light. We demonstrate an
x-ray plenoptic microscope that uses a concentrating micro-capillary array
instead of a micro-lens array and can simultaneously acquire from one hundred
to one thousand x-ray projections of imaged volumes that are located in the
focal spot region of the micro-capillary array. Hence, tomographic slices at
various depths near the focal plane can be reconstructed in a way similar to
tomosynthesis, but from a single x-ray exposure. The microscope enables
depth-resolved imaging of small subvolumes in large samples and can be used for
imaging of weakly absorbing artificial and biological objects by means of
propagation phase-contrast.Comment: The following article has been accepted by Applied Physics Letter
Conformational spread as a mechanism for cooperativity in the bacterial flagellar switch
The bacterial flagellar switch that controls the direction of flagellar rotation during chemotaxis has a highly cooperative response. This has previously been understood in terms of the classic two-state, concerted model of allosteric regulation. Here, we used high-resolution optical microscopy to observe switching of single motors and uncover the stochastic multistate nature of the switch. Our observations are in detailed quantitative agreement with a recent general model of allosteric cooperativity that exhibits conformational spread—the stochastic growth and shrinkage of domains of adjacent subunits sharing a particular conformational state. We expect that conformational spread will be important in explaining cooperativity in other large signaling complexes
Steps in the bacterial flagellar motor
The bacterial flagellar motor is a highly efficient rotary machine used by
many bacteria to propel themselves. It has recently been shown that at low
speeds its rotation proceeds in steps [Sowa et al. (2005) Nature 437,
916--919]. Here we propose a simple physical model that accounts for this
stepping behavior as a random walk in a tilted corrugated potential that
combines torque and contact forces. We argue that the absolute angular position
of the rotor is crucial for understanding step properties, and show this
hypothesis to be consistent with the available data, in particular the
observation that backward steps are smaller on average than forward steps. Our
model also predicts a sublinear torque-speed relationship at low torque, and a
peak in rotor diffusion as a function of torque
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