background and purpose: many workers are exposed to workplace hazards. many occupational diseases are preventable by personal protective devices (ppds). though many workers do not use ppds or their protection by ppds is not sufficient. this study was designed to assess the quality of ppds usage among industrial workers. materials and methods: in a cross-sectional study, 648 workers from four ma...

abortion traditionally means miscarriage and is still known as a problem, which societies have been trying to reduce its rate by using legal means. despite the fact that  pregnant women and fetuses have been historically supported;  abortion  was firstly criminalized in 1926 in iran, 20 years after establishment of modern legal system. during next 53 years this situation changed dramatically, t...

Prequential testing of a forecaster is known to be manipulable if the test must pass an informed forecaster for all possible true distributions. Stewart (2011) provides a non-manipulable prequential likelihood test that only fails an informed forecaster on a small, category I, set of distributions. We present a prequential test based on calibration that also fails the informed forecaster on at ...

The Prime Power Conjecture (PPC) states that abelian planar difference sets of order n exist only for n a prime power. Lander and others have shown that orders divisible by certain composites can be eliminated. In this paper we show how to extend this list of excluded orders.

We investigate here the computational complexity of three natural problems in directed acyclic graphs. We prove their NP Completeness and consider their restrictions to linear orders.