Descriptional Complexity of Three-Nonterminal Scattered Context Grammars: An Improvement

Recently, it has been shown that every recursively enumerable language can be generated by a scattered context grammar with no more than three nonterminals. However, in that construction, the maximal number of nonterminals simultaneously rewritten during a derivation step depends on many factors, such as the cardinality of the alphabet of the generated language and the structure of the generated language itself. This paper improves the result by showing that the maximal number of nonterminals simultaneously rewritten during any derivation step can be limited by a small constant regardless of other factors

Registration of the transition radiation with GaAs detector: Data/MC comparison

New developments of pixel detectors based on GaAs sensors offer effective registration of the transition radiation (TR) X-rays and perform simultaneous measurements of their energies and emission angles. This unique feature opens new possibilities for particle identification on the basis of maximum available information about generated TR photons. Results of studies of TR energy-Angular distributions using a 500 |j.m thick GaAs sensor attached to a Timepix3 chip are presented. Measurements, analysis techniques and a comparison with Monte Carlo (MC) simulations are described and discussed

Determination of fission barrier height of Fr 210 and Ra 210 via neutron measurement

Fission barrier heights of short-lived nuclei away from line of β stability are not known reliably. Low-energy fission of Fr210 and Ra210, produced by (d,p) and (d,n) transfer reaction on the re-accelerated unstable beam Fr209 was investigated at HIE-ISOLDE. Four Timepix3 pixel detectors were installed on the body of the ACTAR TPC demonstrator chamber. Polyethylene converters were used for the detection of fast neutrons. Since no significant background was observed, it was possible to measure the spatial distribution of emitted neutrons reflecting the fission excitation function. Subsequent simulations employing the results of the talys code and available data on fission fragment distributions allowed to estimate directly the value of the fission barrier height for the neutron-deficient nucleus Fr210. This first direct measurement confirmed the reduction of the fission barrier compared to available theoretical calculations by 15-30%

Exploring Alternative Conceptions in our Environmental Education Classroom

Teaching is an inexact science. Even experienced teachers have difficulty assessing the effectiveness of their lessons and students mastery of concept. Teachers must be particularly careful to avoid introducing or reinforcing student misconceptions. The following describes how we scrutinized and modified our own environmental education teaching practices to ensure that our students were learning what we were teaching. Our inquiry into students’ alternative conceptions about the environment was a very enlightening experience for both of us. Th e process revealed some beliefs that surprised us. However, the real surprise came when we realized that our own lessons reinforced (and sometimes formed) many of our students’ alternative conceptions. With our new insights, gained from listening to our students, we developed a better way to teach environmental education