3,186 research outputs found
The co-pyrolysis of flame retarded high impact polystyrene and polyolefins
The co-pyrolysis of brominated high impact polystyrene (Br-HIPS) with polyolefins using a fixed bed reactor has been investigated, in particular, the effect that different types brominated aryl compounds and antimony trioxide have on the pyrolysis products. The pyrolysis products were analysed using FT-IR, GC-FID, GC-MS, and GC-ECD. Liquid chromatography was used to separate the oils/waxes so that a more detailed analysis of the aliphatic, aromatic, and polar fractions could be carried out. It was found that interaction occurs between Br-HIPS and polyolefins during co-pyrolysis and that the presence of antimony trioxide influences the pyrolysis mass balance. Analysis of the Br-HIPS + polyolefin co-pyrolysis products showed that the presence of polyolefins led to an increase in the concentration of alkyl and vinyl mono-substituted benzene rings in the pyrolysis oil/wax resulting from Br-HIPS pyrolysis. The presence of Br-HIPS also had an impact on the oil/wax products of polyolefin pyrolysis, particularly on the polyethylene oil/wax composition which converted from being a mixture of 1-alkenes and n-alkanes to mostly n-alkanes. Antimony trioxide had very little impact on the polyolefin wax/oil composition but it did suppress the formation of styrene and alpha-methyl styrene and increase the formation of ethylbenzene and cumene during the pyrolysis of the Br-HIPS
Preparation and Potential Applications of Evacuated Closed-Cell Plastic Foams
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67368/2/10.1177_0021955X9002600201.pd
Pedagogy and History: Ujamaa and Learner-Centered Pedagogy in Tanzania
Social issues of today are rooted in history, and the study of contemporary issues would thus benefit from tracing their history. In Tanzania, Nyerere’s ujamaa philosophy and the accompanying education for self-reliance (ESR) policy offer a criterion relevant today in pedagogical analysis. Tanzania is currently implementing learner-centered pedagogy (LCP). This article considers the logic of ujamaa, which ostensibly appears to be compatible with LCP principles, and explores through empirical evidence the consistencies and inconsistencies between ujamaa/ESR, LCP, and the pedagogical approaches valued by present-day teachers. The teachers espoused the idea of self-reliance promoted through ujamaa, implying that pedagogies similar to LCP will produce self-reliant graduates. Instead of forcibly transmitting a universal form of ideal pedagogy, the cultural and historical connection between ujamaa and LCP could suggest appropriate forms of teaching and learning in the Tanzanian context
Critical Scale-invariance in Healthy Human Heart Rate
We demonstrate the robust scale-invariance in the probability density
function (PDF) of detrended healthy human heart rate increments, which is
preserved not only in a quiescent condition, but also in a dynamic state where
the mean level of heart rate is dramatically changing. This scale-independent
and fractal structure is markedly different from the scale-dependent PDF
evolution observed in a turbulent-like, cascade heart rate model. These results
strongly support the view that healthy human heart rate is controlled to
converge continually to a critical state.Comment: 9 pages, 3 figures. Phys. Rev. Lett., to appear (2004
First quantized approaches to neutrino oscillations and second quantization
Neutrino oscillations are treated from the point of view of relativistic
first quantized theories and compared to second quantized treatments. Within
first quantized theories, general oscillation probabilities can be found for
Dirac fermions and charged spin 0 bosons. A clear modification in the
oscillation formulas can be obtained and its origin is elucidated and confirmed
to be inevitable from completeness and causality requirements. The left-handed
nature of created and detected neutrinos can also be implemented in the first
quantized Dirac theory in presence of mixing; the probability loss due to the
changing of initially left-handed neutrinos to the undetected right-handed
neutrinos can be obtained in analytic form. Concerning second quantized
approaches, it is shown in a calculation using virtual neutrino propagation
that both neutrinos and antineutrinos may also contribute as intermediate
particles. The sign of the contributing neutrino energy may have to be chosen
explicitly without being automatic in the formalism. At last, a simple second
quantized description of the flavor oscillation phenomenon is devised. In this
description there is no interference terms between positive and negative
components, but it still gives simple normalized oscillation probabilities. A
new effect appearing in this context is an inevitable but tiny violation of the
initial flavor of neutrinos. The probability loss due to the conversion of
left-handed neutrinos to right-handed neutrinos is also presented.Comment: version accepted for publicatio
- …