8,312 research outputs found
[Review of] David Mason, ed. Explaining Ethnic Differences: Changing Patterns of Disadvantage in Britain
A series of communal disturbances took place in several north of England towns during the spring and summer of 2001. They were notable for the participation of young, male Asians, a significant proportion of them Muslims...as against African-Caribbeans (21)
How and Why lslamophobia is tied to English Nationalism but not to Scottish Nationalism
Muslim minorities throughout Europe are under threat of collateral damage from the Blair/Bush \u27War on Terror.\u27 In Scotland they also have to cope with the added possibility that Scottish nationalism might develop an \u27ethnic\u27 as well as a \u27civic\u27 dimension. But is Scottish nationalism part of the problem or part of the solution? Paradoxically, Muslims are under less pressure in Scotland than in England, despite Scotland\u27s move over recent decades--psychologically as well as institutionally--towards nationalism
Crystallization of hard aspherical particles
We use numerical simulations to study the crystallization of monodisperse
systems of hard aspherical particles. We find that particle shape and
crystallizability can be easily related to each other when particles are
characterized in terms of two simple and experimentally accessible order
parameters: one based on the particle surface-to-volume ratio, and the other on
the angular distribution of the perturbations away from the ideal spherical
shape. We present a phase diagram obtained by exploring the crystallizability
of 487 different particle shapes across the two-order-parameter spectrum.
Finally, we consider the physical properties of the crystalline structures
accessible to aspherical particles, and discuss limits and relevance of our
results.Comment: 4 pages, 3 figures. Published in the Journal of Chemical Physics
Exploiting classical nucleation theory for reverse self-assembly
In this paper we introduce a new method to design interparticle interactions
to target arbitrary crystal structures via the process of self-assembly. We
show that it is possible to exploit the curvature of the crystal nucleation
free-energy barrier to sample and select optimal interparticle interactions for
self-assembly into a desired structure. We apply this method to find
interactions to target two simple crystal structures: a crystal with simple
cubic symmetry and a two-dimensional plane with square symmetry embedded in a
three-dimensional space. Finally, we discuss the potential and limits of our
method and propose a general model by which a functionally infinite number of
different interaction geometries may be constructed and to which our reverse
self-assembly method could in principle be applied.Comment: 7 pages, 6 figures. Published in the Journal of Chemical Physic
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Single-molecule spectroscopic studies of conjugated polymers
A semiconductor is a type of material which has electrical properties in between an
insulator and a conductor. A conductor can be thought of as a group of atoms surrounded
by a sea of free electrons, which are free to move throughout the material; in contrast,
the electrons in an insulator are tightly localized on a specific atom or molecule.
In a semiconductor, the electrons are localized as in insulators; however, with the
addition of energy, the electrons in semiconductors are easily excited into a state where
they are free to move throughout the material as in a conductor. Thus, with the proper
combination of materials, electrons can flow from the semiconductor into a circuit when
light strikes it. This is the basis behind solar energy, in which a current is generated
when sunlight hits silicon-based panels known as photovoltaic cells.
Materials known as conjugated organic polymers are semiconductors made up of elements
like carbon, hydrogen, and nitrogen. A polymer is a chain of small repeated
units known as monomers. In a conjugated polymer, the electrons of the molecule are
shared across several atoms in the polymer; when these electrons are excited, they are
then free to move essentially along the entire length of the polymer. Theoretically, then,
conjugated polymers could be used for applications like solar energy, as well.
In order to study single conjugated polymer molecules, a technique known as singlemolecule
spectroscopy (SMS) was used. In SMS, light from a laser is focused to a very
small spot ( 10 nm) on a sample composed of individual, isolated single molecules. This
laser light excites electrons in the molecules; when the electrons relax back to their ground
(lowest-energy) state, they re-release the energy as a characteristic group of wavelengths
of light known as a spectrum.
I studied the spectroscopy of the conjugated polymers F8BT and MEH-PPV. For
F8BT, I studied the effect of polymer size and temperature on the fluorescence of the
polymer. The spectrum of F8BT displays a bimodal distribution: some molecules have
a peak in their emission spectrum at approximately 570 nm (“red”), while some have
it at 530 nm (“blue”).
This bimodal distribution collapses at low temperatures to a single emission peak.
Furthermore, small F8BT molecules emit almost entirely in the blue, while many more
large F8BT molecules emit in the red form. This indicates that there is some type of
low-energy electron “trap” that becomes more abundant as the polymer gets larger. The
most commonly-proposed mechanism for this trap is contact between different parts of
the polymer chain.
For MEH-PPV, I studied 100-molecule aggregates of MEH-PPV polymers. These
aggregates contain enough molecules to display characteristics of bulk MEH-PPV with
on the order of 1023 molecules, but are small enough to be essentially homogeneous –
that is, all of the molecules within a single aggregate have identical environments. MEHPPV
shows a similar bimodal emission distribution to that of F8BT; the aggregates emit
almost exclusively in the “red” form of MEH-PPV. This further supports the hypothesis
that chain-chain contact makes a large contribution to the formation of low-energy traps.
Solar energy production is just one of many areas where conjugated polymers such as
F8BT and MEH-PPV could have a huge impact on the world. If good efficiencies can be
achieved in converting sunlight into electrical current, things like photovoltaic cells could
be much cheaper, easier to produce, and more environmentally friendly.Chemistr
LESS FEDERAL GOVERNMENT INVOLVEMENT IN SOIL AND WATER CONSERVATION
Resource /Energy Economics and Policy,
Results of the 2001 Becoming an Outdoor-Woman Survey
INHS Human Dimensions Research Program and Illinois Department of Natural Resourcesunpublishednot peer reviewedOpe
Results of the 2003-2004 Illinois Youth Hunter Survey
Federal Aid Project Number W-112-R-13, Job Number 103.1, Wildlife Restoration Fund, July
1, 2003 - Sept. 30, 2004Report issued on: December 22, 200
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