2,568 research outputs found
Raising the (metastable) bar: 100% photo-switching in [Pd(Bu4dien)(η1-O2)]+ approaches ambient temperature
100% nitro–nitrito linkage isomerism is reported in single-crystals of the Pd(II)–nitrite system [Pd(Bu4dien)(η1-O2)]BPh4 (Bu4dien = N,N,N′,N′-tetrabutyldiethylenetriamine, BPh4 = tetraphenylborate). Complete conversion to a metastable endo-nitrito-(η1-NO) isomer is achieved after just 15 min irradiation with 400 nm LED light. The system is entirely metastable below 240 K, while pseudo-steady-state photocrystallographic experiments confirm that the excited state isomer is retained, at substantial conversion levels, under continuous illumination until 260 K. These results show promise for new linkage isomer systems, based on heavier transition metal centres, which display full functionality under near-ambient conditions
Orbit Spaces of Gradient Vector Fields
We study orbit spaces of generalized gradient vector fields for Morse
functions. Typically, these orbit spaces are non-Hausdorff. Nevertheless, they
are quite structured topologically and are amenable to study. We show that
these orbit spaces are locally contractible. We also show that the quotient map
associated to each such orbit space is a weak homotopy equivalence and has the
path lifting property.Comment: 16 pages, 4 figures; strengthened a main result (Corollary 3.5) and
updated the introduction and the conclusio
Where in the World? Adult Educator Learning and Professional Development Leading Study Abroad Programs
In this summary of on-going research, we discuss our investigation about adult educator motivations and professional development to lead study abroad programs for adults
Schrijver graphs and projective quadrangulations
In a recent paper [J. Combin. Theory Ser. B}, 113 (2015), pp. 1-17], the
authors have extended the concept of quadrangulation of a surface to higher
dimension, and showed that every quadrangulation of the -dimensional
projective space is at least -chromatic, unless it is bipartite.
They conjectured that for any integers and , the
Schrijver graph contains a spanning subgraph which is a
quadrangulation of . The purpose of this paper is to prove the
conjecture
Quantum statistics on graphs
Quantum graphs are commonly used as models of complex quantum systems, for
example molecules, networks of wires, and states of condensed matter. We
consider quantum statistics for indistinguishable spinless particles on a
graph, concentrating on the simplest case of abelian statistics for two
particles. In spite of the fact that graphs are locally one-dimensional, anyon
statistics emerge in a generalized form. A given graph may support a family of
independent anyon phases associated with topologically inequivalent exchange
processes. In addition, for sufficiently complex graphs, there appear new
discrete-valued phases. Our analysis is simplified by considering combinatorial
rather than metric graphs -- equivalently, a many-particle tight-binding model.
The results demonstrate that graphs provide an arena in which to study new
manifestations of quantum statistics. Possible applications include topological
quantum computing, topological insulators, the fractional quantum Hall effect,
superconductivity and molecular physics.Comment: 21 pages, 6 figure
Analyzing Morton's Typology of Service Paradigms and Integrity
Research on college students found limited support for Morton’s (1995) hypothesis that students have a preference for one distinct type of service orientation (i.e., charity, project, social change). The findings did replicate previous findings that college students prefer the charity paradigm. A measure of integrity was developed and two dimensions were identified that possessed distinct correlates. As Morton predicted, as the degree of integrity increased the preference for a distinct type of service became blurred, suggesting that developing integrity should be an intentional educational goal and it might be aided by exposing students to all three approaches to community service. Implications for service-learning educators are discussed
Quantized Response and Topology of Insulators with Inversion Symmetry
We study three dimensional insulators with inversion symmetry, in which other
point group symmetries, such as time reversal, are generically absent. Their
band topology is found to be classified by the parities of occupied states at
time reversal invariant momenta (TRIM parities), and by three Chern numbers.
The TRIM parities of any insulator must satisfy a constraint: their product
must be +1. The TRIM parities also constrain the Chern numbers modulo two. When
the Chern numbers vanish, a magneto-electric response parameterized by "theta"
is defined and is quantized to theta= 0, 2pi. Its value is entirely determined
by the TRIM parities. These results may be useful in the search for magnetic
topological insulators with large theta. A classification of inversion
symmetric insulators is also given for general dimensions. An alternate
geometrical derivation of our results is obtained by using the entanglement
spectrum of the ground state wave-function.Comment: 12 pages main text; 12 pages appendices; 11 figures. Added new refs.
in 2nd versio
Should sex ratio distorting parasites abandon horizontal transmission?
BACKGROUND: Sex-ratio distorting parasites are of interest due to their effects upon host population dynamics and their potential to influence the evolution of host sex determination systems. In theory, the ability to distort host sex-ratios allows a parasite with efficient vertical (hereditary) transmission to dispense completely with horizontal (infectious) transmission. However, recent empirical studies indicate that some sex-ratio distorting parasites have retained the capability for horizontal transmission. RESULTS: Numerical simulations using biologically realistic parameters suggest that a feminising parasite is only likely to lose the capability for horizontal transmission if its host occurs at low density and/or has a male-biased primary sex ratio. It is also demonstrated that even a small amount of horizontal transmission can allow multiple feminising parasites to coexist within a single host population. Finally it is shown that, by boosting its host's rate of population growth, a feminising parasite can increase its own horizontal transmission and allow the invasion of other, more virulent parasites. CONCLUSIONS: The prediction that sex-ratio distorting parasites are likely to retain a degree of horizontal transmission has important implications for the epidemiology and host-parasite interactions of these organisms. It may also explain the frequent co-occurrence of several sex-ratio distorting parasite species in nature
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