6,720 research outputs found
Chemico-therapeutic approach to prevention of dental caries
The program of chemical preventive dentistry is based primarily upon the development of a procedure for stabilizing stannous fluoride in solution by forcing it into glycerin. New topical fluoride treatment concentrates, fluoride containing gels and prophylaxis pastes, as well as a completely stable stannous fluoride dentifrice are made possible by the development of a rather complicated heat application method to force stannous fluoride into solution in glycerin. That the stannous fluoride is clinically effective in such a preparation is demonstrated briefly on orthodontic patients
Some Observations for Mean-Field Spin Glass Models
We obtain bounds to show that the pressure of a two-body, mean-field spin
glass is a Lipschitz function of the underlying distribution of the random
coupling constants, with respect to a particular semi-norm. This allows us to
re-derive a result of Carmona and Hu, on the universality of the SK model, by a
different proof, and to generalize this result to the Viana-Bray model. We also
prove another bound, suitable when the coupling constants are not independent,
which is what is necessary if one wants to consider ``canonical'' instead of
``grand canonical'' versions of the SK and Viana-Bray models. Finally, we
review Viana-Bray type models, using the language of L\'evy processes, which is
natural in this context.Comment: 15 pages, minor revision
Lossless quantum data compression and variable-length coding
In order to compress quantum messages without loss of information it is
necessary to allow the length of the encoded messages to vary. We develop a
general framework for variable-length quantum messages in close analogy to the
classical case and show that lossless compression is only possible if the
message to be compressed is known to the sender. The lossless compression of an
ensemble of messages is bounded from below by its von-Neumann entropy. We show
that it is possible to reduce the number of qbits passing through a quantum
channel even below the von-Neumann entropy by adding a classical side-channel.
We give an explicit communication protocol that realizes lossless and
instantaneous quantum data compression and apply it to a simple example. This
protocol can be used for both online quantum communication and storage of
quantum data.Comment: 16 pages, 5 figure
Incomplete quantum process tomography and principle of maximal entropy
The main goal of this paper is to extend and apply the principle of maximum
entropy (MaxEnt) to incomplete quantum process estimation tasks. We will define
a so-called process entropy function being the von Neumann entropy of the state
associated with the quantum process via Choi-Jamiolkowski isomorphism. It will
be shown that an arbitrary process estimation experiment can be reformulated in
a unified framework and MaxEnt principle can be consistently exploited. We will
argue that the suggested choice for the process entropy satisfies natural list
of properties and it reduces to the state MaxEnt principle, if applied to
preparator devices.Comment: 8 pages, comments welcome, references adde
Information Content of Spontaneous Symmetry Breaking
We propose a measure of order in the context of nonequilibrium field theory
and argue that this measure, which we call relative configurational entropy
(RCE), may be used to quantify the emergence of coherent low-entropy
configurations, such as time-dependent or time-independent topological and
nontopological spatially-extended structures. As an illustration, we
investigate the nonequilibrium dynamics of spontaneous symmetry-breaking in
three spatial dimensions. In particular, we focus on a model where a real
scalar field, prepared initially in a symmetric thermal state, is quenched to a
broken-symmetric state. For a certain range of initial temperatures,
spatially-localized, long-lived structures known as oscillons emerge in
synchrony and remain until the field reaches equilibrium again. We show that
the RCE correlates with the number-density of oscillons, thus offering a
quantitative measure of the emergence of nonperturbative spatiotemporal
patterns that can be generalized to a variety of physical systems.Comment: LaTeX, 9 pages, 5 figures, 1 tabl
When do generalized entropies apply? How phase space volume determines entropy
We show how the dependence of phase space volume of a classical
system on its size uniquely determines its extensive entropy. We give a
concise criterion when this entropy is not of Boltzmann-Gibbs type but has to
assume a {\em generalized} (non-additive) form. We show that generalized
entropies can only exist when the dynamically (statistically) relevant fraction
of degrees of freedom in the system vanishes in the thermodynamic limit. These
are systems where the bulk of the degrees of freedom is frozen and is
practically statistically inactive. Systems governed by generalized entropies
are therefore systems whose phase space volume effectively collapses to a
lower-dimensional 'surface'. We explicitly illustrate the situation for
binomial processes and argue that generalized entropies could be relevant for
self organized critical systems such as sand piles, for spin systems which form
meta-structures such as vortices, domains, instantons, etc., and for problems
associated with anomalous diffusion.Comment: 5 pages, 2 figure
A note on entropic uncertainty relations of position and momentum
We consider two entropic uncertainty relations of position and momentum
recently discussed in literature. By a suitable rescaling of one of them, we
obtain a smooth interpolation of both for high-resolution and low-resolution
measurements respectively. Because our interpolation has never been mentioned
in literature before, we propose it as a candidate for an improved entropic
uncertainty relation of position and momentum. Up to now, the author has
neither been able to falsify nor prove the new inequality. In our opinion it is
a challenge to do either one.Comment: 2 pages, 2 figures, 2 references adde
Creative Science Through Inquiry: Improving Teacher Self-Efficacy and Outcome Expectancy Through Adaptable, Mystery-Based Professional Development
Teacher self-efficacy is an important contributor to student outcomes, school climate and teacher retention. Outcome expectancy, a construct studied more commonly in health- and behaviour-related fields, may also positively impact school-related outcomes. Research shows that professional development can increase teacher confidence, but few studies have considered this connection for science-focused professional development, specifically. Our study assesses the impact of a science-focused, mystery-based professional development workshop for upper-elementary to high-school teachers. The hands-on, collaborative nature of this workshop allowed for generalisability to classrooms of various ability levels. Using the Science Teaching Efficacy Belief Instrument-A (STEBI-A) as a measure of science-teaching self-efficacy and outcome expectancy, we found that participants’ self-reported self-efficacy and outcome expectancy significantly increased (p < .001 for each) over the course of the two-week workshop. This outcome is especially relevant to schools and districts interested in improving student outcomes, school climate and teacher retention rates
Octupolar order in the multiple spin exchange model on a triangular lattice
We show how a gapless spin liquid with hidden octupolar order arises in an
applied magnetic field, in a model applicable to thin films of 3He with
competing ferromagnetic and antiferromagnetic (cyclic) exchange interactions.
Evidence is also presented for nematic -- i.e., quadrupolar -- correlations
bordering on ferromagnetism in the absence of a magnetic field.Comment: 4 pages, 5 figure
Substrate-specific Effect on Sirtuin Conformation and Oligomerization
Human sirtuins are a family of nicotinamide adenine dinucleotide (NAD +)-dependent enzymes that are responsible for removing acyl modifications from lysine residues. Sirtuins are involved in the formation and proliferation of cancers and are thought to regulate the progression of neurodegenerative diseases. Although sirtuins can be pharmacologically targeted by small molecules, it is not easy to modulate the substrate selectivity of sirtuins despite the chemical diversity of their substrates. Here, we report substrate-specific effects on sirtuin conformation and oligomerization that regulate enzyme deacylase activity. We used fluorescent acyl peptide probes to study substrate interactions with two sirtuin isoforms: SIRT2 and SIRT6. We observed that some of the fluorescent acyl peptides bind sirtuins and change their conformation, whereas other probes bind sirtuins without causing such structural changes. Our fluorescent probes also revealed that SIRT2 forms a dimer at relevant cellular concentrations (~100 nM) in contrast to SIRT6, which is exclusively monomeric. SIRT2 undergoes a conformational transition from dimer to monomer when bound to myristoyl-substrate which slows its demyristoylase reaction, but SIRT2 remains dimeric when performing its deacetylase reaction. Our fluorescent peptide probes will continue to be used to examine substrate specific effects on sirtuin structure and function in order to understand how to pharmacologically modulate sirtuin substrate selectivity
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