41 research outputs found
The second law of thermodynamics, TCP, and Einstein causality in anti-de Sitter space-time
If the vacuum is passive for uniformly accelerated observers in anti-de
Sitter space-time (i.e. cannot be used by them to operate a "perpetuum
mobile"), they will (a) register a universal value of the Hawking-Unruh
temperature, (b) discover a TCP symmetry, and (c) find that observables in
complementary wedge-shaped regions are commensurable (local) in the vacuum
state. These results are model independent and hold in any theory which is
compatible with some weak notion of space-time localization.Comment: 8 pages, slightly improved results, minor changes in the expository
part, new title; to appear in "Classical and Quantum Gravity
Intermediate statistics in quantum maps
We present a one-parameter family of quantum maps whose spectral statistics
are of the same intermediate type as observed in polygonal quantum billiards.
Our central result is the evaluation of the spectral two-point correlation form
factor at small argument, which in turn yields the asymptotic level
compressibility for macroscopic correlation lengths
Adjusting the melting point of a model system via Gibbs-Duhem integration: application to a model of Aluminum
Model interaction potentials for real materials are generally optimized with
respect to only those experimental properties that are easily evaluated as
mechanical averages (e.g., elastic constants (at T=0 K), static lattice
energies and liquid structure). For such potentials, agreement with experiment
for the non-mechanical properties, such as the melting point, is not guaranteed
and such values can deviate significantly from experiment. We present a method
for re-parameterizing any model interaction potential of a real material to
adjust its melting temperature to a value that is closer to its experimental
melting temperature. This is done without significantly affecting the
mechanical properties for which the potential was modeled. This method is an
application of Gibbs-Duhem integration [D. Kofke, Mol. Phys.78, 1331 (1993)].
As a test we apply the method to an embedded atom model of aluminum [J. Mei and
J.W. Davenport, Phys. Rev. B 46, 21 (1992)] for which the melting temperature
for the thermodynamic limit is 826.4 +/- 1.3K - somewhat below the experimental
value of 933K. After re-parameterization, the melting temperature of the
modified potential is found to be 931.5K +/- 1.5K.Comment: 9 pages, 5 figures, 4 table
Dendritic Polyglycerol Amine: An Enhanced Substrate to Support Long-Term Neural Cell Culture
Long-term stable cell culture is a critical tool to better understand cell function. Most adherent cell culture models require a polymer substrate coating of poly-lysine or poly-ornithine for the cells to adhere and survive. However, polypeptide-based substrates are degraded by proteolysis and it remains a challenge to maintain healthy cell cultures for extended periods of time. Here, we report the development of an enhanced cell culture substrate based on a coating of dendritic polyglycerol amine (dPGA), a non-protein macromolecular biomimetic of poly-lysine, to promote the adhesion and survival of neurons in cell culture. We show that this new polymer coating provides enhanced survival, differentiation and long-term stability for cultures of primary neurons or neurons derived from human induced pluripotent stem cells (hiPSCs). Atomic force microscopy analysis provides evidence that greater nanoscale roughness contributes to the enhanced capacity of dPGA-coated surfaces to support cells in culture. We conclude that dPGA is a cytocompatible, functionally superior, easy to use, low cost and highly stable alternative to poly-cationic polymer cell culture substrate coatings such as poly-lysine and poly-ornithine.
Summary statement
Here, we describe a novel dendritic polyglycerol amine-based substrate coating, demonstrating superior performance compared to current polymer coatings for long-term culture of primary neurons and neurons derived from induced pluripotent stem cells
Reference frames, superselection rules, and quantum information
Recently, there has been much interest in a new kind of ``unspeakable''
quantum information that stands to regular quantum information in the same way
that a direction in space or a moment in time stands to a classical bit string:
the former can only be encoded using particular degrees of freedom while the
latter are indifferent to the physical nature of the information carriers. The
problem of correlating distant reference frames, of which aligning Cartesian
axes and synchronizing clocks are important instances, is an example of a task
that requires the exchange of unspeakable information and for which it is
interesting to determine the fundamental quantum limit of efficiency. There
have also been many investigations into the information theory that is
appropriate for parties that lack reference frames or that lack correlation
between their reference frames, restrictions that result in global and local
superselection rules. In the presence of these, quantum unspeakable information
becomes a new kind of resource that can be manipulated, depleted, quantified,
etcetera. Methods have also been developed to contend with these restrictions
using relational encodings, particularly in the context of computation,
cryptography, communication, and the manipulation of entanglement. This article
reviews the role of reference frames and superselection rules in the theory of
quantum information processing.Comment: 55 pages, published versio
Felony Murder and Capital Punishment: an Examination of the Deterrence Question
A proper test of the deterrent effect of the death penalty must consider capital homicides. However, the criterion variable in most investigations has been total homicides—most of which bear no legal or theoretical relationship to capital punishment. To address this fundamental data problem, this investigation used Federal Bureau of Investigation data for 1976–1987 to examine the relationship between capital punishment and felony murder, the most common type of capital homicide. We conducted time series analyses of monthly felony murder rates, the frequency of executions, and the amount and type of television coverage of executions over the period. The analyses revealed occasional departures (for vehicle theft and narcotics killings) from the null hypotheses. However, on balance, and in line with the vast majority of capital punishment studies, this investigation found no consistent evidence that executions and the television coverage they receive are associated significantly with rates for total, index, or different types of felony murder
Sources of variation in cuticular hydrocarbons in the ant formica exsecta
Phenotypic variation arises from interactions between genotype and environment, although how variation is produced and then maintained remains unclear. The discovery of the nest-mate recognition system in Formica exsecta ants has allowed phenotypic variation in chemical profiles to be quantified across a natural population of 83 colonies. We investigated if this variation was correlated or not with intrinsic (genetic relatedness), extrinsic (location, light, temperature) or social (queen number) factors. (Z)-9-Alkenes and n-alkanes showed different patterns of variance: island (location) explained only 0.2% of the variation in (Z)-9-alkenes, but 21¬–29% in n-alkanes, whereas colony of origin explained 96% and 45–49% of the variation in (Z)-9-alkenes and n-alkanes, respectively. By contrast, within-colony variance of (Z)-9-alkenes was 4%, and 23–34% in n-alkanes, supporting the function of the former as recognition cues. (Z)-9-Alkene and n-alkane profiles were correlated with the genetic distance between colonies. Only n-alkane profiles diverged with increasing spatial distance. Sampling year explained a small (5%), but significant, amount of the variation in the (Z)-9-alkenes, but there was no consistent directional trend. Polygynous colonies and populous monogynous colonies were dominated by a rich C23:1 profile. We found no associations between worker size, mound exposure, or humidity, although effect sizes for the latter two factors were considerable. The results support the conjecture that genetic factors are the most likely source of between-colony variation in cuticular hydrocarbons
Comparing GABA-dependent physiological measures of inhibition with proton magnetic resonance spectroscopy measurement of GABA using ultra-high-field MRI
Imbalances in glutamatergic (excitatory) and GABA (inhibitory) signalling within key brain networks are thought to underlie many brain and mental health disorders, and for this reason there is considerable interest in investigating how individual variability in localised concentrations of these molecules relate to brain disorders. Magnetic resonance spectroscopy (MRS) provides a reliable means of measuring, in vivo, concentrations of neurometabolites such as GABA, glutamate and glutamine that can be correlated with brain function and dysfunction. However, an issue of much debate is whether the GABA observed and measured using MRS represents the entire pool of GABA available for measurement (i.e., metabolic, intracellular, and extracellular) or is instead limited to only some portion of it. GABA function can also be investigated indirectly in humans through the use of non-invasive transcranial magnetic stimulation (TMS) techniques that can be used to measure cortical excitability and GABA-mediated physiological inhibition. To investigate this issue further we collected in a single session both types of measurement, i.e., TMS measures of cortical excitability and physiological inhibition and ultra-high-field (7 Tesla) MRS measures of GABA, glutamate and glutamine, from the left sensorimotor cortex of the same group of right-handed individuals. We found that TMS and MRS measures were largely uncorrelated with one another, save for the plateau of the TMS IO curve that was negatively correlated with MRS-Glutamate (Glu) and intra-cortical facilitation (10ms ISI) that was positively associated with MRS-Glutamate concentration. These findings are consistent with the view that the GABA concentrations measured using MRS largely represent pools of GABA that are linked to tonic rather than phasic inhibition and thus contribute to the inhibitory tone of a brain area rather than GABAergic synaptic transmission
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International Waters – Delivering Results
This publication is the fourth in a series of knowledge publications prepared by the UNDP-GEF International Waters programme that document and highlight key results and achievements at the project and portfolio level, comprising four ‘signature’ programme areas: Large Marine Ecosystems; Lakes, Rivers and Aquifers; Integrated Water Resources and Coastal Area Management; and Global Programmes. The portfolio continues to make progress in sustaining the world’s most significant shared water systems for the billions of people who depend on these ecosystems for their livelihoods and security