525 research outputs found
Master-equation approach to the study of phase-change processes in data storage media
We study the dynamics of crystallization in phase-change materials using a master-equation approach in which the state of the crystallizing material is described by a cluster size distribution function. A model is developed using the thermodynamics of the processes involved and representing the clusters of size two and greater as a continuum but clusters of size one (monomers) as a separate equation. We present some partial analytical results for the isothermal case and for large cluster sizes, but principally we use numerical simulations to investigate the model. We obtain results that are in good agreement with experimental data and the model appears to be useful for the fast simulation of reading and writing processes in phase-change optical and electrical memories
The complement receptor C5aR controls acute inflammation and astrogliosis following spinal cord injury
This study investigated the role of the complement activation fragment C5a in secondary pathology following contusive spinal cord injury (SCI). C5ar(-/-) mice, which lack the signaling receptor for C5a, displayed signs of improved locomotor recovery and reduced inflammation during the first week of SCI compared with wild-type mice. Intriguingly, the early signs of improved recovery in C5ar(-/-) mice deteriorated from day 14 onward, with absence of C5aR ultimately leading to poorer functional outcomes, larger lesion volumes, reduced myelin content, and more widespread inflammation at 35 d SCI. Pharmacological blockade of C5aR with a selective antagonist (C5aR-A) during the first 7 d after SCI improved recovery compared with vehicle-treated mice, and this phenotype was sustained up to 35 d after injury. Consistent with observations made in C5ar(-/-) mice, these improvements were, however, lost if C5aR-A administration was continued into the more chronic phase of SCI. Signaling through the C5a-C5aR axis thus appears injurious in the acute period but serves a protective and/or reparative role in the post-acute phase of SCI. Further experiments in bone marrow chimeric mice suggested that the dual and opposing roles of C5aR on SCI outcomes primarily relate to its expression on CNS-resident cells and not infiltrating leukocytes. Additional in vivo and in vitro studies provided direct evidence that C5aR signaling is required during the postacute phase for astrocyte hyperplasia, hypertrophy, and glial scar formation. Collectively, these findings highlight the complexity of the inflammatory response to SCI and emphasize the importance of optimizing the timing of therapeutic interventions
Education and articulation: Laclau and Mouffeâs radical democracy in school
This paper outlines a theory of radical democratic education by addressing a key concept in Laclau and Mouffeâs Hegemony and Socialist Strategy: articulation. Through their concept of articulation, Laclau and Mouffe attempt to liberate Gramsciâs theory of hegemony from Marxist economism, and adapt it to a political sphere inhabited by a plurality of struggles and agents none of which is predominant. However, while for Gramsci the political process of hegemony formation has an explicit educational dimension, Laclau and Mouffe ignore this dimension altogether. My discussion starts with elaborating the concept of articulation and analysing it in terms of three dimensions: performance, connection and transformation. I then address the role of education in Gramsciâs politics, in which the figure of the intellectual is central, and argue that radical democratic education requires renouncing that figure. In the final section, I offer a theory of such education, in which both teacher and students articulate their political differences and identities
The ferric leaching kinetics of arsenopyrite
Abstract In this investigation batch, ferric leaching experiments were carried out in a 100 m l l jacketed vessel maintained at 258C. The parameters varied during the course of the experimental program included the initial redox potential, the total iron concentration, the solids concentration and the pH of the leaching solution. The initial redox potential used ranged from 625 to 470 mV, the overall iron concentration ranged from 8 to 32 g. l l y1 , the mineral concentration ranged from 5 to 20 g. l l y1 and the initial pH used ranged from 1.10 to 1.45. The redox potential of the leach solution was monitored continuously using a redox probe connected to a computer. The leach rates were calculated from the measured change in the redox potential of the leaching solution. The variation in the ferric leaching rate of the arsenopyrite as a function of the solution redox potential displayed similar trends, irrespective of the conditions employed. The ferric leaching rate of the arsenopyrite decreased with decreasing redox potential of the leaching solution and could be accurately described using a modified Butler-Volmer equation; yr s r e y . High concentrations of ferric iron and protons, and a reduction in the solids Ćœ concentration were found to impede the leach rate. The 'rest potential' i.e., the redox potential at . which the dissolution of arsenopyrite stops of the arsenopyrite was found to be higher under these conditions. However, no occluding sulphur layer could be detected on the surface of mineral particles, hence the results suggest that the reactivity of the mineral decreases with an increase in the effective concentration of the ferric iron species. Therefore, although the results suggest the Ćœ . PII: S 0 3 0 4 -3 8 6 X 9 9 0 0 0 0 7 -9 ( ) R. Ruitenberg et al.r Hydrometallurgy 52 1999 37-53 38 likelihood of an electrochemical mechanism being operative, it is necessary to modify the Butler-Volmer-based model to account for the above observations in order to obtain a model capable of predicting the ferric leaching rate of arsenopyrite across a broad range of operating conditions.
Experimental loophole-free violation of a Bell inequality using entangled electron spins separated by 1.3 km
For more than 80 years, the counterintuitive predictions of quantum theory
have stimulated debate about the nature of reality. In his seminal work, John
Bell proved that no theory of nature that obeys locality and realism can
reproduce all the predictions of quantum theory. Bell showed that in any local
realist theory the correlations between distant measurements satisfy an
inequality and, moreover, that this inequality can be violated according to
quantum theory. This provided a recipe for experimental tests of the
fundamental principles underlying the laws of nature. In the past decades,
numerous ingenious Bell inequality tests have been reported. However, because
of experimental limitations, all experiments to date required additional
assumptions to obtain a contradiction with local realism, resulting in
loopholes. Here we report on a Bell experiment that is free of any such
additional assumption and thus directly tests the principles underlying Bell's
inequality. We employ an event-ready scheme that enables the generation of
high-fidelity entanglement between distant electron spins. Efficient spin
readout avoids the fair sampling assumption (detection loophole), while the use
of fast random basis selection and readout combined with a spatial separation
of 1.3 km ensure the required locality conditions. We perform 245 trials
testing the CHSH-Bell inequality and find . A
null hypothesis test yields a probability of that a local-realist
model for space-like separated sites produces data with a violation at least as
large as observed, even when allowing for memory in the devices. This result
rules out large classes of local realist theories, and paves the way for
implementing device-independent quantum-secure communication and randomness
certification.Comment: Raw data will be made available after publicatio
A fusion of minicircle DNA and nanoparticle delivery technologies facilitates therapeutic genetic engineering of autologous canine olfactory mucosal cells
Olfactory ensheathing cells (OECs) promote axonal regeneration and improve locomotor function when transplanted into the injured spinal cord. A recent clinical trial demonstrated improved motor function in domestic dogs with spinal injury following autologous OEC transplantation. Their utility in canines offers promise for human translation, as dogs are comparable to humans in terms of clinical management and genetic/environmental variation. Moreover, the autologous, minimally invasive derivation of OECs makes them viable for human spinal injury investigation. Genetic engineering of transplant populations may augment their therapeutic potential, but relies heavily on viral methods which have several drawbacks for clinical translation. We present here the first proof that magnetic particles deployed with applied magnetic fields and advanced DNA minicircle vectors can safely bioengineer OECs to secrete a key neurotrophic factor, with an efficiency approaching that of viral vectors. We suggest that our alternative approach offers high translational potential for the delivery of augmented clinical cell therapies
Recommended from our members
The notion of contextual locking: Previously learnt items are not accessible as such when appearing in a less common context
We examined the effect of context on the learning of spatial coding in four experiments. Two partially overlapping sets of stimuli, which had the very same stimulusâresponse spatial coding, were presented in unique contexts. Results show contextual lockingâthat is, response times to the very same item in a more common context (80%) were significantly shorter than those in a less common context (20%). Contextual locking was obtained both when the context was more salient (Experiments 1 and 2) and less salient (Experiments 3 and 4). In addition, results were obtained even when contextualization seemed less necessary (Experiments 2 and 4). Binding of information to context is discussed in relation to chunking, transfer effects, and practical applications pertaining to professional training
Inhibition of activation induced CD154 on CD4+ CD25- cells: a valid surrogate for human Treg suppressor function
Natural Regulatory T cells (Tregs) are defined by stable expression of the cell surface proteins CD4 and CD25, low surface expression of CD127 and expression of the transcription factor FOXP3. The contribution of Treg to the prevention of autoimmunity and the maintenance of immune homoestasis is the subject of ongoing interest, as alterations in Treg numbers and function are implicated in a wide range of diseases. The in vitro benchmark for determining Treg function is suppression of proliferation of unmatched effector T cells in a mixed lymphocyte reaction (MLR) over a 3â6-day time period. As an alternative to this assay, we show that a 7-h CD154 expression assay is rapid, simple and provides a reliable readout of suppressor function. Using multiple Treg-like cell types including natural (n)Treg, inducible (i)Treg and Treg cell lines, we show that suppression of CD154 expression is a surrogate for suppression of proliferation. We propose this as a suitable alternative to the MLR assay, as it is rapid and may be more amenable to high-throughput screening, analysing large cohorts of clinical samples or assaying transiently suppressive populations. Keywords: regulatory T cells; functional assays; iTreg; nTregDanika Hill, Nicola Eastaff-Leung, Suzanne Bresatz-Atkins, Noel Warner, Joyce Ruitenberg, Dorren Krumbiegel, Steve Pederson, Natasha McInnes, Cheryl Y. Brown, Timothy Sadlon and Simon C. Barr
- âŠ