7,416 research outputs found
Marx in Miami: Reflections on Teaching and the Confrontation with Ideology
In composing this piece we hope to detail some of our strategies and pedagogical experiences teaching Marx and Marxism in Miami, Florida. Although Miami is certainly a special case regarding the intensity and character of ideological fervor against Leftist political and social theory, we believe the lessons adapted to this specific environment can be generalized for instructors regardless of geography. Teaching Marx in the United States often poses unique challenges. In Miami, those obstacles feel frequently amplified
Dynamics of hard-sphere suspension using Dynamic Light Scattering and X-Ray Photon Correlation Spectroscopy: dynamics and scaling of the Intermediate Scattering Function
Intermediate Scattering Functions (ISF's) are measured for colloidal hard
sphere systems using both Dynamic Light Scattering (DLS) and X-ray Photon
Correlation Spectroscopy (XPCS). We compare the techniques, and discuss the
advantages and disadvantages of each. Both techniques agree in the overlapping
range of scattering vectors. We investigate the scaling behaviour found by
Segre and Pusey [1] but challenged by Lurio et al. [2]. We observe a scaling
behaviour over several decades in time but not in the long time regime.
Moreover, we do not observe long time diffusive regimes at scattering vectors
away from the peak of the structure factor and so question the existence of a
long time diffusion coefficients at these scattering vectors.Comment: 21 pages, 11 figure
Calibrated Sub-Bundles in Non-Compact Manifolds of Special Holonomy
This paper is a continuation of math.DG/0408005. We first construct special
Lagrangian submanifolds of the Ricci-flat Stenzel metric (of holonomy SU(n)) on
the cotangent bundle of S^n by looking at the conormal bundle of appropriate
submanifolds of S^n. We find that the condition for the conormal bundle to be
special Lagrangian is the same as that discovered by Harvey-Lawson for
submanifolds in R^n in their pioneering paper. We also construct calibrated
submanifolds in complete metrics with special holonomy G_2 and Spin(7)
discovered by Bryant and Salamon on the total spaces of appropriate bundles
over self-dual Einstein four manifolds. The submanifolds are constructed as
certain subbundles over immersed surfaces. We show that this construction
requires the surface to be minimal in the associative and Cayley cases, and to
be (properly oriented) real isotropic in the coassociative case. We also make
some remarks about using these constructions as a possible local model for the
intersection of compact calibrated submanifolds in a compact manifold with
special holonomy.Comment: 20 pages; for Revised Version: Minor cosmetic changes, some
paragraphs rewritten for improved clarit
Environmental Clustering of New Zealand Dairy Herds
Previous studies have found that milk yield (a proxy for feeding level) and temperature-humidity index (THI) are important factors in explaining genotype x environment (G x E) interactions, indicating differences between the abilities of genotypes to forage or consume concentrates effectively or to cope with thermal stress (Ravagnolo and Misztal, 2000; Zwald et al., 2003). The objective of this study was to quantify and cluster (CL) herd environments within New Zealand (NZ) based on production levels, a summer heat load index (HLI) and geographical location
Evidence of volcanic ash at a K-T boundary section: Ocean drilling program hole 690 C, Maud Rise, Weddell Sea off East Antarctica
Rare vitric volcanogenic ash but more abundant clay minerals considered volcanogenic in origin are associated with an expanded and essentially complete K-T boundary sequence from Ocean Drilling Project (ODP) Hole 690 C on Maud Rise in the Weddell Sea off East Antarctica. Results at this writing are preliminary and are still based to some extent on shipboard descriptions. Further shore-based studies are in progress. It would appear, however, that the presence of volcanic ash and altered ash in the Danian section beginning at the biostratigraphically and paleomagnetically determined K-T boundary on Maud Rise can be cited as evidence of significant volcanic activity within the South Atlantic-Indian Ocean sector of the Southern Ocean coincident with the time of biotic crises at the end of the Maestrichtian. This is a postulated time of tectonic and volcanic activity within this Southern Hemisphere region, including possible initiation of the Reunion hot spot and a peak in explosive volcanism on Walvis Ridge (1) among other events. A causal relationship with the biotic crisis is possible and volcanism should be given serious consideration as a testable working hypothesis to explain these extinctions
PHOTOCHEMISTRY OF PHYCOBILIPROTEINS
Native PEC from the cyanobacterium, Mastigocladus laminosus, and its isolated α-subunit show photoreversibly photochromic reactions with difference-maxima around 502 and 570 nm in the spectral region of the α-84 phycoviolobilin chromophore. (b) Native PEC and its ÎČ-subunit show little if any reversible photochemistry in the 600â620 nm region, where the phycocyanobilin chromophores on the ÎČ-subunit absorb maximally, (c) Reversible photochemistry is retained in ureadenatured PEC at pH = 7.0 or pH †3. The difference maxima are shifted to 510 and 600 nm, and the amplitudes are decreased. An irreversible absorbance increase occurs around 670 nm (pH †3). (d) The amplitude of the reversible photoreaction difference spectrum is maximum in the presence of 4â5 M urea or 1 M KSCN, conditions known to dissociate phycobiliprotein aggregates into monomers. At the same time, the phycocyanobilin chromophore(s) are bleached irreversibly, (e) The amplitude becomes very small in high aggregates, e.g. in phycobilisomes. (f) In a reciprocal manner, the phototransformation of native PEC leads to a reversible shift of its aggregation equilibrium between trimer and monomer. The latter is favored by orange, the former by green light, (g) It is concluded that the phycoviolobilin chromophore of PEC is responsible for reversible photochemistry in PEC, and that there is not only an influence of aggregation state on photochemistry, but also vice versa an effect of the status of the chromophore on aggregation state. This could constitute a primary signal in the putative function as sensory pigment, either directly, or indirectly via the release of other polypeptides, via photodynamic effects, or the like
Differential Dynamic Microscopy of Bacterial Motility
We demonstrate 'differential dynamic microscopy' (DDM) for the fast, high
throughput characterization of the dynamics of active particles. Specifically,
we characterize the swimming speed distribution and the fraction of motile
cells in suspensions of Escherichia coli bacteria. By averaging over ~10^4
cells, our results are highly accurate compared to conventional tracking. The
diffusivity of non-motile cells is enhanced by an amount proportional to the
concentration of motile cells.Comment: 4 pages, 4 figures. In this updated version we have added simulations
to support our interpretation, and changed the model for the swimming speed
probability distribution from log-normal to a Schulz distribution. Neither
modification significantly changes our conclusion
Compact Einstein Spaces based on Quaternionic K\"ahler Manifolds
We investigate the Einstein equation with a positive cosmological constant
for -dimensional metrics on bundles over Quaternionic K\"ahler base
manifolds whose fibers are 4-dimensional Bianchi IX manifolds. The Einstein
equations are reduced to a set of non-linear ordinary differential equations.
We numerically find inhomogeneous compact Einstein spaces with orbifold
singularity.Comment: LaTeX 28 pages, 5 eps figure
Machine Learning Approaches to Determine Feature Importance for Predicting Infant Autopsy Outcome
Introduction:
Sudden unexpected death in infancy (SUDI) represents the commonest presentation of postneonatal death. We explored whether machine learning could be used to derive data driven insights for prediction of infant autopsy outcome.
Methods:
A paediatric autopsy database containing >7,000 cases, with >300 variables, was analysed by examination stage and autopsy outcome classified as âexplained (medical cause of death identified)â or âunexplainedâ. Decision tree, random forest, and gradient boosting models were iteratively trained and evaluated.
Results:
Data from 3,100 infant and young child (<2 years) autopsies were included. NaĂŻve decision tree using external examination data had performance of 68% for predicting an explained death. Core data items were identified using model feature importance. The most effective model was XG Boost, with overall predictive performance of 80%, demonstrating age at death, and cardiovascular and respiratory histological findings as the most important variables associated with determining medical cause of death.
Conclusion:
This study demonstrates feasibility of using machine-learning to evaluate component importance of complex medical procedures (paediatric autopsy) and highlights value of collecting routine clinical data according to defined standards. This approach can be applied to a range of clinical and operational healthcare scenario
Influence of chromophores on quarternary structure of phycobiliproteins from the cyanobacterium, Mastigocladus laminosus
Chromophores of C-phycocyanin and phycoerythrÎż-cyanin have been chemically modified by reduction to
rubins , bleaching , photoisomerization , or perturbation
with bulky substituents. Pigments containing modified
chromophores, or hybrids containing modified and unmodified chromophores in individual protomers have been prepared. All modifications inhibit the association of the
(aĂ)-protomers of these pigments to higher aggregates. The
results demonstrate a pronounced effect of the state of
the chromophores on biliprotein quaternary structure. It
may be important in phycobi1isome assembly , and also in
the dual function of biliproteins as (i) antenna pigments
for photosynthesis and (ii) reaction centers for photomor-phogenesis
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