517 research outputs found
Generalizations of Ripley's K-function with Application to Space Curves
The intensity function and Ripley's K-function have been used extensively in
the literature to describe the first and second moment structure of spatial
point sets. This has many applications including describing the statistical
structure of synaptic vesicles. Some attempts have been made to extend Ripley's
K-function to curve pieces. Such an extension can be used to describe the
statistical structure of muscle fibers and brain fiber tracks. In this paper,
we take a computational perspective and construct new and very general variants
of Ripley's K-function for curves pieces, surface patches etc. We discuss the
method from [Chiu, Stoyan, Kendall, & Mecke 2013] and compare it with our
generalizations theoretically, and we give examples demonstrating the
difference in their ability to separate sets of curve pieces.Comment: 9 pages & 8 figure
Rotational dynamics of a superhelix towed in a Stokes fluid
Motivated by the intriguing motility of spirochetes (helically-shaped
bacteria that screw through viscous fluids due to the action of internal
periplasmic flagella), we examine the fundamental fluid dynamics of
superhelices translating and rotating in a Stokes fluid. A superhelical
structure may be thought of as a helix whose axial centerline is not straight,
but also a helix. We examine the particular case where these two superimposed
helices have different handedness, and employ a combination of experimental,
analytic, and computational methods to determine the rotational velocity of
superhelical bodies being towed through a very viscous fluid. We find that the
direction and rate of the rotation of the body is a result of competition
between the two superimposed helices; for small axial helix amplitude, the body
dynamics is controlled by the short-pitched helix, while there is a cross-over
at larger amplitude to control by the axial helix. We find far better, and
excellent, agreement of our experimental results with numerical computations
based upon the method of Regularized Stokeslets than upon the predictions of
classical resistive force theory
Dignity and Narrative Medicine
Critiques of the dehumanising aspects of contemporary medical practice have generated increasing interest in the ways in which health care can foster a holistic sense of wellbeing. We examine the relationship between two areas of this humanistic endeavour: narrative and dignity. This paper makes two simple arguments that are intuitive but have not yet been explored in detail: that narrative competence of carers is required for maintaining or recreating dignity, and that dignity promotion in health care practice is primarily narrative in form. The multiple meanings that dignity has in a person’s life are what give the concept power and can only be captured by narrative. This has implications for health care practice where narrative work will be increasingly required to support patient dignity in under-resourced and over-subscribed health care system
Communication and trust in the bounded confidence model
The communication process in a situation of emergency is discussed within the
Scheff theory of shame and pride. The communication involves messages from
media and from other persons. Three strategies are considered: selfish (to
contact friends), collective (to join other people) and passive (to do
nothing). We show that the pure selfish strategy cannot be evolutionarily
stable. The main result is that the community structure is statistically
meaningful only if the interpersonal communication is weak.Comment: 6 pages, 5 figures, RevTeX, for ICCCI-201
Fiber-Flux Diffusion Density for White Matter Tracts Analysis: Application to Mild Anomalies Localization in Contact Sports Players
We present the concept of fiber-flux density for locally quantifying white
matter (WM) fiber bundles. By combining scalar diffusivity measures (e.g.,
fractional anisotropy) with fiber-flux measurements, we define new local
descriptors called Fiber-Flux Diffusion Density (FFDD) vectors. Applying each
descriptor throughout fiber bundles allows along-tract coupling of a specific
diffusion measure with geometrical properties, such as fiber orientation and
coherence. A key step in the proposed framework is the construction of an FFDD
dissimilarity measure for sub-voxel alignment of fiber bundles, based on the
fast marching method (FMM). The obtained aligned WM tract-profiles enable
meaningful inter-subject comparisons and group-wise statistical analysis. We
demonstrate our method using two different datasets of contact sports players.
Along-tract pairwise comparison as well as group-wise analysis, with respect to
non-player healthy controls, reveal significant and spatially-consistent FFDD
anomalies. Comparing our method with along-tract FA analysis shows improved
sensitivity to subtle structural anomalies in football players over standard FA
measurements
Improved Parameterized Algorithms for the Kemeny Aggregation Problem
We give improvements over fixed parameter tractable (FPT) algo-rithms to solve the Kemeny aggregation problem, where the task is to summarize a multi-set of preference lists, called votes, over a set of alternatives, called candidates, into a single preference list that has the minimum total τ-distance from the votes. The τ-distance between two preference lists is the number of pairs of candidates that are or-dered differently in the two lists. We study the problem for preference lists that are total orders. We develop algorithms of running times O∗(1.403kt), O∗(5.823kt/m) ≤ O∗(5.823kavg) and O∗(4.829kmax) for the problem, ignoring the polynomial factors in the O ∗ notation, where kt is the optimum total τ-distance, m is the number of votes, and kavg (resp, kmax) is the average (resp, maximum) over pairwise τ-distances of votes. Our algorithms improve the best previously known running times of O∗(1.53kt) and O∗(16kavg) ≤ O∗(16kmax) [4, 5], which also implies an O∗(164kt/m) running time. We also show how to enumerate all optimal solutions in O∗(36kt/m) ≤ O∗(36kavg) time.
Initial Characterization of the FlgE Hook High Molecular Weight Complex of
The spirochete periplasmic flagellum has many unique attributes. One unusual characteristic is the flagellar hook. This structure serves as a universal joint coupling rotation of the membrane-bound motor to the flagellar filament. The hook is comprised of about 120 FlgE monomers, and in most bacteria these structures readily dissociate to monomers (∼ 50 kDa) when treated with heat and detergent. However, in spirochetes the FlgE monomers form a large mass of over 250 kDa [referred to as a high molecular weight complex (HMWC)] that is stable to these and other denaturing conditions. In this communication, we examined specific aspects with respect to the formation and structure of this complex. We found that the Lyme disease spirochete Borrelia burgdorferi synthesized the HMWC throughout the in vitro growth cycle, and also in vivo when implanted in dialysis membrane chambers in rats. The HMWC was stable to formic acid, which supports the concept that the stability of the HMWC is dependent on covalent cross-linking of individual FlgE subunits. Mass spectrometry analysis of the HMWC from both wild type periplasmic flagella and polyhooks from a newly constructed ΔfliK mutant indicated that other proteins besides FlgE were not covalently joined to the complex, and that FlgE was the sole component of the complex. In addition, mass spectrometry analysis also indicated that the HMWC was composed of a polymer of the FlgE protein with both the N- and C-terminal regions remaining intact. These initial studies set the stage for a detailed characterization of the HMWC. Covalent cross-linking of FlgE with the accompanying formation of the HMWC we propose strengthens the hook structure for optimal spirochete motility
Advances in the Direct Study of Carbon Burning in Massive Stars
The C12+C12 fusion reaction plays a critical role in the evolution of massive stars and also strongly impacts various explosive astrophysical scenarios. The presence of resonances in this reaction at energies around and below the Coulomb barrier makes it impossible to carry out a simple extrapolation down to the Gamow window-the energy regime relevant to carbon burning in massive stars. The C12+C12 system forms a unique laboratory for challenging the contemporary picture of deep sub-barrier fusion (possible sub-barrier hindrance) and its interplay with nuclear structure (sub-barrier resonances). Here, we show that direct measurements of the C12+C12 fusion cross section may be made into the Gamow window using an advanced particle-gamma coincidence technique. The sensitivity of this technique effectively removes ambiguities in existing measurements made with gamma ray or charged-particle detection alone. The present cross-section data span over 8 orders of magnitude and support the fusion-hindrance model at deep sub-barrier energies
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