3,817 research outputs found
Conformal Parametrisation of Loxodromes by Triples of Circles
We provide a parametrisation of a loxodrome by three specially arranged
cycles. The parametrisation is covariant under fractional linear
transformations of the complex plane and naturally encodes conformal properties
of loxodromes. Selected geometrical examples illustrate the usage of
parametrisation. Our work extends the set of objects in Lie sphere
geometry---circle, lines and points---to the natural maximal
conformally-invariant family, which also includes loxodromes.Comment: 14 pages. 9 PDF in four figures, AMS-LaTe
Improving the cost-effectiveness of visual devices for the control of Riverine tsetse flies, the major vectors of Human African Trypanosomiasis
Control of the Riverine (Palpalis) group of tsetse flies is normally achieved with stationary artificial devices such as traps or insecticide-treated targets. The efficiency of biconical traps (the standard control device), 161 m black targets and small 25625 cm targets with flanking nets was compared using electrocuting sampling methods. The work was done on Glossina tachinoides and G. palpalis gambiensis (Burkina Faso), G. fuscipes quanzensis (Democratic Republic of Congo), G. f. martinii (Tanzania) and G. f. fuscipes (Kenya). The killing effectiveness (measured as the catch per m2 of cloth) for small targets plus flanking nets is 5.5–15X greater than for 1 m2 targets and 8.6–37.5X greater than for biconical traps. This has important implications for the costs of control of the Riverine group of tsetse vectors of sleeping sickness
Microfluidics-based approaches to the isolation of African trypanosomes
African trypanosomes are responsible for significant levels of disease in both humans and
animals. The protozoan parasites are free-living flagellates, usually transmitted by arthropod vectors,
including the tsetse fly. In the mammalian host they live in the bloodstream and, in the case of
human-infectious species, later invade the central nervous system. Diagnosis of the disease requires
the positive identification of parasites in the bloodstream. This can be particularly challenging
where parasite numbers are low, as is often the case in peripheral blood. Enriching parasites
from body fluids is an important part of the diagnostic pathway. As more is learned about the
physicochemical properties of trypanosomes, this information can be exploited through use of
different microfluidic-based approaches to isolate the parasites from blood or other fluids. Here,
we discuss recent advances in the use of microfluidics to separate trypanosomes from blood and to
isolate single trypanosomes for analyses including drug screening
Correlated dynamics in egocentric communication networks
We investigate the communication sequences of millions of people through two
different channels and analyze the fine grained temporal structure of
correlated event trains induced by single individuals. By focusing on
correlations between the heterogeneous dynamics and the topology of egocentric
networks we find that the bursty trains usually evolve for pairs of individuals
rather than for the ego and his/her several neighbors thus burstiness is a
property of the links rather than of the nodes. We compare the directional
balance of calls and short messages within bursty trains to the average on the
actual link and show that for the trains of voice calls the imbalance is
significantly enhanced, while for short messages the balance within the trains
increases. These effects can be partly traced back to the technological
constrains (for short messages) and partly to the human behavioral features
(voice calls). We define a model that is able to reproduce the empirical
results and may help us to understand better the mechanisms driving technology
mediated human communication dynamics.Comment: 7 pages, 6 figure
Using a Recurrent Neural Network To Inform the Use of Prostate-specific Antigen (PSA) and PSA Density for Dynamic Monitoring of the Risk of Prostate Cancer Progression on Active Surveillance
The global uptake of prostate cancer (PCa) active surveillance (AS) is steadily increasing. While prostate-specific antigen density (PSAD) is an important baseline predictor of PCa progression on AS, there is a scarcity of recommendations on its use in follow-up. In particular, the best way of measuring PSAD is unclear. One approach would be to use the baseline gland volume (BGV) as a denominator in all calculations throughout AS (nonadaptive PSAD, PSADNA), while another would be to remeasure gland volume at each new magnetic resonance imaging scan (adaptive PSAD, PSADA). In addition, little is known about the predictive value of serial PSAD in comparison to PSA. We applied a long short-term memory recurrent neural network to an AS cohort of 332 patients and found that serial PSADNA significantly outperformed both PSADA and PSA for follow-up prediction of PCa progression because of its high sensitivity. Importantly, while PSADNA was superior in patients with smaller glands (BGV ≤55 ml), serial PSA was better in men with larger prostates of >55 ml. Patient summary: Repeat measurements of prostate-specific antigen (PSA) and PSA density (PSAD) are the mainstay of active surveillance in prostate cancer. Our study suggests that in patients with a prostate gland of 55 ml or smaller, PSAD measurements are a better predictor of tumour progression, whereas men with a larger gland may benefit more from PSA monitoring
Social justice: The missing link in school administrators’ perspectives on teacher induction
Critical scholars view schooling as one piece of a larger struggle for democracy and social justice. We investigated 41 school administrators‟ perceptions about the role and importance of equity, diversity and social justice in new teacher induction in the province of Ontario. Interviews reveal that principals were interested in shaping teacher induction programming in their schools and school districts, but that they regularly prioritized technical issues like classroom management and pedagogy over systemic issues like equity and social justice. When asked directly about equity, principals spoke about learning styles, special needs and differentiated instruction, but they regularly ignored new teachers‟ abilities to counter systemic oppression—racism, sexism, and classism. Our findings suggest that without an explicit focus on equity and social justice in provincial policy documents, teacher induction programming runs the risk of reproducing a transmission model of new teacher education
Altered hemodynamics and vascular reactivity in a mouse model with severe pericyte deficiency
Pericytes are the mural cells of the microvascular network that are in close contact with underlying endothelial cells. Endothelial-secreted PDGFB leads to recruitment of pericytes to the vessel wall, but this is disrupted in Pdgfb mice when the PDGFB retention motif is deleted. This results in severely reduced pericyte coverage on blood vessels. In this study, we investigated vascular abnormalities and hemodynamics in Pdgfb mice throughout the cerebrovascular network and in different cortical layers by in vivo two-photon microscopy. We confirmed that Pdgfb mice are severely deficient in pericytes throughout the vascular network, with enlarged brain blood vessels and a reduced number of vessel branches. Red blood cell velocity, linear density, and tube hematocrit were reduced in Pdgfb mice, which may impair oxygen delivery to the tissue. We also measured intravascular PO and found that concentrations were higher in cortical Layer 2/3 in Pdgfb mice, indicative of reduced blood oxygen extraction. Finally, we found that Pdgfb mice had a reduced capacity for vasodilation in response to an acetazolamide challenge during functional MRI imaging. Taken together, these results suggest that severe pericyte deficiency can lead to vascular abnormalities and altered cerebral blood flow, reminiscent of pathologies such as arteriovenous malformations
Metalevel algorithms for variant satisfiability
Variant satisfiability is a theory-generic algorithm to decide quantifier-free satisfiability in an initial algebra when its corresponding theory has the finite variant property and its constructors satisfy a compactness condition. This paper: (i) gives a precise definition of several meta-level sub-algorithms needed for variant satisfiability; (ii) proves them correct; and (iii) presents a reflective implementation in Maude 2.7 of variant satisfiability using these sub-algorithms.NSF CNS 13-19109Ope
Coherent spinor dynamics in a spin-1 Bose condensate
Collisions in a thermal gas are perceived as random or incoherent as a
consequence of the large numbers of initial and final quantum states accessible
to the system. In a quantum gas, e.g. a Bose-Einstein condensate or a
degenerate Fermi gas, the phase space accessible to low energy collisions is so
restricted that collisions be-come coherent and reversible. Here, we report the
observation of coherent spin-changing collisions in a gas of spin-1 bosons.
Starting with condensates occupying two spin states, a condensate in the third
spin state is coherently and reversibly created by atomic collisions. The
observed dynamics are analogous to Josephson oscillations in weakly connected
superconductors and represent a type of matter-wave four-wave mixing. The
spin-dependent scattering length is determined from these oscillations to be
-1.45(18) Bohr. Finally, we demonstrate coherent control of the evolution of
the system by applying differential phase shifts to the spin states using
magnetic fields.Comment: 19 pages, 3 figure
Disturbance and stress - different meanings in ecological dynamics?
There is an increasing frequency of papers
addressing disturbance and stress in ecology without
clear delimitation of their meaning. Some authors
use the terms disturbance and stress exclusively as
impacts, while others use them for the entire process,
including both causes and effects. In some studies, the
disturbance is considered as a result of a temporary
impact, which is positive for the ecosystem, while
stress is a negative, debilitating impact. By developing
and testing simple theoretical models, the authors
propose to differentiate disturbance and stress by
frequency. If the frequency of the event enables the
variable to reach a dynamic equilibrium which might
be exhibited without this event, then the event (plus its
responses) is a disturbance for the system. If frequency
prevents the variable’s return to similar pre-event
dynamics and drives or shifts it to a new trajectory,
then we are facing stress. The authors propose that
changes triggered by the given stimuli can be evaluated
on an absolute scale, therefore, direction of change of the variable must not be used to choose one
term or the other, i.e. to choose between stress and
disturbance
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