1,203 research outputs found
Deriving Telescope Mueller Matrices Using Daytime Sky Polarization Observations
Telescopes often modify the input polarization of a source so that the
measured circular or linear output state of the optical signal can be
signficantly different from the input. This mixing, or polarization
"cross-talk", is defined by the optical system Mueller matrix. We describe here
an efficient method for recovering the input polarization state of the light
and the full 4 x 4 Mueller matrix of the telescope with an accuracy of a few
percent without external masks or telescope hardware modification. Observations
of the bright, highly polarized daytime sky using the Haleakala 3.7m AEOS
telescope and a coude spectropolarimeter demonstrate the technique.Comment: Accepted for publication in PAS
Like trainer, like bot? Inheritance of bias in algorithmic content moderation
The internet has become a central medium through which `networked publics'
express their opinions and engage in debate. Offensive comments and personal
attacks can inhibit participation in these spaces. Automated content moderation
aims to overcome this problem using machine learning classifiers trained on
large corpora of texts manually annotated for offence. While such systems could
help encourage more civil debate, they must navigate inherently normatively
contestable boundaries, and are subject to the idiosyncratic norms of the human
raters who provide the training data. An important objective for platforms
implementing such measures might be to ensure that they are not unduly biased
towards or against particular norms of offence. This paper provides some
exploratory methods by which the normative biases of algorithmic content
moderation systems can be measured, by way of a case study using an existing
dataset of comments labelled for offence. We train classifiers on comments
labelled by different demographic subsets (men and women) to understand how
differences in conceptions of offence between these groups might affect the
performance of the resulting models on various test sets. We conclude by
discussing some of the ethical choices facing the implementers of algorithmic
moderation systems, given various desired levels of diversity of viewpoints
amongst discussion participants.Comment: 12 pages, 3 figures, 9th International Conference on Social
Informatics (SocInfo 2017), Oxford, UK, 13--15 September 2017 (forthcoming in
Springer Lecture Notes in Computer Science
A spinal organ of proprioception for integrated motor action feedback
Proprioception is essential for behavior and provides a sense of our body movements in physical space. Proprioceptor organs are thought to be only in the periphery. Whether the central nervous system can intrinsically sense its own movement remains unclear. Here we identify a segmental organ of proprioception in the adult zebrafish spinal cord, which is embedded by intraspinal mechanosensory neurons expressing Piezo2 channels. These cells are late-born, inhibitory, commissural neurons with unique molecular and physiological profiles reflecting a dual sensory and motor function. The central proprioceptive organ locally detects lateral body movements during locomotion and provides direct inhibitory feedback onto rhythm-generating interneurons responsible for the central motor program. This dynamically aligns central pattern generation with movement outcome for efficient locomotion. Our results demonstrate that a central proprioceptive organ monitors self-movement using hybrid neurons that merge sensory and motor entities into a unified network
Exchange Field Induced Magnetoresistance in Colossal Magnetoresistance Manganites
The effect of an exchange field on electrical transport in thin films of
metallic ferromagnetic manganites has been investigated. The exchange field was
induced both by direct exchange coupling in a ferromagnet/antiferromagnet
multilayer and by indirect exchange interaction in a ferromagnet/paramagnet
superlattice. The electrical resistance of the manganite layers was found to be
determined by the absolute value of the vector sum of the effective exchange
field and the external magnetic field.Comment: 5 pages, 4 figure
The mixed problem for the Laplacian in Lipschitz domains
We consider the mixed boundary value problem or Zaremba's problem for the
Laplacian in a bounded Lipschitz domain in R^n. We specify Dirichlet data on
part of the boundary and Neumann data on the remainder of the boundary. We
assume that the boundary between the sets where we specify Dirichlet and
Neumann data is a Lipschitz surface. We require that the Neumann data is in L^p
and the Dirichlet data is in the Sobolev space of functions having one
derivative in L^p for some p near 1. Under these conditions, there is a unique
solution to the mixed problem with the non-tangential maximal function of the
gradient of the solution in L^p of the boundary. We also obtain results with
data from Hardy spaces when p=1.Comment: Version 5 includes a correction to one step of the main proof. Since
the paper appeared long ago, this submission includes the complete paper,
followed by a short section that gives the correction to one step in the
proo
Aspects of structural health and condition monitoring of offshore wind turbines
Wind power has expanded significantly over the past years, although reliability of wind turbine systems, especially of offshore wind turbines, has been many times unsatisfactory in the past. Wind turbine failures are equivalent to crucial financial losses. Therefore, creating and applying strategies that improve the reliability of their components is important for a successful implementation of such systems. Structural health monitoring (SHM) addresses these problems through the monitoring of parameters indicative of the state of the structure examined. Condition monitoring (CM), on the other hand, can be seen as a specialized area of the SHM community that aims at damage detection of, particularly, rotating machinery. The paper is divided into two parts: in the first part, advanced signal processing and machine learning methods are discussed for SHM and CM on wind turbine gearbox and blade damage detection examples. In the second part, an initial exploration of supervisor control and data acquisition systems data of an offshore wind farm is presented, and data-driven approaches are proposed for detecting abnormal behaviour of wind turbines. It is shown that the advanced signal processing methods discussed are effective and that it is important to adopt these SHM strategies in the wind energy sector
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N-WASP Is Essential for the Negative Regulation of B Cell Receptor Signaling
Negative regulation of receptor signaling is essential for controlling cell activation and differentiation. In B-lymphocytes, the down-regulation of B-cell antigen receptor (BCR) signaling is critical for suppressing the activation of self-reactive B cells; however, the mechanism underlying the negative regulation of signaling remains elusive. Using genetically manipulated mouse models and total internal reflection fluorescence microscopy, we demonstrate that neuronal Wiskott–Aldrich syndrome protein (N-WASP), which is coexpressed with WASP in all immune cells, is a critical negative regulator of B-cell signaling. B-cell–specific N-WASP gene deletion causes enhanced and prolonged BCR signaling and elevated levels of autoantibodies in the mouse serum. The increased signaling in N-WASP knockout B cells is concurrent with increased accumulation of F-actin at the B-cell surface, enhanced B-cell spreading on the antigen-presenting membrane, delayed B-cell contraction, inhibition in the merger of signaling active BCR microclusters into signaling inactive central clusters, and a blockage of BCR internalization. Upon BCR activation, WASP is activated first, followed by N-WASP in mouse and human primary B cells. The activation of N-WASP is suppressed by Bruton's tyrosine kinase-induced WASP activation, and is restored by the activation of SH2 domain-containing inositol 5-phosphatase that inhibits WASP activation. Our results reveal a new mechanism for the negative regulation of BCR signaling and broadly suggest an actin-mediated mechanism for signaling down-regulation
Functional assessment for clinical use of serum-free adapted NK-92 cells
Natural killer (NK) cells stand out as promising candidates for cellular immunotherapy due to their capacity to kill malignant cells. However, the therapeutic use of NK cells is often dependent on cell expansion and activation with considerable amounts of serum and exogenous cytokines. We aimed to develop an expansion protocol for NK-92 cells in an effort to generate a cost-efficient, xeno-free, clinical grade manufactured master cell line for therapeutic applications. By making functional assays with NK-92 cells cultured under serum-free conditions (NK-92(SF)) and comparing to serum-supplemented NK-92 cells (NK-92(S)) we did not observe significant alterations in the viability, proliferation, receptor expression levels, or in perforin and granzyme levels. Interestingly, even though NK-92(SF) cells displayed decreased degranulation and cytotoxicity against tumor cells in vitro, the degranulation capacity was recovered after overnight incubation with 20% serum in the medium. Moreover, lentiviral vector-based genetic modification efficiency of NK-92(SF) cells was comparable with NK-92(S) cells. The application of similar strategies can be useful in reducing the costs of manufacturing cells for clinical use and can help us understand and implement strategies towards chemically defined expansion and genetic modification protocols
On the Lagrangian Dynamics of Atmospheric Zonal Jets and the Permeability of the Stratospheric Polar Vortex
The Lagrangian dynamics of zonal jets in the atmosphere are considered, with
particular attention paid to explaining why, under commonly encountered
conditions, zonal jets serve as barriers to meridional transport. The velocity
field is assumed to be two-dimensional and incompressible, and composed of a
steady zonal flow with an isolated maximum (a zonal jet) on which two or more
travelling Rossby waves are superimposed. The associated Lagrangian motion is
studied with the aid of KAM (Kolmogorov--Arnold--Moser) theory, including
nontrivial extensions of well-known results. These extensions include
applicability of the theory when the usual statements of nondegeneracy are
violated, and applicability of the theory to multiply periodic systems,
including the absence of Arnold diffusion in such systems. These results,
together with numerical simulations based on a model system, provide an
explanation of the mechanism by which zonal jets serve as barriers to
meridional transport of passive tracers under commonly encountered conditions.
Causes for the breakdown of such a barrier are discussed. It is argued that a
barrier of this type accounts for the sharp boundary of the Antarctic ozone
hole at the perimeter of the stratospheric polar vortex in the austral spring.Comment: Submitted to Journal of the Atmospheric Science
Patient participation: A qualitative study of immigrant women and their experiences
Patient participation in healthcare is a neglected area of interest in the rather extensive amount of research on immigrant so-called Selma patients in Swedish health care as well as worldwide. The aim is to explore the phenomenon “patient participation” in the context of the Swedish health care from the perspective of immigrants non-fluent in Swedish. A phenomenological lifeworld approach was chosen. Data were collected from patients within a municipal home care setting in Sweden. Eight women agreed to participate. In seven interviews, an interpreter was necessary for the translation of the interview. Five authorized interpreters were used. Data were analysed in accordance to a descriptive phenomenological method for caring research. The analysis led to an essence of the phenomenon with three constituents, “to experience participation,” “to refrain from participation,” and “to be deprived of participation.” Patient participation from the perspective of immigrant women means that patients are involved and active in their own health and caring processes. For these women, it is particularly important to have the opportunity to express themselves. Patient participation presupposes professional caregivers who act in a way that increases the patients' opportunities to take part. A skilled interpreter is often necessary in order to enable the patient participation
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