4,464 research outputs found
On the stimulus duty cycle in steady state visual evoked potential
Brain-computer interfaces (BCI) are useful devices that allow direct control of external devices using thoughts, i.e. brain's electrical activity. There are several BCI paradigms, of which steady state visual evoked potential (SSVEP) is the most commonly used due to its quick response and accuracy. SSVEP stimuli are typically generated by varying the luminance of a target for a set number of frames or display events. Conventionally, SSVEP based BCI paradigms use magnitude (amplitude) information from frequency domain but recently, SSVEP based BCI paradigms have begun to utilize phase information to discriminate between similar frequency targets. This paper will demonstrate that using a single frame to modulate a stimulus may lead to a bi-modal distribution of SSVEP as a consequence of a user attending both transition edges. This incoherence, while of less importance in traditional magnitude domain SSVEP BCIs becomes critical when phase is taken into account. An alternative modulation technique incorporating a 50% duty cycle is also a popular method for generating SSVEP stimuli but has a unimodal distribution due to user's forced attention to a single transition edge. This paper demonstrates that utilizing the second method results in significantly enhanced performance in information transfer rate in a phase discrimination SSVEP based BCI
Depletion of chondrocyte primary cilia reduces the compressive modulus of articular cartilage
Primary cilia are slender, microtubule based structures found in the majority of cell types with one cilium per cell. In articular cartilage, primary cilia are required for chondrocyte mechanotransduction and the development of healthy tissue. Loss of primary cilia in Col2aCre;ift88(fl/fl) transgenic mice results in up-regulation of osteoarthritic (OA) markers and development of OA like cartilage with greater thickness and reduced mechanical stiffness. However no previous studies have examined whether loss of primary cilia influences the intrinsic mechanical properties of articular cartilage matrix in the form of the modulus or just the structural properties of the tissue. The present study describes a modified analytical model to derive the viscoelastic moduli based on previous experimental indentation data. Results show that the increased thickness of the articular cartilage in the Col2aCre;ift88(fl/fl) transgenic mice is associated with a reduction in both the instantaneous and equilibrium moduli at indentation strains of greater than 20%. This reveals that the loss of primary cilia causes a significant reduction in the mechanical properties of cartilage particularly in the deeper zones and possibly the underlying bone. This is consistent with histological analysis and confirms the importance of primary cilia in the development of a mechanically functional articular cartilage
Defect unbinding in active nematics
We formulate the statistical dynamics of topological defects in the active
nematic phase, formed in two dimensions by a collection of self-driven
particles on a substrate. An important consequence of the non-equilibrium drive
is the spontaneous motility of strength +1/2 disclinations. Starting from the
hydrodynamic equations of active nematics, we derive an interacting particle
description of defects that includes active torques. We show that activity,
within perturbation theory, lowers the defect-unbinding transition temperature,
determining a critical line in the temperature-activity plane that separates
the quasi-long-range ordered (nematic) and disordered (isotropic) phases. Below
a critical activity, defects remain bound as rotational noise decorrelates the
directed dynamics of +1/2 defects, stabilizing the quasi-long-range ordered
nematic state. This activity threshold vanishes at low temperature, leading to
a re-entrant transition. At large enough activity, active forces always exceed
thermal ones and the perturbative result fails, suggesting that in this regime
activity will always disorder the system. Crucially, rotational diffusion being
a two-dimensional phenomenon, defect unbinding cannot be described by a
simplified one-dimensional model.Comment: 15 pages (including SI), 4 figures. Significant technical
improvements without changing the result
A Dynamic Renormalization Group Study of Active Nematics
We carry out a systematic construction of the coarse-grained dynamical
equation of motion for the orientational order parameter for a two-dimensional
active nematic, that is a nonequilibrium steady state with uniaxial, apolar
orientational order. Using the dynamical renormalization group, we show that
the leading nonlinearities in this equation are marginally \textit{irrelevant}.
We discover a special limit of parameters in which the equation of motion for
the angle field of bears a close relation to the 2d stochastic Burgers
equation. We find nevertheless that, unlike for the Burgers problem, the
nonlinearity is marginally irrelevant even in this special limit, as a result
of of a hidden fluctuation-dissipation relation. 2d active nematics therefore
have quasi-long-range order, just like their equilibrium counterpartsComment: 31 pages 6 figure
Constitutive modeling for isotropic materials
The unified constitutive theories for application to typical isotropic cast nickel base supperalloys used for air-cooled turbine blades were evaluated. The specific modeling aspects evaluated were: uniaxial, monotonic, cyclic, creep, relaxation, multiaxial, notch, and thermomechanical behavior. Further development of the constitutive theories to model thermal history effects, refinement of the material test procedures, evaluation of coating effects, and verification of the models in an alternate material will be accomplished in a follow-on for this base program
Global Optimization by Adiabatic Switching
We apply a recently introduced method for global optimization to determine the ground state energy and configuration for model metallic clusters. The global minimum for a given N-atom cluster is found by following the damped dynamics of the N particle system on an evolving potential energy surface. In this application, the time dependent interatomic potential interpolates adiabatically between the Lennard-Jones (LJ) and the Sutton-Chen (SC) forms. Starting with an ensemble of initial conditions corresponding to the ground state configuration of the Lennard-Jones cluster, the system asymptotically reaches the ground state of the Sutton-Chen cluster. We describe the method and present results for specific cluster size N=15, when the ground state symmetry of LJ and SC differ
Local module identification in dynamic networks with correlated noise: the full input case
The identification of local modules in dynamic networks with known topology
has recently been addressed by formulating conditions for arriving at
consistent estimates of the module dynamics, typically under the assumption of
having disturbances that are uncorrelated over the different nodes. The
conditions typically reflect the selection of a set of node signals that are
taken as predictor inputs in a MISO identification setup. In this paper an
extension is made to arrive at an identification setup for the situation that
process noises on the different node signals can be correlated with each other.
In this situation the local module may need to be embedded in a MIMO
identification setup for arriving at a consistent estimate with maximum
likelihood properties. This requires the proper treatment of confounding
variables. The result is an algorithm that, based on the given network topology
and disturbance correlation structure, selects an appropriate set of node
signals as predictor inputs and outputs in a MISO or MIMO identification setup.
As a first step in the analysis, we restrict attention to the (slightly
conservative) situation where the selected output node signals are predicted
based on all of their in-neighbor node signals in the network.Comment: Extended version of paper submitted to the 58th IEEE Conf. Decision
and Control, Nice, 201
Factors associated with sterilization use among women leaving a U.S. jail: a mixed methods study
Abstract
Background
Despite the high rates of reported sterilization use among women who have spent time in correctional facilities, little is known about the context in which women in this population choose this option. The objective of our study was to use both quantitative and qualitative methods to understand factors associated with sterilization use among women leaving a U.S. jail.
Methods
We administered a cross-sectional survey with 102 jailed women who were participating in a study about contraceptive use after release from jail, and then conducted semi-structured interviews with 29 of those women after their release from jail. We used logistic regression and analytic induction to assess factors associated with self-reported sterilization use.
Results
In our cross-sectional survey, one-third of our sample reported a history of sterilization use. Controlling for age and past pregnancies, the only factor associated with sterilization use was physical abuse history before age 16. In semi-structured interviews, we found that women’s primary motivation for sterilization was the desire to limit childbearing permanently, in some cases where other contraceptive methods had failed them. The decision for sterilization was generally supported by family, partners, and providers. Many women who opted for sterilization expressed financial concern about supporting children and/or reported family histories of sterilization.
Conclusions
The decision to use the permanent method of sterilization as a contraceptive method is a complex one. Results from this study suggest that while explicit coercion may not be a factor in women’s choice for sterilization, interpersonal relationship histories, negative experiences with contraceptives, and structural constraints, such as financial concerns and ongoing criminal justice involvement, seem to influence sterilization use among the vulnerable group of women with criminal justice histories. Public health programs that connect women to reproductive health services should acknowledge constraints on contraceptive decision-making in vulnerable populations.Peer Reviewe
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