12,525 research outputs found
Ethics of Genetic and Biomarker Test Disclosures in Neurodegenerative Disease Prevention Trials
OBJECTIVE:
Prevention trials for neurodegenerative diseases use genetic or other risk marker tests to select participants but there is concern that this could involve coercive disclosure of unwanted information. This has led some trials to use blinded enrollment (participants are tested but not told of their risk marker status). We examined the ethics of blinded vs transparent enrollment using well-established criteria for assessing the ethics of clinical research.
METHODS:
Normative analysis applying 4 key ethical criteria-favorable risk-benefit ratio, informed consent, fair subject selection, and scientific validity-to blinded vs transparent enrollment, using current evidence and state of Alzheimer disease (AD) and other prevention trials.
RESULTS:
Current evidence on the psychosocial impact of risk marker disclosure and considerations of scientific benefit do not support an obligation to use blinded enrollment in prevention trials. Nor does transparent enrollment coerce or involve undue influence of potential participants. Transparent enrollment does not unfairly exploit vulnerable participants or limit generalizability of scientific findings of prevention trials. However, if the preferences of a community of potential participants would affect the rigor or feasibility of a prevention trial using transparent enrollment, then investigators are required by considerations of scientific validity to use blinded enrollment.
CONCLUSIONS:
Considerations of risks and benefits, informed consent, and fair subject selection do not require the use of blinded enrollment for AD prevention trials. Blinded enrollment in AD prevention trials may sometimes be necessary because of the need for scientific validity, not because it prevents coercion or undue influence
Polarization Switching Dynamics Governed by Thermodynamic Nucleation Process in Ultrathin Ferroelectric Films
A long standing problem of domain switching process - how domains nucleate -
is examined in ultrathin ferroelectric films. We demonstrate that the large
depolarization fields in ultrathin films could significantly lower the
nucleation energy barrier (U*) to a level comparable to thermal energy (kBT),
resulting in power-law like polarization decay behaviors. The "Landauer's
paradox": U* is thermally insurmountable is not a critical issue in the
polarization switching of ultrathin ferroelectric films. We empirically find a
universal relation between the polarization decay behavior and U*/kBT.Comment: 5 pages, 4 figure
The Influence of Acoustic Impedance Mismatch on Post-Stenotic Pulsed-Doppler Ultrasound Measurements in a Coronary Artery Model
Acoustic impedance mismatch at the fluid-wall interface was shown to affect the spectra from an intravascular Doppler device in an in vitro model with a diameter typical of human coronary arteries. Measurements were obtained first under Poiseuille flow conditions with impedance mismatches of 0%, 7% and 12%, and then under stenosed conditions for the 0% and 7% mismatch cases. For the zero mismatch case, the Doppler spectra could be readily interpreted in terms of fluid mechanical phenomena. When mismatch was present, the spectra from Poiseuille flow exhibited multiple peaks which could not be directly related to the velocity profile. Also, the spectra from stenosed flow with a mismatch of 7% were similar to those from the zero mismatch case but did not exhibit the specific flow-related features as clearly. These results indicate that the impedance mismatch alters the acoustic environment inside the model and that this causes artifact in the Doppler spectra
Ethics of sham surgery: Perspective of patients
Sham surgery is used as a control condition in neurosurgical clinical trials in Parkinson's disease (PD) but remains controversial. This study aimed to assess the perspective of patients with PD and the general public on the use of sham surgery controls. We surveyed consecutive patients from a university-based neurology outpatient clinic and a community-based general internal medicine practice. Background information was provided regarding PD and two possible methods of testing the efficacy of a novel gene transfer procedure, followed by questions that addressed participants' opinions related to the willingness to participate and permissibility of blinded and unblinded trial designs. Two hundred eighty-eight (57.6%) patients returned surveys. Patients with PD expressed less willingness to participate in the proposed gene transfer surgery trials. Unblinded studies received greater support, but a majority would still allow the use of sham surgery. Those in favor of sham surgery were more educated and more likely to use societal perspective rationales. Patients with PD are more cautious about surgical research participation than patients with non-PD. Their policy views were similar to others', with a majority supporting the use of sham controls. Future research needs to determine whether eliciting more considered judgments of laypersons would reveal different levels of support for sham surgery. © 2007 Movement Disorder SocietyPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57916/1/21775_ftp.pd
Unveiling the ac Dynamics of Ferroelectric Domains by Investigating the Frequency Dependence of Hysteresis Loops
We investigated nonequilibrium domain wall dynamics under an ac field by
measuring the hysteresis loops of epitaxial ferroelectric capacitors at various
frequencies and temperatures. Polarization switching is induced mostly by
thermally activated creep motion at lower frequencies, and by viscous flow
motion at higher frequencies. The dynamic crossover between the creep and flow
regimes unveils two frequency-dependent scaling regions of hysteresis loops.
Based on these findings, we constructed a dynamic phase diagram for hysteretic
ferroelectric domain dynamics in the presence of ac fields.Comment: 3 figure
Search for Anisotropy of Ultra-High Energy Cosmic Rays with the Telescope Array Experiment
We study the anisotropy of Ultra-High Energy Cosmic Ray (UHECR) events
collected by the Telescope Array (TA) detector in the first 40 months of
operation. Following earlier studies, we examine event sets with energy
thresholds of 10 EeV, 40 EeV, and 57 EeV. We find that the distributions of the
events in right ascension and declination are compatible with an isotropic
distribution in all three sets. We then compare with previously reported
clustering of the UHECR events at small angular scales. No significant
clustering is found in the TA data. We then check the events with E>57 EeV for
correlations with nearby active galactic nuclei. No significant correlation is
found. Finally, we examine all three sets for correlations with the large-scale
structure of the Universe. We find that the two higher-energy sets are
compatible with both an isotropic distribution and the hypothesis that UHECR
sources follow the matter distribution of the Universe (the LSS hypothesis),
while the event set with E>10 EeV is compatible with isotropy and is not
compatible with the LSS hypothesis at 95% CL unless large deflection angles are
also assumed. We show that accounting for UHECR deflections in a realistic
model of the Galactic magnetic field can make this set compatible with the LSS
hypothesis.Comment: 10 pages, 9 figure
Mathematical modeling of the metastatic process
Mathematical modeling in cancer has been growing in popularity and impact
since its inception in 1932. The first theoretical mathematical modeling in
cancer research was focused on understanding tumor growth laws and has grown to
include the competition between healthy and normal tissue, carcinogenesis,
therapy and metastasis. It is the latter topic, metastasis, on which we will
focus this short review, specifically discussing various computational and
mathematical models of different portions of the metastatic process, including:
the emergence of the metastatic phenotype, the timing and size distribution of
metastases, the factors that influence the dormancy of micrometastases and
patterns of spread from a given primary tumor.Comment: 24 pages, 6 figures, Revie
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