1,000 research outputs found
119— The Role of Post-Encoding Retrieval on Cognitive and Neural Representations of Spatial Environments
Spatial memory is an important ability for navigating around one’s surrounding environment. However, due to the challenges of developing experimental paradigms that utilize large scale, real-world environments, little research has analyzed, in detail, the development of cognitive maps over time. Past research in rodents has shown that hippocampal place-cells replay during periods of quiet wakefulness, suggesting that mental replay of recent spatial experiences is tied to the development of cognitive maps. In humans, we hypothesize that the development of cognitive maps could therefore be manipulated by having participants selectively recall recent navigational experiences. We analyzed the development of cognitive maps for novel, real-world spatial environments in two groups, a spatial sequencing group (SSG) and rote-retrieval group (RRG), over a period of 2 weeks using Google Street View software. After navigating through the environment, participants’ spatial memories were tested with either rote retrieval or spatial sequencing recognition tests. Our preliminary results suggest the RRG was more successful navigating previously learned routes than the SSG with more practice on the trained routes, whereas the SSG may have developed some ability to discover shortcuts by being encouraged to think more broadly about the routes they were learning, and not rely on memorization
Optimizing astrophotonic spatial reformatters using simulated on-sky performance
One of the most useful techniques in astronomical instrumentation is image
slicing. It enables a spectrograph to have a more compact angular slit, whilst
retaining throughput and increasing resolving power. Astrophotonic components
like the photonic lanterns and photonic reformatters can be used to replace
bulk optics used so far. This study investigates the performance of such
devices using end-to-end simulations to approximate realistic on-sky
conditions. It investigates existing components, tries to optimize their
performance and aims to understand better how best to design instruments to
maximize their performance. This work complements the recent work in the field
and provides an estimation for the performance of the new components.Comment: Conference proceedings in SPIE 2018 Austin Texa
Numerical modeling of mixed sediment resuspension, transport, and deposition during the March 1998 episodic events in southern Lake Michigan
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95016/1/jgrc10260.pd
High sensitivity cantilevers for measuring persistent currents in normal metal rings
We propose a new approach to measuring persistent currents in normal metal
rings. By integrating micron-scale metal rings into sensitive micromechanical
cantilevers and using the cantilevers as torque magnetometers, it should be
possible to measure the rings' persistent currents with greater sensitivity
than the SQUID-based and microwave resonator-based detectors used in the past.
In addition, cantilever-based detectors may allow for measurements in a cleaner
electromagnetic environment. We have fabricated ultra sensitive cantilevers
with integrated rings and measured their mechanical properties. We present an
estimate of the persistent current sensitivity of these cantilever-based
detectors, focusing on the limits set by the cantilever's Brownian motion and
the shot noise in the laser interferometer that monitors the cantilever
Chandra & HST Imaging of the Quasars PKS B0106+013 & 3C345: Inverse Compton X-rays and Magnetized Jets
We present results from deep (70 ks) Chandra ACIS observations and Hubble
Space Telescope ACS F475W observations of two highly optically polarized
quasars belonging to the MOJAVE blazar sample, viz., PKS B0106+013 and 1641+399
(3C345). These observations reveal X-ray and optical emission from the jets in
both sources. X-ray emission is detected from the entire length of the 0106+013
radio jet, which shows clear bends or wiggles - the X-ray emission is brightest
at the first prominent kpc jet bend. A picture of a helical kpc jet with the
first kpc-scale bend representing a jet segment moving close(r) to our line of
sight, and getting Doppler boosted at both radio and X-ray frequencies, is
consistent with these observations. The X-ray emission from the jet end however
peaks at about 0.4" (~3.4 kpc) upstream of the radio hot spot. Optical emission
is detected both at the X-ray jet termination peak and at the radio hot spot.
The X-ray jet termination peak is found upstream of the radio hot spot by
around 0.2" (~1.3 kpc) in the short projected jet of 3C345. HST optical
emission is seen in an arc-like structure coincident with the bright radio hot
spot, which we propose is a sharp (apparent) jet bend instead of a terminal
point, that crosses our line of sight and consequently has a higher Doppler
beaming factor. A weak radio hot spot is indeed observed less than 1"
downstream of the bright radio hot spot, but has no optical or X-ray
counterpart. By making use of the pc-scale radio and the kpc-scale radio/X-ray
data, we derive constraints on the jet Lorentz factors (Gamma_jet) and
inclination angles (theta): for a constant jet speed from pc- to kpc-scales, we
obtain a Gamma_jet of ~70 for 0106+013, and ~40 for 3C345. On relaxing this
assumption, we derive a Gamma_jet of ~2.5 for both the sources. Upper limits on
theta of ~13 degrees are obtained for the two quasars. (ABRIDGED)Comment: 46 pages, 11 figures, Accepted for publication in Ap
Cervical Cancer Screening at a Crossroads: Learnings from the Past Driving Change for the Future
Cervical cancer screening has been one of the most impactful human interventions in medical history, saving the lives of countless thousands of women since the introduction of organized cytology screening programs. Today, we stand at a crossroads in the fight against cervical cancer, with several countries actively engaged in introducing primary human papillomavirus (HPV) testing and vaccination as more effective means of prevention. This chapter discusses the history of organized screening and how this led to HPV test methods to detect cervical cancer. We go on to examine the technologies used to screen for high-risk HPV types and how they affect clinical performance. We examine the evidence for primary HPV screening and review recent self-collection initiatives to reach underserved women, including the use of urine as novel sample type. In addition, we critically examine the evolution of HPV test methods and make the case for the use of extended genotyping as an improved risk stratification tool for guiding clinical management. Finally, we look to the future of cervical cancer screening and consider options for future management programs
Anxiety and anxious-depression in Parkinson's disease over a 4-year period: A latent transition analysis
Background: Depression and anxiety in Parkinson's disease are common and frequently co-morbid, with significant impact on health outcome. Nevertheless, management is complex and often suboptimal. The existence of clinical subtypes would support stratified approaches in both research and treatment.
Method: Five hundred and thirteen patients with Parkinson's disease were assessed annually for up to 4 years. Latent transition analysis (LTA) was used to identify classes that may conform to clinically meaningful subgroups, transitions between those classes over time, and baseline clinical and demographic features that predict common trajectories.
Results: In total, 64.1% of the sample remained in the study at year 4. LTA identified four classes, a 'Psychologically healthy' class (approximately 50%), and three classes associated with psychological distress: one with moderate anxiety alone (approximately 20%), and two with moderate levels of depression plus moderate or severe anxiety. Class membership tended to be stable across years, with only about 15% of individuals transitioning between the healthy class and one of the distress classes. Stable distress was predicted by higher baseline depression and psychiatric history and younger age of onset of Parkinson's disease. Those with younger age of onset were also more likely to become distressed over the course of the study.
Conclusions: Psychopathology was characterized by relatively stable anxiety or anxious-depression over the 4-year period. Anxiety, with or without depression, appears to be the prominent psychopathological phenotype in Parkinson's disease suggesting a pressing need to understanding its mechanisms and improve management
Two populations of X-ray pulsars produced by two types of supernovae
Two types of supernova are thought to produce the overwhelming majority of neutron stars in the Universe. The first type, iron-core collapse supernovae, occurs when a high-mass star develops a degenerate iron core that exceeds the Chandrasekhar limit. The second type, electron-capture supernovae, is associated with the collapse of a lower-mass oxygen-neon-magnesium core as it loses pressure support owing to the sudden capture of electrons by neon and/or magnesium nuclei. It has hitherto been impossible to identify the two distinct families of neutron stars produced in these formation channels. Here we report that a large, well-known class of neutron-star-hosting X-ray pulsars is actually composed of two distinct sub-populations with different characteristic spin periods, orbital periods and orbital eccentricities. This class, the Be/X-ray binaries, contains neutron stars that accrete material from a more massive companion star. The two sub-populations are most probably associated with the two distinct types of neutron-star-forming supernovae, with electron-capture supernovae preferentially producing system with short spin period, short orbital periods and low eccentricity. Intriguingly, the split between the two sub-populations is clearest in the distribution of the logarithm of spin period, a result that had not been predicted and which still remains to be explaine
Besov priors for Bayesian inverse problems
We consider the inverse problem of estimating a function from noisy,
possibly nonlinear, observations. We adopt a Bayesian approach to the problem.
This approach has a long history for inversion, dating back to 1970, and has,
over the last decade, gained importance as a practical tool. However most of
the existing theory has been developed for Gaussian prior measures. Recently
Lassas, Saksman and Siltanen (Inv. Prob. Imag. 2009) showed how to construct
Besov prior measures, based on wavelet expansions with random coefficients, and
used these prior measures to study linear inverse problems. In this paper we
build on this development of Besov priors to include the case of nonlinear
measurements. In doing so a key technical tool, established here, is a
Fernique-like theorem for Besov measures. This theorem enables us to identify
appropriate conditions on the forward solution operator which, when matched to
properties of the prior Besov measure, imply the well-definedness and
well-posedness of the posterior measure. We then consider the application of
these results to the inverse problem of finding the diffusion coefficient of an
elliptic partial differential equation, given noisy measurements of its
solution.Comment: 18 page
- …