2,263 research outputs found
Direct Policy Optimization using Deterministic Sampling and Collocation
We present an approach for approximately solving discrete-time stochastic
optimal-control problems by combining direct trajectory optimization,
deterministic sampling, and policy optimization. Our feedback motion-planning
algorithm uses a quasi-Newton method to simultaneously optimize a reference
trajectory, a set of deterministically chosen sample trajectories, and a
parameterized policy. We demonstrate that this approach exactly recovers LQR
policies in the case of linear dynamics, quadratic objective, and Gaussian
disturbances. We also demonstrate the algorithm on several nonlinear,
underactuated robotic systems to highlight its performance and ability to
handle control limits, safely avoid obstacles, and generate robust plans in the
presence of unmodeled dynamics.Comment: revisions for RA-L 202
Variation of receptor status in cancer of the breast.
One hundred and nineteen patients with breast cancer had 2 or more lesions removed for oestrogen (REc) or progesterone receptor (RPc) assay, either synchronously (on 38 occasions) or after an interval (on 91 occasions). In all but 7 both receptors were assayed for each lesion. The assays did not agree on the presence or absence of REc alone, RPc alone or the combination of both receptors in 11, 13 and 16% respectively of the synchronous samples, compared with 23, 30 and 43% of the asynchronous samples. The differences between the synchronous and asynchronous samples were significant for the combined receptors (P = 0.007) but not for REc (P = 0.176) or RPc alone (P = 0.077). Variation between asynchronous biopsies was greater when the earlier lesion contained RPc (18/37 disagreed) than when it did not (8/50) disagreed, P = 0.0023). This was not true for oestrogen receptor. In those remaining receptor positive there was only a weak correlation between the first and second values (Spearman rank correlation coefficient, rho = 0.39 for REc, P less than 0.02, and 0.45 for RPc, 0.05 less than P less than 0.1). Receptor levels and receptor status may change with time. Biopsy is most appropriate at the time when systemic treatment is proposed
Functional network changes and cognitive control in schizophrenia
Cognitive control is a cognitive and neural mechanism that contributes to managing the complex demands of day-to-day life. Studies have suggested that functional impairments in cognitive control associated brain circuitry contribute to a broad range of higher cognitive deficits in schizophrenia. To examine this issue, we assessed functional connectivity networks in healthy adults and individuals with schizophrenia performing tasks from two distinct cognitive domains that varied in demands for cognitive control, the RiSE episodic memory task and DPX goal maintenance task. We characterized general and cognitive control-specific effects of schizophrenia on functional connectivity within an expanded frontal parietal network (FPN) and quantified network topology properties using graph analysis. Using the network based statistic (NBS), we observed greater network functional connectivity in cognitive control demanding conditions during both tasks in both groups in the FPN, and demonstrated cognitive control FPN specificity against a task independent auditory network. NBS analyses also revealed widespread connectivity deficits in schizophrenia patients across all tasks. Furthermore, quantitative changes in network topology associated with diagnostic status and task demand were observed. The present findings, in an analysis that was limited to correct trials only, ensuring that subjects are on task, provide critical insights into network connections crucial for cognitive control and the manner in which brain networks reorganize to support such control. Impairments in this mechanism are present in schizophrenia and these results highlight how cognitive control deficits contribute to the pathophysiology of this illness
XMM-Newton and optical follow-up observations of three new polars from the Sloan Digital Sky Survey
We report follow-up XMM-Newton and optical observations of three new polars
found in the Sloan Digital Sky Survey. Simple modeling of the X-ray spectra,
and consideration of the details of the X-ray and optical lightcurves
corroborate the polar nature of these three systems and provide further
insights into their accretion characteristics. During the XMM-Newton
observation of SDSS J072910.68+365838.3, X-rays are undetected apart from a
probable flare event, during which we find both the typical hard X-ray
bremsstrahlung component and a very strong line O VII (E=0.57 keV), but no
evidence of a soft blackbody contribution. In SDSS J075240.45+362823.2 we
identify an X-ray eclipse at the beginning of the observation, roughly in phase
with the primary minimum of the optical broad band curve. The X-ray spectra
require the presence of both hard and soft X-ray components, with their
luminosity ratio consistent with that found in other recent XMM-Newton results
on polars. Lastly, SDSS J170053.30+400357.6 appears optically as a very typical
polar, however its large amplitude optical modulation is 180 degrees out of
phase with the variation in our short X-ray lightcurve.Comment: 9 pages, 9 figures, accepted for publication in the ApJ (January
2005
Differentiable Physics Simulation of Dynamics-Augmented Neural Objects
We present a differentiable pipeline for simulating the motion of objects
that represent their geometry as a continuous density field parameterized as a
deep network. This includes Neural Radiance Fields (NeRFs), and other related
models. From the density field, we estimate the dynamical properties of the
object, including its mass, center of mass, and inertia matrix. We then
introduce a differentiable contact model based on the density field for
computing normal and friction forces resulting from collisions. This allows a
robot to autonomously build object models that are visually and
\emph{dynamically} accurate from still images and videos of objects in motion.
The resulting Dynamics-Augmented Neural Objects (DANOs) are simulated with an
existing differentiable simulation engine, Dojo, interacting with other
standard simulation objects, such as spheres, planes, and robots specified as
URDFs. A robot can use this simulation to optimize grasps and manipulation
trajectories of neural objects, or to improve the neural object models through
gradient-based real-to-simulation transfer. We demonstrate the pipeline to
learn the coefficient of friction of a bar of soap from a real video of the
soap sliding on a table. We also learn the coefficient of friction and mass of
a Stanford bunny through interactions with a Panda robot arm from synthetic
data, and we optimize trajectories in simulation for the Panda arm to push the
bunny to a goal location
XO-2b: Transiting Hot Jupiter in a Metal-rich Common Proper Motion Binary
We report on a V=11.2 early K dwarf, XO-2 (GSC 03413-00005), that hosts a
Rp=0.98+0.03/-0.01 Rjup, Mp=0.57+/-0.06 Mjup transiting extrasolar planet,
XO-2b, with an orbital period of 2.615857+/-0.000005 days. XO-2 has high
metallicity, [Fe/H]=0.45+/-0.02, high proper motion, mu_tot=157 mas/yr, and has
a common proper motion stellar companion with 31" separation. The two stars are
nearly identical twins, with very similar spectra and apparent magnitudes. Due
to the high metallicity, these early K dwarf stars have a mass and radius close
to solar, Ms=0.98+/-0.02 Msolar and Rs=0.97+0.02/-0.01 Rsolar. The high proper
motion of XO-2 results from an eccentric orbit (Galactic pericenter, Rper<4
kpc) well confined to the Galactic disk (Zmax~100 pc). In addition, the phase
space position of XO-2 is near the Hercules dynamical stream, which points to
an origin of XO-2 in the metal-rich, inner Thin Disk and subsequent dynamical
scattering into the solar neighborhood. We describe an efficient Markov Chain
Monte Carlo algorithm for calculating the Bayesian posterior probability of the
system parameters from a transit light curve.Comment: 14 pages, 10 Figures, Accepted in ApJ. Negligible changes to XO-2
system properties. Removed Chi^2 light curve analysis section, and simplified
MCMC light curve analysis discussio
The Grizzly, April 12, 2018
The Distance Between Us : Ursinus Welcomes Mexican-American Author Reyna Grande ⢠Lantern Launch Celebrates All Things Creative About Ursinus ⢠Berman Museum Opens Annual Student Exhibition ⢠International Perspective: Easter Festivities in Prague Recall Student\u27s Childhood Celebrations ⢠Senior Awarded Fulbright Scholarship ⢠Students Present at Celebration of Student Achievement ⢠Summer Looks Bright for Dr. Lori Daggar ⢠Opinions: Ursinus Needs More Science Labs for Humanities Students; Facebook\u27s Data Scandal Reveals Need for Privacy Protection ⢠Men\u27s Lax Maintains Optimism Amid Rocky Season ⢠T&F Impresses in Outdoor Openerhttps://digitalcommons.ursinus.edu/grizzlynews/1644/thumbnail.jp
Transgressing the moral economy: Wheelerism and management of the nationalised coal industry in Scotland
This article illuminates the links between managerial style and political economy in post-1945 Britain, and explores the origins of the 1984â1985 miners' strike, by examining in longer historical context the abrasive attitudes and policies of Albert Wheeler, Scottish Area Director of the National Coal Board (NCB). Wheeler built on an earlier emphasis on production and economic criteria, and his micro-management reflected pre-existing centralising tendencies in the industries. But he was innovative in one crucial aspect, transgressing the moral economy of the Scottish coalfield, which emphasised the value of economic security and changes by joint industrial agreement
Practical actions to strengthen capacity for deep-water research in Africa
While Africa's deep marine biodiversity offers economic prospects it also supports crucial ecosystem services and sustainable development is dependent on knowledge of these systems. Building understanding of deep-water ecosystems is key, but there are substantial discrepancies in countries' abilities to achieve this. Coinciding with the 2024 Ocean Decade Conference, the Challenger 150 African Network of Deep-water Researchers is pleased to release a report on âPractical Actions to Strengthen Capacity for Deep-water Research in Africaâ. Through a series of online workshops, the ANDR brought together 98 individuals from 19 African nations to discuss challenges for deep-water research in Africa, identify solutions to overcome these and propose practical actions going forward
Understanding parentsâ emotional experiences for neonatal education:A narrative, interpretive approach
Aims and objectives: To explore the emotional experiences of parents who have had premature babies to inform and educate neonatal nurses and health professionals in this field. Background: Parents find the neonatal unit a daunting and unfamiliar place leading to anxiety, uncertainty and fear about the future of their baby. Parents have significant emotional needs in relation to assisting them to cope with their neonatal experience. In line with a family-centred approach to neonatal education, it is essential to teach health professionals about the emotional impact of neonatal care based on an appreciation of the parent experience. Design: A narrative-based, interpretive approach was undertaken in line with constructivist learning theory. Methods: Twenty narrative interviews took place, with a total of 23 parents of premature babies. Following core story creation to create coherent stories from the raw transcripts, thematic analysis of the narrative constructs using the principles of Braun and Clarke's, International Journal of Qualitative Studies on Health and Well-Being, 2014, 9, 1, framework was undertaken. The study methods were compliant with the consolidated criteria for reporting qualitative research (COREQ). Findings: Thematic analysis revealed key themes relating to the following: parentsâ emotions through the whole neonatal experience, feelings towards the baby, the environment, the staff and the transitions through the different phases of neonatal care. Both negative and positive experiences were reported. Conclusion: Understanding the emotional experience from the parent's perspective, following birth of their premature baby, informs empathic, family-centred teaching and learning within the neonatal education arena. Relevance to clinical practice: Students and health professionals alike can learn what is important in the delivery of care that addresses the emotional needs of parents and families. Educators can use narratives and key messages from parents, both negative and positive, to teach family-centred principles to nurses and health professionals as a core component of a narrative curricula and potentially to enhance empathy
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