6,617 research outputs found
Visibility based hospital inpatient unit design.
Patient fall is one of the adverse events in an inpatient unit of a hospital that can lead to disability and/or mortality. Healthcare literature suggests that increased visibility of patients by unit nurses is essential to improve patient monitoring and, in turn, reduce falls. However, such research has been descriptive in nature and does not provide an understanding of the characteristics of an optimal inpatient unit layout from a visibility-standpoint. This dissertation fills significant voids in this domain and adds much-needed realism to develop insights that hospital decision-makers can use to design their inpatient unit layout. Our first contribution (Chapter 2) adopts an interdisciplinary approach that combines the human field of regard with facility layout design approaches. Specifically, we propose a bi-objective optimization model that jointly determines the optimal (i) location of a nurse in a nursing station and (ii) orientation of a patient\u27s bed in a room for a given layout. The two objectives are maximizing the total visibility of all patients across patient rooms and minimizing inequity in visibility among those patients. We consider three different layout types, L-, I-, and R-shaped; these shapes exhibit the section of an inpatient unit that a nurse oversees. To estimate visibility, we employ the ray casting algorithm to quantify the visibility of a target in a room when viewed by the nurse from the nursing station. This algorithm considers nurses\u27 horizontal visual field and their depth of vision. We also propose a Multi-Objective Particle Swarm Optimization (MOPSO) heuristic to find (near) optimal solutions to the bi-objective optimization model. Our findings suggest that the R-shaped layout outperforms the other two layouts on these visibility-based objectives. Further, the position of the patient\u27s bed plays a role in maximizing the visibility of the patient\u27s room. In our second contribution, we extend the model in the first contribution to now include position of the bed in patient rooms as a decision variable and consider various door positions. We consider four distinct layout types, L–shaped, U-shaped, R-shaped, and I-shaped, with eight patient rooms and a nurse-to-patient ratio of 1:4. We propose an ε-constrained approach to convert the corresponding bi-objective optimization model into a single objective optimization model, prioritizing equity as an objective function. We propose a progressive refinement algorithm to solve this optimization model within a reasonable time. Our findings suggest that a significant improvement in the equity score of a layout can be obtained through the joint determination of patient beds and nurse positions. We also perform a comparative analysis of equity offered by various layout types and observed that angular layout types are a promising output. We also observed that higher spatial distance between nurses is beneficial in achieving higher equity measures when obstruction is high in the case of angular layouts. There are several implications of our findings to practice. The insights from our study related to the impact of layout shapes, bed locations, and obstruction levels on patient visibility can help decision-makers in both greenfield and retrofitting of existing inpatient unit layout designs. Our models can quickly identify highly visible layouts, avoiding costly trial and error in layout changes. Improved decision-making in inpatient unit design will facilitate better patient experiences through equitable visibility distribution and enhanced quality of care
Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. IV. Reduced Inner Working Angle and Increased Robustness to Low-Order Aberrations
The Apodized Pupil Lyot Coronagraph (APLC) is a diffraction suppression
system installed in the recently deployed instruments Palomar/P1640,
Gemini/GPI, and VLT/SPHERE to allow direct imaging and spectroscopy of
circumstellar environments. Using a prolate apodization, the current
implementations offer raw contrasts down to at 0.2 arcsec from a star
over a wide bandpass (20\%), in the presence of central obstruction and struts,
enabling the study of young or massive gaseous planets. Observations of older
or lighter companions at smaller separations would require improvements in
terms of inner working angle (IWA) and contrast, but the methods originally
used for these designs were not able to fully explore the parameter space. We
here propose a novel approach to improve the APLC performance. Our method
relies on the linear properties of the coronagraphic electric field with the
apodization at any wavelength to develop numerical solutions producing
coronagraphic star images with high-contrast region in broadband light. We
explore the parameter space by considering different aperture geometries,
contrast levels, dark-zone sizes, bandpasses, and focal plane mask sizes. We
present an application of these solutions to the case of Gemini/GPI with a
design delivering a raw contrast at 0.19 arcsec and offering a
significantly reduced sensitivity to low-order aberrations compared to the
current implementation. Optimal solutions have also been found to reach
contrast in broadband light regardless of the telescope aperture
shape (in particular the central obstruction size), with effective IWA in the
range, therefore making the APLC a suitable option for the
future exoplanet direct imagers on the ground or in space.Comment: 14 pages, 10 figures, accepted in Ap
Apodized pupil Lyot coronagraphs for arbitrary apertures. V. Hybrid Shaped Pupil designs for imaging Earth-like planets with future space observatories
We introduce a new class of solutions for Apodized Pupil Lyot Coronagraphs
(APLC) with segmented aperture telescopes to remove broadband diffracted light
from a star with a contrast level of . These new coronagraphs provide
a key advance to enabling direct imaging and spectroscopy of Earth twins with
future large space missions. Building on shaped pupil (SP) apodization
optimizations, our approach enables two-dimensional optimizations of the system
to address any aperture features such as central obstruction, support
structures or segment gaps. We illustrate the technique with a design that
could reach contrast level at 34\,mas for a 12\,m segmented telescope
over a 10\% bandpass centered at a wavelength 500\,nm. These
designs can be optimized specifically for the presence of a resolved star, and
in our example, for stellar angular size up to 1.1\,mas. This would allow
probing the vicinity of Sun-like stars located beyond 4.4\,pc, therefore fully
retiring this concern. If the fraction of stars with Earth-like planets is
\eta_{\Earth}=0.1, with 18\% throughput, assuming a perfect, stable wavefront
and considering photon noise only, 12.5 exo-Earth candidates could be detected
around nearby stars with this design and a 12\,m space telescope during a
five-year mission with two years dedicated to exo-Earth detection (one total
year of exposure time and another year of overheads). Our new hybrid APLC/SP
solutions represent the first numerical solution of a coronagraph based on
existing mask technologies and compatible with segmented apertures, and that
can provide contrast compatible with detecting and studying Earth-like planets
around nearby stars. They represent an important step forward towards enabling
these science goals with future large space missions.Comment: 9 pages, 6 figures, ApJ accepted on 01/04/201
High-contrast imager for Complex Aperture Telescopes (HiCAT): 1. Testbed design
Searching for nearby habitable worlds with direct imaging and spectroscopy
will require a telescope large enough to provide angular resolution and
sensitivity to planets around a significant sample of stars. Segmented
telescopes are a compelling option to obtain such large apertures. However,
these telescope designs have a complex geometry (central obstruction, support
structures, segmentation) that makes high-contrast imaging more challenging. We
are developing a new high-contrast imaging testbed at STScI to provide an
integrated solution for wavefront control and starlight suppression on complex
aperture geometries. We present our approach for the testbed optical design,
which defines the surface requirements for each mirror to minimize the
amplitude-induced errors from the propagation of out-of-pupil surfaces. Our
approach guarantees that the testbed will not be limited by these Fresnel
propagation effects, but only by the aperture geometry. This approach involves
iterations between classical ray-tracing optical design optimization, and
end-to-end Fresnel propagation with wavefront control (e.g. Electric Field
Conjugation / Stroke Minimization). The construction of the testbed is planned
to start in late Fall 2013.Comment: Proc. of the SPIE 8864, 10 pages, 3 figures, Techniques and
Instrumentation for Detection of Exoplanets V
An Agent-Based Approach to Self-Organized Production
The chapter describes the modeling of a material handling system with the
production of individual units in a scheduled order. The units represent the
agents in the model and are transported in the system which is abstracted as a
directed graph. Since the hindrances of units on their path to the destination
can lead to inefficiencies in the production, the blockages of units are to be
reduced. Therefore, the units operate in the system by means of local
interactions in the conveying elements and indirect interactions based on a
measure of possible hindrances. If most of the units behave cooperatively
("socially"), the blockings in the system are reduced.
A simulation based on the model shows the collective behavior of the units in
the system. The transport processes in the simulation can be compared with the
processes in a real plant, which gives conclusions about the consequencies for
the production based on the superordinate planning.Comment: For related work see http://www.soms.ethz.c
Extinction controlled adaptive phase-mask coronagraph
Context. Phase-mask coronagraphy is advantageous in terms of inner working
angle and discovery space. It is however still plagued by drawbacks such as
sensitivity to tip-tilt errors and chromatism. A nulling stellar coronagraph
based on the adaptive phase-mask concept using polarization interferometry is
presented in this paper. Aims. Our concept aims at dynamically and
achromatically optimizing the nulling efficiency of the coronagraph, making it
more immune to fast low-order aberrations (tip-tilt errors, focus, ...).
Methods. We performed numerical simulations to demonstrate the value of the
proposed method. The active control system will correct for the detrimental
effects of image instabilities on the destructive interference. The mask
adaptability both in size, phase and amplitude also compensates for
manufacturing errors of the mask itself, and potentially for chromatic effects.
Liquid-crystal properties are used to provide variable transmission of an
annulus around the phase mask, but also to achieve the achromatic {\pi} phase
shift in the core of the PSF by rotating the polarization by 180 degrees.
Results. We developed a new concept and showed its practical advantages using
numerical simulations. This new adaptive implementation of the phase-mask
coronagraph could advantageously be used on current and next-generation
adaptive optics systems, enabling small inner working angles without
compromising contrast.Comment: 7 pages, 6 figure
Wire mesh design
We present a computational approach for designing wire meshes, i.e., freeform surfaces composed of woven wires arranged in a regular grid. To facilitate shape exploration, we map material properties of wire meshes to the geometric model of Chebyshev nets. This abstraction is exploited to build an efficient optimization scheme. While the theory of Chebyshev nets suggests a highly constrained design space, we show that allowing controlled deviations from the underlying surface provides a rich shape space for design exploration. Our algorithm balances globally coupled material constraints with aesthetic and geometric design objectives that can be specified by the user in an interactive design session. In addition to sculptural art, wire meshes represent an innovative medium for industrial applications including composite materials and architectural façades. We demonstrate the effectiveness of our approach using a variety of digital and physical prototypes with a level of shape complexity unobtainable using previous methods
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