426 research outputs found
Optimization of Single-Sided Charge-Sharing Strip Detectors
Simulation of the charge sharing properties of single-sided CZT strip detectors with small anode pads are presented. The effect of initial event size, carrier repulsion, diffusion, drift, trapping and detrapping are considered. These simulations indicate that such a detector with a 150 µm pitch will provide good charge sharing between neighboring pads. This is supported by a comparison of simulations and measurements for a similar detector with a coarser pitch of 225 µm that could not provide sufficient sharing. The performance of such a detector used as a gamma-ray imager is discussed
Continued Studies of Single-Sided Charge-Sharing CZT Strip Detectors
In this paper, we report progress in the study of thick single-sided charge-sharing cadmium zinc telluride (CZT) strip detector modules designed to perform gammaray spectroscopy and 3-D imaging. We report on continuing laboratory and simulation measurements of prototype detectors with 11×11 unit cells (15×15×7.5mm3 ). We report preliminary measurements of the 3-D spatial resolution. Our studies are aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma measurements while minimizing the number and complexity of the electronic readout channels. This is particularly important in space-based coded aperture and Compton telescope instruments that require large area, large volume detector arrays. Such arrays will be required for the NASA’s Black Hole Finder Probe (BHFP) and Advanced Compton Telescope (ACT). This design requires an anode pattern with contacts whose dimensions and spacing are roughly the size of the ionization charge cloud. The first prototype devices have 125µm anode contacts on 225µm pitch. Our studies conclude that finer pitch contacts will be required to improve imaging efficiency
Further studies of single-sided charge-sharing CZT strip detectors
We report progress in the study of a thick CZT strip detector module designed to perform gamma-ray spectroscopy and 3-D imaging. We report preliminary performance measurements of 7.5 mm thick single-sided charge-sharing strip detector prototype devices. This design features both row and column contacts on the anode surface. This electron-only approach addresses problems associated with poor hole transport in CZT that limit the thickness and energy range of double-sided strip detectors. This work includes laboratory and simulation studies aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma measurements while minimizing the number and complexity of the electronic readout channels. This is particularly important in space-based coded aperture and Compton telescope instruments that require large area, large volume detector arrays. Such arrays will be required for the NASA Black Hole Finder Probe (BHFP)and Advanced Compton Telescope (ACT). This new design requires an anode pattern with contacts whose dimensions and spacing are roughly the size of the ionization charge cloud. The first prototype devices have 125 μm anode contacts on 225 μm pitch. Our results demonstrate the principle of operation but suggest that even finer anode contact feature sizes will be necessary to achieve the desired performance
Improved thermal isolation of silicon suspended platforms for an all-silicon thermoelectric microgenerator based on large scale integration of Si nanowires as thermoelectric material
Special suspended micro-platforms have been designed as a part of silicon compatible planar thermoelectric microgenerators. Bottom-up grown silicon nanowires are going to bridge in the future such platforms to the surrounding silicon bulk rim. They will act as thermoelectric material thus configuring an all-silicon thermoelectric device. In the new platform design other additional bridging elements (usually auxiliary support silicon beams) are substituted by low conductance thin film dielectric membranes in order to maximize the temperature difference developed between both areas. These membranes follow a sieve-like design that allows fabricating them with a short additional wet anisotropic etch step. © Published under licence by IOP Publishing Ltd.Peer ReviewedPostprint (published version
Single-sided CZT strip detectors
We report progress in the study of thick CZT strip detectors for 3-d imaging and spectroscopy and discuss two approaches to device design. We present the spectroscopic, imaging, detection efficiency and response uniformity performance of prototype devices. Unlike double-sided strip detectors, these devices feature both row and column contacts implemented on the anode surface. This electron-only approach circumvents problems associated with poor hole transport in CZT that normally limit the thickness and energy range of double-sided strip detectors. These devices can achieve similar performance to pixel detectors. The work includes laboratory and simulation studies aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma radiation measurements. The low channel count strip detector approach can significantly reduce the complexity and power requirements of the readout electronics. This is particularly important in space-based coded aperture or Compton telescope instruments requiring large area, large volume detector arrays. Such arrays will be required for NASA\u27s Black Hole Finder Probe (BHFP) and Advanced Compton Telescope (ACT)
Selecting Metrics to Evaluate Human Supervisory Control Applications
The goal of this research is to develop a methodology to select supervisory control metrics. This
methodology is based on cost-benefit analyses and generic metric classes. In the context of this research,
a metric class is defined as the set of metrics that quantify a certain aspect or component of a system.
Generic metric classes are developed because metrics are mission-specific, but metric classes are
generalizable across different missions. Cost-benefit analyses are utilized because each metric set has
advantages, limitations, and costs, thus the added value of different sets for a given context can be
calculated to select the set that maximizes value and minimizes costs. This report summarizes the
findings of the first part of this research effort that has focused on developing a supervisory control metric
taxonomy that defines generic metric classes and categorizes existing metrics. Future research will focus
on applying cost benefit analysis methodologies to metric selection.
Five main metric classes have been identified that apply to supervisory control teams composed
of humans and autonomous platforms: mission effectiveness, autonomous platform behavior efficiency,
human behavior efficiency, human behavior precursors, and collaborative metrics. Mission effectiveness
measures how well the mission goals are achieved. Autonomous platform and human behavior efficiency
measure the actions and decisions made by the humans and the automation that compose the team.
Human behavior precursors measure human initial state, including certain attitudes and cognitive
constructs that can be the cause of and drive a given behavior. Collaborative metrics address three
different aspects of collaboration: collaboration between the human and the autonomous platform he is
controlling, collaboration among humans that compose the team, and autonomous collaboration among
platforms. These five metric classes have been populated with metrics and measuring techniques from
the existing literature.
Which specific metrics should be used to evaluate a system will depend on many factors, but as a
rule-of-thumb, we propose that at a minimum, one metric from each class should be used to provide a
multi-dimensional assessment of the human-automation team. To determine what the impact on our
research has been by not following such a principled approach, we evaluated recent large-scale
supervisory control experiments conducted in the MIT Humans and Automation Laboratory. The results
show that prior to adapting this metric classification approach, we were fairly consistent in measuring
mission effectiveness and human behavior through such metrics as reaction times and decision
accuracies. However, despite our supervisory control focus, we were remiss in gathering attention
allocation metrics and collaboration metrics, and we often gathered too many correlated metrics that were
redundant and wasteful. This meta-analysis of our experimental shortcomings reflect those in the general
research population in that we tended to gravitate to popular metrics that are relatively easy to gather,
without a clear understanding of exactly what aspect of the systems we were measuring and how the
various metrics informed an overall research question
Assessing the Impact of Haptic Peripheral Displays for UAV Operators
Objectives: A pilot study was conducted to investigate the effectiveness of continuous haptic
peripheral displays in supporting multiple UAV supervisory control. Background: Previous
research shows that continuous auditory peripheral displays can enhance operator performance in
monitoring events that are continuous in nature, such as monitoring how well UAVs stay on their
pre-planned courses. This research also shows that auditory alerts can be masked by other
auditory information. Command and control operations are generally performed in noisy
environments with multiple auditory alerts presented to the operators. In order to avoid this
masking problem, another potentially useful sensory channel for providing redundant
information to UAV operators is the haptic channel. Method: A pilot experiment was conducted
with 13 participants, using a simulated multiple UAV supervisory control task. All participants
completed two haptic feedback conditions (continuous and threshold), where they received alerts
based on UAV course deviations and late arrivals to targets. Results: Threshold haptic feedback
was found to be more effective for late target arrivals, whereas continuous haptic feedback
resulted in faster reactions to course deviations. Conclusions: Continuous haptic feedback
appears to be more appropriate for monitoring events that are continuous in nature (i.e., how well
a UAV keeps its course). In contrast, threshold haptic feedback appears to better support
response to discrete events (i.e., late target arrivals). Future research: Because this is a pilot
study, more research is needed to validate these preliminary findings. A direct comparison
between auditory and haptic feedback is also needed to provide better insights into the potential
benefits of multi-modal peripheral displays in command and control of multiple UAVs.Prepared for Charles River Analytics, Inc
Single-sided CZT strip detectors
We report progress in the study of thick CZT strip detectors for 3-D imaging and spectroscopy and discuss two approaches to device design. Unlike double-sided strip detectors, these devices feature both row and column contacts implemented on the anode surface. This electron-only approach circumvents problems associated with poor hole transport in CZT that normally limit the thickness and energy range of double-sided strip detectors. The work includes laboratory and simulation studies aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma radiation measurements while minimizing the number and complexity of the electronic readout channels. These devices can achieve similar performance to pixel detectors for both 3-D imaging and spectroscopy. The low channel count approach can significantly reduce the complexity and power requirements of the readout electronics. This is particularly important in applications requiring large area detector arrays. We show two single-sided strip detector concepts. One, previously reported, features rows established with collecting contacts and columns with noncollecting contacts. Another, introduced here, operates on a charge sharing principle and establishes both rows and columns with collecting contacts on the anode surface. In previous work using the earlier strip detector concept we reported simulations and measurements of energy and spatial resolution for prototype 5- and 10-mm-thick CZT detectors. We now present the results of detection efficiency and uniformity measurements conducted on 5-mm-thick detectors using a specific configuration of the front-end electronics and event trigger. We discuss the importance of the detector fabrication processes when implementing this approach
Arterial, neural and muscular variations in the upper limb
During our routine dissection studies we observed arterial, neural and muscular
variations in the upper limbs of an adult male cadaver. In this case we observed
the superficial brachial artery origination from the third part of the axillary artery,
communications between the musculocutaneous and median nerves, variant
formation of the brachial plexus, origination of the profunda brachii artery
from the posterior circumflex humeral artery and supernumerary tendons of the
abductor pollicis longus muscle. We think that such variations should be kept in
mind during surgical and diagnostic procedures
Development of CZT strip detector modules for 0.05- to 1-MeV gamma-ray imaging and spectroscopy
We report progress in our study of cadmium zinc telluride (CZT) strip detectors featuring orthogonal coplanar anode contacts. We specifically report on the performance, characterization and stability of 5 and 10 mm thick prototype CZT detectors fabricated using material from several manufacturers. Our ongoing work includes laboratory and simulation studies aimed at optimizing and developing compact, efficient, high performance detector modules for 0.05 to 1 MeV gamma radiation measurements with space-based instrumentation. The coplanar anode strip configuration retains many of the performance advantages of pixel detectors yet requires far fewer electronic channels to perform both 3-d imaging and spectroscopy. Minimizing the channel count is important for large balloon or space instruments including coded aperture telescopes (such as MARGIE or EXIST) and Compton imaging telescopes (such as TIGRE or ACT). We also present plans for developing compact, space qualified imaging modules designed for integration into closely packed large area detector arrays. We discuss issues associated with detector module and array electronics design and development
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