Geb W. Thomas

Using Sensor Networks to Study the Effect of Peripatetic Healthcare Workers on the Spread of Hospital-Associated Infections

BACKGROUND Super-spreading events, in which an individual with measurably high connectivity is responsible for infecting a large number of people, have been observed. Our goal is to determine the impact of hand hygiene noncompliance among peripatetic (eg, highly mobile or highly connected) healthcare workers compared with less-connected workers. METHODS We used a mote-based sensor network to record contacts among healthcare workers and patients in a 20-bed intensive care unit. The data collected from this network form the basis for an agent-based simulation to model the spread of nosocomial pathogens with various transmission probabilities. We identified the most- and least-connected healthcare workers. We then compared the effects of hand hygiene noncompliance as a function of connectedness. RESULTS The data confirm the presence of peripatetic healthcare workers. Also, agent-based simulations using our real contact network data confirm that the average number of infected patients was significantly higher when the most connected healthcare worker did not practice hand hygiene and significantly lower when the least connected healthcare workers were noncompliant. CONCLUSIONS Heterogeneity in healthcare worker contact patterns dramatically affects disease diffusion. Our findings should inform future infection control interventions and encourage the application of social network analysis to study disease transmission in healthcare settings.

Developing Nomad for Robotic Exploration of the Atacama Desert

Recent years have seen renewed attention to planetary exploration, and robotics is recognized as essential to many upcoming missions. In this article we describe the ongoing efforts of the Nomad project to develop robots for planetary and terrestrial exploration. The project is developing, demonstrating, and evaluating systems capable of long-distance, long-duration missions. In 1997 this work has resulted in the Atacama Desert Trek, in which a mobile robot named Nomad, explored the Atacama Desert of northern Chile. Nomads 45-day objective was to travel 200 km across the rugged, barren landscape. We then will describe the technologies for Nomads transforming chassis, high data-rate communication, safeguarded teleoperation and autonomy, panoramic imaging and visualization, and remote science. We then focus on issues of long-distance, long-duration exploration and describe the events and results of the Atacama Desert Trek.

The effect of fingertip microstructures on tactile edge perception

People rely on tactile edge localization to ascertain the location and structure of edges. When pressure is applied to the skin, skin mechanoreceptors convert compressive stress/strain into neural signals. Many attempts to model this conversion neglect intermediate ridges, on the inside of the stiff epidermis. The receptors associated with detecting compressive and shear stresses reside at the tips of these ridges, suggesting a functional importance in the detection of stress. This work considers how underlying microstructure affects the mechanical propagation of stress to receptors. Two unique indenters are applied to two finite element models of idealized, fingerpad skin - one with ridge microstructure. Findings indicate that microstructure produces high, local stress concentrations at ridge tips near receptors. Because stress is focused at ridges beneath edges, there is a higher contrast of stress between ridge tips near the indenters edge and those adjacent. This lensing effect mechanism appears to help distinguish edges.

Life in the Atacama: Searching for life with rovers (science overview)

[1] The Life in the Atacama project investigated the regional distribution of life and habitats in the Atacama Desert of Chile. We sought to create biogeologic maps through survey traverses across the desert using a rover carrying biologic and geologic instruments. Elements of our science approach were to: Perform ecological transects from the relatively wet coastal range to the arid core of the desert; use converging evidence from science instruments to reach conclusions about microbial abundance; and develop and test exploration strategies adapted to the search of scattered surface and shallow subsurface microbial oases. Understanding the ability of science teams to detect and characterize microbial life signatures remotely using a rover became central to the project. Traverses were accomplished using an autonomous rover in a method that is technologically relevant to Mars exploration. We present an overview of the results of the 2003, 2004, and 2005 field investigations. They include: The confirmed identification of microbial habitats in daylight by detecting fluorescence signals from chlorophyll and dye probes; the characterization of geology by imaging and spectral measurement; the mapping of life along transects; the characterization of environmental conditions; the development of mapping techniques including homogeneous biological scoring and predictive models of habitat location; the development of exploration strategies adapted to the search for life with an autonomous rover capable of up to 10 km of daily traverse; and the autonomous detection of life by the rover as it interprets observations on-the-fly and decides which targets to pursue with further analysis.

3D and 2D Marginal Fit of Pressed and CAD/CAM Lithium Disilicate Crowns Made from Digital and Conventional Impressions

PURPOSE This in vitro study evaluated the 3D and 2D marginal fit of pressed and computer-aided-designed/computer-aided-manufactured (CAD/CAM) all-ceramic crowns made from digital and conventional impressions. MATERIALS AND METHODS A dentoform tooth (#30) was prepared for an all-ceramic crown (master die). Thirty type IV definitive casts were made from 30 polyvinyl siloxane (PVS) impressions. Thirty resin models were produced from thirty Lava Chairside Oral Scanner impressions. Thirty crowns were pressed in lithium disilicate (IPS e.max Press; 15/impression technique). Thirty crowns were milled from lithium disilicate blocks (IPS e.max CAD; 15/impression technique) using the E4D scanner and milling engine. The master die and the intaglio of the crowns were digitized using a 3D laser coordinate measurement machine with accuracy of ±0.00898 mm. For each specimen a separate data set was created for the Qualify 2012 software. The digital master die and the digital intaglio of each crown were merged using best-fitting alignment. An area above the margin with 0.75 mm occlusal-gingival width circumferentially was defined. The 3D marginal fit of each specimen was an average of all 3D gap values on that area. For the 2D measurements, the marginal gap was measured at two standardized points (on the margin and at 0.75 mm above the margin), from standardized facial-lingual and mesial-distal digitized sections. One-way ANOVA with post hoc Tukeys honestly significant difference and two-way ANOVA tests were used, separately, for statistical analysis of the 3D and 2D marginal data (alpha = 0.05). RESULTS One-way ANOVA revealed that both 3D and 2D mean marginal gap for group A: PVS impression/IPS e.max Press (0.048 mm ± 0.009 and 0.040 mm ± 0.009) were significantly smaller than those obtained from the other three groups (p < 0.0001), while no significant differences were found among groups B: PVS impression/IPS e.max CAD (0.088 mm ± 0.024 and 0.076 mm ± 0.023), C: digital impression/IPS e.max Press (0.089 mm ± 0.020 and 0.075 mm ± 0.015) and D: digital impression/IPS e.max CAD (0.084 mm ± 0.021 and 0.074 mm ± 0.026). The results of two-way ANOVA revealed a significant interaction between impression techniques and crown fabrication methods for both 3D and 2D measurements. CONCLUSIONS The combination of PVS impression method and press fabrication technique produced the most accurate 3D and 2D marginal fits.

Inter-comparison of low-cost sensors for measuring the mass concentration of occupational aerosols

ABSTRACT Low-cost sensors are effective for measuring the mass concentration of ambient aerosols and second-hand smoke in homes, but their use at concentrations relevant to occupational settings has not been demonstrated. We measured the concentrations of four aerosols (salt, Arizona road dust, welding fume, and diesel exhaust) with three types of low-cost sensors (a DC1700 from Dylos and two commodity sensors from Sharp), an aerosol photometer, and reference instruments at concentrations up to 6500 µg/m3. Raw output was used to assess sensor precision and develop equations to compute mass concentrations. EPA and NIOSH protocols were used to assess the mass concentrations estimated with low-cost sensors compared to reference instruments. The detection efficiency of the DC1700 ranged from 0.04% at 0.1 µm to 108% at 5 µm, as expected, although misclassification of fine and coarse particles was observed. The raw output of the DC1700 had higher precision (lower coefficient of variation, CV = 7.4%) than that of the two sharp devices (CV = 25% and 17%), a finding attributed to differences in manufacturer calibration. Aerosol type strongly influenced sensor response, indicating the need for on-site calibration to convert sensor output to mass concentration. Once calibrated, however, the mass concentration estimated with low-cost sensors was highly correlated with that of reference instruments (R2= 0.99). These results suggest that the DC1700 and Sharp sensors are useful in estimating aerosol mass concentration for aerosols at concentrations relevant to the workplace.

Augmented reality cues and elderly driver hazard perception

Objective: The aim of this study was to evaluate the effectiveness of augmented reality (AR) cues in improving driving safety among elderly drivers who are at increased crash risk because of cognitive impairments. Background: Cognitively challenging driving environments pose a particular crash risk for elderly drivers. AR cuing is a promising technology to mitigate risk by directing driver attention to roadway hazards. We investigate whether AR cues improve or interfere with hazard perception in elderly drivers with age-related cognitive decline. Method: A total of 20 elderly (M = 73 years, SD = 5) licensed drivers with a range of cognitive abilities measured by a speed-of-processing (SOP) composite participated in a 1-hr drive in an interactive, fixed-base driving simulator. Each participant drove through six straight, 6-mile-long, rural roadway scenarios following a lead vehicle. AR cues directed attention to potential roadside hazards in three of the scenarios, and the other three were uncued (baseline) drives. Effects of AR cuing were evaluated with respect to (a) detection of hazardous target objects, (b) interference with detecting nonhazardous secondary objects, and (c) impairment in maintaining safe distance behind a lead vehicle. Results: AR cuing improved the detection of hazardous target objects of low visibility. AR cues did not interfere with detection of nonhazardous secondary objects and did not impair ability to maintain safe distance behind a lead vehicle. SOP capacity did not moderate those effects. Conclusion: AR cues show promise for improving elderly driver safety by increasing hazard detection likelihood without interfering with other driving tasks, such as maintaining safe headway.

Fingerprint lines may not directly affect SA-I mechanoreceptor response

Understanding how skin microstructure affects slowly adapting type I (SA-I) mechanoreceptors in encoding edge discontinuities is fundamental to understanding our sense of touch. Skin microstructure, in particular papillary ridges, has been thought to contribute to edge and gap sensation. Caunas 1954 model of touch sensibility describes a functional relationship between papillary ridges and edge sensation. His lever arm model proposes that the papillary ridge (exterior fingerprint line) and underlying intermediate ridge operate as a single unit, with the intermediate ridge acting as a lever which magnifies indentation imposed at the papillary ridge. This paper contests the validity of the lever arm model. While correctly representing the anatomy, this mechanism inaccurately characterizes the function of the papillary ridges. Finite element analysis and assessment of the critical anatomy indicate that papillary ridges have little direct effect on how SA-I receptors respond to the indentation of static edges. Our analysis supports a revised (stiff shell–elastic bending support) interpretation where the epidermis is split into two major layers with a stiff, deformable shell over an elastic bending support. Recent physiological, electrophysiological, and psychophysical findings support our conclusion that the function of the intermediate ridge is distinct from the function of the papillary ridge.

Virtual tools for supervisory and collaborative control of robots

Often, robotics has failed to meet industry expectations because programming robots is tedious, requires specialists, and often does not provide enough real flexibility to be worth the investment. In order to advance beyond a possible robotics plateau, an integrating technology will need to emerge that can take advantage of complex new robotic capabilities while making systems easier for nonrobotics people to use. This research introduces virtual tools with robotic attributes, and collaborative control concepts, that enable experts in areas other than robotics to simply point and direct sophisticated robots and machines to do new tasks. A system of robots that are directed using such virtual tools is now in place at the Pennsylvania State University (Penn State) and has been replicated at Sandia National Laboratories. (Mpeg movies from the Penn State Virtual Tools and Robotics Laboratory are at http://virtuoso.psu.edu/ mpeg_page.html.) Virtual tools, which appear as graphic representations of robot endeffectors interwoven into live video, carry robotic attributes that define trajectory details and determine how to interpret sensor readings for a particular type of task. An operator, or team of experts, directs robot tasks by virtually placing these tool icons in the scene. The operator(s) direct tasks involving attributes in the same natural way that supervisors direct human subordinates to, for example, put that there, dig there, cut there, and grind there. In this human-machine interface, operators do not teach entire tasks via virtual telemanipulation. They define key action points. The virtual tool attributes allow operators to stay at a supervisory level, doing what humans can do best in terms of task perceptualization, while robots plan appropriate trajectories and a variety of tool-dependent executions. Neither the task experts (e.g., in hazardous environments) nor the plant supervisors (e.g., in remote manufacturing applications) must turn over control to specialized robot technicians for long periods. Within this concept, shutting down a plant to reprogram robots to produce a new product, for example, is no longer required. Further, even though several key collaborators may be in different cities for a particular application, they may work with other experts over a project net that is formed for a particular mission. (We link simply by sending video frames over Netscape.) Using a shared set of virtual tools displayed simultaneously on each of the collaborator workstations, experts virtually enter a common videographic scene to direct portions of a task while graphically and verbally discussing alternatives with the other experts. In the process of achieving collaborative consensus, the robots are automatically programmed as a byproduct of using the virtual tools to decide what should be done and where. The robots can immediately execute the task for all to see once consensus is reached. Virtual tools and their attributes achieve robotic flexibility without requiring specialized programming or telemanipulation on the part of in situ operators. By sharing the virtual tools over project nets, noncollocated experts may now contribute to robot and intelligent machine tasks. To date, we have used virtual tools to direct a large gantry robot at Sandia National Laboratories from Penn State. We will soon have multiple collaborators sharing the virtual tools remotely, with a protocol for participants to take turns placing and moving virtual tools to define portions of complex tasks in other industrial, space-telerobotic, and educational environments. Attributes from each area of robotics research are envisioned with virtual tools as a repository for combining these independently developed robotic capabilities into integrated entities that are easy for an operator to understand, use, and modify.

Primary human bone cultures from older patients do not respond at continuum levels of in vivo strain magnitudes

Osteoporosis is characterized by excessive loss of bone mass, while exercise is believed to maintain or enhance bone mass. Since exercise marginally affects osteoporosis, we wondered whether bone cells from osteoporotic patients would fail to respond to strain. Primary human bone-like cultures were obtained from females over age 60 with hip arthroplasty procedures performed for either osteoporotic fracture (n = 8) or non-osteoporotic osteoarthrosis (n = 5). Cultures (96,000 cell/cm2) were strained in rectangular optically clear silastic wells. Three periods of uniaxial substratum strain (1000 micro-strain, 1 Hz, 10,000 cycles, sine wave) were provided every 24 h using a four-point bending, computer-controlled device. Results at a frequency of 1 Hz were compared to cultures exposed to 20 Hz with bone cells derived from one osteoarthritic subject. Alterations in protein level expression of bone-related proteins were determined using a semi-quantitative confocal approach along with enzyme (alkaline phosphatase) activity and enzyme mRNA copy number using cRNA RT-PCR. Strain did not alter levels of bone-related protein levels, enzyme activity, or steady state copy number per cell in response to strain in either group. Strained cultures from osteoporotic patients exhibited little variation from unstrained controls, while individual cultures from osteoarthritic patients exhibited increases in one protein or the other. The results suggest that bone cells from older individuals may not be responsive to continuum levels of strain anticipated with vigorous activity.