Kevin C. Baldwin

Visual and cognitive deficits predict stopping or restricting driving: the Salisbury Eye Evaluation Driving Study (SEEDS)

PURPOSE To determine the visual and other factors that predict stopping or restricting driving in older drivers. METHODS A group of 1425 licensed drivers aged 67 to 87 years, who were residents of greater Salisbury, participated. At 1 year after enrollment, this group was categorized into those who had stopped driving, drove only within their neighborhood, or continued to drive beyond their neighborhood. At baseline, a battery of structured questionnaires, vision, and cognitive tests were administered. Multivariate analysis determined the factors predictive of stopping or restricting driving 12 months later. RESULTS Of the 1425 enrolled, 1237 (87%) were followed up at 1 year. Excluding those who were already limiting their driving at baseline (n = 35), 1.5% (18/1202) had stopped and 3.4% (41/1202) had restricted their driving. The women (odds ratio [OR], 4.01; 95% confidence interval [CI], 2.05-8.20) and those who prefer to be driven (OR, 3.91; 95% CI, 1.91-8.00) were more likely to stop or restrict driving. Depressive symptoms increased likelihood of restricting or stopping driving (OR, 1.08; 95% CI, 1.009-1.16 per point Geriatric Depression Scale). Slow visual scanning and psychomotor speed (Trail Making Test, Part A: OR, 1.02; 95% CI, 1.01-1.03), poor visuoconstructional skills (Beery-Buktenica Test of Visual Motor Integration: OR, 1.14; 95% CI, 1.05-1.25), and reduced contrast sensitivity (OR, 1.15; 95% CI, 1.03-1.28) predicted stopping or reducing driving. Visual field loss and visual attention were not associated. The effect of vision on changing driving behavior was partially mediated by cognition, depression, and baseline driving preferences. CONCLUSIONS In this cohort, contrast sensitivity and cognitive function were independently associated with incident cessation or restriction of driving space. These data suggest drivers with functional deficits make difficult decisions to restrict or stop driving.

Older Drivers and Failure to Stop at Red Lights

Background Despite sensational news reports, few studies have quantified the rates of poor driving performance among older drivers and the predictors of poor performance. We determined the rate of running red traffic lights among older drivers and the relationship of failure to stop to measures of vision and cognition. Methods Multiple measures of vision and cognition were collected at the baseline examination of a population of 1,425 drivers aged 67–87 years in greater Salisbury, Maryland. Each driver had real-time data collected on 5 days of driving performance at baseline and again at 1 year. Failure to stop at a red traffic light was the primary outcome. Results Overall, 3.8% of older drivers failed to stop at red traffic lights, with 15% of those who ran the light having failed 10% or more of the traffic lights they encountered. A narrowing of the attentional visual field (AVF; the extent of peripheral vision in which objects are detected while attention is also centrally fixated) was associated with failure to stop at traffic lights at baseline and predictive 1 year later (incidence rate ratio = 1.09 per degree lost, 95% confidence interval = 1.01–1.16). Persons with smaller vertical AVF were more likely to fail to stop. No demographic or vision variable was related to failure to stop. Conclusions Failure to stop at red lights was a relatively uncommon event in older drivers and associated with reduced ability to pay attention to visual events in the vertical field of vision.

Narrowband laser generation/air-coupled detection: ultrasonic system for on-line process control of composites

A hybrid laser generation/air-coupled detection ultrasonic system is presented which capitalizes on matching the source and receiver bandwidth. Laser generation of narrowband (approximately 1.2 MHz) ultrasound is achieved through a spatial modulation technique. The frequency of the generated ultrasound is chosen to match the response characteristics of a micromachined air-coupled capacitance transducer for good signal throughput. The system has proven sensitive to surface defects in composite materials, and is well suited for on-line process control applications, with standoff distance for the transmitter and receiver greater than 2 cm, while retaining single-shot operation. The system provides a significant reduction in cost and complexity relative to laser-in/laser-out systems.

Visual and Cognitive Predictors of Performance on Brake Reaction Test: Salisbury Eye Evaluation Driving Study

Objectives: Concern for driving safety has prompted research into understanding factors related to performance. Brake reaction speed (BRS), the speed with which persons react to a sudden change in driving conditions, is a measure of performance. Our aim is to determine the visual, cognitive, and physical factors predicting BRS in a population sample of 1425 older drivers. Methods: The Maryland Department of Motor Vehicles roster of persons aged 67–87 and residing in Salisbury, MD, was used for recruitment of the study population. Procedures included the following: habitual, binocular visual acuity using ETDRS charts, contrast sensitivity using a Pelli-Robson chart, visual fields assessed with a 81-point screening Humphrey field at a single intensity threshold, and a questionnaire to ascertain medical conditions. Cognitive status was assessed using a standard battery of tests for attention, memory, visuo-spatial, and scanning. BRS was assessed using a computer-driven device that measured separately the initial reaction speed (IRS) (from light change to red until removing foot from accelerator) and physical response speed (PRS) (removing foot from accelerator to full brake depression). Five trial times were averaged, and time was converted to speed. Results: The median brake reaction time varied from 384 to 5688 milliseconds. Age, gender, and cognition predicted total BRS, a non-informative result as there are two distinct parts to the task. Once separated, decrease in IRS was associated with low scores on cognitive factors and missing points on the visual field. A decrease in PRS was associated with having three or more physical complaints related to legs and feet, and poorer vision search. Vision was not related to PRS. Conclusion: We have demonstrated the importance of segregating the speeds for the two tasks involved in brake reaction. Only the IRS depends on vision. Persons in good physical condition may perform poorly on brake reaction tests if their vision or cognition is compromised.

Laser ultrasonic chirp sources for low damage and high detectability without loss of temporal resolution

Linear frequency-modulated (chirped) acoustic signals have been generated using a pulsed laser spatially modulated by an absorption mask at the surface of a test material. By distributing the laser energy over an area, instead of focusing it to a point or line source, the peak power density of the laser source can be kept below the damage threshold of the material. The corresponding chirped ultrasonic surface wave packet produced by the source, although extended in time, is detected and processed using a matched filtering technique which compresses the packet into a pulse, thus preserving temporal resolution for accurate time-of-flight measurements. Matched filter processing of the chirped wave packet has been compared with the same processing applied to a narrow-band tone burst wave packet. Processing of the chirped signal permits easy separation of overlapped return echoes which could not be resolved when narrow-band signals were used. Finally, by compressing the energy within a chirped signal to a sing...

Digital Hammurabi: design and development of a 3D scanner for cuneiform tablets

Cuneiform is an ancient form of writing in which wooden reeds were used to impress shapes upon moist clay tablets. Upon drying, the tablets preserved the written script with remarkable accuracy and durability. There are currently hundreds of thousands of cuneiform tablets spread throughout the world in both museums and private collections. The global scale of these artifacts presents several problems for scholars who wish to study them. It may be difficult or impossible to obtain access to a given collection. In addition, photographic records of the tablets many times prove to be inadequate for proper examination. Photographs lack the ability to alter the lighting conditions and view direction. As a solution to these problems, we describe a 3D scanner capable of acquiring the shape, color, and reflectance of a tablet as a complete 3D object. This data set could then be stored in an online library and manipulated by suitable rendering software that would allow a user to specify any view direction and lighting condition. The scanner utilizes a camera and telecentric lens to acquire images of the tablet under varying controlled illumination conditions. Image data are processed using photometric stereo and structured light techniques to determine the tablet shape; color information is reconstructed from primary color monochrome image data. The scanned surface is sampled at 26.8 μm lateral spacing and the height information is calculated on a much smaller scale. Scans of adjacent tablet sides are registered together to form a 3D surface model.

Neutron irradiation of sapphire for compressive strengthening. II. Physical properties changes

Abstract Irradiation of sapphire with fast neutrons (0.8–10 MeV) at a fluence of 1022/m2 increased the c-axis compressive strength and the c-plane biaxial flexure strength at 600 °C by a factor of ∼2.5. Both effects are attributed to inhibition of r-plane twin propagation by damage clusters resulting from neutron impact. The a-plane biaxial flexure strength and four-point flexure strength in the c- and m-directions decreased by 10–23% at 600 °C after neutron irradiation. Neutron irradiation had little or no effect on thermal conductivity, infrared absorption, elastic constants, hardness, and fracture toughness. A featureless electron paramagnetic resonance signal at g=2.02 was correlated with the strength increase: This signal grew in amplitude with increasing neutron irradiation, which also increased the compressive strength. Annealing conditions that reversed the strengthening also annihilated the g=2.02 signal. A signal associated with a paramagnetic center containing two Al nuclei was not correlated with strength. Ultraviolet and visible color centers also were not correlated with strength in that they could be removed by annealing at temperatures that were too low to reverse the compressive strengthening effect of neutron irradiation.

Shape characteristics of biological spores

Calculation of scattering properties of biological materials has classically been addressed using numerical calculations based on T-matrix theory. These calculations use bulk optical properties, particle size distribution, and a limited selection of shape descriptors to calculate the resulting aerosol properties. However, the most applicable shape available in T-matrix codes, the spheroid, is not the best descriptor of most biological materials. Based on imagery of the spores of Bacillus atrophaeus and Bacillus anthracis, capsule and egg shapes are mathematically described and programmed into the Amsterdam Discrete Dipole Approximation (ADDA). Spectrally dependent cross sections and depolarization ratios are calculated and a comparison made to spheroidal shapes of equivalent sizes.

Laser ultrasonic techniques for assessment of tooth structure

Dental health care and research workers require a means of imaging the structures within teeth in vivo. For example, there is a need to image the margins of a restoration for the detection of poor bonding or voids between the restorative material and the dentin. With conventional x-ray techniques, it is difficult to detect cracks and to visualize interfaces between hard media. This due to the x-ray providing only a 2 dimensional projection of the internal structure (i.e. a silhouette). In addition, a high resolution imaging modality is needed to detect tooth decay in its early stages. If decay can be detected early enough, the process can be monitored and interventional procedures, such as fluoride washes and controlled diet, can be initiated which can help the tooth to re-mineralize itself. Currently employed x-ray imaging is incapable of detecting decay at a stage early enough to avoid invasive cavity preparation followed by a restoration with a synthetic material. Other clinical applications include the visualization of periodontal defects, the localization of intraosseous lesions, and determining the degree of osseointegration between a dental implant and the surrounding bone. A means of assessing the internal structure of the tooth based upon use of high frequency, highly localized ultrasound (acoustic waves) generated by a laser pulse is discussed. Optical interferometric detection of ultrasound provides a complementary technique with a very small detection footprint. Initial results using laser-based ultrasound for assessment of dental structures are presented. Discussion will center on the adaptability of this technique to clinical applications.

Laser ultrasonics for process control: issues for implementation

Laser ultrasonic techniques for in-process materials characterization show significant potential for applications where rapid, remote sensing is a requirement. While the potential is great, relatively few on-line industrial systems currently exist owing to difficulty associated with designing and implementing robust laser ultrasonic systems. Although laser-based ultrasound is becoming widely used as a laboratory tool for materials characterization, transitioning this technology into a robust industrial process control system poses several problems. Chief among these are suitable lasers for ultrasound generation, ultrasound detection, interferometer design, required signal processing, and overall system performance. This manuscript addresses each of these issues in turn, and gibes examples of industrial process control implementations where appropriate. Finally, recent advances in increasing laser based ultrasonic sensitivity are discussed.