Data recorded by several infrasound sensor arrays deployed in the southeastern United States during the spring of 2018 have been analyzed during a period when a storm front passed through and spawned several tornado touchdowns. The tornadoes ranged from EF-0 to EF-2. Accurate bearings have been obtained, corresponding to tornadoes at ranges up to more than 100 km. Earlier in the day, a convective storm cell passed and triggered a tornado warning but no verified tornado touchdowns. During this earlier passage, a weaker signal was detected with bearings that tracked this convective storm cell. The analyses reveal that on the systems deployed, the dominant band of coherent infrasound measured from the tornadic storms was between 2 and 6 Hz. Atmospheric conditions are known to have a significant influence on signal detection because of propagation effects and local wind noise conditions. Propagation modeling and wind noise analysis were undertaken and are observed to be consistent with signal detection from the tornadoes. Because of the static sources, as well as the multiple strong cells that were in the region simultaneously, it was necessary to use array signal processing methods that are capable of resolving multiple sources.

Hydrological terrain analysis is important for applications such as environmental resource, agriculture, and flood risk management. It is based on processing of high-resolution, tiled digital elevation model (DEM) data for geographic regions of interest. A major challenge in global hydrological terrain analysis is addressing cross-tile dependencies that arise from the tiled nature of the underlying DEM data, which is too large to hold in memory as a single array. We are not aware of existing tools that can accurately and efficiently perform global terrain analysis within current memory and computational constraints. We solved this problem by implementing a new algorithm in Python, which uses a simple but robust file-based locking mechanism to coordinate the work flow between an arbitrary number of independent processes operating on separate

We have designed and fabricated an anatomically accurate human head phantom that is capable of generating realistic electric scalp potential patterns. This phantom was developed for performance evaluation of new electroencephalography (EEG) caps, hardware, and measurement techniques that are designed for environments high in electromagnetic and mechanical noise. The phantom was fabricated using conductive composite materials that mimic the electrical and mechanical properties of scalp, skull, and brain. The phantom prototype was calibrated and testing was conducted using a 32-electrode EEG cap. Test results show that the phantom is able to generate diverse scalp potential patterns using a finite number of dipole antennas internal to the phantom. This phantom design could provide a valuable test platform for wearable EEG technology.

Workers operating in extreme noise may need levels of hearing protection that are beyond that possible with double hearing protection comprising earplugs and circumaural hearing protectors. In such noise fields, sound conducted along bone-conduction transmission paths that bypass the ear canal can be sufficient to cause hearing damage. To provide sufficient protection beyond this bone-conduction limit, hearing protectors must attenuate sound that is transmitted to the cochlea via bypass mechanisms. The design of a passive hearing protection helmet that provides protection beyond the bone-conduction limit is described here. The helmet was developed for Navy aircraft carrier deck crews who are exposed to extreme sound levels of 150 dB during aircraft launch operations. The helmet design was based on extensive measurements with human subjects and with a human head simulator built to measure bone-conducted sound. These measurements demonstrated that a helmet shell fitted with an edge seal that created an acoustic seal between the shell and the head was effective in attenuating bone-conducted sound. Measured attenuation data are presented in addition to fit and performance data from tests in the laboratory and the field. Lessons learned from this development effort are also discussed. [Work sponsored by the U.S. Navy].

: This manual describes the features and functionality of the Creare Diver Health Monitoring System (DHMS). The Creare DHMS is a body-worn sensor system for monitoring a diver's physiologic condition, as well as of his environment. Currently, the DHMS consists of a single body-worn sensor that measures the divers electrocardiogram (ECG). The DHMS sensor records the ECG and determines the diver's current heart rate. The device logs the data for later retrieval and it also broadcasts the data in real time over a wireless link to a nearby computer. The use of the DHMS system is aimed at researchers performing experiments on divers. The system can be used wet or dry, at the surface or at depth. The DHMS is composed of three components: (1) one or more body-worn sensors. (2) a general purpose PC running a custom-written application to control the sensors and to receive the data, and (3) a dock for recharging the body-worn sensors.

Maintenance of a secure perimeter around military camps is a significant problem. Detecting foot-borne intruders is a particularly difficult aspect of this problem. Visual surveillance and electronic imaging currently serve as the primary surveillance modalities. Seismic sensors, however, offer an attractive alternative and several commercial seismic surveillance products are available. These systems usually employ a small seismic sensor (geophone) combined with on-board signal processing algorithms to automatically detect personnel and vehicles. The performance of the existing seismic sensor systems, however, is often limited by local interference sources. Under funding from the U.S. Army ERDC-CRREL, Creare has been developing a seismic monitoring system that employs innovative data processing algorithms to overcome some of the limitations of the existing systems. In particular, we have developed adaptive noise cancellation (ANC) algorithms that have proved effective against certain classes of interference sources. In the work presented here, we performed controlled field tests with interference from a nearby diesel tractor engine and from a nearby gasoline power generator. Despite this interference, our ANC algorithms enabled the automatic detection of walking intruders at a range of more than 100 feet.

Experiments conducted to determine the resistance of demountable HTS lap joints with variations in compressive stress are reported here. A joint fixture was constructed that enabled the simultaneous testing of multiple joints of different configurations. The joint fixture was installed in a loading facility, comprising a pneumatic press mounted in a vacuum bell jar and connected to a GM cryocooler. The resistance across each joint was measured by means of voltage taps over a range of compressive joint forces. The test results demonstrated that joint resistances less than 2 muOmega were possible with only light joint loading.

The development and testing of a flow cooling system for high-temperature superconducting (HTS) magnets is described. The system includes a turbo-Brayton cryocooler, a magnet thermal interface, and a magnet thermal isolation and support system. The target application is the Variable Specific Impulse Magnetoplasma Rocket (VASIMR). Turbo-Brayton coolers are well suited to such spacecraft applications, as they are compact, modular, lightweight, and efficient, with long maintenance-free lifetimes. Furthermore, the technology scales well to high-cooling capacities. The feasibility of using turbo-Brayton coolers in this application was proven in a design exercise in which existing cooler designs were scaled to provide cooling for the magnet sets required by 200 kW and 1 MW VASIMR engines. The performance of the concepts for the thermal interface and the thermal isolation and support system were measured in separate laboratory tests with a demonstration system built about a representative HTS magnet. Cooling for these tests was provided by a flow cooling loop comprising a compressor, recuperator and GM cryocooler, with the flow pressure, temperature, and mass flow rate selected to effectively simulate the turbo-Brayton operating condition. During system testing, the magnet was cooled below its design operating temperature of 35 K, and good thermal uniformity (<0.4 K) and low thermal loads (<0.5 W) were demonstrated.

A team comprised of the Tai-Yang Research Company, Creare, Inc., and the Advanced Space Propulsion Laboratory at NASA has designed, fabricated and tested a high-temperature superconducting magnet and flow cooling system for a space propulsion application. The magnet bore is 16 cm dia., 5.5 cm long, and generates 0.5 T, with a design operating current of 126 A. The magnet is wound with brass laminated 1 G BSCCO conductor, epoxy impregnated, then thermally connected to a flow cooling loop with a compressor, recuperator and GM cryocooler. Flow conditions are selected to simulate operation with a space proven turbo-Brayton cryocooler. This test demonstrates that design and integration of an HTS magnet with flow cooling is feasible, and offers the advantages of compactness, low weight, high efficiency and high reliability. Design details of the magnet and cooling system and results of successful system qualification tests are reported.

High-resolution ultrasound imaging of the anterior portion of the eye has been shown to provide important information for sizing of intraocular lens implants, diagnosis of pathological conditions, and creation of detailed maps of corneal topography to guide refractive surgery. Current ultrasound imaging systems rely on mechanical scanning of a single acoustic element over the surface of the eye to create the three-dimensional information needed by clinicians. This mechanical scanning process is time-consuming and subject to errors caused by eye movement during the scanning period. This paper describes development of linear ultrasound imaging arrays intended to increase the speed of image acquisition and reduce problems associated with ocular motion. The arrays consist of a linear arrangement of high-frequency transducer elements designed to operate in the 50 - 75 MHz frequency range. The arrays are produced using single-crystal lithium niobate piezoelectric material, thin film electrodes, and epoxy-based acoustic layers. The array elements have been used to image steel test structures and bovine cornea.