Stable, narrow-linewidth laser system with a broad frequency tunability and a fast switching time.

For a Rydberg atom-based sensor to change its sensing frequency, the wavelength of the Rydberg state excitation laser must be altered. The wavelength shifts required can be on the order of 10 nm. A fast-tunable narrow-linewidth laser with broadband tuning capability is required. Here, we present a demonstration of a laser system that can rapidly switch a coupling laser as much as 8 nm in less than 50 µs. The laser system comprises a frequency-stabilized continuous wave laser and an electro-optic frequency comb. A filter enables selection of individual comb lines. A high-speed electro-optic modulator is used to tune the selected comb line to a specific frequency, i.e., an atomic transition. Through Rydberg atom-based sensing experiments, we demonstrate frequency hopping between two Rydberg states and a fast switching time of 400 µs, which we show can be reduced to ∼50 µs with a ping-pong scheme. If updating the RF frequency is not required during frequency hopping, a 200 ns switching time can be achieved. These results showcase the potential of the laser system for advanced Rydberg atom-based radio frequency sensing applications, like communications and radar.

Implementing an electronic sideband offset lock for isotope shift spectroscopy in radium.

We demonstrate laser frequency stabilization with at least 6 GHz of offset tunability using an in-phase/quadrature (IQ) modulator to generate electronic sidebands (ESB) on a titanium sapphire laser at 714 nm and we apply this technique to perform isotope shift spectroscopy of 226Ra and 225Ra. By locking the laser to a single resonance of a high finesse optical cavity and adjusting the lock offset, we determine the frequency difference between the magneto-optical trap (MOT) transitions in the two isotopes to be 2630.0 ± 0.3 MHz, a factor of 29 more precise than the previously available data. Using the known value of the hyperfine splitting of the 3P1 level, we calculate the isotope shift for the 1S0 to 3P1 transition to be 2267.0 ± 2.2 MHz, a factor of 8 more precise than the best available value. Our technique could be applied to countless other atomic systems to provide unprecedented precision in isotope shift spectroscopy and other relative frequency comparisons.

An evaluation of industrial ventilation branch screening methods for obstructions in working exhaust systems.

This research evaluated the effectiveness of screening methods in identifying obstructed branches in industrial ventilation systems. These methods were divided into two categories: pressure comparisons and pressure ratio comparisons. The first category contained techniques that compare measured static pressures with the corresponding design static pressures or with previously measured pressures. Certain aspects of the method suggested in the Industrial Ventilation Manual were also tested. The second category compares the ratios of two measured pressures and includes the new reference ratio method. Data were collected from six industrial ventilation systems. Four of the systems were used to control wood dust, and two were used to control metal shavings from a saw-sharpening operation. Each system was tested for naturally occurring or deliberately inserted obstructions. Appropriate static and velocity pressures were measured to calculate each troubleshooting method's parameter. The change in the parameter was compared with a range of thresholds for the test cases. Receiver operator characteristic curves and bootstrapping techniques were used to identify the best method for determining the presence of obstructions or alterations. The pressure ratio methods were found to be substantially superior to the pressure comparison methods at detecting obstructions.

An evaluation of industrial ventilation troubleshooting methods in experimental systems.

This study determined the efficacy of specific methods of identifying and locating obstructions and alterations to industrial exhaust ventilation systems under challenging conditions when measurement errors were minimized. Two traditional screening methods were evaluated: (1) two variations of the hood static pressure method and (2) a severely modified version of the "Check-out" method. Three proposed pressure ratio methods also were evaluated and compared with the traditional methods. Two full-sized experimental ventilation systems in two ventilation laboratories were tested. One system had five branch ducts, the other had eight, with branch duct diameters ranging from 4 to 7 inches. To create challenge, each system received multiple alterations and, in some cases, the airflow level was changed throughout the system. For each round of measurements (1) different combinations of alterations were made to some ducts; (2) on a given system, relevant pressures and flows were determined for each duct using calibrated pressure sensors and standard pitot tubes held in a traversing device; and (3) the numbers of true and false positives and negatives for each screening method were computed for a broad range of threshold values. Sensitivities were plotted against the false positive rates for all thresholds for each method. The area (AROC) under the resulting "receiver operating characteristic curves" was computed for each method. Variability was simulated using bootstrap methods to determine significance of differences. In addition, the thresholds that would achieve 10 and 20% false positive rates were determined for each method and the accompanying sensitivities compared. The pressure ratio methods detected nearly all nontrivial obstructions with nearly zero false positives (AROC=1). The direct pressure comparison methods showed substantially inferior performance for the substantial challenges presented in these tests. The latter may be useful under less challenging conditions but were of dubious utility in locating obstructions under the ranges of conditions tested.

Hard metal exposures. Part 1: Observed performance of three local exhaust ventilation systems.

Not every ventilation system performs as intended; much can be learned when they do not. The purpose of this study was to compare observed initial performance to expected levels for three saw-reconditioning shop ventilation systems and to characterize the changes in performance of the systems over a one-year period. These three local exhaust ventilation systems were intended to control worker exposures to cobalt, cadmium, and chromium during wet grinding, dry grinding, and welding/brazing activities. Prior to installation the authors provided some design guidance based on Industrial Ventilation, a Manual of Recommended Practice. However, the authors had limited influence on the actual installation and operation and no line authority for the systems. In apparent efforts to cut costs and to respond to other perceived needs, the installed systems deviated from the specifications used in pressure calculations in many important aspects, including adding branch ducts, use of flexible ducts, the choice of fans, and the construction of some hoods. After installation of the three systems, ventilation measurements were taken to determine if the systems met design specifications, and worker exposures were measured to determine effectiveness. The results of the latter will be published as a companion article. The deviations from design and maintenance failures may have adversely affected performance. From the beginning to the end of the study period the distribution of air flow never matched the design specifications for the systems. The observed air flows measured within the first month of installation did not match the predicated design air flows for any of the systems, probably because of the differences between the design and the installed system. Over the first year of operation, hood air flow variability was high due to inadequate cleaning of the sticky process materials which rapidly accumulated in the branch ducts. Poor distribution of air flows among branch ducts frequently produced individual hood air flows that were far below specified design levels even when the total air flow through that system was more than adequate. To experienced practitioners, it is not surprising that deviations from design recommendations and poor maintenance would be associated with poor system performance. Although commonplace, such experiences have not been documented in peer-reviewed publications to date. This publication is a first step in providing that documentation.

Comparison of pitot traverses taken at varying distances downstream of obstructions.

This study determined the deviations between pitot traverses taken under "ideal" conditions--at least seven duct diameter's lengths (i.e., distance = 7D) from obstructions, elbows, junction fittings, and other disturbances to flows--with those taken downstream from commonplace disturbances. Two perpendicular 10-point, log-linear velocity pressure traverses were taken at various distances downstream of tested upstream conditions. Upstream conditions included a plain duct opening, a junction fitting, a single 90 degrees elbow, and two elbows rotated 90 degrees from each other into two orthogonal planes. Airflows determined from those values were compared with the values measured more than 40D downstream of the same obstructions under ideal conditions. The ideal measurements were taken on three traverse diameters in the same plane separated by 120 degrees in honed drawn-over-mandrel tubing. In all cases the pitot tubes were held in place by devices that effectively eliminated alignment errors and insertion depth errors. Duct velocities ranged from 1500 to 4500 ft/min. Results were surprisingly good if one employed two perpendicular traverses. When the averages of two perpendicular traverses was taken, deviations from ideal value were 6% or less even for traverses taken as close as 2D distance from the upstream disturbances. At 3D distance, deviations seldom exceeded 5%. With single diameter traverses, errors seldom exceeded 5% at 6D or more downstream from the disturbance. Interestingly, percentage deviations were about the same at high and low velocities. This study demonstrated that two perpendicular pitot traverses can be taken as close as 3D from these disturbances with acceptable (< or = 5%) deviations from measurements taken under ideal conditions.

The management of athletes with myositis ossificans traumatica.

Myositis ossificans traumatica (MOT) is often encountered by young male athletes participating in contact sports. The purpose of this paper is to review this disorder, characterized by a localized bone formation within muscle and other connective tissues as a result of a single or repeated contusion. MOT merits close attention because it may cause protracted disability and absence from competitive and recreational activities. Moreover, it may be mistaken for serious pathologies such as sarcoma. Confusion regarding the optimal management of MOT may also arise because the literature proposes conservative, experimental and surgical treatment approaches.