Waveguiding properties in Yb:YAG crystals implanted with protons and carbon ions.

We report the fabrication and analysis of optical waveguides in Yb:YAG crystals using either proton or carbon ion implantation. Planar waveguides were obtained by implanting the whole surface of the crystals. Channel waveguides were defined using an electroformed mask with apertures of 10, 15, and 20 micrometers in width. The waveguiding properties of the structures were analyzed, showing good light confinement based on the transversal mode distribution and optical transmission measurements. The spectroscopic properties of the Yb ions in the YAG host are preserved after the implantation process, which demonstrates the potential of this technique for tailoring microcomponents for integrated optics applications. In particular, the Yb:YAG waveguides have the potential to operate as miniature lasers.

Surface morphology of amorphous SiO2 substrates bombarded with 1.0 MeV Si+ ions.

Surface pattern formation on amorphous SiO2 substrates by implantation of 1.0 MeV Si+ ions at a current of 1.3 µA at 70° angle is reported. Surface micrometer sized ripples perpendicular to the ion beam direction are formed, observed by scanning electron microscopy and atomic force microscopy. The morphological features are more or less similar for different fluences. The formation of surface ripples at this energy is discussed in terms of ion stopping mechanisms and patterns obtained within the low- and medium-energy ranges.

Laser emission in proton-implanted Nd:YAG channel waveguides.

The performance of lasers based on channel waveguides produced by proton implantation in Nd:YAG crystals through an electroformed mask is reported. The fabrication method used can produce several waveguide lasers in the crystal by a single implantation process with very good optical performance. The analysis and comparison of the main laser emission features, as well as the propagation losses of these waveguides, by using different output couplers in the laser cavity is also presented.

Optical channel waveguides by proton and carbon implantation in Nd:YAG crystals.

In this work the formation of optical channel waveguides in Nd:YAG crystals by either proton or carbon implantation is reported. The channel waveguides were obtained by a single implantation process through an electroformed mask of nickel-cobalt alloy. Experimental measurements of the optical properties of these waveguides are presented.

Study of gel materials as radioactive 222Rn gas detectors.

Commercial hair gel material (polyvinyl pyrolydone triethanolamine carbopol in water) and bacteriological agar (phycocolloid extracted from a group of red-purple algae, usually Gelidium sp.) have been studied as radioactive radon gas detectors. The detection method is based on the diffusion of the radioactive gas in the gel material, and the subsequent measurement of trapped products of the natural decay of radon by gamma spectrometry. From the several radon daughters with gamma radiation emission (214Pb, 214Bi, 214Po, 210Pb, 210Po), two elements, 214Pb (0.352 MeV) and 214Bi (0.609 MeV), were chosen for the analysis in this work; in order to determine the best sensitivity, corrections were made for the short half-life of the analysed isotopes. For the gamma spectrometry analysis, a hyperpure germanium solid state detector was used, associated with a PC multichannel analyser card with Maestro and Microsoft Excel software. The results show the viability of the method: a linear response in a wide radon concentration range (450-10,000 Bq m(-3)), reproducibility of data, easy handling and low cost of the gel material. This detection methodology opens new possibilities for measurements of radon and other radioactive gases.

Low dose carbon implanted waveguides in Nd:YAG.

For the first time to our knowledge, carbon implantation into YAG crystals doped with Nd has been used to produce optical waveguides. A considerable index decrease in the nuclear region (i.e., the region where the energetic ions stop) of ~ 2.5% was obtained with a low dose implant, while giving an index enhancement in the guiding region of ~ 0.35%. After an annealing step necessary to recover the transparency of the crystals, the layer of reduced refractive index produced by implantation is preserved. Spectroscopic studies carried out in a waveguiding configuration show that emission bands coming from the 4F3/2 level present a slight broadening, while its associated lifetime is similar to that reported in bulk crystals (240 ms).

Planar waveguide lasers by proton implantation in Nd:YAG crystals.

The performance of CW Nd:YAG waveguide lasers operating at 1.06 microm at room temperature is described. The waveguides were fabricated by proton implantation and the main differences in the process of fabrication were the angle of implantation and the total dose implanted. The characterization of the waveguide refractive index profile induced by proton implantation and the main laser characteristics i.e., slope efficiency and threshold are presented.

Myoelectric signal measurement during prolonged computer terminal work.

Myoelectric signal (MES) behaviour was studied during prolonged, sustained, low level contractions using a portable system with limited data storage capacity. A pre-processing technique is described which overcomes memory and data storage limitations in a portable multichannel MES data logger. This technique for data reduction was used to study MES behaviour in four muscle groups during prolonged computer terminal work. Myoelectric signal parameters were recorded from eighteen individuals while they performed computer work both without breaks, and with "microbreaks" (short rest breaks of 30 seconds duration) at twenty minute intervals. Myoelectric signal (MES) data were collected from the cervical paraspinal extensors, the lumbar erector spinae, the upper trapezius, and the forearm extensors while participants performed their usual computer work activities. No significant slope for either amplitude or mean frequency was determined in either the break or no break trials over an eighty minute recording period. Instead, most data sets revealed a cyclic trend in terms of frequency and amplitude parameters of the MES. Characteristic values were compared between trials when subjects did and did not take microbreaks. It was found that the overall median value of mean frequency was higher for the "break" than the "no break" protocol only in the cervical extensors, although the clinical significance of this finding is not well understood. By far, the most interesting finding of this work was the discovery of a cyclic trend in the mean frequency of the myoelectric signals studied. This trend was present even when participants did not take breaks. The trend is a potential indicator of the cyclic recruitment of motor units during sustained postural contractions, and is the primary area to be investigated in future studies by the authors.

Nuclear tracks in CR-39 produced by carbon, oxygen, aluminium and titanium ions.

This work describes the response of CR-39 (allyl diglycol polycarbonate) to different ions (C, O, Al and Ti) produced by the Instituto de Fisica 3 MV 9SDH-2 Pelletron accelerator and backscattered from a thin Au film on a C support. The ion energies were chosen in series such that the ranges of the different ions in the detector were 2, 3, 4, 5, 6, 7 and 8 microm respectively for each series. Once exposed, the detectors were etched with a solution of 6.25 M KOH at 60 degrees C, and the reading was carried out using a digital image analysis system. An analysis of the measured track diameters of all the types of ions indicates that, for a given range, track kinetics are independent of type of ion, energy and stopping power.

Computer terminal work and the benefit of microbreaks.

Microbreaks are scheduled rest breaks taken to prevent the onset or progression of cumulative trauma disorders in the computerized workstation environment. The authors examined the benefit of microbreaks by investigating myoelectric signal (MES) behavior, perceived discomfort, and worker productivity while individuals performed their usual keying work. Participants were randomly assigned to one of three experimental groups. Each participant provided data from working sessions where they took no breaks, and from working sessions where they took breaks according to their group assignment: microbreaks at their own discretion (control), microbreaks at 20 min intervals, and microbreaks at 40 min intervals. Four main muscle areas were studied: the cervical extensors, the lumbar erector spinae, the upper trapezius/supraspinatus, and the wrist and finger extensors. The authors have previously shown that when computer workers remained seated at their workstation, the muscles performing sustained postural contractions displayed a cyclic trend in the mean frequency (MNF) of the MES (McLean et al., J. Electrophysiol. Kinesiol. 10 (1) (2000) 33). The data provided evidence (p < 0.05) that all microbreak protocols were associated with a higher frequency of MNF cycling at the wrist extensors, at the neck when microbreaks were taken by the control and 40 min protocol groups, and at the back when breaks were taken by the 20 and 40 min protocol groups. No significant change in the frequency of MNF cycling was noted at the shoulder. It was determined (p < 0.05) that microbreaks had a positive effect on reducing discomfort in all areas studied during computer terminal work, particularly when breaks were taken at 20 min intervals. Finally, microbreaks showed no evidence of a detrimental effect on worker productivity. The underlying cause of MNF cycling, and its relationship to the development of discomfort or cumulative trauma disorders remains to be determined.

Effect of joystick stiffness, movement speed and movement direction on joystick and upper limb kinematics when using hydraulic-actuation joystick controls in heavy vehicles.

Despite the widespread use of hydraulic-actuation joysticks in mobile North American construction, mining and forestry vehicles, the biomechanical effects that joysticks have on their human operators has not been studied extensively. Using nine unskilled joystick operators and a laboratory mock-up with a commonly used North American heavy off-road equipment hydraulic-actuation joystick and operator seat, the purpose of this work was to quantify and compare the effects of three hydraulic-actuation joystick stiffnesses and two movement speeds on upper limb and joystick kinematics as one of the initial steps towards the development of a hydraulic-actuation joystick design protocol. In addition to providing a detailed description of the kinematics of a constrained occupational task, coupled with the corresponding effects of the task on operator upper limb kinematics, results from principal component analysis and ANOVA procedures revealed a number of differences in joystick and upper limb angle ranges and movement curve shapes resulting from the various joystick stiffness-speed combinations tested. For the most part, these joystick motion alterations were caused by small, insignificant changes in one or more upper limb joint angles. The two exceptions occurred for forward movements of the joystick; the fast speed - light stiffness condition movement pattern shape change was caused primarily by an alteration of the elbow flexion-extension movement pattern. Similarly, the fast speed - normal stiffness condition movement curve shape perturbation - was caused principally by a combination of significant movement curve shape alterations to elbow flexion-extension, external-internal shoulder rotation and flexion-extension of the shoulder. The finding that joystick stiffness and speed alterations affect joystick and upper limb kinematics minimally indicates that the joystick design approach of modelling the joystick and operator upper limb as a closed linkage system should be pursued. This approach would allow one to simulate the upper limb and joystick kinematics that result from virtual changes to upper limb and joystick lengths.

Off-road machine controls: investigating the risk of carpal tunnel syndrome.

Occupationally induced hand and wrist repetitive strain injuries (RSI) such as carpal tunnel syndrome (CTS) are a growing problem in North America. The purpose of this investigation was to apply a modification of the wrist flexion/ extension models of Armstrong and Chaffin (1978, 1979) to determine if joystick controller use in off-road machines could contribute to the development of CTS. A construction equipment cab in the laboratory was instrumented to allow force, displacement and angle measurements from 10 operators while they completed an approximately 30-min joystick motion protocol. The investigation revealed that both the external fingertip and predicted internal wrist forces resulting from the use of these joysticks were very low, indicating that the CTS risk associated with this factor was slight. However, the results also indicated that, particularly for the 'forward' and 'left' right side motions and for all left side motions, force was exerted by other portions of the fingers and hand, thereby under-predicting the tendon tension and internal wrist forces. Wrist angles observed were highest for motions that moved the joysticks to the sides rather than front to back. Thus, the 'right' and 'left' motions for both hands posed a higher risk for CTS development. When the right hand moved into the 'right' position and the left hand moved into the 'left' position, the wrist went into extension in both cases. Results indicate that neither learning nor fatigue affected the results.