Repetition

Bending or twisting during manual handling slippery, or sloped 

Source Courtesy of Occupational Safety and Health Administration. 

Ergonomic risk factors are the aspects of a job or task that impose a biomechanical stress on the worker. Ergonomic risk factors are the synergistic elements of MSD hazards. The following ergonomic risk factors are most likely to cause or contribute to an MSD  

Force Vibration Repetition Contact stress Awkward postures Cold temperatures Static postures 

These risk factors are described briefly in the following sections. 

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In Austria, as well as all over Europe, the first and repetition tests of all pressure equipments including steam drums are required for security reasons within fixed time intervals. These repetitive inspections are done differently in the most European countries, but most time these inspections include, according to the European Pressure Equipment Directive" and the specific national law any kind of over-pressurisation (e.g. hydrotest) and visual inside inspection. 

For the repetitive inspections the required hydrotest can only be performed for a limited number of the small cylinders, and even then the drums have to be removed from the line and the cylinders will be supported in defined distances for the weight of the water and the pressurisation. For the new and long cylinders even this is impossible, because they loose due to the additional weight of the water and the over-pressurisation their roundness and balances. Therefore the law in the most countries within and outside of the EU accept as a replacement of the hydrotest an additional application of different NDT methods, which were often done by an ultrasonic measurement of the wall thickness of the cylindrical part and a MT of the flat covers. 

It obvious a today s demand on repetitive inspections to predict the safety of pressure equipments during the oncoming service period. The acceptance from the industry for this kind of testing is accessible, if you can fulfil this requirement an enlarge in this way the competitiveness. 

In order to verify the repetitiveness of the results, each test will be realized twice. 

A single cut of the tested object is generated in a single scan. Generation of additional cuts demands the repetition of the exposure. 

The source of radiation is a linear accelerator with selectable primary energies of 6, 9 or 11 MeV ( VARIAN Linatron 3000 A). The output of the LINAC at 9 MV is 3000 rad ( 30 Gy) per minute. The pulse length is 3.8 microseconds with repetition frequencies between 50 and 250 Hertz. 

PRF. Defines the pulse repetition frequency (PRF), in Hz, of the probe firing. 

The sample frequency of the ADC (analogue to digital converter) should be 8 times higher than the test frequency (centre frequency of the spectrum). In dependence of the application, different ADC- boards are used. A standard board (20520) provides 8 bit resolution and up to 100 Msamples/s in single shot mode. For manual tests, up to 400 Msamples/s can be reached in the repetition mode. For scanning systems with high frequencies boards up to 400 Msamples/s (single shot) are available. 

The screen shows the predefined area to be scanned and filled to ensure maximum coverage The transmitter operates with a frequency of 40 kHz and with a pulse repetition frequency of 200 Hz. This gives the system an accuracy in positioning of better than 1 mm. 

The microcanonical ensemble is a certain model for the repetition of experiments in every repetition, the system has exactly the same energy, Wand F but otherwise there is no experimental control over its microstate. Because the microcanonical ensemble distribution depends only on the total energy, which is a constant of motion, it is time independent and mean values calculated with it are also time independent. This is as it should be for an equilibrium system. Besides the ensemble average value (il), another coimnonly used average is the most probable value, which is the value of tS(p, q) that is possessed by the largest number of systems in the ensemble. The ensemble average and the most probable value are nearly equal if the mean square fluctuation is small, i.e. if... 

Dadap J I, Hu X F, Russell N M, Ekerdt J G, Lowell J Kand Downer M C 1995 Analysis of second-harmonic generation by unamplified, high-repetition-rate, ultrashort laser pulses at Si(OOI) interfaces/ J. Selected Topics Quantum Electron 1 1145-55... 

The latter may be fiirther subdivided into transient experiments, in which the current and potential vary with time in a non-repetitive fashion steady-state experiments, in which a unique interrelation between current and potential is generated, a relation that does not involve time or frequency and in which the steady-state current achieved is independent of the method adopted and periodic experiments, in which current and potential vary periodically with time at some imposed frequency. 

The most connnon commercially prepared amplifier systems are pumped by frequency-doubled Nd-YAG or Nd-YLF lasers at a 1-5 kHz repetition rate a continuously pumped amplifier that operates typically in the 250 kHz regime has been described and implemented connnercially [40]. The average power of all of the connnonly used types of Ti-sapphire amplifier systems approaches 1 W, so the energy per pulse required for an experiment effectively detennines the repetition rate. 

Knox W H, Downer M C, Fork R L and Shank C V 1984 Amplified femtosecond optical pulses and continuum generation at 5 kHz repetition rate Qpt. Lett. 9 552-4... 

Rudd J V, Korn G, Kane S, Squier J, Mourou G and Bade P 1993 Chirped-pulse amplification of 55 fs pulses at a 1 kHz repetition rate in a TIAI203 regenerative amplifier Opt. Lett. 18 2044-6... 

Hz repetition rate of the lasers and is usually sampled with a gated integrator, whose output is reeorded with a laboratory eomputer. Analogue, rather than digital, eleetronies is usually employed beeause of pile-up of the deteeted photon eounts in an experiment with reasonable produet intensities. 

These experiments yield T2 which, in the case of fast exchange, gives the ratio (Aoi) /k. However, since the experiments themselves have an implicit timescale, absolute rates can be obtained in favourable circumstances. For the CPMG experiment, the timescale is the repetition time of the refocusing pulse for the Tjp experiment, it is the rate of precession around the effective RF field. If this timescale is fast witli respect to the exchange rate, then the experiment effectively measures T2 in the absence of exchange. If the timescale is slow, the apparent T2 contains the effects of exchange. Therefore, the apparent T2 shows a dispersion as the... 

An alternative to split operator methods is to use iterative approaches. In these metiiods, one notes that the wavefiinction is fomially "tt(0) = exp(-i/7oi " ), and the action of the exponential operator is obtained by repetitive application of //on a function (i.e. on the computer, by repetitive applications of the sparse matrix... 

There is a special keyword - loop - which enables repetition of data. This keyword is used mainly when there are several data items with the same type of content (e.g.. description of the atoms within a molecule). 

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