Time window

The rate of re-oxidation of mechanically treated metals depends on the metal, the presence of oxygen and the level of humidity. Guidelines for common metal substrates under ambient conditions without dehumidification in a northern European climate are  

30 minutes for stainless steel, aluminium, brass, bronze and zinc and only 2 minutes (approximately) for magnesium 

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The key quantity in barrier crossing processes in tiiis respect is the barrier curvature Mg which sets the time window for possible influences of the dynamic solvent response. A sharp barrier entails short barrier passage times during which the memory of the solvent environment may be partially maintained. This non-Markov situation may be expressed by a generalized Langevin equation including a time-dependent friction kernel y(t) [ ]... 

When a time window twice the duration of the delay time is used, perfect coincidence is at the centre of the time window and it is possible to make an accurate assessment of the background by considering the region to either side of the perfect coincidence region. An example of a time spectrum is shown m figure Bl.10.8. 

There are a number of observations to be drawn from the above fomuila the relative uncertainty can be reduced to an arbitrarily small value by increasing T, but because the relative uncertainty is proportional to /s/f, a reduction in relative uncertainty by a factor of two requires a factor of four increase in collection time. The relative uncertainty can also be reduced by reducing At. Flere, it is understood that At is the smallest time window that just includes all of the signal. At can be decreased by using the fastest possible detectors, preamplifiers and discriminators and minimizing time dispersion in the section of the experiment ahead of the detectors. 

Examples of typical TOF spectra obtained from 4 keV Ar impinging on a Si 100] surface with chemisorbed FI2O and FI2 are shown in figure B 1.23.6 [35]. Peaks due to Ar scattering from Si and recoiled FI, O and Si are observed. The intensities necessary for stnictural analysis are obtamed by integrating the areas of fixed time windows under these peaks. 

During gc/ms or liquid chromatography/mass spectrometry (Ic/ms) acquisitions, it is possible to perform a mixture of the experiments described in Table 2 for different time windows, with the experimental parameters, such as the coUision energy, optimized for each analyte. 

Although energy resolution is rarely employed in positron camera systems, scatter is not normally a problem. This is because of the very short time window within which two photons must arrive in order to be counted. At low decay rates, the incidence of accidental events is very low, rising only slightly for those that occur as the result of scatter. Some systems employ time-of-flight measurements of the time difference between the arrival of the two photons to obtain additional information about the location of an annihilation along the line. This has been used to improve resolution and statistical accuracy. Resolution is in the range of 3—4 mm and is less dependent on position than is SPECT (16). 

In the event that eertain faults oeeur in the eleetrieal equipment of the generator, the load eireuit breaker must be opened immediately. The result is that the maehine train is aeeelerated with the full power of the expander. Only if the inlet valves are elosed within 0.6 see ean exeessive overspeed be avoided. Eor this reason, both inlet valves must be able to elose within this time window in the event of an emergeney trip. 

Human reliability [lata NJUREG/CR-1278 was supplemented by judgment of system analysts and plant personnel. Human error probabilities were developed from NUREG/CR-12 8, human action time windows from system analysis and some recovery limes from analysis of plant specific experience. Data sources were WASH-1400 HEPs,Fullwood and Gilbert assessment ot I S power reactor Bxp., NUREG/ CR -127K. and selected acro ptice li.it.j... 

A 100% on-time delivery performance means that your subcontractors must deliver supplies within the time window you specify. Unless you so specify, they do not need to operate a just-in-time system but it is obviously less costly to you if they do. It all depends... 

Figure 12.5 Effect of shifting the time window for the ti ansfer. Operation in the SEC-GC analysis of polymer additives in a poly styene matrix, shown foi the following fractions ...

Failure to assess adverse events occurring outside a scheduled time window... 

However, several important studies have shown that intravenous thrombolysis may be beneficial more than 3 hours after stroke onset, provided that only patients with a significant diffusion-perfusion mismatch are treated. In one such smdy, Ribo et al. found that patients with a significant diffusion-perfusion mismatch could be treated safely and effectively in the 3-6-hour time period. In phase II of the desmo-teplase in acute stroke (DIAS) trial, patients with diffusion-perfusion mismatch were treated with desmoteplase up to 9 hours after stroke onset, and showed better outcomes than patients given placebo, with only a minimal incidence of symptomatic hemorrhage. Similar success was achieved in the same time window by the dose escalation study of desmoteplase in acute ischemic stroke (DEDAS). ... 

These studies raise the possibility that, one day, imaging-based treatment protocols may allow for intravenous thrombolysis in patients well outside of the now-accepted 3-hour window, provided they demonstrate substantial diffusion-perfusion mismatch. Such protocols could allow for treatment of a vastly larger number of patients than are currently treated. It has been estimated that only 1-7% of acute stroke patients currently receive thrombolytic medication, and that, in up to 95% of cases, they are ineligible because they present outside of the 3-hour time window. As many as 80% of patients who present 6 hours after stroke onset may demonstrate a significant diffusion-perfusion mismatch. "... 

This section will review the phase III clinical trials of IV thrombolytic agents for acute ischemic stroke, organized by the type of agent and the time window from stroke onset to study drug delivery (Table 3.1). The 1995 National Institute of Neurological Disorders and Stroke (NINDS) rt-PA trial is presented first because it showed that IV rt-PA, given within 3 hours of stroke onset, reduced stroke-related disability. This trial was the basis for the United States Food and Drug Administration (FDA) approval for rt-PA for use in acute ischemic stroke. 

The most common reason for lack of rt-PA use in otherwise eligible patients remains, however, delay in presentation to the hospital. The California Acute Stroke Pilot Registry (CASPR) investigators examined the effect of various hypothetical interventions on the rate of rt-PA use. Their data suggested that if all patients with a known time of onset presented to medical attention immediately, the expected overall rate of thrombolytic treatment within 3 hours would have increased from 4.3% to 28.6%. By comparison, the expected rate of treatment that would result from instantaneous prehospital response was 5.5%, from perfect hospital care was 11.5%, and from extension of time window to 6 hours was 8.3%. 

Combination GP Ilb/IIIa and rt-PA Therapy for Acute Stroke The combination of antiplatelet and thrombolytic drugs has proven efficacy in the setting of myocardial ischemia where an additive effect is seen. In acute stroke thrombolysis with a very narrow time window and less than 50% optimal reperfusion rates,adjunctive therapy with antiplatelets may be a promising approach. However, MAST-I concluded that the group of patients receiving streptokinase plus aspirin had a marked increase in 10-day mortality. 

Fig. 34.25. Time windows in which compounds are present in a composite 4-component peak, with the ranks of the data matrices formed by adding rows to a top matrix To (top down) or to a bottom matrix B(, (bottom up).

MS detection does not necessarily require as highly resolved GC separations as in the case of selective detectors because the likelihood of an overlapping mass spectral peak among pesticides with the same retention time is less than the likelihood of an overlapping peak from the same element. Unfortunately, this advantage cannot always be optimized because SIM and current gas chromatography/tandem mass spectrometry (GC/MS/MS) methods, it is difficult to devise sequential SIM or MS/MS retention time windows to achieve fast GC separations for approximately > 50 analytes in a single method. 

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