Threshold Currents

If acetal resins are processed at temperatures substantially above those recommended for the particular grade, minor amounts of formaldehyde may be Hberated. Formaldehyde (qv) is a colorless, lacrimatory gas with a pungent odor and is intensely irritating to mucous membranes. The human nose is sensitive to concentrations in the range of 0.1 to 0.5 ppm. The current threshold limit value for formaldehyde is 1 ppm. 

The threshold for the current comparator is set by the output of the voltage error amplifier. If the voltage error amplifier indicates that the output voltage is too low, then the current threshold is raised to allow more energy to reach the load. The converse is true too. 

Figure 3.6-1 shows the electrochemical window of a 76-24 mol % [BMMIM][(GF3S02)2N]/Li[(GF3S02)2N] ionic liquid at both GG and Pt working electrodes [15]. For the purposes of assessing the electrochemical window, the current threshold for both the anodic and cathodic limits was set at an absolute value of 100 pA cm . ... 

Filter samples can be prepared to airborne workplace concentrations by spiking each filter with aqueous solution containing elements with concentrations gravimetrically traceable to ultrapure metals or stoidiiometricaUy well defined oxides. The amormts correspond for some of the materials to current threshold limit values of contaminants in workroom atmospheres provided that the simulated filter has been exposed to one cubic meter of air. The certified values are based on a gravimetric procedure, i.e. weight per volume composition of the primary reference material dissolved in high purity sub-dis-tiUed acids. The National Institute of Occupational Health in Oslo, Norway, has produced several batches of such materials certified for 20 elements. Additionally, information values are reported for four other elements see Table 6.2. 

Campara P, D Andrea F, Micciolo R, et al. 1984. Psychological performance of workers with blood-lead concentration below the current threshold limit value. Int Arch Occup Environ Health 53 233-246. 

To protect humans and other mammals, proposed air-quality criteria range from 0.01 to less than 1.0 mg/m3 for metallic nickel and slightly soluble nickel compounds, 0.015-0.5 mg/m3 for water soluble nickel compounds, and 0.005 to 0.7 mg/m3 for nickel carbonyl (Table 6.10). Inhalation of nickel subsulfide concentrations (0.11 to 1.8 mg Ni/m3) near the current threshold limit value of 1 mg Ni/m3 can produce detrimental changes in the respiratory tract of rats after only a few days of exposure (Benson et al. 1995). Additional animal studies are recommended to identify minimally effective inhalation exposure levels for the various nickel compounds (USPHS 1993). Continued monitoring of nickel refining, nickel-cadmium battery manufacture, and nickel powder metallurgy installations is recommended because ambient air levels of bioavailable nickel at these... 

Figure 6.6. Laser diode intensity as a function of temperature and current. Threshold for this diode at 25 C is 60 mA and the maximum current is 90 mA. Redrawn from Melles Griot product literature.

Note that the x axis is logarithmic to allow a wide range of frequencies to be shown. The y axis is the current threshold at which adverse physiological events (dysrhythmias etc.) may occur. The highest risk of an adverse event occurs at current frequencies of around 50 Hz, which is the UK mains frequency. At diathermy frequencies, the threshold for an adverse event is massively raised. 

It has been reported that after withdrawal from twelve-to-twenty-four-hour binges of intravenous cocaine self-administration, current thresholds for electrical brain stimulation reward are elevated in animals (Markou and Koob 1991,1992). In addition, levels of extracellular DA are decreased in Acb following withdrawal from prolonged cocaine self-administration (Weiss et al. 1992b). Long-term cocaine use can decrease tyrosine hydroxylase levels, leading to decreased DA synthesis (Trulson et al. 1987). 

Another physiological toxicokinetic model (Tardif et al., 1993b, 1997) has been used to predict potential interactions between, e.g., toluene, ethylbenzene and we/tr-xylene the model and experimental data from exposed volunteers indicate that no biologically significant changes in their toxicokinetics will occur if these three solvents are present in the air as a mixture within the permissible concentrations for mixtures (Tardif et al., 1997). A model approach also predicted that interactions between dichloromethane and toluene at their current threshold limit values are not relevant for humans (Pclekis Krishnan, 1997). 

An example of a nonoccupational exposure is methanol, which is formed endogenously, probably as the result of the activities of intestinal flora or enzymatic processes. It is present in a number of consumer products. Methanol may be present in low concentrations in some foods, juices, and alcoholic beverages. Methanol can also be derived from the intestinal enzymatic hydrolysis of the artificial sweetener aspartame, which results in methanol absorption from the intestine (Butchko et al. 2002). It is estimated that a 355-mL serving of aspartame-sweetened beverages and of various fruit and tomato juices may contribute about 20-100 mg of dietary methanol (Butchko et al. 2002). For comparison purposes, exposure at the current Threshold Limit Value time-weighted average of methanol (262 mg/m3) would result in a daily dose of about 1,500 mg, assuming an 8-hour inhaled volume of 10 m3 of air and absorption of 57%. 

Evaluation of worker exposure requires samples in the breathing zone and in general room air or rest area. To define a potential hazard, check compliance with regulations or obtain data for control purposes, samples would normally be collected in the vicinity of the operation itself. In general, samples are collected in the vicinity of the workers directly exposed and also workers remote from the exposure who voice complaints. Sample duration requires that the sample contain sufficient matter for an accurate analysis and is based on the sensitivity of the analytical procedure and the estimated air concentration, as well as the current threshold limit value for the contaminant. Table 1 contains appropriate sampling duration, sample flow rates and sample volume. 

Similar ideas can be used for statistically branched polymers let us, for instance, consider the case of large distances b between branch points, i.e. strong confinement as defined by the inequality (20). Then the tube (of cross section D2) can be subdivided into (D/ )2 subtubes , and the chain, in each of them, is subjected to the tension r[v . When the tension equals the threshold force, this leads again to Eq.(34). Here, the current threshold Jc is much larger than Jcl, and rupture may often occur. To avoid this, we need to operate in situations of mild compression, i.e. with D/Rg not too small. 

Increases the current threshold for testing of new substances from 10 kg to 1 tonne. 

The increase in current threshold to produce thrombi that a test drug elicits becomes the measure of its antithrombotic efficiency. Preliminary in vitro tests with a platelet aggre-gometer that measures light transmission through platelet-rich plasma can also be done. 

Lupanine has been substituted on the 2 (keto)-position, forming benzyl-lupanol and further altered to phenyldehydrosparteine by removal of a molecule of water from the 2 and 3 carbon atoms forming a double bond. With either of these derivatives, a tenfold increase in potency of effects on the isolated frog heart is obtained. Lower concentrations cause ventricular standstill (arrest), sinus bradycardia, and an increase in electrical current (threshold) producing fibrillation (78). 

Some of the early detailed work on this subject was published in 1936 by Ferris, King, Spence and Williams. Much work has been published by Dalziel and his co-authors from about 1941 and 1972, see Reference 1, Chapter 20 Bibliography for details. In this reference [B26] and [B29] showed that the current threshold withstand versus time duration characteristic has an 7-squared-i form, as follows -... 

Buckley and coworkers (1985) have investigated the inhalation toxicity of dimethy-lamine in F-344 rats and B6C3F1 mice. Animals exposed to 175 ppm for 6 h/day, 5 days/week for 12 months showed significant lesions in the nasal passages. Rats developed more extensive olfactory lesions than did mice. The study indicated that olfactory sensory cells were highly sensitive to dimethylamine. Even at a concentration of 10 ppm, the current threshold limit value, the rodents developed minor lesions from exposure. 

To Increase the saturation current threshold of the array, allowing one to maximize Integration time (minimize scan rate) one can use larger area diodes, a decision which must be made prior to an optical design. 

Koch, C., O. Bernander, and R.J. Douglas (1995). Do neurons have a voltage or a current threshold for action potential initiation J. Comput. Neurosci. 2,63-82. 

Sauter AR, Dodgson MS, Kalv0y H, Grimnes S, Stubhaug A, Klaastad 0. 2009. Current threshold for nerve stimulation depends on electrical impedance of the tissue A study of ultrasound-guided electrical nerve stimulation of the median nerve. Anesth Analog 108(4), 1338-1343. 

Many modern semiconductor devices comprise alternating layers of different materials forming superlattices and multiple quantum wells. One well-known example of such structures is the diode laser, a mass-produced device. This device depends on confinement of charges in the two-dimensional structures for enhanced laser output at lowered current thresholds. Such alternating semiconductor layers are usually manufactured either by chemical vapor deposition or by molecular beam epitaxy. The thickness of the layers can be closely controlled in both techniques. As mentioned earlier, electrodeposition also allows good control of thickness. 

A spatial summation effect in the nervous system. The current density is reduced when the same current is spread by a larger electrode, but at the same time a larger number of nerve endings are excited. Consequently, the current threshold is not so much altered when electrode area is changed... 

The second level (1 mA) is due to the direct electric excitation of nerve endings, which must be a function of the local current (density). The electric current threshold of perception with firm hand grip contact and contact area several square centimeters, is around 1 mA. Threshold current has a surprisingly small dependence on contact area. The reason for this is mentioned previously in the chapter on DC perception. With a small area contact around... 

Let-go current threshold (15 mA at 50/60 Hz) is the current level when the current density in muscles and nerves is so large that file external current controls the muscles. Just as the grip muscles are stronger than the opening muscles of the hand, a grip around the current carrying conductor cannot be loosened by the person himself. Let-go current levels are therefore the most important data for safety analysis. The result on Figure 10.20 shows that 1% of the population has a let-go threshold as low as 9 mA at power line frequencies. 

Current Threshold Voltage Threshold Very Approximate Organs Affected Type Comments... 

In online model-based FDI, ARRs are evaluated using measurements from the real system being subject to disturbances. The time evolution of ARR residuals serve as fault indicators. For hybrid systems, ARRs are system mode dependent. Hence, an unobserved mode change invalidates the actual set of ARRs. As a result, computed values of fault indicators may exceed current thresholds indicating faults in some system components that have not happened. ARR residuals derived from a bond graph can not only serve as fault indicators but may also be used for model-based system mode identification. 

Hohnberg et al. and Tikkanen considered workers substantially exposed if their estimated continuous exposure had been at least one-third of the current TLV concentration or if the estimated peak exposure had reached the TLV concentration. Similarly, Ng described high concentrations of toluene (mean 88, range 50-150 ppm) exceeding current standards. All these exposure levels for toluene exceed the current threshold limit value. lOL toluene exposure levels are considerably lower than any value reported in the literafrue. 

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