Effects of Oxidation in Everyday Life
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The World Health Organization defines life skills as "abilities for adaptive and positive behaviour that enable individuals to deal effectively with the demands and challenges of everyday life." In primary and secondary education, life skills may refer to a skill set that accommodates more specific needs of modern industrialized life; examples include money management, food preparation, hygiene, basic literacy and numeracy, and organizational skills. Life skills are sometimes, but not always, distinguished from occupational skills.
The United Nations Children's Fund (UNICEF) and the United Nations Educational, Scientific and Cultural Organization (UNESCO) divide life skills into subsets of categories:
Learning to know: Cognitive abilities
Decision making / problem solving skills
- Information gathering skills
- Evaluating future consequences of present actions for self and others
- Determining alternative solutions to problems
- Analysis skills regarding the influence of values and attitudes of self and others on motivation
Critical thinking skills
- Analyzing peer and media influences
- Analyzing attitudes, values, social norms and beliefs and factors affecting these
- Identifying relevant information and information sources
Learning to be: Personal abilities
Skills for increasing internal locus of control
- Self-esteem and confidence-building skills
- Self-awareness skills including awareness of rights, influences, values, attitudes, strengths and weaknesses
- Goal-setting skills
- Self-evaluation, self-assessment, and self-monitoring skills
Skills for managing feelings
Skills for managing stress
Learning to live together: Interpersonal abilities
Interpersonal communication skills
- Verbal and nonverbal communication
- Active listening
- Expressing feelings; giving feedback (without blaming) and receiving feedback
Negotiation and refusal skills
- Ability to listen to and understand another's needs and circumstances and express that understanding
Cooperation and teamwork
- Expressing respect for others' contributions and different styles
- Assessing one's own abilities and contributing to the group
A varistor is an electronic component with a "diode-like" nonlinearcurrentâ€“voltage characteristic. The name is a portmanteau of variable resistor. Varistors are often used to protectcircuits against excessive transient voltages by incorporating them into the circuit in such a way that, when triggered, they will shunt the current created by the high voltage away from the sensitive components. A varistor is also known as Voltage Dependent Resistor or VDR. A varistorâ€™s function is to conduct significantly increased current when voltage is excessive.
Metal oxide varistor
The most common type of varistor is the Metal Oxide Varistor (MOV). This contains a ceramic mass of zinc oxide grains, in a matrix of other metal oxides (such as small amounts of bismuth, cobalt, manganese) sandwiched between two metal plates (the electrodes). The boundary between each grain and its neighbour forms a diode junction, which allows current to flow in only one direction. The mass of randomly oriented grains is electrically equivalent to a network of back-to-back diode pairs, each pair in parallel with many other pairs. When a small or moderate voltage is applied across the electrodes, only a tiny current flows, caused by reverse leakage through the diode junctions. When a large voltage is applied, the diode junction breaks down due to a combination of thermionic emission and electron tunneling, and a large current flows. The result of this behavior is a highly nonlinear current-voltage characteristic, in which the MOV has a high resistance at low voltages and a low resistance at high voltages.
Follow-through current as a result of a lightning strike may generate excessive current that permanently damages a varistor. In general, the primary case of varistor breakdown is localized heating caused as an effect of thermal runaway. This is due to a lack of conformality in individual grain-boundary junctions, which leads to the failure of dominant current paths under thermal stress.
Varistors can absorb part of a surge. How much effect this has on risk to connected equipment depends on the equipment and details of the selected varistor. Varistors do not absorb a significant percentage of a lightning strike, as energy that must be conducted elsewhere is many orders of magnitude greater than what is absorbed by the small device.
A varistor remains non-conductive as a shunt mode device during normal operation when voltage remains well below its "clamping voltage". If a transient pulse (often measured in joules) is too high, the device may melt, burn, vaporize, or otherwise be damaged or destroyed. This (catastrophic) failure occurs when "Absolute Maximum Ratings" in manufacturer's datasheet are significantly exceeded. Varistor degradation is defined by manufacturer's life expectancy charts using curves that relate current, time, and number of transient pulses. A varistor fully degrades typically when its "clamping voltage" has changed by 10%. A fully degraded varistor remains functional (no catastrophic failure) and is not visibly damaged.
Ballpark number for varistor life expectancy is its energy rating. As MOV joules increase, the number of transient pulses increases and the "clamping voltage" during each transient decreases. The purpose of this shunt mode device is to divert a transient so that pulse energy will be dissipated elsewhere. Some energy is also absorbed by the varistor because a varistor is not a perfect conductor. Less energy is absorbed by a varistor, the varistor is more conductive, and its life expectancy increases exponentially as varistor energy rating is increased. Catastrophic failure can be avoided by significantly increasing varistor energy ratings either by using a varistor of higher joules or by connecting more of these shunt mode devices in parallel.
Important parameters are the varistor's energy rating in joules, operating voltage, response time, maximum current, and breakdown (clamping) voltage. Energy rating is often defined using standardized transients such as 8/20 microseconds or 10/1000 microseconds, where 8 microseconds is the transient's front time and 20 microseconds is the time to half value.
To protect communications lines (such as telephone lines) transient suppression devices such as 3 mil carbon blocks (IEEE C62.32), ultra-low capacitance varistors or avalanche diodes are used. For higher frequencies such as radio communication equipment, a gas discharge tube (GDT) may be utilized.
A typical surge protectorpower strip is built using MOVs. A cheapest kind may use just one varistor, from hot (live, active) to neutral. A better protector would contain at least three varistors; one across each of the three pairs of conductors (hot-neutral, hot-ground, neutral-ground). A power strip protector in the United States should have a UL1449 3rd edition approval so that catastrophic MOV failure would not create a fire hazard.
While a MOV is designed to conduct significant power for very short durations (â‰ˆ 8/20 microseconds), such as caused by lightning strikes, it typically does not have the capacity to conduct sustained energy. Under normal utility voltage conditions, this is not a problem. However, certain types of faults on the utility power grid can result in sustained over-voltage conditions. Examples include a loss of a neutral conductor or shorted lines on the high voltage system. Application of sustained over-voltage to a MOV can cause high dissipation, potentially resulting in the MOV device catching fire. The National Fire Protection Association (NFPA) has documented many cases of catastrophic fires that have been caused by MOV devices in surge suppressors, and has issued bulletins on the issue.
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Answers:Hi I'll get back to you with the answer when my daughter returns with her books from school . Hi I'm back as promised - Acid rain can cause serious damage. It kills trees and destroys many wildlife habitats. Areas of forest in eastern North America, central Europe and parts of Asia are dying because rain. When acid rain falls into lakes and rivers, it harms the fish, plants and other freshwater life. Wetland species of birds such as the Japaneses crane and the whooping crane are thretened by acid rain as it destroys their habitat.This couldmake them extinct. In cities, acid rain can even attack the stonework of buildings, an example of this is the Taj Mahal in India which is made of marble - It's starting to turn yellow because of the acid rain.