Page Box 4. The continued growth has placed high demand on an unstable water supply network, designed to extract most of the city's water 72 percent from the Mexico City Aquifer, which underlies the metropolitan area.
The largest group of emitted compounds are hydrocarbons including aromatic ones: A significant contribution also originates from esters of short-chain organic acids, terpenes, formaldehyde and phenols.
However, correct evaluation of outdoor and indoor air is not an easy task. Air is a quite complicated system subjected to changes even in a short period of time.
Recently observed dynamic progress in analytical methods and analytical instruments is a basis for obtaining reliable information on indoor and outdoor air condition and quality.
However, this progress leads to an increase in the cost of monitoring and air quality evaluation, which significantly limits their widespread application.
Hence, alternative methods of acquisition of the information on air quality are being sought. Special attention is paid to sensor techniques [ 222324 ]. Numerous advantages of the chemical sensors include: VOCs concentration level in air determines selection of the chemical sensors for their measurement.
In the case of measurement of exhaust gases and indoor air at workplace, applicability of the chemical sensors is relatively high due to practical and economic advantages of these sensors.
The authors of this paper want to present up-to-date solutions available on the market as far as the chemical sensors for measurement of volatile organic compounds in outdoor and indoor air are concerned.
Characteristics of the Chemical Sensors for Detection of VOCs In the case of commercially available chemical sensors for detection of volatile organic compounds one can distinguish two main approaches: The latter group intended for detection of toxic gases belonging to VOCs includes electrochemical, semiconductor with solid electrolyte and PID-type sensors photoionization detectors [ 2526 ].
Obviously, the main objective of the manufacturers is elaboration of a sensor with the best selective properties and with the low limit of quantification LOQ. Figure 1 presents the concentration range of VOCs present in ambient air, indoor air at workplace and in exhaust gases.
The figure also shows, which commercially available sensors are designated for detection and measurement of VOCs in ambient air, indoor air at workplace and in exhaust gases. Design and operation principle of these sensors were described below.
Electrochemical Amperometric Sensors In these sensors analyte particles diffuse through a membrane separating gas environment from an internal electrolyte and the internal electrolyte most frequently aqueous solution of strong acids or bases, although mixtures with aprotic solvent are also utilized towards the surface of a working electrode suitably polarized with respect to a reference electrode.
Electrochemical reaction occurs at the working electrode, whereas a counter electrode experiences the reaction providing electron balance.
A result of the redox reaction is generation of electric current being a sensor signal. This signal is proportional to concentration of the analyte present in direct vicinity of the sensor gas environment [ 2728 ].
Figure 2 schematically illustrates design of the electrochemical sensor in a three-electrode version with the working measurement electrode, counter electrode and reference electrode of constant potential with respect to the working electrode. Table 1 presents commercially available electrochemical amperometric sensors by Environmental Sensors Co.
Metal Oxide Semiconductor Sensors In these sensors analyte particles diffuse towards the receptor surface, which is metal oxide maintained at suitable temperature using heater where they undergo chemisorption.
This interaction results in change of resistance of the receptor element. Two types of metal oxide semiconductors are utilized in measurement practice: The sensing mechanism of semiconducting n-type metal oxides is based on a phenomenon of chemisorption of oxygen contained in air on the metal oxide layer.
Adsorbed oxygen molecules trap the electrons from a conducting band of the semiconductor. It results in formation of energetic barriers between the grains of metal oxides, which block a flow of electrons.
The consequence is an increase in resistance of the chemically sensitive layer of the sensor. Resistance of the chemically sensitive layer drops when gas molecules of reducing character appear.
They react with bound oxygen leading to liberation of electrons. Reverse principle of operation occurs for p-type metal oxides, which identify oxidizing gases.
The molecules of gas compounds remove electrons from the chemically sensitive layer, thus forming electron holes charge carriers. The process of signal generation change of resistance in the semiconductor sensors is not fully recognized. It is complex and consists of a number of co-existing phenomena:Yet, there is no logical reason to associate the term innovation with large-scale discontinuous change.
Consistent with a dictionary definition, innovation is best associated with creative solutions, and these can occur at a small as well as a large scale, and can be more, or less, discontinuous.
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All in all, Military Innovation in the Interwar Period is a major contribution to today’s key institutional challenge. It highlights invaluable lessons about how the Marine Corps can adapt in a fluid age of murky threats and revolutionary technological change.
Managing for the Future management methods and structures are failing to adequately accommodate a complexity-based world view, which is characterized by discontinuous change, hyper competition and the exponential explosion of information science. Automation is the technology by which a process or procedure is performed with minimum human assistance.
Automation or automatic control is the use of various control systems for operating equipment such as machinery, processes in factories, boilers and heat treating ovens, switching on telephone networks, steering and stabilization of ships, aircraft and other applications and vehicles .
â€œOutline and discuss the concept of rapid, volatile, discontinuous change and its impact on the strategic management of organisations You are asked to write and submit a short, scholarly essay, using an academic essay format, on the following topic: â€œOutline and discuss the concept of rapid, volatile, discontinuous change and its.