ItemLECTURES IN BIOMEDICAL ENGINEERING MEDICAL GASES OXYGEN CONCENTRATORS SUCTION PUMPS VENTILATORS 2020(UHANDISI WA BIOMEDICAL, 2020) ItemX-ray diagnostic equipment(EWH, 1990)X-rays are invisible. Because of their high energy and short wavelength they can penetrate almost all materials, but are absorbed to a different extent by different tissues. In the human body, absorption is high for bones, and low for muscles and other soft tissues. These differences in absorption can be shown on a photographic film as differences in density: the result is a radiograph. Thus, radiographic examination consists of irradiating a part of the patient with a uniform beam of X—rays and recording the emerging rays on a double emulsion film sandwiched between a pair of fluorescent screens. The screens convert the X-rays into light, which in turn exposes the X-ray film. The screens and the film are enclosed in a cassette for protection from daylight. After the exposure, the film must be processed, manually or automatically, in a darkroom by means of developer and fixer solutions. X-ray examinations should be ordered only by physicians or experienced clinical health workers. "Routine" examinations are seldom indicated. A few of the more common indications and examinations that can be performed with diagnostic X-ray equipment are listed below (this is not a complete list). ItemThe WHO Basic Radiological System (WHO-BRS)(WHO, 1995)The rugged, high-quality X-ray equipment specified for the W H O Basic Radio logical System (BRS) is ideally suited for small clinics, health stations, first-referral hospitals, and general practices under the supervision of a general practitioner. In these situations, the population served is often in the range 10 000—100 000. At this level, no fluoroscopy should be undertaken. ItemPipettes, Autopipettes, and Dispensers(WHO, 2005)Mechanical micropipettes (Fig. 2.22) can only be recommended where a reliable supply of new disposable tips is readily available. They are used for the delivery and/or dilution of biological samples in the volume range 5-1000 |al. They are usually of air displacement (indirect) or direct displacement design. To avoid contamination between consecutive samples, most pipettes have a disposable tip that is discarded after each delivery. This greatly increases the cost per test. The practice of washing and reusing disposable tips is not recommended, as any cleaning procedures will change the "wettability" of the plastic. In addition, drying at only slightly elevated temperatures may distort the tip, and prevent a good pneumatic seal with the pipette body. ItemOphthalmoscopes and otoscopes(WHO, 1995)If the instrument is not in use for any length of time, remove the batteries to prevent corrosion. Removal of batteries that have corroded can be difficult. If the rheostat assembly can be removed from the handle, soaking the handle in boiling water helps to dislodge the batteries. Some handles have a hole in the bottom; in this case introduce a punch through the hole to tap the batteries out. A fter removal of the batteries, thoroughly clean the handle. ItemFlame photometers(WHO, 1995)Flame photometers are used routinely for the measurement of lithium (Li), sodium (Na), and potassium (K) in body fluids. More sophisticated instruments can also measure calcium (Ca). In flame photometry, an aqueous salt solution is dispersed in air. The salt in the dispersed droplets is transferred into a gaseous state by heating with a flame, and then quickly disintegrates into gaseous atoms. Above a critical temperature the atoms absorb energy, which excites the electrons into higher energy states. When the excited electrons return to their original state, they emit the absorbed energy as light. The wavelength of the light emitted by each metal is characteristic for that element. The intensity of the light emitted at the given wavelength is proportional to the number of excited metal atoms and can be measured with a suitable optical filter and photodetector. ItemLessons In Electric Circuits, Volume VI – Experiments(2010) Kuphaldt, TonyElectronics is a science, and a very accessible science at that. With other areas of scientific study, expensive equipment is generally required to perform any non-trivial experiments. Not so with electronics. Many advanced concepts may be explored using parts and equipment totaling under a few hundred US dollars. This is good, because hands-on experimentation is vital to gaining scientific knowledge about any subject. When I started writing Lessons In Electric Circuits, my intent was to create a textbook suitable for introductory college use. However, being mostly self-taught in electronics myself, I knew the value of a good textbook to hobbyists and experimenters not enrolled in any formal electronics course. Many people selflessly volunteered their time and expertise in helping me learn electronics when I was younger, and my intent is to honor their service and love by giving back to the world what they gave to me. In order for someone to teach themselves a science such as electronics, they must engage in hands-on experimentation. Knowledge gleaned from books alone has limited use, especially in scientific endeavors. If my contribution to society is to be complete, I must include a guide to experimentation along with the text(s) on theory, so that the individual learning on their own has a resource to guide their experimental adventures. A formal laboratory course for college electronics study requires an enormous amount of work to prepare, and usually must be based around specific parts and equipment so that the 1 2 CHAPTER1. INTRODUCTION experiments will be sufficient detailed, with results sufficiently precise to allow for rigorous comparison between experimental and theoretical data. A process of assessment, articulated through a qualified instructor, is also vital to guarantee that a certain level of learning has taken place. Peer review (comparison of experimental results with the work of others) is an- other important component of college-level laboratory study, and helps to improve the quality of learning. Since I cannot meet these criteria through the medium of a book, it is impractical for me to present a complete laboratory course here. In the interest of keeping this experiment guide reasonably low-cost for people to follow, and practical for deployment over the internet, I am forced to design the experiments at a lower level than what would be expected for a college lab course. ItemLessons In Electric Circuits, Volume V – Reference(2007) Kuphaldt, TonyConverting between units is easy if you have a set of equivalencies to work with. Suppose we wanted to convert an energy quantity of 2500 calories into watt-hours. What we would need to do is find a set of equivalent figures for those units. In our reference here, we see that 251.996 calories is physically equal to 0.293071 watt hour. To convert from calories into watt-hours, we must form a ”unity fraction” with these physically equal figures (a fraction composed of different figures and different units, the numerator and denominator being physically equal to one another), placing the desired unit in the numerator and the initial unit in the denominator, and then multiply our initial value of calories by that fraction. Since both terms of the ”unity fraction” are physically equal to one another, the fraction as a whole has a physical value of 1, and so does not change the true value of any figure when multiplied by it. When units are canceled, however, there will be a change in units. ItemLessons In Electric Circuits, Volume IV – Digital(2007) Kuphaldt, TonyThe expression of numerical quantities is something we tend to take for granted. This is both a good and a bad thing in the study of electronics. It is good, in that we’re accustomed to the use and manipulation of numbers for the many calculations used in analyzing electronic circuits. On the other hand, the particular system of notation we’ve been taught from grade school onward is not the system used internally in modern electronic computing devices, and learning any different system of notation requires some re-examination of deeply ingrained assumptions. First, we have to distinguish the difference between numbers and the symbols we use to represent numbers. A number is a mathematical quantity, usually correlated in electronics to a physical quantity such as voltage, current, or resistance. There are many different types of numbers. ItemLessons In Electric Circuits, Volume III – Semiconductors(2009) Kuphaldt, TonyThis third volume of the book series Lessons In Electric Circuits makes a departure from the former two in that the transition between electric circuits and electronic circuits is formally crossed. Electric circuits are connections of conductive wires and other devices whereby the uniform flow of electrons occurs. Electronic circuits add a new dimension to electric circuits in that some means of control is exerted over the flow of electrons by another electrical signal, either a voltage or a current. ItemLessons In Electric Circuits, Volume II – AC(2007) Kuphaldt, TonyMost students of electricity begin their study with what is known as direct current (DC), which is electricity flowing in a constant direction, and/or possessing a voltage with constant polarity. DC is the kind of electricity made by a battery (with definite positive and negative terminals), or the kind of charge generated by rubbing certain types of materials against each other. As useful and as easy to understand as DC is, it is not the only “kind” of electricity in use. Certain sources of electricity (most notably, rotary electro-mechanical generators) naturally produce voltages alternating in polarity, reversing positive and negative over time. Either as a voltage switching polarity or as a current switching direction back and forth, this “kind” of electricity is known as Alternating Current (AC): Figure 1.1 Whereas the familiar battery symbol is used as a generic symbol for any DC voltage source, the circle with the wavy line inside is the generic symbol for any AC voltage source. One might wonder why anyone would bother with such a thing as AC. It is true that in some cases AC holds no practical advantage over DC. In applications where electricity is used to dissipate energy in the form of heat, the polarity or direction of current is irrelevant, so long as there is enough voltage and current to the load to produce the desired heat (power dissipation). However, with AC it is possible to build electric generators, motors and power distribution systems that are far more efficient than DC, and so we find AC used predominately across the world in high power applications. To explain the details of why this is so, a bit of background knowledge about AC is necessary. ItemLessons In Electric Circuits, Volume I – DC(2006) Kuphaldt, TonyOne pioneering researcher, Benjamin Franklin, came to the conclusion that there was only one fluid exchanged between rubbed objects, and that the two different ”charges” were nothing more than either an excess or a deficiency of that one fluid. After experimenting with wax and wool, Franklin suggested that the coarse wool removed some of this invisible fluid from the smooth wax, causing an excess of fluid on the wool and a deficiency of fluid on the wax. The resulting disparity in fluid content between the wool and wax would then cause an attractive force, as the fluid tried to regain its former balance between the two materials. Postulating the existence of a single ”fluid” that was either gained or lost through rubbing accounted best for the observed behavior: that all these materials fell neatly into one of two categories when rubbed, and most importantly, that the two active materials rubbed against each other always fell into opposing categories as evidenced by their invariable attraction to one another. In other words, there was never a time where two materials rubbed against each other both became either positive or negative.