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ONLINE BOOK Principles of Direct Current Machines
Electric machines have a ubiquitous presence in our modern daily lives, from the generators that supply electricity to motors of all sizes that power countless applications. Providing a balanced treatment of the subject, Electric Machines and Drives: Principles, Control, Modeling, and Simulation takes a ground-up approach that emphasizes fundamental principles. The author carefully deploys physical insight, mathematical rigor, and computer simulation to clearly and effectively present electric machines and drive systems.
Suitable for a one semester class at the senior undergraduate or a graduate level, the text supplies simulation cases that can be used as a base and can be supplemented through simulation assignments and small projects. It includes end-of-chapter problems designed to pick up on the points presented in chapters and develop them further or introduce additional aspects. The book provides an understanding of the fundamental laws of physics upon which electric machines operate, allowing students to master the mathematical skills that their modeling and analysis requires.
Why a.c has name as a.c ???Its reason is based on the fact of direction ...In USA the alternating current has frequency of 60Hertz which means the the coil rotates 60Times and in each rotation/Rearly revolution the direction of current changes 120 times...But Why D.C...has Name As d.c
The ACM Learning Center offers ACM members access to lifelong learning tools and resources. Our E-Learning collections offer complimentary access to more than 55,000 online books and videos from top content publishers. The ACM TechTalk series brings leading computing luminaries and visionaries to your screen. Members enjoy exclusive offers and discounts on IT industry certifications and vendor-specific training.
The Code is designed to inspire and guide the ethical conduct of all computing professionals, including current and aspiring practitioners, instructors, students, influencers, and anyone who uses computing technology in an impactful way. Additionally, the Code serves as a basis for remediation when violations occur. The Code includes principles formulated as statements of responsibility, based on the understanding that the public good is always the primary consideration. Each principle is supplemented by guidelines, which provide explanations to assist computing professionals in understanding and applying the principle.
The Wage and Hour Division (WHD) is pleased to announce that online training is now available to assist all federal, state and local contracting agencies with information on federal rules concerning prevailing wages and other labor law requirements. The training modules, presented by WHD staff and its federal agency partners, provide contracting officials with information on the process of obtaining wage determinations; adding classifications to wage determinations (conformances); compliance principles, and enforcement process under both the Davis-Bacon Act (DBA) and the McNamara Service Contract Act (SCA).
Specifically, two training modules are currently being offered online. A four-hour session for the DBA and a second four-hour session on the SCA. These training modules and accompanying PowerPoint presentations are available in their entirety at the following links:
The scope of applications of UD in Higher Education (UDHE) includes all products and environments that directly or indirectly support teaching and learning in higher education. Examples of more narrowly defined scopes are applications of UD to online learning, informal science learning, student services, IT, or physical spaces.
The combination of the principles discussed above can be used to universally design almost any product or environment. In higher education, for example the combined set can be applied to make more inclusive physical spaces, instruction, and online resources. Rather than memorize the fourteen principles that underpin universal design in education (UDE), however, practitioners work toward compliance with them by following three simple guidelines:
One of the challenges in the current state of applications of UD, UDL, UD of IT, is the three different communities engaged in most efforts in each category rarely talk to one another. UD advocates have made strides in the movement to design living spaces that are are usable by people with disabilities or as they age, but not so much in the design of labs and other academic facilities; UDL advocates sometimes apply the three principles but use inaccessible IT in doing so; and UD of IT advocates often look at the design of technology used b educational settings, but not how it interacts with the pedagogy used to deliver instruction.
A great example of how these three sets of principles can be integrated together is when designing a class. Whether the class is in-person or online, the design of the class should strive to be inclusive to all students, including those with disabilities, and allow all students to access the content of the course and fully participate in class activities. Universal design principles can apply to lectures, classroom discussions, group work, handouts, web-based instruction, fieldwork, and other academic activities. The 7 Principles of UD are particularly helpful when designing instructional facilities like computer labs; the 3 Principles of UDL guide the development of teaching curriculum and pedagogy; and the 4 Principles for the UD of IT that underpin the WCAG guide the creation and use of IT used in any application to ensure that it is accessible to, usable by, and inclusive of everyone, including those with disabilities.
The simple motors you see explained in science books are based on apiece of wire bent into a rectangular loop, which is suspended between thepoles of a magnet. (Physicists would call this acurrent-carrying conductor sitting in a magnetic field.) Whenyou hook up a wire like this to a battery, a direct current (DC) flows through it, producing a temporary magnetic field all around it. This temporary fieldrepels the original field from the permanent magnet, causing the wireto flip over.
Normally the wire would stop at that point and then flip back again,but if we use an ingenious, rotating connectioncalled a commutator, we can make the current reverse every time thewire flips over, and that means the wire will keep rotating in thesame direction for as long as the current keeps flowing. That's theessence of the simple DC electric motor, which was conceived in the1820s by Michael Faraday andturned into a practical invention abouta decade later by William Sturgeon. (You'll find more detail in our introductory article on electric motors.)
Artwork: A DC electric motor is based on a loop of wire turning around inside the fixed magnetic field produced by a permanent magnet. The commutator (a split ring) and brushes (carbon contacts to the commutator) reverse the electric current every time the wire turns over, which keeps it rotating in the same direction.
Unlike toys and flashlights, most homes, offices,factories, and other buildings aren't powered by little batteries:they're not supplied with DC current, but with alternating current(AC), which reverses its direction about 50 times per second(with a frequency of 50 Hz). If you want to run a motor from your household AC electricity supply,instead of from a DC battery, you need a different design of motor.
Thus, the current system is based on a few guiding principles, rather than an extensive list of specific rules. While the handbook still describes how to cite sources, it is organized according to the process of documentation, rather than by the sources themselves. This gives writers a flexible method that is near-universally applicable.
Each element should be followed by the corresponding punctuation mark shown above. Earlier editions of the handbook included the place of publication and required different punctuation (such as journal editions in parentheses and colons after issue numbers) depending on the type of source. In the current version, punctuation is simpler (only commas and periods separate the elements), and information about the source is kept to the basics.
In HIV testing, a blood or saliva specimen is collected for testing, typically using indirect ELISA-based tests. The ELISA is a screening tool for HIV detection, but not diagnostic. Diagnosis requires further testing by Western blot due to potential false positives.[4][14] Another virus, Molluscum contagiosum virus (MCV), which commonly infects the skin of children and young adults, can be detected by ELISA testing. ELISA testing in this setting is currently being evaluated for the assessment of global MCV seroprevalence.[15]
To understand the principlesof modern traction power control systems, it is worth a look at the basics of DC and ACcircuitry. DC is direct current - it travels in one direction only along aconductor. AC is alternating current - so called because it changes direction,flowing first one way along the conductor, then the other. It does this veryrapidly. The number of times it changes direction per second is called thefrequency and is measured in Hertz (Hz). It used to be called cycles per second, incase you've read of this in historical papers. In a diagrammatic representation, thetwo types of current appear as shown in the diagram above left.
A diode is a device with nomoving parts, known as a semi-conductor, which allows current to flow through it in onedirection only. It will block any current which tries to flow in the oppositedirection. Four diodes arranged in a bridge configuration, as shown below,use this property to convert AC into DC or to "rectify" it. It is called a"bridge rectifier". Diodes quickly became popular for railway applicationsbecause they represent a low maintenance option. They first appeared inthe late 1960s when diode rectifiers were introduced on 25 kV AC electric locomotives. 2ff7e9595c
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