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Over the years, OS X and iOS have provided increasingly simple ways for developers to manage their code. Two of these features are blocks, which allow you to store chunks of code in variables and call them later, and operation queues, which dramatically simplify how you write applications that do multiple things at once.
These two features are closely tied together, and, once mastered, quickly become indispensable in developing applications.
In this chapter, you’ll learn how to code with blocks, what they’re good for, and how to use them in conjunction with operation queues, a powerful tool for performing tasks in the background.
It’s often useful to be able to store code in variables. Consider the following code sample:
In Objective-C, this is called a block. Blocks store code, and can be assigned to variables, passed to functions, and generally treated like any other value. The big feature is that blocks can be called like functions, and they capture the state of things as they were when the block was created.See All Chapters
|Hamid R. Arabnia, Leonidas Deligiannidis, Jane You, George Jandieri, Ashu M. G. Solo, and Fernando G. Tinetti||CSREA Press|
Int'l Conf. Modeling, Sim. and Vis. Methods | MSV'14 |
Simulink Model of a Full State Observer for a
DC Motor Position, Speed, and Current
Louiza Sellami, Department of Electrical and Computer Engineering
US Naval Academy, Annapolis, MD, 21402, USA
Abstract— In this paper we develop a state observer model for the armature of a DC motor based on the well-known equivalent circuit model, and torque and speed equations. Towards this end, and as a first step, we derive a state space representation for the circuit model, and demonstrate its controllability and observability properties. Using the Luenberger full state observer technique, we derive and implement the latter in
MATLAB/Simulink for position control of the motor, and verify its operation.
Keywords—Circuit Model, State Space, DC Motors, Armature,
Rotor, Luenberger Sate Observer, Simulink.
DC motors are classified into two categories: the permanent magnet type and the electromagnet type, based on how the magnetic field is created. The latter category is further subdivided into self-excited and separately excited, depending on whether there is a physical connection or not between the field windings and the armature windings. If the two windings are connected in series, this is referred to as a series motor.See All Chapters
|John Viega||O'Reilly Media||ePub|
Software has security flaws, as we well know, and we've seen a lot about why it can take time to get software fixed. But most of the time, fixes come out when a vulnerability is announced, and then the bad guys have a field day. Usually, they have at least a month in which they will have little problem finding people who haven't patched.
But why can't we get everybody to patch in a timely manner? After all, don't most programs these days include auto-updaters so we don't have to remember to go check for new software?
There are a couple of problems. In corporate environments, people like to make sure that patches are stable before allowing them to be deployed so as not to impact productivity. A security flaw that isn't being actively exploited, or one that presents a low risk (perhaps because users are mainly behind the firewall, or perhaps users are just expected not to open random documents from around the Net) may not be as risky as installing an unstable patch that causes the program to crash a lot, thereby destroying productivity across an enterprise.See All Chapters
|Elizabeth Jennings||Carcanet Press Ltd.|
Me damage – possibly an act of love
Not fully felt, leaving frustration and
Imagination. We are made up of
Such acts as these. So what has gone awry?
Imprudence or impatience, or perhaps
Simply the ordinary, human traps?
It does not matter; not, at least, if one
Can feel and then accept and further yet,
Learn from the hurt experience has done.
And most of all, maybe, one should forget
And let poems come like flowers which need the sun.
We need to know, we need to feel.
There are great purposes about
And much confusion, much to doubt.
Somebody has to help, to heal.
And personal love is tainted with
A strange despair. I do not know
What forces bring this kind of death.
Animals, flowers, content to grow
In simple ignorance seem all
This planet bears of innocence.
Compassion is the only way
Back to new knowledge and contents.
The stars are out and clear tonight,
The moon is halved. It seems a time
When revelations swiftly come.
Yet it deceives, this light, this light.
We who are lucky calmly live,
Or fairly calmly. Round the worldSee All Chapters
|Mario Dirks||Rocky Nook-IPS||ePub|
The United States Capitol in the blue hour · I wanted to shoot from a frontal perspective with the subject as central and symmetrical as possible. I used a cable release and turned on my camera’s mirror-lock setting to avoid unnecessary vibrations. 28 mm · ISO 200 · f/18 · 8 sec
Jetlag! It’s 5:30 in the morning and the five-hour time difference is making itself known. I can’t sleep another minute for the life of me so I jump up and take a shower. At such an early hour, I decide on a piece of dry toast for breakfast while I prepare myself for the day with a travel guide and an iPad. Researching sights to visit, transit connections, weather, sun conditions, museums, and countless other things about the city are just as critical as making sure I have fully loaded camera batteries, empty memory cards, and a purposeful selection of lenses. The weather is fantastic: a blue sky with the sun shining and no indication of the forecasted snow chaos.
My first outing brings me to the White House. Wow, what an impressive building! Click, click—my first photos of the tour. I attach my polarizing filter to intensify the blue sky. A quick change of perspective...click, click...portrait, click...landscape, click, click. I’m also impressed that there are no other tourists around. Why is that? Finally, I realize that the building in front of me is the US Department of the Treasury. There’s a certain similarity between the two buildings, but the actual White House is about 500 yards to the left. Embarrassing.See All Chapters
Business & Economics