Is the speed of a satellite self maintained ? Or it needs anything to be done externally ?  Condition : The satellite is in the orbit where it is held in equilibrium by the force of gravity and its centrifugal force.
The orbit of satellites around Earth eventually decays, or so I read. This is typically caused either by atmospheric drag, or by tides. I would assume most satellites have a limited service life in orbit. Hence the question - What is the typical orbital life of a satellite? How long before it's successor must be launched into orbit ?  EDIT: For instance, a weather satellite
Is there an Amazon.com API to retrieve product reviews? What are the main reasons the elves did not show up in force to defeat Sauron? During The Great Battle of the Last Alliance, there were an estimated 100,000 elves that fought with the armies of Isildur. This was one of the first scenes in the first LOTR movie. However, in the trilogy, it appears that only a small number of elves show up to Helms Deep and overall left the majority of the fighting to the humans. Why did the elves not participate during the rest of the war? How full is too full for mechanical hard drives? I have heard many claim that it doesn't matter how full a drive is until it starts cutting into temp and virtual memory space.  This doesn't make sense to me, given the nature of how the data is transacted on a hard drive. The inside of the platter presents less data per revolution than the outside of the drive does, by significant factors. The inside 40% of the radius of full size hard drive is used for the spindle, so only the outside 60% is used for data storage, but that still means that the inside track of a hard drive presents data 60% slower than the outside track.  By my calculation, a Hard drive that is only 10% full should perform about 2.25 times faster than a hard drive that is 90% full, assuming that the flow is constrained by other factors.  Am I wildly off base here? For all the drives I know, even the top speeds of the first 1% of the drive would be well within the bandwidth provided by a SATA 2 connection. Find Oracle JDBC driver in Maven repository Changing password? I would like to change my password.  I have followed the instructions in  but I cannot find the "my logins" hyperlink. I need to grant select permission for all tables owned by a specific user to another user.  Can I do this with a single command along the lines of:  Grant Select on OwningUser.* to ReceivingUser   Or do I have to generate the sql for each table with something along the lines of:   Select 'GRANT SELECT ON OwningUser.'||Table_Name||'TO ReceivingUser'   From All_Tables Where Owner='OWNINGUSER' I am trying to get an intuitive idea of how the  affects Quantum computation. My understanding is that given a qubit $Q$ in superposition $Q_0 \left| 0 \right&gt; + Q_1 \left| 1 \right&gt;$, NCT states another Qubit $S$ cannot be designed such that $S$ is equivalent to the state of $Q$.   Now the catch is, what does Equivalent mean? It could mean either that:   $S = S_0 \left| 0 \right&gt; + S_1 \left| 1 \right&gt;$ such that $S_0 = Q_0, S_1 = Q_1$. Or it could mean that $S = Q$, meaning that if $S$ is observed to be some value ( for example 0) then $Q$ MUST be that same value, and vice versa.    So it seems that point 2, occurs anyways in entangled systems (particularly cat-states), so I can eliminate that option and conclude that that No Cloning states, given a qubit $Q$, it's impossible to make another qubit $S$ such that:  $S = S_0 \left| 0 \right&gt; + S_1 \left| 1 \right&gt;$ such that $S_0 = Q_0, S_1 = Q_1$.  Is this correct? There are two syntaxes for command substitution: with dollar-parentheses and with backticks. Running top -p $(pidof init) and top -p `pidof init` gives the same output. Are these two ways of doing the same thing, or are there differences? Do I need a Japanese transit visa when arriving at Narita and departing from Haneda? I'm arriving from New Delhi, India (Indian passport) with JAL at Narita on 11th July at 07:30 and departing for San Francisco with JAL at 00:05 on 12th July from Haneda. Do I need a transit visa as I'll be switching airports and spending a few hours at JAL City Haneda Airport Hotel?  Previously I had connecting flights from Narita to San Francisco and obtained shore passes to relax at Narita Nikko Hotel. Now I'm travelling with my elderly Mom and do not want complications at Narita immigration or later in the day while going from Narita Airport to Haneda airport. Please advise. dual boot missing files on ntfs I have 3 partitions: one for Windows 7 (ntfs), one for Ubuntu (ext4) and one just for data (ntfs so both operating systems can see them).  My problem is that I had stored some files on the data partition using Ubuntu and when I booted Windows 7 all that data was gone! After that I couldn't find the files even when using Ubuntu.  My files were simply GONE :(  Is there something I can do in Ubuntu or is it just windows problem? I am having trouble with the following problem.      Let $R$ be an integral domain, and let $a \in R$ be a non-zero element. Let $D = \{1, a, a^2, ...\}$. I need to show that $R_D \cong R[x]/(ax-1)$.    I just want a hint.  Basically, I've been looking for a surjective homomorphism from $R[x]$ to $R_D$, but everything I've tried has failed. I think the fact that $f(a)$ is a unit, where $f$ is our mapping, is relevant, but I'm not sure. Thanks Internal or external oscillator I always use the internal oscillator that pics have as I have never found the need to run anything at higher frequency than 8 MHz (which is the fastest the pics I use tend to be able to go). Are there any reasons, beyond going above 8 MHz, that mean I should use an external oscillator? It just seems like one more thing to go wrong to me but I'd be interested to hear what others do. Steady-State Current I am in the process of completing some homework and have come across a question that says: "What is the steady-state current?" It is asking in reference to a circuit that includes two capacitors in parrallel and a DC source of 24V and an AC source given by $\epsilon = 20 \cos(120 \pi t)\ \text{V}$, where $t$ is in seconds. I assume that it is asking when the current is constant. Because naturally the current is not constant due to the AC source, would I just consider the DC source for this? How to do selective-color in Photoshop? How to make the single color in a photography to be color and other parts changed to B&amp;W?.  Don't know exactly the name of the effect, to be more clear in the following photo I want the green part to be green and other parts( leg and sandal) in B&amp;W..    How to achieve that effect in Photoshop? The   echo one; echo two &gt; &gt;(cat); echo three;    command gives unexpected output.  I read this:  and many other articles about process substitution on the internet, but don't understand why it behaves this way.  Expected output:  one two three   Real output:  prompt$ echo one; echo two &gt; &gt;(cat); echo three; one three prompt$ two   Also, this two commands should be equivalent from my point of view, but they don't:  ##### first command - the pipe is used. prompt$ seq 1 5 | cat 1 2 3 4 5 ##### second command - the process substitution and redirection are used. prompt$ seq 1 5 &gt; &gt;(cat) prompt$ 1 2 3 4 5   Why I think, they should be the same? Because, both connects the seq output to the cat input through the anonymous pipe - .  Question: Why it behaves this way? Where is my error? The comprehensive answer is desired (with explanation of how the bash does it under the hood). Windows 7 sleeping during operations I've got Windows 7 set up on my media box.  It's set to sleep after 30 mins of inactivity, but it doesn't seem to work as advertised. In the last two weeks it's gone to sleep during a file copy operation and again while encoding an MP4 file.  Is there any way to get Windows to realise that it's actually busy? Continuous extension of a real function Related;    This is the theorem i need to prove;  "Let $E(\subset \mathbb{R})$ be closed subset and $f:E\rightarrow \mathbb{R}$ be a contiuous function. Then there exists a continuous function $g:\mathbb{R} \rightarrow \mathbb{R}$ such that $g(x)=f(x), \forall x\in E$."  I have tried hours to prove this, but couldn't. I found some solutions, but ridiculously all are wrong. Every solution states that "If $x\in E$ and $x$ is not an interior point of $E$, then $x$ is an endpoint of a segment of at most countable collection of disjoint segments.". However, this is indeed false! (Check Arthur's argument in the link above)  Wrong solution Q4.5;    Just like the argument in this solution, i can see that $g$ is continuous on $E^c$ and $Int(E)$. But how do i show that $g$ is continuous on $E$? What is the optimal order of post-processing steps? What is the procedure for taking down Titans? LINQ Select Distinct with Anonymous Types So I have a collection of objects.  The exact type isn't important.  From it I want to extract all the unique pairs of a pair of particular properties, thusly:  myObjectCollection.Select(item=&gt;new                                 {                                      Alpha = item.propOne,                                      Bravo = item.propTwo                                 }                  ).Distinct();   So my question is:  Will Distinct in this case use the default object equals (which will be useless to me, since each object is new) or can it be told to do a different equals (in this case, equal values of Alpha and Bravo => equal instances)?  Is there any way to achieve that result, if this doesn't do it?