I'm looking at connecting relays,  In the schematic found on this site, the diode is placed in parallel. Why would this be the case? If the diode is there to circumvent large voltage flow back, wouldn't this skip pass the diode and go straight to the arduino?
In most electrical circuits with a relay, a diode is connected in parallel to the coil of the relay. Why? Is it always a good practice?
Best practices for making a WordPress site "movable"? I'm planning to buy a domain and install a WordPress site on it at a web-hosting company.  But first I'll need to iron-out some bugs...  I got a working LAMP-stack at my home-computer, so I'm thinking about first installing my site locally - off the Internet.  I'll be mostly tweaking and making "test-posts" to check that everything works, but I'll probably also make some posts I'd like to keep when I move the site and take it online.  When I'm done chasing bugs; I guess I'll just package the public_html|www directory-tree and upload it to the web-hosting company, and also export the database from my home-computer to the web-hosting.    What I'm wondering if there are some "best practices", some do-s and don't-s, some major pits to take note of?    For example, how can ensure the smooth transition of domain-name in posts and links as such, from localhost to whatever-i-end-up-buying.com (I know from previous attempt of running WordPress at my home computer, that this didn't always work quite well...). After some searching, I find very little on the incorporation of observation weights/measurement errors into principal components analysis. What I do find tends to rely on iterative approaches to include weightings (e.g., ). My question is why is this approach necessary? Why can't we use the eigenvectors of the weighted covariance matrix? Which PHP function can return the current date/time? How do I run executable scripts in Nautilus? Automatically highlight undefined references Query to list number of records in each table in a database I am looking for a method to process a remote sensing image and extract the crown areas of the individual trees from the image.   I have both visual wavelength areal imagery, and lidar data from the area. The location in question is a desert area, so the tree cover isn't as dense as a forest area. The resolution of the aerial imagery is 0.5 feet by 0.5 feet. The lidar resolution is approximately 1 x 1 feet. Both the visual data and the lidar come from a Pima County, Arizona dataset. A sample of the type of aerial imagery I have is at the end of this post.   This question  seems to be the same issue, but there does not seem to be a good answer there.  I can obtain a reasonable classification of the vegetation types (and information about the overall percent cover) in the area by using the Iso Cluster classification in Arcmap, but this provides little information on individual trees. The closest I have to what I want is the results of passing the output of the isocluster classification through the Raster to Polygon feature in Arcmap. The problem is that this method merges near by trees into a single polygon.   Edit: I probably should have included some more detail about what I have. The raw datasets I have are:    Full las data, and a tiff raster generated from it. Visual imagery (like the sample image shown, but covering a much wider area)  Manual direct measurements of a subset of the trees in the area.    From these I have generated:    The ground/vegetation classifications. The DEM/DSM rasters. I'm trying to solve this problem from Hatcher 3.3.24.  Let $M$ be a closed connected 3-manifold, and write $H_1(M, \mathbb{Z})$ as $\mathbb{Z^r} \oplus T$ where $T$ is torsion. Show that $H_2(M, \mathbb{Z})$ is $\mathbb{Z^r}$ if $M$ is orientable or $\mathbb{Z^{r-1}} \oplus \mathbb{Z_2}$ if $M$ is not orientable. In particular $r \geq 1$ if $M$ is not orientable. Using exercise 6 construct examples showing there are no other restrictions on the homology groups of closed 3-manifolds. (In the nonorientable case consider the manifold $N$ obtained from $S^2 \times I$ by identifying $S^2 \times \{0\}$ with $S^2 \times \{1\}$ via a reflection of $S^2$.)  I think I've solved the first part, here's my proof:   First note the following theorem: If $M$ is a closed connected and orientable n-manifold then $H_n(M, \mathbb{Z}) = \mathbb{Z}$ and $Tors(H_{n-1}(M, \mathbb{Z})) = 0$. If nonorientable, then $H_n(M, \mathbb{Z}) = 0$, $Tors(H_{n-1}(M, \mathbb{Z})) = \mathbb{Z_2}$.  Now note by Poincare duality and UCT we have that $H_2(M) \cong H^1(M) \cong \mathbb{Z^r} \oplus T_0 \cong \mathbb{Z^r}$.   In the nonorientable case consider the exact sequence:  $0 \longrightarrow H_2(M) \longrightarrow H_1(M) \longrightarrow H_0(M) \longrightarrow 0$  But we know $H_1(M) = \mathbb{Z^r} \oplus Z_2$ from the earlier theorem and $H_0(M) = \mathbb{Z}$.   Therefore $H_2(M) \cong ker(\mathbb{Z^r} \oplus Z_2 \rightarrow \mathbb{Z}) \cong \mathbb{Z^{r-1}} \oplus \mathbb{Z_2}$.   For the rest of the question I'm quite lost. How do I remove duplicate "Open With" context menu items in Finder.app? For whatever reason, the "Open With" context menu in Finder is always listing every app four times (exactly).     I've read about (and tried) rebuilding the Launch Services database to restore the context menu to its initial state, but nothing seems to work. I've also used Onyx.app to clear user and system caches, but I'm still left with four repetitions of each app under the "Open With" service. I have restarted the system a few times just to be sure it was not some temporary corruption of the list.  I'm running OS X 10.6.6 on a 2011 17" MacBook Pro with a fresh install of OS X (i.e. I didn't use Migration Assistant.app or a Time Machine backup). I did, however, sync all my preferences and other files using MobileMe like I always do, so I imagine it's feasible that a preference file somewhere is causing problems? I didn't notice whether this was happening before or after my MobileMe sync.  How can I fix this so one app shows? What's the origin of referring to female superior officers as "sir"? It is well established in Star Trek: The Next Generation that female superior officers are normally referred to as sir.  This is applied to Dr. Crusher, Counselor Troi, Cmdr. Shelby, Maj. Kira, Lt. Dax, and numerous admirals.   This obviously fits in well with the egalitarian ideals of Star Trek. This convention is made explicit in &quot;Thine Own Self&quot;:  DATA: Counsellor, have you been promoted in my absence? TROI: That's right. Which means from now on you can call me sir. DATA: Yes, sir.  In Addition, the first episode of Star Trek: Voyager, &quot;Caretaker&quot; contains this dialog:  KIM: Thank you, sir. JANEWAY: Mister Kim, at ease before you sprain something. Ensign, despite Starfleet protocol, I don't like being addressed as sir. KIM: I'm sorry, ma'am. JANEWAY: Ma'am is acceptable in a crunch, but I prefer Captain. We're getting ready to leave. Let me show you to the bridge.  which again establishes that sir is the norm, although Capt. Janeway doesn't prefer it. Did this usage of the honorific sir start with ST: TNG or does it predate TNG in either sci-fi or the real world?  Related: Is there a way to set the gnome-terminal title from within the terminal itself without having to right click on the tab. Something like:  active-terminal --title "Foo"   There was a related question previously with an answer that almost lets you do this:  but that doesn't set the gnome-terminal tab title only the window title. Multicollinearity in Decision Tree Can anybody please explain the affect of multicollinearity on Decision Tree algorithms (Classification and regression). I have done some searching but was not able to find the right answer as some say it affects it and others say it doesn't. How to prove that compact subspaces of the Sorgenfrey line are countable? How to prove that every compact subspace of the  is countable? Recovering from a move of /home when it's encrypted (ecryptfs) I had a 20GB / partition at work that dual-booted with Windows and it quickly ran out of space. I usually do 20GB / and 160GB (or whatever the rest of the hard drive is) as /home, so I intended on recovering the space Windows was taking up and turning that into /home.  That went fine and I was able to mount the partition and rsync all my files over.  However, I forgot that the partition was encrypted, so now all my files are sitting in /home/.ecrypt and /home/$USER is empty.  How can I recover my files from /home/.ecrypt and move them to /home/$USER?  I followed this tutorial: Convert continuous numeric values to discrete categories defined by intervals What's the difference between a Long Term Support Release and a Normal Release? Cardinality of the set of all real functions of real variable How does one compute the cardinality of the set of functions $f:\mathbb{R} \to \mathbb{R}$ (not necessarily continuous)? Compute the integral $\int\frac{dx}{(x^2-x+1)\sqrt{x^2+x+1}}$ Lightning tags in beta I came across some lightning tags that are still in beta, ex: lightning:input (Beta) lightning:tabset (Beta) etc  Not sure for how long they were in beta, is it advisable to use them for building UI and deploy to production? Material will not assign to selected vertices