can you guys show me the most considerable differences between the meaning/usage of excuse me and I'm sorry?
Is it ok to say 'sorry' where you otherwise would use 'excuse me'?  Example: "Sorry, but could you show me the way to the next train station?"
I'm trying to work out what value resistor to use in a LED circuit. The equation I'd use to do this is:  $$ R = \frac{V_{cc} - V_f}{I_f} $$  Seems logical, and makes complete sense. The answers to the question  confirm this too.  I have the following LEDs:   \$ V_f = 3.3V \$ \$ I_{f_{typ}} = 20mA \$   Using a 5V power supply:   \$ V_{cc} = 5V \$   Plugging these into the above equation gives:  $$ \begin{eqnarray} R &amp; = &amp; \frac{V_{cc} - V_f}{I_f} \\   &amp; = &amp; \frac{5V - 3.3V}{20mA} \\   &amp; = &amp; 85\Omega \end{eqnarray} $$  All good so far.  However, if I use the calculator at , that gives me 100&Omega;. If I use the ElectroDroid app on my phone, that gives me 85&Omega;.  So, I assume that the linear1 calculator is using a different method of calculating this resistor value; is there some better way of doing this? Applying for a Canadian ETA after previous visits without one How to check the count of .txt files in a folder (dir command)? How can use dir command to check how many .txt files there are in a folder (for example,  C:\Temp\)? I know that a gas is made of atoms or molecules moving freely in space.  When these particles hit the walls of where they're kept in they cause something called pressure.  But these particles never pile up on each other and push a surface down by their weight so that we can measure it as weight, not pressure.  So why do gases have weight? What are review tests (audits) and how do they work? I recently received this rather amusing message while reviewing a user's first post:  Congratulations! This was only a test, designed to make sure you were paying attention. This post has already been removed, but thanks for taking time to leave feedback for the author.   What is the purpose of this test? How does the audit work? What happens if I fail? Why was the system expecting me to negatively review a good post, or positively review a bad post? A review is obviously an audit. Should I report it? Do review audits count toward the Reviewer badge? Do robo-reviewers dream of electric sheep? Eigen Values Proof a.) Let A and B be $n$ x $n$ matrices. Prove that the matrix products   $AB$  and $BA$ have the same eigenvalues.      b.) Prove that every eigenvalue of a matrix A is also an eigenvalue of   its transpose $A^T$. Also, prove that if v is an eigenvector of A with   eigenvalue $\lambda$ and w is an eigenvector of $A^T$ with a different   eigenvalue $\mu \ne \lambda$, then v and w are orthogonal vectors with   respect to the dot product.   For a, I know that if their eigenvalues are the same then their eigenvectors must relate too.    For the first part of b, is it similar to proving that the $det(A) =det (A^T)$? And, I do not know how to do the second part. Can gravity be interpreted as the acceleration of spacetime towards an object? Greetings StackExchange!  We were having a conversation with a peer about stupid ways of interpreting theories. We would go to and fro with an interpretations, but we would always find a way to disprove them. There was one, however, that we couldn't refute:  Gravity on a plane in a bidimensional space can be interpreted as the acceleration of spacetime towards an object.   We tried to invalidate in saying that the inertial mass and gravitational mass would be different, thus violating GR, but after some thought this couldn't be. The gravitational mass would accelerate spacetime towards it. If that object we were to be pushed, the pulling of spacetime would make it difficult for it to move.   We know for a fact this can't be true, and we would greatly appreciate any refutation of this thought. I can clarify if needed, or do a sketch. I apologise in advance as I'm not a native speaker. In a very small static universe with only a particle, does it make sense to talk about time? I am sorry if this question is silly; it′s just one of those things I wished I asked before leaving university.  If there were a static universe only as big as the size of two particles, say electrons, and there were one electron in it going back and forth from point A to point B: would time also go back and forth in the future (point B) and in the past (point A), or would it be considered to  go forward as it does for us? would it be possible to know how long that electron stayed at point A or point B, would it even make sense to ask? I guess what I am asking is: does time move forward only because there are so many particles moving in this enormous space that it is almost impossible they would all be back in the same position they held at least once before relative to each other? does time exist only as a consequence of a lot of particles and their position relative to each other, and the space for them, just like heat? Unable to check a mdadm RAID1 array, says the file system's read only? I recently migrated a RAID1 from a CentOS 5 system to a CentOS 6 system and ever since when I attempt to perform a check I get the following:  $ echo 'check' &gt; /sys/block/md127/md/sync_action -bash: /sys/block/md127/md/sync_action: Read-only file system   This actually shows up from a CRON too, specifically, /etc/cron.d/raid-check. this is included in the mdadm RPM:  $ rpm -ql mdadm | head -5 /etc/cron.d/raid-check /etc/rc.d/init.d/mdmonitor /etc/sysconfig/raid-check /lib/udev/rules.d/63-md-raid-arrays.rules /lib/udev/rules.d/65-md-incremental.rules   Here I'm running the same command that's used by the CRON:  $ raid-check /usr/sbin/raid-check: line 96: /sys/block/md127/md/sync_action: Read-only file system   This typically runs once a week and sends an email which is what originally alerted me to the issue. But at any rate I'm at a loss why this RAID seems to be unable to be checked.  The RAID seems fine on inspection though.  $ cat /proc/mdstat  Personalities : [raid1]  md127 : active raid1 sda1[0] sdb1[1]       976759936 blocks [2/2] [UU]  unused devices: &lt;none&gt;   I point this out only because while googling I found this thread regarding a bug in mdadm but this was for a older version of mdadm.      Version info  $ lsb_release -d Description:    CentOS release 6.6 (Final)  $ rpm -q mdadm mdadm-3.3-6.el6_6.1.x86_64  $ mdadm --version mdadm - v3.3 - 3rd September 2013 Why can't this be done with Master Theorem Apparently recurrences like this cannot be solved with the Master Theorem:  $T(n) = 2T\left(\frac{n}{2}\right) + \frac{n}{\log(n)}$  Because $n^{\log_b(a)} = n^1$ is not a polynomial multiple of $f(n) = \frac{n}{\log(n)}$ since $\frac{n}{\frac{n}{\log(n)}} = \log(n)$, which is less than $n^\epsilon$ for any positive $\epsilon$.  But when is this really even an issue?   For example why wouldn't the time complexity be $n \log n$ using case 2 of the Master Theorem? Unrolling the recursion:  $$T(n) = n\sum_{k=1}^{\log_2(n)} \frac{1}{\log_2(2^k)}$$  $$T(n) = n\sum_{k=1}^{\log_2(n)} \frac{1}{k}$$  Doesn't this suggest $\Theta(n \log n)$ even though it supposedly cannot be done with Master Theorem? How do I disable notifications in my personal profile for activity on pages I am an admin of? I'm an admin of several pages on Facebook (for technical stuff like RSS imports, etc.), but neither do I contribute content nor do I care about their content.  Still, as an admin, I get notifications (upper left hand, the globe icon) about activity (someone liked this, someone posted that) on those pages in my personal (!) profile .  Does anyone have the same issue? Is there any way to explicitly disable notifications for certain pages?  (This behavior seems to be new, by the way; I'm only seeing those notifications for a few weeks now.) Comparison of backup tools This question exists because it has historical significance, but it is not considered a good, on-topic question for this site, so please do not use it as evidence that you can ask similar questions here.  While you are encouraged to help maintain its answers, please understand that "big list" questions are not generally allowed on Ask Ubuntu and will be closed per the .   Backup is incredibly important. Obviously there's no best backup tool, but a comparison of the options would be very interesting.   Graphical Interface? Command line? Incremental backups? Automatic backups? Install method: In standard repositories? PPA? How to split a string in sql server 2008 using stored procedure and insert the data to table How can I find the location of an icon of a launcher in use? How to export/backup Notes in macOS in one go I have a lot of Notes on my machine which I don't want to loose. It's not logical to export them one by one. Is there any way to export them in one go, which would make me either use them on my new   I learned that I could backup ~/Library/Group Containers/group.com.apple.notes but I am not really sure if this would be helpful. This is what I get as for this directory.  $ du -sh ./* 4.0K    ./Library 256K    ./NoteStore.sqlite  32K    ./NoteStore.sqlite-shm 3.0M    ./NoteStore.sqlite-wal   I am running macOS Mojave. Lithium-6 isotope has an approximate magnetic momentum of $0.88\ \mu_N$ in its fundamental nuclear state. I'm trying to find its angular momentum and parity.  I found in a standard table: $I=1^+$ and while I get the parity part, I don't understand the rest. What I have done is filling the shells separately for protons and neutrons and finding that both have their outer particle in the $1 P_{3/2}$ state. Sum of these gives possible total angular momenta to be either $0$, $1$, $2$ or $3$.  So my question is: how do you choose between these to find the real value $I=1$? How do I improve boot speed? I noticed that I got some initial traffic problems at the point where the initial highway is connected to my city. At the beginning I simply elongated both roads that came from that highway, but this doesn't seem to scale.  What I wanted to do now is to create a single six-lane highway from these two four-lane roads. I'd be open to continue to use two roads in parallel here, but I didn't manage to add any way of crossing between the lanes when I tried that idea.  So, how do I merge two one-way roads into a single two-way road? Or, if my idea is really bad, what is a good way to connect the initial highway access to my fledgling city?  Here's a screenshot of the roads I want to connect, if my description wasn't entirely clear: How to duplicate a div in JavaScript How can I start the Blood on the Ice quest? I am currently part of the Stormcloaks and just finished Rescue from Fort Neugard. The Jarl wants to make me a thane and is telling me to buy a house, but his steward is telling me the house is unavailable due to some unpleasantness. I have already completed the 5 quests to help people of Eastmarch.  From what I can see online, I need to begin the Blood on the Ice quest. It is supposed to begin by walking in the windhelm graveyard at night, however every time I go there I don't see anyone.  Someone online said it's possible to miss the scene that triggers the quest if you go into Windhelm and leave without triggering it, but I am hoping this isn't the case. I am in Windhelm a lot because the Enchanting table, Blacksmith, and Fence are all in one location, so find it very convenient. The lady who is supposed to be murdered in the Graveyard (Susanna) is still alive in Candlehearth Hall, so I think I'm not bugged.  The wiki suggests that you have to "The quest will initiate after you entered Windhelm four times from another hold", however I have entered and left quite a few times during the course of my game and know I've been here way over 4 times.  I tried pickpocketing the key, however I don't automatically get the quest on entering the house, and there are a bunch of "Investigate InvestigationTarget" spots in the house. Also, I was reading the Butcher's journal and he was saying he almost caught Susanna when she left Candlehearth, however I have never seen her leave Candlehearth. Perhaps my glitch is she never leaves? I'll have to head to Windhelm on another character and check it out.  Also, I saw something online saying this quest won't trigger if you go past 245 in-game days. Would someone be able to confirm this for me? (Have the XBox version, so waiting 245 days is annoying)  Can someone tell me the exact steps to begin this quest?