Throughout my life I've been told that an inertial frame is one that is not accelerating and I was satisfied with that. Well up to this day, until I asked: accelerating with respect to what ? Now this seems as a flawed definition to me.  Another definition states that an inertial frame is one in which a body remains at rest or moves at constant velocity unless acted upon by forces. This definition seems to be flawed too, don't we usually tell whether or not a force is acting on a body by measuring its acceleration ? How can we switch to doing the opposite so quickly ?  Wikipedia defines an  as:     In classical physics and special relativity, an inertial frame of reference (also inertial reference frame or inertial frame, Galilean reference frame or inertial space) is a frame of reference that describes time and space homogeneously, isotropically, and in a time-independent manner.[1] The physics of a system in an inertial frame have no causes external to the system.[2]   Well this looks too complicated for me, can any one help explaining it in simpler terms please ? How can time and space be "homogeneous", "isotropic", and "time-independent" ?  Finally, can we define an inertial frame as the one in which Newton's three laws of mechanics hold?
I understand that you can (in principle) measure whether "free particles" (no forces) experience accelerations in order to tell whether a frame is inertial. But fundamentally, what determines which frames are inertial (i.e. what principle selects in which frames free particles will not appear to accelerate)? I've been told that the cosmic microwaves determine the ultimate rest frame of the universe, but that doesn't make sense to me, since one can still ask why that frame is an inertial frame.  Also, I understand that there are no real inertial frames in general relativity, but it seems like there certainly exists approximate inertial frames and we can ask why those frames are approximately inertial and not others. For example, in the frame of a person riding a merry go round, free particles appear to greatly accelerate; while in the frame of someone standing next to the merry go round there are no such great accelerations. Why does the guy (or gal) on the merry go round see free particles accelerating while the other guy doesn't.   And if you're gonna tell me that it's "the rest of the stuff in the universe" that determines whether the person on the merry go round sees free particles accelerate, I'll ask how you know that all that stuff is not spinning.  I hope this question sort of makes sense, it's been bothering me for a while and my study of relativity (most of special relativity and just the outline of general relativity) hasn't really clarified it for me much.
Illustrator Vector Graphics Appearing Pixellated This has been puzzling me for a few days now, and I asked a graphic designer I knew before trying here and haven't been able to solve it yet. It's quite weird so please bear with me for a bit.  I am using Adobe Illustrator to create a logo, and I have something that can potentially work. I have used only the pen tool with strokes (no fill), but the issue is, when I view the logo at 100%, it looks pixellated! I know vectors should not even be able to appear pixellated, but they are. Here is the screenshot from AI, without exporting to anything:     That was just done using the snipping tool within Windows, and it's at 100% zoom.  I have anti-aliasing turned on from Edit > Preferences > General, and the document resolution is at 300 ppi (I get the same result with 72 ppi).   Could anyone help me with this?   If relevant: Using CS6, and have a 24 inch Dell U2412M at 1920x1200 resolution. I do have a 21.6" Samsung at 1680x1050 and I get the same result there as well. Let me know if you need any other settings, or if you would like the file, I'd be happy to provide it to be able to solve this problem. This time when I used certbot it created a certificate for "www.$website" instead of $website. This is not what I need.  Here it is:    $ website="my_website123.com"   $ sudo certbot certonly --standalone -d $website -d www.$website --email admin@$website              Saving debug log to /var/log/letsencrypt/letsencrypt.log   Plugins selected: Authenticator standalone, Installer None   Starting new HTTPS connection (1): acme-v01.api.letsencrypt.org   Cert not yet due for renewal    You have an existing certificate that has exactly the same domains or certificate name you requested and isn't close to expiry.   (ref: /etc/letsencrypt/renewal/www.my_website123.com.conf)    What would you like to do?   -------------------------------------------------------------------------------   1: Keep the existing certificate for now   2: Renew &amp; replace the cert (limit ~5 per 7 days)   -------------------------------------------------------------------------------   Select the appropriate number [1-2] then [enter] (press 'c' to cancel): 2   Renewing an existing certificate   Performing the following challenges:   http-01 challenge for my_website123.com   http-01 challenge for www.my_website123.com   Waiting for verification...   Cleaning up challenges    IMPORTANT NOTES:    - Congratulations! Your certificate and chain have been saved at:      /etc/letsencrypt/live/www.my_website123.com/fullchain.pem      Your key file has been saved at:      /etc/letsencrypt/live/www.my_website123.com/privkey.pem      Your cert will expire on 2018-10-18. To obtain a new or tweaked      version of this certificate in the future, simply run certbot      again. To non-interactively renew *all* of your certificates, run      "certbot renew"    - If you like Certbot, please consider supporting our work by:       Donating to ISRG / Let's Encrypt:   https://letsencrypt.org/donate      Donating to EFF:                    https://eff.org/donate-le   Why did it create one for "www" instead of the bare domain?   On all my own servers this exactly command has always created a cert. without "www" - this is what I need. I even tried yesterday on a different server -- without "wwww".  How can I make it create a cert. without "www"? Django templates offer the builtin tag cycle for alternating between several values at different points in a template (or for loop in a template) but this tag does not reset when it is accessed in a scope outside of the cycles definition.  I.e., if you have two or more lists in your template, the rows of all of which you'd like to use some css definitions odd and even, the first row of a list will pick up where the last left off, not with a fresh iteration from the choices (odd and even)  E.g., in the following code, if the first blog has an odd number of entries, then the first entry in a second blog will start as even, when I want it to start at odd.  {% for blog in blogs %}   {% for entry in blog.entries %}     &lt;div class="{% cycle 'odd' 'even' %}" id="{{entry.id}}"&gt;       {{entry.text}}     &lt;/div&gt;   {% endfor %} {% endfor %}   I've tried obviating this by patching with the resetcycle tag offered here:    to no avail.  (The code didn't work for me.)  I've also tried moving my inner loop into a custom tag, but this also did not work, perhaps because the compile/render cycle moves the loop back into the outer loop?  (Regardless of why, it didn't work for me.)  How can I accomplish this simple task!?  I'd prefer not to create a data structure in my view with this information pre-compiled; that seems unnecessary.  Thanks in advance. I want to make a full focus on the body, for example: I need to have a clear focus on the each balls in the photo. I used just single point focus.    In this picture I used:   shutter speed: 8 aperture: F/4 ISO: 200 2 flashes, one in the right and one on the top of project camera: nikon d300s lens : 105mm micro 2.8   Thanks Path connectedness of the set $\{(x,y):(x+1)^{2}+y^{2}\leq 1\}\cup\{(x,y):y=x\sin(\frac{1}{x}),x>0\}$ Let $A$ be the following subset of $\mathbb{R}^{2}$:$$A=\{(x,y):(x+1)^{2}+y^{2}\leq 1\}\cup\{(x,y):y=x\sin(\frac{1}{x}),x&gt;0\}$$ Then  $1.$ $A$ is connected.  $2.$ $A$ is compact.  $3.$ $A$ is path connected.  $4.$ $A$ is bounded.  It is clear that $A$ is unbounded as the graph of $x\sin(\frac{1}{x})$, so option $2$nd and $4$th are not correct. Again $A$ is connected by using the fact that closure of connected set is connected. But i am confused about path connectedness of $A$. Please help me about path connectedness of $A.$ Thanking you. Rerouting stdin and stdout from C Where to find cross section data for $e^{-}$ + $p$ $\longrightarrow$  $p$ + $e^{-}$ ?  does not include it. Is it possible to play FIFA 2015, 4v4 on 2 Consoles? I've the following situation: My friends and I, we're 8 in total, want to play Fifa 15 4v4. I know that the Playstation 4 just supports 4 controllers and thats why we think about a 2 console + 2 TV's setup, so 4 players per console.   So my question is: Is it possible or is there a game mode available were we could play such a setup?  Update: After I got the first answer I've to add that I know that the only way to play on 2 consoles would be through the psn online features. So we did not plan to play on Lan. We just want to sit in the same room with 2 consoles and play against each other over psn. An incorrect proof by exhaustion How are ssl certificates verified? What is the series of steps needed to securely verify a ssl certificate?  My (very limited) understanding is that when you visit an https site, the server sends a certificate to the client (the browser) and the browser gets the certificate's issuer information from that certificate, then uses that to contact the issuerer, and somehow compares certificates for validity.     How exactly is this done?  What about the process makes it immune to man-in-the-middle attacks? What prevents some random person from setting up their own verification service to use in man-in-the-middle attacks, so everything "looks" secure? I've generated some JSON and I'm trying to pull it into an object in JavaScript. I keep getting errors. Here's what I have:  var data = '{"count" : 1, "stack" : "sometext\n\n"}'; var dataObj = eval('('+data+')');   This gives me an error:   unterminated string literal   With JSON.parse(data), I see similar error messages: "Unexpected token ↵" in Chrome, and "unterminated string literal" in Firefox and IE.  When I take out the \n after sometext the error goes away in both cases. I can't seem to figure out why the \n makes eval and JSON.parse fail. Is there a function or method to give the last day of a month? For example if the date is 27 feb 2013, the last date should be 28 feb 2013 , it become 29 if its a leap year. if the date was 2 jan then it should return 31 Jan.  If there is no function then any ideas on how we can get this?  Thanks We are seeing this error in a Winform application.  Can anyone help on why you would see this error, and more importantly how to fix it or avoid it from happening.   System.ComponentModel.Win32Exception: Error creating window handle.    at System.Windows.Forms.NativeWindow.CreateHandle(CreateParams cp)    at System.Windows.Forms.Control.CreateHandle()    at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)    at System.Windows.Forms.Control.CreateControl()    at System.Windows.Forms.Control.OnVisibleChanged(EventArgs e)    at System.Windows.Forms.ButtonBase.OnVisibleChanged(EventArgs e) Is there any way to make a method with more than one instance? Obtaining zero-length string from strtok() Horizontal line of custom length like an — Plot Summary/Details  A human spacecraft lands on an alien world.  I'm not sure if they are exploring, or touched down for repairs. The world is a foreboding place, and home to a vicious predator that somewhat resembles a panther, or other big terrestrial cat. The creature is quite cunning, and ambushes several crewmen when they are scouting the planet or doing some other activity that would have them isolated and away from the ship. It sticks in my mind the creature is very strong, and able to bite through the heavy spacesuits the men wear with ease.  The creature has an unusual nutritional requirement of some sort. As such, it doesn't eat its victims, but somehow drains them of a particular element or chemical substance. I can't remember what it is, though I think it had something to do with the skeletal structure of the men. Calcium, maybe?  I have only very general recollections of how the story ends/is resolved. The humans become aware of the threat, and I believe they ultimately slay the beast. I can't recall anything more specific than that, unfortunately.  Timeframe of Publication  This one is old, I'm sure of that. I can remember the writing style and some of the descriptions being very "old school" - spacemen, rocketship, that sort of thing. Almost like something you'd see in an old sci-fi movie serial, to use a film analogy. If I had to guess, I'd say 1950's at the latest. Do I need a transit visa in Zurich on the way to India? I am travelling from US to India, with an Indian passport but expired F1 visa and going there to get my H1B visa stamping. I have a stop at Zurich for 2 hours while flying to India. Do I need a transit visa for my trip? How do "pet" Walkers help ward off other Walkers? In both the comics and the show, Michonne first appears with two walkers that she essentially keeps as pets.    The comics sort of half-explain this - as per :     She notices walkers don't attack one another and hacks off the arms and lower jaws of Mike and Terry. She chains them up by their necks to use them as escorts for an escape that was successful.   In , we see that even if they still sort of smell like Walkers, the Walkers can smell/detect the living and will attack.  In ,      We see Andrea effectively making a new "pet" so that she can use to deter the Walkers that she comes across on her trip to the prison. Along the trip, she is shown to come within close range of Walkers, but they give her space when she points the "pets" in the right direction.   Why would the Walkers not just attempt to go around the "pets"? What about them creates an effective protective barrier? Isle vs. Island