qid int64 1 74.7M | question stringlengths 12 33.8k | date stringlengths 10 10 | metadata list | response_j stringlengths 0 115k | response_k stringlengths 2 98.3k |
|---|---|---|---|---|---|
4,368 | The lock side is great, however, shoes does not stay on the platform side. Your leg always slip out from the pedals during pedaling. Any solution to improve it? | 2011/06/21 | [
"https://bicycles.stackexchange.com/questions/4368",
"https://bicycles.stackexchange.com",
"https://bicycles.stackexchange.com/users/1676/"
] | Some people have modded the pedals to add set-screws which provide better grip. Typically this involves drilling a hole, tapping it for threads, and adding a set screw of the desired length.
For example, here's an a530 with 2x set screws added:
 | Perhaps you need to change your pedalling style when you're riding without clips: push (only) down onto the pedal, instead of spinning.
That's why you *have* clips. |
4,368 | The lock side is great, however, shoes does not stay on the platform side. Your leg always slip out from the pedals during pedaling. Any solution to improve it? | 2011/06/21 | [
"https://bicycles.stackexchange.com/questions/4368",
"https://bicycles.stackexchange.com",
"https://bicycles.stackexchange.com/users/1676/"
] | I'm not sure there is a good answer to this question. It probably depends most on what type of shoes you wear. Have you tried using trainers/sneakers with a rubber sole? I wouldn't want to try and modify the pedals as you may risk damaging them.
If you want a really good reliable pedal connection on the platform side, I reckon the [Shimano M324 pedals](http://www.wiggle.co.uk/shimano-m324-combination-pedals/) are more likely to suit. | This seems an easy solution pretty easy to take on and off:
 |
4,368 | The lock side is great, however, shoes does not stay on the platform side. Your leg always slip out from the pedals during pedaling. Any solution to improve it? | 2011/06/21 | [
"https://bicycles.stackexchange.com/questions/4368",
"https://bicycles.stackexchange.com",
"https://bicycles.stackexchange.com/users/1676/"
] | Some people have modded the pedals to add set-screws which provide better grip. Typically this involves drilling a hole, tapping it for threads, and adding a set screw of the desired length.
For example, here's an a530 with 2x set screws added:
 | This seems an easy solution pretty easy to take on and off:
 |
4,368 | The lock side is great, however, shoes does not stay on the platform side. Your leg always slip out from the pedals during pedaling. Any solution to improve it? | 2011/06/21 | [
"https://bicycles.stackexchange.com/questions/4368",
"https://bicycles.stackexchange.com",
"https://bicycles.stackexchange.com/users/1676/"
] | I wired a piece of rubber tubing around the front and back beams on mine and it helped a lot. I like the skateboard tape idea and will try it. These pedals are beautifully finished but the edges of all the lugs are rounded over and then hardcoat anodized resulting in a really slippery pedal; your feet tend to slide sideways and go off the outside edge periodically. Wearing SPD MTB shoes on the flat side is the worst, especially when the cleat reaches the outside edge. Running shoes are definitely better. None of this has anything to do with technique; I have old style metal and rubber pedals that you slide off of if you hit a large bump, otherwise you're fine, but these are slippery enough that you can nail your ankle pretty easily. There are a bunch of pedals like the mentioned Shimano M 324 that I think should be better, mostly at the expense of increaded wieght. | Perhaps you need to change your pedalling style when you're riding without clips: push (only) down onto the pedal, instead of spinning.
That's why you *have* clips. |
4,368 | The lock side is great, however, shoes does not stay on the platform side. Your leg always slip out from the pedals during pedaling. Any solution to improve it? | 2011/06/21 | [
"https://bicycles.stackexchange.com/questions/4368",
"https://bicycles.stackexchange.com",
"https://bicycles.stackexchange.com/users/1676/"
] | Some people have modded the pedals to add set-screws which provide better grip. Typically this involves drilling a hole, tapping it for threads, and adding a set screw of the desired length.
For example, here's an a530 with 2x set screws added:
 | I'm not sure there is a good answer to this question. It probably depends most on what type of shoes you wear. Have you tried using trainers/sneakers with a rubber sole? I wouldn't want to try and modify the pedals as you may risk damaging them.
If you want a really good reliable pedal connection on the platform side, I reckon the [Shimano M324 pedals](http://www.wiggle.co.uk/shimano-m324-combination-pedals/) are more likely to suit. |
34,255 | We all know there are still vulnerable code out there even though they may or may not get exploited and found for hacking attempts. I've seen people do it countless times and have a possibly plausible solution I've been working on for this. The only thing I lack is possibilities and opinions for this idea.
Based off of the [Web Application Firewall](https://www.owasp.org/index.php/Web_Application_Firewall), I planned on creating a vBulletin plugin (first) in order to detect unsanatized code by including functions for all possible unsanatized code and sandbox it. In order to lower privileges of anyone without a key (either user defined or generated), either the forum owner will manually access the control panel and disallow what code gets filtered/blocked or automatically detect what known vulnerabilities the code may have and give a 404 to any user that inputs arbitrary exploitable code such as SQLi (accessing a table other than the one on the page allows) and others.
Since people have told me that using a Web Application Firewall has many bypasses that are just annoying to the hacker, I was wondering whether or not sandboxing and lowering privileges is a good idea if I improve the functionality on vBulletin through numerous plugins/products so it can be at least 90% versatile over time?
Opinions are welcome as well. Another question is known bad coding practices. I don't know everything, but I know my mistakes and people have broken and hacked their way through my code to show me. What bad coding practices are known and uncommon/known and common in PHP/JS?
Thanks for the time.
If this would fit in another SE site, sorry & many thanks if it gets migrated.
**Edit**
I was wondering whether or not protecting the additions to a site before protecting the site overall is a good idea. If we look at vBulletin as it stands right now, people are still creating plugins and products that aren't 100% secured and lead to finding that there may be unnecessary code, improper sanitation, and/or unsanatized input. This would wrap the code and protect it through privilege restrictions. The cons about this is less knowledge about security to the owner(s), but more time knowing your website is protected whether you're vulnerable or not. | 2013/04/12 | [
"https://security.stackexchange.com/questions/34255",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/22024/"
] | >
> whether or not sandboxing and lowering privileges is a good idea
>
>
>
**ALWAYS!!!** Every time, everywhere (English is weird), isolate your processes. In an ideal world, we'd SELinux the hell out of every application, user, file, etc.
A properly established mandatory access control provides both protection against exploits and detection of compromise when you see patterns in your audit logs that just shouldn't be there, which of course you're always reviewing to correct bad rules or notice something unwanted has happened.
WAF, MAC, firewalls, etc. are body armor for your web server. They make you heavier and slower, and chest armor doesn't stop you from being shot in the arm, but it does improve your survival odds.
AppArmor is a simpler interface to the Linux security modules, and a decent substitute for corralling specific applications that you consider high-risk if SELinux is melting your brain.
>
> whether or not protecting the additions to a site before protecting the site overall is a good idea
>
>
>
Yes again! The more compartmentalized you can make things, the better off you are. If the a module only needs access to the posts table, provide it a context where it can't access the credential table, etc. It's a lot harder to leak the access you don't have than the access you do have. | There's good info in some of the other answers, for sure. I'd add that you can defeat almost all low-level code injections with a simple trick: use a non-x86 processor. Malware or payload written for x86 simply does not work on non-x86 processor. Linux and some BSD's have been ported to many processor architectures. If you use a portable web stack, then you can just compile it for those architectures and deploy a web application on top of it. Configure things correctly and now you just worry about application level attacks.
Some will accuse it of being security by obscurity. Not true. This is obfuscation and it has proven value. It works so long as it's not widely adopted to the point that hackers put a bunch of effort into the tactic. It's worked for me and many others, including huge NUMA/mainframe markets, for almost ten years. That's saying something. Most attackers use premade kits. And almost all people making kits write x86 desktop/server or ARM mobile. There's simply not a substantial labor force available to easily exploit your stuff running on POWER, Alpha, MIPS, SPARC, etc. So, it's kind of economics + obfuscation working to your advantage.
Remember, though, to combine this trick with good security practices in area of choice of software, configuration, permissions, monitoring, etc. Obfuscation alone isn't enough to prevent all issues. Just a bunch of them. ;)
Note: I'd also try to avoid using platforms that are easy to bypass or inject code into. PHP has a bad history with that kind of thing. The static, type safe, managed runtimes are usually the easiest to secure from problematic code. You just have less to worry about with them and we have tricks like SFI and Native Client for dealing with native code on those platforms if one is so inclined. |
188,763 | We start with one small (but perfectly formed) planetoid. Just for the sake of discussion, we'll say it's Mercury. This planet is more or less useless to me, being too small and too close to the sun. Fortunately, I've got this big building project in mind...and I need materials.
Not-Mercury is therefore slated for deconstruction. I have massive mobile excavator/refinery complexes that are eating steadily away at the crust, processing the rock into useful components, and transporting them to orbit for use in my Dyson Swarm.
However, the core of the planet is still extremely hot - not as hot as Earth's core, and not hot enough to drive tectonic activity, but certainly hot enough to cause critical components of my excavators to become inconveniently runny. What I'd like to do, then, is have some process in place that can transport the heat away from the depths of the planet, keeping the surface cool enough for my machines to work efficiently.
The population of the planet live in subterranean, multi-level tunnel-cities (similar to Zion in the Matrix series). Ideally these cities should be a part of whatever system we put in place to cool the core, but that's not strictly required. Tech level is advanced enough to allow routine interplanetary travel, but not interstellar; fusion reactors, mass drivers, arcologies, etc, but no FTL, matter replication, or transporters. The system is almost completely bare of Handwavium, so ideally tech should be conceivable today.
So - **How can I cool down a planetary core on a timescale of centuries?** | 2020/10/23 | [
"https://worldbuilding.stackexchange.com/questions/188763",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/28786/"
] | The direct answer to your question: Same way we currently cool space ships: By using a heat exchange to capture and transport heat, and radiating that heat off as IR radiation. A solar shade to limit incoming heat from the sun is also helpful.
However I don't think we'll need a planetary core cooling system. Dismantling a planet can't really be done depth first (i.e., speed run to the core), the excavation will be gradual and distributed (shaving a dozen meters off equally around the sphere every year sort of thing). As this is done, hotter rocks are allowed to radiate into space over time and cool down.
You dig another 1m down. Process everything. Accelerate it into space, and move on to another region. When you come back to this region, it's radiated a lot of energy into space and is cooler now.
As you're digging, you're constantly building new refining and launch infrastructure at lower elevations and then dismantling the old, higher elevation one.
Another massive practical reason for doing this is access and power efficiency. Hauling rock up slopes takes a tonne of energy. Hauling rock along flatish ground is relatively cheap. Your robots can move rock better with wheels along smooth near-horizontal ramps than up cliffs.
I've always pictured this project done by an entirely robotic workforce with humans in orbit controlling their strategic moves, the robots being autonomous in tactical moves. No need for a habitat if no humans step foot on the ground. | If you can build a Dyson Swarm, you can use other planetoids. May I suggest using Not-Europa, Not-Ganymede, Not-Calisto, Not-Enceladus, Not-Triton etc.?
They are [literally covered in ice](https://en.wikipedia.org/wiki/Icy_moon), which is kinda cool[pun intended], on top of their rocky cores. They are also around half the radius of Not-Mercury or smaller, and farther from the sun than Not-Mercury[citation needed], which means they won't be so hot. |
188,763 | We start with one small (but perfectly formed) planetoid. Just for the sake of discussion, we'll say it's Mercury. This planet is more or less useless to me, being too small and too close to the sun. Fortunately, I've got this big building project in mind...and I need materials.
Not-Mercury is therefore slated for deconstruction. I have massive mobile excavator/refinery complexes that are eating steadily away at the crust, processing the rock into useful components, and transporting them to orbit for use in my Dyson Swarm.
However, the core of the planet is still extremely hot - not as hot as Earth's core, and not hot enough to drive tectonic activity, but certainly hot enough to cause critical components of my excavators to become inconveniently runny. What I'd like to do, then, is have some process in place that can transport the heat away from the depths of the planet, keeping the surface cool enough for my machines to work efficiently.
The population of the planet live in subterranean, multi-level tunnel-cities (similar to Zion in the Matrix series). Ideally these cities should be a part of whatever system we put in place to cool the core, but that's not strictly required. Tech level is advanced enough to allow routine interplanetary travel, but not interstellar; fusion reactors, mass drivers, arcologies, etc, but no FTL, matter replication, or transporters. The system is almost completely bare of Handwavium, so ideally tech should be conceivable today.
So - **How can I cool down a planetary core on a timescale of centuries?** | 2020/10/23 | [
"https://worldbuilding.stackexchange.com/questions/188763",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/28786/"
] | The direct answer to your question: Same way we currently cool space ships: By using a heat exchange to capture and transport heat, and radiating that heat off as IR radiation. A solar shade to limit incoming heat from the sun is also helpful.
However I don't think we'll need a planetary core cooling system. Dismantling a planet can't really be done depth first (i.e., speed run to the core), the excavation will be gradual and distributed (shaving a dozen meters off equally around the sphere every year sort of thing). As this is done, hotter rocks are allowed to radiate into space over time and cool down.
You dig another 1m down. Process everything. Accelerate it into space, and move on to another region. When you come back to this region, it's radiated a lot of energy into space and is cooler now.
As you're digging, you're constantly building new refining and launch infrastructure at lower elevations and then dismantling the old, higher elevation one.
Another massive practical reason for doing this is access and power efficiency. Hauling rock up slopes takes a tonne of energy. Hauling rock along flatish ground is relatively cheap. Your robots can move rock better with wheels along smooth near-horizontal ramps than up cliffs.
I've always pictured this project done by an entirely robotic workforce with humans in orbit controlling their strategic moves, the robots being autonomous in tactical moves. No need for a habitat if no humans step foot on the ground. | **Launch hot material into space**
Basically, there are only three methods to transfer heat: conduction, convection, and radiation. In space, only the method #3 works. Hot object mush exhaust itself radiating heat into space. While this works, this is very slow. You will have to wait for thousand years for a planet-sized object to cool a fraction of a degree. Building big heat-emitting radiators might help, but those radiators must be also planet-sized.
Conduction and convention methods won't work, because there is no other body to conduct the heat to, and there is no atmosphere. But what if you create a convection (or, rather, direct transfer of overheated gas) out of the planet? This would effectively transfer away all of the excess heat.
Your operation then would go like this:
1. Digging machines would excavate planetary material, vaporizing it in the process. The process would actually become simpler when you get the hotter core;
2. Vapor would get ionized and transferred to an orbital launch ionic "cannon", which would accelerate material to the first cosmic velocity (which, for Mercury-sized planet is only about 3 km/s) and launch this plasma into the orbit;
3. The plasma would form a disk around the planet, and due to its low density would quickly cool down, forming dust;
4. Your orbital operations would collect the dust and transfer it to some other place in the system where you need it. |
188,763 | We start with one small (but perfectly formed) planetoid. Just for the sake of discussion, we'll say it's Mercury. This planet is more or less useless to me, being too small and too close to the sun. Fortunately, I've got this big building project in mind...and I need materials.
Not-Mercury is therefore slated for deconstruction. I have massive mobile excavator/refinery complexes that are eating steadily away at the crust, processing the rock into useful components, and transporting them to orbit for use in my Dyson Swarm.
However, the core of the planet is still extremely hot - not as hot as Earth's core, and not hot enough to drive tectonic activity, but certainly hot enough to cause critical components of my excavators to become inconveniently runny. What I'd like to do, then, is have some process in place that can transport the heat away from the depths of the planet, keeping the surface cool enough for my machines to work efficiently.
The population of the planet live in subterranean, multi-level tunnel-cities (similar to Zion in the Matrix series). Ideally these cities should be a part of whatever system we put in place to cool the core, but that's not strictly required. Tech level is advanced enough to allow routine interplanetary travel, but not interstellar; fusion reactors, mass drivers, arcologies, etc, but no FTL, matter replication, or transporters. The system is almost completely bare of Handwavium, so ideally tech should be conceivable today.
So - **How can I cool down a planetary core on a timescale of centuries?** | 2020/10/23 | [
"https://worldbuilding.stackexchange.com/questions/188763",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/28786/"
] | The direct answer to your question: Same way we currently cool space ships: By using a heat exchange to capture and transport heat, and radiating that heat off as IR radiation. A solar shade to limit incoming heat from the sun is also helpful.
However I don't think we'll need a planetary core cooling system. Dismantling a planet can't really be done depth first (i.e., speed run to the core), the excavation will be gradual and distributed (shaving a dozen meters off equally around the sphere every year sort of thing). As this is done, hotter rocks are allowed to radiate into space over time and cool down.
You dig another 1m down. Process everything. Accelerate it into space, and move on to another region. When you come back to this region, it's radiated a lot of energy into space and is cooler now.
As you're digging, you're constantly building new refining and launch infrastructure at lower elevations and then dismantling the old, higher elevation one.
Another massive practical reason for doing this is access and power efficiency. Hauling rock up slopes takes a tonne of energy. Hauling rock along flatish ground is relatively cheap. Your robots can move rock better with wheels along smooth near-horizontal ramps than up cliffs.
I've always pictured this project done by an entirely robotic workforce with humans in orbit controlling their strategic moves, the robots being autonomous in tactical moves. No need for a habitat if no humans step foot on the ground. | I think you're dealing with a non-problem here. You're giving a time scale of centuries.
You **can't** simply dig down in one spot, it won't take too much distance before your dig collapses. You have to spread your digging out all over the planet. As you dig away material what's underneath is warmer but not greatly so. By the time you get back to that spot it will have cooled naturally.
Besides, your big problem is the waste energy from lifting all that material to space, not the energy of the planetary core. |
188,763 | We start with one small (but perfectly formed) planetoid. Just for the sake of discussion, we'll say it's Mercury. This planet is more or less useless to me, being too small and too close to the sun. Fortunately, I've got this big building project in mind...and I need materials.
Not-Mercury is therefore slated for deconstruction. I have massive mobile excavator/refinery complexes that are eating steadily away at the crust, processing the rock into useful components, and transporting them to orbit for use in my Dyson Swarm.
However, the core of the planet is still extremely hot - not as hot as Earth's core, and not hot enough to drive tectonic activity, but certainly hot enough to cause critical components of my excavators to become inconveniently runny. What I'd like to do, then, is have some process in place that can transport the heat away from the depths of the planet, keeping the surface cool enough for my machines to work efficiently.
The population of the planet live in subterranean, multi-level tunnel-cities (similar to Zion in the Matrix series). Ideally these cities should be a part of whatever system we put in place to cool the core, but that's not strictly required. Tech level is advanced enough to allow routine interplanetary travel, but not interstellar; fusion reactors, mass drivers, arcologies, etc, but no FTL, matter replication, or transporters. The system is almost completely bare of Handwavium, so ideally tech should be conceivable today.
So - **How can I cool down a planetary core on a timescale of centuries?** | 2020/10/23 | [
"https://worldbuilding.stackexchange.com/questions/188763",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/28786/"
] | The direct answer to your question: Same way we currently cool space ships: By using a heat exchange to capture and transport heat, and radiating that heat off as IR radiation. A solar shade to limit incoming heat from the sun is also helpful.
However I don't think we'll need a planetary core cooling system. Dismantling a planet can't really be done depth first (i.e., speed run to the core), the excavation will be gradual and distributed (shaving a dozen meters off equally around the sphere every year sort of thing). As this is done, hotter rocks are allowed to radiate into space over time and cool down.
You dig another 1m down. Process everything. Accelerate it into space, and move on to another region. When you come back to this region, it's radiated a lot of energy into space and is cooler now.
As you're digging, you're constantly building new refining and launch infrastructure at lower elevations and then dismantling the old, higher elevation one.
Another massive practical reason for doing this is access and power efficiency. Hauling rock up slopes takes a tonne of energy. Hauling rock along flatish ground is relatively cheap. Your robots can move rock better with wheels along smooth near-horizontal ramps than up cliffs.
I've always pictured this project done by an entirely robotic workforce with humans in orbit controlling their strategic moves, the robots being autonomous in tactical moves. No need for a habitat if no humans step foot on the ground. | **Use the Sundiver Approach**
As in the David Brin book. Excess heat is converted to high frequency laser light and either beamed to the surface machinery or into space for other uses. The power is generated using the temperature difference between the surface and sub-surface layers. |
188,763 | We start with one small (but perfectly formed) planetoid. Just for the sake of discussion, we'll say it's Mercury. This planet is more or less useless to me, being too small and too close to the sun. Fortunately, I've got this big building project in mind...and I need materials.
Not-Mercury is therefore slated for deconstruction. I have massive mobile excavator/refinery complexes that are eating steadily away at the crust, processing the rock into useful components, and transporting them to orbit for use in my Dyson Swarm.
However, the core of the planet is still extremely hot - not as hot as Earth's core, and not hot enough to drive tectonic activity, but certainly hot enough to cause critical components of my excavators to become inconveniently runny. What I'd like to do, then, is have some process in place that can transport the heat away from the depths of the planet, keeping the surface cool enough for my machines to work efficiently.
The population of the planet live in subterranean, multi-level tunnel-cities (similar to Zion in the Matrix series). Ideally these cities should be a part of whatever system we put in place to cool the core, but that's not strictly required. Tech level is advanced enough to allow routine interplanetary travel, but not interstellar; fusion reactors, mass drivers, arcologies, etc, but no FTL, matter replication, or transporters. The system is almost completely bare of Handwavium, so ideally tech should be conceivable today.
So - **How can I cool down a planetary core on a timescale of centuries?** | 2020/10/23 | [
"https://worldbuilding.stackexchange.com/questions/188763",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/28786/"
] | If you can build a Dyson Swarm, you can use other planetoids. May I suggest using Not-Europa, Not-Ganymede, Not-Calisto, Not-Enceladus, Not-Triton etc.?
They are [literally covered in ice](https://en.wikipedia.org/wiki/Icy_moon), which is kinda cool[pun intended], on top of their rocky cores. They are also around half the radius of Not-Mercury or smaller, and farther from the sun than Not-Mercury[citation needed], which means they won't be so hot. | I think you're dealing with a non-problem here. You're giving a time scale of centuries.
You **can't** simply dig down in one spot, it won't take too much distance before your dig collapses. You have to spread your digging out all over the planet. As you dig away material what's underneath is warmer but not greatly so. By the time you get back to that spot it will have cooled naturally.
Besides, your big problem is the waste energy from lifting all that material to space, not the energy of the planetary core. |
188,763 | We start with one small (but perfectly formed) planetoid. Just for the sake of discussion, we'll say it's Mercury. This planet is more or less useless to me, being too small and too close to the sun. Fortunately, I've got this big building project in mind...and I need materials.
Not-Mercury is therefore slated for deconstruction. I have massive mobile excavator/refinery complexes that are eating steadily away at the crust, processing the rock into useful components, and transporting them to orbit for use in my Dyson Swarm.
However, the core of the planet is still extremely hot - not as hot as Earth's core, and not hot enough to drive tectonic activity, but certainly hot enough to cause critical components of my excavators to become inconveniently runny. What I'd like to do, then, is have some process in place that can transport the heat away from the depths of the planet, keeping the surface cool enough for my machines to work efficiently.
The population of the planet live in subterranean, multi-level tunnel-cities (similar to Zion in the Matrix series). Ideally these cities should be a part of whatever system we put in place to cool the core, but that's not strictly required. Tech level is advanced enough to allow routine interplanetary travel, but not interstellar; fusion reactors, mass drivers, arcologies, etc, but no FTL, matter replication, or transporters. The system is almost completely bare of Handwavium, so ideally tech should be conceivable today.
So - **How can I cool down a planetary core on a timescale of centuries?** | 2020/10/23 | [
"https://worldbuilding.stackexchange.com/questions/188763",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/28786/"
] | If you can build a Dyson Swarm, you can use other planetoids. May I suggest using Not-Europa, Not-Ganymede, Not-Calisto, Not-Enceladus, Not-Triton etc.?
They are [literally covered in ice](https://en.wikipedia.org/wiki/Icy_moon), which is kinda cool[pun intended], on top of their rocky cores. They are also around half the radius of Not-Mercury or smaller, and farther from the sun than Not-Mercury[citation needed], which means they won't be so hot. | **Use the Sundiver Approach**
As in the David Brin book. Excess heat is converted to high frequency laser light and either beamed to the surface machinery or into space for other uses. The power is generated using the temperature difference between the surface and sub-surface layers. |
188,763 | We start with one small (but perfectly formed) planetoid. Just for the sake of discussion, we'll say it's Mercury. This planet is more or less useless to me, being too small and too close to the sun. Fortunately, I've got this big building project in mind...and I need materials.
Not-Mercury is therefore slated for deconstruction. I have massive mobile excavator/refinery complexes that are eating steadily away at the crust, processing the rock into useful components, and transporting them to orbit for use in my Dyson Swarm.
However, the core of the planet is still extremely hot - not as hot as Earth's core, and not hot enough to drive tectonic activity, but certainly hot enough to cause critical components of my excavators to become inconveniently runny. What I'd like to do, then, is have some process in place that can transport the heat away from the depths of the planet, keeping the surface cool enough for my machines to work efficiently.
The population of the planet live in subterranean, multi-level tunnel-cities (similar to Zion in the Matrix series). Ideally these cities should be a part of whatever system we put in place to cool the core, but that's not strictly required. Tech level is advanced enough to allow routine interplanetary travel, but not interstellar; fusion reactors, mass drivers, arcologies, etc, but no FTL, matter replication, or transporters. The system is almost completely bare of Handwavium, so ideally tech should be conceivable today.
So - **How can I cool down a planetary core on a timescale of centuries?** | 2020/10/23 | [
"https://worldbuilding.stackexchange.com/questions/188763",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/28786/"
] | **Launch hot material into space**
Basically, there are only three methods to transfer heat: conduction, convection, and radiation. In space, only the method #3 works. Hot object mush exhaust itself radiating heat into space. While this works, this is very slow. You will have to wait for thousand years for a planet-sized object to cool a fraction of a degree. Building big heat-emitting radiators might help, but those radiators must be also planet-sized.
Conduction and convention methods won't work, because there is no other body to conduct the heat to, and there is no atmosphere. But what if you create a convection (or, rather, direct transfer of overheated gas) out of the planet? This would effectively transfer away all of the excess heat.
Your operation then would go like this:
1. Digging machines would excavate planetary material, vaporizing it in the process. The process would actually become simpler when you get the hotter core;
2. Vapor would get ionized and transferred to an orbital launch ionic "cannon", which would accelerate material to the first cosmic velocity (which, for Mercury-sized planet is only about 3 km/s) and launch this plasma into the orbit;
3. The plasma would form a disk around the planet, and due to its low density would quickly cool down, forming dust;
4. Your orbital operations would collect the dust and transfer it to some other place in the system where you need it. | I think you're dealing with a non-problem here. You're giving a time scale of centuries.
You **can't** simply dig down in one spot, it won't take too much distance before your dig collapses. You have to spread your digging out all over the planet. As you dig away material what's underneath is warmer but not greatly so. By the time you get back to that spot it will have cooled naturally.
Besides, your big problem is the waste energy from lifting all that material to space, not the energy of the planetary core. |
188,763 | We start with one small (but perfectly formed) planetoid. Just for the sake of discussion, we'll say it's Mercury. This planet is more or less useless to me, being too small and too close to the sun. Fortunately, I've got this big building project in mind...and I need materials.
Not-Mercury is therefore slated for deconstruction. I have massive mobile excavator/refinery complexes that are eating steadily away at the crust, processing the rock into useful components, and transporting them to orbit for use in my Dyson Swarm.
However, the core of the planet is still extremely hot - not as hot as Earth's core, and not hot enough to drive tectonic activity, but certainly hot enough to cause critical components of my excavators to become inconveniently runny. What I'd like to do, then, is have some process in place that can transport the heat away from the depths of the planet, keeping the surface cool enough for my machines to work efficiently.
The population of the planet live in subterranean, multi-level tunnel-cities (similar to Zion in the Matrix series). Ideally these cities should be a part of whatever system we put in place to cool the core, but that's not strictly required. Tech level is advanced enough to allow routine interplanetary travel, but not interstellar; fusion reactors, mass drivers, arcologies, etc, but no FTL, matter replication, or transporters. The system is almost completely bare of Handwavium, so ideally tech should be conceivable today.
So - **How can I cool down a planetary core on a timescale of centuries?** | 2020/10/23 | [
"https://worldbuilding.stackexchange.com/questions/188763",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/28786/"
] | **Launch hot material into space**
Basically, there are only three methods to transfer heat: conduction, convection, and radiation. In space, only the method #3 works. Hot object mush exhaust itself radiating heat into space. While this works, this is very slow. You will have to wait for thousand years for a planet-sized object to cool a fraction of a degree. Building big heat-emitting radiators might help, but those radiators must be also planet-sized.
Conduction and convention methods won't work, because there is no other body to conduct the heat to, and there is no atmosphere. But what if you create a convection (or, rather, direct transfer of overheated gas) out of the planet? This would effectively transfer away all of the excess heat.
Your operation then would go like this:
1. Digging machines would excavate planetary material, vaporizing it in the process. The process would actually become simpler when you get the hotter core;
2. Vapor would get ionized and transferred to an orbital launch ionic "cannon", which would accelerate material to the first cosmic velocity (which, for Mercury-sized planet is only about 3 km/s) and launch this plasma into the orbit;
3. The plasma would form a disk around the planet, and due to its low density would quickly cool down, forming dust;
4. Your orbital operations would collect the dust and transfer it to some other place in the system where you need it. | **Use the Sundiver Approach**
As in the David Brin book. Excess heat is converted to high frequency laser light and either beamed to the surface machinery or into space for other uses. The power is generated using the temperature difference between the surface and sub-surface layers. |
188,763 | We start with one small (but perfectly formed) planetoid. Just for the sake of discussion, we'll say it's Mercury. This planet is more or less useless to me, being too small and too close to the sun. Fortunately, I've got this big building project in mind...and I need materials.
Not-Mercury is therefore slated for deconstruction. I have massive mobile excavator/refinery complexes that are eating steadily away at the crust, processing the rock into useful components, and transporting them to orbit for use in my Dyson Swarm.
However, the core of the planet is still extremely hot - not as hot as Earth's core, and not hot enough to drive tectonic activity, but certainly hot enough to cause critical components of my excavators to become inconveniently runny. What I'd like to do, then, is have some process in place that can transport the heat away from the depths of the planet, keeping the surface cool enough for my machines to work efficiently.
The population of the planet live in subterranean, multi-level tunnel-cities (similar to Zion in the Matrix series). Ideally these cities should be a part of whatever system we put in place to cool the core, but that's not strictly required. Tech level is advanced enough to allow routine interplanetary travel, but not interstellar; fusion reactors, mass drivers, arcologies, etc, but no FTL, matter replication, or transporters. The system is almost completely bare of Handwavium, so ideally tech should be conceivable today.
So - **How can I cool down a planetary core on a timescale of centuries?** | 2020/10/23 | [
"https://worldbuilding.stackexchange.com/questions/188763",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/28786/"
] | I think you're dealing with a non-problem here. You're giving a time scale of centuries.
You **can't** simply dig down in one spot, it won't take too much distance before your dig collapses. You have to spread your digging out all over the planet. As you dig away material what's underneath is warmer but not greatly so. By the time you get back to that spot it will have cooled naturally.
Besides, your big problem is the waste energy from lifting all that material to space, not the energy of the planetary core. | **Use the Sundiver Approach**
As in the David Brin book. Excess heat is converted to high frequency laser light and either beamed to the surface machinery or into space for other uses. The power is generated using the temperature difference between the surface and sub-surface layers. |
92,320 | As you know, the Academy of Motion Pictures, Arts and Sciences has announced that they will be including a new category called 'Outstanding Achievement in Popular Film' in their award agenda as of 2020. And I was watching an interview in which two film critics exchange their ideas pertaining to the matter in question like "Is it any good for the Academy or bad?"
One of the critics said to the other that Oscars do not hold much importance to some directors in the industry anymore. The other one replied: "What you said is not quite true because getting nominated for an Oscar and receiving one has still considerable significance for some names working in the industry such as Scorsese." Followingly he made a joke saying: "Okay maybe not for Woody Allen. He does not care about the Oscars at all."
So what I'd like to know is why the Oscars are unimportant for Woody Allen. I know that there had been some award ceremonies where Allen was not in the attendance but some of them he did attend like the one in 2002.
Could Woody Allen's disinterestedness be related with him not considering himself a Hollywood personality or is there another reason for it? | 2018/09/06 | [
"https://movies.stackexchange.com/questions/92320",
"https://movies.stackexchange.com",
"https://movies.stackexchange.com/users/65940/"
] | Woody Allen has been known to ignore Oscars and never attends them. [According to his biographer](https://www.npr.org/2012/02/24/147367956/why-woody-allen-is-always-mia-at-oscars), Eric Lax;
>
> LAX: It's really almost impossible, as he puts it, to judge art, that
> it's so subjective, you can't really say, well, this performance is
> better than that or that writing is better than this and that, if you
> get caught in that trap of relying on other people, however great they
> are, to tell you whether you're any good, you're either going to
> consciously or subconsciously start playing to that group.
>
>
> | In addition to the factual and technical notes by Johnny Bones, let's also consider what an award is in the first place.
In many cases, an award is presented and distributed by an agency standing apart from the groups qualified for being awarded. In some cases, like the AMPAS the committee is supposedly a collection of professionals within the organization but really, who knows for sure? Who gets nominated and why is a matter of contention, but it ultimately follows a set of rules which are not important to list here. Some believe the probability of being nominated is offset by the amount of money one budgets for campaigning for such things.
Whether or not it's all true is not as important as whether or not it's all just a bunch of useless noise to people who are more interested in the work they produce. Some film makers and writers do it because they love doing it, must do it, or their work speaks for itself and their futures are not contingent on the number of accolades they have collected over the years.
Psychologically speaking, it is possible that Woody Allen just didn't care to pander to a ritual that makes no sense to him. I agree, as I could not care less if I was awarded anything. Nobel, Congressional Medal of Honor, Oscar. They all mean absolutely nothing to me and I am unknown in a field where having such awards may actually benefit my so called career. I wouldn't even respond if I was nominated. Even though there are numerous quotes from Woody Allen on the subject, the foundation for his disinterest is most likely in a confidence in his own work that never needed affirmation from anyone else. Like a comedian who makes the whole room laugh - that alone is the affirmation they needed, whether or not a panel of goof balls decided to give them a small statue to recognize this.
Not to be an A-Hole, but there's also the notion of who else holds this award. How do we know he doesn't just despise someone or many who have been awarded? Maybe he thinks of himself apart, or above some of the industry standards defined by who has been awarded in the past. To him, winning an oscar might be akin to "polishing a turd" ... Like if Adolf Hitler was awarded a Nobel prize. Every other holder pretty much throws that award in the trash at that point.
Any official notation on the subject is pretty easily found through Google searching. I added this blurb just to give a personal note. I work for an agency that just won the top award at some thing I don't care about. But my not caring about it is why I can relate to Woody Allen on this subject. I simply cannot find it in me to concern myself with what a panel of people have decided is the best. It seems so self serving, and reciprocal. What a silly little game. |
50,981 | In *Batman vs Superman*, why does the Batman have no trouble in killing goons while rescuing Martha Kent, when we know that the Dark Knight is inclined towards lawfully trying criminals rather than killing them, from previous Batman outings? | 2016/03/29 | [
"https://movies.stackexchange.com/questions/50981",
"https://movies.stackexchange.com",
"https://movies.stackexchange.com/users/4083/"
] | This question has arisen quite a lot since *Dawn of Justice* came out, and while I think it's a fair criticism of Zach Snyder's Batman, the question is usually framed in a way that has a few problems: the idea that this Batman kills for no reason, the idea that the movie never explains why this Batman "changed", and the idea that Batman in general doesn't kill people.
First of all, it's important to keep in mind, as with every other reboot of Batman, that this is a *brand new character*, created by DC Extended Universe "creative director" Zach Snyder and his various writers for *Dawn of Justice* and it's sequels. Obviously, he is using the name and likeness and general backstory from the DC comics character his movies are based on. But just like Kal El was given a new personality, Bruce Wayne has his own new, original personality in this movie. So it's not valid to say that his behavior is inconsistent with any prior actions or philosophy, because there are none. The DCEU Bruce Wayne has never been in any other movie before this, so his actions in *Dawn of Justice* are all we have to go on.
Second, the movie tries (but maybe doesn't succeed) to get across the idea that Batman was not always like this. Alfred repeatedly chastises Bruce for what he's doing and how he's doing it, and there are multiple conversations about the idea that Gotham ultimately corrupts all good men. Though they don't go much into the backstory of Batman yet, the very strong implication is that The Joker has done something incredibly horrible -- probably involving the death of Robin, who's suit we see in the movie -- that even led Bruce to retire from crime fighting. It was only the arrival of Superman and the destruction he caused that led Bruce to go back into business, and his experiences have made him dark and jaded and angry. So, as Batman, he's now *doing the wrong thing* because he's allowing his anger to overcome him.
The final scene in the movie, between Bruce and Diana, practically comes out and says this. Bruce claims that he had let Clark down with his actions, but he's going to do better, and make it up to him. Snyder seems to be leading Bruce on a process of character development where he recognizes the danger and fallout of his previous behavior, and strives to do better.
Third, and possibly most important, Batman is *not* always averse to killing people. Batman in *Dawn of Justice* may be more overt about it, and they may show it more obviously on-screen, but in pretty much [every Batman movie to date](https://www.youtube.com/watch?v=psVIG7YvdjM) Batman has done things that can't possibly have left the target alive, up to and including firing missiles at people from the Batmobile. Batman, in the source comic material, has a "moral code" against killing people, but a lot of that is momentum stemming back to the Golden Age of comics, and particularly during the dominance of the CCA, when the hero would *never be allowed* to hurt someone on-panel. Even then, there has been [more than one](http://www.cracked.com/article_20111_the-6-most-brutal-murders-committed-by-batman.html) incident in the comics -- as far back as pre-CCA-era 1940's -- where Batman clearly kills someone in cold blood. | KutuluMike answered it quite well but here is what Zack Snyder said himself :
>
> I tried to do it in a technical way. There’s a great YouTube video that shows all the kills in the Christopher Nolan movies even though we would perceive them as movies where he doesn’t kill anyone. I think there’s 42 potential kills that Batman does! Also, it goes back and includes even the Tim Burton Batman movies where this reputation as a guy that doesn’t kill comes from.
>
>
> So, I tried to do it by proxy. Shoot the car they’re in, the car blows up or the grenade would go off in the guy’s hand, or when he shoots the tank and the guy pretty much lights the tank [himself]. I perceive it as him not killing directly, but if the bad guy’s are associated with a thing that happens to blow up, he would say that that’s not really my problem.
>
>
> A little more like manslaughter than murder, although I would say that in the Frank Miller comic book that I reference, he kills all the time. There’s a scene from the graphic novel where he busts through a wall, takes the guy’s machine gun…I took that little vignette from a scene in The Dark Knight Returns, and at the end of that, he shoots the guy right between the eyes with the machine gun. One shot. Of course, I went to the gas tank, and all of the guys I work with were like, ‘You’ve gotta shoot him in the head’ because they’re all comic book dorks, and I was like, ‘I’m not gonna be the guy that does that! - { Source: [heyuguys.com](http://www.heyuguys.com/exclusive-zack-snyder-explains-detail-dark-knight-kills-batman-v-superman/)}
>
>
>
Here is that video:
Even KutuluMike's answer mentioned this video.
And below is the full interview of Zack Snyder: |
2,982,404 | I've been looking at these too, both seem to provide fully functional XMPP servers in Java. I know Tigase is designed in a very modular way, not looked at Openfire in as much detail yet.
My intended use would be to create a custom IM-based app, using XMPP for convenience rather than to open my server up to talk to other XMPP servers.
I'm trying to evaluate my needs based on the following, roughly in order of importance:
1. Documentation coverage & community
2. How easy to plug in own functionality
3. Licensing/cost - I don't plan to release my code
4. Maturity and stability | 2010/06/05 | [
"https://Stackoverflow.com/questions/2982404",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/197229/"
] | Tigase is GPL(even version 3) licensed opposed to OpenFire being under Apache license ... for closed source application is OpenFire the go.
It is embaddable and proven to be reliable - 1000s of concurrent users. It even has gateways to communicate with legacy networks - like ICQ.
Only drawback I can se here is that it can handle only one domain per instance(port), however from your description that should not be a problem. | Concerning openfire ... it seems to be more or less abandoned and certainly not because of lack bugs to fix ;) |
2,982,404 | I've been looking at these too, both seem to provide fully functional XMPP servers in Java. I know Tigase is designed in a very modular way, not looked at Openfire in as much detail yet.
My intended use would be to create a custom IM-based app, using XMPP for convenience rather than to open my server up to talk to other XMPP servers.
I'm trying to evaluate my needs based on the following, roughly in order of importance:
1. Documentation coverage & community
2. How easy to plug in own functionality
3. Licensing/cost - I don't plan to release my code
4. Maturity and stability | 2010/06/05 | [
"https://Stackoverflow.com/questions/2982404",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/197229/"
] | Tigase is GPL(even version 3) licensed opposed to OpenFire being under Apache license ... for closed source application is OpenFire the go.
It is embaddable and proven to be reliable - 1000s of concurrent users. It even has gateways to communicate with legacy networks - like ICQ.
Only drawback I can se here is that it can handle only one domain per instance(port), however from your description that should not be a problem. | And Openfire 3.7.0.beta is out since some days now.
Lots of bug fixes, now also support Solaris as host system. |
2,982,404 | I've been looking at these too, both seem to provide fully functional XMPP servers in Java. I know Tigase is designed in a very modular way, not looked at Openfire in as much detail yet.
My intended use would be to create a custom IM-based app, using XMPP for convenience rather than to open my server up to talk to other XMPP servers.
I'm trying to evaluate my needs based on the following, roughly in order of importance:
1. Documentation coverage & community
2. How easy to plug in own functionality
3. Licensing/cost - I don't plan to release my code
4. Maturity and stability | 2010/06/05 | [
"https://Stackoverflow.com/questions/2982404",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/197229/"
] | Do not use Openfire if you expect to scale beyond a couple of thousand concurrent connections.
Tigase is amazing at handling hundreds of thousands concurrent connections and is wonderfully architected for largely distributed platforms where XMPP is simply the external interface. It comes with a price of rather poor documentation. You often need to go and read the source code to understand what's going on.
Openfire is perfect for small setups and its API is simple and very well documented. Unfortunately, it's not architected to scale even nearly close to what tigase is capable of. | Tigase is GPL(even version 3) licensed opposed to OpenFire being under Apache license ... for closed source application is OpenFire the go.
It is embaddable and proven to be reliable - 1000s of concurrent users. It even has gateways to communicate with legacy networks - like ICQ.
Only drawback I can se here is that it can handle only one domain per instance(port), however from your description that should not be a problem. |
2,982,404 | I've been looking at these too, both seem to provide fully functional XMPP servers in Java. I know Tigase is designed in a very modular way, not looked at Openfire in as much detail yet.
My intended use would be to create a custom IM-based app, using XMPP for convenience rather than to open my server up to talk to other XMPP servers.
I'm trying to evaluate my needs based on the following, roughly in order of importance:
1. Documentation coverage & community
2. How easy to plug in own functionality
3. Licensing/cost - I don't plan to release my code
4. Maturity and stability | 2010/06/05 | [
"https://Stackoverflow.com/questions/2982404",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/197229/"
] | And Openfire 3.7.0.beta is out since some days now.
Lots of bug fixes, now also support Solaris as host system. | Concerning openfire ... it seems to be more or less abandoned and certainly not because of lack bugs to fix ;) |
2,982,404 | I've been looking at these too, both seem to provide fully functional XMPP servers in Java. I know Tigase is designed in a very modular way, not looked at Openfire in as much detail yet.
My intended use would be to create a custom IM-based app, using XMPP for convenience rather than to open my server up to talk to other XMPP servers.
I'm trying to evaluate my needs based on the following, roughly in order of importance:
1. Documentation coverage & community
2. How easy to plug in own functionality
3. Licensing/cost - I don't plan to release my code
4. Maturity and stability | 2010/06/05 | [
"https://Stackoverflow.com/questions/2982404",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/197229/"
] | Do not use Openfire if you expect to scale beyond a couple of thousand concurrent connections.
Tigase is amazing at handling hundreds of thousands concurrent connections and is wonderfully architected for largely distributed platforms where XMPP is simply the external interface. It comes with a price of rather poor documentation. You often need to go and read the source code to understand what's going on.
Openfire is perfect for small setups and its API is simple and very well documented. Unfortunately, it's not architected to scale even nearly close to what tigase is capable of. | Concerning openfire ... it seems to be more or less abandoned and certainly not because of lack bugs to fix ;) |
2,982,404 | I've been looking at these too, both seem to provide fully functional XMPP servers in Java. I know Tigase is designed in a very modular way, not looked at Openfire in as much detail yet.
My intended use would be to create a custom IM-based app, using XMPP for convenience rather than to open my server up to talk to other XMPP servers.
I'm trying to evaluate my needs based on the following, roughly in order of importance:
1. Documentation coverage & community
2. How easy to plug in own functionality
3. Licensing/cost - I don't plan to release my code
4. Maturity and stability | 2010/06/05 | [
"https://Stackoverflow.com/questions/2982404",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/197229/"
] | I totally agree with @Yuriy in that Tigase is great for high scalability whereas Openfire is more suitable for small, novice IT running chat for a SMB. I have gone into more detail on this in my blog on [Tigase vs Openfire](http://glennengstrand.info/blog/?p=143). | Concerning openfire ... it seems to be more or less abandoned and certainly not because of lack bugs to fix ;) |
2,982,404 | I've been looking at these too, both seem to provide fully functional XMPP servers in Java. I know Tigase is designed in a very modular way, not looked at Openfire in as much detail yet.
My intended use would be to create a custom IM-based app, using XMPP for convenience rather than to open my server up to talk to other XMPP servers.
I'm trying to evaluate my needs based on the following, roughly in order of importance:
1. Documentation coverage & community
2. How easy to plug in own functionality
3. Licensing/cost - I don't plan to release my code
4. Maturity and stability | 2010/06/05 | [
"https://Stackoverflow.com/questions/2982404",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/197229/"
] | Do not use Openfire if you expect to scale beyond a couple of thousand concurrent connections.
Tigase is amazing at handling hundreds of thousands concurrent connections and is wonderfully architected for largely distributed platforms where XMPP is simply the external interface. It comes with a price of rather poor documentation. You often need to go and read the source code to understand what's going on.
Openfire is perfect for small setups and its API is simple and very well documented. Unfortunately, it's not architected to scale even nearly close to what tigase is capable of. | And Openfire 3.7.0.beta is out since some days now.
Lots of bug fixes, now also support Solaris as host system. |
2,982,404 | I've been looking at these too, both seem to provide fully functional XMPP servers in Java. I know Tigase is designed in a very modular way, not looked at Openfire in as much detail yet.
My intended use would be to create a custom IM-based app, using XMPP for convenience rather than to open my server up to talk to other XMPP servers.
I'm trying to evaluate my needs based on the following, roughly in order of importance:
1. Documentation coverage & community
2. How easy to plug in own functionality
3. Licensing/cost - I don't plan to release my code
4. Maturity and stability | 2010/06/05 | [
"https://Stackoverflow.com/questions/2982404",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/197229/"
] | I totally agree with @Yuriy in that Tigase is great for high scalability whereas Openfire is more suitable for small, novice IT running chat for a SMB. I have gone into more detail on this in my blog on [Tigase vs Openfire](http://glennengstrand.info/blog/?p=143). | And Openfire 3.7.0.beta is out since some days now.
Lots of bug fixes, now also support Solaris as host system. |
2,982,404 | I've been looking at these too, both seem to provide fully functional XMPP servers in Java. I know Tigase is designed in a very modular way, not looked at Openfire in as much detail yet.
My intended use would be to create a custom IM-based app, using XMPP for convenience rather than to open my server up to talk to other XMPP servers.
I'm trying to evaluate my needs based on the following, roughly in order of importance:
1. Documentation coverage & community
2. How easy to plug in own functionality
3. Licensing/cost - I don't plan to release my code
4. Maturity and stability | 2010/06/05 | [
"https://Stackoverflow.com/questions/2982404",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/197229/"
] | Do not use Openfire if you expect to scale beyond a couple of thousand concurrent connections.
Tigase is amazing at handling hundreds of thousands concurrent connections and is wonderfully architected for largely distributed platforms where XMPP is simply the external interface. It comes with a price of rather poor documentation. You often need to go and read the source code to understand what's going on.
Openfire is perfect for small setups and its API is simple and very well documented. Unfortunately, it's not architected to scale even nearly close to what tigase is capable of. | I totally agree with @Yuriy in that Tigase is great for high scalability whereas Openfire is more suitable for small, novice IT running chat for a SMB. I have gone into more detail on this in my blog on [Tigase vs Openfire](http://glennengstrand.info/blog/?p=143). |
93,340 | The context is below.
>
> Bansal is the famous coaching center to clear Engineering Entrance test. **Bansal students had a chip on their shoulder, even though they weren't technically even in a college**
>
>
>
The meaning for the phrase **chip on their shoulder** is **a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight**. I can understand its meaning refers to they are so much alert to face any question or puzzle related to engineering entrance test. But why author added the clause **even though they weren't technically even in a college**? It confuses me. Does it mean only students those goes to college should pocess that kind of attribute or mindset? | 2012/12/05 | [
"https://english.stackexchange.com/questions/93340",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/30645/"
] | I'll go into the semantics here since I have a wee bit of a knowledge of what is being talked about here.
If you're from India, you have the perception, thanks to media, that the students who take classes for engineering entrance to make it to IITs are perceived as the so-called 'inferiors'. It is this that is being referred to here. These students are yet to make it to some college and yet they already know that they might be perceived as the not-so-good ones among their peers.
I hope I'm clear with my thoughts here. | Having a chip on one's shoulder refers to when someone is part of a group or institution that is perceived as being inferior, but its members believe that reputation is unfair.
In your case, the attendees of that school feel that attending a prepatory school makes others view them poorly, but the members do not believe they should be viewed poorly. |
93,340 | The context is below.
>
> Bansal is the famous coaching center to clear Engineering Entrance test. **Bansal students had a chip on their shoulder, even though they weren't technically even in a college**
>
>
>
The meaning for the phrase **chip on their shoulder** is **a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight**. I can understand its meaning refers to they are so much alert to face any question or puzzle related to engineering entrance test. But why author added the clause **even though they weren't technically even in a college**? It confuses me. Does it mean only students those goes to college should pocess that kind of attribute or mindset? | 2012/12/05 | [
"https://english.stackexchange.com/questions/93340",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/30645/"
] | First, this is a [metaphor](http://www.umich.edu/~jlawler/Metaphors.pdf). Like all metaphors it has a number of possible interpretations. It's not literal, and people do not in fact put a physical *chip* on their physical *shoulder*. I'm 70 years old, and I've never seen any actual human being who literally had a chip on their shoulder.
Second, this metaphor refers to any person who seems to take offense easily -- to be seeking out offenses to challenge, in fact. The image has to do with a challenge to "knock this chip off my shoulder," as the first blow in a personal fight. Anybody who said such a thing would have been determined to fight in the first place, and was merely looking for a provoking event. Similar remarks apply to similar metaphors like [*drawing a line on the ground/in the sand*](https://english.stackexchange.com/q/93316/15299).
Third, it is often assumed (because it is so common and so human) that such irascibility is rooted in a personal sense of inferiority of some sort. It can be a matter of backing the wrong team, or being in the wrong social class, or something more personal. In fact, it is hard to separate personal from social inferiority, and many people don't try. But that's not the only possible meaning, merely a frequent accompaniment to such aggressive display. | Having a chip on one's shoulder refers to when someone is part of a group or institution that is perceived as being inferior, but its members believe that reputation is unfair.
In your case, the attendees of that school feel that attending a prepatory school makes others view them poorly, but the members do not believe they should be viewed poorly. |
93,340 | The context is below.
>
> Bansal is the famous coaching center to clear Engineering Entrance test. **Bansal students had a chip on their shoulder, even though they weren't technically even in a college**
>
>
>
The meaning for the phrase **chip on their shoulder** is **a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight**. I can understand its meaning refers to they are so much alert to face any question or puzzle related to engineering entrance test. But why author added the clause **even though they weren't technically even in a college**? It confuses me. Does it mean only students those goes to college should pocess that kind of attribute or mindset? | 2012/12/05 | [
"https://english.stackexchange.com/questions/93340",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/30645/"
] | Having a chip on one's shoulder refers to when someone is part of a group or institution that is perceived as being inferior, but its members believe that reputation is unfair.
In your case, the attendees of that school feel that attending a prepatory school makes others view them poorly, but the members do not believe they should be viewed poorly. | Surely thi phrase started from the Wink Wink brand of chips, which were popular with college teachers. Over time the phrase came to mean any learned individuals who have rather sloppy snack eating habits. |
93,340 | The context is below.
>
> Bansal is the famous coaching center to clear Engineering Entrance test. **Bansal students had a chip on their shoulder, even though they weren't technically even in a college**
>
>
>
The meaning for the phrase **chip on their shoulder** is **a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight**. I can understand its meaning refers to they are so much alert to face any question or puzzle related to engineering entrance test. But why author added the clause **even though they weren't technically even in a college**? It confuses me. Does it mean only students those goes to college should pocess that kind of attribute or mindset? | 2012/12/05 | [
"https://english.stackexchange.com/questions/93340",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/30645/"
] | First, this is a [metaphor](http://www.umich.edu/~jlawler/Metaphors.pdf). Like all metaphors it has a number of possible interpretations. It's not literal, and people do not in fact put a physical *chip* on their physical *shoulder*. I'm 70 years old, and I've never seen any actual human being who literally had a chip on their shoulder.
Second, this metaphor refers to any person who seems to take offense easily -- to be seeking out offenses to challenge, in fact. The image has to do with a challenge to "knock this chip off my shoulder," as the first blow in a personal fight. Anybody who said such a thing would have been determined to fight in the first place, and was merely looking for a provoking event. Similar remarks apply to similar metaphors like [*drawing a line on the ground/in the sand*](https://english.stackexchange.com/q/93316/15299).
Third, it is often assumed (because it is so common and so human) that such irascibility is rooted in a personal sense of inferiority of some sort. It can be a matter of backing the wrong team, or being in the wrong social class, or something more personal. In fact, it is hard to separate personal from social inferiority, and many people don't try. But that's not the only possible meaning, merely a frequent accompaniment to such aggressive display. | I'll go into the semantics here since I have a wee bit of a knowledge of what is being talked about here.
If you're from India, you have the perception, thanks to media, that the students who take classes for engineering entrance to make it to IITs are perceived as the so-called 'inferiors'. It is this that is being referred to here. These students are yet to make it to some college and yet they already know that they might be perceived as the not-so-good ones among their peers.
I hope I'm clear with my thoughts here. |
93,340 | The context is below.
>
> Bansal is the famous coaching center to clear Engineering Entrance test. **Bansal students had a chip on their shoulder, even though they weren't technically even in a college**
>
>
>
The meaning for the phrase **chip on their shoulder** is **a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight**. I can understand its meaning refers to they are so much alert to face any question or puzzle related to engineering entrance test. But why author added the clause **even though they weren't technically even in a college**? It confuses me. Does it mean only students those goes to college should pocess that kind of attribute or mindset? | 2012/12/05 | [
"https://english.stackexchange.com/questions/93340",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/30645/"
] | I'll go into the semantics here since I have a wee bit of a knowledge of what is being talked about here.
If you're from India, you have the perception, thanks to media, that the students who take classes for engineering entrance to make it to IITs are perceived as the so-called 'inferiors'. It is this that is being referred to here. These students are yet to make it to some college and yet they already know that they might be perceived as the not-so-good ones among their peers.
I hope I'm clear with my thoughts here. | Surely thi phrase started from the Wink Wink brand of chips, which were popular with college teachers. Over time the phrase came to mean any learned individuals who have rather sloppy snack eating habits. |
93,340 | The context is below.
>
> Bansal is the famous coaching center to clear Engineering Entrance test. **Bansal students had a chip on their shoulder, even though they weren't technically even in a college**
>
>
>
The meaning for the phrase **chip on their shoulder** is **a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight**. I can understand its meaning refers to they are so much alert to face any question or puzzle related to engineering entrance test. But why author added the clause **even though they weren't technically even in a college**? It confuses me. Does it mean only students those goes to college should pocess that kind of attribute or mindset? | 2012/12/05 | [
"https://english.stackexchange.com/questions/93340",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/30645/"
] | I'll go into the semantics here since I have a wee bit of a knowledge of what is being talked about here.
If you're from India, you have the perception, thanks to media, that the students who take classes for engineering entrance to make it to IITs are perceived as the so-called 'inferiors'. It is this that is being referred to here. These students are yet to make it to some college and yet they already know that they might be perceived as the not-so-good ones among their peers.
I hope I'm clear with my thoughts here. | Having a 'chip on your shoulder' *generally* refers to someone begrudging an opposing person/party. It can be for many reasons - jealously, resentment, bitterness conceived from what the person feels has been a wrongdoing against them by this person/party, an inferiority complex, or indeed general ignorance that has been inherited from peers/parents.
I would need to see what's written before the paragraph you've posted as to why they have a 'chip on their shoulder', as nothing in that paragraph gives it away as to what has caused this issue except for the possibility that the reputation of the centre isn't great and they therefore suffer from an inferiority complex. |
93,340 | The context is below.
>
> Bansal is the famous coaching center to clear Engineering Entrance test. **Bansal students had a chip on their shoulder, even though they weren't technically even in a college**
>
>
>
The meaning for the phrase **chip on their shoulder** is **a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight**. I can understand its meaning refers to they are so much alert to face any question or puzzle related to engineering entrance test. But why author added the clause **even though they weren't technically even in a college**? It confuses me. Does it mean only students those goes to college should pocess that kind of attribute or mindset? | 2012/12/05 | [
"https://english.stackexchange.com/questions/93340",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/30645/"
] | First, this is a [metaphor](http://www.umich.edu/~jlawler/Metaphors.pdf). Like all metaphors it has a number of possible interpretations. It's not literal, and people do not in fact put a physical *chip* on their physical *shoulder*. I'm 70 years old, and I've never seen any actual human being who literally had a chip on their shoulder.
Second, this metaphor refers to any person who seems to take offense easily -- to be seeking out offenses to challenge, in fact. The image has to do with a challenge to "knock this chip off my shoulder," as the first blow in a personal fight. Anybody who said such a thing would have been determined to fight in the first place, and was merely looking for a provoking event. Similar remarks apply to similar metaphors like [*drawing a line on the ground/in the sand*](https://english.stackexchange.com/q/93316/15299).
Third, it is often assumed (because it is so common and so human) that such irascibility is rooted in a personal sense of inferiority of some sort. It can be a matter of backing the wrong team, or being in the wrong social class, or something more personal. In fact, it is hard to separate personal from social inferiority, and many people don't try. But that's not the only possible meaning, merely a frequent accompaniment to such aggressive display. | Surely thi phrase started from the Wink Wink brand of chips, which were popular with college teachers. Over time the phrase came to mean any learned individuals who have rather sloppy snack eating habits. |
93,340 | The context is below.
>
> Bansal is the famous coaching center to clear Engineering Entrance test. **Bansal students had a chip on their shoulder, even though they weren't technically even in a college**
>
>
>
The meaning for the phrase **chip on their shoulder** is **a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight**. I can understand its meaning refers to they are so much alert to face any question or puzzle related to engineering entrance test. But why author added the clause **even though they weren't technically even in a college**? It confuses me. Does it mean only students those goes to college should pocess that kind of attribute or mindset? | 2012/12/05 | [
"https://english.stackexchange.com/questions/93340",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/30645/"
] | First, this is a [metaphor](http://www.umich.edu/~jlawler/Metaphors.pdf). Like all metaphors it has a number of possible interpretations. It's not literal, and people do not in fact put a physical *chip* on their physical *shoulder*. I'm 70 years old, and I've never seen any actual human being who literally had a chip on their shoulder.
Second, this metaphor refers to any person who seems to take offense easily -- to be seeking out offenses to challenge, in fact. The image has to do with a challenge to "knock this chip off my shoulder," as the first blow in a personal fight. Anybody who said such a thing would have been determined to fight in the first place, and was merely looking for a provoking event. Similar remarks apply to similar metaphors like [*drawing a line on the ground/in the sand*](https://english.stackexchange.com/q/93316/15299).
Third, it is often assumed (because it is so common and so human) that such irascibility is rooted in a personal sense of inferiority of some sort. It can be a matter of backing the wrong team, or being in the wrong social class, or something more personal. In fact, it is hard to separate personal from social inferiority, and many people don't try. But that's not the only possible meaning, merely a frequent accompaniment to such aggressive display. | Having a 'chip on your shoulder' *generally* refers to someone begrudging an opposing person/party. It can be for many reasons - jealously, resentment, bitterness conceived from what the person feels has been a wrongdoing against them by this person/party, an inferiority complex, or indeed general ignorance that has been inherited from peers/parents.
I would need to see what's written before the paragraph you've posted as to why they have a 'chip on their shoulder', as nothing in that paragraph gives it away as to what has caused this issue except for the possibility that the reputation of the centre isn't great and they therefore suffer from an inferiority complex. |
93,340 | The context is below.
>
> Bansal is the famous coaching center to clear Engineering Entrance test. **Bansal students had a chip on their shoulder, even though they weren't technically even in a college**
>
>
>
The meaning for the phrase **chip on their shoulder** is **a form of physical challenge, inviting opponents to knock the chip off and so provoke a fight**. I can understand its meaning refers to they are so much alert to face any question or puzzle related to engineering entrance test. But why author added the clause **even though they weren't technically even in a college**? It confuses me. Does it mean only students those goes to college should pocess that kind of attribute or mindset? | 2012/12/05 | [
"https://english.stackexchange.com/questions/93340",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/30645/"
] | Having a 'chip on your shoulder' *generally* refers to someone begrudging an opposing person/party. It can be for many reasons - jealously, resentment, bitterness conceived from what the person feels has been a wrongdoing against them by this person/party, an inferiority complex, or indeed general ignorance that has been inherited from peers/parents.
I would need to see what's written before the paragraph you've posted as to why they have a 'chip on their shoulder', as nothing in that paragraph gives it away as to what has caused this issue except for the possibility that the reputation of the centre isn't great and they therefore suffer from an inferiority complex. | Surely thi phrase started from the Wink Wink brand of chips, which were popular with college teachers. Over time the phrase came to mean any learned individuals who have rather sloppy snack eating habits. |
29,829 | I have a few specific questions, but I think they can all be sufficiently generalized as follows:
**Do cursed items which activate upon being worn, held or seen affect creatures that do not willingly wear, hold or look at such cursed items?**
Normally I try to avoid playing rules lawyer, but I'm somewhat curious about this. Specific examples follow.
1. Necklace of strangulation: an assassin sneaks up behind you and successfully executes a melee touch attack, combat maneuver, etc. to place the necklace around your neck. You then die in HP/6 rounds, unless somebody comes up with a way to get it off, of which there don't appear to be many.
2. Poisonous cloak and/or robe of powerlessness: a hero rushes into the evil arch mage's lair, upon which the mage cackles, raises his hand, and causes the vestment to fly up from behind the hero, giving a reflex save to avoid being robed/cloaked.
3. Scarab of death: the grand hero is sleeping, paralyzed, unconscious, or otherwise sufficiently weakened that the BBEG is able to put the little guy into the palm of the hero's hand. Happy saving throw! | 2013/10/30 | [
"https://rpg.stackexchange.com/questions/29829",
"https://rpg.stackexchange.com",
"https://rpg.stackexchange.com/users/8737/"
] | Cursed magic items are just normal magic items with hidden, usually negative, magic properties. Therefore they should function just like normal magical items, except for when trying to detect the properties of the item.
If the BBEG is able to equip/place the item on the player appropriatly, then the curse should take affect.
If not, then [Dimensional Shackles](http://www.d20pfsrd.com/magic-items/wondrous-items/wondrous-items/c-d/dimensional-shackles) would lose a lot of their intended functionality.
>
> These shackles have magical runes traced across their cold iron links.
>
>
> Any creature bound within them is affected as if a dimensional anchor
> spell were cast upon it (no save). They fit any Small to Large
> creature. The DC to break or slip out of the shackles is 30.
>
>
> | It's possible. But the thing to keep in mind is that "cursed item" is a misnomer: they're just items with a use that doesn't intuitively match with what they look like, and happens to make the *intuitive* use of the item dangerous. Clever players *will* find ways to make these things useful.
Your *necklace of strangulation* and *scarab of death* are perfect examples of this: fire-and-forget tools of assassination. I'm a little less sure of your *poisonous cloak*, just because I'm not sure most telekinesis effects grant enough control to actually get them properly onto a person, but that's only an implementation detail: there are other ways to get the job done.
You can fight this with rules, but it rapidly gets strange. Better to just roll with it. Let players figure out awesome uses for "cursed" items a few times. Then stories of their deeds start to spread, and other folks start to get inspired by them... including folks that the players might wish hadn't heard. This is where you get to have your fun: I don't recommend using cursed stuff directly against the players (too much), but they can be used in the background as plot hooks. Consider an assassin who swapped out the crown prince's sword for a berserking sword just before an important battle: the poor prince charged headlong into enemy lines and got himself killed. |
29,829 | I have a few specific questions, but I think they can all be sufficiently generalized as follows:
**Do cursed items which activate upon being worn, held or seen affect creatures that do not willingly wear, hold or look at such cursed items?**
Normally I try to avoid playing rules lawyer, but I'm somewhat curious about this. Specific examples follow.
1. Necklace of strangulation: an assassin sneaks up behind you and successfully executes a melee touch attack, combat maneuver, etc. to place the necklace around your neck. You then die in HP/6 rounds, unless somebody comes up with a way to get it off, of which there don't appear to be many.
2. Poisonous cloak and/or robe of powerlessness: a hero rushes into the evil arch mage's lair, upon which the mage cackles, raises his hand, and causes the vestment to fly up from behind the hero, giving a reflex save to avoid being robed/cloaked.
3. Scarab of death: the grand hero is sleeping, paralyzed, unconscious, or otherwise sufficiently weakened that the BBEG is able to put the little guy into the palm of the hero's hand. Happy saving throw! | 2013/10/30 | [
"https://rpg.stackexchange.com/questions/29829",
"https://rpg.stackexchange.com",
"https://rpg.stackexchange.com/users/8737/"
] | Cursed magic items are just normal magic items with hidden, usually negative, magic properties. Therefore they should function just like normal magical items, except for when trying to detect the properties of the item.
If the BBEG is able to equip/place the item on the player appropriatly, then the curse should take affect.
If not, then [Dimensional Shackles](http://www.d20pfsrd.com/magic-items/wondrous-items/wondrous-items/c-d/dimensional-shackles) would lose a lot of their intended functionality.
>
> These shackles have magical runes traced across their cold iron links.
>
>
> Any creature bound within them is affected as if a dimensional anchor
> spell were cast upon it (no save). They fit any Small to Large
> creature. The DC to break or slip out of the shackles is 30.
>
>
> | Pathfinder seems to have even encouraged this use of such items with the bard spell Beguiling Gift
<http://paizo.com/pathfinderRPG/prd/advanced/spells/beguilingGift.html#_beguiling-gift>
Save vs. will or get messed up, all at first level!
So, pick your opponents weakest saving throw and cackle maniacally. |
198,022 | This sentence just came to mind right after I watched the sentence :
>
> Do you need anything?
>
>
>
So, do these two sentences have the same meaning, or is the one in the title totally redundant? | 2019/02/23 | [
"https://ell.stackexchange.com/questions/198022",
"https://ell.stackexchange.com",
"https://ell.stackexchange.com/users/89944/"
] | Semantically, the two sentences might actually be considered the *opposite* of each other. (Although not necessarily.)
Let's say I'm about to cook a meal that requires ten different ingredients. A friend might ask me:
>
> Do you *need* anything?
>
>
>
The meaning of this is roughly the same as:
>
> Is there something you *don't* have but *do* need me to get for you?
>
>
>
The emphasis is put on asking about things that are missing, not things that exist.
---
But your other sentence seems to convey the opposite emphasis:
>
> Do you *have* anything you need?
>
>
>
Which is roughly the same as:
>
> Is there anything you *do* have and *don't* need me to get for you?
>
>
>
---
In short, *Do you need anything?* puts the emphasis on assuming you *have* most things and might only need a few, whereas *Do you have anything you need?* puts the emphasis on assuming you are *missing* most things and might need a lot.
---
Idiomatically, it's actually these two questions that would be the equivalent:
>
> Do you *need* ***anything***?
>
> Do you *have* ***everything***?
>
>
> | The one in the title is grammatical, but does not mean the same as the one in the question. In fact, it's pretty unlikely anyone would use it.
The sentence in the title is best understood by considering it as having implied words:
>
> Do you have anything *that is* needed?
>
>
>
Literally, I would take that to mean "do you have anything that you need?", which isn't much use as a question. |
121,210 | In my country it is very common for courses to consist of two types of classes: lectures primarily focus on theoretical aspects of a topic and then after each lecture comes a corresponding “practice” class which covers practical aspects of the material from the preceding lecture, such as how to use it to solve exercises. These latter classes can be taught by the same professor or, quite often, by graduate students.
Is there a term for this kind of classes? If you are from another country, how can I concisely explain to you what these classes are for? How do I indicate in my CV that I was a teacher of such a “practical” part of a course?
---
As a person responsible for “practice” classes you have to plan them on your own (it is generally assumed that the topic of each class will be the same as that of the preceding lecture, but it is not a hard requirement and sometimes you might need to deviate); explain techniques and practical considerations; prove theorems (yourself or engaging the students) which didn’t fit into lectures because they were not required for the theoretical narration but rather have practical implications; solve exercises or have students solve them with your hints; etc. You are also responsible for designing and grading homework assignments, projects, tests.
In essence, professor “outsources” part of the course to you and then in the end gets your input about each student’s performance in it. The primary purpose is to divide students into smaller groups (of around 15 or less), each assigned to a separate teacher, so that each student gets more personal attention. | 2018/12/07 | [
"https://academia.stackexchange.com/questions/121210",
"https://academia.stackexchange.com",
"https://academia.stackexchange.com/users/8872/"
] | Try "tutorial".
Example [writeup on what tutorials are](https://student.unsw.edu.au/tutorials) from the University of New South Wales. | These are also called "quiz sections" at my university. |
121,210 | In my country it is very common for courses to consist of two types of classes: lectures primarily focus on theoretical aspects of a topic and then after each lecture comes a corresponding “practice” class which covers practical aspects of the material from the preceding lecture, such as how to use it to solve exercises. These latter classes can be taught by the same professor or, quite often, by graduate students.
Is there a term for this kind of classes? If you are from another country, how can I concisely explain to you what these classes are for? How do I indicate in my CV that I was a teacher of such a “practical” part of a course?
---
As a person responsible for “practice” classes you have to plan them on your own (it is generally assumed that the topic of each class will be the same as that of the preceding lecture, but it is not a hard requirement and sometimes you might need to deviate); explain techniques and practical considerations; prove theorems (yourself or engaging the students) which didn’t fit into lectures because they were not required for the theoretical narration but rather have practical implications; solve exercises or have students solve them with your hints; etc. You are also responsible for designing and grading homework assignments, projects, tests.
In essence, professor “outsources” part of the course to you and then in the end gets your input about each student’s performance in it. The primary purpose is to divide students into smaller groups (of around 15 or less), each assigned to a separate teacher, so that each student gets more personal attention. | 2018/12/07 | [
"https://academia.stackexchange.com/questions/121210",
"https://academia.stackexchange.com",
"https://academia.stackexchange.com/users/8872/"
] | In the US, we used the term *Recitation Section* for such things. A TA and around 15-20 students would work together to make the lectures more personal in some way. In my experience (45 years) it was often used. Such a section would be stable in that the same TA would work with the same students over the course of a term. | Try "tutorial".
Example [writeup on what tutorials are](https://student.unsw.edu.au/tutorials) from the University of New South Wales. |
121,210 | In my country it is very common for courses to consist of two types of classes: lectures primarily focus on theoretical aspects of a topic and then after each lecture comes a corresponding “practice” class which covers practical aspects of the material from the preceding lecture, such as how to use it to solve exercises. These latter classes can be taught by the same professor or, quite often, by graduate students.
Is there a term for this kind of classes? If you are from another country, how can I concisely explain to you what these classes are for? How do I indicate in my CV that I was a teacher of such a “practical” part of a course?
---
As a person responsible for “practice” classes you have to plan them on your own (it is generally assumed that the topic of each class will be the same as that of the preceding lecture, but it is not a hard requirement and sometimes you might need to deviate); explain techniques and practical considerations; prove theorems (yourself or engaging the students) which didn’t fit into lectures because they were not required for the theoretical narration but rather have practical implications; solve exercises or have students solve them with your hints; etc. You are also responsible for designing and grading homework assignments, projects, tests.
In essence, professor “outsources” part of the course to you and then in the end gets your input about each student’s performance in it. The primary purpose is to divide students into smaller groups (of around 15 or less), each assigned to a separate teacher, so that each student gets more personal attention. | 2018/12/07 | [
"https://academia.stackexchange.com/questions/121210",
"https://academia.stackexchange.com",
"https://academia.stackexchange.com/users/8872/"
] | Try "tutorial".
Example [writeup on what tutorials are](https://student.unsw.edu.au/tutorials) from the University of New South Wales. | Best described as a "Tutorial" in my experience. |
121,210 | In my country it is very common for courses to consist of two types of classes: lectures primarily focus on theoretical aspects of a topic and then after each lecture comes a corresponding “practice” class which covers practical aspects of the material from the preceding lecture, such as how to use it to solve exercises. These latter classes can be taught by the same professor or, quite often, by graduate students.
Is there a term for this kind of classes? If you are from another country, how can I concisely explain to you what these classes are for? How do I indicate in my CV that I was a teacher of such a “practical” part of a course?
---
As a person responsible for “practice” classes you have to plan them on your own (it is generally assumed that the topic of each class will be the same as that of the preceding lecture, but it is not a hard requirement and sometimes you might need to deviate); explain techniques and practical considerations; prove theorems (yourself or engaging the students) which didn’t fit into lectures because they were not required for the theoretical narration but rather have practical implications; solve exercises or have students solve them with your hints; etc. You are also responsible for designing and grading homework assignments, projects, tests.
In essence, professor “outsources” part of the course to you and then in the end gets your input about each student’s performance in it. The primary purpose is to divide students into smaller groups (of around 15 or less), each assigned to a separate teacher, so that each student gets more personal attention. | 2018/12/07 | [
"https://academia.stackexchange.com/questions/121210",
"https://academia.stackexchange.com",
"https://academia.stackexchange.com/users/8872/"
] | In the US, we used the term *Recitation Section* for such things. A TA and around 15-20 students would work together to make the lectures more personal in some way. In my experience (45 years) it was often used. Such a section would be stable in that the same TA would work with the same students over the course of a term. | These are also called "quiz sections" at my university. |
121,210 | In my country it is very common for courses to consist of two types of classes: lectures primarily focus on theoretical aspects of a topic and then after each lecture comes a corresponding “practice” class which covers practical aspects of the material from the preceding lecture, such as how to use it to solve exercises. These latter classes can be taught by the same professor or, quite often, by graduate students.
Is there a term for this kind of classes? If you are from another country, how can I concisely explain to you what these classes are for? How do I indicate in my CV that I was a teacher of such a “practical” part of a course?
---
As a person responsible for “practice” classes you have to plan them on your own (it is generally assumed that the topic of each class will be the same as that of the preceding lecture, but it is not a hard requirement and sometimes you might need to deviate); explain techniques and practical considerations; prove theorems (yourself or engaging the students) which didn’t fit into lectures because they were not required for the theoretical narration but rather have practical implications; solve exercises or have students solve them with your hints; etc. You are also responsible for designing and grading homework assignments, projects, tests.
In essence, professor “outsources” part of the course to you and then in the end gets your input about each student’s performance in it. The primary purpose is to divide students into smaller groups (of around 15 or less), each assigned to a separate teacher, so that each student gets more personal attention. | 2018/12/07 | [
"https://academia.stackexchange.com/questions/121210",
"https://academia.stackexchange.com",
"https://academia.stackexchange.com/users/8872/"
] | In the US I have heard them referred to as "discussion sections," "lab sections," or "fourth hour." Discussion implies a small group where students often work together to make sense of the material, although it may be more or less collaborative. Lab implies that they are working on practice problems or scenarios. Lab is more often used for science classes, although I had lab sections for some mathematics classes as well. The term "fourth hour" comes from a standard class meeting time taking 1.5 hours. Two meetings then would be 3 hours, and might be accompanied by a shorter class meeting to add another hour of time each week.
In the US, your job title would be Teaching Assistant or "TA" as it's often known. It is important to specify the variety of work that you have done, especially the curriculum design tasks. TAs in the US range from essentially teaching an entire course, including many lectures. Other TAs have almost no responsibility. They might take attendance, grade tests, and hold office hours to answer questions. And everything in between. | These are also called "quiz sections" at my university. |
121,210 | In my country it is very common for courses to consist of two types of classes: lectures primarily focus on theoretical aspects of a topic and then after each lecture comes a corresponding “practice” class which covers practical aspects of the material from the preceding lecture, such as how to use it to solve exercises. These latter classes can be taught by the same professor or, quite often, by graduate students.
Is there a term for this kind of classes? If you are from another country, how can I concisely explain to you what these classes are for? How do I indicate in my CV that I was a teacher of such a “practical” part of a course?
---
As a person responsible for “practice” classes you have to plan them on your own (it is generally assumed that the topic of each class will be the same as that of the preceding lecture, but it is not a hard requirement and sometimes you might need to deviate); explain techniques and practical considerations; prove theorems (yourself or engaging the students) which didn’t fit into lectures because they were not required for the theoretical narration but rather have practical implications; solve exercises or have students solve them with your hints; etc. You are also responsible for designing and grading homework assignments, projects, tests.
In essence, professor “outsources” part of the course to you and then in the end gets your input about each student’s performance in it. The primary purpose is to divide students into smaller groups (of around 15 or less), each assigned to a separate teacher, so that each student gets more personal attention. | 2018/12/07 | [
"https://academia.stackexchange.com/questions/121210",
"https://academia.stackexchange.com",
"https://academia.stackexchange.com/users/8872/"
] | These are also called "quiz sections" at my university. | Best described as a "Tutorial" in my experience. |
121,210 | In my country it is very common for courses to consist of two types of classes: lectures primarily focus on theoretical aspects of a topic and then after each lecture comes a corresponding “practice” class which covers practical aspects of the material from the preceding lecture, such as how to use it to solve exercises. These latter classes can be taught by the same professor or, quite often, by graduate students.
Is there a term for this kind of classes? If you are from another country, how can I concisely explain to you what these classes are for? How do I indicate in my CV that I was a teacher of such a “practical” part of a course?
---
As a person responsible for “practice” classes you have to plan them on your own (it is generally assumed that the topic of each class will be the same as that of the preceding lecture, but it is not a hard requirement and sometimes you might need to deviate); explain techniques and practical considerations; prove theorems (yourself or engaging the students) which didn’t fit into lectures because they were not required for the theoretical narration but rather have practical implications; solve exercises or have students solve them with your hints; etc. You are also responsible for designing and grading homework assignments, projects, tests.
In essence, professor “outsources” part of the course to you and then in the end gets your input about each student’s performance in it. The primary purpose is to divide students into smaller groups (of around 15 or less), each assigned to a separate teacher, so that each student gets more personal attention. | 2018/12/07 | [
"https://academia.stackexchange.com/questions/121210",
"https://academia.stackexchange.com",
"https://academia.stackexchange.com/users/8872/"
] | In the US, we used the term *Recitation Section* for such things. A TA and around 15-20 students would work together to make the lectures more personal in some way. In my experience (45 years) it was often used. Such a section would be stable in that the same TA would work with the same students over the course of a term. | In the US I have heard them referred to as "discussion sections," "lab sections," or "fourth hour." Discussion implies a small group where students often work together to make sense of the material, although it may be more or less collaborative. Lab implies that they are working on practice problems or scenarios. Lab is more often used for science classes, although I had lab sections for some mathematics classes as well. The term "fourth hour" comes from a standard class meeting time taking 1.5 hours. Two meetings then would be 3 hours, and might be accompanied by a shorter class meeting to add another hour of time each week.
In the US, your job title would be Teaching Assistant or "TA" as it's often known. It is important to specify the variety of work that you have done, especially the curriculum design tasks. TAs in the US range from essentially teaching an entire course, including many lectures. Other TAs have almost no responsibility. They might take attendance, grade tests, and hold office hours to answer questions. And everything in between. |
121,210 | In my country it is very common for courses to consist of two types of classes: lectures primarily focus on theoretical aspects of a topic and then after each lecture comes a corresponding “practice” class which covers practical aspects of the material from the preceding lecture, such as how to use it to solve exercises. These latter classes can be taught by the same professor or, quite often, by graduate students.
Is there a term for this kind of classes? If you are from another country, how can I concisely explain to you what these classes are for? How do I indicate in my CV that I was a teacher of such a “practical” part of a course?
---
As a person responsible for “practice” classes you have to plan them on your own (it is generally assumed that the topic of each class will be the same as that of the preceding lecture, but it is not a hard requirement and sometimes you might need to deviate); explain techniques and practical considerations; prove theorems (yourself or engaging the students) which didn’t fit into lectures because they were not required for the theoretical narration but rather have practical implications; solve exercises or have students solve them with your hints; etc. You are also responsible for designing and grading homework assignments, projects, tests.
In essence, professor “outsources” part of the course to you and then in the end gets your input about each student’s performance in it. The primary purpose is to divide students into smaller groups (of around 15 or less), each assigned to a separate teacher, so that each student gets more personal attention. | 2018/12/07 | [
"https://academia.stackexchange.com/questions/121210",
"https://academia.stackexchange.com",
"https://academia.stackexchange.com/users/8872/"
] | In the US, we used the term *Recitation Section* for such things. A TA and around 15-20 students would work together to make the lectures more personal in some way. In my experience (45 years) it was often used. Such a section would be stable in that the same TA would work with the same students over the course of a term. | Best described as a "Tutorial" in my experience. |
121,210 | In my country it is very common for courses to consist of two types of classes: lectures primarily focus on theoretical aspects of a topic and then after each lecture comes a corresponding “practice” class which covers practical aspects of the material from the preceding lecture, such as how to use it to solve exercises. These latter classes can be taught by the same professor or, quite often, by graduate students.
Is there a term for this kind of classes? If you are from another country, how can I concisely explain to you what these classes are for? How do I indicate in my CV that I was a teacher of such a “practical” part of a course?
---
As a person responsible for “practice” classes you have to plan them on your own (it is generally assumed that the topic of each class will be the same as that of the preceding lecture, but it is not a hard requirement and sometimes you might need to deviate); explain techniques and practical considerations; prove theorems (yourself or engaging the students) which didn’t fit into lectures because they were not required for the theoretical narration but rather have practical implications; solve exercises or have students solve them with your hints; etc. You are also responsible for designing and grading homework assignments, projects, tests.
In essence, professor “outsources” part of the course to you and then in the end gets your input about each student’s performance in it. The primary purpose is to divide students into smaller groups (of around 15 or less), each assigned to a separate teacher, so that each student gets more personal attention. | 2018/12/07 | [
"https://academia.stackexchange.com/questions/121210",
"https://academia.stackexchange.com",
"https://academia.stackexchange.com/users/8872/"
] | In the US I have heard them referred to as "discussion sections," "lab sections," or "fourth hour." Discussion implies a small group where students often work together to make sense of the material, although it may be more or less collaborative. Lab implies that they are working on practice problems or scenarios. Lab is more often used for science classes, although I had lab sections for some mathematics classes as well. The term "fourth hour" comes from a standard class meeting time taking 1.5 hours. Two meetings then would be 3 hours, and might be accompanied by a shorter class meeting to add another hour of time each week.
In the US, your job title would be Teaching Assistant or "TA" as it's often known. It is important to specify the variety of work that you have done, especially the curriculum design tasks. TAs in the US range from essentially teaching an entire course, including many lectures. Other TAs have almost no responsibility. They might take attendance, grade tests, and hold office hours to answer questions. And everything in between. | Best described as a "Tutorial" in my experience. |
4,109,035 | Let's say you are planning to design a hash function which will generate keys between 0-256. Will using first 2 digits of MD5-digest be a great idea for a uniform distribution? What do you think on this? Is it expensive to md5() some word (2-10 letters)?
I know it is a rough definition of requirements but it would be great to discuss this. | 2010/11/05 | [
"https://Stackoverflow.com/questions/4109035",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/54929/"
] | There's no reason to use a cryptographic strength hash for something as simple as generating 3 digit hashes. You're better off using a more simple hash there.
I'm not certain specifically how expensive MD5 is relative to others, but there are plenty of better ways to create a small hash (see [this article](http://www.partow.net/programming/hashfunctions/) for some algorithm ideas). | MD5 is designed to uniformaly spread the input over all the output bytes so it's as good as any other general hash function - sounds like a bit of overkill if you only want 256 values.
Note the output of MD5 is 128bytes (16bytes), it's only the text representation that is hex digits - so there is really no first two digits of MD5 - just use the bottom 8bits. |
4,109,035 | Let's say you are planning to design a hash function which will generate keys between 0-256. Will using first 2 digits of MD5-digest be a great idea for a uniform distribution? What do you think on this? Is it expensive to md5() some word (2-10 letters)?
I know it is a rough definition of requirements but it would be great to discuss this. | 2010/11/05 | [
"https://Stackoverflow.com/questions/4109035",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/54929/"
] | MD5 is designed to uniformaly spread the input over all the output bytes so it's as good as any other general hash function - sounds like a bit of overkill if you only want 256 values.
Note the output of MD5 is 128bytes (16bytes), it's only the text representation that is hex digits - so there is really no first two digits of MD5 - just use the bottom 8bits. | You haven't explained how you're going to use the hash, and what you're going to do with the collisions that are inevitable given that you have only 256 output values.
I think even MD5 (which is not cryptographically secure any more) is overkill for the likely applications.
I'd probably go with a [CRC](https://secure.wikimedia.org/wikipedia/en/wiki/Cyclic_redundancy_check) (cyclic redundancy check) algorithm that would generate a 16-bit or 32-bit number for you, and would likely give you good enough distribution. |
4,109,035 | Let's say you are planning to design a hash function which will generate keys between 0-256. Will using first 2 digits of MD5-digest be a great idea for a uniform distribution? What do you think on this? Is it expensive to md5() some word (2-10 letters)?
I know it is a rough definition of requirements but it would be great to discuss this. | 2010/11/05 | [
"https://Stackoverflow.com/questions/4109035",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/54929/"
] | You could try [calculating](http://www.miscel.dk/MiscEl/CRCcalculations.html) an 8-bit [CRC](http://en.wikipedia.org/wiki/Cyclic_redundancy_check). | MD5 is designed to uniformaly spread the input over all the output bytes so it's as good as any other general hash function - sounds like a bit of overkill if you only want 256 values.
Note the output of MD5 is 128bytes (16bytes), it's only the text representation that is hex digits - so there is really no first two digits of MD5 - just use the bottom 8bits. |
4,109,035 | Let's say you are planning to design a hash function which will generate keys between 0-256. Will using first 2 digits of MD5-digest be a great idea for a uniform distribution? What do you think on this? Is it expensive to md5() some word (2-10 letters)?
I know it is a rough definition of requirements but it would be great to discuss this. | 2010/11/05 | [
"https://Stackoverflow.com/questions/4109035",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/54929/"
] | There's no reason to use a cryptographic strength hash for something as simple as generating 3 digit hashes. You're better off using a more simple hash there.
I'm not certain specifically how expensive MD5 is relative to others, but there are plenty of better ways to create a small hash (see [this article](http://www.partow.net/programming/hashfunctions/) for some algorithm ideas). | You haven't explained how you're going to use the hash, and what you're going to do with the collisions that are inevitable given that you have only 256 output values.
I think even MD5 (which is not cryptographically secure any more) is overkill for the likely applications.
I'd probably go with a [CRC](https://secure.wikimedia.org/wikipedia/en/wiki/Cyclic_redundancy_check) (cyclic redundancy check) algorithm that would generate a 16-bit or 32-bit number for you, and would likely give you good enough distribution. |
4,109,035 | Let's say you are planning to design a hash function which will generate keys between 0-256. Will using first 2 digits of MD5-digest be a great idea for a uniform distribution? What do you think on this? Is it expensive to md5() some word (2-10 letters)?
I know it is a rough definition of requirements but it would be great to discuss this. | 2010/11/05 | [
"https://Stackoverflow.com/questions/4109035",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/54929/"
] | You could try [calculating](http://www.miscel.dk/MiscEl/CRCcalculations.html) an 8-bit [CRC](http://en.wikipedia.org/wiki/Cyclic_redundancy_check). | There's no reason to use a cryptographic strength hash for something as simple as generating 3 digit hashes. You're better off using a more simple hash there.
I'm not certain specifically how expensive MD5 is relative to others, but there are plenty of better ways to create a small hash (see [this article](http://www.partow.net/programming/hashfunctions/) for some algorithm ideas). |
4,109,035 | Let's say you are planning to design a hash function which will generate keys between 0-256. Will using first 2 digits of MD5-digest be a great idea for a uniform distribution? What do you think on this? Is it expensive to md5() some word (2-10 letters)?
I know it is a rough definition of requirements but it would be great to discuss this. | 2010/11/05 | [
"https://Stackoverflow.com/questions/4109035",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/54929/"
] | You could try [calculating](http://www.miscel.dk/MiscEl/CRCcalculations.html) an 8-bit [CRC](http://en.wikipedia.org/wiki/Cyclic_redundancy_check). | You haven't explained how you're going to use the hash, and what you're going to do with the collisions that are inevitable given that you have only 256 output values.
I think even MD5 (which is not cryptographically secure any more) is overkill for the likely applications.
I'd probably go with a [CRC](https://secure.wikimedia.org/wikipedia/en/wiki/Cyclic_redundancy_check) (cyclic redundancy check) algorithm that would generate a 16-bit or 32-bit number for you, and would likely give you good enough distribution. |
1,076,959 | We have 2 physical servers (A and B), each with ESXI 7.0 installed. We'd like to manage them with vCenter. Can we install vCenter on one of those servers? Is it advisable? | 2021/09/08 | [
"https://serverfault.com/questions/1076959",
"https://serverfault.com",
"https://serverfault.com/users/824135/"
] | >
> Can we install vCenter on one of those servers?
>
>
>
Yes absolutely, in fact that's kind of the default scenario.
>
> Is it advisable?
>
>
>
Sure, why not.
I'll give you a little more info. For larger installations - tens/hundred of hosts what you often see is a small 'management' cluster to run these central VMware tool VMs (vCenter, vROps, Log Insight, NSX controllers etc.), usually 4 hosts or so, maybe 6-8). Then you have one or more workload clusters with the rest of your hosts. All of these servers are managed by the vCenter. The reason you separate these out is that often these management VMs have slightly different use case than the general computer clusters - as an example if your vCenter crashes (and you're not running in HA mode) then you need to find which host is running the vCenter (due to DRS moves) so you can restart it and deal with any issues with it. It's easier to find it if it's a small 4-8 host cluster than a larger one. Also you don't want to run NSX on the hosts that are running the NSX controllers typically.
So for larger installation then yes, I'd have a small management cluster to run the vCenter, but if you only have two servers then you don't have that luxury, in which case then yeah, just get on with it, you'll be fine! | You can install vcenter on any of the two physical server you have, but it's generally not advisable to do so because during the maintenance of the host on which vcenter is installed you will loose connectivity to vcneter. |
15,972,612 | I am calling a RESTFUL web services which returns JSON data. The response contains a numeric value(without quotes) 10000000000223169, but after getting the JavaScript object against this response I get 10000000000223168.
The JSON response shown directly in the browser also shows 10000000000223168 but the FireBug HTTP response in content tab shows the correct value i.e. 10000000000223169 | 2013/04/12 | [
"https://Stackoverflow.com/questions/15972612",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1474941/"
] | That's because numbers in JavaScript are [IEEE754 double precision floats](http://en.wikipedia.org/wiki/Double_precision).
Integers can only be all represented up to 2^53.
Your number is too big to be sent as number, you should send it as string.
If you need to do computation with this number in your browser, the easiest solution would be to use a big number dedicated library (see [this related question](https://stackoverflow.com/questions/4288821/how-to-deal-with-big-numbers-in-javascript)). | 10000000000223169 is beyond the range that may be represented as an exact integer in JavaScript (and hence JSON). It's roughly *2 ^ 53.151* and IEEE 754 only permits 53 bits of resolution in the mantissa of a double precision floating point number.
To transport it without modification it would need to be sent as a string.
In the client that's using this code, it'll also need to be stored either as a string, or as a 64-bit integer (assuming you're using a language with such a data type).
If you try to store it in an IEEE 754 float (which is the default numeric type in JS it'll still get rounded to 53 bits of precision as soon as you attempt to perform any mathematical operation on it. |
218,569 | I've got some NT boxes located on EC2 that I'd like to monitor. The problem is that the Nagios box needs to know an IP address it can connect to in order to do the monitoring, and the IPs of the instances change every time they start.
Is there a good way of doing this or am I going to be forced into writing a program that will poll EC2's API? | 2011/01/04 | [
"https://serverfault.com/questions/218569",
"https://serverfault.com",
"https://serverfault.com/users/23936/"
] | You can use Dynamic DNS. Install a Dynamic-DNS client on every one of your servers and the IP will be updated when it changes.
You'll have to configure Nagios with hostnames instead of IPs. Probably you want a low TTL on the DNS server to avoid the old IP being cached too long. | You can look in to [Elastic IPs](http://aws.amazon.com/articles/1346?_encoding=UTF8&jiveRedirect=1) if you need static IP addresses. These are IPs owned by your AWS account that you can assign to any instance you run.
>
> Elastic IP addresses are static IP addresses designed for dynamic cloud computing. An Elastic IP address is associated with your account, not a particular instance, and you control that address until you choose to explicitly release it. Unlike traditional static IP addresses, however, Elastic IP addresses allow you to mask instance or availability zone failures by programmatically remapping your public IP addresses to any instance associated with your account.
>
>
> |
218,569 | I've got some NT boxes located on EC2 that I'd like to monitor. The problem is that the Nagios box needs to know an IP address it can connect to in order to do the monitoring, and the IPs of the instances change every time they start.
Is there a good way of doing this or am I going to be forced into writing a program that will poll EC2's API? | 2011/01/04 | [
"https://serverfault.com/questions/218569",
"https://serverfault.com",
"https://serverfault.com/users/23936/"
] | You can look in to [Elastic IPs](http://aws.amazon.com/articles/1346?_encoding=UTF8&jiveRedirect=1) if you need static IP addresses. These are IPs owned by your AWS account that you can assign to any instance you run.
>
> Elastic IP addresses are static IP addresses designed for dynamic cloud computing. An Elastic IP address is associated with your account, not a particular instance, and you control that address until you choose to explicitly release it. Unlike traditional static IP addresses, however, Elastic IP addresses allow you to mask instance or availability zone failures by programmatically remapping your public IP addresses to any instance associated with your account.
>
>
> | We use Nagios for monitoring our Windows instances on EC2:
1. Get Elastic IPs (you need static IP addresses).
2. Open ping in the EC2 firewall (blocked by default)
3. Done! |
218,569 | I've got some NT boxes located on EC2 that I'd like to monitor. The problem is that the Nagios box needs to know an IP address it can connect to in order to do the monitoring, and the IPs of the instances change every time they start.
Is there a good way of doing this or am I going to be forced into writing a program that will poll EC2's API? | 2011/01/04 | [
"https://serverfault.com/questions/218569",
"https://serverfault.com",
"https://serverfault.com/users/23936/"
] | You can look in to [Elastic IPs](http://aws.amazon.com/articles/1346?_encoding=UTF8&jiveRedirect=1) if you need static IP addresses. These are IPs owned by your AWS account that you can assign to any instance you run.
>
> Elastic IP addresses are static IP addresses designed for dynamic cloud computing. An Elastic IP address is associated with your account, not a particular instance, and you control that address until you choose to explicitly release it. Unlike traditional static IP addresses, however, Elastic IP addresses allow you to mask instance or availability zone failures by programmatically remapping your public IP addresses to any instance associated with your account.
>
>
> | Groundwork Open Source 6.4 has a Cloud Connector which uses the EC2 API to autodiscover and add/remove hosts - handy for app/websites which scale up and down. |
218,569 | I've got some NT boxes located on EC2 that I'd like to monitor. The problem is that the Nagios box needs to know an IP address it can connect to in order to do the monitoring, and the IPs of the instances change every time they start.
Is there a good way of doing this or am I going to be forced into writing a program that will poll EC2's API? | 2011/01/04 | [
"https://serverfault.com/questions/218569",
"https://serverfault.com",
"https://serverfault.com/users/23936/"
] | You can use Dynamic DNS. Install a Dynamic-DNS client on every one of your servers and the IP will be updated when it changes.
You'll have to configure Nagios with hostnames instead of IPs. Probably you want a low TTL on the DNS server to avoid the old IP being cached too long. | We use Nagios for monitoring our Windows instances on EC2:
1. Get Elastic IPs (you need static IP addresses).
2. Open ping in the EC2 firewall (blocked by default)
3. Done! |
218,569 | I've got some NT boxes located on EC2 that I'd like to monitor. The problem is that the Nagios box needs to know an IP address it can connect to in order to do the monitoring, and the IPs of the instances change every time they start.
Is there a good way of doing this or am I going to be forced into writing a program that will poll EC2's API? | 2011/01/04 | [
"https://serverfault.com/questions/218569",
"https://serverfault.com",
"https://serverfault.com/users/23936/"
] | You can use Dynamic DNS. Install a Dynamic-DNS client on every one of your servers and the IP will be updated when it changes.
You'll have to configure Nagios with hostnames instead of IPs. Probably you want a low TTL on the DNS server to avoid the old IP being cached too long. | Groundwork Open Source 6.4 has a Cloud Connector which uses the EC2 API to autodiscover and add/remove hosts - handy for app/websites which scale up and down. |
218,569 | I've got some NT boxes located on EC2 that I'd like to monitor. The problem is that the Nagios box needs to know an IP address it can connect to in order to do the monitoring, and the IPs of the instances change every time they start.
Is there a good way of doing this or am I going to be forced into writing a program that will poll EC2's API? | 2011/01/04 | [
"https://serverfault.com/questions/218569",
"https://serverfault.com",
"https://serverfault.com/users/23936/"
] | We use Nagios for monitoring our Windows instances on EC2:
1. Get Elastic IPs (you need static IP addresses).
2. Open ping in the EC2 firewall (blocked by default)
3. Done! | Groundwork Open Source 6.4 has a Cloud Connector which uses the EC2 API to autodiscover and add/remove hosts - handy for app/websites which scale up and down. |
652,817 | I am still fairly new to Linux and Ubuntu, so I will apologize ahead of time for my ignorance. I am using working with Ubuntu 14.04 LTS. I have been using Ubuntu for a little over a year now, I am still learning coding and commands, and learning the Ubuntu desktop. My issue is this:
Ubuntu has been working fine until the recent updates I allowed it to update to. I so far have not been able to figure out what is happening.
After the most recent updates I lose all functionality of the desktop, the sidebar has empty white icons and title bar has no functionality for the power icon, wifi icon and Bluetooth icon, if they even show at all. Sometimes the desktop image will show, and sometimes it won't.
On my original install of 14.04 LTS I had a similar issue, which I eventually found was a improper video driver. After repairing, my issue was resolved. However, since the updates this repair is not working. I was thinking it might be an issue with unity, Ubuntu-desktop, or compiz, but have removed and reinstalled all, along with my NVidia driver and no improvement. I also am starting to believe it may be an issue with the most recent kernel update.
If any one has ideas or know of any recent kernel issues, I am open to anything. Just what ever you suggest please be descriptive as possible, as I stated I am still learning Linux and Ubuntu.
Any help would be great, at this point I am lost. | 2015/07/26 | [
"https://askubuntu.com/questions/652817",
"https://askubuntu.com",
"https://askubuntu.com/users/273904/"
] | The issue was with my Internet Service Provider.
The problem is that I tried using Google DNS and OpenDNS but it didn't work and I ruled out ISP issues.
Even using other DNS' my ISP (GVT-Brasil) still pointed Google sites to its problematic IPs.
But in the end I was able to fix using another DNS provider (GigaDNS) so it was indeed an ISP issue. | As other answer noted, this problem can happen due to ISP issue or DNS issues.
I tried following and it worked for me (Ubuntu 17.04).
1. Open a terminal and type "ping google.com" & "ping gmail.com"; If the internet works, then most likely this ping will also work
2. It should show some IP address while pinging; e.g. To me it showed 216.58.197.78 & 172.217.26.165)
3. Copy those IP addresses, paste them in the browser address bar & hit enter
4. If URL resolves to google.com etc., then this issue should be resolved on its own |
6,037 | I'm trying to get a sense if this is an issue for others or every input/output should be labeled so user is not confused and just go with it?
I think almost everyone pronounces it as "LatLon".
Who started it?
Is it because it's in alphabetical order compared to "LonLat"?
Mapping Lat and Lon to Cartesian plane Lon is "x" and Lat is "y" so since we say "(x,y)" it should be said as "LonLat". And now for display of information.
Should the status bar on a mapping application display La,Lo or Lo,Lat?
Should it just be labeled as one way and let user deal with it?
And same with input, what's the right way to order the fields?
KML's format is Lon,Lat,Altitude. While other apps is Lat,Lon and so have to be very vigilant about when converting formats.
Is there a standard? | 2011/02/10 | [
"https://gis.stackexchange.com/questions/6037",
"https://gis.stackexchange.com",
"https://gis.stackexchange.com/users/51/"
] | You should take a look at the ISO standard 6709. Here's the wikipedia entry: [ISO 6709](http://en.wikipedia.org/wiki/ISO_6709)
The main item is that order should always be latitude longitude.
>
> Latitude comes before longitude
>
>
>
[edit now that I have a copy of 6709:2008]
For data interchange, use DD, but for backwards compatibility, sexagesimal is valid.
There's a section called "Latitude and longitude coordinates are not unique" complete with picture.
There is very strong wording about the coordinate order for *display* (not interchange). It says that navigators have traditionally used latitude longitude order and to change the order could compromise safety. Use sexagesimal, direction symbols rather than +/-, etc. Z values follow longitude. Grid/planar values should use the order specified in the CRS definition.
34°05'09.76"N 117°02'01.23"W 829.1m
(Hah! I started to write out a sample and automatically wrote the longitude value first) | This is a common problem, here is another previous discussion:
* [Why some coordinate systems define x-axis as northings and some as easting?](https://gis.stackexchange.com/questions/99769/why-some-coordinate-systems-define-x-axis-as-northings-and-some-as-easting/99781#99781)
There is a very exhaustive discussion at <http://wiki.osgeo.org/wiki/Axis_Order_Confusion>
@wwnick provided the above information as a comment to a duplicate question |
6,037 | I'm trying to get a sense if this is an issue for others or every input/output should be labeled so user is not confused and just go with it?
I think almost everyone pronounces it as "LatLon".
Who started it?
Is it because it's in alphabetical order compared to "LonLat"?
Mapping Lat and Lon to Cartesian plane Lon is "x" and Lat is "y" so since we say "(x,y)" it should be said as "LonLat". And now for display of information.
Should the status bar on a mapping application display La,Lo or Lo,Lat?
Should it just be labeled as one way and let user deal with it?
And same with input, what's the right way to order the fields?
KML's format is Lon,Lat,Altitude. While other apps is Lat,Lon and so have to be very vigilant about when converting formats.
Is there a standard? | 2011/02/10 | [
"https://gis.stackexchange.com/questions/6037",
"https://gis.stackexchange.com",
"https://gis.stackexchange.com/users/51/"
] | You should take a look at the ISO standard 6709. Here's the wikipedia entry: [ISO 6709](http://en.wikipedia.org/wiki/ISO_6709)
The main item is that order should always be latitude longitude.
>
> Latitude comes before longitude
>
>
>
[edit now that I have a copy of 6709:2008]
For data interchange, use DD, but for backwards compatibility, sexagesimal is valid.
There's a section called "Latitude and longitude coordinates are not unique" complete with picture.
There is very strong wording about the coordinate order for *display* (not interchange). It says that navigators have traditionally used latitude longitude order and to change the order could compromise safety. Use sexagesimal, direction symbols rather than +/-, etc. Z values follow longitude. Grid/planar values should use the order specified in the CRS definition.
34°05'09.76"N 117°02'01.23"W 829.1m
(Hah! I started to write out a sample and automatically wrote the longitude value first) | This posed a big problem for me for years on AutoCAD 2D compounded by the fact that autocad reads angles anticlockwise with 0 degrees starting at the 90d position. For a while I liked to believe I had solved it by changing the UCS such that x became northing and y easting. As long as I continued to produce 2D property plans I never really got to face my error: the z axis was pointed the wrong way.
Of course my dimension text were usually reading right to left but I felt it was a small price to pay for correct angle reading and more to the point, putting x and y in their intuitive places (as per Northing/Easting, Lat./Lon. conventions). Then I graduated to Autocad Civil 3d and tried to perform the trick again and came face to face with the bottom line: y is north/lat and x is East/long. Accept that. |
6,037 | I'm trying to get a sense if this is an issue for others or every input/output should be labeled so user is not confused and just go with it?
I think almost everyone pronounces it as "LatLon".
Who started it?
Is it because it's in alphabetical order compared to "LonLat"?
Mapping Lat and Lon to Cartesian plane Lon is "x" and Lat is "y" so since we say "(x,y)" it should be said as "LonLat". And now for display of information.
Should the status bar on a mapping application display La,Lo or Lo,Lat?
Should it just be labeled as one way and let user deal with it?
And same with input, what's the right way to order the fields?
KML's format is Lon,Lat,Altitude. While other apps is Lat,Lon and so have to be very vigilant about when converting formats.
Is there a standard? | 2011/02/10 | [
"https://gis.stackexchange.com/questions/6037",
"https://gis.stackexchange.com",
"https://gis.stackexchange.com/users/51/"
] | This is a common problem, here is another previous discussion:
* [Why some coordinate systems define x-axis as northings and some as easting?](https://gis.stackexchange.com/questions/99769/why-some-coordinate-systems-define-x-axis-as-northings-and-some-as-easting/99781#99781)
There is a very exhaustive discussion at <http://wiki.osgeo.org/wiki/Axis_Order_Confusion>
@wwnick provided the above information as a comment to a duplicate question | This posed a big problem for me for years on AutoCAD 2D compounded by the fact that autocad reads angles anticlockwise with 0 degrees starting at the 90d position. For a while I liked to believe I had solved it by changing the UCS such that x became northing and y easting. As long as I continued to produce 2D property plans I never really got to face my error: the z axis was pointed the wrong way.
Of course my dimension text were usually reading right to left but I felt it was a small price to pay for correct angle reading and more to the point, putting x and y in their intuitive places (as per Northing/Easting, Lat./Lon. conventions). Then I graduated to Autocad Civil 3d and tried to perform the trick again and came face to face with the bottom line: y is north/lat and x is East/long. Accept that. |
470,592 | I have a project that uses the serial port, and it requires two files to run, the win32.dll file (which is in the java runtime environment bin folder) and the javax.comm.properties file (which is in the java runtime environment lib folder). When I run the project from eclipse it works, but when I try to build a jar file for distribution, it won't work. I suspect this is because the dll and properties files aren't included in the jar. How do I specify that they need to be there? | 2009/01/22 | [
"https://Stackoverflow.com/questions/470592",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1585/"
] | I think javax.comm.properties just need to be on your classpath. You may can add it to the top level of a jar you delivery.
InputStream is = MainClass.class.getResourceAsStream("javax.comm.properties");
if (is == null) {properties missing....}
I think win32.dll just need to be on the %PATH%(windows) or $LD\_LIBRARY\_PATH(unix)...... | A jar file is just a normal zip file. If you want to add files to it, just use a tool such as winzip. |
470,592 | I have a project that uses the serial port, and it requires two files to run, the win32.dll file (which is in the java runtime environment bin folder) and the javax.comm.properties file (which is in the java runtime environment lib folder). When I run the project from eclipse it works, but when I try to build a jar file for distribution, it won't work. I suspect this is because the dll and properties files aren't included in the jar. How do I specify that they need to be there? | 2009/01/22 | [
"https://Stackoverflow.com/questions/470592",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1585/"
] | I think javax.comm.properties just need to be on your classpath. You may can add it to the top level of a jar you delivery.
InputStream is = MainClass.class.getResourceAsStream("javax.comm.properties");
if (is == null) {properties missing....}
I think win32.dll just need to be on the %PATH%(windows) or $LD\_LIBRARY\_PATH(unix)...... | With Ant, you can pack everything in your Jar you want to. So let Ant create your Jar, not Eclipse :) |
58,181,766 | I'm getting this log in my logcat
>
> I/zygote: Background concurrent copying GC freed 148531(5MB) AllocSpace objects, 18(936KB) LOS objects, 32% free, 12MB/18MB, paused 3.758ms total 217.199ms
>
>
>
is this something that needs to be addressed or it is can be ignored | 2019/10/01 | [
"https://Stackoverflow.com/questions/58181766",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/6699103/"
] | This is not an error, it's just an **Android log message** notifying you about when garbage collection takes place. Everything's normal. The log messages don't harm your app. It's only a problem if you go out of memory, or you see performance hiccups due to garbage collection.
If you are seeing this frequently (or consistently), then you are likely allocating too many objects. A common cause is allocating many (or a few large) objects within a loop
Every time we hit this loop, we allocate one hundred new Bitmap objects.
The best way to prevent GC sweeps is to not allocate objects. Of course you have to allocate objects in Java, so you need to ensure that you are not allocating unnecessarily.
Finally, you can always filter or ignore the logs. :D | This page may help you with further research: <https://blog.gceasy.io/2017/05/09/understanding-android-gc-logs/> |
5,849,688 | In Apple's developer guide, they state: "A split view controller must always be the root of any interface you create" ([see here](http://developer.apple.com/library/ios/#featuredarticles/ViewControllerPGforiPhoneOS/iPadControllers/iPadControllers.html)). I was curious if anyone knew why they decided that. I have a tab navigator-based application and it makes sense for the content in one of the tabs to be presented in a split view. Why would Apple be opposed to that kind of design? Thanks in advance for your answers.
-Max
PS I'm not looking for ways to put a split view controller in a tab navigator controller (that much I can figure out, even if the code does look sloppy). I'm more curious if anyone has any idea why Apple frowns on it. | 2011/05/01 | [
"https://Stackoverflow.com/questions/5849688",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/733462/"
] | I don't think that this is necessarily a user experience decision as much as it is a technical restriction. UIKit makes a number of assumptions about how UIViewControllers will be used. Including the idea that only a single UIViewController instance has its view visible in given window at any given time. Now since Apple has access to the implementation they have been able to make exceptions for their own "container view controller" classes (UINavigationController, UITabBarController, and UISplitViewController). We can't tell exactly how much of a special case these controllers are or what they needed to do to support displaying nested sub view controllers correctly but one consequence seems to be that both UITabBarController and UISplitViewController are not intended to be used except as the root view controller of a window. Attempting to nest them within other container view controllers may cause unexpected or unreliable behavior.
I tried to cover these restrictions on the use of view controllers and some possible alternatives here: <http://blog.carbonfive.com/2011/03/09/abusing-uiviewcontrollers/> Hopefully that's of some use to you but I'm afraid the only reliable way to get the UI you seem to be looking for it to implement your own split view style display within the view of a single UIViewController. | Please ignore my answer:
Because you can't resize UISplitViewController's subviews with touches? |
5,849,688 | In Apple's developer guide, they state: "A split view controller must always be the root of any interface you create" ([see here](http://developer.apple.com/library/ios/#featuredarticles/ViewControllerPGforiPhoneOS/iPadControllers/iPadControllers.html)). I was curious if anyone knew why they decided that. I have a tab navigator-based application and it makes sense for the content in one of the tabs to be presented in a split view. Why would Apple be opposed to that kind of design? Thanks in advance for your answers.
-Max
PS I'm not looking for ways to put a split view controller in a tab navigator controller (that much I can figure out, even if the code does look sloppy). I'm more curious if anyone has any idea why Apple frowns on it. | 2011/05/01 | [
"https://Stackoverflow.com/questions/5849688",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/733462/"
] | I don't think that this is necessarily a user experience decision as much as it is a technical restriction. UIKit makes a number of assumptions about how UIViewControllers will be used. Including the idea that only a single UIViewController instance has its view visible in given window at any given time. Now since Apple has access to the implementation they have been able to make exceptions for their own "container view controller" classes (UINavigationController, UITabBarController, and UISplitViewController). We can't tell exactly how much of a special case these controllers are or what they needed to do to support displaying nested sub view controllers correctly but one consequence seems to be that both UITabBarController and UISplitViewController are not intended to be used except as the root view controller of a window. Attempting to nest them within other container view controllers may cause unexpected or unreliable behavior.
I tried to cover these restrictions on the use of view controllers and some possible alternatives here: <http://blog.carbonfive.com/2011/03/09/abusing-uiviewcontrollers/> Hopefully that's of some use to you but I'm afraid the only reliable way to get the UI you seem to be looking for it to implement your own split view style display within the view of a single UIViewController. | Apple has always placed high value on consistent use of user interface elements. Having all applications work in the same way helps the user to immediately understand how an app works even if they've never seen it before. Establishing a conceptual hierarchy of view controller containers makes a lot of sense when you're trying to help the user predict behavior. |
11,963,262 | I'm new to Android so I want to make sure that the following solution is the correct one.
The problem:
I want to sync the device's local database with a database on my server, via a webservice, every 10 minutes. I already have a web service call that I can make that returns the new/updated records. What I'm wondering is what is the best way to schedule this task. I want the databases to sync even when the application is not running.
My solution (is this the correct route to go?):
I will have one BroadcastReceiver that listens for android.intent.action.BOOT\_COMPLETED, in it's onReceive I will create an AlarmManager that sends a message to MyReceiver (via a PendingIntent) every 10 minutes. Also, in my application's startup I will do the same (create an alarm to send messages to the MyReceiver via a PendingIntent) - Since both alarms are sending messages to MyReceiver and their corresponding PendingIntents are initialized with PendingIntent.FLAG\_UPDATE\_CURRENT will the new alarm override the old one? (this is what I want to do, in case for some reason the alarm gets cancelled after device boot it should be restarted when the application starts).
In MyReceiver's onReceive() I will create a MyIntentService (this instance will make the webservice call and update the local database).
Is this a good solution? Any suggestions?
Thanks | 2012/08/15 | [
"https://Stackoverflow.com/questions/11963262",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1086530/"
] | Solution is fine...Actually all the AlarmManager instances get cleared when device turned off and rebooted.
The simple way is that...
First create AlarmManager when application started.
Second in onReceive of BOOT\_COMPLETED BroadcastReceiver.
Its enough, PendingIntent.FLAG\_UPDATE\_CURRENT will make sure of having only one activated alarm at a time.
In this way, alarm registered when your application started. There will be no issue if its already registered via BOOT\_COMPLETED. Activated alarm will deactivated when you turn off your device, but BroadcastReceiver to BOOT\_COMPLETED will take care of registration new alarm at next boot.
If you decide that this answers your question, please mark it as "accepted". This will raise both your and my reputation score.
Also you need to review your interval to use network, it might be very resource consuming for device and user. One policy might be to have longer period of interval and check for update when user starts your app (this might not be user friendly but can save many system resources and battery power as well). Try to find some better policy according to your needs. | Using FLAG\_UPDATE\_CURRENT in that manner will override the existing PendingIntent if one exists. I'm not positive but I believe that as soon as you get into onReceive, the PendingIntent is consumed so it's no longer there to be overridden. In either case, it sounds like this is the functionality you are looking for and yes it's a good way to solve this kind of problem. My only other suggestion would be if the 10 minute interval timing is not absolutely critical then use one of the INTERVAL\_ schedules (INTERVAL\_FIFTEEN\_MINUTES for example) in your AlarmManager to help conserve battery life; basically it lets allows all apps that run on intervals to "batch" their work together and wake the device up less frequently. |
176,731 | So during the Last Jedi
>
> Luke does his force projection and faces Kylo Ren. He has a brief conversation with Leia obviously before he does this.
>
> Whilst he's fighting Kylo, Poe says something along the lines of it seems like a distraction so they can escape.
>
> Now in my mind I think Luke knew that Kylo would want to face him. He probably didn't anticipate Kylo trying to shoot him with everything he had first (which probably would have wiped him out if he was actually there). But at no point did he say to any of the rebels. "Hey, I'm not actually here but everyone thinks I am, so I'll distract Kylo Ren and you guys escape out the back, and boom, Bob's your uncle and no one is hurt".
>
> If Luke was creating a distraction for everyone to escape, why didn't he say so rather than relying on someone to figure it out, regardless as to whether he was actually there or not. People could clearly see and interact with him. For all he knows they could have thought all hope was lost and just decided to watch the battle hoping for the best.
>
>
>
I'm looking for an in-universe answer/explanation rather than cinematic reasons. | 2017/12/18 | [
"https://scifi.stackexchange.com/questions/176731",
"https://scifi.stackexchange.com",
"https://scifi.stackexchange.com/users/38450/"
] | In Universe
===========
Luke was creating a legend of himself which is why he stylized himself looking younger and more of a Jedi look than earlier. I think he knew Kylo Ren wanted him dead and so guessed walking out to face them would cause them to shoot. By surviving the shooting he makes himself a legend a man that walked out and survived a barrage of shots from the First Order.
If he had told everyone what he was doing they wouldn't have been impressed, I mean it's amazing but he's a Master Jedi should be easy right? He creates a bigger legend for himself if no one knows the truth. This is evidenced at the end of the film where the children are retelling the story.
Pure speculation on this but I believe Leia knew he wasn't there, she's force sensitive and obviously has a strong connection with Luke. Also Han's dice probably meant a lot to her so if they were the real ones I doubt she would have left them behind.
Out of Universe
===============
It doesn't make for as very good cinematic experience or reveal if Luke says "Hey I'm not actually here don't worry about them shooting me" before he goes out. | **He wanted good reactions**
Luke needed the reactions of the Resistance to be authentic. Ben could have felt it if Poe and the others were not worried but also impressed. The First Order might have seen their reactions on their scopes, and might have suspected something. If they left immediately because they knew Luke wouldn't need their help, and were not curious about what he was going to do, that would have been even more telling.
Also, withholding information from your allies is an ancient Jedi tradition. |
176,731 | So during the Last Jedi
>
> Luke does his force projection and faces Kylo Ren. He has a brief conversation with Leia obviously before he does this.
>
> Whilst he's fighting Kylo, Poe says something along the lines of it seems like a distraction so they can escape.
>
> Now in my mind I think Luke knew that Kylo would want to face him. He probably didn't anticipate Kylo trying to shoot him with everything he had first (which probably would have wiped him out if he was actually there). But at no point did he say to any of the rebels. "Hey, I'm not actually here but everyone thinks I am, so I'll distract Kylo Ren and you guys escape out the back, and boom, Bob's your uncle and no one is hurt".
>
> If Luke was creating a distraction for everyone to escape, why didn't he say so rather than relying on someone to figure it out, regardless as to whether he was actually there or not. People could clearly see and interact with him. For all he knows they could have thought all hope was lost and just decided to watch the battle hoping for the best.
>
>
>
I'm looking for an in-universe answer/explanation rather than cinematic reasons. | 2017/12/18 | [
"https://scifi.stackexchange.com/questions/176731",
"https://scifi.stackexchange.com",
"https://scifi.stackexchange.com/users/38450/"
] | It's very likely that Leia knew Luke wasn't there, and that this was Luke's intention. It is established from Luke's fight with Kylo that physical contact reveals the illusion for what it is (matter passes right through). This is why Luke "dodges" Kylo's attacks, rather than parries them.
Therefore, when Luke first appears and gives Leia Han's dice, she would immediately know they weren't real. This is later supported when she leaves them behind, which (if they were real) she surely wouldn't have done. Also, when Kylo "picks up" the dice, he too understands them to be an illusion. In addition, when Luke kisses Leia on the head, she would have known him to not be present as well.
With this knowledge, Leia would have known about Luke's plan even if Poe hadn't jumped on it. But, since he did, she let him lead. The whole film she was trying to teach him to be a leader, not a hero, and once he takes up the role, she's not going to steal his thunder. But Luke wasn't aware of her goals with Poe, so he naturally informs his sister of his plan in a very subtle, Jedi-Master-y way. | **He wanted good reactions**
Luke needed the reactions of the Resistance to be authentic. Ben could have felt it if Poe and the others were not worried but also impressed. The First Order might have seen their reactions on their scopes, and might have suspected something. If they left immediately because they knew Luke wouldn't need their help, and were not curious about what he was going to do, that would have been even more telling.
Also, withholding information from your allies is an ancient Jedi tradition. |
46,508 | If humans were to muster all their weapons together would it be possible to move Earth's orbit? If we were able to manage it, how far and fast would it travel? Most likely it would kill all inhabitants of Earth and these weapons are of the current technology. | 2016/07/07 | [
"https://worldbuilding.stackexchange.com/questions/46508",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/2358/"
] | Yes, theoretically.
But not by any amount that could be measured. The mass of earth and the orbital velocity around the sun is so huge that any conceivable weapon would give it such a tiny nudge you would never notice.
Remember that to change the orbit you need to launch something away at escape velocity. Firing a gun into the air won't do it, you need to be launching projectiles at 11.2km/s and then somehow stopping the air from slowing them down.
Now compare the mass of that projectile to the mass of the earth and you see the problem.
Even something like an enormous explosion that splits the planet in two (which we couldn't generate anyway) won't change the orbit unless substantial amounts of the planet are launched at a speed above escape velocity. The two halves of the planet would just continue in the same orbit rotating around each other and either join back together or form into a binary. | How much would you want to move the orbit for it to be considered significant?
Back in October 2013, the [Juno](https://en.wikipedia.org/wiki/Juno_(spacecraft)) probe stole some of Earth's momentum as it flew by in a gravity assist, altering it's orbit. The amount was infinitesimally small, but still measurable to a degree.
Given that you talk about weapons, the method would be different from a gravity assist, but the change would be there all the same. However, the effects would be completely unnoticeable compared to the effects of the weapons themselves, which would wipe out life before you could even notice the orbit had changed. |
46,508 | If humans were to muster all their weapons together would it be possible to move Earth's orbit? If we were able to manage it, how far and fast would it travel? Most likely it would kill all inhabitants of Earth and these weapons are of the current technology. | 2016/07/07 | [
"https://worldbuilding.stackexchange.com/questions/46508",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/2358/"
] | Yes, theoretically.
But not by any amount that could be measured. The mass of earth and the orbital velocity around the sun is so huge that any conceivable weapon would give it such a tiny nudge you would never notice.
Remember that to change the orbit you need to launch something away at escape velocity. Firing a gun into the air won't do it, you need to be launching projectiles at 11.2km/s and then somehow stopping the air from slowing them down.
Now compare the mass of that projectile to the mass of the earth and you see the problem.
Even something like an enormous explosion that splits the planet in two (which we couldn't generate anyway) won't change the orbit unless substantial amounts of the planet are launched at a speed above escape velocity. The two halves of the planet would just continue in the same orbit rotating around each other and either join back together or form into a binary. | Think of it another way. Instead of trying to directly move the Earth, with our current weapons could we nudge an asteroid into a near earth "miss" that would gravitationally drag Earth a little bit?
Probably, but it would require a lot of careful preparation and the margin of error would be minute. Then we would be potentially increasing the number of big things with an orbit that crosses the Earth (assuming the big rock will circle back around to pass by the Earth again), never a wise decision. Ideally there is one already out there we could slightly adjust for our purpose.
Plus it would be a LONG process as any asteroid we could move with our current weapons/rockets wouldn't be very large, so the drag it could place on the Earth would be very small. We would have to repeatedly nudge the asteroid, pass after pass, to keep the Earth moving in the desired direction (away from the expanding sun, presumably). "Weapons" (like nuclear explosives) probably aren't the best things for this, but anything with the power to shift an asteroids orbit can be considered a weapon (be it nuclear thrust, a laser, or mass driver coilgun). |
46,508 | If humans were to muster all their weapons together would it be possible to move Earth's orbit? If we were able to manage it, how far and fast would it travel? Most likely it would kill all inhabitants of Earth and these weapons are of the current technology. | 2016/07/07 | [
"https://worldbuilding.stackexchange.com/questions/46508",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/2358/"
] | Yes, theoretically.
But not by any amount that could be measured. The mass of earth and the orbital velocity around the sun is so huge that any conceivable weapon would give it such a tiny nudge you would never notice.
Remember that to change the orbit you need to launch something away at escape velocity. Firing a gun into the air won't do it, you need to be launching projectiles at 11.2km/s and then somehow stopping the air from slowing them down.
Now compare the mass of that projectile to the mass of the earth and you see the problem.
Even something like an enormous explosion that splits the planet in two (which we couldn't generate anyway) won't change the orbit unless substantial amounts of the planet are launched at a speed above escape velocity. The two halves of the planet would just continue in the same orbit rotating around each other and either join back together or form into a binary. | I'm going to go ahead and assume that by "dislodge earth's orbit" you mean "escape the gravity of the sun." Correct me if I am incorrect, of course.
To answer your question: Unfortunately, no, we can't even hope to do that, even if we waive the survival of life as a requirement.
In order to effectively break from orbit around the sun, we have to reach what is called Escape Velocity. This is the minimum speed at which an object must be travelling in order for that object not to be slowed and reversed by the gravity of the body it is trying to escape. Think of throwing a ball into the air. The faster you throw it, the farther up it travels before falling back to the ground. If you throw it *fast* enough, it will never return. This speed is escape velocity.
The Solar Escape Velocity is 42.1 km/s. That's fast. The Earth actually already moves at about 30 km/s though, so if we wanted to eject the Earth from her Solar Orbit, we need an effective Delta-V of 12.1 km/s. Let's do some quick math to see how much energy will be needed to achieve that change in velocity.
Kinetic Energy is calculated with the formula E = (1/2)mv^2 where m is the mass of the object and v is its velocity. The mass of the earth is 5.972x10^24 kg. The velocity of the earth, as I stated, is 30,000 m/s. Inserting those into the equation yields a kinetic energy of 2.6874x10^33 Joules. This is the *current* kinetic energy of the Earth.
To find out how much energy we will need, we need to calculate the hypothetical kinetic energy of the earth at escape velocity, then subtract the current energy to get the difference. Running the numbers using solar escape velocity gives a kinetic energy of 5.2924x10^33 Joules. That's something like double the current energy of the earth. To be exact, we'll need to increase the earth's kinetic energy by 2.605x10^33 Joules.
So how much energy IS 2.605x10^33 Joules? If we write out that number in a more familiar way, it looks like this: 2,675,000,000,000,000,000,000,000,000,000,000 J. To be honest, there is really no way the human mind can grasp that sort of number. The entire energy consumption of human civilization of the Earth is something like 10^19 J in one year. The Estimated reserves of energy bound in oil is 10^22 J. Magnitude ~9 Earthquakes put out similar energy. The meteor strike that "killed" the Dinosaurs released about 10x that amount. Here's the thing about this sort of estimation, though. 10^23 might seem only slightly less than 10^33, but in reality each single increase in the exponent increases the number by 10 times. 10^33 is 10 BILLION times greater than 10^23.
Going back to the Earthquake example, a magnitude 9 Earthquake is horribly intense, and it's not even close to enough energy. An estimated magnitude 12 is what was caused during the above mentioned meteor strike in the Yucatan, and even THAT is way too small. The level of energy we would need to break the Earth free from the sun would register as a magnitude *19* on the Richter Scale. This is literally Earth Shattering. So even if humanity DID possess enough energy to achieve this goal (we don't), then attempting it would literally destroy the earth.
But that's all assuming we wanted to do it all at once. Obviously we don't launch rockets using one giant bomb, we distribute the energy flow over the course of the launch. Let's assume we mounted a massive rocket engine on one side of the Earth, and lit it off with the hope of launching the Earth away from the sun after a long burn. If we limited the energy output of the rocket to something reasonable (let's say ~5x10^16 Watts, which would feel like a constant magnitude 8 earthquake) then the rocket would burn for a *billion years* before the Earth had enough velocity to escape the sun's gravity.
So unfortunately, I can't really say that moving the Earth is a viable option. Her mass is just Too Damn High! |
46,508 | If humans were to muster all their weapons together would it be possible to move Earth's orbit? If we were able to manage it, how far and fast would it travel? Most likely it would kill all inhabitants of Earth and these weapons are of the current technology. | 2016/07/07 | [
"https://worldbuilding.stackexchange.com/questions/46508",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/2358/"
] | Think of it another way. Instead of trying to directly move the Earth, with our current weapons could we nudge an asteroid into a near earth "miss" that would gravitationally drag Earth a little bit?
Probably, but it would require a lot of careful preparation and the margin of error would be minute. Then we would be potentially increasing the number of big things with an orbit that crosses the Earth (assuming the big rock will circle back around to pass by the Earth again), never a wise decision. Ideally there is one already out there we could slightly adjust for our purpose.
Plus it would be a LONG process as any asteroid we could move with our current weapons/rockets wouldn't be very large, so the drag it could place on the Earth would be very small. We would have to repeatedly nudge the asteroid, pass after pass, to keep the Earth moving in the desired direction (away from the expanding sun, presumably). "Weapons" (like nuclear explosives) probably aren't the best things for this, but anything with the power to shift an asteroids orbit can be considered a weapon (be it nuclear thrust, a laser, or mass driver coilgun). | How much would you want to move the orbit for it to be considered significant?
Back in October 2013, the [Juno](https://en.wikipedia.org/wiki/Juno_(spacecraft)) probe stole some of Earth's momentum as it flew by in a gravity assist, altering it's orbit. The amount was infinitesimally small, but still measurable to a degree.
Given that you talk about weapons, the method would be different from a gravity assist, but the change would be there all the same. However, the effects would be completely unnoticeable compared to the effects of the weapons themselves, which would wipe out life before you could even notice the orbit had changed. |
46,508 | If humans were to muster all their weapons together would it be possible to move Earth's orbit? If we were able to manage it, how far and fast would it travel? Most likely it would kill all inhabitants of Earth and these weapons are of the current technology. | 2016/07/07 | [
"https://worldbuilding.stackexchange.com/questions/46508",
"https://worldbuilding.stackexchange.com",
"https://worldbuilding.stackexchange.com/users/2358/"
] | I'm going to go ahead and assume that by "dislodge earth's orbit" you mean "escape the gravity of the sun." Correct me if I am incorrect, of course.
To answer your question: Unfortunately, no, we can't even hope to do that, even if we waive the survival of life as a requirement.
In order to effectively break from orbit around the sun, we have to reach what is called Escape Velocity. This is the minimum speed at which an object must be travelling in order for that object not to be slowed and reversed by the gravity of the body it is trying to escape. Think of throwing a ball into the air. The faster you throw it, the farther up it travels before falling back to the ground. If you throw it *fast* enough, it will never return. This speed is escape velocity.
The Solar Escape Velocity is 42.1 km/s. That's fast. The Earth actually already moves at about 30 km/s though, so if we wanted to eject the Earth from her Solar Orbit, we need an effective Delta-V of 12.1 km/s. Let's do some quick math to see how much energy will be needed to achieve that change in velocity.
Kinetic Energy is calculated with the formula E = (1/2)mv^2 where m is the mass of the object and v is its velocity. The mass of the earth is 5.972x10^24 kg. The velocity of the earth, as I stated, is 30,000 m/s. Inserting those into the equation yields a kinetic energy of 2.6874x10^33 Joules. This is the *current* kinetic energy of the Earth.
To find out how much energy we will need, we need to calculate the hypothetical kinetic energy of the earth at escape velocity, then subtract the current energy to get the difference. Running the numbers using solar escape velocity gives a kinetic energy of 5.2924x10^33 Joules. That's something like double the current energy of the earth. To be exact, we'll need to increase the earth's kinetic energy by 2.605x10^33 Joules.
So how much energy IS 2.605x10^33 Joules? If we write out that number in a more familiar way, it looks like this: 2,675,000,000,000,000,000,000,000,000,000,000 J. To be honest, there is really no way the human mind can grasp that sort of number. The entire energy consumption of human civilization of the Earth is something like 10^19 J in one year. The Estimated reserves of energy bound in oil is 10^22 J. Magnitude ~9 Earthquakes put out similar energy. The meteor strike that "killed" the Dinosaurs released about 10x that amount. Here's the thing about this sort of estimation, though. 10^23 might seem only slightly less than 10^33, but in reality each single increase in the exponent increases the number by 10 times. 10^33 is 10 BILLION times greater than 10^23.
Going back to the Earthquake example, a magnitude 9 Earthquake is horribly intense, and it's not even close to enough energy. An estimated magnitude 12 is what was caused during the above mentioned meteor strike in the Yucatan, and even THAT is way too small. The level of energy we would need to break the Earth free from the sun would register as a magnitude *19* on the Richter Scale. This is literally Earth Shattering. So even if humanity DID possess enough energy to achieve this goal (we don't), then attempting it would literally destroy the earth.
But that's all assuming we wanted to do it all at once. Obviously we don't launch rockets using one giant bomb, we distribute the energy flow over the course of the launch. Let's assume we mounted a massive rocket engine on one side of the Earth, and lit it off with the hope of launching the Earth away from the sun after a long burn. If we limited the energy output of the rocket to something reasonable (let's say ~5x10^16 Watts, which would feel like a constant magnitude 8 earthquake) then the rocket would burn for a *billion years* before the Earth had enough velocity to escape the sun's gravity.
So unfortunately, I can't really say that moving the Earth is a viable option. Her mass is just Too Damn High! | How much would you want to move the orbit for it to be considered significant?
Back in October 2013, the [Juno](https://en.wikipedia.org/wiki/Juno_(spacecraft)) probe stole some of Earth's momentum as it flew by in a gravity assist, altering it's orbit. The amount was infinitesimally small, but still measurable to a degree.
Given that you talk about weapons, the method would be different from a gravity assist, but the change would be there all the same. However, the effects would be completely unnoticeable compared to the effects of the weapons themselves, which would wipe out life before you could even notice the orbit had changed. |
532,897 | As the answer to a question of mine I was referred to a website ([see here please](http://www.wolframalpha.com/input/?i=limit%20%281%20%2b%20sec%283x%29%29%5E%28cot%28x%29%29%20at%20pi/2))
How can WolframAlpha do it like humans? | 2013/10/20 | [
"https://math.stackexchange.com/questions/532897",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/100812/"
] | For the specific system (Mathematica) that you mentioned, there are descriptions of its internals on [these web pages](http://reference.wolfram.com/mathematica/tutorial/TheInternalsOfMathematicaOverview.html) and [these](http://reference.wolfram.com/mathematica/tutorial/SomeNotesOnInternalImplementation.html). But Mathematica is a commercial system, so its internal workings are proprietary, which is why the descriptions don't provide much detail.
While these systems might appear to work "the same way as a human", they really don't. Human beings often use clever creative tricks to solve problems. Computers in general (and computer algebra systems in particular) typically use brute-force systematic methods, as described in the referenced materials. See the description of how Mathematica finds indefinite integrals, for example.
The best results are obtained by a combination of a powerful brute-force computing and intelligent guidance provided by a human being. Computer algebra systems are enormously useful, but they only do what you tell them to do :-) | The internal implementation of symbolic systems are closely related to how compilers work and you can find a lot of the internal implementation details in this Wikipedia article: <https://en.wikipedia.org/wiki/Computer_algebra> but to really understand it or implement a simplified version of something of that caliber you will probably need to get experience with some functional programming language like Haskell and then gain a lot of knowledge of how compilers in general(and specifically for functional languages) work. |
491,864 | I'm writing a sentence, and I'm not sure if it's grammatically correct.
>
> Here are my partner, Jane Doe, and I's completed assignment.
>
>
>
Would this be alright? I never know how to properly use possessives when I'm including myself and someone else.
Also, in case you didn't see my comment below, I *need* to include my partner's name. It can't just be "me and my partner's completed assignment". Otherwise, I wouldn't have an issue. | 2019/03/29 | [
"https://english.stackexchange.com/questions/491864",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/342062/"
] | Without more substantial rephrasing, it will sound strange even if it *is* technically correct.
It would be more natural if you simply drop the use of the possessive:
>
> Here is the completed assignment of my partner, Jane Doe, and me.
>
>
> | To me, the most grammatical “translation” would be:
>
> Here’s my wife’s, Jane Doe’s, and my assignment.
>
>
>
I feel both components of the apposition should be possessive in order to be correct. |
491,864 | I'm writing a sentence, and I'm not sure if it's grammatically correct.
>
> Here are my partner, Jane Doe, and I's completed assignment.
>
>
>
Would this be alright? I never know how to properly use possessives when I'm including myself and someone else.
Also, in case you didn't see my comment below, I *need* to include my partner's name. It can't just be "me and my partner's completed assignment". Otherwise, I wouldn't have an issue. | 2019/03/29 | [
"https://english.stackexchange.com/questions/491864",
"https://english.stackexchange.com",
"https://english.stackexchange.com/users/342062/"
] | Without more substantial rephrasing, it will sound strange even if it *is* technically correct.
It would be more natural if you simply drop the use of the possessive:
>
> Here is the completed assignment of my partner, Jane Doe, and me.
>
>
> | Basically agreeing with Michael Harvey's offering: Here’s my partner Jane Doe’s, and my assignment.
But the comma of apposition is surely not necessary as "partner Jane Doe's" is a complete phrase. such as: Here is x's and my assignment, where x = partner Jane Doe. (Consider "partner" here as a title, rather than "Jane Doe" being in apposition to partner.)
I propose the correct written form would be:
Here’s my partner Jane Doe’s and my assignment. |
7,983,082 | I created a sample hello world application using Flash Builder 4.5.1 (with the update for iOS and AIR SDK version 2.6) for Android.
It went fine, when creating a new mobile project and run the output in desktop mode (launch method - as emulator). But when i try to install the app in the device using USB mode, iam not able to do that. Problem is when i launch the application using project run configurations and selecting Launch method as "On Device" , i am not able to get the device in Flash Builder which was connected through USB.
I tried connecting HTC Inspire device and the corresponding driver has been installed. When i try using Java eclipse (Native code), iam able to detect and deploy the code and check. But when i do the same using Flash Builder 4.5.1, iam not able to see the connected devices.
Went through most of the links in the google and found that we need to add the device hardware id in the 'flashbuilder4.5/utilities/drivers/android/android\_winusb.inf' file. But after adding the device and restarted FLash Builder, still teh same issue.
Also while trying to solve the issue, i found in most of the links and video that on launch from FLash builder there will be a option for Launch Method "Select Debug via USB" before 'device connection help'(hyperlink). But in the installed version of mine, i didn't able to find the option like that. Do we need to any other update to get the option.
Used Software versions:
1. FLash Builder - 4.5.1 (trial version)
1. AIR SDK 2.6
2. HTC Inspire (android 2.2)
Please let me know, does any one faced this issue before.
Thanks in Advance,
Regards
Srinivasan.C | 2011/11/02 | [
"https://Stackoverflow.com/questions/7983082",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/651834/"
] | Thanks for your replies..
I tried in different PC and uninstalled previous version of flash builder (which we have used for testing during preview release). After that, downloaded latest SDK and run the project in Android mobile (HTC - using USB drivers) and desktop it works fine..
The issue in the machine has OS as 'Windows Vista Business' and not able to fix the USB connectivity issue. So i tried in other machine which has OS as 'Windows XP' where i can see the proper installation of USB drivers for HTC and other devices.
Also after proper installation, when we packed and published the project for iOS and Android, it works well in both the platforms without any error.
Thanks,
Srinivasan | Can you check if you have "USB debugging" enabled in your device ?
Go to "Settings->Applications->Development->Enable USB debugging" . You need to enable USB debugging to run and debug any app on the device. |
8,662,560 | I am wanting to learn Java, particularly for Android development since I am getting a new tablet but also for many of the other things Java can do (Struts, network development, JWebSockets, and others). I am a fairly experienced developer with PHP, Javascript and .NET, mostly (I would say I am about an intermediate coder).
My issue is that I prefer to learn from books since I feel they give a more all-inclusive learning experience than trying to patch together a whole bunch of tutorials. I also just enjoy reading technical books! However, I have found a book that looks good to me at a discount book store near me called "Learning Java, 3rd Ed." by Niemeyer and Knudsen. It looks like exactly what I am looking for since it doesn't seem to be a beginner book that spends 500+ pages explaining OO, variables and methods. But it is for Java SE 5!
So now there is a Java SE 6 version, SE 7 and I think there is even a beta of SE 8. How far behind would it put me to learn the Java class library (and generally how to program Java) of Java SE 5?
I found this question: [How difficult is it to learn Java SE 6 from J2SE 5.0?](https://stackoverflow.com/questions/5657042/how-difficult-is-it-to-learn-java-se-6-from-j2se-5-0) but it seems that it was only referring to Java SE 5 vs. SE 6. But now there will soon be 2 more versions beyond that. I have also looked over feature lists of new versions, but without knowing the language better, I can't really tell how important the new versions are, or if they are mostly syntactic sugar. At the best, will I just need to maybe read some tutorials for upgrading developers, or at worst, would my SE 5 code break in SE 6, 7 or 8? Any and all help is appreciated! | 2011/12/28 | [
"https://Stackoverflow.com/questions/8662560",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1120174/"
] | Java 6 has some significant library improvements over Java 5 but few changes to syntax outside some improvements to the way annotations are done, so it won't be hard to pick up 6 incrementally.
Java 7 and (likely) 8 are much bigger changes, but you'd probably be learning them at the same time as the rest of the Java community. Java 7 is still early in the adoption cycle. | I don't think Oracle would do anything that would break Java 5 code in later versions of Java, provided that you didn't use any proprietary or deprecated API's.
With respect to Android, it has its own set of libraries which are not completely the same as any particular version of Java offered by Oracle.
Learning Java 5, and then going through the Android tutorials, and finally looking up the API when you need it should be sufficient for Android. |
8,662,560 | I am wanting to learn Java, particularly for Android development since I am getting a new tablet but also for many of the other things Java can do (Struts, network development, JWebSockets, and others). I am a fairly experienced developer with PHP, Javascript and .NET, mostly (I would say I am about an intermediate coder).
My issue is that I prefer to learn from books since I feel they give a more all-inclusive learning experience than trying to patch together a whole bunch of tutorials. I also just enjoy reading technical books! However, I have found a book that looks good to me at a discount book store near me called "Learning Java, 3rd Ed." by Niemeyer and Knudsen. It looks like exactly what I am looking for since it doesn't seem to be a beginner book that spends 500+ pages explaining OO, variables and methods. But it is for Java SE 5!
So now there is a Java SE 6 version, SE 7 and I think there is even a beta of SE 8. How far behind would it put me to learn the Java class library (and generally how to program Java) of Java SE 5?
I found this question: [How difficult is it to learn Java SE 6 from J2SE 5.0?](https://stackoverflow.com/questions/5657042/how-difficult-is-it-to-learn-java-se-6-from-j2se-5-0) but it seems that it was only referring to Java SE 5 vs. SE 6. But now there will soon be 2 more versions beyond that. I have also looked over feature lists of new versions, but without knowing the language better, I can't really tell how important the new versions are, or if they are mostly syntactic sugar. At the best, will I just need to maybe read some tutorials for upgrading developers, or at worst, would my SE 5 code break in SE 6, 7 or 8? Any and all help is appreciated! | 2011/12/28 | [
"https://Stackoverflow.com/questions/8662560",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1120174/"
] | Java 6 has some significant library improvements over Java 5 but few changes to syntax outside some improvements to the way annotations are done, so it won't be hard to pick up 6 incrementally.
Java 7 and (likely) 8 are much bigger changes, but you'd probably be learning them at the same time as the rest of the Java community. Java 7 is still early in the adoption cycle. | The differences between Java5 and Java6/7 language wise are minimal. There's some new syntactical sugar (let's see: Diamond operator, string switch,.. can't think of anything else) in Java7 but that's about it.
Java5 already includes the most important changes to Java in a long time: Generics and enums.
The only thing that was really improved with Java6/7 (6 especially) is library support: There are lots of classes in the JDK you won't find in Java5, but that shouldn't worry you too much when learning the language. |
8,662,560 | I am wanting to learn Java, particularly for Android development since I am getting a new tablet but also for many of the other things Java can do (Struts, network development, JWebSockets, and others). I am a fairly experienced developer with PHP, Javascript and .NET, mostly (I would say I am about an intermediate coder).
My issue is that I prefer to learn from books since I feel they give a more all-inclusive learning experience than trying to patch together a whole bunch of tutorials. I also just enjoy reading technical books! However, I have found a book that looks good to me at a discount book store near me called "Learning Java, 3rd Ed." by Niemeyer and Knudsen. It looks like exactly what I am looking for since it doesn't seem to be a beginner book that spends 500+ pages explaining OO, variables and methods. But it is for Java SE 5!
So now there is a Java SE 6 version, SE 7 and I think there is even a beta of SE 8. How far behind would it put me to learn the Java class library (and generally how to program Java) of Java SE 5?
I found this question: [How difficult is it to learn Java SE 6 from J2SE 5.0?](https://stackoverflow.com/questions/5657042/how-difficult-is-it-to-learn-java-se-6-from-j2se-5-0) but it seems that it was only referring to Java SE 5 vs. SE 6. But now there will soon be 2 more versions beyond that. I have also looked over feature lists of new versions, but without knowing the language better, I can't really tell how important the new versions are, or if they are mostly syntactic sugar. At the best, will I just need to maybe read some tutorials for upgrading developers, or at worst, would my SE 5 code break in SE 6, 7 or 8? Any and all help is appreciated! | 2011/12/28 | [
"https://Stackoverflow.com/questions/8662560",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1120174/"
] | For what it's worth, Java 7 was only [recently released](http://blogs.oracle.com/javase/entry/java_7_has_released), and I wouldn't expect Java 8 to be released anytime soon.
From a Java versions perspective, the release from Java 1.4 to Java 5 was the biggest change, in my opinion - enough that Sun started referring to Java 1.5 as "Java 5". This was the version that introduced new core features such as Generics, Annotations, etc. The jump from Java 5 onward won't be as big of a change compared to the earlier revisions, in comparison; mostly Java 6 & 7 add to the standard libraries, as well as some new syntactic sugar such as try-with-resources.
Either way, I'd say go for the book. Java 5 is a good start, and once you understand the language you can move on to the new features that Java 6 & 7 provide, such as java.util.concurrency, nio, blah, blah, blah... | Java 6 has some significant library improvements over Java 5 but few changes to syntax outside some improvements to the way annotations are done, so it won't be hard to pick up 6 incrementally.
Java 7 and (likely) 8 are much bigger changes, but you'd probably be learning them at the same time as the rest of the Java community. Java 7 is still early in the adoption cycle. |
8,662,560 | I am wanting to learn Java, particularly for Android development since I am getting a new tablet but also for many of the other things Java can do (Struts, network development, JWebSockets, and others). I am a fairly experienced developer with PHP, Javascript and .NET, mostly (I would say I am about an intermediate coder).
My issue is that I prefer to learn from books since I feel they give a more all-inclusive learning experience than trying to patch together a whole bunch of tutorials. I also just enjoy reading technical books! However, I have found a book that looks good to me at a discount book store near me called "Learning Java, 3rd Ed." by Niemeyer and Knudsen. It looks like exactly what I am looking for since it doesn't seem to be a beginner book that spends 500+ pages explaining OO, variables and methods. But it is for Java SE 5!
So now there is a Java SE 6 version, SE 7 and I think there is even a beta of SE 8. How far behind would it put me to learn the Java class library (and generally how to program Java) of Java SE 5?
I found this question: [How difficult is it to learn Java SE 6 from J2SE 5.0?](https://stackoverflow.com/questions/5657042/how-difficult-is-it-to-learn-java-se-6-from-j2se-5-0) but it seems that it was only referring to Java SE 5 vs. SE 6. But now there will soon be 2 more versions beyond that. I have also looked over feature lists of new versions, but without knowing the language better, I can't really tell how important the new versions are, or if they are mostly syntactic sugar. At the best, will I just need to maybe read some tutorials for upgrading developers, or at worst, would my SE 5 code break in SE 6, 7 or 8? Any and all help is appreciated! | 2011/12/28 | [
"https://Stackoverflow.com/questions/8662560",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1120174/"
] | For what it's worth, Java 7 was only [recently released](http://blogs.oracle.com/javase/entry/java_7_has_released), and I wouldn't expect Java 8 to be released anytime soon.
From a Java versions perspective, the release from Java 1.4 to Java 5 was the biggest change, in my opinion - enough that Sun started referring to Java 1.5 as "Java 5". This was the version that introduced new core features such as Generics, Annotations, etc. The jump from Java 5 onward won't be as big of a change compared to the earlier revisions, in comparison; mostly Java 6 & 7 add to the standard libraries, as well as some new syntactic sugar such as try-with-resources.
Either way, I'd say go for the book. Java 5 is a good start, and once you understand the language you can move on to the new features that Java 6 & 7 provide, such as java.util.concurrency, nio, blah, blah, blah... | I don't think Oracle would do anything that would break Java 5 code in later versions of Java, provided that you didn't use any proprietary or deprecated API's.
With respect to Android, it has its own set of libraries which are not completely the same as any particular version of Java offered by Oracle.
Learning Java 5, and then going through the Android tutorials, and finally looking up the API when you need it should be sufficient for Android. |
8,662,560 | I am wanting to learn Java, particularly for Android development since I am getting a new tablet but also for many of the other things Java can do (Struts, network development, JWebSockets, and others). I am a fairly experienced developer with PHP, Javascript and .NET, mostly (I would say I am about an intermediate coder).
My issue is that I prefer to learn from books since I feel they give a more all-inclusive learning experience than trying to patch together a whole bunch of tutorials. I also just enjoy reading technical books! However, I have found a book that looks good to me at a discount book store near me called "Learning Java, 3rd Ed." by Niemeyer and Knudsen. It looks like exactly what I am looking for since it doesn't seem to be a beginner book that spends 500+ pages explaining OO, variables and methods. But it is for Java SE 5!
So now there is a Java SE 6 version, SE 7 and I think there is even a beta of SE 8. How far behind would it put me to learn the Java class library (and generally how to program Java) of Java SE 5?
I found this question: [How difficult is it to learn Java SE 6 from J2SE 5.0?](https://stackoverflow.com/questions/5657042/how-difficult-is-it-to-learn-java-se-6-from-j2se-5-0) but it seems that it was only referring to Java SE 5 vs. SE 6. But now there will soon be 2 more versions beyond that. I have also looked over feature lists of new versions, but without knowing the language better, I can't really tell how important the new versions are, or if they are mostly syntactic sugar. At the best, will I just need to maybe read some tutorials for upgrading developers, or at worst, would my SE 5 code break in SE 6, 7 or 8? Any and all help is appreciated! | 2011/12/28 | [
"https://Stackoverflow.com/questions/8662560",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/1120174/"
] | For what it's worth, Java 7 was only [recently released](http://blogs.oracle.com/javase/entry/java_7_has_released), and I wouldn't expect Java 8 to be released anytime soon.
From a Java versions perspective, the release from Java 1.4 to Java 5 was the biggest change, in my opinion - enough that Sun started referring to Java 1.5 as "Java 5". This was the version that introduced new core features such as Generics, Annotations, etc. The jump from Java 5 onward won't be as big of a change compared to the earlier revisions, in comparison; mostly Java 6 & 7 add to the standard libraries, as well as some new syntactic sugar such as try-with-resources.
Either way, I'd say go for the book. Java 5 is a good start, and once you understand the language you can move on to the new features that Java 6 & 7 provide, such as java.util.concurrency, nio, blah, blah, blah... | The differences between Java5 and Java6/7 language wise are minimal. There's some new syntactical sugar (let's see: Diamond operator, string switch,.. can't think of anything else) in Java7 but that's about it.
Java5 already includes the most important changes to Java in a long time: Generics and enums.
The only thing that was really improved with Java6/7 (6 especially) is library support: There are lots of classes in the JDK you won't find in Java5, but that shouldn't worry you too much when learning the language. |
7,366,444 | I want to know list of advantages of using Entity framework over data access layer.
My website is host in shared hosting and i don't have access to IIS
Considering that i am working shared hosting world, is it feasible to work with entity framework? | 2011/09/09 | [
"https://Stackoverflow.com/questions/7366444",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/179123/"
] | Microsoft has publicly stated that Entity Framework will be the preffered data access technology for the .NET platform. Given your experience I feel like Entity Framework would be a huge asset to your ability to rapidly develop applications. Shared hosting is completely irrelevant to the fact that you are using entity framework. Just make sure that the hosting company supports .Net 4 framework (or w/e framework version you work with). | Entity Framework is a data access layer. Specifically it's an Object Relational Mapper.
So it basically comes down to - do you want to write your own DAL? - or would you rather spend your time building out the Data Model, and then having Entity create your entities and classes, etc.. for you. |
76,235 | I'm practicing making conceptual databases and I would like to know of I'm on the right track. I've been trying to create an ERD for a scenario as follows:
---
A hotel can take bookings for weddings, conferences and theme nights, as well as regular regular rooms. All bookings have a date, time, booking code, name of staff member that took the booking, deposit paid and payment method.
Weddings bookings record the name of bride and groom, as well as client info (full name, address, phone number and email), who is making the booking and the date of the wedding reception. Number of guests, food menu (3 different alternatives), if the reception is in the evening, if it's open bar and if a photographer is needed. There is two available suites to hold the weddings, Plaza or Ballroom.
Conference bookings require the same client info, as well as name and address of the organisation that holds the conference. Number if participants and which food menu (4 different choices) is desired is also recorded. A conference have access to the same venues as weddings, but can book more than one. There is also 5 smaller conference rooms that can be booked. These can hold 15-20 people, have 2 different layouts and some contain electronic facilities and some have tea/coffee facilities.
Theme nights record the same client details, the number of participants and have access to one of the two venues.
Clients can also book individual rooms, either single or double sized room and most have en-suite facilities. The same client details are stored for this booking as well.
---
What I have managed to model so far is the one below, am I on the right track here?
[](https://i.stack.imgur.com/KYbfo.png)
I know I am missing cardinality, mainly because I haven't figured out any nice way to do it in draw.io which I'm using at the moment.
I feel rather unsure on how to use the generalization/specialization (the arrows), is this done in a good way?
**EDIT:** I´ve updated the ERD with Primary keys but I'm not very sure I'm taking the right approach with it...
**EDIT 2:** I have made some changes to the ERD with some consideration on the answers for this questions. I know some of the issues raised still are there, the one I mainly would consider is combining Meeting\_Room and Suite but I'm not sure how to do it while keeping the constraint of the meeting rooms only being available to the conferences.
One thing that got misinterpreted was the Booker entity due to a mistake from my part. It didn't refer to the staff member taking the booking, but the person that did the booking.
>
> "Weddings bookings record the name of bride and groom, as well as client info (full name, address, phone number and email), **who is ~~taking~~ making the booking** and the date of the wedding reception."
>
>
>
I removed this entity and put it as a field referring to Person instead as the only relevant information about the person taking the booking is the name (for this scenario).
 | 2014/09/10 | [
"https://dba.stackexchange.com/questions/76235",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/47182/"
] | I think you're creating more tables than necessary.
First, why do you need a table for "bridal couple"? Why not just include the bride and groom fields in wedding\_booking table? The only reason to break this out into a separate table would be if you expected to book multiple weddings for the same couple, which seems rather unlikely. If they're getting re-married, it's probably not a second wedding to each other.
Why have tables for "bride" and "groom"? All these do is serve as an extra stepping stone to get from bride and groom id's to their names. Why not just have wedding\_booking have fields for bride\_name\_id and groom\_name\_id?
Why is name separate from client? Why not just put the name fields in the client table? Okay, you also use name for the employee who does the booking. Really you need an employee table and a client table, with each including a name. With just two fields making up the name, there's little gained by breaking this out into a separate table.
I don't see any reason for room\_booking to be a separate table. Booking should simply point to a room.
"Plaza" and "Ballroom" are not fields in suite. They are two different records. Maybe there's "description" that can have the value of "plaza" or "ballroom".
If I understand your intent, every wedding\_booking must be linked to a booking. So there's no need to have a client\_id in wedding\_booking as it's already in booking.
Likewise staff\_member in booking appears to be the same thing as booker\_id in wedding\_booking. It belongs just once, in booking.
Participants, delegates, and guests all appear to be the same idea: how many people are attending this event. I'd combine these into a single field in event\_booking.
If a conference can use either a meeting room or a suite, and possibly multiples, it gets awkward to break these into two tables. I'd combine meeting\_room and suite into a single table. If weddings and theme nights can book meeting rooms, fine, add a flag in there that says which it is, and then suites are available to all three types of events while meeting rooms are available only to conferences.
Many database designers would challenge me on this, but: I'd seriously consider combining theme night, conference, and wedding into a single table and having a type flag that indicates which it is. Most of what you need to record for these events is the same: how many people are coming, what room or rooms are they using, who's name is it under. A few fields only apply to one or the other, like conferences probably don't have flowers. But if somebody organizing a conference said they wanted to have flowers, would you tell them they can't because it's not a wedding? A conference or a theme night could have an open bar, I would think. Etc. My point is, there's no point limiting the services your hotel can offer to just certain types of events because you think they are unlikely to be wanted at other types of events -- unless there's really some reason why you just can't do it, legal restrictions or something. Also, if you later come up with another type of event you might book -- a birthday party or a bar mitzvah or a politician's victory party or whatever -- you just add another type, you don't have to struggle with creating a whole new table. You can even toss in an "other" type to allow for it so you don't have to scramble to reprogram the first time it happens.
Well, that's probably enough comments for the first round. :-) | Your use of shared primary keys makes sense to me. I note especially that the three specialized variants of a Booking all share a primary key with the generalized Event\_booking. This concept of shared primary key is generally quite useful. It enforces the one to one nature of the gen-spec relationship. It provides quick and easy joins between each spec table and the gen table. And it obviates the need for a type field in the gen table.
I wonder why Suite\_ID has to be in both Event\_Booking and Conference\_Booking.
As to whether you are on the right track at the conceptual level, that is a question of whether your conceptual level agrees with the way things are done in the real world. You'll have to get input from subject matter experts, and it may even work differently in different hotel chains.
Note: moved from the duplicate to here. |
365,023 | Why do EM propagate forward in time, but not backward in time? Stated differently, why does EM radiation not "ripple inwards" and collect at some point? These are perfectly possible, by time-reversal.
I'm assuming the explanation will invoke entropy somehow, but it's not yet clear to me how, as we explain similar problems in Stat Mech that way. Maybe it's baked into the initial conditions of the universe (as our Stat Mech explanations require)?
EDIT: I've thought about it some more, and I think my question is this one: why in Quantum Mechanics are we free to use the advanced Greene's Function in place of the retarded one, but not here? (Are we?) Maybe the advanced/retarded potentials result in different physically arrangements of the fields, while the advanced/retarded Greene's functions don't result in physically different wavefunctions? I think that answering this would resolve my question. (Insofar as I would know why we throw out advanced potentials, but certainly it would be unresolved why this area in particular violates time-symmetry. Isn't time-symmetry a major principle? Why would we say the universe is time-symmetric if it isn't in E+M?) | 2017/10/25 | [
"https://physics.stackexchange.com/questions/365023",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/126995/"
] | >
> Stated differently, why does EM radiation not "ripple inwards" and collect at some point? These are perfectly possible, by time-reversal.
>
>
>
Well, in most cases observed or measured, EM radiation does not ripple outwards from a *point* either; usually, the radiation is connected to a body with non-zero spatial dimensions. In fact, radiation of point charges may contain advanced field component but macroscopically *look like* the retarded solution - see the Feynman-Wheeler theory.
I suppose you are interested in the following question:
*since there are well known processes in which EM waves are created in and propagate outwards from physical bodies out to distant space (such as radiating antenna), why are there not also inverse processes, where the EM waves propagate from the distant space towards some physical bodies and collapse on them?*
We know that Maxwell's equations in some simple scenarios (such as continuous motion of a point charge) have solutions like that (called advanced fields as opposed to retarded fields), so why aren't we observing such collapsing spherical waves at least *somewhere*?
**Short answer**: the reason can be sought either in:
* the state of the EM field in the past (a special initial condition that does not lead to macroscopic advanced waves); past is not a part of physical laws, it must be assumed as a separate assumption;
or
* it can be sought in a separate physical law that restricts the fields of charged particles to be the retarded solutions of field equations with their individual source terms.
**Long attempt at an answer:**
If we knew the state of the field everywhere at some point of time and if we knew the subsequent motion of the charges, we could predict the field into the future. If we fix the motion of the charges, the field would be determined by the initial condition.
The initial condition could be, in principle, such that field in vicinity of charged bodies would evolve like an ingoing wave, coming from far away and collapsing on those bodies.
Another initial condition could be such that the opposite would happen; the field would evolve like an outgoing wave, getting away from the bodies to infinity.
There are infinity of other initial conditions which are different from the above; in general, the difference between them is a "free field" - a solution of Maxwell's equations without any sources.
The appropriateness of initial condition in macroscopic theory is to be judged based on experience; there is no physical law that would require one or the other.
Absence of ingoing EM waves in our experience means that certain class of initial conditions for fields is to be avoided or even rejected in macroscopic EM theory.
But this does not easily translate into microscopic theory. Let us assume that total EM field is composed of elementary EM fields of very big number of charged particles.
It is possible to have macroscopically retarded fields that are made of microscopic fields which are not purely retarded but contain advanced field. And it is possible to simulate macroscopic advanced field with a special arrangement of microscopic fields that are purely retarded.
An interesting but not the only possible version of EM theory is that the microscopic fields are completely symmetrical combination of retarded and advanced waves (Tetrode, Frenkel or Feynman-Wheeler models and their variations), but when these are used to explain our experience with macroscopic bodies, things are not so simple anymore: if the elementary fields are symmetrical combination of retarded and advanced waves, how come we do not see such symmetrical EM wave around an antenna? (People actually proposed an experiment and verified that the EM field is not such symmetrical one. Experience suggests that EM field near antenna is well given by the retarded solution.)
In the Feynman-Wheeler model, they came up with an interesting idea: they introduced a boundary condition into the theory (so-called absorber condition) which formally allowed them to arrive at realistic description of EM field where the observable field *seems* to be almost retarded and where the correction supposedly explains radiation reaction. I find the absorber condition very formal and unnatural, and their explanation of radiation reaction (which relies on that condition) as ill motivated and unnecessary for point particles. Still, the idea of symmetrical half-retarded, half-advanced field has some interesting implications, for example, systems of opposite charges are much more stable, because now the waves go both in and out and there is no intense radiation of EM energy to surrounding space from such systems as would be expected based on Larmor's formula (which is not valid here). It is possible that the symmetrical microscopical fields with the right probabilistic assumptions can be consistent with our macroscopic experience with retarded fields, even if we abandon the somehow unnatural absorber condition.
The most simple and natural stance currently is that the elementary fields are retarded and the advanced solutions are unphysical - the second variant from the short answer. This simple choice is quite intuitive - elementary waves only ever propagate outwards from the particles. It explains why macroscopic waves are retarded without further assumptions such as the Feynman-Wheeler absorber condition. True, a collapsing approximately spherical wave could be created if lots of particles danced in a special way, but such correlated motion across great distances is quite improbable, so this poses no challenge for the model. | Not sure anyone answered the question. The reason being their concept of time. There is no such place as the past nor the future. There is only the present. Einstein developed some interesting theories-he did so in 'his' present. He tried to tell everyone time depends upon your frame of reference. Neil Armstrong walked on the moon in 'his' present time. A photon has momentum but no mass. Assume you are a photon 13 billion miles away. It would take 13 billion years to get here. However, if you were that photon then the trip would be instant(frame of reference). Someday man may walk on the plains of Mars. They can only do so in their present.There has never been an instance where [anything]has gone back in time. |
365,023 | Why do EM propagate forward in time, but not backward in time? Stated differently, why does EM radiation not "ripple inwards" and collect at some point? These are perfectly possible, by time-reversal.
I'm assuming the explanation will invoke entropy somehow, but it's not yet clear to me how, as we explain similar problems in Stat Mech that way. Maybe it's baked into the initial conditions of the universe (as our Stat Mech explanations require)?
EDIT: I've thought about it some more, and I think my question is this one: why in Quantum Mechanics are we free to use the advanced Greene's Function in place of the retarded one, but not here? (Are we?) Maybe the advanced/retarded potentials result in different physically arrangements of the fields, while the advanced/retarded Greene's functions don't result in physically different wavefunctions? I think that answering this would resolve my question. (Insofar as I would know why we throw out advanced potentials, but certainly it would be unresolved why this area in particular violates time-symmetry. Isn't time-symmetry a major principle? Why would we say the universe is time-symmetric if it isn't in E+M?) | 2017/10/25 | [
"https://physics.stackexchange.com/questions/365023",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/126995/"
] | >
> Stated differently, why does EM radiation not "ripple inwards" and collect at some point? These are perfectly possible, by time-reversal.
>
>
>
Well, in most cases observed or measured, EM radiation does not ripple outwards from a *point* either; usually, the radiation is connected to a body with non-zero spatial dimensions. In fact, radiation of point charges may contain advanced field component but macroscopically *look like* the retarded solution - see the Feynman-Wheeler theory.
I suppose you are interested in the following question:
*since there are well known processes in which EM waves are created in and propagate outwards from physical bodies out to distant space (such as radiating antenna), why are there not also inverse processes, where the EM waves propagate from the distant space towards some physical bodies and collapse on them?*
We know that Maxwell's equations in some simple scenarios (such as continuous motion of a point charge) have solutions like that (called advanced fields as opposed to retarded fields), so why aren't we observing such collapsing spherical waves at least *somewhere*?
**Short answer**: the reason can be sought either in:
* the state of the EM field in the past (a special initial condition that does not lead to macroscopic advanced waves); past is not a part of physical laws, it must be assumed as a separate assumption;
or
* it can be sought in a separate physical law that restricts the fields of charged particles to be the retarded solutions of field equations with their individual source terms.
**Long attempt at an answer:**
If we knew the state of the field everywhere at some point of time and if we knew the subsequent motion of the charges, we could predict the field into the future. If we fix the motion of the charges, the field would be determined by the initial condition.
The initial condition could be, in principle, such that field in vicinity of charged bodies would evolve like an ingoing wave, coming from far away and collapsing on those bodies.
Another initial condition could be such that the opposite would happen; the field would evolve like an outgoing wave, getting away from the bodies to infinity.
There are infinity of other initial conditions which are different from the above; in general, the difference between them is a "free field" - a solution of Maxwell's equations without any sources.
The appropriateness of initial condition in macroscopic theory is to be judged based on experience; there is no physical law that would require one or the other.
Absence of ingoing EM waves in our experience means that certain class of initial conditions for fields is to be avoided or even rejected in macroscopic EM theory.
But this does not easily translate into microscopic theory. Let us assume that total EM field is composed of elementary EM fields of very big number of charged particles.
It is possible to have macroscopically retarded fields that are made of microscopic fields which are not purely retarded but contain advanced field. And it is possible to simulate macroscopic advanced field with a special arrangement of microscopic fields that are purely retarded.
An interesting but not the only possible version of EM theory is that the microscopic fields are completely symmetrical combination of retarded and advanced waves (Tetrode, Frenkel or Feynman-Wheeler models and their variations), but when these are used to explain our experience with macroscopic bodies, things are not so simple anymore: if the elementary fields are symmetrical combination of retarded and advanced waves, how come we do not see such symmetrical EM wave around an antenna? (People actually proposed an experiment and verified that the EM field is not such symmetrical one. Experience suggests that EM field near antenna is well given by the retarded solution.)
In the Feynman-Wheeler model, they came up with an interesting idea: they introduced a boundary condition into the theory (so-called absorber condition) which formally allowed them to arrive at realistic description of EM field where the observable field *seems* to be almost retarded and where the correction supposedly explains radiation reaction. I find the absorber condition very formal and unnatural, and their explanation of radiation reaction (which relies on that condition) as ill motivated and unnecessary for point particles. Still, the idea of symmetrical half-retarded, half-advanced field has some interesting implications, for example, systems of opposite charges are much more stable, because now the waves go both in and out and there is no intense radiation of EM energy to surrounding space from such systems as would be expected based on Larmor's formula (which is not valid here). It is possible that the symmetrical microscopical fields with the right probabilistic assumptions can be consistent with our macroscopic experience with retarded fields, even if we abandon the somehow unnatural absorber condition.
The most simple and natural stance currently is that the elementary fields are retarded and the advanced solutions are unphysical - the second variant from the short answer. This simple choice is quite intuitive - elementary waves only ever propagate outwards from the particles. It explains why macroscopic waves are retarded without further assumptions such as the Feynman-Wheeler absorber condition. True, a collapsing approximately spherical wave could be created if lots of particles danced in a special way, but such correlated motion across great distances is quite improbable, so this poses no challenge for the model. | This problem has not really impinged on my attention, but I think you are correct that [entropy](https://en.wikipedia.org/wiki/Entropy_(statistical_thermodynamics)) can explain it, when expressed as a number of microstates.
I quote from the relevant conclusion of the answer by Ján Lalinský :
>
> Collapsing spherical waves can still exist, but only as a special situation involving specially correlated particle motions in the past, far from the center.
>
>
>
For simplicity take a single source. The [electromagnetic field emerges](http://motls.blogspot.com/2011/11/how-classical-fields-particles-emerge.html) from a confluence of a large number of photons. Conceptually the wave functions of the individual photons in superposition build up the E and B fields of Maxwell's equations. The photons, as elementary particles are countable. As they spread in the universe the number of microstates increases or remains the same , unless it spreads in completely empty space , which classically is possible , but quantum mechanically the photons will meet vacuum fluctuations, this will involve increasing numbers of microstates.
In order for an advanced wave to reproduce and focus on the same spot, in fact make an inverse source, the photons must interact with the same order of vacuum fluctuations, because the photons will travel the same distance to end up at the same (x,y,z). It will have accumulated entropy of the order of the entropy acquired by the outgoing retarded wave . But the redarded waves source at an (x,y,z) is a at a lower entropy at the start of radiation, the reurned has gathered all the microstates on the way into its entropy, so there has not really been a time reversal to the original solution.
I think this is a [reductio ad absurdum](https://en.wikipedia.org/wiki/Reductio_ad_absurdum) argument, which might be combed to be presentable. |
365,023 | Why do EM propagate forward in time, but not backward in time? Stated differently, why does EM radiation not "ripple inwards" and collect at some point? These are perfectly possible, by time-reversal.
I'm assuming the explanation will invoke entropy somehow, but it's not yet clear to me how, as we explain similar problems in Stat Mech that way. Maybe it's baked into the initial conditions of the universe (as our Stat Mech explanations require)?
EDIT: I've thought about it some more, and I think my question is this one: why in Quantum Mechanics are we free to use the advanced Greene's Function in place of the retarded one, but not here? (Are we?) Maybe the advanced/retarded potentials result in different physically arrangements of the fields, while the advanced/retarded Greene's functions don't result in physically different wavefunctions? I think that answering this would resolve my question. (Insofar as I would know why we throw out advanced potentials, but certainly it would be unresolved why this area in particular violates time-symmetry. Isn't time-symmetry a major principle? Why would we say the universe is time-symmetric if it isn't in E+M?) | 2017/10/25 | [
"https://physics.stackexchange.com/questions/365023",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/126995/"
] | >
> Stated differently, why does EM radiation not "ripple inwards" and collect at some point? These are perfectly possible, by time-reversal.
>
>
>
Well, in most cases observed or measured, EM radiation does not ripple outwards from a *point* either; usually, the radiation is connected to a body with non-zero spatial dimensions. In fact, radiation of point charges may contain advanced field component but macroscopically *look like* the retarded solution - see the Feynman-Wheeler theory.
I suppose you are interested in the following question:
*since there are well known processes in which EM waves are created in and propagate outwards from physical bodies out to distant space (such as radiating antenna), why are there not also inverse processes, where the EM waves propagate from the distant space towards some physical bodies and collapse on them?*
We know that Maxwell's equations in some simple scenarios (such as continuous motion of a point charge) have solutions like that (called advanced fields as opposed to retarded fields), so why aren't we observing such collapsing spherical waves at least *somewhere*?
**Short answer**: the reason can be sought either in:
* the state of the EM field in the past (a special initial condition that does not lead to macroscopic advanced waves); past is not a part of physical laws, it must be assumed as a separate assumption;
or
* it can be sought in a separate physical law that restricts the fields of charged particles to be the retarded solutions of field equations with their individual source terms.
**Long attempt at an answer:**
If we knew the state of the field everywhere at some point of time and if we knew the subsequent motion of the charges, we could predict the field into the future. If we fix the motion of the charges, the field would be determined by the initial condition.
The initial condition could be, in principle, such that field in vicinity of charged bodies would evolve like an ingoing wave, coming from far away and collapsing on those bodies.
Another initial condition could be such that the opposite would happen; the field would evolve like an outgoing wave, getting away from the bodies to infinity.
There are infinity of other initial conditions which are different from the above; in general, the difference between them is a "free field" - a solution of Maxwell's equations without any sources.
The appropriateness of initial condition in macroscopic theory is to be judged based on experience; there is no physical law that would require one or the other.
Absence of ingoing EM waves in our experience means that certain class of initial conditions for fields is to be avoided or even rejected in macroscopic EM theory.
But this does not easily translate into microscopic theory. Let us assume that total EM field is composed of elementary EM fields of very big number of charged particles.
It is possible to have macroscopically retarded fields that are made of microscopic fields which are not purely retarded but contain advanced field. And it is possible to simulate macroscopic advanced field with a special arrangement of microscopic fields that are purely retarded.
An interesting but not the only possible version of EM theory is that the microscopic fields are completely symmetrical combination of retarded and advanced waves (Tetrode, Frenkel or Feynman-Wheeler models and their variations), but when these are used to explain our experience with macroscopic bodies, things are not so simple anymore: if the elementary fields are symmetrical combination of retarded and advanced waves, how come we do not see such symmetrical EM wave around an antenna? (People actually proposed an experiment and verified that the EM field is not such symmetrical one. Experience suggests that EM field near antenna is well given by the retarded solution.)
In the Feynman-Wheeler model, they came up with an interesting idea: they introduced a boundary condition into the theory (so-called absorber condition) which formally allowed them to arrive at realistic description of EM field where the observable field *seems* to be almost retarded and where the correction supposedly explains radiation reaction. I find the absorber condition very formal and unnatural, and their explanation of radiation reaction (which relies on that condition) as ill motivated and unnecessary for point particles. Still, the idea of symmetrical half-retarded, half-advanced field has some interesting implications, for example, systems of opposite charges are much more stable, because now the waves go both in and out and there is no intense radiation of EM energy to surrounding space from such systems as would be expected based on Larmor's formula (which is not valid here). It is possible that the symmetrical microscopical fields with the right probabilistic assumptions can be consistent with our macroscopic experience with retarded fields, even if we abandon the somehow unnatural absorber condition.
The most simple and natural stance currently is that the elementary fields are retarded and the advanced solutions are unphysical - the second variant from the short answer. This simple choice is quite intuitive - elementary waves only ever propagate outwards from the particles. It explains why macroscopic waves are retarded without further assumptions such as the Feynman-Wheeler absorber condition. True, a collapsing approximately spherical wave could be created if lots of particles danced in a special way, but such correlated motion across great distances is quite improbable, so this poses no challenge for the model. | For fundamental questions you must not only limit to a consideration of coordinate time, but you also have to take into account proper time which is the fundamental concept which is underlying the concept of coordinate time of spacetime.
The proper time of lightlike phenomena such as EM waves is zero. That means that lightlike phenomena are **time-symmetric**, there is no intrinsic time direction. By consequence, any definition of a time direction is stemming from the observer who is observing the EM wave moving at velocity c forward in time.
That means simply that lightlike EM waves are interacting with their observer in the time direction of the observer. Based on this conclusion we could speculate that - if there are objects moving in the opposite time direction - that these objects would observe EM waves moving in the opposite time direction. |
365,023 | Why do EM propagate forward in time, but not backward in time? Stated differently, why does EM radiation not "ripple inwards" and collect at some point? These are perfectly possible, by time-reversal.
I'm assuming the explanation will invoke entropy somehow, but it's not yet clear to me how, as we explain similar problems in Stat Mech that way. Maybe it's baked into the initial conditions of the universe (as our Stat Mech explanations require)?
EDIT: I've thought about it some more, and I think my question is this one: why in Quantum Mechanics are we free to use the advanced Greene's Function in place of the retarded one, but not here? (Are we?) Maybe the advanced/retarded potentials result in different physically arrangements of the fields, while the advanced/retarded Greene's functions don't result in physically different wavefunctions? I think that answering this would resolve my question. (Insofar as I would know why we throw out advanced potentials, but certainly it would be unresolved why this area in particular violates time-symmetry. Isn't time-symmetry a major principle? Why would we say the universe is time-symmetric if it isn't in E+M?) | 2017/10/25 | [
"https://physics.stackexchange.com/questions/365023",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/126995/"
] | This problem has not really impinged on my attention, but I think you are correct that [entropy](https://en.wikipedia.org/wiki/Entropy_(statistical_thermodynamics)) can explain it, when expressed as a number of microstates.
I quote from the relevant conclusion of the answer by Ján Lalinský :
>
> Collapsing spherical waves can still exist, but only as a special situation involving specially correlated particle motions in the past, far from the center.
>
>
>
For simplicity take a single source. The [electromagnetic field emerges](http://motls.blogspot.com/2011/11/how-classical-fields-particles-emerge.html) from a confluence of a large number of photons. Conceptually the wave functions of the individual photons in superposition build up the E and B fields of Maxwell's equations. The photons, as elementary particles are countable. As they spread in the universe the number of microstates increases or remains the same , unless it spreads in completely empty space , which classically is possible , but quantum mechanically the photons will meet vacuum fluctuations, this will involve increasing numbers of microstates.
In order for an advanced wave to reproduce and focus on the same spot, in fact make an inverse source, the photons must interact with the same order of vacuum fluctuations, because the photons will travel the same distance to end up at the same (x,y,z). It will have accumulated entropy of the order of the entropy acquired by the outgoing retarded wave . But the redarded waves source at an (x,y,z) is a at a lower entropy at the start of radiation, the reurned has gathered all the microstates on the way into its entropy, so there has not really been a time reversal to the original solution.
I think this is a [reductio ad absurdum](https://en.wikipedia.org/wiki/Reductio_ad_absurdum) argument, which might be combed to be presentable. | Not sure anyone answered the question. The reason being their concept of time. There is no such place as the past nor the future. There is only the present. Einstein developed some interesting theories-he did so in 'his' present. He tried to tell everyone time depends upon your frame of reference. Neil Armstrong walked on the moon in 'his' present time. A photon has momentum but no mass. Assume you are a photon 13 billion miles away. It would take 13 billion years to get here. However, if you were that photon then the trip would be instant(frame of reference). Someday man may walk on the plains of Mars. They can only do so in their present.There has never been an instance where [anything]has gone back in time. |
365,023 | Why do EM propagate forward in time, but not backward in time? Stated differently, why does EM radiation not "ripple inwards" and collect at some point? These are perfectly possible, by time-reversal.
I'm assuming the explanation will invoke entropy somehow, but it's not yet clear to me how, as we explain similar problems in Stat Mech that way. Maybe it's baked into the initial conditions of the universe (as our Stat Mech explanations require)?
EDIT: I've thought about it some more, and I think my question is this one: why in Quantum Mechanics are we free to use the advanced Greene's Function in place of the retarded one, but not here? (Are we?) Maybe the advanced/retarded potentials result in different physically arrangements of the fields, while the advanced/retarded Greene's functions don't result in physically different wavefunctions? I think that answering this would resolve my question. (Insofar as I would know why we throw out advanced potentials, but certainly it would be unresolved why this area in particular violates time-symmetry. Isn't time-symmetry a major principle? Why would we say the universe is time-symmetric if it isn't in E+M?) | 2017/10/25 | [
"https://physics.stackexchange.com/questions/365023",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/126995/"
] | It's counterinuitive, but I think the question
>
> Stated differently, why does EM radiation not "ripple inwards" and collect at some point?
>
>
>
can be answered thusly:
>
> It does.
>
>
>
Or rather, one could choose to see the same system in terms of 'rippling outward', or in terms of 'rippling inward', without changing the underlying physics. In other words, the question
>
> why in Quantum Mechanics are we free to use the advanced Greene's Function in place of the retarded one, but not here? (Are we?)
>
>
>
Can be answered:
>
> We are.
>
>
>
For example, imagine an idealised model of a point source of radiation surrounded at some finite distance by absorbing walls. The obvious description is in terms of retarded waves radiating outwards from the point source, but if one were so inclined one could instead see the same solution as a sum of infinitely many advanced waves converging onto each point on the absorbing boundary. Admittedly I haven't done a calculation to check, but I think it should be possible to do this such that the sum of all these advanced waves gives exactly the same solution as the single retarded wave.
Of course, in this example and many others it is much more convenient to think in terms of retarded waves than advanced ones, and there is also an important question about why this should be the case. This I think has to do with causality. In the example above, if we move the point source we will change the whole radiation field, but if we move the boundary around we will not. We're able to directly manipulate the sources of radiation, but we can only manipulate radiation sinks indirectly, by manipulating the sources.
This seems slightly strange and mysterious in the context of electromagnetic radiation, but it's not really any different from any other physical process --- quite universally, we can only manipulate initial conditions and not final ones. (As an aside, it is possible to derive the second law from more or less this fact alone.{1})
I came to these conclusions while reading {2}, which covers this issue in some depth. However, I read it a long time ago and can't remember if my conclusion is the same one the author comes to.
{1} Jaynes, E. T., 1965, `[Gibbs vs Boltzmann Entropies](http://bayes.wustl.edu/etj/articles/gibbs.vs.boltzmann.pdf),' Am. J. Phys., 33, 391;
{2} Huw Price *[Time's Arrow and Archimedes' Point](http://prce.hu/w/TAAP.html)*, Oxford University Press, 1996 | Not sure anyone answered the question. The reason being their concept of time. There is no such place as the past nor the future. There is only the present. Einstein developed some interesting theories-he did so in 'his' present. He tried to tell everyone time depends upon your frame of reference. Neil Armstrong walked on the moon in 'his' present time. A photon has momentum but no mass. Assume you are a photon 13 billion miles away. It would take 13 billion years to get here. However, if you were that photon then the trip would be instant(frame of reference). Someday man may walk on the plains of Mars. They can only do so in their present.There has never been an instance where [anything]has gone back in time. |
16,460 | A customer wants to launch an ICO which should accept contributions in Ethers, Bitcoins, and fiat via credit cards and wire transfer.
Anyone was able to solve this? I know that this isn't an Ethereum problem but it seems to be an issue for ICOs since most accept only Ethers. | 2017/05/22 | [
"https://ethereum.stackexchange.com/questions/16460",
"https://ethereum.stackexchange.com",
"https://ethereum.stackexchange.com/users/1670/"
] | There's no easy way to fix this, and it may be impossible.
Ideally you should stop using that machine immediately. At the very least, try not to write anything to the hard drive. The contents of the file you need might still be present on the hard drive in unallocated space. Each new file you or Windows creates might overwrite the data you want.
Check out this page and read the *"The Safest Way to Recover a Deleted File"* or *"The Quicker, Riskier Way to Recover a Deleted File"* section:
<https://www.howtogeek.com/169344/how-to-recover-a-deleted-file-the-ultimate-guide/> | I'm sorry, hopefully it wasn't much. If you don't have a backup of your key file or a seed phrase for your accounts, the only thing would be trying data rescue software, maybe you're lucky. There is nothing else you can do, unfortunately. Have a nice day though, and don't forget to backup your wallets next time ! :) |
1,549,928 | I started learning Standard ML recently out of curiosity. So what I know is that is has an efficient compiler (MLton) which allows us to freely use abstractions without worrying about performance.
It would be perfect if I could do some GUI programming with Standard ML, too. Is there anything like Gtk, Qt, or WxWidgets binding for Standard ML?
Thank you very much. | 2009/10/11 | [
"https://Stackoverflow.com/questions/1549928",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/159759/"
] | Here's [a paper](http://www.usenix.org/event/usenix04/tech/freenix/full_papers/larsen/larsen.pdf) describing the [mGTK](http://mgtk.sourceforge.net/) project, which is a Standard ML binding to GTK. There are also a couple of [interfaces to OpenGL](http://mlton.org/OpenGL), although this is more 2 and 3D graphics-oriented rather than specifically a GUI toolkit. [eXene](http://people.cis.ksu.edu/~stough/eXene/index.html) is a toolkit for X Windows. [sml\_tk](http://www.informatik.uni-bremen.de/~cxl/sml_tk/) is an interface to Tk. | There are bindings for foreign toolkits, but the [eXene](http://people.cis.ksu.edu/~stough/eXene/index.html) toolkit was designed to be native for SML and to exploit the features of Concurrent ML. I used it years ago and found it a very smooth fit for the language and a pleasure to use. But it does not have the ginormous library of components that you find in the more widely used toolkits. |
1,549,928 | I started learning Standard ML recently out of curiosity. So what I know is that is has an efficient compiler (MLton) which allows us to freely use abstractions without worrying about performance.
It would be perfect if I could do some GUI programming with Standard ML, too. Is there anything like Gtk, Qt, or WxWidgets binding for Standard ML?
Thank you very much. | 2009/10/11 | [
"https://Stackoverflow.com/questions/1549928",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/159759/"
] | Here's [a paper](http://www.usenix.org/event/usenix04/tech/freenix/full_papers/larsen/larsen.pdf) describing the [mGTK](http://mgtk.sourceforge.net/) project, which is a Standard ML binding to GTK. There are also a couple of [interfaces to OpenGL](http://mlton.org/OpenGL), although this is more 2 and 3D graphics-oriented rather than specifically a GUI toolkit. [eXene](http://people.cis.ksu.edu/~stough/eXene/index.html) is a toolkit for X Windows. [sml\_tk](http://www.informatik.uni-bremen.de/~cxl/sml_tk/) is an interface to Tk. | [Giraffe Library](http://giraffelibrary.org/) provides SML bindings to libraries that support [GObject Introspection](https://gi.readthedocs.io/en/latest/), which includes GTK. At the time of writing, bindings are available for the GTK 3 stack. Although the cairo graphics library does not support GObject Introspection, Giraffe Library provides bindings to some cairo functions.
Although SML has a very precise definition, the definition does not include an FFI, and there is considerable variation between compilers. At the time of writing, Giraffe Library supports only the FFIs of [MLton](http://mlton.org/) and [Poly/ML](https://www.polyml.org/). |
1,549,928 | I started learning Standard ML recently out of curiosity. So what I know is that is has an efficient compiler (MLton) which allows us to freely use abstractions without worrying about performance.
It would be perfect if I could do some GUI programming with Standard ML, too. Is there anything like Gtk, Qt, or WxWidgets binding for Standard ML?
Thank you very much. | 2009/10/11 | [
"https://Stackoverflow.com/questions/1549928",
"https://Stackoverflow.com",
"https://Stackoverflow.com/users/159759/"
] | There are bindings for foreign toolkits, but the [eXene](http://people.cis.ksu.edu/~stough/eXene/index.html) toolkit was designed to be native for SML and to exploit the features of Concurrent ML. I used it years ago and found it a very smooth fit for the language and a pleasure to use. But it does not have the ginormous library of components that you find in the more widely used toolkits. | [Giraffe Library](http://giraffelibrary.org/) provides SML bindings to libraries that support [GObject Introspection](https://gi.readthedocs.io/en/latest/), which includes GTK. At the time of writing, bindings are available for the GTK 3 stack. Although the cairo graphics library does not support GObject Introspection, Giraffe Library provides bindings to some cairo functions.
Although SML has a very precise definition, the definition does not include an FFI, and there is considerable variation between compilers. At the time of writing, Giraffe Library supports only the FFIs of [MLton](http://mlton.org/) and [Poly/ML](https://www.polyml.org/). |
1,218,493 | On June 3rd, Windows 10 installed the Feature update version 1703.
Since then, my MS USB wheel mouse started to play up, disconnecting and reconnecting at random.
I followed the advice found in an old answer to the same problem, where it was suggested it was linked to Power Saving, Sure enough, switching off was enabled, which is silly, really, as I'm using a desktop PC with several monitors, wifi connections, etc.
After turning off the Power Saver option for all USB hubs, mouse and UI, I still found the mouse switched off and on at random. On at least one occasion, the device was also reinstalled automatically - with the power save switch and wake-up box reinstated.
I have tried a non-MS mouse (Swann brand) which I plugged into different USB ports (USB 2 and 3), but that was also switched off at random.
In the end, I uninstalled the mouse completely and went back to the MS wheeler. Restarted the PC.
This may have fixed the problem - it's now been stable for half an hour. fingers crossed :)
Microsoft haven't replied yet.
All I can say is, the mouse had been working fine until the day after the Windows 10 update. It took me a while until I found this website, and the suggestion to check USB hubs' power management settings.
as a PS: The mouse has been well behaved all day today.
A big Thanks to Aaaaayu for <https://superuser.com/posts/66467/revisions>
It didn't last after all - back to start.
every few seconds, the device stop and device restart sounds chirp in the background. And the mouse cursor disappears. Even Solitaire becomes frustrating. | 2017/06/12 | [
"https://superuser.com/questions/1218493",
"https://superuser.com",
"https://superuser.com/users/737819/"
] | Finally, it seems to have been fixed.
After Microsoft's latest Windows-10 update (dated 13 June) was delivered and installed, I haven't been able to reproduce the dropouts.
Easy to verify: Lifting the mouse and turning it upside-down would turn off the light; it no longer does.
Correction: the disconnect/reconnect music has restarted. And it is consistent across USB ports.
(still no answer from Microsoft either) | was having the same problem. This worked for me:
1. Open device manager
2. click on Universal serial bus controllers
3. right click on each one
4. open power management window
5. check to see if the "allow this computer to turn off this device to save power" box is checked
6. uncheck the box and close the window. |
1,218,493 | On June 3rd, Windows 10 installed the Feature update version 1703.
Since then, my MS USB wheel mouse started to play up, disconnecting and reconnecting at random.
I followed the advice found in an old answer to the same problem, where it was suggested it was linked to Power Saving, Sure enough, switching off was enabled, which is silly, really, as I'm using a desktop PC with several monitors, wifi connections, etc.
After turning off the Power Saver option for all USB hubs, mouse and UI, I still found the mouse switched off and on at random. On at least one occasion, the device was also reinstalled automatically - with the power save switch and wake-up box reinstated.
I have tried a non-MS mouse (Swann brand) which I plugged into different USB ports (USB 2 and 3), but that was also switched off at random.
In the end, I uninstalled the mouse completely and went back to the MS wheeler. Restarted the PC.
This may have fixed the problem - it's now been stable for half an hour. fingers crossed :)
Microsoft haven't replied yet.
All I can say is, the mouse had been working fine until the day after the Windows 10 update. It took me a while until I found this website, and the suggestion to check USB hubs' power management settings.
as a PS: The mouse has been well behaved all day today.
A big Thanks to Aaaaayu for <https://superuser.com/posts/66467/revisions>
It didn't last after all - back to start.
every few seconds, the device stop and device restart sounds chirp in the background. And the mouse cursor disappears. Even Solitaire becomes frustrating. | 2017/06/12 | [
"https://superuser.com/questions/1218493",
"https://superuser.com",
"https://superuser.com/users/737819/"
] | To me, it would appear the you might be experiencing *interference* from other radio devices. Have you introduced new equipment into your environment? To your Laptop/Computer? Have you *moved* any of your equipment? This (your problem) can easily occur if channels of your wireless devices *overlap*. In those cases, the most powerful (radio signal) device wins.
I think the Windows update may just be a coincidence. | was having the same problem. This worked for me:
1. Open device manager
2. click on Universal serial bus controllers
3. right click on each one
4. open power management window
5. check to see if the "allow this computer to turn off this device to save power" box is checked
6. uncheck the box and close the window. |
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