HDPE as the body of a 3-D Printer?

Question: I've been working on my own DIY 3-D printer recently, and I've been trying to experiment a little with different materials for the body. Someone suggested using HDPE (high-density polyethylene), since it works well on a CNC machine, which would make creating a number of prototypes easy. I know HDPE can also be used for filament, but I've never tried it before. Does anybody have any input on HDPE, or other potential materials for the body? I'm trying to avoid using wood, as I've had some poor experiences with it.
Comment: Really hard to beat aluminum extrusion frames. Are you particularly wanting a cut-sheet construction printer?
Comment: Not necessarily, but I have a lot of experience with CAD/CAM programs, so I'm trying to use this as an oppurtunity to stretch my design muscles a little.
Answer: The main consideration when building the body/frame of a 3D printer is the stiffness.  The stiffer the material, the less the frame will deform under load, and the more accurate and repeatable your results will be.
UHMW has a Tensile Modulus of Elasticity around 120,000 psi (http://www.polytechindustrial.com/products/plastic-stock-shapes/uhmw-polyethylene)
Aluminium has a Modulus of Elasticity around 10,000,000 psi (Mott, Applied Strength of Materials, 5th Edition, depends on the specific alloy)
Aluminium is around 100 times stiffer than UHMW.
Comment: I'd be curious to know how the figures compare for lexan sheet at 3 or 6 mm thickness, considering how many 3d printers use it for construction.
Comment: Lexan (Polycarbonate) has a modulus around 340,000 psi (http://www.sabic-ip.com/resins/DataSheet/Internet/PDF/1002002131_1002003947_1002038344_SI.pdf)
Comment: Loving the 'Lets apply science' answer.
Comment: One piece of the science I'd like to see applied is what happens to the stiffness of acrylic when the bolts are tightened enough to keep the geometry of the frame from changing. I would expect that the cracks will propagate into the frame and destroy the stiffness.

I'd also suggest that one can crank down pretty heavily on bolts in UHMW-PE without cracking.
Answer: I've used what is commonly described as UHMW-PE, aka, Ultra-high Molecular Weight Polyethylene for various projects. You may know this material is often used in cutting boards, as it cleans easily and doesn't cut easily.
it does machine in a manner similar to aluminum, although the tool should be cooled/lubricated to prevent a build-up of melted plastic on the cutting edges. You can get away without coolant or lubricant if cutting speeds are slow and the swarf is cleared away from the cutter.
I'd not considered such a material for constructing a 3d printer, as it's expensive, but I've also not compared the prices to equivalent sizes of aluminum.
I'd consider that the use in a 3d printer would be a good substitute for lexan, as one can tighten the bolts without fear of cracking. For bolts subject to rotation or vibration, self-locking nuts are a good idea. If you have use of a broach, cutting out a pocket for the nuts would be easily accomplished.
I have downloaded the plans for the open-source 3d printer known as DICE, which calls for aluminum, but the pricing I've found was excessive for the right quantities. I think I'll explore the same bill of materials in HDPE or UHMW-PE (which may be different names for the same substance).
Equally useful to know is that the material is very slippery, effectively self-lubricating under the right conditions. Unfortunately, for a 3d printer application, I don't believe the self-lubricating part would work for carriages but might be fun to try with linear slides.
It is not as stiff as aluminum, so where stiffness is needed and not provided by the architecture, a thicker piece may be indicated. I can just barely bend with my fingers a piece of 3 mm (1/8") a small amount, but cannot do so for aluminum.
Here's the result of a quick search for UHMWPE:
https://www.interstateplastics.com/Uhmw-Natural-Virgin-Sheet-UHMNV~~SH.php?thickness=0.125&dim2=12&dim3=24 which gives a price for 1/8" white sheet 24 x 12" as US\$ 26.06 while the black version is available only as thin as 1/4" for about US$ 28.00
The equivalent size in aluminum 6061T6 at onlinemetals.com is about US\$ 3.00 more expensive. That is lower than I expected, skewing the idea farther away from UHMWPE than one might hope. The equivalent for 1/4" is almost US\$ 60, quite a bit higher.
It would appear that if you need the thicker stuff, the price is better for plastic, not so good for the aluminum.
Comment: My biggest problem currently is trying to determine how thick I want/need the sheets to be in order to create a solid object, that's capable of handling the constant vibrations of a 3-D printer, without causing any problems, so until I have a better idea of the exact dimensions, I probably won't be purchasing any materials. Either way, I appreciate the info!
Comment: I'm happy to have helped. If you want to perform some inexpensive tests, purchase cutting boards from the local big box store. I'm able to get quite thick material of some size locally at less than ten dollars per board.

If you believe my answer qualifies, please click the check box icon. Thanks
Answer: I've tried this material (8 mm thickness) for a Prusa i3 clone of my own design but needed to abandon using it as it doesn't allow to be cut by laser easily on my friends laser cutting machine (not a hobby laser cutting machine, it is his business).
HDPE requires lower speed than cutting Plexiglas or Acrylic resulting in more heat input and a small top cut and a large bottom cut width leaving the edges far from being straight.

HDPE as the body of a 3-D Printer?


Discouraging voles from entering my compost bin

Question: I believe there are voles getting into my compost bin.  I am not putting kitchen waste in the bin but no cooked food or meat.  I can't prevent voles from getting into the compost bin, so my questions are: How can I discourage voles from getting attracted?  What type of food should I not put in the bin?  Are voles detrimental to the compost or will the compost still be usable in my organic vegetable garden?  Should I put tea leaves, banana peels, watermelon rind, etc in the compost bin or will that attract voles?  For the most part, this is a cold compost bin because I don't think I am able to heat it up naturally (that is a different issue).
Comment: Are the voles a problem?  They are probably tunneling and aerating your compost piles for you.  As well as eating and pooping out even better crap for your compost.  Compost in the process of decomposition is self-heating.  Voles will get into the mulch around roses for instance and could girdle the roses if hungry.  Kill one vole and you'll get 10 to replace it...same with mice. The voles are there BECAUSE of the heat from decomposition and the food.  Does anyone know of any downside to having these little guys involved with a compost pile?
Comment: Could be rats. Not positive.
Comment: Not a problem as yet.  Just an observation that I wanted to get clarified so it does not become a problem.
Comment: Let's just see what others come up with, you must know by now I am not a control freak and am a complete woose with little furry lives.  Have never had a problem with any of them.  In fact being the idiot I am, I have been feeding the wild bunnies and although the death rate is huge, we are getting a little population going.  I've yet to find a problem with having a 'bunny spa and ranch' gig going!  I give them all our leftovers and they poop it out and spread 'fertilizer' everywhere for this wilderness chunk of land.  Voles and moles...even squirrels and gophers I've never had any problems.
Comment: Are you certain that it is voles? Could it be rats?
Comment: Check for worms or grubs in the compost. That's what the rodents may be after. If the pH is high, you might have a lot of earthworms. Grubs are a different story. Other insects like soldier fly larvae are also food sources
Comment: No earthworms or grubs. See some small insects but not sure what they are.
Comment: One potential solution is to try to put up an owl box or two. I'm putting some up this year and hope I get takers. They'll keep the entire rodent population down, including the voles or rats.
Answer: As the comments indicate, voles in compost might not be a bad idea in principle, and in fact might help the process. Use whatever materials you think are suitable. However voles in the garden are a completely different issue; while locating a compost pile close to an active garden might appear to be a good idea since then you don't have far to cart the waste and final compost, you might have to deal with vole damage in the garden.
Effects I have seen from voles in a Canadian garden:

Runs in grass plots visible as the snow cover melts; damage is cosmetic, and a good indication of where they are currently active and might be hiding
Chewed potatoes and tomatoes; voles will scrabble in the soil once they learn where the potato patch is to chew at the exposed tubers, and will get at your low hanging toms particularly in dry spells
Pole beans snipped off at ground level once they get to medium height; the foliage gives cover for them to hide under while they chew at the base. Again I think this is access to moisture, I think they drink the sap oozing from the cut end in dry spells
Bark girdling of fruit trees; in one particularly hard winter I lost 90% of my tree collection to girdling. The only trees spared were the pears.

From this I learn that voles in compost close to the garden (but not the orchard) once the season is over is fine, but as soon as the new season starts the remaining compost is moved far from where I am growing things.
PS allow foxes to get to the compost, if it fits with your other goals. It is fun to watch foxes prancing on the snow to get the voles and mice to reveal themselves.


I couldn't deauth any devices using aireplay-ng command in kali linux

Question: I am using Kali linux. I've updated all tools and services by apt-get update and apt-get upgrade.
I was using aircrack-ng for pentesting my wlan network.
I wanted to deauth any device connected to my mobile hotspot using aireplay-ng. syntax was correct and it started running, but, no device is being disconnected from my mobile hotspot.
I used airmon-ng start wlan0 to initiate my wlan for aircrack-ng.
Then, airodump-ng wlan0mon to list all the networks in its vicinity.
I used airodump-ng -c [channel of router] --bssid [bssid of router] wlan0mon to show the details of devices connected to that router.
Then, I used aireplay-ng --deauth 0 60 -a [bssid of router] wlan0mon to disconnect all the devices connected to that router.
It repeated "Sending deAuth to broadcast - - BSSID [bssid of router]" the same line for 60 times, but not even a single device got disconnected from the hotspot.
I even tried to deauth a specific device form router by aireplay-ng --deauth 0 60 -a [bssid of router] -c [mac address of device] wlan0mon, but still,the same case got repeated as above.
Any help would be appreciated :>)
Comment: Devices generally tend to reauthenticate immediately. The purpose of deauthentication is the ability to listen in on reauthentication handshake, which can be cracked.
Comment: Why is there "0 60" after deauth? Having both arguments doesn't make sense. You are supplying "0" to deauth, which means to send continuously, not "60".
Comment: @Nomad Then, how could we verify whether the got de authenticated... because when my friends tried this in his laptop, there was a clear result showing that devices connected got to zero.
Comment: @Nomad I even verified that whether my wireless card is capable of wireless injection or not! The results were positive.
Comment: @multithr3at3d I even tried with just '0' but, that didn't make any improvement.!
Answer: First of all the command starts like this aireplay-ng --deauth 60 or aireplay-ng -0 60 for 60 packets or to send it continuously (DoS) aireplay-ng --deauth 0 or aireplay-ng -0 0. Anyway if you see an output it mean that you typed it right.
Second, have you tried the basic troubleshooting?

Why does deauthentication not work?
There can be several reasons and one or more can affect you:

You are physically too far away from the client(s). You need enough transmit power for the packets to reach and be heard by the clients. If you do a full packet capture, each packet sent to the client should result in an "ack" packet back. This means the client heard the packet. If there is no "ack" then likely it did not receive the packet.

Wireless cards work in particular modes such b, g, n and so on. If your card is in a different mode then the client card there is good chance that the client will not be able to correctly receive your transmission. See the previous item for confirming the client received the packet.

Some clients ignore broadcast deauthentications. If this is the case, you will need to send a deauthentication directed at the particular client. (I see that you already tried this one, some AP have a protection that if you're not "authenticated" it will drop a deauth from a random/unknown source for obvious reasons so always try to add the -c [target_mac] flag)

Clients may reconnect too fast for you to see that they had been disconnected. If you do a full packet capture, you will be able to look for the reassociation packets in the capture to confirm deauthentication worked. (Have you opened the packet capture?)

Taken from Aircrack-ng documentation
Please try all this and share what you wanted to achieve, what have you tried, what where the inputs and outputs.
Answer: I believe what is happening is that the deauth packets are successfully being sent to the router and the devices are successfully being disconnected, but since devices tend to connect back to the AP automatically you are not noticing anything. Try sending an infinite number of deauth that pretend to come from the AP and check if clients connected to it cannot access the internet or it gets significantly slower. The command for this is:
aireplay-ng -0 0 -a [bssid] [interface]
This will send deauth packets to all clients connected to an AP, the packets appear to be from the access point, thus jam the WiFi network for all devices. You can use -c to specific which devices. You can verify this by looking to see if the WiFi network is jammed and devices cannot connect to the internet. If this is the case then congrats! Your deauth packets are being sent successfully.
You can also try to get the WPA2 handshake after de authenticating clients connected to the router to verify it. If you successfully get the handshake saved to a file then the deauth packets are working.


Is it possible for a popular centralised app like Twitter to port to EOS?

Question: If the possibility for Twitter to become decentralized on the EOS blockchain exists, what are the point-by-point steps it should take to become a dApp? What will happen to their existing users, how will they even login? And what will happen data they have created - Tweets, Retweets, Images etc? Can they be moved to the blockchain without user involvement?
Answer: In theory, Twitter could move all their data to EOS, using the blockchain purely as a replacement for their cloud services. They have just signed a contract with Amazon Web Services to do just this, so it is unlikely they will be moving to EOS anytime soon. However if they did, the move would be invisible to their users, who would not even realise they had moved to blockchain based dapp unless they read about it.
Crucially, twitter users would not necessarily need EOS accounts for such a dapp to work. Unless twitter wanted them to for some reason.
The questions they would need to answer is whether EOS based storage:

Is economically competitive compared to traditional cloud.
Has sufficient reliability and capacity. Something they may need to evaluate after EOS has been live for a time.
Data security. How to store user passwords and other sensitive data? BlockChain and IPFS mean data is available to all. All encryption will only last for a finite time until it is broken. This can be a problem even in data-centers and cloud storage providers, where access is limited to a relatively small number. Some combination of private/cloud storage, breaking data to store via EOS block producers into small encrypted chunks, may mitigate risks. Recommending users change passwords upon every upgrade to a newer encryption algorithm, even if the old one isn't broken yet, is probably also a good idea.

Edit
Third section on security issues added to answer concerns of @leo-ribbero in comments.
Comment: If the users does not need an account, how do they login? Also, where the authentication data will be stored (like user/password)? Finally, how would they store sensitive data like emails?
Comment: They login in to their regular twitter account. They wouldn't need an EOS account, unless twitter decided they did. But that would be up to the app maker. Sensitive data could be encrypted, the same way it would have to be for storing on Amazon Cloud.
Comment: So you are saying that the auth data would be outside the blockchain or the auth data will be stored encrypted in a smart contract table? The problem with encryption in blockchain is that in the future, we will be able to read these data, because you know, encryption is always broken with hardware evolution - and blockchain is forever...
Comment: As I understand it, a lot of data storage in EOS is handled off the blockchain using IPFS. Only the contracts are stored on the chain.
Comment: Of course, even IPFS might not be secure enough for password hashes, for similar reasons. Although trusting third party cloud providers, or even private data centers, as an alternative, might be a false security, as there will still be a number of employees with access. At some point ANY form of password storage will be broken if you wait long enough.
Answer: Before an existing business built on the current paradigm of a centralized server can migrate to a decentralized backend, they are likely going to need to completely revise their business model.  In the case of Twitter, the reason for the business to exist is that they are able to sell ads at a high enough margin to justify the expense of their business operations.  In a decentralized model - where users have ownership of their data and some control over how it is used by advertisers - the entire reason for the business to exist shifts.
Content and accounts could theoretically migrate, but the business that manages them would need a pretty compelling reason to move.


"all the same" and "all different", versus "the same" and "different"

Question: What is the difference between these two sentences:
1- Our shirts are all the same size but they're all different colours.
2- Our shirts are the same size but different colours.
* I cannot understand why should one use "all" in the first sentence, while it could be written without it (I know it's an adverb, but I cannot understand its meaning).
Comment: It's not an adverb; it's a determinative [link](https://simple.wiktionary.org/wiki/all). It is not part of the NP "the same size" but an optional quantificational adjunct in clause structure.
Comment: The parsing of your specific example is ***ambiguous***, because ***all different colours*** could either mean *every shirt is a different colour to every other shirt* (no two shirts are the same colour), OR *we have shirts in every colour which it's possible to have* (and we might have several shirts in certain colours).
Comment: Thank you FumbleFingers and BillJ for trying to help me.
Answer: All is an intensifier here.
In the case of same it doesn't really change the meaning, just emphasises the sameness.
In the case of different, it is still an intensifier, but it potentially changes the meaning a bit; unfortunately in an ambiguous way:
It might attach to "shirts" and mean that each shirt is a different colour from all the rest.
More likely, it attaches to "different colours", and emphasises the range of colours. It certainly implies that there are more than two colours, and probably more than three. But it is not precise, and not necessarily saying that each colour is different from all the rest.
Comment: Thank you for your response.
Answer: For the most part, they are the same but with a minor implication (at least to me)

1- Our shirts are all the same size but they're all different colours.

There are any number of shirts (but most likely 3 or more, it would seem awkward to say it for just two). Each shirt is the same size, but each shirt is a different color. If there are seven different shirts, they are seven different colors.

2- Our shirts are the same size but different colours.

This could either be used for two or several shirts. If it was used for more than a few, (let's say for a choir or a team), I think the implication would be that they are all the same size and a variety of colors, but each color may not be unique.
Comment: Thank you very much


Why do I experience a second, floating body when body scanning?

Question: When I did the 10 day Vipassana meditation retreat, sometimes I would find that when I was body scanning, I would suddenly realize I was scanning a second, floating body maybe a foot in front and above from my actual body.  I could feel my sensations in the second body, but it was very disconcerting because it FELT like me, but was a projection.  I felt distrustful of my own experience.  If I recognized it, I could get my attention to return to my actual body and the projection would  go away.
What was that and why did it happen?  Should I have just kept on doing what I was doing and observed, or (sort of) forcibly returned my attention to my actual body, as I did?
Comment: If it was a goenka retreat it doesnt surprise me.  Those retreats are too ascetic. You become sleep derived and are made to sit for many hours at a stretch that disassociation from the body is probably a natural way to cope. Its like when they put prisoners in solitary confinement.
Answer: That's really interesting.  I would say that because Goenka and the ATs (and the Buddha as well) say to scan the actual bodily sensations, the reality, it was the right thing to do to return to the body itself.  Did you talk to one of the ATs about this, by the way?
Answer: This is interesting to me, because I experienced the same thing and it turned into a bad habit that took a while to get rid of. My response was to return to the body once I realized what was happening, and that is also what the AT said.
What I experienced was that the projection had some flaws... I could easily map strong sensations to it, but I could not map subtle sensations to it. It took some time before I even realized that I was working on a map or projection rather than just sensing actual body. It also took a while to break the habit. I chalked it up to beginner's fumbling.
Answer: What is ones "act-ual", or real body?
It's good to experiment, even look what (kind of regard) is lesser stressful, if certain regard still contains stress, and not so good to assume preoccupations (ideas of phenomenas or the phenomena itself) as "this is real, this is mine, this is my self, this is what I am".
Understand, Nyom Kara.
Do that much, and no need then to ask if certain phenomena was right and real afterwards. Look and investigate again.
[Note: This is a gift of Dhamma and not meant for commercial purpose or other low wordily gains by means of trade and exchange.]


Covering estate tax on US assets for non-resident alien

Question: I am a non-resident alien holding a brokerage account in the USA but residing outside the USA. My country does not have an estate tax treaty with the USA. So my estate is liable for a significant estate tax up to 40%. Is there any way to avoid or to cover this tax? I thought of buying term insurance for myself, but I am not sure whether US companies will sell term insurance to a non-resident. I want to buy insurance from a US company because I want the death benefit to be in USD. Can someone suggest as to what the best way to approach this issue is?
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/109944/discussion-on-question-by-user2371765-covering-estate-tax-on-us-assets-for-non-r).
Answer: Beneficiaries don't pay estate tax in the US; the estate does. What the beneficiary gets is whatever is left of the estate after the estate tax has been paid from the assets of the estate. The executor of the estate might need to sell some of the stocks in the brokerage account to raise the cash to pay the estate tax, and the money/stocks or whatever is left in the brokerage account passes to the beneficiary free of any kind of (US) tax. Furthermore, as per US law, the basis of the stocks inherited by the beneficiary is the market value of the stocks as of the date of your death and so the beneficiary only needs to pay capital gains on the stock to the extent that the stock price increased during the time the beneficiary held the stock; all (unrealized) gains that occurred during the time that the deceased held the stock before death are "forgiven" since the estate paid estate taxes on these gains.  Now, what all this means to the beneficiary if the beneficiary is also a nonresident of the US is a whole 'nuther matter. Finally, all the above is for brokerage accounts that are not held as IRA or 401(k) accounts.
Comment: The executor of the estate will inform the beneficiary of the valuation of the stocks as of the date of death. The beneficiary doesn't get to just take over the brokerage account (that is, it is not just a matter of substituting "Beneficiary Name" for "Owner's Name"on the brokerage website; it is more complicated than that).
Comment: I came to know a while ago that one could set up a trust account to address the estate tax issue. But I don't know the details.
Comment: I corrected the question. Since the estate tax is on the account value and not on the capital gains (although its purpose could be only to tax unrealized gains) it is a huge amount for non-residents. My question was about how to minimize it or to cover it. When the account holder is alive, they are going to pay tax on the realized capital gains in their country. It is conceivable that if the unrealized capital gains at the time of death are small in proportion to the account not only the whole of them but also a significant chunk of the principal might be paid out in estate tax.
Comment: Also, how will the beneficiary keep track of the market value at the time of inheritance? It is just not practical. The statements will always report the actual basis.
Comment: No matter how large the unrealized capital gains are, a 40% estate tax will always ensure that the effective capital gains tax rate is at least 40%. Practically speaking, the latter will be way more than 40%.
Comment: It may be better to gift the assets earlier, if still before death, to avoid the estate tax. Run the numbers.
Comment: Trust likewise hast to be set up while still alive


rename all children objects with prefix from parent

Question: I'm converting voxel art to blender for animation and render. All the cubes import automatically named cube.001, cube.002, ect. I then parent all those cubes to an empty to animate their movement and name the empty what ever the object is. only problem is when I import new objects even from other blender scenes, the imported cubes rename themselves so that they aren't duplicating names, so cube.001 becomes cube.234 and so on. Problem is that my friend is talking about potentially building a video game with these assets so accidentally renaming objects like this could be problematic in the future. Is there a way to rename all the children objects so they have a prefix that matches the parent name? For example parent: "space-bug" would rename the cubes "space-bug-cube.001" and so on.
Comment: Try this: create new mesh (which has vertices, other than empty like circle or any thing) and name it. Select all objects and last select the new mesh with the name and press Cltr+J  to merge into single object. Then go into edit mode and select all vertices and press P-> separate by loose parts. Now the objects have .001 ,.002... with name given to new mesh. It may work.
Answer: <code>import bpy

current_object = bpy.data.objects
i = 0
for ob in bpy.context.scene.objects:
    # check if parent exist
    existing_parent = current_object[ob.name].parent
    if existing_parent:
        # check if it has been already renamed from parent
        if not current_object[ob.name].parent.name == current_object[ob.name].name.split('.')[0]:
        # change the name of the object to the name of parent
            current_object[ob.name].name = existing_parent.name + '_' + str(i).zfill(2)
            print(ob.name, existing_parent.name)
            i += 1
        else:
            print('nothing to do')
</code>
this script renames the objects in the scene according to their parent. if they share already the same name (meaning probably it has been already renamed) it does nothing. far from by polished though as for know it adds a numerical sequence to all the scene not per object.
Answer: Found a solution using an add-on that batch renames all selected objects when you hit ctrl+r.
https://github.com/p2or/blender-viewport-rename


Is it good idea to change Simple Recover Model into Bulk-Logged on ETL system?

Question: We are having an ETL process which inserts lots of data into tables. This database is set to Simple Recovery Model and the transaction log is growing a lot. I was thinking that would it help to set this database into Bulk-Logged Recovery Model? We are taking full backups on daily basis. So is there some operations which are not logged in Bulk-Logged Recovery Model compared to Simple Recovery Model?
Comment: Your current recovery model has the least amount of logging. BULK-LOGGED offers more logging as it keeps track of modifed extents performed by bulk operations.
Answer: If you log grows on ETL in simple mode it means your inserts are not minimally logged. The requirements for minimal logging are described in Operations That Can Be Minimally Logged and Prerequisites for Minimal Logging in Bulk Import:

Minimal logging requires that the target [of a INSERT BULK operation] table meets the following conditions:

The table is not being replicated.
Table locking is specified (using
  TABLOCK).

The Data Loading Performance Guide also mentions the TF 610 effects and how it affects minimal logging.
Answer: Bulk Logged will not help you in this situation.  Your transaction log is growing because you are performing large transactions.  In simple mode, the log is truncated after a checkpoint.
Depending on how you are loading your data, you may need to break it up into smaller chunks.  Make sure you are not loading all the data in one large transaction.
Answer: If at all, your log size will grow when changing from simple recovery to bulk logged. You may be having log running transactions, or uncommitted/runaway transactions that are keeping a hold of your log file, causing it to grow.


SQL Database Snapshot before code depolyment faster than backup

Question: We have code deployments every Thursday, some of the changes involve database changes - before the code is depolyed we do a SQL backup in case there are errors, this usually takes 45 minutes and everyone has to wait till it finishes.  Could I take advantage of taking a database snapshot, and if the code tests good just delete the snapshot, if there is a problem use the snapshot to roll back any changes made?
Comment: We do this often, take snapshot before change and delete if no issues ON TOP of regular backup though (plus 1-minute TLOG backup). DB Snapshot is a godsend in those cases. We've had multiple VMware upgrade redo's (upgrade, error, fix error, restore snapshot, try again)
Answer: Depending on the changes being performed, database snapshots are a viable alternative to backups. You need to ensure you're meeting the prerequisites and that you won't be impacted by the limitations for the source and snapshot (see here).
There are limitations around certain feature usage, such as no MEMORY_OPTIMIZED_DATA filegroups, that prevent snapshots. In addition, some features like FILESTREAM filegroups and Full Text Indexes are unavailable in the snapshot database.
You also need to ensure you have sufficient disk space available when undergoing post-deployment testing because the snapshot will grow as you change data.
You also can't drop database files from the source DB after a snapshot is created. In circumstances where this is happening, backup is the solution.


Do odds depend the the number of hands folded preflop?

Question: In a game with 8 players where 6 fold, two players went all in pre flop, one had JJ and the other had KJ. I know JJ means that you are ahead before the cards are played and the probability of winning is around 66%, I am wondering though whether this probability should differ at all given that there were 6 other hands dealt out? That is, does the 66% figure refer to a heads up situation, or is it independent of the number of cards left in the deck?
Comment: The question is depended on game type, I guess your talking about hold'em however the answer would be very different for stud poker.
Comment: Probability is a measure of *information*. All that matters is which cards are known and which are unknown. Their physical locations, whether they are dealt or undealt, etc., doesn't matter.
Answer: Assuming you know nothing about the cards dealt, they don't matter, so the 66% holds up. In most calculations we would just ignore the folded cards since we don't have any definite information about them. If you want to factor them in, you can no longer calculate your exact pot equity, since you don't know how often your opponents are folding hands like Ax, KT, and K9, (and this would also depend how the betting played out preflop).
You can infer that the probability of any of your opponents having had hands like AA, KK, QQ, AK, AQ is slim, so you can expect there to be a very slightly increased probability of A's, K's, and Q's appearing on the board than you would expect if you had no additional information. This means that the KJ has a slightly increased chance of hitting a straight, however this will have a pretty small impact on your probability of winning with JJ. In fact, hitting his straight will allow you to chop if he has paired his K, so the improvement to his hand by factoring in the folded cards is even smaller.
It is almost always the case that factoring in the folded cards will have a very small impact on your pot equity, and it is impossible to measure exactly unless your opponents are playing like robots and you know their exact hand ranges. For these reasons, it is usually impractical to do so.
Answer: The short answer is that the other cards don't matter? Why, because the cards are just as likely to have been folded, as they are to still be in the stub of cards to be dealt out. You can't differentiate the cards in that way, so you don't need to account for them in any special way.


Plot a point at a user input distance perpendicular to a polyline

Question: I have a straight polyline and the distances in metres of the points I want to plot perpendicular to that line. The points are all different distances and should be measured from a different point along the polyline. Is there a simple way to get these points plotted?
Comment: Can you post a picture and expand a bit?  It's a bit unclear what you're asking for.
Comment: It is a problem of analytical geometry and  for the principles, look at [How to draw perpendicular lines in QGIS?](http://gis.stackexchange.com/a/59196/2581)
Answer: Linear referencing is the way to go for this problem.  If the Route measures are based on the length of the line then all you need is a table that contains the Route Name, the distance along the line increasing from the end where you start your measures, and a distance offset.  By using the Make Route Event Layer tool or table context menu option you can create a layer of points at those positions on the line with the offset specified.  Offsets have to be positive or negative to offset to either the left or right of the line.  There are settings that can change which side of the line uses positive offsets and which uses negative offsets.  Since your line is straight, that is the ideal use of this approach.
However, there is a limitation when you apply this and other techniques to lines that are not straight.  The perpendicular offset is always relative to just one pair of vertices, never three or more vertices.  So if a position occurs at the point of angle deflection between three vertices, the perpendicular offset will only consider two of those vertices and create a 90 degree angle relative to those vertices.  It will not derive an average angle using three vertices that would result in an intermediate angle between the three vertices.  Also if the offset would be affected by the curve created by a buffer of that offset distance near changes in the line's bearing, that is not considered by the tool.  Outside of a tool I created for my personal use, I have not seen any tool that considers more than two vertices when determining a perpendicular angle to a line.
Comment: I tried using this tool and it succeeded but there are no points plotted. It has made a sheet with the distances and offsets I specified but no points plotted. In the attribute table for the layer created there is a column that says LOC_ERROR and for each point it says route not found. Is it acceptable to use an excel table?
Comment: Please disregard the above comment, I just had the wrong information in the route identifier field


Can you trim rim tape once installed?

Question: I installed my rim tape then noticed was too wide so I trimmed it with a razor knife. Would this have caused any damage to the rim bead?
Comment: What kind of rim do you have? I seriously doubt anything bad can happen unless you run CF rims or tubeless.
Comment: I've done this once or twice, with stock AL rims.  I see no problem (though it does irritate one that it's so hard to find the right size rim tape).
Answer: Probably not, depends how careful you are and if they are carbon rims.
I always do a 3cm test to get the best width, then take my time and gracefully cut the width of the entire roll with a cutter.
Now you have a entire roll of the correct width and you just apply what you need.
Answer: You can though I can say that in 40+ years or riding and many years of working in shops I've never once had to do this. Rim tapes come in various widths from various makers so you should be able to find one that will fit. Also a little too wide is far preferable to a tape that is a little too narrow.

Can you trim rim tape once installed?


How do you calculate the "true" chemical potential in classical density functional theory?

Question: In classical density functional theory, one traditionally calculates the chemical potential by taking the variational derivative,
\begin{equation}
\mu_{i} = \frac{\delta F}{\delta \rho_{i}}
\end{equation}
of the Helmholtz free energy
\begin{equation}
F[\rho] = \int d\textbf{r} f(\rho, \nabla \rho, ...) \textrm{.}
\end{equation}
However, this is not directly analogous to the chemical potential in classical thermodynamics. In the latter theory, the chemical potential is defined as a partial derivative with respect to the number of moles,
\begin{equation}
\hat{\mu}_{i} = \frac{\partial A}{\partial n_{i}}
\end{equation}
where $A$ is the homogeneous Helmholtz free energy analogous to $F$.
Importantly, $n_{i}$ is an extrinsic quantity (e.g. $n_{i} = \rho_{i} V$, where $V$ is the system volume). This means that $\mu_{i}$, defined in DFT is actually analogous to the derivative
\begin{equation}
\mu_{i} = \frac{\partial A}{\partial \rho_{i}}
\end{equation}
How then does one obtain the actual analogue,
\begin{equation}
\hat{\mu}_{i} = \frac{\delta F}{\delta n_{i}}
\end{equation}
to the traditional chemical potential?
Is this generalization correct? If so, how does one go about computing such a quantity when the number of moles $n_{i}$ is now itself a functional of the density,
\begin{equation}
n_{i} = \int d\textbf{r} \rho_{i}(\textbf{r})
\end{equation}
Aside:

It is clear that $\partial A/\partial \rho_{i}$ is related to the difference between chemical potentials for an incompressible, multicomponent system, e.g. http://dx.doi.org/10.1103/PhysRevE.83.061602. Because of this, it is sometimes called an "exchange" chemical potential, e.g. https://doi.org/10.1039/C6SM02839J.
There is also a connection between the exchange chemical potentials and the osmotic pressure, $\pi = \partial A/\partial V$. It is not clear to me how one can calculate the osmotic pressure from a functional either, since it is also an extrinsic quantity.

Related:

https://math.stackexchange.com/q/3016507/
https://math.stackexchange.com/q/3697883/
Comment: In case this question does not attract many answers (I don't think there are many computational chemists/materials people here), I would try posting it here: https://materials.stackexchange.com/
Comment: Thanks @Godzilla123. I didn't realize there was a materials forum. Posted: https://materials.stackexchange.com/questions/1147/how-do-you-calculate-the-true-chemical-potential-in-classical-density-function
Answer: This isn't a detailed answer; hopefully I can come back and answer it more fully later. However, here is a simple explanation that might help.
Instead of taking the functional derivative of the Helmholtz free energy, you can consider taking the functional derivative the free energy density. Essentially, this is just taking the thermodynamic derivative
$$ \hat{\mu_i}=\frac{\partial A}{\partial N_i} $$
and dividing both the numerator and denominator by the volume $V$.


What happened to Poe?

Question: Poe (Ann Danielewski) had a rising music career in the late 1990s, but then she completely vanished from the public eye. I've heard a variety of stories about her disappearance, ranging from corporate mergers to mismanagement to financial and legal trouble. Many stories claim that she was not allowed to record or perform music. How is that possible, and what actually happened?
Comment: This gives an overview of wat happened: http://www.agentassociation.com/media/asset/SDOC0365.pdf
Comment: Take a listen to her collaboration with Conjure one called center of the sun....it's amazing!
Answer: As you stated in the question itself its due to the merger of
recording company and legal fights.

Poe's three album deal is lost in Atlantic/AOL Time Warner merger. In November 2000, Atlantic/AOL Time Warner first chose to drop the
Modern/FEI, and as a result were contractually obligated to pay
Modern/FEI an undisclosed amount of money, and effectively release
themselves from any further fiduciary responsibilities to Modern/ FEI
and/or Poe.
Modern/FEI's agreed to give Atlantic a two-year grace period during which Modern/FEI agreed not to do anything commercially with any of
Poe's master recordings, enabling Atlantic to sell off their stock of
already produced copies of "Haunted." As a result, "Haunted" received
no further promotional support and the album faded from the market
place.
In 2004, Modern/ FEI sold the Poe Masters for "Hello" and "Haunted" to Sheridan Square Music who merged in 2005 with V2 Records, which
cataloged the Poe masters under a sub-label called Indie Blue. Indie
Blue and Sheridan Square Music were acquired by E-One Music in 2009.
Though Modern/ FEI kept ownership of Poe's masters until 2004, in 2001 as "Haunted" was climbing the charts, the label sold its interest
in Poe as an artist and in Poe's future recordings, in a questionable
deal to wealthy oil executive and author Robert M. Edsel who bought
her contract and kept Poe tied up in court, unable to release new
music or perform professionally for nearly a decade. What music Poe
did release during that time was generally done under the pseudonym
"Jane."

The contract eventually ended after 10 years of legal wrangling, when
The Labor Commission of California ruled in favor of Poe. New York
Post writer, Miriam Katz, quoted Poe in her 2011 article, "A Decade of
Silence," about Poe's ten-year legal battles, "My entire life was
suddenly under the control of a very powerful man whom I didn't know,
and who didn't [seem to] mean well. It was a horror story from which I
am just beginning to recover.
(Source: Wikipedia)

This all conditions made her 10 years of disappearance and even after it she doesn't have came up with any grand thing yet. On September 12, 2012, Poe posted a one-minute song and video on a new mobile platform called PTCH; however, no announcement was made about an official release date.
Comment: I was hoping to get some information that wasn't already in the Wikipedia article linked from the question. Basically I don't get how this results in a musician being unable to perform for *over ten years.*
Comment: @BraddSzonye if singer has contracted signed with a company stating that she can't perform outside the company then she can't without breaking contract which is not that easy and even she performed under the pseudonym "Jane" under the hood of Robert.
Comment: Sadly, this not an uncommon story in the music business, although having it last ten full years is unusual. Over the years many recording artists under contract have found themselves contractually prohibited from releasing and selling, or in many cases even *recording* any new music. The nature of the artist signing a contract with a record label or music publishing company is that of "indentured servitude" under California and USA law.

What happened to Poe?


Why is the population so high in Kali yuga?

Question: It is said that one gets the human form after collecting a lot of good karma, then how the population has increased to such? As it is Kali yuga and good is very scanty and will go down even further as time goes by, number of human beings should be decreasing day by day.
Comment: here is an analogy for this inspired by the Great Swami Vivekanandaji (this is just a positive-view of looking at things). You go to the gym. In the gym everything is difficult. You have to lift weights, you have to run on the treadmill, you have to actually work hard! But still you go, why? It is because by toiling hard at the gym, it provides great opportunity to grow. Similarly Kali Yuga is the best time to be born, because it is like a giant gym. Everything is difficult, if you can be good now, then you are the best of men! That's why many souls take birth in Kali Yuga.
Comment: Actually many bhakti-yogis also say that this is the best yuga, because in this yuga chanting of God's names alone is quite enough to take one across the ocean of Bhavasagar. (Although this is easier said). Also for really pious souls who have attained the realm of Divinity Itself, for them this is the best age, Kali Yuga, people are falling off their Dharma, this is the time they need Help. Thus great saints take birth in hundreds in this age to help those souls which are in need of spiritual rescue. God is equally present in all yugas These are the many many positives of Kali Yuga !!!!
Comment: Ah I see your question now, anyway pointing out some positives. If you live your life now and you do some good deeds, then some bad deeds, it does not mean you are immediately born as a beast! After doing some good deeds, the soul gets born as a human. That does not mean that after doing a single bad deed, it becomes a beast again. Many souls in Kali Yuga are pious-enough (although you cannot call them perfect) to be reborn as human beings. Yes war exists, yes killing is more than before, but not everyone descends to such extremes!! This is just one view I am sure there are many others
Comment: as for why saints descend even though they know it is destiny of Kali Yuga. Well that is what is called Love/Compassion/Mercy and that is why these souls are called merciful or having lot of love for us. If one loves his friend, then he will be there for him, even if he knows that the friend is getting what he is destined to get. We are suffering, whether because of destiny or not. The saints still come down for us, they can hear our call. That is their destiny you can say. That is their mission, to share with us the same elixir that they have drank from the True Self or God!
Comment: I see that you are trying to show me the brighter side but that does not answer the question. If human form is so difficult to get then how come everybody is getting a human form and human beings are increasing day by day, does that mean all these people who are born were great souls in the past lives and that's how they got human form, otherwise they could have become any other creature.
Comment: Yeah I see your point, but isn't Kalyuga destined to be like this, bad and all sorts of evil will prevail, that's how it's described then why all this help from these saints you are talking about.
Comment: Even with human form, you can be physically or mentally handicapped which is as bad as becoming an animal or a bird or an insect or a fish... Also, not being born is the best thing if you are in Indra's kingdom with the GODs.
Comment: High population is not only in Kali Yuga, it can be in other yugas also. Kali Yuga had less population compared to the present age of Dwapara.
Comment: Related [souls and population](http://hinduism.stackexchange.com/q/8346/277) also see last line at http://hinduism.stackexchange.com/q/8443/277.
Answer: Who gets human form on this earth?
Generally, the cases are:

Some one could be evolving upwards from lower species of life.
Some one may have fallen from higher planets after enjoying the results of good
karma as stated in the Gita verse below.

When they have thus enjoyed vast heavenly sense pleasure and the
results of their pious activities are exhausted, they return to this
mortal planet again. Bhagvad Gita 9.21

So we cannot assume that population must decrease in Kali yuga. There is exit and entry going on continously.
Also kali-yuga is not all bad for those interested in self realization. According to Srimad Bhavatam 1.17.38 and 1.17.39 influence of Kali is there only in places where gambling, drinking, prostitution, animal slaughter and accumulation of gold (for material enjoyment) is there.
The process of self-realization in kali yuga is also very easy. Just by chanting the holy names of Krishna one can attain perfection. This is confirmed in Srimad Bhagavatam 12.3.51

kaler dosa-nidhe rajann
asti hy eko mahan gunah
kirtanad eva krsnasya
 mukta-sangah param vrajet
My dear King, although Kali-yuga is an ocean of faults, there is still
one good quality about this age: Simply by chanting the Hare Krsna
maha-mantra, one can become free from material bondage and be promoted
to the transcendental kingdom.
Comment: Is there a reason why it should not? In Dvapara-yuga just Krishna's immediate children + grandchildren were more than 1.6 million.
Comment: Do you mean to say the population was as high as kalyuga even in other ages ?
Answer: <code>Why the population is so high in Kali-Yuga ?
</code>
The  answer  to this question is given indirectly in Shreemad Bhagvat Purana at various places.I will explain the cause through those Shlokas (verses).Before giving that let me give a brief backgroud about Kaliyuga.

There is a story of King Parikshita & Kaliyuga.In which king
  parikshita gave four places for kaliyuga to live  they are 1) Gambling
2) Wine or Alcohol 3) violence 4) Sexual cheating or (Vyabhichara ,
  व्याभिचार)). These are the sanskrit verses from Shreemad Bhagvat Purana
  telling us the characteristics of kaliyuga.

So What exactly is Kaliyuga-: According to Bhagvatam Kaliyuga means.

यदा मायानृतं तन्द्रायदा मायानृतं तन्द्रा निद्रा हिंसा विषादनम।
  शोको मोहो भयं दैन्यं स कालिस्तामस: स्मृत ॥30॥
yadā māyānṛtaṁ tandrā nidrā hiṁsā viṣādanam śoka-mohau bhayaṁ
  dainyam sa kalis tāmasaḥ smṛtaḥ
Meaning - When there is a predominance of cheating, lying, sloth, sleepiness, violence, depression, lamentation, bewilderment, fear and
  poverty, that age is Kali, the age of the mode of ignorance.
SB 12.3.30

characteristics of this Kaliyuga

दस्यूत्कृष्टा जनपदा वेदा: पाखण्डदूषिता:। राजनश्च प्रजाभक्षा:
  शिश्नोदपरा द्विजा:॥32॥
dasyūtkṛṣṭā janapadā vedāḥ pāṣaṇḍa-dūṣitāḥ rājānaś ca
  prajā-bhakṣāḥ śiśnodara-parā dvijāḥ
Meaning - Cities will be dominated by thieves, the Vedas will be
  contaminated by speculative interpretations of atheists, political
  leaders will virtually consume the citizens, and the so-called priests
  and intellectuals will be devotees of their bellies and genitals.
SB 12.3.32
पितृभ्रातृसुहॄज्ज्ञातीन हित्वा सौरतसौह्यदा:। ननान्द्रुश्यालसंवादा
  दीना: स्त्रैणा: कलौ नरा:॥37॥
pitṛ-bhrātṛ-suhṛj-jñātīn hitvā saurata-sauhṛdāḥ
  nanāndṛ-śyāla-saṁvādā dīnāḥ straiṇāḥ kalau narāḥ
Meaning- In Kali-yuga men will be wretched and controlled by women. They will reject their fathers, brothers, other relatives and
  friends and will instead associate with the sisters and brothers of
  their wives. Thus their conception of friendship will be based
  exclusively on sexual ties.
 SB 12.3.37
न रक्षिष्यन्ति मनुजा: स्थविरौ पितरावपि । पुत्रान सर्वार्थकुशलान
  क्षुद्रा:शिश्नोदरम्भरा॥42॥
na rakṣiṣyanti manujāḥ sthavirau pitarāv api putrān bhāryāṁ ca
  kula-jām kṣudrāḥ śiśnodaraṁ-bharāḥ
Meaning - Men will no longer protect their elderly parents, their children or their respectable wives. Thoroughly degraded, they will
  care only to satisfy their own bellies and genitals.
SB 12.3.42

So from above shlokas(verses) we come to know that in Kaliyuga People's mind are corrupted due to excessive materialistic desires.They are   more sexual pleasure oriented. They are only thinking of satisfying there sense's or sexual desires.
And I think that is one of the reason of high population in Kaliyuga.
Comment: pushkar your answer is ok but this is about the souls increment problem if souls are not created newly then why population increases very much and if souls in animals are born as humans then humans will also be born as animals but animal population is decreasing at a vast rate, only human population is increasing so what is the reason.This is the question friend
Comment: @sakthi - I think animal population is not decreasing.Yes Animal ,bird , insects  species are getting lost at alarming rate.But since we here on Hinduism SE generally refer population as human population , unless specifically mentioned about other population.So the answer is human centric.
Answer: Firstly, the concept of population control, materialistic competition, abortion, sexual gratification, rape, cheating, divorce, etc. are all normal concepts for Kali Yuga, where people have no respect or inclination or rather that intellect required for spiritual learning and knowledge of the Self.
A detailed analysis of Kali Yuga's symptoms is given in the Srimad Bhagavatam, which is one of the famous Puranas.

12.2.3
dāmpatye 'bhirucir hetur
  māyaiva vyāvahārike
  strītve puḿstve ca hi ratir
  vipratve sūtram eva hi

Men and women will live together merely because of superficial
    attraction, and success in business will depend on deceit. Womanliness
    and manliness will be judged according to one's expertise in sex, and
    a man will be known as a brahmana just by his wearing a thread.

EXPLANATION : Just as human life as a whole has a great and serious
  purpose -- namely spiritual liberation -- fundamental human
  institutions such as marriage and child-rearing should also be
  dedicated to that great objective. Unfortunately, in the present age
  the satisfaction of the sex impulse has become the overriding, if not
  the exclusive, reason for marriage.
The sexual impulse, which induces the male and female of almost every
  species to combine physically, and in higher species also emotionally,
  is ultimately not a natural urge, because it is based on the unnatural
  identification of the self with the body. Life itself is a spiritual
  phenomenon. It is the soul that lives and gives apparent life to the
  biological machine called the body. Consciousness is the soul's
  manifest energy, and thus consciousness, awareness itself, is
  originally an entirely spiritual event. When life, or consciousness,
  is confined within a biological machine and falsely mistakes itself to
  be that machine, material existence occurs and sex desire arises.
12.2.5
anāḍhyataivāsādhutve
  sādhutve dambha eva tu
  svīkāra eva codvāhe
  snānam eva prasādhanam

A person will be judged unholy if he does not have money, and
    hypocrisy will be accepted as virtue. Marriage will be arranged simply
    by verbal agreement, and a person will think he is fit to appear in
    public if he has merely taken a bath.

12.2.6
dūre vāry-ayanaḿ tīrthaḿ
  lāvaṇyaḿ keśa-dhāraṇam
  udaraḿ-bharatā svārthaḥ
  satyatve dhārṣṭyam eva hi
  dākṣyaḿ kuṭumba-bharaṇaḿ
  yaśo 'rthe dharma-sevanam

A sacred place will be taken to consist of no more than a reservoir of
    water located at a distance, and beauty will be thought to depend on
    one's hairstyle. Filling the belly will become the goal of life, and
    one who is audacious will be accepted as truthful. He who can maintain
    a family will be regarded as an expert man, and the principles of
    religion will be observed only for the sake of reputation.

12.2.7
evaḿ prajābhir duṣṭābhir
  ākīrṇe kṣiti-maṇḍale
  brahma-viṭ-kṣatra-śūdrāṇāḿ
  yo balī bhavitā nṛpaḥ

As the earth thus becomes crowded with a corrupt population, whoever among any of the social classes shows himself to be the strongest will
    gain political power.

12.2.11
triḿśad viḿśati varṣāṇi
  paramāyuḥ kalau nṛṇām

The maximum duration of life for human beings in Kali-yuga will become
    fifty years.

So as we see here, texts absolutely prove how gratifying the procreating sense pleasures lead us to absolute blindness about God and the spiritual reality. Hence taking procreation for granted, we find the population high. As a balance, Prakriti also caused their lifespans to decrease vastly from earlier yugas.
Answer: Looks like more than the current population existed during Mahabharata:
Mahabharata 11.26.8

jīvatāṃ parimāṇajñaḥ sainyānām asi pāṇḍava
hatānāṃ yadi jānīṣe parimāṇaṃ vadasva me

Vaishampayana said, 'If, O son of Pandu, thou knowest it, tell me the
    number of those that have fallen in this battle, as also of those that
    have escaped with life!'

Mahabharata 11.26.9

daśāyutānām ayutaṃ sahasrāṇi ca viṃśatiḥ
koṭyaḥ ṣaṣṭiś ca ṣaṭ caiva ye 'smin rājamṛdhe hatāḥ
"Yudhishthira answered, 'One billion 660 million and 20,000 men have
  fallen in this battle. Of the heroes that have escaped, the number is
  240,165.'

More than 166 crore men have died in Mahabharata. Many men survived. I think they were soldiers.If soldiers were lived in this huge number, then think about the population. So, your question on why population is high in Kali Yuga is likely invalid.
Answer: There is an obscure rule of karma:
When a human kills an animal intentionally, it generally gets reborn as a human. If the human is degenerate, he may slip back and be born as what he killed.
An analogous truth can be easily found in the scriptures: when God incarnates, and slays whichever Asura is causing havoc, the Asura is liberated; he attains proximity with God (born in a high loka), and becomes enlightened.
When a human kills an animal, the animal attains human form. This is one of the reasons why it is not good to kill as many animals as we do; too many humans have to be born as a result of that, which upsets the dharma (order) on earth.
But hey, the dharma of kali-yuga is to destroy dharma.
Comment: Welcome to Hinduism SE! You should cite sources.
Comment: friends i agree with the animals being born as humans but at the same time humans will also be born as animals but in kali yuga other animals population is decreasing in a great rate there is no constant population itself and about 70 or 80 percent of humans kill animals or eat them by buying. If your saying is ok then by now animal population will atleast 3 times of our population but it is decreasing only.


How do I use a Bluetooth keyboard on bios

Question: I have a Raspberry Pi 2 B+.  I have a wireless mouse and a wireless internet stick. My keyboard is also Bluetooth but without an adapter.  I can use it only when i type in a code that is needed to connect the first time.  But I am already stuck in bios so how can I navigate with only the mouse? I bought this keyboard because it does not require a cable but I forgot that you cant use it at the beginning. So I am looking for a solution. I have a laptop. Can I use my laptop to configure everything so I can use my keyboard on the next boot?  You guys know how this work? I am a beginner.
Comment: **There is no BIOS to be stuck in** so you should *describe what is actually happening,* not what you think is happening.
Comment: @goldilocks I think he mistook the command line or `raspi-config` as the BIOS.
Comment: It does sound as though the OP needs to configure something on the Pi which will needs a keyboard - but his keyboard may not work without that configuration -  a [Catch-22](https://en.wikipedia.org/wiki/Catch-22) situation?
Comment: What software is on the SD card for the Pi is it "Raspbian"?  Did you have a kit with some stuff on the Card already or did you put stuff on there with your laptop.  The reason I ask is that if you have Raspbian on the card already you ought to be able to SSH into it - if your laptop is a Windows one you will want to install [Putty](http://www.putty.org/) on THAT first as a first step... IIRC you can get away with just a mouse if there is [NOOBS](https://www.raspberrypi.org/downloads/) or NOOBS+Raspian on the card.
Answer: There are two types of wireless keyboard/ mouse kits available.
The one you seem to have is where the Operating System needs to start Bluetooth Utilities and connect to HID (Human Interface Device) This is a standard Bluetooth pairing system. Any device with Bluetooth will be able to connect to your kit AFTER pairing.
So you would need to use a wired USB keyboard to configure your Raspberry Pi first. After that "BIOS" screen, which is probaly just raspi-config you will need to log in, enable Bluetooth utilities, pair your Keyboard to the Bluetooth and enable a script to restart the Bluetooth Services on EVERY reboot.

The other type is just called Wireless (No Bluetooth in the name) and it also uses the 2.4ghz frequency band, but without pairing. This type of kit sometimes requires you to press a synchronise button on the mouse/keyboard but more commonly it is factory locked to a specific set already and doesn't require any buttons to be pressed.  This is the type of keyboard and mouse kit you require for it to work in "BIOS"/EFI on x86 type systems or SoC type systems with USB interface initialised in the firmware or early stages of bootloading.
The reason the second type works is because the pairing happens on the hardware and the USB emulates a PS/2 keyboard. This emulation of PS/2 allows you to use your Wireless keyboard and mouse almost straight away after power on as its a really old keyboard/mouse standard that is supported by everything. It doesn't require extra drivers. (The "driver" is baked in to the USB specification, and is really just a standard, but that is why it works so well and early in boot)

In Windows the drivers show up as HID just because that is how
  Microsoft wants it to be. But on Unix type devices, or even BIOS, it
  shows up as PS/2

I for example have the Microsoft Wireless Keyboard and Mouse 3000 set. I can plug this into the Pi and have mouse and keyboard access straight after plugging in the USB. The USB is locked to a single set of keyboard and mouse, so you just put batteries in. I also successfully used this keyboard on Android with OTG, my TV and various other devices. Just because the USB emulates PS/2


Question about reality; different events having impact on further events that one usually would not possibly relate to one another?

Question: So I am wondering about how some events have future effect on other events. For example, if someone offers someone else a piece of chocolate 10 years before, it may somehow relate to something else that happens 10 years in the future. For example, say I broke my leg when I was 10, if I had not broke my leg, there would be a totally different outcome correct? And say as a different thing that.... I don't know, say someone decided to smoke weed one time in their life, it could drastically have changed the outcome if they had never smoked that weed before. Like even trivial things as simple as what color shirt one wears, whether someone decides to say hi or not to a stranger they pass by on the street, deciding to eat certain foods, etc. can have drastic impact on two different realities. Say even really small things like thinking a certain thought, listening to a certain song, going to the bathroom, all can impact the future. My question here is wondering about if we are all broken into a bunch of separate realities and if in theory if those realities all are playing out right now, and if my theory about big things or even miniscule things actually can alter the future. For example, if JFK had not been assassinated, or if 9/11 never had happened, its possible that people born after 1963 wouldn't have been born, after 2001 wouldn't have been born, totally different realities, etc. Even though they both are bad things. And if Hitler hadn't risen to power we probably never would have been born either because one event will affect other events, and I doubt that most of the people on here are 85+ years old. In theory, we actually may have been saved and brought into existence by moral purposes that would have been considered terrible, its not what you want to hear but it is the truth. Were they still bad people? Sure,but in theory we would have to kind of thank them in a way because otherwise we would not exist to begin with most likely. And no, I am not planning a destructive event against humanity, but it is just interesting to contemplate how different things could have turned out. I myself perceive multiple different realities are playing out right this moment, however it is impossible to communicate with them due to laws of physics or that such. Am I over thinking this, or what do you think on this? Is my theory correct?
Comment: One big question in such theories: what qualifies as "the same event?"  Defining that turns out to be rather tricky without major assumptions.
Answer: Essentially what you're describing is the butterfly effect. The butterfly effect is the idea that a seemingly small action can cause large effects. The classic example is that the flap of a butterfly's wings in China sets off a tornado in Texas. This of course ignores the fact that the flap of a butterfly's wings could have prevented a tornado in Texas. Both would be equally likely.
The butterfly effect comes about from Chaos Theory, in that even a tiny change in initial conditions bring about drastic differences in the future and that there is no equation or model to predict where the system will be based on the initial conditions.
I would say you are right to think that the actions we take can have a drastic impact on the future, but it's just impossible to say what those impacts will be.
I also find it interesting to think about the Many-worlds interpretation of quantum mechanics. This is the idea that any and every possible thing that could happen, does happen. So like you're saying, it's possible that the person could or could not have eaten that piece of chocolate. Both are possible within the laws of physics, and any "decision" is equally real. This goes down to the subatomic level in that quantum mechanics is governed by probabilistic events. Instead of a person making a decision, there are many "random" paths that a particle can take. There is no way to know which one will happen, only that it is more likely that one will happen over another. Quantum mechanics does not tell us which path it will take since they are all possible, so they are all equally "real". The people that subscribe to the many-worlds interpretation argue that since every single possibility is "real" then basically at every event, the universe "splits" into a universe where possibility A happened, and another where possibility B happened. We simultaneously exist in all realities where it is possible that we could have existed.
These ideas can also come into the debate between determinism and free will. If the universe is completely governed by the laws of physics (and therefore people and their decisions) do we really have the capacity to decide to do one thing versus another? Is every decision we make really a decision or were we bound to do it anyway based on past events going back all the way to the big bang?
Comment: aww gee Dr Byrnes, i'd like to think i got the idea myself, b-but i definitely didn't learn it in school. I guess rick destroying my old reality kinda, i guess, you know, gave me the first hand experience
Comment: Great answer Morty. Perhaps you got the idea from Rick Sanchez?


Do these rotors pass inspection?

Question:
Hello all,
Bit urgent as I'm trying my best to help my mother. She needed a safety performed so she can go from a lease to buying her car directly from Honda. Honda is also the one that performed the safety (and failed it). They were not happy she would be buying it, given how the market is now. They wanted the lease to just end and them to have possession back. As I picked her up and was waiting with her, they called and said her 2 back rotors are rusted and need replacing to pass the safety. It's a 2018 Civic with 18,000 kilometers (11,000 miles) on it. She doesn't drive it much. They said with taxes it would be $630 total, including the safety. She was expecting just the $100ish for the safety. My personal mechanic said it has to be really rusted and "over 25% rust on the contact area" to fail. I took this photo when they still had it up, and I didn't see noticeable rust, but I'm also not a mechanic. I drove her car and it honestly feels new and the brakes are super smooth, way better than my car. Based on the photo above, is there any reason she should've paid the $630 for the rotors to be replaced just to pass inspection? They didn't know of my involvement until I arrived after to look/question it, were they just trying to taken advantage of a 65yo lady? Just based off the photos, of course. Any input appreciated. Thank you.
Comment: Those would be an instant fail in my country and I would not even consider submitting for test until they had been replaced. So, no they are not taking advantage.
Comment: Agree with @SolarMike, it's a genuine issue. The swept area of the rotor should not show rust or grooves. The calipers could be partially seized up from driving so little. An independent shop could be cheaper, and for $630 I hope they replaced (or will replace?) both the rotors and the calipers.
Comment: UPDATE: They passed safety with independent shop after driving for 2 days, $113 bill instead of $630. Safe to say my Mom is happy!
Comment: My friend had a "safety" done by an independent one time - passed with flying colors... BUT it started to rain just after he parked it and when he picked it up after the "test" the blacktop was dry under the car... and it was still raining. We never used that place again.
Answer: From the photo above, the answer is: No. These will not pass inspection. The reason I say this is because of the deep gouging of the surface. You can also tell there isn't much contact between the brake pad and the rotor. And from what I'm seeing, there IS a lot of rust there. This isn't going to be much braking power there. If this were a good looking rotor, you'd have to expect about 80% of the surface to be clean and without the scoring. For them to suggest replacement is not beyond the pale.
If the rest of them look about the same, then it's not going to be a cheap job. You usually do the job in pairs. Since you're in Canada, the price is going to be higher than here in the States. $630C is about $500USD ... with the safety, that could account for a bit of the cost. Really, I don't think it's too far out of line.
Answer: UPDATE: They passed safety with independent shop after driving for 2 days, $113 bill instead of $630. Safe to say my Mom is happy!
Answer: Actually, I'll dare to provide an answer different from the one posted by the 134k reputation guy.
I had problems where my car stuck and required small force from the engine to cause it to suddenly release. Initially I thought it maybe was the parking pawl sticking. The problem occasionally returned for maybe 5 times. However, at one point where the car was driven very little, and not driven at all in areas with stoplights (only countryside areas where I didn't have to brake except maybe using the regenerative braking in my hybrid), and the weather was rainy, it stuck again. This time the problem became worse and required massive engine force to release the car.
Then I realized something's wrong, it shouldn't be that way, and looked at all the wheels. The rear wheels had brake rotors which almost exactly looked like your rotors.
I began a fixing regime: I drove the car with aggressive braking. Gradually the rear brake rotors became better. There was one minor setback, one case where I didn't drive the car for a day in rainy weather, and it suffered from very minor brake stick, but nothing as bad as the horrible sticking when the car was driven only in countryside areas. Finally I managed to fix the last setback.
Now the rear brake rotors look much better. It took about three months of hard braking to get from the horrible state to the current acceptable state.
The mandatory inspection was exactly two weeks ago. They didn't complain anything about rear brake rotors. The only minor complaint was bit over 20% difference in force of rear parking brake (allowed difference is 70%), and that was caused because the parking brake is implemented by using a secondary brake drum, not the main disc brakes, and I had never used the parking brake to slow the car down so it's understandable there's going to be some difference in the forces of the non-used brake. The rear main brake had exactly 0% difference in braking forces.
You can fix it like I fixed it! Three months (I drove about 4000 km in those three months total), with lots of hard braking, may be able to rescue your brake rotors.
Comment: So, basically you want a 65 year old lady to do an "Italian service" on public roads?
Comment: UPDATE: They passed safety with independent shop after driving for 2 days, $113 bill instead of $630. Safe to say my Mom is happy!
Comment: Glad that the Italian service did work! 2 days of driving is quite little though, very surprised they went acceptable so fast.

Do these rotors pass inspection?


How to reduce star trailing when taking long exposure photographs?

Question: My telescope's sidereal tracking is lousy: it just doesn't work. To overcome this, when taking long-exposure photographs through it, what's the best way to reduce star trailing?
Answer: Sounds like you should get a new mount. :-)
Being more serious, even expensive mounts have periodic tracking errors (due to manufacturing tolerance of gears and moving equipment) that need to be corrected. These are the basic ways to do the corrections:

Add a guide scope to the side of your scope, use an eyepiece with cross-hairs, and watch a star while you take a photo. When the scope drifts, you push buttons to move the scope to keep the star centered.
Do the same thing with a guide scope but use a dedicated guide camera that provides the corrections to the tracking.
There are also guide cameras that you can insert just in front of the camera. They use a small "pick-off" mirror to look at a star in the field (off axis guider). The guide camera provides the corrections to the tracking.

Of course, all of these methods require a mount that can be moved slowly and smoothly in both right-ascension and declination to keep the guide star centered. Also, the mount needs to be an equatorial mount and accurately aligned. (More expensive mounts can be alt-azimuth mounts and use a gadget to rotate the camera during the exposure.)
Comment: After using it tonight, it seems to be working perfectly. I must have been aligning it wrongly in the past :D
Comment: Those with the small pick-off mirror are called "off axis guider". Could you please edit your answer?
Answer: This is not quite a full answer, but a useful addition to your image processing stack are deconvolution methods designed with astronomy in mind.
There's a free software tool for image processing called Iris which includes some useful deconvolution methods not available in typical image processing applications.
Here's a brief tutorial showing what's possible with these tool.  Note in particular the RL2 method, rather than the RL method.
Note that these tool should not be used generally to correct long exposure star trails, but can correct small trails.


How to sort Apache Solr search results?

Question: I want to make possible for the user to SORT Apache Solr results based on some taxonomy terms.How can I do that?
I also want to make possible for a user to change the number of the results on the page.
How can I achieve both of them?
Thanks in advance
Comment: It's usually a bad idea to ask multiple questions, especially in this case, where the way you solve the first question will effect how you can solve the second question.
Answer: I good way to utilize Solr for search with Drupal, is to use the Search API, is has a Solr integration module, which will allow you to setup a View with exposed filters and full text search. With the flexibility of Views, you should be able to setup the view to allow the users to sort as they wish.
Answer: I guess this comes too late for you but maybe will help someone else:
(1) Sorting can be handled with Facets:
    Facet API  ( facetapi )
(2) # of results per page sounds like a Drupal configuration thing, maybe handled in the configuration of the Block in which you show the search results
Comment: Hello and welcome. This looks a bit more like speculation than a real answer. Could you please expand it a bit, especially first part, as you seem to know it pretty well?
Comment: Hello,
re: (1) I tried Facet API module & it provides ways to drill down in search. You can sort by relevancy, date, author, date... customized in the Facet tab in ApacheSolr settings (if Facet is enabled).

When these terms are exposed, they become available in Blocks.

Taxonomy ("Filter by field of type taxonomy_term_reference.") is one of the items exposed.
I haven't used it, but it's there.

Perhaps I misunderstood Sokratis' question?

re:(2) # of results, I was wrong, they are not configured in Blocks. Looks like it's in the 'configure display' link for whatever term is exposed.
Comment: Thank you for explanation. Could you please edit it inside your answer? I would like to do it myself, but I'm afraid to mess it up.

How to sort Apache Solr search results?


Replacing LED lights with LED lights but 2 out of 5 has issues

Question: I have recessed lights in kitchen.  I placed LED lights in them several year ago, spot/flood screw in.  I just replaced all five with the updated, lighter weight, technology.  When I hit the switch all lights came on.  Click it off and two of the lights did not come back on.  Checked the socket/light by placing the old but working light back in and the light came on. Concluded it was a bad light...but tow of the?  Took back to Lowes and exchange for two new lights.  Place the two exchanged new lights in the sockets did not work.  Took the non working light swapped it with a working "new" light and it worked.  So lights are good, sockets are good as the old lights come on in the sockets.  The only thing I can observe is the contact point on the new lights is slightly wider and the actual contact point is slightly recessed more than the old LED's.  Any suggestions?
Comment: Hello, and welcome to Stack Exchange. You aren't quite clear: are you saying that all five sockets work with the old bulbs, but two of the five sockets consistently have trouble with the new bulbs?
Answer: My bet is that the middle contact isn't sprung enough to be consistent.
First, turn the breaker off.
Then, gently tug at the central contact in the middle of the light fixture's socket to bend it a tiny bit further forward. Needlenose pliers can work well for this.
Don't bend it too hard; otherwise you'll have a broken light fixture to deal with.
Comment: I have seen this quite often and agree. Some lamps just don't screw in enough to make good contact and adjusting the center contact usually works well. +


Is Sher-Wood T90 considered a pro stock hockey stick?

Question: Is Sher-Wood T90 considered a pro stock hockey stick? Do some NHL players use it?
Comment: PSA: this question is being discussed on [meta](https://sports.meta.stackexchange.com/questions/826/is-this-question-considered-as-localized/).
Comment: Please look at answer provided if that's not what you intended to know, comment and suggest clarification.
Comment: I guess I wanted to find out if any professional hockey players have used this stick.
Answer: Mentioned Sher-Wood T90 hockey stick, doesn't appear to be pro stock hockey but is retail version (followed the link of the picture to prohockeylife.com).
ProStockHockey website shows a difference between pro stock and retail version, and there is a pro version of Sher-Wood T90 hockey stick branded under New York Islanders player Steve Bernier.


Price update in Add to cart functionality from product detail page to cart page

Question: Can anyone tell me in magento, when we click Add to Cart button in product detail page, where and how is Product Price and Qty input multiplied and updated in shopping cart page Subtotal column. I want to customize the action for my custom pricing module.
Comment: what you mean by `customize the action for my custom pricing module.`
Comment: By default, magento takes the **prod price** and **qty** as separate parameters and multiply them during **Add to Cart** event to display **subtotal** in cart page. But I am performing custom price calculation in product page itself and updating the custom price using ajax. Now I want my custom price to be displayed in cart page sub total column alone. But the same price is displayed both in unit **price** and **subtotal** columns. Also I want to **prevent default multiply action** on Add to cart.
Comment: Amit pl let me know if u can help me with this issue.
Comment: that means you can change cart item price and subtotal?
Answer: The subtotal logic on the cart page is implemented in the below template file.
app/design/frontend/rwd/default/template/checkout/cart/item/default.phtml

Override this file into your local and modify it as per your requirement.
Comment: thank you for the reply.. can u pls tell me how does the subtotal in cart page logic goes in while clicking **Add to Cart** in PDP **(product price * qty)**
Comment: check my updated answer
Comment: btw is it poss for u to answer my another query too?
Answer: Guess that
You  want to change cart item unit price.I
So in this case,you can use magento event/observer.
Basically  there are two events,by which you can change the cart price of that products:

checkout_cart_product_add_after
checkout_cart_update_items_after
checkout_cart_product_update_after

This 3 event is need because of:
Event1:checkout_cart_product_add_after
This event is fire when first time a product is cart for current session of current input values from frontend
Event2:checkout_cart_product_update_after
This event is fire when a current exiting cart item edited from  edit link  of  cart item.
Event3:checkout_cart_update_items_after
This event is fire whenever cart items update from cart page.
As per as magento system, a cart item price change using setter functions setCustomPrice(), setOriginalCustomPrice of cart item Object.
Just like:
$EachCartitem->setCustomPrice($price);
$EachCartitem->setOriginalCustomPrice($price);
// Enable super mode on the product.
$EachCartitem->getProduct()->setIsSuperMode(true);

If you can cart each unit price then automatically change subtotal
An example: Custom options operations
Comment: Thank u Amit. I have set the new price and it's updated in quote table using event/obs. The problem is, I'm changing the Prod Price displayed in my pdp using ajax when my customer enters a number. Along with tat I'm using several parameters and calculating the custom prod price. It's updated in the same div where magento displays the unit price frm backend. So when I add to cart, the unit price in cart is getting updated as my custom price. I wanna stop it. Also I need to prevent the **prod price * qty** functionality.


Controlling multiple solenoids with arduino

Question: I was wondering how I could connect multiple 12v solenoids (more than the 53 allowed on mega because of the pins) on the Arduino Mega 2560 to get it to control the keys on a piano/keyboard/organ. Would 74HC595 shift register work for it with the 12v? (Many of them) Because there are so many high voltage solenoids is it possible to control a few of them at a time? I was wondering if someone has a link to somewhere that I could refer to. Thanks
Comment: you could also use a 74HCT259 or a PCF8574 to expand the number of pins
Answer: Arduino I/O pins, and the output pins of 74HC595 shift registers are logic-level outputs, and are not intended to drive power-hungry items like solenoids. In either case (direct I/O or shift registers) you need to use the logic signal from the output pin to drive something else that switches the 12V source.
That something else can be a MOSFET or a relay, though often even relay coils are themselves driven by a MOSFET or other transistor that is switched by a microcontroller output pin.
One of the many search results that describe this is at http://hades.mech.northwestern.edu/index.php/Driving_using_a_single_MOSFET
Comment: Ok thanks for the link and explanation - it'll help with the project!
Answer: the shift register has 2 features that will help you:

a latch pin. When a the storage register pin is kept low the outputs won't change this allows you to shift in a new value without perturbing the outputs.
a Qh' output this is the output from the last bit that bypasses the normal output. If you connect that to the next shift register you can daisy chain several registers.

The outputs of the chip are not meant to driver significant currents. Instead use them to drive a mosfet that in turn drives the relay. There are boards that contain all the support circuitry needed to drive relays using low power signals.


Why do devices stop operating properly in extreme cold?

Question: I have noticed that a lot of smart phones say that they won't operate under -4 degrees F (-20 degrees C). Can anyone explain to me what happens when the phones get cold that stops them from operating?
Comment: Batteries become chemically inactive in the cold. Heat them, or get a crank and use yourself as a power source. Seriously, this can be mitigated just by having the device in your inner coat pocket.
Comment: The first smartphone I used had its LCD become solid at -3°C
Comment: Here's [another question](https://electronics.stackexchange.com/questions/35663/minimum-operating-temperature-outer-space) that is little bit related. - Might be somewhat interesting for you.
Answer: -4 F is -20C, which is a standard low limit for chips and electrical components. Some of that is just because it is very hard to test chips at low temperature, but there are real issues you can run into, which include:

Batteries degrade at low temperatures, depending on their chemistry.

The battery output voltage is lower, meaning you need more current to get the same power
The battery internal resistance can increase. The added resistance can heat up the board, but it also wastes power and makes the battery output voltage less stable, as it will change with current draw.
The heat caused by the extra resistance can potentially damage the battery, since you are heating up the inside while the outside is cold, creating a thermal gradient which adds mechanical stress.

Thermal cycling of parts can become worse. Things break when you make them cold and heat them up because of thermal expansion. I believe this issue is worse at lower temperatures, possible related to metals becoming brittle when they are very cold.
Chips can draw more current at low temperatures. This issue compounds the other two, since more current becomes more heat, which increasing thermal cycling.
Chip timing changes. Digital circuits have special timing rules to ensure that all signals are in the right place at the right time. Lowering the temperature changes all that and can create a race condition.
Comment: The battery point's a little confusing... since "*they will get hotter as you draw more current*" so wouldn't that solve the low temperature problem?
Comment: I am disappointed when the chip doesn't work while I single-step the clock.
Comment: **"I am disappointed when the chip doesn't work while I single-step the clock."** There are two type of timing error in a digital circuits: set-up timing error and hold timing error. The latter is independent of the clock frequency so it will fail on single stepping too.
Comment: @Xen2050 KyranF is right, the system will eventually warm up, but there are related issues of wasted power (that heat has to come from somewhere) and, potentially, a temperature gradient is not the best thing, because of mechanical issues.

No designer should say "let's warm this board up by heating the inside of our battery". I will clarify my original answer.
Comment: @Xen2050 the battery heating (or the chips heating) may self-protect the entire device if the enclosure the device is in is relatively well insulated - as in, it may have taken days to get down to such a low temp, and after the cold-start period the device may warm up enough to keep itself within operating temp
Comment: The higher internal resistance of the battery could prevent the device from running altogether - the short circuit current is the max current that you can draw from a battery, and this decreases as the internal resistance increases.  Not to mention voltage drop, as the short circuit current is the current at 0v output - the device will stop working long before the short circuit current reaches the minimum current required to operate.
Answer: For most of these devices it's the display...
LCDs don't like the cold.

Typically, standard LCD character and graphics modules provide a temperature range of 0°C to +50°C. However, several display manufacturers offer extreme temperature models with operating temperatures of -40°C to +80 or +85°C. There also is a wide selection of standard versions that range from -20°C to +70°

Source
The newer OLED types do have a much better temperature tolerance though, -40°C to +80°C.
Comment: @SpehroPefhany hey fellow Hoser, as my answer states, some can be made to work at -40C, but automotive parts and cheap phone parts are not in the same class. The heat generated from the backlight helps a lot to keep the liquid fluid too. If you let them freeze they can and will crack though.
Comment: In my experience with laptop LCDs in the cold (around -10°C) the picture gets grainy and slow but it still works. There are rugged laptops with heated displays to work around this problem. Some smartphones have OLED displays, do they have the same issues?
Comment: @Michael OLEDs do have a wider temp range since there is no fluid to thicken or freeze. " -40°C to +80°C. " OLEDs do have other issues though.
Comment: As a card-carrying Canadian, I can verify that the LCDs in my car dashboard work just fine at -20°C.
Answer: Batteries dislike cold.
Generally all batteries lose capacity and current in the very cold.   (However, using them often warms them up.).  Lithiums have a particular problem with being charged in the very cold.
Also, devices are concerned about condensation occurring inside the device from humid air entering the headphone jack etc.
Answer: Crystal oscillators may not start up; or the crystal resonant frequency, which has a temperature coefficient, may be outside the guaranteed Automatic Frequency Control (afc) range, needed to ensure the data packets start on expected time slots even after some hours of operation and phase slipping.
Answer: To add my 2 cents on all the great answers (which would apply not only to electronic devices but generally all electric devices) - the temperature drop results in change of material resistance (namely for metals they become less resistant), while this might seem a minor thing, in industrial equipment this is one of the items accounted for. Electronic devices would suffer most at that because many microchips rely on resistors between some of their lines to be of specific value, if that value changes the microchip may start misbehaving or completely shutdown.
Answer: Analog circuits can also have problems at low temperatures. Resistance changes across temperature, and so do transistor threshold voltages and transconductances. If a reference voltage or current goes out of spec, it can affect other analog circuits that depend on it (like an ADC or a charge pump).
When you're simulating a design and (later) characterizing and testing hardware, you have to pick a lower bound for temperature. There may not be any actual problems if you go a little below that temperature, but the manufacturer can only guarantee correct operation if you stay within the tested limits.
That being said, for smartphones the battery and display are probably the bigger concerns, as the other answers show.
Answer: When you get into minus figures things start to slow down, there is something called ABSOLUTE ZERO which is 0 degrees Kelvin or minus 273 C. @ 0 Kelvin nothing moves, including protons and electrons, it basically freezes electricity (not sure what happens with photons).  Eventually chip speeds will slow down but not at the same rate so the sync is lost.
Comment: that should be -273 Cent, 0 K, or -460 Farenheit, or 0 Rankin.
Answer: My 2 cents is that there is a "Diode Equation" (google it!) that includes current, voltage and temperature. So a semiconductors behaviour depends on temperature. Useful in a digital thermometer, but must be counteracted by adding trace elements and other magic by the manufacturers of ordinary chips to make them work "straight". But this works only within a limited temp. range depending on budget and usage. So I guess it would be possible to make a phone that works well only between -220C and -150C, for example.


Should tenant be allowed to have rent due on x days past start of the lease?

Question: A tenant ask if he could pay rent on the 10th of the month when the lease starts on the first. Is this common or be allowed? Seems like he is asking for 10 days of courtesy habitation.
Comment: Is he asking to pay the rent _every_ month on the tenth or just the first one? Do you change rent in advance or in arrears (meaning is the payment for the prior month or the next one)?
Answer: In most jurisdictions you have quite a bit of latitude in what you and your tenant agree to. Some people like monthly expenses to hit at a time other than the 1st because of the timing of their paychecks and/or other monthly expenses.
I take it as a sign they might be living paycheck to paycheck which is not ideal, but up to you to decide if you're comfortable with their financial situation.
If you do agree to a non-standard payment schedule you'd probably either have them pay 10-days worth up front and then a full month on the 10th, or a larger first payment on the 10th. Not giving them 10-days for free.
Answer: Presumably rent is paid monthly in advance?
Then the first month's rent will be for 1 month + 10 days, and continue monthly thereafter.
Answer: Unless explicitly stated that they want ten days free, this usually means they want to make a first, smaller payment (they pay on the tenth of their first month for the first ten days), or they make a larger payment for the first month on the tenth of the next month that adds the ten days. After either of these options you then revert to a normal monthly cycle paid on the tenth.
You can obviously argue back and forth if you dislike any of this, and depending on the contract and locale can probably play hard ball on it if you really don't want it, but run the risk of an angry tenant. Angry tenant's are basically always bad, as a lack of care of the property can cause you a lot more loss than ten days rent.
Answer:
Seems like he is asking for 10 days of courtesy habitation.

Not necessarily. You can see it from different angles, and essentially, they match each other in the sum.
As others suggested, you might want to charge them ⅓ of the monthly rent upfront. But then, you have to consider that in the last month they live there, they only have to pay ⅔ of the amount due.
You might as well accept a continuous delay: they pay on the 10th, but for the current month. It might be the easiest way of seeing it.
Both perspectives are equivalent in the end.
Surely you will hold a security deposit anyway; maybe you can agree to a higher amount than usual.