comparison of atmospheric correction methods

Question: I have noticed that dos methods for atmospheric corrections are in the section of radiometric correction i.*.toar on GRASS GIS. Does that means that dark object subtraction (DOS) is a method for doing radiometric and atmospheric corrections at once? Input images for that method have to be in DN format I would suspect. I want to compare the results with 6s algorithm.
Answer: The DOS methods are for atmospheric correction only, not radiometric correction.
The i.*.toar modules allow you to combine in one step radiometric correction with some additional DOS atmospheric correction method. The input to the i.*.toar modules is the original DN values.
The default to i.*.toar is "uncorrected", so normally you would use i.*.toar to get a radiometric corrected image, then run that thru i.atcor (which implements 6S) to get your atmospheric correction.
Comment: I have done the 6s but I wasn't sure about DOS. So DOS performing radiometric and atmospheric correction at once?
Comment: No, as I said, DOS methods are atmospheric correction only. But if you are running the i.\*.toar module, then you can choose to do both radiometric correction, and atmospheric correction thru one of the DOS methods.


need to connect my same apps with one database

Question: i have 3 servers for three applications on aws ec2 using MySql database,
now each of the application is having amember that is client subscription app,
it connects with sql databse that is created in each instance
so in this way every amamber app is having diffrent database in each server,
now we are working with a device ROKU we need to pass the XML attributes from amember to it
to varify the user so he can watch online streaming tv.
the objective
now i need to make one database that will be connected with each server using amember
so each server access one database .
Options
my options are aws RDS ,dynamoDb
Now can anyone put me in the right direction, for that.
in simple Words
need to connect my multiple apps (same app) with one database
 HELLLLP
Answer: If you need to connect to a mysql database, DynamoDB is not the answer. It isn't a mysql database.
RDS is a mysql database. It connects like any other mysql database. You haven't mentioned what language[s] you are using, however. Googling "connect to mysql with [language]" should help.
Answer: I think it would be best to stick with relational databases such as MySQL.
Amazon RDS is a managed MySQL solution, but you don't have to use it for your needs.
You can use one of your EC2 instances or a new EC2 instance as the central DB and connect all the other servers to it for quires. There are pros and cons for choosing RDS over your own SQL server. If you have any questions there, feel free to edit your question and add them.
EDIT according to comment
In order to connect your application with the local MySQL. Your are probably using a connection string that points to either "localhost" or "127.0.0.1"... That is the IP of your local machine. You will have to change it to the remote IP of the machine where the DB is stored remotely.
Comment: thanks Chen but can you give me littel more on that, like if i have created an instance name ABC (its DB) and i want to point my application on XYZ instance to ABC localhost, then how should i tell my application to connect db remotly,


QGIS Polygon Selection

Question: I want to select a polygon using QGIS. The polygon is only represented via it's boundaries (I chose not to fill the area in order to highlight the problem). Why are not all lines that surround the polygon selected? See picture below. A similar problem occurs when two polygons overlap: only one polygon is highlighted.
Comment: Are those blue lines actuylly polygons as well or just lines?
Comment: they are polygons. The area colour is inivisble (no fill).
Answer: This is due to the drawing order of your polygon.  The other ones are probably drawn after the selected one.  The last drawn is rendered on top of the others.  That's why the border of the selected one is partialy hidden
Comment: @kalakaru Yes. In Symbology Tab there is a small text saying "Layer Rendering" at the bottom. Open it and now check the box next to "Control feature rendering order". Now you can click the box with the "AZ and Arrow" Symbol and choose an attribute that controls the rendering order.
Comment: if you set your fill as semi-transparant, the polygons underneath will show up
Comment: Is there a way I can change the order of the polygons? Because polygons underneath a polygon are for example hidden.
Comment: @PieterB that solved my problem. Thank you!! :)
Answer: It look like you have a line layer delimiting polygons otherwise the whole area would appear selected (you can check the layer geometry with a right click on the layer name then select property then looking for the information tab and checking the Geometry)
If that's the case you may have information in the attribute table that may let you select whole boundary if not you will have to manually select all the line that limit your area.
If you give us more detail (like how this layer was made or what's in the attribute table) you will get more helpful answers

QGIS Polygon Selection


How to take KML locations and add information inside of them in qgis to build one layer?

Question: I have two files, the first one has information and the second one has KML locations, So the idea is that I need to take every KML location that I have in the second file and add data on it that I have in the first file, so how I can create one Qgis Layer that include all the KML locations with their information.
Comment: Can you share these files with us? Both of them are KMLs, is not it?
Comment: No, not both of them, one has KML LOCATIONS, and the other one just has a report that contains information that I should add to every KML location as a table of attributes in qgis.
Comment: Bring them both into QGIS, and perform a simple join (if possible)
Answer: Sounds like you might want to do a "Table Join" to bring together a geographic dataset with a tabular data source... something that QGIS and other GIS packages can do.  You'll need to make sure that your KML file can be imported into QGIS, so it should have only one geometry type (points, lines or polygons).  And you'll want your "information" file to be tabular like a spreadsheet or CSV file with uniform rows and columns of data.  Finally, you will need to have unique identifiers in both files, to match the features in the KML file with the rows in the "information" file.  If you have all those things, then you should be able to "Join" the tabular data to the KML, and export it all as a new KML, a shapefile, or some other format. IF your "information" isn't in a tabular form, and/or doesn't have unique identifiers that match your KML features, then can you create a table/spreadsheet like that from it?  You can look up Joins in QGIS, like here: https://www.qgistutorials.com/en/docs/performing_table_joins.html
Comment: All right that sounds great thanks Christiaan


Transformer getting hot

Question: I have build an LED array consisting of 75leds, 5 connected in series with a 39ohm-1/4watt resistor and 15 such series connected in parallel to the rectifier circuit having 2-IN5408 diodes and 1- 25V_4700µF capacitor. The transformer is 12-0-12v_3A. The leds forward voltage is 3.3v-3.4v and forward current is 60mA. As the whole fixture is for an aquarium i have to run it continously for 6 hrs and the transformer gets quite hot (cannot touch it for more than 5 secs)? Is the rectifier circuit and the transformer not adequate for running the leds?
Comment: Please draw a schematic!
Answer: It should be adequate.
Measure the voltage across the 39-ohm resistors and you should get ~2.34V. If it is significantly more then you should increase the resistor values to get ~60mA.
Answer: That is not too hot.  You may be able to reduce the heat with an improved rectifier, by reducing current, or using a more efficient number of LEDs in the strings.
Efficiency is mostly a function of how close the supply voltage is to the LED string's forward voltage.
You measure the DC forward voltage of the LED strings and the supply voltage.
Then select a current that gives you the desired LED intensity.
This online calculator will give you the efficiency based on the measured values.

Transformer getting hot


What is a Layered Tiff

Question: I've been asked to provide layered Tiff files from Illustrator. However, when I re-open the Tiff in Illustrator, it's just a flat image, which I'd expect but then why is the client asking for it in layers or am I missing a step?
Comment: It is a bit of a weird request. Wanting layers indicates the desire to be able to edit, but wanting tiff, which is a raster format, indicates that the vector graphics must be rasterized and therefore not entirely editable anymore.
Comment: Just explain to the client that the file is a vector, Illustrator, file not a Photoshop file and a tiff would actually *degrade* the quality... but you *can* send an editable Illustrator file. (Hopefully you're charging appropriately for delivering editable files).
Comment: Maybe time to educate your client about the difference between vector and raster graphics. Sounds like they are confused. And yes you are right, Illustrator can't export layered TIFFs. It just flattens them.  It can however export a layered PSD, but every object would need to be on a separate layer (not just sub-layers), and of course, each layer would be rasterized.
Comment: Not clear from the question, but they may be asking for an alpha channel to be included in the TIFF (if applicable).
Comment: Thanks for all your help everybody!  We've cleared things now. The client thought I'd designed the pattern in Photoshop, which will export layers to Tiff and and now I'm sending a layered PDF from Illustrator.
Answer: Layered Tiff files are essentially a bastardized, Adobe-proprietary, setting for the TIFF format.
If one chooses Save As in Photoshop for a file containing layers, and then chooses the Tiff format, there is an option to save Layers....

These layers inside the TIFF will only be seen by Adobe products. Layers are not part of the standard TIFF specification.
Opening a layered TIFF file in non-Adobe software merely presents a flat TIFF based upon the appearance of a flat file. (As if layers were flattened in Photoshop before saving the TIFF.)

Adobe is odd in that they add Adobe-only specifications to some formats while ignoring other, globally allowed, specifications. For example, with Photoshop one can save a layered TIFF files, but Photoshop doesn't understand or save the common, allowed, specification of multi-page TIFFs.

For vector files in Illustrator, there is no method of saving a layered TIFF. Illustrator can export/save a TIFF, but only a flat TIFF. If one needs a "layered TIFF" and all that is present is Illustrator artwork, then either the AI file would need to be exported (with layers) to Photoshop, or objects manually copy/pasted and reconstructed in Photoshop - and then a layered TIFF saved using Photoshop. As far as I'm aware, only Photoshop is capable of saving "layered" TIFFs.

Truth of the matter is, one probably should take the opportunity to educated the client a bit and explain that you have a vector file, which is generally more editable than a Photoshop file and you can provide that as opposed to a Layered TIFF.
Clients will tend to try and speak to the designer's level if they have a little knowledge. Chances are the client is merely aware that Photoshop is often a tool used by designers. So, they ask for what they've received in the past, not necessarily what's most appropriate.
Answer: Tiff files are not vector based and is very similar to .psd (Photoshop files). You will need to open it in photoshop to see if the layers are exported correctly (not sure if Illustrator flattens tiff images on export). If so you maybe have to export layers separately and combine them again in Photoshop.
Comment: I see, thank you. I think the confusion I have comes form the fact that I've designed my repeat tile in Illustrator and the client has presumed I used Photoshop, where a layered Tiff can easily be generated, but I think I  can export to PDF and maintain the layers.

What is a Layered Tiff


List of active users and their access rights to O.S. in Windows Server 2003

Question: How I can get a list of active users and their profiles (access rights) to O.S. in Windows Server 2003 ?
Answer: It depends on what you mean by "active" and by "profiles" and by "access rights". It also depends on whether you are interested in local users or domain users.
For local users, you can use net user at a command prompt.
C:\Users\MyUser>net user

User accounts for \\TestMachine

-------------------------------------------------------------------------------
DefaultAccount           defaultuser0             Administrator
JohnSmith                SallyJones               MyUser

To tell whether each one is active (and in this case, Windows uses "active" to mean "enabled" -- it has nothing to do with whether they are currently logged on, or when they most recently interacted with the system), you can use net user <username>.
C:\Users\MyUser>net user administrator
User name                    administrator
Full Name                    administrator
Comment                      Administrator Account
User's comment
Country/region code          000 (System Default)
Account active               No
Account expires              Never

[...]

Local Group Memberships      *Administrators       *Performance Log Users

[...]

The command completed successfully.

And then you can parse out the "Account active" portion. But Powershell makes it easier.
Get-LocalUser

That'll give you all local users. To filter for only active (enabled) users:
Get-LocalUser | Where Enabled -eq "True"

As for access rights (that's not the same thing as a profile, but I'm gonna assume you are looking for access rights), the net user <username> command will give you a list of the local groups that the user is a member of. (But finding exactly what object those groups (or the users directly) have access to will require looping through all securable objects.)
If you can clarify what it is that you are trying to accomplish, this answer can probably be improved.


User authentication using MySQL and GRANT or custom software solution?

Question: I'm a long time programmer but have done very little database design.  So I'm seeking some feedback on a solution I'm developing.
Description
I will have several (10 to 20) customers storing sensitive data on  my remote server.  A customer is an organization that has users.  Access is done via  piece of java software running on the server accessing a MySQL server.  A separate client java program accesses the server and does the interchange.
Data privacy is very important, so I am planning on a separate DB (schema) for each customer.  Within each database there are three user levels: input, query, and admin. A user fits into one of those levels and gets various permissions on the DB.  I'm planning to do everything with stored procedures, so really they are getting access to a set of stored procedures on a specific DB.
The biggest challenge is that the customer's Admin users have to be able to add (or remove) additional users that only have access to the customer's database.  Users should be unique to the DB, but not to the MySQL instance.  Each customer should be about to have a user named 'bob' for example.
Question
So I have two ways currently of approaching this.  The one I currently prefer is to have each user be a real MySQL user that can have privileges GRANTed.  This makes sure they can only execute what their role specifies right at the MySQL level.  The problem is name collision since MySQL usernames are global to all DBs.  I solved that by having a "root" table that maps a User's customerID (unique to each customer, not each user) to a DB, then a table in that DB maps the user's name to a userID, which is then the actual MySQL user.  The java server software would connect to the DB using the mapped userID and user's password, and go about business.  It's a good bit of effort and hoop jumping to do this, but I like it from a security standpoint.
The other way is just to have a couple of base users in the DB for the java software to connect and then write our own auth by storing usernames and passwords in each customer's DB.  It would be up to the software to make sure only the right DBs are modified, only the right functions are called, etc since nothing in MySQL would be able to prevent it.  The base users would have to have all permissions for all user types, so a software glitch or compromise in the java software could lead to bad things for the DB.  Makes the DB easier but the software somewhat more complex.
Feedback
So do any DB veterans have some feedback on this?  Has anyone solved an issue like this in a better way?  Trying to get some ideas before we commit to something.
Thanks, Matt
Answer:
The other way is just to have a couple of base users in the DB for the java software to connect and then ...

Use LDAP to store users, schema associations, privileges, roles, authorizations, etc., etc.
It is always up to the software -- via authorization rules -- to make sure only the right DBs are modified, only the right functions are called, etc
The base users would have to appropriate permissions for specific user types,

so a software glitch or compromise in the java software could lead to bad things for the DB.

That's always true.  So use testing to prevent this mysterious "glitch".
The database is not magically "more secure" or magically "less subject to software glitches".  DB security is just as trustworthy as application security.  Both are just as trustworthy as the administrative procedures and human factors.
Use application-level authorization.  Use LDAP.
Don't impute magical powers to RDBMS authorization schemes.  They're not "better" or "more trustworthy".
Application authorization checks -- in most languages and frameworks -- are single line-of-code decorators (or if statements) that explicitly define what group of users has access to the functionality.  It's not difficult.  It's not subject to "glitches".
Comment: Not keen on that.  LDAP adds another service to maintain and backup.  And code that has to be written into the server software to allow the customer to add and remove users from LDAP.  The users have to be kept in sync with the DB.  I'm not assuming magic powers in MySQL, but it already has the ability to add a layer of security by limiting what a user can do.  MySQL has the benefit of millions of installs testing and ensuring its security.  I'd like to leverage that in parallel with my own.
Comment: @ZaXa: "adds another service to maintain and backup".  Cost is approximately zero.  "add and remove users from LDAP".  Readily available libraries make that cost nearly zero.  "users have to be kept in sync with the DB".  False.  DB uses LDAP.  "in parallel with my own. "?  As in, "in parallel with my own security framework which duplicates existing security frameworks?"  My point is this.  It's been written.  Use what's available.  Do not invent your own.


How to efficiently compute similarity between documents in a stream of documents

Question: I gather Text documents (in Node.js) where one document i is represented as a list of words.
What is an efficient way to compute the similarity between these documents, taking into account that new documents are coming as a sort of stream of documents?
I currently use cos-similarity on the Normalized Frequency of the words within each document. I don't use the TF-IDF (Term frequency, Inverse document frequency) because of the scalability issue since I get more and more documents.
Initially
My first version was to start with the currently available documents, compute a big Term-Document matrix A, and then compute S = A^T x A so that S(i, j) is (after normalization by both norm(doc(i)) and norm(doc(j))) the cos-similarity between documents i and j whose word frequencies are respectively doc(i) and doc(j).
For new documents
What do I do when I get a new document doc(k)? Well, I have to compute the similarity of this document with all the previous ones, which doesn't require to build a whole matrix. I can just take the inner-product of doc(k) dot doc(j) for all previous j, and that result in S(k, j), which is great.
The troubles

Computing S in Node.js is really long. Way too long in fact! So I decided to create a C++ module which would do the whole thing much faster. And it does! But I cannot wait for it, I should be able to use intermediate results. And what I mean by "not wait for it" is both
a. wait for the computation to be done, but also
b. wait for the matrix A to be built (it's a big one).

Computing new S(k, j) can take advantage of the fact that documents have way less words than the set of all the given words (which I use to build the whole matrix A). Thus, it looks faster to do it in Node.js, avoiding a lot of extra-resource to be taken to access the data.

But is there any better way to do that?
Note : the reason I started computing S is that I can easily build A in Node.js where I have access to all the data, and then do the matrix multiplication in C++ and get it back in Node.js, which speeds the whole thing a lot. But now that computing S gets impracticable, it looks useless.
Note 2 : yep, I don't have to compute the whole S, I can just compute the upper-right elements (or the lower-left ones), but that's not the issue. The time computation issue is not of that order.
Comment: Have you had a look at random projection lsh?
Answer: If one has to solve it today, just use pre-trained word vectors from fasttext or word2vec


Is it possible to customize the GParted toolbar so that the icons include text?

Question: I installed GParted 0.12.1 in ubuntu. There is no text description under the toolbar icons. Is there a way to display text under the icons in the toolbar as can be seen on the various tutorial web pages and the GParted page at Wikipedia?
Answer: If you install dconf-editor (sudo apt-get install dconf-editor) and run it you can change this default.
Simply navigate to org/gnome/desktop/interface and change the value that says toolbar-style to "both" (by default it is both-horiz).
Do note, however, that this is a change that affects all applications, not just GParted.
Answer: Githlar has the right answer, but like he said it will affect all of your applications. If you do not want to make that change, you might be satisfied with different icons.
Installing unity-tweak-tool will allow you to change your icon theme. Gnome-tweak-tool will work as well but I don't like it nearly as much.
sudo apt-get install unity-tweak-tool
Find and download icons. I like getting them from gnome-look.org. Then unpack them to /usr/share/icons.
Now you just launch the tweak tool and change your icons. This way you can find some icons that help you identify the functions of gparted without adding text to all of your programs' title bars.


How to stop mobogenie auto-download in Android?

Question: mobogenie application auto download in my mobile. My cellphone is Sony Xperia J and my Android version is 4.1.2. Once, I removed it from my device, but it's downloaded automatically again. How to stop that?
Comment: Hi, I realize this is an old question, but it'd help if you could clarify the detail a little bit. By "downloading", did you mean downloading the APK file only, or downloading (and installing) from market app? Based on the answer, I'd assume the former since the APK was downloaded by rogue ads? (similar to https://forums.androidcentral.com/samsung-galaxy-note-2/352043-how-stop-mobogenie-auto-download.html)
Answer: Go to Setting -> Accounts & Sync -> Google -> Ads( Reset the Advertising ID ) + Ads setting ( Google Ads Manager and Opt out )


Airodump-ng occationally not showing networks near me

Question: I'm brand new to the field of pen testing, so please excuse my ignorance and the potential asking of a question that already exists. As I stated in the title, there are times when I run airodump-ng [interface] and no networks are displayed. And to be clear, I do not mean that certain networks show up sometimes and not others; I mean that zero networks are displayed. I am using the Alfa AWUS036NEH network adapter with the Ralink RT2870/RT3070 chipset, and I know of three ways in which to switch this adapter to Monitor mode (excluding code to turn off wireless adapter and turn it back on):

iwconfig wlan0 mode monitor
airmon-ng start wlan0
airmon-ng check kill followed by airmon-ng start wlan0

When I try to use any of these various methods, I get varied results. Sometimes the second approach will work and other times it won't. Same with the other methods.
My question, then, is whether this is normal or not. From what I have found online, the network adapter I am using is not one of the most popular ones, so I'm willing to buy a new one if that's the reason. But knowing that it might just be me not fully understanding how everything works, I was hoping to get some insight from this community.
For what it's worth, I'm using Airbase-ng 1.2 rc4 and running cat /etc/issue shows Kali GNU/Linux Rolling \n \l. Please let me know if more information is needed.
Comment: Yes. Sometimes you just need to... poke... the card first. Some shitty drivers this will cause a kernel panic on though so watch out.
Comment: This isn't normal. I have the same card as you and I have a script with this card which starts it up in monitor mode on boot (raspberry pi monitoring station). Have you tried just doing `ifconfig wlan0 down; ifconfig wlan up` before doing any of this?
Comment: I have not. Is the suggestion to then do: `ifconfig wlan0 down; ifconfig wlan0 up; ifconfig wlan0 down; iwconfig wlan0 mode monitor; ifconfig wlan0 up`?
Answer: Try running airmon-ng first followed by airmon-ng check kill. If that does not work try killing the processes manually by typing kill [pid of the process]. And if all that does not work try "rfkill unblock all", this will unblock your adapter if it was being blocked by the firmware as it is not a very famous adapter and may not have the proper drivers installed.
Try all of the above methods and if all of them fail then your adapter may not be compatible or may partially be compatible, i suggest getting a TP-Link WN722N v-1.0. It is a budget adapter and i personally use it besides alfa adapters. Make sure you get the v-1.0 because v-2.0 is not compatible.
Comment: Welcome on the Security SE! Note, all capital nicks don't look very well, I suggest to become simply "The Yogovo".
Answer: I would suggest using Kali 2018.2. I could not find anything with a clear solution, but the RT2870/RT3070 chipset appeared not to be compatible with the Linux kernel a year ago, and only had closed source drivers. Kali Linux 2.0 Compatible USB Adapter Test and issue with RT3070 chipset may give perspective.


Annoying shrill outgoing Facetime ring tone

Question: Is there anyway to stop the FaceTime ringtone heard on an outgoing call? I have tried the iPhone mute button and FaceTime mute icon with no success.
Answer: No, this is not possible without switching output device to another connected device which is muted, such as a bluetooth speaker or car stereo, or jailbreaking to delete the audio file from the filesystem.
Answer: You can't actually mute it but you can reduce to a very low level, simply with the volume buttons. It will remember your settings for future calls.
Answer: Use earphones whilst it's calling and when it's connecting take them out.


Find out the bottleneck for windows remote desktop server (Terminal server)

Question: I have Windows server 2008 R2 (SP1) installed on my VMware Host to work as RDS server. Sometimes my remote users can see the lagging/delay on RDS server. Can anyone tell me from their experience what are the best practices to find the bottleneck for this server?
Comment: What have you done to try to track down the latency?  Are the clients on a local network? Network equipment composition? Do they all lag at the same time? Server resources; processor(s), RAM, disk? Performance monitor? Client versions, extension, RemoteFX?
Comment: If you are running a TS, as a VM, then how many virtual CPUs did you assign?  You may be better off with multiple VMs with a smaller number of CPUs.
Comment: Thank you for the suggestions. I have not done anything to track down the latency. Will try to figure out step by step...
Answer: As Chris S mentioned, there are several things that can contribute to poor remote desktop performance. From my experience, these are the main causes, in order of likelihood.
Bandwidth
The #1 cause of poor performance with remote desktop is lack of bandwidth. Depending on exactly what is being done, a session can use anywhere from a a few Kbps to a few Mbps of bandwidth. My own tests have shown that scrolling through a PDF will use up to 3 Mbps. As available bandwidth decreases, so does perceived performance.
You first need to determine the bandwidth needs of your application. This requires testing in a controlled LAN environment, then measuring the bandwidth use as you perform normal tasks. I personally had success with NetLimiter on my personal workstation. You can also approach the problem from another angle, and use NetLimiter to force your connection speed down to whatever your WAN connection is rated at. This should give a good indication of what your remote users are seeing.
Once you know how much bandwidth your application wants, you need to determine whether it is the limiting factor. First, measure the available bandwidth between the client and the server. An excellent tool for this is iperf. I'll assume that you have sufficient bandwidth available during a controlled test.
Next, you will want to set up some kind of bandwidth monitoring to see whether user-reported problems correlate with spikes in traffic or other undesirables. My preference is to dump traffic from a switch or router into ntop, as it provides useful realtime and historic reports on bandwidth usage.
If you're encountering bandwidth problems, one easy change is to change the "Experience" settings on the remote desktop connection. Disable visual styles and animations, and many desktop operations will seem magically faster.
Latency
Another common issue with remote desktop connections is latency. There needs to be a reasonably quick round-trip time between the client and server, or people will be able to perceive a delay. As a rule of thumb, most people start to notice problems between 50 and 100 ms ping times.
Luckily, this is usually easy to diagnose. You can set up monitoring tools like SmokePing or PRTG Network Monitor to provide reports on the latency between your monitoring server and any other arbitrary host. You can even just use the built-in ping -t command for short sessions. Normally you want to locate the monitoring server on the same LAN as your remote desktop server, then set up monitoring against both the server and your clients. Try to correlate problem reports with incidents of high ping time.
If you're having problems with high ping times, use traceroute to find out where the delay is being introduced. If you determine that the problem resides within your own network, consider introducing QoS filtering to prioritize realtime traffic like Remote Desktop.
Also, be wary of anybody who is connecting over a wireless medium, whether that is 802.11 (WiFi), or worse, a satellite connection. Wireless connections are prone to environmental interference that can cause extreme latency problems under various conditions, and for varying periods of time. And using remote desktop through a satellite always sucks.
Local CPU or memory
And finally, it's possible that your server is simply overburdened. Monitor the CPU and memory usage, especially during peak hours, to ensure that the server is capable of meeting requests in a timely fashion.
One of the tools mentioned above (PRTG) can be set up to monitor CPU and memory usage of a server over time, and can produce graphs that make it easy to correlate problem problem reports with specific faults.
Bonus tip: If your users are having trouble typing, especially with regard to modifier keys not applying properly, try changing your keyboard settings on the Remote Desktop connection shortcut so that Apply Windows key combinations is set to On the local computer.
Comment: Nice answer. I manage a farm of 20 TS servers and the 2 most common causes of performance problems that we see are the 2 you listed first in your answer: bandwidth and latency. These 2 factors have the greatest impact on performance (or perceived performance) in my opinion. My own testing showed that a user running several Office applications, IE, and opening PDF files consumed an average of 100Kbps over an 8 hour period. That's what our planning number is in terms of bandwidth allocation per user and that's what we recommend our customers have in order to have "well performing" sessions.
Comment: Hi Nic, Thank you very much for the nice detailed answer. I will go through it and will try to figure it out.. Thanks a bunch for the answer. Thanks to Joeqwerty also for comments..
Comment: I manage a small farm and I agree. We also use PRTG to look at see if historic data matches reported issues. Our number two issues are bandwitch (local/ISP issues) and CPU (bad programs on low core count servers). The best way to quickly see if it bandwidth is to ask the users if text input seems to lag.
Comment: You mentioned a lot of great tools, but how much of a sessions bandwidth requirements can be gathered through WMI? or even better performance counters?  I'm new to TS, but been tasked to surface various stats on a session. Thks in advance for your time.
Answer: Check out the RDS Best Practises Analyzer.


MapInfo to layered pdf with linked layered legends

Question: I am trying to make a layered pdf of Rock geochemistry thematic map from MapInfo of several different elements on same base so I can present a clean 1 page pdf map with the ability to view or unview the different elements values with the appropriate legend with one click.  I get it all to work except the legends will not come in as separate layers attached to proper map. Can anyone help?
Answer: I came across that issue, too, a while back.
I don't think MapInfo Pro links the legends to the layers in the map in the PDF. So there's no way to hide the legend for a single layer when you turn that layers visibility to off.
You will have to view all legends all the time.
The only possible solution that comes to my mind is to have multiple maps each with one thematic map in the layout.
This would make it possible to show/hide the individual maps in the PDF


How many databases can SQL server express handle

Question: I'm running a SQL EXPRESS 2005 server currently hosting ~50 databases. The databases serve clients' CMS/eCommerce websites. The connections are to a single instance, no user attached instances are being used. Median DB size is 5MB, the largest 20MB. The website are mostly low traffic, the CPU utilization is < 10%, and the SQL process uses at most 350MB RAM.
For now I'm well within the SQL server express limits of 1CPU/1GB RAM. In the upcoming expansion the number of databases may double. If I assume linear growth in requirements, the 1GB limit still wont be reached. But I'm concerned the number (> 100) of databases may become an issue. I'm not sure if this usage scenario is what Microsoft had in mind for express.
Is there any information or preferably real-world experience regarding SQL server express capability to handle lots of small databases? Can I expect it to run 150 databases, or should I start working on migrating to other database servers/file-based databases?
Answer: That answer is NOT true. SQL express will use one CPU as per socket. This means ALL cores are used. It clearly states this on the licensing schemes for SQL and on the SQL express page, here: http://support.microsoft.com/default.aspx/kb/914278 Therefore all cores will be used and if the chip uses hyper threading all those will be used also. It is limited to only one PHYSICAL CPU regardless of cores and multithreading.
Answer: Not real world but...
According to Beginning SQL server 2005 Express database applications By Rick Dobson
"The maximum number of databases per database server is 32767"
The 1GB memory restriction would be my worry.  I am sure there is someone out there running express with over 100 db's, hopefully they will read this.
Answer: There isn't a limit to the number of databases, however there is a 4GB per database limit.  Although how you're getting by without the SQL Server Agent is beyond me.  My guess is that you're going to run into the memory limit before you run into any SQL server limit.
Edited to add

The 1 GB RAM limit is the memory limit
  available for the buffer pool. The
  buffer pool is used to store data
  pages and other information. However,
  memory needed to keep track of
  connections, locks, and so on is not
  counted toward the buffer pool limit.
  It is therefore possible that the
  server will use more than 1 GB in
  total, but it will never use more than
  1 GB for the buffer pool. Address
  Windowing Extensions (AWE) or 3 GB
  data access is not supported or
  needed.

From here.
Comment: I'm using ExpressMaint + Windows Task Scheduler as lame substitute for Agent.
Comment: Please note: These days the db limit is 10GB, and has been for a few editions now.
Answer: According to the SQL Server 2005 Express edition overview:

there are no limits to the number of
  databases that can be attached to the
  server.

So, the limit is how much performance you can utilise of the server. Consider that as the express edition will only use one CPU core, if you have a quad core processor it can not use more than 25%.
If you later on find that you need to utilise more of the server's performance, you can quite easily upgrade to a different version of SQL Server.
Comment: interesting, this KB article contradicts the link above, stating that it will use multiple cores of a single physical cpu. "On a computer that has a multiple-core CPU, SQL Server 2005 Express Edition starts a separate scheduler for each core." http://support.microsoft.com/kb/914278


Monitors used for Recording IRs for Small Objects.

Question: I know you can record IRs with transient sounds but since recording the sine sweeps is the best way to go about I was wondering if playing the sine sweep through small computer monitors work in case I am recording IR for a wine bottle or a tin can etc.? Or do I need to have a professional set of monitors to play it? Will the choice of monitors have an effect on the final IR? I haven't recorded IRs before and I am planning to record a few soon. So wanted to be sure before I started.
Thank You.
Comment: I believe a majority of smaller object based IRs are created without sweeps, simply by striking the object and using the hit as an IR. I imagine a smaller speaker will impart a bit of a pinched sound on the results, but I'd be curious to hear about your results.
Answer: Yes, the choice of speaker will definitely have an impact on the resulting IR. You can think of your speaker as a filter in the signal chain; all irregularities in the frequency response of the speaker will be present in the final IR as well. Distortion will complicate the matter even more. That's why Altiverb has different import settings depending on what speaker or slate you used to record the sweep or impulse -- they analyzed sweeps/impulses from those sources and are therefore able to compensate.
That, however, doesn't mean that you can't get awesome results with less than stellar speakers. It just means that the IR will not be a faithful representation of the space (unless you compensate for it, as Altiverb does).


Substance below Critical Temperature but above Critial Pressure

Question: I know that above the critical temperature and pressure, at the boundary between the liquid and gas phase disappears. But does this also hold when temperature is below critical temperature but pressure is above critical pressure? Or do we observe a different phenomenon?
Answer: If the temperature is below critical temp and the pressure is also below its critical value then there is a possibility that we see an equilibrium between the liquid and gaseous states.
When one of them is above their critical value it is impossible to change the state of the substance from gas to liquid by merely changing the other parameter. For instance if $T > T_c$, then no matter how much you try to increase the pressure, the gas will not liquefy. Similarly if $P > P_c$, you can't have a gas-liquid equilibrium in any temperature. It's clear from the given picture.
Comment: So for the case in my question, will the substance exist as a gas or liquid?
Comment: It will be a liquid, if the volume is small. If you increase volume it will suddenly become gas.
Answer: I insist you look at the P-T curve of the system. Below Tc and above Pc is not beyond (Pc,Tc). So you are in one of the phase(liquid in this case).


What is the maximum number of rows a fast lookup in a flow can return

Question: I can't find it in the docs, but there has to be a maximum. In a salesforce flow, what is the maximum number of records a fast lookup can return. What happens if the number is higher than the max?
Comment: This doesn't seem to be explicitly mentioned in the documentation as I have tried going through the Developer docs. I suspect it will be linked to the Apex limitation on the maximum heap size or the SOQL limit of 50,000 rows https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_gov_limits.htm#total_heap_size_limit_desc
Answer: I just tested this, and there's no limit for the number of rows a Fast Lookup can return directly, but you are bound by the governor limits in Apex Code and Visualforce: heap size, query row limits, query limits, view state size, and CPU time. Attempting to update those records may also run into other limits, such as the DML statement limit and the DML total record limit (plus any of the previously mentioned limits).
Comment: Thanks and it turns out that looping through them the most likely limit that will be hit is:

Maximum number of executed elements at run time 2,000

so it's very likely less than 2000 rows that can be handled and dependent on the complexity of the flow. The more complex, the lower the number of rows that can be handled, rendering it only useful for very simple cases, anything else is better off as a trigger.
Comment: @ScottMorrison Mostly true. However, every "screen" is a separate transaction, which is how you could still process more than 2k records (I've actually built something like this), but then you still risk the other limits, depending on how it's laid out.
Comment: If it's an auto-executing flow triggered from process builder there aren't any screens so in that case everything appears to be in the same transaction
Answer: It's a bit late to be chiming in on this, however, I'll comment in case anyone finds this thread in the future.
If you are in an auto-executing flow, you can put in a wait element and that will reset the transaction counter the same as a screen will.


Can the test set of attributes be a subset of the training set's attributes?

Question: I'm currently writing an application for a trick-based card game, where agents are assigned points based on the accuracy of their predictions of how many hands they're going to win. The number of tricks predicted will display a level of confidence to the other agents as well as also potentially allowing the agent to choose the Trump suit.
I've compiled a set of attributes (such as cards in hand, score sum total in hand) that will be useful in the prediction, but it would be ideal if I could include previous predictions in the training set.
My question is can my test data [attributes] be a subset of the training data [attributes ∩ predictions] both of which are predicting the number of hands that the agent will win?
Comment: If you train your classifier on properties not actually available when applying it, then you might run into problems.
Answer: Well, if the test data would be the same from training data, your machine learning algorithm may overfit. Because you test your model with your training data it may perform very well, as it may see the pattern even in noise. And then it won't generalize on new data.
You should separate the test data (with which you see the accuracy) to the training data.


Pyramid with reCaptcha: how to implement?

Question: I want to add the most popular captcha client on my site - reCaptcha.
But I didn't found any examples or tutorials in internet...
Maybe somebody knows how to do it?
I'll be very appreciate for any help!!!
Answer: There is full API documentation available for reCATPCHA here. It probably has sample code, too.
I found this by going to the reCAPTCHA website and clicking on the FAQ link.
And of course, you sign up for the service here. That's pretty obvious from the home page.
Comment: Yes, I did it within 2 hours! Thanks!
Answer: You need to do two things:
1) Display the widget on your site. Copy the html and javascript code on this reCaptcha documentation page.
2) Validate the user's response. You can use the python client for this.
There is an example on how to use this in this stackoverflow post.
Good luck!


What's the role of bromelain in pineapple?

Question: Bromelain refers to one of two proteases found in pineapple and its relatives. Like other proteases, many believe it has therapeutic uses and it's the subject of a lot of research. But what role does it play in the pineapple itself? Why does pineapple (or papaya, for that matter) generate large quantities of protease when other plants do not?
Answer: Antifungal properties? as tested in below article.
López‐García, B., Hernández, M. and Segundo, B.S., 2012. Bromelain, a cysteine protease from pineapple (Ananas comosus) stem, is an inhibitor of fungal plant pathogens. Letters in applied microbiology, 55(1), pp.62-67. Available here
Comment: @PolypipeWrangler Please reread theforestecologist's comment, this is site policy not one person's opinion. Link only answers are frowned upon and decrease the quality of StackExchange. An answer doesn't need to become "long" to include more than just a link.
Comment: Please cite scientific papers fully using a formal citation guide. (Google Scholar does all the work for you if you want): see [here](https://scholar.google.com/scholar?hl=en&as_sdt=0%2C36&q=Bromelain%2C+a+cysteine+protease+from+pineapple+%28Ananas+comosus%29+stem%2C+is+an+inhibitor+of+fungal+plant+pathogens%22&btnG=)
Comment: Citing is absolutely necessary here, so thank you for pointing toward a reputable study (though see my comment above and my edits). However, posts citing other's work need to summarize, quote, or otherwise explain the rationale for including the citation (especially if no further explanation is provided as part of the answer). Answers on SE need to be complete in and of themselves -- as in someone 5 years from now should be able to view your answer and feel like they had the question adequately answered without needing to leave the site. External links and citations can be for further reading
Comment: I thought the name of the paper was a good answer already, didn't want to waste peoples time reading long answers.


Identify vintage bicycle brand

Question: I don't know much about bicycles but I came across one that I want to offer to my nephew since he is into vintage race bikes. I would like to know the original brand of the bicycle/frame since I want to replicate it with the right decals. I was told the frame tubes are Reynolds 531 and from the equipment (Mafac, Simplex, Belleri) I assume the bicycle is probably French from the 70s after several searches enter image description here. Thank you in advance for your help.
Comment: It's a nice looking bike! The better French bikes from that era usually Vitus tubing for frames, the better Italian frames usually used Columbus, and the British and U.S. bicycles generally used Reynolds 531 tubing. This bike has been repainted. Reynolds stickers can be purchased or made. The sticker is not a reliable indicator for what the frame is made of. Parts are interchangeable and are not a reliable indicator for country of origin, date of manufacture or manufacturer. If there were some unique characteristic of the frame - dropouts, lugs, construction - we might get a match
Comment: If a conclusive answer doesn't turn up, then avoid guessing.  Instead leave it bare, exactly as-is, or if you must dress it with decals, get your nephew's name as a water-transfer decal and use that on the downtube. I'd appreciate the personal touch.
Comment: The threading of the bottom bracket may be an indicator for French, Italian or British origin, although not to be taken for an absolute truth.
Comment: Late 1970s, but fairly generic for that era.
Comment: It would be great if you could post details such as the BB threading, the brand of dropouts, and the seatpost size. The seatpost in particular is a good indication of the quality of the tubing. You might also consider posting in the classic and vintage forum on bikeforums.net. There are many vintage bike experts there who can identify frames based on lug patterns and tubing.
Answer: Not particularly fine lugwork. Look like Prugnat lugs, but not S4s. Fork crown isn't too finely filed either. Can't tell the brand of ends from the shots. Straight brake bridge with no tangs at the stays. Can't see BB very well at all. Nor chainstay bridge. Is Campag brazeon cable guides? Can't see. Are forks replacements? Does the fork raking look like it's cheaply done? Match the quality of the lugwork? Fork ends match the stay ends? What else could narrow down its country of origin?
Comment: Might most of this be better as a comment?  There's just the lugs info, and the rest is all requests for clarifications.

Identify vintage bicycle brand


Nexus 4 Notification bar unresponsive

Question: My notification bar has suddenly become unresponsive. I have been unable to swipe down the bar no matter the orientation of my phone (regular and in landscape). I've played around with chrome to test the touch screen responsiveness and everything works fine. Is there a way I may have accidentally turned my notification bar off? Has anyone had this issue and know how to fix it? Thank you!
Comment: @Izzy Even if it does not persist after reboot, that is a relevant bug. I have experienced it with my  3 days old Nexus 4. Maybe it's worth to file a bug report
Comment: Does that unresponsiveness persist after a reboot? Maybe some service went havoc.
Comment: @mdelolmo Agreed, if you can reproduce it. But here's the wrong place for "bug reports", as we cannot fix them. All we can do is help to figure out, and find possible work-arounds :)
Comment: Many owners of Nexus 4 experience this problem. See: https://productforums.google.com/forum/?hl=en#!msg/mobile/3g6ZnYxKl_w/yhGAvDt1uGcJ
Comment: I experience it from time to time; quite annoying.
Answer: Try doing a hard reboot (Power off the phone and power it back on). I had this problem just two minutes ago and that seemed to resolve it. Cheers!
Comment: This solves the problem for some users but not all. My friend who also has a Nexus 4 is able to solve it with a reboot, but it doesn't help on my phone

Nexus 4 Notification bar unresponsive


Do bigger telescopes equal better results?

Question: There are many large reflecting/optical telescopes around the world, just to name a few: the Very Large Telescope, Large Zenith Telescope, and European Extremely Large Telescope.
My question is does actually building larger telescopes improve visibility of the universe, quality of an image, and various other attributes of a telescope?
Well it does seem kind of obvious that a larger telescope may have more magnification and better imaging, however if that is true than why don't we just build a super large one (think really really big, unlike the size of the current large ones) so we can see the universe in HD - so to speak?
Since we haven't done this yet (I think) is it because of financial issues or is it because simply building a bigger telescope won't improve much to visibility and image quality?
Comment: I'm not really into telescope building plans, but much of the work leading up to deciding whether or not a given telescope should be built is done by people who both have other duties, and who are employed for typically two years before moving on to something else.
Comment: @kiilkid: The Giant Magellan Telescope has 7 mirrors which are spin-cast. There is one facility that can make them and it seems to take about a year to get a cool, finished mirror blank. Then it needs to be ground and figured. Ignoring the first mirror which took 7 years because it was the pathfinder, it looks like it will take ten or so years to cast and figure the other six (plus one spare).
Comment: Side note: The European Extremely Large Telescope isn't really a telescope yet. It won't have first light until in ten years or so.
Comment: Good question. There are practicalities such as foreseeing whether the current technology will be severely outdated by future technology before the telescope is finished, but unfortunately I think it's mostly a question about money and management.
Comment: @pela yes, I've noticed that, also the one their building in South America, I believe its the GMT, won't be done until 2026 (i think). Why does it take so long to build a telescope?
Answer: Magnification is not the main purpose of a telescope. A very small telescope will have a lower resolution than a larger one, but for larger ones, the atmosphere limits the amount of detail visible.
Large telescopes capture more light than small telescopes. More light means that dimmer objects are visible, and there is more light to be analysed. A very dim object, such as a planet orbiting another star, needs a very large mirror to collect enough light to analyse spectroscopically. And this is the reason why larger telescopes are made. Of course larger telescopes cost a lot, and cost is the reason that telescopes like the "Overwhelmingly large telescope" was not built.
Much of the development in telescopes in the last 25 years has been not in ever larger mirrors, but in adaptive optics, or using two telescopes together as an interferometric telescope.
Comment: For some things, bigger is better. But as there are limited resources, there are choices to make. A 100m telescope could do some fantastic things, but I'd rather have a functional JWST (6.5m) than a OWT.  Obligitory xkcd: https://xkcd.com/1294/
Comment: Thank you for your answer. So essentially a larger telescope would be better right? I had a feeling costs played a role and it sucks that it is the reason why we haven't built an "Overwhelminingly large telescope" yet.
Comment: @JamesK how does the Relight criterion play a role here. Say for a large optical reflecting telescope what would $D$ and $\theta = 1.22\frac{\lambda}{D}$ be? More light is one of the reasons for a large mirror, but the resolution should also be affected by it. The focal length $f$ should be also somehow made small, since the spatial resolution is $l = 1.22\frac{\lambda \cdot f}{D}$
Answer: You've pretty much answered it yourself.
Very large telescopes are expensive to build, and there are diminishing returns for large instruments operating under Earth's atmosphere.
Air turbulence (what is known as "seeing") limits the resolving power of the telescope - its ability to distinguish small details and make high resolution images. It's an essentially random phenomenon, so sometimes it gets better, but generally speaking large instruments are more strongly affected by turbulence.
Light pollution is the glow caused by all artificial light sources (city lights, industrial lights), which are making it difficult to see very faint, very distant objects. It is drowning the faint objects in artificial glow.
The bigger the telescope is, the better its resolving power, and the better its light gathering ability (the ability to see faint objects). But seeing and light pollution are affecting both. You could fight seeing with adaptive optics, with decent results. You could fight light pollution by installing the instrument far from cities. Or you could fight both by launching the instrument into space.
All these solutions cost money. Large instruments are expensive. Adaptive optics are expensive. Running an observatory in the middle of nowhere also adds costs. Finally, launching things into space is not cheap either.
However, each one of these methods is used in one case or another. For each kind of application, astronomers need to make a decision for what methods they could use to improve performance, and then match that up with the money available to the project. It's a complex overall decision that takes a long time, lots of discussions, often politics gets involved, etc.
So what gets built is a compromise between what astronomers want, and what is actually doable from a financial, political, and technological standpoint.

BTW, "magnification" is not a parameter that astronomers use to define an instrument. Any instrument can give you any magnification you want - just use a different eyepiece. The relevant parameter here is the resolving power - the ability of the instrument to distinguish fine details. This depends on the instrument size - the diameter (or "aperture") of the telescope. Bigger scope = better resolving power (all else being equal). As I said above, seeing (air turbulence) is a major limiting factor here.
Answer: I'd like to add more inputs on the physics behind telescope resolution. The telescope resolution is given by its primary mirror size which produces a "quasi" punctual image for each light source it sees, that is called a airy disk. The airy disk size is inversely proportional to the telescope primary mirror diameter and like pixels on a LCD screen the lower the pixel size the better the resolution. However, the limiting factor on the ground is the atmospheric turbulence, this is why huge telescope of few meters wide cannot see better than a 500mm amateur telescope resolution wise (see Fried parameter). So in order to reach the telescope full resolution potential we need to build adaptive optics or better we could send the telescope to space.
Comment: Keep in mind that atmospheric turbulence is a random phenomenon. Under normal conditions, a very large telescope cannot see better than a smaller one - however, periods of calm occur randomly, and therefore the image could improve dramatically once in a while. Of course, it's not entirely predictable when this happens. So, yes, adaptive optics or space based telescopes are the true answer to this issue.
Comment: You are right Florin this is why lucky imaging technique can be used to grasp these elusive moments of stable air flow. Still larger telescope are more affected by turbulence than smaller ones, just imagine how chaotic looks a tiny airy spot shaken by air currents compared to a larger one.
Answer: BIG Telescopes afford two luxuries
More refined mirrors spread over a larger area permit Greater image resolution. They capture MORE light, even the faintest weakest light.
And being bigger means the telescope get's more comprehensive views of the night sky.
Answer: Just a small supplementary -- there is no point in building a larger telescope unless you can manufacture a mirror that big without any kind of flaw or deformation and then mount it so that it doesn't change shape as you point it in different directions. This is a whole pile of really hard engineering problems which have also limited the size of telescopes that could be built at various times, or at the very least shifted the price-performance tradeoff.


Visual Studio Full Screen Mode

Question: Is it possible to remove VS's menu from the full screen mode  Shift + Alt + Enter
Answer: Microsoft released this extension that hides the menu bars.
Answer: Someone else found a way to do it, but it apperently was buggy:
http://www.vbdotnetforums.com/ide/34228-real-fullscreen-hide-menu.html
Maybe follow the Microsoft link and see if the bug was fixed, or try the code again in the newest versions of VS.
Edit:  Also, this is probably not what you are wanting, but if you didn't know, you can double click an opened file's tab, making it a popout window, then double click it's title bar again and it will fullscreen just that file.  There is no menu, but the bar at the top still exists.
Comment: thanks.  It's too bad there isn't a native VS setting for hiding menus like in SharpDevelope.

Visual Studio Full Screen Mode


What other pairs of wars have had a ~25 year interval?

Question: The I and II world wars are 25 years apart, which is within the length of one generation. This is interesting, because it creates a premise for an entire part of a generation to be both without fathers and grandfathers. Have there been other wars separated by the length of one generation (20-30 years)?
Comment: How exactly did you measure that 25 years between one war and the second? If you count 1914 and 1939, then it would still be 25 years even if WWI lasted for two decades...
Comment: First, it is difficult to say that these wars had a ~25 year interval of peace between them.  Many of the countries that fought in WWI and WWII fought in wars between that time, both in their colonies and within Europe (the Spanish Civil War, for example). In general, even when isolating by country it is difficult to make such clear cut delineations.
Comment: Marshal Foch on Versailles: "This is not a peace. It is an armistice for twenty years". The point here is that the end of WW1 didn't resolve the reasons for conflict. However, this question seems like it's just concerned with time proximity of wars, rather than that type of relationship.
Answer: There were plenty: E.g. the Austro-Prussian War (1866) and the Franco-Prussian War  (1870–1871) form such a pair. Obviously Prussia (soon to become center of the German Empire as proclaimed by Wilhelm I in 1871) participated in both.
As a European who has been born in the 1960s I rather often comment to my friends that it has been extraordinary good fortune for us members of an  generation that hasn't had to witness war (from up-close) during their lifetimes (keeping fingers crossed.) I give credit partly to the shocks of the two WWs (on the destructive side) and the developments leading up to the founding of the EU (on the constructive side) each.
UPDATE: I now realize that I have answered a slightly different question by mistake, i.e. one for pairs of wars with a time span of 25 years or less (sic!) in between. Sorry for that.
Answer: How about the Punic Wars? The first war was 264 to 241 BC. The second was 218 to 201 and the third 149 to 146. There were 23 years between the first two and 52 between the last two.
Answer: What about three generations in a row?
From the series of Polish-Teutonic Wars that took place between 14th and 16th century, I would refer to three periods of time. 1409-11 (with the Battle of Grunwald, which was one of the largest military engagements of medieval Europe) during the rules of Władysław II Jogaila, then a generation later, 1431-35, at the end of his reigns, and finally another generation later, Thirteen Years War (1454-66), in the times of Casimir IV Jagiellon.
Answer: The French Revolution begun in 1789 and the Battle of Waterloo was 1815, 25 years later. I think you could also find many examples during Hundred-Years War.
Also crusades can be set in 10-30 year steps:

2nd (1150)
3rd (1190)
4th (1202)
children's (1212)
5th (1220)
6th (1230)
7th (1250)
8th (1270)

(dates rounded, full list eg. in Wikipedia)
Answer: The French Revolution (begun in 1789) happened around a decade before the Napoleonic Wars (late 1700s-1814). That's a clear case, too, of the one leading to the other, as the instability surrounding the Reign of Terror and so on led directly to Napoleon gaining power in France.
One could argue that there's a similar link between the Russo-Japanese War of the early 1900s and the Great War, as it demonstrated that Russia was weak and could be taken. As with the French Revolution / Napoleonic campaigns, though, that might be too close for you, as you had more or less the same cohort fighting in each instance.
My other example was going to be the Punic Wars, although those too have already been mentioned. If ever one conflict led to another...
Comment: France was at war almost without interruption between 1791 and 1815.
Answer: In the U.S., the French and Indian War, 1754-1763 was about one generation ahead of the American Revolution 1776-1783. If you take the Texas Revolution of 1836 as the "start" of the Mexican-American War, the 1836 start was 25 years ahead the Civil War (1861-65).
The argument is that the earlier wars "incubated" the later wars, as some historians believe was the case with World War I and II. The French and Indian War caused the taxation (and set up a potential alliance with France), that led to the American Revolution. And the wars of Texas and America against Mexico sharpened the slavery issue, helping to incubate the Civil War.
The "third wars" in these sequences were the War of 1812 after the American Revolution, and the Korean War after World War II. There was no "third war" after the Civil War because of the  exhaustion of the Americans.
Comment: What aboutnthe Cuban War?
Comment: @FelixGoldberg: I could consider that a precursor of the NEXT cycle (World War I, World War II, Korean War. The Spanish-American war was also associated with the Philippines and Asia. In any event, Cuba was "offshore" the U.S., not part of the north American continent. Nor was it part of the slavery debate.
Comment: The Indian Wars were the follow on to the Mexican-Civil-Indian war cycle, determining how the United States would develop west of the Mississippi.


plsr output RMSEP increasing as number of components

Question: I have a dataset with 20 rows and 480 columns. When I run plsr command with validation="LOO" my output shows RMSEP or CV is increasing with number of components and stabilizing after 6 components. My impression is that RMSEP should decrease. Confused! Help!
Answer: You are right, generally RMSECV is supposed to decrease first, followed by stabilization or increment or very slow decrement. If you are observing a steady increment of RMSECV starting from first component, it is likely:

Your dependent and independent variables are not linearly related to each other(enough).
You have insufficient number of observations to reveal the relationship between dependent and independent variables.
You really need only 1 component to model the data.
Comment: Thank you! Looks like I need to investigate at least (1),(2) and (3) above. However, in terms of variance capture it looks as though I need about 7 components (captures 99% of variance) and RMSEP is stabilizing at this point. I know my sample size is very small - but gasoline has almost similar sample size. I think I shall try non-linear first.


Do the benefits of ridge regression diminish with larger datasets?

Question: I have a question about ridge regression and about its benefits (relative to OLS) when the datasets are big. Do the benefits of ridge regression disappear when the datasets are larger (e.g. 50,000 vs 1000)? When the dataset is large enough, wouldn't the normal OLS model be able to determine which parameters are more important, thus reducing the need for the penalty term? Ridge regression makes sense when the data sets are small and there is scope for high variance, but do we expect its intended benefits (relative to OLS) to disappear for large datasets?
Answer: One thing that you might be overlooking with your reasoning is the fact that increased predictors does not necessarily lead to a better model. In this case, the more predictors you have the higher the risk of collinearity that there is between them - thus increasing the utility of ridge regression.
In fact, a second point:
The larger the number of predictors that you have in your model the more useful techniques like ridge regression are. This is because with so many predictors it is very difficult to determine if collinearity or other relationships exist between predictors. When you have a smaller model with say 5 predictors, you could verify this fairly easily. With 1,000 predictors this would be much more difficult.
In the case of the Lasso regression, the benefits are even more obvious. Since predictor coefficients values can be shrunk fully to zero this acts as a form of feature selection. Here, you are potentially removing predictors that capture redundant information.
Also - in answer to the second part of your question - OLS does not perform any form of feature selection. Therefore, it will not be able to pick out which parameters are the most important by adding more. The more parameters you add to your model the higher the variance gets. Why is this? You have more estimations to make and therefore collectively your model is less reliable. Consequently, your model will likely inflate the coefficients on the predictors giving undue "weight" or importance to certain predictors.
Comment: Okay thank you very much! (I would upvote the post but I do not have enough reputation)
Comment: Thanks for this response. When I said 'larger datasets', I was referring to number of data points rather than parameters. You are correct that OLS doesn't have feature selection. Generally speaking, for a dataset of size 50,000 (with ~10 parameters) would we still expect ridge regression to outperform as significantly as it might to with a dataset of size 1,000? Thanks for the help!
Comment: I think a generalization in this regard is somewhat difficult to draw as it will depend on the data that comprises each of the data sets. I would say that depends. If you have a data set or 50k intuition would suggest that we might get a better fit, however since OLS is at high risk of being effected by outliers perhaps if there are many present in that data set the fit will be worse. If the dataset of 1k however follows a linear pattern almost exactly the fit might be better.
Comment: Consequently, it would be difficult to say whether ridge regression would or would not perform better in either of these cases without trying it both ways to see.


Restorable-from-scratch Backup of Windows XP onto backuppc

Question: How can I take reverse-incremental backups into backuppc of Windows XP machines?  These need to include state information, open files, etc a la VSS (the disk access method, not Source Safe) / shadow copy.  We need them to be restorable from backup and programmatically transformable into a bootable XenServer image.  This is for continuity.  The systems are running MS SQL Server, SQLLite databases, java apps, Access-database-using apps, etc, serving files over the network, leaving tons of files open at once, etc.
Comment: What is a reverse-incremental backup?
Comment: See Wikipedia under incremental backup.
Basically, the most recent one is the full backup, and backups before that are incremental going back in time.
ON UNIX, ie backuppc, backup is done even better.  Everything is a full backup, but duplicates are removed via the filesystem.
The backups are usually stored on disk using hard links so that the exponential backoffs (12h, 24h, 2d, 4d, 8d, 14d, 4w, 8w, 16w, 26w, 1y, 2y) are ALL there and appear complete.
Comment: Seriously, no answers?
Answer: As stated on the official BackupPC documentation, you can't have backup suitable for bare metal restores.
This is for two reasons:

BackupPC backups only files, no other disk information, like partition tables o mbr, so your disk layout is not saved.
BackupPC does not backup Windows ACLs, so your NTFS file permissions are not saved

I'm looking for a similar solution, and the best options that I have found are:

Use a VSS approach as described at BackupPC Wiki: User Scripts - Client - Windows VSS - backuppc
Use this old unmantained Windows Client, that states to be Windows specific: Keene Enterprises :: Open Source :: BackupPCd
Answer: Windows Bare Metal restore is possible with backuppc, but is not a direct option for it... it's just taking a full backup made with VSS and restore to a HD and recover that HD to boot.
I boot from a linux live CD, build the partitions and filesystem, restore all files, boot from a windows liveCD (like hiren's CD), restore the acls with SetACL (http://helgeklein.com/) and fix the MBR and fix the boot.ini. After this, you take a black chicken, offer it to the your god, dance around the room, pray and reboot. then start fixing if something fails :)
if you start from a already installed windows and replace the files, its usually easier
This is also another method, its the same restore, but using windows, instead of the linux.
Check this site for more info:
http://www.goodjobsucking.com/?p=219
Yep, windows is hard to restore, compared with linux :)
What i recommend is to use the drive snapshot (http://www.drivesnapshot.de/en/) to build windows images (bare installs or up-to-date backups)  and restore then with the static-restore-only snapshot for linux, using a live CD and then restore any changes file i need from backuppc


How do i get a hedge to thicken and fill out?

Question: The lower part of the hedge is thin and bare, ie bare branches. The top is flourishing with new growth.
Comment: Hi Chris, a picture that shows what plant the hedge is made of would help and your location.
Comment: If a hedge is only pruned at the top, essentially all growth will be at the top. Sounds like improper pruning.
Answer: At the level of detail provided in the question:
Narrow the top so the bottom gets sunlight.
However, depending on the plant, that may be "too little, too late" to actually bring back where branches have died back to the trunk, in which case the answer is to replace with new plants and keep them trimmed "narrow on the top" to keep them in active growth on the bottom.
Hedges which are vertical or spread outwards on the top do tend to die out on the bottom, primarily due to lack of light.
Comment: Yes, two basic principles: 1) hedges get denser if they are pruned frequently; 2) hedges die off at the bottom if they aren't significantly wider at the bottom than at the top.
Answer: I was wondering if you have tried epsom salt on or around your hedges? With pruning it regularly, this could be a sufficient filling for your shrubs!
Comment: Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer).


Kahler structure on flag manifolds

Question: Does every complex flag manifold have a natural Kähler structure? If so, what is it?
Comment: Surely the question is only about *complex* flag manifolds.  The real flag manifolds are not even hermitian.
Comment: Yes, of course. I've put this in the question.
Comment: KKS metric on complex flag manifolds is Kahler. In fact any flag manifold can be seen as symplectic quotient of Kahler manifold. Since the symplectic  quotient of Kahler manifold is Kahler, hence flag manifold is Kahler manifold
Answer: Yes. Use Plucker embedding to embed it into $CP^n$ then restrict Fubini-Study metric.
Comment: More concretely, let $\lambda$ be a dominant weight of $G$, and $V_\lambda$ its corresponding irrep. Then the unique closed $G$-orbit on ${\mathbb P}V$ is a flag manifold $G/P$, now projectively embedded. (Which $P$ arises depends on which wall of the Weyl chamber $\lambda$ lies on.)
Answer: Every flag manifold $M=G^{\mathbb{C}}/P=G/C(S)$ where $P$ is a parabolic subgroup and $C(S)=P\cap G$ is the centralizer of a torus $S\subset G$, admits a finite number of
invariant Kähler structures.  In particular the complex  presentation $G^{\mathbb{C}}/P$
gives rise to an finite number of invariant complex structures (i.e. integrable almost complex structures  commuting with the isotropy representation of $M$).  Any such complex structure is determined by an invariant ordering $R_{M}^{+}$ on the set of complementary roots
$R_{M}=R\backslash R_{K}$ of $M$ and explicitly is given by
$$
J_{o}E_{\pm \alpha}=\pm i E_{\pm\alpha},   \quad a\in R_{M}^{+}
$$
where $E_{\alpha}$ are root vectors with respect a Weyl basis of $\frak{g}^{\mathbb{C}}$.
On the other hand, the real presentation $G/C(S)$ makes $M$ a (homogeneous) Kähler manifold,
as a (co)-adjoint orbit of an element $w\in\frak{g}$ in the Lie algebra $\frak{g}$ of the compact connected (semi)simple Lie group.  Flag manifolds exhaust all compact homogeneous Kähler manifolds corresponding to a compact connected semi-simple Lie group.
To be more specific,  $M$ admits a finite number of Kähler structures which are parametrized by the well-known $\frak{t}$-chambers (connected components of the set of regular elements of $\frak{t}$) where
$$
{\frak{t}} =( H\in{\frak{h}} : (H, \Pi_{0})=0  )
 $$
is a real form of the center ${\frak{z}}$ of the isotropy subgroup $K=C(S)$.
Here $\frak{h}$ is the Cartan subalgebra corresponding to a maximal torus $T$ of $G$ which contains $S$, and $\Pi_{0}\subset\Pi$ is the subgroup of simple roots which define (the semi-simple part of) the complexification  $\frak{k}^{\mathbb{C}}$ (note that $K=C(S)=P\cap G$ is a reductive Lie group).  We have
$$
{\frak{z}}^{\mathbb{C}}={\frak{t}}\oplus i {\frak{t}}, \ \ \ {\frak{k}}^{\mathbb{C}}={\frak{z}}^{\mathbb{C}}\oplus{\frak{k}}_{ss}^{\mathbb{C}}
$$
where ${\frak{z}}^{\mathbb{C}}$ is the complexification of the center ${\frak{z}}$ and ${\frak{k}}_{ss}^{\mathbb{C}}$ is the semi-simple part of the reductive complex Lie subalgebra ${\frak{k}}^{\mathbb{C}}$
In particular, there exists a natural 1-1 correspondence between elements from ${\frak{t}}$ and
closed invariant 2-forms on $M$.  Symplectic 2-forms (non-degenerate) correspond to regular elements $t$ of ${\frak{t}}$.
Note that the corresponding symplectic form corresponding to a regular element $t_{0}$ is   the Kirillov-Kostant-Souriau 2-form in the (co)-adjoint orbit $Ad(G)t_{0}$, that is
$$
\omega_{t_{0}}(X, Y)=B(t_{0}, [X, Y]),  \ \ X, Y\in T_{t_{0}}M.
$$
For more details see: D. Alekseevsky: Flag manifolds (11. Yugoslav Geometrical seminar, Divcibare, 10-17 October 1993, 3-35.
This article is a very good review on the geometry of flag manifolds.
Comment: While the space of $G$-invariant complex structures on the flag manifold is finite, the space of $G$-invariant compatible Kähler structures is only *finite dimensional* in general, rather than finite.  For example, consider the simplest flag variety $F_{1,2} = \mathrm{SU}(3)/\mathbb{T}^2$.  The space $S$ of closed, $\mathrm{SU}(3)$-invariant $2$-forms on $F_{1,2}$ has dimension $2$, and, for each of the $\mathrm{SU}(3)$-invariant complex structures $J$, there is an open set $S_J\subset S$ that consists of Kähler forms compatible with $J$.
Comment: The quoted paper of Alekseevsky is online here: http://elib.mi.sanu.ac.rs/pages/browse_issue.php?db=zr&rbr=14
Comment: Clearly no complex manifold admits a finite number of Kähler structures, unless that number is zero, as you can rescale a Kähler metric.
Answer: The question has already been answered by Bugs Bunny, but I thought I'd point out that there is a nice paper by H.-C. Wang from the 1950s that discusses the complex structure of homogeneous manifolds in some detail. One of the results proved there is that a compact, simply connected complex homogeneous manifold (such as a complex flag manifold) is Kähler if and only if it has nonzero (ordinary) Euler characteristic. That complex flag manifolds have nonzero Euler characteristics follows, for example, from the Bruhat decomposition.

Kahler structure on flag manifolds


I have a leaky shower. Builder thinks a total renovation to bathroom is needed to waterproof whole bathroom

Question: So the builder I got in thinks I should remove shower, vanity and toilet. Basically a renovation of the whole bathroom upstairs to waterproof the bathroom. The leak is obvious that it is from the shower. Is what he's saying excessive?
Comment: How can we possibly answer this? Bring in a second (and third) contractor! Get a second opinion from someone ONSITE.
Comment: Not even a chance without good pictures, but regardless you'll need a second opinion.
Answer: If there is an access panel below the shower you can look for yourself and see exactly where its comming from. If it is just the drain pipe seal it can be resealed without tearing the whole place up. Did the contractor open up the ceiling below the shower?  I agree a second opinion is needed.
Comment: Thanks. I got a second and third opinion.  One from a waterproofer who thinks we can rip the tiles off the shower floor and 2 rows off the sides, put new shower in ($2000). The other one is to do what you suggested Dave which is cut up an access hole in the ceiling and see what it is..etc The ceiling has to be fixed regardless so he thinks to start there and then get plumber to do testing etc..(unknown depends on findings). The major bathroom renovation quote was ($11,000)...I know I don't want to do the major renovation if I can help it.


Coulomb's Law Question

Question: The presentation of Coulomb's Law in various books occasionally has a note that the test charge, q2, must be small enough that it doesn"t alter the field of the first charge, q1. The same limitation applies to a test charge in any other stationary electric field. If those are the facts of life, then fine, but how can anyone confidently calculate the force between two macroscopic bodies, each with its own charge distribution? What are reasonable limits on charge level, physical size, and separating distance? It seems that one could correctly perform any and all required volume integrations and occasionally, if not often, produce invalid results. Moreover, for actual physical charged bodies, won't the electric field(s) alter the charge distribution on those material bodies? Is the solution to these issues simply some non-linear formulation that I just haven't seen yet?
Comment: If you have two bodies with a certain charge distribution, the net force that each body acts over itself is equal to zero due to Newton's third law. In this kind of problems it is usually considered that the charge distributions are fixed (i.e. the bodies are insulators), but you could solve the problem computationally applying the laws you already know.
Comment: I guess I asked two questions at once. Sorry. My basic question is, since Coulomb's Law requires the test charge to be small enough that it doesn't change the electric field from the other charge, how can that Law be of practical use when calculating force values? Also, any formulations derived from Coulomb's Law have the same limitation.
Answer: Some of them could be complicated, if they don't have symmetry. The good starting point is by assuming symmetry. For example, Gauss' law can be used to solve for the electric field due to a sphere, plane charge density, cylinder etc.
These derivations use Coulomb's law as a starting point.

Coulomb's Law Question


Changing fill after Extrude and Bevel, Expand ILLUSTRATOR

Question: In Illustrator, I have an object that is curved and which I created with extrude and bevel, and then Object⇾Expand.
Is there a way to now change the color of the object and keep the shading of Extrude and Bevel tools?
Comment: Probably... but there's no indication of what *software* you are using.
Comment: @Scott sorry, first post
Answer: If you can accept a single color with no hue nor saturation variety you get it easily by inserting a top shape which colorizes the original below. An example:

The shape to be extruded

Extruded shape, Expand Appearance is applied

Clipping mask released, ungrouped 4 times, united to one item by applying Pathfinder panel's Unite

New fill color selected

Copies of (2) and (4) are aligned, (4) is on the top and has got blending mode Color.

Blending modes are selected in the transparency panel. It opens automatically if one clicks "Opacity" in the appearance panel. Blending mode Color applies the hue and saturation of the top object, the brightness variations of the bottom object stay. Try also other blending modes, at least Overlay, Color Burn, and Hard light. Some of them may give an useful result.
More possiblities can be got by using color editing, but that's quite limited in my legacy Illustrator, so I skip it. Hopefully someone shows what's possible in modern Illustrator.
I have Edit > Edit Colors > Recolor, but there's no other global adjustments than brightness. The lack of global adjustments and the high number of the splinters in the expanded shape makes color editing very difficult.
Altering contrast without color editing:
You can reduce the contrast by adding a single color (=united) copy on top with blending mode normal. Reduce the opacity to make original brightness variations partially visible.
Increase the contrast with blending mode Hard Light:

The expanded shape in the left is duplicated (=copy, paste in place) and the top version has got blending mode Hard light. It brightens bright and darkens dark. Applying the trick twice doubles it. Reducing the opacity of the top object reduces the effect.
Rasterizing: Copy and paste the expanded object as pixels to an empty image in Photoshop and use all Photoshop's power to colorize and change the contrast. Then you can save the result as PNG or PSD and place it to Illustrator as a raster image. Copying and pasting back to Illustrator removes the transparency, so save and place!
You do not lose any quality if you know beforehand what's the biggest size of the image and the image in Photoshop has high enough pixel dimensions. Most of us avoid this route because rasterizing removes the free scalability.
Not asked: The most powerful way to to get a new color is to recolor the original shape and extrude again, maybe with adjusted light settings in the extrusion dialog. I guess the original is now unavailable or there's so many extruded and expanded objects that the questioner searches something easier than guessing the right extrusion settings for everyone.


Is this mortar or concrete subfloor under my bathroom tile?

Question: I am redoing my second floor bathroom because of a leak under the tub which over many years has caused a leak downstairs. I thought it would be easy changing a rotten wooden subfloor… But when i started removing the old tiles, it was mortar or concrete? I cannot tell.. I attached a pic. Will this make the subfloor replacement harder or easier? Since its mortar or concrete can i just plug the hole with mortar and retile? Or does the whole subfloor need to be removed and filled with new mortar?
Comment: You've stumbled on the origin of the term "thin set" (mortar). It's the modern alternative to this conventional full mortar base.
Comment: When we renovated our 1939 upstairs bathroom the entire floor was laid on poured concrete a few inches thick. We had the same problem with a leaky tub ruining the ceiling below. Even some of the water pipes were embedded in it. The whole slab had to be removed. But we were doing a full renovation and expanded the bathroom about a foot.
Answer: Presumably from the description it's a thick mortar bed method tile floor, typical for 1950s and earlier tile work.
You'll have to determine if the framing (likely wood, if the house is wood framed) holding it up (well below the floor level of the rest of the second floor) is rotten or not. That might be easiest from below, where you presumably need to fix the damaged ceiling anyway.
Despite being outdated, it's a good tile support - out of style these days since newer methods are faster and don't require the vastly different floor level at framing time. If what's holding it up is not rotten, patching with mortar should be all that's needed. Tile floors that have lasted 100+ years were typically put in this way.
Comment: +1 to 'check the framing for rot'. Open up a big section of the ceiling below to fully understand that scope of the problem.


reference for elementary mortgage math

Question: I have a student doing a project on  default rate & prepayment rate for mortgages.  She would like to include a section on how the quantities affect pricing, & so would like to reference a formula that gives the value of a mortgage in terms of them, say for constant values of them.  I think it used to be possible to find them in one or both of Fabozzi's books, (fixed income handbook and mortgage handbook) but the editions she found in the library did not in fact have them.
So the QUESTION is does someone know a readily available source that has a formula for the value of a mortgage in terms of these quantities or basically the same thing, psa, smm etc.
Answer: I would recommend the following text:

Mortgage-Backed Securities: Products, Structuring, and Analytical Techniques, 2nd Edition - Frank Fabozzi.

Part II: Prepayment and Default Metrics and Behavior covers the topics you mentioned, and I have been using it recently as a basis for making models based on agency MBS products. This introduces the 100 PSA model, and general pricing using default and prepayment curves.
Answer: The best book i can think of are from FRM Quant program. The concepts for which you are seeking answers could be easily found in FRM part 1 books (Initial chapters). These are pretty expensive, but if you could get your hands on any older versions, that should be fine.
Any MBS book would have these topics. But the reader must have keen intent to extract the information.
All Interest rates and MBS primarily depend on few formula "KE to the power of RT" and "P(1 + r/n)to the power of n*t". Most formula's are based on the above two. These could be slightly tweaked to customize as per requirements to include constant costs, recurring costs and any special costs.
Comment: what is FRM Quant program?
Answer: https://www.youtube.com/watch?v=aEnjFFFVhGs Credit goes to the CFA institute.

reference for elementary mortgage math


How do I know what image type to use?

Question: I'm working on a website which will use images in several different applications, from action buttons to avatars to larger detail images. What factors should I take into consideration to decide whether these images should be jpgs, gifs, or pngs?
Answer:
JPG for photos or high color differences
PNG for images with gradual transparency (fade from 1 color to clear)
GIF for images with small color palettes

Obviously give each image a try and see what comes out to the smallest file size. The smaller the size the better. Also don't worry about transparency in IE6 for your PNG's, grandma isn't as concerned how your site looks just that she can see pictures of you on it.
Answer: File size. The smaller the file size the faster it will download for your users. So go for the smallest file size that doesn't affect your image quality.
(Generally speaking JPGs are used for photographs and PNGs/GIFs are used for icon-like images)
Comment: I would add that for UI screenshots/non-photos - use PNG. JPEG tends to horribly pixelate non-photo images.
Answer: Browser Support. I think it's IE6 or IE7 and older do not support png based images with a transparent background properly. It usually adds some funky background color.
Comment: Only IE6 has problems with transparent PNGs. IE7-9 is fine with them.
Comment: IE4 and newer support *paletted* PNG *with transparency*: http://calendar.perfplanet.com/2010/png-that-works/#paletted

How do I know what image type to use?


DIY or Custom Quadcopter

Question: I want a quadcopter with (2)lb payload capacity, (5)mi range, 30mph min. speed, long-range fpv, waypoints, & ZERO enforced geofencing. I am willing to use/accept any combination of hardware/software as long as above specs are met. Can anyone suggest a specific product, build a setup meeting the requirements for me for around $1,500, or point me to someone who will, or suggest a product that can be modified to these requirements?
Answer: It sounds like you are dropping some cell phones in prison fences.
I will hit these point by point:
2lb capacity: Anything 5"+ can do it.
5mi range:
You will need a BVLoS waiver to be legal. Good luck; they run about \$20k in legal fees last time I looked. Of course, that will also need a commercial license. Not gonna lie; a legal BVLoS flight is pretty much impossible.
Digital FPV will cover you but can be sketchy at a distance. Many factors, such as geography, quality of gear, and EM noise floor.  5 miles is a big ask and most commonly seen away from urban areas (less EM noise).
No geofencing: Build your own
No such specific OTS product exists. SkyDio is close, but they are just Chinese crap (they assemble in the USA).  Also big \$.
\$1500 budget-- good luck - some round numbers:  Digital goggles w/upgrades $800, Underlying custom drone \$500, \$100 release mechanism, \$200 transmitter. \$250 batteries and charger (to start), \$100 charger, \$500 flight controller and GPS gear (minimum), FPV transmitter + antenna \$100.  Closer to \$3k to start.

DIY or Custom Quadcopter


what is a networking protocol?

Question: i just want to  start by saying that I  classify my self as a beginner in networking  and my only hope is to become  very good  as you are,so  i was reading this book and i didn't understand the term very well a "networking protocol"" and it continue saying that a network has a  lot of  networking protocols
so i just want  a simple definition of a protocol.
thank you very very much in advance.
Answer:
A network protocol defines rules and conventions for communication between network devices.  Network protocols include mechanisms for devices to identify and make connections with each other, as well as formatting rules that specify how data is packaged into messages sent and received. Some protocols also support message acknowledgment and data compression designed for reliable and/or high-performance network communication.

Network Protocol Description
Comment: Duffman Thank  you so much for the great explication , so  a networking protocol is like a language  and Each function or service of a network like (http , smtp , telnet ) has its own language  like
human languages, some are similar to each other while others are quite unique right ?
Answer: For understanding protocols, I usually suggestion reading the mail transport protocol first (esp Example 1 of RFC 821), then actually trying it with your own mail servers: it's designed for a person to type it for diagnosing email problems.  Then comparing it against something like file transfer FTP (esp example in Section 7 of RFC 959).
Understanding binary protocols and the transport protocols follows naturally from there.  It's hard to understand any of the protocols if you don't understand what problem they are solving: hence much easier with sending mail and files.
Answer: Network protocols state the order and kind of messages that two network entities exchange each other.
The two network entities (or sometimes more than two, but anyway you can always imagine it's two entities at a time) can be two routers, two compuers, a router and a computer...etc.

what is a networking protocol?


Is American put Gamma always greater than the European one in the non-early-exercise domain?

Question: Consider a pair of American and European puts with the same specifications except the former has the continuous early exercise right. Has anyone plotted the Gamma's of both as functions of the underlying price and time to expiry for the underlying greater than the critical exercise price? Is the American put Gamma necessarily greater than or equal to that of the European counterpart in this domain? I would like a mathematical proof if it is true. I suspect the negative answer may predominantly come from the region where the underlying is close to and above the critical exercise price.
Comment: Does [this question](https://quant.stackexchange.com/q/35163/41821) help?
Comment: @Kevin: Yes, it does. Thank you. I am now more interested in a proof if this inequality is always true.
Answer: I think the argument of continuity as suggested by the deleted post does apply.  American options should be continuous in all their Greeks across "boundaries", because it is a free boundary.  Given continuity , the statement fails.  For example the following diagram makes it pretty obvious.  Not a math proof I
Comment: This is false. $\frac{\partial^2 P}{\partial S^2}$ is not necessarily continuous across the exercise, or free, boundary. In fact, in most cases it is discontinuous across the boundary. Your diagram just shows the continuity of $\frac{\partial P}{\partial S}$.