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  • Ubuntu installation error on a windows machine

    - by Rahul
    Was trying to install Ubuntu from a CD on a machine which already has windows on it, choose the option of "Resize IDE1 master (hda) and use freed space" during the "Install the base system" step. After that i get the error- "Unable to install initrd-tools. An error was returned while trying to install the initrd-tools package into the target system. Check /target/var/log/bootstrap.log for details. The problem is one one hand i cannot proceed with the complete installation and on other hand if i remove the CD, am not able to boot windows as it says No bootable device. Would highly appreciate for any recommendations.

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  • jqGrid - dynamically load different drop down values for different rows depending on another column value

    - by Renso
    Goal: As we all know the jqGrid examples in the demo and the Wiki always refer to static values for drop down boxes. This of course is a personal preference but in dynamic design these values should be populated from the database/xml file, etc, ideally JSON formatted. Can you do this in jqGrid, yes, but with some custom coding which we will briefly show below (refer to some of my other blog entries for a more detailed discussion on this topic). What you CANNOT do in jqGrid, referrign here up and to version 3.8.x, is to load different drop down values for different rows in the jqGrid. Well, not without some trickery, which is what this discussion is about. Issue: Of course the issue is that jqGrid has been designed for high performance and thus I have no issue with them loading a  reference to a single drop down values list for every column. This way if you have 500 rows or one, each row only refers to a single list for that particuolar column. Nice! SO how easy would it be to simply traverse the grid once loaded on gridComplete or loadComplete and simply load the select tag's options from scratch, via ajax, from memory variable, hard coded etc? Impossible! Since their is no embedded SELECT tag within each cell containing the drop down values (remeber it only has a reference to that list in memory), all you will see when you inspect the cell prior to clicking on it, or even before and on beforeEditCell, is an empty <TD></TD>. When trying to load that list via a click event on that cell will temporarily load the list but jqGrid's last internal callback event will remove it and replace it with the old one, and you are back to square one. Solution: Yes, after spending a few hours on this found a solution to the problem that does not require any updates to jqGrid source code, thank GOD! Before we get into the coding details, the solution here can of course be customized to suite your specific needs, this one loads the entire drop down list that would be needed across all rows once into global variable. I then parse this object that contains all the properties I need to filter the rows depending on which ones I want the user to see based off of another cell value in that row. This only happens when clicking the cell, so no performance penalty. You may of course to load it via ajax when the user clicks the cell, but I found it more effecient to load the entire list as part of jqGrid's normal editoptions: { multiple: false, value: listingStatus } colModel options which again keeps only a reference to the sinlge list, no duplciation. Lets get into the meat and potatoes of it.         var acctId = $('#Id').val();         var data = $.ajax({ url: $('#ajaxGetAllMaterialsTrackingLookupDataUrl').val(), data: { accountId: acctId }, dataType: 'json', async: false, success: function(data, result) { if (!result) alert('Failure to retrieve the Alert related lookup data.'); } }).responseText;         var lookupData = eval('(' + data + ')');         var listingCategory = lookupData.ListingCategory;         var listingStatus = lookupData.ListingStatus;         var catList = '{';         $(lookupData.ListingCategory).each(function() {             catList += this.Id + ':"' + this.Name + '",';         });         catList += '}';         var lastsel;         var ignoreAlert = true;         $(item)         .jqGrid({             url: listURL,             postData: '',             datatype: "local",             colNames: ['Id', 'Name', 'Commission<br />Rep', 'Business<br />Group', 'Order<br />Date', 'Edit', 'TBD', 'Month', 'Year', 'Week', 'Product', 'Product<br />Type', 'Online/<br />Magazine', 'Materials', 'Special<br />Placement', 'Logo', 'Image', 'Text', 'Contact<br />Info', 'Everthing<br />In', 'Category', 'Status'],             colModel: [                 { name: 'Id', index: 'Id', hidden: true, hidedlg: true },                 { name: 'AccountName', index: 'AccountName', align: "left", resizable: true, search: true, width: 100 },                 { name: 'OnlineName', index: 'OnlineName', align: 'left', sortable: false, width: 80 },                 { name: 'ListingCategoryName', index: 'ListingCategoryName', width: 85, editable: true, hidden: false, edittype: "select", editoptions: { multiple: false, value: eval('(' + catList + ')') }, editrules: { required: false }, formatoptions: { disabled: false} }             ],             jsonReader: {                 root: "List",                 page: "CurrentPage",                 total: "TotalPages",                 records: "TotalRecords",                 userdata: "Errors",                 repeatitems: false,                 id: "0"             },             rowNum: $rows,             rowList: [10, 20, 50, 200, 500, 1000, 2000],             imgpath: jQueryImageRoot,             pager: $(item + 'Pager'),             shrinkToFit: true,             width: 1455,             recordtext: 'Traffic lines',             sortname: 'OrderDate',             viewrecords: true,             sortorder: "asc",             altRows: true,             cellEdit: true,             cellsubmit: "remote",             cellurl: editURL + '?rows=' + $rows + '&page=1',             loadComplete: function() {               },             gridComplete: function() {             },             loadError: function(xhr, st, err) {             },             afterEditCell: function(rowid, cellname, value, iRow, iCol) {                 var select = $(item).find('td.edit-cell select');                 $(item).find('td.edit-cell select option').each(function() {                     var option = $(this);                     var optionId = $(this).val();                     $(lookupData.ListingCategory).each(function() {                         if (this.Id == optionId) {                                                       if (this.OnlineName != $(item).getCell(rowid, 'OnlineName')) {                                 option.remove();                                 return false;                             }                         }                     });                 });             },             search: true,             searchdata: {},             caption: "List of all Traffic lines",             editurl: editURL + '?rows=' + $rows + '&page=1',             hiddengrid: hideGrid   Here is the JSON data returned via the ajax call during the jqGrid function call above (NOTE it must be { async: false}: {"ListingCategory":[{"Id":29,"Name":"Document Imaging & Management","OnlineName":"RF Globalnet"} ,{"Id":1,"Name":"Ancillary Department Hardware","OnlineName":"Healthcare Technology Online"} ,{"Id":2,"Name":"Asset Tracking","OnlineName":"Healthcare Technology Online"} ,{"Id":3,"Name":"Asset Tracking","OnlineName":"Healthcare Technology Online"} ,{"Id":4,"Name":"Asset Tracking","OnlineName":"Healthcare Technology Online"} ,{"Id":5,"Name":"Document Imaging & Management","OnlineName":"Healthcare Technology Online"} ,{"Id":6,"Name":"Document Imaging & Management","OnlineName":"Healthcare Technology Online"} ,{"Id":7,"Name":"EMR/EHR Software","OnlineName":"Healthcare Technology Online"}]} I only need the Id and Name for the drop down list, but the third column in the JSON object is important, it is the only that I match up with the OnlineName in the jqGrid column, and then in the loop during afterEditCell simply remove the ones I don't want the user to see. That's it!

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  • Typical collision detection

    - by marcg11
    I would like to know how is the typical collision detection of most games. For example, you control a character which can move in 2 dimensional directions (except up and down). Now lets asume he walks into a wall, most of the games depending on character angle and the BB normal face will only stop the player in one axis, but will continue moving in the other along the wall axis. How is that done? I've only managed to stop the character from going through the wall by seting the position to the last one in the past frame if the new position colllisions the bounding box. But this just makes the player stop sharply and unrealisticly.

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  • Managing Files/Folder in Content Repositories or File Systems with Oracle ADF and WebCenter

    - by Shay Shmeltzer
    One more entry in a set of entries (1,2,3) about the capabilities that WebCenter adds to ADF applications. WebCenter is basically the new Portal framework in the Oracle stack - and one key thing that portals do is work with content, allowing you to compose and publish content from files as well as save and store content. In this demo you'll see how using a set of taskflows provided by WebCenter you can add a file management, creation and viewing capabilities to a regular ADF application. To try this out you don't need any fancy content management system - we'll just use your file system for now. All you need is the WebCenter extension installed in JDeveloper, and then you can follow the demo on your own JDeveloper instance. You'll define a connection to your content repository you'll be able to add a bunch of pre-built WebCenter taskflows into your page. And suddenly you can upload/download/create and view document directly from your applicaiton. Check it out:

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  • 12.04 boots fine, with graphical splash screen, but then Monitor "out of range"

    - by Jim Bednar
    I see dozens of posts from people whose monitors are saying "out of range" under Ubuntu; seems like there are some serious problems in Ubuntu with autodetection of monitor capabilities. :-( But none of the many, many suggestions I found have solved my problem, and right now I can't use anything graphical on this machine! History: I installed Ubuntu 12.04 on my HP Proliant Microserver N40L, which worked reasonably at the default resolution across several reboots. At some point I noticed that the proprietary video driver was not in use, and tried to install one to get better window-drawing speeds, but it failed with some sort of error, and I gave up on that. A few weeks later when I next rebooted, it showed the usual BIOS screen and various boot loading screens (including GRUB), and then the usual purple Ubuntu splash screen with the dots showing that things were loading, but when it finished booting the monitor went black and eventually showed "Out of range" (with no other information). Given that there were several weeks between reboots (it's a server, after all), I've no idea if it was some system update, trying to install the proprietary drivers, or something else that caused the problem. Anyway, the system has booted fine, as I can do Ctrl-Alt-F1 to get a text prompt and can log in there. But Ctrl-Alt-F7 goes back to the out of range error. Some posters said to try Ctrl-Alt-- (minus) to cycle through resolutions until one works, but that didn't have any visible effect. Many, many others said it was a grub problem, which seems unlikely given that grub's screen looks fine, but I tried editing /etc/default/grub to set a particular resolution (trying many of them) and running update-grub, with no apparent effect. Rebooting into failsafe mode works the same as regular mode. Replacing xorg.conf with xorg.conf.failsafe works the same too. I'm at my wits' end! Isn't there anything I can do to convince Ubuntu to choose a mode that the monitor supports? E.g. the one that it is using for the splash screen? I don't need great resolution on this machine, just anything that works!!!!! Help!!!!!! Please!!!!

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  • Calculate gears rotation for a realtime simulation

    - by nkint
    Hi I'm trying to do a game with real time simulations of gears. There is a big Gear with inside a smaller gear. I managed to draw gears with different diameters but equal size teeth, but if i try to move the smaller one inside the bigger one the movement is odd. see the animated gif. the biggest gear is in center C1 and the small in the center C2. I calculate C2 position in this way: C2.x = C1.x + C1_RADIUS-C2_RADIUS) * cos(t); C2.y = C1.y - C1_RADIUS-C2_RADIUS) * sin(t); for t that goes from 0 to TWO_PI in n steps. I apply as rotation the angle t, but maybe it is wrong and i have to calculate another rotation for get a perfect joint

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  • Removing Menu Items from Window Tabs

    - by Geertjan
    So you're working on your NetBeans Platform application and you notice that when you right-click on tabs in the predefined windows, e.g., the Projects window, you see a long list of popup menus. For whatever the reason is, you decide you don't want those popup menus. You right-click the application and go to the Branding dialog. There you uncheck the checkboxes that are unchecked below: As you can see above, you've removed three features, all of them related to closing the windows in your application. Therefore, "Close" and "Close Group" are now gone from the list of popup menus: But that's not enough. You also don't want the popup menus that relate to maximizing and minimizing the predefined windows, so you uncheck those checkboxes that relate to that: And, hey, now they're gone too: Next, you decide to remove the feature for floating, i.e., undocking the windows from the main window: And now they're gone too: However, even when you uncheck all the remaining checkboxes, as shown here... You're still left with those last few pesky popup menu items that just will not go away no matter what you do: The reason for the above? Those actions are hardcoded into the action list, which is a bug. Until it is fixed, here's a handy workaround: Set an implementation dependency on "Core - Windows" (core.window). That is, set a dependency and then specify that it is an implementation dependency, i.e., that you'll be using an internal class, not one of the official APIs. In one of your existing modules, or in a new one, make sure you have (in addition to the above) a dependency on Lookup API and Window System API. And then, add the class below to the module: import javax.swing.Action; import org.netbeans.core.windows.actions.ActionsFactory; import org.openide.util.lookup.ServiceProvider; import org.openide.windows.Mode; import org.openide.windows.TopComponent; @ServiceProvider(service = ActionsFactory.class) public class EmptyActionsFactory extends ActionsFactory { @Override public Action[] createPopupActions(TopComponent tc, Action[] actions) { return new Action[]{}; } @Override public Action[] createPopupActions(Mode mode, Action[] actions) { return new Action[]{}; } } Hurray. Farewell to superfluous popup menu items on your window tabs. In the screenshot below, the tab of the Projects window is being right-clicked and no popup menu items are shown, which is true for all the other windows, those that are predefined as well as those that you add afterwards:

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  • Is there a quasi-standard set of attributes to annotate thread safety, immutability etc.?

    - by Eugene Beresovksy
    Except for a blog post here and there, describing the custom attributes someone created, but that do not seem to get any traction - like one describing how to enforce immutability, another one on Documenting Thread Safety, modeling the attributes after JCIP annotations - is there any standard emerging? Anything MS might be planning for the future? This is something that should be standard, if there's to be any chance of interoperability between libraries concurrency-wise. Both for documentation purposes, and also to feed static / dynamic test tools. If MS isn't doing anything in that direction, it could be done on CodePlex - but I couldn't find anything there, either. <opinion>Concurrency and thread safety are really hard in imperative and object-languages like C# and Java, we should try to tame it, until we hopefully switch to more appropriate languages.</opinion>

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  • When can I be sure a directed graph is acyclic?

    - by Daniel Scocco
    The definition for directed acyclic graph is this: "there is no way to start at some vertex v and follow a sequence of edges that eventually loops back to v again." So far so good, but I am trying to find some premises that will be simpler to test and that will also guarantee the graph is acyclic. I came up with those premises, but they are pretty basic so I am sure other people figured it out in the past (or they are incorrect). The problem is I couldn't find anything related on books/online, hence why I decided to post this question. Premise 1: If all vertices of the graph have an incoming edge, then the graph can't be acyclic. Is this correct? Premise 2: Assume the graph in question does have one vertex with no incoming edges. In this case, in order to have a cycle, at least one of the other vertices would need to have two or more incoming edges. Is this correct?

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  • If-Else V.S. Switch end of flow

    - by Chris Okyen
    I was wondering the if if-else statements, is like a switch statement that does not have a break statement.To clarify with an example, will the if-else statement go through all the boolean expressions even if comes to one that is true before the final one... I.E., if boolean_expression_1 was true, would it check if boolean_expression_2 is true? If not, why do switch statements need break statements but if-else statements do not? And if they do, I ask the opposite sort question proposed in the previous sentence. if( boolean_expression_1 ) statement_1 else if( boolean_expression_2 ) statement_2 else default_statement switch( controlling_expression ) { case: ( A ) .... case: ( z ) }

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  • Is there a Visual Studio style tool/IDE?

    - by Tim
    I have been developing in the windows space with Visual Studio for a while now with work, but I have also been using Ubuntu for a while and am keen to get into some software development for linux. I should also note. I am not looking for .NET and I am aware of mono. I am also familiar with c++ development and some python, so the language isn't so much relevant as the "all in one" aspect. I was interested to know if there is a useful all in one code/debug/design(gui) IDE similar to something like Visual Studio but for linux?

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  • Testing Reference Data Mappings

    - by Michael Stephenson
    Background Mapping reference data is one of the common scenarios in BizTalk development and its usually a bit of a pain when you need to manage a lot of reference data whether it be through the BizTalk Cross Referencing features or some kind of custom solution. I have seen many cases where only a couple of the mapping conditions are ever tested. Approach As usual I like to see these things tested in isolation before you start using them in your BizTalk maps so you know your mapping functions are working as expected. This approach can be used for almost all of your reference data type mapping functions where you can take advantage of MSTests data driven tests to test lots of conditions without having to write millions of tests. Walk Through Rather than go into the details of this here, I'm going to call out to one of my colleagues who wrote a nice little walk through about using data driven tests a while back. Check out Callum's blog: http://callumhibbert.blogspot.com/2009/07/data-driven-tests-with-mstest.html

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  • Habanero

    - by csharp-source.net
    An Enterprise Application Framework for .Net that is ideally suited for developing applications in an agile manner. The framework is used for producing an application from the data layer through to the front-end. Free open source under the LGPL license, it includes ORM, code generation and runtime UI generation to create one application for the desktop & web. Features: * ORM: Map database tables to objects in code * Persist property values to and from the database * Define all mapping in a single XML file * Switch between database vendors with one setting * Support for MySQL, MS Sql Server, MS Access, Oracle, PostgreSQL, SQLite, Firebird * FireStarter GUI class definitions xml manager * Generate user interfaces and map properties to controls * Develop for both desktop (with Windows Forms) and web (with Gizmox' Visual WebGUI) * Generate new projects and code files * Generate UI forms from templates * Reverse engineer class definitions from existing databases * Support variable data sources, including an in-memory database. Ships with Firestarter a free database reverse engineering, Domain Modelling and Code Generator.

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  • can't see myself in Skype video call

    - by seb
    I'm running 12.04 and I've installed skype via the software centre. As with 11.10 everything works fine with 12.04 as well. There is only one thing that does not work. I can't see myself in Skype video calls. The video call works fine, I can see the other side the other side can see me. Buid in microphone works. If I click on 'show myself' during the video call nothing happens. I know that it works on Ubuntu in general as I had it working a while back on a different machine (Xubuntu 11.04). Could that be related to the GPU? I'm now on a intel/nvidia one. Any Ideas where I can hunt for some options or tweaking?

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  • Now Instagram lets you record and share 15 seconds video with awesome filters

    - by Gopinath
    Instagram is one of the most popular photo sharing applications and it is very popular for amazing filters that turn an ordinary photo in to an incredible one. Today Instagram extended the filters and sharing options to videos. With the latest version of Instagram application for iOS/Android you can record videos, apply filters and share them. Recording and sharing videos on Instagram is much similar to photos and. You can capture videos up to 15 seconds and there are 13 filters to choose for processing. Wondering why the limit is at 15 seconds? Pundits are saying that TV ads are in general 15 seconds and Instagram is preparing for video ads in near future. Anyways within hours of video sharing features, Instagram is flooded with short videos and the Explore section has very interesting ones to browse through. Just like photos, you can share the captured videos to your Twitter, Facebook and other social stream from Instagram.

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  • Low complexity shader to indicate the sides of a polyline

    - by Pris
    I have a bunch of polylines that I draw using GL_LINES. They can have thousands of points. They actually represent the separation of land and water on a map. I don't have complete polygons, just the ordered set of points. I'm looking for a neat but efficient way to visually convey Side A and Side B as being different. For example I could offset the polyline in one direction a few times and fade it out (but every offset is doubling the number of points), or offset it once to make a "ribbon" and give one side a 'glow' like effect to mimic the outer glow or shadow of a polygon). This is for a mobile application and I'm using OpenGL ES 2. I'd like to keep the effect as simple as possible from a complexity stand point. I'm looking for some additional ideas; maybe there's a clever shader technique out there or a visual effect I haven't considered.

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  • Conflict between Change Control and ASL Mapping

    - by Jie Chen
    Yesterday I got one strange report that on Agile 9.3.1.2, adding a Supplier into Item's Supplier tab will always remove all the data from Item.PageTwo.MultiList01 field which is assigned to a User Group list. The detailed problem description is like below. In JavaClient, MultiList01 attribute on Parts class's PageTwo tab is enabled and assigned with User Group list. On WebClient, user created a new Part and assign MultiList01 with two UserGroups: "Global User Group Test1" and "Personal Group_Test1". Then go to Suppliers tab to add three Suppliers. Switch back to Part's TitleBlock, will see MultiList01 loses the User Group data. To confirm if MultiList01 really loses the data or it saves with other wrong data, I need to check the database and find strange data that MultiList01 saves wrong data ",7976911,7976907,7976959,", which are exactly the ID of these three Suppliers. Then I can suspect the Supplier attribute on Suppliers tab must be mapped to MultiList01. However when I check Supplier in JavaClient, the "ASL mapped to" is blank. More interesting thing is the database clearly shows Supplier attribute (Base ID =2000004219) is mapped to 2090, which is PageTwo.MultiList01 Base ID. Till now, we can get a conclusion that Supplier data is really mapped to MultiList01, though we assign MultiList01 to User Group list and Supplier does not set "ASL mapped to". It must be another function which overrides "ASL mapped to" visibility in JavaClient with high priority. That is the "Change Controlled" function. We immediately see "ASL mapped to" with value "MultiList01" when we disable Change Controlled for Multilist01 If one attribute is Change Controlled, Supplier data cannot be mapped to this attribute theoretically because Supplier could be dynamically modified by users, not by Changes. In real situation of Agile 9.3.1.2, it could be a Code Defect. We can imagine the scenario customer met. He setup Parts.PageTwo.Multilist01 assigned with Supplier list, then in Parts.Suppliers.Supplier attribute, he set "ASL mapped to" to "Multilist01". Later company business is changed, so he set Multilist01 with Change Controlled and re-assign with User Group list. He forgot to remove "ASL mapped to" before he did modifications to Multilist01. Finally we know the solution, it depends on real business. If still need to mapping Supplier to Parts.PageTwo attribute, should modify "ASL mapped to" to other one attribute which already has assigned with Suppliers list. If do not need "ASL mapped to" function, should delete the data from database level. We cannot do it from JavaClient UI. delete propertytable where id in (select p.id from propertytable p, nodetable n where p.parentid =n.id and n.inherit=2000004219 and propertyid=794)

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  • How to install Visual Studio 2010 Search References and Pro Power Tools side by side

    - by Daniel Cazzulino
    The new Visual Studio 2010 Pro Power Tools bring a new Add Reference dialog that completely replaces the classic one when you click the familiar Add Reference command: It seems like a nice dialog that is more aligned with the new Add New dialog and the Extension Manager one. But for this particular case, I believe it's awfully overkill (what's the use of that right sidebar? what's the use for the categories of assemblies split between Framework and Extensions?). The (also new) Search References extension which I blogged about earlier, gives you the familiar classic dialog enhanced with the must-have Search capability:...Read full article

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  • Netbook partitioning scheme suggestions

    - by David B
    I got a new Asus EEE PC 1015PEM with 2GB RAM and a 250GB HD. After playing with the netbook edition a little, I would like to install the desktop edition I'm used to. In addition to ubunto partition(s), I would like to have one separate partition for data (documents, music, etc.), so I could try other OSs in the future without losing the data. What partition scheme would you recommend? I usually like to let the installation do it by itself, but when I try to that I can only use the entire disk, so I don't get the desired data partition. I wish there was a way to see the recommended default partitioning scheme, then just tweak it a bit to fit your needs (instead of building one from scratch). So, how would you recommend I partition my HD? Please be specific since I never manually partitioned before. Thanks!

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  • Dotted subdomain name or new domain?

    - by Catalin Ilinca
    I have a company website hosted at www.BRAND.com (where BRAND is a generic name). The company want to develop a "micro website" for one of their campaigns, named "Inspired By BRAND". I have two directions: inspired.by.BRAND.com - which I personally don't like too much. I don't know why but I don't recall any web address similar to this one subdomain.subdomain.domain.com. inspired.BRAND.com - which I this is best suited for it. Fewer dots and similar to "more friendly" addresses subdomain.domain.com. Any hints, guidelines, any thoughts is well appreciated. Thanks in advance

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  • Computer Networks UNISA - Chap 8 &ndash; Wireless Networking

    - by MarkPearl
    After reading this section you should be able to Explain how nodes exchange wireless signals Identify potential obstacles to successful transmission and their repercussions, such as interference and reflection Understand WLAN architecture Specify the characteristics of popular WLAN transmission methods including 802.11 a/b/g/n Install and configure wireless access points and their clients Describe wireless MAN and WAN technologies, including 802.16 and satellite communications The Wireless Spectrum All wireless signals are carried through the air by electromagnetic waves. The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. The wireless spectrum falls between 9KHZ and 300 GHZ. Characteristics of Wireless Transmission Antennas Each type of wireless service requires an antenna specifically designed for that service. The service’s specification determine the antenna’s power output, frequency, and radiation pattern. A directional antenna issues wireless signals along a single direction. An omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions The geographical area that an antenna or wireless system can reach is known as its range Signal Propagation LOS (line of sight) uses the least amount of energy and results in the reception of the clearest possible signal. When there is an obstacle in the way, the signal may… pass through the object or be obsrobed by the object or may be subject to reflection, diffraction or scattering. Reflection – waves encounter an object and bounces off it. Diffraction – signal splits into secondary waves when it encounters an obstruction Scattering – is the diffusion or the reflection in multiple different directions of a signal Signal Degradation Fading occurs as a signal hits various objects. Because of fading, the strength of the signal that reaches the receiver is lower than the transmitted signal strength. The further a signal moves from its source, the weaker it gets (this is called attenuation) Signals are also affected by noise – the electromagnetic interference) Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. Frequency Ranges Older wireless devices used the 2.4 GHZ band to send and receive signals. This had 11 communication channels that are unlicensed. Newer wireless devices can also use the 5 GHZ band which has 24 unlicensed bands Narrowband, Broadband, and Spread Spectrum Signals Narrowband – a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies Broadband – uses a relatively wide band of the wireless spectrum and offers higher throughputs than narrowband technologies The use of multiple frequencies to transmit a signal is known as spread-spectrum technology. In other words a signal never stays continuously within one frequency range during its transmission. One specific implementation of spread spectrum is FHSS (frequency hoping spread spectrum). Another type is known as DSS (direct sequence spread spectrum) Fixed vs. Mobile Each type of wireless communication falls into one of two categories Fixed – the location of the transmitted and receiver do not move (results in energy saved because weaker signal strength is possible with directional antennas) Mobile – the location can change WLAN (Wireless LAN) Architecture There are two main types of arrangements Adhoc – data is sent directly between devices – good for small local devices Infrastructure mode – a wireless access point is placed centrally, that all devices connect with 802.11 WLANs The most popular wireless standards used on contemporary LANs are those developed by IEEE’s 802.11 committee. Over the years several distinct standards related to wireless networking have been released. Four of the best known standards are also referred to as Wi-Fi. They are…. 802.11b 802.11a 802.11g 802.11n These four standards share many characteristics. i.e. All 4 use half duplex signalling Follow the same access method Access Method 802.11 standards specify the use of CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to access a shared medium. Using CSMA/CA before a station begins to send data on an 802.11 network, it checks for existing wireless transmissions. If the source node detects no transmission activity on the network, it waits a brief period of time and then sends its transmission. If the source does detect activity, it waits a brief period of time before checking again. The destination node receives the transmission and, after verifying its accuracy, issues an acknowledgement (ACT) packet to the source. If the source receives the ACK it assumes the transmission was successful, – if it does not receive an ACK it assumes the transmission failed and sends it again. Association Two types of scanning… Active – station transmits a special frame, known as a prove, on all available channels within its frequency range. When an access point finds the probe frame, it issues a probe response. Passive – wireless station listens on all channels within its frequency range for a special signal, known as a beacon frame, issued from an access point – the beacon frame contains information necessary to connect to the point. Re-association occurs when a mobile user moves out of one access point’s range and into the range of another. Frames Read page 378 – 381 about frames and specific 802.11 protocols Bluetooth Networks Sony Ericson originally invented the Bluetooth technology in the early 1990s. In 1998 other manufacturers joined Ericsson in the Special Interest Group (SIG) whose aim was to refine and standardize the technology. Bluetooth was designed to be used on small networks composed of personal communications devices. It has become popular wireless technology for communicating among cellular telephones, phone headsets, etc. Wireless WANs and Internet Access Refer to pages 396 – 402 of the textbook for details.

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  • Retail in New York - a walk down 5th Avenue

    - by sarah.taylor(at)oracle.com
    It's the week of the NRF Big Show and all eyes in the retail industry are on New York. The Big Apple is famous for Big Retail -with a proliferation of incredibly iconic stores. The environment is exciting and familiar even to people visiting this small island for the first time. Most of us have travelled down Fifth Avenue watching movies and TV even if we have never set foot on American soil. I find it one of the most exciting retail cities in the world and I am thrilled this year to be here with so many of Oracle's International retail customers who are joining us for the Retail Exchange. The Oracle program brings retailers from all over the planet together to share ideas and be inspired by New York retail and the NRF event. The show celebrates its 100th year in 2011 and New York itself has been recognized globally as the capital of innovative retail for just as long.  Fifth Avenue is where many global brands have placed their flagship stores, and businesses are in constant competition to set themselves apart from their competitors - both in the store and from the street.  These flag ship retail destinations present what today's customers are finding most exciting and delightful about retail. For the tourist market, they may only visit these stores once, but the impression that a trip to a flagship store leaves with a customer can last a lifetime.  One of the stores that is currently turning heads on Fifth Avenue is Hollister, sister brand to Abercrombie and Fitch, which has filled its shop front with a massive live video (and audio) feed of surfers on the beach in California.  To complete the effect, they also have troughs of water in front of the video screens to bring the sea to the street.  And this isn't the only kind of surfing that retailers are considering today and multi-channel retail is a hot topic that all of the retailers joining the Retail Exchange are considering.   The rest of the world looks to the brands along Fifth Avenue for inspiration - how they take advantage of new opportunities, how they set themselves apart from their competitors and how they keep their products fresh and desirable. With these inspiring pioneers in New York, it's little wonder that NRF's Big Show is so popular, and that New York is viewed as one of the retail capitals of the world. It is a pleasure to be here with so many of the world's greatest international retailers.

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  • How can I choose between Linux and Windows hosting?

    - by Mohamad
    I am a relative beginner when it comes to choosing web servers and hosting plans. I'm about to signup for a hosting plan with GoDaddy. My main requirement is ColdFusion and MySQL. The plans on offer include Linux and Windows based plans. Which one should I choose, and why? I don't have a lot of requirements other than what I mentioned above. I never used Linux before but I doubt I'll ever need to do anything beyond tampering with my account. What are the main advantages of one over the other?

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  • Build an Inexpensive but Polished Sous Vide Cooker for Geeky Culinary Fun

    - by Jason Fitzpatrick
    Kitchen craft has taken a turn for the geekier in the last few years with all manner of DIY projects; this DIY Sous Video cooker stands apart from the average hacked-together model and is polished enough to leave on the counter. We see a lot of cooking related hacks in our news feeds and this one is definitely one of the cleaner builds. It sports a clean display, nice case, and and easy to use interface–perfect for Sous Vide’ing yourself a delicious streak or other culinary treat. Hit up the link below for a full run down on the build. DIY Sous Vide Immersion Cooker On The Cheap [via Make] How To Customize Your Wallpaper with Google Image Searches, RSS Feeds, and More 47 Keyboard Shortcuts That Work in All Web Browsers How To Hide Passwords in an Encrypted Drive Even the FBI Can’t Get Into

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