Recent Open Source Physics Releases

NVT-Molecular Dynamics Model

Sun, 19 May 2013 18:33:32 EST

The NVT-Molecular Dynamics Model performs molecular dynamics simulations at constant temperature of 32, 108, 256 or 500 molecules interacting through the Lennard-Jones potential, in a wide range of densities and temperatures covering liquid, vapor and solid states. Thermodynamic properties, radial and speed distribution functions, velocity autocorrelation functions (vcf's) and their Fourier spectra, and mean square displacements (msd's) are calculated and displayed. Self-diffusion coefficients are worked out from the vcf's and msd's. Self space-time correlation functions (sstcf's) are estimated and compared with the Gaussian approximation. The 3D molecular motions can also be visualized. The motion equations are integrated by two methods, at user's choice: the damped-force with leap-frog Verlet's algorithm, and the "ad-hoc" rescaling with the velocity Verlet algorithm. The model allows to assess the role of the potential cut-off distance, the number of steps in equilibration runs, the time-step and the gap between time origins for vcf's, msd's and sstcf's.

The NVT-Molecular Dynamics Model was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Re: Re: Augmented reality with remote cammera

Sat, 18 May 2013 11:52:55 EST

Open Source Physics Forum: EJS Modeling
Thread: Remote camera
Author: Diego Racero

Andres, thank you for your help.

I haven't got an IP cammera, I'm was trying to use VLC, but a founf a problem because I don't know what codec I may use in order to get the image displayed.

Have you got any adavice.

Thanks in advance.

Instantaneous Frequency Stock Market Model

Fri, 17 May 2013 09:42:02 EST

The Instantaneous Frequency Stock Model estimates a stock's cyclical fluctuations over a three-day period to determine how fast the market is moving. The instantaneous frequency of an input signal is calculated by modeling an input function's most recent data points as a sin wave and performing a Fourier transform to derive the function's frequency. This model implements different velocity indicators on daily closing prices of a few common companies, and allows the user to compare values of the indicators at different times.

The Instantaneous Frequency model was developed by Matt Mohorn using the Easy Java Simulations (EJS) modeling tool. You can examine and modify the physical model for this simulation if you have Ejs installed by right-clicking within the plot and selecting "Open Ejs Model" from the pop-up menu.

Re: Augmented reality with remote cammera

Thu, 16 May 2013 08:05:45 EST

Open Source Physics Forum: EJS Modeling
Thread: Remote camera
Author: Andres Mejias

Diego,

you need an IP camera and, in the remore AR system (from the View 3D palette in EJS) , you must define the camera URL. For example, I use an Axis IP camera, and a valid URL could be:

http://127.0.0.1:8083/axis-cgi/mjpg/video.cgi

(change it with your IP address and port if you have one)

The URL depends on camera model and brand. If you don't have an IP camera, you need an streaming server in order to use an USB or local camera as an IP camera. For example, videoLan (VLC) is a good choice. This option is more complicated, because you use a camera, a computer and the streaming server. With an IP camera, you just need to connect it to the wired LAN.

Regards

Andres Mejias

Augmented reality with remote cammera

Wed, 15 May 2013 12:19:09 EST

Open Source Physics Forum: EJS Modeling
Thread: Remote camera
Author: Diego Racero

I'm working with the augmented reality module with directly connected cammera and everything went ok, but I just can't figure out how to configure the remote module in order to place the cammera connected through wired LAN.
Could someone help me to find a solution?

Thanks in advance

Re: Re: Resetting certain variables with reset button but not all the variables

Thu, 09 May 2013 13:21:01 EST

Open Source Physics Forum: EJS Modeling
Thread: Resetting certain variables with reset button but not all the variables
Author: fergal wallace

worked great paco :-)
Many thanks!!

Re: Resetting certain variables with reset button but not all the variables

Wed, 08 May 2013 18:16:44 EST

Open Source Physics Forum: EJS Modeling
Thread: Resetting certain variables with reset button but not all the variables
Author: Francisco Esquembre

_reset() does the following:
- sets all variables to the values indicated in the tables of variables
- runs the Initialization code (+ Fixed relations)

however, initialise() only runs the Initialization code (+ Fixed relations)

By setting the value of some variables (and not others) in the Initialization pages, you can call initialise(9 to get what you want.

Cheers,

Paco

Resetting certain variables with reset button but not all the variables

Wed, 08 May 2013 10:16:06 EST

Open Source Physics Forum: EJS Modeling
Thread: Resetting certain variables with reset button but not all the variables
Author: fergal wallace

I'm trying to reset some of my variables with the rest button but not all the variables. Basically what i want to do is choose which variables are reset when the reset button is clicked.
_reset() is just resetting everything. I want to reset just three variables.
Seems like such an easy thing to do in my head but i've just had trouble with it.
Any help much appreciated!!

Re: using number fields

Tue, 07 May 2013 07:50:13 EST

Open Source Physics Forum: EJS Modeling
Thread: number fields
Author: Jean-Philippe Grivet

Problem solved!
One has to hit to validate any modfication
JP Grivet

using number fields

Tue, 07 May 2013 05:48:35 EST

Open Source Physics Forum: EJS Modeling
Thread: number fields
Author: Jean-Philippe Grivet

Hello,
I am learning how to use EJS to creat simulations. I have tried to run the simulation

\EJS_4.3\workspace\source\users\ehu\jma\oscillations\oscillator.xml

The compilation and generation are done without problem, the simulation runs quite well,
except for the following. In the nice display, there is a column of number fields provided to
alter various parameters. However, these fields are not active: modifying any of them changes
nothing in the simulation.

What should I do to make these fields active, and the simulation really effective ?

TIA

JP Grivet

file naming convention

Fri, 03 May 2013 10:34:43 EST

Open Source Physics Forum: EJS Modeling
Thread: Help about files
Author: Jean-Philippe Grivet

My first attempts at EJS programming produced files with a .XML suffix. I have now written a slightly more complex program which EJS stores with a .ejs suffix; why ? Further, if I change the suffix to .xml, EJS opens the file in the Win notebook and shows unformatted xml ??

another question: I don't understand how I can choose files to be exported as HTML.

Thank you in advance for your time and help
JP Grivet

bug report on Equation EJS_4.3.7_130310 and EJS_4.3.6_120219

Wed, 01 May 2013 21:28:24 EST

Open Source Physics Forum: EJS Modeling
Thread: bug report on Equation EJS_4.3.7_130310 and EJS_4.3.6_120219
Author: lookang

bug report on Equation EJS_4.3.7_130310 and EJS_4.3.6_120219.

hi professors,

it seems the equation is bugged.

i added the equation and the EJS cannot read the file correctly now.

this is the correct file without equations https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejs_GFieldandPotential1Dv7EarthMoon.jar

this is the bug after adding equations

https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejs_GFieldandPotential1Dv9EarthMoon.jar

https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejs_GFieldandPotential1Dv8EarthMoon.jar

the desired look of the simulation with latex equation is like this

version april 30 2013 http://weelookang.blogspot.sg/2010/08/ejs-open-source-gravitational-field_10.html
picture of computer model of Earth and Moon gravity system,
added white backgroundoption for printing on lecture notes, fixed bug of g2 showing, latex (appears to be not working yet) for g and phi,menu for EarthMoon configuration instead of just MoonEarth previously
https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejs_GFieldandPotential1Dv8EarthMoon.jarauthor: lookang and andrew based on andrew duffy early model

Post edited May 1, 2013 at 9:33 PM EST.

Re: adding checkbox for multiple radioactive sources

Wed, 01 May 2013 21:22:06 EST

Open Source Physics Forum: EJS Modeling
Thread: adding checkbox for multiple radioactive sources
Author: lookang

hi fergal,

u can refer to the source code in this model for the checkbox option. http://www.compadre.org/osp/items/detail.cfm?ID=9707

or the updated version available here

http://weelookang.blogspot.sg/p/physics-applets-virtual-lab.html

31 October 2011 added magnify and random length objects to challenge students to think more, hopefully more fun to figure out for themselves! http://weelookang.blogspot.sg/2010/06/ejs-open-source-vernier-calipers-java.html https://dl.dropbox.com/u/44365627/lookangEJSworkspace/export/ejs_AAPTVernierCaliper.jar author: Fu-Kwun and lookang (this remix version)

Post edited April 19, 2013 at 3:48 AM EST.

Post edited April 19, 2013 at 3:49 AM EST.

Post edited April 19, 2013 at 3:50 AM EST.

adding checkbox for multiple radioactive sources

Wed, 01 May 2013 08:43:45 EST

Open Source Physics Forum: EJS Modeling
Thread: adding checkbox for multiple radioactive sources
Author: fergal wallace

I'm trying to add a checkbox containing three radioactive sources to demonstrate the attenuation coefficient of gamma rays with matter. I have the simulation working fine with just a cobalt60 source but i want to expand on this now and add strontium and cesium using the same coding but different variable values for the new sources when they are selected.
Any help would be much appreciated

Re: Re: Re: Re: Re: Re: image's center of rotation

Sat, 27 Apr 2013 03:21:02 EST

Open Source Physics Forum: EJS Modeling
Thread: Center of rotation
Author: way better

try an image programme to see if is working dynamically. rotate the image's center is not an easy job for us new to image app.

gold find :)

Fri, 26 Apr 2013 01:36:58 EST

Resource Title: Teaching with Moodle and OSP Plugins
Author: lookang

the moodle in davidson is packed with lots of public resources that can help anyone learn.
love it!

Re: Re: combobox how to use the tool?

Tue, 23 Apr 2013 18:10:52 EST

Open Source Physics Forum: EJS Modeling
Thread: ComboBox
Author: Gabriel Ribeiro

The file is attached.
Thank you.

Gabriel Ribeiro

Re: Re: EJS_4.3.7_130310 Editors do not start

Sun, 21 Apr 2013 10:42:08 EST

Open Source Physics Forum: EJS Modeling
Thread: EJS_4.3.7_130310 Editors do not start
Author: Francisco Esquembre

That's fine. The important is that you can now run EJS.

Paco

Re: EJS_4.3.7_130310 Editors do not start

Sun, 21 Apr 2013 06:18:34 EST

Open Source Physics Forum: EJS Modeling
Thread: EJS_4.3.7_130310 Editors do not start
Author: Cleon Teunissen

Trying java -jar EjsConsole.jar (in the appropriate directory) seemed to indicate a Windows permission problem.

I re-downloaded and unzipped, and that version started correctly. (As always on first use of software Comodo Defense+ software prompted me whether to allow the program to proceed.)

But later with the same EJS the editors didn't start anymore.
It occurred to me I had renamed the directory (Defense+ identification includes the path).

Often when I want to test I open the Comodo Security menu, and I click 'exit', to exclude security software interference. Did that, and then checked, and I saw this time Comodo was still running. Apparently, when I click 'exit', Comodo doesn't actually exit (or not always).
So I tried setting Defence+ to 'disabled'.
Then EJS started normally.

I opened a Comodo configurator window, and added an explicit 'allow' rule for EJS and everything in its subdirectories.
After that EJS started normally.

Conclusion: Comodo Security was the cause of the denial of permission, it wasn't an EJS error.
Paco, I owe you an apology. I failed in making sure it wasn't Security software interference.

Teaching with Moodle and OSP Plugins

Fri, 19 Apr 2013 15:16:15 EST

This talk describes Moodle courseware created at Davidson College for introductory physics and astronomy courses that, in addition to standard Moodle content, incorporate in-class polling and simulations using open source Moodle plugins. We will show how we use the In-class Polling for All Learners (IPAL) plugin developed by Bill Junkin to download questions from a databank in the ComPADRE digital library. We will also show how to use the EJSApp plugin developed by Rubén Heradio and Luis de la Torre Cubillo at the National Distance Education University (UNED) in Madrid to embed Easy Java Simulations (EJS) applications (such as simulations, virtual and remote laboratories) into a Moodle course. These tools allow teachers to easily incorporate computer-based modeling into their curriculum by providing an open and extensible solution for incorporating interactive engagement pedagogies into their Moodle courses.

Function to return an integer problem

Fri, 19 Apr 2013 09:01:04 EST

Open Source Physics Forum: EJS Modeling
Thread: Problem with code in On Release of a Slider View
Author: Eoghan Miggan

Hey, so I wrote a function to get a random number between two value ranges as so:

public int getRandomNumber(int lowest, int highest){

int num = highest - lowest;

Random rand = new Random();
int i = rand.nextInt(num) + lowest;

return i;

}

For example if I was to say N = getRandomNumber(340, 385); and call this in the evolution page then it works and returns a random number between 340-385 over and over and over when play() it clicked.

But when I call this function in the On Release code of a Slider view, it only returns int's of values 1-9.

Does anyone know why this is?

Re: combobox how to use the tool?

Fri, 19 Apr 2013 03:45:43 EST

Open Source Physics Forum: EJS Modeling
Thread: ComboBox
Author: lookang

hi gabriel, u can refer to the source code in this model for the checkbox option. http://www.compadre.org/osp/items/detail.cfm?ID=9707

or the updated version available here

http://weelookang.blogspot.sg/p/physics-applets-virtual-lab.html

Post edited April 19, 2013 at 3:48 AM EST.

Post edited April 19, 2013 at 3:49 AM EST.

Post edited April 19, 2013 at 3:50 AM EST.

Re: Re: EJS_4.3.7_130310 Editors do not start

Thu, 18 Apr 2013 16:04:16 EST

Open Source Physics Forum: EJS Modeling
Thread: EJS_4.3.7_130310 Editors do not start
Author: Francisco Esquembre

Cleon,

The only thing I can think of is that you start the console from a command window using:
C:\> java -jar EjsConsole.jar
and see if this command window shows any error message. If so, please , send this message to me or post it here.

Paco

Re: EJS_4.3.7_130310 Editors do not start

Thu, 18 Apr 2013 15:59:53 EST

Open Source Physics Forum: EJS Modeling
Thread: EJS_4.3.7_130310 Editors do not start
Author: Cleon Teunissen

Paco,

thank you for your effort.

You mention: 'errors should show in the EJS console'.
Unfortunately, what I get in the output tab of the EJS console is devoid of clues.
The usual output in the EJS console consists of three lines, and the first two are as follows:

RMI registry started at port: 2008
EjsConsole server is ready to listen at port: 2008

And the third line with all the technical information.

On my setup (W7 Pro, JRE 1.7 update 21) the output in the EJS console output tab reads as follows:

RMI registry started at port: 2008
EjsConsole server is ready to listen at port: 2008
The Program selected is NOT running

That is all. So there is no clue.

My best guess is that the Oracle Java Virtual Machine behaves differently on different platforms. I assume that running a VM in a Mac is not the same as running Windows directly.

EDIT:
I forgot to mention: I also tried the same setup with the Internet Firewall program that I use shut down, to see if maybe the problem was due to some sort of firewall interference. Same error.

Cleon

Post edited April 18, 2013 at 4:04 PM EST.

Re: EJS_4.3.7_130310 Editors do not start

Thu, 18 Apr 2013 14:30:48 EST

Open Source Physics Forum: EJS Modeling
Thread: EJS_4.3.7_130310 Editors do not start
Author: Francisco Esquembre

Cleon,

I just tested with Java 1.7 release 10 and then updated to the latest (21) to do the test again. No problem at all with EJS 4.3.7 130310 just downloaded from the EJS web page. I tested both in a 64 bits Mac OS X Mountain Lion and a 32 bits Windows 7 (running in a VM in my Mac with Parallel Desktop).
You are right that EJS does not use the Java logging mechanism, though. But errors shoudl show in the EJS console.

I am running my EJS in 1.7 regularly since it appeared. And I have found no problems.

Paco