Articles

Checking whether a class is defined in CSS

Wednesday, 16 June 2010 22:03 |

Written by tushev |

Most of modern JS frameworks allow to check, whether an element has a particular class. However, I could not find something in jQuery related to checking, whether ther's a particular class in CSS. So, after googling for a while, I found the function which does this extremely well. I'm republishing it to save your time:

function getDefinedCss(s){
 if(!document.styleSheets) return '';
 if(typeof s== 'string') s= RegExp('\\b'+s+'\\b','i'); // IE capitalizes html selectors 

 var A, S, DS= document.styleSheets, n= DS.length, SA= [];
 while(n){
 S= DS[--n];
 A= (S.rules)? S.rules: S.cssRules;
 for(var i= 0, L= A.length; i<L; i++){
 tem= A[i].selectorText? [A[i].selectorText, A[i].style.cssText]: [A[i]+''];
 if(s.test(tem[0])) SA[SA.length]= tem;
 }
 }
 return SA.join('\n\n');
}

This function accepts an name of class or id(sure, without . or # ). In case it founds something, it returns the citation from CSS. Try it yourself!

Replacement for standart Windows Task Manager

Friday, 04 June 2010 16:56 |

Written by tushev |

Despite Windows Task Manager is a well-balanced program, there are more options to be desired. First of all, I'd like to be able to see the whole process structure - including hidden processes and the sequence of calling. As well I'd like to see more information on each process - including it's libraries, open network connections, perfomance statistics, command line parameters etc.

Process Explorer from Sysinternals has all of this features. It's a lightweight (~4MB, 1.5 MB zipped) and useful program. It can be downloaded from Microsoft TechNet - http://technet.microsoft.com/en-us/sysinternals/bb896653.aspx.

I installed this program once, and never more used ordinary task manager. Process explorer completele replaces its functionallty, as well adding a bunch of new capabilities and tools. So I activated Options->Replace Task Manager ;-)

Using Recovery console to restore and backup system registry

Friday, 04 June 2010 16:18 |

Written by tushev |

We all know that it's diffucult to make backup of Windows registry. This is because OS prevents direct access to the files, even for reading, so we have to use an alternate tools. But when you are running a Recovery console (as well as any other OS) you can access those files, copy and replace them.

Putting yourself on a safe ground - installing a recovery console

Friday, 04 June 2010 16:09 |

Written by tushev |

This tip is suitable only if you are running Windows XP, 2000, 2003 Server, MCE 2005. Windows Vista and 7 do not include this feature - look here for more info: http://windowslive.com/Connect/Post/E8E5CC039D51E3DB-2123982

Windows Recovery console is a tool that helps you to recover your OS from serious errors. In fact, it's a small operating system from Microsoft (but incapable of running any programs, except several built-in commands). It is available from some installation CDs (when booting from them), but as well you can always install it on a hard drive - indo a hidden folder, cmdcons, on a boot partition.

To install it, press Win+R, type cmd, press ok, then type X:\i386\winnt32 /cmdcons (replace X with actual letter of your optical drive). After installation, a new option appears in your boot menu - it's a Recovery console. If a problem occures, you can use it to fix the issues.

Using command line to close hanged apps

Friday, 04 June 2010 16:07 |

Written by tushev |

Sometimes we find ourseleves in situation, in which an app hanged up(especially a full screen one), but we still have control over the machine - we can use start menu, other app etc. However, we cannot see what's going on because of the hanged app (and remove it from running processes in Task Manager (or Process Explorer).

Choosing a telescope

Friday, 14 May 2010 21:50 |

Written by tushev |

Choosing a telescope, especially the first one, is always a very important question. What will you be able to see, almost all your emotions and comfort depend on the instrument, so you have to choose it carefully.

The most important thing, I suppose, is the quality of optics. You will not get any pleasure from using a scope with wide-diameter, but not very good mirror or lens. So always try to get the best thing you can afford, and there's some reason in buying less smaller, but more qualitative telescope.

Optical system

First of all, you shold know that all telescopes are divided into three main groups: refractors (those use lens as a primary optical element), reflectors (mirror), and catadioptric (combining lens and mirror). Reflectors are easiest to produce (there's only one surface to be made), and, consequently, the cheapest. Almost all large telescopes are reflectors.

Refractor

Reflector

Catadioptric

There are hot discussions of choosing a type of scope. I'm not going to cite all the things, just name some most important facts:

Reflectors are cheaper => you can get bigger diameter and see more objects (see below)
Reflectors have less weight
Reflectors provide upturned image. There's practically no difference for vieving celestial objects, but this may be inconvinient for ground observations.
Refractors are less sensitive to humidity, temperature, there's less air turbulence in the tube
Refractors have practically no reflected light inside their tube, so the sky seems darker and you can distinguish more faint objects
Refractors do not have central mirror that screens a part of the objective, so they utilise almost 100% of following light (except percents of light reflected and absorbed in lens)
Catadioptrics provide the best image
Catadioptrics are the most compact scopes, and the most expensive

So, for a beginner, I'd recommend a following rule:

If you are going to buy a telescope with a diameter less than 100mm, take refractor, greate than 100 mm - take reflector.

As well, if you are going to buy a telescope with aperture greater than 150mm, you may take a catadioptric system (or a reflector, if you cannot afford catadioptric).

Objective diameter (aperture)

This is a diameter of your telescope primary optical surface (a lens or a mirror). The bigger is it, the more light collects your telescope, and the more faint objects become available to distinguish.

For a beginner, optimal diameter is 110-150 mm. However, if you are eager for watching deep-sky objects, like nebulaes, galaxies etc, take as greater aperture as you can.

Telescope mount

A mount is a system that support your telescope and allows its pointing into different direction. It consists of a stationary part (usually a tripod or a pole) and a moving one.

There are two main types of mounts: equatorial and azimuthal. The last one is a simple structure that allows you to rotate the scope around vertical axis - to different corners of earth, and point it higher or lower. It's very easy to use and understand. However, it requires constant adoption of telescope direction because of rotation of the sky.

Equatorial mount is free of this weakness. It has an axis pointed to the celestial pole (e.g., nearby a Polar Star in Nothern hemisphere). As you know, all the sky rotates around this pole, so rotating the scope around polar axis with the speed of Earth rotation (~7.29 × 10⁻⁵ radians per second) will keep the scope pointed to the same point of the sky all the time.

Look here for more info: Equatorial coordinate system, Celestial coordinates, Equatorial mount.

I'd strongly recommend to purchase an equatorial mount. An azimuthal mount may be suitable only if you are plannning to do ground observations as well.

There are several typical mounts on the market. For amateur scopes there are EQ1, EQ2 and EQ3. EQ1 is the cheapest, but it's sensitive to vibrations. For most scopes an EQ2 will be optimal.

These three parts are constituitive for a scope. As well as there are another things, such as a set of oculars, aceessoires, finder, hour drive, authomatization etc. But those are a theme for a separate article.

tushev.org

Articles

Checking whether a class is defined in CSS

Replacement for standart Windows Task Manager

Using Recovery console to restore and backup system registry

Putting yourself on a safe ground - installing a recovery console

Using command line to close hanged apps

Choosing a telescope