نکته

On 14th December 1900, German theoretical physicist Max Plank published his seminal paper on the Quantum Theory of Radiation, and quantum physics was born! In the early years of the 20th century, quantum physics was further developed and applied to explain several other experiments by Albert Einstein, Paul Dirac, Neils Bohr and many others.

Quantum theory is extremely non-intuitive, and came as a shock to the physics community, shaking the foundations of scientific knowledge. American physicist Richard Feynman once said, “I think I can safely say that nobody understands quantum mechanics.”

Though a century old now, its interpretations still puzzle scientists and students alike, making it a hot topic for research, with new ‘theories’ coming up all the time!

Sass: Syntactically Awesome Style Sheets

Angular Gaurd

برای اینکه وسط یک کاری یک کاری انجام دهد مثلا وقتی کاربر یک آدرس را می اورد با استفاده از روت ها چک کند که آیا دسترسی دارد یا نه یا مثلا لاگ کند.

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SET versus SELECT when assigning variables?

SET is the ANSI standard for variable assignment, SELECT is not.

SET can only assign one variable at a time, SELECT can make multiple assignments at once.

If assigning from a query, SET can only assign a scalar value. If the query returns multiple values/rows then SET will raise an error. SELECT will assign one of the values to the variable and hide the fact that multiple values were returned (so you'd likely never know why something was going wrong elsewhere - have fun troubleshooting that one)

When assigning from a query if there is no value returned then SET will assign NULL, where SELECT will not make the assignment at all (so the variable will not be changed from its previous value)

As far as speed differences - there are no direct differences between SET and SELECT. However SELECT's ability to make multiple assignments in one shot does give it a slight speed advantage over SET.

نمایش دیراک

شخصی به نام پل آدریان موریس دیراک (Paul Adrien Maurice Dirac)، نمادگذاری جمع و جور و قدرتمندی را معرفی کرد که هم در فضای برداری و هم در فضای هیلبرت کاربرد دارد. به هر تابع موج ψ یک بردار حالت نسبت داده می‌شود که به آن «کت» گفته می‌شود. هم‌چنین به هر مزدوج مختلطِ تابع موجِ φ، یعنیφ* ، یک بردار حالت نسبت داده می‌شود که «برا» نام دارد. ضرب داخلی(φ,ψ) ، با «برا-کت»  نشان داده می‌شود.

Qubit

http://asiac.ir/?p=1382

قانون جابجایی ویلهلم وین فیزیکدان آلمانی:

 

حاصلضرب دمای مطلق یک جسم و طول موج تابش شده از آن یک مقدار ثابت است.

λ_max × T = C مقدار C در این فرمول 0.002897mK می باشد.

 

این موارد در فیزیک کلاسیک قابل توضیح نبودند که منجر به ایجاد فیزیک کوانتوم شد:

1. تابش جسم سیاه
2. پدیده فتو الکتریک
3. اثر کامپتون

Ultraviolet catastrophe

In the beginning there was continuous flow, and then Max Planck came along and proposed quantization. Quantization basically just means, that instead of being continuous, things such as EM radiation, can only exist in multiples of certain values. It’s a little bit like having a tube of smarties. The whole tube represents a beam of light. Inside it you have the smarties. You can split the tube, so you can have less smarties in there, or you can get another tube and have smarties, but you have to have a whole number of smarties, because they can’t be split (if anyone e-mails me suggesting I squash/crush/split a smartie, I will hunt them down and make them pay!).

Planck came to this conclusion when working on the “Ultraviolet Catastrophe”. According to classical electromagnetism, the number of ways an electromagnetic wave can vibrate a in a 3-dimensional cavity, per unit frequency, is proportional to the square of the frequency. This means that the power you would get out per unit frequency should follow the Rayleigh-Jeans law, which means that the power would be proportional to the frequency squared. So if you put the frequency up higher and higher the power would be unlimited. Planck said that electromagnetic energy did not follow the classical description. He said that it could only be emitted in discrete packets of energy proportional to the frequency

oblivious

Us : /əˈblɪviəs/   Uk : /əˈblɪvɪəs/

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(معمولا با: of یا to) بی خبر (از)، بی اعتنا (به)، فراموشکار، بی توجه