Screening Definition and 38 Threads

In the Jellium model, it is customary to evaluate the exchange term of the Hartree-Fock equation for plane waves ##\varphi_{\mathbf{k}_i}## as a correction to the energy of the non-interacting electron gas obtaining $$\hat{U}^{ex} \varphi_{\mathbf{k}_i}=-e^2 \left( \int \dfrac{\mathrm{d}^3k}{2...

Consider a 5 m diamter trampoline. It has an area of not quite 20 m2 If a jumper sinks 1 meter into the mat at center, the volume of the displacement cone is 6.5 m3 (1/3 base of cone times height) Because air as to move in over the top, as well as get out from under, the air moved per jump...

This weekend (June 26-28) the IEEE Information Theory Society is showing a free screening of The Bit Player - a movie about Claude Shannon (the "father" of information theory) The website below has the link and password for Vimeo...

Check out the full lecture on the Royal Institution YouTube channel.

I get the basics of green screening. The processing software recognizes a small range of green and can substitute a different image where it occurs. Here's what I don't get: if a subject is standing in front of a green screen, they will have reflections of green. Notice that, in the...

Hi, I have difficulty understanding the term screening. Screening is reducing of the electric field, as far as I have understood until now. 1. Why does screening occurs? Is it due to collective interaction of plasmons? 2. If we have a slow electric field, will screening occur or will it not...

What is the procedure for full male STD screening? Is it painful?

Books say 3 possibilities for this situation as insert within Lacz, insert outside Lacz, no inserted vectors, then these goes the transformation with Ecoli. But we can't know transformation yield %100. Thus, if we make blue white screening there is more possibilities. Lacz-- inserted within...

Homework Statement The aim of a laboratory course was to measure the x-ray fluorescene spectra of 20 metallic samples. By comparison of the peaks in the energy spectra with known electronic transitions (e.g. ##K_α## of ##Cu##) the materials were identified. After that, Moseley's law $$...

Hi All, I needed some help or guidance starting my MSc reading, as there is tonnes of literature out there and it's difficult to understand what is necessary. I am beginning to look at applying screening models to a 2D system, such as the Thomas-Fermi continuum screening model, to a 2D system...

The following article says virtual particles don't exist or are just book keeping device. https://www.physicsforums.com/insights/physics-virtual-particles If that's the case, then how do you explain charge screening? We observe the charge of an electron to be less than the bare charge, or what...

Hello! I read today about the screening in QED and vacuum polarization. And the image they used to explain it was an electron surrounded by a ring of positrons and then by a ring of electron, which makes sense. Now, the Gauss's law outside and inside the 2 rings will give the same result, as the...

In multiple-electron atoms the effective charge of nucleus for a given electron, is reduced by the presence of other electrons (including those from more external shells, against the shell theorem): Z_eff = Z - s where the screening constant s depends on Z and the concerning orbital. It is...

Can anyone explain in simple terms what the term screening means? My intuition is that a metal is a good screener because in the presence of an external electric field its free electrons will rearrange themselves such that the electric field is zero inside the metal. But I am having a hard time...

Hi All, It is said that iron has a high "permeability" for the magnetic field, it let's the magnetic field pass through it more easily. But it is also said that iron screens the magnetic field? Don't these two contradict themselves? Thanks, Ionel

If a material is doped (introducing positive dopants to the lattice) there will be a build up of negative cahrge around them, screening. I have a couple of questions that seem obvious but I'm still a little unsure: 1) how would more screening effect resistivity? I would assume that a build up...

if I have a not necessarily homogenous electric field of a charge distribution in an electrolyte and i want to find out what the electric field at some position in the electrolyte is. is there any equation that i could use to consider also electric screening by the ions, so that I will get a...

Why exactly does an increase in the oxidation state of an element (i.e., higher positive states) reduce the screening of core electrons? For example, why would fewer electrons in a d state alter (increase) the effective charge experienced by a p state?

Dear physics forums users, I'm reading a paper saying "For hole density p\sim 10^{17} - 10^{18}/cm^3, the screening length in silicon, \lambda_{Si}, is ~1-2nm." For this, the paper references Sze's, Physics of Semiconductor Devices. I'm unable to find the formula by which the authors seem to...

I got quite confused with the math in Thomas-Fermi's approximation. I thought it was supposed to approximate a length but the math from a textbook gives energy instead. I don't understand what is it trying to approximate. My professor told me that normal conductors screen electric field...

Somewhat unusual question: Do you think LMP7721MA would get degraded by xrays used for luggage screening? It is an electrometer opamp with extremely low input bias current: http://www.national.com/pf/LM/LMP7721.html#Overview Normally the electronics is not affected by the xrays but this...

Hi! I have to understand how this integral is evaluated (it is taken from Fetter - Quantum theory of many particle systems)(14.24): http://dl.dropbox.com/u/158338/fis/fetter.pdf" in particular, i don't know how the log brach cuts are defined.. as far as I know, log branch cuts can be...

Homework Statement I have a multichoice past exam that does not come with answers. Please help with the following: The reason why alkali metals have the largest radii but smallest ionisation energies is best described by the fact: a) screening is least effective for a lone electron...

I'm reading The Lightness of Being by Frank Wilczek. In a footnote talking about screening of a (real) positive charge by virtual particles (p47), he says "Thus the force falls off faster than 1 over the distance squared, as you'd have without screening" (by virtual particles). How then...

Why is the screening effect of d orbital electrons less than that of s and p electrons?

Homework Statement I'm supposed to show that the Lindhard dielectric functions gives a contribution to the effective potential of a metals as U_{eff}( \vec{r} ) \propto \frac{cos( 2 k_{F}r)}{r^{3}} in the limit of r\rightarrow\infty for d = 3 (3 dimensions) Homework Equations...

Could anyone give me a couple of sentences to what it is?

Hello, Chemistry grad student here about to start a physics-y project...so trying to learn about condensed matter physics. I get how screening works when you add a single charge to a gas of electrons, but what happens in a metal when you have a whole lattice, ie, a background charge density...

Why is there no notices regarding JEST 2010? Its conducted in february each year i heard. Why haven't they started asking for applications yet? And will it be conducted on the same date as GATE?

"Electron screening" came up in a homework assignment, and I'm not sure what it means exactly. All I've been able to find on the general topic is that it relates to charge (which I may very well have misunderstood). The homework question is about terms in the SWE for Li which represent...

Dears How Electron screening occurs and what it is mean? does it affect the cross secction of the fusion? Regards

Homework Statement In xenon (Z = 54), what is the effective charge Zeff experienced by an electron in the M (n=3) shell? Homework Equations Zeff = Z - total electrons in K and L shells The Attempt at a Solution I think total electrons in K shell are 8 and in L shell are 18...

In lecture today, we were going through Griffith's QM, Chapter 7, The Variational Principle. The particular case is the ground state of Helium, where we consider the electron-electron interaction as a potential in the Hamiltonian. When all is said and done, we go further and kind of...

Ok I've had this problem with this last part of this one question. Show that Moseley's Law for Ka radiation may be expressed as sqrt(f)=[sqrt((3/4)*(13.6/h))]*(Z-1) where f is the x-ray frequency and z is the atomic number. (b) Check the agreement of the original 1914 data shown in Figure...

How much would a DNA screen reveal about someone's personality and intelligence? :confused:

Not a live performance :frown: ALL LOCATIONS ARE ON SALE NOW: New York (Farmingdale) - Farmingdale Multiplex in Long Island http://www.movietickets.com/pre_purchase.asp?house_id=1095&movie_id=51759&showdate=7 Los Angeles - Universal CityWalk Theatres...

My friend's family has a history of cancer, could she be screened for (genetic) markers that indicate high risk for certain cancers or something and how much would that cost and how helpful would it be thanks

Airports are thinking about installing new backscatter X-ray machines for screening passengers (http://www.campaignfortruth.com/Eclub/210703/CTM-airportxray.htm These screeners see through clothes, but bounce off metal and skin, leaving the traveller essentially naked to the person...