Allen Majewski


Department of Physics, University of Florida

Temperature Effects in Nuclear Quadrupole Resonance Spectroscopy


Temperature Dependence of Solid State Nuclear Quadrupole Resonance

Design of Impedance Matching Networks for NMR and NQR Studies in the HF Band

FULL TEXT (PDF)

Search for Nuclear Quadrupole Resonance in an Organic Quantum Magnet

FULL TEXT (PDF)

By ALLEN R. MAJEWSKI
A QUALIFYING EXAM PAPER PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
2015

Bitcoin-data manipulaton and plotting in python

Screen Shot 2015-05-30 at 9.08.52 AM

I wrote a python mini-api to manipulate and visualize the price of bitcoin historically using the coinbase version 1 api. See my blog post or fork it on github

How random is /dev/random? Visualizing the output of /dev/random using hexdump, dd, and python

I wrote a python script that will plot the output of /dev/random in a few ways so you can see just how random it is.

Make a line plot:

Screen Shot 2015-05-30 at 9.08.52 AM

Make a histogram

Screen Shot 2015-05-30 at 9.08.02 AM  

Options

Edit the block size and/or block count in *.sh to change the output resolution:

Screen Shot 2015-05-30 at 8.33.37 AM

Remember that on OSX, /dev/random and /dev/urandom are identical. On linux, to get 100 blocks as I have, you may have to use /dev/urandom (unlimited random). The linux case is probably more interesting as the outputs are different. How exactly DO they differ?

OSX is known to use Yarrow-160 a cryptographic algorithm that makes use of hash functions (specifically SHA1) to create "unlimited" seemingly-random bits from a finite entropy pool.

As far as I know, linux does not. Linux will wait for more entropy when /dev/random is used as opposed to /dev/urandom.

See blog post and github repository.


NQR: forthcoming qualifying exam presentation slides on NQR possiblities in solids

... especially dichloro-tetrakis-thiourea-nickel, a Bose-Einstein condensate quantum magnet


Theory of nuclear quadrupole moment - field interactions, and transitions frequencies

... a quantitative exploration of the soelectric field gradient tensor's coupling to the quadrupole moment of nuclear sites in solids ... ... Consider a particle of charge q in the vicinity of a localized charge distributoon ρ(x). The electrostatic energy of the stystem can be written in terms of the multipole moments ...


Calculations-of-the-EFG-tensor-in-DTN-using-GIPAW-with-CASTEP-and-QE-software

... One important difference between NQR and NMR is that for NQR, the transition frequency is site specific and cannot be chosen by the experimenter. In NMR studies, the excitation frequency of the nucleus is just the gyromagnetic ratio times the applied field. Thus, the difficulty in NMR is controlling the uniformity of the applied static B. However, the experimenter is free to choose an operating frequency by adjusting B. For NQR, the transition frequency is proportional to the electric field gradient (EFG) at the nuclear site, which is entirely a property of the substance and a function of temperature. While it is theoretically possible to apply a prescribed EFG in the lab, it is unfeasible as the EFG's in crystal strcutures are often on the order of many kV/m^2. Thus the particular difficulty in NQR spectroscopy is locating the resonance in the first place, which is difficult if not hopeless if the apparatus runs at a fixed frequency and the search space is several orders of magnitude in frequency. The home made pulsed superheterodyne spectrometer used in the trial experiments has proven to have excellent resolution. However, it has essentially no ability to perform frequency sweeps ...


35Cl and 14N Nuclear Quadrupole Resonance in Paradichlorobenzene, Sodium Chlorate, and Hexamethylenetetramine

... Pulsed nuclear quadrupole resonance studies were carried out in sodium chlorate, para-dichlorobenzene in 35Cl. The 14N nuclear quadrupole resonance (NQR) in hexamethylenetetramine was observed using pulsed techniques on a home built superheterodyne spectrometer with a hybrid tee bridge configuration. High S/N was achieved with robust isolation techniques, high quality fast recovery amplifiers, and high Q resonant tank. All studies were conducted using the same apparatus. The superheterodyne was largely unchanged for the three studies except for the tank section and the pulse protection circuitry between the power amplifier and the receiver section. An exact calculation of probe parameters was made. Evidence of an non-zero assymetry parameter in HMT was observed, but more research is needed...


Does a copy of Hamlet lie buried within the digits of pi?

Yes...yes it does.


Easy impedance matching in NMR tanks using L-networks

A method of reducing the number of free parameters from 2 to 1 for matching


A JFET preamp for the LM386

Cigar box guitar amp with LM386 + JFET preamp guide with LTSpice guide


Are sawtooth waves a complete set?

Here I represent a sine as a sum of sawtooth waves and note the weird convergence


Hexadecimal word games

As it turns out, !fail=forsee


Sad grep

:-(


Generating arbitrary sounds from waveforms on a pc

Home made synthesizer on a raspberry pi with mathematica



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