44,955 research outputs found
The municipal archives of the City of New York
Ith some 100,000 cubic feet of civic documents, vital and building records, libers, films and photographs, New York City's Municipal Archives is a magnet for researchers. Among those who benefit from centralized access to the wealth of material deposited in the Archives by city government agencies are genealogists,
urban scholars and architectural historians
A globally convergent flow for computing the best low rank approximation of a matrix
We work in the space of -by- real matrices with the Frobenius inner
product. Consider the following
Problem: Given an m-by-n real matrix A and a positive integer k, find the
m-by-n matrix with rank k that is closest to A.
I discuss a rank-preserving differential equation (d.e.) which solves this
problem. If X(t) is a solution of this d.e., then the distance between
and decreases as t increases; this distance function is a Lyapunov function
for the d.e. If has distinct positive singular values (which is a generic
condition) then this d.e. has only one stable equilibrium point. The other
equilibrium points are finite in number and unstable. In other words, the basin
of attraction of the stable equilibrium point on the manifold of matrices with
rank consists of almost all matrices. This special equilibrium point is the
solution of the given problem. Usually constrained optimization problems have
many local minimums (most of which are undesirable). So the constrained
optimization problem considered here is very special
Time-spliced X-ray Diffraction Imaging
Diffraction imaging of non-equilibrium dynamics at atomic resolution is
becoming possible with X-ray free-electron lasers. However, there are
unresolved problems with applying this method to objects that are confined in
only one dimension. Here I show that one-dimensional coherent diffraction
imaging is possible by splicing together images recovered from different delays
in a time-resolved experiment. This is used to image the time and space
evolution of antiferromagnetic order in a complex oxide heterostructure from
measurements of a resonant soft X-ray diffraction peak. Mid-infrared excitation
of the substrate is shown to lead to a magnetic front that propagates at a
velocity exceeding the speed of sound, a critical observation for the
understanding of driven phase transitions in complex condensed matter
The Legend of the Wehrmacht’s “Clean Hands”: The Attempt to Remove Nazism from the German Military
The legend of the Wehrmacht’s “clean hands” was created with the Himmerdoer Memorandum of 1950 and sought to disassociate the German military with its Nazi past. The legend gained popularity in the minds of the German people and successfully led to Germany’s rearmament after World War Two. Beginning in 1990, the legend was destroyed as the actions of the Wehrmacht during World War Two created a different picture than that of the legend. The Wehrmacht’s hands were far from “clean” and instead were very dirty
Personnel and the Library School
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