2,444 research outputs found
Crystal cleaving machine
A machine is disclosed for cleaving hard crystals. A typical example of which is lithium fluoride, with prcision and uniformity and includes vertical axis positioning control means for an adjustable spring tension guided hammer mechanism employed to strike an anvil. A crystal cleaving shock wave transmitted to a cleaving blade is generated having an angulated cleaving edge in contact with one corner of the crystal. Connection between the anvil and the blade is by means of a pair of vertical shafts held in substantially friction free engagement by two pairs of adjustable linear bearings. An underlying crystal holding fixture with horizontal position control means includes a zero reference stop face for the crystal and opposing spring-loaded clamping and vertical positioning elements which are precisely guided
Workpiece positioning vise
A pair of jaw assemblies simultaneously driven in opposed reciprocation by a single shaft has oppositely threaded sections to automatically center delicate or brittle workpieces such as lithium fluoride crystal beneath the blade of a crystal cleaving machine. Both jaw assemblies are suspended above the vise bed by a pair of parallel guide shafts attached to the vise bed. Linear rolling bearings, fitted around the guide shafts and firmly held by opposite ends of the jaw assemblies, provide rolling friction between the guide shafts and the jaw assemblies. A belleville washer at one end of the drive shaft and thrust bearings at both drive shaft ends hold the shaft in compression between the vise bed, thereby preventing wobble of the jaw assemblies due to wear between the shaft and vise bed
Method and apparatus for slicing crystals
The crystal slicing method is described as follows. A crystal is sliced in a plane parallel to flat, opposed parallel end faces of the crystal. The end faces of the crystal are gripped by a pair of opposed, perforated platens of a pair of vacuum chambers, one of which is translatable relative to the other. A blade cuts the crystal through the desired plane. A spring biases one of the vacuum chambers away from the other vacuum chamber while both of the faces are gripped by the vacuum chambers and the blade is cleaving the crystal. A sliced portion of the crystal gripped by one of the vacuum chambers is pulled away from the remainder of the crystal gripped by the second vacuum chamber when the crystal was cleaved by the blade through the plane
Quantum phase transition between one-channel and two-channel Kondo polarons
For a mobile spin-1/2 impurity, coupled antiferromagnetically to a
one-dimensional gas of fermions, perturbative ideas have been used to argue in
favor of two-channel Kondo behavior of the impurity spin. Here we combine
general considerations and extensive numerical simulations to show that the
problem displays a novel quantum phase transition between two-channel and
one-channel Kondo screening upon increasing the Kondo coupling. We construct a
ground-state phase diagram and discuss the various non-trivial crossovers as
well as possible experimental realizations.Comment: 5+4 pages, 5+3 fig
Dynamical Mean Field Theory with the Density Matrix Renormalization Group
A new numerical method for the solution of the Dynamical Mean Field Theory's
self-consistent equations is introduced. The method uses the Density Matrix
Renormalization Group technique to solve the associated impurity problem. The
new algorithm makes no a priori approximations and is only limited by the
number of sites that can be considered. We obtain accurate estimates of the
critical values of the metal-insulator transitions and provide evidence of
substructure in the Hubbard bands of the correlated metal. With this algorithm,
more complex models having a larger number of degrees of freedom can be
considered and finite-size effects can be minimized.Comment: 5 pages, 4 figure
Mott transition in the Hubbard model away from particle-hole symmetry
We solve the Dynamical Mean Field Theory equations for the Hubbard model away
from the particle-hole symmetric case using the Density Matrix Renormalization
Group method. We focus our study on the region of strong interactions and
finite doping where two solutions coexist. We obtain precise predictions for
the boundaries of the coexistence region. In addition, we demonstrate the
capabilities of this precise method by obtaining the frequency dependent
optical conductivity spectra.Comment: 4 pages, 4 figures; updated versio
Using Narrative Inquiry to Explore Critical Reflection and Self-Awareness in Equity Leadership Development
Critical reflection and self-awareness are two of the most crucial components in developing equity-centered leaders (Dugan and Humbles, 2018; Madsen, 2020; Patti, Madrazo, Senge, and Stern, 2015). Leading for equity requires the leader to face both personal bias and professional challenges (Boske, 2014). Many leaders are willing to engage in the work of leading for equity but lack clarity about where to start and how to proceed, often seeking out external tools. Using narrative inquiry, this study collected leaders’ stories to understand the participants’ perspective of self, the understanding of their own journey, and the connections to their leadership work
State-of-the-art techniques for calculating spectral functions in models for correlated materials
The dynamical mean field theory (DMFT) has become a standard technique for
the study of strongly correlated models and materials overcoming some of the
limitations of density functional approaches based on local approximations. An
important step in this method involves the calculation of response functions of
a multiorbital impurity problem which is related to the original model.
Recently there has been considerable progress in the development of techniques
based on the density matrix renormalization group (DMRG) and related matrix
product states (MPS) implying a substantial improvement to previous methods. In
this article we review some of the standard algorithms and compare them to the
newly developed techniques, showing examples for the particular case of the
half-filled two-band Hubbard model.Comment: 8 pages, 4 figures, to be published in EPL Perspective
Features of spin-charge separation in the equilibrium conductance through finite rings
We calculate the conductance through rings with few sites described by
the model, threaded by a magnetic flux and weakly coupled to
conducting leads at two arbitrary sites. The model can describe a circular
array of quantum dots with large charging energy in comparison with the
nearest-neighbor hopping . We determine analytically the particular values
of for which a depression of the transmittance is expected as a
consequence of spin-charge separation. We show numerically that the equilibrium
conductance at zero temperature is depressed at those particular values of
for most systems, in particular at half filling, which might be easier
to realize experimentally.Comment: 8 pages, 7 figure
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