52,220 research outputs found
Transition metal oxides using quantum Monte Carlo
The transition metal-oxygen bond appears prominently throughout chemistry and
solid-state physics. Many materials, from biomolecules to ferroelectrics to the
components of supernova remnants contain this bond in some form. Many of these
materials' properties strongly depend on fine details of the TM-O bond and
intricate correlation effects, which make accurate calculations of their
properties very challenging. We present quantum Monte Carlo, an explicitly
correlated class of methods, to improve the accuracy of electronic structure
calculations over more traditional methods like density functional theory. We
find that unlike s-p type bonding, the amount of hybridization of the d-p bond
in TM-O materials is strongly dependant on electronic correlation.Comment: 20 pages, 4 figures, to appear as a topical review in J. Physics:
Condensed Matte
Stopping Sexual Harassment in the Empire State: Past, Present, and a Possible Future
This report maps current patterns of workplace sexual harassment and their impact in New York State. It also provides a broader frame for understanding how efforts to confront sexual and gender-based harassment and assault have evolved over time, and charts possible directions for future organizing, policy, and research in New York and beyond.
The findings presented here are drawn from the 2018 Empire State Poll, an annual statewide survey of 800 New Yorkers conducted by the Cornell Survey Research Institute. Questions added to the survey reflecting existing legal definitions of workplace sexual harassment reveal the following: 10.9 percent of New York residents have experienced quid pro quo workplace sexual harassment, and 21.9 percent have experienced workplace sexual harassment that created a hostile work environment; 31.1 percent of women and 18.9 percent of men have experienced at least one of these forms of harassment. 13.9 percent of people of color and people of Hispanic origin have experienced quid pro quo workplace sexual harassment, as opposed to 8.5 percent of non-Hispanic whites. 38.9 percent of those experiencing at least one form of workplace sexual harassment say it impacted their work or careers; 48.9 percent who experienced quid pro quo harassment reported such an impact. 83.4 percent of New York residents think their leaders should do more to address workplace sexual harassment. There is notable variation by politics and ideology, but regardless of worldview, strong majorities think leaders should do more.
In addition to sharing the survey findings, the report discusses experiences and responses of survivors and how they are shaped by different identities and relations of power. It highlights black women’s leadership in propelling wide-reaching shifts in law and culture; efforts initiated by diverse survivors to effect change in specific industries; and culture change work engaging men and women as allies
Crossover from a square to a hexagonal pattern in Faraday surface waves
We report on surface wave pattern formation in a Faraday experiment operated
at a very shallow filling level, where modes with a subharmonic and harmonic
time dependence interact. Associated with this distinct temporal behavior are
different pattern selection mechanisms, favoring squares or hexagons,
respectively. In a series of bifurcations running through a pair of
superlattices the surface wave pattern transforms between the two incompatible
symmetries. The close analogy to 2D and 3D crystallography is pointed out.Comment: 4 pages, 4 figure
Point-Defect Optical Transitions and Thermal Ionization Energies from Quantum Monte Carlo Methods: Application to F-center Defect in MgO
We present an approach to calculation of point defect optical and thermal
ionization energies based on the highly accurate quantum Monte Carlo methods.
The use of an inherently many-body theory that directly treats electron
correlation offers many improvements over the typically-employed density
functional theory Kohn-Sham description. In particular, the use of quantum
Monte Carlo methods can help overcome the band gap problem and obviate the need
for ad-hoc corrections. We demonstrate our approach to the calculation of the
optical and thermal ionization energies of the F-center defect in magnesium
oxide, and obtain excellent agreement with experimental and/or other
high-accuracy computational results
Quantum Monte Carlo for minimum energy structures
We present an efficient method to find minimum energy structures using energy
estimates from accurate quantum Monte Carlo calculations. This method involves
a stochastic process formed from the stochastic energy estimates from Monte
Carlo that can be averaged to find precise structural minima while using
inexpensive calculations with moderate statistical uncertainty. We demonstrate
the applicability of the algorithm by minimizing the energy of the H2O-OH-
complex and showing that the structural minima from quantum Monte Carlo
calculations affect the qualitative behavior of the potential energy surface
substantially.Comment: 7 pages, 4 figure
S-wave quantum entanglement in a harmonic trap
We analyze the quantum entanglement between two interacting atoms trapped in
a spherical harmonic potential. At ultra-cold temperature, ground state
entanglement is generated by the dominated s-wave interaction. Based on a
regularized pseudo-potential Hamiltonian, we examine the quantum entanglement
by performing the Schmidt decomposition of low-energy eigenfunctions. We
indicate how the atoms are paired and quantify the entanglement as a function
of a modified s-wave scattering length inside the trap.Comment: 10 pages, 5 figures, to be apear in PR
Analysis of photon-atom entanglement generated by Faraday rotation in a cavity
Faraday rotation based on AC Stark shifts is a mechanism that can entangle
the polarization variables of photons and atoms. We analyze the structure of
such entanglement by using the Schmidt decomposition method. The
time-dependence of entanglement entropy and the effective Schmidt number are
derived for Gaussian amplitudes. In particular we show how the entanglement is
controlled by the initial fluctuations of atoms and photons.Comment: 6 pages, 3 figure
Phase relaxation of Faraday surface waves
Surface waves on a liquid air interface excited by a vertical vibration of a
fluid layer (Faraday waves) are employed to investigate the phase relaxation of
ideally ordered patterns. By means of a combined frequency-amplitude modulation
of the excitation signal a periodic expansion and dilatation of a square wave
pattern is generated, the dynamics of which is well described by a Debye
relaxator. By comparison with the results of a linear theory it is shown that
this practice allows a precise measurement of the phase diffusion constant.Comment: 5 figure
Loss of purity by wave packet scattering at low energies
We study the quantum entanglement produced by a head-on collision between two
gaussian wave packets in three-dimensional space. By deriving the two-particle
wave function modified by s-wave scattering amplitudes, we obtain an
approximate analytic expression of the purity of an individual particle. The
loss of purity provides an indicator of the degree of entanglement. In the case
the wave packets are narrow in momentum space, we show that the loss of purity
is solely controlled by the ratio of the scattering cross section to the
transverse area of the wave packets.Comment: 7 pages, 1 figur
Experimental studies of hypersonic boundary-layer transition and effects of wind tunnel disturbances
Boundary layer transition data on cones and free stream disturbance levels were measured in a hypersonic wind tunnel and Mach 8 variable density hypersonic tunnel. Transition data were obtained by using different conical models and techniques for detecting the location of transition. The disturbance levels were measured by using hot wire anemometry and pressure transducers. The transition Reynolds numbers obtained from the tests correlated well when the fluctuating pressures measured at the surface of conical models were used as a correlating parameter
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