3,722 research outputs found
Transport through a vibrating quantum dot: Polaronic effects
We present a Green's function based treatment of the effects of
electron-phonon coupling on transport through a molecular quantum dot in the
quantum limit. Thereby we combine an incomplete variational Lang-Firsov
approach with a perturbative calculation of the electron-phonon self energy in
the framework of generalised Matsubara Green functions and a Landauer-type
transport description. Calculating the ground-state energy, the dot
single-particle spectral function and the linear conductance at finite carrier
density, we study the low-temperature transport properties of the vibrating
quantum dot sandwiched between metallic leads in the whole electron-phonon
coupling strength regime. We discuss corrections to the concept of an
anti-adiabatic dot polaron and show how a deformable quantum dot can act as a
molecular switch.Comment: 10 pages, 8 figures, Proceedings of "Progress in Nonequilibrium
Green's Function IV" Conference, Glasgow 200
Phonon-affected steady-state transport through molecular quantum dots
We consider transport through a vibrating molecular quantum dot contacted to
macroscopic leads acting as charge reservoirs. In the equilibrium and
nonequilibrium regime, we study the formation of a polaron-like transient state
at the quantum dot for all ratios of the dot-lead coupling to the energy of the
local phonon mode. We show that the polaronic renormalization of the dot-lead
coupling is a possible mechanism for negative differential conductance.
Moreover, the effective dot level follows one of the lead chemical potentials
to enhance resonant transport, causing novel features in the inelastic
tunneling signal. In the linear response regime, we investigate the impact of
the electron-phonon interaction on the thermoelectrical properties of the
quantum dot device.Comment: 11 pages, 7 figures, FQMT11 Proceeding
ASSESSMENT OF THE TRAINING AND CONTINUING EDUCATION NEEDS OF A REGIONAL PUBLIC HEALTH WORKFORCE
A large Midwestern university recently received accreditation for its Master of Public Health (MPH) degree program from the Council on Education for Public Health (CEPH). Requirements of the accreditation include the periodic assessment of the regional public health workforce’s professional development needs and the delivery of training and continuing education to meet those needs. To that end, this study’s primary purpose was to describe the professional development needs of the regional public health workforce and to develop recommendations for the provision of professional development activities to meet those needs. Fifty-eight respondents from 27 regional public health departments and 7 regional health coalitions completed the survey, identifying priority public health topical training needs as well as priority community health education competency training needs. Additionally, respondents indicated a preference for the delivery of trainings, with offsite, face-to-face training sessions offering continuing education units (CEUs) in a series of half-day or full-day workshops being favored
Hooke's law correlation in two-electron systems
We study the properties of the Hooke's law correlation energy (\Ec),
defined as the correlation energy when two electrons interact {\em via} a
harmonic potential in a -dimensional space. More precisely, we investigate
the ground state properties of two model systems: the Moshinsky atom (in
which the electrons move in a quadratic potential) and the spherium model (in
which they move on the surface of a sphere). A comparison with their Coulombic
counterparts is made, which highlights the main differences of the \Ec in
both the weakly and strongly correlated limits. Moreover, we show that the
Schr\"odinger equation of the spherium model is exactly solvable for two values
of the dimension (), and that the exact wave function is
based on Mathieu functions.Comment: 7 pages, 5 figure
Uniform electron gases
We show that the traditional concept of the uniform electron gas (UEG) --- a
homogeneous system of finite density, consisting of an infinite number of
electrons in an infinite volume --- is inadequate to model the UEGs that arise
in finite systems. We argue that, in general, a UEG is characterized by at
least two parameters, \textit{viz.} the usual one-electron density parameter
and a new two-electron parameter . We outline a systematic
strategy to determine a new density functional across the
spectrum of possible and values.Comment: 8 pages, 2 figures, 5 table
Excited states of spherium
We report analytic solutions of a recently discovered quasi-exactly solvable
model consisting of two electrons, interacting {\em via} a Coulomb potential,
but restricted to remain on the surface of a -dimensional sphere.
Polynomial solutions are found for the ground state, and for some higher
() states. Kato cusp conditions and interdimensional degeneracies are
discussed.Comment: 6 pages, 2 figures, to appear in Mol. Phy
Phonon affected transport through molecular quantum dots
To describe the interaction of molecular vibrations with electrons at a
quantum dot contacted to metallic leads, we extend an analytical approach that
we previously developed for the many-polaron problem. Our scheme is based on an
incomplete variational Lang-Firsov transformation, combined with a perturbative
calculation of the electron-phonon self-energy in the framework of generalised
Matsubara functions. This allows us to describe the system at weak to strong
coupling and intermediate to large phonon frequencies. We present results for
the quantum dot spectral function and for the kinetic coefficient that
characterises the electron transport through the dot. With these results we
critically examine the strengths and limitations of our approach, and discuss
the properties of the molecular quantum dot in the context of polaron physics.
We place particular emphasis on the importance of corrections to the concept of
an antiadiabatic dot polaron suggested by the complete Lang-Firsov
transformation.Comment: 30 pages, 15 figures, revised version including new figure
Invariance of the correlation energy at high density and large dimension in two-electron systems
We prove that, in the large-dimension limit, the high-density correlation
energy \Ec of two opposite-spin electrons confined in a -dimensional space
and interacting {\em via} a Coulomb potential is given by \Ec \sim -1/(8D^2)
for any radial confining potential . This result explains the observed
similarity of \Ec in a variety of two-electron systems in three-dimensional
space.Comment: 4 pages, 1 figure, to appear in Phys. Rev. Let
Compression of sub-relativistic space-charge-dominated electron bunches for single-shot femtosecond electron diffraction
We demonstrate compression of 95 keV, space-charge-dominated electron bunches
to sub-100 fs durations. These bunches have sufficient charge (200 fC) and are
of sufficient quality to capture a diffraction pattern with a single shot,
which we demonstrate by a diffraction experiment on a polycrystalline gold
foil. Compression is realized by means of velocity bunching as a result of a
velocity chirp, induced by the oscillatory longitudinal electric field of a 3
GHz radio-frequency cavity. The arrival time jitter is measured to be 80 fs
Identity in the Writings of Lucian of Samosata
The second-century CE Greek sophist, rhetorician, and satirist Lucian of Samosata (c. 120-185 CE) presents a complex figure in his writings. A native of the province of Syria who wrote in Greek under the Roman Empire, Lucian’s identity and perspective on the world around him seems complex and often self-contradictory in his works. In light of Lucian’s complexity, readers and later scholars have sometimes tried to pigeonhole his identity into simple terms of “Greek,” “Syrian,” or “Roman.” This thesis offers an alternative view, applying the postcolonial lens of “discrepant identities” to Lucian’s literary personae in his writings. Lucian’s self-portrayal shifted between his works due to a variety of factors stemming from Roman imperial rule. Through a series of case studies of Lucian’s works (De Dea Syria, Heracles, De Mercede Conductis, Apologia, and Patriae Encomium) this thesis shows the malleability of Lucian’s self-presentation within his literary corpus due to his evolving circumstances, the broader context of the Roman Empire, and the pressures of unfavorable stereotypes. Finally, as a figure with a sizable literary record, Lucian offers an excellent model of how the identities of other provincials may have shifted as a response to the necessities of life in the heterogeneous Roman Empire.History, Department ofHonors Colleg
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