592 research outputs found
Variational Monte Carlo for Interacting Electrons in Quantum Dots
We use a variational Monte Carlo algorithm to solve the electronic structure
of two-dimensional semiconductor quantum dots in external magnetic field. We
present accurate many-body wave functions for the system in various magnetic
field regimes. We show the importance of symmetry, and demonstrate how it can
be used to simplify the variational wave functions. We present in detail the
algorithm for efficient wave function optimization. We also present a Monte
Carlo -based diagonalization technique to solve the quantum dot problem in the
strong magnetic field limit where the system is of a multiconfiguration nature.Comment: 34 pages, proceedings of the 1st International Meeting on Advances in
Computational Many-Body Physics, to appear in Journal of Low Temperature
Physics (vol. 140, nos. 3/4
Half-Integer Filling Factor States in Quantum Dots
Emergence of half-integer filling factor states, such as nu=5/2 and 7/2, is
found in quantum dots by using numerical many-electron methods. These states
have interesting similarities and differences with their counterstates found in
the two-dimensional electron gas. The nu=1/2 states in quantum dots are shown
to have high overlaps with the composite fermion states. The lower overlap of
the Pfaffian state indicates that electrons might not be paired in quantum dot
geometry. The predicted nu=5/2 state has high spin polarization which may have
impact on the spin transport through quantum dot devices.Comment: 4 pages, accepted to Phys. Rev. Let
Vortices in quantum droplets: Analogies between boson and fermion systems
The main theme of this review is the many-body physics of vortices in quantum
droplets of bosons or fermions, in the limit of small particle numbers. Systems
of interest include cold atoms in traps as well as electrons confined in
quantum dots. When set to rotate, these in principle very different quantum
systems show remarkable analogies. The topics reviewed include the structure of
the finite rotating many-body state, universality of vortex formation and
localization of vortices in both bosonic and fermionic systems, and the
emergence of particle-vortex composites in the quantum Hall regime. An overview
of the computational many-body techniques sets focus on the configuration
interaction and density-functional methods. Studies of quantum droplets with
one or several particle components, where vortices as well as coreless vortices
may occur, are reviewed, and theoretical as well as experimental challenges are
discussed.Comment: Review article, 53 pages, 53 figure
Influence of the Catalyst Particle Size on the Aqueous Phase Reforming of n-Butanol Over Rh/ZrO2
Butanol is a by-product obtained from biomass that can be valorized through aqueous phase reforming. Rh/ZrO2 catalysts were prepared and characterized, varying the size of the support particles. The results showed a relatively mild effect of internal mass transport on butanol conversion. However, the influence of internal transport limitations on the product distribution was much stronger, promoting consecutive reactions, i.e., dehydrogenation, hydrogenolysis, and reforming of propane and ethane. Hydrogen consuming reactions, i.e., hydrogenolysis, were more strongly enhanced than hydrogen producing reactions due to internal concentration gradients. Large support particles deactivated faster, attributed to high concentrations of butyraldehyde inside the catalyst particles, enhancing deposit formation via aldol condensation reactions. Consequently, also the local butyric acid concentration was high, decreasing the local pH, enhancing Rh leaching. The influence of internal transfer limitation on product distribution and stability is discussed based on a reaction scheme with three main stages, i.e., (1) formation of liquid intermediates via dehydrogenation, (2) formation of gas via decarbonylation/decarboxylation reactions, and (3) hydrocarbon hydrogenolysis/reforming/dehydrogenation
Ground-state of two-dimensional finite electron systems in the Quantum Hall regime
We study electronic structures of quasi-two-dimensional finite electron
systems in high magnetic fields. The solutions in the fractional quantum Hall
regime are interpreted as quantum liquids of electrons and off-electron
vortices. The ground states are classified according to the number of vortices
inside the electron droplet. The theory predicts observable effects due to
vortex formation in the chemical potentials and magnetization of electron
droplets. We compare the transitions in the theory to those found in electron
transport experiments on a quantum dot device and find significant
correspondence.Comment: 4 pages, 4 figures (3 in colour), revised in response to referees'
comments, to appear in Phys. Rev. let
Glutathione s-transferase omega in the lung and sputum supernatants of COPD patients
BACKGROUND: The major contribution to oxidant related lung damage in COPD is from the
oxidant/antioxidant imbalance and possibly impaired antioxidant defence. Glutathione (GSH) is one
of the most important antioxidants in human lung and lung secretions, but the mechanisms
participating in its homeostasis are partly unclear. Glutathione-S-transferase omega (GSTO) is a
recently characterized cysteine containing enzyme with the capability to bind and release GSH in
vitro. GSTO has not been investigated in human lung or lung diseases.
METHODS: GSTO1-1 was investigated by immunohistochemistry and Western blot analysis in 72
lung tissue specimens and 40 sputum specimens from non-smokers, smokers and COPD, in
bronchoalveolar lavage fluid and in plasma from healthy non-smokers and smokers. It was also
examined in human monocytes and bronchial epithelial cells and their culture mediums in vitro.
RESULTS: GSTO1-1 was mainly expressed in alveolar macrophages, but it was also found in airway
and alveolar epithelium and in extracellular fluids including sputum supernatants, bronchoalveolar
lavage fluid, plasma and cell culture mediums. The levels of GSTO1-1 were significantly lower in the
sputum supernatants (p = 0.023) and lung homogenates (p = 0.003) of COPD patients than in nonsmokers.
CONCLUSION: GSTO1-1 is abundant in the alveolar macrophages, but it is also present in
extracellular fluids and in airway secretions, the levels being decreased in COPD. The clinical
significance of GSTO1-1 and its role in regulating GSH homeostasis in airway secretions, however,
needs further investigations
Vortex Clusters in Quantum Dots
We study electronic structures of two-dimensional quantum dots in strong magnetic fields using mean-field density-functional theory and exact diagonalization. Our numerically accurate mean-field solutions show a reconstruction of the uniform-density electron droplet when the magnetic field flux quanta enter one by one the dot in stronger fields. These quanta correspond to repelling vortices forming polygonal clusters inside the dot. We find similar structures in the exact treatment of the problem by constructing a conditional operator for the analysis. We discuss important differences and limitations of the methods used.Peer reviewe
Rectangular quantum dots in high magnetic fields
We use density-functional methods to study the effects of an external
magnetic field on two-dimensional quantum dots with a rectangular hard-wall
confining potential. The increasing magnetic field leads to spin polarization
and formation of a highly inhomogeneous maximum-density droplet at the
predicted magnetic field strength. At higher fields, we find an oscillating
behavior in the electron density and in the magnetization of the dot. We
identify a rich variety of phenomena behind the periodicity and analyze the
complicated many-electron dynamics, which is shown to be highly dependent on
the shape of the quantum dot.Comment: 6 pages, 6 figures, submitted to Phys. Rev.
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