2,598 research outputs found
Berry phase of the composite-fermion Fermi Sea: Effect of Landau-level mixing
We construct explicit lowest-Landau-level wave functions for the
composite-fermion Fermi sea and its low energy excitations following a recently
developed approach [Pu, Wu and Jain, Phys. Rev. B 96, 195302 (2018)] and
demonstrate them to be very accurate representations of the Coulomb
eigenstates. We further ask how the Berry phase associated with a closed loop
around the Fermi circle, predicted to be in a Dirac composite fermion
theory satisfying particle-hole symmetry [D. T. Son, Phys. Rev. X 5, 031027
(2015)], is affected by Landau level mixing. For this purpose, we consider a
simple model wherein we determine the variational ground state as a function of
Landau level mixing within the space spanned by two basis functions: the
lowest-Landau-level projected and the unprojected composite-fermion Fermi sea
wave functions. We evaluate Berry phase for a path around the Fermi circle
within this model following a recent prescription, and find that it rotates
rapidly as a function of Landau level mixing. We also consider the effect of a
particle-hole symmetry breaking three-body interaction on the Berry phase while
confining the Hilbert space to the lowest Landau level. Our study deepens the
connection between the Berry phase and the exact particle-hole symmetry
in the lowest Landau level.Comment: 13 pages, 6 figure
Search for exact local Hamiltonians for general fractional quantum Hall states
We report on our systematic attempts at finding local interactions for which
the lowest-Landau-level projected composite-fermion wave functions are the
unique zero energy ground states. For this purpose, we study in detail the
simplest non-trivial system beyond the Laughlin states, namely bosons at
filling and identify local constraints among clusters of
particles in the ground state. By explicit calculation, we show that no
Hamiltonian up to (and including) four particle interactions produces this
state as the exact ground state, and speculate that this remains true even when
interaction terms involving greater number of particles are included.
Surprisingly, we can identify an interaction, which imposes an energetic
penalty for a specific entangled configuration of four particles with relative
angular momentum of , that produces a unique zero energy solution (as
we have confirmed for up to 12 particles). This state, referred to as the
-state, is not identical to the projected composite-fermion state, but
the following facts suggest that the two might be topologically equivalent: the
two sates have a high overlap; they have the same root partition; the quantum
numbers for their neutral excitations are identical; and the quantum numbers
for the quasiparticle excitations also match. On the quasihole side, we find
that even though the quantum numbers of the lowest energy states agree with the
prediction from the composite-fermion theory, these states are not separated
from the others by a clearly identifiable gap. This prevents us from making a
conclusive claim regarding the topological equivalence of the state
and the composite-fermion state. Our study illustrates how new candidate states
can be identified from constraining selected many particle configurations and
it would be interesting to pursue their topological classification.Comment: 21 pages, 11 figure
Accuracy of DNA Repair During Replication in Saccharomyces Cerevisiae
DNA repair is a crucial part of organismal survival. The repair process is carried out by DNA polymerases and mismatch repair proteins. Things don’t always go as planned in DNA repair, and sometimes DNA repair is inaccurate. Inaccurate DNA repair can potentially lead to the loss of the genes important for cell division and replication. There has been much research into the efficiency of these DNA polymerases, yet there has been no thorough research into how the accuracy of repair is distributed among all of the different types of homologous recombination. The goal of this article is to review the literature on the accuracy of DNA repair during replication in Saccharomyces cerevisiae
Magnetic and mechanical effects of Mn substitutions in AlFe2B2
The mechanical and magnetic properties of the newly discovered MAB-phase
class of materials based upon AlFe2B2 were investigated. The samples were
synthesised from stoichiometric amounts of all constituent elements. X-ray
diffraction shows that the main phase is orthorhombic with an elongated b-axis,
similar to AlFe2B2. The low hardness and visual inspection of the samples after
deformation indicate that these compounds are deformed via a delamination
process. When substituting iron in AlFe2B2 with manganese, the magnetism in the
system goes from being ferro- to antiferromagnetic via a disordered
ferrimagnetic phase exhibited by AlFeMnB2. Density functional theory
calculations indicate a weakening of the magnetic interactions among the
transitions metal ions as iron is substituted by manganese in AlFe2B2. The
Mn-Mn exchange interactions in AlMn2 B2 are found to be very small
Identification of transcriptional and metabolic programs related to mammalian cell size
SummaryBackgroundRegulation of cell size requires coordination of growth and proliferation. Conditional loss of cyclin-dependent kinase 1 in mice permits hepatocyte growth without cell division, allowing us to study cell size in vivo using transcriptomics and metabolomics.ResultsLarger cells displayed increased expression of cytoskeletal genes but unexpectedly repressed expression of many genes involved in mitochondrial functions. This effect appears to be cell autonomous because cultured Drosophila cells induced to increase cell size displayed a similar gene-expression pattern. Larger hepatocytes also displayed a reduction in the expression of lipogenic transcription factors, especially sterol-regulatory element binding proteins. Inhibition of mitochondrial functions and lipid biosynthesis, which is dependent on mitochondrial metabolism, increased the cell size with reciprocal effects on cell proliferation in several cell lines.ConclusionsWe uncover that large cell-size increase is accompanied by downregulation of mitochondrial gene expression, similar to that observed in diabetic individuals. Mitochondrial metabolism and lipid synthesis are used to couple cell size and cell proliferation. This regulatory mechanism may provide a possible mechanism for sensing metazoan cell size
- …