1,522 research outputs found
Frustrated Hubbard ladders and superconductivity in -BEDT-TTF organic compounds
Half-filled two-leg Hubbard ladders have spin-gapped short-range
antiferromagnetic correlations while three-leg ladders have power law
antoferromagnetic correlations, and both systems have d_{x^2-y^2}-power law
pairing correlations when they are doped. Thus these ladders exhibit some of
the phenomenology seen in the layered cuprates. Here we report results for
half-filled frustrated Hubbard ladders, based upon ladder segments taken from a
tight-binding model of kappa-BEDT-TTF. Although these ladders are half-filled,
varying the degree of frustration can drive them across an insulator-metal
transition. We suggest that the spin, charge and pairing correlations of these
frustrated ladders near the insulator-metal transition provide support for the
notion that kappa-BEDT-TTF is a strongly correlated superconductor
Phase diagram of the one-dimensional Holstein model of spinless fermions
The one-dimensional Holstein model of spinless fermions interacting with
dispersionless phonons is studied using a new variant of the density matrix
renormalisation group. By examining various low-energy excitations of finite
chains, the metal-insulator phase boundary is determined precisely and agrees
with the predictions of strong coupling theory in the anti-adiabatic regime and
is consistent with renormalisation group arguments in the adiabatic regime. The
Luttinger liquid parameters, determined by finite-size scaling, are consistent
with a Kosterlitz-Thouless transition.Comment: Minor changes. 4 pages, 4 figures. To appear in Physical Review
Letters 80 (1998) 560
The identification of mitochondrial DNA variants in glioblastoma multiforme
Background:
Mitochondrial DNA (mtDNA) encodes key proteins of the electron transfer chain (ETC), which produces ATP through oxidative phosphorylation (OXPHOS) and is essential for cells to perform specialised functions. Tumor-initiating cells use aerobic glycolysis, a combination of glycolysis and low levels of OXPHOS, to promote rapid cell proliferation and tumor growth. Glioblastoma multiforme (GBM) is an aggressively malignant brain tumor and mitochondria have been proposed to play a vital role in GBM tumorigenesis.
Results:
Using next generation sequencing and high resolution melt analysis, we identified a large number of mtDNA variants within coding and non-coding regions of GBM cell lines and predicted their disease-causing potential through in silico modeling. The frequency of variants was greatest in the D-loop and origin of light strand replication in non-coding regions. ND6 was the most susceptible coding gene to mutation whilst ND4 had the highest frequency of mutation. Both genes encode subunits of complex I of the ETC. These variants were not detected in unaffected brain samples and many have not been previously reported. Depletion of HSR-GBM1 cells to varying degrees of their mtDNA followed by transplantation into immunedeficient mice resulted in the repopulation of the same variants during tumorigenesis. Likewise, de novo variants identified in other GBM cell lines were also incorporated. Nevertheless, ND4 and ND6 were still the most affected genes. We confirmed the presence of these variants in high grade gliomas.
Conclusions:
These novel variants contribute to GBM by rendering the ETC. partially dysfunctional. This restricts metabolism to anaerobic glycolysis and promotes cell proliferation
Density Matrix Renormalization Group Study of the S=1/2 Anisotropic Antiferromagnetic Heisenberg Chains with Quasiperiodic Exchange Modulation
The low energy behavior of the S=1/2 antiferromagnetic XY-like XXZ chains
with precious mean quasiperiodic exchange modulation is studied by the density
matrix renormalization group method. It is found that the energy gap of the
chain with length N scales as with nonuniversal exponent
if the Ising component of the exhange coupling is antiferromagnetic.
This behavior is expected to be the characteristic feature of the quantum spin
chains with relevant aperiodicity. This is in contrast to the XY chain for
which the precious mean exchange modulation is marginal and the gap scales as
. On the contrary, it is also verified that the energy gap scales as
if the Ising component of the exhange coupling is ferromagnetic. Our
results are not only consistent with the recent bosonization analysis of Vidal,
Mouhanna and Giamarchi but also clarify the nature of the strong coupling
regime which is inaccesssible by the bosonization approach.Comment: 8 pages, 15 figures, 1 table; Proceedings of the workshop 'Frontiers
in Magnetism', Kyoto, Oct. 199
Analytical approach to the quantum-phase transition in the one-dimensional spinless Holstein model
We study the one-dimensional Holstein model of spinless fermions interacting
with dispersion-less phonons by using a recently developed projector-based
renormalization method (PRM). At half-filling the system shows a
metal-insulator transition to a Peierls distorted state at a critical
electron-phonon coupling where both phases are described within the same
theoretical framework. The transition is accompanied by a phonon softening at
the Brillouin zone boundary and a gap in the electronic spectrum. For different
filling, the phonon softening appears away from the Brillouin zone boundary and
thus reflects a different type of broken symmetry state.Comment: 8 pages, 4 figures included; v2: completely revised and extended; v3:
minor changes, final version, to be published in Eur. Phys. J.
Effect of the Cretaceous Serra Geral igneous event on the temperatures and heat flow of the Parana Basin, southern Brazil
We investigate the effects of the cooling of intrusive and extrusive igneous bodies on the temperature history and surface heat flow of the Parana Basin. The Serra Geral igneous event (130â135 Ma) covered most of this basin with flood basalts. Associated with this event numerous sills and dykes intruded the sediments and basement, and extensive underplating may have occurred in the lower crust and upper mantle beneath the basin. We develop an analytical model of the conductive cooling of tabular intrusive bodies and use it to calculate temperatures within the sediments as a function of time since emplacement. Depending on the thickness of these igneous bodies and the timing of sequential emplacement, the thermal history of a given locus in the basin can range from a simple extended period of higher temperatures to multiple episodes of peak temperatures separated by cooling intervals. The cooling of surface flood basalts, sills and dykes is capable of maintaining temperatures abovc the normal geothermal gradient temperatures for a few hundred thousand years, while large-scale underplating may influence temperatures for up to 10 million years. We conclude that any residual heat from the cooling of the Serra Geral igneous rocks has long since decayed to insignificant values and that present-day temperatures and heat flow are not affected. However, the burial of the sediments beneath the thick basalt cap caused a permanent temperature increase of up to 50°C in the underlying sediments since the beginning of the Cretaceous.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72088/1/j.1365-2117.1994.tb00087.x.pd
Recommended from our members
Matching roots to their environment
Background Plants form the base of the terrestrial food chain and provide medicines, fuel, fibre and industrial materials to humans. Vascular land plants rely on their roots to acquire the water and mineral elements necessary for their survival in nature or their yield and nutritional quality in agriculture. Major biogeochemical fluxes of all elements occur through plant roots, and the roots of agricultural crops have a significant role to play in soil sustainability, carbon sequestration, reducing emissions of greenhouse gasses, and in preventing the eutrophication of water bodies associated with the application of mineral fertilisers.
â Scope This article provides the context for a Special Issue of Annals of Botany on âMatching Roots to Their Environmentâ. It first examines how land plants and their roots evolved, describes how the ecology of roots and their rhizospheres contributes to the acquisition of soil resources, and discusses the influence of plant roots on biogeochemical cycles. It then describes the role of roots in overcoming the constraints to crop production imposed by hostile or infertile soils, illustrates root phenotypes that improve the acquisition of mineral elements and water, and discusses high-throughput methods to screen for these traits in the laboratory, glasshouse and field. Finally, it considers whether knowledge of adaptations improving the acquisition of resources in natural environments can be used to develop root systems for sustainable agriculture in the future
Metal-insulator transition in the one-dimensional Holstein model at half filling
We study the one-dimensional Holstein model with spin-1/2 electrons at
half-filling. Ground state properties are calculated for long chains with great
accuracy using the density matrix renormalization group method and extrapolated
to the thermodynamic limit. We show that for small electron-phonon coupling or
large phonon frequency, the insulating Peierls ground state predicted by
mean-field theory is destroyed by quantum lattice fluctuations and that the
system remains in a metallic phase with a non-degenerate ground state and
power-law electronic and phononic correlations. When the electron-phonon
coupling becomes large or the phonon frequency small, the system undergoes a
transition to an insulating Peierls phase with a two-fold degenerate ground
state, long-range charge-density-wave order, a dimerized lattice structure, and
a gap in the electronic excitation spectrum.Comment: 6 pages (LaTex), 10 eps figure
Posterior cricoid region fluoroscopic findings: the posterior cricoid plication.
The region posterior to the cricoid cartilage is challenging to assess fluoroscopically. The purpose of this investigation is to critically evaluate the posterior cricoid (PC) region on fluoroscopy and describe patterns of common findings. This was a case control study. All fluoroscopic swallowing studies performed between June 16, 2009, and February 9, 2010, were reviewed for features seen in the PC region. These findings were categorized into distinct patterns and compared to fluoroscopic studies performed in a cohort of normal volunteers. Two hundred patient studies and 149 healthy volunteer studies were reviewed. The mean age of the referred patient cohort and the volunteer cohort was 57 years (±19) and 61 years (±16), respectively (p > 0.05). The patient cohort was 53% male and the control cohort was 56% female (p > 0.05). Four groups were identified. Pharyngoesophageal webs were seen in 7% (10/149) of controls and 14% (28/200) of patients (p = 0.03). A PC arch impression was seen in 16% of patients (32/200) and controls (24/149) (p = 1). A PC plication was demonstrated in 23% (34/149) of controls and 30% (60/200) of patients (p = 0.13). No distinctive PC region findings were seen in 54% (81/149) of controls and 42% (84/200) of referred patients (p = 0.02). Four patients (2%) had both a web and a PC plication. Four categories of PC region findings were identified (unremarkable PC region, web, PC arch impression, and PC plication). Both patients referred for swallowing studies and healthy volunteers demonstrated esophageal webs, PC arch impressions, and PC plications. Only webs were more common in patients than in control subjects (p = 0.03). The PC impression and PC plication are likely to represent normal variants that may be identified on fluoroscopic swallow studies
- âŠ