68 research outputs found
Block-Spin Approach to Electron Correlations
We consider an expansion of the ground state wavefunction of quantum lattice
many-body systems in a basis whose states are tensor products of block-spin
wavefunctions. We demonstrate by applying the method to the antiferromagnetic
spin-1/2 chain that by selecting the most important many-body states the
technique affords a severe truncation of the Hilbert space while maintaining
high accuracy.Comment: 17 pages, 3 Postscript figure
Diabetes and colorectal cancer risk: A new look at molecular mechanisms and potential role of novel antidiabetic agents
Epidemiological data have demonstrated a significant association between the presence of type 2 diabetes mellitus (T2DM) and the development of colorectal cancer (CRC). Chronic hyperglycemia, insulin resistance, oxidative stress, and inflammation, the processes inherent to T2DM, also play active roles in the onset and progression of CRC. Recently, small dense low-density lipoprotein (LDL) particles, a typical characteristic of diabetic dyslipidemia, emerged as another possible underlying link between T2DM and CRC. Growing evidence suggests that antidiabetic medications may have beneficial effects in CRC prevention. According to findings from a limited number of preclinical and clinical studies, glucagon-like peptide-1 receptor agonists (GLP-1RAs) could be a promising strategy in reducing the incidence of CRC in patients with diabetes. However, available findings are inconclusive, and further studies are required. In this review, novel evidence on molecular mechanisms linking T2DM with CRC development, progression, and survival will be discussed. In addition, the potential role of GLP-1RAs therapies in CRC prevention will also be evaluated
Temperature dependent band structure of the Kondo insulator
We present a Qantum Monte Carlo (QMC) study of the temperature dependent
dynamics of the Kondo insulator. Working at the so-called symmetrical point
allows to perform minus-sign free QMC simulations and thus reach temperatures
of less than 1% of the conduction electron bandwidth. Study of the temperature
dependence of the single particle Green's function and dynamical spin
correlation function shows a surprisingly intricate low temperature band
structure and gives evidence for two characteristic temperatures, which we
identify with the Kondo and coherence temperature, respectively. In particular,
the data show a temperature induced metal-insulator transition at the coherence
temperature.Comment: RevTex-file, 4 PRB pages with 4 eps figures. Hardcopies of figures
(or the entire manuscript) can be obtained by e-mail request to:
[email protected]
Atherosclerosis development and progression: the role of atherogenic small, dense LDL.
Atherosclerosis is responsible for large cardiovascular mortality in many countries globally. It has been shown over the last decades that the reduction of atherosclerotic progression is a critical factor for preventing future cardiovascular events. Low-density lipoproteins (LDL) have been successfully targeted, and their reduction is one of the key preventing measures in patients with atherosclerotic disease. LDL particles are pivotal for the formation and progression of atherosclerotic plaques; yet, they are quite heterogeneous, and smaller, denser LDL species are the most atherogenic. These particles have greater arterial entry and retention, higher susceptibility to oxidation, as well as reduced affinity for the LDL receptor. Increased proportion of small, dense LDL particles is an integral part of the atherogenic lipoprotein phenotype, the most common form of dyslipidemia associated with insulin resistance. Recent data suggest that both genetic and epigenetic factors might induce expression of this specific lipid pattern. In addition, a typical finding of increased small, dense LDL particles was confirmed in different categories of patients with elevated cardiovascular risk. Small, dense LDL is an independent risk factor for cardiovascular diseases, which emphasizes the clinical importance of both the quality and the quantity of LDL. An effective management of atherosclerotic disease should take into account the presence of small, dense LDL in order to prevent cardiovascular complications
A New Look at Novel Cardiovascular Risk Biomarkers: The Role of Atherogenic Lipoproteins and Innovative Antidiabetic Therapies
The presence of residual cardiovascular disease (CVD) risk is a current dilemma in clinical practice; indeed, despite optimal management and treatment, a considerable proportion of patients still undergo major CV events. Novel lipoprotein biomarkers are suggested as possible targets for improving the outcomes of patients at higher risk for CVD, and their impact on major CV events and mortality have previously been investigated. Innovative antidiabetic therapies have recently shown a significant reduction in atherogenic lipoproteins, beyond their effects on glucose parameters; it has also been suggested that such anti-atherogenic effect may represent a valuable mechanistic explanation for the cardiovascular benefit of, at least, some of the novel antidiabetic agents, such as glucagon-like peptide-1 receptor agonists. This emphasizes the need for further research in the field in order to clearly assess the effects of innovative treatments on different novel biomarkers, including atherogenic lipoproteins, such as small dense low-density lipoprotein (LDL), lipoprotein(a) (Lp(a)) and dysfunctional high-density lipoprotein (HDL). The current article discusses the clinical importance of novel lipid biomarkers for better management of patients in order to overcome residual cardiovascular risk
Electronic Correlations Near a Peierls-CDW Transition
Results of a phenomenological Monte carlo calculation for a 2D
electron-phonon Holstein model near a Peierls-CDW transition are presented.
Here the zero Matsubara frequency part of the phonon action is dominant and we
approximated it by a phenomenological form that as an Ising-like Peierls-CDW
transition. The resulting model is studied on a 32 by 32 lattice. The single
particle spectral weight A(k,\omega), the density of states N(\omega), and the
real part of the conductivity \sigma_1(\omega) all show evidence of a pseudogap
which develops in the low-energy electronic degrees of freedom as the
Peierls-CDW transition is approachedComment: 14 pages, 7 figure
Spin, Charge and Quasiparticle Gaps in the One-Dimensional Kondo Lattice with f^2 Configuration
The ground state properties of the one-dimensional Kondo lattice with an f^2
configuration at each site are studied by the density matrix renormalization
group method. At half-filling, competition between the Kondo exchange J and the
antiferromagnetic intra f-shell exchange I leads to reduction of energy gaps
for spin, quasi-particle and charge excitations. The attractive force among
conduction electrons is induced by the competition and the bound state is
formed. As J/I increases the f^2 singlet gives way to the Kondo singlet as the
dominant local correlation. The remarkable change of the quasi-particle gap is
driven by the change of the spin-1/2 excitation character from the itinerant
one to the localized one. Possible metal-insulator transition is discussed
which may occur as the ratio J/I is varied by reference to mean-field results
in the f^2 lattice system and the two impurity Kondo system.Comment: 7 pages, 7 figures, submitted to J. Phys. Soc. Jp
Coexisting Kondo singlet state with antiferromagnetic long-range order: A possible ground state for Kondo insulators
The ground-state phase diagram of a half-filled anisotropic Kondo lattice
model is calculated within a mean-field theory. For small transverse exchange
coupling , the ground state shows an antiferromagnetic
long-range order with finite staggered magnetizations of both localized spins
and conduction electrons. When , the long-range order
is destroyed and the system is in a disordered Kondo singlet state with a
hybridization gap. Both ground states can describe the low-temperature phases
of Kondo insulating compounds. Between these two distinct phases, there may be
a coexistent regime as a result of the balance between local Kondo screening
and magnetic interactions.Comment: four pages, Revtex, one figure; to be published in Phys. Rev. B, 1
July issue, 200
Charge ordering in the spinels AlVO and LiVO
We develop a microscopic theory for the charge ordering (CO) transitions in
the spinels AlVO and LiVO (under pressure). The high degeneracy
of CO states is lifted by a coupling to the rhombohedral lattice deformations
which favors transition to a CO state with inequivalent V(1) and V(2) sites
forming Kagom\'e and trigonal planes respectively. We construct an extended
Hubbard type model including a deformation potential which is treated in
unrestricted Hartree Fock approximation and describes correctly the observed
first-order CO transition. We also discuss the influence of associated orbital
order. Furthermore we suggest that due to different band fillings AlVO
should remain metallic while LiVO under pressure should become a
semiconductor when charge disproportionation sets in
Friedel Oscillations and Charge Density Waves in Chains and Ladders
The density matrix renormalization group method for ladders works much more
efficiently with open boundary conditions. One consequence of these boundary
conditions is groundstate charge density oscillations that often appear to be
nearly constant in magnitude or to decay only slightly away from the
boundaries. We analyse these using bosonization techniques, relating their
detailed form to the correlation exponent and distinguishing boundary induced
generalized Friedel oscillations from true charge density waves. We also
discuss a different approach to extracting the correlation exponent from the
finite size spectrum which uses exclusively open boundary conditions and can
therefore take advantage of data for much larger system sizes. A general
discussion of the Friedel oscillation wave-vectors is given, and a convenient
Fourier transform technique is used to determine it. DMRG results are analysed
on Hubbard and t-J chains and 2 leg t-J ladders. We present evidence for the
existence of a long-ranged charge density wave state in the t-J ladder at a
filling of n=0.75 and near J/t \approx 0.25.Comment: Revtex, 15 pages, 15 postscript figure
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