142 research outputs found
Dynamical correlations and quantum phase transition in the quantum Potts model
We present a detailed study of the finite temperature dynamical properties of
the quantum Potts model in one dimension.Quasiparticle excitations in this
model have internal quantum numbers, and their scattering matrix {\gf deep} in
the gapped phases is shown to take a simple {\gf exchange} form in the
perturbative regimes. The finite temperature correlation functions in the
quantum critical regime are determined using conformal invariance, while {\gf
far from the quantum critical point} we compute the decay functions
analytically within a semiclassical approach of Sachdev and Damle [K. Damle and
S. Sachdev, Phys. Rev. B \textbf{57}, 8307 (1998)]. As a consequence, decay
functions exhibit a {\em diffusive character}. {\gf We also provide robust
arguments that our semiclassical analysis carries over to very low temperatures
even in the vicinity of the quantum phase transition.} Our results are also
relevant for quantum rotor models, antiferromagnetic chains, and some spin
ladder systems.Comment: 18 PRB pages added correction
On scaling fields in Ising models
We study the space of scaling fields in the symmetric models with the
factorized scattering and propose simplest algebraic relations between form
factors induced by the action of deformed parafermionic currents. The
construction gives a new free field representation for form factors of
perturbed Virasoro algebra primary fields, which are parafermionic algebra
descendants. We find exact vacuum expectation values of physically important
fields and study correlation functions of order and disorder fields in the form
factor and CFT perturbation approaches.Comment: 2 Figures, jetpl.cl
Jorge A. Swieca's contributions to quantum field theory in the 60s and 70s and their relevance in present research
After revisiting some high points of particle physics and QFT of the two
decades from 1960 to 1980, I comment on the work by Jorge Andre Swieca. I
explain how it fits into the quantum field theory during these two decades and
draw attention to its relevance to the ongoing particle physics research. A
particular aim of this article is to direct thr readers mindfulness to the
relevance of what at the time of Swieca was called "the Schwinger Higgs
screening mechanism". which, together with recent ideas which generalize the
concept of gauge theories, has all the ingredients to revolutionize the issue
of gauge theories and the standard model.Comment: 49 pages, expansion and actualization of text, improvement of
formulations and addition of many references to be published in EPJH -
Historical Perspectives on Contemporary Physic
Gene-specific repair of Pt/DNA lesions and induction of apoptosis by the oral platinum drug JM216 in three human ovarian carcinoma cell lines sensitive and resistant to cisplatin
JM216, an oral platinum drug entering into phase III clinical trial, exhibited comparable cytotoxicity to cisplatin in three human ovarian carcinoma cell lines: the sensitive (CH1), acquired resistant (CH1cisR) and intrinsically resistant (SKOV-3). Platinum accumulation and binding to DNA were similar in each of the three cell lines at equimolar doses, indicating that the resistant cell lines could tolerate higher intracellular platinum levels and platinum bound to DNA at IC50 concentrations of drug. Comparison with cisplatin demonstrated that intracellular platinum levels were marginally higher with JM216, but that platinum binding to DNA was similar for the two drugs in each of the cell lines. Each of the cell lines exhibited an ability to repair JM216 induced platinum/DNA lesions in the N-ras gene (gene-specific repair) at equitoxic concentrations of drug. However, this occurred to a greater extent in the two resistant cell lines such that by 24 h the CH1cisR and SKOV-3 had removed 72% and 67% respectively compared with approximately 32% for the CH1. Reduced gene-specific repair capacity in CH1 cells was also seen following incubation with 25 μM (or 5 μM – 2 × IC50) cisplatin, whereas the CH1cisR and SKOV-3 cell lines were repair proficient. JM216 induced apoptosis in the three cell lines following a 2h incubation with 2 × the IC50 of drug. Fluorescent microscopy of cells stained with propidium iodide showed that the detached cell population displayed typical apoptotic nuclei. Furthermore, field inversion gel electrophoresis demonstrated the presence of DNA fragments approximately 23–50 kb in size, indicative of apoptosis, in the detached cells. JM216 induced an S phase slow down in each of the three cell lines accompanied by a G2 block in the CH1 pair. Incubation with this concentration of JM216 also resulted in the induction of p53 in the CH1 and CH1cisR. These studies suggest that the relative sensitivity of the CH1 cell line to cisplatin and JM216 is at least partly attributable to a deficiency in gene-specific repair. The oral platinum drug, JM216, exerts its cytotoxic effects through the induction of apoptosis following a slow-down in S phase in both the sensitive and resistant lines. © 1999 Cancer Research Campaig
Targeted correction of a thalassemia-associated β-globin mutation induced by pseudo-complementary peptide nucleic acids
β-Thalassemia is a genetic disorder caused by mutations in the β-globin gene. Triplex-forming oligonucleotides and triplex-forming peptide nucleic acids (PNAs) have been shown to stimulate recombination in mammalian cells via site-specific binding and creation of altered helical structures that provoke DNA repair. However, the use of these molecules for gene targeting requires homopurine tracts to facilitate triple helix formation. Alternatively, to achieve binding to mixed-sequence target sites for the induced gene correction, we have used pseudo-complementary PNAs (pcPNAs). Due to steric hindrance, pcPNAs are unable to form pcPNA–pcPNA duplexes but can bind to complementary DNA sequences via double duplex-invasion complexes. We demonstrate here that pcPNAs, when co-transfected with donor DNA fragments, can promote single base pair modification at the start of the second intron of the beta-globin gene. This was detected by the restoration of proper splicing of transcripts produced from a green fluorescent protein-beta globin fusion gene. We also demonstrate that pcPNAs are effective in stimulating recombination in human fibroblast cells in a manner dependent on the nucleotide excision repair factor, XPA. These results suggest that pcPNAs can be effective tools to induce heritable, site-specific modification of disease-related genes in human cells without purine sequence restriction
BLOOD VESSELS IN GANGLIA IN HUMAN ESOPHAGUS MIGHT EXPLAIN THE HIGHER FREQUENCY OF MEGAESOPHAGUS COMPARED WITH MEGACOLON
Integrable sigma models with theta=pi
A fundamental result relevant to spin chains and two-dimensional disordered
systems is that the sphere sigma model with instanton coupling theta=pi has a
non-trivial low-energy fixed point and a gapless spectrum. This result is
extended to two series of sigma models with theta=pi: the SU(N)/SO(N) sigma
models flow to the SU(N)_1 WZW theory, while the O(2N)/O(N)\times O(N) models
flow to O(2N)_1 (2N free Majorana fermions). These models are integrable, and
the exact quasiparticle spectra and S matrices are found. One interesting
feature is that charges fractionalize when theta=pi. I compute the energy in a
background field, and verify that the perturbative expansions for \theta=0 and
pi are the same as they must be. I discuss the flows between the two sequences
of models, and also argue that the analogous sigma models with Sp(2N) symmetry,
the Sp(2N)/U(N) models, flow to Sp(2N)_1.Comment: 31 pages, 2 figures. v2: corrects many typos. v3: corrects more
typos, adds referenc
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