346 research outputs found
Auxiliary fields approach to shift-symmetric theories: the derivative theory and the crumpled-to-flat transition of membranes at two-loop order
We introduce a technique relying on the use of auxiliary fields in order to
eliminate explicit field-derivatives that plague the high orders
renormalization group treatment of shift-symmetric, derivative, theories. This
technique simplifies drastically the computation of fluctuations in such
theories. This is illustrated by deriving the two-loop renormalization group
equations and the three-loop anomalous dimension of the derivative
theory in , which is also relevant to describe the
crumpled-to-flat transition of polymerized membranes. Some features of this
transition are provided.Comment: 7 page
Multi-Armed Bandits for Correlated Markovian Environments with Smoothed Reward Feedback
We study a multi-armed bandit problem in a dynamic environment where arm
rewards evolve in a correlated fashion according to a Markov chain. Different
than much of the work on related problems, in our formulation a learning
algorithm does not have access to either a priori information or observations
of the state of the Markov chain and only observes smoothed reward feedback
following time intervals we refer to as epochs. We demonstrate that existing
methods such as UCB and -greedy can suffer linear regret in such
an environment. Employing mixing-time bounds on Markov chains, we develop
algorithms called EpochUCB and EpochGreedy that draw inspiration from the
aforementioned methods, yet which admit sublinear regret guarantees for the
problem formulation. Our proposed algorithms proceed in epochs in which an arm
is played repeatedly for a number of iterations that grows linearly as a
function of the number of times an arm has been played in the past. We analyze
these algorithms under two types of smoothed reward feedback at the end of each
epoch: a reward that is the discount-average of the discounted rewards within
an epoch, and a reward that is the time-average of the rewards within an epoch.Comment: Significant revision of prior version including deeper discussion of
related work, gap-independent regret bounds, and regret bounds for discounted
reward
Monte Carlo renormalization group study of the Heisenberg and XY antiferromagnet on the stacked triangular lattice and the chiral model
With the help of the improved Monte Carlo renormalization-group scheme, we
numerically investigate the renormalization group flow of the antiferromagnetic
Heisenberg and XY spin model on the stacked triangular lattice (STA-model) and
its effective Hamiltonian, 2N-component chiral model which is used in
the field-theoretical studies. We find that the XY-STA model with the lattice
size exhibits clear first-order behavior. We also
find that the renormalization-group flow of STA model is well reproduced by the
chiral model, and that there are no chiral fixed point of
renormalization-group flow for N=2 and 3 cases. This result indicates that the
Heisenberg-STA model also undergoes first-order transition.Comment: v1:15 pages, 15 figures v2:updated references v3:added comments on
the higher order irrelevant scaling variables v4:added results of larger
sizes v5:final version to appear in J.Phys.Soc.Jpn Vol.72, No.
Spin-stiffness and topological defects in two-dimensional frustrated spin systems
Using a {\it collective} Monte Carlo algorithm we study the low-temperature
and long-distance properties of two systems of two-dimensional classical tops.
Both systems have the same spin-wave dynamics (low-temperature behavior) as a
large class of Heisenberg frustrated spin systems. They are constructed so that
to differ only by their topological properties. The spin-stiffnesses for the
two systems of tops are calculated for different temperatures and different
sizes of the sample. This allows to investigate the role of topological defects
in frustrated spin systems. Comparisons with Renormalization Group results
based on a Non Linear Sigma model approach and with the predictions of some
simple phenomenological model taking into account the topological excitations
are done.Comment: RevTex, 25 pages, 14 figures, Minor changes, final version. To appear
in Phys.Rev.
Optimization of the derivative expansion in the nonperturbative renormalization group
We study the optimization of nonperturbative renormalization group equations
truncated both in fields and derivatives. On the example of the Ising model in
three dimensions, we show that the Principle of Minimal Sensitivity can be
unambiguously implemented at order of the derivative expansion.
This approach allows us to select optimized cut-off functions and to improve
the accuracy of the critical exponents and . The convergence of the
field expansion is also analyzed. We show in particular that its optimization
does not coincide with optimization of the accuracy of the critical exponents.Comment: 13 pages, 9 PS figures, published versio
Non-Perturbative Renormalization Group for Simple Fluids
We present a new non perturbative renormalization group for classical simple
fluids. The theory is built in the Grand Canonical ensemble and in the
framework of two equivalent scalar field theories as well. The exact mapping
between the three renormalization flows is established rigorously. In the Grand
Canonical ensemble the theory may be seen as an extension of the Hierarchical
Reference Theory (L. Reatto and A. Parola, \textit{Adv. Phys.}, \textbf{44},
211 (1995)) but however does not suffer from its shortcomings at subcritical
temperatures. In the framework of a new canonical field theory of liquid state
developed in that aim our construction identifies with the effective average
action approach developed recently (J. Berges, N. Tetradis, and C. Wetterich,
\textit{Phys. Rep.}, \textbf{363} (2002))
Partial loss of function of the GHRH Receptor leads to mild Growth Hormone Deficiency
OBJECTIVE: Recessive mutations in GHRHR are associated with severe isolated growth hormone deficiency (IGHD), with a final height in untreated patients of 130 cm ± 10 cm (-7.2 ± 1.6 SDS; males) and 114 ± 0.7 cm (-8.3 ± 0.1 SDS; females). DESIGN: We hypothesized that a consanguineous Pakistani family with IGHD in three siblings (two males, one female) would have mutations in GH1 or GHRHR. RESULTS: Two novel homozygous missense variants [c.11G>A (p.R4Q), c.236C>T (p.P79L)] at conserved residues were identified in all three siblings. Both were absent from control databases, aside from pR4Q appearing once in heterozygous form in the Exome Aggregation Consortium Browser. The brothers were diagnosed with GH deficiency at 9.8 and 6.0 years (height SDS: -2.24 and -1.23, respectively), with a peak GH of 2.9 μg/liter with low IGF-1/IGF binding protein 3. Their sister presented at 16 years with classic GH deficiency (peak GH <0.1 μg/liter, IGF-1 <3.3 mmol/liter) and attained an untreated near-adult height of 144 cm (-3.0 SDS); the tallest untreated patient with GHRHR mutations reported. An unrelated Pakistani female IGHD patient was also compound homozygous. All patients had a small anterior pituitary on magnetic resonance imaging. Functional analysis revealed a 50% reduction in maximal cAMP response to stimulation with GHRH by the p.R4Q/p.P79L double mutant receptor, with a 100-fold increase in EC50. CONCLUSION: We report the first coexistence of two novel compound homozygous GHRHR variants in two unrelated pedigrees associated with a partial loss of function. Surprisingly, the patients have a relatively mild IGHD phenotype. Analysis revealed that the pP79L mutation is associated with the compromise in function, with the residual partial activity explaining the mild phenotype
Regulation of proliferating cell nuclear antigen ubiquitination in mammalian cells
After exposure to DNA-damaging agents that block the progress of the replication fork, monoubiquitination of proliferating cell nuclear antigen (PCNA) mediates the switch from replicative to translesion synthesis DNA polymerases. We show that in human cells, PCNA is monoubiquitinated in response to methyl methanesulfonate and mitomycin C, as well as UV light, albeit with different kinetics, but not in response to bleomycin or camptothecin. Cyclobutane pyrimidine dimers are responsible for most of the PCNA ubiquitination events after UV-irradiation. Failure to ubiquitinate PCNA results in substantial sensitivity to UV and methyl methanesulfonate, but not to camptothecin or bleomycin. PCNA ubiquitination depends on Replication Protein A (RPA), but is independent of ATR-mediated checkpoint activation. After UV-irradiation, there is a temporal correlation between the disappearance of the deubiquitinating enzyme USP1 and the presence of PCNA ubiquitination, but this correlation was not found after chemical mutagen treatment. By using cells expressing photolyases, we are able to remove the UV lesions, and we show that PCNA ubiquitination persists for many hours after the damage has been removed. We present a model of translesion synthesis behind the replication fork to explain the persistence of ubiquitinated PCNA
Weak quenched disorder and criticality: resummation of asymptotic(?) series
In these lectures, we discuss the influence of weak quenched disorder on the
critical behavior in condensed matter and give a brief review of available
experimental and theoretical results as well as results of MC simulations of
these phenomena. We concentrate on three cases: (i) uncorrelated random-site
disorder, (ii) long-range-correlated random-site disorder, and (iii) random
anisotropy.
Today, the standard analytical description of critical behavior is given by
renormalization group results refined by resummation of the perturbation theory
series. The convergence properties of the series are unknown for most
disordered models. The main object of these lectures is to discuss the
peculiarities of the application of resummation techniques to perturbation
theory series of disordered models.Comment: Lectures given at the Second International Pamporovo Workshop on
Cooperative Phenomena in Condensed Matter (28th July - 7th August 2001,
Pamporovo, Bulgaria). 51 pages, 12 figures, 1 style files include
Bypass of mutagenic O 6 -Carboxymethylguanine DNA Adducts by Human Y- and B-Family Polymerases
The generation of chemical alkylating agents from nitrosation of glycine and bile acid conjugates in the gastrointestinal tract is hypothesized to initiate carcinogenesis. O6-carboxymethylguanine (O6-CMG) is a product of DNA alkylation derived from nitrosated glycine. Although the tendency of the structurally related adduct O6-methylguanine to code for the misincoporation of TTP during DNA replication is well-established, the impact of the presence of the O6-CMG adduct in a DNA template on the efficiency and fidelity of translesion DNA synthesis (TLS) by human DNA polymerases (Pols) has hitherto not been described. Herein, we characterize the ability of the four human TLS Pols η, ι, κ, and ζ and the replicative Pol δ to bypass O6-CMG in a prevalent mutational hot-spot for colon cancer. The results indicate that Pol η replicates past O6-CMG, incorporating dCMP or dAMP, whereas Pol κ incorporates dCMP only, and Pol ι incorporates primarily dTMP. Additionally, the subsequent extension step was carried out with high efficiency by TLS Pols η, κ, and ζ, while Pol ι was unable to extend from a terminal mismatch. These results provide a first basis of O6-CMG-promoted base misincorporation by Y- and B-family polymerases potentially leading to mutational signatures associated with colon cancer
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