459 research outputs found
Universal conductivity and dimensional crossover in multi-layer graphene
We show, by exact Renormalization Group methods, that in multi-layer graphene
the dimensional crossover energy scale is decreased by the intra-layer
interaction, and that for temperatures and frequencies greater than such scale
the conductivity is close to the one of a stack of independent layers up to
small corrections
Fermi liquid behavior in the 2D Hubbard model at low temperatures
We prove that the weak coupling 2D Hubbard model away from half filling is a
Landau Fermi liquid up to exponentially small temperatures. In particular we
show that the wave function renormalization is an order 1 constant and
essentially temperature independent in the considered range of temperatures and
that the interacting Fermi surface is a regular convex curve. This result is
obtained by deriving a convergent expansion (which is not a power series) for
the two point Schwinger function by Renormalization Group methods and proving
at each order suitable power counting improvements due to the convexity of the
interacting Fermi surface. Convergence follows from determinant bounds for the
fermionic expectations.Comment: 66 pages, 10 figure
Extended scaling relations for planar lattice models
It is widely believed that the critical properties of several planar lattice
models, like the Eight Vertex or the Ashkin-Teller models, are well described
by an effective Quantum Field Theory obtained as formal scaling limit. On the
basis of this assumption several extended scaling relations among their indices
were conjectured. We prove the validity of some of them, among which the ones
by Kadanoff, [K], and by Luther and Peschel, [LP].Comment: 32 pages, 7 fi
Non perturbative Adler-Bardeen Theorem
The Adler-Bardeen theorem has been proved only as a statement valid at all
orders in perturbation theory, without any control on the convergence of the
series. In this paper we prove a nonperturbative version of the Adler-Bardeen
theorem in by using recently developed technical tools in the theory of
Grassmann integration.Comment: 28 pages, 14 figure
Establishment of prophylactic enoxaparin dosing recommendations to achieve targeted anti-factor Xa concentrations in children with CHD
Background
Enoxaparin may be used to prevent central venous catheter-related thrombosis in patients with CHD. We aimed to determine whether current enoxaparin dosing regimens effectively achieve anti-factor Xa concentrations within prophylactic goal ranges in this patient population.
Methods
We implemented a formal protocol aimed at reducing central venous catheter-related thrombosis in children with CHD in January, 2016. Standard empiric prophylactic enoxaparin dosing regimens were used – for example, 0.75 mg/kg/dose every 12 hours for patients <2 months of age and 0.5 mg/kg/dose every 12 hours for patients ⩾2 months of age – with anti-factor Xa goal range of 0.25–0.49 IU/ml. Patients <2 years of age who received enoxaparin and had at least one valid steady-state anti-factor Xa measurement between 25 January, 2016 and 31 August, 2016 were retrospectively reviewed.
Results
During the study period, 47 patients had 186 anti-factor Xa concentrations measured, of which 20 (11%) were above and 112 (60%) were below the prophylactic goal range. Anti-factor Xa concentrations within the goal range were ultimately achieved in 31 patients. Median dose required to achieve anti-factor Xa concentrations within the prophylactic range was 0.89 mg/kg/dose (25, 75%: 0.75, 1.11) for patients <2 months (n=23 patients) and 0.79 mg/kg/dose (25, 75%: 0.62, 1.11) for patients â©ľ2 months (n=8 patients).
Conclusions
Enoxaparin doses required to achieve prophylactic anti-factor Xa concentrations in young children with CHD were consistently higher than the currently recommended prophylactic dosing regimens. Further study is needed to determine whether dose titration to achieve prophylactic anti-factor Xa concentrations is effective in preventing central venous catheter-related thrombosis
Ward Identities and chiral anomalies for coupled fermionic chains
Coupled fermionic chains are usually described by an effective model written
in terms of bonding and anti-bonding spinless fields with linear dispersion in
the vicinities of the respective Fermi points. We derive for the first time
exact Ward Identities (WI) for this model, proving the existence of chiral
anomalies which verify the Adler-Bardeen non-renormalization property. Such WI
are expected to play a crucial role in the understanding of the thermodynamic
properties of the system. Our results are non-perturbative and are obtained
analyzing Grassmann functional integrals by means of Constructive Quantum Field
Theory methods.Comment: TeX file, 26 pages, 7 figures. Published version, new section added
to answer referee remarks and derive the Ward Identites, no modifications in
the main resul
Modelling CO emission from hydrodynamic simulations of nearby spirals, starbursting mergers, and high-redshift galaxies
We model the intensity of emission lines from the CO molecule, based on
hydrodynamic simulations of spirals, mergers, and high-redshift galaxies with
very high resolutions (3pc and 10^3 Msun) and detailed models for the
phase-space structure of the interstellar gas including shock heating, stellar
feedback processes and galactic winds. The simulations are analyzed with a
Large Velocity Gradient (LVG) model to compute the local emission in various
molecular lines in each resolution element, radiation transfer and opacity
effects, and the intensity emerging from galaxies, to generate synthetic
spectra for various transitions of the CO molecule. This model reproduces the
known properties of CO spectra and CO-to-H2 conversion factors in nearby
spirals and starbursting major mergers. The high excitation of CO lines in
mergers is dominated by an excess of high-density gas, and the high turbulent
velocities and compression that create this dense gas excess result in broad
linewidths and low CO intensity-to-H2 mass ratios. When applied to
high-redshift gas-rich disks galaxies, the same model predicts that their
CO-to-H2 conversion factor is almost as high as in nearby spirals, and much
higher than in starbursting mergers. High-redshift disk galaxies contain giant
star-forming clumps that host a high-excitation component associated to gas
warmed by the spatially-concentrated stellar feedback sources, although CO(1-0)
to CO(3-2) emission is overall dominated by low-excitation gas around the
densest clumps. These results overall highlight a strong dependence of CO
excitation and the CO-to-H2 conversion factor on galaxy type, even at similar
star formation rates or densities. The underlying processes are driven by the
interstellar medium structure and turbulence and its response to stellar
feedback, which depend on global galaxy structure and in turn impact the CO
emission properties.Comment: A&A in pres
Renormalization Group and Asymptotic Spin--Charge separation for Chiral Luttinger liquids
The phenomenon of Spin-Charge separation in non-Fermi liquids is well
understood only in certain solvable d=1 fermionic systems. In this paper we
furnish the first example of asymptotic Spin-Charge separation in a d=1 non
solvable model. This goal is achieved using Renormalization Group approach
combined with Ward-Identities and Schwinger-Dyson equations, corrected by the
presence of a bandwidth cut-offs. Such methods, contrary to bosonization, could
be in principle applied also to lattice or higher dimensional systems.Comment: 45 pages, 11 figure
The scaling limit of the energy correlations in non integrable Ising models
We obtain an explicit expression for the multipoint energy correlations of a
non solvable two-dimensional Ising models with nearest neighbor ferromagnetic
interactions plus a weak finite range interaction of strength , in a
scaling limit in which we send the lattice spacing to zero and the temperature
to the critical one. Our analysis is based on an exact mapping of the model
into an interacting lattice fermionic theory, which generalizes the one
originally used by Schultz, Mattis and Lieb for the nearest neighbor Ising
model. The interacting model is then analyzed by a multiscale method first
proposed by Pinson and Spencer. If the lattice spacing is finite, then the
correlations cannot be computed in closed form: rather, they are expressed in
terms of infinite, convergent, power series in . In the scaling limit,
these infinite expansions radically simplify and reduce to the limiting energy
correlations of the integrable Ising model, up to a finite renormalization of
the parameters. Explicit bounds on the speed of convergence to the scaling
limit are derived.Comment: 75 pages, 11 figure
Incommensurate Charge Density Waves in the adiabatic Hubbard-Holstein model
The adiabatic, Holstein-Hubbard model describes electrons on a chain with
step interacting with themselves (with coupling ) and with a classical
phonon field \f_x (with coupling \l). There is Peierls instability if the
electronic ground state energy F(\f) as a functional of \f_x has a minimum
which corresponds to a periodic function with period , where
is the Fermi momentum. We consider irrational so that
the CDW is {\it incommensurate} with the chain. We prove in a rigorous way in
the spinless case, when \l,U are small and {U\over\l} large, that a)when
the electronic interaction is attractive there is no Peierls instability
b)when the interaction is repulsive there is Peierls instability in the
sense that our convergent expansion for F(\f), truncated at the second order,
has a minimum which corresponds to an analytical and periodic
\f_x. Such a minimum is found solving an infinite set of coupled
self-consistent equations, one for each of the infinite Fourier modes of
\f_x.Comment: 16 pages, 1 picture. To appear Phys. Rev.
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