399 research outputs found
A generalized Kac-Ward formula
The Kac-Ward formula allows to compute the Ising partition function on a
planar graph G with straight edges from the determinant of a matrix of size 2N,
where N denotes the number of edges of G. In this paper, we extend this formula
to any finite graph: the partition function can be written as an alternating
sum of the determinants of 2^{2g} matrices of size 2N, where g is the genus of
an orientable surface in which G embeds. We give two proofs of this generalized
formula. The first one is purely combinatorial, while the second relies on the
Fisher-Kasteleyn reduction of the Ising model to the dimer model, and on
geometric techniques. As a consequence of this second proof, we also obtain the
following fact: the Kac-Ward and the Fisher-Kasteleyn methods to solve the
Ising model are one and the same.Comment: 23 pages, 8 figures; minor corrections in v2; to appear in J. Stat.
Mech. Theory Ex
Gauge Invariant Cutoff QED
A hidden generalized gauge symmetry of a cutoff QED is used to show the
renormalizability of QED. In particular, it is shown that corresponding Ward
identities are valid all along the renormalization group flow. The exact
Renormalization Group flow equation corresponding to the effective action of a
cutoff lambda phi^4 theory is also derived. Generalization to any gauge group
is indicated.Comment: V1: 18 pages, 2 figures; V2: Discussions improved. Version accepted
for publication in Physica Script
On Finite Noncommutativity in Quantum Field Theory
We consider various modifications of the Weyl-Moyal star-product, in order to
obtain a finite range of nonlocality. The basic requirements are to preserve
the commutation relations of the coordinates as well as the associativity of
the new product. We show that a modification of the differential representation
of the Weyl-Moyal star-product by an exponential function of derivatives will
not lead to a finite range of nonlocality. We also modify the integral kernel
of the star-product introducing a Gaussian damping, but find a nonassociative
product which remains infinitely nonlocal. We are therefore led to propose that
the Weyl-Moyal product should be modified by a cutoff like function, in order
to remove the infinite nonlocality of the product. We provide such a product,
but it appears that one has to abandon the possibility of analytic calculation
with the new product.Comment: 13 pages, reference adde
once weekly administration of high dosage etanercept in patients with plaque psoriasis results of a pilot experience power study
Abstract Etanercept is a soluble tumour necrosis factor receptor fusion protein which is approved for the treatment of plaque psoriasis at the dose of either 25mg twice weekly (BIW) or, for the initial 12 weeks, 50mg BIW. Alternative dosing regimens have not been evaluated in psoriasis. In this study, we compare the efficacy and tolerability of two etanercept dosing regimens--50mg BIW and 100mg once weekly (OW)--for 12 weeks in 108 patients with moderate-to-severe recalcitrant psoriasis. Efficacy measures included Psoriasis Area and Severity Index (PASI), severity of pruritus recorded on a visual analogue scale (VAS) and the influence on quality of life assessed by means of Dermatology Life Quality Index (DLQI). Both etanercept regimens caused a significant change in all the efficacy parameters after 4 weeks and 12 weeks, at a comparable rate. At week 12, a PASI improvement of at least 50% from baseline (PASI 50) was achieved by 74% of patients treated with 50mg BIW and 78% of patients treated with 100mg OW. A PASI 75 response was obtained in 54% and 50% of patients treated with 50mg BIW and 100mg OW, respectively. Treatment was well tolerated with similar type and frequency of adverse events between the two groups
Translation Invariance, Commutation Relations and Ultraviolet/Infrared Mixing
We show that the Ultraviolet/Infrared mixing of noncommutative field theories
with the Gronewold-Moyal product, whereby some (but not all) ultraviolet
divergences become infrared, is a generic feature of translationally invariant
associative products. We find, with an explicit calculation that the phase
appearing in the nonplanar diagrams is the one given by the commutator of the
coordinates, the semiclassical Poisson structure of the non commutative
spacetime. We do this with an explicit calculation for represented generic
products.Comment: 24 pages, 1 figur
Finite-size scaling of the quasiespecies model
We use finite-size scaling to investigate the critical behavior of the
quasiespecies model of molecular evolution in the single-sharp-peak replication
landscape. This model exhibits a sharp threshold phenomenon at Q=Q_c=1/a, where
Q is the probability of exact replication of a molecule of length L and a is
the selective advantage of the master string.
We investigate the sharpness of the threshold and find that its
characteristic persist across a range of Q of order L^(-1) about Q_c.
Furthermore, using the data collapsing method we show that the normalized mean
Hamming distance between the master string and the entire population, as well
as the properly scaled fluctuations around this mean value, follow universal
forms in the critical region.Comment: 8 pages,tex. Submitted to Physical Review
Graviton Spectra in String Cosmology
We propose to uncover the signature of a stringy era in the primordial
Universe by searching for a prominent peak in the relic graviton spectrum. This
feature, which in our specific model terminates an increase and
initiates an decrease, is induced during the so far overlooked
bounce of the scale factor between the collapsing deflationary era (or pre-Big
Bang) and the expanding inflationary era (or post-Big Bang). We evaluate both
analytically and numerically the frequency and the intensity of the peak and we
show that they may likely fall in the realm of the new generation of
interferometric detectors. The existence of a peak is at variance with
ordinarily monotonic (either increasing or decreasing) graviton spectra of
canonical cosmologies; its detection would therefore offer strong support to
string cosmology.Comment: 14 pages, RevTex source and 6 figures.p
Network intelligence vs. jamming in underwater networks: how learning can cope with misbehavior
In this paper, we present a machine-learning technique to counteract jamming attacks in underwater networks. Indeed, this is relevant in security applications where sensor devices are located in critical regions, for example, in the case of national border surveillance or for identifying any unauthorized intrusion. To this aim, a multi-hop routing protocol that relies on the exploitation of a Q-learning methodology is presented with a focus on increasing reliability in data communication and network lifetime. Performance results assess the effectiveness of the proposed solution as compared to other efficient state-of-the-art approaches
- âŠ