Double neutral pion photoproduction at threshold

We consider the chiral expansion of the threshold amplitude for the reaction $\gamma p \to \pi^0 \pi^0 p$ to order ${\cal O}(M_\pi^2)$. We substantiate a claim that this photoproduction channel is significantly enhanced close to threshold due to pion loops. A precise measurement of the corresponding cross sections is called for which allows to test chiral perturbation theory.Comment: 8 pp, LaTe

Residual mean first-passage time for jump processes: theory and applications to L\'evy flights and fractional Brownian motion

We derive a functional equation for the mean first-passage time (MFPT) of a generic self-similar Markovian continuous process to a target in a one-dimensional domain and obtain its exact solution. We show that the obtained expression of the MFPT for continuous processes is actually different from the large system size limit of the MFPT for discrete jump processes allowing leapovers. In the case considered here, the asymptotic MFPT admits non-vanishing corrections, which we call residual MFPT. The case of L/'evy flights with diverging variance of jump lengths is investigated in detail, in particular, with respect to the associated leapover behaviour. We also show numerically that our results apply with good accuracy to fractional Brownian motion, despite its non-Markovian nature.Comment: 13 pages, 8 figure

Defective transport properties of three-terminal carbon nanotube junctions

We investigate the transport properties of three terminal carbon based nanojunctions within the scattering matrix approach. The stability of such junctions is subordinated to the presence of nonhexagonal arrangements in the molecular network. Such "defective" arrangements do influence the resulting quantum transport observables, as a consequence of the possibility of acting as pinning centers of the correspondent wavefunction. By investigating a fairly wide class of junctions we have found regular mutual dependencies between such localized states at the carbon network and a strikingly behavior of the conductance. In particular, we have shown that Fano resonances emerge as a natural result of the interference between defective states and the extended continuum background. As a consequence, the currents through the junctions hitting these resonant states might experience variations on a relevant scale with current modulations of up to 75%.Comment: 8 pages, 8 figure

Global mean first-passage times of random walks on complex networks

We present a general framework, applicable to a broad class of random walks on complex networks, which provides a rigorous lower bound for the mean first-passage time of a random walker to a target site averaged over its starting position, the so-called global mean first-passage time (GMFPT). This bound is simply expressed in terms of the equilibrium distribution at the target, and implies a minimal scaling of the GMFPT with the network size. We show that this minimal scaling, which can be arbitrarily slow for a proper choice of highly connected target, is realized under the simple condition that the random walk is transient at the target site, and independently of the small-world, scale free or fractal properties of the network. Last, we put forward that the GMFPT to a specific target is not a representative property of the network, since the target averaged GMFPT satisfies much more restrictive bounds, which forbid any sublinear scaling with the network size.Comment: 4 pages, 1 figur

Periodontal and Dental Status in Packs of Spanish Dogs

While periodontal disease (PD) is the most common canine oral pathology, its prevalence varies according to diagnosis methodology, breed, and age. We intended to increase understanding of canine PD by studying dogs that are managed in a specific way: pack dogs in Spain. They received a mixed diet (home-prepared food, commercial dry food, stale bread and bones). Thirty-two conscious individuals from two packs of dogs in Northeastern Spain (30/32 crossbred hunting dogs and 2/32 Siberian Husky; 26 males and 6 females; 27.75 ± 5.807 kgs; 5.48 ± 2.818 years) received visual dental examination for assessment of absent teeth (AT), dental calculus (DC) grade, gingival recession (GR), periodontal disease (PD), tooth fracture (TF), and dental attrition (DA). DC was the most prevalent oral problem (75%), followed by TF/DA (68.75%), AT (34.37%), GR (31.25%), and, finally, PD (15.62%). Low individual affectation values were found for AT, GR, and PD (<1 tooth/individual); mean DC grade per individual was 0.06 ± 0.063; and TF and DA were found in 1.63 and 4.72 teeth/individual, respectively. Low prevalence and extent of PD was attributed to diagnosis methodology, bodyweight effect, breed, and, ultimately, diet. Individuals affected by DC remained under veterinary surveillance due to PD development

Luminescence Spectra of Quantum Dots in Microcavities. I. Bosons

We provide a unified theory of luminescence spectra of coupled light-matter systems realized with semiconductor heterostructures in microcavities, encompassing: i) the spontaneous emission case, where the system decays from a prepared (typically pure) initial state, and ii) luminescence in the presence of a continuous, incoherent pump. While the former case has been amply discussed in the literature (albeit mainly for the case of resonance), no consideration has been given to the influence of the incoherent pump. We show how, by provoking a self-consistent quantum state, the pump considerably alters the emission spectra, even at vanishing intensities. The main outcome of our analysis is to unambiguously identify strong-coupling in situations where it appears in disguise or only seems to appear. Here, we consider bosonic matter fields, in which case fully analytical solutions can be obtained. This describes the case of quantum wells or large quantum dots, or the limit of low excitation where the average populations remain much smaller than one