Nonperturbative results on the quark-gluon vertex

We present analytical and numerical results for the Dirac form factor of the quark-gluon vertex in the quark symmetric limit, where the incoming and outgoing quark momenta have the same magnitude but opposite sign. To accomplish this, we compute the relevant components of the quark-ghost scattering kernel at the one-loop dressed approximation, using as basic ingredients the full quark propagator, obtained as a solution of the quark gap equation, and the gluon propagator and ghost dressing function, obtained from large-volume lattice simulations.Comment: 8 pages, 6 figures. Talk presented by A.C.A at Xth Quark Confinement and the Hadron Spectrum, 8-12 October 2012, TUM Campus Garching, Munich, German

Development of polymer network of phenolic and epoxies resins mixed with linseed oil: pilot study

Epoxy resin was mixed with phenolic resins in different percentages by weight. Composite 40/60 means the proportion by weight of epoxy resin is 40 percent. It was found that only composites 50/50 and 40/60 could be cured in ambient conditions. Dynamic mechanical analysis showed that only these two composites form interpenetrating polymer network. The addition of linseed oil to the two resins results also in the formation of interpenetrating network irrespective of proportion by weight of the resins; the mechanical properties will only be better when the percentage by weight of epoxy resin is higher; the aim of reducing cost and at the same time maintaining the mechanical properties cannot be fully achieved because epoxy resin is much more expensive than its counterpart

Anomalies of the infrared-active phonons in underdoped YBCO as an evidence for the intra-bilayer Josephson effect

The spectra of the far-infrared c-axis conductivity of underdoped YBCO crystals exhibit dramatic changes of some of the phonon peaks when going from the normal to the superconducting state. We show that the most striking of these anomalies can be naturally explained by changes of the local fields acting on the ions arising from the onset of inter- and intra-bilayer Josephson effects.Comment: Revtex, epsf, 6 pages, 3 figures encapsulated in tex

Trinets encode tree-child and level-2 phylogenetic networks

Phylogenetic networks generalize evolutionary trees, and are commonly used to represent evolutionary histories of species that undergo reticulate evolutionary processes such as hybridization, recombination and lateral gene transfer. Recently, there has been great interest in trying to develop methods to construct rooted phylogenetic networks from triplets, that is rooted trees on three species. However, although triplets determine or encode rooted phylogenetic trees, they do not in general encode rooted phylogenetic networks, which is a potential issue for any such method. Motivated by this fact, Huber and Moulton recently introduced trinets as a natural extension of rooted triplets to networks. In particular, they showed that level-1 level-1 phylogenetic networks are encoded by their trinets, and also conjectured that all “recoverable” rooted phylogenetic networks are encoded by their trinets. Here we prove that recoverable binary level-2 networks and binary tree-child networks are also encoded by their trinets. To do this we prove two decomposition theorems based on trinets which hold for all recoverable binary rooted phylogenetic networks. Our results provide some additional evidence in support of the conjecture that trinets encode all recoverable rooted phylogenetic networks, and could also lead to new approaches to construct phylogenetic networks from trinets

Electronic and phononic Raman scattering in detwinned YBa2_2Cu3_3O6.95_{6.95} and Y0.85_{0.85}Ca0.15_{0.15}Ba2_2Cu3_3O6.95_{6.95}: s-wave admixture to the dx2−y2d_{x^2-y^2}-wave order parameter

Inelastic light (Raman) scattering has been used to study electronic excitations and phonon anomalies in detwinned, slightly overdoped YBa$_2$Cu$_3$O$_{6.95}$ and moderately overdoped Y$_{0.85}$Ca$_{0.15}$Ba$_2$Cu$_3$O$_{6.95}$ single crystals. In both samples modifications of the electronic pair-breaking peaks when interchanging the a- and b-axis were observed. The lineshapes of several phonon modes involving plane and apical oxygen vibrations exhibit pronounced anisotropies with respect to the incident and scattered light field configurations. Based on a theoretical model that takes both electronic and phononic contributions to the Raman spectra into account, we attribute the anisotropy of the superconductivity-induced changes in the phonon lineshapes to a small s-wave admixture to the $d_{x^2-y^2}$ pair wave-function. Our theory allows us to disentangle the electronic Raman signal from the phononic part and to identify corresponding interference terms. We argue that the Raman spectra are consistent with an s-wave admixture with an upper limit of 20 percent.Comment: accepted in Phys. Rev. B, 11 page

Efficiency Centered Maintenance of Preheat Train of a Crude Oil Distillation Unit

Nowadays, maintenance is based on the synergistic integration of operational reliability and timely maintenance, which guarantees the required availability and optimal cost. Operational reliability implies producing more, better performance, longer life, and availability. Timely maintenance involves the least time out of service, fewer maintenance costs, fewer operating costs, and less money. In this work, we study the preheating train of a crude distillation unit of a refinery, which processes 994 m3/h, which presents a formation of a foulinglayer inside it. Among the impacts of fouling is the reduction in the effectiveness of heat transfer, the increase in fuel consumption, the increase in CO2 emissions, the increase in maintenance costs, and the decrease in the profit margin of process. An appropriate cleaning program of the surface of the heat exchanger network is necessary to preserve its key performance parameters, preferably close to design values. This paper presents the maintenance method centered on energy efficiency, to plan the intervention of the preheating train equipment maintenance, which considers the economic energy improvement and the cost of the type of maintenance. The method requires the calculation of the fouling evolution from which the global heat transfer coefficient is obtained, and the heat flux is determined as a function of time. It was observed that, as time passes, the resistance provided by fouling increases and that the overall heat transfer coefficient decreases. The energy efficiency centered maintenance has an indicator of economic justification (factor J) that relates the economic-energy improvement achieved when performing maintenance, taking into account the economic effort invested. Depending on the cost of the type of maintenance to be performed, a threshold should be chosen, from which the maintenance activity is justified. The effectiveness values of the heat exchanger (e) and the J indicator are used to form a criticality matrix, which allows prioritizing maintenance activities in each equipment. The planning of the implementation dates of the maintenance of each heat exchanger, from the maintenance method centered on energy efficiency applied to the crude distillation unit's, preheat train, constitutes a contribution in this specific field. The conceptual design of the maintenance method centered on energy efficiency presented in this work is feasible for other heat transfer equipment used in oil refineries and industry in general. The procedure developed uses real operation values, and with its implementation, a saving of 150000 US dollars was achieved. © 2020 ASME

Spittlebugs: Bioecology, Host Plant Resistance and Advances in IPM

Several species and genera of spittlebugs (Homoptera: Cercopidae) are economic pests of grasses in tropical America. These insects compete with grazing animals by reducing forage availability and quality. They may cause serious losses on millions of hectares of improved pastures based on cultivars of several species of Brachiaria (signal grasses). Except for the cultivar Marandu, most of the available commercial cultivars of Brachiaria are susceptible to spittlebugs. In spite of their economic importance, much research need to be done yet. Such insect-plant system encompasses a diverse group of spittlebug species, a diverse group of forage grass species, which are under different management systems, in a broad range of ecological zones. Control efforts have been directed to host plant resistance, alternative that has been recognized as being of easy adoption and of low cost to farmers. It is probably the best control measure for controlling insect pests in low value crops, like pastures, widely established over vast areas. Screening for spittlebug resistance has been conducted both at CIAT and Embrapa-Beef Cattle Center, and promising accessions have been found. It is important however, that additional biological and behavioral studies of these insects, together with evaluations of other control techniques, like biological control and cultural practices, are also performed. Promising control measures and future research needs are discussed

Electroreflectance spectroscopy in self-assembled quantum dots: lens symmetry

Modulated electroreflectance spectroscopy $\Delta R/R$ of semiconductor self-assembled quantum dots is investigated. The structure is modeled as dots with lens shape geometry and circular cross section. A microscopic description of the electroreflectance spectrum and optical response in terms of an external electric field (${\bf F}$) and lens geometry have been considered. The field and lens symmetry dependence of all experimental parameters involved in the $\Delta R/R$ spectrum have been considered. Using the effective mass formalism the energies and the electronic states as a function of ${\bf F}$ and dot parameters are calculated. Also, in the framework of the strongly confined regime general expressions for the excitonic binding energies are reported. Optical selection rules are derived in the cases of the light wave vector perpendicular and parallel to $$. Detailed calculation of the Seraphin coefficients and electroreflectance spectrum are performed for the InAs and CdSe nanostructures. Calculations show good agreement with measurements recently performed on CdSe/ZnSe when statistical distribution on size is considered, explaining the main observed characteristic in the electroreflectance spectra

Electron--Electron Scattering in Quantum Wires and it's Possible Suppression due to Spin Effects

A microscopic picture of electron-electron pair scattering in single mode quantum wires is introduced which includes electron spin. A new source of `excess' noise for hot carriers is presented. We show that zero magnetic field `spin' splitting in quantum wires can lead to a dramatic `spin'-subband dependence of electron--electron scattering, including the possibility of strong suppression. As a consequence extremely long electron coherence lengths and new spin-related phenomena are predicted. Since electron bands in III-V semiconductor quantum wires are in general spin-split in zero applied magnetic field, these new transport effects are of general importance.Comment: 11 pages, LaTeX and APS-RevteX 2, Rep.No. GF66,Figures from author, Physical Review Letters, scheduled for 7 June 199

Electron-phonon renormalization of the absorption edge of the cuprous halides

Compared to most tetrahedral semiconductors, the temperature dependence of the absorption edges of the cuprous halides (CuCl, CuBr, CuI) is very small. CuCl and CuBr show a small increase of the gap $E_0$ with increasing temperature, with a change in the slope of $E_0$ vs. $T$ at around 150 K: above this temperature, the variation of $E_0$ with $T$ becomes even smaller. This unusual behavior has been clarified for CuCl by measurements of the low temperature gap vs. the isotopic masses of both constituents, yielding an anomalous negative shift with increasing copper mass. Here we report the isotope effects of Cu and Br on the gap of CuBr, and that of Cu on the gap of CuI. The measured isotope effects allow us to understand the corresponding temperature dependences, which we also report, to our knowledge for the first time, in the case of CuI. These results enable us to develop a more quantitative understanding of the phenomena mentioned for the three halides, and to interpret other anomalies reported for the temperature dependence of the absorption gap in copper and silver chalcogenides; similarities to the behavior observed for the copper chalcopyrites are also pointed out.Comment: 14 pages, 5 figures, submitted to Phys. Rev.