On the character degree graph of finite groups

Given a finite group G, let cd (G) denote the set of degrees of the irreducible complex characters of G. The character degree graph of G is defined as the simple undirected graph whose vertices are the prime divisors of the numbers in cd (G) , two distinct vertices p and q being adjacent if and only if pq divides some number in cd (G). In this paper, we consider the complement of the character degree graph, and we characterize the finite groups for which this complement graph is not bipartite. This extends the analysis of Akhlaghi et al. (Proc Am Math Soc 146:1505\u20131513, 2018), where the solvable case was treated

Essays in macroeconomics

Esta tesis consta de tres capítulos, cada uno de los cuales analiza temas relevantes en el campo de la Macroeconomía. La investigación realizada en los tres capítulos se basa en la metodología de los modelos dinámicos de equilibrio general. Los fundamentos microeconómicos se encuentran en el núcleo de este tipo de modelos, en los que los agentes forman sus expectativas sobre el futuro de manera racional. Esta metodología ha demostrado ser una herramienta poderosa para abordar un gran conjunto de problemas económicos. El primer capítulo, ``Risk Aversion, Entrepreneurship and Wealth Distribution'', explora el efecto de la heterogeneidad en la aversión al riesgo sobre el emprendimiento, el comportamiento del ahorro y la distribución de la riqueza. La distribución de la riqueza es uno de los temas más debatidos no solo en la política contemporánea, sino también en los medios de comunicación y en ámbitos académicos. En particular, la gran concentración de riqueza en la parte superior de la distribución, que se observa en muchas economías avanzadas, se ha situado en el centro del debate. La relevancia de este problema no se ha visto socavada a pesar de la dificultad que supone estimar los niveles de riqueza acumulada en manos de los hogares más ricos. Apoyado por razones empíricas, el marco teórico para analizar la distribución de la riqueza debe incluir tanto el emprendimiento como la heterogeneidad de las preferencias. Con este objetivo, en el primer capítulo se desarrolla un modelo de elección ocupacional con agentes heterogéneos en el que los hogares varían en su aversión al riesgo, se enfrentan a perturbaciones idiosincrásicas no asegurables, tienen restricciones financieras y deben decidir si convertirse en trabajadores o en emprendedores. Esta decisión se basa en una combinación de la aversión al riesgo individual, las habilidades específicas en cada ocupación y los niveles de riqueza acumulados. Como resultado se obtiene que la aversión al riesgo tiene un efecto directo e indirecto en la decisión de ahorro y en la ocupación de los agentes. Por un lado, una mayor aversión al riesgo disuade a los agentes de convertirse en emprendedores y, por lo tanto, los ahorros destinados a superar las restricciones financieras son menores. Por otro lado, una mayor aversión al riesgo también conduce a un mayor ahorro por motivo de precaución que, indirectamente, atenúa las restricciones financieras y hace que la opción de convertirse en emprendedor sea más atractiva. En el modelo desarrollado, el último efecto domina, y los agentes con mayor aversión al riesgo acumulan mayores niveles de riqueza y también se convierten en emprendedores. La contribución más importante de este modelo es que permite desentrañar los efectos que la aversión al riesgo y las fricciones financieras tienen sobre el emprendimiento, que es un factor clave para explicar la desigualdad en la acumulación de la riqueza. El segundo capítulo se titula ``Long-term business relationships, bargaining and monetary policy'' y es un trabajo conjunto con Mirko Abbritti y Tommaso Trani. Su motivación se deriva de la creciente literatura empírica que documenta la importancia de las relaciones comerciales a largo plazo y los procesos de negociación sobre la rigidez de los precios y las dinámicas empresariales. Este artículo introduce relaciones comerciales entre empresas (B2B) a largo plazo y procesos de negociación de precios en un modelo monetario de equilibrio general dinámico estocástico (DSGE) estándar. El modelo se basa en dos suposiciones. Primero, tanto los productores mayoristas como los minoristas necesitan gastar recursos para formar nuevas relaciones comerciales. Segundo, una vez que se forma una relación comercial, el precio se establece en una negociación bilateral entre las empresas. El modelo proporciona un marco riguroso para estudiar el efecto de las relaciones comerciales a largo plazo y los procesos de negociación sobre la política monetaria y la dinámica del ciclo económico. Además, se demuestra que estas relaciones comerciales reducen tanto el papel de asignación de los precios intermedios como los efectos reales de las perturbaciones de la política monetaria. También encontramos que el modelo hace un gran trabajo al replicar los segundos momentos y las correlaciones cruzadas de los datos, y que mejora con respecto al modelo de referencia Neo Keynesiano en explicar dichos estadísticos. El tercer y último capítulo de esta tesis, ``On Staggered Prices and Optimal Inflation'', es coautoreado con uno de mis directores, Miguel Casares. En este artículo se calcula la tasa de inflación óptima en estado estacionario bajo dos especificaciones de rigidez de precios diferentes, Calvo (1983) y Taylor (1980), en un modelo con competencia monopolística. Encontramos que la tasa óptima de inflación en estado estacionario es siempre positiva. Este resultado es robusto a los cambios en el grado de rigidez de los precios. En ambos casos con rigidez de precios, la tasa de inflación óptima es aproximadamente igual al cociente entre la tasa de descuento y la elasticidad de Dixit-Stiglitz. Para calibraciones estándar, el coste de bienestar de la inflación es cuantitativamente pequeño, pero significativamente más alto si los precios son rígidos a la Calvo que si son rígidos a la Taylor.Fundación Banco Sabadell, Fundación Bancaria Caja Navarra y Universidad Pública de NavarraPrograma de Doctorado en Economía, Empresa y Derecho (RD 99/2011)Ekonomiako, Enpresako eta Zuzenbideko Doktoretza Programa (ED 99/2011

Measuring the nonlinear refractive index of graphene using the optical Kerr effect method

© 2016 Optical Society of America.By means of the ultrafast optical Kerr effect method coupled to optical heterodyne detection (OHD-OKE), we characterize the third-order nonlinear response of graphene and compare it to experimental values obtained by the Z-scan method on the same samples. From these measurements, we estimate a negative nonlinear refractive index for monolayer graphene, n2 = -1.1 × 10-13 m2/W. This is in contradiction to previously reported values, which leads us to compare our experimental measurements obtained by the OHD-OKE and the Z-scan method with theoretical and experimental values found in the literature and to discuss the discrepancies, taking into account parameters such as doping

Fibrotic remodeling of colonic tunica muscularis is associated with vascular network activation in ulcerative colitis

Intestinal fibrosis in inflammatory bowel disease is a dynamic, multifactorial process, which involve multiple cell types and interconnected events [1]. Angiogenesis is a hallmark of active gut disease and closely related to fibrogenetic processes. Endothelial cells and pericytes of neovessels have been found to be able to differentiate into fibroblasts and can be considered good candidates for fibrogenesis also in the intestinal tract [2]. This study was aimed to study whether the fibrotic processes occurring within the tunica muscularis of UC patients are associated with vascular remodeling. Full-thickness left colonic samples were obtained from patients with established, severe and pharmacologically unresponsive UC, who underwent bowel resection. Routine histology, histochemistry and immunohistochemistry were conducted in paraffin cross-sections. Collagen and elastic fiber distribution was evaluated within the tunica muscularis by both histochemical and immunohistochemical assays. The vascular network pattern was analyzed by revealing the expression of CD31, CD105 and nestin by immunofluorescence applied to laser confocal microscopy. A significant increase in collagen fibers and a decrease in elastin content were detected in the tonaca muscularis of UC inflamed colon, as compared with controls. In particular, enhanced collagen deposition were found at level of the longitudinal muscle and circular muscle layer, and in perivascular spaces. By contrast, elastic fiber pattern was significantly decreased throughout the whole muscle compartment. Increased blood vessel density was observed in the colonic tunica muscularis of UC samples compared with samples from healthy control individuals. In particular, the neovessels of inflamed colon showed the activation of both endothelial cells and pericytes, which overexpressed CD105 and nestin, respectively. A significant vascular remodelling (i.e., angiogenesis, endothelial proliferation and pericyte activation) has been observed in the fibrotic tunica muscularis of colon from UC patients. On the basis of the present findings, it is possible to argue that cells of newly formed vessels within the tunica muscularis may contribute to the UC-associated fibrosis by cell transition to mesenchymal phenotype

Persistent enteric murine norovirus infection is associated with functionally suboptimal virus-specific CD8 T cell responses

Norovirus (NV) gastroenteritis is a major contributor to global morbidity and mortality, yet little is known about immune mechanisms leading to NV control. Previous studies using the murine norovirus (MNV) model have established a key role for T cells in MNV clearance. Despite these advances, important questions remain regarding the magnitude, location, and dynamics of the MNV-specific T cell response. To address these questions, we identified MNV-specific major histocompatibility complex (MHC) class I immunodominant epitopes using an overlapping peptide screen. One of these epitopes (amino acids 519 to 527 of open reading frame 2 [ORF2(519-527)]) was highly conserved among all NV genogroups. Using MHC class I peptide tetramers, we tracked MNV-specific CD8 T cells in lymphoid and mucosal sites during infection with two MNV strains with distinct biological behaviors, the acutely cleared strain CW3 and the persistent strain CR6. Here, we show that enteric MNV infection elicited robust T cell responses primarily in the intestinal mucosa and that MNV-specific CD8 T cells dynamically regulated the expression of surface molecules associated with activation, differentiation, and homing. Furthermore, compared to MNV-CW3 infection, chronic infection with MNV-CR6 resulted in fewer and less-functional CD8 T cells, and this difference was evident as early as day 8 postinfection. Finally, MNV-specific CD8 T cells were capable of reducing the viral load in persistently infected Rag1(−/−) mice, suggesting that these cells are a crucial component of NV immunity. Collectively, these data provide fundamental new insights into the adaptive immune response to two closely related NV strains with distinct biological behaviors and bring us closer to understanding the correlates of protective antiviral immunity in the intestine

Riluzole exerts distinct antitumor effects from a metabotropic glutamate receptor 1-specific inhibitor on breast cancer cells

Recent evidence suggests that glutamate signaling plays an important role in cancer. Riluzole is a glutamate release inhibitor and FDA-approved drug for the treatment of amyotrophic lateral sclerosis. It has been investigated as an inhibitor of cancer cell growth and tumorigenesis with the intention of repurposing it for the treatment of cancer. Riluzole is thought to act by indirectly inhibiting glutamate signaling. However, the specific effects of riluzole in breast cancer cells are not well understood. In this study, the anti-cancer effects of riluzole were explored in a panel of breast cancer cell lines in comparison to the metabotropic glutamate receptor 1-specific inhibitor BAY 36-7620. While both drugs inhibited breast cancer cell proliferation, there were distinct functional effects suggesting that riluzole action may be metabotropic glutamate receptor 1-independent. Riluzole induced mitotic arrest independent of oxidative stress while BAY 36-7620 had no measurable effect on mitosis. BAY 36-7620 had a more pronounced and significant effect on DNA damage than riluzole. Riluzole altered cellular metabolism as demonstrated by changes in oxidative phosphorylation and cellular metabolite levels. These results provide a better understanding of the functional action of riluzole in the treatment of breast cancer

Morpho-functional alterations of colonic neuromuscular compartment in experimental Parkinson’s disease

Parkinson’s disease (PD) is a degenerative neurological disorder, which is often associated with gastrointestinal symptoms. Among these disturbances, constipation has received considerable attention owing to its potential value as early marker of disease onset [1, 2]. Our study aims at evaluating motor dysfunctions and neurochemical coding of colonic neuromuscular compartment in a rat model of PD. Experimental PD was induced in rats by unilateral injection of 6-idroxydopamine (6-OHDA) into two sites of the right medial forebrain bundle. Functional and morphological studies were carried out 28 and 56 days after treatment. Colonic circular muscle contractions were revorded in organ baths after electrical stimulation or in the presence of exogenous substance P (SP). Colonic samples were examined by immunohistochemistry for the following parameters: density of myenteric HuC/D+ neurons and GFAP+ glial cells; distribution pattern and quantitative expression of SP, tyrosine hidroxylase (TH) and choline acethyltransferase (ChAT). Contractions elicited by electrically evoked tachykinin release as well as by exogenous SP were enhanced at both day 28 and 56, as compared to controls. Myenteric ganglia of PD animals displayed a significant increase in HuC/D+ neuron density, but no alteration in GFAP+ expression. SP+ myenteric neurons progressively increased over time, while the expression of TH and ChAT were significantly reduced at both time points. Experimental PD, elicited by nigrostriatal dopaminergic degeneration, is associated with functional and histopathological/neurochemical changes of the colonic neuromuscular compartment. The enhanced tachykinenergic motor control, associated with an upregulation of neuronal SP expression, together with reduced expression of TH and ChAT, may account for the colonic motor dysfunctions often associated to PD

Colonic inflammation in experimental Parkinson’s disease

Parkinson’s disease (PD) is characterized by degeneration and loss of dopaminergic nigrostriatal neurons, responsible for neurologic symptoms. Besides motor signs, most PD patients experience gastrointestinal (GI) disturbances, including dyspepsia and constipation, which impair severely their quality of life. The pathophysiology of digestive disturbances in PD is largely unknown, but recently a link between PD and colonic inflammation has been observed in human biopsies [1]. Our study aims at evaluating some inflammatory patterns in colonic whole wall in a rat model of PD. PD was induced in rats by unilateral injection of 6-idroxydopamine (6-OHDA) into two sites of the right medial forebrain bundle. Studies were carried out 28 and 56 days after treatment on full-thickness samples from distal colon. The following parameters were examined: tissue malondialdehyde (MDA), an index of membrane lipid peroxidation; tumor necrosis factor (TNF), an index of inflammatory cytokine release; inflammatory cells (eosinophils, mast cells); glial fibrillar acid protein (GFAP) and substance P (SP) expression in myenteric ganglia by immunohistochemical staining. At both time points 6-OHDA-induced nigrostriatal denervation was associated with significant increase in: a) tissue levels of MDA (membrane oxidative stress) and TNF (tissue inflammation); b) density of eosinophil and mast cell in tunica mucosa and submucosa (inflammatory infiltration); b) GFAP expression in myenteric ganglia of tunica muscularis (enteric glia activation); c) SP expression in myenteric neurons, which is compatible with an enhanced tachykinenergic motor control as shown by preliminary functional studies on colonic muscle strips from PD rats. Our findings suggest that experimental PD, elicited by nigrostriatal dopaminergic degeneration, is associated with an inflammation of the colonic wall involving all layers. These results support the view that peripheral enteric neuroinflammation may account for GI motor dysfunctions in PD