Some results on injectivity and multistationarity in chemical reaction networks

The goal of this paper is to gather and develop some necessary and sufficient criteria for injectivity and multistationarity in vector fields associated with a chemical reaction network under a variety of more or less general assumptions on the nature of the network and the reaction rates. The results are primarily linear algebraic or matrix-theoretic, with some graph-theoretic results also mentioned. Several results appear in, or are close to, results in the literature. Here, we emphasise the connections between the results, and where possible, present elementary proofs which rely solely on basic linear algebra and calculus. A number of examples are provided to illustrate the variety of subtly different conclusions which can be reached via different computations. In addition, many of the computations are implemented in a web-based open source platform, allowing the reader to test examples including and beyond those analysed in the paper

The inheritance of nondegenerate multistationarity in chemical reaction networks

We study how the properties of allowing multiple positive nondegenerate equilibria (MPNE) and multiple positive linearly stable equilibria (MPSE) are inherited in chemical reaction networks (CRNs). Specifically, when is it that we can deduce that a CRN admits MPNE or MPSE based on analysis of its subnetworks? Using basic techniques from analysis we are able to identify a number of situations where MPNE and MPSE are inherited as we build up a network. Some of these modifications are known while others are new, but all results are proved using the same basic framework, which we believe will yield further results. The results are presented primarily for mass action kinetics, although with natural, and in some cases immediate, generalisation to other classes of kinetics

Combinatorial approaches to Hopf bifurcations in systems of interacting elements

We describe combinatorial approaches to the question of whether families of real matrices admit pairs of nonreal eigenvalues passing through the imaginary axis. When the matrices arise as Jacobian matrices in the study of dynamical systems, these conditions provide necessary conditions for Hopf bifurcations to occur in parameterised families of such systems. The techniques depend on the spectral properties of additive compound matrices: in particular, we associate with a product of matrices a signed, labelled digraph termed a DSR^[2] graph, which encodes information about the second additive compound of this product. A condition on the cycle structure of this digraph is shown to rule out the possibility of nonreal eigenvalues with positive real part. The techniques developed are applied to systems of interacting elements termed “interaction networks”, of which networks of chemical reactions are a special case

Pheochromocytoma – clinical manifestations, diagnosis and current perioperative management

Pheochromocytoma is a neuroendocrine tumor characterized by the excessive production of catecholamines (epinephrine, norepinephrine, and dopamine). The diagnosis is suspected due to hypertensive paroxysms, associated with vegetative phenomena, due to the catecholaminergic hypersecretion. Diagnosis involves biochemical tests that reveal elevated levels of catecholamine metabolites (metanephrine and normetanephrine). Functional imaging, such as 123I-metaiodobenzylguanidine scintigraphy (123I-MIBG), has increased specificity in identifying the catecholamine-producing tumor and its metastases. The gold-standard treatment for patients with pheochromocytoma is represented by the surgical removal of the tumor. Before surgical resection, it is important to optimize blood pressure and intravascular volume in order to avoid negative hemodynamic events

Cardio metabolic risk factors for atrial fibrillation in type 2 diabetes mellitus: Focus on hypertension, metabolic syndrome and obesity

Objective. Atrial fibrillation (AF) in type 2 diabetes mellitus (T2DM) has been little explored so far. However, there are several cardio metabolic risk factors for AF in T2DM patients, such as arterial hypertension, obesity or the metabolic syndrome. Our objective was to evaluate cardio metabolic risk factors for AF in T2DM patients. Methods. We studied the medical records of T2DM patients hospitalized in the Internal Medicine department of an emergency referral hospital in Bucharest, Romania. The study was observational, retrospective and carried out between January-June 2018. Results. The study group included 221 T2DM patients (with a mean age of 68.65 ± 10.64, ranging between 37-93 years): 116 women (52.49%; with a mean age of 70.53 ± 10.69, ranging between 37-93 years) and 105 men (47.51%; with a mean age of 66.57 ± 10.23, ranging between 38-91 years). 92 patients had AF (41.63%): 40 women (34.48%) and 52 men (49.52%). 180 patients (81.45%) were hypertensive: 103 women (88.79%) and 77 men (73.33%). 113 patients (51.13%) had metabolic syndrome: 58 women (50.00%) and 55 men (52.38%). 77 patients (34.84%) were obese: 45 women (38.79%) and 32 men (30.48%). AF patients associated obesity in 26 cases (28.26%), hypertension in 73 cases (79.35%) and metabolic syndrome in 56 cases (60.87%). Conclusions. Out of the study group, 92 T2DM patients (41.63%) had AF, men being more likely to suffer from AF than women (p=0.0288). Hypertension affected 180 patients (81.45%) and in greater proportion women vs. men (p=0.0051). The metabolic syndrome and obesity were discovered in 113 patients (51.13%) and 77 patients (34.84%), respectively, with no significant differences in terms of gender. In our research, the highest cardio metabolic risk factors for AF in T2DM were hypertension (OR = 3.6675) and the metabolic syndrome (OR = 3.3388)

Characterization of defect structures in nanocrystalline materials by X-ray line profile analysis

X-ray line profile analysis is a powerful alternative tool for determining dislocation densities, dislocation type, crystallite and subgrain size and size-distributions, and planar defects, especially the frequency of twin boundaries and stacking faults. The method is especially useful in the case of submicron grain size or nanocrystalline materials, where X-ray line broadening is a well pronounced effect, and the observation of defects with very large density is often not easy by transmission electron microscopy. The fundamentals of X-ray line broadening are summarized in terms of the different qualitative breadth methods, and the more sophisticated and more quantitative whole pattern fitting procedures. The efficiency and practical use of X-ray line profile analysis is shown by discussing its applications to metallic, ceramic, diamond-like and polymer nanomaterials

The effect of waiters’ occupational identity on employee turnover within the context of Michelin-starred restaurants

Although restaurants employ a high number of employees across the UK, accounting for 4.5% of total UK employment, this figure masks the relatively high degree of employee turnover. There is limited information about work engagement and turnover amongst waitering staff (servers). This study analyzed which antecedents (e.g., employer brand, extraversion and stereotype) impact servers’ occupational identity, and how this relationship affects work engagement and employee turnover within a theoretically-informed conceptual framework. A sample of servers in London based Michelin-starred restaurants was used (N=398). Although extraversion and stereotype reactance were not found to be relevant to occupational identity, employer brand was. The notion that the construction of occupational identity has consequences for work engagement and employee turnover was supported, as positive relationships were found. This research has practical implications for restaurant management strategy, and informs further investigations within the field

Nanocrystalline materials studied by powder diffraction line profile analysis

X-ray powder diffraction is a powerful tool for characterising the microstructure of crystalline materials in terms of size and strain. It is widely applied for nanocrystalline materials, especially since other methods, in particular electron microscopy is, on the one hand tedious and time consuming, on the other hand, due to the often metastable states of nanomaterials it might change their microstructures. It is attempted to overview the applications of microstructure characterization by powder diffraction on nanocrystalline metals, alloys, ceramics and carbon base materials. Whenever opportunity is given, the data provided by the X-ray method are compared and discussed together with results of electron microscopy. Since the topic is vast we do not try to cover the entire field