Yield and Dynamics of Tri-Trophic Food Chains

Strong relationships between top productivity and dynamic behavior of tri-trophic food chains are pointed out by analyzing the classical Rosenzweig-MacArthur model. On one hand, food chains are subdivided into under-supplied and over-supplied, the first being those in which a marginal increase of nutrient supply to the bottom produces a marginal increase of mean top productivity. On the other hand, a detailed bifurcation analysis proves that dynamics complexity first increases with nutrient supply (from stationary to low-frequency cyclic regime and, finally, to chaos) and then decreases (from chaos to high-frequency cyclic regime). A careful comparison of the two analyses supports the conclusion that food chains cycling at high-frequency are over-supplied, while all others are under-supplied. A straightforward consequence of this result is that maximization of top productivity requires a chaotic regime. This regime turns out to be very often on the edge of a potential catastrophic collapse of food yield. In other words, optimality implies very complex and dangerous dynamics, as stated long ago for di-trophic food chains by Rosenzweig in his famous paper on the paradox of enrichment

Belyakov homoclinic bifurcations in a tritrophic food chain model

Complex dynamics of the most frequently used tritrophic food chain model are investigated in this paper. First it is shown that the model admits a sequence of pairs of Belyakov bifurcations (codimension-two homoclinic orbits to a critical node). Then fold and period-doubling cycle bifurcation curves associated to each pair of Belyakov points are computed and analyzed. The overall bifurcation scenario explains why stable limit cycles and strange attractors with dierent geometries can coexist. The analysis is conducted by combining numerical continuation techniques with theoretical arguments

A Model for QCD at High Density and Large Quark Mass

We study the high density region of QCD within an effective model obtained in the frame of the hopping parameter expansion and choosing Polyakov type of loops as the main dynamical variables representing the fermionic matter. To get a first idea of the phase structure, the model is analyzed in strong coupling expansion and using a mean field approximation. In numerical simulations, the model still shows the so-called sign problem, a difficulty peculiar to non-zero chemical potential, but it permits the development of algorithms which ensure a good overlap of the Monte Carlo ensemble with the true one. We review the main features of the model and present calculations concerning the dependence of various observables on the chemical potential and on the temperature, in particular of the charge density and the diquark susceptibility, which may be used to characterize the various phases expected at high baryonic density. We obtain in this way information about the phase structure of the model and the corresponding phase transitions and cross over regions, which can be considered as hints for the behaviour of non-zero density QCD.Comment: 21 pages, 29 figure

Phase diagram of the lattice Wess-Zumino model from rigorous lower bounds on the energy

We study the lattice N=1 Wess-Zumino model in two dimensions and we construct a sequence $\rho^{(L)}$ of exact lower bounds on its ground state energy density $\rho$, converging to $\rho$ in the limit $L\to\infty$. The bounds $\rho^{(L)}$ can be computed numerically on a finite lattice with $L$ sites and can be exploited to discuss dynamical symmetry breaking. The transition point is determined and compared with recent results based on large-scale Green Function Monte Carlo simulations with good agreement.Comment: 32 pages, 12 figure

Singular Homoclinic Bifurcations in Tri-trophic Food Chains

The Rosenzweig-MacArthur food chain model is proved to have homoclinic orbits. The proof is in two steps. First we use a geometric approach based on singular perturbation and detect singular homoclinic orbits as well as parameter combinations for which these orbits exist. Then we show, numerically, that for slightly different parameter values there exist also non singular homoclinic orbits which tend toward the singular ones when the time responses of the three trophic levels are extremely diversified. The analysis is performed systematically, without exploiting too deeply the mathematical structure of the Rosenzweig-MacArthur model. This is done intentionally, in order to facilitate readers interested more in the methodology than in the application to food chains

Role of PET gamma detection in radioguided surgery: a systematic review

Purpose This systematic review aimed to collect published studies concerning intraoperative gamma detection of positronemitting tracers for radioguided surgery (RGS) applications. Methods A systematic literature search of studies published until October 2022 was performed in Pubmed, Web Of Science, Central (Cochrane Library) and Scopus databases, including the following keywords: “Positron Emission Tomography” OR “PET” AND “Gamma” OR “γ” AND “Probe” AND “Radioguided Surgery” OR “RGS”. The included studies had to concern RGS procedures performed in at least 3 patients, regardless of the administered radiopharmaceutical and the field of application. Results Among to the 17 selected studies, all published between 2000 and 2022, only 2 investigations were conducted with gallium-68 (68Ga)-labeled somatostatin analogues, with fluorine-18-fluoro-2-deoxyglucose ([ 18F]FDG) being the most commonly used agent for RGS applications. Almost all studies were performed in oncologic patients, with only one paper also including inflammatory and infectious findings. The analysis showed that the largest part of procedures was performed through the intraoperative use of conventional gamma probes, not specifically designed for the detection of annihilation photons (n = 9), followed by PET gamma probes (n = 5) and with only three studies involving electronic collimation. Conclusions Regardless of the intraoperative devices, RGS with positron emitters seems to lead to significant improvements in surgeons’ ability to obtain a complete resection of tumors, even if the nature of photons resulting from positron–electron collision still remains extremely challenging and requires further technical advances

Study of Bio-Pharmaceutical and Antimicrobial Properties of Pomegranate (Punica granatum L.) Leathery Exocarp Extract

Pomegranate (Punica granatum L.) fruits are important sources of vitamins and minerals and widely used in the dietary supplement industry. An aqueous extract of its leathery exocarp (LEP) was obtained by a solid-phase micro-extraction method. The antifungal activity was examined against the phytopathogenic fungi, Fusarium oxysporum, Phytophthora cinnamomi, Penicillium digitatum and Botrytis cinerea, and the antibacterial activity was evaluated against Escherichia coli, Xanthomonas campestris, Bacillus megaterium and Clavibacter michiganensis. The antimicrobial assays showed, in some cases, a promising antimicrobial effect compared to the synthetic drugs. The possible antiacetylcholinesterase and antioxidant activities of the LEP extract were investigated by the Ellman’s assay and 2,2-diphenyl-1-picrylhydrazyl (DPPH) test, respectively, and their results showed that the LEP extract has an effective anti-acetylcholinesterase inhibitory effect and an antioxidant activity. Thus, the LEP extract could be valid as a candidate for further studies on the use of pomegranate in neurodegenerative diseases as a food preservative and a suitable substitute to control several phytopathogens

Apparent Diffusion Coefficient Assessment of Brain Development in Normal Fetuses and Ventriculomegaly

Diffusion neuro-MRI has benefited significantly from sophisticated pre-processing procedures aimed at improving image quality and diagnostic. In this work, diffusion-weighted imaging (DWI) was used with artifact correction and the apparent diffusion coefficient (ADC) was quantified to investigate fetal brain development. The DWI protocol was designed in order to limit the acquisition time and to estimate ADC without perfusion bias. The ADC in normal fetal brains was compared to cases with isolated ventriculomegaly (VM), a common fetal disease whose DWI studies are still scarce. DWI was performed in 58 singleton fetuses (Gestational age (GA) range: 19–38w) at 1.5T. In 31 cases, VM was diagnosed on ultrasound. DW-Spin Echo EPI with b-values = 50, 200, 700 s/mm2 along three orthogonal axes was used. All images were corrected for noise, Gibbs-ringing, and motion artifacts. The signal-to-noise ratio (SNR) was calculated and the ADC was measured with a linear least-squared algorithm. A multi-way ANOVA was used to evaluate differences in ADC between normal and VM cases and between second and third trimester in different brain regions. Correlation between ADC and GA was assessed with linear and quadratic regression analysis. Noise and artifact correction considerably increased SNR and the goodness-of-fit. ADC measurements were significantly different between second and third trimester in centrum semiovale, frontal white matter, thalamus, cerebellum and pons of both normal and VM brains (p ≤ 0.03). ADC values were significantly different between normal and VM in centrum semiovale and frontal white matter (p ≤ 0.02). ADC values in centrum semiovale, thalamus, cerebellum and pons linearly decreased with GA both in normal and VM brains, while a quadratic relation with GA was found in basal ganglia and occipital white matter of normal brains and in frontal white matter of VM (p ≤ 0.02). ADC values in all fetal brain regions were lower than those reported in literature where DWI with b = 0 was performed. Conversely, they were in agreement with the results of other authors who measured perfusion and diffusion contributions separately. By optimizing our DWI protocol we achieved an unbiased quantification of brain ADC in reasonable scan time. Our findings suggested that ADC can be a useful biomarker of brain abnormalities associated with VM