Dynamics of a structured slug population model in the absence of seasonal variation

We develop a novel, nonlinear structured population model for the slug Deroceras reticulatum, a highly significant agricultural pest of great economic impact, in both organic and non-organic settings. In the absence of seasonal variations, we numerically explore the effect of life history traits that are dependent on an individual's size and measures of population biomass. We conduct a systematic exploration of parameter space and highlight the main mechanisms and implications of model design. A major conclusion of this work is that strong size dependent predation significantly adjusts the competitive balance, leading to non-monotonic steady state solutions and slowly decaying transients consisting of distinct generational cycles. Furthermore, we demonstrate how a simple ratio of adult to juvenile biomass can act as a useful diagnostic to distinguish between predated and non-predated environments, and may be useful in agricultural settings

Influence Of Quantum Well Barrier Height On The Amplitude-phase Coupling And The Spectral Linewidth In Quantum Well Lasers

Recently, it has been found both theoretically and experimentally that the differential gain in quantum well lasers is significantly affected by the unavoidable thermal population of injected carriers in the upper subbands of the quantum well structure, especially in the states of the separate confinement heterostructure region (state filling effect). The differential gain depends on the rate of increase of the quasi Fermi energies with increasing injected carrier density. The presence of upper subbands with large density of states tends to clamp the Fermi energies thus leading to a low differential gain. The state filling effect also significantly affects the amplitude-phase coupling and the spectral linewidth in quantum well lasers as a direct consequence of its influence on the differential gain

Primary versus delayed repair for bile duct injuries sustained during cholecystectomy: results of a survey of the Association Francaise de Chirurgie

BACKGROUND: Bile duct injuries (BDIs) sustained during a cholecystectomy still remain a major surgical problem, and it is still not clear whether the injury should be repaired immediately or a delayed repair is preferred. METHODS: A retrospective national French survey was conducted to compare the results of immediate (at time of cholecystectomy), early (within 45 days after a cholecystectomy) and late (beyond 45 days after a cholecystectomy) surgical repair for BDI sustained during a cholecystectomy. RESULTS: Forty-seven surgical centres provided 640 cases of bile duct injury sustained during a cholecystectomy of which 543 were analysed for the purpose of the present study. The timing of repair was immediate in 194 cases (35.7%), early in 216 cases (39.8%) and late in 133 cases (24.5%). The type of repair was a suture repair in 157 cases (81%), and a bilio-digestive reconstruction in 37 cases (19%) for immediate repair; a suture repair in 119 cases (55.1%) and a bilio-digestive anastomosis in 96 cases (44.9%) for the early repair; and a bilio-digestive reconstruction in 129 cases (97%) and a suture repair in 4 cases (3%) for late repair. A second procedure was required in 110 cases (56.7%) for immediate repair, 80 cases (40.7%) for early repair (P < 0.05) and in 9 cases (6.8%) for late repair (P < 0.001). CONCLUSION: The timing of surgical repair for a bile duct injury sustained during a cholecystectomy influences significantly the rate of a second procedure and a late repair should be preferred option

B-type natriuretic peptide as a biochemical marker of left ventricular diastolic function: Assessment in asymptomatic patients 1 year after valve replacement for aortic stenosis.

Objectives: Left ventricular (LV) diastolic dysfunction after aortic valve replacement (AVR) carries a substantial risk of development of heart failure and reduced survival. In addition to echocardiography, B-type natriuretic peptide (BNP) provides a powerful incremental assessment of diastolic function. This study evaluates BNP as a marker of LV diastolic dysfunction in a cohort of patients with preserved LV ejection fraction who underwent AVR for pure aortic stenosis and the relationship between BNP values and the grade of LV diastolic dysfunction. Methods A total of 113 patients were included in the study. Echocardiographic evaluation was performed preoperatively, 5 days postoperatively and at 12-month follow-up, to assess LV dimensional and functional parameters. Diastolic function was labelled as normal, mild, moderate or severe dysfunction. Concomitantly, BNP levels were evaluated. Results Mild to severe diastolic dysfunction occurred preoperatively in all patients. At 12-month follow-up, 65 (62.5%) patients had mild and 25 (24.1%) moderate to severe diastolic dysfunction. BNP values, categorized for quartile distribution, correlated with diastolic dysfunction grade (P < 0.001 for each comparison). At receiver operating characteristic analysis, the BNP level of 120 pg/ml was 91% sensitive and 85% specific for diastolic disease, while 300 pg/ml was 80% sensitive and 91% specific for moderate or severe diastolic dysfunction. Twelve months after AVR, BNP values were strongly correlated with the significant echocardiographic parameters suggestive of diastolic dysfunction (P ≤ 0.006 in all cases). Conclusions The BNP level following AVR is related to diastolic disease severity and may complement echocardiographic evaluation when symptoms are unclear and LV function is difficult to interpret

Kinetic theory of age-structured stochastic birth-death processes

Classical age-structured mass-action models such as the McKendrick-von Foerster equation have been extensively studied but are unable to describe stochastic fluctuations or population-size-dependent birth and death rates. Stochastic theories that treat semi-Markov age-dependent processes using, e.g., the Bellman-Harris equation do not resolve a population's age structure and are unable to quantify population-size dependencies. Conversely, current theories that include size-dependent population dynamics (e.g., mathematical models that include carrying capacity such as the logistic equation) cannot be easily extended to take into account age-dependent birth and death rates. In this paper, we present a systematic derivation of a new, fully stochastic kinetic theory for interacting age-structured populations. By defining multiparticle probability density functions, we derive a hierarchy of kinetic equations for the stochastic evolution of an aging population undergoing birth and death. We show that the fully stochastic age-dependent birth-death process precludes factorization of the corresponding probability densities, which then must be solved by using a Bogoliubov-–Born–-Green–-Kirkwood-–Yvon-like hierarchy. Explicit solutions are derived in three limits: no birth, no death, and steady state. These are then compared with their corresponding mean-field results. Our results generalize both deterministic models and existing master equation approaches by providing an intuitive and efficient way to simultaneously model age- and population-dependent stochastic dynamics applicable to the study of demography, stem cell dynamics, and disease evolution

Treatment of a rapidly expanding thoracoabdominal aortic aneurysm after endovascular repair of descending thoracic aortic aneurysm in an old patient.

Background: Aortic pathology progression and/or procedure related complications following endovascular repair should always be considered mostly in older patients. We herein describe a hybrid procedure for treatment of rapidly expanding thoracoabdominal aneurysm following endovascular treatment of a descending thoracic aortic aneurysm in an older patient. Case presentation: A 82-year-old man at 18 months after endovascular surgery for a contained rupture of descending thoracic aortic aneurysm revealed a type IV thoracoabdominal aneurysm with significant increase of the aortic diameters at superior mesenteric and renal artery levels. A hybrid approach consisting of preventive visceral vessel revascularization and endovascular repair of entire abdominal aorta was performed. Under general anaesthesia and by xyphopubic laparotomy, the infrarenal aneurysmatic aorta and common iliac arteries were replaced by a bifurcated woven prosthetic graf. From each of the prosthetic branches two reverse 14x7 mm bifurcated PTFE prosthetic grafts were anastomized to both renal arteries and to the celiac axis and superior mesenteric artery, respectively. Vessel ischemia was restricted to the time required for anastomosis. Three 10 cm Gore endovascular stent-grafts for a total length of 15 cm, were used. The overlapping of the stent-grafts was carried out from the bottom upwards, starting from the aorto-iliac prosthetic body up to the healthy segment of thoracic aorta, 40 mm from the previous stent-grafts. The patient was discharged on the 9th postoperative day. Conclusion: This technique offers the advantage of a less invasive treatment, reducing the risk of paraplegia, visceral ischaemia and pulmonary complications, mostly in older patients

Experimental evidence of stochastic resonance without tuning due to non Gaussian noises

In order to test theoretical predictions, we have studied the phenomenon of stochastic resonance in an electronic experimental system driven by white non Gaussian noise. In agreement with the theoretical predictions our main findings are: an enhancement of the sensibility of the system together with a remarkable widening of the response (robustness). This implies that even a single resonant unit can reach a marked reduction in the need of noise tuning.Comment: 4 pages, 3 figure

Treatment challenges in and outside a network setting: Head and neck cancers

Head and neck cancer (HNC) is a rare disease that can affect different sites and is characterized by variable incidence and 5-year survival rates across Europe. Multiple factors need to be considered when choosing the most appropriate treatment for HNC patients, such as age, comorbidities, social issues, and especially whether to prefer surgery or radiation-based protocols. Given the complexity of this scenario, the creation of a highly specialized multidisciplinary team is recommended to guarantee the best oncological outcome and prevent or adequately treat any adverse effect. Data from literature suggest that the multidisciplinary team-based approach is beneficial for HNC patients and lead to improved survival rates. This result is likely due to improved diagnostic and staging accuracy, a more efficacious therapeutic approach and enhanced communication across disciplines. Despite the benefit of MTD, it must be noted that this approach requires considerable time, effort and financial resources and is usually more frequent in highly organized and high-volume centers. Literature data on clinical research suggest that patients treated in high-accrual centers report better treatment outcomes compared to patients treated in low-volume centers, where a lower radiotherapy-compliance and worst overall survival have been reported. There is general agreement that treatment of rare cancers such as HNC should be concentrated in high volume, specialized and multidisciplinary centers. In order to achieve this goal, the creation of international collaboration network is fundamental. The European Reference Networks for example aim to create an international virtual advisory board, whose objectives are the exchange of expertise, training, clinical collaboration and the reduction of disparities and enhancement of rationalize migration across Europe. The purpose of our work is to review all aspects and challenges in and outside this network setting planned for the management of HNC patients

Comparison of AFITPAC versus NOS and a Packet Radio Network Design

This thesis encompasses two themes: (1) A comparison of the Network Operating System (NOS) software package, developed by Phil Karn and others, and AFITPAC, written by Marsh and Geier at the Air Force Institute of Technology. The comparison is based on the Air Force Logistics Command\u27s requirements for the development of a Packet Radio Network program. The results of the comparison are a recommendation that use of the NOS package be pursued because it can meet all twelve of the requirements and compiles with five of the Military Standard Protocols. (2) The design of a personal computer Packet Radio Network Simulator used to analyze the network performance of AFITPAC and NOS is proposed. The proposal concludes with a discussion of problems in development of the simulation which used MODSIM IITM, C++, and a 80386/25Mhz personal computer. Recommendations are made for pursuing the simulation effort on other hardware platforms and for improvements to the design

Steady states in a structured epidemic model with Wentzell boundary condition

We introduce a nonlinear structured population model with diffusion in the state space. Individuals are structured with respect to a continuous variable which represents a pathogen load. The class of uninfected individuals constitutes a special compartment that carries mass, hence the model is equipped with generalized Wentzell (or dynamic) boundary conditions. Our model is intended to describe the spread of infection of a vertically transmitted disease, for example Wolbachia in a mosquito population. Therefore the (infinite dimensional) nonlinearity arises in the recruitment term. First we establish global existence of solutions and the Principle of Linearised Stability for our model. Then, in our main result, we formulate simple conditions, which guarantee the existence of non-trivial steady states of the model. Our method utilizes an operator theoretic framework combined with a fixed point approach. Finally, in the last section we establish a sufficient condition for the local asymptotic stability of the positive steady state