Semigroup analysis of structured populations with distributed states-at-birth arising in mathematical aquaculture

Motivated by the modelling of structured parasite populations in aquaculture we consider a class of physiologically structured population models, where individuals may be recruited into the population at different sizes in general. That is, we consider a size-structured population model with distributed states-at-birth. The mathematical model which describes the evolution of such a population is a first order nonlinear partial integro-differential equation of hyperbolic type. First, we use positive perturbation arguments and utilise results from the spectral theory of semigroups to establish conditions for the existence of a positive equilibrium solution of our model. Then we formulate conditions that guarantee that the linearised system is governed by a positive quasicontraction semigroup on the biologically relevant state space. We also show that the governing linear semigroup is eventually compact, hence growth properties of the semigroup are determined by the spectrum of its generator. In case of a separable fertility function we deduce a characteristic equation and investigate the stability of equilibrium solutions in the general case using positive perturbation arguments.

Optimal latent period in a bacteriophage population model structured by infection-age

We study the lysis timing of a bacteriophage population by means of a continuously infection-age-structured population dynamics model. The features of the model are the infection process of bacteria, the natural death process, and the lysis process which means the replication of bacteriophage viruses inside bacteria and the destruction of them. We consider that the length of the lysis timing (or latent period) is distributed according to a general probability distribution function. We have carried out an optimization procedure and we have found the latent period corresponding to the maximal fitness (i.e. maximal growth rate) of the bacteriophage population.

Stochastic demography and the neutral substitution rate in class-structured populations.

The neutral rate of allelic substitution is analyzed for a class-structured population subject to a stationary stochastic demographic process. The substitution rate is shown to be generally equal to the effective mutation rate, and under overlapping generations it can be expressed as the effective mutation rate in newborns when measured in units of average generation time. With uniform mutation rate across classes the substitution rate reduces to the mutation rate.

Magnetic resonance coronary lumen and vessel wall imaging.

Coronary magnetic resonance angiography (MRA) is a technique aimed at establishing a noninvasive test for the assessment of significant coronary stenoses. There are certain boundary conditions that have hampered the clinical success of coronary MRA and coronary vessel wall imaging. Recent advances in hardware and software allow for consistent visualization of the proximal and mid portions of the native coronary arteries. Current research focuses on the use of intravascular MR contrast agents and black blood coronary angiography. One common goal is to create a noninvasive test which might allow for screening for major proximal and mid coronary artery disease. These novel approaches will represent a major step forward in diagnostic cardiology.

Oscillations in a molecular structured cell population model

We consider a nonlinear cyclin content structured model of a cell population divided into proliferative and quiescent cells. We show, for particular values of the parameters, existence of solutions that do not depend on the cyclin content. We make numerical simulations for the general case obtaining, for some values of the parameters convergence to the steady state but also oscillations of the population for others.

Gastroschisis - what should be told to parents?

Gastroschisis is a common congenital abdominal wall defect. It is almost always diagnosed prenatally thanks to routine maternal serum screening and ultrasound screening programs. In the majority of cases, the condition is isolated (i.e. not associated with chromosomal or other anatomical anomalies). Prenatal diagnosis allows for planning the timing, mode and location of delivery. Controversies persist concerning the optimal antenatal monitoring strategy. Compelling evidence supports elective delivery at 37 weeks' gestation in a tertiary pediatric center. Cesarean section should be reserved for routine obstetrical indications. Prognosis of infants with gastroschisis is primarily determined by the degree of bowel injury, which is difficult to assess antenatally. Prenatal counseling usually addresses gastroschisis issues. However, parental concerns are mainly focused on long-term postnatal outcomes including gastrointestinal function and neurodevelopment. Although infants born with gastroschisis often endure a difficult neonatal course, they experience few long-term complications. This manuscript, which is structured around common parental questions and concerns, reviews the evidence pertaining to the antenatal, neonatal and long-term implications of a fetal gastroschisis diagnosis and is aimed at helping healthcare professionals counsel expecting parents. © 2013 John Wiley & Sons, Ltd.

Unexpected left ventricular free-wall rupture following an aortic catheter-valve implantation.

Our experience with the Sapien trans-apical aortic valve (Edwards Lifesciences Inc., Irvine, CA, USA) has been straightforward without per-procedural mortality except in 1/16 consecutive cases who developed non-apical haemorrhage early after valve implantation. We describe the case of an 84-year-old female carrying a very high operative risk (logistic EuroScore of 44%), who underwent a trans-apical stent-valve implantation for severe and symptomatic aortic valve stenosis (23 mm). Due to massive blood loss, an emergency sternotomy and cannulation for cardiopulmonary bypass resuscitation were necessary to treat (without success) an unusual and unexpected subaortic left ventricular free-wall rupture that occurred few minutes after the stent-valve positioning and implantation. To the best of our knowledge, this is the first described case of a left ventricular free-wall rupture occurring after an otherwise non-complicated standard catheter-based aortic valve replacement.

Coronary MR imaging: lumen and wall.

Coronary MR imaging is a promising noninvasive technique for the combined assessment of coronary artery anatomy and function. Anomalous coronary arteries and aneurysms can reliably be assessed in clinical practice using coronary MR imaging and the presence of significant left main or proximal multivessel coronary artery disease detected. Technical challenges that need to be addressed are further improvements in motion suppression and abbreviated scanning times aimed at improving spatial resolution and patient comfort. The development of new and specific contrast agents, high-field MR imaging with improved spatial resolution, and continued progress in MR imaging methods development will undoubtedly lead to further progress toward the noninvasive and comprehensive assessment of coronary atherosclerotic disease.

Gadolinium Enhanced MR Coronary Vessel Wall Imaging at 3.0 Tesla.

Purpose. We evaluated the influence of the time between low-dose gadolinium (Gd) contrast administration and coronary vessel wall enhancement (LGE) detected by 3T magnetic resonance imaging (MRI) in healthy subjects and patients with coronary artery disease (CAD). Materials and Methods. Four healthy subjects (4 men, mean age 29 ± 3 years and eleven CAD patients (6 women, mean age 61 ± 10 years) were studied on a commercial 3.0 Tesla (T) whole-body MR imaging system (Achieva 3.0 T; Philips, Best, The Netherlands). T1-weighted inversion-recovery coronary magnetic resonance imaging (MRI) was repeated up to 75 minutes after administration of low-dose Gadolinium (Gd) (0.1 mmol/kg Gd-DTPA). Results. LGE was seen in none of the healthy subjects, however in all of the CAD patients. In CAD patients, fifty-six of 62 (90.3%) segments showed LGE of the coronary artery vessel wall at time-interval 1 after contrast. At time-interval 2, 34 of 42 (81.0%) and at time-interval 3, 29 of 39 evaluable segments (74.4%) were enhanced. Conclusion. In this work, we demonstrate LGE of the coronary artery vessel wall using 3.0 T MRI after a single, low-dose Gd contrast injection in CAD patients but not in healthy subjects. In the majority of the evaluated coronary segments in CAD patients, LGE of the coronary vessel wall was already detectable 30-45 minutes after administration of the contrast agent.

Conclusions on the measurement of arterial wall thickness: anatomic, physiologic and methodologic considerations

AIM: To discuss the use of new ultrasonic techniques that make it possible to visualize elastic (carotid) and muscular (radial) capacitance arteries non-invasively. RESULTS OF DATA REVIEW: Measurements of carotid wall thickness and the detection of atheromas are related to arterial pressure, to other risk factors and to the risk of subsequent complications. The use of high-frequency ultrasound (7.5-10 MHz), measurements of far wall thicknesses in areas free of atheromas at end-diastole (by ECG gating or pressure waveform recording) and descriptions of the size and characteristics of atherosclerotic plaques allow a non-invasive assessment of vascular hypertrophy and atherosclerosis in hypertensive patients. CONCLUSIONS: Careful attention to methodologic and physiologic factors is needed to provide accurate information about the anatomy of the dynamically pulsating arterial tree.

Structured output SVM for remote sensing image classification

In the recent years, kernel methods have revealed very powerful tools in many application domains in general and in remote sensing image classification in particular. The special characteristics of remote sensing images (high dimension, few labeled samples and different noise sources) are efficiently dealt with kernel machines. In this paper, we propose the use of structured output learning to improve remote sensing image classification based on kernels. Structured output learning is concerned with the design of machine learning algorithms that not only implement input-output mapping, but also take into account the relations between output labels, thus generalizing unstructured kernel methods. We analyze the framework and introduce it to the remote sensing community. Output similarity is here encoded into SVM classifiers by modifying the model loss function and the kernel function either independently or jointly. Experiments on a very high resolution (VHR) image classification problem shows promising results and opens a wide field of research with structured output kernel methods.

An approximate mathematical model for solidification of a flowing liquid in a microchannel

A mathematical model is developed to analyse the combined flow and solidification of a liquid in a small pipe or two-dimensional channel. In either case the problem reduces to solving a single equation for the position of the solidification front. Results show that for a large range of flow rates the closure time is approximately constant, and the value depends primarily on the wall temperature and channel width. However, the ice shape at closure will be very different for low and high fluxes. As the flow rate increases the closure time starts to depend on the flow rate until the closure time increases dramatically, subsequently the pipe will never close.

Effect of testosterone on immunocompetence, parasite load, and metabolism in the common wall lizard (Podarcis muralis)

Testosterone can benefit individual fitness by increasing ornament colour, aggressiveness, and sperm quality, but it can also impose both metabolic and immunological costs. However, evidence that testosterone causes immuno suppression in freely living populations is scant. We studied the effects of testosterone on one component of the immune system (i.e., the cell-mediated response to phytohaemagglutinin), parasite load, and metabolic rate in the common wall lizard, Podarcis muralis (Laurenti, 1768). For analyses of immunocompetence and parasitism, male lizards were implanted at the end of the breeding season with either empty or testosterone implants and were returned to their site of capture for 5-6 weeks before recapture. For analyses of the effects of testosterone on metabolic rate, male lizards were captured and implanted before hibernation and were held in the laboratory for 1 week prior to calorimetry. Experimental treatment with testosterone decreased the cell-mediated response to the T-cell mitogen phytohemagglutinin and increased mean metabolic rate. No effects of testosterone on the number of ectoparasites, hemoparasites, and resting metabolic rate could be detected. These results are discussed in the framework of the immunocompetence handicap hypothesis and the immuno-redistribution process hypothesis. [Authors]