Stochastic Spatial Models in Ecology: A Statistical Physics Approach

Ecosystems display a complex spatial organization. Ecologists have long tried to characterize them by looking at how different measures of biodiversity change across spatial scales. Ecological neutral theory has provided simple predictions accounting for general empirical patterns in communities of competing species. However, while neutral theory in well-mixed ecosystems is mathematically well understood, spatial models still present several open problems, limiting the quantitative understanding of spatial biodiversity. In this review, we discuss the state of the art in spatial neutral theory. We emphasize the connection between spatial ecological models and the physics of non-equilibrium phase transitions and how concepts developed in statistical physics translate in population dynamics, and vice versa. We focus on non-trivial scaling laws arising at the critical dimension of spatial neutral models, and their relevance for biological populations inhabiting two-dimensional environments. We conclude by discussing models incorporating non-neutral effects in the form of spatial and temporal disorder, and analyze how their predictions deviate from those of purely neutral theories.MAM is grateful to the Spanish-MINECO for financial support (under Grant FIS2013-43201-P; FEDER funds

The use of the temporalis muscle flap in facial and craniofacial reconstructive surgery. A review of 182 cases.

The authors report on their 16-year experience of reconstruction with the temporalis myofascial flap in 182 cases. All aspects of reconstructive cranio-maxillofacial surgery are covered: trauma, deformities, tumours, TMJ ankylosis, facial paralysis. The temporalis myofascial flap was used both as a single and as a composite flap with cranial bone, coronoid process or skin island. Major complications were not observed. On the basis of their experience, the authors confirm the reliability, versatility and reproducibility of the use of this flap. This is due both to its rich blood supply and to its proximity to the reconstruction site. It is suggested that the use of the temporalis muscle flap should be taken into consideration before deciding on more extensive reconstructive procedures

Pediatric cranio-facial surgery. First-year's experience with a gun applying bioabsorbable tacks

AIM: In 2001 a prototype of a gun to apply bioabsorbable tacks in cranio-facial surgery has been developed. METHODS: From May 2001 to May 2002 this device has been used in the University Hospital of Innsbruck (Austria) for different cranioplasty procedures, in 34 children, showing its reliability for cranio-facial bone fixation. The children were affected by isolated craniosynostosis or by syndromical synostosis (Apert, Crouzon) and in a case of benign tumor of the parietal skull vault. The range of age, at the time of surgery, was between 3 months and 204 months of age. Bone segments were fixed using self-reinforced polylactide plates and tacks. RESULTS: Firm fixation was obtained intra-operatively and the operative time was reduced about 25-30 minutes as compared to use of plates and screws. This device has just one limitation in its own spring force: sometimes the bone thinner than 1 mm has been broken applying the tacks. CONCLUSION: After the first-year's experience it is possible to confirm that this device reduces, in selected cases, operative time, blood loss, risk of infection and, as a result, the costs

Guidelines for the optimization of microsurgery in atherosclerotic patients

We review the pathogenesis of atherosclerosis and the issues that must be taken into consideration when performing microsurgery in atherosclerotic patients. Atherosclerosis is a systemic disease, and may affect the success of microsurgery. Atherosclerotic patients have a tendency toward thrombosis, because the nature of the arteries is changed. Such patients are usually old and have additional medical problems. To increase the success rate of microsurgery in atherosclerotic patients, special precautions should be considered. Patients must be evaluated properly for the suitability of microsurgery. The microsurgical technique requires a meticulous approach, and various technical tricks can be used to avoid thrombosis. Recipient-vessel selection, anastomotic technique, and the use of vein grafts are all important issues. Prophylactic anticoagulation is recommended in severely atherosclerotic patients. Close monitoring of the patient and flap is necessary after the operation, as with routine microvascular free-tissue transfers. We conclude that atherosclerosis is not a contraindication for microsurgery. If the microsurgeon knows how to deal with the difficulties in atherosclerotic patients, microsurgery can be performed safely

Use of defibrotide in preventing vascular thrombosis in experimental pancreas transplantation

Venous thrombosis is one of the more frequent complications in pancreas transplantation. The efficacy of a new antithrombotic substance has been studied in an experimental model of pancreas transplantation. Sixteen miniature swines with streptozotocin induced diabetes underwent whole pancreas transplantation from a non sibling donor. Half of these animals were treated with defibrotide, a polideoxyribonucleotide obtained by controlling depolymerization of mammalian lung deoxyribonucleic acid. The others did not receive any antithrombotic treatment. Blood glucose and insulin levels were monitored. Seven days post transplant, the grafts were removed and examined for vascular thrombosis. A lower incidence of venous thrombosis was observed in the group treated with defibrotide in comparison to the control group. No differences in pancreatic function, coagulation parameters morphological aspects of the grafts were observed in the two groups. Defibrotide appears to be a useful drug to prevent vascular thrombosis in pancreas transplantation

Glucagon test in the diagnosis of rejection in pancreas transplantation in pigs

Pancreas transplantation is today a valid alternative to insulin therapy in type I diabetes. However one of the major problems related to this treatment is the difficulty in the diagnosis of rejection because of the lack of a valid functional index. In this experimental study, we have evaluated the utility of the glucagon test in monitoring rejection in pancreas transplants. Seven animals with streptozotocin induced diabetes, underwent whole pancreas transplantation in extraperitoneal location. Daily monitoring of blood glucose and blood insulin determinations before and after glucagon stimulus were performed. Blood glucose, which was normalized after transplantation, did not show significant alterations during the study. On the contrary, the glucagon test evidenced a good insulinemic response to the stimulus on the 3rd postoperative day, whereas on the 6th postoperative day the test demonstrated an altered pancreatic function. Thus the glucagon test has proved to be a more sensitive test than blood glucose determination in the functional evaluation of pancreas transplantation

A new technique for substernal colon transposition with a breast dissector: report of 39 cases

This paper investigates the effectiveness of the breast dissector to create a substernal space for oesophageal reconstruction. The surgeon must be extremely careful while dissecting the tissue below the sternum in order to avoid pneumothorax. The endoscopically assisted preparation of the substernal route is safe but it requires appropriate training. A retrospective study on 68 patients who underwent oesophageal reconstruction was done analysing the patients’ records. In 39 cases, the breast dissector was used. In 29 cases, the substernal tunnel was created with hand dissection only. All 68 colon segments were successfully transferred in the two groups of patients. In all 39 the cases where the breast dissector was used no pneumothorax followed. In 10 (34%) patients of the control group pneumothorax occurred. Concluding, no more pneumothorax has occurred during the substernal oesophageal reconstruction since we started using the breast dissector