Influence of the First Preparation Steps on the Properties of GaN Layers Grown on 6H-SIC by Mbe

AbstractThe Gan heteroepitaxy on 6H-SiC is affected by the bad morphology of the substrate surface. We performed a hydrogen etching at 1550°C on the 6H-SiC(0001) substrates to obtain atomically flat terraces. An improvement of the structural properties of GaN grown by MBE on such substrates after deposition of a LT-AIN buffer layer is observed. A value of less than 220 arcsec of the FWHM of the XRD rocking curve, showing a reduced screw dislocations density, is comparable with the best results reported until now for thick GaN samples. Photoluminescence showed a structured near band edge emission spectrum with evidence of the A, B and C free exciton recombinations

OCCUPATIONAL INJURIES AMONG EMERGENCY MEDICAL SERVICES PERSONNEL, SEUS 118 PROVINCE OF LECCE. OBSERVATION PERIOD FROM 2005 TO 2010 AND EVALUATION OF ORGANIZATIONAL AND ECONOMIC EFFECTS

Background: the risk of injury to Emergency Medical Services personnel (SEUS) is still being explored. Objectives: to describe the epidemiology of occupational injuries among SEUS personnel, calculate injury rates, characterize the types of occupational exposure to risks and injuries reported by SEUS workers and evaluate organizational and economic effects. Methods: this is a retrospective study of all injury records of SEUS workers in the Province of Lecce (Italy) from January 1, 2005 to December 31, 2010. There is also an evaluation of economic and organizational effects that injuries had on 118 SEUS personnel of Lecce in 2010. Results: during the period observed, 92 files were reported. Nurses were the most involved workers (46%, p = 0.019). The main cause of occupational injury was mechanical (91%, p = 0.0001), and biological (6%), and three cases were related to heated discussions. The first cause of injury was car accidents (25%). "Sprains” and “strains” were the most frequent types of injuries (37%) among Emergency medical personnel. The 92 cases resulted in 1,851 workdays lost. Nursing personnel is the category that weighs heavily on the global cost. The phenomenon of occupational injuries has made the already critical situation worse. Conclusions: the phenomenon of occupational injuries among SEUS workers is related to the peculiar environment and to specific causes such as car accidents when operating in external locations, that turn out to be hostile and the psychological impact due to intervention conditions. Investigation on this subject may help the management of health organizations to identify more detailed prevention strategies. Economic effects of the phenomenon are very important. Organizational difficulties cannot be exclusively charged to the phenomenon of occupational injuries, but the phenomenon has worsened the situation which has been critical for several years. The gravity of this phenomenon is not helping the organizational structure which is on the brink of collapse and certainly will need great determination to return to a normal situation. References • Sterud T, Ekeberg Ø, Hem E. Health status in the ambulance services: a systematic review. BMC Health Serv Res. 2006; 6:82. • Heick R, Young T, Peek-Asa C. Occupational injuries among emergency medical ervice providers in the United States. Journal of Occupational and Environmental medicine/ American College of Occup Environ Med. 2009; 51(8): 963-968

Shaping epigenetic memory via genomic bookmarking

Reconciling the stability of epigenetic patterns with the rapid turnover of histone modifications and their adaptability to external stimuli is an outstanding challenge. Here, we propose a new biophysical mechanism that can establish and maintain robust yet plastic epigenetic domains via genomic bookmarking (GBM). We model chromatin as a recolourable polymer whose segments bear non-permanent histone marks (or colours) which can be modified by 'writer' proteins. The three-dimensional chromatin organisation is mediated by protein bridges, or 'readers', such as Polycomb Repressive Complexes and Transcription Factors. The coupling between readers and writers drives spreading of biochemical marks and sustains the memory of local chromatin states across replication and mitosis. In contrast, GBM-targeted perturbations destabilise the epigenetic patterns. Strikingly, we demonstrate that GBM alone can explain the full distribution of Polycomb marks in a whole Drosophila chromosome. We finally suggest that our model provides a starting point for an understanding of the biophysics of cellular differentiation and reprogramming

Fluidodynamic evaluation of arteriovenous fistulae for hemodialysis

Arteriovenous fistulae (AVF) are commonly used in dialysis treatment of uremic patients. However, many AVF create problems and have to be re-examined. Problems arise in the cannulation site and must be treated with antibiotics, and stenosis, both in the arterial and in the venous side of the AVF. In the worst case, the AVF must be replaced for treatment to continue. However, this can only be repeated once before the AVF site is no longer viable. This increases the discomfort, the morbidity and the mortality of the dialysis patient. Several kinds of AVF were studied to determine whether flow disturbances give rise to these complications. Many studies have already demonstrated the importance of hemodynamic factors in vascular disease pathogenesis. These factors include: the pulsatility of flow, the elasticity of the vessel, the non-Newtonian blood, flow behavior and, very importantly for AVF, the vessel geometry. In model studies, intimal changes have been observed in bends and bifurcations, regions of vessel construction and vessel stenosis. In these regions, blood flow changes abruptly and this contributes to arterial disease. We prepared several one-to-one, true-to-scale elastic silicon rubber models of different AVF. The AVF models were based on angiographic studies of chronic dialysis patients and on AVF from the arms of cadavers. The models had a similar compliance to that of the human blood vessel. Flow was visualized using photoelasticity apparatus and a birefringent blood-like fluid. This method is suitable to analyze the spatial configuration of flow profiles, to differentiate laminar flow from disturbed flow, and to visualize flow separation, vortex formation and secondary flow. It was found that AVF create disturbances that are not found under normal physiological flow conditions. The X-formed AVF was very unsatisfactory, creating significant flow disturbances. The AVF had high velocity fluctuations. These could lead, for example, to aneurysm formation. A better configuration would be an end-to-end AVF. However, this formation creates other complications. For example, there is not enough blood to the hand and parts of the hand lose feeling. The recommended AVF would be an end-to-side anastomosis. In this case, attention is needed for placement geometry, to minimize additional flow disturbances. Several models as well as patient angiographic studies are discussed