Fracture mechanics testing for environmental stress cracking in thermoplastics

Under the combined influence of an aggressive environment and applied stress, engineering thermoplastics may undergo a phenomenon known as environmental stress cracking (ESC). This can result in adverse effects such as embrittlement and premature failure in service, due to the growth of environmentally-induced cracks to critical sizes, with little to no fluid absorption in the bulk material. Fracture mechanics is proposed as a suitable scheme to study and quantify ESC, with the aim being to obtain characterising data for different polymer-fluid combinations of interest, as well as to develop a reliable fracture mechanics test protocol. In the proposed method, slow crack growth is monitored to assess the effect of a range of applied crack driving forces (K, or alternatively G) on observed crack speeds, as opposed to simply measuring time-to-failure. This paper presents the results of experiments performed on the following materials: linear low density polyethylene (LLDPE) in Igepal solution and high impact polystyrene (HIPS) in sunflower oil. A discussion of the various issues surrounding the data analysis for these long-term tests is also included, as the attainment of consistent and repeatable results is critical for a method to be internationally standardised, which is a goal of the European Structural Integrity Society (ESIS) Technical Committee 4 from whose interest this work is drawn

An investigation of the structure beneath Magadi area in southern Kenya rift using gravimetric data

Magadi area is located in the southern part of the Kenyan rift, an activecontinental rift that is part of the East African Rift system. Local seismic activity monitored previously around Lake Magadi revealed an earthquake cluster caused by swarm activity in the rift centre at shallow depths, which was probably triggered by magma movements. There was need for a follow-up to locate any body at depth with sufficient density contrast that may represent magmatic intrusions. Gravity measurements were carried out in 58 established stations and data from 52 other stations merged from existing coverage of previous measurements. Necessary corrections were applied to the gravity data and a Bouguer contour map prepared. Euler deconvolution technique was used to image depth to the causative bodies along selected profiles on the Bouguer anomaly map. Two  dimensional gravity forward models of the subsurface structure were generated by using Euler depth solutions in the start models. Among others, a unique body of density of 3.20 gcm-3 was modelled on the northern region near little Magadi at a depth of approximately 0.4 km. The location of the body coincides with the area where earthquake swarm occurs. Such a body of high density contrasts may be caused by mafic intrusions into the crust. Discontinuities in Euler solution cluster along the profiles indicated buried faults in the volcanic rift infill. The high seismicity may hence be associated to magma intrusions.Key words: Gravity, Bouguer anomaly, Euler Deconvolution, Keny

Spectral analysis of ground magnetic data in Magadi area, Southern Kenya rift

The area surrounding Lake Magadi in the southern Kenya rift is characterized by hot springs that issue from fractures distributed along the shores of the lake. Presence of earthquake swarms that cluster in northern margin of Lake Magadi strongly indicate magmatic activity in the area. This study was done as a follow-up to investigate depth to the heat source possibly causing high seismic activity and high heat flow in the area. A ground magnetic survey was conducted to investigate geothermal potential of the area and a magnetic anomaly contour map prepared. Spectral analysis involving determining power spectrum was applied to magnetic data along selected profiles cutting through discerned anomalies. Spectral analysis results suggest that the Curie-point isotherm depth under Magadi ranges from 5.20 km to 8.30 km. Estimated vertical temperature gradients along the profiles ranges from 111.53°C/km to 69.92°C/km. The hightemperature gradients and relatively shallow Curie point depths indicates high heat flow which suggests presence of a hot magmatic intrusion

Endovenous laser ablation therapy in children: applications and outcomes

BACKGROUND: Endovenous laser ablation is well recognized as the first-line treatment for superficial venous reflux with varicose veins in adults. It is not widely reported and is not an established practice in pediatric patients. OBJECTIVE: To illustrate a variety of pediatric venous conditions in which endovenous laser ablation can be utilized and to demonstrate its feasibility and safety in children. MATERIALS AND METHODS: We conducted a retrospective review of endovenous laser ablation procedures performed between January 2007 and July 2014 at two large pediatric institutions. RESULTS: We included 35 patients (17 males) who underwent endovenous laser ablation to 43 veins. Median age at first treatment was 14 years (range: 3-18 years). Median weight was 56 kg (range: 19-97 kg). Underlying diagnoses were common venous malformation (15), Klippel-Trenaunay syndrome (8), superficial venous reflux with varicose veins (5), verrucous hemangioma-related phlebectasia (4), venous varix (2) and arteriovenous fistula (1). The most common aim of treatment was to facilitate sclerotherapy. Thirty-four patients had treatment in the lower limbs and one patient in an upper limb. Ten of the veins treated with endovenous laser ablation had an additional procedure performed to close the vein. Complications attributable to endovenous laser ablation occurred in two patients (6%). One patient experienced post-procedural pain and one patient developed a temporary sensory nerve injury. Median clinical follow-up was 13 months (range: 28 days-5.7 years). The aim of the treatment was achieved in 29 of the 35 (83%) patients. CONCLUSION: Endovenous laser ablation is technically feasible and safe in children. It can be used in the management of a range of pediatric venous diseases with good outcomes

REFRACTIVE-INDEX DEPENDENCE ON FREE-CARRIERS FOR GAAS

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REFRACTIVE-INDEX PROFILE AND RESONANT MODES IN GAAS-LASERS

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Efficacy and Harms of Direct Oral Anticoagulants in the Elderly for Stroke Prevention in Atrial Fibrillation and Secondary Prevention of Venous Thromboembolism

Background-Evidence regarding use of direct oral anticoagulants (DOACs) in the elderly, particularly bleeding risks, is unclear despite the presence of greater comorbidities, polypharmacy and altered pharmacokinetics in this age group. Methods and Results-We performed a systematic review and meta-analysis of randomised trials of DOACs (dabigatran, apixaban, rivaroxaban, edoxaban) for efficacy and bleeding outcomes compared to VKA (vitamin k antagonists) in elderly participants (aged ≥75 years) treated for acute venous thromboembolism or stroke prevention in atrial fibrillation. Nineteen studies were eligible for inclusion but only 11 reported data specifically for elderly participants. Efficacy in managing thrombotic risks for each DOAC was similar or superior to VKA in the elderly. A non-significantly, higher risk of major bleeding than VKA was observed with dabigatran 150mg (Odds Ratio 1.18, 95% confidence interval 0.97-1.44) but not with the 110mg dose. Significantly higher gastrointestinal bleeding risks with dabigatran 150mg (1.78, 1.35-2.35) and 110mg (1.40, 1.04-1.90) and lower intracranial bleeding risks than VKA for dabigatran 150mg (0.43, 0.26-0.72) and dabigatran 110mg (0.36, 0.22-0.61) were also observed. A significantly lower major bleeding risk compared to VKA was observed for apixaban (0.63, 0.51-0.77), edoxaban 60mg (0.81, 0.67-0.98) and 30mg (0.46, 0.38-0.57) while rivaroxaban showed similar risk. Conclusion-DOACs demonstrated at least equal efficacy to VKA in managing thrombotic risks in the elderly however bleeding patterns were distinct. In particular, dabigatran was associated with a higher risk of gastrointestinal bleeding than VKA. Insufficient published data for apixaban, edoxaban and rivaroxaban indicates further work is needed to clarify their bleeding risks in the elderly

Trace-gas metabolic versatility of the facultative methanotroph Methylocella silvestris

The climate-active gas methane is generated both by biological processes and by thermogenic decomposition of fossil organic material, which forms methane and short-chain alkanes, principally ethane, propane and butane1, 2. In addition to natural sources, environments are exposed to anthropogenic inputs of all these gases from oil and gas extraction and distribution. The gases provide carbon and/or energy for a diverse range of microorganisms that can metabolize them in both anoxic3 and oxic zones. Aerobic methanotrophs, which can assimilate methane, have been considered to be entirely distinct from utilizers of short-chain alkanes, and studies of environments exposed to mixtures of methane and multi-carbon alkanes have assumed that disparate groups of microorganisms are responsible for the metabolism of these gases. Here we describe the mechanism by which a single bacterial strain, Methylocella silvestris, can use methane or propane as a carbon and energy source, documenting a methanotroph that can utilize a short-chain alkane as an alternative to methane. Furthermore, during growth on a mixture of these gases, efficient consumption of both gases occurred at the same time. Two soluble di-iron centre monooxygenase (SDIMO) gene clusters were identified and were found to be differentially expressed during bacterial growth on these gases, although both were required for efficient propane utilization. This report of a methanotroph expressing an additional SDIMO that seems to be uniquely involved in short-chain alkane metabolism suggests that such metabolic flexibility may be important in many environments where methane and short-chain alkanes co-occur