In the past, many have considered the production and use of hydrogen, assuming that it is just another gaseous fuel and can be handled much like natural gas in today's energy economy. With this study we present an analysis of the energy required to operate an elemental hydrogen economy, with particular reference to road transport. High-grade electricity from renewable or nuclear sources is needed not only to generate hydrogen, but also for all the other essential stages. However, because of the molecular structure of hydrogen, the infrastructure is much more energy-intensive than in an oil and natural gas economy.In a "Hydrogen Economy" the hydrogen, like any other commercial product, is subject to several stages between production and use. Hydrogen has to be packaged by compression or liquefaction, transported by surface vehicles or pipelines, stored, and transferred to the end user. Whether generated by electrolysis or by chemistry, and even if produced locally at filling stations, the gaseous or liquid hydrogen has to undergo these market processes before it can be used by the customer. Hydrogen can also be derived chemically at relatively low cost from natural gas or other hydrocarbons. However, because there are no energetic or environmental advantages, we do not consider this option.In this study, the energy consumed by each stage is related to the true energy content-the higher heating value (HHV)-of the delivered hydrogen. The analysis reveals that much more energy is needed to operate a hydrogen economy than is required for fossil energy supply and distribution today. In fact, the input of electrical energy to make, package, transport, store and transfer hydrogen may easily exceed the hydrogen Downloaded by [University of Newcastle, Australia] at 16:42 27 December 2014 30 Cogeneration and Distributed Generation Journal energy delivered to the end user-implying a well-to-tank efficiency of less than 50%. However, precious energy can be saved by packaging hydrogen chemically in a synthetic liquid hydrocarbon like methanol or ethanol. To decouple energy use from global warming, the use of "geocarbons" from fossil sources should be avoided. However, carbon atoms from biomass, organic waste materials or recycled carbon dioxide could become the carriers for hydrogen atoms. Furthermore, energy intensive electrolysis may be partially replaced by the less energy intensive chemical transformation of water and carbon to natural and synthetic hydrocarbons, including bio-methanol and bio-ethanol. Hence, the closed natural hydrogen (water) cycle and the closed natural carbon (CO 2 ) cycle may be used to produce synthetic hydrocarbons for a post-fossil fuel energy economy. As long as the carbon comes from the biosphere ("bio-carbon"), the synthetic hydrocarbon economy would be far better than the elemental hydrogen economy-both energetically and thus environmentally.
No abstract
In the treatment of abdominal sacral colpopexy mesh erosion, we recommend maintaining a high index of suspicion for secondary infections.
Objectives The primary objective was to evaluate 1-year anterior wall anatomic success rates for vaginal uterosacral ligament suspension (USLS) and minimally invasive sacral colpopexy (SCP) using delayed-absorbable suture. Secondary objectives included assessment of apical success, mesh or suture exposure, and postoperative quality of life (QoL) measures 12 months after surgery. Methods This was a retrospective cohort study including women who underwent a hysterectomy with concomitant USLS or SCP with delayed-absorbable suture from January 2011 to December 2015 with 1-year follow-up. Successful anterior vaginal wall support was defined as Ba of less than 0. Successful apical support was defined as no apical descent (point C) greater than one half of the total vaginal length. In addition, 1-year QoL questionnaires were measured postoperatively. Results A total of 282 women were identified. Sixty-two women (31 vaginal USLS and 31 SCP) met inclusion criteria. Demographics were similar between groups except for a higher body mass index in the USLS group (27.5 ± 5.6 kg/m2 vs 24.1 ± 3.3 kg/m2, P < 0.05). Preoperative POP-Q was mostly stage II and III. At 1-year, anatomic success rates for the anterior compartment were 66.7% versus 90.3% for USLS and SCP groups, respectively (P = 0.02). There was no significant difference in apical success (P = 1.00) or QoL scores between groups at 1 year. Conclusions Anatomic success rates at 1 year using delayed-absorbable suture were better for SCP when using the anterior wall as a measure of success, but there were no significant differences in apical success rates, mesh or suture exposure, and QoL measures between groups.
Objective: To compare postoperative vaginal incision separation and healing in patients undergoing posterior repair with perforated porcine dermal grafts with those that received grafts without perforations. Secondarily, the tensile properties of the perforated and non-perforated grafts were measured and compared. Materials and Methods: This was a non-randomized retrospective cohort analysis of women with stage II or greater rectoceles who underwent posterior repair with perforated and non-perforated porcine dermal grafts (Pelvicol TM CR Bard Covington, GA USA). The incidence of postoperative vaginal incision separation (dehiscence) was compared. A secondary analysis to assess graft tensile strength, suture pull out strength, and flexibility after perforation was performed using standard test method TM 0133 and ASTM bending and resistance protocols. Results: Seventeen percent of patients (21/127) who received grafts without perforations developed vaginal incision dehiscence compared to 7% (5/71) of patients who received perforated grafts (p = 0.078). Four patients with vaginal incision dehiscence with non-perforated grafts required surgical revision to facilitate healing. Neither tensile strength or suture pull out strength were significantly different between perforated and non-perforated grafts (p = 0.81, p = 0.29, respectively). There was no difference in the flexibility of the two grafts (p = 0.20). Conclusion: Perforated porcine dermal grafts retain their tensile properties and are associated with fewer vaginal incision dehiscences.
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