• Energy Research
• Closed Access close
• US close
• AU close
• FR close
• ID close

AbstractA new approach for the replacement of heart valves consists of obtaining an acellular matrix from animal aortic valves that performs mechanically, is nonantigenic, and is free from calcification and fibroblast proliferation. Novel biochemical treatments must be developed for this purpose. In this work, we focus on the characterization of collagen in acellular bovine cardiovascular tissues, fresh or glutaraldehyde treated, and stored in different solutions [phosphate‐buffered saline (PBS), ethanol, octanol, and glutaraldehyde], to determine whether the resulting fibrous material is structurally preserved. The preservation of the triple helical structure of collagen is checked by differential scanning calorimetry (DSC), which is a well suited technique to analyze thermal transitions in proteins, such as denaturation. To get insight into the molecular dynamics of collagen in the nanometric range, we used thermally stimulated currents, a dielectric technique running at low frequency, that measure the dipolar reorientations in proteins submitted to a static electrical field. The combined use of these two techniques allowed us to evaluate the physical structure and conformation of collagen after the different chemical treatments. We have found that the glutaraldehyde treatment followed by octanol storage preserves the triple helical conformation of the polypeptidic chains of collagen, contrary to the ethanol and PBS storage that induce drastic changes in the thermal and dielectric behavior of the protein. Moreover, this particular chemical treatment stabilizes the collagen structure (shift toward high temperature of the collagen denaturation and stiffening of the chains by a cross‐linking action) when compared to the control sample, and so could provide interesting fibrous material for the conception of bioprosthetic heart valve. © 2002 Wiley Periodicals, Inc., J Biomed Mater Res 64A: 330–338, 2003

Abstract An ATP-activated transhydrogenase which catalyzes the reduction of TPN + by DPNH has been demonstrated in the microsomal fraction from the endosperm of immature Echinocystis macrocarpa seeds. The activity is specifically dependent on the presence of ATP ( K m of approximately 0.1 m m ) of several nucleotides tested. The reaction is stimulated by MgCl 2 addition up to concentrations of 6 m m . When 10 −2 m EDTA is added to the assay mixture in the absence of added MgCl 2 , a transhydrogenation reaction is observed which no longer shows any dependence on added ATP. A TPN + -dependent ATPase activity can be demonstrated in these preparations, but no fixed stoichiometry between ATP cleavage and TPNH formation could be established. A lag in attaining the maximal rate of transhydrogenation is seen unless the enzyme is preincubated for 10 min with ATP before initiating the reaction. It can further be shown that preincubation of the enzyme with ATP followed by removal of the ATP on a Dowex 1 column produces an enzyme capable of catalyzing the transhydrogenation without the further addition of ATP. 2,4-Dinitrophenol and thyroxin are effective inhibitors of the transhydrogenase and 2,4-dinitrophenol was shown to inhibit the activating effect of ATP during the preincubation period. It is concluded that the role of ATP is in the modification of the enzyme rather than direct participation in the transhydrogenation. The transhydrogenase is inhibited by ADP and AMP. This results in a response of the enzyme to adenylate energy charge in a manner characteristic for regulatory enzymes which participate in ATP-utilizing metabolic sequences.

This paper presents an experimental study of indoor thermal environment near a full-scale glass facade with different types of shading devices under varying climatic conditions in winter. Interior glazing and shading temperature, operative temperature and radiant temperature asymmetry were measured for facade sections with roller shades and venetian blinds at different positions. Interior glass surface temperatures can be high during sunny days with low outdoor temperature. Shading systems significantly improved operative temperature and radiant temperature asymmetry during cold sunny days, depending on their properties and tilt angle. During cloudy days the impact was smaller, however the shading layers could still decrease the amount of heat loss through the facade. A transient building thermal model, which also calculates indoor environmental indices under the presence of solar radiation, was developed and compared with the experimental measurements. Part II of this paper uses this validated model with a transient, two-node thermal comfort model (including transmitted solar radiation) for assessment of indoor environmental conditions with different building envelope and shading properties, facade location and orientation.

Bioenergy is considered a sustainable substitute to fossil-fuel resources and the development of a prudent combination of renewable and innovative conversion technologies are essential for the valorization and effective conversion of biowaste to value-added commodities. Here, a negative pressure-induced carbonization process was proposed for the valorization of lignin-enriched biowaste precursor to bio-oil and environmental materials (biochar) at various temperatures. The high heating values (HHV) of the as-prepared biochars from the lignin enriched precursor under negative pressure (low-medium vacuum) were within 25.9-31.5 MJ/kg, which matched satisfactorily to the commercial charcoal. Whereas, the bio-oils produced from the lignin enriched precursor under vacuum conditions was a blend of complex aromatic and straight-chain hydro-carbons, including aldehyde, ketone, phenol, and furans, exhibiting ability as potential heating-oil with HHV within 21.2-28.2 MJ/kg. Moreover, the biochars produced under vacuum environments at higher temperature showed greater stability (22.5-35.9%) than those produced under N2 atmosphere.

Abstract As a consequence of deregulation, competition and problems in securing capital outlays for expansion of the infrastructure, modern power systems are operating at ever-smaller capacity and stability margins. Traditional entities involved in securing adequate protection and control for the system may soon become inadequate, and the emergence of the new participants (non-utility generation, transmission and distribution companies) requires coordinated approach and careful coordination of the new operating conditions. The paper reviews the key issues and design considerations for the present and new generation of SPS and emergency control schemes, and evaluates the strategies for their implementation.

Abstract The Liquefied natural gas (LNG) cryogenic submerged pump, the core power equipment for the transportation of liquefied natural gas, is prone to cavitation. However, based on the traditional analysis of the pressure drop, the irreversible loss after cavitation can barely be displayed quantitatively. To solve this problem, an entropy production diagnostic model (EPDM) by the contribution of viscous entropy production (VEP), turbulent entropy production (TEP) and wall entropy production (WEP) for the cavitation flow was established to calculate the energy loss. The cryogenic cavitation model and proposed EPDM were proved to be reliable after comparing results with Hord’s experiment in an ogive and cavitation experiment in a centrifugal pump. Then, by studying the total entropy production, it was found that the EPDM could well predict the occurrence of the critical cavitation and the deterioration of cavitation. When compared with TEP and WEP, the effect of VEP is negligible. As the cavitation area expands from the suction surface of inducer (id) to the first-stage impeller (impA), the cavitation process can be divided into three stages and the total energy loss increases significantly from the first stage to the third one. Through the global distribution of energy loss, it was found that the faster growth of the loss in the second-stage impeller (impB) and the second-stage guide vane (gvB), not in id and impA, contributes more to the energy loss after cavitation. Finally, from the variation of ratio of TEP to WEP, it reveals that cavitation has a greater effect on the WEP rate for the impB, but the turbulent viscous dissipation is still dominant, while the eddy dissipation and resistance loss in gvB with the evolution of cavitation are both crucial.

Main advantage of electric vehicles (EV) compared to vehicles using fossil fuels is that does not produce air pollution. One day the existence of conventional vehicles will be replaced by EV. EV gets electricity supply from batteries. When using EV, one day the electrical energy in the batteries will run out. To recharge batteries, important components such as the Electrical Vehicle Charger (EVC) are needed. EVC provides the impact of voltage drop on the electric power system bus during the charging process. This voltage drop caused by the power supply from generators cannot meet the needs of loads, including chargers and batteries. To maintain the voltage so it remains at its safe operating voltage, the same bus with EVC is interconnected with renewable energy sources. Renewable energy sources used in this study are four types of wind turbine power plants. Safe range of operating voltage in this research from 95% to 105%. This paper analyzes the change in voltage in the electric power system when the wind power plant fills EVC. The research methods section uses several scenarios. The aim is to determine the effect of each type of wind power plant on the bus voltage and EVC. Simulation results show that scenario 3 has the best results than the other scenarios. In scenario 3, voltage in bus 12 is 98,08%, voltage in bus 13 is 98,66%, and voltage in bus 14 is 98,42%. All three buses in safe limits of the operating voltage.

A procedure for optimizing the sizes of soil heat accumulators is presented together with technical and economic solutions the use of which allows the construction cost of such facilities to be minimized. Calculation examples are given.

Abstract This paper formulates a model that assesses the economic and policy implications of the adoption and operation of microgrids. The recent climate agreement between the US and China as well as the historic Lima accord on climate change are prompting a massive demand in climate-friendly technologies. Given the increasing demand for electricity and the mounting costs of electricity supply associated with maximizing system performance through an optimal economic scheduling of microgrids, decision makers and policymakers are already facing the problem of sketching energy management strategies for localized operation and grid penetration. We employ a modified Benders' decomposition approach to explore the optimal scheduling of supply from different technology units in the microgrid in the face of supply and demand uncertainties. We guarantee that the power generated by the units meets systemic load while satisfying the primary operational and technological constraints. We implement our model in a quantitative numerical analysis where we investigate the operational regulation in the light of a public environmental policy. We extend prior research on this subject by uncovering a greater reliance on the grid under simultaneous uncertainties in demand and supply. We unlock a strategy for a proper mitigation of the effects of emissions. We find that carbon abatement policy can be used to motivate microgrids operators to invest in fuel cells and natural gas technologies when dealing with uncertainty.

Abstract Background Parabolic Trough Solar Collector (PTSC) is one of the most popular and an effective device that converts solar radiation into a heat or useful energy. However, it suffers from high temperature gradient and low thermal efficiency. The solution for this problem is to use new advanced coolants (hybrid nanofluids) in order to enhance PTSC's thermal efficiency. Methods A numerical analysis on the thermo-hydraulic performance of a PTSC receiver's tube equipped with conical turbulators is presented. The Navier-Stokes equations are solved using Finite Volume Method (FVM) coupled with Monte Carlo Ray Tracing (MCRT) method. The flow and thermal characteristics as well as entropy generation of the PTSC's receiver tube are investigated for three hybrid nanofluids (Ag-SWCNT, Ag-MWCNT, and Ag-MgO) having a mixing ratio of (50:50) dispersed in Syltherm oil 800, Reynolds number (5000 to 100,000) and fluid inlet temperatures (400 to 650 K). Significant findings The conical turbulators effectively augmented the thermal performance by 233.4% utilising Ag-SWCNT/Syltherm oil instead of pure Syltherm oil. The performance evaluation criterion is found to be in the range of 0.9–1.82. The thermal and exergetic efficiencies increased by 11.5% and 18.2%, respectively. The maximum decrement in the entropy generation rate and entropy generation ratio are 42.7% and 33.7%.