998 resultados para Fuel trade
Resumo:
First principles calculations with molecular dynamics are
utilized to simulate a simplified electrical double layer formed in the
active electric potential region during the electrocatalytic oxidation of
ethanol on Pd electrodes running in an alkaline electrolyte. Our
simulations provide an atomic level insight into how ethanol oxidation
occurs in fuel cells: New mechanisms in the presence of the simplified
electrical double layer are found to be different from the traditional
ones; through concerted-like dehydrogenation paths, both acetaldehyde
and acetate are produced in such a way as to avoid a variety of
intermediates, which is consistent with the experimental data obtained
from in situ FTIR spectroscopy. Our work shows that adsorbed OH on
the Pd electrode rather than Pd atoms is the active center for the
reactions; the dissociation of the C−H bond is facilitated by the
adsorption of an OH− anion on the surface, resulting in the formation
of water. Our calculations demonstrate that water dissociation rather than H desorption is the main channel through which
electrical current is generated on the Pd electrode. The effects of the inner Helmholtz layer and the outer Helmholtz layer are
decoupled, with only the inner Helmholtz layer being found to have a significant impact on the mechanistics of the reaction. Our
results provide atomic level insight into the significance of the simplified electrical double layer in electrocatalysis, which may be
of general importance.
Resumo:
The most active binary PtSn catalyst for direct ethanol fuel cell applications has been studied at 20 oC and 60 oC, using variable temperature electrochemical in-situ FTIR. In comparison with Pt, binary PtSn inhibits ethanol dissociation to CO(a), but promotes partial oxidation to acetaldehyde and acetic acid. Increasing the temperature from 20 oC to 60 oC facilitates both ethanol dissociation to CO(a) and their further oxidation to CO2, leading to an increased selectivity towards CO2; however, acetaldehyde and acetic acid are still the main products. Potential-dependent phase diagrams for surface oxidants of OH(a) formation on Pt(111), Pt(211) and Sn modified Pt(111) and Pt(211) surfaces have been determined using density functional theory (DFT) calculations. It is shown that Sn promotes the formation of OH(a) with a lower onset potential on the Pt(111) surface, whereas an increase in the onset potential is found on modification of the (211) surface. In addition, Sn inhibits the Pt(211) step edge with respect to ethanol C-C bond breaking compared with that found on the pure Pt, which reduces the formation of CO(a). Sn was also found to facilitate ethanol dehydrogenation and partial oxidation to acetaldehyde and acetic acid which, combined with the more facile OH(a) formation on the Pt(111) surface, gives us a clear understanding of the experimentally determined results. This combined electrochemical in-situ FTIR and DFT study, provides, for the first time, an insight into the long-term puzzling features of the high activity but low CO2 production found on binary PtSn ethanol fuel cell catalysts.
Resumo:
The EU is considered to be one of the main proponents of what has been called the deep trade agenda—that is, the push for further trade liberalization with an emphasis on the removal of domestic non-tariff regulatory measures affecting trade, as opposed to the traditional focus on the removal of trade barriers at borders. As negotiations on the Doha Development Round have stalled, the EU has attempted to achieve these aims by entering into comprehensive free trade agreements (FTAs) that are not only limited exclusively to tariffs but also extend to non-tariff barriers, including services, intellectual property rights (IPRs), competition, and investment. These FTAs place great emphasis on regulatory convergence as a means to secure greater market openings. The paper examines the EU's current external trade policy in the area of IP, particularly its attempts to promote its own regulatory model for the protection of IP rights through trade agreements. By looking at the IP enforcement provisions of such agreements, the article also examines how the divisive issues that are currently hindering the progress of negotiations at WTO level, including the demands from developing countries to maintain a degree of autonomy in the area of IP regulation as well as the need to balance IP protection with human rights protection, are being dealt with in recent EU FTAs.
Resumo:
How are resources split between caring for offspring and self-maintenance? Is the timing of immune challenge important? In burying beetles challenging the immune system prior to breeding does not affect the total number and quality of offspring produced during the individual's lifetime. However, the immune system is suppressed during breeding and if an immune challenge is presented during this time the beetle will upregulate its immune system, but at the detriment to the number of offspring produced during that breeding opportunity.We know that parental investment and immune investment are costly processes, but it is unclear which trait will be prioritized when both may be required. Here, we address this question using the burying beetle Nicrophorus vespilloides, carrion breeders that exhibit biparental care of young. Our results show that immunosuppression occurs during provision of parental care. We measured phenoloxidase (PO) on Days 1-8 of the breeding bout and results show a clear decrease in PO immediately from presentation of the breeding resource onward. Having established baseline immune investment during breeding we then manipulated immune investment at different times by applying a wounding challenge. Beetles were wounded prior to and during the parental care period and reproductive investment quantified. Different effects on reproductive output occur depending on the timing of wounding. Challenging the immune system with wounding prior to breeding does not affect reproductive output and subsequent lifetime reproductive success (LRS). LRS is also unaffected by applying an immune elicitor prior to breeding, though different arms of the immune system are up/downregulated, perhaps indicating a trade-off between cellular and humoral immunity. In contrast, wounding during breeding reduces reproductive output and to the greatest extent if the challenge is applied early in the breeding bout. Despite being immunosuppressed, breeding beetles can still respond to wounding by increasing PO, albeit not to prebreeding levels. This upregulation of PO during breeding may affect parental investment, resulting in a reduction in reproductive output. The potential role of juvenile hormone in controlling this trade-off is discussed.
Resumo:
In this paper, we present a unique cross-layer design framework that allows systematic exploration of the energy-delay-quality trade-offs at the algorithm, architecture and circuit level of design abstraction for each block of a system. In addition, taking into consideration the interactions between different sub-blocks of a system, it identifies the design solutions that can ensure the least energy at the "right amount of quality" for each sub-block/system under user quality/delay constraints. This is achieved by deriving sensitivity based design criteria, the balancing of which form the quantitative relations that can be used early in the system design process to evaluate the energy efficiency of various design options. The proposed framework when applied to the exploration of energy-quality design space of the main blocks of a digital camera and a wireless receiver, achieves 58% and 33% energy savings under 41% and 20% error increase, respectively. © 2010 ACM.
Resumo:
Polar codes are one of the most recent advancements in coding theory and they have attracted significant interest. While they are provably capacity achieving over various channels, they have seen limited practical applications. Unfortunately, the successive nature of successive cancellation based decoders hinders fine-grained adaptation of the decoding complexity to design constraints and operating conditions. In this paper, we propose a systematic method for enabling complexity-performance trade-offs by constructing polar codes based on an optimization problem which minimizes the complexity under a suitably defined mutual information based performance constraint. Moreover, a low-complexity greedy algorithm is proposed in order to solve the optimization problem efficiently for very large code lengths.
Resumo:
Power dissipation and tolerance to process variations pose conflicting design requirements. Scaling of voltage is associated with larger variations, while Vdd upscaling or transistor up-sizing for process tolerance can be detrimental for power dissipation. However, for certain signal processing systems such as those used in color image processing, we noted that effective trade-offs can be achieved between Vdd scaling, process tolerance and "output quality". In this paper we demonstrate how these tradeoffs can be effectively utilized in the development of novel low-power variation tolerant architectures for color interpolation. The proposed architecture supports a graceful degradation in the PSNR (Peak Signal to Noise Ratio) under aggressive voltage scaling as well as extreme process variations in. sub-70nm technologies. This is achieved by exploiting the fact that some computations are more important and contribute more to the PSNR improvement compared to the others. The computations are mapped to the hardware in such a way that only the less important computations are affected by Vdd-scaling and process variations. Simulation results show that even at a scaled voltage of 60% of nominal Vdd value, our design provides reasonable image PSNR with 69% power savings.
Alkali Activated Fuel Ash and Slag Mixes:Optimization Study from Mortars to Concrete Building Blocks
Resumo:
Alkali activated binders, based on ash and slag, also known as geopolymers, can play a key role in reducing the carbon footprint of the construction sector by replacing ordinary Portland cement in some concretes. Since 1970s, research effort has been ongoing in many research institutions. In this study, pulverized fuel ash (PFA) from a UK power plant, ground granulated blast furnace slag (GGBS) and combinations of the two have been investigated as geopolymer binders for concrete applications. Activators used were sodium hydroxide and sodium silicate solutions. Mortars with sand/binder ratio of 2.75 with several PFA and GGBS combinations have been mixed and tested. The optimization of alkali dosage (defined as the Na2O/binder mass ratio) and modulus (defined as the Na2O/SiO2 mass ratio) resulted in strengths in excess of 70 MPa for tested mortars. Setting time and workability have been considered for the identification of the best combination of PFA/GGBS and alkali activator dosage for different precast concrete products. Geopolymer concrete building blocks have been replicated in laboratory and a real scale factory trial has been successfully carried out. Ongoing microstructural characterization is aiming to identify reaction products arising from PFA/GGBS combinations.
Resumo:
Developed countries, led by the EU and the US, have consistently called for ‘deeper integration’ over the course of the past three decades i.e., the convergence of ‘behind-the-border’ or domestic polices and rules such as services, competition, public procurement, intellectual property (“IP”) and so forth. Following the collapse of the Doha Development Round, the EU and the US have pursued this push for deeper integration by entering into deep and comprehensive free trade agreements (“DCFTAs”) that are comprehensive insofar as they are not limited to tariffs but extend to regulatory trade barriers. More recently, the EU and the US launched negotiations on a Transatlantic Trade and Investment Partnership (“TTIP”) and a Trade in Services Agreement (“TISA”), which put tackling barriers resulting from divergences in domestic regulation in the area of services at the very top of the agenda. Should these agreements come to pass, they may well set the template for the rules of international trade and define the core features of domestic services market regulation. This article examines the regulatory disciplines in the area of services included in existing EU and US DCFTAs from a comparative perspective in order to delineate possible similarities and divergences and assess the extent to which these DCFTAs can shed some light into the possible outcome and limitations of future trade negotiations in services. It also discusses the potential impact of such negotiations on developing countries and, more generally, on the multilateral process.
Resumo:
Globally vehicle operators are experiencing rising fuel costs and increased
running expenses as governments around the world attempt to decrease carbon dioxide emissions and fossil fuel consumption, due to global warming and the drive to reduce dependency on fossil fuels. Recent advances in hybrid vehicle design have made great strides towards more efficient operation, with regenerative braking being widely used to capture otherwise lost energy. In this paper a hybrid series bus is developed a step further, by installing another method of energy capture on the vehicle. In this case, it is in the form of the Organic Rankine Cycle (ORC). The waste heat expelled to the exhaust and coolant streams is recovered and converted to electrical energy which is then stored in the hybrid vehicles batteries. The electrical energy can then be used for the auxiliary power circuit or to assist in vehicle propulsion, thus reducing the load on the engine, thereby improving the overall fuel economy of the vehicle and reducing carbon dioxide emissions.