1,370 research outputs found
Corrigendum to “High-pressure adsorptive storage of hydrogen in MIL-101 (Cr) and AX-21 for mobile applications: Cryocharging and cryokinetics” [Mater & Des 89 (2016) 1086–1094]
No full textRefers To Nuno Bimbo, Wesley Xu, Jessica E. Sharpe, Valeska P. Ting, Timothy J. Mays High-pressure adsorptive storage of hydrogen in MIL-101 (Cr) and AX-21 for mobile applications: Cryocharging and cryokinetics Materials & Design, Volume 89, 5 January 2016, Pages 1086-1094 The authors regret to inform that….. The Supplementary Information should have been included in the original paper and is now provided with this corrigendum. All the data and figures, contained in the manuscript and supporting information, are available and can be accessed free of charge at http://dx.doi.org/10.15125/BATH-00099. Any questions related to the data should be addressed to the corresponding author. Authors would like to apologize for the inconvenience caused
Old Friends in a New Dress
No full textSee my copy of the 1826 third edition, which added Part II. (Perhaps the first edition was in 1807.) This fifth edition makes several important changes. First, it admits at last who the author is: R.S. Sharpe. Secondly, it cuts the title back by leaving out or Select Fables of Aesop in Verse. Thirdly, it adds a third section of fourteen more stories, Additional Fables, 1837. (It seems also to have dropped one from Part II and to have rearranged the order of fables in both the first and second parts.) Fourthly, it is the first edition of this book to add cuts, eighty-two of them spread over the three parts of the book. Fifthly, Chalmers and Collins in Glasgow have dropped out of the picture as publishers. Finally, the book has grown to 264 pages. See my comments there. I continue to enjoy the artistry of these fables. Perhaps I have been reading so many original fables lately that it is a special pleasure to come back to good traditional stories. I read the new fourteen fables. They are a mix of the well known and the less well known. Their main lesson is, as so often in nineteenth-century fable books, that children obey their parents. The new vignettes are good. Some good examples are Two Goats (112), TT (121), FG (180), and WSC (248). The moral to FG advises doubting the things we cannot gain and being happy without them (180). There is a T of C at the beginning, after the commendations of an earlier edition of the book. The binding has separated completely from the interior of the book. The cover features a gilt arrangement of fable animals around the title. Curiously, the price is stamped in gilt on both the cover and the spine.This is a hardbound book (hard cover)Fifth editionBy R.S. Sharpe
Bootstrap-based bias correction for the out-of-sample Sharpe ratio
No full textLooking for making an investment, one objective could be to find a portfolio where the Sharpe ratio for in the future, known as the out-of-sample Sharpe ratio, is maximized. Since future data is not avail-able, the Sharpe ratio needs to be predicted using historical data, the in-sample data. This is often done using the Sharpe Ratio Information Criterion, which determines the bias for the in-sample Sharpe ratio to es-timate the out-of-sample Sharpe ratio. However, this approach assumes that the covariance matrix is known. In portfolio management, the covariance matrix is typically unknown and can only be estimated. This project will use the bootstrap method to estimate the out-of-sample Sharpe ratio using the estimated co-variance matrix and analogous methods used for the Akaike Information Criterion. By eliminating the assumption of a known covariance matrix, this method becomes more applicable. Simulations will also be done with a known covariance matrix, demonstrating that the bootstrap method is an effective approach for estimating the out-of-sample Sharpe ratio. We then look at some extensions for the bootstrap method and finally we will apply the bootstrap method to stocks in the Dutch and American stock markets, showing that the in-sample Sharpe ratio is often overly optimistic compared to the out-of-sample Sharpe ratio. We reached our goal that we found an effective way to estimate the out-of-sample Sharpe ratio without the assumption that the covariance matrix is known, resulting this method becomes much more suitable for predicting the Sharpe ratio in the future.1Applied Mathematic
In Memory of Dr. Roger Sharpe
Get PDFIn Memory of Dr. Roger Sharpe
Nebraska Ornithologists\u27 Union member, author and educator Roger Sharpe passed away on June 27, 2003. He is survived by his wife Beverly, three daughters and one son.
Dr. Sharpe was born on March 31, 1941. His Ph.D. was in Vertebrate Zoology from the University of Nebraska at Lincoln. He was an instructor at the University of Nebraska at Omaha from 1968 until his retirement in 2000. He was a professor of ornithology, environmental biology and conservation biology, and he began and continued to coordinate the Environmental Studies Program there.
Dr. Sharpe also originated an exchange program with Charles University in Prague, Czechoslovakia, for both faculty and students. He was part of a team of scientists assembled to help combat pollution in Czechoslovakia
In Memory of Dr. Roger Sharpe
Get PDFIn Memory of Dr. Roger Sharpe
Nebraska Ornithologists\u27 Union member, author and educator Roger Sharpe passed away on June 27, 2003. He is survived by his wife Beverly, three daughters and one son.
Dr. Sharpe was born on March 31, 1941. His Ph.D. was in Vertebrate Zoology from the University of Nebraska at Lincoln. He was an instructor at the University of Nebraska at Omaha from 1968 until his retirement in 2000. He was a professor of ornithology, environmental biology and conservation biology, and he began and continued to coordinate the Environmental Studies Program there.
Dr. Sharpe also originated an exchange program with Charles University in Prague, Czechoslovakia, for both faculty and students. He was part of a team of scientists assembled to help combat pollution in Czechoslovakia
Analysis of optimal conditions for adsorptive hydrogen storage in microporous solids
No full textThere is much current interest in the storage of hydrogen in porous materials for mobile energy applications. Despite significant hydrogen storage capacities having been observed recently for some synthesised materials, the identification of optimal operating conditions (pressure and temperature) is perhaps an even more important consideration from an engineering and applied science perspective. There will be pressure and temperature limits for effective use of an adsorptive storage system, because the adsorbent will always displace a volume in the storage container, and so at very high pressures the amount of hydrogen stored at a given temperature will be greater for a container with no adsorbent. In order for an adsorbent to be used there has to be some gain in the amount of the hydrogen stored to compensate for the cost and mass of the solid. We present a methodology by which the pressure and temperature ranges where it is advantageous to use adsorptive storage can be easily identified and the real gain of using such systems in terms of the absolute amount of hydrogen stored can be quantified. Using a well-characterised commercial activated carbon as an example system, we modelled high pressure hydrogen sorption isotherms and identified the operating conditions for which there is a significant increase in storage capacity from using an adsorbent as opposed to storage in the same volume via compression of hydrogen at the same temperature. A novel comparison of the density enhancement in the micropores with respect to the bulk hydrogen gas, as well as the influence of incorporating different amounts of adsorbent into a high pressure storage container is also presented. (C) 2012 Elsevier B.V. All rights reserved
Isosteric enthalpies for hydrogen adsorbed on nanoporous materials at high pressures
Get PDFA sound understanding of any sorption system requires an accurate determination of the enthalpy of adsorption. This is a fundamental thermodynamic quantity that can be determined from experimental sorption data and its correct calculation is extremely important for heat management in adsorptive gas storage applications. It is especially relevant for hydrogen storage, where porous adsorptive storage is regarded as a competing alternative to more mature storage methods such as liquid hydrogen and compressed gas. Among the most common methods to calculate isosteric enthalpies in the literature are the virial equation and the Clausius-Clapeyron equation. Both methods have drawbacks, for example, the arbitrary number of terms in the virial equation and the assumption of ideal gas behaviour in the Clausius-Clapeyron equation. Although some researchers have calculated isosteric enthalpies of adsorption using excess amounts adsorbed, it is arguably more relevant to applications and may also be more thermodynamically consistent to use absolute amounts adsorbed, since the Gibbs excess is a partition, not a thermodynamic phase. In this paper the isosteric enthalpies of adsorption are calculated using the virial, Clausius-Clapeyron and Clapeyron equations from hydrogen sorption data for two materials-activated carbon AX-21 and metal-organic framework MIL-101. It is shown for these two example materials that the Clausius-Clapeyron equation can only be used at low coverage, since hydrogen's behaviour deviates from ideal at high pressures. The use of the virial equation for isosteric enthalpies is shown to require care, since it is highly dependent on selecting an appropriate number of parameters. A systematic study on the use of different parameters for the virial was performed and it was shown that, for the AX-21 case, the Clausius-Clapeyron seems to give better approximations to the exact isosteric enthalpies calculated using the Clapeyron equation than the virial equation with 10 variable parameters
How to compare market efficiency? The Sharpe ratio based on the ARMA-GARCH forecast
No full textThis paper derives a new method for comparing the weak-form efficiency of markets. The author derives the formula of the Sharpe ratio from the ARMA-GARCH model and finds that the Sharpe ratio just depends on the coefficients of the AR and MA terms and is not affected by the GARCH process. For empirical purposes, the Sharpe ratio can be formulated with a monotonic increasing function of R-squared if the sample size is large enough. One can utilize the Sharpe ratio to compare weak-form efficiency among different markets. The results of stochastic simulation demonstrate the validity of the proposed method. The author also constructs empirical AR-GARCH models and computes the Sharpe ratio for S&P 500 Index and the SSE Composite Index
Modelling the potential of adsorbed hydrogen for use in aviation
Get PDFA novel method for modelling the amount of hydrogen in high-pressure tanks containing varying quantities of adsorbent has been extended to allow calculation of the energy density and the specific energy of the storage system. An example calculation, using TE7 activated carbon beads as an adsorbent, has been conducted over a range of temperatures and compared to alternative energy storage methods, including conventional high-pressure methods. The results indicate that adsorption of hydrogen yields a higher energy density than direct compression up to a certain pressure, which is dependent on the temperature. A preliminary comparison shows adsorbed hydrogen to be superior to battery storage technologies for both energy density and specific energy stored, although further calculations are required to expand the system boundaries used. Adsorbed hydrogen in a range of materials resulted in much lower energy density and specific energy than standard jet fuels such as kerosene, proving that advancement in the materials is required, especially intrinsic hydrogen storage capacity, before adsorption becomes a competitive energy storage technology for aviation. (C) 2014 Elsevier Inc. All rights reserved
High-pressure adsorptive storage in hydrogen in MIL-101 (Cr) and AX-21 for mobile applications : cryocharging and cryokinetics
Get PDFCurrent state-of-the-art methods consist of containing highpressure compressed hydrogen in composite cylinders, with solid-state hydrogen storage materials an alternative that could improve on storage performance by enhancing volumetric densities. A new strategy that uses cryogenic temperatures to load hydrogen (cryocharging) is proposed and analysed in this work, comparing densities and final storage pressures for empty cylinders and containers with the high-surface area materials MIL-101 (Cr) and AX-21. Results show cryocharging as a viable option, as it can substantially lower the charging (at 77 K) and final pressures (at 298 K) for the majority of the cases considered. Kinetics are an equally important requirement for hydrogen storage systems, so the effective diffusivities at these conditions for both materials were calculated, and showed values comparable to the ones estimated in metal-organic frameworks and zeolites from quasielastic neutron scattering and molecular simulations. High-surface area materials tailored for hydrogen storage are a promising route for storage in mobile applications and results show that cryocharging is a promising strategy for hydrogen storage systems, since it increases volumetric densities and avoids energy penalties of operating at high pressures and/or low temperatures
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