Shear deformation of amorphous and nanocrystalline copper microstructures via atomistic simulation

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.Includes bibliographical references (p. 24).In the well-known Hall-Petch behavior, yield and flow stresses in polycrystalline metals increase with a decrease in grain size. As grain size continues to decrease, mechanical strength peaks. As grain size further decreases, mechanical strength begins to decrease. As grain size approaches zero, the total structure is composed of an increasingly high percentage of grain boundaries, which exhibit the properties of an amorphous structure. Molecular dynamics simulations, with the goal of exploring this behavior, were performed on nanocrystalline and amorphous microstructures using the embedded atom potential developed by Mishin et al. A 0.2 shear strain was applied to each of the nanocrystalline and amorphous samples. From these simulations, we have observed the inverse Hall-Petch behavior of nanocrystalline structures. We have also shown that the amorphous structure as zero grain size is reasonable as the limiting case for the inverse Hall-Petch trends in nanocrystalline structures.by David R. Gandy.S.B

Emigdiano Blues: The California Indigenous Pigment Palette and an In Situ Analysis of an Exotic Colour

The Native inhabitants of South Central California produced rock art containing red, orange, black, white, green and blue colours using a range of mineral and organic materials. Many of these same colours were used on material culture and body painting. This paper focuses on a sub-group of the Chumash, called the Emigdiano, who produced an enigmatic blue colour used in the creation of rock art. Here, we focus on the blue pigment at the rock shelter site of Three Springs in the Wind Wolves Preserve in South Central California. The composition of blue pigments has previously been the focus of discussion with suggestions that they were produced either using European pigments taken from Spanish missions, or that azurite from a local quarry was the source. Previous experimental work had demonstrated that it was possible for the blue to be produced from locally available azurite. Here we present the in situ analyses of these enigmatic blue pigments using handheld X-ray Fluorescence (pXRF). Results from pXRF analysis of rock art, quarried azurite samples and experimental rock art reconstructions showed that the Emigdiano Blue at Three Springs were not azurite based and was composed of optical blue (a mixture of black and white or grey materials which mimic the appearance of blue). This paper discusses the surprising implications of the use, given the availability of a ‘true’ blue pigment, and the wider ontological importance of combining multiple colours to produce the effect of blue in a rock art panel

Including Aortic Valve Morphology in Computational Fluid Dynamics Simulations: Initial Findings and Application to Aortic Coarctation

Computational fluid dynamics (CFD) simulations quantifying thoracic aortic flow patterns have not included disturbances from the aortic valve (AoV). 80% of patients with aortic coarctation (CoA) have a bicuspid aortic valve (BAV) which may cause adverse flow patterns contributing to morbidity. Our objectives were to develop a method to account for the AoV in CFD simulations, and quantify its impact on local hemodynamics. The method developed facilitates segmentation of the AoV, spatiotemporal interpolation of segments, and anatomic positioning of segments at the CFD model inlet. The AoV was included in CFD model examples of a normal (tricuspid AoV) and a post-surgical CoA patient (BAV). Velocity, turbulent kinetic energy (TKE), time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) results were compared to equivalent simulations using a plug inlet profile. The plug inlet greatly underestimated TKE for both examples. TAWSS differences extended throughout the thoracic aorta for the CoA BAV, but were limited to the arch for the normal example. OSI differences existed mainly in the ascending aorta for both cases. The impact of AoV can now be included with CFD simulations to identify regions of deleterious hemodynamics thereby advancing simulations of the thoracic aorta one step closer to reality

Corporate Governance in Financial Institutions

On 29th - 30th March 2007, SUERF and the Central Bank of Cyprus jointly organized a Seminar: Corporate Governance in Financial Institutions. The papers in the present publication are based on a sample of the presentations at the Seminar. Together, the papers illuminate a number of key issues in corporate governance in a variety of financial firms. In the first paper based on a keynote address, Spyros G. Stavrinakis, Central Bank of Cyprus gives an overview of the legal framework for corporate governance in financial institutions in Cyprus. According to a Central BankDirective issued in 2006, implementation of corporate governance principles is mandatory for all banks incorporated in Cyprus and their overseas branches and for some Cyprus branches of foreign banks domiciled outside the European Economic Area. Banks are obliged to have a robust internal governance framework, consistent lines of reporting and effective risk identification, management, monitoring and reporting procedures for all the risks to which credit institutions are actually or potentially exposed. The board of directors should take the lead in establishing and approving ethical standards and corporate values for itself and for the bank's senior executive management. Potential conflicts of interest should be identified, prevented or appropriately managed. Each bank should maintain a compliance function that monitors compliance with rules, regulations and policies. Clear lines of responsibility and accountability should be set and enforced. New members of the board of directors as well as the senior executive managers of banks have to be vetted and approved by the Central Bank of Cyprus for their " fitness and properness." In order to ensure transparency concerning the implementation of the principles, each bank's corporate governance framework should be disclosed in the bank's annual report and on its public website. In the second paper by Christian Harm, University of Muenster, "The Governance of the Banking Firm" the author builds on the literatures on corporate governance and financial regulation. In relation to governance of financial institutions, agency theory has both merits and shortcomings. It provides good explanations in many delegation situations but it has severe difficulties in dealing with institutions with several stakeholders and complex objective functions for the management. Firms guided by shareholder value may work more effectively than firms guided by stakeholder cacophony. Depositors are important stakeholders in banks. Since they are typically incapable of managing the supervision of their claims on the bank, they rely on regulators to do it for them. Remuneration systems for bank managers should provide proper incentives. According to the author, incentives should be structured such as to reward particular strategic achievements. Banks can apply executive stock option plans, but should confine options to a secondary place behind other long-term incentives based on success criteria that further shareholder interests without compromising the regulatory mission. Such an incentive framework tends, however, to be very complex so that the general ambiguities associated with the concept of governance could imply that in the banking firm, selecting managers with a proper intrinsic motivation may be superior to defining complex remuneration programs. In the third paper "Corporate Governance Issues in Non-Shareholder Value Financial Institutions: ACase Study of Mutual Building Societies in the UK", David T. Llewellyn, Loughborough University, focuses on corporate governance in non-incorporated financial firms. The author describes the relevant stakeholders and the nature of agency problems in different types of financial firms. He compares monitoring mechanisms, incentives, abilities and feasibilities of managers and members of mutuals. Mutuality raises specific corporate governance issues: Corporate governance is less clearly defined because the firm's objectives are less clearly defined. Conflicts of interest between managers and owners are less easily identified and it is more difficult to create management incentives. The almost exclusive source of capital is retained profits and each member has a non-exclusive and non-marketable claim to residual net worth. Voting rights are typically not proportional to the size of the ownership stake. There is no market in ownership claims and therefore no effective market in corporate control. Consequently, there is ample scope for mutuals to be inefficient. There is, however, no evidence that the efficiency and performance of mutuals are poorer that that of incorporated financial firms. In the fourth paper "Corporate Governance in Emerging Market Banks", Bridget Gandy, Fitch Ratings Ltd., and her co-authors from the rating agency look at the framework for corporate governance of banks in a sample of emerging market countries. Since the crisis in the late 1990s in Latin America and Asia, there has been a marked improvement in corporate governance of financial institutions in the regions under observation. Many countries have taken legal steps to develop functioning market economies with a view to the need to satisfy the demands of international capital markets. Several banks have listed their shares on stock exchanges in developed markets and foreign bank ownership and involvement in local banking systems have increased. In Central and Eastern Europe, countries' desire for EU-accession has impacted on the development of their corporate governance systems. At the individual bank level, Fitch Ratings looks at bank board independence and quality, oversight and the importance of related party transactions, the integrity of the audit process, acceptability of executive and director remuneration, ownership structures and transparency. In evaluating the quality of governance at the country level, the authors apply a three-pillar approach in line with Montesquieu: Powers and responsibilities need to be separated between a representative legislature, a competent and accountable executive branch and a fair and independent judiciary. The paper contains an interesting table in which a number of key regulatory initiatives in a sample of emerging market countries are compared. The authors point out that large scale privatizations have reduced the importance of state-owned banks in many countries. There are, however, still several examples with complex holding structures involving banks with potential negative implications for corporate governance quality and problems with related party transactions. Acquisitions by foreign banks with developed corporate governance standards have generally had a positive impact and also listing of bank shares on foreign stock exchanges with tough disclosure and transparency requirements have contributed positively to the quality of corporate governance in emerging market banks. Read together, the four papers give a good overview of the development of corporate governance practices and remaining problems in financial institutions of different types and with domicile in different countries

Investigating the biological properties of carbohydrate derived fulvic acid (CHD-FA) as a potential novel therapy for the management of oral biofilm infections.

Background: A number of oral diseases, including periodontitis, derive from microbial biofilms and are associated with increased antimicrobial resistance. Despite the widespread use of mouthwashes being used as adjunctive measures to control these biofilms, their prolonged use is not recommended due to various side effects. Therefore, alternative broad-spectrum antimicrobials that minimise these effects are highly sought after. Carbohydrate derived fulvic acid (CHD-FA) is an organic acid which has previously demonstrated to be microbiocidal against Candida albicans biofilms, therefore, the aims of this study were to evaluate the antibacterial activity of CHD-FA against orally derived biofilms and to investigate adjunctive biological effects.<p></p> Methods: Minimum inhibitory concentrations were evaluated for CHD-FA and chlorhexidine (CHX) against a range of oral bacteria using standardised microdilution testing for planktonic and sessile. Scanning electron microscopy was also employed to visualise changes in oral biofilms after antimicrobial treatment. Cytotoxicity of these compounds was assessed against oral epithelial cells, and the effect of CHD-FA on host inflammatory markers was assessed by measuring mRNA and protein expression.<p></p> Results: CHD-FA was highly active against all of the oral bacteria tested, including Porphyromonas gingivalis, with a sessile minimum inhibitory concentration of 0.5%. This concentration was shown to kill multi-species biofilms by approximately 90%, levels comparable to that of chlorhexidine (CHX). In a mammalian cell culture model, pretreatment of epithelial cells with buffered CHD-FA was shown to significantly down-regulate key inflammatory mediators, including interleukin-8 (IL-8), after stimulation with a multi-species biofilm.<p></p> Conclusions: Overall, CHD-FA was shown to possess broad-spectrum antibacterial activity, with a supplementary function of being able to down-regulate inflammation. These properties offer an attractive spectrum of function from a naturally derived compound, which could be used as an alternative topical treatment strategy for oral biofilm diseases. Further studies in vitro and in vivo are required to determine the precise mechanism by which CHD-FA modulates the host immune response.<p></p&gt

A Bayesian approach to star-galaxy classification

Star-galaxy classification is one of the most fundamental data-processing tasks in survey astronomy, and a critical starting point for the scientific exploitation of survey data. For bright sources this classification can be done with almost complete reliability, but for the numerous sources close to a survey's detection limit each image encodes only limited morphological information. In this regime, from which many of the new scientific discoveries are likely to come, it is vital to utilise all the available information about a source, both from multiple measurements and also prior knowledge about the star and galaxy populations. It is also more useful and realistic to provide classification probabilities than decisive classifications. All these desiderata can be met by adopting a Bayesian approach to star-galaxy classification, and we develop a very general formalism for doing so. An immediate implication of applying Bayes's theorem to this problem is that it is formally impossible to combine morphological measurements in different bands without using colour information as well; however we develop several approximations that disregard colour information as much as possible. The resultant scheme is applied to data from the UKIRT Infrared Deep Sky Survey (UKIDSS), and tested by comparing the results to deep Sloan Digital Sky Survey (SDSS) Stripe 82 measurements of the same sources. The Bayesian classification probabilities obtained from the UKIDSS data agree well with the deep SDSS classifications both overall (a mismatch rate of 0.022, compared to 0.044 for the UKIDSS pipeline classifier) and close to the UKIDSS detection limit (a mismatch rate of 0.068 compared to 0.075 for the UKIDSS pipeline classifier). The Bayesian formalism developed here can be applied to improve the reliability of any star-galaxy classification schemes based on the measured values of morphology statistics alone.Comment: Accepted 22 November 2010, 19 pages, 17 figure

Acute dosing of latrepirdine (Dimebon), a possible Alzheimer therapeutic, elevates extracellular amyloid-beta levels in vitro and in vivo.

BACKGROUND: Recent reports suggest that latrepirdine (Dimebon, dimebolin), a retired Russian antihistamine, improves cognitive function in aged rodents and in patients with mild to moderate Alzheimer's disease (AD). However, the mechanism(s) underlying this benefit remain elusive. AD is characterized by extracellular accumulation of the amyloid-beta (Abeta) peptide in the brain, and Abeta-lowering drugs are currently among the most popular anti-amyloid agents under development for the treatment of AD. In the current study, we assessed the effect of acute dosing of latrepirdine on levels of extracellular Abeta using in vitro and in vivo experimental systems. RESULTS: We evaluated extracellular levels of Abeta in three experimental systems, under basal conditions and after treatment with latrepirdine. Mouse N2a neuroblastoma cells overexpressing Swedish APP were incubated for 6 hr in the presence of either vehicle or vehicle + latrepirdine (500pM-5 muM). Synaptoneurosomes were isolated from TgCRND8 mutant APP-overexpressing transgenic mice and incubated for 0 to 10 min in the absence or presence of latrepirdine (1 muM or 10 muM). Drug-naïve Tg2576 Swedish mutant APP overexpressing transgenic mice received a single intraperitoneal injection of either vehicle or vehicle + latrepirdine (3.5 mg/kg). Picomolar to nanomolar concentrations of acutely administered latrepirdine increased the extracellular concentration of Abeta in the conditioned media from Swedish mutant APP-overexpressing N2a cells by up to 64% (p = 0.01), while a clinically relevant acute dose of latrepirdine administered i.p. led to an increase in the interstitial fluid of freely moving APP transgenic mice by up to 40% (p = 0.01). Reconstitution of membrane protein trafficking and processing is frequently inefficient, and, consistent with this interpretation, latrepirdine treatment of isolated TgCRND8 synaptoneurosomes involved higher concentrations of drug (1-10 muM) and led to more modest increases in extracellular Abeta(x-42 )levels (+10%; p = 0.001); of note, however, was the observation that extracellular Abeta(x-40 )levels did not change. CONCLUSIONS: Here, we report the surprising association of acute latrepirdine dosing with elevated levels of extracellular Abeta as measured in three independent neuron-related or neuron-derived systems, including the hippocampus of freely moving Tg2576 mice. Given the reported association of chronic latrepirdine treatment with improvement in cognitive function, the effects of chronic latrepirdine treatment on extracellular Abeta levels must now be determined.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Importance subsampling for power system planning under multi-year demand and weather uncertainty

This paper introduces a generalised version of importance subsampling for time series reduction/aggregation in optimisation-based power system planning models. Recent studies indicate that reliably determining optimal electricity (investment) strategy under climate variability requires the consideration of multiple years of demand and weather data. However, solving planning models over long simulation lengths is typically computationally unfeasible, and established time series reduction approaches induce significant errors. The importance subsampling method reliably estimates long-term planning model outputs at greatly reduced computational cost, allowing the consideration of multi-decadal samples. The key innovation is a systematic identification and preservation of relevant extreme events in modeling subsamples. Simulation studies on generation and transmission expansion planning models illustrate the method’s enhanced performance over established "representative days" clustering approaches. The models, data and sample code are made available as open-source software

Importance subsampling: improving power system planning under climate-based uncertainty

Recent studies indicate that the effects of inter-annual climate-based variability in power system planning are significant and that long samples of demand & weather data (spanning multiple decades) should be considered. At the same time, modelling renewable generation such as solar and wind requires high temporal resolution to capture fluctuations in output levels. In many realistic power system models, using long samples at high temporal resolution is computationally unfeasible. This paper introduces a novel subsampling approach, referred to as importance subsampling, allowing the use of multiple decades of demand & weather data in power system planning models at reduced computational cost. The methodology can be applied in a wide class of optimisation based power system simulations. A test case is performed on a model of the United Kingdom created using the open-source modelling framework Calliope and 36 years of hourly demand and wind data. Standard data reduction approaches such as using individual years or clustering into representative days lead to significant errors in estimates of optimal system design. Furthermore, the resultant power systems lead to supply capacity shortages, raising questions of generation capacity adequacy. In contrast, importance subsampling leads to accurate estimates of optimal system design at greatly reduced computational cost, with resultant power systems able to meet demand across all 36 years of demand & weather scenarios