Biomechanical model of human cornea based on stromal microstructure

The optical characteristics of the human cornea depends on the mechanical balance between the intra-ocular pressure and intrinsic tissue stiffness. A wide range of ophthalmic surgical procedures alter corneal biomechanics to induce local or global curvature changes for the correction of visual acuity. Due to the large number of surgical interventions performed every day, a deeper understanding of corneal biomechanics is needed to improve the safety of these procedures and medical devices. The aim of this study is to propose a biomechanical model of the human cornea, based on stromal microstructure. The constitutive mechanical law includes collagen fiber distribution based on X-ray scattering analysis, collagen cross-linking, and fiber uncrimping. Our results showed that the proposed model reproduced inflation and extensiometry experimental data [Elsheikh et al., Curr. Eye Res., 2007; Elsheikh et al., Exp. Eye Res., 2008] successfully. The mechanical properties obtained for different age groups demonstrated an increase in collagen cross-linking for older specimens. In future work such a model could be used to simulate non-symmetric interventions, and provide better surgical planning.

Numerical model of the human cornea based on stromal microstructure: identification of mechanical properties for two age groups

The optical quality of the human eye mainly depends on the refractive performance of the cornea. The shape of the cornea is a mechanical balance between intraocular pressure and tissue intrinsic stiffness. Several surgical procedures in ophthalmology alter the biomechanics of the cornea to provoke local or global curvature changes for vision correction. Legitimated by the large number of surgical interventions performed every day, the demand for a deeper understanding of corneal biomechanics is rising to improve the safety of procedures and medical devices. The aim of our work is to propose a numerical model of corneal biomechanics, based on the stromal microstructure. Our novel anisotropic constitutive material law features a probabilistic weighting approach to model collagen fiber distribution as observed on human cornea by Xray scattering analysis (Aghamohammadzadeh et. al., Structure, February 2004). Furthermore, collagen cross-linking was explicitly included in the strain energy function. Results showed that the proposed model is able to successfully reproduce both inflation and extensiometry experimental data (Elsheikh et. al., Curr Eye Res, 2007; Elsheikh et. al., Exp Eye Res, May 2008). In addition, the mechanical properties calculated for patients of different age groups (Group A: 65-79 years; Group B: 80-95 years) demonstrate an increased collagen cross-linking, and a decrease in collagen fiber elasticity from younger to older specimen. These findings correspond to what is known about maturing fibrous biological tissue. Since the presented model can handle different loading situations and includes the anisotropic distribution of collagen fibers, it has the potential to simulate clinical procedures involving nonsymmetrical tissue interventions. In the future, such mechanical model can be used to improve surgical planning and the design of next generation ophthalmic devices.

A Surface Displacement Analysis for Volcan Pacaya from October 2001 through March 2013 by Means of 3-D Modeling of Precise Position GPS Data

Volcán Pacaya is one of three currently active volcanoes in Guatemala. Volcanic activity originates from the local tectonic subduction of the Cocos plate beneath the Caribbean plate along the Pacific Guatemalan coast. Pacaya is characterized by generally strombolian type activity with occasional larger vulcanian type eruptions approximately every ten years. One particularly large eruption occurred on May 27, 2010. Using GPS data collected for approximately 8 years before this eruption and data from an additional three years of collection afterwards, surface movement covering the period of the eruption can be measured and used as a tool to help understand activity at the volcano. Initial positions were obtained from raw data using the Automatic Precise Positioning Service provided by the NASA Jet Propulsion Laboratory. Forward modeling of observed 3-D displacements for three time periods (before, covering and after the May 2010 eruption) revealed that a plausible source for deformation is related to a vertical dike or planar surface trending NNW-SSE through the cone. For three distinct time periods the best fitting models describe deformation of the volcano: 0.45 right lateral movement and 0.55 m tensile opening along the dike mentioned above from October 2001 through January 2009 (pre-eruption); 0.55 m left lateral slip along the dike mentioned above for the period from January 2009 and January 2011 (covering the eruption); -0.025 m dip slip along the dike for the period from January 2011 through March 2013 (post-eruption). In all bestfit models the dike is oriented with a 75° westward dip. These data have respective RMS misfit values of 5.49 cm, 12.38 cm and 6.90 cm for each modeled period. During the time period that includes the eruption the volcano most likely experienced a combination of slip and inflation below the edifice which created a large scar at the surface down the northern flank of the volcano. All models that a dipping dike may be experiencing a combination of inflation and oblique slip below the edifice which augments the possibility of a westward collapse in the future.

[Lung volume reduction in severe emphysema]

BACKGROUND: Lung volume reduction (LVR) surgery is an effective and organ-preserving treatment option for patients suffering from severe dyspnea due to endstage emphysema. METHOD: Resection of functionally inactive lung parenchyma reduces over-inflation and restores the elastic recoil of the lungs. Thus it results in improvement of dyspnea, mobility and pulmonary function. Patient selection is crucial. Of simliar importance is pulmonary rehabilitation, as well as sufficient expertise in the treatment of endstage chronic respiratory failure. RESULTS AND CONCLUSION: The in-hospital morbidity and mortality after LVR are acceptable (0 to 5%) and the good results seem to last at least 18 to 24 months. LVR can be offered to selected patients either as an alternative or as bridge to lung transplantation.

Does the Federal Reserve Follow a Non-Linear Taylor Rule?

The Taylor rule has become one of the most studied strategies for monetary policy. Yet, little is known whether the Federal Reserve follows a non-linear Taylor rule. This paper employs the smooth transition regression model and asks the question: does the Federal Reserve change its policy-rule according to the level of inflation and/or the output gap? I find that the Federal Reserve does follow a non-linear Taylor rule and, more importantly, that the Federal Reserve followed a non-linear Taylor rule during the golden era of monetary policy, 1985-2005, and a linear Taylor rule throughout the dark age of monetary policy, 1960-1979. Thus, good monetary policy is associated with a non-linear Taylor rule: once inflation approaches a certain threshold, the Federal Reserve adjusts its policy-rule and begins to respond more forcefully to inflation.

HEALTH CARE COST INCREASES IN METROPOLITAN AREAS

The research project is an extension of the economic theory to the health care field and health care research projects evaluating the influence of demand and supply variables upon medical care inflation. The research tests a model linking the demographic and socioeconomic characteristics of the population, its community case mix, and technology, the prices of goods and services other than medical care, the way its medical services are delivered and the health care resources available to its population to different utilization patterns which, consequently, lead to variations in health care prices among metropolitan areas. The research considers the relationship of changes in community characteristics and resources and medical care inflation.^ The rapidly increasing costs of medical care have been of great concern to the general public, medical profession, and political bodies. Research and analysis of the main factors responsible for the rate of increase of medical care prices is necessary in order to devise appropriate solutions to cope with the problem. An understanding of the community characteristics and resources-medical care costs relationships in the metropolitan areas potentially offers guidance in individual plan and national policy development.^ The research considers 145 factors measuring community milieu (demographic, social, educational, economic, illness level, prices of goods and services other than medical care, hospital supply, physicians resources and techological factors). Through bivariate correlation analysis, the number of variables was reduced to a set of 1 to 4 variables for each cost equation. Two approaches were identified to track inflation in the health care industry. One approach measures costs of production which accounts for price and volume increases. The other approach measures price increases. One general and four specific measures were developed to represent each of the major approaches. The general measure considers the increase on medical care prices as a whole and the specific measures deal with hospital costs and physician's fees. The relationships among changes in community characteristics and resources and health care inflation were analyzed using bivariate correlation and regression analysis methods. It has been concluded that changes in community characteristics and resources are predictive of hospital costs and physician's fees inflation, but are not predictive of increases in medical care prices. These findings provide guidance in the formulation of public policy which could alter the trend of medical care inflation and in the allocation of limited Federal funds.^

The Long-Run Phillips Curve: A Structural VAR Investigation

Both cointegration methods, and non-cointegrated structural VARs identified based on either long-run restrictions, or a combination of long-run and sign restrictions, are used in order to explore the long-run trade-off between inflation and the unemployment rate in the post-WWII U.S., U.K., Euro area, Canada, and Australia. Overall, neither approach produces clear evidence of a non-vertical trade-off. The extent of uncertainty surrounding the estimates is however substantial, thus implying that a researcher holding alternative priors about what a reasonable slope of the long-run trade-off might be will likely not see her views falsified

ANALISANDO A RELAÇÃO DOS VOLUMES DE EXPORTAÇÃO E DE IMPORTAÇÃO, PIB, TAXAS DE CÂMBIO E INFLAÇÃO NO PERÍODO DE 2004 A 2014.

Esta dissertação visa deslumbrar uma análise macroeconômica do Brasil, especialmente no que se refere à relação dos índices mensais dos volumes das exportações e das importações com os volumes mensais do PIB, da Taxa SELIC e as Taxas de Câmbio, conforme dados coletados no período de janeiro de 2004 a dezembro de 2014, através de pesquisa literária referente aos históricos sobre cada conceito envolvido no âmbito da macroeconomia das varáveis estudadas. Foi realizado um estudo de caso embasado em dados de sites governamentais, no período delimitado, empregando-se o método de regressão linear, com base na Teoria da correlação de Pearson, demonstrando os resultados obtidos no período do estudo para as varáveis estudadas. Desta maneira, conseguiu-se estudar e analisar como as variáveis dependentes (resposta): volume das exportações e volume das importações estão relacionadas com as varáveis independentes (explicativas): PIB, Taxa Selic e taxa de Câmbio. Os resultados apurados no presente estudo permitem identificar que existe correlação moderada e negativa, quando analisadas a Taxa Selic e a Taxa de Câmbio com os volumes das exportações e das importações, enquanto o PIB apresenta correlação forte e positiva na análise com os volumes das exportações e das importações

Choques de oferta e política monetária na economia brasileira: Uma análise do impacto dos preços das commodities na inflação entre 2002 e 2014

Há mais de uma década o controle dos níveis de preço na economia brasileira é realizado dentro do escopo do Regime de Metas de Inflação, que utiliza modelos macroeconômicos como instrumentos para guiar as tomadas de decisões sobre política monetária. Após um período de relativo êxito (2006 - 2009), nos últimos anos apesar dos esforços das autoridades monetárias na aplicação das políticas de contenção da inflação, seguindo os mandamentos do regime de metas, esta tem se mostrado resistente, provocando um debate em torno de fatores que podem estar ocasionando tal comportamento. Na literatura internacional, alguns trabalhos têm creditado aos choques de oferta, especialmente aos desencadeados pela variação dos preços das commodities, uma participação significativa na inflação, principalmente em economias onde os produtos primários figuram como maioria na pauta exportadora. Na literatura nacional, já existem alguns trabalhos que apontam nesta mesma direção. Sendo assim, buscou-se, como objetivo principal para o presente estudo, avaliar como os choques de oferta, mais especificamente os choques originados pelos preços das commodities, têm impactado na inflação brasileira e como e com que eficiência a política monetária do país tem reagido. Para tanto, foi estimado um modelo semiestrutural contendo uma curva de Phillips, uma curva IS e duas versões da Função de Reação do Banco Central, de modo a verificar como as decisões de política monetária são tomadas. O método de estimação empregado foi o de Autorregressão Vetorial com Correção de Erro (VEC) na sua versão estrutural, que permite uma avaliação dinâmica das relações de interdependência entre as variáveis do modelo proposto. Por meio da estimação da curva de Phillips foi possível observar que os choques de oferta, tanto das commodities como da produtividade do trabalho e do câmbio, não impactam a inflação imediatamente, porém sua relevância é crescente ao longo do tempo chegando a prevalecer sobre o efeito autorregressivo (indexação) verificado. Estes choques também se apresentaram importantes para o comportamento da expectativa de inflação, produzindo assim, uma indicação de que seus impactos tendem a se espalhar pelos demais setores da economia. Através dos resultados da curva IS constatou-se a forte inter-relação entre o hiato do produto e a taxa de juros, o que indica que a política monetária, por meio da fixação de tal taxa, influencia fortemente a demanda agregada. Já por meio da estimação da primeira função de reação, foi possível perceber que há uma relação contemporânea relevante entre o desvio da expectativa de inflação em relação à meta e a taxa Selic, ao passo que a relação contemporânea do hiato do produto sobre a taxa Selic se mostrou pequena. Por fim, os resultados obtidos com a segunda função de reação, confirmaram que as autoridades monetárias reagem mais fortemente aos sinais inflacionários da economia do que às movimentações que acontecem na atividade econômica e mostraram que uma elevação nos preços das commodities, em si, não provoca diretamente um aumento na taxa básica de juros da economia.

Report of committee for the form of quarter bills, 1778 December 12

This one-and-a-half page handwritten draft of a report on a folio-sized leaf outlines a six-point process for drafting and authorizing student quarter bills. The procedures consolidate the billing areas, detail the Treasurer's responsibilities, and expand the oversight of the President and Tutors. The report, dated December 12, 1778, is signed by President Samuel Langdon. The draft includes two differently worded versions of the sixth proposal, one of which is struck through.

Les enjeux de la libéralisation des comptes de capital dans les pays du sud de la Méditerranée. = Challenges arising from Capital Account Liberalisation in the Countries of the South Mediterranean Region. MEDPRO Technical Report No. 11/March 2012

This MEDPRO Technical Report confirms the importance of commercial openness and macroeconomic performance (i.e. the control of inflation and stability of current account balance and exchange rate) on growth dynamics in the south Mediterranean countries. In particular, the positive impact of capital account liberalisation is conditioned by the imperative reinforcement of institutional quality, country risk reduction, and government stability. An examination of the Tunisian case shows that only sectors subject to tariff dismantlement within the framework of the Association Agreement with the EU appear to benefit from capital account liberalisation. Furthermore, the report shows that a scenario of capital account liberalisation requires the anticipation of monetary policy reaction functions. It follows that the mechanisms for interest rate adjustment, or inter alia, the interest rates’ reaction to price fluctuations, are weakly volatile. In turn, the analysis shows that an active control of inflation mismatches occurs essentially through exchange rate corrections, thus highlighting the greater interest central banks have in exchange rate stability over real stability. A capital account liberalisation scenario would hence impose a tightening of monetary policy.

The financial stability risks of ultra-loose monetary policy. Bruegel Policy Contribution Issue 2015/03

Ultra-loose monetary policies, such as very low or even negative interest rates, large-scale asset purchases, long-maturity lending to banks and forward guidance in central bank communication, aim to increase inflation and output, to the benefit of financial stability. But at the same time, these measures pose various risks and might create challenges for financial institutions. • By assessing the theoretical literature and developments in the United States, United Kingdom and Japan, where very expansionary monetary policies were adopted during the past six years, and by examining the euro-area situation, we conclude that the risks to financial stability of ultra-loose monetary policy in the euro area could be low. However, vigilance is needed. • While monetary policy should focus on its primary mandate of area-wide price stability, other policies should be deployed whenever the financial cycle deviates from the economic cycle or when heterogeneous financial developments in the euro area require financial tightening in some but not all countries. These policies include micro-prudential supervision, macro-prudential oversight, fiscal policy and regulation of sectors that pose risks to financial stability, such as construction.

2016 already puts its mark on the economic map of Europe. CEPS Essay No. 22/8 January 2016

The start of 2016 brought highly symbolic changes to the trade policy map of Europe between the EU- and Russian-led blocs, as the EU’s Deep and Comprehensive Free Trade Area (DCFTA) with Ukraine entered into force provisionally, while Russia moved in precisely the opposite direction by scrapping its free trade agreement with Ukraine. However the ongoing changes go far wider and deeper. The energy sector and major industries see disengagement between Ukraine and Russia, and Russia’s share in Ukrainian trade is falling substantially. New transport corridors with China may offer synergies with trade opportunities for all three DCFTA states, with Georgia first in line. Visa liberalisation for the entire DCFTA space is now firmly in prospect. Divergent macroeconomic trends between a recovering eurozone and recession in Russia will accentuate the changes in trade structures. A better organisation of the pan-European economic space is surely desirable, but prospects for links between the EU and the Eurasian Economic Union remain problematic.

Multi-level zero-inflated Poisson regression modelling of correlated count data with excess zeros

Count data with excess zeros relative to a Poisson distribution are common in many biomedical applications. A popular approach to the analysis of such data is to use a zero-inflated Poisson (ZIP) regression model. Often, because of the hierarchical Study design or the data collection procedure, zero-inflation and lack of independence may occur simultaneously, which tender the standard ZIP model inadequate. To account for the preponderance of zero counts and the inherent correlation of observations, a class of multi-level ZIP regression model with random effects is presented. Model fitting is facilitated using an expectation-maximization algorithm, whereas variance components are estimated via residual maximum likelihood estimating equations. A score test for zero-inflation is also presented. The multi-level ZIP model is then generalized to cope with a more complex correlation structure. Application to the analysis of correlated count data from a longitudinal infant feeding study illustrates the usefulness of the approach.