Interpreting Oxygenation-Based Neuroimaging Signals: The Importance and the Challenge of Understanding Brain Oxygen Metabolism

Functional magnetic resonance imaging is widely used to map patterns of brain activation based on blood oxygenation level dependent (BOLD) signal changes associated with changes in neural activity. However, because oxygenation changes depend on the relative changes in cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2), a quantitative interpretation of BOLD signals, and also other functional neuroimaging signals related to blood or tissue oxygenation, is fundamentally limited until we better understand brain oxygen metabolism and how it is related to blood flow. However, the positive side of the complexity of oxygenation signals is that when combined with dynamic CBF measurements they potentially provide the best tool currently available for investigating the dynamics of CMRO2. This review focuses on the problem of interpreting oxygenation-based signals, the challenges involved in measuring CMRO2 in general, and what is needed to put oxygenation-based estimates of CMRO2 on a firm foundation. The importance of developing a solid theoretical framework is emphasized, both as an essential tool for analyzing oxygenation-based multimodal measurements, and also potentially as a way to better understand the physiological phenomena themselves. The existing data, integrated within a simple theoretical framework of O2 transport, suggests the hypothesis that an important functional role of the mismatch of CBF and CMRO2 changes with neural activation is to prevent a fall of tissue pO2. Future directions for better understanding brain oxygen metabolism are discussed

Confundiendo Guerra Civil con Guerra en la Stasis Griega

[ES] La violencia ha sido considerada uno de los grandes ejes que explican el devenir de la humanidad desde los comienzos de la ciencia historiográfica. Nos repele y nos atrae, deseamos olvidarla pero no debemos dejar que caiga en el olvido, aparenta estar ligada a momentos históricos concretos pero atraviesa nuestro día a día… Quizás por estas razones la violencia, en todas sus posibles manifestaciones, lejos de ser un tema obsoleto, continúa teniendo un gran potencial como cuestión historiográfica, tal y como muestran las investigaciones que conforman este libro. De la mano de diferentes especialistas, y en un recorrido que va desde la Prehistoria hasta la Edad Contemporánea, este volumen colectivo analiza las violencias históricas desde la antropología física, la historia militar, la iconografía, o la historia de la infancia entre otros puntos de vista. Guerras, conflictos políticos y religiosos y sus significados simbólicos, o la violencia como espectáculo son algunas de las cuestiones que abordan sus páginas. Si bien existen pocos temas que hayan sido más estudiados por la historiografía que la violencia, este libro, fruto del Congreso Internacional La Violencia en la Historia, celebrado en la Universidad de Salamanca en octubre de 2019, es una muestra de que las preguntas históricas nunca se agotan y de que las violencias pasadas deben seguir siendo revisitadas desde nuevos enfoques

A novel method of combining blood oxygenation and blood flow sensitive magnetic resonance imaging techniques to measure the cerebral blood flow and oxygen metabolism responses to an unknown neural stimulus.

Simultaneous implementation of magnetic resonance imaging methods for Arterial Spin Labeling (ASL) and Blood Oxygenation Level Dependent (BOLD) imaging makes it possible to quantitatively measure the changes in cerebral blood flow (CBF) and cerebral oxygen metabolism (CMRO(2)) that occur in response to neural stimuli. To date, however, the range of neural stimuli amenable to quantitative analysis is limited to those that may be presented in a simple block or event related design such that measurements may be repeated and averaged to improve precision. Here we examined the feasibility of using the relationship between cerebral blood flow and the BOLD signal to improve dynamic estimates of blood flow fluctuations as well as to estimate metabolic-hemodynamic coupling under conditions where a stimulus pattern is unknown. We found that by combining the information contained in simultaneously acquired BOLD and ASL signals through a method we term BOLD Constrained Perfusion (BCP) estimation, we could significantly improve the precision of our estimates of the hemodynamic response to a visual stimulus and, under the conditions of a calibrated BOLD experiment, accurately determine the ratio of the oxygen metabolic response to the hemodynamic response. Importantly we were able to accomplish this without utilizing a priori knowledge of the temporal nature of the neural stimulus, suggesting that BOLD Constrained Perfusion estimation may make it feasible to quantitatively study the cerebral metabolic and hemodynamic responses to more natural stimuli that cannot be easily repeated or averaged

IMPACT OF DAIRY PRODUCT IMPORTS ON U.S. MILK PRICE

Demand and Price Analysis, International Relations/Trade, Livestock Production/Industries,

Investigation of strategic capacity issues in the aerospace sector

The business environment is changing fast and radically. Traditional capacity planning has limitations in today’s dynamic environments, particularly from a strategic perspective in the aerospace sector. This document sets out to identify the unique characteristics of the aerospace industry and compare the traditional views of capacity planning and modern concepts in SCP relevant to the sector. Key findings are summarised from an analysis of the literature on strategic capacity planning. The importance of considering demand uncertainty, technology uncertainty and supply uncertainty is highlighted. Two case studies in the aero- engine sector are presented. A collaborative virtual organisation requires Strategic Capacity Planning (SCP) that focuses not only on economies of scale but also on coordination, flexibility and responsiveness. An integrated framework for addressing SCP in the aerospace industry is presented

Streamlining the formation of virtual enterprises in the aerospace industry

The virtual enterprise is an ideal solution to the pace of change in modern markets, where increasingly well-informed customers demand high performance, customised products, with continuing downward pressure on prices and lead times. In meeting customer requirements of this kind, the level of investment demanded of an individual manufacturer may be prohibitive, but success can be achieved through collaboration between businesses. Engineering across organisational boundaries poses many problems, but these have been the subject of study for some years, and are relatively well-supported by systems such as e-business portals, neutral file formats and shared data environments. If lead times are to be further reduced, it may be wise to target the virtual enterprise formation stage, rather than the operations that are to be conducted once the enterprise has formed. Within the VIVACE (Value Improvement through a Virtual Aeronautical Collaborative Enterprise) project, one task is to demonstrate how a significant reduction in the time required for a virtual company to create a business proposal might be achieved. This paper identifies some key obstacles, and discusses potential solutions

Investigation of strategic capacity issues in the aerospace sector

The business environment is changing fast and radically. Traditional capacity planning has limitations in today’s dynamic environments, particularly from a strategic perspective in the aerospace sector. This document sets out to identify the unique characteristics of the aerospace industry and compare the traditional views of capacity planning and modern concepts in SCP relevant to the sector. Key findings are summarised from an analysis of the literature on strategic capacity planning. The importance of considering demand uncertainty, technology uncertainty and supply uncertainty is highlighted. Two case studies in the aero- engine sector are presented. A collaborative virtual organisation requires Strategic Capacity Planning (SCP) that focuses not only on economies of scale but also on coordination, flexibility and responsiveness. An integrated framework for addressing SCP in the aerospace industry is presented

Streamlining the formation of virtual enterprises in the aerospace industry

The virtual enterprise is an ideal solution to the pace of change in modern markets, where increasingly well-informed customers demand high performance, customised products, with continuing downward pressure on prices and lead times. In meeting customer requirements of this kind, the level of investment demanded of an individual manufacturer may be prohibitive, but success can be achieved through collaboration between businesses. Engineering across organisational boundaries poses many problems, but these have been the subject of study for some years, and are relatively well-supported by systems such as e-business portals, neutral file formats and shared data environments. If lead times are to be further reduced, it may be wise to target the virtual enterprise formation stage, rather than the operations that are to be conducted once the enterprise has formed. Within the VIVACE (Value Improvement through a Virtual Aeronautical Collaborative Enterprise) project, one task is to demonstrate how a significant reduction in the time required for a virtual company to create a business proposal might be achieved. This paper identifies some key obstacles, and discusses potential solutions