Lagrangian Matroids: Representations of Type BnB_n

We introduce the concept of orientation for Lagrangian matroids represented in the flag variety of maximal isotropic subspaces of dimension N in the real vector space of dimension 2N+1. The paper continues the study started in math.CO/0209100.Comment: Requires amssymb.sty; 17 page

Lagrangian Pairs and Lagrangian Orthogonal Matroids

Represented Coxeter matroids of types $C_n$ and $D_n$, that is, symplectic and orthogonal matroids arising from totally isotropic subspaces of symplectic or (even-dimensional) orthogonal spaces, may also be represented in buildings of type $C_n$ and $D_n$, respectively. Indeed, the particular buildings involved are those arising from the flags or oriflammes, respectively, of totally isotropic subspaces. There are also buildings of type $B_n$ arising from flags of totally isotropic subspaces in odd-dimensional orthogonal space. Coxeter matroids of type $B_n$ are the same as those of type $C_n$ (since they depend only upon the reflection group, not the root system). However, buildings of type $B_n$ are distinct from those of the other types. The matroids representable in odd dimensional orthogonal space (and therefore in the building of type $B_n$) turn out to be a special case of symplectic (flag) matroids, those whose top component, or Lagrangian matroid, is a union of two Lagrangian orthogonal matroids. These two matroids are called a Lagrangian pair, and they are the combinatorial manifestation of the ``fork'' at the top of an oriflamme (or of the fork at the end of the Coxeter diagram of $D_n$). Here we give a number of equivalent characterizations of Lagrangian pairs, and prove some rather strong properties of them.Comment: Requires amssymb.sty; 12 pages, 2 LaTeX figure

Epidemic orientalism: social construction and the global management of infectious disease

This dissertation examines how certain epidemic outbreaks become "global threats", that is, diseases that become the focus of international regulations and organized responses while others do not. To answer this question, this dissertation draws upon archival data collected at the World Health Organization (WHO) archives in Geneva, the Western Cape Archives in Cape Town, the British Library, British National Archives, the Wellcome Library Archives in London, and twelve qualitative interviews with senior global health actors in order to analyze five cases when disease threats were prioritized internationally as well as how these constructions patterned responses to outbreaks. I begin by exploring the formation of the first international disease controls in the 19th century, the International Sanitary Conventions, created to prevent the spread of three diseases- plague, cholera and yellow fever. I probe how these earliest conventions patterned responses to diseases covered under them and limited responses to those beyond their scope. Examining how these conventions transformed, I explore why the same disease priorities were maintained by the WHO in their International Sanitary Regulations of the 1950's. Finally, I analyze the transformation of the International Health Regulations in 2005 and its effects on the assessment of disease threat. This dissertation shows that three factors structure the construction of disease threat: epidemic orientalism, economic concerns and field dynamics. Epidemic Orientalism, a discourse motivating the construction of disease threat that first emerged in the 17th, 18th and 19th centuries, positioned the colonized world as the space from which Europe and the Imperial powers needed to be protected. This orientalist gaze prioritizes the control of diseases emanating from colonial sites that threaten international trade and commerce and has been re-inscribed in all past and present regulations. These factors explain how and why plague, cholera and yellow fever came to be maintained as the primary diseases of international concern until the 21st century. As the WHO has recently been challenged in its authority to manage disease threats, these two factors are also mediated by the WHO's manipulation of symbolic power within a new field of infectious disease management which conditions responses to outbreaks today

High and Low-Speed Streaks in Turbulent Wedge Spreading

Boundary-layer transition triggered by a roughness element generates a turbulent wedge that spreads laterally as the flow proceeds downstream. The spreading half angle is about $6^{\circ}$ in zero-pressure-gradient flows regardless of Reynolds number and roughness shape. Recent simulations and experiments have sought to explain the lateral-spreading mechanism and have observed high- and low-speed streaks along the flanks of the wedge that appear central to the spreading process. To better elucidate the role of streaks, a naphthalene flow-visualization survey and hotwire measurements are conducted over a wider range of Reynolds numbers and a longer streamwise domain than previous experiments. The results reconfirm the spreading half angle is insensitive to Reynolds numbers based on roughness location, $Re_{x,k}$, and roughness height, $Re_{kk}$. When made nondimensional by the unit Reynolds number, the distance from the roughness to the effective origin of the turbulent wedge and to the first high-speed flanking streaks depends on $Re_{kk}$ but not $Re_{x,k}$. The distance between the first and second high-speed streaks is also observed to depend on $Re_{kk}$. In spite of a long measurement domain, third streaks are not observed and it remains unknown whether subsequent streak-to-streak distances collapse to a universal value. The reason downstream streaks are not observed may be low-frequency meandering of streak structures. Hotwire measurements confirm breakdown to turbulence first occurs via a shear-layer instability above low-speed streaks. Farther downstream, high-intensity broadband fluctuations are observed in equivalent positions on secondary low-speed streaks

DEVELOPMENT OF A FIRE DANGER INDEX FOR EUCALYPT PLANTATIONS IN THE NORTHERN COAST OF BAHIA, BRAZIL

Economic losses caused by fires in commercial plantations of eucalypt forest has led to the development of new fire-fighting systems and methodologies. This study aimed to develop a fire danger index for eucalypt plantations in the Copener Forestal Ltda. areas located in the north coast of Bahia, Brazil, in order to improve fire control efforts. For this purpose, eight years of meteorological data were collected and correlated to forest fire occurrence through multivariate logistic regression. The proposed model (White Model) presented a better statistical performance than other models generally used in Brazil, recommended for operational use in focused area.Keywords: Fire danger rating; fire prevention; fire suppression; fire safety. ResumoDesenvolvimento de um índice de perigo de ocorrência de incêndios florestais para plantações de eucalipto no litoral norte da Bahia, Brasil. Em função das perdas econômicas causadas pelo fogo em plantações comerciais de eucalipto, novas metodologias e sistemas de prevenção e combate ao fogo têm sido criados. Este estudo buscou desenvolver um índice de perigo de ocorrência de incêndio florestal em plantações de eucalipto da empresa Copener Florestal Ltda., localizada no litoral norte da Bahia, Brasil, a fim de aprimorar os sistemas de prevenção e combate ao fogo. Para tal, oito anos de dados meteorológicos foram coletados e correlacionados com a ocorrência de incêndios florestais através da regressão logística multivariada. O modelo proposto neste trabalho (Modelo White) obteve um melhor desempenho estatístico que outros modelos comumente utilizados no Brasil e, portanto, é recomendado para utilização operacional na área de estudo.Palavras-chave: Índice de perigo; prevenção e combate ao fogo; segurança florestal.Economic losses caused by fires in commercial plantations of eucalypt forest has led to the development of new fire-fighting systems and methodologies. This study aimed to develop a fire danger index for eucalypt plantations in the Copener Forestal Ltda. areas located in the north coast of Bahia, Brazil, in order to improve fire control efforts. For this purpose, eight years of meteorological data were collected and correlated to forest fire occurrence through multivariate logistic regression. The proposed model (White Model) presented a better statistical performance than other models generally used in Brazil, recommended for operational use in focused area.Keywords: Fire danger rating; fire prevention; fire suppression; fire safety

Weak Lensing of the CMB by Large-Scale Structure

Several recent papers have studied lensing of the CMB by large-scale structures, which probes the projected matter distribution from $z=10^3$ to $z\simeq 0$. This interest is motivated in part by upcoming high resolution, high sensitivity CMB experiments, such as APEX/SZ, ACT, SPT or Planck, which should be sensitive to lensing. In this paper we examine the reconstruction of the large-scale dark matter distribution from lensed CMB temperature anisotropies. We go beyond previous work in using numerical simulations to include higher order, non-Gaussian effects and study how well the quadratic estimator of \cite{Hu01a} is able to recover the input field. We also study contamination by kinetic Sunyaev-Zel'dovich signals, which is spectrally indistinguishable from lensed CMB anisotropies. We finish by estimating the sensitivity of the previously cited experiments.Comment: 26 pages, 13 figures, replaced to match the minor revisions of the accepted versio

Optophysiological characterisation of inner retina responses with high-resolution optical coherence tomography

Low coherence laser interferometry has revolutionised quantitative biomedical imaging of optically transparent structures at cellular resolutions. We report the first optical recording of neuronal excitation at cellular resolution in the inner retina by quantifying optically recorded stimulus-evoked responses from the retinal ganglion cell layer and comparing them with an electrophysiological standard. We imaged anaesthetised paralysed tree shrews, gated image acquisition, and used numerical filters to eliminate noise arising from retinal movements during respiratory and cardiac cycles. We observed increases in contrast variability in the retinal ganglion cell layer and nerve fibre layer with flash stimuli and gratings. Regions of interest were subdivided into three-dimensional patches (up to 5-15μm in diameter) based on response similarity. We hypothesise that these patches correspond to individual cells, or segments of blood vessels within the inner retina. We observed a close correlation between the patch optical responses and mean electrical activity of afferent visual neurons. While our data suggest that optical imaging of retinal activity is possible with high resolution OCT, the technical challenges are not trivial