Fluidic packaging of microengine and microrocket devices for high pressure and high temperature operation

The fluidic packaging of Power MEMS devices such as the MIT microengine and microrocket requires the fabrication of hermetic seals capable of withstanding temperature in the range 20-600/spl deg/C and pressures in the range 100-300 atm. We describe an approach to such packaging by attaching Kovar metal tubes to a silicon device using glass seal technology. Failure due to fracture of the seals is a significant reliability concern in the baseline process: microscopy revealed a large number of voids in the glass, pre-cracks in the glass and silicon, and poor wetting of the glass to silicon. The effects of various processing and materials parameters on these phenomena were examined. A robust procedure, based on the use of metal-coated silicon substrates, was developed to ensure good wetting. The bending strength of single-tube specimens was determined at several temperatures. The dominant failure mode changed from fracture at room temperature to yielding of the glass and Kovar at 600/spl deg/C. The strength in tension at room temperature was analyzed using Weibull statistics; these results indicate a probability of survival of 0.99 at an operational pressure of 125 atm at room temperature for single tubes and a corresponding probability of 0.9 for a packaged device with 11 joints. The residual stresses were analyzed using the method of finite elements and recommendations for the improvement of packaging reliability are suggested

An Editor for Helping Novices to Learn Standard ML

This paper describes a novel editor intended as an aid in the learning of the functional programming language Standard ML. A common technique used by novices is programming by analogy whereby students refer to similar programs that they have written before or have seen in the course literature and use these programs as a basis to write a new program. We present a novel editor for ML which supports programming by analogy by providing a collection of editing commands that transform old programs into new ones. Each command makes changes to an isolated part of the program. These changes are propagated to the rest of the program using analogical techniques. We observed a group of novice ML students to determine the most common programming errors in learning ML and restrict our editor such that it is impossible to commit these errors. In this way, students encounter fewer bugs and so their rate of learning increases. Our editor, C Y NTHIA, has been implemented and is due to be tested on st..

Cryptococcus neoformans ex vivo capsule size is associated with intracranial pressure and host immune response in HIV-associated cryptococcal meningitis

<p>Background. The Cryptococcus neoformans polysaccharide capsule is a well-characterised virulence factor with immunomodulatory properties. The organism and/or shed capsule is postulated to raise intracranial pressure(ICP) in cryptococcal meningitis(CM) by mechanical obstruction of cerebrospinal fluid(CSF) outflow. Little is known regarding capsule phenotype in human cryptococcosis. We investigated the relationship of ex vivo CSF capsular phenotype with ICP and CSF immune response, as well as in vitro phenotype.</p> <p>Methods. 134 HIV-infected Ugandan adults with CM had serial lumbar punctures with measurement of CSF opening pressures, quantitative cultures, ex vivo capsule size and shedding, viscosity, and CSF cytokines. 108 had complete data. Induced capsular size and shedding were measured in vitro for 48 C. neoformans isolates.</p> <p>Results. Cryptococcal strains producing larger ex vivo capsules in the baseline(pre-treatment) CSF correlated with higher ICP(P=.02), slower rate of fungal clearance(P=.02), and paucity of CSF inflammation, including decreased CSF white blood cell(WBC) count(P<.001), interleukin(IL)-4(P=.02), IL-6(P=.01), IL-7(P=.04), IL-8(P=.03), and interferon-gamma(P=.03). CSF capsule shedding did not correlate with ICP. On multivariable analysis, capsule size remained independently associated with ICP. Ex vivo capsular size and shedding did not correlate with that of the same isolates grown in vitro.</p> <P>Conclusions. Cryptococcal capsule size ex vivo is an important contributor to virulence in human cryptococcal meningitis.</P&gt

Renal pericytes: regulators of medullary blood flow

Regulation of medullary blood flow (MBF) is essential in maintaining normal kidney function. Blood flow to the medulla is supplied by the descending vasa recta (DVR), which arise from the efferent arterioles of juxtamedullary glomeruli. DVR are composed of a continuous endothelium, intercalated with smooth muscle-like cells called pericytes. Pericytes have been shown to alter the diameter of isolated and in situ DVR in response to vasoactive stimuli that are transmitted via a network of autocrine and paracrine signalling pathways. Vasoactive stimuli can be released by neighbouring tubular epithelial, endothelial, red blood cells and neuronal cells in response to changes in NaCl transport and oxygen tension. The experimentally described sensitivity of pericytes to these stimuli strongly suggests their leading role in the phenomenon of MBF autoregulation. Because the debate on autoregulation of MBF fervently continues, we discuss the evidence favouring a physiological role for pericytes in the regulation of MBF and describe their potential role in tubulo-vascular cross-talk in this region of the kidney. Our review also considers current methods used to explore pericyte activity and function in the renal medulla

Intensive care utilisation and outcomes after high-risk surgery in Scotland: a population based cohort study.

Chief Scientist’s Office Scotland (grant no. CHZ/821/4)

Virus shapes and buckling transitions in spherical shells

We show that the icosahedral packings of protein capsomeres proposed by Caspar and Klug for spherical viruses become unstable to faceting for sufficiently large virus size, in analogy with the buckling instability of disclinations in two-dimensional crystals. Our model, based on the nonlinear physics of thin elastic shells, produces excellent one parameter fits in real space to the full three-dimensional shape of large spherical viruses. The faceted shape depends only on the dimensionless Foppl-von Karman number \gamma=YR^2/\kappa, where Y is the two-dimensional Young's modulus of the protein shell, \kappa is its bending rigidity and R is the mean virus radius. The shape can be parameterized more quantitatively in terms of a spherical harmonic expansion. We also investigate elastic shell theory for extremely large \gamma, 10^3 < \gamma < 10^8, and find results applicable to icosahedral shapes of large vesicles studied with freeze fracture and electron microscopy.Comment: 11 pages, 12 figure

Prevalence of diffuse pancreatic beta islet cell disease with hyperinsulinism: Problems in recognition and management

Among 77 patients with endogenous hyperinsulinism seen in 2 medical centers, diffuse islet cell disease accounted for 17 (22%) patients. Since diffuse islet cell disease poses special problems in management, its prevalence is emphasized in this report. Among these patients with diffuse islet cell disease, there were 11 patients with adenomatosis, 4 with nesidioblastosis, and 2 with islet cell hyperplasia. Six of the 77 patients were found in multiple endocrine neoplasia, type I kindreds; diffuse islet cell disease was documented in 4 of these patients. We outline principles of management in patients with diffuse islet cell disease. Frozen section microscopy failed to identify nesidioblastosis or islet cell hyperplasia. Chez 77 malades, provenant de 2 centres médicaux, qui présentaient un hyperinsulinisme endogène, 17 cas de lésions diffuses des îlots de Langerhans ont été dénombrés. Ce fait est donc loin d'être exceptionnel et cette étude a pour but de le souligner. Parmi ces 17 malades, 11 présentaient des adénomes multiples (adénomatoses), 4 des nésidoblastomes (anomalies tissulaires multifocales), 2 des hyperplasies cellulaires insulaires. Chez ces 77 malades, 6 cas de MEN type I furent individualisés, 4 d'entre eux présentaient une maladie insulaire diffuse. Les auteurs, forts de cette expériences insistent sur les principes du traitement de ce type d'affection. Ils insistent sur le fait que l'étude histologique extemporanée ne permet pas d'identifier les nésidoblastomes et les hyperplasies cellulaires insulaires et que dans 70%–80% des cas les résections pancréatiques ne permettent pas d'obtenir la guérison. Un problema constante para el cirujano que opera pacientes con hiperinsulinismo endógeno es el de qué hacer cuando no se encuentre patología en el curso de la operación una vez realizada la exploración preliminar del páncreas. Los adenomas solitarios de células beta pueden pasar desapercibidos cuando no son palpables; la identificación de la enfermedad difusa de las células insulares plantea muchos problemas. Reconocemos tres alteraciones principales de tipo difuso: adenomatosis de células beta, nesidioblastosis e hiperplasia pancreática de células beta. Además, múltiples macroadenomas pueden coexistir o no con microadenomatosis o con hiperplasia en ciertos pacientes con hiperinsulinismo. Los desórdenes de células insulares de tipo multifocal son particularmente frecuentes en pacientes con Neoplasia Endocrina Multiple Tipo I.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41314/1/268_2005_Article_BF01654942.pd

On the history and future of soil organic phosphorus research:a critique across three generations

Soil organic phosphorus has broad agronomic and ecological significance, but remains a neglected topic of research. This opinion paper reflects a collaborative discussion between three generations of scientists who have collectively studied soil organic phosphorus for almost 50 years. We discuss personal reflections on our involvement in the field, opinions about progress and promising opportunities for future research. We debate an apparent overemphasis on analytical methodology at the expense of broader questions, and whether this has stifled progress in recent decades. We reiterate the urgent need to understand organic phosphorus cycling in the environment to address fundamental questions about phosphate supply, crop nutrition, water quality and ecosystem ecology. We also contend that we must encourage and integrate the study of organic phosphorus across all scales, from molecular chemistry to global cycling. Our discussion among three generations of researchers shows the value of a long-term perspective, emphasizes the changing nature of this field of research, and reinforces the importance of continuing to be curious about the dynamics of organic phosphorus in the environment

Maximally incompressible neutron star matter

Relativistic kinetic theory, based on the Grad method of moments as developed by Israel and Stewart, is used to model viscous and thermal dissipation in neutron star matter and determine an upper limit on the maximum mass of neutron stars. In the context of kinetic theory, the equation of state must satisfy a set of constraints in order for the equilibrium states of the fluid to be thermodynamically stable and for perturbations from equilibrium to propagate causally via hyperbolic equations. Application of these constraints to neutron star matter restricts the stiffness of the most incompressible equation of state compatible with causality to be softer than the maximally incompressible equation of state that results from requiring the adiabatic sound speed to not exceed the speed of light. Using three equations of state based on experimental nucleon-nucleon scattering data and properties of light nuclei up to twice normal nuclear energy density, and the kinetic theory maximally incompressible equation of state at higher density, an upper limit on the maximum mass of neutron stars averaging 2.64 solar masses is derived.Comment: 8 pages, 2 figure

Large-scale Bright Fronts in the Solar Corona: A Review of "EIT waves"

``EIT waves" are large-scale coronal bright fronts (CBFs) that were first observed in 195 \AA\ images obtained using the Extreme-ultraviolet Imaging Telescope (EIT) onboard the \emph{Solar and Heliospheric Observatory (SOHO)}. Commonly called ``EIT waves", CBFs typically appear as diffuse fronts that propagate pseudo-radially across the solar disk at velocities of 100--700 km s$^{-1}$ with front widths of 50-100 Mm. As their speed is greater than the quiet coronal sound speed ($c_s\leq$200 km s$^{-1}$) and comparable to the local Alfv\'{e}n speed ($v_A\leq$1000 km s$^{-1}$), they were initially interpreted as fast-mode magnetoacoustic waves ($v_{f}=(c_s^2 + v_A^2)^{1/2}$). Their propagation is now known to be modified by regions where the magnetosonic sound speed varies, such as active regions and coronal holes, but there is also evidence for stationary CBFs at coronal hole boundaries. The latter has led to the suggestion that they may be a manifestation of a processes such as Joule heating or magnetic reconnection, rather than a wave-related phenomena. While the general morphological and kinematic properties of CBFs and their association with coronal mass ejections have now been well described, there are many questions regarding their excitation and propagation. In particular, the theoretical interpretation of these enigmatic events as magnetohydrodynamic waves or due to changes in magnetic topology remains the topic of much debate.Comment: 34 pages, 19 figure