Optical diagnostic investigation of low Reynolds number nozzle flows

The objectives are to obtain temperature, density and velocity profile measurements in the expansion region of low Reynolds number nozzles through the use of optical diagnostics. An LIF system will be used to probe the expansion of a microwave-heated expansion in the Center vacuum facility. The experimental measurements made in this program will be compared to numerical predictions obtained by Drs. Charles Merkle and Lyle Long

Coupling between fluid dynamics and energy addition in arcjet and microwave thrusters

A new approach to numerically solving the problem of the constricted electric arcjet is presented. An Euler Implicit finite difference scheme is used to solve the full compressible Navier Stokes equations in two dimensions. The boundary and initial conditions represent the constrictor section of the arcjet, and hydrogen is used as a propellant. The arc is modeled as a Gaussian distribution across the centerline of the constrictor. Temperature, pressure and velocity profiles for steady state converged solutions show both axial and radial changes in distributions resulting from their interaction with the arc energy source for specific input conditions. The temperature rise is largest at the centerline where there is a the greatest concentration arc energy. The solution does not converge for all initial inputs and the limitations in the range of obtainable solutions are discussed

Incidência de coccidiosis em diferentes sistemas de criação de coelhos

Amostras fecais de coelhos foram examinadas pela técnica de flutuação para a presença e contagem de oocistos do gênero Eimeria, de acordo com a técnica McMaster, em uma investigação com o objetivo de comparar um sistema alternativo não medicamentoso de criação de coelhos e sistemas convencionais com diferentes níveis de controle higiênico. A presença de oocistos nas diferentes explorações foi baixa, mas muito variável. As maiores concentrações de oocistos foram encontradas nas explorações cujas condições higiênicas não foram boas, independentemente do tratamento ou não com anticoccidiano, ou do sistema de criação. Os melhores resultados foram observados no sistema alternativo com boas condições higiênicas. Neste sistema, a concentração de oocistos nos láparos desmamados, que deveriam apresentar máxima susceptibilidade à infecção por Eimeria, foi muito baixa. Estes resultados indicam que o estrito respeito às condições higiênicas é suficiente para o controle da coccidiose e que a profilaxia farmacológica poderia ser evitada sempre que fossem adotadas altas condições higiênicas so sistema criatório ao ar livre, baseado em células subterrâneas exploráveis (tocas

Resonant electron transmission through a finite quantum spin chain

Electron transport in a finite one dimensional quantum spin chain (with ferromagnetic exchange) is studied within an $s-d$ exchange Hamiltonian. Spin transfer coefficients strongly depend on the sign of the $s-d$ exchange constant. For a ferromagnetic coupling, they exhibit a novel resonant pattern, reflecting the salient features of the combined electron-spin system. Spin-flip processes are inelastic and feasible at finite voltage or at finite temperature.Comment: 4 pages including 4 .eps figure

Are Keratoacanthomas Variants of Squamous Cell Carcinomas? A Comparison of Chromosomal Aberrations by Comparative Genomic Hybridization

Keratoacanthoma (KA) is a benign keratinocytic neoplasm that usually presents as a solitary nodule on sun-exposed areas, develops within 6–8 weeks and spontaneously regresses after 3–6 months. KAs share features such as infiltration and cytological atypia with squamous cell carcinomas (SCCs). Furthermore, there are reports of KAs that have metastasized, invoking the question of whether or not KA is a variant of SCC. To date no reported criteria are sensitive enough to discriminate reliably between KA and SCC, and consequently there is a clinical need for discriminating markers. We screened fresh frozen material from 132 KAs and 37 SCCs for gross chromosomal aberrations by using comparative genomic hybridization (CGH). Forty-nine KAs (37.1%) and 31 SCCs (83.7%) showed genomic aberrations, indicating a higher degree of chromosomal instability in SCCs. Gains of chromosomal material from 1p, 14q, 16q, 20q, and losses from 4p were seen significantly more frequently in SCCs compared with KAs (P-values 0.0033, 0.0198, 0.0301, 0.0017, and 0.0070), whereas loss from 9p was seen significantly more frequently in KAs (P-value 0.0434). The patterns of recurrent aberrations were also different in the two types of neoplasms, pointing to different genetic mechanisms involved in their developments

CD4 Depletion in SIV-Infected Macaques Results in Macrophage and Microglia Infection with Rapid Turnover of Infected Cells

In rhesus macaques (RMs), experimental depletion of CD4+ T-cells prior to SIV infection results in higher viremia and emergence of CD4-independent SIV-envelopes. In this study we used the rhesus recombinant anti-CD4 antibody CD4R1 to deplete RM CD4+ T-cells prior to SIVmac251 infection and investigate the sources of the increased viral burden and the lifespan of productively infected cells. CD4-depleted animals showed (i) set-point viral load two-logs higher than controls; (ii) macrophages constituting 80% of all SIV vRNA+ cells in lymph node and mucosal tissues; (iii) substantial expansion of pro-inflammatory monocytes; (iv) aberrant activation and infection of microglial cells; and (v) lifespan of productively infected cells significantly longer in comparison to controls, but markedly shorter than previously estimated for macrophages. The net effect of CD4+ T-cell depletion is an inability to control SIV replication and a shift in the tropism of infected cells to macrophages, microglia, and, potentially, other CD4-low cells which all appear to have a shortened in vivo lifespan. We believe these findings have important implications for HIV eradication studies

Optimization of energy transfer in microwave electrothermal thrusters

Results are presented from preliminary tests conducted to evaluate the performance of a prototype microwave electrothermal thruster. The primary component of the device is a microwave resonant cavity. The device produces stable axial plasmas within a pressurized section of the cavity with the plasma positioned in the inlet region of the nozzle. Plasma stability is enhanced by axial power coupling, an optimal distribution of electric power density within the cavity, and a propellant gas flow which has a large vortical velocity component. The thruster has been operated with a number of propellant gases: helium, nitrogen, ammonia, and hydrogen. Plasmas can be formed in a reliable manner at cavity pressures of 1 kPa and incident power levels ranging from 50 W to 350 W, depending on the gas used, and can be operated at pressures up to 300 kPa at power levels up to 2200 W. Ideal performance results of vacuum Isp and thermal efficiency vs. specific power are presented for each gas. Representative results of this preliminary work are: He - Isp = 625 s, eta-thermal = 90 percent; N2 - Isp = 270 s, eta-thermal = 41 percent; NH3 - Isp = 475 s, eta-thermal= 55 percent; H2 - Isp = 1040 s, eta-thermal = 53 percent

Off the Map: Modes of Spatial Representation in the Indigenous Icelandic riddarasögur

Until relatively recent times, the late medieval Icelandic romances, or frumsamdar riddarasögur (indigenous riddarasögur) have been considered to be of little critical value. Some of the defining features of the genre, such as exotic settings, supernatural beings, and unrealistic plots have prevented a full understanding of the texts as important expressions of their time. The success that the riddarasögur enjoyed in the Late Middle Ages and their abundant use of foreign narrative modes have often been associated with the Icelanders’ need to retreat into escapism and fantasy after the loss of political independence between 1262 and 1264. In the past decades, however, new critical perspectives have encouraged a positive re-evaluation of the genre. This project intends to contribute to the valorisation of the riddarasögur by investigating the modes of representation of fictional space in the earliest extant romances dating back to the fourteenth century. Foreign inspirations and entertainment are only two sides of Icelandic romances, which are in fact much more complex literary products and witnesses to the Icelanders’ continuous commitment to the business of storytelling. A focus on the medieval sources will facilitate the analysis of the historical background in which the riddarasögur were produced as well as the formulation of hypotheses about their function in their parent culture. The fundamental premise of the thesis is that learned Icelanders actively contributed to the great material and cultural exchanges that characterised late medieval Europe despite the political disappointments of the late thirteenth century. The centrality of travels and world descriptions in the texts has encouraged my methodological approach, which focuses firstly on the question of whether Western Europe shared a logic, a common pattern of conceiving and organising space as one of the most meaningful dimensions of the human experience. After addressing Henri Lefebvre’s general spatial theory, the basic parameters that guided the production and interpretation of space in medieval Christian Europe shall be defined on ideological grounds, especially through the works of St. Augustine. Then, the fictional space of three selected case studies (Sigurðar saga þögla, Ectors saga, and Nitida saga) will be investigated alongside their possible sources, both learned and popular, local and foreign. A careful analysis of the texts will confirm the adoption in Iceland of a paradigm of spatial thinking that was widespread in religious and highly learned environments, showing an interest of Icelandic intellectuals for complex and allegorical compositions only partially destined to the entertainment of the readers. In fact, the creative engagement of Icelandic authors with new literary trends will reveal their partaking in the ii vibrant cultural scenario of the Late Middle Ages thereby finally exorcising the ghost of literary divertissement.Riddarasögur frá síðmiðöldum – þær sem við köllum frumsamdar riddarasögur – voru lengi vel lítils metnar meðal íslenskra bókmennta. Vera má að hin helstu einkenni bókmenntagreinarinnar, þættir á borð við framandi sögusvið, óraunsæjan söguþráð og yfirnáttúrulegar vættir, hafi valdið því að fólk hætti að líta á textana sem mikilvægan tjáningarmiðil síns tíma. Oftar en ekki hefur verið litið á erlend áhrif á frásagnargerð sagnanna og vinsældir þeirra á síðmiðöldum sem vitnisburð um veruleikaflótta – að Íslendingar hafi í menningarsköpun sinni flúið á vit ímyndunaraflsins við fall þjóðveldisins á árunum 1262–1264. Á síðustu áratugum hafa fræðilegar nálganir þó náð að kynda undir jákvæðu endurmati á riddarasögum og fræðimenn hafa þá m.a. leitast við að sýna fram á hvernig þær endurspegla samfélag sitt. Það verkefni sem hér um ræðir kemur til með að byggja á þessu endurmati og fylla myndina hvað varðar hlutverk og merkingu riddarasagna, en áhersla verður lögð á að rannsaka birtingarmynd frásagnarýmis í textum frá 14. öld, þegar elstu sögurnar urðu til. Erlend áhrif og afþreying eru hins vegar einungis tvær hliðar á hinum íslensku riddarasögum, og í raun og veru eru þær mun flóknari bókmenntaverk, auk þess sem þær bera vott um áframhaldandi og stöðugan áhuga Íslendinga á sagnaskemmtun. Með því að beina athyglinni að miðaldaheimildunum sjálfum, riddarasögum frá 14. öld, má greina þann sögulega grundvöll sem þær spruttu úr, og gerir okkur kleift að leggja fram tilgátur um hlutverk sagnanna í menningarlegu samhengi. Sú grunnforsenda sem gengið er út frá er að lærðir Íslendingar hafi – þrátt fyrir hinar pólitíku sviptingar í lok 13. aldar – lagt drjúgan skerf til þeirrar efnismiðlunar og menningarlegu samskipta sem áttu sér stað í Evrópu á síðmiðöldum. Sú fræðilega nálgun sem hér er beitt er að mörgu leyti mótuð af hinu miðlæga þema sagnanna sem snýr að ferðalögum og lýsingu á staðháttum víða um heim, en fyrst mun ég leitast við að varpa ljósi á þá spurningu hvort Vestur-Evrópubúar hafi deilt hugmyndum sínum um rými, og hvort þeir hafi búið yfir sambærilegu hugsanamynstri þegar kemur að því að ímynda sér og skipuleggja rými sem eina af grunnvíddum mannlegs veruleika. Eftir það mun ég ræða hina almennu rýmiskenningu Henris Lefebvre, og skilgreina þá þætti sem stýrðu mótun og túlkun rýmis í kristnum hugmyndaheimi evrópskra miðalda, einkum í gegnum guðfræði heilags Ágústínusar og annarra kirkjufeðra. Að því loknu mun ég greina og rannsaka frásagnarlegt rými þriggja riddarasagna, eða Sigurðar sögu þögla, Ectors sögu og Nitida sögu, og fjalla um mögulegar heimildir þeirra, íslenskar sem erlendar og lærðar jafnt sem alþýðlegar. Sýnt verður fram á hvernig íslenskir höfundar unnu með hin nýstárlegu sagnaform síðmiðalda og með iv hvaða hætti sögurnar bera vott um þátttöku þeirra í hinni litríku menningarflóru evrópskra síðmiðalda. Með þessu má vonandi kveða niður gamlan draug; klisjuna um veruleikaflótta Íslendinga við fall þjóðveldisins.Háskólasjóður Eimskipafélags Ísland

Shear coaxial injector instability mechanisms

There is no definitive knowledge of which of several concurrent processes ultimately results in unstable combustion within liquid rocket chambers employing shear coaxial injectors. Possible explanations are a detrimental change in the atomization characteristics due to a decrease in the gas-to-liquid velocity ratio, a change in the gas side injector pressure drop allowing acoustic coupling to the propellant feed system or the disappearance of a stabilizing recirculation region at the base of the LOX post. The aim of this research effort is to investigate these proposed mechanisms under conditions comparable to actual engine operation. Spray characterization was accomplished with flash photography and planar laser imaging to examine the overall spray morphology and liquid jet breakup processes and with a PDPA to quantify the spatial distribution of droplet size and mean axial velocity. A simplified stability model based on the Rayleigh criterion was constructed for the flow dynamics occurring within the chamber and injector to evaluate the potential coupling between the chamber and injector acoustic modes and was supported by high frequency measurements of chamber and injector pressure oscillations. To examine recirculation within the LOX post recess, velocity measurements were performed in the recess region by means of LDV. Present experiments were performed under noncombusting conditions using LOX/GH2 stimulants at pressures up to 4 MPa

Adult enteric nervous system in health is maintained by a dynamic balance between neuronal apoptosis and neurogenesis

According to current dogma, there is little or no ongoing neurogenesis in the fully developed adult enteric nervous system. This lack of neurogenesis leaves unanswered the question of how enteric neuronal populations are maintained in adult guts, given previous reports of ongoing neuronal death. Here, we confirm that despite ongoing neuronal cell loss because of apoptosis in the myenteric ganglia of the adult small intestine, total myenteric neuronal numbers remain constant. This observed neuronal homeostasis is maintained by new neurons formed in vivo from dividing precursor cells that are located within myenteric ganglia and express both Nestin and p75NTR, but not the pan-glial marker Sox10. Mutation of the phosphatase and tensin homolog gene in this pool of adult precursors leads to an increase in enteric neuronal number, resulting in ganglioneuromatosis, modeling the corresponding disorder in humans. Taken together, our results show significant turnover and neurogenesis of adult enteric neurons and provide a paradigm for understanding the enteric nervous system in health and disease