1,721,906 research outputs found
Christopher Mark Tanner gravemarker and decorations, Logan, Utah, 1999
No full textChristopher Mark Tanner gravemarker in the Logan, Utah, Cemetery (1000 North 1200 East). Image is of a headstone that has mountains and ducks and cattails engraved on it. A plant in a pot (now wilted) has been placed to the side of the stone. There are also two toys: a plastic yellow toy bulldozer and dump truck, set in front of the headstone
The statics and dynamics of sessile bubbles on inclined surfaces
No full textThesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND AEROBibliography: leaves 93-94.by Christopher Mark Greiner.M.S
Small scale physical processes and phytoplankton growth in self seas
No full textDetailed physical and biological observations collected in shelf sea regions, dominated by tidal mixing fronts or internal tides, are analysed in terms of the effect of physical forcing on phytoplankton growth. Microstructure measurements are used to quantify differences in vertical mixing and hence nutrient and light supply across regimes. The Fast Repetition Rate Fluorometer (FRRF) is used to obtain high-resolution data on the physiological state of the associated phytoplankton communities, with the aim of testing hypotheses relating growth to changing environmental conditions. Observations were made during three research cruises, RRS Challenger, in the Western English Channel, 1999 and RV Kaharoa, off the North East New Zealand coast, 1998 and 2000. The work represents one of the first attempts to collect and interpret FRRF data in a defined physical context within natural ecosystems.Results from the 1999 cruise indicate that physical forcing in the region of a tidal mixing front has a pronounced influence on the physiology of the associated phytoplankton communities. FRRF based observations were consistent with nutrient limitation towards the stratified side of tidal mixing fronts, while deep vertical mixing caused light limitation within the mixed region. The observed enhancement of chlorophyll in the region of tidal mixing fronts therefore results, at least partly, from in situ growth.Results from the 1998 and 2000 cruises demonstrate that internal tide dissipation can be responsible for high vertical nitrate fluxes and pronounced variations in phytoplankton light climate. Interpretation of physiological data from the 2000 cruise was difficult due to the complexity of the physical processes observed. However, physiological variability due to vertical motions and upwelling in the region is demonstrated.Changes in FRRF derived photophysiology, as described by the photosynthetic efficiency (Fv/Fm) and the functional absorption cross section (σPSH), are shown to be related to photosynthetic parameters measured by 14C derived carbon fixation. In particular a striking inverse correlation between FRRF derived σPSH and 14C P* vs. E derived maximal photosynthetic rates (P*max) was observed. FRRF derived photosynthetic rates are shown to compare favourably with 14C derived rates, given the limitations of both techniques.</p
Vertical sequences in turbidite successions : fact or fiction?
No full textThe Angola Basin, cored during DSDP (Deep Sea Drilling Project) Leg 75, reveals datasets from two distinctly different turbidite systems - the Cretaceous gren fan and the Upper Miocene to Recent brown fan. More quantitative techniques with a higher resolution data-set enable the detection of more intricate smaller-scale sequence trends and also enables an assessment of previously documented broader sequences. The general interpretation of fan development is subsequently modified to account for the increased sequence definition. The results of vertical sequence analysis upon two Upper Miocene to Pliocene cores from ODP (Ocean Drilling Program) Leg 116 in the distal Bengal Fan illustrate the interplay between turbidite deposition and tectonics. This study shows how periodic times of active faulting and associated local uplift, affect the production of differential sequence architecture between terminal lobe successions. The study also elucidates the role of topography and flow restricting barriers upon turbidite thickness. Another area of study, in the Late Oligocene Izu Bonin forearc basin, included the sequence analysis of volcaniclastic turbidites and debrites cored from three laterally equivalent sites. These were selected because active forearc basin settings are not widely documented and therefore poorly understood. The results of the study of sequences in the basin show quantitative proof of seismic controls upon gravity flow propagation.Despite the increasing knowledge of the planform geometries and processes acting in modern-day deep-water systems, most sequence types are always related to old models based upon field studies. Two investigations were included in the thesis to document the types of sequences found in two well studied field areas and to offer support to the studies on the extensive vertical cores. Firstly, the validity of compensation cycles, which have been identified and commonly referred to in studies of lobe and lobe-fringe settings, was assessed through the study of successions from the Hecho Basin, south-central Pyrenees. The present study found no evidence that documented cyclic thickening-upwards sequences exist in such settings. This is thought to be a function of the greater complexity which exists as a result of a number of intrabasinal controls upon lobe deposition. (DX191317)</p
Unsteady hot-wire and hot-film wake measurements of automobile-like bluff bodies
Get PDFThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1990.Title as it appears in the M.I.T. Graduate List, Feb. 1990: Unsteady hot-film and hot-wire wake measurements of automobile-like bluff bodies.Includes bibliographical references (leaves 213-214).by Christopher Mark Greiner.Ph.D
Vibration-induced white finger in dockyard employees
No full textVibration-induced white finger (VWF) is a vascular condition associated with occupational exposure to hand-transmitted vibration. The fingers are prone to intermittent blanching attacks which may be triggered by cold conditions and are usually accompanied by numbness and tingling or pain. VWF has been associated with the use of various tools and processes, among which are the percussive and rotary metal-working tools used in ship repair work. This thesis describes a study of dose-effect relationships for VWF in dockyard employees.A review of the literature revealed more than 40 epidemiological studies of VWF in workers using hand-held metal-working tools. Measurements of tool vibration have also been reported, but few researchers have combined epidemiological studies of VWF with measurements of the vibration exposures Involved. Some dose-effect relationships have been suggested and current standards contain tentative dose effect guidance. Some recent authors have suggested that the frequency weighting and time-dependencies assumed In current standards are inadequate.Methods for the measurement of hand-transmitted vibration were assessed. The vibration characteristics of sixteen pneumatic tools commonly used in dockyard work were measured in the laboratory. Repeated measurements were made In three axes at each hand position and analysis included the computation of narrow-band spectra, acceleration magnitudes in octave bands and overall frequency-weighted and unweighted acceleration magnitudes.A survey of vibration-exposed employees in a dockyard was conducted by questionnaire. Information related to symptoms of VWF, and the history of use of vibrating tools was obtained from each individual. The severity of blanching in each affected individual was recorded using a scoring system.The severity and prevalence of symptoms were related to various measures of vibration 'dose' (i.e. combinations of measured vibration magnitudes and reported exposure times) by logistic regression and survival analysis. A highly significant relationship between VWF severity and exposure time was demonstrated. However, the use of frequency-weighted acceleration in dose calculations reduced the goodness of fit, while unweighted acceleration gave a small improvement in some cases. This suggests that higher frequencies in the range 6.3 Hz to 1250 Hz are of greater Importance than current standards imply. The effect of vibration magnitude was found to be small compared with that of exposure time and no clear effect of vibration direction or vibration frequency was demonstrated.No evidence was found for a time-dependency of the form assumed in current standards. It is possible that the risk of VWF may not be directly related to the vibration magnitude, but that a 'threshold' magnitude exists, below which the hazard is small and above which it is proportional to a function of the exposure time. Further Investigation of this hypothesis is recommended
Periastron accretion in high mass X-ray binaries: comparing supergiant fast X-ray transients and Be/X-ray binaries
No full textHigh Mass X-ray Binaries (HXMBs) are some of the brightest objects in the X-ray sky and test our understanding of accretion physics in extreme stellar environments.In this thesis, characterisation of the accretion processes around periastron in two Supergiant Fast X-ray Transients (SFXTs) and one Be/X-ray Binary (BeXRB) is presented. A combined XMM-Newton and INTEGRAL study of the SFXT SAX J1818.6-1703 reveals the source to be in an active state, presenting a low luminosity phase that can be explained by the onset of a subsonic propeller or transition to the radiative regime of quasi-spherical accretion (QSA). The strongest flaring activity coincides with significant spectral hardening and the associated luminosities of this phase suggest a potential transition to the Compton regime of QSA. Spectral analysis also reveals strong intrinsic absorption, an order of magnitude higher than previously observed and among the highest measured in an SFXT. Observations of the SFXT IGR J18450-0435 with XMM-Newton also show low luminosity phases that can be explained by the onset of the radiative regime of QSA. Fast flaring behaviour is attributed to transition to the Compton regime and evidence of the accretion of magnetised stellar wind is presented. Spectral analysis again reveals enhanced local absorption up to five times greater than previous reported. A multi-wavelength study of the BeXRB IGR J01217-7257 allows the discovery of X-ray periodicities of 82.5±0.7 days and 2.1562±0.0001 seconds attributed to the neutron star orbital and spin periods respectively. Detected X-ray outbursts are put into an orbital context and found to be consistent with Type-I outbursts. Analysis of long-baseline optical data reveals short periodicities (∼ 1 day) that are attributed to non-radial pulsations (NRPs) of the companion and an association between the NRPs, decretion disc growth and the onset of Type-I outbursts is suggested
Investigating the function of the retention/retrieval, ERp57-binding and glycan-binding sites of calreticulin in MHC class I antigen presentation
No full textCalreticulin (CRT) is an Endoplasmic Reticulum (ER) resident protein involved in intracellular calcium homeostasis and the folding of newly synthesised glycoproteins. CRT also forms part of the peptide loading complex (PLC) where it assists in Major Histocompatibility Complex (MHC) class I folding, maturation and peptide loading with the assistance of ERp57. CRT's localisation is kept in check through a C-terminal Lys-Asp-Glu-Leu (KDEL) sequence that retrieves it to the ER through the KDEL receptor. The CRT -/- mouse fibroblast cell line K42 loads MHC class I molecules and presents endogenous antigens to cytotoxic T lymphocytes inefficiently ~Gao et al 2002). Importantly, the trafficking speed of the endogenous class I alleles (H-2Kb and H-2D ) to the cell surface was shown to be faster in K42 than in its CRT +/+ counterpart K4I; furthermore fewer MHC I were incorporated into the PLC in K42 (Gao et aI., 2002), similar to a class I Tl34K mutant that fails to present antigen efficiently (Lewis et aI., 1996). This suggests that CRT influences MHC I trafficking rate and may recruit MHC I to the PLC, ensuring efficient MHC I antigen presentation. In this study, the role of CRT was further dissected using a series of mutant constructs that were expressed in K42 and their effects on MHC I antigen presentation determined. The mutants were designed to address three questions: the role of the c-terminus and KDEL in MHC I retention / retrieval; the importance of the interaction between CRT and ERp57; and the effect of mutation of CRT's glycan-binding site on MHC I antigen presentation. Unexpectedly, the glycan-binding CRT mutant fully restored MHC I antigen presentation, suggesting that polypeptide interactions define CRT substrate specificity. However, efficient MHC I assembly with the PLC was shown to require an interaction between CRT and ERp57. The trafficking rate of MHC I was influenced not just by the KDEL sequence but also by the interaction between CRT and ERp57 and by undefined residues within the 11 c-terminal amino acids of CRT, consistent with a role in MHC I retention / retrieval. Cumulatively, results show that the CRT's c-terminus, KDEL sequence and ERp57 binding site, but not CRT's glycan-binding site, are obligatory for efficient MHC I antigen presentation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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