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Search Results: 1 - 10 of 252140 matches for " John R. Webb "
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Inflammation-Associated Nitrotyrosination Affects TCR Recognition through Reduced Stability and Alteration of the Molecular Surface of the MHC Complex
Chaithanya Madhurantakam, Adil D. Duru, Tatyana Sandalova, John R. Webb, Adnane Achour
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0032805
Abstract: Nitrotyrosination of proteins, a hallmark of inflammation, may result in the production of MHC-restricted neoantigens that can be recognized by T cells and bypass the constraints of immunological self-tolerance. Here we biochemically and structurally assessed how nitrotyrosination of the lymphocytic choriomeningitis virus (LCMV)-associated immunodominant MHC class I-restricted epitopes gp33 and gp34 alters T cell recognition in the context of both H-2Db and H-2Kb. Comparative analysis of the crystal structures of H-2Kb/gp34 and H-2Kb/NY-gp34 demonstrated that nitrotyrosination of p3Y in gp34 abrogates a hydrogen bond interaction formed with the H-2Kb residue E152. As a consequence the conformation of the TCR-interacting E152 was profoundly altered in H-2Kb/NY-gp34 when compared to H-2Kb/gp34, thereby modifying the surface of the nitrotyrosinated MHC complex. Furthermore, nitrotyrosination of gp34 resulted in structural over-packing, straining the overall conformation and considerably reducing the stability of the H-2Kb/NY-gp34 MHC complex when compared to H-2Kb/gp34. Our structural analysis also indicates that nitrotyrosination of the main TCR-interacting residue p4Y in gp33 abrogates recognition of H-2Db/gp33-NY complexes by H-2Db/gp33-specific T cells through sterical hindrance. In conclusion, this study provides the first structural and biochemical evidence for how MHC class I-restricted nitrotyrosinated neoantigens may enable viral escape and break immune tolerance.
A segmental radiological study of the spine and rib – cage in children with progressive Infantile Idiopathic Scoliosis
Theodoros B Grivas, Geoffrey R Burwell, Elias S Vasiliadis, John K Webb
Scoliosis , 2006, DOI: 10.1186/1748-7161-1-17
Abstract: In the posteroanterior (PA) spinal radiographs of 24 patients with progressive IIS, with a mean age of 4.1 years old, the Thoracic Ratios (TRs) (segmental convex and concave TRs), the Cobb angle, the segmental vertebral rotation and vertebral tilt were measured. In 233 subjects, with a mean age of 5.1 years old, who were used as a control group, the segmental left and right TRs and the total width of the chest (left plus right TRs) were measured in PA chest radiographs. Statistical analysis included Mann-Whitney, Spearman correlation coefficient, multiple linear regression analysis and ANOVA.The comparison shows that the scoliotic thorax is significantly narrower than that of the controls at all spinal levels. The upper chest in IIS is funnel-shaped and the vertebral rotation at T4 early in management correlates significantly with the apical vertebral rotation at follow up.The IIS thorax is narrower than that of the controls, the upper chest is funnel-shaped and there is a predictive value of vertebral rotation at the upper limit of the thoracic curve of IIS, which reflects, impaired rib control of spinal rotation possibly due to neuromuscular factors, which contribute also to the funnel-shaped chest.A study of children aged 1–5 years with progressive infantile idiopathic scoliosis (IIS) shows that a two stage anterior and posterior surgical procedure leads to deterioration of the spine during follow up [1-3].By reviewing the literature, no publication was found on rib growth in children with IIS. Dansereau et al [4] examined rib length asymmetry by using a stereoradiographic method in children with adolescent idiopathic scoliosis.These findings caused us to undertake a segmental radiological study of the spine and rib – cage in children with progressive IIS.The effect of upper thoracic cage on pulmonary function in IIS is an additional interesting issue. A report on diminished pulmonary function following arthrodesis of the thoracic spine before age 5 noted strong
The Dormice (Myoxidae) of Southern Africa
Peter Webb,John Skinner
Hystrix : the Italian Journal of Mammalogy , 1995, DOI: 10.4404/hystrix-6.1-2-4042
Abstract: Very little is known about the dormice of Africa south of the Sahara, even their current classification is suspect. This paper summarises the information available in the literature on the four (probable) species of dormouse found in southern Africa. Mean body masses are approximately >55 g, 50 g, 27 g and <27 g in Graphiurus ocularis, G. platyops, G. murinus, and G. parvus respectively. All four species are silver-grey dorsally and buffy-white ventrally with varying degress of black around the eyes. G. ocularis and G. platyops prefer rocky hillsides and koppies while G. murinus and G. parvus are primarily arboreal. Breeding in southern Africa is probably limited to the warm, wet summer months with a normal litter size of three or four and one or two litters per year. At least in G. ocularis breeding pairs appear to be territorial. Torpor can be induced in individuals in captivity but the use and extent of hibernation in the wild depends on local climatic conditions. G. ocularis seems to be purely carnivorous while the other three species are omnivores. Riassunto I Mioxidi del Sud Africa - Molto poco è conosciuto sui mioxidi dell'Africa a sud del Sahara, persino la loro classificazione attuale è dubbia. Nel presente lavoro vengono riassunte le informazioni disponibili in letteratura sulle quattro (probabili) specie di mioxidi del Sud Africa. I pesi corporei medi sono approssimativamente superiori a 55 g, 50 g, 27 g ed inferiori a 27 g in Graphiurus ocularis, G. platyops, G. murinus e G. parvus rispettivamente. Tutte e quattro le specie presentano una colorazione grigio-argentea dorsalmente e bianco-marrone ventralmente con gradi variabili di nero intorno agli occhi. G. ocularis e G. parvus sono essenzialmente arborei. La riproduzione in sud Africa è probabilmente limitata ai caldi e umidi mesi estivi con una o due figliate per anno, costituite da tre o quattro piccoli. Almeno in G. ocularis le coppie riproduttive sembrano essere territoriali. I1 torpore può essere indotto in individui in cattività ma l'uso ed il grado di letargo in condizioni naturali dipendono da condizioni climatiche locali. G. ocularis sembra essere esclusivamente carnivoro mentre le altre tre specie sono onnivore.
Scoliosis - The current concepts
Sengupta Dilip,Webb John
Indian Journal of Orthopaedics , 2010,
Abundances in the Lyman--alpha clouds
Sandra Savaglio,John Webb
Physics , 1995,
Abstract: We have re--examined the chemical composition of \lya clouds using the composite--cloud technique, in which each \lya line in a spectrum is shifted to its rest frame wavelength and all rest frame spectra are co--added to form an `averaged' \lya cloud spectrum. We illustrate how various estimates of the spectrum and redshift evolution of the background ionizing UV flux lead to very different predictions for the relative strengths of heavy element lines in the forest clouds. We also show how the potential abundance limits depend on the various observational quantities and how different procedures may be required for OVI and CIV. Preliminary results are presented from an analysis of two high redshift QSO echelle spectra.
Nonlinear optics of fibre event horizons
Karen E. Webb,Miro Erkintalo,Yiqing Xu,Neil G. R. Broderick,John M. Dudley,Goery Genty,Stuart G. Murdoch
Physics , 2014, DOI: 10.1038/ncomms5969
Abstract: The nonlinear interaction of light in an optical fibre can mimic the physics at an event horizon. This analogue arises when a weak probe wave is unable to pass through an intense soliton, despite propagating at a different velocity. To date, these dynamics have been described in the time domain in terms of a soliton-induced refractive index barrier that modifies the velocity of the probe. Here, we complete the physical description of fibre-optic event horizons by presenting a full frequency-domain description in terms of cascaded four-wave mixing between discrete single-frequency fields, and experimentally demonstrate signature frequency shifts using continuous wave lasers. Our description is confirmed by the remarkable agreement with experiments performed in the continuum limit, reached using ultrafast lasers. We anticipate that clarifying the description of fibre event horizons will significantly impact on the description of horizon dynamics and soliton interactions in photonics and other systems.
A new analysis of fine-structure constant measurements and modelling errors from quasar absorption lines
Michael R. Wilczynska,John K. Webb,Julian A. King,Michael T. Murphy,Matthew B. Bainbridge,Victor V. Flambaum
Physics , 2015, DOI: 10.1093/mnras/stv2148
Abstract: We present an analysis of 23 absorption systems along the lines of sight towards 18 quasars in the redshift range of $0.4 \leq z_{abs} \leq 2.3$ observed on the Very Large Telescope (VLT) using the Ultraviolet and Visual Echelle Spectrograph (UVES). Considering both statistical and systematic error contributions we find a robust estimate of the weighted mean deviation of the fine-structure constant from its current, laboratory value of $\Delta\alpha/\alpha=\left(0.22\pm0.23\right)\times10^{-5}$, consistent with the dipole variation reported in Webb et al. and King et al. This paper also examines modelling methodologies and systematic effects. In particular we focus on the consequences of fitting quasar absorption systems with too few absorbing components and of selectively fitting only the stronger components in an absorption complex. We show that using insufficient continuum regions around an absorption complex causes a significant increase in the scatter of a sample of $\Delta\alpha/\alpha$ measurements, thus unnecessarily reducing the overall precision. We further show that fitting absorption systems with too few velocity components also results in a significant increase in the scatter of $\Delta\alpha/\alpha$ measurements, and in addition causes $\Delta\alpha/\alpha$ error estimates to be systematically underestimated. These results thus identify some of the potential pitfalls in analysis techniques and provide a guide for future analyses.
Could We Detect Molecular Oxygen in the Atmosphere of a Transiting Extra-Solar Earth-Like Planet?
John K. Webb,Imma Wormleaton
Physics , 2001, DOI: 10.1071/AS01037
Abstract: Although the extra-solar planets discovered so far are of the giant, gaseous, type, the increased sensitivity of future surveys will result in the discovery of lower mass planets. The detection of O2 in the atmosphere of a rocky extra-solar planet would be a potential indicator of a life. In this paper we address the specific issue of whether we would be able to detect the O2 A-band absorption feature in the atmosphere of a planet similar to the Earth, if it were in orbit around a nearby star. Our method is empirical, in that we use observations of the Earth's O2 A-band, with a simple geometric modification for a transiting extra-solar planet, allowing for limb-darkening of the host star. We simulate the spectrum of the host star with the superposed O2 A-band absorption of the transiting planet, assuming a spectral resolution of 7 km/s (typical of current echelle spectrographs), for a range of spectral signal-to-noise ratios. The main result is that we could reliably detect the O2 A-band of the transiting planet for host stars with radii 0.3 solar or less. However, using existing instrumentation and 8m telescopes, this requires target M stars with m(V) of approximately 10 or brighter for integration times of about 10 hours or less. The number of such stars over the sky is small. Larger aperture telescopes and/or improved instrumentation efficiency would enable surveys of M stars down to m(V) = 13 and greatly improve the chances of discovering life elsewhere.
On spaces of modular forms spanned by eta-quotients
Jeremy Rouse,John J. Webb
Mathematics , 2013,
Abstract: An eta-quotient of level $N$ is a modular form of the shape $f(z) = \prod_{\delta | N} \eta(\delta z)^{r_{\delta}}$. We study the problem of determining levels $N$ for which the graded ring of holomorphic modular forms for $\Gamma_{0}(N)$ is generated by (holomorphic, respectively weakly holomorphic) eta-quotients of level $N$. In addition, we prove that if $f(z)$ is a holomorphic modular form that is non-vanishing on the upper half plane and has integer Fourier coefficients at infinity, then $f(z)$ is an integer multiple of an eta-quotient. Finally, we use our results to determine the structure of the cuspidal subgroup of $J_{0}(2^{k})(\mathbb{Q})$.
The appropriate role of colloids in managing fluid imbalance: a critical review of recent meta-analytic findings
Andrew R Webb
Critical Care , 2000, DOI: 10.1186/cc967
Abstract: The recent publication of three meta-analyses [1,2,3] has intensified the long-standing debate regarding the merits of colloids to expand the plasma space in critically ill patients. Two of these meta-analyses concluded that excess mortality was associated with the use of colloids generally [1] and of albumin specifically [2], and proposed that such use be curtailed outside the context of RCTs. The third meta-analysis concluded there was no overall mortality difference associated with colloid versus crystalloid resuscitation [3]. Furthermore, due to methodologic limitations, evidence-based clinical recommendations were not deemed to be warranted on the basis of the meta-analysis [3].Critical care physicians must now assess what impact, if any, these meta-analyses should exert upon current clinical practice. This assessment needs to include a close and rigorous examination of the meta-analyses and the RCTs underlying them.The systematic review by Schierhout and Roberts [1] identified 26 RCTs [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29] encompassing 1622 patients receiving colloid or crystalloid. Mortality was adopted as the main outcome measure in the meta-analysis of these RCTs. Mortality among patients receiving colloid was found to be greater than that of crystalloid recipients by 4%, with a 95% CI of 0-8%. The corresponding relative risk of death was 1.19 (95% CI, 0.98-1.45). This difference was not significant since the 95% CI for relative risk included 1.One of the major problems pervading this meta-analysis was that of heterogeneity among the included RCTs. Patients with any of various hypovolaemic insults received any of various colloids or crystalloids at differing concentrations. Yet the outcome of hypovolaemia is likely to be influenced by the cause of the hypovolaemia. There is, furthermore, little basis to postulate that different colloids, with disparate biochemical properties, will have similar effects on outcome. There is
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