Biomedical subjects

N Amos

Publications and source records attributed to N Amos.

At least 19 recordsLinked to original sources

PubMed2002

Search for R-parity violating supersymmetry in two-muon and four-jet topologies.

We present results of a search for R-parity-violating decay of the neutralino chi;01, taken as the lightest supersymmetric particle, to a muon and two jets. The decay proceeds through a lepton-number violating coupling lambda(')(2jk) (j=1,2; k=1,2,3), with R-parity conservation in all other production and decay processes. In the absence of candidate events from 77.5+/-3.9 pb(-1) of data collected by the D0 experiment at the Fermilab Tevatron in pp collisions at sqrt[s]=1.8 TeV, and with an expected background of 0.18+/-0.03+/-0.02 events, we set limits on squark and gluino masses within the framework of the minimal low-energy supergravity-supersymmetry model.

Journal Article↗

PubMed2002

Search for leptoquark pairs decaying into nunu+jets in pp collisions at square root[s] = 1.8 TeV.

We present the results of a search for leptoquark (LQ) pairs in (85.2+/-3.7) pb(-1) of pp* collider data collected by the D0 experiment at the Fermilab Tevatron. We observe no evidence for leptoquark production and set a limit on sigma(pp*-->LQLQ-->nunu+jets) as a function of the mass of the leptoquark (m(LQ)). Assuming the decay LQ-->nuq, we exclude scalar leptoquarks for m(LQ) < 98 GeV/c(2), and vector leptoquarks for m(LQ) < 200 GeV/c(2) and coupling which produces the minimum cross section, at a 95% confidence level.

Journal Article↗

PubMed2002

Search for the scalar top quark in pp collisions at square root[s] = 1.8 TeV.

We have performed a search for scalar top quark (stop) pair production in the inclusive electron-muon-missing transverse energy final state, using a sample of pp events corresponding to 108.3 pb(-1) of data collected with the D0 detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the sneutrino is the lightest supersymmetric particle. For the dominant decays of the lightest stop, t-->b chi+1 and t-->blnu, no evidence for signal is found. We derive cross-section limits as a function of stop ( t ), chargino ( chi+1), and sneutrino ( nu) masses.

Journal Article↗

PubMed2002

Direct search for charged higgs bosons in decays of top quarks.

We present a search for charged Higgs bosons in decays of pair-produced top quarks in pp collisions at sqrt[s] = 1.8 TeV recorded by the D0 detector at the Fermilab Tevatron collider. With no evidence for signal, we exclude most regions of the ( M(H+/-),tan(beta)) parameter space where the decay t--> H(+)b has a branching fraction >0.36 and B(H+/--->tau(nu)(tau)) is large.

Journal Article↗

PubMed2002

A comparative study to assess the clinical use of Fluorescein Meniscus Time (FMT) with Tear Break up Time (TBUT) and Schirmer's tests (ST) in the diagnosis of dry eyes.

INTRODUCTION: The clinical diagnosis of dry-eye is confirmed by a suitable test of tear production and the technique commonly used today to diagnose dry eye is the Schirmer's test (ST). Although the ST is easy to perform it gives variable results, poor reproducibility and low sensitivity for detecting dry eyes. Another test, the tear break up time (TBUT) is used to assess the stability of tears which if abnormal may also cause symptomatic dry-eye. We present the results of both these tests and a new test, which shows greater sensitivity than the ST in detecting aqueous tear deficiency. The fluorescein meniscus time (FMT) is a new test developed in conjunction with one of the authors (CL) and the Department of Ophthalmology at the University Hospital of Wales. The FMT is a measure of the rate at which a fluorescent tear meniscus is formed using 2% sodium fluorescein, a stopwatch and suitable illumination with a slit lamp. METHOD: An open controlled study in 62 patients and 51 controls was conducted to compare the ability of ST, FMT and TBUT to detect dry-eye in a group of patients diagnosed with rheumatoid arthritis and symptomatic dry eyes for a minimum period of 6 months. A separate control group of 15 subjects was tested on three separate occasions to assess the reproducibility of the FMT test. RESULTS: All three tests showed a statistically significant difference between the patient and control populations; Mann-Whitney P < 0.001. There was a correlation between the right and left eye for all three tests in the control group (ST r(2) = 0.77, FMT r(2) = 0.98, TBUT r(2) = 0.94). This correlation was markedly reduced for FMT and TBUT in the patient population and was in keeping with the symptoms reported as being worse on one side in a proportion of the patients (FMT r(2) = 0.52, TBUT r(2) = 0.54, ST r(2) = 0.75). A correlation with age was also observed for all the three tests in the control group (ST r(2) = 0.74, FMT r(2)= 0.92, TBUT r(2) = 0.51), but not in the patient population (ST r(2) = 0.06, FMT r(2) = 0.18, TBUT r(2) = 0.03). A significant correlation was observed between the ST and FMT in both the control (ST vs FMT r(2) = 0.65) and patient population (ST vs FMT r(2) = 0.44). There was no value greater than 200 seconds for FMT recorded in the control group. Using this value to define an abnormal FMT, 85% of the patients (72% of the eyes tested) had an abnormal result. This was in contrast to 35% of patients (26% of the eyes tested) with abnormal results detected by ST. Using ANOVA and Student's paired t-test, there were no significant differences between the three sets of values recorded serially over 3 months to assess the reproducibility of the FMT. The average standard error of the mean was 2.72% and the average co-efficient of variation 4.07%. CONCLUSION: Our study suggests that the FMT is a more sensitive test with good reproducibility compared to the Schirmer's test. The FMT correlates with the ST and suggests that both tests measure aqueous tear deficiency. The FMT therefore is a better alternative to ST currently being used to test aqueous tear deficiency.

Adolescent↗

PubMed2001

Early graft function after pediatric liver transplantation: comparison between in situ split liver grafts and living-related liver grafts.

BACKGROUND: The systematic application of living-related and cadaveric, in situ split-liver transplantation has helped to alleviate the critical shortage of suitable-sized, pediatric donors. Undoubtedly, both techniques are beneficial and advantageous; however, the superiority of either graft source has not been demonstrated directly. Because of the potential living-donor risks, we reserve the living donor as the last graft option for pediatric recipients awaiting liver transplantation. Inasmuch as no direct comparison between these two graft types has been performed, we sought to perform a comparative analysis of the functional outcomes of left lateral segmental grafts procured from these donor sources to determine whether differences do exist. METHODS: A retrospective analysis of all liver transplants performed at a single institution between February 1984 and January 1999 was undertaken. Only pediatric (<18 years) recipients of left lateral segmental grafts procured from either living-related (LRD) or cadaveric, in situ split-liver (SLD) donors were included. A detailed analysis of preoperative, intraoperative, and postoperative variables was undertaken. Survival was estimated using the Kaplan-Meier method, and comparison of variables between groups was undertaken using the t test of Wilcoxon rank sum test. RESULTS: There were no significant differences in the preoperative variables between the 39 recipients of SLD grafts and 34 recipients of LRD grafts. The donors did differ significantly in mean age, ABO blood group matching, and preoperative liver function testing. Postoperative liver function testing revealed significant early differences in aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, prothrombin time, and alkaline phosphatase, with grafts from LRD performing better than those from SLD. SLD grafts also had significantly longer ischemia times and a higher incidence of graft loss owing to primary nonfunction and technical complications (9 vs. 2, P<0.05). However, six of these graft losses in the SLD group were because of technical or immunologic causes, which, theoretically, should not differ between the two groups. Furthermore, these graft losses did not negatively impact early patient survival as most patients were successfully rescued with retransplantation (30-day actuarial survival, 97.1% SLD vs. 94.1% LRD, P=0.745). In the surviving grafts, the early differences in liver function variables normalized. CONCLUSIONS: Inherent differences in both donor sources exist and account for differences seen in preoperative and intraoperative variables. Segmental grafts from LRD clearly performed better in the first week after transplantation as demonstrated by lower liver function variables and less graft loss to primary nonfunction. However, the intermediate function (7-30 days) of both grafts did not differ, and the early graft losses did not translate into patient death. Although minimal living-donor morbidity was seen in this series, the use of this donor type still carries a finite risk. We therefore will continue to use SLD as the primary graft source for pediatric patients awaiting liver transplantation.

Adult↗

PubMed2001

Ratio of isolated photon cross sections in pp macro collisions at square root of s = 630 and 1800 GeV.

The inclusive cross section for production of isolated photons has been measured in pp macro collisions at square root of s = 630 GeV with the D0 detector at the Fermilab Tevatron Collider. The photons span a transverse energy (E(T)) range from 7-49 GeV and have pseudorapidity absolute value of eta < 2.5. This measurement is combined with the previous D0 result at square root of s = 1800 GeV to form a ratio of the cross sections. Comparison of next-to-leading-order QCD with the measured cross section at 630 GeV and the ratio of cross sections show satisfactory agreement in most of the E(T) range.

Journal Article↗

PubMed2001

Search for new physics using QUAERO: a general interface to D0 event data.

We describe QUAERO, a method that (i) enables the automatic optimization of searches for physics beyond the standard model, and (ii) provides a mechanism for making high energy collider data generally available. We apply QUAERO to searches for standard model WW, ZZ, and t t macro production, to searches for these objects produced through a new heavy resonance, and to the first direct search for W'-->WZ. Through this interface, we make three data sets collected by the D0 experiment at square root of [s] = 1.8 TeV publicly available.

Journal Article↗

PubMed2001

Search for heavy particles decaying into electron-positron pairs in pp collisions.

We present results of searches for technirho (rho(T)), techniomega (omega(T)), and Z' particles, using the decay channels rho(T),omega(T),Z'-->e(+)e(-). The search is based on 124.8 pb(-1) of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes pp-->rho(T),omega(T),Z'-->e(+)e(-) as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate rho(T) and omega(T) states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.

Journal Article↗

PubMed2001

Quasi-model-independent search for new high p(T) physics at D0.

We apply a quasi-model-independent strategy ("Sleuth") to search for new high p(T) physics in approximately 100 pb(-1) of pp collisions at square root of (s) = 1.8 TeV collected by the D0 experiment during 1992-1996 at the Fermilab Tevatron. We systematically analyze many exclusive final states and demonstrate sensitivity to a variety of models predicting new phenomena at the electroweak scale. No evidence of new high p(T) physics is observed.

Journal Article↗

PubMed2001

Ratio of jet cross sections at square root of s = 630 GeV and 1800 GeV.

The D0 Collaboration has measured the inclusive jet cross section in barpp collisions at square root of s = 630 GeV. The results for pseudorapidities (eta)<0.5 are combined with our previous results at square root of s = 1800 GeV to form a ratio of cross sections with smaller uncertainties than either individual measurement. Next-to-leading-order QCD predictions show excellent agreement with the measurement at 630 GeV; agreement is also satisfactory for the ratio. Specifically, despite a 10% to 15% difference in the absolute magnitude, the dependence of the ratio on jet transverse momentum is very similar for data and theory.

Journal Article↗

PubMed2001

Ratios of multijet Cross Sections in p p collisions at radical(s) = 1.8 TeV.

We report on a study of the ratio of inclusive three-jet to inclusive two-jet production cross sections as a function of total transverse energy in p&pmacr; collisions at a center-of-mass energy sqrt[s] = 1.8 TeV, using data collected with the D0 detector during the 1992-1993 run of the Fermilab Tevatron Collider. The measurements are used to deduce preferred renormalization scales in perturbative O(alpha(3)(s)) QCD calculations in modeling soft-jet emission.

Journal Article↗

PubMed2001

Inclusive jet production in pp(macro) collisions.

We report a new measurement of the pseudorapidity (eta) and transverse-energy ( E(T)) dependence of the inclusive jet production cross section in pp(macro) collisions at square root of s = 1.8 TeV using 95 pb(-1) of data collected with the D0 detector at the Fermilab Tevatron. The differential cross section d(2)sigma/(dE(T)d eta) is presented up to eta = 3, significantly extending previous measurements. The results are in good overall agreement with next-to-leading order predictions from QCD and indicate a preference for certain parton distribution functions.

Journal Article↗

PubMed2001

Search for large extra dimensions in dielectron and diphoton production.

We report a search for effects of large extra spatial dimensions in pp collisions at a center-of-mass energy of 1.8 TeV with the D0 detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% C.L. on the effective Planck scale between 1.0 and 1.4 TeV for several formalisms and numbers of extra dimensions.

Journal Article↗

PubMed2001

Functional differences between influenza A-specific cytotoxic T lymphocyte clones expressing dominant and subdominant TCR.

We have shown that the dominance of CD8+ T cells expressing TCR Vbeta17 in the adult HLA-A*0201-restricted influenza A/M1(58-66)-specific response is acquired following first antigen exposure. Despite the acquired dominance of Vbeta17+ cells, subdominant M1(58-66)-specific clones expressing non-Vbeta17+ TCR persist in all individuals. To determine whether the affinity of the expressed TCR for the HLA-A*0201/M1(58-66) complex could influence functional properties, M1(58-66)-specific clones expressing subdominant (non-Vbeta17+) TCR were compared to cytotoxic T lymphocyte (CTL) clones expressing dominant (Vbeta17+) TCR. The Vbeta17+ CTL required up to 10,000-fold lower amounts of M1 peptide to mediate lysis compared to CTL clones expressing other Vbeta gene segments. All Vbeta17+ CTL clones tested bound HLA-A*0201/M1(58-66) tetramer, but two of three CTL clones expressing other TCR did not bind tetramer. The inability of non-Vbeta17+ CTL to bind tetramer did not correlate with phenotype, CD8 dependence or with cytokine production profiles. This suggests a limitation for the use of tetramers in examining subdominant T cell responses. Together these findings suggest that Vbeta17+ CTL which dominate the HLA-A*0201-restricted CTL response against influenza A are not functionally distinct from subdominant non-Vbeta17+ CTL. The dominance of Vbeta17+ CTL is likely to result from a competitive advantage due to superior CTL avidity for the HLA-A*0201/M1(58-66) complex.

Adult↗

PubMed2001

Minocycline-induced lupus: clinical features and response to rechallenge.

OBJECTIVE: To describe the spectrum of clinical features in patients with minocycline-induced lupus (MIL) and determine their response to rechallenge. METHODS: The clinical features and laboratory findings of 23 patients with MIL were recorded. Ten patients were rechallenged, and their C-reactive protein (CRP) levels were monitored. RESULTS: All subjects complained of polyarthralgia; three had metacarpophalangeal and proximal interphalangeal joint synovitis and one had bilateral knee effusions. Elevated hepatic transaminases were noted in eight subjects. Cutaneous vasculitis was a feature in two cases. None had renal or central nervous system disease, although five patients complained of impaired concentration and poor memory and a single patient had a peripheral sensory neuropathy. The following serological abnormalities were detected: antinuclear antibodies (19/23 patients); antibodies to double-stranded DNA (4/23); perinuclear antineutrophil cytoplasmic antibodies (10/15); IgG anti-cardiolipin antibodies (6/23); hypergammaglobulinaemia (12/19). Anti-histone antibodies were negative in 9/9 cases. Rechallenge resulted in rapid recurrence of symptoms and elevation of CRP levels. CONCLUSION: MIL is associated with a wide spectrum of clinical and serological features. The diagnosis can be confirmed by rechallenge, which results in rapid reappearance of symptoms and a rise in CRP.

Adolescent↗

PubMed2001

Serum soluble interleukin 2 receptor levels and radiological progression in early rheumatoid arthritis.

OBJECTIVE: To investigate the association between serum soluble interleukin 2 receptor (sIL-2R) levels and radiological changes in patients with early rheumatoid arthritis (RA). METHODS: sIL-2R levels from 155 patients with active RA were measured by immunoassay over a 2 year period and the associations with radiological change and other measures of disease activity were analyzed. RESULTS: The area under the curve for sIL-2R is weakly associated with the change in the modified Larsen score over a 2 year period; this is weaker than the association of radiological change with serum C-reactive protein. CONCLUSION: We found no significant association of sIL-2R levels with erosive change in early RA.

Arthritis, Rheumatoid↗

PubMed2000

Measurement of the W-->taunu production cross section in pp collisions at square root s=1.8 TeV.

We report on a measurement of sigma(pp-->W+X)B(W-->taunu) in pp collisions at sqrt[s]=1.8 TeV at the Fermilab Tevatron. The measurement is based on an integrated luminosity (lum) of 18 pb-1 of data collected with the D0 detector during 1994-1995. We find that sigma(pp-->W+X)B(W-->taunu)=2.22+/-0.09 (stat)+/-0. 10 (syst)+/-0.10 (lum) nb. Lepton universality predicts that the ratio of the tau and electron electroweak charged current couplings to the W boson, gWtau/gWe, be unity. We find gWtau/gWe=0.980+/-0.031, in agreement with lepton universality.

Journal Article↗