Displaying publications 41 - 60 of 120 in total

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  1. Heo HY, Tee YK, Harston G, Leigh R, Chappell MA
    NMR Biomed, 2023 Jun;36(6):e4734.
    PMID: 35322482 DOI: 10.1002/nbm.4734
    Amide proton transfer (APT) imaging, a variant of chemical exchange saturation transfer MRI, has shown promise in detecting ischemic tissue acidosis following impaired aerobic metabolism in animal models and in human stroke patients due to the sensitivity of the amide proton exchange rate to changes in pH within the physiological range. Recent studies have demonstrated the possibility of using APT-MRI to detect acidosis of the ischemic penumbra, enabling the assessment of stroke severity and risk of progression, monitoring of treatment progress, and prognostication of clinical outcome. This paper reviews current APT imaging methods actively used in ischemic stroke research and explores the clinical aspects of ischemic stroke and future applications for these methods.
    Matched MeSH terms: Protons
  2. Msayib Y, Harston GWJ, Tee YK, Sheerin F, Blockley NP, Okell TW, et al.
    Neuroimage Clin, 2019;23:101833.
    PMID: 31063943 DOI: 10.1016/j.nicl.2019.101833
    BACKGROUND: Amide proton transfer (APT) imaging may help identify the ischaemic penumbra in stroke patients, the classical definition of which is a region of tissue around the ischaemic core that is hypoperfused and metabolically stressed. Given the potential of APT imaging to complement existing imaging techniques to provide clinically-relevant information, there is a need to develop analysis techniques that deliver a robust and repeatable APT metric. The challenge to accurate quantification of an APT metric has been the heterogeneous in-vivo environment of human tissue, which exhibits several confounding magnetisation transfer effects including spectrally-asymmetric nuclear Overhauser effects (NOEs). The recent literature has introduced various model-free and model-based approaches to analysis that seek to overcome these limitations.

    OBJECTIVES: The objective of this work was to compare quantification techniques for CEST imaging that specifically separate APT and NOE effects for application in the clinical setting. Towards this end a methodological comparison of different CEST quantification techniques was undertaken in healthy subjects, and around clinical endpoints in a cohort of acute stroke patients.

    METHODS: MRI data from 12 patients presenting with ischaemic stroke were retrospectively analysed. Six APT quantification techniques, comprising model-based and model-free techniques, were compared for repeatability and ability for APT to distinguish pathological tissue in acute stroke.

    RESULTS: Robustness analysis of six quantification techniques indicated that the multi-pool model-based technique had the smallest contrast between grey and white matter (2%), whereas model-free techniques exhibited the highest contrast (>30%). Model-based techniques also exhibited the lowest spatial variability, of which 4-pool APTR∗ was by far the most uniform (10% coefficient of variation, CoV), followed by 3-pool analysis (20%). Four-pool analysis yielded the highest ischaemic core contrast-to-noise ratio (0.74). Four-pool modelling of APT effects was more repeatable (3.2% CoV) than 3-pool modelling (4.6% CoV), but this appears to come at the cost of reduced contrast between infarct growth tissue and normal tissue.

    CONCLUSION: The multi-pool measures performed best across the analyses of repeatability, spatial variability, contrast-to-noise ratio, and grey matter-white matter contrast, and might therefore be more suitable for use in clinical imaging of acute stroke. Addition of a fourth pool that separates NOEs and semisolid effects appeared to be more biophysically accurate and provided better separation of the APT signal compared to the 3-pool equivalent, but this improvement appeared be accompanied by reduced contrast between infarct growth tissue and normal tissue.

    Matched MeSH terms: Protons*
  3. Abbasi MA, Ijaz M, Aziz-Ur-Rehman -, Siddiqui SZ, Ali Shah SA, Shahid M, et al.
    Pak J Pharm Sci, 2020 Jul;33(4):1609-1616.
    PMID: 33583794
    In the planned research work, the nucleophilic substitution reaction of 1-[(E)-3-phenyl-2-propenyl]piperazine (1) was carried out with different sulfonyl chlorides (2a-g) at pH 9-10 to synthesize its different N-sulfonated derivatives (3a-g). The structures of the synthesized compounds were characterized by their proton-nuclear magnetic resonance (1H-NMR), carbon-nuclear magnetic resonance (13C-NMR) and Infra Red (IR) spectral data, along with CHN analysis. The inhibition potential of the synthesized molecules was ascertained against two bacterial pathogenic strains i.e. Bacillus subtilis and Escherichia coli. It was inferred from the results that some of the compounds were very suitable inhibitors of these bacterial strains. Moreover, their cytotoxicity was also profiled and it was outcome that most of these molecules possessed moderate cytotoxicity.
    Matched MeSH terms: Protons
  4. Ishola, K. S., Adeoti, L., Sawyerr, F., Adiat, K. A. N
    MyJurnal
    Detailed geophysical investigations have been carried out using integrated geophysical methods with a view to characterising the subsurface lithologic features that might indicate suitable places for structural developments. An overview of the subsurface resistivity distribution has been achieved employing 8Vertical Electrical Soundings with the Schlumberger array and 4 2D resistivity imaging using Wenner array. In order to constrain the results of the electrical resistivity methods, we carried out a ground magnetic survey along E-W direction using the Proton precession magnetometer at 1m sampling interval. Analysis of well logs data available and VES results showed 4 to 5 geoelectric layers corresponding to sand, clayey sand, clay, silty sand and sandy clay. The 2D resistivity imaging sections showed relative decrease of apparent resistivity with depth implying a geological transition from sand with high resistivity value of about 508Ωm to clay with low resistivity value 16Ωm at depths of 0-20m and 25-50m respectively. The magnetic profiles showed that the study area was characterised by short wavelengths and amplitudes ranging from –3800 to 700 nT. The highs and lows of the magnetic responses occasioned by lithological variations and structural features were magnetically resolved. In view of the identified subsurface structures, the suggested depth to the competent layer is about 20m for low to medium structures while above 50m would be suitable for heavy or massive engineering structures. The use of integrated geophysical methods for the delineation, identification and imaging of the subsurface geological structures which could provide clues to the nature and type of foundation suitable for the development of the study area has been successfully achieved.
    Matched MeSH terms: Protons
  5. Oh AL, Tan AG, Phan HS, Lee BC, Jumaat N, Chew SP, et al.
    Pharm Pract (Granada), 2015 Apr-Jun;13(3):633.
    PMID: 26445624 DOI: 10.18549/PharmPract.2015.03.633
    Proton-pump inhibitors (PPI) and histamine-2 receptor antagonists (H2RA) are common acid suppressants used in gastrointestinal disorders. The trend of usage in Malaysia has changed from predominantly H2RA to PPI from 2007 to 2008, 3.46 versus 2.87 and 2.99 versus 3.24 DDD (Defined Daily Dose)/1000 population/day respectively. This raises concerns as PPI overutilization amounts to higher cost expenditure and are associated with various untoward consequences such as Clostridium difficile-associated diarrhea, pneumonia, and osteoporosis.
    Matched MeSH terms: Protons
  6. Khachatryan V, Sirunyan AM, Tumasyan A, Adam W, Bergauer T, Dragicevic M, et al.
    Phys Rev Lett, 2015 Feb 13;114(6):061801.
    PMID: 25723204
    A search for new long-lived particles decaying to leptons is presented using proton-proton collisions produced by the LHC at √[s]=8  TeV. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 19.7  fb(-1). Events are selected with an electron and muon with opposite charges that both have transverse impact parameter values between 0.02 and 2 cm. The search has been designed to be sensitive to a wide range of models with nonprompt e-μ final states. Limits are set on the "displaced supersymmetry" model, with pair production of top squarks decaying into an e-μ final state via R-parity-violating interactions. The results are the most restrictive to date on this model, with the most stringent limit being obtained for a top squark lifetime corresponding to cτ=2  cm, excluding masses below 790 GeV at 95% confidence level.
    Matched MeSH terms: Protons
  7. Chatrchyan S, Khachatryan V, Sirunyan AM, Tumasyan A, Adam W, Bergauer T, et al.
    Phys Rev Lett, 2014 Apr 25;112(16):161802.
    PMID: 24815637
    Results are presented of a search for a "natural" supersymmetry scenario with gauge mediated symmetry breaking. It is assumed that only the supersymmetric partners of the top quark (the top squark) and the Higgs boson (Higgsino) are accessible. Events are examined in which there are two photons forming a Higgs boson candidate, and at least two b-quark jets. In 19.7  fb-1 of proton-proton collision data at s=8  TeV, recorded in the CMS experiment, no evidence of a signal is found and lower limits at the 95% confidence level are set, excluding the top squark mass below 360 to 410 GeV, depending on the Higgsino mass.
    Matched MeSH terms: Protons
  8. Khachatryan V, Sirunyan AM, Tumasyan A, Adam W, Asilar E, Bergauer T, et al.
    Phys Rev Lett, 2016 Feb 19;116(7):071801.
    PMID: 26943527 DOI: 10.1103/PhysRevLett.116.071801
    A search for narrow resonances in proton-proton collisions at sqrt[s]=13  TeV is presented. The invariant mass distribution of the two leading jets is measured with the CMS detector using a data set corresponding to an integrated luminosity of 2.4  fb^{-1}. The highest observed dijet mass is 6.1 TeV. The distribution is smooth and no evidence for resonant particles is observed. Upper limits at 95% confidence level are set on the production cross section for narrow resonances with masses above 1.5 TeV. When interpreted in the context of specific models, the limits exclude string resonances with masses below 7.0 TeV, scalar diquarks below 6.0 TeV, axigluons and colorons below 5.1 TeV, excited quarks below 5.0 TeV, color-octet scalars below 3.1 TeV, and W^{'} bosons below 2.6 TeV. These results significantly extend previously published limits.
    Matched MeSH terms: Protons
  9. Khachatryan V, Sirunyan AM, Tumasyan A, Adam W, Asilar E, Bergauer T, et al.
    Phys Rev Lett, 2016 Jan 22;116(3):032301.
    PMID: 26849587 DOI: 10.1103/PhysRevLett.116.032301
    The production cross sections of the B^{+}, B^{0}, and B_{s}^{0} mesons, and of their charge conjugates, are measured via exclusive hadronic decays in p+Pb collisions at the center-of-mass energy sqrt[s_{NN}]=5.02  TeV with the CMS detector at the CERN LHC. The data set used for this analysis corresponds to an integrated luminosity of 34.6  nb^{-1}. The production cross sections are measured in the transverse momentum range between 10 and 60  GeV/c. No significant modification is observed compared to proton-proton perturbative QCD calculations scaled by the number of incoherent nucleon-nucleon collisions. These results provide a baseline for the study of in-medium b quark energy loss in Pb+Pb collisions.
    Matched MeSH terms: Protons
  10. Khachatryan V, Sirunyan AM, Tumasyan A, Adam W, Bergauer T, Dragicevic M, et al.
    Phys Rev Lett, 2015 Mar 13;114(10):101801.
    PMID: 25815923
    Results are presented from a search for new decaying massive particles whose presence is inferred from an imbalance in transverse momentum and which are produced in association with a single top quark that decays into a bottom quark and two light quarks. The measurement is performed using 19.7  fb^{-1} of data from proton-proton collisions at a center-of-mass energy of 8 TeV, collected with the CMS detector at the CERN LHC. No deviations from the standard model predictions are observed and lower limits are set on the masses of new invisible bosons. In particular, scalar and vector particles, with masses below 330 and 650 GeV, respectively, are excluded at 95% confidence level, thereby substantially extending a previous limit published by the CDF Collaboration.
    Matched MeSH terms: Protons
  11. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys Rev Lett, 2020 Sep 04;125(10):102001.
    PMID: 32955327 DOI: 10.1103/PhysRevLett.125.102001
    The first study of charm quark diffusion with respect to the jet axis in heavy ion collisions is presented. The measurement is performed using jets with p_{T}^{jet}>60  GeV/c and D^{0} mesons with p_{T}^{D}>4  GeV/c in lead-lead (Pb-Pb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of sqrt[s_{NN}]=5.02  TeV, recorded by the CMS detector at the LHC. The radial distribution of D^{0} mesons with respect to the jet axis is sensitive to the production mechanisms of the meson, as well as to the energy loss and diffusion processes undergone by its parent parton inside the strongly interacting medium produced in Pb-Pb collisions. When compared to Monte Carlo event generators, the radial distribution in pp collisions is found to be well described by pythia, while the slope of the distribution predicted by sherpa is steeper than that of the data. In Pb-Pb collisions, compared to the pp results, the D^{0} meson distribution for 4
    Matched MeSH terms: Protons
  12. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Bergauer T, Dragicevic M, et al.
    Phys Rev Lett, 2020 Oct 09;125(15):152001.
    PMID: 33095627 DOI: 10.1103/PhysRevLett.125.152001
    Using a data sample of proton-proton collisions at sqrt[s]=13  TeV, corresponding to an integrated luminosity of 140  fb^{-1} collected by the CMS experiment in 2016-2018, the B_{s}^{0}→X(3872)ϕ decay is observed. Decays into J/ψπ^{+}π^{-} and K^{+}K^{-} are used to reconstruct, respectively, the X(3872) and ϕ. The ratio of the product of branching fractions B[B_{s}^{0}→X(3872)ϕ]B[X(3872)→J/ψπ^{+}π^{-}] to the product B[B_{s}^{0}→ψ(2S)ϕ]B[ψ(2S)→J/ψπ^{+}π^{-}] is measured to be [2.21±0.29(stat)±0.17(syst)]%. The ratio B[B_{s}^{0}→X(3872)ϕ]/B[B^{0}→X(3872)K^{0}] is found to be consistent with one, while the ratio B[B_{s}^{0}→X(3872)ϕ]/B[B^{+}→X(3872)K^{+}] is two times smaller. This suggests a difference in the production dynamics of the X(3872) in B^{0} and B_{s}^{0} meson decays compared to B^{+}. The reported observation may shed new light on the nature of the X(3872) particle.
    Matched MeSH terms: Protons
  13. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys Rev Lett, 2018 May 18;120(20):202005.
    PMID: 29864318 DOI: 10.1103/PhysRevLett.120.202005
    A search for resonancelike structures in the B_{s}^{0}π^{±} invariant mass spectrum is performed using proton-proton collision data collected by the CMS experiment at the LHC at sqrt[s]=8  TeV, corresponding to an integrated luminosity of 19.7  fb^{-1}. The B_{s}^{0} mesons are reconstructed in the decay chain B_{s}^{0}→J/ψϕ, with J/ψ→μ^{+}μ^{-} and ϕ→K^{+}K^{-}. The B_{s}^{0}π^{±} invariant mass distribution shows no statistically significant peaks for different selection requirements on the reconstructed B_{s}^{0} and π^{±} candidates. Upper limits are set on the relative production rates of the X(5568) and B_{s}^{0} states times the branching fraction of the decay X(5568)^{±}→B_{s}^{0}π^{±}. In addition, upper limits are obtained as a function of the mass and the natural width of possible exotic states decaying into B_{s}^{0}π^{±}.
    Matched MeSH terms: Protons
  14. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys Rev Lett, 2018 May 18;120(20):201801.
    PMID: 29864370 DOI: 10.1103/PhysRevLett.120.201801
    A search for narrow resonances decaying to bottom quark-antiquark pairs is presented, using a data sample of proton-proton collisions at sqrt[s]=8  TeV corresponding to an integrated luminosity of 19.7  fb^{-1}. The search is extended to masses lower than those reached in typical searches for resonances decaying into jet pairs at the LHC, by taking advantage of triggers that identify jets originating from bottom quarks. No significant excess of events is observed above the background predictions. Limits are set on the product of cross section and branching fraction to bottom quarks for spin 0, 1, and 2 resonances in the mass range of 325-1200 GeV. These results improve on the limits for resonances decaying into jet pairs in the 325-500 GeV mass range.
    Matched MeSH terms: Protons
  15. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys Rev Lett, 2018 Dec 14;121(24):241802.
    PMID: 30608761 DOI: 10.1103/PhysRevLett.121.241802
    Three of the most significant measured deviations from standard model predictions, the enhanced decay rate for B→D^{(*)}τν, hints of lepton universality violation in B→K^{(*)}ℓℓ decays, and the anomalous magnetic moment of the muon, can be explained by the existence of leptoquarks (LQs) with large couplings to third-generation quarks and masses at the TeV scale. The existence of these states can be probed at the LHC in high energy proton-proton collisions. A novel search is presented for pair production of LQs coupled to a top quark and a muon using data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9  fb^{-1}, recorded by the CMS experiment. No deviation from the standard model prediction has been observed and scalar LQs decaying exclusively into tμ are excluded up to masses of 1420 GeV. The results of this search are combined with those from previous searches for LQ decays into tτ and bν, which excluded scalar LQs below masses of 900 and 1080 GeV. Vector LQs are excluded up to masses of 1190 GeV for all possible combinations of branching fractions to tμ, tτ and bν. With this analysis, all relevant couplings of LQs with an electric charge of -1/3 to third-generation quarks are probed for the first time.
    Matched MeSH terms: Protons
  16. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys Rev Lett, 2018 Nov 30;121(22):221802.
    PMID: 30547617 DOI: 10.1103/PhysRevLett.121.221802
    The first evidence of events consistent with the production of a single top quark in association with a photon is reported. The analysis is based on proton-proton collisions at sqrt[s]=13  TeV and recorded by the CMS experiment in 2016, corresponding to an integrated luminosity of 35.9  fb^{-1}. Events are selected by requiring the presence of a muon (μ), a photon (γ), an imbalance in transverse momentum from an undetected neutrino (ν), and at least two jets (j) of which exactly one is identified as associated with the hadronization of a b quark. A multivariate discriminant based on topological and kinematic event properties is employed to separate signal from background processes. An excess above the background-only hypothesis is observed, with a significance of 4.4 standard deviations. A fiducial cross section is measured for isolated photons with transverse momentum greater than 25 GeV in the central region of the detector. The measured product of the cross section and branching fraction is σ(pp→tγj)B(t→μνb)=115±17(stat)±30(syst)  fb, which is consistent with the standard model prediction.
    Matched MeSH terms: Protons
  17. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Bergauer T, Dragicevic M, et al.
    Phys Rev Lett, 2020 Oct 09;125(15):151802.
    PMID: 33095594 DOI: 10.1103/PhysRevLett.125.151802
    The first observation is reported of the combined production of three massive gauge bosons (VVV with V=W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV. The analysis is based on a data sample recorded by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 137  fb^{-1}. The searches for individual WWW, WWZ, WZZ, and ZZZ production are performed in final states with three, four, five, and six leptons (electrons or muons), or with two same-sign leptons plus one or two jets. The observed (expected) significance of the combined VVV production signal is 5.7 (5.9) standard deviations and the corresponding measured cross section relative to the standard model prediction is 1.02_{-0.23}^{+0.26}. The significances of the individual WWW and WWZ production are 3.3 and 3.4 standard deviations, respectively. Measured production cross sections for the individual triboson processes are also reported.
    Matched MeSH terms: Protons
  18. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Bergauer T, Dragicevic M, et al.
    Phys Rev Lett, 2020 Nov 27;125(22):222001.
    PMID: 33315428 DOI: 10.1103/PhysRevLett.125.222001
    Ultrarelativistic heavy ion collisions recreate in the laboratory the thermodynamical conditions prevailing in the early universe up to 10^{-6}  sec, thereby allowing the study of the quark-gluon plasma (QGP), a state of quantum chromodynamics (QCD) matter with deconfined partons. The top quark, the heaviest elementary particle known, is accessible in nucleus-nucleus collisions at the CERN LHC, and constitutes a novel probe of the QGP. Here, we report the first evidence for the production of top quarks in nucleus-nucleus collisions, using lead-lead collision data at a nucleon-nucleon center-of-mass energy of 5.02 TeV recorded by the CMS experiment. Two methods are used to measure the cross section for top quark pair production (σ_{tt[over ¯]}) via the selection of charged leptons (electrons or muons) and bottom quarks. One method relies on the leptonic information alone, and the second one exploits, in addition, the presence of bottom quarks. The measured cross sections, σ_{tt[over ¯]}=2.54_{-0.74}^{+0.84} and 2.03_{-0.64}^{+0.71}  μb, respectively, are compatible with expectations from scaled proton-proton data and QCD predictions.
    Matched MeSH terms: Protons
  19. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys Rev Lett, 2019 Mar 29;122(12):121803.
    PMID: 30978057 DOI: 10.1103/PhysRevLett.122.121803
    This Letter describes a search for Higgs boson pair production using the combined results from four final states: bbγγ, bbττ, bbbb, and bbVV, where V represents a W or Z boson. The search is performed using data collected in 2016 by the CMS experiment from LHC proton-proton collisions at sqrt[s]=13  TeV, corresponding to an integrated luminosity of 35.9  fb^{-1}. Limits are set on the Higgs boson pair production cross section. A 95% confidence level observed (expected) upper limit on the nonresonant production cross section is set at 22.2 (12.8) times the standard model value. A search for narrow resonances decaying to Higgs boson pairs is also performed in the mass range 250-3000 GeV. No evidence for a signal is observed, and upper limits are set on the resonance production cross section.
    Matched MeSH terms: Protons
  20. Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, et al.
    Phys Rev Lett, 2019 Apr 19;122(15):151802.
    PMID: 31050519 DOI: 10.1103/PhysRevLett.122.151802
    For the first time, a search for the rare decay of the W boson to three charged pions has been performed. Proton-proton collision data recorded by the CMS experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 77.3  fb^{-1}, have been analyzed. No significant excess is observed above the background expectation. An upper limit of 1.01×10^{-6} is set at 95% confidence level on the branching fraction of the W boson to three charged pions. This provides a strong motivation for theoretical calculations of this branching fraction.
    Matched MeSH terms: Protons
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