366 research outputs found
Epidemiology of the viral hepatitis B and C in female prisoners of Metropolitan Regional Prison Complex in the State of GoiĂĄs, Central Brazil
Anterior surgical management of the cervicothoracic junction lesions at T1 and T2 vertebral bodies
The exchange activities of [Fe]Â hydrogenase (ironâsulfur-cluster-free hydrogenase) from methanogenic archaea in comparison with the exchange activities of [FeFe] and [NiFe]Â hydrogenases
[Fe]Â hydrogenase (ironâsulfur-cluster-free hydrogenase) catalyzes the reversible reduction of methenyltetrahydromethanopterin (methenyl-H4MPT+) with H2 to methylene-H4MPT, a reaction involved in methanogenesis from H2 and CO2 in many methanogenic archaea. The enzyme harbors an iron-containing cofactor, in which a low-spin iron is complexed by a pyridone, two CO and a cysteine sulfur. [Fe]Â hydrogenase is thus similar to [NiFe] and [FeFe]Â hydrogenases, in which a low-spin iron carbonyl complex, albeit in a dinuclear metal center, is also involved in H2 activation. Like the [NiFe] and [FeFe]Â hydrogenases, [Fe]Â hydrogenase catalyzes an active exchange of H2 with protons of water; however, this activity is dependent on the presence of the hydride-accepting methenyl-H4MPT+. In its absence the exchange activity is only 0.01% of that in its presence. The residual activity has been attributed to the presence of traces of methenyl-H4MPT+ in the enzyme preparations, but it could also reflect a weak binding of H2 to the iron in the absence of methenyl-H4MPT+. To test this we reinvestigated the exchange activity with [Fe]Â hydrogenase reconstituted from apoprotein heterologously produced in Escherichia coli and highly purified iron-containing cofactor and found that in the absence of added methenyl-H4MPT+ the exchange activity was below the detection limit of the tritium method employed (0.1Â nmol minâ1Â mgâ1). The finding reiterates that for H2 activation by [Fe]Â hydrogenase the presence of the hydride-accepting methenyl-H4MPT+ is essentially required. This differentiates [Fe]Â hydrogenase from [FeFe] and [NiFe]Â hydrogenases, which actively catalyze H2/H2O exchange in the absence of exogenous electron acceptors
Recommended from our members
Luminosity determination using Z boson production at the CMS experiment
Data Availability Statement - This manuscript has no associated data or
the data will not be deposited. [Authorsâ comment: Release and preser
vation of data used by the CMS Collaboration as the basis for publi
cations is guidedbytheCMSpolicyasstatedinhttps://cms-docdb.cern.
ch/cgibin/PublicDocDB/RetrieveFile?docid=6032&filename=CMSD
ataPolicyV1.2.pdf&version=2. CMS data preservation,re-use and open
access policy.]The measurement of ZÂ boson production is presented as a method to determine the integrated luminosity of CMS data sets. The analysis uses protonâproton collision data, recorded by the CMS experiment at the CERN LHC in 2017 at a center-of-mass energy of 13 TeV . Events with ZÂ bosons decaying into a pair of muons are selected. The total number of ZÂ bosons produced in a fiducial volume is determined, together with the identification efficiencies and correlations from the same data set, in small intervals of 20 pb-1 of integrated luminosity, thus facilitating the efficiency and rate measurement as a function of time and instantaneous luminosity. Using the ratio of the efficiency-corrected numbers of ZÂ bosons, the precisely measured integrated luminosity of one data set is used to determine the luminosity of another. For the first time, a full quantitative uncertainty analysis of the use of Z bosons for the integrated luminosity measurement is performed. The uncertainty in the extrapolation between two data sets, recorded in 2017 at low and high instantaneous luminosity, is less than 0.5%. We show that the ZÂ boson rate measurement constitutes a precise method, complementary to traditional methods, with the potential to improve the measurement of the integrated luminosity.SCOAP
Recommended from our members
Search for nonresonant Higgs boson pair production in the four leptons plus two b jets final state in proton-proton collisions at = 13 TeV
A preprint version of the article is available at arXiv:2206.10657v2 [hep-ex], https://arxiv.org/abs/2206.10657 . Comments: Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at this http URL (CMS Public Pages). Report number: CMS-HIG-20-004, CERN-EP-2022-114.The first search for nonresonant production of Higgs boson pairs (HH) with one H decaying into four leptons and the other into a pair of b quarks is presented, using proton-proton collisions recorded at a center-of-mass energy of s = 13 TeV by the CMS experiment. The analyzed data correspond to an integrated luminosity of 138 fbâ1. A 95% confidence level upper limit of 32.4 is set on the signal strength modifier ÎŒ, defined as the ratio of the observed HH production rate in the HHâ ZZâb b ÂŻ â 4 âb b ÂŻ decay channel to the standard model (SM) expectation. Possible modifications of the H trilinear coupling λ HHH with respect to the SM value are investigated. The coupling modifier Îșλ, defined as λ HHH divided by its SM prediction, is constrained to be within the observed (expected) range â8.8 (â9.8) < Îșλ < 13.4 (15.0) at 95% confidence level. [Figure not available: see fulltext.].SCOAP3
Recommended from our members
Search for long-lived particles decaying to a pair of muons in proton-proton collisions at âs = 13 TeV
A preprint version of the article is available at arXiv:2205.08582v2 [hep-ex], https://arxiv.org/abs/2205.08582 . Comments: Replaced with the published version. Added the journal reference and the DOI. All the figures and tables, including additional supplementary figures and tables, can be found at https://cms-results.web.cern.ch/cms-results/public-results/publications/EXO-21-006 (CMS Public Pages).An inclusive search for long-lived exotic particles decaying to a pair of muons is presented. The search uses data collected by the CMS experiment at the CERN LHC in proton-proton collisions at s = 13 TeV in 2016 and 2018 and corresponding to an integrated luminosity of 97.6 fbâ1. The experimental signature is a pair of oppositely charged muons originating from a common secondary vertex spatially separated from the pp interaction point by distances ranging from several hundred ÎŒm to several meters. The results are interpreted in the frameworks of the hidden Abelian Higgs model, in which the Higgs boson decays to a pair of long-lived dark photons ZD, and of a simplified model, in which long-lived particles are produced in decays of an exotic heavy neutral scalar boson. For the hidden Abelian Higgs model with m(ZD) greater than 20 GeV and less than half the mass of the Higgs boson, they provide the best limits to date on the branching fraction of the Higgs boson to dark photons for cÏ(ZD) (varying with m(ZD)) between 0.03 and â0.5 mm, and above â0.5 m. Our results also yield the best constraints on long-lived particles with masses larger than 10 GeV produced in decays of an exotic scalar boson heavier than the Higgs boson and decaying to a pair of muons. [Figure not available: see fulltext.].SCOAP3
- âŠ