In this study, a new idea that electrogenic transporters determine cell resting state is presented. The previous assumption was that pumps, especially the sodium one, determine it. The latter meets ...difficulties, because it violates the law of conservation of energy; also a significant deficit of pump activity is reported. The amount of energy carried by a single ATP molecule reflects the potential of the inner mitochondrial membrane, which is about −200 mV. If pumps enforce a resting membrane potential that is more than twice smaller, then the majority of energy stored in ATP would be dissipated by each pump turning. However, this problem could be solved if control is transferred from pumps to something else, e.g., electrogenic transporters. Then pumps would transfer the energy to the ionic gradient without losses, while the cell surface membrane potential would be associated with the reversal potential of some electrogenic transporters. A minimal scheme of this type would include a sodium-calcium exchanger as well as sodium and calcium pumps. However, note that calcium channels and pumps are positioned along both intracellular organelles and the surface membrane. Therefore, the above-mentioned scheme would involve them as well as possible intercellular communications. Such schemes where various kinds of pumps are assumed to work in parallel may explain, to a great extent, the slow turning rate of the individual members. Interaction of pumps and transporters positioned at distant biological membranes with various forms of energy transfer between them may thus result in hypoxic/reperfusion injury, different kinds of muscle fatigue, and nerve-glia interactions.
This article presents a general statistical mechanical approach to describe self-folding together with the hybridization between a pair of finite length DNA or RNA molecules. The model takes into ...account the entire ensemble of single- and double-stranded species in solution and their mole fractions at different temperatures. The folding and hybridization models deal with matched pairs, mismatches, symmetric and asymmetric interior loops, bulges, and single-base stacking that might exist at duplex ends or at the ends of helices. All possible conformations of the single- and double-stranded species are explored. Only intermolecular basepairs are considered in duplexes at this stage. In particular we focus on the role of stacking between neighboring nucleotide residues of single unfolded strands as an important source of enthalpy change on helix formation which has not been modeled computationally thus far. Changes in the states of the single strands with temperature are shown to lead to a larger heat effect at higher temperature. An important consequence of this is that predictions of enthalpies, which are based on databases of nearest-neighbor energy parameters determined for molecules or duplexes with lower melting temperatures compared with the melting temperatures of the oligos for which they are used as a predictive tool, will be underestimated.
The membrane transporters (pumps and co-transporters) are the main players in maintaining the cell homeostasis. Models of various types, each with their own drawbacks, describe transporter behavior. ...The aim of this study is to find the link between the biophysically based and empirical models to face and solve their specific problems. Instead of decreasing the number of states and using few complex rate constants as is usually done, we use the number of states as great as possible. Then, each transition in the cycle can represent an elementary process and we can apply the mass action law, according to which if rate constants depend on concentrations the dependence is linear. Thus, the expression for the steady state transporter current can be transformed from a function of rate constants into a function of concentrations. When transporter states form a single cycle, it can be characterized by two modes of action – forward and backward ones. Specific mode is realized depending on the available free energy. Each mode of action is characterized by a set of transporter affinities together with a parameter that describes the maximal turning rate. Except standard affinities corresponding to the substances that are binding to the transporter, affinities for the substances that are released are also defined. Such scheme provides great possibilities to construct approximations as each individual affinity could be estimated from experiments as precisely as possible. The approximations may be used for not only description and study of the transporter current but also in cellular models that attempt to describe wide variety of processes in excitable cells.
•General form of the steady state current valid for arbitrary transporter is proposed.•Expression for transporter current valid under very general assumptions is obtained.•Link between biophysically based and empirical models of pump is demonstrated.•A framework for expanding complexity of empirical models is proposed.
We have cloned, expressed, and characterized the full-length and various soluble fragments of the SARS-CoV (Tor2 isolate) S glycoprotein. Cells expressing S fused with receptor-expressing cells at ...neutral pH suggesting that the recombinant glycoprotein is functional, its membrane fusogenic activity does not require other viral proteins, and that low pH is not required for triggering membrane fusion; fusion was not observed at low receptor concentrations. S and its soluble ectodomain, S
e, were not cleaved to any significant degree. They ran at about 180–200
kDa in SDS gels suggesting post-translational modifications as predicted by previous computer analysis and observed for other coronaviruses. Fragments containing the N-terminal amino acid residues 17–537 and 272–537 but not 17–276 bound specifically to Vero E6 cells and purified soluble receptor, ACE2, recently identified by M. Farzan and co-workers Nature 426 (2003) 450–454. Together with data for inhibition of binding by antibodies developed against peptides from S, these findings suggest that the receptor-binding domain is located between amino acid residues 303 and 537. These results also confirm that ACE2 is a functional receptor for the SARS virus and may help in the elucidation of the mechanisms of SARS-CoV entry and in the development of vaccine immunogens and entry inhibitors.
A new approach for the preparation of approx. 5 nm sized ytterbium fluoride nanoparticles based on the fluorolytic sol-gel route is reported. DLS, TEM, IR and XRD were used to characterize the ...particles as well as the aging behavior of the sols. Furthermore, a new Yb(III) complex was isolated from the precursor solution and characterized by X-ray single crystal structure determination.
CMS iRPC FEB development and validation Gouzevitch, M.; El Sawy, M.; Alves, G.A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2024, Letnik:
1064
Journal Article
Recenzirano
Odprti dostop
In view of the High Luminosity upgrade of the CERN LHC, the forward CMS Muon spectrometer will be extended with two new stations of improved Resistive Plate Chambers (iRPC) covering the ...pseudorapidity range from 1.8 to 2.4. Compared to the present RPC system, the gap thickness is reduced to lower the avalanche charge, and an innovative 2D strip readout geometry is proposed. These improvements will allow iRPC detector to cope with higher background rates. A new Front-End-Board (FEB) is designed to readout iRPC signals with a threshold as low as 30fC and an integrated Time Digital Converter with a resolution of 30ps. In addition, the communication bandwidth is significantly increased by using optical fibers. The history, final design, certification, and calibration of this FEB are presented.
Pressure correction study for the CMS iRPC detector Abdelhameid, T.; Gouzevitch, M.; Tytgat, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2024, Letnik:
1059, Številka:
C
Journal Article
Machine Learning based tool for CMS RPC currents quality monitoring Shumka, E.; El Sawy, M.; Alves, G.A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2023, Letnik:
1054, Številka:
C
Journal Article
Recenzirano
Odprti dostop
The muon system of the CERN Compact Muon Solenoid (CMS) experiment includes more than a thousand Resistive Plate Chambers (RPC). They are gaseous detectors operated in the hostile environment of the ...CMS underground cavern on the Large Hadron Collider where pp luminosities of up to 2×1034cm−2s−1 are routinely achieved. The CMS RPC system performance is constantly monitored and the detector is regularly maintained to ensure stable operation. The main monitorable characteristics are dark current, efficiency for muon detection, noise rate etc. Herein we describe an automated tool for CMS RPC current monitoring which uses Machine Learning techniques. We further elaborate on the dedicated generalized linear model proposed already and add autoencoder models for self-consistent predictions as well as hybrid models to allow for RPC current predictions in a distant future.
The molten salt electrolytic method for the preparation of nano-structured carbon materials has been subjected to a systematic investigation. It has been confirmed that the electrolysis of molten ...lithium chloride in the presence of a graphite cathode generates a carbonaceous product that contains nano-structured constituents like particles, fibres and tubes. It has furthermore been found that the precise composition of the product depends critically on a number of process parameters, namely, type of graphite material, reaction temperature, electrochemical polarisation regime, and reaction time. After careful optimisation of these parameters, it has become possible to achieve a content of nanotubes in the carbonaceous product of approximately 80%. This exceeds by far the results of all previous studies using this approach. The nanotubes synthesised are multi-walled with varying diameters and highly curved, and they occur in the form of aggregates of considerable size.
The present Compact Muon Solenoid Resistive Plate Chambers system has been worked efficiently during Run I and Run II of data taking period (Shah et al., 2020) 1. In the coming years of operation ...with the High Luminosity LHC (HL-LHC), the expected rate and integrated charge are expected to be about 600 Hz/cm2 and 840 mC/cm2, respectively (including a safety factor of three). Therefore, the HL-LHC phase will be a challenge for the RPC system since the expected operating conditions are much harsher than those for which the detectors have been designed, and could introduce non-recoverable aging effects which can alter the detector properties. A longevity test has been started at the CERN Gamma Irradiation Facility to estimate the impact of HL-LHC conditions on the RPC detector performance in order to determine whether the RPC system will survive the harsher background conditions expected at HL-LHC. The latest results of the irradiation test will be presented.
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