83 research outputs found
Semi-Inclusive Distributions in Statistical Models
The semi-inclusive properties of the system of neutral and charged particles
with net charge equal to zero are considered in the grand canonical, canonical
and micro-canonical ensembles as well as in micro-canonical ensemble with
scaling volume fluctuations. Distributions of neutral particle multiplicity and
charged particle momentum are calculated as a function of the number of charged
particles. Different statistical ensembles lead to qualitatively different
dependencies. They are being compared with the corresponding experimental data
on multi-hadron production in interactions at high energies.Comment: Two subsections are added: "Average multiplicities, fluctuations and
correlations" and "Quantum statistics
Power Law in Micro-Canonical Ensemble with Scaling Volume Fluctuations
Volume fluctuations are introduced in a statistical modelling of relativistic
particle collisions. The micro-canonical ensemble is used, and the volume
fluctuations are assumed to have the specific scaling properties. This leads to
the KNO scaling of the particle multiplicity distributions as measured in p+p
interactions. A striking prediction of the model is a power law form of the
single particle momentum spectrum at high momenta. Moreover, the mean
multiplicity of heavy particles also decreases as a function of the particle
mass according to a power law. Finally, it is shown that the dependence of the
momentum spectrum on the particle mass and momentum reduces to the dependence
on the particle energy. These results resemble the properties of particle
production in collisions of high energy particles
Charged-Particle Multiplicity in Proton-Proton Collisions
This article summarizes and critically reviews measurements of
charged-particle multiplicity distributions and pseudorapidity densities in
p+p(pbar) collisions between sqrt(s) = 23.6 GeV and sqrt(s) = 1.8 TeV. Related
theoretical concepts are briefly introduced. Moments of multiplicity
distributions are presented as a function of sqrt(s). Feynman scaling, KNO
scaling, as well as the description of multiplicity distributions with a single
negative binomial distribution and with combinations of two or more negative
binomial distributions are discussed. Moreover, similarities between the energy
dependence of charged-particle multiplicities in p+p(pbar) and e+e- collisions
are studied. Finally, various predictions for pseudorapidity densities, average
multiplicities in full phase space, and multiplicity distributions of charged
particles in p+p(pbar) collisions at the LHC energies of sqrt(s) = 7 TeV, 10
TeV, and 14 TeV are summarized and compared.Comment: Invited review for Journal of Physics G -- version 2: version after
referee's comment
Opportunities in multimodal neuroimaging for optimizing thrombolytic therapy for ischemic stroke
The main purpose of examination of patients before thrombolytic therapy for ischemic stroke (IS) is to timely identify contraindications to the use of recombinant tissue plasminogen activator.Objective: to estimate opportunities and benefits in applying multimodal magnetic resonance imaging (MRI) to improve clinical outcomes in acute stroke, among other processes, by enhancing the efficiency and safety of thrombolytic therapy.Patients and methods. The clinical experience of the S.M. Kirov Military Medical Academy in using multimodal MRI of the brain since 2004 was analyzed in patients with stroke.Results. Comprehensive assessment of the results of perfusion-weighted MRI of the brain and those of transcranial Doppler ultrasound identified five clinically significant variants of perfusion changes in IS: normal perfusion; postischemic hyperemia; persistent hypoperfusion; acute pathological hyperperfusion, and unrecovered perfusion. With an irreversible tissue damage volume of >60 cm3 on day 1 of stroke, as evidenced by diffusion-weighted MRI, the odd ratio for cerebral edema in the acutest period of the disease is 39.4% (95% CI 2.57–2436; p<0.05). The risk of hemorrhagic transformation increases with a measured diffusion coefficient in the area of the nucleus of developing nonlacunar infarct <35×10-5 mm2/sec within the first 24 hours after disease onset (p<0.005).Conclusion. The data of local clinical practice and the results of international clinical trials show that multimodal MRI of the brain is a reliable tool for the detailed evaluation of the expected efficiency and safety of thrombolytic therapy for IS. When persistent hypoperfusion is detected, the determination of perfusion-diffusion mismatch is of no informative value in deciding on whether thrombolytic therapy can be performed. Estimating the volume of pathological changes on diffusion-weighted images and the measured diffusion coefficient in the area of the nucleus of developing nonlacunar infarct in the measured diffusion coefficient maps allows the risk of major intracranial complications due to IS to be identified
Results of thrombectomy in lower-extremity ischemia in patients with COVID-19 and respiratory failure of different severity
Aim. To analyze the results of thrombectomy in lower-extremity ischemia in patients with coronavirus disease 2019 (COVID-19) and respiratory failure of different severity.Material and methods. This retrospective, cohort, comparative study for the period from May 1, 2020 to March 1, 2022 included 305 patients with acute lower-extremity ischemia and COVID-19. Depending on the type of oxygen support, three groups of patients were formed: group 1 (n=168) — nasal oxygen insufflation; group 2 (n=92) — non-invasive ventilation (NIV); group 3 (n=45) — artificial ventilation (AV). Thrombectomy was carried out according to the standard technique using Fogarty catheters (3F-6F — depending on the vessel size). After the diagnosis was established before and after the start of surgical treatment, all patients received the following therapy: Unfractionated IV heparin infusion at an initial rate of 1000 U/r, adjusted to maintain the activated partial thromboplastin time at 2-3 times the normal value; 2. Oral acetylsalicylic acid 125 mg; 3. Analgesics.Results. Myocardial infarction and ischemic stroke were not detected in the total sample. The highest number of deaths (group 1: 5,3%, n=9; group 2: 72,8%, n=67; group 3: 100%, n=45; p<0,0001), retrombosis (group 1 : 18,4%, n=31; group 2: 69,5%, n=64; group 3: 91,1%, n=41; p<0,0001) and limb amputations (group 1: 9,5%, n=16; group 2: 56,5%, n=52; group 3: 91,1%, n=41; p<0,0001) was recorded in group 3 patients.Conclusion. In patients receiving mechanical ventilation, COVID-19 have more aggressive course, which is expressed in an increase in laboratory para- meters (C-reactive protein, ferritin, interleukin-6, D-dimer), the severity of pneumonia and location of thrombosis in the tibial arteries. Among patients with COVID-19 receiving mechanical ventilation, the greatest number of rethromboses (91,1%), limb amputations (91,1%), and deaths (100%) are noted, which suggests the expediency of abandoning open thrombectomy in favor of anticoagulant/antiplatelet therapy in this cohort of patients. The development of arterial thrombosis in patients with COVID-19 receiving mechanical ventilation is an indicator of a high risk of death. Open thrombectomy in combination with anticoagulant/antiplatelet therapy is most effective in patients on nasal oxygen insufflation or NIV
Lambda hyperons produced in central nucleus-nucleus interactions at 4.5 GeV/c momentum per incident nucleon
Transverse momenta and rapidities of Lambda 's produced in central nucleus-nucleus collisions at 4.5 GeV/c·u (C-C,...,O-Pb) were studied and compared with those from inelastic He-Li interactions at the same incident momentum. Polarization of the Lambda hyperons was found to be consistent with zero ( alpha P=-0.06=0.11 for Lambda 's from central collisions). An upper limit of the Lambda -bar / Lambda production ratio was estimated to be less than 4.5 x 10-3. The experiment was performed in a triggered streamer chamber
Hadronization in Z0 decay
The confinement transition from the quark and gluon degrees of freedom
appropriate in perturbation theory to the hadrons observed by real world
experiments is poorly understood. In this strongly interacting transition
regime we presently rely on models, which to varying degrees reflect possible
scenarios for the QCD dynamics. Because of the absence of beam and target
remnants, and the clean experimental conditions and high event rates, e+e-
annihilation to hadrons at the Z0 provides a unique laboratory, both
experimentally and theoretically, for the study of parton hadronization. This
review discusses current theoretical understanding of the hadronization of
partons, with particular emphasis on models of the non-perturbative phase, as
implemented in Monte Carlo simulation programs. Experimental results at LEP and
SLC are summarised and considered in the light of the models. Suggestions are
given for further measurements which could help to produce more progress in
understanding hadronization.Comment: Topical review, to appear in J.Phys.G, 80 page
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