290 research outputs found
Changes in the human blood coagulating system during prolonged hypokinesia
Changes in the coagulating system of the blood were studied in six subjects during prolonged hypokinesia. Thrombogenic properties of the blood rose in all cases on the 8th day. These changes are explained by stress reaction due to unusual conditions for a healthy person. Changes in the blood coagulating system in the group subjected to physical exercise and without it ran a practically parallel course. Apparently physical exercise is insufficient to prevent such changes that appear in the coagulating system of the blood during prolonged hypokinesia
Новые поликарбонатсилоксаны на основе силоксан-N-фталимидинов
Objectives. Polymeric carbonate siloxanes containing a siloxane-N-phthalimidine group in the chain frame are new synthetic comb-like macromolecule systems. This work aims to study the possibility of applying them in the form of film materials for heat-resistant, high-performance gas-permeable membranes.Methods. Comb-like polycarbonate siloxanes of the siloxane-containing polyether class were obtained using various polycondensation methods. i.e., by the polymer-analogous transformation of polycarbonate-allyl-N-phthalimidines, using their reaction in an alkyl hydride siloxane solution; polycondensation of N-(3-(pentamethyldisiloxane)-propyl)-3,3-bis-(4'-hydroxyphenyl)phthalimidine with diphenylolpropane bis-chloroformate in a solution using triethylamine as an acceptor of hydrochloric acid; interphase polycondensation of the above reagents in a dichloromethane aqueous alkali system. The structures of the obtained initial and polymeric compounds were confirmed by proton nuclear magnetic resonance spectroscopy and elemental analysis. All of the synthesized comb-like copolymers had good solubility in several available solvents and film formations.Results. The new comb-like polycarbonate siloxanes had high thermal stability. According to thermogravimetric analysis, the introduction of up to 20 wt % siloxane units makes it possible to increase the heat resistance of polycarbonate siloxanes by 25 °C. Concurrently, their glasstransition temperature reaches 160 °C. Copolymers of polycarbonate siloxanes in the form of films have a high tensile strength above 50 MPa and an elastic modulus of up to 2000 MPa. The permeability coefficients of gases through a copolymer of polycarbonate siloxanes in the form of a film for several gases surpass the permeability of industrial polycarbonate from diphenylolpropane and fluorine-containing siloxane polycarbonate.Conclusions. The results achieved indicate the possibility of creating new polymeric combshaped siloxane systems with a variable structure that can contribute to obtaining the properties desired from them. Combined with high selectivity gas separation, this makes it possible to use such comb-shaped polycarbonate siloxanes as film membrane materials with an increased operating temperature range.Цели. Полимерные карбонатсилоксаны, содержащие в обрамлении цепи силоксан-N-фталимидиновую группировку, являются новыми синтетическими гребнеобразными системами макромолекул. Цель работы – изучить возможность их применения в виде пленочных материалов для термостойких высокоэффективных газопроницаемых мембран.Методы. Гребнеобразные поликарбонатсилоксаны класса силоксан-содержащих полиэфиров были получены различными поликонденсационными методами: полимераналогичным превращением поликарбонат-аллил-N-фталимидинов их реакцией в растворе с алкилгидридсилоксанами; поликонденсацией N-(3-(пентаметилдисилокси)-пропил)-3,3-бис-(4'-окси-фенил)фталимидина с бис-хлорформиатом дифенилолпропана в растворе, используя триэтиламин в качестве акцептора соляной кислоты или межфазной поликонденсацией указанных реагентов в системе метиленхлорид–водная щелочь. Структуры полученных исходных и полимерных соединений были подтверждены спектроскопией ядерного магнитного резонанса 1 H и элементным анализом. Свойством всех синтезированных гребнеобразных сополимеров является их хорошая растворимость в ряде доступных растворителях и пленкообразование.Результаты. Показано, что новые гребнеобразные поликарбонатсилоксаны обладают высокой термической устойчивостью. По данным термогравиметрического анализа введение в сополимер до 20 масс. % силоксановых звеньев позволяет повысить термостойкость поликарбонатсилоксанов на 25 °C. При этом, температура стеклования их достигает 160 °C. Сополимеры поликарбонатсилоксанов в виде пленок обладают высокой прочностью на разрыв выше 50 МПа и модулем упругости до 2000 МПа. Коэффициенты проницаемости газов через coполимер поликарбонатсилоксанов в виде пленки по ряду газов превосходят проницаемость для промышленного поликарбоната из дифенилолпропана и фторсодержащего силоксанового поликарбоната.Выводы. Достигнутые результаты свидетельствуют о возможности создания новых полимерных гребнеобразных силоксановых систем с варьируемой структурой, которая способствует для них получению заданных свойств. В сочетании с высокой селективностью разделения газов это позволяет использовать новые гребнеобразные поликарбонатсилоксаны в качестве пленочных мембранных материалов с повышенным интервалом рабочих температур
Determination of the b quark mass at the M_Z scale with the DELPHI detector at LEP
An experimental study of the normalized three-jet rate of b quark events with
respect to light quarks events (light= \ell \equiv u,d,s) has been performed
using the CAMBRIDGE and DURHAM jet algorithms. The data used were collected by
the DELPHI experiment at LEP on the Z peak from 1994 to 2000. The results are
found to agree with theoretical predictions treating mass corrections at
next-to-leading order. Measurements of the b quark mass have also been
performed for both the b pole mass: M_b and the b running mass: m_b(M_Z). Data
are found to be better described when using the running mass. The measurement
yields: m_b(M_Z) = 2.85 +/- 0.18 (stat) +/- 0.13 (exp) +/- 0.19 (had) +/- 0.12
(theo) GeV/c^2 for the CAMBRIDGE algorithm. This result is the most precise
measurement of the b mass derived from a high energy process. When compared to
other b mass determinations by experiments at lower energy scales, this value
agrees with the prediction of Quantum Chromodynamics for the energy evolution
of the running mass. The mass measurement is equivalent to a test of the
flavour independence of the strong coupling constant with an accuracy of 7
permil.Comment: 24 pages, 10 figures, Accepted by Eur. Phys. J.
Study of Inclusive J/psi Production in Two-Photon Collisions at LEP II with the DELPHI Detector
Inclusive J/psi production in photon-photon collisions has been observed at
LEP II beam energies. A clear signal from the reaction gamma gamma -> J/psi+X
is seen. The number of observed N(J/psi -> mu+mu-) events is 36 +/- 7 for an
integrated luminosity of 617 pb^{-1}, yielding a cross-section of
sigma(J/psi+X) = 45 +/- 9 (stat) +/- 17 (syst) pb. Based on a study of the
event shapes of different types of gamma gamma processes in the PYTHIA program,
we conclude that (74 +/- 22)% of the observed J/psi events are due to
`resolved' photons, the dominant contribution of which is most probably due to
the gluon content of the photon.Comment: 13 pages, 8 figures, Accepted by Phys. Lett.
Study of Leading Hadrons in Gluon and Quark Fragmentation
The study of quark jets in e+e- reactions at LEP has demonstrated that the
hadronisation process is reproduced well by the Lund string model. However, our
understanding of gluon fragmentation is less complete. In this study enriched
quark and gluon jet samples of different purities are selected in three-jet
events from hadronic decays of the Z collected by the DELPHI experiment in the
LEP runs during 1994 and 1995. The leading systems of the two kinds of jets are
defined by requiring a rapidity gap and their sum of charges is studied. An
excess of leading systems with total charge zero is found for gluon jets in all
cases, when compared to Monte Carlo Simulations with JETSET (with and without
Bose-Einstein correlations included) and ARIADNE. The corresponding leading
systems of quark jets do not exhibit such an excess. The influence of the gap
size and of the gluon purity on the effect is studied and a concentration of
the excess of neutral leading systems at low invariant masses (<~ 2 GeV/c^2) is
observed, indicating that gluon jets might have an additional hitherto
undetected fragmentation mode via a two-gluon system. This could be an
indication of a possible production of gluonic states as predicted by QCD.Comment: 19 pages, 6 figures, Accepted by Phys. Lett.
Measurement and Interpretation of Fermion-Pair Production at LEP energies above the Z Resonance
This paper presents DELPHI measurements and interpretations of
cross-sections, forward-backward asymmetries, and angular distributions, for
the e+e- -> ffbar process for centre-of-mass energies above the Z resonance,
from sqrt(s) ~ 130 - 207 GeV at the LEP collider. The measurements are
consistent with the predictions of the Standard Model and are used to study a
variety of models including the S-Matrix ansatz for e+e- -> ffbar scattering
and several models which include physics beyond the Standard Model: the
exchange of Z' bosons, contact interactions between fermions, the exchange of
gravitons in large extra dimensions and the exchange of sneutrino in R-parity
violating supersymmetry.Comment: 79 pages, 16 figures, Accepted by Eur. Phys. J.
Evidence for an Excess of Soft Photons in Hadronic Decays of Z^0
Soft photons inside hadronic jets converted in front of the DELPHI main
tracker (TPC) in events of qqbar disintegrations of the Z^0 were studied in the
kinematic range 0.2 < E_gamma < 1 GeV and transverse momentum with respect to
the closest jet direction p_T < 80 MeV/c. A clear excess of photons in the
experimental data as compared to the Monte Carlo predictions is observed. This
excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/-
0.27) x 10^{-3} gamma/jet in the specified kinematic region, while the expected
level of the inner hadronic bremsstrahlung (which is not included in the Monte
Carlo) is (0.340 +/- 0.001 +/- 0.038) x 10^{-3} gamma/jet. The ratio of the
excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8),
which is similar in strength to the anomalous soft photon signal observed in
fixed target experiments with hadronic beams.Comment: 37 pages, 9 figures, Accepted by Eur. Phys. J.
A Determination of the Centre-of-Mass Energy at LEP2 using Radiative 2-fermion Events
Using e+e- -> mu+mu-(gamma) and e+e- -> qqbar(gamma) events radiative to the
Z pole, DELPHI has determined the centre-of-mass energy, sqrt{s}, using energy
and momentum constraint methods. The results are expressed as deviations from
the nominal LEP centre-of-mass energy, measured using other techniques. The
results are found to be compatible with the LEP Energy Working Group estimates
for a combination of the 1997 to 2000 data sets.Comment: 20 pages, 6 figures, Accepted by Eur. Phys. J.
A Precise Measurement of the Tau Lifetime
The tau lepton lifetime has been measured with the e+e- -> tau+tau- events
collected by the DELPHI detector at LEP in the years 1991-1995. Three different
methods have been exploited, using both one-prong and three-prong tau decay
channels. Two measurements have been made using events in which both taus decay
to a single charged particle. Combining these measurements gave tau_tau (1
prong) = 291.8 +/- 2.3 (stat) +/- 1.5 (sys) fs. A third measurement using taus
which decayed to three charged particles yielded tau_tau (3 prong) = 288.6 +/-
2.4 (stat) +/- 1.3 (sys) fs. These were combined with previous DELPHI results
to measure the tau lifetime, using the full LEP1 data sample, to be tau_tau =
290.9 +/- 1.4 (stat) +/- 1.0 (sys) fs.Comment: 27 pages, 7 figure
Study of Tau-pair Production in Photon-Photon Collisions at LEP and Limits on the Anomalous Electromagnetic Moments of the Tau Lepton
Tau-pair production in the process e+e- -> e+e-tau+tau- was studied using
data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000.
The corresponding integrated luminosity is 650 pb^{-1}. The values of the
cross-section obtained are found to be in agreement with QED predictions.
Limits on the anomalous magnetic and electric dipole moments of the tau lepton
are deduced.Comment: 20 pages, 9 figures, Accepted by Eur. Phys. J.
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