4,411 research outputs found
Strongly Enhanced Low Energy Alpha-Particle Decay in Heavy Actinide Nuclei and Long-Lived Superdeformed and Hyperdeformed Isomeric States
Relatively low energy and very enhanced alpha-particle groups have been
observed in various actinide fractions produced via secondary reactions in a
CERN W target which had been irradiated with 24-GeV protons. In particular,
5.14, 5.27 and 5.53 MeV alpha-particle groups with corresponding half-lives of
3.8(+ -)1.0 y, 625(+ -)84 d and 26(+ -)7 d, have been seen in Bk, Es and Lr-No
sources, respectively. The measured energies are a few MeV lower than the known
g.s. to g.s. alpha-decays in the corresponding neutron-deficient actinide
nuclei. The half-lives are 4 to 7 orders of magnitude shorter than expected
from the systematics of alpha-particle decay in this region of nuclei. The
deduced evaporation residue cross sections are in the mb region, about 4 orders
of magnitude higher than expected. A consistent interpretation of the data is
given in terms of production of long-lived isomeric states in the second and
third wells of the potential-energy surfaces of the parent nuclei, which decay
to the corresponding wells in the daughters. The possibility that the isomeric
states in the third minimum are actually the true or very near the true ground
states of the nuclei, and consequences regarding the production of the
long-lived superheavy elements, are discussed.Comment: 27 pages including 8 figures and 4 table
Combustion behaviour of some biodesulphurized coals assessed by TGA/DTA
Thermal analysis, i.e. TGA/DTA is used to study the changes in the combustion behaviour of microbially treated coals. In view of their high sulphur content and industrial significance three samples are under consideration, i.e. one lignite and two subbituminous from different region in Bulgaria. The differences
in burning profiles can be related to structural changes resulted from biological treatments. The overall biological treatment generates these changes probably due to the oxidation process. Concerning organic sulphur biodesulphurization there is no change in any drastic mannerof the thermal characteristic parameters. In general, applied biotreatments provoke a complex influence on combustion coal behaviour. From one side a better ignition performance, a minor decrease in higher heating value and diminishing peak
temperature of maximum weight loss rate for all biotreated samples are observed. From other side some decrease in the combustibility indicated by an increase in the combustion time and the end of combustion temperature are obvious. Also well determined decrease of self-heating temperature after biotreatments evolves high risk of spontaneous unmanageable coal combustion
Density resummation of perturbation series in a pion gas to leading order in chiral perturbation theory
The mean field (MF) approximation for the pion matter, being equivalent to
the leading ChPT order, involves no dynamical loops and, if self-consistent,
produces finite renormalizations only. The weight factor of the Haar measure of
the pion fields, entering the path integral, generates an effective Lagrangian
which is generally singular in the continuum limit.
There exists one parameterization of the pion fields only, for which the weight
factor is equal to unity and , respectively. This
unique parameterization ensures selfconsistency of the MF approximation. We use
it to calculate thermal Green functions of the pion gas in the MF approximation
as a power series over the temperature. The Borel transforms of thermal
averages of a function of the pion
fields with respect to the scalar pion density are found to be
. The perturbation series over the scalar
pion density for basic characteristics of the pion matter such as the pion
propagator, the pion optical potential, the scalar quark condensate
, the in-medium pion decay constant , and the
equation of state of pion matter appear to be asymptotic ones. These series are
summed up using the contour-improved Borel resummation method. The quark scalar
condensate decreases smoothly until MeV. The temperature
is the maximum temperature admissible for thermalized non-linear
sigma model at zero pion chemical potentials. The estimate of is
above the chemical freeze-out temperature MeV at RHIC and above
the phase transition to two-flavor quark matter MeV,
predicted by lattice gauge theories.Comment: Replaced with revised and extended version. Results are compared to
lattice gauge theories. 16 pages REVTeX, 13 eps figure
The role of echocardiography in the diagnosis of fetal and pediatric cardiac tumors
В исторически план развитието на образните методи на изследване при сърдечните тумори позволи преминаването от аутопсионна към прижизнено поставена диагноза. Ехокардиографията е лесно достъпен, неинвазивен и високо информативен диагностичен метод на първи избор.Представени са възможностите на съвременното комплексно ехокардиографско изследване за ранно, включително и пренатално, откриване на туморите на сърцето, придружаващите сърдечни аномалии и извършването на коректна хемодинамична оценка. Включени са и наши собствени наблюдения на пациенти с различни по вид сърдечни тумори, диагностицирани както фетално, така и след раждането.Ехокардиографското изследване е утвърден, бърз, удобен и информативен метод за пре- и постнатално диагностициране на сърдечните тумори в детската възраст, както и за тяхното пре- и постоперативно проследяване.The development of different imaging techniques allows the diagnosis of cardiac tumors to be made before the death of a person, and not as it used to be made - following a post mortem. Echocardiography is easily available, noninvasive and a highly informative diagnostic method of choice.We`re presenting the possibilities of current echocardiography examination for the early, including prenatal, diagnosis of cardiac tumors, concomitant congenital heart diseases and hemodynamic evaluation. In this report we also include the observations of our own patients with different kinds of cardiac tumors, which were diagnosed prenatally and after birth. Echocardiography is an approved, quick, convenient and informative prenatal, and postnatal, diagnostic method for cardiac tumors in childhood, as well as for their preoperative and postoperative follow-up
Numerical investigation of high-pressure combustion in rocket engines using Flamelet/Progress-variable models
The present paper deals with the numerical study of high pressure LOx/H2 or
LOx/hydrocarbon combustion for propulsion systems. The present research effort
is driven by the continued interest in achieving low cost, reliable access to
space and more recently, by the renewed interest in hypersonic transportation
systems capable of reducing time-to-destination. Moreover, combustion at high
pressure has been assumed as a key issue to achieve better propulsive
performance and lower environmental impact, as long as the replacement of
hydrogen with a hydrocarbon, to reduce the costs related to ground operations
and increase flexibility. The current work provides a model for the numerical
simulation of high- pressure turbulent combustion employing detailed chemistry
description, embedded in a RANS equations solver with a Low Reynolds number
k-omega turbulence model. The model used to study such a combustion phenomenon
is an extension of the standard flamelet-progress-variable (FPV) turbulent
combustion model combined with a Reynolds Averaged Navier-Stokes equation
Solver (RANS). In the FPV model, all of the thermo-chemical quantities are
evaluated by evolving the mixture fraction Z and a progress variable C. When
using a turbulence model in conjunction with FPV model, a probability density
function (PDF) is required to evaluate statistical averages of chemical
quantities. The choice of such PDF must be a compromise between computational
costs and accuracy level. State- of-the-art FPV models are built presuming the
functional shape of the joint PDF of Z and C in order to evaluate
Favre-averages of thermodynamic quantities. The model here proposed evaluates
the most probable joint distribution of Z and C without any assumption on their
behavior.Comment: presented at AIAA Scitech 201
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