Search

The article observes the main provisions of the clinical recommendations for prevention, anesthesia and intensive care for postpartum hemorrhage. The main risk factors, possible complications, principles of clinical and laboratory diagnosis in this pathology are consistently presented. Particular attention is paid to issues of infusion, transfusion therapy and correction of coagulopathic disorders. The problems of estimating the amount of blood loss, diagnosing disorders of the hemostatic system, regulation of hemodynamics in hemorrhagic shock are discussed. The use of recombinant coagulation factors in coagulopathy on the background of massive blood loss has been substantiated.

A complex chaotic dynamics in a gyrotron was experimentally observed under conditions of high supercriticality corresponding to 1000–1500-fold excess of the beam current parameter over the starting value. At electron beam currents typical of gyrotron test setups, this excess has been achieved by a transition to excitation of the lowest mode of a cylindrical waveguide. Chaotic generation regimes were observed in a 33 GHz frequency range with a spectral width of 500 MHz and record narrow relative width below 1.5% These results imply considerable progress in comparison to previous experiments with gyrotron type devices and are in good agreement with theoretical analysis based on a system of averaged evolution equations derived with allowance for finiteness of the transit time of electrons via the interaction space.

The ordered alloys of Fe with nominally non-magnetic 4d/5d (Rh, Pd, Pt) elements demonstrate an array of an attractive magnetic properties. The high magnetic anisotropy energy (MAE) of the ordered L1 0 FePt is considered as particularly important property for achieving small thermally stable magnetic grains [1]. Recent progress in fabrication and characterization of nano-granular and nano-particulate FePt films puts emphasize on understanding of the temperature dependence of MAE [2]. Theoretical framework for the temperature dependence of the MAE was summarized by Callen and Callen [3]. This theory predicts universal parametric dependence between K 1 (T) and M S (T) which for the uniaxial magnet simply given by the K 1 (M S (T)) ∼ M S 3 in the low temperature region. Measurements on epitaxial FePt films, however, demonstrate K(T) ∼ M S 2 scaling in the wide temperature range [2]. The origin of this behavior was found to be in the magnetic interactions mediated by the Pt induced spin moment [4]. In FePt anisotropic exchange mediated by the induced Pt spin moment appears to be dominating over the Fe contribution and thus leading to the K 1 ∼ M s 2.1 low temperature scaling behavior [4]. In this work we present results of the magnetic measurements for a single variant highly ordered L1 0 FePd crystals. This chemical analog of the FePt is known for its significantly lower ordering temperature (950 vs. 1910 K) and somewhat smaller MAE K 1 of about 2'107 erg/cc. We present results of K 1 (T) measurements on single ordering domain FePd samples which clearly demonstrate different than reported for the FePt thin films scaling behavior K(T) ∼ M3.8. We discuss initial theoretical interpretation provided on the basis of recently measured ordering defects in the form of intermediate disordered phase [5,6].

The first stage of the experimental study of a frequency adjustable FEM-oscillator with a broadband microwave system based on the effect of microwave beams multiplication is presented. Operability of the key element of this system (wide-band reflector) was tested in the “hot” experiment. The 45 GHz FEM-oscillator with a microwave system of the new type was driven by a 500 keV, 120 A, 20 ns electron beam and generated 7 MW of radiation with a 12% efficiency. A new double-resonance operating regime of the FEM with combined - undulator and homogeneous guide - magnetic field, when both the undulator and the cyclotron resonance conditions are fulfilled simultaneously, was realized.

Operability of the wide-band reflector based on the effect of microwave beams multiplication was tested in the "hot" experiment. A microwave system of the new type including such a reflector was used in a free electron maser (FEM)-oscillator with a guide magnetic field. The high-current accelerator "Sinus-6" forming a 500 keV/120 A electron beam was used as the FEM driver. The double-resonance regime, when both the undulator and the cyclotron resonance conditions were fulfilled simultaneously, provided maximum output power 7 MW and electron efficiency 12% at the designed frequency 45 GHz.

A new scheme of self-exciting single-cavity gyromultiplier is tested in a preliminary mm-range experiment. Such a scheme is prospective for realization in THz range.

Electronic efficiency of 26%, close to the value calculated for a perfect electron beam in a type of FEM based on the stimulated electron cyclotron radiation, has been obtained for the first time.

The paper presents recent test results on low relativistic (20-80 kV) gyro-TWT and gyro-BWO based on a microwave system in the form of a waveguide with helical surface. In particular, in experiments the Ka-band gyro-TWT showed the following output parameters: pulse power up to 180 kW, gain 25-30 dB, instant frequency band 10%, efficiency at second harmonic operation 27%. The gyro-BWO was designed for CW operation with output power of 5-7 kW at frequencies around 24 GHz. Smooth frequency tuning in the band of 10% was demonstrated.

The paper presents recent test results on low relativistic (20-80 kV) gyro-TWT and gyro-BWO based on a microwave system in the form of a waveguide with helical surface. In particular, in experiments the gyro-TWT showed the following output parameters: pulse power up to 180 kW, gain 25-30 dB, instant frequency band 10%, efficiency at second harmonic operation 27%.

Summary form only given. The gyrotron traveling wave tube (gyro-TWT) is a well-known amplifier variety of the gyro-devices, which may have a wide instantaneous frequency bandwidth because of the operation with an electromagnetic wave possessing large group velocity. For a microwave system in the form of a smooth cylindrical waveguide a large wave group velocity inevitably leads to a large axial wavenumber, which makes this device significantly more sensitive to particle velocity spread in comparison with a gyrotron. The most favorable wave dispersion for a gyro-TWT is that when the wave group velocity is sufficiently large and constant in the region of close-to-zero axial wavenumber. A similar dispersion can be realized in an oversized circular waveguide with special helical ripples of its inner surface A theoretical analysis demonstrates important advantages of the "helical" gyro-TWTs over the analogous "smooth" ones in sensitivity to electron velocity spread, frequency bandwidth and stability to parasitic self-oscillations. The proof-of-principle experiments exploiting moderately relativistic (200-300 keV) short-pulse (20-100 ns) field-emission electron beams have proved the main theoretical predictions. Based on the first successful experiments and the developed theory, a project was started aimed at the creation of a more applicable device. The main goal of this project is the realization of a Ka-band gyro-TWT with a low-relativistic electron beam produced by a gun with a thermionic cathode.

Simultaneous generation at the second and fourth cyclotron harmonics has been obtained from a single-cavity self-excited gyromultiplier. Output power of the short-wavelength radiation amounts to 100 W at a frequency of 75 GHz. The proposed scheme seems to be promising for the terahertz frequency range.

A second-order time-differential equation is proposed for the approximate solution of the time-dependent Schrodinger equation with a limited basis. The resulting nonunitary solutions allow for a flux of probability into the excluded space. Simple examples are used in demonstration.

A time-dependent imaginary optical potential is used to approximate the Schr\"odinger time evolution in a necessarily truncated subspace. The flux of probability into the neglected space, for which the ordinary unitary subspace Schr\"odinger solution does not account, can generally be well reproduced by an optical potential that is diagonal in energy and linear in time. This is demonstrated in a number of examples including the Lipkin model, Gaussian Hamiltonians, and a schematic heavy-ion collision model.

A simple microscopic determinantal type basis is used to generate oscillator-like wave functions and associated rotational bands. These wave functions can be used to investigate other phenomena.

Approximations to the Schrodinger time evolution in a highly truncated subspace are studied as an alternative to the time-dependent Hartree-Fock approximation. We derive a differential equation of second order in time, that involves the subspace matrix elements of the square of the Hamiltonian. The equation is completely defined and soluble within an arbitrarily truncated subspace. The solutions are non-unitary and allow for a flux of probability between the subspace and the excluded space. The accuracy of the approximation is studied in a number of examples.

It is demonstrated that the extent of density clustering in light A =4n nuclei, as given by Hartee-Fock calculations, depends rather sensitively upon the saturating mechanism of the interactions being used. The example carried through in detail is that of 20 Ne.

Variational calculations find that the first excited state of 160 O is predominently a prolately deformed 2p-2h excitation for a central force which saturates at the correct energy, but the excitation energy is much too high.

A variational approach is used to obtain the Mariscotti, Scharff-Goldhaber and Buck prescription for analyzing rotational spectra. Results of two and three boson microscope calculations are used to illustrate the ideas used.

The two-body matrix element for a Gaussian force is obtained in closed form using cylindrical harmonic oscillator wave functions. The result is completely general allowing all possible cylindrical states and allowing different oscillator constants for each state. These include matrix elements which cannot be determined by the usual methods of separation into relative and centre-of-mass coordinates.

The existence of more than one collective 0 + state in deformed nuclei due to the separation of ‘oblate’ and ‘prolate’ matrix elements is demonstrated by means of a model calculation and calculations using 240 Pu single particle wave functions.

The direct and exchange potential matrix elements are shown to be either insensitive to nuclear deformation or to have opposing behaviour. Therefore, the total potential energy behaviour as the system deforms depends rather sensitively on the exchange properties of the nuclear force. Reasonable saturating forces which are related to scattering data result in exchange mixtures which make the total potential energy insensitive to reasonable deformations. The minimization of the total energy (essentially the kinetic energy) leads to results similar to the Nilsson model. The 20Ne nucleus and the 4p-4h 16O excited state are used as illustrations.

The equilibrium ground state energies of the 1p shell nuclei are calculated by diagonalizing the full many-particle Hamiltonian with saturating forces in an M , rather than J , Slater determinant representation. The single-particle wave functions have variable oscillator constants which preserve cylindrical symmetry. The ground state energy is minimized with respect to the different oscillator constants. This is equivalent to minimizing the ground state energy with respect to nuclear volume, nuclear deformation, and, in a limited sense, to the form of the single-particle radial functions. In the zero-deformation limit, the diagonalization and minimization with respect to nuclear size is equivalent to finding the best intermediate coupling result for the ground state energy consistent with the force being used. Most 1p shell nuclei are found to be deformed with the deformation being a sensitive function of the amount of Majorana exchange in the force mixture. For light 1p shell nuclei the 1p orbitals are considerably larger relative to the 1s orbitals than predicted by the usual simple harmonic single-particle potential.

It is shown that symmetric deformed nuclei are unstable to asymmetric deformation at sufficiently high angular momentum. Forking and backbending are natural consequences of this instability.

The suitability of density and momentum dependent delta function forces in nuclear calculations is studied using Hartee-Fock calculations in the 2s-1d shell. The effect of the compressibility upon deformation and rms radius is investigated.

The use of a density dependent NN force reduces the theoretically determined Λ binding energy 1p shell nuclei by approximately 0.2 to 0.4 MeV due to compressibility effects. Different odd state ΛN interactions can change these results.

The variable moment of inertia model is shown to be applicable to odd-even nuclei when Coriolis coupling effects are small. Under appropriate circumstances the odd-even moments of inertia should be nearly equal to those of an adjoining even-even nucleus.

28 Si ground state is found to be prolate when density dependent forces are used in Hartree-Fock calculations instead of oblate as in the case for non-density dependent forces.

We derive non-determinantalapproximations to the Schrodinger time-evolution in a necessarily truncated subspace, that allow for a flux of probability between the subspace and the excluded space.

The customary time-dependent Hartree--Fock problem is shown to be ambiguous up to an arbitrary function of time additive to H/sub HF/, and, consequently, up to an arbitrary time-dependent phase for the solution, PHI(t). The ''constant'' (H)'' phase is proposed as the best resolution of this ambiguity. It leads to the following attractive features: (a) the time-dependent Hartree--Fock (TDHF) Hamiltonian, H/sub HF/, becomes a quantity whose expectation value is equal to the average energy and, hence, constant in time; (b) eigenstates described exactly by determinants, have time-dependent Hartree--Fock solutions identical with the exact time-dependent solutions; (c) among all possible TDHF solutions this choice minimizes the norm of the quantity (H--i dirac constant delta/delta t) operating on the ket PHI, and guarantees optimal time evolution over an infinitesimal period; (d) this choice corresponds both to the stationary value of the absolute difference between (H) and (i dirac constant delta/delta t) and simultaneously to its absolute minimal value with respect to choice of the time-dependent phase. The source of the ambiguity is discussed. It lies in the time-dependent generalization of the freedom to transform unitarily among the single-particle states of a determinant at the (physically irrelevant for stationary states) cost of altering onlymore » a factor of unit magnitude.« less

The time-dependent Hartree-Fock (TDHF) variational principle is shown to yield a unique solution with no indeterminacy in its time-dependent phase. The long-standing contrary opinion arises from an impermissible restriction to norm-preserving variations. 9 references.