4,145 research outputs found
Inversionless light amplification and optical switching controlled by state-dependent alignment of molecules
We propose a method to achieve amplification without population inversion by
anisotropic molecules whose orientation by an external electric field is
state-dependent. It is based on decoupling of the lower-state molecules from
the resonant light while the excited ones remain emitting. The suitable class
of molecules is discussed, the equation for the gain factor is derived, and the
magnitude of the inversionless amplification is estimated for the typical
experimental conditions. Such switching of the sample from absorbing to
amplifying via transparent state is shown to be possible both with the aid of
dc and ac control electric fields.Comment: AMS-LaTeX v1.2, 4 pages with 4 figure
Inversionless gain in a three-level system driven by a strong field and collisions
Inversionless gain in a three-level system driven by a strong external field
and by collisions with a buffer gas is investigated. The mechanism of
populating of the upper laser level contributed by the collision transfer as
well as by relaxation caused by a buffer gas is discussed in detail. Explicit
formulae for analysis of optimal conditions are derived. The mechanism
developed here for the incoherent pump could be generalized to other systems.Comment: RevTeX, 9 pages, 4 eps figure
Priority areas of development of resources of hydrocarbons of Hlynskyi and Solokhivskyi oil and gas region of Dnipro and Donetsk basin
The resource potential of the Hlynsko-Solokhivskyi oil and gas region, selected area of oil and gas accumulation (OGA) was described. By means of graphical analysis the extent of the area resource potential development and selected areas of OGA was defined. The analysis of non-discovered resources (including localized) in areas, promising and producing complexes and deeps was made. The most promising areas were determined. The appropriate recommendations on further geology exploration for the purpose of improving the efficiency on oil and gas were given
Folded modes in the infrared spectra of the spin-Peierls phase of CuGeO_3
Polarized far-infrared transmittance spectra of CuGeO_3 single crystals were
measured at different temperatures (6K < T < 300K). Two spectral lines, at
284.2 cm-1 in E||c polarization and at 311.7 cm-1 in E||b polarization, appear
at the temperature of the spin-Peierls transition and grow in intensity with
decreasing temperature. Both of them are, most probably, folded modes of the
dimerized lattice. We discuss a possible role of the spin-phonon interaction in
the formation of the 311.7 cm-1 feature.Comment: 4 pages, 5 figures, 1 table; Submitted to Phys.Rev.B Second revision.
Figures and text were slightly change
Postoperative Cardiac Complications in Patients Undergoing Laryngectomies
Introduction: The European Society of Cardiology provides guidelines for preoperative cardiac risk assessment in patients undergoing laryngectomies. Cardiovascular risk factors: chronic congestive heart failure, ischemic heart disease, severe arrhythmias, have important prognostic significance for major surgical interventions and must be carefully evaluated preoperatively.The Aim of the study is to determine the most common postoperative cardiac complications in patients undergoing laryngectomies.Materials and Methods: A clinical prospective cohort study including 120 patients undergoing total laryngectomy, in the Department of Otorhinolaryngology at the University Hospital „Queen Giovanna“ – ISUL, Sofia, 2014-2017.Results and discussion: The most common postoperative cardiac complications in patients undergoing laryngectomies are arterial hypertension, angina pectoris, and tachycardia.Conclusion: There are many cardiac risk factors in patients undergoing laryngectomies that can lead to postoperative complications, respectively prolong the hospital stay and increase medical expenses
Lattice vibrations of alpha'-NaV_2O_5 in the low-temperature phase. Magnetic bound states?
We report high resolution polarized infrared studies of the quarter-filled
spin ladder compound alpha'-NaV_2O_5 as a function of temperature (5K <= T <=
300K). Numerous new modes were detected below the temperature T_c=34K of the
phase transition into a charge ordered nonmagnetic state accompanied by a
lattice dimerization. We analyse the Brillouin zone (BZ) folding due to lattice
dimerization at T_c and show that some peculiarities of the low-temperature
vibrational spectrum come from quadruplets folded from the BZ point (1/2, 1/2,
1/4). We discuss an earlier interpretation of the 70, 107, and 133cm-1 modes as
magnetic bound states and propose the alternative interpretation as folded
phonon modes strongly interacting with charge and spin excitations.Comment: 15 pages, 13 Postscript figure
Raman, infrared and optical spectra of the spin-Peierls compound NaV_2O_5
We have measured polarized spectra of Raman scattering, infrared and optical
transmission of NaV_2O_5 single crystals above the temperature of the
spin-Peierls transition Tsp=35 K. Some of the far-infrared (FIR) phonon lines
are strongly asymmetric, due to the spin-phonon interaction. In addition to the
phonon lines, a broad band was observed in the c(aa)c Raman spectrum and in the
E||a FIR transmission spectrum. A possible origin of these bands is discussed.
The absorption band at 10000 cm-1 1.25 eV is attributed to vanadium d-d
electronic transitions while the absorption edge above 3 eV is supposed to
correspond to the onset of charge-transfer transitions.Comment: 7 figures, 8 page
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