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

Optical properties, electron-phonon coupling, and Raman scattering of vanadium ladder compounds

The electronic structure of two V-based ladder compounds, the quarter-filled NaV$_2$O$_5$ in the symmetric phase and the iso-structural half-filled CaV$_2$O$_5$ is investigated by ab initio calculations. Based on the bandstructure we determine the dielectric tensor $\epsilon(\omega)$ of these systems in a wide energy range. The frequencies and eigenvectors of the fully symmetric A$_{g}$ phonon modes and the corresponding electron-phonon and spin-phonon coupling parameters are also calculated from first-principles. We determine the Raman scattering intensities of the A$_g$ phonon modes as a function of polarization and frequency of the exciting light. All results, i.e. shape and magnitude of the dielectric function, phonon frequencies and Raman intensities show very good agreement with available experimental data.Comment: 11 pages, 10 figure

Charge ordering in quarter-filled ladder systems coupled to the lattice

We investigate charge ordering in the presence of electron-phonon coupling for quarter-filled ladder systems by using Exact Diagonalization. As an example we consider NaV2O5 using model parameters obtained from first-principles band-structure calculations. The relevant Holstein coupling to the lattice considerably reduces the critical value of the nearest-neighbor Coulomb repulsion at which formation of the zig-zag charge-ordered state occurs, which is then accompanied by a static lattice distortion. Energy and length of a kink-like excitation on the background of the distorted lattice are calculated. Spin and charge spectra on ladders with and without static distortion are obtained, and the charge gap and the effective spin-spin exchange parameter J are extracted. J agrees well with experimental results. Analysis of the dynamical Holstein model, restricted to a small number of phonons, shows that low frequency lattice vibrations increase the charge order, accompanied by dynamically produced zig-zag lattice distortions.Comment: 11 pages, 17 figures, revised version as to appear in Phys. Rev.

Experimental implementation of a four-level N-type scheme for the observation of Electromagnetically Induced Transparency

A nondegenerate four-level N-type scheme was experimentally implemented to observe electromagnetically induced transparency (EIT) at the $^{87}$Rb D$_{2}$ line. Radiations of two independent external-cavity semiconductor lasers were used in the experiment, the current of one of them being modulated at a frequency equal to the hyperfine-splitting frequency of the excited 5P$_{3/2}$ level. In this case, apart from the main EIT dip corresponding to the two-photon Raman resonance in a three-level $\Lambda$-scheme, additional dips detuned from the main dip by a frequency equal to the frequency of the HF generator were observed in the absorption spectrum. These dips were due to an increase in the medium transparency at frequencies corresponding to the three-photon Raman resonances in four-level N-type schemes. The resonance shapes are analyzed as functions of generator frequency and magnetic field.Comment: 3 pages, 2 figure

Autler - Townes doublet probed by strong field

This paper deals with the Autler - Townes doublet structure. Applied driving and probing laser fields can have arbitrary intensities. The explanation is given of the broadening of doublet components with the growth of probing field intensity, which was observed in experiment. The effects of Doppler averaging are discussed.Comment: 12 pages, RevTeX, 5 figures in 9 file

Первая клиническая пересадка сердца в истории отечественной и зарубежной медицины

The first human heart transplant immediately exposed many unsolved problems of organ transplant existing at an early stage of the development of that kind of medical technology. The review of historical, legal and philosophical aspects of the first human heart transplantation in Russia and abroad is presented. Special attention is paid to the role and destiny of the pioneers of heart transplantation. The dramatic lives of Vladimir Demikhov and famous South African surgeon Christiaan Barnard are compared. The hard way of the heart transplantation founders is not lost, worthy successors continued their work, saving the lives of hundreds and thousands of patients.Статья посвящена 50-летию первой операции по трансплантации сердца человеку в 1967 г., значение которой рассматривается в контексте истории медицины. Освещается беспрецедентная реакция на нее мировых масс-медиа. Первая трансплантация сердца сразу же обнажила множество нерешенных проблем трансплантологии того времени. Анализируются философско-этические проблемы донорства органов и границы между экспериментальной и клинической стадиями трансплантации органов. В статье проведен анализ исторического пути развития трансплантации сердца от эксперимента к массовому клиническому применению технологии. Рассмотрены бурные дискуссии в обществе, вызванные первыми клиническими пересадками сердца. Особый интерес представляет роль и судьба пионеров трансплантации сердца. Сравнивается драматическая судьба В.П. Демихова и научный путь южноафриканского хирурга К. Барнарда

Электрофоретическая подвижность эритроцитов у больных с тяжелыми формами интоксикации

Objective: to study the diagnostic and prognostic value of changes in red blood cell electrophoretic mobility (RBCEM) in patients with infectious and noninfectious forms of intoxication.Materials and methods. A cytoferometer (Opton) was used to determine RBCEM; venous blood samples taken on heparin were studied. Thirty patients with peritonitis (infectious intoxication) and 22 patients with a pancreatic tumor and mechanical jaundice (noninfectious intoxication) were examined. All the patients received standard therapy for this disease. Eight out of 30 patients died on days 3—10 postoperatively.Results. On postoperative days 1—2, the values of RBCEM were outside the lower normal range in 90% of the patients with peritonitis (p<0.01). At the same time the patients with a good outcome of the disease differed from those who subsequently died (p<0.05), but they did not differ in the severity of the disease (APACHE II scale) and the results of laboratory and clinical blood tests. On days 7—14 versus days 1—2 after surgery, the survivors, unlike the deceased, showed an increase in RBCEM (p<0.05) and a reduction in disease severity by the APACHE II scale (p<0.05). On admission, in 95% of patients with pancreatic tumor, the values of RBCEM were beyond the lower normal range (p<0.01). Seven-day disintoxicant therapy caused a rise in this index.Conclusion. Intoxication with infectious and noninfectious agents leads to lower RBCEM. In patients with general peritonitis, the values of this index and its changes are of diagnostic and prognostic value in evaluating the severity and outcome of the disease and the efficiency of performed therapeutic measures. Цель. Изучение диагностической и прогностической значимости изменений электрофоретической подвижности эритроцитов (ЭФПЭ) у больных с инфекционной и неинфекционной формами интоксикации организма.Материалы и методы. Для определения ЭФПЭ был использован цитоферометр фирмы «Opton», материалом для исследования служила венозная кровь, взятая на гепарине. Обследование проведено у 30 больных с перитонитом (инфекционная форма интоксикации) и у 22 больных опухолью поджелудочной железы с механической желтухой (неинфекционная форма интоксикации). Всем больным проводили стандартизированную терапию для данного заболевания. Из 30 больных перитонитом 8 умерли на 3—10 сутки после операции.Результаты. На 1—2-е сутки после операции у 90% больных с перитонитом величины ЭФПЭ находились за пределами нижней границы нормы (р<0,01). При этом больные с благоприятным исходом заболевания отличались от впоследствии умерших более высокими значениями этого показателя (р<0,05), но не различались по тяжести состояния (шкала АРАСНЕ II), результатам лабораторно-клинического анализа крови. На 7—14-е сутки после операции у выживших больных, в отличие от умерших, наблюдалось увеличение ЭФПЭ (р<0,05) и уменьшение тяжести их состояния по шкале АРАСНЕ II (р<0,05) по сравнению с 1—2 сутками послеоперационного периода. При поступлении в стационар у 95% больных с опухолью поджелудочной железы величины ЭФПЭ были меньше нижней границы нормы (р<0,01). Проведение дезинтоксикационной терапии в течение 7 суток сопровождалось увеличением значений этого показателя.Заключение. Интоксикация организма инфекционными и неинфекционными агентами приводит к снижению ЭФПЭ. У больных с разлитым перитонитом значения этого показателя и его динамика имеют диагностическую и прогностическую значимость для оценки тяжести и исхода заболевания, эффективности проводимых лечебных мероприятий.