Ara Abovyan - Academia.edu (original) (raw)

Papers by Ara Abovyan

Vestnik khirurgii imeni I. I. Grekova, 2021

The objective was to retrospectively analyze the dependence of long-term results of laparoscopic ... more The objective was to retrospectively analyze the dependence of long-term results of laparoscopic Roux-en-Y gastric bypass surgery according to the size of the formed gastric stumpMethods and materials. We retrospectively analyzed the long-term results of 207 morbidly obese patients who underwent laparoscopic Roux-en-Y gastric bypass surgery by two different techniques. The median follow-up was 36 months. Two groups of patients were identified according to the method of formation of the gastric stump: using 2 (1st group) or 3 (2nd group) stapler cassettes and performing of computed tomography volumetry to determine thevolume of the created gastric stump.Results. Statistically significant differences in the volume of the formed gastric stump, depending on the method of operation, were as follows: 23.8 ml (8.9–37.3 ml) in the 1st group and 47.7 ml (31.9–72.8 ml) in the 2nd group (p<0.0001). Significant differences were observed in the following indicators: relapse of weight gain or ...

Physical Review A, 2013

We analyze the dynamics of a superconducting qubit and the phenomenon of multiorder Rabi oscillat... more We analyze the dynamics of a superconducting qubit and the phenomenon of multiorder Rabi oscillations in the presence of a time-modulated external field. Such a field is also presented as a bichromatic field consisting of two spectral components, which are symmetrically detuned from the qubit resonance frequency. This approach leads to obtaining qualitative quantum effects beyond those for the case of monochromatic excitation of qubits. We calculate Floquet states and quasienergies of the composite system "superconducting qubit plus time-modulated field" for various resonant regimes. We analyze the dependence of quasienergies from the amplitude of an external field, demonstrating the zeros of difference between quasienergies. We show that, as a rule, populations of qubit states exhibit aperiodic oscillations, but we demonstrate the specific important regimes in which dynamics of populations becomes periodically regular.

Deflection of an atomic beam passing through two crossed standing light waves is proposed for stu... more Deflection of an atomic beam passing through two crossed standing light waves is proposed for studies of transition through the Raman resonance in Λ -atomic systems. Considering different regimes of excitation of Λ -atoms by offresonant standing waves, we demonstrate that the deflection patterns, in the plane perpendicular to the direction of the center of atomic mass motion, are essentially different for the cases of one-photon and two-photon excitations. Visualization of the quantum superposition states of low atomic levels on the two-dimensional spatial patterns of atomic deflection is performed.

We study qubit manipulations by a train of pulses in a systematic approach based on the Magnus ex... more We study qubit manipulations by a train of pulses in a systematic approach based on the Magnus expansion and Furry representation in quantum electrodynamics. Furry–Magnus expansion gives approximate exponential representation of a time-evolution operator without the Dyson time-ordering procedure for interactions with external fields of arbitrary intensity and allows us to obtain general expression for single-qubit populations as a function of time-dependent Rabi frequency. The concrete calculations are performed for tunneling quantum dynamics, for multiphoton resonance interactions of qubits, as well as for off-resonance excitations of qubits driven by Gaussian pulses beyond rotating wave approximation. In this way, the populations of qubit states are investigated for various operational regimes, including single-pulse excitation and two-pulse excitation with a phase shift between pulse envelopes being the controlling parameter, and for excitation with sequential pulses. In the last...

IOP Conference Series: Materials Science and Engineering, 2021

The urgent task which is addressed in this work is the development of methods for determining the... more The urgent task which is addressed in this work is the development of methods for determining the frequencies and forms of vibrations, as well as dynamic reactions of thin slabs with various support systems, including those supported on point supports. The aim of the work is to develop experimental methods for determining the frequencies and forms of natural oscillations of slabs with holes and thin point-supported square solid ones. In this work, the frequencies of square slabs with free edges resting on point supports are determined; the dependences of the vibration frequencies of slabs from the coordinates of point supports and the dimensions of symmetrically placed holes; the arrangement of point supports, wherein the basic frequency of free vibrations of the slab is maximum; the frequencies, shapes, and decrements of vibrations of square slabs supported on four point supports were determined experimentally, as well as the influence of the presence of holes and the degree of pin...

Grekov's Bulletin of Surgery

INTRODUCTION. Bariatric operations lead to changes in body composition. The desired fat loss may ... more INTRODUCTION. Bariatric operations lead to changes in body composition. The desired fat loss may be accompanied by decrease of muscle mass, thus raising the risk of sarcopenia.The OBJECTIVE was to evaluate the long-term results of surgical treatment of morbid obesity and concomitant comorbid conditions, as well as a decrease of muscle mass in the pre - and long-term postoperative period.METHODS AND MATERIALS. This prospective randomized controlled blind trial included the results of treatment of 241 patients. Patients were divided into 2 groups depending on the type of surgical treatment. The first group consisted of 116 people who underwent RYGB; the second group included 125 patients who underwent OAGB/MGB. 83 patients from the first group and 95 patients from the control group at the preoperative stage and 24 months after the operation randomly underwent bioelectrical impedance with the determination of skeletal muscle mass (SMM) and skeletal muscle mass index (SMMI)=SMM/Height2....

Modern technologies in ophtalmology

Physical Review A

The deflection of atoms in a Λ-type configuration passing through two crossed standing light wave... more The deflection of atoms in a Λ-type configuration passing through two crossed standing light waves is proposed for the probing and visualization of atomic superposition states. For this goal, we use both the large-dispersive and Raman-resonant regimes of atom-field interaction, giving rise to position-dependent phase shifts of fields, and perform double simultaneous spatial measurements on an atom. In this way, it is demonstrated that the deflection spatial patterns of atoms in a Λ-configuration passing through modes of standing waves are essentially modified if the atoms are initially prepared in coherent superpositions of their low-level states as well as when the superposition states are created during the process of deflection. There are similar results for the joint momentum distributions of atoms. Furthermore, considering both one-photon- and two-photon-excitation regimes of Λ atoms, we also illustrate that the two-dimensional patterns of defected atoms qualitatively reflect t...

Vestnik khirurgii imeni I. I. Grekova, 2021

The objective was to retrospectively analyze the dependence of long-term results of laparoscopic ... more The objective was to retrospectively analyze the dependence of long-term results of laparoscopic Roux-en-Y gastric bypass surgery according to the size of the formed gastric stumpMethods and materials. We retrospectively analyzed the long-term results of 207 morbidly obese patients who underwent laparoscopic Roux-en-Y gastric bypass surgery by two different techniques. The median follow-up was 36 months. Two groups of patients were identified according to the method of formation of the gastric stump: using 2 (1st group) or 3 (2nd group) stapler cassettes and performing of computed tomography volumetry to determine thevolume of the created gastric stump.Results. Statistically significant differences in the volume of the formed gastric stump, depending on the method of operation, were as follows: 23.8 ml (8.9–37.3 ml) in the 1st group and 47.7 ml (31.9–72.8 ml) in the 2nd group (p<0.0001). Significant differences were observed in the following indicators: relapse of weight gain or ...

Physical Review A, 2013

We analyze the dynamics of a superconducting qubit and the phenomenon of multiorder Rabi oscillat... more We analyze the dynamics of a superconducting qubit and the phenomenon of multiorder Rabi oscillations in the presence of a time-modulated external field. Such a field is also presented as a bichromatic field consisting of two spectral components, which are symmetrically detuned from the qubit resonance frequency. This approach leads to obtaining qualitative quantum effects beyond those for the case of monochromatic excitation of qubits. We calculate Floquet states and quasienergies of the composite system "superconducting qubit plus time-modulated field" for various resonant regimes. We analyze the dependence of quasienergies from the amplitude of an external field, demonstrating the zeros of difference between quasienergies. We show that, as a rule, populations of qubit states exhibit aperiodic oscillations, but we demonstrate the specific important regimes in which dynamics of populations becomes periodically regular.

Deflection of an atomic beam passing through two crossed standing light waves is proposed for stu... more Deflection of an atomic beam passing through two crossed standing light waves is proposed for studies of transition through the Raman resonance in Λ -atomic systems. Considering different regimes of excitation of Λ -atoms by offresonant standing waves, we demonstrate that the deflection patterns, in the plane perpendicular to the direction of the center of atomic mass motion, are essentially different for the cases of one-photon and two-photon excitations. Visualization of the quantum superposition states of low atomic levels on the two-dimensional spatial patterns of atomic deflection is performed.

We study qubit manipulations by a train of pulses in a systematic approach based on the Magnus ex... more We study qubit manipulations by a train of pulses in a systematic approach based on the Magnus expansion and Furry representation in quantum electrodynamics. Furry–Magnus expansion gives approximate exponential representation of a time-evolution operator without the Dyson time-ordering procedure for interactions with external fields of arbitrary intensity and allows us to obtain general expression for single-qubit populations as a function of time-dependent Rabi frequency. The concrete calculations are performed for tunneling quantum dynamics, for multiphoton resonance interactions of qubits, as well as for off-resonance excitations of qubits driven by Gaussian pulses beyond rotating wave approximation. In this way, the populations of qubit states are investigated for various operational regimes, including single-pulse excitation and two-pulse excitation with a phase shift between pulse envelopes being the controlling parameter, and for excitation with sequential pulses. In the last...

IOP Conference Series: Materials Science and Engineering, 2021

The urgent task which is addressed in this work is the development of methods for determining the... more The urgent task which is addressed in this work is the development of methods for determining the frequencies and forms of vibrations, as well as dynamic reactions of thin slabs with various support systems, including those supported on point supports. The aim of the work is to develop experimental methods for determining the frequencies and forms of natural oscillations of slabs with holes and thin point-supported square solid ones. In this work, the frequencies of square slabs with free edges resting on point supports are determined; the dependences of the vibration frequencies of slabs from the coordinates of point supports and the dimensions of symmetrically placed holes; the arrangement of point supports, wherein the basic frequency of free vibrations of the slab is maximum; the frequencies, shapes, and decrements of vibrations of square slabs supported on four point supports were determined experimentally, as well as the influence of the presence of holes and the degree of pin...

Grekov's Bulletin of Surgery

INTRODUCTION. Bariatric operations lead to changes in body composition. The desired fat loss may ... more INTRODUCTION. Bariatric operations lead to changes in body composition. The desired fat loss may be accompanied by decrease of muscle mass, thus raising the risk of sarcopenia.The OBJECTIVE was to evaluate the long-term results of surgical treatment of morbid obesity and concomitant comorbid conditions, as well as a decrease of muscle mass in the pre - and long-term postoperative period.METHODS AND MATERIALS. This prospective randomized controlled blind trial included the results of treatment of 241 patients. Patients were divided into 2 groups depending on the type of surgical treatment. The first group consisted of 116 people who underwent RYGB; the second group included 125 patients who underwent OAGB/MGB. 83 patients from the first group and 95 patients from the control group at the preoperative stage and 24 months after the operation randomly underwent bioelectrical impedance with the determination of skeletal muscle mass (SMM) and skeletal muscle mass index (SMMI)=SMM/Height2....

Modern technologies in ophtalmology

Physical Review A

The deflection of atoms in a Λ-type configuration passing through two crossed standing light wave... more The deflection of atoms in a Λ-type configuration passing through two crossed standing light waves is proposed for the probing and visualization of atomic superposition states. For this goal, we use both the large-dispersive and Raman-resonant regimes of atom-field interaction, giving rise to position-dependent phase shifts of fields, and perform double simultaneous spatial measurements on an atom. In this way, it is demonstrated that the deflection spatial patterns of atoms in a Λ-configuration passing through modes of standing waves are essentially modified if the atoms are initially prepared in coherent superpositions of their low-level states as well as when the superposition states are created during the process of deflection. There are similar results for the joint momentum distributions of atoms. Furthermore, considering both one-photon- and two-photon-excitation regimes of Λ atoms, we also illustrate that the two-dimensional patterns of defected atoms qualitatively reflect t...