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Search Results: 1 - 10 of 386 matches for " Petko Todorov "
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Detection of slow atoms confined in a Cesium vapor cell by spatially separated pump and probe laser beams
Petko Todorov,Nikoolay Petrov,Isabelle Maurin,Solomon Saltiel,Daniel Bloch
Physics , 2013, DOI: 10.1117/12.2014930
Abstract: The velocity distribution of atoms in a thermal gas is usually described through a Maxwell-Boltzman distribution of energy, and assumes isotropy. As a consequence, the probability for an atom to leave the surface under an azimuth angle {\theta} should evolve as cos {\theta}, in spite of the fact that there is no microscopic basis to justify such a law. The contribution of atoms moving at a grazing incidence towards or from the surface, i.e. atoms with a small normal velocity, here called "slow" atoms, reveals essential in the development of spectroscopic methods probing a dilute atomic vapor in the vicinity of a surface, enabling a sub-Doppler resolution under a normal incidence irradiation. The probability for such "slow" atoms may be reduced by surface roughness and atom-surface interaction. Here, we describe a method to observe and to count these slow atoms relying on a mechanical discrimination, through spatially separated pump and probe beams. We also report on our experimental progresses toward such a goal.
A 2D nanosphere array for atomic spectroscopy
Marco Romanelli,Isabelle Maurin,Petko Todorov,Chia-Hua Chan,Daniel Bloch
Physics , 2007, DOI: 10.1051/anphys:2008024
Abstract: We are interested in the spectroscopic behaviour of a gas confined in a micrometric or even nanometric volume. Such a situation could be encountered by the filling-up of a porous medium, such as a photonic crystal, with an atomic gas. Here, we discuss the first step of this program, with the generation and characterization of a self-organized 2D film of nanospheres of silica. We show that an optical characterization by laser light diffraction permits to extract some information on the array structure and represents an interesting complement to electron microscopy.
Dicke Coherent Narrowing in Two-Photon and Raman Spectroscopy of Thin Vapour Cells
Gabriel Dutier,Petko Todorov,Ismahène Hamdi,Isabelle Maurin,Solomon Saltiel,Daniel Bloch,Martial Ducloy
Physics , 2005, DOI: 10.1103/PhysRevA.72.040501
Abstract: The principle of coherent Dicke narrowing in a thin vapour cell, in which sub-Doppler spectral lineshapes are observed under a normal irradiation for a l/2 thickness, is generalized to two-photon spectroscopy. Only the sum of the two wave vectors must be normal to the cell, making the two-photon scheme highly versatile. A comparison is provided between the Dicke narrowing with copropagating fields, and the residual Doppler-broadening occurring with counterpropagating geometries. The experimental feasibility is discussed on the basis of a first observation of a two-photon resonance in a 300 nm-thick Cs cell. Extension to the Raman situation is finally considered.
Testing the distance-dependence of the van der Waals interaction between an atom and a surface through spectroscopy in a vapor nanocell
Athanasdios Laliotis,Isabelle Maurin,Petko Todorov,Ismahène Hamdi,Gabriel Dutier,Alexander Yarovitski,Solomon Saltiel,Marie-Pascale Gorza,Michèle Fichet,Martial Ducloy,Daniel Bloch
Physics , 2007, DOI: 10.1117/12.726798
Abstract: This paper presents our current measurements in a vapor nanocell aiming at a test of the distance-dependence of the atom-surface interaction, when simple asymptotic descriptions may turn to be not valid. A state-of-the-art of atom-surface interaction measurements is provided as an introduction, along with the comparison with the theory of the van der Waals (or Casimir-Polder) interaction; it is followed by a presentation of the most salient features of nanocell spectroscopy
Exploring the van der Waals Atom-Surface attraction in the nanometric range
Michèle Fichet,Gabriel Dutier,Alexander Yarovitski,Petko Todorov,Ismahène Hamdi,Isabelle Maurin,Solomon Saltiel,David Sarkisyan,Marie-Pascale Gorza,Daniel Bloch,Martial Ducloy
Physics , 2006, DOI: 10.1209/0295-5075/77/54001
Abstract: The van der Waals atom-surface attraction, scaling as C3 z-3 for z the atom-surface distance, is expected to be valid in the distance range 1-1000 nm, covering 8-10 orders of magnitudes in the interaction energy. A Cs vapour nanocell allows us to analyze the spectroscopic modifications induced by the atom-surface attraction on the 6P3/2->6D5/2 transition. The measured C3 value is found to be independent of the thickness in the explored range 40-130 nm, and is in agreement with an elementary theoretical prediction. We also discuss the specific interest of exploring short distances and large interaction energy.
Drag Forces, Neutral Wind and Electric Conductivity Changes in the Ionospheric E Region
Petko Nenovski
Physics , 2014,
Abstract: The neutrals in the Earth environment are in fact free and subjected to drag forces (by ions). In this study we show that drag or friction forces in the ionosphere-thermosphere system initiate changes in the plasma flow, neutral wind, and the conductivity, as well. Ions and electrons embedded in neutral wind field of velocity u acquire drifts perpendicular both to the initial neutral wind velocity and to the ambient magnetic field producing a perpendicular electric current. This perpendicular electric current is defined by a conductivity derived previously and the polarization electric field u x B. Self-consistently, the free neutrals acquires an additional neutral velocity component perpendicular to the initial neutral wind velocity u. The Pedersen and Hall currents wane within a specific time inversely proportional to neutral-ion collision frequency. These findings are relevant to a better understanding of electric current generation, distribution and closure in weakly ionized plasmas where charged particles (plasma) and neutrals are not bound (free) as the ionosphere and thermosphere in the Earth environment, the solar atmosphere-chromosphere region and even dusty plasmas. The theoretical results supposedly address to recent observations of meso-scale neutral wind rotation in the vicinity of auroral arcs (Kosch et al, 2010).
Global surface wave resonances of the earth magnetosphere and their possible manifestation
Petko Nenovski
Physics , 2014,
Abstract: In this paper global surface wave modes supported by plasma discontinuities at both the magnetopause and the plasmapause are considered. The ionosphere at the ends of the magnetic field lines of the earth outer magnetosphere is considered as reflecting boundaries of the surface waves that propagate along the plasma boundaries. As a result a standing wave structure along the magnetic field fluxes of the outer magnetosphere, i.e. surface wave resonance structure can be formed. Due to quantized wavenumbers along the magnetic field lines, the surface wave resonance possesses quantified frequencies in a following way: f = nfres, where fres is frequency of the corresponding fundamental surface wave resonance and n is an integer. Global Pc5 pulsations have been observed and interpreted mostly as cavity modes of the earth magnetosphere. The global Pc5 pulsations however could alternatively be interpreted as ultra low-frequency surface wave resonances of the earth magnetosphere that do not necessarily involve the cavity mode-field aligned resonance transformation concept.
Method for Tentative Evaluation of Membrane Permeability Coefficients for Sodium and Potassium Ions in Unicellular Organisms  [PDF]
Atanas Todorov Atanasov
Open Journal of Biophysics (OJBIPHY) , 2013, DOI: 10.4236/ojbiphy.2013.31A012
Abstract:

The membrane permeability coefficient for sodium and potassium ions in unicellular organisms can be calculated using the data for cell volume, surface and mean generation time during growth and dividing of cells by binary. Accordingly theory of proposed method, the membrane permeability coefficients for passed trough outer cell membrane sodium and potassium ions, is equal to the volume of unicellular organism divided to product between cell surface and mean generation time of cells. The calculated by this way diapason of values overlaps with experimentally measured diapason of values of permeability coefficient for sodium and potassium ions. The deviation between the theoretically calculated and experimentally measured values of permeability coefficient does not exceed one order of magnitude.

Length of Periods in the Nasal Cycle during 24-Hours Registration  [PDF]
Atanas Todorov Atanasov
Open Journal of Biophysics (OJBIPHY) , 2014, DOI: 10.4236/ojbiphy.2014.43010
Abstract:
The periodic congestion and decongestion of the nasal venous sinuses and an alternation of airflow from one side of the nose to the other are known in literature as “nasal cycle”. It is established that nasal cycle during 24-hours registration contains from 4 to 8 time full periods, length of which varies from 0.80 h to 5.75 h. The mean length of all full periods is 2.80 ± 0.17 h. The mean length of full periods of left nostril is 3.07 h and the mean length of periods of right nostril is 2.43 h. The result suggests that there is any asymmetry in length of periods of airflow trough left and right nostrils about 40 min. The longer periods of left nostril can be connected with higher metabolic and functional activity of brain and human organism during active work.
Nasal Cycle Dilemma: Nasal Cycle Is Associated to Brain Wake/REM States or Is Associated to Conscious State in Them?  [PDF]
Atanas Todorov Atanasov
Open Journal of Biophysics (OJBIPHY) , 2019, DOI: 10.4236/ojbiphy.2019.91001
Abstract: Experimental and theoretical arguments have been described in favor of the hypothesis that the nasal cycle reversals of the nostril’s airflow occurs only in the consciousness states of the brain (during awake/wake state, REM state and during dreams in St.1, 2 of the non-REM sleep). This finding gives possibility to use nasal cycle as “marker for consciousness states”. An idea for clinical application of the hypothesis is proposed.
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