Coherent interaction of laser pulses in a resonant optically dense extended medium under the regime of strong field-matter coupling

Nonstationary pump-probe interaction between short laser pulses propagating in a resonant optically dense coherent medium is considered. A special attention is paid to the case, where the density of two-level particles is high enough that a considerable part of the energy of relatively weak external laser-fields can be coherently absorbed and reemitted by the medium. Thus, the field of medium reaction plays a key role in the interaction processes, which leads to the collective behavior of an atomic ensemble in the strongly coupled light-matter system. Such behavior results in the fast excitation interchanges between the field and a medium in the form of the optical ringing, which is analogous to polariton beating in the solid-state optics. This collective oscillating response, which can be treated as successive beats between light wave-packets of different group velocities, is shown to significantly affect propagation and amplification of the probe field under its nonlinear interaction with a nearly copropagating pump pulse. Depending on the probe-pump time delay, the probe transmission spectra show the appearance of either specific doublet or coherent dip. The widths of these features are determined by the density-dependent field-matter coupling coefficient and increase during the propagation. Besides that, the widths of the coherent features, which appear close to the resonance in the broadband probe-spectrum, exceed the absorption-line width, since, under the strong-coupling regime, the frequency of the optical ringing exceeds the rate of incoherent relaxation. Contrary to the stationary strong-field effects, the density- and coordinate-dependent transmission spectra of the probe manifest the importance of the collective oscillations and cannot be obtained in the framework of the single-atom model.Comment: 10 pages, 8 figures, to be published in Phys. Rev.

Resonant nonstationary amplification of polychromatic laser pulses and conical emission in an optically dense ensemble of neon metastable atoms

Experimental and numerical investigation of single-beam and pump-probe interaction with a resonantly absorbing dense extended medium under strong and weak field-matter coupling is presented. Significant probe beam amplification and conical emission were observed. Under relatively weak pumping and high medium density, when the condition of strong coupling between field and resonant matter is fulfilled, the probe amplification spectrum has a form of spectral doublet. Stronger pumping leads to the appearance of a single peak of the probe beam amplification at the transition frequency. The greater probe intensity results in an asymmetrical transmission spectrum with amplification at the blue wing of the absorption line and attenuation at the red one. Under high medium density, a broad band of amplification appears. Theoretical model is based on the solution of the Maxwell-Bloch equations for a two-level system. Different types of probe transmission spectra obtained are attributed to complex dynamics of a coherent medium response to broadband polychromatic radiation of a multimode dye laser.Comment: 9 pages, 13 figures, corrected, Fig.8 was changed, to be published in Phys. Rev.

Decoherence and Noise in Loschmidt Echo Experiments

We discuss some recent results concerning the decoherence in controlled quantum open systems within the mathematical setting corresponding to motion reversal experiments (the Loschmidt echo). We compare the case of randomly chosen sequence of unitary dynamical maps with the case of a constant dynamics corresponding to a classically chaotic evolution. The interplay between chaos and decoherence is illustrated by the new numerical results on the quantum Arnold cat map perturbed by a measurement process. Open problems related to the simple operational characterization of the decoherence strength are discussed

The ecological and material-saving technology for producing brake blocks with stable parameters of quality. Part 2. Verification of modernized technology under real conditions

Prezentowany artykuł jest drugim z cyklu omawiającym prace badawcze związane z udoskonaleniem technologii produkcji wstawek hamulcowych dla kolejnictwa w odlewni Spomel w Lęborku. Współpraca z Instytutem rozpoczęła się od realizacji projektu modernizacji procesu wytwarzania odlewów nowej generacji nieiskrzących wstawek hamulcowych dla potrzeb kolejnictwa w latach 2000−2001. W ramach tego projektu opracowana została ekologiczna i materiałooszczędna technologia wytwarzania nieiskrzących wstawek hamulcowych o wysokich parametrach jakościowych. Wyniki badań nad opracowaniem tej technologii przedstawiono w niniejszym artykule. Badania te obejmowały między innymi opracowanie metod zasilania odlewu, dobór składu mas formierskich i rdzeniowych zapewniających uzyskanie poprawy dokładności wymiarowej oraz jakości powierzchni odlewów, stabilizację parametrów technologicznych wykonywania form odlewniczych, badania struktury, właściwości mechanicznych i ścieralności tworzywa odlewów testowych, a także określenie parametrów technologicznych procesu odlewniczego.The presented article is the second in the series, which presents research related to the improvement of technology for producing brake blocks for the railway industry in the Spomel foundry in Lębork. The cooperation with the Foundry Research Institute started with the implementation of a project which modernised the process for producing casts of a new generation of non-sparking brake blocks for the needs of the railway industry in the years 2000−2001. Within the framework of this project an ecological and material-saving technology was developed for producing non-sparking brake blocks with high quality parameters. The research results obtained from the development of the technology are presented in the present article. The research included, among other things, the development of a method for feeding the cast, the selection of moulding and core sands which ensure improved dimensional accuracy and quality of surfaces of casts, stabilisation of technological parameters of produced casting moulds, the research of the structure, mechanical properties and abrasion of examined cast material, as well as determination of technological parameters for the casting process

The ecological and material-saving technology for producing brake blocks with stable parameters of quality. Part 1. Technology modernization using computer simulation

Prezentowany artykuł jest pierwszym z cyklu omawiającym prace badawcze związane z udoskonaleniem technologii produkcji wstawek hamulcowych dla kolejnictwa w odlewni Spomel w Lęborku. Współpraca z Instytutem rozpoczęła się od realizacji projektu modernizacji procesu wytwarzania odlewów nowej generacji nieiskrzących wstawek hamulcowych dla potrzeb kolejnictwa w latach 2000−2001. W ramach tego projektu opracowana została ekologiczna i materiałooszczędna technologia wytwarzania nieiskrzących wstawek hamulcowych o wysokich parametrach jakościowych. Wyniki badań nad opracowaniem tej technologii przedstawiono w niniejszym artykule. Badania te obejmowały między innymi opracowanie metod zasilania odlewu, dobór składu mas formierskich i rdzeniowych zapewniających uzyskanie poprawy dokładności wymiarowej oraz jakości powierzchni odlewów, stabilizację parametrów technologicznych wykonywania form odlewniczych, badania struktury, właściwości mechanicznych i ścieralności tworzywa odlewów testowych, a także określenie parametrów technologicznych procesu odlewniczego.The presented article is the first in the series, which presents research related to the improvement of technology for producing brake blocks for the railway industry in the Spomel foundry in Lębork. The cooperation with the Foundry Research Institute started with the implementation of a project which modernised the process for producing casts of a new generation of non-sparking brake blocks for the needs of the railway industry in the years 2000−2001. Within the framework of this project an ecological and material-saving technology was developed for producing non-sparking brake blocks with high quality parameters. The research results obtained from the development of the technology are presented in the present article. The research included, among other things, the development of a method for feeding the cast, the selection of moulding and core sands which ensure improved dimensional accuracy and quality of surfaces of casts, stabilisation of technological parameters of produced casting moulds, the research of the structure, mechanical properties and abrasion of examined cast material, as well as determination of technological parameters for the casting process

Generalised heart rate statistics reveal neurally mediated homeostasis transients

Distributions of accelerations and decelerations, obtained from increments of heart rate recorded during a head-up tilt table (HUTT) test provide short-term characterization of the complex cardiovascular response to a rapid controlled dysregulation of homeostasis. A generalised statistic is proposed for evaluating the neural reflexes responsible for restoring the homeostatic dynamics. An evaluation of the effects on heart rate of the neural regulation involved in achieving homeostasis indicates a distinction between vasovagal patients and healthy subjects who are not susceptible to spontaneous fainting. A healthy cardiovascular response to the HUTT test is identified in the sympathetic tone appropriately punctuated by vagal activity