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When studying the spin-noise-induced fluctuations of Kerr rotation in a quantum-well microcavity, we have found a dramatic increase of the noise signal (by more than two orders of magnitude) in the vicinity of anti-crossing of the polariton branches. The effect is explained by nonlinear optical instability of the microcavity giving rise to the light-power-controlled amplification of the polarization noise signal. In the framework of the developed model of built-in amplifier, we also interpret the nontrivial spectral and intensity-related properties of the observed noise signal below the region of anti-crossing of polariton branches. The discovered effect of optically controllable amplification of broadband polarization signals in microcavities in the regime of optical instability may be of interest for detecting weak oscillations of optical anisotropy in fundamental research and for other applications in optical information processing. [ABSTRACT FROM AUTHOR]

In a cohort of 106 donors, we analyzed correlations in the binding of natural antibodies to human glycans in a composition of the glycan array. Along with trivial relationships (between structurally similar glycans), we found a high positive correlation between completely unrelated glycans. The most intriguing among the negative is the correlation of average strength (close to –0.5) between antibodies to Galβ1-3GlcNAc and antibodies to lactosamines (Galβ1-4GlcNAc)n. The reason for the functional antagonism between these antibodies is not yet clear. [ABSTRACT FROM AUTHOR]

We present results of numerical simulations of the kinetics of exciton-exciton annihilation of weakly localized one-dimensional Frenkel excitons at low temperatures. We find that the kinetics is represented by two well-distinguished components: a fast short-time decay and a very slow long-time tail. The former arises from excitons that initially reside in states belonging to the same localization segment of the chain, while the slow component is caused by excitons created on different localization segments. We show that the usual bimolecular theory fails in the description of the behavior found. We also present a qualitative analytical explanation of the nonexponential behavior observed in both the short- and the long-time decay components. Finally, it is shown that our theoretical estimate for the annihilation time of the fast component is in good agreement with data obtained from transient absorption experiments on J-aggregates of pseudoisocyanine. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Cooperative radiation emitted by an ensemble of three-level optical systems with a doublet in the ground state (Λ scheme), which is placed into a cyclic cavity, is studied theoretically. In contrast to the two-level model of emitters, this process with such a configuration of operating transitions may occur without population inversion in the whole, if the doublet is prepared at the initial instant in a superposition (coherent) state. In the ideal case of a Hamilton system, in which the cavity losses and relaxation in the radiator ensemble are disregarded, the conservation laws are derived, which allow a substantial reduction of the dimension of the phase space of the model (ℝ → ℝ) and the application of methods of dynamics of nonlinear systems for analyzing the three-level superradiance under these conditions. The possibility of different (both quasiperiodic and chaotic) scenarios of the three-level superradiance is demonstrated on the basis of Poincaré's mappings. Global bifurcation of the system upon a transition from the conventional superradiance regime to inversionless one is revealed. The effects of cavity losses, as well as homogeneous and inhomogeneous broadening in the system of radiators on the regularities found are also discussed. [ABSTRACT FROM AUTHOR]

Superradiance of three-level optical systems with a doublet in the ground state (Λ-scheme) placed in a high- Q cavity is studied theoretically. The conservation laws are obtained, which allow to considerably reduce the dimension of the phase space of the examined model (R→R). In the particular case of a degenerate doublet, a mapping that makes it possible to reduce the problem of the three-level superradiance to a Duffing oscillator model (R→R) is found. It is shown the possibility to initiate the superradiance generation even in the case when the population of the upper level is smaller than the total population of the lower doublet, i.e., without population inversion on the whole. [ABSTRACT FROM AUTHOR]

We exploit the potential of the spin noise spectroscopy (SNS) for studies of nuclear spin dynamics in n-GaAs. The SNS experiments were performed on bulk n-type GaAs layers embedded into a high-finesse microcavity at negative detuning. In our experiments, nuclear spin polarisation initially prepared by optical pumping is monitored in real time via a shift of the peak position in the electron spin noise spectrum. We demonstrate that this shift is a direct measure of the Overhauser field acting on the electron spin. The dynamics of nuclear spin is shown to be strongly dependent on the electron concentration. [ABSTRACT FROM AUTHOR]

A dual‐band shared‐aperture antenna with a frequency ratio of 3 is presented in the letter. A low‐band antenna consists of two printed dipoles. An artificial magnetic conductor (AMC) is used to reduce the height of the low‐band antenna. A high‐band antenna consists of four printed dipoles. It is placed between the AMC elements and the antenna ground plane. The AMC elements and antenna ground plane form a Fabry–Perot cavity and allow increasing gain of the high‐band antenna. An additional structure is inserted between the antenna ground plane and the AMC elements to decrease heights of the Fabry–Perot cavity and the high‐band antenna simultaneously. The total size of the proposed antenna is 1.02λL × 1.02λL × 0.103λL (λL is the central wavelength of the low operating band). Simulated and measured results show that the designed antenna has 57% and 16.7% bandwidths in the low‐ and high‐frequency bands. [ABSTRACT FROM AUTHOR]

The optical gyrotropy noise of a high-finesse semiconductor Bragg microcavity with an embedded quantum well (QW) is studied at different detunings of the photon mode with respect to the QW exciton resonances. A strong suppression of the noise magnitude for the photon mode frequencies lying above exciton resonances is found. We show that such a critical behavior of the observed optical noise power is specific to asymmetric Fabry-Perot resonators. As follows from our analysis, at a certain level of intracavity loss, the reflectivity of the asymmetric resonator vanishes, while the polarimetric sensitivity to the gyrotropy changes dramatically when moving across the critical point. The results of model calculations are in a good agreement with our experimental data on the spin noise in a single-quantum-well microcavity and are confirmed also by the spectra of the photoinduced Kerr rotation in the pump-probe experiments. [ABSTRACT FROM AUTHOR]

We report on an experimental observation of spin noise in a single semiconductor quantum well embedded into a microcavity. The great cavity-enhanced sensitivity to fluctuations of optical anisotropy has allowed us to measure the Kerr rotation and ellipticity noise spectra in the strong-coupling regime. The spin noise spectra clearly show two resonant features: a conventional magnetoresonant component shifting towards higher frequencies with a magnetic field and an unusual "nonmagnetic" component centered at zero frequency and getting suppressed with an increasing magnetic field. We attribute the first of them to the Larmor precession of free electron spins, whereas, the second one is presumably due to hyperfine electron-nuclei spin interactions. [ABSTRACT FROM AUTHOR]

A cavity-like regime of superradiance for a double-layer medium populated by atoms with the A-scheme of transitions is considered in a semiclassical approximation under the condition that the layers are arranged symmetrically with respect to initial characteristics of the field and atomic system populating the layers. An analytical law for the linear stage of the superradiance process is found that agrees well with numerical solution of the differential equations of the model under consideration for any initial conditions nearly up to the peak of the appropriate characteristic of the field intensity module. For the case of degenerate lower doublet, the resonant character of the dependence of the superradiance pulse time delay on the distance between the layers is studied. [ABSTRACT FROM AUTHOR]

We have measured fission fragment-mass yields for neutron-induced fission of 232Th and 238U at energies 32.8, 45.3, and 59.9 MeV. The experiments were done at quasimonoenergetic neutron beams of the Cyclotron Research Center at Louvain-la-Neuve. To detect the fission fragments, a multisection Frisch-gridded ionization chamber was used. The measurement and data analysis techniques are discussed in detail. The obtained mass yields are compared to model calculations with the intermediate-energy nuclear reaction code MCFX. The MCFX code is used to calculate the fraction of fissioning nuclei after cascade, preequilibrium, and statistical reaction stages. The formation of mass distributions is considered as a result of oscillations of the mass-asymmetry degree of freedom in the potential well calculated with the temperature-dependent shell correction method. The experimental results as well as the results of the model calculations demonstrate that the probability of symmetric fission increases with incident neutron energy for both nuclei. The comparison also shows that the symmetric fission is more enhanced for thorium than for uranium with increasing neutron energy. We also compare 238U results with available experimental data; the 232Th data were measured for the first time. [ABSTRACT FROM AUTHOR]

In spin noise spectroscopy, the magnetic susceptibility spectrum is known to be provided by the spin-system untouched by any external perturbation, or, better to say, disturbed only by its thermal bath. We propose a new version of spin noise spectroscopy, with the detected magnetization (Faraday-rotation) noise being "stimulated" by an external fluctuating magnetic field with a quasiwhite spectrum. An experimental study of the stimulated spin noise performed on a BaF 2 : U 3 + crystal in a longitudinal magnetic field has revealed specific features of this approach and allowed us to identify the Van-Vleck and population-related contributions to the AC susceptibility of the system and to discover unusual magnetic-field dependence of the longitudinal spin relaxation rate in low magnetic fields. It is shown that spectra of the stimulated and spontaneous spin noise, being both closely related to the spin-system magnetic susceptibility, are still essentially different. Distinctions between the two types of the spin-noise spectra and two approaches to spin noise spectroscopy are discussed. [ABSTRACT FROM AUTHOR]

The effect of the local field on the competition of transitions in the superradiance of an incompletely excited thin layer of three-level atoms (A-diagram of working transitions) is studied. The analysis made proves that the upper sublevel of the lower doublet is initially unpopulated. It is shown that the Raman transition, in the local-field regime, is ahead of the development of the superradiance pulse and causes the transfer of populations between sublevels of the lower doublet. [ABSTRACT FROM AUTHOR]

Excitation of stimulated photon echo by two incoherent pulses obtained from one source and one coherent pulse is considered. The dependence of the average amplitude of stimulated echo on the parameters of noise pulses is determined. The results can be used for analysis of the corresponding algorithm of excitation of stimulated spin echo, as well as in calculations of characteristics of the signal processors based on the phenomena of photon and spin echoes. [ABSTRACT FROM AUTHOR]

The effect of a local field on the transition competition in the process of superradiance of a thin layer of three-level atoms (Γ-configuration of working transitions) in the presence of an initial coherence of the lower doublet is investigated. It is shown that under the action of a local field, a coherent Raman transition between sublevels of the lower doublet can take place. [ABSTRACT FROM AUTHOR]

We analyze the possibility of superradiance in an ensemble of three-level atoms in the absence of population inversion. We show that in the case of a A configuration of the active transitions this effect can occur for an initially coherent superposition of the states of the lower doublet. We also study how splitting of the lower levels influences this effect and discuss ways of creating low-frequency coherence. [ABSTRACT FROM AUTHOR]

Objective: Synthetic lipophilic constructs (Function–Spacer–Lipids, FSLs) are excellent tools for modification of cell surface with almost any molecular fragment. The aim of this research is synthesis of FSLs containing both glycan and fluorescent tag introduced in the structure of the construct independently to each other. Such compounds allow to avoid treatment with fluorescently labeled antibodies prior to visualization of inserted glycans by confocal microscopy thus opening the wide range of possibilities for studying biological processes involving these glycans. Methods: Two FSLs containing same glycan, A (type 2) tetrasaccharide, and spacerlipid block, CMG (carboxymethylglycine) spacer-arm and DOPE (dioleoylphosphatidylethanolamine) lipid, and various fluorescent tags, fluoresceine and sulfo-Cyanine-3, were synthesized. Derivatives of α- or ε-azido lysine were used as central blocks, to which all other fragments were attached. Two various approaches differing in the order of introduction of components were employed. Conjugation via CuAAC reaction was used in both synthetic schemes. Results and Discussion: The first approach (the following order of attachment of components: glycan, then spacer-lipid, then fluorescent tag) allowed to obtain target FSL according to proposed synthetic plan. When the second approach was employed (the following order of attachment: fluorescent tag, then glycan, then spacer–lipid), side reaction of racemization of central lysine block was observed during conjugation of glycan part. To overcome this problem, synthetic sequence was changed: amino group in lysine unit was protected and glycan was introduced prior to fluorescent tag. This modification allowed to avoid undesired racemization. Conclusions: Two FSL constructs containing A (type 2) tetrasaccharide, CMG–DOPE spacer-lipid block, and fluorescent tag (fluoresceine or sulfo-Cyanine-3) were obtained. Independent manner of attachment of glycan and fluorophore allows to study interaction of glycan with carbohydrate binding proteins directly in the cell membrane. [ABSTRACT FROM AUTHOR]

We study theoretically the nonlinear optical response of a monolayer of regularly arranged three-level identical quantum emitters with a doublet in the excited state to the action of a monochromatic electromagnetic field quasi-resonant to optical transitions in the emitter. The total retarded dipole–dipole interaction of the emitters is accounted for in the mean-field approximation. This interaction plays the role of a positive feedback, which (in combination with the immanent nonlinearity of emitters themselves) leads to multistability of the monolayer response. The stability of different response branches is analyzed using the Lyapunov exponents method. It is found that the instability type depends on the doublet splitting and changes from self-oscillations to chaos upon increasing the splitting. Another important property of the monolayer is its high (almost 100%) reflectance in a certain frequency range; i.e., within this range, the monolayer operates as a perfect nanometer mirror; moreover, reflection can be switched to transmission changing slightly the incident field amplitude (bistability). The possibility of application of the above mentioned monolayer optical properties in nanophotonics is discussed. [ABSTRACT FROM AUTHOR]

Synthetic analogs of glycolipids are widely used for modification of the cell membrane with glycans. Constructs capable of selective (or even specific) insertion into membrane rafts are of special interest because various molecules (transmembrane proteins, their cofactors, and glycosphingolipids) essential for cellular processes are concentrated in these domains. A suitable lipid part for such constructs is a cholesterol derivative that retain the ability of the 3β-substituent to form the hydrogen bonds in the plasma membrane. Herein, synthesis of lipophilic construct containing 3β-cholesterylamine as a lipid part and blood group A (type 2) tetrasaccharide as a glycan part is described. [ABSTRACT FROM AUTHOR]

We report on experimental study of the exciton-polariton emission (PE) polarization noise below and above the polariton lasing threshold under continuous-wave nonresonant excitation. The experiments were performed with a high-Q graded 5λ/2 GaAs/AlGaAs microcavity with four sets of three quantum wells in the strong-coupling regime. The PE polarization noise substantially exceeded in magnitude the shot-noise level and, in the studied frequency range (up to 650 MHz), had a flat spectrum. We have found that the polarization and intensity noise dependences on the pump power are strongly different. This difference is ascribed to the bosonic stimulation effect in spin-dependent scattering of the polaritons to the condensate. A theoretical model describing the observed peculiarity of the PE polarization noise is proposed. [ABSTRACT FROM AUTHOR]

Glycolipids are components of the cell membrane capable of transport both from it and in the opposite direction, i.e. from the intercellular matrix to the membrane. The latter opens up the possibility of studying the functioning of glycolipids by their inserting into the cell membrane. In practice, synthetic analogs of glycolipids are significantly more suitable than natural glycolipids for such application, because one can vary properties, modifying their structure, as well as conjugating to other bioactive components, in addition to glycans. This study describes the synthesis of the eight glycolipids containing the same glycan part (A (type 2) tetrasaccharide) but varying in the composition of the lipid part as well as analogs of glycolipids carrying several identical carbohydrate moieties. The resulting series of synthetic analogs of glycolipids opens up the possibility of studying the immunological presentation of the glycan and its recognition by antibodies in the real microenvironment (glycocalyx) of a living cell. [ABSTRACT FROM AUTHOR]

We attract attention to the fact that the ultimate (shot-noise-limited) polanmetric sensitivity can be enhanced by orders of magnitude leaving the photon flux incident onto the photodetector on the same low level. This opportunity is of crucial importance for present-day spin noise spectroscopy, where a direct increase of sensitivity by increasing the probe beam power is strongly restricted by the admissible input power of the broadband photodetectors. The gain in sensitivity is achieved by replacing the 45° polarization geometry commonly used in conventional schemes with balanced detectors by geometries with stronger polarization extinction. The efficiency of these high-extinction polarization geometries with enhancement of the detected signal by more than an order of magnitude is demonstrated by measurements of the spin noise spectra of bulk n:GaAs in the spectral range 835-918 nm. It is shown that the inevitable growth of the probe beam power with the sensitivity gain makes spin noise spectroscopy much more perturbative, but, at the same time, opens up fresh opportunities for studying nonlinear interactions of strong light fields with spin ensembles. [ABSTRACT FROM AUTHOR]

The network of adhesion/growth-regulatory galectins in chicken (chicken galectin, CG) has only one tandemrepeat-type protein, CG8. Using a cell-based assay and probing galectin reactivity with a panel of fluorescent neoglycoconjugates (glycoprobes), its glycan-binding profile was determined. For internal validation, human galectin-8 (HG8) was tested. In comparison to HG8, CG8 showed a rather similar specificity: both galectins displayed high affinity to blood group ABH antigens as well as to 3′-sialylated and 3′-sulfated lactosamine chains. The most remarkable difference was found to be an ability of HG8 (but not CG8) to bind the disaccharide Galβ1-3GlcNAc (Le) as well as branched and linear oligolactosamines. The glycan-binding profile was shown to be influenced by glycocalix of the cell, where the galectin is anchored. Particularly, glycosidase treatment of galectin-loaded cells led to the change of the profile. Thus, we suppose the involvement of cis-glycans in the interaction of cell-anchored galectins with external glycoconjugates. [ABSTRACT FROM AUTHOR]

The effect of the sample extent in the process of superradiance and superradiance without population inversion of a thin (L ≤ λ) layer of three-level atoms (Λ-configuration of working transitions) is investigated. The limits of applicability of the spatially homogeneous approximation are determined. The consideration of the extent is shown to introduce new effects into the kinetics of populations and the field. [ABSTRACT FROM AUTHOR]

A simple and practical 10-step synthesis is reported for previously unknown diastereomers of C‑methylated spermine (Spm) analogue, 1,12-diamino-3,10-dimethyl-4,9-diazadodecane (3,10-Me2Spm), starting from commercially available enantiomers of 2-(Boc-amino)-1-propanol. Title compounds were prepared in gram scale, in excellent overall yields and enantiomeric purity. Since biochemical properties of 3,10‑Me2Spm can be regulated by changing the configuration of chiral center(s), these analogues are of obvious value for studying not only cellular functions of spermine, but even diseases associated with the disturbances of spermine metabolism. [ABSTRACT FROM AUTHOR]

It is shown analytically that the introduction of the law 'On the Management of Radioactive Waste' and the start of the active phase of the decommissioning of NPP have changed goal-setting in the waste management system and actualized the task of modernizing the system. The necessary conditions for improving the technological platform for managing radioactive waste at NPP (R&D status, experience in using in practice the advances made in science, commercial accessibility of the required materials and technical means) have mostly been formulated. Modernization of the waste management system, as a rule, does not require radical revisions of the design solutions or high material costs. [ABSTRACT FROM AUTHOR]

The report encompasses capabilities of scanning electron microscopy for quantitative diagnostics of morphology and ultimate composition of soft matter nanostructures in the mode of scattered electron registration with energy selection. [ABSTRACT FROM AUTHOR]

We develop a method of nonperturbative optical control over adiabatic remagnetization of the nuclear spin system and apply it to verify the spin temperature concept in GaAs microcavities. The nuclear spin system is shown to exactly follow the predictions of the spin temperature theory, despite the quadrupole interaction that was earlier reported to disrupt nuclear spin thermalization. These findings open a way for the deep cooling of nuclear spins in semiconductor structures, with the prospect of realizing nuclear spin-ordered states for high-fidelity spin-photon interfaces. [ABSTRACT FROM AUTHOR]

Nuclear spin relaxation is studied in n-GaAs thick layers and microcavity samples with different electron densities. We reveal that both in metallic samples where electrons are free and mobile, and in insulating samples where electrons are localized, nuclear spin relaxation is strongly enhanced at low magnetic fields. The origin of this effect could reside in the quadrupole interaction between nuclei and fluctuating electron charges, that has been proposed to govern nuclear spin dynamics at low magnetic fields in the insulating samples. The characteristic values of these magnetic fields are given by dipole-dipole interaction between nuclei in bulk samples, and are greatly enhanced in microcavities, presumably due to additional strain, inherent to microstructures and nanostructures. [ABSTRACT FROM AUTHOR]