Preparation of Partially Degraded Copolymers of Acrylamide with (Acrylamidopropyl)trimethylammonium Chloride in the Presence of Radical Initiators

Chain degradation of copolymers of acrylamide with (acrylamidopropyl)trimethylammonium chloride at 25-50°C in aqueous solutions under the action of radical degradative agents was studied viscometrically. The effiency of controlling the molecular weight of the copolymers was evaluated.     

Optical performance of materials for X‐ray refractive optics in the energy range 8–100 keV

A quantitative analysis of the crucial characteristics of currently used and promising materials for X‐ray refractive optics is performed in the extended energy range 8–100 keV. According to the examined parameters, beryllium is the material of choice for X‐ray compound refractive lenses (CRLs) in the energy range 8–25 keV. At higher energies the use of CRLs made of diamond and the cubic phase of boron nitride (c‐BN) is beneficial. It was demonstrated that the presence of the elements of the fourth (or higher) period has a fatal effect on the functional X‐ray properties even if low‐Z elements dominate in the compound, like in YB₆₆. Macroscopic properties are discussed: much higher melting points and thermal conductivities of C and c‐BN enable them to be used at the new generation of synchrotron radiation sources and X‐ray free‐electron lasers. The role of crystal and internal structure is discussed: materials with high density are preferable for refractive applications while less dense phases are suitable for X‐ray windows. Single‐crystal or amorphous glass‐like materials based on Li, Be, B or C that are free of diffuse scattering from grain boundaries, voids and inclusions are the best candidates for applications of highly coherent X‐ray beams.     

Obtaining DNA aptamers to human interleukin-6 for biomagnetic immunoassay nanosensors

We used aptamers, which are functional equivalents of antibodies, in order to develop a nanosensor immunoassay system based on magnetic nanoparticles and a SQUID magnetometer. Selection was used to obtain DNA aptamers to interleukin-6; their affinity to the target protein was characterized by surface plasmon resonance. It was shown that the biotinylated aptamer binds to magnetic nanoparticles that were functionalized with streptavidin.     

Hard QCD processes and impact-parameter dependence of parton energy losses in ultrarelativistic nuclear collisions

Special features of particle and jet production in hard QCD processes induced by ultrarelativistic heavy-ion collisions are investigated. The energy loss of partons produced in hard collisions that is due to their multiple scattering in dense quark-gluon matter is analyzed as a function of the impact parameter of a nucleus-nucleus collision. The possibility of experimentally observing effects that are expected in this connection and which include different impact-parameter dependences of radiative and collision hard-jet energy losses, a modification to the shape of the impact-parameter distribution of dijets, and the suppression of the yield of muon pairs having large invariant masses is discussed.     

Protective radiolucent aluminium oxide coatings for beryllium X‐ray optics

Beryllium, being one of the most transparent materials to X‐ray radiation, has become the material of choice for X‐ray optics instrumentation at synchrotron radiation sources and free‐electron laser facilities. However, there are concerns due to its high toxicity and, consequently, there is a need for special safety regulations. The authors propose to apply protective coatings in order to seal off beryllium from the ambient atmosphere, thus preventing degradation processes providing additional protection for users and prolonging the service time of the optical elements. This paper presents durability test results for Be windows coated with atomic‐layer‐deposition alumina layers run at the European Synchrotron Radiation Facility. Expositions were performed under monochromatic, pink and white beams, establishing conditions that the samples could tolerate without radiation damage. X‐ray treatment was implemented in various environments, i.e. vacuum, helium, nitrogen, argon and dry air at different pressures. Post‐process analysis revealed their efficiency for monochromatic and pink beams.     

Self-assembly of colloidal cubes via vertical deposition

The vertical deposition technique for creating crystalline microstructures is applied for the first time to nonspherical colloids in the form of hollow silica cubes. Controlled deposition of the cubes results in large crystalline films with variable symmetry. The microstructures are characterized in detail with scanning electron microscopy and small-angle X-ray scattering. In single layers of cubes, distorted square to hexagonal ordered arrays are formed. For multilayered crystals, the intralayer ordering is predominantly hexagonal with a hollow site stacking, similar to that of the face centered cubic lattice for spheres. Additionally, a distorted square arrangement in the layers is also found to form under certain conditions. These crystalline films are promising for various applications such as photonic materials.     

Resonant interaction of femtosecond radiation with a cloud of cold <Superscript>87</Superscript>Rb atoms

The resonant interaction of ⁸⁷Rb atoms in a magneto-optical trap with femtosecond laser radiation in the spectral range 760–820 nm has been investigated experimentally. It has been demonstrated that femtosecond laser radiation with a spectral width of 10 nm interacts with an atomic ensemble as a set of spectrally narrow modes and as an ionizing laser field simultaneously. The dynamics of trap loading in the presence of ionization by femtosecond radiation has been studied, and the 5D _5/2 level population produced by an additional weak laser field has been measured.     

Classical gluon fields and collective dynamics of color-charge systems

Physics of Atomic Nuclei - An investigation of color fields that arise in collisions of relativistic heavy ions reveals that, in the non-Abelian case, a change in the color charge leads to the...     

Structural state of second-generation HTSCs obtained by laser ablation

The structure of buffer layers and deposited YBa₂Cu₃O _x (Y123) films with a high critical current density (～10⁶ A/cm²) has been investigated by different methods. These superconducting films and buffer layers are found to have a fine-grained structure, which, along with the high texture of Y123 films of the (001) type, is believed to be responsible for the high critical current density. An unusual texture is revealed in buffer layers, which differs from that of substrates and Y123 films. The superconducting films deposited on buffer CeO₂ layers exhibit a system of orthogonal lines; in the case under consideration, this is a manifestation of a domain structure with Y123 particles at boundaries.     

Nuclear geometry of jet quenching

The most suitable way to study jet quenching as a function of the distance traversed is varying the impact parameter b of the ultrarelativistic nucleus–nucleus collision (the initial energy density in the nuclear overlapping zone is almost independent of b up to ). It is shown that the b-dependences of the medium-induced radiative and collisional energy losses of a hard parton jet propagating through dense QCD matter are very different. The experimental verification of this phenomenon could be performed for a jet with non-zero cone size based on the essential difference between the angular distributions of the collisional and radiative energy losses. Received: 10 February 2000 / Revised version: 18 April 2000 / Published online: 6 July 2000