Instability of string models of baryons: Character and manifestations

The character of the instability of a rotational state (rotation of the system at a constant speed) against small perturbations is studied in detail for the Y string model of the baryon. It is shown that the existing instability is due to the presence of repeated real-valued frequencies in the spectrum of small perturbations and that there are no complex-valued frequencies in this spectrum. This leads to a linear growth of small-perturbation amplitudes. A comparison of the Y configuration with the q-q-q linear string model of the baryon reveals a difference in the character of the instability of rotational states of these systems and in the manifestations of this instability. In particular, there are exponentially growing modes in the excitation spectrum of the linear model, which lead to an additional contribution to the baryon-state width.     

Closed relativistic strings in geometrically nontrivial spaces

We find exact solutions of the equations of motion for a closed relativistic string that carries a point mass and moves in the space given by the direct product of Minkowski space and a compact manifold (multidimensional torus). We investigate physical characteristics of the system states described by these solutions.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 142, No. 1, pp. 72–82, January, 2005.     

Instability of the Y string baryon model within classical dynamics

For the three-string baryon model (Y configuration), the known exact solution to the classical equations of motion that describes the rotational motion of the system at a constant speed is investigated for stability. In the spectrum of small perturbations of this solution, modes growing exponentially with time are found, whereby the instability of rotational motion is proven for the Y configuration. This result is confirmed within an alternative approach that makes it possible to determine the classical motion of the system from a specific initial position and initial velocities of string points. A comparison of the Y configuration with the model of a relativistic string with massive ends, in which case rotational motion is stable in the linear approximation, aids in revealing the most adequate string model from the point of view of describing baryon excitations on Regge trajectories.     

Determination of the world surface of a relativistic string from the trajectory of a massive end

It is shown that the world surface of a relativistic string can be uniquely recovered from the trajectory of a massive end of it if the trajectory is specified in Minkowski space in the form of an arbitrary curve of constant curvature with timelike tangent vector. Conditions are determined for the existence on the world surface of a line that can be identified with the trajectory of the other end of the string and also for the possibility of physical realization of the model in the case when there is no such line.State University, Tver. Translated from Teoreticheskayi i Matematicheskaya Fizika, Vol. 102, No. 1, pp. 150–159, January, 1995.     

Classification of motions admitting linearization of boundary conditions for the relativistic string with massive ends

For the relativistic string with masses at its ends, a classification of motions (world surfaces) admitting a parametrization under which the equations of motion and the boundary conditions are linear (due to the fact that the parameter for the trajectories of the string ends is proportional to the natural parameter) is carried out. These motions can be represented as Fourier series with respect to the eigenfunctions of a generalized Sturm-Liouville problem. The completeness of the family of these eigenfunctions in class C is proved. It is shown that in Minkowski spaces of dimensions2+1 and3+1, the motions in question reduce to a uniform rotation of one or several (spatially coincident) rectilinear strings (the world surface is a helicoid). In spaces of higher dimensions, some other nontrivial motions of this type are also possible.Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 109, No. 2, pp. 187–201, November, 1996.     

Peptide cysteine thiyl radicals abstract hydrogen atoms from surrounding amino acids: the photolysis of a cystine containing model peptide

Peptide cysteine thiyl radicals were generated through UV-photolysis of disulfide precursors, in order to follow intramolecular reactions of those radicals with neighboring amino acids. When reactions were carried out in D(2)O, there was a significant incorporation of deuterium specifically into the C(alpha)-H bonds of glycine residues in positions i+1 and i-1 to the Cys residue, indicating a fast reversible H-atom transfer. This H-atom transfer occurred prior to the formation of final, nonradical products including free thiol, thioaldehyde, and aldehyde. Such fast H-atom transfer is relevant to biologic conditions of oxidative stress and to the stabilization of proteins against oxidation, where the formation of carbon-centered radicals in proteins may lead to fragmentation, intramolecular cross-linking, aggregation and/or epimerization.     

Capillary neutron optics for prompt-gamma activation analysis

A neutron lens has been constructed to focus cold neutrons from the exit of a⁵⁸Ni neutron guide, which delivers a beam to the Prompt-Gamma Activation Analysis (PGAA) station at the NIST Cold Neutron Research Facility. The lens compresses a neutron beam of cross section 50 mm× 45 mm onto a focal spot of diameter 0.53 mm (fwhm) wich an average gain of 80 in neutron current density. PGAA measurements have been performed to demonstrate the enhanced sensitivity and detection limits for various elements and the spatial resolution in one transverse dimension. For the two test particles (a gadolinium glass bead and cadmium metal of sizes less than 0.5 mm), the gain in the -count rate with the lens is a factor of 60, and the detection limit is improved by a factor of 20. The system can be used for two-dimensional mapping of samples on a sub-millimeter scale to complement other analytical techniques such as neutron depth profiling (NDP).     

Solubility of cadmium in lead tellurides

The solubility of cadmium in PbTe was determined using microhardness and hydrostatic density measurements and by electron microscopy and electron probe microanalysis. All these methods indicate that the existence region of Pb_{1 − x} Cd _x Te solid solutions (ss) extends to x = 0.08 at 670°C. As the cadmium concentration of the solid solution increases, microhardness shifts up, whereas density shifts down.