Conceptual leadership models: success in the life philosophy of modern leaders

The article analyzes the conceptual models of leadership. The specificity of the leader's perception by the followers in various conceptual schemes-versions is revealed. An idea is outlined that unites the conceptual schemes of leadership concepts existing at the turn of the 20th – 21st centuries: one of the signs of the life philosophy of modern leaders is an orientation towards success, understood as a process that includes an ideal model of the future. The leader, as shown in the study, assesses the real situation and is able to determine the degree of the gap in the relationship “present – ideal future”. This assessment of the gap for a successful leader is the basis for motivating change, through which the gap is invariably reduced

Electron spin synchronization induced by optical nuclear magnetic resonance feedback

We predict a new physical mechanism explaining the electron spin precession frequency focusing effect observed recently in singly charged quantum dots exposed to a periodic train of resonant circularly polarized short optical pulses [A. Greilich et al, Science 317, 1896 (2007), Ref. 1]. We show that electron spin precession in an external magnetic field and a field of nuclei creates a Knight field oscillating at the frequency of nuclear spin resonance. This field drives the projection of the nuclear spin onto magnetic field to the value that makes the electron spin precession frequency a multiple of the train cyclic repetition frequency, which is the condition at which the Knight field vanishes.Comment: 4+ pages, 3 figure

Effect of external magnetic field on electron spin dephasing induced by hyperfine interaction in quantum dots

We investigate the influence of an external magnetic field on spin phase relaxation of single electrons in semiconductor quantum dots induced by the hyperfine interaction. The basic decay mechanism is attributed to the dispersion of local effective nuclear fields over the ensemble of quantum dots. The characteristics of electron spin dephasing is analyzed by taking an average over the nuclear spin distribution. We find that the dephasing rate can be estimated as a spin precession frequency caused primarily by the mean value of the local nuclear magnetic field. Furthermore, it is shown that the hyperfine interaction does not fully depolarize electron spin. The loss of initial spin polarization during the dephasing process depends strongly on the external magnetic field, leading to the possibility of effective suppression of this mechanism.Comment: 10 pages, 2 figure

Spin- and entanglement-dynamics in the central spin model with homogeneous couplings

We calculate exactly the time-dependent reduced density matrix for the central spin in the central-spin model with homogeneous Heisenberg couplings. Therefrom, the dynamics and the entanglement entropy of the central spin are obtained. A rich variety of behaviors is found, depending on the initial state of the bath spins. For an initially unpolarized unentangled bath, the polarization of the central spin decays to zero in the thermodynamic limit, while its entanglement entropy becomes maximal. On the other hand, if the unpolarized environment is initially in an eigenstate of the total bath spin, the central spin and the entanglement entropy exhibit persistent monochromatic large-amplitude oscillations. This raises the question to what extent entanglement of the bath spins prevents decoherence of the central spin.Comment: 8 pages, 2 figures, typos corrected, published versio

Long-term Dynamics of the Electron-nuclear Spin System of a Semiconductor Quantum Dot

A quasi-classical theoretical description of polarization and relaxation of nuclear spins in a quantum dot with one resident electron is developed for arbitrary mechanisms of electron spin polarization. The dependence of the electron-nuclear spin dynamics on the correlation time $\tau_c$ of electron spin precession, with frequency $\Omega$, in the nuclear hyperfine field is analyzed. It is demonstrated that the highest nuclear polarization is achieved for a correlation time close to the period of electron spin precession in the nuclear field. For these and larger correlation times, the indirect hyperfine field, which acts on nuclear spins, also reaches a maximum. This maximum is of the order of the dipole-dipole magnetic field that nuclei create on each other. This value is non-zero even if the average electron polarization vanishes. It is shown that the transition from short correlation time to $\Omega\tau_c>1$ does not affect the general structure of the equation for nuclear spin temperature and nuclear polarization in the Knight field, but changes the values of parameters, which now become functions of $\Omega\tau_c$. For correlation times larger than the precession time of nuclei in the electron hyperfine field, it is found that three thermodynamic potentials ($\chi$, $\bm{\xi}$, $\varsigma$) characterize the polarized electron-nuclear spin system. The values of these potentials are calculated assuming a sharp transition from short to long correlation times, and the relaxation mechanisms of these potentials are discussed. The relaxation of the nuclear spin potential is simulated numerically showing that high nuclear polarization decreases relaxation rate.Comment: RevTeX 4, 12 pages, 9 figure

Game species fodder conditions in Eastern Siberia and Amur region

Hunting farms can serve as a source of primary data on the state of natural resources. Taking into account the increasing anthropogenic impact on the environment, it is necessary to constantly monitor the situation with food for ungulates and predators in order to be able to take timely measures to improve the quality of habitat for wild fauna. Populations of wild large animals live in the host landscapes of so reduced that animals population become extremely vulnerable and unstable, signs of crisis can be seen in the data on the number of animals. Lack of natural food is a serious deterrent, especially in difficult times of the year, such as winter and spring. An analysis of the situation with food for a particular species will allow hunting farms to properly plan their feeding and other activities throughout the year in order to maintain a population of certain species on their territory and minimize the migration of species outside the protected areas. The aim of our work was to create a baseline for tracking data on the characteristics of wildlife animals. The research results allow hunting farms to use the data of animal feeding preferences during different seasons of the year for better organization of their biotechnical measures and improvement of feeding conditions for such species as red deer (Cervus elaphus), elk (Cervus canadensis), roe deer (Capreolus pygargus) and bear(Ursus arctos)