461 research outputs found
Loss of quantum coherence due to non-stationary glass fluctuations
Low-temperature dynamics of insulating glasses is dominated by a macroscopic
concentration of tunneling two-level systems (TTLS). The distribution of the
switching/relaxation rates of TTLS is exponentially broad, which results in
non-equilibrium state of the glass at arbitrarily long time-scales. Due to the
electric dipolar nature, the switching TTLS generate fluctuating
electromagnetic fields. We study the effect of the non-thermal slow fluctuators
on the dephasing of a solid state qubit. We find that at low enough
temperatures, non-stationary contribution can dominate the stationary (thermal)
one, and discuss how this effect can be minimized.Comment: 4 page
Zero-bias anomalies of point contact resistance due to adiabatic electron renormalization of dynamical defects
We study effect of the adiabatic electron renormalization on the parameters
of the dynamical defects in the ballistic metallic point contact. The upper
energy states of the ``dressed'' defect are shown to give a smaller
contribution to a resistance of the contact than the lower energy ones. This
holds both for the "classical" renormalization related to defect coupling with
average local electron density and for the "mesoscopic" renormalization caused
by the mesoscopic fluctuations of electronic density the dynamical defects are
coupled with. In the case of mesoscopic renormalization one may treat the
dynamical defect as coupled with Friedel oscillations originated by the other
defects, both static and mobile. Such coupling lifts the energy degeneracy of
the states of the dynamical defects giving different mesoscopic contribution to
resistance, and provides a new model for the fluctuator as for the object
originated by the electronic mesoscopic disorder rather than by the structural
one. The correlation between the defect energy and the defect contribution to
the resistance leads to zero-temperature and zero-bias anomalies of the point
contact resistance.
A comparison of these anomalies with those predicted by the Two Channel Kondo
Model (TCKM) is made. It is shown, that although the proposed model is based on
a completely different from TCKM physical background, it leads to a zero-bias
anomalies of the point contact resistance, which are qualitatively similar to
TCKM predictions.Comment: 6 pages, to be published in Phys. Rev.
ЛІНГВОСТИЛІСТИЧНІ ОСОБЛИВОСТІ АНГЛІЙСЬКОЇ ПІСНІ ЯК ТЕКСТУ МАЛОЇ ФОРМИ. (Linguistical and stylistical peculiarities of the English song as a text of small form.)
Стаття присвячена дослідженню лінгвостилістичних особливостей англомовної пісні як тексту малої форми і зумовлена спрямуванням сучасних лінгвістичних досліджень на поглиблення дослідницької парадигми лінгвістики тексту новим знанням про механізми систематизації структурних, функціональних та лінгвальних ознак тексту взагалі та його малої форми зокрема.
(The article deals with the study of linguostylistic peculiarities of English songs. It is stipulated by the interest of modern linguistic investigations in deepening the research paradigm of text linguistics with new knowledge about the mechanisms of systematization of structural, functional and linguistic features of the text in general and short texts in particular.
Low-frequency noise in tunneling through a single spin
We propose measurements of low-frequency noise in the tunneling current
through a single molecule with a spin as an experimental probe for identifying
a mechanism of the spin-dependent tunneling. A specific tail near the zero
frequency in the noise spectrum is predicted; the amplitude and the width of
being of the same order of magnitude as the recently reported peak in the noise
spectrum at the spin Larmor frequency. The ratio of the spectrum amplitudes at
zero- and Larmor frequencies is shown to be a convenient tool for testing
theoretical predictions.Comment: 4 pages, 3 figures. In the replaced version some mistakes are fixe
Josephson transport through a Hubbard impurity center
We investigate the Josephson transport through a thin semiconductor barrier
containing impurity centers with the on-site Hubbard interaction of an
arbitrary sign and strength. We find that in the case of the repulsive
interaction the Josephson current changes sign with the temperature increase if
the energy of the impurity level (measured from the Fermi energy of
superconductors) falls in the interval . We predict strong temporal
fluctuations of the current if only a few centers present within the junction.
In the case of the attractive impurity potential () and at low
temperatures, the model is reduced to the effective two level Hamiltonian
allowing thus a simple description of the nonstationary Josephson effect in
terms of pair tunneling processes
Improvement of forms and methods of teaching in higher education
Розглянуто поняття форм і методів навчання у вищому навчальному
закладі як складових компонентів авторських педагогічних систем та розглянуто
їх характеристику. Виділено організаційні форми навчання, які одночасно є
способами безперервного управління пізнавальною діяльністю студентів. До них
відносять: лекції, семінарські заняття, лабораторні роботи, практикуми,
самостійну роботу, науково-дослідну роботу студентів, різного виду практику
тощо. Показано, що ефективність навчання безпосередньо залежить від форм і
методів, які викладач буде використовувати в навчально-виховному процесі. Вміле
їх поєднання дозволить активізувати студента і викликати в ньому інтерес до
процесу навчання.The concepts of forms and methods of teaching in higher education as constituent
components of the author's pedagogical systems were considered and their
characteristics were considered too. Organizational forms of education were given. They
are method of continuous management of cognitive activity of the students. These include: lectures, seminars, laboratory works, self-work, research work of students,
various types of practice, etc. It is shown that the effectiveness of teaching depends
directly on the forms and methods that the teacher will use in the educational process.
Skillful combination of them will allow activating the student and arouse interest in him
in the learning process
Zero-bias anomalies on SrLaCuO thin films
High-impedance contacts made on the surface of SrLaCuO
superconducting thin films systematically display a zero-bias anomaly. We
consider two-level systems (TLS) as the origin of this anomaly. We observe that
the contribution of some TLS to the contact resistance is weakened by a
magnetic field. We show that this could result from the increase of the TLS
relaxation rate in the superconducting state, due to its ability to create
pairs of quasiparticles out of the condensate, when located close to the
surface of the film
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