High-frequency oscillations in low-dimensional conductors and semiconductor superlattices induced by current in stack direction

A narrow energy band of the electronic spectrum in some direction in low-dimensional crystals may lead to a negative differential conductance and N-shaped I-V curve that results in an instability of the uniform stationary state. A well-known stable solution for such a system is a state with electric field domain. We have found a uniform stable solution in the region of negative differential conductance. This solution describes uniform high-frequency voltage oscillations. Frequency of the oscillation is determined by antenna properties of the system. The results are applicable also to semiconductor superlattices.Comment: 8 pages, 3 figure

Gifting representations’ analysis in the digital environment of Moscow museums

The article presents the research results of gifting online-representations of 170 museums in Moscow (federal, regional, private). Data collection and its interpretation were structured around the duality of the museum gift as a semantic unit representing the following categories: 1) appeals and requests from museums for different types of property support (new items or monetary donations); 2) gifts previously given to the museum, presented in electronic catalogues. The data collected from the materials of Moscow museums’ websites showed that appeals for assistance to museums, regardless of the type of charity, are the lot of a minority (8–15 %). In turn, 82 museums have systematized electronic catalogues, among them only 13 % clearly distinguish information about the way of items’ arrival and through a gift, including in a separate category of description. Considering a long history of philanthropists’ influence on the formation and development of museums, and evidence of existing museum support practices, the author does not argue about low intensity of donations in museum institutions, but offers to draw a conclusion about the relationship between low articulation of gift intentions and donations in the collections and functioning of the museum field in Moscow, its rules and shared norms

Stable Spin Precession at one Half of Equilibrium Magnetization in Superfluid 3He-B

New stable modes of spin precession have been observed in superfluid 3He-B. These dynamical order parameter states include precession with a magnetization S=pS_{eq} which is different from the equilibrium value S_{eq}. We have identified modes with p=1, 1/2 and \approx 0. The p=1/2 mode is the second member of phase correlated states of a spin superfluid. The new states can be excited in the temperature range 1-T/T_c \lesssim 0.02 where the energy barriers between the different local minima of the spin-orbit energy are small. They are stable in CW NMR due to low dissipation close to T_c.Comment: submitted to Physical Review Letters, 4 pages, revtex, 4 Figures in ftp://boojum.hut.fi/pub/publications/lowtemp/LTL-96005.p

Fractional and unquantized dc voltage generation in THz-driven semiconductor superlattices

We consider the spontaneous creation of a dc voltage across a strongly coupled semiconductor superlattice subjected to THz radiation. We show that the dc voltage may be approximately proportional either to an integer or to a half- integer multiple of the frequency of the applied ac field, depending on the ratio of the characteristic scattering rates of conducting electrons. For the case of an ac field frequency less than the characteristic scattering rates, we demonstrate the generation of an unquantized dc voltage.Comment: 6 pages, 3 figures, RevTEX, EPSF. Revised version v3: corrected typo

QCD Heat Kernel in Covariant Gauge

We report the calculation of the fourth coefficient in an expansion of the heat kernel of a non-minimal, non-abelian kinetic operator in an arbitrary background gauge in arbitrary space-time dimension. The fourth coefficient is shown to bring a nontrivial gauge dependence due to the contribution of the lowest order off-shell gauge invariant structure.Comment: 6 pages + title page, standart LaTe

Urethral doubling in children and adolescents

Urethral doubling is a rare congenital malformation of the lower urinary tract. A little more than 200 cases of various forms of this defect have been described in the literature worldwide. We present a rare clinical case of duplication of the urethra in combination with the megaureter of the only functioning kidney. In this patient, we encountered a previously undescribed anomaly within the generally accepted classification of the kidney collecting system in combination with a true diverticulum of the bladder and a descending orthotopic ureterocele