Positive and negative magnetostatic coupling in two-layer magnetic films

The energy of positive and negative magnetostatic coupling has been measured in two-layer Fe-Ni-Co ¦SiO¦ Fe-Ni-Mo films for intermediate SiO layers having thicknesses of from 100 to 1500 Å. The intermediate-layer thickness corresponding to a transition from positive to negative coupling was determined for a series of films having a constant magneticlayer thickness.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 11–16, November, 1969.     

Loss due to magnetic-rotation hysteresis in bismuth calcium vanadium iron garnet

The field and temperature dependences of the loss due to magnetic-rotation hysteresis have been determined by the rotational-moment method in a (Bi_0.32Ca_2.68Fe_3.66V_1.34O₁₂) single crystal. In the temperature range between –183 and +25 °C, the loss increases with increasing field, reaching a maximum at 2500–6000 Oe; then it decreases, vanishing completely in high fields. The loss behavior can be described well at all temperatures studied by an exponential dependence on the field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 12, No. 2, pp. 65–69, February, 1969.     

Propagation of elastic waves along the fibers in oriented glass-reinforced plastics

The dispersion equation is derived for axisymmetric (longitudinal and torsional) normal vibrations in oriented glass-reinforced plastics. The low-frequency case is examined in detail. The frequency limits of applicability of the method of substituting a homogeneous medium for the composite (GRP) are estimated. The dependence of the vibration propagation velocity on glass content is calculated.Leningrad Zonal Scientific-Research Institute of Experimental Design of Public and Residential Buildings. Translated from Mekhanika Polimerov, No. 6, pp. 976–983, November–December, 1973.     

Magnetoresistive effect in a rotating magnetic field for nickel and cobalt films

The longitudinal and transverse effects (Thomson effect) have been investigated in nickel and cobalt films from 600 to 1500 Å thick. The change in electrical resistance in a rotating magnetic field has been studied. Certain singularities of the magnetoresistive effect R/R have been observed for cobalt as compared with nickel films. The data for thin films are compared with those for bulk materials.     

Measurement of Cell Volume Changes by Fluorescence Self-Quenching

At high concentrations, certain fluorophores undergo self-quenching, i.e., fluorescence intensity decreases with increasing fluorophore concentration. Accordingly, the self-quenching properties can be used for measuring water volume changes in lipid vesicles. In cells, quantitative determination of water transport using fluorescence self-quenching has been complicated by the requirement of relatively high (mM) and often toxic loading concentrations. Here we report a simple method that uses low (M) loading concentrations of calcein-acetoxymethyl ester (calcein-AM) to obtain intracellular concentrations of the fluorophore calcein suitable for measurement of changes in cell water volume by self-quenching. The relationship between calcein fluorescence intensity, when excited at 490 nm (its excitation maximum), and calcein concentration was investigated in vitro and in various cultured cell types. The relationship was bell-shaped, with the negative slope in the concentration range where the fluorophore undergoes fluorescence self-quenching. In cultured retinal pigment epithelial cells, calcein fluorescence and extracellular osmolarity were linearly related. A 25-mOsm hypertonic challenge corresponded to a decrease in calcein fluorescence with high signal-to-noise ratio (>15). Similar results were obtained with the fluorophore BCECF when excited at its isosbestic wavelength (436 nm). The present results demonstrate the usefulness of fluorescence self-quenching to measure rapid changes in cell water volume.     

On a multidimensional version of the tomographic problem

The main result: If the dimension of a Euclidean space with measure is high enough, only the first observation from a long series of observations with random independent choice of projection gives essential information on the measure. Bibliography: 8 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 244, 1997, pp. 295–301. Translated by V. Sudakov.     

Large almost monochromatic subsets in hypergraphs

We show that for all ℓ and ε > 0 there is a constant c = c(ℓ, ε) > 0 such that every ℓ-coloring of the triples of an N-element set contains a subset S of size $ c\sqrt {\log N} $ c\sqrt {\log N} such that at least 1 − ε fraction of the triples of S have the same color. This result is tight up to the constant c and answers an open question of Erdős and Hajnal from 1989 on discrepancy in hypergraphs. For ℓ ≥ 4 colors, it is known that there is an ℓ-coloring of the triples of an N-element set whose largest monochromatic subset has cardinality only Θ(log log N). Thus, our result demonstrates that the maximum almost monochromatic subset that an ℓ-coloring of the triples must contain is much larger than the corresponding monochromatic subset. This is in striking contrast with graphs, where these two quantities have the same order of magnitude. To prove our result, we obtain a new upper bound on the ℓ-color Ramsey numbers of complete multipartite 3-uniform hypergraphs, which answers another open question of Erdős and Hajnal.     

Matrix methods for the calculation of stability diagrams in quadrupole mass spectrometry

The theory of the computer calculation of the stability of ion motion in periodic quadrupole fields is considered. A matrix approach for the numerical solution of the Hill equation and examples of calculations of stability diagrams are described. The advantage of this method is that it can be used for any periodic waveform. The stability diagrams with periodic rectangular waveform voltages are calculated with this approach. Calculations of the conventional stability diagram of the 3-D ion trap and the first six regions of stability of a mass filter with this method are presented. The stability of the ion motion for the case of a trapping voltage with two or more frequencies is also discussed. It is shown that quadrupole excitation with the rational angular frequency omega = Nomega/P (where N, P are integers and omega is the angular frequency of the trapping field) leads to splitting of the stability diagram along iso-beta lines. Each stable region of the unperturbed diagram splits into P stable bands. The widths of the unstable resonance lines depend on the amplitude of the auxiliary voltage and the frequency. With a low auxiliary frequency splitting of the stability diagram is greater near the boundaries of the unperturbed diagram. It is also shown that amplitude modulation of the trapping RF voltage by an auxiliary signal is equivalent to quadrupole excitation with three frequencies. The effect of modulation by a rational frequency is similar to the case of quadrupole excitation, although splitting of the stability diagram differs to some extent. The methods and results of these calculations will be useful for studies of higher stability regions, resonant excitation, and non-sinusoidal trapping voltages.