Smadar Shatz

ESR Detection of 1O2 Reveals Enhanced Redox Activity in Illuminated Cell Cultures

Low-energy visible light (LEVL) has previously been found to modulate various processes in different biological systems. One explanation for the stimulatory effect of LEVL is light-induced reactive oxygen species formation. In the present study, both sperm and skin cells were illuminated with LEVL and were found to generate singlet oxygen (1O2). The detection of 1O2 was performed using a trapping probe, 2,2,6,6-tetramethyl-4-piperidone, coupled with electron paramagnetic resonance spectroscopy. In addition, we have shown that, together with 1O2 generation, LEVL illumination increases the reductive capacity of the cells, which explains the difficulties encountered in 1O2 detection. The potential of visible light to change the cellular redox state may explain the recently observed biostimulative effects exerted by LEVL.

Characterization of Y-Ba-Cu-O thin films using their nonlinear magnetic response

Measurement of the third harmonic component in the ac magnetic response was used to investigate the multiphase nature of Y‐Ba‐Cu‐O thin films grown epitaxially on single‐crystal wafers of SrTiO3. Films prepared by electron beam evaporation and by activated reactive evaporation techniques exhibit several peaks in the harmonic amplitude versus temperature, indicating multiple phase transitions. The film prepared by laser ablation technique exhibits a sharp single peak, indicating a single phase transition. These results, corroborated by x‐ray diffraction and x‐ray photoelectron spectroscopy, demonstrate the usefulness of third harmonic measurements in characterizing thin‐film samples.

The effect of intercalants on the host liposome.

When phospholipids are vigorously dispersed in water, liposomes are formed. In the present study, we have explored the effect of intercalant concentration on various properties of unilamellar liposomes. Liposomes were sonically intercalated with vitamin E acetate (VitEAc) and hypericin (Hy) until no difference in light transmission was observed, which reflects the formation of liposomes of minimal diameter. Our studies indicate that the intercalant structure and concentration have an influence on the liposome diameter, which could be directly measured by cryogenic transmittance electronic microscopy. Thus, intercalated VitEAc substantially decreased the diameter of unilamellar dimyristoylphosphatidylcholine liposomes, whereas Hy did not. In addition, we followed peak intensities in the absorbance and fluorescence spectra of Hy as a function of intercalant concentration in the liposomal solution. Initially, the fluorescence intensity increased linearly with concentration; however, the curve then arched asymptotically, followed by a decrease in fluorescence at yet higher concentrations. Because the Hy monomer is the only species that emits fluorescence, we believe that the decrease of fluorescence intensity is the result of Hy aggregation.

The effect of non-local electron scattering on the current-perpendicular-to-plane-mode magnetoresistance of magnetic multilayers

We have carried out an experimental and theoretical study of non-local electron scattering in magnetic multilayers by measuring the magnetoresistance MR(H) in the CPP (current-perpendicular-to-plane) mode for two samples consisting of different magnetic layers (M1, M2) separated by non-magnetic layers (NM). For the two samples, the ordering of the layers was as follows: [M1/NM/M2/NM]N and [M1/NM]N[M2/NM]N. If the non-local character of the electron scattering were unimportant, the two samples would yield identical curves for MR(H) in the CPP mode. However, our measured MR(H) curves are completely different for the two samples. This demonstrates the importance of non-local electron scattering. For our measurements, M1 = Fe(50 A), M2 = Co(20 A), NM = Cu(200 A) for Fe-Co samples, and M1 = Co(10 A), M2 = Co(60 A), NM = Cu(200 A) for the Co-Co samples. To confirm our ideas, we calculated MR(H), including the effect of non-local electron scattering, and obtained quantitative agreement with experiment.

Magnetoresistance of interleaved and separated Co/Cu multilayers in the CPP mode

We have measured the field dependence of the magnetoresistance MR(H) in the CPP mode for two types of magnetic multilayers that differ only in the ordering of the magnetic layers: [Co (10 A)/Cu/Co (60 A)/Cu]N and [Co (10 A)/Cu]N [Co (60 A)/Cu]N, with the Cu layers always being 200 A. The series resistor model predicts that in the CPP mode, MR(H) is independent of the ordering of the layers. Nevertheless, the MR(H) curves measured were found to be completely different for the two cases. We suggest that the reason for this difference is that the electron mean free path is long enough that the potential that scatters the electrons is due to pairs of neighboring magnetic layers, which differ for the two types of magnetic multilayers.We have measured the field dependence of the magnetoresistance MR(H) in the CPP mode for two types of magnetic multilayers that differ only in the ordering of the magnetic layers: [Co (10 A)/Cu/Co (60 A)/Cu]N and [Co (10 A)/Cu]N [Co (60 A)/Cu]N, with the Cu layers always being 200 A. The series resistor model predicts that in the CPP mode, MR(H) is independent of the ordering of the layers. Nevertheless, the MR(H) curves measured were found to be completely different for the two cases. We suggest that the reason for this difference is that the electron mean free path is long enough that the potential that scatters the electrons is due to pairs of neighboring magnetic layers, which differ for the two types of magnetic multilayers.

Overtone Spectra of Gongs used in Music Therapy

Abstract Fast Fourier Transform (FFT) study of gong sound spectrograms was carried out on four gongs manufactured by Paiste Company, Switzerland. The results show complex spectra, presented in detail in the present work, that explain the extraordinary sound of the gongs. Each gong has its unique spectrum and its unique time-decay characteristics. The overtone series of the gongs include consonant and dissonant intervals, and have no relation to the harmonic overtone series of musical tones. The theory of an ideal circular membrane was applied in computation of the overtone spectrum of one gong (“World” gong), leading to very good agreement between computed and measured data. Comparison of gongs to other percussions is discussed, and, in particular, a comparison is made with spectra of church bells, vibraphone, and Tibetan singing bowl. The overtone series of the various gongs were found to provide satisfactory explanation to the effect of the gongs on patients subjected to music therapy with gongs. In addition, a special case history of an effect of certain percussion sounds, of interest to music therapy, is described and interpreted with the help of results of FFT analysis.

Magnetoresistance of magnetic multilayers: understanding Ohm's law

The magnetic-field dependence of the magnetoresistance MR(H) of magnetic multilayers in the CPP mode (current perpendicular to the layers) was recently measured for two samples that differ only in the ordering of the layers: [Fe/Cu/Co/Cu]N and [Fe/Cu]N[Co/Cu]N, where N denotes the number of repeats. Ohms law states that MR(H) should be the same for these two samples because in a series circuit, the resistance is independent of the ordering of the resistors. However, the measured MR(H) curves were found to be completely different for the two samples. We show that this unexpected result can be explained as follows. The mean free path is sufficiently long that MR(H) is due to the scattering of electrons by pairs of neighbouring magnetic layers, which differ for the two samples. To confirm these ideas, we carried out calculations of MR(H) and obtained quantitative agreement with experiment.

New results for the dependence of the magnetoresistance of magnetic multilayers on the layer thickness

We measured the dependence of the giant magnetoresistance on the thickness of the magnetic layers for a magnetic multilayer comprising two types of magnetic layers, oriented in the CPP mode (current perpendicular to the plane of the layers). The thickness dependence was found to be very different for thin and thick multilayers and for the interleaved and the separated configurations. An explanation for these differences is presented.

Magnetoresistance of magnetic multilayers: a phenomenological approach

A phenomenological approach is presented for the giant magnetoresistance (GMR) of magnetic multilayers oriented in the CPP mode (current perpendicular to the plane of the layers). New results are found for the dependence of the GMR on the number of repeats of the multilayer.

Fractals in Monte Carlo simulations of a short polyelectrolyte

Fractal dimensionalities, , for charged polymers are calculated over a continuous range of Bjerrum length for chains with various numbers of beads, N. Drastically decreasing values of , characteristic of a phase transition, are found as increases from zero in the range A. The fractal dimensionality approaches unity as predicted by de Gennes et al (de Gennes P-G, Pincus P, Valesco R M and Brochard F 1976 J. Physique 37 1461) close to the onset of order. A newly developed smoothing algorithm yields a substantial improvement in the MC results and reveals an interesting fan-shaped behaviour of exponents and prefactor components at slightly above zero. It also enables discernment of a non-monotonic behaviour of versus N at and close to zero. Differences found in bending between short and long chains may provide an additional explanation for the stability of benzene and the low stability of conjugated rings of N>6. Based on fractal concepts, monomer densities are derived at various and it is suggested that the drastic density changes at A are evidence of the first-order nature of this phase transition.