Mode of action of antitumour antibiotics-III: Modulation of permeability of nuclear membrane in the presence of the antibiotics

The binding characteristics of the antibiotics to nuclei and their effect on the permeability of nuclear membrane with respect to histones and ribonucleic acids have been investigated. The binding constant for chromomycin A3 was found to be 1.4 × 104M?1 and number of binding sites was equal to 3.48 ± 1.08 × 1012 molecules/nuclei. The antibiotic chromomycin A3 enhanced the uptake of lysine-rich histone, actinomycin D decreased the uptake and ethidium bromide had no effect. Chromomycin A3 also enhanced the release of acid insoluble fraction containing RNA from the nuclei, actinomycin D and ethidium bromide inhibited the release of acid insoluble fraction containing RNA. The relevance of this finding to the role of nuclear envelope in understanding the mechanism of action of the antibiotic has been discussed.

Directional solidification of aluminum-nickel eutectic alloys using electroslag remelting

Attempts were made to produce directionally solidified, specifically grain aligned Al-6 wt pct Ni eutectic alloy using a laboratory scale ESR unit. For this purpose sand cast alloy electrodes were electroslag remelted under different mold conditions. The grain structure of the ingots obtained from these meltings showed that insulated silica molds gave the best vertical alignment of grains along the length of the ingot. The NiAl3 fibers within the grains tended to fan out and there was only a preferred alignment of fibers along the growth direction under the conditions of our experiments. The ESR parameters most suitable for vertical alignment of eutectic grains have been identified. In some electroslag remelting trials ingots were grown on a seed ingot. This resulted in a fewer vertical grains compared to the case when no seed ingot was used. The sand cast specimen of the eutectic exhibited a maximum tensile strength of around 88.2 MN/m2 (9.0 kg/mm2) whereas conventional ESR using water cooled mold gave strength value of 98.0 MN/m2 (10 kg/mm2). The directionally solidified ESR material showed longitudinal tensile strength as high as 213.7 MN/m2 (21.8 kg/mm2) which could be further increased to 220.6 MN/m2 (22.5 kg/mm2) by using the seed ingot. The average growth rate was varied between 5 to 25 mm/min during electroslag remelting in this study. The flow stresses, tangent modulus and ultimate tensile strength of directionally solidified eutectic increased with increasing growth rates.

Design of clutter-rejecting compact pulse bursts with amplitude modulation and frequency-shift keying

A method is presented for the design of compact pulse burst signals, with amplitude and frequency stepping between individual pulses, for optimum rejection of radar clutter distributed arbitrarily in range. The method is illustrated by an example. It is shown that amplitude stepping plays a useful role only when the reciprocal of the individual pulse width is not insignificant compared to the bandwidth permitted to the signal. As an important and useful subclass of the amplitude-and-frequency-stepped signals, constant amplitude FSK bursts are studied and the extent of loss of clutter performance due to amplitude flattening is evaluated.

Oestrogen-induced synthesis of thiamin-binding protein in immature chicks. Kinetics of induction, hormonal specificity and modulation

A specific radioimmunoassay procedure was developed to monitor the plasma concentrations of thiamin-binding protein, a minor yolk constituent of the chicken egg. By using this sensitive assay, the kinetics of oestrogen-induced elaboration of this specific protein in immature chicks was investigated. After a single injection of the steroid hormone, with an initial lag period of 4–5h the thiamin-binding protein rapidly accumulated in the plasma, attaining peak concentrations around 75h and declining thereafter. A 4-fold amplification of the response was noticed during the secondary stimulation, and this increased to 9-fold during the tertiary stimulation with the steroid hormone. The magnitude of the response was dependent on the hormone dose, and the initial latent period and the duration of the ascending phase of induction were unchanged for the hormonal doses tested during both the primary and secondary stimulations. The circulatory half-life of the protein was 6h as calculated from the measurement of the rate of disappearance of the exogenously administered 125I-labelled protein. Simultaneous administration of progesterone, dihydrotestosterone or corticosterone did not alter the pattern of induction. On the other hand, hyperthyroidism markedly decreased the oestrogenic response, whereas propylthiouracil-induced hypothyroidism had the opposite effect. The anti-oestrogen E- and Z-clomiphene citrates, administered 30min before oestrogen, effectively blocked the hormonal induction. a-Amanitin and cycloheximide administered along with or shortly after the sex steroid severely curtailed the protein elaboration. A comparison of the kinetics of induction of thiamin- and riboflavin-binding proteins by oestrogen revealed that, beneath an apparent similarity, a clear-cut difference exists between the two vitamin-binding proteins, particularly with regard to hormonal dose-dependent sensitivity of induction and the half-life in circulation. The steroid-mediated elaboration of the two yolk proteins thus appears to be not strictly co-ordinated, despite several common regulatory features underlying their induction.

Out-of-equilibrium microrheology using optical tweezers to probe directional viscoelastic properties under shear

Many wormlike micellar systems exhibit appreciable shear thinning due to shear-induced alignment. As the micelles get aligned introducing directionality in the system, the viscoelastic properties are no longer expected to be isotropic. An optical-tweezers-based active microrheology technique enables us to probe the out-of-equilibrium rheological properties of a wormlike micellar system simultaneously along two orthogonal directions-parallel to the applied shear, as well as perpendicular to it. While the displacements of a trapped bead in response to active drag force carry signature of conventional shear thinning, its spontaneous position fluctuations along the perpendicular direction manifest an orthogonal shear thickening, an effect hitherto unobserved. Copyright (C) EPLA, 2010

Influence of Raman scattering on the cross phase modulation in optical fibers

The effect of Raman scattering on co-propagation of two short optical pulses is considered. The intra pulse Raman scattering causes the self-frequency shift of each pulse. The effect of the inter pulse Raman scattering is to enhance the frequency shift while the stimulated Raman scattering (SRS) term suppresses (enhances) the frequency shift if the center frequency difference between the optical pulses falls to the right (left) of the Raman gain peak. An expression for the frequency shift as a function of the propagation distance is obtained.

The modulation of radiation in an electron-positron plasma

The modulational instability of a large-amplitude, linearly polarized electromagnetic wave propagating in an electron-positron plasma is considered, including the combined effect of relativistic mass variation of the plasma particles, harmonic generation, and the non-resonant, finite-frequency electrostatic density perturbations, all caused by the large-amplitude radiation field. The radiation from many strong sources, such as AGN and pulsars, has been observed to vary over a host of time-scales. It is possible that the extremely rapid variations in the non-thermal continuum of AGN, as well as in the non-thermal radio radiation from pulsars, can be accounted for by the modulational instabilities to which radiation may be subjected during its propagation out of the emission region.

Crystallography of solid-liquid interface and evolution of texture during directional solidification of Tb0.3Dy0.7Fe1.95 alloy

The effect of growth texture on the magnetostriction of ternary Tb0.3Dy0.7Fe1.95 was studied by conducting unidirectional solidification experiments using a zoning set-up. Detailed texture evolutions were studied using X-ray diffraction on samples obtained by varying growth rates from 18 to 72 cm/h, under a temperature gradient of 100 degrees C/cm. The estimated texture co-efficient and pole figures of the samples indicate that during the onset of the solidification, < 110 > and < 331 >/'rotated < 110 >' texture components nucleate and grow in all the samples. However, as the solidification progresses, < 112 > texture component becomes dominant at higher growth rate. This results in an improvement of magnetostriction from 1000 to 1300 microstrains for samples grown at growth rates of 18 and 72 cm/h respectively. The transition of preferred growth direction occurs through intermediate orientations < 123 >. An attempt has been made in this paper to explain the occurrence of different growth texture by considering the stability of growing interface, its planar packing fraction and atomic stacking sequence of several low index planes. (C) 2010 Elsevier Ltd. All rights reserved.

Dimorphism and structural modulation in quinoxaline

The Z' = 1 and Z' = 5 structures of quinoxaline are compared. The nature of the intermolecular interactions in the Z' = 5 structure is studied by means of variable-temperature single-crystal X-ray diffraction. The C-H center dot center dot center dot N and pi ... pi it interactions in these structures are of a stabilizing nature. The high Z' structure has the better interactions, whereas the low Z' structure has the better stability. This trade-off is a recurrent theme in molecular crystals and is a manifestation of the distinction between thermodynamically and kinetically favoured crystal forms.

Hormonal modulation of secretion of immunoreactive riboflavin carrier protein by adult rat Leydig cells in vitro

Adult rat Leydig cells in culture synthesize and secrete riboflavin carrier protein (RCP) as demonstrated by [S-35]-methionine incorporation into newly synthesized proteins followed by immunoprecipitation as well as specific radioimmunoassay. LH stimulates the secretion of RCP 4-fold which could be inhibited upto 75% by an aromatase inhibitor. 8-bromo-cyclic AMP and cholera toxin could mimic the LH stimulated secretion of the carrier protein. The extent of stimulation of RCP secretion brought about by exogenous estradiol-17 beta is comparable to that of LH. The antiestrogen tamoxifen, when added along with either LH or estrogen, inhibited the stimulated levels significantly. These results show that the estrogen-inducible riboflavin carrier is secreted by Leydig cells under positive regulation of LH.

Modulation of vesicular properties by variation of shapes of bolaform counter ions in hybrid-ion paired surfactants

Four new vesicle-forming bolaphile/amphiphile ion pairs are synthesized; the bolaphile shapes in such hybrid systems strongly control their vesicular properties.

Effect of sliding speed on friction and wear of uni-directional aramid fibre-phenolic resin composite

A previous study on the tribological performance of a compression-moulded aramid fibre-phenolic resin composite, containing 30% continuous fibre, showed that this composite provides a reasonable combination of the friction coefficient and wear rate to be used as a friction component, such as a brake shoe. In the present work, the effect of sliding speed on the friction and wear behaviour of this composite has been investigated. The sliding experiments were conducted in a speed range of 0.1-6 m s(-1) at two normal pressure levels of 1.0 and 4.9 MPa. The coefficient of friction was found to be stable over a wide range of sliding speeds and normal pressures. The wear of the composite was found to be insensitive to changes in the speed in the higher speed range. The results have been supplemented with scanning electron micrographs to help understand possible friction and wear mechanisms.

Space vector pulsewidth modulation — A status review

The technique of space vector pulsewidth modulation (SVM) is reviewed. The basic principle of SVM is derived and is compared with sine-triangle PWM. Operation in the overmodulation range is explained. Extension of SVM to other inverter-motor combinations such as three level inverters and split phase motors are discussed.