Organogelation and cytotoxic evolution of phosphonate ester functionalised hydrophobic alkanediamide motifs

Here we report various rigid alkanediamide derivatives, with three different substitution patterns of phosphonate ester for investigation of organogelation properties. The gelation properties of these compounds can be tuned by altering the number and position of the phosphonate esters. It was found that supramolecular self-assembly of the bisphosphonate esters (1a, 1d, 1h and 2a–b) resulted gel formation, whereas that of the tetraphosphonate esters (3a, 3d, 3h) resulted in construction of nanospheres and microspheres. The diverse morphology of the gel formation appears to depend predominantly on the substituted phenyl ring of the phosphonate ester functionality. Subsequent in vitro cytotoxic screening against four human tumour cell lines (A549, MDA-MB-231, MCF-7 and HeLa) using MTT assays revealed that derivatives 1f–h and 3a show cytotoxic potencies at concentrations less than 5 μM (IC₅₀ values). Compounds 1f–h exhibited promising activity against A549 cell line, 1g–h were highly effective against MDA-MB-231, 1f and 3a show potential against MCF-7 and 1f–g were active against the HeLa cell line.     

Phase stability of gyroklystron amplifier

Expressions are derived for RF phase stability in conventional klystrons and gyroklystrons. Phase noise is found to depend on electron energy in a completely different way for the two types of devices, due to the inherent differences in gun dynamics and interaction mechanisms. In general, phase stability is better in gyroklystrons operating at voltage ⩽100 kV, while klystrons have somewhat better phase stability at higher operating voltage. An experimental study of phase stability in a four-cavity, 7.5-kV conventional klystron and in a three-cavity, 30-kV gyroklystron confirmed theoretical predictions. Phase sensitivity in the conventional klystron was 13° per percent change in voltage, and in gyroklystron was 4° per percent change in voltage. The magnitude and frequency of the measured phase jitter was well correlated with the droop and ripple on the beam voltage. Phase sensitivity to other parameters such as input power, magnetic field strength, and input frequency were also studied experimentally     

Phase-locking of a second-harmonic gyrotron oscillator using aquasi-optical circulator to separate injection and output signals

Phase-locking in a 34.5-GHz special complex cavity gyrotron oscillator operating at the second harmonic of the electron cyclotron frequency was studied. Injection of the locking power was made via a quasi-optical circulator connected to the gyrotron output. Locking bandwidth was measured by comparing the phase of the injection signal and output signal using a balanced mixer. Locking was observed with input power level as low as 40 dB below the gyrotron output power. The locking bandwidth is, however, narrower than in gyrotrons operating at the fundamental cyclotron frequency which may be attributed to the longer resonant cavity in the second harmonic gyrotron and the corresponding larger value of external quality factor. The measurements are roughly in agreement with predictions of Adler's phase-locking equation which is given for our system in terms of powers propagating in the output waveguide toward and away from the gyrotron cavity     

Effect of cross-link density on the morphology,thermal and mechanical properties of flexible molded polyurea/urethane foams and films

The effect of cross-link density on the morphology and properties of two flexible molded foam samples was studied. Film samples based on the same foam formulations were also fabricated to study the feasibility of using them for the characterization of complex foam products. Fourier transform infrared spectroscopy (FTIR) and small angle X-ray scattering (SAXS) data show that films and foam samples have entirely different hard domain ordering. The results of the study of morphology indicate that an increase in cross-link density appears to increases phase mixing in film and foam samples. Differential scanning calorimetry (DSC) studies indicate that the soft segment glass transition temperature (T_g) is independent of cross-link density (at levels studied). But for both film and foam samples, morphology clearly dicates the manner in which moisture interacts with the hard domains. Results of the stress-strain behavior indicate that an increase in cross-link density increases the modulus and decreases the elongation at break. Mooney-Rivilin modeling of the stress-elongation behavior of film shows that the higher cross-link density sample gives more nonaffine behavior, possibly due to a heterogeneous distribution of hard domains. Similar modeling of the foams was not possible because of their linear stress response to surprisingly high elongation. The results of the power law modeling of stress relaxation response indicates that with an increase in cross-link density (covalent and virtual), the power law exponent decreases as expected. At levels of cross-linking and hard segment content studied, stroke-controlled equilibrium hysteresis was independent of cross-link density. Normalized dynamic mechanical spectra (DMS) show that the film samples have higher rubbery plateau modulus. The magnitude of the area under the tan δ curve at T_g indicates greater flexibility of polymer segments in foam sample. Structure-property relationships of cellular materials can be established by characterizing film samples because a parallel trend exists between each group. © 1994 John Wiley & Sons, Inc.     

The signal-to-noise ratio for speech intelligibility—An auditorium acoustics design index

The Signal-to-Noise Ratio devised by Lochner and Burger contributed an objective design index for predicting speech intelligibility. Their index provided a measure of useful and detrimental reflected speech energy according to the integration and masking characteristics of hearing, and enabled predictions to be made from impulse measurements in models. However, it was found necessary to extend the Signal-to-Noise Ratio theory to account for the effect of fluctuating ambient background noise on speech intelligibility. A modified Signal-to-Noise Ratio was derived from a best-fitting empirical correlation with speech intelligibility in a series of measurements in existing auditoria. In the modified Signal-to-Noise Ratio ambient background noise is no longer considered in terms of its steady state characteristics but more specifically in terms of its transient and spectral characteristics given by the concept of the L₁₀ PNC level. The index has been applied as design criteria to prediction and to evaluation techniques.     

TEM-induced structural evolution in amorphous Fe oxide nanoparticles

Exposure to the high energy electron beam of a TEM changes the morphology of amorphous Fe oxide nanoparticles from solid spheres to hollow shells. Amorphous Fe oxide nanoparticles prepared via high-temperature methods using hexadecylamine and trioctylphosphine oxide surfactants were compared to crystalline gamma-Fe2O3 particles of similar size. Both sets of particles are fully characterized via SQUID magnetometry, X-ray powder diffraction, BET surface analysis, EPR spectroscopy, high-resolution transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). Time-resolved TEM images reveal that the amorphous Fe oxide particles evolve from solid spheres into hollow shells in <2 min, whereas crystalline gamma-Fe2O3 are unaffected by the electron beam. The resulting nanocrystalline Fe oxide shells bear striking resemblance to core-shell nanocrystals, but are a result of a morphology change attributed to restructuring of particle voids and defects induced by quasi-melting in the TEM. These results thus imply that caution is necessary when using TEM to analyze nanoparticle core-shell and heterostructured nanoparticles.     

Nanoporous WO3 from anodized RF sputtered tungsten thin films

We report the first electrochemical anodization of RF (radio-frequency) sputtered tungsten (W) thin films. High pressure sputtering was utilized to produce W films of low intrinsic stress with a high degree of adhesion to the transparent substrates. Structurally and uniformly porous tungsten trioxide (WO₃) films were obtained under optimised anodization conditions in fluoride ion-containing electrolyte. Crystalline WO₃ was obtained after annealing the films at 450 °C. SEM and XRD characterisation techniques were used to determine the surface morphology and crystal structure of the non-anodized and anodized films.     

AC space-charge effects in gyroklystron amplifiers

The effects of AC space charge on multicavity gyroklystron amplifiers are studied. It is found that when AC space charge is included in the analysis of weakly relativistic multicavity gyroklystron amplifiers, the optimized nonlinear efficiency becomes a function of beam current. For a cold beam (no velocity spread), the efficiency is maximum at zero current and decreases monotonically as the current increases. The zero current limit of the optimized efficiency when AC space-charge effects are included is not the same as the optimized efficiency with no space charge; it is significantly higher. This behavior is regularized when velocity spread is taken into account; in that case, the nonlinear efficiency increases with beam current until it reaches a maximum, then falls off slowly. The increase in efficiency is attributed to enhanced bunching associated with the saturation of the space-charge instability in the drift region; the reduction in efficiency at high current occurs because space charge induces an additional velocity spread in the beam