Impressive Gelation in Organic Solvents by Synthetic, Low Molecular Mass, Self-Organizing Urethane Amides of L-Phenylalanine

Synthetic routes leading to 12 L-phenylalanine based mono- and bipolar derivatives (1-12) and an in-depth study of their structure-property relationship with respect to gelation have been presented. These include monopolar systems such as N-[(benzyloxy)carbonyl]-L-phenylalanine-N-alkylamides and the corresponding bipolar derivatives with flexible and rigid spacers such as with 1,12-diaminododecane and 4,4'-diaminodiphenylmethane, respectively. The two ends of the latter have been functionalized with N-[(benzyloxy)carbonyl]-L-phenylalanine units via amide connection. Another bipolar molecule was synthesized in which the middle portion of the hydrocarbon segment contained polymerizable diacetylene unit. To ascertain the role of the presence of urethane linkages in the gelator molecule protected L-phenylalanine derivatives were also synthesized in which the (benzyloxy)carbonyl group has been replaced with (tert-butyloxy)carbonyl, acetyl, and benzoyl groups, respectively. Upon completion of the synthesis and adequate characterization of the newly described molecules, we examined the aggregation and gelation properties of each of them in a number of solvents and their mixtures. Optical microscopy and electron microscopy further characterized the systems that formed gels. Few representative systems, which showed excellent gelation behavior was, further examined by FT-IR, calorimetric, and powder X-ray diffraction studies. To explain the possible reasons for gelation, the results of molecular modeling and energy-minimization studies were also included. Taken together these results demonstrate the importance of the presence of (benzyloxy)carbonyl unit, urethane and secondary amide linkages, chiral purities of the headgroup and the length of the alkyl chain of the hydrophobic segment as critical determinants toward effective gelation.

Studies on low-intensity oxy-fuel burner

This paper presents experimental and computational results of oxy-fuel burner operating on classical flame and lameless mode for heat release rate of 26 kW/m3. The uniqueness of the burner arises from a slight asymmetric injection of oxygen at near sonic velocities. Measurements of emperature, species, total heat flux, radiative heat flux and NOx emission were carried out inside the furnace and the flow field was computationally analyzed. The flame studies were carried out for coaxial flow of oxygen and fuel jets with similar inlet velocities. This configuration results in slow mixing between fuel and oxygen and the flame is developed at distance away from the burner and the flame is bright/white in colour. In the flameless mode a slight asymmetric injection of the high velocity oxygen jet leads to a large asymmetric recirculation pattern with the recirculation ratio of 25 and the resulting flame is weak bluish in colour with little soot and acetylene formation. The classical flame in comparison is characterised by soot and acetylene formation, higher NOx and noise generation. The distribution of temperature and heat flux in the furnace is more uniform with flameless mode than with flame mode.

Trehalose Toxicity in Cuscuta refexal Correlation With low Trehalase Activity

A toxic effect of a,a-trehalose in an angiospermic plant, Cuscuta reflexa (dodder), Is described. This disaccharide and Its analogs, 2-aminotrehalose and 4-aminotbhakose, induced a raid blackening of the terminal region of the vine which is Involved in elongation growth. From the results of in vitro growth of several angkiopermic plants and determination of trehalase activity in them, it is concluded that the toxic effect of trehalose in Cucaa is because of the very low trehalas activity In the vine. As a result, trehalose accumulates In the vine and interferes with some process closely associated with growth. The growth potential of Lemma (a duckweed) in a medium containing trehalose as the carbon source was ihreversibly lost upon addition of trealosamine, an Inhibitor of trehalase activity. It is concluded that, if allowed to accumulate within the tissue, trehalose may be potentiaMly toxic or inhibitory to higher plants in generaL The presence of trhalase actvity in plants, where Its substrate has not been found to occur, is envisged to relieve the plant from the toxic effects of trehalose which it may encounter in soil or during association with fungi or insects.

Partial discharges at low pressures in a dielectric interface between uniform field electrodes

Partial discharges in a gaseous interface due to the presence of a dielectric between two uniform field electrodes in air at different pressures from 0.5 to 685 mm Hg have been studied and measurements of inception and extinction voltages, number of pulses and their charge magnitudes at inception are reported. It has been observed that the extinction voltage can be as low as 70% of the inception voltage suggesting that the working voltage in such cases should be about 30% lower than the observed inception voltage. Small magnitude pulses are found to be more in number than large magnitude pulses. The charge is found to be pressure dependent. The results have been explained on the basis of an equivalent circuit consisting of resistance and capacitance in which the discharge gap functions as a switch.

Co-2-Ions In A Low-Pressure Glow-Discharge Of Carbon-Dioxide

$CO_2^{-}$ ions have been detected in the gas phase and measured by a mass spectrometer with a flight time of 30 µs in the positive column of carbondioxide glow discharge.

High-Pressure Low-Temperature Locknut Cell For Both Electron-Paramagnetic-Res And Nmr-Studies To 10 Kilobars And 77-K

A locked high-pressure cell with working pressure range up to 10 kbars suitable for low-temperature studies to 77 K has been described. It can be used for both EPR and NMR studies of single crystals (and other solid samples). The high-pressure seal and all other aspects of the cell remain the same for either application. Only a change of the bottom plug is required for a switch from a nuclear-magnetic-resonance (NMR) to an electron-paramagnetic-resonance (EPR) experiment. Details of the procedure for the calibration of pressure inside the cell at various temperatures are discussed. The performance of the cell in EPR (Cr3+ion) and NMR (27Al nucleus) studies is reported.

On the short-range order in Al-Mn quasicrystals during low-temperature ageing

We report the evolution of diffuse intensity during the low-temperature ageing of Al-Mn quasicrystals. This is taken as evidence of short-range order in the icosahedral phase prior to its decomposition. The implication of these diffuse intensities is discussed.

Low temperature fluorination of sulphur compounds with elemental fluorine

Low temperature fluorination technique is adopted for fluorination of the following sulphur compounds in freon-11 medium (1) Sulphur dioxide (2) Thionyl chloride (3) Sulphuryl chloride (4) Tetrasulphur tetra nitride and (5) Sulphur bromide. All the compounds undergo oxidative fluorination to give rise to sulphur-fluorine compounds except sulphuryl chloride which resists fluorination. Sulphuryl chloride thus behaves as a good solvent medium for fluorination of other reactive compounds like elemental sulphur. Details of the experimental procedures adopted and the identification of the products will be presented.

Low-intensity differential photocapacitance of MOS structures

Some new observations on the phenomenon of photocapacitane on n-type silicon MOS structures under low intensities of illumination are reported. The difference between the illuminated and dark C---characteristics is automatically followed as a function of the applied bias thereby obtaining the differential photocapacitance and the resulting characteristics has been termed as the Low Intensity Differential Photocapacitance (LIDP). For an MOS capacitor, the LIDP characteristics is seen to go through a well defined maximum. The phenomenon has been investigated under different ambient conditions like light intensity, temperature, dependance of the frequency of the light etc. and it has been found that the phenomenon is due to a band excband excitation. In this connection, a novel sensitive technique for the measurement of the capacitance based upon following the frequency changes of a tank circuit is also described in some detail. It is also shown that the phenomenon can be understood by a simple theoretical model.

Dependence of low-lying energy eigenvalues on the short- and long-range parts of confining potentials

The potential description of a quark-antiquark system seems to work very well in describing a number of hadronic properties. However, the precise form of the potential is unknown. The changes in the low-lying eigenvalues as a result of changes in the long-range part of the potential are investigated in a non-perturbative manner. It is shown by considering a variety of examples that the low-lying eigenvalues are insensitive to the long-range part of the potential.

Low-temperature and high-pressure Raman and x-ray studies of pyrochlore Tb2Ti2O7: Phonon anomalies and possible phase transition

We have carried out temperature- and pressure-dependent Raman and x-ray measurements on single crystals of Tb2Ti2O7. We attribute the observed anomalous temperature dependence of phonons to phonon-phonon anharmonic interactions. The quasiharmonic and anharmonic contributions to the temperature-dependent changes in phonon frequencies are estimated quantitatively using mode Grüneisen parameters derived from pressure-dependent Raman experiments and bulk modulus from high-pressure x-ray measurements. Further, our Raman and x-ray data suggest a subtle structural deformation of the pyrochlore lattice at ~9 GPa. We discuss possible implications of our results on the spin-liquid behavior of Tb2Ti2O7.

Simplified Mathematical Model for Effects of Freezing on the Low-Temperature Performance of the Lead-Acid Battery

Discharge periods of lead-acid batteries are significantly reduced at subzero centigrade temperatures. The reduction is more than what can he expected due to decreased rates of various processes caused by a lowering of temperature and occurs despite the fact that active materials are available for discharge. It is proposed that the major cause for this is the freezing of the electrolyte. The concentration of acid decreases during battery discharge with a consequent increase in the freezing temperature. A battery freezes when the discharge temperature falls below the freezing temperature. A mathematical model is developed for conditions where charge-transfer reaction is the rate-limiting step. and Tafel kinetics are applicable. It is argued that freezing begins from the midplanes of electrodes and proceeds toward the reservoir in-between. Ionic conduction stops when one of the electrodes freezes fully and the time taken to reach that point, namely the discharge period, is calculated. The predictions of the model compare well to observations made at low current density (C/5) and at -20 and -40 degrees C. At higher current densities, however, diffusional resistances become important and a more complicated moving boundary problem needs to be solved to predict the discharge periods. (C) 2009 The Electrochemical Society.

Low PAPR Square STBCs from Complex Partial-Orthogonal Designs (CPODs)

Space-time codes from complex orthogonal designs (CODs) with no zero entries offer low Peak to Average Power Ratio (PAPR) and avoid the problem of switching off antennas. But square CODs for 2(a) antennas with a + 1. complex variables, with no zero entries were discovered only for a <= 3 and if a + 1 = 2(k), for k >= 4. In this paper, a method of obtaining no zero entry (NZE) square designs, called Complex Partial-Orthogonal Designs (CPODs), for 2(a+1) antennas whenever a certain type of NZE code exists for 2(a) antennas is presented. Then, starting from a so constructed NZE CPOD for n = 2(a+1) antennas, a construction procedure is given to obtain NZE CPODs for 2n antennas, successively. Compared to the CODs, CPODs have slightly more ML decoding complexity for rectangular QAM constellations and the same ML decoding complexity for other complex constellations. Using the recently constructed NZE CODs for 8 antennas our method leads to NZE CPODs for 16 antennas. The class of CPODs do not offer full-diversity for all complex constellations. For the NZE CPODs presented in the paper, conditions on the signal sets which will guarantee full-diversity are identified. Simulation results show that bit error performance of our codes is same as that of the CODs under average power constraint and superior to CODs under peak power constraint.

Reduction of Permittivity in Epoxy Nanocomposites at Low Nano-filler Loadings

Experimental studies reveal a reduction in the values of permittivity for epoxy nanocomposites; at low filler loadings as compared to neat epoxy over a wide frequency range. This permittivity reduction is attributed to the interaction dynamics between nanoparticles: and epoxy chains at the interface region and interestingly, this interaction has also been found to influence the glass transition temperatures (T-g) of the examined nanocomposite systems. Accordingly, a dual nanolayer interface model for an epoxy based nanocomposite system is analyzed to explain the obtained permittivity characteristics.