Framework‐Substituted Bismuth Zeolite‐P: Synthesis and Characterization

Bismuth‐modified zeolite‐P (Bi‐ZP) was synthesized by hydrothermal methods during the phase transformation of analcime to zeolite‐P. The evolution of phase transformation of pure analcime to Bi‐ZP was investigated. The results showed that bismuth atoms were incorporated into the framework of the microporous zeolite‐P. The effect of various Bi/Al (0–3) and Si/Bi (1–5) mole ratios on the synthesis of bismuth modified zeolite were studied by X‐ray diffraction (XRD) technique and FT‐IR spectroscopy. Evolution of the growth process of Bi‐ZP spheres was carried out at different time intervals with XRD patterns and FE‐SEM images. The energy dispersive X‐ray (EDX) spectrum indicated the existence of bismuth atoms in the synthesized Bi‐ZP. Framework substitutions of bismuth were evidenced by a set of complementary characterizations such as diffusive reflectance UV/Vis (DRS) and Raman spectroscopy on the synthesized Bi‐ZP (Si/Bi = 1).     

Power absorbed during whole-body fore-and-aft vibration: Effects of sitting posture,backrest, and footrest

Although the discomfort or injury associated with whole-body vibration cannot be predicted directly from the power absorbed during exposure to vibration, the absorbed power may contribute to understanding of the biodynamics involved in such responses. From measurements of force and acceleration at the seat, the feet, and the backrest, the power absorbed at these three locations was calculated for subjects sitting in four postures (feet hanging, maximum thigh contact, average thigh contact, and minimum thigh contact) both with and without a rigid vertical backrest while exposed to four magnitudes (0.125, 0.25, 0.625, and 1.25 m s^?2 rms) of random fore-and-aft vibration. The power absorbed by the body at the supporting seat surface when there was no backrest showed a peak around 1 Hz and another peak between 3 and 4 Hz. Supporting the back with the backrest decreased the power absorbed at the seat at low frequencies but increased the power absorbed at high frequencies. Foot support influenced both the magnitude and the frequency of the peaks in the absorbed power spectra as well as the total absorbed power. The measurements of absorbed power are consistent with backrests being beneficial during exposure to low frequency fore-and-aft vibration but detrimental with high frequency fore-and-aft vibration.     

Some boundary properties of holomorphic functions of several complex variables

A local uniqueness theorem and analogs of the theorem on removable singularities under the hypothesis of boundedness are proved for functions satisfying the tangential Cauchy-Riemann conditions on hypersurfaces in Cⁿ. The results can be interpreted as giving certain boundary properties of holomorphic functions of several complex variables.Translated from Matematicheskie Zametki, Vol. 23, No. 6, pp. 839–844, June, 1978.In conclusion I express my thanks to B. V. Shabat for his contant interest in this work.     

Simulating the equation of state of model globular proteins adsorbed at a surface

Monte Carlo computer simulation is used to follow the adsorption of a model globular and disordered protein at a hard surface and to simulate the surface equation of state for these molecules. The simulation utilizes the deformable globule model where the "protein" is treated as a collection of interacting subunits. Disordered globules are modeled as athermal molecules, whereas globular molecules have a strong attractive interaction between subunits. The surface equation of state is modeled by applying a known pressure to an adsorbed globule and following the changes in adsorbed conformation. Simulated equations of state for the disordered and globular molecules show features that are observed in experimental surface pressure versus area plots. In particular the simulated equations of state show "kinks" that correspond to regions where the adsorbed globules undergo conformational changes as they lift away from the surface in response to the increased pressure. The model proteins follow Bull's equation at low surface pressures in a way that is broadly in line with results from experiment, and the changes in conformation as a function of surface pressure are in line with predictions by DeFeijter and Benjamins made using a soft-particle model for adsorbed proteins.     

The first use of a Rh(III) complex as a novel ionophore for thiocyanate-selective polymeric membrane electrodes

The feasibility of a newly synthesized Rh(III) complex, Rh[(trpy)(bpy)Cl](PF₆)₂, as a novel ionophore for the preparation of anion-selective polymeric membrane electrodes was tested. The ionophore exhibited anti-Hofmeister behavior with enhanced potentiometric selectivity toward thiocyanate ion compared to other anions. The influence of some experimental parameters such as membrane composition, nature and amount of plasticizer and additive and concentration of internal solution on the potential response of the SCN⁻ sensor were investigated. The electrode exhibits a Nernstian response for SCN⁻ over a wide concentration range (1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M) with a slope −58.7 ± 0.5 mV per decade and a detection limit of 4.0 × 10⁻⁶ M (0.23 ppm). It could be used in a pH range of 3.0-8.0 and has a fast response time of about 15 s. The proposed sensor was used for the determination of thiocyanate ions in real samples such as urine and saliva of smokers and nonsmokers and, as an indicator electrode, in potentiometric titrations of SCN⁻ ion.     

The use of dilute solution viscometry to characterize the network properties of carbopol microgels

We used dilute solution viscometry, specifically, measurements of intrinsic viscosity and overlap concentration to characterize two members of the carbopol family, carbopols 940 and 941. These measured quantities were then used to calculate the swollen-to-dry volume ratios for both resins over a range of ionic strengths. The variation in this ratio is representative of the swelling equilibria of the micronetwork and is modeled using standard network theory with modifications for non-Gaussian chain statistics and for fixed charges on the chains. By fitting to experimental data, the cross-link density is determined as 1450 monomer units between cross-link sites for carbopol 940 and 3300 units for carbopol 941. The shear modulus of the microgel domain is then predicted from the swelling data and found to be an order of magnitude greater than the elastic modulus measured on concentrated carbopol dispersions. We argue that this discrepancy is due to a large number of defects which reduce the cycle rank of the network. Current microgel technology specifies that their rheological behavior can be predicted once the domain cross-link density is known. Simple dilute solution viscometry appears capable of providing this prerequisite.     

Osmotic deswelling of microgels by linear polyelectrolytes

Polyacrylate microgels used as absorbers or viscosifiers in water are known to have these useful qualities reduced in the presence of linear poly-electrolytes. An osmotic deswelling mechanism is postulated whereby the counterions from linear chains sterically excluded from the gel act to draw solvent from the gel phase. This postulate is tested using intrinsic viscosity measurements of Carbopol microgels, made with the linear polyelectrolyte considered as parr of the solvent. The intrinsic viscosity is used to calculate the swollen-to-dry volume ratio for the microgel in the presence or absence of 0.1% linear sodium polyacrylate over a range in ionic strength. Simultaneously, a standard treatment for the free energy of a network of non-Gaussian chains containing fixed charges is modified to include the osmotic effect of the excluded counterions. In the absence of linear polymer, the theory is fit to the data, the fitting parameter being the 3100 monomer units between crosslink sites in the network. In the presence of high (350 000) molecular weight linear polymer, good agreement is found between the observed deswelling and that predicted if the linear chains are totally excluded. Lower molecular weight linear chains are found to give a reduced deswelling which is shown to be self-consistent with their partitioning into the network.Presented in part at the 64th Colloid and Surface Science Symposium, Lehigh University, June 1990     

A Partial CSI Estimation Approach for Downlink FDD massive-MIMO System with Different Base Transceiver Station Topologies

Massive multiple-input multiple-output (massive-MIMO) is a promising technology for next generation wireless communications systems due to its capability to increase the data rate and meet the enormous ongoing data traffic explosion. However, in non-reciprocal channels, such as those encountered in frequency division duplex (FDD) systems, channel state information (CSI) estimation using downlink (DL) training sequence is to date very challenging issue, especially when the channel exhibits a shorter coherence time. In particular, the availability of sufficiently accurate CSI at the base transceiver station (BTS) allows an efficient precoding design in the DL transmission to be achieved, and thus, reliable communication systems can be obtained. In order to achieve the aforementioned objectives, this paper presents a feasible DL training sequence design based on a partial CSI estimation approach for an FDD massive-MIMO system with a shorter coherence time. To this end, a threshold-based approach is proposed for a suitable DL pilot selection by exploring the statistical information of the channel covariance matrix. The mean square error of the proposed design is derived, and the achievable sum rate and bit-error-rate for maximum ratio transmitter and regularized zero forcing precoding is investigated over different BTS topologies with uniform linear array and uniform rectangular array. The results show that a feasible performance in the DL FDD massive-MIMO systems can be achieved even when a large number of antenna elements are deployed by the BTS and a shorter coherence time is considered.

     

Use of iridium oxide films as hydrogen gas evolution cathodes in aqueous media

Hydrous iridium oxide films are highly resistant to reduction under cathodic, hydrogen gas evolution, conditions in aqueous acid or base. Such behavior is not in agreement with simple thermodynamic (Pourbaix) data based on the assumption that the system behaves in a reversible manner. The barrier to reduction is attributed, as discussed earlier for RuO₂, to the involvement of high-energy intermediates (iridium atoms or microclusters of same) which can only be generated at unusually negative overpotential values evidently far into the hydrogen gas evolution region. Thermally prepared IrO₂/Ti electrodes are possible candidates for hydrogen gas evolution cathodes in water electrolysis cells; however, under extended operating conditions, the performance of these cathodes was found to deteriorate due to gradual shedding of the active oxide layer.