Characterization of porous materials by small-angle scattering

Characterization of porous materials by small-angle scattering has been extensively pursued for several years now as the pores are often of mesoscopic size and compatible with the length scale accessible by the technique using both neutrons and X-rays as probing radiation. With the availability of ultra small-angle scattering instruments, one can investigate porous materials in the sub-micron length scale. Because of the increased accessible length scale vis-a-vis the multiple scattering effect, conventional data analysis procedures based on single scattering approximation quite often fail. The limitation of conventional data analysis procedures is also pronounced in the case of thick samples and long wavelength of the probing radiation. Effect of multiple scattering is manifested by broadening the scattering profile. Sample thickness for some technologically important materials is often significantly high, as the experimental samples have to replicate all its essential properties in the bulk material. Larger wavelength of the probing radiation is used in some cases to access large length scale and also to minimize the effect of double Bragg reflections.     

Synthesis and solution properties of a new pH‐responsive polymer containing amino propanesulfonic acid residues

The reaction of diallyl amine with 1,3‐propane sultone led to the synthesis of the zwitterionic monomer 3‐(N,N‐diallylammonio)propanesulfonate. The sulfobetaine was cyclopolymerized in water in the presence of sodium chloride with t‐butylhydroperoxide as an initiator to afford a polysulfobetaine (PSB) in very good yield. PSB, upon treatment with sodium hydroxide, was converted into an anionic polyelectrolyte (APE). Although APE was readily soluble in salt‐free water, PSB needed the presence of low‐molecular‐weight salts (e.g., NaCl, KI, etc., in the range of 0.135–1.04 N) for its dissolution. The solution properties of PSB and APE were investigated with potentiometric and viscometric techniques. The basicity constant of the amine was apparent and followed the modified Henderson–Hasselbalch equation; as the degree of protonation (α) of the whole macromolecule increases, the protonation of the amine nitrogens becomes increasingly more difficult. The composition and phase diagram of the aqueous two‐phase systems of APE/PSB and poly(ethylene glycol) were also explored. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 172–184, 2003     

Digital circuit applications of resonant tunneling devices

Many semiconductor quantum devices utilize a novel tunneling transport mechanism that allows picosecond device switching speeds. The negative differential resistance characteristic of these devices, achieved due to resonant tunneling, is also ideally suited for the design of highly compact, self-latching logic circuits. As a result, quantum device technology is a promising emerging alternative for high-performance very-large-scale-integration design. The bistable nature of the basic logic gates implemented using resonant tunneling devices has been utilized in the development of a gate-level pipelining technique, called nanopipelining, that significantly improves the throughput and speed of pipelined systems. The advent of multiple-peak resonant tunneling diodes provides a viable means for efficient design of multiple-valued circuits with decreased interconnect complexity and reduced device count as compared to multiple-valued circuits in conventional technologies. This paper details various circuit design accomplishments in the area of binary and multiple-valued logic using resonant tunneling diodes (RTD's) in conjunction with high-performance III-V devices such as heterojunction bipolar transistors (HBT's) and modulation doped field-effect transistors (MODFET's). New bistable logic families using RTD+HBT and RTD+MODFET gates are described that provide a single-gate, self-latching majority function in addition to basic NAND, NOR, and inverter gates     

Distinct Proton and Water Reduction Behavior with a Cobalt(III) Electrocatalyst Based on Pentadentate Oximes

A new pentadentate oxime has been designed to drive the preferential coordination favored by Co^I in catalysts used for proton/water reduction. The ligand incorporates water upon metal coordination and is water soluble. This Co^III species is doubly reduced to Co^I and exhibits H⁺ reduction activity in the presence of weak acids in MeCN and evolves H₂ upon protonation suggesting that the ligand design increases catalyst effectiveness. Superior catalysis is observed in water with a turnover number (TON) of 5700 over 18 h. However, the catalyst yields Co‐based nanoparticles, indicating that the solvent media may dictate the nature of the catalyst.     

Auxiliary-directed oxidation of ursolic acid by ‘Ru’-porphyrins: chemical modulation of cytotoxicity against tumor cell lines

Derivatization of ursolic acid, one of the natural ursene-type pentacyclic triterpenes, was investigated by the oxidation with dioxoruthenium(VI) tetraphenylporphyrins. Oxidation selectivity on the terpene structure was modulated by the auxiliaries introduced on the tetraphenylporphyrin. Chemical oxidation of the ursolic acid affected the cytotoxic activity against tumor cell lines.     

Fractal morphology in porous membranes: A small-angle X-Ray scattering investigation

This paper reports the small-angle X-ray scattering (SAXS) study and flow- rate measurements of semipermeable porous polysulfone (PS) and sulfonated polycarbonate-doped polysulfone (SPC-PS) membranes. Flow rates of sodium chloride, sodium sulfate, and polyethylene glycol solutions through these membranes have been measured. For all the solutions, the flux through the SPC-PS membrane was found to be close to 1.65 times that through the PS membrane. SAXS measurements show that the pore morphologies of two membranes are mass fractal in nature with different fractal dimensions. The difference in flow rates through these membranes is explained in terms of porosity and fractal dimension.     

Time-domain modeling of high-speed interconnects by modified methodof characteristics

In this paper, a new model of lossy transmission lines is presented for the time-domain simulation of high-speed interconnects. This model is based on the modified method of characteristics (MMC). The characteristic functions are first approximated by applying lower order Taylor series in the frequency domain, and then a set of simple recursive formulas are obtained in the time domain. The formulas, which involve tracking performances between two ends of a transmission line, are similar to those derived by the method of characteristics for lossless and undistorted lossy transmission lines. The algorithm, based on the proposed MMC model, can efficiently evaluate transient responses of high-speed interconnects. It only uses the quantities at two ends of the lines, requiring less computation time and less memory space than required by other methods. Examples indicate that the new method has high accuracy and is very efficient for the time-domain simulation of interconnects in high-speed integrated circuits     

Interleaved PWM with discontinuous space-vector modulation

This paper describes the effect of interleaved discontinuous space-vector modulation (SVM) in paralleled three-phase systems using three-phase pulsewidth modulation (PWM) rectifiers as an example. At the discontinuous point of the SVM, the phase shift between the switching signals of the paralleled modules generates a zero-sequence excitation to the system. Because the conventional control in a balanced three-phase system with only dq channels cannot reject this disturbance, a beat-frequency circulating current will develop on the zero axis. Based on this observation, a SVM without using zero vectors is used to eliminate the cause of pure zero-sequence current for parallel operation. Using this SVM, the circulating current is observable in dq channels. It can be suppressed dynamically by strong current loops of power-factor-correction (PFC) circuits. The concept is verified experimentally on a breadboard system     

9(R)‐[6(R)‐Hydroxy­methyl‐1‐oxa‐4‐thia­cyclo­hexan‐2‐yl]hypoxanthine–water (4/3), a nucleoside analogue

The title compound, 9(R)‐[6(R)‐hydroxy­methyl‐1‐oxa‐4‐thia­cyclo­hexan‐2‐yl]‐1,9‐di­hydro‐6H‐purin‐6‐one–water (4/3), C₁₀H₁₂N₄O₃S·0.75H₂O, crystallizes in the triclinic space group P1 with four mol­ecules in the asymmetric unit and 0.75 waters of hydration per mol­ecule. The structure was refined to an R value of 0.072 for 3382 observed reflections. The four crystallographically independent mol­ecules are designated A, B, C and D. All four oxa­thia­ne rings adopt the chair conformation and the purine bases are in an anti orientation with respect to the sugar moieties. Molecules A and D and mol­ecules C and B are base paired by a single hydrogen bond of the type N—H?N. These base pairs are again hydrogen bonded to their translated pairs in the direction of a cell diagonal.     

Theoretical and experimental investigation of the fast- andslow-scale instabilities of a DC-DC converter

We use an exact formulation based on nonlinear maps to investigate both the fast-scale and slow-scale instabilities of a voltage-mode buck converter operating in the continuous conduction mode and its interaction with a filter. Comparing the results of the exact model with those of the averaged model shows the shortcomings of the latter in predicting fast-scale instabilities. We show the impact of parasitics on the onset of chaos using a high-frequency model. The experimentally validated theoretical results of this paper provide an improved understanding of the dynamics of the converter beyond the linear regime and this may lead to less conservative control design and newer applications