Cassette mutagenesis of Aspergillus awamori glucoamylase near its general acid residue to probe its catalytic and pH properties

Nine single amino add mutations in the active site of Aspergillusawamori glucoamylase were made by cassette mutagenesis to alterthe pH dependence of the enzyme and to determine possible functionsof the mutated residues. The Glul79-Asp mutation expressed inyeast led to a very large decrease in k_cat but to no changein K_m, verifying this residue's catalytic function. Aspl76-Gluand Glul80-Asp mutations affected K_m a more than k_cat, implyingthat Aspl76 and Glul80 are involved in substrate binding orstructural integrity. The Leul77-Asp mutation decreased k_catonly moderately, probably by changing the position of the generalacid catalytic group, and did not affect K_m. The Trpl78-Aspmutation greatly decreased k_cat while increasing K_m, showingthe importance of Trpl78 in the active site. Vall81-Asp andAsnl82-Asp mutations changed kinetk values little, suggestingthat Vall81 and Asnl82 are of minor catalytic and structuralimportance. Finally, insertions of Asp or Gly between residues176 and 177 resulted in almost complete loss of activity, probablycaused by destruction of the active site structure. No largechanges in pH dependence occurred in those mutations where kineticvalues could be determined, in spite of the increase in mostcases of the total negative charge. Increases in activationenergy of maltoheptaose hydrolysis in most of the mutant glucoamylasessuggested cleavage of individual hydrogen bonds in enzyme-substratecomplexes.     

Systems with a switch and estimation of absolute stability region

Two methods are proposed for estimation of absolute stability region in the space of parameters. The first method uses nontrivial necessary conditions, which follow from stability of switching systems. The second method is a modification of the harmonic balance approach; it is used for approximate determination of existence of periodic modes that arise when stability is lost.     

On absolute stability of discrete systems

Modernization is considered of the criterion of absolute stability of discrete systems [1, 2], which uses the method of quadratic transformation of the state vector. The modernization aim is to obtain the criterion form that does not explicitly depend on the notions of this method. The new formulation permits performing all calculations in the space of the initial dimension, which reduces the complexity of the problem solution. This work represents the development of the approach suggested in [3] for continuous systems.     

Ligating behavior and metal uptake of N‐sulphonylpolyamine chelating resins anchored on polystyrene‐divinylbenzene beads

Amberlite XAD‐2 has been functionalized by coupling through –SO₂‐with ethylenediamine, propylenediamine, and diethylenetriamine to give the corresponding polyamine chelating resins I–III. The solid metallopolymer complexes of the synthesized chelating resins with Cu²⁺, Zn²⁺, Cd²⁺, and Pb²⁺ were synthesized. The polyamine derivatives and their metal complexes were characterized by elemental analysis, spectral (IR, UV/V, and ESR), and magnetic studies. The batch equilibrium method was utilized for using the chelating polyamines for the removal of Cu⁺², Zn⁺², Cd⁺², and Pb⁺² ions from aqueous solutions at different pH values and different shaking times at room temperature. The selective extraction of Cu⁺² from a mixture of the four metal ions and the metal capacities of the chelating resins were evaluated using atomic absorption spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1839–1846, 2005     

A filter design method for minimizing ringing in a region of interest in MR spectroscopic images

Magnetic resonance spectroscopic imaging (MRSI) requires a relatively long time to sample k-space (the spatial frequency domain), effectively lowpass filtering the resulting reconstructed image. Ringing is especially problematic when a region of interest (ROI) is close to a bright region outside the ROI, since the bright region tends to create a ringing artifact into the ROI due to the lowpass nature of the data. In this paper, we propose a method that reduces the effect of a stronger signal region on a weaker signal in a nearby ROI by designing a postprocessing filter that steers the strong interference away from the ROI. The proposed method is computationally simple both in the design stage and in applying it to images. We present experiments that illustrate the value of the technique.     

An investigation of information system utilization

This investigation focuses upon the information utilization process; i.e., what it means for a decision-maker to utilize an information system. A definition of utilization is adopted that states that an information system is utilized if the output from the information system is included in the Human Information Processing system of a decision-maker. The definition of utilization is further refined by segmenting utilization into two distinct subsystems, a Human Information Processing system and a Data Selection system. As an initial investigation of the utilization process, it was decided specifically to study the relationship of the Data Selection system to the Human Information Processing system. The primary aim of this investigation was to determine whether factors that are internal to a decision-maker may affect the data selection process. “Cognitive style” was chosen as representative of internal factors. Measures of data selection and cognitive style were created with particular emphasis placed on the development of an instrument to measure cognitive style. An experiment was designed to investigate the effect of this factor on data selection. The results of this experiment indicate there is a strong relationship between cognitive style and data selection.     

Scan blindness phenomenon in conformal finite phased arrays of printed dipoles

Scan blindness phenomenon for finite phased arrays of printed dipoles on material coated, electrically large circular cylinders is investigated. Effects on the scan blindness mechanism of several array and supporting structure parameters, including curvature effects, are observed and discussed. A full-wave solution, based on a hybrid method of moments/Green's function technique in the spatial domain, is used to achieve the aforementioned goals. Numerical results show that the curvature affects the surface waves and hence the mutual coupling between array elements. As a result, the array current distribution of arrays mounted on coated cylinders are considerably different compared to similar arrays on planar platforms. Therefore, finite phased arrays of printed dipoles on coated cylinders show different behavior in terms of scan blindness phenomenon compared to their planar counterparts. Furthermore, this phenomenon is completely different for axially and circumferentially oriented printed dipoles on coated cylinders suggesting that particular element types might be important for cylindrical arrays.     

Fabrication and Characterization of Electrical Interconnects and Microfluidic Cooling for 3D ICS With Silicon Interposer

Heat generation in high-performance three-dimensional integrated circuits (3D ICs) is a significant challenge due to limited heat removal paths and high power density. To address this challenge, this paper presents an embedded microfluidic heat sink (MFHS) for such high-performance 3D ICs. In the proposed 3D IC system, each tier contains an embedded MFHS, along with high-aspect-ratio (23:1) through-silicon vias (TSVs) routed through the MFHS. In each tier, solder-based electrical and fluidic inputs/outputs are co-fabricated with wafer-level batch fabrication. Moreover, microfluidic cooling experiments of staggered micropin-fins with embedded TSVs are presented for the first time.