Alpha‐Cyclodextrin Production using Cyclodextrin Glycosyltransferase from Klebsiella pneumoniae AS‐22

Alpha‐cyclodextrin (α‐CD) production, using cyclodextrin glycosyltransferase (CGTase) from Klebsiella pneumoniae AS‐22, was investigated in the presence of various complexing agents using raw wheat starch and dextrin as substrates. The addition of many alcohols resulted in increased conversion of both raw wheat starch and dextrin to α‐CD. With 125 g/L raw wheat starch, 42.5% (w/w) conversion to CDs was obtained in the presence of 2% (v/v) butan‐1‐ol. The ratio of α:β‐CD formed was 97:3, with negligible formation of γ‐CD and malto‐oligosaccharides. The production of α‐CD was optimized using two‐level factorial designs in three variables: dextrin, hexan‐1‐ol and enzyme concentrations. Under optimum conditions, 12.1% (w/w) conversion of 500 g/L dextrin to total‐CDs was achieved. The ratio of α:β:γ‐CD formed was 91:3:6, with negligible production of malto‐oligosaccharides. This CGTase was strongly inhibited by α:‐CD; 50% inhibition of reaction rate was observed at an initial concentration of 4 g/L α:‐CD. The effectiveness of an ultrafiltration membrane bioreactor for continuous removal of product was also tested.     

Attitude Controller for Steady Hover of a Rotary-Wing Flying Robot

This paper presents an attitude controller for steady hover of CMERI’s Rotary-Wing Flying Robot. The main objective is to control the dynamic behaviour of the robot, which is complex in shape and motion as nonlinear aerodynamic forces and gravity acts on the system. Due to limited accuracy of the dynamic model, the attitude dynamics is conditionally stable where a minimum amount of attitude feedback is required for system stability. To compensate for conditional stability with improved disturbance rejection, an attitude controller is developed adopting cascade control loop architecture. The INS system feedback is used for outer control loop while the gyro feedback is adopted for the inner control loop to attain a high bandwidth, ensuring attitude stability with accelerated response required for a steady hover. The defined controller has introduced corrective control to mitigate the disturbance as sensed by the gyros before they actually do affect the output as the cascade control loop is more responsive than simply the INS loop feedback. In the proposed approach, the robot is modelled using well known “NASA Minimum Complexity Math Model” where robot dynamics is decoupled into Single Input Single Output system. Kalman filter is used to estimate the attitude from the high frequency based gyros aided by INS system feedback data while a matched pole-zero method is used to perform discretization. The stability of the system is evaluated using closed loop identification. The provided solution is tested on Hirobo Scheadu50 model and the system performance is analyzed using the proposed controller.     

Fast ray-tracing of human eye optics on Graphics Processing Units

We present a new technique for simulating retinal image formation by tracing a large number of rays from objects in three dimensions as they pass through the optic apparatus of the eye to objects. Simulating human optics is useful for understanding basic questions of vision science and for studying vision defects and their corrections. Because of the complexity of computing such simulations accurately, most previous efforts used simplified analytical models of the normal eye. This makes them less effective in modeling vision disorders associated with abnormal shapes of the ocular structures which are hard to be precisely represented by analytical surfaces. We have developed a computer simulator that can simulate ocular structures of arbitrary shapes, for instance represented by polygon meshes. Topographic and geometric measurements of the cornea, lens, and retina from keratometer or medical imaging data can be integrated for individualized examination. We utilize parallel processing using modern Graphics Processing Units (GPUs) to efficiently compute retinal images by tracing millions of rays. A stable retinal image can be generated within minutes. We simulated depth-of-field, accommodation, chromatic aberrations, as well as astigmatism and correction. We also show application of the technique in patient specific vision correction by incorporating geometric models of the orbit reconstructed from clinical medical images.     

Understanding the Plasticity of the α/β Hydrolase Fold: Lid Swapping on the Candida antarctica Lipase B Results in Chimeras with Interesting Biocatalytic Properties

The best of both worlds . Long molecular dynamics (MD) simulations of Candida antarctica lipase B (CALB) confirmed the function of helix α5 as a lid structure. Replacement of the helix with corresponding lid regions from CALB homologues from Neurospora crassa and Gibberella zeae resulted in new CALB chimeras with novel biocatalytic properties. The figure shows a snapshot from the MD simulation.

     

Pre-charging of module capacitors of MMC when the module switches are driven by a source derived from the module capacitor

A modular multilevel converter (MMC) is one of the latest multilevel converters used for high and medium-voltage power conversion. It is based on cascade connection of multiple identical modules using IGBTs as switching devices. Module switches of MMC are preferably driven by a source derived from the module capacitor. In each MMC module, the control circuit, consisting of gate drivers, is powered from a dc supply derived from the local capacitor. The module capacitors need to be pre-charged, to power the control circuit. The problem faced while doing so experimentally for MMC with two modules per arm and a solution have been reported earlier. If a fly-back converter is used to generate the power supply for driving the control circuit, the module capacitor voltages become unstable during uncontrolled pre-charging. It has been reported earlier that the reason for this is approximately constant power load on the module capacitor. This work provides theoretical understanding of the problem and shows by analysis that the power supply can be made stable if the load on the module capacitor is made a positive resistance load. As the complexity of MMC with more than two modules per arm is higher, the phenomenon is studied by simulation for MMC with four modules per arm. It shows that when a fly-back converter is used for generating the power supply, similar instability occurs in MMC with four modules per arm. It shows that when the module capacitor is made to have a load with positive resistance characteristics, the module capacitor voltages and consequently the power supplies stabilize even for MMC with four modules per arm. It further shows that even if the load on the module capacitor is negative resistance type, when fly-back converter is used to generate the module power supply, by switching devices in those modules where power supply becomes available first, followed by sorting algorithm, stable power supplies can be developed on all the modules and the capacitors can be fully charged to the desired voltage.     

Active serine involved in the stabilization of the active site loop in the Humicola lanuginosa lipase

We have investigated the binding properties of and dynamics in Humicola lanuginosa lipase (Hll) and the inactive mutant S146A (active Ser146 substituted with Ala) using fluorescence spectroscopy and molecular dynamics simulations, respectively. Hll and S146A show significantly different binding behavior for phosphatidylcholine (PC) and phosphatidylglycerol (PG) liposomes. Generally, higher binding affinity is observed for Hll than the S146A mutant. Furthermore, depending on the matrix, the addition of the transition state analogue benzene boronic acid increases the binding affinity of S146A, whereas only small changes are observed for Hll suggesting that the active site lid in the latter opens more easily and hence more lipase molecules are bound to the liposomes. These observations are in agreement with molecular dynamics simulations and subsequent essential dynamics analyses. The results reveal that the hinges of the active site lid are more flexible in the wild-type Hll than in S146A. In contrast, larger fluctuations are observed in the middle region of the active site loop in S146A than in Hll. These findings reveal that the single mutation (S146A) of the active site serine leads to substantial conformational alterations in the H. lanuginosa lipase and different binding affinities.     

Synthesis and characterization of oxime resin of poly(4-viny1, 2′-carboxybenzophenone) and its metal polychelates

The synthesis and characterization of oxime resin of poly(4-vinyl, 2′-carboxybenzophenone) is described and its exchange properties for Cu(II), Ni(II), and Co(II) are studied. The metal poiycheiates are investigated by magnetic measurements, diffuse reflectance spectroscopy, and infrared spectroscopy. © 1995 John Wiley & Sons, Inc.     

Effect of diethylene glycol (DEG) on the crystallization behavior of poly(ethylene terephthalate) (PET)

The effect of diethylene glycol (DEG) on the crystallization of poly(ethylene terephthalate) (PET) was studied under isothermal and dynamic conditions. The strain-induced crystallization of PET and its relationship to DEG content was also studied. The samples were isothermally and dynamically crystallized in the differential scanning calorimeter (DSC). The thermograms were then analyzed to determine the kinetic parameters. Strain-induced crystallization was studied by stretching samples at different strain rates. These samples were then annealed for various periods of time and quenched to room temperature. Birefringence and density were measured on the annealed samples. Results indicate that the DEG content reduces the rate of crystallization of PET when crystallizing from the melt, isothermally and dynamically. When crystallizing from the glassy state, the effects of DEG are not prominent. The mechanism of crystallization is not affected by the amount of DEG, within the range of DEG contents evaluated. In the case of strain-induced crystallization, increased DEG content reduces the crystallinity of PET at intermediate strain rates, but at higher strain rates, the crystallinity is not affected by the DEG content. © 1993 John Wiley & Sons, Inc.