Functional group dependent site specific fragmentation of molecules by low energy electrons

Functional group dependence is observed in the dissociative electron attachment (DEA) to various organic molecules in which the DEA features seen in the precursor molecules of the groups are retained in the bigger molecules. This functional group dependence is seen to lead to site-selective fragmentation of these molecules at the hydrogen sites. The results are explained in terms of the formation of core-excited Feshbach resonances. The results point to a simple way of controlling chemical reactions as well as interpreting the DEA data from bigger biological molecules.     

How Do Metal Ions Modulate the Rate-Determining Electron-Transfer Step in Cytochrome P450 Reactions?

Cytochrome P450 (CYP450) enzymes play important roles in maintaining human health and their reaction rates are dependent on the first electron transfer from the reduction partner. Interestingly, experimental work has shown that this step is highly influenced by the addition of metal ions. To understand the effect of external perturbations on the CYP450 first reduction step, we have performed a computational study with model complexes in the presence of metal and organic ions, solvent molecules, and an electric field. The results show that these medium-range interactions affect the driving force as well as electron-transfer rates dramatically. Based on the location, distance, and direction of the ions/electric field, the catalytic reaction rates are enhanced or impaired. Calculations on a large crystal structure with bonded alkali metal ions indicated inhibition patterns of the ions. Therefore, we predict that the active forms of the natural CYP450 isozymes will not have more than one alkali metal ion bound in the second-coordination sphere. As such, this study provides an insight into the activity of CYP450 enzymes and the effects of ions and electric field perturbations on their activity.     

Knapsack problems with sigmoid utilities: Approximation algorithms via hybrid optimization

We study a class of non-convex optimization problems involving sigmoid functions. We show that sigmoid functions impart a combinatorial element to the optimization variables and make the global optimization computationally hard. We formulate versions of the knapsack problem, the generalized assignment problem and the bin-packing problem with sigmoid utilities. We merge approximation algorithms from discrete optimization with algorithms from continuous optimization to develop approximation algorithms for these NP-hard problems with sigmoid utilities.     

Design and development of a neutron/X-ray combined computed tomography system at Missouri S&T

A new method for non-destructive analysis has been developed using a combined neutron/X-ray imaging system at the Missouri Science & Technology Reactor (MSTR). The interactions of neutrons and X-ray photons with matter produce differing characteristic information, resulting in distinctly different visual images. In order to obtain a more comprehensive picture of the structural and compositional data for a desired object, a prototype imaging system has been designed which utilizes neutron and X-ray imaging simultaneously without obstructing the beam geometry for each imaging mechanism. The current system is optimized for the imaging of small to medium sized objects of 0.5–50 mm. This new imaging capability in place at the MSTR promises great advances in the field of non-destructive testing, especially for nuclear engineering, nuclear medical science, and material science research. In an imaging object, a range of atomic number values and thermal cross-sections may be present. Where multiple materials having similar atomic number and differing thermal cross-section or vice versa may be present, exclusive neutron or X-ray analysis may exhibit shortcomings in distinguishing interfaces. However, fusing the neutron image and X-ray image into a combined image offers the strengths of both and may provide a superior method of analysis. In this paper, a novel combined X-ray and neutron imaging system will be introduced for superior analysis of certain imaging objects. Design details of experimental set-up and examples of preliminary imaging tests from individual modality will be detailed.     

Determination of salutary parameters to facilitate bio-energy production from three uncommon biomasses using thermogravimetric analysis

Fuels derived from biomass are renewable as well as environment friendly. In this study, three biomasses viz. husk of areca nut (Areca catheu), trunks of moj (Albizzia lucida), and bon bogori (Ziziphus rugosus) available in North-East region of India were tested as potential biofuel sources. The accentuation of this study was to determine the kinetic parameters using thermogravimetric (TG) technique under air and nitrogen atmosphere. The experiments were carried out within temperature range 300–973 K under air and nitrogen atmosphere at four different heating rates viz. 5, 10, 15, and 20 K min^?1, respectively. The mass losses at different lumps in the TG graphs were estimated. The first-order kinetic parameters such as activation energy and pre-exponential factor were calculated for different reaction zones for all the three biomass samples. Effects of atmosphere on combustion characteristics (e.g., peak temperature, ignition temperature, and reactivity index) of biomasses were also determined in this study. Areca nut husk has highest ignition temperature (526.38 K) and reactivity index (0.21) but moj has highest peak temperature (597.91 K) along with highest activation energy (348.04 kJ mol^?1) and pre-exponential factor (1.12 × 10²⁴ min^?1), respectively.     

Facile Tetrahydropyranylation of Alcohols and Phenols Using Anhydrous Calcium Chloride under Mild and Neutral Conditions

Summary.  Treatment of 3,4-dihydro-2H-pyran with various alcohols and phenols in the presence of a catalytic amount of anhydrous calcium chloride in dichloromethane furnished tetrahydropyranyl ethers under almost neutral conditions. Corresponding author. E-mail: bandgar_bp@yahoo.com Received January 25, 2002; accepted (revised) March 20, 2002