196,129 research outputs found
RESISTANCE AND PROPULSION OF AN ICEBREAKING VESSEL IN ULTRA-SHALLOW WATER
No full textThis paper highlights main aspects of the shallow water effects on resistance, hull-propeller interaction and propulsive qualities of anicebreaking emergency and evacuation vessel(IBEEVs). The IBEEV is a smallsized, shallow draft vessel, owned and operated by AGIP KCO on the sea basin in the Kazakhstan sector of the Northern Caspian Sea. It was designed specifically to evacuate personnel from offshore oil installations in emergency situations taking also into account a potential hydrocarbon/toxic environment. Because of generally unsatisfactory behavior of first prototypes in full-scale operations, a comprehensive research project was planned by AGIP KCO aimed at assessing overall performanceof the IBEEV as-it-is in order to plan a possible retrofit. A number of activities sequentially involving Navalprogettiand Krylov State Research Center were implemented with the key support from the first author. These activities encompassed analytical and numerical computations, model tests in deep and shallow water. The ultra-shallow water depth showed dramatic influence on the vessel’s resistance, hull-propeller interaction, and bollard pull capability. Finally, the rope pull capability of IBEEV was assessed on the basis of resistance and self-propulsion tests
Computational Evidence for the Catalytic Mechanism of Human Glutathione S-Transferase A3-3: A QM/MM Investigation
No full textA Quantum Mechanics/Molecular Mechanics (QM/MM) computational investigation of the catalytic mechanism of the human glutathione transferase A3-3 (hGSTA3-3) has been carried out. The results demonstrate that the isomerization reaction is concerted, but highly asynchronous: in the first reaction phase the glutathione (GSH) negative sulfur (thiolate) acts as a base and deprotonates carbon C4 of the substrate Δ5-androstene-3,17-dione (Δ5-AD); in the second reaction phase the hydroxyl proton of the tyrosine fragment Y9 is transferred to C6 affording the Δ4-androstene-3,17-dione product (Δ4-AD). The initial state of the enzyme is subsequently restored by transferring a proton from the GSH sulfur to the tyrosine negative oxygen. There is no evidence for a “genuine” stepwise mechanism involving the formation of a real dienolate intermediate as suggested in previous papers. Furthermore, our computations have evidenced that, when we consider the whole process (including the restoring of the enzyme), GSH behaves as a base/acid catalyst (as hypothesized by some authors), but it requires the participation of the tyrosine Y9 acting as a proton shuttle. A “fingerprint analysis” has been used to rank the electrostatic effects on the catalysis of the various residues surrounding the active site. This analysis highlights the role played by the arginine residue R15 in stabilizing the initial complex in agreement with previous suggestions based on crystal structures
A Rational Approach Towards a New Ferrocenyl Pyrrolidine for Stereoselective Enamine Catalysis
No full textProline and pyrrolidine derivatives (Hayashi– Jørgensen catalysts) are considered “work horses” in organocatalysis. This report describes a new effective ferrocenyl pyrrolidine catalyst that is able to perform well in benchmark organocatalytic reactions (see figure). The ferrocene moiety controls the conformational space and a simple alkyl group effectively covers a face of the derived enamine. This new framework can find applications in organocatalysis, and in general, in new ligand desig
Short term prognosis of stroke in a clinical series of 94 patients
No full textWe conducted a study on the factors predictive of early mortality (within 30 days of onset of symptoms) in a clinical series of 94 patients at their first stroke. Irrespective of the type of stroke, ischemic or hemorrhagic, early mortality proved to correlate with clinical parameters, such as coma at onset, presence of paralysis, changes in ocular motility, and neuroradiological parameters (lesion size on the CT scan) indicative of stroke severity
A tunable QM/MM approach to chemical reactivity, structure and physico-chemical properties prediction
No full textThis contribution describes a new implementation of a general hybrid approach with a modular structure (called COBRAMM: Computations at Bologna Relating Ab‐initio and Molecular Mechanic Methods) that is able to integrate some specialized programs and acts as a flexible computational environment, thus increasing the flexibility/efficiency of both QM, and MM, and QM/MM calculations. Specifically, QM/MM ground and excited states geometry optimizations, frequency calculations, conical intersection searches and adiabatic/non‐adiabatic molecular dynamics can be performed on a large molecular system, that can be split up to three different layers corresponding to different levels of accuracy
Shedding a new light on photolyases: Accurate molecular modeling as a tool for undestanding DNA repairing enzymes
No full textRing-Opening/Ring-Closing Protocols from Nitrothiophenes: Six-Membered versus Unusual Eight-Membered Sulfur Heterocycles through Michael-Type Addition on Nitrobutadienes
No full textWhen Ar is a low-aromaticity homo- or heterosystem. the sulfonyl-stabilized anion of nitrobutadienes 4 (which derive from the initial ring opening, of 3-nitrothiophene) undergoes a rather surprising addition onto the aromatic ring itself, thereby leading to the construction of an unusual eight-membered sulfur heterocycle condensed with the original Ar ring. The competitiveness of such a pathway with respect to the formation of the thiopyran ring (i.e., addition onto the nitrovinyl moiety) is favored at low temperatures, thus revealing its nature as a kinetically controlled process
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
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