Steric Hindrance as a Mechanistic Probe for Olefin Reactivity: Variability of the Hydrogenic Canopy over the Isomeric Adamantylideneadamantane/Sesquihomoadamantene Pair (A Combined Experimental and Theoretical Study)

Access to each CC face of adamantylideneadamantane (AA) and sesquihomoadamantene (SA) is hindered by the hydrogenic canopy consisting of four β-hydrogens; otherwise, these olefins have quite normal environments. X-ray crystallography and density functional (DFT) calculations show a 0.5 Å larger annular opening in the protective cover of AA than that in SA. This contributes to the remarkable differences in reactivity toward various reagents, not only by limiting access to the olefin site in SA but also by inhibiting reactions which force these hydrogens closer together. Thus, AA is subject to typical olefin-addition reactions with bromine, sulfuryl chloride, m-chloroperbenzoic acid, dioxygen, and so forth, albeit sometimes at attenuated rates. On the other hand, SA is singularly unreactive under identical reaction conditions, except for the notable exceptions that include Brønsted (protonic) acids, a nitrosonium cation, and dichlorine. The exceptions are characterized as three sterically limited (electrophilic) reagents whose unique reactivity patterns are shown to be strongly influenced by steric access to the CC center. As such, the different degrees of steric encumbrance in the isomeric donors AA and SA shed considerable light on the diverse nature of olefinic reactions. In particular, they evoke mechanistic features in electrophilic addition versus electron transfer, which are otherwise not readily discernible with other less hindered olefinic donors. Transient structures of the olefinic-reaction intermediates such as the protonated carbocations AA−H+ and SA−H+ as well as the cation radicals AA•+ and SA•+ are probed by the combination of X-ray crystallographic analyses and density functional theoretical computations

Study of Mach reflection in inviscid flows

In this paper, we study the Mach reflection phenomenon in inviscid flows using a higher order discontinuous Galerkin method and overset grids. We use the shock capturing procedure proposed in Siva Prasad Kochi et al. using overset grids to capture the discontinuities occurring in the supersonic flow over a wedge accurately. In this procedure, we obtain a coarse grid solution first and using the troubled cell data, we construct an overset grid which is approximately aligned to all the discontinuities. We rerun the solver with the coarse grid solution as the initial condition while using the troubled cell indicator and the limiter only on the overset grid. This allows us to capture the discontinuities accurately. Using this procedure, we have obtained the solution for Mach $3.0$ and $4.0$ flow over a wedge for various wedge angles and determined the detachment criterion and the Von Neumann condition accurately. We have also determined the Mach stem height for various wedge angles for these Mach numbers. We have also demonstrated the hysteresis that occurs in the transition from regular reflection to Mach reflection.Comment: 11 pages, 8 Figures, 2 Table

The cross-frequency mediation mechanism of intracortical information transactions

In a seminal paper by von Stein and Sarnthein (2000), it was hypothesized that "bottom-up" information processing of "content" elicits local, high frequency (beta-gamma) oscillations, whereas "top-down" processing is "contextual", characterized by large scale integration spanning distant cortical regions, and implemented by slower frequency (theta-alpha) oscillations. This corresponds to a mechanism of cortical information transactions, where synchronization of beta-gamma oscillations between distant cortical regions is mediated by widespread theta-alpha oscillations. It is the aim of this paper to express this hypothesis quantitatively, in terms of a model that will allow testing this type of information transaction mechanism. The basic methodology used here corresponds to statistical mediation analysis, originally developed by (Baron and Kenny 1986). We generalize the classical mediator model to the case of multivariate complex-valued data, consisting of the discrete Fourier transform coefficients of signals of electric neuronal activity, at different frequencies, and at different cortical locations. The "mediation effect" is quantified here in a novel way, as the product of "dual frequency RV-coupling coefficients", that were introduced in (Pascual-Marqui et al 2016, http://arxiv.org/abs/1603.05343). Relevant statistical procedures are presented for testing the cross-frequency mediation mechanism in general, and in particular for testing the von Stein & Sarnthein hypothesis.Comment: https://doi.org/10.1101/119362 licensed as CC-BY-NC-ND 4.0 International license: http://creativecommons.org/licenses/by-nc-nd/4.0

Comparison of complications of spinal and general anesthasia in percutaneous kidney stone removal

While the complications of spinal anesthesia are much less than general anesthesia, percutaneous nephrolithotomy (PCNL) is still performed under general anesthesia in most centers. Therefore, in this study spinal anesthesia is compared with general anesthesia in patients undergoing PCNL. This research was a double-blind clinical trial study which was conducted on 130 patients with inclusion criteria. Patients were nonrandomly assigned into two general anesthesia (n=65) and spinal anesthesia (n=65) groups and underwent PCNL surgery.In group A, patients were given intravenously midazolam (2 mg), fentanyl (100 μg), atracurium (0.5 mg/kg), propofol (2 mg/kg) and morphine (10 mg) and then were incubated. In group B, Marcaine 0.5% (15 mg) was injected into the L3-L4 or L4-L5 lumbar spinal space in a sitting position. Patient’s blood pressure was measured and recorded at various times and in recovery as well as in the surgery room. Intra-operative bleeding, pain in the surgery area, nausea and vomiting, shortness of breath and sore throat were recorded for the two groups in the ward and during hospitalization.Changes of blood pressure were the same in both groups. In the general anesthesia group, intra-operative bleeding, pain at the site of the surgery, nausea and vomiting, shortness of breath and sore throat and duration of hospitalization were significantly higher. Changes in other tests were equal in both groups. Spinal anesthesia might be a safer method than general anesthesia for PCNL surgery.Keywords: Complication, Spinal Anesthesia, General Anesthesia, Kidney Stone Removal, Percutaneou