1,128 research outputs found
2-Thiabicyclo[3.2.0]hepta-3,6-Dienes. 1. Aluminum Chloride Catalyzed Thermal [2 + 2] Cycloaddition of 2-Butynedinitrile with Alkyl-Substituted Thiophenes
Tetra- and Trialkylthiophenes 4–6 React with 2-Butynedinitrile in the Presence of 1 Equiv of Aluminum Chloride in Dichloromethane at 0 °C Via [2 + 2] Cycloaddition to 2-3.2.0] hepta-3,6-Diene-6,7-Dicarbonitriles 7–10 as the Major Products. Reaction of 4 and 5 Also Gave Small Amounts (4% and 6%) of 1,2-Benzenedicarbonitriles 11 and 12 Which Result from [4 + 2] Cycloaddition and Subsequent Extrusion of Sulfur. 4,5,6,7-Tetrahydro-1,3-Dimethylbenzo[C]thiophene (6) Reacts with 2-Butynedinitrile under the Same Conditions to Give an Ene Adduct (13) in Addition to the [2 + 2] Cycloadduct 10. 2,5-Dimethylthiophene (3) Gave a 2:1 Reaction Product 14, the Formation of Which Can Be Explained Via Friedel-Crafts Alkylation of 3 by the Initially Formed [2 + 2] Cycloadduct. the 2-3.2.0] hepta-3,6-Dienes 7–10 and the Ene Adduct 13 Show Intramolecular Charge-Transfer Absorptions in the UV Spectra. © 1982, American Chemical Society. All Rights Reserved
New hairy black hole solutions with a dilaton potential
We consider black hole solutions with a dilaton field possessing a nontrivial
potential approaching a constant negative value at infinity. The asymptotic
behaviour of the dilaton field is assumed to be slower than that of a localized
distribution of matter. A nonabelian SU(2) gauge field is also included in the
total action. The mass of the solutions admitting a power series expansion in
at infinity and preserving the asymptotic anti-de Sitter geometry is
computed by using a counterterm subtraction method. Numerical arguments are
presented for the existence of hairy black hole solutions for a dilaton
potential of the form , special attention being paid to the case of
gauged supergravity model of Gates and Zwiebach.Comment: 12 pages, 4 figures; v2:references added, typos corrected, small
changes in Section
2-Thiabicyclo[3.2.0]-hepta-3,6-dienes. 2. Thermal and photochemical isomerization of 2-thiabicyclo[3.2.0]hepta-3,6-dienes. An example of the antarafacial-antarafacial Cope rearrangement
Thermal Rearrangement of 2-3.2.0] hepta-3,6-Diene-6,7-Dicarbonitrile8 1–3 to their 4,5-Dicarbonitrile Isomers 4–6 Takes Place at 110–140 °C in Yields of 82–84%. the Reactions Are First Order with Rates Almost Independent of the Polarity of the Solvent. Activation Parameters (ΔH‡ = 120–140 KJ Mol−1 and ΔS‡ ≈ 0 J K−1 Mol−1) Are in Agreement with a Concerted Symmetry-Allowed Antarafacial-Antarafacial Cope Rearrangement. Compounds 1–3 Rearrange Photochemically Via Cleavage of the C-1-S Bond to the 1,7-Dicarbonitrile Isomers 7–9. Isomer 9 Rearranges Further on Prolonged Irradiation to Give 10. a Tentative Mechanism for This Rearrangement is Given. © 1982, American Chemical Society. All Rights Reserved
Inotropic effects of propofol, thiopental, midazolam, etomidate, and ketamine on isolated human atrial muscle
Background: Cardiovascular instability after intravenous induction of anesthesia may be explained partly by direct negative inotropic effects. The direct inotropic influence of etomidate, ketamine, midazolam, propofol, and thiopental on the contractility of isolated human atrial tissue was determined. Effective concentrations were compared with those reported clinically. Methods: Atrial tissue was obtained from 16 patients undergoing coronary bypass surgery. Each fragment was divided into three strips, and one anesthetic was tested per strip in increasing concentrations (10 -6 to 10 - 2 M). Strips were stimulated at 0.5 Hz, and maximum isometric force was measured. Induction agents were studied in two groups, group 1 (n = 7) containing thiopental, midazolam, and propofol, and group 2 (n = 9) consisting of etomidate, ketamine, and propofol. Results: The tested anesthetics caused a concentration-dependent depression of contractility resulting in complete cessation of contractions at the highest concentrations. The IC 50s (mean ± SEM; μM) for inhibition of the contractility were: thiopental 43 ± 7.6, propofol 235 ± 48 (group 1), and 246 ± 42 (group 2), midazolam 145 ± 54, etomidate 133 ± 13, and ketamine 303 ± 54. Conclusions: This is the first study demonstrating a concentration-dependent negative inotropic effect of intravenous anesthetics in isolated human atrial muscle. NO inhibition of myocardial contractility was found in the clinical concentration ranges of propofol, midazolam, and etomidate. In contrast, thiopental showed strong and ketamine showed slight negative inotropic properties. Thus, negative inotropic effects may explain in part the cardiovascular depression on induction of anesthesia with thiopental but not with propofol, midazolam, and etomidate. Improvement of hemodynamics after induction of anesthesia with ketamine cannot be explained by intrinsic cardiac stimulation
Long Range Order at Low Temperature in Dipolar Spin Ice
Recently it has been suggested that long range magnetic dipolar interactions
are responsible for spin ice behavior in the Ising pyrochlore magnets and . We report here numerical
results on the low temperature properties of the dipolar spin ice model,
obtained via a new loop algorithm which greatly improves the dynamics at low
temperature. We recover the previously reported missing entropy in this model,
and find a first order transition to a long range ordered phase with zero total
magnetization at very low temperature. We discuss the relevance of these
results to and .Comment: New version of the manuscript. Now contains 3 POSTSCRIPT figures as
opposed to 2 figures. Manuscript contains a more detailed discussion of the
(i) nature of long-range ordered ground state, (ii) finite-size scaling
results of the 1st order transition into the ground state. Order of authors
has been changed. Resubmitted to Physical Review Letters Contact:
[email protected]
Quantum evolution across singularities: the case of geometrical resolutions
We continue the study of time-dependent Hamiltonians with an isolated
singularity in their time dependence, describing propagation on singular
space-times. In previous work, two of us have proposed a "minimal subtraction"
prescription for the simplest class of such systems, involving Hamiltonians
with only one singular term. On the other hand, Hamiltonians corresponding to
geometrical resolutions of space-time tend to involve multiple operator
structures (multiple types of dependence on the canonical variables) in an
essential way.
We consider some of the general properties of such (near-)singular
Hamiltonian systems, and further specialize to the case of a free scalar field
on a two-parameter generalization of the null-brane space-time. We find that
the singular limit of free scalar field evolution exists for a discrete subset
of the possible values of the two parameters. The coordinates we introduce
reveal a peculiar reflection property of scalar field propagation on the
generalized (as well as the original) null-brane. We further present a simple
family of pp-wave geometries whose singular limit is a light-like hyperplane
(discontinuously) reflecting the positions of particles as they pass through
it.Comment: 25 pages, 1 figur
Nonabelian solutions in N=4, D=5 gauged supergravity
We consider static, nonabelian solutions in N=4, D=5 Romans' gauged
supergravity model. Numerical arguments are presented for the existence of
asymptotically anti-de Sitter configurations in the version of the
theory, with a dilaton potential presenting a stationary point. Considering the
version of the theory with a Liouville dilaton potential, we look for
configurations with unusual topology. A new exact solution is presented, and a
counterterm method is proposed to compute the mass and action.Comment: 15 pages, 4 figure
Supporting First Grade Students Learning Number Facts Up to 10 Using a Parrot Game
Knowing number facts up to 10 become crucial if we want students to solve addition and subtraction problems using more abbreviated strategies. Otherwise, students will keep counting one-by-one until they get an answer. One of important number facts is number pairs that make ten because it is an important ‘benchmark' that students will refer to constantly. Considering the important of number facts up to 10, we designed a parrot game activity to supports students learning process. We designed an instructional activity based on Realistic Mathematics Education (RME) approach. We tried this instructional activity with twenty seven first grade students in SDN 179 Palembang. As a result, we found that many first grade students were able to know number facts up to 10, but they still need models to support their thinking
- …