2,168 research outputs found
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Synthesis and Coordination Compounds of A Bis(Imino)Acenaphthene (Bian)-Supported N-Heterocyclic Carbene
The bis(imino)acenaphthene-supported N-heterocyclic carbene IPr(BIAN) has been prepared by deprotonation of the precursor imidazolium chloride. Treatment of IPr(BIAN) imidazolium chloride with Ag(2)O afforded the silver complex [IPr(BIAN)]AgCl which can be converted into the corresponding gold complex [IPr(BIAN)]AuCl by reaction with (tht)AuCl (tht = tetrahydrothiophene). The iridium complex [IPr(BIAN)]Ir(COD)Cl was prepared by reaction of the imidazolium chloride with KO(t)Bu and [Ir(COD)Cl](2) and subsequently converted to the carbonyl complex [IPr(BIAN)]Ir(CO)(2)Cl by exposure to an atmosphere of CO. All new compounds were characterized by single-crystal X-ray diffraction, multinuclear NMR, MS and HRMS data.Robert A. Welch Foundation F-0003National Science Foundation 0741973Chemistr
Synthesis, Crystal Structure and Photophysical Properties of Lanthanide Coordination Polymers of 4- 4-(9H-Carbazol-9-Yl)Butoxy Benzoate: The Effect of Bidentate Nitrogen Donors on Luminescence
A new aromatic carboxylate ligand, 4-[4-(9H-carbazol-9-yl)butoxy]benzoic acid (HL), has been synthesized by the replacement of the hydroxyl hydrogen of 4-hydroxy benzoic acid with a 9-butyl-9H-carbazole moiety. The anion derived from HL has been used for the support of a series of lanthanide coordination compounds [Ln = Eu (1), Gd (2) and Tb (3)]. The new lanthanide complexes have been characterized by a variety of spectroscopic techniques. Complex 3 was structurally authenticated by single-crystal X-ray diffraction and found to exist as a solvent-free 1D coordination polymer with the formula [Tb(L)(3)](n). The structural data reveal that the terbium atoms in compound 3 reside in an octahedral ligand environment that is somewhat unusual for a lanthanide. It is interesting to note that each carboxylate group exhibits only a bridging-bidentate mode, with a complete lack of more complex connectivities that are commonly observed for extended lanthanide-containing solid-state structures. Examination of the packing diagram for 3 revealed the existence of two-dimensional molecular arrays held together by means of CH-pi interactions. Aromatic carboxylates of the lanthanides are known to exhibit highly efficient luminescence, thus offering the promise of applicability as optical devices. However, due to difficulties that arise on account of their polymeric nature, their practical application is somewhat limited. Accordingly, synthetic routes to discrete molecular species are highly desirable. For this purpose, a series of ternary lanthanide complexes was designed, synthesized and characterized, namely [Eu(L)(3)(phen)] (4), [Eu(L)(3)(tmphen)] (5), [Tb(L)(3)(phen)] (6) and [Tb(L)(3)(tmphen)] (7) (phen = 1,10-phenanthroline and tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline). The photophysical properties of the foregoing complexes in the solid state at room temperature have been investigated. The quantum yields of the ternary complexes 4 (9.65%), 5 (21.00%), 6 (14.07%) and 7 (32.42%), were found to be significantly enhanced in the presence of bidentate nitrogen donors when compared with those of the corresponding binary compounds 1 (0.11%) and 3 (1.45%). Presumably this is due to effective energy transfer from the ancillary ligands.Council of Scientific and Industrial Research (CSIR-TAPSUN Project) SSL, NWP-55CSIR, New DelhiRobert A. Welch Foundation F-0003Chemistr
Consistent Approximations for the Optimal Control of Constrained Switched Systems
Though switched dynamical systems have shown great utility in modeling a
variety of physical phenomena, the construction of an optimal control of such
systems has proven difficult since it demands some type of optimal mode
scheduling. In this paper, we devise an algorithm for the computation of an
optimal control of constrained nonlinear switched dynamical systems. The
control parameter for such systems include a continuous-valued input and
discrete-valued input, where the latter corresponds to the mode of the switched
system that is active at a particular instance in time. Our approach, which we
prove converges to local minimizers of the constrained optimal control problem,
first relaxes the discrete-valued input, then performs traditional optimal
control, and then projects the constructed relaxed discrete-valued input back
to a pure discrete-valued input by employing an extension to the classical
Chattering Lemma that we prove. We extend this algorithm by formulating a
computationally implementable algorithm which works by discretizing the time
interval over which the switched dynamical system is defined. Importantly, we
prove that this implementable algorithm constructs a sequence of points by
recursive application that converge to the local minimizers of the original
constrained optimal control problem. Four simulation experiments are included
to validate the theoretical developments
A Killing tensor for higher dimensional Kerr-AdS black holes with NUT charge
In this paper, we study the recently discovered family of higher dimensional
Kerr-AdS black holes with an extra NUT-like parameter. We show that the inverse
metric is additively separable after multiplication by a simple function. This
allows us to separate the Hamilton-Jacobi equation, showing that geodesic
motion is integrable on this background. The separation of the Hamilton-Jacobi
equation is intimately linked to the existence of an irreducible Killing
tensor, which provides an extra constant of motion. We also demonstrate that
the Klein-Gordon equation for this background is separable.Comment: LaTeX, 14 pages. v2: Typo corrected and equation added. v3: Reference
added, introduction expanded, published versio
SCC characterization of AL-Li-Cu-x Alloys
In the past several decades many Al-Li-X alloys have been studied to understand the fracture properties due to its superior specific strength and modulus over the currently dominated 2024 & 7075 type aircraft structural alloys. It is also observed that their stress corrosion resistance is also good in the peak aged condition depending on the (Li/Cu) ratio. To understand its behavior with respect to its heat treatment, a systematic collection of data is required from the published literature.
We have collected such systematic data for three alloys from the early 1980’s on Al-3Li, Al-2Li-3Cu and Al-1.5Li-4.5Cu, all with 0.12Zr to keep the grain structure predominantly un-recrystalized. Such alloys were tested in the S-T direction in 3.5%NaCl solution to obtain the plateau velocities (da/dt) and threshold KIscc. It is observed that in all the alloys, (da/dt) decreased with aging heat treatment time, the decrease increased with (Li/Cu) ratio. This decrease is interpreted in terms of the degree of anodic dissolution of the grain boundary precipitates. The results are compared with theSCCbehavior of 7050 and 2024 alloys. Additional data where reversion aging treatment was given shows that grain boundary precipitates play an important role in theSCCbehavior. The overall trend in theSCCbehavior is discussed in light of the current understanding of the aluminum alloy behavior in terms of anodic dissolution and the role of hydrogen
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Aseptic Barriers Allow a Clean Contact for Contaminated Stethoscope Diaphragms.
Objective:To determine whether a single-use stethoscope diaphragm barrier surface remains aseptic when placed on pathogen-contaminated stethoscopes. Methods:From May 31 to August 5, 2019, we tested 2 separate barriers using 3 different strains of 7 human pathogens, including extended-spectrum β-lactamase-producing Escherichia coli, methicillin-resistant Staphylococcus aureus, and vancomycin resistant Enterococcus faecium. Results:For all diaphragms with either of the 2 barriers tested, no growth was recorded for any of the pathogens. Stethoscopes with aseptic barriers remained sterile for up to 24 hours. These single-use barriers also provided aseptic surfaces when stethoscope diaphragms were inoculated with human specimens, including saliva, stool, urine, and sputum. Conclusion:Disposable aseptic diaphragm barriers may provide robust and efficient solutions to reduce transmission of pathogens via stethoscopes
Separability and Killing Tensors in Kerr-Taub-NUT-de Sitter Metrics in Higher Dimensions
A generalisation of the four-dimensional Kerr-de Sitter metrics to include a
NUT charge is well known, and is included within a class of metrics obtained by
Plebanski. In this paper, we study a related class of Kerr-Taub-NUT-de Sitter
metrics in arbitrary dimensions D \ge 6, which contain three non-trivial
continuous parameters, namely the mass, the NUT charge, and a (single) angular
momentum. We demonstrate the separability of the Hamilton-Jacobi and wave
equations, we construct a closely-related rank-2 Staeckel-Killing tensor, and
we show how the metrics can be written in a double Kerr-Schild form. Our
results encompass the case of the Kerr-de Sitter metrics in arbitrary
dimension, with all but one rotation parameter vanishing. Finally, we consider
the real Euclidean-signature continuations of the metrics, and show how in a
limit they give rise to certain recently-obtained complete non-singular compact
Einstein manifolds.Comment: Author added, title changed, references added, focus of paper changed
to Killing tensors and separability. Latex, 13 page
Larvicidal effects of crude extracts of dried ripened fruits of Piper nigrum against Culex quinquefasciatus larval instars
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