4,963 research outputs found
Di-μ-benzoato-κ3 O,O′:O;κ3 O:O,O′-bis[(benzoato-κ2 O,O′)(1,10-phenanthroline-κ2 N,N′)lead(II)]
In the centrosymmetric dinuclear title compound, [Pb2(C7H5O2)4(C12H8N2)2], two Pb2+ ions are connected by two tridentate bridging benzoate anions. The Pb2+ ion is seven-coordinated by five O atoms from three benzoate anions and two N atoms from the 1,10-phenanthroline ligands. The benzoate anions adopt two different coordination modes, one bidentate–chelating and one tridentate bridging–chelating. The three-dimensional supramolecular framework is achieved by intermolecular π–π stacking interactions, with a shortest centroid–centroid distance of 3.617 (4) Å
Poly[[triaqua(μ3-4-oxidopyridine-2,6-dicarboxylato)thulium(III)] monohydrate]
In the title coordination polymer, {[Tm(C7H2NO5)(H2O)3]·H2O}n, the TmIII atom is eight-coordinated by a tridentate 4-oxidopyridine-2,6-dicarboxylate trianion, two monodentate anions and three water molecules, forming a distorted bicapped trigonal–prismatic TmNO7 coordination geometry. The anions bridge adjacent TmIII ions into double chains. Adjacent chains are further connected into sheets. O—H⋯O hydrogen bonds involving both coordinated and uncoordinated water molecules generate a three-dimensional supramolecular framework
Gravitational Lensing Effects of Fermion-Fermion Stars: I. Strong Field Case
We investigate a two-component model for gravitational lenses, i.e., the
fermion-fermion star as a dark matter self-gravitating system made from two
kinds of fermions with different masses. We calculate the deflection angles
varying from arcseconds to even degrees. There is one Einstein ring. In
particular, we find three radial critical curves for radial magnifications and
four or five images of a point source. These are different from the case of the
one-component model such as the fermion stars and boson stars. This is due to
the fermion-fermion star being a two-component concentric sphere. Our results
suggest that any possible observations of the number of images more than 3
could imply a polytropic distribution of the mass inside the lens in the
universe.Comment: 7 pages, LaTex and PostScript; 4 figures, PostScrip
Di-μ-benzoato-κ3 O,O′:O′;κ3 O:O,O′-bis[(benzoato-κ2 O,O′)(1,10-phenanthroline-κ2 N,N′)cadmium]
The dinuclear title compound, [Cd2(C7H5O2)4(C12H8N2)2], lies on a crystallographic twofold axis. The CdII ions are connected by two bridging benzoate anions and each ion is seven-coordinated by five O atoms from three benzoate ligands and by two N atoms from 1,10-phenanthroline. The benzoate ligands adopt two different coordination modes, acting as bidentate and bridging tridentate ligands. The discrete neutral molecules further extend their structure into a three-dimensional supramolecular framework by intermolecular π–π [interplanar distances of 3.392 (4) Å] and C—H⋯π stacking interactions [H–mean plane = 2.567 (4) and 2.781 (4) Å]
Poly[diaquatris(μ4-1,3-phenylenediacetato)dicerium(III)]
In the title coordination polymer, [Ce2(C10H8O4)3(H2O)2]n, each CeIII atom is nine-coordinated by eight O atoms from six different 1,3-phenylenediacetate (pda) bivalent anions and one O atom from a coordinated water molecule, forming a distorted tricapped trigonal–prismatic coordination geometry. Eight CeIII ions and twelve pda ligands form a large [Ce8(pda)12] ring, and four CeIII ions and six pda ligands form a small [Ce4(pda)6] ring. The rings are further connected by the coordination interactions of pda ligands and CeIII, generating a three-dimensional supramolecular framework
Poly[[triaqua(μ3-4-oxidopyridine-2,6-dicarboxylato)holmium(III)] monohydrate]
In the title coordination polymer, {[Ho(C7H2NO5)(H2O)3]·H2O}n, the HoIII atom is eight-coordinated by a tridentate 4-oxidopyridine-2,6-dicarboxylate trianion, two monodentate anions and three water molecules, forming a distorted bicapped trigonal–prismatic HoNO7 coordination geometry. The anions bridge adjacent HoIII ions into double chains. Adjacent chains are further connected into sheets. O—H⋯O hydrogen bonds involving both coordinated and uncoordinated water molecules generate a three-dimensional supramolecular framework
DFT-Spread Spectrally Overlapped Hybrid OFDM-Digital Filter Multiple Access IMDD PONs
A novel transmission technique—namely, a DFT-spread spectrally overlapped hybrid OFDM–digital filter multiple access (DFMA) PON based on intensity modulation and direct detection (IMDD)—is here proposed by employing the discrete Fourier transform (DFT)-spread technique in each optical network unit (ONU) and the optical line terminal (OLT). Detailed numerical simulations are carried out to identify optimal ONU transceiver parameters and explore their maximum achievable upstream transmission performances on the IMDD PON systems. The results show that the DFT-spread technique in the proposed PON is effective in enhancing the upstream transmission performance to its maximum potential, whilst still maintaining all of the salient features associated with previously reported PONs. Compared with previously reported PONs excluding DFT-spread, a significant peak-to-average power ratio (PAPR) reduction of over 2 dB is achieved, leading to a 1 dB reduction in the optimal signal clipping ratio (CR). As a direct consequence of the PAPR reduction, the proposed PON has excellent tolerance to reduced digital-to-analogue converter/analogue-to-digital converter (DAC/ADC) bit resolution, and can therefore ensure the utilization of a minimum DAC/ADC resolution of only 6 bits at the forward error correction (FEC) limit (1 × 10−3). In addition, the proposed PON can improve the upstream power budget by >1.4 dB and increase the aggregate upstream signal transmission rate by up to 10% without degrading nonlinearity tolerances
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