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