Cage-like ordered silica with large mesopore volume synthesized by doubling amount of polymer, adding sodium chloride and lowering acid concentration

Cage-like ordered mesoporous silica, FDU-1, with about twice the pore volume and a narrower pore size distribution compared with those for previously reported samples was synthesized in a much shorter time by doubling the amount of block copolymer, adding sodium chloride and lowering the acid concentration.     

160 GHz harmonic mode-locked AlGaInAs 1.55 μm strained quantum-well compound-cavity laser

We characterized the reflectivity and the modal discrimination of intracavity reflectors (ICRs) with different numbers of slots and presented harmonic mode-locking operation of a monolithic semiconductor laser comprising a compound cavity formed by a single deeply etched slot ICR fabricated from 1.55 μm AlGaInAs strained quantum well material. Gaussian pulses were generated at a 161.8 GHz repetition rate with a pulse duration of 1.67 ps and a time-bandwidth product of 0.81.     

Ionic-like behavior of oppositely charged nanoparticles

Mixtures of oppositely charged nanoparticles of various sizes and charge ratios precipitate only at the point of electroneutrality. This phenomenon-specific to the nanoscale and reminiscent of threshold precipitation of ions-is a consequence of the formation of core-and-shell nanoparticle aggregates, in which the shells are composed of like-charged particles and are stabilized by efficient electrostatic screening.     

Tightness in contact metric 3-manifolds

This paper begins the study of relations between Riemannian geometry and global properties of contact structures on 3-manifolds. In particular we prove an analog of the sphere theorem from Riemannian geometry in the setting of contact geometry. Specifically, if a given three dimensional contact manifold (M,ξ) admits a complete compatible Riemannian metric of positive 4/9-pinched curvature then the underlying contact structure ξ is tight; in particular, the contact structure pulled back to the universal cover is the standard contact structure on S ³. We also describe geometric conditions in dimension three for ξ to be universally tight in the nonpositive curvature setting.     

Alkali metal halogenides coordination compounds with hexamethylenetetramine

Six coordination compounds: [Li(H₂O)₄]⁺·hmta·Cl^?, [Li(H₂O)₄]⁺·hmta·I^?, [Na(H₂O)₄(hmta)] ²⁺₂ ·2H₂O·2Br^?, [Na(H₂O)₄(hmta)] ²⁺₂ ·2H₂O·2I^?, [K(H₂O)(hmta)I] _n and [Rb(H₂O)(hmta)I] _n , have been synthesized and characterised by IR spectroscopy, thermogravimetry coupled with differential thermal analysis, elemental analysis and X-ray crystallography. Both the sodium compounds are isostructural in a solid state, an isostructurality is also observed between compounds containing potassium and rubidium iodides. The sodium compounds exist as dimers (dinuclear core of the complex ion is created by two sodium cations and two water molecules). The molecules of potassium and rubidium compounds are assembled to the two dimensional hybrid nets. The each potentially multifunctional ligand (the hmta) exists in the outer coordination sphere in lithium compounds, acts in a monodentate mode in sodium compounds and in bidentate-bridging modes in potassium and rubidium compounds. The lithium ions are four coordinated, and the sodium, potassium and rubidium ions are six coordinated. Thermal analyses show that the investigated compounds decompose gradually with the formation of alkali metal halides which, during the further heating, are totally removed or they undergo partial decomposition to oxides.

     

Tight Beltrami fields with symmetry

Let M be a compact orientable Seifered fibered 3-manifold without a boundary, and α an S ¹-invariant contact form on M. In a suitable adapted Riemannian metric to α, we provide a bound for the volume Vol(M) and the curvature, which implies the universal tightness of the contact structure ξ = ker α.      

Preconcentration of trace lead via formation of the bis(2,2-bipyridyl) complex and its adsorption on oxidized multiwalled carbon nanotubes

A solid phase extraction method is presented for the preconcentration of trace lead ions on oxidized multiwalled carbon nanotubes (ox-MWCNTs). In the first step, the cationic Pb(II) complex of 2,2-bipyridyl is formed which, in a second step, is adsorbed on ox-MWCNTs mainly due to electrostatic and van der Waals interactions. The Pb(II) ions were then eluted with dilute nitric acid and quantified by FAAS. The effects of pH value, mass of sorbent, concentration of 2,2-bipyridyl, stirring time, of type, concentration and volume of eluent, of eluent flow rate and sample volume were examined. Most other ions do not affect the recovery of Pb(II). The limits of detection are 240 and 60 ng L^?1 for sample volumes of 100 and 400 mL, respectively. The recovery and relative standard deviation are >95 % and 2.4 %, respectively. Other figures of merit include a preconcentration factor of 160 and a maximum adsorption capacity of 165 mg g^?1. The method was successfully applied to the determination of Pb(II) in spiked tap water samples. The accuracy of the method was verified by correctly analyzing a certified reference material (NCS ZC85006; lead in tomatoes).