A loop-by-loop defect rectification procedure for optimal synthesis of Stephenson III path generators

This paper presents a formulation of constraints for the synthesis of Stephenson III mechanism and a loop-by-loop defect-rectification procedure. The procedure divides the Stephenson III mechanism into two loops, namely, Loop I, i.e., four-bar, and Loop II, i.e., five-bar mechanisms. Then, the defects are identified using the established methodology to formulate the defect-specific constraints in the simplified form. Based on the constraints, an optimization problem is formulated to synthesize a Stephenson III mechanism for path generation. A well-established meta-heuristic algorithm is used to solve the constrained optimization problem. For demonstrating the effectiveness of the formulated constraints, two numerical examples are considered, in which Stephenson III path generator mechanisms are synthesized. It is found that the mechanisms synthesized using the proposed procedure are defect-free when constraints are imposed, which is verified using the stick-diagram.

     

Tuning the Reactivity of N,O,O,O‐Non‐Metallocene Catalysts for α‐Olefin Polymerization: Issues Related to Ligand Symmetry and Derivatization

Summary: Titanium‐based precatalysts, bearing C₃ or pseudo‐C_s symmetric aminotriol ligands, upon activation with methylaluminoxane, polymerize hex‐1‐ene to give polymers of high molecular weight, i.e., 50 000 and 600 000, respectively, with low dispersity, 1.2–1.4, and high isotacticity, 85–60%, depending on the overall symmetry of the precatalysts, but when one arm of the aminotriol ligands is methylated to yield C₂ or meso aminodiol ligands, their corresponding titanium catalysts gave higher‐molecular‐weight polyhexenes, 300 000 to 250 000, with lower dispersities, 1.07–1.11, which possibly suggests living polymerization, with activities 200–500 times greater than that of the parent C₃ and pseudo‐C_s catalysts.

     

Relation between the activation parameters of low-temperature slip and the mean-square amplitude of atomic vibrations in cubic metals

The available data on various activation parameters of low-temperature slip in 9 body-centred cubic and 5 face-centred cubic elements have been examined as a function of a single microscopic parameter, namely mean-square amplitude of atomic vibrations <u ²>, specific to the material. It is found that for a given crystal structure, the microscopic parameters of the unit activation process of yielding, e.g. the initial length of dislocation segment, the critical height of the kink-pair nucleated, the associated activation volume, the binding energy per interatomic spacing along the glide dislocation on the slip plane etc. correlate well with the mean-square amplitude of atomic vibrations <u ²> through a power regression formula.     

Synthesis of Titanatranes Containing Bis(aryloxo)-(alkoxo)amines and their Use in Catalysis for Ethylene Polymerization

Syntheses of titanatranes containing [(O-2,4-Me₂C₆H₂-6-CH₂)₂-{O(CH₂)_nCH₂}]N³⁻ (n = 1,2) have been explored. Catalytic activity for ethylene polymerization by Ti₂(OⁱPr)₂{[(O-2,4-Me₂C₆H₂-6-CH₂)₂(µ₂-OCH₂-CH₂)]N}₂ ( 1a ) - MAO catalyst increased at high temperature; the activity also increased upon addition of AlMe₃. Ti(O- 2,6-ⁱPr₂C₆H₃){[(O-2,4-Me₂C₆H₂-6-CH₂)₂(OCH₂CH₂)]N} ( 1c ) showed higher activity than 1a under the same conditions. Ti{[(O-2,4-Me₂C₆H₂-6-CH₂)₂(HOCH₂CH₂CH₂)]N}₂ was isolated from the reaction of Ti(OⁱPr)₄ with bis(2-hydroxy-3,5-dimethylbenzyl)-propanolamine; the structure was determined by X-ray crystallography.     

Hollow‐Core Magnetic Colloidal Nanocrystal Clusters with Ligand‐Exchanged Surface Modification as Delivery Vehicles for Targeted and Stimuli‐Responsive Drug Release

The fabrication of hierarchical magnetic nanomaterials with well‐defined structure, high magnetic response, excellent colloidal stability, and biocompatibility is highly sought after for drug‐delivery systems. Herein, a new kind of hollow‐core magnetic colloidal nanocrystal cluster (HMCNC) with porous shell and tunable hollow chamber is synthesized by a one‐pot solvothermal process. Its novelty lies in the “tunability” of the hollow chamber and of the pore structure within the shell through controlled feeding of sodium citrate and water, respectively. Furthermore, by using the ligand‐exchange method, folate‐modified poly(acrylic acid) was immobilized on the surface of HMCNCs to create folate‐targeted HMCNCs (folate‐HMCNCs), which endowed them with excellent colloidal stability, pH sensitivity, and, more importantly, folate receptor‐targeting ability. These assemblages exhibited excellent colloidal stability in plasma solution. Doxorubicin (DOX), as a model anticancer agent, was loaded within the hollow core of these folate‐HMCNCs (folate‐HMCNCs‐DOX), and drug‐release experiments proved that the folate‐HMCNCs‐DOX demonstrated pH‐dependent release behavior. The folate‐HMCNCs‐DOX assemblages also exhibited higher potent cytotoxicity to HeLa cells than free doxorubicin. Moreover, folate‐HMCNCs‐DOX showed rapid cell uptake apart from the enhanced cytotoxicity to HeLa cells. Experimental results confirmed that the synthesized folate‐HMCNCs are smart nanovehicles as a result of their improved folate receptor‐targeting abilities and also because of their combined pH‐ and magnetic‐stimuli response for applications in drug delivery.     

Thermal conduction through porous and dispersed three-phase systems

A loose three-phase system made of metal, non-metal and air is considered resulting from small successive dispersions in effective continuous medium (ecm). The effective thermal conductivity of loose three-phase systems is estimated by extending theecm approach to multi-phase systems. The unsteady state line source (needle) method is employed to determine the effective thermal conductivity of some selected three-phase materials. The calculated and observed values show good agreement suggesting that the continuous medium approach can be applied to estimate effective thermal conductivity of multi-phase systems.     

Some stereochemical effects in gaseous ion decompositions

Stereochemical effects were observed in the electron ionization, methane, isobutane and ammonia positive ion chemical ionization and hydroxy negative ion chemical ionization behaviour of some isomeric triaryl nitrocyclohexenes. cis-Eliminations leading to loss of HNO₂, H₂NO₂ and arene were found to be stereochemically preferred in gaseous ions.     

Facile synthesis,growth mechanism,and optical properties of CdSe nanoparticles in self-assembled micellar media and their efficient conjugation with proteins

This article demonstrates the influence of various surfactants of different polarities—anionic, sodium dodecyl sulfate, cationic, hexadecyltrimethylammonium bromide and non-ionic, and polyoxyethylene iso-octyl phenyl ether (TX-100)—on the formation of CdSe nanoparticles in aqueous solutions. The surfactant-stabilizing effect has been monitored using transmission electron microscopy. Spectral properties of CdSe nanoparticles have been investigated; the structure of the long-wave edge of the fundamental absorption band of CdSe nanoparticles has been analyzed. It has been shown that the variation of the synthesizing conditions (stabilizer’s nature and concentration, CdSe concentration, etc.) allows the tailoring of the CdSe nanoparticle size in the range of 8–17 nm. Lifshitz–Slyrzov–Wagner kinetic analysis has also been performed using the size variation according to ripening temperature and time period. The differences in the stabilization ability of tested substances are discussed with respect to their structure and possible mechanism of the surface interaction with the nanoparticles. The flexible surface chemistry of the CdSe-micelles causes them to be water soluble and allows their further conjugation with protein molecules through electrostatic attraction. The interaction between functionalized CdSe nanoparticles with protein molecules have been investigated using fluorescence spectroscopy.     

Ag2O as nucleating agent in the crystallization of superconducting phase in Bi2Sr2Ca4Cu5γ glass composition

The nucleating action of silver oxide (1 mol% Ag₂O) in the crystallization of superconducting phase in Bi₂Sr₂Ca₄Cu₅O_γ system is quite remarkable. The characteristics of these glass ceramics are found to depend chiefly upon the formation conditions of the initial glass composition and a subsequent phase separation. We observe from the SEM studies the evidence of highly textured growth. The presence of long platelet and square-like platelet-type particles could be explained on the basis of an orientation effect. Besides being influencing the structural properties markedly, the nucleating agent also affects the physical properties, in particular, the normal state resistivity (). The above effects result in broadening of X-ray diffraction lines and a change in slope, in the normal state region (190–220 K) of (T) plots. Out of the three procedures used to fit the (T) data, the usual linear fit (χT) does not work out at all over the temperature range 140–300 K. On the other hand non-linear fits, χTⁿ (n=0.5) and the piece-wise linear fits (140–200 K and 220–300 K) work out much better. These results are interpreted on the basis of a possible intergrowth of two superconducting phases.