Highly sensitive bend sensor with hybrid long-period and tilted fiber Bragg grating

We demonstrate a new type of fiber optic bend sensor with a hybrid structure made up of a long period grating (LPG) and a tilted fiber Bragg grating (TFBG). The sensing mechanism is based on the spectrum of power transfers between the core and cladding modes from a TFBG located downstream from a LPG. We show that the curvature of a beam can be determined by the reflected power difference between the core mode and the recoupled cladding modes. We further provide design rules for the LPG and TFBG to optimize and linearize the sensor response. In addition, the temperature cross-sensitivities of this configuration are also investigated for two different types of fiber.     

On the Origin of Primitive Cells: From Nutrient Intake to Elongation of Encapsulated Nucleotides

Recent major discoveries in membrane biophysics hold the key to a modern understanding of the origin of life on Earth. Membrane bilayer vesicles have been shown to provide a multifaceted microenvironment in which protometabolic reactions could have developed. Cell‐membrane‐like aggregates of amphiphilic molecules capable of retaining encapsulated oligonucleotides have been successfully created in the laboratory. Sophisticated laboratory studies on the origin of life now show that elongation of the DNA primer takes place inside fatty acid vesicles when activated nucleotide nutrients are added to the external medium. These studies demonstrate that cell‐like vesicles can be sufficiently permeable to allow for the intake of charged molecules such as activated nucleotides, which can then take part in copying templates in the protocell interior. In this Review we summarize recent experiments in this area and describe a possible scenario for the origin of primitive cells, with an emphasis on the elongation of encapsulated nucleotides.     

Side Products in Nucleotide Chemistry

Abstract

Alkyl bisaminophosphorodiamidites¹ (1) has been shown to be versatile reagents for in situ preparation of d-nucleoside-3-phosphoramidites^2,3,4 (2.)     

SELECTIVE S-ALKYLATION IN PHASE TRANSFER CATALYSIS OF 2-PYRIDINE-, -PYRIMIDINE- AND BENZOXAZOLE-THIONE

Abstract

Alkylation via phase transfer catalysis of several ambident anions of the |N–C–S|^? type leads exclusively to S-substitution. Yields obtained are better or equal to those given by conventional methods and experimental work-up is very much simplified compared to the latter.     

Effect of Aging on the Mechanical Properties of Polymeric Materials

Abstract

Aging can modify polymer structure at the molecular, macromolecular, and/or the morphological level and thus induce changes in the mechanical properties. Stiffness is generally not modified for nonrubbery materials, except for mass transfer (solvent plasticization or plasticizer loss) in amorphous polymers or phase transfer (crystallization or crystal destruction) in semicrystalline polymers. The most significant modulus changes occur in the radiochemical aging of semicrystalline polymers whose amorphous phase is in the rubbery state. Yield properties generally vary in the same way as stiffness. Physical aging at T < T _g can lead to a significant increase in the yield stress. Very general features can be observed for rupture properties, for instance: 1) Only ultimate elongation ε is a pertinent variable in kinetic studies of aging involving tensile testing and related methods, 2) the amplitude of ε variation for a given degradation conversion is considerably higher for initially ductile materials than for brittle ones, and 3) the rupture envelope σ = f(ε), i.e., the ultimate stress, is often very close to the initial tensile curve except for rubbery materials undergoing predominant crosslinking. The mechanisms of ultimate property changes are reviewed. A kinetic approach is proposed for the very important case of heterogeneous, diffusion-controlled aging.     

Calixarenes as Polyhapto-aromatic Ligands: Alkali Metal Ions and Sulfonated Calixarenes

Crystal structure determinations for the hexarubidium and octacesium derivatives of calix[6]arene hexasulfonic acid, as well as of a new solvate of the pentasodium derivative of calix[4]arene tetrasulfonic acid, and comparison with structural data from the literature for alkali metal complexes of sulfonated calixarenes, have provided further evidence for the importance of interactions with aromatic ~ -electrons for the heavier alkali metal cations. There is evidence as well that this interaction can be enhanced by extended ionization of the sulfonated calixarene.