Effects of loading conditions and temperature on environmental stress cracking of low-density polyethylene

Fracture mechanics was used to investigate the environmental stress cracking (ESC) of low density polyethylene (LDPE). Annealed and quenched samples were prepared; a single edge notch was made and the samples were fractured under constant load in a liquid methanol environment. The relation between the stress intensity factor K and the crack speed ? has been investigated. There is a large difference between annealed and quenched samples in the variation of this relation with temperature and applied load. The cause of this difference is discussed in detail. We propose that thermally activated molecular motion is essential to ESC of the annealed LDPE while stress concentration contributes markedly to ESC of the quenched LDPE.     

On the stable posture of a pair of parallel cylinders in a uniform flow *

The stable posture of a pair of parallel circular cylinders in a uniform flow was experimentally studied when it was free to rotate about an axis at the middle of the two cylinders. The cylinder pair comes to rest facing the oncoming flow side by side, the line connecting the centers of the two cylinders being perpendicular to the flow, when s/d = 0.5, where s is the distance between the center of rotation and the central axis of each cylinder and d is the diameter of the cylinder. When s/d = 1.0 or 1.5, the cylinder pair is stable both in tandem, with one cylinder behind the other, and in side-by-side arrangements to the oncoming flow. When s/d 2.0, the cylinder pair is stable only in tandem arrangements.     

Beta-1,3-glucan polysaccharide (schizophyllan) acting as a one-dimensional host for creating supramolecular dye assemblies

We have demonstrated that one-dimensional supramolecular dye assemblies with a uniform diameter can be created by utilizing schizophyllan (SPG) as a one-dimensional host. In the supramolecular nanofibers, the dye molecules are assembled into the different aggregation modes depending on the preparation procedures. The findings establish that SPG is useful for creating the supramolecular nanofibers, where temporal superstructures can be stabilized by the SPG-specific helical higher-order structure. [structure: see text].     

Cofactor Biogenesis in Cysteamine Dioxygenase: C−F Bond Cleavage with Genetically Incorporated Unnatural Tyrosine

Cysteamine dioxygenase (ADO) is a thiol dioxygenase whose study has been stagnated by the ambiguity as to whether or not it possesses an anticipated protein‐derived cofactor. Reported herein is the discovery and elucidation of a Cys‐Tyr cofactor in human ADO, crosslinked between Cys220 and Tyr222 through a thioether (C?S) bond. By genetically incorporating an unnatural amino acid, 3,5‐difluoro‐tyrosine (F₂‐Tyr), specifically into Tyr222 of human ADO, an autocatalytic oxidative carbon–fluorine bond activation and fluoride release were identified by mass spectrometry and ¹⁹F NMR spectroscopy. These results suggest that the cofactor biogenesis is executed by a powerful oxidant during an autocatalytic process. Unlike that of cysteine dioxygenase, the crosslinking results in a minimal structural change of the protein and it is not detectable by routine low‐resolution techniques. Finally, a new sequence motif, C‐X‐Y‐Y(F), is proposed for identifying the Cys‐Tyr crosslink.     

Carbohydrate-appended curdlans as a new family of glycoclusters with binding properties both for a polynucleotide and lectins

Beta-1,3-glucans having carbohydrate-appendages (alpha-D-mannoside, N-acetyl-beta-D-glucosaminide and beta-lactoside) at the C6-position of every repeating unit can be readily prepared from curdlan (a linear beta-1,3-glucan) through regioselective bromination/azidation to afford 6-azido-6-deoxycurdlan followed by chemo-selective Cu(i)-catalyzed [3 + 2]-cycloaddition with various carbohydrate modules having a terminal alkyne. The resultant carbohydrate-appended curdlans can interact with polycytosine to form stable macromolecular complexes consistent with two polysaccharide strands and one polycytosine strand. Furthermore, these macromolecular complexes show strong and specific affinity toward carbohydrate-binding proteins (lectins). Therefore, one can utilize these carbohydrate-appended curdlans as a new family of glycoclusters.     

Photolysis of triphenyl phosphate in aqueous methanol

Upon UV irradiation in methanol, triphenyl phosphate ( 1a ) gave biphenylyl phenyl phosphate ( 2a ) as the main product, whereas the addition of water to the solution caused an increase of the yield of biphenyl ( 3a ). These products were formed through a singlet excited state and an intramolecular excimer, respectively. © 1996 John Wiley & Sons, Inc.     

Specifications of a neutron exposure accelerator system for biological effects experiments (NASBEE) in NIRS

We developed a neutron irradiation facility, neutron exposure accelerator system for biological effect experiments (NASBEE) for biological studies in National Institute of Radiological Sciences, Japan. Irradiation field of 2 MeV average neutrons generated by a Be(d–n)B reaction is established. Dose uniformity of 240 mm in diameter irradiation field is producible within ±2.5% with a dose rate of 0.87 Gy/h at sample target distance of 1170 mm. Two irradiation rooms, a specific pathogen-free (SPF) conditioned one and a conventional, are now available. Irradiation protocols for in vitro experiments are now established and demonstrated by obtaining a relative biological effectiveness (RBE) of cell inactivation measured to be 3.54 with 10% survival dose (D₁₀).