Elastic response of single DNA molecules exhibits a reentrant collapsing transition

We measured the elastic response of single DNA molecules at various concentrations of the trivalent cation, spermidine. When added spermidine caused the DNA to collapse, the force-extension curves showed either plateaus or stick-release patterns depending on the concentration. The periodic stick-release response determines a characteristic length, which may reflect toroidal supercoiling. At high concentrations of spermidine, we observed the reelongation of single molecules of collapsed DNA. Thus condensation occurs between lower and upper critical concentrations, verifying that the transition is reentrant as theoretically predicted.     

Room-temperature grating-based morphological hole burning in Sm2+-doped glass powders

We have observed grating-based morphological hole burning in Sm2+-doped glass powders at room temperature. When photobleaching on the 4f(6)-4f(5)5d transition of Sm2+ is combined with multiple light scattering, holes are produced in frequency and wave-vector domains. The hole profile depends on the amount of light absorption of Sm2+; it sharpens as the absorption decreases. The variation of the hole shape is explained theoretically based on a diffusion approximation.     

Strain-induced regioselectivities in reactions of benzyne possessing a fused four-membered ring

[reaction: see text] A fused four-membered ring has a powerful directing ability in effecting the regioselective reactions of benzyne with ketene silyl acetal, nucleophile, and alpha-alkoxyfuran.     

Conversion of D-glucose to cyclitol with hydroxymethyl substituent via intramolecular silyl nitronate cycloaddition reaction: application to total synthesis of (+)-cyclophellitol

[reaction: see text] A diastereoisomeric mixture of 1-nitro-6-heptene-2,3,4,5-tetraol derivative (A) was prepared by Henry reaction between d-glucose-based aldehyde and nitromethane. Only the (2S)-isomer of A led to cyclitol (B) via nitronate-olefin cycloaddition on treatment with TMS-Cl and Et(3)N in the presence of catalytic DMAP followed by acid treatment. (+)-Cyclophellitol (1) was synthesized from B in eight steps.     

Velocity measurement of clay intrusion through a sudden contraction step using a tagging pulse sequence

Magnetic resonance imaging (MRI) with a spatial tagging sequence was used to measure the velocity distribution of clay that was forced past a sudden contraction. A spatial tagging sequence provided magnetic resonance images of clay that allowed measurement of the velocity distribution in the clay, which can provide profound insights on the deformation process of clay during the intrusion process. The experiments were conducted using a specially-designed vessel that could operate at up to 30 MPa. The vessel offers a rectangle test section with a sudden contraction step that had a ratio of contraction of 2:1. The vessel was installed into a commercial magnetic resonance imaging equipment and then the fluid motion of clay flowing into the narrow contracted channel was quantitatively investigated to examine behaviors of flowing clay as non-Newtonian fluid. MRI results are compared with those obtained by computational fluid dynamics (CFD) calculation. Velocity distributions obtained from each tag displacement did not well agree with those predicted by CFD results near the contraction step where the fluid accelerated rapidly. However, a post-processing on calculation results, in which virtual tag displacement is calculated, gave better agreement with experiment and enabled us to compare MRI results with CFD results.     

Correspondence between higher order energy derivative formalisms for restricted Hartree-Fock and correlated wavefunctions

This paper takes the form of a review including some original contributions. Analytic higher energy derivative expressions for configuration interaction (CI) wavefunctions have been used to obtain the corresponding energy derivative formulae for multi-configuration self-consistent-field (MCSCF), general open-shell and closed-shell restricted Hartree-Fock (RHF) wavefunctions by explicitly imposing the variational and orthonormality conditions on the molecular orbital (MO) space. The general structure of the reduction procedure used here is thusCI MCSCF General RHF Closed-shell HF.The equations expressing the correspondence among correlated and RHF wavefunctions have been presented to interrelate various conditions and definitions involved in the energy derivative expressions. Practical formulae for the energy derivatives of the above mentioned wavefunctions up to fourth order are explicitly given.     

New visualization method of progressive acoustic wavefronts using a Köster prism

Visualization of a progressive acoustic wave is explained and verified experimentally. A Köster prism set in an image-forming system works so that the optical wave fields emerging from two points across the exit plane of an acoustic column may be superposed at a point in the image plane. The image intensity changes with a period of half the acoustic wavelength magnified suitably. The visibility of the image intensity takes values between 0 and 0.54 if the acoustic power is made to change. No practical frequency limitation is present in the lower frequency range of the acoustic wave.     

On methods for generating uniform random points on the surface of a sphere

Some methods for generating random points uniformly distributed on the surface of ann-sphere have been proposed to simulate spherical processes on computer. A standard method is to normalize random points inside of the sphere, see M. Muller [5]. Improved methods were given by J. M. Cook [1] and G. Marsaglia [4] in three and four dimensions, and computational methods in higher dimensions by J. S. Hicks and R. F. Wheeling [3] and M. Sibuya [6]. In this paper we shall offer direct methods for generating uniform random points on the surface of a unitn-sphere, which can be easily combined with Marsaglia's idea for getting more improved methods. Our method in even dimensions was obtained by M. Sibuya [6], but a differential-geometric view-point will make analyses simpler, even in odd dimensions.     

Illumination with a moving light source

Image formation is discussed under the condition that an object is illuminated with a moving light source and a time-averaged image is observed. An optical system with such illumination works as if the object were illuminated with spatially, partially coherent light from a certain fixed source.     

Observation of antinormally ordered Hanbury Brown-Twiss correlations

We have measured antinormally ordered Hanbury Brown-Twiss correlations for coherent states of the electromagnetic field by using a stimulated parametric down-conversion process. Photons were detected by stimulated emission, rather than by absorption, so that the detection responded not only to actual photons but also to zero-point fluctuations via spontaneous emission. The observed correlations were distinct from normally ordered ones as they showed excess positive correlations, i.e., photon bunching effects, which arose from the thermal nature of zero-point fluctuations.