Fundamental imaging properties of transillumination laser computed tomography based on coherent detection imaging method.

The coherent detection imaging (CDI) method uses the optical heterodyne detection technique. CW and single frequency lasers having long coherence lengths are used to exploit the maximum advantages of heterodyne detection, such as high directionality, selectivity and sensitivity. The CDI method based on optical heterodyne detection enables selective filtering of the directional coherence-retaining emergent photons, which leads to image reconstruction from projections, similar to X-ray computed tomography (CT). So far we have demonstrated the advantages and capabilities of the measurement technique for transillumination optical computed tomography in biomedicine. Here, we investigate the fundamental imaging properties of CDI method, such as its high directionality and quantitativeness, with preliminary physical phantom experiments. The results show that the CDI method satisfies the requirements for CT reconstruction under the first order approximation, and enables quantitative measurements in the sense that the relationship between estimated and actual concentration retains a satisfactory linearity.     

Low-temperature specific heat study of SrCu2(BO3)2 with an exactly solvable ground state

The specific heat of a two-dimensional spin gap system SrCu₂(BO₃)₂ realizing the Shastry-Suther-land model was measured between 1.3 and 25 K under various magnetic fields up to 12 T. The analysis based on an isolated dimer model in a low temperature region revealed that the value of the spin gap at zero field is Δ = 34.4 K. It turned out that Δ decreases in proportion to H due to the Zeeman splitting of the excited triplet levels. This simplest model, however, fails to reproduce the result in a high-temperature region, suggesting rather strong spin-spin correlation of the system.     

Computation of transition to turbulence in the compression stage of a reciprocating engine

The transition to turbulent flow in the compression stage of a reciprocating engine is studied by obtaining the finite-difference numerical solutions to the governing Navier-Stokes equations without using explicit turbulence models. A computational method is developed under the assumption that the flow is in a low-subsonic regime with strong compression. The numerical method is a simple extension of the well known MAC method. Computations were performed for three different chamber geometries at the engine speed of 1400 rpm. The results of the computations clearly demonstrate the transient process in which large tumbling vortices break down into smaller ones near the end of the compression process. The transition process is also caught experimentally by using Mach-Zehnder interferometry.     

Electrophilic glycosidation employing 3,5-O-(di-tert-butylsilylene)-erythro-furanoid glycal leads to exclusive formation of the β-anomer: synthesis of 2′-deoxynucleosides and its 1′-branched analogues

Stereoselectivity in N-iodosuccimide (NIS)-mediated electrophilic glycosidation was examined by employing 2,4-bis-O-(trimethylsilyl)thymine and three different silyl-protected erythro-furanoid glycals 12, 16, and 18. As a result, it was found that 3,5-O-(di-t-butylsilylene)-protected 18 gave only the β-anomer (21). The remarkable stereoselectivity observed by employing 18 is discussed on the basis of its X-ray crystallographic analysis. 1-Substituted glycals gave the corresponding β-anomer, again exclusively, to provide access to 1′-branched 2′-deoxynucleosides.     

The first asymmetric total syntheses of both enantiomers of cryptocaryone

The first asymmetric total syntheses of the (+)- and (−)-cryptocaryones are described. Removal of the acetal unit of the enone acetal 5, which was obtained in our previous study from the cyclohexadiene acetal 3, afforded the enone acetal 8 in a one-pot procedure. The acylation of 8 with cinnamoyl chloride and subsequent hydrolysis of the resulting acetal gave the lactol 11. Its oxidation with NIS and tetra-n-butylammonium iodide (TBAI) finally furnished the natural (+)-cryptocaryone 2. The same procedure from ent-3 afforded the unnatural one 1.