Experimental investigation of the buckling of shallow spherical shells

In the present paper, the buckling behavior of clamped thin shallow spherical shells under external pressure is studied. Seventy-nine plastic shells formed by thermovacuum process were tested. The distributions of initial geometrical imperfections and vertical displacements were minutely measured with a differential transformer. It was possible to control the symmetrical initial geometrical imperfection of each specimen.Results indicate that the buckling phenomena of shallow spherical shells vary greatly with the symmetrical initial imperfection parameter η. In the case of the geometrical parameter λ larger than 5.5, the amplitude of the asymmetrical displacement component with the bifurcation buckling wave calculated by Huang becomes large immediately before buckling. The validity of Huang's theory for an initially perfect shell is experimentally demonstrated.     

Heavy muon as a possible cause of two anomalies

We propose to explain two observed anomalies that suggest extension of the minimal gauge scheme, the eμ production in the e⁺e^? reaction and the anomalous y-distribution in $\text{ν}{}_{\mathrm{\mu }}$ reactions, as being caused by a single object, a heavy muon. With more accurate neutrino data this explanation can readily be distinguished from that of a new quark production.     

Theoretical investigation of the stability of highly charged C60 molecules produced with intense near-infrared laser pulses

We theoretically investigated the stability of highly charged C(60) (z+) cations produced from C(60) with an ultrashort intense laser pulse of lambda approximately 1800 nm. We first calculated the equilibrium structures and vibrational frequencies of C(60) (z+) as well as C(60). We then calculated key energies relevant to dissociation of C(60) (z+), such as the excess vibrational energy acquired upon sudden tunnel ionization from C(60). By comparing the magnitudes of the calculated energies, we found that C(60) (z+) cations up to z approximately 12 can be produced as a stable or quasistable (microsecond-order lifetime) intact parent cation, in agreement with the recent experimental report by V. R. Bhardwaj et al. [Phys. Rev. Lett. 93, 043001 (2004)] that almost only intact parent C(60) (z+) cations up to z=12 are detected by a mass spectrometer. The results of Rice-Ramsperger-Kassel-Marcus calculation suggest that the lifetime of C(60) (z+) drastically decreases by ten orders of magnitude as z increases from z=11 to z=13. Using the time-dependent adiabatic state approach, we also investigated the vibrational excitation of C(60) and C(60) (z+) by an intense near-infrared pulse. The results indicate that large-amplitude vibration with energy of >10 eV is induced in the delocalized h(g)(1)-like mode of C(60) (z+).     

Observation of negative and positive trions in the electrochemically carrier-doped single-walled carbon nanotubes

Understanding of electronic and optical features of single-walled carbon nanotubes (SWNTs) has been a central issue in science and nanotechnology of carbon nanotubes. We describe the detection of both the positive trion (positively charged exciton) and negative trion (negatively charged exciton) as a three-particle bound state in the SWNTs at room temperature by an in situ photoluminescence spectroelectrochemistry method for an isolated SWNT film cast on an ITO electrode. The electrochemical hole and electron dopings enable us to detect such trions on the SWNTs. The large energy difference between the singlet bright exciton and the negative and positive trions showing a tube diameter dependence is determined by both the exchange splitting energy and the trion binding energy. In contrast to conventional compound semiconductors, on the SWNTs, the negative trion has almost the same binding energy to the positive trion, which is attributed to nearly identical effective masses of the holes and electrons.     

Design, synthesis, evaluation, and structure of vitamin D analogues with furan side chains

Based on the crystal structures of human vitamin D receptor (hVDR) bound to 1α,25-dihydroxy-vitamin D(3) (1,25 D) and superagonist ligands, we previously designed new superagonist ligands with a tetrahydrofuran ring at the side chain that optimize the aliphatic side-chain conformation through an entropy benefit. Following a similar strategy, four novel vitamin D analogues with aromatic furan side chains (3a, 3b, 4a, 4b) have now been developed. The triene system has been constructed by an efficient stereoselective intramolecular cyclization of an enol triflate (A-ring precursor) followed by a Suzuki-Miyaura coupling of the resulting intermediate with an alkenyl boronic ester (CD-side chain, upper fragment). The furan side chains have been constructed by gold chemistry. These analogues exhibit significant pro-differentiation effects and transactivation potency. The crystal structure of 3a in a complex with the ligand-binding domain of hVDR revealed that the side-chain furanic ring adopts two conformations.     

Theoretical verification of nonthermal microwave effects on intramolecular reactions

There have been a growing number of articles that report dramatic improvements in the experimental performance of chemical reactions by microwave irradiation compared to that under conventional heating conditions. We theoretically examined whether nonthermal microwave effects on intramolecular reactions exist or not, in particular, on Newman-Kwart rearrangements and intramolecular Diels-Alder reactions. The reaction rates of the former calculated by the transition state theory, which consider only the thermal effects of microwaves, agree quantitatively with experimental data, and thus, the increases in reaction rates can be ascribed to dielectric heating of the solvent by microwaves. In contrast, for the latter, the temperature dependence of reaction rates can be explained qualitatively by thermal effects but the possibility of nonthermal effects still remains regardless of whether competitive processes are present or not. The effective intramolecular potential energy surface in the presence of a microwave field suggests that nonthermal effects arising from potential distortion are vanishingly small in intramolecular reactions. It is useful in the elucidation of the reaction mechanisms of microwave synthesis to apply the present theoretical approach with reference to the experiments where thermal and nonthermal effects are separated by screening microwave fields.     

Stereoselective convergent synthesis of 24,25-dihydroxyvitamin D3 metabolites: a practical approach

Vitamin D3 active metabolites 24R,25-(OH)2-D3, 24S,25-(OH)2-D3, and 1 alpha, 24R,25-(OH)3-D3 were synthesized by a convergent and stereoselective approach. In the synthetic route, the stereogenic center at C-24 was generated through ultrasonically induced aqueous conjugate addition of iodide 6 to Seebach's dioxolanone 5, and the vitamin D triene system was constructed using the Lythgoe approach. The synthesis, which is both short (seven steps from iodide 6) and efficient (32-40% overall yield), allows the preparation of large quantities of the metabolites and provides a novel example of a highly stereoselective reaction promoted by the zinc-copper couple in aqueous media.