We report on, in this letter, a phenomenon that the central zerointensity point of a doughnut beam, caused by phase singularity, disappears in the focus, when such a beam is focused by a high numerical-aperture objective in free space. In addition, the focal shape of the doughnut beam of a given topological charge exhibits the increased ring intensity in the direction orthogonal to the incident polarization state and an elongation in the polarization direction. These phenomena are caused by the effect of depolarization, associated with a high numerical-aperture objective, and become pronounced by the use of a central obstruction in the objective aperture.

It is shown that embedding of flipped $\mathrm{SU}(5)$ in a five-dimensional $\mathrm{SO}(10)$ enables exact unification of the gauge coupling constants. The demand for unification uniquely determines both the compactification scale and the cutoff scale. These are found to be ${M}_{C}\ensuremath{\approx}5.5\ifmmode\times\else\texttimes\fi{}{10}^{14}\mathrm{GeV},$ and ${M}_{*}\ensuremath{\approx}1.0\ifmmode\times\else\texttimes\fi{}{10}^{17}\mathrm{GeV},$ respectively. The theory explains the absence of $d=5$ proton-decay operators through the implementation of the missing partner mechanism. On the other hand, the presence of $d=6$ proton-decay operators points towards the bulk localization of the first and second families of matter fields.

In vitro cultures of five moss species were established on hormone-free MS medium, or on MS medium supplemented with different concentrations of 2,4-dichlorophenoxyacetic acid and kinetin. In vitro culture of Eurhynchium praelongum (Hedw.) B., S. & G., has been initiated from the apical shoots of the gametophytes, and the cultures of Aloina aloides (K.F.Schultz) Kindb. Brachythecium velutinum (Hedw.) B., S. & G., Ceratodon purpureus (Hedw.) Brid. and Grimmia pulvinata (Hedw.) Sm. were initiated from the spores of immature sporophytes. In secondary protonema culture of Eurhynchium praelongum, spontaneous regeneration occurred successfully. Protonema cultures of Aloina aloides, Brachythecium velutinum and Ceratodon purpureus reversed to caulonema culture where bud formation occurred. Grimmia pulvinata cultures remained at the protonema stage. Aloina aloides (K.F.Schultz) Kindb., Brachythecium velutinum (Hedw.) B.S. & G., Ceratodon purpureus (Hedw.) Brid., Eurhynchium praelongum (Hedw.) B.S. & G. ve Grimmia pulvinata (Hedw.) Sm. Yosunlarinin ‹n vitro Kulturu Ozet: Hormonsuz veya farkli konsantrasyonlarda oksin ve sitokinin iceren besi ortamlarinda (MS) yaflamlari tehlikede olmayan cok sayidaki yosun turu icin in vitro kulturleri oluflturulmufltur. Eurhynchium praelongum (Hedw.) B.S. & G.'nin in vitro kulturune gametofitlerin uc surgunlerinden, Aloina aloides (K.F.Schultz) Kindb., Brachythecium velutinum (Hedw.) B.S. & G., Ceratodon purpureus (Hedw.) Brid. ve Grimmia pulvinata(Hedw.) Sm.'nin in vitro kulturlerine ise olgunlaflmamifl saprofitlerin sporlarindan alinarak bafllanmifltir. Eurhynchium praelongum'nin sekonder protonema kulturu do?al olarak baflarili bir flekilde oluflmaktadir. Aloina aloides, Brachythecium velutinum ve Ceratodon purpureus'nin protonema kulturleri tomurcuk formasyonunun gerceklefltii kaulonema kulturune donuflmufl, Grimmia pulvinata ise protonema evresinde kalmifltir. Anahtar Sozcukler: Yosunlar, in vitro kulturu, Aloina aloides, Brachythecium velutinum, Ceratodon purpureus, Eurhynchium praelongum, Grimmia pulvinata