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We study the thermal Markovian diffusion of tracer particles in a 2D medium with spatially varying diffusivity D(r), mimicking recently measured, heterogeneous maps of the apparent diffusion coefficient in biological cells. For this heterogeneous diffusion process (HDP) we analyse the mean squared displacement (MSD) of the tracer particles, the time averaged MSD, the spatial probability density function, and the first passage time dynamics from the cell boundary to the nucleus. Moreover we examine the non-ergodic properties of this process which are important for the correct physical interpretation of time averages of observables obtained from single particle tracking experiments. From extensive computer simulations of the 2D stochastic Langevin equation we present an in-depth study of this HDP. In particular, we find that the MSDs along the radial and azimuthal directions in a circular domain obey anomalous and Brownian scaling, respectively. We demonstrate that the time averaged MSD stays linear as a function of the lag time and the system thus reveals a weak ergodicity breaking. Our results will enable one to rationalise the diffusive motion of larger tracer particles such as viruses or submicron beads in biological cells.
On the role of fluoro-substituted nucleosides in DNA radiosensitization for tumor radiation therapy
(2014)
Gemcitabine (2′,2′-difluorocytidine) is a well-known radiosensitizer routinely applied in concomitant chemoradiotherapy. During irradiation of biological media with high-energy radiation secondary low-energy (<10 eV) electrons are produced that can directly induce chemical bond breakage in DNA by dissociative electron attachment (DEA). Here, we investigate and compare DEA to the three molecules 2′-deoxycytidine, 2′-deoxy-5-fluorocytidine, and gemcitabine. Fluorination at specific molecular sites, i.e., nucleobase or sugar moiety, is found to control electron attachment and subsequent dissociation pathways. The presence of two fluorine atoms at the sugar ring results in more efficient electron attachment to the sugar moiety and subsequent bond cleavage. For the formation of the dehydrogenated nucleobase anion, we obtain an enhancement factor of 2.8 upon fluorination of the sugar, whereas the enhancement factor is 5.5 when the nucleobase is fluorinated. The observed fragmentation reactions suggest enhanced DNA strand breakage induced by secondary electrons when gemcitabine is incorporated into DNA.
The Beruriah Incident
(2014)
The story known as the Beruriah Incident, which appears in Rashi’s commentary on bAvodah Zarah 18b (related to ATU types 920A* and 823A*), describes the failure and tragic end of R. Meir and his wife Beruriah, two tannaic role-models. This article examines the authenticity of the story by tracking the method of distribution in traditional Jewish society before the modern era, and comparing the story’s components with rabbinic literature and international folklore.
The development of the current liturgical music used in the Belgrade synagogue is (in the last decades) heavily influenced by foreign traditions (mostly levantine) that are brought to Belgrade by modern communication systems. Therefore it is nearly impossible to speak of a status quo that might be possibly obsolete by tomorrow – at least with respect to the melodies. The great changes within the liturgical music occurred not due to acculturation into the Serbian majority but due to the personal preferences of the religious leaders of the Belgrade Jews. The alterations are a conscious process which is precisely the consequence of the musical taste of the local Rabbi and Cantor and not occurring autonomously. In order to understand the new nusah sepharadiyerushalmi that took the place of the forlorn nusah after the downfall of the Communist regime it is deemed necessary to look towards Israel where the rite developed.