ALBERT

Description: We present a new upper-mantle tomographic model derived solely from hum seismic data. Phase correlograms between station pairs are computed to extract phase-coherent signals. Correlograms are then stacked using the time–frequency phase-weighted stack method to build-up empirical Green's functions. Group velocities and uncertainties are measured in the wide period band of 30–250 s, following a resampling approach. Less data are required to extract reliable group velocities at short periods than at long periods, and 2 yr of data are necessary to measure reliable group velocities for the entire period band. Group velocities are first regionalized and then inverted versus depth using a simulated annealing method in which the number and shape of splines that describes the S -wave velocity model are variable. The new S -wave velocity tomographic model is well correlated with models derived from earthquakes in most areas, although in India, the Dharwar craton is shallower than in other published models.

Description: We analyse the photopolarimetric response measured in Comet C/1975 V1 (West) using model agglomerated debris particles. Such particles have highly irregular morphology and volume density with properties that are consistent with the samples retrieved by Stardust from Comet 81P/Wild 2. We find that an entire set of observational data including phase function, phase dependence of the degree of linear polarization, photometric, and polarimetric colour in Comet C/1975 V1 (West) can be quantitatively reproduced with a two-component mixture of weakly and highly absorbing particles, having refractive indices m  = 1.5+0 i or 1.6+0.0005 i and 2.43+0.59 i , respectively. These refractive indices are consistent with Mg-rich silicates and amorphous carbon, two species considered to be abundant in comets. Our modelling predicts the volume ratio of these materials being about 1:3. We note that in situ mass spectrometry measurements of Comet 1P/Halley suggested a similar ratio of weakly to highly absorbing particles, with a large uncertainty. The best fit to observations is obtained for a polydisperse ensembles of particles that obey the power-law size distribution r –1.5 and r –2 . Such a distribution also is in good agreement with in situ studies of Comet 1P/Halley. While our modelling can reproduce the photopolarimetric properties of Comet C/1975 V1 (West), it also is one of the simplest approach, since it has fewer free parameters than other approaches.

Description: P and S receiver functions (PRF and SRF) from 19 seismograph stations in the Gibraltar Arc and the Iberian Massif reveal new details of the regional deep structure. Within the high-velocity mantle body below southern Spain the 660-km discontinuity is depressed by at least 20 km. The Ps phase from the 410-km discontinuity is missing at most stations in the Gibraltar Arc. A thin (~50 km) low- S -velocity layer atop the 410-km discontinuity is found under the Atlantic margin. At most stations the S410p phase in the SRFs arrives 1.0–2.5 s earlier than predicted by IASP91 model, but, for the propagation paths through the upper mantle below southern Spain, the arrivals of S410p are delayed by up to +1.5 s. The early arrivals can be explained by elevated Vp / Vs ratio in the upper mantle or by a depressed 410-km discontinuity. The positive residuals are indicative of a low (~1.7 versus ~ 1.8 in IASP91) Vp / Vs ratio. Previously, the low ratio was found in depleted lithosphere of Precambrian cratons. From simultaneous inversion of the PRFs and SRFs we recognize two types of the mantle: ‘continental’ and ‘oceanic’. In the ‘continental’ upper mantle the S -wave velocity in the high-velocity lid is 4.4–4.5 km s –1 , the S -velocity contrast between the lid and the underlying mantle is often near the limit of resolution (0.1 km s –1 ), and the bottom of the lid is at a depth reaching 90–100 km. In the ‘oceanic’ domain, the S -wave velocities in the lid and the underlying mantle are typically 4.2–4.3 and ~ 4.0 km s –1 , respectively. The bottom of the lid is at a shallow depth (around 50 km), and at some locations the lid is replaced by a low S -wave velocity layer. The narrow S–N-oriented band of earthquakes at depths from 70 to 120 km in the Alboran Sea is in the ‘continental’ domain, near the boundary between the ‘continental’ and ‘oceanic’ domains, and the intermediate seismicity may be an effect of ongoing destruction of the continental lithosphere.

Description: We investigate the magnetic field which is generated by turbulent motions of a weakly ionized gas. Galactic molecular clouds give us an example of such a medium. As in the Kazantsev–Kraichnan model we assume a medium to be homogeneous and a neutral gas velocity field to be isotropic and correlated in time. We take into consideration the presence of a mean magnetic field, which defines a preferred direction in space and eliminates isotropy of magnetic field correlators. Evolution equations for the anisotropic correlation function are derived. Isotropic cases with zero mean magnetic field as well as with small mean magnetic field are investigated. It is shown that stationary bounded solutions exist only in the presence of the mean magnetic field for the Kolmogorov neutral gas turbulence. The dependence of the magnetic field fluctuations amplitude on the mean field is calculated. The stationary anisotropic solution for the magnetic turbulence is also obtained for large values of the mean magnetic field.

Description: Integrase strand transfer inhibitors (INSTIs) are highly effective against HIV infections. Co-crystal structures of the prototype foamy virus intasome have shown that all three FDA-approved drugs, raltegravir (RAL), elvitegravir and dolutegravir (DTG), act as interfacial inhibitors during the strand transfer (ST) integration step. However, these structures give only a partial sense for the limited inhibition of the 3'-processing reaction by INSTIs and how INSTIs can be modified to overcome drug resistance, notably against the G140S-Q148H double mutation. Based on biochemical experiments with modified oligonucleotides, we demonstrate that both the viral DNA +1 and –1 bases, which flank the 3'-processing site, play a critical role for 3'-processing efficiency and inhibition by RAL and DTG. In addition, the G140S-Q148H (SH) mutant integrase, which has a reduced 3'-processing activity, becomes more active and more resistant to inhibition of 3'-processing by RAL and DTG in the absence of the –1 and +1 bases. Molecular modeling of HIV-1 integrase, together with biochemical data, indicate that the conserved residue Q146 in the flexible loop of HIV-1 integrase is critical for productive viral DNA binding through specific contacts with the virus DNA ends in the 3'-processing and ST reactions. The potency of integrase inhibitors against 3'-processing and their ability to overcome resistance is discussed.

Description: PIP3 is synthesized by the Class I PI3Ks and regulates complex cell responses, such as growth and migration. Signals that drive long-term reshaping of cell phenotypes are difficult to resolve because of complex feedback networks that operate over extended times. PIP 3 -dependent modulation of mRNA accumulation is clearly important in this process but is poorly understood. We have quantified the genome-wide mRNA-landscape of non-transformed, breast epithelium-derived MCF10a cells and its response to acute regulation by EGF, in the presence or absence of a PI3Kα inhibitor, compare it to chronic activation of PI3K signalling by cancer-relevant mutations (isogenic cells expressing an oncomutant PI3Kα allele or lacking the PIP 3 -phosphatase/tumour-suppressor, PTEN). Our results show that whilst many mRNAs are changed by long-term genetic perturbation of PIP3 signalling (‘butterfly effect’), a much smaller number do so in a coherent fashion with the different PIP3 perturbations. This suggests a subset of more directly regulated mRNAs. We show that mRNAs respond differently to given aspects of PIP3 regulation. Some PIP3-sensitive mRNAs encode PI3K pathway components, thus suggesting a transcriptional feedback loop. We identify the transcription factor binding motifs SRF and PRDM1 as important regulators of PIP3-sensitive mRNAs involved in cell movement.

Description: Circular polarization in cometary continuum bands has been observed for more than 30 years. Recently, imaging data on circular polarization have been obtained for more than 10 comets using the 6-m Big Telescope Alt-azimuthal (BTA) telescope (Russia). However, despite the accumulation of significant amounts of data, the mechanisms that form circular polarization in the cometary environment are still a mystery. Regular mechanisms, such as multiple scattering in an optically thick medium or the domination of particles or materials of a specific mirror asymmetry (including homochirality), could not explain the observations. Particle alignment was considered the most feasible mechanism; however, the cause of the particle alignment was not clear. The most reasonable mechanism, alignment in a magnetic field, was considered doubtful, as comets do not have their own magnetic field and, according to the in situ results for comet Halley, the solar magnetic field could not penetrate deeply into the coma. However, new theoretical studies of cometary coma interaction with the solar magnetic field and, especially, Rosetta observations of the diamagnetic cavity of comet 67P/Churyumov–Gerasimenko showed that the solar wind magnetic field can penetrate as close to the nucleus as several dozen kilometres. This allows us to suggest alignment in the solar magnetic field as a reason for the observed circular polarization. Based on the data obtained for comet 67P, we estimate the time necessary for the alignment of cometary particles in the solar magnetic field. The estimates obtained are consistent with the observations of cometary circular polarization.