Efficiency of thermal relaxation by radiative processes in protoplanetary discs: constraints on hydrodynamic turbulence

Hydrodynamic, non-magnetic instabilities can provide turbulent stress in the regions of protoplanetary discs, where the MRI can not develop. The induced motions influence the grain growth, from which formation of planetesimals begins. Thermal relaxation of the gas constrains origins of the identified hydrodynamic sources of turbulence in discs. We estimate the radiative relaxation timescale of temperature perturbations and study the dependence of this timescale on the perturbation wavelength, the location within the disc, the disc mass, and the dust-to-gas mass ratio. We then apply thermal relaxation criteria to localise modes of the convective overstability, the vertical shear instability, and the zombie vortex instability. Our calculations employed the latest tabulated dust and gas mean opacities and we account for the collisional coupling to the emitting species. The relaxation criterion defines the bulk of a typical T Tauri disc as unstable to the development of linear hydrodynamic instabilities. The midplane is unstable to the convective overstability from at most 2\mbox{ au} and up to 40\mbox{ au}, as well as beyond 140\mbox{ au}. The vertical shear instability can develop between 15\mbox{ au} and 180\mbox{ au}. The successive generation of (zombie) vortices from a seeded noise can work within the inner 0{.}8\mbox{ au}. Dynamic disc modelling with the evolution of dust and gas opacities is required to clearly localise the hydrodynamic turbulence, and especially its non-linear phase.Comment: 13 pages, 8 figure

Conditioned Unitary Transformation on biphotons

A conditioned unitary transformation ($90^o$ polarization rotation) is performed at single-photon level. The transformation is realized by rotating polarization for one of the photons of a polarization-entangled biphoton state (signal photon) by means of a Pockel's cell triggered by the detection of the other (idler) photon after polarization selection. As a result, polarization degree for the signal beam changes from zero to the value given by the idler detector quantum efficiency. This result is relevant to practical realization of various quantum information schemes and can be used for developing a new method of absolute quantum efficiency calibration

Absolute calibration of Analog Detectors using Stimulated Parametric Down Conversion

Spontaneous parametric down conversion has been largely exploited as a tool for absolute calibration of photon counting detectors, photomultiplier tubes or avalanche photodiodes working in Geiger regime. In this work we investigate the extension of this technique from very low photon flux of photon counting regime to the absolute calibration of analog photodetectors at higher photon flux. Moving toward higher photon rate, i.e. at high gain regime, with the spontaneous parametric down conversion shows intrinsic limitations of the method, while the stimulated parametric down conversion process, where a seed beam properly injected into the crystal in order to increase the photon generation rate in the conjugate arm, allows us to work around this problem. A preliminary uncertainty budget is discussed

Human ribosomal protein S13 regulates expression of its own gene at the splicing step by a feedback mechanism

The expression of ribosomal protein (rp) genes is regulated at multiple levels. In yeast, two genes are autoregulated by feedback effects of the protein on pre-mRNA splicing. Here, we have investigated whether similar mechanisms occur in eukaryotes with more complicated and highly regulated splicing patterns. Comparisons of the sequences of ribosomal protein S13 gene (RPS13) among mammals and birds revealed that intron 1 is more conserved than the other introns. Transfection of HEK 293 cells with a minigene-expressing ribosomal protein S13 showed that the presence of intron 1 reduced expression by a factor of four. Ribosomal protein S13 was found to inhibit excision of intron 1 from rpS13 pre-mRNA fragment in vitro. This protein was shown to be able to specifically bind the fragment and to confer protection against ribonuclease cleavage at sequences near the 5′ and 3′ splice sites. The results suggest that overproduction of rpS13 in mammalian cells interferes with splicing of its own pre-mRNA by a feedback mechanism

Twin-photon techniques for photo-detector calibration

The aim of this review paper is to enlighten some recent progresses in quantum optical metrology in the part of quantum efficiency measurements of photo-detectors performed with bi-photon states. The intrinsic correlated nature of entangled photons from Spontaneous Parametric Down Conversion phenomenon has opened wide horizons to a new approach for the absolute measurement of photo-detector quantum efficiency, outgoing the requirement for conventional standards of optical radiation; in particular the simultaneous feature of the creation of conjugated photons led to a well known technique of coincidence measurement, deeply understood and implemented for standard uses. On the other hand, based on manipulation of entanglement developed for Quantum Information protocols implementations, a new method has been proposed for quantum efficiency measurement, exploiting polarisation entanglement in addition to energy-momentum and time ones, that is based on conditioned polarisation state manipulation. In this review, after a general discussion on absolute photo-detector calibration, we compare these different methods, in order to give an accurate operational sketch of the absolute quantum efficiency measurement state of the art

International Transport Corridors of Eurasia and the Silk Road Economic Belt

The paper discusses the interaction of Eurasian Economic Union and the Silk Road Economic Belt within the framework of transport routes and international transport corridors development. Today’s Eurasian international transport corridors are reviewed together with the discussion of rebuild and renovated transport infrastructure, considering corresponding realization issues. The paper gives the perspective of collaboration in the transport section of planned Big Eurasian Partnership, which is virtually realized within the framework of the Shanghai Cooperation Organization

A central fragment of ribosomal protein S26 containing the eukaryote-specific motif YxxPKxYxK is a key component of the ribosomal binding site of mRNA region 5′ of the E site codon

The eukaryotic ribosomal protein S26e (rpS26e) lacking eubacterial counterparts is a key component of the ribosomal binding site of mRNA region 5′ of the codon positioned at the exit site. Here, we determined the rpS26e oligopeptide neighboring mRNA on the human 80S ribosome using mRNA analogues bearing perfluorophenyl azide-derivatized nucleotides at designed locations. The protein was cross-linked to mRNA analogues in specific ribosomal complexes, in which the derivatized nucleotide was located at positions −3 to −9. Digestion of cross-linked rpS26e with various specific proteolytic agents followed by identification of the resulting modified oligopeptides made it possible to map the cross-links to fragment 60–71. This fragment contains the motif YxxPKxYxK conserved in eukaryotic but not in archaeal rpS26e. Analysis of X-ray structure of the Tetrahymena thermophila 40S subunit showed that this motif is not implicated in the intraribosomal interactions, implying its involvement in translation process in a eukaryote-specific manner. Comparison of the results obtained with data on positioning of ribosomal ligands on the 40S subunit lead us to suggest that this motif is involved in interaction with both the 5′-untranslated region of mRNA and the initiation factor eIF3 specific for eukaryotes, providing new insights into molecular mechanisms of translation in eukaryotes