Protein Phosphatase 1 (PP1) Is a Post-Translational Regulator of the Mammalian Circadian Clock

Circadian clocks coordinate the timing of important biological processes. Interconnected transcriptional and post-translational feedback loops based on a set of clock genes generate and maintain these rhythms with a period of about 24 hours. Many clock proteins undergo circadian cycles of post-translational modifications. Among these modifications, protein phosphorylation plays an important role in regulating activity, stability and intracellular localization of clock components. Several protein kinases were characterized as regulators of the circadian clock. However, the function of protein phosphatases, which balance phosphorylation events, in the mammalian clock mechanism is less well understood. Here, we identify protein phosphatase 1 (PP1) as regulator of period and light-induced resetting of the mammalian circadian clock. Down-regulation of PP1 activity in cells by RNA interference and in vivo by expression of a specific inhibitor in the brain of mice tended to lengthen circadian period. Moreover, reduction of PP1 activity in the brain altered light-mediated clock resetting behavior in mice, enhancing the phase shifts in either direction. At the molecular level, diminished PP1 activity increased nuclear accumulation of the clock component PER2 in neurons. Hence, PP1, may reduce PER2 phosphorylation thereby influencing nuclear localization of this protein. This may at least partially influence period and phase shifting properties of the mammalian circadian clock

Physicochemical characterisation of pottery from the Vinca culture, Serbia, regarding the firing temperature and decoration techniques

A study of decorated Neolithic pottery samples from the excavation site Plocnik, Serbia, was performed using X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR) and X-ray fluorescence (XRF) spectroscopy. The investigated samples belong to the era of the Vinca culture that existed in the central Balkan region from the mid VI until the first half of the V millennium BCE. The mineralogical composition of the pottery samples and comparison of the investigated pottery with thermally treated local clay indicated firing temperatures in the range from 600 to 800 degrees C. Two different types of white pigments were identified in white incrusted decorations: calcium carbonate and bone white (composed of crushed bones). This is the first evidence of the use of bones for decorations in pottery of the Vinca culture from the excavation site Plocnik. In addition to this, it was revealed that the potters used the iron reduction technique for obtaining black decorations

Spectroscopic investigation of two Serbian icons painted on canvas

A multianalytical study of two Serbian icons, The Virgin and Child and St. Petka, painted on canvas by unknown authors was performed in order to identify the materials used as pigments, binders and the ground layer. The investigated icons belong to the Museum of the Serbian Orthodox Church in Belgrade. Samples, collected from different parts of the icons, were analysed by: optical microscopy (OM), energy dispersive X-Ray fluorescence (EDXRF), Fourier transform infrared (FTIR) and micro-Raman spectroscopy. The obtained results revealed the presence of the following pigments: Prussian Blue, ultramarine, Green Earth, iron oxides, Lead White and Zinc White. Linseed oil was used as the binder. The materials used for the ground layers were gypsum, calcite, baryte and Lead White. The gilded surface of the icon The Virgin and Child was made of gold. The gilded surface on the frame of this icon was made of imitation of gold, i.e., Schlagmetal, since EDXRF spectroscopy showed the presence of copper and zinc, while gold was not detected. Based on the style and the consideration of an art historian, as well as on the obtained results for the corresponding pigments and binder, both icons were most probably made at the end of 19th or the beginning of the 20th century

Regularization of the circular restricted three-body problem using 'similar' coordinate systems

The regularization of a new problem, namely the three-body problem, using 'similar' coordinate system is proposed. For this purpose we use the relation of 'similarity', which has been introduced as an equivalence relation in a previous paper (see \cite{rom11}). First we write the Hamiltonian function, the equations of motion in canonical form, and then using a generating function, we obtain the transformed equations of motion. After the coordinates transformations, we introduce the fictitious time, to regularize the equations of motion. Explicit formulas are given for the regularization in the coordinate systems centered in the more massive and the less massive star of the binary system. The 'similar' polar angle's definition is introduced, in order to analyze the regularization's geometrical transformation. The effect of Levi-Civita's transformation is described in a geometrical manner. Using the resulted regularized equations, we analyze and compare these canonical equations numerically, for the Earth-Moon binary system.Comment: 24 pages, 7 figures; Accepted for publication in Astrophysics and Space Scienc