High peak power sub-60 fs Yb:KGW laser

A high power sub-60 fs mode-locked diode-pumped Yb: KGW laser based on hybrid action of an InGaAs quantum-dot saturable absorber mirror and Kerr-lens mode locking was demonstrated. The laser delivered 56 fs pulses with 1.95 W of average power corresponding to 450 kW of peak power. The spectral bandwidth of the pulse was 20.5 nm, which was near the gain bandwidth limit of the Yb:KGW crystal. To the best of our knowledge, these are the shortest pulses generated from the monoclinic double tungstate crystals (and Yb:KGW laser crystal in particular) and the most powerful in the sub-60 fs regime. At the same time they are also the shortest pulses produced to date with the help of a quantum-dot-based saturable absorber

Non-conservative Evolution of Cataclysmic Variables

We suggest a new mechanism to account for the loss of angular momentum in binaries with non-conservative mass exchange. It is shown that in some cases the loss of matter can result in increase of the orbital angular momentum of a binary. If included into consideration in evolutionary calculations, this mechanism appreciably extends the range of mass ratios of components for which mass exchange in binaries is stable. It becomes possible to explain the existence of some observed cataclysmic binaries with high donor/accretor mass ratio, which was prohibited in conservative evolution models.Comment: LaTeX, 32 pages, to be published in Astron. Z

DEMOGRAPHIC POLICY OF FRANCE

Presently, demographic policy is of great importance for solving the problem of depopulation. The article reviews the experience of France in solving this challenge, analyzes the various methods used in this country to deal with population decline. Special attention has been paid to the state support of families and children through the provision of social payments and benefits. Trends and forecasts of demographic processes in France have been considered also, taking into account the measures taken by the state to support the family. Based on the study, conclusions have been made about the effectiveness of demographic policy in France

Lys98 Substitution in Human AP Endonuclease 1 Affects the Kinetic Mechanism of Enzyme Action in Base Excision and Nucleotide Incision Repair Pathways

Human apurinic/apyrimidinic endonuclease 1 (APE1) is a key enzyme in the base excision repair (BER) and nucleotide incision repair (NIR) pathways. We recently analyzed the conformational dynamics and kinetic mechanism of wild-type (wt) protein, in a stopped-flow fluorescence study. In this study, we investigated the mutant enzyme APE1K98A using the same approach. Lys98 was known to hydrogen bond to the carboxyl group of Asp70, a residue implicated in binding the divalent metal ion. Our data suggested that the conformational selection and induced fit occur during the enzyme action. We expanded upon the evidence that APE1 can pre-exist in two conformations. The isomerization of an enzyme-product complex in the BER process and the additional isomerization stage of enzyme-substrate complex in the NIR process were established for APE1K98A. These stages had not been registered for the wtAPE1. We found that the K98A substitution resulted in a 12-fold reduction of catalytic constant of 5′-phosphodiester bond hydrolysis in (3-hydroxytetrahydrofuran-2-yl)methyl phosphate (F, tetrahydrofuran) containing substrate, and in 200-fold reduction in 5,6-dihydrouridine (DHU) containing substrate. Thus, the K98A substitution influenced NIR more than BER. We demonstrated that the K98A mutation influenced the formation of primary unspecific enzyme-substrate complex in a complicated manner, depending on the Mg2+ concentration and pH. This mutation obstructed the induced fit of enzyme in the complex with undamaged DNA and F-containing DNA and appreciably decreased the stability of primary complex upon interaction of enzyme with DNA, containing the natural apurinic/apyrimidinic (AP) site. Furthermore, it significantly delayed the activation of the less active form of enzyme during NIR and slowed down the conformational conversion of the complex of enzyme with the cleavage product of DHU-substrate. Our data revealed that APE1 uses the same active site to catalyze the cleavage of DHU- and AP-substrates

In-band pumped conical refraction Nd:KGW laser

We have demonstrated an in-band pumped conical refraction (CR) Nd: KGW laser. The CR laser was diode-pumped at 910 nm and produced an output power of 1.15 W at 1069 nm

Conical refraction output from a Nd:YVO4 laser with an intracavity conerefringent element

A conical refraction (CR) laser based on an a-cut Nd:YVO4 laser was demonstrated. By using a KGW crystal as a CR element, a typical laser with a Gaussian intensity output profile was transformed into a laser with conically refracted output. The CR laser delivered 220 mW of output power for 500 mW of pump power. The separation of the laser gain medium and the CR element reduced the complexity of the pumping scheme, and resulted in the generation of well-behaved CR laser beams with outstanding quality. The presented approach is power scalable and offers a unique possibility of studying the transformation of a Gaussian laser mode into a conically refracted one in a laser cavity

Diode-pumped Yb:CALGO laser with conical refraction output

A high power conical refraction (CR) laser was demonstrated based on Yb:CALGO laser crystal with a separate intracavity CR element. The CR laser delivered the maximum output power of 6.25 W at 25 W of incident pump power which is the highest output power for the CR lasers to date. The separation of the CR element from the laser gain medium reduced the complexity of laser pumping. The generated CR laser beam exhibited excellent quality with well-resolved concentric rings and the Poggendorff dark ring

Interaction of the general transcription factor TnrA with the PII-like protein GlnK and glutamine synthetase in Bacillus subtilis

TnrA is a master transcription factor regulating nitrogen metabolism in Bacillus subtilis under conditions of nitrogen limitation. When the preferred nitrogen source is in excess, feedback-inhibited glutamine synthetase (GS) has been shown to bind TnrA and disable its activity. In cells grown with an energetically unfavorable nitrogen source such as nitrate, TnrA is fully membrane-bound via a complex of AmtB and GlnK, which are the transmembrane ammonium transporter and its cognate regulator, respectively, originally termed NrgA and NrgB. The complete removal of nitrate from the medium leads to rapid degradation of TnrA in wild-type cells. In contrast, in AmtB-deficient or GlnK-deficient strains, TnrA is neither membrane-bound nor degraded in response to nitrate depletion. Here, we show that TnrA forms either a stable soluble complex with GlnK in the absence of AmtB, or constitutively binds to GS in the absence of GlnK. In vitro, the TnrA C-terminus is responsible for interactions with either GS or GlnK, and this region appears also to mediate proteolysis, suggesting that binding of GlnK or GS protects TnrA from degradation. Surface plasmon resonance detection assays have demonstrated that GS binds to TnrA not only in its feedback-inhibited form, but also in its non-feedback-inhibited form, although less efficiently. TnrA binding to GlnK or GS responds differentially to adenylate nucleotide levels, with ATP weakening interactions with both partners. Structured digital abstract to by () to by () to by () to by () with by () to by () with by () with by () with by () to by () to by () The present paper reveals a novel mechanism for regulating the stability of the general nitrogen-stress transcription factor TnrA in Bacillus subtilis. TnrA remains resistant to intracellular proteolysis as long as it is complexed to either GlnK or glutamine synthetase (GS). Interaction with both proteins occurs via the C-terminus of TnrA, which is also recognized by the proteolytic activity © 2011 The Authors Journal compilation