Laser-driven quantum magnonics and THz dynamics of the order parameter in antiferromagnets

The impulsive generation of two-magnon modes in antiferromagnets by femtosecond optical pulses, so-called femto-nanomagnons, leads to coherent longitudinal oscillations of the antiferromagnetic order parameter that cannot be described by a thermodynamic Landau-Lifshitz approach. We argue that this dynamics is triggered as a result of a laser-induced modification of the exchange interaction. In order to describe the oscillations we have formulated a quantum mechanical description in terms of magnon pair operators and coherent states. Such an approach allowed us to} derive an effective macroscopic equation of motion for the temporal evolution of the antiferromagnetic order parameter. An implication of the latter is that the photo-induced spin dynamics represents a macroscopic entanglement of pairs of magnons with femtosecond period and nanometer wavelength. By performing magneto-optical pump-probe experiments with 10 femtosecond resolution in the cubic KNiF$_3$ and the uniaxial K$_2$NiF$_4$ collinear Heisenberg antiferromagnets, we observed coherent oscillations at the frequency of 22 THz and 16 THz, respectively. The detected frequencies as a function of the temperature ideally fit the two-magnon excitation up to the N\'eel point. The experimental signals are described as dynamics of magnetic linear dichroism due to longitudinal oscillations of the antiferromagnetic vector.Comment: 25 pages, 10 figure

Contribution of <i>AGTR</i> 1 Promoter Region Polymorphism to the Progression and Outcome of Sepsis in Patients with Various Comorbidities

Blood pressure dysregulation and circulatory failure are major contributors to the progression of sepsis and especially septic shock. One of the genes affecting the vascular endothelium and arteriolar tone is the angiotensin II receptor 1 gene (AGTR1). The AGTR1 rs275651 single-nucleotide polymorphism is associated with the development of angina, high altitude pulmonary edema, and hypertension. The significance of the AGTR1 rs275651 polymorphism in sepsis, particularly in patients with significant comorbidity, has not been studied previously.The aim of the study was to determine the impact of AGTR1 functional polymorphism on sepsis outcome in patients with various comorbidities, including cardiovascular disease and type 2 diabetes mellitus.Material and methods. A prospective study included 144 ICU patients of two clinical hospitals in Moscow, aged 18-75 years with clinical signs of sepsis (Sepsis-3, 2016).Results. In the group of patients with cardiovascular diseases, carriers of the TT AGTR1 rs275651 genotype had a lower mortality rate compared with carriers of the A allele (25 deaths out of 33 versus 16 out of 16, respectively, P=0.041, Fisher's exact test; P=0.0019, log-rank test). In the group of patients with diabetes mellitus (n=62), we also found significant differences in sepsis outcome based on the AGTR1 rs275651 genotype variant. The subgroup of TT AGTR1 rs275651 genotype carriers demonstrated significantly lower mortality compared with TA, AA genotypes carriers (27 deaths out of 41 and 20 out of 21, respectively, P=0.012, Fisher's exact test; OR=10.37; 95% CI: 1.26 to 85.5; P&lt;0.0001, log-rank test).Conclusion. We found an association of the functional polymorphism AGTR1 -777 T&gt;A (rs275651) with sepsis outcome in ICU patients with high-value baseline comorbidity: carriers of the more common TT genotype had lower mortality compared to carriers of the minor A allele

Defects as a reason of continuity of normal-incommensurate phase transitions

Almost all normal-incommensurate phase transitions observed experimentally are continuous. We show that there is not any theoretical reason for this general behaviour in perfect crystals. A normal-incommensurate phase transition that is not too far from the mean-field tricritical point should be discontinuous and it is highly improbable that so far reported normal-incommensurate phase transitions lie very far from this point. To understand this behaviour we study influence of defects on a hypothetical first-order normal-incommensurate phase transition in a pure material. We have found that this influence is strikingly different from that on other kinds of first-order phase transitions. The change of the discontinuity of the order parameter at the transition is negative and formally diverges within our approximate theory. At the same time the diminishing of the phase transition temperature remains finite. We interpret these results as an indication that at least some of the observed seemingly second-order normal-incommensurate transitions would be first-order transitions in defectless crystals.Comment: 17 pages, 1 figur

Very high frequency gravitational wave background in the universe

Astrophysical sources of high frequency gravitational radiation are considered in association with a new interest to very sensitive HFGW receivers required for the laboratory GW Hertz experiment. A special attention is paid to the phenomenon of primordial black holes evaporation. They act like black body to all kinds of radiation, including gravitons, and, therefore, emit an equilibrium spectrum of gravitons during its evaporation. Limit on the density of high frequency gravitons in the Universe is obtained, and possibilities of their detection are briefly discussed.Comment: 14 page

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

Observations of water masses and circulation with focus on the Eurasian Basin of the Arctic Ocean from the 1990s to the late 2000s

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