166 research outputs found
On the backreaction issue for the black hole in de Sitter space-time
We consider quantum real massive scalar field in the de Sitter-Schwarzschild
space-time backround. To have an analytic head way we study in detail the
two-dimensional case, assuming that the situation in four dimensions will not
be much different conceptually. It is assumed, that quantum field is in a
thermal state i.e. described by the planckian distribution for the exact modes
in the geometry under consideration. We calculate approximately the expectation
value of stress-energy tensor near the cosmological and black hole horizons. It
is shown that for a generic temperature backreaction from quantum fields on the
geometry cannot be neglected. Thus, de Sitter-Schwarzschild space-time geometry
inevitably is strongly modified by the quantum fluctuations of the matter
fields.Comment: 10 pages, references, comments and calculation details adde
New phase structure of the Nambu -- Jona - Lasinio model at nonzero chemical potential
It is shown that in the Nambu -- Jona - Lasinio model at nonzero chemical
potential there are two different massive phases with spontaneously broken
chiral symmetry. In one of them particle density is identically zero, in
another phase it is not equal to zero. The transition between phases is a phase
transition of the second order.Comment: 8 pages, LaTeX, no figures
Benchmarking of 3D space charge codes using direct phase space measurements from photoemission high voltage DC gun
We present a comparison between space charge calculations and direct
measurements of the transverse phase space for space charge dominated electron
bunches after a high voltage photoemission DC gun followed by an emittance
compensation solenoid magnet. The measurements were performed using a
double-slit setup for a set of parameters such as charge per bunch and the
solenoid current. The data is compared with detailed simulations using 3D space
charge codes GPT and Parmela3D with initial particle distributions created from
the measured transverse and temporal laser profiles. Beam brightness as a
function of beam fraction is calculated for the measured phase space maps and
found to approach the theoretical maximum set by the thermal energy and
accelerating field at the photocathode.Comment: 11 pages, 23 figures. submitted to Phys Rev ST-A
Synthesis, crystal structure, and thermal stability of double borate Na3ErB2O6
Received: 05.10.2021. Revised: 18.10.2021. Accepted: 18.10.2021. Available online: 20.10.2021.Double borate Na3ErB2O6 was synthesized by the solid-state reaction. The crystal structure of Na3ErB2O6 was refined by the Rietveld method: P21/c, a = 6.49775(14) Å, b = 8.50424(17) Å, c = 12.0067(3) Å, β = 118.4797(9)°, Z = 4. The crystal structure of Na3ErB2O6 consists of –[ErO6]∞-chains along the "b" axis, which are linked by BO3 triangles in a three-dimensional framework. Sodium atoms occupy empty positions inside the channels. The thermal behavior of Na3ErB2O6 was studied in detail in the range of 25–1150 °C range by DSC and TG methods. Na3ErB2O6 congruently melts at 1116 °C. Based on the results of DSC measurements, three reversible phase transitions were found for Na3ErB2O6.The work was supported by Basic Project of BINM SB RAS № 0273-2021-0008. X-ray powder diffraction and thermal analysis were obtained using the equipment of the Collective Use Center BINM SB RAS
Beam-Breakup Instability Theory for Energy Recovery Linacs
Here we will derive the general theory of the beam-breakup instability in
recirculating linear accelerators, in which the bunches do not have to be at
the same RF phase during each recirculation turn. This is important for the
description of energy recovery linacs (ERLs) where bunches are recirculated at
a decelerating phase of the RF wave and for other recirculator arrangements
where different RF phases are of an advantage. Furthermore it can be used for
the analysis of phase errors of recirculated bunches. It is shown how the
threshold current for a given linac can be computed and a remarkable agreement
with tracking data is demonstrated. The general formulas are then analyzed for
several analytically solvable cases, which show: (a) Why different higher order
modes (HOM) in one cavity do not couple so that the most dangerous modes can be
considered individually. (b) How different HOM frequencies have to be in order
to consider them separately. (c) That no optics can cause the HOMs of two
cavities to cancel. (d) How an optics can avoid the addition of the
instabilities of two cavities. (e) How a HOM in a multiple-turn recirculator
interferes with itself. Furthermore, a simple method to compute the orbit
deviations produced by cavity misalignments has also been introduced. It is
shown that the BBU instability always occurs before the orbit excursion becomes
very large.Comment: 12 pages, 6 figure
Who is in the driver's seat in 8p12 amplifications? ZNF703 in luminal B breast tumors
Two recent reports identify ZNF703 as an oncogene driving selection of frequent chromosome 8p12 amplifications in luminal B breast tumors. The estrogen-responsive ZNF703 gene encodes a transcriptional cofactor that, when overexpressed, induces cell proliferation and interferes with transforming growth factor beta signaling. In MCF7 cells, increased ZNF703 expression results in activation of genes involved in stem cell self-renewal - while in primary human mammary epithelial cells, ZNF703 increases the ratio of luminal to basal progenitors. Expression of the murine homolog of ZNF703 reduces cell adhesion and promotes metastasis. ZNF703 overexpression thus alters regulation of proliferation and differentiation in luminal B tumors
Phylogenetic analysis of the microbial mat in the hot spring Garga (Baikal rift zone) and the diversity of natural peptidases
Hydrolytic bacteria (in particular, proteolytics) are the primary destructors in hot springs. The proteolytic bacteria are able to secrete enzymes that are active in wide ranges of pH and temperature. The aim of this work was to study the taxonomic composition, the structure of the bacterial microbial mat, and to study the distribution of peptidases in the thermophilic microbial Garga community. For the study, we sampled the microbial mat at a water temperature of 54.2 °C and a pH of 8.3. Hydrochemical analysis of water showed a high content of sulfates, 390 mg/dm3. The microelement composition of water showed that the Garga water had increased concentrations of B, Rb, Li, Ba, Sr. We analyzed the taxonomic diversity of the microbial community in the hot spring Garga at a temperature zone of 54 °C. The structure of the microbial mat is represented by various phylogenetic groups of mesophilic and thermophilic bacteria, with various metabolic and ecological functions. The dominant group in this community was the phylum Firmicutes (64 %). The analysis of the collected metagenomic sequences of the microbial community allowed the detected peptidases in the microbial community in the hot spring Garga to be for the first time systematized and characterized. Comparisons of metagenomic sequences of representative data showed a dominance of serine peptidase class enzymes. Natural peptidases in the investigated microbial community ensure the hydrolysis of biopolymers at the first stages of the destruction of organic matter and may have biotechnological relevance
Exploration of structural, thermal, vibrational and spectroscopic properties of new noncentrosymmetric double borate Rb3NdB6O12
New noncentrosymmetric rare earth borate Rb3NdB6O12 is found in the ternary system Rb2O–Nd2O3–B2O3. The Rb3NdB6O12 powder was fabricated by solid state synthesis at 1050 K for 72 h and the crystal structure was obtained by the Rietveld method. Rb3NdB6O12 crystallized in space group R32 with unit cell parameters a = 13.5236(4), c = 31.162(1) Å, Z = 3. From DSC measurements, the reversible phase transition (I type) in Rb3NdB6O12 is observed at 852–936 K. The 200 μm thick tablet is transparent over the spectral range of 0.3–6.5 μm and the band gap is found as Eg ∼ 6.29 eV. Nonlinear optical response of Rb3NdB6O12 tested via SHG is estimated to be higher than that of K3YB6O12. Blue shift of Nd luminescent lines is found in comparison with other borates. The vibrational parameters of Rb3NdB6O12 are evaluated by experimental methods
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