66 research outputs found
Improved ring potential of QED at finite temperature and in the presence of weak and strong magnetic field
Using the general structure of the vacuum polarization tensor
in the infrared (IR) limit, , the
ring contribution to QED effective potential at finite temperature and non-zero
magnetic field is determined beyond the static limit, . The resulting ring potential is then studied in
weak and strong magnetic field limit. In the limit of weak magnetic field, at
high temperature and for , the improved ring potential consists of
a term proportional to , in addition to the expected
term arising from the static limit. Here, is the
fine structure constant. In the limit of strong magnetic field, where QED
dynamics is dominated by the lowest Landau level (LLL), the ring potential
includes a novel term consisting of dilogarithmic function
. Using the ring improved
(one-loop) effective potential including the one-loop effective potential and
ring potential in the IR limit, the dynamical chiral symmetry breaking of QED
is studied at finite temperature and in the presence of strong magnetic field.
The gap equation, the dynamical mass and the critical temperature of QED in the
regime of LLL dominance are determined in the improved IR as well as in the
static limit. For a given value of magnetic field, the improved ring potential
is shown to be more efficient in decreasing the critical temperature arising
from one-loop effective potential.Comment: V1: 39 pages, 2 figures, 2 tables, LaTeX format; V2: 53 pages, 3
figures, 1 table, Sect. IV revised, results are unchanged, 3 appendices and
references added, version accepted for publication in Phys. Rev.
Hospital outbreak of carbapenem-resistant Enterobacterales associated with a bla OXA-48 plasmid carried mostly by Escherichia coli ST399
A hospital outbreak of carbapenem-resistant Enterobacterales was detected by routine surveillance. Whole genome sequencing and subsequent analysis revealed a conserved promiscuous blaOXA-48 carrying plasmid as the defining factor within this outbreak. Four different species of Enterobacterales were involved in the outbreak. Escherichia coli ST399 accounted for 35 of all the 55 isolates. Comparative genomics analysis using publicly available E. coli ST399 genomes showed that the outbreak E. coli ST399 isolates formed a unique clade. We developed a mathematical model of pOXA-48-like plasmid transmission between host lineages and used it to estimate its conjugation rate, giving a lower bound of 0.23 conjugation events per lineage per year. Our analysis suggests that co-evolution between the pOXA-48-like plasmid and E. coli ST399 could have played a role in the outbreak. This is the first study to report carbapenem-resistant E. coli ST399 carrying blaOXA-48 as the main cause of a plasmid-borne outbreak within a hospital setting. Our findings suggest complementary roles for both plasmid conjugation and clonal expansion in the emergence of this outbreak
Photocurrent in strontium titanate films on silicon substrates
Using the sol-gel method, strontium titanate films were prepared
(strontium titanate xerogels) on monocrystalline silicon substrates at 750°C
annealing temperature. Nickel upper electrodes were deposited by
magnetron sputtering, and the current–voltage characteristics were
measured for the prepared structures with two upper electrodes and a
Schottky barrier. Significant changes in the current–voltage characteristics
were observed after illuminating the diode structure with a halogen lamp
characterized by 57 mW/cm2 intensity and 3123°C color temperature of the
tungsten filament. For a 65-nm thick strontium titanate film under reverse
bias voltage of –3 V the photocurrent is 80 μA, whereas without illumination
the reverse current is close to zero. Under direct illumination and a voltage
of 3 V the photocurrent is 190 μA, while without illumination the current
does not exceed 22.5 μA
Low-resistance and high-resistance states in strontium titanate films formed by the sol–gel method
A change in the resistance of strontium titanate structures formed by
the sol–gel method has been demonstrated. The transition of a strontium
titanate film with a thickness of about 300 nm from the highresistance to
low-resistance state occurs when the bias voltage on the silicon/titanium
dioxide/platinum/strontium titanate/nickel capacitor structure reaches the
values of about 10 V. The resistance changes from several ohms to several
tens of kiloohms. For a thicker film (~400 nm), the switching voltage
increases while the resistance of the structure in the high-resistance state
reaches several hundreds of kiloohms. Supposedly, the main role in
changing the resistance is played by deep levels whose population changes
by the applied voltage. The prospects for the application of strontium
titanate films in memory memristor elements have been discussed
Optical characteristics of strontium titanate films formed by sol-gel method on quartz substrates
The transmission spectra of films of strontium titanate up to 200 nm thick produced on quartz glass substrates by the sol-gel method were investigated in the region of 200–1100 nm. The sol was prepared from strontium acetate, titanium tetraisopropoxide, acetic acid, and ethylene glycol monomethyl ether. The strontium titanate films were formed by successive deposition of five layers with intermediate drying of each layer and final heat treatment at temperatures in the range of 500–700oC. From analysis of the transmission spectra it was established that the obtained films are characterized by a wide forbidden band decreasing from 4.46 to 3.84 eV in the transition from x-ray amorphous films to crystalline films with refractive index of 1.996 (λ = 620 nm) due to the high packing density of up to 81.5% of that for monocrystalline strontium titanate
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