53 research outputs found
Optical response of a titanium-based cold-electron bolometer
We present experimental results on the testing of cold-electron bolometer (CEB) detectors comprised of a thin Ti film absorber and two SIN junctions integrated with a planar antenna. The CEB performance was tested in a He-3 sorption cryostat HELIOX-AC-V at bath temperatures of 280-305 mK. The optical response was measured using the hot/cold load method by flipping a Cu reflector opposite a blackbody surface inside a 3 K shield and using a thermal source with variable temperature. In the first experiment, the detector chip was mounted in an optical sample-holder whose aperture was switched towards or away from a blackbody source changing the incident radiation temperature from 3 K to 270 mK. As a result, we measured the optical response to a 3 K/270 mK radiation temperature change. The measured voltage response value for the detector integrated in a double-dipole antenna was Delta V-out = 120 mu V. This corresponds to a noise equivalent power of NEP = V-n/(dV/dP) = 3.5 x 10(-17) W Hz(-1/2), where dV/dP is the voltage to power response obtained from the incoming power estimation based on the Planck formula
High-precision molecular dynamics simulation of UO2-PuO2: superionic transition in uranium dioxide
Our series of articles is devoted to high-precision molecular dynamics
simulation of mixed actinide-oxide (MOX) fuel in the rigid ions approximation
using high-performance graphics processors (GPU). In this article we assess the
10 most relevant interatomic sets of pair potential (SPP) by reproduction of
the Bredig superionic phase transition (anion sublattice premelting) in uranium
dioxide. The measurements carried out in a wide temperature range from 300K up
to melting point with 1K accuracy allowed reliable detection of this phase
transition with each SPP. The {\lambda}-peaks obtained are smoother and wider
than it was assumed previously. In addition, for the first time a pressure
dependence of the {\lambda}-peak characteristics was measured, in a range from
-5 GPa to 5 GPa its amplitudes had parabolic plot and temperatures had linear
(that is similar to the Clausius-Clapeyron equation for melting temperature).Comment: 7 pages, 6 figures, 1 tabl
Fabrication of nis and sis nanojunctions with aluminum electrodes and studies of magnetic field influence on iv curves
Samples of superconductor–insulator–superconductor (SIS) and normal metal–insulator– superconductor (NIS) junctions with superconducting aluminum of different thickness were fabricated and experimentally studied, starting from conventional shadow evaporation with a suspended resist bridge. We also developed alternative fabrication by magnetron sputtering with twostep direct e-beam patterning. We compared Al film grain size, surface roughness, resistivity deposited by thermal evaporation and magnetron sputtering. The best-quality NIS junctions with large superconducting electrodes approached a resistance R(0)/R(V2Δ) factor ratio of 1000 at 0.3 K and over 10,000 at 0.1 K. At 0.1 K, R(0) was determined completely by the Andreev current. The contribution of the single-electron current dominated at V > VΔ/2. The single-electron resistance extrapolated to V = 0 exceeded the resistance R(V2Δ) by 3
7 109. We measured the influence of the magnetic field on NIS junctions and described the mechanism of additional conductivity due to induced Abrikosov vortices. The modified shape of the SINIS bolometer IV curve was explained by Joule overheating via NIN (normal metal–insulator–normal metal) channels
Non-Thermal Absorption and Quantum Efficiency of SINIS Bolometer
We study mechanisms of absorption in two essentially different types of superconductor-insulator-normal metal-insulator-superconductor (SINIS) bolometers with absorber directly placed on Si wafer and with absorber suspended above the substrate. The figure of merit for quantum photon absorption is quantum efficiency equal to the number of detected electrons for one photon. The efficiency of absorption is dramatically dependent on phonon losses to substrate and electrodes, and electron energy losses to electrodes through tunnel junctions. The maximum quantum efficiency can approach n = hf/kT = 160 at f = 350 GHz T = 0.1 K, and current responsivity dI/dP = e/kT in quantum gain bolometer case, contrary to photon counter mode with quantum efficiency of n = 1 and responsivity dI/dP = e/hf. In experiments, we approach intrinsic quantum efficiency up to n = 80 electrons per photon in bolometer with suspended absorber, contrary to quantum efficiency of about one for absorber on the substrate. In the case of suspended Cu and Pd absorber, Kapitsa resistance protect from power leak to Al electrodes
ATTACK DETECTION IN ENTERPRISE NETWORKS BY MACHINE LEARNING METHODS
Detection of network attacks is currently one of the most important problems of secure use of enterprise networks. Network signature-based intrusion detection systems cannot detect new types of attacks. Thus, the urgent task is to quickly classify network traffic to detect network attacks. The article describes algorithms for detecting attacks in enterprise networks based on data analysis that can be collected in them. The UNSW-NB15 data set was used to compare machine learning methods for classifying attack or-normal traffic, as well as to identify nine more popular classes of typical attacks, such as Fuzzers, Analysis, Backdoors, DoS, Exploits, Generic, Reconnaissance, Shellcode and Worms. Balanced accuracy is used as the main metric for assessing the accuracy of the classification. The main advantage of this metric is an adequate assessment of the accuracy of classification algorithms given the strong imbalance in the number of marked records for each class of data set. As a result of the experiment, it was found that the best algorithm for identifying the presence of an attack is RandomForest, to clarify its type - AdaBoost
Public participation in planning a comfortable urban environment on the example of the Arkhangelsk region
The article analyzes the experience of public participation in the planning of a comfortable urban environment. The forms of public involvement in the formation of a comfortable urban environment and their implementation are considered on the example of the Arkhangelsk region. The method of complex analysis of the theory and practice of public communications helps the article to present a qualitative as-sessment of public involvement in the improvement of the urban environment. It is shown that the existing methods of interaction between the authorities and citizens represent a one-sided process and often they are reduced to the formal fulfillment of legal requirements by municipalities. To improve the efficiency of public participation, the authors propose to develop a communicative model of urban space management based on constant interaction between municipal authorities and citizens. This model will allow establishing a dialogue between all stakeholders, which will ultimately lead to the successful implementation of the urban environmental program and improve the quality of life of citizens
Colossal magnetoresistance in EuZnP and its electronic and magnetic structure
We investigate single crystals of the trigonal antiferromagnet EuZnP
() by means of electrical transport, magnetization
measurements, X-ray magnetic scattering, optical reflectivity, angle-resolved
photoemission spectroscopy (ARPES) and ab-initio band structure calculations
(DFT+U). We find that the electrical resistivity of EuZnP increases
strongly upon cooling and can be suppressed in magnetic fields by several
orders of magnitude (CMR effect). Resonant magnetic scattering reveals a
magnetic ordering vector of , corresponding to an
-type antiferromagnetic (AFM) order, below . We
find that the moments are canted out of the plane by an angle of about
degrees and tilted away from the [100] - direction
by . We observe nearly isotropic magnetization
behavior for low fields and low temperatures which is consistent with the
magnetic scattering results. The magnetization measurements show a deviation
from the Curie-Weiss behavior below , the temperature below
which also the field dependence of the material's resistivity starts to
increase. An analysis of the infrared reflectivity spectrum at
allows us to resolve the main phonon bands and intra-/interband transitions,
and estimate indirect and direct band gaps of
and ,
respectively, which are in good agreement with the theoretically predicted
ones. The experimental band structure obtained by ARPES is nearly
-independent above and below . The comparison of the theoretical
and experimental data shows a weak intermixing of the Eu 4 states close to
the point with the bands formed by the phosphorous 3 orbitals
leading to an induction of a small magnetic moment at the P sites
Site- and spin-dependent coupling at the highly ordered h-BN/Co(0001) interface
Using photoelectron diffraction and spectroscopy, we explore the structural and electronic properties of the hexagonal boron nitride (h-BN) monolayer epitaxially grown on the Co(0001) surface. Perfect matching of the lattice parameters allows formation of a well-defined interface where the B atoms occupy the hollow sites while the N atoms are located above the Co atoms. The corrugation of the h-BN monolayer and its distance from the substrate were determined by means of R-factor analysis. The obtained results are in perfect agreement with the density functional theory (DFT) predictions. The electronic structure of the interface is characterized by a significant mixing of the h-BN and Co states. Such hybridized states appear in the h-BN band gap. This allows to obtain atomically resolved scanning tunneling microscopy (STM) images from the formally insulating 2D material being in contact with ferromagnetic metal. The STM images reveal mainly the nitrogen sublattice due to a dominating contribution of nitrogen orbitals to the electronic states at the Fermi level. We believe that the high quality, well-defined structure and interesting electronic properties make the h-BN/Co(0001) interface suitable for spintronic applications.L.V.Ya. acknowledges the RSF (Grant No. 16-42-01093). A.V.T., V.O.S., K.A.B., O.Yu.V., and D.Yu.U. acknowledge St. Petersburg State University for research Grant No. 11.65.42.2017. M.V.K. and I.I.O. acknowledge the RFBR (Grant No. 16-29-06410). C.L. acknowledges the DFG (Grant Nos. LA655-17/1 and LA655-19/1).Peer reviewe
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