Accurate low temperature charge transport measurements in combination with high-precision x-ray diffraction experiments have allowed detection of the symmetry lowering in the single domain ...Tm0.19Yb0.81B12 crystals that belong to the family of dodecaborides with metal-insulator transition. Based on the fine structure analysis we discover the formation of dynamic charge stripes within the semiconducting matrix of Tm0.19Yb0.81B12. The charge dynamics in these conducting nano-size channels is characterized by broad-band optical spectroscopy that allowed estimating the frequency (~2.4 × 1011 Hz) of quantum motion of the charge carriers. It is suggested that cooperative Jahn-Teller effect in the boron sublattice is a cause of the large-amplitude rattling modes of the Tm and Yb ions responsible for the 'modulation' of the conduction band along one of the directions through the variation of 5d-2p hybridization of electron states.
The research is focused on the ignition of solid fuels in a heated air flow. The experimental conditions correspond closely to solid fuel combustion in coal-fired boiler furnaces. Charcoal, wood, ...brown and bituminous coals were used as independent solid fuels and as fuel mixture components. The particle sizes of these fuels were less than 40 μm, 40–140 μm, 140–250 μm, 250–375 μm and 375–800 μm. They were ignited under the conditions of radiant-convective heating as they were moving in a heated air flow with a temperature of 500–800 °C and at a velocity of 5 m/s. The ignition delay time was the main investigated characteristic, recorded by a high-speed video camera. The induction period of bituminous coal shortens by 25–35% when 25–50% brown coal or wood in an air-dry state is added. The lowest ignition delay times were established for the fuel mixtures of bituminous coal with dry charcoal. The experimental curves of the ignition delay times of fuels and their mixtures versus the heated air temperature were presented as approximation equations. Based on the conducted research findings, a muffle burner design with a vortex structure of the fuel-air flow was proposed for the fuel oil-free start-up of coal-fired boilers.
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•Oil-free start-up of coal-fired boilers can be put into practice.•Adding 25–50% of highly reactive components to the main solid fuel reduces ignition time by 25–35%.•Particle size of fuel mixtures should not exceed 250 μm.•They are reliably ignited within 0.1–0.2 s at an oxidizer flow temperature of 500–800 °C.•Design of a burner unit for fuel oil-free start-up of a coal-fired boiler was proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Randomness and frustration are believed to be two crucial criteria for the formation of spin glass state. However, the spin freezing occurs in some well-ordered crystals below the related ...temperature
T
f
due to the instability of each spin state, which induces the variation of either magnetic moment value or exchange energy. Here we explore the new mechanism of the in-site originated disorder in antiferromagnets Gd
0.73
La
0.27
B
6
and GdB
6
, which is caused by the random mutual shifts of Gd
3+
spins from the centrally symmetrical positions in the regular cubic lattice. The universal scaling of ESR linewidth temperature dependencies to the power law
ΔH
(
T
) ~ ((
T
−
T
D
)
/T
D
)
α
with
α
= − 1.1 ± 0.05 in the paramagnetic phase of both compounds demonstrates the identity of the origin of magnetic randomness. In Gd
0.73
La
0.27
B
6
the resulting random spin configurations freeze at
T
f
≈ 10.5 K where the maximum of magnetization is observed. Below
T
f
the splitting of ZFC and FC magnetization curves takes place as well as the magnetic state depends on the antecedent sample history. In the case of GdB
6
the coherent displacement of Gd ions compete with these random shifts forming an antiferromagnetic (AFM) phase at
T
N
= 15.5 K, which prevails over the spin freezing at
T
f
≈ 13 K, expected from the ESR data. The observation of the hysteresis of the ESR spectrum in the AFM phase suggests that its properties may be determined by the competition of two types of AFM orders, which results in formation of stable magnetic domains with nonequivalent positions of AFM Gd pairs at
T
< 10 K.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Methods of preparing heterogeneous gel fuels have been elaborated on the basis of oil-free and oil-filled cryogels, containing coal dust particles with a size no more than 140μm. Mechanical ...properties of 20-mm fuel pellets have been analyzed. The ignition mechanisms of heterogeneous gel fuels have been experimentally discovered in a high-temperature (600–1000°C) oxidizer medium, and the influence of the initial fuel temperature (from −85 to 20°C) on the fuel ignition characteristics has been researched. The multi-component composition of the oil-filled cryogels with coal dust particles is the reason for microexplosions that leads to the fuel sample dispersion and intensification both the ignition and burnout. Such fuel compositions are characterized by 1.5–2-fold lower ignition delay times (1–6s vs. 2–12s) than the compositions based on cryogels containing only coal particles, other things being equal.
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•We prepared gel fuels based on oil-free and oil-filled cryogels containing coal dust particles.•Ignition mechanisms of gel fuels in a high-temperature air medium were established.•It combines processes that occur during metal dust explosion and combustion of single coal particle.•The microexplosions intensify both the ignition and burnout of oil-filled cryogels.•Initial fuel temperature from −85 to 20°С was found to affect ignition characteristics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Lateral distribution functions of particles in extensive air showers with the energy
eV recorded by ground-based and underground scintillation detectors with a threshold of
GeV at the Yakutsk array ...during the continuous observations from 1986 to 2016 have been analyzed using events with zenith angles θ ≤ 60°. Experimental functions have been compared to the predictions obtained with the QGSJet-01-d hadron interaction model by applying the CORSIKA code. The entire dataset indicates that cosmic rays consist predominantly of protons.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We report a measurement of the neutron lifetime using ultracold neutrons stored in a magneto-gravitational trap made of permanent magnets. Neutrons surviving in the trap after fixed storage times ...have been counted and the trap losses have continuously been monitored during storage by detecting neutrons leaking from the trap. The value of the neutron lifetime resulting from this measurement is τ
n
= (878.3 ± 1.6
stat
± 1.0
syst
) A unique feature of this experiment is the monitoring of leaking neutrons providing a robust control of the main systematic loss.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
Introducing of topological insulator concept for fluctuating valence compound – samarium hexaboride – has recently initiated a new round of studies aimed to clarify the nature of the ground ...state in this extraordinary system with strong electron correlations. Here we discuss the data of magnetic resonance in the pristine single crystals of SmB
6
measured in 60 GHz cavity experiments at temperatures 1.8–300 K. The microwave study as well as the DC resistivity and Hall effect measurements performed for the different states of SmB
6
110 surface prove definitely the existence of the layer with metallic conductivity increasing under lowering temperature below 5 K. Four lines with the g-factors g ≈ 2 are found to contribute to the ESR-like absorption spectrum that may be attributed to intrinsic paramagnetic centers on the sample’s surface, which are robust with respect to the surface treatment. The temperature dependence of integrated intensity
I
(
T
) for main paramagnetic signal is found to demonstrate anomalous critical behavior
I
(
T
) ~ (
T
*
−
T
)
ν
with characteristic temperature
T
*
= 5.34 ± 0.05 K and exponent ν = 0.38 ± 0.03 indicating possible magnetic transition at the SmB
6
110 surface. Additional resonant magnetoabsorption line, which may be associated with either donor-like defects or cyclotron resonance mode corresponding to the mass
m
c
~ 1.2
m
0
, is reported.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The consistent relativistic energy approach to atoms in a strong realistic laser field, based on the Gell-Mann and Low S-matrix formalism, is applied in the study of resonant multiphoton ionization ...of krypton by intense uv laser radiation and for the computation of the resonance shift and width in krypton. The approach to the treatment of the multiphoton resonances in nuclei is outlined for the 57Fe nucleus.
The lateral distribution of particles in extensive air showers from cosmic rays with energy above 10
17
eV registered at the Yakutsk complex array was analyzed. Experimentally measured particle ...densities were compared to the predictions obtained within frameworks of three ultra-high energy hadron interaction models. The cosmic ray mass composition estimated from the readings of surface-based and underground detectors of the array is consistent with estimations obtained from measurements of lateral distribution of the air showers Cherenkov light emission. A comparison was made with the results of direct measurement of the muon component performed at the Pierre Auger Observatory. It is demonstrated that the densities of muon flux measured at Yakutsk array are consistent with results of fluorescent light measurements and disagree with results on muons obtained at the Auger array.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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