HoFe1-xMnxO3 (0 < x < 1) single crystals have been grown by the optical floating zone technique. A structural transition from the orthorhombic to hexagonal modification has been established in the ...crystals in the concentration range of 0.7-0.8, which has been confirmed by the X-ray diffraction data. For a series of the rhombic crystals, the room-temperature Mossbauer study and magnetic measurements in the temperature range of 4.2-1000 K have been carried out. It has been observed that, with an increase in the manganese content in the samples, the temperature of the spin-reorientation transition increases significantly: from 60 K in the HoFeO3 compound to room temperature in HoFe0.6Mn0.4O3. The magnetic measurements have shown that, upon substitution of manganese for iron, the magnetic orientational type transition changes from a second-order transition (AxFyGz -> CxGyFz) to first-order one (AxFyGz -> GxCyAz) with a weak ferromagnetic moment only in the b direction (for Pnma notation). The growth of the spin-reorientation transition temperature has been attributed to the change in the value of the indirect exchange in the iron subsystem under the action of manganese, which has been found when studying the Mossbauer effect in the HoFe1-xMnxO3 (x < 0.4) compound.
In order to clarify the mechanism of hysteretic behavior of magnetoresistance of granular HTSC the magnetoresistance curves R(H) and time evolution of the resistance in constant applied magnetic ...fields have been studied in granular YBCO at T=77 K. It was found that on ascending branch of R(H) dependence the resistance at H=const decreased with time while on the descending branch the resistance increased with time in applied constant magnetic field. For the range of low magnetic fields (below the minimum point of the descending branch of R(H) dependence) the resistance at H=const decreased again. The behavior observed is well described by the model of granular HTSC, where the intergrain space is in effective magnetic field which is the superposition of the applied field and the field induced by superconducting grains. The time evolution of resistance reflects processes of time relaxation of magnetization of HTSC grains due to the intragrain flux creep.
The time evolution of the magnetoresistance of bulk YBCO + CuO composites at
T
=
4.2
K
in constant applied magnetic fields was studied to clarify the mechanism of hysteretic behavior of ...magnetoresistance
R
(
H
)
of granular HTSC. The composites represent “model” granular HTSC with weakened Josephson coupling between superconducting (YBCO) crystallites. It was found for the first time that on the ascending branch of
R
(
H
)
dependence, the resistance at
H
=
const
decreased with time while on the descending branch, the resistance increased with time in an applied constant magnetic field. In the range of low magnetic fields (below the minimum point of the descending branch of the R(H) dependence), the resistance at
H
=
const
decreased again. Similar measurements performed on pure polycrystalline YBCO at
T
=
77.4
K
have shown that the behavior of evolution of resistance with time is similar to that observed for the composite. This proves the peculiarity of time evolution of magnetoresistance to be a common feature of granular HTSCs. The behavior revealed is well described by the model of granular HTSC, where the intergrain media is in an effective magnetic field which is the superposition of the external field and the field induced by superconducting grains. The time evolution of resistance reflects the time relaxation of magnetization of HTSC grains due to the intragrain flux creep processes.
Hysteresis and relaxation of magnetoresistance and magnetization of substituted (La
0.5
Eu
0.5
)
0.7
Pb
0.3
MnO
3
lanthanum manganite in a low-temperature region (<40 K) are investigated. It is shown ...that at these temperature features of the magnetoresistive effect are determined mainly by spin-dependent tunnelling of carriers via insulating grain boundaries. As was demonstrated previously, the grain boundaries may be antiferromagnetically ordered. Therefore, relaxation of magnetization and resistance is determined by the processes of relative orientation of the magnetic moments of ferromagnetic domains neighbouring the antiferromagnetic boundary of ferromagnetic domains under the action of temperature fluctuations. It is shown that relaxation follows the logarithmic law within the time interval
t
∼ 10
2
–3×10
3
s. A comparison between time evolutions of the magnetic moment and resistance shows that magnetoresistance and magnetization are related as δ
R
= δ
M
n
, where
n
= 2.5. The obtained value
n
is close to the characteristic value
n
= 2 for tunnel magnetoresistance of granular
ferromagnetic metal/insulator
systems.
The article describes the materials on the development of intelligent algorithms, hardware and software configuration of information-measuring system that automates the stand for the operational life ...testing of hydraulic machines - oil sediment and motors. The cRIO was selected as a basic hardware platform with a set of input-output modules interacting with a personal computer via Ethernet interface to start the test and display the results. The intelligence of the system is provided by the implementation of artificial neural networks that analyze the stand values and make decisions on its operation.
Large differences in the composition of diet between early development and adulthood can have detrimental effects on obesity risk. We examined the effects of an intermittent high fat/sucrose diet ...(HFS) on satiety hormone and serum metabolite response in disparate diets. Wistar rat pups were fed control (C), high prebiotic fiber (HF) or high protein (HP) diets (weaning to 16 weeks), HFS diet challenged (6 weeks), and finally reverted to their respective C, HF, or HP diet (4 weeks). At conclusion, measurement of body composition and satiety hormones was accompanied by 1H NMR metabolic profiles in fasted and postprandial states. Metabolomic profiling predicted dietary source with >90% accuracy. The HF group was characterized by lowest body weight and body fat (P < 0.05) and increased satiety hormone levels (glucagon-like peptide 1 and peptide-YY). Regularized modeling confirmed that the HF diet is associated with higher gut hormone secretion that could reflect the known effects of prebiotics on gut microbiota and their fementative end products, the short chain fatty acids. Rats reared on a HF diet appear to experience fewer adverse effects from an intermittent high fat diet in adulthood when rematched to their postnatal diet. Metabolite profiles associated with the diets provide a distinct biochemical signature of their effects.
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