New approach of phosphate–sulfate synthesis, preventing sulfur elimination was proposed. It implies sulfur encasement into intermediate with heightened thermal resistance, thus the synthesis ...temperature of phosphate–sulfate could be increased, and crystallization can be performed. This method is considered to be capable by example of obtaining of Pb
2/3
FeZr(PO
4
)
7/3
(SO
4
)
2/3
ceramic. It was synthesized by means of sol–gel method via formation of intermediate PbSO
4
, which encased sulfur and eventually led to formation of mentioned before phosphate–sulfate. Obtained sample was characterized via X-ray, IR, combined DTA–TG, SEM and microprobe electron analysis. Crystal structure and unit cell parameters were derived from least-squares refinement of powder X-ray diffraction data (NZP-type, sp. gr.
R
3
¯
c
,
a
= 8.6339 Å,
c
= 23.2991 Å, V = 1504.1 Å
3
). Thermal expansion (
α
a
= 0.96·10
−6
,
α
c
= 3.24·10
−6
,
α
av
= 1.76·10
−6
K
−1
) of compound also has been studied. There is a wide area of interest, due to development of ceramics with low thermal expansion.
Graphical Abstract
—
This paper presents results of investigation of core–clad optical fibers based on rare-earth-doped multicomponent chalcogenide glasses of the Ge–Ga(In)–As(Sb)–Se systems. Optical, emission, and ...lasing characteristics of such fibers in the IR spectral region demonstrate advantages of their materials over foreign analogues owing to low concentrations of regulated impurities.
The influence of rare earth dopant concentration on selenide laser glass quality was investigated. A problem to be solved was identified – an increase in rare earth doping level leads to optical ...losses due to light scattering by heterogeneous inclusions and to the decrease of the optical damage threshold. The room temperature laser system consisting of 4.6 μm pulsed Fe:ZnSe pump laser and Ce3+:Ge20Sb10Ga5Se65 bulk glass was demonstrated. The slope efficiency of Ce3+:glass laser with respect to the absorbed pump energy reached 25% with a maximum output energy of 45 mJ.
Features of the molecular beam epitaxy growth of the AlSb/InAs heterostructures with a high-mobility two-dimensional electron gas for microwave transistors with ultralow power consumption are ...described. The main stages of fabrication of the transistors based on the AlSb/InAs heterostructures are outlined. The drain and drain–gate characteristics of the transistors are reported and discussed.
—
The crystallization kinetics of extrapure bismuth-doped Ge–S glasses, GeS
x
〈
n
Bi〉 (1.25 ≤
х
≤ 1.6,
n
= 1 at %), have been studied by differential scanning calorimetry (DSC) in the range 320–1000 ...K. A technique proposed for analysis of crystallization peaks offers the possibility of describing them with an accuracy comparable to that of the Erofeev semiempirical model and includes analytical expressions for the degree of crystallization, α(
t,
Т
), further developing a simplified version of the Kolmogorov–Johnson–Mehl theory. The kinetic characteristics of glass crystallization in α(
t,
Т
) found using this technique and graphical representation of the data in the form of a time–temperature–transition (TTT) diagram make it possible to optimize the optical fiber drawing temperature and time.
Compounds Mn
0.5
Ti
2
(PO
4
)
3
and Mn
0.5
Zr
2
(PO
4
)
3
and Mn
0.5+2
x
Zr
2 –
x
(PO
4
)
3
(0 <
x
≤0.35) solid solution were prepared by two variants of the sol-gel method using inorganic and ...organic reagents and were characterized using X-ray diffraction and IR spectroscopy. Mn
0.5
Ti
2
(PO
4
)
3
, a compound with an NaZr
2
(PO
4
)
3
(NZP) structure, is formed at 600°C and is stable up to 950°C. Mn
0.5
Zr
2
(PO
4
)
3
has dimorphism; its low-temperature phase having the Sc
2
(WO
4
)
3
(SW) structure was prepared at 650°C, and the high-temperature NZP phase, at 1200°C. Mn
0.5
+
2
x
Zr
2−
x
(PO
4
)
3
solid solution crystallizes in an SW-type structure; it is thermally unstable at temperatures above 900°C. The thermal stability of samples decays as
x
rises. p The numbers of the stretching and bending vibrations in an
PO
4
3
−
ion in the IR spectra of NZP and SW ortho-phosphates agree with factor-group analysis for space group
R
3̅ and
P
2
1
/
n
. Structure refinement was carried out for the low-temperature Mn
0.5
Zr
2
(PO
4
)
3
phase (space group P2
1
/
n, a
= 8.861(3) Å,
b
= 8.869(2) Å,
c
= 12.561(3) Å, β = 89.51(2)°) and for the solid solution. The basis of the structures is a framework built of corner-sharing tetrahedra PO
4
and octahedra ZrO
6
or (Mn,Zr)O
6
. The framework interstices are occupied by cations Mn
2
+ in tetrahedral oxygen coordination. A comparative crystal-chemical analysis of the morpho-tropic series of M
0.5
Zr
2
(PO
4
)
3
phosphates (M stands for a metal in the oxidation state +2) elucidated a relationship between structural features.
It has been established that rare earth elements (REE), as alloying additives, are a significant source of hydrogen and oxygen impurity in glasses of Ge – S and Ge – As – S systems. A method has been ...developed that includes loading germanium in the form of monosulfide and high-temperature annealing of REE and their compounds in sulfur vapor, reducing content of absorbing impurities in sulfide-germanium glasses. Samples of especially pure glasses of Ge42.5S57.5 and Ge35As10S55 composition doped with praseodymium up to 1450 ppm(at) were prepared. The impurity content of hydrogen and oxygen in the form of SH-groups and Ge–O in the best glass samples was 0.02–0.06 ppm(wt) and <0.1– 0.2 ppm(wt), respectively. The absorption coefficients and the absorption cross section were determined for various energy states of the Pr3+ ion in Ge35As10S55 glass. The luminescence intensity of Pr3+ ions in the spectral ranges 2.0–2.8 and 3.5–5.8 µm in Ge42.5S57.5 glasses is by 3 orders of magnitude higher than in Ge35As10S55 glasses.
Two realisations of the pump-probe method have been used to study the time-resolved non-linear optical response of glassy chalcogenides at frequencies near their single-photon and two-photon ...bandgaps. Photo-excitation of gap states has been revealed as a determining effect for structural, electronic, thermal and optical changes in a glass sample.
The Ga5GeSx85I10 glasses with x=1.5, 1.7, 2.0, 2.3 and 2.6 are prepared; their thermal and optical properties and stability against crystallization are investigated. The values of glass transition ...temperature, energy bandgap and volume fraction of crystalline phase in glasses after annealing have nonmonotonic dependence on the macro-composition with a maximum value at x=2.0. In the DSC curves of glasses with x=2.0, 2.3 and 2.6, two glass transition temperatures are registered. The glass samples containing 1.2ppm(at) hydrogen impurity in the form of SH-group and <1ppm(at) oxygen impurity in the form of GeO were produced.
•The pure Ga5GeSx85I10 glasses with x=1.5, 1.7, 2.0, 2.3 and 2.6 were prepared.•The thermal, optical and crystallization properties of Ga5GeSx85I10 glasses were investigated.•The glasses in the Ga5GeSx85I10 system with low tendency to crystallization were determined.•The single-index Ga5GeS1.585I10 and Ga5GeS1.785I10 glass fibers were drawn.
MMM – The molecular model of memory Zeltser, Gregory; Sukhanov, Ilya M.; Nevorotin, Alexey J.
Journal of theoretical biology,
09/2022, Letnik:
549
Journal Article
Recenzirano
Display omitted
•Traditional understanding of the mechanisms of memory associated with the electrical signals having a unique combination of frequency and amplitude.•Apart from neuronal circuits, a ...diversity of the molecular memory carriers, are essential for memory performance.•The “memory alphabet” molecules are conformationally changed by the frequency-tunable electrical oscillations.•Bidirectional translocations of these molecules across lipid/water barriers of the neuronal plasma membrane responsible for acquisition and retrieval of the information bits.
Identifying mechanisms underlying neurons ability to process information including acquisition, storage, and retrieval plays an important role in the understanding of the different types of memory, pathogenesis of many neurological diseases affecting memory and therapeutic target discovery. However, the traditional understanding of the mechanisms of memory associated with the electrical signals having a unique combination of frequency and amplitude does not answer the question how the memories can survive for life-long periods of time, while exposed to synaptic noise. Recent evidence suggests that, apart from neuronal circuits, a diversity of the molecular memory (MM) carriers, are essential for memory performance. The molecular model of memory (MMM) is proposed, according to which each item of incoming information (the elementary memory item – eMI) is encoded by both circuitries, with the unique for a given MI electrical parameters, and also the MM carriers, unique by its molecular composition. While operating as the carriers of incoming information, the MMs, are functioning within the neuron plasma membrane. Inactive (latent) initially, during acquisition each of the eMIs is activated to become a virtual copy of some real fact or events bygone. This activation is accompanied by the considerable remodeling of the MM molecule associated with the resonance effect.
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