Homogeneous Crystals Research Articles

Development of a Matrix Sublimation Device with Controllable Crystallization Temperature for MALDI Mass Spectrometry Imaging.

The size and distribution of matrix crystals deposited on the surface of a tissue section play a key role in the performance of MALDI mass spectrometry imaging (MALDI-MSI). In this study, uniform distribution and a restricted size of matrix crystals were achieved via a homemade matrix sublimation device with controllable crystallization temperature. The crystallization temperature was stably controlled at a subzero temperature, and homogeneous matrix crystals with diameters <0.2 μm were generated on the sample surface. Typical MALDI-MSI experiments of endogenous and exogenous components in the tissues of strawberries, kidneys, and mussels were conducted to examine the performance of the sublimator. Good reproducibility of MALDI-MSI was achieved, and the quality of ion images was significantly improved. These results demonstrate that the developed sublimator should have potential in matrix deposition for further high resolution MALDI-MSI application.

Infrared properties of interstitial oxygen in homogeneous bulk Si1−XGeX crystals

Homogeneous concentration Si1-XGeX crystals (0.3 ≤ X ≤ 0.9) with 20 mm in diameter were grown using the Travelling Liquidus Zone (TLZ) method. Infrared (IR) absorption spectra of the SiGe crystals were measured at room temperature, which revealed the interstitial oxygen Oi related SiOiSi absorption peak shifted −25.7x cm−1 from 9.09 µm (1100 cm−1) for Si0.7Ge0.3 to 9.18 µm (1089 cm−1) for Si0.3Ge0.7. That shift gives the Mode-Grüneisen parameter of SiOiSi vibration of 0.67 + 0.03x. The oxygen concentration in the four Si1−XGeX (x ~ 0.3) crystals was measured using secondary ion mass spectroscopy (SIMS). The correlation coefficient used to convert the oxygen concentration into the SiOiSi absorption peak intensity of Si1−XGeX (x ~ 0.3) was 2.56 × 1017 atoms/cm2.

Electron microscopy investigations on the mineral lorándite (TlAsS2) from Allchar in Macedonia

Abstract In this paper, we report on electron microscopy studies of single crystals of the natural mineral lorándite, TlAsS2. The main focus of this investigation was to address the question as to whether those lorándite crystals are chemically and structurally homogeneous, in order to be utilized as an effective neutrino detector within the lorándite experiment (LOREX) project. Apart from few secondary minerals, being present only at the surface of the lorándite samples, scanning electron microscopy (SEM) indicated homogeneous crystals. Similarly, transmission electron microscopy (TEM) imaging revealed a homogenous and undisturbed crystal structure, with the only exception of local coffee-bean contrasts; however, rarely observed. These specific contrast variations are known to be a typical strain indicator caused by a local deformation of the crystal lattice. Energy-dispersive X-ray spectroscopy (EDS) in conjunction with electron energy-loss spectroscopy (EELS) did not show any significant chemical difference when analysing regions on or off those coffee-bean features, indicating a chemically homogenous mineral. Since the presence of lattice disturbing secondary phase precipitates could be excluded by imaging and complementary chemical analysis, crystal defects such as dislocations and stacking faults or minor fluid inclusions are discussed as the probable origin of this local elastic strain. The experimental results confirm that the studied lorándite single crystals fulfil all structural and chemical requirements to be employed as the natural mineral that allows to determine solar neutrino fluxes. In addition, critical issues regarding the rather challenging sample preparation of lorándite are reported and a quantification of the maximum tolerable electron dose in the TEM is presented, since lorándite was found to be sensitive with respect to electron beam irradiation. Furthermore, the limits of EDS measurements due to peak overlapping are shown and discussed utilizing the case of Pb in lorándite. In this regard, a comparison with the Tl- and Pb-containing natural mineral hutchinsonite, TlPbAs5S9, is also included.

Ultramagnesian Olivine in the Monchepluton (Fo96) and Pados-Tundra (Fo93) Layered Intrusions (Kola Peninsula)

Abstract —The paper focuses on compositional variations of olivine and chromian spinel in the Monchepluton and Pados-Tundra layered intrusions, which host significant chromitite mineralization. Ore-bearing dunite (with up to 25–30 vol.% Mcr) in the Sopcheozerskoe chromite deposit from the Monchepluton complex, Kola Peninsula, Russia, bears an assemblage of phases with exceptionally high magnesium contents: Fo96 + augite (Mg# = 94) + magnesiochromite, Mcr (Mg# ≈ 65); Mg# = 100·Mg/(Mg + Fe2+ + Mn). However, olivine in the host dunite has normal maximum values of Mg# comparable to those in cumulus olivine from layered intrusions worldwide (Fo≤91–92). The Fo96 phase in the Sopcheozerskoe deposit shows the most primitive composition ever reported from any layered intrusion. Magnesiochromite occurs as unzoned homogeneous euhedral crystals unaffected by subsolidus exchange or metasomatic effects. Olivine in ore-bearing dunite (20–25 vol.% magnesian chromite) from the Pados-Tundra complex attains Fo93, with the Mg# value notably higher than the range (Fo85.5–90.6) in olivine from orthopyroxenite, harzburgite, and dunite within the intrusion. Olivine and chromian spinel in the two complexes behave coherently, with covarying patterns of Mg# and Ni contents in olivine at R = 0.75 (n = 160) and positive correlation between Mg# in coexisting chromian spinel and olivine grains at R = 0.8 (n = 150). This behavior indicates that the two phases attained equilibrium during crystallization. It appears unlikely that the extremely high Mg enrichment in olivine (Fo96), as well as in all associated phases of the Monchepluton complex, would result from a subsolidus reaction between olivine and chromian spinel or low-temperature alteration of olivine. We suggest a more realistic explanation that the olivine (+ high-Mg augite)–chromian spinel assemblage crystallized from komatiitic magma under the conditions of progressively increasing oxygen fugacity (fO2). The high Mg# in the Mcr-chromite-enriched system, above the maximum values common in cumulus olivine from layered intrusions (up to Fo96 against Fo≤91–92), may be caused by shortage of ferrous iron.

Predicting process design spaces for spray drying amorphous solid dispersions

Amorphous solid dispersions (ASDs) are commonly manufactured using spray-drying processes. The product quality can be decisively influenced by the choice of process parameters. Following the quality-by-design approach, the identification of the spray-drying process design space is thus an integral task in drug product development. Aiming a solvent-free and homogeneous ASD, API crystallization and amorphous phase separation needs to be avoided during drying. This publication provides a predictive approach for determining spray-drying process conditions via considering thermodynamic driving forces for solvent drying as well as ASD-specific API/polymer/solvent interactions and glass transitions. The ternary API/polymer/solvent phase behavior was calculated using the Perturbed-Chain Statistical Associating Theory (PC-SAFT) and combined with mass and energy balances to find appropriate spray-drying conditions. A process design space was identified for the ASDs of ritonavir and naproxen with either poly(vinylpyrrolidone) or poly(vinylpyrrolidone-co-vinylacetate) spray dried from the solvents acetone, dichloromethane, or ethanol.

Modification of crystallization in Cu2ZnSn(S,Se)4 films using Al2O3 capping layers

In this paper, we reported a modified preparation process for Cu2ZnSn(S,Se)4 (CZTSSe) films. For this process, Al2O3 capping layers were deposited on precursor films before selenization. It was found the capping layer can prevent the formation of separate CuxSe phase on top of the film and facilitate a homogeneous growth of the crystalline grains during selenization. Detailed characterizations revealed the reason: the Al2O3 capping layers can inhibit the incorporation of Se into the film in low-temperature region (below 350 °C). So the reaction between Se and Cu, which is thermodynamically preferential in this temperature region, can be prevented. As the disappearance of CuxSe, the traditional top-to-down crystallization mode was substituted by a homogeneous crystallization mode. Therefore, CZTSSe films with homogeneous crystallization properties were achieved. By using the capping layers, the efficiencies of the solar cells were improved. In particular, the open-circuit voltage (VOC) of the solar cell increased by ~18% by using the capping layers.

Chemical precipitation at extreme fluoride concentration and potential recovery of CaF2 particles by fluidized-bed homogenous crystallization process

Excessive and industrial advances have increased fluoride quantity in the effluents. However, the environmental carrying capacity for fluoride is relatively slim immediately affecting both aquatic and terrestrial animals while its transport can further contaminate the water source. To protect the public and the environment, different environmental agencies globally set their respective effluent standard restricting F- concentration to 15 mg/L as the median value. However, various processes from previous investigations have mostly been limited in treating 100–1000 mg F-/L with secondary pollution commonly overlooked. Re-assessing the available defluoridation technologies, chemical precipitation has still been the most feasible among the technologies, especially extremely high fluoride concentrations. In this study, fluoride removal through chemical precipitation was investigated using conventional precipitation and fluidized-bed homogeneous crystallization. Parameters such as a wide range of initial concentrations from 100 to10,000 mg/L and pH 2.0–11.0 under conventional precipitation were varied and analyzed. To reduce high water content sludge, a 550-mL cylindrical glass was modified to simulate a fluidized-bed reactor to investigate homogenous crystallization varying influent concentration, bed-support size, and fluid flow. Results showed that chemical precipitation could effectively remove fluoride even at very high fluoride concentrations ranging from 1,000 to 10,000 mg/L. Alternatively in the fluidized-bed granulation process, an initial very low flow without recirculation flow was required to initiate particle formation. The predominant size of the recovered particle was < 0.2 mm which was relatively heavy atypically not reaching the upper region of the reactor. Under the observed optimum condition with an initial fluoride concentration of 450 mg/L, both total removal and crystallization ratio could reach ∼ 98% efficiency lowering fluoride concentration to < 15.0 mg F-/L within 7 days.

Analysis of a 2D Periodic Array of Metal Cylinders with Lumped Elements in Passband

Eigenwaves of a homogeneous electromagnetic crystal (EMC) that represents a 2D array of metal cylinders with gaps containing lumped elements (LEs) forming a parallel LC circuit are studied. The array of cylinders with LEs is installed inside a planar waveguide (PW). Variations in the parameters of the EMC eigenwaves due to variations in the capacitance are analyzed. The problem of eigenwaves is solved with the aid of numerical electrodynamic simulation in the HFSS system using periodic boundary conditions. Dependences of the main technical parameters, in particular, passband on the geometrical parameters of the structure and circuit parameters are considered. It is shown that a decrease in the height of the PW filled with a dielectric material can be used to improve the EMC quality parameters. Excitation of a finite-width EMC layer is considered. It is shown that the main results obtained for the regime of eigenwaves are proven by the solution to the problem of the EMC excitation.

Lattice-Matched Metal-Semiconductor Heterointerface in Monolayer Cu2Te.

The interface between metals and semiconductors plays an essential role in two-dimensional electronic heterostructures, which has provided an alternative opportunity to realize next-generation electronic devices. Lattice-matched two-dimensional heterointerfaces have been achieved in polymorphic 2D transition-metal dichalcogenides MX2 with M = (W, Mo) and X = (Te, Se, S) through phase engineering; yet other transition-metal chalcogenides have been rarely reported. Here we show that a single layer of hexagonal Cu2Te crystal could be synthesized by one-step liquid-solid interface growth and exfoliation. Characterizations of atomically resolved scanning tunneling microscope reveal that the Cu2Te monolayer consists of two lattice-matched distinct phases, similar to the 1T and 1T' phases of MX2. The scanning tunneling spectra identify the coexistence of the metallic 1T and semiconducting 1T' phases within the chemically homogeneous Cu2Te crystals, as confirmed by density functional theory calculations. Moreover, the two phases could form nanoscale lattice-matched metal-semiconductor junctions with atomically sharp interfaces. These results suggest a promising potential for exploiting atomic-scale electronic devices in 2D materials.

Nutrients recovery from urine through struvite formation using lab-scale fluidized-bed homogeneous crystallization reactor

Phosphorus (P) is considered the most important micro-element needed for every living thing. Even though they have limited amount, P and nitrogen (N) are responsible for eutrophication in water bodies. This paper aimed to give an insight into the removal efficiency of nutrients and struvite crystallization of slowly soluble fertilizer MgNH4PO4.6H2O, which is also called NH4+-struvite. Besides, using fluidized bed homogeneous crystallization (FBHC) system can reduce impurities in granular struvite generated during the reaction as the advantage function itself. The results showed the changes in pH, magnesium (Mg2+), phosphate (PO43--P), ammonium (NH4+-N), and appearance of spontaneous struvite precipitation over time. Using synthesis urine sample with adjusted pH and Mg2+ concentration to determine the optimal conditions for granular NH4+-struvite recovery to maintain Mg and P removal efficiency up to 99% in steady state. In this study, the removal efficiency of N was about 80 – 85% maximum. The initial results indicated the feasibility of simultaneous crystallizing NH4+-struvite which is mentioned above. It could easily form at pH around 8 – 9. On the other hand, urea hydrolysis makes a pH increase in urine from 6.5 to less than 9.0 at room temperature. This might cause a heavy impact on the NH4+-N crystallization during the formation of granular struvite if there has no suitable NH4+-N pretreatment options. For Mg recovery, the concentration of Mg is detrimental in the creation of struvite. This will bring better removal efficiency if there is an available Mg source in nature which can be reused directly in an environmentally eco-friendly way. The total mass of struvite precipitate obtained in the form of nuclei corresponds to 200 g/m3 of urine during 24 days operation.

TEMPERATURE ASPECTS OF A CUBOID CRYSTAL IN PHOTOACOUSTIC INTERACTION

When a solid crystal undergoes photoacoustic effect, excitation process occurs due to a fraction of incident radiation absorbed by that sample. The nature of excitation depends on the energy of incident radiation. The relaxation processes, generally non-radiative in nature, are observed. Alternate processes of absorption and non- radiative relaxation cause variation in translational temperature in atoms of the crystal. In this paper, the thermal aspects of an isotropic cuboid crystal of elastic material in photoacoustic interaction are presented. This theoretical determination is carried out by applying the finite Marchi–Fasulo integral transform method within the crystal size limitations of a homogeneous cuboid crystal. The results are obtained in terms of infinite series, and the numerical calculations are carried out by using MATHCAD-7 software. The transient translational temperature on the surface of the cuboid crystal in photoacoustic interaction is mathematically determined in terms of thermal conductivity of the elastic material of the crystal.

Li-Be-Nb-Ta mineralogy of the Kuqu leucogranite and pegmatite in the Eastern Himalaya, Tibet, and its implication

稀有金属矿物记录了花岗伟晶岩成岩成矿的重要信息。喜马拉雅是全球著名的淡色花岗岩带，库曲岩体位于喜马拉雅东段的特提斯喜马拉雅岩系中。本文调查了库曲岩体的二云母花岗岩、白云母花岗岩、电气石花岗岩和花岗伟晶岩，其中，花岗伟晶岩涉及花岗岩的伟晶岩相和独立伟晶岩脉。库曲岩体产出的稀有金属矿物包括锂辉石、锂绿泥石、绿柱石、铌铁矿-钽铁矿、钇铀钽烧绿石和细晶石，它们主要赋存于似文象伟晶岩、石英-钠长石-白云母伟晶岩、块体长石-钠质细晶岩、块体长石-电气石钠质细晶岩、锂辉石-块体长石-细晶岩、白云母花岗岩的伟晶岩相以及电气石花岗岩内。显微镜观察、电子探针和LA-ICP-MS测试结果显示锂辉石具有四种产状，包括粗粒锂辉石自形-半自形晶、细粒锂辉石-石英镶嵌晶、中细粒锂辉石-钾长石-钠长石-云母镶嵌晶以及发育锂绿泥石的粗粒锂辉石，揭示了其形成时复杂的熔流体动荡结晶环境。绿柱石背散射电子图像（BSE）下呈均一结构和不均一结构（蚀变边、不规则分带和补丁分带），元素替代机制包括通道-八面体替代、通道-四面体替代以及通道中碱金属阳离子间的置换。铌铁矿族矿物包括原生、蚀变边和不规则分带结构，部分被钇铀钽烧绿石和细晶石交代。与原生铌铁矿相比，蚀变边和不规则分带铌铁矿族矿物总体上富钽贫锰，显示了结晶分异、过冷却引起的过饱和以及流体作用。根据稀有金属矿物揭示的成因信息，独立伟晶岩脉（似文象伟晶岩）、白云母花岗岩的伟晶岩相和电气石花岗岩在岩浆分异程度、经历的演化过程、以及流体活动方面存在差异，很可能是不同期次岩浆活动的产物。库曲岩体绿柱石的Rb和Zn含量、以及铌铁矿族矿物的Sc₂O₃、SiO₂和PbO含量，与已有指示标志存在相关性，作为潜在指示标志仍需开展更多的研究工作。综合含锂辉石伟晶岩的产出、岩浆分异演化程度、多期花岗质岩浆活动、复杂的流体作用以及所属锂丰度高值区等因素，库曲岩体是喜马拉雅东段找锂的有利地段。;The rare-element minerals record important information of rock-forming process and metallogenesis. Himalaya is a famous leucogranite belt. The Kuqu intrusion is located in the Tethys Himalayan sedimentary sequence in the Eastern Himalaya. This study investigated two-mica granite, muscovite granite, tourmaline granite and granitic pegmatites in the Kuqu intrusion. The granitic pegmatites refer to either the pegmatite rocks that are included in and related to granite or the pegmatite zones that make up a single pegmatite dyke. The rare-element minerals identified in the Kuqu intrusion include spodumene, cookeite, beryl, columbite-tantalite, Y-hatchettolite and microlite. They are distributed in quartz-feldspar-muscovite pegmatite, quartz-albite-muscovite pegmatite, blocky feldspar-aplite, block feldspar-tourmaline aplite, spodumene-blocky feldspar-aplite, pegmatite rock in muscovite granite, and tourmaline granite. The EMPA and LA-ICP-MS analytical results indicate that spodumenes show four occurrences which consists of coarse-grained subhedral to euhedral spodumene, fine-grained symplectitic reaction border composed of spodumene and quartz, middle to fine-grained mosaic structure of spodumene, K-feldspar, albite and muscovite, and coarse-grained spodumene filled by cookeite veins. These occurrences of spodumene reveal a complex and fluid-rich unstable crystallization environment. There are homogeneous and heterogeneous beryl crystals in the intrusion. The internal zonation patterns for heterogeneous beryls are alteration border, patches and complex irregular zoning in BSE images. The substitution mechanisms of beryl in the Kuqu intrusion are channel-octahedral, channel-tetrahedral and alkali cations in channel. The columbite-group mineral crystals are composed of primary part and alteration border or display irregular zoning pattern, some of which are altered by Y-hatchettolite and microlite. Compared with primary parts, the alteration border and irregular zoned crystals have higher Ta/(Nb+Ta) values and lower Mn/(Fe+Mn) values, indicating fractional crystallization, supersaturation caused by strong undercooling, and fluid activities. Based on the studies of rare-element minerals, the single pegmatite dyke (quartz-feldspar-muscovite pegmatite), pegmatite rock in muscovite granite and tourmaline granite display differences on the degree of fractionation of magma, evolution processes and fluid activities and they might be magma products of different stages. The Rb and Zn contents of beryl, and Sc₂O₃, SiO₂ and PbO contents of columbite-group minerals show correlation with the existed indicators for evolution degree of magma, but more studies are needed to carry out for them to be possible indicators. Considering the spodumene-bearing pegmatite indentified in the intrusion, the high degree of magma evolution, multistage of magmatism, complex fluid activities and being in a high lithium abundance value area, the Kuqu intrusion is an important potential area for future lithium prospecting in the Eastern Himalaya.

Salt precipitation and evaporative flux on sandy soil with saline groundwater under different evaporation demand conditions

Context Salt precipitation and its influence on evaporation have been widely studied in recent years. However, the evolution process of salt precipitation and evaporative flux is poorly understood under various evaporation demand (ED) rate condition, which is defined as the evaporation rate of distilled water from soil under constant radiation conditions. Aims and methods This study investigated the evolution of salt crust and evaporative flux on sand soil columns with fixed saline groundwater at a depth of 20 cm under four ED conditions (29.5, 21.5, 9.0 and 4.0 mm day−1). Key results Evaporation rate significantly decreased in all treatments because the salt crust was elevated and salt domes formed, but the salt patterns of salt precipitation and evaporation exhibited significant differences between different EDs. The homogeneous fine powder crystals precipitated under relatively high ED conditions (29.5 and 21.5 mm day−1), and tended to aggregate and form an elevated salt crust in the initial period of salt precipitation. Consequently, it resulted in a sharp decrease in evaporation during the initial period of salt precipitation. In contrast, discrete and large crystals observed under low ED conditions (9.0 and 4.0 mm day−1), resulted in a stable evaporation stage during the initial period of salt precipitation. The highest relative evaporation rate was observed under the lowest ED condition when the evaporation rate reached stability, which was attributed to the formation of small and discrete salt domes, indicating that both the upward and lateral growth of salt precipitation were influenced by ED. Conclusions and implications The physics of salt crust formation needs to be considered in understanding how salt precipitates on the soil surface.

Time crystallinity and finite-size effects in clean Floquet systems

A cornerstone assumption that most literature on discrete time crystals has relied on is that homogeneous Floquet systems generally heat to a featureless infinite temperature state, an expectation that motivated researchers in the field to mostly focus on many-body localized systems. Some works have however shown that the standard diagnostics for time crystallinity apply equally well to clean settings without disorder. This fact raises the question whether an homogeneous discrete time crystal is possible in which the originally expected heating is evaded. Studying both a localized and an homogeneous model with short-range interactions, we clarify this issue showing explicitly the key differences between the two cases. On the one hand, our careful scaling analysis confirms that, in the thermodynamic limit and in contrast to localized discrete time crystals, homogeneous systems indeed heat. On the other hand, we show that, thanks to a mechanism reminiscent of quantum scars, finite-size homogeneous systems can still exhibit very crisp signatures of time crystallinity. A subharmonic response can in fact persist over timescales that are much larger than those set by the integrability-breaking terms, with thermalization possibly occurring only at very large system sizes (e.g., of hundreds of spins). Beyond clarifying the emergence of heating in disorder-free systems, our work casts a spotlight on finite-size homogeneous systems as prime candidates for the experimental implementation of nontrivial out-of-equilibrium physics.

Homogeneous Floquet time crystal from weak ergodicity breaking

Recent works on observation of discrete time-crystalline signatures throw up major puzzles on the necessity of localization for stabilizing such out-of-equilibrium phases. Motivated by these studies, we delve into a clean interacting Floquet system, whose quasi-spectrum conforms to the ergodic Wigner-Dyson distribution, yet with an unexpectedly robust, long-lived time-crystalline dynamics in the absence of disorder or fine-tuning. We relate such behavior to a measure zero set of nonthermal Floquet eigenstates with long-range spatial correlations, which coexist with otherwise thermal states at near-infinite temperature and develop a high overlap with a family of translationally invariant, symmetry-broken initial conditions. This resembles the notion of "dynamical scars" that remain robustly localized throughout a thermalizing Floquet spectrum with fractured structure. We dub such a long-lived discrete time crystal formed in partially nonergodic systems, "scarred discrete time crystal" which is distinct by nature from those stabilized by either many-body localization or prethermalization mechanism.

Homogeneous Crystallization in Cyclically Sheared Frictionless Grains.

Many experiments over the past half century have shown that, for a range of protocols, granular materials compact under pressure and repeated small disturbances. A recent experiment on cyclically sheared spherical grains showed significant compaction via homogeneous crystallization (Rietz etal., 2018). Here we present numerical simulations of frictionless, purely repulsive spheres undergoing cyclic simple shear via Newtonian dynamics with linear viscous drag at fixed vertical load. We show that for sufficiently small strain amplitudes, cyclic shear gives rise to homogeneous crystallization at a volume fraction ϕ=0.646±0.001. This result indicates that neither friction nor gravity is essential for homogeneous crystallization in driven granular media. Understanding how crystal formation is initiated within a homogeneous disordered state gives key insights into the old open problem of glass formation in fluids.

Molecular Dynamics Simulation of Calcium Sulfate Nucleation in Homogeneous and Heterogeneous Crystallization Conditions: An Application in Water Flooding

During water flooding of the oil reservoir, deposition of calcium sulfate on the pore surface causes formation damage and affects oil recovery efficiency. Thus, a clear understanding of this scale’...

Effect of sucrose ester S370 on interfacial layers and fat crystals network of whipped cream

The effect of sucrose ester S370 on the interfacial layers and fat crystals network of whipped cream has been studied in this work. The addition of S370 showed a little effect on the droplets size, interfacial protein concentration and viscosity of emulsion samples before whipping. However, the addition of S370, as a heterogeneous nucleating agent, could induce nucleation and lead to the formation of more small crystals in the bulk mixture and emulsions. These small crystals, which were not able to pierce the interface of fat droplets effectively, would retard fat coalescence during whipping process. The addition of S370 resulted in lower degree of fat coalescence, lower interfacial protein concentration, shorter optimum whipping time (top) and lower overrun of whipped cream. At lower S370 concentration (<0.05 wt%), large-size crystals and inhomogeneous fat crystals network led to lower firmness and less bubbles stability of whipped cream samples. At 0.05 wt% S370 concentration, homogeneous crystals network, resulted in whipped cream with high firmness and bubbles stability. However, lower interfacial protein concentration and small-size crystals were observed at higher concentration of S370 (>0.05 wt%). As a result, the aerated structure was not strong enough to stabilize whipped cream.

Role of Dislocations in the Process of Degradation of Semiconductor Lasers with Electronic Energy Pumping. Experimental Research

Light self-destruction-degradation of the second type has been observed in samples of semiconductor lasers with electronic energy pumping with high optical homogeneity and good quality of surface treatment. In these samples, damage appeared in the form of cords perpendicular to the ends of the resonator. According to the current understanding of the passage of powerful light streams through various media, the emergence of narrow light channels is due to the phenomenon of self-focusing. It refers to the fundamental physical mechanisms of propagation of laser radiation and is caused by nonlinear phenomena arising in a medium under the influence of high-power laser radiation. The physical reason for self-focusing is an increase in the refractive index n in a strong light field. Thermal self-focusing is the most probable cause of radiation redistribution in the active region of the crystal. However, it is possible that in the initial stage of the appearance of light channels a certain role is played by the growth of the intensity of radiation in certain sections of the crystal because of the instability of generation or small fluctuations in the pump current density. Then the process acquires an avalanche character, since the localization of the ray in the channel increases the density of light radiation which can lead to overheating of the substance and the activation of the thermal self-focusing mechanism. The experiments performed in this paper have shown that optically homogeneous crystals possess maximum resistance to degradation processes. In them, the critical power of light destruction is determined by the self-focusing threshold of radiation in a material. Since the nonlinear addition to the refractive index Δn = n2E2 at the self-focusing threshold is determined by the change in the concentration of non-equilibrium carriers ΔN(E2), the value of the maximum fluctuation DΔNmax itself is proportional to the value of the non-equilibrium carrier concentration at the generation threshold ΔNpores and the relative excess of the generation threshold J = (j – jn)/jn. Thus, a low threshold concentration of non-equilibrium carriers is one of the conditions for increasing material resistance to degradation processes. In doped crystals ΔNpores is less than in pure materials. This, perhaps, explains the rather higher value of Pcritial in the optimally doped homogeneous n-GaAs. Smaller values of Pcritial in p-type samples doped with zinc can be associated not only with the inhomogeneity of these crystals, but also with large generation thresholds. In addition, the cross section for absorption of radiation by holes is about 3–4 times larger than by electrons, which can also reduce the self-destruction threshold of lasers. At Т = 300 K, the lasing thresholds are higher that naturally reduces the value of the self-focusing threshold.

Анализ влияния легирования на структурные дефекты в LiNbO3.

Changes in a structural state of homogeneous doped lithium niobate crystals with magnesium in the region of 5 mol. % were studied by X-ray diffraction methods. It was found that the changes in the structure of LiNbO3: Mg occured not only in the region of the impurity defect, but also in the region of the main motive of the structure. Bond lengths in the octahedra of the main motive and the Nb–Li distance along the polar axis of the crystal changed. The magnesium introduced into the vacant lithium octahedron distorted the shape of the octahedron more strongly than niobium.