Асимптотическая стадия роста автокаталитических III-V нитевидных нанокристаллов методом молекулярно-пучковой эпитаксии

A new analytic theory is developed for asymptotic stage of self-catalyzed growth of III-V nanowires (NWs) by molecular beam epitaxy (MBE), where NWs collect all group III atoms deposited from vapor. The shadowing NW length is derived which corresponds for the full shadowing of the substrate surface in MBE. The NW length and radius are derived depending on the effective deposition thickness and MBE growth parameters. It is shown that the NW length increases, and their length decreases with decreasing the array pitch and increasing the V/III flux ratio.

Study of the initial stage of GaAs growth on FIB-modified silicon substrates

In this work, we studied the effect of the deposition thickness, growth rate, arsenic flux, and implantation dose on the morphology of the GaAs nanostructures grown on modified Si areas. It is shown that an increase in the growth rate at the initial stages of the growth process leads to the transition of the growth regime from layered-like to one-dimensional with the formation of nanowires. Studies of the effect of As4 pressure have shown that a change in the equivalent As4 flux in the range of 3.7 - 5.0 ML/s does not lead to any significant change in the structure of the GaAs layer in the modified areas. An increase in the implantation dose during processing with a focused ion beam led to disordering of the directions of the grown nanowires due to the degradation of the substrate crystal structure.

Slicing strategy and process of laser direct metal deposition (DMD) of the inclined thin-walled part under open-loop control

Purpose The purpose of this paper is to improve the dimensional accuracy of inclined thin-walled parts fabricated by laser direct metal deposition (DMD) under an open-loop control system. Design/methodology/approach In this study, a novel method of the adaptive slicing method and DMD process with feedback adjustment of deposition height has been developed to successively fabricate complex inclined thin-walled square tube elbow parts. The defocus amount was used as a variable to the matching between the deposition thickness and the adaptive slicing height. Findings The low relative error of dimensional accuracy between experimental and designed parts shows that the matching of the single-layer deposition thickness and the adaptive slicing height can be realized by optimizing the defocusing amount. The negative feedback of the thin-wall part height can be achieved when the defocus amount and the z-axis increment are less than deposition thickness. The improvement of dimensional accuracy of inclined thin-walled parts is also attributed to the optimized scanning strategy. Practical implications The slicing method and deposition process can provide technical guidance for other additive manufacturing (AM) systems to fabricate metal thin-walled parts with high dimensional accuracy because the feedback control of deposition height can be realized only by the optimized process. Originality/value This study provides a novel adaptive slice method and corresponding the deposition process, and expands the slicing method of AM metal parts.

Geomorphologic Evolution of Northern Tibetan Plateau in the Quaternary: Tectonic and Climatic Controls

Situated in the northwestern Qinghai-Tibet Plateau, the Qaidam Basin is the largest Cenozoic terrestrial intermountain basin in the world. It is an ideal place for understanding the coupling control of tectonics and climate on sedimentary evolution. Although numerous studies on the Quaternary sedimentary evolution of the Qaidam Basin have been done, most of which are of local, conceptual and qualitative in nature. In this study, we investigated the entire Qaidam Basin and its surrounding mountains quantitatively as a single entity to probe the Quaternary evolution of the basin-range system in the northern Qinghai-Tibet Plateau. We used a Basin and Landscape Dynamics (Badlands) modeling algorithm that is capable of modeling landscape evolution by simulating erosion, sediment transport and deposition in a source-to-sink context by considering climate changes and tectonic uplift. We have simulated the evolution of the Qaidam Basin and its surrounding mountains since 2.5 Ma quantitatively. Both tectonic uplift and climate changes appear to have a direct impact on the denudation and deposition rates, but the impact varies through time. The deposition in the Qaidam Basin was mainly affected by tectonic movement during the period of 2.5 Ma to 0.6 Ma, reaching a maximum deposition thickness of 2130 m at the end of 0.6 Ma, but was prevailed by climate after 0.6 Ma during the last four glacials-interglacials, reaching a maximum deposition thickness of 3200 m. The Qilian Mountains and the Kunlun Mountains contributed the bulk sediments to the Qaidam Basin around 35% and 40%, respectively. The Altun Mountains made a significant contribution to the sediments in the Qaidam Basin during the early Quaternary from 2.5 Ma to 2.4 Ma due to a high denudation rate. The findings provide new insights for analyzing geomorphic and landscape evolution as well as source-to-sink systems in the Northern Qinghai-Tibet Plateau.

Cement Slurry Plugging Law and Optimal Plugging Flow Rate at a High Hydraulic Gradient

With the continuous development of coal and rock mass engineering, water inrush grouting has become an urgent problem in engineering disaster management. Herein, a theoretical model of the optimal plugging flow rate was established, and a comparative theoretical analysis was performed based on the results of indoor model tests. The particle incipient velocity was defined as the optimal plugging flow rate. The effects of hydrodynamic velocity, water-cement ratio, grouting pressure, and fracture aperture on the cement slurry grouting plugging were studied, and the optimal threshold of the plugging flow rate was obtained for theoretical model verification. Results showed that, at a high hydraulic gradient, the plugging effect of the grout was mainly affected by the hydrodynamic velocity, water-cement ratio, and grouting pressure (listed in the order of importance). When the hydrodynamic velocity was low, the difference in the slurry deposition thickness was large under different water–cement ratios and pipe diameters. When the hydrodynamic velocity was increased, the influence of various factors on the slurry deposition thickness decreased. Through a comparative analysis of the experimental and theoretical values, the optimal plugging velocity of pure cement slurry was 0.5–0.55 m·s−1 under different conditions, and the error between the experimental and theoretical values was less than 0.1 m·s−1, which confirmed the rationality of the proposed model.

The Concept of Need for a Downhole Scale Inspection Tool: An Appraisal for an Emerging Technology in Scale Management

Monitoring techniques in oilfield scale management are expensive, susceptible to error, are not conducted in real-time, and they are non-in situ. Most scale prediction tools (i.e., water analysis and computer-based algorithms) have their deficiency and the need for accurately correlate calculated scaling tendencies with actual field data is evident. Lack of info about type, severity and location of scale deposits can lead to the failure of well intervention jobs. This work aims to serve as an opportunity to provide fertile ground and basis for utilizing new emerging technology for scale management in downhole application. Research into utilizing sensors along with an advanced computerized imaging procedure in the downhole application has not been explored to the same extent as other applications, such as scale monitoring in pipelines and surface facilities. Downhole Scale Inspection Tool (DSIT) is a new emerging technology which promises to enhance considerably our ability to detect deposits and scale with the aim of sensors and tomography technology. DSIT has enormous potential for application in downhole condition as it uses slickline unit alongside with routine well intervention jobs. The acquired data by DSIT such as temperature, pressure, depth, deposition thickness and permittivity are utilized for downhole scale analysis, monitoring and detection. When the type of scale is known, it is easier to take the correct steps in preventive maintenance or a cleaning process. Using DSIT, the trend of deposition thickness can be detected and immediately known if it is growing or shrinking. This will help to optimize any chemical feed and also generate substantial savings over time. This paper gives an overview of developing cutting-edge technology in downhole applications for scale management and possible barriers to new technology implementation. Using DSIT can lead to better data acquisition from downhole and contribute to a higher success rate of scale removal in downhole. This technique offers many benefits for scale treatment, monitoring and prediction when filed data is necessary for validation of scaling tendencies.

STUDY OF PLACENTAS OF HYPERTENSIVE MOTHERS ASSISTED IN TWO PUBLIC MATERNITIES OF RECIFE-PE

Objective: Perform the histomorphometric study of the following regions: areas of perivillous fibrin deposition; thickness of the endothelial layer of the vessels; analysis of Tenney-Parker changes. Analyze the Placental Index (IP). Results: It was seen that the weight of the placentas increased according to the weight of the newborn, however, when the variable PI was analyzed as being decisive for the development of a risk-free pregnancy, it was found that this parameter was not significant between the groups studied. (p <0.05). It was found that there is a significant difference in relation to the areas of fibrin deposition (P <0.05) between the groups and that it possibly converges with the data found in the literature in which it could be established that in the GrH there is a different relationship in this pattern. The findings of the thickness of the middle layer were significant in the GrH when compared to the GrN (p <0.05), when this parameter is compared between the Hypertensive Disorders of Pregnancy (HDP) groups, microscopically the PE cases showed prominent changes. I n the present study, Tenney-Parker changes were prominent and discreet in 75% of the GrH placentas versus 20% in the GrN. However, there are contradictions in the literature regarding the consideration of this finding seen only in Hematoxylin-Eosin staining. Conclusion: Given the above, the presence of syncytial knots, the difference between vessel thickness and areas of fibrin deposition are possibly involved in the pathogenesis of Hypertensive Syndromes, regardless of age and established classifications. In order to evaluate syncytial knots, further studies are needed in this population.

STUDY OF PLACENTAS OF HYPERTENSIVE MOTHERS ASSISTED IN TWO PUBLIC MATERNITIES OF RECIFE-PE

Objective: Perform the histomorphometric study of the following regions: areas of perivillous fibrin deposition; thickness of the endothelial layer of the vessels; analysis of Tenney-Parker changes. Analyze the Placental Index (IP). Results: It was seen that the weight of the placentas increased according to the weight of the newborn, however, when the variable PI was analyzed as being decisive for the development of a risk-free pregnancy, it was found that this parameter was not significant between the groups studied. (p <0.05). It was found that there is a significant difference in relation to the areas of fibrin deposition (P <0.05) between the groups and that it possibly converges with the data found in the literature in which it could be established that in the GrH there is a different relationship in this pattern. The findings of the thickness of the middle layer were significant in the GrH when compared to the GrN (p <0.05), when this parameter is compared between the Hypertensive Disorders of Pregnancy (HDP) groups, microscopically the PE cases showed prominent changes. I n the present study, Tenney-Parker changes were prominent and discreet in 75% of the GrH placentas versus 20% in the GrN. However, there are contradictions in the literature regarding the consideration of this finding seen only in Hematoxylin-Eosin staining. Conclusion: Given the above, the presence of syncytial knots, the difference between vessel thickness and areas of fibrin deposition are possibly involved in the pathogenesis of Hypertensive Syndromes, regardless of age and established classifications. In order to evaluate syncytial knots, further studies are needed in this population.