The Third-Order Elastic Constants and Mechanical Properties of 30° Partial Dislocation in Germanium: A Study from the First-Principles Calculations and the Improved Peierls−Nabarro Model

The elastic constants, core width and Peierls stress of partial dislocation in germanium has been investigated based on the first-principles calculations and the improved Peierls−Nabarro model. Our results suggest that the predictions of lattice constant and elastic constants given by LDA are in better agreement with experiment results. While the lattice constant is overestimated at about 2.4% and most elastic constants are underestimated at about 20% by the GGA method. Furthermore, when the applied deformation is larger than 2%, the nonlinear elastic effects should be considered. And with the Lagrangian strains up to 8%, taking into account the third-order terms in the energy expansion is sufficient. Except the original γ—surface generally used before (given by the first-principles calculations directly), the effective γ—surface proposed by Kamimura et al. derived from the original one is also used to study the Peierls stress. The research results show that when the intrinsic−stacking−fault energy (ISFE) is very low relative to the unstable−stacking−fault energy (USFE), the difference between the original γ—surface and the effective γ—surface is inapparent and there is nearly no difference between the results of Peierls stresses calculated from these two kinds of γ—surfaces. As a result, the original γ—surface can be directly used to study the core width and Peierls stress when the ratio of ISFE to the USFE is small. Since the negligence of the discrete effect and the contribution of strain energy to the dislocation energy, the Peierls stress given by the classical Peierls−Nabarro model is about one order of magnitude larger than that given by the improved Peierls−Nabarro model. The result of Peierls stress estimated by the improved Peierls−Nabarro model agrees well with the 2~3 GPa reported in the book of Solid State Physics edited by F. Seitz and D. Turnbull.

Finite element modeling of coupling characteristics of directional coupler for multiplexer and de-multiplexer application

Numerical simulation of directional coupler that is based on the finite element method was conducted using the COMSOL Multiphysics software. The distributions of electric field and power flow of light propagates in two cores of directional coupler were analyzed. The results showed the dependencies of coupling length and maximum transfer power between cores on the cores separation and the wavelength, the characteristic of a subwavelength directional coupler can be used for photonic integrated circuits. Asymmetric directional coupler was also designed by changing in the device dimension, as the core width. The variation of coupling length with the core width were analysed. It was found that the power switching between cores is reduced when introducing a small difference in the one core width of directional coupler, followed by increased coupling length. At the same time, the coupling length can be decreased efficiently by increasing the difference in one core width; therefore, a directional coupler with large core width is more convenient to reduce the power switching between cores than the smaller core width. This study is useful for determining the coupling characteristics between the cores that may be used as a platform for future photonic integrated circuits in optical communication systems.

Micro Ring Resonator based CO2 Gas Sensor using PbSe Quantum Dots

In this paper, we introduce a micro-ring resonator-based highly sensitive carbon dioxide sensor. For this purpose, a valley is created in the core of the ring and PbSe quantum dots (QDs) are deposited in the valley and the sensor is exposed to CO2 gas. In this way, the refractive index of the PbSe QDs increases with an increase in the concentration of gas flow, and then the resonance frequency of the ring resonator shifts. The designed sensor operates almost linearly over a wide range of concentrations for CO2 gas and shows a high resonance shift at different concentrations of CO2 gas. The detection limit for the designed sensor is 0.001% of CO2 gas which is more sensitive than previously reported sensors based on microring resonators. The frequency shifts are investigated by changing the width of the valley. The minimum width of the valley was determined for the evanescent field in which only the outer core of the ring affects the resonant frequency. Also, the modal analysis of the designed ring resonator waveguide is investigated to determine the minimum core width.

Heat and water fluxmodeling in an earth dam

This study aims to identify the water flux in an earth dam using heat flux due to convection. Sixteen earth dams model was constructed in a hydraulic flume by varyinggeometrical and flow input parameters to identify heat and water flux.Homogeneous as well was earth dam with the clay core was built-in a hydraulic flume. Temperature measurements were doneto calculate heat flux in the experimental model. A finite element model of the earth dam using Seep/w was developed to obtain water flux,while temp/wwas to obtain heat flux. These results were used as input in Temp/w and Seep/w in Geostudio 2020. Significant reduction of the heat and water fluxwas seen while comparing the homogeneous models with central impervious core models. An increase in the heat and water flux was observed on increasing the downstream filter's length, longitudinal slope,and vice versa with the upstream slope and the thickness of the clay core. Comparing fluxesina homogeneous dam model (model 1) with the clay core model (model 9) with top width 2.4 m and bottom width 18 m in model 9, both water flux and heat flux were reduced78.46%. While comparing it with model 10, with bottom core width of 18 m and top core width of 1.9 m, both water flux and heat flux reduced by 77.72%. Heat flux measurements were found a valuable alternative to detecting water flux and seepage in an earth dam at a reduced cost.

Photonics Rib Waveguide Dimension Dependent Charge Distribution and Loss Characterization

The simulation of behaviour of the charge distribution and the loss characteristic for rib-waveguide is demonstrated by using silicon-on-insulator (SOI). In this simulation, the rib waveguide is designed at a core width of 450nm, core height of 250nm, rib height of 50nm and buried oxide height of 100nm. These dimensions are set as reference. The aspiration of designing rib waveguide instead of other type of waveguide such as ridge waveguide is from the higher light confinement that can be accomplished by rib waveguide as the refractive index difference is huge and the designing of an active device can be realized. In this analysis, free carrier-injection effect was implemented in the first part of the simulation to study the distribution charges of rib-based waveguide structure based on basic dimensions. In this analysis, electrical voltage was varied from 0V to 1.2V in steps of 0.2V for the analysis of distribution of electron. In the second part of the simulation, four design parameters had been amended which included the core width and height, rib height and buried oxide height. Physical dimensions of the waveguide were altered to achieve smaller device footprint with optimized performance affecting large Free Spectral Range (FSR) and high Q-factor. With proper waveguide physical dimensions design, a good performance Micro-Ring Resonator (MRR) exhibits the principles of wide FSR and Q-factor can be achieved.

Hybrid models of dislocations

In a Volterra dislocation the relative displacement by the Burgers vector appears abruptly in the dislocation core so that the core has no width. This leads to divergent stresses and strains, which are unrealistic. Hybrid models correct this failure by considering a balance of forces that results in a finite core width, and finite stresses and strains throughout. Interatomic forces tend to constrict the core and elastic forces tend to widen it. The Frenkel-Kontorova model comprises two interacting linear chains of atoms as a representation of an edge dislocation, with linear springs between adjacent atoms of each chain. The Peierls-Nabarro model assumes the core is confined to two parallel atomic planes sandwiched between elastic continua. This model enables the stress to move the dislocation to be calculated, and it leads to the concept of dislocation kinks. These models highlight the role of atomic interactions in affecting ductility.

MORPHOLOGICAL AND CHEMICAL CHARACTERISTICS OF VARIOUS PUMMELO (Citrus maxima (Burm.) Merr.) ACCESSIONS FROM MAGETAN REGENCY

Magetan Regency was the production centre of pummelo that have many accessions with various morphological and chemical characteristics, but only a few of them were identificated. This study was aimed at identifying morphological and chemical characteristics of pummelo fruits in Magetan Regency. The study was conducted in the Biology Laboratory of Djuanda University, Bogor from May to July 2015. Results showed with regard to their morphological characteristic, pomelo plants in this region were found to have spheroid and spheroid-pyriform fruits and the weight of their fruit parts, fruit core width, mesocarp thickness, fruit circle before peeling, fruit circle after peeling, number of fruit segments, number of developed seeds, and edible parts of the fruit were varied. Chemical characteristics were also found to be varied with vitamin C content of 29.80−44.66 mg/100g, total soluble solids (TSS) content of 8.10−9.72°Brix, total titratable acidity (TAA) of 0.31−0.53 g/100 ml, and TSS/ TAA ratio of 17.69−28.58. Key words: production centre of pummelo, spheroid, vitamin C, TSS

Experimental Studies on the Formation of Air-core inside the Drop Shaft

In this study, the drainage efficiency of the multi-stage intake structure, which transports flood to the underground storage, was investigated from the laboratory experiments. The multi-stage intake structure was designed based on the tangential intake and the steps on the bed were purposes to decrease the energy of approaching flow. The experimental results show that the maximum water depth was effectively decreased in the entrance of the drop shaft. The measurements results of the air core width in the drop shaft show that the flow was stably drained without the choking. Furthermore, the air core width tends to increase with the Froude number, and these results indicate that the multi-stage intake structure is applicable to convey the approaching flow with relatively high velocity.

Development of Security and Safety Fuel for Pu-Burner HTGR: Part 3 — Preliminary Reactor Safety Analyses Under Depressurization Accidents

Preliminary reactor safety analyses were performed for the Pu-burner HTGR (High Temperature Gas-cooled Reactor) to investigate plutonium fuel influence on reactor thermal and kinetic behavior for the depressurization accident which is design base accident, and the depressurization accident without scram, which is beyond design base accident. The analytical results of depressurization accident show that the reactor thermal power is restricted lower than the reference reactor with uranium fuel, because the core width is wider for better Pu-burning performance. The analytical results of depressurization accident without scram show that the re-criticality is delayed compare to the reference reactor with uranium-fueled core, due to its temperature reactivity coefficient. The delay of re-criticality brings that operators have more margins for accident management, for example, manual insertion of shutdown devices to the reactor core.