Mapping the potential within a nanoscale undoped GaAs region using a scanning electron microscope

Semiconductor dopant profiling using secondary electron imaging in a scanning electron microscope (SEM) has been developed in recent years. In this paper, we show that the mechanism behind it also allows mapping of the electric potential of undoped regions. By using an unbiased GaAs/AlGaAs heterostructure, this article demonstrates the direct observation of the electrostatic potential variation inside a 90nm wide undoped GaAs channel surrounded by ionized dopants. The secondary electron emission intensities are compared with two-dimensional numerical solutions of the electric potential.Comment: 7 pages, 3 figure

Community Involvement in Flood Mitigation: A Survey-Based Approach in Marion County, SC

Marion County is located in northern South Carolina between the Great Pee Dee and Little Pee Dee Rivers. Because Marion County was the location of severe flooding during hurricanes Matthew (2016) and Florence (2018), the South Carolina Floodwater Commission identified Marion County as a location for drainage system improvement by the Infrastructure and Shoreline Armoring Task Force. In order to align plans for drainage system improvement with the needs of the local communities, commission chairman Thomas Mullikin requested a community survey to gauge the residents\u27 personal experiences and views on what changes should be made to address the problem. The purpose of this survey is not only to guide the Infrastructure and Shoreline Armoring Task Force in making and implementing decisions about drainage system improvement, but also to establish a connection with Marion County using a method that can be implemented in other flood-prone communities in the future. 320 individual survey responses were collected between May and September 2019, with respondents answering questions on topics such as their experiences with flooding and property damage over the past ten years, their knowledge of flood zones and flood insurance, and their opinions about flood mitigation strategies and responsibility in community recovery. Survey responses were digitally coded, individual question results were recorded, and the impact of demographic factors on select questions was examined using univariate analysis. The results indicate that, while few respondents know their flood zone or have implemented property-scale flood prevention measures, there is a significant interest in further education as well as support for building code updates and rezoning based on recent flooding. Older respondents reported more frequent flooding over the past ten years, and were more likely to know their flood zone, to support rezoning and building code updates, to report taking flood warnings seriously, and to express interest in further education than younger respondents. The results suggest that more educational outreach is necessary for residents to understand the extensive history and likely future of flooding in Marion County, whether their personal property is at risk for future flooding, and how to access flood insurance and resources for flood recovery and mitigation

(1RS,2SR,7RS,8RS)-N-Benzoyltricyclo[6.2.2.0²,⁷]dodeca-9,11-diene-1,10-dicarboximide

The title 1,4-photoadduct, C₂₁H₁₉NO₃, was formed on irradiation of N-benzoylphthalimide in dichloromethane containing cyclohexene. The bond lengths and angles are generally within the normal ranges. A notable feature of the molecule is the presence within it of four contiguous chiral centres

Computer program development for the analysis of inelastic beam and soil behaviour in geotechnical design

Computer-aided engineering requires the correct implementation of design methods in computer programs so as to play a beneficial role in engineering practice. This thesis describes the development of a computer program to analyse geotechnical engineering problems based on the principles of beam-soil interaction where the beam is supported by a single or two-layer soil system. In 1867, a foundation model was proposed by Winkler in which the elastic foundation beneath a horizontal beam could be viewed as a series of independent springs. Foundation reaction to beam deflection is, therefore, linear. A stiffness matrix, for use in matrix methods of structural analysis, has been developed to define this beam-soil interaction, and such a method can be incorporated into a computer program. Furthermore, an iterative technique was created to allow for inelastic soil response when using the elastic stiffness matrix. However, such a technique did not consider realistic soil behaviour, and has limitations is used for practical design. This research' work describes how use can be made of the pressure-displacement response relationship for a soil to bring greater realism to beam-soil modelling and analysis. Such a relationship is commonly determined in geotechnical design procedures through a plate load test in the field. In addition, the iterative technique is extended to include non-linear beam behaviour as well, and plastic hinging of the beam material is incorporated to enable limitation of inelastic response. While previous research has only considered foundations of a single soil only, a procedure to model a two-layered system is developed. Two-layered foundations are required for proper modelling of soldier pile support systems, an area of structural design in geotechnics chosen to demonstrate realistic design potential for the computer program. The two-layered principle is based on the derivation of a control parameter to differentiate between response from just the upper soil layer, and a combined response from both soil layers. The procedure is relatively simple, and no extra information is required other than the two pressure displacement relationships for the individual soil layers. A desktop computer program is described which incorporates the inelastic analysis features, as well as the two-layered soil system. The program makes use of a graphical user interface to offer the user an easy, interactive environment for analysing beam-on-soil foundation problems. As such, the program can be used directly, or for further research into beam-soil interaction. The program is applied in the analysis of both field and laboratory tests to ascertain its accuracy in predicting beam-soil interaction. The laboratory test measures the deflection of a horizontal beam on a single soil foundation medium, where the beam is loaded by a single jack at approximately mid-span. Computer predictions for such a test were in very close agreement with the laboratory observations, despite the small magnitude of beam displacements, and the fact the beam-soil system suffered a bearing capacity failure which affected the beam deflection. The field test was performed to investigate the performance of a flexible soldier pile under high anchor loading. Results of the computer analyses again show the program's predictions to be in very close agreement with the field measurements. Currently, the program does not include the facility to model soil layers behind a soldier pile, but the method developed in this thesis can easily incorporate multiple pressure-displacement curves for different soils. Final conclusions drawn express a need for more research into soldier pile systems before the techniques of this work can be used for routine design. Nevertheless, the development of the program has made a significant contribution to advancing the use of computer-aided design in this field of geotechnical engineering

4',5',6',7'-Tetrachlorospiro[cyclohex-2-ene-1,2'-indan]-1',3'-dione

The title compound, C₁₄H₈Cl₄O₂, has been isolated following irradiation of a dichloromethane solution of N-acetyltetrachlorophthalimide and cyclohexene. The structure refinement is slightly compromised by the disorder over two positions of equal occupancy of a methylene groupβ to the spiro C atom

Studies in the transformations of austenite

The work described in this section is a study of one aspect of the effect of austenitic inhomogeneity on the transformation of austenite during the heat treatment of plain carbon steels containing about 0.4 carbon. To begin with it was intended to make a study of the austenpering process and it was shown that the change in electrical resistance accompanying the precipitation of carbide could be used to follow the breakdown of austenite. The use of this method meant that a nonconducting quenching bath must be used since it was not feasible to provide an insulating cover for the test piece. Salt bath and hot air blast quenching were both tried but proved to be too slow to supress completely the formation of pearlite. Attention was then transferred to a more direct study of the effect of inhomogeneity by microscopical methods. Specimens were reacted isothermally in an attempt to detect any differences in reaction times due to differing degree of homogeneity. The results were inconsistent, due probably to variations in the temperature of the lead bath used, and no correlation between austenising time and reaction time could be established. Differences in the appearance of specimens air cooled after varying times in the furnace suggested that a comparison of the appearance of normalised specimens which had initial structures of varying degrees of coarseness might give an approximate idea of the time required to eliminate the effect of varying initial structure. The specimens employed had the carbide in the form of pearlite of approximately the same degree of fineness but the ferrite areas differed An size, one having an ASTM grain size 2-3 and the other 8. It was found that after three minutes at 850 °C followed by air cooling the structures obtained showed marked differences but that after eight minutes no difference was visible. It seems, therefore, that between,JJJ three and eight minutes carbon has diffused sufficiently to remove the effect of the ferrite corresponding to the coarser grain. No conclusion can be drawn regarding the time taken for solution of carbide. Tensile tests on specimens prepared in the same way showed differences, after three minutes at temperatureswhich were markedly reduced after eight minutes, supporting the conclusion above. End quenched test pieces showed the effect of inhomogeneity due to ferrite on transformation during more rapid cooling. In this case the presence of areas, of low carbon content was shown to result in the formation of pearlite at cooling rates too great to allow of its formation by the normal grain boundary nucleation. Starting with a ferrite-pearlite structure with grain size L1., the low carbon areas resulting from the ferrite in the original structure are eliminated after two minutes at 850 °C, at least to the extent that they no longer act more powerfully than the normal grain boundary nuclei in inducing the formation of pearlite. No conclusion can be drawn with any degree of condifence regarding the time required to dissolve cementite completely and remove the resulting inhomogeneity but it seems probable that it is less than the time required to remove inhomogeneity due to the original presence of ferrite. This would not be the case if the original structure contained cementite in larger particles than was the case in these experiments. The practical conclusion to be drawn from these experiments in that in the heat treatment of 0.4% to 0.5% carbon steel where the carbon is present in the form of sorbitic or finely lamellar pearlite, the time required at a given temperature for practical homogeneity to be reached is determined by the time required for carbon to diffuse into the pre-existing ferrite areas. This time depends on the size of those areas but is quite short, of the order of two minutes at 850 °C where the ferrite network corresponds to A. S. T. M. grain size 4. Unless the piece being heat treated is very small, the time required for homogenisation will be so short compared with the time required to raise the temperature that in most cases it will be negligible

Lithological and Foraminiferal Characteristics of Shoreface and Shallow Shelf Facies off Bogue Banks, NC

Fossil foraminiferal assemblages are used by paleontologists to determine the depositional environment of the strata in which the assemblages are found. This allows for the reconstruction of past environments and climates working under the assumption that specific foraminiferal assemblages are diagnostic to the depositional environment. However, foraminiferal assemblages of several coastal subenvironments (e.g., beach, shoreface, ebb tide delta, inner shelf) have yet to be extensively studied. In this study, Holocene sediments from vibracores taken off the coast of Bogue Banks, NC, were analyzed for their lithology and foraminiferal assemblages to study the differences before shoreface and inner shelf environments. Two 3 m vibracores from each environment were logged using a method that is independent from composition, and samples of sediment from Holocene units were taken for foraminiferal analysis. Sand and mud content were determined by sieving. The 63-710 micron fraction of the samples were floated in a sodium polytungstate solution to concentrate foraminiferal tests. Approximately 100 specimens were randomly picked from each sample and the relative percentages of three major foraminiferal taxonomic groups were recorded. In shelf sediment samples, assemblages comprised 95% to 100% Rotaliina. By comparison, in shoreface sediment samples, assemblages comprised 85% to 90% Rotaliina, with 10% to 15% Miliolina. These results suggest that a potential method for distinguishing the two subenvironments could be found in the presence of absence of genera within the suborder Miliolina

Benzylammonium 2,4-bis(dicyanomethylene)-2,3-dihydroisoindolide

The cation and anion of the title salt, C⁷H₁₀N⁺.C₁₄H₄N₅-, are both bisected by a crystallographic mirror plane. Extensive hydrogen bonding, with the R₆⁶(28) graph-set motif, connects the ions into layers