Monte Carlo Simulation of Comptonization in Inhomogeneous Media

Comptonization is the process in which photon spectrum changes due to multiple Compton scatterings in the electronic plasma. It plays an important role in the spectral formation of astrophysical X-ray and gamma-ray sources. There are several intrinsic limitations for the analytical method in dealing with the Comptonization problem and Monte Carlo simulation is one of the few alternatives. We describe an efficient Monte Carlo method that can solve the Comptonization problem in a fully relativistic way. We expanded the method so that it is capable of simulating Comptonization in the media where electron density and temperature varies discontinuously from one region to the other and in the isothermal media where density varies continuously along photon paths. The algorithms are presented in detail to facilitate computer code implementation. We also present a few examples of its application to the astrophysical research.Comment: 12 pages, 4 figures, Postscript file, in press ("Computers in Physics", Vol. 11, No. 6

Understanding the Roles of sketching in product design

Sketching is an essential part of the tradition and practice of design. However, despite the extensive literature on the subject, the roles of sketching in the design are still not fully understood. Therefore, this PhD study was carried out to understand the roles of sketching in the product design field and to develop the means to support the design sketching process. Hypotheses emerged from the review of the literature and led to three descriptive studies: a pilot study to identify the roles of sketching in design; a survey of design students; a survey of design professionals. Data collected from these studies were used to test and verify the hypotheses. It was found that the major roles of sketching in design were related to design ideation and design communication. The comparison between design students and professionals showed that they tend to perceive the major roles of sketching differently, but shared similar opinions on the major roles of talking sketches, sketching expertise and as a practical supporting tool. In addition, an Ideation Segment Model was proposed, which describes the process that sketching ideas evolve into final design outcomes and locates the potential supporting tools in the sketching process. Consequently, a practical supporting tool was developed to enhance understanding of design sketching, to provide external stimuli, and to improve sketching expertise. The supporting tool, entitled the PD-Sketching Primer and PD-Sketching Toolkit, was tested with education and positive feedback was received. This research has contributed towards understanding the roles of sketching in design, e.g. it is the first empirical study of ‘non-working sketches’ in the design field. It has generated new knowledge and tools to support the design sketching process. This supporting tool is one of only a few resources designed to support sketching activity and creative performance in the product design field.Open Acces

Structural auditing methodologies for controlled terminologies

Several auditing methodologies for large controlled terminologies are developed. These are applied to the Unified Medical Language System XXXX and the National Cancer Institute Thesaurus (NCIT). Structural auditing methodologies are based on the structural aspects such as IS-A hierarchy relationships groups of concepts assigned to semantic types and groups of relationships defined for concepts. Structurally uniform groups of concepts tend to be semantically uniform. Structural auditing methodologies focus on concepts with unlikely or rare configuration. These concepts have a high likelihood for errors. One of the methodologies is based on comparing hierarchical relationships between the META and SN, two major knowledge sources of the UMLS. In general, a correspondence between them is expected since the SN hierarchical relationships should abstract the META hierarchical relationships. It may indicate an error when a mismatch occurs. The UMLS SN has 135 categories called semantic types. However, in spite of its medium size, the SN has limited use for comprehension purposes because it cannot be easily represented in a pictorial form, it has many (about 7,000) relationships. Therefore, a higher-level abstraction for the SN called a metaschema, is constructed. Its nodes are meta-semantic types, each representing a connected group of semantic types of the SN. One of the auditing methodologies is based on a kind of metaschema called a cohesive metaschema. The focus is placed on concepts of intersections of meta-semantic types. As is shown, such concepts have high likelihood for errors. Another auditing methodology is based on dividing the NCIT into areas according to the roles of its concepts. Moreover, each multi-rooted area is further divided into pareas that are singly rooted. Each p-area contains a group of structurally and semantically uniform concepts. These groups, as well as two derived abstraction networks called taxonomies, help in focusing on concepts with potential errors. With genomic research being at the forefront of bioscience, this auditing methodology is applied to the Gene hierarchy as well as the Biological Process hierarchy of the NCIT, since processes are very important for gene information. The results support the hypothesis that the occurrence of errors is related to the size of p-areas. Errors are more frequent for small p-areas

Phase Difference and Coherence as Diagnistics of Accreting Compact Sources

We present calculations of the time lags and the coherence function of X-ray photons for a novel model of radiation emission from accretion powered, high-energy sources. Our model involves only Comptonization of soft photons injected near the compact object in an extended but non-uniform atmosphere around the compact object. Our results show that this model produces time lags between the hard and soft bands of the X-ray spectrum which increase with Fourier period, in agreement with recent observations; it also produces a coherence function equal to one over a wide range of frequencies if the system parameters do not have significant changes, also in agreement with the limited existing observations. We explore various conditions that could affect coherence functions. We indicate that measurements of these statistical quantities could provide diagnostics of the radial structure of the density of this class of sources.Comment: 15 pages, Latex, using AAS macro, to be published in Astrophysical Journal Letters

Organising the socio-economic relevance of university research: the case of nanomaterials research in Taiwan

This thesis is concerned with academics’ behaviour when organising research aimed at being relevant. More specifically, this study combines a sociological approach and an extensive bibliometric analysis, investigating the relationships between scientists’ perceptions of relevance, their research behaviours and their publishing activities in terms of organising nanomaterials research in Taiwan. By introducing a resource-based concept of the notion of relevance from a scientist’s perspective, it contributes to intellectual debates on changes to knowledge production and the relationship between scientific excellence and socio-economic relevance. The study finds that the ways nanomaterials scientists perceive and organise their research, specifically in terms of research orientation, industry involvement and interdisciplinary collaboration, are not entirely oriented towards socio-economic concerns. Scientists tend to adapt to the demand for relevance by demonstrating potential research applications and forming interdisciplinary collaborations. Nevertheless, they are more persistent in terms of not having industry involved in the research process. Balancing adaptation and persistence reflects scientists’ concerns with securing financial, intellectual and symbolic resources in order to establish their academic credibility. The bibliometric analysis broadly confirms the qualitative results findings, showing an increasing trend towards publishing in applied and targeted basic journals, and towards interdisciplinary collaboration. Yet, the proportion of university-industry papers has been rather stable over time. While our interviews suggest that senior scientists tend to consider interdisciplinary collaboration as a way to facilitate application, the bibliometric analysis shows that interdisciplinary co-authored papers tend to be more basic and receive more citations. The analysis also finds that junior scientists tend to feel more pressure to achieve a strong academic performance, thereby pushing them away from activities concerning achieving the envisioned socio-economic relevance of their research. Given the ambiguous notion of relevance and the inconsistency of policy practices, this thesis suggests that the real pressure is more to do with the demand for excellence than for relevance

Compton backscattered annihilation line emission: A new diagnostic of accreting compact sources

It is shown that Compton scattering of 511 keV electron-positron annihilation radiation produces a line like feature at approx. 170 keV from backscattered photons. Assuming a simple model of an accretion disk around a compact source, the spectrum is explored of the spectrum of Compton scattered annihilation line emission for a range of conditions. It is further shown that such Compton baskscattering of annihilation line emission from the inner edge of an accretion disk could account for the previously unidentified 170 keV line emission and high energy continuum observed from a variable, compact source, or sources, of annihilation radiation near the Galactic Center. Identification of the observed 170 keV line as an annihilation line reflection feature provides strong new evidence that the source of the emission is an accreting compact object. Further study of these features in existing spectra and in forthcoming GRO observation of these and other sources can provide unique new diagnostics of the innermost regions of accretion disks around compact objects