992 resultados para small dependence


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In this paper, the influence of the impact energy on the initial fabrication of thin films formed by low energy cluster deposition was investigated by molecular dynamics simulation of All 3 clusters depositing on Ni(0 0 1) substrate. In the case of soft-landing, (0.01 eV/atom), clusters are rearranged from I-h symmetry into fcc-like clusters on the surface. Then they aggregate each other, which result in thin film growing in 3D island mode. While, growth will be in layer-by-layer mode at the impact energy of a few electron volt due to the transient lateral spread of cluster atoms induced by dense collision cascade. This effect has been traced to collision cascade inside the cluster. which is enhanced by collision with a hard Ni substrate. (C) 2002 Elsevier Science B.V. All rights reserved.

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The deposition of hyperthermal CH3 on diamond (001)-(2×1) surface at room temperature has been studied by means of molecular dynamics simulation using the many-body hydrocarbon potential. The energy threshold effect has been observed. That is, with fixed collision geometry, chemisorption can occur only when the incident energy of CH3 is above a critical value (Eth). Increasing the incident energy, dissociation of hydrogen atoms from the incident molecule was observed. The chemisorption probability of CH3 as a function of its incident energy was calculated and compared with that of C2H2. We found that below 10 eV, the chemisorption probability of C2H2 is much lower than that of CH3 on the same surface. The interesting thing is that it is even lower than that of CH3 on a hydrogen covered surface at the same impact energy. It indicates that the reactive CH3 molecule is the more important species than C2H2 in diamond synthesis at low energy, which is in good agreement with the experimental observation.

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Ions play an important role in affecting climate and particle formation in the atmosphere. Small ions rapidly attach to particles in the air and, therefore, studies have shown that they are suppressed in polluted environments. Urban environments, in particular, are dominated by motor vehicle emissions and, since motor vehicles are a source of both particles and small ions, the relationship between these two parameters is not well known. In order to gain a better understanding of this relationship, an intensive campaign was undertaken where particles and small ions of both signs were monitored over two week periods at each of three sites A, B and C that were affected to varying degrees by vehicle emissions. Site A was close to a major road and reported the highest particle number and lowest small ion concentrations. Precursors from motor vehicle emissions gave rise to clear particle formation events on five days and, on each day this was accompanied by a suppression of small ions. Observations at Site B, which was located within the urban airshed, though not adjacent to motor traffic, showed particle enhancement but no formation events. Site C was a clean site, away from urban sources. This site reported the lowest particle number and highest small ion concentration. The positive small ion concentration was 10% to 40% higher than the corresponding negative value at all sites. These results confirm previous findings that there is a clear inverse relationship between small ions and particles in urban environments dominated by motor vehicle emissions.

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Introduction: The use of amorphous-silicon electronic portal imaging devices (a-Si EPIDs) for dosimetry is complicated by the effects of scattered radiation. In photon radiotherapy, primary signal at the detector can be accompanied by photons scattered from linear accelerator components, detector materials, intervening air, treatment room surfaces (floor, walls, etc) and from the patient/phantom being irradiated. Consequently, EPID measurements which presume to take scatter into account are highly sensitive to the identification of these contributions. One example of this susceptibility is the process of calibrating an EPID for use as a gauge of (radiological) thickness, where specific allowance must be made for the effect of phantom-scatter on the intensity of radiation measured through different thicknesses of phantom. This is usually done via a theoretical calculation which assumes that phantom scatter is linearly related to thickness and field-size. We have, however, undertaken a more detailed study of the scattering effects of fields of different dimensions when applied to phantoms of various thicknesses in order to derive scattered-primary ratios (SPRs) directly from simulation results. This allows us to make a more-accurate calibration of the EPID, and to qualify the appositeness of the theoretical SPR calculations. Methods: This study uses a full MC model of the entire linac-phantom-detector system simulated using EGSnrc/BEAMnrc codes. The Elekta linac and EPID are modelled according to specifications from the manufacturer and the intervening phantoms are modelled as rectilinear blocks of water or plastic, with their densities set to a range of physically realistic and unrealistic values. Transmissions through these various phantoms are calculated using the dose detected in the model EPID and used in an evaluation of the field-size-dependence of SPR, in different media, applying a method suggested for experimental systems by Swindell and Evans [1]. These results are compared firstly with SPRs calculated using the theoretical, linear relationship between SPR and irradiated volume, and secondly with SPRs evaluated from our own experimental data. An alternate evaluation of the SPR in each simulated system is also made by modifying the BEAMnrc user code READPHSP, to identify and count those particles in a given plane of the system that have undergone a scattering event. In addition to these simulations, which are designed to closely replicate the experimental setup, we also used MC models to examine the effects of varying the setup in experimentally challenging ways (changing the size of the air gap between the phantom and the EPID, changing the longitudinal position of the EPID itself). Experimental measurements used in this study were made using an Elekta Precise linear accelerator, operating at 6MV, with an Elekta iView GT a-Si EPID. Results and Discussion: 1. Comparison with theory: With the Elekta iView EPID fixed at 160 cm from the photon source, the phantoms, when positioned isocentrically, are located 41 to 55 cm from the surface of the panel. At this geometry, a close but imperfect agreement (differing by up to 5%) can be identified between the results of the simulations and the theoretical calculations. However, this agreement can be totally disrupted by shifting the phantom out of the isocentric position. Evidently, the allowance made for source-phantom-detector geometry by the theoretical expression for SPR is inadequate to describe the effect that phantom proximity can have on measurements made using an (infamously low-energy sensitive) a-Si EPID. 2. Comparison with experiment: For various square field sizes and across the range of phantom thicknesses, there is good agreement between simulation data and experimental measurements of the transmissions and the derived values of the primary intensities. However, the values of SPR obtained through these simulations and measurements seem to be much more sensitive to slight differences between the simulated and real systems, leading to difficulties in producing a simulated system which adequately replicates the experimental data. (For instance, small changes to simulated phantom density make large differences to resulting SPR.) 3. Comparison with direct calculation: By developing a method for directly counting the number scattered particles reaching the detector after passing through the various isocentric phantom thicknesses, we show that the experimental method discussed above is providing a good measure of the actual degree of scattering produced by the phantom. This calculation also permits the analysis of the scattering sources/sinks within the linac and EPID, as well as the phantom and intervening air. Conclusions: This work challenges the assumption that scatter to and within an EPID can be accounted for using a simple, linear model. Simulations discussed here are intended to contribute to a fuller understanding of the contribution of scattered radiation to the EPID images that are used in dosimetry calculations. Acknowledgements: This work is funded by the NHMRC, through a project grant, and supported by the Queensland University of Technology (QUT) and the Royal Brisbane and Women's Hospital, Brisbane, Australia. The authors are also grateful to Elekta for the provision of manufacturing specifications which permitted the detailed simulation of their linear accelerators and amorphous-silicon electronic portal imaging devices. Computational resources and services used in this work were provided by the HPC and Research Support Group, QUT, Brisbane, Australia.

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Knowledge Integration (KI) is one of the major aspects driving innovation within an organisation. In this paper, we attempt to develop a better understanding of the challenges of knowledge integration within the innovation process in technology-based firms. Using four technology-based Australian firms, we investigated how knowledge integration may be managed within the context of innovation in technology firms. The literature highlights the role of four KI tasks that affect the innovation capability within technology-oriented firms, namely team building capability, capturing tacit knowledge, role of KM systems and technological systemic integration. Our findings indicate that in addition to the four tasks, a strategic approach to integrating knowledge for innovation as well as leadership and management are essential to achieving effective KI across multiple levels of engagement. Our findings also offer practical insights of how knowledge can be integrated within innovation process.

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Stereo visual odometry has received little investigation in high altitude applications due to the generally poor performance of rigid stereo rigs at extremely small baseline-to-depth ratios. Without additional sensing, metric scale is considered lost and odometry is seen as effective only for monocular perspectives. This paper presents a novel modification to stereo based visual odometry that allows accurate, metric pose estimation from high altitudes, even in the presence of poor calibration and without additional sensor inputs. By relaxing the (typically fixed) stereo transform during bundle adjustment and reducing the dependence on the fixed geometry for triangulation, metrically scaled visual odometry can be obtained in situations where high altitude and structural deformation from vibration would cause traditional algorithms to fail. This is achieved through the use of a novel constrained bundle adjustment routine and accurately scaled pose initializer. We present visual odometry results demonstrating the technique on a short-baseline stereo pair inside a fixed-wing UAV flying at significant height (~30-100m).

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On 21 September 1999 Division 152 was inserted into the Income Tax Assessment Act (1997) (ITAA 1997). It was subsequently subject to amendments in 2006. Division 152 contains the small business CGT concessions, which enables eligible small business taxpayers to reduce the amount of tax payable on capital gains arising from certain CGT events (including the sale of the small business itself) that occur after 11:45 am on 21 September 1999. One of the stated principal objectives of the legislation was to provide a concessionary regime for small business owners who did not have the same ability to access the concessionary superannuation regime (particularly the superannuation guarantee charge) generally available to employees. The then Federal Treasurer, Mr Peter Costello, when announcing the introduction of the concessions, specifically stated that the object of Div 152 was to provide “small business people with access to funds for retirement or expansion”. The purpose of this project is to: one, assess the extent to which small business taxpayers understand the CGT small business concessions, particularly when considering sale of their business; two, determine which of the four small business CGT concessions are being adopted and/or recommended by tax advisors to clients; and three, determine whether the recent superannuation changes announced by the Federal Government in relation to the capping of the concessional superannuation thresholds have had an impact on the use of the small business retirement concession. It is anticipated that the results of this study will reveal that that small business owners are reliant on their tax advisors to explain the operation of Division 152. It is plausible that give the complexity of the CGT concessions, most small business owners are completely unaware of the four small business CGT concessions contained in Division 152 and do not understand how these concessions apply. Our study will also reveal the extent to which each CGT small business concession has been adopted (and reasons why). In particular, emphasis will be placed on the adoption of the small business retirement concession contained in Subdivision 152-D (and specific reasons for its adoption). This study also seeks to understand whether the recent (and impending) changes to the concessional superannuation cap has resulted in the retirement concession being more widely adopted (or recommended) by tax advisors. We would expect that the results of our study to confirm this to be the case, particularly coupled with the recent economic downturn, which has led to lower superannuation fund balances. By providing accounting firms with this information, small business owners will benefit from the information, becoming better placed to be long-term self funded retirees, providing not only financial benefits to the individuals and the country, but a significant increase in social self-assurance by these members of the community.

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This paper presents a recursive strategy for online detection of actuator faults on a unmanned aerial system (UAS) subjected to accidental actuator faults. The proposed detection algorithm aims to provide a UAS with the capability of identifying and determining characteristics of actuator faults, offering necessary flight information for the design of fault-tolerant mechanism to compensate for the resultant side-effect when faults occur. The proposed fault detection strategy consists of a bank of unscented Kalman filters (UKFs) with each one detecting a specific type of actuator faults and estimating corresponding velocity and attitude information. Performance of the proposed method is evaluated using a typical nonlinear UAS model and it is demonstrated in simulations that our method is able to detect representative faults with a sufficient accuracy and acceptable time delay, and can be applied to the design of fault-tolerant flight control systems of UASs.

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A Neutral cluster and Air Ion Spectrometer (NAIS) was used to monitor the concentration of airborne ions on 258 full days between Nov 2011 and Dec 2012 in Brisbane, Australia. The air was sampled from outside a window on the sixth floor of a building close to the city centre, approximately 100 m away from a busy freeway. The NAIS detects all ions and charged particles smaller than 42 nm. It was operated in a 4 min measurement cycle, with ion data recorded at 10 s intervals over 2 min during each cycle. The data were analysed to derive the diurnal variation of small, large and total ion concentrations in the environment. We adapt the definition of Horrak et al (2000) and classify small ions as molecular clusters smaller than 1.6 nm and large ions as charged particles larger than this size...

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This thesis studied the source of instability in optical phase modulators used in high accuracy laser measurement systems. The nonlinear origin of the amplitude noise helped further reducing this instability in applications that rely on phase modulators to function. This outcome will have positive impacts on the development of new methods in the amplitude noise suppression.

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This study aimed to investigate drink driving in a sample of general drivers and convicted drunk driving offenders in Guangzhou, China. The study also aimed to explore some potential factors that impact on alcohol-related driving behaviour. Samples of 406 general drivers and 101 drunk driving offenders were recruited between May and October 2012. A survey was used to collect information about demographic characteristics, knowledge, attitudes and practices related to drink driving. The Alcohol Use Disorders Identification Test (AUDIT) was used to assess possible drinking problems. The average age reported for starting to drink alcohol for both groups of participants was around 19 years old. The mean AUDIT score of general drivers was 7.4 (SD = 5.4) representing a low level of alcohol problems, and for convicted drunk driving offenders was 11.1 (SD = 5.9) representing a medium level of alcohol problems (significant difference between means, t = 5.75, p < 0.001). AUDIT scores indicated that a substantial proportion (65%) of the offenders had medium to high levels of alcohol use disorders, compared with 38.5% among general drivers. Offenders who knew the drunk driving legal limit had a lower AUDIT score (M = 9.8, SD = 5.16) than those who did not know it (M = 12.2, SD = 6.257, t = -1.987. p = 0.05). In addition, offenders who were novice drivers (licensed less than 2 years) had a higher AUDIT score (M = 16.4, SD = 7.6) than the other three driver experience categories used.

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This series of research vignettes is aimed at sharing current and interesting research findings from our team of international Entrepreneurship researchers. This vignette, written by Dr. Rene Bakker, examines the evidence on the effects of a entrepreneurs’ personal networks on small firm performance, and the factors that moderate this relationship.

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Our results demonstrate that photorefractive residual amplitude modulation (RAM) noise in electro-optic modulators (EOMs) can be reduced by modifying the incident beam intensity distribution. Here we report an order of magnitude reduction in RAM when beams with uniform intensity (flat-top) profiles, generated with an LCOS-SLM, are used instead of the usual fundamental Gaussian mode (TEM00). RAM arises from the photorefractive amplified scatter noise off the defects and impurities within the crystal. A reduction in RAM is observed with increasing intensity uniformity (flatness), which is attributed to a reduction in space charge field on the beam axis. The level of RAM reduction that can be achieved is physically limited by clipping at EOM apertures, with the observed results agreeing well with a simple model. These results are particularly important in applications where the reduction of residual amplitude modulation to 10^-6 is essential.

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The market of building retrofits is increasingly more intensified as existing buildings are aging. The building retrofit projects involve existing buildings which impose constraints on stakeholders throughout the project process. They are also risky, complex, less predictable and difficult to be well planned with on-site waste becoming one of the critical issues. Small and Medium Enterprises (SMEs) carry out most of the work in retrofit projects as subcontractors, but they often do not have adequate resources to deal with the specific technical challenges and project risks related to waste. This paper first discusses the requirements of waste management in building retrofit projects considering specific project characteristics and work natures, and highlights the importance of involving SMEs in waste planning and management through an appropriate way. By utilizing semi-structured interviews, this research develops a process model for SMEs to be applied in waste management. A collaboration scenario is also developed for collaborative waste planning and management by SMEs as subcontractors and large companies as main contractors. Findings from the paper will promote coordination of project delivery and waste management in building retrofit projects, and improve the involvement and performance of SMEs in dealing with waste problems.

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In vivo small molecules as necessary intermediates are involved in numerous critical metabolic pathways and biological processes associated with many essential biological functions and events. There is growing evidence that MS-based metabolomics is emerging as a powerful tool to facilitate the discovery of functional small molecules that can better our understanding of development, infection, nutrition, disease, toxicity, drug therapeutics, gene modifications and host-pathogen interaction from metabolic perspectives. However, further progress must still be made in MS-based metabolomics because of the shortcomings in the current technologies and knowledge. This technique-driven review aims to explore the discovery of in vivo functional small molecules facilitated by MS-based metabolomics and to highlight the analytic capabilities and promising applications of this discovery strategy. Moreover, the biological significance of the discovery of in vivo functional small molecules with different biological contexts is also interrogated at a metabolic perspective.