Small Design Changes Research Articles

Dosimetry revisited for the HDR brachytherapy source model mHDR‐v2

Recently, the manufacturer of the HDR 192Ir mHDR-v2 brachytherapy source reported small design changes (referred to herein as mHDR-v2r) that are within the manufacturing tolerances but may alter the existing dosimetric data for this source. This study aimed to (1) check whether these changes affect the existing dosimetric data published for this source; (2) obtain new dosimetric data in close proximity to the source, including the contributions from 192Ir electrons and considering the absence of electronic equilibrium; and (3) obtain scatter dose components for collapsed cone treatment planning system implementation. Three different Monte Carlo (MC) radiation transport codes were used: MCNP5, PENELOPE2008, and GEANT4. The source was centrally positioned in a 40 cm radius water phantom. Absorbed dose and collision kerma were obtained using 0.1 mm (0.5 mm) thick voxels to provide high-resolution dosimetry near (far from) the source. Dose-rate distributions obtained with the three MC codes were compared. Simulations of mHDR-v2 and mHDR-v2r designs performed with three radiation transport codes showed agreement typically within 0.2% for r > or = 0.25 cm. Dosimetric contributions from source electrons were significant for r < 0.25 cm. The dose-rate constant and radial dose function were similar to those from previous MC studies of the mHDR-v2 design. The 2D anisotropy function also coincided with that of the mHDR-v2 design for r > or = 0.25 cm. Detailed results of dose distributions and scatter components are presented for the modified source design. Comparison of these results to prior MC studies showed agreement typically within 0.5% for r > or = 0.25 cm. If dosimetric data for r < 0.25 cm are not needed, dosimetric results from the prior MC studies will be adequate.

Improving bending stress in spur gears using asymmetric gears and shape optimization

Bending stress plays a significant role in gear design wherein its magnitude is controlled by the nominal bending stress and the stress concentration due to the geometrical shape. The bending stress is indirectly related to shape changes made to the cutting tool. This work shows that the bending stress can be reduced significantly by using asymmetric gear teeth and by shape optimizing the gear through changes made to the tool geometry. However, to obtain the largest possible stress reduction a custom tool must be designed depending on the number of teeth, but the stress reductions found are not very sensitive to small design changes. This observation suggests the use of two new standard cutting tools.

Rotary Molecular Motors: A Large Increase in Speed through a Small Change in Design

Reducing the steric interaction between the upper-half and the lower-half of a light-driven rotary molecular motor by decreasing the size of the aromatic moiety in the upper-half from a naphthalene to a benzothiophene results in an almost 3500 times faster rotation.

Negative or positive effects of plantation and intensive forestry on biodiversity: A matter of scale and perspective

Terrestrial biodiversity is closely linked to forest ecosystems but anthropogenic reductions in forest cover and changes in forest structure and composition jeopardize their biodiversity. Several forest species are threatened because of reduced habitat quality and fragmentation or even habitat loss as a result of forest management activities. In response to this threat, integrated forest management (IFM) was developed in the early 1990s and has been applied over large spatial scales ever since. While IFM seeks to satisfy both human resource demands and ecosystem integrity, the whole forest matrix is affected and this may also have negative impacts on biodiversity. The concept of forest zoning (e.g., Triad) avoids these issues by physically separating land uses from each other. The zoning approach has been developed in the same period as IFM, but there are still very few examples of large-scale applications. This may be because its distinctiveness from IFM may not always seem clear and because forest zoning is not easily implemented. Here we explain these differences and show that IFM and the zoning approach are indeed different management paradigms. We advocate the use of high-yield plantations within the zoning paradigm as a means for biodiversity conservation and review the literature (with an emphasis on the northern hemisphere and on plantation forestry within a land-zoning approach) on impacts of forest management activities on biodiversity. Furthermore, we give advice on issues that require consideration when implementing forest zoning at both the stand and the landscape levels. We recommend several small changes in design and management of forest plantations as a means to significantly increase their biodiversity value. We conclude that while forest zoning seems an adequate strategy for the Canadian forestry sector, a shift in paradigm must carry over to policy-makers and legislation if this approach is to succeed. Key words: biodiversity, landbase zoning, forest management, intensive silviculture, plantation forests

Modeling of dynamic behavior of a single-point moored submersible fish cage under currents

The submergence behavior of a small volume fish cage in a single-point mooring system under currents is investigated using a numerical model. Results are validated by comparing to a scaled physical model tow test. The current induced submergence depth, as a function of net chamber solidity for various water velocities is examined. The system remains at the surface at low water velocities until the solidity dependent threshold is reached. At higher currents, the system enters an unstable submergence regime where a small change in the system design could significantly impact the predicted submergence depth. The distribution of current throughout the water column also plays an important role in the steady state response of the structure.Analytical formulas to approximate the dependence of normal drag coefficient for cylinders and spheres on Reynolds number (Re) are proposed. The formulas for cylinders expand the expressions of Choo and Casarella (1971) to account for the decrease in drag forces experimentally observed for 2×105<Re<106. Modeling of this effect is important for proper interpretation of Froude scale physical modeling data.

The morphology of integrated self-assembled monolayers and their impact on devices – A computational and experimental approach

We report on a combined experimental and computational study on self-assembled monolayers (SAMs). The dielectric properties of SAMs based on n-alkyl phosphonic acids in large area thin film devices (organic field-effect transistors with good hole mobilities up to 0.3 cm 2 V −1 s −1 at −1 V and capacitors) depend on their chain length, but not consistently to theoretical pictures of tunneling through saturated n-alkanes. An unexpected saturation of current density with increasing chain length was obtained in devices, what impact on the leakage current in transistors and current density in capacitors. This is attributed to different self-assembled monolayer morphology ranging from an amorphous state for short alkyl chains to a quasi-crystalline state for longer alkyl chains. Molecular dynamics (MD) simulations provide a deeper insight into the nature of the three-dimensional intermolecular interactions and support the proposed SAM morphology. The change in morphology leads to a reduced effective SAM thickness in devices, which could be described by a Simmons approach quantitatively. The morphological aspect of self-assembled molecules is of enormous importance beyond the applications of SAMs in low-voltage, high mobility organic transistors because of it’s relevance for the hole field of molecular scale electronics. It demonstrates that even small changes in the molecular design can change the molecular interactions and monolayer assembly.

Household Response to the 2008 Tax Rebate: Survey Evidence and Aggregate Implications

Only about one‐fifth of respondents in the Reuters/University of Michigan survey report that the 2008 tax rebates led them to mostly increase spending, whereas over half said it would lead them to mostly pay off debt. Of those in the mostly‐spend category, the response was swift, with over 80% reporting increasing their spending within 3 months of receiving their rebate. Older households, households with higher wealth and higher income, and those expecting future income growth were generally more likely to spend the rebates. A review of other surveys confirms the general pattern of results and suggests that small changes in survey design do not have a major effect on the distribution of responses. The distribution of survey answers corresponds to an aggregate marginal propensity to consume (MPC) after 1 year of about one‐third. The paper combines this survey‐based estimate of the MPC and the survey‐based estimate of the timing of spending to show that the rebates help explain the aggregate movements in saving, spending, and debt in 2008. Because the rebate was large and was distributed over a short period, it had a nontrivial effect on total spending in the second and third quarters of 2008. Nonetheless, the results imply that the rebates provided only a modest stimulus to spending per dollar of rebate.

Modeling and Validating the Effective Hydraulic Detention Time for a 10 mgd Ozone Contactor at the Lake Washington Surface Water Treatment Plant, Melbourne, Florida

Ozonation has been added to the treatment process at the 20 mgd Lake Washington Surface Water Treatment Plant (SWTP), Melbourne, Florida to improve finished water quality, control taste and odor, and provide greater than 0.5-log credit for inactivation of Cryptosporidium. The new ozone contactors (2 parallel 10 mgd trains) are located between the existing ActifloTM clarifiers and the filters on a relatively congested site. Prior to construction, a Computational Fluid Dynamics (CFD) study indicated that the proposed contactor design was not optimized to provide the targeted Cryptosporidium log inactivation. Based on the CFD modeling, the design was modified to reduce the baffle heights (increasing end gaps at turns) and the baffle ends were chamfered to improve flow patterns within the contactor. Internal access platforms were rotated from parallel to the flow (along outside walls) to perpendicular to the flow (along baffle walls). These small design changes increased the modeled effective detention time (t10) for disinfection and the corresponding hydraulic efficiency (baffling factor) by 22 %. In addition, the dosing location for the ozone quenching chemical (hydrogen peroxide) was modified to provide extra ozone detention. The ozone contactors were then constructed to incorporate the design changes optimized from the modeling. During the start up of the ozone system, fluoride tracer tests were completed to validate the effective detention time (and baffling factor) calculated by CFD. Furthermore, a series of modifications are planned for the ozonated water sampling regime to take greater advantage of Ct10 credits and reduce the required ozone dose, thereby saving energy and operating costs. This paper discusses several calculation methods for Cryptosporidium inactivation Ct10 reporting in compliance with the Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) and the LT2ESWTR Pre-proposal Draft Regulatory Language for Stakeholder Review (USEPA, 2002). The selection of the method will depend upon ease of implementation, modifications required to the ozone-in-water residual sampling system, long-term results of bromate sampling and actual Cryptosporidium bin classification under the LT2ESWTR. The article describes the CFD studies, improvements made to the contactor design, the tracer validation of the design, Ct10 reporting methods and modifications to the ozone residual sampling system that the City is considering.

Household Response to the 2008 Tax Rebate: Survey Evidence and Aggregate Implications

Only about one-fifth of respondents in the Reuters/University of Michigan survey report that the 2008 tax rebates led them to mostly increase spending, while over half said it would lead them to mostly pay off debt. Of those in the mostly-spend category, the response was swift, with over 80 percent reporting increasing their spending within three months of receiving their rebate. Older households, households with higher wealth and higher income, and those expecting future income growth were generally more likely to spend the rebates. A review of other surveys confirms the general pattern of results and suggests that small changes in survey design do not have a major effect on the distribution of responses. The distribution of survey answers corresponds to an aggregate MPC after one year of about one-third. The paper combines this survey-based estimate of the MPC and the survey-based estimate of the timing of spending to show that the rebates help explain the aggregate movements in saving, spending, and debt in 2008. Because the rebate was large and distributed over a short period, we estimate that it had a non-trivial effect on total spending in the second and third quarters of 2008. Nonetheless, the results imply that the rebates provided only a modest stimulus to spending per dollar of rebate.

Effect of uncertainties on substructure coupling: Modelling and reduction strategies

Different strategies for modelling and reducing the effect of uncertainties on the dynamic behaviour of coupled structures are discussed in this paper. In assembled structures, each component satisfies specifications about material properties and dimensional tolerances. Variability of design specifications within the tolerance field may affect the dynamic behaviour of the assembled structure more than that of any individual component substructure. Among modelling strategies, non-predictive techniques such as post-processing of data from a set of randomly assembled structures and analysis of sensitivities to uncertain variables are considered. However, emphasis is placed on a less trivial yet simple strategy such as the use of design of experiments to fit a regression model. Different reduction strategies are considered according to whether small design changes (even revised tolerance allocation) are still possible or not. In the latter case, selective assembly is extended to problems where the performance requirement is not the clearance between two parts, but a prescribed dynamic behaviour.

Evaluation of Pictorial Assembly Instructions for Young Children

We examined the usability of common formats of pictorial toy assembly instructions for 6- and 9-year-old children. Interlocking building toys and models are increasingly prevalent and important for developing spatial abilities and fine motor skills among children. Little is known about how effectively the intended child users can interpret and carry out the instructions. Twenty-four children used five sets of manufacturer-supplied pictorial toy assembly instructions. We evaluated the impact of toy instruction set, age, gender, and previous experience on usability problems, assembly speed and accuracy, instruction gaze time, and subjective ratings. The children had difficulty with all but the simplest instructions and assemblies. As predicted, older participants assembled more quickly, with fewer errors and fewer instruction looks. However, the 6-year-old girls assembled the fewest parts correctly, and the 9-year-old girls reported having the least fun. Instruction look time and frequency revealed differences in instruction complexity and were correlated with subjective ratings of fun. Thirty-two usability problems were observed, and 10 are described in detail. Product age recommendations may not reflect developmentally appropriate instructions. Small design changes should contribute to improved instruction usability among young children. For instance, designers should avoid complex graphic syntax, depict colors accurately, select clear angles of view, and support natural tendencies to assemble top to bottom. This research provides pictorial assembly instruction guidelines to inform instruction designers and describes performance and look-time benchmarks for future usability studies.

The Printing Culture in Shakespeare's Age as Reflected in the First Quartos of Venus and Adonis &amp; The Rape of Lucrece

The Printing Culture in Shakespeare's Age as Reflected in the First Quartos of Venus and Adonis &amp; The Rape of Lucrece

Using an advance organizer to facilitate change in students’ conceptualisation of the role of creativity in science

An advance organizer pertaining to the nature of science (NOS) aspect of the role creativity plays in science was incorporated into a problem-based laboratory activity of an undergraduate first-year chemistry curriculum. The advance organizer was presented in one of three versions to different sections of students: (1) definite explication of the NOS learning outcome, (2) indefinite explication, and (3) no explication. An NOS survey was administered to 235 students prior to implementation of the advance organizer and to 136 students after completion of the instructional activity involving the advance organizer. The results of this study indicate that the different versions of the advance organizer differ with respect to altering students’ conceptualisation of creativity: specifically, only the indefinite explication of the intended learning outcome led to a significant change in the percentage of students holding more informed views. This finding suggests that a relatively small change in instructional design can advance improvement in achieving NOS learning outcomes within a large-scale content-based science course.

The interfacial structure and Young's modulus of peptide films having switchable mechanical properties.

We report the structure and Young's modulus of switchable films formed by peptide self-assembly at the air-water interface. Peptide surfactant AM1 forms an interfacial film that can be switched, reversibly, from a high- to low-elasticity state, with rapid loss of emulsion and foam stability. Using neutron reflectometry, we find that the AM1 film comprises a thin (approx. 15A) layer of ordered peptide in both states, confirming that it is possible to drastically alter the mechanical properties of an interfacial ensemble without significantly altering its concentration or macromolecular organization. We also report the first experimentally determined Young's modulus of a peptide film self-assembled at the air-water interface (E=80MPa for AM1, switching to E<20MPa). These findings suggest a fundamental link between E and the macroscopic stability of peptide-containing foam. Finally, we report studies of a designed peptide surfactant, Lac21E, which we find forms a stronger switchable film than AM1 (E=335MPa switching to E<4MPa). In contrast to AM1, Lac21E switching is caused by peptide dissociation from the interface (i.e. by self-disassembly). This research confirms that small changes in molecular design can lead to similar macroscopic behaviour via surprisingly different mechanisms.

Heuristics and Biases in Retirement Savings Behavior

Standard economic theories of saving implicitly assume that households have the cognitive ability to solve the relevant optimization problem and the willpower to execute the optimal plan. Both of the implicit assumptions are suspect. Even among economists, few spend much time calculating a personal optimal savings rate. Instead, most people cope by adopting simple heuristics, or rules of thumb. In this paper, we investigate both the heuristics and the biases that emerge in the area of retirement savings. We examine the decisions employees make about whether to join a savings plan, how much to contribute, and how to invest. Saving for retirement is a difficult problem, and most employees have little training upon which to draw in making the relevant decisions. Perhaps as a result, investors are relatively passive. They are slow to join advantageous plans; they make infrequent changes; and they adopt naive diversification strategies. In short, they need all the help they can get. We discuss the possible role of interventions aiming to improve retirement decision making. Fortunately, many effective ways to help participants are also the least costly interventions: namely, small changes in plan design, sensible default options, and opportunities to increase savings rates and rebalance portfolios automatically.

Parallel-plate Rheometer Calibration Using Oil and Computer Simulation

Fluid flow patterns in traditional rotational rheometers are generally well known and rheological parameters such as viscosity can be easily calculated from experimental data of single phase fluids and analytical solutions of the patterns. However, when the fluid is a suspension, where some of the particles are as large as 2 mm in diameter, these rheometers need to be modified. The distance between the shearing planes needs to be increased, which necessitates additional physical confinement of the fluid. This causes the flow pattern to be not analytically soluble leading to an inability to correctly compute the viscosity. This paper presents a modified parallel plate rheometer, and proposes means of calibration using standard oils and numerical simulation of the flow. A lattice Boltzmann method was used to simulate the flow in the modified rheometer, thus using an accurate numerical solution in place of the intractable analytical solution. The simulations reproduced experimental results by taking into account the actual rheometer geometry. The numerical simulations showed that small changes in the rheometer design can have a significant impact on how the rheological data should be extracted from the experimental results.

A novel approach to DFM in toolmaking: a case study

A novel approach to avoid the knowledge gap between design and production is presented in this paper. The main idea is to build a system in the form of a computer program whose core is the manufacturing expert systems to be used by the product designer. The system reveals critical features of the designed product from the manufacturing point of view and points them out to the product designer. The product designer can decide whether to change the critical part of the product or not. The system presented in this paper is prepared for the toolmaking, where a lot of relatively cheap products are made by one relatively expensive tool. Since the shape of the cavity in the tool is the negative shape of the product, small changes in the product design can significantly reduce the manufacturing costs of the tool.

Advancing the Hexapole Cs-Corrector for the Scanning Transmission Electron Microscope

Aberration correctors using hexapole fields have proven useful to correct for the spherical aberration in electron microscopy. We investigate the limits of the present design for the hexapole corrector with respect to minimum probe size for the scanning transmission electron microscope and discuss several ways in which the design could be improved by rather small and incremental design changes for the next generation of advanced probe-forming systems equipped with a gun monochromator.

Fast Meshless Reanalysis Using Combined Approximations, Preconditioned Conjugate Gradient, and Taylor Series

Multiple design iterations often require repeated stress analyses to be performed as the design is modified slightly. A method is presented that combines the meshless stress analysis method with a reanalysis technique to avoid repeating the time-consuming steps of remeshing and solving for small design changes. An iterative reanalysis method based on the preconditioned conjugate gradient method is introduced and compared to the linear Taylor series, simple iteration, and combined approximations reanalysis methods. The asymptotic running time is presented for each reanalysis method, and accuracy is compared for two example problems: a cantilever beam and a hole-in-plate. Results show the Taylor series to have the fastest run time, followed in order by simple iteration, preconditioned conjugate gradient, and combined approximations. For the two example problems, accuracy of the simple iteration method is poor for design changes greater than 5%. Taylor series accuracy depends greatly on the choice of the design variable, the example problem, and the method for computing the sensitivity. The combined approximations and preconditioned conjugate gradient methods both demonstrate less than 10% error up to a 100% change in height for the cantilever beam and 30% change in radius for the hole-in-plate example.

The impact of interface roughness scattering and degeneracy in relaxed and strained Si n-channel MOSFETs

The continual scaling of the conventional MOSFET architecture is reaching its fundamental limit, requiring intolerably thin gate oxides and high channel doping that lead to low device performance and high leakage. Meeting the requirements of the next generation technology nodes requires a departure from the standard MOSFET design both in terms of new materials and architectures. One of the most the promising candidates is strained Si which delivers significant enhancements in device performance with relatively small changes in the overall device design and technology. A major advantage of the strained Si MOSFET architecture is that the overall CMOS performance may be improved due to the enhanced transport of both electrons and holes within the strained layer. In this work we use Monte Carlo simulations to study the performance improvements in nano-scale strained Si MOSFETs. We present useful interpolation formulae for the essential material parameters necessary for accurate device simulation of the strained n-channel Si/SiGe material system. Our Ensemble Monte Carlo simulations indicate that the experimentally observed improvements in surface n-channel strained Si devices are partially related to a smoother strained Si/SiO 2 interface compared to the relaxed Si/SiO 2 interface. The use of degenerate carrier-statistics is crucial in the understanding of carrier transport not only in the high-doped regions which occur in modern scale strained Si-MOSFETs, but also in the strained channel with its reduced density of states.