Schematic Example Research Articles

A SAR ADC with current steering DAC and voltage input

A successive-approximation register analog-to-digital converter with current steering digital-to-analog converter (DAC) and voltage input is presented. Passive current-to-voltage conversion is used at the DAC output. A technique for increasing the settling speed without extra current consumption is proposed. Simulations of schematic example confirm the improvement.

Explicating concepts in reasoning from function to form by two-step innovative abductions

AbstractThe mechanism of design reasoning from function to form is suggested to consist of a two-step inference of the innovative abduction type. First is an inference from a desired functional aspect to an idea, concept, or solution principle to satisfy the function. This is followed by a second innovative abduction, from the latest concept to form, structure, or mechanism. The intermediate entity in the logical reasoning, the concept, is thus made explicit, which is significant in following and understanding a specific design process, for educating designers, and to build a logic-based computational model of design. The idea of a two-step abductive reasoning process is developed from the critical examination of several propositions made by others. We use the notion of innovative abduction in design, as opposed to such abduction where the question is about selecting among known alternatives, and we adopt a previously proposed two-step process of abductive reasoning. However, our model is different in that the two abductions used follow the syllogistic pattern of innovative abduction. In addition to using a schematic example from the literature to demonstrate our derivation, we apply the model to an existing, empirically derived method of conceptual design called “parameter analysis” and use two examples of real design processes. The two synthetic steps of the method are shown to follow the proposed double innovative abduction scheme, and the design processes are presented as sequences of double abductions from function to concept and from concept to form, with a subsequent deductive evaluation step.

Analysis of excessive deformations in tunnels for safety evaluation

Tunnel construction is increasing worldwide in mining and civil engineering. There have been several accidents that resulted in delays, cost overruns, some with more severe consequences. To help minimize these accidents, it is necessary to assess and manage the risks associated with tunnel construction and exploration. A particular type of accident, or undesirable event, which can occur during tunnel construction and operation, is associated with the occurrence of excessive deformations occurring inside the tunnel. This can happen due to deficient design, construction defects, and high in situ stresses or due to specific swelling and squeezing grounds. Deep coal mines where large deformations can occur during and after excavations due to the soft properties of the rock and the high in situ stresses, are particularly vulnerable to this type of event. The associated non-linear problems are related with geomechanical behavior of the rock mass, changes in the geometry of cavities and in some cases with developing surface contacts due to large strains. In this paper, the phenomena involved in large material deformations are analyzed in detail and the basic equations for the Chen’s large deformation theory are presented. The application of an FEM based method to simulate large material deformations, the Material Point Method (MPM) to the simulation of large deformation that occurs in tunnels when failure occurs, is also described. An application of MPM to the Jiahe Coal Mine, in China is presented, and the numerical results obtained with MPM compared with solutions using Chen’s large deformation theory. Safety considerations about the excessive deformation scenario in tunnels are drawn and a risk assessment methodology with special use of Bayesian networks is proposed. A simplified schematic example was presented for two case scenarios.

Consequences of Candidate Omission

Consequences of Candidate Omission

Judgements of time to contact are affected by rate of appearance of visible texture

More fine-grained texture becomes visible if the distance between an observer and an object or surface is reduced. This article illustrates with a schematic example that the inverse rate of the relative appearance of visible texture provides information about time to contact if the observer has a constant visual acuity and the texture has a certain scale-independent structure. An experiment is reported in which texture appearance was manipulated. Participants were asked to make forced-choice time-to-contact judgements. A small but significant effect indicates that the judgements were affected by the rate of appearance of the texture. It is concluded that observers use this type of information.

Genomic Analysis of Left Ventricular Remodeling

The left ventricle (LV) of the heart remodels in response to hemodynamic load through the processes of physiological or pathophysiological hypertrophy.1–3 Despite extensive study of the molecular basis of cardiac hypertrophy and LV remodeling,1,4 the mainstay of medical treatment of maladaptive remodeling remains based on therapies initially devised for treating hypertension. The limited progress in the development of specific therapies for LV remodeling has led some to refer to “the impossible task of developing a new treatment for heart failure” and is the reason why, in part, device therapies have received such recent attention.5–8 To gain a better understanding of the biology of maladaptive LV remodeling, with a view to identifying therapeutic targets, new paradigms and experimental approaches are needed, and genomics provides one such methodology. Genomics is the study of genome-scale data sets, at the DNA or RNA level, and when combined with studies of physiological traits or disease phenotypes, genomics can be used to infer molecular insights. Unlike single-gene studies, which are the favored hypothesis-driven design,4 genomic approaches examine variation in up to gigabases of sequences to find statistical associations between transcripts and traits in a hypothesis-free system. These hypothesis-free studies have often been criticized as unfocused, but following the successes of genome-wide association studies (GWAS) and the recent achievements of integrated genetic and genomic analyses, a new era of genomic experimentation presents itself.9–14 It is notable that GWAS and integrated genomic studies in humans often identify regions associated with disease rather than specific genes and that effect sizes are small; nevertheless, these data remain highly informative.15–17 In this article, we review the genomic analysis of LV remodeling in the context of the recent past, the state of the art, and the imminent use of next-generation sequencing. A glossary of terms is …

Retrieval of the complex reflection coefficient from nano scale thin films by using polarized neutrons and magnetic substrates

A method is proposed for overcoming the famous ‘phase problem’ in neutron specular reflectometry. It is shown that the complex reflection coefficient of any unknown non magnetic layer, with real scattering length density, can be determined by using a magnetic transmitted media and by measuring the polarization of the reflected beam relative to the incident beam. The method follows directly from a recent one which is limited to a one-dimensional neutron polarization. Here, the theory is generalized for a neutron polarization of arbitrary direction. We show that some combinations between the polarization of the incident and reflected beam must be used to determine the reflection coefficient. Also, it is shown that instead of full polarization or reflectivity analysis, some combinations between polarization and reflectivity can be used in the analysis process. The method is supplemented with a schematic example to test the method and its stability in the presence of experimental uncertainties and roughness of the interfaces.

Exact determination of phase information in spin-polarized neutron specular reflectometry

A method is proposed to determine the complex reflection coefficient of any real scattering length density (i.e., in the case where there is no effective absorption, which is a good approximation for neutrons) in neutron specular reflectometry. The method makes use of a magnetic reference layer mediated between the substrate and an unknown sample and measurements of the polarization direction of the reflected beam or a suitable choice of polarization and reflectivity analysis of the reflected beam. It corresponds to the concept proposed recently, but has been derived in the formalism of the transfer matrix. The method is based upon relations between the polarization of the incident and reflected beams, and the transfer matrix elements of the unknown and known layers. Thus, in this manner, only by final polarization orientation measurement can we find the reflection coefficient of any unknown sample which is surrounded on both sides by a uniform medium. Apart from the final polarization orientation measurement of the reflected beam, which is hampered by complications in selecting the physical solution, we show that the reflection coefficient can be determined by more flexible ways using a suitable choice of possible measurements of reflectivity and polarization of the reflected beam. A schematic example is presented to illustrate the method.

Retrieval of the reflection coefficient in spin-polarized neutron specular reflectometry

A method is proposed which allows a complete determination of the complex reflectioncoefficient for any free unknown real potential (i.e., in the case where there is no effectiveabsorption). It exploits the interference of the spin components of a polarizedneutron beam in the presence of a magnetic reference layer mediated betweensubstrate and sample. Following the recent investigations, the method requirespolarization analysis of the reflected beam instead of reflectivity analysis. However, ourmethod is based on the transfer matrix formalism. In this method we use therelations between the polarization and the reflectivity of the reflected beam andthe transfer matrix elements for the known and unknown samples. Using theserelations we show that instead of fully polarization measurement, some suitablechoice of polarization and reflectivity measurements can be used to determine thereflection coefficient. The method is supplemented with a schematic example.

Unique reconstruction of depth profiles in neutron specular reflectometry: practical aspects

The possibility of a full determination of the reflection coefficient (modulus and phase) in neutron specular reflection is discussed. Specifically, the proposed solution of the phase problem based on polarization measurements and a magnetic reference layer is considered. A procedure and the corresponding formulae are worked out to extract the maximum of accessible information from measurements with available reflectometers, taking into account their limitations in the polarization analysis and the preparation of the beam. Albeit the incompleteness of the polarization measurements results in ambiguities of the reflection coefficient, the physical one can in most cases be identified by additional knowledge about the profile. This is shown in a schematic example with simulated incomplete data.

Organizational Warning Systems: A Probabilistic Approach to Optimal Design

The optimization of warning systems includes the choice of signals to be monitored, the sensitivity of the alert level and the response to these signals. In organizations that design or manage complex, risk-critical systems, the problem is not only the observation of a signal, but also its accurate communication to the appropriate decision maker, and the actions that he or she can take upon receiving the signals given the state of deterioration of the physical system at that time. In this paper, we describe an analytical framework focused on organization performance, based on decision analysis and probability, to design and optimize such a warning system from a management perspective. The probability of failure during the time it takes to observe a signal, decide of its importance, and communicate a warning, and the time elapsed between the occurrence of an accident initiator and the events that follow, including the action taken in response, are computed in parallel, using a dynamic probabilistic risk analysis, assuming a Markov (or semi-Markov) evolution process when appropriate. The analysis then allows optimization of the choice of signals to be observed, the design of the communication chain, the filtering of the information, and the response at the appropriate management level. The questions are thus: What is the value (in terms of risk reduction) of a warning system of given structure and procedures? And what is its optimal configuration? The optimization model presented here reflects the nature of the engineering system to be monitored, the communication structure within the organization that designs or manages it, errors that can occur in the communication phase, the best action(s) of the decision maker once he or she receives a warning signal, and the expected value of the costs, including those of system failure. The schematic example of inspection and maintenance of an airplane is used throughout the paper to illustrate, at a very simplified level, the creation and evaluation of this model.

Calculations of theoretical strength: State of the art and history

Current state and historical evolution of theoretical strength calculations is presented as a brief overview completed by a database of selected theoretical and experimental results. Principles of a sophisticated analysis of mechanical stability of crystals are elucidated by means of a schematic example. Stability conditions and Jacobian matrixes are presented for selected crystalline symmetries and deformation paths. The importance of this analysis for understanding micromechanics of fracture is shown against the background of the influence of crystal defects. Differences between theoretical and experimental theoretical strength (TS) values are discussed and some challenging tasks are outlined for the near future.

ACCURACY AND RELIABILITY OF NUMERICAL RIVER MODELS1

ABSTRACT: Over the last 20 years, our possibilities to model river flows numerically have increased enormously. In this paper, the question is addressed whether a more sophisticated model is always better than a simpler one. Increased detail, both in finer resolution and in physical processes taken into account, has its price in more computer time, higher data need, and perhaps more unknown coefficients to be calibrated. Moreover, uncertainty in actual physical conditions (e.g., bottom roughness), inflow and parameters remains, which may dominate the uncertainty of the results. Also, the questions asked by a decision maker may not always be very precise. For a schematic but relevant example, we show that a better model does not necessarily give more reliable results because some of the basic uncertainties remain. It is concluded that we should use the simplest model that will answer the question as to the accuracy needed, taking into account uncertainties in the data

APRAM: an advanced programmatic risk analysis method

While engineering projects are expected to accomplish more with fewer resources, the dependencies among these projects have continually increased. At NASA, for example, faster-better-cheaper (FBC) projects are being grouped into programmes to enhance the benefits of synergies among smaller projects, and to attenuate, through diversification, the risks of single large missions. Under strict resource constraints, FBC project managers must balance several types of failure risks including the effect of their project's performance on future missions. Existing risk analysis models generally focus on the quantification of either technical or management risks. These tools, while beneficial, are generally used in isolation, and tightening the constraints generally encourages decisions that can increase the risks of technical failure. Since it is difficult to balance simultaneously cost, schedule and performance of a given project as well as their effects on other projects, managers who face these problems can benefit from an integrated programmatic risk analysis. In this paper, we present an advanced programmatic risk analysis model (APRAM) that is based on probability and systems analysis. It includes both managerial and technical risks, and can support decisions such as the choice of a design and of a budget reserve at the onset of a project. The model starts with the analysis of the trade-off between reserves and system development, then incorporates the effects of testing and reviews, partial mission failures, and project dependencies within programmes. The method is illustrated by the schematic example of two projects in an unmanned space programme.

THE HETEROGENEITY OF RIGHTS

If there is a constitutional right to R, and a law L by its terms prohibits R, L cannot be validly applied to some person P’s exercise of R. For at least two reasons, however, most cases involving claims of constitutional right are substantially more difficult than this schematic example. First, lawmakers rarely act so brashly as to proscribe rights in so many words.But see Board of Airport Comm’rs v. Jews for Jesus, Inc., 482 U.S. 569 (1987) (invalidating a ban on all “First Amendment activities” at the main terminal of the Los Angeles International Airport). Second, even facially invalid laws typically include within their sweep much unprotected activity.For example, a law forbidding “prayers or offerings to any god but the Christian God” prohibits, inter alia, involuntary human sacrifice to the Aztec god Huehueteotl, see Johanna Broda et al., THE GREAT TEMPLE OF TENOCHTITLAN 68–70 (1988), which ought to be unprotected even under the broadest reading of the Free Exercise Clause.

The impact of fluctuations in intensity patterns on the number of monitor units and the quality and accuracy of intensity modulated radiotherapy.

The purpose of this work is to examine the potential impact of the frequency and amplitude of fluctuations ("complexity") in intensity distributions on intensity-modulated radiotherapy (IMRT) dose distributions. The intensity-modulated beams are efficiently delivered using a multileaf collimator (MLC). Radiation may be delivered through a continuous (dynamic mode) or discrete (step-and-shoot) sequence of windows formed by the leaves. Algorithms and software that convert optimized intensity distributions into leaf trajectories apply approximate empirical corrections to account for the various effects associated with MLC characteristics, such as the rounded leaf tips, tongue-and-groove leaf design, leaf transmission, leaf scatter, and collimator scatter upstream from the MLC. Typically, the difference between inter- and intraleaf transmissions is ignored. In this paper, using a schematic example of IMRT for head and neck carcinomas, we demonstrate that complex anatomy and severe optimization constraints produce complex intensity patterns. Using idealized intensity patterns we also demonstrate that, for complex intensity patterns, the average window width tends to be smaller and, for the same dose received by the tumor, the number of MUs is larger. We found that as the complexity increases, so does the contribution of radiation transmitted through and scattered from the leaves ("indirect radiation") to the total delivered dose. As a consequence, the lowest deliverable intensity in complex intensity patterns may be significantly greater than that required to provide adequate protection for some normal tissues. Furthermore, since corrections for leaf transmission and scatter effects are approximate and the difference between inter- and intraleaf transmission is ignored, the accuracy of the delivered dose may be affected. Using the results of a simple experiment and a typical intensity-modulated beam for a head and neck case as examples, we show the effect of window width and complexity on the accuracy and deliverability of intensity patterns. Some possible strategies for improving the accuracy and for relaxing the lower limit on deliverable intensity are discussed.

Radiobiological considerations in the design of fractionation strategies for intensity-modulated radiation therapy of head and neck cancers

Purpose: The dose distributions of intensity-modulated radiotherapy (IMRT) treatment plans can be shown to be significantly superior in terms of higher conformality if designed to simultaneously deliver high dose to the primary disease and lower dose to the subclinical disease or electively treated regions. We use the term “simultaneous integrated boost” (SIB) to define such a treatment. The purpose of this paper is to develop suitable fractionation strategies based on radiobiological principles for clinical trials and routine use of IMRT of head and neck (HN) cancers. The fractionation strategies are intended to allow escalation of tumor dose while adequately sparing normal tissues outside the target volume and considering the tolerances of normal tissues embedded within the primary target volume. Methods and Materials: IMRT fractionation regimens are specified in terms of “normalized total dose” (NTD), i.e., the biologically equivalent dose given in 2 Gy/fx. A linear-quadratic isoeffect formula is applied to convert NTDs into “nominal” prescription doses. Nominal prescription doses for a high dose to the primary disease, an intermediate dose to regional microscopic disease, and lower dose to electively treated nodes are used for optimizing IMRT plans. The resulting nominal dose distributions are converted back into NTD distributions for the evaluation of treatment plans. Similar calculations for critical normal tissues are also performed. Methods developed were applied for the intercomparison of several HN treatment regimens, including conventional regimens used currently and in the past, as well as SIB strategies. This was accomplished by comparing the biologically equivalent NTD values for the gross tumor and regional disease, and bone, muscle, and mucosa embedded in the gross tumor volume. Results: (1) A schematic HN example was used to demonstrate that dose distributions for SIB IMRT are more conformal compared to dose distributions when IMRT is divided into a large-field phase and a boost phase. Both were shown to be significantly superior compared to dose distributions obtained using conventional beams for the large-field phase followed by IMRT for the boost phase. (2) The relationship between NTD and nominal dose for HN tumors was found to be quite sensitive to the choice of tumor clonogen doubling time but relatively insensitive to other parameters. (3) For late effect normal tissues embedded in the tumor volume and assumed to receive the same dose as the tumor, the biologically equivalent NTD for the SIB IMRT may be significantly higher. (4) Normal tissues outside the target volume receive lower dose due to the higher conformality of the IMRT plans. The biologically equivalent NTDs are even lower due to the lower dose per fraction in the SIB strategy. Conclusions: IMRT dose distributions are most conformal when designed to be delivered as SIB. Using isoeffect radiobiological relationships and published HN data, fractionation strategies can be designed in which the nominal dose levels to the primary, regional disease and electively treated volumes are appropriately adjusted, each receiving different dose/fx. Normal tissues outside the treated volumes are at reduced risk in such strategies since they receive lower total dose as well as lower dose/fx. However, the late effect toxicities of tissues embedded within the primary target volume and assumed to receive the same dose as the primary may pose a problem. The efficacy and safety of the proposed fractionation strategies will need to be evaluated with careful clinical trials.

Isoscalar and isovector pair correlations in an isospin-invariant pairing plus quadrupole model

Isovector and isoscalar correlations are investigated using an isospin-invariant pairing plus quadrupole model with inclusion of an isoscalar pairing force. An exact shell model calculation is carried out on the ${(g}_{9/2}{)}_{p}{(g}_{9/2}{)}_{n}$ shell, as a schematic example. We study isoscalar $(\ensuremath{\tau}=0)$ and isovector $(\ensuremath{\tau}=1)$ pair correlations in the ground state and excited states, and examine the interplay between isoscalar and isovector correlations. Under the single ${g}_{9/2}$ shell approximation, it is found that, for the $N=Z$ even-even system, the number of $\ensuremath{\tau}=1, J=8$ pairs increases drastically in a state with total spin $I=8$ along the yrast line. For $N=Z$ odd-odd systems, there is a crossing of an even-spin ground band by an odd-spin band at $I=1$ along the yrast line. The $\ensuremath{\tau}=0, J=9$ proton-neutron correlations increase suddenly at $I=7.$ This can be interpreted as the alignment of a proton-neutron pair. Finally, we examine the $J=0$ pair correlations in ground states of even-even and odd-odd systems.

Cities and the real world

Abstract It is generally recognized that modern cities pose many problems for their inhabitants and contribute to environmental damage. However, neither planners nor scientists give adequate consideration to cities’ place in the evolutionary process and the planet's ecological system. By recognizing these connections and natural laws, planning would become more realistic, and meaningful progress could be made in solving serious social and environmental problems. Some basic problems influencing urban form are discussed, and a schematic example of how we might approach the planning of urban settlements is presented.

A proposal for the determination of the phases in specular neutron reflection

A method is proposed for solving the phase problem in specular neutron reflection. A differential equation for the reflection phase is derived and solved in terms of the reflectivity and the dwell time. This opens the possibility of determining surface profiles from measured quantities by inversion. A schematic example is presented.