Ideal Constraints Research Articles

Characterization of Daily Shifts and Their Correlation With Plan Quality for Treatments With a 1.5T MR-Linac

Patient daily translational errors are corrected by shifting beam apertures–versus shifting patient–with certain novel image-guided radiation therapy (RT) technologies without laser alignment systems (LAS). In the presence of non-flat beams, recovering reference plan quality is performed by plan adaptation. We sought to characterize shifts within a cohort of patients undergoing treatment without a LAS using a 1.5T MR-equipped linear accelerator (MR-Linac). We further sought to identify correlations between shift magnitude and RT plan quality. Patients treated on a MR-Linac were aggregated and shifts for each fraction, in 3 dimensions, were collected. Plan quality was assessed via PTV coverage (in %), % global max, and number of organs at risk (OARs) outside ideal constraints. Demographic variables felt to potentially influence the magnitude of shifts were recorded. Patient-level variables were summarized using mean, standard deviation, median, and range for continuous variables; frequency and percentage for categorical variables. There was no missing data among analytic variables. Correlations were described using scatter plots. The degree of correlation was assessed using Spearman’s rank correlation coefficient (rho). Robust standard errors for Spearman’s rho were obtained using bootstrap procedures. The bootstrap was performed by sampling patients with replacement (as opposed to sampling individual measurements) for 1000 bootstrap replicates. 41 patients were included, totaling 406 treatment fractions. Mean patient height was 169.92 cm (SD 8.85), mean weight was 83.24 kg (SD 17.72), and median number of unique fractions was 5 (range 2-30). Mean shift magnitudes (in cm) measured per site: liver 1.58 (SD 0.93), pancreas 1.51 (SD 0.78), brain 0.55 (SD 0.27), oropharynx 0.36 (SD 0.12), retroperitoneum 1.78 (SD 0.64), prostate 1.47 (SD 0.90), adrenal gland 1.48 (SD 0.57), lung 1.53 (SD 0.79), rectum 1.46 (SD 0.52), abdominal nodes 2.34 (SD1.30). There was no correlation between patient weight or height and shift magnitude (Rho 0.11, p-value 0.573) and (Rho 0.06, p-value 0.671), respectively. Shift magnitude was not correlated with PTV coverage (Rho -0.02, p-value 0.878), % global max (Rho -0.09, p-value 0.697), or OARs outside ideal (Rho -0.40, p-value 0.116). Greater shift magnitudes did correlate with plan scaling (Rho -0.22, p-value 0.045). When evaluating correlation between scale and plan quality, no significance difference was identified. We have characterized the magnitudes of shifts present for patients undergoing treatment on 1.5T MR-Linac without conventional LAS or couch shifting. Such descriptive magnitudes may help determine acceptable ranges of shift tolerance. Plan adaptation with rescaling successfully minimized degradation of daily plan quality in the presence of large shifts and non-flat beams.

A dosimetric evaluation of a single urethral constraint for high-dose-rate prostate brachytherapy

PurposeThe American Brachytherapy Society (ABS) consensus guidelines for high-dose-rate (HDR) prostate brachytherapy suggest 11 different dose constraints for the urethra. The purpose of this study is to evaluate whether a single urethral constraint of D0.1 cm3 < 110% could meet all the proposed ABS urethral constraints and to evaluate the heterogeneity and similarities of other portions of the dose-volume histogram (DVH) when only optimizing to a single constraint. MethodsThis is a retrospective study of 18 consecutively treated HDR prostate brachytherapy patients treated between May 2018 to November 2018. Nine patients underwent HDR brachytherapy combined with external beam radiation therapy, and nine underwent HDR brachytherapy as monotherapy. Additional DVH values were extracted for the whole, proximal, middle, and distal urethra and compared for differences. ResultsNone of the ABS suggested constraints were violated when optimizing the urethra D0.1 cm3 dose to be less than 110% of the prescription. An evaluation of the DVHs for the whole, proximal, middle, and distal urethra showed a large variation in the shape of the remainder of the DVH for all parts of the urethra. The largest standard deviations in dose to the whole and middle urethra were at the V14 dose level, and that to the proximal and distal urethra were at the V10 dose level. ConclusionA single urethral dose constraint of D0.1 cm3 < 110% can meet all the proposed ABS constraints. There is high variability in other parts of the urethra DVH when only using a single constraint. Additional data is needed to determine ideal constraints for the entirety of the urethra DVH.

Transient dynamics in strongly nonlinear systems: optimization of initial conditions on the resonant manifold.

We consider a system of two linear and linearly coupled oscillators with ideal impact constraints. Primary resonant energy exchange is investigated by analysis of the slow flow using the action-angle (AA) formalism. Exact inversion of the action-energy dependence for the linear oscillator with impact constraints is not possible. This difficulty, typical for many models of nonlinear oscillators, is circumvented by matching the asymptotic expansions for the linear and impact limits. The obtained energy-action relation enables the complete analysis of the slow flow and the accurate description of the critical delocalization transition. The transition from the localization regime to the energy-exchange regime is captured by prediction of the critical coupling value. Accurate prediction of the delocalization transition requires a detailed account of the coupling energy with appropriate redefinition and optimization of the limiting phase trajectory on the resonant manifold.This article is part of the theme issue 'Nonlinear energy transfer in dynamical and acoustical systems'.

Smart Secured Real Time Agriculture Monitoring System

Embedded systems in Agriculture play a vital role in unifying the work involved and improve conservations. Designing a smart as well as a cost efficient and more user-friendly system will be idealistic challenge. The following system that has been proposed is designed with those ideal constraints in mind. It consists of a Raspberry pi3 as a gateway that links the sensor networks with the cloud. To improve security an MQTT protocol is used for cloud connectivity. The communication between the sensor networks is managed by NRF24L01. The Sensor network is a separate entity that can used like a plug and play device and is built by a micro controller with a LCD display and an interfaced GPS. Multicasting is also possible between sensor networks and the gateway. The processed data from the sensor networks is sent through NRF24L01 to the gateway. The gateway further processes and encapsulates the data and through MQTT the data gets stored on the cloud. This cloud data can be accessed through computer or mobile device

A reduced-order approach to the adaptive fuzzy sliding mode control of the constrained manipulator

A reduced-order approach to the adaptive fuzzy sliding mode control of the constrained manipulator is proposed. Based on the Udwadia–Kalaba motion constraint equation, the dynamic equation of the constrained manipulator with both ideal and non-ideal constraints is obtained. Considering the uncertainty of the terminal non-ideal constrained force and the chattering phenomenon of sliding mode control, the adaptive fuzzy and the sliding mode control method are combined to control the constrained manipulator. Because the system is constrained, the model order reduction method is innovatively used in the control algorithm. The stability of the system is proved by Lyapunov theorem. For demonstrating the effectiveness of the control algorithm, the 2-degree-of-freedom manipulator is taken as the research object. Finally, the high-precision control of the manipulator is achieved and the chattering phenomenon caused by the sliding mode control is weakened.

Absolute plate motions relative to deep mantle plumes

Advances in whole waveform seismic tomography have revealed the presence of broad mantle plumes rooted at the base of the Earth's mantle beneath major hotspots. Hotspot tracks associated with these deep mantle plumes provide ideal constraints for inverting absolute plate motions as well as testing the fixed hotspot hypothesis. In this paper, 27 observed hotspot trends associated with 24 deep mantle plumes are used together with the MORVEL model for relative plate motions to determine an absolute plate motion model, in terms of a maximum likelihood optimization for angular data fitting, combined with an outlier data detection procedure based on statistical tests. The obtained T25M model fits 25 observed trends of globally distributed hotspot tracks to the statistically required level, while the other two hotspot trend data (Comores on Somalia and Iceland on Eurasia) are identified as outliers, which are significantly incompatible with other data. For most hotspots with rate data available, T25M predicts plate velocities significantly lower than the observed rates of hotspot volcanic migration, which cannot be fully explained by biased errors in observed rate data. Instead, the apparent hotspot motions derived by subtracting the observed hotspot migration velocities from the T25M plate velocities exhibit a combined pattern of being opposite to plate velocities and moving towards mid-ocean ridges. The newly estimated net rotation of the lithosphere is statistically compatible with three recent estimates, but differs significantly from 30 of 33 prior estimates.

On Vector Form of Differential Variational Principles of Mechanics

We introduce variation of a vector δx which can be interpreted either as a virtual displacement of a system, or as variation of the velocity of a system, or as variation of the acceleration of a system. This vector is used to obtain a unified form of differential variational principles of mechanics from the scalar representative equations of motion. Conversely, this notation implies the original equations of motion, which enables one to consider the obtained scalar products as principles of mechanics. Using the same logical scheme, one constructs a differential principle on the basis of the vector equation of constrained motion of a mechanical system. In this form of notation, it is proposed to conserve the zero scalar products of reactions of ideal constraints and the vector δx. This enables one to obtain also the equations involving generalized constrained forces from this form of notation.

Managing complexity: from visual perception to sustainable transitions\u2014contributions of Brunswik\u2019s Theory of Probabilistic Functionalism

Coping with the multitude of information, relationships, and dynamics of the biotic and abiotic environment is a fundamental prerequisite for the survival of any organismic system. This paper discusses what contribution the Theory of Probabilistic Functionalism (TPF) of Egon Brunswik (1903–1955), which was originally developed for visual perception (including certain cognitive processes) and later for judgment, may provide today. The present paper elaborates that the principles of TPF go beyond the common weighting and regression analysis-based model of information processing that has been associated with the Brunswikian Lens Model. We argue that Brunswik’s TPF rather provides basic principles of how organisms interact with complex environmental systems when processing cues (instead of information) and thus are able to produce evolutionarily stable representations of and judgments about the environment. TPF was formulated with no references to physiological processes. The present paper aims to demonstrate how well these principles correspond with current biophysical and neurophysiological findings, models, and simulations of sensation. We then discuss in what ways planning groups may be seen as organisms and how groups resemble and differ from (biological) organisms on the level of the individual and below. Based on this, we suggest how the principles of TPF can be used to describe planning groups’ activities when constructing planning variants or scenarios for sustainable transitioning. We illustrate the ways in which (under ideal constraints that may be provided in ideal transdisciplinary processes) planning groups follow principles such as vicarious mediation. Here, we reflect on the ways decision theoretic tools (such as Formative Scenario Analysis and Multi-Attribute Decision Analysis) can serve to construct robust (i.e., “evolutionarily stable”) orientations for the future. It is difficult to validate big theories such as TPF. Thus, special attention is paid to the question of how strategies of validation (according to normal scientific principles) for different principles and TPF as such can be developed. We conclude that (in the context of sustainable transitioning) TPF can be utilized from a descriptive, prescriptive, and normative perspective. All three perspectives call for different strategies of validation.

Integrating Modelling Approaches for Understanding Telecoupling: Global Food Trade and Local Land Use

The telecoupling framework is an integrated concept that emphasises socioeconomic and environmental interactions between distant places. Viewed through the lens of the telecoupling framework, land use and food consumption are linked across local to global scales by decision-making agents and trade flows. Quantitatively modelling the dynamics of telecoupled systems like this could be achieved using numerous different modelling approaches. For example, previous approaches to modelling global food trade have often used partial equilibrium economic models, whereas recent approaches to representing local land use decision-making have widely used agent-based modelling. System dynamics models are well established for representing aggregated flows and stores of products and values between distant locations. We argue that hybrid computational models will be useful for capitalising on the strengths these different modelling approaches each have for representing the various concepts in the telecoupling framework. However, integrating multiple modelling approaches into hybrid models faces challenges, including data requirements and uncertainty assessment. To help guide the development of hybrid models for investigating sustainability through the telecoupling framework here we examine important representational and modelling considerations in the context of global food trade and local land use. We report on the development of our own model that incorporates multiple modelling approaches in a modular approach to negotiate the trade-offs between ideal representation and modelling resource constraints. In this initial modelling our focus is on land use and food trade in and between USA, China and Brazil, but also accounting for the rest of the world. We discuss the challenges of integrating multiple modelling approaches to enable analysis of agents, flows, and feedbacks in the telecoupled system. Our analysis indicates differences in representation of agency are possible and should be expected in integrated models. Questions about telecoupling dynamics should be the primary driver in selecting modelling approaches, tempered by resource availability. There is also a need to identify appropriate modelling assessment and analysis tools and learn from their application in other domains.

The impact of imaging modality (CT vs MRI) and patient position (supine vs prone) on tangential whole breast radiation therapy planning

PurposeThe purpose of this study was to evaluate the impact of magnetic resonance imaging (MRI) versus computed tomography (CT)-derived planning target volumes (PTVs), in both supine and prone positions, for whole breast (WB) radiation therapy. Methods and materialsFour WB radiation therapy plans were generated for 28 patients in which PTVs were generated based on CT or MRI data alone in both supine and prone positions. A 6-MV tangential intensity modulated radiation therapy technique was used, with plans designated as ideal, acceptable, or noncompliant. Dose metrics for PTVs and organs at risk were compared to analyze any differences based on imaging modality (CT vs MRI) or patient position (supine vs prone). ResultsWith respect to imaging modality 2/11 whole breast planning target volume (WB_PTV) dose metrics (percentage of PTV receiving 90% and 110% of prescribed dose) displayed statistically significant differences; however, these differences did not alter the average plan compliance rank. With respect to patient positioning, the odds of having an ideal plan versus a noncompliant plan were higher for the supine position compared with the prone position (P = .026). The minimum distance between the seroma cavity planning target volume (SC_PTV) and the chest wall was increased with prone positioning (P < .001, supine and prone values 1.1 mm and 8.7 mm, respectively). Heart volume was greater in the supine position (P = .005). Heart doses were lower in the supine position than prone (P < .01, mean doses 3.4 ± 1.55 Gy vs 4.4 ± 1.13 Gy for supine vs prone, respectively). Mean lung doses met ideal dose constraints in both positions, but were best spared in the prone position. The contralateral breast maximum dose to 1cc (D1cc) showed significantly lower doses in the supine position (P < .001, 4.64 Gy vs 9.51 Gy). ConclusionsPlanning with PTVs generated from MRI data showed no clinically significant differences from planning with PTVs generated from CT with respect to PTV and doses to organs at risk. Prone positioning within this study reduced mean lung dose and whole heart volumes but increased mean heart and contralateral breast doses compared with supine.

Teaching Practice in B. Ed: Prospective Teachers’ Perception of Theory and Practice

Teaching practice is the core component of whole teacher training process. This part not only allows prospective teachers to use their skills and enhance their abilities, but it also trains them for future job placement. Here the question arises that does teaching practice help prospective teachers to learn all teaching techniques, which is essential to gain mastery in teaching process or they get caught between the loopholes of theoretical ideal views and constraints of real classroom situations. The purpose of the study was to investigate the gap between theory taught during course-work and practical implementation of that knowledge during teaching practice. Another objective of the study was to assess the competency level of prospective teachers for teaching practice. It was hypothesized that prospective teachers do have sufficient content knowledge, awareness of pedagogical teaching strategies and teaching practice before the commencement of teaching practice. Sixty alumni of B.ED program, who passed out during last five years were randomly selected as samples for the following study. A structured questionnaire consisted of 25 items including content knowledge and understanding, pedagogical content knowledge, and application of gained knowledge and learned skills were designed to gather data. The questionnaire was based on a Lickert scale to gather responses. The data were analyzed by using the percentage method. After analysis of results, it can be recommended that teacher in-charges should also be assessed for their skills to apprise prospective teachers. Furthermore, there should be a comprehensive exam of prospective teachers before the commencement of teaching practice that should be designed and conducted under direct supervision of NACTE or its appointed team. It will be a great step to ensure quality teaching in teacher education programs.

Instantaneous impulses in multibody dynamics

This paper considers instantaneous impulses in multibody dynamics. Instantaneous impulses may act on the multibody from its exterior or they may appear in its interior as a consequence of two of its parts interacting by an impact imposed by a unilateral constraint. The theory is based on the Euler laws of instantaneous impulses, which may be seen as a complement to the Euler laws for regular motions. Based on these laws, and specific continuum properties of the quantities involved, local balance laws for momentum and moment of momentum, involving instantaneous impulses and introducing the Cauchy impulse tensor, are derived. Thermodynamical restrictions on the impulse tensor are formulated based on the dissipation inequality. By stating a principle of virtual work for instantaneous impulses, and demonstrating its equivalence to Euler’s laws, Lagrange’s equations are derived. Lagrange’s equations are convenient to use in the case of multibody dynamics containing rigid as well as flexible parts. A central theme of this paper is the discussion of the interaction between parts of the multibody and their relation to geometrical and kinematical constraints. This interaction is severely affected by the presence of friction, which is notoriously difficult to handle. In a preparation for this discussion we first consider the one-point impact between two rigid bodies. The importance of the so-called impact tensor for this problem is demonstrated. In order to be able to handle the impact laws of Poisson and Stonge, an impact process, governed by a system of ordinary differential equations, is defined. Within this model phenomena, such as slip stop, slip start and slip direction reversal, may be handled. For a multibody with an arbitrary number of parts and multiple impacts, the situation is much more complicated and certain simplifications have to be introduced. Equations of motion for a multibody, consisting of rigid parts and in the presence of ideal bilateral constraints and unilateral constraints involving friction, are formulated. Unique solutions are obtained, granted that the mass matrix of the multibody system is non-singular, the constraint matrices satisfy specific full rank conditions and that the friction is not too high.

New families of asymptotically optimal doubly periodic arrays with ideal correlation constraints

We present q new asymptotically optimal families of doubly periodic arrays with ideal auto and cross correlation constraints, derived from the Moreno-Maric construction for frequency hopping applications. These new families possess the same properties that make the Moreno-Maric construction suitable for communications systems and digital watermarking, size (q+1)×(q+1), weight ?=q+1, family size q?2, and correlation 2, where q is a power of a prime. These new families are asymptotically optimal.

Late toxicity and quality of life after definitive treatment of prostate cancer: redefining optimal rectal sparing constraints for intensity-modulated radiation therapy.

The objective of this study was to assess late toxicity and quality of life (QOL) for patients receiving definitive intensity-modulated radiotherapy (IMRT) and image-guided radiation therapy (IGRT) with regard to normal tissue sparing objectives. Three hundred and seventy-two consecutive men treated with definitive IMRT for prostate adenocarcinoma. Toxicity was graded by CTC v3.0 genitourinary (GU) and gastrointestinal (GI) toxicity at each follow-up visit. Patient-reported QOL (EPIC-26) was prospectively collected for a subset of men. Dosimetric data for bladder and rectum were compared to toxicity and QOL global domain scores, specifically analyzing outcomes for men who met ideal rectal constraints (V70 <10%, V65 <20%, V40 <40%). The median age and prescription dose was 69 years and 76 Gy, respectively. Median follow-up was 47 months. At 4 years, freedom from Grade 2 (FFG2) GI toxicity was 92% and FFG2 GU toxicity was 76%. On univariate analysis, current smoking, larger bladder volume, and higher RT dose were associated with decreased FFG2 GU toxicity, while use of anticoagulation, increasing age, and not meeting ideal rectal constraints were associated with decreased FFG2 GI toxicity (all P ≤ 0.05). Bowel QOL remained stable over the 2-year follow-up period and was higher for patients who met ideal rectal constraints (P = 0.05). IMRT with IGRT is associated with low rates of severe toxicity and a high GI and GU QOL. The use of strict rectal constraints can further improve GI QOL and reduce GI toxicity.

Image-guided intensity-modulated radiotherapy for prostate cancer: Dose constraints for the anterior rectal wall to minimize rectal toxicity

Rectal adverse events (AEs) are a major concern with definitive radiotherapy (RT) treatment for prostate cancer. The anterior rectal wall is at the greatest risk of injury as it lies closest to the target volume and receives the highest dose of RT. This study evaluated the absolute volume of anterior rectal wall receiving a high dose to identify potential ideal dose constraints that can minimize rectal AEs. A total of 111 consecutive patients with Stage T1c to T3a N0 M0 prostate cancer who underwent image-guided intensity-modulated RT at our institution were included. AEs were graded according to the Common Terminology Criteria for Adverse Events, version 4.0. The volume of anterior rectal wall receiving 5 to 80Gy in 2.5-Gy increments was determined. Multivariable Cox regression models were used to identify cut points in these volumes that led to an increased risk of early and late rectal AEs. Early AEs occurred in most patients (88%); however, relatively few of them (13%) were grade ≥2. At 5 years, the cumulative incidence of late rectal AEs was 37%, with only 5% being grade ≥2. For almost all RT doses, we identified a threshold of irradiated absolute volume of anterior rectal wall above which there was at least a trend toward a significantly higher rate of AEs. Most strikingly, patients with more than 1.29, 0.73, or 0.45cm3 of anterior rectal wall exposed to radiation doses of 67.5, 70, or 72.5Gy, respectively, had a significantly increased risk of late AEs (relative risks [RR]: 2.18 to 2.72; p ≤ 0.041) and of grade ≥ 2 early AEs (RR: 6.36 to 6.48; p = 0.004). Our study provides evidence that definitive image-guided intensity-modulated radiotherapy (IG-IMRT) for prostate cancer is well tolerated and also identifies dose thresholds for the absolute volume of anterior rectal wall above which patients are at greater risk of early and late complications.

A Software Architecture and Application for Reporting on and Analyzing Radiation Plans for Concordance With Ideal Dose Constraints as a Quality Assurance Parameter

A Software Architecture and Application for Reporting on and Analyzing Radiation Plans for Concordance With Ideal Dose Constraints as a Quality Assurance Parameter

Exploiting wheel slips of mobile robots to improve navigation performance

Improving navigation performance of autonomous wheeled mobile robot (WMR) in a dynamic unstructured environment requires improved maneuverability. In such cases, the dynamics of wheel slip may violate the ideal no-slip kinematic constraints generally used to model nonholonomic WMR. In this paper, a new method is proposed to tackle the modeling inadequacy that arises when slip is neglected by including both longitudinal and lateral slip dynamics into the overall dynamics of the WMR. This new model of the WMR provides a realistic simulation environment that can be utilized to develop model-based controllers to improve WMR navigation. In this paper, a dynamic planner with a path-following controller is designed to allow the WMR to navigate efficiently by autonomously regulating the generated traction force due to wheel slip. Extensive simulation results demonstrate the importance of the proposed modeling technique to capture slip phenomenon and the efficacy of the presented control technique to exploit such slip for better navigation performance.

Equilibrium and stability of tensegrity structures: A convex analysis approach

In this paper, tensegrity structures are modeled by introducing suitable energy convex functions. These allow to enforce both ideal and non-ideal constraints, gathering compatibility, equilibrium, and stability problems, as well as their duality relationships, in the same functional framework. Arguments of convex analysis allow to recover consistently a number of basic results, as well as to formulate new interpretations and analysis criterions.

Dynamical masses of early-type galaxies at z ~ 2

AbstractThe evolution of masses and sizes of passive (early-type) galaxies with redshift provides ideal constraints to galaxy formation models. These parameters can in principle be obtained for large galaxy samples from multi-band photometry alone. However the accuracy of photometric masses is limited by the non-universality of the IMF. Galaxy sizes can be biased at high redshift due to the inferior quality of the imaging data. Both problems can be avoided using galaxy dynamics, and in particular by measuring the galaxies stellar velocity dispersion. Here we provide an overview of the efforts in this direction.

On the brachistochronic motion of mechanical systems with unilateral constraints

The problem of brachistochronic motion of a two-degree of freedom mechanical system is considered. The ideal bilateral constraints and one unilateral constraint with Coulomb friction are imposed on the system. It has been assumed that the components of the metric tensor are constant. After introducing the transformation of generalized coordinates, whereby the quadratic form of kinetic energy is reduced to a canonical form, the considered problem is geometrically interpreted as the motion of a representative point in a two-dimensional Euclidean space. Thus, the analogy with the brachistochronic motion of a particle along a curve which is treated as a unilateral constraint is achieved. The results are illustrated via an example.