Constrained Clustering With Nonnegative Matrix Factorization.
Zhang, Xianchao; Zong, Linlin; Liu, Xinyue; Luo, Jiebo
2016-07-01
Nonnegative matrix factorization (NMF) and symmetric NMF (SymNMF) have been shown to be effective for clustering linearly separable data and nonlinearly separable data, respectively. Nevertheless, many practical applications demand constrained algorithms in which a small number of constraints in the form of must-link and cannot-link are available. In this paper, we propose an NMF-based constrained clustering framework in which the similarity between two points on a must-link is enforced to approximate 1 and the similarity between two points on a cannot-link is enforced to approximate 0. We then formulate the framework using NMF and SymNMF to deal with clustering of linearly separable data and nonlinearly separable data, respectively. Furthermore, we present multiplicative update rules to solve them and show the correctness and convergence. Experimental results on various text data sets, University of California, Irvine (UCI) data sets, and gene expression data sets demonstrate the superiority of our algorithms over existing constrained clustering algorithms.
Constrained Nonnegative Matrix Factorization for Image Representation.
Liu, Haifeng; Wu, Zhaohui; Li, Xuelong; Cai, Deng; Huang, Thomas S
2012-07-01
Nonnegative matrix factorization (NMF) is a popular technique for finding parts-based, linear representations of nonnegative data. It has been successfully applied in a wide range of applications such as pattern recognition, information retrieval, and computer vision. However, NMF is essentially an unsupervised method and cannot make use of label information. In this paper, we propose a novel semi-supervised matrix decomposition method, called Constrained Nonnegative Matrix Factorization (CNMF), which incorporates the label information as additional constraints. Specifically, we show how explicitly combining label information improves the discriminating power of the resulting matrix decomposition. We explore the proposed CNMF method with two cost function formulations and provide the corresponding update solutions for the optimization problems. Empirical experiments demonstrate the effectiveness of our novel algorithm in comparison to the state-of-the-art approaches through a set of evaluations based on real-world applications.
Pairwise constrained concept factorization for data representation.
He, Yangcheng; Lu, Hongtao; Huang, Lei; Xie, Saining
2014-04-01
Concept factorization (CF) is a variant of non-negative matrix factorization (NMF). In CF, each concept is represented by a linear combination of data points, and each data point is represented by a linear combination of concepts. More specifically, each concept is represented by more than one data point with different weights, and each data point carries various weights called membership to represent their degrees belonging to that concept. However, CF is actually an unsupervised method without making use of prior information of the data. In this paper, we propose a novel semi-supervised concept factorization method, called Pairwise Constrained Concept Factorization (PCCF), which incorporates pairwise constraints into the CF framework. We expect that data points which have pairwise must-link constraints should have the same class label as much as possible, while data points with pairwise cannot-link constraints will have different class labels as much as possible. Due to the incorporation of the pairwise constraints, the learning quality of the CF has been significantly enhanced. Experimental results show the effectiveness of our proposed novel method in comparison to the state-of-the-art algorithms on several real world applications.
Constrained Fisher Scoring for a Mixture of Factor Analyzers
2016-09-01
ARL-TR-7836• SEP 2016 US Army Research Laboratory Constrained Fisher Scoring for a Mixture of Factor Analyzers by Gene T Whipps, Emre Ertin, and...TR-7836• SEP 2016 US Army Research Laboratory Constrained Fisher Scoring for a Mixture of Factor Analyzers by Gene T Whipps Sensors and Electron... Research Laboratory Sensors and Electron Devices Directorate ATTN: RDRL-SES-A Adelphi, MD 20783 primary author’s email: <gene.t.whipps.civ@mail.mil>. This
3-D Lung Segmentation by Incremental Constrained Nonnegative Matrix Factorization.
Hosseini-Asl, Ehsan; Zurada, Jacek M; Gimelfarb, Georgy; El-Baz, Ayman
2016-05-01
Accurate lung segmentation from large-size 3-D chest-computed tomography images is crucial for computer-assisted cancer diagnostics. To efficiently segment a 3-D lung, we extract voxel-wise features of spatial image contexts by unsupervised learning with a proposed incremental constrained nonnegative matrix factorization (ICNMF). The method applies smoothness constraints to learn the features, which are more robust to lung tissue inhomogeneities, and thus, help to better segment internal lung pathologies than the known state-of-the-art techniques. Compared to the latter, the ICNMF depends less on the domain expert knowledge and is more easily tuned due to only a few control parameters. Also, the proposed slice-wise incremental learning with due regard for interslice signal dependencies decreases the computational complexity of the NMF-based segmentation and is scalable to very large 3-D lung images. The method is quantitatively validated on simulated realistic lung phantoms that mimic different lung pathologies (seven datasets), in vivo datasets for 17 subjects, and 55 datasets from the Lobe and Lung Analysis 2011 (LOLA11) study. For the in vivo data, the accuracy of our segmentation w.r.t. the ground truth is 0.96 by the Dice similarity coefficient, 9.0 mm by the modified Hausdorff distance, and 0.87% by the absolute lung volume difference, which is significantly better than for the NMF-based segmentation. In spite of not being designed for lungs with severe pathologies and of no agreement between radiologists on the ground truth in such cases, the ICNMF with its total accuracy of 0.965 was ranked fifth among all others in the LOLA11. After excluding the nine too pathological cases from the LOLA11 dataset, the ICNMF accuracy increased to 0.986.
Constraining isoprene emission factors using airborne flux measurements during CABERNET
NASA Astrophysics Data System (ADS)
Misztal, P. K.; Karl, T.; Jiang, X.; Avise, J. C.; Scott, K.; Jonsson, H.; Guenther, A. B.; Goldstein, A. H.
2012-12-01
An aircraft flux study was conducted to assess biogenic volatile organic compound (BVOC) emissions from California ecosystems targeting oak woodlands and isoprene for most transects. The direct eddy covariance approach featured high speed proton transfer reaction mass spectrometry onboard a CIRPAS (Center for Interdisciplinary Remotely-Piloted Aircraft Studies) Twin Otter aircraft during June 2011 as part of the CABERNET (California Airborne BVOC Emission Research in Natural Ecosystem Transects) project. Isoprene fluxes were calculated using wavelet analysis and scaled to surface fluxes using a divergence term obtained by measuring fluxes at multiple altitudes over homogenous oak terrain. By normalization of fluxes to standard temperature and photosynthetically active radiation levels using standard BVOC modeling equations, the resulting emission factors could be directly compared with those used by MEGAN (Model of Emissions of Gases and Aerosols from Nature) and BEIGIS (Biogenic Emission Inventory Geographic Information System) models which are the most commonly used BVOC emission models for California. As expected, oak woodlands were found to be the dominant source of isoprene in all areas surrounding and in the Central Valley of California. The airborne fluxes averaged to 2 km spatial resolution matched remarkably well with current oak woodland distributions driving the models and hence the correspondence of modeled and aircraft derived emission factors was also good, although quantitative differences were encountered depending on the region and driving variables used. Fluxes measured from aircraft proved to be useful for the improvement of the accuracy of modeled predictions for isoprene and other important ozone and aerosol precursor compounds. These are the first regional isoprene flux measurements using direct eddy covariance on aircraft.
The Evolution of a Teacher Community of Practice: Identifying Facilitating and Constraining Factors
ERIC Educational Resources Information Center
Borg, Tracey
2012-01-01
This paper presents findings from a larger, qualitative study that explored the potential of a school-based teacher community of practice as a model for a transformative form of teacher professional development. This paper reports on initial findings from a grounded theory exploration of the factors that facilitated and constrained the evolution…
ERIC Educational Resources Information Center
Jääskelä, Päivikki; Häkkinen, Päivi; Rasku-Puttonen, Helena
2017-01-01
Higher education calls for reform, but deeper knowledge about the prerequisites for teaching development and pedagogical change is missing. In this study, 51 university teachers' experiences of supportive or constraining factors in teaching development were investigated in the context of Finland's multidisciplinary network. The findings reveal…
Unsupervised unmixing of hyperspectral imagery using the constrained positive matrix factorization
NASA Astrophysics Data System (ADS)
Masalmah, Yahya M.; Vélez-Reyes, Miguel
2006-04-01
This paper presents an approach for simultaneous determination of endmembers and their abundances in hyperspectral imagery unmixing using a constrained positive matrix factorization (PMF). The algorithm presented here solves the constrained PMF using Gauss-Seidel method. This algorithm alternates between the endmembers matrix updating step and the abundance estimation step until convergence is achieved. Preliminary results using a subset of a HYPERION image taken in SW Puerto Rico are presented. These results show the potential of the proposed method to solve the unsupervised unmixing problem.
Constraining Factors of Research among faculty members at Hormozgan University of Medical Sciences
Nejatizadeh, Azim; Sarnayzadeh, Majid; Kahnouji, Kobra; Ghasemi, Rachel; Nakhodaei, Nahid
2016-01-01
Introduction In recent decades, the major criteria for development in countries were defined mostly by research position. The first step in organizing the research subject in societies is gaining a correct perception of abilities, available facilities, and finding the strengths and weaknesses of research programs. This research was conducted to determine the constraining factors of research among faculty members. Methods In this cross-sectional study in 2013, the population was Hormozgan Medical Science faculty members, and samples were selected based on the Morgan table (138 individuals). A researcher-made questionnaire after determining validity and confirming reliability was distributed among them. The data were analyzed by SPSS using descriptive and inferential statistics, such as Pearson’s product-moment correlation. Results Among organizational factors, lack of data presentation to researchers from organization sections with 81.2% was the most effective factor. The lack of facilitating national and international research exchange with 80.5% and the lack of research workshops based on needs with 77.9% were the next ones. Among the personal constraining factors, 64% of the faculty declared that having inadequate time for research due to the educational activities was the main factor. Conclusions According to the faculty’s comments, research activities encounter different constraining factors. It can be said that, by promoting a data registration system, collaborating on contract agreements and improving national and international research exchange, empowering members’ research (need-based workshops), and decreasing the faculty’s clinical and educational activities can overcome these constraints. PMID:27382451
NASA Astrophysics Data System (ADS)
Clougherty, Jane E.; Houseman, E. Andres; Levy, Jonathan I.
Recent studies have used land use regression (LUR) techniques to explain spatial variability in exposures to PM 2.5 and traffic-related pollutants. Factor analysis has been used to determine source contributions to measured concentrations. Few studies have combined these methods, however, to construct and explain latent source effects. In this study, we derive latent source factors using confirmatory factor analysis constrained to non-negative loadings, and develop LUR models to predict the influence of outdoor sources on latent source factors using GIS-based measures of traffic and other local sources, central site monitoring data, and meteorology. We collected 3-4 day samples of nitrogen dioxide (NO 2) and PM 2.5 outside of 44 homes in summer and winter, from 2003 to 2005 in and around Boston, Massachusetts. Reflectance analysis, X-ray fluorescence spectroscopy (XRF), and high-resolution inductively-coupled plasma mass spectrometry (ICP-MS) were performed on particle filters to estimate elemental carbon (EC), trace element, and water-soluble metals concentrations. Within our constrained factor analysis, a five-factor model was optimal, balancing statistical robustness and physical interpretability. This model produced loadings indicating long-range transport, brake wear/traffic exhaust, diesel exhaust, fuel oil combustion, and resuspended road dust. LUR models largely corroborated factor interpretations through covariate significance. For example, 'long-range transport' was predicted by central site PM 2.5 and season; 'brake wear/traffic exhaust' and 'resuspended road dust' by traffic and residential density; 'diesel exhaust' by percent diesel traffic on nearest major road; and 'fuel oil combustion' by population density. Results suggest that outdoor residential PM 2.5 source contributions can be partially predicted using GIS-based terms, and that LUR techniques can support factor interpretation for source apportionment. Together, LUR and factor analysis
Ng, Felicia S L; Schütte, Judith; Ruau, David; Diamanti, Evangelia; Hannah, Rebecca; Kinston, Sarah J; Göttgens, Berthold
2014-12-16
Combinatorial transcription factor (TF) binding is essential for cell-type-specific gene regulation. However, much remains to be learned about the mechanisms of TF interactions, including to what extent constrained spacing and orientation of interacting TFs are critical for regulatory element activity. To examine the relative prevalence of the 'enhanceosome' versus the 'TF collective' model of combinatorial TF binding, a comprehensive analysis of TF binding site sequences in large scale datasets is necessary. We developed a motif-pair discovery pipeline to identify motif co-occurrences with preferential distance(s) between motifs in TF-bound regions. Utilizing a compendium of 289 mouse haematopoietic TF ChIP-seq datasets, we demonstrate that haematopoietic-related motif-pairs commonly occur with highly conserved constrained spacing and orientation between motifs. Furthermore, motif clustering revealed specific associations for both heterotypic and homotypic motif-pairs with particular haematopoietic cell types. We also showed that disrupting the spacing between motif-pairs significantly affects transcriptional activity in a well-known motif-pair-E-box and GATA, and in two previously unknown motif-pairs with constrained spacing-Ets and Homeobox as well as Ets and E-box. In this study, we provide evidence for widespread sequence-specific TF pair interaction with DNA that conforms to the 'enhanceosome' model, and furthermore identify associations between specific haematopoietic cell-types and motif-pairs. © The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.
A robust endmember constrained non-negative matrix factorization method for hyperspectral unmixing
NASA Astrophysics Data System (ADS)
Liu, Jinjun
2016-03-01
This paper presents a new method based non-negative matrix factorization (NMF) for hyperspectral unmixing, termed robust endmember constrained NMF (RECNMF). The objective function of RECNMF can not only reduce the effect of noise and outliers but also can reduce the size of convex formed by the endmembers and the correlation between the endmembers. The algorithm is solved by the projected gradient method. The effectiveness of RECNMF is illustrated by comparing its performance with the state-of-the-art algorithms in simulated data.
Obstetric perineal injury: risk factors and prevalence in a resource-constrained setting.
Naidoo, T D; Moodley, J
2015-10-01
The prevalence of obstetric perineal injuries and risk factors vary between affluent and resource-constrained settings. This prospective observational study reports on the factors associated with perineal lacerations in a cohort of Black African and Indian women delivering at two regional hospitals in South Africa. Binary logistic regression analysis was used to test for associations between independent variables and the dependent variable on multivariate analysis. All variables significant on bivariate analysis (P < 0.05) were included in the multivariate model. There were 202 (16.2%) perineal tears. Variables significant with having a perineal tear on bivariate and multivariate analysis included: Black African race (OR: 2.4; 95% CI: 1.2-4.6); duration of labour ≥6.3h (OR: 1.5; 95% CI: 1.1-2.1); and epidural analgesia (OR: 2.9; 95% CI: 1.9-4.7). Having an episiotomy was protective against perineal tears (OR: 0.06; 95% CI: 0.03-0.1). Obstetric perineal injury commonly occurs in our resourced-constrained setting and the risk factors are similar to those in well-resourced settings. Identification of those at risk may reduce obstetric perineal injury. © The Author(s) 2015.
Method for exploiting bias in factor analysis using constrained alternating least squares algorithms
Keenan, Michael R.
2008-12-30
Bias plays an important role in factor analysis and is often implicitly made use of, for example, to constrain solutions to factors that conform to physical reality. However, when components are collinear, a large range of solutions may exist that satisfy the basic constraints and fit the data equally well. In such cases, the introduction of mathematical bias through the application of constraints may select solutions that are less than optimal. The biased alternating least squares algorithm of the present invention can offset mathematical bias introduced by constraints in the standard alternating least squares analysis to achieve factor solutions that are most consistent with physical reality. In addition, these methods can be used to explicitly exploit bias to provide alternative views and provide additional insights into spectral data sets.
Edge, Sara; Newbold, K Bruce; McKeary, Marie
2014-09-01
Studies on youth health and well-being are predominantly quantitative and expert-driven with less attention given to how youth understand what it means to be healthy themselves and the role of socio-cultural factors in shaping this. Knowledge on the perceptions and experiences of refugee youth is particularly lacking and notable given their unique stressors related to migratory, settlement and integration experiences. We contribute a better understanding of how refugee youth themselves define and contextualize health, with particular emphasis given to socio-cultural factors that enable or constrain health promotion efforts and individual health agency. This research was undertaken at a downtown drop-in centre in Hamilton, Ontario, Canada that provided settlement and integration services to newcomer youth. We employ a grounded theory approach and draw upon participant observation, focus groups and in-depth interviews. Twenty-six youth (age 18-25 years), representing 12 different countries of origin participated. The youth defined health very broadly touching upon many typical determinants of health (e.g. education, income, etc.). Yet factors of most importance (as demonstrated by the frequency and urgency in which they were discussed by youth) included a sense of belonging, positive self-identity, emotional well-being, and sense of agency or self-determination. We conceptualize these as "mediating" factors given the youth argued they enabled or constrained their ability to cope with adversities related to other health determinant categories. The youth also discussed what we interpret as "facilitators" that encourage mediating factors to manifest positively (e.g. informal, non-biomedical settings and programs that nurture trust, break down access barriers, and promote a sense of community amongst peers, mentors, and health professionals). When creating health promotion strategies for refugee youth (and perhaps youth more generally) it is important to understand the
Multi-factor Constrained Information Analysis Method for Landslide Hazard Risk
NASA Astrophysics Data System (ADS)
Tao, Kunwang; Wang, Liang; Qian, Xinlin
2015-04-01
Landslide hazard cause enormous damage to human life, property, and the environment. The most effective way to mitigate the effects of landslides is to evaluate the risk of the landslides, and take measures to avoid the loss in advance. Various factors should be considered for the landslides' risk assessment, so the assessment has great complexity and uncertainty. According to landslides, the multiple factors constrained method for landslides risk assessment was proposed at the same time, which with three step to carried it out, first using the GIS technology to divide the analysis grid as the base analysis unit, second, according to the available information, slope, lithology, faults, landuse, etc. as the multiple evaluation factors, finally, based on years of landslides in the observed data, the risk assessment analysis of landslides were realized with of multiple factors constrained assessment model, which the weight value of every factor was determined by the information model. The region of Gongliu was selected as the experimental area which located in Xinjiang Ili River basin and the altitude of 600 to 4000 meters, with the special terrain characteristics of long at the east to west, narrow at north to south. The unique topography characters is the abundant rainfall which causing frequent landslides. By selecting 500m * 500m as an analysis grid which covering the whole study area, based on the multiple factors constrained method for the landslides risk assessment, a comprehensive assessment of the landslides risk in this region were computed out, and the landslide hazard classification map was realized at the end. From the experimental results of the statistical perspective, the proportion of landslide hazard point is 94.04% at a little high risk and high risk areas. And the proportion of 4.64% at the low risk zone, 1.32% at the most low risk zone. The results showed a high probability of landslides at high level of the assess region, which showed that
Gagliardi, Anna R; Lehoux, Pascale; Ducey, Ariel; Easty, Anthony; Ross, Sue; Bell, Chaim M; Trbovich, Patricia; Takata, Julie; Urbach, David R
2017-04-01
Patient engagement (PE) is warranted when treatment risks and outcomes are uncertain, as is the case for higher risk medical devices. Previous research found that patients were not engaged in discussions or decisions about implantable medical devices. This study explored physician views about engaging patients in such discussions. Qualitative interviews using a basic descriptive approach. Canada. Practicing cardiovascular and orthopaedic physicians. Level, processes and determinants of PE in medical device discussions and decisions. Views were largely similar among 10 cardiovascular and 12 orthopaedic physicians interviewed. Most said that it was feasible to inform and sometimes involve patients in discussions, but not to partner with them in medical device decision-making. PE was constrained by patient (comfort with PE, technical understanding, physiologic/demographic characteristics, prognosis), physician (device preferences, time), health system (purchasing contracts) and device factors (number of devices on market, comparative advantage). A framework was generated to help physicians engage patients in discussions about medical devices, even when decisions may not be preference sensitive due to multiple constraints on choice. This study identified that patients are not engaged in discussions or decisions about implantable medical devices. This may be due to multiple constraints. Further research should establish the legitimacy, prevalence and impact of constraining factors, and examine whether and how different levels and forms of PE are needed and feasible.
Unsupervised unmixing of hyperspectral imagery using the constrained positive matrix factorization
NASA Astrophysics Data System (ADS)
Masalmah, Yahya M.
In hyperspectral imaging, hundreds of images are taken at narrow and contiguous spectral bands providing us with high spectral resolution spectral signatures that can be used to discriminate between objects. In many applications, the measured spectral signature is a mixture of the object of interest, and other objects within the field of view of the sensor. To determine which objects are in the field of view of the sensor, we need to decompose the measured spectral signature in its constituents and their contribution to the measured signal. This research dealt with the unsupervised determination of the constituents and their fractional abundance in each pixel in a hyperspectral image using a constrained positive matrix factorization (cPMF). Different algorithms are presented to compute the cPMF. Tests and validation with real and simulated data show the effectiveness of the method. Application of the approach to environmental remote sensing and microscopic imaging is shown.
NASA Astrophysics Data System (ADS)
Xia, Jianghai; Xu, Yixian; Miller, Richard D.; Ivanov, Julian
2012-07-01
Quality factors (Q) of near-surface materials are as important as velocities of the materials in many applications. Only phase information of surface-wave data is utilized when high-frequency (≥ 2 Hz) surface-wave data are routinely inverted to determine near-surface shear (S)-wave velocities. Amplitude information of high-frequency surface-wave data can be used to determine quality factors of near-surface materials. Given S-wave velocity, compressional (P)-wave velocity, and Rayleigh-wave phase velocities, it is feasible to solve for S-wave quality factor QS and P-wave quality factor QP (for some specific velocity models) down to 30 m below the ground surface in many settings by inverting high-frequency Rayleigh-wave attenuation coefficients in a layered earth model. Amplitude of seismic data is an exponential function of attenuation coefficients. When calculating attenuation coefficients from changes in amplitude, this nonlinear nature would result in that small variations in amplitude cause huge changes in attenuation coefficients. This result suggests data (attenuation coefficients) that normally possess large errors could eventually transfer to a model (quality factors); therefore, constraints (or a priori information) on models are necessary. Because an inversion system to solve this problem is unstable, a regularization parameter must be introduced into an inversion algorithm to stabilize the inversion. These characteristics of the inversion problem allow us to solve the problem as a constrained and regularized linear system. Usually, a set of models that meet the defined constraints can be obtained by solving the system. Based on the linear nature of the inversion system, a smooth model can be selected from the set of models as a solution of the inversion using the L-curve method. This approach is a trade-off solution between data misfit and model length. Several real-world examples demonstrate the importance of constraints in finding acceptable realistic
Bell, Linda; Lacombe, Marie; Yergeau, Eric; Moutquin, Jean-Marie; Tribble, Denise St-cyr; Royer, Francine; Garant, Marie-Pierre
2008-01-01
To document breastfeeding rates from birth to six months as well as the factors facilitating and constraining the continuation of breastfeeding in women in the Eastern Townships of Quebec and to compare these to the results obtained in 1999. Postal questionnaire sent to 374 mothers who had breastfed and analysis of archival data. Breastfeeding rates were 86.3% at birth and 75% at discharge from hospital in all mothers who gave birth to a child in 2004-2005. Breastfeeding rates in the 272 mothers who answered the questionnaire were reported to be 67.3% and 47.4% at three and six months respectively. Results indicate that 8.9% of infants were still receiving breast milk exclusively after the third month. However, 27.9% of the mothers had stopped breastfeeding during the infant's first week. Support from the nurses was the primary factor facilitating breastfeeding. The main reasons the mothers gave for stopping breastfeeding were problems with breastfeeding and fatigue. Breastfeeding rates in this area of Quebec have increased significantly in the past five years and are comparable with those in the rest of Canada. Breastfeeding exclusively up to six months is rare, and initiatives to support breastfeeding mothers in the hospital and in the community are having success.
ERIC Educational Resources Information Center
Bower, Matt; Lee, Mark J. W.; Dalgarno, Barney
2017-01-01
This article presents the outcomes of a pilot study investigating factors that supported and constrained collaborative learning in a blended reality environment. Pre-service teachers at an Australian university took part in a hybrid tutorial lesson involving a mixture of students who were co-located in the same face-to-face (F2F) classroom along…
ERIC Educational Resources Information Center
Bower, Matt; Lee, Mark J. W.; Dalgarno, Barney
2017-01-01
This article presents the outcomes of a pilot study investigating factors that supported and constrained collaborative learning in a blended reality environment. Pre-service teachers at an Australian university took part in a hybrid tutorial lesson involving a mixture of students who were co-located in the same face-to-face (F2F) classroom along…
Kettinger, Adam O; Kannengiesser, Stephan A R; Breuer, Felix A; Vidnyanszky, Zoltan; Blaimer, Martin
2017-09-01
Parallel imaging generally entails a reduction in the signal-to-noise ratio of the final image. Phase-constrained methods aim to improve reconstruction quality by using symmetry properties of k-space. Noise amplification in phase-constrained reconstruction depends heavily on the object background phase. The purpose of this work is to present a new approach of using tailored radiofrequency pulses to optimize the object phase distribution in order to maximize the benefit of phase-constrained reconstruction, and to minimize the noise amplification. Intrinsic object phase and coil sensitivity profiles are measured in a prescan. Optimal phase distribution is computed to maximize signal-to-noise ratio in the given setup. Tailored radiofrequency pulses are designed to introduce the optimal phase map in the following accelerated acquisitions, subsequently reconstructed by phase-constrained methods. The potential of the method is demonstrated in vivo with in-plane accelerated (8x) and simultaneous multislice (3x) acquisitions. Mean g-factors are reduced by up to a factor of 2 compared with conventional techniques when an appropriate phase-constrained reconstruction is applied to phase-optimized acquisitions, enhancing the signal-to-noise ratio of the final images and the visibility of small details. Combining phase-constrained reconstruction and phase optimization by tailored radiofrequency pulses can provide notable improvement in the signal-to-noise ratio and reconstruction quality of accelerated MRI. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.
Lu, Na; Li, Tengfei; Pan, Jinjin; Ren, Xiaodong; Feng, Zuren; Miao, Hongyu
2015-05-01
Electroencephalogram (EEG) provides a non-invasive approach to measure the electrical activities of brain neurons and has long been employed for the development of brain-computer interface (BCI). For this purpose, various patterns/features of EEG data need to be extracted and associated with specific events like cue-paced motor imagery. However, this is a challenging task since EEG data are usually non-stationary time series with a low signal-to-noise ratio. In this study, we propose a novel method, called structure constrained semi-nonnegative matrix factorization (SCS-NMF), to extract the key patterns of EEG data in time domain by imposing the mean envelopes of event-related potentials (ERPs) as constraints on the semi-NMF procedure. The proposed method is applicable to general EEG time series, and the extracted temporal features by SCS-NMF can also be combined with other features in frequency domain to improve the performance of motor imagery classification. Real data experiments have been performed using the SCS-NMF approach for motor imagery classification, and the results clearly suggest the superiority of the proposed method. Comparison experiments have also been conducted. The compared methods include ICA, PCA, Semi-NMF, Wavelets, EMD and CSP, which further verified the effectivity of SCS-NMF. The SCS-NMF method could obtain better or competitive performance over the state of the art methods, which provides a novel solution for brain pattern analysis from the perspective of structure constraint. Copyright © 2015 Elsevier Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Sturtz, Timothy M.
Source apportionment models attempt to untangle the relationship between pollution sources and the impacts at downwind receptors. Two frameworks of source apportionment models exist: source-oriented and receptor-oriented. Source based apportionment models use presumed emissions and atmospheric processes to estimate the downwind source contributions. Conversely, receptor based models leverage speciated concentration data from downwind receptors and apply statistical methods to predict source contributions. Integration of both source-oriented and receptor-oriented models could lead to a better understanding of the implications sources have on the environment and society. The research presented here investigated three different types of constraints applied to the Positive Matrix Factorization (PMF) receptor model within the framework of the Multilinear Engine (ME-2): element ratio constraints, spatial separation constraints, and chemical transport model (CTM) source attribution constraints. PM10-2.5 mass and trace element concentrations were measured in Winston-Salem, Chicago, and St. Paul at up to 60 sites per city during two different seasons in 2010. PMF was used to explore the underlying sources of variability. Information on previously reported PM10-2.5 tire and brake wear profiles were used to constrain these features in PMF by prior specification of selected species ratios. We also modified PMF to allow for combining the measurements from all three cities into a single model while preserving city-specific soil features. Relatively minor differences were observed between model predictions with and without the prior ratio constraints, increasing confidence in our ability to identify separate brake wear and tire wear features. Using separate data, source contributions to total fine particle carbon predicted by a CTM were incorporated into the PMF receptor model to form a receptor-oriented hybrid model. The level of influence of the CTM versus traditional PMF was
Constraining the Astrophysical S Factor of the 3He(α,γ)7Be Reaction
NASA Astrophysics Data System (ADS)
Carmona-Gallardo, M.; Rojas, A.; Nara Singh, B. S.; Akers, C.; Aviv, O.; Borge, M. J. G.; Christian, G.; Davids, B.; Fallis, J.; Fulton, B. R.; Hager, U.; Haquin, G.; Hass, M.; Hutcheon, D. A.; Nir-El, Y.; Ottewell, D.; Ruiz, C.; Sjue, S. K. L.; Tengblad, O.; Yaniv, R.; Yungreis, Z.
The cross section of the 3He(α,γ)7Be reaction has been widely studied both from the theoretical and the experimental fronts due to its relevance to the standard solar model and to the Big Bang Nucleosynthesis calculations. We report here on cross section measurements in the energy region Ec.m. = 1-3 MeV using the direct recoil counting method in an attempt to resolve the discrepancies among the previous data sets and calculations in this energy region and thus to constrain the extrapolations of the S34(E) curve to astrophysical energies.
NASA Astrophysics Data System (ADS)
Druken, Bridget Kinsella
Lesson study, a teacher-led vehicle for inquiring into teacher practice through creating, enacting, and reflecting on collaboratively designed research lessons, has been shown to improve mathematics teacher practice in the United States, such as improving knowledge about mathematics, changing teacher practice, and developing communities of teachers. Though it has been described as a sustainable form of professional development, little research exists on what might support teachers in continuing to engage in lesson study after a grant ends. This qualitative and multi-case study investigates the sustainability of lesson study as mathematics teachers engage in a district scale-up lesson study professional experience after participating in a three-year California Mathematics Science Partnership (CaMSP) grant to improve algebraic instruction. To do so, I first provide a description of material (e.g. curricular materials and time), human (attending district trainings and interacting with mathematics coaches), and social (qualities like trust, shared values, common goals, and expectations developed through relationships with others) resources present in the context of two school districts as reported by participants. I then describe practices of lesson study reported to have continued. I also report on teachers' conceptions of what it means to engage in lesson study. I conclude by describing how these results suggest factors that supported and constrained teachers' in continuing lesson study. To accomplish this work, I used qualitative methods of grounded theory informed by a modified sustainability framework on interview, survey, and case study data about teachers, principals, and Teachers on Special Assignment (TOSAs). Four cases were selected to show the varying levels of lesson study practices that continued past the conclusion of the grant. Analyses reveal varying levels of integration, linkage, and synergy among both formally and informally arranged groups of
Levy, Jonathan I; Clougherty, Jane E; Baxter, Lisa K; Houseman, E Andres; Paciorek, Christopher J
2010-12-01
multiple indicators of traffic using Massachusetts Highway Department (MHD) data and traffic counts collected outside the residences where the air monitoring was conducted. We used a standardized questionnaire to collect data on home characteristics and occupant behaviors. Additional housing information was collected through property tax records. Ambient concentrations of pollutants as well as meteorological data were collected from centrally located ambient monitors. We used GIS-based LUR models to explain spatial and temporal variability in residential outdoor concentrations of PM2.5, EC, and NO2. We subsequently derived latent-source factors for residential outdoor concentrations using confirmatory factor analysis constrained to nonnegative loadings. We developed LUR models to determine whether GIS covariates and other predictors explain factor variability and thereby support initial factor interpretations. To evaluate indoor concentrations, we developed physically interpretable regression models that explored the relationship between measured indoor and outdoor concentrations, relying on questionnaire data to characterize indoor sources and activities. Because outdoor pollutant concentrations measured directly outside of homes are unlikely to be available for most large epidemiologic studies, we developed regression models to explain indoor concentrations of PM2.5, EC, and NO2 as a function of other, more readily available data: GIS covariates, questionnaire data reflecting both sources and ventilation, and central site monitoring data. As we did for outdoor concentrations, we then derived latent-source factors for residential indoor concentrations and developed regression models explaining variability in these indoor latent-source factors. Finally, to provide insight about the effects of improved characterization of exposures for the results of subsequent epidemiologic investigations, we developed a simulation framework to quantitatively compare the implications of
Castonguay, Julie; Vézina, Aline; Sévigny, Andrée
2014-03-01
The reality of volunteering in nonprofit organizations who offer services to seniors at home was observed from the viewpoint of two types of actors: volunteers and coordinators. Our results suggest that there are three decisive stages in volunteering: recruitment, realization of volunteer activity, and pursuit of this commitment. For each of them, some factors are more influential than others. Their presence or absence makes possible or not the initiation of this commitment and its pursuit. In this context, a constant negotiation takes place between the actors. Each of them has to adapt himself to others. Nevertheless, this adaptation is limited. So, stability between the position of the organization and that of the volunteer is necessary.
Minimum-volume-constrained nonnegative matrix factorization: enhanced ability of learning parts.
Zhou, Guoxu; Xie, Shengli; Yang, Zuyuan; Yang, Jun-Mei; He, Zhaoshui
2011-10-01
Nonnegative matrix factorization (NMF) with minimum-volume-constraint (MVC) is exploited in this paper. Our results show that MVC can actually improve the sparseness of the results of NMF. This sparseness is L(0)-norm oriented and can give desirable results even in very weak sparseness situations, thereby leading to the significantly enhanced ability of learning parts of NMF. The close relation between NMF, sparse NMF, and the MVC_NMF is discussed first. Then two algorithms are proposed to solve the MVC_NMF model. One is called quadratic programming_MVC_NMF (QP_MVC_NMF) which is based on quadratic programming and the other is called negative glow_MVC_NMF (NG_MVC_NMF) because it uses multiplicative updates incorporating natural gradient ingeniously. The QP_MVC_NMF algorithm is quite efficient for small-scale problems and the NG_MVC_NMF algorithm is more suitable for large-scale problems. Simulations show the efficiency and validity of the proposed methods in applications of blind source separation and human face images analysis. © 2011 IEEE
Morioka, Yoko; Casari, Caterina; Wohner, Nikolett; Cho, Sungyun; Kurata, Sachiko; Kitano, Ayumi; Christophe, Olivier D; Lenting, Peter J; Li, Renhao; Denis, Cécile V; Prévost, Nicolas
2014-05-22
Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease that presents with thrombocytopenia, disseminated thrombosis, hemolytic anemia, and organ dysfunction. The etiology of TTP has revealed that patients share a deficiency in plasma protease a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13), the enzyme responsible for cleaving ultra-large von Willebrand factor (VWF) multimers into nonthrombogenic fragments. Therefore, existing TTP mouse models were developed by targeted disruption of the ADAMTS13 gene. ADAMTS13(-/-) mice are mostly asymptomatic in the absence of a trigger, as redundant proteases appear to take on VWF processing. As an alternative approach to creating one such model, we devised a strategy based on the expression of a cleavage-resistant VWF mutant in mice. The creation of a disulfide bond within the A2 domain of VWF was found to render VWF multimers resistant to proteolysis by plasma proteases under flow. Furthermore, mice expressing the murine VWF/p.S1494C-p.A1534C mutant present with symptoms characteristics of acute TTP such as thrombocytopenia, red cell shredding, accumulation of VWF-rich thrombi in the microvasculature, and advanced TTP symptoms such as renal dysfunction and splenomegaly. Because this model appears to faithfully emulate the pathophysiology of TTP, it should prove most useful in the study of microangiopathic diseases and their treatment. © 2014 by The American Society of Hematology.
Lapping, Karin; Frongillo, Edward A; Nguyen, Phuong H; Coates, Jennifer; Webb, Patrick; Menon, Purnima
2014-09-01
Translating national policies and guidelines into effective action at the subnational level (e.g., province or region) is a prerequisite for ensuring an impact on nutrition. In several countries, including Vietnam, the focus of this paper, this process is affected by the quality of the decentralized process of planning and action. This study examined how provincial planning processes for nutrition occurred in Vietnam during 2009 and 2010. Key goals were to understand variability in processes across provinces, identify factors that influenced the process, and assess the usefulness of the process for individuals involved in planning and action. A qualitative case-study methodology was used. Data were drawn from interviews with 51 government officials in eight provinces. The study found little variability in the planning process among these eight provinces, probably due to a planning process that was predominantly a fiscal exercise within the confines of a largely centralized structure. Respondents were almost unanimous about the main barriers: a top-down approach to planning, limited human capacity for effective planning at subnational levels, and difficulty in integrating actions from multiple sectors. Provincial-level actors were deeply dissatisfied with the nature of their role in the process. Despite the rhetoric to the contrary, too much power is probably still retained at the central level. A strategic multiyear approach is needed to strengthen the provincial planning process and address many of the key barriers identified in this study.
Cheung, Vincent C K; Devarajan, Karthik; Severini, Giacomo; Turolla, Andrea; Bonato, Paolo
2015-08-01
The non-negative matrix factorization algorithm (NMF) decomposes a data matrix into a set of non-negative basis vectors, each scaled by a coefficient. In its original formulation, the NMF assumes the data samples and dimensions to be independently distributed, making it a less-than-ideal algorithm for the analysis of time series data with temporal correlations. Here, we seek to derive an NMF that accounts for temporal dependencies in the data by explicitly incorporating a very simple temporal constraint for the coefficients into the NMF update rules. We applied the modified algorithm to 2 multi-dimensional electromyographic data sets collected from the human upper-limb to identify muscle synergies. We found that because it reduced the number of free parameters in the model, our modified NMF made it possible to use the Akaike Information Criterion to objectively identify a model order (i.e., the number of muscle synergies composing the data) that is more functionally interpretable, and closer to the numbers previously determined using ad hoc measures.
Smith, Timothy D; Rossie, James B; Cooper, Gregory M; Carmody, Kelly A; Schmieg, Robin M; Bonar, Christopher J; Mooney, Mark P; Siegel, Michael I
2010-01-01
The air filled cavities of paranasal sinuses are thought by some to appear opportunistically in spatial "gaps" within the craniofacial complex. Anthropoid primates provide excellent natural experiments for testing this model, since not all species possess a full complement of paranasal sinuses. In this study, two genera of monkeys (Saguinus and Cebuella) which form maxillary sinuses (MS) as adults were compared to squirrel monkeys (Saimiri spp.), in which a MS does not form. Using microCT and histomorphometric methods, the spatial position of paranasal spaces was assessed and size of the adjacent dental sacs was measured. In Saguinus, secondary pneumatization is underway perinatally, and the sinus extends alongside deciduous premolars (dp). The MS overlaps all permanent molars in the adult. In Saimiri, the homologous space (maxillary recess) extends no farther posterior than the first deciduous premolar at birth and extends no farther than the last premolar in the adult. Differences in dental size and position may account for this finding. For example, Saimiri has significantly larger relative dp volumes, and enlarged orbits, which encroach on the internasal space to a greater degree when compared to Saguinus. These factors limit space for posterior expansion of the maxillary recess. These findings support the hypothesis that secondary pneumatization is a novel, opportunistic growth mechanism that removes "unneeded" bone. Moreover, paranasal spaces occur in association with semiautonomous skeletal elements that border more than one functional matrix, and the spatial dynamics of these units can act as a constraint on pneumatic expansion of paranasal spaces.
Kreutzwiser, Reid; de Loë, Rob; Imgrund, Krystian; Conboy, Mary Jane; Simpson, Hugh; Plummer, Ryan
2011-04-01
Regulatory frameworks to ensure municipal drinking water safety exist in most North American jurisdictions. However, similar protection is rarely provided to people reliant on water provided from private wells. In Canada, approximately 4 million people depend on privately owned, domestic wells for their drinking water. Numerous studies have shown that people who rely on private wells for their water supplies are at risk from nitrate and bacterial contamination. Given the fact that regulations relating to private wells tend to be weak or poorly enforced, actions taken by well owners to protect their own drinking water safety are extremely important. Drawing on one of the largest and most comprehensive surveys of private well owners ever conducted in Canada or elsewhere, this paper explores factors that influence well owner stewardship behaviour. Key behaviours examined included annual testing of well water and inspection of wells, measures to protect water quality, and proper decommissioning of unused wells. A geographically-stratified survey, sent to 4950 well owners in Ontario, Canada, resulted in an effective response rate of 34% (n = 1567). Logistic regression analyses revealed that motivations for well stewardship behaviours included reassurance, the perception of problems, and knowledge of the environment. Knowing how to perform stewardship behaviours was an important antecedent to action. Barriers to stewardship included complacency, inconvenience, ignorance, cost, and privacy concerns. To promote stewardship, local initiatives, better educational materials, and enforcement through real estate laws are all required. Ultimately, drinking water safety for people reliant on private wells is shown to be a responsibility shared by governments and private well owners. Copyright © 2010 Elsevier Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Bertone, Peter Felix
Achieving a sufficiently precise experimental determination of the astrophysical S-factor for the 14N(p, gamma) 15O reaction remains one of the most enduring and important problems in the field of experimental nuclear astrophysics. This reaction regulates the rate of energy generation during the main-sequence phase in stars with masses greater than approximately 1.5 M⊙ , for all stars at the termination of the main sequence, and for all stars during the red-giant phase. This fact has numerous ramifications in other aspects of stellar evolution including globular cluster age estimation, solar neutrino production, and carbon star evolution. The first attempt to directly measure the cross section for the 14N(p, gamma)15 O reaction took place in 1951. After more than five decades and several attempts, a sufficiently precise direct measurement of this reaction still eludes researchers. Given the vanishingly small cross section for this reaction at stellar energies and the inherent limitations of detection technology, there is some reason to suspect that the direct approach to measuring this reaction will likely not markedly improve the situation in the future, thereby necessitating the exploration of indirect approaches to constraining the best estimate of the 14N(p , gamma)15O astrophysical S-factor. These were the considerations that motivated this dissertation. Prior to this study, there were several unresolved questions concerning the nuclear structure of 15O which, if measured precisely enough, could substantially improve the best estimate of the S-factor for the 14N(p, gamma) 15O reaction. In particular, it was thought that the width of the Ex = 6793-keV sub-threshold level in 15O resulted in a large contribution from this state to the 14N(p, gamma) 15O S-factor at stellar energies, but this width had never been measured. Also, accepted best practice in the analysis of experimental S-factor data involves inclusion of elastic scattering data for higher lying
NASA Astrophysics Data System (ADS)
Travis, K.; Jacob, D. J.; Fisher, J. A.; Marais, E. A.; Kim, S.; Zhu, L.; Yu, K.; Yantosca, R.; Payer Sulprizio, M.; Paulot, F.; Mao, J.; Wennberg, P. O.; Crounse, J.; Ryerson, T. B.; Wisthaler, A.; Huey, L. G.; Thompson, A. M.
2014-12-01
The Southeast United States (SEUS) is unique in its atmospheric chemistry and the difficulty of models in reproducing observed ozone (O3) (Fiore et al, 2009). Unlike the Western U.S., O3 variability is more heavily influenced by anthropogenic impacts than background sources such as wildfires, foreign transport, and stratospheric intrusions (Zhang et al, 2011). In addition, the SEUS has biogenic VOC emissions, important O3 precursors, which are among the highest in the world. We use observations from the SEAC4RS campaign over the SEUS in summer 2013, interpreted with the global chemical transport model GEOS-Chem, to evaluate the factors controlling O3 in this region. We use the GEOS-Chem model version v9-02 with significant updates, including improved treatment of isoprene nitrates (Lee et al, 2014), revised yields of MVK and MACR (Liu et al, 2013), improved treatment of isoprene epoxides (Bates et al, 2014), and faster deposition of isoprene oxidation products. The model significantly over predicts the observed O3, particularly in isoprene-rich, low-NOx regions. Properly capturing the fate of the isoprene peroxy radical (RO2) is essential to modeling O3 during the campaign. The amount of NOx in the SEUS is mainly driven by anthropogenic emissions with a smaller contribution from lightning and soil NOx, in addition to the amount of NOx recycled by isoprene nitrates. The variability in the amount of HOx available in the model can be influenced by the recycling of OH assumed in the GEOS-Chem chemical mechanism. We use the ratio of measured isoprene hydroxyperoxide (ISOPOOH) to isoprene nitrates (ISOPN) to constrain the modeled branching between the RO2 + HO2 and RO2 + NO2 pathways. Based on this ratio, we find that the RO2 + HO2 pathway is underestimated in our current chemical mechanism. Moreover, our NOx emissions may be overestimated by comparison with satellite tropospheric NO2 columns. We increase the importance of the RO2 + HO2 pathway with the inclusion of HONO
NASA Astrophysics Data System (ADS)
Laborda López, Casto; López Sánchez-Vizcaíno, Vicente; Marchesi, Claudio; Gómez-Pugnaire, María Teresa; Garrido, Carlos J.; Jabaloy-Sánchez, Antonio; Padrón-Navarta, José Alberto
2017-04-01
Rodingites are Ca-, Al-enriched and Si-undersaturated rocks formed from mafic precursors enclosed in peridotites. Formation of both rodingites and serpentinites occurs simultaneously during serpentinization. Therefore, rodingites are common rocks associated with serpentinites in exhumed terrains, which experienced subduction and HP metamorphism. However, uncertainties remain about the factors that constrain the diverse mineral associations occurring in meta-rodingites as well as their response to devolatilization and redox reactions during subduction. In the Cerro del Almirez ultramafic massif (S-Spain) meta-rodingite bodies are enclosed both in Atg-serpentinite and Chl-harzburgite, which are separated by a transitional zone that represents the front of prograde serpentinite dehydration during subduction. Different types of meta-rodingites are found associated with these two ultramafic lithologies: Grandite-meta-rodingite (type 1) within Atg-serpentinite, Epidote-meta-rodingite (type 2) within both of them, especially in the vicinity of the dehydration front, and Pyralspite-meta-rodingite (type 3) within Chl-harzburgite. Type 1 consists of garnet, chlorite and clinopyroxene with minor titanite, magnetite and ilmenite. Several garnet generations are found within this meta-rodingite type: Grt1 (Ti-rich hydrogrossular, 78-90 wt% grossular), Grt2 (6-20 wt% pyralspite, 80-93 wt% grandite), and Grt3 (Ti-rich grandite, 38-40 wt% andradite). Type 2 meta-rodingite consists of epidote and clinopyroxene with minor titanite, garnet and chlorite. It appears partially transforming type 1 rocks within Atg-serpentinite and its amount increases gradually towards the dehydration front. Just across this front, in the Chl-harzburgite domain, all meta-rodingites are type 2. Type 3 meta-rodingite overgrew type 2 assemblages and consists of garnet (Grt4, 38-50 wt% almandine, 12-31% pyrope, 17-35% grossular), epidote, clinopyroxene, amphibole, chlorite, titanite and rutile. All meta
Kunz, Martin; Liddle, Andrew R.; Parkinson, David; Gao Changjun
2009-10-15
Cosmological observations are normally fit under the assumption that the dark sector can be decomposed into dark matter and dark energy components. However, as long as the probes remain purely gravitational, there is no unique decomposition and observations can only constrain a single dark fluid; this is known as the dark degeneracy. We use observations to directly constrain this dark fluid in a model-independent way, demonstrating, in particular, that the data cannot be fit by a dark fluid with a single constant equation of state. Parametrizing the dark fluid equation of state by a variety of polynomials in the scale factor a, we use current kinematical data to constrain the parameters. While the simplest interpretation of the dark fluid remains that it is comprised of separate dark matter and cosmological constant contributions, our results cover other model types including unified dark energy/matter scenarios.
Transcription of the histone H5 gene is regulated by three differentiation-specific enhancers.
Rousseau, S; Asselin, M; Renaud, J; Ruiz-Carrillo, A
1993-01-01
Histone H5, an early marker of the avian erythroid lineage, is expressed at low levels in early erythroid precursors and at higher levels in more mature cells. We show that the increase in H5 expression is due to transcriptional activation of the H5 gene following differentiation of precursor CFU(E). We have found and characterized two upstream enhancers, E1 (between -2233 and -1878 from the site of transcription initiation, +1) and E3 (between -1321 and -1163), and confirmed the presence of a downstream enhancer (C. D. Trainor, S. J. Stamler, and J. D. Engel, Nature [London] 328:827-830, 1987) E7 (between +846 and +1181) which are responsible for the increase in H5 gene transcription. The enhancers had a weak effect in nondifferentiated CFU(E) but a strong effect when the cells were induced to differentiate. Cooperation among the three enhancers, however, was not required for H5 gene activity in the differentiated cells. The enhancers contain binding sites for several ubiquitous and erythroid cell-specific nuclear proteins, including GATA-1, as demonstrated with GATA-1-specific antibodies. Although the GATA sites were required for enhancer function, the concentration of GATA-1, GATA-2, and GATA-3 decreased during cell differentiation, and overexpression of these factors had little effect on H5 transcription. Hence, the differentiation-specific effect of the enhancers is not mediated by changes in relative levels of the GATA factors. Functional analysis of the H5 promoter indicated that the requirement of several elements, including a GC box necessary for transcription enhancement, did not change during the early stages of CFU(E) differentiation. However, the UPE, a positive element in proliferating CFU(E) recognized by the transcription factor H4TF2, was dispensable in the differentiated cells. These results suggest that as the cells enter the final stages of differentiation, there is a reprogramming of the regulatory factors that control H5 transcription and that
ERIC Educational Resources Information Center
Temple, Viviene A.; Walkley, Jeff W.
2007-01-01
Background: Physical activity influences health in individuals and within populations. This study explored factors perceived as enabling or inhibiting participation in physical activity by adults with intellectual disability from a health promotion perspective. Method: Six focus group interviews were conducted: adults with intellectual disability…
NASA Astrophysics Data System (ADS)
Masalmah, Yahya M.; Veléz-Reyes, Miguel
2008-04-01
This paper presents a full algorithm to compute the solution for the unsupervised unmixing problem based on the positive matrix factorization. The algorithm estimates the number of endmembers as the rank of the matrix. The algorithm has an initialization stage using the SVD subset selection algorithm. Testing and validation with real and simulated data show the effectiveness of the method. Application of the approach to environmental remote sensing is shown.
Espin, S; Lingard, L; Baker, G R; Regehr, G
2006-06-01
This paper explores the factors that influence the persistence of unsafe practice in an interprofessional team setting in health care, towards the development of a descriptive theoretical model for analyzing problematic practice routines. Using data collected during a mixed method interview study of 28 members of an operating room team, participants' approaches to unsafe practice were analyzed using the following three theoretical models from organizational and cognitive psychology: Reason's theory of "vulnerable system syndrome", Tucker and Edmondson's concept of first and second order problem solving, and Amalberti's model of practice migration. These three theoretical approaches provide a critical insight into key trends in the interview data, including team members' definition of error as the breaching of standards of practice, nurses' sense of scope of practice as a constraint on their reporting behaviours, and participants' reports of the forces influencing tacit agreements to work around safety regulations. However, the relational factors underlying unsafe practice routines are poorly accounted for in these theoretical approaches. Incorporating an additional theoretical construct such as "relational coordination" to account for the emotional human features of team practice would provide a more comprehensive theoretical approach for use in exploring unsafe practice routines and the forces that sustain them in healthcare team settings.
NASA Astrophysics Data System (ADS)
Lu, H.; Hu, G.; Vanderveen, J.; Liu, C.; Ratcliffe, C.; Ripmeester, J.
2011-12-01
CO2 replacement of CH4 from methane hydrate has been proposed as a method to produce gas from natural gas hydrate by taking advantage of both the production of natural gas and the sequestration of CO2. To examine the validity of this method DOE/Conoco-Philips is considering having a field test in Alaska. The reaction of CO2 replacing CH4 from methane hydrate has been confirmed to be thermodynamically feasible, but concern is always raised about the reaction kinetics. Some kinetic studies in the system of methane hydrate and liquid or gaseous CO2 have found that the reaction proceeds at a very low rate. Natural gas hydrate occurs in sediments with multi-components and complex structure, so matters will be even more complicated. Up to now, few investigations have been carried out concerning the factors affecting the reaction process of CO2 replacing CH4 from methane hydrate. Experiments were implemented with sands, which were recovered from Mallik 5L-38 well, Mackenzie Delta, Northwest Territory, Canada, sediment that previously contained hydrate although it had been dried completely before our experiments. The water-saturated sands were tightly charged into a plastic bottle (90 mm deep and 60 mm wide), and then this test specimen was sealed in a pressure cell. After methane hydrate was synthesized in the test specimen for 108 days under a pressure of 11 to 8 MPa and a temperature of 3 degrees Celsius, liquid CO2 was introduced into the pressure cell. The conditions under which CO2 was reacted with methane hydrate were ~5.3 MPa and 5 degrees Celsius. After reacting for 15 days, the test specimen was recovered. The test specimen was cut into ~10 mm thick discs, and sub-samples were further taken from each of the discs. In addition to the determination of hydrate saturation and the gas composition, Raman spectroscopic studies were carried out for the sub-samples obtained. The results revealed: 1) less CO2 replacement in the bottom disc of the test specimen as compared
Dorman, Michael F.; Cook, Sarah; Spahr, Tony; Zhang, Ting; Loiselle, Louise; Schramm, David; Whittingham, JoAnne; Gifford, Rene
2014-01-01
Many studies have documented the benefits to speech understanding when cochlear implant (CI) patients can access low-frequency acoustic information from the ear opposite the implant. In this study we assessed the role of three factors in determining the magnitude of bimodal benefit -- (i) the level of CI-only performance, (ii) the magnitude of the hearing loss in the ear with low-frequency acoustic hearing and (iii) the type of test material. The patients had low-frequency PTAs (average of 125, 250 and 500 Hz) varying over a large range (<30 dB HL to >70 dB HL) in the ear contralateral to the implant. The patients were tested with (i) CNC words presented in quiet (n=105) (ii) AzBio sentences presented in quiet (n=102), (iii) AzBio sentences in noise at +10 dB signal-to-noise ratio (SNR) (n=69), and (iv) AzBio sentences at +5 dB SNR (n=64). We find maximum bimodal benefit when (i) CI scores are less than 60 percent correct, (ii) hearing loss is less than 60 dB HL in low-frequencies and (iii) the test material is sentences presented against a noise background. When these criteria are met, some bimodal patients can gain 40-60 percentage points in performance relative to performance with a CI. PMID:25285624
Ugare, G U; Bassey, I E; Udosen, J E; Ndifon, W; Ndoma-Egba, R; Asuquo, M; Undie, G
2014-01-01
The objective of the following study is to analyze the trauma type (causes), injury pattern and factors that may have contributed to death within 72 h of admission into our emergency department (E.D). An 18 month prospective observational study, done from April 2009 to September 2010. All the patients were that admitted for 72 h following a full assessment by the attending clinician were enlisted for the study. The demographic data of each patient, time of arrival at the E.D, type of injury sustained, time of incident, previous care at any peripheral hospital, clinical state of the patient, Glasgow coma scale (GCS), Injury severity score (ISS) and treatment offered before death were entered into a Proforma. This was done using EPI-Info statistical programme version 3.4.3 of 2007(by CDC Atlanta Georgia , USA). A total of 4011 patients were seen in the E.D during the period. 1943 (48.4%), were trauma emergencies, with a (147; 41.4%) mortality. Their ages ranged from 4 to 87 years, with an average of 34.5 years. The male:female ratio was 7:1. The assessed GCS ranged from 6 to 15, with an average of 9.1, the ISS ranged from 9 to 75 with an average of 31.3. Road traffic accidents (RTAs) accounted for 118 (80.3%) of the deaths, assaults 14.3%, falls from height 4.0% and gunshot injuries 1.4%. The overall mortality was 17.1%. The major source of trauma death was RTA; The most frequently injured part of the body was head, with death resulting clinically hemorrhage. The 17.1% mortality is multifactorial: The late presentation (in some cases occasioned by interference by persons not knowledgeable in the basics of trauma care) lack of trained personnel and the systemic deficiencies.
NASA Astrophysics Data System (ADS)
Mozaffar, A.; Schoon, N.; Digrado, A.; Bachy, A.; Delaplace, P.; du Jardin, P.; Fauconnier, M.-L.; Aubinet, M.; Heinesch, B.; Amelynck, C.
2017-03-01
Because of its high abundance and long lifetime compared to other volatile organic compounds in the atmosphere, methanol (CH3OH) plays an important role in atmospheric chemistry. Even though agricultural crops are believed to be a large source of methanol, emission inventories from those crop ecosystems are still scarce and little information is available concerning the driving mechanisms for methanol production and emission at different developmental stages of the plants/leaves. This study focuses on methanol emissions from Zea mays L. (maize), which is vastly cultivated throughout the world. Flux measurements have been performed on young plants, almost fully grown leaves and fully grown leaves, enclosed in dynamic flow-through enclosures in a temperature and light-controlled environmental chamber. Strong differences in the response of methanol emissions to variations in PPFD (Photosynthetic Photon Flux Density) were noticed between the young plants, almost fully grown and fully grown leaves. Moreover, young maize plants showed strong emission peaks following light/dark transitions, for which guttation can be put forward as a hypothetical pathway. Young plants' average daily methanol fluxes exceeded by a factor of 17 those of almost fully grown and fully grown leaves when expressed per leaf area. Absolute flux values were found to be smaller than those reported in the literature, but in fair agreement with recent ecosystem scale flux measurements above a maize field of the same variety as used in this study. The flux measurements in the current study were used to evaluate the dynamic biogenic volatile organic compound (BVOC) emission model of Niinemets and Reichstein. The modelled and measured fluxes from almost fully grown leaves were found to agree best when a temperature and light dependent methanol production function was applied. However, this production function turned out not to be suitable for modelling the observed emissions from the young plants
Koerber, S C; Gulyas, J; Lahrichi, S L; Corrigan, A; Craig, A G; Rivier, C; Vale, W; Rivier, J
1998-12-03
We hypothesized that covalent constraints such as side-chain to side-chain lactam rings would stabilize an alpha-helical conformation shown to be important for the recognition and binding of the human corticotropin-releasing factor (hCRF) C-terminal 33 residues to CRF receptors. These studies led to the discovery of cyclo(20-23)[DPhe12,Glu20,Lys23,Nle21,38]hCRF (12-41) and of astressin ¿cyclo(30-33)[DPhe12,Nle21,38,Glu30,Lys33]hCR F(12-41)¿, two potent CRF antagonists, and of cyclo(30-33)[Ac-Leu8,DPhe12,Nle21, Glu30,Lys33,Nle38]hCRF(8-41), the shortest sequence equipotent to CRF reported to date (Rivier et al. J. Med. Chem. 1998, 41, 2614-2620 and references therein). To test the hypothesis that the Glu20-Lys23 and Glu30-Lys33 lactam rings were favoring an alpha-helical conformation rather than a turn, we introduced a D-amino acid at positions 22, 31, and 32 in the respective rings. Whereas the introduction of a D-residue at position 31 was only marginally deleterious to potency (ca. 2-fold decrease in potency), introduction of a D-residue at position 22 and/or 32 was favorable (up to 2-fold increase in potency) in most of the cyclic hCRF, alpha-helical CRF, urotensin, and urocortin agonists and antagonists that were tested and was also favorable in linear agonists but not in linear antagonists; this suggested a unique and stabilizing role for the lactam ring. Introduction of a [DHis32] (6) or acetylation of the N-terminus (7) of astressin had a minor deleterious or a favorable influence, respectively, on duration of action. In the absence of structural data on these analogues, we conducted molecular modeling on an Ac-Ala13-NH2 scaffold in order to quantify the structural influence of specific L- and DAla6 and L- and DAla7 substitutions in [Glu5,Lys8]Ac-Ala13-NH2 in a standard alpha-helical configuration. Models of the general form [Glu5,LAla6 or DAla6,LAla7 or DAla7,Lys8]Ac-Ala13-NH2 were subjected to high-temperature molecular dynamics followed by annealing
NASA Astrophysics Data System (ADS)
Sofowote, Uwayemi M.; Su, Yushan; Dabek-Zlotorzynska, Ewa; Rastogi, Ankit K.; Brook, Jeff; Hopke, Philip K.
2015-05-01
The Canadian National Air Pollution Surveillance (NAPS) network operates five fine particulate matter (PM2.5) speciation sites in Ontario. Data from 2005 to 2010 from these sites were subjected to constrained positive matrix factorization (PMF) to obtain factors of particulate matter pollution. Eight factors were found to be common across the sites. These constrained factors were particulate sulfate and nitrate, aged combustion aerosols, biomass/wood combustion, non-ferrous metal smelting, crustal matter, steel works, and road salt. Other factors found at these sites were largely related to local sources in their respective neighbourhoods. Diagnostic results from constraining the PMF factors could be used to select the appropriate post-PMF analyses as they reveal the factors that were expected to have regional or local sources. Interpretation of the spatial trends of factors was guided by the extent of similarity of target ratios across the five sites as determined by their coefficient of variation (C.V.). On average, particulate sulfate had PM2.5 mass contributions that ranged from 7% (Wallaceburg) to 36% (Simcoe) and nitrate species ranged from 7% (Simcoe) to 23% (Windsor). A clear low rural - high urban divide for particulate nitrate was also observed. These non-uniform impacts across the sites indicate that a single representative location is not suitable for studying PM2.5 in Ontario. Temporal variations showed greater abundance of particulate sulfate in the summer and particulate nitrate in the winter respectively. Yearly median values of the sulfate factor that is largely energy-related have been declining for most sites since peaking in 2007. A trajectory ensemble model, simplified quantitative transport bias analysis (sQTBA) was used to identify potential source regions of the constrained sulfate and nitrate factors while radial plots of the conditional probability function (CPF) were used to explore the more locally-sourced factors. The US Midwest, east
Raguideau, Sébastien; Plancade, Sandra; Pons, Nicolas; Leclerc, Marion
2016-01-01
Whole Genome Shotgun (WGS) metagenomics is increasingly used to study the structure and functions of complex microbial ecosystems, both from the taxonomic and functional point of view. Gene inventories of otherwise uncultured microbial communities make the direct functional profiling of microbial communities possible. The concept of community aggregated trait has been adapted from environmental and plant functional ecology to the framework of microbial ecology. Community aggregated traits are quantified from WGS data by computing the abundance of relevant marker genes. They can be used to study key processes at the ecosystem level and correlate environmental factors and ecosystem functions. In this paper we propose a novel model based approach to infer combinations of aggregated traits characterizing specific ecosystemic metabolic processes. We formulate a model of these Combined Aggregated Functional Traits (CAFTs) accounting for a hierarchical structure of genes, which are associated on microbial genomes, further linked at the ecosystem level by complex co-occurrences or interactions. The model is completed with constraints specifically designed to exploit available genomic information, in order to favor biologically relevant CAFTs. The CAFTs structure, as well as their intensity in the ecosystem, is obtained by solving a constrained Non-negative Matrix Factorization (NMF) problem. We developed a multicriteria selection procedure for the number of CAFTs. We illustrated our method on the modelling of ecosystemic functional traits of fiber degradation by the human gut microbiota. We used 1408 samples of gene abundances from several high-throughput sequencing projects and found that four CAFTs only were needed to represent the fiber degradation potential. This data reduction highlighted biologically consistent functional patterns while providing a high quality preservation of the original data. Our method is generic and can be applied to other metabolic processes in
Aslam, M; Perkins, S J
2001-06-22
Factor H (FH) is a regulatory cofactor for the protease factor I in the breakdown of C3b in the complement system of immune defence, and binds to heparin and other polyanionic substrates. FH is composed of 20 short consensus/complement repeat (SCR) domains, for which the overall arrangement in solution is unknown. As previous studies had shown that FH can form monomeric or dimeric structures, X-ray and neutron scattering was accordingly performed with FH in the concentration range between 0.7 and 14 mg ml(-1). The radius of gyration of FH was determined to be 11.1-11.3 nm by both methods, and the radii of gyration of the cross-section were 4.4 nm and 1.7 nm. The distance distribution function P(r) showed that the overall length of FH was 38 nm. The neutron data showed that FH was monomeric with a molecular mass of 165,000(+/-17,000) Da. Analytical ultracentrifugation data confirmed this, where sedimentation equilibrium curve fits gave a mean molecular mass of 155,000(+/-3,000) Da. Sedimentation velocity experiments using the g*(s) derivative method showed that FH was monodisperse and had a sedimentation coefficient of 5.3(+/-0.1) S. In order to construct a full model of FH for scattering curve and sedimentation coefficient fits, homology models were constructed for 17 of the 20 SCR domains using knowledge of the NMR structures for FH SCR-5, SCR-15 and SCR-16, and vaccinia coat protein SCR-3 and SCR-4. Molecular dynamics simulations were used to generate a large conformational library for each of the 19 SCR-SCR linker peptides. Peptides from these libraries were combined with the 20 SCR structures in order to generate stereochemically complete models for the FH structure. Using an automated constrained fit procedure, the analysis of 16,752 possible FH models showed that only those models in which the 20 SCR domains were bent back upon themselves were able to account for the scattering and sedimentation data. The best-fit models showed that FH had an overall length
Constraining Galileon inflation
Regan, Donough; Anderson, Gemma J.; Hull, Matthew; Seery, David E-mail: G.Anderson@sussex.ac.uk E-mail: D.Seery@sussex.ac.uk
2015-02-01
In this short paper, we present constraints on the Galileon inflationary model from the CMB bispectrum. We employ a principal-component analysis of the independent degrees of freedom constrained by data and apply this to the WMAP 9-year data to constrain the free parameters of the model. A simple Bayesian comparison establishes that support for the Galileon model from bispectrum data is at best weak.
Choosing health, constrained choices.
Chee Khoon Chan
2009-12-01
In parallel with the neo-liberal retrenchment of the welfarist state, an increasing emphasis on the responsibility of individuals in managing their own affairs and their well-being has been evident. In the health arena for instance, this was a major theme permeating the UK government's White Paper Choosing Health: Making Healthy Choices Easier (2004), which appealed to an ethos of autonomy and self-actualization through activity and consumption which merited esteem. As a counterpoint to this growing trend of informed responsibilization, constrained choices (constrained agency) provides a useful framework for a judicious balance and sense of proportion between an individual behavioural focus and a focus on societal, systemic, and structural determinants of health and well-being. Constrained choices is also a conceptual bridge between responsibilization and population health which could be further developed within an integrative biosocial perspective one might refer to as the social ecology of health and disease.
Constrained Stochastic Extended Redundancy Analysis.
DeSarbo, Wayne S; Hwang, Heungsun; Stadler Blank, Ashley; Kappe, Eelco
2015-06-01
We devise a new statistical methodology called constrained stochastic extended redundancy analysis (CSERA) to examine the comparative impact of various conceptual factors, or drivers, as well as the specific predictor variables that contribute to each driver on designated dependent variable(s). The technical details of the proposed methodology, the maximum likelihood estimation algorithm, and model selection heuristics are discussed. A sports marketing consumer psychology application is provided in a Major League Baseball (MLB) context where the effects of six conceptual drivers of game attendance and their defining predictor variables are estimated. Results compare favorably to those obtained using traditional extended redundancy analysis (ERA).
Neave, Matthew J; Rachmawati, Rita; Xun, Liping; Michell, Craig T; Bourne, David G; Apprill, Amy; Voolstra, Christian R
2017-01-01
Reef-building corals are well regarded not only for their obligate association with endosymbiotic algae, but also with prokaryotic symbionts, the specificity of which remains elusive. To identify the central microbial symbionts of corals, their specificity across species and conservation over geographic regions, we sequenced partial SSU ribosomal RNA genes of Bacteria and Archaea from the common corals Stylophora pistillata and Pocillopora verrucosa across 28 reefs within seven major geographical regions. We demonstrate that both corals harbor Endozoicomonas bacteria as their prevalent symbiont. Importantly, catalyzed reporter deposition–fluorescence in situ hybridization (CARD–FISH) with Endozoicomonas-specific probes confirmed their residence as large aggregations deep within coral tissues. Using fine-scale genotyping techniques and single-cell genomics, we demonstrate that P. verrucosa harbors the same Endozoicomonas, whereas S. pistillata associates with geographically distinct genotypes. This specificity may be shaped by the different reproductive strategies of the hosts, potentially uncovering a pattern of symbiont selection that is linked to life history. Spawning corals such as P. verrucosa acquire prokaryotes from the environment. In contrast, brooding corals such as S. pistillata release symbiont-packed planula larvae, which may explain a strong regional signature in their microbiome. Our work contributes to the factors underlying microbiome specificity and adds detail to coral holobiont functioning. PMID:27392086
Constrained control allocation
NASA Technical Reports Server (NTRS)
Durham, Wayne C.
1992-01-01
This paper addresses the problem of the allocation of several flight controls to the generation of specified body-axis moments. The number of controls is greater than the number of moments being controlled, and the ranges of the controls are constrained to certain limits. The controls are assumed to be individually linear in their effect throughout their ranges of motion, and independent of one another in their effects. The geometries of the subset of the constrained controls and of its image in moment space are examined. A direct method of allocating these several controls is presented, that guarantees the maximum possible moment is generated within the constraints of the controls. The results are illustrated by an example problem involving three controls and two moments.
Constrained noninformative priors
Atwood, C.L.
1994-10-01
The Jeffreys noninformative prior distribution for a single unknown parameter is the distribution corresponding to a uniform distribution in the transformed model where the unknown parameter is approximately a location parameter. To obtain a prior distribution with a specified mean but with diffusion reflecting great uncertainty, a natural generalization of the noninformative prior is the distribution corresponding to the constrained maximum entropy distribution in the transformed model. Examples are given.
NASA Astrophysics Data System (ADS)
Sofowote, Uwayemi M.; Su, Yushan; Dabek-Zlotorzynska, Ewa; Rastogi, Ankit K.; Brook, Jeff; Hopke, Philip K.
2015-05-01
Rotational ambiguity in factor analyses leads to solutions that are not always consistent with reality. The inherent non-negativity constraints in positive matrix factorization (PMF) help to prevent factor solutions from becoming overly unrealistic, but they are not sufficient to prevent unwanted rotations that could manifest in factors that should have similar compositions varying across multiple sites. The Canadian National Air Pollution Surveillance (NAPS) network operates five fine particulate matter (PM2.5) speciation sites in Ontario. Data from these sites from 2005 to 2010 were subjected to PMF to obtain factors representing sources of particulate matter. Eight factors were found to be common across these sites. These factors had profiles that varied greatly from one site to the other, suggesting that the PMF solutions were impacted by some rotational ambiguity. New features in the EPA PMF V5 program allow the use of a priori information to impose mathematical constraints that guide the evolution of the factor solutions. These constraints reduce the rotational space. In situations where major emissions sources are known and located in the neighborhood of receptors, or emissions inventories and literature source profiles exist, it is easy to use these profiles to force the factor solutions to conform to the expected signatures. In our case, reported source profiles were neither available nor applicable due to the large spatial span of potential sources and receptor sites. This work describes how such constraints can be generated and used in these complex situations. The fundamental principle explored in this work is the concept of 'stiffness' of PMF solutions to identify the desirable non-rotating factors.
McCaughan, K K; Poole, E S; Pel, H J; Mansell, J B; Mannering, S A; Tate, W P
1998-07-01
There have been contrasting reports of whether the positioning of a translational stop signal immediately after a start codon in a single oligonucleotide can act as a model template to support efficient in vitro termination. This paradox stimulated this study of what determines the constraints on the positioning of the components in the termination complex. The mini mRNA, AUGUGAA, was unable to support efficient in vitro termination in contrast to separate AUG/UGA(A) codons, unless the ribosomal interaction of the stop signal with the decoding factor, release factor 2, was stimulated with ethanol or with nucleotide-free release factor 3, or by using (L11-)-ribosomes which have a higher affinity for release factor 2, or unless the fMet-tRNA was first bound to 30S subunits independently of the mini mRNA. An additional triplet stop codon could restore activity of the mini mRNA, indicating that its recognition was not sterically restrained by the stop signal already within it. This suggests that in an initiation complex an adjoining start/stop signal is not positioned to support efficient decoding by release factor unless it is separated from the start codon. Site-directed crosslinking from mRNAs to components of the termination complex has shown that mRNA elements like the Shine-Dalgarno sequence and the codon preceding the stop signal can affect the crosslinking to release factor, and presumably the orientation of the signal to the factor.
Bayesian evaluation of inequality constrained hypotheses.
Gu, Xin; Mulder, Joris; Deković, Maja; Hoijtink, Herbert
2014-12-01
Bayesian evaluation of inequality constrained hypotheses enables researchers to investigate their expectations with respect to the structure among model parameters. This article proposes an approximate Bayes procedure that can be used for the selection of the best of a set of inequality constrained hypotheses based on the Bayes factor in a very general class of statistical models. The software package BIG is provided such that psychologists can use the approach proposed for the analysis of their own data. To illustrate the approximate Bayes procedure and the use of BIG, we evaluate inequality constrained hypotheses in a path model and a logistic regression model. Two simulation studies on the performance of our approximate Bayes procedure show that it results in accurate Bayes factors. PsycINFO Database Record (c) 2014 APA, all rights reserved
Liang, Yun-Feng; Zhou, Bei; He, Hao-Ning; Fan, Yi-Zhong; Wei, Da-Ming; Tam, Pak-Hin Thomas
2014-02-01
GRB 130821A was detected by Fermi-GBM/LAT, Konus-WIND, SPI-ACS/INTEGRAL, RHESSI and Mars Odyssey-HEND. Although the data of GRB 130821A are very limited, we show in this work that the high energy γ-ray emission (i.e., above 100 MeV) alone imposes tight constraint on the density profile of the circum-burst medium as well as the initial Lorentz factor of the outflow. The temporal behavior of the high energy γ-ray emission is consistent with the forward shock synchrotron radiation model, and the circum-burst medium likely has a constant-density profile. The Lorentz factor is about a few hundred, similar to other bright GRBs.
Constrained space camera assembly
Heckendorn, Frank M.; Anderson, Erin K.; Robinson, Casandra W.; Haynes, Harriet B.
1999-01-01
A constrained space camera assembly which is intended to be lowered through a hole into a tank, a borehole or another cavity. The assembly includes a generally cylindrical chamber comprising a head and a body and a wiring-carrying conduit extending from the chamber. Means are included in the chamber for rotating the body about the head without breaking an airtight seal formed therebetween. The assembly may be pressurized and accompanied with a pressure sensing means for sensing if a breach has occurred in the assembly. In one embodiment, two cameras, separated from their respective lenses, are installed on a mounting apparatus disposed in the chamber. The mounting apparatus includes means allowing both longitudinal and lateral movement of the cameras. Moving the cameras longitudinally focuses the cameras, and moving the cameras laterally away from one another effectively converges the cameras so that close objects can be viewed. The assembly further includes means for moving lenses of different magnification forward of the cameras.
Vassar, R.; Rosenberg, M.; Tyner, A.; Fuchs, E. ); Ross, S. )
1989-03-01
A construct containing {approx}2,500 base pairs (bp) of 5{prime} upstream and {approx}700 bp of 3{prime} downstream sequence was used to drive the expression of an intronless human K14 gene in vitro and in vivo. To track the expression of the gene, a small sequence encoding the antigenic portion of neuropeptide substance P was inserted in frame 5{prime} to the TGA translation stop codon of the gene. Surprisingly, this gene was expressed promiscuously in a wide variety of cultured cells transiently transfected with the construct. In contrast, when introduced into the germ line of transgenic mice, the construct was expressed in a fashion analogous to the endogenous K14 gene--namely, in the basal layer of stratified squamous epithelia. The results suggest that some regulatory mechanism is overridden as a consequence of transient transfection but that sequences that can control proper K14 expression are present in the construct. The appropriate tissue-specific and differentiation-specific expression of K14{center dot}P in transgenic mice is an important first step in characterizing a promoter that could be employed to drive the foreign expression of drug-related genes in the epidermis of skin grafts.
Constraining the Littlest Higgs
Petriello, Frank J
2002-11-18
Little Higgs models offer a new way to address the hierarchy problem, and give rise to a weakly-coupled Higgs sector. These theories predict the existence of new states which are necessary to cancel the quadratic divergences of the Standard Model. The simplest version of these models, the Littlest Higgs, is based on an SU(5)/SO(5) non-linear sigma model and predicts that four new gauge bosons, a weak isosinglet quark, t{prime}, with Q=2/3, as well as an isotriplet scalar field exist at the TeV scale. We consider the contributions of these new states to precision electroweak observables, and examine their production at the Tevatron. We thoroughly explore the parameter space of this model and find that small regions are allowed by the precision data where the model parameters take on their natural values. These regions are, however, excluded by the Tevatron data. Combined, the direct and indirect effects of these new states constrain the ''decay constant'' f {approx}> 3.5 TeV and m{sub t{prime}} {approx}> 10 TeV. These bounds imply that significant fine-tuning be present in order for this model to resolve the hierarchy problem.
NASA Astrophysics Data System (ADS)
Verde, Licia; Bellini, Emilio; Pigozzo, Cassio; Heavens, Alan F.; Jimenez, Raul
2017-04-01
We investigate our knowledge of early universe cosmology by exploring how much additional energy density can be placed in different components beyond those in the ΛCDM model. To do this we use a method to separate early- and late-universe information enclosed in observational data, thus markedly reducing the model-dependency of the conclusions. We find that the 95% credibility regions for extra energy components of the early universe at recombination are: non-accelerating additional fluid density parameter ΩMR < 0.006 and extra radiation parameterised as extra effective neutrino species 2.3 < Neff < 3.2 when imposing flatness. Our constraints thus show that even when analyzing the data in this largely model-independent way, the possibility of hiding extra energy components beyond ΛCDM in the early universe is seriously constrained by current observations. We also find that the standard ruler, the sound horizon at radiation drag, can be well determined in a way that does not depend on late-time Universe assumptions, but depends strongly on early-time physics and in particular on additional components that behave like radiation. We find that the standard ruler length determined in this way is rs = 147.4 ± 0.7 Mpc if the radiation and neutrino components are standard, but the uncertainty increases by an order of magnitude when non-standard dark radiation components are allowed, to rs = 150 ± 5 Mpc.
Constrained space camera assembly
Heckendorn, F.M.; Anderson, E.K.; Robinson, C.W.; Haynes, H.B.
1999-05-11
A constrained space camera assembly which is intended to be lowered through a hole into a tank, a borehole or another cavity is disclosed. The assembly includes a generally cylindrical chamber comprising a head and a body and a wiring-carrying conduit extending from the chamber. Means are included in the chamber for rotating the body about the head without breaking an airtight seal formed therebetween. The assembly may be pressurized and accompanied with a pressure sensing means for sensing if a breach has occurred in the assembly. In one embodiment, two cameras, separated from their respective lenses, are installed on a mounting apparatus disposed in the chamber. The mounting apparatus includes means allowing both longitudinal and lateral movement of the cameras. Moving the cameras longitudinally focuses the cameras, and moving the cameras laterally away from one another effectively converges the cameras so that close objects can be viewed. The assembly further includes means for moving lenses of different magnification forward of the cameras. 17 figs.
Power-constrained supercomputing
NASA Astrophysics Data System (ADS)
Bailey, Peter E.
As we approach exascale systems, power is turning from an optimization goal to a critical operating constraint. With power bounds imposed by both stakeholders and the limitations of existing infrastructure, achieving practical exascale computing will therefore rely on optimizing performance subject to a power constraint. However, this requirement should not add to the burden of application developers; optimizing the runtime environment given restricted power will primarily be the job of high-performance system software. In this dissertation, we explore this area and develop new techniques that extract maximum performance subject to a particular power constraint. These techniques include a method to find theoretical optimal performance, a runtime system that shifts power in real time to improve performance, and a node-level prediction model for selecting power-efficient operating points. We use a linear programming (LP) formulation to optimize application schedules under various power constraints, where a schedule consists of a DVFS state and number of OpenMP threads for each section of computation between consecutive message passing events. We also provide a more flexible mixed integer-linear (ILP) formulation and show that the resulting schedules closely match schedules from the LP formulation. Across four applications, we use our LP-derived upper bounds to show that current approaches trail optimal, power-constrained performance by up to 41%. This demonstrates limitations of current systems, and our LP formulation provides future optimization approaches with a quantitative optimization target. We also introduce Conductor, a run-time system that intelligently distributes available power to nodes and cores to improve performance. The key techniques used are configuration space exploration and adaptive power balancing. Configuration exploration dynamically selects the optimal thread concurrency level and DVFS state subject to a hardware-enforced power bound
NASA Astrophysics Data System (ADS)
Abrahamse, Augusta
2010-12-01
Future advances in cosmology will depend on the next generation of cosmological observations and how they shape our theoretical understanding of the universe. Current theoretical ideas, however, have an important role to play in guiding the design of such observational programs. The work presented in this thesis concerns the intersection of observation and theory, particularly as it relates to advancing our understanding of the accelerated expansion of the universe (or the dark energy). Chapters 2 - 4 make use of the simulated data sets developed by the Dark Energy Task Force (DETF) for a number of cosmological observations currently in the experimental pipeline. We use these forecast data in the analysis of four quintessence models of dark energy: the PNGB, Exponential, Albrecht-Skordis and Inverse Power Law (IPL) models. Using Markov Chain Monte Carlo sampling techniques we examine the ability of each simulated data set to constrain the parameter space of these models. We examine the potential of the data for differentiating time-varying models from a pure cosmological constant. Additionally, we introduce an abstract parameter space to facilitate comparison between models and investigate the ability of future data to distinguish between these quintessence models. In Chapter 5 we present work towards understanding the effects of systematic errors associated with photometric redshift estimates. Due to the need to sample a vast number of deep and faint galaxies, photometric redshifts will be used in a wide range of future cosmological observations including gravitational weak lensing, baryon accoustic oscillations and type 1A supernovae observations. The uncertainty in the redshift distributions of galaxies has a significant potential impact on the cosmological parameter values inferred from such observations. We introduce a method for parameterizing uncertainties in modeling assumptions affecting photometric redshift calculations and for propagating these
Optimal constrained layer damping with partial coverage
NASA Astrophysics Data System (ADS)
Marcelin, J.-L.; Trompette, Ph.; Smati, A.
1992-12-01
This paper deals with the optimal damping of beams constrained by viscoelastic layers when only one or several portions of the beam are covered. An efficient finite element model for dynamic analysis of such beams is used. The design variables are the dimensions and prescribed locations of the viscoelastic layers and the objective is the maximum viscoelastic damping factor. The method for nonlinear programming in structural optimization is the so-called method of moving asymptotes.
Line constrained between two curves
NASA Astrophysics Data System (ADS)
Ahmad, Afida; Ali, Jamaludin Md.
2013-04-01
In this paper, the method of finding the line constrained between two quadratic Bezier curves and also finding the line constrained between a quadratic Bezier curve and a circle is presented. The application of the line constrained can be used in the construction of railway tracks between any obstacle or rolling a ball to the other side of a wall in a way that it just touches the wall. The method used is by using equal root properties of a quadratic equation in order to find one point where the line touches the curve. The work examples involved different curve orientations and different circle positions. Mathematica software is used to compute the solutions for the line constrained and present the solutions graphically. By using the method proposed, the number of intersection points obtained is used to determine the number of lines constrained between two curves and between a curve and a circle. The conclusion on whether all lines are acceptable to be considered as the line constrained are depending on the application of the line.
McGehee, R E; Habener, J F
1995-04-01
The differentiation-specific element (DSE) is a cis-acting transcriptional element located at nucleotide--1000 in the 5'-flanking promoter of the angiotensinogen gene. It is required for the irreversible and sustained increase in transcription of the angiotensinogen gene that occurs during differentiation of 3T3-L1 adipoblasts into adipocytes induced by a 3-day hormonal pulse. We report here the cloning of 3T3-L1 adipocyte cDNA encoding a 150 kilodalton protein designated Differentiation Specific Element Binding Protein (DSEB) that exhibits sequence-specific binding to a DSE oligonucleotide. Two DSEB mRNAs (3.6 and 4.2 kilobases) are observed in adipose, brain, kidney, testis, liver, and lung. Both DSEB mRNA and protein are induced during, and remain elevated after, 3T3-L1 cell adipogenesis. Analysis of adipoblasts by immunocytochemistry with an antiserum directed to bacterial expressed DSEB reveals that DSEB is localized to the nucleus and is induced during differentiation. DNA-binding assays show that binding is specific and exhibits high affinity and specificity for the DSE. Deletional analyses of bacterial expressed recombinant DSEB identifies a DNA-binding domain of 120 amino acids that contains two predicted helical regions. A sequence of 72 amino acids within the DNA-binding domain of DSEB is 60% identical to domains found in the sequences of several bacterial ligases. Further, DSEB is homologous to several proteins reported recently that are proposed to be a component(s) of the DNA replication-C complex raising the possibility that DSEB may be both a transcription factor and a DNA-replication factor.
CONSTRAINING SOURCE REDSHIFT DISTRIBUTIONS WITH GRAVITATIONAL LENSING
Wittman, D.; Dawson, W. A.
2012-09-10
We introduce a new method for constraining the redshift distribution of a set of galaxies, using weak gravitational lensing shear. Instead of using observed shears and redshifts to constrain cosmological parameters, we ask how well the shears around clusters can constrain the redshifts, assuming fixed cosmological parameters. This provides a check on photometric redshifts, independent of source spectral energy distribution properties and therefore free of confounding factors such as misidentification of spectral breaks. We find that {approx}40 massive ({sigma}{sub v} = 1200 km s{sup -1}) cluster lenses are sufficient to determine the fraction of sources in each of six coarse redshift bins to {approx}11%, given weak (20%) priors on the masses of the highest-redshift lenses, tight (5%) priors on the masses of the lowest-redshift lenses, and only modest (20%-50%) priors on calibration and evolution effects. Additional massive lenses drive down uncertainties as N{sub lens}{sup -1/2}, but the improvement slows as one is forced to use lenses further down the mass function. Future large surveys contain enough clusters to reach 1% precision in the bin fractions if the tight lens-mass priors can be maintained for large samples of lenses. In practice this will be difficult to achieve, but the method may be valuable as a complement to other more precise methods because it is based on different physics and therefore has different systematic errors.
Constraining the mass of the Local Group
NASA Astrophysics Data System (ADS)
Carlesi, Edoardo; Hoffman, Yehuda; Sorce, Jenny G.; Gottlöber, Stefan
2017-03-01
The mass of the Local Group (LG) is a crucial parameter for galaxy formation theories. However, its observational determination is challenging - its mass budget is dominated by dark matter that cannot be directly observed. To meet this end, the posterior distributions of the LG and its massive constituents have been constructed by means of constrained and random cosmological simulations. Two priors are assumed - the Λ cold dark matter model that is used to set up the simulations, and an LG model that encodes the observational knowledge of the LG and is used to select LG-like objects from the simulations. The constrained simulations are designed to reproduce the local cosmography as it is imprinted on to the Cosmicflows-2 data base of velocities. Several prescriptions are used to define the LG model, focusing in particular on different recent estimates of the tangential velocity of M31. It is found that (a) different vtan choices affect the peak mass values up to a factor of 2, and change mass ratios of MM31 to MMW by up to 20 per cent; (b) constrained simulations yield more sharply peaked posterior distributions compared with the random ones; (c) LG mass estimates are found to be smaller than those found using the timing argument; (d) preferred Milky Way masses lie in the range of (0.6-0.8) × 1012 M⊙; whereas (e) MM31 is found to vary between (1.0-2.0) × 1012 M⊙, with a strong dependence on the vtan values used.
Optimization of retinotopy constrained source estimation constrained by prior
Hagler, Donald J.
2015-01-01
Studying how the timing and amplitude of visual evoked responses (VERs) vary between visual areas is important for understanding visual processing but is complicated by difficulties in reliably estimating VERs in individual visual areas using non-invasive brain measurements. Retinotopy constrained source estimation (RCSE) addresses this challenge by using multiple, retinotopically-mapped stimulus locations to simultaneously constrain estimates of VERs in visual areas V1, V2, and V3, taking advantage of the spatial precision of fMRI retinotopy and the temporal resolution of magnetoencephalography (MEG) or electroencephalography (EEG). Nonlinear optimization of dipole locations, guided by a group-constrained RCSE solution as a prior, improved the robustness of RCSE. This approach facilitated the analysis of differences in timing and amplitude of VERs between V1, V2, and V3, elicited by stimuli with varying luminance contrast in a sample of eight adult humans. The V1 peak response was 37% larger than that of V2 and 74% larger than that of V3, and also ~10–20 msec earlier. Normalized contrast response functions were nearly identical for the three areas. Results without dipole optimization, or with other nonlinear methods not constrained by prior estimates were similar but suffered from greater between-subject variability. The increased reliability of estimates offered by this approach may be particularly valuable when using a smaller number of stimulus locations, enabling a greater variety of stimulus and task manipulations. PMID:23868690
Interactive graphics nonlinear constrained optimization
NASA Technical Reports Server (NTRS)
Saouma, V. E.; Sikiotis, E. S.
1984-01-01
An interactive computer graphics environment was used for nonlinear constrained optimization analysis. It is found that by combining the power of a digital computer with the subtlety of engineering judgment during program execution, final results can be substantially better than the ones achieved by the numerical algorithm by itself.
NASA Astrophysics Data System (ADS)
Ng, Pin T.; Maechler, Martin
2015-05-01
COBS (COnstrained B-Splines), written in R, creates constrained regression smoothing splines via linear programming and sparse matrices. The method has two important features: the number and location of knots for the spline fit are established using the likelihood-based Akaike Information Criterion (rather than a heuristic procedure); and fits can be made for quantiles (e.g. 25% and 75% as well as the usual 50%) in the response variable, which is valuable when the scatter is asymmetrical or non-Gaussian. This code is useful for, for example, estimating cluster ages when there is a wide spread in stellar ages at a chosen absorption, as a standard regression line does not give an effective measure of this relationship.
Constrained Multiobjective Biogeography Optimization Algorithm
Mo, Hongwei; Xu, Zhidan; Xu, Lifang; Wu, Zhou; Ma, Haiping
2014-01-01
Multiobjective optimization involves minimizing or maximizing multiple objective functions subject to a set of constraints. In this study, a novel constrained multiobjective biogeography optimization algorithm (CMBOA) is proposed. It is the first biogeography optimization algorithm for constrained multiobjective optimization. In CMBOA, a disturbance migration operator is designed to generate diverse feasible individuals in order to promote the diversity of individuals on Pareto front. Infeasible individuals nearby feasible region are evolved to feasibility by recombining with their nearest nondominated feasible individuals. The convergence of CMBOA is proved by using probability theory. The performance of CMBOA is evaluated on a set of 6 benchmark problems and experimental results show that the CMBOA performs better than or similar to the classical NSGA-II and IS-MOEA. PMID:25006591
Constrained minimization for monotonic reconstruction
Rider, W.J.; Kothe, D.B.
1996-08-20
The authors present several innovations in a method for monotonic reconstructions. It is based on the application of constrained minimization techniques for the imposition of monotonicity on a reconstruction. In addition, they present extensions of several classical TVD limiters to a genuinely multidimensional setting. In this case the linear least squares reconstruction method is expanded upon. They also clarify data dependent weighting techniques used with the minimization process.
HCV management in resource-constrained countries.
Lim, Seng Gee
2017-02-21
With the arrival of all-oral directly acting antiviral (DAA) therapy with high cure rates, the promise of hepatitis C virus (HCV) eradication is within closer reach. The availability of generic DAAs has improved access to countries with constrained resources. However, therapy is only one component of the HCV care continuum, which is the framework for HCV management from identifying patients to cure. The large number of undiagnosed HCV cases is the biggest concern, and strategies to address this are needed, as risk factor screening is suboptimal, detecting <20% of known cases. Improvements in HCV confirmation through either reflex HCV RNA screening or ideally a sensitive point of care test are needed. HCV notification (e.g., Australia) may improve diagnosis (proportion of HCV diagnosed is 75%) and may lead to benefits by increasing linkage to care, therapy and cure. Evaluations for cirrhosis using non-invasive markers are best done with a biological panel, but they are only moderately accurate. In resource-constrained settings, only generic HCV medications are available, and a combination of sofosbuvir, ribavirin, ledipasvir or daclatasvir provides sufficient efficacy for all genotypes, but this is likely to be replaced with pangenetypic regimens such as sofosbuvir/velpatasvir and glecaprevir/pibrentaasvir. In conclusion, HCV management in resource-constrained settings is challenging on multiple fronts because of the lack of infrastructure, facilities, trained manpower and equipment. However, it is still possible to make a significant impact towards HCV eradication through a concerted effort by individuals and national organisations with domain expertise in this area.
Compositionally Constraining Elysium Lava Fields
NASA Astrophysics Data System (ADS)
Karunatillake, S.; Button, N. E.; Skok, J. R.
2013-12-01
Chemical provinces of Mars defined recently [1-3] became possible with the maps of elemental mass fractions generated with Mars Odyssey Gamma and Neutron Spectrometer (GS) data [4,5]. These provide a unique perspective by representing compositional signatures distinctive of the regolith vertically at decimeter depths and laterally at hundreds of kilometer scale. Some provinces overlap compellingly with regions highlighted by other remote sensing observations, such as the Mars Radar Stealth area [3]. The spatial convergence of mutually independent data with the consequent highlight of a region provides a unique opportunity of insight not possible with a single type of remote sensing observation. Among such provinces, previous work [3] highlighted Elysium lava flows as a promising candidate on the basis of convergence with mapped geologic units identifying Elysium's lava fields generally, and Amazonian-aged lava flows specifically. The South Eastern lava flows of Elysium Mons, dating to the recent Amazonian epoch, overlap compellingly with a chemical province of K and Th depletion relative to the Martian midlatitudes. We characterize the composition, geology, and geomorphology of the SE Elysium province to constrain the confluence of geologic and alteration processes that may have contributed to its evolution. We compare this with the North Western lava fields, extending the discussion on chemical products from the thermal evolution of Martian volcanism as discussed by Baratoux et al. [6]. The chemical province, by regional proximity to Cerberus Fossae, may also reflect the influence of recently identified buried flood channels [7] in the vicinity of Orcus Patera. Despite the compelling chemical signature from γ spectra, fine grained unconsolidated sediment hampers regional VNTIR (Visible, Near, and Thermal Infrared) spectral analysis. But some observations near scarps and fresh craters allow a view of small scale mineral content. The judicious synthesis of
SENSE Phase-Constrained Magnitude Reconstruction With Iterative Phase Refinement
Lew, Calvin; Pineda, Angel R.; Clayton, David; Spielman, Dan; Chan, Frandics; Bammer, Roland
2012-01-01
Conventional sensitivity encoding (SENSE) reconstruction is based on equations in the complex domain. However, for many MRI applications only the magnitude is relevant. If there exists an estimate of the underlying phase information, a magnitude-only phase-constrained reconstruction can help to improve the conditioning of the SENSE reconstruction problem. Consequently, this reduces g-factor-related noise enhancement. In previous attempts at phase-constrained SENSE reconstruction, image quality was hampered by strong aliasing artifacts resulting from inadequate phase estimates and high sensitivity to phase errors. If a full-resolution phase image is used, a significant reduction in aliasing errors and better noise properties compared to SENSE can be obtained. An iterative scheme that improves the phase estimate to better approximate the phase is presented. The mathematical framework of the new approach is provided together with comparisons of conventional SENSE, phase-constrained SENSE, and the new phase-refinement method. Both theory and experimental verification demonstrate significantly better noise performance at high reduction factors, i.e., close to the theoretical limit. For applications that need only magnitude data, an iterative phase-constrained SENSE reconstruction can provide substantial SNR improvement over SENSE reconstruction and less artifacts than phase-constrained SENSE. PMID:17969127
Constraining Lorentz violation with cosmology.
Zuntz, J A; Ferreira, P G; Zlosnik, T G
2008-12-31
The Einstein-aether theory provides a simple, dynamical mechanism for breaking Lorentz invariance. It does so within a generally covariant context and may emerge from quantum effects in more fundamental theories. The theory leads to a preferred frame and can have distinct experimental signatures. In this Letter, we perform a comprehensive study of the cosmological effects of the Einstein-aether theory and use observational data to constrain it. Allied to previously determined consistency and experimental constraints, we find that an Einstein-aether universe can fit experimental data over a wide range of its parameter space, but requires a specific rescaling of the other cosmological densities.
Constraining relativistic viscous hydrodynamical evolution
Martinez, Mauricio; Strickland, Michael
2009-04-15
We show that by requiring positivity of the longitudinal pressure it is possible to constrain the initial conditions one can use in second-order viscous hydrodynamical simulations of ultrarelativistic heavy-ion collisions. We demonstrate this explicitly for (0+1)-dimensional viscous hydrodynamics and discuss how the constraint extends to higher dimensions. Additionally, we present an analytic approximation to the solution of (0+1)-dimensional second-order viscous hydrodynamical evolution equations appropriate to describe the evolution of matter in an ultrarelativistic heavy-ion collision.
Constraining walking and custodial technicolor
Foadi, Roshan; Frandsen, Mads T.; Sannino, Francesco
2008-05-01
We show how to constrain the physical spectrum of walking technicolor models via precision measurements and modified Weinberg sum rules. We also study models possessing a custodial symmetry for the S parameter at the effective Lagrangian level - custodial technicolor - and argue that these models cannot emerge from walking-type dynamics. We suggest that it is possible to have a very light spin-one axial (vector) boson. However, in the walking dynamics the associated vector boson is heavy while it is degenerate with the axial in custodial technicolor.
Method of constrained global optimization
NASA Astrophysics Data System (ADS)
Altschuler, Eric Lewin; Williams, Timothy J.; Ratner, Edward R.; Dowla, Farid; Wooten, Frederick
1994-04-01
We present a new method for optimization: constrained global optimization (CGO). CGO iteratively uses a Glauber spin flip probability and the Metropolis algorithm. The spin flip probability allows changing only the values of variables contributing excessively to the function to be minimized. We illustrate CGO with two problems-Thomson's problem of finding the minimum-energy configuration of unit charges on a spherical surface, and a problem of assigning offices-for which CGO finds better minima than other methods. We think CGO will apply to a wide class of optimization problems.
Quantum Annealing for Constrained Optimization
NASA Astrophysics Data System (ADS)
Hen, Itay; Spedalieri, Federico M.
2016-03-01
Recent advances in quantum technology have led to the development and manufacturing of experimental programmable quantum annealers that promise to solve certain combinatorial optimization problems of practical relevance faster than their classical analogues. The applicability of such devices for many theoretical and real-world optimization problems, which are often constrained, is severely limited by the sparse, rigid layout of the devices' quantum bits. Traditionally, constraints are addressed by the addition of penalty terms to the Hamiltonian of the problem, which, in turn, requires prohibitively increasing physical resources while also restricting the dynamical range of the interactions. Here, we propose a method for encoding constrained optimization problems on quantum annealers that eliminates the need for penalty terms and thereby reduces the number of required couplers and removes the need for minor embedding, greatly reducing the number of required physical qubits. We argue the advantages of the proposed technique and illustrate its effectiveness. We conclude by discussing the experimental feasibility of the suggested method as well as its potential to appreciably reduce the resource requirements for implementing optimization problems on quantum annealers and its significance in the field of quantum computing.
Quantum Annealing for Constrained Optimization
NASA Astrophysics Data System (ADS)
Hen, Itay; Spedalieri, Federico
Recent advances in quantum technology have led to the development and manufacturing of experimental programmable quantum annealers that could potentially solve certain quadratic unconstrained binary optimization problems faster than their classical analogues. The applicability of such devices for many theoretical and practical optimization problems, which are often constrained, is severely limited by the sparse, rigid layout of the devices' quantum bits. Traditionally, constraints are addressed by the addition of penalty terms to the Hamiltonian of the problem, which in turn requires prohibitively increasing physical resources while also restricting the dynamical range of the interactions. Here we propose a method for encoding constrained optimization problems on quantum annealers that eliminates the need for penalty terms and thereby removes many of the obstacles associated with the implementation of these. We argue the advantages of the proposed technique and illustrate its effectiveness. We then conclude by discussing the experimental feasibility of the suggested method as well as its potential to boost the encodability of other optimization problems.
Constrained sampling method for analytic continuation
NASA Astrophysics Data System (ADS)
Sandvik, Anders W.
2016-12-01
A method for analytic continuation of imaginary-time correlation functions (here obtained in quantum Monte Carlo simulations) to real-frequency spectral functions is proposed. Stochastically sampling a spectrum parametrized by a large number of δ functions, treated as a statistical-mechanics problem, it avoids distortions caused by (as demonstrated here) configurational entropy in previous sampling methods. The key development is the suppression of entropy by constraining the spectral weight to within identifiable optimal bounds and imposing a set number of peaks. As a test case, the dynamic structure factor of the S =1 /2 Heisenberg chain is computed. Very good agreement is found with Bethe ansatz results in the ground state (including a sharp edge) and with exact diagonalization of small systems at elevated temperatures.
Constrained sampling method for analytic continuation.
Sandvik, Anders W
2016-12-01
A method for analytic continuation of imaginary-time correlation functions (here obtained in quantum Monte Carlo simulations) to real-frequency spectral functions is proposed. Stochastically sampling a spectrum parametrized by a large number of δ functions, treated as a statistical-mechanics problem, it avoids distortions caused by (as demonstrated here) configurational entropy in previous sampling methods. The key development is the suppression of entropy by constraining the spectral weight to within identifiable optimal bounds and imposing a set number of peaks. As a test case, the dynamic structure factor of the S=1/2 Heisenberg chain is computed. Very good agreement is found with Bethe ansatz results in the ground state (including a sharp edge) and with exact diagonalization of small systems at elevated temperatures.
A constrained EM algorithm for independent component analysis.
Welling, M; Weber, M
2001-03-01
We introduce a novel way of performing independent component analysis using a constrained version of the expectation-maximization (EM) algorithm. The source distributions are modeled as D one-dimensional mixtures of gaussians. The observed data are modeled as linear mixtures of the sources with additive, isotropic noise. This generative model is fit to the data using constrained EM. The simpler "soft-switching" approach is introduced, which uses only one parameter to decide on the sub- or supergaussian nature of the sources. We explain how our approach relates to independent factor analysis.
Fast Energy Minimization of large Polymers Using Constrained Optimization
Todd D. Plantenga
1998-10-01
A new computational technique is described that uses distance constraints to calculate empirical potential energy minima of partially rigid molecules. A constrained minimuzation algorithm that works entirely in Cartesian coordinates is used. The algorithm does not obey the constraints until convergence, a feature that reduces ill-conditioning and allows constrained local minima to be computed more quickly than unconstrained minima. Computational speedup exceeds the 3-fold factor commonly obtained in constained molecular dynamics simulations, where the constraints must be strictly obeyed at all times.
Formal language constrained path problems
Barrett, C.; Jacob, R.; Marathe, M.
1997-07-08
In many path finding problems arising in practice, certain patterns of edge/vertex labels in the labeled graph being traversed are allowed/preferred, while others are disallowed. Motivated by such applications as intermodal transportation planning, the authors investigate the complexity of finding feasible paths in a labeled network, where the mode choice for each traveler is specified by a formal language. The main contributions of this paper include the following: (1) the authors show that the problem of finding a shortest path between a source and destination for a traveler whose mode choice is specified as a context free language is solvable efficiently in polynomial time, when the mode choice is specified as a regular language they provide algorithms with improved space and time bounds; (2) in contrast, they show that the problem of finding simple paths between a source and a given destination is NP-hard, even when restricted to very simple regular expressions and/or very simple graphs; (3) for the class of treewidth bounded graphs, they show that (i) the problem of finding a regular language constrained simple path between source and a destination is solvable in polynomial time and (ii) the extension to finding context free language constrained simple paths is NP-complete. Several extensions of these results are presented in the context of finding shortest paths with additional constraints. These results significantly extend the results in [MW95]. As a corollary of the results, they obtain a polynomial time algorithm for the BEST k-SIMILAR PATH problem studied in [SJB97]. The previous best algorithm was given by [SJB97] and takes exponential time in the worst case.
Exploring constrained quantum control landscapes
NASA Astrophysics Data System (ADS)
Moore, Katharine W.; Rabitz, Herschel
2012-10-01
The broad success of optimally controlling quantum systems with external fields has been attributed to the favorable topology of the underlying control landscape, where the landscape is the physical observable as a function of the controls. The control landscape can be shown to contain no suboptimal trapping extrema upon satisfaction of reasonable physical assumptions, but this topological analysis does not hold when significant constraints are placed on the control resources. This work employs simulations to explore the topology and features of the control landscape for pure-state population transfer with a constrained class of control fields. The fields are parameterized in terms of a set of uniformly spaced spectral frequencies, with the associated phases acting as the controls. This restricted family of fields provides a simple illustration for assessing the impact of constraints upon seeking optimal control. Optimization results reveal that the minimum number of phase controls necessary to assure a high yield in the target state has a special dependence on the number of accessible energy levels in the quantum system, revealed from an analysis of the first- and second-order variation of the yield with respect to the controls. When an insufficient number of controls and/or a weak control fluence are employed, trapping extrema and saddle points are observed on the landscape. When the control resources are sufficiently flexible, solutions producing the globally maximal yield are found to form connected "level sets" of continuously variable control fields that preserve the yield. These optimal yield level sets are found to shrink to isolated points on the top of the landscape as the control field fluence is decreased, and further reduction of the fluence turns these points into suboptimal trapping extrema on the landscape. Although constrained control fields can come in many forms beyond the cases explored here, the behavior found in this paper is illustrative of
ERIC Educational Resources Information Center
Hutchison, Amy C.; Woodward, Lindsay
2014-01-01
The Common Core State Standards produce a need to understand how digital tools can support literacy instruction. The purpose of this case study was to explore how a language arts teacher's integration of computers and iPads empowered and constrained her and the resulting classroom instruction. Constraining factors included (a) inadequate…
ERIC Educational Resources Information Center
Hutchison, Amy C.; Woodward, Lindsay
2014-01-01
The Common Core State Standards produce a need to understand how digital tools can support literacy instruction. The purpose of this case study was to explore how a language arts teacher's integration of computers and iPads empowered and constrained her and the resulting classroom instruction. Constraining factors included (a) inadequate…
Constraining QGP properties with CHIMERA
NASA Astrophysics Data System (ADS)
Garishvili, Irakli; Abelev, Betty; Cheng, Michael; Glenn, Andrew; Soltz, Ron
2011-10-01
Understanding essential properties of strongly interacting matter is arguably the most important goal of the relativistic heavy-ion programs both at RHIC and the LHC. In particular, constraining observables such as ratio of shear viscosity to entropy density, η/s, initial temperature, Tinit, and energy density is of critical importance. For this purpose we have developed CHIMERA, Comprehensive Heavy Ion Model Reporting and Evaluation Algorithm. CHIMERA is designed to facilitate global statistical comparison of results from our multi-stage hydrodynamics/hadron cascade model of heavy ion collisions to the key soft observables (HBT, elliptic flow, spectra) measured at RHIC and the LHC. Within this framework the data representing multiple different measurements from different experiments are compiled into single format. One of the unique features of CHIMERA is, that in addition to taking into account statistical errors, it also treats different types of systematic uncertainties. The hydrodynamics/hadron cascade model used in the framework incorporates different initial state conditions, pre-equilibrium flow, the UVH2+1 viscous hydro model, Cooper-Frye freezeout, and the UrQMD hadronic cascade model. The sensitivity of the observables to the equation of state (EoS) is explored using several EoS's in the hydrodynamic evolution. The latest results from CHIMERA, including data from the LHC, will be presented.
Gyrification from constrained cortical expansion
Tallinen, Tuomas; Chung, Jun Young; Biggins, John S.; Mahadevan, L.
2014-01-01
The exterior of the mammalian brain—the cerebral cortex—has a conserved layered structure whose thickness varies little across species. However, selection pressures over evolutionary time scales have led to cortices that have a large surface area to volume ratio in some organisms, with the result that the brain is strongly convoluted into sulci and gyri. Here we show that the gyrification can arise as a nonlinear consequence of a simple mechanical instability driven by tangential expansion of the gray matter constrained by the white matter. A physical mimic of the process using a layered swelling gel captures the essence of the mechanism, and numerical simulations of the brain treated as a soft solid lead to the formation of cusped sulci and smooth gyri similar to those in the brain. The resulting gyrification patterns are a function of relative cortical expansion and relative thickness (compared with brain size), and are consistent with observations of a wide range of brains, ranging from smooth to highly convoluted. Furthermore, this dependence on two simple geometric parameters that characterize the brain also allows us to qualitatively explain how variations in these parameters lead to anatomical anomalies in such situations as polymicrogyria, pachygyria, and lissencephalia. PMID:25136099
Constraining the Europa Neutral Torus
NASA Astrophysics Data System (ADS)
Smith, Howard T.; Mitchell, Donald; mauk, Barry; Johnson, Robert E.; clark, george
2016-10-01
"Neutral tori" consist of neutral particles that usually co-orbit along with their source forming a toroidal (or partial toroidal) feature around the planet. The distribution and composition of these features can often provide important, if not unique, insight into magnetospheric particles sources, mechanisms and dynamics. However, these features can often be difficult to directly detect. One innovative method for detecting neutral tori is by observing Energetic Neutral Atoms (ENAs) that are generally considered produced as a result of charge exchange interactions between charged and neutral particles.Mauk et al. (2003) reported the detection of a Europa neutral particle torus using ENA observations. The presence of a Europa torus has extremely large implications for upcoming missions to Jupiter as well as understanding possible activity at this moon and providing critical insight into what lies beneath the surface of this icy ocean world. However, ENAs can also be produced as a result of charge exchange interactions between two ionized particles and in that case cannot be used to infer the presence of neutral particle population. Thus, a detailed examination of all possible source interactions must be considered before one can confirm that likely original source population of these ENA images is actually a Europa neutral particle torus. For this talk, we examine the viability that the Mauk et al. (2003) observations were actually generated from a neutral torus emanating from Europa as opposed to charge particle interactions with plasma originating from Io. These results help constrain such a torus as well as Europa source processes.
Order-constrained linear optimization.
Tidwell, Joe W; Dougherty, Michael R; Chrabaszcz, Jeffrey S; Thomas, Rick P
2017-02-27
Despite the fact that data and theories in the social, behavioural, and health sciences are often represented on an ordinal scale, there has been relatively little emphasis on modelling ordinal properties. The most common analytic framework used in psychological science is the general linear model, whose variants include ANOVA, MANOVA, and ordinary linear regression. While these methods are designed to provide the best fit to the metric properties of the data, they are not designed to maximally model ordinal properties. In this paper, we develop an order-constrained linear least-squares (OCLO) optimization algorithm that maximizes the linear least-squares fit to the data conditional on maximizing the ordinal fit based on Kendall's τ. The algorithm builds on the maximum rank correlation estimator (Han, 1987, Journal of Econometrics, 35, 303) and the general monotone model (Dougherty & Thomas, 2012, Psychological Review, 119, 321). Analyses of simulated data indicate that when modelling data that adhere to the assumptions of ordinary least squares, OCLO shows minimal bias, little increase in variance, and almost no loss in out-of-sample predictive accuracy. In contrast, under conditions in which data include a small number of extreme scores (fat-tailed distributions), OCLO shows less bias and variance, and substantially better out-of-sample predictive accuracy, even when the outliers are removed. We show that the advantages of OCLO over ordinary least squares in predicting new observations hold across a variety of scenarios in which researchers must decide to retain or eliminate extreme scores when fitting data.
BICEP2 constrains composite inflation
NASA Astrophysics Data System (ADS)
Channuie, Phongpichit
2014-07-01
In light of BICEP2, we re-examine single field inflationary models in which the inflation is a composite state stemming from various four-dimensional strongly coupled theories. We study in the Einstein frame a set of cosmological parameters, the primordial spectral index ns and tensor-to-scalar ratio r, predicted by such models. We confront the predicted results with the joint Planck data, and with the recent BICEP2 data. We constrain the number of e-foldings for composite models of inflation in order to obtain a successful inflation. We find that the minimal composite inflationary model is fully consistent with the Planck data. However it is in tension with the recent BICEP2 data. The observables predicted by the glueball inflationary model can be consistent with both Planck and BICEP2 contours if a suitable number of e-foldings are chosen. Surprisingly, the super Yang-Mills inflationary prediction is significantly consistent with the Planck and BICEP2 observations.
Constrained navigation for unmanned systems
NASA Astrophysics Data System (ADS)
Vasseur, Laurent; Gosset, Philippe; Carpentier, Luc; Marion, Vincent; Morillon, Joel G.; Ropars, Patrice
2005-05-01
The French Military Robotic Study Program (introduced in Aerosense 2003), sponsored by the French Defense Procurement Agency and managed by Thales as the prime contractor, focuses on about 15 robotic themes which can provide an immediate "operational add-on value". The paper details the "constrained navigation" study (named TEL2), which main goal is to identify and test a well-balanced task sharing between man and machine to accomplish a robotic task that cannot be performed autonomously at the moment because of technological limitations. The chosen function is "obstacle avoidance" on rough ground and quite high speed (40 km/h). State of the art algorithms have been implemented to perform autonomous obstacle avoidance and following of forest borders, using scanner laser sensor and standard localization functions. Such an "obstacle avoidance" function works well most of the time, BUT fails sometimes. The study analyzed how the remote operator can manage such failures so that the system remains fully operationally reliable; he can act according to two ways: a) finely adjust the vehicle current heading; b) take the control of the vehicle "on the fly" (without stopping) and bring it back to autonomous behavior when motion is secured again. The paper also presents the results got from the military acceptance tests performed on French 4x4 DARDS ATD.
Constrained Allocation Flux Balance Analysis
Mori, Matteo; Hwa, Terence; Martin, Olivier C.
2016-01-01
New experimental results on bacterial growth inspire a novel top-down approach to study cell metabolism, combining mass balance and proteomic constraints to extend and complement Flux Balance Analysis. We introduce here Constrained Allocation Flux Balance Analysis, CAFBA, in which the biosynthetic costs associated to growth are accounted for in an effective way through a single additional genome-wide constraint. Its roots lie in the experimentally observed pattern of proteome allocation for metabolic functions, allowing to bridge regulation and metabolism in a transparent way under the principle of growth-rate maximization. We provide a simple method to solve CAFBA efficiently and propose an “ensemble averaging” procedure to account for unknown protein costs. Applying this approach to modeling E. coli metabolism, we find that, as the growth rate increases, CAFBA solutions cross over from respiratory, growth-yield maximizing states (preferred at slow growth) to fermentative states with carbon overflow (preferred at fast growth). In addition, CAFBA allows for quantitatively accurate predictions on the rate of acetate excretion and growth yield based on only 3 parameters determined by empirical growth laws. PMID:27355325
Leonard, Michelle; Zhang, Liping; Zhai, Ni; Cader, Ahmad; Chan, Yim; Nowak, Roberta B; Fowler, Velia M; Menko, A Sue
2011-01-15
Extensive elongation of lens fiber cells is a central feature of lens morphogenesis. Our study investigates the role of N-cadherin junctions in this process in vivo. We investigate both the molecular players involved in N-cadherin junctional maturation and the subsequent function of these junctions as epicenters for the assembly of an actin cytoskeleton that drives morphogenesis. We present the first evidence of nascent cadherin junctions in vivo, and show that they are a prominent feature along lateral interfaces of undifferentiated lens epithelial cells. Maturation of these N-cadherin junctions, required for lens cell differentiation, preceded organization of a cortical actin cytoskeleton along the cells' lateral borders, but was linked to recruitment of α-catenin and dephosphorylation of N-cadherin-linked β-catenin. Biochemical analysis revealed differentiation-specific recruitment of actin regulators cortactin and Arp3 to maturing N-cadherin junctions of differentiating cells, linking N-cadherin junctional maturation with actin cytoskeletal assembly during fiber cell elongation. Blocking formation of mature N-cadherin junctions led to reduced association of α-catenin with N-cadherin, prevented organization of actin along lateral borders of differentiating lens fiber cells and blocked their elongation. These studies provide a molecular link between N-cadherin junctions and the organization of an actin cytoskeleton that governs lens fiber cell morphogenesis in vivo.
Lee, Hangnoh; Ragusano, Linda; Martinez, Ana; Gill, Jagdip; Dimova, Dessislava K
2012-06-01
E2F and RB proteins regulate the expression of genes involved in cell cycle progression, apoptosis, differentiation, and development. Recent studies indicate that they function as part of an evolutionarily conserved multiprotein complex termed dREAM/DREAM/LINC. Here we characterize the role of the Drosophila complex, dREAM, in the regulation of differentiation-specific E2F target genes in actively proliferating cells. These genes are regulated differently from cell cycle-related E2F targets, they do not depend on E2F activation, and E2F/RB repression is maintained throughout the cell cycle. In proliferating cells, their repression is dependent on dREAM. We find that dREAM plays a dual role in their regulation. First, it is required for the stability of the repressive dE2F2/RBF complexes at their promoters during S phase. Second, we find that dREAM is indispensable for both transcriptional repression mechanisms employed at these genes.
Constrained Peptides as Miniature Protein Structures
Yin, Hang
2012-01-01
This paper discusses the recent developments of protein engineering using both covalent and noncovalent bonds to constrain peptides, forcing them into designed protein secondary structures. These constrained peptides subsequently can be used as peptidomimetics for biological functions such as regulations of protein-protein interactions. PMID:25969758
Sparsity constrained contrast source inversion.
Ramirez, Ana B; van Dongen, Koen W A
2016-09-01
Ultrasound imaging is used for detecting and characterizing breast lesions. A state of the art imaging method is the contrast source inversion (CSI), which solves the full wave nonlinear inverse problem. However, when the measurements are acquired in noisy environments, CSI can diverge from the correct solution after several iterations. Problems associated with noisy data were originally solved by including total variation (TV) regularization. Unfortunately, for very noisy data, TV regularization alone is not sufficient. In this work, compressed sensing ideas are used to regularize the inversion process by restricting the solution of the CSI method to be sparse in a transformation domain. The proposed method estimates the contrast source and contrast function by minimizing the mean squared error between the measured and modeled data. An extra penalty term is added to measure sparsity in the transformation domain. A second method that combines sparsity of the contrast source and minimal TV in the contrast function is also presented. The proposed methods are tested on noise-free and noisy synthetic data sets representing a scan of a cancerous breast. Numerical experiments show that, for measurements contaminated with 1% noise, the sparsity constrained CSI improves the normalized mean squared error of the reconstructed speed-of-sound profiles up to 36% in comparison with traditional CSI. Also, for measurements contaminated with 5% noise, the proposed methods improve the quality of the reconstruction up to 70% in comparison with the traditional CSI method. Experimental results also show that the methods remain convergent to the correct speed-of-sound profile as the number of iterations increases.
HYPR: constrained reconstruction for enhanced SNR in dynamic medical imaging
NASA Astrophysics Data System (ADS)
Mistretta, C.; Wieben, O.; Velikina, J.; Wu, Y.; Johnson, K.; Korosec, F.; Unal, O.; Chen, G.; Fain, S.; Christian, B.; Nalcioglu, O.; Kruger, R. A.; Block, W.; Samsonov, A.; Speidel, M.; Van Lysel, M.; Rowley, H.; Supanich, M.; Turski, P.; Wu, Yan; Holmes, J.; Kecskemeti, S.; Moran, C.; O'Halloran, R.; Keith, L.; Alexander, A.; Brodsky, E.; Lee, J. E.; Hall, T.; Zagzebski, J.
2008-03-01
During the last eight years our group has developed radial acquisitions with angular undersampling factors of several hundred that accelerate MRI in selected applications. As with all previous acceleration techniques, SNR typically falls as least as fast as the inverse square root of the undersampling factor. This limits the SNR available to support the small voxels that these methods can image over short time intervals in applications like time-resolved contrast-enhanced MR angiography (CE-MRA). Instead of processing each time interval independently, we have developed constrained reconstruction methods that exploit the significant correlation between temporal sampling points. A broad class of methods, termed HighlY Constrained Back PRojection (HYPR), generalizes this concept to other modalities and sampling dimensions.
Assessing working memory capacity through time-constrained elementary activities.
Lucidi, Annalisa; Loaiza, Vanessa; Camos, Valérie; Barrouillet, Pierre
2014-01-01
Working memory (WM) capacity measured through complex span tasks is among the best predictors of fluid intelligence (Gf). These tasks usually involve maintaining memoranda while performing complex cognitive activities that require a rather high level of education (e.g., reading comprehension, arithmetic), restricting their range of applicability. Because individual differences in such complex activities are nothing more than the concatenation of small differences in their elementary constituents, complex span tasks involving elementary processes should be as good of predictors of Gf as traditional tasks. The present study showed that two latent variables issued from either traditional or new span tasks involving time-constrained elementary activities were similarly correlated with Gf. Moreover, a model with a single unitary WM factor had a similar fit as a model with two distinct WM factors. Thus, time-constrained elementary activities can be integrated in WM tasks, permitting the assessment of WM in a wider range of populations.
Conjugate Gradient Methods for Constrained Least Squares Problems
1990-01-01
TINO Hi!AGL . edi"o ar m m Conjugate Gradient Methods for Constrained Least Squares Problems by Douglas James A thesis 3ubmitted to the Graduate Faculty...Breakdown of Incomplete QR Factorizations The research which led to this dissertation began with a look at incomplete QR preconditioners for ordinary...AFIT/CI/CIA- 90-013D 6a. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7&. NAME OF MONITORING ORGANIZATION AFIT STUDENT AT (if applicable) AFIT/CIA
Constrained Galerkin variational integrators and modified constrained symplectic Runge-Kutta methods
NASA Astrophysics Data System (ADS)
Wenger, Theresa; Ober-Blöbaum, Sina; Leyendecker, Sigrid
2017-07-01
The presented constrained Galerkin variational integrators base on the higher order variational integrators in [1], now applied to holonomically constrained systems and are an extension of the constrained Galerkin methods in [2]. Sufficient conditions are given to obtain a stiffly accurate integration scheme, its structure preserving properties are analysed and the convergence order as well as the computational efficiency are investigated numerically. The equivalence to constrained symplectic Runge-Kutta methods is shown, with focus on a modified constrained symplectic Runge-Kutta method, that was first introduced in [3], there for the unconstrained case.
Temporally constrained reconstruction applied to MRI temperature data.
Todd, Nick; Adluru, Ganesh; Payne, Allison; DiBella, Edward V R; Parker, Dennis
2009-08-01
The monitoring of thermal ablation procedures would benefit from an acceleration in the rate at which MRI temperature maps are acquired. Constrained reconstruction techniques have been shown to be capable of generating high quality images using only a fraction of the k-space data. Here, we present a temporally constrained reconstruction (TCR) algorithm applied to proton resonance frequency shift (PRF) data. The algorithm generates images from undersampled data by iteratively minimizing a cost function. The unique challenges of using an iterative constrained reconstruction technique to generate real-time images were addressed. For a set of eight heating experiments on ex vivo porcine tissue, a maximum reduction factor of 4 was achieved while keeping the root mean square error (RMSE) of the temperature below 0.5 degrees C. For a set of three heating experiments on in vivo canine muscle tissue, the maximum reduction factor achieved was 3 while keeping the temperature RMSE below 1.0 degrees C. At these reduction factors, the TCR algorithm underpredicted the thermal dose by an average of 6% for the ex vivo data and 28% for the in vivo data. Compared with sliding window and low resolution reconstructions, the RMSE of the TCR algorithm was significantly lower (P < 0.05 in all cases).
Constraining inflation with future galaxy redshift surveys
Huang, Zhiqi; Vernizzi, Filippo; Verde, Licia E-mail: liciaverde@icc.ub.edu
2012-04-01
With future galaxy surveys, a huge number of Fourier modes of the distribution of the large scale structures in the Universe will become available. These modes are complementary to those of the CMB and can be used to set constraints on models of the early universe, such as inflation. Using a MCMC analysis, we compare the power of the CMB with that of the combination of CMB and galaxy survey data, to constrain the power spectrum of primordial fluctuations generated during inflation. We base our analysis on the Planck satellite and a spectroscopic redshift survey with configuration parameters close to those of the Euclid mission as examples. We first consider models of slow-roll inflation, and show that the inclusion of large scale structure data improves the constraints by nearly halving the error bars on the scalar spectral index and its running. If we attempt to reconstruct the inflationary single-field potential, a similar conclusion can be reached on the parameters characterizing the potential. We then study models with features in the power spectrum. In particular, we consider ringing features produced by a break in the potential and oscillations such as in axion monodromy. Adding large scale structures improves the constraints on features by more than a factor of two. In axion monodromy we show that there are oscillations with small amplitude and frequency in momentum space that are undetected by CMB alone but can be measured by including galaxy surveys in the analysis.
Constrained tricritical phenomena in two dimensions.
Deng, Youjin; Heringa, Jouke R; Blöte, Henk W J
2005-03-01
We investigate several tricritical models on the square lattice by means of Monte Carlo simulations. These include the Blume-Capel model, Baxter's hard-square model, and the q=1 , 3, and 4 Potts models with vacancies. We use a combination of the Wolff and geometric cluster methods, which conserves the total number of vacancies or lattice-gas particles and suppresses critical slowing down. Several quantities are sampled, such as the specific heat C and the structure factor C(s) , which accounts for the large-scale spatial inhomogeneity of the energy fluctuations. We find that the constraint strongly modifies some of the critical singularities. For instance, the specific heat C reaches a finite value at tricriticality, while C(s) remains divergent as in the unconstrained system. We are able to explain these observed constrained phenomena on the basis of the Fisher renormalization mechanism generalized to include a subleading relevant thermal scaling field. In this context, we find that, under the constraint, the leading thermal exponent y(t1) is renormalized to 2- y(t1) , while the subleading exponent y(t2) remains unchanged.
Founder niche constrains evolutionary adaptive radiation.
Flohr, Régis C E; Blom, Carsten J; Rainey, Paul B; Beaumont, Hubertus J E
2013-12-17
Adaptive radiation of a lineage into a range of organisms with different niches underpins the evolution of life's diversity. Although the role of the environment in shaping adaptive radiation is well established, theory predicts that the evolvability and niche of the founding ancestor are also of importance. Direct demonstration of a causal link requires resolving the independent effects of these additional factors. Here, we accomplish this using experimental bacterial populations and demonstrate how the dynamics of adaptive radiation are constrained by the niche of the founder. We manipulated the propensity of the founder to undergo adaptive radiation and resolved the underlying causal changes in both its evolvability and niche. Evolvability did not change, but the propensity for adaptive radiation was altered by changes in the position and breadth of the niche of the founder. These observations provide direct empirical evidence for a link between the niche of organisms and their propensity for adaptive radiation. This general mechanism may have rendered the evolutionary dynamics of extant adaptive radiations dependent on chance events that determined their founding ancestors.
2012-01-01
Background The enzyme acetyl-CoA carboxylase-alpha (ACC-α) is rate limiting for de novo fatty acid synthesis. Among the four promoters expressing the bovine gene, promoter IA (PIA) is dominantly active in lipogenic tissues. This promoter is in principal repressed but activated under favorable nutritional conditions. Previous analyses already coarsely delineated the repressive elements on the distal promoter but did not resolve the molecular nature of the repressor. Knowledge about the molecular functioning of this repressor is fundamental to understanding the nutrition mediated regulation of PIA activity. We analyzed here the molecular mechanism calibrating PIA activity. Results We finely mapped the repressor binding sites in reporter gene assays and demonstrate together with Electrophoretic Mobility Shift Assays that nuclear factor-Y (NF-Y) and CCAAT/enhancer binding protein-β (C/EBPβ) each separately repress PIA activity by binding to their cognate low affinity sites, located on distal elements of the promoter. Simultaneous binding of both factors results in strongest repression. Paradoxically, over expression of NFY factors, but also - and even more so - of C/EBPβ significantly activated the promoter when bound to high affinity sites on the proximal promoter. However, co-transfection experiments revealed that NF-Y may eventually diminish the strong stimulatory effect of C/EBPβ at the proximal PIA in a dose dependent fashion. We validated by chromatin immunoprecipitation, that NF-Y and C/EBP factors may physically interact. Conclusion The proximal promoter segment of PIA appears to be principally in an active state, since even minute concentrations of both, NF-Y and C/EBPβ factors can saturate the high affinity activator sites. Higher factor concentrations will saturate the low affinity repressive sites on the distal promoter resulting in reduced and calibrated promoter activity. Based on measurements of the mRNA concentrations of those factors in different
NASA Astrophysics Data System (ADS)
Hofer, Christoph; Papritz, Andreas
2011-10-01
The article describes the R-package constrainedKriging, a tool for spatial prediction problems that involve change of support. The package provides software for spatial interpolation by constrained (CK), covariance-matching constrained (CMCK), and customary universal (UK) kriging. CK and CMCK yield approximately unbiased predictions of nonlinear functionals of target quantities under change of support and are therefore an attractive alternative to conditional Gaussian simulations. The constrainedKriging package computes CK, CMCK, and UK predictions for points or blocks of arbitrary shape from data observed at points in a two-dimensional survey domain. Predictions are computed for a random process model that involves a nonstationary mean function (modeled by a linear regression) and a weakly stationary, isotropic covariance function (or variogram). CK, CMCK, and UK require the point-block and block-block averages of the covariance function if the prediction targets are blocks. The constrainedKriging package uses numerically efficient approximations to compute these averages. The article contains, apart from a brief summary of CK and CMCK, a detailed description of the algorithm used to compute the point-block and block-block covariances, and it describes the functionality of the software in detail. The practical use of the package is illustrated by a comparison of universal and constrained lognormal block kriging for the Meuse Bank heavy metal data set.
Active constrained clustering by examining spectral Eigenvectors
NASA Technical Reports Server (NTRS)
Wagstaff, Kiri L.; desJardins, Marie; Xu, Qianjun
2005-01-01
This work focuses on the active selection of pairwise constraints for spectral clustering. We develop and analyze a technique for Active Constrained Clustering by Examining Spectral eigenvectorS (ACCESS) derived from a similarity matrix.
Constrained density functional for noncollinear magnetism
NASA Astrophysics Data System (ADS)
Ma, Pui-Wai; Dudarev, S. L.
2015-02-01
Energies of arbitrary small- and large-angle noncollinear excited magnetic configurations are computed using a highly accurate constrained density functional theory approach. Numerical convergence and accuracy are controlled by the choice of Lagrange multipliers λI entering the constraining conditions. The penalty part Ep of the constrained energy functional at its minimum is shown to be inversely proportional to λI, enabling a simple, robust, and accurate iterative procedure to be followed to find a convergent solution. The method is implemented as a part of ab initio vasp package, and applied to the investigation of noncollinear B2-like and <001 > double-layer antiferromagnetic configurations of bcc iron, Fe2 dimer, and amorphous iron. Forces acting on atoms depend on the orientations of magnetic moments, and the proposed approach enables constrained self-consistent noncollinear magnetic and structural relaxation of large atomic systems to be carried out.
Active constrained clustering by examining spectral Eigenvectors
NASA Technical Reports Server (NTRS)
Wagstaff, Kiri L.; desJardins, Marie; Xu, Qianjun
2005-01-01
This work focuses on the active selection of pairwise constraints for spectral clustering. We develop and analyze a technique for Active Constrained Clustering by Examining Spectral eigenvectorS (ACCESS) derived from a similarity matrix.
Energetic Materials Optimization via Constrained Search
2015-06-01
ARL-TR-7304• JUN 2015 US Army Research Laboratory Energetic Materials Optimization via Constrained Search by Berend Christopher Rinderspacher...Army Research Laboratory Energetic Materials Optimization via Constrained Search by Berend Christopher Rinderspacher Weapons and Materials Research...burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching
On the Constrained Attitude Control Problem
NASA Technical Reports Server (NTRS)
Hadaegh, Fred Y.; Kim, Yoonsoo; Mesbahi, Mehran; Singh, Gurkipal
2004-01-01
In this paper, we consider various classes of constrained attitude control (CAC) problem in single and multiple spacecraft settings. After categorizing attitude constraints into four distinct types, we provide an overview of the existing approaches to this problem. We then proceed to further expand on a recent algorithmic approach to the CAC problem. The paper concludes with an example demonstrating the viability of the proposed algorithm for a multiple spacecraft constrained attitude reconfiguration scenario.
On the Constrained Attitude Control Problem
NASA Technical Reports Server (NTRS)
Hadaegh, Fred Y.; Kim, Yoonsoo; Mesbahi, Mehran; Singh, Gurkipal
2004-01-01
In this paper, we consider various classes of constrained attitude control (CAC) problem in single and multiple spacecraft settings. After categorizing attitude constraints into four distinct types, we provide an overview of the existing approaches to this problem. We then proceed to further expand on a recent algorithmic approach to the CAC problem. The paper concludes with an example demonstrating the viability of the proposed algorithm for a multiple spacecraft constrained attitude reconfiguration scenario.
Shared developmental programme strongly constrains beak shape diversity in songbirds.
Fritz, Joerg A; Brancale, Joseph; Tokita, Masayoshi; Burns, Kevin J; Hawkins, M Brent; Abzhanov, Arhat; Brenner, Michael P
2014-04-16
The striking diversity of bird beak shapes is an outcome of natural selection, yet the relative importance of the limitations imposed by the process of beak development on generating such variation is unclear. Untangling these factors requires mapping developmental mechanisms over a phylogeny far exceeding model systems studied thus far. We address this issue with a comparative morphometric analysis of beak shape in a diverse group of songbirds. Here we show that the dynamics of the proliferative growth zone must follow restrictive rules to explain the observed variation, with beak diversity constrained to a three parameter family of shapes, parameterized by length, depth and the degree of shear. We experimentally verify these predictions by analysing cell proliferation in the developing embryonic beaks of the zebra finch. Our findings indicate that beak shape variability in many songbirds is strongly constrained by shared properties of the developmental programme controlling the growth zone.
An algorithm for mass matrix calculation of internally constrained molecular geometries.
Aryanpour, Masoud; Dhanda, Abhishek; Pitsch, Heinz
2008-01-28
Dynamic models for molecular systems require the determination of corresponding mass matrix. For constrained geometries, these computations are often not trivial but need special considerations. Here, assembling the mass matrix of internally constrained molecular structures is formulated as an optimization problem. Analytical expressions are derived for the solution of the different possible cases depending on the rank of the constraint matrix. Geometrical interpretations are further used to enhance the solution concept. As an application, we evaluate the mass matrix for a constrained molecule undergoing an electron-transfer reaction. The preexponential factor for this reaction is computed based on the harmonic model.
Outcome and complications of constrained acetabular components.
Yang, Cao; Goodman, Stuart B
2009-02-01
Constrained acetabular liners were developed for the surgical treatment of recurrent instability by holding the femoral head captive within the socket. This article summarizes the data describing constrained component designs, indications, outcome, and complications. Different designs accept head sizes of varying diameter and have differing amounts of rim elevation and offset, allowing slight variations in the range of movement allowed. Complications of constrained acetabular components can be divided into three categories. The first category is directly related to the constraining mechanism such as dislocation, head dissociation from the stem, liner dissociation from the acetabular device, and impingement with or without locking ring breakage. The second category is related to increased constraint such as aseptic component loosening and osteolysis and periprosthetic fracture. The third category includes those cases not associated with increased constraint such as infection, deep vein thrombosis, and periprosthetic fracture. This device is effective at achieving hip stability, but the complications related to the constraining mechanism and increased constraint are of concern. These devices should be used as a salvage measure for the treatment of severe instability.
Groundwater availability as constrained by hydrogeology and environmental flows.
Watson, Katelyn A; Mayer, Alex S; Reeves, Howard W
2014-01-01
Groundwater pumping from aquifers in hydraulic connection with nearby streams has the potential to cause adverse impacts by decreasing flows to levels below those necessary to maintain aquatic ecosystems. The recent passage of the Great Lakes-St. Lawrence River Basin Water Resources Compact has brought attention to this issue in the Great Lakes region. In particular, the legislation requires the Great Lakes states to enact measures for limiting water withdrawals that can cause adverse ecosystem impacts. This study explores how both hydrogeologic and environmental flow limitations may constrain groundwater availability in the Great Lakes Basin. A methodology for calculating maximum allowable pumping rates is presented. Groundwater availability across the basin may be constrained by a combination of hydrogeologic yield and environmental flow limitations varying over both local and regional scales. The results are sensitive to factors such as pumping time, regional and local hydrogeology, streambed conductance, and streamflow depletion limits. Understanding how these restrictions constrain groundwater usage and which hydrogeologic characteristics and spatial variables have the most influence on potential streamflow depletions has important water resources policy and management implications. © 2013, National Ground Water Association.
Groundwater availability as constrained by hydrogeology and environmental flows
Watson, Katelyn A.; Mayer, Alex S.; Reeves, Howard W.
2014-01-01
Groundwater pumping from aquifers in hydraulic connection with nearby streams has the potential to cause adverse impacts by decreasing flows to levels below those necessary to maintain aquatic ecosystems. The recent passage of the Great Lakes-St. Lawrence River Basin Water Resources Compact has brought attention to this issue in the Great Lakes region. In particular, the legislation requires the Great Lakes states to enact measures for limiting water withdrawals that can cause adverse ecosystem impacts. This study explores how both hydrogeologic and environmental flow limitations may constrain groundwater availability in the Great Lakes Basin. A methodology for calculating maximum allowable pumping rates is presented. Groundwater availability across the basin may be constrained by a combination of hydrogeologic yield and environmental flow limitations varying over both local and regional scales. The results are sensitive to factors such as pumping time, regional and local hydrogeology, streambed conductance, and streamflow depletion limits. Understanding how these restrictions constrain groundwater usage and which hydrogeologic characteristics and spatial variables have the most influence on potential streamflow depletions has important water resources policy and management implications.
Constraining weak annihilation using semileptonic D decays
Ligeti, Zoltan; Luke, Michael; Manohar, Aneesh V.
2010-08-01
The recently measured semileptonic D{sub s} decay rate can be used to constrain weak annihilation (WA) effects in semileptonic D and B decays. We revisit the theoretical predictions for inclusive semileptonic D{sub (s)} decays using a variety of quark mass schemes. The most reliable results are obtained if the fits to B decay distributions are used to eliminate the charm quark mass dependence, without using any specific charm mass scheme. Our fit to the available data shows that WA is smaller than commonly assumed. There is no indication that the WA octet contribution (which is better constrained than the singlet contribution) dominates. The results constrain an important source of uncertainty in the extraction of |V{sub ub}| from inclusive semileptonic B decays.
Liang Enwei; Yi Shuangxi; Lue Houjun; Zhang Jin; Zhang Binbin; Zhang Bing E-mail: zhang@physics.unlv.ed
2010-12-20
The onset of gamma-ray burst (GRB) afterglow is characterized by a smooth bump in the early afterglow light curve as the GRB fireball is decelerated by the circumburst medium. We extensively search for GRBs with such an onset feature in their optical and X-ray light curves from the literature and from the catalog established with the Swift/XRT. Twenty optically selected GRBs and 12 X-ray-selected GRBs are obtained, among which 17 optically selected and 2 X-ray-selected GRBs have redshift measurements. We fit these light curves with a smooth broken power law and measure the width (w), rising timescale (t{sub r}), and decaying timescale (t{sub d}) at full width at half-maximum. Strong mutual correlations among these timescales and with the peak time (t{sub p}) are found. The ratio t{sub r}/t{sub d} is almost universal among bursts, but the ratio t{sub r}/t{sub p} varies from 0.3 to {approx}1. The optical peak luminosity in the R band (L{sub R,p}) is anti-correlated with t{sub p} and w in the burst frame, indicating a dimmer and broader bump peaking at a later time. The isotropic prompt gamma-ray energy (E{sub {gamma},iso}) is also tightly correlated with L{sub R,p} and t{sub p} in the burst frame. Assuming that the bumps signal the deceleration of the GRB fireballs in a constant density medium, we calculate the initial Lorentz factor ({Gamma}{sub 0}) and the deceleration radius (R{sub d}) of the GRBs with redshift measurements. The derived {Gamma}{sub 0} is typically a few hundreds, and the deceleration radius is R{sub dec} {approx} 2 x 10{sup 17} cm. More intriguingly, a tight correlation between {Gamma}{sub 0} and E{sub {gamma},iso} is found, namely {Gamma}{sub 0} {approx_equal} 182(E{sub {gamma},iso}/10{sup 52} erg){sup 0.25}. This correlation also applies to the small sample of GRBs which show the signature of the afterglow onset in their X-ray afterglow, and to two bursts (GRBs 990123 and 080319B) whose early optical emission is dominated by a reverse shock. The
Pattern Search Methods for Linearly Constrained Minimization
NASA Technical Reports Server (NTRS)
Lewis, Robert Michael; Torczon, Virginia
1998-01-01
We extend pattern search methods to linearly constrained minimization. We develop a general class of feasible point pattern search algorithms and prove global convergence to a Karush-Kuhn-Tucker point. As in the case of unconstrained minimization, pattern search methods for linearly constrained problems accomplish this without explicit recourse to the gradient or the directional derivative. Key to the analysis of the algorithms is the way in which the local search patterns conform to the geometry of the boundary of the feasible region.
Spacecraft inertia estimation via constrained least squares
NASA Technical Reports Server (NTRS)
Keim, Jason A.; Acikmese, Behcet A.; Shields, Joel F.
2006-01-01
This paper presents a new formulation for spacecraft inertia estimation from test data. Specifically, the inertia estimation problem is formulated as a constrained least squares minimization problem with explicit bounds on the inertia matrix incorporated as LMIs [linear matrix inequalities). The resulting minimization problem is a semidefinite optimization that can be solved efficiently with guaranteed convergence to the global optimum by readily available algorithms. This method is applied to data collected from a robotic testbed consisting of a freely rotating body. The results show that the constrained least squares approach produces more accurate estimates of the inertia matrix than standard unconstrained least squares estimation methods.
Spacecraft inertia estimation via constrained least squares
NASA Technical Reports Server (NTRS)
Keim, Jason A.; Acikmese, Behcet A.; Shields, Joel F.
2006-01-01
This paper presents a new formulation for spacecraft inertia estimation from test data. Specifically, the inertia estimation problem is formulated as a constrained least squares minimization problem with explicit bounds on the inertia matrix incorporated as LMIs [linear matrix inequalities). The resulting minimization problem is a semidefinite optimization that can be solved efficiently with guaranteed convergence to the global optimum by readily available algorithms. This method is applied to data collected from a robotic testbed consisting of a freely rotating body. The results show that the constrained least squares approach produces more accurate estimates of the inertia matrix than standard unconstrained least squares estimation methods.
Pattern Search Algorithms for Bound Constrained Minimization
NASA Technical Reports Server (NTRS)
Lewis, Robert Michael; Torczon, Virginia
1996-01-01
We present a convergence theory for pattern search methods for solving bound constrained nonlinear programs. The analysis relies on the abstract structure of pattern search methods and an understanding of how the pattern interacts with the bound constraints. This analysis makes it possible to develop pattern search methods for bound constrained problems while only slightly restricting the flexibility present in pattern search methods for unconstrained problems. We prove global convergence despite the fact that pattern search methods do not have explicit information concerning the gradient and its projection onto the feasible region and consequently are unable to enforce explicitly a notion of sufficient feasible decrease.
Constrained tri-sphere kinematic positioning system
Viola, Robert J
2010-12-14
A scalable and adaptable, six-degree-of-freedom, kinematic positioning system is described. The system can position objects supported on top of, or suspended from, jacks comprising constrained joints. The system is compatible with extreme low temperature or high vacuum environments. When constant adjustment is not required a removable motor unit is available.
Constrained superfields from inflation to reheating
NASA Astrophysics Data System (ADS)
Dalianis, Ioannis; Farakos, Fotis
2017-10-01
We construct effective supergravity theories from customized constrained superfields which provide a setup consistent both for the description of inflation and the subsequent reheating processes. These theories contain the minimum degrees of freedom in the bosonic sector required for single-field inflation.
A Model for Optimal Constrained Adaptive Testing.
ERIC Educational Resources Information Center
van der Linden, Wim J.; Reese, Lynda M.
1998-01-01
Proposes a model for constrained computerized adaptive testing in which the information in the test at the trait level (theta) estimate is maximized subject to the number of possible constraints on the content of the test. Test assembly relies on a linear-programming approach. Illustrates the approach through simulation with items from the Law…
Rhythmic Grouping Biases Constrain Infant Statistical Learning
ERIC Educational Resources Information Center
Hay, Jessica F.; Saffran, Jenny R.
2012-01-01
Linguistic stress and sequential statistical cues to word boundaries interact during speech segmentation in infancy. However, little is known about how the different acoustic components of stress constrain statistical learning. The current studies were designed to investigate whether intensity and duration each function independently as cues to…
Automation of constrained-value business forms
Carson, M.L.; Beaumariage, T.G.; Greitzer, F.L.
1993-05-01
Expert systems can improve many business tasks. However, the nature of a constrained-value business form can result in a rule base that contains circular reasoning, unsuitable for expert system implementation. A methodology is presented for restructuring such a rule base for compatibility with a backward-chaining expert system.
Constrained Subjective Assessment of Student Learning
ERIC Educational Resources Information Center
Saliu, Sokol
2005-01-01
Student learning is a complex incremental cognitive process; assessment needs to parallel this, reporting the results in similar terms. Application of fuzzy sets and logic to the criterion-referenced assessment of student learning is considered here. The constrained qualitative assessment (CQA) system was designed, and then applied in assessing a…
Constrained Subjective Assessment of Student Learning
ERIC Educational Resources Information Center
Saliu, Sokol
2005-01-01
Student learning is a complex incremental cognitive process; assessment needs to parallel this, reporting the results in similar terms. Application of fuzzy sets and logic to the criterion-referenced assessment of student learning is considered here. The constrained qualitative assessment (CQA) system was designed, and then applied in assessing a…
How We Can Constrain Aerosol Type Globally
NASA Technical Reports Server (NTRS)
Kahn, Ralph
2016-01-01
In addition to aerosol number concentration, aerosol size and composition are essential attributes needed to adequately represent aerosol-cloud interactions (ACI) in models. As the nature of ACI varies enormously with environmental conditions, global-scale constraints on particle properties are indicated. And although advanced satellite remote-sensing instruments can provide categorical aerosol-type classification globally, detailed particle microphysical properties are unobtainable from space with currently available or planned technologies. For the foreseeable future, only in situ measurements can constrain particle properties at the level-of-detail required for ACI, as well as to reduce uncertainties in regional-to-global-scale direct aerosol radiative forcing (DARF). The limitation of in situ measurements for this application is sampling. However, there is a simplifying factor: for a given aerosol source, in a given season, particle microphysical properties tend to be repeatable, even if the amount varies from day-to-day and year-to-year, because the physical nature of the particles is determined primarily by the regional environment. So, if the PDFs of particle properties from major aerosol sources can be adequately characterized, they can be used to add the missing microphysical detail the better sampled satellite aerosol-type maps. This calls for Systematic Aircraft Measurements to Characterize Aerosol Air Masses (SAM-CAAM). We are defining a relatively modest and readily deployable, operational aircraft payload capable of measuring key aerosol absorption, scattering, and chemical properties in situ, and a program for characterizing statistically these properties for the major aerosol air mass types, at a level-of-detail unobtainable from space. It is aimed at: (1) enhancing satellite aerosol-type retrieval products with better aerosol climatology assumptions, and (2) improving the translation between satellite-retrieved aerosol optical properties and
Constrained target controllability of complex networks
NASA Astrophysics Data System (ADS)
Guo, Wei-Feng; Zhang, Shao-Wu; Wei, Ze-Gang; Zeng, Tao; Liu, Fei; Zhang, Jingsong; Wu, Fang-Xiang; Chen, Luonan
2017-06-01
It is of great theoretical interest and practical significance to study how to control a system by applying perturbations to only a few driver nodes. Recently, a hot topic of modern network researches is how to determine driver nodes that allow the control of an entire network. However, in practice, to control a complex network, especially a biological network, one may know not only the set of nodes which need to be controlled (i.e. target nodes), but also the set of nodes to which only control signals can be applied (i.e. constrained control nodes). Compared to the general concept of controllability, we introduce the concept of constrained target controllability (CTC) of complex networks, which concerns the ability to drive any state of target nodes to their desirable state by applying control signals to the driver nodes from the set of constrained control nodes. To efficiently investigate the CTC of complex networks, we further design a novel graph-theoretic algorithm called CTCA to estimate the ability of a given network to control targets by choosing driver nodes from the set of constrained control nodes. We extensively evaluate the CTC of numerous real complex networks. The results indicate that biological networks with a higher average degree are easier to control than biological networks with a lower average degree, while electronic networks with a lower average degree are easier to control than web networks with a higher average degree. We also show that our CTCA can more efficiently produce driver nodes for target-controlling the networks than existing state-of-the-art methods. Moreover, we use our CTCA to analyze two expert-curated bio-molecular networks and compare to other state-of-the-art methods. The results illustrate that our CTCA can efficiently identify proven drug targets and new potentials, according to the constrained controllability of those biological networks.
Vibration control of cylindrical shells using active constrained layer damping
NASA Astrophysics Data System (ADS)
Ray, Manas C.; Chen, Tung-Huei; Baz, Amr M.
1997-05-01
The fundamentals of controlling the structural vibration of cylindrical shells treated with active constrained layer damping (ACLD) treatments are presented. The effectiveness of the ACLD treatments in enhancing the damping characteristics of thin cylindrical shells is demonstrated theoretically and experimentally. A finite element model (FEM) is developed to describe the dynamic interaction between the shells and the ACLD treatments. The FEM is used to predict the natural frequencies and the modal loss factors of shells which are partially treated with patches of the ACLD treatments. The predictions of the FEM are validated experimentally using stainless steel cylinders which are 20.32 cm in diameter, 30.4 cm in length and 0.05 cm in thickness. The cylinders are treated with ACLD patches of different configurations in order to target single or multi-modes of lobar vibrations. The ACLD patches used are made of DYAD 606 visco-elastic layer which is sandwiched between two layers of PVDF piezo-electric films. Vibration attenuations of 85% are obtained with maximum control voltage of 40 volts. Such attenuations are attributed to the effectiveness of the ACLD treatment in increasing the modal damping ratios by about a factor of four over those of conventional passive constrained layer damping (PCLD) treatments. The obtained results suggest the potential of the ACLD treatments in controlling the vibration of cylindrical shells which constitute the major building block of many critical structures such as cabins of aircrafts, hulls of submarines and bodies of rockets and missiles.
CONSTRAINED SPECTRAL CLUSTERING FOR IMAGE SEGMENTATION
Sourati, Jamshid; Brooks, Dana H.; Dy, Jennifer G.; Erdogmus, Deniz
2013-01-01
Constrained spectral clustering with affinity propagation in its original form is not practical for large scale problems like image segmentation. In this paper we employ novelty selection sub-sampling strategy, besides using efficient numerical eigen-decomposition methods to make this algorithm work efficiently for images. In addition, entropy-based active learning is also employed to select the queries posed to the user more wisely in an interactive image segmentation framework. We evaluate the algorithm on general and medical images to show that the segmentation results will improve using constrained clustering even if one works with a subset of pixels. Furthermore, this happens more efficiently when pixels to be labeled are selected actively. PMID:24466500
Constraining the Braneworld with Gravitational Wave Observations
McWilliams, Sean T.
2010-04-09
Some braneworld models may have observable consequences that, if detected, would validate a requisite element of string theory. In the infinite Randall-Sundrum model (RS2), the AdS radius of curvature, l, of the extra dimension supports a single bound state of the massless graviton on the brane, thereby reproducing Newtonian gravity in the weak-field limit. However, using the AdS/CFT correspondence, it has been suggested that one possible consequence of RS2 is an enormous increase in Hawking radiation emitted by black holes. We utilize this possibility to derive two novel methods for constraining l via gravitational wave measurements. We show that the EMRI event rate detected by LISA can constrain l at the {approx}1 {mu}m level for optimal cases, while the observation of a single galactic black hole binary with LISA results in an optimal constraint of l{<=}5 {mu}m.
Constraining the braneworld with gravitational wave observations.
McWilliams, Sean T
2010-04-09
Some braneworld models may have observable consequences that, if detected, would validate a requisite element of string theory. In the infinite Randall-Sundrum model (RS2), the AdS radius of curvature, l, of the extra dimension supports a single bound state of the massless graviton on the brane, thereby reproducing Newtonian gravity in the weak-field limit. However, using the AdS/CFT correspondence, it has been suggested that one possible consequence of RS2 is an enormous increase in Hawking radiation emitted by black holes. We utilize this possibility to derive two novel methods for constraining l via gravitational wave measurements. We show that the EMRI event rate detected by LISA can constrain l at the approximately 1 microm level for optimal cases, while the observation of a single galactic black hole binary with LISA results in an optimal constraint of l < or = 5 microm.
Constraining the Braneworld with Gravitational Wave Observations
NASA Technical Reports Server (NTRS)
McWilliams, Sean T.
2011-01-01
Some braneworld models may have observable consequences that, if detected, would validate a requisite element of string theory. In the infinite Randall-Sundrum model (RS2), the AdS radius of curvature, L, of the extra dimension supports a single bound state of the massless graviton on the brane, thereby reproducing Newtonian gravity in the weak-field limit. However, using the AdS/CFT correspondence, it has been suggested that one possible consequence of RS2 is an enormous increase in Hawking radiation emitted by black holes. We utilize this possibility to derive two novel methods for constraining L via gravitational wave measurements. We show that the EMRI event rate detected by LISA can constrain L at the approximately 1 micron level for optimal cases, while the observation of a single galactic black hole binary with LISA results in an optimal constraint of L less than or equal to 5 microns.
Compilation for critically constrained knowledge bases
Schrag, R.
1996-12-31
We show that many {open_quotes}critically constrained{close_quotes} Random 3SAT knowledge bases (KBs) can be compiled into disjunctive normal form easily by using a variant of the {open_quotes}Davis-Putnam{close_quotes} proof procedure. From these compiled KBs we can answer all queries about entailment of conjunctive normal formulas, also easily - compared to a {open_quotes}brute-force{close_quotes} approach to approximate knowledge compilation into unit clauses for the same KBs. We exploit this fact to develop an aggressive hybrid approach which attempts to compile a KB exactly until a given resource limit is reached, then falls back to approximate compilation into unit clauses. The resulting approach handles all of the critically constrained Random 3SAT KBs with average savings of an order of magnitude over the brute-force approach.
Cosmogenic photons strongly constrain UHECR source models
NASA Astrophysics Data System (ADS)
van Vliet, Arjen
2017-03-01
With the newest version of our Monte Carlo code for ultra-high-energy cosmic ray (UHECR) propagation, CRPropa 3, the flux of neutrinos and photons due to interactions of UHECRs with extragalactic background light can be predicted. Together with the recently updated data for the isotropic diffuse gamma-ray background (IGRB) by Fermi LAT, it is now possible to severely constrain UHECR source models. The evolution of the UHECR sources especially plays an important role in the determination of the expected secondary photon spectrum. Pure proton UHECR models are already strongly constrained, primarily by the highest energy bins of Fermi LAT's IGRB, as long as their number density is not strongly peaked at recent times.
The totally constrained model: three quantization approaches
NASA Astrophysics Data System (ADS)
Gambini, Rodolfo; Olmedo, Javier
2014-08-01
We provide a detailed comparison of the different approaches available for the quantization of a totally constrained system with a constraint algebra generating the non-compact group. In particular, we consider three schemes: the Refined Algebraic Quantization, the Master Constraint Programme and the Uniform Discretizations approach. For the latter, we provide a quantum description where we identify semiclassical sectors of the kinematical Hilbert space. We study the quantum dynamics of the system in order to show that it is compatible with the classical continuum evolution. Among these quantization approaches, the Uniform Discretizations provides the simpler description in agreement with the classical theory of this particular model, and it is expected to give new insights about the quantum dynamics of more realistic totally constrained models such as canonical general relativity.
Constraining SUSY GUTs and Inflation with Cosmology
Rocher, Jonathan
2006-11-03
In the framework of Supersymmetric Grand Unified Theories (SUSY GUTs), the universe undergoes a cascade of symmetry breakings, during which topological defects can be formed. We address the question of the probability of cosmic string formation after a phase of hybrid inflation within a large number of models of SUSY GUTs in agreement with particle and cosmological data. We show that cosmic strings are extremely generic and should be used to relate cosmology and high energy physics. This conclusion is employed together with the WMAP CMB data to strongly constrain SUSY hybrid inflation models. F-term and D-term inflation are studied in the SUSY and minimal SUGRA framework. They are both found to agree with data but suffer from fine tuning of their superpotential coupling ({lambda} (less-or-similar sign) 3 x 10-5 or less). Mass scales of inflation are also constrained to be less than M < or approx. 3 x 1015 GeV.
Constraining Neutron Star Matter with Quantum Chromodynamics
NASA Astrophysics Data System (ADS)
Kurkela, Aleksi; Fraga, Eduardo S.; Schaffner-Bielich, Jürgen; Vuorinen, Aleksi
2014-07-01
In recent years, there have been several successful attempts to constrain the equation of state of neutron star matter using input from low-energy nuclear physics and observational data. We demonstrate that significant further restrictions can be placed by additionally requiring the pressure to approach that of deconfined quark matter at high densities. Remarkably, the new constraints turn out to be highly insensitive to the amount—or even presence—of quark matter inside the stars.
On the path integral of constrained systems
Muslih, Sami I.
2004-10-04
Constrained Hamiltonian systems are investigated by using Gueler's method. Integration of a set of equations of motion and the action function is discussed. It is shown that the canonical path integral quantization is obtained directly as an integration over the canonical phase-space coordinates without any need to enlarge the initial phase-space by introducing extra- unphysical variables as in the Batalin-Fradkin-Tyutin (BFT) method. The abelian Proca model is analyzed by the two methods.
Constraining neutron star matter with quantum chromodynamics
Kurkela, Aleksi; Fraga, Eduardo S.; Schaffner-Bielich, Jürgen; Vuorinen, Aleksi
2014-07-10
In recent years, there have been several successful attempts to constrain the equation of state of neutron star matter using input from low-energy nuclear physics and observational data. We demonstrate that significant further restrictions can be placed by additionally requiring the pressure to approach that of deconfined quark matter at high densities. Remarkably, the new constraints turn out to be highly insensitive to the amount—or even presence—of quark matter inside the stars.
Constraining neutrino decays with CMBR data
NASA Astrophysics Data System (ADS)
Hannestad, Steen
1998-07-01
The decay of massive neutrinos to final states containing only invisible particles is poorly constrained experimentally. In this letter we describe the constraints that can be put on neutrino mass and lifetime using CMBR measurements. We find that very tight lifetime limits on neutrinos in the mass range 10 eV - 100 keV can be derived using CMBR data from upcoming satellite measurements.
Synthesis of constrained analogues of tryptophan
Negrato, Marco; Abbiati, Giorgio; Dell’Acqua, Monica
2015-01-01
Summary A Lewis acid-catalysed diastereoselective [4 + 2] cycloaddition of vinylindoles and methyl 2-acetamidoacrylate, leading to methyl 3-acetamido-1,2,3,4-tetrahydrocarbazole-3-carboxylate derivatives, is described. Treatment of the obtained cycloadducts under hydrolytic conditions results in the preparation of a small library of compounds bearing the free amino acid function at C-3 and pertaining to the class of constrained tryptophan analogues. PMID:26664620
Constrained Implants in Total Knee Replacement.
Touzopoulos, Panagiotis; Drosos, Georgios I; Ververidis, Athanasios; Kazakos, Konstantinos
2015-05-01
Total knee replacement (TKR) is a successful procedure for pain relief and functional restoration in patients with advanced osteoarthritis. The number of TKRs is increasing, and this has led to an increase in revision surgeries. The key to long-term success in both primary and revision TKR is stability, as well as adequate and stable fixation between components and underlying bone. In the vast majority of primary TKRs and in some revision cases, a posterior cruciate retaining or a posterior cruciate substituting device can be used. In some primary cases with severe deformity or ligamentous instability and in most of the revision cases, a more constrained implant is required. The purpose of this paper is to review the literature concerning the use of condylar constrained knee (CCK) and rotating hinge (RH) implants in primary and revision cases focusing on the indications and results. According to this review, although excellent and very good results have been reported, there are limitations of the existing literature concerning the indications for the use of constrained implants, the absence of long-term results, and the limited comparative studies.
Constrained and joint inversion on unstructured meshes
NASA Astrophysics Data System (ADS)
Doetsch, J.; Jordi, C.; Rieckh, V.; Guenther, T.; Schmelzbach, C.
2015-12-01
Unstructured meshes allow for inclusion of arbitrary surface topography, complex acquisition geometry and undulating geological interfaces in the inversion of geophysical data. This flexibility opens new opportunities for coupling different geophysical and hydrological data sets in constrained and joint inversions. For example, incorporating geological interfaces that have been derived from high-resolution geophysical data (e.g., ground penetrating radar) can add geological constraints to inversions of electrical resistivity data. These constraints can be critical for a hydrogeological interpretation of the inversion results. For time-lapse inversions of geophysical data, constraints can be derived from hydrological point measurements in boreholes, but it is difficult to include these hard constraints in the inversion of electrical resistivity monitoring data. Especially mesh density and the regularization footprint around the hydrological point measurements are important for an improved inversion compared to the unconstrained case. With the help of synthetic and field examples, we analyze how regularization and coupling operators should be chosen for time-lapse inversions constrained by point measurements and for joint inversions of geophysical data in order to take full advantage of the flexibility of unstructured meshes. For the case of constraining to point measurements, it is important to choose a regularization operator that extends beyond the neighboring cells and the uncertainty in the point measurements needs to be accounted for. For joint inversion, the choice of the regularization depends on the expected subsurface heterogeneity and the cell size of the parameter mesh.
An English language interface for constrained domains
NASA Technical Reports Server (NTRS)
Page, Brenda J.
1989-01-01
The Multi-Satellite Operations Control Center (MSOCC) Jargon Interpreter (MJI) demonstrates an English language interface for a constrained domain. A constrained domain is defined as one with a small and well delineated set of actions and objects. The set of actions chosen for the MJI is from the domain of MSOCC Applications Executive (MAE) Systems Test and Operations Language (STOL) directives and contains directives for signing a cathode ray tube (CRT) on or off, calling up or clearing a display page, starting or stopping a procedure, and controlling history recording. The set of objects chosen consists of CRTs, display pages, STOL procedures, and history files. Translation from English sentences to STOL directives is done in two phases. In the first phase, an augmented transition net (ATN) parser and dictionary are used for determining grammatically correct parsings of input sentences. In the second phase, grammatically typed sentences are submitted to a forward-chaining rule-based system for interpretation and translation into equivalent MAE STOL directives. Tests of the MJI show that it is able to translate individual clearly stated sentences into the subset of directives selected for the prototype. This approach to an English language interface may be used for similarly constrained situations by modifying the MJI's dictionary and rules to reflect the change of domain.
Constrained inversion of seismo-volcanic events
NASA Astrophysics Data System (ADS)
Nocerino, Luciano; D'Auria, Luca; Giudicepietro, Flora; Martini, Marcello
2014-05-01
The inversion of seismo-volcanic events is performed to retrieve the source geometry and to determine volumetric budgets of the source. Such observations have shown to be an important tool for the seismological monitoring of volcanoes. We developed a novel technique for the non-linear constrained inversion of low frequency seismo-volcanic events. Unconstrained linear inversion methods work well when a dense network of broadband seismometers is available. We propose a new constrained inversion technique, which has shown to be efficient also in a reduced network configuration and a low signal-noise ratio. The waveform inversion is performed in the frequency domain, constraining the source mechanism during the event to vary only in its magnitude. The eigenvectors orientation and the eigenvalue ratio are kept constant. This significantly reduces the number of parameters to invert, making the procedure more stable. The method has been tested over a synthetic dataset, reproducing realistic very-long-period (VLP) signals Stromboli volcano. We have applied the method to a VLP dataset recorded on Stromboli volcano and to low-frequency earthquakes recorded on Mt.Vesuvius.
Constraining the North Pacific carbon sink: biological and physical processes
NASA Astrophysics Data System (ADS)
Ayers, J.; Lozier, M.
2010-12-01
The transition zone region of the North Pacific is a notably large sink for atmospheric carbon dioxide on a mean annual basis, though seasonally the region varies between strong wintertime uptake and weak summertime outgassing. Because the direction of air-sea carbon flux is effectively set by the sea surface pCO2, we seek to identify and quantify those processes most responsible for its variability in this region. While changes in temperature, salinity, dissolved inorganic carbon, and alkalinity are all factors that impact sea surface pCO2 on a seasonal basis, on a mean annual basis the region must be maintained as a sink by processes that remove carbon from surface waters: biological drawdown as well as the result of advection/mixing. In this work we constrain the quantitative contribution of each of these processes throughout an annual cycle. The least constrained of these processes is the biological pump, which we estimate in two independent ways: bottom-up, using satellite data-based primary productivity models coupled with export estimates from literature; and top-down, by determining what the biological pump would need to be to maintain the observed sea surface pCO2 values in the region, given our estimates of all the other regulatory processes.
21 CFR 888.3780 - Wrist joint polymer constrained prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Wrist joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3780 Wrist joint polymer constrained prosthesis. (a) Identification. A wrist joint polymer constrained prosthesis is a device made...
21 CFR 888.3720 - Toe joint polymer constrained prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Toe joint polymer constrained prosthesis. 888.3720... (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3720 Toe joint polymer constrained prosthesis. (a) Identification. A toe joint polymer constrained prosthesis is a device made of...
21 CFR 888.3720 - Toe joint polymer constrained prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Toe joint polymer constrained prosthesis. 888.3720... (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3720 Toe joint polymer constrained prosthesis. (a) Identification. A toe joint polymer constrained prosthesis is a device made of...
21 CFR 888.3230 - Finger joint polymer constrained prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Finger joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3230 Finger joint polymer constrained prosthesis. (a) Identification. A finger joint polymer constrained prosthesis is a device...
21 CFR 888.3780 - Wrist joint polymer constrained prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Wrist joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3780 Wrist joint polymer constrained prosthesis. (a) Identification. A wrist joint polymer constrained prosthesis is a device made...
21 CFR 888.3230 - Finger joint polymer constrained prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Finger joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3230 Finger joint polymer constrained prosthesis. (a) Identification. A finger joint polymer constrained prosthesis is a device...
21 CFR 888.3720 - Toe joint polymer constrained prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Toe joint polymer constrained prosthesis. 888.3720... (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3720 Toe joint polymer constrained prosthesis. (a) Identification. A toe joint polymer constrained prosthesis is a device made of silicone...
21 CFR 888.3780 - Wrist joint polymer constrained prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Wrist joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3780 Wrist joint polymer constrained prosthesis. (a) Identification. A wrist joint polymer constrained prosthesis is a device made of...
21 CFR 888.3780 - Wrist joint polymer constrained prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Wrist joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3780 Wrist joint polymer constrained prosthesis. (a) Identification. A wrist joint polymer constrained prosthesis is a device made of...
21 CFR 888.3780 - Wrist joint polymer constrained prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Wrist joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3780 Wrist joint polymer constrained prosthesis. (a) Identification. A wrist joint polymer constrained prosthesis is a device made of...
21 CFR 888.3720 - Toe joint polymer constrained prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Toe joint polymer constrained prosthesis. 888.3720... (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3720 Toe joint polymer constrained prosthesis. (a) Identification. A toe joint polymer constrained prosthesis is a device made of silicone...
21 CFR 888.3720 - Toe joint polymer constrained prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Toe joint polymer constrained prosthesis. 888.3720... (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3720 Toe joint polymer constrained prosthesis. (a) Identification. A toe joint polymer constrained prosthesis is a device made of silicone...
21 CFR 888.3230 - Finger joint polymer constrained prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Finger joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3230 Finger joint polymer constrained prosthesis. (a) Identification. A finger joint polymer constrained prosthesis is a device intended...
21 CFR 888.3230 - Finger joint polymer constrained prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Finger joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3230 Finger joint polymer constrained prosthesis. (a) Identification. A finger joint polymer constrained prosthesis is a device intended...
21 CFR 888.3230 - Finger joint polymer constrained prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Finger joint polymer constrained prosthesis. 888... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3230 Finger joint polymer constrained prosthesis. (a) Identification. A finger joint polymer constrained prosthesis is a device intended...
2010-01-01
Background The peroxisome proliferator activated receptor (PPAR) subgroup of the nuclear hormone receptor superfamily is activated by a variety of natural and synthetic ligands. PPARs can heterodimerize with retinoid X receptors, which have homology to other members of the nuclear receptor superfamily. Ligand binding to PPAR/RXRs results in recruitment of transcriptional coactivator proteins such as steroid receptor coactivator 1 (SRC-1) and CREB binding protein (CBP). Both SRC-1 and CBP are histone acetyltransferases, which by modifying nucleosomal histones, produce more open chromatin structure and increase transcriptional activity. Nuclear hormone receptors can recruit limiting amounts of coactivators from other transcription factor binding sites such as AP-1, thereby inhibiting the activity of AP-1 target genes. PPAR and RXR ligands have been used in experimental breast cancer therapy. The role of coactivator expression in mammary tumorigenesis and response to drug therapy has been the subject of recent studies. Methods We examined the effects of loss of SRC-1 on MMTV-neu mediated mammary tumorigenesis. Results SRC-1 null mutation in mammary tumor prone mice increased the tumor latency period, reduced tumor proliferation index and metastasis, inhibited response to PPAR and RXR ligands, and induced genes involved in mammary gland differentiation. We also examined human breast cancer cell lines overexpressing SRC-1 or CBP. Coactivator overexpression increased cellular proliferation with resistance to PPAR and RXR ligands and remodeled chromatin of the proximal epidermal growth factor receptor promoter. Conclusions These results indicate that histone acetyltransferases play key roles in mammary tumorigenesis and response to anti-proliferative therapies. PMID:21080969
NASA Technical Reports Server (NTRS)
Williams, Brian; Hudson, Nicolas; Tweddle, Brent; Brockers, Roland; Matthies, Larry
2011-01-01
A Feature and Pose Constrained Extended Kalman Filter (FPC-EKF) is developed for highly dynamic computationally constrained micro aerial vehicles. Vehicle localization is achieved using only a low performance inertial measurement unit and a single camera. The FPC-EKF framework augments the vehicle's state with both previous vehicle poses and critical environmental features, including vertical edges. This filter framework efficiently incorporates measurements from hundreds of opportunistic visual features to constrain the motion estimate, while allowing navigating and sustained tracking with respect to a few persistent features. In addition, vertical features in the environment are opportunistically used to provide global attitude references. Accurate pose estimation is demonstrated on a sequence including fast traversing, where visual features enter and exit the field-of-view quickly, as well as hover and ingress maneuvers where drift free navigation is achieved with respect to the environment.
Constrained inflaton due to a complex scalar
Budhi, Romy H. S.; Kashiwase, Shoichi; Suematsu, Daijiro
2015-09-14
We reexamine inflation due to a constrained inflaton in the model of a complex scalar. Inflaton evolves along a spiral-like valley of special scalar potential in the scalar field space just like single field inflation. Sub-Planckian inflaton can induce sufficient e-foldings because of a long slow-roll path. In a special limit, the scalar spectral index and the tensor-to-scalar ratio has equivalent expressions to the inflation with monomial potential φ{sup n}. The favorable values for them could be obtained by varying parameters in the potential. This model could be embedded in a certain radiative neutrino mass model.
Newton modified barrier method in constrained optimization
NASA Technical Reports Server (NTRS)
Polyak, R.
1990-01-01
In this paper, we develop and investigate the Newton method for solving constrained (non-smooth) optimization problems. This approach is based on the modified barrier functions (MBF) theory and on the global converging step-size version of the Newton method for smooth unconstrained optimization. Due to the excellent properties of the MBF near primal-dual solution, the Newton modified barrier method (NMBM) has a better rate of convergence, better complexity bound, and is much more stable in the final stage of the computational process than the methods which are based on the classical barrier functions (CBF).
Incomplete Dirac reduction of constrained Hamiltonian systems
Chandre, C.
2015-10-15
First-class constraints constitute a potential obstacle to the computation of a Poisson bracket in Dirac’s theory of constrained Hamiltonian systems. Using the pseudoinverse instead of the inverse of the matrix defined by the Poisson brackets between the constraints, we show that a Dirac–Poisson bracket can be constructed, even if it corresponds to an incomplete reduction of the original Hamiltonian system. The uniqueness of Dirac brackets is discussed. The relevance of this procedure for infinite dimensional Hamiltonian systems is exemplified.
Quantization of soluble classical constrained systems
Belhadi, Z.; Menas, F.; Bérard, A.; Mohrbach, H.
2014-12-15
The derivation of the brackets among coordinates and momenta for classical constrained systems is a necessary step toward their quantization. Here we present a new approach for the determination of the classical brackets which does neither require Dirac’s formalism nor the symplectic method of Faddeev and Jackiw. This approach is based on the computation of the brackets between the constants of integration of the exact solutions of the equations of motion. From them all brackets of the dynamical variables of the system can be deduced in a straightforward way.
Constraining nucleon high momentum in nuclei
NASA Astrophysics Data System (ADS)
Yong, Gao-Chan
2017-02-01
Recent studies at Jefferson Lab show that there are a certain proportion of nucleons in nuclei have momenta greater than the so-called nuclear Fermi momentum pF. Based on the transport model of nucleus-nucleus collisions at intermediate energies, nucleon high momentum caused by the neutron-proton short-range correlations in nuclei is constrained by comparing with π and photon experimental data and considering some uncertainties. The high momentum cutoff value pmax ≤ 2pF is obtained.
ERIC Educational Resources Information Center
Cornish, Kim; Cole, Victoria; Longhi, Elena; Karmiloff-Smith, Annette; Scerif, Gaia
2012-01-01
Basic attentional processes and their impact on developmental trajectories in fragile X syndrome were assessed in a 3-year prospective study. Although fragile X syndrome is a monogenic X-linked disorder, there is striking variability in outcomes even in young boys with the condition. Attention is a key factor constraining interactions with the…
ERIC Educational Resources Information Center
Cornish, Kim; Cole, Victoria; Longhi, Elena; Karmiloff-Smith, Annette; Scerif, Gaia
2012-01-01
Basic attentional processes and their impact on developmental trajectories in fragile X syndrome were assessed in a 3-year prospective study. Although fragile X syndrome is a monogenic X-linked disorder, there is striking variability in outcomes even in young boys with the condition. Attention is a key factor constraining interactions with the…
Intersecting transcription networks constrain gene regulatory evolution
Sorrells, Trevor R; Booth, Lauren N; Tuch, Brian B; Johnson, Alexander D
2015-01-01
Epistasis—the non-additive interactions between different genetic loci—constrains evolutionary pathways, blocking some and permitting others1–8. For biological networks such as transcription circuits, the nature of these constraints and their consequences are largely unknown. Here we describe the evolutionary pathways of a transcription network that controls the response to mating pheromone in yeasts9. A component of this network, the transcription regulator Ste12, has evolved two different modes of binding to a set of its target genes. In one group of species, Ste12 binds to specific DNA binding sites, while in another lineage it occupies DNA indirectly, relying on a second transcription regulator to recognize DNA. We show, through the construction of various possible evolutionary intermediates, that evolution of the direct mode of DNA binding was not directly accessible to the ancestor. Instead, it was contingent on a lineage-specific change to an overlapping transcription network with a different function, the specification of cell type. These results show that analyzing and predicting the evolution of cis-regulatory regions requires an understanding of their positions in overlapping networks, as this placement constrains the available evolutionary pathways. PMID:26153861
Multiple Manifold Clustering Using Curvature Constrained Path
Babaeian, Amir; Bayestehtashk, Alireza; Bandarabadi, Mojtaba
2015-01-01
The problem of multiple surface clustering is a challenging task, particularly when the surfaces intersect. Available methods such as Isomap fail to capture the true shape of the surface near by the intersection and result in incorrect clustering. The Isomap algorithm uses shortest path between points. The main draw back of the shortest path algorithm is due to the lack of curvature constrained where causes to have a path between points on different surfaces. In this paper we tackle this problem by imposing a curvature constraint to the shortest path algorithm used in Isomap. The algorithm chooses several landmark nodes at random and then checks whether there is a curvature constrained path between each landmark node and every other node in the neighborhood graph. We build a binary feature vector for each point where each entry represents the connectivity of that point to a particular landmark. Then the binary feature vectors could be used as a input of conventional clustering algorithm such as hierarchical clustering. We apply our method to simulated and some real datasets and show, it performs comparably to the best methods such as K-manifold and spectral multi-manifold clustering. PMID:26375819
Constraining torsion with Gravity Probe B
Mao Yi; Guth, Alan H.; Cabi, Serkan; Tegmark, Max
2007-11-15
It is well-entrenched folklore that all torsion gravity theories predict observationally negligible torsion in the solar system, since torsion (if it exists) couples only to the intrinsic spin of elementary particles, not to rotational angular momentum. We argue that this assumption has a logical loophole which can and should be tested experimentally, and consider nonstandard torsion theories in which torsion can be generated by macroscopic rotating objects. In the spirit of action=reaction, if a rotating mass like a planet can generate torsion, then a gyroscope would be expected to feel torsion. An experiment with a gyroscope (without nuclear spin) such as Gravity Probe B (GPB) can test theories where this is the case. Using symmetry arguments, we show that to lowest order, any torsion field around a uniformly rotating spherical mass is determined by seven dimensionless parameters. These parameters effectively generalize the parametrized post-Newtonian formalism and provide a concrete framework for further testing Einstein's general theory of relativity (GR). We construct a parametrized Lagrangian that includes both standard torsion-free GR and Hayashi-Shirafuji maximal torsion gravity as special cases. We demonstrate that classic solar system tests rule out the latter and constrain two observable parameters. We show that Gravity Probe B is an ideal experiment for further constraining nonstandard torsion theories, and work out the most general torsion-induced precession of its gyroscope in terms of our torsion parameters.
Constraining the Mass of A Galaxy Cluster
NASA Astrophysics Data System (ADS)
Cemenenkoff, Nicholas; Rines, Kenneth J.; Geller, Margaret J.; Diaferio, Antonaldo
2017-01-01
Accurate cluster masses are critical for understanding dark matter and for using clusters to constrain cosmological parameters. We use the observed surface number density profile and velocity dispersion profile of galaxies in the Coma cluster to constrain its mass profile via Jeans analysis. In particular, we evaluate the robustness of the mass estimate M_200 by using different parametric forms for the distribution of mass and galaxies as well as different models of the orbital anisotropy parameter β (r) . Allowing for variation between the scale radii of the mass profile and the galaxy profile (i.e. relaxing the assumption that galaxies trace mass) does not significantly change the estimate of M 200 . We use a Bayesian approach to construct probability distribution functions of M 200, scale radius, and beta via Markov Chain Monte Carlo (MCMC) sampling. We apply this approach to ensemble clusters stacked by either their Sunyaev-Zel'dovich (SZ) signals or X-ray luminosities to measure the scaling relations of dynamical mass estimates with these mass proxies. Specifically, we test the hypothesis that the apparent deficit of SZ clusters (compared to predictions based on observations of the microwave background) can be explained by a bias of ˜ 60% in the normalization of the scaling relation between SZ signal and mass.
New General Tools for Constrained Geometry Optimizations.
De Vico, Luca; Olivucci, Massimo; Lindh, Roland
2005-09-01
A modification of the constrained geometry optimization method by Anglada and Bofill (Anglada, J. M.; Bofill, J. M. J. Comput. Chem. 1997, 18, 992-1003) is designed and implemented. The changes include the choice of projection, quasi-line-search, and the use of a Rational Function optimization approach rather than a reduced-restricted-quasi-Newton-Raphson method in the optimization step. Furthermore, we show how geometrical constrains can be implemented in an approach based on nonredundant curvilinear coordinates avoiding the inclusion of the constraints in the set of redundant coordinates used to define the internal coordinates. The behavior of the new implementation is demonstrated in geometry optimizations featuring single or multiple geometrical constraints (bond lengths, angles, etc.), optimizations on hyperspherical cross sections (as in the computation of steepest descent paths), and location of energy minima on the intersection subspace of two potential energy surfaces (i.e. minimum energy crossing points). In addition, a novel scheme to determine the crossing point geometrically nearest to a given molecular structure is proposed.
Constraining the halo mass function with observations
NASA Astrophysics Data System (ADS)
Castro, Tiago; Marra, Valerio; Quartin, Miguel
2016-12-01
The abundances of dark matter haloes in the universe are described by the halo mass function (HMF). It enters most cosmological analyses and parametrizes how the linear growth of primordial perturbations is connected to these abundances. Interestingly, this connection can be made approximately cosmology independent. This made it possible to map in detail its near-universal behaviour through large-scale simulations. However, such simulations may suffer from systematic effects, especially if baryonic physics is included. In this paper, we ask how well observations can constrain directly the HMF. The observables we consider are galaxy cluster number counts, galaxy cluster power spectrum and lensing of Type Ia supernovae. Our results show that Dark Energy Survey is capable of putting the first meaningful constraints on the HMF, while both Euclid and J-PAS (Javalambre-Physics of the Accelerated Universe Astrophysical Survey) can give stronger constraints, comparable to the ones from state-of-the-art simulations. We also find that an independent measurement of cluster masses is even more important for measuring the HMF than for constraining the cosmological parameters, and can vastly improve the determination of the HMF. Measuring the HMF could thus be used to cross-check simulations and their implementation of baryon physics. It could even, if deviations cannot be accounted for, hint at new physics.
Regular Language Constrained Sequence Alignment Revisited
NASA Astrophysics Data System (ADS)
Kucherov, Gregory; Pinhas, Tamar; Ziv-Ukelson, Michal
Imposing constraints in the form of a finite automaton or a regular expression is an effective way to incorporate additional a priori knowledge into sequence alignment procedures. With this motivation, Arslan [1] introduced the Regular Language Constrained Sequence Alignment Problem and proposed an O(n 2 t 4) time and O(n 2 t 2) space algorithm for solving it, where n is the length of the input strings and t is the number of states in the non-deterministic automaton, which is given as input. Chung et al. [2] proposed a faster O(n 2 t 3) time algorithm for the same problem. In this paper, we further speed up the algorithms for Regular Language Constrained Sequence Alignment by reducing their worst case time complexity bound to O(n 2 t 3/logt). This is done by establishing an optimal bound on the size of Straight-Line Programs solving the maxima computation subproblem of the basic dynamic programming algorithm. We also study another solution based on a Steiner Tree computation. While it does not improve the run time complexity in the worst case, our simulations show that both approaches are efficient in practice, especially when the input automata are dense.
Glassy dynamics of kinetically constrained models
NASA Astrophysics Data System (ADS)
Ritort, F.; Sollich, P.
2003-06-01
We review the use of kinetically constrained models (KCMs) for the study of dynamics in glassy systems. The characteristic feature of KCMs is that they have trivial, often non-interacting, equilibrium behaviour but interesting slow dynamics due to restrictions on the allowed transitions between configurations. The basic question which KCMs ask is therefore how much glassy physics can be understood without an underlying 'equilibrium glass transition'. After a brief review of glassy phenomenology, we describe the main model classes, which include spin-facilitated (Ising) models, constrained lattice gases, models inspired by cellular structures such as soap froths, models obtained via mappings from interacting systems without constraints, and finally related models such as urn, oscillator, tiling and needle models. We then describe the broad range of techniques that have been applied to KCMs, including exact solutions, adiabatic approximations, projection and mode-coupling techniques, diagrammatic approaches and mappings to quantum systems or effective models. Finally, we give a survey of the known results for the dynamics of KCMs both in and out of equilibrium, including topics such as relaxation time divergences and dynamical transitions, nonlinear relaxation, ageing and effective temperatures, cooperativity and dynamical heterogeneities, and finally non-equilibrium stationary states generated by external driving. We conclude with a discussion of open questions and possibilities for future work.
Physically constrained maximum likelihood mode filtering.
Papp, Joseph C; Preisig, James C; Morozov, Andrey K
2010-04-01
Mode filtering is most commonly implemented using the sampled mode shapes or pseudoinverse algorithms. Buck et al. [J. Acoust. Soc. Am. 103, 1813-1824 (1998)] placed these techniques in the context of a broader maximum a posteriori (MAP) framework. However, the MAP algorithm requires that the signal and noise statistics be known a priori. Adaptive array processing algorithms are candidates for improving performance without the need for a priori signal and noise statistics. A variant of the physically constrained, maximum likelihood (PCML) algorithm [A. L. Kraay and A. B. Baggeroer, IEEE Trans. Signal Process. 55, 4048-4063 (2007)] is developed for mode filtering that achieves the same performance as the MAP mode filter yet does not need a priori knowledge of the signal and noise statistics. The central innovation of this adaptive mode filter is that the received signal's sample covariance matrix, as estimated by the algorithm, is constrained to be that which can be physically realized given a modal propagation model and an appropriate noise model. Shallow water simulation results are presented showing the benefit of using the PCML method in adaptive mode filtering.
The Constrained Crystallization of Nylon-6
NASA Astrophysics Data System (ADS)
Mohan, Anushree; Tonelli, Alan
2008-10-01
Non-covalently bonded crystalline inclusion compounds (ICs) have been formed by threading host cyclic starches, cyclodextrins (CDs) onto guest nylon 6 (N6) chains. When excess N6 is employed, non-stoichiometric (n-s)-N6-CD-ICs with partially uncovered and dangling N6 chains result. While the crystalline CD lattice is stable to ˜300 C, the uncovered and dangling, yet constrained, N6 chains may crystallize below or, as shown below, be molten above ˜225 C. We have been studying the constrained crystallization of the dangling N6 chains in (n-S)-N6-CD-ICs, with comparison to bulk N6 samples, as a function of N6 molecular weights, lengths of uncovered N6 chains, and the CD host used. In the IC channels formed with host α- and γ-CDs containing 6 and 8 glucose units, respectively, single and pairs of side-by-side N6 chains are threaded and included. In the α-CD-ICs the ˜ 0.5 nm channels are separated by ˜ 1.4 nm, while in γ-CD-ICs the ˜ 1 nm channels are ˜ 1.7 nm apart, with each γ-CD channel including 2 N6 chains. N6 chains in the bulk and in the dense (n-s)-N6-CD-IC brushes show distinctly different kinetic and thermodynamic crystallization behaviors.
Stall Recovery Guidance Algorithms Based on Constrained Control Approaches
NASA Technical Reports Server (NTRS)
Stepanyan, Vahram; Krishnakumar, Kalmanje; Kaneshige, John; Acosta, Diana
2016-01-01
Aircraft loss-of-control, in particular approach to stall or fully developed stall, is a major factor contributing to aircraft safety risks, which emphasizes the need to develop algorithms that are capable of assisting the pilots to identify the problem and providing guidance to recover the aircraft. In this paper we present several stall recovery guidance algorithms, which are implemented in the background without interfering with flight control system and altering the pilot's actions. They are using input and state constrained control methods to generate guidance signals, which are provided to the pilot in the form of visual cues. It is the pilot's decision to follow these signals. The algorithms are validated in the pilot-in-the loop medium fidelity simulation experiment.
A directionally constrained adaptive array with phase-only control
NASA Astrophysics Data System (ADS)
Kikuma, N.; Takao, K.
1985-05-01
An adaptive antenna array system with phase-only control and under the principle of DCMP (directionally constrained minimization of power) is discussed. A new penalty function is introduced for the system in order to take into consideration the protection of the desired signal while minimizing the unwanted interference and/or noise. Because of the analytical limitation, computer simulation experiments are extensively carried out. The constraint coefficient that is the most important factor of the penalty function is especially investigated, and the optimum choice is given. It is also shown that the theoretical consideration leads to the same value. Finally, the quantization of phaseshifters is attempted, and the limit of its performance is shown.
A constrained EM algorithm for principal component analysis.
Ahn, Jong-Hoon; Oh, Jong-Hoon
2003-01-01
We propose a constrained EM algorithm for principal component analysis (PCA) using a coupled probability model derived from single-standard factor analysis models with isotropic noise structure. The single probabilistic PCA, especially for the case where there is no noise, can find only a vector set that is a linear superposition of principal components and requires postprocessing, such as diagonalization of symmetric matrices. By contrast, the proposed algorithm finds the actual principal components, which are sorted in descending order of eigenvalue size and require no additional calculation or postprocessing. The method is easily applied to kernel PCA. It is also shown that the new EM algorithm is derived from a generalized least-squares formulation.
Constraining omega and bias from the Stromlo-APM survey
Loveday, J.
1995-05-01
Galaxy redshift surveys provide a distorted picture of the universe due to the non-Hubble component of galaxy motions. By measuring such distortions in the linear regime one can constrain the quantity {beta} = {Omega}{sup 0.6} where {Omega} is the cosmological density parameter and b is the (linear) bias factor for optically-selected galaxies. In this paper we estimate {beta} from the Stromlo-APM redshift survey by comparing the amplitude of the direction-averaged redshift space correlation function to the real space correlation function. We find a 95% confidence upper limit of {beta} = 0.75, with a `best estimate` of {beta} {approx} 0.48. A bias parameter b {approx} 2 is thus required if {Omega} {equivalent_to} 1. However, higher-order correlations measured from the APM galaxy survey indicate a low value for the bias parameter b {approx} 1, requiring that Q {approx_lt} 0.6.
Nonlinear hyperspectral unmixing based on constrained multiple kernel NMF
NASA Astrophysics Data System (ADS)
Cui, Jiantao; Li, Xiaorun; Zhao, Liaoying
2014-05-01
Nonlinear spectral unmixing constitutes an important field of research for hyperspectral imagery. An unsupervised nonlinear spectral unmixing algorithm, namely multiple kernel constrained nonnegative matrix factorization (MKCNMF) is proposed by coupling multiple-kernel selection with kernel NMF. Additionally, a minimum endmemberwise distance constraint and an abundance smoothness constraint are introduced to alleviate the uniqueness problem of NMF in the algorithm. In the MKCNMF, two problems of optimizing matrices and selecting the proper kernel are jointly solved. The performance of the proposed unmixing algorithm is evaluated via experiments based on synthetic and real hyperspectral data sets. The experimental results demonstrate that the proposed method outperforms some existing unmixing algorithms in terms of spectral angle distance (SAD) and abundance fractions.
Constrained reverse diffusion for thick slice interpolation of 3D volumetric MRI images.
Neubert, Aleš; Salvado, Olivier; Acosta, Oscar; Bourgeat, Pierrick; Fripp, Jurgen
2012-03-01
Due to physical limitations inherent in magnetic resonance imaging scanners, three dimensional volumetric scans are often acquired with anisotropic voxel resolution. We investigate several interpolation approaches to reduce the anisotropy and present a novel approach - constrained reverse diffusion for thick slice interpolation. This technique was compared to common methods: linear and cubic B-Spline interpolation and a technique based on non-rigid registration of neighboring slices. The methods were evaluated on artificial MR phantoms and real MR scans of human brain. The constrained reverse diffusion approach delivered promising results and provides an alternative for thick slice interpolation, especially for higher anisotropy factors.
Disappearance and Creation of Constrained Amorphous Phase
NASA Astrophysics Data System (ADS)
Cebe, Peggy; Lu, Sharon X.
1997-03-01
We report observation of the disappearance and recreation of rigid, or constrained, amorphous phase by sequential thermal annealing. Tempera- ture modulated differential scanning calorimetry (MDSC) is used to study the glass transition and lower melting endotherm after annealing. Cold crystallization of poly(phenylene sulfide), PPS, at a temperature just above Tg creates an initial large fraction of rigid amorphous phase (RAP). Brief, rapid annealing to a higher temperature causes RAP almost to disappear completely. Subsequent reannealing at the original lower temperature restores RAP to its original value. At the same time that RAP is being removed, Tg decreases; when RAP is restored, Tg also returns to its initial value. The crystal fraction remains unaffected by the annealing sequence.
Printer model inversion by constrained optimization
NASA Astrophysics Data System (ADS)
Cholewo, Tomasz J.
1999-12-01
This paper describes a novel method for finding colorant amounts for which a printer will produce a requested color appearance based on constrained optimization. An error function defines the gamut mapping method and black replacement method. The constraints limit the feasible solution region to the device gamut and prevent exceeding the maximum total area coverage. Colorant values corresponding to in-gamut colors are found with precision limited only by the accuracy of the device model. Out-of- gamut colors are mapped to colors within the boundary of the device gamut. This general approach, used in conjunction with different types of color difference equations, can perform a wide range of out-of-gamut mappings such as chroma clipping or for finding colors on gamut boundary having specified properties. We present an application of this method to the creation of PostScript color rendering dictionaries and ICC profiles.
Constrained Aerothermodynamic Design of Hypersonic Vehicles
NASA Technical Reports Server (NTRS)
Gally, Tom; Campbell, Dick
2002-01-01
An investigation was conducted into possible methods of incorporating a hypersonic design capability with aerothermodynamic constraints into the CDISC aerodynamic design tool. The work was divided into two distinct phases: develop relations between surface curvature and hypersonic pressure coefficient which are compatible with CDISC's direct-iterative design method; and explore and implement possible methods of constraining the heat transfer rate over all or portions of the design surface. The main problem in implementing this method has been the weak relationship between surface shape and pressure coefficient at the stagnation point and the need to design around the surface blunt leading edge where there is a slope singularity. The final results show that some success has been achieved, but further improvements are needed.
Remote gaming on resource-constrained devices
NASA Astrophysics Data System (ADS)
Reza, Waazim; Kalva, Hari; Kaufman, Richard
2010-08-01
Games have become important applications on mobile devices. A mobile gaming approach known as remote gaming is being developed to support games on low cost mobile devices. In the remote gaming approach, the responsibility of rendering a game and advancing the game play is put on remote servers instead of the resource constrained mobile devices. The games rendered on the servers are encoded as video and streamed to mobile devices. Mobile devices gather user input and stream the commands back to the servers to advance game play. With this solution, mobile devices with video playback and network connectivity can become game consoles. In this paper we present the design and development of such a system and evaluate the performance and design considerations to maximize the end user gaming experience.
Constraining the Interior Earth Objects population
NASA Astrophysics Data System (ADS)
Fuentes, Cesar; Trilling, David E.; Knight, Matthew M.; Mommert, Michael; Hechenleitner, Federico
2016-10-01
Interior Earth Objects (IEOs) are among the least known populations in the Solar Sytem. Ground-based surveys are extremely inefficient in surveying them as most of the time IEOs are located inside the orbit of the Earth. We present observational constraints to the IEO population from STEREO (Solar TErrestrial RElations Observatory). This is the first result of searching through the archival STEREO data. Although after analyzing a year's worth of data we found no new IEOs, we observed hundreds of known asteroids. Our survey efficiency is computed with known and implanted synthetic objects, yielding a limiting magnitude of V~14.5. We constrain different IEO population models, yielding an upper limit for the total number of IEOs in line with previous estimates.
The asymptotics of large constrained graphs
NASA Astrophysics Data System (ADS)
Radin, Charles; Ren, Kui; Sadun, Lorenzo
2014-05-01
We show, through local estimates and simulation, that if one constrains simple graphs by their densities ɛ of edges and τ of triangles, then asymptotically (in the number of vertices) for over 95% of the possible range of those densities there is a well-defined typical graph, and it has a very simple structure: the vertices are decomposed into two subsets V1 and V2 of fixed relative size c and 1 - c, and there are well-defined probabilities of edges, gjk, between vj ∈ Vj, and vk ∈ Vk. Furthermore the four parameters c, g11, g22 and g12 are smooth functions of (ɛ, τ) except at two smooth ‘phase transition’ curves.
How alive is constrained SUSY really?
Bechtle, Philip; Desch, Klaus; Dreiner, Herbert K.; ...
2016-05-31
Constrained supersymmetric models like the CMSSM might look less attractive nowadays because of fine tuning arguments. They also might look less probable in terms of Bayesian statistics. The question how well the model under study describes the data, however, is answered by frequentist p-values. Thus, for the first time, we calculate a p-value for a supersymmetric model by performing dedicated global toy fits. We combine constraints from low-energy and astrophysical observables, Higgs boson mass and rate measurements as well as the non-observation of new physics in searches for supersymmetry at the LHC. Furthermore, using the framework Fittino, we perform globalmore » fits of the CMSSM to the toy data and find that this model is excluded at the 90% confidence level.« less
How alive is constrained SUSY really?
Bechtle, Philip; Desch, Klaus; Dreiner, Herbert K.; Hamer, Matthias; Kramer, Michael; O'Leary, Ben; Porod, Werner; Sarrazin, Bjorn; Stefaniak, Tim; Uhlenbrock, Mathias; Wienemann, Peter
2016-05-31
Constrained supersymmetric models like the CMSSM might look less attractive nowadays because of fine tuning arguments. They also might look less probable in terms of Bayesian statistics. The question how well the model under study describes the data, however, is answered by frequentist p-values. Thus, for the first time, we calculate a p-value for a supersymmetric model by performing dedicated global toy fits. We combine constraints from low-energy and astrophysical observables, Higgs boson mass and rate measurements as well as the non-observation of new physics in searches for supersymmetry at the LHC. Furthermore, using the framework Fittino, we perform global fits of the CMSSM to the toy data and find that this model is excluded at the 90% confidence level.
Spatially constrained propulsion in jumping archer fish
NASA Astrophysics Data System (ADS)
Mendelson, Leah; Techet, Alexandra
2016-11-01
Archer fish jump multiple body lengths out of the water for prey capture with impressive accuracy. Their remarkable aim is facilitated by jumping from a stationary position directly below the free surface. As a result of this starting position, rapid acceleration to a velocity sufficient for reaching the target occurs with only a body length to travel before the fish leaves the water. Three-dimensional measurements of jumping kinematics and volumetric velocimetry using Synthetic Aperture PIV highlight multiple strategies for such spatially constrained acceleration. Archer fish rapidly extend fins at jump onset to increase added mass forces and modulate their swimming kinematics to minimize wasted energy when the body is partially out of the water. Volumetric measurements also enable assessment of efficiency during a jump, which is crucial to understanding jumping's role as an energetically viable hunting strategy for the fish.
Sampling Motif-Constrained Ensembles of Networks
NASA Astrophysics Data System (ADS)
Fischer, Rico; Leitão, Jorge C.; Peixoto, Tiago P.; Altmann, Eduardo G.
2015-10-01
The statistical significance of network properties is conditioned on null models which satisfy specified properties but that are otherwise random. Exponential random graph models are a principled theoretical framework to generate such constrained ensembles, but which often fail in practice, either due to model inconsistency or due to the impossibility to sample networks from them. These problems affect the important case of networks with prescribed clustering coefficient or number of small connected subgraphs (motifs). In this Letter we use the Wang-Landau method to obtain a multicanonical sampling that overcomes both these problems. We sample, in polynomial time, networks with arbitrary degree sequences from ensembles with imposed motifs counts. Applying this method to social networks, we investigate the relation between transitivity and homophily, and we quantify the correlation between different types of motifs, finding that single motifs can explain up to 60% of the variation of motif profiles.
Fluctuation theorem for constrained equilibrium systems.
Gilbert, Thomas; Dorfman, J Robert
2006-02-01
We discuss the fluctuation properties of equilibrium chaotic systems with constraints such as isokinetic and Nosé-Hoover thermostats. Although the dynamics of these systems does not typically preserve phase-space volumes, the average phase-space contraction rate vanishes, so that the stationary states are smooth. Nevertheless, finite-time averages of the phase-space contraction rate have nontrivial fluctuations which we show satisfy a simple version of the Gallavotti-Cohen fluctuation theorem, complementary to the usual fluctuation theorem for nonequilibrium stationary states and appropriate to constrained equilibrium states. Moreover, we show that these fluctuations are distributed according to a Gaussian curve for long enough times. Three different systems are considered here: namely, (i) a fluid composed of particles interacting with Lennard-Jones potentials, (ii) a harmonic oscillator with Nosé-Hoover thermostatting, and (iii) a simple hyperbolic two-dimensional map.
Fluctuation theorem for constrained equilibrium systems
NASA Astrophysics Data System (ADS)
Gilbert, Thomas; Dorfman, J. Robert
2006-02-01
We discuss the fluctuation properties of equilibrium chaotic systems with constraints such as isokinetic and Nosé-Hoover thermostats. Although the dynamics of these systems does not typically preserve phase-space volumes, the average phase-space contraction rate vanishes, so that the stationary states are smooth. Nevertheless, finite-time averages of the phase-space contraction rate have nontrivial fluctuations which we show satisfy a simple version of the Gallavotti-Cohen fluctuation theorem, complementary to the usual fluctuation theorem for nonequilibrium stationary states and appropriate to constrained equilibrium states. Moreover, we show that these fluctuations are distributed according to a Gaussian curve for long enough times. Three different systems are considered here: namely, (i) a fluid composed of particles interacting with Lennard-Jones potentials, (ii) a harmonic oscillator with Nosé-Hoover thermostatting, and (iii) a simple hyperbolic two-dimensional map.
Statistical mechanics of budget-constrained auctions
NASA Astrophysics Data System (ADS)
Altarelli, F.; Braunstein, A.; Realpe-Gomez, J.; Zecchina, R.
2009-07-01
Finding the optimal assignment in budget-constrained auctions is a combinatorial optimization problem with many important applications, a notable example being in the sale of advertisement space by search engines (in this context the problem is often referred to as the off-line AdWords problem). On the basis of the cavity method of statistical mechanics, we introduce a message-passing algorithm that is capable of solving efficiently random instances of the problem extracted from a natural distribution, and we derive from its properties the phase diagram of the problem. As the control parameter (average value of the budgets) is varied, we find two phase transitions delimiting a region in which long-range correlations arise.
Perceived visual speed constrained by image segmentation
NASA Technical Reports Server (NTRS)
Verghese, P.; Stone, L. S.
1996-01-01
Little is known about how or where the visual system parses the visual scene into objects or surfaces. However, it is generally assumed that the segmentation and grouping of pieces of the image into discrete entities is due to 'later' processing stages, after the 'early' processing of the visual image by local mechanisms selective for attributes such as colour, orientation, depth, and motion. Speed perception is also thought to be mediated by early mechanisms tuned for speed. Here we show that manipulating the way in which an image is parsed changes the way in which local speed information is processed. Manipulations that cause multiple stimuli to appear as parts of a single patch degrade speed discrimination, whereas manipulations that perceptually divide a single large stimulus into parts improve discrimination. These results indicate that processes as early as speed perception may be constrained by the parsing of the visual image into discrete entities.
Constrained fits with non-Gaussian distributions
NASA Astrophysics Data System (ADS)
Frühwirth, R.; Cencic, O.
2016-10-01
Non-normally distributed data are ubiquitous in many areas of science, including high-energy physics. We present a general formalism for constrained fits, also called data reconciliation, with data that are not normally distributed. It is based on Bayesian reasoning and implemented via MCMC sampling. We show how systems of both linear and non-linear constraints can be efficiently treated. We also show how the fit can be made robust against outlying observations. The method is demonstrated on a couple of examples ranging from material flow analysis to the combination of non-normal measurements. Finally, we discuss possible applications in the field of event reconstruction, such as vertex fitting and kinematic fitting with non-normal track errors.
Explaining evolution via constrained persistent perfect phylogeny.
Bonizzoni, Paola; Carrieri, Anna Paola; Della Vedova, Gianluca; Trucco, Gabriella
2014-01-01
The perfect phylogeny is an often used model in phylogenetics since it provides an efficient basic procedure for representing the evolution of genomic binary characters in several frameworks, such as for example in haplotype inference. The model, which is conceptually the simplest, is based on the infinite sites assumption, that is no character can mutate more than once in the whole tree. A main open problem regarding the model is finding generalizations that retain the computational tractability of the original model but are more flexible in modeling biological data when the infinite site assumption is violated because of e.g. back mutations. A special case of back mutations that has been considered in the study of the evolution of protein domains (where a domain is acquired and then lost) is persistency, that is the fact that a character is allowed to return back to the ancestral state. In this model characters can be gained and lost at most once. In this paper we consider the computational problem of explaining binary data by the Persistent Perfect Phylogeny model (referred as PPP) and for this purpose we investigate the problem of reconstructing an evolution where some constraints are imposed on the paths of the tree. We define a natural generalization of the PPP problem obtained by requiring that for some pairs (character, species), neither the species nor any of its ancestors can have the character. In other words, some characters cannot be persistent for some species. This new problem is called Constrained PPP (CPPP). Based on a graph formulation of the CPPP problem, we are able to provide a polynomial time solution for the CPPP problem for matrices whose conflict graph has no edges. Using this result, we develop a parameterized algorithm for solving the CPPP problem where the parameter is the number of characters. A preliminary experimental analysis shows that the constrained persistent perfect phylogeny model allows to explain efficiently data that do not
Constraining Paleoearthquake Slip Distributions with Coral Microatolls
NASA Astrophysics Data System (ADS)
Lindsay, A.; McCloskey, J.; nic Bhloscaidh, M.; Murphy, S.
2014-12-01
Key to understanding the threat posed by large megathrust earthquakes is identifying where the potential for these destructive events exists. Studying extended sequences of earthquakes, Slip Deficit and Stress Evolution modelling techniques may hold the key to locating areas of concern. However, as well as using recent instrumentally constrained slip distributions they require the production of high resolution source models for pre-instrumental events. One place we can attempt this longer term modelling is along the Sunda Trench with its record of large megathrust earthquakes dating back centuries. Coral microatolls populating the intertidal areas of the Sumatran Forearc act as long-term geodetic recorders of tectonic activity. Repeated cycles of stress accumulation and release alter relative sea levels around these islands. Growth of corals, controlled by the level of the lowest tide, exploit interseismic rises in sea level. In turn, they experience die-offs when coseismic drops in sea level lead to subaerially exposure. Examination of coral stratigraphy reveals a history of displacements from which information of past earthquakes can be inferred. We have developed a Genetic Algorithm Slip Estimator (GASE) to rapidly produce high resolution slip distributions from coral displacement data. GASE recombines information held in populations of randomly generated slip distributions, to create superior models, satisfying observed displacements. Non-unique solutions require multiple iterations of the algorithm, producing a suite of models from which an ensemble slip distribution is drawn. Systematic testing of the algorithm demonstrates its ability to reliably estimate both known synthetic and instrumentally constrained slip distributions based on surface displacements. We will present high-resolution source models satisfying published displacement data for a number recent and paleoearthquakes along the Sunda trench, including the great 1797 and 1833 events.
A Path Algorithm for Constrained Estimation
Zhou, Hua; Lange, Kenneth
2013-01-01
Many least-square problems involve affine equality and inequality constraints. Although there are a variety of methods for solving such problems, most statisticians find constrained estimation challenging. The current article proposes a new path-following algorithm for quadratic programming that replaces hard constraints by what are called exact penalties. Similar penalties arise in l1 regularization in model selection. In the regularization setting, penalties encapsulate prior knowledge, and penalized parameter estimates represent a trade-off between the observed data and the prior knowledge. Classical penalty methods of optimization, such as the quadratic penalty method, solve a sequence of unconstrained problems that put greater and greater stress on meeting the constraints. In the limit as the penalty constant tends to ∞, one recovers the constrained solution. In the exact penalty method, squared penalties!are replaced by absolute value penalties, and the solution is recovered for a finite value of the penalty constant. The exact path-following method starts at the unconstrained solution and follows the solution path as the penalty constant increases. In the process, the solution path hits, slides along, and exits from the various constraints. Path following in Lasso penalized regression, in contrast, starts with a large value of the penalty constant and works its way downward. In both settings, inspection of the entire solution path is revealing. Just as with the Lasso and generalized Lasso, it is possible to plot the effective degrees of freedom along the solution path. For a strictly convex quadratic program, the exact penalty algorithm can be framed entirely in terms of the sweep operator of regression analysis. A few well-chosen examples illustrate the mechanics and potential of path following. This article has supplementary materials available online. PMID:24039382
Constrained sampling experiments reveal principles of detection in natural scenes.
Sebastian, Stephen; Abrams, Jared; Geisler, Wilson S
2017-07-11
A fundamental everyday visual task is to detect target objects within a background scene. Using relatively simple stimuli, vision science has identified several major factors that affect detection thresholds, including the luminance of the background, the contrast of the background, the spatial similarity of the background to the target, and uncertainty due to random variations in the properties of the background and in the amplitude of the target. Here we use an experimental approach based on constrained sampling from multidimensional histograms of natural stimuli, together with a theoretical analysis based on signal detection theory, to discover how these factors affect detection in natural scenes. We sorted a large collection of natural image backgrounds into multidimensional histograms, where each bin corresponds to a particular luminance, contrast, and similarity. Detection thresholds were measured for a subset of bins spanning the space, where a natural background was randomly sampled from a bin on each trial. In low-uncertainty conditions, both the background bin and the amplitude of the target were fixed, and, in high-uncertainty conditions, they varied randomly on each trial. We found that thresholds increase approximately linearly along all three dimensions and that detection accuracy is unaffected by background bin and target amplitude uncertainty. The results are predicted from first principles by a normalized matched-template detector, where the dynamic normalizing gain factor follows directly from the statistical properties of the natural backgrounds. The results provide an explanation for classic laws of psychophysics and their underlying neural mechanisms.
Constraining mantle properties using dynamic topography and gravity
NASA Astrophysics Data System (ADS)
Zhou, Q.; Chang, C.; Liu, L.
2016-12-01
Dynamic topography influences both the present-day continental elevation and its past evolution. However, both the mechanism and magnitude of dynamic topography are not entirely clear. This is because mantle dynamic properties, i.e. density and viscosity structures, the most important factors controlling dynamic topography, are uncertain. With the increasing resolution of seismic tomography, it is possible to better constrain the mantle density and viscosity structures and the associated dynamic topography by better matching gravity and landscape evolution. The recent high-resolution tomography images over the United States (U.S.) provide an ideal opportunity for constraining dynamic topography and its mantle origin. We compute the history of dynamic topography using time-dependent mantle convection models. We design a two-step procedure. First, we attempt to match the present-day gravity observations, in order to obtain a density structure that is consistent with gravity Second, we try to match the time-dependent dynamic topography with observational records, and use this process to place more constraints on mantle density and viscosity. We iteratively repeat procedure until our model can match both gravity and dynamic topography. Over the western U.S., we use proxies for surface vertical motion history as constraints for dynamic topography predictions. Over the eastern U.S., we use dynamic topography to force river evolution and compare the resulting drainage and sedimentation patterns with observation. Our preliminary results suggest that the Miocene-present uplift history of Sierra Nevada is due to the intrusion of the hot oceanic asthenosphere. The bowl-shaped Colorado Plateau topography reflects largely dynamic uplift due to eastward encroachment of the hot asthenosphere around the edge of the plateau. The good match between these predictions and observations suggest that the sub-lithospheric mantle density and viscosity structures are largely correct. More
Newton's method for large bound-constrained optimization problems.
Lin, C.-J.; More, J. J.; Mathematics and Computer Science
1999-01-01
We analyze a trust region version of Newton's method for bound-constrained problems. Our approach relies on the geometry of the feasible set, not on the particular representation in terms of constraints. The convergence theory holds for linearly constrained problems and yields global and superlinear convergence without assuming either strict complementarity or linear independence of the active constraints. We also show that the convergence theory leads to an efficient implementation for large bound-constrained problems.
Asynchronous parallel generating set search for linearly-constrained optimization.
Lewis, Robert Michael; Griffin, Joshua D.; Kolda, Tamara Gibson
2006-08-01
Generating set search (GSS) is a family of direct search methods that encompasses generalized pattern search and related methods. We describe an algorithm for asynchronous linearly-constrained GSS, which has some complexities that make it different from both the asynchronous bound-constrained case as well as the synchronous linearly-constrained case. The algorithm has been implemented in the APPSPACK software framework and we present results from an extensive numerical study using CUTEr test problems. We discuss the results, both positive and negative, and conclude that GSS is a reliable method for solving small-to-medium sized linearly-constrained optimization problems without derivatives.
Resource Management in Constrained Dynamic Situations
NASA Astrophysics Data System (ADS)
Seok, Jinwoo
Resource management is considered in this dissertation for systems with limited resources, possibly combined with other system constraints, in unpredictably dynamic environments. Resources may represent fuel, power, capabilities, energy, and so on. Resource management is important for many practical systems; usually, resources are limited, and their use must be optimized. Furthermore, systems are often constrained, and constraints must be satisfied for safe operation. Simplistic resource management can result in poor use of resources and failure of the system. Furthermore, many real-world situations involve dynamic environments. Many traditional problems are formulated based on the assumptions of given probabilities or perfect knowledge of future events. However, in many cases, the future is completely unknown, and information on or probabilities about future events are not available. In other words, we operate in unpredictably dynamic situations. Thus, a method is needed to handle dynamic situations without knowledge of the future, but few formal methods have been developed to address them. Thus, the goal is to design resource management methods for constrained systems, with limited resources, in unpredictably dynamic environments. To this end, resource management is organized hierarchically into two levels: 1) planning, and 2) control. In the planning level, the set of tasks to be performed is scheduled based on limited resources to maximize resource usage in unpredictably dynamic environments. In the control level, the system controller is designed to follow the schedule by considering all the system constraints for safe and efficient operation. Consequently, this dissertation is mainly divided into two parts: 1) planning level design, based on finite state machines, and 2) control level methods, based on model predictive control. We define a recomposable restricted finite state machine to handle limited resource situations and unpredictably dynamic environments
Eulerian Formulation of Spatially Constrained Elastic Rods
NASA Astrophysics Data System (ADS)
Huynen, Alexandre
Slender elastic rods are ubiquitous in nature and technology. For a vast majority of applications, the rod deflection is restricted by an external constraint and a significant part of the elastic body is in contact with a stiff constraining surface. The research work presented in this doctoral dissertation formulates a computational model for the solution of elastic rods constrained inside or around frictionless tube-like surfaces. The segmentation strategy adopted to cope with this complex class of problems consists in sequencing the global problem into, comparatively simpler, elementary problems either in continuous contact with the constraint or contact-free between their extremities. Within the conventional Lagrangian formulation of elastic rods, this approach is however associated with two major drawbacks. First, the boundary conditions specifying the locations of the rod centerline at both extremities of each elementary problem lead to the establishment of isoperimetric constraints, i.e., integral constraints on the unknown length of the rod. Second, the assessment of the unilateral contact condition requires, in principle, the comparison of two curves parametrized by distinct curvilinear coordinates, viz. the rod centerline and the constraint axis. Both conspire to burden the computations associated with the method. To streamline the solution along the elementary problems and rationalize the assessment of the unilateral contact condition, the rod governing equations are reformulated within the Eulerian framework of the constraint. The methodical exploration of both types of elementary problems leads to specific formulations of the rod governing equations that stress the profound connection between the mechanics of the rod and the geometry of the constraint surface. The proposed Eulerian reformulation, which restates the rod local equilibrium in terms of the curvilinear coordinate associated with the constraint axis, describes the rod deformed configuration
Zeng, Sanyou; Jiao, Ruwang; Li, Changhe; Li, Xi; Alkasassbeh, Jawdat S
2017-09-01
A novel multiobjective technique is proposed for solving constrained optimization problems (COPs) in this paper. The method highlights three different perspectives: 1) a COP is converted into an equivalent dynamic constrained multiobjective optimization problem (DCMOP) with three objectives: a) the original objective; b) a constraint-violation objective; and c) a niche-count objective; 2) a method of gradually reducing the constraint boundary aims to handle the constraint difficulty; and 3) a method of gradually reducing the niche size aims to handle the multimodal difficulty. A general framework of the design of dynamic constrained multiobjective evolutionary algorithms is proposed for solving DCMOPs. Three popular types of multiobjective evolutionary algorithms, i.e., Pareto ranking-based, decomposition-based, and hype-volume indicator-based, are employed to instantiate the framework. The three instantiations are tested on two benchmark suites. Experimental results show that they perform better than or competitive to a set of state-of-the-art constraint optimizers, especially on problems with a large number of dimensions.
Explaining evolution via constrained persistent perfect phylogeny
2014-01-01
Background The perfect phylogeny is an often used model in phylogenetics since it provides an efficient basic procedure for representing the evolution of genomic binary characters in several frameworks, such as for example in haplotype inference. The model, which is conceptually the simplest, is based on the infinite sites assumption, that is no character can mutate more than once in the whole tree. A main open problem regarding the model is finding generalizations that retain the computational tractability of the original model but are more flexible in modeling biological data when the infinite site assumption is violated because of e.g. back mutations. A special case of back mutations that has been considered in the study of the evolution of protein domains (where a domain is acquired and then lost) is persistency, that is the fact that a character is allowed to return back to the ancestral state. In this model characters can be gained and lost at most once. In this paper we consider the computational problem of explaining binary data by the Persistent Perfect Phylogeny model (referred as PPP) and for this purpose we investigate the problem of reconstructing an evolution where some constraints are imposed on the paths of the tree. Results We define a natural generalization of the PPP problem obtained by requiring that for some pairs (character, species), neither the species nor any of its ancestors can have the character. In other words, some characters cannot be persistent for some species. This new problem is called Constrained PPP (CPPP). Based on a graph formulation of the CPPP problem, we are able to provide a polynomial time solution for the CPPP problem for matrices whose conflict graph has no edges. Using this result, we develop a parameterized algorithm for solving the CPPP problem where the parameter is the number of characters. Conclusions A preliminary experimental analysis shows that the constrained persistent perfect phylogeny model allows to
Constraining electromagnetic core-mantle coupling
NASA Astrophysics Data System (ADS)
Wicht, J.; Jault, D.
1999-02-01
Electromagnetic core-mantle coupling is one candidate for explaining length of day (LOD) variations on decadal time scales. This coupling has traditionally been calculated from models of core surface flow /U-->, but core flow inversions are not unique. Unfortunately, the main torque contribution depends on the toroidal part /∇×r-->Φ of the vector field (U-->Br), which is left undetermined by the radial induction equation that links core flows to magnetic field data under the frozen-flux hypothesis. (Br is the radial magnetic field at the core surface.) We have developed a new method that bypasses flow inversions. Using the vector field (U-->Br) directly, we estimate its toroidal part by imposing that (U-->Br) vanishes where Br=0. The calculation of the electromagnetic torque is also hindered by the uncertainty in the conductivity structure of the lower mantle. However, we conclude that the conductivity of the lower mantle has to be much larger than current estimates derived from diamond anvil cell experiments to make the electromagnetic torque significant. The region beneath Africa and the mid-Atlantic (where there is the most significant (Br=0) curve apart from the magnetic equator) is particularly important. Here, the field Φ is relatively well constrained, and this is the single region that contributes most to the torque. Following Holme [Holme, R., 1998a. Electromagnetic core-mantle coupling 1: explaining decadal changes in the length of day. Geophys. J. Int. (132) 167-180.], we show nevertheless that small changes to Φ suffice to recover the torque ΓLOD required to explain LOD variations provided that the lower mantle conductivity is high enough. We find a value similar to Holme [Holme, R., 1998b. Electromagnetic core-mantle coupling 2: probing deep mantle conductance. In: Gunis, M., Wysession, M.E., Knittel, E., Buffett, B.A. (Eds.), The Core-Mantle Boundary Region. AGU, pp. 139-151.] for the minimum conductance (108 S). However, we were not able to
Sequential unconstrained minimization algorithms for constrained optimization
NASA Astrophysics Data System (ADS)
Byrne, Charles
2008-02-01
The problem of minimizing a function f(x):RJ → R, subject to constraints on the vector variable x, occurs frequently in inverse problems. Even without constraints, finding a minimizer of f(x) may require iterative methods. We consider here a general class of iterative algorithms that find a solution to the constrained minimization problem as the limit of a sequence of vectors, each solving an unconstrained minimization problem. Our sequential unconstrained minimization algorithm (SUMMA) is an iterative procedure for constrained minimization. At the kth step we minimize the function G_k(x)=f(x)+g_k(x), to obtain xk. The auxiliary functions gk(x):D ⊆ RJ → R+ are nonnegative on the set D, each xk is assumed to lie within D, and the objective is to minimize the continuous function f:RJ → R over x in the set C=\\overline D , the closure of D. We assume that such minimizers exist, and denote one such by \\hat x . We assume that the functions gk(x) satisfy the inequalities 0\\leq g_k(x)\\leq G_{k-1}(x)-G_{k-1}(x^{k-1}), for k = 2, 3, .... Using this assumption, we show that the sequence {f(xk)} is decreasing and converges to f({\\hat x}) . If the restriction of f(x) to D has bounded level sets, which happens if \\hat x is unique and f(x) is closed, proper and convex, then the sequence {xk} is bounded, and f(x^*)=f({\\hat x}) , for any cluster point x*. Therefore, if \\hat x is unique, x^*={\\hat x} and \\{x^k\\}\\rightarrow {\\hat x} . When \\hat x is not unique, convergence can still be obtained, in particular cases. The SUMMA includes, as particular cases, the well-known barrier- and penalty-function methods, the simultaneous multiplicative algebraic reconstruction technique (SMART), the proximal minimization algorithm of Censor and Zenios, the entropic proximal methods of Teboulle, as well as certain cases of gradient descent and the Newton-Raphson method. The proof techniques used for SUMMA can be extended to obtain related results for the induced proximal
Unsymmetric ordering using a constrained Markowitz scheme
Amestoy, Patrick R.; Xiaoye S.; Pralet, Stephane
2005-01-18
We present a family of ordering algorithms that can be used as a preprocessing step prior to performing sparse LU factorization. The ordering algorithms simultaneously achieve the objectives of selecting numerically good pivots and preserving the sparsity. We describe the algorithmic properties and challenges in their implementation. By mixing the two objectives we show that we can reduce the amount of fill-in in the factors and reduce the number of numerical problems during factorization. On a set of large unsymmetric real problems, we obtained the median reductions of 12% in the factorization time, of 13% in the size of the LU factors, of 20% in the number of operations performed during the factorization phase, and of 11% in the memory needed by the multifrontal solver MA41-UNS. A byproduct of this ordering strategy is an incomplete LU-factored matrix that can be used as a preconditioner in an iterative solver.
Constraining the global bromomethane budget from carbon stable isotopes
NASA Astrophysics Data System (ADS)
Bahlmann, Enno; Wittmer, Julian; Greule, Markus; Zetzsch, Cornelius; Seifert, Richard; Keppler, Frank
2016-04-01
Despite intense research in the last two decades, the global bromomethane (CH3Br) budget remains unbalanced with the known sinks exceeding the known sources by about 25%. The reaction with OH is the largest sink for CH3Br. We have determined the kinetic isotope effects for the reactions of CH3Br with the OH and Cl radical in order to better constrain the global CH3Br budget from an isotopic perspective. The isotope fractionation experiments were performed at 20±1°C in a 3500 L Teflon smog-chamber with initial CH3Br mixing ratios of about 2 and 10 ppm and perflourohexane (25 ppb) as internal standard. Atomic chlorine (Cl) was generated via photolysis of molecular chlorine (Cl2) using a solar simulator with an actinic flux comparable to that of the sun in mid-summer in Germany. OH radicals were generated via the photolysis of ozone (O3) at 253.7 nm in the presence of water vapor (RH = 70%).The mixing ratios of CH3Br, and perflourohexane were monitored by GC-MS with a time resolution of 15 minutes throughout the experiments. From each experiment 10 to 15 sub samples were taken in regular time intervals for subsequent carbon isotope ratio determinations by GC-IRMS performed at two independent laboratories in parallel. We found a kinetic isotope effect (KIE) of 17.6±3.3‰ for the reaction of CH3Br with OH and a KIE of 9.8±1.4 ‰ for the reaction with Cl*. We used these fractionation factors along with new data on the isotopic composition of CH3Br in the troposphere (-34±7‰) and the surface ocean (-26±7‰) along with reported source signatures, to constrain the unknown source from an isotopic perspective. The largest uncertainty in estimating the isotopic composition of the unknown source arises from the soil sink. Microbial degradation in soils is the second largest sink and assigned with a large fractionation factors of about 50‰. However, field experiments revealed substantially smaller apparent fractionation factors ranging from 11 to 22‰. In addition
Pinel-Giroux, Fanny-Maud; de Guise, Jacques A.; Labelle, Hubert
2007-01-01
Sagittal curvatures of the spine can be assessed using the constrained or non-constrained Cobb techniques. However, there is no study that specifically compares these two techniques. The objective of this study is to assess the reproducibility and clinical relevance of the non-constrained Cobb technique (non-constrained limit vertebrae) compared to the constrained Cobb technique (constrained limit vertebrae). Standing sagittal radiographs of the spine of ten adolescents with idiopathic scoliosis, ten adolescents with spondylolisthesis and ten normal adolescents were selected. Thoracic kyphosis (TK) and lumbar lordosis (LL) were measured twice by three observers using both constrained and non-constrained Cobb techniques. Pearson’s correlation coefficients, as well as intra- and inter-observer intra-class correlation coefficients (ICC) were calculated. Inter-observer ICCs were similar for TK and LL with both techniques, ranging from 0.84 to 0.89. Intra-observer ICCs for both techniques were between 0.74 and 0.92 for TK, while they were between 0.87 and 0.97 for LL. The two techniques were highly correlated for the measurement of the TK (r = 0.96) and LL (r = 0.94). Computer-assisted assessment of the sagittal profile using the non-constrained Cobb technique provides excellent reproducibility. As opposed to the constrained Cobb technique, the non-constrained Cobb technique takes into account the variability in the level of transition between the TK and LL. However, adequate use of this technique requires accurate identification of the limit vertebrae in the thoracolumbar spine. Consequently, a computer-assisted technique is recommended when using the non-constrained Cobb technique. PMID:17426991
Constraining the Evolution of ZZ Ceti
NASA Technical Reports Server (NTRS)
Mukadam, Anjum S.; Kepler, S. O.; Winget, D. E.; Nather, R. E.; Kilic, M.; Mullally, F.; vonHippel, T.; Kleinman, S. J.; Nitta, A.; Guzik, J. A.
2003-01-01
We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213.13 s observed in ZZ Ceti drifts at a rate dP/dt 5 (5.5 plus or minus 1.9) x 10(exp -15) ss(sup -1), after correcting for proper motion. Our results are consistent with previous P values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is |P||P(raised dot)|greater than or equal to 1.2 Gyr, comparable to the theoretical cooling timescale for the star. Our current stability limit for the period 213.13 s is only slightly less than the present measurement for another DAV, G117-B15A, for the period 215.2 s, establishing this mode in ZZ Ceti as the second most stable optical clock known, comparable to atomic clocks and more stable than most pulsars. Constraining the cooling rate of ZZ Ceti aids theoretical evolutionary models and white dwarf cosmochronology. The drift rate of this clock is small enough that we can set interesting limits on reflex motion due to planetary companions.
Constrained Markovian Dynamics of Random Graphs
NASA Astrophysics Data System (ADS)
Coolen, A. C. C.; de Martino, A.; Annibale, A.
2009-09-01
We introduce a statistical mechanics formalism for the study of constrained graph evolution as a Markovian stochastic process, in analogy with that available for spin systems, deriving its basic properties and highlighting the role of the `mobility' (the number of allowed moves for any given graph). As an application of the general theory we analyze the properties of degree-preserving Markov chains based on elementary edge switchings. We give an exact yet simple formula for the mobility in terms of the graph's adjacency matrix and its spectrum. This formula allows us to define acceptance probabilities for edge switchings, such that the Markov chains become controlled Glauber-type detailed balance processes, designed to evolve to any required invariant measure (representing the asymptotic frequencies with which the allowed graphs are visited during the process). As a corollary we also derive a condition in terms of simple degree statistics, sufficient to guarantee that, in the limit where the number of nodes diverges, even for state-independent acceptance probabilities of proposed moves the invariant measure of the process will be uniform. We test our theory on synthetic graphs and on realistic larger graphs as studied in cellular biology, showing explicitly that, for instances where the simple edge swap dynamics fails to converge to the uniform measure, a suitably modified Markov chain instead generates the correct phase space sampling.
Constraining Simulated Photosynthesis with Fluorescence Observations
NASA Astrophysics Data System (ADS)
Baker, I. T.; Berry, J. A.; Lee, J.; Frankenberg, C.; Denning, S.
2012-12-01
The measurement of chlorophyll fluorescence from satellites is an emerging technology. To date, most applications have compared fluorescence to light use efficiency models of Gross Primary Productivity (GPP). A close correspondence between fluorescence and GPP has been found in these comparisons. Here, we 'go the other way' and calculate fluorescence using an enzyme kinetic photosynthesis model (the Simple Biosphere Model; SiB), and compare to spectral retrievals. We utilize multiple representations for model phenology as a sensitivity test, obtaining leaf area index (LAI) and fraction of photosynthetically active radiation absorbed (fPAR) from both MODIS-derived products as well as a prognostic model of LAI/fPAR based on growing season index (PGSI). We find that bidirectional reflectance distribution function (BRDF), canopy radiative transfer, and leaf-to-canopy scaling all contribute to variability in simulated fluorescence. We use our results to evaluate discrepancies between light use efficiency and enzyme kinetic models across latitudinal, vegetation and climatological gradients. Satellite retrievals of fluorescence will provide insight into photosynthetic process and constrain simulations of the carbon cycle across multiple spatiotemporal scales.
Constraining the oblateness of Kepler planets
Zhu, Wei; Huang, Chelsea X.; Zhou, George; Lin, D. N. C.
2014-11-20
We use Kepler short-cadence light curves to constrain the oblateness of planet candidates in the Kepler sample. The transits of rapidly rotating planets that are deformed in shape will lead to distortions in the ingress and egress of their light curves. We report the first tentative detection of an oblate planet outside the solar system, measuring an oblateness of 0.22{sub −0.11}{sup +0.11} for the 18 M{sub J} mass brown dwarf Kepler 39b (KOI 423.01). We also provide constraints on the oblateness of the planets (candidates) HAT-P-7b, KOI 686.01, and KOI 197.01 to be <0.067, <0.251, and <0.186, respectively. Using the Q' values from Jupiter and Saturn, we expect tidal synchronization for the spins of HAT-P-7b, KOI 686.01, and KOI 197.01, and for their rotational oblateness signatures to be undetectable in the current data. The potentially large oblateness of KOI 423.01 (Kepler 39b) suggests that the Q' value of the brown dwarf needs to be two orders of magnitude larger than that of the solar system gas giants to avoid being tidally spun down.
Proximity Navigation of Highly Constrained Spacecraft
NASA Technical Reports Server (NTRS)
Scarritt, S.; Swartwout, M.
2007-01-01
Bandit is a 3-kg automated spacecraft in development at Washington University in St. Louis. Bandit's primary mission is to demonstrate proximity navigation, including docking, around a 25-kg student-built host spacecraft. However, because of extreme constraints in mass, power and volume, traditional sensing and actuation methods are not available. In particular, Bandit carries only 8 fixed-magnitude cold-gas thrusters to control its 6 DOF motion. Bandit lacks true inertial sensing, and the ability to sense position relative to the host has error bounds that approach the size of the Bandit itself. Some of the navigation problems are addressed through an extremely robust, error-tolerant soft dock. In addition, we have identified a control methodology that performs well in this constrained environment: behavior-based velocity potential functions, which use a minimum-seeking method similar to Lyapunov functions. We have also adapted the discrete Kalman filter for use on Bandit for position estimation and have developed a similar measurement vs. propagation weighting algorithm for attitude estimation. This paper provides an overview of Bandit and describes the control and estimation approach. Results using our 6DOF flight simulator are provided, demonstrating that these methods show promise for flight use.
Optimization of input-constrained systems
NASA Astrophysics Data System (ADS)
Malki, Suleyman; Spaanenburg, Lambert
2009-05-01
The computational demands of algorithms are rapidly growing. The naive implementation uses extended doubleprecision floating-point numbers and has therefore extreme difficulties in maintaining real-time performance. For fixedpoint numbers, the value representation pushes in two directions (value range and step size) to set the applicationdependent word size. In the general case, checking all combinations of all different values on all system inputs will easily become computationally infeasible. Checking corner cases only helps to reduce the combinatorial explosion, as still checking for accuracy and precision to limit word size remains a considerable effort. A range of evolutionary techniques have been tried where the sheer size of the problem withstands an extensive search. When the value range can be limited, the problem becomes tractable and a constructive approach becomes feasible. We propose an approach that is reminiscent of the Quine-Mc.Cluskey logic minimization procedure. Next to the conjunctive search as popular in Boolean minimization, we investigate the disjunctive approach that starts from a presumed minimal word size. To eliminate the occurrence of anomalies, this still has to be checked for larger word sizes. The procedure has initially been implemented using Java and Matlab. We have applied the above procedure to feed-forward and to cellular neural networks (CNN) as typical examples of input-constrained systems. In the case of hole-filling by means of a CNN, we find that the 1461 different coefficient sets can be reduced to 360, each giving robust behaviour on 7-bits internal words.
Scheduling Aircraft Landings under Constrained Position Shifting
NASA Technical Reports Server (NTRS)
Balakrishnan, Hamsa; Chandran, Bala
2006-01-01
Optimal scheduling of airport runway operations can play an important role in improving the safety and efficiency of the National Airspace System (NAS). Methods that compute the optimal landing sequence and landing times of aircraft must accommodate practical issues that affect the implementation of the schedule. One such practical consideration, known as Constrained Position Shifting (CPS), is the restriction that each aircraft must land within a pre-specified number of positions of its place in the First-Come-First-Served (FCFS) sequence. We consider the problem of scheduling landings of aircraft in a CPS environment in order to maximize runway throughput (minimize the completion time of the landing sequence), subject to operational constraints such as FAA-specified minimum inter-arrival spacing restrictions, precedence relationships among aircraft that arise either from airline preferences or air traffic control procedures that prevent overtaking, and time windows (representing possible control actions) during which each aircraft landing can occur. We present a Dynamic Programming-based approach that scales linearly in the number of aircraft, and describe our computational experience with a prototype implementation on realistic data for Denver International Airport.
Joint Chance-Constrained Dynamic Programming
NASA Technical Reports Server (NTRS)
Ono, Masahiro; Kuwata, Yoshiaki; Balaram, J. Bob
2012-01-01
This paper presents a novel dynamic programming algorithm with a joint chance constraint, which explicitly bounds the risk of failure in order to maintain the state within a specified feasible region. A joint chance constraint cannot be handled by existing constrained dynamic programming approaches since their application is limited to constraints in the same form as the cost function, that is, an expectation over a sum of one-stage costs. We overcome this challenge by reformulating the joint chance constraint into a constraint on an expectation over a sum of indicator functions, which can be incorporated into the cost function by dualizing the optimization problem. As a result, the primal variables can be optimized by a standard dynamic programming, while the dual variable is optimized by a root-finding algorithm that converges exponentially. Error bounds on the primal and dual objective values are rigorously derived. We demonstrate the algorithm on a path planning problem, as well as an optimal control problem for Mars entry, descent and landing. The simulations are conducted using a real terrain data of Mars, with four million discrete states at each time step.
Distributed Constrained Optimization with Semicoordinate Transformations
NASA Technical Reports Server (NTRS)
Macready, William; Wolpert, David
2006-01-01
Recent work has shown how information theory extends conventional full-rationality game theory to allow bounded rational agents. The associated mathematical framework can be used to solve constrained optimization problems. This is done by translating the problem into an iterated game, where each agent controls a different variable of the problem, so that the joint probability distribution across the agents moves gives an expected value of the objective function. The dynamics of the agents is designed to minimize a Lagrangian function of that joint distribution. Here we illustrate how the updating of the Lagrange parameters in the Lagrangian is a form of automated annealing, which focuses the joint distribution more and more tightly about the joint moves that optimize the objective function. We then investigate the use of "semicoordinate" variable transformations. These separate the joint state of the agents from the variables of the optimization problem, with the two connected by an onto mapping. We present experiments illustrating the ability of such transformations to facilitate optimization. We focus on the special kind of transformation in which the statistically independent states of the agents induces a mixture distribution over the optimization variables. Computer experiment illustrate this for &sat constraint satisfaction problems and for unconstrained minimization of NK functions.
Constrained Graph Optimization: Interdiction and Preservation Problems
Schild, Aaron V
2012-07-30
The maximum flow, shortest path, and maximum matching problems are a set of basic graph problems that are critical in theoretical computer science and applications. Constrained graph optimization, a variation of these basic graph problems involving modification of the underlying graph, is equally important but sometimes significantly harder. In particular, one can explore these optimization problems with additional cost constraints. In the preservation case, the optimizer has a budget to preserve vertices or edges of a graph, preventing them from being deleted. The optimizer wants to find the best set of preserved edges/vertices in which the cost constraints are satisfied and the basic graph problems are optimized. For example, in shortest path preservation, the optimizer wants to find a set of edges/vertices within which the shortest path between two predetermined points is smallest. In interdiction problems, one deletes vertices or edges from the graph with a particular cost in order to impede the basic graph problems as much as possible (for example, delete edges/vertices to maximize the shortest path between two predetermined vertices). Applications of preservation problems include optimal road maintenance, power grid maintenance, and job scheduling, while interdiction problems are related to drug trafficking prevention, network stability assessment, and counterterrorism. Computational hardness results are presented, along with heuristic methods for approximating solutions to the matching interdiction problem. Also, efficient algorithms are presented for special cases of graphs, including on planar graphs. The graphs in many of the listed applications are planar, so these algorithms have important practical implications.
Flexible constrained de Finetti reductions and applications
NASA Astrophysics Data System (ADS)
Lancien, Cécilia; Winter, Andreas
2017-09-01
De Finetti theorems show how sufficiently exchangeable states are well-approximated by convex combinations of independent identically distributed states. Recently, it was shown that in many quantum information applications, a more relaxed de Finetti reduction (i.e., only a matrix inequality between the symmetric state and one of the de Finetti forms) is enough and that it leads to more concise and elegant arguments. Here we show several uses and general flexible applicability of a constrained de Finetti reduction in quantum information theory, which was recently discovered by Duan, Severini, and Winter. In particular, we show that the technique can accommodate other symmetries commuting with the permutation action and permutation-invariant linear constraints. We then demonstrate that, in some cases, it is also fruitful with convex constraints, in particular separability in a bipartite setting. This is a constraint particularly interesting in the context of the complexity class QMA(2) of interactive quantum Merlin-Arthur games with unentangled provers, and our results relate to the soundness gap amplification of QMA(2) protocols by parallel repetition. It is also relevant for the regularization of certain entropic channel parameters. As an aside, we present an alternative way of attacking this problem, relying on an entanglement measure theory rather than the de Finetti approach. Finally, we explore an extension to infinite-dimensional systems, which usually pose inherent problems to de Finetti techniques in the quantum case.
Joint Chance-Constrained Dynamic Programming
NASA Technical Reports Server (NTRS)
Ono, Masahiro; Kuwata, Yoshiaki; Balaram, J. Bob
2012-01-01
This paper presents a novel dynamic programming algorithm with a joint chance constraint, which explicitly bounds the risk of failure in order to maintain the state within a specified feasible region. A joint chance constraint cannot be handled by existing constrained dynamic programming approaches since their application is limited to constraints in the same form as the cost function, that is, an expectation over a sum of one-stage costs. We overcome this challenge by reformulating the joint chance constraint into a constraint on an expectation over a sum of indicator functions, which can be incorporated into the cost function by dualizing the optimization problem. As a result, the primal variables can be optimized by a standard dynamic programming, while the dual variable is optimized by a root-finding algorithm that converges exponentially. Error bounds on the primal and dual objective values are rigorously derived. We demonstrate the algorithm on a path planning problem, as well as an optimal control problem for Mars entry, descent and landing. The simulations are conducted using a real terrain data of Mars, with four million discrete states at each time step.
Pressure compensated transducer system with constrained diaphragm
NASA Astrophysics Data System (ADS)
Percy, Joseph L.
1992-08-01
An acoustic source apparatus has an acoustic transducer that is enclosed in a substantially rigid and watertight enclosure to resist the pressure of water on the transducer and to seal the transducer from the water. The enclosure has an opening through which acoustic signals pass and over which is placed a resilient, expandable and substantially water-impermeable diaphragm. A net stiffens and strengthens the diaphragm as well as constrains the diaphragm from overexpansion or from migrating due to buoyancy forces. Pressurized gas, regulated at slightly above ambient pressure, is supplied to the enclosure and the diaphragm to compensate for underwater ambient pressures. Gas pressure regulated at above ambient pressure is used to selectively tune the pressure levels within the enclosure and diaphragm so that diaphragm resonance can be achieved. Controls are used to selectively fill, as well as vent the enclosure and diaphragm during system descent and ascent, respectively. A signal link is used to activate these controls and to provide the driving force for the acoustic transducer.
Computational studies of spatially constrained DNA
Olson, W.K.; Westcott, T.P.; Liu, Guo-Hua
1996-12-31
Closed loops of double stranded DNA are ubiquitous in nature, occurring in systems ranging from plasmids, bacterial chromosomes, and many viral genomes, which form single closed loops, to eukaryotic chromosomes and other linear DNAs, which appear to be organized into topologically constrained domains by DNA-binding proteins. The topological constraints in the latter systems are determined by the spacing of the bound proteins along the contour of the double helix along with the imposed turns and twists of DNA in the intermolecular complexes. As long as the duplex remains unbroken, the linking number Lk, or number of times the two strands of the DNA wrap around one another, is conserved. If one of the strands is nicked and later re-sealed, the change in overall folding that accompanies DNA-protein interactions leads to a change in Lk. The supercoiling brought about by such protein action, in turn, determines a number of key biological events, including replication, transcription, and recombination. 51 refs., 5 figs., 1 tab.
Constrained Sypersymmetric Flipped SU (5) GUT Phenomenology
Ellis, John; Mustafayev, Azar; Olive, Keith A.; /Minnesota U., Theor. Phys. Inst. /Minnesota U. /Stanford U., Phys. Dept. /SLAC
2011-08-12
We explore the phenomenology of the minimal supersymmetric flipped SU(5) GUT model (CFSU(5)), whose soft supersymmetry-breaking (SSB) mass parameters are constrained to be universal at some input scale, Min, above the GUT scale, M{sub GUT}. We analyze the parameter space of CFSU(5) assuming that the lightest supersymmetric particle (LSP) provides the cosmological cold dark matter, paying careful attention to the matching of parameters at the GUT scale. We first display some specific examples of the evolutions of the SSB parameters that exhibit some generic features. Specifically, we note that the relationship between the masses of the lightest neutralino {chi} and the lighter stau {tilde {tau}}{sub 1} is sensitive to M{sub in}, as is the relationship between m{sub {chi}} and the masses of the heavier Higgs bosons A,H. For these reasons, prominent features in generic (m{sub 1/2}, m{sub 0}) planes such as coannihilation strips and rapid-annihilation funnels are also sensitive to Min, as we illustrate for several cases with tan {beta} = 10 and 55. However, these features do not necessarily disappear at large Min, unlike the case in the minimal conventional SU(5) GUT. Our results are relatively insensitive to neutrino masses.
Constrained spheroids for prolonged hepatocyte culture.
Tong, Wen Hao; Fang, Yu; Yan, Jie; Hong, Xin; Hari Singh, Nisha; Wang, Shu Rui; Nugraha, Bramasta; Xia, Lei; Fong, Eliza Li Shan; Iliescu, Ciprian; Yu, Hanry
2016-02-01
Liver-specific functions in primary hepatocytes can be maintained over extended duration in vitro using spheroid culture. However, the undesired loss of cells over time is still a major unaddressed problem, which consequently generates large variations in downstream assays such as drug screening. In static culture, the turbulence generated by medium change can cause spheroids to detach from the culture substrate. Under perfusion, the momentum generated by Stokes force similarly results in spheroid detachment. To overcome this problem, we developed a Constrained Spheroids (CS) culture system that immobilizes spheroids between a glass coverslip and an ultra-thin porous Parylene C membrane, both surface-modified with poly(ethylene glycol) and galactose ligands for optimum spheroid formation and maintenance. In this configuration, cell loss was minimized even when perfusion was introduced. When compared to the standard collagen sandwich model, hepatocytes cultured as CS under perfusion exhibited significantly enhanced hepatocyte functions such as urea secretion, and CYP1A1 and CYP3A2 metabolic activity. We propose the use of the CS culture as an improved culture platform to current hepatocyte spheroid-based culture systems.
Optimization of constrained density functional theory
NASA Astrophysics Data System (ADS)
O'Regan, David D.; Teobaldi, Gilberto
2016-07-01
Constrained density functional theory (cDFT) is a versatile electronic structure method that enables ground-state calculations to be performed subject to physical constraints. It thereby broadens their applicability and utility. Automated Lagrange multiplier optimization is necessary for multiple constraints to be applied efficiently in cDFT, for it to be used in tandem with geometry optimization, or with molecular dynamics. In order to facilitate this, we comprehensively develop the connection between cDFT energy derivatives and response functions, providing a rigorous assessment of the uniqueness and character of cDFT stationary points while accounting for electronic interactions and screening. In particular, we provide a nonperturbative proof that stable stationary points of linear density constraints occur only at energy maxima with respect to their Lagrange multipliers. We show that multiple solutions, hysteresis, and energy discontinuities may occur in cDFT. Expressions are derived, in terms of convenient by-products of cDFT optimization, for quantities such as the dielectric function and a condition number quantifying ill definition in multiple constraint cDFT.
Constraining Amazonian Methane Emission from Wetlands
NASA Astrophysics Data System (ADS)
Boesch, Hartmut; Parker, Robert; Webb, Alex; Wilson, Chris; Chipperfield, Martyn; Gloor, Emanuel; Feng, Liang; Palmer, Paul
2017-04-01
The Amazon Basin contains large wetland ecosystems which are important sources of methane (CH4). Spaceborne observations provide detailed information about the spatio-temporal distributions of atmospheric methane over the Amazon Basin which will provide a strong constrain on the underlying emissions and their year to year variations. Methane observations from space are available from the Japanese GOSAT instrument since 2009. We use the proxy retrieval method which provides much greater coverage over the Amazon region compared to so-called Full-Physics methods due to their lower sensitivity to thin clouds. Validation of GOSAT retrieval over the Amazon using the ground-based TCCON network is currently not possible due to a lack of data and we have used routine aircraft profiles to show that GOSAT columns are sufficiently accurate for estimating surface flux for the region. Using a variational flux inverse system together with the 3-D atmospheric chemical transport model TOMCAT, we infer surface fluxes for the Amazon region from GOSAT observations which are used to analyse the spatial distribution of methane wetlands emissions as well as annual variations in emissions with a focus on periods 2011/2012 and 2013/14 which are characterized by large variations in rainfall.
Constraining Cosmological Models with Different Observations
NASA Astrophysics Data System (ADS)
Wei, J. J.
2016-07-01
With the observations of Type Ia supernovae (SNe Ia), scientists discovered that the Universe is experiencing an accelerated expansion, and then revealed the existence of dark energy in 1998. Since the amazing discovery, cosmology has became a hot topic in the physical research field. Cosmology is a subject that strongly depends on the astronomical observations. Therefore, constraining different cosmological models with all kinds of observations is one of the most important research works in the modern cosmology. The goal of this thesis is to investigate cosmology using the latest observations. The observations include SNe Ia, Type Ic Super Luminous supernovae (SLSN Ic), Gamma-ray bursts (GRBs), angular diameter distance of galaxy cluster, strong gravitational lensing, and age measurements of old passive galaxies, etc. In Chapter 1, we briefly review the research background of cosmology, and introduce some cosmological models. Then we summarize the progress on cosmology from all kinds of observations in more details. In Chapter 2, we present the results of our studies on the supernova cosmology. The main difficulty with the use of SNe Ia as standard candles is that one must optimize three or four nuisance parameters characterizing SN luminosities simultaneously with the parameters of an expansion model of the Universe. We have confirmed that one should optimize all of the parameters by carrying out the method of maximum likelihood estimation in any situation where the parameters include an unknown intrinsic dispersion. The commonly used method, which estimates the dispersion by requiring the reduced χ^{2} to equal unity, does not take into account all possible variances among the parameters. We carry out such a comparison of the standard ΛCDM cosmology and the R_{h}=ct Universe using the SN Legacy Survey sample of 252 SN events, and show that each model fits its individually reduced data very well. Moreover, it is quite evident that SLSNe Ic may be useful
NUCLEI SEGMENTATION VIA SPARSITY CONSTRAINED CONVOLUTIONAL REGRESSION
Zhou, Yin; Chang, Hang; Barner, Kenneth E.; Parvin, Bahram
2017-01-01
Automated profiling of nuclear architecture, in histology sections, can potentially help predict the clinical outcomes. However, the task is challenging as a result of nuclear pleomorphism and cellular states (e.g., cell fate, cell cycle), which are compounded by the batch effect (e.g., variations in fixation and staining). Present methods, for nuclear segmentation, are based on human-designed features that may not effectively capture intrinsic nuclear architecture. In this paper, we propose a novel approach, called sparsity constrained convolutional regression (SCCR), for nuclei segmentation. Specifically, given raw image patches and the corresponding annotated binary masks, our algorithm jointly learns a bank of convolutional filters and a sparse linear regressor, where the former is used for feature extraction, and the latter aims to produce a likelihood for each pixel being nuclear region or background. During classification, the pixel label is simply determined by a thresholding operation applied on the likelihood map. The method has been evaluated using the benchmark dataset collected from The Cancer Genome Atlas (TCGA). Experimental results demonstrate that our method outperforms traditional nuclei segmentation algorithms and is able to achieve competitive performance compared to the state-of-the-art algorithm built upon human-designed features with biological prior knowledge. PMID:28101301
Constrained Subjective Assessment of Student Learning
NASA Astrophysics Data System (ADS)
Saliu, Sokol
2005-09-01
Student learning is a complex incremental cognitive process; assessment needs to parallel this, reporting the results in similar terms. Application of fuzzy sets and logic to the criterion-referenced assessment of student learning is considered here. The constrained qualitative assessment (CQA) system was designed, and then applied in assessing a past course in microcomputer system design (MSD). CQA criteria were articulated in fuzzy terms and sets, and the assessment procedure was cast as a fuzzy inference rule base. An interactive graphic interface provided for transparent assessment, student "backwash," and support to the teacher when compiling the tests. Grade intervals, obtained from a departmental poll, were used to compile a fuzzy "grade" set. Assessment results were compared to those of a former standard method and to those of a modified version of it (but with fewer criteria). The three methods yielded similar results, supporting the application of CQA. The method improved assessment reliability by means of the consensus embedded in the fuzzy grade set, and improved assessment validity by integrating fuzzy criteria into the assessment procedure.
String theory origin of constrained multiplets
NASA Astrophysics Data System (ADS)
Kallosh, Renata; Vercnocke, Bert; Wrase, Timm
2016-09-01
We study the non-linearly realized spontaneously broken supersymmetry of the (anti-)D3-brane action in type IIB string theory. The worldvolume fields are one vector A μ , three complex scalars ϕ i and four 4d fermions λ 0, λ i. These transform, in addition to the more familiar {N}=4 linear supersymmetry, also under 16 spontaneously broken, non-linearly realized supersymmetries. We argue that the worldvolume fields can be packaged into the following constrained 4d non-linear {N}=1 multiplets: four chiral multiplets S, Y i that satisfy S 2 = SY i =0 and contain the worldvolume fermions λ 0 and λ i ; and four chiral multiplets W α , H i that satisfy S{W}_{α }=S{overline{D}}_{overset{\\cdotp }{α }}{overline{H}}^{overline{imath}}=0 and contain the vector A μ and the scalars ϕ i . We also discuss how placing an anti-D3-brane on top of intersecting O7-planes can lead to an orthogonal multiplet Φ that satisfies S(Φ -overline{Φ})=0 , which is particularly interesting for inflationary cosmology.
The Pendulum: From Constrained Fall to the Concept of Potential
ERIC Educational Resources Information Center
Bevilacqua, Fabio; Falomo, Lidia; Fregonese, Lucio; Giannetto, Enrico; Giudice, Franco; Mascheretti, Paolo
2006-01-01
Kuhn underlined the relevance of Galileo's gestalt switch in the interpretation of a swinging body from constrained fall to time metre. But the new interpretation did not eliminate the older one. The constrained fall, both in the motion of pendulums and along inclined planes, led Galileo to the law of free fall. Experimenting with physical…
Constrained spectral clustering under a local proximity structure assumption
NASA Technical Reports Server (NTRS)
Wagstaff, Kiri; Xu, Qianjun; des Jardins, Marie
2005-01-01
This work focuses on incorporating pairwise constraints into a spectral clustering algorithm. A new constrained spectral clustering method is proposed, as well as an active constraint acquisition technique and a heuristic for parameter selection. We demonstrate that our constrained spectral clustering method, CSC, works well when the data exhibits what we term local proximity structure.
Regularized Partial and/or Constrained Redundancy Analysis
ERIC Educational Resources Information Center
Takane, Yoshio; Jung, Sunho
2008-01-01
Methods of incorporating a ridge type of regularization into partial redundancy analysis (PRA), constrained redundancy analysis (CRA), and partial and constrained redundancy analysis (PCRA) were discussed. The usefulness of ridge estimation in reducing mean square error (MSE) has been recognized in multiple regression analysis for some time,…
Regularized Partial and/or Constrained Redundancy Analysis
ERIC Educational Resources Information Center
Takane, Yoshio; Jung, Sunho
2008-01-01
Methods of incorporating a ridge type of regularization into partial redundancy analysis (PRA), constrained redundancy analysis (CRA), and partial and constrained redundancy analysis (PCRA) were discussed. The usefulness of ridge estimation in reducing mean square error (MSE) has been recognized in multiple regression analysis for some time,…
The Pendulum: From Constrained Fall to the Concept of Potential
ERIC Educational Resources Information Center
Bevilacqua, Fabio; Falomo, Lidia; Fregonese, Lucio; Giannetto, Enrico; Giudice, Franco; Mascheretti, Paolo
2006-01-01
Kuhn underlined the relevance of Galileo's gestalt switch in the interpretation of a swinging body from constrained fall to time metre. But the new interpretation did not eliminate the older one. The constrained fall, both in the motion of pendulums and along inclined planes, led Galileo to the law of free fall. Experimenting with physical…
Probability Statements Extraction with Constrained Conditional Random Fields.
Deleris, Léa A; Jochim, Charles
2016-01-01
This paper investigates how to extract probability statements from academic medical papers. In previous work we have explored traditional classification methods which led to numerous false negatives. This current work focuses on constraining classification output obtained from a Conditional Random Field (CRF) model to allow for domain knowledge constraints. Our experimental results indicate constraining leads to a significant improvement in performance.
Smooth Constrained Heuristic Optimization of a Combinatorial Chemical Space
2015-05-01
ARL-TR-7294•MAY 2015 US Army Research Laboratory Smooth ConstrainedHeuristic Optimization of a Combinatorial Chemical Space by Berend Christopher...7294•MAY 2015 US Army Research Laboratory Smooth ConstrainedHeuristic Optimization of a Combinatorial Chemical Space by Berend Christopher...
The constrained reinitialization equation for level set methods
NASA Astrophysics Data System (ADS)
Hartmann, Daniel; Meinke, Matthias; Schröder, Wolfgang
2010-03-01
Based on the constrained reinitialization scheme [D. Hartmann, M. Meinke, W. Schröder, Differential equation based constrained reinitialization for level set methods, J. Comput. Phys. 227 (2008) 6821-6845] a new constrained reinitialization equation incorporating a forcing term is introduced. Two formulations for high-order constrained reinitialization (HCR) are presented combining the simplicity and generality of the original reinitialization equation [M. Sussman, P. Smereka, S. Osher, A level set approach for computing solutions to incompressible two-phase flow, J. Comput. Phys. 114 (1994) 146-159] in terms of high-order standard discretization and the accuracy of the constrained reinitialization scheme in terms of interface displacement. The novel HCR schemes represent simple extensions of standard implementations of the original reinitialization equation. The results evidence the significantly increased accuracy and robustness of the novel schemes.
Constraining the Evolution of Poor Clusters
NASA Astrophysics Data System (ADS)
Broming, Emma J.; Fuse, C. R.
2012-01-01
There currently exists no method by which to quantify the evolutionary state of poor clusters (PCs). Research by Broming & Fuse (2010) demonstrated that the evolution of Hickson compact groups (HCGs) are constrained by the correlation between the X-ray luminosities of point sources and diffuse gas. The current investigation adopts an analogous approach to understanding PCs. Plionis et al. (2009) proposed a theory to define the evolution of poor clusters. The theory asserts that cannibalism of galaxies causes a cluster to become more spherical, develop increased velocity dispersion and increased X-ray temperature and gas luminosity. Data used to quantify the evolution of the poor clusters were compiled across multiple wavelengths. The sample includes 162 objects from the WBL catalogue (White et al. 1999), 30 poor clusters in the Chandra X-ray Observatory archive, and 15 Abell poor clusters observed with BAX (Sadat et al. 2004). Preliminary results indicate that the cluster velocity dispersion and X-ray gas and point source luminosities can be used to highlight a weak correlation. An evolutionary trend was observed for multiple correlations detailed herein. The current study is a continuation of the work by Broming & Fuse examining point sources and their properties to determine the evolutionary stage of compact groups, poor clusters, and their proposed remnants, isolated ellipticals and fossil groups. Preliminary data suggests that compact groups and their high-mass counterpart, poor clusters, evolve along tracks identified in the X-ray gas - X-ray point source relation. While compact groups likely evolve into isolated elliptical galaxies, fossil groups display properties that suggest they are the remains of fully coalesced poor clusters.
Constraining Cosmic Evolution of Type Ia Supernovae
Foley, Ryan J.; Filippenko, Alexei V.; Aguilera, C.; Becker, A.C.; Blondin, S.; Challis, P.; Clocchiatti, A.; Covarrubias, R.; Davis, T.M.; Garnavich, P.M.; Jha, S.; Kirshner, R.P.; Krisciunas, K.; Leibundgut, B.; Li, W.; Matheson, T.; Miceli, A.; Miknaitis, G.; Pignata, G.; Rest, A.; Riess, A.G.; /UC, Berkeley, Astron. Dept. /Cerro-Tololo InterAmerican Obs. /Washington U., Seattle, Astron. Dept. /Harvard-Smithsonian Ctr. Astrophys. /Chile U., Catolica /Bohr Inst. /Notre Dame U. /KIPAC, Menlo Park /Texas A-M /European Southern Observ. /NOAO, Tucson /Fermilab /Chile U., Santiago /Harvard U., Phys. Dept. /Baltimore, Space Telescope Sci. /Johns Hopkins U. /Res. Sch. Astron. Astrophys., Weston Creek /Stockholm U. /Hawaii U. /Illinois U., Urbana, Astron. Dept.
2008-02-13
We present the first large-scale effort of creating composite spectra of high-redshift type Ia supernovae (SNe Ia) and comparing them to low-redshift counterparts. Through the ESSENCE project, we have obtained 107 spectra of 88 high-redshift SNe Ia with excellent light-curve information. In addition, we have obtained 397 spectra of low-redshift SNe through a multiple-decade effort at Lick and Keck Observatories, and we have used 45 ultraviolet spectra obtained by HST/IUE. The low-redshift spectra act as a control sample when comparing to the ESSENCE spectra. In all instances, the ESSENCE and Lick composite spectra appear very similar. The addition of galaxy light to the Lick composite spectra allows a nearly perfect match of the overall spectral-energy distribution with the ESSENCE composite spectra, indicating that the high-redshift SNe are more contaminated with host-galaxy light than their low-redshift counterparts. This is caused by observing objects at all redshifts with similar slit widths, which corresponds to different projected distances. After correcting for the galaxy-light contamination, subtle differences in the spectra remain. We have estimated the systematic errors when using current spectral templates for K-corrections to be {approx}0.02 mag. The variance in the composite spectra give an estimate of the intrinsic variance in low-redshift maximum-light SN spectra of {approx}3% in the optical and growing toward the ultraviolet. The difference between the maximum-light low and high-redshift spectra constrain SN evolution between our samples to be < 10% in the rest-frame optical.
Quasi-optical constrained lens amplifiers
NASA Astrophysics Data System (ADS)
Schoenberg, Jon S.
1995-09-01
A major goal in the field of quasi-optics is to increase the power available from solid state sources by combining the power of individual devices in free space, as demonstrated with grid oscillators and grid amplifiers. Grid amplifiers and most amplifier arrays require a plane wave feed, provided by a far field source or at the beam waist of a dielectric lens pair. These feed approaches add considerable loss and size, which is usually greater than the quasi-optical amplifier gain. In addition, grid amplifiers require external polarizers for stability, further increasing size and complexity. This thesis describes using constrained lens theory in the design of quasi optical amplifier arrays with a focal point feed, improving the power coupling between the feed and the amplifier for increased gain. Feed and aperture arrays of elements, input/output isolation and stability, amplifier circuitry, delay lines and bias distribution are all contained on a single planar substrate, making monolithic circuit integration possible. Measured results of X band transmission lenses and a low noise receive lens are presented, including absolute power gain up to 13 dB, noise figure as low as 1.7 dB, beam scanning to +/-30 deg, beam forming and beam switching of multiple sources, and multiple level quasi-optical power combining. The design and performance of millimeter wave power combining amplifier arrays is described, including a Ka Band hybrid array with 1 watt output power, and a V Band 36 element monolithic array with a 5 dB on/off ratio.
Mars, Moon, Mercury: Magnetometry Constrains Planetary Evolution
NASA Astrophysics Data System (ADS)
Connerney, John E. P.
2015-04-01
We have long appreciated that magnetic measurements obtained about a magnetized planet are of great value in probing the deep interior. The existence of a substantial planetary magnetic field implies dynamo action requiring an electrically conducting, fluid core in convective motion and a source of energy to maintain it. Application of the well-known Lowe's spectrum may in some cases identify the dynamo outer radius; where secular variation can be measured, the outer radius can be estimated using the frozen flux approximation. Magnetic induction may be used to probe the electrical conductivity of the mantle and crust. These are useful constraints that together with gravity and/or other observables we may infer the state of the interior and gain insight into planetary evolution. But only recently has it become clear that space magnetometry can do much more, particularly about a planet that once sustained a dynamo that has since disappeared. Mars is the best example of this class: the Mars Global Surveyor spacecraft globally mapped a remanent crustal field left behind after the demise of the dynamo. This map is a magnetic record of the planet's evolution. I will argue that this map may be interpreted to constrain the era of dynamo activity within Mars; to establish the reversal history of the Mars dynamo; to infer the magnetization intensity of Mars crustal rock and the depth of the magnetized crustal layer; and to establish that plate tectonics is not unique to planet Earth, as has so often been claimed. The Lunar magnetic record is in contrast one of weakly magnetized and scattered sources, not easily interpreted as yet in terms of the interior. Magnetometry about Mercury is more difficult to interpret owing to the relatively weak field and proximity to the sun, but MESSENGER (and ultimately Beppi Columbo) may yet map crustal anomalies (induced and/or remanent).
The cost-constrained traveling salesman problem
Sokkappa, P.R.
1990-10-01
The Cost-Constrained Traveling Salesman Problem (CCTSP) is a variant of the well-known Traveling Salesman Problem (TSP). In the TSP, the goal is to find a tour of a given set of cities such that the total cost of the tour is minimized. In the CCTSP, each city is given a value, and a fixed cost-constraint is specified. The objective is to find a subtour of the cities that achieves maximum value without exceeding the cost-constraint. Thus, unlike the TSP, the CCTSP requires both selection and sequencing. As a consequence, most results for the TSP cannot be extended to the CCTSP. We show that the CCTSP is NP-hard and that no K-approximation algorithm or fully polynomial approximation scheme exists, unless P = NP. We also show that several special cases are polynomially solvable. Algorithms for the CCTSP, which outperform previous methods, are developed in three areas: upper bounding methods, exact algorithms, and heuristics. We found that a bounding strategy based on the knapsack problem performs better, both in speed and in the quality of the bounds, than methods based on the assignment problem. Likewise, we found that a branch-and-bound approach using the knapsack bound was superior to a method based on a common branch-and-bound method for the TSP. In our study of heuristic algorithms, we found that, when selecting modes for inclusion in the subtour, it is important to consider the neighborhood'' of the nodes. A node with low value that brings the subtour near many other nodes may be more desirable than an isolated node of high value. We found two types of repetition to be desirable: repetitions based on randomization in the subtour buildings process, and repetitions encouraging the inclusion of different subsets of the nodes. By varying the number and type of repetitions, we can adjust the computation time required by our method to obtain algorithms that outperform previous methods.
Motor Demands Constrain Cognitive Rule Structures
Collins, Anne Gabrielle Eva; Frank, Michael Joshua
2016-01-01
Study of human executive function focuses on our ability to represent cognitive rules independently of stimulus or response modality. However, recent findings suggest that executive functions cannot be modularized separately from perceptual and motor systems, and that they instead scaffold on top of motor action selection. Here we investigate whether patterns of motor demands influence how participants choose to implement abstract rule structures. In a learning task that requires integrating two stimulus dimensions for determining appropriate responses, subjects typically structure the problem hierarchically, using one dimension to cue the task-set and the other to cue the response given the task-set. However, the choice of which dimension to use at each level can be arbitrary. We hypothesized that the specific structure subjects adopt would be constrained by the motor patterns afforded within each rule. Across four independent data-sets, we show that subjects create rule structures that afford motor clustering, preferring structures in which adjacent motor actions are valid within each task-set. In a fifth data-set using instructed rules, this bias was strong enough to counteract the well-known task switch-cost when instructions were incongruent with motor clustering. Computational simulations confirm that observed biases can be explained by leveraging overlap in cortical motor representations to improve outcome prediction and hence infer the structure to be learned. These results highlight the importance of sensorimotor constraints in abstract rule formation and shed light on why humans have strong biases to invent structure even when it does not exist. PMID:26966909
Ductile failure of a constrained metal foil
NASA Astrophysics Data System (ADS)
Varias, A. G.; Suo, Z.; Shih, C. F.
A METAL foil bonded between stiff ceramic blocks may fail in a variety of ways, including de-adhesion of interfaces, cracking in the ceramics and ductile rupture of the metal. If the interface bond is strong enough to allow the foil to undergo substantial plastic deformation dimples are usually present on fracture surfaces and the nominal fracture energy is enhanced. Ductile fracture mechanisms responsible for such morphology include (i) growth of near-tip voids nucleated at second-phase particles and or interface pores, (ii) cavitation and (iii) interfacial debonding at the site of maximum stress which develops at distances of several foil thicknesses ahead of the crack tip. For a crack in a low to moderately hardening bulk metal, it is known that the maximum mean stress which develops at a distance of several crack openings ahead of the tip does not exceed about three times the yield stress. In contrast, the maximum mean stress that develops at several foil thicknesses ahead of the crack tip in a constrained metal foil can increase continuously with the applied load. Mean stress and interfacial traction of about four to six times the yield of the metal foil can trigger cavitation and/or interfacial debonding. The mechanical fields which bear on the competition between failure mechanisms are obtained by a large deformation finite element analysis. Effort is made to formulate predictive criteria indicating, for a given material system, which one of the several mechanisms operates and the relevant parameters that govern the nominal fracture work. The shielding of the crack tip in the context of ductile adhesive joints, due to the non-proportional deformation in a region of the order of the foil thickness, is also discussed.
Constraining the source of mantle plumes
NASA Astrophysics Data System (ADS)
Cagney, N.; Crameri, F.; Newsome, W. H.; Lithgow-Bertelloni, C.; Cotel, A.; Hart, S. R.; Whitehead, J. A.
2016-02-01
In order to link the geochemical signature of hot spot basalts to Earth's deep interior, it is first necessary to understand how plumes sample different regions of the mantle. Here, we investigate the relative amounts of deep and shallow mantle material that are entrained by an ascending plume and constrain its source region. The plumes are generated in a viscous syrup using an isolated heater for a range of Rayleigh numbers. The velocity fields are measured using stereoscopic Particle-Image Velocimetry, and the concept of the 'vortex ring bubble' is used to provide an objective definition of the plume geometry. Using this plume geometry, the plume composition can be analysed in terms of the proportion of material that has been entrained from different depths. We show that the plume composition can be well described using a simple empirical relationship, which depends only on a single parameter, the sampling coefficient, sc. High-sc plumes are composed of material which originated from very deep in the fluid domain, while low-sc plumes contain material entrained from a range of depths. The analysis is also used to show that the geometry of the plume can be described using a similarity solution, in agreement with previous studies. Finally, numerical simulations are used to vary both the Rayleigh number and viscosity contrast independently. The simulations allow us to predict the value of the sampling coefficient for mantle plumes; we find that as a plume reaches the lithosphere, 90% of its composition has been derived from the lowermost 260-750 km in the mantle, and negligible amounts are derived from the shallow half of the lower mantle. This result implies that isotope geochemistry cannot provide direct information about this unsampled region, and that the various known geochemical reservoirs must lie in the deepest few hundred kilometres of the mantle.
Laterally constrained inversion for CSAMT data interpretation
NASA Astrophysics Data System (ADS)
Wang, Ruo; Yin, Changchun; Wang, Miaoyue; Di, Qingyun
2015-10-01
Laterally constrained inversion (LCI) has been successfully applied to the inversion of dc resistivity, TEM and airborne EM data. However, it hasn't been yet applied to the interpretation of controlled-source audio-frequency magnetotelluric (CSAMT) data. In this paper, we apply the LCI method for CSAMT data inversion by preconditioning the Jacobian matrix. We apply a weighting matrix to Jacobian to balance the sensitivity of model parameters, so that the resolution with respect to different model parameters becomes more uniform. Numerical experiments confirm that this can improve the convergence of the inversion. We first invert a synthetic dataset with and without noise to investigate the effect of LCI applications to CSAMT data, for the noise free data, the results show that the LCI method can recover the true model better compared to the traditional single-station inversion; and for the noisy data, the true model is recovered even with a noise level of 8%, indicating that LCI inversions are to some extent noise insensitive. Then, we re-invert two CSAMT datasets collected respectively in a watershed and a coal mine area in Northern China and compare our results with those from previous inversions. The comparison with the previous inversion in a coal mine shows that LCI method delivers smoother layer interfaces that well correlate to seismic data, while comparison with a global searching algorithm of simulated annealing (SA) in a watershed shows that though both methods deliver very similar good results, however, LCI algorithm presented in this paper runs much faster. The inversion results for the coal mine CSAMT survey show that a conductive water-bearing zone that was not revealed by the previous inversions has been identified by the LCI. This further demonstrates that the method presented in this paper works for CSAMT data inversion.
Constrained Inversion of Enceladus Interaction Observations
NASA Astrophysics Data System (ADS)
Herbert, Floyd; Khurana, K. K.
2007-10-01
Many detailed and sophisticated ab initio calculations of the electrodynamic interaction of Enceladus' plume with Saturn's corotating magnetospheric plasma flow have been computed. So far, however, all such calculations have been forward models, that assume the properties of the plume and compute perturbations to the magnetic (and in some cases, flow velocity) field. As a complement to the forward calculations, work reported here explores the inverse approach, of using simplified physical models of the interaction for computationally inverting the observed magnetic field perturbations of the interaction, in order to determine the cross-B-field conductivity distribution near Enceladus, and from that, the neutral gas distribution. Direct inversion of magnetic field observations to current systems is, of course, impossible, but adding the additional constraint of the interaction physics greatly reduces the non-uniqueness of the computed result. This approach was successfully used by Herbert (JGR 90:8241, 1985) to constrain the atmospheric distribution on Io and the Io torus mass density at the time of the Voyager encounter. Work so far has derived the expected result that there is a cone-shaped region of enhanced cross-field conductivity south of Enceladus, through which currents are driven by the motional electric field. That is, near Enceladus' south pole the cross-field currents are localized, but more widely spread at greater distance. This cross-field conductivity is presumably both pickup and collisional (Pedersen and Hall). Due to enforcement of current conservation, Alfven-wing-like currents north of the main part of the interaction region seem to close partly around Enceladus (assumed insulating) and also to continue northward with attenuated intensity, as though there were a tenuous global exosphere on Enceladus providing additional cross-field conductivity. FH thanks the NASA Outer Planets Research, Planetary Atmospheres, and Geospace Science Programs for
Hee, S.; Vázquez, J. A.; Handley, W. J.; Hobson, M. P.; Lasenby, A. N.
2016-12-01
Data-driven model-independent reconstructions of the dark energy equation of state w(z) are presented using Planck 2015 era CMB, BAO, SNIa and Lyman-α data. These reconstructions identify the w(z) behaviour supported by the data and show a bifurcation of the equation of state posterior in the range 1.5 < z < 3. Although the concordance ΛCDM model is consistent with the data at all redshifts in one of the bifurcated spaces, in the other a supernegative equation of state (also known as ‘phantom dark energy’) is identified within the 1.5σ confidence intervals of the posterior distribution. In order to identify the power of different datasets in constraining the dark energy equation of state, we use a novel formulation of the Kullback–Leibler divergence. Moreover, this formalism quantifies the information the data add when moving from priors to posteriors for each possible dataset combination. The SNIa and BAO datasets are shown to provide much more constraining power in comparison to the Lyman-α datasets. Furthermore, SNIa and BAO constrain most strongly around redshift range 0.1 - 0.5, whilst the Lyman-α data constrains weakly over a broader range. We do not attribute the supernegative favouring to any particular dataset, and note that the ΛCDM model was favoured at more than 2 log-units in Bayes factors over all the models tested despite the weakly preferred w(z) structure in the data.
Constraining big bang lithium production with recent solar neutrino data
NASA Astrophysics Data System (ADS)
Takács, Marcell P.; Bemmerer, Daniel; Szücs, Tamás; Zuber, Kai
2015-06-01
The 3He (α ,γ )7Be reaction affects not only the production of 7Li in big bang nucleosynthesis, but also the fluxes of 7Be and 8B neutrinos from the Sun. This double role is exploited here to constrain the former by the latter. A number of recent experiments on 3He α ,γ )7Be provide precise cross section data at E =0.5 - 1.0 MeV center-of-mass energies. However, there is a scarcity of precise data at big bang energies, 0.1-0.5 MeV, and below. This problem can be alleviated, based on precisely calibrated 7Be and 8B neutrino fluxes from the Sun that are now available, assuming the neutrino flavor oscillation framework to be correct. These fluxes and the standard solar model are used here to determine the 3He α ,γ )7Be astrophysical S -factor at the solar Gamow peak, S34ν(2 3-5+6 keV ) =0.548 ±0.054 keV b . This new data point is then included in a reevaluation of the 3He α ,γ )7Be S -factor at big bang energies, following an approach recently developed for this reaction in the context of solar fusion studies. The reevaluated S -factor curve is then used to redetermine the 3He α ,γ )7Be thermonuclear reaction rate at big bang energies. The predicted primordial lithium abundance is 7Li H =5.0 ×10-10 , far higher than the Spite plateau.
Constraining duty cycles through a Bayesian technique
NASA Astrophysics Data System (ADS)
Romano, P.; Guidorzi, C.; Segreto, A.; Ducci, L.; Vercellone, S.
2014-12-01
The duty cycle (DC) of astrophysical sources is generally defined as the fraction of time during which the sources are active. It is used to both characterize their central engine and to plan further observing campaigns to study them. However, DCs are generally not provided with statistical uncertainties, since the standard approach is to perform Monte Carlo bootstrap simulations to evaluate them, which can be quite time consuming for a large sample of sources. As an alternative, considerably less time-consuming approach, we derived the theoretical expectation value for the DC and its error for sources whose state is one of two possible, mutually exclusive states, inactive (off) or flaring (on), as based on a finite set of independent observational data points. Following a Bayesian approach, we derived the analytical expression for the posterior, the conjugated distribution adopted as prior, and the expectation value and variance. We applied our method to the specific case of the inactivity duty cycle (IDC) for supergiant fast X-ray transients, a subclass of flaring high mass X-ray binaries characterized by large dynamical ranges. We also studied IDC as a function of the number of observations in the sample. Finally, we compare the results with the theoretical expectations. We found excellent agreement with our findings based on the standard bootstrap method. Our Bayesian treatment can be applied to all sets of independent observations of two-state sources, such as active galactic nuclei, X-ray binaries, etc. In addition to being far less time consuming than bootstrap methods, the additional strength of this approach becomes obvious when considering a well-populated class of sources (Nsrc ≥ 50) for which the prior can be fully characterized by fitting the distribution of the observed DCs for all sources in the class, so that, through the prior, one can further constrain the DC of a new source by exploiting the information acquired on the DC distribution derived
Microgrid Optimal Scheduling With Chance-Constrained Islanding Capability
Liu, Guodong; Starke, Michael R.; Xiao, B.; ...
2017-01-13
To facilitate the integration of variable renewable generation and improve the resilience of electricity sup-ply in a microgrid, this paper proposes an optimal scheduling strategy for microgrid operation considering constraints of islanding capability. A new concept, probability of successful islanding (PSI), indicating the probability that a microgrid maintains enough spinning reserve (both up and down) to meet local demand and accommodate local renewable generation after instantaneously islanding from the main grid, is developed. The PSI is formulated as mixed-integer linear program using multi-interval approximation taking into account the probability distributions of forecast errors of wind, PV and load. With themore » goal of minimizing the total operating cost while preserving user specified PSI, a chance-constrained optimization problem is formulated for the optimal scheduling of mirogrids and solved by mixed integer linear programming (MILP). Numerical simulations on a microgrid consisting of a wind turbine, a PV panel, a fuel cell, a micro-turbine, a diesel generator and a battery demonstrate the effectiveness of the proposed scheduling strategy. Lastly, we verify the relationship between PSI and various factors.« less
Constrained circulation at Endeavour ridge facilitates colonization by vent larvae.
Thomson, Richard E; Mihály, Steven F; Rabinovich, Alexander B; McDuff, Russell E; Veirs, Scott R; Stahr, Frederick R
2003-07-31
Understanding how larvae from extant hydrothermal vent fields colonize neighbouring regions of the mid-ocean ridge system remains a major challenge in oceanic research. Among the factors considered important in the recruitment of deep-sea larvae are metabolic lifespan, the connectivity of the seafloor topography, and the characteristics of the currents. Here we use current velocity measurements from Endeavour ridge to examine the role of topographically constrained circulation on larval transport along-ridge. We show that the dominant tidal and wind-generated currents in the region are strongly attenuated within the rift valley that splits the ridge crest, and that hydrothermal plumes rising from vent fields in the valley drive a steady near-bottom inflow within the valley. Extrapolation of these findings suggests that the suppression of oscillatory currents within rift valleys of mid-ocean ridges shields larvae from cross-axis dispersal into the inhospitable deep ocean. This effect, augmented by plume-driven circulation within rift valleys having active hydrothermal venting, helps retain larvae near their source. Larvae are then exported preferentially down-ridge during regional flow events that intermittently over-ride the currents within the valley.
Partially Blended Constrained Rational Cubic Trigonometric Fractal Interpolation Surfaces
NASA Astrophysics Data System (ADS)
Chand, A. K. B.; Tyada, K. R.
2016-08-01
Fractal interpolation is an advance technique for visualization of scientific shaped data. In this paper, we present a new family of partially blended rational cubic trigonometric fractal interpolation surfaces (RCTFISs) with a combination of blending functions and univariate rational trigonometric fractal interpolation functions (FIFs) along the grid lines of the interpolation domain. The developed FIFs use rational trigonometric functions pi,j(θ) qi,j(θ), where pi,j(θ) and qi,j(θ) are cubic trigonometric polynomials with four shape parameters. The convergence analysis of partially blended RCTFIS with the original surface data generating function is discussed. We derive sufficient data-dependent conditions on the scaling factors and shape parameters such that the fractal grid line functions lie above the grid lines of a plane Π, and consequently the proposed partially blended RCTFIS lies above the plane Π. Positivity preserving partially blended RCTFIS is a special case of the constrained partially blended RCTFIS. Numerical examples are provided to support the proposed theoretical results.
Constrained variability of modeled T:ET ratio across biomes
NASA Astrophysics Data System (ADS)
Fatichi, Simone; Pappas, Christoforos
2017-07-01
A large variability (35-90%) in the ratio of transpiration to total evapotranspiration (referred here as T:ET) across biomes or even at the global scale has been documented by a number of studies carried out with different methodologies. Previous empirical results also suggest that T:ET does not covary with mean precipitation and has a positive dependence on leaf area index (LAI). Here we use a mechanistic ecohydrological model, with a refined process-based description of evaporation from the soil surface, to investigate the variability of T:ET across biomes. Numerical results reveal a more constrained range and higher mean of T:ET (70 ± 9%, mean ± standard deviation) when compared to observation-based estimates. T:ET is confirmed to be independent from mean precipitation, while it is found to be correlated with LAI seasonally but uncorrelated across multiple sites. Larger LAI increases evaporation from interception but diminishes ground evaporation with the two effects largely compensating each other. These results offer mechanistic model-based evidence to the ongoing research about the patterns of T:ET and the factors influencing its magnitude across biomes.
Constrained Choices: Adolescents Speak on Sexuality in Peru
Bayer, Angela M.; Tsui, Amy O.; Hindin, Michelle J.
2011-01-01
While numerous studies have explored adolescent sexual behavior in Peru, to date, none have explored how adolescents situate sexuality within the context of their broader lives. This information is needed to inform policies and programs. Life history interviews were conducted with 20 12–17 year-old females and males from a low-income settlement near Lima, Peru. Data were analyzed using holistic content analysis and grounded theory. Sexuality had a strong presence in adolescents’ lives. However, adolescents viewed the complete expression of their sexuality as a constrained choice. Constraints are due to the belief that sexual intercourse always results in pregnancy; the nature of sex education; the provision of proscriptive advice; and the family tensions, economic problems, racism and violence present in adolescents’ lives. Social and cultural factors seem to surpass and often suppress the physical and psychological dimensions of adolescents’ sexuality. The results of this study can inform policies and programs to support adolescents as they construct their sexuality and make sexuality-related decisions. PMID:20526920
Carbon constrains fungal endophyte assemblages along the timberline.
Yang, Teng; Weisenhorn, Pamela; Gilbert, Jack A; Ni, Yingying; Sun, Ruibo; Shi, Yu; Chu, Haiyan
2016-09-01
The alpha diversity of foliar fungal endophytes (FEs) in leaves of Betula ermanii in a subalpine timberline ecotone on Changbai Mountain, China increased with elevation. There were also significant differences in beta diversity along the elevation gradient. Among the environmental variables analysed, leaf carbon significantly increased with elevation, and was the most significant environmental factor that constrained the alpha and beta diversity in the FE communities. Tree height and the cellulose, lignin, and carbon/nitrogen ratio of the leaves also affected the FE assemblages. When controlled for the effects of elevation, leaf carbon was still the main driver of changes in evenness, Shannon diversity and FE community composition. The results offered clues of the carbon acquisition strategy of the foliar FEs across this cold terrain. There was strong multicollinearity between both annual precipitation and temperature, with elevation (|Pearson r| > 0.986), so the effects of these climatic variables were impossible to separate; however, they may play key roles, and the direct effects of both warrant further investigation. As pioneer decomposers of leaf litter, variations in diversity and community composition of FE measured here may feedback and influence carbon cycling and dynamics in these forest ecosystems. © 2015 Society for Applied Microbiology and John Wiley & Sons Ltd.
Folding of Small Proteins Using Constrained Molecular Dynamics
Balaraman, Gouthaman S.; Park, In-Hee; Jain, Abhinandan; Vaidehi, Nagarajan
2011-01-01
The focus of this paper is to examine whether conformational search using constrained molecular dynamics (MD) method is more enhanced and enriched towards “native-like” structures compared to all-atom MD for the protein folding as a model problem. Constrained MD methods provide an alternate MD tool for protein structure prediction and structure refinement. It is computationally expensive to perform all-atom simulations of protein folding because the processes occur on a timescale of microseconds. Compared to the all-atom MD simulation, constrained MD methods have the advantage that stable dynamics can be achieved for larger time steps and the number of degrees of freedom is an order of magnitude smaller, leading to a decrease in computational cost. We have developed a generalized constrained MD method that allows the user to “freeze and thaw” torsional degrees of freedom as fit for the problem studied. We have used this method to perform all-torsion constrained MD in implicit solvent coupled with the replica exchange method to study folding of small proteins with various secondary structural motifs such as, α-helix (polyalanine, WALP16), β-turn (1E0Q), and a mixed motif protein (Trp-cage). We demonstrate that constrained MD replica exchange method exhibits a wider conformational search than all-atom MD with increased enrichment of near native structures. “Hierarchical” constrained MD simulations, where the partially formed helical regions in the initial stretch of the all-torsion folding simulation trajectory of Trp-cage were frozen, showed a better sampling of near native structures than all-torsion constrained MD simulations. This is in agreement with the zipping-and-assembly folding model put forth by Dill and coworkers for folding proteins. The use of hierarchical “freeze and thaw” clustering schemes in constrained MD simulation can be used to sample conformations that contribute significantly to folding of proteins. PMID:21591767
Constraining dark energy from the abundance of weak gravitational lenses
NASA Astrophysics Data System (ADS)
Weinberg, Nevin N.; Kamionkowski, Marc
2003-05-01
We examine the prospect of using the observed abundance of weak gravitational lenses to constrain the equation-of-state parameter w=p/ρ of dark energy. Dark energy modifies the distance-redshift relation, the amplitude of the matter power spectrum, and the rate of structure growth. As a result, it affects the efficiency with which dark-matter concentrations produce detectable weak-lensing signals. Here we solve the spherical-collapse model with dark energy, clarifying some ambiguities found in the literature. We also provide fitting formulae for the non-linear overdensity at virialization and the linear-theory overdensity at collapse. We then compute the variation in the predicted weak-lens abundance with w. We find that the predicted redshift distribution and number count of weak lenses are highly degenerate in w and the present matter density Ω0. If we fix Ω0 the number count of weak lenses for w=-2/3 is a factor of ~2 smaller than for the Λ cold dark matter (CDM) model w=-1. However, if we allow Ω0 to vary with w such that the amplitude of the matter power spectrum as measured by the Cosmic Background Explorer (COBE) matches that obtained from the X-ray cluster abundance, the decrease in the predicted lens abundance is less than 25 per cent for -1 <=w< -0.4. We show that a more promising method for constraining dark energy - one that is largely unaffected by the Ω0-w degeneracy as well as uncertainties in observational noise - is to compare the relative abundance of virialized X-ray lensing clusters with the abundance of non-virialized, X-ray underluminous, lensing haloes. For aperture sizes of ~15 arcmin, the predicted ratio of the non-virialized to virialized lenses is greater than 40 per cent and varies by ~20 per cent between w=-1 and -0.6. Overall, we find that, if all other weak-lensing parameters are fixed, a survey must cover at least ~40 deg2 in order for the weak-lens number count to differentiate a ΛCDM cosmology from a dark-energy model with w
Constrained reduced-order models based on proper orthogonal decomposition
Reddy, Sohail R.; Freno, Brian Andrew; Cizmas, Paul G. A.; ...
2017-04-09
A novel approach is presented to constrain reduced-order models (ROM) based on proper orthogonal decomposition (POD). The Karush–Kuhn–Tucker (KKT) conditions were applied to the traditional reduced-order model to constrain the solution to user-defined bounds. The constrained reduced-order model (C-ROM) was applied and validated against the analytical solution to the first-order wave equation. C-ROM was also applied to the analysis of fluidized beds. Lastly, it was shown that the ROM and C-ROM produced accurate results and that C-ROM was less sensitive to error propagation through time than the ROM.
Onomatopoeia characters extraction from comic images using constrained Delaunay triangulation
NASA Astrophysics Data System (ADS)
Liu, Xiangping; Shoji, Kenji; Mori, Hiroshi; Toyama, Fubito
2014-02-01
A method for extracting onomatopoeia characters from comic images was developed based on stroke width feature of characters, since they nearly have a constant stroke width in a number of cases. An image was segmented with a constrained Delaunay triangulation. Connected component grouping was performed based on the triangles generated by the constrained Delaunay triangulation. Stroke width calculation of the connected components was conducted based on the altitude of the triangles generated with the constrained Delaunay triangulation. The experimental results proved the effectiveness of the proposed method.
Residual flexibility test method for verification of constrained structural models
NASA Technical Reports Server (NTRS)
Admire, John R.; Tinker, Michael L.; Ivey, Edward W.
1992-01-01
A method is presented for deriving constrained modes and frequencies from a model correlated to a set of free-free test modes and a set of measured residual flexibilities. The method involves a simple modification of the MacNeal and Rubin component mode representation to allow verification of a constrained structural model. Results for two spaceflight structures show quick convergence of constrained modes using an easily measurable set of free-free modes plus the residual flexibility matrix or its boundary partition. This paper further validates the residual flexibility approach as an alternative test/analysis method when fixed-base testing proves impractical.
Quantum dynamics by the constrained adiabatic trajectory method
Leclerc, A.; Jolicard, G.; Guerin, S.; Killingbeck, J. P.
2011-03-15
We develop the constrained adiabatic trajectory method (CATM), which allows one to solve the time-dependent Schroedinger equation constraining the dynamics to a single Floquet eigenstate, as if it were adiabatic. This constrained Floquet state (CFS) is determined from the Hamiltonian modified by an artificial time-dependent absorbing potential whose forms are derived according to the initial conditions. The main advantage of this technique for practical implementation is that the CFS is easy to determine even for large systems since its corresponding eigenvalue is well isolated from the others through its imaginary part. The properties and limitations of the CATM are explored through simple examples.
York, William S; Yi, Xiaobing
2004-08-01
A computer program CONDORR (CONstrained Dynamics of Rigid Residues) was developed for molecular dynamics simulations of large and/or constrained molecular systems, particularly carbohydrates. CONDORR efficiently calculates molecular trajectories on the basis of 2D or 3D potential energy maps, and can generate such maps based on a simple force field. The simulations involve three translational and three rotational degrees of freedom for each rigid, asymmetrical residue in the model. Total energy and angular momentum are conserved when no stochastic or external forces are applied to the model, if the time step is kept sufficiently short. Application of Langevin dynamics allows longer time steps, providing efficient exploration of conformational space. The utility of CONDORR was demonstrated by application to a constrained polysaccharide model and to the calculation of residual dipolar couplings for a disaccharide. [Figure: see text]. Molecular models (bottom) are created by cloning rigid residue archetypes (top) and joining them together. As defined here, the archetypes AX, HM and BG respectively correspond to an alpha-D-Xyl p residue, a hydroxymethyl group, and a beta-D-Glc p residue lacking O6, H6a and H6b. Each archetype contains atoms (indicated by boxes) that can be shared with other archetypes to form a linked structure. For example, the glycosidic link between the two D-Glc p residues is established by specifying that O1 of the nonreducing beta-D-Glc p (BG) residue (2) is identical to O4 of the reducing Glc p (BG) residue (1). The coordinates of the two residues are adjusted so as to superimpose these two (nominally distinct) atoms. Flexible hydroxymethyl (HM) groups (3 and 4) are treated as separate residues, and the torsional angles (normally indicated by the symbol omega) that define their geometric relationships to the pyranosyl rings of the BG residues are specified as psi3 and psi4, respectively. The torsional angles phi3 and phi4, defined solely to
Mantle Convection Models Constrained by Seismic Tomography
NASA Astrophysics Data System (ADS)
Durbin, C. J.; Shahnas, M.; Peltier, W. R.; Woodhouse, J. H.
2011-12-01
Perovskite-post-Perovskite transition (Murakami et al., 2004, Science) that appears to define the D" layer at the base of the mantle. In this initial phase of what will be a longer term project we are assuming that the internal mantle viscosity structure is spherically symmetric and compatible with the recent inferences of Peltier and Drummond (2010, Geophys. Res. Lett.) based upon glacial isostatic adjustment and Earth rotation constraints. The internal density structure inferred from the tomography model is assimilated into the convection model by continuously "nudging" the modification to the input density structure predicted by the convection model back towards the tomographic constraint at the long wavelengths that the tomography specifically resolves, leaving the shorter wavelength structure free to evolve, essentially "slaved" to the large scale structure. We focus upon the ability of the nudged model to explain observed plate velocities, including both their poloidal (divergence related) and toroidal (strike slip fault related) components. The true plate velocity field is then used as an additional field towards which the tomographically constrained solution is nudged.
Is oil consumption constrained by industrial structure? Evidence from China
NASA Astrophysics Data System (ADS)
Jia, Y. Q.; Duan, H. M.
2017-08-01
This paper examines whether oil consumption is constrained by output value, applying a cointegration test and an ECM to the primary, secondary, and tertiary sectors in China during 1985-2013. The empirical results indicate that oil consumption in China is constrained by the industrial structure both in the short run and in the long run. Regardless of the time horizon considered, the oil consumption constraint is the lowest for the primary sector as well as the highest for the tertiary sector. This is because the long-term industrial structure formation and the technological level of each sector underlines the existence of long run equilibrium and short run fluctuations of output value and oil consumption, with the latter being constrained by adjustments in industrial structure. In order to decrease the constraining effect of output value on oil consumption, the government should take some measures to improve the utilization rate, reducing the intensity of oil consumption, and secure the supply of oil.
A Constrained Spline Estimator of a Hazard Function.
ERIC Educational Resources Information Center
Bloxom, Bruce
1985-01-01
A constrained quadratic spline is proposed as an estimator of the hazard function of a random variable. A maximum penalized likelihood procedure is used to fit the estimator to a sample of psychological response times. (Author/LMO)
Vibration control through passive constrained layer damping and active control
NASA Astrophysics Data System (ADS)
Lam, Margaretha J.; Inman, Daniel J.; Saunders, William R.
1997-05-01
To add damping to systems, viscoelastic materials (VEM) are added to structures. In order to enhance the damping effects of the VEM, a constraining layer is attached. When this constraining layer is an active element, the treatment is called active constrained layer damping (ACLD). Recently, the investigation of ACLD treatments has shown it to be an effective method of vibration suppression. In this paper, the treatment of a beam with a separate active element and passive constrained layer (PCLD) element is investigated. A Ritz- Galerkin approach is used to obtain discretized equations of motion. The damping is modeled using the GHM method and the system is analyzed in the time domain. By optimizing on the performance and control effort for both the active and passive case, it is shown that this treatment is capable of lower control effort with more inherent damping, and is therefore a better approach to damp vibration.
Thin-shell wormholes constrained by cosmological observations
NASA Astrophysics Data System (ADS)
Wang, Deng; Meng, Xin-He
2017-09-01
We investigate the thin-shell wormholes constrained by cosmological observations for the first time in the literature. Without loss of generality, we study the thin-shell wormholes in ωCDM model and analyze their stability under perturbations preserving the symmetry. Firstly, we constrain the ωCDM model using a combination of Union 2.1 SNe Ia data, the latest H(z) data and CMB data. Secondly, we use the constrained dark energy equation of state (EoS) ω which lies in [ - 1 . 05 , - 0 . 89 ] to investigate thin-shell wormholes generated by various black hole spacetimes. We find that the stable Schwarzschild and Reinssner-Nordström thin-shell wormholes constrained by cosmological observations do not exist. In addition, the method we developed can be applied in exploring the stable thin-shell wormholes from any black hole spacetime in the framework of any cosmological theory.
FXR agonist activity of conformationally constrained analogs of GW 4064
Akwabi-Ameyaw, Adwoa; Bass, Jonathan Y.; Caldwell, Richard D.; Caravella, Justin A.; Chen, Lihong; Creech, Katrina L.; Deaton, David N.; Madauss, Kevin P.; Marr, Harry B.; McFadyen, Robert B.; Miller, Aaron B.; Navas, III, Frank; Parks, Derek J.; Spearing, Paul K.; Todd, Dan; Williams, Shawn P.; Wisely, G. Bruce
2010-09-27
Two series of conformationally constrained analogs of the FXR agonist GW 4064 1 were prepared. Replacement of the metabolically labile stilbene with either benzothiophene or naphthalene rings led to the identification of potent full agonists 2a and 2g.
Constrained Adaptive Beamforming for Improved Contrast in Breast Ultrasound
2006-06-01
have led us to utilize a recently proposed method, Spatial Processing Optimized and Constrained ( SPOC ). In initial simulations this method not only...6 Summary of First Year Progress……………………………………6 Conventional Beamformer Optimization………….…………….….7 SPOC Progress...and hundreds of papers published in this area, only the SPOC (Spatial Processing Optimized and Constrained) algorithm could be readily modified to meet
Constrained Adaptive Beamforming for Improved Contrast in Breast Ultrasound
2008-06-01
us to modify the Spatial Processing Optimized and Constrained algorithm ( SPOC ) to yield the Time-Domain Optimized Near-field Estimator (TONE). In...beamformers - Improvement and evaluation of adaptive imaging algorithms based loosely on SPOC - Invention and testing of the basic TONE algorithm...named the Time-domain Optimized Near-Filed Estimator, or TONE. The novel ABF was developed from Spatial Processing: Optimized and Constrained ( SPOC
Constrained minimization of smooth functions using a genetic algorithm
NASA Technical Reports Server (NTRS)
Moerder, Daniel D.; Pamadi, Bandu N.
1994-01-01
The use of genetic algorithms for minimization of differentiable functions that are subject to differentiable constraints is considered. A technique is demonstrated for converting the solution of the necessary conditions for a constrained minimum into an unconstrained function minimization. This technique is extended as a global constrained optimization algorithm. The theory is applied to calculating minimum-fuel ascent control settings for an energy state model of an aerospace plane.
Geometric constrained variational calculus. II: The second variation (Part I)
NASA Astrophysics Data System (ADS)
Massa, Enrico; Bruno, Danilo; Luria, Gianvittorio; Pagani, Enrico
2016-10-01
Within the geometrical framework developed in [Geometric constrained variational calculus. I: Piecewise smooth extremals, Int. J. Geom. Methods Mod. Phys. 12 (2015) 1550061], the problem of minimality for constrained calculus of variations is analyzed among the class of differentiable curves. A fully covariant representation of the second variation of the action functional, based on a suitable gauge transformation of the Lagrangian, is explicitly worked out. Both necessary and sufficient conditions for minimality are proved, and reinterpreted in terms of Jacobi fields.
Constraining compartmental models using multiple voltage recordings and genetic algorithms.
Keren, Naomi; Peled, Noam; Korngreen, Alon
2005-12-01
Compartmental models with many nonlinearly and nonhomogeneous distributions of voltage-gated conductances are routinely used to investigate the physiology of complex neurons. However, the number of loosely constrained parameters makes manually constructing the desired model a daunting if not impossible task. Recently, progress has been made using automated parameter search methods, such as genetic algorithms (GAs). However, these methods have been applied to somatically recorded action potentials using relatively simple target functions. Using a genetic minimization algorithm and a reduced compartmental model based on a previously published model of layer 5 neocortical pyramidal neurons we compared the efficacy of five cost functions (based on the waveform of the membrane potential, the interspike interval, trajectory density, and their combinations) to constrain the model. When the model was constrained using somatic recordings only, a combined cost function was found to be the most effective. This combined cost function was then applied to investigate the contribution of dendritic and axonal recordings to the ability of the GA to constrain the model. The more recording locations from the dendrite and the axon that were added to the data set the better was the genetic minimization algorithm able to constrain the compartmental model. Based on these simulations we propose an experimental scheme that, in combination with a genetic minimization algorithm, may be used to constrain compartmental models of neurons.
Gravitational-wave limits from pulsar timing constrain supermassive black hole evolution.
Shannon, R M; Ravi, V; Coles, W A; Hobbs, G; Keith, M J; Manchester, R N; Wyithe, J S B; Bailes, M; Bhat, N D R; Burke-Spolaor, S; Khoo, J; Levin, Y; Osłowski, S; Sarkissian, J M; van Straten, W; Verbiest, J P W; Wang, J-B
2013-10-18
The formation and growth processes of supermassive black holes (SMBHs) are not well constrained. SMBH population models, however, provide specific predictions for the properties of the gravitational-wave background (GWB) from binary SMBHs in merging galaxies throughout the universe. Using observations from the Parkes Pulsar Timing Array, we constrain the fractional GWB energy density (Ω(GW)) with 95% confidence to be Ω(GW)(H0/73 kilometers per second per megaparsec)(2) < 1.3 × 10(-9) (where H0 is the Hubble constant) at a frequency of 2.8 nanohertz, which is approximately a factor of 6 more stringent than previous limits. We compare our limit to models of the SMBH population and find inconsistencies at confidence levels between 46 and 91%. For example, the standard galaxy formation model implemented in the Millennium Simulation Project is inconsistent with our limit with 50% probability.
Clements, John H.; DeLorbe, John E.; Benfield, Aaron P.; Martin, Stephen F.
2010-01-01
Structures of the Grb2 SH2 domain complexed with a series of pseudopeptides containing flexible (benzyl succinate) and constrained (aryl cyclopropanedicarboxylate) replacements of the phosphotyrosine (pY) residue in tripeptides derived from Ac-pYXN-NH2 (where X = V, I, E and Q) were elucidated by X-ray crystallography. Complexes of flexible/constrained pairs having the same pY + 1 amino acid were analyzed in order to ascertain what structural differences might be attributed to constraining the phosphotyrosine replacement. In this context, a given structural dissimilarity between complexes was considered to be significant if it was greater than the corresponding difference in complexes coexisting within the same asymmetric unit. The backbone atoms of the domain generally adopt a similar conformation and orientation relative to the ligands in the complexes of each flexible/constrained pair, although there are some significant differences in the relative orientations of several loop regions, most notably in the BC loop that forms part of the binding pocket for the phosphate group in the tyrosine replacements. These variations are greater in the set of complexes of constrained ligands than in the set of complexes of flexible ligands. The constrained ligands make more direct polar contacts to the domain than their flexible counterparts, whereas the more flexible ligand of each pair makes more single-water-mediated contacts to the domain; there was no correlation between the total number of protein–ligand contacts and whether the phosphotyrosine replacement of the ligand was preorganized. The observed differences in hydrophobic interactions between the complexes of each flexible/constrained ligand pair were generally similar to those observed upon comparing such contacts in coexisting complexes. The average adjusted B factors of the backbone atoms of the domain and loop regions are significantly greater in the complexes of constrained ligands than in the complexes of
NASA Astrophysics Data System (ADS)
Balamurugan, V.; Narayanan, S.
2003-10-01
In the present paper, the active-passive hybrid vibration control performance due to Enhanced Smart Constrained Layer Damping (ESCLD) treatment as proposed by Liao and Wang on plate like structures has been considered. This treatment consists of a viscoelastic layer constrained between a smart piezoelectric layer and the base structure being controlled. Also, the smart constraining layer is clamped to the base structure. This type of damping treatment has got both active and passive component of damping. The passive damping is through cyclic shearing of viscoelastic constrained layer which is further enhanced by activating the smart piezoelectric constraining layer and the active component of the damping is through the transfer of control moments from the piezoelectric layer to the base structure through the viscoelastic layer and also bypassed through the clamps. A plate finite element has been formulated using first order shear deformation theory, including the effect of transverse shear and rotary inertia. The effect of the viscoelastic shear layer and piezoelectric constraining layer on the mass and stiffness has been included in the model. The viscoelastic shear layer is modeled usig Golla-Hughes-McTavish (GHM) method, which is a time domain approach. The clamps (edge elements) are modeled as equivalent springs connecting the smart piezoelectric constraining layer with the structure to be controlled. LQR optimal control strategy is used to obtain optimal control gains. The effect of the viscoelastic material properties (shear modulus and loss factor) on the hybrid vibration control performance is studied for both SCLD (without edge elements) and ESCLD systems.
Constraining canopy biophysical simulations with MODIS reflectance data
NASA Astrophysics Data System (ADS)
Drewry, D. T.; Duveiller, G.
2013-05-01
Modern vegetation models incorporate ecophysiological details that allow for accurate estimates of carbon dioxide uptake, water use and energy exchange, but require knowledge of dynamic structural and biochemical traits. Variations in these traits are controlled by genetic factors as well as growth stage and nutrient and moisture availability, making them difficult to predict and prone to significant error. Here we explore the use of MODIS optical reflectance data for constraining key canopy- and leaf-level traits required by forward biophysical models. A multi-objective optimization algorithm is used to invert the PROSAIL canopy radiation transfer model, which accounts for the effects of leaf-level optical properties, foliage distribution and orientation on canopy reflectance across the optical range. Inversions are conducted for several growing seasons for both soybean and maize at several sites in the Central US agro-ecosystem. These inversions provide estimates of seasonal variations, and associated uncertainty, of variables such as leaf area index (LAI) that are then used as inputs into the MLCan biophysical model to conduct forward simulations. MLCan characterizes the ecophysiological functioning of a plant canopy at a half-hourly timestep, and has been rigorously validated for both C3 and C4 crops against observations of canopy CO2 uptake, evapotranspiration and sensible heat exchange across a wide range of meteorological conditions. The inversion-derived canopy properties are used to examine the ability of MODIS data to characterize seasonal variations in canopy properties in the context of a detailed forward canopy biophysical model, and the uncertainty induced in forward model estimates as a function of the uncertainty in the inverted parameters. Special care is made to ensure that the satellite observations match adequately, in both time and space, with the coupled model simulations. To do so, daily MODIS observations are used and a validated model of
CMB polarization can constrain cosmology better than CMB temperature
NASA Astrophysics Data System (ADS)
Galli, Silvia; Benabed, Karim; Bouchet, François; Cardoso, Jean-François; Elsner, Franz; Hivon, Eric; Mangilli, Anna; Prunet, Simon; Wandelt, Benjamin
2014-09-01
We demonstrate that for a cosmic variance limited experiment, cosmic microwave background (CMB) E polarization alone places stronger constraints on cosmological parameters than CMB temperature. For example, we show that CℓEE can constrain parameters better than CℓTT by up to a factor 2.8 when a multipole range of ℓ=30-2500 is considered. We expose the physical effects at play behind this remarkable result and study how it depends on the multipole range included in the analysis. In most relevant cases, CℓTE or CℓEE surpass the CℓTT-based cosmological constraints. This result is important as the small-scale astrophysical foregrounds are expected to have a much reduced impact on polarization, thus opening the possibility of building cleaner and more stringent constraints of the ΛCDM model. This is relevant especially for proposed future CMB satellite missions, such as CORE or PRISM, that are designed to be cosmic variance limited in polarization till very large multipoles. We perform the same analysis for a Planck-like experiment, and conclude that even in this case CℓTE alone should determine the constraint on Ωch2 better than CℓTT by ˜15%, while determining Ωbh2, ns and θ with comparable accuracy. Finally, we explore a few classical extensions of the ΛCDM model and show again that CMB polarization alone provides more stringent constraints than CMB temperature in the case of a cosmic variance limited experiment.
Constrained Source Space MR Spectroscopy: Multiple Voxels, No Gradient Readout.
Landheer, K; Sahgal, A; Das, S; Graham, S J
2015-08-01
Our goal was to develop a novel technique for measuring a small number of localized spectra simultaneously and in a time-efficient manner. Using appropriate radiofrequency pulses, the magnetization from multiple voxels is excited simultaneously and then separated (reconstructed) by using the individual coil-sensitivity profiles from a multichannel receiver coil. Because no gradients are used for k-space encoding, constrained source space MR spectroscopy provides a time advantage over conventional spectroscopic imaging and an improved signal-to-noise ratio per square root of unit time over single-voxel spectroscopy applied at each successive location. In the present work, we considered prototype application of constrained source space MR spectroscopy for 2 voxels. Experimental data from healthy volunteers and simulation results showed that constrained source space MR spectroscopy is effective at extracting 2 independent spectra even in the challenging scenario of the voxels being closely spaced. Also, from 6 patients with various types of brain cancer we obtained 2-voxel constrained source space MR spectroscopy data, which showed spectra of clinical quality in half the time required to perform successive single-voxel MR spectroscopy. Constrained source space MR spectroscopy provides clinical quality spectra and could be used to probe multiple voxels simultaneously in combination with Hadamard encoding for further scan-time reductions. © 2015 by American Journal of Neuroradiology.
Variational contact symmetries of constrained Lagrangians
NASA Astrophysics Data System (ADS)
Terzis, Petros A.; Dimakis, N.; Christodoulakis, T.; Paliathanasis, Andronikos; Tsamparlis, Michael
2016-03-01
The investigation of contact symmetries of re-parametrization invariant Lagrangians of finite degrees of freedom and quadratic in the velocities is presented. The main concern of the paper is those symmetry generators which depend linearly in the velocities. A natural extension of the symmetry generator along the lapse function N(t) , with the appropriate extension of the dependence in N ˙ (t) of the gauge function, is assumed; this action yields new results. The central finding is that the integrals of motion are either linear or quadratic in velocities and are generated, respectively by the conformal Killing vector fields and the conformal Killing tensors of the configuration space metric deduced from the kinetic part of the Lagrangian (with appropriate conformal factors). The freedom of re-parametrization allows one to appropriately scale N(t) , so that the potential becomes constant; in this case the integrals of motion can be constructed from the Killing fields and Killing tensors of the scaled metric. A rather interesting result is the non-necessity of the gauge function in Noether's theorem due to the presence of the Hamiltonian constraint.
Constraining decaying dark matter with neutron stars
NASA Astrophysics Data System (ADS)
Pérez-García, M. Ángeles; Silk, Joseph
2015-05-01
The amount of decaying dark matter, accumulated in the central regions in neutron stars together with the energy deposition rate from decays, may set a limit on the neutron star survival rate against transitions to more compact objects provided nuclear matter is not the ultimate stable state of matter and that dark matter indeed is unstable. More generally, this limit sets constraints on the dark matter particle decay time, τχ. We find that in the range of uncertainties intrinsic to such a scenario, masses (mχ /TeV) ≳ 9 ×10-4 or (mχ /TeV) ≳ 5 ×10-2 and lifetimes τχ ≲1055 s and τχ ≲1053 s can be excluded in the bosonic or fermionic decay cases, respectively, in an optimistic estimate, while more conservatively, it decreases τχ by a factor ≳1020. We discuss the validity under which these results may improve with other current constraints.
Reliable Delay Constrained Multihop Broadcasting in VANETs
NASA Astrophysics Data System (ADS)
Koubek, Martin; Rea, Susan; Pesch, Dirk
2010-12-01
Vehicular communication is regarded as a major innovative feature for in-car technology. While improving road safety is unanimously considered the major driving factor for the deployment of Intelligent Vehicle Safety Systems, the challenges relating to reliable multi-hop broadcasting are exigent in vehicular networking. In fact, safety applications must rely on very accurate and up-to-date information about the surrounding environment, which in turn requires the use of accurate positioning systems and smart communication protocols for exchanging information. Communications protocols for VANETs must guarantee fast and reliable delivery of information to all vehicles in the neighbourhood, where the wireless communication medium is shared and highly unreliable with limited bandwidth. In this paper, we focus on mechanisms that improve the reliability of broadcasting protocols, where the emphasis is on satisfying the delay requirements for safety applications. We present the Pseudoacknowledgments (PACKs) scheme and compare this with existing methods over varying vehicle densities in an urban scenario using the network simulator OPNET.
Liao, Ho-Tang; Yau, Yu-Chen; Huang, Chun-Sheng; Chen, Nathan; Chow, Judith C; Watson, John G; Tsai, Shih-Wei; Chou, Charles C-K; Wu, Chang-Fu
2017-08-01
Exposure to air pollutants such as volatile organic compounds (VOCs) and fine particulate matter (PM2.5) are associated with adverse health effects. This study applied multiple time resolution data of hourly VOCs and 24-h PM2.5 to a constrained Positive Matrix Factorization (PMF) model for source apportionment in Taipei, Taiwan. Ninety-two daily PM2.5 samples and 2208 hourly VOC measurements were collected during four seasons in 2014 and 2015. With some a priori information, we used different procedures to constrain retrieved factors toward realistic sources. A total of nine source factors were identified as: natural gas/liquefied petroleum gas (LPG) leakage, solvent use/industrial process, contaminated marine aerosol, secondary aerosol/long-range transport, oil combustion, traffic related, evaporative gasoline emission, gasoline exhaust, and soil dust. Results showed that solvent use/industrial process was the largest contributor (19%) to VOCs while the largest contributor to PM2.5 mass was secondary aerosol/long-range transport (57%). A robust regression analysis showed that secondary aerosol was mostly contributed by regional transport related factor (25%). Copyright © 2017 Elsevier Ltd. All rights reserved.
Foster, Sarah; Giles-Corti, Billie
2008-09-01
Personal safety is commonly cited in qualitative research as a barrier to local walking, yet the relationship between safety and constrained physical activity has received mixed support in quantitative studies. This paper reviews the quantitative evidence to date, seeking to explain the inconsistencies, and offers recommendations for future research. A social-ecological framework was adopted to explore the evidence linking crime-related safety, and factors that influence real and perceived safety, with constrained physical activity. Perceived safety tends to affect the physical activity of groups already known to exhibit greater anxiety about crime; and some elements of the built environment that influence safety appear to constrain physical activity. However the evidence is somewhat inconsistent, and this may be partly attributed to measurement limitations. Many studies employ generic safety measures that make implicit references to crime or use composite variables that lack specificity. Physical activity outcomes also require consideration, as only activities occurring locally outdoors are likely to be affected by neighborhood crime. Further research is required to tease out associations between real and perceived crime-related safety and physical activity, ideally employing behaviour and crime-specific measures, and addressing the moderating role of the social and built environments.
Constrained growth flips the direction of optimal phenological responses among annual plants.
Lindh, Magnus; Johansson, Jacob; Bolmgren, Kjell; Lundström, Niklas L P; Brännström, Åke; Jonzén, Niclas
2016-03-01
Phenological changes among plants due to climate change are well documented, but often hard to interpret. In order to assess the adaptive value of observed changes, we study how annual plants with and without growth constraints should optimize their flowering time when productivity and season length changes. We consider growth constraints that depend on the plant's vegetative mass: self-shading, costs for nonphotosynthetic structural tissue and sibling competition. We derive the optimal flowering time from a dynamic energy allocation model using optimal control theory. We prove that an immediate switch (bang-bang control) from vegetative to reproductive growth is optimal with constrained growth and constant mortality. Increasing mean productivity, while keeping season length constant and growth unconstrained, delayed the optimal flowering time. When growth was constrained and productivity was relatively high, the optimal flowering time advanced instead. When the growth season was extended equally at both ends, the optimal flowering time was advanced under constrained growth and delayed under unconstrained growth. Our results suggests that growth constraints are key factors to consider when interpreting phenological flowering responses. It can help to explain phenological patterns along productivity gradients, and links empirical observations made on calendar scales with life-history theory.
Constrained Violent Relaxation to a Spherical Halo
NASA Astrophysics Data System (ADS)
Mangalam, A.; Nityananda, R.; Sridhar, S.
1999-10-01
Violent relaxation during the collapse of a galaxy halo is known to be incomplete in realistic cases such as cosmological infall or mergers. We adopt a physical picture of strong but short-lived interactions between potential fluctuations and particle orbits, using the broad framework outlined earlier for incorporating incompleteness of the relaxation. We are guided by results from plasma physics, viz., the quasilinear theory of Landau damping, but allow for significant differences in our case. Crucially, wave particle scattering does not drive the system to an equilibrium distribution function of the exponential type, even in regions of phase space allowed by the constraints. The physical process is mixing without friction in ``action'' space, for which the simplest possible model is a constant phase space density modulated by the constraints. Our distribution function does not use the exponential functions of the energy prevalent in other work, which we regard as inappropriate to collisionless systems. The dynamical constraint of a finite short period of the relaxation process is argued to lead to a 1/Tr factor in the distribution function, where Tr is the radial period. The notion of strong potential fluctuations in a core is built in as a cutoff in pericenter (which we find preferable to one angular momentum, the other alternative we explored). The halo of the self-consistent, parameter-free solutions show an r-4 behavior in density at large r, an r1/4 surface brightness profile in the region 0.1re-8re, and a radially anisotropic velocity dispersion profile outside an isotropic core. The energy distribution seen in simulations N(E) singles out the pericenter cutoff model as the most realistic among the variants we have explored. The results are robust to modifications of the period dependence keeping the same asymptotic behavior or to the use of binding energy raised to the power of 3/2 in place of 1/Tr.
Using extracellular action potential recordings to constrain compartmental models.
Gold, Carl; Henze, Darrell A; Koch, Christof
2007-08-01
We investigate the use of extracellular action potential (EAP) recordings for biophysically faithful compartmental models. We ask whether constraining a model to fit the EAP is superior to matching the intracellular action potential (IAP). In agreement with previous studies, we find that the IAP method under-constrains the parameters. As a result, significantly different sets of parameters can have virtually identical IAP's. In contrast, the EAP method results in a much tighter constraint. We find that the distinguishing characteristics of the waveform--but not its amplitude-resulting from the distribution of active conductances are fairly invariant to changes of electrode position and detailed cellular morphology. Based on these results, we conclude that EAP recordings are an excellent source of data for the purpose of constraining compartmental models.
Undulatory buckling of a rod constrained by an elastic matrix
NASA Astrophysics Data System (ADS)
Liu, Jia; Su, Tianxiang; Lopez-Pamies, Oscar; Reis, Pedro; Bertoldi, Katia
2012-02-01
Elastic instabilities of rods constrained by an elastic matrix and subjected to axial compression have long been recognized as essential for structural applications in the context of failure mitigation and, more recently, towards exploitation of functionality. Relevant fields for this class of problems include drilling, biomedical instrumentation and root growth in plants. We explore the two possible scenarios observed when, above a threshold load, compression is applied to a rod constrained by a matrix: i) the rod can develop a planar oscillatory solution (sinusoidal buckling) or ii) it can take the configuration of a helix (helical buckling). We identify the principal parameters of this system, perform a systematic parametric study and rationalize the phase diagram through a hybrid of theoretical and numerical analyses. Particular attention is devoted to the effect of the mechanical properties of the constraining matrix which is found to have a critical influence on this buckling scenario.
Residual flexibility test method for verification of constrained structural models
NASA Technical Reports Server (NTRS)
Admire, John R.; Tinker, Michael L.; Ivey, Edward W.
1994-01-01
A method is described for deriving constrained modes and frequencies from a reduced model based on a subset of the free-free modes plus the residual effects of neglected modes. The method involves a simple modification of the MacNeal and Rubin component mode representation to allow development of a verified constrained (fixed-base) structural model. Results for two spaceflight structures having translational boundary degrees of freedom show quick convergence of constrained modes using a measureable number of free-free modes plus the boundary partition of the residual flexibility matrix. This paper presents the free-free residual flexibility approach as an alternative test/analysis method when fixed-base testing proves impractical.
Hee, S.; Vázquez, J. A.; Handley, W. J.; ...
2016-12-01
Data-driven model-independent reconstructions of the dark energy equation of state w(z) are presented using Planck 2015 era CMB, BAO, SNIa and Lyman-α data. These reconstructions identify the w(z) behaviour supported by the data and show a bifurcation of the equation of state posterior in the range 1.5 < z < 3. Although the concordance ΛCDM model is consistent with the data at all redshifts in one of the bifurcated spaces, in the other a supernegative equation of state (also known as ‘phantom dark energy’) is identified within the 1.5σ confidence intervals of the posterior distribution. In order to identify themore » power of different datasets in constraining the dark energy equation of state, we use a novel formulation of the Kullback–Leibler divergence. Moreover, this formalism quantifies the information the data add when moving from priors to posteriors for each possible dataset combination. The SNIa and BAO datasets are shown to provide much more constraining power in comparison to the Lyman-α datasets. Furthermore, SNIa and BAO constrain most strongly around redshift range 0.1 - 0.5, whilst the Lyman-α data constrains weakly over a broader range. We do not attribute the supernegative favouring to any particular dataset, and note that the ΛCDM model was favoured at more than 2 log-units in Bayes factors over all the models tested despite the weakly preferred w(z) structure in the data.« less
Shah, Sweta; Nelemans, Gijs
2014-08-01
The space-based gravitational wave (GW) detector, evolved Laser Interferometer Space Antenna (eLISA) is expected to observe millions of compact Galactic binaries that populate our Milky Way. GW measurements obtained from the eLISA detector are in many cases complimentary to possible electromagnetic (EM) data. In our previous papers, we have shown that the EM data can significantly enhance our knowledge of the astrophysically relevant GW parameters of Galactic binaries, such as the amplitude and inclination. This is possible due to the presence of some strong correlations between GW parameters that are measurable by both EM and GW observations, for example, the inclination and sky position. In this paper, we quantify the constraints in the physical parameters of the white-dwarf binaries, i.e., the individual masses, chirp mass, and the distance to the source that can be obtained by combining the full set of EM measurements such as the inclination, radial velocities, distances, and/or individual masses with the GW measurements. We find the following 2σ fractional uncertainties in the parameters of interest. The EM observations of distance constrain the chirp mass to ∼15%-25%, whereas EM data of a single-lined spectroscopic binary constrain the secondary mass and the distance with factors of two to ∼40%. The single-line spectroscopic data complemented with distance constrains the secondary mass to ∼25%-30%. Finally, EM data on double-lined spectroscopic binary constrain the distance to ∼30%. All of these constraints depend on the inclination and the signal strength of the binary systems. We also find that the EM information on distance and/or the radial velocity are the most useful in improving the estimate of the secondary mass, inclination, and/or distance.
A constrained von Mises distribution to describe fiber organization in thin soft tissues.
Gouget, Cecile L M; Girard, Michael J; Ethier, C Ross
2012-03-01
The semi-circular von Mises distribution is widely used to describe the unimodal planar organization of fibers in thin soft tissues. However, it cannot accurately describe the isotropic subpopulation of fibers present in such tissues, and therefore an improved mathematical description is needed. We present a modified distribution, formed as a weighted mixture of the semi-circular uniform distribution and the semi-circular von Mises distribution. It is described by three parameters: β, which weights the contribution from each mixture component; k, the fiber concentration factor; and θ ( p ), the preferred fiber orientation. This distribution was used to fit data obtained by small-angle light scattering experiments from various thin soft tissues. Initial use showed that satisfactory fits of fiber distributions could be obtained (error generally < 1%), but at the cost of non-physically meaningful values of k and β. To address this issue, an empirical constraint between the parameters k and β was introduced, resulting in a constrained 2-parameter fiber distribution. Compared to the 3-parameter distribution, the constrained 2-parameter distribution fits experimental data well (error generally < 2%) and had the advantage of producing physically meaningful parameter values. In addition, the constrained 2-parameter approach was more robust to experimental noise. The constrained 2-parameter fiber distribution can replace the semi-circular von Mises distribution to describe unimodal planar organization of fibers in thin soft tissues. Inclusion of such a function in constitutive models for finite element simulations should provide better quantitative estimates of soft tissue biomechanics under normal and pathological conditions.
NASA Astrophysics Data System (ADS)
Hee, S.; Vázquez, J. A.; Handley, W. J.; Hobson, M. P.; Lasenby, A. N.
2017-04-01
Data-driven model-independent reconstructions of the dark energy equation of state w(z) are presented using Planck 2015 era cosmic microwave background, baryonic acoustic oscillations (BAO), Type Ia supernova (SNIa) and Lyman α (Lyα) data. These reconstructions identify the w(z) behaviour supported by the data and show a bifurcation of the equation of state posterior in the range 1.5 < z < 3. Although the concordance Λ cold dark matter (ΛCDM) model is consistent with the data at all redshifts in one of the bifurcated spaces, in the other, a supernegative equation of state (also known as 'phantom dark energy') is identified within the 1.5σ confidence intervals of the posterior distribution. To identify the power of different data sets in constraining the dark energy equation of state, we use a novel formulation of the Kullback-Leibler divergence. This formalism quantifies the information the data add when moving from priors to posteriors for each possible data set combination. The SNIa and BAO data sets are shown to provide much more constraining power in comparison to the Lyα data sets. Further, SNIa and BAO constrain most strongly around redshift range 0.1-0.5, whilst the Lyα data constrain weakly over a broader range. We do not attribute the supernegative favouring to any particular data set, and note that the ΛCDM model was favoured at more than 2 log-units in Bayes factors over all the models tested despite the weakly preferred w(z) structure in the data.
Value, Cost, and Sharing: Open Issues in Constrained Clustering
NASA Technical Reports Server (NTRS)
Wagstaff, Kiri L.
2006-01-01
Clustering is an important tool for data mining, since it can identify major patterns or trends without any supervision (labeled data). Over the past five years, semi-supervised (constrained) clustering methods have become very popular. These methods began with incorporating pairwise constraints and have developed into more general methods that can learn appropriate distance metrics. However, several important open questions have arisen about which constraints are most useful, how they can be actively acquired, and when and how they should be propagated to neighboring points. This position paper describes these open questions and suggests future directions for constrained clustering research.
Augmented Lagrangian method for constrained nuclear density functional theory
NASA Astrophysics Data System (ADS)
Staszczak, A.; Stoitsov, M.; Baran, A.; Nazarewicz, W.
2010-10-01
The augmented Lagrangiam method (ALM), widely used in quantum chemistry constrained optimization problems, is applied in the context of the nuclear Density Functional Theory (DFT) in the self-consistent constrained Skyrme Hartree-Fock-Bogoliubov (CHFB) variant. The ALM allows precise calculations of multi-dimensional energy surfaces in the space of collective coordinates that are needed to, e.g., determine fission pathways and saddle points; it improves the accuracy of computed derivatives with respect to collective variables that are used to determine collective inertia; and is well adapted to supercomputer applications.
Constraining dark energy with Sunyaev-Zel'dovich cluster surveys.
Weller, Jochen; Battye, Richard A; Kneissl, Rüdiger
2002-06-10
We discuss the prospects of constraining the properties of a dark energy component, with particular reference to a time varying equation of state, using future cluster surveys selected by their Sunyaev-Zel'dovich effect. We compute the number of clusters expected for a given set of cosmological parameters and propogate the errors expected from a variety of surveys. In the short term they will constrain dark energy in conjunction with future observations of type Ia supernovae, but may in time do so in their own right.
Value, Cost, and Sharing: Open Issues in Constrained Clustering
NASA Technical Reports Server (NTRS)
Wagstaff, Kiri L.
2006-01-01
Clustering is an important tool for data mining, since it can identify major patterns or trends without any supervision (labeled data). Over the past five years, semi-supervised (constrained) clustering methods have become very popular. These methods began with incorporating pairwise constraints and have developed into more general methods that can learn appropriate distance metrics. However, several important open questions have arisen about which constraints are most useful, how they can be actively acquired, and when and how they should be propagated to neighboring points. This position paper describes these open questions and suggests future directions for constrained clustering research.
Augmented Lagrangian Method for Constrained Nuclear Density Functiional Theory
Staszczak, A.; Stoitsov, Mario; Baran, Andrzej K; Nazarewicz, Witold
2010-01-01
The augmented Lagrangian method (ALM), widely used in quantum chemistry constrained optimization problems, is applied in the context of the nuclear Density Functional Theory (DFT) in the self-consistent constrained Skyrme Hartree-Fock-Bogoliubov (CHFB) variant. The ALM allows precise calculations of multidimensional energy surfaces in the space of collective coordinates that are needed to, e.g., determine fission pathways and saddle points; it improves accuracy of computed derivatives with respect to collective variables that are used to determine collective inertia and is well adapted to supercomputer applications.
Constraining the scalar septet model through vector boson scattering
NASA Astrophysics Data System (ADS)
Harris, Mary-Jean; Logan, Heather E.
2017-05-01
The scalar septet model extends the standard model Higgs sector by an isospin septet with hypercharge chosen to preserve ρ ≡MW2/MZ2cos2θW=1 . In this paper we constrain the model at high septet masses using perturbative unitarity of longitudinal vector boson scattering amplitudes. We also apply the constraints from LHC searches for doubly-charged Higgs bosons produced in vector boson fusion, which constrain the model at lower septet masses. We point out some important differences between the septet model and extended Higgs models that preserve custodial symmetry in the scalar spectrum.
A Novel Approach to Constraining Uncertain Stellar Evolution Models
NASA Astrophysics Data System (ADS)
Rosenfield, Philip; Girardi, Leo; Dalcanton, Julianne; Johnson, L. C.; Williams, Benjamin F.; Weisz, Daniel R.; Bressan, Alessandro; Fouesneau, Morgan
2017-01-01
Stellar evolution models are fundamental to nearly all studies in astrophysics. They are used to interpret spectral energy distributions of distant galaxies, to derive the star formation histories of nearby galaxies, and to understand fundamental parameters of exoplanets. Despite the success in using stellar evolution models, some important aspects of stellar evolution remain poorly constrained and their uncertainties rarely addressed. We present results using archival Hubble Space Telescope observations of 10 stellar clusters in the Magellanic Clouds to simultaneously constrain the values and uncertainties of the strength of core convective overshooting, metallicity, interstellar extinction, cluster distance, binary fraction, and age.
Constrained optimization for image restoration using nonlinear programming
NASA Technical Reports Server (NTRS)
Yeh, C.-L.; Chin, R. T.
1985-01-01
The constrained optimization problem for image restoration, utilizing incomplete information and partial constraints, is formulated using nonlinear proramming techniques. This method restores a distorted image by optimizing a chosen object function subject to available constraints. The penalty function method of nonlinear programming is used. Both linear or nonlinear object function, and linear or nonlinear constraint functions can be incorporated in the formulation. This formulation provides a generalized approach to solve constrained optimization problems for image restoration. Experiments using this scheme have been performed. The results are compared with those obtained from other restoration methods and the comparative study is presented.
Constrained modes in control theory - Transmission zeros of uniform beams
NASA Technical Reports Server (NTRS)
Williams, T.
1992-01-01
Mathematical arguments are presented demonstrating that the well-established control system concept of the transmission zero is very closely related to the structural concept of the constrained mode. It is shown that the transmission zeros of a flexible structure form a set of constrained natural frequencies for it, with the constraints depending explicitly on the locations and the types of sensors and actuators used for control. Based on this formulation, an algorithm is derived and used to produce dimensionless plots of the zero of a uniform beam with a compatible sensor/actuator pair.
A filter-based evolutionary algorithm for constrained optimization.
Clevenger, Lauren M.; Hart, William Eugene; Ferguson, Lauren Ann
2004-02-01
We introduce a filter-based evolutionary algorithm (FEA) for constrained optimization. The filter used by an FEA explicitly imposes the concept of dominance on a partially ordered solution set. We show that the algorithm is provably robust for both linear and nonlinear problems and constraints. FEAs use a finite pattern of mutation offsets, and our analysis is closely related to recent convergence results for pattern search methods. We discuss how properties of this pattern impact the ability of an FEA to converge to a constrained local optimum.
Constrained optimization for image restoration using nonlinear programming
NASA Technical Reports Server (NTRS)
Yeh, C.-L.; Chin, R. T.
1985-01-01
The constrained optimization problem for image restoration, utilizing incomplete information and partial constraints, is formulated using nonlinear proramming techniques. This method restores a distorted image by optimizing a chosen object function subject to available constraints. The penalty function method of nonlinear programming is used. Both linear or nonlinear object function, and linear or nonlinear constraint functions can be incorporated in the formulation. This formulation provides a generalized approach to solve constrained optimization problems for image restoration. Experiments using this scheme have been performed. The results are compared with those obtained from other restoration methods and the comparative study is presented.
A lexicographic approach to constrained MDP admission control
NASA Astrophysics Data System (ADS)
Panfili, Martina; Pietrabissa, Antonio; Oddi, Guido; Suraci, Vincenzo
2016-02-01
This paper proposes a reinforcement learning-based lexicographic approach to the call admission control problem in communication networks. The admission control problem is modelled as a multi-constrained Markov decision process. To overcome the problems of the standard approaches to the solution of constrained Markov decision processes, based on the linear programming formulation or on a Lagrangian approach, a multi-constraint lexicographic approach is defined, and an online implementation based on reinforcement learning techniques is proposed. Simulations validate the proposed approach.
Can X-ray constrained Hartree-Fock wavefunctions retrieve electron correlation?
Genoni, Alessandro; Dos Santos, Leonardo H R; Meyer, Benjamin; Macchi, Piero
2017-03-01
The X-ray constrained wavefunction (XC-WF) method proposed by Jayatilaka [Jayatilaka & Grimwood (2001) ▸, Acta Cryst. A57, 76-86] has attracted much attention because it represents a possible third way of theoretically studying the electronic structure of atoms and molecules, combining features of the more popular wavefunction- and DFT-based approaches. In its original formulation, the XC-WF technique extracts statistically plausible wavefunctions from experimental X-ray diffraction data of molecular crystals. A weight is used to constrain the pure Hartree-Fock solution to the observed X-ray structure factors. Despite the wavefunction being a single Slater determinant, it is generally assumed that its flexibility could guarantee the capture, better than any other experimental model, of electron correlation effects, absent in the Hartree-Fock Hamiltonian but present in the structure factors measured experimentally. However, although the approach has been known for long time, careful testing of this fundamental hypothesis is still missing. Since a formal demonstration is impossible, the validation can only be done heuristically and, to accomplish this task, X-ray constrained Hartree-Fock calculations have been performed using structure factor amplitudes computed at a very high correlation level (coupled cluster) for selected molecules in isolation, in order to avoid the perturbations due to intermolecular interactions. The results show that a single-determinant XC-WF is able to capture the electron correlation effects only partially. The largest amount of electron correlation is extracted when: (i) a large external weight is used (much larger than what has normally been used in XC-WF calculations using experimental data); and (ii) the high-order reflections, which carry less information on the electron correlation, are down-weighted (or even excluded), otherwise they would bias the fitting towards the unconstrained Hartree-Fock wavefunction.
Can X-ray constrained Hartree–Fock wavefunctions retrieve electron correlation?
Genoni, Alessandro; Dos Santos, Leonardo H. R.; Meyer, Benjamin; Macchi, Piero
2017-01-01
The X-ray constrained wavefunction (XC-WF) method proposed by Jayatilaka [Jayatilaka & Grimwood (2001) ▸, Acta Cryst. A57, 76–86] has attracted much attention because it represents a possible third way of theoretically studying the electronic structure of atoms and molecules, combining features of the more popular wavefunction- and DFT-based approaches. In its original formulation, the XC-WF technique extracts statistically plausible wavefunctions from experimental X-ray diffraction data of molecular crystals. A weight is used to constrain the pure Hartree–Fock solution to the observed X-ray structure factors. Despite the wavefunction being a single Slater determinant, it is generally assumed that its flexibility could guarantee the capture, better than any other experimental model, of electron correlation effects, absent in the Hartree–Fock Hamiltonian but present in the structure factors measured experimentally. However, although the approach has been known for long time, careful testing of this fundamental hypothesis is still missing. Since a formal demonstration is impossible, the validation can only be done heuristically and, to accomplish this task, X-ray constrained Hartree–Fock calculations have been performed using structure factor amplitudes computed at a very high correlation level (coupled cluster) for selected molecules in isolation, in order to avoid the perturbations due to intermolecular interactions. The results show that a single-determinant XC-WF is able to capture the electron correlation effects only partially. The largest amount of electron correlation is extracted when: (i) a large external weight is used (much larger than what has normally been used in XC-WF calculations using experimental data); and (ii) the high-order reflections, which carry less information on the electron correlation, are down-weighted (or even excluded), otherwise they would bias the fitting towards the unconstrained Hartree–Fock wavefunction. PMID:28250952
21 CFR 888.3210 - Finger joint metal/metal constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Finger joint metal/metal constrained cemented... metal/metal constrained cemented prosthesis. (a) Identification. A finger joint metal/metal constrained..., 1996 for any finger joint metal/metal constrained cemented prosthesis that was in...
21 CFR 888.3210 - Finger joint metal/metal constrained cemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Finger joint metal/metal constrained cemented... metal/metal constrained cemented prosthesis. (a) Identification. A finger joint metal/metal constrained..., 1996 for any finger joint metal/metal constrained cemented prosthesis that was in...
21 CFR 888.3210 - Finger joint metal/metal constrained cemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Finger joint metal/metal constrained cemented... metal/metal constrained cemented prosthesis. (a) Identification. A finger joint metal/metal constrained..., 1996 for any finger joint metal/metal constrained cemented prosthesis that was in...
21 CFR 888.3210 - Finger joint metal/metal constrained cemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Finger joint metal/metal constrained cemented... metal/metal constrained cemented prosthesis. (a) Identification. A finger joint metal/metal constrained..., 1996 for any finger joint metal/metal constrained cemented prosthesis that was in...
21 CFR 888.3300 - Hip joint metal constrained cemented or uncemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Hip joint metal constrained cemented or uncemented... metal constrained cemented or uncemented prosthesis. (a) Identification. A hip joint metal constrained... Administration on or before December 26, 1996 for any hip joint metal constrained cemented or...
21 CFR 888.3210 - Finger joint metal/metal constrained cemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Finger joint metal/metal constrained cemented... metal/metal constrained cemented prosthesis. (a) Identification. A finger joint metal/metal constrained..., 1996 for any finger joint metal/metal constrained cemented prosthesis that was in...
A new spatially constrained NMF with application to fMRI.
Ferdowsi, Saideh; Abolghasemi, Vahid; Makkiabadi, Bahador; Sanei, Saeid
2011-01-01
In this paper the problem of BOLD detection is addressed. The focus here is on non-negative matrix factorization (NMF), which is a data driven method and able to provide part-based representation of data. A new constrained optimization problem is proposed for the purpose of BOLD detection. The proposed constraint imposes some prior spatial information of active area inside the brain, on the decomposition process. The constraint is built up based on the type of stimulus and available physiological knowledge of the brain performance. The simulation results on both synthetic and real fMRI data show that applying the proposed constraint improves the BOLD detection performance.
Constraining Sommerfeld enhanced annihilation cross-sections of dark matter via direct searches
NASA Astrophysics Data System (ADS)
Arina, Chiara; Josse-Michaux, François-Xavier; Sahu, Narendra
2010-08-01
In a large class of models we show that the light scalar field responsible for the Sommerfeld enhancement in the annihilation of dark matter leads to observable direct detection rates, due to its mixing with the standard model Higgs. As a result the large annihilation cross-section of dark matter at present epoch, required to explain the observed cosmic ray anomalies, can be strongly constrained by direct searches. In particular Sommerfeld boost factors of order of a few hundred are already out of the CDMS-II upper bound at 90% confidence level for reasonable values of the model parameters.
Halo effective field theory constrains the solar 7Be + p → 8B + γ rate
Zhang, Xilin; Nollett, Kenneth M.; Phillips, D. R.
2015-11-06
In this study, we report an improved low-energy extrapolation of the cross section for the process 7Be(p,γ)8B, which determines the 8B neutrino flux from the Sun. Our extrapolant is derived from Halo Effective Field Theory (EFT) at next-to-leading order. We apply Bayesian methods to determine the EFT parameters and the low-energy S-factor, using measured cross sections and scattering lengths as inputs. Asymptotic normalization coefficients of 8B are tightly constrained by existing radiative capture data, and contributions to the cross section beyond external direct capture are detected in the data at E < 0.5 MeV. Most importantly, the S-factor at zeromore » energy is constrained to be S(0) = 21.3 ± 0.7 eV b, which is an uncertainty smaller by a factor of two than previously recommended. That recommendation was based on the full range for S(0) obtained among a discrete set of models judged to be reasonable. In contrast, Halo EFT subsumes all models into a controlled low-energy approximant, where they are characterized by nine parameters at next-to-leading order. These are fit to data, and marginalized over via Monte Carlo integration to produce the improved prediction for S(E).« less
Constrained Adaptive Beamforming for Improved Contrast in Breast Ultrasound
2005-06-01
led us to utilize a recently proposed method, Spatial Processing Optimized and Constrained ( SPOC ). In initial simulations this method not only...6 Review of the Adaptive Beamforming Literature ................... 7 SPOC Progress...given the parameters of in vivo ultrasound imaging. SPOC Progress: Most of the Adaptive Beamforming algorithms previously described fail when applied to
Applications of a Constrained Mechanics Methodology in Economics
ERIC Educational Resources Information Center
Janova, Jitka
2011-01-01
This paper presents instructive interdisciplinary applications of constrained mechanics calculus in economics on a level appropriate for undergraduate physics education. The aim of the paper is (i) to meet the demand for illustrative examples suitable for presenting the background of the highly expanding research field of econophysics even at the…
A spatially constrained ecological classification: rationale, methodology and implementation
Franz Mora; Louis Iverson; Louis Iverson
2002-01-01
The theory, methodology and implementation for an ecological and spatially constrained classification are presented. Ecological and spatial relationships among several landscape variables are analyzed in order to define a new approach for a landscape classification. Using ecological and geostatistical analyses, several ecological and spatial weights are derived to...
Extended Shadow Test Approach for Constrained Adaptive Testing. Research Report.
ERIC Educational Resources Information Center
Veldkamp, Bernard P.; Ariel, Adelaide
Several methods have been developed for use on constrained adaptive testing. Item pool partitioning, multistage testing, and testlet-based adaptive testing are methods that perform well for specific cases of adaptive testing. The weighted deviation model and the Shadow Test approach can be more generally applied. These methods are based on…
Constrained Hartree-Fock and quasi-spin projection
NASA Astrophysics Data System (ADS)
Cambiaggio, M. C.; Plastino, A.; Szybisz, L.
1980-08-01
The constrained Hartree-Fock approach of Elliott and Evans is studied in detail with reference to two quasi-spin models, and their predictions compared with those arising from a projection method. It is found that the new approach works fairly well, although limitations to its applicability are encountered.
Extracting electron transfer coupling elements from constrained density functional theory
NASA Astrophysics Data System (ADS)
Wu, Qin; Van Voorhis, Troy
2006-10-01
Constrained density functional theory (DFT) is a useful tool for studying electron transfer (ET) reactions. It can straightforwardly construct the charge-localized diabatic states and give a direct measure of the inner-sphere reorganization energy. In this work, a method is presented for calculating the electronic coupling matrix element (Hab) based on constrained DFT. This method completely avoids the use of ground-state DFT energies because they are known to irrationally predict fractional electron transfer in many cases. Instead it makes use of the constrained DFT energies and the Kohn-Sham wave functions for the diabatic states in a careful way. Test calculations on the Zn2+ and the benzene-Cl atom systems show that the new prescription yields reasonable agreement with the standard generalized Mulliken-Hush method. We then proceed to produce the diabatic and adiabatic potential energy curves along the reaction pathway for intervalence ET in the tetrathiafulvalene-diquinone (Q-TTF-Q) anion. While the unconstrained DFT curve has no reaction barrier and gives Hab≈17kcal /mol, which qualitatively disagrees with experimental results, the Hab calculated from constrained DFT is about 3kcal /mol and the generated ground state has a barrier height of 1.70kcal/mol, successfully predicting (Q-TTF-Q)- to be a class II mixed-valence compound.
How well can future CMB missions constrain cosmic inflation?
Martin, Jérôme; Vennin, Vincent; Ringeval, Christophe E-mail: christophe.ringeval@uclouvain.be
2014-10-01
We study how the next generation of Cosmic Microwave Background (CMB) measurement missions (such as EPIC, LiteBIRD, PRISM and COrE) will be able to constrain the inflationary landscape in the hardest to disambiguate situation in which inflation is simply described by single-field slow-roll scenarios. Considering the proposed PRISM and LiteBIRD satellite designs, we simulate mock data corresponding to five different fiducial models having values of the tensor-to-scalar ratio ranging from 10{sup -1} down to 10{sup -7}. We then compute the Bayesian evidences and complexities of all Encyclopædia Inflationaris models in order to assess the constraining power of PRISM alone and LiteBIRD complemented with the Planck 2013 data. Within slow-roll inflation, both designs have comparable constraining power and can rule out about three quarters of the inflationary scenarios, compared to one third for Planck 2013 data alone. However, we also show that PRISM can constrain the scalar running and has the capability to detect a violation of slow roll at second order. Finally, our results suggest that describing an inflationary model by its potential shape only, without specifying a reheating temperature, will no longer be possible given the accuracy level reached by the future CMB missions.
Excision technique in constrained formulations of Einstein equations: collapse scenario
NASA Astrophysics Data System (ADS)
Cordero-Carrión, I.; Vasset, N.; Novak, J.; Jaramillo, J. L.
2015-04-01
We present a new excision technique used in constrained formulations of Einstein equations to deal with black hole in numerical simulations. We show the applicability of this scheme in several scenarios. In particular, we present the dynamical evolution of the collapse of a neutron star to a black hole, using the CoCoNuT code and this excision technique.
Multiply-Constrained Semantic Search in the Remote Associates Test
ERIC Educational Resources Information Center
Smith, Kevin A.; Huber, David E.; Vul, Edward
2013-01-01
Many important problems require consideration of multiple constraints, such as choosing a job based on salary, location, and responsibilities. We used the Remote Associates Test to study how people solve such multiply-constrained problems by asking participants to make guesses as they came to mind. We evaluated how people generated these guesses…
Constrained Quantum Mechanics: Chaos in Non-Planar Billiards
ERIC Educational Resources Information Center
Salazar, R.; Tellez, G.
2012-01-01
We illustrate some of the techniques to identify chaos signatures at the quantum level using as guiding examples some systems where a particle is constrained to move on a radial symmetric, but non-planar, surface. In particular, two systems are studied: the case of a cone with an arbitrary contour or "dunce hat billiard" and the rectangular…
Reflections on How Color Term Acquisition Is Constrained
ERIC Educational Resources Information Center
Pitchford, Nicola J.
2006-01-01
Compared with object word learning, young children typically find learning color terms to be a difficult linguistic task. In this reflections article, I consider two questions that are fundamental to investigations into the developmental acquisition of color terms. First, I consider what constrains color term acquisition and how stable these…
Constrained quantum mechanics: chaos in non-planar billiards
NASA Astrophysics Data System (ADS)
Salazar, R.; Téllez, G.
2012-07-01
We illustrate some of the techniques to identify chaos signatures at the quantum level using as guiding examples some systems where a particle is constrained to move on a radial symmetric, but non-planar, surface. In particular, two systems are studied: the case of a cone with an arbitrary contour or dunce hat billiard and the rectangular billiard with an inner Gaussian surface.
Multiply-Constrained Semantic Search in the Remote Associates Test
ERIC Educational Resources Information Center
Smith, Kevin A.; Huber, David E.; Vul, Edward
2013-01-01
Many important problems require consideration of multiple constraints, such as choosing a job based on salary, location, and responsibilities. We used the Remote Associates Test to study how people solve such multiply-constrained problems by asking participants to make guesses as they came to mind. We evaluated how people generated these guesses…
Constrained Transport vs. Divergence Cleanser Options in Astrophysical MHD Simulations
NASA Astrophysics Data System (ADS)
Lindner, Christopher C.; Fragile, P.
2009-01-01
In previous work, we presented results from global numerical simulations of the evolution of black hole accretion disks using the Cosmos++ GRMHD code. In those simulations we solved the magnetic induction equation using an advection-split form, which is known not to satisfy the divergence-free constraint. To minimize the build-up of divergence error, we used a hyperbolic cleanser function that simultaneously damped the error and propagated it off the grid. We have since found that this method produces qualitatively and quantitatively different behavior in high magnetic field regions than results published by other research groups, particularly in the evacuated funnels of black-hole accretion disks where Poynting-flux jets are reported to form. The main difference between our earlier work and that of our competitors is their use of constrained-transport schemes to preserve a divergence-free magnetic field. Therefore, to study these differences directly, we have implemented a constrained transport scheme into Cosmos++. Because Cosmos++ uses a zone-centered, finite-volume method, we can not use the traditional staggered-mesh constrained transport scheme of Evans & Hawley. Instead we must implement a more general scheme; we chose the Flux-CT scheme as described by Toth. Here we present comparisons of results using the divergence-cleanser and constrained transport options in Cosmos++.
Testing a Constrained MPC Controller in a Process Control Laboratory
ERIC Educational Resources Information Center
Ricardez-Sandoval, Luis A.; Blankespoor, Wesley; Budman, Hector M.
2010-01-01
This paper describes an experiment performed by the fourth year chemical engineering students in the process control laboratory at the University of Waterloo. The objective of this experiment is to test the capabilities of a constrained Model Predictive Controller (MPC) to control the operation of a Double Pipe Heat Exchanger (DPHE) in real time.…
Joint Force Interdependence for a Fiscally Constrained Future
2013-03-01
Army 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Dr. Richard Meinhart ...Joint Force Interdependence For A Fiscally Constrained Future by Colonel Daniel P. Ray United States Army ...United States Army War College Class of 2013 DISTRIBUTION STATEMENT: A Approved for Public Release Distribution is Unlimited
Improved Differential Evolution with Shrinking Space Technique for Constrained Optimization
NASA Astrophysics Data System (ADS)
Fu, Chunming; Xu, Yadong; Jiang, Chao; Han, Xu; Huang, Zhiliang
2017-05-01
Most of the current evolutionary algorithms for constrained optimization algorithm are low computational efficiency. In order to improve efficiency, an improved differential evolution with shrinking space technique and adaptive trade-off model, named ATMDE, is proposed to solve constrained optimization problems. The proposed ATMDE algorithm employs an improved differential evolution as the search optimizer to generate new offspring individuals into evolutionary population. For the constraints, the adaptive trade-off model as one of the most important constraint-handling techniques is employed to select better individuals to retain into the next population, which could effectively handle multiple constraints. Then the shrinking space technique is designed to shrink the search region according to feedback information in order to improve computational efficiency without losing accuracy. The improved DE algorithm introduces three different mutant strategies to generate different offspring into evolutionary population. Moreover, a new mutant strategy called "DE/rand/best/1" is constructed to generate new individuals according to the feasibility proportion of current population. Finally, the effectiveness of the proposed method is verified by a suite of benchmark functions and practical engineering problems. This research presents a constrained evolutionary algorithm with high efficiency and accuracy for constrained optimization problems.
Information Retrieval by Constrained Spreading Activation in Semantic Networks.
ERIC Educational Resources Information Center
Cohen, Paul R.; Kjeldsen, Rick
1987-01-01
Describes GRANT, an expert system for finding sources of funding given research proposals. The architecture of GRANT and the implementation of constrained spreading activation (a modified search algorithm based on semantic memory) are described, and recall and precision rates are analyzed. (Author/LRW)
Constrained Quantum Mechanics: Chaos in Non-Planar Billiards
ERIC Educational Resources Information Center
Salazar, R.; Tellez, G.
2012-01-01
We illustrate some of the techniques to identify chaos signatures at the quantum level using as guiding examples some systems where a particle is constrained to move on a radial symmetric, but non-planar, surface. In particular, two systems are studied: the case of a cone with an arbitrary contour or "dunce hat billiard" and the rectangular…
Achieving Procurement Efficiencies in a Budget-Constrained Environment
2015-05-13
Copyright © 2015 Boeing. All rights reserved. . Corporate Contracts Darryl Scott Corporate Vice President, Contracts May 13, 2015 Naval...Budget-Constrained Environment T2012 Panel March 12, 2012 Copyright © 2012 Boeing. All rights reserved. Copyright © 2015 Boeing. All rights reserved...Corporate | Contracts Comparison of Commercial and Military Production Satellites Copyright © 2012 Boeing. All rights reserved. $407M ~58 mo
Solution of a Complex Least Squares Problem with Constrained Phase.
Bydder, Mark
2010-12-30
The least squares solution of a complex linear equation is in general a complex vector with independent real and imaginary parts. In certain applications in magnetic resonance imaging, a solution is desired such that each element has the same phase. A direct method for obtaining the least squares solution to the phase constrained problem is described.
Bayesian Item Selection in Constrained Adaptive Testing Using Shadow Tests
ERIC Educational Resources Information Center
Veldkamp, Bernard P.
2010-01-01
Application of Bayesian item selection criteria in computerized adaptive testing might result in improvement of bias and MSE of the ability estimates. The question remains how to apply Bayesian item selection criteria in the context of constrained adaptive testing, where large numbers of specifications have to be taken into account in the item…
Hamiltonian dynamics and constrained variational calculus: continuous and discrete settings
NASA Astrophysics Data System (ADS)
de León, Manuel; Jiménez, Fernando; Martín de Diego, David
2012-05-01
The aim of this paper is to study the relationship between Hamiltonian dynamics and constrained variational calculus. We describe both using the notion of Lagrangian submanifolds of convenient symplectic manifolds and using the so-called Tulczyjew triples. The results are also extended to the case of discrete dynamics and nonholonomic mechanics. Interesting applications to the geometrical integration of Hamiltonian systems are obtained.
Using Diagnostic Text Information to Constrain Situation Models
ERIC Educational Resources Information Center
Dutke, Stephan; Baadte, Christiane; Hahnel, Andrea; von Hecker, Ulrich; Rinck, Mike
2010-01-01
During reading, the model of the situation described by the text is continuously accommodated to new text input. The hypothesis was tested that readers are particularly sensitive to diagnostic text information that can be used to constrain their existing situation model. In 3 experiments, adult participants read narratives about social situations…
Applications of a Constrained Mechanics Methodology in Economics
ERIC Educational Resources Information Center
Janova, Jitka
2011-01-01
This paper presents instructive interdisciplinary applications of constrained mechanics calculus in economics on a level appropriate for undergraduate physics education. The aim of the paper is (i) to meet the demand for illustrative examples suitable for presenting the background of the highly expanding research field of econophysics even at the…
Constrained variational calculus for higher order classical field theories
NASA Astrophysics Data System (ADS)
Campos, Cédric M.; de León, Manuel; Martín de Diego, David
2010-11-01
We develop an intrinsic geometrical setting for higher order constrained field theories. As a main tool we use an appropriate generalization of the classical Skinner-Rusk formalism. Some examples of applications are studied, in particular to the geometrical description of optimal control theory for partial differential equations.
Testing a Constrained MPC Controller in a Process Control Laboratory
ERIC Educational Resources Information Center
Ricardez-Sandoval, Luis A.; Blankespoor, Wesley; Budman, Hector M.
2010-01-01
This paper describes an experiment performed by the fourth year chemical engineering students in the process control laboratory at the University of Waterloo. The objective of this experiment is to test the capabilities of a constrained Model Predictive Controller (MPC) to control the operation of a Double Pipe Heat Exchanger (DPHE) in real time.…
Constrained optimization schemes for geophysical inversion of seismic data
NASA Astrophysics Data System (ADS)
Sosa Aguirre, Uram Anibal
Many experimental techniques in geophysics advance the understanding of Earth processes by estimating and interpreting Earth structure (e.g., velocity and/or density structure). These techniques use different types of geophysical data which can be collected and analyzed separately, sometimes resulting in inconsistent models of the Earth depending on data quality, methods and assumptions made. This dissertation presents two approaches for geophysical inversion of seismic data based on constrained optimization. In one approach we expand a one dimensional (1-D) joint inversion least-squares (LSQ) algorithm by introducing a constrained optimization methodology. Then we use the 1-D inversion results to produce 3-D Earth velocity structure models. In the second approach, we provide a unified constrained optimization framework for solving a 1-D inverse wave propagation problem. In Chapter 2 we present a constrained optimization framework for joint inversion. This framework characterizes 1-D Earth's structure by using seismic shear wave velocities as a model parameter. We create two geophysical synthetic data sets sensitive to shear velocities, namely receiver function and surface wave dispersion. We validate our approach by comparing our numerical results with a traditional unconstrained method, and also we test our approach robustness in the presence of noise. Chapter 3 extends this framework to include an interpolation technique for creating 3-D Earth velocity structure models of the Rio Grande Rift region. Chapter 5 introduces the joint inversion of multiple data sets by adding delay travel times information in a synthetic setup, and leave the posibility to include more data sets. Finally, in Chapter 4 we pose a 1-D inverse full-waveform propagation problem as a PDE-constrained optimization program, where we invert for the material properties in terms of shear wave velocities throughout the physical domain. We facilitate the implementation and comparison of different
Experimentally constraining the boundary conditions for volcanic ash aggregation
NASA Astrophysics Data System (ADS)
Kueppers, U.; Auer, B.; Cimarelli, C.; Scolamacchia, T.; Guenthel, M.; Dingwell, D. B.
2011-12-01
Volcanic ash is the primary product of various volcanic processes. Due to its size, ash can remain in the atmosphere for a prolonged period of time. Aggregation processes are a first-order influence on the residence time of ash in the atmosphere and its dispersion from the vent. Due to their internal structure, ash aggregates have been classified as ash pellets or accretionary lapilli. Although several concomitant factors may play a role during aggregation, there is a broad consensus that both 1) particle collision and 2) humidity are required for particles to aggregate. However, direct observation of settling aggregates and record of the boundary conditions favourable to their formation are rare, therefore limiting our understanding of the key processes that determine ash aggregates formation. Here, we present the first results from experiments aimed at reproducing ash aggregation by constraining the required boundary conditions. We used a ProCell Lab System of Glatt Ingenieurtechnik GmbH that is conventionally used for food and chemical applications. We varied the following parameters: 1) air flow speed [40-120 m3/h], 2) air temperature [30-60°C], 3) relative humidity [20-50 %], and 4) liquid droplets composition [water and 25% water glass, Na2SiO3]. The starting material (125-90 μm) is obtained by milling natural basaltic lapilli (Etna, Italy). We found that the experimental duration and the chosen conditions were not favourable for the production of stable aggregates when using water as spraying liquid. Using a 25% water-glass solution as binder we could successfully generate and investigate aggregates of up to 2 mm size. Many aggregates are spherical and resemble ash pellets. In nature, ash pellets and accretionary lapilli are the product of complex processes taking place at very different conditions (temperature, humidity, ash concentration, degree of turbulence). These experiments shed some first light on the ash agglomeration process for which direct
Geometry parameterization and multidisciplinary constrained optimization of coronary stents.
Pant, Sanjay; Bressloff, Neil W; Limbert, Georges
2012-01-01
Coronary stents are tubular type scaffolds that are deployed, using an inflatable balloon on a catheter, most commonly to recover the lumen size of narrowed (diseased) arterial segments. A common differentiating factor between the numerous stents used in clinical practice today is their geometric design. An ideal stent should have high radial strength to provide good arterial support post-expansion, have high flexibility for easy manoeuvrability during deployment, cause minimal injury to the artery when being expanded and, for drug eluting stents, should provide adequate drug in the arterial tissue. Often, with any stent design, these objectives are in competition such that improvement in one objective is a result of trade-off in others. This study proposes a technique to parameterize stent geometry, by varying the shape of circumferential rings and the links, and assess performance by modelling the processes of balloon expansion and drug diffusion. Finite element analysis is used to expand each stent (through balloon inflation) into contact with a representative diseased coronary artery model, followed by a drug release simulation. Also, a separate model is constructed to measure stent flexibility. Since the computational simulation time for each design is very high (approximately 24 h), a Gaussian process modelling approach is used to analyse the design space corresponding to the proposed parameterization. Four objectives to assess recoil, stress distribution, drug distribution and flexibility are set up to perform optimization studies. In particular, single objective constrained optimization problems are set up to improve the design relative to the baseline geometry-i.e. to improve one objective without compromising the others. Improvements of 8, 6 and 15% are obtained individually for stress, drug and flexibility metrics, respectively. The relative influence of the design features on each objective is quantified in terms of main effects, thereby suggesting the
Constraining the Antarctic contribution to interglacial sea-level rise
NASA Astrophysics Data System (ADS)
Naish, T.; Mckay, R. M.; Barrett, P. J.; Levy, R. H.; Golledge, N. R.; Deconto, R. M.; Horgan, H. J.; Dunbar, G. B.
2015-12-01
Observations, models and paleoclimate reconstructions suggest that Antarctica's marine-based ice sheets behave in an unstable manner with episodes of rapid retreat in response to warming climate. Understanding the processes involved in this "marine ice sheet instability" is key for improving estimates of Antarctic ice sheet contribution to future sea-level rise. Another motivating factor is that far-field sea-level reconstructions and ice sheet models imply global mean sea level (GMSL) was up to 20m and 10m higher, respectively, compared with present day, during the interglacials of the warm Pliocene (~4-3Ma) and Late Pleistocene (at ~400ka and 125ka). This was when atmospheric CO2 was between 280 and 400ppm and global average surface temperatures were 1- 3°C warmer, suggesting polar ice sheets are highly sensitive to relatively modest increases in climate forcing. Such magnitudes of GMSL rise not only require near complete melt of the Greenland Ice Sheet and the West Antarctic Ice Sheet, but a substantial retreat of marine-based sectors of East Antarctic Ice Sheet. Recent geological drilling initiatives on the continental margin of Antarctica from both ship- (e.g. IODP; International Ocean Discovery Program) and ice-based (e.g. ANDRILL/Antarctic Geological Drilling) platforms have provided evidence supporting retreat of marine-based ice. However, without direct access through the ice sheet to archives preserved within sub-glacial sedimentary basins, the volume and extent of ice sheet retreat during past interglacials cannot be directly constrained. Sediment cores have been successfully recovered from beneath ice shelves by the ANDRILL Program and ice streams by the WISSARD (Whillans Ice Stream Sub-glacial Access Research Drilling) Project. Together with the potential of the new RAID (Rapid Access Ice Drill) initiative, these demonstrate the technological feasibility of accessing the subglacial bed and deeper sedimentary archives. In this talk I will outline the
Constrained Laboratory vs. Unconstrained Steering-Induced Rollover Crash Tests.
Kerrigan, Jason R; Toczyski, Jacek; Roberts, Carolyn; Zhang, Qi; Clauser, Mark
2015-01-01
The goal of this study was to evaluate how well an in-laboratory rollover crash test methodology that constrains vehicle motion can reproduce the dynamics of unconstrained full-scale steering-induced rollover crash tests in sand. Data from previously-published unconstrained steering-induced rollover crash tests using a full-size pickup and mid-sized sedan were analyzed to determine vehicle-to-ground impact conditions and kinematic response of the vehicles throughout the tests. Then, a pair of replicate vehicles were prepared to match the inertial properties of the steering-induced test vehicles and configured to record dynamic roof structure deformations and kinematic response. Both vehicles experienced greater increases in roll-axis angular velocities in the unconstrained tests than in the constrained tests; however, the increases that occurred during the trailing side roof interaction were nearly identical between tests for both vehicles. Both vehicles experienced linear accelerations in the constrained tests that were similar to those in the unconstrained tests, but the pickup, in particular, had accelerations that were matched in magnitude, timing, and duration very closely between the two test types. Deformations in the truck test were higher in the constrained than the unconstrained, and deformations in the sedan were greater in the unconstrained than the constrained as a result of constraints of the test fixture, and differences in impact velocity for the trailing side. The results of the current study suggest that in-laboratory rollover tests can be used to simulate the injury-causing portions of unconstrained rollover crashes. To date, such a demonstration has not yet been published in the open literature. This study did, however, show that road surface can affect vehicle response in a way that may not be able to be mimicked in the laboratory. Lastly, this study showed that configuring the in-laboratory tests to match the leading-side touchdown conditions
The medium term outcome of the Omnifit constrained acetabular cup.
Bigsby, Ewan; Whitehouse, Michael R; Bannister, Gordon C; Blom, Ashley W
2012-01-01
Recurrent dislocation requiring revision surgery occurs in approximately 4% of primary total hip arthroplasties (THAs). To reduce this risk, or to treat those patients who recurrently dislocate, a constrained acetabular component may be used, however there are concerns over the success of such components due to increased mechanical stresses. The purpose of this study was to analyse the survivorship and radiological results for the Omnifit constrained acetabular component, providing a longer patient reported outcome follow-up than previous studies. 117 patients (median age 82 years) underwent a THA with an Omnifit constrained acetabular component. Of these, 45 were primary replacements and 72 were revisions. Survivorship analysis was performed and patients were assessed both radiologically and functionally. At follow-up, 53 patients (45.3%) had died at a median time of 33 months from operation. The median overall follow-up was 7.0 (5.5-8.2) years. Survivors (median age 83 years) reported a median Oxford Hip Score (OHS) of 16.6 (0-48), 87.8% were satisfied with their surgery. 45 (91.8%) of the acetabular components were stable radiologically, 48 (96%) of the femoral components were stable (5 uncemented, 43 cemented) and two possibly unstable. Four of the 117 patients underwent further surgery. Only one required revision of the prosthesis and this was for a periprosthetic fracture. In the medium term the Omnifit constrained acetabular component prevents dislocation and does not cause excessive loosening of either the acetabular or femoral components in our patient population. Our results support the use of the Omnifit constrained acetabular component in elderly patients at risk of dislocation with low functional demand.
Ghan, Steven; Wang, Minghuai; Zhang, Shipeng; Ferrachat, Sylvaine; Gettelman, Andrew; Griesfeller, Jan; Kipling, Zak; Lohmann, Ulrike; Morrison, Hugh; Neubauer, David; Partridge, Daniel G; Stier, Philip; Takemura, Toshihiko; Wang, Hailong; Zhang, Kai
2016-05-24
A large number of processes are involved in the chain from emissions of aerosol precursor gases and primary particles to impacts on cloud radiative forcing. Those processes are manifest in a number of relationships that can be expressed as factors dlnX/dlnY driving aerosol effects on cloud radiative forcing. These factors include the relationships between cloud condensation nuclei (CCN) concentration and emissions, droplet number and CCN concentration, cloud fraction and droplet number, cloud optical depth and droplet number, and cloud radiative forcing and cloud optical depth. The relationship between cloud optical depth and droplet number can be further decomposed into the sum of two terms involving the relationship of droplet effective radius and cloud liquid water path with droplet number. These relationships can be constrained using observations of recent spatial and temporal variability of these quantities. However, we are most interested in the radiative forcing since the preindustrial era. Because few relevant measurements are available from that era, relationships from recent variability have been assumed to be applicable to the preindustrial to present-day change. Our analysis of Aerosol Comparisons between Observations and Models (AeroCom) model simulations suggests that estimates of relationships from recent variability are poor constraints on relationships from anthropogenic change for some terms, with even the sign of some relationships differing in many regions. Proxies connecting recent spatial/temporal variability to anthropogenic change, or sustained measurements in regions where emissions have changed, are needed to constrain estimates of anthropogenic aerosol impacts on cloud radiative forcing.
Hirayama, Jun-ichiro; Hyvärinen, Aapo; Kiviniemi, Vesa; Kawanabe, Motoaki; Yamashita, Okito
2016-01-01
Characterizing the variability of resting-state functional brain connectivity across subjects and/or over time has recently attracted much attention. Principal component analysis (PCA) serves as a fundamental statistical technique for such analyses. However, performing PCA on high-dimensional connectivity matrices yields complicated “eigenconnectivity” patterns, for which systematic interpretation is a challenging issue. Here, we overcome this issue with a novel constrained PCA method for connectivity matrices by extending the idea of the previously proposed orthogonal connectivity factorization method. Our new method, modular connectivity factorization (MCF), explicitly introduces the modularity of brain networks as a parametric constraint on eigenconnectivity matrices. In particular, MCF analyzes the variability in both intra- and inter-module connectivities, simultaneously finding network modules in a principled, data-driven manner. The parametric constraint provides a compact module-based visualization scheme with which the result can be intuitively interpreted. We develop an optimization algorithm to solve the constrained PCA problem and validate our method in simulation studies and with a resting-state functional connectivity MRI dataset of 986 subjects. The results show that the proposed MCF method successfully reveals the underlying modular eigenconnectivity patterns in more general situations and is a promising alternative to existing methods. PMID:28002474
NASA Astrophysics Data System (ADS)
Zhang, Xuewu; Du, Yunyan; Su, Fenzhen; Wen, Wei
2009-10-01
With quick development of economy, spatial distribution and specialization level of China large scale commodity exchange markets whose turnover are more than 100 million Yuan, have changed greatly. And influencing factors which distribute in the research region have attribute information and spatial information and do not satisfy statistical independence. Commodity exchange market specialization index is brought forward to measure specialization degree, based on the former research and constrained co-local spatial association rule is used to analyze symbiotic pattern between specialization level and influencing factors. Constrained predicate templates and association rule templates can improve mining efficiency greatly. As the result shown, large scale commodity exchange market specialization level on country-region spatial scale went down from 2000 to 2005 and rose at 2006. The interesting association rules extracted based on defined minimum support and confident can provide officers of region governments with rational advices on large scale commodity exchange markets planning and construction.
Bayesian methods for the analysis of inequality constrained contingency tables.
Laudy, Olav; Hoijtink, Herbert
2007-04-01
A Bayesian methodology for the analysis of inequality constrained models for contingency tables is presented. The problem of interest lies in obtaining the estimates of functions of cell probabilities subject to inequality constraints, testing hypotheses and selection of the best model. Constraints on conditional cell probabilities and on local, global, continuation and cumulative odds ratios are discussed. A Gibbs sampler to obtain a discrete representation of the posterior distribution of the inequality constrained parameters is used. Using this discrete representation, the credibility regions of functions of cell probabilities can be constructed. Posterior model probabilities are used for model selection and hypotheses are tested using posterior predictive checks. The Bayesian methodology proposed is illustrated in two examples.
Inadequacy of single-impulse transfers for path constrained rendezvous
NASA Technical Reports Server (NTRS)
Stern, S. A.; Soileau, K. M.
1987-01-01
The use of single-impulse techniques to maneuver from point to point about a large space structure (LSS) with an arbitrary geometrical configuration and spin is examined. Particular consideration is given to transfers with both endpoints on the forbidden zone surface. Clohessy-Wiltshire equations of relative motion are employed to solve path constrained rendezvous problems. External and internal transfers between arbitrary points are analyzed in terms of tangential departure and arrival conditions. It is observed that single-impulse techniques are inadequate for transferring about the exterior of any LSS; however, single-impulse transfers are applicable for transfers in the interior of LSSs. It is concluded that single-impulse transducers are not applicable for path constrained rendezvous guidance.
Constraining the Noncommutative Spectral Action via Astrophysical Observations
Nelson, William; Ochoa, Joseph; Sakellariadou, Mairi
2010-09-03
The noncommutative spectral action extends our familiar notion of commutative spaces, using the data encoded in a spectral triple on an almost commutative space. Varying a rather simple action, one can derive all of the standard model of particle physics in this setting, in addition to a modified version of Einstein-Hilbert gravity. In this Letter we use observations of pulsar timings, assuming that no deviation from general relativity has been observed, to constrain the gravitational sector of this theory. While the bounds on the coupling constants remain rather weak, they are comparable to existing bounds on deviations from general relativity in other settings and are likely to be further constrained by future observations.
Lilith: a tool for constraining new physics from Higgs measurements
NASA Astrophysics Data System (ADS)
Bernon, Jérémy; Dumont, Béranger
2015-09-01
The properties of the observed Higgs boson with mass around 125 GeV can be affected in a variety of ways by new physics beyond the Standard Model (SM). The wealth of experimental results, targeting the different combinations for the production and decay of a Higgs boson, makes it a non-trivial task to assess the patibility of a non-SM-like Higgs boson with all available results. In this paper we present Lilith, a new public tool for constraining new physics from signal strength measurements performed at the LHC and the Tevatron. Lilith is a Python library that can also be used in C and C++/ ROOT programs. The Higgs likelihood is based on experimental results stored in an easily extensible XML database, and is evaluated from the user input, given in XML format in terms of reduced couplings or signal strengths.The results of Lilith can be used to constrain a wide class of new physics scenarios.
Functional coupling constrains craniofacial diversification in Lake Tanganyika cichlids
Tsuboi, Masahito; Gonzalez-Voyer, Alejandro; Kolm, Niclas
2015-01-01
Functional coupling, where a single morphological trait performs multiple functions, is a universal feature of organismal design. Theory suggests that functional coupling may constrain the rate of phenotypic evolution, yet empirical tests of this hypothesis are rare. In fish, the evolutionary transition from guarding the eggs on a sandy/rocky substrate (i.e. substrate guarding) to mouthbrooding introduces a novel function to the craniofacial system and offers an ideal opportunity to test the functional coupling hypothesis. Using a combination of geometric morphometrics and a recently developed phylogenetic comparative method, we found that head morphology evolution was 43% faster in substrate guarding species than in mouthbrooding species. Furthermore, for species in which females were solely responsible for mouthbrooding the males had a higher rate of head morphology evolution than in those with bi-parental mouthbrooding. Our results support the hypothesis that adaptations resulting in functional coupling constrain phenotypic evolution. PMID:25948565
Matter coupling in partially constrained vielbein formulation of massive gravity
Felice, Antonio De; Mukohyama, Shinji; Gümrükçüoğlu, A. Emir; Heisenberg, Lavinia E-mail: emir.gumrukcuoglu@nottingham.ac.uk E-mail: shinji.mukohyama@ipmu.jp
2016-01-01
We consider a linear effective vielbein matter coupling without introducing the Boulware-Deser ghost in ghost-free massive gravity. This is achieved in the partially constrained vielbein formulation. We first introduce the formalism and prove the absence of ghost at all scales. As next we investigate the cosmological application of this coupling in this new formulation. We show that even if the background evolution accords with the metric formulation, the perturbations display important different features in the partially constrained vielbein formulation. We study the cosmological perturbations of the two branches of solutions separately. The tensor perturbations coincide with those in the metric formulation. Concerning the vector and scalar perturbations, the requirement of absence of ghost and gradient instabilities yields slightly different allowed parameter space.
CONMIN: A FORTRAN program for constrained function minimization: User's manual
NASA Technical Reports Server (NTRS)
Vanderplaats, G. N.
1973-01-01
CONMIN is a FORTRAN program, in subroutine form, for the solution of linear or nonlinear constrained optimization problems. The basic optimization algorithm is the Method of Feasible Directions. The user must provide a main calling program and an external routine to evaluate the objective and constraint functions and to provide gradient information. If analytic gradients of the objective or constraint functions are not available, this information is calculated by finite difference. While the program is intended primarily for efficient solution of constrained problems, unconstrained function minimization problems may also be solved, and the conjugate direction method of Fletcher and Reeves is used for this purpose. This manual describes the use of CONMIN and defines all necessary parameters. Sufficient information is provided so that the program can be used without special knowledge of optimization techniques. Sample problems are included to help the user become familiar with CONMIN and to make the program operational.
Constraining new physics models with isotope shift spectroscopy
NASA Astrophysics Data System (ADS)
Frugiuele, Claudia; Fuchs, Elina; Perez, Gilad; Schlaffer, Matthias
2017-07-01
Isotope shifts of transition frequencies in atoms constrain generic long- and intermediate-range interactions. We focus on new physics scenarios that can be most strongly constrained by King linearity violation such as models with B -L vector bosons, the Higgs portal, and chameleon models. With the anticipated precision, King linearity violation has the potential to set the strongest laboratory bounds on these models in some regions of parameter space. Furthermore, we show that this method can probe the couplings relevant for the protophobic interpretation of the recently reported Be anomaly. We extend the formalism to include an arbitrary number of transitions and isotope pairs and fit the new physics coupling to the currently available isotope shift measurements.
Colorimetric characterization of LCD based on constrained least squares
NASA Astrophysics Data System (ADS)
LI, Tong; Xie, Kai; Wang, Qiaojie; Yao, Luyang
2017-01-01
In order to improve the accuracy of colorimetric characterization of liquid crystal display, tone matrix model in color management modeling of display characterization is established by using constrained least squares for quadratic polynomial fitting, and find the relationship between the RGB color space to CIEXYZ color space; 51 sets of training samples were collected to solve the parameters, and the accuracy of color space mapping model was verified by 100 groups of random verification samples. The experimental results showed that, with the constrained least square method, the accuracy of color mapping was high, the maximum color difference of this model is 3.8895, the average color difference is 1.6689, which prove that the method has better optimization effect on the colorimetric characterization of liquid crystal display.
Matter coupling in partially constrained vielbein formulation of massive gravity
Felice, Antonio De; Gümrükçüoğlu, A. Emir; Heisenberg, Lavinia; Mukohyama, Shinji
2016-01-04
We consider a linear effective vielbein matter coupling without introducing the Boulware-Deser ghost in ghost-free massive gravity. This is achieved in the partially constrained vielbein formulation. We first introduce the formalism and prove the absence of ghost at all scales. As next we investigate the cosmological application of this coupling in this new formulation. We show that even if the background evolution accords with the metric formulation, the perturbations display important different features in the partially constrained vielbein formulation. We study the cosmological perturbations of the two branches of solutions separately. The tensor perturbations coincide with those in the metric formulation. Concerning the vector and scalar perturbations, the requirement of absence of ghost and gradient instabilities yields slightly different allowed parameter space.
Constraining the nuclear equation of state at subsaturation densities.
Khan, E; Margueron, J; Vidaña, I
2012-08-31
Only one-third of the nucleons in 208Pb occupy the saturation density area. Consequently, nuclear observables related to the average properties of nuclei, such as masses or radii, constrain the equation of state not at the saturation density but rather around the so-called crossing density, localized close to the mean value of the density of nuclei: ρ is approximately equal to 0.11 fm(-3). This provides an explanation for the empirical fact that several equation of state quantities calculated with various functionals cross at a density significantly lower than the saturation one. The third derivative M of the energy per unit of volume at the crossing density is constrained by the giant monopole resonance measurements in an isotopic chain rather than the incompressibility at saturation density. The giant monopole resonance measurements provide M=1100±70 MeV (6% uncertainty), whose extrapolation gives K(∞)=230±40 MeV (17% uncertainty).
Moving Forward to Constrain the Shear Viscosity of QCD Matter
Denicol, Gabriel; Monnai, Akihiko; Schenke, Björn
2016-05-26
In this work, we demonstrate that measurements of rapidity differential anisotropic flow in heavy-ion collisions can constrain the temperature dependence of the shear viscosity to entropy density ratio η/s of QCD matter. Comparing results from hydrodynamic calculations with experimental data from the RHIC, we find evidence for a small η/s ≈ 0.04 in the QCD crossover region and a strong temperature dependence in the hadronic phase. A temperature independent η/s is disfavored by the data. We further show that measurements of the event-by-event flow as a function of rapidity can be used to independently constrain the initial state fluctuations in three dimensions and the temperature dependent transport properties of QCD matter.
Moving Forward to Constrain the Shear Viscosity of QCD Matter.
Denicol, Gabriel; Monnai, Akihiko; Schenke, Björn
2016-05-27
We demonstrate that measurements of rapidity differential anisotropic flow in heavy-ion collisions can constrain the temperature dependence of the shear viscosity to entropy density ratio η/s of QCD matter. Comparing results from hydrodynamic calculations with experimental data from the RHIC, we find evidence for a small η/s≈0.04 in the QCD crossover region and a strong temperature dependence in the hadronic phase. A temperature independent η/s is disfavored by the data. We further show that measurements of the event-by-event flow as a function of rapidity can be used to independently constrain the initial state fluctuations in three dimensions and the temperature dependent transport properties of QCD matter.
Functional coupling constrains craniofacial diversification in Lake Tanganyika cichlids.
Tsuboi, Masahito; Gonzalez-Voyer, Alejandro; Kolm, Niclas
2015-05-01
Functional coupling, where a single morphological trait performs multiple functions, is a universal feature of organismal design. Theory suggests that functional coupling may constrain the rate of phenotypic evolution, yet empirical tests of this hypothesis are rare. In fish, the evolutionary transition from guarding the eggs on a sandy/rocky substrate (i.e. substrate guarding) to mouthbrooding introduces a novel function to the craniofacial system and offers an ideal opportunity to test the functional coupling hypothesis. Using a combination of geometric morphometrics and a recently developed phylogenetic comparative method, we found that head morphology evolution was 43% faster in substrate guarding species than in mouthbrooding species. Furthermore, for species in which females were solely responsible for mouthbrooding the males had a higher rate of head morphology evolution than in those with bi-parental mouthbrooding. Our results support the hypothesis that adaptations resulting in functional coupling constrain phenotypic evolution.
A second-generation constrained reaction volume shock tube.
Campbell, M F; Tulgestke, A M; Davidson, D F; Hanson, R K
2014-05-01
We have developed a shock tube that features a sliding gate valve in order to mechanically constrain the reactive test gas mixture to an area close to the shock tube endwall, separating it from a specially formulated non-reactive buffer gas mixture. This second-generation Constrained Reaction Volume (CRV) strategy enables near-constant-pressure shock tube test conditions for reactive experiments behind reflected shocks, thereby enabling improved modeling of the reactive flow field. Here we provide details of the design and operation of the new shock tube. In addition, we detail special buffer gas tailoring procedures, analyze the buffer/test gas interactions that occur on gate valve opening, and outline the size range of fuels that can be studied using the CRV technique in this facility. Finally, we present example low-temperature ignition delay time data to illustrate the CRV shock tube's performance.
The genetic code constrains yet facilitates Darwinian evolution.
Firnberg, Elad; Ostermeier, Marc
2013-08-01
An important goal of evolutionary biology is to understand the constraints that shape the dynamics and outcomes of evolution. Here, we address the extent to which the structure of the standard genetic code constrains evolution by analyzing adaptive mutations of the antibiotic resistance gene TEM-1 β-lactamase and the fitness distribution of codon substitutions in two influenza hemagglutinin inhibitor genes. We find that the architecture of the genetic code significantly constrains the adaptive exploration of sequence space. However, the constraints endow the code with two advantages: the ability to restrict access to amino acid mutations with a strong negative effect and, most remarkably, the ability to enrich for adaptive mutations. Our findings support the hypothesis that the standard genetic code was shaped by selective pressure to minimize the deleterious effects of mutation yet facilitate the evolution of proteins through imposing an adaptive mutation bias.
A Novel Neural Network for Generally Constrained Variational Inequalities.
Gao, Xingbao; Liao, Li-Zhi
2016-06-13
This paper presents a novel neural network for solving generally constrained variational inequality problems by constructing a system of double projection equations. By defining proper convex energy functions, the proposed neural network is proved to be stable in the sense of Lyapunov and converges to an exact solution of the original problem for any starting point under the weaker cocoercivity condition or the monotonicity condition of the gradient mapping on the linear equation set. Furthermore, two sufficient conditions are provided to ensure the stability of the proposed neural network for a special case. The proposed model overcomes some shortcomings of existing continuous-time neural networks for constrained variational inequality, and its stability only requires some monotonicity conditions of the underlying mapping and the concavity of nonlinear inequality constraints on the equation set. The validity and transient behavior of the proposed neural network are demonstrated by some simulation results.
A Projection Neural Network for Constrained Quadratic Minimax Optimization.
Liu, Qingshan; Wang, Jun
2015-11-01
This paper presents a projection neural network described by a dynamic system for solving constrained quadratic minimax programming problems. Sufficient conditions based on a linear matrix inequality are provided for global convergence of the proposed neural network. Compared with some of the existing neural networks for quadratic minimax optimization, the proposed neural network in this paper is capable of solving more general constrained quadratic minimax optimization problems, and the designed neural network does not include any parameter. Moreover, the neural network has lower model complexities, the number of state variables of which is equal to that of the dimension of the optimization problems. The simulation results on numerical examples are discussed to demonstrate the effectiveness and characteristics of the proposed neural network.
ConStrains identifies microbial strains in metagenomic datasets.
Luo, Chengwei; Knight, Rob; Siljander, Heli; Knip, Mikael; Xavier, Ramnik J; Gevers, Dirk
2015-10-01
An important fraction of microbial diversity is harbored in strain individuality, so identification of conspecific bacterial strains is imperative for improved understanding of microbial community functions. Limitations in bioinformatics and sequencing technologies have to date precluded strain identification owing to difficulties in phasing short reads to faithfully recover the original strain-level genotypes, which have highly similar sequences. We present ConStrains, an open-source algorithm that identifies conspecific strains from metagenomic sequence data and reconstructs the phylogeny of these strains in microbial communities. The algorithm uses single-nucleotide polymorphism (SNP) patterns in a set of universal genes to infer within-species structures that represent strains. Applying ConStrains to simulated and host-derived datasets provides insights into microbial community dynamics.
Moving Forward to Constrain the Shear Viscosity of QCD Matter
Denicol, Gabriel; Monnai, Akihiko; Schenke, Björn
2016-05-26
In this work, we demonstrate that measurements of rapidity differential anisotropic flow in heavy-ion collisions can constrain the temperature dependence of the shear viscosity to entropy density ratio η/s of QCD matter. Comparing results from hydrodynamic calculations with experimental data from the RHIC, we find evidence for a small η/s ≈ 0.04 in the QCD crossover region and a strong temperature dependence in the hadronic phase. A temperature independent η/s is disfavored by the data. We further show that measurements of the event-by-event flow as a function of rapidity can be used to independently constrain the initial state fluctuations inmore » three dimensions and the temperature dependent transport properties of QCD matter.« less
Moving Forward to Constrain the Shear Viscosity of QCD Matter
Denicol, Gabriel; Monnai, Akihiko; Schenke, Björn
2016-05-26
In this work, we demonstrate that measurements of rapidity differential anisotropic flow in heavy-ion collisions can constrain the temperature dependence of the shear viscosity to entropy density ratio η/s of QCD matter. Comparing results from hydrodynamic calculations with experimental data from the RHIC, we find evidence for a small η/s ≈ 0.04 in the QCD crossover region and a strong temperature dependence in the hadronic phase. A temperature independent η/s is disfavored by the data. We further show that measurements of the event-by-event flow as a function of rapidity can be used to independently constrain the initial state fluctuations in three dimensions and the temperature dependent transport properties of QCD matter.
Image coding using entropy-constrained residual vector quantization
NASA Technical Reports Server (NTRS)
Kossentini, Faouzi; Smith, Mark J. T.; Barnes, Christopher F.
1993-01-01
The residual vector quantization (RVQ) structure is exploited to produce a variable length codeword RVQ. Necessary conditions for the optimality of this RVQ are presented, and a new entropy-constrained RVQ (ECRVQ) design algorithm is shown to be very effective in designing RVQ codebooks over a wide range of bit rates and vector sizes. The new EC-RVQ has several important advantages. It can outperform entropy-constrained VQ (ECVQ) in terms of peak signal-to-noise ratio (PSNR), memory, and computation requirements. It can also be used to design high rate codebooks and codebooks with relatively large vector sizes. Experimental results indicate that when the new EC-RVQ is applied to image coding, very high quality is achieved at relatively low bit rates.
Topoisomerase V relaxes supercoiled DNA by a constrained swiveling mechanism
Taneja, Bhupesh; Schnurr, Bernhard; Slesarev, Alexei; Marko, John F.; Mondragón, Alfonso
2007-01-01
Topoisomerase V is a type I topoisomerase without structural or sequence similarities to other topoisomerases. Although it belongs to the type I subfamily of topoisomerases, it is unrelated to either type IA or IB enzymes. We used real-time single-molecule micromechanical experiments to show that topoisomerase V relaxes DNA via events that release multiple DNA turns, employing a constrained swiveling mechanism similar to that for type IB enzymes. Relaxation is powered by the torque in the supercoiled DNA and is constrained by friction between the protein and the DNA. Although all type IB enzymes share a common structure and mechanism and type IA and type II enzymes show marked structural and functional similarities, topoisomerase V represents a different type of topoisomerase that relaxes DNA in a similar overall manner as type IB molecules but by using a completely different structural and mechanistic framework. PMID:17804808
Hadroproduction experiments to constrain accelerator-based neutrino fluxes
NASA Astrophysics Data System (ADS)
Zambelli, Laura
2017-09-01
The precise knowledge of (anti-)neutrino fluxes is one of the largest limitation in accelerator-based neutrino experiments. The main limitations arise from the poorly known production properties of neutrino parents in hadron-nucleus interactions. Strategies used by neutrino experiment to constrain their fluxes using external hadroproduction data will be described and illustrated with an example of a tight collaboration between T2K and NA61/SHINE experiments. This enabled a reduction of the T2K neutrino flux uncertainty from ∼25% (without external constraints) down to ∼10%. On-going developments to further constrain the T2K (anti-)neutrino flux are discussed and recent results from NA61/SHINE are reviewed. As the next-generation long baseline experiments aim for a neutrino flux uncertainty at a level of a few percent, the future data-taking plans of NA61/SHINE are discussed.
Spectral finite-element methods for parametric constrained optimization problems.
Anitescu, M.; Mathematics and Computer Science
2009-01-01
We present a method to approximate the solution mapping of parametric constrained optimization problems. The approximation, which is of the spectral finite element type, is represented as a linear combination of orthogonal polynomials. Its coefficients are determined by solving an appropriate finite-dimensional constrained optimization problem. We show that, under certain conditions, the latter problem is solvable because it is feasible for a sufficiently large degree of the polynomial approximation and has an objective function with bounded level sets. In addition, the solutions of the finite-dimensional problems converge for an increasing degree of the polynomials considered, provided that the solutions exhibit a sufficiently large and uniform degree of smoothness. Our approach solves, in the case of optimization problems with uncertain parameters, the most computationally intensive part of stochastic finite-element approaches. We demonstrate that our framework is applicable to parametric eigenvalue problems.
Control of the constrained planar simple inverted pendulum
NASA Technical Reports Server (NTRS)
Bavarian, B.; Wyman, B. F.; Hemami, H.
1983-01-01
Control of a constrained planar inverted pendulum by eigenstructure assignment is considered. Linear feedback is used to stabilize and decouple the system in such a way that specified subspaces of the state space are invariant for the closed-loop system. The effectiveness of the feedback law is tested by digital computer simulation. Pre-compensation by an inverse plant is used to improve performance.
Control of the constrained planar simple inverted pendulum
NASA Technical Reports Server (NTRS)
Bavarian, B.; Wyman, B. F.; Hemami, H.
1983-01-01
Control of a constrained planar inverted pendulum by eigenstructure assignment is considered. Linear feedback is used to stabilize and decouple the system in such a way that specified subspaces of the state space are invariant for the closed-loop system. The effectiveness of the feedback law is tested by digital computer simulation. Pre-compensation by an inverse plant is used to improve performance.
Differentially Constrained Motion Planning with State Lattice Motion Primitives
2012-02-01
requirements for the degree of Doctor of Philosophy in Robotics The Robotics Institute Carnegie Mellon University Pittsburgh, Pennsylvania 15213 February 2012 ...Thesis Committee Alonzo Kelly, Chair Matt Mason Tony Stentz Steve LaValle, University of Illinois Copyright c© 2012 by Mihail N. Pivtoraiko. All...REPORT DATE FEB 2012 2. REPORT TYPE 3. DATES COVERED 00-00- 2012 to 00-00- 2012 4. TITLE AND SUBTITLE Differentially Constrained Motion Planning
Constraining dark energy through the stability of cosmic structures
Pavlidou, V.; Tetradis, N.; Tomaras, T.N. E-mail: ntetrad@phys.uoa.gr
2014-05-01
For a general dark-energy equation of state, we estimate the maximum possible radius of massive structures that are not destabilized by the acceleration of the cosmological expansion. A comparison with known stable structures constrains the equation of state. The robustness of the constraint can be enhanced through the accumulation of additional astrophysical data and a better understanding of the dynamics of bound cosmic structures.
Simple Comb Generator Design for SWaP Constrained Applications
2016-01-26
Simple Comb Generator Design for SWaP-Constrained Applications Kenneth E. Kolodziej MIT Lincoln Laboratory, Lexington, Massachusetts, USA Abstract...compact comb generator circuit using a step recovery diode is analyzed and the prototype results presented in this paper. This simple circuit...to most wireless devices. Index Terms— Comb generator , pulse generator , step re- covery diode, SRD. I. INTRODUCTION Comb generator circuits are used to
Social Emotional Optimization Algorithm for Nonlinear Constrained Optimization Problems
NASA Astrophysics Data System (ADS)
Xu, Yuechun; Cui, Zhihua; Zeng, Jianchao
Nonlinear programming problem is one important branch in operational research, and has been successfully applied to various real-life problems. In this paper, a new approach called Social emotional optimization algorithm (SEOA) is used to solve this problem which is a new swarm intelligent technique by simulating the human behavior guided by emotion. Simulation results show that the social emotional optimization algorithm proposed in this paper is effective and efficiency for the nonlinear constrained programming problems.
Critical transition in the constrained traveling salesman problem
NASA Astrophysics Data System (ADS)
Andrecut, M.; Ali, M. K.
2001-04-01
We investigate the finite size scaling of the mean optimal tour length as a function of density of obstacles in a constrained variant of the traveling salesman problem (TSP). The computational experience pointed out a critical transition (at ρc~85%) in the dependence between the excess of the mean optimal tour length over the Held-Karp lower bound and the density of obstacles.
Anti-B-B Mixing Constrains Topcolor-Assisted Technicolor
Burdman, Gustavo; Lane, Kenneth; Rador, Tonguc
2000-12-06
We argue that extended technicolor augmented with topcolor requires that all mixing between the third and the first two quark generations resides in the mixing matrix of left-handed down quarks. Then, the anti-B_d--B_d mixing that occurs in topcolor models constrains the coloron and Z' boson masses to be greater than about 5 TeV. This implies fine tuning of the topcolor couplings to better than 1percent.
Image restoration by constrained total variation minimization and variants
NASA Astrophysics Data System (ADS)
Chambolle, Antonin; Lions, Pierre-Louis
1995-09-01
We study a signal or image restoration method proposed by Rudin and Osher, namely, the constrained total variation (TV) minimization. This very powerful method gives excellent results on nearly piecewise constant signals, but fails on more complicated data. We propose a very general way to combine convex potentials like the TV, and in this setting we introduce a variant that performs better on piecewise regular--but non constant-- signals.
Constraining the Solubility of Aerosol Fe using US GEOTRACES Data
NASA Astrophysics Data System (ADS)
Aguilar-Islas, A. M.; Buck, C. S.; Rember, R.; Landing, W. M.
2016-02-01
Atmospheric deposition represents an important input of micronutrients to surface waters, and is of particular interest as an input for the limiting micronutrient iron. The solubility of aerosol iron after deposition is not well constrained, and it has been shown to vary principally with aerosol composition, although dissolution methodologies also contribute to the observed variability. To address procedural artifacts and arrive at a better constrained estimate of aerosol iron fractional solubility, a flow-through on-board protocol designed to minimize experimental artifacts and to simulate conditions experienced by deposited aerosols was used during the US Atlantic GEOTRACES cruises and compared to laboratory leaching methods. Here we present results of the fractional solubility of aerosol iron obtained during the US GEOTRACES Atlantic and Pacific cruises, and suggest revising estimates for this parameter. Our data provides a more constrained upwardly adjusted estimate in the range of 8% to 14% solubility for iron in aerosols dominated by lithogenic sources, and a fractional solubility of 15% to 25% for iron in aerosols from air masses impacted by anthropogenic sources. Greater variability (6% to 55%) was observed in the solubility of iron in aerosols from maritime air masses.
The dynamics of folding instability in a constrained Cosserat medium
Gourgiotis, Panos A.
2017-01-01
Different from Cauchy elastic materials, generalized continua, and in particular constrained Cosserat materials, can be designed to possess extreme (near a failure of ellipticity) orthotropy properties and in this way to model folding in a three-dimensional solid. Following this approach, folding, which is a narrow zone of highly localized bending, spontaneously emerges as a deformation pattern occurring in a strongly anisotropic solid. How this peculiar pattern interacts with wave propagation in the time-harmonic domain is revealed through the derivation of an antiplane, infinite-body Green’s function, which opens the way to integral techniques for anisotropic constrained Cosserat continua. Viewed as a perturbing agent, the Green’s function shows that folding, emerging near a steadily pulsating source in the limit of failure of ellipticity, is transformed into a disturbance with wavefronts parallel to the folding itself. The results of the presented study introduce the possibility of exploiting constrained Cosserat solids for propagating waves in materials displaying origami patterns of deformation. This article is part of the themed issue ‘Patterning through instabilities in complex media: theory and applications.’ PMID:28373382
CONSTRAINING INTRACLUSTER GAS MODELS WITH AMiBA13
Molnar, Sandor M.; Umetsu, Keiichi; Ho, Paul T. P.; Koch, Patrick M.; Victor Liao, Yu-Wei; Lin, Kai-Yang; Liu, Guo-Chin; Nishioka, Hiroaki; Birkinshaw, Mark; Bryan, Greg; Haiman, Zoltan; Shang, Cien; Hearn, Nathan
2010-11-10
Clusters of galaxies have been extensively used to determine cosmological parameters. A major difficulty in making the best use of Sunyaev-Zel'dovich (SZ) and X-ray observations of clusters for cosmology is that using X-ray observations it is difficult to measure the temperature distribution and therefore determine the density distribution in individual clusters of galaxies out to the virial radius. Observations with the new generation of SZ instruments are a promising alternative approach. We use clusters of galaxies drawn from high-resolution adaptive mesh refinement cosmological simulations to study how well we should be able to constrain the large-scale distribution of the intracluster gas (ICG) in individual massive relaxed clusters using AMiBA in its configuration with 13 1.2 m diameter dishes (AMiBA13) along with X-ray observations. We show that non-isothermal {beta} models provide a good description of the ICG in our simulated relaxed clusters. We use simulated X-ray observations to estimate the quality of constraints on the distribution of gas density, and simulated SZ visibilities (AMiBA13 observations) for constraints on the large-scale temperature distribution of the ICG. We find that AMiBA13 visibilities should constrain the scale radius of the temperature distribution to about 50% accuracy. We conclude that the upgraded AMiBA, AMiBA13, should be a powerful instrument to constrain the large-scale distribution of the ICG.
The dynamics of folding instability in a constrained Cosserat medium
NASA Astrophysics Data System (ADS)
Gourgiotis, Panos A.; Bigoni, Davide
2017-04-01
Different from Cauchy elastic materials, generalized continua, and in particular constrained Cosserat materials, can be designed to possess extreme (near a failure of ellipticity) orthotropy properties and in this way to model folding in a three-dimensional solid. Following this approach, folding, which is a narrow zone of highly localized bending, spontaneously emerges as a deformation pattern occurring in a strongly anisotropic solid. How this peculiar pattern interacts with wave propagation in the time-harmonic domain is revealed through the derivation of an antiplane, infinite-body Green's function, which opens the way to integral techniques for anisotropic constrained Cosserat continua. Viewed as a perturbing agent, the Green's function shows that folding, emerging near a steadily pulsating source in the limit of failure of ellipticity, is transformed into a disturbance with wavefronts parallel to the folding itself. The results of the presented study introduce the possibility of exploiting constrained Cosserat solids for propagating waves in materials displaying origami patterns of deformation. This article is part of the themed issue 'Patterning through instabilities in complex media: theory and applications.'
Short-Term Results of Novel Constrained Total Hip Arthroplasty
Pace, Thomas; Finley, Stephen; Snider, Rebecca; Looper, Jayme; Tanner, Stephanie
2015-01-01
Constrained acetabular components have only been recommended as a salvage option for the persistently unstable total hip arthroplasty (THA), due to limited range of motion and less than satisfactory component failure rates. This is a retrospective review of 137 patients with 154 consecutive primary constrained THAs performed between November 2003 and August 2007. We reviewed serial radiographs, postoperative complications, groin/thigh pain, and compared preoperative and postoperative Harris Hip Scores. With a mean follow-up of 6 years, there was 1.9% dislocation rate, 0% component failure rate, and 2.6% infection rate. Seven patients reported continued groin pain, and three had continued thigh pain. One patient showed radiographic evidence of 1 mm polyethylene wear. Radiographic review showed no evidence of osteolysis or stem subsidence. Harris Hip Scores improved from a mean of 68.8 (range 58-87) preoperatively to 98.9 (range 65-100) at final clinical assessment. This constrained acetabular prosthesis had a dislocation rate of less than 2%, with 0% component failure rate at a minimum of 2 years of follow-up suggesting this prosthesis may be a viable alternative for patients at risk for instability or those known to have recurrent instability. PMID:26330992
A TV-constrained decomposition method for spectral CT
NASA Astrophysics Data System (ADS)
Guo, Xiaoyue; Zhang, Li; Xing, Yuxiang
2017-03-01
Spectral CT is attracting more and more attention in medicine, industrial nondestructive testing and security inspection field. Material decomposition is an important issue to a spectral CT to discriminate materials. Because of the spectrum overlap of energy channels, as well as the correlation of basis functions, it is well acknowledged that decomposition step in spectral CT imaging causes noise amplification and artifacts in component coefficient images. In this work, we propose materials decomposition via an optimization method to improve the quality of decomposed coefficient images. On the basis of general optimization problem, total variance minimization is constrained on coefficient images in our overall objective function with adjustable weights. We solve this constrained optimization problem under the framework of ADMM. Validation on both a numerical dental phantom in simulation and a real phantom of pig leg on a practical CT system using dual-energy imaging is executed. Both numerical and physical experiments give visually obvious better reconstructions than a general direct inverse method. SNR and SSIM are adopted to quantitatively evaluate the image quality of decomposed component coefficients. All results demonstrate that the TV-constrained decomposition method performs well in reducing noise without losing spatial resolution so that improving the image quality. The method can be easily incorporated into different types of spectral imaging modalities, as well as for cases with energy channels more than two.
Constraining ecosystem processes from tower fluxes and atmospheric profiles.
Hill, T C; Williams, M; Woodward, F I; Moncrieff, J B
2011-07-01
The planetary boundary layer (PBL) provides an important link between the scales and processes resolved by global atmospheric sampling/modeling and site-based flux measurements. The PBL is in direct contact with the land surface, both driving and responding to ecosystem processes. Measurements within the PBL (e.g., by radiosondes, aircraft profiles, and flask measurements) have a footprint, and thus an integrating scale, on the order of 1-100 km. We use the coupled atmosphere-biosphere model (CAB) and a Bayesian data assimilation framework to investigate the amount of biosphere process information that can be inferred from PBL measurements. We investigate the information content of PBL measurements in a two-stage study. First, we demonstrate consistency between the coupled model (CAB) and measurements, by comparing the model to eddy covariance flux tower measurements (i.e., water and carbon fluxes) and also PBL scalar profile measurements (i.e., water, carbon dioxide, and temperature) from Canadian boreal forest. Second, we use the CAB model in a set of Bayesian inversions experiments using synthetic data for a single day. In the synthetic experiment, leaf area and respiration were relatively well constrained, whereas surface albedo and plant hydraulic conductance were only moderately constrained. Finally, the abilities of the PBL profiles and the eddy covariance data to constrain the parameters were largely similar and only slightly lower than the combination of both observations.
CONSTRAINING SOLAR FLARE DIFFERENTIAL EMISSION MEASURES WITH EVE AND RHESSI
Caspi, Amir; McTiernan, James M.; Warren, Harry P.
2014-06-20
Deriving a well-constrained differential emission measure (DEM) distribution for solar flares has historically been difficult, primarily because no single instrument is sensitive to the full range of coronal temperatures observed in flares, from ≲2 to ≳50 MK. We present a new technique, combining extreme ultraviolet (EUV) spectra from the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory with X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), to derive, for the first time, a self-consistent, well-constrained DEM for jointly observed solar flares. EVE is sensitive to ∼2-25 MK thermal plasma emission, and RHESSI to ≳10 MK; together, the two instruments cover the full range of flare coronal plasma temperatures. We have validated the new technique on artificial test data, and apply it to two X-class flares from solar cycle 24 to determine the flare DEM and its temporal evolution; the constraints on the thermal emission derived from the EVE data also constrain the low energy cutoff of the non-thermal electrons, a crucial parameter for flare energetics. The DEM analysis can also be used to predict the soft X-ray flux in the poorly observed ∼0.4-5 nm range, with important applications for geospace science.
Constrained novelty search: a study on game content generation.
Liapis, Antonios; Yannakakis, Georgios N; Togelius, Julian
2015-01-01
Novelty search is a recent algorithm geared toward exploring search spaces without regard to objectives. When the presence of constraints divides a search space into feasible space and infeasible space, interesting implications arise regarding how novelty search explores such spaces. This paper elaborates on the problem of constrained novelty search and proposes two novelty search algorithms which search within both the feasible and the infeasible space. Inspired by the FI-2pop genetic algorithm, both algorithms maintain and evolve two separate populations, one with feasible and one with infeasible individuals, while each population can use its own selection method. The proposed algorithms are applied to the problem of generating diverse but playable game levels, which is representative of the larger problem of procedural game content generation. Results show that the two-population constrained novelty search methods can create, under certain conditions, larger and more diverse sets of feasible game levels than current methods of novelty search, whether constrained or unconstrained. However, the best algorithm is contingent on the particularities of the search space and the genetic operators used. Additionally, the proposed enhancement of offspring boosting is shown to enhance performance in all cases of two-population novelty search.
Constraining Solar Flare Differential Emission Measures with EVE and RHESSI
NASA Astrophysics Data System (ADS)
Caspi, Amir; McTiernan, James M.; Warren, Harry P.
2014-06-01
Deriving a well-constrained differential emission measure (DEM) distribution for solar flares has historically been difficult, primarily because no single instrument is sensitive to the full range of coronal temperatures observed in flares, from lsim2 to gsim50 MK. We present a new technique, combining extreme ultraviolet (EUV) spectra from the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory with X-ray spectra from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), to derive, for the first time, a self-consistent, well-constrained DEM for jointly observed solar flares. EVE is sensitive to ~2-25 MK thermal plasma emission, and RHESSI to gsim10 MK together, the two instruments cover the full range of flare coronal plasma temperatures. We have validated the new technique on artificial test data, and apply it to two X-class flares from solar cycle 24 to determine the flare DEM and its temporal evolution; the constraints on the thermal emission derived from the EVE data also constrain the low energy cutoff of the non-thermal electrons, a crucial parameter for flare energetics. The DEM analysis can also be used to predict the soft X-ray flux in the poorly observed ~0.4-5 nm range, with important applications for geospace science.
Applications of a constrained mechanics methodology in economics
NASA Astrophysics Data System (ADS)
Janová, Jitka
2011-11-01
This paper presents instructive interdisciplinary applications of constrained mechanics calculus in economics on a level appropriate for undergraduate physics education. The aim of the paper is (i) to meet the demand for illustrative examples suitable for presenting the background of the highly expanding research field of econophysics even at the undergraduate level and (ii) to enable the students to gain a deeper understanding of the principles and methods routinely used in mechanics by looking at the well-known methodology from the different perspective of economics. Two constrained dynamic economic problems are presented using the economic terminology in an intuitive way. First, the Phillips model of the business cycle is presented as a system of forced oscillations and the general problem of two interacting economies is solved by the nonholonomic dynamics approach. Second, the Cass-Koopmans-Ramsey model of economical growth is solved as a variational problem with a velocity-dependent constraint using the vakonomic approach. The specifics of the solution interpretation in economics compared to mechanics is discussed in detail, a discussion of the nonholonomic and vakonomic approaches to constrained problems in mechanics and economics is provided and an economic interpretation of the Lagrange multipliers (possibly surprising for the students of physics) is carefully explained. This paper can be used by the undergraduate students of physics interested in interdisciplinary physics applications to gain an understanding of the current scientific approach to economics based on a physical background, or by university teachers as an attractive supplement to classical mechanics lessons.
Effects of constrained trunk movement on frontal plane gait kinematics.
Arvin, Mina; van Dieën, Jaap H; Bruijn, Sjoerd M
2016-09-06
Previously it has been shown that constraining step width in gait coincides with decreased trunk displacements. Conversely, external stabilization of the upper body in gait coincides with decreased step width, but this may in part be due to changes in passive dynamics of the leg. In the present study, trunk kinematics during gait were constrained without external stabilization by using an orthosis, to investigate whether step width and dynamic gait stability in the ML direction are changed in relation to trunk kinematics. Nine healthy young adults walked on a treadmill at three different speeds with no intervention and while wearing a thoracolumbar orthosis. Based on marker trajectories, trunk COM displacement, body COM displacement and velocity, step width, and margin-of-stability in ML direction were calculated. The results showed that the orthosis significantly reduced trunk and body COM displacements. As hypothesized, the restriction of trunk movement coincided with significantly decreased step width, while the margin-of-stability was not affected. These findings indicate that, when trunk movements are constrained, humans narrow step width, while maintaining a constant margin-of-stability. In conclusion, the present results in combination with previous work imply that in gait a reciprocal coupling between trunk kinematics and foot placement in the frontal plane subserves control of stability in the frontal plane. Copyright © 2016 Elsevier Ltd. All rights reserved.
The statistical challenge of constraining the low-mass IMF in Local Group dwarf galaxies
NASA Astrophysics Data System (ADS)
El-Badry, Kareem; Weisz, Daniel R.; Quataert, Eliot
2017-06-01
We use Monte Carlo simulations to explore the statistical challenges of constraining the characteristic mass (mc) and width (σ) of a lognormal sub-solar initial mass function (IMF) in Local Group dwarf galaxies using direct star counts. For a typical Milky Way (MW) satellite (MV = -8), jointly constraining mc and σ to a precision of ≲ 20 per cent requires that observations be complete to ≲ 0.2 M⊙, if the IMF is similar to the MW IMF. A similar statistical precision can be obtained if observations are only complete down to 0.4 M⊙, but this requires measurement of nearly 100× more stars, and thus, a significantly more massive satellite (MV ˜ -12). In the absence of sufficiently deep data to constrain the low-mass turnover, it is common practice to fit a single-sloped power law to the low-mass IMF, or to fit mc for a lognormal while holding σ fixed. We show that the former approximation leads to best-fitting power-law slopes that vary with the mass range observed and can largely explain existing claims of low-mass IMF variations in MW satellites, even if satellite galaxies have the same IMF as the MW. In addition, fixing σ during fitting leads to substantially underestimated uncertainties in the recovered value of mc (by a factor of ˜4 for typical observations). If the IMFs of nearby dwarf galaxies are lognormal and do vary, observations must reach down to ˜mc in order to robustly detect these variations. The high-sensitivity, near-infrared capabilities of the James Webb Space Telescope and Wide-Field Infrared Survey Telescope have the potential to dramatically improve constraints on the low-mass IMF. We present an efficient observational strategy for using these facilities to measure the IMFs of Local Group dwarf galaxies.
Using qflux to constrain modeled Congo Basin rainfall in the CMIP5 ensemble
NASA Astrophysics Data System (ADS)
Creese, A.; Washington, R.
2016-11-01
Coupled models are the tools by which we diagnose and project future climate, yet in certain regions they are critically underevaluated. The Congo Basin is one such region which has received limited scientific attention, due to the severe scarcity of observational data. There is a large difference in the climatology of rainfall in global coupled climate models over the basin. This study attempts to address this research gap by evaluating modeled rainfall magnitude and distribution amongst global coupled models in the Coupled Model Intercomparison Project 5 (CMIP5) ensemble. Mean monthly rainfall between models varies by up to a factor of 5 in some months, and models disagree on the location of maximum rainfall. The ensemble mean, which is usually considered a "best estimate" of coupled model output, does not agree with any single model, and as such is unlikely to present a possible rainfall state. Moisture flux (qflux) convergence (which is assumed to be better constrained than parameterized rainfall) is found to have a strong relationship with rainfall; strongest correlations occur at 700 hPa in March-May (r = 0.70) and 850 hPa in June-August, September-November, and December-February (r = 0.66, r = 0.71, and r = 0.81). In the absence of observations, this relationship could be used to constrain the wide spectrum of modeled rainfall and give a better understanding of Congo rainfall climatology. Analysis of moisture transport pathways indicates that modeled rainfall is sensitive to the amount of moisture entering the basin. A targeted observation campaign at key Congo Basin boundaries could therefore help to constrain model rainfall.
NASA Technical Reports Server (NTRS)
Nicely, Julie M.; Anderson, Daniel C.; Canty, Timothy P.; Salawitch, Ross J.; Wolfe, Glenn M.; Apel, Eric C.; Arnold, Steve R.; Atlas, Elliot L.; Blake, Nicola J.; Bresch, James F.; Campos, Teresa L.; Dickerson, Russell R.; Duncan, Bryan; Emmons, Louisa K.; Evans, Mathew J.; Fernandez, Rafael P.; Flemming, Johannes; Hall, Samuel R.; Hanisco, Thomas F.; Honomichl, Shawn B.; Hornbrook, Rebecca S.; Huijnen, Vincent; Kaser, Lisa; Kinnison, Douglas E.; Lamarque, Jean-Francois; Mao, Jingqui; Monks, Sarah A.; Montzka, Denise D.; Pan, Laura L.; Riemer, Daniel D.; Saiz-Lopez, Alfonso; Steenrod, Stephen D.; Stell, Meghan H.; Tilmes, Simone; Turquety, Solene; Ullmann, Kirk; Weinheimer, Andrew J.
2016-01-01
Hydroxyl radical (OH) is the main daytime oxidant in the troposphere and determines the atmospheric lifetimes of many compounds. We use aircraft measurements of O3, H2O, NO, and other species from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, which occurred in the tropical western Pacific (TWP) during January-February 2014, to constrain a photochemical box model and estimate concentrations of OH throughout the troposphere. We find that tropospheric column OH (OHCOL) inferred from CONTRAST observations is 12 to 40% higher than found in chemical transport models (CTMs), including CAM-chem-SD run with 2014 meteorology as well as eight models that participated in POLMIP (2008 meteorology). Part of this discrepancy is due to a clear-sky sampling bias that affects CONTRAST observations; accounting for this bias and also for a small difference in chemical mechanism results in our empirically based value of OHCOL being 0 to 20% larger than found within global models. While these global models simulate observed O3 reasonably well, they underestimate NOx (NO +NO2) by a factor of 2, resulting in OHCOL approx.30% lower than box model simulations constrained by observed NO. Underestimations by CTMs of observed CH3CHO throughout the troposphere and of HCHO in the upper troposphere further contribute to differences between our constrained estimates of OH and those calculated by CTMs. Finally, our calculations do not support the prior suggestion of the existence of a tropospheric OH minimum in the TWP, because during January-February 2014 observed levels of O3 and NO were considerably larger than previously reported values in the TWP.
NASA Technical Reports Server (NTRS)
Nicely, Julie M.; Anderson, Daniel C.; Canty, Timothy P.; Salawitch, Ross J.; Wolfe, Glenn M.; Apel, Eric C.; Arnold, Steve R.; Atlas, Elliot L.; Blake, Nicola J.; Bresch, James F.;
2016-01-01
Hydroxyl radical (OH) is the main daytime oxidant in the troposphere and determines the atmospheric lifetimes of many compounds. We use aircraft measurements of O3, H2O, NO, and other species from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, which occurred in the tropical western Pacific (TWP) during January-February 2014, to constrain a photochemical box model and estimate concentrations of OH throughout the troposphere. We find that tropospheric column OH (OHCOL) inferred from CONTRAST observations is 12 to 40% higher than found in chemical transport models (CTMs), including CAM-chem-SD run with 2014 meteorology as well as eight models that participated in POLMIP (2008 meteorology). Part of this discrepancy is due to a clear-sky sampling bias that affects CONTRAST observations; accounting for this bias and also for a small difference in chemical mechanism results in our empirically based value of OHCOL being 0 to 20% larger than found within global models. While these global models simulate observed O3 reasonably well, they underestimate NOx (NO +NO2) by a factor of 2, resulting in OHCOL approx.30% lower than box model simulations constrained by observed NO. Underestimations by CTMs of observed CH3CHO throughout the troposphere and of HCHO in the upper troposphere further contribute to differences between our constrained estimates of OH and those calculated by CTMs. Finally, our calculations do not support the prior suggestion of the existence of a tropospheric OH minimum in the TWP, because during January-February 2014 observed levels of O3 and NO were considerably larger than previously reported values in the TWP.
An observationally constrained evaluation of the oxidative capacity in the tropical western Pacific troposphere
NASA Astrophysics Data System (ADS)
Nicely, Julie M.; Anderson, Daniel C.; Canty, Timothy P.; Salawitch, Ross J.; Wolfe, Glenn M.; Apel, Eric C.; Arnold, Steve R.; Atlas, Elliot L.; Blake, Nicola J.; Bresch, James F.; Campos, Teresa L.; Dickerson, Russell R.; Duncan, Bryan; Emmons, Louisa K.; Evans, Mathew J.; Fernandez, Rafael P.; Flemming, Johannes; Hall, Samuel R.; Hanisco, Thomas F.; Honomichl, Shawn B.; Hornbrook, Rebecca S.; Huijnen, Vincent; Kaser, Lisa; Kinnison, Douglas E.; Lamarque, Jean-Francois; Mao, Jingqiu; Monks, Sarah A.; Montzka, Denise D.; Pan, Laura L.; Riemer, Daniel D.; Saiz-Lopez, Alfonso; Steenrod, Stephen D.; Stell, Meghan H.; Tilmes, Simone; Turquety, Solene; Ullmann, Kirk; Weinheimer, Andrew J.
2016-06-01
Hydroxyl radical (OH) is the main daytime oxidant in the troposphere and determines the atmospheric lifetimes of many compounds. We use aircraft measurements of O3, H2O, NO, and other species from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, which occurred in the tropical western Pacific (TWP) during January-February 2014, to constrain a photochemical box model and estimate concentrations of OH throughout the troposphere. We find that tropospheric column OH (OHCOL) inferred from CONTRAST observations is 12 to 40% higher than found in chemical transport models (CTMs), including CAM-chem-SD run with 2014 meteorology as well as eight models that participated in POLMIP (2008 meteorology). Part of this discrepancy is due to a clear-sky sampling bias that affects CONTRAST observations; accounting for this bias and also for a small difference in chemical mechanism results in our empirically based value of OHCOL being 0 to 20% larger than found within global models. While these global models simulate observed O3 reasonably well, they underestimate NOx (NO + NO2) by a factor of 2, resulting in OHCOL ~30% lower than box model simulations constrained by observed NO. Underestimations by CTMs of observed CH3CHO throughout the troposphere and of HCHO in the upper troposphere further contribute to differences between our constrained estimates of OH and those calculated by CTMs. Finally, our calculations do not support the prior suggestion of the existence of a tropospheric OH minimum in the TWP, because during January-February 2014 observed levels of O3 and NO were considerably larger than previously reported values in the TWP.
Prior image constrained image reconstruction in emerging computed tomography applications
NASA Astrophysics Data System (ADS)
Brunner, Stephen T.
Advances have been made in computed tomography (CT), especially in the past five years, by incorporating prior images into the image reconstruction process. In this dissertation, we investigate prior image constrained image reconstruction in three emerging CT applications: dual-energy CT, multi-energy photon-counting CT, and cone-beam CT in image-guided radiation therapy. First, we investigate the application of Prior Image Constrained Compressed Sensing (PICCS) in dual-energy CT, which has been called "one of the hottest research areas in CT." Phantom and animal studies are conducted using a state-of-the-art 64-slice GE Discovery 750 HD CT scanner to investigate the extent to which PICCS can enable radiation dose reduction in material density and virtual monochromatic imaging. Second, we extend the application of PICCS from dual-energy CT to multi-energy photon-counting CT, which has been called "one of the 12 topics in CT to be critical in the next decade." Numerical simulations are conducted to generate multiple energy bin images for a photon-counting CT acquisition and to investigate the extent to which PICCS can enable radiation dose efficiency improvement. Third, we investigate the performance of a newly proposed prior image constrained scatter correction technique to correct scatter-induced shading artifacts in cone-beam CT, which, when used in image-guided radiation therapy procedures, can assist in patient localization, and potentially, dose verification and adaptive radiation therapy. Phantom studies are conducted using a Varian 2100 EX system with an on-board imager to investigate the extent to which the prior image constrained scatter correction technique can mitigate scatter-induced shading artifacts in cone-beam CT. Results show that these prior image constrained image reconstruction techniques can reduce radiation dose in dual-energy CT by 50% in phantom and animal studies in material density and virtual monochromatic imaging, can lead to radiation
Towards better constrained models of the solar magnetic cycle
NASA Astrophysics Data System (ADS)
Munoz-Jaramillo, Andres
2010-12-01
The best tools we have for understanding the origin of solar magnetic variability are kinematic dynamo models. During the last decade, this type of models has seen a continuous evolution and has become increasingly successful at reproducing solar cycle characteristics. The basic ingredients of these models are: the solar differential rotation -- which acts as the main source of energy for the system by shearing the magnetic field; the meridional circulation -- which plays a crucial role in magnetic field transport; the turbulent diffusivity -- which attempts to capture the effect of convective turbulence on the large scale magnetic field; and the poloidal field source -- which closes the cycle by regenerating the poloidal magnetic field. However, most of these ingredients remain poorly constrained which allows one to obtain solar-like solutions by "tuning" the input parameters, leading to controversy regarding which parameter set is more appropriate. In this thesis we revisit each of those ingredients in an attempt to constrain them better by using observational data and theoretical considerations, reducing the amount of free parameters in the model. For the meridional flow and differential rotation we use helioseismic data to constrain free parameters and find that the differential rotation is well determined, but the available data can only constrain the latitudinal dependence of the meridional flow. For the turbulent magnetic diffusivity we show that combining mixing-length theory estimates with magnetic quenching allows us to obtain viable magnetic cycles and that the commonly used diffusivity profiles can be understood as a spatiotemporal average of this process. For the poloidal source we introduce a more realistic way of modeling active region emergence and decay and find that this resolves existing discrepancies between kinematic dynamo models and surface flux transport simulations. We also study the physical mechanisms behind the unusually long minimum of
Color constrains depth in da Vinci stereopsis for camouflage but not occlusion.
Wardle, Susan G; Gillam, Barbara J
2013-12-01
Monocular regions that occur with binocular viewing of natural scenes can produce a strong perception of depth--"da Vinci stereopsis." They occur either when part of the background is occluded in one eye, or when a nearer object is camouflaged against a background surface in one eye's view. There has been some controversy over whether da Vinci depth is constrained by geometric or ecological factors. Here we show that the color of the monocular region constrains the depth perceived from camouflage, but not occlusion, as predicted by ecological considerations. Quantitative depth was found in both cases, but for camouflage only when the color of the monocular region matched the binocular background. Unlike previous reports, depth failed even when nonmatching colors satisfied conditions for perceptual transparency. We show that placing a colored line at the boundary between the binocular and monocular regions is sufficient to eliminate depth from camouflage. When both the background and the monocular region contained vertical contours that could be fused, some observers appeared to use fusion, and others da Vinci constraints, supporting the existence of a separate da Vinci mechanism. The results show that da Vinci stereopsis incorporates color constraints and is more complex than previously assumed.
Relative frequencies of constrained events in stochastic processes: An analytical approach.
Rusconi, S; Akhmatskaya, E; Sokolovski, D; Ballard, N; de la Cal, J C
2015-10-01
The stochastic simulation algorithm (SSA) and the corresponding Monte Carlo (MC) method are among the most common approaches for studying stochastic processes. They relies on knowledge of interevent probability density functions (PDFs) and on information about dependencies between all possible events. Analytical representations of a PDF are difficult to specify in advance, in many real life applications. Knowing the shapes of PDFs, and using experimental data, different optimization schemes can be applied in order to evaluate probability density functions and, therefore, the properties of the studied system. Such methods, however, are computationally demanding, and often not feasible. We show that, in the case where experimentally accessed properties are directly related to the frequencies of events involved, it may be possible to replace the heavy Monte Carlo core of optimization schemes with an analytical solution. Such a replacement not only provides a more accurate estimation of the properties of the process, but also reduces the simulation time by a factor of order of the sample size (at least ≈10(4)). The proposed analytical approach is valid for any choice of PDF. The accuracy, computational efficiency, and advantages of the method over MC procedures are demonstrated in the exactly solvable case and in the evaluation of branching fractions in controlled radical polymerization (CRP) of acrylic monomers. This polymerization can be modeled by a constrained stochastic process. Constrained systems are quite common, and this makes the method useful for various applications.
Constrained Versions of DEDICOM for Use in Unsupervised Part-Of-Speech Tagging
Dunlavy, Daniel; Chew, Peter A.
2016-05-01
This reports describes extensions of DEDICOM (DEcomposition into DIrectional COMponents) data models [3] that incorporate bound and linear constraints. The main purpose of these extensions is to investigate the use of improved data models for unsupervised part-of-speech tagging, as described by Chew et al. [2]. In that work, a single domain, two-way DEDICOM model was computed on a matrix of bigram fre- quencies of tokens in a corpus and used to identify parts-of-speech as an unsupervised approach to that problem. An open problem identi ed in that work was the com- putation of a DEDICOM model that more closely resembled the matrices used in a Hidden Markov Model (HMM), speci cally through post-processing of the DEDICOM factor matrices. The work reported here consists of the description of several models that aim to provide a direct solution to that problem and a way to t those models. The approach taken here is to incorporate the model requirements as bound and lin- ear constrains into the DEDICOM model directly and solve the data tting problem as a constrained optimization problem. This is in contrast to the typical approaches in the literature, where the DEDICOM model is t using unconstrained optimization approaches, and model requirements are satis ed as a post-processing step.
Grouping puts figure-ground assignment in context by constraining propagation of edge-assignment
Brooks, Joseph L.; Driver, Jon
2010-01-01
Figure-ground organization involves assignment of edges to a figural shape on one or the other side of each dividing edge. Established visual cues for edge-assignment primarily concern relatively local rather than contextual factors. Here we show that assignment for a locally-unbiased edge can be affected by assignment of a remote contextual edge that has its own locally-biased assignment. We find that such propagation of edge-assignment from the biased remote context occurs only when the biased and unbiased edges are grouped. This new principle, whereby grouping constrains propagation of figural edge-assignment, emerges from both subjective reports and from an objective short-term edge-matching task. It generalizes from moving displays involving grouping by common fate and collinearity, to static displays with grouping by similarity of edge-contrast polarity, or apparent occlusion. Our results identify a new contextual influence upon edge-assignment. They also identify a new mechanistic relation between grouping and figure-ground processes, whereby grouping between remote elements can constrain propagation of edge-assignment between those elements. PMID:20436200
Focusing Events and Constrains on Policy Addressing Long-Term Climate Change Risks
NASA Astrophysics Data System (ADS)
O'Donovan, K.
2014-12-01
When policy makers are aware of immediate and long-term risks to communities, what do they do to plan for and mitigate the effects of climate change? This paper addresses that question in two ways. First, as an organizing framework it presents an overview of the empirical evidence on focusing events. Focusing events are defined as sudden, rare events that reveal harm or the potential for future harm that the general public and policy makers become aware of simultaneously. These large-scale events are typically natural and disasters, crisis, or technological accidents. This paper considers the empirical evidence of the relationship between focusing events, the harm revealed by the event and policy change aimed at reducing future risk of harm. Second, this paper reviews the case of flood mitigation policy in the United States from 1968 to 2008. It considers the ways in which policy makers have and have not integrated future flood risks into mitigation policy and planning, particularly after large-scale floods. It analyzes the political, intergovernmental, demographic and geographic factors that have promoted and constrained long-term flood mitigation policy. This paper concludes with a discussion of the meaning and implications of potential focusing events and constrains on policy for long-term climate change concerns.
Perkins, Stephen J.; Okemefuna, Azubuike I.; Nan, Ruodan; Li, Keying; Bonner, Alexandra
2009-01-01
X-ray and neutron-scattering techniques characterize proteins in solution and complement high-resolution structural studies. They are useful when either a large protein cannot be crystallized, in which case scattering yields a solution structure, or a crystal structure has been determined and requires validation in solution. These solution structures are determined by the application of constrained modelling methods based on known subunit structures. First, an appropriate starting model is generated. Next, its conformation is randomized to generate thousands of models for trial-and-error fits. Comparison with the experimental data identifies a small family of best-fit models. Finally, their significance for biological function is assessed. We illustrate this in application to structure determinations for secretory immunoglobulin A, the most prevalent antibody in the human body and a first line of defence in mucosal immunity. We also discuss the applications to the large multi-domain proteins of the complement system, most notably its major regulator factor H, which is important in age-related macular degeneration and renal diseases. We discuss the importance of complementary data from analytical ultracentrifugation, and structural studies of protein–protein complexes. We conclude that constrained scattering modelling makes useful contributions to our understanding of antibody and complement structure and function. PMID:19605402
Tolerance-based OPC and solution to MRC-constrained OPC
NASA Astrophysics Data System (ADS)
Ping, Yang; Li, Xiaohai; Jang, Stephen; Kwa, Denny; Zhang, Yunqiang; Lugg, Robert
2011-04-01
Model based optical proximity correction (MB-OPC) has been widely used in advanced lithography process today. However controlling the edge placement error (EPE) and critical dimension (CD) has become harder as the k1 process factor decreases and design complexity increases. Especially, for high-NA lithography using strong off-axis illumination (OAI), ringing effects on 2D layout makes CD control difficult. In addition, mask rule check (MRC) limits also prevent good OPC convergence where two segment edges are corrected towards each other to form a correction-conflicting scenario because traditional OPC only consider the impact of the current edge when calculating the edge movement. A more sophisticated OPC algorithm that considers the interaction between segments is necessary to find a solution that is both MRC and convergence compliant. This paper first analyzes the phenomenon of MRC-constrained OPC. Then two multiple segment correction techniques for tolerance-based OPC and MRC-constrained OPC are discussed. These correction techniques can be applied to selected areas with different lithographic specifications. The feasibility of these techniques is demonstrated by quantifying the EPE convergence through iterations and by comparing the simulated contour results.
Perkins, Stephen J; Okemefuna, Azubuike I; Nan, Ruodan; Li, Keying; Bonner, Alexandra
2009-10-06
X-ray and neutron-scattering techniques characterize proteins in solution and complement high-resolution structural studies. They are useful when either a large protein cannot be crystallized, in which case scattering yields a solution structure, or a crystal structure has been determined and requires validation in solution. These solution structures are determined by the application of constrained modelling methods based on known subunit structures. First, an appropriate starting model is generated. Next, its conformation is randomized to generate thousands of models for trial-and-error fits. Comparison with the experimental data identifies a small family of best-fit models. Finally, their significance for biological function is assessed. We illustrate this in application to structure determinations for secretory immunoglobulin A, the most prevalent antibody in the human body and a first line of defence in mucosal immunity. We also discuss the applications to the large multi-domain proteins of the complement system, most notably its major regulator factor H, which is important in age-related macular degeneration and renal diseases. We discuss the importance of complementary data from analytical ultracentrifugation, and structural studies of protein-protein complexes. We conclude that constrained scattering modelling makes useful contributions to our understanding of antibody and complement structure and function.
Application of constrained-layer damping to a precision kinematic coupling
Jensen, S A; Hale, L C
2000-10-10
This paper addresses the need to support a very precise optical instrument while causing essentially no influence to its natural shape. Such influences could come from a number of sources, such as manufacturing tolerances, temperature changes, over-constrained structural members, or ground motion. Kinematic couplings have long been used for purposes of repeatable location and minimal influence to the supported object, however these couplings typically offer very little damping. This paper presents a kinematic coupling that utilizes constrained-layer damping techniques to damp out the first three modes of vibration of a precision optical instrument. Finite element analysis was used to aid in the design and tuning of the dampers for the kinematic coupling. Experimental tests were conducted and confirmed the effectiveness of the dampers. The quality factor (Q), which measure the amplification at resonance, dropped from 33.3 to 5.9 on the first mode, from 156.3 to 7.1 on the second mode, and from 147.1 to 18.5 on the third mode. These dampers help to ensure that the stringent vibration requirements necessary to produce high quality optical images are met.
Relative frequencies of constrained events in stochastic processes: An analytical approach
NASA Astrophysics Data System (ADS)
Rusconi, S.; Akhmatskaya, E.; Sokolovski, D.; Ballard, N.; de la Cal, J. C.
2015-10-01
The stochastic simulation algorithm (SSA) and the corresponding Monte Carlo (MC) method are among the most common approaches for studying stochastic processes. They relies on knowledge of interevent probability density functions (PDFs) and on information about dependencies between all possible events. Analytical representations of a PDF are difficult to specify in advance, in many real life applications. Knowing the shapes of PDFs, and using experimental data, different optimization schemes can be applied in order to evaluate probability density functions and, therefore, the properties of the studied system. Such methods, however, are computationally demanding, and often not feasible. We show that, in the case where experimentally accessed properties are directly related to the frequencies of events involved, it may be possible to replace the heavy Monte Carlo core of optimization schemes with an analytical solution. Such a replacement not only provides a more accurate estimation of the properties of the process, but also reduces the simulation time by a factor of order of the sample size (at least ≈104 ). The proposed analytical approach is valid for any choice of PDF. The accuracy, computational efficiency, and advantages of the method over MC procedures are demonstrated in the exactly solvable case and in the evaluation of branching fractions in controlled radical polymerization (CRP) of acrylic monomers. This polymerization can be modeled by a constrained stochastic process. Constrained systems are quite common, and this makes the method useful for various applications.
Locality Constrained Joint Dynamic Sparse Representation for Local Matching Based Face Recognition
Wang, Jianzhong; Yi, Yugen; Zhou, Wei; Shi, Yanjiao; Qi, Miao; Zhang, Ming; Zhang, Baoxue; Kong, Jun
2014-01-01
Recently, Sparse Representation-based Classification (SRC) has attracted a lot of attention for its applications to various tasks, especially in biometric techniques such as face recognition. However, factors such as lighting, expression, pose and disguise variations in face images will decrease the performances of SRC and most other face recognition techniques. In order to overcome these limitations, we propose a robust face recognition method named Locality Constrained Joint Dynamic Sparse Representation-based Classification (LCJDSRC) in this paper. In our method, a face image is first partitioned into several smaller sub-images. Then, these sub-images are sparsely represented using the proposed locality constrained joint dynamic sparse representation algorithm. Finally, the representation results for all sub-images are aggregated to obtain the final recognition result. Compared with other algorithms which process each sub-image of a face image independently, the proposed algorithm regards the local matching-based face recognition as a multi-task learning problem. Thus, the latent relationships among the sub-images from the same face image are taken into account. Meanwhile, the locality information of the data is also considered in our algorithm. We evaluate our algorithm by comparing it with other state-of-the-art approaches. Extensive experiments on four benchmark face databases (ORL, Extended YaleB, AR and LFW) demonstrate the effectiveness of LCJDSRC. PMID:25419662
NASA Astrophysics Data System (ADS)
Lankau, Timm; Yu, Chin-Hui
2013-06-01
A constrained reduced-dimensionality algorithm can be used to efficiently locate transition states and products in reactions involving conformational changes. The search path (SP) is constructed stepwise from linear combinations of a small set of manually chosen internal coordinates, namely the predictors. The majority of the internal coordinates, the correctors, are optimized at every step of the SP to minimize the total energy of the system so that the path becomes a minimum energy path connecting products and transition states with the reactants. Problems arise when the set of predictors needs to include weak coordinates, for example, dihedral angles, as well as strong ones such as bond distances. Two principal constraining methods for the weak coordinates are proposed to mend this situation: static and dynamic constraints. Dynamic constraints are automatically activated and revoked depending on the state of the weak coordinates among the predictors, while static ones require preset control factors and act permanently. All these methods enable the successful application (4 reactions are presented involving cyclohexane, alanine dipeptide, trimethylsulfonium chloride, and azafulvene) of the reduced dimensionality method to reactions where the reaction path covers large conformational changes in addition to the formation/breaking of chemical bonds. Dynamic constraints are found to be the most efficient method as they require neither additional information about the geometry of the transition state nor fine tuning of control parameters.
NASA Astrophysics Data System (ADS)
Liu, Kailong; Li, Kang; Zhang, Cheng
2017-04-01
Battery temperature is a primary factor affecting the battery performance, and suitable battery temperature control in particular internal temperature control can not only guarantee battery safety but also improve its efficiency. This is however challenging as current controller designs for battery charging have no mechanisms to incorporate such information. This paper proposes a novel battery charging control strategy which applies the constrained generalized predictive control (GPC) to charge a LiFePO4 battery based on a newly developed coupled thermoelectric model. The control target primarily aims to maintain the battery cell internal temperature within a desirable range while delivering fast charging. To achieve this, the coupled thermoelectric model is firstly introduced to capture the battery behaviours in particular SOC and internal temperature which are not directly measurable in practice. Then a controlled auto-regressive integrated moving average (CARIMA) model whose parameters are identified by the recursive least squares (RLS) algorithm is developed as an online self-tuning predictive model for a GPC controller. Then the constrained generalized predictive controller is developed to control the charging current. Experiment results confirm the effectiveness of the proposed control strategy. Further, the best region of heat dissipation rate and proper internal temperature set-points are also investigated and analysed.
21 CFR 888.3220 - Finger joint metal/polymer constrained cemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Finger joint metal/polymer constrained cemented... metal/polymer constrained cemented prosthesis. (a) Identification. A finger joint metal/polymer..., 1996 for any finger joint metal/polymer constrained cemented prosthesis that was in...
21 CFR 888.3220 - Finger joint metal/polymer constrained cemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Finger joint metal/polymer constrained cemented... metal/polymer constrained cemented prosthesis. (a) Identification. A finger joint metal/polymer..., 1996 for any finger joint metal/polymer constrained cemented prosthesis that was in...
21 CFR 888.3220 - Finger joint metal/polymer constrained cemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Finger joint metal/polymer constrained cemented... metal/polymer constrained cemented prosthesis. (a) Identification. A finger joint metal/polymer..., 1996 for any finger joint metal/polymer constrained cemented prosthesis that was in...
21 CFR 888.3120 - Ankle joint metal/polymer non-constrained cemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Ankle joint metal/polymer non-constrained cemented... metal/polymer non-constrained cemented prosthesis. (a) Identification. An ankle joint metal/polymer non... December 26, 1996 for any ankle joint metal/polymer non-constrained cemented prosthesis that was in...
21 CFR 888.3100 - Ankle joint metal/composite semi-constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Ankle joint metal/composite semi-constrained... Ankle joint metal/composite semi-constrained cemented prosthesis. (a) Identification. An ankle joint metal/composite semi-constrained cemented prosthesis is a device intended to be implanted to replace an...
Resource-Driven Mission-Phasing Techniques for Constrained Agents in Stochastic Environments
2010-07-01
adopted a Lagrangian and dual LP approach to solve constrained MDPs with total cost criteria. Feinberg (2000) analyzed the complexity of constrained...agents mechanically implement mode-transition and resource- reconfiguration actions. 6. Conclusion The work in this paper designed, analyzed, and...lize resource reconfiguration opportunities. It provides a new computationally efficient resource-reconfiguration mechanism for resource-constrained
21 CFR 888.3500 - Knee joint femorotibial metal/composite semi-constrained cemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
...-constrained cemented prosthesis. 888.3500 Section 888.3500 Food and Drugs FOOD AND DRUG ADMINISTRATION... § 888.3500 Knee joint femorotibial metal/composite semi-constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/composite semi-constrained cemented prosthesis is a two-part...
21 CFR 888.3490 - Knee joint femorotibial metal/composite non-constrained cemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
...-constrained cemented prosthesis. 888.3490 Section 888.3490 Food and Drugs FOOD AND DRUG ADMINISTRATION... § 888.3490 Knee joint femorotibial metal/composite non-constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/composite non-constrained cemented prosthesis is a device...
21 CFR 888.3500 - Knee joint femorotibial metal/composite semi-constrained cemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
...-constrained cemented prosthesis. 888.3500 Section 888.3500 Food and Drugs FOOD AND DRUG ADMINISTRATION... § 888.3500 Knee joint femorotibial metal/composite semi-constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/composite semi-constrained cemented prosthesis is a two-part...
21 CFR 888.3490 - Knee joint femorotibial metal/composite non-constrained cemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
...-constrained cemented prosthesis. 888.3490 Section 888.3490 Food and Drugs FOOD AND DRUG ADMINISTRATION... § 888.3490 Knee joint femorotibial metal/composite non-constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/composite non-constrained cemented prosthesis is a device...
21 CFR 888.3500 - Knee joint femorotibial metal/composite semi-constrained cemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
...-constrained cemented prosthesis. 888.3500 Section 888.3500 Food and Drugs FOOD AND DRUG ADMINISTRATION... § 888.3500 Knee joint femorotibial metal/composite semi-constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/composite semi-constrained cemented prosthesis is a two-part...
21 CFR 888.3490 - Knee joint femorotibial metal/composite non-constrained cemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
...-constrained cemented prosthesis. 888.3490 Section 888.3490 Food and Drugs FOOD AND DRUG ADMINISTRATION... § 888.3490 Knee joint femorotibial metal/composite non-constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/composite non-constrained cemented prosthesis is a device...
21 CFR 888.3650 - Shoulder joint metal/polymer non-constrained cemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Shoulder joint metal/polymer non-constrained... Shoulder joint metal/polymer non-constrained cemented prosthesis. (a) Identification. A shoulder joint metal/polymer non-constrained cemented prosthesis is a device intended to be implanted to replace...
21 CFR 888.3800 - Wrist joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Wrist joint metal/polymer semi-constrained... Wrist joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. A wrist joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace a wrist...
21 CFR 888.3310 - Hip joint metal/polymer constrained cemented or uncemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Hip joint metal/polymer constrained cemented or... Hip joint metal/polymer constrained cemented or uncemented prosthesis. (a) Identification. A hip joint metal/polymer constrained cemented or uncemented prosthesis is a device intended to be implanted...
21 CFR 888.3220 - Finger joint metal/polymer constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Finger joint metal/polymer constrained cemented... metal/polymer constrained cemented prosthesis. (a) Identification. A finger joint metal/polymer..., 1996 for any finger joint metal/polymer constrained cemented prosthesis that was in...
21 CFR 888.3510 - Knee joint femorotibial metal/polymer constrained cemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Knee joint femorotibial metal/polymer constrained... Knee joint femorotibial metal/polymer constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/polymer constrained cemented prosthesis is a device intended to be implanted to replace...
21 CFR 888.3650 - Shoulder joint metal/polymer non-constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Shoulder joint metal/polymer non-constrained... Shoulder joint metal/polymer non-constrained cemented prosthesis. (a) Identification. A shoulder joint metal/polymer non-constrained cemented prosthesis is a device intended to be implanted to replace...
21 CFR 888.3160 - Elbow joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Elbow joint metal/polymer semi-constrained... Elbow joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. An elbow joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace an...
21 CFR 888.3800 - Wrist joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Wrist joint metal/polymer semi-constrained... Wrist joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. A wrist joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace a wrist...
21 CFR 888.3310 - Hip joint metal/polymer constrained cemented or uncemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Hip joint metal/polymer constrained cemented or... Hip joint metal/polymer constrained cemented or uncemented prosthesis. (a) Identification. A hip joint metal/polymer constrained cemented or uncemented prosthesis is a device intended to be implanted...
21 CFR 888.3110 - Ankle joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Ankle joint metal/polymer semi-constrained... Ankle joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. An ankle joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace an...
21 CFR 888.3120 - Ankle joint metal/polymer non-constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Ankle joint metal/polymer non-constrained cemented... metal/polymer non-constrained cemented prosthesis. (a) Identification. An ankle joint metal/polymer non... December 26, 1996 for any ankle joint metal/polymer non-constrained cemented prosthesis that was...
21 CFR 888.3510 - Knee joint femorotibial metal/polymer constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Knee joint femorotibial metal/polymer constrained... Knee joint femorotibial metal/polymer constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/polymer constrained cemented prosthesis is a device intended to be implanted to replace...
21 CFR 888.3660 - Shoulder joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Shoulder joint metal/polymer semi-constrained... Shoulder joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. A shoulder joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace...
21 CFR 888.3660 - Shoulder joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Shoulder joint metal/polymer semi-constrained... Shoulder joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. A shoulder joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace...
21 CFR 888.3790 - Wrist joint metal constrained cemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Wrist joint metal constrained cemented prosthesis... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3790 Wrist joint metal constrained cemented prosthesis. (a) Identification. A wrist joint metal constrained cemented prosthesis is...
21 CFR 888.3200 - Finger joint metal/metal constrained uncemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Finger joint metal/metal constrained uncemented... metal/metal constrained uncemented prosthesis. (a) Identification. A finger joint metal/metal... Administration on or before December 26, 1996 for any finger joint metal/metal constrained uncemented...
21 CFR 888.3790 - Wrist joint metal constrained cemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Wrist joint metal constrained cemented prosthesis... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3790 Wrist joint metal constrained cemented prosthesis. (a) Identification. A wrist joint metal constrained cemented prosthesis is...
21 CFR 888.3200 - Finger joint metal/metal constrained uncemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Finger joint metal/metal constrained uncemented... metal/metal constrained uncemented prosthesis. (a) Identification. A finger joint metal/metal... Administration on or before December 26, 1996 for any finger joint metal/metal constrained uncemented...
21 CFR 888.3790 - Wrist joint metal constrained cemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Wrist joint metal constrained cemented prosthesis... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3790 Wrist joint metal constrained cemented prosthesis. (a) Identification. A wrist joint metal constrained cemented prosthesis is...
21 CFR 888.3200 - Finger joint metal/metal constrained uncemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Finger joint metal/metal constrained uncemented... metal/metal constrained uncemented prosthesis. (a) Identification. A finger joint metal/metal... Administration on or before December 26, 1996 for any finger joint metal/metal constrained uncemented...
21 CFR 888.3100 - Ankle joint metal/composite semi-constrained cemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Ankle joint metal/composite semi-constrained... Ankle joint metal/composite semi-constrained cemented prosthesis. (a) Identification. An ankle joint metal/composite semi-constrained cemented prosthesis is a device intended to be implanted to replace...
21 CFR 888.3200 - Finger joint metal/metal constrained uncemented prosthesis.
Code of Federal Regulations, 2010 CFR
2010-04-01
... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Finger joint metal/metal constrained uncemented... metal/metal constrained uncemented prosthesis. (a) Identification. A finger joint metal/metal... Administration on or before December 26, 1996 for any finger joint metal/metal constrained uncemented...
21 CFR 888.3790 - Wrist joint metal constrained cemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Wrist joint metal constrained cemented prosthesis... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3790 Wrist joint metal constrained cemented prosthesis. (a) Identification. A wrist joint metal constrained cemented prosthesis is...
21 CFR 888.3790 - Wrist joint metal constrained cemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Wrist joint metal constrained cemented prosthesis... SERVICES (CONTINUED) MEDICAL DEVICES ORTHOPEDIC DEVICES Prosthetic Devices § 888.3790 Wrist joint metal constrained cemented prosthesis. (a) Identification. A wrist joint metal constrained cemented prosthesis is...
21 CFR 888.3200 - Finger joint metal/metal constrained uncemented prosthesis.
Code of Federal Regulations, 2011 CFR
2011-04-01
... 21 Food and Drugs 8 2011-04-01 2011-04-01 false Finger joint metal/metal constrained uncemented... metal/metal constrained uncemented prosthesis. (a) Identification. A finger joint metal/metal... Administration on or before December 26, 1996 for any finger joint metal/metal constrained uncemented...
21 CFR 888.3120 - Ankle joint metal/polymer non-constrained cemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Ankle joint metal/polymer non-constrained cemented... metal/polymer non-constrained cemented prosthesis. (a) Identification. An ankle joint metal/polymer non... December 26, 1996 for any ankle joint metal/polymer non-constrained cemented prosthesis that was in...
21 CFR 888.3510 - Knee joint femorotibial metal/polymer constrained cemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Knee joint femorotibial metal/polymer constrained... Knee joint femorotibial metal/polymer constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/polymer constrained cemented prosthesis is a device intended to be implanted to replace part...
21 CFR 888.3110 - Ankle joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Ankle joint metal/polymer semi-constrained... Ankle joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. An ankle joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace an ankle...
21 CFR 888.3110 - Ankle joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Ankle joint metal/polymer semi-constrained... Ankle joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. An ankle joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace an ankle...
21 CFR 888.3110 - Ankle joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Ankle joint metal/polymer semi-constrained... Ankle joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. An ankle joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace an ankle...
21 CFR 888.3120 - Ankle joint metal/polymer non-constrained cemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Ankle joint metal/polymer non-constrained cemented... metal/polymer non-constrained cemented prosthesis. (a) Identification. An ankle joint metal/polymer non... December 26, 1996 for any ankle joint metal/polymer non-constrained cemented prosthesis that was in...
21 CFR 888.3160 - Elbow joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Elbow joint metal/polymer semi-constrained... Elbow joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. An elbow joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace an elbow...
21 CFR 888.3510 - Knee joint femorotibial metal/polymer constrained cemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Knee joint femorotibial metal/polymer constrained... Knee joint femorotibial metal/polymer constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/polymer constrained cemented prosthesis is a device intended to be implanted to replace part...
21 CFR 888.3160 - Elbow joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2014 CFR
2014-04-01
... 21 Food and Drugs 8 2014-04-01 2014-04-01 false Elbow joint metal/polymer semi-constrained... Elbow joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. An elbow joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace an elbow...
21 CFR 888.3510 - Knee joint femorotibial metal/polymer constrained cemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Knee joint femorotibial metal/polymer constrained... Knee joint femorotibial metal/polymer constrained cemented prosthesis. (a) Identification. A knee joint femorotibial metal/polymer constrained cemented prosthesis is a device intended to be implanted to replace part...
21 CFR 888.3120 - Ankle joint metal/polymer non-constrained cemented prosthesis.
Code of Federal Regulations, 2013 CFR
2013-04-01
... 21 Food and Drugs 8 2013-04-01 2013-04-01 false Ankle joint metal/polymer non-constrained cemented... metal/polymer non-constrained cemented prosthesis. (a) Identification. An ankle joint metal/polymer non... December 26, 1996 for any ankle joint metal/polymer non-constrained cemented prosthesis that was in...
21 CFR 888.3160 - Elbow joint metal/polymer semi-constrained cemented prosthesis.
Code of Federal Regulations, 2012 CFR
2012-04-01
... 21 Food and Drugs 8 2012-04-01 2012-04-01 false Elbow joint metal/polymer semi-constrained... Elbow joint metal/polymer semi-constrained cemented prosthesis. (a) Identification. An elbow joint metal/polymer semi-constrained cemented prosthesis is a device intended to be implanted to replace an elbow...
Constrained dynamics approach for motion synchronization and consensus
NASA Astrophysics Data System (ADS)
Bhatia, Divya
In this research we propose to develop constrained dynamical systems based stable attitude synchronization, consensus and tracking (SCT) control laws for the formation of rigid bodies. The generalized constrained dynamics Equations of Motion (EOM) are developed utilizing constraint potential energy functions that enforce communication constraints. Euler-Lagrange equations are employed to develop the non-linear constrained dynamics of multiple vehicle systems. The constraint potential energy is synthesized based on a graph theoretic formulation of the vehicle-vehicle communication. Constraint stabilization is achieved via Baumgarte's method. The performance of these constrained dynamics based formations is evaluated for bounded control authority. The above method has been applied to various cases and the results have been obtained using MATLAB simulations showing stability, synchronization, consensus and tracking of formations. The first case corresponds to an N-pendulum formation without external disturbances, in which the springs and the dampers connected between the pendulums act as the communication constraints. The damper helps in stabilizing the system by damping the motion whereas the spring acts as a communication link relaying relative position information between two connected pendulums. Lyapunov stabilization (energy based stabilization) technique is employed to depict the attitude stabilization and boundedness. Various scenarios involving different values of springs and dampers are simulated and studied. Motivated by the first case study, we study the formation of N 2-link robotic manipulators. The governing EOM for this system is derived using Euler-Lagrange equations. A generalized set of communication constraints are developed for this system using graph theory. The constraints are stabilized using Baumgarte's techniques. The attitude SCT is established for this system and the results are shown for the special case of three 2-link robotic manipulators
Constrained model predictive control, state estimation and coordination
NASA Astrophysics Data System (ADS)
Yan, Jun
In this dissertation, we study the interaction between the control performance and the quality of the state estimation in a constrained Model Predictive Control (MPC) framework for systems with stochastic disturbances. This consists of three parts: (i) the development of a constrained MPC formulation that adapts to the quality of the state estimation via constraints; (ii) the application of such a control law in a multi-vehicle formation coordinated control problem in which each vehicle operates subject to a no-collision constraint posed by others' imperfect prediction computed from finite bit-rate, communicated data; (iii) the design of the predictors and the communication resource assignment problem that satisfy the performance requirement from Part (ii). Model Predictive Control (MPC) is of interest because it is one of the few control design methods which preserves standard design variables and yet handles constraints. MPC is normally posed as a full-state feedback control and is implemented in a certainty-equivalence fashion with best estimates of the states being used in place of the exact state. However, if the state constraints were handled in the same certainty-equivalence fashion, the resulting control law could drive the real state to violate the constraints frequently. Part (i) focuses on exploring the inclusion of state estimates into the constraints. It does this by applying constrained MPC to a system with stochastic disturbances. The stochastic nature of the problem requires re-posing the constraints in a probabilistic form. In Part (ii), we consider applying constrained MPC as a local control law in a coordinated control problem of a group of distributed autonomous systems. Interactions between the systems are captured via constraints. First, we inspect the application of constrained MPC to a completely deterministic case. Formation stability theorems are derived for the subsystems and conditions on the local constraint set are derived in order to
Constrained Spectral Conditioning for spatial sound level estimation
NASA Astrophysics Data System (ADS)
Spalt, Taylor B.; Brooks, Thomas F.; Fuller, Christopher R.
2016-11-01
Microphone arrays are utilized in aeroacoustic testing to spatially map the sound emitted from an article under study. Whereas a single microphone allows only the total sound level to be estimated at the measurement location, an array permits differentiation between the contributions of distinct components. The accuracy of these spatial sound estimates produced by post-processing the array outputs is continuously being improved. One way of increasing the estimation accuracy is to filter the array outputs before they become inputs to a post-processor. This work presents a constrained method of linear filtering for microphone arrays which minimizes the total signal present on the array channels while preserving the signal from a targeted spatial location. Thus, each single-channel, filtered output for a given targeted location estimates only the signal from that location, even when multiple and/or distributed sources have been measured simultaneously. The method is based on Conditioned Spectral Analysis and modifies the Wiener-Hopf equation in a manner similar to the Generalized Sidelobe Canceller. This modified form of Conditioned Spectral Analysis is embedded within an iterative loop and termed Constrained Spectral Conditioning. Linear constraints are derived which prevent the cancellation of targeted signal due to random statistical error as well as location error in the sensor and/or source positions. The increased spatial mapping accuracy of Constrained Spectral Conditioning is shown for a simulated dataset of point sources which vary in strength. An experimental point source is used to validate the efficacy of the constraints which yield preservation of the targeted signal at the expense of reduced filtering ability. The beamforming results of a cold, supersonic jet demonstrate the qualitative and quantitative improvement obtained when using this technique to map a spatially-distributed, complex, and possibly coherent sound source.
Fast alternating projection methods for constrained tomographic reconstruction.
Liu, Li; Han, Yongxin; Jin, Mingwu
2017-01-01
The alternating projection algorithms are easy to implement and effective for large-scale complex optimization problems, such as constrained reconstruction of X-ray computed tomography (CT). A typical method is to use projection onto convex sets (POCS) for data fidelity, nonnegative constraints combined with total variation (TV) minimization (so called TV-POCS) for sparse-view CT reconstruction. However, this type of method relies on empirically selected parameters for satisfactory reconstruction and is generally slow and lack of convergence analysis. In this work, we use a convex feasibility set approach to address the problems associated with TV-POCS and propose a framework using full sequential alternating projections or POCS (FS-POCS) to find the solution in the intersection of convex constraints of bounded TV function, bounded data fidelity error and non-negativity. The rationale behind FS-POCS is that the mathematically optimal solution of the constrained objective function may not be the physically optimal solution. The breakdown of constrained reconstruction into an intersection of several feasible sets can lead to faster convergence and better quantification of reconstruction parameters in a physical meaningful way than that in an empirical way of trial-and-error. In addition, for large-scale optimization problems, first order methods are usually used. Not only is the condition for convergence of gradient-based methods derived, but also a primal-dual hybrid gradient (PDHG) method is used for fast convergence of bounded TV. The newly proposed FS-POCS is evaluated and compared with TV-POCS and another convex feasibility projection method (CPTV) using both digital phantom and pseudo-real CT data to show its superior performance on reconstruction speed, image quality and quantification.
Pattern recognition constrains mantle properties, past and present
NASA Astrophysics Data System (ADS)
Atkins, S.; Rozel, A. B.; Valentine, A. P.; Tackley, P.; Trampert, J.
2015-12-01
Understanding and modelling mantle convection requires knowledge of many mantle properties, such as viscosity, chemical structure and thermal proerties such as radiogenic heating rate. However, many of these parameters are only poorly constrained. We demonstrate a new method for inverting present day Earth observations for mantle properties. We use neural networks to represent the posterior probability density functions of many different mantle properties given the present structure of the mantle. We construct these probability density functions by sampling a wide range of possible mantle properties and running forward simulations, using the convection code StagYY. Our approach is particularly powerful because of its flexibility. Our samples are selected in the prior space, rather than being targeted towards a particular observation, as would normally be the case for probabilistic inversion. This means that the same suite of simulations can be used for inversions using a wide range of geophysical observations without the need to resample. Our method is probabilistic and non-linear and is therefore compatible with non-linear convection, avoiding some of the limitations associated with other methods for inverting mantle flow. This allows us to consider the entire history of the mantle. We also need relatively few samples for our inversion, making our approach computationally tractable when considering long periods of mantle history. Using the present thermal and density structure of the mantle, we can constrain rheological and compositional parameters such as viscosity and yield stress. We can also use the present day mantle structure to make inferences about the initial conditions for convection 4.5 Gyr ago. We can constrain initial mantle conditions including the initial concentration of heat producing elements in the mantle and the initial thickness of primordial material at the CMB. Currently we use density and temperature structure for our inversions, but we can
Hygro-thermal mechanical behavior of Nafion during constrained swelling
NASA Astrophysics Data System (ADS)
Silberstein, Meredith N.; Boyce, Mary C.
Durability is a major limitation of current proton exchange membrane fuel cells. Mechanical stress due to hygro-thermal cycling is one failure mechanism of the polymer electrolyte membrane. In previous work the cyclic rate, temperature, and hydration dependent elastic-viscoplastic mechanical behavior of Nafion has been extensively investigated in uniaxial and biaxial tension, serving as a data basis and means of validation for a three-dimensional constitutive model. Here, the important effect of loading via constrained swelling is studied. Specifically, two types of loading are investigated: partially constrained swelling via a bimaterial swelling test and hygro-thermal cycling within a fuel cell. The bimaterial swelling conditions are examined via experiments in conjunction with modeling. Nafion/GDL bimaterial strips were hydrated and observed to curl significantly with the membrane on the convex side due to the large Nafion hygro-expansion coefficient. Upon drying the bimaterial strips developed a slight reverse curvature with the membrane on the concave side due to the plastic deformation which had occurred in the membrane during hydration. Finite element simulations utilizing the Nafion constitutive model successfully predicted the behavior during hydration and drying, providing insight on the constrained swelling physics and the ability of the model to predict such events. Simulations of in situ fuel cell hygro-thermal cycling are performed via a simplified two-dimensional fuel cell model. The simulation results confirm the finding of other studies that a tensile stress develops in the membrane during drying. Further, a concentration of negative hydrostatic pressure is found to develop just inside the channel region in the dried state supporting the theory of hygro-thermal driven mechanical stresses causing pinhole formation in the channel. The amplitude of the pressure cycling is found to be large and sensitive to both hygro-thermal ramp time and hold time