2,549 research outputs found
A note on the differences between Drucker-Prager and Mohr-Coulomb shear strength criteria
No full textA systematic approach to measure the differences between Mohr-Coulomb (MC) and Drucker-Prager (DP) shear strength criteria used commonly in soil and rock mechanics is presented. It is shown that the DP criterion generates a shear strength between 0.6 and 3 times the MC strength, for the same friction angle and cohesion parameters. The appropriate conditions for obtaining equal shear strengths are given. Moreover, some new DP failure surfaces are proposed which minimize the differences relative to the MC predictions. The equivalence of the DP and MC criteria under plane strain conditions is also examined
Advances In Ecological Data Integration And Management [avanços Na Integração E Gerenciamento De Dados Ecológicos]
No full text[No abstract available]91115120Berkley, C., (2001) Metacat: a schema-independent XML database system, pp. 171-179. , Proceedings of the 13th International Conference on Scientific and Statistical Database Management2001Fairfax, Virginia USA. Fairfax: George Mason University, IEEE Computer SocietyBerry, R.J., Ecology: where genes and geography meet (1989) Journal of Animal Ecology, 58, pp. 733-759. , http://dx.doi.org/10.2307/5121De By, R.A., Drucker, D.P., Santos, L.C., Base de dados para inventários de biodiversidade (2008) Reserva Ducke: A biodiversidade amazônica através de uma grade, pp. 145-160. , http://ppbio.inpa.gov.br/Port/public/LivroRFAD_ebook.pdf/, Oliveira ML et al., organizadores. Manaus: Attema Design Editorial Available fromCosta, F.R.C., Magnusson, W.E., The need for large-scale, integrated studies of biodiversity - the experience of the Program for Biodiversity Research in Brazilian Amazonia (2010) Natureza & Conservação, 8 (1), pp. 3-12Costello, M.J., Motivating online publication of data (2009) BioScience, 59, pp. 418-427. , http://dx.doi.org/10.1525/bio.2009.59.5.9Fegraus, E.H., Maximizing the value of ecological data with structured metadata: An introduction to ecological metadata language (EML) and principles for metadata creation (2005) Bulletin of the Ecological Society of America, 86, pp. 158-168. , http://dx.doi.org/10.1890/0012-9623(2005)86[158:MTVOED]2.0.CO;2Hackett, E., Ecology transformed: the National Center for Ecological Analysis and Synthesis and the changing patterns of ecological research (2008) Scientific collaboration on the internet, pp. 277-296. , Olson G, Zimmerman A & Bos N, editors. Boston: Massachusetts Institute of TechnologyHalpern, B.S., Floeter, S.R., Functional diversity responses to changing species richness in reef fish communities (2008) Marine Ecology Progress Series, 364, pp. 147-156. , http://dx.doi.org/10.3354/meps07553Higgins, D., Berkley, C., Jones, M.B., (2002) Managing heterogeneous ecological data using Morpho, , Proceedings of the 14th International Conference on Scientific and Statistical Database Management2002Edinburgh, Scotland, UK. Edinburgh: IEEE Computer SocietyJackson, J.B.C., Historical overfishing and the recent collapse of coastal ecosystems (2001) Science, 293, pp. 629-638. , http://dx.doi.org/10.1126/science.1059199Jones, M.B., The new bioinformatics: integrating ecological data from the gene to the biosphere (2006) Annual Review of Ecology, Evolution, and Systematics, 37, pp. 519-544. , http://dx.doi.org/10.1146/annurev.ecolsys.37.091305.110031Joly, C.A., As parcelas permanentes do Projeto Temático BIOTA Gradiente Funcional: Composição florística, estrutura e funcionamento da Floresta Ombrófila Densa dos Núcleos Picinguaba e Santa Virgínia do Parque Estadual da Serra do Mar, São Paulo, Brasil (2008) Experiências de monitoramento no bioma Mata Atlântica com uso de parcelas permanentes, pp. 109-148. , Sanquetta CA, editor. Curitiba: Programa PELD-CNPq & MultigraphLewinsohn, T.M., Prado, P.I., (2002) Biodiversidade Brasileira: Síntese do Estado Atual do Conheciment, , São Paulo: Editora ContextoLynch, C., How do your data grow (2008) Nature, 455, pp. 28-29. , http://dx.doi.org/10.1038/455028aMadin, J.S., Advancing ecological research with ontologies (2008) Trends in Ecology and Evolution, 23 (3), pp. 159-168. , http://dx.doi.org/10.1016/j.tree.2007.11.007Michener, W.K., Nongeospatial metadata for the ecological sciences (1997) Ecological Applications, 7, pp. 330-342. , http://dx.doi.org/10.1890/1051-0761(1997)007[0330:NMFTES]2.0.CO;2Michener, W.K., Long term ecological research and information management (2011) Ecological Informatics, 6 (1), pp. 13-24. , http://dx.doi.org/10.1016/j.ecoinf.2010.11.005Parmesan, C., Yohe, G., A globally coherent fingerprint of climate change impacts across natural systems (2003) Nature, 421, pp. 37-42. , http://dx.doi.org/10.1038/nature01286Piwowar, H.A., Day, R.S., Fridsma, D.B., Sharing detailed research data is associated with increased citation rate (2007) PLoS ONE, 2 (3), pp. e308. , http://dx.doi.org/10.1371/journal.pone.0000308Prado, P.I., Distribuições de abundâncias de espécies: avanços analíticos para entender um padrão básico em ecologia (2009) Ciência e Ambiente, 39, pp. 121-136Sagarin, R., Pauchard, A., Observational approaches in ecology open new ground in a changing world (2010) Frontiers in Ecology and the Environment, 8, pp. 379-386. , http://dx.doi.org/10.1890/090001Reichman, O.J., Jones, M.B., Schildhauer, M.P., Challenges and opportunities of open data in ecology (2011) Science, 331, pp. 703-705. , http://dx.doi.org/10.1126/science.1197962Whitlock, M.C., Data archiving (2010) American Naturalist, 175, pp. 145-146. , http://dx.doi.org/10.1086/65034
岩土常规三轴 Drucker-Prager 准则
No full text隨著三維數值極限分析得到日益關注，亟需發展適用于巖土常規三軸應力狀態的Drucker-Prager（DP）準則。當前尚無適用于巖土常規三軸條件的DP準則的精確解，而是使用近似的等面積圓DP-31準則，該準則偏安全。基于巖土三剪能量準則，推導了該準則最高點（即該準則與摩爾-庫侖準則的切點）對應的羅德角的表達式，進而通過最高點建立了巖土常規三軸DP-32準則，并將其應用于常規三軸條件下土體的極限荷載計算與邊坡穩定性分析。研究表明：DP-32準則計算的常規三軸下土體極限荷載為實測值的87%～97%,DP-32準則與DP-31準則計算的極限荷載之比可達1.19，且隨著圍壓減小、黏聚力c增大或者內摩擦角φ增大，二者計算結果的差異增大；DP-32準則計算的土質邊坡穩定安全系數為DP-31準則計算結果的1.01～1.04倍，且二者差異隨著坡度增大而增大。這些結果表明DP-32準則適用于巖土常規三軸應力狀態下的數值極限分析。 With the increasing attention paid to three-dimensional numerical limit analysis, there is an urgent need to develop a new Drucker-Prager (DP) criterion suitable for geomaterials under conventional triaxial stress condition. Yet, an exact DP criterion for geomaterials under conventional triaxial stress condition does not exist. Instead, an approximate equal-area-circle DP-31 criterion has been used traditionally, which is relatively safe. This study developed a new DP-32 criterion for geomaterials under conventional triaxial stress condition based on the tri-shear energy yield criterion. The theoretical formulation was derived to determine the highest point of the criterion (i.e., the tangent point between the criterion and the Mohr-Coulomb criterion). Then, the conventional triaxial DP-32 criterion was established through the highest point. Thereafter, this new criterion was used to determine the ultimate load of soil under conventional triaxial condition and slope stability analysis. The ultimate load of soil under conventional triaxial condition determined by the DP-32 criterion was found to be about 87%–97% of the measured value. Moreover, the maximum ratio of ultimate load computed by the DP-32 criterion to the DP-31 criterion was 1.19, and it increased with decreasing confining pressure, increasing cohesion c, or increasing internal friction angle φ. The factor of safety (FOS) of soil slopes determined by the DP-32 criterion was approximately 1.01–1.04 times that determined by the DP-31 criterion. Furthermore, the difference increased at larger slope angles. These results suggest that the DP-32 criterion is suitable for numerical limit analysis of geomaterials under conventional triaxial stress condition
A common HLA-DPA1 variant is associated with hepatitis B virus infection but fails to distinguish active from inactive Caucasian carriers
No full textBackground and Aims: Chronic infection with the hepatitis B virus (HBV) is a major health issue worldwide. Recently, single nucleotide polymorphisms (SNPs) within the human leukocyte antigen (HLA)-DP locus were identified to be associated with HBV infection in Asian populations. Most significant associations were observed for the A alleles of HLA-DPA1 rs3077 and HLA-DPB1 rs9277535, which conferred a decreased risk for HBV infection. We assessed the implications of these variants for HBV infection in Caucasians.
Methods: Two HLA-DP gene variants (rs3077 and rs9277535) were analyzed for associations with persistent HBV infection and with different clinical outcomes, i.e., inactive HBsAg carrier status versus progressive chronic HBV (CHB) infection in Caucasian patients (n = 201) and HBsAg negative controls (n = 235).
Results: The HLA-DPA1 rs3077 C allele was significantly associated with HBV infection (odds ratio, OR = 5.1, 95% confidence interval, CI: 1.9–13.7; p = 0.00093). However, no significant association was seen for rs3077 with progressive CHB infection versus inactive HBsAg carrier status (OR = 2.7, 95% CI: 0.6–11.1; p = 0.31). In contrast, HLA-DPB1 rs9277535 was not associated with HBV infection in Caucasians (OR = 0.8, 95% CI: 0.4–1.9; p = 1).
Conclusions: A highly significant association of HLA-DPA1 rs3077 with HBV infection was observed in Caucasians. However, as a differentiation between different clinical courses of HBV infection was not possible, knowledge of the HLA-DPA1 genotype cannot be translated into personalized anti-HBV therapy approaches
On the effects of non-linearities in DP systems
No full textIn offshore operations a trend is forming where vessels are more often required to do multiple short operations within a small-time frame. Traditional mooring systems require execution time far beyond the operation time. Dynamic positioning systems offer great advantages for short time span operations such as crew transfer or lift operations. Currently operations are planned based on DP capability plots and experience of captain and DPO. DP capability plots have little operational value as this is a static calculation and only provide information for average station keeping capability. During operations, the displacements made by the vessel around the DP set-point, also referred to as DP offset, are of great importance to determine the operability of an operation. Currently, the only way of calculating the DP offset is by conducting extensive time domain simulations, which are hard to integrate in the operational workflow of a DP vessel involved in walk-to-work operations. Therefore, a new approach is developed which predicts the vessel’s DP offset in the frequency domain, which enables a quick and robust calculation of the DP offset which is suited to merge into the on-board workflow. A frequency domain model is per definition a linear model. This leads to the main challenge of this research. A vessel operating on DP is non-linear. Currently there is no insight in what the effect is of non-linear components present in a DP system, on the linear approximation of a frequency domain model. To investigate the effect of non-linear components onto the DP frequency domain model, a time domain model is developed that is capable of systematically enabling/disabling different non-linear components. The time domain model will serve as the ’truth’ in this research as no actual vessel data is available. Furthermore, this helps identify the effects more easily, as the input for both models are identical. From the time domain model transfer functions can be derived that serve as the basis for the frequency domain model. The transfer function is a linear relation between two variables. In this case, between second order wave drift forces and displacement of the vessel in surge, sway and yaw direction. The following non-linear components are investigated in this research: Thruster ramp up, thruster turning rate, forbidden zones, saturation and thruster allocation. Thruster allocation is present in each model that will be tested, as this is an essential part of a DP system. Using two methods of determining transfer functions the model and the effects of all non-linear components are tested. The model is subjected to a variety sea-state, with different wave directions. Both methods offer similar results even though different approaches to determine the transfer functions are used. The selected method is capable of accurately predicting vessel offsets, although some extreme offsets are not captured. It is concluded that the presence of non-linear components have little to no effect on the DP offset as calculated by the time domain model. Because natural frequencies characteristic to these non-linear components are expected to exist at much higher frequencies that naturally present in second order wave drift forces. Thus, making a linear frequency domain model suitable for DP offset forecasting. It is advised to investigate the effect of including 2D input spectra as this is expected to improve the current model.<br/
Differentially Private GAN for Time Series
No full textGenerative Adversarial Networks (GANs) are a modern solution aiming to encourage public sharing of data, even if the data contains inherently private information, by generating synthetic data that looks like, but is not equal to, the data the GAN was trained on. However, GANs are prone to remembering samples from the training data, therefore additional care is needed to guarantee privacy. Differentially Private (DP) GANs offer a solution to this problem by protecting user privacy through a mathematical guarantee, achieved by adding carefully constructed noise at specific points in the training process. A state-of-the-art example of such a GAN is Gradient Sanitized Wasserstein GAN, (GS-WGAN), \cite{chen2021gswgan}. This model is shown to create higher quality synthetic images than other DP GANs. To extend the applicability of GS-WGAN we first reproduce and extend the evaluation, verifying that the model outperforms DP-CGAN by an average of 40\% when assessed across three qualitative metrics and two datasets. Secondly we propose improvements to the architecture and training procedure to make GS-WGAN applicable on timeseries data. The experimental results show that GS-WGAN is fit for generating synthetic timeseries through promising experimental results.[1] D. Chen, T. Orekondy, and M. Fritz, “Gs-wgan: A gradient-sanitized approach for learning differentially private generators,” 2021CSE3000 Research ProjectComputer Science and Engineerin
BNN-DP: Robustness Certification of Bayesian Neural Networks via Dynamic Programming
No full textIn this paper, we introduce BNN-DP, an efficient algorithmic framework for analysis of adversarial robustness of Bayesian Neural Networks (BNNs). Given a compact set of input points T ⊂ Rn, BNN-DP computes lower and upper bounds on the BNN's predictions for all the points in T. The framework is based on an interpretation of BNNs as stochastic dynamical systems, which enables the use of Dynamic Programming (DP) algorithms to bound the prediction range along the layers of the network. Specifically, the method uses bound propagation techniques and convex relaxations to derive a backward recursion procedure to over-approximate the prediction range of the BNN with piecewise affine functions. The algorithm is general and can handle both regression and classification tasks. On a set of experiments on various regression and classification tasks and BNN architectures, we show that BNN-DP outperforms state-of-the-art methods by up to four orders of magnitude in both tightness of the bounds and computational efficiency.Team Luca Laurent
Identification of material parameters for Drucker–Prager plasticity model for FRP confined circular concrete columns
No full textAbstractExisting research works have established that Drucker–Prager (DP) plasticity model is capable of modeling stress–strain behavior of confined concrete. However, accuracy of the model largely depends on adequate evaluation of its parameters that determine the yield criterion, hardening/softening rule and flow rule. Through careful analytical studies of test results of FRP confined concrete columns under theoretical framework of the DP model, it is found that: (1) the hardening/softening rule is governed by plastic strains and the FRP stiffness ratio; (2) the friction angle decreases slightly with an increase in plastic deformation; and (3) the plastic dilation angle is a function of both axial plastic strain and the FRP stiffness ratio. Explicit models for these properties are developed from analytical studies. By implementing the proposed models in ABAQUS, finite element analyses can well predict stress–strain responses of FRP confined concrete columns
Linking agrobiodiversity data through metadata standards.
No full textTrabalho apresentado na TDWG 2020 annual conference. e58928
Identification of material parameters for Drucker-Prager plasticity model for FRP confined circular concrete columns
No full textExisting research works have established that Drucker-Prager (DP) plasticity model is capable of modeling stress-strain behavior of confined concrete. However, accuracy of the model largely depends on adequate evaluation of its parameters that determine the yield criterion, hardening/softening rule and flow rule. Through careful analytical studies of test results of FRP confined concrete columns under theoretical framework of the DP model, it is found that: (1) the hardening/softening rule is governed by plastic strains and the FRP stiffness ratio; (2) the friction angle decreases slightly with an increase in plastic deformation; and (3) the plastic dilation angle is a function of both axial plastic strain and the FRP stiffness ratio. Explicit models for these properties are developed from analytical studies. By implementing the proposed models in ABAQUS, finite element analyses can well predict stress-strain responses of FRP confined concrete columns
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