Numerical and experimental assessment of the modal curvature method for damage detection in plate structures

This paper is concerned with the use of numerically obtained modal curvatures for damage detection in both isotropic and composite laminated plates. Numerical simulations are carried out by using COMSOL Multiphysics as FEM solver of the governing equations, in which a Mindlin-Reissner plate model is assumed and defects are introduced as localized smoothed variations of the baseline (healthy) configuration. Experiments are also performed on steel and aluminum plates using scanning laser vibrometry. This study confirms that the central difference method greatly amplifies the measurement errors and its application leads to ineffective predictions for damage detection, even after denoising. As a consequence, different numerical techniques should be explored to allow the use of numerically obtained modal curvatures for structural health monitoring. Herein, the Savitzky-Golay filter (or least-square smoothing filter) is considered for the numerical differentiation of noisy data

Cooperative Decision Making : a methodology based on collective preferences aggregation

National audienceThe benefice of a collective decisions process mainly rests upon the possibility for the participants to confront their respective points of views. To this end, they must have cognitive and technical tools that ease the sharing of the reasons that motivate their own preferences, while accounting for information and feelings they should keep for their own. The paper presents the basis of such a cooperative decision making methodology that allows sharing information by accurately distinguishing the components of a decision and the steps of its elaboration

Numerical and experimental assessment of the modal curvature method for damage detection in plate structures

Use of modal curvatures obtained from modal displacement data for damage detection in isotropic and composite laminated plates is addressed through numerical examples and experimental tests. Numerical simulations are carried out employing COMSOL Multiphysics as finite element solver of the equations governing the Mindlin-Reissner plate model. Damages are introduced as localized non-smooth variations of the bending stiffness of the baseline (healthy) configuration. Experiments are also performed on steel and aluminum plates using scanning laser vibrometry. The obtained results confirm that use of the central difference method to compute modal curvatures greatly amplifies the measurement errors and its application leads to unreliable predictions for damage detection, even after denoising. Therefore, specialized ad hoc numerical techniques must be suitably implemented to enable structural health monitoring via modal curvature changes. In this study, the Savitzky-Golay filter (also referred to as least-square smoothing filter) is considered for the numerical differentiation of noisy data. Numerical and experimental results show that this filter is effective for the reliable computation of modal curvature changes in plate structures due to defects and/or damages

Identification of plastic constitutive parameters at large deformations from three dimensional displacement fields

The aim of this paper is to provide a general procedure to extract the constitutive parameters of a plasticity model starting from displacement measurements and using the Virtual Fields Method. This is a classical inverse problem which has been already investigated in the literature, however several new features are developed here. First of all the procedure applies to a general three-dimensional displacement field which leads to large plastic deformations, no assumptions are made such as plane stress or plane strain although only pressure-independent plasticity is considered. Moreover the equilibrium equation is written in terms of the deviatoric stress tensor that can be directly computed from the strain field without iterations. Thanks to this, the identification routine is much faster compared to other inverse methods such as finite element updating. The proposed method can be a valid tool to study complex phenomena which involve severe plastic deformation and where the state of stress is completely triaxial, e.g. strain localization or necking occurrence. The procedure has been validated using a three dimensional displacement field obtained from a simulated experiment. The main potentialities as well as a first sensitivity study on the influence of measurement errors are illustrated

WiseEye: next generation expandable and programmable camera trap platform for wildlife research

Funding: The work was supported by the RCUK Digital Economy programme to the dot.rural Digital Economy Hub; award reference: EP/G066051/1. The work of S. Newey and RJI was part funded by the Scottish Government's Rural and Environment Science and Analytical Services (RESAS). Details published as an Open Source Toolkit, PLOS Journals at: http://dx.doi.org/10.1371/journal.pone.0169758Peer reviewedPublisher PD

Macrophage Tropism and Cytopathicity of HIV-1 Variants Isolated Sequentially from a Long-Term Survivor Infected with nef-Deleted Virus

Long-term survival of human immunodeficiency virus type 1 (HIV-1) infection has been noted in rare cohorts of individuals infected with nef-deleted virus. Enhanced macrophage tropism and cytopathicity contribute to pathogenicity of wild type HIV-1. To better understand the pathogenesis of nef-deleted HIV-1, we analyzed the replication capacity and macrophage cytopathicity of nef-deleted HIV-1 isolated sequentially from a long-term survivor during progression to AIDS (n=6 isolates). Compared with controls, all nef-deleted viruses replicated to low levels in peripheral blood mononu-clear cells and monocyte-derived macrophages (MDM). One nef-deleted virus that was isolated on the development of AIDS caused high levels of syncytia in MDM similar to control viruses, but five viruses isolated from earlier times prior to AIDS onset caused only minimal cytopathicity. Together, these results suggest that enhanced cytopathicity of nef-deleted HIV-1 for MDM can occur independently of replication capacity, and may contribute to the pathogenesis of nef-deleted HIV-1 infection

Conformational alterations in the CD4 binding cavity of HIV-1 gp120 influencing gp120-CD4 interactions and fusogenicity of HIV-1 envelopes derived from brain and other tissues

<p>Abstract</p> <p>Background</p> <p>CD4-binding site (CD4bs) alterations in gp120 contribute to HIV-1 envelope (Env) mediated fusogenicity and the ability of gp120 to utilize low levels of cell-surface CD4. In a recent study, we constructed three-dimensional models of gp120 to illustrate CD4bs conformations associated with enhanced fusogenicity and enhanced CD4-usage of a modestly-sized panel of blood-derived HIV-1 Envs (n = 16). These conformations were characterized by a wider aperture of the CD4bs cavity, as constrained by the inner-most atoms at the gp120 V1V2 stem and the V5 loop. Here, we sought to provide further validation of the utility of these models for understanding mechanisms that influence Env function, by characterizing the structure-function relationships of a larger panel of Envs derived from brain and other tissues (n = 81).</p> <p>Findings</p> <p>Three-dimensional models of gp120 were generated by our recently validated homology modelling protocol. Analysis of predicted CD4bs structures showed correlations between the aperture width of the CD4bs cavity and ability of the Envs to mediate cell-cell fusion, scavenge low-levels of cell-surface CD4, bind directly to soluble CD4, and bind to the Env mAb IgG1b12 whose epitope overlaps the gp120 CD4bs. These structural alterations in the CD4bs cavity were associated with repositioning of the V5 loop.</p> <p>Conclusions</p> <p>Using a large, independent panel of Envs, we can confirm the utility of three-dimensional gp120 structural models for illustrating CD4bs alterations that can affect Env function. Furthermore, we now provide new evidence that these CD4bs alterations augment the ability of gp120 to interact with CD4 by increasing the exposure of the CD4bs.</p

In vivo emergence of HIV-1 highly sensitive to neutralizing antibodies.

BACKGROUND: The rapid and continual viral escape from neutralizing antibodies is well documented in HIV-1 infection. Here we report in vivo emergence of viruses with heightened sensitivity to neutralizing antibodies, sometimes paralleling the development of neutralization escape. METHODOLOGY/PRINCIPAL FINDINGS: Sequential viral envs were amplified from seven HIV-1 infected men monitored from seroconversion up to 5 years after infection. Env-recombinant infectious molecular clones were generated and tested for coreceptor use, macrophage tropism and neutralization sensitivity to homologous and heterologous serum, soluble CD4 and monoclonal antibodies IgG1b12, 2G12 and 17b. We found that HIV-1 evolves sensitivity to contemporaneous neutralizing antibodies during infection. Neutralization sensitive viruses grow out even when potent autologous neutralizing antibodies are present in patient serum. Increased sensitivity to neutralization was associated with susceptibility of the CD4 binding site or epitopes induced after CD4 binding, and mediated by complex envelope determinants including V3 and V4 residues. The development of neutralization sensitive viruses occurred without clinical progression, coreceptor switch or change in tropism for primary macrophages. CONCLUSIONS: We propose that an interplay of selective forces for greater virus replication efficiency without the need to resist neutralizing antibodies in a compartment protected from immune surveillance may explain the temporal course described here for the in vivo emergence of HIV-1 isolates with high sensitivity to neutralizing antibodies

Phenotype and envelope gene diversity of nef-deleted HIV-1 isolated from long-term survivors infected from a single source

<p>Abstract</p> <p>Background</p> <p>The Sydney blood bank cohort (SBBC) of long-term survivors consists of multiple individuals infected with attenuated, <it>nef</it>-deleted variants of human immunodeficiency virus type 1 (HIV-1) acquired from a single source. Long-term prospective studies have demonstrated that the SBBC now comprises slow progressors (SP) as well as long-term nonprogressors (LTNP). Convergent evolution of <it>nef </it>sequences in SBBC SP and LTNP indicates the <it>in vivo </it>pathogenicity of HIV-1 in SBBC members is dictated by factors other than <it>nef</it>. To better understand mechanisms underlying the pathogenicity of <it>nef</it>-deleted HIV-1, we examined the phenotype and <it>env </it>sequence diversity of sequentially isolated viruses (n = 2) from 3 SBBC members.</p> <p>Results</p> <p>The viruses characterized here were isolated from two SP spanning a three or six year period during progressive HIV-1 infection (subjects D36 and C98, respectively) and from a LTNP spanning a two year period during asymptomatic, nonprogressive infection (subject C18). Both isolates from D36 were R5X4 phenotype and, compared to control HIV-1 strains, replicated to low levels in peripheral blood mononuclear cells (PBMC). In contrast, both isolates from C98 and C18 were CCR5-restricted. Both viruses isolated from C98 replicated to barely detectable levels in PBMC, whereas both viruses isolated from C18 replicated to low levels, similar to those isolated from D36. Analysis of <it>env </it>by V1V2 and V3 heteroduplex tracking assay, V1V2 length polymorphisms, sequencing and phylogenetic analysis showed distinct intra- and inter-patient <it>env </it>evolution.</p> <p>Conclusion</p> <p>Independent evolution of <it>env </it>despite convergent evolution of <it>nef </it>may contribute to the <it>in vivo </it>pathogenicity of <it>nef</it>-deleted HIV-1 in SBBC members, which may not necessarily be associated with changes in replication capacity or viral coreceptor specificity.</p