Structural characterization of isobar selenium containing contaminant in a commercially available selenomethionine standard using electrospray – Ion Mobility Time of Flight Mass Spectrometry

Poster (2011, April)

Structural Chemistry and Magnetic Properties of Nd18Li8Fe5-xMxO39 (M = Mn, Co),

in Inorganic Chemistry (2009), 48

The structural complexity of phosphates in the Li-Fe2+-Fe3+ (+ PO4) system

Conference (2012, September 03)

Structural confirmation of the French version of the Oldenburg Burnout Inventory (OLBI)

Conference (2013, May 23)

This study refers to the validation of the Oldenburg Burnout Inventory (OLBI) in a Belgian population. Data gathered from nine samples were used. This represented nearly 4000 participants from different ... [more ▼]

This study refers to the validation of the Oldenburg Burnout Inventory (OLBI) in a Belgian population. Data gathered from nine samples were used. This represented nearly 4000 participants from different activity sectors. First, the traditional two-factor structure of the instrument, an alternative two-factor model and a one-factor structure were tested. Stability and generalizability of these models were then investigated using replications across various samples. The final objective was to determine relations between OLBI’s two dimensions and constructs such as positive and negative occupational states, intention to quit, job satisfaction, supervisor’s support and routinization. Confirmatory factor analysis showed that the traditional two-factor model as well as the alternative two-factor structure fits the data better than a one-factor model. Moreover, convergent and discriminant validity assumptions are confirmed. [less ▲]

Structural damage detection based on PCA of vibration measurements

in 58th Meeting of the Soc. for Mach. Failure Prevention Tech, Virginia Beach, 2004 (2004)

This paper deals with the application of statistical process control techniques based on principal component analysis to vibration-based damage diagnosis of structures. Principal component analysis of the ... [more ▼]

This paper deals with the application of statistical process control techniques based on principal component analysis to vibration-based damage diagnosis of structures. Principal component analysis of the sensor time-responses allows to extract principal directions (i.e. features) which define a subspace that is representative of the dynamics of the instrumented structure. Any change in the response of a single sensor will affect the subspace spanned by the complete sensor response set. It follows that the subspace corresponding to the current state of the structure can be compared to the subspace of the initial state of the structure, assumed to be healthy, in order to diagnose possible damage. Principal component analysis may also be performed for every potential subset of damaged sensors in order to identify the involved sensor, and, therefore, the damaged substructure. In this paper, the problem of structural damage detection is addressed in the case of environmental vibration testing. A direct application is presented for a test item submitted to random vibration testing by means of an electro-dynamic shaker. [less ▲]

Structural damage diagnosis under changing environmental conditions

in 7th International Conference on Motion and Vibration Control, Saint Louis, 2004 (2004)

A method is proposed to perform structural health monitoring under varying environmental and operational conditions. The method is based on principal component analysis (PCA) applied to a data set ... [more ▼]

A method is proposed to perform structural health monitoring under varying environmental and operational conditions. The method is based on principal component analysis (PCA) applied to a data set containing vibration characteristics identified during the monitoring of the structure. The advantage of the method is that it does not require the measurement of environmental parameters that are taken into account as embedded variables. As the influence of environmental effects may be effectively eliminated, the residual error of the PCA prediction model remains small if the structure is healthy, and increases significantly when structural damage occurs. Novelty analysis on the residual errors provides a statistical indication of damage. The PCA-based damage detection method is illustrated using experimental data. It will also be shown that when the relationship between the vibration characteristics becomes nonlinear, PCA is advantageously replaced by one of its nonlinear generalizations. [less ▲]

Structural damage diagnosis under varying environmental conditions - Part II: local PCA for non-linear cases

in Mechanical Systems & Signal Processing (2005), 19(4), 865-880

It is well known that changes in vibration features of structures due to damage may be masked by the effects of environmental variations. This influence has to be eliminated in the structural health ... [more ▼]

It is well known that changes in vibration features of structures due to damage may be masked by the effects of environmental variations. This influence has to be eliminated in the structural health-monitoring process, especially when a long-term in situ monitoring is expected. In the companion paper [1] a linear method based on principal component analysis (PCA) has been proposed and has shown encouraging results for linear or even weakly non-linear cases. The present paper concerns a further extension of the proposed method to handle non-linear cases, which may be encountered in some complex structures. The method involves a two-step procedure, namely a clustering of the data space into several regions and then the application of PCA La each local region. The application of local PCA allows performing a piecewise linearisation of the non-linear problem. A close look at the choice of the distortion function used in data clustering leads to two new clustering strategies. Whereas the first strategy is specifically suitable for the application treated in this paper, the second one is more general. The local PCA-based damage detection method is applied for the structural health monitoring of a real bridge using vibration data measured in situ over a one-year period. 2005 Elsevier Ltd. All rights reserved. [less ▲]

Structural damage localization by combining flexibility and stiffness methods

in Engineering Structures (2005), 27(12), 1752-1761

A damage diagnosis technique based on changes in dynamically measured flexibility and stiffness of structures is presented. The objective is not only to detect the existence of damage, but also to locate ... [more ▼]

A damage diagnosis technique based on changes in dynamically measured flexibility and stiffness of structures is presented. The objective is not only to detect the existence of damage, but also to locate it. The covariance-driven subspace identification technique is applied to identify structural modal parameters, and these are then used to assemble the flexibility matrix of dimensions corresponding to the measured degrees of freedom. The corresponding stiffness matrix is obtained by a pseudo-inversion of the flexibility matrix. Damage localization is achieved by a combined assessment of changes in these two measured matrices in moving from the reference state to the damaged state. Since the location of damage is given directly by the position of sensors, no geometrical measurements and finite element models are needed. When using output-only measurement data, an approximate mass-normalization of the mode shapes is adopted and an appropriate correction procedure is proposed. Numerical and experimental applications are considered, in order to examine the efficiency and limitations of the presented method. [less ▲]

Structural Determinants of Cold Adaptation and Stability in a Large Protein

in Journal of Biological Chemistry (2001), 276(28), 25791-6

The heat-labile alpha-amylase from an antarctic bacterium is the largest known protein that unfolds reversibly according to a two-state transition as shown by differential scanning calorimetry. Mutants of ... [more ▼]

The heat-labile alpha-amylase from an antarctic bacterium is the largest known protein that unfolds reversibly according to a two-state transition as shown by differential scanning calorimetry. Mutants of this enzyme were produced, carrying additional weak interactions found in thermostable alpha-amylases. It is shown that single amino acid side chain substitutions can significantly modify the melting point T(m), the calorimetric enthalpy Delta H(cal), the cooperativity and reversibility of unfolding, the thermal inactivation rate constant, and the kinetic parameters k(cat) and K(m). The correlation between thermal inactivation and unfolding reversibility displayed by the mutants also shows that stabilizing interactions increase the frequency of side reactions during refolding, leading to intramolecular mismatches or aggregations typical of large proteins. Although all mutations were located far from the active site, their overall trend is to decrease both k(cat) and K(m) by rigidifying the molecule and to protect mutants against thermal inactivation. The effects of these mutations indicate that the cold-adapted alpha-amylase has lost a large number of weak interactions during evolution to reach the required conformational plasticity for catalysis at low temperatures, thereby producing an enzyme close to the lowest stability allowing maintenance of the native conformation. [less ▲]

Structural Determinants of Specificity and Catalytic Mechanism in mammalian 25-kDa Thiamine Triphosphatase

in Biochimica et Biophysica Acta - General Subjects (in press)

Background: Thiamine triphosphate (ThTP) is present in most organisms and might be involved in intracellular signaling. In mammalian cells, the cytosolic ThTP level is controlled by a specific thiamine ... [more ▼]

Background: Thiamine triphosphate (ThTP) is present in most organisms and might be involved in intracellular signaling. In mammalian cells, the cytosolic ThTP level is controlled by a specific thiamine triphosphatase (ThTPase), belonging to the CYTH superfamily of proteins. CYTH proteins are present in all superkingdoms of life and act on various triphosphorylated substrates. Methods: Using crystallography, mass spectrometry and mutational analysis, we identified the key structural determinants of the high specificity and catalytic efficiency of mammalian ThTPase. Results: Triphosphate binding requires three conserved arginines while the catalytic mechanism relies on an unusual lysine-tyrosine dyad. By docking of the ThTP molecule in the active site, we found that Trp-53 should interact with the thiazole part of the substrate molecule, thus playing a key role in substrate recognition and specificity. Sea anemone and zebrafish CYTH proteins, which retain the corresponding Trp residue, are also specific ThTPases. Surprisingly, the whole chromosome region containing the ThTPase gene is lost in birds. Conclusion: The specificity for ThTP is linked to a stacking interaction between the thiazole heterocycle of thiamine and a tryptophan residue. The latter likely plays a key role in the secondary acquisition of ThTPase activity in early metazoan CYTH enzymes, in the lineage leading from cnidarians to mammals. General significance: We show that ThTPase activity is not restricted to mammals as previously thought but is an acquisition of early metazoans. This, and the identification of critically important residues, allows us to draw an evolutionary perspective of the CYTH family of proteins. [less ▲]