bluuebunny/crossref_metadata_2025 huggingface dataset:
Channelrhodopsin: Potential Applications in Vision Restoration
Authors: Pan Zhuo‐Hua , Dizhoor Alexander M
Published: September 2009

Channelrhodopsins, the directly light‐gated ion channels from green algae, provide a powerful tool for basic research in neuroscience as well as potential applications for treating neurological diseases and disorders. One of the promising clinical applications is to cure blindness caused by the death of rod and cone photoreceptors.

Key concepts:

Light, through multiple conformational changes caused by reversible isomerization of retinal chromophore group, transiently creates ion conductance in microbial retinal binding proteins, channelrhodopsins.

Photocycle of channelrhodopsins remains preserved when they are heterologously expressed in animal and human cells.

Channelrhodoposins are directly light‐gated cation channels with million second activation and deactivation kinetics.

A sufficient number of functional channelrhodopsins can be formed in animal neurons, with endogenous chromophore groups as supplied by regular diet. Thus, only introducing a single gene of channelrhodopsins is required to turn various types of animal neurons into artificial photoreceptor cells.

Converting surviving inner retinal neurons into directly photosensitive cells is a new strategy to treating blindness after the death of rod and cone photoreceptors.

Using delivery by adeno‐associated viral vectors, long‐term expression of channelrhodopsin‐2 can be achieved in rodent inner retinal neurons

in vivo

.

Expression of channelrhodopsin‐2 in surviving inner retinal neurons of a mouse model with retinal degeneration can restore the ability of the retina to encode light signals and transmit the light signals to the visual cortex.
Thermosensation
Authors: Mak Stephanie , Zhang Xuming , McNaughton Peter
Published: September 2009

Detection of temperature, both of the surroundings and of the body itself, is critical for maintaining normal physiological functioning. To date, a number of thermo‐sensitive ion channels have been reported to be involved in thermosensation, six of which belong to the transient receptor potential (TRP) superfamily of nonselective cation channels. Each of these operates over a distinct temperature range and many respond to natural compounds that elicit sensations of heat or cold. The best studied is TRP vanilloid 1 (TRPV1), which is both a receptor for capsaicin, the active principle of chilli peppers, and a painful heat receptor which responds to temperatures over 42°C. Our understanding of cold transduction has also rapidly increased in recent years with the intriguing discovery of the cold receptors TRP melastatin 8 (TRPM8) and TRP ankyrin 1 (TRPA1).

Key concepts

Our current understanding of thermosensation comes mainly from the identification of six temperature‐sensitive ion channels (thermo‐TRP channels) belonging to the transient receptor potential (TRP) superfamily of nonselective calcium channels.

Each thermo‐TRP operates over a distinct temperature range. Four of them (TRPV1–4) are activated by heat, and two of them (TRPM8 and TRPA1) are activated by cold.

Thermo‐TRPs also respond to natural compounds that elicit corresponding psychophysical sensations of heat or cold.

The response of these channels is regulated after tissue damage and is subjected to modulation by inflammatory mediators released at the site of injury. The altered sensitivity of these channels accounts for the phenomenon of thermal hyperalgesia.

Inflammatory mediators sensitize TRPV1 via the activation of protein kinases such as protein kinase C (PKC), protein kinase A (PKA) and Src. The modulation of TRPV1 by PKC and PKA depends on the correct positioning of the kinases by a scaffolding protein, AKAP79/150.

There are other possible mechanisms involved in thermosensation, for example, modulation of potassium channels such as TREK‐2.
Paraneoplastic Neurologic Syndromes
Authors: Maat Peter , Sillevis Smitt Peter AE
Published: September 2009

Paraneoplastic neurologic syndromes (PNS) are remote effects of cancer. Immunological factors appear important in the pathogenesis of PNS since the detection of antineuronal autoantibodies. Detection of paraneoplastic antibodies is very helpful in diagnosing an unexplained neurological syndrome as paraneoplastic and in directing the search towards the underlying neoplasm. There are seven well‐characterized paraneoplastic antibodies reactive with the onconeural Hu, Yo, Ri, Ma2, CV2, amphiphysin and recoverin antigens. Recently, anti‐VGKC and anti‐NMDA receptor antibodies were identified in patients with limbic encephalitis (LE). Thirty per cent of patients with anti‐VGKC and LE have an underlying tumour, while most patients with anti‐NMDAR and LE are young women with an ovarian teratoma. Both VGKC‐ and NMDAR‐related LE respond well to immunotherapy. In contrast, the effect of immunotherapy in patients with PNS associated with antibodies against the intracellular onconeural antigens is disappointing. These patients benefit most from early detection and treatment of the underlying tumour.
Molecular Genetics of Hereditary Spastic Paraplegias
Authors: Novelli Giuseppe , Contino Gianmarco
Published: September 2009

Hereditary spastic paraplegias (HSPs) are a group of single‐gene disorders in which the axons of the corticospinal tract either fail to develop normally or undergo progressive degeneration. The main clinical feature of all HSPs is a bilateral, symmetrical, slowly progressive spastic paraparesis predominantly of the lower extremities, which occurs in relative isolation in pure or uncomplicated HSPs (PHSPs) or in combination with other features in complicated HSPs (CHSPs). So far, about 40 different chromosomal HSP loci have been identified by genetic linkage analysis and an increasing number of gene mutations are being identified, representing one of the most significant examples of genetic heterogeneity. Autosomal and X‐linked patterns of inheritance, both dominant and recessive, have been described. Defects in intracellular trafficking and transport in myelination and abnormalities of mitochondrial proteins have been involved in HSP pathogenesis.

Key Concepts:

Hereditary spastic paraplegias (HSP) are a group of single‐gene disorders characterized by bilateral, symmetrical, slowly progressive spastic paraparesis predominantly of the lower extremities (pure or uncomplicated HSPs).

The phenotype can be complicated by additional features (complicated HSPs).

HSPs affect 1/10 000 individuals.

Pathogenesis depends on abnormalities in intracellular trafficking, trasnsport and endocytosis, neural cell recognition and signalling, myelination and mitochondrial proteins.

About 40 different chromosomal loci and 20 genes have been identified indicating the extraordinarly strong genetic heterogeneity.

Patterns of inheritance include autosomal and X‐linked, both recessive and dominant.

Mutations in
Spastin
(SPG4) account for approximately 40% of autosomal dominant HSPs, and more then any other HSP defect. Autosomal recessive HSP account for approximately 15–20% of all types of HSPs.

Genotype–phenotype correlation and penetrance can be extremely variable even among the same family and/or gene defect.

Genetic counselling is particularly challenging because of genetic heterogeneity and should take in consideration pattern of inheritance, geographical epidemiology and clinical evaluation with a multidisciplinary approach.

To date, treatment of HSPs is primarily directed symptomatically towards reducing muscle spasticity.
Biallelic Germline Mutations of Mismatch‐Repair Genes and Paediatric Malignancies
Authors: Wimmer Katharina , Etzler Julia
Published: September 2009

Constitutional impairment of the human
deoxyribonucleic acid
(DNA) mismatch repair (MMR) system due to biallelic germline mutations in one of the MMR genes

MLH1

,

MSH2

,

MSH6

or

PMS2

causes a condition that may best be described as constitutional MMR‐deficiency (CMMR‐D) syndrome. Clinically, the syndrome is characterized by a strong predisposition to various paediatric malignancies, primarily haematological malignancies, brain tumours and early onset colorectal cancer as well as signs reminiscent of neurofibromatosis type 1 (NF1). This phenotypic overlap of CMMR‐D syndrome and NF1 may hamper or delay proper diagnosis of the underlying genetic condition, thus bearing a challenge for clinicians and geneticists alike. The article briefly reports the clinical findings in the so far described CMMR‐D syndrome patients and points out possible phenotype–genotype correlations with respect to tumour spectrum and age of malignancy onset.

Key concepts

The DNA MMR system is responsible for the correction of single base pair mismatches and small misalignments that continuously arise during DNA replication.

Defective MMR will lead to the accumulation of uncorrected mismatches in the genome and may ultimately result in cancer development.

In humans, biallelic germline mutations in one of the MMR genes
MLH1
,
MSH2
,
MSH6
and
PMS2
cause a strong predisposition to paediatric malignancies.

The condition may best be termed CMMR‐D syndrome.

Children affected by CMMR‐D syndrome primarily develop haematological malignancies, brain tumours and early onset colorectal cancers as well as
café‐au‐lait
spots (CLS) and other signs reminiscent of neurofibromatosis type 1.

The phenotypic overlap of CMMR‐D syndrome and neurofibromatosis type 1 (NF1), one of the most common autosomal dominant genetic disorders, might hamper or delay proper diagnosis of the condition.

There are indications that CMMR‐D syndrome patients carrying biallelic
MLH1/MSH2
and
MSH6/PMS2
mutations, respectively, might differ in tumour types and age of malignancy onset.

Microsatellite instability testing and/or immunohistochemical expression analysis for the MMR genes as well as reliable mutation analysis of
MLH1
,
MSH2
,
MSH6
and
PMS2
is important not only for proper diagnosis of CMMR‐D syndrome patients but also has implications for their relatives, as heterozygous germline mutations in these MMR genes are known to cause hereditary nonpolyposis colorectal cancer (HNPCC).
HIV
Vaccine Approaches
Authors: McKnight Á , Pennington Daniel J
Published: September 2009

The goal of vaccination is to establish long‐term immunological readiness that allows rapid protection against infectious disease. All current successful vaccines achieve this by inducing neutralizing antibodies, which are effective against acute, cytopathic infections that could otherwise prove fatal. By contrast, potential vaccines against highly variable pathogens that establish persistent infections, such as HIV, have been unsuccessful, as responses in addition to neutralizing antibodies, directed to specific anatomical locations, are probably necessary. Human studies on
human immunovirus
(HIV)‐exposed/infected long‐term nonprogressors to acquired immunodeficiency syndrome (AIDS) are beginning to reveal the correlates of immune protection that new vaccines should attempt to reproduce. Coupled with exciting new vaccine design and delivery strategies, these novel HIV vaccine approaches offer real hope that the HIV/AIDS pandemic can finally be overcome.
Death Receptors
Authors: Krammer Peter H , Lavrik Inna N
Published: September 2009

Apoptosis or programmed cell death is a common property of all multicellular organisms. It can be triggered by a number of factors including ultraviolet (UV) or γ‐irradiation, chemotherapeutic drugs or growth factor withdrawal. A death signal can either be induced by death receptors (extrinsic pathway) or via the mitochondria (intrinsic pathway). The death receptor (DR) family is the subfamily of the tumour necrosis factor receptor (TNFR) superfamily. Stimulation of the death receptors results in the transduction of either apoptotic or survival signals. Here we present a general overview of death receptor signalling and describe the main mechanisms leading to activation of death receptor signalling pathways.

Key concepts:

Stimulation of the death receptors (DR) leads to apoptosis.

All DR are distinguished by the presence of the death domain.

Crosslinking of DR with death ligands results in formation of the death‐inducing signalling complex (DISC).

Caspases play the central role in the transduction of death receptor apoptotic signal.

As a result of DISC formation procaspase‐8 is activated with the formation of the active caspase‐8 heterotetramer, which then triggers apoptotic signal.

c‐FLIP proteins block caspase‐8 activation at the DISC and thereby death receptor‐induced apoptosis.

There are two types of apoptotic signalling: Type I and Type II cells.

Stimulation of DR also might lead to the induction of nonapoptotic pathways.
The Apoptosome: The Executioner of Mitochondria‐mediated Apoptosis
Authors: Ferraro Elisabetta , Cecconi Francesco
Published: September 2009

The apoptosome is a molecular complex of two major components – the adapter protein
apoptotic protease
activating factor 1 (
Apaf1
) and the protease caspase‐9. These are assembled during apoptosis upon
Apaf1
interaction with cytochrome
c
, which is released from the intermembrane space of mitochondria under precise cell death stimuli. Apoptosome assembly triggers effector caspase activation, which – in turn – drives cell demise. Several proteins bind and regulate apoptosome. This complex is found in vertebrates, even though similar functions are played by ortholog proteins through slightly different mechanisms also in lower eukaryotes. Given the involvement of apoptosome dysfunctions in human diseases, this complex is also a relevant molecular target in biomedicine.

Key concepts

It was a stunning discovery to find out that cytochrome
c
, essential for adenosine triphosphate (ATP) production and cell life, was involved in a cell death pathway.

Apoptosis regulation is essential for avoiding unwanted cell death and allowing the correct development and homoeostasis of the whole organism. Therefore there are several regulators of apoptosome activity.

Caspases and Apaf1 have a key phylogenetically conserved role in apoptosis.

Apoptosis is evolutionary well‐conserved in terms of its basic mechanisms; however, the role of mitochondria in apoptosis of organisms other than vertebrates needs to be clearly defined.
Mitochondria Fusion and Fission
Authors: Benard Giovanni , Peng Guihong , Karbowski Mariusz
Published: September 2009

Mitochondrial structural dynamics is regulated by the fusion or fission of these organelles. Recently published evidence indicates the vital role of mitochondrial fusion and fission in cellular physiology, including progression of apoptosis. These reports indicate that in addition to intimate link between mitochondrial morphogenesis machineries and regulation of mitochondrial steps in apoptosis, certain proteins vital for the regulation of mitochondrial steps in apoptosis can also regulate mitochondrial fusion and fission in healthy cells. In this article, we focus on the regulation of mitochondrial network dynamics. The emerging evidence indicating that proteins implicated in mitochondrial network dynamics are vital for the mitochondrial steps in apoptosis is presented here, as well. Furthermore, the data demonstrating an unexpected role for the B‐cell lymphoma (Bcl)‐2 family members in the regulation of mitochondrial morphogenesis are also discussed.

Key concepts:

In healthy cells, mitochondrial cycle between several shapes, their morphology result from the equilibrium between mitochondrial fusion and fission.

The unique feature of mitochondrial fusion is the necessity of merging double membrane systems from the two fusing mitochondria. This process is mediated by the outer mitochondrial membrane‐associated mitofusin proteins (Mfn1 and Mfn2), and the inner mitochondrial membrane‐associated Opa1.

Regulation of mitochondrial fusion and fission has a significant impact on cell viability and early development.

The mitochondrial fragmentation occurs concomitantly with the outer mitochondrial membrane (OMM) permeabilization, a critical step in apoptosis.

The cooperation between proteins involved in mitochondrial fusion and fission and Bcl‐2 family proteins during apoptosis suggests that changes in mitochondrial network dynamics contribute to apoptotic signalling.

The mechanistic link between the core mitochondrial fusion and fission regulating proteins (e.g. Drp1, Mfn2 and Opa1) and proteins from Bcl‐2 family, suggest that Bcl‐2 family proteins also regulate mitochondrial dynamics in healthy cells.
Phylogenetic Relationships Deduced from Whole Genome Comparisons
Authors: Boussau Bastien
Published: September 2009

In the second half of the twentieth century, gene sequences have been used to study their evolution as well as the history of species. A decade ago, progress in sequencing techniques provided the opportunity to use whole genome sequences for reconstructing species phylogeny. Several phylogenomic methods have been used to exploit these large amounts of data, and those that are based on homologous or orthologous characters have been favoured. Among these, the supertree and supermatrix approaches have been very successful at resolving parts of the tree of life. However, these methods discard a great proportion of the evolutionary information present in genomes. New integrative models of genome evolution could make a better use of whole genome sequences and thus improve the resolution of the tree of life.

Key concepts

Genomes contain a very large amount of information relevant for reconstructing their history and the history of species.

Among phylogenomic methods, only those based on homologous/orthologous characters can reconstruct a species tree.

Rare genomic changes, supertree and supermatrice methods have been the most extensively used.

Genome‐sized datasets have permitted confirming key phylogenies, and have also provided new insights into important parts of the tree of life.

New methods that combine different types of genomic information could further improve the resolution of the tree of life.
Nonpathogenic Epsilonproteobacteria
Authors: Nakagawa Satoshi , Takaki Yoshihiro
Published: September 2009

The Epsilonproteobacteria is a class within the phylum Proteobacteria and has been primarily recognized as a group of pathogenic microorganisms. However, nonpathogenic Epsilonproteobacteria has been increasingly of great biological importance. They represent bacteria with the highest metabolic versatility. Nonpathogenic Epsilonproteobacteria occurs dominantly in various redoxclines such as deep‐sea vents, stratified ocean, terrestrial sulfidic caves, and oil fields as both epi‐ or endosymbionts and free‐living microorganisms. Recent genome analysis has revealed that some virulence determinants and the genomic plasticity of the pathogenic Epsilonproteobacteria appear to have roots in nonpathogenic, chemoautotrophic Epsilonproteobacteria. These work advantageously for pathogenic Epsilonproteobacteria to be efficiently and persistently infectious and for nonpathogenic Epsilonproteobacteria to thrive in extreme habitats. In the genomic era, previously unrecognized evolutionary links are emerging between important human/animal pathogens and their nonpathogenic, symbiotic, chemoautotrophic relatives.

Key concepts

The Epsilonproteobacteria is the class within the phylum Proteobacteria and represented by important human/animal pathogens.

The perception of the class Epsilonproteobacteria has recently changed dramatically.

The Epsilonproteobacteria comprise numerous nonpathogenic bacteria with diverse ecophysiology and phylogeny.

Nonpathogenic Epsilonproteobacteria play key roles in biogeochemical cycles in various extreme environments on earth.

Nonpathogenic Epsilonproteobacteria provide new insights into the origin of animal/human pathogens.
Fundamentals of Guided Elastic Waves in Solids
Authors: Cesnik Carlos E. S. , Raghavan Ajay
Published: September 2009

Guided‐wave (GW) approaches have shown good promise as structural health monitoring (SHM) algorithms. However, to achieve their full potential, a sound understanding of the fundamentals of GWs in solids is very desirable and that is the objective of this article. After a brief introduction to the field of GW SHM, it starts with the simplest equation of elastic waves, that of one‐dimensional (1D) waves in a taut string. It covers basic concepts of 1D elastic waves to enable an understanding of fundamental concepts and nomenclature relating to wave theory. It then builds on these ideas to derive the 3D elasticity equations of free GWs (Lamb and horizontal shear waves) in isotropic plates. The notion of dispersiveness of GWs is then explained. This is followed by a brief derivation of the GW field excited by finite‐dimensional piezoelectric wafer transducers in isotropic plates based on the authors' earlier work. Subsequently, the equations of bulk waves in transversely isotropic solids are covered and these are used to build the solution for free GWs in multilayered fibrous composite laminates using the global matrix approach. The concept of GW steering in composites is discussed. Finally, more complex research issues in GW SHM are briefly introduced.
Civil Infrastructure Load Models for Structural Health Monitoring
Authors: Peil Udo
Published: September 2009

Load models play an important role in structural health monitoring (SHM). On the one hand, loads and load models are needed for system identification, which is the first step in obtaining a measure of structural health. Different possible loading procedures and their models are discussed in relation to the planned identification outcomes. On the other hand, the characteristics of realistic loads acting on a structure must be known to allow a precise lifetime prediction. In this article, only traffic and wind load models are discussed. Unexpected loads such as earthquakes, blasts, etc., cannot be predicted very accurately; thus, a lifetime assessment is not feasible. A similar situation exists with wind‐induced vibrations, e.g., due to vortex shedding, galloping, flutter, etc. These vibrations are usually always dangerous for a structure and may cause fatigue or other types of damage; thus, wind‐induced vibrations must be prevented rather than predicted.
Data Interrogation Approaches with Strain and Load Gauge Sensor Arrays
Authors: Todd Michael D.
Published: September 2009

This article considers how strain gauges and load gauges are being used as sensors (hardware) in conjunction with feature extraction algorithms (software) in structural health monitoring and damage prognosis applications. A concise review of mature strain gauge and load gauge technologies is presented, followed by a discussion on how the community has implemented data mining with these specific types of sensor arrays to make a system assessment of some kind. Examples from current SHM literature are provided for illustration where appropriate.
Nonlinear Acoustic Methods
Authors: Donskoy Dimitri M.
Published: September 2009

The nonlinear acoustic technique (NAT) developed for detecting and characterizing structural and material defects is an emerging field with unique advantages and challenges. NAT exploits nonlinear dynamic behavior produced by contact interfaces and micro‐ and mesoscopic inhomogeneities associated with structural defects and damages including cracks, disbonds, and delaminations. Nonlinearities across the defects lead to noticeable nonlinear transformations of the interrogating acoustic signals such as harmonic distortions, frequency mixing, modulations, etc. Digital signal processing is used to experimentally capture these transformations unlocking the potential of the NAT to monitor and characterize nonlinear defects and damages in a wide variety of materials and structures.
Guided‐Wave Array Methods
Authors: Wilcox Paul D.
Published: September 2009

Guided waves are an attractive mechanism for detecting localized damage in structural health monitoring (SHM) applications because the damage can be remote from sensor locations. There are various techniques for transmitting and detecting guided waves using monolithic devices, but greater flexibility and superior performance can be achieved using arrays of transducer elements in conjunction with digital signal processing. In this article, the requirements for both deployable and permanently attached guided‐wave arrays are described and the differences between arrays used on one‐dimensional and two‐dimensional waveguides are highlighted. A distinction is made between compact arrays where the elements are in close proximity to one another, often in the same package, and sparse distributed arrays. The mathematical principles that are used to achieve mode separation and directionality with compact arrays are summarized and the practical consequences for array design are reviewed with reference to appropriate examples drawn from the literature. The final section of the article examines the somewhat different requirements of a permanently attached sparse array of sensors. Here the suppression of artifacts from structural features is the key challenge to be overcome for a successful SHM system, and it is shown how this dictates the maximum intersensor spacing that can be used.
Fiber‐Optic Sensor Principles
Authors: Peters Kara
Published: September 2009

This article presents the fundamental principles common to all optical fiber sensors, as well as general issues concerning their application to structural health monitoring systems. More detailed descriptions of specific optical fiber sensors can be found in
Intensity‐, Interferometric‐, and Scattering‐based Optical‐fiber Sensors
and
Fiber Bragg Grating Sensors
. Lightwave propagation through an optical fiber is described with an emphasis on mode propagation constants and energy distributions. The four primary sensing mechanisms exploiting these parameters are presented: intensity, phase, spectrum, and polarization encoding. Common sensor uses for different optical fiber types are presented including single‐mode, multimode, high‐birefringence, and polymer optical fibers. Commonly applied laser sources are also described. Finally, the integration of optical fiber sensors into structural components is discussed including the strength and attenuation properties of the optical fibers themselves. Included are methods for embedment in composite laminates and concrete structures, the strain transfer between the host structure and the embedded sensor, and the integrity of composite structures with embedded optical fiber sensor networks.
Sensor Technologies for Direct Health Monitoring of Tires
Authors: Moffitt Ronald D. , Bland Scott M. , Sunny Mohammad R. , Kapania Rakesh K.
Published: September 2009

Structural health monitoring of tires is increasingly becoming very important and a number of studies have been or are being conducted to develop appropriate means to accomplish this very difficult task. A key to achieving this goal would be the development of appropriate sensors for predicting, and thus ultimately preventing, onset of failure in tires. The failure modes in tires are many and it may require a large number of sensors to detect onset of these failure modes. This article summarizes some of the sensors that are currently available for sensing strain in tires. Specifically, we review noncontacting sensors such as the sidewall torsion sensor, the developments of the Apollo project, a laser‐sensing system, micropower impulse radar, ultrawideband (UWB) radar–based health monitoring, chromasonic sensors based on acoustic emission, acceleration sensing, force/friction sensing, and strain sensing.
Ship and Offshore Structures
Authors: Kim Myung Hyun , Kim Do Hyung
Published: September 2009

Structural health monitoring techniques for ship and offshore structures are summarized in this article. Owing to the increasing accidents associated with bulk carriers and large oil tankers, international regulating committees have recommended the use of hull stress monitoring systems for bulk carriers of 20 000 dwt and above to reduce the risks of structural failure since 1994. In this article, typical hull stress monitoring systems (HMS) and common sensors with monitored parameters are discussed. Long‐based strain gauge (LBSG), accelerometers, and other types of sensors, such as motion sensors and pressure sensors, that are employed in HMS are introduced. Particular requirements for HMS are summarized for each classification societies such as LR (Lloyed Register), ABS (American Bureau of Shipping), DNV (Det Norske Veritas), and IACS (International Association of Classification Societies). Moreover, emerging new technologies applicable for ship and offshore structures are also introduced. The basic principles and the application of fiber‐optic sensors (FOS), acoustic emission sensors (AE), and crack detection sensors (CD) are reviewed in the later part of this chapter. Finally, new requirements and trends in terms of structural health monitoring in marine industries are introduced. In particular, the importance of structural health monitoring technology that is applicable in cryogenic environment is presented.
Noncontact Rail Monitoring by Ultrasonic Guided Waves
Authors: Rizzo Piervincenzo , Coccia Stefano , Bartoli Ivan , di Scalea Francesco Lanza
Published: September 2009

Recent train accidents have reaffirmed the need for developing more effective rail defect detection systems than those used today. One of the recent developments in rail inspection is the use of ultrasonic guided waves and noncontact probing techniques to target transverse‐type defects. Besides the obvious advantages of noncontact probing, which include robustness and potential for large inspection speed, such a system can theoretically detect transverse defects under horizontal shelling or head checks. A rail inspection prototype based on these concepts and funded by the Federal Railroad Administration (FRA) is under development at the University of California at San Diego (UCSD). The first field test was carried out in March 2006. The second field test took place in April 2007. This article first presents the main aspects of ultrasonic guided‐wave inspection of rails, including wave propagation modeling and noncontact ultrasound probing. The discussion then focuses on the UCSD/FRA prototype and its defect detection performance as determined in both laboratory tests and field tests.
Statistical Time Series Methods forSHM
Authors: Fassois Spilios D. , Sakellariou John S.
Published: September 2009

Statistical time series methods for structural health monitoring utilize random excitation and/or vibration response signals, statistical model building, and statistical decision making for inferring the health state of a structure. This includes fault detection, identification (localization), as well as magnitude estimation. The principles and operation of methods that utilize the time or frequency domains on a periodic inspection basis are explained, and the methods are classified into various categories under the general nonparametric and parametric classes. Representative methods from each category are outlined and their use is illustrated on a laboratory structure.
Nonlinear Features forSHMApplications
Authors: Nichols Jonathan M. , Todd Michael D.
Published: September 2009

In structural health monitoring, it is often the case that the dynamics of the structure being monitored are appropriately described by a nonlinear model. The statistical properties of the structural response data are therefore different from those contained in a linear structure's response. Taking these properties into account when computing damage‐sensitive features results in a more powerful approach to assessing damage presence, magnitude, location, and type over methods that rely on linear statistical properties. This article describes a variety of ways in which nonlinearity appears in structural dynamics and reviews a number of strategies for incorporating nonlinearity in the feature‐extraction process.
Dimensionality Reduction Using Linear and Nonlinear Transformation
Authors: Kerschen Gaëtan , Golinval Jean‐Claude
Published: September 2009

With a clear trend toward very large experimental data sets, dimensionality reduction has become an important step of structural health monitoring. The objective of this article is to support that the proper orthogonal decomposition and its nonlinear generalizations are a meaningful addition to the dynamicist's toolbox in this context. The techniques are demonstrated using two application examples, namely, reduced‐order modeling and damage detection under varying environmental conditions.
Damage Detection Using theHilbert–Huang Transform
Authors: Pines Darryll J. , Salvino Liming W.
Published: September 2009

In this article, a new structural health monitoring and damage identification method is presented. The method developed here exploits a new time–frequency signal‐processing analysis tool now commonly referred to as theempirical mode decompositionmethod coupled with the Hilbert–Huang transform. The empirical mode decomposition is a time‐series analysis method that extracts a custom set of basis functions to describe the vibratory response of a system. The ability of the empirical mode decomposition to extract embedded oscillations, to reveal hidden reflections in the data and to provide a high‐resolution energy–time–frequency spectrum is used to characterize guided Lamb wave interactions with various damaged regions. Case studies are used to illustrate the effectiveness of the empirical mode decomposition method and various damage detection metrics to infer damage in one‐ and two‐dimensional structures.
Artificial Neural Networks
Authors: Reed Steve
Published: September 2009

Artificial neural networks (ANNs) are able to learn from experience, generalize from examples, and identify underlying information from within noisy data. These characteristics, and the explosion in ANN techniques over the past 15 or 20 years, have led to an ever‐increasing role for ANNs within structural health monitoring (SHM) systems. Within this article, the development of ANNs and the basic principles behind their functionality, training, and deployment are described. Emphasis is placed upon the multilayer perceptron (MLP), as the workhorse of ANN methods; however, other techniques, including radial basis functions (RBF) and self‐organizing feature maps (SOFMs), are also detailed. Examples of the use of ANNs within SHM systems are presented and reference has been made to a wide range of texts throughout this article.
Data Fusion of Multiple Signals from the Sensor Network
Authors: Su Zhongqing , Wang Xiaoming , Ye Lin
Published: September 2009

Data fusion
is a
multilevel
and
multifaceted
process of combining
multiple
features extracted from a
multitude
of spatially distributed
independent
sources, so as to provide capabilities in automatic detection, classification, and identification. The goal of this article is to introduce the currently prevailing data fusion approaches with the purpose of structural health monitoring (SHM). Emphases are particularly placed on the principle of data fusion, fusion architecture, and major fusion algorithms. Representative case studies for evaluating structural damage by using fusion algorithms including correlation measures (CMs), artificial neural network (ANN), and Bayesian inference (BI) are followed.
Uncertainty Analysis
Authors: Manson Graeme , Worden Keith , Pierce S. Gareth , Denoeux Thierry
Published: September 2009

This article considers the issue of uncertainty analysis in general and also its relevance to structural health monitoring. Brief descriptions of the most popular of the many frameworks for uncertainty representation are given. The three main uncertainty‐related problems of relevance to structural dynamics, namely, quantification, fusion, and propagation, are then discussed. In order to illustrate the preceding ideas in a realistic scenario, two case studies conducted on an aerospace structure, namely the wing of a Gnat trainer aircraft, are provided. The first case study considers the issue of attaining certification for the artificial neural network damage classifiers through the assessment of the network's robustness to uncertainty. This case study involves the propagation of intervals through the network structure and it was found that it is likely that the networks which would be considered as optimal, in the traditional sense, would not be the network that is most robust to uncertainty. The second case study considers evidence‐based classifiers as an alternative to probabilistic classifiers for the problem of damage location. The Dempster–Shafer theory is employed to construct neural network classifiers with the potential to admit ignorance, rather than misclassify. Issues of propagation and fusion in an evidence‐based framework are considered. It was also found that Dempster–Shafer networks give a slight improvement over their probabilistic counterparts.
Constitutive Modeling of Magnetostrictive Materials
Authors: Gopalakrishnan Srinivasan
Published: September 2009

The constitutive model for a magnetostrictive material is presented in this article. An example of a magnetostrictive material is Terfenol‐D. Like the piezoelectric material, this material has two constitutive laws, one of which is the sensing law and the other the actuation law, both of which are highly coupled and nonlinear. For the purpose of analysis, the constitutive laws can be characterized as coupled or uncoupled and linear or nonlinear. The coupled model is studied without assuming any explicit direct relationship with the magnetic field. In the linear‐coupled model, which is assumed to preserve the magnetic flux line continuity, the elastic modulus, the permeability, and magnetoelastic constant are assumed as constant. In the nonlinear‐coupled model, the nonlinearity is decoupled and solved separately for the magnetic domain and the mechanical domain using two nonlinear curves, namely, the stress versus strain curve and the magnetic flux density versus magnetic field curve. This is performed by two different methods. In the first, the magnetic flux density is computed iteratively, while in the second, the artificial neural network is used, wherein the trained network gives the necessary strain and magnetic flux density for a given magnetic field and stress level. The effect of nonlinearity is demonstrated on a simple magnetostrictive rod.
Modeling Aspects in Finite Elements
Authors: Gopalakrishnan Srinivasan
Published: September 2009

This article presents some of the modeling aspects in finite element (FE) analysis for structural health monitoring (SHM) problems. First, the procedure to select a proper FE mesh size for a given frequency content of a predefined input is given. A relationship between the damage sizes and the frequency content of the predefined input signal is then established. Different methods of modeling flaws in finite element method (FEM) and their utility in SHM studies are explained in detail through numerical examples. Limitations of FEM for SHM and their possible remedies are discussed. The article ends with a summary and some useful modeling suggestions.
Development of Fuzzy Rules for Damage Detection and Location
Authors: Ganguli Ranjan
Published: September 2009

Work done in using fuzzy logic for structural damage detection is reviewed. An introduction to fuzzy logic is given and the process of developing rules is illustrated using two examples for damage detection in cantilever beams made of isotropic and composite materials, respectively. It is shown that fuzzy logic provides a practical alternative to neural network and genetic algorithm–based damage detection approaches popular with structural health monitoring researchers. Fuzzy logic–based damage detection algorithms can detect, locate, and identify the size of damage from noisy data. Moreover, the process of rule development in fuzzy systems can be automated via learning algorithms leading to genetic fuzzy systems.
Loads Monitoring in Aerospace Structures
Authors: Reed Steve
Published: September 2009

Loads monitoring can be defined as
a structural usage substantiation activity
. This activity involves the capture, analysis, and reporting of representative, directly measured strain data or derived loads and associated flight parameters from a sample of suitably instrumented in‐service air vehicles within a fleet. The aim of this article is to describe the philosophy behind operational loads monitoring in aerospace structures, within the context of in‐service structural health monitoring.
Loads and Temperature Effects on a Bridge
Authors: Wang Ming L.
Published: September 2009

A number of efforts had been made to instrument bridges for the purpose of structural monitoring and assessment. The outcome of these efforts, as gauged by advances in the understanding of the definition of structural damage and their role in sensor selection as well as in the design of cost and data‐effective monitoring systems, has itself been difficult to assess. The authors experience with the design, calibration, and operation of a monitoring system for the Kishwaukee Bridge in Illinois has provided several lessons that bear upon these concerns. The systems have performed well in providing a continuous, low‐cost monitoring platform for bridge engineers with immediate relevant information. Specifically, load and environmental effects are addressed in detail.
Maintenance Principles for Civil Structures
Authors: Frangopol Dan M. , Messervey Thomas B.
Published: September 2009

This chapter explores the rapidly evolving field related to incorporating information obtained through structural health monitoring (SHM) into the design, maintenance, and management of civil structures. Herein, the employment of monitoring technologies is investigated with respect to the following topics: development of a strategic, top‐down monitoring approach; collecting the most critical information, at the right time, with the right instrument; probabilistic formulation of the analysis; conducting structural assessment; updating with monitoring information; life‐cycle costing; and inclusion of risk. Simple examples are utilized to highlight the issues related to the use of monitoring technologies as a natural part of design and management. In this article, the need for performance‐based design, several examples of monitoring‐based structural assessment, and calculating life‐cycle costs are treated in detail. In the end, the reader should gain an appreciation of recent progress in the rapidly developing field of SHM, some of the considerations for its implementation, and needs for further study.
Usage Management of Military Aircraft Structures
Authors: Neunaber Rolf H.
Published: September 2009

The aircraft structure is designed and certified for an allowable number of flight hours in a specific usage environment. Deviation from the certified usage spectrum has effects on the allowable number of flights. This is owing to the fatigue behavior of the metallic structure, which is highly sensitive to variations in load spectra. Such variations are particularly common in the use of military aircraft, because of frequent changes in configurations and role.

Structural health monitoring (SHM) allows the monitoring of structural degradation. This is not only for flight safety but with an increasing tendency for reasons of material conservation, e.g., the planning of structural inspections and modifications.

This article starts with a more general differentiation of load and condition‐acquisition systems. Furthermore, as an example of load‐acquisition systems, the tracking concept for the German Tornado aircraft is explained; this is built on flight parameter recording followed by the evaluation of the gathered data.

The results generated in this way are interpreted, on one hand, for reasons of material conservation like nonperiodic inspection planning and modification planning and, on the other hand, for the fleet management.

Furthermore, the associated tasks, analytical condition monitoring, and fleet leader inspections, are explained.

Finally, the considerable saving in cost, which can be achieved by the use of SHM, is illustrated using an appropriate example.
Monitoring Marine Structures
Authors: Salvino Liming W. , Collette Matthew D.
Published: September 2009

Technologies and methodologies need to be developed to monitor ship hull and structural integrity as US navy and maritime industry designs increasingly rely on lightweight materials such as composites and aluminum for ship structures to meet future high‐speed/high‐performance goals. Wave loadings at high speeds result in pressure fields that challenge local and global structural integrity to a degree not supported by traditional navy or commercial design approaches. There is little generic experience related to maintaining structural performance of lightweight high‐speed ships. This is especially true as they age. There is a fast growing interest in equipping high‐speed vessels with an operational real‐time structural health monitoring system. Currently, there are several US navy research and development programs that contain the development of ship and hull structural health monitoring systems. Examples of such will be given. Previous and current efforts as well as required technologies for health monitoring of ship structures will be reviewed. The importance and the roles of an effective structural health monitoring system throughout the life cycle of a ship are discussed. The continued advancement of pertinent technologies will ultimately enable a comprehensive structural health monitoring system that includes diagnostic methods and prognostic capabilities to proactively manage future ship hull and structures.
History ofSHMfor Commercial Transport Aircraft
Authors: Ikegami Roy , Boller Christian
Published: September 2009

For the commercial transport aircraft industry, structural health monitoring (SHM) is a relatively new technology, and significant effort is required to define, develop, validate, and certify SHM systems for specific structural applications. Additionally, the systems must be demonstrated to be reliable over an aircraft service life of 30 years with low maintenance costs. This article describes some of the past activities on the part of commercial aircraft original equipment manufacturers (OEMs), the aircraft operators, and SHM equipment suppliers to evaluate, develop, and certify SHM technologies for potential application to new commercial aircraft designs and the aging commercial aircraft fleet currently in service.
Fatigue Monitoring in Military Fixed‐Wing Aircraft
Authors: Buderath Matthias
Published: September 2009

This article elaborates on the principles applied in the development of fatigue and usage monitoring systems for military fixed wing aircraft. Various airframe fatigue life monitoring concepts have been applied to the fatigue management of the Tornado aircraft. Experience gained from such aircraft have lead the way for innovative approaches for preceding aircraft such as the Eurofighter and A400M. In these cases the principles of fatigue and usage monitoring are more or less the same but we can see many of improvements in the information fusion, integration, processing, and information management technologies. This is seen as key to manage structural integrity, aircraft/fleet availability, and the reduction of operation and support costs. We have seen that in particular operational availability cannot be dissociated from the related costs going alone with corrective and scheduled maintenance actions. Significant operation and support reductions can only be achieved at aircraft level having a comprehensive view about aircraft, system, and structural performance. The more the information can be integrated into a maintenance information system, the more operational and cost benefit becomes obvious. The next generation of military aircraft will have hopefully a combined usage‐ and damage monitoring system implemented.