bluuebunny/crossref_metadata_2025 huggingface dataset:
Apoptosis: Inherited Disorders
Authors: Su Helen C , Lenardo Michael J
Published: September 2009

Apoptosis is a mechanism of programmed cell death used in organ remodelling during development and for eliminating unnecessary or dangerous cells. In the immune system, apoptosis maintains homeostasis by limiting lymphocyte responses. Genetic defects in apoptosis leads to disturbed lymphocyte homeostasis and, potentially, autoimmunity or neoplasia. An important apoptosis disorder in humans involves the death receptor Fas. However, recently, disorders in the apoptosis pathways triggered by trophic factor withdrawal ordeoxyribonucleic acid(DNA) damage have also been described. Dual roles of certain molecules for both apoptotic and normal nonapoptotic lymphocyte function can account for combined apoptosis and immunodeficiency disorders.

Key concepts

Lymphocytes undergo propriocidal regulation, in which the cells that are actively proliferating are most susceptible to programmed cell death. This form of negative regulation limits the maximal intensity of immune responses and establishes the basal state of homeostasis after an immune response.

Apoptosis occurs when T lymphocytes become activated to express death receptors, undergo repeated antigenic stimulation through the T‐cell receptor, or cease to produce growth factors such as IL‐2. Apoptotic pathways stimulated by death receptors, and those stimulated by intracellular derangements, are both utilized.

Mice and humans who have defective apoptosis display progressive accumulation of lymphocytes, systemic autoimmunity and a predisposition to lymphoid malignancy.

Most genetic lesions responsible for the prototypical disease in humans, autoimmune lymphoproliferative syndrome (ALPS), involve the Fas death receptor that mediates extrinsic apoptosis. ALPS can also result from a mutation in NRAS that impairs Bim‐mediated apoptosis during cytokine deprivation.

Humans with caspase‐8 or SH2D1A (SAP) deficiencies have lymphoproliferative disease and immunodeficiency, illustrating the dual roles of these molecules for lymphocyte apoptosis and nonapoptotic lymphocyte function.

p53 mutations responsible for cancer susceptibility in the Li–Fraumeni syndrome impair genotoxic stress‐induced apoptosis, through effects on Puma and other Bcl‐2 family members.
‘Race’,
IQ
and Genes
Authors: Carson Michael , Beckwith Jon
Published: September 2009

Dominant social classes have often used scientific arguments to explain their privileged status. With the development of intelligence quotient (IQ) tests and the founding of the field of genetics, some researchers explained racial differences in behaviours such as IQ test performance as due to genetic differences. Recent discoveries in molecular genetics have provided evidence that human variation at the
deoxyribonucleic acid
(DNA) level is slight; much more variation exists within the members of any single group than between two different population groups. However, as the DNA of populations worldwide has been further characterized, some have assumed that racial differences in intelligence or other social behaviours can be ascribed to those slight interracial genetic differences. Scientists must remain vigilant and expose misrepresentations of scientific data that overemphasize the genetics of group differences and that support genetically deterministic explanations for complex behaviours, such as intelligence.

Key Concepts

Science, through measurements of brain size and IQ test scores, has been misused to support the idea of presumed racial hierarchies in intelligence.

The search for gene variants associated with complex behavioural traits, including intelligence, has been largely unsuccessful.

Environment plays a major role in the manifestation of most genetic traits.

Recent discoveries in molecular genetics have shown that most of the genetic variation that is found among human beings around the world is found in all racial and ethnic groups and only a small amount is found in specific groups.

Using large numbers of genetic variants that differ only slightly in proportion between population groups, researchers can assort individuals into major continental geographic clusters with a high degree of accuracy.

Aside from a small fraction of genes influencing apparent, visible physical features distinguishing people, the distribution of genetic variation does not support a biological basis for the concept of human races.

Preliminary and faulty scientific studies on issues relating to race and intelligence are often rapidly and unjustifiably translated into calls for changes in social policy.

Scientists have a responsibility to help ensure that studies on the genetics of group differences are not misused and misrepresented to support racist theories regarding human behaviours.
Genetic Counselling for Muslim Families of Pakistani and Bangladeshi Origin in Britain
Authors: Shaw Alison
Published: September 2009

An elevated risk of recessive conditions associated with the practice of consanguineous marriage may be relevant for some couples of Pakistani and Bangladeshi Muslim origin, but counsellors need to avoid stigmatizing couples who are consanguineous and should focus instead on establishing risk and strategies for risk management. Patients' prior understandings of illness causality, inheritance and risk; their religious beliefs; their language use and aspects of their family structure may also influence their access to and use of genetic information in important ways. However, these factors are not static markers of ‘ethnic’ or ‘cultural’ difference but are subject to continual negotiation within and between families and their significance varies from case to case. Genetic counsellors need to be aware of the range of ideas that patients may bring to a genetics consultation, without presuming that any particular set of ideas will apply in any given case.

Key concepts

An effective counselling service for British Pakistani and Bangladeshi Muslim families should avoid giving undue negative emphasis to cousin marriages.

Genetic counsellors should be sensitive to the range of understandings of illness causality and inheritance that patients may bring to a genetics consultation.

A patient's gender, status and position in their family can influence their access to and interpretation of genetic risk information.

Genetic counsellors should avoid stereotyping Muslim patients and be sensitive to the range of personal and religious considerations involved in the use of medical technologies in pregnancy.

Access to services would be improved by employing appropriately trained bilingual genetic professionals and interpreters.
Molecular Genetics of Predisposition to Respiratory Disorders in Newborn
Authors: Tulassay Tivadar , Treszl Andras , Vasarhelyi Barna
Published: September 2009

During the perinatal period, preterm neonates face severe complications. These include disorders of the lung such as respiratory distress syndrome and chronic lung disease. The risk of complications depends on maturity, but data also suggest the existence of an inherited susceptibility. This may be due to genetic polymorphisms and inherited mutations. Reported associations between lung disease and polymorphisms of genes encoding proteins that regulate inflammation, vasoregulation and lung development helped the identification of specific genetic elements in perinatal respiratory disorders. In a minority of newborns inherited mutations such as those of surfactant protein encoding gene may be responsible for the development of perinatal lung disorders. Further studies are required to assess those genetic patterns that can be used for the identification of patients at risk.

Key concepts:

Perinatal respiratory disorders affect primarily preterm infants.

These include idiopathic respiratory disorder, bronchopulmonary dysplasia.

Inherited genetic polymorphisms may be a risk factor of these complications.

Genetic polymorphisms with an impact on immune response, vasoregulation and lung development are extensively tested.

Several associations between polymorphisms and disease were reported.

Other data support the contribution of genetics to other perinatal complications that are risk factors for respiratory disorders.

Rare mutations may also cause perinatal lung disorders in some infants.

One day the results of these studies may serve as a basis for individualized therapy and risk assessment; currently we are far from this goal.
History of the Electron Microscope in Cell Biology
Authors: Masters Barry R
Published: September 2009

In the years following World War II there was an explosion in the biological sciences with the rapid emergence of cell biology, molecular biology and biophysics. These events were affected by the development and use of new technologies for cellular fractionation and imaging, specifically the electron microscope, which provided a resolution, that is, unobtainable with light microscopes. Electron microscopes made visible the fine structure of cells and their organelles, the structure of viruses. Now cryo‐electron microscopy is emerging as a key tool to visualize and localize the proteins in an entire cell, the organization of actin filaments in the cytoskeleton, and molecular complexes such as nuclear pores.
Inhibitor of Apoptosis (
IAP
) and
BIR
‐containing Proteins
Authors: Vaux David L
Published: September 2009

The inhibitor of apoptosis (IAP) family of proteins are characterized by presence of one or more baculoviral IAP Repeat (BIR) domains, so they are also termed BIRCs, for ‘BIR‐containing’ proteins. The first IAPs were identified in insect‐attacking viruses, which use them to inhibit defensive apoptosis of the host cell. Subsequently, other BIR‐containing proteins have been found in organisms from yeasts to mammals. The human IAP XIAP can block apoptosis by directly inhibiting caspases, whereas cIAP1 and cIAP2 inhibit apoptosis by reducing caspase‐activating signals from tumour necrosis factor (TNF) receptor superfamily members. As the genes for some IAPs are amplified in cancers, they appear to be able to act as oncogenes. IAP‐antagonist compounds modelled on the IAP antagonist Smac/Diablo are being developed for the treatment of cancer, and are currently undergoing clinical trials.

Key concepts

All IAPs bear at least one BIR domain, but not all BIR‐containing proteins are inhibitors of apoptosis.

XIAP can block apoptosis by directly inhibiting caspases, but cIAP1 and cIAP2 inhibit apoptosis by reducing caspase‐activating signals from TNF receptor superfamily members, and by promoting activation of canonical NFκB pathways rather than noncanonical NFκB pathways.

Genes for some IAPs are amplified in cancers, and IAP‐antagonist compounds modelled on the IAP antagonist Smac/Diablo are being developed for the treatment of cancer.

Survivin and BRUCE are not apoptosis inhibitors, but are needed for cell division.
Autophagy in Nonmammalian Systems
Authors: Hill Jahda H , Baehrecke Eric H
Published: September 2009

Autophagy, or ‘self‐eating’, is a catabolic process that enables lysosome‐mediated degradation of cytoplasmic contents and recycling of macromolecules to be used in essential cellular processes. This process enables cells to survive during nutrient restriction, participates in cell death during development, and functions in clearance of protein aggregates and intracellular pathogens. Autophagy has been widely studied in yeast,

Drosophila

and

Caenorhabditis elegans

, and studies in these organisms have revealed regulation by multiple cellular pathways. These include cell growth regulators, such as the Class I
PI3 kinase
and target of rapamycin (TOR), as well as cell death regulators, including caspases. Defects in autophagy are associated with cancer, neurodegeneration and reduced lifespan. Genetic experiments in

Drosophila

and

C. elegans

have been critical in determining how impairment of autophagy functions in these diseases.

Key concepts

Several yeast screens in the 1990s revealed genes required for autophagy.

Over 30
atg
genes have been shown to regulate autophagy.

Autophagy is induced in response to starvation and oxidative stress, enabling cells to recycle macromolecules and degrade damaged organelles.

Autophagy is required for steroid‐triggered removal of larval tissues during

Drosophila melanogaster

development.

Autophagosomes can sequester intracellular pathogens, which evade the cell's phagocytic machinery, and traffic them to the lysosome for degradation.

Decreased autophagy leads to an inability to clear protein aggregates and mutant polyglutamine containing proteins from neurons in fly and worm neurodegeneration models.

Induction of autophagy in the adult fly brain by transgenic expression of ATG8 can extend lifespan, whereas knock down of

atg7

or

atg8

leads to increased neuronal cell death and reduced lifespan.
History of Cell Biology
Authors: Dröscher Ariane
Published: September 2009

Although egg cells are visible to the naked eye, the history of cell biology is closely coupled to that of microscopy. In nearly 350 years, cell research has produced an extraordinary rich panorama of studies, concepts and representations. Robert Hooke's 1665 analogy to monk cells, the transition from ‘cellular tissue’ to single ‘cells’ around the year 1800, Schleiden and Schwann's identification of the cell as the elementary unit of life, the prominent status it gained during cytology's expansion to the other fields of biomedical inquiry, Schultze's definition as ‘a clump of protoplasm containing a nucleus’, the worlds of endocellular and ultrastructural organization, the ‘compartimentalization’ of the cell in the 1950s and 1960s, its role as map for biochemical and molecular research, all these are just few of the many historical answers to the question ‘what is a cell and what is it good for?’.

Key concepts:

For the beginning of cell biology as a new research field it was not sufficient to be merely able to see cells.

The development of cell biology was coupled with the evolution of optical instruments and of anatomical theory.

One indispensable prerequisite for the formulation of the first cell theory was the shift from the concept of cellular tissue to that of cells as single units.

Cell research underwent ‘golden ages’ whenever cells were considered the basic units of life.

Many outstanding life scientists did not attribute central importance to cells.

The study of cells was (and still is) extraordinarily rich in different ways of seeing, describing, depicting and conceiving.

Though it originated from a specific theory, the history of cell biology is characterized by its growing independence from general theory.

Throughout its history cell biology was characterized by its ability to expand into neighbouring research fields and to integrate their concepts and methods.
Virus‐induced Tumourigenesis
Authors: Duensing Stefan
Published: September 2009

Some of the deadliest and most frequent malignant tumours worldwide are caused by microbes. It has been estimated that viruses contribute to approximately 15–20% of all malignancies in humans. Tumour viruses are not only a global health problem, they have also been instrumental for seminal discoveries in fundamental cancer research and helped to shape the current concepts of multistep tumourigenesis and malignant progression. This article will summarize the basic principles of viral oncogenesis followed by examples of known and emerging human tumour viruses.

Key concepts:

Oncogenic viruses are a major cause of cancer‐related death worldwide.

Oncogenic viruses have evolved to target key regulatory pathways of infected host cells through different mechanisms including insertional mutagenesis, gene piracy and specialized viral proteins, which target host cellular proteins (oncoproteins).

The most common host cell signalling pathways targeted by tumour viruses are the retinoblastoma (pRB) and p53 tumour suppressor pathways.

Tumour viruses frequently subvert host cell control of the cell division cycle, apoptosis, genome integrity and immune recognition.

Human tumour viruses include DNA viruses (HPV, EBV, KSHV and HBV) and RNA viruses (HTLV‐I and HCV).

The most recently discovered emerging human tumour virus is Merkel cell polyomavirus (MCPyV).
Caspases in Inflammation and Immunity
Authors: LeBlanc Philippe M , Saleh Maya
Published: September 2009

Two of the main challenges that eukaryotic multicellular organisms faced during evolution were to cope with invading microorganisms and to eliminate infected cells. The immune system evolved to handle both tasks. Intertwined with immunity is programmed cell death that tailors the immune response and provides an effective way to remove infected cells. Caspases, effectors of inflammation and programmed cell death cascades, are perfectly suited to regulate the host response to invaders and injury. Their activity as inflammatory and killer proteases is regulated by direct binding to sensors of pathogens or danger, they can be modified following activation of signalling cascades by feedback mechanisms to terminate the inflammatory response and control cell survival, and they associate with coactivators and corepressors whose expression is closely linked to the needs of the cell.

Key concepts

Cell death and innate immunity are ancient evolutionarily conserved processes that utilize a number of related effectors and parallel signal transduction mechanisms.

Innate immunity provides first line defences against pathogens and acts as a sentinel that primes adaptive immunity.

Innate immunity depends on evolutionarily conserved germline‐encoded pattern recognition receptors (PRRs) that ‘sense’ pathogen‐associated molecular patterns (PAMPs) and ‘danger’ signals.

The role of caspases in innate immunity is conserved through evolution.

Caspase‐1, the prototypical member of the inflammatory caspase subfamily, contributes to host defence through different interrelated mechanisms, notably cell repair, inflammation and cell death.

Caspase‐1 activity is necessary for host resistance to pathogens; however, when deregulated, it is at the basis of multiple inflammatory diseases.

Inflammatory caspases are activated in NLR‐scaffolded multiprotein complexes termed ‘inflammasomes’ that are reminiscent of the apoptosome. Caspase‐12, an inflammatory caspase related to caspase‐1, is an endogenous inhibitor of the inflammasome.

Apoptosis tailors adaptive immunity. Mutations in
Casp‐8
and
Casp‐10
cause autoimmune lymphoproliferative syndrome (ALPS).

Excessive apoptotic caspase activity contributes to the pathogenesis of inflammatory diseases such as severe sepsis.
Free and Forced Vibration Models
Authors: Haroon Muhammad
Published: September 2009

This article provides an overview of vibrations‐based structural health monitoring (SHM). The framework of vibrations‐based SHM is discussed by using Newton's Law to interpret the various aspects, including data types and classes of techniques available. The process of SHM is illustrated by discussing experimental and numerical examples of loads and damage identification drawn from the literature and the use of this SHM information in the development of empirical damage prognosis models.
Static Damage Phenomena and Models
Authors: Sundararaman Shankar
Published: September 2009

This article provides an overview of static damage phenomena and the physical models utilized to identify damage using measured data. Static damage models provide an understanding of the underlying physics associated with damage, which is usually described in terms of boundary conditions, loading conditions, and material, geometric, electromagnetic, and thermodynamic properties. Examples that apply static damage models to examine changes due to damage in elastic waves in structural materials are discussed. Additionally, as a sample sensitivity analysis study, damage in metallic, orthotropic, and composite plates is modeled as variations in local geometry, stiffness, damping, and mass density using two‐dimensional and three‐dimensional wave propagation models based on the local interaction simulation approach (LISA).
Damage Evolution Phenomena and Models
Authors: Grandt Alten F.
Published: September 2009

The goal of this article is to overview some of the structural health monitoring issues associated with the development and growth of structural damage. A brief summary of various structural failure modes is provided, with particular emphasis on cyclic fatigue. Although fatigue is one of the commonly recognized failure modes, it is problematic for structural health monitoring. The complexity of this mechanism leads to many subtle load history effects that must be recognized and captured to obtain an accurate prognosis of remaining fatigue life. The article concludes with a proposed “witness sample” method that could provide a cost‐effective approach for monitoring structures for evidence of potential fatigue damage.
Applications of Acoustic Emission forSHM: A Review
Authors: Wevers Martine , Lambrighs Kasper
Published: September 2009

This article reviews the application of acoustic emission (AE) for structural health monitoring. The basic principles of AE are explained and a historical background is given. The different types of AE, the wave propagation, the detection, the Kaiser effect and the Felicity ratio, the signal analysis, and the localization and discrimination methods are described in detail. This is followed by a literature review on the most common applications of AE for structural health monitoring. The article concludes with some future prospects of AE.
Ultrasonic Methods
Authors: Hillger Wolfgang
Published: September 2009

Ultrasonic testing (UT) is a well‐established nondestructive technique. It is based on ultrasonic waves in a frequency range usually from 0.5 to 20 MHz. UT provides a quality control, determination of material properties, and a flaw detection with location in all three dimensions. Using echo technique, only a one‐sided access of the test component is necessary. A flaw detector provides instantaneous results. Automated systems deliver images like C‐scans (top view) and B‐scans (view in cross‐section direction) of hidden defects. In this article, the physical principles of UT are explained and the parts of an imaging system are described.
Piezoelectric Impedance Methods for Damage Detection and Sensor Validation
Authors: Park Gyuhae , Farrar Charles R.
Published: September 2009

This article presents an overview and recent applications in impedance‐based structural health monitoring (SHM). The basic principle behind this technique is to apply high‐frequency structural excitations (typically greater than 30 kHz) through surface‐bonded piezoelectric transducers, and measure the local mechanical impedance by monitoring the current and voltage applied to the piezoelectric transducers. Changes in impedance indicate changes in the structure, which in turn can indicate that damage has occurred. Previous experimental studies are summarized to demonstrate how this technique can be efficiently used to detect structural damage in real time. The impedance method also has applications in the field of sensor self‐diagnostics and validation in determining the operational status of piezoelectric active sensors used in SHM. The feasibility of this sensor validation procedure is demonstrated by analytical studies and experimental examples, where the functionality of surface‐mounted piezoelectric sensors was continuously deteriorated.
Thermal Imaging Methods
Authors: Balageas Daniel L.
Published: September 2009

Thermal imaging methods, more particularly infrared (IR) thermography, are commonly used techniques in nondestructive evaluation. They are also beginning to be used in experimental mechanics. They could be very useful for structural health monitoring purposes, although they cannot be totally embedded in the structures. Two main approaches exist for using these techniques as structural health monitoring tools.

The first approach is based on the fact that all mechanical phenomena are accompanied by correlated thermal effects (thermomechanical coupling). These effects can be reversible or irreversible. The reversible thermal phenomena are a link to the strain (and stress) state of structures. Generally, irreversible phenomena are the signature of the occurrence of damage. Mapping the thermal state of a structure is a means to detect abnormalities in the mechanical behavior of the structure.

The second approach comes from classical nondestructive evaluation: damages are detected, localized, and characterized by the disturbances they introduce in the local thermal properties (heat conduction, heat diffusion, heat capacity, effusivity, interface thermal resistance) of the structure.

The physical principles of IR radiometry and the state of the art IR thermography are recalled. The analysis of the thermographic process shows how to perform a quantitative measurement, a requisite for the identification of structural health and the characterization of damages. The different ways to perform structural health monitoring with IR thermography are finally detailed: diagnostic elaboration based on a thermomechanical analysis (strain mapping and fatigue detection), and damage detection and characterization by stimulated thermography.
Eddy‐Current Methods
Authors: Goldfine Neil , Washabaugh Andrew , Sheiretov Yanko , Windoloski Mark
Published: September 2009

In the context of structural health monitoring (SHM), eddy‐current testing (ET) is one of several techniques that the maintainers of high‐value assets can select as part of an asset life management program. In this article, conventional ET and advanced ET methods are described. The focus is on scanning and point‐by‐point ET using handheld or automated systems. This article also describes an advanced ET method called the
MWM‐Array
in detail and associated multivariate inverse methods called
grid methods
. In a companion article on eddy‐current
in situ
sensors, the focus is on surface‐mounted and embedded sensors for SHM, using onboard instrumentation or portable data‐acquisition units.
Full‐Field Sensing: Three‐Dimensional Computer Vision and Digital Image Correlation for Noncontacting Shape and Deformation Measurements
Authors: Sutton Michael A.
Published: September 2009

Computer vision methods using digital image correlation for image matching, with emphasis on stereovision systems for three‐dimensional shape and displacement measurements, are described. Basic theoretical developments and details regarding a recent application of the methodology to quantify deformations in structural components are presented. Results indicate that vision‐based methods can be used successfully to quantify shape and deformation in a wide range of structural and component configurations.
Electric and Electromagnetic Properties Sensing
Authors: Lemistre Michel B.
Published: September 2009

A new family of electromagnetic techniques allowing to obtain information on the health of structures made of composite materials has been developed recently. These techniques, easily transposable in the domain of structural health monitoring (SHM), consist of determining the state of the health of a structure by measuring its two main electric parameters (i.e. the electric conductivity and/or the dielectric permittivity), the main damages inducing locally a significant variation of these two parameters. After a short recall of the elements of electromagnetic theory, necessary to fully understand these techniques, the various methods are explained and examples of application are provided.
Fiber Bragg Grating Sensors
Authors: Peters Kara
Published: September 2009

This article reviews the principles and application of optical fiber Bragg gratings (FBGs) as strain and temperature sensors for structural health monitoring applications. FBG sensors have many advantages for strain sensing in such applications including their small size, the potential to multiplex hundreds of sensors with a single ingress/egress fiber, their immunity to electromagnetic interference, and their corrosion resistance. The spectral properties of FBGs and their response to applied strain and temperature fields are derived. Multiplexing and interrogation strategies for large sensor networks are presented. Special focus is placed on the response of FBGs to multiaxis strain fields and rapidly varying strain fields such as near the location of structural damage. Common approaches to invert the spectral response of an FBG subjected to a complex strain field are also reviewed. Finally, this article reviews common fabrication techniques for FBGs and their relative impacts on the strength of these sensors.
Novel Fiber‐Optic Sensors
Authors: Peters Kara
Published: September 2009

This article reviews novel fiber‐optic sensors for the measurement of strain and temperature that are based on recently developed optical fiber technologies. Sensors based on surface relief gratings and sapphire optical fibers for high‐temperature environments are presented. Additionally, the response of fiber Bragg gratings in extremely low‐temperature environments is discussed. The optical and mechanical response of newly developed single‐mode polymer optical fibers over large‐strain ranges is explained, along with the fabrication of FBGs in such fibers. As compared to conventional silica fibers, single‐mode polymer optical fibers demonstrate increased phase sensitivity to strain and negative phase sensitivity to temperature. Recently fabricated microstructured optical fibers, which demonstrate little or no temperature sensitivity and can incorporate a variety of sensors with novel properties, are also reviewed. Multicore optical fibers, which have been applied for the measurement of local curvatures and networked for the measurement of the shape of flexible structures, are also discussed. Finally, recent examples of the application of microelectromechanical system (MEMS) technology to the fabrication of optical fiber sensors, including focused ion beam machining, are presented.
Intensity‐, Interferometric‐, and Scattering‐Based Optical‐Fiber Sensors
Authors: Peters Kara
Published: September 2009

This article presents the sensing mechanics, strain and temperature sensitivity, and data‐acquisition techniques for optical‐fiber sensors based on intensity, phase shifts, and intrinsic scattering. Such sensors are well suited for health‐monitoring applications. The utilization of standard optical fibers for the measurement of strain through fiber fractures or microbending is described. Afterward, the equation for the phase shift in a lightwave propagating through an optical fiber is derived. The sensitivity of this phase shift to external parameters such as strain and temperature is also derived and typical values for fused silica optical fibers cited. The measurement of this phase shift through Mach–Zehnder and Michelson in‐fiber interferometer configurations is presented. Active and passive homodyne techniques for the interrogation of these periodic phase shift signals to alleviate directional ambiguity and signal fading near quadrature points are described. The alternative interferometer configurations of low‐coherence and Fabry–Perot interferometers are described, which provide absolute measurements of strain and/or temperature for large structural applications. Finally, the measurement of distributed strain and temperatures through intrinsic scattering phenomena with the optical fiber and, in particular, stimulated Brillouin scattering is summarized.
Piezoelectric Wafer Active Sensors
Authors: Yu Lingyu , Giurgiutiu Victor
Published: September 2009

Embedded ultrasonic nondestructive evaluation (NDE) permits active structural health monitoring (SHM), i.e., the on‐demand interrogation of the structure to determine its current state of structural health. The enabling element of embedded ultrasonic NDE is the piezoelectric wafer active sensor (PWAS). We begin with reviewing the PWAS operational principles. Then the mechanism of using PWAS as guided‐wave transmitters and receivers is presented. PWAS interacts with the host structure through the shear‐lag model. Lamb wave mode tuning can be achieved by the judicious combination of PWAS dimensions, frequency value, and Lamb mode characteristics. The use of pitch‐catch, pulse‐echo, and phased‐array ultrasonic methods for Lamb wave SHM is addressed. Next, the use of electromechanical (E/M) impedance method with PWAS is described. The local dynamics of the structure can be identified directly through the E/M impedance spectrum of the PWAS permanently mounted to the structure. Simulation studies using analytical and finite element methods are run to predict the structural responses and verified with experimental results. Finally, novel PWAS developments are briefly addressed, including thein situfabricated PWAS and thin‐film PWAS. The article concludes with a discussion on the current status and the future directions for PWAS transducers.
Directed Energy Sensors/Actuators
Authors: Blackshire James L.
Published: September 2009

Directed energy sensing methods have found increased use as inspection tools over the last several decades. To a large degree, this is due to the abundance of new energy sources and detectors, which span the entire electromagnetic spectrum. In this brief review article, the key underlying principles of directed energy sensing are presented with a special emphasis on recent developments related to material inspections, nondestructive evaluation, and structural health monitoring. For most applications, directed energy approaches are best classified by their wavelength/frequency, which along with incident energy/power levels determines how the directed energy interacts with the material of interest. In keeping with this theme, specific technology examples will be provided for short‐wavelength X ray, midwave visible, long‐wave infrared, and ultra‐long‐wave terahertz/microwave inspection approaches. The interested reader is encouraged to refer to the numerous cited articles and books for additional information and details, which are covered in the article.
Signal Processing for Damage Detection
Authors: Staszewski Wieslaw J. , Worden Keith
Published: September 2009

This article is intended to provide motivation for the study of signal processing methods in the context of Structural health monitoring (SHM). Apart from providing a brief discussion of the main areas of SHM in which signal processing is required in order to make progress, the article provides a roadmap for the signal processing part of the Encyclopedia and guides the reader to the more detailed expositions of the various topics.
Data Preprocessing for Damage Detection
Authors: Halfpenny Andrew
Published: September 2009

An effective structural health monitoring (SHM) system relies on good quality measurement data. All measured data are susceptible to noise or errors, which are introduced at various stages along the signal path. Some errors gradually develop as the system ages, while others are apparent only under certain operating conditions. In this article, we introduce the most common types of measurement errors and discuss methods for detecting and, where possible, removing them to recover the original measured signal.

The article begins with an overview describing stages along the signal path and the types of errors commonly introduced. We describe the most common configuration errors associated with SHM data acquisition and show how errors can be identified, remedied, or avoided through good system design. The term
noise
is used to describe an undesirable component within the signal. The article continues by categorizing the types of noise, identifying the cause of noise, and presenting methods of denoising measured data. We conclude by describing techniques that are particularly suited to the analysis of rotating machinery.
Cepstral Methods of Operational Modal Analysis
Authors: Randall Robert B.
Published: September 2009

The cepstrum is the inverse Fourier transform of the logarithmic spectrum. For SIMO (single input, multiple output) systems, the cepstrum of each output signal is the sum of the cepstra of the forcing function and the system properties. Where the input log spectrum is reasonably smooth and flat (impulsive or broadband random), the input is concentrated in the low part of the cepstrum and the high part can be curve fitted for the system poles and zeros. For minimum‐phase systems, the complex cepstrum can be derived from response autospectra only. The so‐called differential cepstrum has the advantage that it can be calculated from a time signal directly and also that its mathematical formulation allows the poles and zeros to be obtained using methods designed for fitting impulse response functions. For excitation by a series of (say burst random) pulses, the “mean differential cepstrum” gives a more accurate result. For MIMO (multiple input, multiple output) systems, which virtually always apply in practice, two approaches are currently being investigated: blind source separation to separate the response to one of the inputs (thus SIMO) and a matrix decomposition analogous to the mean differential cepstrum. The advantage of the cepstral techniques is the potential for obtaining scaled mode shapes because of obtaining zeros as well as poles.
Wavelet Analysis
Authors: Robertson Amy N. , Basu Biswajit
Published: September 2009

Wavelet analysis, as a time–frequency analysis tool, has shown great promise in recent years. The advantage of the wavelet transform over other time–frequency transforms is in its capabilities of flexible time windowing and computational efficiency. It is evidenced from the reported literature in this article that the wavelet transform has immense potential for application in the area of structural health monitoring (SHM). The theoretical foundations of continuous, discrete wavelet transform (DWT) and orthogonal wavelet transform have been presented. The construction of a multiresolution analysis (MRA)‐based fast algorithm for calculating the DWT and its relation to filtering of signals is discussed. Also presented is the concept of wavelet packets and a brief discussion on the choice of wavelets to suit applications. Examples are presented that show the applications of continuous, discrete, and orthogonal wavelets for the detection of damage by analysis of Lamb wave propagation, and the application of wavelet packets for the identification of stiffness variation in structural systems.
Model‐Based Statistical Signal Processing for Change and Damage Detection
Authors: Basseville Michèle
Published: September 2009

Handling parameterized models for monitoring structures or processes is a natural approach to damage or fault detection and diagnosis. Modeling damages and faults as deviations in the parameter vector with respect to its nominal value in safe conditions calls for the use of statistical change detection and isolation methods. Such methods share the ability of handling noises and uncertainties with other statistical approaches.

The purpose of this article is to describe the key elements in the design of change detection algorithms. Basic concepts (likelihood ratio, estimation, and innovation) are introduced. These tools involve a number of familiar operations (integration, averaging, sensitivity, adaptive thresholds, and windows). It is suggested that a statistical framework enlightens the meaning and increases the power of those operations. Vibration‐based structural health monitoring is addressed within this framework.
Statistical Pattern Recognition
Authors: Sohn Hoon , Oh Chang Kook
Published: September 2009

Structural health monitoring (SHM) problems can often be cast in the context of a statistical pattern recognition paradigm. In this article, a suite of statistical pattern recognition tools applicable to various levels of SHM are introduced. First, multivariate analyses and dimensionality reduction techniques are introduced for effective feature extraction. Here, feature extraction is a step of mining features, which are sensitive to damage of interest, from measured raw signals. Secondly, training data are used to build a statistical model in the inference stage, and the model is used for subsequent decision making for classification and regression problems. If data are available from both undamaged and damaged systems, supervised learning techniques can be used to detect changes in system features extracted from these data that are indicative of damage. If data are only available from the undamaged system, unsupervised learning approaches to subsequent data can be used to identify damage. Finally, ongoing research efforts to address data normalization are presented. Data normalization is a process of separating signal changes caused by operational and environmental variations of the system from those due to structural damage.
Optimization Techniques for Damage Detection
Authors: Worden Keith , Staszewski Wieslaw , Manson Graeme , Ruotulo Aldo , Surace Cecilia
Published: September 2009

This article is concerned with techniques for optimization problems in the context of structural health monitoring. Many techniques are available for solving various classes of problems, including the computationally demanding combinatorial optimization problems which arise in principled approaches to feature selection or sensor optimization. This article briefly describes the classical, gradient‐based approaches that are well represented in the mathematical literature, and then goes on to discuss, in much more detail, the heuristic methods inspired by physics and biology, which have (comparatively) recently proved to be very powerful for combinatorial problems.
Finite Elements: Modeling of Piezoceramic and Magnetostrictive Sensors and Actuators
Authors: Gopalakrishnan Srinivasan
Published: September 2009

In this article, finite element modeling of smart structures with built‐in smart sensors and actuators is presented. Three different smart material sensors/actuators, namely, the piezoelectric (PZT—lead–zirconate–titanate), magnetostrictive (Terfenol‐D), and piezofiber composite material patches used as sensors/actuators, are considered for modeling in this article. The first part of the article briefly describes the constitutive models for these materials (which is dealt extensively in previous articles in this section), which is followed by the finite element formulation of 1‐D and 2‐D finite elements. Also, finite element model for a thin‐walled beam element is presented. Some numerical examples using the formulated element are presented to demonstrate the abilities of the formulated element.
Modeling for Detection of Degraded Zones in Metallic and Composite Structures
Authors: Ostachowicz Wiesław , Krawczuk Marek
Published: September 2009

This paper presents the state of the art of modeling and detection of damages in metallic and composite structures. The continuous, discrete‐continuous, and discrete models available in the literature are described. Also, the influence of damages on vibration behavior of structures is presented, along with possibilities of damage detection based on changes in dynamic characteristics of structures.
Modeling of
L
amb Waves in Composite Structures
Authors: Chakraborty Abir
Published: September 2009

An overview of the modeling aspects of Lamb waves in composite structure is presented. Lamb wave modes are computed using two methods: one by directly solving the two‐dimensional elasticity equation and the second by using various higher order beam theories. The performance of different beam theories is discussed in comparison to the solution of the original equation. Relative merits and demerits of each method are discussed. Along with the mode computation, a procedure is also outlined to obtain the simulation of propagating Lamb wave modes. The method also includes the solution of the governing elastodynamic equation for layered media subjected to arbitrary loading and boundary conditions. Lamb wave modes are provided for unidirectional laminated plies, and the procedure for general ply stacking is outlined.
Operational Loads Sensors
Authors: Ranson William F. , Vachon Reginald I.
Published: September 2009

Load sensors for Structural Health Monitoring (SHM) are discussed. The general theory for the major types of accelerometers and strain gauges are presented. Specific examples of monitoring devices and applications are presented.
Nondestructive Evaluation/Nondestructive Testing/Nondestructive Inspection (NDE/NDT/NDI) Sensors—Eddy Current, Ultrasonic, and Acoustic Emission Sensors
Authors: Blodgett Mark , Lindgren Eric , Sathish Shamachary , Jata Kumar V.
Published: September 2009

Material state characterization is often performed using nondestructive evaluation (NDE) techniques with an objective to either understand or evaluate the microstructural state of the material or indirectly determine the damage that may have occurred in the material during manufacturing or service. Understanding material state is crucial, since material properties define the material's ability to perform its designed function. A number of nondestructive evaluation/nondestructive testing/nondestructive inspection (NDE/NDT/NDI) sensors are available to measure properties of a material. Basic laws of physics dictate the function of the sensor. This article attempts to explain the physics behind eddy current, ultrasonic, and acoustic emission sensors routinely used in NDI of aircraft structures.
Eddy‐Currentin situSensors forSHM
Authors: Goldfine Neil , Zilberstein Vladimir , Schlicker Darrell , Grundy Dave
Published: September 2009

This article describes capabilities of surface‐mounted and embedded eddy‐current sensors for onboard structural health monitoring (SHM), including detection and monitoring of damage as well as monitoring of usage state variables such as stresses and temperatures. The focus is on flexible, model‐based SHM sensors such as MWM‐Arrays, which are placed at selected locations to provide enhanced observability of damage and usage state variables as well as enable diagnostics—specifically to support life management decisions.
Miniaturized Sensors Employing Micro‐ and Nanotechnologies
Authors: Loh Kenneth J. , Lynch Jerome P.
Published: September 2009

Microelectromechanical systems (MEMSs) represent a revolutionary approach to the miniaturization of sensors designed for structural health monitoring (SHM) applications. The characteristic of MEMS sensors is their size, which can be on the order of a few micrometers in scale. Such sensors also enjoy low fabrication costs, low power demands, and high sensitivity. In this article, the application of MEMS sensors, namely, accelerometers, strain sensors, acoustic emission (AE) sensors, corrosion sensors, and wireless interdigital transducers are described. While MEMS has made major inroads into SHM applications, future miniaturization of sensors will be derived from the nanotechnology domain. Nanotechnology and its associated tools offer engineers an unprecedented opportunity to design sensing materials at atomistic length‐scales; the results are multifunctional materials capable of sensing their response to loads.
Design of Active Sensor Network and Multilevel Data Fusion
Authors: Wang Xiaoming , Su Zhongqing
Published: September 2009

Design of a sensing network, and subsequently, the interpretation of data acquired from sensors, are two critical issues in structural health monitoring (SHM). It is understood that the process to identify structural health status is basically an inverse problem, often mathematically ill‐posed. This article has the goal of introducing the active sensor network, a spatially distributed sensing structure, designed to deal with the problem of SHM. Data fusion, especially multilevel data fusion, is then presented to face the challenges in data interpretation, which can be considered as a process to establish a posterior belief about a set of propositions like structural damage events on the basis of a set of prior beliefs that are possessed by sensors. A data fusion process is utilized to increase the robustness and reliability of structural condition identification algorithms by reducing imprecision, uncertainties, and incompleteness. There is a wide range of approaches in data fusion, including the algorithms based on voting scheme, Bayesian theory, Dempster–Schafer rules, fuzzy inference, and artificial neural network.