Material Flaw Populations and Component Strength Distributions in the Context of the Weibull Function.

A clear relationship between the population of brittle-fracture controlling flaws generated in a manufactured material and the distribution of strengths in a group of selected components is established. Assumptions regarding the strength-flaw size relationship, the volume of the components, and the number in the group, are clarified and the contracting effects of component volume and truncating effects of group number on component strength empirical distribution functions highlighted. A simple analytical example is used to demonstrate the forward prediction of population → distribution and the more important reverse procedure of empirical strength distribution → underlying flaw population. Three experimental examples are given of the application of the relationships to state-of-the-art micro- and nano-scale strength distributions to experimentally determine flaw populations: two on etched microelectromechanical systems (MEMS) structures and one on native and oxidized silicon nanowires. In all examples, the minimum threshold strength and conjugate maximum flaw size are very well estimated and the complete flaw population, including the minimum flaw size, are very poorly estimated, although etching, bimodal, and oxidation effects were clearly discernible. The results suggest that the best use of strength distribution information for MEMS manufacturers and designers might be in estimation of the strength threshold.

Rapid detection of equine infectious anaemia virus nucleic acid by insulated isothermal RT-PCR assay to aid diagnosis under field conditions.

BACKGROUND: Control of equine infectious anaemia (EIA) currently depends on serological diagnosis of infected equids. However, recently infected equids may not produce detectable anti-EIAV antibodies up to 157 days post infection and so present a high transmission risk. Therefore, direct nucleic acid detection methods are urgently needed to improve EIAV surveillance and management programs in counties where the disease is endemic. OBJECTIVES: To evaluate a field-deployable, reverse transcription-insulated isothermal PCR (RT-iiPCR) assay targeting the conserved 5' untranslated region (5' UTR)/exon 1 of the tat gene of EIAV. STUDY DESIGN: The analytical and clinical performance of the newly developed EIAV RT-iiPCR was evaluated by comparison with a EIAV real-time RT-PCR (RT-qPCR) along with the AGID test. METHODS: Analytical sensitivity was determined using in vitro transcribed RNA containing the target area of the 5' UTR/tat gene and samples from two EIAV-positive horses. Specificity was verified using nine common equine viruses. Clinical performance was evaluated by comparison with EIAV RT-qPCR and AGID using samples derived from 196 inapparent EIAV carrier horses. RESULTS: EIAV RT-iiPCR did not react with other commonly encountered equine viruses and had equivalent sensitivity (95% detection limit of eight genome equivalents), with a concordance of 95.41% to conventional EIAV RT-qPCR. However, the RT-qPCR and RT-iiPCR had sensitivities of 43.75 and 50.00%, respectively, when compared to the AGID test. MAIN LIMITATIONS: Low viral loads commonly encountered in inapparent EIAV carriers may limit the diagnostic sensitivity of RT-PCR-based tests. CONCLUSIONS: Although EIAV RT-iiPCR is not sufficiently sensitive to replace the current AGID test, it can augment control efforts by identifying recently exposed or "serologically silent" equids, particularly as the latter often represent a significant transmission risk because of high viral loads. Furthermore, the relatively low cost and field-deployable design enable utilisation of EIAV RT-iiPCR even in remote regions.

Quantitative Scanning Probe Microscopy for Nanomechanical Forensics.

Atomic force microscopy (AFM) was used to assess the indentation modulus Ms and pull-off force Fpo in four case studies of distinct evidence types, namely hair, questioned documents, fingerprints, and explosive particle-surface interactions. In the hair study, Ms decreased and Fpo increased after adding conditioner and bleach to the hair. For the questioned documents, Ms and Fpo of two inks were markedly different; ballpoint pen ink exhibited smaller variations relative to the mean value than printer ink. The fingerprint case study revealed that both maximum height and Fpo decreased over a three-day period. Finally, the study on explosive particle-surface interactions illustrated that two fabrics exhibited similar Ms, but different Fpo. Overall, it was found that AFM addresses needs in forensic science as defined by several federal agencies, in particular an improved ability to expand the information extracted from evidence and to quantify its evidentiary value.

Deep sequencing and variant analysis of an Italian pathogenic field strain of equine infectious anaemia virus.

Equine infectious anaemia virus (EIAV) is a lentivirus with an almost worldwide distribution that causes persistent infections in equids. Technical limitations have restricted genetic analysis of EIAV field isolates predominantly to gag sequences resulting in very little published information concerning the extent of inter-strain variation in pol, env and the three ancillary open reading frames (ORFs). Here, we describe the use of long-range PCR in conjunction with next-generation sequencing (NGS) for rapid molecular characterization of all viral ORFs and known transcription factor binding motifs within the long terminal repeat of two EIAV isolates from the 2006 Italian outbreak. These isolates were from foals believed to have been exposed to the same source material but with different clinical histories: one died 53 days post-infection (SA) while the other (DE) survived 5 months despite experiencing multiple febrile episodes. Nucleotide sequence identity between the isolates was 99.358% confirming infection with the same EIAV strain with most differences comprising single nucleotide polymorphisms in env and the second exon of rev. Although the synonymous:non-synonymous nucleotide substitution ratio was approximately 2:1 in gag and pol, the situation is reversed in env and ORF3 suggesting these sequences are subjected to host-mediated selective pressure. EIAV proviral quasispecies complexity in vivo has not been extensively investigated; however, analysis suggests it was relatively low in SA at the time of death. These results highlight advantages of NGS for molecular characterization of EIAV namely it avoids potential artefacts generated by traditional composite sequencing strategies and can provide information about viral quasispecies complexity.

In situ spectroscopic study of the plastic deformation of amorphous silicon under non-hydrostatic conditions induced by indentation.

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline ß-tin phase within the a-Si network.

Designing a standard for strain mapping: HR-EBSD analysis of SiGe thin film structures on Si.

Patterned SiGe thin film structures, heteroepitaxially deposited on Si substrates, are investigated as potential reference standards to establish the accuracy of high resolution electron backscattered diffraction (HR-EBSD) strain measurement methods. The proposed standards incorporate thin films of tetragonally distorted epitaxial Si1-xGex adjacent to strain-free Si. Six films of three different nominal compositions (x=0.2, 0.3, and 0.4) and various thicknesses were studied. Film composition and out-of-plane lattice spacing measurements, by x-ray photoelectron spectroscopy and x-ray diffraction, respectively, provided independent determinations of film epitaxy and predictions of tetragonal strain for direct comparison with HR-EBSD strain measurements. Films assessed to be coherent with the substrate exhibited tetragonal strain values measured by HR-EBSD identical to those predicted from the composition and x-ray diffraction measurements, within experimental relative uncertainties of order 2%. Such films thus provide suitable prototypes for designing a strain reference standard.

Dual implantation of a radio-telemeter and vascular access port allows repeated hemodynamic and pharmacological measures in conscious lean and obese rats.

Expansion of physiological knowledge increasingly requires examination of processes in the normal, conscious state. The current study describes a novel approach combining surgical implantation of radio-telemeters with vascular access ports (VAPs) to allow repeated hemodynamic and pharmacological measures in conscious rats. Dual implantation was conducted on 16-week-old male lean and obese Zucker rats. Continued viability one month after surgery was observed in 67% of lean and 44% of obese animals, giving an overall 54% completion rate. Over the five-week measurement period, reliable and reproducible basal mean arterial pressure and heart rate measures were observed. VAP patency and receptor-independent vascular reactivity were confirmed by consistent hemodynamic responses to sodium nitroprusside (6.25 µg/kg). Acutely, minimal hemodynamic responses to repeated bolus administration of 0.2 mL saline indicated no significant effect of increased blood volume or administration stress, making repeated acute measures viable. Similarly, repeated administration of the ß-adrenoceptor agonist dobutamine (30 µg/kg) at 10 min intervals resulted in reproducible hemodynamic changes in both lean and obese animals. Therefore, our study demonstrates that this new approach is viable for the acute and chronic assessment of hemodynamic and pharmacological responses in both lean and obese conscious rats. This technique reduces the demand for animal numbers and allows hemodynamic measures with minimal disruption to animals' welfare, while providing reliable and reproducible results over several weeks. In conclusion, dual implantation of a radio-telemeter and VAP introduces a valuable technique for undertaking comprehensive studies involving repeated pharmacological tests in conscious animals to address important physiological questions.

Equine infectious anemia and equine infectious anemia virus in 2013: a review.

A detailed description of equine infectious anemia virus and host responses to it are presented. Current control and eradication of the infection are discussed with suggestions for improvements to increase their effectiveness.

Development of a precision nanoindentation platform.

The design, construction, and performance of a surface-referenced nanoindentation instrument, termed a precision nanoindentation platform (PNP), are presented. The PNP is a symmetrically designed instrument with a centrally located indenter tip attached to a force cell for measuring the forces between the tip and a specimen. Penetration of the indenter tip into the specimen surface is measured using two proximity sensors placed symmetrically about the indenter. Each proximity sensor is attached to a piezoelectric actuator that is servo controlled to maintain the sensor and the reference frame to which it is attached at a constant height relative to the specimen surface. As the indenter tip penetrates the specimen surface, the movement of the tip relative to the two surface reference frames is measured using capacitance gauges and the average of these displacements is used as a measure of penetration depth. The current indenter is capable of applying indentation forces of up to 150 mN with a noise floor below 2 µN rms for a sampling rate of 1 kHz, and measuring displacement with 0.4 nm rms noise for the same sampling rate. The proximity sensors are capable of maintaining surface height variations of less than 1.0 nm with penetration depths of up to 10 µm. Long-term stability tests indicate a total uncertainty in indentation depth less than 10 nm for periods as long as 12 h. To demonstrate instrument accuracy, repeated indention cycles were performed on a fused silica specimen using incrementally increasing indention force. From this test, an average value of 72 GPa ± 1.5 GPa for the Young's modulus was obtained from the elastic unloading curves for 10 measurements ranging in maximum force from 5 mN to 50 mN. To demonstrate longer-term instrument stability, a poly(methyl methacrylate) specimen was subjected to a fixed 5 mN indentation force for 4 h; two distinct creep-like mechanisms were observed.

Challenges and proposed solutions for more accurate serological diagnosis of equine infectious anaemia.

Serological diagnosis of equine infectious anaemia virus (EIAV) infections has depended mainly on the agar gel immunodiffusion test (AGIDT). This study documents the presence of EIAV genetic sequences in a number of persistently infected horses and mules whose serums were interpreted as negative/equivocal on AGIDT, but positive on more than one ELISA test and in immunoblot tests. Strategies designed to take advantage of the combined strengths of the ELISA and AGIDT are shown effective in a national surveillance program for EIA in Italy where 17 per cent (25/149) of the equids considered to be infected with EIAV on combined/comparative serological data had reactions in the AGIDT that were interpreted as negative or equivocal. These data document the benefits of using a three-tiered laboratory system for the diagnosis of EIA. Although the ELISA-first strategy introduces some confusing results, the discovery of up to 20 per cent more cases of EIA makes it compelling. In our opinion, it is better and more defensible to find two samples in 1000 with resolvable but falsely positive ELISA tests for EIA than to release two to three horses in 10,000 with falsely negative test results for EIA (the rates seen in the Italian surveillance presented here).

Mechanical properties and structure of the biological multilayered material system, Atractosteus spatula scales.

During recent decades, research on biological systems such as abalone shell and fish armor has revealed that these biological systems employ carefully arranged hierarchical multilayered structures to achieve properties of high strength, high ductility and light weight. Knowledge of such structures may enable pathways to design bio-inspired materials for various applications. This study was conducted to investigate the spatial distribution of structure, chemical composition and mechanical properties in mineralized fish scales of the species Atractosteus spatula. Microindentation tests were conducted, and cracking patterns and damage sites in the scales were examined to investigate the underlying protective mechanisms of fish scales under impact and penetration loads. A difference in nanomechanical properties was observed, with a thinner, stiffer and harder outer layer (indentation modulus ∼69 GPa and hardness ∼3.3 GPa) on a more compliant and thicker inner layer (indentation modulus ∼14.3 GPa and hardness ∼0.5 GPa). High-resolution scanning electron microscopy imaging of a fracture surface revealed that the outer layer contained oriented nanorods embedded in a matrix, and that the nanostructure of the inner layer contained fiber-like structures organized in a complex layered pattern. Damage patterns formed during microindentation show complex deformation mechanisms. Images of cracks identify growth through the outer layer, then deflection along the interface before growing and arresting in the inner layer. High-magnification images of the crack tip in the inner layer show void-linking and fiber-bridging exhibiting inelastic behavior. The observed difference in mechanical properties and unique nanostructures of different layers may have contributed to the resistance of fish scales to failure by impact and penetration loading.

Ultimate bending strength of Si nanowires.

Test platforms for the ideal strength of materials are provided by almost defect-free nanostructures (nanowires, nanotubes, nanoparticles, for example). In this work, the ultimate bending strengths of Si nanowires with radii in the 20-60 nm range were investigated by using a new bending protocol. Nanowires simply held by adhesion on flat substrates were bent through sequential atomic force microscopy manipulations. The bending states prior to failure were analyzed in great detail to measure the bending dynamics and the ultimate fracture strength of the investigated nanowires. An increase in the fracture strengths from 12 to 18 GPa was observed as the radius of nanowires was decreased from 60 to 20 nm. The large values of the fracture strength of these nanowires, although comparable with the ideal strength of Si, are explained in terms of the surface morphology of the nanowires.

Detection, molecular characterization and phylogenetic analysis of full-length equine infectious anemia (EIAV) gag genes isolated from Shackleford Banks wild horses.

The genetically distinct wild horse herds inhabiting Shackleford Banks, North Carolina are probably the direct descendents of Spanish stock abandoned after failed attempts to settle mid-Atlantic coastal regions of North America in the Sixteenth Century. In a 1996 island survey, 41% of the gathered horses were discovered seropositive for Equine Infectious Anemia Virus (EIAV) with additional cases identified in 1997 and 1998. As a result of their unique genetic heritage, EIAV seropositive individuals identified in the two latter surveys were transferred to a quarantine facility on the mainland. In September 2008 two of the horses SB1 and SB2 after 10 and 11 years in quarantine respectively, developed clinical signs of EIA. In the case of SB2 these were so severe that the only humane option was euthanasia. Although SB1, survived it experienced a second clinical episode one month later. In May 2009, a third horse in quarantine, SB3, developed extremely severe clinical EIA and was euthanized. This demonstrates naturally infected long-term inapparent carriers can experience recrudescence of very severe disease many years after initial exposure to EIAV. Phylogenetic analysis of complete EIAV gag gene sequences obtained from each of three Shackleford horses demonstrated they were infected with very closely related viruses. Although these were distinguishable from all other strains examined, they belong to a monophyletic group comprising almost exclusively of New World isolates that is distinct from a number of recently characterized Central European EIAV strains.

Indentation device for in situ Raman spectroscopic and optical studies.

Instrumented indentation is a widely used technique to study the mechanical behavior of materials at small length scales. Mechanical tests of bulk materials, microscopic, and spectroscopic studies may be conducted to complement indentation and enable the determination of the kinetics and physics involved in the mechanical deformation of materials at the crystallographic and molecular level, e.g., strain build-up in crystal lattices, phase transformations, and changes in crystallinity or orientation. However, many of these phenomena occurring during indentation can only be observed in their entirety and analyzed in depth under in situ conditions. This paper describes the design, calibration, and operation of an indentation device that is coupled with a Raman microscope to conduct in situ spectroscopic and optical analysis of mechanically deformed regions of Raman-active, transparent bulk material, thin films or fibers under contact loading. The capabilities of the presented device are demonstrated by in situ studies of the indentation-induced phase transformations of Si thin films and modifications of molecular conformations in high density polyethylene films.

High resolution surface morphology measurements using EBSD cross-correlation techniques and AFM.

The surface morphology surrounding wedge indentations in (001) Si has been measured using electron backscattered diffraction (EBSD) and atomic force microscopy (AFM). EBSD measurement of the lattice displacement field relative to a strain-free reference location allowed the surface uplift to be measured by summation of lattice rotations about the indentation axis. AFM was used in intermittent contact mode to determine surface morphology. The height profiles across the indentations for the two techniques agreed within 1 nm. Elastic uplift theory is used to model the data.

Isolation and characterization of ß-haemolytic-Streptococci from endometritis in mares.

The objective of this manuscript was to validate published PCR-based methods for detection of ß-haemolytic Streptococci by comparison with established bacteriological techniques using 85 clinical isolates recovered from uterine swabs of mares with clinical signs of endometritis and to determine the distribution of SeeL/SeeM and SzeL/SzeM superantigens in isolates of Streptococcus equi subsp. equi (S. equi) and S. equi subsp. zooepidemicus (S. zooepidemicus). The conventional bacteriological techniques showed the vast majority of these isolates (78) were S. zooepidemicus with just 5 Streptococcus dysgalactiae subsp. equisimilis (S. equisimilis) and 2 S. equi strains detected. The PCR analyses confirmed the bacteriological results demonstrating the reliability of the 16S rRNA PCR assay for detecting Streptococci, the multiplex PCR for differentiating between S. zooepidemicus, and S. equi, and PCR assays based on streptokinase genes for identification of S. equisimilis. PCRs for genes encoding superantigens revealed seeL and seeM specific amplicons with size of approximately 800 and 810 bp respectively for the S. equi strains and for 2 S. zooepidemicus strains. To our knowledge, this is the first report of szeL and szeM possession by S. zooepidemicus isolates derived from endometritis in mares.

Compressive stress effect on the radial elastic modulus of oxidized Si nanowires.

Detailed understanding and optimal control of the properties of Si nanowires are essential steps in developing Si nanoscale circuitry. In this work, we have investigated mechanical properties of as-grown and oxidized Si nanowires as a function of their diameter. From contact-resonance atomic force microscopy measurements, the effect of the compressive stress at the Si-SiO(2) interface was revealed in the diameter dependence of the elastic modulus of Si nanowires oxidized at 900 and 1000 degrees C. A modified core-shell model that includes the interface stress developed during oxidation captures the diameter dependence observed in the measured elastic moduli of these oxidized Si nanowires. The values of strain and stress as well as the width of the stressed transition region at the Si-SiO(2) interface agree with those reported in simulations and experiments.

Elastic moduli of faceted aluminum nitride nanotubes measured by contact resonance atomic force microscopy.

A new methodology for determining the radial elastic modulus of a one-dimensional nanostructure laid on a substrate has been developed. The methodology consists of the combination of contact resonance atomic force microscopy (AFM) with finite element analysis, and we illustrate it for the case of faceted AlN nanotubes with triangular cross-sections. By making precision measurements of the resonance frequencies of the AFM cantilever-probe first in air and then in contact with the AlN nanotubes, we determine the contact stiffness at different locations on the nanotubes, i.e. on edges, inner surfaces, and outer facets. From the contact stiffness we have extracted the indentation modulus and found that this modulus depends strongly on the apex angle of the nanotube, varying from 250 to 400 GPa for indentation on the edges of the nanotubes investigated.

Contact-resonance atomic force microscopy for nanoscale elastic property measurements: Spectroscopy and imaging.

Quantitative measurements of the elastic modulus of nanosize systems and nanostructured materials are provided with great accuracy and precision by contact-resonance atomic force microscopy (CR-AFM). As an example of measuring the elastic modulus of nanosize entities, we used the CR-AFM technique to measure the out-of-plane indentation modulus of tellurium nanowires. A size-dependence of the indentation modulus was observed for the investigated tellurium nanowires with diameters in the range 20-150nm. Over this diameter range, the elastic modulus of the outer layers of the tellurium nanowires experienced significant enhancement due to a pronounced surface stiffening effect. Quantitative estimations for the elastic moduli of the outer and inner parts of tellurium nanowires of reduced diameter are made with a core-shell structure model. Besides localized elastic modulus measurements, we have also developed a unique CR-AFM imaging capability to map the elastic modulus over a micrometer-scale area. We used this CR-AFM capability to construct indentation modulus maps at the junction between two adjacent facets of a tellurium microcrystal. The clear contrast observed in the elastic moduli of the two facets indicates the different surface crystallography of these facets.