The PASCAL Visual Object Classes Challenge

This paper reviews the past, present, and future of the hydroxyapatite (HAp)-based biomaterials from the point of view of preparation of hard tissue replacement implants. Properties of the hard tissues are also described. The mechanical reliability of the pure HAp ceramics is low, therefore it cannot be used as artificial teeth or bones. For these reasons, various HAp-based composites have been fabricated, but only the HAp-coated titanium alloys have found wide application. Among the others, the microstructurally controlled HAp ceramics such as fibers/whiskers-reinforced HAp, fibrous HAp-reinforced polymers, or biomimetically fabricated HAp/collagen composites seem to be the most suitable ceramic materials for the future hard tissue replacement implants.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400042527

Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants

Mathematical Handbook for Scientists and Engineers

Bone substitutes are being increasingly used in surgery as over two millions bone grafting procedures are performed worldwide per year. Autografts still represent the gold standard for bone substitution, though the morbidity and the inherent limited availability are the main limitations. Allografts, i.e. banked bone, are osteoconductive and weakly osteoinductive, though there are still concerns about the residual infective risks, costs and donor availability issues. As an alternative, xenograft substitutes are cheap, but their use provided contrasting results, so far. Ceramic-based synthetic bone substitutes are alternatively based on hydroxyapatite (HA) and tricalcium phosphates, and are widely used in the clinical practice. Indeed, despite being completely resorbable and weaker than cortical bone, they have exhaustively proved to be effective. Biomimetic HAs are the evolution of traditional HA and contains ions (carbonates, Si, Sr, Fl, Mg) that mimic natural HA (biomimetic HA). Injectable cements represent another evolution, enabling mininvasive techniques. Bone morphogenetic proteins (namely BMP2 and 7) are the only bone inducing growth factors approved for human use in spine surgery and for the treatment of tibial nonunion. Demineralized bone matrix and platelet rich plasma did not prove to be effective and their use as bone substitutes remains controversial. Experimental cell-based approaches are considered the best suitable emerging strategies in several regenerative medicine application, including bone regeneration. In some cases, cells have been used as bioactive vehicles delivering osteoinductive genes locally to achieve bone regeneration. In particular, mesenchymal stem cells have been widely exploited for this purpose, being multipotent cells capable of efficient osteogenic potential. Here we intend to review and update the alternative available techniques used for bone fusion, along with some hints on the advancements achieved through the experimental research in this field.

/pdf/bone-substitutes-in-orthopaedic-surgery-from-basic-science-1n4hkut079.pdf

Bone substitutes in orthopaedic surgery: from basic science to clinical practice

Mother-of-pearl, also known as nacre, is the iridescent material which forms the inner layer of seashells from gastropods and bivalves. It is mostly made of microscopic ceramic tablets densely packed and bonded together by a thin layer of biopolymer. The hierarchical microstructure of this biological material is the result of millions of years of evolution, and it is so well organized that its strength and toughness are far superior to the ceramic it is made of. In this work the structure of nacre is described over several length scales. The tablets were found to have wavy surfaces, which were observed and quantified using various experimental techniques. Tensile and shear tests performed on small samples revealed that nacre can withstand relatively large inelastic strains and exhibits strain hardening. In this article we argue that the inelastic mechanism responsible for this behavior is sliding of the tablets on one another accompanied by transverse expansion in the direction perpendicular to the tablet planes. Three dimensional representative volume elements, based on the identified nacre microstructure and incorporating cohesive elements with a constitutive response consistent with the interface material and nanoscale features were numerically analyzed. The simulations revealed that even in the absence of nanoscale hardening mechanism at the interfaces, the microscale waviness of the tablets could generate strain hardening, thereby spreading the inelastic deformation and suppressing damage localization leading to material instability. The formation of large regions of inelastic deformations around cracks and defects in nacre are believed to be an important contribution to its toughness. In addition, it was shown that the tablet junctions (vertical junctions between tablets) strengthen the microstructure but do not contribute to the overall material hardening. Statistical variations within the microstructure were found to be beneficial to hardening and to the overall mechanical stability of nacre. These results provide new insights into the microstructural features that make nacre tough and damage tolerant. Based on these findings, some design guidelines for composites mimicking nacre are proposed.

http://barthelat-lab.mcgill.ca/files/papers/nacreJMPS2006.pdf

On the mechanics of mother-of-pearl: a key feature in the material hierarchical structure

Synthesis of nanophase hydroxyapatite/collagen composite

The deformation, fracture and toughening mechanisms of nacre from a kind of fresh-water bivalve mollusc (Cristaria plicata) were studied by SEM, TEM and microindentation tests. Experimental results revealed a strong anisotropy of the damage behaviour reflecting the microstructural character of nacre. The fractured surface parallel to the cross-sectional surface of nacre was much more tortuous than that parallel to the platelet surface. The crack line on the cross-sectional surface was step-like, while that on the platelet surface was polygonal. Sliding of aragonite layer combined with the plastic deformation of organic matrix is the main plastic deformation mechanism of nacre. Three main toughening mechanisms have been found acting in concert: crack deflection, fibre pull-out and organic matrix bridging.

Observations of damage morphologies in nacre during deformation and fracture

Harmonic estimation is an important topic in power system signal processing. Windowed interpolation fast Fourier transformation (WIFFT) is an efficient algorithm for power system harmonic estimation, which can eliminate the errors caused by spectral leakage and picket fence effect. However, the fitting polynomial in the interpolation procedure contains both even and odd terms, and this increases the computational burden. This paper proposes a simple symmetrical interpolation FFT algorithm, where the even terms are removed from the fitting polynomial based on the triangular self-convolution windows (TSCW). The polynomials for frequency and amplitude computations are provided. Considerable leakage errors and harmonic interferences can be suppressed by the TSCW. Accurate estimations of harmonic parameters can be obtained via the fitting polynomial and the TSCW, both with adjustable order to fulfill different accuracy and speed requirements of practical power harmonic measurement. Simulation results and measurements have validated the proposed method.

Harmonic Estimation Using Symmetrical Interpolation FFT Based on Triangular Self-Convolution Window

Correct identification of the origins of herbal medical products is becoming increasingly important in tandem with the growing interest in alternative medicine. However, visual inspection of raw material is still the most widely used method, and newer scientific approaches are needed. To develop a more objective and efficient tool for discriminating herbal origins, particularly Korean and Chinese, we employed a nuclear magnetic resonance (NMR)-based metabolomics approach combined with an orthogonal projections to latent structure-discriminant analysis (OPLS-DA) multivariate analysis. We first analyzed the constituent metabolites of Scutellaria baicalensis through NMR studies. Subsequent holistic data analysis with OPLS-DA yielded a statistical model that could cleanly discriminate between the sample groups even in the presence of large structured noise. An analysis of the statistical total correlation spectroscopy (STOCSY) spectrum identified citric acid and arginine as the key discriminating metabolites for Korean and Chinese samples. As a validation of the discrimination model, we performed blind prediction tests of sample origins using an external test set. Our model correctly predicted the origins of all of the 11 test samples, demonstrating its robustness. We tested the wider applicability of the developed method with three additional herbal medicines from Korea and China and obtained very high prediction accuracy. The solid discriminatory power and statistical validity of our method suggest its general applicability for determining the origins of herbal medicines.

Application of a 1H nuclear magnetic resonance (NMR) metabolomics approach combined with orthogonal projections to latent structure-discriminant analysis as an efficient tool for discriminating between Korean and Chinese herbal medicines.

There is an ongoing debate about the fundamental security of existing quantum key exchange schemes. This debate indicates not only that there is a problem with security but also that the meanings of perfect, imperfect, conditional and unconditional (information theoretic) security in physically secure key exchange schemes are often misunderstood. It has been shown recently that the use of two pairs of resistors with enhanced Johnson-noise and a Kirchhoff-loop - i.e., a Kirchhoff-Law-Johnson-Noise (KLJN) protocol - for secure key distribution leads to information theoretic security levels superior to those of today's quantum key distribution. This issue is becoming particularly timely because of the recent full cracks of practical quantum communicators, as shown in numerous peer-reviewed publications. The KLJN system is briefly surveyed here with discussions about the essential questions such as (i) perfect and imperfect security characteristics of the key distribution, and (ii) how these two types of securities can be unconditional (or information theoretical).

/pdf/unconditional-security-by-the-laws-of-classical-physics-2ys9i022k7.pdf

He Wen

Papers

Synthesis of nanophase hydroxyapatite/collagen composite

Observations of damage morphologies in nacre during deformation and fracture

Harmonic Estimation Using Symmetrical Interpolation FFT Based on Triangular Self-Convolution Window

Application of a 1H nuclear magnetic resonance (NMR) metabolomics approach combined with orthogonal projections to latent structure-discriminant analysis as an efficient tool for discriminating between Korean and Chinese herbal medicines.

Unconditional Security by the Laws of Classical Physics