Diamond like carbon coatings for potential application in biological implants – a review

Production of wear debris has been linked to the failure of numerous hip implants. With the current focus on increasing the implant longevity, thus wear and corrosion resistance is important. Hard coatings have the potential to reduce the wear and corrosion. Diamond like Carbon (DLC) coatings exhibit properties that could make them viable for implants. This paper critically reviews previously published research into usage of DLC coatings for implants. Overall DLCs seem to be an effective coating for implants but with the variance in results, further testing is required for clarification of us

Non-linear Yang-Mills instantons from strings are π\pi-stable D-branes

We show that B-type $\Pi$-stable D-branes do not in general reduce to the (Gieseker-) stable holomorphic vector bundles used in mathematics to construct moduli spaces. We show that solutions of the almost Hermitian Yang--Mills equations for the non-linear deformations of Yang--Mills instantons that appear in the low-energy geometric limit of strings exist iff they are $\pi$-stable, a geometric large volume version of $\Pi$-stability. This shows that $\pi$-stability is the correct physical stability concept. We speculate that this string-canonical choice of stable objects, which is encoded in and derived from the central charge of the string-\emph{algebra}, should find applications to algebraic geometry where there is no canonical choice of stable \emph{geometrical} objects.Comment: v3: Minor revision; 14 page

D-Branes on K3-Fibrations

B-type D-branes are constructed on two different K3-fibrations over IP_1 using boundary conformal field theory at the rational Gepner points of these models. The microscopic CFT charges are compared with the Ramond charges of D-branes wrapped on holomorphic cycles of the corresponding Calabi-Yau manifold. We study in particular D4-branes and bundles localized on the K3 fibers, and find from CFT that each irreducible component of a bundle on K3 gains one modulus upon fibration over IP_1. This is in agreement with expectations and so provides a further test of the boundary CFT.Comment: 16p, harvmac, tables.tex; typos corrected, refs added, discussion about moduli spaces improve

Determinants of food insecurity among smallholder farmer households in Central America: recurrent versus extreme weather-driven events

To ensure food security among rural communities under a changing climate, policymakers need information on the prevalence and determinants of food insecurity, the role of extreme weather events in exacerbating food insecurity,and the strategies that farmers use to cope with food insecurity. Using household surveys in Guatemala and Honduras, we explore the prevalence of food insecurity among smallholder farmers on both a recurrent (seasonal)and episodic (resulting from extreme weather events) basis, analyze the factors associated with both types of food insecurity, and document farmer coping strategies. Of the 439 households surveyed, 56% experienced recurrent foodinsecurity, 36% experienced episodic food insecurity due to extreme weather events, and 24% experienced both types. Food insecurity among smallholder farmers was correlated with sociodemographic factors (e.g., age, education,migration) and asset ownership. The factors affecting food insecurity differed between type and prevalence of food insecurity. Our results highlight the urgent need for policies and programs to help smallholder farmers improve theiroverall food security and resilience to extreme weather shocks. Such policies should focus on enhancing farmer education levels, securing land tenure, empowering women, promoting generational knowledge exchange, and providing emergency food support in the lean season or following extreme weather events

D-Branes on ALE Spaces and the ADE Classification of Conformal Field Theories

The spectrum of D2-branes wrapped on an ALE space of general ADE type is determined, by representing them as boundary states of N=2 superconformal minimal models. The stable quantum states have RR charges which precisely represent the gauge fields of the corresponding Lie algebra. This provides a simple and direct physical link between the ADE classification of N=2 superconformal field theories, and the corresponding root systems. An affine extension of this structure is also considered, whose boundary states represent the D2-branes plus additional D0-branes.Comment: 12p, harvmac, minor corrrections and ref adde

Transgenic and Knockout Mice Models to Reveal the Functions of Tumor Suppressor Genes

Cancer is caused by multiple genetic alterations leading to uncontrolled cell proliferation through multiple pathways. Malignant cells arise from a variety of genetic factors, such as mutations in tumor suppressor genes (TSGs) that are involved in regulating the cell cycle, apoptosis, or cell differentiation, or maintenance of genomic integrity. Tumor suppressor mouse models are the most frequently used animal models in cancer research. The anti-tumorigenic functions of TSGs, and their role in development and differentiation, and inhibition of oncogenes are discussed. In this review, we summarize some of the important transgenic and knockout mouse models for TSGs, including Rb, p53, Ink4a/Arf, Brca1/2, and their related genes

A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy-Ion Physics

In a previous paper, we calculated the fully quantum-mechanical cross section for electromagnetic excitation during peripheral heavy-ion collisions. Here, we examine the sensitivity of that cross section to the detailed structure of the projectile and target nuclei. At the transition energies relevant to nuclear physics, we find the cross section to be weakly dependent on the projectile charge radius, and to be sensitive to only the leading momentum-transfer dependence of the target transition form factors. We exploit these facts to derive a quantum-mechanical ``equivalent-photon spectrum'' valid in the long-wavelength limit. This improved spectrum includes the effects of projectile size, the finite longitudinal momentum transfer required by kinematics, and the response of the target nucleus to the off-shell photon.Comment: 19 pages, 5 figure

Product-Group Unification in Type IIB String Thoery

The product-group unification is a model of unified theories, in which masslessness of the two Higgs doublets and absence of dimension-five proton decay are guaranteed by a symmetry. It is based on SU(5) x U(N) (N=2,3) gauge group. It is known that various features of the model are explained naturally, when it is embedded in a brane world. This article describes an idea of how to accommodate all the particles of the model in Type IIB brane world. The GUT-breaking sector is realized by a D3--D7 system, and chiral quarks and leptons arise from intersection of D7-branes. The D-brane configuration can be a geometric realization of the non-parallel family structure of quarks and leptons, an idea proposed to explain the large mixing angles observed in the neutrino oscillation. The tri-linear interaction of the next-to-minimal supersymmetric standard model is obtained naturally in some cases.Comment: 33 pages, 5 figure