The Chemistry-Process-Structure Relationships of a Functionally Graded Ti-6Al-4V/Ti-1B Alloy Processed with Laser-Engineered Net Shaping Creates Borlite.

We quantify the chemistry-process-structure-property relationships of a Ti-6Al-4V alloy in which titanium-boron alloy (Ti-B) was added in a functionally graded assembly through a laser-engineered net shaping (LENS) process. The material gradient was made by pre-alloyed powder additions to form an in situ melt of the prescribed alloy concentration. The complex heterogeneous structures arising from the LENS thermal history are completely discussed for the first time, and we introduce a new term called "Borlite", a eutectic structure containing orthorhombic titanium monoboride (TiB) and titanium. The ß-titanium grain size decreased nonlinearly until reaching the minimum when the boron weight fraction reached 0.25%. Similarly, the transformed α-titanium grain size decreased nonlinearly until reaching the minimum level, but the grain size was approximately 2 µm when the boron weight fraction reached 0.6%. Alternatively, the α-titanium grain size increased nonlinearly from 1 to 5 µm as a function of the aluminum concentration increasing from 0% to 6% aluminum by weight and vanadium increasing from 0% to 4% by weight. Finally, the cause-effect relationships related to the creation of unwanted porosity were quantified, which helps in further developing additively manufactured metal alloys.

A Multiphysics Thermoelastoviscoplastic Damage Internal State Variable Constitutive Model including Magnetism.

We present a macroscale constitutive model that couples magnetism with thermal, elastic, plastic, and damage effects in an Internal State Variable (ISV) theory. Previous constitutive models did not include an interdependence between the internal magnetic (magnetostriction and magnetic flux) and mechanical fields. Although constitutive models explaining the mechanisms behind mechanical deformations caused by magnetization changes have been presented in the literature, they mainly focus on nanoscale structure-property relations. A fully coupled multiphysics macroscale ISV model presented herein admits lower length scale information from the nanoscale and microscale descriptions of the multiphysics behavior, thus capturing the effects of magnetic field forces with isotropic and anisotropic magnetization terms and moments under thermomechanical deformations. For the first time, this ISV modeling framework internally coheres to the kinematic, thermodynamic, and kinetic relationships of deformation using the evolving ISV histories. For the kinematics, a multiplicative decomposition of deformation gradient is employed including a magnetization term; hence, the Jacobian represents the conservation of mass and conservation of momentum including magnetism. The first and second laws of thermodynamics are used to constrain the appropriate constitutive relations through the Clausius-Duhem inequality. The kinetic framework employs a stress-strain relationship with a flow rule that couples the thermal, mechanical, and magnetic terms. Experimental data from the literature for three different materials (iron, nickel, and cobalt) are used to compare with the model's results showing good correlations.

Mechanical resonances of helically coiled carbon nanowires.

Despite their wide spread applications, the mechanical behavior of helically coiled structures has evaded an accurate understanding at any length scale (nano to macro) mainly due to their geometrical complexity. The advent of helically coiled micro/nanoscale structures in nano-robotics, nano-inductors, and impact protection coatings has necessitated the development of new methodologies for determining their shear and tensile properties. Accordingly, we developed a synergistic protocol which (i) integrates analytical, numerical (i.e., finite element using COMSOL) and experimental (harmonic detection of resonance; HDR) methods to obtain an empirically validated closed form expression for the shear modulus and resonance frequency of a singly clamped helically coiled carbon nanowire (HCNW), and (ii) circumvents the need for solving 12th order differential equations. From the experimental standpoint, a visual detection of resonances (using in situ scanning electron microscopy) combined with HDR revealed intriguing non-planar resonance modes at much lower driving forces relative to those needed for linear carbon nanotube cantilevers. Interestingly, despite the presence of mechanical and geometrical nonlinearities in the HCNW resonance behavior the ratio of the first two transverse modes f2/f1 was found to be similar to the ratio predicted by the Euler-Bernoulli theorem for linear cantilevers.

Functional anatomy of distant-acting mammalian enhancers.

Transcriptional enhancers are a major class of functional element embedded in the vast non-coding portion of the human genome. Acting over large genomic distances, enhancers play critical roles in the tissue and cell type-specific regulation of genes, and there is mounting evidence that they contribute to the aetiology of many human diseases. Methods for genome-wide mapping of enhancer regions are now available, but the functional architecture contained within human enhancer elements remains unclear. Here, we review recent approaches aimed at understanding the functional anatomy of individual enhancer elements, using systematic qualitative and quantitative assessments of mammalian enhancer variants in cultured cells and in vivo. These studies provide direct insight into common architectural characteristics of enhancers including the presence of multiple transcription factor-binding sites and the mixture of both transcriptionally activating and repressing domains within the same enhancer. Despite such progress in understanding the functional composition of enhancers, the inherent complexities of enhancer anatomy continue to limit our ability to predict the impact of sequence changes on in vivo enhancer function. While providing an initial glimpse into the mutability of mammalian enhancers, these observations highlight the continued need for experimental enhancer assessment as genome sequencing becomes routine in the clinic.

Severe neural tube defect syndrome from the Early Archaic of Florida.

The Early Archaic Windover site is on the east coast of mid-peninsular Florida. A subadult skeleton (about 15 years old at time of death) was recovered with multiple pathologies related to spina bifida aperta of the neural arch at the L3-S2 level of the spine. Other evidence indicates s.b. cystica, although the degree of severity of the dysraphic neural tube syndrome cannot be directly determined. In addition to spina bifida, the lumbar region is scoliotic from malformation of zygapophyses. The defect is accompanied by severe infection of the right tibia and fibula, and disuse atrophy of long bones. It is hypothesized the NTD (neural tube defect) led to progressive sensory deprivation, which in turn led to increased loss of mobility, ulceration, and risk of serious infections. Other "minor" anomalies such as cone-shaped epiphyses, enlarged nutrient foramina, and vental vertebral cavitation are also discussed. The chronic nature of these defects provide insight on the high level of long-term care and attention provided a severely handicapped individual 7,500 years ago.

Anatomical, cellular and molecular analysis of 8,000-yr-old human brain tissue from the Windover archaeological site.

Recovery and analysis of ancient tissue and bone of human origin has long been extensively investigated. Only recently, however, has it been technically possible to recover genetic material from ancient human and animal samples. As both previous studies involved dried tissue, it is important to determine whether other conditions may also preserve ancient tissue and genetic material. We describe here an analysis of preserved human bone and soft matter discovered in 1984-85 buried in a small swampy pond in central Florida. The recovered skeletal material represented a minimum of 40 individuals of both sexes and various ages. Corrected radiocarbon dates directly from bone and from peat matrix gave consistent ages in the range of 7,790 to 8,290 yr before present (BP). Nine individuals with intracranial soft matter were recovered and, in five of these, material recognizable as preserved or replaced brain tissue was present. Further analysis demonstrated gross anatomical features, remnant cellular structure and human DNA. As this find appears to be the oldest-known example of preserved human cell structure and DNA, it represents a significant resource for both anthropological and genetic studies.