The Influence of Alloying and Fabrication Techniques on the Mechanical Properties, Biodegradability and Biocompatibility of Zinc: A Comprehensive Review

Zinc has been identified as one of the most promising biodegradable metal along with magnesium and iron. Zinc appears to address some of the core engineering problems associated with magnesium and iron when applied to biomedical implant applications; hence the increase in the number of research done on the metal in the last few years. In this review, the current state-of-the-art on biodegradable Zn, including recent developments, current opportunities and future directions of research are discussed. The discussions are presented with a specific focus on reviewing the relationship of mechanical properties, biodegradability, and biocompatibility of zinc with alloying and fabrication techniques. This work hopes to guide future studies on biodegradable Zn that will help in the advancement of the field. STATEMENT OF SIGNIFICANCE: (i) The review offers an up-to-date and comprehensive review of the influence of alloying and fabrication technique on mechanical properties, biodegradability and biocompatibility; (ii) The work cites the most relevant biodegradable Zn fabrication processes including additive manufacturing techniques; (iii) The review includes a listing of research gap and future research directions for the field of biodegradable Zn

First principles calculations for vacancies and antisites in PbSe and PbTe: bulk and nanowire.

The energetic stability and the electronic properties of vacancies (VX) and antisites (XY) in PbSe and PbTe are investigated. PbSe and PbTe are narrow band gap semiconductors and have the potential to be used in infrared detectors, laser, and diodes. They are also of special interest for thermoelectric devices (TE). The calculations are based in the Density Functional Theory (DFT) and the General Gradient Approximation (GGA) for the exchange-correlation term, as implemented in the VASP code. The core and valence electrons are described by the Projected Augmented Wave (PAW) and the Plane Wave (PW) methods, respectively. The defects are studied in the bulk and nanowire (NW) system. Our results show that intrinsec defects (vacancies and antisites) in PbTe have lower formation energies in the NW as compared to the bulk and present a trend in migrate to the surface of the NW. For the PbSe we obtain similar results when compare the formation energy for the bulk and NW. However, the Pb vacancy and the antisites are more stable in the core of the NW. The intrinsec defects are shallow defects for the bulk system. For both PbSe and PbTe VPb is a shallow acceptor defect and VSe and VT e are shallow donor defects for the PbSe and PbTe, respectively. Similar electronic properties are observed for the antisites. For the Pb in the anion site we obtain an n-type semiconductor for both PbSe and PbTe, SeP b is a p-type for the PbSe, and T eP b is a n-type for PbTe. Due the quantum con¯nement effects present in the NW (the band gap open), these defects have different electronic properties for the NW as compared to the bulk. Now these defects give rise to electronic levels in the band gap of the PbTe NW and the VT e present a metallic character. For the PbSe NW a p-type and a n-type semiconductor is obtained for the VP b and P bSe, respectively. On the other hand, deep electronic levels are present in the band gap for the VSe and SePb. These results show that due an enhanced in the electronic density of states (DOS) near the Fermi energy, the defective PbSe and PbTe are candidates for efficient TE devices

Imprisonment and internment: Comparing penal facilities North and South

Recent references to the ‘warehouse prison’ in the United States and the prisión-depósito in Latin America seem to indicate that penal confinement in the western hemisphere has converged on a similar model. However, this article suggests otherwise. It contrasts penal facilities in North America and Latin America in terms of six interrelated aspects: regimentation; surveillance; isolation; supervision; accountability; and formalization. Quantitatively, control in North American penal facilities is assiduous (unceasing, persistent and intrusive), while in Latin America it is perfunctory (sporadic, indifferent and cursory). Qualitatively, North American penal facilities produce imprisonment (which enacts penal intervention through confinement), while in Latin America they produce internment (which enacts penal intervention through release). Closely entwined with this qualitative difference are distinct practices of judicial involvement in sentencing and penal supervision. Those practices, and the cultural and political factors that underpin them, represent an interesting starting point for the explanation of the contrasting nature of imprisonment and internment

Epitaxial growth in dislocation-free strained alloy films: Morphological and compositional instabilities

The mechanisms of stability or instability in the strained alloy film growth are of intense current interest to both theorists and experimentalists. We consider dislocation-free, coherent, growing alloy films which could exhibit a morphological instability without nucleation. We investigate such strained films by developing a nonequilibrium, continuum model and by performing a linear stability analysis. The couplings of film-substrate misfit strain, compositional stress, deposition rate, and growth temperature determine the stability of film morphology as well as the surface spinodal decomposition. We consider some realistic factors of epitaxial growth, in particular the composition dependence of elastic moduli and the coupling between top surface and underlying bulk of the film. The interplay of these factors leads to new stability results. In addition to the stability diagrams both above and below the coherent spinodal temperature, we also calculate the kinetic critical thickness for the onset of instability as well as its scaling behavior with respect to misfit strain and deposition rate. We apply our results to some real growth systems and discuss the implications related to some recent experimental observations.Comment: 26 pages, 13 eps figure

Self-Organized Growth of Alloy Superlattices

We predict theoretically and demonstrate experimentally the spontaneous formation of a superlattice during crystal growth. When a strained alloy grows by "step flow", the steps at the surface form periodic bunches. The resulting modulated strain biases the incorporation of the respective alloy components at different steps in the bunch, leading to the formation of a superlattice. X-ray diffraction and electron microscopy for SiGe grown on Si give clear evidence for such spontaneous superlattice formation

Levels of Trace Metals in the Clam, Polymesoda solida (Philippi, 1846) (Bivalvia: Cyrenidae), from the Strait of Lake

Abstract: This study determined concentrations of arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), selenium (Se), vanadium (V), and zinc (Zn) in the clam Polymesoda solida, collected in nine different sites in the Strait of Lake Maracaibo and Bahía El Tablazo, to assess the spatial distribution of metals, and the safety of clam consumption by humans. Overall average concentrations ± standard deviations in µg/g dw were 8.34 ± 1.51 for As, 0.59 ± 0.28 for Cd, 13.80 ± 6.13 for Cu, 1.22 ± 0.51 for Pb, 2.29 ± 0.62 for Se, 2.59 ± 1.55 for V, and 24.70 ± 4.98 for Zn. No distinct trend in the spatial distribution of metals was observed, and levels in clams were below maximum permissible values for seafood consumption. Positive correlations of V with Pb, and Cd suggest common pollution sources, and their levels were comparable to other bivalve species from contaminated aquatic systems

Intervalley scattering by acoustic phonons in two-dimensional MoS2 revealed by double-resonance Raman spectroscopy

Double-resonance Raman scattering is a sensitive probe to study the electron-phonon scattering pathways in crystals. For semiconducting two-dimensional transition-metal dichalcogenides, the double-resonance Raman process involves different valleys and phonons in the Brillouin zone, and it has not yet been fully understood. Here we present a multiple energy excitation Raman study in conjunction with density functional theory calculations that unveil the double-resonance Raman scattering process in monolayer and bulk MoS2. Results show that the frequency of some Raman features shifts when changing the excitation energy, and first-principle simulations confirm that such bands arise from distinct acoustic phonons, connecting different valley states. The double-resonance Raman process is affected by the indirect-to-direct bandgap transition, and a comparison of results in monolayer and bulk allows the assignment of each Raman feature near the M or K points of the Brillouin zone. Our work highlights the underlying physics of intervalley scattering of electrons by acoustic phonons, which is essential for valley depolarization in MoS2