Shock Deformation in Zircon, a Comparison of Results from Shock-Reverberation and Single-Shock Experiments

The utility of the mineral zircon, ZrSiO4, as a shock-metamorphic geobarometer and geochronometer, has been steadily growing within the planetary science community. Zircon is an accessory phase found in many terrestrial rock types, lunar samples, lunar meteorites, martian meteorites and various other achondrites. Because zircon is refractory and has a high closure temperature for Pb diffusion, it has been used to determine the ages of some of the oldest material on Earth and elsewhere in the Solar System. Furthermore, major (O) and trace-element (REE, Ti, Hf) abundances and isotope compositions of zircon help characterize the petrogenetic environments and sources from which they crystallized. The response of zircon to impact-induced shock deformation is predominantly crystallographic, including dislocation creep and the formation of planar and sub-planar, low-angle grain boundaries; the formation of mechanical {112} twins; transformation to the high pressure polymorph reidite; the development of polycrystalline microtextures; and dissociation to the oxide constituents SiO2 and ZrO2. Shock microstructures can also variably affect the U- Pb isotope systematics of zircon and, in some instances, be used to constrain the impact age. While numerous studies have characterized shock deformation in zircon recovered from a variety of terrestrial impact craters and ejecta deposits and Apollo samples, experimental studies of shock deformation in zircon are limited to a handful of examples in the literature. In addition, the formation conditions (e.g., P, T) of various shock microstructures, such as planar-deformation bands, twins, and reidite lamellae, remain poorly con-strained. Furthermore, previous shocked-zircon experimental charges have not been analyzed using modern analytical equipment. This study will therefore under-take an new set of zircon shock experiments, which will then be microstructurally characterized using state-of-the-art instrumentation within the Astromaterials Research and Exploration Science Division (ARES), NASA Johnson Space Center

Atomic kinetic energy, momentum distribution and structure of solid neon at zero-temperature

We report on the calculation of the ground-state atomic kinetic energy, $E_{k}$, and momentum distribution of solid Ne by means of the diffusion Monte Carlo method and Aziz HFD-B pair potential. This approach is shown to perform notably for this crystal since we obtain very good agreement with respect to experimental thermodynamic data. Additionally, we study the structural properties of solid Ne at densities near the equilibrium by estimating the radial pair-distribution function, Lindemann's ratio and atomic density profile around the positions of the perfect crystalline lattice. Our value for $E_{k}$ at the equilibrium density is $41.51(6)$ K, which agrees perfectly with the recent prediction made by Timms {\it et al.}, $41(2)$ K, based on their deep-inelastic neutron scattering experiments carried out over the temperature range $4 - 20$ K, and also with previous path integral Monte Carlo results obtained with the Lennard-Jones and Aziz HFD-C2 atomic pairwise interactions. The one-body density function of solid Ne is calculated accurately and found to fit perfectly, within statistical uncertainty, to a Gaussian curve. Furthermore, we analyze the degree of anharmonicity of solid Ne by calculating some of its microscopic ground-state properties within traditional harmonic approaches. We provide insightful comparison to solid $^4$He in terms of the Debye model, in order to size the relevance of anharmonic effects in Ne.Comment: 20 pages, 7 figures. To be published in Physical Review

Effects of prenatal exposure to xenobiotic estrogen and the development of endometriosis in adulthood

Abstract only availableEndometriosis is an estrogen-dependent disease that affects millions of women worldwide, causing pain and infertility. While it is known that retrograde menstruation places endometrial tissue in the peritoneal cavity, it is unclear why it invades and proliferates in women with endometriosis. Studies have shown that other hormone-dependent diseases have a fetal basis (e.g. breast cancer), suggesting that the presence of different hormones before birth may alter the incidence of endometriosis in adulthood. For example, women whose mothers took the synthetic estrogen diethylstilbestrol (DES) during pregnancy had an eighty percent increased incidence of endometriosis. Thus, our hypothesis is that prenatal exposure to xenobiotic estrogen will increase the severity of endometriosis in adulthood in a mouse model of surgically-induced endometriosis. To test this hypothesis, mice were time mated and dosed with vehicle control, 100 ng/kg DES or 10,000 ng/kg DES from days 11-17 of gestation. Surgical induction of endometriosis was performed in adulthood by autotransplantation of one uterine horm. The horn was removed, opened, divided into three pieces, and sutured to the arterial cascade of the intestinal mesentery. The implants became vascularized and formed endometriotic lesions. The mice were then collected at 2 or 4 weeks post-surgery, and the following endpoints were measured: 1) uterine weight; 2) implant size; and 3) implant weight. Additionally, implants were set aside for further analysis of 1) histology; 2) estrogen receptor indicator reporter gene activity; and 3) endometriosis-related gene expression. At the conclusion of this ongoing study, we expect to show whether there is an estrogen-mediated fetal component to endometriosis.Life Sciences Undergraduate Research Opportunity Progra

Proteomic profiling of neuromas reveals alterations in protein composition and local protein synthesis in hyper-excitable nerves

Neuropathic pain may arise following peripheral nerve injury though the molecular mechanisms associated with this are unclear. We used proteomic profiling to examine changes in protein expression associated with the formation of hyper-excitable neuromas derived from rodent saphenous nerves. A two-dimensional difference gel electrophoresis ( 2D-DIGE) profiling strategy was employed to examine protein expression changes between developing neuromas and normal nerves in whole tissue lysates. We found around 200 proteins which displayed a > 1.75-fold change in expression between neuroma and normal nerve and identified 55 of these proteins using mass spectrometry. We also used immunoblotting to examine the expression of low-abundance ion channels Nav1.3, Nav1.8 and calcium channel alpha 2 delta-1 subunit in this model, since they have previously been implicated in neuronal hyperexcitability associated with neuropathic pain. Finally, S(35)methionine in vitro labelling of neuroma and control samples was used to demonstrate local protein synthesis of neuron-specific genes. A number of cytoskeletal proteins, enzymes and proteins associated with oxidative stress were up-regulated in neuromas, whilst overall levels of voltage-gated ion channel proteins were unaffected. We conclude that altered mRNA levels reported in the somata of damaged DRG neurons do not necessarily reflect levels of altered proteins in hyper-excitable damaged nerve endings. An altered repertoire of protein expression, local protein synthesis and topological re-arrangements of ion channels may all play important roles in neuroma hyper-excitability

Lath Structured Monazite from Haughton Dome, Canada Reveals Shock-Induced Tetragonal High Pressure Polymorph of REEPO4

Shock deformed monazite, mono-clinic rare earth element (REE) phosphate, from the Haughton Dome impact structure, Nunavut, Canada, contain lath-structured lamellae. Microstructural phase heritage indicate the former presence of a previously unreported, shock-produced, tetragonal-structured, high pressure polymorph of REEPO4. This study presents an electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) study of shock deformed monazite from the historic sample DIG-9, a shock stage III, biotite sillimanite gneiss sample from near the central uplift of the Haughton Dome (7522'20"N, 8940'50"W), in which shock features in monazite were first described

A Genetic Screen Identifies a Critical Role for the WDR81-WDR91 Complex in the Trafficking and Degradation of Tetherin.

Tetherin (BST2/CD317) is a viral restriction factor that anchors enveloped viruses to host cells and limits viral spread. The HIV-1 Vpu accessory protein counteracts tetherin by decreasing its cell surface expression and targeting it for ubiquitin-dependent endolysosomal degradation. Although the Vpu-mediated downregulation of tetherin has been extensively studied, the molecular details are not completely elucidated. We therefore used a forward genetic screen in human haploid KBM7 cells to identify novel genes required for tetherin trafficking. Our screen identified WDR81 as a novel gene required for tetherin trafficking and degradation in both the presence and absence of Vpu. WDR81 is a BEACH-domain containing protein that is also required for the degradation of EGF-stimulated epidermal growth factor receptor (EGFR) and functions in a complex with the WDR91 protein. In the absence of WDR81 the endolysosomal compartment appears swollen, with enlarged early and late endosomes and reduced delivery of endocytosed dextran to cathepsin-active lysosomes. Our data suggest a role for the WDR81-WDR91 complex in the fusion of endolysosomal compartments and the absence of WDR81 leads to impaired receptor trafficking and degradation.This work was supported by the Wellcome Trust, through a Principal Research Fellowship to PJL (084957/Z/08/Z) and Ph.D studentship to RR (079895/Z/06/Z), by MRC research grant MR/M010007/1 to JPL and by a BBSRC industrial CASE studentship with GSK Research and Development Ltd to LJD. The CIMR is in receipt of a Wellcome Trust strategic award 100140.This is the final version of the article. It first appeared from Wiley via https://doi.org/10.1111/tra.1240