142 research outputs found
Atomistic origin of stress overshoots and serrations in a CuZr metallic glass
In this work we use molecular dynamics simulations to study the stress
overshoots of metallic glass CuZr in three scenarios
(unloading-reloading, slide-stop-slide, and stress serrations) that are
associated with shear band relaxation. We found that, after the elastic
recovery effect is factored out, atomic volume in the shear band barely changes
during compressive relaxation but decreases during tensile relaxation, while
local fivefold symmetry increases consistently for both cases. We propose that
the atomistic mechanism for the related stress overshoots is due to the
relaxation of structural symmetry, instead of free volume, in the shear band.
Upon unloading, a propagating shear band continues for some time before
arrested, which results in a stress undershoot and could contribute to material
fatigue under cyclic elastic loads. We did not directly observe stress
serrations via molecular dynamics simulations due to the very high simulated
strain rates. While athermal quasistatic simulations produce serrated flow
stress, we note that such serrations result from global avalanches of shear
events rather than the relaxation of the shear band
Zr-Co-Al bulk metallic glass composites containing B2 ZrCo via rapid quenching and annealing
As a promising remedy for overcoming the limited ductility and work softening
of bulk metallic glasses (BMGs), BMG composites incorporating a B2 crystalline
phase have attracted considerable attention. Here, we explore the formation of
Zr-Co-Al BMG composites by quenching alloys ZrCoAl,
ZrCoAl, ZrCoAl,
ZrCoAl, and ZrCoAl. We found the
first alloy fully amorphous whereas the fifth was fully crystallized upon
quenching. The other three were quenched to generate composite structures, with
a higher fraction of B2 ZrCo phase with increasing Co/Zr ratio and decreasing
Al content. For comparison, the formation of B2 ZrCo in annealed
ZrCoAl was also studied. For both approaches the influence
of crystalline phases on hardness was examined
A Search for Li in Stars with Planets
Using very high-resolution (R 125,000) and high quality (S/N
350) spectra, we have searched for Li in stars hosting extra-solar
planets. From detailed profile-fitting of the Li {\sc i} resonance line at
6707.7 \AA, we find no significant amount of Li relative to the Li
for any of 8 planet bearing stars (Li/Li 0.0 - 0.03) with a
strong Li {\sc i} lines. In particular, we do not confirm the presence of
Li with Li/Li = 0.13 reported by Israelian et al.(2001) for
HD 82943, a star with two known planets. Several of the 8 stars plus HD 219542
A, the planet-less primary of a binary, have been identified in the literature
as possible recipients of accreted terrestrial material. For all of the
planet-hosting stars and an additional 5 planet-less stars, we find no
Li.Comment: Accepted for MNRAS, 18 pages (12 figures included
Vu Villa Staircase Structural Repair
The Vu Villa in uptown Butte has a staircase leading to the second floor that is beginning to sag and needs structural support to fix the sag in the stairs
Submission 238 to: Australia's Science and Research Priorities - Conversation Starter
Australia plans to obtain, build, and operate nuclear propelled submarines. The immense challenges brought about by this change in national defence strategy, along with the ambition to create a 20,000 strong nuclear science and engineering capable workforce, must be reflected in the National Science and Research Priorities, and the National Science Statement. We therefore recommend the inclusion of Nuclear Technology as a contemporary National Science and Research Priority, for consideration by the Science Strategy and Priorities Taskforce
The Guinea Pig as a Model for Sporadic Alzheimer\u27s Disease (AD): The Impact of Cholesterol Intake on Expression of AD-Related Genes
We investigated the guinea pig, Cavia porcellus, as a model for Alzheimer’s disease (AD), both in terms of the conservation of genes involved in AD and the regulatory responses of these to a known AD risk factor - high cholesterol intake. Unlike rats and mice, guinea pigs possess an Ab peptide sequence identical to human Ab. Consistent with the commonality between cardiovascular and AD risk factors in humans, we saw that a high cholesterol diet leads to up-regulation of BACE1 (b-secretase) transcription and down-regulation of ADAM10 (a-secretase) transcription which should increase release of Ab from APP. Significantly, guinea pigs possess isoforms of AD-related genes found in humans but not present in mice or rats. For example, we discovered that the truncated PS2V isoform of human PSEN2, that is found at raised levels in AD brains and that increases c-secretase activity and Ab synthesis, is not uniquely human or aberrant as previously believed. We show that PS2V formation is up-regulated by hypoxia and a high-cholesterol diet while, consistent with observations in humans, Ab concentrations are raised in some brain regions but not others. Also like humans, but unlike mice, the guinea pig gene encoding tau, MAPT, encodes isoforms with both three and four microtubule binding domains, and cholesterol alters the ratio of these isoforms. We conclude that AD-related genes are highly conserved and more similar to human than the rat or mouse. Guinea pigs represent a superior rodent model for analysis of the impact of dietary factors such as cholesterol on the regulation of AD-related genes
Lithium in the Intermediate-Age Open Cluster, NGC 3680
High-dispersion spectra centered on the Li 6708 A line have been obtained for
70 potential members of the open cluster NGC 3680, with an emphasis on stars in
the turnoff region. A measurable Li abundance has been derived for 53 stars, 39
of which have radial velocities and proper motions consistent with cluster
membership. After being transferred to common temperature and abundance scales,
previous Li estimates have been combined to generate a sample of 49 members, 40
of which bracket the cluster Li-dip. Spectroscopic elemental analysis of 8
giants and 5 turnoff stars produces [Fe/H] = -0.17 +/- 0.07 (sd) and -0.07 +/-
0.02 (sd), respectively. We also report measurements of Ca, Si and Ni which are
consistent with scaled-solar ratios within the errors. Adopting [Fe/H] = -0.08
(Sect. 3.6), Y^2 isochrone comparisons lead to an age of 1.75 +/- 0.10 Gyr and
an apparent modulus of (m-M) = 10.30 +/- 0.15 for the cluster, placing the
center of the Li-dip at 1.35 +/- 0.03 solar masses. Among the giants, 5 of 9
cluster members are now known to have measurable Li with A(Li) near 1.0. A
combined sample of dwarfs in the Hyades and Praesepe is used to delineate the
Li-dip profile at 0.7 Gyr and [Fe/H] = +0.15, establishing its center at 1.42
+/- 0.02 solar masses and noting the possible existence of secondary dip on its
red boundary. When evolved to the typical age of the clusters NGC 752, IC 4651
and NGC 3680, the Hyades/Praesepe Li-dip profile reproduces the observed
morphology of the combined Li-dip within the CMD's of the intermediate-age
clusters while implying a metallicity dependence for the central mass of the
Li-dip given by Mass = (1.38 +/-0.04) + (0.4 +/- 0.2)[Fe/H]. The implications
of the similarity of the Li-dichotomy among giants in NGC 752 and IC 4651 and
the disagreement with the pattern among NGC 3680 giants are discussed.Comment: Latex ms. is 56 pages, including 10 figures and 4 tables. Accepted
for the Astronomical Journa
A Polygenic Risk Score Derived From Episodic Memory Weighted Genetic Variants Is Associated With Cognitive Decline in Preclinical Alzheimer's Disease
Studies of Alzheimer's disease risk-weighted polygenic risk scores (PRSs) for cognitive performance have reported inconsistent associations. This inconsistency is particularly evident when PRSs are assessed independent of APOE genotype. As such, the development and assessment of phenotype-specific weightings to derive PRSs for cognitive decline in preclinical AD is warranted. To this end a episodic memory-weighted PRS (emPRS) was derived and assessed against decline in cognitive performance in 226 healthy cognitively normal older adults with high brain Aβ-amyloid burden participants from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study. The effect size for decline in a verbal episodic memory was determined individually for 27 genetic variants in a reference sample (n = 151). These were then summed to generate a emPRS either including APOE (emPRSc̅APOE) or excluding APOE (emPRSs̅APOE ). Resultant emPRS were then evaluated, in a test sample (n = 75), against decline in global cognition, verbal episodic memory and a pre-Alzheimer's cognitive composite (AIBL-PACC) over 7.5 years. The mean (SD) age of the 226 participants was 72.2 (6.6) years and 116 (51.3%) were female. Reference and test samples did not differ significantly demographically. Whilst no association of emPRSs were observed with baseline cognition, the emPRSc̅ APOE was associated with longitudinal global cognition (-0.237, P = 0.0002), verbal episodic memory (-0.259, P = 0.00003) and the AIBL-PACC (-0.381, P = 0.02). The emPRSs̅ APOE was also associated with global cognition (-0.169, P = 0.021) and verbal episodic memory (-0.208, P = 0.004). Stratification by APOE ε4 revealed that the association between the emPRS and verbal episodic memory was limited to carriage of no ε4 or one ε4 allele. This was also observed for global cognition. The emPRS and rates of decline in AIBL-PACC were associated in those carrying one ε4 allele. Overall, the described novel emPRS has utility for the prediction of decline in cognition in preclinical AD. This study provides evidence to support the further use and evaluation of phenotype weightings in PRS development
- …