1,397 research outputs found
GrĂŒneisen parameter of hcpâFe to 171 GPa
We measured the phonon density of states (DOS) of hexagonal close-packed iron (É-Fe) with high statistical quality using nuclear resonant inelastic X-ray scattering and in situ X-ray diffraction experiments between pressures of 30 GPa and 171 GPa and at 300 K, with a neon pressure medium up to 69 GPa. The shape of the phonon DOS remained similar at all compression points, while the maximum (cutoff) energy increased regularly with decreasing volume. As a result, we present a generalized scaling law to describe the volume dependence of É-Fe's total phonon DOS which, in turn, is directly related to the ambient temperature vibrational GrĂŒneisen parameter (Îł_(vib)). Fitting our individual Îł_(vib) data points with Îł_(vib) = Îł_(vib),0(V/V0)^q, a common parameterization, we found an ambient pressure Îł_(vib,0) = 2.0 ± 0.1 for the range q = 0.8 to 1.2. We also determined the Debye sound velocity (v_D) from the low-energy region of the phonon DOS and our in situ measured volumes, and used the volume dependence of v_D to determine the commonly discussed Debye GrĂŒneisen parameter (Îł_D). Comparing our Îł_(vib)(V) and Îł_D(V), we found Îł_(vib) to be âŒ10% larger than Îł_D at any given volume. Finally, applying our Îł_(vib)(V) to a Mie-GrĂŒneisen type relationship and an approximate form of the empirical Lindemann melting criterion, we predict the vibrational thermal pressure and estimate the high-pressure melting behavior of É-Fe at Earth's core pressures
Fibril polymorphism affects immobilized non-amyloid flanking domains of huntingtin exon1 rather than its polyglutamine core
Polyglutamine expansion in the huntingtin protein is the primary genetic cause of Huntington's disease (HD). Fragments coinciding with mutant huntingtin exon1 aggregate in vivo and induce HD-like pathology in mouse models. The resulting aggregates can have different structures that affect their biochemical behaviour and cytotoxic activity. Here we report our studies of the structure and functional characteristics of multiple mutant htt exon1 fibrils by complementary techniques, including infrared and solid-state NMR spectroscopies. Magic-angle-spinning NMR reveals that fibrillar exon1 has a partly mobile α-helix in its aggregation-accelerating N terminus, and semi-rigid polyproline II helices in the proline-rich flanking domain (PRD). The polyglutamine-proximal portions of these domains are immobilized and clustered, limiting access to aggregation-modulating antibodies. The polymorphic fibrils differ in their flanking domains rather than the polyglutamine amyloid structure. They are effective at seeding polyglutamine aggregation and exhibit cytotoxic effects when applied to neuronal cells
The axial ratio of hcp iron at the conditions of the Earth's inner core
We present ab initio calculations of the high-temperature axial c/a ratio of
hexagonal-close-packed (hcp) iron at Earth's core pressures, in order to help
interpret the observed seismic anisotropy of the inner core. The calculations
are based on density functional theory, which is known to predict the
properties of high-pressure iron with good accuracy. The temperature dependence
of c/a is determined by minimising the Helmholtz free energy at fixed volume
and temperature, with thermal contributions due to lattice vibrations
calculated using harmonic theory. Anharmonic corrections to the harmonic
predictions are estimated from calculations of the thermal average stress
obtained from ab initio molecular dynamics simulations of hcp iron at the
conditions of the inner core. We find a very gradual increase of axial ratio
with temperature. This increase is much smaller than found in earlier
calculations, but is in reasonable agreement with recent high-pressure,
high-temperature diffraction measurements. This result casts doubt on an
earlier interpretation of the seismic anisotropy of the inner core
Carbon-fiber tips for scanning probe microscopes and molecular electronics experiments
We fabricate and characterize carbon-fiber tips for their use in combined
scanning tunneling and force microscopy based on piezoelectric quartz tuning
fork force sensors. An electrochemical fabrication procedure to etch the tips
is used to yield reproducible sub-100-nm apex. We also study electron transport
through single-molecule junctions formed by a single octanethiol molecule
bonded by the thiol anchoring group to a gold electrode and linked to a carbon
tip by the methyl group. We observe the presence of conductance plateaus during
the stretching of the molecular bridge, which is the signature of the formation
of a molecular junction.Comment: Conference Proceeding (Trends in NanoTechnology 2011, Tenerife
SPAIN); Nanoscale Research Letters, (2012) 7:25
International primate neuroscience research regulation, public engagement and transparency opportunities
Scientific excellence is a necessity for progress in biomedical research. As research becomes ever more international, establishing international collaborations will be key to advancing our scientific knowledge. Understanding the similarities in standards applied by different nations to animal research, and where the differences might lie, is crucial. Cultural differences and societal values will also contribute to these similarities and differences between countries and continents. Our overview is not comprehensive for all species, but rather focuses on non-human primate (NHP) research, involving New World marmosets and Old World macaques, conducted in countries where NHPs are involved in neuroimaging research. Here, an overview of the ethics and regulations is provided to help assess welfare standards amongst primate research institutions. A comparative examination of these standards was conducted to provide a basis for establishing a common set of standards for animal welfare. These criteria may serve to develop international guidelines, which can be managed by an International Animal Welfare and Use Committee (IAWUC). Internationally, scientists have a moral responsibility to ensure excellent care and welfare of their animals, which in turn, influences the quality of their research. When working with animal models, maintaining a high quality of care (âculture of careâ) and welfare is essential. The transparent promotion of this level of care and welfare, along with the results of the research and its impact, may reduce public concerns associated with animal experiments in neuroscience research
The AFLOW Fleet for Materials Discovery
The traditional paradigm for materials discovery has been recently expanded
to incorporate substantial data driven research. With the intent to accelerate
the development and the deployment of new technologies, the AFLOW Fleet for
computational materials design automates high-throughput first principles
calculations, and provides tools for data verification and dissemination for a
broad community of users. AFLOW incorporates different computational modules to
robustly determine thermodynamic stability, electronic band structures,
vibrational dispersions, thermo-mechanical properties and more. The AFLOW data
repository is publicly accessible online at aflow.org, with more than 1.7
million materials entries and a panoply of queryable computed properties. Tools
to programmatically search and process the data, as well as to perform online
machine learning predictions, are also available.Comment: 14 pages, 8 figure
Potential health impacts of heavy metals on HIV-infected population in USA.
Noninfectious comorbidities such as cardiovascular diseases have become increasingly prevalent and occur earlier in life in persons with HIV infection. Despite the emerging body of literature linking environmental exposures to chronic disease outcomes in the general population, the impacts of environmental exposures have received little attention in HIV-infected population. The aim of this study is to investigate whether individuals living with HIV have elevated prevalence of heavy metals compared to non-HIV infected individuals in United States. We used the National Health and Nutrition Examination Survey (NHANES) 2003-2010 to compare exposures to heavy metals including cadmium, lead, and total mercury in HIV infected and non-HIV infected subjects. In this cross-sectional study, we found that HIV-infected individuals had higher concentrations of all heavy metals than the non-HIV infected group. In a multivariate linear regression model, HIV status was significantly associated with increased blood cadmium (p=0.03) after adjusting for age, sex, race, education, poverty income ratio, and smoking. However, HIV status was not statistically associated with lead or mercury levels after adjusting for the same covariates. Our findings suggest that HIV-infected patients might be significantly more exposed to cadmium compared to non-HIV infected individuals which could contribute to higher prevalence of chronic diseases among HIV-infected subjects. Further research is warranted to identify sources of exposure and to understand more about specific health outcomes
Active Site Mutations Change the Cleavage Specificity of Neprilysin
Neprilysin (NEP), a member of the M13 subgroup of the zinc-dependent endopeptidase family is a membrane bound peptidase capable of cleaving a variety of physiological peptides. We have generated a series of neprilysin variants containing mutations at either one of two active site residues, Phe563 and Ser546. Among the mutants studied in detail we observed changes in their activity towards leucine5-enkephalin, insulin B chain, and amyloid ÎČ1â40. For example, NEPF563I displayed an increase in preference towards cleaving leucine5-enkephalin relative to insulin B chain, while mutant NEPS546E was less discriminating than neprilysin. Mutants NEPF563L and NEPS546E exhibit different cleavage site preferences than neprilysin with insulin B chain and amyloid Ă1â40 as substrates. These data indicate that it is possible to alter the cleavage site specificity of neprilysin opening the way for the development of substrate specific or substrate exclusive forms of the enzyme with enhanced therapeutic potential
BIM Methodology and Tools Implementation for Construction Companies (GreenBIM Project)
Building Information Modelling (BIM) is recognized as one of the leading innovations in the construction sector. However, some studies highlight how BIM implementation is lagging behind in small and medium enterprises (SMEs). Moreover, the majority of the research is focused on the construction phase and there is a need for further studies able to demonstrate the possibilities associated with the introduction of BIM in construction companies. This paper presents the first set of results from the GreenBIM project focused on the development of a BIM implementation framework from SMEs in the construction sector. In this context, the paper focuses on the quantity estimation starting from building information models analyzed by the construction company
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