937 research outputs found
Spray Ejected from the Lunar Surface by Meteoroid Impact
Fragments ejected from lunar surface by meteoroid impact analyzed on basis of studies of hypervelocity impact in rock and san
Consequences of asteroid fragmentation during impact hazard mitigation
The consequences of the fragmentation of an Earth-threatening asteroid due to an attempted deflection are examined in this paper. The minimum required energy for a successful impulsive deflection of a threatening object is computed and compared to the energy required to break up a small size asteroid. The results show that the fragmentation of an asteroid that underwent an impulsive deflection, such as a kinetic impact or a nuclear explosion, is a very plausible event.Astatistical model is used to approximate the number and size of the fragments as well as the distribution of velocities at the instant after the deflection attempt takes place. This distribution of velocities is a function of the energy provided by the deflection attempt, whereas the number and size of the asteroidal fragments is a function of the size of the largest fragment. The model also takes into account the gravity forces that could lead to a reaggregation of the asteroid after fragmentation. The probability distribution of the pieces after the deflection is then propagated forward in time until the encounter with Earth. A probability damage factor (i.e., expected damage caused by a given size fragment multiplied by its impact probability) is then computed and analyzed for different plausible scenarios, characterized by different levels of deflection energies and lead times
Modular detergents tailor the purification and structural analysis of membrane proteins including G-protein coupled receptors
Detergents enable the purification of membrane proteins and are indispensable reagents instructural biology. Even though a large variety of detergents have been developed in the lastcentury, the challenge remains to identify guidelines that allowfine-tuning of detergents forindividual applications in membrane protein research. Addressing this challenge, here weintroduce the family of oligoglycerol detergents (OGDs). Native mass spectrometry (MS)reveals that the modular OGD architecture offers the ability to control protein purificationand to preserve interactions with native membrane lipids during purification. In addition to abroad range of bacterial membrane proteins, OGDs also enable the purification and analysisof a functional G-protein coupled receptor (GPCR). Moreover, given the modular design ofthese detergents, we anticipatefine-tuning of their properties for specific applications instructural biology. Seen from a broader perspective, this represents a significant advance forthe investigation of membrane proteins and their interactions with lipids
Revisiting stress-corrosion cracking and hydrogen embrittlement in 7xxx-Al alloys at the near-atomic-scale
Atomic scale evolution of the surface chemistry in Li[Ni,Mn,Co]O2 cathode for Li-ion batteries stored in air
Layered LiMO2 (M = Ni, Co, Mn, and Al mixture) cathode materials used for Li-ion batteries are reputed to be highly reactive through their surface, where the chemistry changes rapidly when exposed to ambient air. However, conventional electron/spectroscopy-based techniques or thermogravimetric analysis fails to capture the underlying atom-scale chemistry of vulnerable Li species. To study the evolution of the surface composition at the atomic scale, here we use atom probe tomography and probed the surface species formed during exposure of a LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material to air. The compositional analysis evidences the formation of Li2CO3. Site specific examination from a cracked region of an NMC811 particle also suggests the predominant presence of Li2CO3. These insights will help to design improved protocols for cathode synthesis and cell assembly, as well as critical knowledge for cathode degradatio
UVB radiation induced effects on cells studied by FTIR spectroscopy
We have made a preliminary analysis of the results about the eVects on
tumoral cell line (lymphoid T cell line Jurkat) induced by UVB radiation (dose
of 310 mJ/cm^2) with and without a vegetable mixture. In the present study, we
have used two techniques: Fourier transform infrared spectroscopy (FTIR) and
flow cytometry. FTIR spectroscopy has the potential to provide the
identiWcation of the vibrational modes of some of the major compounds (lipid,
proteins and nucleic acids) without being invasive in the biomaterials. The
second technique has allowed us to perform measurements of cytotoxicity and to
assess the percentage of apoptosis. We already studied the induction of
apoptotic process in the same cell line by UVB radiation; in particular, we
looked for correspondences and correlations between FTIR spetroscopy and flow
cytometry data finding three highly probable spectroscopic markers of apoptosis
(Pozzi et al. in Radiat Res 168:698-705, 2007). In the present work, the
results have shown significant changes in the absorbance and spectral pattern
in the wavenumber protein and nucleic acids regions after the treatments
Crater formation by fast ions: comparison of experiment with Molecular Dynamics simulations
An incident fast ion in the electronic stopping regime produces a track of
excitations which can lead to particle ejection and cratering. Molecular
Dynamics simulations of the evolution of the deposited energy were used to
study the resulting crater morphology as a function of the excitation density
in a cylindrical track for large angle of incidence with respect to the surface
normal. Surprisingly, the overall behavior is shown to be similar to that seen
in the experimental data for crater formation in polymers. However, the
simulations give greater insight into the cratering process. The threshold for
crater formation occurs when the excitation density approaches the cohesive
energy density, and a crater rim is formed at about six times that energy
density. The crater length scales roughly as the square root of the electronic
stopping power, and the crater width and depth seem to saturate for the largest
energy densities considered here. The number of ejected particles, the
sputtering yield, is shown to be much smaller than simple estimates based on
crater size unless the full crater morphology is considered. Therefore, crater
size can not easily be used to estimate the sputtering yield.Comment: LaTeX, 7 pages, 5 EPS figures. For related figures/movies, see:
http://dirac.ms.virginia.edu/~emb3t/craters/craters.html New version uploaded
5/16/01, with minor text changes + new figure
Exploring Views from University Faculty and Cooperating Teachers on General Music Teacher Preparation
The purpose of this exploratory study was to examine perspectives of experienced university faculty and cooperating teachers in general music education. The co-authorsâ four guiding research questions were: (a) What are the ideal components of preservice general music teacher preparation; (b) What do cooperating teachers and university supervisors expect of preservice music teachers; (c) How may preservice general music teacher preparation be improved; and (d) What are the possible roadblocks and solutions for improving preservice music teacher preparation? For this case study, 11 university faculty and 19 cooperating teachers completed a researcher-designed, open-ended survey (N = 30). Using a downward coding process to identify diversity within the data, followed by upward coding to determine synthesis within the data, three themes emerged: enabling conditions, inhibiting conditions, and curriculum reorganization. Research questions (a) and (b) matched with enabling conditions, when present, and inhibiting conditions, when absent. Curricular reorganization responses matched with question (c), while inhibiting conditions and elements of curricular reorganization matched with question (d). The co-authors discuss implications of their findings for music teacher education and make recommendations for further research to extend this exploratory study
NanoglassâNanocrystal Composite - a Novel Material Class for Enhanced Strength-Plasticity Synergy
NanoglassâNanocrystal Composite - a Novel Material Class for Enhanced StrengthâPlasticity Synergy
The properties of a material can be engineered by manipulating its atomic and chemical architecture. Nanoglasses which have been recently invented and comprise nanosized glassy particles separated by amorphous interfaces, have shown promising properties. A potential way to exploit the structural benefits of nanoglasses and of nanocrystalline materials is to optimize the composition to obtain crystals forming within the glassy particles. Here, a metastable Feâ10 at% Sc nanoglass is synthesized. A complex hierarchical microstructure is evidenced experimentally at the atomic scale. This bulk material comprises grains of a FeSc amorphous matrix separated by an amorphous interfacial network enriched and likely stabilized by hydrogen, and propertyâenhancing pureâFe nanocrystals selfâassembled within the matrix. This composite structure leads a yield strength above 2.5 GPa with an exceptional quasiâhomogeneous plastic flow of more than 60% in compression. This work opens new pathways to design materials with even superior properties
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