13,783 research outputs found
The stress-corrosion behavior of Al-Li-Cu alloys: A comparison of test methods
Two powder metallurgy processed (Al-Li-Cu) alloys with and without Mg addition were studied in aqueous 3.5% NaCl solution during the alternate immersion testing of tuning fork specimens, slow crack growth tests using fracture mechanics specimens, and the slow strain rate testing of straining electrode specimens. Scanning electron microscopy and optical metallography were used to demonstrate the character of the interaction between the Al-Li-Cu alloys and the selected environment. Both alloys are susceptible to SC in an aqueous 3.5% NaCl solution under the right electrochemical and microstructural conditions. Each test method yields important information on the character of the SC behavior. Under all conditions investigated, second phase particles strung out in rows along the extrusion direction in the alloys were rapidly attacked, and played principal role in the SC process. With time, larger pits developed from these rows of smaller pits and under certain electrochemical conditions surface cracks initiated from the larger pits and contributed directly to the fracture process. Evidence to support slow crack growth was observed in both the slow strain rate tests and the sustained immersion tests of precracked fracture mechanics specimens. The possible role of H2 in the stress corrosion cracking process is suggested
MENGA: a new comprehensive tool for the integration of neuroimaging data and the Allen human brain transcriptome atlas
Brain-wide mRNA mappings offer a great potential for neuroscience research as they can provide information about system proteomics. In a previous work we have correlated mRNA maps with the binding patterns of radioligands targeting specific molecular systems and imaged with positron emission tomography (PET) in unrelated control groups. This approach is potentially applicable to any imaging modality as long as an efficient procedure of imaging-genomic matching is provided. In the original work we considered mRNA brain maps of the whole human genome derived from the Allen human brain database (ABA) and we performed the analysis with a specific region-based segmentation with a resolution that was limited by the PET data parcellation. There we identified the need for a platform for imaging-genomic integration that should be usable with any imaging modalities and fully exploit the high resolution mapping of ABA dataset.In this work we present MENGA (Multimodal Environment for Neuroimaging and Genomic Analysis), a software platform that allows the investigation of the correlation patterns between neuroimaging data of any sort (both functional and structural) with mRNA gene expression profiles derived from the ABA database at high resolution.We applied MENGA to six different imaging datasets from three modalities (PET, single photon emission tomography and magnetic resonance imaging) targeting the dopamine and serotonin receptor systems and the myelin molecular structure. We further investigated imaging-genomic correlations in the case of mismatch between selected proteins and imaging targets
Vacuum magnetic linear birefringence using pulsed fields: the BMV experiment
We present the current status of the BMV experiment. Our apparatus is based
on an up-to-date resonant optical cavity coupled to a transverse magnetic
field. We detail our data acquisition and analysis procedure which takes into
account the symmetry properties of the raw data with respect to the orientation
of the magnetic field and the sign of the cavity birefringence. The measurement
result of the vacuum magnetic linear birefringence k_\mathrm{CM}8 \times 10^{-21}^{-2}3\sigma$ confidence level
Chemical evolution in the environment of intermediate mass young stellar objects: NGC7129--FIRS2 and LkH234
We have carried out a molecular survey of the Class 0 IM protostar NGC 7129
-- FIRS 2 (hereafter FIRS 2) and the Herbig Be star LkH 234 with the
aim of studying the chemical evolution of the envelopes of intermediate-mass
(IM) young stellar objects (YSOs). Both objects have similar luminosities (~500
Lsun) and are located in the same molecular cloud which minimizes the chemical
differences due to different stellar masses or initial cloud conditions.
Moreover, since they are located at the same distance, we have the same spatial
resolution in both objects. A total of 17 molecular species (including rarer
isotopes) have been observed in both objects and the structure of their
envelopes and outflows is determined with unprecedent detail.
Our results show that the protostellar envelopes are dispersed and warmed up
during the evolution to become a pre-main sequence star. In fact, the envelope
mass decreases by a factor >5 from FIRS 2 to LkH234, while the kinetic
temperature increases from ~13K to 28K. On the other hand, there is no
molecular outflow associated with LkH234. The molecular outflow seems
to stop before the star becomes visible. These physical changes strongly affect
the chemistry of their envelopes.
Based on our results in FIRS2 and LkH 234, we propose some abundance
ratios that can be used as chemical clocks for the envelopes of IM YSOs. The
SiO/CS, CN/N2H+, HCN/N2H+, DCO+/HCO+ and D2CO/DCO+ ratios are good diagnostics
of the protostellar evolutionary stage.Comment: 24 pages, 17 figure
Higgs Properties in the Fourth Generation MSSM: Boosted Signals Over the 3G Plan
The generalization of the MSSM to the case of four chiral fermion generations
(4GMSSM) can lead to significant changes in the phenomenology of the otherwise
familiar Higgs sector. In most of the 3GMSSM parameter space, the lighter
CP-even is GeV and mostly Standard Model-like while
are all relatively heavy. Furthermore, the ratio of Higgs vevs,
, is relatively unconstrained. In contrast to this, in the 4GMSSM,
heavy fourth generation fermion loops drive the masses of to large
values while the CP-odd boson, , can remain relatively light and is restricted to the range 1/2 \lsim \tan \beta \lsim 2 due to
perturbativity requirements on Yukawa couplings. We explore this scenario in
some detail, concentrating on the collider signatures of the light CP-odd Higgs
at both the Tevatron and LHC. We find that while may lead to a
potential signal in the channel at the LHC, may first be
observed in the channel due to a highly loop-enhanced cross
section that can be more than an order of magnitude greater than that of a SM
Higgs for masses of and . We find that the
CP-even states are highly mixed and can have atypical branching
fractions. Precision electroweak constraints, particularly for the light
parameter space region, are examined in detail.Comment: 20 pages, 7 figures; typos fixed, refs adde
A Multiscale Investigation of Habitat Use and Within-river Distribution of Sympatric Sand Darter Species
The western sand darter Ammocrypta clara, and eastern sand darter Ammocrypta pellucida are sand-dwelling fishes of conservation concern. Past research has emphasized the importance of studying individual populations of conservation concern, while recent research has revealed the importance of incorporating landscape scale processes that structure habitat mosaics and local populations. We examined habitat use and distributions of western and eastern sand darters in the lower Elk River of West Virginia. At the sandbar habitat use scale, western sand darters were detected in sandbars with greater area, higher proportions of coarse grain sand and faster bottom current velocity, while the eastern sand darter used a wider range of sandbar habitats. The landscape scale analysis revealed that contributing drainage area was an important predictor for both species, while sinuosity, which presumably represents valley type also contributed to the western sand darter’s habitat suitability. Sandbar quality (area, grain size, and velocity) and fluvial geomorphic variables (drainage area and valley type) are likely key driving factors structuring sand darter distributions in the Elk River. This multiscale study of within-river species distribution and habitat use is unique, given that only a few sympatric populations are known of western and eastern sand darters
Two Graviton Production at and Hadron Hadron Colliders in the Randall-Sundrum Model
We compute the pair production cross section of two Kaluza Klein modes in the
Randall-Sundrum model at and hadron hadron colliders. These processes
are interesting because they get dominant contribution from the graviton
interaction at next to leading order. Hence they provide a nontrivial test of
the low scale gravity models. All the Feynman rules at next to leading order
are also presented. These rules may be useful for many phenomenological
applications including the computation of higher order loop corrections.Comment: 24 pages, 11 figures, some typos correcte
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