8,690 research outputs found
Piezoelectric-based apparatus for strain tuning
We report the design and construction of piezoelectric-based apparatus for
applying continuously tuneable compressive and tensile strains to test samples.
It can be used across a wide temperature range, including cryogenic
temperatures. The achievable strain is large, so far up to 0.23% at cryogenic
temperatures. The apparatus is compact and compatible with a wide variety of
experimental probes. In addition, we present a method for mounting
high-aspect-ratio samples in order to achieve high strain homogeneity.Comment: 8 pages, 8 figure
Synthetic Antimicrobial Peptides Exhibit Two Different Binding Mechanisms to the Lipopolysaccharides Isolated from and
Circular dichroism and 1H NMR were used to investigate the interactions of a
series of synthetic antimicrobial peptides (AMPs) with lipopolysaccharides (LPS) isolated from
Pseudomonas aeruginosa and Klebsiella pneumoniae. Previous CD studies with AMPs
containing only three Tic-Oic dipeptide units do not exhibit helical characteristics upon
interacting with small unilamellar vesicles (SUVs) consisting of LPS. Increasing the number of
Tic-Oic dipeptide units to six resulted in five analogues with CD spectra that exhibited helical
characteristics on binding to LPS SUVs. Spectroscopic and in vitro inhibitory data suggest that
there are two possible helical conformations resulting from two different AMP-LPS binding
mechanisms. Mechanism one involves a helical binding conformation where the AMP binds
LPS very strongly and is not efficiently transported across the LPS bilayer resulting in the loss of
inhibitory activity. Mechanism two involves a helical binding conformation where the AMP
binds LPS very loosely and is efficiently transported across the LPS bilayer resulting in an
increase in inhibitory activity. Mechanism three involves a nonhelical binding conformation
where the AMP binds LPS very loosely and is efficiently transported across the LPS bilayer
resulting in an increase in inhibitory activity
The Keck/OSIRIS Nearby AGN Survey (KONA) I. The Nuclear K-band Properties of Nearby AGN
We introduce the Keck Osiris Nearby AGN survey (KONA), a new adaptive
optics-assisted integral-field spectroscopic survey of Seyfert galaxies. KONA
permits at ~0.1" resolution a detailed study of the nuclear kinematic structure
of gas and stars in a representative sample of 40 local bona fide active
galactic nucleus (AGN). KONA seeks to characterize the physical processes
responsible for the coevolution of supermassive black holes and galaxies,
principally inflows and outflows. With these IFU data of the nuclear regions of
40 Seyfert galaxies, the KONA survey will be able to study, for the first time,
a number of key topics with meaningful statistics. In this paper we study the
nuclear K-band properties of nearby AGN. We find that the luminosities of the
unresolved Seyfert 1 sources at 2.1 microns are correlated with the hard X-ray
luminosities, implying that the majority of the emission is non-stellar. The
best-fit correlation is logLK = 0.9logL2-10 keV + 4 over 3 orders of magnitude
in both K-band and X-ray luminosities. We find no strong correlation between
2.1 microns luminosity and hard X-ray luminosity for the Seyfert 2 galaxies.
The spatial extent and spectral slope of the Seyfert 2 galaxies indicate the
presence of nuclear star formation and attenuating material (gas and dust),
which in some cases is compact and in some galaxies extended. We detect
coronal-line emission in 36 galaxies and for the first time in five galaxies.
Finally, we find 4/20 galaxies that are optically classified as Seyfert 2 show
broad emission lines in the near-IR, and one galaxy (NGC 7465) shows evidence
of a double nucleus.Comment: Accepted for publication in ApJ, 19 pages with 18 figure
A Multiwavelength Analysis of the Strong Lensing Cluster RCS 022434-0002.5 at z=0.778
We present the results of two (101 ks total) Chandra observations of the
z=0.778 optically selected lensing cluster RCS022434-0002.5, along with weak
lensing and dynamical analyses of this object. An X-ray spectrum extracted
within R(2500) (362 h(70)^(-1) kpc) results in an integrated cluster
temperature of 5.1 (+0.9,-0.5) keV. The surface brightness profile of
RCS022434-0002.5 indicates the presence of a slight excess of emission in the
core. A hardness ratio image of this object reveals that this central emission
is primarily produced by soft X-rays. Further investigation yields a cluster
cooling time of 3.3 times 10^9 years, which is less than half of the age of the
universe at this redshift given the current LCDM cosmology. A weak lensing
analysis is performed using HST images, and our weak lensing mass estimate is
found to be in good agreement with the X-ray determined mass of the cluster.
Spectroscopic analysis reveals that RCS022434-0002.5 has a velocity dispersion
of 900 +/- 180 km/s, consistent with its X-ray temperature. The core gas mass
fraction of RCS022434-0002.5 is, however, found to be three times lower than
expected universal values. The radial distribution of X-ray point sources
within R(200) of this cluster peaks at ~0.7 R(200), possibly indicating that
the cluster potential is influencing AGN activity at that radius. Correlations
between X-ray and radio (VLA) point source positions are also examined.Comment: 32 pages, 9 figures. Accepted for publication in The Astrophysical
Journa
Public exhibit for demonstrating the quantum of electrical conductance
We present a new robust setup that explains and demonstrates the quantum of
electrical conductance for a general audience and which is continuously
available in a public space. The setup allows users to manually thin a gold
wire of several atoms in diameter while monitoring its conductance in real
time. During the experiment, a characteristic step-like conductance decrease
due to rearrangements of atoms in the cross-section of the wire is observed.
Just before the wire breaks, a contact consisting of a single atom with a
characteristic conductance close to the quantum of conductance can be
maintained up to several seconds. The setup is operated full-time, needs
practically no maintenance and is used on different educational levels
Symmetry breaking in commensurate graphene rotational stacking; a comparison of theory and experiment
Graphene stacked in a Bernal configuration (60 degrees relative rotations
between sheets) differs electronically from isolated graphene due to the broken
symmetry introduced by interlayer bonds forming between only one of the two
graphene unit cell atoms. A variety of experiments have shown that non-Bernal
rotations restore this broken symmetry; consequently, these stacking varieties
have been the subject of intensive theoretical interest. Most theories predict
substantial changes in the band structure ranging from the development of a Van
Hove singularity and an angle dependent electron localization that causes the
Fermi velocity to go to zero as the relative rotation angle between sheets goes
to zero. In this work we show by direct measurement that non-Bernal rotations
preserve the graphene symmetry with only a small perturbation due to weak
effective interlayer coupling. We detect neither a Van Hove singularity nor any
significant change in the Fermi velocity. These results suggest significant
problems in our current theoretical understanding of the origins of the band
structure of this material.Comment: 7 pages, 6 figures, submitted to PR
- …