8,883 research outputs found
Dust in the Local Group
How dust absorbs and scatters starlight as a function of wavelength (known as
the interstellar extinction curve) is crucial for correcting for the effects of
dust extinction in inferring the true luminosity and colors of reddened
astrophysical objects. Together with the extinction spectral features, the
extinction curve contains important information about the dust size
distribution and composition. This review summarizes our current knowledge of
the dust extinction of the Milky Way, three Local Group galaxies (i.e., the
Small and Large Magellanic Clouds, and M31), and galaxies beyond the Local
Group.Comment: 21 pages, 11 figures; invited review article published in "LESSONS
FROM THE LOCAL GROUP -- A Conference in Honour of David Block and Bruce
Elmegreen" eds. Freeman, K.C., Elmegreen, B.G., Block, D.L. & Woolway, M.
(SPRINGER: NEW YORK), pp. 85-10
The Mid-Infrared Extinction Law and its Variation in the Coalsack Nebula
In recent years the wavelength dependence of interstellar extinction from the
ultraviolet (UV), optical, through the near- and mid-infrared (IR) has been
studied extensively. Although it is well established that the UV/optical
extinction law varies significantly among the different lines of sight, it is
not clear how the IR extinction varies among various environments. In this
work, using the color-excess method and taking red giants as the extinction
tracer, we determine the interstellar extinction Alambda in the four
Spitzer/IRAC bands of the Coalsack nebula, a nearby starless dark cloud, based
on the data obtained from the 2MASS and Spitzer/GLIMPSE surveys. We select five
individual regions across the nebula that span a wide variety of physical
conditions, ranging from diffuse, translucent to dense environments, as traced
by the visual extinction, the Spitzer/MIPS 24micron emission, and CO emission.
We find that Alambda/AKs, the mid-IR extinction relative to AKs, decreases from
diffuse to dense environments, which may be explained in terms of ineffective
dust growth in dense regions. The mean extinction (relative to AKs) is
calculated for the four IRAC bands as well, which exhibits a flat mid-IR
extinction law, consistent with previous determinations for other regions. The
extinction in the IRAC 4.5micron band is anomalously high, much higher than
that of the other three IRAC bands. It cannot be explained in terms of CO and
CO2 ices. The mid-IR extinction in the four IRAC bands have also been derived
for four representative regions in the Coalsack Globule 2 which respectively
exhibit strong ice absorption, moderate or weak ice absorption, and very weak
or no ice absorption. The derived mid-IR extinction curves are all flat, with
Alambda/AKs increasing with the decrease of the H2O ice absorption optical
depth.Comment: 39 pages, 13 figures, accepted by Ap
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Nanoparticles for live cell microscopy: A surface-enhanced Raman scattering perspective.
Surface enhanced Raman scattering (SERS) nanoparticles are an attractive alternative to fluorescent probes for biological labeling because of their photostability and multiplexing capabilities. However, nanoparticle size, shape, and surface properties are known to affect nanoparticle-cell interactions. Other issues such as the formation of a protein corona and antibody multivalency interfere with the labeling properties of nanoparticle-antibody conjugates. Hence, it is important to consider these aspects in order to validate such conjugates for live cell imaging applications. Using SERS nanoparticles that target HER2 and CD44 in breast cancer cells, we demonstrate labeling of fixed cells with high specificity that correlates well with fluorescent labels. However, when labeling live cells to monitor surface biomarker expression and dynamics, the nanoparticles are rapidly uptaken by the cells and become compartmentalized into different cellular regions. This behavior is in stark contrast to that of fluorescent antibody conjugates. This study highlights the impact of nanoparticle internalization and trafficking on the ability to use SERS nanoparticle-antibody conjugates to monitor cell dynamics
Interfacial thermal transport in atomic junctions
We study ballistic interfacial thermal transport across atomic junctions.
Exact expressions for phonon transmission coefficients are derived for thermal
transport in one-junction and two-junction chains, and verified by numerical
calculation based on a nonequilibrium Green's function method. For a
single-junction case, we find that the phonon transmission coefficient
typically decreases monotonically with increasing freqency. However, in the
range between equal frequency spectrum and equal acoustic impedance, it
increases first then decreases, which explains why the Kapitza resistance
calculated from the acoustic mismatch model is far larger than the experimental
values at low temperatures. The junction thermal conductance reaches a maximum
when the interfacial coupling equals the harmonic average of the spring
constants of the two semi-infinite chains. For three-dimensional junctions, in
the weak coupling limit, we find that the conductance is proportional to the
square of the interfacial coupling, while for intermediate coupling strength
the conductance is approximately proportional to the interfacial coupling
strength. For two-junction chains, the transmission coefficient oscillates with
the frequency due to interference effects. The oscillations between the two
envelop lines can be understood analytically, thus providing guidelines in
designing phonon frequency filters.Comment: 10 pages, 13 figures. Accepted by Phys. Rev.
A novel coaxial magnetic gear using bulk HTS for industrial applications
In this paper, a novel coaxial magnetic gear (CMG) using bulk high temperature superconductors (HTS) is proposed. By substituting bulk HTS for ferromagnetic material, a novel stationary ring is resulted, which can not only provide the desired field modulation effect but also suppress the end-effects that commonly occurred in the traditional CMG. The performance of the proposed bulk HTS CMG is assessed and then verified by using finite element analysis. © 2006 IEEE.published_or_final_versio
Toward understanding the 3.4 micron and 9.7 micron extinction feature variations from the local diffuse interstellar medium to the Galactic center
Observationally, both the 3.4micron aliphatic hydrocarbon C--H stretching
absorption feature and the 9.7micron amorphous silicate Si--O stretching
absorption feature show considerable variations from the local diffuse
interstellar medium (ISM) to Galactic center (GC): both the ratio of the visual
extinction (A_V) to the 9.7micron Si--O optical depth (\tausil) and the ratio
of A_V to the 3.4micron C--H optical depth (\tauahc) of the solar neighborhood
local diffuse ISM are about twice as much as that of the GC. In this work, we
try to explain these variations in terms of a porous dust model consisting of a
mixture of amorphous silicate, carbonaceous organic refractory dust (as well as
water ice for the GC dust).Comment: 6 pages, 6 figures, uses eps.cls. Accepted for publication in "Earth,
Planets and Space" (special issue on Cosmic Dust
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