22,743 research outputs found
VLT near- to mid-IR imaging and spectroscopy of the M17 UC1-IRS5 region
We investigate the surroundings of the hypercompact HII region M17 UC1 to
probe the physical properties of the associated young stellar objects and the
environment of massive star formation. Five of the seven point sources in this
region show -band excess emission. Geometric match is found between the H_2
emission and near-IR polarized light in the vicinity of IRS5A, and between the
diffuse mid-IR emission and near-IR polarization north of UC1. The H_2 emission
is typical for dense PDRs, which are FUV pumped initially and repopulated by
collisional de-excitation. The spectral types of IRS5A and B273A are B3-B7
V/III and G4-G5 III, respectively. The observed infrared luminosity L_IR in the
range 1-20 micron is derived for three objects; we obtain 2.0x10^3 L_\sun for
IRS5A, 13 L_\sun for IRS5C, and 10 L_\sun for B273A. IRS5 might be a young
quadruple system. Its primary star IRS5A is confirmed to be a high-mass
protostellar object (~ 9 M_\sun, ~1x10^5 yrs); it might have terminated
accretion due to the feedback from the stellar activities (radiation pressure,
outflow) and the expanding HII region of M17. UC1 might also have terminated
accretion because of the expanding hypercompact HII region ionized by itself.
The disk clearing process of the low-mass YSOs in this region might be
accelerated by the expanding HII region. The outflows driven by UC1 are running
in south-north with its northeastern side suppressed by the expanding
ionization front of M17; the blue-shifted outflow lobe of IRS5A is seen in two
types of tracers along the same line of sight in the form of H_2 emission
filament and mid-emission. The H_2 line ratios probe the properties of M17 SW
PDR, which is confirmed to have a clumpy structure with two temperature
distributions: warm, dense molecular clumps with n_H>10^5 cm^-3 and T~575 K and
cooler atomic gas with n_H~3.7x10^3-1.5x10^4 cm-3 and T~50-200 K.Comment: accepted for publication in A&A, 19 pages, 15 figures, 5 table
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Attenuation of hedgehog/GLI signaling by NT1721 extends survival in pancreatic cancer.
BackgroundPancreatic cancer is one of the most lethal malignancies due to frequent late diagnosis, aggressive tumor growth and metastasis formation. Continuously raising incidence rates of pancreatic cancer and a lack of significant improvement in survival rates over the past 30 years highlight the need for new therapeutic agents. Thus, new therapeutic agents and strategies are urgently needed to improve the outcome for patients with pancreatic cancer. Here, we evaluated the anti-tumor activity of a new natural product-based epidithiodiketopiperazine, NT1721, against pancreatic cancer.MethodsWe characterized the anticancer efficacy of NT1721 in multiple pancreatic cancer cell lines in vitro and in two orthotopic models. We also compared the effects of NT1721 to clinically used hedgehog inhibitors and the standard-of-care drug, gemcitabine. The effect of NT1721 on hedgehog/GLI signaling was assessed by determining the expression of GLI and GLI target genes both in vitro and in vivo.ResultsNT1721 displayed IC50 values in the submicromolar range in multiple pancreatic cancer cell lines, while largely sparing normal pancreatic epithelial cells. NT1721 attenuated hedgehog/GLI signaling through downregulation of GLI1/2 transcription factors and their downstream target genes, which reduced cell proliferation and invasion in vitro and significantly decreased tumor growth and liver metastasis in two preclinical orthotopic mouse models of pancreatic cancer. Importantly, treatment with NT1721 significantly improved survival times of mice with pancreatic cancer compared to the standard-of-care drug, gemcitabine.ConclusionsFavorable therapeutics properties, i.e. 10-fold lower IC50 values than clinically used hedgehog inhibitors (vismodegib, erismodegib), a 90% reduction in liver metastasis and significantly better survival times compared to the standard-of-care drug, gemcitabine, provide a rational for testing NT1721 in the clinic either as a single agent or possibly in combination with gemcitabine or other therapeutic agents in PDAC patients overexpressing GLI1/2. This could potentially result in promising new treatment options for patients suffering from this devastating disease
Tuning the emission wavelength of Si nanocrystals in SiO2 by oxidation
Si nanocrystals (diameter 2–5 nm) were formed by 35 keV Si + implantation at a fluence of 6 × 1016 Si/cm2 into a 100 nm thick thermally grown SiO2 film on Si (100), followed by thermal annealing at 1100 °C for 10 min. The nanocrystals show a broad photoluminescence spectrum, peaking at 880 nm, attributed to the recombination of quantum confined excitons. Rutherford backscattering spectrometry and transmission electron microscopy show that annealing these samples in flowing O2 at 1000 °C for times up to 30 min results in oxidation of the Si nanocrystals, first close to the SiO2 film surface and later at greater depths. Upon oxidation for 30 min the photoluminescence peak wavelength blueshifts by more than 200 nm. This blueshift is attributed to a quantum size effect in which a reduction of the average nanocrystal size leads to emission at shorter wavelengths. The room temperature luminescence lifetime measured at 700 nm increases from 12 µs for the unoxidized film to 43 µs for the film that was oxidized for 29 min
Charge and spin Hall conductivity in metallic graphene
Graphene has an unusual low-energy band structure with four chiral bands and
half-quantized and quantized Hall effects that have recently attracted
theoretical and experimental attention. We study the Fermi energy and disorder
dependence of its spin Hall conductivity. In the metallic regime we find that
vertex corrections enhance the intrinsic spin Hall conductivity and that skew
scattering can lead to its values that exceed the quantized ones expected when
the chemical potential is inside the spin-orbit induced energy gap. We predict
that large spin Hall conductivities will be observable in graphene even when
the spin-orbit gap does not survive disorder.Comment: 4 pages, 2 figure
Generalized Stacking Fault Energy Surfaces and Dislocation Properties of Silicon: A First-Principles Theoretical Study
The generalized stacking fault (GSF) energy surfaces have received
considerable attention due to their close relation to the mechanical properties
of solids. We present a detailed study of the GSF energy surfaces of silicon
within the framework of density functional theory. We have calculated the GSF
energy surfaces for the shuffle and glide set of the (111) plane, and that of
the (100) plane of silicon, paying particular attention to the effects of the
relaxation of atomic coordinates. Based on the calculated GSF energy surfaces
and the Peierls-Nabarro model, we obtain estimates for the dislocation
profiles, core energies, Peierls energies, and the corresponding stresses for
various planar dislocations of silicon.Comment: 9 figures (not included; send requests to [email protected]
Stable Equilibrium Based on L\'evy Statistics: Stochastic Collision Models Approach
We investigate equilibrium properties of two very different stochastic
collision models: (i) the Rayleigh particle and (ii) the driven Maxwell gas.
For both models the equilibrium velocity distribution is a L\'evy distribution,
the Maxwell distribution being a special case. We show how these models are
related to fractional kinetic equations. Our work demonstrates that a stable
power-law equilibrium, which is independent of details of the underlying
models, is a natural generalization of Maxwell's velocity distribution.Comment: PRE Rapid Communication (in press
Singlet superfield extension of the minimal supersymmetric standard model with Peccei-Quinn symmetry and a light pseudoscalar Higgs boson at the LHC
Motivated by the mu-problem and the axion solution to the strong CP-problem,
we extend the MSSM with one more chiral singlet field . The underlying
PQ-symmetry allows only one more term in the superpotential. The
spectrum of the Higgs system includes a light pseudoscalar (in addition
to the standard CP-even Higgs boson), predominantly decaying to two photons:
. Both Higgs bosons might be in the range accessible to
current LHC experiments.Comment: 5 pages with 3 figure
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