10,224 research outputs found
Slowly-growing gap-opening planets trigger weaker vortices
The presence of a giant planet in a low-viscosity disc can create a gap edge
in the disc's radial density profile sharp enough to excite the Rossby Wave
Instability. This instability may evolve into dust-trapping vortices that might
explain the "banana-shaped" features in recently observed asymmetric transition
discs with inner cavities. Previous hydrodynamical simulations of
planet-induced vortices have neglected the timescale of hundreds to thousands
of orbits to grow a massive planet to Jupiter-size. In this work, we study the
effect of a giant planet's runaway growth timescale on the lifetime and
characteristics of the resulting vortex. For two different planet masses (1 and
5 Jupiter masses) and two different disc viscosities (=3 and 3), we compare the vortices induced by planets with
several different growth timescales between 10 and 4000 planet orbits. In
general, we find that slowly-growing planets create significantly weaker
vortices with lifetimes and surface densities reduced by more than . For
the higher disc viscosity, the longest growth timescales in our study inhibit
vortex formation altogether. Additionally, slowly-growing planets produce
vortices that are up to twice as elongated, with azimuthal extents well above
in some cases. These unique, elongated vortices likely create a
distinct signature in the dust observations that differentiates them from the
more concentrated vortices that correspond to planets with faster growth
timescales. Lastly, we find that the low viscosities necessary for vortex
formation likely prevent planets from growing quickly enough to trigger the
instability in self-consistent models.Comment: 12 pages, 7 figures, Accepted by MNRA
Observational diagnostics of elongated planet-induced vortices with realistic planet formation timescales
Gap-opening planets can generate dust-trapping vortices that may explain some
of the latest discoveries of high-contrast crescent-shaped dust asymmetries in
transition discs. While planet-induced vortices were previously thought to have
concentrated shapes, recent computational work has shown that these features
naturally become much more elongated in the gas when simulations account for
the relatively long timescale over which planets accrete their mass. In this
work, we conduct two-fluid hydrodynamical simulations of vortices induced by
slowly-growing Jupiter-mass planets in discs with very low viscosity (). We simulate the dust dynamics for four particle sizes
spanning 0.3 mm to 1 cm in order to produce synthetic ALMA images. In our
simulations, we find that an elongated vortex still traps dust, but not
directly at its center. With a flatter pressure bump and disruptions from the
planet's overlapping spiral density waves, the dust instead circulates around
the vortex. This motion (1) typically carries the peak off-center, (2) spreads
the dust out over a wider azimuthal extent , (3) skews the
azimuthal profile towards the front of the vortex, and (4) can also create
double peaks in newly-formed vortices. In particular, we expect that the most
defining observational signature, a peak offset of more than ,
should be detectable of the time in observations with a beam diameter
of at most the planet's separation from its star.Comment: Accepted to MNRAS. 13 pages, 8 figures. Movies available at:
https://lavinia.as.arizona.edu/~mhammer/vortex_signatures.htm
Electronic transport in quasi-one-dimensional arrays of gold nanocrystals
We report on the fabrication and current-voltage (IV) characteristics of very
narrow, strip-like arrays of metal nanoparticles. The arrays were formed from
gold nanocrystals self-assembled between in-plane electrodes. Local
cross-linking of the ligands by exposure to a focused electron beam and
subsequent removal of the unexposed regions produced arrays as narrow as four
particles wide and sixty particles long, with high degree of structural
ordering. Remarkably, even for such quasi-one-dimensional strips, we find
nonlinear, power-law IV characteristics similar to that of much wider
two-dimensional (2D) arrays. However, in contrast to the robust behavior of 2D
arrays, the shape of the IV characteristics is much more sensitive to
temperature changes and temperature cycling. Furthermore, at low temperatures
we observe pronounced two-level current fluctuations, indicative of discrete
rearrangements in the current paths. We associate this behavior with the
inherent high sensitivity of single electron tunneling to the polarization
caused by the quenched offset charges in the underlying substrate.Comment: 5 pages, 4 figure
Recommended from our members
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
Innate immune system activation in zebrafish and cellular models of Diamond Blackfan Anemia.
Deficiency of ribosomal proteins (RPs) leads to Diamond Blackfan Anemia (DBA) associated with anemia, congenital defects, and cancer. While p53 activation is responsible for many features of DBA, the role of immune system is less defined. The Innate immune system can be activated by endogenous nucleic acids from non-processed pre-rRNAs, DNA damage, and apoptosis that occurs in DBA. Recognition by toll like receptors (TLRs) and Mda5-like sensors induces interferons (IFNs) and inflammation. Dying cells can also activate complement system. Therefore we analyzed the status of these pathways in RP-deficient zebrafish and found upregulation of interferon, inflammatory cytokines and mediators, and complement. We also found upregulation of receptors signaling to IFNs including Mda5, Tlr3, and Tlr9. TGFb family member activin was also upregulated in RP-deficient zebrafish and in RPS19-deficient human cells, which include a lymphoid cell line from a DBA patient, and fetal liver cells and K562 cells transduced with RPS19 shRNA. Treatment of RP-deficient zebrafish with a TLR3 inhibitor decreased IFNs activation, acute phase response, and apoptosis and improved their hematopoiesis and morphology. Inhibitors of complement and activin also had beneficial effects. Our studies suggest that innate immune system contributes to the phenotype of RPS19-deficient zebrafish and human cells
Exploration of nonlocalities in ensembles consisting of bipartite quantum states
It is revealed that ensembles consisting of multipartite quantum states can
exhibit different kinds of nonlocalities. An operational measure is introduced
to quantify nonlocalities in ensembles consisting of bipartite quantum states.
Various upper and lower bounds for the measure are estimated and the exact
values for ensembles consisting of mutually orthogonal maximally entangled
bipartite states are evaluated.Comment: The title and some contents changed, 4 pages, no figure
Dynamical Self-assembly during Colloidal Droplet Evaporation Studied by in situ Small Angle X-ray Scattering
The nucleation and growth kinetics of highly ordered nanocrystal
superlattices during the evaporation of nanocrystal colloidal droplets was
elucidated by in situ time resolved small-angle x-ray scattering. We
demonstrated for the first time that evaporation kinetics can affect the
dimensionality of the superlattices. The formation of two-dimensional
nanocrystal superlattices at the liquid-air interface of the droplet has an
exponential growth kinetics that originates from interface "crushing".Comment: 4 pages, 4 figure
Percolating through networks of random thresholds: Finite temperature electron tunneling in metal nanocrystal arrays
We investigate how temperature affects transport through large networks of
nonlinear conductances with distributed thresholds. In monolayers of
weakly-coupled gold nanocrystals, quenched charge disorder produces a range of
local thresholds for the onset of electron tunneling. Our measurements
delineate two regimes separated by a cross-over temperature . Up to
the nonlinear zero-temperature shape of the current-voltage curves survives,
but with a threshold voltage for conduction that decreases linearly with
temperature. Above the threshold vanishes and the low-bias conductance
increases rapidly with temperature. We develop a model that accounts for these
findings and predicts .Comment: 5 pages including 3 figures; replaced 3/30/04: minor changes; final
versio
Isomorphism of graph classes related to the circular-ones property
We give a linear-time algorithm that checks for isomorphism between two 0-1
matrices that obey the circular-ones property. This algorithm leads to
linear-time isomorphism algorithms for related graph classes, including Helly
circular-arc graphs, \Gamma-circular-arc graphs, proper circular-arc graphs and
convex-round graphs.Comment: 25 pages, 9 figure
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