1,089 research outputs found
Bubbling with -almost constant mean curvature and an Alexandrov-type theorem for crystals
A compactness theorem for volume-constrained almost-critical points of
elliptic integrands is proven. The result is new even for the area functional,
as almost-criticality is measured in an integral rather than in a uniform
sense. Two main applications of the compactness theorem are discussed. First,
we obtain a description of critical points/local minimizers of elliptic
energies interacting with a confinement potential. Second, we prove an
Alexandrov-type theorem for crystalline isoperimetric problems
Corruption and climate change policies: do the bad old days matter?
We study the effect of countriesâ historical legacy with corruption on recent climate change policies and on global cooperation. Current policy outcomes build on policy choices made in previous years, and these choices were likely affected by the degree of corruption at the time. Our empirical findings using data for up to 131 countries suggest that accumulated historical experience with corruption is important for todayâs policy outcomes, and appears to be more important than the current level of corruption
Triaxial orbit-based modelling of the Milky Way Nuclear Star Cluster
We construct triaxial dynamical models for the Milky Way nuclear star cluster
using Schwarzschild's orbit superposition technique. We fit the stellar
kinematic maps presented in Feldmeier et al. (2014). The models are used to
constrain the supermassive black hole mass M_BH, dynamical mass-to-light ratio
M/L, and the intrinsic shape of the cluster. Our best-fitting model has M_BH =
(3.0 +1.1 -1.3)x10^6 M_sun, M/L = (0.90 +0.76 -0.08) M_sun/L_{sun,4.5micron},
and a compression of the cluster along the line-of-sight. Our results are in
agreement with the direct measurement of the supermassive black hole mass using
the motion of stars on Keplerian orbits. The mass-to-light ratio is consistent
with stellar population studies of other galaxies in the mid-infrared. It is
possible that we underestimate M_BH and overestimate the cluster's triaxiality
due to observational effects. The spatially semi-resolved kinematic data and
extinction within the nuclear star cluster bias the observations to the near
side of the cluster, and may appear as a compression of the nuclear star
cluster along the line-of-sight. We derive a total dynamical mass for the Milky
Way nuclear star cluster of M_MWNSC = (2.1 +-0.7)x10^7 M_sun within a sphere
with radius r = 2 x r_eff = 8.4 pc. The best-fitting model is tangentially
anisotropic in the central r = 0.5-2 pc of the nuclear star cluster, but close
to isotropic at larger radii. Our triaxial models are able to recover complex
kinematic substructures in the velocity map.Comment: 14 pages, 10 figures. Accepted for publication in MNRA
VLT Diffraction Limited Imaging and Spectroscopy in the NIR: Weighing the black hole in Centaurus A with NACO
We present high spatial resolution near-infrared spectra and images of the
nucleus of Centaurus A (NGC 5128) obtained with NAOS-CONICA at the VLT. The
adaptive optics corrected data have a spatial resolution of 0.06" (FWHM) in K-
and 0.11" in H-band, four times higher than previous studies. The observed gas
motions suggest a kinematically hot disk which is orbiting a central object and
is oriented nearly perpendicular to the nuclear jet. We model the central
rotation and velocity dispersion curves of the [FeII] gas orbiting in the
combined potential of the stellar mass and the (dominant) black hole. Our
physically most plausible model, a dynamically hot and geometrically thin gas
disk, yields a black hole mass of M_bh = (6.1 +0.6/-0.8) 10^7 M_sun. As the
physical state of the gas is not well understood, we also consider two limiting
cases: first a cold disk model, which completely neglects the velocity
dispersion; it yields an M_bh estimate that is almost two times lower. The
other extreme case is to model a spherical gas distribution in hydrostatic
equilibrium through Jeans equation. Compared to the hot disk model the best-fit
black hole mass increases by a factor of 1.5. This wide mass range spanned by
the limiting cases shows how important the gas physics is even for high
resolution data. Our overall best-fitting black hole mass is a factor of 2-4
lower than previous measurements. With our revised M_bh estimate, Cen A's
offset from the M_bh-sigma relation is significantly reduced; it falls above
this relation by a factor of ~2, which is close to the intrinsic scatter of
this relation. (Abridged)Comment: 12 pages, 14 figures, including minor changes following the referee
report; accepted for publication in The Astrophysical Journa
ALMA Observations of the Physical and Chemical Conditions in Centaurus A
Centaurus A, with its gas-rich elliptical host galaxy, NGC 5128, is the
nearest radio galaxy at a distance of 3.8 Mpc. Its proximity allows us to study
the interaction between an active galactic nucleus, radio jets, and molecular
gas in great detail. We present ALMA observations of low J transitions of three
CO isotopologues, HCN, HCO, HNC, CN, and CCH toward the inner projected
500 pc of NGC 5128. Our observations resolve physical sizes down to 40 pc. By
observing multiple chemical probes, we determine the physical and chemical
conditions of the nuclear interstellar medium of NGC 5128. This region contains
molecular arms associated with the dust lanes and a circumnuclear disk (CND)
interior to the molecular arms. The CND is approximately 400 pc by 200 pc and
appears to be chemically distinct from the molecular arms. It is dominated by
dense gas tracers while the molecular arms are dominated by CO and its
rare isotopologues. The CND has a higher temperature, elevated CN/HCN and
HCN/HNC intensity ratios, and much weaker CO and CO emission than
the molecular arms. This suggests an influence from the AGN on the CND
molecular gas. There is also absorption against the AGN with a low velocity
complex near the systemic velocity and a high velocity complex shifted by about
60 km s. We find similar chemical properties between the CND in emission
and both the low and high velocity absorption complexes implying that both
likely originate from the CND. If the HV complex does originate in the CND,
then that gas would correspond to gas falling toward the supermassive black
hole
Refugees, not economic migrants:Why do asylum seekers register in Hungary?
The article analyses why asylumâseekers choose Hungary as an entry point to the European Union. Among the Central and Eastern European countries Hungary has been by far the most popular choice for asylumâseekers between 2002 and 2016, yet surprisingly, it has been neglected by the literature. Using a panel dataset and fixed effects regressions, the article finds that beyond being âconvenientlyâ located on the Balkans migration route, variables related to Hungary's immigration policy are the most significant determinants of asylumâseeker choices. The article finds no evidence to support recent claims by the Hungarian government that arrivals to the country are actually economic migrants and not asylumâseekers; quite the contrary, the results indicate that on average asylumâseekers entering Hungary are fleeing violent conflict in their countries of origin
Phosphorylation of Targeting Protein for Xenopus Kinesin-like Protein 2 (TPX2) at Threonine 72 in Spindle Assembly
The human ortholog of the targeting protein for Xenopus kinesin-like protein 2 (TPX2) is a cytoskeletal protein that plays a major role in spindle assembly and is required for mitosis. During spindle morphogenesis, TPX2 cooperates with Aurora A kinase and Eg5 kinesin to regulate microtubule organization. TPX2 displays over 40 putative phosphorylation sites identified from various high-throughput proteomic screenings. In this study, we characterize the phosphorylation of threonine 72 (Thr(72)) in human TPX2, a residue highly conserved across species. We find that Cdk1/2 phosphorylate TPX2 in vitro and in vivo. Using homemade antibodies specific for TPX2 phosphorylated at Thr(72), we show that this phosphorylation is cell cycle-dependent and peaks at M phase. Endogenous TPX2 phosphorylated at Thr(72) does not associate with the mitotic spindle. Furthermore, ectopic GFP-TPX2 T72A preferentially concentrates on the spindle, whereas GFP-TPX2 WT distributes to both spindle and cytosol. The T72A mutant also increases the proportion of cells with multipolar spindles phenotype. This effect is associated with increased Aurora A activity and abnormally elongated spindles, indicative of higher Eg5 activity. In summary, we propose that phosphorylation of Thr(72) regulates TPX2 localization and impacts spindle assembly via Aurora A and Eg5.X11109Ysciescopu
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