7,774 research outputs found
The distribution of [/Fe] in the Milky Way disc
Using a sample of red giant stars from the Apache Point Observatory Galactic
Evolution Experiment (APOGEE) Data Release 16, we infer the conditional
distribution in the Milky Way disk
for the -elements Mg, O, Si, S, and Ca. In each bin of [Fe/H] and
Galactocentric radius , we model as a sum of two
Gaussians, representing "low-" and "high-" populations with
scale heights and , respectively.
By accounting for age-dependent and -dependent selection effects in APOGEE,
we infer the [/Fe] distributions that would be found for a fair sample
of long-lived stars covering all . Near the Solar circle, this distribution
is bimodal at sub-solar [Fe/H], with the low- and high- peaks
clearly separated by a minimum at intermediate [/Fe]. In agreement with
previous results, we find that the high- population is more prominent
at smaller , lower [Fe/H], and larger , and that the sequence
separation is smaller for Si and Ca than for Mg, O, and S. We find significant
intrinsic scatter in [/Fe] at fixed [Fe/H] for both the low-
and high- populations, typically -dex. The means,
dispersions, and relative amplitudes of this two-Gaussian description, and the
dependence of these parameters on , [Fe/H], and -element, provide a
quantitative target for chemical evolution models and a test for hydrodynamic
simulations of disk galaxy formation. We argue that explaining the observed
bimodality will probably require one or more sharp transitions in the disk's
gas accretion, star formation, or outflow history in addition to radial mixing
of stellar populations.Comment: Accepted for publication in MNRA
BKM Lie superalgebras from counting twisted CHL dyons
Following Sen[arXiv:0911.1563], we study the counting of (`twisted') BPS
states that contribute to twisted helicity trace indices in four-dimensional
CHL models with N=4 supersymmetry. The generating functions of half-BPS states,
twisted as well as untwisted, are given in terms of multiplicative eta products
with the Mathieu group, M_{24}, playing an important role. These multiplicative
eta products enable us to construct Siegel modular forms that count twisted
quarter-BPS states. The square-roots of these Siegel modular forms turn out be
precisely a special class of Siegel modular forms, the dd-modular forms, that
have been classified by Clery and Gritsenko[arXiv:0812.3962]. We show that each
one of these dd-modular forms arise as the Weyl-Kac-Borcherds denominator
formula of a rank-three Borcherds-Kac-Moody Lie superalgebra. The walls of the
Weyl chamber are in one-to-one correspondence with the walls of marginal
stability in the corresponding CHL model for twisted dyons as well as untwisted
ones. This leads to a periodic table of BKM Lie superalgebras with properties
that are consistent with physical expectations.Comment: LaTeX, 32 pages; (v2) matches published versio
Loss of Melanoregulin (MREG) Enhances Cathepsin-D Secretion by the Retinal Pigment Epithelium
Cathepsin-D (Cat-D) is a major proteolytic enzyme in phagocytic cells. In the retinal pigment epithelium (RPE), it is responsible for the daily degradation of photoreceptor outer segments (POSs) to maintain retinal homeostasis. Melanoregulin (MREG)-mediated loss of phagocytic capacity has been linked to diminished intracellular Cat-D activity. Here, we demonstrate that loss of MREG enhances the secretion of intermediate Cat-D (48 kDa), resulting in a net enhancement of extracellular Cat-D activity. These results suggest that MREG is required to maintain Cat-D homeostasis in the RPE and likely plays a protective role in retinal health. In this regard, in the Mreg dsu/dsu mouse, we observe increased basal laminin. Loss of the Mreg dsu allele is not lethal and therefore leads to slow age-dependent changes in the RPE. Thus, we propose that this model will allow us to study potential dysregulatory functions of Cat-D in retinal disease
Lattice Green's function approach to the solution of the spectrum of an array of quantum dots and its linear conductance
In this paper we derive general relations for the band-structure of an array
of quantum dots and compute its transport properties when connected to two
perfect leads. The exact lattice Green's functions for the perfect array and
with an attached adatom are derived. The expressions for the linear conductance
for the perfect array as well as for the array with a defect are presented. The
calculations are illustrated for a dot made of three atoms. The results derived
here are also the starting point to include the effect of electron-electron and
electron-phonon interactions on the transport properties of quantum dot arrays.
Different derivations of the exact lattice Green's functions are discussed
Loss of Melanoregulin (MREG) Enhances Cathepsin-D Secretion by the Retinal Pigment Epithelium
Abstract Cathepsin-D (Cat-D) is a major proteolytic enzyme in phagocytic cells. In the retinal pigment epithelium (RPE), it is responsible for the daily degradation of photoreceptor outer segments (POSs) to maintain retinal homeostasis. Melanoregulin (MREG)-mediated loss of phagocytic capacity has been linked to diminished intracellular Cat-D activity. Here, we demonstrate that loss of MREG enhances the secretion of intermediate Cat-D (48 kDa), resulting in a net enhancement of extracellular Cat-D activity. These results suggest that MREG is required to maintain Cat-D homeostasis in the RPE and likely plays a protective role in retinal health. In this regard, in the Mreg dsu/dsu mouse, we observe increased basal laminin. Loss of the Mreg dsu allele is not lethal and therefore leads to slow age-dependent changes in the RPE. Thus, we propose that this model will allow us to study potential dysregulatory functions of Cat-D in retinal disease. Copyright © Cambridge University Press, 2013
The Contribution of Melanoregulin to Microtubule-Associated Protein 1 Light Chain 3 (LC3) Associated Phagocytosis in Retinal Pigment Epithelium
A main requisite in the phagocytosis of ingested material is a coordinated series of maturation steps which lead to the degradation of ingested cargo. Photoreceptor outer segment (POS) renewal involves phagocytosis of the distal disk membranes by the retinal pigment epithelium (RPE). Previously, we identified melanoregulin (MREG) as an intracellular cargo-sorting protein required for the degradation of POS disks. Here, we provide evidence that MREG-dependent processing links both autophagic and phagocytic processes in LC3-associated phagocytosis (LAP). Ingested POS phagosomes are associated with endogenous LC3 and MREG. The LC3 association with POSs exhibited properties of LAP; it was independent of rapamycin pretreatment, but dependent on Atg5. Loss of MREG resulted in a decrease in the extent of LC3-POS association. Studies using DQâą-BSA suggest that loss of MREG does not compromise the association and fusion of LC3-positive phagosomes with lysosomes. Furthermore, the mechanism of MREG action is likely through a protein complex that includes LC3, as determined by colocalization and immunoprecipitation in both RPE cells and macrophages. We posit that MREG participates in coordinating the association of phagosomes with LC3 for content degradation with the loss of MREG leading to phagosome accumulation. © 2014, Springer Science+Business Media New York
Linking land and lake: Using novel geochemical techniques to understand biological response to environmental change
The exploitation of lakes has led to large-scale contemporary impacts on freshwater systems, largely in response to catchment clearance. Such clearance is causing changes to carbon dynamics in tropical lakes which may have significance for wider carbon budgets, depending on the changes in carbon sequestration and mineralisation driven by changing roles of terrestrial and aquatic carbon in lakes over time. Despite increasing awareness of the pivotal role of carbon source in carbon dynamics, discriminating the source of carbon from a palaeolimnological record is rarely undertaken. Here we use novel geochemical techniques (brGDGTs, n-alkanes, Rock-Eval pyrolysis), paired with traditional analyses (diatoms, pollen), to elucidate changing sources of carbon through time and ecosystem response. Environmental changes at Lake Nyamogusingiri can be divided into three phases: Phase I (CE 1150-1275), a shallow and productive lake, where a diverse terrestrial environment is, initially, the main carbon source, before switching to an aquatic source; Phase II (CE 1275-1900), variable lake levels (generally in decline) with increasing productivity, and carbon is autochthonous in source; Phase III (CE 1900-2007), lake level declines, and the carbon is of a mixed source, though the terrestrially derived carbon is from a less diverse source. The organic geochemical analyses provide a wealth of data regarding the complexity of aquatic response to catchment and with-in lake changes. These data demonstrate show that small, tropical lake systems have the potential to bury high quantities of carbon, which has implications for the disruption of local biogeochemical cycles (C, P, N, and Si) both in the past, and the future as human and climate pressures increase
The Contribution of Melanoregulin to Microtubule-Associated Protein 1 Light Chain 3 (LC3) Associated Phagocytosis in Retinal Pigment Epithelium
A main requisite in the phagocytosis of ingestedmaterial is a coordinated series of maturation steps which leadto the degradation of ingested cargo. Photoreceptor outersegment (POS) renewal involves phagocytosis of the distaldisk membranes by the retinal pigment epithelium (RPE).Previously, we identified melanoregulin (MREG) as an intra-cellular cargo-sorting protein required for the degradation ofPOS disks. Here, we provide evidence that MREG-dependentprocessing links both autophagic and phagocytic processes inLC3-associated phagocytosis (LAP). Ingested POSphagosomes are associated with endogenous LC3 andMREG. The LC3 association with POSs exhibited propertiesof LAP; it was independent of rapamycin pretreatment, butdependent on Atg5. Loss of MREG resulted in a decrease inthe extent of LC3-POS association. Studies using DQâą-BSAsuggest that loss of MREG does not compromise the associ-ation and fusion of LC3-positive phagosomes with lysosomes.Furthermore, the mechanism of MREG action is likelythrough a protein complex that includes LC3, as determinedby colocalization and immunoprecipitation in both RPE cellsand macrophages. We posit that MREG participates incoordinating the association of phagosomes with LC3 forcontent degradation with the loss of MREG leading tophagosome accumulation
Traveling waves for nonlinear Schr\"odinger equations with nonzero conditions at infinity, II
We prove the existence of nontrivial finite energy traveling waves for a
large class of nonlinear Schr\"odinger equations with nonzero conditions at
infinity (includindg the Gross-Pitaevskii and the so-called "cubic-quintic"
equations) in space dimension . We show that minimization of the
energy at fixed momentum can be used whenever the associated nonlinear
potential is nonnegative and it gives a set of orbitally stable traveling
waves, while minimization of the action at constant kinetic energy can be used
in all cases. We also explore the relationship between the families of
traveling waves obtained by different methods and we prove a sharp nonexistence
result for traveling waves with small energy.Comment: Final version, accepted for publication in the {\it Archive for
Rational Mechanics and Analysis.} The final publication is available at
Springer via http://dx.doi.org/10.1007/s00205-017-1131-
Non-Supersymmetric Stringy Attractors
In this paper we examine the stability of non-supersymmetric attractors in
type IIA supergravity compactified on a Calabi-Yau manifold, in the presence of
sub-leading corrections to the N=$ pre-potential. We study black hole
configurations carrying D0-D6 and D0-D4 charges. We consider the O(1)
corrections to the pre-potential given by the Euler number of the Calabi-Yau
manifold. We argue that such corrections in general can not lift the zero modes
for the D0-D6 attractors. However, for the attractors carrying the D0-D4
charges, they affect the zero modes in the vector multiplet sector. We show
that, in the presence of such O(1) corrections, the D0-D4 attractors can either
be stable or unstable depending on the geometry of the underlying Calabi-Yau
manifold, and on the specific values of the charges they carry.Comment: corrected typos, minor modification
- âŠ