377 research outputs found
A conserved filamentous assembly underlies the structure of the meiotic chromosome axis.
The meiotic chromosome axis plays key roles in meiotic chromosome organization and recombination, yet the underlying protein components of this structure are highly diverged. Here, we show that 'axis core proteins' from budding yeast (Red1), mammals (SYCP2/SYCP3), and plants (ASY3/ASY4) are evolutionarily related and play equivalent roles in chromosome axis assembly. We first identify 'closure motifs' in each complex that recruit meiotic HORMADs, the master regulators of meiotic recombination. We next find that axis core proteins form homotetrameric (Red1) or heterotetrameric (SYCP2:SYCP3 and ASY3:ASY4) coiled-coil assemblies that further oligomerize into micron-length filaments. Thus, the meiotic chromosome axis core in fungi, mammals, and plants shares a common molecular architecture, and likely also plays conserved roles in meiotic chromosome axis assembly and recombination control
Dual Massive Gravity
The linearized massive gravity in three dimensions, over any maximally
symmetric background, is known to be presented in a self-dual form as a first
order equation which encodes not only the massive Klein-Gordon type field
equation but also the supplementary transverse-traceless conditions. We
generalize this construction to higher dimensions. The appropriate dual
description in d dimensions, additionally to a (non-symmetric) tensor field
, involves an extra rank-(d-1) field equivalently represented by
the torsion rank-3 tensor. The symmetry condition for arises
on-shell as a consequence of the field equations. The action principle of the
dual theory is formulated. The focus has been made on four dimensions. Solving
one of the fields in terms of the other and putting back in the action one
obtains two other equivalent formulations of the theory in which the action is
quadratic in derivatives. In one of these representations the theory is
formulated entirely in terms of a rank-2 non-symmetric tensor .
This quadratic theory is not identical to the Fierz-Pauli theory and contains
the coupling between the symmetric and antisymmetric parts of .
Nevertheless, the only singularity in the propagator is the same as in the
Fierz-Pauli theory so that only the massive spin-2 particle is propagating. In
the other representation, the theory is formulated in terms of the torsion
rank-3 tensor only. We analyze the conditions which follow from the field
equations and show that they restrict to 5 degrees of freedom thus producing an
alternative description to the massive spin-2 particle. A generalization to
higher dimensions is suggested.Comment: 14 pages; v2: modifications in Appendix, more references adde
A First Look at White Dwarf - M Dwarf Pairs in the Sloan Digital Sky Survey (SDSS)
We have identified 109 White Dwarf (WD) - M dwarf pairs in the Sloan Digital
Sky Survey (SDSS) with g < 20th magnitude. For each system we determined the
temperature of the WD primary and the spectral type of the M dwarf secondary.
Using H-alpha emission as a proxy for the chromospheric activity level of the M
dwarf, we investigated correlations between the activity level and properties
of the system. Compared with field M dwarfs (Hawley et al. 1996), we see a
slightly higher active fraction of early-type stars, with activity levels
similar to the field.
We have conducted followup observations at the ARC 3.5m telescope to obtain
radial velocity information and to search for short period binaries, which may
be on the verge of interacting. We report on one system with a 4.1 hour period,
and several additional systems with significant velocity variations.Comment: 23 pages with 10 figures. Accepted by AJ, to appear in May 2003 issu
A conserved filamentous assembly underlies the structure of the meiotic chromosome axis
The meiotic chromosome axis plays key roles in meiotic chromosome organization and recombination, yet the underlying protein components of this structure are highly diverged. Here, we show that 'axis core proteins' from budding yeast (Red1), mammals (SYCP2/SYCP3), and plants (ASY3/ASY4) are evolutionarily related and play equivalent roles in chromosome axis assembly. We first identify 'closure motifs' in each complex that recruit meiotic HORMADs, the master regulators of meiotic recombination. We next find that axis core proteins form homotetrameric (Red1) or heterotetrameric (SYCP2:SYCP3 and ASY3:ASY4) coiled-coil assemblies that further oligomerize into micron-length filaments. Thus, the meiotic chromosome axis core in fungi, mammals, and plants shares a common molecular architecture, and likely also plays conserved roles in meiotic chromosome axis assembly and recombination control
Spectroscopic Properties of Cool Stars in the SDSS: An Analysis of Magnetic Activity and a Search for Subdwarfs
We present a spectroscopic analysis of nearly 8000 late-type dwarfs in the
Sloan Digital Sky Survey. Using the Halpha emission line as an activity
indicator, we investigate the fraction of active stars as a function of
spectral type and find a peak near type M8, confirming previous results. In
contrast to past findings, we find that not all M7-M8 stars are active. We show
that this may be a selection effect of the distance distributions of previous
samples, as the active stars appear to be concentrated near the Galactic Plane.
We also examine the activity strength (ratio of the luminosity emitted in
Halpha to the bolometric luminosity) for each star, and find that the mean
activity strength is constant over the range M0-M5 and declines at later types.
The decline begins at a slightly earlier spectral type than previously found.
We explore the effect that activity has on the broadband photometric colors and
find no significant differences between active and inactive stars. We also
carry out a search for subdwarfs using spectroscopic metallicity indicators,
and find 60 subdwarf candidates. Several of these candidates are near the
extreme subdwarf boundary. The spectroscopic subdwarf candidates are redder by
\~0.2 magnitudes in g-r compared to disk dwarfs at the same r-i color.Comment: 17 pages, 9 figures, accepted for publication in A
Manipulating ultracold atoms with a reconfigurable nanomagnetic system of domain walls
The divide between the realms of atomic-scale quantum particles and
lithographically-defined nanostructures is rapidly being bridged. Hybrid
quantum systems comprising ultracold gas-phase atoms and substrate-bound
devices already offer exciting prospects for quantum sensors, quantum
information and quantum control. Ideally, such devices should be scalable,
versatile and support quantum interactions with long coherence times.
Fulfilling these criteria is extremely challenging as it demands a stable and
tractable interface between two disparate regimes. Here we demonstrate an
architecture for atomic control based on domain walls (DWs) in planar magnetic
nanowires that provides a tunable atomic interaction, manifested experimentally
as the reflection of ultracold atoms from a nanowire array. We exploit the
magnetic reconfigurability of the nanowires to quickly and remotely tune the
interaction with high reliability. This proof-of-principle study shows the
practicability of more elaborate atom chips based on magnetic nanowires being
used to perform atom optics on the nanometre scale.Comment: 4 pages, 4 figure
Low-Mass Dwarf Template Spectra from the Sloan Digital Sky Survey
We present template spectra of low-mass (M0-L0) dwarfs derived from over
4,000 Sloan Digital Sky Survey (SDSS) spectra. These composite spectra are
suitable for use as medium-resolution (R ~ 1,800) radial velocity standards. We
report mean spectral properties (molecular bandhead strengths,equivalent
widths) and use the templates to investigate the effects of magnetic activity
and metallicity on the spectroscopic and photometric properties of low-mass
stars.Comment: 16 pages, 11 Figures, accepted to the Astronomical Journal,
low-resolution figures included. Full-resolution images can be found at
http://www.astro.washington.edu/bochansk/lowmass.pd
A blood-based diagnostic test incorporating plasma Aβ42/40 ratio, ApoE proteotype, and age accurately identifies brain amyloid status: Findings from a multi cohort validity analysis
BACKGROUND: The development of blood-based biomarker tests that are accurate and robust for Alzheimer\u27s disease (AD) pathology have the potential to aid clinical diagnosis and facilitate enrollment in AD drug trials. We developed a high-resolution mass spectrometry (MS)-based test that quantifies plasma Aβ42 and Aβ40 concentrations and identifies the ApoE proteotype. We evaluated robustness, clinical performance, and commercial viability of this MS biomarker assay for distinguishing brain amyloid status.
METHODS: We used the novel MS assay to analyze 414 plasma samples that were collected, processed, and stored using site-specific protocols, from six independent US cohorts. We used receiver operating characteristic curve (ROC) analyses to assess assay performance and accuracy for predicting amyloid status (positive, negative, and standard uptake value ratio; SUVR). After plasma analysis, sites shared brain amyloid status, defined using diverse, site-specific methods and cutoff values; amyloid PET imaging using various tracers or CSF Aβ42/40 ratio.
RESULTS: Plasma Aβ42/40 ratio was significantly (p \u3c 0.001) lower in the amyloid positive vs. negative participants in each cohort. The area under the ROC curve (AUC-ROC) was 0.81 (95% CI = 0.77-0.85) and the percent agreement between plasma Aβ42/40 and amyloid positivity was 75% at the optimal (Youden index) cutoff value. The AUC-ROC (0.86; 95% CI = 0.82-0.90) and accuracy (81%) for the plasma Aβ42/40 ratio improved after controlling for cohort heterogeneity. The AUC-ROC (0.90; 95% CI = 0.87-0.93) and accuracy (86%) improved further when Aβ42/40, ApoE4 copy number and participant age were included in the model.
CONCLUSIONS: This mass spectrometry-based plasma biomarker test: has strong diagnostic performance; can accurately distinguish brain amyloid positive from amyloid negative individuals; may aid in the diagnostic evaluation process for Alzheimer\u27s disease; and may enhance the efficiency of enrolling participants into Alzheimer\u27s disease drug trials
- …