1,817 research outputs found
The Versatile Molecular Complex Component LC8 Promotes Several Distinct Steps of Flagellar Assembly
LC8 is present in various molecular complexes. However, its role in these complexes remains unclear. We discovered that although LC8 is a subunit of the radial spoke (RS) complex in Chlamydomonas flagella, it was undetectable in the RS precursor that is converted into the mature RS at the tip of elongating axonemes. Interestingly, LC8 dimers bound in tandem to the N-terminal region of a spoke phosphoprotein, RS protein 3 (RSP3), that docks RSs to axonemes. LC8 enhanced the binding of RSP3 N-terminal fragments to purified axonemes. Likewise, the N-terminal fragments extracted from axonemes contained LC8 and putative spoke-docking proteins. Lastly, perturbations of RSP3’s LC8-binding sites resulted in asynchronous flagella with hypophosphorylated RSP3 and defective associations between LC8, RSs, and axonemes. We propose that at the tip of flagella, an array of LC8 dimers binds to RSP3 in RS precursors, triggering phosphorylation, stalk base formation, and axoneme targeting. These multiple effects shed new light on fundamental questions about LC8-containing complexes and axoneme assembly
Neutral hydrogen in dwarf galaxies. II. The kinematics of HI
This paper is the second in a series presenting a sample of 29 late-type
dwarf galaxies observed with the Westerbork Synthesis Radio Telescope in the
21-cm line of neutral hydrogen (HI). Here we present rotation curves, maps of
the velocity field and maps of the velocity dispersion across the sample
galaxies.Comment: 16 pages; accepted by A&
Real-time evolution for weak interaction quenches in quantum systems
Motivated by recent experiments in ultracold atomic gases that explore the
nonequilibrium dynamics of interacting quantum many-body systems, we
investigate the nonequilibrium properties of a Fermi liquid. We apply an
interaction quench within the Fermi liquid phase of the Hubbard model by
switching on a weak interaction suddenly; then we follow the real-time dynamics
of the momentum distribution by a systematic expansion in the interaction
strength based on the flow equation method. In this paper we derive our main
results, namely the applicability of a quasiparticle description, the
observation of a new type of quasi-stationary nonequilibrium Fermi liquid like
state and a delayed thermalization of the momentum distribution. We explain the
physical origin of the delayed relaxation as a consequence of phase space
constraints in fermionic many-body systems. This brings about a close relation
to similar behavior of one-particle systems which we illustrate by a discussion
of the squeezed oscillator; we generalize to an extended class of systems with
discrete energy spectra and point out the generic character of the
nonequilibrium Fermi liquid results for weak interaction quenches. Both for
discrete and continuous systems we observe that particular nonequilibrium
expectation values are twice as large as their corresponding analogues in
equilibrium. For a Fermi liquid, this shows up as an increased
correlation-induced reduction of the quasiparticle residue in nonequilibrium.Comment: 54 page
Assessment of Surface Water Contamination from Coalbed Methane Fracturing-Derived Volatile Contaminants in Sullivan County, Indiana, USA
There is a growing concern over the contamination of surface water and the associated environmental and public health consequences from the recent proliferation in hydraulic fracturing in the USA. Petroleum hydrocarbon-derived contaminants of concern [benzene, toluene, ethylbenzene, and xylene (BTEX)] and various dissolved cations and anions were spatially determined in surface waters around 14 coalbed methane fracking wells in Sullivan County, IN, USA. At least one BTEX was detected in 69% of sampling sites (n=13) and 23% of sampling sites were found to be contaminated with all of the BTEX. Toluene was the most common BTEX compound detected across all sites, both upstream and downstream from coalbed methane fracking sites. The calcium (~60 ppm) and sulfates (~175 ppm) were the dominant cations and anions, respectively, in surface water around the fracking sites. This study represents the first report of BTEX contamination in surface water from coalbed methane hydraulic fracturing wells
Quantum phase transitions in the interacting boson model
This review is focused on various properties of quantum phase transitions
(QPTs) in the Interacting Boson Model (IBM) of nuclear structure. The model in
its infinite-size limit exhibits shape-phase transitions between spherical,
deformed prolate, and deformed oblate forms of the ground state. Finite-size
precursors of such behavior are verified by robust variations of nuclear
properties (nuclear masses, excitation energies, transition probabilities for
low lying levels) across the chart of nuclides. Simultaneously, the model
serves as a theoretical laboratory for studying diverse general features of
QPTs in interacting many-body systems, which differ in many respects from
lattice models of solid-state physics. We outline the most important fields of
the present interest: (a) The coexistence of first- and second-order phase
transitions supports studies related to the microscopic origin of the QPT
phenomena. (b) The competing quantum phases are characterized by specific
dynamical symmetries and novel symmetry related approaches are developed to
describe also the transitional dynamical domains. (c) In some parameter
regions, the QPT-like behavior can be ascribed also to individual excited
states, which is linked to the thermodynamic and classical descriptions of the
system. (d) The model and its phase structure can be extended in many
directions: by separating proton and neutron excitations, considering
odd-fermion degrees of freedom or different particle-hole configurations, by
including other types of bosons, higher order interactions, and by imposing
external rotation. All these aspects of IBM phase transitions are relevant in
the interpretation of experimental data and important for a fundamental
understanding of the QPT phenomenon.Comment: a review article, 71 pages, 18 figure
Use of SF6 to estimate anthropogenic CO2 in the upper ocean
The highest concentrations of anthropogenic carbon (C_ant) are found in the upper layers of the world ocean. However, this is where seasonal variability of inorganic carbon and related parameters due to thermal and biological effects complicates use of back-calculation approaches for C ant . Tracer based approaches to C_ant estimation are unaffected by biological variability and have found wide application. However, slow-down, even reversal, of the atmospheric growth of chlorofluorocarbons (CFCs) restricts use of these tracers for C ant estimation for waters ventilated since the mid 1990s. Here we apply SF6, a tracer that continues to increase in the atmosphere, as a basis for the C_ant estimation, using samples collected in the midlatitude North Atlantic in 2004. C ant estimates derived from water mass transit time distributions (TTDs) calculated with SF6 are compared to those based on CFC-12. For recently ventilated waters (pCFC-12 > ∼450 ppt), the uncertainty of SF6 based estimates of C_ant is ∼6 μmol kg−1 less than that of CFC-12 based estimates. CFC-12 based estimates remain more reliable for older (deeper) water masses, as a result of the longer input history and more readily detectable concentrations of CFC-12. Historical data suggest that the near-surface saturation of CFC-12 has increased over time, in inverse proportion to its atmospheric growth rate. Use of a time-dependent saturation of CFC-12 in TTD calculations appears to provide more reliable estimation of C_ant
The Hide-and-Seek of Grain Boundaries from Moire Pattern Fringe of Two-Dimensional Graphene
Grain boundaries (GBs) commonly exist in crystalline materials and affect various properties of materials. The facile identification of GBs is one of the significant requirements for systematical study of polycrystalline materials including recently emerging two-dimensional materials. Previous observations of GBs have been performed by various tools including high resolution transmission electron microscopy. However, a method to easily identify GBs, especially in the case of low-angle GBs, has not yet been well established. In this paper, we choose graphene bilayers with a GB as a model system and investigate the effects of interlayer rotations to the identification of GBs. We provide a critical condition between adjacent moire fringe spacings, which determines the possibility of GB recognition. In addition, for monolayer graphene with a grain boundary, we demonstrate that low-angle GBs can be distinguished easily by inducing moire patterns deliberately with an artificial reference overlayopen0
Dynamics of Starbursting Dwarf Galaxies. II. UGC 4483
UGC 4483 is a nearby Blue Compact Dwarf (BCD) galaxy. HST observations have
resolved the galaxy into single stars and this has led to the derivation of its
star formation history and to a direct estimate of its stellar mass. We have
analysed archival VLA observations of the 21 cm line and found that UGC 4483
has a steeply-rising rotation curve which flattens in the outer parts at a
velocity of ~20 km/s. Radial motions of ~5 km/s may also be present. As far as
we know, UGC 4483 is the lowest-mass galaxy with a differentially rotating HI
disk. The steep rise of the rotation curve indicates that there is a strong
central concentration of mass. We have built mass models using the HST
information on the stellar mass to break the disk-halo degeneracy: old stars
contribute ~50 of the observed rotation velocity at 2.2 disk scale-lengths.
Baryons (gas and stars) constitute an important fraction of the total dynamical
mass. These are striking differences with respect to typical dwarf irregular
galaxies (dIrrs), which usually have slowly-rising rotation curves and are
thought to be entirely dominated by dark matter. BCDs appear to be different
from non-starbursting dIrrs in terms of their HI and stellar distributions and
their internal dynamics. To their high central surface brightnesses and high
central HI densities correspond strong central rotation-velocity gradients.
This implies that the starburst is closely related with the gravitational
potential and the concentration of gas. We discuss the implications of our
results on the properties of the progenitors/descendants of BCDs.Comment: Published on Astronomy & Astrophysics (11 pages, 10 figures). Typos
fixe
Pre-operative pulmonary assessment for patients with hip fracture
Hip fracture is a common injury among the elderly. Although patients who receive hip fracture surgery carry the best functional recovery compared to other treatment modalities, the presence of postoperative pulmonary complications, such as atelectasis, pneumonia, and pulmonary thromboembolism, may contribute to increased length of hospital stay, perioperative morbidity, and mortality. This review aims to provide evidence-based recommendations for preoperative assessment and perioperative strategies to reduce the risk of pulmonary complications after hip fracture surgery. Clinical assessment and basic laboratory results are sufficient to stratify the risk of postoperative pulmonary complications. Well-documented risk factors for pulmonary complications include advanced age, poor general health status, current infections, pre-existing cardiopulmonary diseases, hypoalbuminemia, and impaired renal function. Apart from optimizing the patient's medical conditions, interventions such as lung expansion maneuvers and thromboprophylaxis have been proven to be effective in reducing the risk of pulmonary complications after hip fracture surgery
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