16,339 research outputs found
Could 2S 0114+650 be a magnetar?
We investigate the spin evolution of the binary X-ray pulsar 2S 0114+650,
which possesses the slowest known spin period of hours. We argue
that, to interpret such long spin period, the magnetic field strength of this
pulsar must be initially \gsim 10^{14} G, that is, it was born as a magnetar.
Since the pulsar currently has a normal magnetic field G, our
results present support for magnetic field decay predicted by the magnetar
model.Comment: 7 pages, 1 figure, accepted for publication in ApJ
Ultrasonic tracking of a sinking ball in a vibrated dense granular suspension
Observing and understanding the movement of an intruder through opaque dense
suspensions such as quicksand remains a practical and conceptual challenge.
Here we use an ultrasonic probe to investigate the dynamics of a steel ball
sinking in a 3D dense glass bead packing saturated by water. We show that the
frictional model developed for dry granular media can be used to describe the
ball motion induced by horizontal vibration. From this rheology we infer the
static friction coefficient and effective viscosity that decrease when
increasing the vibration intensity. Our main finding is that the
vibration-induced reduction of the yield stress and increase of the sinking
depth are presumably due to induced slipping at the grain contacts but without
visible plastic rearrangements of grains, in contrast to dry granular packings.
To explain these results, we propose a mechanism of acoustic lubrication that
reduces the inter-particle friction and leads to a decrease of the yield
stress. This scenario is different from the mechanism of liquefaction usually
invoked in loosely packed quicksands where the vibration-induced compaction
increases the pore pressure and decreases the confining pressure on the solid
skeleton, thus reducing the granular resistance to external load.Comment: 9 pages and 5 figures, plus the supplemental information (1 page, 2
movies, 1 figure
Cortical and structural connectivity damage correlated with impaired syntactic processing
Problems with sentence processing and production are not exclusive to speakers with agrammatic aphasia. Besides peripheral problems with auditory processing or articulatory control, lexical retrieval, attention and short-term memory deficits may all underlie difficulties with organizing words into sentences, applying inflectional morphology and correctly accessing and processing verb argument structure. Lesions that result in sentence processing problems are therefore not homogeneously limited to a small region. However, sentence processing and production can be broken up into components, in order to investigate the brain-behavior relationship in greater detail. The Northwestern Assessment of Verbs and Sentences (NAVS) allows for such investigations, as it consists of several tasks that tap into different components of syntactic processing (Cho-Reyes & Thompson, 2012). In particular, the NAVS focuses on the pivotal role of verbs and verb argument structure in sentence (de)construction.
With respect to structural syntactic features that affect sentence processing, it is of interest to investigate deficits that are characterized by greater problems with noncanonical sentence structures, compared to canonical structures. Patients with such a pattern of impairment may be considered to have a specific deficit in complex syntactic processing. Brain-behavior investigations that focus on such patterns may yield greater insight into regions and/or networks that serve a particular role in the syntactic computations that underlie the relation between canonical and noncanonical sentences (Magnusdottir et al., 2013).
As part of a larger study into correlations between brain damage and functional deficits, we submitted participants to an MRI scanning protocol that included anatomical scans, diffusion tensor imaging, resting state functional imaging, and perfusion imaging. Such a combination of methods reduces the chance of underestimating the extent of stroke-induced brain damage and its effect on patient symptoms. We investigated correlations with performance on NAVS subtests, as well as with the ratio of performance on canonical versus noncanonical sentence structures
A New Estimation of Mass Accumulation Efficiency in Helium Shell Flashes toward Type Ia Supernova Explosions
We have calculated the mass accumulation efficiency during helium shell
flashes to examine whether or not a carbon-oxygen white dwarf (C+O WD) grows up
to the Chandrasekhar mass limit to ignite a Type Ia supernova explosion. It has
been frequently argued that luminous super-soft X-ray sources and symbiotic
stars are progenitors of SNe Ia. In such systems, a C+O WD accretes
hydrogen-rich matter from a companion and burns hydrogen steadily on its
surface. The WD develops a helium layer underneath the hydrogen-rich envelope
and undergoes periodic helium shell flashes. Using OPAL opacity, we have
reanalyzed a full cycle of helium shell flashes on a 1.3 M_\odot C+O WD and
confirmed that the helium envelope of the WD expands to blow a strong wind. A
part of the accumulated matter is lost by the wind.
The mass accumulation efficiency is estimated as \eta_{He} = -0.175 (\log
\dot M + 5.35)^2 + 1.05, for -7.3 < \log \dot M < -5.9, where the mass
accretion rate \dot M is in units of M_\odot yr^{-1}. In relatively high mass
accretion rates as expected in recent SN Ia progenitor models, the mass
accumulation efficiency is large enough for C+O WDs to grow to the
Chandrasekhar mass, i.e., \eta_{He} = 0.9 for \log \dot M = -6.3, and
\eta_{He}=0.57 for \log \dot M = -7.0. The wind velocity (\sim 1000 km/s) is
much faster than the orbital velocity of the binary (< 300 km/s) and therefore,
the wind cannot be accelerated further by the companion's motion.Comment: 11 pages including 4 eps-files, accepted for publication in ApJ
Letter
The development of a resource-efficient photovoltaic system
This paper presents the measures taken in the demonstration of the photovoltaic case study developed within the European project ‘Towards zero waste in industrial networks’ (Zerowin), integrating the D4R (Design for recycling, repair, refurbishment and reuse) criteria at both system and industrial network level. The demonstration is divided into three phases. The first phase concerns the development of a D4R photovoltaic concept, the second phase focused on the development of a specific component of photovoltaic systems and the third phase was the demonstration of the D4R design in two complete photovoltaic systems (grid-connected and stand-alone). This paper includes a description of the installed photovoltaic systems, including a brief summary at component level of the lithium ion battery system and the D4R power conditioning system developed for the pilot installations. Additionally, industrial symbioses within the network associated with the photovoltaic systems and the production model for the network are described
NlpI-Prc Proteolytic Complex Mediates Peptidoglycan Synthesis and Degradation via Regulation of Hydrolases and Synthases in <i>Escherichia coli</i>
Balancing peptidoglycan (PG) synthesis and degradation with precision is essential for bacterial growth, yet our comprehension of this intricate process remains limited. The NlpI-Prc proteolytic complex plays a crucial but poorly understood role in the regulation of multiple enzymes involved in PG metabolism. In this paper, through fluorescent D-amino acid 7-hydroxycoumarincarbonylamino-D-alanine (HADA) labeling and immunolabeling assays, we have demonstrated that the NlpI-Prc complex regulates the activity of PG transpeptidases and subcellular localization of PBP3 under certain growth conditions. PBP7 (a PG hydrolase) and MltD (a lytic transglycosylase) were confirmed to be negatively regulated by the NlpI-Prc complex by an in vivo degradation assay. The endopeptidases, MepS, MepM, and MepH, have consistently been demonstrated as redundantly essential “space makers” for nascent PG insertion. However, we observed that the absence of NlpI-Prc complex can alleviate the lethality of the mepS mepM mepH mutant. A function of PG lytic transglycosylases MltA and MltD as “space makers” was proposed through multiple gene deletions. These findings unveil novel roles for NlpI-Prc in the regulation of both PG synthesis and degradation, shedding light on the previously undiscovered function of lytic transglycosylases as “space makers” in PG expansion
Macroscopic limit cycle via pure noise-induced phase transition
Bistability generated via a pure noise-induced phase transition is reexamined
from the view of bifurcations in macroscopic cumulant dynamics. It allows an
analytical study of the phase diagram in more general cases than previous
methods. In addition using this approach we investigate patially-extended
systems with two degrees of freedom per site. For this system, the analytic
solution of the stationary Fokker-Planck equation is not available and a
standard mean field approach cannot be used to find noise induced phase
transitions. A new approach based on cumulant dynamics predicts a noise-induced
phase transition through a Hopf bifurcation leading to a macroscopic limit
cycle motion, which is confirmed by numerical simulation.Comment: 8 pages, 8 figure
Out of Equilibrium Solutions in the -Hamiltonian Mean Field model
Out of equilibrium magnetised solutions of the -Hamiltonian Mean Field
(-HMF) model are build using an ensemble of integrable uncoupled pendula.
Using these solutions we display an out-of equilibrium phase transition using a
specific reduced set of the magnetised solutions
- …