1,172 research outputs found
09461 Abstracts Collection -- Algorithms and Applications for Next Generation SAT Solvers
From 8th to 13th November 2009, the Dagstuhl Seminar 09461 "Algorithms and Applications for Next Generation SAT Solvers" was held in Schloss Dagstuhl--Leibniz Center for Informatics. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts, slides or full papers are provided, if available
Dictyostelium Myosin-IE Is a Fast Molecular Motor Involved in Phagocytosis
Class I myosins are single-headed motor proteins, implicated in various motile processes including organelle translocation, ion-channel gating, and cytoskeleton reorganization. Here we describe the cellular localization of myosin-IE and its role in the phagocytic uptake of solid particles and cells. A complete analysis of the kinetic and motor properties of Dictyostelium discoideum myosin-IE was achieved by the use of motor domain constructs with artificial lever arms. Class I myosins belonging to subclass IC like myosin-IE are thought to be tuned for tension maintenance or stress sensing. In contrast to this prediction, our results show myosin-IE to be a fast motor. Myosin-IE motor activity is regulated by myosin heavy chain phosphorylation, which increases the coupling efficiency between the actin and nucleotide binding sites tenfold and the motile activity more than fivefold. Changes in the level of free Mg(2+) ions, which are within the physiological range, are shown to modulate the motor activity of myosin-IE by inhibiting the release of adenosine diphosphate
Positron annihilation as a cosmic-ray probe
Recently, the gamma-ray telescopes AGILE and Fermi observed several
middle-aged supernova remnants (SNRs) interacting with molecular clouds. A
plausible emission mechanism of the gamma rays is the decay of neutral pions
produced by cosmic ray (CR) nuclei (hadronic processes). However, observations
do not rule out contributions from bremsstrahlung emission due to CR electrons.
TeV gamma-ray telescopes also observed many SNRs and discovered many
unidentified sources. It is still unclear whether the TeV gamma-ray emission is
produced via leptonic processes or hadronic processes. In this Letter, we
propose that annihilation emission of secondary positrons produced by CR nuclei
is a diagnostic tool of the hadronic processes. We investigate MeV emissions
from secondary positrons and electrons produced by CR protons in molecular
clouds. The annihilation emission of the secondary positrons from SNRs can be
robustly estimated from the observed gamma-ray flux. The expected flux of the
annihilation line from SNRs observed by AGILE and Fermi is sufficient for the
future Advanced Compton Telescope to detect. Moreover, synchrotron emission
from secondary positrons and electrons and bremsstrahlung emission from CR
protons can be also observed by the future X-ray telescope NuSTAR and ASTRO-H.Comment: 6 pages, 4 figures, accepted for publication in the MNRAS letter
Internet Service Providers' and Individuals' Attitudes, Barriers, and Incentives to Secure IoT
Internet of Things (IoT) play a vital role in securing IoT.
However, encouraging them to do so is hard. Our study investigates ISPsâ and individualsâ attitudes towards the security
of IoT, the obstacles they face, and their incentives to keep
IoT secure, drawing evidence from Japan.
Due to the complex interactions of the stakeholders, we
follow an iterative methodology where we present issues and
potential solutions to our stakeholders in turn. For ISPs, we
survey 27 ISPs in Japan, followed by a workshop with representatives from government and 5 ISPs. Based on the findings
from this, we conduct semi-structured interviews with 20 participants followed by a more quantitative survey with 328
participants. We review these results in a second workshop
with representatives from government and 7 ISPs. The appreciation of challenges by each party has lead to findings that
are supported by all stakeholders.
Securing IoT devices is neither usersâ nor ISPsâ priority.
Individuals are keen on more interventions both from the
government as part of regulation and from ISPs in terms of
filtering malicious traffic. Participants are willing to pay for
enhanced monitoring and filtering. While ISPs do want to help
users, there appears to be a lack of effective technology to
aid them. ISPs would like to see more public recognition for
their efforts, but internally they struggle with executive buy-in
and effective means to communicate with their customers.
The majority of barriers and incentives are external to ISPs
and individuals, demonstrating the complexity of keeping IoT
secure and emphasizing the need for relevant stakeholders in
the IoT ecosystem to work in tandem
Transport of <i>Sporosarcina pasteurii</i> in sandstone and its significance for subsurface engineering technologies
The development of microbially mediated technologies for subsurface remediation and rock engineering is steadily increasing; however, we are lacking experimental data and models to predict bacterial movement through rock matrices. Here, breakthrough curves (BTCs) were obtained to quantify the transport of the ureolytic bacterium, Sporosarcina pasteurii, through sandstone cores, as a function of core length (1.8â7.5 cm), bacterial density (4 Ă 10<sup>6</sup> to 9 Ă 10<sup>7</sup> cells/ml) and flow rate (5.8â17.5 m/s). <i>S. pasteurii</i> was easily immobilised within the homogeneous sandstone matrix (>80%) in comparison to a packed sand column (<20%; under similar experimental conditions), and percentage recovery decreased almost linearly with increasing rock core length. Moreover, a decrease in bacterial density or flow rate enhanced bacterial retention. A numerical model based on 1D advection dispersion models used for unconsolidated sand was fitted to the BTC data obtained here for sandstone. Good agreement between data and model was obtained at shorter rock core lengths (<4 cm), suggesting that physicochemical filtration processes are similar in homogeneous packed sand and sandstones at these lengths. Discrepancies were, however observed at longer core lengths and with varying flow rates, indicating that the attributes of consolidated rock might impact bacterial transport progressively more with increasing core length. Implications of these results on microbial mineralisation technologies currently being developed for sealing fluid paths in subsurface environment is discussed
Cosmological Feedback from High-Redshift Dwarf Galaxies
We model how repeated supernova explosions in high-redshift dwarf starburst
galaxies drive superbubbles and winds out of the galaxies. We compute the
efficiencies of metal and mass ejection and energy transport from the galactic
potentials, including the effect of cosmological infall of external gas. The
starburst bubbles quickly blow out of small, high-redshift, galactic disks, but
must compete with the ram pressure of the infalling gas to escape into
intergalactic space. We show that the assumed efficiency of the star formation
rate dominates the bubble evolution and the metal, mass, and energy feedback
efficiencies. With star formation efficiency f*=0.01, the ram pressure of
infall can confine the bubbles around high-redshift dwarf galaxies with
circular velocities v_c>52 km/s. We can expect high metal and mass ejection
efficiencies, and moderate energy transport efficiencies in halos with
v_c~30-50 km/s and f*~0.01 as well as in halos with v_c~100 km/s and f*>>0.01.
Such haloes collapse successively from 1-2 sigma peaks in LambdaCDM Gaussian
density perturbations as time progresses. These dwarf galaxies can probably
enrich low and high-density regions of intergalactic space with metals to
10^-3-10^-2 Zsun as they collapse at z~8 and z<5 respectively. They also may be
able to provide adequate turbulent energy to prevent the collapse of other
nearby halos, as well as to significantly broaden Lyman-alpha absorption lines
to v_rms~20-40 km/s. We compute the timescales for the next starbursts if gas
freely falls back after a starburst, and find that, for star formation
efficiencies as low as f*<0.01, the next starburst should occur in less than
half the Hubble time at the collapse redshift. This suggests that episodic star
formation may be ubiquitous in dwarf galaxies.Comment: Accepted for ApJ v613, 60 pages, 15 figure
Radion Stabilization In 5D SUGRA
We present a detailed study of radion stabilization within 5D conformal SUGRA
compactified on an orbifold. We use an effective 4D superfield
description developed in our previous work. The effects of tree level bulk and
boundary couplings, and in particular of one loop contributions and of a non
perturbative correction on the radion stabilization are investigated. We find
new examples of radion stabilization in non SUSY and (meta-stable) SUSY
preserving Minkowski vacua.Comment: LaTex. Some comments and references added, version to appear in NP
Tracing the Reionization-Epoch Intergalactic Medium with Metal Absorption Lines
IGM metal absorption lines observed in z>6 spectra offer the opportunity to
probe early feedback processes, the nature of enriching sources, and the
topology of reionization. We run high-resolution cosmological simulations
including galactic outflows to study the observability and physical properties
of 5 ions (C II, C IV, O I, Si II, Si IV) in absorption between z=8->5. We
apply three cases for ionization conditions: Fully neutral, fully reionized,
and a patchy model based on the flux from the nearest galaxy. We find that our
simulations broadly fit available z~5-6 IGM metal-line data, although all
observations cannot be accommodated with a single ionization condition.
Variations in O I absorbers among sight lines seen by Becker et al. (2006)
suggest significant neutral IGM patches down to z~6. Strong C IV absorbers at
z~6 may be the result of ionization by their parent galaxy. Our outflows have
typical speeds of ~200 km/s and mass loading factors of ~6. Such high mass
loading is critical for enriching the IGM to the observed levels while
curtailing star formation to match the observed z~6 rest-frame UV luminosity
function. The volume filling factor of metals increases during this epoch, but
only reaches ~1% for Z>10^(-3) Zsolar by z=5. C IV is an ideal tracer of IGM
metals at z~5-6, with dropping global ionization fractions to either higher or
lower redshifts. This results in a strongly increasing global Omega(C IV) from
z=8->5, in contrast to its relative constancy from z=5->2. Our simulations do
not support widespread early IGM enrichment from e.g. Pop III stars. High-z
absorbers arise from metals on their first outward journey from galaxies, at
distances less than 50 kpc. The galaxies responsible for early IGM enrichment
have typical M*=10^(7.0-8.5) Msolar.Comment: Accepted to MNRAS, 34 pages, 24 figures, 1 table (Sections 5.5,
6.3.1, & 6.3.2 added as well as 5 figures and 1 table
Escape fraction of ionizing photons from high-redshift galaxies in cosmological SPH simulations
Combing the three-dimensional radiative transfer (RT) calculation and
cosmological SPH simulations, we study the escape fraction of ionizing photons
(f_esc) of high-redshift galaxies at z=3-6. Our simulations cover the halo mass
range of M_h = 10^9 - 10^12 M_sun. We postprocess several hundred simulated
galaxies with the Authentic Radiative Transfer (ART) code to study the halo
mass dependence of f_esc. In this paper, we restrict ourselves to the transfer
of stellar radiation from local stellar population in each dark matter halo. We
find that the average f_esc steeply decreases as the halo mass increases, with
a large scatter for the lower mass haloes. The low mass haloes with M_h ~ 10^9
M_sun have large values of f_esc (with an average of ~ 0.4), whereas the
massive haloes with M_h ~ 10^11 M_sun show small values of f_esc (with an
average of ~ 0.07). This is because in our simulations, the massive haloes show
more clumpy structure in gas distribution, and star-forming regions are
embedded inside these clumps, making it more difficult for the ionizing photons
to escape. On the other hand, in low mass haloes, there are often conical
regions of highly ionized gas due to the shifted location of young star
clusters from the center of dark matter halo, which allows the ionizing photons
to escape more easily than in the high-mass haloes. By counting the number of
escaped ionizing photons, we show that the star-forming galaxies can ionize the
intergalactic medium at z=3-6. The main contributor to the ionizing photons is
the haloes with M_h < 10^10 M_sun owing to their high f_esc. The large
dispersion in f_esc suggests that there may be various sizes of H{\sc ii}
bubbles around the haloes even with the same mass in the early stages of
reionization. We also examine the effect of UV background radiation field on
f_esc using simple, four different treatment of UV background.Comment: 13 pages, 13 figures, accepted for publication in MNRAS, A full
resolution version is available at
http://www.ccs.tsukuba.ac.jp/Astro/Members/yajima/Yajima2010.pd
A Deep HST Search for Escaping Lyman Continuum Flux at z~1.3: Evidence for an Evolving Ionizing Emissivity
We have obtained deep Hubble Space Telescope far-UV images of 15 starburst
galaxies at z~1.3 in the GOODS fields to search for escaping Lyman continuum
photons. These are the deepest far-UV images m_{AB}=28.7, 3\sigma, 1" diameter)
over this large an area (4.83 arcmin^2) and provide the best escape fraction
constraints for any galaxy at any redshift. We do not detect any individual
galaxies, with 3\sigma limits to the Lyman Continuum (~700 \AA) flux 50--149
times fainter (in f_nu) than the rest-frame UV (1500 \AA) continuum fluxes.
Correcting for the mean IGM attenuation (factor ~2), as well as an intrinsic
stellar Lyman Break (~3), these limits translate to relative escape fraction
limits of f_{esc,rel}<[0.03,0.21]. The stacked limit is
f_{esc,rel}(3\sigma)<0.02. We use a Monte Carlo simulation to properly account
for the expected distribution of IGM opacities. When including constraints from
previous surveys at z~1.3 we find that, at the 95% confidence level, no more
than 8% of star--forming galaxies at z~1.3 can have relative escape fractions
greater than 0.50. Alternatively, if the majority of galaxies have low, but
non-zero, escaping Lyman Continuum, the escape fraction can not be more than
0.04. Both the stacked limits, and the limits from the Monte Carlo simulation
suggest that the average ionizing emissivity (relative to non-ionizing UV
emissivity) at z~1.3 is significantly lower than has been observed in Lyman
Break Galaxies (LBGs) at z~3. If the ionizing emissivity of star-forming
galaxies is in fact increasing with redshift, it would help to explain the high
photoionization rates seen in the IGM at z>4 and reionization of the
intergalactic medium at z>6. [Abridged]Comment: Submitted to ApJ (Nov. 6) Comments Welcome. 11 pages, 8 figure
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