10,506 research outputs found
Unfolding Rates for the Diffusion-Collision Model
In the diffusion-collision model, the unfolding rates are given by the
likelihood of secondary structural cluster dissociation. In this work, we
introduce an unfolding rate calculation for proteins whose secondary structural
elements are -helices, modeled from thermal escape over a barrier which
arises from the free energy in buried hydrophobic residues. Our results are in
good agreement with currently accepted values for the attempt rate.Comment: Shorter version of cond-mat/0011024 accepted for publication in PR
Spreading The Char: The Importance of Local Compatibility in the Diffusion of Biochar Systems to the Smallholder Agriculture Community Context
This thesis enters the context of smallholder agriculture communities in the developing world. It explores the potentials of biochar and what biochar systems could bring to the smallholder communities while simultaneously bringing environmental benefits. It then acknowledges the challenges of diffusion –the spreading of an unfamiliar innovation. It seeks to answer the question of what will make diffusion of biochar systems more successful in the smallholder context, fixating on the characteristic of compatibility as well as the role local community members can play in making a new biochar system more visible to the rest of the communities
Size effects in multiferroic BiFeO3 nanodots: A first-principles-based study
An effective Hamiltonian scheme is developed to investigate structural and
magnetic properties of BiFeO3 nanodots under short-circuit-like electrical
boundary conditions. Various striking effects are discovered. Examples include
(a) scaling laws involving the inverse of the dots' size for the magnetic and
electric transition temperatures; (b) the washing out of some structural phases
present in the bulk via size effects; (c) the possibility of tailoring the
difference between the Neel and Curie temperatures, by playing with the size
and electrical boundary conditions; and (d) an universal critical thickness of
the order of 1.6 nm below which the dots do not possess any long-range ordering
for the electrical and magnetic dipoles, as well as, for the oxygen octahedral
tiltings.Comment: 3 figure
1RXS J180408.9-342058: an ultra compact X-ray binary candidate with a transient jet
We present a detailed NIR/optical/UV study of the transient low mass X-ray
binary 1RXS J180408.9-342058 performed during its 2015 outburst, aimed at
determining the nature of its companion star. We obtained three optical spectra
at the 2.1 m San Pedro Martir Observatory telescope (Mexico). We performed
optical and NIR photometric observations with both the REM telescope and the
New Technology Telescope (NTT) in La Silla. We obtained optical and UV
observations from the Swift archive. Finally, we performed optical polarimetry
of the source by using the EFOSC2 instrument mounted on the NTT. The optical
spectrum of the source is almost featureless since the hydrogen and He I
emissions lines, typically observed in LMXBs, are not detected. Similarly,
carbon and oxygen lines are neither observed. We marginally detect the He II
4686 AA emission line, suggesting the presence of helium in the accretion disc.
No significant optical polarisation level was observed. The lack of hydrogen
and He I emission lines in the spectrum implies that the companion is likely
not a main sequence star. Driven by the tentative detection of the He II 4686
AA emission line, we suggest that the system could harbour a helium white
dwarf. If this is the case, 1RXS J180408.9-342058 would be an ultra-compact
X-ray binary. By combining an estimate of the mass accretion rate together with
evolutionary tracks for a He white dwarf, we obtain a tentative orbital period
of ~ 40 min. On the other hand, we also built the NIR-optical-UV spectral
energy distribution (SED) of the source at two different epochs. One SED was
gathered when the source was in the soft X-ray state, and it is consistent with
the presence of a single thermal component. The second SED, obtained when the
source was in the hard X-ray state, shows a thermal component together with a
tail in the NIR, likely indicating the presence of a (transient) jet.Comment: 8 pages, 5 figures, 4 tables. Accepted for publication in Astronomy &
Astrophysics (Section 7
Independent Configurable Architecture for Reliable Operation of Unmanned Systems with Distributed Onboard Services
This paper presents the development of ICAROUS-2 (Independent Configurable Architecture for Reliable Operation of Unmanned Systems with Distributed Onboard Services), the second generation of a software architecture that integrates several algorithms as distributed onboard services to enable robust autonomous UAS applications. In particular, the ICAROUS architecture defines a framework to perform detect and avoid, geofencing, path monitoring, path planning, and autonomous decision making to ensure safety and mission progress. Most of the core algorithms implemented in ICAROUS are formally verified using an interactive theorem prover. These algorithms are composed together using a plan execution engine, whose operational semantics is formally specified. A description of the integrated architecture, services currently available, and flight test results highlighting the capability of ICAROUS are presented
Young Super Star Clusters in the Starburst of M82: The Catalogue
Recent results from Hubble Space Telescope (HST) have resolved starbursts as
collections of compact young stellar clusters. Here we present a photometric
catalogue of the young stellar clusters in the nuclear starburst of M82,
observed with the HST WFPC2 in Halpha (F656N) and in four optical broad-band
filters. We identify 197 young super stellar clusters. The compactness and high
density of the sources led us to develop specific techniques to measure their
sizes. Strong extinction lanes divide the starburst into five different zones
and we provide a catalogue of young super star clusters for each of these. In
the catalogue we include relative coordinates, radii, fluxes, luminosities,
masses, equivalent widths, extinctions, and other parameters. Extinction values
have been derived from the broad-band images. The radii range between 3 and 9
pc, with a mean value of 5.7 +/- 1.4pc, and a stellar mass between 10e4 and
10e6 Mo. The inferred masses and mean separation, comparable to the size of
super star clusters, together with their high volume density, provides strong
evidence for the key ingredients postulated by Tenorio et al. (2003) as
required for the development of a supergalactic wind.Comment: 45 pages, 5 figures, 12 tables. Accepted for publication in ApJ.
Added Erratu
Spin injection in a single metallic nanoparticle: a step towards nanospintronics
We have fabricated nanometer sized magnetic tunnel junctions using a new
nanoindentation technique in order to study the transport properties of a
single metallic nanoparticle. Coulomb blockade effects show clear evidence for
single electron tunneling through a single 2.5 nm Au cluster. The observed
magnetoresistance is the signature of spin conservation during the transport
process through a non magnetic cluster.Comment: 3 page
Radio continuum properties of luminous infrared galaxies. Identifying the presence of an AGN in the radio
Luminous infrared galaxies are systems enshrouded in dust, which absorbs most
of their optical/UV emission and re-radiates it in the mid- and far-infrared.
Radio observations are largely unaffected by dust obscuration, enabling us to
study the central regions of LIRGs in an unbiased manner. The main goal of this
project is to examine how the radio properties of local LIRGs relate to their
infrared spectral characteristics. Here we present an analysis of the radio
continuum properties of a subset of the Great Observatories All-sky LIRG Survey
(GOALS), which consists of 202 nearby systems (z<0.088). Our radio sample
consists of 35 systems, or 46 individual galaxies, that were observed at both
1.49 and 8.44 GHz with the VLA with a resolution of about 1 arcsec (FWHM). The
aim of the project is to use the radio imagery to probe the central kpc of
these LIRGs in search of active galactic nuclei. We used the archival data at
1.49 and 8.44 GHz to create radio-spectral-index maps using the standard
relation between flux density Sv and frequency v, S~v^-a, where a is the radio
spectral index. By studying the spatial variations in a, we classified the
objects as radio-AGN, radio-SB, and AGN/SB (a mixture). We identified the
presence of an active nucleus using the radio morphology, deviations from the
radio/infrared correlation, and spatially resolved spectral index maps, and
then correlated this to the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII]
line ratios and EQW of the 6.2 um PAH feature) and optical (BPT diagram) AGN
diagnostics. We find that 21 out of the 46 objects in our sample are radio-AGN,
9 are classified as starbursts (SB), and 16 are AGN/SB. After comparing to
other AGN diagnostics we find 3 objects out of the 46 that are identified as
AGN based on the radio analysis, but are not classified as such based on the
mid-infrared and optical AGN diagnostics presented in this study.Comment: 33 pages, 7 figures, 5 tables, to appear in A&
VALES: IV. Exploring the transition of star formation efficiencies between normal and starburst galaxies using APEX/SEPIA Band-5 and ALMA at low redshift
In this work we present new APEX/SEPIA Band-5 observations targeting the CO
() emission line of 24 Herschel-detected galaxies at .
Combining this sample {with} our recent new Valpara\'iso ALMA Line Emission
Survey (VALES), we investigate the star formation efficiencies (SFEs =
SFR/) of galaxies at low redshift. We find the SFE of our sample
bridges the gap between normal star-forming galaxies and Ultra-Luminous
Infrared Galaxies (ULIRGs), which are thought to be triggered by different star
formation modes. Considering the as the SFR and the
ratio, our data show a continuous and smooth increment as a function of
infrared luminosity (or star formation rate) with a scatter about 0.5 dex,
instead of a steep jump with a bimodal behaviour. This result is due to the use
of a sample with a much larger range of sSFR/sSFR using LIRGs, with
luminosities covering the range between normal and ULIRGs. We conclude that the
main parameters controlling the scatter of the SFE in star-forming galaxies are
the systematic uncertainty of the conversion factor, the gas
fraction and physical size.Comment: 9pages, 7 figures, 1 table, accepted for publication in MNRA
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