1,419 research outputs found
Laboratory observations of slow earthquakes and the spectrum of tectonic fault slip modes
Slow earthquakes represent an important conundrum in earthquake physics. While regular
earthquakes are catastrophic events with rupture velocities governed by elastic wave speed,
the processes that underlie slow fault slip phenomena, including recent discoveries of tremor,
slow-slip and low-frequency earthquakes, are less understood. Theoretical models and sparse
laboratory observations have provided insights, but the physics of slow fault rupture remain
enigmatic. Here we report on laboratory observations that illuminate the mechanics of
slow-slip phenomena. We show that a spectrum of slow-slip behaviours arises near the
threshold between stable and unstable failure, and is governed by frictional dynamics via the
interplay of fault frictional properties, effective normal stress and the elastic stiffness of the
surrounding material. This generalizable frictional mechanism may act in concert with other
hypothesized processes that damp dynamic ruptures, and is consistent with the broad range
of geologic environments where slow earthquakes are observed
C ion-implanted TiO2 thin film for photocatalytic applications
Third-generation TiO2 photocatalysts were prepared by implantation of C+ ions into 110 nm thick TiO2 films. An accurate structural investigation was performed by Rutherford backscattering spectrometry, secondary ion mass spectrometry, X-ray diffraction, Raman-luminescence spectroscopy, and UV/VIS optical characterization. The C doping locally modified the TiO2 pure films, lowering the band-gap energy from 3.3 eV to a value of 1.8 eV, making the material sensitive to visible light. The synthesized materials are photocatalytically active in the degradation of organic compounds in water under both UV and visible light irradiation, without the help of any additional thermal treatment. These results increase the understanding of the C-doped titanium dioxide, helpful for future environmental applications. (C) 2015 AIP Publishing LLC
The visitors' perception of authenticity at the museums: Archaeology versus modern art
The aim of this paper is to analyse quantitatively the visitors' perception of authenticity in two different types of museums: archaeology versus modern and contemporary art. The research is based on 1288 questionnaires collected from June to September 2011 among the visitors of the South Tyrol Museum of Archaeology (ĂTZI) in Bolzano and the Museum of Modern and Contemporary Art (MART) in Trento-Rovereto. Logit models were used in order to estimate the set of independent variables that significantly influence both the perception of the authenticity and the 'virtual' choice between the two types of museums considered. The results suggested that the authenticity perception was related to peculiar authenticity-related factors and by specific socio-demographic characteristics of the interviewee, although some common elements emerge. In particular, ĂTZI authenticity is linked to its uniqueness in the world, whereas MART visitors relate authenticity to the museum's building and the perception that it was not just a tourist attraction. The empirical evidence confirms the well-known concept that authenticity perception is a dynamic experience, depending on the peculiar characteristics of the attraction analysed. © 2012 © 2012 Taylor & Francis
Visitors to two types of museums: Do expenditure patterns differ?
The authors study the determinants of the expenditure behaviour of visitors to two types of museums. Ad hoc surveys were conducted between June and September 2011 of visitors to the South Tyrol Museum of Archaeology and the Museum of Modern and Contemporaneous Art of Trento and Rovereto (MART). These are the two principal museums in the Italian provinces of Bolzano and Trento. The double-hurdle model is used via the Heien and Wessels two-step estimator. This procedure splits the process of spending decision into the stages of 'selection' and 'outcome', and also results in consistent estimates. The findings highlight two distinct profiles. The spending of visitors to the modern art museum is positively related to its cultural interest, whereas the expenditure profile of the archaeological museum visitors is more 'generalist'
A vigorous activity cycle mimicking a planetary system in HD200466
Stellar activity can be a source of radial velocity (RV) noise and can
reproduce periodic RV variations similar to those produced by an exoplanet. We
present the vigorous activity cycle in the primary of the visual binary
HD200466, a system made of two almost identical solar-type stars with an
apparent separation of 4.6 arcsec at a distance of 44+/-2 pc. High precision RV
over more than a decade, adaptive optics (AO) images, and abundances have been
obtained for both components. A linear trend in the RV is found for the
secondary. We assumed that it is due to the binary orbit and once coupled with
the astrometric data, it strongly constrains the orbital solution of the binary
at high eccentricities (e~0.85) and quite small periastron of ~21 AU. If this
orbital motion is subtracted from the primary radial velocity curve, a highly
significant (false alarm probability <0.1%) period of about 1300 d is obtained,
suggesting in a first analysis the presence of a giant planet, but it turned
out to be due to the stellar activity cycle. Since our spectra do not include
the Ca~II resonance lines, we measured a chromospheric activity indicator based
on the Halpha line to study the correlation between activity cycles and
long-term activity variations. While the bisector analysis of the line profile
does not show a clear indication of activity, the correlation between the
Halpha line indicator and the RV measurements identify the presence of a strong
activity cycle.Comment: Accepted on Astronomy and Astrophysics Main Journal 2014, 16 pages,
18 figure
© Author(s) 2008. This work is distributed under the Creative Commons Attribution 3.0 License. Natural Hazards and Earth System Sciences
Abstract. A major impediment to an understanding of the links between climate and landscape change, has been the relatively coarse resolution of landscape response measures (rates of weathering, sediment production, erosion and transport) relative to the higher resolution of the climatic signal (precipitation and temperature on hourly to annual time scales). A combination of high temporal and spatial resolution dendroclimatic and dendrogeomorphic approaches were used to study relationships between climatic variability and hillslope and valley floor dynamics in a small drainage basin in the Colorado Plateau of northeastern Arizona, USA Dendrogeomorphic and vegetation evidence from slopes and valley bottoms, including root exposure, bending of trunks, change in plant cover and burial and exhumation of valley bottom trees and shrubs, suggest that the currently observe
Radio emission from the high-mass X-ray binary BP Cru: first detection
BP Cru is a well known high-mass X-ray binary composed of a late B hypergiant
(Wray 977) and a neutron star, also observed as the X-ray pulsar GX 301-2. No
information about emission from BP Cru in other bands than X-rays and optical
has been reported to date in the literature, though massive X-ray binaries
containing black holes can have radio emission from a jet. In order to assess
the presence of a radio jet, we searched for radio emission towards BP Cru
using the Australia Compact Array Telescope during a survey for radio emission
from Be/X-ray transients. We probed the 41.5d orbit of BP Cru with the
Australia Telescope Compact Array not only close to periastron but also close
to apastron. BP Cru was clearly detected in our data on 4, possibly 6, of 12
occasions at 4.8 and 8.6 GHz. Our data suggest that the spectral index of the
radio emission is modulated either by the X-ray flux or the orbital phase of
the system. We propose that the radio emission of BP Cru probably arises from
two components: a persistent component, coming from the mass donor Wray 977,
and a periodic component connected to the accretion onto the neutron star,
possibly coming from a (weak and short lived) jet.Comment: 2 figures, accepted for publication in A+A letter
Astrocyte function is affected by aging and not Alzheimer's disease: A preliminary investigation in hippocampi of 3xTg-AD mice
Old age is a risk factor for Alzheimer's disease (AD), which is characterized by hippocampal impairment together with substantial changes in glial cell functions. Are these alterations due to the disease progression or are they a consequence of aging? To start addressing this issue, we studied the expression of specific astrocytic and microglial structural and functional proteins in a validated transgenic model of AD (3ĂTg-AD). These mice develop both amyloid plaques and neurofibrillary tangles, and initial signs of the AD-like pathology have been documented as early as three months of age. We compared male 3ĂTg-AD mice at 6 and 12 months of age with their wild-type age-matched counterparts. We also investigated neurons by examining the expression of both the microtubule-associated protein 2 (MAP2), a neuronal structural protein, and the brain-derived neurotrophic factor (BDNF). The latter is indeed a crucial indicator for synaptic plasticity and neurogenesis/ neurodegeneration. Our results show that astrocytes are more susceptible to aging than microglia, regardless of mouse genotype. Moreover, we discovered significant agedependent alterations in the expression of proteins responsible for astrocyte-astrocyte and astrocyte-neuron communication, as well as a significant age-dependent decline in BDNF expression. Our data promote further research on the unexplored role of astroglia in both physiological and pathological aging
Isolated, Massive Supergiants near the Galactic Center
We have carried out a pilot project to assess the feasibility of using radio,
infrared, and X-ray emission to identify young, massive stars located between 1
and 25 pc from the Galactic center. We first compared catalogs compiled from
the Very Large Array, the Chandra X-ray Observatory, and 2MASS. We identified
two massive, young stars: the previously-identified star that is associated
with the radio HII region H2, and a newly-identified star that we refer to as
CXOGC J174516.1-290315. The infrared spectra of both stars exhibit very strong
Br-gamma and He I lines, and resemble those of massive supergiants that have
evolved off of the main sequence, but not yet reached the Wolf-Rayet phase. We
estimate that each star has a bolometric luminosity >10^6 L_sun. The detection
of these two sources in X-rays is surprising, because stars at similar
evolutionary states are not uniformly bright X-ray sources. Therefore, we
suggest that both stars are in binary systems that contain either OB stars
whose winds collide with those of the luminous supergiants, or compact objects
that are accreting from the winds of the supergiants. We also identify X-ray
emission from a nitrogen-type Wolf-Rayet star and place upper limits on the
X-ray luminosities of three more evolved, massive stars that previously have
been identified between 1 and 25 pc from Sgr A*. Finally, we briefly discuss
the implications that future searches for young stars will have for our
understanding of the recent history of star formation near the Galactic center.
(abridged)Comment: 9 pages, including 8 figures. Submitted to ApJ, and modified in
response to referee's repor
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