4,864 research outputs found
Analysis of Different Methodologies to Calculate Bouguer Gravity Anomalies in the Argentine Continental Margin
We have tested and used two methods to determine the Bouguer gravity anomaly in the area of the Argentine continental margin. The first method employs the relationship between the topography and gravity anomaly in the Fourier transform domain using Parker’s expression for different orders of expansion. The second method computes the complete Bouguer correction (Bullard A, B and C) with the Fortran code FA2BOUG2. The Bouguer slab correction (Bullard A), the curvature correction (Bullard B) and the terrain correction (Bullard C) are computed in several zones according to thedistances between the topography and the calculation point. In each zone, different approximations of the gravitationalattraction of rectangular or conic prisms are used according to the surrounding topography. Our calculations show that the anomaly generated by the fourth order in Parker’s expansion is actually compatible with the traditional Bouguer anomaly calculated with FA2BOUG, and that higher orders do not introduce significant changes. The comparison reveals that the difference between both methods in the Argentine continental margin has a quasi bimodal statistical distribution. The main disadvantage in using routines based on Parker's expansion is that an average value of the topography is needed for the calculation and, as the margin has an abrupt change of the topography in the continental slope area, it causes a bimodal distribution. It is worth noticing that, as expected, the most important differences between both methods are located over the continental slope both in complex structures such as part of the shared margin, as well as in isolated points where there are contributions from short wavelength or rugged topography.Fil: Pedraza de Marchi, Ana Carolina. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y GeofÃsicas; ArgentinaFil: Ghidella, Marta E.. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; ArgentinaFil: Tocho, Claudia. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y GeofÃsicas; Argentin
On the Globular Cluster IMF below 1 Solar Mass
(Abridged) Accurate luminosity functions (LF) for a dozen globular clusters
have now been measured at or just beyond their half-light radius using HST.
They span almost the entire cluster main sequence below ~ 0.75 Msolar. All
these clusters exhibit LF that rise continuously from an absolute I magnitude
M_I ~ 6 to a peak at M_I ~ 8.5-9 and then drop with increasing M_I.
Transformation of the LF into mass functions (MF) by means of the most recent
mass luminosity relations that are consistent with all presently available data
on the physical properties of low mass, low metallicity stars shows that all
the LF observed so far can be obtained from MF having the shape of a log-normal
distribution with characteristic mass m_c=0.33 +/- 0.03 Msolar and standard
deviation sigma = 1.81 +/- 0.19. After correction for the effects of mass
segregation, the variation of the ratio of the number of higher to lower mass
stars with cluster mass or any simple orbital parameter or the expected time to
disruption recently computed for these clusters shows no statistically
significant trend over a range of this last parameter of more than a factor of
100. We conclude that the global MF of these clusters have not been measurably
modified by evaporation and tidal interactions with the Galaxy and, thus,
should reflect the initial distribution of stellar masses. Since the log-normal
function that we find is also very similar to the one obtained independently
for much younger clusters and to the form expected theoretically, the
implication seems to be unavoidable that it represents the true stellar IMF for
this type of stars in this mass range.Comment: Accepted for publication in The Astrophysical Journal. Contains 28
pages with 6 figure
Why haven't loose globular clusters collapsed yet?
We report on the discovery of a surprising observed correlation between the
slope of the low-mass stellar global mass function (GMF) of globular clusters
(GCs) and their central concentration parameter c=log(r_t/r_c), i.e. the
logarithmic ratio of tidal and core radii. This result is based on the analysis
of a sample of twenty Galactic GCs with solid GMF measurements from deep HST or
VLT data. All the high-concentration clusters in the sample have a steep GMF,
most likely reflecting their initial mass function. Conversely,
low-concentration clusters tend to have a flatter GMF implying that they have
lost many stars via evaporation or tidal stripping. No GCs are found with a
flat GMF and high central concentration. This finding appears
counter-intuitive, since the same two-body relaxation mechanism that causes
stars to evaporate and the cluster to eventually dissolve should also lead to
higher central density and possibly core-collapse. Therefore, more concentrated
clusters should have lost proportionately more stars and have a shallower GMF
than low concentration clusters, contrary to what is observed. It is possible
that severely depleted GCs have also undergone core collapse and have already
recovered a normal radial density profile. It is, however, more likely that GCs
with a flat GMF have a much denser and smaller core than suggested by their
surface brightness profile and may well be undergoing collapse at present. In
either case, we may have so far seriously underestimated the number of post
core-collapse clusters and many may be lurking in the Milky Way.Comment: Four pages, one figure, accepted for publication in ApJ Letter
Partition of unity interpolation using stable kernel-based techniques
In this paper we propose a new stable and accurate approximation technique
which is extremely effective for interpolating large scattered data sets. The
Partition of Unity (PU) method is performed considering Radial Basis Functions
(RBFs) as local approximants and using locally supported weights. In
particular, the approach consists in computing, for each PU subdomain, a stable
basis. Such technique, taking advantage of the local scheme, leads to a
significant benefit in terms of stability, especially for flat kernels.
Furthermore, an optimized searching procedure is applied to build the local
stable bases, thus rendering the method more efficient
RBF approximation of large datasets by partition of unity and local stabilization
We present an algorithm to approximate large dataset by Radial Basis Function
(RBF) techniques. The method couples a fast domain decomposition procedure with a
localized stabilization method. The resulting algorithm can efficiently deal with large
problems and it is robust with respect to the typical instability of kernel methods
The Mass Function of Main Sequence Stars in NGC6397 from Near IR and Optical High Resolution HST Observations
We have investigated the properties of the stellar mass function in the
globular cluster NGC6397 using a large set of HST observations that include
WFPC2 images in V and I, obtained at ~4' and 10' radial distances, and a series
of deep images in the J and H bands obtained with the NIC2 and NIC3 cameras of
NICMOS pointed to regions located ~4.5' and ~3.2' from the center. These
observations span the region from ~1 to ~3 times the cluster's half-light
radius. All luminosity functions, derived from color magniutde diagrams,
increase with decreasing luminosity up to a peak at M_I~8.5 or M_H~7 and then
precipitously drop well before photometric incompleteness becomes significant.
Within the observational uncertainties, at M_I~12 or M_H~10.5 (~0.09 Msun) the
luminosity functions are compatible with zero. By applying the best available
mass- luminosity relation appropriate to the metallicity of NGC6397 to both the
optical and IR data, we obtain a mass function that shows a break in slope at
\~0.3 Msun. No single exponent power-law distribution is compatible with these
data, regardless of the value of the exponent. We find that a dynamical model
of the cluster can simultaneously reproduce all the luminosity functions
observed throughout the cluster only if the IMF rises as m**-1.6 in the range
0.8-0.3 Msun and then drops as m**0.2 below ~0.3 Msun. Adopting a more physical
log-normal distribution for the IMF, all these data taken together imply a best
fit distribution with characteristic mass m_c~0.3 and sigma~1.8.Comment: 18 pages, 6 figures (ps). Accepted for publication in Ap
Late movement of basin-edge lobate scarps on Mercury
Basin-edge lobate scarps are a sub-type of tectonic shortening structure on the surface of Mercury that have formed at the edge of volcanic units that fill or partly fill impact basins. We have performed a global survey of these features and find that they are widespread in basins across the planet. We obtained model ages from crater size–frequency distribution analysis for a subset of our surveyed basins, for both the smooth plains infill and for the last resolvable tectonic activity on the associated basin-edge scarps. Our results indicate that some of these lobate scarps were still accumulating strain in the late Mansurian (approximately 1 Ga). From a photogeological assessment, we find that the orientations of these basin-edge lobate scarps are similar to those reported for the global population of lobate scarps in earlier studies, appearing to align ∼north–south at low latitudes and ∼east–west at higher latitudes. However, reassessing these landforms’ orientation with artificially illuminated topographic data does not allow us to rule out the effect of illumination bias. We propose that these landforms, the result of crustal shortening in response to global contraction, formed along the interface between the basin floor and the smooth plains unit, which acted as a mechanical discontinuity along which shortening strains were concentrated
The Effect of Narrow-Band Transmission on Recognition of Paralinguistic Information From Human Vocalizations
Practically, no knowledge exists on the effects of speech coding and recognition for narrow-band transmission of speech signals within certain frequency ranges especially in relation to the recognition of paralinguistic cues in speech. We thus investigated the impact of narrow-band standard speech coders on the machine-based classification of affective vocalizations and clinical vocal recordings. In addition, we analyzed the effect of speech low-pass filtering by a set of different cut-off frequencies, either chosen as static values in the 0.5-5-kHz range or given dynamically by different upper limits from the first five speech formants (F1-F5). Speech coding and recognition were tested, first, according to short-term speaker states by using affective vocalizations as given by the Geneva Multimodal Emotion Portrayals. Second, in relation to long-term speaker traits, we tested vocal recording from clinical populations involving speech impairments as found in the Child Pathological Speech Database. We employ a large acoustic feature space derived from the Interspeech Computational Paralinguistics Challenge. Besides analysis of the sheer corruption outcome, we analyzed the potential of matched and multicondition training as opposed to miss-matched condition. In the results, first, multicondition and matched-condition training significantly increase performances as opposed to mismatched condition. Second, downgrades in classification accuracy occur, however, only at comparably severe levels of low-pass filtering. The downgrades especially appear for multi-categorical rather than for binary decisions. These can be dealt with reasonably by the alluded strategies
The effects of the target material properties and layering on the crater chronology: the case of Raditladi and Rachmaninoff basins on Mercury
In this paper we present a crater age determination of several terrains
associated with the Raditladi and Rachmaninoff basins. These basins were
discovered during the first and third MESSENGER flybys of Mercury,
respectively. One of the most interesting features of both basins is their
relatively fresh appearance. The young age of both basins is confirmed by our
analysis on the basis of age determination via crater chronology. The derived
Rachmaninoff and Raditladi basin model ages are about 3.6 Ga and 1.1 Ga,
respectively. Moreover, we also constrain the age of the smooth plains within
the basins' floors. This analysis shows that Mercury had volcanic activity
until recent time, possibly to about 1 Ga or less. We find that some of the
crater size-frequency distributions investigated suggest the presence of a
layered target. Therefore, within this work we address the importance of
considering terrain parameters, as geo-mechanical properties and layering, into
the process of age determination. We also comment on the likelihood of the
availability of impactors able to form basins with the sizes of Rachmaninoff
and Raditladi in relatively recent times.Comment: Accepted by PSS, to appear on MESSENGER Flybys special issu
Disastri Naturali e Dynamic Capabilities nel Commercio
Il presente contributo descrive i primi risultati emersi da un’indagine esplorativa volta ad esaminare l’impatto che il terremoto del 2012 ha prodotto sulle attività commerciali al dettaglio della bassa emiliana. L’obiettivo specifico è quello di analizzare la capacità di risposta di tali tipologie di imprese all’evento critico adottando la prospettiva teorica delle capacità dinamiche. Si tratta di temi che la letteratura corrente non ha affrontato in modo sistematico ed adeguato in condizioni di criticità , soprattutto con riferimento al contesto della distribuzione al dettaglio.
La metodologia scelta si è basata sull’utilizzo di strumenti di analisi qualitativa quali focus group e interviste semi-strutturate a un campione di dettaglianti colpiti dal sisma, caratterizzati da diverse specializzazioni merceologiche e parametri dimensionali. I primi risultati hanno evidenziato le risorse e le competenze ritenute necessarie per essere competitivi prima del sisma (qualità del servizio e assistenza alla clientela nel momento della vendita), nella gestione dell’evento critico (tempestività di reazione, creatività e flessibilità nella gestione dell’emergenza, sia nei rapporti con la clientela che con i fornitori; la necessità di rivedere l’offerta e di modificare l’assortimento) e in prospettiva futura (capacità di lettura del mercato, innovazione, acquisizione di nuove competenze tramite percorsi di formazione). Ne emergono alcune implicazioni manageriali e di policy
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