3,313 research outputs found
Resource-driven Substructural Defeasible Logic
Linear Logic and Defeasible Logic have been adopted to formalise different
features relevant to agents: consumption of resources, and reasoning with
exceptions. We propose a framework to combine sub-structural features,
corresponding to the consumption of resources, with defeasibility aspects, and
we discuss the design choices for the framework
Ice melting and earthquake suppression in Greenland
It has been suggested that the Greenland ice sheet is the cause of earthquake
suppression in the region. With few exceptions, the observed seismicity
extends only along the continental margins of Greenland, which almost
coincide with the ice sheet margin. This pattern has been put forward as
further validation of the earthquake suppression hypothesis. In this review,
new evidence in terms of ice melting, post-glacial rebound and earthquake
occurrence is gathered and discussed to re-evaluate the connection between
ice mass unloading and earthquake suppression. In Greenland, the spatiotemporal
distribution of earthquakes indicates that seismicity is mainly con-
fined to regions where the thick layer of ice is absent and where significant ice
melting is presently occurring. A clear correlation between seismic activity
and ice melting in Greenland is not found. However, earthquake locations
and corresponding depth distributions suggest two distinct governing mechanisms:
post-glacial rebound promotes moderate-size crustal earthquakes at
Greenland’s regional scale, while current ice melting promotes shallow low
magnitude seismicity locall
Intermittent Sea Level Acceleration
Using instrumental observations from the Permanent Service for Mean Sea Level (PSMSL), we provide a new assessment of the global sea{level acceleration for the last 2 centuries (1820-2010). Our results, obtained
by a stack of tide gauge time series, con firm the existence of a global sea level acceleration (GSLA) and, coherently with independent assessments so far, they point to a value close to 0:01 mm/yr2. However, di fferently from
previous studies, we discuss how change points or abrupt inflections in individual sea level time series have contributed to the GSLA. Our analysis,
based on methods borrowed from econometrics, suggests the existence of
two distinct driving mechanisms for the GSLA, both involving a minority
of tide gauges globally. The first effectively implies a gradual increase in the rate of sea level rise at individual tide gauges, while the second is manifest
through a sequence of catastrophic variations of the sea level trend. These occurred intermittently since the end of the 19th century and became more frequent during the last four decades
Anomalous secular sea-level acceleration in the Baltic Sea caused by isostatic adjustment
Observations from the global array of tide gauges show that global sealevel
has been rising at an average rate of 1.5-2 mm/yr during the last
~150 years [Douglas 1991, Spada and Galassi 2012]. Although a global
sea-level acceleration was initially ruled out [Douglas 1992], subsequent
studies [Douglas 1997, Church and White 2006, Jevrejeva et al.
2008, Church and White 2011] have coherently proposed values of ~1
mm/year/century [Olivieri and Spada 2013]. More complex non-linear
trends and abrupt sea-level variations have now also been recognized.
Globally, these could manifest a regime shift between the late Holocene
and the current rhythms of sea-level rise [Gehrels and Woodworth 2013],
while locally they result from ocean circulation anomalies, steric effects
and wind stress [Bromirski et al. 2011, Merrifield 2011]. Although isostatic
readjustment affects the local rates of secular sea-level change
[Milne and Mitrovica 1998, Peltier 2004], a possible impact on regional
acceleration has been so far discounted [Douglas 1992, Jevrejeva et al.
2008, Woodworth et al. 2009] since the process evolves on a millennium
time scale [Turcotte and Schubert 2002]. Here we report a previously unnoticed
anomaly in the long-term sea-level acceleration of the Baltic Sea
tide gauge records, and we explain it by the classical post-glacial rebound
theory and numerical modeling of glacial isostasy. Contrary to previous
assumptions, our findings demonstrate that isostatic compensation plays
a role in the regional secular sea-level acceleration
Empirical mode decomposition of long-term polar motion observation
We use the Empirical Mode Decomposition (EMD) method to study the decadal variations in polar motion and its long-term trend since year 1900. The existence of the so-called “Markowitz wobble”, a multidecadal fluctuation of the mean pole of rotation whose nature has long been debated since its discovery in 1960, is confirmed. In the EMD approach, the Markowitz wobble naturally arises as an empirical oscillatory term in polar motion, showing significant amplitude variations and a period of approximately 3 decades. The path of the time-averaged, non-cyclic component of polar motion matches the results of previous investigations based on classical spectral methods. However, our analysis also reveals previously unnoticed steep variations (change points) in the rate and the direction of secular polar motion
Quality aware selective ECC for approximate DRAM
Approximate DRAMs are DRAM memories where energy saving techniques have been implemented by trading off bit-cell error rate with power consumption. They are considered part of the building blocks in the larger area of approximate computing. Relaxing refresh rate has been proposed as an interesting solution to achieve better efficiency at the expense of rising error rate. However, some works have demonstrated that much better results are achieved if at word-level some bits are retained without errors (i.e. their cells are refreshed at nominal rate), resulting in architectures using multiple refresh rates. In this paper we present a technique that can be applied to approximate DRAMs under reduced refresh rate. It allows to trim error rate at word-level, while still performing the refresh operation at the same rate for all cells. The number of bits that are protected is configurable and depends on output quality degradation that can be accepted by the application
Metastability and small eigenvalues in Markov chains
In this letter we announce rigorous results that elucidate the relation
between metastable states and low-lying eigenvalues in Markov chains in a much
more general setting and with considerable greater precision as was so far
available. This includes a sharp uncertainty principle relating all low-lying
eigenvalues to mean times of metastable transitions, a relation between the
support of eigenfunctions and the attractor of a metastable state, and sharp
estimates on the convergence of probability distribution of the metastable
transition times to the exponential distribution.Comment: 5pp, AMSTe
The FDA “black box” warning on antidepressant suicide risk in young adults: More harm than benefits?
The decision made in the year 2004 by the U.S. Food and Drug Administration (FDA) to require a boxed warning on antidepressants regarding the risk of suicidality in young adults still represents a matter of controversy. The FDA warning was grounded on industry-sponsored trials carried one decade ago or earlier. However, within the past decade, an increasing number of reports have questioned the actual validity of the FDA warning, especially considering a decline in the prescription of the antidepressant drugs associated with an increase in the rate of suicidal events among people with severe depression. The present report provides an overview of the FDA black box warning, also documenting two Major Depressive Disorder patients whose refusal to undergo a pharmacological antidepressant treatment possibly led to an increased risk for suicidal behaviors. The concerns raised by the FDA black box warning need to be considered in real-world clinical practice, stating the associated clinical and public health implications
Sea-level rise along the Emilia-Romagna coast (Northern Italy) in 2100: scenarios and impacts
As a consequence of climate change and land subsidence, coastal zones are
directly impacted by sea-level rise. In some particular areas, the effects on
the ecosystem and urbanisation are particularly enhanced. We focus on the
Emilia-Romagna (E-R) coastal plain in Northern Italy, bounded by the Po river
mouth to the north and by the Apennines to the south. The plain is
∼ 130 km long and is characterised by wide areas below mean sea
level, in part made up of reclaimed wetlands. In this context, several
morphodynamic factors make the shore and back shore unstable. During next
decades, the combined effects of land subsidence and of the sea-level rise as
a result of climate change are expected to enhance the shoreline instability,
leading to further retreat. The consequent loss of beaches would impact the
economy of the region, which is tightly connected with tourism
infrastructures. Furthermore, the loss of wetlands and dunes would threaten
the ecosystem, which is crucial for the preservation of life and the
environment. These specific conditions show the importance of a precise
definition of the possible local impacts of the ongoing and future climate
variations. The aim of this work is the characterisation of vulnerability in
different sectors of the coastal plain and the recognition of the areas in
which human intervention is urgently required. The Intergovernmental Panel on
Climate Change (IPCC) Fifth Assessment Report (AR5) sea-level scenarios are
merged with new high-resolution terrain models, current data for local
subsidence and predictions of the flooding model in_CoastFlood in
order to develop different scenarios for the impact of sea-level rise
projected to year 2100. First, the potential land loss due to the combined
effect of subsidence and sea-level rise is extrapolated. Second, the increase
in floodable areas as a result of storm surges is quantitatively determined.
The results are expected to support the regional mitigation and adaptation
strategies designed in response to climate change
Metastable States, Relaxation Times and Free-energy Barriers in Finite Dimensional Glassy Systems
In this note we discuss metastability in a long-but-finite range disordered
model for the glass transition. We show that relaxation is dominated by
configuration belonging to metastable states and associate an in principle
computable free-energy barrier to the equilibrium relaxation time. Adam-Gibbs
like relaxation times appear naturally in this approach.Comment: 4 pages, 2 figures. Typos correcte
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