393 research outputs found
A Model of Dynamic Resource Allocation in Workflow Systems
Current collaborative work environments are characterized by dynamically changing organizational structures. Although there have been several efforts to refine work distribution, especially in workflow management, most literature assumes a static database approach which captures organizational roles, groups and hierarchies and implements a dynamic roles based agent assignment protocol. However, in practice only partial information may be available for organizational models, and in turn a large number of exceptions may emerge at the time of work assignment. In this paper we present an organizational model based on a policy based normative system. The model is based on a combination of an intentional logic of agency and a flexible, but computationally feasible, non-monotonic formalism (Defeasible Logic). Although this paper focuses on the model specification, the proposed approach to modelling agent societies provides a means of reasoning with partial and unpredictable information as is typical of organizational agents in workflow system
Modelling dialogues for optimal legislation
This paper presents a framework for modelling legislative deliberation in the form of dialogues. Roughly, in legislative dialogues coalitions can dynamically change and propose rule-based theories associated with different utility functions, depending on the legislative theory the coalitions are trying to determine
High-resolution 40Ar/39Ar chronostratigraphy of the post-caldera (<20 ka) volcanic activity at Pantelleria, Sicily Strait
The island of Pantelleria (Sicily Strait), the type locality for pantellerite, has been the locus of major calderaforming
eruptions that culminated, ca. 50 ka ago, in the formation of the Cinque Denti caldera produced by the
Green Tuff eruption. The post-caldera silicic activity since that time has been mostly confined inside the caldera
and consists of smaller-energy eruptions represented by more than twenty coalescing pantelleritic centers
structurally controlled by resurgence and trapdoor faulting of the caldera floor. A high-resolution 40Ar/39Ar
study was conducted on key units spanning the recent (post-20 ka) intracaldera activity to better characterize
the present-day status (and forecast the short-term behavior of) the system based on the temporal evolution of
the latest eruptions. The new 40Ar/39Ar data capture a long-term (N15 ka) decline in eruption frequency with a
shift in eruptive pace from 3.5 ka−1 to 0.8 ka−1 associated with a prominent paleosol horizon marking the only
recognizable volcanic stasis around 12–14 ka. This shift in extraction frequency occurswithoutmajor changes in
eruptive style, and is paralleled by a subtle trend of decreasingmelt differentiation index. We speculate that this
decline probably occurred (i) without short-term variations in melt production/differentiation rate in a steadystate
compositionally-zoned silicic reservoir progressively tapped deeper through the sequence, and (ii) that it
was possibly modulated by outboard eustatic forcing due to the 140 m sea level rise over the past 21 ka. The
intracaldera system is experiencing a protracted stasis since 7 ka. Coupled with recent geodetic evidence of
deflation and subsidence of the caldera floor, the system appears today to be on a wane with no temporal
evidence for a short-term silicic eruption
An overview of the geochemical characteristics of oceanic carbonatites: New insights from Fuerteventura carbonatites (Canary islands)
The occurrence of carbonatites in oceanic settings is very rare if compared with their continental counterpart, having been reported only in Cape Verde and Canary Islands. This paper provides an overview of the main geochemical characteristics of oceanic carbonatites, around which many debates still exist regarding their petrogenesis. We present new data on trace elements in minerals and whole-rock, together with the first noble gases isotopic study (He, Ne, Ar) in apatite, calcite, and clinopyroxene from Fuerteventura carbonatites (Canary Islands). Trace elements show a similar trend as Cape Verde carbonatites, almost tracing the same patterns on multi-element and REE abundance diagrams.3He/4He isotopic ratios of Fuerteventura carbonatites reflect a shallow (sub-continental lithospheric mantle, SCLM) He signature in their petrogenesis, and they clearly differ from Cape Verde carbonatites, i.e., fluids from a deep and low degassed mantle with a primitive plume-derived He signature are involved in their petrogenesis
First measurements of the Fe oxidation state of spinel inclusions in olivine single crystals from Vulture (Italy) with the in situ synchrotron micro-Mössbauer technique
The redox state of the Earth's upper mantle (i.e., oxygen
fugacity, fO2) is a key variable that influences numerous processes
occurring at depth like the mobility of volatile species, partial melting,
and metasomatism. It is linked to the oxidation state of peridotite rocks,
which is normally determined through the available oxythermobarometers
after measuring the chemical composition of equilibrated rock-forming
minerals and the Fe3+ in redox-sensitive minerals like spinel or
garnet. To date, accurate measurements of Fe3+ / ∑Fe in peridotites
have been limited to those peridotites (e.g., harzburgites and lherzolites) for
which an oxythermobarometer exists and where spinel (or garnet) crystals
can be easily separated and measured by conventional 57Fe Mössbauer
spectroscopy. Wehrlitic rocks have been generally formed by the interaction of a
lherzolite with carbonatitic melts and, therefore, have recorded the passage of
(metasomatic) fluids at mantle conditions. However, no oxythermobarometer
exists to determine their equilibrium fO2.
The aim of this study was to retrieve the fO2 of the mantle beneath
Mt. Vulture volcano (Italy) through the study of a wehrlitic lapillus emitted
during the last eruption (∼ 140 kyr ago) that contain olivines
with multiple tiny spinel inclusions with sizes < 40 µm. To
our knowledge, the Fe oxidation state of these inclusions has been never
determined with the Mössbauer technique due to their small sizes.
Here, we present measurements of the Fe3+ / ∑Fe using in situ
synchrotron Mössbauer spectroscopy coupled with chemical and
spectroscopic analysis of both host olivine and spinel inclusions.
The results show Fe3+ / ∑Fe ratios of 0.03–0.05 for olivine and
0.40–0.45 for the included spinels, the latter of which appear higher than
those reported in literature for mantle spinel harzburgites and lherzolites.
Given the evidence of the mantle origin of the trapped spinels, we
propose that the high fO2 (between 0.81 and 1.00 log above the
fayalite–magnetite–quartz buffer; FMQ) likely results from the interaction
between the pristine spinel lherzolite and a CO2-rich metasomatic
agent prior to the spinel entrapment in olivines at mantle depths.</p
Diffuse and focused carbon dioxide and methane emissions from the Sousaki geothermal system, Greece
We report first data on chemical composition of the gas
emitted by the geothermal system of Sousaki, Greece. Gas
manifestations display typical geothermal gas composition
with CO2 as the main component and CH4 and H2S as
minor species. Soil gas composition derives from the
mixing of two end-members (atmospheric air and
geothermal gas). Soil CO2 fluxes range from<2 to
33,400 g m2 d1. The estimated diffuse output of
hydrothermal CO2, estimated for an area of 0.015 km2, is
about 630 g s1, while a tentative estimation of CH4 diffuse
output gave a value of about 1.15 g s
Septate uterus: nosographic overview and endoscopic treatment
To comment on the prevalence, diagnosis, and treatment of the septate uterus, with special reference to hysteroscopic metroplasty and its effect on reproductive outcome, we searched publications in PubMed and Embase. Original articles, meta-analysis, reviews, and opinion articles were selected. The studies suggest that the prevalence of the septate uterus is increased in women with repeated pregnancy loss and infertility. Reliable diagnosis depends on accurate assessment of the uterine fundal contour and uterine cavity by means of magnetic resonance and three-dimensional ultrasound. Pertinent published data comparing pregnancy outcome before and after hysteroscopic metroplasty indicated a marked improvement after surgery. Magnetic resonance and three-dimensional ultrasound represent the gold standard for diagnosis of septate uterus. Hysteroscopic metroplasty with its simplicity, minimal postoperative sequelae, and improved reproductive outcome is the gold standard for treatment, not only in patients with recurrent pregnancy loss and premature labor but also in patients with infertility, especially if in vitro fertilization is being contemplated
Timescale of Emplacement and Rheomorphism of the Green Tuff Ignimbrite (Pantelleria, Italy)
We present a multidisciplinary study based on Differential Scanning Calorimetry (DSC), paleomagnetic analysis, and numerical modeling to gain information on the timescales of syn- and post-depositional ductile deformation of the strongly welded and rheomorphic Green Tuff ignimbrite (GT; Pantelleria, Italy). DSC measurements allow the determination of glass fictive temperatures (Tf; i.e., the parameter accounting for the cooling dependence of glass structure and properties). Using a Tf-based geospeedometry procedure, we infer the cooling rate (qc) experienced by the glassy phases in different lithofacies within the GT formation. Glass shards from the basal pumice fall deposit record a fast qc of ∼10°C/s. In contrast, the ignimbrite body returns slow qc values depending on the stratigraphic position and lithofacies (basal/upper vitrophyres, fiamme-rich and rheomorphic layers), ranging from ∼10−2 to ∼10−6 °C/s. Moreover, paleomagnetic analyses of the natural remanent magnetization of ignimbrite matrix and embedded lithic clasts indicate an emplacement temperature higher than 550–600°C. By integrating calorimetric and paleomagnetic datasets, we constrain a conductive cooling model, describing the ignimbrite's temperature-time-viscosity (T–t–η) evolution from the eruptive temperature to below Tf. Outcomes suggest that the upper and basal vitrophyres deformed and quenched over hours, indicating that the entire GT underwent intense syn-depositional ductile deformation. Furthermore, the central body remained above Tf for a much longer timespan (>1 month), enabling post-emplacement rheomorphic flow. Lastly, we discuss the critical role of mechanisms such as shear heating and retrograde solubility of volatiles, in locally controlling the rheological behavior of the GT
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