49 research outputs found
Phosphorus-rich pyroxene in mantle xenoliths
No full textNumerous recent reports of detailed crystal zoning
patterns and anomalous enrichment in phosphorus (P) have
focused mainly on olivine from various settings [1-4]. P
enrichment and zoning in olivine have been attributed to
rapid crystal growth and development of disequilibrium as
well as to growth from P-rich melts. Here we report the
comparatively novel observation of elevated P in pyroxenes
from glass-bearing veins and pockets in a previously
undescribed xenolith from Cima Volcanic Field-CVF,
California; H.G. Wilshire (sample Ci-1-105) and in newly
collected mantle xenoliths from the Middle Atlas, Morocco.
Analytical techniques included optical microscopy, electron
microprobe and laser-ablation Inductively Coupled Plasma
Mass Spectrometry. We examine whether the P
concentrations in pyroxene (Px), although unusual, are in fact
anomalous compared to the adjacent glass concentration,
consider possible mechanisms for P enrichment, and correlate
the P enrichment in Px with indicators of metasomatism.
The petrogenetic history of each glassy region involves
melt intrusion, reaction with host minerals, cooling
accompanied by crystal growth, quench of glass, and possibly
later modifications. Secondary P-rich pyroxenes (P2O5 ~ 0.6
wt%) in a glassy pocket in the CVF xenolith are
homogeneous and surrounded by P-rich glass. They reflect
fairly slow near-equilibrium pyroxene growth after the melt
temperature became close to the host rock, with P
concentration in the melt buffered by apatite saturation. In the
Moroccan xenoliths, pyroxenes in a glassy vein exhibit
concentric zoning with P2O5 from 0.05 wt% (core) to ca. 0.3
wt% (intermediate) and then from 0.8 wt% (inner rim) to 1.2
wt% (outer rim). We attribute this to an accelerating rate of
crystal growth, with onset of a diffusive boundary layer pileup
effect and excess P incorporation near the pyroxene rim
Phosphorus-rich olivines in a composite xenolith from Morocco: implications for growth processes
No full textPhosphorus(P)-rich zones in olivine may reflect incorporation of P in excess of equilibrium
partitioning during rapid growth (e.g. Milman-Barris et al. 2008). We investigated (by optical
microscopy and electron microprobe) a composite mantle xenolith from the Middle Atlas
Mountains (Morocco) containing two lithologies, wehrlite and harzburgite, in direct contact. The
host alkali basalt (El Messbahi et al. 2015) is present on the margins of the hand sample but not
included in our thin section. Both lithologies display porphyroclastic texture and contain interstitial
devitrified glass. Large primary matrix olivine in both wehrlite and harzburgite has P2O5
concentrations ≤0.09 wt.% and nearly constant composition, Fo90, except for Fe-rich reaction rims
in contact with the interstitial devitrified glass. The P-rich interstitial spaces between these primary
matrix olivines consist of devitrified glass, secondary olivine, clinopyroxene, spinel, and apatite.
The secondary olivine ranges between Fo86-93 and is obviously enriched in P2O5, with
concentrations from 0.36-1.98 wt.%. Whereas matrix clinopyroxene in the wehrlite forms isolated
subhedral to euhedral crystals, the interstitial regions contain elongated and dendritic
clinopyroxene up to 10 μm long as well as replacive clinopyroxene rims on matrix minerals. Spinel
occurs as tiny discrete grains associated with the devitrified glass. Apatite is found only as very
small crystals embedded in devitrified glass.
High-resolution X-ray mapping of P in olivine reveals both alternating P-rich bands parallel to
crystal elongation and patchy zoning. P5+ correlates negatively with Si4+ (R = –0.90) and positively
with Na+ (R = +0.73). Correlation with total divalent cations (Mg2++Mn2++Fe2++Ca2++Ni2+) is weakly
negative (R = –0.44). Although correlation of P5+ and Al3+ is weak (R = -0.42), the combination
P5++Al3+ displays a better anticorrelation with Si4+ (R = –0.92). Overall, the observed correlations
suggest the predominant substitution mechanism is 2 IVSi4+ <=> IVP5+ + IVR3+, with some additional
accommodation by IVSi4+ +VIM2+ <=> IVP5+ + VINa+.
Because no glass was observed, the apparent olivine/melt partition coefficient could not be
directly measured. However, using the maximum P2O5 contents (1.05, 1.18 and 2.31 wt%) measured in glass in melt veins from other xenoliths from the a nearby Moroccan volcanic flow
(Baziotis et al. 2019) and the P-rich olivines from the present study, we infer a DP
ol/melt range
0.85-1.88. The most probable value is greater than unity, despite P being incompatible in olivine
during equilibrium growth. Such an apparent partitioning suggests that olivine crystallization was
rapid enough, ~1-10 K/hour, to develop a P-rich diffusive boundary layer from which the growing
olivine incorporated P in excess of equilibrium partitioning with the bulk melt pocket (Grant &
Kohn, 2013).
We consider several scenarios for the formation of the interstitial pockets, including partial melting
of the xenolith, intrusion of a metasomatic melt in an event earlier than eruption, and reaction
with the host lava during ascent
On the Color and Genesis of Prase (Green Quartz) and Amethyst from the Island of Serifos, Cyclades, Greece
No full textThe color of quartz and other minerals can be either caused by defects in the crystal structure or by finely dispersed inclusions of other minerals within the crystals. In order to investigate the mineral chemistry and genesis of the famous prase (green quartz) and amethyst association from Serifos Island, Greece, we used electron microprobe analyses and oxygen isotope measurements of quartz. We show that the color of these green quartz crystals is caused by small and acicular amphibole inclusions. Our data also shows that there are two generations of amphibole inclusions within the green quartz crystals, which indicate that the fluid, from which both amphiboles and quartz have crystallized, must have had a change in its chemical composition during the crystallization process. The electron microprobe data also suggests that traces of iron may be responsible for the amethyst coloration. Both quartz varieties are characterized by isotopic compositions that suggest mixing of magmatic and meteoric/marine fluids. The contribution of meteoric fluid is more significant in the final stages and reflects amethyst precipitation under more oxidizing conditions
Stamatis remarks on Freeman Article
No full textThis collection includes:
• Shaikh, A. (1984, April 7). Discussion of Willi Semmler and Peter Flashel on prices, profit, and sales [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (1983, March 7). Note on joint production: Differentiated capital [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (1984, April 6). Duncan Foley’s “Prices of production in a general model of production” [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (n.d.). Seminar/discussion notes with comments on the work of Duncan Foley, Peter Flashel, Gérard Duménil, and Bertram Schefold [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (1984, April 5–6). Marxian competition, neoclassical competition, and some implications: Response to Steedman/Morishima critique [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (1984, April 6). Joint production: Allocation of overhead costs for fixed capital and joint products [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (n.d.). Prices of production as centers of gravity, profitability, and traditional approaches to depreciation [Handwritten notes, citing Charles Landen, Dale Gerboth, & Thomas McRae, Accounting for depreciable assets (1975)]. Manuscript in possession of the author.
• Shaikh, A. (1984, April 5). Joint production: Equations and discussion of Flashel’s and Ian Steedman’s methods [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (n.d.). Piero Sraffa’s method, choice of technique, and prices of production [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (1977, March 21). Steedman on joint production [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (n.d.). Steedman example, referencing L. Mainwaring on the Sraffa joint-production system [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (n.d.). Schefold seminar: Joint product systems, pure fixed capital, competition, and accumulation [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (n.d.). Anomaly in aggregating production processes and infinite investment patterns [Handwritten notes]. Manuscript in possession of the author.
• Shaikh, A. (1984, April 6). S. P.: Duménil on the concept of negative value [Handwritten notes]. Manuscript in possession of the author
Replication Data for: Evaporation of Boron from Aluminoborosilicate Melt
No full textKey Points:
- Experiments on B2O3 evaporation from Ca- and Mg-bearing aluminoborosilicate melts were conducted at 1250 and 1350 °C for 60-1020 hours, under varying oxygen fugacities (FMQ-6 to FMQ+1.5) and in air.
- Results indicate that B evaporation increases by an order of magnitude under higher oxygen fugacities compared to reducing conditions, with two possible gas-phase speciation reactions for B2O3 suggested by Gibbs free energy minimization.
- B2O3 evaporation rate constants were calculated from the final glass compositions, showing slower evaporation rates than diffusion rates, indicating that evaporation is the rate-limiting process
Replication Data for: The stability of antigorite in subduction zones revisited: the effect of F on antigorite stability and its breakdown reactions at high pressures and high temperatures, with implications for the geochemical cycles of halogens
No full textWe present new experimental data on the effect of F on the stability of antigorite and its breakdown products at high pressures (2–6 GPa) and high temperatures (570–850 °C). The experiments show that F does not affect the stability of antigorite, but addition of F to the system affects which minerals are formed when antigorite breaks down. In a F-free system and in a system with intermediate F contents (2 wt% F), antigorite breaks down to olivine and orthopyroxene, but in a F-rich system (5 wt% F), antigorite breaks down to other hydrous and F-bearing mineral assemblages which include chlorite, clinohumite and humite-group minerals (HGM). Since the latter mineral phases are stable at higher pressures and temperatures, and contain more F than antigorite, significant amounts of F and potentially other halogens can be retained in the subducting slab and transported deep into the mantle and possibly even into the Earth’s transition zone
Traffic Safety of Disabled Pedestrians at Signalized Crosswalks
No full textMobility of disabled people has as a basic guarantee the traffic safety. Walking for disabled may have improved considerably compared to the past, but there are stillissues such as the safe crossing at signalized crosswalks. Also, the availability of studies on safe crossing for disabled pedestrians is limited. While it has been understood how pedestrians perceive safety at crosswalks, no similar study has been done for disabled pedestrians. The main purpose of this study is to fill the gap and make it more understandable how disabled pedestrians perceive traffic safety at signalized crosswalks. The literature showed significant factors that influence the pedestrian crossing behavior, such as the gender, the kind of disability, the presence of traffic lights at crosswalks, and weather conditions. Most ofthese factors are significantly related to the perception of safety.The main methodology included the interviews, and the survey, using the statistical analysis with the hypothesis tests and the Generalized Linear Model for the process of the data. The results proved that factors such as gender, age, kind of disability, the walking frequency had a significant impact on the perceived safety of disabled pedestrians. Yet, the study brought up important solutions that can improve safety perception, such as technological solutions like artificial intelligence traffic lights and infrastructure solutions such as the construction of underground crosswalks and refuges islands at long distance crosswalks. A recommendation is that the authorities and transport planners should emphasize to the solutions proposed to improve safety. A further scientific recommendation would the study of the objective safety in the future, comparing it with the perceived safety. This study has contributed significantly to the understanding of the issues faced by disabled pedestrians at crosswalks and it can be a starting point for further improvements in the mobility of disabled pedestrians and their lives in the future.Transport, Infrastructure and Logistic
Mechanical and corrosion behaviour of 3D printed aluminium bronzes produced by wire+arc additive manufacturing: In collaboration with RAMLAB
No full textThe emerging field of 3D printing has expanded to the fabrication of metallic components during the last decade. Among the most prominent applications is the production of aluminium bronze marine propellers by the Wire+Arc Additive Manufacturing (WAAM) method. This method incorporates a welding system attached to a robotic arm. The final product results after sequential bead depositions. The main assets of the method are the efficient material usage and the minimization of lead time, which both have a positive environmental and economic impact. The aim of this project is to evaluate the feasibility to produce 3D printed aluminium bronze (CMA and NAB alloys) blocks with the WAAM method and compare the mechanical and corrosion properties of the blocks with the market requirements. In order to achieve that, rectangular blocks were manufactured at the facilities of Delft University of Technology and at Rotterdam Additive Manufacturing Fieldlab (RAMLAB). Cross sectional areas were extracted and used for microstructural investigation and for hardness measurement. Subsequently, the blocks were machined to produce tensile and Charpy specimens along the built height. Finally, corrosion tests were performed, including open circuit potential measurements, polarization experiments and Scanning Kelvin Probe (SKP) tests.The microstructural investigation revealed that the 3D printed CMA block consisted of a banded structure. The deposited layers consisted of two dominant phases, α and β, and a variety of precipitates. The Widmanstätten α phase nucleates at the grain boundaries mainly. The tempering promotes the growth of the α phase, making the grain boundaries more indistinguishable, while the β phase decomposes.The mechanical testing results depicted that the hardness, the tensile strength and the absorption energy of the 3D printed blocks exceeded the specifications of the cast products, according to the ASTM standards. The built height direction is weaker than the welding direction; however, the deposition height plays no significant role in the mechanical properties. Samples were also tested after a heat treatment of 675 °C for 6 hours, as recommended in the literature. The result was a 25% reduction of the tensile yield strength and a 10% reduction of the ultimate tensile strength. However, the scatter in the measured values was reduced too. Regarding the corrosion results, the built height has little effect on the corrosion susceptibility, according to the polarization curves. The material exhibits a remarkable low corrosion rate, which justifies its use in marine applications. The Scanning Kelvin Probe (SKP) tests illustrated the beneficial aspect of the tempering heat treatment, which alleviates the large potential differences of adjacent deposited areas.It can be concluded that the CMA alloys are tolerable to the oscillations of the production parameters, making them appealing to the additive manufacturing industry. The mechanical properties achieved, outmatch not only the specifications for the cast CMA products, but also the performance of similar 3D printed aluminium bronze structures, found in the literature.Materials Science and Engineerin
Pesticide inputs from the sewage treatment plant of Agrinio to River Acheloos, western Greece: occurrence and removal
No full textPublisher‘s note. We regret that the published version of this article erroneously denoted the first author as corresponding author; in fact the formal corresponding author of this paper is Professor Ioannis Konstantinou, whose address is repeated below.</jats:p
Microgrid expansion planning using simulation-based optimization and reinforcement learning
No full textThis dissertation provides an analytical framework for tackling the long-term microgrid expansion planning problem. In the wake of the highly electrified future that is ahead of us, the need for reliable and economical power supply will become more urgent than ever. The role of microgrids in fulfilling this need is expected to be highly crucial. While there is a lot of active research going on related to developing optimization models for such systems, the current work innovates by considering both economic and reliability aspects, as well as the stochastic nature of various components in the energy industry. Furthermore, the fact that the microgrids will be placed at the core of the future energy systems will naturally give birth to another important problem from the planning perspective; this problem concerns the derivation of optimal strategies when expanding the microgrids, both in storage and power capacity. The criticality of formulating systematic, analytical and novel methodologies to tackle this problem can be easily justified by considering the steady growth of load demand, the technological advancements continuously being made, and the high operating costs incurred in these processes. The research work that can be found currently in the literature lacks in considering several peculiarities of microgrids. Moreover, many proposed approaches fail to provide realistic and complex-enough formulations due to the incompetence of traditional solution techniques in handling problems of that scale. The current research work serves as the first attempt to formulate a highly detailed long-term expansion planning problem in microgrid setting and solve it using advanced artificial intelligence techniques. Towards this direction, a simulation-based approach is developed to determine cost-optimal battery sizing under preset reliability constraints, and a unified dynamic optimization framework is built and used to derive holistic optimal expansion strategies. Overall, the goal of the present research work is to provide novel baseline models that give a well-shaped structure to the stochastic problem of long-term expansion planning, while utilizing advanced machine learning tools and techniques.Ph.D.Includes bibliographical reference
