696 research outputs found
Physical and chemical effects of CO₂ storage in saline aquifers of the southern North Sea
Full text linkOne of the most promising mitigation strategies for greenhouse gas accumulation in
the atmosphere is carbon capture and storage (CCS). Deep saline aquifers are seen as the most efficient carbon dioxide (CO₂) storage sites, mainly because of their vast
size and worldwide distribution. Injecting CO₂ into brine filled media will cause a
physical and chemical disequilibrium in the formation. This PhD thesis documents
the investigation of some of the resulting effects which occur at the beginning of the
injection, during the injection period and millions of years after injection.
When CO₂ is injected into a brine filled reservoir, large amounts of in situ brine will
be displaced away from the injection well. This causes a pressure increase in the
vicinity of the well which may compromise the injection process. The simulation of this pressure increase was performed with the black-oil simulator Eclipse10 (Schlumberger) while using a number of recent formulas to predict the mutual
dissolution and the fluid properties of CO₂ and brine. The results show that the
pressure increase can exceed the maximum sustainable pore pressure and will cause
fracturing of the reservoir formation. The pore pressure increase is dependent on
parameters such as temperature and salinity because they change the fluid properties
of the CO₂ and brine, but also the capability of the fluids to dissolve mutually. The
mutual dissolution has generally a pressure reducing effect although its impact is
regarded to be overestimated. This is mainly because reservoir engineering software
cannot simulate the shock front realistically. Undulations, which appear on the
injection pressure profile are not a result of model instabilities but can either be
related to enhanced mutual dissolution due to grid effects, or to the software which
may overestimate or underestimate the pressure and dissolution. A detailed
investigation of those undulations is vital for the interpretation of the injection
pressure.
High fluid pressure can be an important parameter for the estimation of the CO₂
storage capacity of saline aquifers such as the offshore Bunter Sandstone Formation,
in the UK southern North Sea. Based on fluid pressure, the 1 storage capacity was
calculated using the ECLIPSE compositional simulation package and a simple
analytical equation. The estimated storage capacity is 6.55 to 7.17 Gt of CO₂
calculated with the analytical and the numerical approach respectively. By
comparing the results, the differences are relatively moderate and therefore the
application of the numerical simulator is not regarded as necessary. This is mainly
due to the effective pressure flow which prevents pressure accumulations underneath
the cap rock. Although the CO₂ storage capacity of the Bunter Sandstone Formation
remains high, a previous survey, which was not based on fluid pressure, calculated a
storage capacity approximately twice as high as the results presented here.
In theory, due to the increase in CO₂ concentration, CO₂ bearing carbonate minerals
could precipitate when CO₂ is injected into an aquifer such as the Rotliegend aquifer
in the southern North Sea. Geochemical models often predict a relatively rapid
growth of carbonate minerals as the most secure form of long term engineered CO₂
storage. But validation of model-results remains difficult due to the long periods of
time involved. Natural analogue studies can bridge the gap between experiments and
real-world storage. The Fizzy field, a southern North Sea (UK) gas accumulation
with a high natural CO₂ content (c. 50%) provides an ideal opportunity to study the
long term effect of CO₂ related mineral reaction. However all such reservoirs contain
‘normal’ diagenetic dolomite, so that distinguishing sequestration related dolomite is
a challenge. CO₂ was stepwise extracted from dolomite from both the Fizzy field and
the Orwell Rotliegend sandstone in order to reveal any zonation of the crystals which
could be related to enhanced dolomite precipitation due to the high CO₂
concentration. According to the method between 0 and 22 % of the dolomite in the
Fizzy field precipitated due to the high CO₂ concentration. Therefore, between 0 and
19 % of the CO₂, which is related to the relatively recent high CO₂ concentration, is
‘trapped’ in the ‘sequestration dolomite’. The wide range of this estimate is mainly
related to rock heterogeneity
[[alternative]]Niklas Luhmann’s Theory of Social Systems and Its Implication to the Educational Analysis
No full text[[abstract]]Niklas Luhmann’s Theory of Social Systems and Its Implication to the Educational Analysis
Abstract
This thesis aims to study Niklas Luhmann’s theory of social systems and its educational implications. The first chapter explores major problems and predicament in the study of education. It also points out contributions of Luhmann to educational studies. The second chapter traces sources of Luhmann’s theory of intellectual traditions. The third chapter then explicates the structure of Luhmann’s theory with an analysis of important ideas and concepts implicated in his works.These ideas and concepts include , for example , system , complexity , meaning , function , communication , self-reference and others. The fourth chapter discusses how Luhmann has reflected on current educational systems on the basis of his own theory. In particular,Chapter Five takes up Luhmann’s discussion in Reflexionsprobleme im Erziehungssystem. The last chapter , in conclusion , reviews major themes of this research , identifies the difficulties thus encountered, and suggests possible directions for future studies.
Triple oxygen isotopes of modern terrestrial mammalian tooth enamel – New implications for paleoenvironmental and physiological research
No full textBriefe aus der Verbannung / Tristia. Epistulae ex Ponto : Lateinisch - Deutsch /
No full textIm Jahre 8 n. Chr. wird Ovid aus nicht bekanntem Grund von Kaiser Augustus nach Tomis am Schwarzen Meer verbannt, an den Rand der zivilisierten Welt, in eine trostlose Gegend, in der niemand Latein spricht und die er bis zu seinem Tod 17 n. Chr. nicht mehr verlassen wird. Er beginnt, verzweifelte Briefe zu schreiben - man würde sie heute "Offene Briefe" nennen - und diese nach Rom zur Veröffentlichung zu schicken. Sie sind sorgsam dichterisch komponiert, der Stil ist geschliffen und sie haben nur ein Ziel: die öffentliche Meinung in Rom für ihn einzunehmen; erfolglos, wie wir wissen. Gleichwohl sind die Briefe bewegende Dokumente frühester Exil-Literatur. Sie wurden das ganze Mittelalter über gelesen und haben das moderne Bewusstsein Europas mitgeprägt. Die neue Einführung des Münchner Altphilologen Niklas Holzberg und die neuen besonders ausführlichen Anmerkungen zu den unzähligen versteckten Anspielungen in den Briefen untersuchen sorgfältig, was an Ovids Klagen echt und was "Literatur" ist, wo er unter der Unerträglichkeit des Exils tatsächlich leidet und wo er nur gängigen Vorstellungen über die Wildnis am Pontos Ausdruck verleiht. Eingeleitet und erläutert von Niklas Holzberg.Im Jahre 8 n. Chr. wird Ovid aus nicht bekanntem Grund von Kaiser Augustus nach Tomis am Schwarzen Meer verbannt, an den Rand der zivilisierten Welt, in eine trostlose Gegend, in der niemand Latein spricht und die er bis zu seinem Tod 17 n. Chr. nicht mehr verlassen wird. Er beginnt, verzweifelte Briefe zu schreiben - man würde sie heute "Offene Briefe" nennen - und diese nach Rom zur Veröffentlichung zu schicken. Sie sind sorgsam dichterisch komponiert, der Stil ist geschliffen und sie haben nur ein Ziel: die öffentliche Meinung in Rom für ihn einzunehmen; erfolglos, wie wir wissen. Gleichwohl sind die Briefe bewegende Dokumente frühester Exil-Literatur. Sie wurden das ganze Mittelalter über gelesen und haben das moderne Bewusstsein Europas mitgeprägt. Die neue Einführung des Münchner Altphilologen Niklas Holzberg und die neuen besonders ausführlichen Anmerkungen zu den unzähligen versteckten Anspielungen in den Briefen untersuchen sorgfältig, was an Ovids Klagen echt und was "Literatur" ist, wo er unter der Unerträglichkeit des Exils tatsächlich leidet und wo er nur gängigen Vorstellungen über die Wildnis am Pontos Ausdruck verleiht. Eingeleitet und erläutert von Niklas Holzberg.Electronic reproduction.Mode of access: Internet via World Wide Web.Description based on online resource; title from PDF title page (publisher’s Web site, viewed May 26, 2011
Scandal on campus. Dietrich Schwanitz reads Niklas Luhmann’s systems theory
Full text linkNiklas Luhmann (1927–1998) is one of the most distinguished sociologists of the twentieth cen-tury and the author of systems theory, which to a great extent has been accommodated into lin-guistics. Dietrich Schwanitz (1940–2004), an anglicist, is one of the most interesting interpreters of Luhmann on the basis of literary studies. Schwanitz is also known as a writer and author of the novel Campus (Der Campus, 1995). The main character, a sociologist, Hanno Hackmann, is wrongly accused of the sexual harassment and rape of a student. His reckless romance is exploited by various people in the university milieu to achieve their own goals. In fact, these people are, however, only the representatives of various social systems, especially politics and the media. Striving for re-election, the university rector needs this matter for his campaign, and the media are only interested in a scandalous story to be exploited for some time. Social communication does not reflect reality, and, at the same time, can be described as based on the “reduction of complexi-ty” (“Komplexitätsreduktion”). This is one of the most important concepts in Niklas Luhmann’s work. It turns out that systems theory provides the specific key to interpret the novel
Hydrogen storage in depleted gas fields: capacity and performance
Full text linkThe Paris Agreement to limit anthropogenic warming to 1.5 °C above pre-industrial
levels requires rapid reduction of greenhouse gas emissions. The UK has a large
natural gas demand which varies massively across the year, with peaks in winter up
to five times as high as the lows in summer. Decarbonising this system will require
an emissions-free alternative to natural gas coupled with large-scale seasonal
storage. Hydrogen can be used as an alternative to natural gas as it releases no
CO2 when burned. Hydrogen can also be used to store renewable electricity during
times of surplus, as well as buffering hydrogen production from natural gas coupled
with CCS. The aim of this thesis is to investigate the potential for seasonal storage
of hydrogen in depleted gas fields with a focus on the UK. There are three main
parts to this thesis: a regional capacity estimate for the UK continental shelf; a
reservoir engineering, geological modelling, and hydrogen storage simulation study
of an onshore gas field; and the development of an open-source tool for the
accurate estimation of the flow rates and cushion gas requirements of gas storage
sites.
A high-level assessment of gas fields on the UK continental shelf for hydrogen
storage potential was undertaken, alongside calculations of the seasonal storage
requirement for the 100% replacement of natural gas demand in the UK with
hydrogen. UK natural gas demand over the past five years has exceeded was 800
TWh with peak daily demand in winter reaching almost 5 TWh/day compared to
summer lows of 1 to 1.5 TWh/day. Using monthly demand data an estimate of 150
TWh of seasonal hydrogen storage is required to replace seasonal variations in
natural gas production. A method is determined to screen gas fields and saline
aquifers for suitability, however it is found that the estimates for saline aquifers are
extremely low confidence due to a lack of data. Gas fields are able to hold 13,800
TWh of hydrogen and assuming a cushion gas requirement of 50%, this gives a
value of 6900 TWh working gas capacity for hydrogen across 95 gas fields. Of these
85% are in the Southern North Sea which could utilise existing infrastructure and
large offshore wind developments to develop large-scale offshore hydrogen
production.
As depleted gas fields still contain some natural gas, there is a need to investigate
the effects of storing hydrogen in such a field. The Cousland gas field, a small, 0.9
billion cubic feet (BCF) gas field in Scotland was selected for a simulation study. The
field had previously been earmarked for town gas storage in the 1960s and so a
reservoir engineering study was performed using well testing and production data
from the 1930s to 1960s. From this study, a geological model was developed and
history matched against the results of the reservoir engineering study and
production data. Three one-well, 20 year hydrogen storage scenarios at different
pressures were then simulated. Hydrogen was injected for 2 years, allowed to settle
for 2 years, then 14 storage cycles of injection, storage, extraction, and empty were
completed before a final depletion of the cushion gas over 1 year. The initial volume
injected into the reservoir had little effect on the hydrogen recovery factor, storage
capacity, well flow rates, produced gas composition, and pressure response. The
extracted hydrogen showed less contamination with natural gas over time and the
results show that the mixed zone between the hydrogen and natural gas was
pushed further from the well with each subsequent storage cycle. The field has a
capacity of close to 1000 tonnes of hydrogen with recovery factors higher than 90%.
The natural gas in the reservoir behaved as a cushion gas, and hydrogen purity
could be controlled through injection strategies.
Cushion gas requirements for gas storage sites are important for both deliverability
and economics, and, outside of reservoir simulation studies, cushion gas
requirements are generally assumed. The final chapter of this thesis describes an
open-source program designed to improve these assumptions. The programs uses
basic reservoir parameters (original reservoir pressure, average permeability,
average porosity, formation thickness, depth, gas initially in place, and reservoir
temperature ) for volumetric gas fields to calculate the working and cushion gas
volumes, expected flow rates, and well performance. The program uses an open-source fluid property database (CoolProp) to model the properties of both methane
and hydrogen. LIT (laminar-inertial-turbulent) and pseudopressure equations are
used to solve the generalized radial-flow diffusivity equation which allows the
program to be used on reservoirs of all pressures. Bottom hole flowing pressure is
computed using the average temperature and compressibility method. As the
program is open-source the code can be downloaded and adjusted according to
need. The program is validated using data from four real gas storage sites. The
results from these four sites are used to compare hydrogen and methane gas
storage performance and finds that similar levels of performance can be achieved in
terms of energy deliverability with hydrogen showing significantly lower cushion gas
requirements than methane, particularly for the higher pressure, larger fields. The
results suggest that cushion gas requirements and deliverability are not entirely
dependent on reservoir properties but can be changed significantly by adjusting the
number of wells and well diameter. A simple economics model shows that this has
implications for the optimal number of wells drilled in a storage site
Pore-scale imaging of hydrogen displacement and trapping in porous media
Full text linkHydrogen can act as an energy store to balance supply and demand in the renewable energy sector. Hydrogen storage in subsurface porous media could deliver high storage capacities but the volume of recoverable hydrogen is unknown. We imaged the displacement and capillary trapping of hydrogen by brine in a Clashach sandstone core at 2–7 MPa pore fluid pressure using X-ray computed microtomography. Hydrogen saturation obtained during drainage at capillary numbers o
The Abstract Robot Simulator Manual
No full textRobot Simulator Manual Version 1.0 Sean P. Engelson Niklas Bertani YALEU/DCS/TR-XXX October 1992 This work was partially supported by the Defense Advanced Research Projects Agency, contract number DAAA15-87-K-0001, administered by the Ballistic Research Laboratory. The first author is supported by a fellowship from the Fannie and John Hertz Foundation Ars Magna The Abstract Robot Simulator Manual Version 1.0 Sean P. Engelson Niklas Bertani 0 This work was partially supported by the Defense Advanced Research Projects Agency, contract number DAAA15-87-K-0001, administered by the Ballistic Research Laboratory. The first author is supported by a fellowship from the Fannie and John Hertz Foundation Abstract AI planning research has historically operated in formal abstractions of the real world. This approach was useful in discovering many fundamental issues underlying planning; also, problems in simple domains such as the blocks world can turn out to be surprisingly difficult. Late..
Cross-Topic Author Identification -- a Case Study on Swedish Literature
Full text linkUsing material from the Swedish Literature Bank, we investigate whether common methods of author identification using word frequencies and part of speech frequencies are sensitive to differences in topic. The results show that this is the case, thereby casting doubt on much previous work in author identification. This sets the stage for a broader future study, comparing other methods and generalising the results
Manipulating Embeddings of Stable Diffusion Prompts
No full textSupplementary material of the paper Manipulating Embeddings of Stable Diffusion Prompts.
The paper can be found on arXiv: arXiv:2308.12059
Please cite as:
@Article{deckers:2023b,
author = {Niklas Deckers and Julia Peters and Martin Potthast},
title = {Manipulating Embeddings of Stable Diffusion Prompts},
journal = {CoRR},
volume = {abs/2308.12059},
url = {https://arxiv.org/abs/2308.12059},
month = aug,
year = 2023
- …
