104 research outputs found
The solutions of the 3rd and 4th Clay Millennium problems
In this treatise I present the solutions of the third Clay Millennium problem
in the computational complexity and the fourth Clay Millennium problem in
classical fluid dynamics.Comment: arXiv admin note: text overlap with arXiv:1108.1165 by other author
Synthesis and Characterization of High Temperature Cement-Based Hydroceramic Materials
Cement-based materials are of importance in the construction of geothermal wells
and high-temperature oil and gas wells. These materials fill the annulus between the
well casing and the rock forming a protective layer, known as sealant, which is used
primarily to secure and support the casing inside the well. In addition it prevents
entry of unwanted fluids into the well and communication between formation fluids at
different levels. These cement based sealants need to perform for many years at
high temperatures and in severe chemical environments; conditions which can
cause the material of the well-casing to degrade resulting in reduced strength and
increased permeability.
The aim of this study is to develop new materials which will have the potential
properties (high strength and low permeability) for use as sealants in geothermal
and deep, hot oil wells. In order to do this special cement slurries, based on the
CaO−Al2O3−SiO2−H2O (CASH) hydroceramic system, have been synthesised over
the temperature range 200 to 350 °C (i.e. the typical working temperature of these
wells). The additives used in these cement slurries are silica flour and alumina.
A detailed description of a suite of novel hydroceramic compositions over the
temperature range 200 to 350 °C is given. X-ray diffraction has been used to
determine the mineralogical composition and Rietveld refinement to quantify the
known phases present at different temperatures. In addition the chemistry of some
of the major phases present has been examined using electron probe microanalysis.
Scanning electron microprobe and simulation software have been employed to
study the crystal shape of these major minerals.
The engineering properties of the hydroceramic materials are very important. A
study of the compressive strength and permeability has been carried out over a
range of temperature (200 to 350 °C). In addition permeability has been calculated
using simulation software and the results compared with experimental values.
Hydroceramic formulations with excellent strength and permeability measurements
have been found. Some of these formulations have been tested for durability under
simulated well conditions. These materials have been immersed into different brines
for a certain period of time at temperatures between 200 to 300 °C. Some
preliminary results regarding the changes in mineralogy in these samples are
presented in this thesis. These experiments have been carried out at the
Synchrotron Radiation Source (SRS) using tomographic energy-dispersive
diffraction imaging (TEDII)
Towards the identification of miRNAs targeting the translational machinery as novel cancer therapeutics
Increased protein production is a prerequisite for cell proliferation, thus rendering translation and ribosome deregulation a common hallmark of cancer cell biology. A frequently observed mechanism in malignancies is the overactivation of the translational process. As a consequence, strategies that selectively target the ribosomal machinery bear significant promise as cancer therapeutic approaches. To this end, this report provides a workflow for the identification of novel miRNA molecules with the ability to target and suppress ribosomal activity in cancer cells
A versatile classification tool for galactic activity using optical and infrared colors
(abridged) The overwhelming majority of diagnostic tools for galactic
activity are focused on active galaxies. Passive or dormant galaxies are often
excluded from these diagnostics which usually employ emission line features. In
this work, we use infrared and optical colors in order to build an
all-inclusive galactic activity diagnostic tool that can discriminate between
star-forming, AGN, LINER, composite, and passive galaxies, and which can be
used in local and low-redshift galaxies. We explore classification criteria
based on infrared colors from the 3 WISE bands supplemented with optical colors
from the u, g, and r SDSS bands. From these we aim to find the minimal
combination of colors for optimal results. Furthermore, to mitigate biases
related to aperture effects, we introduce a new WISE photometric scheme combing
different sized apertures. We develop a diagnostic tool using machine learning
methods that includes both active and passive galaxies under one unified scheme
using 3 colors. We find that the combination of W1-W2, W2-W3, and g-r colors
offers good performance while the broad availability of these colors for a
large number of galaxies ensures wide applicability on large galaxy samples.
The overall accuracy is 81% while the achieved completeness for each
class is 81% for star-forming, 56% for AGN, 68% for LINER,
65% for composite, and 85% for passive galaxies. Our diagnostic
provides a significant improvement over existing IR diagnostics by including
all types of active, as well as passive galaxies, and extending them to the
local Universe. The inclusion of the optical colors improves their performance
in identifying low-luminosity AGN which are generally confused with
star-forming galaxies, and helps to identify cases of starbursts with extreme
mid-IR colors which mimic obscured AGN galaxies, a well-known problem for most
IR diagnostics.Comment: Accepted for publication in the A&A journal. The code for the
application of our model can be accessed through the GitHub repository in
https://github.com/BabisDaoutis/GalActivityClassifie
Star-formation rate and stellar mass calibrations based on infrared photometry and their dependence on stellar population age and extinction
The stellar mass () and the star-formation rate (SFR) are among the
most important features that characterize galaxies. Measuring these fundamental
properties accurately is critical for understanding the present state of
galaxies, and their history. This work explores the dependence of the IR
emission of galaxies on their extinction, and the age of their stellar
populations (SPs). It aims at providing accurate IR SFR and
calibrations that account for SP age and extinction while quantifying their
scatter. We use the CIGALE spectral energy distribution (SED) fitting code to
create models of galaxies with a wide range of star-formation histories, dust
content, and interstellar medium properties. We fit the relations between
and SFR with IR and optical photometry of the model-galaxy SEDs with
the MCMC method, and perform a machine-learning random forest analysis on the
same data set in order to validate the latter. This work provides calibrations
for the SFR using a combination of the WISE bands 1 and 3, or the JWST F200W
and F2100W bands. It also provides mass-to-light ratio calibrations based on
the WISE band-1, or the JWST band F200W, along with the optical or
colors. These calibrations account for the biases attributed to the SP age,
while they are given in the form of extinction-dependent and
extinction-independent relations. They show robust estimations while minimizing
the scatter and biases throughout a wide range of SFRs and stellar masses. The
SFR calibration offers better results, especially in dust-free or passive
galaxies where the contributions of old SPs or biases from the lack of dust are
significant. Similarly, the calibration yields significantly better
results for dusty/high-SFR galaxies where dust emission can otherwise bias the
estimations.Comment: 18 pages, 10 figures. Accepted for publication in Astronomy &
Astrophysics on 16 March 202
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The effect of autonomy in sustaining social entrepreneurial intention through management education: the cases of Malaysia and Scotland
he study examines what is the role of autonomy on individual social entrepreneurial intention (EI) for students. Furthermore, it examines the differences between the emerging market setting and developed market to gather an understanding of context differences. Using principal component analysis the study finds that the motivators of EI can be divided into 5 components. Following from that the autonomy variable can be divided into 3 sub components. The results present differences in propensity towards EI in the two country settings along with differences in propensity towards social entrepreneurship. The results are unique as they test EI variables from the literature on social entrepreneurship and in an emerging market context. The role of autonomy as a bridge between education and attitude or intention is presented
A Comparative Performance Evaluation of Algorithms for the Analysis and Recognition of Emotional Content
Sentiment Analysis is highly valuable in Natural Language Processing (NLP) across domains, processing and evaluating sentiment in text for emotional understanding. This technology has diverse applications, including social media monitoring, brand management, market research, and customer feedback analysis. Sentiment Analysis identifies positive, negative, or neutral sentiments, providing insights into decision-making, customer experiences, and business strategies. With advanced machine learning models like Transformers, Sentiment Analysis achieves remarkable progress in sentiment classification. These models capture nuances, context, and variations for more accurate results. In the digital age, Sentiment Analysis is indispensable for businesses, organizations, and researchers, offering deep insights into opinions, sentiments, and trends. It impacts customer service, reputation management, brand perception, market research, and social impact analysis. In the following experimental research, we will examine the Zero-Shot technique on pre-trained Transformers and observe that, depending on the Model we use, we can achieve up to 83% in terms of the model’s ability to distinguish between classes in this Sentiment Analysis problem
Study on the effectiveness of commercial anti‐islanding algorithms in the prospect of mass penetration of PVs in low‐voltage distribution networks
In the coming years, distribution grids will be progressively flooded by renewable energy sources (RES) that will be interconnected with the main grid through power electronic converters. Photovoltaics (PVs) are one of the most promising renewable technologies even for densely built-up areas where space problems are inevitable. The high penetration prospect of PV facilities on low-voltage distribution networks raises questions regarding the necessity of advanced functions that will enable electronically coupled RES to support the operation of distribution grids and to enhance their reliability. In this context, the objective of this study is to investigate the effectiveness of various islanding prevention measures installed in commercial PV inverters, when multiple inverters are operating in parallel with a low-voltage distribution network (LVDN). Extensive experiments were performed under various PV penetration levels, linear/non-linear load and over/under voltage and over/under frequency conditions, as well as for various values of total harmonic distortion of the mains voltage. Further to the primary statistical analysis, the results were analysed in depth by advanced mathematical methods such as box plot and cluster analysis. The findings of this study indicate that commercial anti-islanding techniques present a high probability of failure in the case of multiple PV units at the same point of common coupling, calling for new and more advanced algorithms.European Commission, H2020, 65411
The String Light Cone in the pp-wave Background
In this letter, we determine the particle and the string light cone in the
pp-wave background. The result is a deformed version of the flat one. We point
out the light cone exhibits an intriguing periodicity in the light cone time
direction x^+ with a period \sim 1/ \mu. Our results also suggest that a
quantum theory in the pp-wave background can be formulated consistently only if
the background is periodic in the light cone time x^+.Comment: 10 pages. v2: references and comments adde
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