18 research outputs found
De synthese en rheologie van enige vloeibaar kristallijne zijketen polyacrylaten
No full textApplied SciencesTechnologie van makromolekulaire stoffe
Polymeriseerbaarheid van macromonomeren: Literature study
No full textIn de literatuur wordt vaak twijfel geuit over het vermogen van macromonomeren om te polymeriseren. Macromonomeren zijn monomeren die bestaan uit een polymeerketen met aan het uiteinde een of andere functionele groep. De macromonomeren vormen een belangrijke klasse monomeren omdat ze een eenvoudige route naar de synthese van ent copolymeren verschaffen door copolymerisatie met laagmoleculaire monomeren. Deze scriptie is het resultaat van een literatuurstudie naar de polymeriseerbaarheid van macromonomeren, waarbij vooral de homopolymerisatie is bestudeerd. De synthese van macromonomeren, copolymerisatie met kleine monomeren en de karakterisering van polymacromonomeren worden ook behandeld...Applied SciencesScheikundige Technologie en de MateriaalkundeTechnologie van Macromoleculaire Stoffe
Verbetering van het transportproces - Met minder kosten van productie naar klant
No full textDe begeleider en/of auteur heeft geen toestemming gegeven tot het openbaar maken van de scriptie.
The supervisor and/or the author did not authorize public publication of the thesis.
Conjugate comparison of Super Dual Auroral Radar Network and Cluster electron drift instrument measurements of E × B plasma drift
No full textContinued fractions which correspond to two series expansions and the strong Hamburger moment problem
No full textJust as the denominator polynomials of a J-fraction are
orthogonal polynomials with respect to some moment functional, the
denominator polynomials of an M-fraction are shown to satisfy a skew
orthogonality relation with respect to a stronger moment functional.
Many of the properties of the numerators and denominators of an M-
fraction are also studied using this pseudo orthogonality relation
of the denominator polynomials. Properties of the zeros of the
denominator polynomials when the associated moment functional is
positive definite are also considered.
A type of continued fraction, referred to as a J-fraction, is
shown to correspond to a power series about the origin and to another
power series about infinity such that the successive convergents of
this fraction include two more additional terms of anyone of the
power series. Given the power series expansions, a method of
obtaining such a J-fraction, whenever it exists, is also looked at.
The first complete proof of the so called strong Hamburger moment
problem using a continued fraction is given. In this case the
continued fraction is a J-fraction.
Finally a special class of J-fraction, referred to as positive
definite J-fractions, is studied in detail.
The four chapters of this thesis are divided into sections.
Each section is given a section number which is made up of the
chapter number followed by the number of the section within the
chapter. The equations in the thesis have an equation number
consisting of the section number followed by the number of the
equation within that section.
In Chapter One, in addition to looking at some of the
historical and recent developments of corresponding continued
fractions and their applications, we also present some preliminaries.
Chapter Two deals with a different approach of understanding
the properties of the numerators and denominators of corresponding
(two point) rational functions and, continued fractions. This
approach, which is based on a pseudo orthogonality relation of the
denominator polynomials of the corresponding rational functions,
provides an insight into understanding the moment problems. In
particular, results are established which suggest a possible type
of continued fraction for solving the strong Hamburger moment
problem.
In the third chapter we study in detail the existence
conditions and corresponding properties of this new type of continued
fraction, which we call J-fractions. A method of derivation of one
of these 3-fractions is also considered. In the same chapter we also
look at the all important application of solving the strong Hamburger
moment problem, using these 3-fractions.
The fourth and final chapter is devoted entirely to the study
of the convergence behaviour of a certain class of J-fractions,
namely positive definite J-fractions. This study also provides some
interesting convergence criteria for a real and regular 3-fraction.
Finally a word concerning the literature on continued fractions
and moment problems. The more recent and up-to-date exposition on
the analytic theory of continued fractions and their applications is
the text of Jones and Thron [1980]. The two volumes of Baker and
Graves-Morris [1981] provide a very good treatment on one of the
computational aspects of the continued fractions, namely Pade
approximants. There are also the earlier texts of Wall [1948] and
Khovanskii [1963], in which the former gives an extensive insight
into the analytic theory of continued fractions while the latter,
being simpler, remains the ideal book for the beginner. In his
treatise on Applied and Computational Complex Analysis, Henrici
[1977] has also included an excellent chapter on continued fractions.
Wall [1948] also includes a few chapters on moment problems and
related areas. A much wider treatment of the classical moment
problems is provided in the excellent texts of Shohat and Tamarkin
[1943] and Akhieser [1965]
Silicates with incorporation of NH4+, Rb+, or Cs+
No full textThis thesis presents results of an experimental study on the incorporation of NH4+,
Rb +, and Cs + in micas and feldspars. The studied micas are dioctahedral. The feldspars are
sanidine-like.
In chapter II it is shown that the ammonium analogue of muscovite, called tobelite,
with the formula NH4AlzSi~AlOlO(OHhcan be synthesized using NH3 in water, sal volatile
or urea as donors for NH4 . The synthesis conditions may be quite high, even 500 oC at a
pressure of 4 to 5 kbar. These synthesis pressures are higher than ones reported up to now
in the literature, and they demonstrate that tobelite is not necessarily a mineral that is
restricted to low pressure and temperature environments. All tobelite found so far seem
to have formed at low temperature and pressure. In the literature, tobelite is mentioned to
occur in relationship to fossil fuel deposits, and in chapter II it is elucidated why such a
relationship may occur.
The synthesis of NH4AlSi30 Il, its characterization with XRD, SEM and IRspectroscopy,
its study by thermal analyses, and its morphological description are reported
in Chapter III. NH4AlSi30& is very close in structure to sanidine (KAlSi30 g). The similarities
of NH4AlSi30 g with the mmeral buddingtonite (NH4AlSi30 g.VzH;P) are so striking, that it
is likely that buddingtonite and the ammonium analogue of sanidme are the same. The first
description of buddingtonite reports that it has zeolitic properties. The half mole of lattice
water in NH4AlSi30 g.VzH20 is, according to descriptions in the literature, not present in the
structure in an ordered way.
A detailed study (Chapter IV) of the original samples of buddingtonite, kindly made
available by the principal author of the article in which buddingtonite was described firstly,
shows that the zeolitic properties, as well as the lattice water can be ascribed to an admixture
of montmorillonite, a clay mineral, in the original samples. Buddingtonite is not redefined
in chapter IV, but it is strongly suggested to consider buddingtonite and NH4AlSi30 g as the
same silicates and to disregard the zeolitic half mole of water of buddingtonite.
Chapter V describes the synthesis and characterization of the Rb-analogue of 2M!muscovite
(RbAlzSi3AlOlO(OHh) and comparison of this silicate with muscovite and other
dioctahedral micas. Chapter VI describes the synthesis, characterization, morphology and
structure of the Rb-analogue of sanidine (RbAlSi30 11). To get an indication of the influence of the mcorporation of Rb in muscovite and
sanidine on the reaction of muscovite to sanidine, corundum and water, the location of the
equilibrium of the reaction of RbAlzSi3AlOlO(OHh to RbAlSi1()g, corundum and water
was studied at 2 kbar. The results are also given in chapter VI, and indicate that the
temperature at which the equilibrium is probably situated is only slightly higher (probably
maximal 20 DC) than for the reaction of the K-silicates. If complete replacement of K by Rb
does not have much effect, incorporation of Rb in muscovite and sanidine on trace element
level will probably not influence the position of the equilibrium at all.
In chapter VII, the incorporation of Rb in muscovite by ion-exchange is studied.
Muscovite as well as its Rb-analogue are brought in contact with alkali cWoride solutions to
establish ion exchange of K and Rb. All exchange experiments are carried out at a pressure
of 2 kbar. The most important result is that there exists a solvus between the endmembers
RbAlltSi3AlOlO(OHh and KAlZSi3AlOlO(OHh (muscovite). The exact location of the solvus
remams somewhat unclear, which is probably caused by the ability of micas to form
intergrowths.
Chapter VIII gives an account of the synthesis and characterization of a Cs-containing
mica with a structure resembling that of muscovite. On basis of the data it can not be proven
that the mica is the Cs-analogue of muscovite, because no accurate chemical analyses could
be gathered. The mica is formed at a temperature of 400 DC at 2 kbar and at 400 DC and 500
DC at pressures of 2 and 5 kbar. Investigated conditions are 300, 400, 500 and 600 DC at
pressures of 0.5,2, and 5 kbar. Pollucite (CsAlSiz06) always occurs together with the mica,
as well as another Al-containing phase (boehmite, or diaspore or corundum, depending on
the conditions
An examination of inter-hemispheric conjugacy in a subauroral polarization stream
No full textDuring geomagnetically disturbed conditions the midlatitude ionosphere is subject to intense poleward directed electric fields in the dusk-midnight sector. These electric fields lead to the generation of a latitudinally narrow westward directed flow channel in the subauroral region called a subauroral polarization stream (SAPS). If the magnetic field lines are treated as equipotentials, electrodynamic events such as SAPS are expected to occur simultaneously at magnetically conjugate locations with similar features. In this paper we present simultaneous observations of a SAPS event in both hemispheres made by midlatitude SuperDARN radars with conjugate fields-of-view. We analyze the relation between the geomagnetic conditions and the characteristics of the channels such as latitudinal location, electric field, total potential variations across the channels, and Pedersen current. The results suggest a strong correlation between the strength of the ring current and the latitudinal location of the channel. An inter-hemispheric comparison of the characteristics of the channel indicates that the potential variations across the channels are similar while the electric fields, Pedersen currents and latitudinal widths of the channel exhibit differences that are consistent with equal potential variations. We attribute these differences to seasonal differences in ionospheric conductivity between the hemispheres and magnetic distortion effects in the inner magnetosphere
Latitudinal phytoplankton distribution and the neutral theory of biodiversity
No full textAim
Recent studies have suggested that global diatom distributions are not limited by dispersal, in the case of both extant species and fossil species, but rather that environmental filtering explains their spatial patterns. Hubbell's neutral theory of biodiversity provides a framework in which to test these alternatives. Our aim is to test whether the structure of marine phytoplankton (diatoms, dinoflagellates and coccolithophores) assemblages across the Atlantic agrees with neutral theory predictions. We asked: (1) whether intersite variance in phytoplankton diversity is explained predominantly by dispersal limitation or by environmental conditions; and (2) whether species abundance distributions are consistent with those expected by the neutral model.
Location
Meridional transect of the Atlantic (50° N–50° S).
Methods
We estimated the relative contributions of environmental factors and geographic distance to phytoplankton composition using similarity matrices, Mantel tests and variation partitioning of the species composition based upon canonical ordination methods. We compared the species abundance distribution of phytoplankton with the neutral model using Etienne's maximum-likelihood inference method.
Results
Phytoplankton communities are slightly more determined by niche segregation (24%), than by dispersal limitation and ecological drift (17%). In 60% of communities, the assumption of neutrality in species’ abundance distributions could not be rejected. In tropical zones, where oceanic gyres enclose large stable water masses, most communities showed low species immigration rates; in contrast, we infer that communities in temperate areas, out of oligotrophic gyres, have higher rates of species immigration.
Conclusions
Phytoplankton community structure is consistent with partial niche assembly and partial dispersal and drift assembly (neutral processes). The role of dispersal limitation is almost as important as habitat filtering, a fact that has been largely overlooked in previous studies. Furthermore, the polewards increase in immigration rates of species that we have discovered is probably caused by water mixing conditions and productivity
Dynamic subauroral ionospheric electric fields observed by the Falkland Islands radar during the course of a geomagnetic storm
No full textWe present an analysis of ionospheric electric field data observed during a geomagnetic
storm by the recently deployed HF radar located on the Falkland Islands. On 3 August
2010 at ∼1800 UT evidence of the onset of a geomagnetic storm was observed in ground
magnetometer data in the form of a decrease in the Sym‐H index of ∼100 nT. The
main phase of the storm was observed to last ∼24 hours before a gradual recovery lasting
∼3 days. On 4 August, during the peak magnetic disturbance of the storm, a high velocity
(>1000 m s−1) channel of ionospheric plasma flow, which we interpret as a subauroral
ion drift (SAID), located between 53° and 58° magnetic south and lasting ∼6.5 hours, was
observed by the Falkland Islands radar in the pre‐midnight sector. Coincident flow data
from the DMSP satellites and the magnetically near‐conjugate northern hemisphere
Blackstone HF radar reveal that the SAID was embedded within the broader subauroral
polarization streams (SAPS). DMSP particle data indicate that the SAID location closely
followed the equatorward edge of the auroral electron precipitation boundary, while
remaining generally poleward of the equatorward boundary of the ion precipitation. The
latitude of the SAID varied throughout the interval on similar timescales to variations in
the interplanetary magnetic field and auroral activity, while variations in its velocity were
more closely related to ring current dynamics. These results are consistent with SAID
electric fields being generated by localized charge separation in the partial ring current, but
suggest that their location is more strongly governed by solar wind driving and associated
large‐scale magnetospheric dynamics
