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Performance Evaluation of Powerline Technology on Low Voltage Distribution Networks
Powerline technology (PLT) employs the electrical distribution network to transmit data in addition to supplying power. PLT is currently employed to provide data networking in many domestic environments, and is expected to play a major part in the development of the forthcoming Smart Grid.
Given that the electrical distribution network was not designed with data transmission in mind, electromagnetic radiation from the network can give rise to interference. Regulators and researchers have considered the impact of such widespread radiation, and investigations of the various aspects of powerline have been conducted over the last decade. Despite this prolonged period, however, there remains a lack of agreement on the typical performance of such networks or the implications for regulation policy.
An accurate model of the radio frequency (RF) properties of the typical electrical distribution network would be extremely valuable in developing standards and informing policy. The aim of this thesis is to provide a cohesive approach to determining the RF characteristics of a typical domestic property and applying such parameters to model the performance of PLT.
The thesis reviews the recent development of broadband PLT, the progress made by the more prominent regulators, and the trials undertaken to define the key parameters affecting propagation. A detailed experimental programme carried out both in the laboratory and at typical sites is described.
An empirical model of the RF performance of a UK domestic low voltage distribution network (LVDN) is developed from analysis of the experimental results. It is shown via this analysis that discrete measurements of the conducted and radiated parameters can be related and that the RF performance of the LVDN can be described by Conversion and Radiated Loss. The radiated field is shown to comprise the combined common mode current to the LVDN and common bonding network (CBN).
The thesis concludes with consideration of the future development of powerline technology, particularly in support of the Smart Grid development
Extended radio emission in MOJAVE Blazars: Challenges to Unification
We present the results of a study on the 1.4 GHz kpc-scale radio emission in
the complete flux density limited MOJAVE sample, comprising 135 radio-loud
AGNs. While extended emission is detected in the majority of the sources, about
7% of the sources exhibit only radio core emission. Many BL Lacs exhibit
extended radio power and kpc-scale morphology typical of powerful FRII jets,
while a substantial number of quasars possess radio powers intermediate between
FRIs and FRIIs. This poses challenges to the simple radio-loud unified scheme,
which links BL Lacs to FRIs and quasars to FRIIs. We find a significant
correlation between extended radio emission and pc-scale jet speeds: the more
radio powerful sources possess faster jets. This indicates that the 1.4 GHz (or
low frequency) radio emission is indeed related to jet kinetic power. Various
properties such as extended radio power and apparent pc-scale jet speeds vary
smoothly between different blazar subclasses, suggesting that, at least in
terms of radio jet properties, the distinction between quasars and BL Lac
objects, at an emission-line equivalent width of 5 Angstrom is essentially an
arbitrary one. Based on the assumption that the extended radio luminosity is
affected by the kpc-scale environment, we define the ratio of extended radio
power to absolute optical magnitude as a proxy for environmental effects.
Trends with this parameter suggest that the pc-scale jet speeds and the
pc-to-kpc jet misalignments are not affected by the large-scale environment,
but are more likely to depend upon factors intrinsic to the AGN, or its local
pc-scale environment. We suggest that some of the extremely misaligned MOJAVE
blazar jets could be "hybrid" morphology sources, with an FRI jet on one side
and an FRII jet on the other. (Abridged)Comment: 40 pages, 16 figures, accepted for publication in Ap
Radio-optical scrutiny of compact AGN: Correlations between properties of pc-scale jets and optical nuclear emission
We study the correlations between the Very Long Baseline Array radio emission
at 15 GHz, extended emission at 151 MHz, and optical nuclear emission at 5100
AA for a complete sample of 135 compact jets. We use the partial Kendall's tau
correlation analysis to check the link between radio properties of parsec-scale
jets and optical luminosities of host AGN. We find a significant positive
correlation for 99 quasars between optical nuclear luminosities and total radio
(VLBA) luminosities of unresolved cores at 15 GHz originated at milliarcseconds
scales. For 18 BL Lacs, the optical continuum emission correlates with the
radio emission of the jet at 15 GHz. We suggest that the radio and optical
emission are beamed and originate in the innermost part of the
sub--parsec-scale jet in quasars. Analysis of the relation between the apparent
speed of the jet and the optical nuclear luminosity at 5100 AA supports the
relativistic beaming model for the optical emission generated in the jet, and
allows the peak values of the intrinsic optical luminosity of the jet and its
Lorentz factor to be estimated for the populations of quasars, BL Lacs, and
radio galaxies. The radio-loudness of quasars is found to increase at high
redshifts, which can be a result of lower efficiency of the accretion in AGN
having higher radio luminosities. A strong positive correlation is found
between the intrinsic kinetic power of the jet and the apparent luminosities of
the total and the unresolved core emission of the jet at 15 GHz. This
correlation is interpreted in terms of intrinsically more luminous parsec-scale
jet producing more luminous extended structure which is detectable at low radio
frequencies, 151 MHz. A possibility that the low frequency radio emission is
relativistically beamed in superluminal AGN and therefore correlates with radio
luminosity of the jet at 15 GHz can not be ruled out (abridged).Comment: 16 pages, 10 figuers; minor comments are added; accepted to A&
Polarization of synchrotron emission from relativistic reconfinement shocks with ordered magnetic fields
We calculate the polarization of synchrotron radiation produced at the
relativistic reconfinement shocks, taking into account globally ordered
magnetic field components, in particular toroidal and helical fields. In these
shocks, toroidal fields produce high parallel polarization (electric vectors
parallel to the projected jet axis), while chaotic fields generate moderate
perpendicular polarization. Helical fields result in a non-axisymmetric
distribution of the total and polarized brightness. For a diverging downstream
velocity field, the Stokes parameter U does not vanish and the average
polarization is neither strictly parallel nor perpendicular. A distance at
which the downstream flow is changing from diverging to converging can be
easily identified on polarization maps as the turning point, at which
polarization vectors switch, e.g., from clockwise to counterclockwise.Comment: 10 pages, 6 figures, accepted for publication in A&
Cosmological evolution of compact AGN at 15 GHz
We study the uniformity of the distribution of compact flat-spectrum AGN on
the sky and the evolution of their relativistic jets with cosmic epoch. A
complete sample of compact extragalactic radio sources at 15 GHz was recently
compiled to conduct the MOJAVE program. The MOJAVE sample comprises 133
radio-loud flat-spectrum AGN with compact relativistic outflows detected at
parsec scales. The source counts of compact AGN shows that the MOJAVE sample
represents a flux-limited complete sample. Analysis of the population of
flat-spectrum quasars of the sample reveals that the pc-scale jets of quasars
have intrinsic luminosities in the range between ~10^24 W/Hz and ~10^27 W/Hz
and Lorentz factors distributed between 3 and 30. We find that the apparent
speed (or Lorentz factor) of jets evolves with redshift, increasing from z~0 to
z~1 and then falling at higher redshifts (z~2.5) by a factor of 2.5. The
evolution of apparent speeds does not affect significantly the evolution of the
beamed luminosity function of quasars, which is most likely to be dependent on
the evolution of radio luminosity. Furthermore, the beamed radio luminosity
function suggests that the intrinsic luminosity function of quasars has a
double power-law form: it is flat at low luminosities and steep at high
luminosities. There is a positive evolution of quasars at low redshifts (z<0.5)
and strong negative evolution at redshifts >1.7 with space density decline up
to z~2.5. This implies that the powerful jets were more populous at redshifts
between 0.5 and 1.7. We show that the evolution of compact quasars is
luminosity dependent and it depends strongly on the speed of the jet suggesting
that there are two distinct populations of quasars with slow and fast jets
which evolve differently with redshift.Comment: 9 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
Emission from Hot Dust in the Infrared Spectra of Gamma-ray Bright Blazars
A possible source of -ray photons observed from the jets of blazars
is inverse Compton scattering by relativistic electrons of infrared seed
photons from a hot, dusty torus in the nucleus. We use observations from the
Spitzer Space Telescope to search for signatures of such dust in the infrared
spectra of four -ray bright blazars, the quasars 4C 21.35, CTA102, and
PKS 1510089, and the BL Lacertae object ON231. The spectral energy
distribution (SED) of 4C 21.35 contains a prominent infrared excess indicative
of dust emission. After subtracting a non-thermal component with a power-law
spectrum, we fit a dust model to the residual SED. The model consists of a
blackbody with temperature K, plus a much weaker optically thin
component at K. The total luminosity of the thermal dust emission is
erg s. If the dust lies in an equatorial
torus, the density of IR photons from the torus is sufficient to explain the
-ray flux from 4C 21.35 as long as the scattering occurs within a few
parsecs of the central engine. We also report a tentative detection of dust in
the quasar CTA102, in which the luminosity of the infrared excess is erg s. However, in CTA102 the far-IR spectra are too
noisy to detect the m silicate feature. Upper limits to the luminosity
from thermal emission from dust in PKS 1510-089, and ON231, are,
, and erg s, respectively. These
upper limits do not rule out the possibility of inverse Compton up-scattering
of IR photons to -ray energies in these two sources. The estimated
covering factor of the hot dust in 4C 21.35, 22%, is similar to that of
non-blazar quasars; however, 4C 21.35 is deficient in cooler dust.Comment: 23 Pages, 5 Figures, 2 Tables, 1 Machine Readable Table. Accepted to
Ap
The unfriendly ISM in the radio galaxy 4C12.50 (PKS 1345+12)
The radio source 4C12.50 has often been suggested to be a prime candidate for
the link between ultraluminous infrared galaxies and young radio galaxies. A
VLBI study of the neutral hydrogen in the nuclear regions of this object shows
that most of the gas detected close to the systemic velocity is associated with
an off-nuclear cloud (~50 to 100 pc from the radio core) with a column density
of ~10^22 T_spin/100 K) cm^(-2) and an HI mass of a few times 10^5 to 10^6
M_sun. We consider a number of possibilities to explain the results. In
particular, we discus the possibility that this cloud indicates the presence of
a rich and clumpy interstellar medium in the centre, likely left over from the
merger that triggered the activity and that this medium influences the growth
of the radio source. The location of the cloud -- at the edge of the northern
radio jet/lobe -- suggests that the radio jet might be interacting with a gas
cloud. This interaction could be responsible for bending the young radio jet.
The velocity profile of the gas is relatively broad (~150$ km/s) and we
interpret this as kinematical evidence for interaction of the radio plasma with
the cloud. We also consider the model where the cloud is part of a broader
circumnuclear structure. Only a limited region of this structure would have
sufficient background radio brightness and large enough column depth in neutral
gas to obtain detectable HI absorption against the counterjet. The VLBI study
of the neutral hydrogen in 4C12.50 suggests that HI detected near the systemic
velocity (as it is often the case in radio galaxies) may not necessarily be
connected with a circumnuclear disk or torus (as is very often assumed) but
instead could be a tracer of the large-scale medium that surrounds the active
nucleus and that may influence the growth of the young radio source.Comment: 7 pages, 2 figures. Accepted for publication in A&
Rapid optical variability of TeV blazars
In this first systematic attempt to characterise the intranight optical
variability (INOV) of TeV detected blazars, we have monitored a well defined
set of 9 TeV blazars on total 26 nights during 2004-2010. In this R (or V)-band
monitoring programme only one blazar was monitored per night for a minimum
duration of 4 hours. Using the CCD, an INOV detection threshold of ~ 1-2 % was
achieved in the densely sampled DLCs. We have further expanded the sample by
including another 13 TeV blazars from literature. This enlarged sample of 22
TeV blazars, monitored on a total of 116 nights (including 55 nights newly
reported here), has enabled us to arrive at the first estimate of the INOV duty
cycle of TeV detected blazars. Applying the C-test, the INOV DC is found to be
59 %, which decreases to 47 % if only INOV fractional amplitudes above 3 % are
considered. These observations also permit, for the first time, a comparison of
the INOV characteristics of the two major subclasses of TeV detected BL Lacs,
namely LBLs and HBLs, for which we find the INOV DCs to be ~ 63 % and ~ 38 %,
respectively. This demonstrates that the INOV differential between LBLs and
HBLs persists even when only their TeV detected subsets are considered. Despite
dense sampling, the intranight light curves of the 22 TeV blazars have not
revealed even a single feature on time scale substantially shorter than 1 hour,
even though the inner jets of TeV blazars are believed to have exceptionally
large bulk Lorentz factors (and correspondingly stronger time compression). An
intriguing feature, clearly detected in the light curve of the HBL J1555+1111,
is a 4 per cent `dip' on a 1 hour timescale. This unique feature could have
arisen from absorption in a dusty gas cloud, occulting a superluminally moving
optical knot in the parsec scale jet of this relatively luminous BL Lacs
object.Comment: 39 pages, 3 figures, accepted for publication in MNRA
B2 0954+25A: a typical Fermi blazar or a gamma-loud Narrow Line Seyfert 1
B2 0954+25A, detected by the {\it Fermi} satellite, is a blazar with
interesting observational properties: it has been observed to transit from a
jet dominated to a disk dominated state; its radio spectrum appears flat at all
observing frequencies (down to 74 MHz); optically, the H line profile is
asymmetric. The flatness of radio spectrum suggests that the isotropic emission
from radio lobes is very weak, despite the large size of its jet ( 500
kpc). Its broad--band spectral energy distribution is surprisingly similar to
that of the prototypical --ray, radio loud, Narrow Line Seyfert 1
(--NLS1) galaxy PMN J0948+0022. In this work we revisit the mass
estimates of B2 0954+25A considering only the symmetric component of the
H line and find (1--3) M_{\sun}. In light of our
composite analysis, we propose to classify the source as a transition object
between the class of Flat Spectrum Radio Quasar and --ray, radio loud
NLS1. A comparison with two members of each class (3C 273 and PMN J0948+0022)
is discussed.Comment: MNRAS accepted. 14 pages, 6 figure
Trade unions, civil society organisations and health reforms
This article provides an analysis of resistance to neoliberalism and commodification in the public healthcare sector as seen from a trade union perspective. It uses recent research on social-movement unionism and new labour internationalism to structure a series of case studies examining resistance to different dimensions of healthcare commodification in four countries. The range of alliances trade unions are making do not fit tidily into one model, but give insights into the movement elements of trade unionism. This dimension must be strengthened, but can also be in tension with collective bargaining and other institutional processes. How to constantly reconcile these different positions is the future challenge facing trade unions
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