4,990 research outputs found
An analysis of security issues in building automation systems
The purpose of Building Automation Systems (BAS) is to centralise the management of a wide range of building services, through the use of integrated protocol and communication media. Through the use of IP-based communication and encapsulated protocols, BAS are increasingly being connected to corporate networks and also being remotely accessed for management purposes, both for convenience and emergency purposes. These protocols, however, were not designed with security as a primary requirement, thus the majority of systems operate with sub-standard or non-existent security implementations, relying on security through obscurity. Research has been undertaken into addressing the shortfalls of security implementations in BAS, however defining the threats against BAS, and detection of these threats is an area that is particularly lacking. This paper presents an overview of the current security measures in BAS, outlining key issues, and methods that can be improved to protect cyber physical systems against the increasing threat of cyber terrorism and hacktivism. Future research aims to further evaluate and improve the detection systems used in BAS through first defining the threats and then applying and evaluating machine learning algorithms for traffic classification and IDS profiling capable of operating on resource constrained BAS
Reionization Revisited: Secondary CMB Anisotropies and Polarization
Secondary CMB anisotropies and polarization provide a laboratory to study
structure formation in the reionized epoch. We consider the kinetic
Sunyaev-Zel'dovich effect from mildly nonlinear large-scale structure and show
that it is a natural extension of the perturbative Vishniac effect. If the gas
traces the dark matter to overdensities of order 10, as expected from
simulations, this effect is at least comparable to the Vishniac effect at
arcminute scales. On smaller scales, it may be used to study the thermal
history-dependent clustering of the gas. Polarization is generated through
Thomson scattering of primordial quadrupole anisotropies, kinetic (second order
Doppler) quadrupole anisotropies and intrinsic scattering quadrupole
anisotropies. Small scale polarization results from the density and ionization
modulation of these sources. These effects generically produce comparable E and
B-parity polarization, but of negligible amplitude (0.001-0.01 uK) in adiabatic
CDM models. However, the primordial and kinetic quadrupoles are observationally
comparable today so that a null detection of B-polarization would set
constraints on the evolution and coherence of the velocity field. Conversely, a
detection of a cosmological B-polarization even at large angles does not
necessarily imply the presence of gravity waves or vorticity. For these
calculations, we develop an all-sky generalization of the Limber equation that
allows for an arbitrary local angular dependence of the source for both scalar
and symmetric trace-free tensor fields on the sky.Comment: 14 pages, 12 figures, minor changes and typo fixes reflect published
versio
Semiconductor filled microstructured optical fibres with single mode guidance
Microstructured optical fibre (MOF) technology has generated new opportunities for the implementation of optical fibres with novel properties and functions [1]. It has been shown that silica MOFs make excellent 3D templates for semiconductor material deposition inside the capillary voids [2]. Recently a silicon MOF was designed and fabricated that had a high refractive index micron sized core, but yet only supported two guided modes [3]. This structure was realised via the complete filling of a hollow core photonic bandgap fibre (PBGF) with silicon so that the original air guiding PBGF was converted to a total internal reflection guiding fibre. Here, we extend the investigation by using a finite element method to model the optical properties of semiconductor filled MOFs of similar structures, with the aim to achieve broadband single mode guidance. Strategies to achieve single mode guidance both through the MOF template design and the selective filling of the voids of the original PBGF with semiconductor materials of different indices (silicon, silicon nitride, germanium) are proposed and investigated numerically. In particular, by selectively filling MOF templates with cladding rods that have a slightly raised index over that of the core, index guiding single mode operation can be observed in high index micron sized cores. Small index differences are achievable by controlling the nitrogen content in SiNx and an example of a single mode semiconductor MOF is shown in Figure 1, where the confinement loss of the fundamental mode is ~106 lower than the lowest order cladding mode
Continuing the education of autistic pupils while focusing on family wellbeing during the Coronavirus Pandemic
This advice is given in the form of numbered points in no
particular order. Some will be very relevant and useful to
some autistic children and young people and their families
and others will not. It is for the reader to select those that make most sense and seem worth trying. As this document was developed at the start of the pandemic lockdown, transition back in to school /college was not then at
the top of the priority list. Supporting learners going back
into schools and colleges which may look very different
from their pre pandemic presentation is clearly an important consideration now. The first bullet point raises this
concern which is unpacked further later in the document
Mapping Cluster Mass Distributions via Gravitational Lensing of Background Galaxies
We present a new method for measuring the projected mass distributions of
galaxy clusters. The gravitational amplification is measured by comparing the
joint distribution in redshift and magnitude of galaxies behind the cluster
with that of field galaxies. We show that the total amplification is directly
related to the surface mass density in the weak field limit, and so it is
possible to map the mass distribution of the cluster. The method is shown to be
limited by discreteness noise and galaxy clustering behind the lens. Galaxy
clustering sets a lower limit to the error along the redshift direction, but a
clustering independent lensing signature may be obtained from the magnitude
distribution at fixed redshift. Statistical techniques are developed for
estimating the surface mass density of the cluster. We extend these methods to
account for any obscuration by cluster halo dust, which may be mapped
independently of the dark matter. We apply the method to a series of numerical
simulations and show the feasibility of the approach. We consider approximate
redshift information, and show how the mass estimates are degraded.Comment: ApJ in press. 23 pages of LaTeX plus figs. Text & figs available by
anonymous ftp from resun03.roe.ac.uk in directory /pub/jap/lens (you need
btp.tex and apj.sty
Correlation between the Mean Matter Density and the Width of the Saturated Lyman Alpha Absorption
We report a scaling of the mean matter density with the width of the
saturated Lyman alpha absorptions. This property is established using the
``pseudo-hydro'' technique (Croft et al. 1998). It provides a constraint for
the inversion of the Lyman alpha forest, which encounters difficulty in the
saturated region. With a Gaussian density profile and the scaling relation, a
simple inversion of the simulated Lyman alpha forests shows that the
one-dimensional mass power spectrum is well recovered on scales above 2 Mpc/h,
or roughly k < 0.03 s/km, at z=3. The recovery underestimates the power on
small scales, but improvement is possible with a more sophisticated algorithm.Comment: 7 pages, 9 figures, accepted for publication in MNRAS, replaced by
the version after proo
A technique for correcting ERTS data for solar and atmospheric effects
The author has identified the following significant results. Based on processing ERTS CCTs and ground truth measurements collected on Michigan test site for January through June 1973 the following results are reported: (1) atmospheric transmittance varies from: 70 to 85% in band 4, 77 to 90% in band 5, 80 to 94% in band 6, and 84 to 97% in band 7 for one air mass; (2) a simple technique was established to determine atmospheric scattering seen by ERTS-1 from ground-based measurements of sky radiance. For March this scattering was found to be equivalent to that produced by a target having a reflectance of 11% in band 4, 5% in band 5, 3% in band 6, and 1% in band 7; (3) computer ability to classify targets under various atmospheric conditions was determined. Classification accuracy on some targets (i.e. bare soil, tended grass, etc.) hold up even under the most severe atmospheres encountered, while performance on other targets (trees, urban, rangeland, etc.) degrades rapidly when atmospheric conditions change by the smallest amount
Ultrafast optical control using the Kerr nonlinearity in hydrogenated amorphous silicon microcylindrical resonators
Microresonators are ideal systems for probing nonlinear phenomena at low thresholds due to their small mode volumes and high quality (Q) factors. As such, they have found use both for fundamental studies of light-matter interactions as well as for applications in areas ranging from telecommunications to medicine. In particular, semiconductor-based resonators with large Kerr nonlinearities have great potential for high speed, low power all-optical processing. Here we present experiments to characterize the size of the Kerr induced resonance wavelength shifting in a hydrogenated amorphous silicon resonator and demonstrate its potential for ultrafast all-optical modulation and switching. Large wavelength shifts are observed for low pump powers due to the high nonlinearity of the amorphous silicon material and the strong mode confinement in the microcylindrical resonator. The threshold energy for switching is less than a picojoule, representing a significant step towards advantageous low power silicon-based photonic technologies
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