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

Amplitude and Phase Fluctuations for Gravitational Waves Propagating through Inhomogeneous Mass Distribution in the Universe

When a gravitational wave (GW) from a distant source propagates through the universe, its amplitude and phase change due to gravitational lensing by the inhomogeneous mass distribution. We derive the amplitude and phase fluctuations, and calculate these variances in the limit of a weak gravitational field of density perturbation. If the scale of the perturbation is smaller than the Fresnel scale $\sim 100 {pc} (f/{mHz})^{-1/2}$ ($f$ is the GW frequency), the GW is not magnified due to the diffraction effect. The rms amplitude fluctuation is $1-10$ for $f > 10^{-10}$ Hz, but it is reduced less than 5% for a very low frequency of $f < 10^{-12}$ Hz. The rms phase fluctuation in the chirp signal is $\sim 10^{-3}$ radian at LISA frequency band ($10^{-5} - 10^{-1}$ Hz). Measurements of these fluctuations will provide information about the matter power spectrum on the Fresnel scale $\sim 100$ pc.Comment: 6 pages, 6 figures, refferences added, accepted for publication in Ap

Old Galaxies at High Redshift and the Cosmological Constant

In a recent striking discovery, Dunlop {\bf \it et al} observed a galaxy at redshift z=1.55 with an estimated age of 3.5 Gyr. This is incompatible with age estimates for a flat matter dominated universe unless the Hubble constant is less than $45 kms^{-1}Mpc^{-1}$. While both an open universe, and a universe with a cosmological constant alleviate this problem, I argue here that this result favors a non-zero cosmological constant, especially when considered in light of other cosmological constraints. In the first place, for the favored range of matter densities, this constraint is more stringent than the globular cluster age constraint, which already favors a non-zero cosmological constant. Moreover, the age-redshift relation for redshifts of order unity implies that the ratio between the age associated with redshift 1.55 and the present age is also generally larger for a cosmological constant dominated universe than for an open universe. In addition, structure formation is generally suppressed in low density cosmologies, arguing against early galaxy formation. The additional constraints imposed by the new observation on the parameter space of $h$ vs $\Omega_{matter}$ (where $H= 100 h kms^{-1}Mpc^{-1}$) are derived for both cosmologies. For a cosmological constant dominated universe this constraint is consistent with the range allowed by other cosmological constraints, which also favor a non-zero value.Comment: latex, 10 pages, including two embedded postscript figure

The scale of homogeneity in the Las Campanas Redshift Survey

We analyse the Las Campanas Redshift Survey using the integrated conditional density (or density of neighbors) in volume-limited subsamples up to unprecedented scales (200 Mpc/$h$) in order to determine without ambiguity the behavior of the density field. We find that the survey is well described by a fractal up to 20-30 Mpc/$h$, but flattens toward homogeneity at larger scales. Although the data are still insufficient to establish with high significance the expected homogeneous behavior, and therefore to rule out a fractal trend to larger scales, a fit with a CDM-like spectrum with high normalization well represents the data.Comment: 8 pages, 3 figures, accepted on Ap.J. Letter

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

Weighing the Cosmological Energy Contents with Weak Gravitational Lensing

Bernardeau et al. (1997), using perturbation theory, showed that the skewness of the large-scale lensing-convergence, or projected mass density, could be used to constrain $\Omega_m$, the matter content of the universe. On the other hand, deep weak-lensing field surveys in the near future will likely measure the convergence on small angular scales (< 10 arcmin.), where the signal will be dominated by highly nonlinear fluctuations. We develop a method to compute the small-scale convergence skewness, using a prescription for the highly nonlinear three-point function developed by Scoccimarro and Frieman (1998). This method gives predictions that agree well with existing results from ray-tracing N-body simulations, but is significantly faster, allowing the exploration of a large number of models. We demonstrate that the small-scale convergence skewness is insensitive to the shape and normalization of the primordial (CDM-type) power spectrum, making it dependent almost entirely on the cosmological energy contents, through their influence on the global geometrical distances and fluctuation growth rate. Moreover, nonlinear clustering appears to enhance the differences between predictions of the convergence skewness for a range of models. Hence, in addition to constraining $\Omega_m$, the small-scale convergence skewness from future deep several- degree-wide surveys can be used to differentiate between curvature dominated and cosmological constant ($\Lambda$) dominated models, as well as to constrain the equation of state of a quintessence component, thereby distinguishing $\Lambda$ from quintessence as well. Finally, our method can be easily generalized to other measures such as aperture mass statistics.Comment: 13 pages, 2 ps figures, submitted to ApJ

Second Order Corrections to Weak Lensing by Large-Scale Structure

We calculate corrections to the power spectrum predictions of weak lensing by large scale structure due to higher order effects in the gravitational potential. Using a perturbative approach to third order in transverse displacements, we calculate a second order correction to the angular power spectra of E and B mode shear and convergence resulting from dropping the so-called Born approximation, where one integrates along the unperturbed photon path. We also consider a correction to the power spectra from the coupling between lenses at different redshifts. Both effects generate B-mode shear and the latter also causes a net rotation of the background galaxy images. We show all these corrections are at least two orders of magnitude below the convergence or E-mode power and hence relevant only to future ultra high precision measurements. These analytical calculations are consistent with previous numerical estimates and validate the use of current large scale structure weak lensing predictions for cosmological studies and future use of B-modes as a monitor of systematic effects.Comment: 4 pages, 1 figure, submitted to ApJ

Power Spectrum Correlations Induced by Non-Linear Clustering

Gravitational clustering is an intrinsically non-linear process that generates significant non-Gaussian signatures in the density field. We consider how these affect power spectrum determinations from galaxy and weak-lensing surveys. Non-Gaussian effects not only increase the individual error bars compared to the Gaussian case but, most importantly, lead to non-trivial cross-correlations between different band-powers. We calculate the power-spectrum covariance matrix in non-linear perturbation theory (weakly non-linear regime), in the hierarchical model (strongly non-linear regime), and from numerical simulations in real and redshift space. We discuss the impact of these results on parameter estimation from power spectrum measurements and their dependence on the size of the survey and the choice of band-powers. We show that the non-Gaussian terms in the covariance matrix become dominant for scales smaller than the non-linear scale, depending somewhat on power normalization. Furthermore, we find that cross-correlations mostly deteriorate the determination of the amplitude of a rescaled power spectrum, whereas its shape is less affected. In weak lensing surveys the projection tends to reduce the importance of non-Gaussian effects. Even so, for background galaxies at redshift z=1, the non-Gaussian contribution rises significantly around l=1000, and could become comparable to the Gaussian terms depending upon the power spectrum normalization and cosmology. The projection has another interesting effect: the ratio between non-Gaussian and Gaussian contributions saturates and can even decrease at small enough angular scales if the power spectrum of the 3D field falls faster than 1/k^2.Comment: 34 pages, 15 figures. Revised version, includes a clearer explanation of why the hierarchical ansatz does not provide a good model of the covariance matrix in the non-linear regime, and new constraints on the amplitudes Ra and Rb for general 4-pt function configurations in the non-linear regim

Damped Lyman alpha systems and disk galaxies: number density, column density distribution and gas density

We present a comparison between the observed properties of damped Lyman alpha systems (DLAs) and the predictions of simple models for the evolution of present day disk galaxies, including both low and high surface brightness galaxies. We focus in particular on the number density, column density distribution and gas density of DLAs, which have now been measured in relatively large samples of absorbers. From the comparison we estimate the contribution of present day disk galaxies to the population of DLAs, and how it varies with redshift. Based on the differences between the models and the observations, we also speculate on the nature of the fraction of DLAs which apparently do not arise in disk galaxies.Comment: 11 pages, 10 figures, accepted in MNRA

Measuring the Deviation from the Linear and Deterministic Bias through Cosmic Gravitational Lensing Effects

Since gravitational lensing effects directly probe inhomogeneities of dark matter, lensing-galaxy cross-correlations can provide us important information on the relation between dark matter and galaxy distributions, i.e., the bias. In this paper, we propose a method to measure the stochasticity/nonlinearity of the galaxy bias through correlation studies of the cosmic shear and galaxy number fluctuations. Specifically, we employ the aperture mass statistics $M_{ap}$ to describe the cosmic shear. We divide the foreground galaxy redshift $z_f<z_s$ into several bins, where $z_s$ is the redshift of the source galaxies, and calculate the quantity $^2/$ for each redshift bin. Then the ratio of the summation of $^2/< N_g^2(z_f)>$ over the bins to $$ gives a measure of the nonlinear/stochastic bias. Here $N_g(z_f)$ is the projected surface number density fluctuation of foreground galaxies at redshift $z_f$, and $M_{ap}$ is the aperture mass from the cosmic-shear analysis. We estimate that for a moderately deep weak-lensing survey with $z_s=1$, source galaxy surface number density $n_b=30 \hbox {gal}/\hbox {arcmin}^2$ and a survey area of $25 \hbox {deg}^2$, the effective $r$-parameter that represents the deviation from the linear and deterministic bias is detectable in the angular range of 1'-10' if |r-1|\gsim 10%. For shallow, wide surveys such as the Sloan Digital Sky Survey with $z_s=0.5$, $n_b=5 \hbox {gal}/\hbox {arcmin}^2$, and a survey area of $10^4 \hbox {deg}^2$, a 10% detection of $r$ is possible over the angular range $1'-100'$.Comment: ApJ in pres