Effects of Intermittent Emission: Noise Inventory for Scintillating Pulsar B0834+06

We compare signal and noise for observations of the scintillating pulsar B0834+06, using very-long baseline interferometry and a single-dish spectrometer. Comparisons between instruments and with models suggest that amplitude variations of the pulsar strongly affect the amount and distribution of self-noise. We show that noise follows a quadratic polynomial with flux density, in spectral observations. Constant coefficients, indicative of background noise, agree well with expectation; whereas second-order coefficients, indicative of self-noise, are about 3 times values expected for a pulsar with constant on-pulse flux density. We show that variations in flux density during the 10-sec integration account for the discrepancy. In the secondary spectrum, about 97% of spectral power lies within the pulsar's typical scintillation bandwidth and timescale; an extended scintillation arc contains about 3%. For a pulsar with constant on-pulse flux density, noise in the dynamic spectrum will appear as a uniformly-distributed background in the secondary spectrum. We find that this uniform noise background contains 95% of noise in the dynamic spectrum for interferometric observations; but only 35% of noise in the dynamic spectrum for single-dish observations. Receiver and sky dominate noise for our interferometric observations, whereas self-noise dominates for single-dish. We suggest that intermittent emission by the pulsar, on timescales < 300 microseconds, concentrates self-noise near the origin in the secondary spectrum, by correlating noise over the dynamic spectrum. We suggest that intermittency sets fundamental limits on pulsar astrometry or timing. Accounting of noise may provide means for detection of intermittent sources, when effects of propagation are unknown or impractical to invert.Comment: 38 pages, 10 figure

A sense of self for power side-channel signatures: instruction set disassembly and integrity monitoring of a microcontroller system

Cyber-attacks are on the rise, costing billions of dollars in damages, response, and investment annually. Critical United States National Security and Department of Defense weapons systems are no exception, however, the stakes go well beyond financial. Dependence upon a global supply chain without sufficient insight or control poses a significant issue. Additionally, systems are often designed with a presumption of trust, despite their microelectronics and software-foundations being inherently untrustworthy. Achieving cybersecurity requires coordinated and holistic action across disciplines commensurate with the specific systems, mission, and threat. This dissertation explores an existing gap in low-level cybersecurity while proposing a side-channel based security monitor to support attack detection and the establishment of trusted foundations for critical embedded systems. Background on side-channel origins, the more typical side-channel attacks, and microarchitectural exploits are described. A survey of related side-channel efforts is provided through side-channel organizing principles. The organizing principles enable comparison of dissimilar works across the side-channel spectrum. We find that the maturity of existing side-channel security monitors is insufficient, as key transition to practice considerations are often not accounted for or resolved. We then document the development, maturation, and assessment of a power side-channel disassembler, Time-series Side-channel Disassembler (TSD), and extend it for use as a security monitor, TSD-Integrity Monitor (TSD-IM). We also introduce a prototype microcontroller power side-channel collection fixture, with benefits to experimentation and transition to practice. TSD-IM is finally applied to a notional Point of Sale (PoS) application for proof of concept evaluation. We find that TSD and TSD-IM advance state of the art for side-channel disassembly and security monitoring in open literature. In addition to our TSD and TSD-IM research on microcontroller signals, we explore beneficial side-channel measurement abstractions as well as the characterization of the underlying microelectronic circuits through Impulse Signal Analysis (ISA). While some positive results were obtained, we find that further research in these areas is necessary. Although the need for a non-invasive, on-demand microelectronics-integrity capability is supported, other methods may provide suitable near-term alternatives to ISA

VLBI Imaging of Water Maser Emission from the Nuclear Torus of NGC 1068

We have made the first VLBI synthesis images of the H2O maser emission associated with the central engine of the Seyfert galaxy NGC 1068. Emission extends about +/-300 km/s from the systemic velocity. Images with submilliarcsecond angular resolution show that the red-shifted emission lies along an arc to the northwest of the systemic emission. (The blue-shifted emission has not yet been imaged with VLBI.) Based on the maser velocities and the relative orientation of the known radio jet, we propose that the maser emission arises on the surface of a nearly edge-on torus, where physical conditions are conducive to maser action. The visible part of the torus is axially thick, with comparable height and radius. The velocity field indicates sub-Keplerian differential rotation around a central mass of about 1e7 Msun that lies within a cylindrical radius of about 0.65 pc. The estimated luminosity of the central engine is about 0.5 of the Eddington limit. There is no detectable compact radio continuum emission near the proposed center of the torus (T_B< 5e6 K on size scales of about 0.1 pc), so that the observed flat-spectrum core cannot be direct self-absorbed synchrotron radiation.Comment: 12 pages, 4 figures. To appear in ApJ Part 2. Also available at http://www.physics.ucsb.edu/~vlbiweb

Gravitational Radiation and Very Long Baseline Interferometry

Gravitational waves affect the observed direction of light from distant sources. At telescopes, this change in direction appears as periodic variations in the apparent positions of these sources on the sky; that is, as proper motion. A wave of a given phase, traveling in a given direction, produces a characteristic pattern of proper motions over the sky. Comparison of observed proper motions with this pattern serves to test for the presence of gravitational waves. A stochastic background of waves induces apparent proper motions with specific statistical properties, and so, may also be sought. In this paper we consider the effects of a cosmological background of gravitational radiation on astrometric observations. We derive an equation for the time delay measured by two antennae observing the same source in an Einstein-de Sitter spacetime containing gravitational radiation. We also show how to obtain similar expressions for curved Friedmann-Robertson-Walker spacetimes.Comment: 31 pages plus 3 separate figures, plain TeX, submitted to Ap

Quasar Proper Motions and Low-Frequency Gravitational Waves

We report observational upper limits on the mass-energy of the cosmological gravitational-wave background, from limits on proper motions of quasars. Gravitational waves with periods longer than the time span of observations produce a simple pattern of apparent proper motions over the sky, composed primarily of second-order transverse vector spherical harmonics. A fit of such harmonics to measured motions yields a 95%-confidence limit on the mass-energy of gravitational waves with frequencies <2e-9 Hz, of <0.11/h*h times the closure density of the universe.Comment: 15 pages, 1 figure. Also available at http://charm.physics.ucsb.edu:80/people/cgwinn/cgwinn_group/index.htm

Identification of DHX33 as a mediator of rRNA synthesis and cell growth

In this report, we employed a lentiviral RNA interference screen to discover nucleolar DEAD/DEAH-box helicases involved in RNA polymerase I (Pol I)-mediated transcriptional activity. Our screen identified DHX33 as an important modulator of 47S rRNA transcription. We show that DHX33 is a cell cycle-regulated nucleolar protein that associates with ribosomal DNA (rDNA) loci, where it interacts with the RNA Pol I transcription factor upstream binding factor (UBF). DHX33 knockdown decreased the association of Pol I with rDNA and caused a dramatic decrease in levels of rRNA synthesis. Wild-type DHX33 overexpression, but not a DNA binding-defective mutant, enhanced 47S rRNA synthesis by promoting the association of RNA polymerase I with rDNA loci. In addition, an NTPase-defective DHX33 mutant (K94R) acted as a dominant negative mutant, inhibiting endogenous rRNA synthesis. Moreover, DHX33 deficiency in primary human fibroblasts triggered a nucleolar p53 stress response, resulting in an attenuation of proliferation. Thus, we show the mechanistic importance of DHX33 in rRNA transcription and proliferation