The 21-SPONGE HI Absorption Survey I: Techniques and Initial Results

We present methods and results from "21-cm Spectral Line Observations of Neutral Gas with the EVLA" (21-SPONGE), a large survey for Galactic neutral hydrogen (HI) absorption with the Karl G. Jansky Very Large Array (VLA). With the upgraded capabilities of the VLA, we reach median root-mean-square (RMS) noise in optical depth of $\sigma_{\tau}=9\times 10^{-4}$ per $0.42\rm\,km\,s^{-1}$ channel for the 31 sources presented here. Upon completion, 21-SPONGE will be the largest HI absorption survey with this high sensitivity. We discuss the observations and data reduction strategies, as well as line fitting techniques. We prove that the VLA bandpass is stable enough to detect broad, shallow lines associated with warm HI, and show that bandpass observations can be combined in time to reduce spectral noise. In combination with matching HI emission profiles from the Arecibo Observatory ($\sim3.5'$ angular resolution), we estimate excitation (or spin) temperatures ($\rm T_s$) and column densities for Gaussian components fitted to sightlines along which we detect HI absorption (30/31). We measure temperatures up to $\rm T_s\sim1500\rm\,K$ for individual lines, showing that we can probe the thermally unstable interstellar medium (ISM) directly. However, we detect fewer of these thermally unstable components than expected from previous observational studies. We probe a wide range in column density between $\sim10^{16}$ and $>10^{21}\rm\,cm^{-2}$ for individual HI clouds. In addition, we reproduce the trend between cold gas fraction and average $\rm T_s$ found by synthetic observations of a hydrodynamic ISM simulation by Kim et al. (2014). Finally, we investigate methods for estimating HI $\rm T_s$ and discuss their biases.Comment: Accepted for publication in ApJ; 24 pages, 14 figure

LkCa 15: A Young Exoplanet Caught at Formation?

Young and directly imaged exoplanets offer critical tests of planet-formation models that are not matched by RV surveys of mature stars. These targets have been extremely elusive to date, with no exoplanets younger than 10--20 Myr and only a handful of direct-imaged exoplanets at all ages. We report the direct imaging discovery of a likely (proto)planet around the young (~2 Myr) solar analog LkCa 15, located inside a known gap in the protoplanetary disk (a "transitional disk"). Our observations use non-redundant aperture masking interferometry at 3 epochs to reveal a faint and relatively blue point source ($M_K'=9.1+/-0.2, K'-L'=0.98+/-0.22), flanked by approximately co-orbital emission that is red and resolved into at least two sources (M_L'=7.5+/-0.2, K'-L'=2.7+/-0.3; M_L'=7.4+/-0.2, K'-L'=1.94+/-0.16). We propose that the most likely geometry consists of a newly-formed (proto)planet that is surrounded by dusty material. The nominal estimated mass is ~6 M_{Jup} according to the 1 Myr hot-start models. However, we argue based on its luminosity, color, and the presence of circumplanetary material that the planet has likely been caught at its epoch of assembly, and hence this mass is an upper limit due to its extreme youth and flux contributed by accretion. The projected separations (71.9 +/- 1.6 mas, 100.7 +/- 1.9 mas, and 88.2 +/- 1.8 mas) and deprojected orbital radii (16, 21, and 19 AU) correspond to the center of the disk gap, but are too close to the primary star for a circular orbit to account for the observed inner edge of the outer disk, so an alternate explanation (i.e., additional planets or an eccentric orbit) is likely required. This discovery is the first direct evidence that at least some transitional disks do indeed host newly-formed (or forming) exoplanetary systems, and the observed properties provide crucial insight into the gas giant formation process.Comment: Accepted to ApJ; 15 pages, 4 figures, 2 tabls in emulateapj forma

Cognitive Radio Systems

Cognitive radio is a hot research area for future wireless communications in the recent years. In order to increase the spectrum utilization, cognitive radio makes it possible for unlicensed users to access the spectrum unoccupied by licensed users. Cognitive radio let the equipments more intelligent to communicate with each other in a spectrum-aware manner and provide a new approach for the co-existence of multiple wireless systems. The goal of this book is to provide highlights of the current research topics in the field of cognitive radio systems. The book consists of 17 chapters, addressing various problems in cognitive radio systems

An Optoelectronic Stimulator for Retinal Prosthesis

Retinal prostheses require the presence of viable population of cells in the inner retina. Evaluations of retina with Age-Related Macular Degeneration (AMD) and Retinitis Pigmentosa (RP) have shown a large number of cells remain in the inner retina compared with the outer retina. Therefore, vision loss caused by AMD and RP is potentially treatable with retinal prostheses. Photostimulation based retinal prostheses have shown many advantages compared with retinal implants. In contrary to electrode based stimulation, light does not require mechanical contact. Therefore, the system can be completely external and not does have the power and degradation problems of implanted devices. In addition, the stimulating point is flexible and does not require a prior decision on the stimulation location. Furthermore, a beam of light can be projected on tissue with both temporal and spatial precision. This thesis aims at fi nding a feasible solution to such a system. Firstly, a prototype of an optoelectronic stimulator was proposed and implemented by using the Xilinx Virtex-4 FPGA evaluation board. The platform was used to demonstrate the possibility of photostimulation of the photosensitized neurons. Meanwhile, with the aim of developing a portable retinal prosthesis, a system on chip (SoC) architecture was proposed and a wide tuning range sinusoidal voltage-controlled oscillator (VCO) which is the pivotal component of the system was designed. The VCO is based on a new designed Complementary Metal Oxide Semiconductor (CMOS) Operational Transconductance Ampli er (OTA) which achieves a good linearity over a wide tuning range. Both the OTA and the VCO were fabricated in the AMS 0.35 µm CMOS process. Finally a 9X9 CMOS image sensor with spiking pixels was designed. Each pixel acts as an independent oscillator whose frequency is controlled by the incident light intensity. The sensor was fabricated in the AMS 0.35 µm CMOS Opto Process. Experimental validation and measured results are provided

Near-Infrared Instrumentation and Millimeter-Wave Simulations For Cosmological Surveys.

The evolution of the Universe is well characterized by the concordance lCDM cosmological model where structure formation is seeded by cold dark matter and accelerated expansion is driven by the cosmological constant. Understanding the history and fate of the Universe requires precise measurements of cosmological parameters. Finding them inconsistent may lead to a more fundamental physical theory. I explore observable probes of cosmological parameters as well as instrumental effects that may obfuscate them. I develop a framework for simulating millimeter-wave skies including galaxy clusters' Sunyaev-Zel'dovich (SZ) signature. This framework includes astrophysical and instrumental effects. Its primary use is in testing systematic effects resulting from joining intrinsic profile variations and mass dependencies with observational uncertainties and signal extraction techniques as well as multi-wavelength studies. I demonstrate that the signal recovered using Matched Filter is very sensitive to (SZ) profile shapes and potentially leads to biases. I then consider the impact of galaxy cluster selection and characterization in the maxBCG cluster catalog on recovering a stacked SZ signal in light of recently measured biases. I find that accounting for the mass calibration uncertainty and mis-centering of galaxy clusters may explain the majority of the observed discrepancy. In addition, contrary to others' findings, I conclude that the X-ray sub-sample of maxBCG clusters is similarly affected. My findings suggest that the SZ signal can indeed serve as an alternate mass calibration technique. I finally focus on instrumental effects in near-infrared (NIR) detectors designed for large surveys of the cosmos. I first characterize the flux dependent non-linearity known as reciprocity failure and find that it can be as large as 10% per decade in flux change but is suppressed by cooling the detectors. I then thoroughly study the quantum efficiency (QE) of a single NIR device under different environmental and illumination conditions and conclude that it can vary significantly. Careful accounting of various sources of uncertainty suggests that some observers may be too confident in the quality of their QE measurements.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102326/1/tomaszbi_1.pd

The role of calcium in the destruction of target cells by cytotoxic T cells

Thesis (Ph. D.)--Massachusetts Institute of Technology, Harvard-MIT Divison of Health Sciences and Technology Program in Medical Engineering and Medical Physics, 1987.Title as it appears in M.I.T. Graduate List, June 1987: The role of calcium in the destruction of target cells by cytotoxic T lymphocytes.Bibliography: leaves 224-239.by Nancy L. Allbritton.Ph.D

The detection of microplastics in beach sediments: extraction methods, biases, and results from samples along the German Baltic coast

The spatial and temporal variations of microplastic concentrations in beach sediments at the German Baltic coast are investigated. A total of 11 locations were sampled in the Rostock area, on Ruegen island, in the Oder / Peene estuary, and in the North Sea Jade Bay. Microplastic particle and fibre concentrations were in the range 0-11 coloured pieces/kg sediment, with typical numbers of 1-3 particles/kg. Industrial and urban river discharge, fishing activity, and tourism are identified as the most likely sources for the observed microplastic contaminations.In der Masterarbeit wurde die räumliche und zeitliche Verteilung von Mikroplastik in Strandsedimenten an der deutschen Ostseekueste untersucht. Sedimentproben wurden an 11 Stränden entlang der Rostocker und Ruegener Küsten, im Oder / Peene Ästuar und im Jadebusen an der Nordsee genommen. Die Konzentrationen von Mikroplastik-Partikeln und -Fasern lagen im Bereich 0-11 farbige Teilchen/kg Sediment, mit typischen Konzentrationen von 1-3 Partikeln/kg. Als wahrscheinlichste Eintrittspfade für Mikroplastik in die Ostsee wurden industrielle und städtische Abwässer (Rostock, Stettin), Fischerei (Oder / Peene) und Tourismus (Warnemuende) identifiziert

Permissionless Clock Synchronization with Public Setup

The permissionless clock synchronization problem asks how it is possible for a population of parties to maintain a system-wide synchronized clock, while their participation rate fluctuates --- possibly very widely --- over time. The underlying assumption is that parties experience the passage of time with roughly the same speed, but however they may disengage and engage with the protocol following arbitrary (and even chosen adversarially) participation patterns. This (classical) problem has received renewed attention due to the advent of blockchain protocols, and recently it has been solved in the setting of proof of stake, i.e., when parties are assumed to have access to a trusted PKI setup [Badertscher et al., Eurocrypt ’21]. In this work, we present the first proof-of-work (PoW)-based permissionless clock synchronization protocol. Our construction assumes a public setup (e.g., a CRS) and relies on an honest majority of computational power that, for the first time, is described in a fine-grain timing model that does not utilize a global clock that exports the current time to all parties. As a secondary result of independent interest, our protocol gives rise to the first PoW-based ledger consensus protocol that does not rely on an external clock for the time-stamping of transactions and adjustment of the PoW difficulty