Context-sensitive multimedia

Thesis (M.S.V.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1993.Includes bibliographical references (leaves 98-99).by Nathan Shalom Abramson.M.S.V.S

Design, specification, and implementation of a movie server

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1990.Includes bibliographical references (leaves 63-64).by Nathan S. Abramson.B.S

Convex minorants of random walks and L\'evy processes

This article provides an overview of recent work on descriptions and properties of the convex minorant of random walks and L\'evy processes which summarize and extend the literature on these subjects. The results surveyed include point process descriptions of the convex minorant of random walks and L\'evy processes on a fixed finite interval, up to an independent exponential time, and in the infinite horizon case. These descriptions follow from the invariance of these processes under an adequate path transformation. In the case of Brownian motion, we note how further special properties of this process, including time-inversion, imply a sequential description for the convex minorant of the Brownian meander.Comment: 11 pages, 5 figure

Estimating the Accuracy of Anal Cytology in the Presence of an Imperfect Reference Standard

Background: The study aim is to estimate sensitivity and specificity of anal cytology for histologic HSIL in analyses adjusted for the imperfect biopsy reference standard. Methods and Principal Findings: Retrospective cohort study of an anal dysplasia screening program for HIV infected adults. We estimated the prevalence of histologic HSIL by concurrent cytology category and the associated cytology ROC area. Cytology operating characteristics for HSIL were estimated and adjusted for the imperfect reference standard by 3 methodologies. The study cohort included 261 patients with 3 available measures: (1) referral cytology; (2) HRA cytology; and (3) HRA directed biopsy. The prevalence of biopsy HSIL varied according to the concurrent HRA cytology result: 64.5

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

The Design and Evolution of the dtype Hybrid Programming Environment

The dtype distributed programming environment is a comprehensive set of protocols and libraries that facilitate the easy development of interactive distributed applications. This paper provides an outline of the history and evolution of the dtype programming environment, an examination of several dtype-based applications, and a technical overview of the current implementation of the dtype environment in use at the MIT Media Laboratory and elsewhere. Keywords--- Scheme, multimedia, networking, extension languages, hybrid programming. I. Introduction This paper describes the design and evolution of dtype programming environment, a distributed programming environment developed at the MIT Media Laboratory from 1990--1994. The dtype programming environment provides a number of features to support distributed application design. Although each of these features are present individually in a number of other programming environments, in the dtype environment they combine to make a surprisingl..

Low-Inductance Asymmetrical Hybrid GaN HEMT Switching Cell Design for the FCML Converter in High Step-Down Applications

Proper utilization of GaN devices generally necessitates ultra-low inductance printed circuit board (PCB) layout in the main commutation loop or switching cell of a power converter. The flying c apacitor m ultilevel ( FCML) t opology in particular contains many of these switching cells, thus design optimization becomes critical. A novel asymmetrical cell layout design with sub-1 nH commutation loop inductance is proposed and characterized for the FCML by utilizing a transient- and impedance-based measurement technique in conjunction with 3D field simulation. To validate its efficacy, this switching cell design is demonstrated within a prototype high performance step-down intermediate bus converter supply (vout = 48 V) with wide input voltage range (vin = 48 to 340 V)

A General Analysis of Resonant Switched Capacitor Converters Using Peak Energy Storage and Switch Stress Including Ripple

This work presents a general analytical framework enabling large-signal characterization of resonant switched-capacitor (ReSC) power converters that accounts for passive component voltage and current ripple, for operation at and above resonance. From this, appropriate phase durations for minimized rms currents are derived, in addition to expressions for total passive component volume using an intuitive peak energy method. An example hardware prototype validates both the derived waveforms and timings—as well as total passive volume—through three comparable hardware configurations, one of which minimizes passive component volume. In addition, the proposed technique formulates analytical expressions for both rms currents and peak blocking voltages, facilitating refined loss estimation and component selection. Subsequent calculation of the large-signal Volt–Amp (VA) switch stress metric allows a more accurately quantified trade-off between active and passive components compared to prior work, which has not fully accounted for ripple. Four common ReSC topologies are exemplified throughout, with topology specific parameters documented for reference

Multi-Ratio Operation of Flying Capacitor Multilevel Converters At and Above Resonance

The flying capacitor multilevel (FCML) converter is an attractive candidate for dc/dc step-up and step-down applications due to its relatively low switch stress and greatly reduced inductor volume. It can be operated in either a regulating pulse width modulated (PWM) or fixed-ratio resonant mode. For fixed-ratio operation, the FCML converter is capable of achieving multiple rational conversion ratios (up to a maximum of N:1) with the same switch-capacitor network simply by changing the gating signals of its switches. In addition, the inductance requirement can be further reduced compared to regulated operation, while switching losses at resonance can be mitigated due to the presence of soft-switching. However, there is limited prior analysis of higher level-count (N\geq 3) fixed-ratio FCML converters operating at resonance or above resonance, where the derivation of appropriate phase durations becomes significantly more involved. This work presents a full analytical method to calculate optimal phase durations for the fixed-ratio FCML converter across all rational conversion ratios while operating at or above resonance. Hardware results for an N=5 FCML converter are presented for conversion ratios 5: 1, 5: 2, 5:3 and 5:4, illustrating the ability to use above-resonance operation to optimize the distribution of switching losses and conduction losses in the converter