1,327 research outputs found

    Silicon Atomic Quantum Dots Enable Beyond-CMOS Electronics

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    We review our recent efforts in building atom-scale quantum-dot cellular automata circuits on a silicon surface. Our building block consists of silicon dangling bond on a H-Si(001) surface, which has been shown to act as a quantum dot. First the fabrication, experimental imaging, and charging character of the dangling bond are discussed. We then show how precise assemblies of such dots can be created to form artificial molecules. Such complex structures can be used as systems with custom optical properties, circuit elements for quantum-dot cellular automata, and quantum computing. Considerations on macro-to-atom connections are discussed.Comment: 28 pages, 19 figure

    Algorithmic Jim Crow

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    This Article contends that current immigration- and security-related vetting protocols risk promulgating an algorithmically driven form of Jim Crow. Under the “separate but equal” discrimination of a historic Jim Crow regime, state laws required mandatory separation and discrimination on the front end, while purportedly establishing equality on the back end. In contrast, an Algorithmic Jim Crow regime allows for “equal but separate” discrimination. Under Algorithmic Jim Crow, equal vetting and database screening of all citizens and noncitizens will make it appear that fairness and equality principles are preserved on the front end. Algorithmic Jim Crow, however, will enable discrimination on the back end in the form of designing, interpreting, and acting upon vetting and screening systems in ways that result in a disparate impact

    Application of active controls technology to aircraft bide smoothing systems

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    A critical review of past efforts in the design and testing of ride smoothing and gust alleviation systems is presented. Design trade offs involving sensor types, choice of feedback loops, human comfort, and aircraft handling-qualities criteria are discussed. Synthesis of a system designed to employ direct-lift and side-force producing surfaces is reported. Two STOL aircraft and an executive transport are considered. Theoretically predicted system performance is compared with hybrid simulation and flight test data. Pilot opinion rating, pilot workload, and passenger comfort rating data for the basic and augmented aircraft are included

    A Study of Job Satisfaction and Retention Amongst Public and Private Basic School Teachers in Ghana

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    The teacher is a focal point among the various agents of education who see to the advancement and development of a nation. This comparative study examined the job satisfaction and retention amongst basic school teachers at Ledzokuku Krowor Municipality in the context of Herzberg’s Two Factor Theory. Specifically, the study will explore the impact of motivator and hygiene factors between public and private basic school teachers, identify the significant difference between public and private school teachers in their hygiene factors, measure the level of job satisfaction variables that are responsible to discriminate private and public school teachers and to find out factors of job satisfaction that influence teacher retention between public and private basic school teachers. The adapted version of Minnesota Job Satisfaction Questionnaire was used to collect quantitative data from 210 basic school teachers using descriptive statistics and inferential statistical techniques while the interviews conducted were analysed qualitatively through content analysis. For the qualitative data, 12 senior management teachers and those who indicated they were leaving or had left were purposely selected and interviewed in focus groups. Interviews were recorded using a digital voice recorder (Olympics VN-713PC) then translated verbatim. Interview transcripts were uploaded to NVivo10 software (QSR International Pty Ltd). Different codes were identified into potential themes and all important coded extracts were collated within the identified themes. The independent samples t-test results showed that there is a significant difference in job dissatisfaction variables of basic school teachers. High scores on salary, job security, policy, working conditions and low scores on status, relation with supervisors and subordinate are predictive of private schools teachers. This analysis suggests that private basic school teachers were more dissatisfied with their hygiene factors of job satisfaction than their counterparts in the public sector. It was recommended that the Ministry of Education and other stakeholders should develop a policy framework that will culminate into developing a Teacher Support and Motivation Framework (TSMF). Keywords: Herzberg Theory, Hygiene Factors, Job Satisfaction, Motivator, Private and Public Basic School, Teachers, Retention DOI: 10.7176/JEP/12-3-16 Publication date: January 31st 202

    F-16 Ventral Fin Buffet Alleviation Using Piezoelectric Actuators

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    Buffet-induced vibrations can have a disastrous impact on aircraft structures. Early attempts at combating buffet vibrations included passive methods such as structural enhancements and leading edge fences. Active methods have shown greater promise, including active airflow control, control surface modulation, and active structural control using piezoelectric actuators. Surface mounted piezoelectric actuators impart directional strain reducing the negative effects associated with harmful vibration. The Block-15 F-16 ventral fin represents an aircraft structure prone to failure when subjected to the buffet field from the wake of a LANTIRN pod. This research takes advantage of the susceptibility to buffet vibration of the Block 15 ventral fin in an effort to design an active control system to alleviate vibrations using piezoelectric actuators and sensors and to demonstrate its capability during flight test. It was sponsored by the United States Air Force (USAF) Test Pilot School (TPS). The development of an active control system began with the specification of piezoelectric actuators and sensors to be used in a collocated design to alleviate the vibrations of the first two modes of the ventral fin. A switching amplifier was designed and built to drive the actuators during all phases of testing. For the piezoelectric actuators to be effective, they needed to be located within the regions of highest strain energy and aligned with the principal strain vectors in those regions, the direction of principle strain was experimentally determined to ensure the proper orientation of the piezoelectric hardware on the ventral fin\u27s surface. Two control techniques were used in this research: positive position feedback and Linear Quadratic Gaussian compensator

    Research and technology, Lewis Research Center

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    Aeronautics, space, and terrestrial energy research is covered. Energy conversion processes and systems for propulsion in the atmosphere, in space, and on the ground are reviewed. Electric energy generation and storage for both terrestrial and space applications and materials and structures for such systems are also reviewed

    Large-Signal Stability Criteria in DC Power Grids with Distributed-Controlled Converters and Constant Power Loads

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    The increasing adoption of power electronic devices may lead to large disturbance and destabilization of future power systems. However, stability criteria are still an unsolved puzzle, since traditional small-signal stability analysis is not applicable to power electronics-enabled power systems when a large disturbance occurs, such as a fault, a pulse power load, or load switching. To address this issue, this paper presents for the first time the rigorous derivation of the sufficient criteria for large-signal stability in DC microgrids with distributed-controlled DC-DC power converters. A novel type of closed-loop converter controllers is designed and considered. Moreover, this paper is the first to prove that the well-known and frequently cited Brayton-Moser mixed potential theory (published in 1964) is incomplete. Case studies are carried out to illustrate the defects of Brayton-Moser mixed potential theory and verify the effectiveness of the proposed novel stability criteria

    Tracking and data relay satellite system configuration and tradeoff study. Volume 5: TDRS spacecraft design, part 1

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    A dual spin stabilized TDR spacecraft design is presented for low data rate (LDR) and medium data rate (MDR) user spacecraft telecommunication relay service. The relay satellite provides command and data return channels for unmanned users together with duplex voice and data communication channels for manned user spacecraft. TDRS/ground links are in the Ku band. Command links are provided at UHF for LDR users and S band for MDR users. Voice communication channels are provided at UHF/VHF for LDR users and at S band for MDR users. The spacecraft is designed for launch on the Delta 2914 with system deployment planned for 1978. This volume contains a description of the overall TDR spacecraft configuration, a detailed description of the spacecraft subsystems, a reliability analysis, and a product effectiveness plan
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