For an oscillator that is periodically swept in frequency between some upper and lower bound, the output amplitude may easily be made constant and therefore known with a high degree of certainty. The instantaneous frequency exists only at a point in time and therefore possesses a zero probability of existing at any point. This thesis deals with the development of a method for interchanging the probability density functions of amplitude and frequency so that the latter becomes known with certainty while the former is known only to the extent that it is within a certain range. The method developed makes practical the use of the fast tuned voltage controlled oscillator as the local oscillator in a frequency scanning superheterodyne receiver. Exact frequency is expressed by a digital word of finite bit length that, in actuality, expresses the value of a quantized amplitude variable whose quantized value represents a precise frequency. Because of the interrelationship of amplitude, frequency, and time through the Fourier Transform, functions of these variables are also interrelated suggesting the possibility that the original certainty of amplitude information may be traded with the original uncertainty of frequency information. The success of the method presented makes use of the precise knowledge of the frequencies of the sidebands generated by the angle modulation process rather than make direct use of the instantaneous frequency. After mathematical development, a design example addresses the actual frequency range in the microwave region where the scanning superheterodyne receiver finds military application. To demonstrate the concept of precise frequency control with words of finite length, a practical frequency model is designed and constructed by scaling megahertz to hertz. Extensive use is made of monolithic waveform generators, balanced mixers, and operational amplifiers used as active filters and time domain summers. All assemblies within the model have practical microwave counterparts. Time and frequency domain waveforms are observed at virtually every major point of the model corresponding to the functional block interfaces and are compared with the mathematical predictions. The ultimate goal of precise frequency selection as a function of an imprecise independent variable is also obtained with the aid of a spectrum analyzer and dual trace oscilloscope. The causes of less than optimum signal level separation of adjacent discrete frequencies are analyzed in a qualitative manner. Reasons for the ineffectiveness of a quantitative critique are also presented. Experimental results, however, are demonstrated proof of the feasibility of the concept of exchanging probability density functions of related variables and that refinement is the only ingredient missing to render the fast scan VCO a useful local oscillator.
To effectively participate in modern collaborations, member organizations should be able to share digital resources with various partners, while ensuring their digital resources are protected from inappropriate access.In the existing literature, a substantial amount of research on centralized access control in the context of a single organization has been carried out.However, research on decentralized access control in a collaborative environment is scarce.To advance research in this area, I implemented a prototype of a decentralized access control system, which supports transparency, auditability, immutability, and equality in a collaboration environment, using the Multichain blockchain platform, RESTful web services, and Java programming language.The prototype was developed to evaluate two primary metrics: average response time and throughput.To achieve this, I carried out a number of experiments to measure both metrics on a Local Area Network (LAN) and on Amazon Web Services (AWS) under 84 different experimental conditions.The LAN setup provides a baseline for system performance under optimal conditions, while the cloud infrastructure represents a real-world use case.With low-system loads (comprising one to thirty concurrent clients and a single server running the system), the LAN setup outperformed the AWS setup by a factor of 2.5 based on throughput.On the other hand, when the system load is significantly increased, with more servers running the system, the AWS and LAN setups showed only a marginal difference in their performance.This demonstrates the potential to horizontally scale the decentralized access control system using blockchain on cloud infrastructure.
This paper discuss the smoke sensor and the relay control in the smart home.STM32 is used as the central part of the whole system and LwIP protocol is also applied to transfer data. The system uses the MQ-2 smoke sensor detect the concentration of combustible gases in air, and uses the SRD-05VDC-SL-C to close and cut off the circuit. The paper also discuss the sensitivity characteristics and the temperature and humidity effect of the smoke sensor. At the end of the paper, it is given the C code in the KEIL MDK environment.