Band Limited Signals Observed Over Finite Spatial and Temporal Windows: An Upper Bound to Signal Degrees of Freedom

The study of degrees of freedom of signals observed within spatially diverse broadband multipath fields is an area of ongoing investigation and has a wide range of applications, including characterising broadband MIMO and cooperative networks. However, a fundamental question arises: given a size limitation on the observation region, what is the upper bound on the degrees of freedom of signals observed within a broadband multipath field over a finite time window? In order to address this question, we characterize the multipath field as a sum of a finite number of orthogonal waveforms or spatial modes. We show that (i) the "effective observation time" is independent of spatial modes and different from actual observation time, (ii) in wideband transmission regimes, the "effective bandwidth" is spatial mode dependent and varies from the given frequency bandwidth. These findings clearly indicate the strong coupling between space and time as well as space and frequency in spatially diverse wideband multipath fields. As a result, signal degrees of freedom does not agree with the well-established degrees of freedom result as a product of spatial degrees of freedom and time-frequency degrees of freedom. Instead, analogous to Shannon's communication model where signals are encoded in only one spatial mode, the available signal degrees of freedom in spatially diverse wideband multipath fields is the time-bandwidth product result extended from one spatial mode to finite modes. We also show that the degrees of freedom is affected by the acceptable signal to noise ratio (SNR) in each spatial mode.Comment: Submitted to IEEE Transactions on Signal Processin

INVESTIGATION INTO THE ADDITION OF BENZOIC ACID AND STYRENE OXIDE & EFFECT OF PHOSPHONIUM SALTS FOR FLAME RETARDANCY IN POLYURETHANE FILMS

INVESTIGATION INTO THE ADDITION OF BENZOIC ACID AND STYRENE OXIDE & EFFECT OF PHOSPHONIUM SALTS FOR FLAME RETARDANCY IN POLYURETHANE FILMS An Abstract of the Thesis by Salehin Mahbub The thesis will be divided into two sections. First, the synthesis of a 1,2-hydroxy ester was performed using styrene oxide and benzoic acid using several different catalysts and solvents. This project was chosen because there is a limited number of studies in literature and they did not report a systematic study. Various catalysts will be used in this study such as tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium fluoride, tetrabutylammonium iodide to determine the effects of the halide on the reaction. The solvents chosen for this research were toluene, isopropanol, butanol and THF to determine solvents effects. Samples were analyzed by Fourier-transform infrared (FT-IR) spectroscopy and Nuclear magnetic resonance (NMR) spectroscopy. FTIR was used to determine reaction completion and NMR was used to determine the ratio of the regioisomers. The second part of the research is the study of the effects of novel phosphonium salts on flame retardancy. New flame resistant materials are required industrially to replace halogenated flame retardants since these compounds have a negative environmental impact. In this study, phosphonium salts and triphenyl phosphate were incorporated into polyurethane films. FT-IR was used to characterize the polymer. Polyurethane films containing phosphonium salts and triphenyl phosphate were characterized by a burn test and thermogravimetric analysis (TGA) to determine their effect on flame retardancy and thermal stability

Socio-political and economic correlates influencing abortion policies across the states in America

In United States abortion has been the divisive issue in social and political front. In June 2022, a long-awaited ruling of US Supreme court officially reversed 1973s ruling on Roe v. Wade that established the constitutional right to abortion. Access to abortion has been facing challenges by the right wing formal and informal socio-political agencies placing reproductive health of women at risk. Pro-life conservative groups across the states have been attempting to make abortion difficult to access through enacting laws prevailing societal norms and patriarchal values based on religiosity. Utilizing the social determinants of health and system perspectives this study measures the cumulative effect of sociopolitical and economic variables on abortion policy scores of the states using multiple linear regression model. Independent variables in the model are state's 2020 presidential election outcome, prevalence of teen abortion, unemployment among women living in poverty, and enrollment of women in higher education. As hypothesized, presidential election outcome was identified as a predictor of state's abortion policy attribute and the extent of policy being supportive or restrictive. Bivariate analyses show significant associations between dependent variables and the predictors in expected direction such as, states with supportive abortion policy had higher enrollment of female in college or graduate school compared to that of states with restrictive abortion policy. Implications and recommendations for future research are provided

Analysis of Degrees of Freedom of Wideband Random Multipath Fields Observed Over Time and Space Windows

In multipath systems, available degrees of freedom can be considered as a key performance indicator, since the channel capacity grows linearly with the available degrees of freedom. However, a fundamental question arises: given a size limitation on the observable region, what is the intrinsic number of degrees of freedom available in a wideband random multipath wavefield observed over a finite time interval? In this paper, we focus on answering this question by modelling the wavefield as a sum of orthogonal waveforms or spatial orders. We show that for each spatial order, (i) the observable wavefield is band limited within an effective bandwidth rather than the given bandwidth and (ii) the observation time varies from the given observation time. These findings show the strong coupling between space and time as well as space and bandwidth. In effect, for spatially diverse multipath wavefields, the classical degrees of freedom result of "time-bandwidth" product does not directly extend to "time-space-bandwidth" product.Comment: 9 pages, 2 figures, Accepted in 2014 IEEE Workshop on Statistical Signal Processin

Impact of mechanical vibration on over-the-air link at upper mmW frequencies

Abstract. Mechanical vibrations will affect the performance of the wireless link especially with coming 6G systems, which will operate at significantly higher frequencies than current 5G networks. The mechanical vibrations affect the frequency generation circuitries of the radio equipment and thus the performance of the radio link. The amount mechanical vibration to the radio or any equipment has been standardized and a short summary of related standards has been given in the thesis. Some practical measurements have been performed to verify the effects of mechanical vibration on wireless link performance. The measurement has been done with a vector signal analyzer that measures the S-parameters of the wireless link. The phase response of the measured S-parameters has been studied to illustrate the phenomena. The mechanical vibration has been measured with a mobile phone application which detects the changes, vibrations, and location changes of the mobile phone when it was placed over the frequency extender. As a result of the selection of frequency extenders, the RF measurement equipment has been able to perform over a greater frequency range than was originally intended. The used mobile phone application was the G-force meter, which is freely available from application stores. The measured S-parameters S11 and S21 were analyzed with Matlab software which was provided for the purpose. The measured S-parameters and vibration results have been time synchronized in the Matlab result post-processing. The measurement results show clearly that mechanical vibrations influence the radio signal phase and thus it needs to be considered in the future development of 6G

Missing Requirements Information and its Impact on Software Architectures: A Case Study

[Context & motivation] In the development of large, software-intensive systems, the system’s requirements are seldom, if ever, concluded upon prior to commencing with systems architecture. Research shows that, in order to manage development and domain complexities, instances of requirements engineering (RE) and systems architecting (SA) processes tend to inter-weave. [Question/problem] However, missing requirements information can cause one to create (or recreate) the needed information during different SA activities. While backtracking in the software development process is known to be costly, the costs associated with missing requirements in the SA process have not been investigated empirically. [Principal ideas/results] We thus conducted a case study where we investigated to what extent requirements or requirements attributes’ information found missing during the SA process and impact of those missing information on SA in terms of effort. The study involved five architecting teams that involve final year undergraduate and graduate students enrolled in the university course on SA, working on architecting a system falls under “banking” domain. Our result shows that, architects did find requirements and requirements attributes’ information missing while architecting. Among requirements information, architects found that, system functionality information, constraints information and system interaction (users/systems) information are missing in requirements at higher percentages. Within requirements’ attributes, architects found requirements priority, dependency and rationale missing at higher percentages. It is also found that, out of total time spent on architecting the system, effort given to recreate missing requirements information is higher for group3 (21.5%), group1 (18%), and group2 (17%) other than group4 (12.37%) and group5(10.18%). [Contribution] The anticipated benefits of the findings are, it can motivate researchers to venture into other areas of software engineering (such as coding, testing, maintenance, etc.) from the view point of missing requirements information and its impact on those areas. This knowledge could help software practitioners to decide what kind of information need to take care of, during RE process, that could possibly ease SA process and later development phases. To the best of my knowledge, this is the first work which focuses on, to what extent requirements and requirements’ attributes information found missing during SA; characteristics and impact of those requirements missing information on SA process in terms of effort