Review of free-space optical communications with diverging beam

The report reviews the technology of Free-space Optical Communication (FSO) and simulation methods for testing the performance of diverged beam in the technology. In addition to the introduction, the theory of turbulence and its effect over laser is also reviewed. In the simulation revision chapter, on-off keying (OOK) and diverged beam is assumed in the transmitter, and in the receiver, avalanche photodiode (APD) is utilized to convert the photon stream into electron stream. Phase screens are adopted to simulate the effect of turbulence over the phase of the optical beam. Apart from this, the method of data processing is introduced and retrospected. In the summary chapter, there is a general explanation of different beam divergence and their performance

Online Social Influence

This dissertation studies the behaviors of consumers in an online, social context. In the first essay, we jointly model the drivers of social media rebroadcasting behavior. Our goal in this research is to propose a framework and model of social media rebroadcasting behavior that integrates the various factors shown to influence rebroadcasting behavior. These include the role of message content and influence, factors that have been studied separately with very little integration. The results from our proposed model show that not only does rebroadcasting activity vary with the content of the original message but also that individuals are more likely to rebroadcast content that closely fits with their own interests. In the second essay, we ask whether online opinions impact consumers' decision quality and assess whether this impact occurs immediately or requires one to undergo learning first. We focus on a setting where consumers have multiple learning episodes based on their experiences with opinions from both uni- and bi-directional ties (i.e. weak and strong ties). We find that the dynamic effects are dependent on the strength of the tie. Additional strong ties (operationalized as bi-directional links) lead to immediate positive effects on decision quality. In contrast, additional weak ties (uni-directional, follower relationships) as a source of information lead initially to lower decision quality. However, highly-experienced consumers receive, ultimately, higher positive effects on decision quality from weak ties as compared with strong ties. Finally, in the third essay, we propose a new framework and model for identifying dimension specific influentials. We explicitly model individuals' preferences by estimating their locations on a market map to disentangle purchase behavior due to homophily from that due to influence. Our results show that it is important to estimate dimension specific influence, based on a comparison of model fit with a baseline model that measures influence along one dimension. We also show that individuals have varying levels of influence across dimensions, and an influencer for one dimension is not always influential on all dimensions

Financial constraints and the value of cash holdings

Financial constraint is an important topic in corporate finance. Previous literatures do researches on how to do measurement on financial constraint and whether it has an impact on investment and cash holdings. The results of these articles indicate that financial constraints do have influence on cash holdings. This dissertation will analyze the association between cash holdings and the value of companies in financially constrained and unconstrained firms based on some existing conclusions. We need to check two problems. One is whether cash holdings more valuable in constrained companies, and the other one is why cash holdings more valuable in these companies. A sample of 42276 firm-year observations from 2004 to 2011 in United State is used to do analysis. Financially constrained and unconstrained companies are divided by three measures, which are payout ratios, size and KZ index. By using univariate test, OLS regression, fixed effect, and two-step least squares in empirical researches, we can reach the following conclusions: In financially constrained companies cash holdings are more valuable. Larger amount of cash holdings can allow companies accept profitable investment projects, which can lead to higher excess stock return. So cash holdings have an impact on the value of firms via investment activities. For some financially constrained companies with higher hedging needs, they will reserve larger amount of cash, and the amount of cash are more valuable in financially constrained companies with stronger hedging needs than financially constrained companies with lower needs for hedging

Corn Yield Prediction based on Remotely Sensed Variables Using Variational Autoencoder and Multiple Instance Regression

In the U.S., corn is the most produced crop and has been an essential part of the American diet. To meet the demand for supply chain management and regional food security, accurate and timely large-scale corn yield prediction is attracting more attention in precision agriculture. Recently, remote sensing technology and machine learning methods have been widely explored for crop yield prediction. Currently, most county-level yield prediction models use county-level mean variables for prediction, ignoring much detailed information. Moreover, inconsistent spatial resolution between crop area and satellite sensors results in mixed pixels, which may decrease the prediction accuracy. Only a few works have addressed the mixed pixels problem in large-scale crop yield prediction. To address the information loss and mixed pixels problem, we developed a variational autoencoder (VAE) based multiple instance regression (MIR) model for large-scaled corn yield prediction. We use all unlabeled data to train a VAE and the well-trained VAE for anomaly detection. As a preprocess method, anomaly detection can help MIR find a better representation of every bag than traditional MIR methods, thus better performing in large-scale corn yield prediction. Our experiments showed that variational autoencoder based multiple instance regression (VAEMIR) outperformed all baseline methods in large-scale corn yield prediction. Though a suitable meta parameter is required, VAEMIR shows excellent potential in feature learning and extraction for large-scale corn yield prediction

Noise control and utility: From regulatory network to spatial patterning

Stochasticity (or noise) at cellular and molecular levels has been observed extensively as a universal feature for living systems. However, how living systems deal with noise while performing desirable biological functions remains a major mystery. Regulatory network configurations, such as their topology and timescale, are shown to be critical in attenuating noise, and noise is also found to facilitate cell fate decision. Here we review major recent findings on noise attenuation through regulatory control, the benefit of noise via noise-induced cellular plasticity during developmental patterning, and summarize key principles underlying noise control

Energy regeneration from suspension dynamic modes and self-powered actuation

Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper concerns energy harvesting from vehicle suspension systems. The generated power associated with bounce, pitch and roll modes of vehicle dynamics is determined through analysis. The potential values of power generation from these three modes are calculated. Next, experiments are carried out using a vehicle with a four jack shaker rig to validate the analytical values of potential power harvest. For the considered vehicle, maximum theoretical power values of 1.1kW, 0.88kW and 0.97kW are associated with the bounce, pitch and roll modes, respectively, at 20 Hz excitation frequency and peak to peak displacement amplitude of 5 mm at each wheel, as applied by the shaker. The corresponding experimentally power values are 0.98kW, 0.74kW and 0.78kW. An experimental rig is also developed to study the behavior of regenerative actuators in generating electrical power from kinetic energy. This rig represents a quarter-vehicle suspension model where the viscous damper in the shock absorber system is replaced by a regenerative system. The rig is able to demonstrate the actual electrical power that can be harvested using a regenerative system. The concept of self-powered actuation using the harvested energy from suspension is discussed with regard to applications of self-powered vibration control. The effect of suspension energy regeneration on ride comfort and road handling is presented in conjunction with energy harvesting associated with random road excitations.Peer reviewedFinal Accepted Versio