Browsing by Author "Zhang, Chen"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Ammonia emissions from broiler houses and mitigating technologies(University of Delaware, 2021) Zhang, ChenIn recent years, increased attentions have been given to ammonia (NH3) emissions from poultry due to its environmental and health impacts. NH3 is generated from the chemical decomposition of bird feces by certain bacteria in the litter. NH3 was considered as a precursor to fine particulate matter (PM2.5), and the US Environmental Protection Agency (EPA) has been petitioned to regulate NH3 as a criteria pollutant. Furthermore, NH3 emission represents a significant loss of valuable nitrogen fertilizer. NH3 can be deposited from the atmosphere, if excess nitrogen (N) is deposited, it may impact the ecosystem negatively. Potential environmental issues associated with exceeding N in the environment include nitrate contamination of drinking water; eutrophication of surface water bodies; vegetation or ecosystem changes due to higher concentrations of N; and soil acidification through nitrification and leaching. Several approaches have been suggested and evaluated for mitigating NH3 emissions from concentrated animal feeding operations (CAFOs). Litter amendment can produce hydrogen irons (H+) when it dissolves and inhibit the free NH3 production by converting it to the ammonium (NH4+). The commonly used litter amendments include aluminum sulfate, sodium bisulfate, and ferric sulfate. Acid scrubber can absorb NH3 from exhausted air emitted from CAFOs. The scrubbers usually filled with packing materials and acid solution. Acid solution is sprayed from the top of the reactor. Mass transfer occurs from gas to liquid phase when the air and solution get contact. The vegetative environmental buffer (VEBs) has been used around CAFOs as a best management practice to reduce downwind gas concentration and emissions. Previous studies show VEBs can also mitigate odor and particulate matters. Some studies have been done with those technologies for the NH3 mitigation from poultry operations. However, the data from broiler operations is still limited. In this project, several different NH3 mitigating technologies, include litter amendment, acid scrubber and VEBs, will be tested and evaluated in broiler operations. The data can be used as a reference for future studies and commercial use.Item Detection of Stealthy Jamming for UAV-Assisted Wireless Communications: An HMM-based Method(IEEE Transactions on Cognitive Communications and Networking, 2023-02-28) Zhang, Chen; Zhang, Leyi; Mao, Tianqi; Xiao, Zhenyu; Han, Zhu; Xia, Xiang-GenDue to the high mobility, low cost and high robustness of line-of-sight (LoS) channels, unmanned aerial vehicles (UAVs) have begun to play an important role in assisting wireless communications. However, the broadcasting nature of wireless communication networks makes the electromagnetic spectrum vulnerable to jamming attacks. To ensure communication security, this paper investigates the jamming detection issue for UAV-assisted wireless communications. Different from the existing works, we consider detection of stealthy jamming with no prior knowledge of legitimate users or channel statistics, which makes the detection more challenging. To solve this problem, we design a hidden Markov model (HMM) based jamming detection (HBJD) method. First, we process the received signals with a sliding window to calculate the logarithmic received energy and use HMM to model the signal transmission under a jamming attack. Specifically, the spectrum state and logarithmic received energy are modeled as the hidden state and observable variable of HMM. Then, the Expectation-Maximization (EM) algorithm is applied to estimate the parameters of HMM. With the estimated parameters, the spectrum state of each logarithmic received energy sample can be decided according to the maximum posterior probability (MAP) criterion. Finally, we design the test statistics and derive the threshold based on the estimated HMM parameters for the final decision. Simulation results demonstrate the superiority of the proposed solution for the detection of stealthy jamming without prior knowledge of legitimate users or the channel statistics.