Matching Items (42)
Description
Nonlinear dispersive equations model nonlinear waves in a wide range of physical and mathematics contexts. They reinforce or dissipate effects of linear dispersion and nonlinear interactions, and thus, may be of a focusing or defocusing nature. The nonlinear Schrödinger equation or NLS is an example of such equations. It appears as a model in hydrodynamics, nonlinear optics, quantum condensates, heat pulses in solids and various other nonlinear instability phenomena. In mathematics, one of the interests is to look at the wave interaction: waves propagation with different speeds and/or different directions produces either small perturbations comparable with linear behavior, or creates solitary waves, or even leads to singular solutions. This dissertation studies the global behavior of finite energy solutions to the $d$-dimensional focusing NLS equation, $i partial _t u+Delta u+ |u|^{p-1}u=0, $ with initial data $u_0in H^1,; x in Rn$; the nonlinearity power $p$ and the dimension $d$ are chosen so that the scaling index $s=frac{d}{2}-frac{2}{p-1}$ is between 0 and 1, thus, the NLS is mass-supercritical $(s>0)$ and energy-subcritical $(s<1).$ For solutions with $ME[u_0]<1$ ($ME[u_0]$ stands for an invariant and conserved quantity in terms of the mass and energy of $u_0$), a sharp threshold for scattering and blowup is given. Namely, if the renormalized gradient $g_u$ of a solution $u$ to NLS is initially less than 1, i.e., $g_u(0)<1,$ then the solution exists globally in time and scatters in $H^1$ (approaches some linear Schr"odinger evolution as $ttopminfty$); if the renormalized gradient $g_u(0)>1,$ then the solution exhibits a blowup behavior, that is, either a finite time blowup occurs, or there is a divergence of $H^1$ norm in infinite time. This work generalizes the results for the 3d cubic NLS obtained in a series of papers by Holmer-Roudenko and Duyckaerts-Holmer-Roudenko with the key ingredients, the concentration compactness and localized variance, developed in the context of the energy-critical NLS and Nonlinear Wave equations by Kenig and Merle. One of the difficulties is fractional powers of nonlinearities which are overcome by considering Besov-Strichartz estimates and various fractional differentiation rules.
ContributorsGuevara, Cristi Darley (Author) / Roudenko, Svetlana (Thesis advisor) / Castillo_Chavez, Carlos (Committee member) / Jones, Donald (Committee member) / Mahalov, Alex (Committee member) / Suslov, Sergei (Committee member) / Arizona State University (Publisher)
Created2011
Description
This thesis outlines the development of a vector retrieval technique, based on data assimilation, for a coherent Doppler LIDAR (Light Detection and Ranging). A detailed analysis of the Optimal Interpolation (OI) technique for vector retrieval is presented. Through several modifications to the OI technique, it is shown that the modified technique results in significant improvement in velocity retrieval accuracy. These modifications include changes to innovation covariance portioning, covariance binning, and analysis increment calculation. It is observed that the modified technique is able to make retrievals with better accuracy, preserves local information better, and compares well with tower measurements. In order to study the error of representativeness and vector retrieval error, a lidar simulator was constructed. Using the lidar simulator a thorough sensitivity analysis of the lidar measurement process and vector retrieval is carried out. The error of representativeness as a function of scales of motion and sensitivity of vector retrieval to look angle is quantified. Using the modified OI technique, study of nocturnal flow in Owens' Valley, CA was carried out to identify and understand uncharacteristic events on the night of March 27th 2006. Observations from 1030 UTC to 1230 UTC (0230 hr local time to 0430 hr local time) on March 27 2006 are presented. Lidar observations show complex and uncharacteristic flows such as sudden bursts of westerly cross-valley wind mixing with the dominant up-valley wind. Model results from Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) and other in-situ instrumentations are used to corroborate and complement these observations. The modified OI technique is used to identify uncharacteristic and extreme flow events at a wind development site. Estimates of turbulence and shear from this technique are compared to tower measurements. A formulation for equivalent wind speed in the presence of variations in wind speed and direction, combined with shear is developed and used to determine wind energy content in presence of turbulence.
ContributorsChoukulkar, Aditya (Author) / Calhoun, Ronald (Thesis advisor) / Mahalov, Alex (Committee member) / Kostelich, Eric (Committee member) / Huang, Huei-Ping (Committee member) / Phelan, Patrick (Committee member) / Arizona State University (Publisher)
Created2013
Description
It is possible in a properly controlled environment, such as industrial metrology, to make significant headway into the non-industrial constraints on image-based position measurement using the techniques of image registration and achieve repeatable feature measurements on the order of 0.3% of a pixel, or about an order of magnitude improvement on conventional real-world performance. These measurements are then used as inputs for a model optimal, model agnostic, smoothing for calibration of a laser scribe and online tracking of velocimeter using video input. Using appropriate smooth interpolation to increase effective sample density can reduce uncertainty and improve estimates. Use of the proper negative offset of the template function has the result of creating a convolution with higher local curvature than either template of target function which allows improved center-finding. Using the Akaike Information Criterion with a smoothing spline function it is possible to perform a model-optimal smooth on scalar measurements without knowing the underlying model and to determine the function describing the uncertainty in that optimal smooth. An example of empiric derivation of the parameters for a rudimentary Kalman Filter from this is then provided, and tested. Using the techniques of Exploratory Data Analysis and the "Formulize" genetic algorithm tool to convert the spline models into more accessible analytic forms resulted in stable, properly generalized, KF with performance and simplicity that exceeds "textbook" implementations thereof. Validation of the measurement includes that, in analytic case, it led to arbitrary precision in measurement of feature; in reasonable test case using the methods proposed, a reasonable and consistent maximum error of around 0.3% the length of a pixel was achieved and in practice using pixels that were 700nm in size feature position was located to within ± 2 nm. Robust applicability is demonstrated by the measurement of indicator position for a King model 2-32-G-042 rotameter.
ContributorsMunroe, Michael R (Author) / Phelan, Patrick (Thesis advisor) / Kostelich, Eric (Committee member) / Mahalov, Alex (Committee member) / Arizona State University (Publisher)
Created2012
Description
Globalization has necessitated cross-cultural communication among groups and individuals alike, often beginning with management. This project considers how the degree of Power Distance, one of Hofstede's cultural dimensions, may change over time as a result of exposure to different, and often opposing, cultural values. We conducted two surveys 12 weeks apart collecting an initial sample of 317 and retaining a secondary sample of 142. We gathered data on demographics, education, on-campus involvement, cultural dimensions, and levels of comfort with different cultures. Through data analysis we found that as a result of exposure to different cultural values, cultural groups adjust their own views on Power Distance. Specifically, we found that the Anglo cultural group and the international cultural subgroup that had been living in the U.S. for less than 10 years trended towards each other on levels of Power Distance. We also found that international female students adjusted to new cultural surroundings faster than their male counterparts. These discoveries have led us to conclusions regarding the influence of awareness of other cultural values through international exposure, specifically that of Power Distance, as well as male versus female differences in cultural adjustment, and how differing views might trend towards each other with recurrent interaction.
ContributorsNiren, Alyssa (Co-author) / Davidson, Rachel (Co-author) / Lee, Peggy (Thesis director) / Zhang, Zhen (Committee member) / Department of Supply Chain Management (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / School of International Letters and Cultures (Contributor) / Department of Information Systems (Contributor) / W. P. Carey School of Business (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
A numerical study of wave-induced momentum transport across the tropopause in the presence of a stably stratified thin inversion layer is presented and discussed. This layer consists of a sharp increase in static stability within the tropopause. The wave propagation is modeled by numerically solving the Taylor-Goldstein equation, which governs the dynamics of internal waves in stably stratified shear flows. The waves are forced by a flow over a bell shaped mountain placed at the lower boundary of the domain. A perfectly radiating condition based on the group velocity of mountain waves is imposed at the top to avoid artificial wave reflection. A validation for the numerical method through comparisons with the corresponding analytical solutions will be provided. Then, the method is applied to more realistic profiles of the stability to study the impact of these profiles on wave propagation through the tropopause.
ContributorsCole, Alexandra Shea (Author) / Moustaoui, Mohamed (Thesis director) / Kostelich, Eric (Committee member) / Mahalov, Alex (Committee member) / School of International Letters and Cultures (Contributor) / School of Geographical Sciences and Urban Planning (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
Description
This work presents a thorough analysis of reconstruction of global wave fields (governed by the inhomogeneous wave equation and the Maxwell vector wave equation) from sensor time series data of the wave field. Three major problems are considered. First, an analysis of circumstances under which wave fields can be fully reconstructed from a network of fixed-location sensors is presented. It is proven that, in many cases, wave fields can be fully reconstructed from a single sensor, but that such reconstructions can be sensitive to small perturbations in sensor placement. Generally, multiple sensors are necessary. The next problem considered is how to obtain a global approximation of an electromagnetic wave field in the presence of an amplifying noisy current density from sensor time series data. This type of noise, described in terms of a cylindrical Wiener process, creates a nonequilibrium system, derived from Maxwell’s equations, where variance increases with time. In this noisy system, longer observation times do not generally provide more accurate estimates of the field coefficients. The mean squared error of the estimates can be decomposed into a sum of the squared bias and the variance. As the observation time $\tau$ increases, the bias decreases as $\mathcal{O}(1/\tau)$ but the variance increases as $\mathcal{O}(\tau)$. The contrasting time scales imply the existence of an ``optimal'' observing time (the bias-variance tradeoff). An iterative algorithm is developed to construct global approximations of the electric field using the optimal observing times. Lastly, the effect of sensor acceleration is considered. When the sensor location is fixed, measurements of wave fields composed of plane waves are almost periodic and so can be written in terms of a standard Fourier basis. When the sensor is accelerating, the resulting time series is no longer almost periodic. This phenomenon is related to the Doppler effect, where a time transformation must be performed to obtain the frequency and amplitude information from the time series data. To obtain frequency and amplitude information from accelerating sensor time series data in a general inhomogeneous medium, a randomized algorithm is presented. The algorithm is analyzed and example wave fields are reconstructed.
ContributorsBarclay, Bryce Matthew (Author) / Mahalov, Alex (Thesis advisor) / Kostelich, Eric J (Thesis advisor) / Moustaoui, Mohamed (Committee member) / Motsch, Sebastien (Committee member) / Platte, Rodrigo (Committee member) / Arizona State University (Publisher)
Created2023
Description
Climate is a critical determinant of agricultural productivity, and the ability to accurately predict this productivity is necessary to provide guidance regarding food security and agricultural management. Previous predictions vary in approach due to the myriad of factors influencing agricultural productivity but generally suggest long-term declines in productivity and agricultural land suitability under climate change. In this paper, I relate predicted climate changes to yield for three major United States crops, namely corn, soybeans, and wheat, using a moderate emissions scenario. By adopting data-driven machine learning approaches, I used the following machine learning methods: random forest (RF), extreme gradient boosting (XGB), and artificial neural networks (ANN) to perform comparative analysis and ensemble methodology. I omitted the western US due to the region's susceptibility to water stress and the prevalence of artificial irrigation as a means to compensate for dry conditions. By considering only climate, the model's results suggest an ensemble mean decline in crop yield of 23.4\% for corn, 19.1\% for soybeans, and 7.8\% for wheat between the years of 2017 and 2100. These results emphasize potential negative impacts of climate change on the current agricultural industry as a result of shifting bio-climactic conditions.
ContributorsSwarup, Shray (Author) / Eikenberry, Steffen (Thesis director) / Mahalov, Alex (Committee member) / Barrett, The Honors College (Contributor) / Computer Science and Engineering Program (Contributor)
Created2023-05
Description企业文化以及中高层员工对企业文化的认同度影响员工工作绩效表现，探讨他们之间的相互作用机理，有利于厘清企业文化的执行效果，方便决策者根据现实情况进行决策调整。在员工工作绩效层面，受限于数据的易得性、代表性与普遍性，以往的研究更多关注于企业发展，同时，很少有学者关注中高层管理人对企业文化认同的影响及决定因素。青山实业子公司众多，中高层管理人员人数达六百多人，提供了足够的研究样本，正是在这样的背景下，本文从剖析核心企业文化以及中高层管理人员对企业文化认同度视角出发，结合内外部因素，探索企业文化认同度与工作绩效、工作满意度的关系，并确定影响企业文化认同的前因，分析其作用机制，并据此对企业为中高层个人发展提供良好平台提出策略和建议。研究发现，归属感需求，外向型性格，工作能力，组织文化强度，团队沟通，分配公平和企业声誉对于组织文化认同度有正面影响，且这些影响因素在控制常见变量的情况下依然呈现出显著性。企业文化认同度对工作绩效和工作满意度都具有显著的正面促进作用。
ContributorsHe, Xiuqin (Author) / Zhu, David (Thesis advisor) / Wu, Fei (Thesis advisor) / Zhang, Zhen (Committee member) / Arizona State University (Publisher)
Created2022
Description2021年初笔者所在公司(D公司)邀请第三方咨询公司实施激励机制变革项目，历经半年完成调研、方案设计与培训落地，同年7月1日正式执行新的激励机制方案。 本文以笔者所在公司为实证调研对象，通过激励机制调整前后的两次问卷调查，与两次问卷调查期间的员工访谈与观察、财务数据监控等，深入探究企业激励机制调整前后公司员工敬业度与员工绩效的具体影响。
基于D公司激励机制调整，研究员工敬业度与员工绩效的具体变化，对D公司来说，第一可以验证激励变革效果，审视并梳理公司激励原则。第二可以关注员工敬业度对员工绩效的的作用机制，指导企业发展变革。相关的研究成果对其他激励变革的企业也有一定的借鉴意义，基于本文的实证研究对员工敬业度与员工绩效的作用机制有一定的理论贡献。
激励变革前后员工敬业度的变化，量表采用知名专业咨询公司盖洛普精心设计的工作环境评测与管理工具Q12，这个调研工具已经在世界上许多个大型公司实施、获得良好效果。Q12是设计用来调查员工对工作环境及员工敬业度的一系列题目。我在此基础上加入性别、年龄、工龄等变量，同时加入员工访谈与观察。激励变革前后员工绩效的具体变化，提取财务数据体现。
ContributorsLiu, Donghui (Author) / Zhu, David (Thesis advisor) / Cheng, Shijun (Thesis advisor) / Zhang, Zhen (Committee member) / Arizona State University (Publisher)
Created2023
Description自雇司机是公路货运司机中比例人数最多、最基层的一员，他们在公路物流行业中扮演着极为重要的角色，他们承担着各种来源的压力。本文以疫情前后按揭购买卡车的自雇司机为研究样本，基于本研究收集到的独特数据，研究发现自雇卡车司机在面临按揭压力时，倾向采取更为激进的经营及驾驶行为，表现为更少的休息天数、更长的工作时长以及更危险的高速驾驶行为，并在一系列稳健性检验中基本结论仍然存在；基于新冠疫情事件研究发现，新冠疫情带来的非预期性经济停摆和收入中断，导致疫情前的发生的按揭贷款的卡车司机面临更强的还款压力，在经济恢复后面对按揭压力更有可能采用激进的经营和驾驶行为；进一步，通过机制检验研究本文发现这种按揭压力主要表现为担心当前或者未来发生不能及时偿还按揭款。再者，基于人格性征和家庭支持的调节效应检验，本文发现神经质人格特征、谨慎尽责性人格特征以及工作压力感没有在按揭压力与自雇卡车司机激进的经营和驾驶选择上起到调节作用，这可能是自雇卡车司机面临的按揭压力都很大，个体性格特征很大程度无法缓和其压力感，而家庭的支持和家庭-工作平衡可以有效缓解自雇卡车司机面临按揭压力时提高工作时长和危险驾驶行为的倾向。
最后，本文设计一项随机对照干预实验，向自雇卡车司机发送短息或者微信，提醒他们避免疲劳驾驶和危险超速驾驶，然后观察发送短信微信前后自雇卡车司机经营及驾驶行为的变化，识别考察外界积极主动的关心和提醒能否起到相应的后果。本文发现对自雇卡车司机获得外部主动积极地的关心和提醒，在面临按揭压力时意识到简单地减少休息增加运营时长以及采用危险驾驶行为抢时间的策略可能给其带来很大的风险，从而相应地缓解对按揭压力的过度反应；进一步调节作用检验表明，短信干预实验在神经质和谨慎尽责性人格司机中起到更大的减缓作用，同时家庭支持较少时短信干预实现效应也更为明显。
ContributorsMa, Liqun (Author) / Shen, Wei (Thesis advisor) / Wu, Fei (Thesis advisor) / Zhang, Zhen (Committee member) / Arizona State University (Publisher)
Created2021