Group Sparse Precoding for Cloud-RAN with Multiple User Antennas

Cloud radio access network (C-RAN) has become a promising network architecture to support the massive data traffic in the next generation cellular networks. In a C-RAN, a massive number of low-cost remote antenna ports (RAPs) are connected to a single baseband unit (BBU) pool via high-speed low-latency fronthaul links, which enables efficient resource allocation and interference management. As the RAPs are geographically distributed, the group sparse beamforming schemes attracts extensive studies, where a subset of RAPs is assigned to be active and a high spectral efficiency can be achieved. However, most studies assumes that each user is equipped with a single antenna. How to design the group sparse precoder for the multiple antenna users remains little understood, as it requires the joint optimization of the mutual coupling transmit and receive beamformers. This paper formulates an optimal joint RAP selection and precoding design problem in a C-RAN with multiple antennas at each user. Specifically, we assume a fixed transmit power constraint for each RAP, and investigate the optimal tradeoff between the sum rate and the number of active RAPs. Motivated by the compressive sensing theory, this paper formulates the group sparse precoding problem by inducing the $\ell_0$-norm as a penalty and then uses the reweighted $\ell_1$ heuristic to find a solution. By adopting the idea of block diagonalization precoding, the problem can be formulated as a convex optimization, and an efficient algorithm is proposed based on its Lagrangian dual. Simulation results verify that our proposed algorithm can achieve almost the same sum rate as that obtained from exhaustive search

New results on the positive solutions of nonlinear second-order differential systems

In this paper, we study the three-point boundary value problems for systems of nonlinear second order ordinary differential equations of the form $$\left\{\begin{aligned} &u''=-f(t,v), \ \ 0< t< 1,\\&v''=-g(t,u), \ \ 0< t< 1\\&u(0)=v(0)=0,\varsigma u(\zeta)=u(1),\varsigma v(\zeta)=v(1),\end{aligned}\right.$$ where $f:(0,1)\times [0,+\infty)\to [0,+\infty),g:[0,1]\times [0,+\infty)\to [0,+\infty),00,$ and $\varsigma\zeta< 1,f$ may be singular at $t = 0$ and/or $t = 1.$ Under some rather simple conditions, by means of monotone iterative technique, a necessary and sufficient condition for the existence of positive solutions is established, a result on the existence and uniqueness of the positive solution and the iterative sequence of solution is given

Symmetric signaling by an asymmetric 1 erythropoietin : 2 erythropoietin receptor complex

Thesis (M. Eng.)--Massachusetts Institute of Technology, Biological Engineering Division, 2008.Includes bibliographical references (p. 43-46).One erythropoietin molecule binds asymmetrically to two identical receptor monomers via erythropoietin site 1 and site 2, although it is unclear how asymmetry affects receptor activation and signaling. Here we report the computational design and experimental validation of two mutant erythropoietin receptors: one that binds only to erythropoietin site 1 but not site 2, and one that binds only to site 2 but not site 1. Expression of either mutant receptor alone in Ba/F3 cells cannot elicit a signal in response to erythropoietin, but when co-expressed, there is a proliferative response and activation of the JAK2 Stat5 signaling pathway. A truncated erythropoietin receptor with only one cytosolic tyrosine (Y343), on only one receptor monomer is sufficient for signaling in response to erythropoietin, regardless of the monomer on which it is located. The same results apply to having only one conserved juxtamembrane hydrophobic L253 or W258 residue, essential for JAK2 activation, in the full-length receptor dimer. We conclude that despite asymmetry in the ligand-receptor dimer interaction, both sides are competent for signaling, and we suggest that the receptors signal equally.by Yingxin Zhang.M.Eng

Engineering polymeric hollow fiber membrane reactors for sustainable chemical transformation reactions

“Over the past decade, laboratory-scale continuous-flow processes have witnessed explosive developments and have attracted a great deal of interest with respect to the significance of the economic and environmentally-sustainable production of pharmaceuticals, fine chemicals, and agrochemicals, as well as upgrading of biomass feedstocks. Immobilization of organocatalysts and metal nanoparticles on continuous-flow microreactors offers an efficient catalytic system that exploits and enhances the advantages of both nanocatalysis and flow chemistry, the so-called flow nanocatalysis approach. Various approaches have been developed for the development of continuous-flow reactions including immobilization and subsequent anchoring of organocatalysts and metal nanoparticles within microfluidic reactors. However, many applications of microfluidic reactor-supported catalysts are still hampered by catalysts decomposition and their subsequent leaching from the microfluidic reactor to the product stream. This dissertation focuses on the investigation of structure/property/performance relations of a new catalytic membrane reactor platform for conducting catalytic reactions in a continuous-flow fashion. More specifically, it focuses on permanent immobilization/impregnation of organic or metal nanoparticle catalysts by covalent bonding within highly swelling-resistant asymmetric polymeric hollow fiber surfaces for non-leaching catalysis. This novel hollow fiber membrane reactor was used as a heterogeneous catalyst and continuous-flow reactor for various reactions including aldol and nitroaldol condensation, Heck coupling, tandem reaction of glucose and fructose to 5-hydroxymethylfurfural, and nitrophenol reduction reactions”--Abstract, page iv

Microencapsulation of omega-3 fatty acid rich oil via complex coacervation

The overall goal of this thesis was to use plant-based materials to encapsulate omega-3 oils to produce microencapsulated powders with improved stability against oxidative stresses. This research includes four studies (Chapter 3, 4, 5 & 6). Chapter 3 examined the complexation behaviour of lentil protein isolate (LPI) and carboxymethyl cellulose (CMC) with different degree of substitution (DS; 0.7, 0.9, and 1.2) and molar mass (MM; 90 and 250 kDa), and their thermodynamic properties. For complexation behaviour, max optical density was conducted at 4:1 LPI: CMC mixing ratio. MM and DS had no significant effect on critical pH values but impacted the size and number of complexes formed. The complexation reactions of all LPI-CMC mixtures at pH 3 was energetically favorable. Chapter 4 and 5 compared the complexation behaviour of LPI with various polysaccharides, including CMC, gum Arabic (GA), alginate (AL), ι-carrageenan (ι-C), and κ-carrageenan (κ-C), and the resulting emulsifying properties. For chapter 4, at 4:1 LPI-polysaccharide mixing ratio, LPI-GA and LPI-CMC mixtures formed coacervate-type of complexes, while precipitate-type of complexes were formed with LPI-AL and LPI-ι-C systems. Their resulting complexes at pHopt were used to make emulsions. LPI-ι-C emulsion displayed the highest emulsion stability (ES) due to its high emulsion viscosity, lower mean droplet sizes, and highly negative-charged droplets. For chapter 5, incorporating ι-C and κ-C into the LPI solution led to suppression of complexes formed. Emulsions prepared with the resulting soluble complexes at pH 6 showed significantly higher stability than those made with insoluble complexes at pH 3.5 for each sample. The greatest ES was attributed to 4:1 LPI-κ-C and LPI-ι-C emulsions at pH 6. Chapter 6 developed the LPI-polysaccharide based microcapsules to encapsulate flaxseed oil. LPI-κ-C and LPI-ι-C emulsions with maltodextrin at pH 6 were prepared, followed by spray-drying or freeze-drying to yield the dried capsules. Spray-dried capsules showed higher oil encapsulation efficiency, but the encapsulated oil was oxidized significantly due to heat effect during drying and lower water activity of the capsules. Flaxseed oil was stable in all freeze-dried capsules during 8 weeks of storage. For in vitro oil release profile, more oil was released from LPI-κ-C powders under simulated gastric fluid, but more oil was released from LPI-ι-C powders under subsequent simulated gastric fluid and simulated intestinal fluid regardless of drying method and oil content. This research suggested that there is great potential to use the resulting emulsions to make plant-based microcapsules to deliver omega-3 oils

Reaction kinetics of NH3-SCR over Cu-CHA from first principles

Ammonia assisted selective catalytic reduction (NH3-SCR) is a leading technology that is used for NOx reduction to N2 and H2O in oxygen excess. Thanks to its high activity, high selectivity, and durability, Cu-CHA is commercialized as an NH3-SCR catalyst. Despite the superior catalytic performance, small amounts of nitrous oxide (N2O) are formed during the NH3-SCR as an unwanted by-product. N2O has a strong greenhouse potential and should be avoided. To further enhance the performance of NH3-SCR catalysts to handle the increasingly stringent emission standards, understanding the mechanism for NH3-SCR and, in particular, N2O formation over Cu-CHA is essential.In this thesis, density functional theory (DFT) calculations and first principles microkinetic simulations are used to investigate the reaction path and the reaction kinetics for low temperature-NH3-SCR. Based on a previously proposed catalytic cycle for NH3-SCR over Cu-CHA, an N2O formation path is put forward. It is proposed that N2O can form over linear [Cu(NH3)2]+ complexes, which are present during low temperature operation. N2O is formed from H2NNO, which is generated via NH2-NO coupling over a Cu-OOH-Cu site. The reaction proceeds with a low barrier and rationalizes the low-temperatureN2O emission peak observed experimentally at high Cu-loadings. N2O formation at high temperatures is instead proposed to occur through the decomposition of NH4NO3.With a catalytic cycle including N2O formation, a first principles microkinetic model is developed to investigate the reaction kinetic of NH3-SCR over Cu-CHA. When developing the model, special attention is paid assessing the change in entropy for each reaction step. The results from the kinetic model show good agreement with the experimental data of apparent activation energies, reaction orders and N2O selectivity. The model links the catalytic performance with structure and forms the basis for further developments of the NH3-SCR technology

A Comprehensive Model for Recommending Personalized Learning Resources for the Development of Linguistic Competence

With the continuous advancement of globalization and informatization, the linguistic competence of college students has become a key index for evaluating their comprehensive quality. Faced with diverse needs of students and educational environments, it is increasingly important and complex to accurately locate the linguistic competence goals of college students. Although existing research methods, such as standardized testing and teacher assessment, provide certain convenience, they rely on single data sources and have a certain degree of subjectivity, which limits their universality and accuracy. This study aimed to solve this problem by doing comprehensive research on two aspects: first, curriculum analysis based on relation extraction. A relation extraction model, such as Casrel, was used for advanced text analysis, which provided educators with more in-depth insights; second, personalized learning material recommendation based on text recommendation. Personalized learning paths were provided for students of different levels using the abstractness-based text recommendation algorithm. This study not only filled the gaps in existing research methods, but also provided a new, scientific and efficient solution, helping improve the quality of education and promote the formulation of scientific education policies

Link-Family Safety Mobile Application Design

The safety and health of children are essential issues not only for households but also for society. Missing Child is a severe strike to a family. It causes severe trauma memory and affects family members both psychologically and physically. Incidents like this also spread a feeling of fear among the local community. Many efforts have been made to help with this problem, such as the Amber Alert system, the location-tracking functions in the operating system in smartphones. There are also many safety apps in the app stores trying to prevent this kind of incident. However, there are still things that these apps do not cover: What should the parents do when they lose contact with their children and feel worried? This project explored ways to provide guidance for parents and tried to find a way to balance the privacy-safety tradeoff

Meta-analysis of the population and phenotypic expression of CYP2C9/2C19 polymorphism on drug metabolism in different ethnicities

The term "pharmacogenetics" has been defined as the scientific study of inherited factors that affect the human drug response. Many pharmacogenetie studies have been published since 1995 and have focussed on the principal enzyme family involved in drug metabolism, the cytochrome P450 family, particularly cytochrome P4502C9 and 2C19. In order to investigate the pharmacogenetic aspect of pharmacotherapy, the relevant studies describing the association of pharmacogenetic factor(s) in drug responses must be retrieved from existing literature using a systematic review approach. In addition, the estimation of variant allele prevalence for the gene under study between different ethnic populations is important for pharmacogenetic studies. In this thesis, the prevalence of CYP2C9/2C19 alleles between different ethnicities has been estimated through meta-analysis and the population genetic principle. The clinical outcome of CYP2C9/2C19 allelic variation on the pharmacotherapy of epilepsy has been investigated; although many new antiepileptic drugs have been launched into the market, carbamazepine, phenobarbital and phenytoin are still the major agents in the pharmacotherapy of epilepsy. Therefore, phenytoin was chosen as a model AED and the effect of CYP2C9/2C19 genetic polymorphism on phenytoin metabolism was further examined.An estimation of the allele prevalence was undertaken for three CYP2C9/2C19 alleles respectively using a meta-analysis of studies that fit the Hardy-Weinberg equilibrium. The prevalence of CYP2C9*1 is approximately 81%, 96%, 97% and 94% in Caucasian, Chinese, Japanese, African populations respectively; the pooled prevalence of CYP2C19*1 is about 86%, 57%, 58% and 85% in these ethnic populations respectively. However, the studies of association between CYP2C9/2C19 polymorphism and phenytoin metabolism failed to achieve any qualitative or quantitative conclusion. Therefore, mephenytoin metabolism was examined as a probe drug for association between CYP2C19 polymorphism and mephenytoin metabolic ratio. Similarly, analysis of association between CYP2C9 polymorphism and warfarin dose requirement was undertaken.It was confirmed that subjects carrying two mutated CYP2C19 alleles have higher S/R mephenytoin ratio due to deficient CYP2C19 enzyme activity. The studies of warfarin and CYP2C9 polymorphism did not provide a conclusive result due to poor comparability between studies.The genetic polymorphism of drug metabolism enzymes has been studied extensively, however other genetic factors, such as multiple drug resistance genes (MDR) and genes encoding ion channels, which may contribute to variability in function of drug transporters and targets, require more attention in future pharmacogenetic studies of antiepileptic drugs