Platinum Electrocatalysts and Their Supports with High Activity and Durability for Low Temperature Fuel Cells

Low temperature fuel cells, including proton-exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC), are now attracting enormous interest as a promising power generation device. However, high cost and low durability of the catalysts limit their wide-spread commercialization. This thesis is focused on increasing the electrocatalytic activity and durability of Pt catalysts on supports. Due to the drawbacks of commercially-used carbon black supports, carbon nanotubes (CNT) and nitrogen-doped carbon nanotubes (CNx) are synthesized as the catalyst supports by the chemical vapor deposition method. The electrocatalytic activities and electrochemical durability of the catalysts on these novel supports are evaluated. And the single H2/02 fuel cell performances are tested. CNT and CNx are compared as the supports of Pt nanoparticles. Smaller size and more uniformly dispersed Pt nanoparticles are deposited on CNx than on CNT without pretreatment. Pt supported on CNx (Pt/CNx) exhibits a larger electrochemical surface area (ECSA) and higher catalytic activity toward oxygen reduction reaction (ORR), in comparison with Pt supported on CNT (Pt/CNT). Pt catalysts supported on CNT and CNx of different nitrogen contents are examined for their electrochemical stabilities with accelerated durability tests for the first time. Based on the loss of ECSA and TEM images of the Pt nanoparticles, Pt/CNx exhibited much higher stabilities than Pt/CNT, and the stability increases with the iii increase of nitrogen contents in the CNx supports. SnO2 nanoparticles are deposited on CNx with the atomic layer deposition (ALD) technique as a co-catalyst of Pt. A three-dimensional Pt-SnO2/CNx/carbon paper composite electrode demonstrates higher electrocatalytic activities over ORR and methanol oxidation reaction (MOR) than Pt/CNx/carbon paper. The pre-deposited SnO2 also increases the electrochemical stability of Pt catalysts. Polycrystalline SnO2 is more effective than the amorphous form in stabilizing Pt catalysts. Pt alloys such as Pt-Ni supported on functionalized CNT are studied. A volcano-shape relationship is observed between the electrocatalytic activities toward ORR and the Ni contents in the PtNi alloy catalysts with different atomic ratios, with Pt75Ni25 exhibiting the highest activity. A geometric effect of Pt-Pt interatomic distance and electronic effect are proposed to explain the enhancement Ofelectrocatalytic activity with Ni introduction

Multiagent model and mean field theory of complex auction dynamics

Acknowledgements We are grateful to Ms Yinan Zhao for providing the data and to Yuzhong Chen and Cancan Zhou for discussions and suggestions. This work was supported by ARO under Grant No. W911NF-14-1-0504 and by NSFC under Grants Nos. 11275003 and 61174165. The visit of QC to Arizona State University was partially sponsored by the State Scholarship Fund of China.Peer reviewedPublisher PD

Regional surname affinity: a spatial network approach

OBJECTIVE We investigate surname affinities among areas of modern‐day China, by constructing a spatial network, and making community detection. It reports a geographical genealogy of the Chinese population that is result of population origins, historical migrations, and societal evolutions. MATERIALS AND METHODS We acquire data from the census records supplied by China's National Citizen Identity Information System, including the surname and regional information of 1.28 billion registered Chinese citizens. We propose a multilayer minimum spanning tree (MMST) to construct a spatial network based on the matrix of isonymic distances, which is often used to characterize the dissimilarity of surname structure among areas. We use the fast unfolding algorithm to detect network communities. RESULTS We obtain a 10‐layer MMST network of 362 prefecture nodes and 3,610 edges derived from the matrix of the Euclidean distances among these areas. These prefectures are divided into eight groups in the spatial network via community detection. We measure the partition by comparing the inter‐distances and intra‐distances of the communities and obtain meaningful regional ethnicity classification. DISCUSSION The visualization of the resulting communities on the map indicates that the prefectures in the same community are usually geographically adjacent. The formation of this partition is influenced by geographical factors, historic migrations, trade and economic factors, as well as isolation of culture and language. The MMST algorithm proves to be effective in geo‐genealogy and ethnicity classification for it retains essential information about surname affinity and highlights the geographical consanguinity of the population.National Natural Science Foundation of China, Grant/Award Numbers: 61773069, 71731002; National Social Science Foundation of China, Grant/Award Number: 14BSH024; Foundation of China of China Scholarships Council, Grant/Award Numbers: 201606045048, 201706040188, 201706040015; DOE, Grant/Award Number: DE-AC07-05Id14517; DTRA, Grant/Award Number: HDTRA1-14-1-0017; NSF, Grant/Award Numbers: CHE-1213217, CMMI-1125290, PHY-1505000 (61773069 - National Natural Science Foundation of China; 71731002 - National Natural Science Foundation of China; 14BSH024 - National Social Science Foundation of China; 201606045048 - Foundation of China of China Scholarships Council; 201706040188 - Foundation of China of China Scholarships Council; 201706040015 - Foundation of China of China Scholarships Council; DE-AC07-05Id14517 - DOE; HDTRA1-14-1-0017 - DTRA; CHE-1213217 - NSF; CMMI-1125290 - NSF; PHY-1505000 - NSF)Published versio

Abrupt climatic events recorded by the Ili loess during the last glaciation in Central Asia: Evidence from grain-size and minerals

The loess record of Central Asia provides an important archive of regional climate and environmental changes. In contrast to the widely investigated loess deposits in the Chinese Loess Plateau, Central Asian loess-paleosol sequences remain poorly understood. Here, we present an aeolian loess section in the southern Ili Basin. Based on granularity and mineralogical analyses, we reconstruct climatic changes during the last glaciation. The results indicated that most of the abrupt climatic events (such as Dansgaard-Oeschger events and Heinrich events) were imprinted in this loess section, although their amplitudes and ages showed some differences. Compared with the millennial oscillations recoded in loess and stalagmites in East Asia, the arid Central Asia responded more sensitively to the warming events than to the cooling events. The shifting trajectory of westerlies across Central Asia played an important role in dust deposition during the stadials. The North Atlantic climatic signals may have been transmitted from Central Asia to the East Asian monsoon regions via the westerlies

Analysis of wealth inequality with a random money transfer model

Increasing gap in wealth distribution is among the key issues that have been discussed worldwide in recent years. In this paper, we use the money transfer model to explain the formation of wealth distribution, by imposing two types of debt constraints, and the analytic function of wealth distribution is derived by adopting Boltzmann statistics. With a limit of individual debt, it is shown that the stationary distribution of wealth follows the exponential law, which is verified by many empirical studies. While the limit is imposed on the total amount of bank loan, the stationary distribution becomes an asymmetric Laplace one. Furthermore, an excellent agreement is found between these analytical probability density functions and numerical results by simulation at the steady state

Retroform Cervical Dystonia: Target Muscle Selection and Efficacy of Botulinum Toxin Injection

IntroductionRetroform cervical dystonia (RCD), which includes retrocaput and retrocollis, is a rare form of cervical dystonia. Few reports have been published on RCD. The present study aimed to characterize the target muscles involved in RCD and the efficacy of botulinum toxin type A (BTX-A) injection.MethodsPatients with consecutive cervical dystonia with RCD as the most problematic feature were retrospectively analyzed over a 10-year period. Target muscles were screened and confirmed based on clinical evaluation, single-photon emission computed tomography, and electromyography. In addition, efficacy and adverse events following BTX-A injection in patients with RCD were evaluated.ResultsA total of 34 patients with RCD were included, 18 of whom presented with retrocaput and 16 with retrocollis. The most frequently injected muscles in RCD were splenius capitis (SPCa, 97.1%) and semispinalis capitis (SSCa, 97.1%), followed by levator scapulae (LS, 50.0%), rectus capitis posterior major (RCPM, 47.1%), trapezius (TPZ, 41.2%), and sternocleidomastoid muscle (SCM, 41.2%). Besides cervical muscles, the erector spinae was also injected in 17.6% of patients. Most muscles were predominantly bilaterally injected. The injection schemes of retrocaput and retrocollis were similar, possibly because in patients with retrocollis, retrocaput was often combined. BTX-A injection achieved a satisfactory therapeutic effect in RCD, with an average symptom relief rate of 69.0 ± 16.7%. Mild dysphagia (17.6%) and posterior cervical muscle weakness (17.6%) were the most common adverse events.ConclusionSPCa, SSCa, LS, RCPM, LS, and SCM were commonly and often bilaterally injected in RCD. Patients with RCD could achieve satisfactory symptom relief after BTX-A injection

Mobility in a Globalised World

The term mobility has different meanings in the following academic disciplines. In economics, mobility is the ability of an individual or a group to improve their economic status in relation to income and wealth within their lifetime or between generations. In information systems and computer science, mobility is used for the concept of mobile computing, in which a computer is transported by a person during normal use. Logistics creates, by the design of logistics networks, the infrastructure for the mobility of people and goods. Electric mobility is one of today’s solutions from engineering perspective to reduce the need of energy resources and environmental impact. Moreover, for urban planning, mobility is the crunch question about how to optimize the different needs for mobility and how to link different transportation systems. The conference “Mobility in a Globalised World” took place in Iserlohn, Germany, on September 14th – 15th, 2011. The aim of this conference was to provide an interdisciplinary forum for the exchange of ideas among practitioners, researchers, and government officials regarding the different modes of mobility in a globalised world, focusing on both domestic and international issues. The proceedings at hand document the results of the presentations and ensuing discussions at the conference

Holocene dust deposition in the Ili Basin and its implications for climate variations in Westerlies-dominated Central Asia

Understanding Holocene paleoclimate in arid Central Asia (ACA) is helpful for predicting future climate. However, Holocene climate patterns and their forcing mechanisms across ACA are vigorously debated in the context of global climate change. Here, we present a Holocene loess profile (SGX) from the Ili Basin in the Westerlies-dominated Central Asia. Based on high-resolution, medium-grained (38-63 mu m) quartz optically stimulated luminescence (OSL) dating, and grain size and color measurements, we reconstruct the Holocene paleoclimate. OSL geochronology indicate that this SGX loess profile covers the last 11.5 ka, and grain size analyses reveal that the sediments are sandy loess, and the environmentally sensitive fractions are < 35.6 mu m and 35.6-252 mu m which represent suspensions after dust storms and proximal deposit components transported mainly during dust storms, respectively. And the redness and yellowness in the loess profile are closely related to the concentrations of hematite (Hm) and goethite (Gt); the ratio Hm/Gt also can be used to reflect the evolution of dry/humid conditions in Central Asian loess. The Holocene Westerlies-dominated climate in ACA is characterized by a dry early Holocene, persistently wet conditions in the middle and late Holocene, and a climatic optimum in the late Holocene. The winter solar insolation at 60 degrees N is considered the major forcing of Holocene climate evolution in ACA