Differential regulation of stiffness, topography, and dimension of substrates in rat mesenchymal stem cells

The physiological microenvironment of the stem cell niche, including the three factors of stiffness, topography, and dimension, is crucial to stem cell proliferation and differentiation. Although a growing body of evidence is present to elucidate the importance of these factors individually, the interaction of the biophysical parameters of the factors remains insufficiently characterized, particularly for stem cells. To address this issue fully, we applied a micro-fabricated polyacrylamide hydrogel substrate with two elasticities, two topographies, and three dimensions to systematically test proliferation, morphology and spreading, differentiation, and cytoskeletal re-organization of rat bone marrow mesenchymal stem cells (rBMSCs) on twelve cases. An isolated but not combinatory impact of the factors was found regarding the specific functions. Substrate stiffness or dimension is predominant in regulating cell proliferation by fostering cell growth on stiff, unevenly dimensioned substrate. Topography is a key factor for manipulating cell morphology and spreading via the formation of a large spherical shape in a pillar substrate but not in a grooved substrate. Although stiffness leads to osteogenic or neuronal differentiation of rBMSCs on a stiff or soft substrate, respectively, topography or dimension also plays a lesser role in directing cell differentiation. Neither an isolated effect nor a combinatory effect was found for actin or tubulin expression, whereas a seemingly combinatory effect of topography and dimension was found in manipulating vimentin expression. These results further the understandings of stem cell proliferation, morphology, and differentiation in a physiologically mimicking microenvironment

PARAMETRIZATION OF HIGH-SPEED TRAIN STREAMLINE SHAPE

In the past decade, the high speed trains (HSTs) in China have experienced a booming development, with the design of CRH380A as a predominant example. A series of brand new HSTs have been developed with high aerodynamic performance, which includes the running resistance, the lift of the trailing car, pressure waves when trains pass by each other, aerodynamic noise in the far field, etc. In order to design HSTs with better aerodynamic performance, it is necessary to perform aerodynamic shape optimization, especially to optimize the streamline shape of HSTs. Parametrization is the basis for the whole optimization process, since good parametrization approach not only affects the optimization strategy, but also determines the design space and optimization efficiency. In the present paper, a series of work related to the streamline shape parametrization performed by the author in recent years have been introduced. Four different parametrization approaches have been exhibited, which are Local Shape Function method (LSF) and Free-Foam Deformation method (FFD), Modified Vehicle Modeling Function method (MVMF), Class function/Shape function Transformation method (CST). These methods could be categorized into two kinds: shape disturbance approach (LSF and FFD) and shape description approach (MVMF and CST). Among these four methods, some are developed by the authors while some are locally modified so as to meet the parametrization of the streamline shape. The detailed process of these four approaches are exhibited in the present paper and the characteristics of these four approaches are compared.</p

Pan-cancer analysis of whole genomes

Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale(1-3). Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4-5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter(4); identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation(5,6); analyses timings and patterns of tumour evolution(7); describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity(8,9); and evaluates a range of more-specialized features of cancer genomes(8,10-18).Peer reviewe

Estimating geocenter motion and changes in the Earth’s dynamic oblateness from GRACE and geophysical models

Geocenter motion and changes in the Earth’s dynamic oblateness (J2) are of great importance in many applications. Among others, they are critical indicators of largescale mass redistributions, which is invaluable to understand ongoing global climate change. The revolutionary Gravity Recovery and Climate Experiment (GRACE) satellite mission enables a constant monitoring of redistributing masses within the Earth’s system. However, it still cannot provide reliable time variations in degree-1 coefficients and degree-2 zonal coefficients, which are directly related to geocenter motion and J2 variations.Physical and Space Geodes

Quasi-vertical Gallium Nitride Diodes for Microwave Power Applications

The deployment of fifth-generation (5G) networks requires more closely spaced wireless infrastructures with a high output power to deal with high-frequency signal attenuation issues. Microwave power limiters have been widely used in the RF front-end in various wireless communication systems. A diode limiter circuit prevents the damage of sensitive receiver components by allowing RF signals below a certain threshold to pass through, while larger signals exceeding the threshold are attenuated. Many studies have been carried out on Si-based diode limiters in recent years; however, they have shown scant room for further improvement as silicon reaches its theoretical limitations. From this perspective, there is a need for new semiconductor materials to satisfy the requirements of devices. Wide-bandgap materials (e.g., gallium nitride) have recently attracted a great deal of interest due to their superior material properties such as wide band-gap, high electron saturation velocity, and high critical electric field.Although lateral-structure GaN devices are staying ahead of the pace of industrialization, they still face several constraints and do not reach the GaN material limit due to requiring a high epitaxial layer quality and precise processing. A vertical structure is a convenient solution in Si- or SiC-based devices, which are also attractive alternatives to GaN devices. Quasi-vertical GaN devices have the freedom to select substrates (such as silicon, sapphire, and SiC) by using hetero-epitaxial growth technology. A planar structure design is easy to integrate with other RF components. This dissertation aimed to develop a quasi-vertical GaN diode for high-power RF and microwave applications which could operate in a wide frequency band and at high input power levels, with easy integration and low cost. The scope of this dissertation involved three aspects: design and fabrication of a quasi-vertical GaN device with mesa etching optimization; suppression of reverse leakage with an enhanced breakdown voltage; demonstration of microwave power applications (limiters and detectors) based on developed GaN diodes.First, a literature summary of the state-of-the-art vertical GaN SBDs is presented in Chapter 2. A trade-off between the &#x1d445;&#x1d45c;&#x1d45b;,&#x1d460;&#x1d45d; and BV of a diode is analyzed to characterize the performance of diodes. We discuss the benchmark of &#x1d445;&#x1d45c;&#x1d45b;,&#x1d460;&#x1d45d; and BV for vertical GaN SBDs with different substrates (Si, sapphire, and GaN) and various edge terminal techniques. The equivalent circuit model of a diode for studying the high-frequency properties is introduced.Second, the optimization of mesa etching for a quasi-vertical GaN SBD by inductively coupled plasma (ICP) etching is comprehensively investigated in this chapter. In particular, the microtrench at the bottom corner of the mesa is eliminated by optimizing etch recipes. For the photoresist (PR) masked GaN samples, high source power is the cause of deteriorated mesa sidewall morphology. Although high-temperature (&gt;140 ℃) hard baking prior to etching can produce a smooth sidewall, the drawbacks are significant and include oblique sidewall profile formation and hard striping. For the &#x1d446;&#x1d456;&#x1d442;2-masked GaN samples, the micro-trench problem at the bottom corner of the mesa can be reduced or eliminated by reducing the source power or by adding &#x1d435;&#x1d436;&#x1d459;3 into the &#x1d436;&#x1d459;2 plasma. After ICP etching, the use of a TMAH wet treatment for samples can obtain a near-90° steep mesa sidewall that is microtrench-free and has a smooth surface. The proposed etching technique can be extended to other GaN nanostructures, such as hexagonal pyramids and nanowire arrays, which is promising for sensors, vertical transistors, optoelectronics, and photovoltaics.Third, a quasi-vertical GaN SBD is developed from the perspective of epilayer design, device layout, device modeling, fabrication, and leakage suppression. The design flow and fabrication process of quasi-vertical GaN diodes for microwave power applications are presented. Three solutions are developed to suppress the leakage current, namely, mesa optimization, argon ion terminations, and post-mesa nitridation. The experiment results show that our diode has the lowest leakage current density at 80% of the BV among the reported vertical GaN SBDs for a BV between 120 and 250 V. Combining mesa optimization and post-mesa nitridation technology effectively enhances the breakdown voltage and achieves excellent conduction characteristics.Fourth, a high-performance quasi-vertical GaN Schottky diode on a sapphire substrate and its application for high-power microwave circuits are investigated. We experimentally demonstrate the use of a vertical GaN SBD for L-band microwave power limiters for the first time ever. The GaN SBD limiter can handle at least 40 dBm of CW input power at 2 GHz without failure, which is comparable to a commercial Si-based diode limiter. Then, we experimentally demonstrate a quasi-vertical GaN SBD with post-mesa nitridation for high-power and broadband microwave detection. The fabricated quasi-vertical GaN diode reaches a high forward current density of 9.19 &#x1d458;&#x1d434;/&#x1d450;&#x1d45a;2 at 3 V, and BV of 106 V. An extremely high output current of 400 mA is obtained when the detected power reaches 38.4 dBm at 3 GHz in pulsed-wave mode.Finally, all of the research content mentioned in this thesis is summarized, and the problems needing to be further investigated with lucubrate direction are indicated.Electronic Components, Technology and Material

Monolithically Inegrated Silicon Bipolar RF Oscillators

Electrical Engineering, Mathematics and Computer Scienc

Egress as Part of Fire Safety in High-rise Buildings

The process of evacuating some large high-rise buildings may take upwards of several hours. One question that needs to be asked, however, is whether it is feasible and desirable to completely evacuate the high-rise building in fires. This research seeks to remedy this problem by proposing one or more efficient egress plan(s) for high-rise buildings. Investigation into a number of Dutch projects, international fire codes and state-of-the-art literature laid the foundation for this study. Four egress plans have been presented from a worldwide perspective for a specific certain building: Koningin Julianaplein in The Hague, the Netherlands. At least ten egress possibilities have been presented with respect to different fire scenarios. Assessment results of all egress possibilities suggest that partial evacuation appears to be the most appropriate strategy for Koningin Julianaplein, which results in a reduction in egress time by as much as 50% (defend-in-place) and 43% (relocation). While for office towers under relatively high occupant loading, phased evacuation has positive effect on the egress efficiency in comparison with traditional simultaneous evacuation.Building Technology and PhysicsStructural EngineeringCivil Engineering and Geoscience

Climate-driven seasonal geocenter motion during the GRACE period

Annual cycles in the geocenter motion time series are primarily driven by mass changes in the Earth’s hydrologic system, which includes land hydrology, atmosphere, and oceans. Seasonal variations of the geocenter motion have been reliably determined according to Sun et al. (J Geophys Res Solid Earth 121(11):8352–8370, 2016) by combining the Gravity Recovery And Climate Experiment (GRACE) data with an ocean model output. In this study, we reconstructed the observed seasonal geocenter motion with geophysical model predictions of mass variations in the polar ice sheets, continental glaciers, terrestrial water storage (TWS), and atmosphere and dynamic ocean (AO). The reconstructed geocenter motion time series is shown to be in close agreement with the solution based on GRACE data supporting with an ocean bottom pressure model. Over 85% of the observed geocenter motion time series, variance can be explained by the reconstructed solution, which allows a further investigation of the driving mechanisms. We then demonstrated that AO component accounts for 54, 62, and 25% of the observed geocenter motion variances in the X, Y, and Z directions, respectively. The TWS component alone explains 42, 32, and 39% of the observed variances. The net mass changes over oceans together with self-attraction and loading effects also contribute significantly (about 30%) to the seasonal geocenter motion in the X and Z directions. Other contributing sources, on the other hand, have marginal (less than 10%) impact on the seasonal variations but introduce a linear trend in the time series.Physical and Space Geodes

An operational simulation framework for modelling the multi-interaction of two-wheelers on mixed-traffic road segments

In recent years, the interest in riding in cities using the two-wheeler (e.g., bicycles, electric bicycles, electric mopeds, etc.) increases. Mixed-traffic road segments are one of the most common traffic scenes where the mixed two-wheeler flows exist. Because the movements are often not restricted by lanes, the two-wheeler uses lateral road space more freely and shows obvious multilateral interactions (i.e. multi-interaction) with others, bringing issues that endanger traffic safety. A precise estimation of its impacts on traffic operation and safety is necessary, while the microscopic simulation model can satisfy the need as a helpful tool. However, most existing simulation models of these three types of two-wheelers are essentially focusing on handling the one-on-one interaction. The capability to deal with the two-wheeler multi-interaction in mixed traffic is still rare, and the description of what endogenous tasks are contained by the multi-interaction has also not given by literature. To this end, this paper first defines what the multi-interaction entails on the operational behaviour level, claiming that it contains three intertwined processes, namely a (mental) perception, a (mental) decision, and a physical process. The (mental) perception and decision processes represent the recognition of interactions and the response to traffic conditions, while the physical process refers to the execution of these mental activities. A three-layer simulation framework has then been developed, where each layer sequentially corresponds to one of the operational behaviour tasks. Integrated component models are also proposed in each layer to cover these operational tasks. A Comfort Zone model is hence put forward to dynamically perceive the multiple interactive road users, while a Bayesian network model is developed to deal with the decision-making process under multi-interaction situations. Meanwhile, a behaviour force model is also proposed to capture the non-lane based movements following the selected behaviour and current interaction states. Finally, we face validate the proposed models by the comparison between simulation results and observations obtained from trajectory dataset. Results indicate the model performance matches the observed interaction and motion well.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport and Plannin

Planning of public housing in modern Tianjin (1928–1945)

European, American, and Japanese debates on public housing served as models for those in modern China, and Chinese scholars and professionals, with the support of the KMT (Kuomintang), developed public housing as a sign of innovation in both societal reform and building typology. Using the under-researched case of Tianjin's public housing during the so-called Nanjing Decade (1928–1937) and then again during the Japanese Occupation (1937–1945) as case studies, the paper first explores how journals, books, and foreign-trained Chinese scholars introduced the concept of public housing to China. It then examines five public housing projects that municipal authorities developed for Tianjin, two in the Nanjing Decade and three during the Japanese Occupation. Analysing the sites, architectural designs, and management rules of these projects, the paper argues that the projects in the Nanjing Decade (both planned and realized) mostly targeted poor families, serving to simultaneously solve housing problems, reform society, and police the poor; while the projects during the Japanese Occupation benefited high-income people or the Japanese, and did not play a role in the relief of the local poor, who suffered most from the housing shortage.OLD History of Architecture & Urban Plannin