David R. Smith

Bio: David R. Smith is an academic researcher from Duke University. The author has contributed to research in topics: Metamaterial & Antenna (radio). The author has an hindex of 110, co-authored 881 publications receiving 91683 citations. Previous affiliations of David R. Smith include Brunel University London & Princeton University.

Friction compensation strategies in large telescopes

Abstract: For large telescopes, management of axis friction presents a significant challenge. In some cases, this is avoided or minimized in the design stage by employing hydrostatic bearings. However, the main axis servo systems of many large telescopes must cope with bearing or wheel friction. This friction affects or limits servo control performance in several ways. The most obvious is the stick-slip limit cycle that is characteristic of trying to hold position with an integrating control system in the presence of friction. If it is not taken into account, friction also introduces effects into the state estimation in model-based controllers. There are several standard approaches to friction compensation. These include dithering (introducing a noise signal to the drive motors), direct Coulomb friction compensation (sending an additional torque based on the rate command), and adaptive techniques based on monitoring of the final drive velocities. In this work, we experimentally compare different friction compensation approaches on the static positioning performance of the Large Millimeter Telescope/Gran Telescopio Milimetrico (LMT). Single and double integrator systems are investigated, as well as direct Coulomb friction compensation.

Design of a Reconfigurable Metasurface Antenna for Dynamic Near-Field Focusing

Abstract: We show the design of a dynamically reconfigurable holographic metasurface antenna for near-field beam-focusing applications. A metasurface layer is used to modulate the guided-mode reference to an aperture field of interest producing the desired radiated wavefront. Exciting the dynamically reconfigurable metasurface layer with the guided-mode reference produces a reconfigurable focus in the near-field of the antenna aperture. The reconfigurable operation is achieved in an-all electronic manner, without the need for any mechanical moving apparatus or phase shifting circuits.

Efficient finite element resolution of gyromagnetic and gyroelectric nonreciprocal electromagnetic problems.

Abstract: We present a rigorous derivation of the weak-form formulation of the Helmholtz equation for electromagnetic structures incorporating general nonreciprocal, dispersive materials such as magnetized ferrites or magnetized free-carrier plasmas. This formulation allows an efficient self-consistent treatment using finite elements of a variety of problems involving magnetic or magneto-optical materials biased by an external DC field where the eigenmodes become nonreciprocal or even unidirectional. The possibilities of this method are illustrated with several examples of TE-polarized modes at microwave frequencies and TM-polarized modes at optical and infrared wavelengths.

Microbiome–Gut Dissociation in the Neonate: Obesity and Coeliac Disease as Examples of Microbiome Function Deficiency Disorder

Abstract: The purpose of this article is to provide a direction for translational research based on an analysis of the nature of complex, immune-related conditions such as obesity and coeliac disease. In essence, it seems that the prevalence of these non-communicable diseases is related to the degradation of the microbiome during the industrialisation of society, and that their nature can be used to infer the functions of the “pre-industrial” microbiome. Based on this analysis, the key point is the necessity for the fully functioning microbiome, acting alongside the parental genetic inheritance of the child, to be in place immediately after birth. In our view, this is achieved by the seemingly accidental process of maternal microbial inheritance during normal birth. Note, however, that this is not possible if the microbiome of the mother is itself degraded following previous problems. Under these conditions the health of a child may be affected from the moment of birth, although, with the exception of atopic diseases, such as eczema and food allergy, the consequences may not become apparent until late childhood or as an adult. In this way, this microbiome function deficiency hypothesis incorporates the epidemiological observations of David Strachan and David Barker in that their onset can be traced to early childhood. Coeliac disease has been chosen as an illustrative example of a multifactorial disorder due to the fact that, in addition to a series of immune system manifestations and a potential problem with food absorption, there is also a significant psychological component. Finally, it is worth noting that an ingestible sensor calibrated to the detection of interkingdom communication molecules (semiochemicals) within the intestine may offer a practical way of assessment and, perhaps, amelioration of at least some of the consequences of non-communicable disease.

Investigation of Transformer Turns Ratio Between Feed and Slot of Aperture Coupled Slot Antenna by Using $S_{11}$ Parameter

Abstract: This communication presents a simplified design approach to obtain the turns ratio nf which models the coupling between the microstrip feed and slot line of an aperture coupled slot antenna by using the S11 parameter. Equations are derived using S11 parameter to determine nf and simulations are carried out at 2 GHz using substrates of PCB FR4, Duroid 5870, and Duroid 6010. Results indicate nf is proportional to the slot length from 0 to 20 mm increasing rapidly with length. Over 20 mm slot length, the trend reduces and the value of nf tends towards 1. In addition, nf varies with the height of substrate but is little affected by dielectric constant of substrate which could therefore be ignored to simplify the design procedure. Measured results show good agreement with the theoretical model.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Surface plasmon subwavelength optics

Abstract: Surface plasmons are waves that propagate along the surface of a conductor. By altering the structure of a metal's surface, the properties of surface plasmons--in particular their interaction with light--can be tailored, which offers the potential for developing new types of photonic device. This could lead to miniaturized photonic circuits with length scales that are much smaller than those currently achieved. Surface plasmons are being explored for their potential in subwavelength optics, data storage, light generation, microscopy and bio-photonics.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These