Nuclear Magnetic Resonance Studies of Silicon Carbide Polytypes

The ²⁹Si MAS NMR spectra of the 2H, 4H, 6H, and 3C polytypes of silicon carbide are presented. An attempt is made to correlate differences in the chemical shifts with local atomic environment. The results of the analysis of the spectra of pure polytypes are used as a basic for the interpretation of the spectra of mixed polytypes and a discussion of the crystallinity and impurity levels of different samples. Carbon-13 chemical shifts obtained from spectra of the same polytypes are also tabulated.     

An improved formalism for quantum computation based on geometric algebra—case study: Grover’s search algorithm

The Grover search algorithm is one of the two key algorithms in the field of quantum computing, and hence it is desirable to represent it in the simplest and most intuitive formalism possible. We show firstly, that Clifford’s geometric algebra, provides a significantly simpler representation than the conventional bra-ket notation, and secondly, that the basis defined by the states of maximum and minimum weight in the Grover search space, allows a simple visualization of the Grover search analogous to the precession of a spin- ${\frac{1}{2}}$ particle. Using this formalism we efficiently solve the exact search problem, as well as easily representing more general search situations. We do not claim the development of an improved algorithm, but show in a tutorial paper that geometric algebra provides extremely compact and elegant expressions with improved clarity for the Grover search algorithm. Being a key algorithm in quantum computing and one of the most studied, it forms an ideal basis for a tutorial on how to elucidate quantum operations in terms of geometric algebra—this is then of interest in extending the applicability of geometric algebra to more complicated problems in fields of quantum computing, quantum decision theory, and quantum information.     

像素与矢量

智能对象的出现使得在Photoshop和Illustrator中使用像素和矢量之间的差别迅速消失。Derek Lea将会在制作一个结构完美且矢量明显的作品的同时为你解释原因。     

The effect of mixed mode I/III on crack evolution in brittle solids

A modification of Sommer's classical experiment [4] has been used to fracture rods of a brittle epoxy resin in mixed mode I/III stress conditions. The nucleation and growth of cracks in an increasing K _III/K _I stress field have been investigated, particularly in relation to the formation of river lines and the evolution of multiple cracks between river lines to form smooth helicoid surfaces. The fractographic features associated with the progressive development of river line patterns involving crack bowing at river line steps, interaction between arrays of cracks and the coalescence of river lines are described. As K _III/K _I increases the scale of the river line patterns increases but the patterns remain self similar. Using principles from differential geometry it is shown that helicoid surfaces can be generated entirely by crack evolution involving tilting without twiting.Emeritus Goldsmiths' Professor of Metallurgy, University of Cambridge, U.K.     

A sampling approach to Debiasing the offline evaluation of recommender systems

Journal of Intelligent Information Systems - Offline evaluation of recommender systems (RSs) mostly relies on historical data, which is often biased. The bias is a result of many confounders that...     

Selective toxicity of hydroxyl-rich carbon nanodots for cancer research

Nano Research - The toxicity of nanoparticles in a biological system is an integration of effects arising from surface functionality, particle size, ionic dissolution, etc. This complexity suggests...     

Thermally compensated temperature sensor capable of highly accurate measurements on surfaces

A thermally compensated temperature sensor capable of highly accurate determination of surface temperatures has been demonstrated. The probe consists of a single crystal Y(3)Al(5)O(12) fiber terminating in a laser-heated Yb(3)Al(5)O(12) phosphor. It has been shown to have a measurement accuracy of approximately 1 degrees C. In principle, this device should work in the proximity as well as the contact mode.     

A millimeter wave frequency synthesizer covering the 40–60 GHz waveguide band

This paper describes a millimeter wave frequency synthesizer based on a single broadband backward wave oscillator tube which is capable of covering the entire 40–60 GHz waveguide band with useful power output, low phase noise, and rapid frequency switching. The synthesizer is controlled by an internal microcomputer which sets the reference oscillator frequency through a General Purpose Interface Bus (GPIB) and generates synthesizer coarse tuning corrections through a programmable digital-to-analog converter. The phase/frequency control system uses a frequency discriminator for capture of the source from large frequency errors and a complementary phase lock for precise phase and frequency control.