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941.
The underlying physics of the generation and detection of terahertz (THz) waves in gases are described. The THz wave generation process takes place in two steps: asymmetric gas ionization by two-frequency laser fields, followed by interaction of the ionized electron wave packets with the surrounding medium, producing an intense ‘echo’ with tunable spectral content. In order to clarify the physical picture at the moment of ionization, the laser–atom interaction is treated through solution of the time-dependent Schrödinger equation, yielding an ab initio understanding of the release of the electron wave packets. The second step, where the electrons interact with the surrounding plasma is treated analytically. The resulting pressure dependence of the THz radiation is explored in detail. The THz wave detection process is shown to be the result of four-wave mixing, leading to analytical expressions of the signal obtained which allow for improved optimization of systems that exploit these effects. 相似文献
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944.
Joseph Nicholas Wills 《Journal of Architectural Education》2013,67(3):39-41
The previous article gives a participant's-eye view of an annual summer event, some years established. This one, by contrast, is concerned with a first: a course offered by Paolo Soleri (who will have become known to those who may not have known of him before as this year's recipient of the AIA Craftsmanship Medal) in the summer session of the Arizona State University School of Architecture. The course, officially designated “Architectural Craft” but generally known as “Siltpile,” was held in the special environment that Soleri has created for his life and work in the desert near Scottsdale. Here it is described and discussed by one of the twenty-three students, from nearly as many schools of architecture, who attended it. Mr Wills is a student at the University of Nebraska. 相似文献
945.
This paper is concerned with the identification of discrete-time, time invariant, state affine state space models driven by an independent identically distributed (IID) random input, and in the presence of process and measurement noise. The identification problem is treated using a cumulant based approach. It is shown that the input-output and input-state crosscumulant equations in the time domain have the form of a linear autonomous system. An algorithmic procedure is then developed, for the computation of the unknown system matrices, based on a standard deterministic linear subspace identification algorithm, provided the input signal has some persistent excitation properties. The special case of Gaussian IID input is also examined. The proposed method is computationally very efficient and its accuracy is illustrated by simulations. 相似文献
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947.
Choo-Yee Ting Helmi Zakariah Fadzilah Kamaludin Darryl Lin-Wei Cheng Nicholas Yu-Zhe Tan Hui-Jia Yee 《计算机、材料和连续体(英文)》2021,67(1):835-848
Ever since the COVID-19 pandemic started in Wuhan, China, much research work has been focusing on the clinical aspect of SARS-CoV-2. Researchers have been leveraging on various Artificial Intelligence techniques as an alternative to medical approach in understanding the virus. Limited studies have, however, reported on COVID-19 transmission pattern analysis, and using geography features for prediction of potential outbreak sites. Predicting the next most probable outbreak site is crucial, particularly for optimizing the planning of medical personnel and supply resources. To tackle the challenge, this work proposed distance-based similarity measures to predict the next most probable outbreak site together with its magnitude, when would the outbreak likely to happen and the duration of the outbreak. The work began with preprocessing of 1365 patient records from six districts in the most populated state named Selangor in Malaysia. The dataset was then aggregated with population density information and human elicited geography features that might promote the transmission of COVID-19. Empirical findings indicated that the proposed unified decision-making approach outperformed individual distance metric in predicting the total cases, next outbreak location, and the time interval between start dates of two similar sites. Such findings provided valuable insights for policymakers to perform Active Case Detection. 相似文献
948.
Yue Sun Yifan Zhang Ye Gao Pan Wang Gang He Nicholas T. Blum Jing Lin Quanhong Liu Xiaobing Wang Peng Huang 《Advanced materials (Deerfield Beach, Fla.)》2020,32(48):2004481
Simultaneous photodynamic therapy (PDT) and photothermal therapy (PTT) can reduce the risks of drug leakage, body burden, and preparation complexity in traditional combination PDT/PTT. Here, a versatile nanoporphyrin (Pp18-lipos) self-assembled from lipid–purpurin 18 conjugates (Pp18-lipids) and pure lipids is presented. The as-prepared Pp18-lipos with 2 mol% Pp18-lipids can perform effective PDT and fluorescence imaging. The Pp18-lipos with 65 mol% Pp18 can perform potent PTT and photoacoustic imaging. The chelation of Mn2+ endows the Pp18-lipids-Mn2+ a high T1-weighted magnetic resonance imaging contrast. Notably, pretreatment of low-dose PDT facilitates the endocytosis and tumor accumulation of Pp18-lipos, thus achieving synergistic PDT/PTT. Upon exposure to a single 705 nm-laser, the combination of PDT/PTT achieves a significantly higher tumor growth inhibition rate than PDT or PTT alone. In addition, it is found that the synergistic PDT/PTT triggers more potent anti-tumor immune response including tumor infiltration of immune cells and release of related cytokines. 相似文献
949.
Amey Apte Kosar Mozaffari Farnaz Safi Samghabadi Jordan A. Hachtel Long Chang Sandhya Susarla Juan Carlos Idrobo David C. Moore Nicholas R. Glavin Dmitri Litvinov Pradeep Sharma Anand B. Puthirath Pulickel M. Ajayan 《Advanced materials (Deerfield Beach, Fla.)》2020,32(24):2000006
Since graphene, a variety of 2D materials have been fabricated in a quest for a tantalizing combination of properties and desired physiochemical behavior. 2D materials that are piezoelectric, i.e., that allow for a facile conversion of electrical energy into mechanical and vice versa, offer applications for sensors, actuators, energy harvesting, stretchable and flexible electronics, and energy storage, among others. Unfortunately, materials must satisfy stringent symmetry requirements to be classified as piezoelectric. Here, 2D ultrathin single-crystal molybdenum oxide (MoO2) flakes that exhibit unexpected piezoelectric-like response are fabricated, as MoO2 is centrosymmetric and should not exhibit intrinsic piezoelectricity. However, it is demonstrated that the apparent piezoelectricity in 2D MoO2 emerges from an electret-like behavior induced by the trapping and stabilization of charges around defects in the material. Arguably, the material represents the first 2D electret material and suggests a route to artificially engineer piezoelectricity in 2D crystals. Specifically, it is found that the maximum out-of-plane piezoresponse is 0.56 pm V−1, which is as strong as that observed in conventional 2D piezoelectric materials. The charges are found to be highly stable at room temperature with a trapping energy barrier of ≈2 eV. 相似文献
950.
James C. Loudon Alison C. Twitchett‐Harrison David Corts‐Ortuo Max T. Birch Luke A. Turnbull Ale tefan
i
Feodor Y. Ogrin Erick O. Burgos‐Parra Nicholas Bukin Angus Laurenson Horia Popescu Marijan Beg Ondrej Hovorka Hans Fangohr Paul A. Midgley Geetha Balakrishnan Peter D. Hatton 《Advanced materials (Deerfield Beach, Fla.)》2019,31(16)
The intense research effort investigating magnetic skyrmions and their applications for spintronics has yielded reports of more exotic objects including the biskyrmion, which consists of a bound pair of counter‐rotating vortices of magnetization. Biskyrmions have been identified only from transmission electron microscopy images and have not been observed by other techniques, nor seen in simulations carried out under realistic conditions. Here, quantitative Lorentz transmission electron microscopy, X‐ray holography, and micromagnetic simulations are combined to search for biskyrmions in MnNiGa, a material in which they have been reported. Only type‐I and type‐II magnetic bubbles are found and images purported to show biskyrmions can be explained as type‐II bubbles viewed at an angle to their axes. It is not the magnetization but the magnetic flux density resulting from this object that forms the counter‐rotating vortices. 相似文献