Transformation media that turn a narrow slit into a large window

Based on the transformation media theory, the authors propose a way to replace a wide window with a narrow slit filled with designed metamaterial to achieve the same transmittance as the one of the window. Numerical simulations for a two dimensional case are given to illustrate the ideas and the performance of the design.Comment: 10 pages, 3 figure

Superscatterer: Enhancement of scattering with complementary media

Based on the concept of complementary media, we propose a novel design which can enhance the electromagnetic wave scattering cross section of an object so that it looks like a scatterer bigger than the scale of the device. Such a ``superscatterer'' is realized by coating a negative refractive material shell on a perfect electrical conductor cylinder. The scattering field is analytically obtained by Mie scattering theory, and confirmed by full-wave simulations numerically. Such a device can be regarded as a cylindrical concave mirror for all angles.Comment: 9 pages, 4 figure

Clustering-guided novel unsupervised domain adversarial network for partial transfer fault diagnosis of rotating machinery

Unsupervised partial transfer fault diagnosis studies of rotating machinery have practical significance, which still exists some challenges, for example, the learned domain-specific statistics and parameters usually influence the learning effect of target-domain features to some degree, and the relatively scattered target-domain features will lead to negative transfer. To overcome those limitations and further improve partial transfer fault diagnosis performance, a clustering-guided novel unsupervised domain adversarial network is proposed in this paper. Firstly, a novel unsupervised domain adversarial network is constructed using domain-specific batch normalization to remove domain-specific information to enhance alignment between source and target domains. Secondly, embedded clustering strategy is designed to learn tightly clustered target-domain features to suppress negative transfer in partial domain adaptation process. Finally, a joint optimization objective function is defined to balance different losses to improve the training and diagnosis performance. Two experimental cases of bevel gearbox and bearing are used to validate the effectiveness and superiority of the proposed method in solving unsupervised partial transfer fault diagnosis problems

An invisibility cloak using silver nanowires

In this paper, we use the parameter retrieval method together with an analytical effective medium approach to design a well-performed invisible cloak, which is based on an empirical revised version of the reduced cloak. The designed cloak can be implemented by silver nanowires with elliptical cross-sections embedded in a polymethyl methacrylate host. This cloak is numerically proved to be robust for both the inner hidden object as well as incoming detecting waves, and is much simpler thus easier to manufacture when compared with the earlier proposed one [Nat. Photon. 1, 224 (2007)].Comment: 7 pages, 4 figures, 2 table

Decoding Sponge City in Shenzhen : resilience program or growth policy?

Thesis: M.C.P., Massachusetts Institute of Technology, Department of Urban Studies and Planning, 2017.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 66-69).Unprecedented urbanization in China, combined with the increase of extreme weather events globally, has led to greater vulnerability of Chinese cities to urban water management issues including non-point source pollution, shortage of fresh water and urban floodings. In response to these problems, a national policy named "Sponge City" was first introduced in early 2014 to form a comprehensive alternative. Since then, two major views of its conceptualization have defined "Sponge City" as (1) a distributed resilience program modeled after Low Impact Development (LID) and Green Infrastructure (GI), and (2) a growth policy justifying the new investment in urban construction sector and the experimental field of financial innovation to involve private investment such as Public-Private Partnerships (PPP). However, a central contradiction has been widely observed in practice as the environmental and economic agendas of "Sponge City" are not always compatible with each other. This thesis examines the phenomenon where local governments, in the face of such dilemmas, have tended to skew "Sponge City" towards pro-growth policies by branding "Sponge New Districts" in urban outskirts, and asks why and how local governments use "Sponge New District" as a potential resolution. This thesis studies the case of Guangming New District in Shenzhen, Guangdong Province and argues two rationales exist behind this strategy. First, the development of such "Sponge New Districts" provides local government with more opportunities for private investors to profit from basic urban infrastructure projects such as roads and amenities. Second, such development justifies the direct intervention of the government in financing and construction by aligning Sponge New Districts with the local expansion agenda. Nonetheless, these "Sponge New Districts" divert the original environmental ideology of Sponge City and suggest that a fundamental gap exists between an idealized resilience program and the execution of pro-growth agendas at the local governmental level in contemporary China.by Hongru Cai.M.C.P

3D printing–assisted preoperative plan of pedicle screw placement for middle-upper thoracic trauma: a cohort study

Abstract Background This study aimed to evaluate the application of 3D printing in assisting preoperative plan of pedicle screw placement for treating middle-upper thoracic trauma. Methods A preoperative plan was implemented in seven patients suffering from middle-upper thoracic (T3–T7) trauma between March 2013 and February 2016. In the 3D printing models, entry points of 56 pedicle screws (Magerl method) and 4 important parameters of the pedicle screws were measured, including optimal diameter (ϕ, mm), length (L, mm), inclined angle (α), head-tilting angle (+β), and tail-tilting angle (−β). In the surgery, bare-hands fixation of pedicle screws was performed using 3D printing models and the measured parameters as guidance. Results A total of seven patients were enrolled, including five men and two women, with the age of 21–62 years (mean age of 37.7 years). The position of the pedicle screw was evaluated postoperatively using a computerized tomography scan. Totally, 56 pedicle screws were placed, including 33 pieces of level 0, 18 pieces of level 1, 4 pieces of level 2 (pierced lateral wall), and 1 piece of level 3 (pierced lateral wall, no adverse consequences), with a fine rate of 91.0%. Conclusions 3D printing technique is an intuitive and effective assistive technology to pedicle screw fixation for treating middle-upper thoracic vertebrae, which improve the accuracy of bare-hands screw placement and reduce empirical errors. Trial registration The trial was approved by the Ethics Committee of the Fujian Provincial Hospital. It was registered on March 1st, 2013, and the registration number was K2013–03-001

Modified DSAN for unsupervised cross-domain fault diagnosis of bearing under speed fluctuation

Existing researches about unsupervised cross-domain bearing fault diagnosis mostly consider global alignment of feature distributions in various domains, and focus on relatively ideal diagnosis scenario under the steady speeds. Therefore, unsupervised feature adaptation between all the corresponding subdomains under speed fluctuation remains great challenges. This paper proposes a modified deep subdomain adaptation network (MDSAN) for more practical and challenging cross-domain diagnostic scenarios from the fluctuating speeds to steady speeds. Firstly, to extract the representative features and effectively suppress negative transfer, a novel shared feature extraction module guided by multi-headed self-attention mechanism is constructed. Then, a new trade-off factor is designed to improve the convergence performance and optimization process of MDSAN. The proposed method is used for analyzing experimental bearing vibration data, and the results show that it has higher diagnostic accuracy, faster convergence, better distribution alignment, and is more suitable for unsupervised cross-domain fault diagnosis under speed fluctuation scenario compared with the existing methods

A momentum flux measuring instrument with the variable-range for exhaust plume

A momentum flux measuring instrument (MFMI), which ranges from 1 mN∼300 N, is designed to measure the parameters related to the momentum flux of exhaust plume of attitude and orbit control thrusters covered electric and chemical thrusters. A MFMI with the variable-range provides an efficient and economy way to study the exhaust plume of both electric and chemical thrusters. The flexural pivots, replaceable strain gauge, replaceable target plate, and force arm with the variable length make it possible. The designed MFMI with the non-displacement measurement can reduce the influence of pipelines and test lines, especially the elastic force and friction due to displacement. The designed MFMI system with the range of 0∼100 mN and 0∼15 N was calibrated separately. The target indirect measurement method is a simple and economical option for measuring the thrust of electric thrusters, and is employed to measure the thrust of the LIPS-200 ion thruster using the designed MFMI. Research indicates that the sputtering contributes to the momentum transfer of plasma-surface interactions. In addition, the high-speed charged ions from the thruster will experience a charge-exchange (CEX) collision with the slow neutral background. Therefore, the influence of the sputtering and CEX on target indirect measurement method is derived in detail, and then the measured thrust is corrected. The measured average thrust, which is 40.1 mN, demonstrates that the designed MFMI is effective. The designed MFMI can also be employed as a thrust stand by directly mounting the thrusters on torsional arm, and a maximum of three thrusters can be installed on the MFMI at the same time

Linking Mentoring and Job Search Behavior: A Moderated Mediation Model

The present research aims to explore the impact of mentoring relationship on college graduates’ job search behavior among Chinese undergraduate students by examining the mediator of job search intention and the moderator of job search self-efficacy. A two-wave survey study was conducted in China (N = 594). Our findings show a positive indirect relation between mentoring and college graduates’ job search behaviors through job search intention. The graduates’ job search self-efficacy positively moderated the indirect relationship such that when job search self-efficacy was higher, the influence of mentoring on behavior via job search intention was stronger. These findings extend the literature by clarifying how and when mentoring facilitates graduates’ job search behaviors and provide practical implications for facilitating a smooth school-to-work transition in China. As the first study that empirically clarifies why (through job search intention) and when (job search self-efficacy) mentoring function is positively related to job search behavior among Chinese undergraduate students, the present study contributes to the existing mentoring and job search literature. Future research is encouraged to extend the findings by integrating theory of planned behavior (TPB) with self-regulation theory toward deepening current understanding of how and when mentoring can contribute to a student’s success in job search behavior

Additional file 2: Typical case 2. Fig. S20. of 3D printing–assisted preoperative plan of pedicle screw placement for middle-upper thoracic trauma: a cohort study

62 years-old male, falling injury with T2/3 fracture type B1. Case 2. Fig. S21. Continuously printed 3D spine model for patient of Case2. Fig. S22. Individually printed 3D spine model for patient of Case2. Fig. S23. Postoperative anteroposterior X-ray showed correction fixation from T1 to T4 of the thoracic vertebrae. Case2. Fig. S24. Pedicle screw distribution was of level 1 at right T1, and of level 0 at left T1. Case2. Fig. S25. Pedicle screw distribution was of level 1 at right T2, and of level 0 at left T2. Case2. Fig. S26. Pedicle screw distribution was of level 0 at T3. Case2. Fig. S27. Pedicle screw distribution was of level 0 at T4. Case2. (ZIP 3450 kb