Explore the vast range of titles available.

A large-scale silicon nanophotonic phased array with more than 4,000 antennas is demonstrated using a state-of-the-art complementary metal-oxide–semiconductor (CMOS) process, enabling arbitrary holograms with tunability, which brings phased arrays to many new technological territories. New dimension to photonic nanoarrays Nanophotonic approaches allow the construction of chip-scale arrays of optical nanoantennas capable of producing radiation patterns in the far field. This could be useful for a range of applications in communications, LADAR (laser detection and ranging) and three-dimensional holography. Until now this technology has been restricted to one-dimensional or small two-dimensional arrays. This paper reports the construction of a large-scale silicon nanophotonic phased array containing 4,096 optical nanoantennas balanced in power and aligned in phase. The array was used to generate a complex radiation pattern—the MIT logo—in the far field. The authors show that this type of nanophotonic phased array can be actively tuned, and in some cases the beam is steerable. Electromagnetic phased arrays at radio frequencies are well known and have enabled applications ranging from communications to radar, broadcasting and astronomy 1 . The ability to generate arbitrary radiation patterns with large-scale phased arrays has long been pursued. Although it is extremely expensive and cumbersome to deploy large-scale radiofrequency phased arrays 2 , optical phased arrays have a unique advantage in that the much shorter optical wavelength holds promise for large-scale integration 3 . However, the short optical wavelength also imposes stringent requirements on fabrication. As a consequence, although optical phased arrays have been studied with various platforms 4 , 5 , 6 , 7 , 8 and recently with chip-scale nanophotonics 9 , 10 , 11 , 12 , all of the demonstrations so far are restricted to one-dimensional or small-scale two-dimensional arrays. Here we report the demonstration of a large-scale two-dimensional nanophotonic phased array (NPA), in which 64 × 64 (4,096) optical nanoantennas are densely integrated on a silicon chip within a footprint of 576 μm × 576 μm with all of the nanoantennas precisely balanced in power and aligned in phase to generate a designed, sophisticated radiation pattern in the far field. We also show that active phase tunability can be realized in the proposed NPA by demonstrating dynamic beam steering and shaping with an 8 × 8 array. This work demonstrates that a robust design, together with state-of-the-art complementary metal-oxide–semiconductor technology, allows large-scale NPAs to be implemented on compact and inexpensive nanophotonic chips. In turn, this enables arbitrary radiation pattern generation using NPAs and therefore extends the functionalities of phased arrays beyond conventional beam focusing and steering, opening up possibilities for large-scale deployment in applications such as communication, laser detection and ranging, three-dimensional holography and biomedical sciences, to name just a few.

The autobiography of astronaut John Young.

Imprint lithography is emerging as an alternative nano-patterning technology to traditional photolithography that permits the fabrication of 2D and 3D structures with <100 nm resolution, patterning and modification of functional materials other than photoresist and is low cost, with operational ease for use in developing bio-devices. Techniques for imprint lithography, categorized as either ‘molding and embossing’ or ‘transfer printing’, will be discussed in the context of microarrays for genomics, proteomics and tissue engineering. Specifically, fabrication by nanoimprint lithography (NIL), UV-NIL, step and flash imprint lithography (S–FIL), micromolding by elastomeric stamps and micro- and nano-contact printing will be reviewed.

This study examined the status of toxic metal contamination of the urban industrial city of Ahvaz in Iran. Two hundred and twenty-seven surface soils from a depth horizon of 0–10 cm were collected from urban areas. In addition, 15 soil samples were collected to recognise the sources of Pb in urban topsoils in Ahvaz city. Mean concentration of Pb, Zn, Cu and As were 181 ± 167, 123 ± 118, 185 ± 167 and 6.9 ± 8.9 mg.kg −1 , respectively. Results of inter-element relationship among studied toxic metals revealed that Pb, Zn and Cu may have the same anthropogenic origin, whilst As originated from different sources. The results of pollution index (PI) and Nemerow pollution index (NPI) implied that Pb, Zn, and Cu had a moderate to high level of pollution. The Pb isotopic composition analysis suggested clear anthropogenic origins of Pb including industrial emission, vehicle exhaust and dust storm with the mean contributions of 47%, 15% and 7%, respectively, by a four-end member model.

A career-spanning documentary on the Rolling Stones, with concert footage from their \"A Bigger Bang\" tour.

Silicon photonics has emerged as the leading candidate for implementing ultralow power wavelength–division–multiplexed communication networks in high-performance computers, yet current components (lasers, modulators, filters and detectors) consume too much power for the high-speed femtojoule-class links that ultimately will be required. Here we demonstrate and characterize the first modulator to achieve simultaneous high-speed (25 Gb s −1 ), low-voltage (0.5  V PP ) and efficient 0.9 fJ per bit error-free operation. This low-energy high-speed operation is enabled by a record electro-optic response, obtained in a vertical p – n junction device that at 250 pm V −1 (30 GHz V −1 ) is up to 10 times larger than prior demonstrations. In addition, this record electro-optic response is used to compensate for thermal drift over a 7.5 °C temperature range with little additional energy consumption (0.24 fJ per bit for a total energy consumption below 1.03 J per bit). The combined results of highly efficient modulation and electro-optic thermal compensation represent a new paradigm in modulator development and a major step towards single-digit femtojoule-class communications. Optical modulators on silicon promise to deliver ultralow power communication networks between or within computer chips. Here, the authors demonstrate a silicon modulator operating with less than one femtojoule energy and are able to compensate for thermal drift over a 7.5 °C temperature range.

Two major oil-producing regions frame this article. The first is the onshore oil world in the global South (the Niger delta in Nigeria as part of the wider Gulf of Guinea), and the second is the offshore world of deepwater oil and gas exploration and production in the United States (specifically, the Gulf of Mexico, and the Deepwater Horizon blowout). Both arenas can be seen as oil frontiers—frontiers of accumulation and dispossession—rooted in the operations of specific oil assemblages. I trace the relations between the deep infrastructures of the oil world—pipelines, rigs, flowstations, tankers, financiers, engineering firms, security forces, and so on—and to the regimes of life and death in the postcolonial South and the advanced capitalist North. Political, economic, and social relations are, as Timothy Mitchell notes, engineered out of the flows of energy. Opening up these sorts of oil frontiers—whether in Angolan or Brazilian deepwater, Russian Siberia, or increasingly now the frozen frontiers of the Arctic—necessitates engagements with place-specific social and political forces, none of which necessarily or easily are compatible with some presumed set of desires of corporate oil capital—political stability, surplus management, price control—or indeed of imperialist oil-consuming states. In one case the terminal point is an insurgency and combustible politics threatening the very operations of the oil industry and the petrostate itself; in the other it is the violence of a blowout—the loss of human and environmental life and livelihoods—and of the deadly consequences of substituting technical and financial over political risks.

Globally, more than 800 million people are undernourished while >2 billion people have one or more chronic micronutrient deficiencies (MNDs). More than 6% of global mortality and morbidity burdens are associated with undernourishment and MNDs. Here we show that, in 2011, 3.5 and 1.1 billion people were at risk of calcium (Ca) and zinc (Zn) deficiency respectively due to inadequate dietary supply. The global mean dietary supply of Ca and Zn in 2011 was 684 ± 211 and 16 ± 3 mg capita −1 d −1 (±SD) respectively. Between 1992 and 2011, global risk of deficiency of Ca and Zn decreased from 76 to 51% and 22 to 16%, respectively. Approximately 90% of those at risk of Ca and Zn deficiency in 2011 were in Africa and Asia. To our knowledge, these are the first global estimates of dietary Ca deficiency risks based on food supply. We conclude that continuing to reduce Ca and Zn deficiency risks through dietary diversification and food and agricultural interventions including fortification, crop breeding and use of micronutrient fertilisers will remain a significant challenge.