Active dielectric antenna on chip for spatial light modulation

• Ciyuan Qiu,
• Jianbo Chen,
• Yang Xia
• & Qianfan Xu

Integrated photonic resonators are widely used to manipulate light propagation in an evanescently-coupled waveguide. While the evanescent coupling scheme works well for planar optical systems that are naturally waveguide based, many optical applications are free-space based, such as imaging, display, holographics, metrology and remote sensing. Here we demonstrate an active dielectric antenna as the interface device that allows the large-scale integration capability of silicon photonics to serve the free-space applications. We show a novel perturbation-base diffractive coupling scheme that allows a high-Q planer resonator to directly interact with and manipulate free-space waves. Using a silicon-based photonic crystal cavity whose resonance can be rapidly tuned with a p-i-n junction, a compact spatial light modulator with an extinction ratio of 9.5 dB and a modulation speed of 150 MHz is demonstrated. Method to improve the modulation speed is discussed.

Energy: Clean stoves already in use in rural India

• Sudhir Kumar

Nature

 

491,

 

333

 

(15 November 2012)

 

doi:10.1038/491333b

Published online

 

14 November 2012

The health and pollution problems caused by primitive heating stoves (Nature 490, 343; 2012) are already being addressed in one rural Indian community.

In the state of Arunachal Pradesh in the eastern Himalayas — a biodiversity hot spot (N. Myers et al. Nature 403, 853–858; 2000) — most people use biomass fuel as their primary source of energy. It is burnt in a safe, energy-efficient and smoke-free stove called a chulha.

This portable iron stove is enclosed, equipped with a heat-intensity control, an ash-collection tray and an exhaust pipe. It costs just 1,500–3,000 rupees (US$28–56), and has a thermal efficiency of 60%, compared with 6–8% for traditional stoves. This translates into a significant saving of around 300 kilograms of wood fuel (biomass) equivalent per year (J. S. Rawat et al. Curr. Sci. 98,1554; 2010).

These improvements have proved to be a boon for rural women living in poor socio-economic conditions.

Counting primary loops in polymer gels

Huaxing Zhou a, Jiyeon Woo a, Alexandra M. Cok a, Muzhou Wang b, Bradley D. Olsen b, and Jeremiah A. Johnson a,1Departments of a Chemistry and b
Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139
Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved October 9, 2012 (received for review July 31, 2012)

Much of our fundamental knowledge related to polymer networks is

built on an assumption of ideal end-linked network structure. Real

networks invariably possess topological imperfections that negatively affect mechanical properties; modifications of classical network theories have been developed to account for these defects.

Despite decades of effort, there are no known experimental protocols for precise quantification of even the simplest topological

network imperfections: primary loops. Here we present a simple

conceptual framework that enables primary loop quantification in

polymeric materials. We apply this framework to measure the

fraction of primary loop junctions in trifunctional PEG-based hydrogels. We anticipate that the concepts described here will open new

avenues of theoretical and experimental research related to polymer

network structure.

Synthetic Lipid Membrane Channels Formed by Designed DNA Nanostructures

1. Martin Langecker¹,*, 
2. Vera Arnaut¹,*, 
3. Thomas G. Martin²,*, 
4. Jonathan List¹, 
5. Stephan Renner¹, 
6. Michael Mayer³,
7. Hendrik Dietz²,†, 
8. Friedrich C. Simmel¹,†

Science 16 November 2012: 
Vol. 338 no. 6109 pp. 932-936 
DOI: 10.1126/science.1225624

ABSTRACT

We created nanometer-scale transmembrane channels in lipid bilayers by means of self-assembled DNA-based nanostructures. Scaffolded DNA origami was used to create a stem that penetrated and spanned a lipid membrane, as well as a barrel-shaped cap that adhered to the membrane, in part via 26 cholesterol moieties. In single-channel electrophysiological measurements, we found similarities to the response of natural ion channels, such as conductances on the order of 1 nanosiemens and channel gating. More pronounced gating was seen for mutations in which a single DNA strand of the stem protruded into the channel. Single-molecule translocation experiments show that the synthetic channels can be used to discriminate single DNA molecules.

Spontaneous Thermoreversible Formation of Cationic Vesicles in a Protic Ionic Liquid

Carlos R. López-Barrón , Dongcui Li , Leo DeRita ,Madivala G. Basavaraj , and Norman J. Wagner *

Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, United States

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja308975e

Publication Date (Web): October 3, 2012

Copyright © 2012 American Chemical Society

The search for stable vesicular structures is a long-standing topic of research because of the usefulness of these structures and the scarcity of surfactant systems that spontaneously form vesicles in true thermodynamic equilibrium. We report the first experimental evidence of spontaneous formation of vesicles for a pure cationic double tail surfactant (didodecyldimethylammonium bromide, DDAB) in a protic ionic liquid (ethylammonium nitrate, EAN). Using small and ultra-small angle neutron scattering, rheology and bright field microscopy, we identify the coexistence of two vesicle containing phases in compositions ranging from 2 to 68 wt %. A low density highly viscous solution containing giant vesicles (D 30 μm) and a sponge (L₃) phase coexists with a dilute high density phase containing large vesicles (D  2.5 μm). Vesicles form spontaneously via different thermodynamic routes, with the same size distribution, which strongly supports that they exist in a true thermodynamic equilibrium. The formation of equilibrium vesicles and the L₃ phase is facilitated by ion exchange between the cationic surfactant and the ionic liquid, as well as the strength of the solvophobic effect in the protic ionic liquid.

Coordination Chemistry and Antisolvent Strategy to Rare-Earth Solid Solution Colloidal Spheres

Cheng Chao Li and Hua Chun Zeng *

Department of Chemical and Biomolecular Engineering, Faculty of Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja307280v

Publication Date (Web): October 23, 2012

Copyright © 2012 American Chemical Society

We have devised in this work a general synthetic strategy for preparation of single- and multicomponent rare-earth coordination polymer colloidal spheres (RE-CPCSs). This strategy is based on an integration of coordination chemistry and antisolvent effect for synchronized precipitation. Highly monodisperse RE-CPCSs with homogeneous mixing of RE elements, which are not readily attainable by any existing methods, have been successfully prepared for the first time. In addition, the type and molar ratio of these colloidal spheres can be adjusted easily in accordance to the variety and dosage of precursor salts. The molar ratio of RE elements in as-prepared colloidal spheres shows a linear relationship to that of starting reactants. Furthermore, the RE-based core/shell colloidal spheres can be facilely prepared by introducing other metal salts (beyond lanthanide elements) owing to their different coordination chemistry and precipitation behavior. By adjusting concentrations of the ionic activators, luminescent properties can be tuned accordingly. Moreover, the RE-CPCSs can be transformed to monodisperse lanthanide oxide spheres via simple heat treatment. We believe that the present synthetic strategy provides a viable route to prepare other lanthanide-containing colloidal spheres that have enormous potential for future applications as optoelectronic devices, catalysts, gas sensors, and solar cells.

Discovery of an Organic Trefoil Knot

1. Nandhini Ponnuswamy¹, 
2. Fabien B. L. Cougnon¹, 
3. Jessica M. Clough¹, 
4. G. Dan Pantoş², 
5. Jeremy K. M. Sanders¹,*

Science 9 November 2012: 
Vol. 338 no. 6108 pp. 783-785 
DOI: 10.1126/science.1227032

ABSTRACT

Molecular knots remain difficult to produce using the current synthetic methods of chemistry because of their topological complexity. We report here the near-quantitative self-assembly of a trefoil knot from a naphthalenediimide-based aqueous disulfide dynamic combinatorial library. The formation of the knot appears to be driven by the hydrophobic effect and leads to a structure in which the aromatic components are buried while the hydrophilic carboxylate groups remain exposed to the solvent. Moreover, the building block chirality constrains the topological conformation of the knot and results in its stereoselective synthesis. This work demonstrates that the hydrophobic effect provides a powerful strategy to direct the synthesis of entwined architectures.

Visualization of Latent Fingermarks by Nanotechnology: Reversed Development on Paper—A Remedy to the Variation in Sweat Composition

1. Dr. Nimer Jaber, 
2. Dr. Adam Lesniewski,
3. Hadar Gabizon, 
4. Sanaa Shenawi, 
5. Prof. Daniel Mandler^*, 
6. Prof. Joseph Almog^*

1. Article first published online: 4 NOV 2012
   DOI: 10.1002/anie.201205259
   Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

   Angewandte Chemie International Edition

Don′t sweat it: “Negative” fingermarks are developed on paper by the application of gold nanoparticles (gold circles) that are capped by a bifunctional ligand, and then silver precipitation. In this process, paper is the substrate and the fingermarks serve as a mask. This approach may contribute to the successful recovery of latent fingermarks by law enforcement agencies.