A multilayer photonic structure is described that strongly reflects incident sunlight while emitting heat selectively through an atmospheric transparency window to outer space; this leads to passive cooling under direct sunlight of 5 degrees Celsius below ambient air temperature, which has potential applications in air-conditioning and energy efficiency.

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Passive radiative cooling below ambient air temperature under direct sunlight

Transparent conductors as solar energy materials: A panoramic review

Most present-day semiconductor devices use inorganic crystalline materials, with single-crystalline silicon dominating other materials like GaAs by about a factor of 1000. Despite the advantages of single-crystalline inorganic semiconductors like high room-temperature mobility (up to 1000 cm2/(V s)) and high stability, these materials are less suitable for low-cost and large-area applications. Additionally, silicon is an indirect semiconductor and therefore is not well suited for optoelectronic applications like light-emitting diodes. Solar cells from silicon are expensive and require a large amount of energy for their fabrication, leading to a long energy payback time. As an alternative, organic semiconductors have recently gained much attention (for review articles, see refs 1 -3 (OLEDs), ref 4 (organic electronics in general), and refs 5 and 6 (organic solar cells)). Originally, much of the research concentrated on single crystals, which can have mobilities of a few cm2/(V s) at room temperature and even much higher values at low temperature, as shown in the pioneering work of Karl et al.7 However, for practical applications, thinfilm organic semiconductors with disordered morphology, such as evaporated small-molecule compounds or polymers processed from solution, are prevailing. Organic semiconductors are already broadly applied as photoconductors for copiers and laser printers. * Corresponding author. E-mail: leo@iapp.de. Web address: www.iapp.de. 1233 Chem. Rev. 2007, 107, 1233−1271

Highly efficient organic devices based on electrically doped transport layers.

Inorganic semiconductor light-emitting diodes (LEDs) are environmentally benign and have already found widespread use as indicator lights, large-area displays, and signage applications. In addition, LEDs are very promising candidates for future energy-saving light sources suitable for office and home lighting applications. Today, the entire visible spectrum can be covered by light-emitting semiconductors: AlGaInP and AlGaInN compound semiconductors are capable of emission in the red to yellow wavelength range and ultraviolet (uv) to green wavelength range, respectively. Currently, two basic approaches exist for white light sources: The combination of one or more phosphorescent materials with a semiconductor LED and the use of multiple LEDs emitting at complementary wavelengths. Both approaches are suitable for high efficiency sources that have the potential to replace incandescent and fluorescent lights. In this article, the properties of inorganic LEDs will be presented, including emission spectra, electrical characteristics, and current-flow patterns. Structures providing high internal quantum efficiency, namely, heterostructures and multiple quantum well structures, will be discussed. Advanced techniques enhancing the external quantum efficiency will be reviewed, including resonant-cavities, die shaping (chip shaping), omnidirectional reflectors, and photonic crystals. Different approaches to white LEDs will be presented and figures-of-merit such as the color rendering index, luminous efficacy, and luminous efficiency will be explained. Finally, the packaging of low power and high power LED dies will be discussed.


Keywords:

light-emitting diodes (LEDs);
solid-state lighting;
compound semiconductors;
device physics;
reflectors;
resonant cavity LEDs;
white LEDs;
packaging

Light Emitting Diodes

Suppose we wish to recover a signal \input amssym $\font\abc=cmmib10\def\bi#1{\hbox{\abc#1}} {\bi x} \in {\Bbb C}^n$ from m intensity measurements of the form , ; that is, from data in which phase information is missing. We prove that if the vectors are sampled independently and uniformly at random on the unit sphere, then the signal x can be recovered exactly (up to a global phase factor) by solving a convenient semidefinite program–-a trace-norm minimization problem; this holds with large probability provided that m is on the order of , and without any assumption about the signal whatsoever. This novel result demonstrates that in some instances, the combinatorial phase retrieval problem can be solved by convex programming techniques. Finally, we also prove that our methodology is robust vis-a-vis additive noise. © 2012 Wiley Periodicals, Inc.

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PhaseLift: Exact and Stable Signal Recovery from Magnitude Measurements via Convex Programming

The authors' experience with the application of the needle optimization technique to the design of optical coating is summarized. A physical interpretation of the technique is provided, and its main features are identified. Guidelines on the application of the needle optimization technique to various types of design problems are given.

Application of the needle optimization technique to the design of optical coatings.

The history of High Performance Computing at the Moscow State University (MSU) began with the creation of the Research Computing Center (RCC) in 1955. Since its inception, the MSU Computing Center was equipped with up-to-the-minute equipment. "Lomonosov" supercomputer was installed at the M. V. Lomonosov Moscow State University in 2009. This supercomputer was created by the Russian company "T-Platforms." At the beginning of 2012, MSU's supercomputing center based on "Lomonosov" had over 550 users from MSU, the Russian Academy of Sciences (RAS), and other organizations. The system network provides communication between parallel application processes in the compute nodes using MPI protocol, and an access to a parallel filesystem for the service servers and all compute nodes. The power of the MSU supercomputer system is widely used for the Russian Federation Presidential Commission Project on the modernization and technological development of the Russian economy: "Supercomputing Education."

"Lomonosov": Supercomputing at Moscow State University

In the phase retrieval problem one seeks to recover an unknown function g(t) from the amplitude mod g(k) mod of its Fourier transform. Since phase and amplitude are, in general, independent of each other, it is necessary to make use of other kinds of information which implicitly or explicitly constrain the admissible solutions g(t). In this paper we survey a variety of results explaining circumstances under which g(t) may be uniquely recovered from mod g(k) mod and supplementary information. A number of explicit formulae for the phase are discussed. We pay particular attention to the phase retrieval problem as it arises in certain inverse-scattering applications.

The phase retrieval problem

Basics of Optics of Multilayer Systems

Design approaches for optical thin films that recognize the key role of a design's total optical thickness are presented. These approaches are based primarily on the needle optimization technique but also utilize other optimization procedures. Using the described design approaches, an optical coating engineer can obtain a set of theoretical designs with different combinations of principal design metrics (merit function value, number of layers, and total design optical thickness); this extends opportunities for choosing the most practical and manufacturable design. We also show that some design problems have multiple solutions with nearly the same combinations of principal design metrics.

Alexander V. Tikhonravov

Papers

Application of the needle optimization technique to the design of optical coatings.

"Lomonosov": Supercomputing at Moscow State University

The phase retrieval problem

Basics of Optics of Multilayer Systems

Optical coating design approaches based on the needle optimization technique.