California Institute of Technology

About: California Institute of Technology is a education organization based out in Pasadena, California, United States. It is known for research contribution in the topics: Galaxy & Redshift. The organization has 57649 authors who have published 146691 publications receiving 8620287 citations. The organization is also known as: Caltech & Cal Tech.

Time-dependent density-matrix renormalization-group using adaptive effective Hilbert spaces

Abstract: An algorithm for the simulation of the evolution of slightly entangled quantum states has been recently proposed as a tool to study time-dependent phenomena in one-dimensional quantum systems. Its key feature is a time-evolving block-decimation (TEBD) procedure to identify and dynamically update the relevant, conveniently small, subregion of the otherwise exponentially large Hilbert space. Potential applications of the TEBD algorithm are the simulation of time-dependent Hamiltonians, transport in quantum systems far from equilibrium and dissipative quantum mechanics. In this paper we translate the TEBD algorithm into the language of matrix product states in order to both highlight and exploit its resemblances to the widely used density-matrix renormalization-group (DMRG) algorithms. The TEBD algorithm, being based on updating a matrix product state in time, is very accessible to the DMRG community and it can be enhanced by using well-known DMRG techniques, for instance in the event of good quantum numbers. More importantly, we show how it can be simply incorporated into existing DMRG implementations to produce a remarkably effective and versatile 'adaptive time-dependent DMRG' variant, that we also test and compare to previous proposals.

Emerging roles for lipids in shaping membrane-protein function

Abstract: Studies of membrane proteins have revealed a direct link between the lipid environment and the structure and function of some of these proteins Although some of these effects involve specific chemical interactions between lipids and protein residues, many can be understood in terms of protein-induced perturbations to the membrane shape The free-energy cost of such perturbations can be estimated quantitatively, and measurements of channel gating in model systems of membrane proteins with their lipid partners are now confirming predictions of simple models

Comet 81P/Wild 2 under a microscope.

Abstract: The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

Overview of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)

Abstract: The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a research facility instrument provided by the Ministry of International Trade and Industry (MITI), Tokyo, Japan to be launched on NASA's Earth Observing System morning (EOS-AM1) platform in 1998. ASTER has three spectral hands in the visible near-infrared (VNIR), six bands in the shortwave infrared (SWIR), and five bands in the thermal infrared (TIR) regions, with 15-, 30-, and 90-m ground resolution, respectively. The VNIR subsystem has one backward-viewing band for stereoscopic observation in the along-track direction. Because the data will have wide spectral coverage and relatively high spatial resolution, it will be possible to discriminate a variety of surface materials and reduce problems in some lower resolution data resulting from mixed pixels. ASTER will, for the first time, provide high-spatial resolution multispectral thermal infrared data from orbit and the highest spatial resolution surface spectral reflectance temperature and emissivity data of all of the EOS-AM1 instruments. The primary science objective of the ASTER mission is to improve understanding of the local- and regional-scale processes occurring on or near the Earth's surface and lower atmosphere, including surface-atmosphere interactions. Specific areas of the science investigation include the following: (1) land surface climatology; (2) vegetation and ecosystem dynamics; (3) volcano monitoring; (4) hazard monitoring; (5) aerosols and clouds; (6) carbon cycling in the marine ecosystem; (7) hydrology; (8) geology and soil; and (9) land surface and land cover change. There are three categories of ASTER data: a global map, regional monitoring data sets, and local data sets to be obtained for requests from individual investigators.