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A combined top-down and bottom-up approach for precise placement of metal nanoparticles on silicon (vol 4, pg 330, 2008)

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SMALL 2008年第4期4卷 393-393页

作者： Choi, W. K. Liew, T. H. Chew, H. G. Zheng, F. Thompson, C. V. Wang, Y. Hong, M. H. Wang, X. D. Li, L. Yun, J. Microelectronics Laboratory Department of Electrical and Computer Engineering National University of Singapore 117576 Singapore Singapore Fax: (+65) 677-911-03 Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge MA 02139 USA ECE-DSI Laser Microprocessing Laboratory Department of Electrical and Computer Engineering National University of Singapore 117576 Singapore Singapore Advanced Materials for Micro- and Nano-Systems Singapore-MIT Alliance 117576 Singapore Singapore

A combined top-down and bottom-up approach was used for precise placement of metal nanoparticles on silicon substrates. The study used laser interference lithography (LIL) technique, to open windows on a silicon wafer with a silicon oxide mask. Inverted pyramids were obtained at the window region, by etching the silicon wafer in KOH under the top-down approach. The bottom-up approach involved the evaporation of a gold (Au) layer on the whole silicon wafer and annealing at elevated temperature. The Au inside the inverted pyramids was coarsened and formed Au dots inside them. The results show that the diameter of the metal nanoparticles can be tuned more effectively, by changing the Au layer thickness, along with the annealing temperature.

关键词： gold nanolithography nanomanipulation nanoparticles silicon surfaces

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Approximate dynamic programming using support vector regression

Approximate dynamic programming using support vector regress...

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IEEE Conference on Decision and Control

作者： Brett Bethke Jonathan P. How Asuman Ozdaglar Department of Aeronautics and Astronautics MIT Cambridge MA USA Department of Aeronautics and Astronautics Massachusetts Institute of Technology USA Department of Electrical Engineering Computer Science Massachusetts Institute of Technology USA

ISBN: (纸本)9781424431236

This paper presents a new approximate policy iteration algorithm based on support vector regression (SVR). It provides an overview of commonly used cost approximation architectures in approximate dynamic programming problems, explains some difficulties encountered by these architectures, and argues that SVR-based architectures can avoid some of these difficulties. A key contribution of this paper is to present an extension of the SVR problem to carry out approximate policy iteration by forcing the Bellman error to zero at selected states. The algorithm does not require trajectory simulations to be performed and is able to utilize a rich set of basis functions in a computationally efficient way. Computational results for an example problem are shown.

关键词： Dynamic programming Function approximation computer architecture Costs Neural networks Space technology Computational modeling Decision making Uncertainty Finance

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Quantum Phase Tomography of a Strongly Driven Qubit

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Physical Review Letters 2008年第19期101卷 190502-190502页

作者： M. S. Rudner A. V. Shytov L. S. Levitov D. M. Berns W. D. Oliver S. O. Valenzuela T. P. Orlando Department of Physics Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA Department of Physics University of Utah Salt Lake City Utah 84112 USA Kavli Institute for Theoretical Physics University of California Santa Barbara California 93106 USA MIT Lincoln Laboratory 244 Wood Street Lexington Massachusetts 02420 USA MIT Francis Bitter Magnet Laboratory Cambridge Massachusetts 02139 USA Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA

The interference between repeated Landau-Zener transitions in a qubit swept through an avoided level crossing results in Stückelberg oscillations in qubit magnetization, a hallmark of the coherent strongly driven regime in two-level systems. The two-dimensional Fourier transforms of the resulting oscillatory patterns are found to exhibit a family of one-dimensional curves in Fourier space, in agreement with recent observations in a superconducting qubit. We interpret these images in terms of time evolution of the quantum phase of the qubit state and show that they can be used to probe dephasing mechanisms.

关键词： Fourier transforms

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Arrayed Si/SiGe Nanowire Heterostructure Formation via Au-catalyzed Wet Chemical Etching Method

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ECS Transactions 2008年第25期16卷

作者： Xiaodong Wang K.L. Pey W.K. Choi C.K.F. Ho Eugene A. Fitzgerald D. Antoniadis Nanyang Technological University School of Electrical and Electronic Engineering Nanyang Technological University Department of Electrical and Computer Engineering National University of Singapore Advanced Materials for Micro- and Nano-Systems Programme Singapore-MIT Alliance MIT Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology

Aligned Si/SiGe nanowire heterostructures have been formed using Au-assisted top-down chemical etching method combined with nanosphere lithography. Since the nanowires are formed from the as-grown films, the heterostructures along the axial axis of the formed nanowires, i.e. axial heterostructures, are replica of the grown layered film structure. Thus SiGe nanowire heterostructures can be readily formed along the axis using an as-grown heterostructured film. By applying a nanosphere lithography technique, the space, diameter, and density of the nanowires can be controlled and readily formed at specifically defined area. Because of the flexibility and simplicity of this method, nanowires with embedded junctions of different doping characteristics and Si/Ge concentrations can be fabricated easily. Si and its Ge alloy nanowires and one dimensional heterostructures formed using this method may have great potential for vertical logic, photovoltaic and memory device applications.

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Arrayed Si/SiGe Nanowire Heterostructure Formation via Au-catalyzed Wet Chemical Etching Method

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ECS Meeting Abstracts 2008年第2期MA2008-02卷

Abstract not Available.

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Astro-comb: revolutionizing precision spectroscopy in astrophysics

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Proceedings of the International Astronomical Union 2008年第S253期4卷 499-501页

作者： Claire E. Cramer Chih-Hao Li Andrew J. Benedick Alexander G. Glenday Franz X. Kärtner David F. Phillips Dimitar Sasselov Andrew Szentgyorgyi Ronald L. Walsworth Dept. of Physics Harvard University Cambridge MA 02138 USA email: ccramer@fas.harvard.edu Harvard-Smithsonian Center for Astrophysics Cambridge MA 02138USA Dept. of Electrical Engineering Computer Science and Research Lab for Electronics MIT Cambridge MA 02138USA Dept. of Astronomy Harvard University Cambridge MA 02138 USA

Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision better than 60cm/s. To find a 1-Earth mass planet in an Earth-like orbit, a precision of 5cm/s is necessary. The combination of a laser frequency comb with a Fabry-Perot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration. Here we report the fabrication of such a filtered laser comb with up to 40 GHz (~1 Angstrom) line spacing, generated from a 1 GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb (astro-comb) is well matched to the resolving power of high-resolution astrophysical spectrographs. The astrocomb should allow a precision as high as 1cm/s in astronomical readial velocity measurements.

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Dependence of orientation tuning on recurrent excitation and inhibition in a network model of V1 08

Dependence of orientation tuning on recurrent excitation and...

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Proceedings of the 22nd International Conference on Neural Information Processing Systems

作者： Klaus Wimmer Marcel Stimberg Robert Martin Lars Schwabe Jorge Mariño James Schummers David C. Lyon Mriganka Sur Klaus Obermayer Bernstein Center for Computational Neuroscience and Technische Universität Berlin Germany Dept of Computer Science and Electrical Engineering University of Rostock Germany Dept of Medicine Neuroscience and Motor Control Group Univ. A Coruña Spain Dept of Brain and Cognitive Sci and Picower Ctr for Learning and Memory MIT Cambridge Dept of Anatomy and Neurobiology University of California Irvine

ISBN: (纸本)9781605609492

The computational role of the local recurrent network in primary visual cortex is still a matter of debate. To address this issue, we analyze intracellular recording data of cat V1, which combine measuring the tuning of a range of neuronal properties with a precise localization of the recording sites in the orientation preference map. For the analysis, we consider a network model of Hodgkin-Huxley type neurons arranged according to a biologically plausible two-dimensional topographic orientation preference map. We then systematically vary the strength of the recurrent excitation and inhibition relative to the strength of the afferent input. Each parametrization gives rise to a different model instance for which the tuning of model neurons at different locations of the orientation map is compared to the experimentally measured orientation tuning of membrane potential, spike output, excitatory, and inhibitory conductances. A quantitative analysis shows that the data provides strong evidence for a network model in which the afferent input is dominated by strong, balanced contributions of recurrent excitation and inhibition. This recurrent regime is close to a regime of "instability", where strong, self-sustained activity of the network occurs. The firing rate of neurons in the best-fitting network is particularly sensitive to small modulations of model parameters, which could be one of the functional benefits of a network operating in this particular regime.

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Message passing and distributed statistical inference 45

Message passing and distributed statistical inference

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45th Annual Allerton Conference on Communication, Control, and Computing 2007

作者： Chandrasekaran, Venkat Johnson, Jason Kreidl, O. Patrick Malioutov, Dmitry Sanghavi, Sujay Willsky, Alan S. Department of Electrical Engineering and Computer Science Laboratory for Information and Decision Systems MIT CambridgeMA United States

ISBN: (纸本)9781605600864

In this paper , we summarize several research directions involving message-passing algorithms and distributed fusion. The starting point is inference for graphical models , but the different constraints and objectives found in sensor networks suggest new questions. In addition to providing pointers to a variety of other parts of our research in this area , we spend most of our time on two research investigations. The irst involves team-theoretic approaches to distributed decision-making and the development of message-passing algorithms for sensor network organization in order to optimize distributed team objectives. The second deals with the exploitation of so-called walk-sum analysis for distributed linear estimation. In particular under an easily checked condition for walk-summability , we can show that essentially any messaging strategy converges to the optimal distributed solution;moreover with modest use of local memory , this remains true in the presence of random message losses. We also describe how this framework leads to a tractable max-spanning tree problem for optimal adaptive message routing-i.e. , for determining a spanning tree for the next wave of messages to reduce an upper bound on estimation error as quickly as possible.

关键词： Sensor networks

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Studying reprogramming of somatic cells via fusion with embryonic stem cells: A massively parallel device for cell fusion 11

Studying reprogramming of somatic cells via fusion with embr...

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11th International Conference on Miniaturized Systems for Chemistry and Life sciences, uTAS 2007

作者： Skelley, Alison M. Kirak, Oktay Jaenisch, Rudolf Voldman, Joel Research Laboratory of Electronics MIT United States Microsystems Technology Laboratories MIT United States Whitehead Institute MIT United States Electrical Engineering and Computer Science MIT United States

ISBN: (纸本)9780979806407

Controlled fusion between an embryonic stem cell and a somatic cell is an important strategy for cellular reprogramming. We have developed a microfluidic system specifically to address the main limitation of current fusion technologies: the positioning and pairing of cells prior to fusion. We present a PDMS device designed to pair cells prior to fusion. Thousands of properly paired cells are obtainable within a mm-sized area, and the device is compatible with both chemical and electrical fusion. Fusion efficiencies obtained with our device demonstrate a significant improvement over current technologies. © 2007 CBMS.

关键词： Stem cells

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Improvements on an out-of-plane MEMS quadrupole for portable mass spectrometry

Improvements on an out-of-plane MEMS quadrupole for portable...

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Technical Digest of the 20th International Vacuum Nanoelectronics Conference, IVNC 07

作者： Valasquez-Garcia, L.F. Cheung, K. Akinwande, A.I. Microsystems Technologies Laboratories MIT Cambridge MA 02139 United States Electrical Engineering and Computer Science MIT Cambridge MA 02139 United States

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ISBN: (纸本)1424411343

No abstract available

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