214 research outputs found

    Comments on T-dualities of Ramond-Ramond Potentials

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    The type IIA/IIB effective actions compactified on T^d are known to be invariant under the T-duality group SO(d, d; Z) although the invariance of the R-R sector is not so direct to see. Inspired by a work of Brace, Morariu and Zumino,we introduce new potentials which are mixture of R-R potentials and the NS-NS 2-form in order to make the invariant structure of R-R sector more transparent. We give a simple proof that if these new potentials transform as a Majorana-Weyl spinor of SO(d, d; Z), the effective actions are indeed invariant under the T-duality group. The argument is made in such a way that it can apply to Kaluza-Klein forms of arbitrary degree. We also demonstrate that these new fields simplify all the expressions including the Chern-Simons term.Comment: 26 pages; LaTeX; major version up; discussion on the Chern-Simons term added; references adde

    Weyl Groups in AdS(3)/CFT(2)

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    The system of D1 and D5 branes with a Kaluza-Klein momentum is re-investigated using the five-dimensional U-duality group E_{6(+6)}(Z). We show that the residual U-duality symmetry that keeps this D1-D5-KK system intact is generically given by a lift of the Weyl group of F_{4(+4)}, embedded as a finite subgroup in E_{6(+6)}(Z). We also show that the residual U-duality group is enhanced to F_{4(+4)}(Z) when all the three charges coincide. We then apply the analysis to the AdS(3)/CFT(2) correspondence, and discuss that among 28 marginal operators of CFT(2) which couple to massless scalars of AdS(3) gravity at boundary, 16 would behave as exactly marginal operators for generic D1-D5-KK systems. This is shown by analyzing possible three-point couplings among 42 Kaluza-Klein scalars with the use of their transformation properties under the residual U-duality group.Comment: 20 pages, 3 figue

    Wideband low-noise optical beam deflection sensor with photothermal excitation for liquid-environment atomic force microscopy

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    閲戞并澶у銉曘儹銉炽儐銈c偄銈点偆銈ㄣ兂銈规妲婭 developed a wideband low-noise optical beam deflection sensor with a photothermal cantilever excitation system for liquid-environment atomic force microscopy. The developed sensor has a 10 MHz bandwidth and 4.7 fm/Hz deflection noise density in water. The theoretically limited noise performance (i.e., the noise level limited only by the photodiode shot noise) has been achieved in liquid for the first time. Owing to the wide bandwidth and the replaceable focus lens design, the sensor is applicable to cantilevers with various dimensions. The deflection noise densities of less than 7.8 fm/Hz have been achieved in water for cantilevers with lengths from 35 to 125 渭m. The ideal amplitude and phase versus frequency curves without distortion are obtained with the developed photothermal excitation system. The excitation system is applicable to relatively stiff cantilevers (>20 N/m) in liquid, making it possible to obtain true atomic-resolution images in liquid. True atomic-resolution imaging of mica in water is demonstrated using the developed deflection sensor and the photothermal excitation system. 漏 2009 American Institute of Physics

    Subnanometer-resolution frequency modulation atomic force microscopy in liquid for biological applications

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    閲戞并澶у銉曘儹銉炽儐銈c偄銈点偆銈ㄣ兂銈规妲婽he spatial resolution and force sensitivity of frequency modulation atomic force microscopy (FM-AFM) in liquid have been dramatically improved in the last a few years. It is now possible to image individual atoms and molecules at a solid/liquid interface with a subnanometerscale resolution and a piconewton-order loading force. This capability enabled the direct visualization of hydration layers and mobile ions on a lipid bilayer and 尾-strands constituting an amyloid fibril. These striking results highlighted the significant potential of FM-AFM in biological research. Here, I summarize the technological innovation that brought about this progress and review biological applications of FM-AFM in liquid. 漏 2009 The Japan Society of Applied Physics

    Instrumentation and biological applications of high-resolution frequency modulation atomic force microscopy in liquid

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    Frequency modulation atomic force microscopy (FM-AFM) has been a powerful tool for imaging atomic-scale structures and properties of various materials including metals, semiconductors, metal oxides, alkali halides and organic systems. Whilst the method has been used mainly in ultrahigh vacuum environments, recent progress in FM-AFM instrumentation made it possible to apply this technique also to investigations in liquid. This technological innovation opened up a variety of applications of FM-AFM in biology and electrochemistry. To date, the improved FM-AFM instrument and technique have been applied to investigations of several biological materials, providing novel information that has not been accessible with other imaging techniques. In this review, I will summarize the recent progress in FM-AFM instrumentation and biological applications in liquid. 漏 (2008) Trans Tech Publications, Switzerland

    Direct imaging of individual intrinsic hydration layers on lipid bilayers with Angstrom resolution

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    The interactions between water and biological molecules have the potential to influence the structure, dynamics, and function of biological systems, hence the importance of revealing the nature of these interactions in relation to the local biochemical environment. We have investigated the structuring of water at the interface of supported dipalmitoylphosphatidylcholine bilayers in the gel phase in phosphate buffer solution using frequency modulation atomic force microscopy (FM-AFM). We present experimental results supporting the existence of intrinsic (i.e., surface-induced) hydration layers adjacent to the bilayer. The force versus distance curves measured between the bilayer and the AFM tip show oscillatory force profiles with a peak spacing of 0.28 nm, indicative of the existence of up to two hydration layers next to the membrane surface. These oscillatory force profiles reveal the molecular-scale origin of the hydration force that has been observed between two apposing lipid bilayers. Furthermore, FM-AFM imaging at the water/lipid interface visualizes individual hydration layers in three dimensions, with molecular-scale corrugations corresponding to the lipid headgroups. The results demonstrate that the intrinsic hydration layers are stable enough to present multiple energy barriers to approaching nanoscale objects, such as proteins and solvated ions, and are expected to affect membrane permeability and transport

    The molecular-scale arrangement and mechanical strength of phospholipid/cholesterol mixed bilayers investigated by frequency modulation atomic force microscopy in liquid

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    閲戞并澶у銉曘儹銉炽儐銈c偄銈点偆銈ㄣ兂銈规妲婥holesterols play key roles in controlling molecular fluidity in a biological membrane, yet little is known about their molecular-scale arrangements in real space. In this study, we have directly imaged lipid-cholesterol complexes in a model biological membrane consisting of dipalmitoylphosphatidylcholine (DPPC) and cholesterols by frequency modulation atomic force microscopy (FM-AFM) in phosphate buffer solution. FM-AFM images of a DPPC/cholesterol bilayer in the liquid-ordered phase showed higher energy dissipation values compared to those measured on a nanoscale DPPC domain in the gel phase, reflecting the increased molecular fluidity due to the insertion of cholesterols. Molecular-resolution FM-AFM images of a DPPC/cholesterol bilayer revealed the existence of a rhombic molecular arrangement (lattice constants: a = 0.46nm, b = 0.71nm) consisting of alternating rows of DPPC and cholesterols as well as the increased defect density and reduced molecular ordering. The mechanical strength of a DPPC/cholesterol bilayer was quantitatively evaluated by measuring a loading force required to penetrate the membrane with an AFM tip. The result revealed the significant decrease of mechanical strength upon insertion of cholesterols. Based on the molecular-scale arrangement found in this study, we propose a model to explain the reduced mechanical strength in relation to the formation of lipid-ion networks. 漏 2009 IOP Publishing Ltd

    Spurious-free cantilever excitation in liquid by piezoactuator with flexure drive mechanism

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    閲戞并澶у銉曘儹銉炽儐銈c偄銈点偆銈ㄣ兂銈规妲媁e have developed a cantilever holder for spurious-free cantilever excitation in liquid by piezoactuator. In the holder, generation and propagation of an acoustic wave are suppressed by "acoustic barriers," i.e., boundaries between two materials having significantly different acoustic impedance while cantilever vibration is excited by "flexure drive mechanism" utilizing elastic deformation of a flexure hinge made of a material having a low elastic modulus. The holder enables to obtain amplitude and phase curves without spurious peaks in liquid using a piezoactuator, which ensures stability and accuracy of dynamic-mode atomic force microscopy in liquid. 漏 2009 American Institute of Physics
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