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  • 1
    Electronic Resource
    Electronic Resource
    Nonequilibrium solvation: An ab initio quantum-mechanical method in the continuum cavity model approximation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7375-7384 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electrostatic relationships necessary for the quantum-mechanical evaluation of the properties of a solute experiencing sudden changes in its internal charge distribution are here presented in a form suitable to perform accurate quantum-mechanical calculations of the solute properties. Attention has been paid to express the boundary conditions in the most convenient form and to avoid further constraints on the elaboration of the computational procedures. The approach exploits the separation of orientational (inertial) and electronic (inertialess) components of the polarization and complements the polarizable continuum method [Chem. Phys. 65, 239 (1982)], usually employed for static descriptions. Examples of application of the method to photoionization and electronic transitions processes are shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464728
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  • 2
    Electronic Resource
    Electronic Resource
    Optimal conditions for imaging in scanning tunneling microscopy: Experimental (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3875-3878 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present a study of the behavior of the texture of surfaces imaged by scanning tunneling microscopy (STM) under different control conditions in the feedback loop. The quality and the reliability of the STM images can be described quantitatively by giving the values of two adimensional parameters that describe the measurement conditions. The analysis of the main surface texture parameters such as the rms roughness and the average wavelength shows that they have a strong dependence on the values of the parameters used in the feedback loop for imaging regardless of the visual quality of the images that can be the same. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149192
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  • 3
    Electronic Resource
    Electronic Resource
    Optimal conditions for imaging in scanning tunneling microscopy: Theory (1998)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 69 (1998), S. 3867-3874 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The scanning tunneling microscopy (STM) feedback system is analyzed to look for the optimal conditions for measurement. The typical feedback circuit normally used in STM and the parameters involved on it are studied, and their relative importance into the loop are discussed. The analysis of the role of each parameter demonstrated the importance of a detailed knowledge of the instrument to assure that the images obtained are reliable. We obtained equations that involve the main parameters of the loop, and yield the optimal conditions for imaging taking into account stability, signal amplitude, and phase shift. Combining the stability conditions with the imaging conditions obtained in this work, we found values for the feedback parameters to perform optimal STM measurements. Moreover, with this work, we highlight the importance to include in further publications the value of the main parameters used to obtain STM images. The conclusion of our work is that in some cases (in particular atomic resolution and fractal analysis) STM users should pay more attention to the setting of the instrument. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149191
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  • 4
    Electronic Resource
    Electronic Resource
    Electrochemical preparation of tungsten tips for a scanning tunneling microscope (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1917-1921 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We present experimental results obtained during the electrochemical preparation of tungsten tips for a scanning tunneling microscope. Experiments were done with direct current and two kinds of electrolytes widely reported in the literature: KOH and NaOH. We report the effects of the applied voltage, time of etching, tip length, electrolyte concentration, wire diameter, and immersed portion as relevant parameters in the process. From the images obtained by a metallurgical microscope and a scanning electron microscope as well as from Auger and electron diffraction x-ray analysis the best conditions for W tip preparation were obtained. We found that KOH is better than NaOH as an electrolyte to prepare tips for scanning tunneling microscopy and that tip quality increases as the wire diameter and the immersed portion increases. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146996
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis of scanning tunneling microscopy feedback system (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3196-3203 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A theoretical analysis of the feedback system in the scanning tunneling microscope (STM) is presented. The proposed model includes all the elements involved in the STM loop. The knowledge of its behavior allow one to accurately determine the region where the unstable STM operation could affect the measurements, and also to set the optimal working parameters. Each element of the feedback circuitry is analyzed and discussed as well as their mutual interactions. Thus the stability region of a STM has been obtained analytically, using all the possible elements in the feedback loop and without using simplifications or rare models for the system. The mathematical models for each element of the loop has been used and the problem has been solved using control theory. Different working conditions are simulated and analyzed. Some relations for stability conditions, considering the value of each component involved in the feedback loop, are proposed and analyzed. The good agreement between theory and experimentation is shown by comparing images taken under conditions of good stability and of instability. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145551
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  • 6
    Electronic Resource
    Electronic Resource
    High-resolution x-ray diffraction study of piezoelectric InGaAs/GaAs multiquantum well p-i-n photodiodes grown on (111)B GaAs (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1574-1576 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-resolution x-ray diffractometry has been applied to the structural characterization of piezoelectric strained InGaAs/GaAs multiquantum well p-i-n diodes grown by molecular beam epitaxy on (111)B GaAs substrates. Reference samples simultaneously grown on (001) GaAs have been also characterized. Diodes with 3, 7, and 10 periods and different well to barrier thickness ratio have been studied. Symmetric and asymmetric reflections at various azimuths were measured and the scans were fitted with theoretical curves obtained through a dynamical simulation program developed in our lab. The comparison between experimental and simulated profiles has enabled us to determine the main structural parameters of the samples. High-resolution x-ray diffractometry provided accurate data about period and capping layer thicknesses, indium content in the wells and state of relaxation, information which cannot be always obtained in (111)B samples from other characterization techniques such as photoluminescence or photocurrent spectroscopies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117034
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  • 7
    Electronic Resource
    Electronic Resource
    Observation of non-trigonal lattice distortion in pseudomorphic InGaAs/GaAs superlattices grown on misoriented (111)B GaAs (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 3297-3305 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate the asymmetric lattice distortion of pseudomorphic superlattices grown on misoriented substrates. High-resolution x-ray diffractometry has been employed to study InGaAs/GaAs superlattices grown by molecular beam epitaxy on (111)B GaAs with a miscut angle of 1°. We observe the nontrigonal deformation of the InGaAs unit cells, while the GaAs cells retain the cubic symmetry. This result is in accord with the behavior predicted by the anisotropic elasticity theory. Consequently, the threefold symmetry of the [1¯1¯1¯] axis is lost and, therefore, the interpretation of the diffraction profiles must take account of the actual Miller indices of the substrate surface and reflecting planes used during each measurement. Otherwise, a non-negligible error in the determination of the period thickness and indium fraction could be introduced. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365637
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  • 8
    Electronic Resource
    Electronic Resource
    α7-Nicotinic acetylcholine receptors mediate an Aβ1−42-induced increase in the level of acetylcholinesterase in primary cortical neurones (2004)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 88 (2004), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The β-amyloid protein (Aβ) is the major protein component of amyloid plaques found in the Alzheimer brain. Although there is a loss of acetylcholinesterase (AChE) from both cholinergic and non-cholinergic neurones in the brain of Alzheimer patients, the level of AChE is increased around amyloid plaques. Previous studies using P19 cells in culture and transgenic mice which overexpress human Aβ have suggested that this increase may be due to a direct action of Aβ on AChE expression in cells adjacent to amyloid plaques. The aim of the present study was to examine the mechanism by which Aβ increases levels of AChE in primary cortical neurones. Aβ1−42 was more potent than Aβ1−40 in its ability to increase AChE in primary cortical neurones. The increase in AChE was unrelated to the toxic effects of the Aβ peptides. The effect of Aβ1−42 on AChE was blocked by inhibitors of α7 nicotinic acetylcholine receptors (α7 nAChRs) as well as by inhibitors of L- or N-type voltage-dependent calcium channels (VDCCs), whereas agonists of α7 nAChRs (choline, nicotine) increased the level of AChE. The results demonstrate that the effect of Aβ1−42 on AChE is due to an agonist effect of Aβ1−42 on the α7 nAChR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.2003.02296.x
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of scanning tunneling microscopy feedback system: Experimental determination of parameters (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 2947-2952 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the experimental work necessary on a scanning tunneling microscopy (STM) system to obtain some important feedback parameters—to have stability and good imaging conditions—such as the mechanical resonance frequency ω0, the delay time τ, and the damping factor ζ. We study and analyze each one of the main components involved on the STM such as the feedback system, the piezoelectric elements, the rigidity of the mechanical structure (the mechanical resonance), and its relation with the scanning rate for imaging. We conclude that it is necessary to obtain these parameters with the STM in tunnel conditions, in order to consider the effects of the tip, surface contamination, and tip sample interaction. We also conclude that tripod based STM can be better than STM based on piezo tubes scanners. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147077
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  • 10
    Electronic Resource
    Electronic Resource
    Solvent effects on the potential energy surface of the 1:1 complex of water and formamide: Application of the polarizable continuum model to the study of nonadditive effects (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5539-5546 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A study of the solvent effect on the potential energy surface of the 1:1 complex of water and formamide have been performed. In the description of the solvent we have employed the polarizable continuum model. The calculations were done at Hartree–Fock ab initio and Møller–Plesset (MP) levels. We found that the geometry of the system is appreciably modified by the solvent. The most important changes are the inversion of the water molecule orientation and the increase of the O(formamide)–H(water) distance by about 0.2 A(ring). In the gas phase binding to the carbonyl is energetically equivalent to binding to the amino group. However, in solution, water binds better to the carbonyl oxygen that to the NH group. The nonadditive contributions are, in general, important and can be related to the change in the monomer energies when one passes from the monomeric to the dimeric reaction potential. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471793
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