We present a broadband dielectric spectroscopy study of potassium tantalate niobate (KTN) crystals, doped with varying amounts of Cu ions. The dielectric landscape in frequency and temperature is rich, with multiple processes in different temperature phases of the crystals. Of particular interest are the processes resulting from Cu and Nb ions in the paraelectric phase of the crystal and from Cu ions in the ferroelectric phase. The linear dependence of the ferroelectric transition temperature in KTN crystals (KTa0.62Nb0.38O3Cu) on the concentration of Nb, as well as the dielectric behavior of the ferroelectric phase transition in these crystals, are well known. We concentrate of the dielectric relaxation resulting from the Cu ions in the crystal lattice. Cu dopants in very small concentrations have been added in the past to enhance the photoreftractive properties of KTN crystals. However the small ionic radius of such dopants, relative to their lattice site, results in virtual dipoles exhibiting dielectric relaxation. The random nature of their distribution throughout the ordered KTN lattice leads to relaxation behavior reminiscent of glass formers. In particular Vogel Fulcher Tammann relaxation of these ions is evident in the paraelectric phase of the crystal. This cooperativity is broken at a critical temperature (T = 354 K) and the relaxation becomes Arrhenius in nature. An explanation in terms of Adam-Gibbs theory is presented where the cooperative cluster is realized by polarized Nb ions linking the widely space Cu ions. At the phase transition (T-c = 295.6 K) this relaxation is ’frozen’ by large internal fields caused by the structural shift of the Nb ion in the unit cell. As the temperature drops the Cu ions undergo a reorganization about the multiwell potential leading to a saddle-like process characteristic of liquids in confined systems. An explanation for this behavior is proposed based on free volume concepts, where the relatively small ionic radius of the Cu ions provides the free volume for the relaxing species. The role of the oxygen octahedra as the relaxing species is discussed. (c) 2005 Published by Elsevier BV.
This research focuses on the internal discourse of the Gush Katif settlers, exposes their socio-political perceptions, and attempts to understand the motives and the socio-psychological reasoning determining the settlers’ conduct. An understanding of the settlers’ discourse entails understanding their perception of “a home” - a geographic location strongly tied with their individual and community identity. The research highlights the frequent tension between the humane, individual and communal discourse and the national-religious discourse.
Association of a drug with chylomicrons in the enterocyte is an essential step in the lymphatic absorption pathway. In this article, the uptake of lipophilic compounds by chylomicrons ex vivo was compared to the corresponding intestinal lymphatic bioavailability reported in rats in order to elucidate the degree of correlation and to evaluate the utilization of this correlation as a predictive measurement of the lymphatic bioavailability potential of lipophilic drugs. Nine lipophilic compounds (Vitamin D(3), Vitamin E, halofantrine, probucol, diazepam, testosterone, cyclosporin A, benzo[a]pyrene and p,p'-DDT) at a concentration of 1.75 x 10(-6)M were incubated for 1h with chylomicron emulsion separated from rat blood. A strong linear correlation was found between the degree of association of compounds with chylomicrons ex vivo and the lymphatic transport reported in rats (r(2)=0.94, P<0.0001), whereas logP and solubility in long chain triglycerides showed only moderate correlation with lymphatic bioavailability. The linear correlation between the degree of uptake of compounds by isolated chylomicrons and intestinal lymphatic transport suggests that the two processes are governed by similar factors. Thus, the degree of association of lipophilic compounds with isolated chylomicrons can be used as a simple screening model for estimation of intestinal lymphatic transport potential of drug molecules. This approach is important in view of the practical difficulties in direct determination of the lymphatic bioavailability in vivo.
This essay details the urban consequences of the Al Aqsa Intifadah and the separation barrier project on Jerusalem. In West Jerusalem, the onset of terror, and specifically a wave of suicide bombings, hastened the city’s decentralization. Rapid decline of the economy and the disappearance of tourism further battered the city’s vitality. Israel’s increased barriering of the city, culminating in the separation barrier project, was a major low for the city’s Arab inhabitants, and the urban fabric of East Jerusalem. Neighborhoods inside and outside the barrier were divided, with massive effects on daily life, work opportunities, property values, and relocation patterns. The paper argues that without a strategic package of urban recovery measures, Jerusalem is in danger of becoming locked in a spiral of decline.
This paper reports an attempt to teach game theory in order to increase students' motivation to learn mathematics. A course in game theory was created in order to introduce students to new mathematical content presented in a different way.
An ab initio method is developed for variational grand-canonical molecular electronic structure of open systems based on the Gibbs–Peierls–Boguliobov inequality. We describe the theory and a practical method for performing the calculations within standard quantum chemistry codes using Gaussian basis sets. The computational effort scales similarly to the ground-state Hartree–Fock method. The quality of the approximation is studied on a hydrogen molecule by comparing to the exact Gibbs free energy, computed using full configuration-interaction calculations. We find the approximation quite accurate, with errors similar to those of the Hartree–Fock method for ground-state zero-temperature calculations. A further demonstration is given of the temperature effects on the bending potential curve for water. Some future directions and applications of the method are discussed. Several appendices give the mathematical and algorithmic details of the method.
The results of harmonic and anharmonic frequency calculations on a guanine-cytosine complex with an enolic structure (a tautomeric form with cytosine in the enol form and with a hydrogen at the 7-position on guanine) are presented and compared to gas-phase IR-UV double resonance spectral data. Harmonic frequencies were obtained at the RI-MP2/cc-pVDZ, RI-MP2/TZVPP, and semiempirical PM3 levels of electronic structure theory. Anharmonic frequencies were obtained by the CC-VSCF method with improved PM3 potential surfaces; the improved PM3 potential surfaces are obtained from standard PM3 theory by coordinate scaling such that the improved PM3 harmonic frequencies are the same as those computed at the RI-MP2/cc-pVDZ level. Comparison of the data with experimental results indicates that the average absolute percentage deviation for the methods is 2.6% for harmonic RI-MP2/cc-pVDZ (3.0% with the inclusion of a 0.956 scaling factor that compensates for anharmonicity), 2.5% for harmonic RI-MP2/TZVPP (2.9% with a 0.956 anharmonicity factor included), and 2.3% for adapted PM3 CC-VSCF; the empirical scaling factor for the ab initio harmonic calculations improves the stretching frequencies but decreases the accuracy of the other mode frequencies. The agreement with experiment supports the adequacy of the improved PM3 potentials for describing the anharmonic force field of the G(...)C base pair in the spectroscopically probed region. These results may be useful for the prediction of the pathways of vibrational energy flow upon excitation of this system. The anharmonic calculations indicate that anharnionicity along single mode coordinates can be significant for simple stretching modes. For several other cases, coupling between different vibrational modes provides the main contribution to anharmonicity. Examples of strongly anharmonically coupled modes are the symmetric stretch and group torsion of the hydrogen-bonded NH2 group on guanine, the OH stretch and torsion of the enol group on cytosine, and the NH stretch and NH out-of-plane bend of the non-hydrogen-bonded NH group on guanine.
We employ an approach wherein the ground state entanglement of a relativistic free scalar field is directly probed in a controlled manner. The approach consists of having a pair of initially nonentangled detectors locally interact with the vacuum for a finite duration T, such that the two detectors remain causally disconnected, and then analyzing the resulting detector mixed state. We show that the correlations between arbitrarily far-apart regions of the vacuum cannot be reproduced by a local hidden-variable model, and that as a function of the distance L between the regions, the entanglement decreases at a slower rate than ∼exp[−(L∕cT)3].
The design and performance of several generations of wavelength-selective 1 X K switches are reviewed. These optical subsystems combine the functionality of a demultiplexer, per-wavelength switch, and multiplexer in a single, low-loss unit. Free-space optics is utilized for spatially separating the constituent wavelength division multiplexing (WDM) channels as well as for space-division switching from an input optical fiber to one of K output fibers (1 X K functionality) on a channel-by-channel basis using a microelectromechanical system (MEMS) micromirror array. The switches are designed to provide wide and flat pass- bands for minimal signal distortion. They can also provide spectral equalization and channel blocking functionality, making them well suited for use in transparent WDM optical mesh networks.
The design and performance of several generations of wavelength-selective 1 X K switches are reviewed. These optical subsystems combine the functionality of a demultiplexer, per-wavelength switch, and multiplexer in a single, low-loss unit. Free-space optics is utilized for spatially separating the constituent wavelength division multiplexing (WDM) channels as well as for space-division switching from an input optical fiber to one of K output fibers (1 X K functionality) on a channel-by-channel basis using a microelectromechanical system (MEMS) micromirror array. The switches are designed to provide wide and flat pass- bands for minimal signal distortion. They can also provide spectral equalization and channel blocking functionality, making them well suited for use in transparent WDM optical mesh networks.
Modern game theory was born in 1928, when John von Neumann published his Minimax Theorem. This theorem ascribes to all two-person zero-sum games a value-what rational players may expect-and optimal strategies-how they should play to achieve that expectation. Seventy-seven years later, strategic game theory has not gotten beyond that initial point, insofar as the basic questions of value and optimal strategies are concerned. Equilibrium theories do not tell players how to play and what to expect; even when there is a unique Nash equilibrium, it it is not at all clear that the players "should" play this equilibrium, nor that they should expect its payoff. Here, we return to square one: abandon all ideas of equilibrium and simply ask, how should rational players play, and what should they expect. We provide answers to both questions, for all n-person games in strategic form.
The fundamental revelations to the founders of the three monotheistic religions, among many other revelation experiences, had occurred on a mountain. These three revelation experiences share many phenomenological components like feeling and hearing a presence, seeing a figure, seeing lights, and feeling of fear. In addition, similar experiences have been reported by non-mystic contemporary mountaineers. The similarities between these revelations on mountains and their appearance in contemporary mountaineers suggest that exposure to altitude might affect functional and neural mechanisms, thus facilitating the experience of a revelation. Different functions relying on brain areas such as the temporo-parietal junction and the prefrontal cortex have been suggested to be altered in altitude. Moreover, acute and chronic hypoxia significantly affect the temporo-parietal junction and the prefrontal cortex and both areas have also been linked to altered own body perceptions and mystical experiences. Prolonged stay at high altitudes, especially in social deprivation, may also lead to prefrontal lobe dysfunctions such as low resistance to stress and loss of inhibition. Based on these phenomenological, functional, and neural findings we suggest that exposure to altitudes might contribute to the induction of revelation experiences and might further our understanding of the mountain metaphor in religion. Mystical and religious experiences are important not only to the mystic himself, but also to many followers, as it was indeed with respect to the leaders of the three monotheistic religions. Yet, concerning its subjective character, mystical experiences are almost never accessible to the scholars interested in examining them. The tools of cognitive neuroscience make it possible to approach religious and mystical experiences not only by the semantical analysis of texts, but also by approaching similar experiences in healthy subjects during prolonged stays at high altitude and/or in cognitive paradigms. Cognitive neurosciences, in turn, might profit from the research of mysticism in their endeavor to further our understanding of mechanisms of corporeal awareness and self consciousness.
Although the fact that the eye is moving constantly has been known for a long time, the role of fixational eye movements (FEM) is still in dispute. Whatever their role, it is structurally clear that, since the eye is a ball, the size of these movements diminishes for locations closer to the poles. Here we propose a new perspective on the role of FEM from which we derive a prediction for a three-way interaction of a stimulus' orientation, location, and spatial frequency. Measuring time-to-disappearance for gratings located in the periphery we find that, as predicted, gratings located to the left and right of fixation fade faster when horizontal than when vertical in low spatial frequencies and faster when vertical than when horizontal in high spatial frequencies. The opposite is true for gratings located above and below fixation.
