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Field Effects (field + effects)
Selected AbstractsCULTURAL ECONOMY AND THE CREATIVE FIELD OF THE CITYGEOGRAFISKA ANNALER SERIES B: HUMAN GEOGRAPHY, Issue 2 2010Allen J. Scott ABSTRACT. I begin with a rough sketch of the incidence of the cultural economy in US cities today. I then offer a brief review of some theoretical approaches to the question of creativity, with special reference to issues of social and geographic context. The city is a powerful fountainhead of creativity, and an attempt is made to show how this can be understood in terms of a series of localized field effects. The creative field of the city is broken down (relative to the cultural economy) into four major components, namely, (a) intra-urban webs of specialized and complementary producers, (b) the local labour market and the social networks that bind workers together in urban space, (c) the wider urban environment, including various sites of memory, leisure, and social reproduction, and (d) institutions of governance and collective action. I also briefly describe some of the path-dependent dynamics of the creative field. The article ends with a reference to some issues of geographic scale. Here, I argue that the urban is but one (albeit important) spatial articulation of an overall creative field whose extent is ultimately nothing less than global. [source] Discovery of the causeway and the mortuary temple of the Pyramid of Amenemhat II using near-surface magnetic investigation, Dahshour, Giza, EgyptGEOPHYSICAL PROSPECTING, Issue 2 2010T. Abdallatif ABSTRACT The main outbuildings of the Amenemhat II pyramid complex in Dahsour were yet to be discovered due to a very long subjection of the area to the military authorities and also the demolition of the pyramid itself. We describe the discovery of some of these outbuildings using near-surface magnetic investigations. A gradiometer survey was conducted in the area east of the pyramid to measure the vertical magnetic gradient with a high resolution instrument at 0.5 m sampling interval. The data showed some undesirable field effects such as grid discontinuities, grid slope, traverse stripe effects, spikes and high frequencies originating from recent ferrous contamination. These undesirable effects were addressed to produce an enhanced display. We have successfully detected four main structures in the area east of the pyramid; the causeway that connected the mortuary temple with the valley temple during the Middle Kingdom of the 12th Dynasty, the mortuary temple and its associated rooms, ruins of an ancient working area and an Egyptian-style tomb structure called a Mastaba. An improved recognition for these structures was accomplished by using the analytic signal and Euler deconvolution techniques. Excavation of a small part within the study area has proven the reliability of magnetic discoveries and the shallowness and composition of the detected features. [source] Heteroatoms and substituent effects: The importance of heteroatom hyperconjugationHETEROATOM CHEMISTRY, Issue 5 2002James F. King We have found that the specific rate of ,-sulfonyl carbanion formation in a ,-substituted sulfone shows a sizable dependence on the HC,C,X torsion angle. Defining kN = (kexch)X/(kexch)model (where the model has X = H or an alkyl group) we observed for a collection of ,-alkoxy sulfones (X = OR) acceptable agreement with the expression log kN = a + b cos2 , (where a = 1.70 and b = 2.62). Extension to other ,-substituents (X = RS, R2N, and R3N+) yields the same pattern, with the last showing very large dependence of kN on the torsion angle (b = 6.3). These observations are ascribed to the presence (in addition to the inductive and field effects) of negative hyperconjugation responsible for accelerations of 1000-fold and more, deriving from donation of the incipient negative charge on carbon into the ,*CX orbital in the transition state. These observations reflect, and at the same time underline, the importance of the low-lying antibonding orbitals present in heteroatomic molecules. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:397,405, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10067 [source] Time-dependent density functional theory calculations of X-ray absorptionINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2003J. J. Rehr Abstract There has been dramatic progress in recent years both in calculations and in the interpretation of X-ray absorption spectra (XAS). Often an independent-electron approximation with final state potentials is adequate. However, for soft X-rays (i.e., energies less than about 1 keV) local field effects can be important. Such local fields arise from the dynamic screening of both the external X-ray field and the coupling to the core hole created in the absorption process. These effects require a theory that goes beyond the independent-electron approximation. We developed an efficient approach for treating such effects in molecules and solids based on a generalization of time-dependent density functional theory (TDDFT), with a local approximation for the screening response. The approach has been implemented in our self-consistent, real-space Green's function code FEFF8 in terms of screened dipole transition matrix elements. Typical results are discussed for the XAS of the N4,5 edges of solid Xe and for the L2,3 edges of 3d transition metals. Our approach accounts for the deviations of the L3/L2 intensity branching ratio from the 2:1 value of the independent electron approximation. For the N4,5 edges of Xe, the approach also accounts for the observed fine structure. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 [source] Extraction Using Moderate Electric FieldsJOURNAL OF FOOD SCIENCE, Issue 1 2004I. SENSOY ABSTRACT: During moderate electric field (MEF) processing, a voltage applied across a food material may affect the permeability of cell membranes. It is known that high electric fields can cause either reversible or irreversible rupture of cell membranes. In this research, the effect of MEF processing on permeability was studied. Effects of frequency and electric field strength were investigated. Cellular structure was investigated by transmission electron microscopy (TEM). Fermented black tea leaves and fresh or dry mint leaves were placed in tea bags or cut in 1 cm2 squares, depending on the experiment, and immersed in an aqueous fluid medium. Control samples were heated on a hot plate. MEF treatments were conducted by applying a voltage across electrodes immersed in opposite sides of the beaker. Control and MEF-treated fresh mint leaf samples heated to 50°C were analyzed by TEM. MEF processing significantly increased the extraction yield for fresh mint leaves because of additional electric field effects during heating. Dried mint leaves and fermented black tea leaves were not affected by the treatment type. Low frequency resulted in higher extraction rates for fresh mint leaves. The electric field strength study showed that electrical breakdown is achieved even at low electric field strengths. MEF treatment shows potential to be used as an alternative to conventional heating for extraction from cellular materials. [source] Magnetic field effects on the copolymerization of water-soluble and ionic monomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2009Ignacio Rintoul Abstract The effect of magnetic field (MF) on the radical copolymerization of a series of water-soluble and ionic monomers is presented including acrylamide (AM), acrylic acid (AA), its ionized form acrylate (A,), and diallyldimethylammonium chloride (DADMAC). The following combinations have been studied: AM/AA, AM/A,, AM/DADMAC, and AA/DADMAC. In addition to the MF, strong electrostatic interactions are present for the majority of monomer combinations and conditions. Although the monomer consumption rate (Rp) increased up to 65% applying a MF of 0.1 Tesla, the composition of the resulting copolymers was not affected under such conditions. Despite this increase of Rp by MF, the electrostatic repulsion between ionic monomers and charged growing radicals dominates Rp and governs the copolymer composition with and without MF. The order of the experimentally obtained reactivity ratios reflects the extent of electrostatic interaction: rAM/AA (1.41) < r (3.10) < rAA/DADMAC (4.25) < rAM/DADMAC (6.95) and rAA/AM (2.20) > rDADMAC/AA (0.25) > r (0.17) > rDADMAC/AM (0.03). Overall, weak MF offers to reduce the production time without modifying the product composition. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 373,383, 2009 [source] 1H chemical shifts in NMR: Part 23,, the effect of dimethyl sulphoxide versus chloroform solvent on 1H chemical shiftsMAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2006Raymond J. Abraham Abstract The 1H chemical shifts of 124 compounds containing a variety of functional groups have been recorded in CDCl3 and DMSO- d6 (henceforth DMSO) solvents. The 1H solvent shift ,, = ,(DMSO) , ,(CDCl3) varies from ,0.3 to +4.6 ppm. This solvent shift can be accurately predicted (rms error 0.05 ppm) using the charge model of ,, ,, , and long-range contributions. The labile protons of alcohols, acids, amines and amides give both, the largest solvent shifts and the largest errors. The contributions for the various groups are tabulated and it is shown that for H.C.C.X ,-effects (X = OH, NH, O, NH.CO) there is a dihedral angle dependence of the ,-effect. The group contributions are discussed in terms of the possible solvent,solute interactions. For protic hydrogens, hydrogen bonding is the dominant interaction, but for the remaining protons solvent anisotropy and electric field effects appear to be the major factors. Copyright © 2006 John Wiley & Sons, Ltd. [source] Computation and analysis of 19F substituent chemical shifts of some bridgehead-substituted polycyclic alkyl fluoridesMAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2003William Adcock Abstract The 19F NMR shieldings for several remotely substituted rigid polycyclic alkyl fluorides with common sets of substituents covering a wide range of electronic effects were calculated using the DFT-GIAO theoretical model. The level of theory, B3LYP/6,311+G(2d,p), was chosen based on trial calculations which gave good agreement with experimental values where known. The optimized geometries were used to obtain various molecular parameters (fluorine natural charges, electron occupancies on fluorine of lone pairs and of the CF bond, and hybridization states) by means of natural bond orbital (NBO) analysis which could help in understanding electronic transmission mechanisms underlying 19F substituent chemical shifts (SCS) in these systems. Linear regression analysis was employed to explore the relationship between the calculated 19F SCS and polar substituent constants and also the NBO derived molecular parameters. The 19F SCS are best described by an electronegativity parameter. The most pertinent molecular parameters appear to be the occupation number of the NBO p-type fluorine lone pair and the occupation number of the CF antibonding orbital. This trend suggests that in these types of rigid saturated systems hyperconjugative interactions play a key role in determining the 19F SCS. Electrostatic field effects appear to be relatively unimportant. Copyright © 2003 John Wiley & Sons, Ltd. [source] Kirschning and Jansen computer-aided design formulae for the analysis of parallel coupled linesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2009J. A. Brandăo Faria Abstract Among the many computer-aided design (CAD) formulae used for the calculation of the wave parameters of coupled microstrip lines where fringing field effects occur, the Kirschning and Jansen equations are the most utilized ones, not only because of their high accuracy, but also because of their wide range of application. Here, we show that, despite the aforementioned advantages, such equations may lack physical meaning. We prove, for the first time, that the utilization of these widespread CAD equations can lead to positive valued mutual capacitances, an unacceptable result from the viewpoint of electromagnetic theory. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2466,2470, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24659 [source] Magnetic field effects on the optical response of corrugated films: Voigt geometryPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2003J. H. Jacobo-Escobar Abstract Using the Rayleigh,Fano modal theory it is investigated the interaction of p -polarized light with the corrugated surface of a metallic film. Calculations of the magnetoreflectance in the presence of an external magnetic field in the Voigt configuration are carried out. Studies are performed on the nonreciprocity property and the coupling of the incident light with the surface magnetoplasmons. It is found that the calculated dispersion relation of the surface magnetoplasmons predicts the possible experimental excitation of such modes. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nonequilibrium quantum anharmonic oscillator and scalar field: high temperature approximationsANNALEN DER PHYSIK, Issue 6 2009R.F. Alvarez-Estrada Abstract We treat a relativistic quantum boson gas, described by a scalar quantum field, with quartic self-interaction (,4) in three spatial dimensions: we review the known equilibrium case and present new proposals off-equilibrium. For high temperature and large spatial scales, the behaviour of the gas at equilibrium simplifies nonperturbatively (equilibrium dimensional reduction or EDR): its thermodynamics is described by classical statistical mechanics with some quantum field effects. By assumption, the initial state of the gas off-equilibrium includes interactions and inhomogeneities and is not far from thermal equilibrium. We employ real-time generating functionals and obtain the free nonequilibrium correlators at non-zero temperature. The nonequilibrium quantum gas appears to simplify nonperturbatively in the regime of high temperature and large temporal and spatial scales (nonequilibrium dimensional reduction or NEDR), its dynamics being described by classical statistical mechanics with some quantum field effects. We outline the renormalization of the ,4 theory, the nonequilibrium statistical mechanics of a quantum anharmonic oscillator and the high temperature simplifications, all of which provide very useful hints for NEDR in the field case. Our main proposals are NEDR and the associated new (renormalized) real-time nonequilibrium generating functionals for the ,4 theory. [source] Radio frequency magnetic field effects on molecular dynamics and iron uptake in cage proteinsBIOELECTROMAGNETICS, Issue 4 2010Oscar Céspedes Abstract The protein ferritin has a natural ferrihydrite nanoparticle that is superparamagnetic at room temperature. For native horse spleen ferritin, we measure the low field magnetic susceptibility of the nanoparticle as 2.2,×,10,6,m3,kg,1 and its Néel relaxation time at about 10,10,s. Superparamagnetic nanoparticles increase their internal energy when exposed to radio frequency magnetic fields due to the lag between magnetization and applied field. The energy is dissipated to the surrounding peptidic cage, altering the molecular dynamics and functioning of the protein. This leads to an increased population of low energy vibrational states under a magnetic field of 30,µT at 1,MHz, as measured via Raman spectroscopy. After 2,h of exposure, the proteins have a reduced iron intake rate of about 20%. Our results open a new path for the study of non-thermal bioeffects of radio frequency magnetic fields at the molecular scale. Bioelectromagnetics 31:311,317, 2010. © 2010 Wiley-Liss, Inc. [source] Expression of HSP72 after ELF-EMF exposure in three cell lines,BIOELECTROMAGNETICS, Issue 7 2007Eric Gottwald Abstract It has been reported that magnetic fields with flux densities ranging from µT to mT are able to induce heat shock factor, HSP72 mRNA or heat shock proteins in various cells. In this study we investigated changes in the HSP72 mRNA transcription level in three cell lines (HL-60, H9c2, and Girardi heart cells) and in the intracellular HSP72 protein content in two cell lines (HL-60 and Girardi heart cells) after treatment schemes using electromagnetic fields with a flux density of 2 µT to 4 mT, a frequency of 50 Hz and exposure times from 15 to 30 min. None of the treatments or modalities showed any significant effect on the HSP72 protein level, although HSP72 mRNA could be induced, at least to some extent, with one of the parameter combinations in all cell lines tested. Obviously, HSP72 mRNA transcription and translation are not necessarily coupled in certain cells. This leads to the conclusion that electromagnetic field effects on HSP72 mRNA levels are not indicative for downstream effects unless increased mRNA levels can be correlated with increased HSP72 protein levels as well. Bioelectromagnetics 28:509,518, 2007. © 2007 Wiley-Liss, Inc. [source] Extremely low frequency magnetic field effects on premorbid behaviors produced by cocaine in the mouseBIOELECTROMAGNETICS, Issue 4 2004Jungdae Kim Abstract We investigated the premorbid behavioral changes produced by the administration of cocaine and acute exposure to extremely low frequency (ELF) magnetic field (MF) in the mouse. ICR mice received intraperitoneal injections of cocaine at two doses (65 and 70 mg/kg) and were subsequently exposed to one of eight ELF-MF fields (2, 3, 4, 8, 10, 15, 25, or 60 Hz) of about 20 G (2 mT) intensity immediately after injection. Twelve mice were used for each of applied cocaine dose and ELF-MF level. For a given dose of cocaine, the applied MF frequencies were randomly ordered, and blind tests were carried out in which the behavior observer did not know the frequencies of MF. The premorbid behaviors were defined in the ICR mice and their changes were observed over the exposure of various ELF-MFs. Our data show that the onset times of stop rearing and tonic-clonic seizure in the 4 Hz MF exposure group are significantly different from those of the sham group. Bioelectromagnetics 25:245,250, 2004. © 2004 Wiley-Liss, Inc. [source] Brief exposure to a 50 Hz, 100 ,T magnetic field: Effects on reaction time, accuracy, and recognition memoryBIOELECTROMAGNETICS, Issue 3 2002John Podd Abstract The present study investigated both the direct and delayed effects of a 50 Hz, 100 ,T magnetic field on human performance. Eighty subjects completed a visual duration discrimination task, half being exposed to the field and the other half sham exposed. The delayed effects of this field were also examined in a recognition memory task that followed immediately upon completion of the discrimination task, Unlike our earlier studies, we were unable to find any effects of the field on reaction time and accuracy in the visual discrimination task. However, the field had a delayed effect on memory, producing a decrement in recognition accuracy. We conclude that after many years of experimentation, finding a set of magnetic field parameters and human performance measures that reliably yield magnetic field effects is proving elusive. Yet the large number of significant findings suggests that further research is warranted. Bioelectromagnetics 23:189,195, 2002. © 2002 Wiley-Liss, Inc. [source] Alternating current electric field effects on neural stem cell viability and differentiation,BIOTECHNOLOGY PROGRESS, Issue 3 2010Marvi A. Matos Abstract Methods utilizing stem cells hold tremendous promise for tissue engineering applications; however, many issues must be worked out before these therapies can be routinely applied. Utilization of external cues for preimplantation expansion and differentiation offers a potentially viable approach to the use of stem cells in tissue engineering. The studies reported here focus on the response of murine neural stem cells encapsulated in alginate hydrogel beads to alternating current electric fields. Cell viability and differentiation was studied as a function of electric field magnitude and frequency. We applied fields of frequency (0.1,10) Hz, and found a marked peak in neural stem cell viability under oscillatory electric fields with a frequency of 1 Hz. We also found an enhanced propensity for astrocyte differentiation over neuronal differentiation in the 1 Hz cultures, as compared to the other field frequencies we studied. Published 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] | ||||||||||||||||