661 research outputs found
The \u3cem\u3eTemascal\u3c/em\u3e and Humoral Medicine in Santa Cruz Mixtepec, Juxtlahuaca, Oaxaca, Mexico
This investigation reports on the present day use of the sweatbath among an indigenous people in Mexico. The purpose of this thesis was to provide evidence that aboriginal medicine in Mexico contained elements which were based on sets of opposing forces, and that these elements are present in the curing rites of the people of Santa Cruz Mixtepec.
Traditional views of the disease causation and curing are described with particular attention given to the postpartum sweatbath ritual or temascal. A comparison of this ritual in Santa Cruz Mixtepec to that seen in neighboring communities suggests that humoral medicine is aboriginal in nature, not solely an introduced trait resulting from acculturation to Spanish culture.
It is recommended that because of the ubiquitous nature of the sweatbath in Mexico, future investigations should consider this trait for studying the amount of aboriginal views that remain in a community\u27s curing techniques and also the amount of acculturation that the community has undergone
Перспективы использования магнезиальных пород
A new operation mode of the lens system in electron energy loss spectrometers is proposed which brings the cardinal plane of the lenses closer to the sample. Experiments as well as electron optical calculations show an intensity gain by a factor of 3-4. The required voltages on the lens elements are calculated as function of the impact energy at the sample. Furthermore, the lens system is characterized with respect to the solid angle probed by the spectrometer and the transmission which enables the evaluation of spectral intensities in terms of the absolute scattering probability for elastic and inelastic scattering. The results apply to most existing electron energy loss spectrometers as they stem from the same design and use identical lens systems. (C) 2012 Elsevier B.V. All rights reserved
Dielectric response effects in attosecond time-resolved streaked photoelectron spectra of metal surfaces
The release of conduction-band electrons from a metal surface by a
sub-femtosecond extreme ultraviolet (XUV) pulse, and their propagation through
the solid, provokes a dielectric response in the solid that acts back on the
photoelectron wave packet. We calculated the (wake) potential associated with
this photoelectron self-interaction in terms of bulk and surface plasmon
excitations and show that it induces a considerable, XUV-frequency-dependent
temporal shift in laser-streaked XUV photoemission spectra, suggesting the
observation of the ultrafast solid-state dielectric response in contemporary
streaked photoemission experiments.Comment: 4 pages and 4 figures, submitted to PR
Variational approach to the scattering of charged particles by a many-electron system
We report a variational approach to the nonlinearly screened interaction of
charged particles with a many-electron system. This approach has been developed
by introducing a modification of the Schwinger variational principle of
scattering theory, which allows to obtain nonperturbative scattering
cross-sections of moving projectiles from the knowledge of the linear and
quadratic density-response functions of the target. Our theory is illustrated
with a calculation of the energy loss per unit path length of slow antiprotons
moving in a uniform electron gas, which shows good agreement with a fully
nonlinear self-consistent Hartree calculation. Since available self-consistent
calculations are restricted to low heavy-projectile velocities, we expect our
theory to have novel applications to a variety of processes where nonlinear
screening plays an important role.Comment: 10 pages, 2 figures; Accepted to Physical Review
Sub-monolayer nucleation and growth of complex oxide heterostructures at high supersaturation and rapid flux modulation
We report on the non-trivial nanoscale kinetics of the deposition of novel
complex oxide heterostructures composed of a unit-cell thick correlated metal
LaNiO3 and dielectric LaAlO3. The multilayers demonstrate exceptionally good
crystallinity and surface morphology maintained over the large number of
layers, as confirmed by AFM, RHEED, and synchrotron X-ray diffraction. To
elucidate the physics behind the growth, the temperature of the substrate and
the deposition rate were varied over a wide range and the results were treated
in the framework of a two-layer model. These results are of fundamental
importance for synthesis of new phases of complex oxide heterostructures.Comment: 13 pages, 6 figure
The Effects of Next-Nearest-Neighbor Interactions on the Orientation Dependence of Step Stiffness: Reconciling Theory with Experiment for Cu(001)
Within the solid-on-solid (SOS) approximation, we carry out a calculation of
the orientational dependence of the step stiffness on a square lattice with
nearest and next-nearest neighbor interactions. At low temperature our result
reduces to a simple, transparent expression. The effect of the strongest trio
(three-site, non pairwise) interaction can easily be incorporated by modifying
the interpretation of the two pairwise energies. The work is motivated by a
calculation based on nearest neighbors that underestimates the stiffness by a
factor of 4 in directions away from close-packed directions, and a subsequent
estimate of the stiffness in the two high-symmetry directions alone that
suggested that inclusion of next-nearest-neighbor attractions could fully
explain the discrepancy. As in these earlier papers, the discussion focuses on
Cu(001).Comment: 8 pages, 3 figures, submitted to Phys. Rev.
Low-Temperature Orientation Dependence of Step Stiffness on {111} Surfaces
For hexagonal nets, descriptive of {111} fcc surfaces, we derive from
combinatoric arguments a simple, low-temperature formula for the orientation
dependence of the surface step line tension and stiffness, as well as the
leading correction, based on the Ising model with nearest-neighbor (NN)
interactions. Our formula agrees well with experimental data for both Ag and
Cu{111} surfaces, indicating that NN-interactions alone can account for the
data in these cases (in contrast to results for Cu{001}). Experimentally
significant corollaries of the low-temperature derivation show that the step
line tension cannot be extracted from the stiffness and that with plausible
assumptions the low-temperature stiffness should have 6-fold symmetry, in
contrast to the 3-fold symmetry of the crystal shape. We examine Zia's exact
implicit solution in detail, using numerical methods for general orientations
and deriving many analytic results including explicit solutions in the two
high-symmetry directions. From these exact results we rederive our simple
result and explore subtle behavior near close-packed directions. To account for
the 3-fold symmetry in a lattice gas model, we invoke a novel
orientation-dependent trio interaction and examine its consequences.Comment: 11 pages, 8 figure
Direct Determination of Electron-Phonon Coupling Matrix Element in a Correlated System
High-resolution electron energy loss spectroscopy measurements have been
carried out on an optimally doped cuprate Bi2Sr2CaCu2O8+{\delta}. The
momentum-dependent linewidth and the dispersion of an A1 optical phonon are
obtained. Based on these data as well as the detailed knowledge of the
electronic structure from angle-resolved photoemission spectroscopy, we develop
a scheme to determine the full structure of electron-phonon coupling for a
specific phonon mode, thus providing a general method for directly resolving
the EPC matrix element in systems with anisotropic electronic structures
Adsorbate-induced surface stress, surface strain and surface reconstruction : S on Cu(100) and Ni(100)
Density functional theory (DFT) calculations have been applied to investigate the known difference in behaviour of S adsorption on Cu(100) and Ni(100). Both surfaces form a 0.25 ML (2 × 2) adsorption phase, but while at higher coverage a 0.5 ML c(2 × 2) phase forms on Ni(100), on Cu(100) only a reconstructed 0.47 ML (√17 × √17)R14° structure occurs. Calculations of the energy, structure, and surface stress of (2 × 2) and c(2 × 2) phases on both substrates show there is an energy advantage on both surfaces to form the higher coverage phase, but that both surfaces show local surface strain around the S atoms in the (2 × 2) phase, a phenomenon previously investigated only on Cu(100). More than forty different structural models of the Cu(100)(√17 × √17)R14°-S phase have been investigated. The pseudo-(100)c(2 × 2) structure previously proposed, containing 16 Cu adatoms per unit mesh in the reconstructed layer, is found to be less energetically favourable than many other possible structures, even after taking account of local structural relaxations. Significantly more favourable is a structure with 12 Cu adatoms per (√17 × √17)R14° unit mesh, previously proposed on the basis of scanning tunnelling microscopy (STM), and found to yield simulated STM images in good agreement with experiment. This model has all S atoms in local 4-fold coordinated hollows relative to the Cu atoms below, half being located above Cu adatoms with the remainder lying above the underlying outermost substrate layer. However, an alternative model with only 4 Cu adatoms and with half the S atoms at 3-fold coordinated sites on the periphery of the Cu adatom cluster, has an even lower energy and gives simulated STM images in excellent agreement with experiment
The role of contacts in graphene transistors: A scanning photocurrent study
A near-field scanning optical microscope is used to locally induce
photocurrent in a graphene transistor with high spatial resolution. By
analyzing the spatially resolved photo-response, we find that in the n-type
conduction regime a p-n-p structure forms along the graphene device due to the
doping of the graphene by the metal contacts. The modification of the
electronic structure is not limited only underneath the metal electrodes, but
extends 0.2-0.3 um into the graphene channel. The asymmetric conduction
behavior of electrons and holes that is commonly observed in graphene
transistors is discussed in light of the potential profiles obtained from this
photocurrent imaging approach. Furthermore, we show that photocurrent imaging
can be used to probe single- / multi-layer graphene interfaces
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