21,955 research outputs found
Metropolitan Maquiladora Econometric Forecast Accuracy
Maquiladora in-bond manufacturing activities occupy positions of collective importance within many regional economies across Mexico. To date, empirical evidence regarding the predictability of maquiladora activities in Mexico has not been attempted. To partially fill that gap in the literature, two sets of in-bond industry econometric forecasts for metropolitan economies in Northern Mexico are analyzed. Empirical results indicate that accurate forecasts of metropolitan maquiladora variables may prove elusive.Regional Maquiladora Forecasting
Psychosis in Azheimer\u27s Disease
Much of the basic science literature on Alzheimer\u27s Disease (AD) reflects ongoing research into pathophysiology and neuropathology. Yet, despite reports of the association between psychotic symptoms and Alzheimer\u27s disease, relatively little is known about why such symptoms develop in certain patients and not in others. Neuroimaging and genetic studies may provide greater understanding of this association and allow clinicians and researchers to prevent, predict and treat the onset of psychotic symptoms in the future. This paper will review the current literature on the topic of psychosis in Alzheimer\u27s disease and focus on current recommendations for interventions by clinicians and caregivers
Seasonal cycling of sulfur and iron in porewaters of a Delaware salt marsh
An extensive pore water data set has been gathered in the Great Marsh, Delaware over various seasons, salinities, and tides. The data all point to a complimentary redox cycle for sulfur and iron which operates seasonally and tidally. Surface oxidizing conditions prevail in summer, with more reducing conditions at depth during the winter. During the spring tides which flood the marsh, pyrite oxidation occurs releasing excess dissolved iron (II) and sulfate to the porewaters, and precipitating authigenic solid iron phases. The redox conditions in the porewaters of the upper zone during the summer is poised between mildly oxidizing and mildly reducing conditions as shown by pE calculations. This redox environment and intermediate iron-sulfur redox species may be important for the stimulation of plant growth (photosynthesis) and sustenance of a viable microbial community (heterotrophy and chemoautropy)
Generating high-order optical and spin harmonics from ferromagnetic monolayers
High-order harmonic generation (HHG) in solids has entered a new phase of
intensive research, with envisioned band-structure mapping on an ultrashort
time scale. This partly benefits from a flurry of new HHG materials discovered,
but so far has missed an important group. HHG in magnetic materials should have
profound impact on future magnetic storage technology advances. Here we
introduce and demonstrate HHG in ferromagnetic monolayers. We find that HHG
carries spin information and sensitively depends on the relativistic spin-orbit
coupling; and if they are dispersed into the crystal momentum space,
harmonics originating from real transitions can be -resolved and carry
the band structure information. Geometrically, the HHG signal is sensitive to
spatial orientations of monolayers. Different from the optical counterpart, the
spin HHG, though probably weak, only appears at even orders, a consequence of
SU(2) symmetry. Our findings open an unexplored frontier -- magneto-high-order
harmonic generation.Comment: 19 pages, 4 figure
Controls on dissolved organic carbon quantity and chemical character in temperate rivers of North America
Understanding the processes controlling the transfer and chemical composition of dissolved organic carbon (DOC) in freshwater systems is crucial to understanding the carbon cycle and the effects of DOC on water quality. Previous studies have identified watershedâscale controls on bulk DOC flux and concentration among small basins but fewer studies have explored controls among large basins or simultaneously considered the chemical composition of DOC. Because the chemical character of DOC drives riverine biogeochemical processes such as metabolism and photodegradation, accounting for chemical character in watershedâscale studies will improve the way bulk DOC variability in rivers is interpreted. We analyzed DOC quantity and chemical character near the mouths of 17 large North American rivers, primarily between 2008 and 2010, and identified watershed characteristics that controlled variability. We quantified DOC chemical character using both specific ultraviolet absorbance at 254ânm (SUVA254) and XADâresin fractionation. Mean DOC concentration ranged from 2.1 to 47âmgâCâLâ1 and mean SUVA254 ranged from 1.3 to 4.7âLâmgâCâ1âmâ1. We found a significant positive correlation between basin wetland cover and both bulk DOC concentration (R2â=â0.78; pâ\u3câ0.0001) and SUVA254 (R2â=â0.91; pâ\u3câ0.0001), while other land use characteristics were not correlated. The strong wetland relationship with bulk DOC concentration is similar to that found by others in small headwater catchments. However, two watersheds with extremely long surface water residence times, the Colorado and St. Lawrence, diverged from this wetland relationship. These results suggest that the role of riverine processes in altering the terrestrial DOC signal at the annual scale was minimal except in river systems with long surface water residence times. However, synoptic DOC sampling of both quantity and character throughout river networks will be needed to more rigorously test this finding. The inclusion of DOC chemical character will be vital to achieving a more complete understanding of bulk DOC dynamics in large river systems
Magnetic spin moment reduction in photoexcited ferromagnets through exchange interaction quenching: Beyond the rigid band approximation
The exchange interaction among electrons is one of the most fundamental
quantum mechanical interactions in nature and underlies any magnetic phenomena
from ferromagnetic ordering to magnetic storage. The current technology is
built upon a thermal or magnetic field, but a frontier is emerging to directly
control magnetism using ultrashort laser pulses. However, little is known about
the fate of the exchange interaction. Here we report unambiguously that
photoexcitation is capable of quenching the exchange interaction in all three
ferromagnetic metals. The entire process starts with a small number of
photoexcited electrons which build up a new and self-destructive potential that
collapses the system into a new state with a reduced exchange splitting. The
spin moment reduction follows a Bloch-like law as , where is
the absorbed photon energy and is a scaling exponent. A good agreement
is found between the experimental and our theoretical results. Our findings may
have a broader implication for dynamic electron correlation effects in
laser-excited iron-based superconductors, iron borate, rare-earth
orthoferrites, hematites and rare-earth transition metal alloys.Comment: 16 pages, 3 figures, one supplementary material fil
Four-wave mixing, quantum control and compensating losses in doped negative-index photonic metamaterials
The possibility of compensating absorption in negative-index metatamterials
(NIMs) doped by resonant nonlinear-optical centers is shown. The role of
quantum interference and extraordinary properties of four-wave parametric
amplification of counter-propagating electromagnetic waves in NIMs are
discussed.Comment: 3 pages, 3 figures, LaTeX, corrected typos in eqs. (1) and (2
- âŚ