Resistive Switching of Individual,Chemically Synthesized TiO2 Nanoparticles

Resistively switching devices are considered promising for next‐generation nonvolatile random‐access memories. Today, such memories are fabricated by means of “top–down approaches” applying thin films sandwiched between nanoscaled electrodes. In contrast, this work presents a “bottom–up approach” disclosing for the first time the resistive switching (RS) of individual TiO₂ nanoparticles (NPs). The NPs, which have sizes of 80 and 350 nm, respectively, are obtained by wet chemical synthesis and thermally treated under oxidizing or vacuum conditions for crystallization, respectively. These NPs are deposited on a Pt/Ir bottom electrode and individual NPs are electrically characterized by means of a nanomanipulator system in situ, in a scanning electron microscope. While amorphous NPs and calcined NPs reveal no switching hysteresis, a very interesting behavior is found for the vacuum‐annealed, crystalline TiO_2–x NPs. These NPs reveal forming‐free RS behavior, dominantly complementary switching (CS) and, to a small degree, bipolar switching (BS) characteristics. In contrast, similarly vacuum‐annealed TiO₂ thin films grown by atomic layer deposition show standard BS behavior under the same conditions. The interesting CS behavior of the TiO_2–x NPs is attributed to the formation of a core–shell‐like structure by re‐oxidation of the reduced NPs as a unique feature.     

A macrokinetic approach to crystallization applied to a new thermoplastic polyimide (New TPI) as a model polymer

The application of a new macrokinetic approach to polymer crystallization is applied in this work to a new thermoplastic polyimide (New TPI) recently developed as a matrix of advanced polymer matrix composites. The slow crystallization kinetics presented by New TPI in the entire range between the glass-transition temperature and the melting point makes TPI an excellent model polymer for testing crystallization models. In the approach presented here the variation of the induction time with the temperature is included in the Nakamura model for nonisothermal crystallization, and a simplified expression of the kinetic constant as a function of the temperature is adopted. The proposed model is verified through a comparison with a complete set of experimental data, ranging from the melting point to the glass-transition temperature of the polymer, obtained in isothermal and nonisothermal conditions. Moreover phase transformation diagrams (TTT and CCT plots) are presented, providing a fundamental tool for understanding the crystallization behavior of semicrystalline matrices and to determine the more appropriate processing conditions. © 1995 John Wiley & Sons, Inc.     

Preisach modeling and reversible magnetization

Methods of dealing with reversible magnetization in the context of Preisach modeling are examined. A generalization of the vector product model which includes reversible effects, as well as the usual irreversible effects, is presented     

Effects of dietary fiber and phytic acid on mineral availability.

In general, it has been shown that dietary fiber may bind metallic cations in both in vitro and in vivo studies. However, there clearly are many unresolved questions on the effects of high-fiber diets on mineral availability. On one side, the effects of fiber on the utilization of nutrients vary greatly with the amount and type of fiber. In addition, there are many agents in both food and the digestive tract that may affect the mineral binding to fiber: some agents may inhibit binding, while others will enhance it. Also, there are several major difficulties in drawing conclusions from the in vitro and in vivo studies due to the different experimental conditions, methods used to follow the mineral balance, etc. Finally, it must be borne in mind that fiber and phytic acid occur together in fiber-rich diets and, thus, it is difficult to separate the effects of fiber and phytate in the utilization of most essential polyvalent metallic ions. The studies summarized in this review show that the recommendation for increasing dietary fiber in Western communities would not be expected to have any adverse effect on mineral absorption if we increase not only the intake of fiber, but also the dietary intake of other food components such as protein (both vegetable and animal protein) and ascorbic, citric, and oxalic acids (in fruits and vegetables). The adequate intake of minerals, fat, and simple sugars are maintained with this type of diet. The recommendations should be best interpreted in such a way as to prevent the consumption of excessive amounts of phytate, particularly for those whose mineral needs are great. Further studies are still needed in this field in order to understand the conflicting results published in the literature regarding the effects of fiber on the utilization of minerals; however, the studies reviewed in this article may give us an idea of the complexity of mineral availability in fiber-rich, phytate-rich diets.     

Comparative effects of the chelators sodium 4,5-dihydroxybenzene-1,3-disulfonate (Tiron) and diethylenetriaminepentaacetic acid (DTPA) on acute uranium nephrotoxicity in rats

The effect of transient, global cerebral ischemia on the distribution of endothelin (ET) in blood-brain barrier (BBB) in CA1 area of hippocampus long-time after ischemia was estimated using post-embedding immunogold technique. ET-like immunoreactivity as a gold particles was localized in all compartments of the blood-brain barrier e.g. in endothelial cells, in pericytes, in periendothelial space including basement membrane, and in astroglial processes. In control animal the density of labelling in all elements of BBB in CA1 area of hippocampus was moderate. ET-like immunoreactivity (ET-like IR) was estimated 1 week-12 months after ischemia. Intense ET-like IR in all elements of BBB was noted 2 and 6 months after ischemia. A potential pathophysiological role of endothelin in cerebral vasospasm in long-time after ischemia is well documented.     

Analysis and parameterisation of wind profiles in the low atmosphere

Knowledge of temporal and spatial variation of the wind is important to obtain accurate calculations of wind power potential. The best estimation method involves direct measurement of wind speed which, however, is not always possible. In such cases, a good parameterisation of wind profile is necessary. A RASS sodar located in Northern Spain has been used in this paper. This device provided a broad database of 10-min averages from August 2002 to January 2004. The vertical range extended from 40 to 500 m in 20 m levels, although the 220 m level was selected as the upper boundary by analysis of wind speed and temperature vertical profiles. Hourly medians were calculated each month in the 10 lower levels, yielding a sharp contrast between day and night. Flat wind speed profiles were clear during day, mainly in summer, due to convection produced by surface heating. However, stable stratification favoured horizontal movement and wind speed values increasing with height were observed during the night. Power and logarithmic laws have been fitted from vertical profiles of hourly wind speed medians. The exponent of the power law showed hourly medians greater than 0.5 during the night and lower than 0.2 during the day. A simple model has been proposed for the parameters of both expressions, consisting of an addition of three harmonic functions with periods of 1 year, 1 day and half a day. Hourly wind speed medians were successfully fitted at the heights of interest, although the fit proved better for the power law. Finally, a slight decrease in fitting at increasing heights was also observed.     

A program for the simulation and analysis of open atmospheric balloon soundings

The equation of motion for a balloon in an atmosphere is generalized but placed in proper context by taking into account some fluid theory results and a few factors not considered in previous works. The design of a computer program becomes necessary to find solutions. A code that allows to perform 2D simulations of open balloons flights is developed. The coupled integrodifferential nature of the problem represented a significant challenge for a satisfactory implementation.     

Gastric resection and subtotal gastrectomy. Principles and updated surgical technique

The Authors describe their last 10 years experience in gastric surgery. They report the results obtained in 12 gastric resections performed for complications following gastric and/or duodenal peptic ulcers, in 33 cases of total gastrectomies (34%), and 48 cases of subtotal gastrectomies (49%) for early and advanced cancer. The results lead to interesting conclusions: first of all achieving a wide jejunojejunostomy between the afferent and the efferent loop the problems related to gastric resection (as postoperative sequelae, dumping syndrome, reflux esophagitis, alkaline gastritis, etc.) are avoided. Problems regarding lymphadenectomy in patients submitted to subtotal gastrectomy (D2-D3) are then reported. After a brief history of gastric reconstruction following gastric resection the evolution in surgical techniques and the results obtained during the last 10 years are described. The good long term results allow to conclude that our strategy in gastric surgery ensures a good quality of life of the patients as well as a radical operation in case of gastric cancer.     

CLASSIFICATION OF MULTI-LOOK POLARIMETRIC SAR IMAGERY AND POLARIZATION CHANNEL OPTIMIZATION

In this paper, a new maximum likelihood (ML) classification algorithm is proposed to classify the multi-look polarimetric synthetic aperture radar (SAR) imagery. Experimental results with the NASA/JPL airborne L-band polarimetric SAR data demonstrate the effectiveness of the new algorithm. Furthermore, when using the algorithm in the classifications with subsets of the multi-look polarimetric SAR data, the polarization-channel optimization for the terrain type classification is implemented.