Bipolar switching in chalcogenide phase change memory.

Phase change materials based on chalcogenides are key enabling technologies for optical storage, such as rewritable CD and DVD, and recently also electrical nonvolatile memory, named phase change memory (PCM). In a PCM, the amorphous or crystalline phase affects the material band structure, hence the device resistance. Although phase transformation is extremely fast and repeatable, the amorphous phase suffers structural relaxation and crystallization at relatively low temperatures, which may affect the temperature stability of PCM state. To improve the time/temperature stability of the PCM, novel operation modes of the device should be identified. Here, we present bipolar switching operation of PCM, which is interpreted by ion migration in the solid state induced by elevated temperature and electric field similar to the bipolar switching in metal oxides. The temperature stability of the high resistance state is demonstrated and explained based on the local depletion of chemical species from the electrode region.

[Nephrolithiasis in patients with intestinal diseases]. / La nefrolitiasi nelle malattie intestinali.

Intestinal diseases may cause the formation of urinary stones through changes in the metabolism of oxalate, calcium, and uric acid. The oxalate that is excreted into urine comes from the catabolism of ascorbic acid and some amino acids or from intestinal absorption of food oxalate. Calcium is absorbed by the gut after the stimulation of active vitamin D and is excreted by the kidney under the control of the bone/parathyroid hormone axis. Uric acid is generated by the oxidation of exogenous and endogenous purine bases, is excreted by the kidney through glomerular filtration/tubular secretion, and is soluble in alkaline urine. Several data indicate that patients with inflammatory bowel diseases are at high risk of urinary stones containing calcium-oxalate salt or uric acid. Calcium-oxalate stones are caused by colonic oxalate hyperabsorption (secondary to intestinal dysfunction) or by parenteral nutrition. Uric acid stones are typical of patients with severe diarrhea and/or intestinal neostomy, that is, in patients with hyperconcentrated acidic urine. Relationships between malabsorptive intestinal diseases and urinary stones are less well defined. Preventive countermeasures are not the same for all disorders. Hyperoxaluria should be controlled by diets with a low content of lipids and oxalate but supplemented with calcium and probiotics. The presence of hyperconcentrated acidic urine should be controlled by correct hydration and administration of citrate.

Gender and performance in athletics.

A comparison of women's and men's performance in swimming, running, and skating is made based on available world record data. The ratio of women's to men's record times is analyzed as a time series, and the asymptotic value of this ratio is discussed in the context of a model. "Rate of improvement curves" are defined over time and by event in a given sport and are compared across gender. The relationship of record time to event distance is estimated and also analyzed across event and gender boundaries. We make three conclusions: 1. The rate of improvement for women has been extraordinary and is larger for longer distance vents. 2. Law-like relations emerge for record times and event lengths. These relations have interesting physical interpretations when examined for various sports. 3. The male physiology is more suited to anaerobic strength events while, given increased access and participation, women can be expected to be more on a par with men in some long-distance aerobic events.

Thermotropic phase transitions at retinal rod outer segments membrane level.

Thermotropic phase transitions (i.e. phase changes induced by heat) were studied at frog ROS membrane level, with the aid of birefringence (phase difference, T) determination. In both dark and light adapted states, an early phase transition was observed (transition temperature, Tt, from +42 divided by 46 degree C). Apparently this change in the physiological state of the membrane precedes the disorientation of the pigment molecules. Following a period of birefringence stabilization a further decrease in birefringence takes place (from +52 divided by 53 degrees C onwards). During the last part of this phase Rho molecules appear to be completely disoriented, as though in solution. The physical changes underlying the transition phenomena seem related to the unbleached and bleached conditions of the ROS; with rising temperatures, the Tt point does not differ significantly in both conditions.