Electronic switching in phase-change memories Pirovano, A.; Lacaita, A.L.; Benvenuti, A. ...
IEEE transactions on electron devices,
03/2004, Letnik:
51, Številka:
3
Journal Article
Recenzirano
A detailed investigation of electronic switching in chalcogenide-based phase-change memory devices is presented. An original bandgap model consistent with the microscopic structure of both ...crystalline and amorphous chalcogenide is described, and a physical picture of the switching mechanism is proposed. Numerical simulations provide, for the first time, a quantitative description of the peculiar current-voltage curve of a Ge/sub 2/Sb/sub 2/Te/sub 5/ resistor, in good agreement with measurements performed on test devices.
A detailed investigation of the time evolution for the low-field resistance R/sub off/ and the threshold voltage V/sub th/ in chalcogenide-based phase-change memory devices is presented. It is ...observed that both R/sub off/ and V/sub th/ increase and become stable with time and temperature, thus improving the cell readout window. Relying on a microscopic model, the drift of R/sub off/ and V/sub th/ is linked to the dynamic of the intrinsic traps typical of amorphous chalcogenides, thus providing for the first time a unified framework for the comprehension of chalcogenide materials transient behavior.
Bipolar disorder (BD) is associated with signs of widespread disruption of white matter (WM) integrity. A polymorphism in the promoter of the serotonin transporter (5‐HTTLPR) influenced functional ...cortico‐limbic connectivity in healthy subjects and course of illness in BD, with the short (s) allele being associated with lower functional connectivity, and with earlier onset of illness and poor response to treatment. We tested the effects of 5‐HTTLPR on diffusion tensor imaging (DTI) measures of WM microstructure in 140 inpatients, affected by a major depressive episode in course of BD, of Italian descent. We used whole brain tract‐based spatial statistics in the WM skeleton with threshold‐free cluster enhancement of DTI measures of WM microstructure: axial, radial and mean diffusivity and fractional anisotropy. Compared with l/l homozygotes, 5‐HTTLPR*s carriers showed significantly increased radial and mean diffusivity in several brain WM tracts, including corpus callosum, cingulum bundle, uncinate fasciculus, corona radiata, thalamic radiation, inferior and superior longitudinal fasciculus and inferior fronto‐occipital fasciculus. An increase of mean and radial diffusivity, perpendicular to the main axis of the WM tract, is thought to signify increased space between fibers, thus suggesting demyelination or dysmyelination, or loss of bundle coherence. The effects of 5‐HTTLPR on the anomalous emotional processing in BD might be mediated by changes of WM microstructure in key WM tracts contributing to the functional integrity of the brain.
White matter microstructure in bipolar disorder is influenced by a serotonin transporter gene polymorphism
The catechol-O-methyltransferase (COMT) enzyme inactivates catecholamines, and the COMT Val(108/158)Met polymorphism (rs4680) influences the enzyme activity. Recent clinical studies found a ...significant effect of rs4680 on antidepressant response to fluoxetine and paroxetine, but several other studies were negative. No study considered drug plasma levels as possible nuisance covariate.
We studied the effect of rs4680 on response to fluvoxamine antidepressant monotherapy.
Forty-one consecutively admitted inpatients affected by a major depressive episode in course of major depressive disorder were administered fluvoxamine for 6 weeks. Changes in severity of depression were assessed with weekly Hamilton Depression ratings and analyzed with repeated measures ANOVA in the context of General Linear Model, with rs4680 and fluvoxamine plasma levels as factors.
rs4680 significantly interacted with time in affecting antidepressant response to fluvoxamine, with outcome being inversely proportional to the enzyme activity: better effects in Met-carriers, worse effects in Val/Val homozygotes. The effect became significant at the fourth week of treatment, and influence final response rates. Fluvoxamine plasma levels had marginal effects on outcome.
This is the first study that reports a positive effect of rs4680 on response to fluvoxamine, and the third independent report of its influence on response to selective 5-HT reuptake inhibitors (SSRIs). Our findings support the hypothesis that factors affecting catecholaminergic neurotransmission might contribute to shape the individual response to antidepressants irrespective of their primary molecular target.
The phase transformation in chalcogenide-based nonvolatile memories is studied by cell electrical characterization. The cell state (amorphous, crystalline, or mixed) is changed by applying electrical ...pulses, then the cell resistance R and the current-voltage characteristics are measured. From the analysis of the electrical parameters of the cell, we provide evidence for a stacked-like phase distribution in the active layer. Results are discussed with reference to the thermal profile during the program pulse in the chalcogenide layer.
Postpartum depression can mark the onset of bipolar disorder. The coding region of Per3 gene contains a variable-number tandem-repeat polymorphism, which has been shown to influence bipolar disorder ...onset and to affect breast cancer risk. We showed a relationship between Per3 polymorphism and postpartum depressive onset in bipolar disorder.
Highlights CLOCK and 5-HTTLPR modulated the relationship between early stress and suicide The effect of CLOCK overcomes the influence of 5-HTTLPR In C carriers higher early stress associates to the ...likelihood of attempting suicide A positive relationship exists between suicide and early stress in l/l-C carriers In the l/l-T/T group suicidality is not related to the amount of childhood stress.
In this letter, we show a compact model that describes the main electrical features of phase change memory (PCM) devices. The model coherently reproduces the behavior of both SET and RESET states ...with the description of the physics of involved phenomena for different bias and temperature conditions. For arbitrary programming pulses, the model is able to generate intermediate states with mixed phase distributions and, thus, with resistance values between the SET and RESET ones. The proposed model is therefore a precious tool for the design of multilevel PCM applications.
Abstract Glutamate is the major excitatory neurotransmitter in the brain, with up to 40% of all synapses being glutamatergic. An altered glutamatergic transmission could play a critical role in ...working memory deficts observed in schizophrenia and could underline progressive changes such as grey matter loss throughout the brain. The aim of the study was to investigate if gray matter volume and working memory could be modulated by a genetic polymorphism related to glutamatergic function. Fifty schizophrenia patients underwent magnetic resonance and working memory testing outside of the scanner and were genotyped for rs4354668 EAAT2 polymorphism. Carriers of the G allele had lower gray matter volumes than T/T homozygote and worse working memory performance. Poor working memory performance was associated with gray matter reduction. Differences between the three genotypes are more relevant among patients showing poor performance at the 2-back task. Since glutamate abnormalities are known to be involved in excitotoxic processes, the decrease in cortical thickness observed in schizophrenia patients could be linked to an excess of extracellular glutamate. The differential effect of EAAT2 observed between good and poor performers suggests that the effect of EEAT2 on gray matter might reveal in the presence of a pathological process affecting gray matter.
