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Background In Parkinson's disease (PD), impulsive-compulsive behaviors (ICBs) may develop as side-effect of dopaminergic medications. Abnormal incentive-driven decision-making, which is supported by the cognitive control and motivation interaction, may represent an ICBs signature. This systematic review explored whether structural and/or functional brain differences between PD patients with vs without ICBs encompass incentive-driven decision-making networks. Methods Structural and functional neuroimaging studies comparing PD patients with and without ICBs, either de novo or medicated, were included. Results Thirty articles were identified. No consistent evidence of structural alteration both in de novo and medicated PD patients were found. Differences in connectivity within the default mode, the salience and the central executive networks predate ICBs development and remain stable once ICBs are fully developed. Medicated PD patients with ICBs show increased metabolism and cerebral blood flow in orbitofrontal and cingulate cortices, ventral striatum, amygdala, insula, temporal and supramarginal gyri. Abnormal ventral striatum connectivity with anterior cingulate cortex and limbic structures was reported in PD patients with ICBs. Discussion Functional brain signatures of ICBs in PD encompass areas involved in cognitive control and motivational encoding networks of the incentive-driven decision-making. Functional alterations predating ICBs may be related to abnormal synaptic plasticity in these networks.

We show that the geodesic flow of a compact Finsler manifold without conjugate points is transitive provided that the universal covering satisfies the uniform Finsler visibility condition. This result is a nontrivial extension of a well known theorem due to Eberlein for Riemannian manifolds. For doing so, we introduce suitable Finsler versions of the concepts of Gromov's δ-hyperbolicity and Eberlein's visibility, and study their consequences.

The experimental analysis of the electrical behavior of Phase Change Memory arrays evidenced a seasoning effect both on SET and RESET state. The previous modeling efforts on this issue were addressed only towards RESET operation. This work presents a SET seasoning model implemented within a numerical simulator starting from the extraction of the characteristic Erase operation kinetic parameters, in order to complete the picture of seasoning modeling in PCM. The analysis of such phenomenon, that is not detrimental to the memory, allows a better comprehension of the transition dynamics from the amorphous to the crystalline phase. The model developed reproduces experimental data obtained with writing waveforms featuring different crystallization approaches.

Travelling back and forth across the Balkans, sharing the tiny spaces of crammed buses or the anguish and the cunning of young and old travellers constitute the analytical basis for a new definition of the concept of border. The article suggests that border is such not so much because it prevents crossing but rather because only some, with determinate characteristics are able to cross. In the Balkans borders actually exist in order to force those who want to cross them to change “at least a little bit”. The perception of the symmetry or asymmetry of the border which depends on negotiation processes in which the power of each party is determined by the interest of the other to have access to the territory is also analyzed. The author remarks that in this present case the interest of the Balkan citizens to be part of the European Union is much superior to the desire of the “European” to have access to the Balkan territories.

In this work we have investigated the seasoning effect in SET state occurring during cycling of multimegabit Phase Change Memory arrays. The impact of the erasing waveform on this phenomenon has been experimentally evaluated. The physical nature of the phenomenon has been discussed in relation to the electro-thermal characteristics of the active material. The study of such phenomenon is also important to comprehend the transition dynamics of the GST material towards its crystalline state and to develop accurate models allowing an estimate of the PCM cells behavior as a function of the operative cycles.

We propose a new methodology for a fast top-down identification of disturbs in large arrays of nonvolatile memories. The new strategy aims at providing the set of all the effective and dangerous disturbs present in a technology with no a priori selection of the physical mechanisms to be targeted. No simulations are needed, and neighbor-cell influence on disturb is empirically taken into account. This top-down strategy requires a limited set of experimental measurements and provides, in a fast "one-shot" approach, a complete disturb assessment, including the effects of new failure mechanisms. Experimental results on nonconventional floating gate Flash test chips are shown and discussed in order to demonstrate the features and the validity of the proposed methodology.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO Neste trabalho provamos que o fluxo geodésico de uma variedade Finsler de dimensão n compacta, sem pontos conjugados e que é uma variedade de visibilidade uniforme é transitivo. Para isso, introduzimos versões Finsler dos conceitos de hiperbolicidade de Gromov e visibilidade de Eberlein e estudamos suas consequências. Como aplicação da transitividade, provamos que superfícies Finsler k-básicas compactas de gênero maior que um, sem pontos conjugados e com fibrados de Green contínuos são Riemannianas. In this work we prove that the geodesic flow of a compact, n-dimensional Finsler manifold without conjugate points and which is an uniform visibility manifold is transitive. For this, we introduce Finsler versions of Gromov s hyperbolicity and Eberlein s visibility concepts and study its consequences. As an application of the transitivity, we prove that compact, k-basic Finsler surfaces without conjugate points, with genus greater than one and with continuous Green bundles are Riemannian.

Experimental data and analysis show that overerase effects in NOR Flash memories increase with the electric field used during erasing. We found that the electric field is an accelerating factor for cell degradation during cycling. Tunnel oxide degradation reaches a critical level above which the cell starts showing erased threshold voltage instabilities possibly leading to single bit failure. Experimental data show that cell degradation during erasing has to be ascribed to hole injection rather than to electron injection and that both hole trapping and detrapping increase with the electric field. The total stress time required to reach the critical degradation level has been found to follow a 1/E/sub ox/ exponential dependence which is similar to the oxide breakdown phenomena thus establishing a physical link between the two phenomena. Anode Hole Injection has been suggested as hole generation and injection mechanism occurring during erasing and it is shown to be consistent with the experimental data.

This paper presents experimental results and statistics about the erratic erase in Flash Memories, setting the basis for any physical modeling of the phenomena and data comparison. Statistical parameters like the reliability function and the failure rate have been measured and modeled by analytical functions showing that all cells of an array may potentially exhibit erratic events. By mapping the physical position of each erratic bit in a sector and using an equivalent cell approach, it has been possible to establish a correlation between the erratic phenomena and the intrinsic amorphous nature of SiO/sub 2/. Tail bits of the erased distribution have been shown to be caused by erratic events suggesting a unique physical cause for the two phenomena. The relation between positive and negative shifts has also been discussed and overerase risks caused by erratic behaviors have been estimated.

This paper presents a new erasing scheme for flash memories based on a sequence of bulk to gate-box pulses with increasing voltage amplitude. It is experimentally and analytically demonstrated that the erasing dynamics always reaches an equilibrium condition where each pulse induces a constant and controllable injected charge and, therefore, constant threshold shifts. The analytical study allows us to express both the final threshold voltage and the oxide electric field as a function of technological, physical, and electrical parameters. Electrical parameters can be conveniently adapted to control both the threshold voltage and the oxide fields, thus reducing oxide stresses. Advantages with respect to the standard box erasing scheme are theoretically and experimentally demonstrated.

We have addressed the problem of threshold voltage (V/sub TH/) variation in flash memory cells after heavy-ion irradiation by using specially designed array structures and test instruments. After irradiation, low V/sub TH/ tails appear in V/sub TH/ distributions, growing with ion linear energy transfer (LET) and fluence. In particular, high LET ions, such as iodine used in this paper, can produce a bit flip. Since the existing models cannot account for large charge losses from the floating gate, we propose a new mechanism, based on the excess of positive charge produced by a single ion, temporarily lowering the tunnel oxide barrier (positive charge assisted leakage current) and enhancing the tunneling current. This mechanism fully explains the experimental data we present.

This work presents experimental results concerning erratic behaviors in flash memories obtained by tracking the threshold voltage dynamics during any single erase operation and providing a deeper insight into their physical nature. The particular shape of the experimental erase curves allows the derivation of a nearly linear relationship between the amplitude of erratic threshold shifts and the equivalent barrier height controlling Fowler-Nordheim injection.

In this paper, we analyze the read current shifts that have been observed after the erase operations in phase change memory arrays. Experimental data analyses allow detecting statistical features of the current shifts in terms of their occurrence and magnitude, which are consistent with the physical interpretation attributed to the presence or absence of secondary percolation path in parallel to the main one created during the crystallization process. Based on the statistical characterization, we develop a model for the read current that reproduces the measured read current distributions after erase, during cycling, and for different erase pulse durations.

The Edge Wordline Disturb (EWD) represented a reliability issue on traditional Flash NAND memories, evidenced as an unwanted positive threshold voltage shift of all the cells belonging to the first wordline (WL0) connected to the Ground Select Transistor (GSL). In this work, throughout the experimental characterization of Multimegabit arrays it has been investigated the presence and the physical nature of the EWD in Charge Trapping (CT) NAND Flash, emphasizing its dependency on parameters such as the programming voltage, the inhibit voltage and device aging.

In this paper we report data on the reliability and performance characterization of a CMOS-based non-volatile memory (NVM) array, the operating principle of which is based on stiction forces within a MEMS switch. Unlike any other NVM technology, the data retention of this technology improves with increasing temperatures. The switches have been proven to operate over an extremely wide temperature range from −150°C to 300°C, in a 4MRad/s radiation environment and can withstand acceleration forces up to 20,000g. The technology is an ideal candidate for highly reliable non-volatile memory in harsh environmental applications, like auto-motive, defense, space, down-well and geo-thermal. This NVM switch and a tunable RF-MEMS capacitor will be the first products based on this CMOS integrated MEMS platform.

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We present a statistical model of erratic behaviors in Flash memory arrays based on a Markov chain model. The model parameters are experimentally evaluated through short-program/erase-cycling characterizations. The model is suitable for Monte Carlo simulations of Flash memory arrays through which the presence of tail bits in the threshold voltage distribution can be correctly predicted. Finally, an application to NAND architectures is discussed in relation to overprogramming issue.

The need to improve nonvolatile memories reliability in embedded systems is a key design concern. We here propose a methodology, managed by the memory controller, that optimizes the data reliability at the physical level for critical data whereas exploiting the transaction performances for noncritical data. The reliability-performance tradeoff is obtained by partitioning the memory addressable space in different functional blocks, each on written by means of a specific optimized writing algorithm. The method feasibility is demonstrated by a case study exploiting phase change memories (PCMs) features.

In this work we have investigated the seasoning effect in SET state occurring during cycling of multimegabit Phase Change Memory arrays. The impact of the erasing waveform on this phenomenon has been experimentally evaluated. The physical nature of the phenomenon has been discussed in relation to the electro-thermal characteristics of the active material. The study of such phenomenon is also important to comprehend the transition dynamics of the GST material towards its crystalline state and to develop accurate models allowing an estimate of the PCM cells behavior as a function of the operative cycles.

The continuous demand for NAND flash memories with higher performance and storage capabilities pushes the manufactures towards the limits of present technologies and to explore new solutions, both from the physical and the architectural point of view.

We present a two-level random telegraph noise (RTN) characterization technique which allows the estimation of RTN model parameters with statistical validity, thus acquiring a deeper insight into the physics of noise-generating process. A two-state Markov chain is used to model the stochastic behavior of RTN. In this way, an easy implementation of Monte Carlo performance and reliability simulations of large populations of electron devices can be performed. The robustness of the methodology has been investigated under different inherent noise conditions.

In this letter, we present a new analytical model of the erasing operation in phase-change memories (PCMs). The model successfully describes the dynamics of the erasing curves of PCM arrays in terms of a filamentation picture of the electronic switching process. We also suggest a physical link between the crystalline fraction concept and the filamentation properties, thus providing a deeper comprehension of the underlying physics. The model is able to take into account both technological and architectural parameters, and it is suitable for the statistical analysis of PCM arrays.

This work shows for the first time the presence of erratic phenomena in p-channel floating gate memories using Fowler Nordheim tunneling for both program and erase operations. A specific p-channel EEPROM architecture is investigated and found to be intrinsically robust against erratic behaviors. A comparison between the p-channel device and a conventional n-channel Flash is discussed and physical interpretations are suggested.

Phase transition of chalcogenide materials from amorphous to crystalline (also known as the erasing mechanism), in phase change memory arrays (PCM), is obtained by an electrothermal induced process. The change of temperature in the programmable volume of a PCM cell, is achieved by a voltage waveform applied to an heater element, which furthermore affect cell active material. Erasing waveform choice is a critical step for memory reliability and strictly depends by the system application where memory is fitted in. This paper is intended to provide a study of the common used erasing waveform, evidencing the crystallization mechanism implemented, performing the parameters extraction of each waveform and then optimize them in order to get best performance.

Highly productive: Grafted monolith silica skeleton microreactors process bulky molecules more efficiently than a batch mode reactor. This efficiency is due to a higher contact area, shorter diffusion path, and lower inhibition by products in the thin monolith skeleton. These materials provide a new approach in the field of heterogeneous catalysis for the synthesis of fine chemicals.