Understanding and Optimization of Pulsed SET Operation in HfO_x-Based RRAM Devices for Neuromorphic Computing Applications

Padovani, Andrea,Woo, Jiyong,Hwang, Hyunsang,Larcher, Luca IEEE 2018 IEEE electron device letters Vol.39 No.5

<P>We use experiments and device simulations to investigate pulsed SET operation of HfO<SUB>2</SUB>-based RRAM devices for their possible use as electronic synapses. The application of a train of identical pulses only allows for an abrupt change of the device current, which is not suitable for synaptic devices. By using simulations, we link the microscopic properties and changes of the conductive filament during the pulsed operation to the measured conductance and its dependence on pulse voltage, width, and number. The results allow us to derive guidelines that we use to design optimized SET pulses (or pulse trains) allowing extending the conventional binary operation of HfO<SUB>2</SUB>-based RRAMs to the multi-level cell operation required by electronic synapses.</P>

Numerical methods for the dynamic analysis of masonry structures

Cristina Padovani,Giuseppe Pasquinelli,Silvia Degl’Innocenti 국제구조공학회 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.22 No.1

The paper deals with the numerical solution of the dynamic problem of masonry structures. Masonry is modelled as a non-linear elastic material with zero tensile strength and infinite compressive strength. Due to the non-linearity of the adopted constitutive equation, the equations of the motion must be integrated directly. In particular, we apply the Newmark or the Hilber-Hughes-Taylor methods implemented in code NOSA to perform the time integration of the system of ordinary differential equations obtained from discretising the structure into finite elements. Moreover, with the aim of evaluating the effectiveness of these two methods, some dynamic problems, whose explicit solutions are known, have been solved numerically. Comparisons between the exact solutions and the corresponding approximate solutions obtained via the Newmark and Hilber-Hughes-Taylor methods show that in the cases under consideration both numerical methods yield satisfactory results.

Linking Conductive Filament Properties and Evolution to Synaptic Behavior of RRAM Devices for Neuromorphic Applications

Jiyong Woo,Padovani, Andrea,Kibong Moon,Myounghun Kwak,Larcher, Luca,Hyunsang Hwang IEEE 2017 IEEE electron device letters Vol.38 No.9

<P>We perform a comparative study of HfO2 and Ta2O5 resistive switching memory (RRAM) devices for their possible application as electronic synapses. By means of electrical characterization and simulations, we link their electrical behavior (digital or analog switching) to the properties and evolution of the conductive filament (CF). More specifically, we identify that bias-polarity-dependent digital switching in HfO2 RRAM is primarily related to the creation and rupture of an oxide barrier. Conversely, the modulation of the CF size in Ta2O5 RRAM allows bias-polarity-independent analog switching with multiple states. Therefore, when the Ta2O5 RRAM is used to implement a synapse in multilayer perceptron neural networks operated by back-propagation algorithms, patterns in handwritten digits can be recognized with high accuracy. Index</P>

Numerical methods for the dynamic analysis of masonry structures

Degl'Innocenti, Silvia,Padovani, Cristina,Pasquinelli, Giuseppe Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.22 No.1

The paper deals with the numerical solution of the dynamic problem of masonry structures. Masonry is modelled as a non-linear elastic material with zero tensile strength and infinite compressive strength. Due to the non-linearity of the adopted constitutive equation, the equations of the motion must be integrated directly. In particular, we apply the Newmark or the Hilber-Hughes-Taylor methods implemented in code NOSA to perform the time integration of the system of ordinary differential equations obtained from discretising the structure into finite elements. Moreover, with the aim of evaluating the effectiveness of these two methods, some dynamic problems, whose explicit solutions are known, have been solved numerically. Comparisons between the exact solutions and the corresponding approximate solutions obtained via the Newmark and Hilber-Hughes-Taylor methods show that in the cases under consideration both numerical methods yield satisfactory results.

A numerical method for the limit analysis of masonry structures

S. Degl'Innocenti,C. Padovani 국제구조공학회 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.1

Case–control study exploring the short-term association of bronchiolitis with high blood pressure and hypertension in hospitalized children

Sophia Giang,Andrew J. Padovani,Lavjay Butani 대한고혈압학회 2022 Clinical Hypertension Vol.28 No.-

Unlike in adults, there are limited pediatric data exploring the association between acute respiratory illnesses and blood pressure abnormalities. The aim of our study was to explore the association of bronchiolitis, a common respiratory illness, with elevated blood pressure in hospitalized children.In this single center retrospective case–control study, we evaluated the association between bronchiolitis and elevated blood pressure and hypertension in hospitalized children, compared to a control group admitted with nonrespiratory conditions, using multivariate regression analyses. Standard published normative data on pediatric blood pressure were used to classify children in various blood pressure categories. A high prevalence of elevated blood pressure (16%) and hypertension (60%) was noted among children with bronchiolitis; this was not statistically different from the control group (18% for elevated blood pressure; 57% for hypertension; P -values, 0.71 and 0.53, respectively). On multivariate regression analyses, only length of stay was associated with hypertension. No patient with blood pressure abnormalities received antihypertensives nor were any nephrology consults documented. A high prevalence of blood pressure abnormalities, without documentation of their recognition, was noted in hospitalized children regardless of diagnosis, pointing to the need for more data on outcomes-driven significance of pediatric inpatient blood pressure measurements.

A numerical method for the limit analysis of masonry structures

Degl'Innocenti, Silvia,Padovani, Cristina Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.18 No.1

The paper presents a numerical method for the limit analysis of structures made of a rigid no-tension material. Firstly, we formulate the constrained minimum problem resulting from the application of the kinematic theorem, which characterizes the collapse multiplier as the minimum of all kinematically admissible multipliers. Subsequently, by using the finite element method, we derive the corresponding discrete minimum problem in which the objective function is linear and the inequality constraints are linear as well as quadratic. The method is then applied to some examples for which the collapse multiplier and a collapse mechanism are explicitly known. Lastly, the solution to the minimum problem calculated via numerical codes for quadratic programming problems, is compared to the exact solution.

Endovascular treatment of residual or recurrent intracranial aneurysms after surgical clipping

da Silva Júnior Nilton Rocha,Trivelato Felipe Padovani,Nakiri Guilherme Seizem,Rezende Marco Túlio Salles,de Castro-Afonso Luís Henrique,Abud Thiago Giansante,Vanzin José Ricardo,Manzato Luciano Bambi 대한뇌혈관외과학회 2021 Journal of Cerebrovascular and Endovascular Neuros Vol.23 No.3

Objective Total aneurysm occlusion is crucial for the prevention of rebleeding of a ruptured aneurysm or to avoid rupture of an unruptured lesion. Both surgical and endovascular embolization fail to achieve complete aneurysm occlusion in all the cases. The objective of the study was to establish the safety and efficacy of endovascular treatment for previously clipped residual or recurrent aneurysms. Methods This was an observational, retrospective study of patients harboring incompletely occluded intracranial aneurysms after clipping who underwent endovascular treatment. Patients were treated using 4 different techniques: (1) simple coiling, (2) balloon remodeling, (3) stent-assisted coiling, and (4) flow diversion. Analyses were performed to identify predictors of total aneurysm occlusion, recanalization and complications. Results Between May 2010 and September 2018, 70 patients harboring incompletely occluded intracranial aneurysms after clipping met the inclusion criteria in 5 centers. The mean residual aneurysm size was 7.5 mm. Fifty-nine aneurysms were unruptured. Total aneurysm occlusion was achieved in 75.3% of the aneurysms after 1 year. All aneurysms treated with flow diversion revealed complete occlusion according to control angiography. Recanalization was observed in 14.5%. Permanent morbidity and mortality occurred in 2.9% and 1.4% of the patients, respectively. Conclusions Endovascular treatment of recurrent or residual aneurysms after surgical clipping was safe and efficacious. Flow diversion seems to be associated with better anatomical results. A more rigid study, a larger group of patients, and long-term follow-up are required to provide stronger conclusions about the best approach for residual clipped aneurysms.

A numerical tool for thermo-mechanical analysis of multilayer stepped structures

Bagnoli, Paolo Emilio,Girardi, Maria,Padovani, Cristina,Pasquinelli, Giuseppe Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.6

An integrated simulation tool for multilayer stepped pyramidal structures is presented. The tool, based on a semi-analytical mathematical strategy, is able to calculate the temperature distributions and thermal stresses at the interfaces between the layers of such structures. The core of the thermal solver is the analytical simulator for power electronic devices, DJOSER, which has been supplemented with a mechanical solver based on the finite-element method. To this end, a new ele-ment is proposed whose geometry is defined by its mean surface and thickness, just as in a plate. The resulting mechanical model is fully three-dimensional, in the sense that the deformability in the direction orthogonal to the mean surface is taken into account. The dedicated finite element code developed for solving the equilibrium problem of structures made up of two or more superimposed plates subjected to thermal loads is applied to some two-layer samples made of silicon and copper. Comparisons performed with the results of standard finite element analyses using a large number of brick elements reveal the soundness of the strategy employed and the accuracy of the tool developed.

A numerical tool for thermo-mechanical analysis of multilayer stepped structures

Paolo Emilio Bagnoli,Maria Girardi,Cristina Padovani,Giuseppe Pasquinelli 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.6

An integrated simulation tool for multilayer stepped pyramidal structures is presented. The tool, based on a semi-analytical mathematical strategy, is able to calculate the temperature distributions and thermal stresses at the interfaces between the layers of such structures. The core of the thermal solver is the analytical simulator for power electronic devices, DJOSER, which has been supplemented with a mechanical solver based on the finite-element method. To this end, a new ele-ment is proposed whose geometry is defined by its mean surface and thickness, just as in a plate. The resulting mechanical model is fully three-dimensional, in the sense that the deformability in the direction orthogonal to the mean surface is taken into account. The dedicated finite element code developed for solving the equilibrium problem of structures made up of two or more superimposed plates subjected to thermal loads is applied to some two-layer samples made of silicon and copper. Comparisons performed with the results of standard finite element analyses using a large number of brick elements reveal the soundness of the strategy employed and the accuracy of the tool developed.