Versatile stochastic dot product circuits based on nonvolatile memories for high performance neurocomputing and neurooptimization.

The key operation in stochastic neural networks, which have become the state-of-the-art approach for solving problems in machine learning, information theory, and statistics, is a stochastic dot-product. While there have been many demonstrations of dot-product circuits and, separately, of stochastic neurons, the efficient hardware implementation combining both functionalities is still missing. Here we report compact, fast, energy-efficient, and scalable stochastic dot-product circuits based on either passively integrated metal-oxide memristors or embedded floating-gate memories. The circuit's high performance is due to mixed-signal implementation, while the efficient stochastic operation is achieved by utilizing circuit's noise, intrinsic and/or extrinsic to the memory cell array. The dynamic scaling of weights, enabled by analog memory devices, allows for efficient realization of different annealing approaches to improve functionality. The proposed approach is experimentally verified for two representative applications, namely by implementing neural network for solving a four-node graph-partitioning problem, and a Boltzmann machine with 10-input and 8-hidden neurons.

Spike-timing-dependent plasticity learning of coincidence detection with passively integrated memristive circuits.

Spiking neural networks, the most realistic artificial representation of biological nervous systems, are promising due to their inherent local training rules that enable low-overhead online learning, and energy-efficient information encoding. Their downside is more demanding functionality of the artificial synapses, notably including spike-timing-dependent plasticity, which makes their compact efficient hardware implementation challenging with conventional device technologies. Recent work showed that memristors are excellent candidates for artificial synapses, although reports of even simple neuromorphic systems are still very rare. In this study, we experimentally demonstrate coincidence detection using a spiking neural network, implemented with passively integrated metal-oxide memristive synapses connected to an analogue leaky-integrate-and-fire silicon neuron. By employing spike-timing-dependent plasticity learning, the network is able to robustly detect the coincidence by selectively increasing the synaptic efficacies corresponding to the synchronized inputs. Not surprisingly, our results indicate that device-to-device variation is the main challenge towards realization of more complex spiking networks.

Implementation of multilayer perceptron network with highly uniform passive memristive crossbar circuits.

The progress in the field of neural computation hinges on the use of hardware more efficient than the conventional microprocessors. Recent works have shown that mixed-signal integrated memristive circuits, especially their passive (0T1R) variety, may increase the neuromorphic network performance dramatically, leaving far behind their digital counterparts. The major obstacle, however, is immature memristor technology so that only limited functionality has been reported. Here we demonstrate operation of one-hidden layer perceptron classifier entirely in the mixed-signal integrated hardware, comprised of two passive 20 × 20 metal-oxide memristive crossbar arrays, board-integrated with discrete conventional components. The demonstrated network, whose hardware complexity is almost 10× higher as compared to previously reported functional classifier circuits based on passive memristive crossbars, achieves classification fidelity within 3% of that obtained in simulations, when using ex-situ training. The successful demonstration was facilitated by improvements in fabrication technology of memristors, specifically by lowering variations in their I-V characteristics.

Corrigendum: A multiply-add engine with monolithically integrated 3D memristor crossbar/CMOS hybrid circuit.

This corrects the article DOI: 10.1038/srep42429.

A multiply-add engine with monolithically integrated 3D memristor crossbar/CMOS hybrid circuit.

Silicon (Si) based complementary metal-oxide semiconductor (CMOS) technology has been the driving force of the information-technology revolution. However, scaling of CMOS technology as per Moore's law has reached a serious bottleneck. Among the emerging technologies memristive devices can be promising for both memory as well as computing applications. Hybrid CMOS/memristor circuits with CMOL (CMOS + "Molecular") architecture have been proposed to combine the extremely high density of the memristive devices with the robustness of CMOS technology, leading to terabit-scale memory and extremely efficient computing paradigm. In this work, we demonstrate a hybrid 3D CMOL circuit with 2 layers of memristive crossbars monolithically integrated on a pre-fabricated CMOS substrate. The integrated crossbars can be fully operated through the underlying CMOS circuitry. The memristive devices in both layers exhibit analog switching behavior with controlled tunability and stable multi-level operation. We perform dot-product operations with the 2D and 3D memristive crossbars to demonstrate the applicability of such 3D CMOL hybrid circuits as a multiply-add engine. To the best of our knowledge this is the first demonstration of a functional 3D CMOL hybrid circuit.

Seed layer technique for high quality epitaxial manganite films.

We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

Self-Adaptive Spike-Time-Dependent Plasticity of Metal-Oxide Memristors.

Metal-oxide memristors have emerged as promising candidates for hardware implementation of artificial synapses - the key components of high-performance, analog neuromorphic networks - due to their excellent scaling prospects. Since some advanced cognitive tasks require spiking neuromorphic networks, which explicitly model individual neural pulses ("spikes") in biological neural systems, it is crucial for memristive synapses to support the spike-time-dependent plasticity (STDP). A major challenge for the STDP implementation is that, in contrast to some simplistic models of the plasticity, the elementary change of a synaptic weight in an artificial hardware synapse depends not only on the pre-synaptic and post-synaptic signals, but also on the initial weight (memristor's conductance) value. Here we experimentally demonstrate, for the first time, an STDP behavior that ensures self-adaptation of the average memristor conductance, making the plasticity stable, i.e. insensitive to the initial state of the devices. The experiments have been carried out with 200-nm Al2O3/TiO2-x memristors integrated into 12 × 12 crossbars. The experimentally observed self-adaptive STDP behavior has been complemented with numerical modeling of weight dynamics in a simple system with a leaky-integrate-and-fire neuron with a random spike-train input, using a compact model of memristor plasticity, fitted for quantitatively correct description of our memristors.

Training and operation of an integrated neuromorphic network based on metal-oxide memristors.

Despite much progress in semiconductor integrated circuit technology, the extreme complexity of the human cerebral cortex, with its approximately 10(14) synapses, makes the hardware implementation of neuromorphic networks with a comparable number of devices exceptionally challenging. To provide comparable complexity while operating much faster and with manageable power dissipation, networks based on circuits combining complementary metal-oxide-semiconductors (CMOSs) and adjustable two-terminal resistive devices (memristors) have been developed. In such circuits, the usual CMOS stack is augmented with one or several crossbar layers, with memristors at each crosspoint. There have recently been notable improvements in the fabrication of such memristive crossbars and their integration with CMOS circuits, including first demonstrations of their vertical integration. Separately, discrete memristors have been used as artificial synapses in neuromorphic networks. Very recently, such experiments have been extended to crossbar arrays of phase-change memristive devices. The adjustment of such devices, however, requires an additional transistor at each crosspoint, and hence these devices are much harder to scale than metal-oxide memristors, whose nonlinear current-voltage curves enable transistor-free operation. Here we report the experimental implementation of transistor-free metal-oxide memristor crossbars, with device variability sufficiently low to allow operation of integrated neural networks, in a simple network: a single-layer perceptron (an algorithm for linear classification). The network can be taught in situ using a coarse-grain variety of the delta rule algorithm to perform the perfect classification of 3 × 3-pixel black/white images into three classes (representing letters). This demonstration is an important step towards much larger and more complex memristive neuromorphic networks.

Ultrahigh vacuum and low-temperature cleaning of oxide surfaces using a low-concentration ozone beam.

We present a novel method of delivering a low-concentration (<15%) ozone beam to an ultra-high vacuum environment for the purpose of cleaning and dosing experimental samples through oxidation processing. The system described is safe, low-cost, and practical and overcomes the limitations of ozone transport in the molecular flow environment of high or ultrahigh vacuum whilst circumventing the use of pure ozone gas which is potentially highly explosive. The effectiveness of this method in removing surface contamination is demonstrated through comparison of high-temperature annealing of a simple oxide (MgO) in ozone and oxygen environments as monitored using quadrupole mass spectroscopy and Auger electron spectroscopy. Additionally, we demonstrate the potential of ozone for obtaining clean complex oxide surfaces without the need for high-temperature annealing which may significantly alter surface structure.

[Psychopathologic risk assessment and self-esteem in patients undergoing hypospadias surgery]. / Valutazione del rischio psicopatologico e dell'autostima in pazienti operati per ipospadia.

AIMS: Although the long-term outcomes ofhypospadias surgery are considered important for psychosexual development, only a few attempts have been made to evaluate patient psico-pathology. MATERIAL AND METHODS: 20 out 40 patients who received under sealed cover two envelopes--the first containing the assessment tools, the other empty and prepaid for the answer--joined the study. The results came from the analysis of anamnestic interview specially created in order to gather information on how to access to surgery and the degree of information that the parents had from the surgeon, from the analysis of the CBCL (Child Behavior CheckList 2001:4-16 years) and TMA (Multidimensional self-esteem Test: the Italian version of the MSCS Multidimensional Self-Concept Scale). Of the 20 patients recruited, 15, aged from 9 to 18 years (mean age 12.5), age at operation between 2 and 5 years (mean age 3.3 yrs), have returned the questionnaires correctly compiled. Patient data were compared with those of a control group not suffering from genital pathology. RESULTS: From the CBCL: the area of the identification of the problems showed no significant differences between the study group and the control. The area of competence, altered in both groups, did not show statistically significant differences. From the analysis of TMA: there were no statistically significant differences between the two groups in sub-domains: Social, Competence, Affect, Family and Physical. Within the subdomain school the two groups differed significantly for low self-esteem in the group of surgical patients. CONCLUSION: The MST test indicate that hypospadias surgery does not change the global self-esteem but, surprisingly, at least in this patient population, only a lower self-esteem in school performance in the age group considered. This study may indicate the importance of psychological support during the transition from adolescence to adulthood.

Surface nanostructures in manganite films.

Ultrathin manganite films are widely used as active electrodes in organic spintronic devices. In this study, a scanning tunnelling microscopy (STM) investigation with atomic resolution revealed previously unknown surface features consisting of small non-stoichiometric islands. Based upon this evidence, a new mechanism for the growth of these complex materials is proposed. It is suggested that the non-stoichiometric islands result from nucleation centres that are below the critical threshold size required for stoichiometric crystalline growth. These islands represent a kinetic intermediate of single-layer growth regardless of the film thickness, and should be considered and possibly controlled in manganite thin-film applications.

[Advantages of the anterior and mid-shaft hypospadias repair in the first year of life]. / Vantaggi del trattamento dell'ipospadia anteriore e medio peniena nel primo anno di vita.

PURPOSE: Only a few studies have been performed on the evaluation of complications strictly related to the age at operation of hypospadias repair. The aim of our study was to evaluate the incidence of complications of surgical treatment of anterior and midshaft hypospadias in relation to the age at operation. MATERIALS AND METHODS: 108 patients from 2005 to 2011 were operated on by the same surgeon (AM) for anterior and mid-shaft hypospadias. The patients were divided into two groups according to their age: group A consisted of 48 patients who had undergone surgery before 12 months, group B consisted of 60 patients in whom surgery was performed after 12 months of age (2months -12 yrs). All patients were corrected with TIPU (Snodgrass technique). For the two groups was evaluated the rate ofperioperative complications (hematoma, edema, hemorrhage), suture dehiscence, fistula, stenosis. For the statistical analysis of complications was used the exact test of chi-square Fischer. RESULTS: At a mean follow-up of 36 months. Group A: 2/48 patients presented fistula after 2-6 weeks. Group B: 15/60 patients presented the following complications: 2 hematomas, 1 postoperative bleeding; 5 fistulas arising after 2-6 weeks, 3 minimal meatal regression; 4 thinning flow. The Fisher test was significant. CONCLUSIONS: The results of our study confirm that patients with hypospadias, operated within the first years of life, have a statistically lower rate of complications than patients treated at later dates. Therefore, the age is believed to be a pivotal prognostic factor for the functional and aesthetic results.

[Laparoscopic treatment of UPJ obstruction in ectopic pelvic kidneys in children]. / Trattamento laparoscopico dell'Ostruzione del Giunto Pielo-Ureterale nei reni ectopici in età pediatrica.

AIMS: To assess the feasibility and safety of a laparoscopic approach to UPJ obstruction (UPJO) in ectopic pelvic kidneys. MATERIAL AND METHODS: In a retrospective analysis we selected 14 children, aged 6 months to 17 years, 12 males, 2 females, who had been treated in our Department between January 2004 and June 2011. 9 patients presented ureteropelvic junction obstruction (in 3 cases pelvic stones coexisted) with normal/moderately reduced (> or = 25%) relative function at radionuclide scan (MAG3), 3 nonfunctioning kidneys associated or not to hypertension, 2 congenital hypo-dysplastic kidneys. The evaluation of each patient involved the medical history, ultrasound examination, VCUG, MAG3 diuresis renogram and MRI in some cases. Of the patients presenting UPJO, 5 underwent dismembered pyeloplasty with pyelolithotomy, if required, and 4 pelvic derotation with straightening of the uretero-pelvic junction. A previous cystoscopic placement of a Double J stent was utilized. This facilitated the identification and dissection around the pelvis. With the patient in Trendelenburg position we utilized an umbilical trocar and two trocar in the right and left iliac fossae; an additional trocar, when required, was inserted more cephalad on the midclavear line contralaterally to the lesion. The derotation of ureteropelvic junction was obtained by freeing the kidney's lower pole and by placing intraperitoneally the junction protected with a Double J stent. This was obtained by suturing the peritoneum behind the ureteropelvic junction resulting in a forward rotation of the major axis of the kidney and a straightening of the junction. The 5 patients presenting nonfunctioning ectopic kidneys underwent laparoscopic nephrectomy. While the removal of congenital hypoplasic kidneys resulted easy, the removal of nonfunctioning kidneys was more difficult due to their complex vascular situation and for the embryonic disposition. RESULTS: The operating time varied between 40 to 200 minutes. No patient required conversion to open surgery. The hypertension resolved after nephrectomy in all cases. 2 cases of dismembered pyeloplasty required a placement of Double J stent due the recurrence of symptoms and ! patient is waiting for redo operation. The pelvic derotation showed an improvement of diuretic MAG3 renogram and the function remained stable and patiens are symptoms-free. CONCLUSION: The UPJO in ectopic pelvic kidneys presents a large spectrum of presentation. The laparoscopic approach provides good surgical exposure, and operative times are acceptable compared to those of laparoscopic procedure in anatomically normal kidneys. It has also proved a very useful tool in the non-functioning kidney nephrectomy thank to the help of magnification in the identification of numerous aberrant vessels that are quite often found in the pelvic kidneys. The derotation of the pelvis seems a useful procedure in moderate obstruction even if a longer followup is needed.

Organic spintronics.

Organic semiconductors are emerging materials in the field of spintronics. Successful achievements include their use as a tunnel barrier in magnetoresistive tunnelling devices and as a medium for spin-polarized current in transport devices. In this paper, we give an overview of the basic concepts of spin transport in organic semiconductors and present the results obtained in the field, highlighting the open questions that have to be addressed in order to improve devices performance and reproducibility. The most challenging perspectives will be discussed and a possible evolution of organic spin devices featuring multi-functional operation is presented.

Pneumovesicoscopic correction of primary vesicoureteral reflux (VUR) in children. Our experience.

AIM: We report our experience with pneumovesicoscopic cross-trigonal ureteral reimplantation to correct primary vesicoureteral reflux (VUR) in children. MATERIAL AND METHODS: 14 children (10 girls, 4 boys, aged 4 to 12 years) with persistent VUR ≥ grade III (5 bilateral, 19 refluxing ureters) underwent pneumovesicoscopic Cohen's cross-trigonal reimplantation. Under cystoscopic control, a first midline 5-mm trocar was introduced for a 0°\30° telescope at the dome of the bladder, and 2 left and right 3- or 5-mm trocars were inserted through the anterolateral wall. The ureter was freed by creating a sharp plane between the detrusor muscle and the ureteral wall. If necessary, the ureter was tailored outside the bladder. Submucosal tunnel(s) were prepared with the help of scissors and graspers. The detrusor at the site of the ureter mobilization was repaired and ureteroneocystomy was performed using 4-5 interrupted absorbable sutures. A 12-Ch Foley catheter was introduced at the site of the dome port. The urethral and suprapubic catheters were removed 2-3 days after the procedure and the patients were discharged on day 3. RESULTS: One boy developed mild suprapubic emphysema postoperatively. Mean operating time was 136 min (range 80-230 min). No patient required conversion to the open technique. Renal US, VCUG, and MAG3 radionuclide scans were obtained in all patients between 3-6 months postoperatively, and provided evidence of reflux resolution in 13 out of 14 patients. CONCLUSION: Our experience seems to confirm that pneumovesicoscopic cross-trigonal ureteral reimplantation can be performed safely and effectively.

Effectiveness of botulinum-A toxin for the treatment of refractory overactive bladder in children.

AIMS: We describe our experience with botulinum-A toxin (BTX-A) in children presenting idiopathic overactive bladder (OAB) refractory to anticholinergic drugs. MATERIAL AND METHODS: 21 patients, aged 8-12 years, were treated over a 3-year period. BTX-A was administered at a dosage of 12.5 UI /kg body weight, without exceeding 200 UI, at 20 detrusor sites. To ensure a stable solution, each 100 UI of botulinum toxin was diluted with 5 cc saline solution just prior to performing the cystoscopy. RESULTS: No patient presented with severe systemic complications or urinary retention after injection therapy; 6 patients presented with slight hematuria for 2-3 days. The clinical results were as follows. At 6 months, 8/21 patients (38%) showed full response, 12/21 (57%) had a partial response after a 2 (nd) injection, and 1/21 (4.7%) showed no response after a 2 (nd) injection. At 12 months, 16 patients (76%) had a full response, 4 (19%) showed a partial response after a 3 (rd) injection, and 1 patient (4.7%) still had no response. At 18 months, 18 patients (85%) showed a full response, 2 patients (9.5%) had a partial response, 1 patient (4.7%) had no response. At the end of this study, 8/21 patients (38%) were symptom-free, after only one botulinum detrusor injection, 13/21 patients (61.9%) received a second botulinum injection because of recurrence of urinary incontinence 6-7 months after the initial treatment, and 4/21 patients (19%) received a third injection 12-14 months after the initial treatment, of whom 2 had a full response and 2 had a partial response. Patient no. 20 refused any further botulinum treatment after the 2 (nd) unsuccessful injection series. CONCLUSION: Intravesical BTX-A injection appears to be safe and useful in children presenting with idiopathic overactive drug-resistant bladder.

[Syringocele in children: an unusual presentation as scrotal mass]. / Il siringocele in età pediatrica: una insolita presentazione come massa scrotale.

Syringocele is a cystic dilation of the excretory bulbourethral Cowper gland duct, and is a rather uncommon finding in pediatric age. It is frequently asymptomatic but sometimes may cause voiding symptoms and urinary tract infection (UTI). This case report describes an unusual manifestation of syringocele presenting with hydrocele. The case concerns a 2-year-old boy who was referred to our Clinic with a diagnosis of hydrocele. The patient underwent hydrocelectomy through a bilateral inguinal incision, but no clear communication with the patent peritoneal vaginal ducts could be demonstrated. The histology evidenced an epidermoid cyst. One year later the scrotal mass relapsed. Sonography, voiding cistography (VCG), computed tomography (CT) scan and magnetic resonance imaging (MRI) were performed. VCG, CT scan and MRI demonstrated the communication between the urethra and the scrotal mass. A surgical excision of the syringocele with endoscopic resection of the collar were performed. Syringocele is a rare entity in pediatrics. To this authors' knowledge there are no reports in the literature describing cases presenting with scrotal mass.