Review of neuromorphic computing based on NAND flash memory.

The proliferation of data has facilitated global accessibility, which demands escalating amounts of power for data storage and processing purposes. In recent years, there has been a rise in research in the field of neuromorphic electronics, which draws inspiration from biological neurons and synapses. These electronics possess the ability to perform in-memory computing, which helps alleviate the limitations imposed by the 'von Neumann bottleneck' that exists between the memory and processor in the traditional von Neumann architecture. By leveraging their multi-bit non-volatility, characteristics that mimic biology, and Kirchhoff's law, neuromorphic electronics offer a promising solution to reduce the power consumption in processing vector-matrix multiplication tasks. Among all the existing nonvolatile memory technologies, NAND flash memory is one of the most competitive integrated solutions for the storage of large volumes of data. This work provides a comprehensive overview of the recent developments in neuromorphic computing based on NAND flash memory. Neuromorphic architectures using NAND flash memory for off-chip learning are presented with various quantization levels of input and weight. Next, neuromorphic architectures for on-chip learning are presented using standard backpropagation and feedback alignment algorithms. The array architecture, operation scheme, and electrical characteristics of NAND flash memory are discussed with a focus on the use of NAND flash memory in various neural network structures. Furthermore, the discrepancy of array architecture between on-chip learning and off-chip learning is addressed. This review article provides a foundation for understanding the neuromorphic computing based on the NAND flash memory and methods to utilize it based on application requirements.

Toward Ideal Low-Frequency Noise in Monolayer CVD MoS2 FETs: Influence of van der Waals Junctions and Sulfur Vacancy Management.

The pursuit of sub-1-nm field-effect transistor (FET) channels within 3D semiconducting crystals faces challenges due to diminished gate electrostatics and increased charge carrier scattering. 2D semiconductors, exemplified by transition metal dichalcogenides, provide a promising alternative. However, the non-idealities, such as excess low-frequency noise (LFN) in 2D FETs, present substantial hurdles to their realization and commercialization. In this study, ideal LFN characteristics in monolayer MoS2 FETs are attained by engineering the metal-2D semiconductor contact and the subgap density of states (DOS). By probing non-ideal contact resistance effects using CuS and Au electrodes, it is uncovered that excess contact noise in the high drain current (ID) region can be substantially reduced by forming a van der Waals junction with CuS electrodes. Furthermore, thermal annealing effectively mitigates sulfur vacancy-induced subgap density of states (DOS), diminishing excess noise in the low ID region. Through meticulous optimization of metal-2D semiconductor contacts and subgap DOS, alignment of 1/f noise with the pure carrier number fluctuation model is achieved, ultimately achieving the sought-after ideal LFN behavior in monolayer MoS2 FETs. This study underscores the necessity of refining excess noise, heralding improved performance and reliability of 2D electronic devices.

Investigation of Deep Spiking Neural Networks Utilizing Gated Schottky Diode as Synaptic Devices.

Deep learning produces a remarkable performance in various applications such as image classification and speech recognition. However, state-of-the-art deep neural networks require a large number of weights and enormous computation power, which results in a bottleneck of efficiency for edge-device applications. To resolve these problems, deep spiking neural networks (DSNNs) have been proposed, given the specialized synapse and neuron hardware. In this work, the hardware neuromorphic system of DSNNs with gated Schottky diodes was investigated. Gated Schottky diodes have a near-linear conductance response, which can easily implement quantized weights in synaptic devices. Based on modeling of synaptic devices, two-layer fully connected neural networks are trained by off-chip learning. The adaptation of a neuron's threshold is proposed to reduce the accuracy degradation caused by the conversion from analog neural networks (ANNs) to event-driven DSNNs. Using left-justified rate coding as an input encoding method enables low-latency classification. The effect of device variation and noisy images to the classification accuracy is investigated. The time-to-first-spike (TTFS) scheme can significantly reduce power consumption by reducing the number of firing spikes compared to a max-firing scheme.

Neuromorphic Computing Using NAND Flash Memory Architecture With Pulse Width Modulation Scheme.

A novel operation scheme is proposed for high-density and highly robust neuromorphic computing based on NAND flash memory architecture. Analog input is represented with time-encoded input pulse by pulse width modulation (PWM) circuit, and 4-bit synaptic weight is represented with adjustable conductance of NAND cells. Pulse width modulation scheme for analog input value and proposed operation scheme is suitably applicable to the conventional NAND flash architecture to implement a neuromorphic system without additional change of memory architecture. Saturated current-voltage characteristic of NAND cells eliminates the effect of serial resistance of adjacent cells where a pass bias is applied in a synaptic string and IR drop of metal wire resistance. Multiply-accumulate (MAC) operation of 4-bit weight and width-modulated input can be performed in a single input step without additional logic operation. Furthermore, the effect of quantization training (QT) on the classification accuracy is investigated compared with post-training quantization (PTQ) with 4-bit weight. Lastly, a sufficiently low current variance of NAND cells obtained by the read-verify-write (RVW) scheme achieves satisfying accuracies of 98.14 and 89.6% for the MNIST and CIFAR10 images, respectively.

On-Chip Training Spiking Neural Networks Using Approximated Backpropagation With Analog Synaptic Devices.

Hardware-based spiking neural networks (SNNs) inspired by a biological nervous system are regarded as an innovative computing system with very low power consumption and massively parallel operation. To train SNNs with supervision, we propose an efficient on-chip training scheme approximating backpropagation algorithm suitable for hardware implementation. We show that the accuracy of the proposed scheme for SNNs is close to that of conventional artificial neural networks (ANNs) by using the stochastic characteristics of neurons. In a hardware configuration, gated Schottky diodes (GSDs) are used as synaptic devices, which have a saturated current with respect to the input voltage. We design the SNN system by using the proposed on-chip training scheme with the GSDs, which can update their conductance in parallel to speed up the overall system. The performance of the on-chip training SNN system is validated through MNIST data set classification based on network size and total time step. The SNN systems achieve accuracy of 97.83% with 1 hidden layer and 98.44% with 4 hidden layers in fully connected neural networks. We then evaluate the effect of non-linearity and asymmetry of conductance response for long-term potentiation (LTP) and long-term depression (LTD) on the performance of the on-chip training SNN system. In addition, the impact of device variations on the performance of the on-chip training SNN system is evaluated.

Pruning for Hardware-Based Deep Spiking Neural Networks Using Gated Schottky Diode as Synaptic Devices.

Deep learning represents state-of-the-art results in various machine learning tasks, but for applications that require real-time inference, the high computational cost of deep neural networks becomes a bottleneck for the efficiency. To overcome the high computational cost of deep neural networks, spiking neural networks (SNN) have been proposed. Herein, we propose a hardware implementation of the SNN with gated Schottky diodes as synaptic devices. In addition, we apply L1 regularization for connection pruning of the deep spiking neural networks using gated Schottky diodes as synap-tic devices. Applying L1 regularization eliminates the need for a re-training procedure because it prunes the weights based on the cost function. The compressed hardware-based SNN is energy efficient while achieving a classification accuracy of 97.85% which is comparable to 98.13% of the software deep neural networks (DNN).

Effect of Word-Line Bias on Linearity of Multi-Level Conductance Steps for Multi-Layer Neural Networks Based on NAND Flash Cells.

NAND flash memory which is mature technology has great advantage in high density and great storage capacity per chip because cells are connected in series between a bit-line and a source-line. Therefore, NAND flash cell can be used as a synaptic device which is very useful for a high-density synaptic array. In this paper, the effect of the word-line bias on the linearity of multi-level conductance steps of the NAND flash cell is investigated. A 3-layer perceptron network (784×200×10) is trained by a suitable weight update method for NAND flash memory using MNIST data set. The linearity of multi-level conductance steps is improved as the word line bias increases from Vth -0.5 to Vth +1 at a fixed bit-line bias of 0.2 V. As a result, the learning accuracy is improved as the word-line bias increases from Vth -0.5 to Vth+1.

Gated Schottky Diode-Type Synaptic Device with a Field-Plate Structure to Reduce the Forward Current.

A gated Schottky diode with a field-plate structure is proposed and investigated as a new low-power synaptic device to suppress the forward current of the Schottky diode. In a hardware-based neural network, unwanted forward current can flow through gated Schottky diode-type synaptic devices during integration operations, possibly causing a malfunction of the neural network and increasing the power consumption. By adopting a field-plate structure, a virtual pn junction to suppress the forward current of the Schottky diode is formed in the poly-Si active layer. As a result, the unwanted forward current of the gated Schottky diode is successfully reduced to less than 1 pA/µm.

Emerging memory technologies for neuromorphic computing.

In this paper, we reviewed the recent trends on neuromorphic computing using emerging memory technologies. Two representative learning algorithms used to implement a hardware-based neural network are described as a bio-inspired learning algorithm and software-based learning algorithm, in particular back-propagation. The requirements of the synaptic device to apply each algorithm were analyzed. Then, we reviewed the research trends of synaptic devices to implement an artificial neural network.

Accurate extraction of WSe2 FETs parameters by using pulsed I-V method at various temperatures.

This work investigates the intrinsic characteristics of multilayer WSe2 field effect transistors (FETs) by analysing Pulsed I-V (PIV) and DC characteristics measured at various temperatures. In DC measurement, unwanted charge trapping due to the gate bias stress results in I-V curves different from the intrinsic characteristic. However, PIV reduces the effect of gate bias stress so that intrinsic characteristic of WSe2 FETs is obtained. The parameters such as hysteresis, field effect mobility (µeff), subthreshold slope (SS), and threshold voltage (Vth) measured by PIV are significantly different from those obtained by DC measurement. In PIV results, the hysteresis is considerably reduced compared with DC measurement, because the charge trapping effect is significantly reduced. With increasing temperature, the field effect mobility (µeff) and subthreshold swing (SS) are deteriorated, and threshold voltage (Vth) decreases.

Meta-analysis comparing outcomes of fixed-bearing and mobile-bearing prostheses in total knee arthroplasty.

Study findings have been inconsistent in confirming advantages for mobile-bearing compared with fixed-bearing prostheses for total knee arthroplasty. Therefore, we did meta-analysis of trials comparing outcomes from using the 2 different designs. Of 5670 citations identified for screening, 10 trials reporting 620 participants (906 knees) at final follow-up were eligible for data extraction and meta-analysis. The meta-analysis did not find a significant difference in the American Knee Society Knee Scores, Knee Society Functional and Pain Scores, range of motion, occurrence of radiolucent lines, prosthesis-related complications, and participant preference. The results suggest that the mobile-bearing prosthesis does not offer clinical or radiologic advantage over the fixed-bearing prosthesis.

The strength of the rotator cuff before and after subacromial injection of lidocaine.

The purpose of this study was to evaluate the strength of the shoulder before and after the impingement test. This study included 153 cases of impingement syndrome, 20 cases of partial-thickness rotator cuff tear, and 60 cases of full-thickness rotator cuff tear. We divided each of the groups into 2 subgroups according to the mean percentage decrease in pain to evaluate the correlation between pain and muscle weakness. We also divided the impingement syndrome group into 2 groups based on stiffness. After the test, the subgroup with stiffness had a greater reduction in pain compared with the subgroup without stiffness. The results show no statistically significant difference in the strength of the shoulder, except for increased external rotation strength in patients with full-thickness rotator cuff tears and increased supraspinatus strength in patients with impingement syndrome with stiffness. In cases in which the continuity of the rotator cuff is maintained, pain is not an important factor in the cause of shoulder weakness. Preoperative muscle testing can be done despite pain, but if a full-thickness rotator cuff tear is confirmed, re-examination of external rotator strength is necessary. In patients with impingement syndrome, particularly with shoulder stiffness, supraspinatus strength can be decreased.

Three-level anterior cervical discectomy and fusion in elderly patients with wedge shaped tricortical autologous graft: A consecutive prospective series.

BACKGROUND: Treatment of multilevel cervical spondylotic myelopathy/radiculopathy is a matter of debate, more so in elderly patients due to compromised physiology. We evaluated the clinical and radiological results of cervical fusion, using wedge-shaped tricortical autologous iliac graft and Orion plate for three-level anterior cervical discectomy in elderly patients. MATERIALS AND METHODS: Twelve elderly patients with mean age of 69.7 years (65-76 years) were treated between April 2000 and March 2005, for three-level anterior cervical discectomy and fusion, using wedge-shaped tricortical autologous iliac graft and Orion plate. Outcome was recorded clinically according to Odom's criteria and radiologically in terms of correction of lordosis angle and intervertebral disc height span at the time of bony union. The mean follow-up was 29.8 months (12-58 months). RESULTS: All the patients had a complete recovery of clinical symptoms after surgery. Postoperative score according to Odom's criteria was excellent in six patients and good in remaining six. Bony union was achieved in all the patients with average union time of 12 weeks (8-20 weeks). The mean of sum of three segment graft height collapse was 2.50 mm (SD = 2.47). The average angle of lordosis was corrected from 18.2 degrees (SD = 2.59 degrees ) preoperatively to 24.9 degrees (SD = 4.54 degrees ) at the final follow-up. This improvement in the radiological findings is statistically significant (P < 0.05). CONCLUSION: Cervical fusion with wedge-shaped tricortical autologous iliac graft and Orion plate for three-level anterior cervical discectomy is an acceptable technique in elderly patients. It gives satisfactory results in terms of clinical outcome, predictable early solid bony union, and maintenance of disc space height along with restoration of cervical lordosis.

Comparison of surgical outcome in impingement syndrome with and without stiff shoulder.

BACKGROUND: In impingment syndrome with associated stiff shoulder the general protocol of management is to conservatively treat the stiff shoulder followed by operative treatment of the impingement syndrome. This consecutive prospective study was carried out to evaluate the functional outcome of surgical management for impingement syndrome associated with stiff shoulder and to compare the results with surgical management of impingement syndrome alone. MATERIALS AND METHODS: We evaluated a total of 100 patients with impingement syndrome, consisting of 76 patients with impingement syndrome alone (Group A) and 24 patients of stiff shoulder associated with impingement syndrome (Group B). Group A patients were treated by subacromial decompression alone and Group B patients were treated by closed manipulation under anesthesia followed by subacromial decompression. RESULTS: According to the American Shoulder and Elbow Surgeons (ASES) evaluation score satisfactory results were obtained in 80% patients of Group A and 67% patients of Group B, while for patients with diabetes [(n = 18), Group A (n = 11), Group B (n = 7)] satisfactory results were achieved in 82% of patients of Group A(9/11) and 43% of Group B(3/7). Overall, Group B patients had a lower range of motion for external rotation postoperatively, thus indicating that procedures to improve the external rotation, such as a release of the rotator interval or anterior capsule, might be considered in conjunction with other surgical procedures in patients with impingement syndrome with associated stiffness to further improve functional outcome. CONCLUSION: Acromioplasty can be performed in stiff shoulder associated with impingement syndrome without fears of further worsening of stiffness from adhesions with the exposed raw undersurface of acromian. Patients with diabetes mellitus and shoulder stiffness tend to have poor clinical outcomes and must receive appropriate counseling preoperatively.

Radial nerve palsy after arthroscopic anterior capsular release for degenerative elbow contracture.

Because the use of arthroscopy has increased recently for the treatment of elbow lesions, reports of complications have become more common. Nerve injury after arthroscopic anterior capsular release is an extremely rare complication, with 4 reported cases worldwide. We usually use a sharp-tipped electrocautery device with a 0.5-mm diameter during arthroscopic capsular release. In this case, because the former was not prepared, we used a ball-tipped electrocautery device with a 3-mm diameter. Herein, we experienced a case of radial nerve palsy after arthroscopic anterior capsular release using a ball-tipped electrocautery device on a degenerative elbow contracture. We supposed that the electrocautery device caused transiently thermal injury of the radial nerve despite proper portal entry site, intra-articular distension, and gentle arthroscopic manipulation. Elbow arthroscopy remains a technically difficult procedure with the potential for neurologic complications. To perform surgery safely, knowledge of the regional neuroanatomy and a thorough understanding of proper instrument usage are required.

Bone age delay patterns in Legg-Calvé-Perthes disease: an analysis using the Tanner and Whitehouse 3 method.

To study the bone age delay patterns in different stages of Perthes disease, 140 hand and corresponding hip radiographs in 83 patients were assessed. In the hand radiographs, the radius, ulna, metacarpals and phalanges (RUS) and carpal bone ages were calculated using the Tanner and Whitehouse 3 method and the Greulich and Pyle (G and P) bone age was assessed using the G and P atlas. From corresponding hip radiographs, the modified Elizabethtown stage was assessed. The RUS and carpal bone age as well as G and P bone age were found to lag behind the chronological age. The 95% confidence interval for the difference between RUS and G and P bone ages was 0.19 to 0.43 years and between carpal and G and P bone ages was -0.516 to -0.14 years, indicating a close agreement between the Tanner and Whitehouse 3 and G and P methods. The RUS bone age delay was maximum in stage Ia (2.00 +/- 1.08 years), whereas carpal delay was maximum in stage IIa (2.15 +/- 1.28 years). Bone maturation acceleration was observed in later stages of the disease as bone age tried to catch up with chronological age. Carpal delay was significantly greater than RUS delay from stage Ib to IIIb (P<0.05), but no significant difference was observed between carpal and RUS delays in stage IV (P=0.21), implying that bone maturation acceleration occurs in the RUS in the earlier stages, and carpal bone age tends to catch up with RUS bone age in the healed stage of the disease. The RUS and carpal bone age delays in stage I were significantly greater in severe (Catterall groups 3 and 4) disease than in mild (Catterall groups 1 and 2) disease. All patients in whom RUS or carpal bone age delay in stage I was greater than 2 years subsequently developed severe disease, indicating a positive correlation between bone age delay in stage I and subsequent extent of involvement of capital femoral epiphysis.

Genetic diversity of Acanthamoeba isolated from ocean sediments.

Genetic diversity of 18 Acanthamoeba isolates from ocean sediments was evaluated by comparing mitochondrial (mt) DNA RFLP, 18S rDNA sequences and by examining their cytopathic effects on human corneal epithelial cells versus reference strains. All isolates belonged to morphologic group II. Total of 16 restriction phenotypes of mtDNA from 18 isolates demonstrated the genetic diversity of Acanthamoeba in ocean sediments. Phylogenetic analysis using 18s rDNA sequences revealed that the 18 isolates were distinct from morphological groups I and III. Fifteen isolates showed close relatedness with 17 clinical isolates and A. castellanii Castellani and formed a lineage equivalent to T4 genotype of Byers group. Two reference strains from ocean sediment, A. hatchetti BH-2 and A. griffini S-7 clustered unequivocally with these 15 isolates. Diversity among isolates was also evident from their cytopathic effects on human corneal cells. This is the first time describing Acanthamoeba diversity in ocean sediments in Korea.

Antioxidant and cytotoxic activities of xanthones from Cudrania tricuspidata.

The new catecholic xanthone, 1,3,7-trihydroxy-4-(1,1-dimethyl-2-propenyl)-5,6-(2,2-dimethylchromeno)-xanthone (1), was isolated from the root bark of Cudrania tricuspidata together with seven known xanthones. The structures were fully characterized by analysis of physical and spectral (UV, IR, mass, and NMR) data. Relationships between the structural characteristics of xanthones and their antioxidant activities (DPPH, superoxide, and hydroxyl radical) were studied. Among the range of catecholic xanthones, 6,7-dihydroxyl xanthones (3-8) exhibited a strong scavenging effect on the DPPH radical. When one of the catecholic hydroxyl groups was protected as in compounds 1 and 2, DPPH radical scavenging activity was markedly decreased (IC(50)>200microM). DPPH activities were consistent with electrochemical response by cyclic voltammetry. Interestingly, compounds (1, 2) which had the weak activities on DPPH, exhibited both potent superoxide and hydroxyl radical scavenging activities. The strong activity on the hydroxyl radical of compounds (1, 2) could be rationalized by their chelating effect with iron (Fe(2+)) due to a redshift of its complex. The catecholic xanthones (3-8), being able to convert quinone methide intermediate, showed potent cytotoxicities against human cancer cell lines (HT-29, HL-60, SK-OV3, AGS, and A549). In particular, compounds 3, 6, and 7 had strong cytotoxic activities against AGS (LD(50)<5microM). DNA fragmentation patterns induced by catecholic xanthones revealed that tumor cell death was due to apoptosis.

Tibial lengthening and concomitant foot deformity correction in 14 patients with permanent deformity after poliomyelitis.

BACKGROUND: In neuromuscular diseases, limb lengthening and foot deformity correction are associated with a high risk of complications associated with distraction callus and joint contracture. We have found no published articles of tibial lengthening and concomitant foot deformity correction using the Ilizarov method or traditional methods. To compare result of gradual distraction with triple arthrodesis for foot deformity combined with tibial lengthening, we investigated healing index and complications of two methods. PATIENTS AND METHODS: We reviewed 14 patients with permanent deformity after poliomyelitis who underwent tibial lengthening and concomitant foot deformity correction using the Ilizarov external fixator. Tibial lengthening over an intramedullary nail was performed in 3 patients and lengthening without a nail was performed in 11 patients. RESULTS: The mean external fixation time was 6 (3.6-10) months without nail and 1.6 (1.5-1.7) months with nail, whereas the mean healing index was 1.8 (0.8-3.1) months/cm without nail and 2 (1.8-2.3) months/cm with nail. Concomitant foot treatments included triple arthrodesis in 7 patients, pantalar arthrodesis in 2 patients with flail ankle, and gradual foot frame distraction without bony foot procedures in 5 patients. Delayed consolidation and recurrent equinus contracture of the ankle requiring additional lengthening of the Achilles tendon were the most common bone and joint complications during tibial lengthening. INTERPRETATION: The gradual foot frame distraction method was associated with major complications, such as recurrent foot deformity, joint luxation, and arthritis. We therefore recommend triple arthrodesis as a concomitant procedure during tibial lengthening

Ex vivo expansion of human umbilical cord blood-derived T-lymphocytes with homologous cord blood plasma.

This study was designed to establish a more effective and safe culture system for adoptive immunotherapy by investigating the use of homologous cord blood plasma (HCBP) instead of fetal bovine serum (FBS), which has various limitations including ethical problems for the ex vivo expansion of human umbilical T lymphocytes. Fresh human umbilical mononuclear cell fractions were isolated by Ficoll-Hypaque density centrifugation. Nonadherent mononuclear cell fractions were cultured with anti-CD3 antibody (5 microg/ml), IL-2 (175 U/ml), and either 10% FBS or 10% HCBP. On day 8, the cellular proliferation rate and cell surface markers were assessed. There was no significant difference in proliferation when human umbilical cord blood T lymphocytes were grown in medium supplemented with FBS or HCBP (p > 0.05). In medium containing FBS, the proportion of CD3(+)CD4(+) (markers for helper T cell), CD3(+)CD8(+) (cytotoxic T cell), CD3(+)CD25(+) (activated T cell), CD3(+)CD38(+) (immature T cell), and CD3(+)CD45RO(+) (memory T cell) cells was significantly increased (p < 0.05), whereas proportion of CD3(+)CD45RA(+) (naive T cell) and CD16(+)CD56(+) (NK cell) cells was significantly decreased (p < 0.05). In HCBP supplemented medium, the proportion of CD3(+)CD8(+), CD3(+)CD25(+), CD3(+)CD45RA(+), and CD3(+)CD45RO(+) cells was significantly increased (p < 0.05). The proportion of CD3(+)CD4(+), CD3(+)CD45RO(+) and CD3(+)CD38(+) cells was significantly higher, but proportion of CD3(+)CD45RA(+) and CD3(+)CD8(+) cells was significantly lower in FBS compared with HCBP supplemented medium (p < 0.05). Our results support the feasibility of ex vivo expansion of human umbilical cord blood T lymphocytes in medium supplemented with HCBP for future adoptive cellular immunotherapy.