On the development of memristive devices for electroforming-free and analog memristive crossbar arrays

Memristive devices can reversibly change their resistance by applying an electrical voltage or current. These thin-film devices have the potential to serve as central components in novel neuromorphic circuits, similar to synapses in the human brain. Unlike traditional neuromorphic systems, they enable a state-based and non-volatile weight between two neurons. This comes very close to the natural model of the human brain, where information is stored and processed together. The aim of this thesis was the development of novel memristive devices and the integration into crossbar arrays. An essential requirement was an analogous resistance change, which allows continuous changes in resistance. It was found, that devices with a combination of tunnel and Schottky barriers are best suited for this purpose. These double barrier devices show an analogous and homogeneous resistance change. As a reference system, filament-based memristive devices have been developed that alter their resistance due the migration of silver. Since the formation of filaments is almost random, they have a significantly higher device variability and very few states between the off- and on-state. Only the high quality of the double barrier component allowed the circuit integration without the need to individually adjust circuit parameters for each memristive device. Due to the non-linear switching characteristics and the advantageous I-V characteristics, the devices were integrated into a space-saving crossbar architecture, which increased the packing density tenfold. Due to the simultaneously simplified electrical connection, it was possible to realize a circuit for pattern classification with 180 memristive devices. The construction of an automated measuring system enabled the characterization of a large number of devices. The development of database-supported measurement and evaluation programs facilitated the analysis of the device and switching properties

Double-Barrier Memristive Devices for Unsupervised Learning and Pattern Recognition

The use of interface-based resistive switching devices for neuromorphic computing is investigated. In a combined experimental and numerical study, the important device parameters and their impact on a neuromorphic pattern recognition system are studied. The memristive cells consist of a layer sequence Al/Al2O3/Nb x O y /Au and are fabricated on a 4-inch wafer. The key functional ingredients of the devices are a 1.3 nm thick Al2O3 tunnel barrier and a 2.5 mm thick Nb x O y memristive layer. Voltage pulse measurements are used to study the electrical conditions for the emulation of synaptic functionality of single cells for later use in a recognition system. The results are evaluated and modeled in the framework of the plasticity model of Ziegler et al. Based on this model, which is matched to experimental data from 84 individual devices, the network performance with regard to yield, reliability, and variability is investigated numerically. As the network model, a computing scheme for pattern recognition and unsupervised learning based on the work of Querlioz et al. (2011), Sheridan et al. (2014), Zahari et al. (2015) is employed. This is a two-layer feedforward network with a crossbar array of memristive devices, leaky integrate-and-fire output neurons including a winner-takes-all strategy, and a stochastic coding scheme for the input pattern. As input pattern, the full data set of digits from the MNIST database is used. The numerical investigation indicates that the experimentally obtained yield, reliability, and variability of the memristive cells are suitable for such a network. Furthermore, evidence is presented that their strong I-V non-linearity might avoid the need for selector devices in crossbar array structures

Relationships among Gas Production, End Products of Rumen Fermentation and Microbial N Produced in vitro at Two Incubation Times

This experiment compared linear relationships among end-products of rumen fermentation measured at the time (t.) at which a feed produces half of its asymptotic gas production) or at 48 h. Meadow hay and corn grain were incubated for t. (16 and 9 h, respectively) or for 48 h into glass bottles. Each bottle (310 ml) was filled with feed sample (0.5 g) and 75 ml of buffered rumen fluid, and incubated at 39.0°C. Gas production (GP) was measured using the ANKOMRF System, and gas accumulated in headspace of bottles was released at 3.4 kPa. At t. or 48 h, fermentation fluids were analysed for ammonia N (N-NH3), volatile fatty acids (VFA), residual NDF and N bound to residual NDF (N-NDF). Values of GP were also predicted from VFA. Microbial N (MN) was computed as the difference between N present at the beginning and at the end of incubation. At 48 h, the relationship between GP measured and predicted from VFA was weak (R2 = 0.67; equation not shown), whereas the linear relationship was better at t. (R2 = 0.94). At t., the relationship between N-NH3 and measured GP was strong (R2 = 0.84), as well as that between MN and measured GP (R2 = 0.92). Conversely, these variables were not well related at 48 h. At t., the valerate content in rumen fluid was negligible. However, relatively large amounts of valerate were measured after 48 h, probably the result of microbial lysis. Results suggest that relationships among end-products of rumen fermentation can be more accurately evaluated at a substrate-specific incubation time (t.) rather than at 48 h

High intensity interval training is associated with greater impact on physical fitness, insulin sensitivity and muscle mitochondrial content in males with overweight/obesity, as opposed to continuous endurance training: a randomized controlled trial

Objectives: To evaluate the effect of high intensity training (HIT) on physical fitness, basal respiratory exchange ratio (bRER), insulin sensitivity and muscle histology in overweight/obese men compared to continuous aerobic training (CAT). Material and methods: 16 male participants with overweight/obesity (age: 42-57 years, body mass index: 28-36 kg/m2) were randomized to HIT (n=8) or CAT (n=8) for 10 weeks, twice a week. HIT was composed of 10 minutes high intensity, 10 minutes continuous aerobic, 10 minutes high intensity exercises. CAT was composed of three times 10 minutes continuous exercising. Changes in anthropometry, physical and metabolic fitness were evaluated. Muscle histology (mitochondria and lipid content) was evaluated by transmission electron microscopy (TEM). Results: HIT showed a significant increase for peak VO2 (P=0.01), for insulin sensitivity (AUC glucose (P<0,001), AUC insulin (P<0,001), OGTT composite score (P=0.007)) and a significant decrease of bRER (P<0.001) compared to CAT. Muscle mitochondrial content was significantly increased after HIT at the subsarcolemmal (P=0.004 number and P=0.001 surface) as well as the intermyofibrillar site (P<0.001 number and P=0.001 surface). Conclusion: High intensity training elicits stronger beneficial effects on physical fitness, basal RER, insulin sensitivity, and muscle mitochondrial content, as compared to continuous aerobic training

Tau protein, A beta 42 and S-100B protein in cerebrospinal fluid of patients with dementia with Lewy bodies

The intra vitam diagnosis of dementia with Lewy bodies (DLB) is still based on clinical grounds. So far no technical investigations have been available to support this diagnosis. As for tau protein and beta-amyloid((1-42)) (Abeta42), promising results for the diagnosis of Alzheimer's disease ( AD) have been reported; we evaluated these markers and S-100B protein in cerebrospinal fluid (CSF), using a set of commercially available assays, of 71 patients with DLB, 67 patients with AD and 41 nondemented controls (NDC) for their differential diagnostic relevance. Patients with DLB showed significantly lower tau protein values compared to AD but with a high overlap of values. More prominent differences were observed in the comparison of DLB patients with all three clinical core features and AD patients. Abeta42 levels were decreased in the DLB and AD groups versus NDC, without significant subgroup differences. S-100B levels were not significantly different between the groups. Tau protein levels in CSF may contribute to the clinical distinction between DLB and AD, but the value of the markers is still limited especially due to mixed pathology. We conclude that more specific markers have to be established for the differentiation of these diseases. Copyright (C) 2005 S. Karger AG, Basel