Connecting Spiking Neurons to a Spiking Memristor Network Changes the Memristor Dynamics

Memristors have been suggested as neuromorphic computing elements. Spike-time dependent plasticity and the Hodgkin-Huxley model of the neuron have both been modelled effectively by memristor theory. The d.c. response of the memristor is a current spike. Based on these three facts we suggest that memristors are well-placed to interface directly with neurons. In this paper we show that connecting a spiking memristor network to spiking neuronal cells causes a change in the memristor network dynamics by: removing the memristor spikes, which we show is due to the effects of connection to aqueous medium; causing a change in current decay rate consistent with a change in memristor state; presenting more-linear $I-t$ dynamics; and increasing the memristor spiking rate, as a consequence of interaction with the spiking neurons. This demonstrates that neurons are capable of communicating directly with memristors, without the need for computer translation.Comment: Conference paper, 4 page

When and where do feed-forward neural networks learn localist representations?

According to parallel distributed processing (PDP) theory in psychology, neural networks (NN) learn distributed rather than interpretable localist representations. This view has been held so strongly that few researchers have analysed single units to determine if this assumption is correct. However, recent results from psychology, neuroscience and computer science have shown the occasional existence of local codes emerging in artificial and biological neural networks. In this paper, we undertake the first systematic survey of when local codes emerge in a feed-forward neural network, using generated input and output data with known qualities. We find that the number of local codes that emerge from a NN follows a well-defined distribution across the number of hidden layer neurons, with a peak determined by the size of input data, number of examples presented and the sparsity of input data. Using a 1-hot output code drastically decreases the number of local codes on the hidden layer. The number of emergent local codes increases with the percentage of dropout applied to the hidden layer, suggesting that the localist encoding may offer a resilience to noisy networks. This data suggests that localist coding can emerge from feed-forward PDP networks and suggests some of the conditions that may lead to interpretable localist representations in the cortex. The findings highlight how local codes should not be dismissed out of hand

Carbon dynamics of surface residue- and root-derived particulate organic matter in the whole soil and aggregate size fractions

The importance of particulate organic matter (POM) in the soil ecosystem has been emphasized by many researchers, but the dynamics of POM and its role in aggregate formation are not well understood. I concluded a simulated no-till experiment which utilized 14C labeled plant material, periodic sampling, and a combination of physical and chemical fractionation methods to measure progressive changes in aggregation and the distribution of new POM C as surface residue and in situ roots decomposed. The main objectives of this dissertation were: (i) to characterize the relative contribution of surface residue- and root-derived C to soil organic matter (SOM) under no-till; (ii) to compare the concentration of new POM C in aggregates of different size and stability; (iii) to quantify changes with time in the amount, concentration, and distribution of surface residue- and root-derived C in free and intraaggregate POM;After one year, 66% of the 14C contained in surface residue on d 0 had been respired as CO2, 12% of the 14C remained in residue on the soil surface, and 16% of the 14C was in the soil. In contrast, 56% of the root-derived 14C was respired as CO2 and 44% of the 14C remained in the soil after one year. The concentration of root-derived POM 14C was significantly higher in stable (slaked) compared to less stable (capillary wetted) macroaggregates, but there was no difference in the concentration of surface residue-derived POM 14C in stable compared to unstable macroaggregates. The disruption of macroaggregates during the first 90 d of the incubation resulted in the release of root-derived intraaggregate POM into the free POM pool. After d 90, most of the root-derived C lost from macroaggregates with slaking was contained within microaggregates. The amount of new, root-derived C associated with microaggregates released from macroaggregates with slaking increased linearly with time which supports the hypothesis that microaggregates form within macroaggregates. The data present compelling evidence that in no-till, aggregate formation and stabilization processes are directly related to the decomposition of root-residue and the dynamics of POM C in the soil

Saving Incentives for Low- and Middle-Income Families: Evidence from a Field Experiment with H&R Block

This paper analyzes the effects of a large randomized field experiment, carried out with H&R Block, offering matching incentives for IRA contributions at the time of tax preparation. About 15,000 H&R Block clients, in 60 offices in predominantly low- and middle-income neighborhoods in St. Louis, were randomly offered a 20 percent match on IRA contributions, a 50 percent match, or no match (the control group). The evaluation generates two broad findings. First, higher match rates significantly raise IRA participation and contributions. Take-up rates were 3 percent for the control group, 10 percent in the 20 percent match group, and 17 percent in the 50 percent match group. Average IRA contributions (excluding the match) for the 20 percent and 50 percent match groups were 4 and 8 times higher than in the control group, respectively. Second, several additional findings are inconsistent with the full-information, rational-saver model, and suggest instead that professional tax assistance, information provision, and ease of saving can play important roles in encouraging IRA contributions among low- and middle-income families. For example, we find more modest effects on take-up and amounts contributed from the existing Saverç—´ Credit, which provides an effective match for retirement saving contributions through the tax code; we suspect that the differences may reflect the complexity of the Saver's Credit as enacted, and the way in which its effective match is presented. Taken together, our results suggest that the combination of a clear and understandable match for saving, easily accessible savings vehicles, the opportunity to use part of an income tax refund to save, and professional assistance could generate a significant increase in retirement saving participation and contributions, even among middle- and low-income households.

A Study of Corporate Real Estate Resource Management

Corporate real estate resources have been estimated at over one quarter of the current market value of the total assets of major American corporations. This study, based upon interviews with corporate real estate executives, examines the current state of corporate real estate resource management practices. It found that while the dominant view of real estate continues to be a production factor within this sample of corporations, there has been significant growth of corporate real estate units. This has been accompanied by increased influence and more active real estate resource management.

Are there any ‘object detectors’ in the hidden layers of CNNs trained to identify objects or scenes?

Various methods of measuring unit selectivity have been developed with the aim of better understanding how neural networks work. But the different measures provide divergent estimates of selectivity, and this has led to different conclusions regarding the conditions in which selective object representations are learned and the functional relevance of these representations. In an attempt to better characterize object selectivity, we undertake a comparison of various selectivity measures on a large set of units in AlexNet, including localist selectivity, precision, class-conditional mean activity selectivity (CCMAS), network dissection,the human interpretation of activation maximization (AM) images, and standard signal-detection measures. We find that the different measures provide different estimates of object selectivity, with precision and CCMAS measures providing misleadingly high estimates. Indeed, the most selective units had a poor hit-rate or a high false-alarm rate (or both) in object classification, making them poor object detectors. We fail to find any units that are even remotely as selective as the 'grandmother cell' units reported in recurrent neural networks. In order to generalize these results, we compared selectivity measures on units in VGG-16 and GoogLeNet trained on the ImageNet or Places-365 datasets that have been described as 'object detectors'. Again, we find poor hit-rates and high false-alarm rates for object classification. We conclude that signal-detection measures provide a better assessment of single-unit selectivity compared to common alternative approaches, and that deep convolutional networks of image classification do not learn object detectors in their hidden layers.Comment: Published in Vision Research 2020, 19 pages, 8 figure

Outcomes of Treated Human Granulocytic Ehrlichiosis Cases

We conducted a case-control study in Wisconsin to determine whether some patients have long-term adverse health outcomes after antibiotic treatment for human granulocytic ehrlichiosis (HGE). A standardized health status questionnaire was administered to patients and controls matched by age group and sex. Consenting patients provided blood samples for serologic testing. Among the 85 previously treated patients, the median interval since onset of illness was 24 months. Compared with 102 controls, patients were more likely to report recurrent or continuous fevers, chills, fatigue, and sweats. Patients had lower health status scores than controls for bodily pain and health relative to 1 year earlier, but there was no significant difference in physical functioning, role limitations, general health, or vitality measures. The HGE antibody titer remained elevated in one patient; two had elevated aspartate aminotransferase levels. HGE may cause a postinfectious syndrome characterized by constitutional symptoms without functional disability or serologic evidence of persistent infection

Differential function and maturation of human stem cell-derived islets after transplantation

Insulin-producing stem cell-derived islets (SC-islets) provide a virtually unlimited cell source for diabetes cell replacement therapy. While SC-islets are less functional when first differentiated in vitro compared to isolated cadaveric islets, transplantation into mice has been shown to increase their maturation. To understand the effects of transplantation on maturation and function of SC-islets, we examined the effects of cell dose, transplantation strategy, and diabetic state in immunocompromised mice. Transplantation of 2 and 5, but not 0.75 million SC-islet cells underneath the kidney capsule successfully reversed diabetes in mice with pre-existing diabetes. SQ and intramuscular injections failed to reverse diabetes at all doses and had undetectable expression of maturation markers, such as MAFA and FAM159B. Furthermore, SC-islets had similar function and maturation marker expression regardless of diabetic state. Our results illustrate that transplantation parameters are linked to SC-islet function and maturation, providing ideal mouse models for preclinical diabetes SC therapy research