The ELM Neuron: an Efficient and Expressive Cortical Neuron Model Can Solve Long-Horizon Tasks

Traditional large-scale neuroscience models and machine learning utilize simplified models of individual neurons, relying on collective activity and properly adjusted connections to perform complex computations. However, each biological cortical neuron is inherently a sophisticated computational device, as corroborated in a recent study where it took a deep artificial neural network with millions of parameters to replicate the input-output relationship of a detailed biophysical model of a cortical pyramidal neuron. We question the necessity for these many parameters and introduce the Expressive Leaky Memory (ELM) neuron, a biologically inspired, computationally expressive, yet efficient model of a cortical neuron. Remarkably, our ELM neuron requires only 8K trainable parameters to match the aforementioned input-output relationship accurately. We find that an accurate model necessitates multiple memory-like hidden states and intricate nonlinear synaptic integration. To assess the computational ramifications of this design, we evaluate the ELM neuron on various tasks with demanding temporal structures, including a sequential version of the CIFAR-10 classification task, the challenging Pathfinder-X task, and a new dataset based on the Spiking Heidelberg Digits dataset. Our ELM neuron outperforms most transformer-based models on the Pathfinder-X task with 77% accuracy, demonstrates competitive performance on Sequential CIFAR-10, and superior performance compared to classic LSTM models on the variant of the Spiking Heidelberg Digits dataset. These findings indicate a potential for biologically motivated, computationally efficient neuronal models to enhance performance in challenging machine learning tasks.Comment: 23 pages, 10 figures, 9 tables, submitted to NeurIPS 202

The Redshift Evolution of the Mean Temperature, Pressure, and Entropy Profiles in 80 SPT-Selected Galaxy Clusters

We present the results of an X-ray analysis of 80 galaxy clusters selected in the 2500 deg2 South Pole Telescope survey and observed with the Chandra X-ray Observatory. We divide the full sample into subsamples of ∼20 clusters based on redshift and central density, performing a joint X-ray spectral fit to all clusters in a subsample simultaneously, assuming self-similarity of the temperature profile. This approach allows us to constrain the shape of the temperature profile over 0 R500) regions than their low-z (0.3 < z < 0.6) counterparts. Combining the average temperature profile with measured gas density profiles from our earlier work, we infer the average pressure and entropy profiles for each subsample. Confirming earlier results from this data set, we find an absence of strong cool cores at high z, manifested in this analysis as a significantly lower observed pressure in the central 0.1R500 of the high-z cool-core subset of clusters compared to the low-z cool-core subset. Overall, our observed pressure profiles agree well with earlier lower-redshift measurements, suggesting minimal redshift evolution in the pressure profile outside of the core. We find no measurable redshift evolution in the entropy profile at r . 0.7R500 – this may reflect a long-standing balance between cooling and feedback over long timescales and large physical scales. We observe a slight flattening of the entropy profile at r & R500 in our high-z subsample. This flattening is consistent with a temperature bias due to the enhanced (∼3×) rate at which group-mass (∼2 keV) halos, which would go undetected at our survey depth, are accreting onto the cluster at z ∼ 1. This work demonstrates a powerful method for inferring spatially-resolved cluster properties in the case where individual cluster signal-to-noise is low, but the number of observed clusters is high.Physic

Sinuous-Antenna coupled TES bolometers for Cosmic Microwave Background Polarimetry

We are developing antenna‐coupled TES bolometers for CMB polarimetry that receive both linear polarizations over nearly two octaves of bandwidth. This ultra‐wide bandwidth is achieved with a novel adaptation of the sinuous antenna that integrates microstrip feed‐lines onto the arms of the antenna and uses a contacting extended hemispherical lens to focus the beam. It is challenging to achieve desirable antenna performance over such a wide band and our version of the sinuous antenna offers a unique solution. We have integrated this antenna with TES‐bolometers and report on a series of optical tests that demonstrate the antenna beams’s high symmetry, cross‐polarization rejection, gain, and optical efficiency over the operating band

Further Optimization of the APEX-SZ TES Bolometer Array

We describe the recent reoptimization of the detector array in the APEX‐SZ receiver, which is currently operating at the APEX telescope in Chile. APEX‐SZ is designed to image the Sunyaev Zel’dovich effect (SZE). Observations are made in a single spectral band centered on 150 GHz, which is where the decrement of the SZE peaks. The APEX‐SZ transition‐edge sensor bolometers are micro‐fabricated in six 55‐element sub arrays, which combine to form the full 330‐element focal plane operating at 280 mK. We report on the newest generation of sub‐arrays that use a λ∕4 silicon‐filled backshort. Compared to the first generation array which used a 3λ∕4 backshort, the new arrays have a broader bandwidth and an increased optical efficiency. We present spectral bandpass and efficiency measurements and compare these to electromagnetic simulations of the bolometer absorption. The overall improvement in optical coupling reduces the noise equivalent temperature (NET) of each bolometer by a factor of approximately 1.5. Several galaxy clusters have been observed using the new detectors and analysis of the data is currently underway. We also present plans for future upgrades to the receive

SPT-SZ: a Sunyaev-ZePdovich survey for galaxy clusters

The SPT‐SZ is, currently, the most powerful instrument for detecting galaxy clusters through the Sunyaev‐Zel’dovich (SZ) effect. The SPT‐SZ focal plane consists of over 700 background limited TES spiderweb bolometers observing in three different pass bands (90 GHz, 150 GHz, and 220 GHz) readout by a frequency domain SQUID multiplexer. Together with the 10‐m South Pole Telescope, SPT‐SZ has realized exceptional sensitivity at arcminute resolution over a one degree field of view and is the first instrument to discover new galaxy clusters through the SZ effect. We will discuss the SPT‐SZ design and deployment, present initial results from the first two seasons, and outline future survey plan