Combining Hebbian and reinforcement learning in a minibrain model

A toy model of a neural network in which both Hebbian learning and reinforcement learning occur is studied. The problem of `path interference', which makes that the neural net quickly forgets previously learned input-output relations is tackled by adding a Hebbian term (proportional to the learning rate $\eta$) to the reinforcement term (proportional to $\rho$) in the learning rule. It is shown that the number of learning steps is reduced considerably if $1/4 < \eta/\rho < 1/2$, i.e., if the Hebbian term is neither too small nor too large compared to the reinforcement term

A split-cavity design for the incorporation of a DC bias in a 3D microwave cavity

We report on a technique for applying a DC bias in a 3D microwave cavity. We achieve this by isolating the two halves of the cavity with a dielectric and directly using them as DC electrodes. As a proof of concept, we embed a variable capacitance diode in the cavity and tune the resonant frequency with a DC voltage, demonstrating the incorporation of a DC bias into the 3D cavity with no measurable change in its quality factor at room temperature. We also characterize the architecture at millikelvin temperatures and show that the split cavity design maintains a quality factor $Q_\text{i} \sim 8.8 \times 10^5$, making it promising for future quantum applications

Observations on waders (Charadriidae) at Scoresby Sund, East Greenland

Populations of waders in three census areas at Scoresby Sund, central East Greenland, were studied during the three breeding seasons of 1973, 1974 and 1975. Ringed Plover (Charadrius hiaticula ), Golden Plover (Pluvialis apricaria), Turnstone (Arenaria interpres), Knot (Calidris canutus), Dunlin (Calidris alpina) and Sanderling (Calidris alba) bred in the census areas, while Purple Sandpiper (Calidris maritima) and Red-necked Phalarope (Phalaropus lobatus) bred elsewhere in the region. Population densities were very low, compared to other areas further north in high arctic Greenland. Extensive, deep and late-thawing snow cover prevents waders from utilizing large areas in June. Time of breeding showed a high correlation with the snow melting conditions in the respective areas and years. Breeding success was generally low; only Ringed Plover had more than 50% nest and egg survival. Nest failures were probably mostly due to predation by Arctic Foxes (Alopex lagopus). Observation and examination of individuals from post-breeding flocks in the second half of July indicated that these flocks contained mainly non-breeders, but failed and successful breeders were also present. Measurements on eggs, pulli and adults are presented

Altered expression of CD44 and DKK1 in the progression of Barrett's esophagus to esophageal adenocarcinoma

Barrett's esophagus (BE) is an acquired condition in which the normal lining of the esophagus is replaced by intestinal metaplastic epithelium. BE can evolve to esophageal adenocarcinoma (EAC) through low-grade dysplasia (LGD) and high-grade dysplasia (HGD). The only generally accepted marker for increased risk of EAC is the presence of HGD, diagnosed on endoscopic biopsies. More specific markers for the prediction of EAC risk are needed. A tissue microarray was constructed comprising tissue samples from BE, LGD, HGD, and EAC. Marker expression was studied by immunohistochemistry using antibodies against CD44, DKK1, CDX2, COX2, SOX9, OCT1, E-cadherin, and β-catenin. Immunostaining was evaluated semi-quantitatively. CD44 expression decreased in HGD and EAC relative to BE and LGD. DKK1 expression increased in HGD and EAC relative to BE and LDG. CDX2 expression increased in HGD but decreased in EAC. COX2 expression decreased in EAC, and SOX9 expression increased only in the upper crypt epithelial cells in HGD. E-cadherin expression decreased in EAC. Nuclear β-catenin was not significantly different between BE, LGD, and HGD. Loss of CD44 and gain of DKK1 expression characterizes progression from BE and LGD to HGD and EAC, and their altered expression might indicate an increased risk for developing an EAC. This observation warrants inclusion of these immunohistochemically detectable markers in a study with a long patient follow-u

The formation of CO2_2 through consumption of gas-phase CO on vacuum-UV irradiated water ice

[Abridged] Observations of protoplanetary disks suggest that they are depleted in gas-phase CO. It has been posed that gas-phase CO is chemically consumed and converted into less volatile species through gas-grain processes. Observations of interstellar ices reveal a CO$_2$ component within H$_2$O ice suggesting co-formation. The aim of this work is to experimentally verify the interaction of gas-phase CO with solid-state OH radicals above the sublimation temperature of CO. Amorphous solid water (ASW) is deposited at 15 K and followed by vacuum-UV (VUV) irradiation to dissociate H$_2$O and create OH radicals. Gas-phase CO is simultaneously admitted and only adsorbs with a short residence time on the ASW. Products in the solid state are studied with infrared spectroscopy and once released into the gas phase with mass spectrometry. Results show that gas-phase CO is converted into CO$_2$, with an efficiency of 7-27%, when interacting with VUV irradiated ASW. Between 40 and 90 K, CO$_2$ production is constant, above 90 K, O$_2$ production takes over. In the temperature range of 40-60 K, the CO$_2$ remains in the solid state, while at temperatures $\geq$ 70 K the formed CO$_2$ is released into the gas phase. We conclude that gas-phase CO reacts with solid-state OH radicals above its sublimation temperature. This gas-phase CO and solid-state OH radical interaction could explain the observed CO$_2$ embedded in water-rich ices. It may also contribute to the observed lack of gas-phase CO in planet-forming disks, as previously suggested. Our experiments indicate a lower water ice dissociation efficiency than originally adopted in model descriptions of planet-forming disks and molecular clouds. Incorporation of the reduced water ice dissociation and increased binding energy of CO on a water ice surfaces in these models would allow investigation of this gas-grain interaction to its full extend.Comment: Accepted for publication in Astronomy & Astrophysic

Mixed-Integer MPC Strategies for Fueling and Density Control in Fusion Tokamaks

Model predictive control (MPC) is promising for fueling and core density feedback control in nuclear fusion tokamaks, where the primary actuators, frozen hydrogen fuel pellets fired into the plasma, are discrete. Previous density feedback control approaches have only approximated pellet injection as a continuous input due to the complexity that it introduces. In this letter, we model plasma density and pellet injection as a hybrid system and propose two MPC strategies for density control: mixed-integer (MI) MPC using a conventional mixed-integer programming (MIP) solver and MPC utilizing our novel modification of the penalty term homotopy (PTH) algorithm. By relaxing the integer requirements, the PTH algorithm transforms the MIP problem into a series of continuous optimization problems, reducing computational complexity. Our novel modification to the PTH algorithm ensures that it can handle path constraints, making it viable for constrained hybrid MPC in general. Both strategies perform well with regards to reference tracking without violating path constraints and satisfy the computation time limit for real-time control of the pellet injection system. However, the computation time of the PTH-based MPC strategy consistently outpaces the conventional MI-MPC strategy

Sound localization with bilateral bone conduction devices

Purpose To investigate sound localization in patients bilaterally fitted with bone conduction devices (BCDs). Additionally, clinically applicable methods to improve localization accuracy were explored. Methods Fifteen adults with bilaterally fitted percutaneous BCDs were included. At baseline, sound localization, (un)aided pure-tone thresholds, device use, speech, spatial and qualities of hearing scale (SSQ) and York hearing-related quality of life (YHRQL) questionnaire were measured. Settings to optimize sound localizing were added to the BCDs. At 1 month, sound localization was assessed again and localization was practiced with a series of sounds with visual feedback. At 3 months, localization performance, device use and questionnaire scores were determined again. Results At baseline, one patient with congenital hearing loss demonstrated near excellent localization performance and four other patients (three with congenital hearing loss) localized sounds (quite) accurately. Seven patients with acquired hearing loss were able to lateralize sounds, i.e. identify whether sounds were coming from the left or right side, but could not localize sounds accurately. Three patients (one with congenital hearing loss) could not even lateralize sounds correctly. SSQ scores were significantly higher at 3 months. Localization performance, device use and YHRQL scores were not significantly different between visits. Conclusion In this study, the majority of experienced bilateral BCD users could lateralize sounds and one third was able to localize sounds (quite) accurately. The localization performance was robust and stable over time. Although SSQ scores were increased at the last visit, optimizing device settings and a short practice session did not improve sound localization