Matrix Product States, Random Matrix Theory and the Principle of Maximum Entropy

Using random matrix techniques and the theory of Matrix Product States we show that reduced density matrices of quantum spin chains have generically maximum entropy.Comment: 11 pages, 4 figure

Representational organization of novel task sets during proactive encoding

Recent multivariate analyses of brain data have boosted our understanding of the organizational principles that shape neural coding. However, most of this progress has focused on perceptual visual regions (Connolly et al., 2012), whereas far less is known about the organization of more abstract, action-oriented representations. In this study, we focused on humans{\textquoteright} remarkable ability to turn novel instructions into actions. While previous research shows that instruction encoding is tightly linked to proactive activations in fronto-parietal brain regions, little is known about the structure that orchestrates such anticipatory representation. We collected fMRI data while participants (both males and females) followed novel complex verbal rules that varied across control-related variables (integrating within/across stimuli dimensions, response complexity, target category) and reward expectations. Using Representational Similarity Analysis (Kriegeskorte et al., 2008) we explored where in the brain these variables explained the organization of novel task encoding, and whether motivation modulated these representational spaces. Instruction representations in the lateral prefrontal cortex were structured by the three control-related variables, while intraparietal sulcus encoded response complexity and the fusiform gyrus and precuneus organized its activity according to the relevant stimulus category. Reward exerted a general effect, increasing the representational similarity among different instructions, which was robustly correlated with behavioral improvements. Overall, our results highlight the flexibility of proactive task encoding, governed by distinct representational organizations in specific brain regions. They also stress the variability of motivation-control interactions, which appear to be highly dependent on task attributes such as complexity or novelty.SIGNIFICANCE STATEMENTIn comparison with other primates, humans display a remarkable success in novel task contexts thanks to our ability to transform instructions into effective actions. This skill is associated with proactive task-set reconfigurations in fronto-parietal cortices. It remains yet unknown, however, how the brain encodes in anticipation the flexible, rich repertoire of novel tasks that we can achieve. Here we explored cognitive control and motivation-related variables that might orchestrate the representational space for novel instructions. Our results showed that different dimensions become relevant for task prospective encoding depending on the brain region, and that the lateral prefrontal cortex simultaneously organized task representations following different control-related variables. Motivation exerted a general modulation upon this process, diminishing rather than increasing distances among instruction representations

Survival and Nesting Ecology of Scaled Quail in the Trans-Pecos, Texas

Scaled quail (Callipepla squamata) are one of the most ecologically and economically important wildlife species in the Trans-Pecos, because they are the primary upland game bird in the Chihuahuan Desert. Using radiotelemetry, we evaluated survival (Kaplan–Meier) and nesting success of quail on 3 study sites in the Trans-Pecos, Texas: one (Santiago Mountain Ranch, central Brewster Co.) was supplemented with milo (Sorghum bicolor) year-round, the second (Lado Ranch, south Culberson Co.) never used supplements, and the third (Apache Ranch, central Culberson Co.) was supplemented with quail blocks. We trapped and radiocollared 164 female quail collectively across all study sites, and followed them for 2 years (May–Sep 2012–2013). There were no survival differences between years within study sites (P = 0.985), so we grouped data across years and compared survival between study sites. Apache Ranch had the lowest survival (55%) compared with the Santiago Mountain Ranch (76.3%) and Lado Ranch (75%). We found 47 nests across the reproductive seasons for 2012 and 2013. On average, scaled quail had high nesting success (72.6%), eggs per nest (11.6), and hatchability (91.25%). Nesting occurred from May to September with peak nesting in June and July. Timing and quantity of rain, combined with range conditions seemed to have the greatest effect on nesting performance

Microstructure Evolution During Powder Compaction

The process of powder compaction consists of the synthesis of loose powders into a solid material. The applications of compaction of granular systems extend to pharmaceuticals, detergents, food, ceramic and metallurgical processes. It is indispensable to have a thorough understanding of the behavior of confined granular systems during compaction because the performance of the final desired product is related to the microstructural features that develop during the compaction process. To have a more realistic description of the compaction, it is also important to include the packing process of granular systems. However, there are different particle packing algorithms that account for the particle filling process. The Discrete Element Method (DEM) had been used to obtain a dynamic solution to this problem but requires high computational power. As an alternative to the computationally expensive DEM approach, a static based algorithm has recently been developed for the modelling and simulation of the particle packing process. The algorithm allows for the modelling of the packing process by placing spheres inside different shapes and sizes of containers. In this study, we present a new version of the nanoHUB Powder Compaction tool. It currently simulates the microstructure evolution of monodisperse, compressible granular systems up to high relative densities. The tool also models the plastic and elastic deformation of single particles described by different contact mechanics models. The new features use a general particle packing algorithm and thus allow the user to choose a particle size distribution in a specified range for the mean, standard deviation and number of particles to fill the die. The information is passed to the solver that in turn simulates the compaction in Purdue’s high-performance computer cluster

Is there evidence for a hotter Universe?

The measurement of present-day temperature of the Cosmic Microwave Background (CMB), $T_0 = 2.72548 \pm 0.00057$ K (1$\sigma$), made by the Far-InfraRed Absolute Spectrophotometer (FIRAS), is one of the most precise measurements ever made in Cosmology. On the other hand, estimates of the Hubble Constant, $H_0$, obtained from measurements of the CMB temperature fluctuations assuming the standard $\Lambda$CDM model exhibit a large ($4.1\sigma$) tension when compared with low-redshift, model-independent observations. Recently, some authors argued that a slightly change in $T_0$ could alleviate or solve the $H_0$-tension problem. Here, we investigate evidence for a hotter or colder universe by performing an independent analysis from currently available temperature-redshift $T(z)$ measurements. Our analysis (parametric and non-parametric) shows a good agreement with the FIRAS measurement and a discrepancy of $\gtrsim 1.9\sigma$ from the $T_0$ values required to solve the $H_0$ tension. This result reinforces the idea that a solution of the $H_0$-tension problem in fact requires either a better understanding of the systematic errors on the $H_0$ measurements or new physics.Comment: 4 pages, 2 figures, 1 table. Accepted for publication in European Physical Journal