SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Degrees of freedom

244

Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850-2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.

Concepts: Ice, Climate, Weather, Climate change, Degrees of freedom, Ocean, Global warming, Latitude

156

Variability in motor performance results from the interplay of error correction and neuromotor noise. This study examined whether visual amplification of error, previously shown to improve performance, affects not only error correction, but also neuromotor noise, typically regarded as inaccessible to intervention. Seven groups of healthy individuals, with six participants in each group, practiced a virtual throwing task for three days until reaching a performance plateau. Over three more days of practice, six of the groups received different magnitudes of visual error amplification; three of these groups also had noise added. An additional control group was not subjected to any manipulations for all six practice days. The results showed that the control group did not improve further after the first three practice days, but the error amplification groups continued to decrease their error under the manipulations. Analysis of the temporal structure of participants' corrective actions based on stochastic learning models revealed that these performance gains were attained by reducing neuromotor noise and, to a considerably lesser degree, by increasing the size of corrective actions. Based on these results, error amplification presents a promising intervention to improve motor function by decreasing neuromotor noise after performance has reached an asymptote. These results are relevant for patients with neurological disorders and the elderly. More fundamentally, these results suggest that neuromotor noise may be accessible to practice interventions.

Concepts: Monotonic function, Function, Degrees of freedom, Amplifier

30

The development of obesity may be aggravated if obesity itself insulates against heat loss and thus diminishes the amount of food burnt for body temperature control. This would be particularly important under normal animal house conditions where mice experience a chronic cold stress (at ≈20 °C). We used Scholander plots (energy expenditure plotted versus ambient temperature) to examine the insulation (thermal conductance) of mice, defined as the slope of the Scholander curve at subthermoneutral temperatures. We verified the method by demonstrating that shaved mice possessed only half the insulation of nonshaved mice. We examined a series of obesity models (mice fed high-fat diets and kept at different temperatures, classical diet-induced obesity mice, ob/ob mice and obesity-prone (C57BL/6) versus obesity-resistant (129S) mice). We found that neither acclimation temperature, nor any kind or degree of obesity affected the thermal insulation of the mice, when analyzed at the whole mouse level or as energy expenditure per lean weight. Calculation per body weight erroneously implied increased insulation in obese mice. We conclude that in contrast to what would be expected, obesity of any kind does not increase thermal insulation in mice, and it does therefore not in itself aggravate the development of obesity. It may be discussed to what degree excess adipose tissue has an insulation effect in humans and especially whether significant metabolic effects are associated with insulation in humans.

Concepts: Energy, Obesity, Adipose tissue, Temperature, Heat, Leptin, Heat transfer, Degrees of freedom

29

Animals adaptively regulate their metabolic rate and hence energy expenditure over the annual cycle to cope with energetic challenges. We studied energy management in greylag geese. In all geese, profound seasonal changes of heart rate (fH) and body temperature (Tb) showed peaks in summer and troughs during winter, and also daily modulation of fH and Tb. Daily mean fH was on average 22% lower at the winter trough than at the summer peak, whereas daily mean Tb at the winter trough was only about 1 °C below the summer peak. Daily means of Tb together with those of air temperature and day length were the most important predictors of daily mean fH, which was further modulated by precipitation, reproductive state, and, to a minor degree, social rank. Peaks of fH and Tb occurred earlier in incubating females compared to males. Leading goslings increased daily mean fH. Our results suggest that in greylag geese, pronounced changes of fH over the year are caused by photoperiod-induced changes of endogenous heat production. Similar to large non-hibernating mammals, tolerance of lower Tb during winter seems the major factor permitting this. On top of these major seasonal changes, fH and Tb are elevated in incubating females.

Concepts: Energy, Temperature, Thermodynamics, Heat, Entropy, Season, Internal energy, Degrees of freedom

28

The crossing of a transition state in a multidimensional reactive system is mediated by invariant geometric objects in phase space: An invariant hyper-sphere that represents the transition state itself and invariant hyper-cylinders that channel the system towards and away from the transition state. The existence of these structures can only be guaranteed if the invariant hyper-sphere is normally hyperbolic, i.e., the dynamics within the transition state is not too strongly chaotic. We study the dynamics within the transition state for the hydrogen exchange reaction in three degrees of freedom. As the energy increases, the dynamics within the transition state becomes increasingly chaotic. We find that the transition state first looses and then, surprisingly, regains its normal hyperbolicity. The important phase space structures of transition state theory will, therefore, exist at most energies above the threshold.

Concepts: Chemical reaction, Fundamental physics concepts, Physics, Transition state, Force, Classical mechanics, Degrees of freedom, Transition state theory

27

The kinetic energy of a force-free granular gas decays monotonously due to inelastic collisions of the particles. For a homogeneous granular gas of identical particles, the corresponding decay of granular temperature is quantified by Haff’s law. Here, we report that for a granular gas of aggregating particles, the granular temperature does not necessarily decay but may even increase. Surprisingly, the increase of temperature is accompanied by the continuous loss of total gas energy. This stunning effect arises from a subtle interplay between decaying kinetic energy and gradual reduction of the number of degrees of freedom associated with the particles' dynamics. We derive a set of kinetic equations of Smoluchowski type for the concentrations of aggregates of different sizes and their energies. We find scaling solutions to these equations and a condition for the aggregation mechanism predicting growth of temperature. Numerical direct simulation Monte Carlo results confirm the theoretical predictions.

Concepts: Energy, Fundamental physics concepts, Temperature, Radioactive decay, Kinetic energy, Classical mechanics, Internal energy, Degrees of freedom

27

In this study, we explore the feasibility of using bioinspired robotics to influence the behaviour of mosquitofish (Gambusia affinis), a social freshwater fish species that is extensively studied for the ecological issues associated with its diffusion in non-native environments. Specifically, in a dichotomous choice test, we investigate the behavioural response of small shoals of mosquitofish to a robotic fish inspired by mosquitofish in its colouration, shape, aspect ratio, and locomotion. Our results indicate that the swimming depth and the aspect ratio of the robotic fish are both determinants of mosquitofish preference. In particular, we find that mosquitofish are never attracted by a robotic fish whose colouration and shape are inspired by live subjects and that the degree of repulsion varies as a function of the swimming depth and the aspect ratio.

Concepts: Psychology, Aspect ratio, Degrees of freedom, Freshwater fish, Poeciliidae, Mosquitofish, Gambusia, Live-bearing fish

15

The identification of causal effects is a fundamental problem in climate change research. Here, a new perspective on climate change causality is presented using the central England temperature (CET) dataset, the longest instrumental temperature record, and a combination of slow feature analysis and wavelet analysis. The driving forces of climate change were investigated and the results showed two independent degrees of freedom -a 3.36-year cycle and a 22.6-year cycle, which seem to be connected to the El Niño-Southern Oscillation cycle and the Hale sunspot cycle, respectively. Moreover, these driving forces were modulated in amplitude by signals with millennial timescales.

Concepts: Fundamental physics concepts, Climate change, Degrees of freedom, Solar cycle

15

Since initial reports regarding the impact of motion artifact on measures of functional connectivity, there has been a proliferation of participant-level confound regression methods to limit its impact. However, many of the most commonly used techniques have not been systematically evaluated using a broad range of outcome measures. Here, we provide a systematic evaluation of 14 participant-level confound regression methods in 393 young adults. Specifically, we compare methods according to four benchmarks, including the residual relationship between motion and connectivity, distance-dependent effects of motion on connectivity, network identifiability, and additional degrees of freedom lost in confound regression. Our results delineate two clear trade-offs among methods. First, methods that include global signal regression minimize the relationship between connectivity and motion, but unmask distance-dependent artifact. In contrast, censoring methods mitigate both motion artifact and distance-dependence, but use additional degrees of freedom. Importantly, less effective de-noising methods are also unable to identify modular network structure in the connectome. Taken together, these results emphasize the heterogeneous efficacy of proposed methods, and suggest that different confound regression strategies may be appropriate in the context of specific scientific goals.

Concepts: Regression analysis, Linear regression, Evaluation, Effectiveness, Statistical terminology, Degrees of freedom, Errors and residuals in statistics, Benchmark

13

To test three proposed models for adaptive thermogenesis in compartments of energy expenditure following different degrees of weight loss. Specifically, (1) there is no adaptive thermogenesis [constant relationship of energy expenditure (EE) to metabolic mass]. (2) There is a fixed degree of adaptive thermogenesis once fat stores are below a “threshold.” (3) The degree of adaptive thermogenesis is proportional to weight loss.

Concepts: Metabolism, Adenosine triphosphate, Energy, Mass, Classical mechanics, Academic degree, Degrees of freedom, Homeostasis