From thermal rectifiers to thermoelectric devices

We discuss thermal rectification and thermoelectric energy conversion from the perspective of nonequilibrium statistical mechanics and dynamical systems theory. After preliminary considerations on the dynamical foundations of the phenomenological Fourier law in classical and quantum mechanics, we illustrate ways to control the phononic heat flow and design thermal diodes. Finally, we consider the coupled transport of heat and charge and discuss several general mechanisms for optimizing the figure of merit of thermoelectric efficiency.Comment: 42 pages, 22 figures, review paper, to appear in the Springer Lecture Notes in Physics volume "Thermal transport in low dimensions: from statistical physics to nanoscale heat transfer" (S. Lepri ed.

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time, and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space. While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes, vast areas of the tropics remain understudied. In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity, but it remains among the least known forests in America and is often underrepresented in biodiversity databases. To worsen this situation, human-induced modifications may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge, it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Long-term outcome of isobutyryl-CoA dehydrogenase deficiency diagnosed following an episode of ketotic hypoglycaemia

Isobutyryl-CoA Dehydrogenase Deficiency (IBDD) is an inherited disorder of valine metabolism caused by mutations in ACAD8. Most reported patients have been diagnosed through newborn screening programmes due to elevated C4-carnitine levels and appear clinically asymptomatic. One reported non-screened patient had dilated cardiomyopathy and anaemia at the age of two years. We report a 13 month old girl diagnosed with IBDD after developing hypoglycaemic encephalopathy (blood glucose 1.9 mmol/l) during an episode of rotavirus-induced gastroenteritis. Metabolic investigations demonstrated an appropriate ketotic response (free fatty acids 2594 μmol/l, 3-hydroxybutyrate 3415 μmol/l), mildly elevated plasma lactate (3.4 mmol/l), increased C4-carnitine on blood spot and plasma acylcarnitine analysis and other metabolic abnormalities secondary to ketosis. After recovery, C4-carnitine remained increased and isobutyrylglycine was detected on urine organic acid analysis. Free carnitine was normal in all acylcarnitine samples. IBDD was confirmed by finding a homozygous c.845C > T substitution in ACAD8. The patient was given, but has not used, a glucose polymer emergency regimen and after ten years' follow-up has had no further episodes of hypoglycaemia nor has she developed cardiomyopathy or anaemia. Psychomotor development has been normal to date. Though we suspect IBDD did not contribute to hypoglycaemia in this patient, patients should be followed-up carefully and glucose polymer emergency regimens may be indicated if recurrent episodes of hypoglycaemia occur

Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

We study the spin-polarized tunneling of electrons from the valence band of GaMnAs into the conduction band of n-type GaAs with Si delta-doping at the interface. The injection of spin-polarized electrons is detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode, corresponding to magneto-optical Kerr effect loops. The angular momentum selection rules are simplified by the strain-induced heavy-hole/light-hole splitting, allowing a direct relation between circular polarization and spin-polarization. Comparison with the influence of Zeeman splitting allow us to conclude a spin-injection from the majority spin-band