Horizontal spreading of planetary debris accreted by white dwarfs

White dwarfs with metal-polluted atmospheres have been studied widely in the context of the accretion of rocky debris from evolved planetary systems. One open question is the geometry of accretion and how material arrives and mixes in the white dwarf surface layers. Using the three-dimensional (3D) radiation hydrodynamics code co5bold, we present the first transport coefficients in degenerate star atmospheres that describe the advection–diffusion of a passive scalar across the surface plane. We couple newly derived horizontal diffusion coefficients with previously published vertical diffusion coefficients to provide theoretical constraints on surface spreading of metals in white dwarfs. Our grid of 3D simulations probes the vast majority of the parameter space of convective white dwarfs, with pure-hydrogen atmospheres in the effective temperature range of 6000–18 000 K and pure-helium atmospheres in the range of 12 000–34 000 K. Our results suggest that warm hydrogen-rich atmospheres (DA; ${\gtrsim} 13\, 000$ K) and helium-rich atmospheres (DB and DBA; ${\gtrsim} 30\, 000$ K) are unable to efficiently spread the accreted metals across their surface, regardless of the time dependence of accretion. This result may be at odds with the current non-detection of surface abundance variations in white dwarfs with debris discs. For cooler hydrogen- and helium-rich atmospheres, we predict a largely homogeneous distribution of metals across the surface within a vertical diffusion time-scale. This is typically less than 0.1 per cent of disc lifetime estimates, a quantity that is revisited in this paper using the overshoot results. These results have relevance for studies of the bulk composition of evolved planetary systems and models of accretion disc physics

Amylin/Calcitonin receptor–mediated signaling in POMC neurons influences energy balance and locomotor activity in chow-fed male mice

Amylin, a pancreatic hormone and neuropeptide, acts principally in the hindbrain to decrease food intake and has recently been shown to act as a neurotrophic factor to control the development of area postrema → nucleus of the solitary tract and arcuate hypothalamic nucleus→ paraventricular nucleus axonal fiber outgrowth. Amylin is also able to activate ERK signaling specifically in POMC neurons independently of leptin. For investigation of the physiological role of amylin signaling in POMC neurons, the core component of the amylin receptor, calcitonin receptor (CTR), was depleted from POMC neurons using an inducible mouse model. The loss of CTR in POMC neurons leads to increased body weight gain, increased adiposity, and glucose intolerance inmale knockoutmice, characterized by decreased energy expenditure (EE) and decreased expression of uncoupling protein 1 (UCP1) in brown adipose tissue. Furthermore, a decreased spontaneous locomotor activity and absent thermogenic reaction to the application of the amylin receptor agonist were observed in male and female mice. Together, these results show a significant physiological impact of amylin/calcitonin signaling in CTR-POMC neurons on energy metabolism and demonstrate the need for sex-specific approaches in obesity research and potentially treatment

Factor Analysis

Schack T, Koester D. Factor Analysis. In: Hackfort D, Schinke RJ, Strauss B, eds. Dictionary of sport psychology. Sport, Exercise, and Performing Arts. London, UK: Academic Press; 2019: 107

Convective overshoot and macroscopic diffusion in pure-hydrogen-atmosphere white dwarfs

We present a theoretical description of macroscopic diffusion caused by convective overshoot in pure-hydrogen DA white dwarfs using 3D, closed-bottom, radiation hydrodynamics (COBOLD)-B-5 simulations. We rely on a new grid of deep 3D white dwarf models in the temperature range 11 400 <= T-eff <= 18 000 K where tracer particles and a tracer density are used to derive macroscopic diffusion coefficients driven by convective overshoot. These diffusion coefficients are compared to microscopic diffusion coefficients from 1D structures. We find that the mass of the fully mixed region is likely to increase by up to 2.5 orders of magnitude while inferred accretion rates increase by a more moderate order of magnitude. We present evidence that an increase in settling time of up to 2 orders of magnitude is to be expected, which is of significance for time-variability studies of polluted white dwarfs. Our grid also provides the most robust constraint on the onset of convective instabilities in DA white dwarfs to be in the effective temperature range from 18 000 to 18 250 K

Monolithically integrated multimode interference coupler-based master oscillator power amplifier with dual-wavelength emission around 830 nm

A monolithically integrated dual-wavelength multimode interference coupler-based master oscillator power amplifier is presented. It consists of two shallowly etched, laterally separated ridge waveguide laser cavities as master oscillators with individual distributed Bragg reflector gratings as cavity mirrors. A deeply etched coupling section containing S-bend shaped waveguides and a multimode interference coupler is used to couple the laser emission of the master oscillators into a shallowly etched single waveguide serving as power amplifier. Changing the etch depth for the coupling section enables a compact device layout. In addition, increased radiation angles of modes not coupled into the power amplifier help to suppress beam steering, otherwise indicated by laterally separated far-field intensity distributions. The device provides 0.5 W of dual-wavelength emission around 830 nm in individual and common operation. As designed, both emission wavelengths are separated by 0.5 nm with spectral widths below 20 pm, limited by the spectral resolution of the spectrometer. Both peak wavelengths remain within spectral windows of 50 pm within the available power range. This enables full flexibility selecting operating points for applications such as shifted excitation Raman difference spectroscopy and the generation of THz emission by photomixing. The emission wavelengths can additionally be non-continuously tuned by applying a heater current to resistors implemented next to the distributed Bragg reflector gratings. As an example, selected spectral distances of 0.5 nm, 1.0 nm, 1.5 nm, and 2.0 nm are demonstrated. Near field widths of 5 μ m and far field angles of 17° result in beam propagation ratios of 1.4 (1/e ^2 ) in all operation modes and enable easy beam shaping or optical single-mode fiber coupling

Patterns of regional brain hypometabolism associated with knowledge of semantic features and categories in Alzheimer's disease

The study of semantic memory in patients with Alzheimer's disease (AD) has raised important questions about the representation of conceptual knowledge in the human brain. It is still unknown whether semantic memory impairments are caused by localized damage to specialized regions or by diffuse damage to distributed representations within nonspecialized brain areas. To our knowledge, there have been no direct correlations of neuroimaging of in vivo brain function in AD with performance on tasks differentially addressing visual and functional knowledge of living and nonliving concepts. We used a semantic verification task and resting 18-fluorodeoxyglucose positron emission tomography in a group of mild to moderate AD patients to investigate this issue. The four task conditions required semantic knowledge of (1) visual, (2) functional properties of living objects, and (3) visual or (4) functional properties of nonliving objects. Visual property verification of living objects was significantly correlated with left posterior fusiform gyrus metabolism (Brodmann's area [BA] 37/19). Effects of visual and functional property verification for nonliving objects largely overlapped in the left anterior temporal (BA 38/20) and bilateral premotor areas (BA 6), with the visual condition extending more into left lateral precentral areas. There were no associations with functional property verification for living concepts. Our results provide strong support for anatomically separable representations of living and nonliving concepts, as well as visual feature knowledge of living objects, and against distributed accounts of semantic memory that view visual and functional features of living and nonliving objects as distributed across a common set of brain area