The influence of forward-scattered light in transmission measurements of (exo)planetary atmospheres

[Abridged] The transmission of light through a planetary atmosphere can be studied as a function of altitude and wavelength using stellar or solar occultations, giving often unique constraints on the atmospheric composition. For exoplanets, a transit yields a limb-integrated, wavelength-dependent transmission spectrum of an atmosphere. When scattering haze and/or cloud particles are present in the planetary atmosphere, the amount of transmitted flux not only depends on the total optical thickness of the slant light path that is probed, but also on the amount of forward-scattering by the scattering particles. Here, we present results of calculations with a three-dimensional Monte Carlo code that simulates the transmitted flux during occultations or transits. For isotropically scattering particles, like gas molecules, the transmitted flux appears to be well-described by the total atmospheric optical thickness. Strongly forward-scattering particles, however, such as commonly found in atmospheres of Solar System planets, can increase the transmitted flux significantly. For exoplanets, such added flux can decrease the apparent radius of the planet by several scale heights, which is comparable to predicted and measured features in exoplanet transit spectra. We performed detailed calculations for Titan's atmosphere between 2.0 and 2.8 micron and show that haze and gas abundances will be underestimated by about 8% if forward-scattering is ignored in the retrievals. At shorter wavelengths, errors in the gas and haze abundances and in the spectral slope of the haze particles can be several tens of percent, also for other Solar System planetary atmospheres. We also find that the contribution of forward-scattering can be fairly well described by modelling the atmosphere as a plane-parallel slab.Comment: Icarus, accepted for publicatio

Quantifying Losses of Understory Forage in Aspen Stands on the Dixie and Fishlake National Forests

The West has lost up to 60% of its historic aspen stands over the last century, probably as a result of the successional tendency of aspen to be replaced by coniferous species in the absence of periodic fires. One of several major impacts of this change is the loss of understory forage as conifer canopy cover increases. I measured understory biomass in aspen stands ranging from 0% to 81 % absolute conifer cover in the canopy Ill and found that understory production declines exponentially as conifers replace aspen. I also did an economic analysis to determine the value of the forage that is not being produced by aspen sites due to a presence of coniferous species within the tree canopy. Study results indicate significant losses in forage, marketable through the sale of livestock, and losses in revenue generated through grazing fees for the USDA Forest Service

Motivations and experiences of UK students studying abroad

This report summarises the findings of research aimed at improving understanding of the motivations behind the international diploma mobility of UK student

Reaching the hydrodynamic regime in a Bose-Einstein condensate by suppression of avalanche

We report the realization of a Bose-Einstein condensate (BEC) in the hydrodynamic regime. The hydrodynamic regime is reached by evaporative cooling at a relative low density suppressing the effect of avalanches. With the suppression of avalanches a BEC containing 120.10^6 atoms is produced. The collisional opacity can be tuned from the collisionless regime to a collisional opacity of more than 3 by compressing the trap after condensation. In the collisional opaque regime a significant heating of the cloud at time scales shorter than half of the radial trap period is measured. This is direct proof that the BEC is hydrodynamic.Comment: Article submitted for Phys. Rev. Letters, 6 figure

Large atom number Bose-Einstein condensate of sodium

We describe the setup to create a large Bose-Einstein condensate containing more than 120x10^6 atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical dark-spot MOT in our experiments contains 2.0x10^10 atoms with a temperature of 320 microK and a density of about 1.0x10^11 atoms/cm^3. The sample is spin polarized in a high magnetic field, before the atoms are loaded in the magnetic trap. Spin polarizing in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by evaporative cooling. To suppress the 3-body losses at the end of the evaporation the magnetic trap is decompressed in the axial direction.Comment: 11 pages, 12 figures, submitted to Review Of Scientific Instrument

Volumes of Restricted Minkowski Sums and the Free Analogue of the Entropy Power Inequality

In noncommutative probability theory independence can be based on free products instead of tensor products. This yields a highly noncommutative theory: free probability . Here we show that the classical Shannon's entropy power inequality has a counterpart for the free analogue of entropy . The free entropy (introduced recently by the second named author), consistently with Boltzmann's formula $S=k\log W$, was defined via volumes of matricial microstates. Proving the free entropy power inequality naturally becomes a geometric question. Restricting the Minkowski sum of two sets means to specify the set of pairs of points which will be added. The relevant inequality, which holds when the set of "addable" points is sufficiently large, differs from the Brunn-Minkowski inequality by having the exponent $1/n$ replaced by $2/n$. Its proof uses the rearrangement inequality of Brascamp-Lieb-L\"uttinger

Nationaal voorzorgsbeleid over magnetische velden van hoogspanningslijnen in België, Frankrijk, Duitsland, Nederland en het Verenigd Koninkrijk

Scientific research points to a possibly increased risk of childhood leukaemia in children who live near overhead power lines. Because of statistical uncertainties and the fact that the disease mechanism is not known, it is not clear whether the magnetic fields of the power lines are the cause. Out of precaution, the Netherlands and several other European countries have developed policies several years ago that aim to reduce the exposure to magnetic fields from new power lines. Different countries deal in different ways with the uncertainties in the available knowledge and strike a different balance between scientific evidence and social, economic and political arguments. These are the findings of an investigation by the National Institute of Public Health and the Environment (RIVM). The report clarifies the policy in the Netherlands on magnetic fields from power lines and compares it with the policies in four nearby countries (Belgium, France, Germany and the United Kingdom). These countries differ in the applied limits and in the locations and types of electricity infrastructure to which the policy applies. For example, the policy in the United Kingdom is the most restrained and is aimed at informing the public and changing the connectivity (phasing) of power lines, for example in power stations, which weakens the magnetic field. Further measures are not deemed proportional to the possible risk. Germany applies a policy that aims to minimise magnetic fields from a broader range of electricity infrastructure, for example also for switch stations and the overhead wires of railways.Wetenschappelijk onderzoek wijst op een mogelijk verhoogd risico op leukemie bij kinderen die in de buurt van bovengrondse hoogspanningslijnen wonen. Door statistische onzekerheden en het onbekende ziektemechanisme is het niet duidelijk of de magnetische velden van de hoogspanningslijnen daar de oorzaak van zijn. Uit voorzorg hebben Nederland en enkele andere Europese landen enkele jaren geleden beleid opgezet om de blootstelling aan de magnetische velden van nieuwe hoogspanningslijnen te beperken. Landen blijken verschillend om te gaan met de onzekerheden in de beschikbare kennis en maken voor hun beleid andere afwegingen tussen de wetenschappelijke bewijslast en sociale, economische en politieke argumenten. Dit blijkt uit onderzoek van het RIVM. Hierin is het Nederlandse beleid over magneetvelden van hoogspanningslijnen verduidelijkt en vergeleken met het beleid in vier omringende landen (België, Duitsland, Frankrijk, Verenigd Koninkrijk). De landen verschillen in de gebruikte limieten en op welke locaties en welk type elektriciteitsvoorzieningen het beleid van toepassing is. Het Verenigd Koninkrijk is bijvoorbeeld het meest terughoudend in beleid en richt zich op publieksvoorlichting en op aanpassingen in de aansluitingpunten van de draden van de hoogspanningslijnen, bijvoorbeeld in de centrale, waardoor het magneetveld zwakker wordt. Verdergaande maatregelen vinden zij niet in verhouding staan tot het mogelijke risico. Duitsland hanteert een beleid dat in bredere zin is ingestoken op het minimaliseren van magnetische velden, dus ook voor bijvoorbeeld transformatorstations en bovenleidingen van treinen.Ministerie van I&