Longitudinal variations, the opposition effect and monochromatic albedos for Mars

Magnitude at zero phase, phase coefficient, and monochromatic albedo computed for Mars as function of wavelengt

Two-photon absorption and broadband optical limiting with bis-donor stilbenes

Large two-photon absorptivities are reported for symmetrical bis-donor stilbene derivatives with dialkylamino or diphenylamino groups. These molecules exhibit strong optical limiting of nanosecond pulses over a broad spectral range in the visible. Relative to bis(di-n-butylamino)stilbene, bis(diphenylamino)stilbene exhibits a 90-nm red shift of its optical limiting band but only a minimal shift of ~13 nm of its lowest one-photon electronic absorption band. Mixtures of these compounds offer an unprecedented combination of broad optical limiting bandwidth and high linear transparency

The MAHB, the Culture Gap, and Some Really Inconvenient Truths

Humanity's failure to take adequate actions to stem a likely environmental collapse calls for extraordinary measures to understand and alter human behavior, argues Paul Ehrlich. His Millennium Assessment of Human Behavior (MAHB) aims to chart the path to a sustainable future

Habitat conversion and global avian biodiversity loss

The magnitude of the impacts of human activities on global biodiversity has been documented at several organizational levels. However, although there have been numerous studies of the effects of local-scale changes in land use (e.g. logging) on the abundance of groups of organisms, broader continental or global-scale analyses addressing the same basic issues remain largely wanting. None the less, changing patterns of land use, associated with the appropriation of increasing proportions of net primary productivity by the human population, seem likely not simply to have reduced the diversity of life, but also to have reduced the carrying capacity of the environment in terms of the numbers of other organisms that it can sustain. Here, we estimate the size of the existing global breeding bird population, and then make a first approximation as to how much this has been modified as a consequence of land-use changes wrought by human activities. Summing numbers across different land-use classes gives a best current estimate of a global population of less than 100 billion breeding bird individuals. Applying the same methodology to estimates of original land-use distributions suggests that conservatively this may represent a loss of between a fifth and a quarter of pre-agricultural bird numbers. This loss is shared across a range of temperate and tropical land-use types

Rigid Singularity Theorem in Globally Hyperbolic Spacetimes

We show the rigid singularity theorem, that is, a globally hyperbolic spacetime satisfying the strong energy condition and containing past trapped sets, either is timelike geodesically incomplete or splits isometrically as space $\times$ time. This result is related to Yau's Lorentzian splitting conjecture.Comment: 3 pages, uses revtex.sty, to appear in Physical Review

Forest albedo in the context of different cloud situations derived from irradiance measurements at the Leipzig floodplain crane: A pilot study

The surface albedo significantly modulates the atmospheric energy budget and, thus, vertical radiation, energy, and mass fluxes. Therefore, it regulates the local and regional effects of climate warming. Over a forest canopy, the surface albedo mainly depends on the seasonal leaf state. Furthermore, for certain surface types, such as snow, it has been shown that the surface albedo changes as a function of cloudiness. A similar effect is expected over forest surfaces, leading to complex feedback loops between forest surfaces and climate. To investigate these processes, a pilot study was performed at the Leipzig floodplain crane to observe the forest canopy albedo under different atmospheric conditions in 2021. First analyses revealed a dependency of the forest albedo from the cloud state, which is slightly stronger in the near-infrared wavelength range compared to the visible wavelength range.Der atmosphärische Strahlungshaushalt und damit auch die vertikale Strahlungsverteilung, Energie- und Massenflüsse werden signifikant durch die Bodenalbedo gesteuert. Diese regulieren somit lokale und regionale Effekte der Klimaerwärmung. Über einem Wald hängt die Bodenalbedo hauptsächlich vom saisonalen Blattstatus ab. Zudem wurde für bestimmte Bodentypen wie Schneeoberflächen gezeigt, dass die Bodenalbedo eine Funktion der Bewölkung ist. Ähnlicher Effekte werden für Waldoberflächen erwartet, welche zu komplexen Rückkopplungseffekten zwischenWaldoberflächen und dem Klima führen. Um diese Prozesse zu untersuchen wurde im Jahr 2021 eine Vorstudie am Leipziger Auwaldkran durchgeführt, um die Waldalbedo unter verschiedenen atmosphärischen Bedingungen zu beobachten. Erste Analysen zeigen, dass auch die Albedo des Waldes von den Bewölkungsbedingungen abhängt. Der Effekt ist dabei etwas stärker im nah-infrarotem als im sichtbaren Wellenlängenbereich zu beobachten

Numerical test of the damping time of layer-by-layer growth on stochastic models

We perform Monte Carlo simulations on stochastic models such as the Wolf-Villain (WV) model and the Family model in a modified version to measure mean separation $\ell$ between islands in submonolayer regime and damping time $\tilde t$ of layer-by-layer growth oscillations on one dimension. The stochastic models are modified, allowing diffusion within interval $r$ upon deposited. It is found numerically that the mean separation and the damping time depend on the diffusion interval $r$, leading to that the damping time is related to the mean separation as ${\tilde t} \sim \ell^{4/3}$ for the WV model and ${\tilde t} \sim \ell^2$ for the Family model. The numerical results are in excellent agreement with recent theoretical predictions.Comment: 4 pages, source LaTeX file and 5 PS figure

Mounding Instability and Incoherent Surface Kinetics

Mounding instability in a conserved growth from vapor is analysed within the framework of adatom kinetics on the growing surface. The analysis shows that depending on the local structure on the surface, kinetics of adatoms may vary, leading to disjoint regions in the sense of a continuum description. This is manifested particularly under the conditions of instability. Mounds grow on these disjoint regions and their lateral growth is governed by the flux of adatoms hopping across the steps in the downward direction. Asymptotically ln(t) dependence is expected in 1+1- dimensions. Simulation results confirm the prediction. Growth in 2+1- dimensions is also discussed.Comment: 4 pages, 4 figure

Lattice Effects in Crystal Evaporation

We study the dynamics of a stepped crystal surface during evaporation, using the classical model of Burton, Cabrera and Frank, in which the dynamics of the surface is represented as a motion of parallel, monoatomic steps. The validity of the continuum approximation treated by Frank is checked against numerical calculations and simple, qualitative arguments. The continuum approximation is found to suffer from limitations related, in particular, to the existence of angular points. These limitations are often related to an adatom detachment rate of adatoms which is higher on the lower side of each step than on the upper side ("Schwoebel effect").Comment: DRFMC/SPSMS/MDN, Centre d'Etudes Nucleaires de Grenoble, 25 pages, LaTex, revtex style. 8 Figures, available upon request, report# UBFF30119

Ecological Impacts of Invasive Species

Nearly 6,500 nonnative species are present in the United States and are responsible for the extinction of over 760 native species. The introduction of invasive species is ongoing and the ecological ramifications of these invasions are diverse but could include competition between invasive and native species, disruption of natural ecological processes, and reduced ecosystem services. While invasive species are able to severely damage vital ecosystems, there are methods of predicting and lessening the impacts. Our goal is to educate our campus community about the impact of invasive species on native ecosystems, including the dangers of invasive species, and how we can prevent future invasions. To accomplish this, we conducted an extensive literature review to examine how invasive species are controlled and managed, and how current preventative measures can be improved upon. We hypothesize that a greater focus on successful preventative measurements will reflect a decrease in overall human transportation and the spread of invasive species. The connection between conservation and invasive species plays an important role in understanding and implementing preventative actions in ecosystems that are potentially susceptible to invasive species and is critical to protecting and maintaining biodiversity on our planet