Emergence of pulled fronts in fermionic microscopic particle models

We study the emergence and dynamics of pulled fronts described by the Fisher-Kolmogorov-Petrovsky-Piscounov (FKPP) equation in the microscopic reaction-diffusion process A + A A$ on the lattice when only a particle is allowed per site. To this end we identify the parameter that controls the strength of internal fluctuations in this model, namely, the number of particles per correlated volume. When internal fluctuations are suppressed, we explictly see the matching between the deterministic FKPP description and the microscopic particle model.Comment: 4 pages, 4 figures. Accepted for publication in Phys. Rev. E as a Rapid Communicatio

Discreteness effects in a reacting system of particles with finite interaction radius

An autocatalytic reacting system with particles interacting at a finite distance is studied. We investigate the effects of the discrete-particle character of the model on properties like reaction rate, quenching phenomenon and front propagation, focusing on differences with respect to the continuous case. We introduce a renormalized reaction rate depending both on the interaction radius and the particle density, and we relate it to macroscopic observables (e.g., front speed and front thickness) of the system.Comment: 23 pages, 13 figure

High reflectivity grating waveguide coatings for 1064nm

We propose thin single-layer grating waveguide structures to be used as high-reflectivity, but low thermal noise, alternative to conventional coatings for gravitational wave detector test mass mirrors. Grating waveguide (GWG) coatings can show a reflectivity of up to 100% with an overall thickness of less than a wavelength. We theoretically investigate GWG coatings for 1064nm based on tantala (Ta2O5) on a Silica substrate focussing on broad spectral response and low thickness

Elastic fluctuations as observed in a confocal slice

Recent confocal experiments on colloidal solids motivate a fuller study of the projection of three-dimensional fluctuations onto a two-dimensional confocal slice. We show that the effective theory of a projected crystal displays several exceptional features, such as non-standard exponents in the dispersion relations. We provide analytic expressions for the effective two-dimensional elastic properties which allow one to work back from sliced experimental observations to three-dimensional elastic constants.Comment: 5 pages, 2 figure

Fluctuating "Pulled" Fronts: the Origin and the Effects of a Finite Particle Cutoff

Recently it has been shown that when an equation that allows so-called pulled fronts in the mean-field limit is modelled with a stochastic model with a finite number $N$ of particles per correlation volume, the convergence to the speed $v^*$ for $N \to \infty$ is extremely slow -- going only as $\ln^{-2}N$. In this paper, we study the front propagation in a simple stochastic lattice model. A detailed analysis of the microscopic picture of the front dynamics shows that for the description of the far tip of the front, one has to abandon the idea of a uniformly translating front solution. The lattice and finite particle effects lead to a ``stop-and-go'' type dynamics at the far tip of the front, while the average front behind it ``crosses over'' to a uniformly translating solution. In this formulation, the effect of stochasticity on the asymptotic front speed is coded in the probability distribution of the times required for the advancement of the ``foremost bin''. We derive expressions of these probability distributions by matching the solution of the far tip with the uniformly translating solution behind. This matching includes various correlation effects in a mean-field type approximation. Our results for the probability distributions compare well to the results of stochastic numerical simulations. This approach also allows us to deal with much smaller values of $N$ than it is required to have the $\ln^{-2}N$ asymptotics to be valid.Comment: 26 pages, 11 figures, to appear in Phys. rev.

Ethnicity, voter alignment and political party affiliation - an African case: Zambia

Conventional wisdom holds that ethnicity provides the social cleavage for voting behav-iour and party affiliation in Africa. Because this is usually inferred from aggregate data of national election results, it might prove to be an ecological fallacy. The evidence based on individual data from an opinion survey in Zambia suggests that ethnicity matters for voter alignment and even more so for party affiliation, but it is certainly not the only factor. The analysis also points to a number of qualifications which are partly methodology-related. One is that the degree of ethnic voting can differ from one ethno-political group to the other depending on various degrees of ethnic mobilisation. Another is that if smaller eth-nic groups or subgroups do not identify with one particular party, it is difficult to find a significant statistical correlation between party affiliation and ethnicity - but that does not prove that they do not affiliate along ethnic lines.Wahlverhalten und Mitgliedschaft in politischen Parteien Afrikas ist nur wenig untersucht worden. Gewöhnlich wird argumentiert, dass Ethnizität als soziale Konfliktlinie das Wahlverhalten und die Parteienmitgliedschaft strukturiert. Da dieses Argument auf hoch aggregierten Wahldaten beruht, kann hier ein ökologischer Fehlschuss vorliegen. Die vorliegende Analyse beruht deshalb auf individuellen Umfragedaten aus Sambia. Das Ergebnis ist, dass Ethnizität tatsächlich eine Rolle für das Wahlverhalten und die Parteienmitgliedschaft spielt, aber keineswegs den einzigen Erklärungsfaktor darstellt. Die Analyse offenbart zudem eine Reihe von Einschränkungen und Qualifizierungen, die teilweise methodischer Natur sind. Eine ist, dass ethnisches Wahlverhalten und Parteienmitgliedschaft von einer ethnischen Gruppe zur anderen unterschiedlich ist, dass, wenn sich kleinere ethnische Gruppen oder Untergruppen mit keiner Partei identifizieren, es schwierig wird, statistisch signifikante Korrelationen zu finden - was indessen noch nicht beweist, dass Ethnizität keine Rolle spielt

The Early Local and Regional Immune Response to Recall Inoculations of Mycobacterium Leprae in the Skin of Rhesus Macaques (Macaca Mulatta).

Epidemiological studies have failed to show any important impact of human immunodeficiency virus (HIV) infection and disease on leprosy, in contrast to the well documented increase in incidence and morbidity with other mycobacteria in these patients, notably Mycobacterium tuberculosis. The early events following exposure and repeated exposure to Mycobacterium leprae (ML) have not still been studied. Previous studies of first inoculations of ML in the skin of rhesus monkeys have indicated delayed recruitment of CD4+ cells and delayed interleukin (IL) 2 secretion in skin inoculation sites in simian immunodeficiency (SIV) positive animals. The development of the secondary immune response against a challenge of ML was studied over a period of 2 months in the skin of 9 rhesus macaques, all inoculated previously with ML, 3 of which were SIV positive slow progressors. Cell recruitment and types of cytokine response in the skin and draining lymph nodes (LN) were investigated using flow cytometry (FC), immunohistochemistry, and reverse transcription polymerase chain reaction to detect relative levels of messenger ribonucleic acid (mRNA) expression for IL2, IL4, interferon gamma (IFNgamma) and IL10. Results were analyzed according to SIV status and persistence of ML infection. An early vigorous expression of IL2 and IFNgamma mRNA, indicative of a strong T helper (Th) 1 cytokine profile, was seen in the skin of macaques that cleared ML infection. Animals that developed persistent ML infection (ML+) had delayed, weak Th1 response, and no evidence of early Th2 response in the skin. In contrast, early up regulation of IL4 was only observed in the LN of ML+ macaques. Recruitment of CD4+ lymphocytes into the skin was significantly lower and delayed in ML+ animals. CD4:CD8 ratio were significantly lower in the blood in SIV+ monkeys. However, no significant differences in CD4+ lymphocyte recruitment or expression of cytokine mRNA were observed between SIV- and SIV+ monkeys. Despite evidence of systemic immunodepression, the slow progressing SIV+ rhesus macaques are still capable of mounting an adequate response to ML re-inoculation in the skin. A Th2 response is not generated in the skin early after re-infection in animals which developed progressive infection

The Benefits and Harms of Transmitting Into Space

Deliberate and unintentional radio transmissions from Earth propagate into space. These transmissions could be detected by extraterrestrial watchers over interstellar distances. Here, we analyze the harms and benefits of deliberate and unintentional transmissions relevant to Earth and humanity. Comparing the magnitude of deliberate radio broadcasts intended for messaging to extraterrestrial intelligence (METI) with the background radio spectrum of Earth, we find that METI attempts to date have much lower detectability than emissions from current radio communication technologies on Earth. METI broadcasts are usually transient and several orders of magnitude less powerful than other terrestrial sources such as astronomical and military radars, which provide the strongest detectable signals. The benefits of radio communication on Earth likely outweigh the potential harms of detection by extraterrestrial watchers; however, the uncertainty regarding the outcome of contact with extraterrestrial beings creates difficulty in assessing whether or not to engage in long-term and large-scale METI.Comment: Published in Space Polic

Major flaws in conflict prevention policies towards Africa : the conceptual deficits of international actors’ approaches and how to overcome them

Current thinking on African conflicts suffers from misinterpretations oversimplification, lack of focus, lack of conceptual clarity, state-centrism and lack of vision). The paper analyses a variety of the dominant explanations of major international actors and donors, showing how these frequently do not distinguish with sufficient clarity between the ‘root causes’ of a conflict, its aggravating factors and its triggers. Specifically, a correct assessment of conflict prolonging (or sustaining) factors is of vital importance in Africa’s lingering confrontations. Broader approaches (e.g. “structural stability”) offer a better analytical framework than familiar one-dimensional explanations. Moreover, for explaining and dealing with violent conflicts a shift of attention from the nation-state towards the local and sub-regional level is needed.Aktuelle Analysen afrikanischer Gewaltkonflikte sind häufig voller Fehlinterpretationen (Mangel an Differenzierung, Genauigkeit und konzeptioneller Klarheit, Staatszentriertheit, fehlende mittelfristige Zielvorstellungen). Breitere Ansätze (z. B. das Modell der Strukturellen Stabilität) könnten die Grundlage für bessere Analyseraster und Politiken sein als eindimensionale Erklärungen. häufig differenzieren Erklärungsansätze nicht mit ausreichender Klarheit zwischen Ursachen, verschärfenden und auslösenden Faktoren. Insbesondere die richtige Einordnung konfliktverlängernder Faktoren ist in den jahrzehntelangen gewaltsamen Auseinandersetzungen in Afrika von zentraler Bedeutung. Das Diskussionspapier stellt die große Variationsbreite dominanter Erklärungsmuster der wichtigsten internationalen Geber und Akteure gegenüber und fordert einen Perspektivenwechsel zum Einbezug der lokalen und der subregionalen Ebene für die Erklärung und Bearbeitung gewaltsamer Konflikte

Switchable Windows - Spectral Transmission and Switching Times

The switching time and spectral transmission in fully clear and fully opaque states of polymer dispersed liquid crystals (PDLC), suspended particle device (SPD) and electrochromic (EC) switchable windows were evaluated to assess their suitability to control solar heat transmission though glazed façade and comfort to building occupants. The transmission measurement on a SPD film showed a very effective absorption modulation in the visible range but fast decrease in the near infrared region. The switching speed was demonstrated to be related strongly to wavelengths. A SPD film with a larger absorption and faster switching speed in the infrared region was shown to be preferable to control solar heat transfer through glazings and thermal comfort. The PDLC window did not modulate transmission but rather modulated scattering. In the opaque state, the PDLC window was highly scattering resulting in spectral transmission varying at short distances from the window while being constant in the far field. The switching speed measurement demonstrated that liquid-based switchable windows can respond as fast as the eye to have the potential to control spontaneous glare. The EC window demonstrated a lower absorbance efficiency than the SPD in the visible range but appeared to have a much higher efficiency in the infrared region measured. EC windows are characterized by their slow switching speed when compared to SPD and PDLC. This makes them unsuitable for spontaneous glare control and are more suited to predictive solar heat gain control over a defined time horizon. With the increasing integration of adaptive technologies into building facades and to predict the energetical and ambient performance of such buildings and the impact on the occupants’ comfort, this paper emphasises on the importance to provide spectral performance information of switchable windows