Evacuation in the Social Force Model is not stationary

An evacuation process is simulated within the Social Force Model. Thousand pedestrians are leaving a room by one exit. We investigate the stationarity of the distribution of time lags between instants when two successive pedestrians cross the exit. The exponential tail of the distribution is shown to gradually vanish. Taking fluctuations apart, the time lags decrease in time till there are only about 50 pedestrians in the room, then they start to increase. This suggests that at the last stage the flow is laminar. In the first stage, clogging events slow the evacuation down. As they are more likely for larger crowds, the flow is not stationary. The data are investigated with detrended fluctuation analysis.Comment: 7 pages, 3 figures; PACS numbers: 89.75.Fb, 05.40.-a, 05.45.Tp, 89.40.B

Survey of Planetary Nebulae at 30 GHz with OCRA-p

We report the results of a survey of 442 planetary nebulae at 30 GHz. The purpose of the survey is to develop a list of planetary nebulae as calibration sources which could be used for high frequency calibration in future. For 41 PNe with sufficient data, we test the emission mechanisms in order to evaluate whether or not spinning dust plays an important role in their spectra at 30 GHz. The 30-GHz data were obtained with a twin-beam differencing radiometer, OCRA-p, which is in operation on the Torun 32-m telescope. Sources were scanned both in right ascension and declination. We estimated flux densities at 30 GHz using a free-free emission model and compared it with our data. The primary result is a catalogue containing the flux densities of 93 planetary nebulae at 30 GHz. Sources with sufficient data were compared with a spectral model of free-free emission. The model shows that free-free emission can generally explain the observed flux densities at 30 GHz thus no other emission mechanism is needed to account for the high frequency spectra.Comment: 10 pages, 7 Postscript figures, to be published in A&

Cross-talk between high light stress and plant defence to the two-spotted spider mite in Arabidopsis thaliana

Little is known about how plants deal with arthropod herbivores under the fluctuating light intensity and spectra which occur in natural environments. Moreover, the role of simultaneous stress such as excess light (EL) in the regulation of plant responses to herbivores is poorly characterized. In the current study, we focused on a mite-herbivore, specifically, the two-spotted spider mite (TSSM), which is one of the major agricultural pests worldwide. Our results showed that TSSM-induced leaf damage (visualized by trypan blue staining) and oviposition rate (measured as daily female fecundity) decreased after EL pre-treatment in wild-type Arabidopsis plants, but the observed responses were not wavelength specific. Thus, we established that EL pre-treatment reduced Arabidopsis susceptibility to TSSM infestation. Due to the fact that a portion of EL energy is dissipated by plants as heat in the mechanism known as non-photochemical quenching (NPQ) of chlorophyll fluorescence, we tested an Arabidopsis npq4-1 mutant impaired in NPQ. We showed that npq4-1 plants are significantly less susceptible to TSSM feeding activity, and this result was not dependent on light pre-treatment. Therefore, our findings strongly support the role of light in plant defence against TSSM, pointing to a key role for a photo-protective mechanism such as NPQ in this regulation. We hypothesize that plants impaired in NPQ are constantly primed to mite attack, as this seems to be a universal evolutionarily conserved mechanism for herbivores

The usefulness of selected linden species (Tilia sp.) for phytoremediation of airborne particulate matter

Rozwijające się urbanizacja, transport i przemysł są źródłem zanieczyszczeń mikropyłowych, które wpływają na pogorszenie jakości powietrza i stanowią zagrożenie dla zdrowia mieszkańców. Drzewa są coraz bardziej doceniane jako naturalne filtry powietrza oczyszczające je z zanieczyszczeń mikropyłowych. Lipy to drzewa bardzo często spotykane w miastach, zarówno w parkach, jak i przy ulicach naszej strefy klimatycznej. W niniejszej pracy porównano wybrane gatunki i odmiany lip, różniące się wyglądem i wymaganiami pod względem ich zdolności do akumulacji zanieczyszczeń mikropyłowych. W doświadczeniach sprawdzano ilość pyłów o średnicy aerodynamicznej cząstek 10−100 μm, 2,5−10 μm oraz 0,2−2,5 μm, jakie zgromadziły się na powierzchni liści i w woskach. Najlepszym fitoremediantem okazała się Tilia cordata Mill. (lipa drobnolistna). Liście lipy holenderskiej „Pallida” również bardzo dobrze gromadziły zanieczyszczenia.Progressing urbanization, development of transport and industry are the sources of particulate matter, which decrease air quality and pose a threat to human health. Plants are the only natural organizm to clean the air. Trees are more and more appreciated as natural air filters that remove particulate matter. Linden are very common in cites, in parks and even near streets in our climatic zone. In this paper, selected species of linden were compared in order to determine their ability to accumulate particulate matter. These linden trees have different morphology and requirements. The accumulation of particulate matter of the size: 10–100 μm, 2.5–10 μm and 0.2–2.5 μm was analysed within this study. Tilia cordata turned out to be the best phytoremediant. Tilia × Europe „Pallida” was also very good in accumulating particulate matter on its leaves