2,023 research outputs found
DNA binding of dinuclear iron(II) metallosupramolecular cylinders. DNA unwinding and sequence preference
[Fe2L3]4+ (L = C25H20N4) is a synthetic tetracationic supramolecular cylinder (with a triple helical architecture) that targets the major groove of DNA and can bind to DNA Y-shaped junctions. To explore the DNA-binding mode of [Fe2L3]4+, we examine herein the interactions of pure enantiomers of this cylinder with DNA by biochemical and molecular biology methods. The results have revealed that, in addition to the previously reported bending of DNA, the enantiomers extensively unwind DNA, with the M enantiomer being the more efficient at unwinding, and exhibit preferential binding to regular alternating purineāpyrimidine sequences, with the M enantiomer showing a greater preference. Also, interestingly, the DNA binding of bulky cylinders [Fe2(L-CF3)3]4+ and [Fe2(L-Ph)3]4+ results in no DNA unwinding and also no sequence preference of their DNA binding was observed. The observation of sequence-preference in the binding of these supramolecular cylinders suggests that a concept based on the use of metallosupramolecular cylinders might result in molecular designs that recognize the genetic code in a sequence-dependent manner with a potential ability to affect the processing of the genetic code
Nearest neighbour models for local and regional avalanche forecasting
International audienceThis paper presents two avalanche forecasting applications NXD2000 and NXD-REG which were developed at the Swiss Federal Institute for Snow and Avalanche Re-search (SLF). Even both are based on the nearest neighbour method they are targeted to different scales. NXD2000 is used to forecast avalanches on a local scale. It is operated by avalanche forecasters responsible for snow safety at snow sport areas, villages or cross country roads. The area covered ranges from 10 km2 up to 100 km2 depending on the climatological homogeneity. It provides the forecaster with ten most similar days to a given situation. The observed avalanches of these days are an indication of the actual avalanche danger. NXD-REG is used operationally by the Swiss avalanche warning service for regional avalanche forecasting. The Nearest Neighbour approach is applied to the data sets of 60 observer stations. The results of each station are then compiled into a map of current and future avalanche hazard. Evaluation of the model by cross-validation has shown that the model can reproduce the official SLF avalanche forecasts in about 52% of the days
Disordered Carbon nanotube alloys in the Effect Medium Super Cell Approximation
We investigate a disordered single-walled carbon nanotube (SWCNT) in an
effective medium super cell approximation (EMSCA).
First type of disorder that we consider is the presence of vacancies.
Our results show that the vacancies induce some bound states on their
neighbor host sites, leading to the creation of a band around the Fermi energy
in the SWCNT average density of states.Second type of disorder considered is a
substitutional alloy due to it's applications in
hetrojunctions. We found that for a fixed boron (nitrogen) concentration, by
increasing the nitrogen (boron) concentration the averaged semiconducting gap,
, decreases and at a critical concentration it disappears. A consequence
of our results for nano electronic devices is that by changing the
boron(nitrogen) concentration, one can make a semiconductor SWCNT with a
pre-determined energy gap.Comment: 4 page
Sub two-cycle soliton-effect pulse compression at 800 nm in Photonic Crystal Fibers
The possibility of soliton self-compression of ultrashort laser pulses down
to the few-cycle regime in photonic crystal fibers is numerically investigated.
We show that efficient sub-two-cycle temporal compression of nanojoule-level
800 nm pulses can be achieved by employing short (typically 5-mm-long)
commercially available photonic crystal fibers and pulse durations of around
100 fs, regardless of initial linear chirp, and without the need of additional
dispersion compensation techniques. We envisage applications in a new
generation of compact and efficient sub-two cycle laser pulse sources.Comment: 16 pages, 6 figure
Modulation Instability of Ultrashort Pulses in Quadratic Nonlinear Media beyond the Slowly Varying Envelope Approximation
We report a modulational instability (MI) analysis of a mathematical model
appropriate for ultrashort pulses in cascaded quadratic-cubic nonlinear media
beyond the so-called slowly varying envelope approximation. Theoretically
predicted MI properties are found to be in good agreement with numerical
simulation. The study shows the possibility of controlling the generation of MI
and formation of solitons in a cascaded quadratic-cubic media in the few cycle
regimes. We also find that stable propagation of soliton-like few-cycle pulses
in the medium is subject to the fulfilment of the modulation instability
criteria
Plasmon signatures in high harmonic generation
High harmonic generation in polarizable multi-electron systems is
investigated in the framework of multi-configuration time-dependent
Hartree-Fock. The harmonic spectra exhibit two cut offs. The first cut off is
in agreement with the well established, single active electron cut off law. The
second cut off presents a signature of multi-electron dynamics. The strong
laser field excites non-linear plasmon oscillations. Electrons that are ionized
from one of the multi-plasmon states and recombine to the ground state gain
additional energy, thereby creating the second plateau.Comment: Major revision, 12 pages, 5 figures, submitted to J. Phys. B (2005),
accepte
Climate and disease in historical urban space: evidence from 19th century PoznaÅ, Poland
This study examines the relationship between temperature levels and precipitation amounts as explanatory variables for the probability of death due to waterborne and airborne diseases in historical urban space. To date, the literature has not focused on the climatological epidemiology of 19th century Polish urban areas. We used individual mortality data from PoznaÅ parish death registers between 1850 and 1900. Each deceased individual was assigned average monthly temperature values and precipitation amounts in the month of death, LAG1 (1-month-lagged) temperature and LAG1 rainfall, and place of residence. We studied the relationship between weather conditions and mortality using formalized statistical models reflecting the discrete nature of the response data (via multinomial logistic regression). Lagged monthly average temperature levels and lagged monthly average precipitation amounts were better predictors of airborne and waterborne disease mortality than the concurrent (non-lagged) monthly averages. The lagged effects of temperature and precipitation on waterborne and airborne diseases were significant (except for the smooth lagged average monthly temperature effect for airborne diseases). There was also significant spatial heterogeneity (differences among city quarters) in the prevalence of deaths due to waterborne and airborne diseases.</p
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