57 research outputs found
Correlating Fourier phase information with real-space higher order statistics
We establish for the first time heuristic correlations between harmonic space
phase information and higher order statistics. Using the spherical full-sky
maps of the cosmic microwave background as an example we demonstrate that known
phase correlations at large spatial scales can gradually be diminished when
subtracting a suitable best-fit (Bianchi-) template map of given strength. The
weaker phase correlations lead in turn to a vanishing signature of anisotropy
when measuring the Minkowski functionals and scaling indices in real-space and
comparing them with surrogate maps being free of phase correlations. Those
investigations can open a new road to a better understanding of signatures of
non-Gaussianities in complex spatial structures by elucidating the meaning of
Fourier phase correlations and their influence on higher order statistics.Comment: 6 pages plus 1 supplemental page, 4 figures, submitte
Wake-mediated propulsion of an upstream particle in two-dimensional plasma crystals
The wake-mediated propulsion of an "extra" particle in a channel of two
neighboring rows of a two-dimensional plasma crystal, observed experimentally
by Du et al. [Phys. Rev. E 89, 021101(R) (2014)], is explained in simulations
and theory. We use the simple model of a pointlike ion wake charge to reproduce
this intriguing effect in simulations, allowing for a detailed investigation
and a deeper understanding of the underlying dynamics. We show that the
nonreciprocity of the particle interaction, owing to the wake charges, is
responsible for a broken symmetry of the channel that enables a persistent
self-propelled motion of the extra particle. We find good agreement of the
terminal extra-particle velocity with our theoretical considerations and with
experiments.Comment: 7 pages, 4 figures, PRL (https://journals.aps.org/prl/), updated
version with correct author affiliation
Probing non-Gaussianities in the CMB on an incomplete sky using surrogates
We demonstrate the feasibility to generate surrogates by Fourier-based
methods for an incomplete data set. This is performed for the case of a CMB
analysis, where astrophysical foreground emission, mainly present in the
Galactic plane, is a major challenge. The shuffling of the Fourier phases for
generating surrogates is now enabled by transforming the spherical harmonics
into a new set of basis functions that are orthonormal on the cut sky. The
results show that non-Gaussianities and hemispherical asymmetries in the CMB as
identified in several former investigations, can still be detected even when
the complete Galactic plane (|b| < 30{\deg}) is removed. We conclude that the
Galactic plane cannot be the dominant source for these anomalies. The results
point towards a violation of statistical isotropy.Comment: 9 pages, 13 figures, accepted by Physical Review
Network analysis of 3D complex plasma clusters in a rotating electric field
Network analysis was used to study the structure and time evolution of driven
three-dimensional complex plasma clusters. The clusters were created by
suspending micron-size particles in a glass box placed on top of the rf
electrode in a capacitively coupled discharge. The particles were highly
charged and manipulated by an external electric field that had a constant
magnitude and uniformly rotated in the horizontal plane. Depending on the
frequency of the applied electric field, the clusters rotated in the direction
of the electric field or remained stationary. The positions of all particles
were measured using stereoscopic digital in-line holography. The network
analysis revealed the interplay between two competing symmetries in the
cluster. The rotating cluster was shown to be more cylindrical than the
nonrotating cluster. The emergence of vertical strings of particles was also
confirmed.Comment: 9 pages, 9 figures; corrected Fig.4 and typo
Dynamics of lane formation in driven binary complex plasmas
The dynamical onset of lane formation is studied in experiments with binary
complex plasmas under microgravity conditions. Small microparticles are driven
and penetrate into a cloud of big particles, revealing a strong tendency
towards lane formation. The observed time-resolved lane formation process is in
good agreement with computer simulations of a binary Yukawa model with Langevin
dynamics. The laning is quantified in terms of the anisotropic scaling index,
leading to a universal order parameter for driven systems.Comment: 4 pages, 3 figures, movies available at
http://www.mpe.mpg.de/pke/lane-formation
Network analysis of 3D complex plasma clusters
Network analysis was used to study the structure and time evolution of driven
three-dimensional complex plasma clusters. The clusters were created by suspending
micron-size particles in a glass box placed on top of the rf electrode in
a capacitively coupled discharge. The particles were highly charged and manipulated
by an external electric �eld that had a constant magnitude and rotated
uniformly in the horizontal plane. Depending on the frequency of the applied electric
�eld, the clusters rotated in the direction of the electric �eld or remained stationary.
The three-dimensional positions of all particles were measured using stereoscopic
digital in-line holography.
The network approach was used to elucidate the structural changes in the cluster
consisting only of a very limited number of particles (64). The Analysis revealed an
interplay between two competing symmetries in the cluster. Spherical and cylindrical
ordering of the particles was examined by comparing network measures of the
experimental data with null models. The null models were arti�cial data with a certain
number of points in perfectly spherical order, and the rest in cylindrical order.
The well established network measures local connectivity, clustering coe�cient and
average path length were considered. Network analysis of the clusters showed
that the rotating cluster was more cylindrical than the nonrotating cluster.
These �ndings were in agreement with the estimate of the radial con�nement
with the aid of a dynamical force balance. Neglecting friction and inertial forces due
to the low particle velocities in the cluster, the pro�le of the electrical con�nement
could be estimated by calculating the repulsing Yukawa-type interaction between
the particles. The radial con�nement was shown to be stronger in the case of cluster
rotation, increasing the cylindricity of the cluster.
The emergence of vertical strings of particles was also con�rmed by using a network
analysis. While the traditional method of a �xed threshold has limitations such
as erroneously including passing by particles and a somewhat arbitrary threshold,
community �nding algorithms yield a more elegant approach of �nding structures
in complex systems. With the aid of multislice networks, it is possible to examine
the whole time series at once and thus resolve the time evolution of the strings.
As we demonstrated, network analysis is a powerful tool to analyze the structure
of complex plasma clusters and may have numerous applications in other complex
systems where the characertization of the spatial structure plays a vital role.
An overview of the current status of CMB observations
In this paper we briefly review the current status of the Cosmic Microwave
Background (CMB) observations, summarising the latest results obtained from CMB
experiments, both in intensity and polarization, and the constraints imposed on
the cosmological parameters. We also present a summary of current and future
CMB experiments, with a special focus on the quest for the CMB B-mode
polarization.Comment: Latest CMB results have been included. References added. To appear in
"Highlights of Spanish Astrophysics V", Proceedings of the VIII Scientific
Meeting of the Spanish Astronomical Society (SEA) held in Santander, 7-11
July, 200
Natural products as starting points for future anti-malarial therapies: going back to our roots?
Abstract Background The discovery and development of new anti-malarials are at a crossroads. Fixed dose artemisinin combination therapy is now being used to treat a hundred million children each year, with a cost as low as 30 cents per child, with cure rates of over 95%. However, as with all anti-infective strategies, this triumph brings with it the seeds of its own downfall, the emergence of resistance. It takes ten years to develop a new medicine. New classes of medicines to combat malaria, as a result of infection by Plasmodium falciparum and Plasmodium vivax are urgently needed. Results Natural product scaffolds have been the basis of the majority of current anti-malarial medicines. Molecules such as quinine, lapachol and artemisinin were originally isolated from herbal medicinal products. After improvement with medicinal chemistry and formulation technologies, and combination with other active ingredients, they now make up the current armamentarium of medicines. In recent years advances in screening technologies have allowed testing of millions of compounds from pharmaceutical diversity for anti-malarial activity in cellular assays. These initiatives have resulted in thousands of new sub-micromolar active compounds – starting points for new drug discovery programmes. Against this backdrop, the paucity of potent natural products identified has been disappointing. Now is a good time to reflect on the current approach to screening herbal medicinal products and suggest revisions. Nearly sixty years ago, the Chinese doctor Chen Guofu, suggested natural products should be approached by dao-xing-ni-shi or ‘acting in the reversed order’, starting with observational clinical studies. Natural products based on herbal remedies are in use in the community, and have the potential unique advantage that clinical observational data exist, or can be generated. The first step should be the confirmation and definition of the clinical activity of herbal medicinal products already used by the community. This first step forms a solid basis of observations, before moving to in vivo pharmacological characterization and ultimately identifying the active ingredient. A large part of the population uses herbal medicinal products despite limited numbers of well-controlled clinical studies. Increased awareness by the regulators and public health bodies of the need for safety information on herbal medicinal products also lends support to obtaining more clinical data on such products. Conclusions The relative paucity of new herbal medicinal product scaffolds active against malaria results discovered in recent years suggest it is time to re-evaluate the ‘smash and grab’ approach of randomly testing purified natural products and replace it with a patient-data led approach. This will require a change of perspective form many in the field. It will require an investment in standardisation in several areas, including: the ethnopharmacology and design and reporting of clinical observation studies, systems for characterizing anti-malarial activity of patient plasma samples ex vivo followed by chemical and pharmacological characterisation of extracts from promising sources. Such work falls outside of the core mandate of the product development partnerships, such as MMV, and so will require additional support. This call is timely, given the strong interest from researchers in disease endemic countries to support the research arm of a malaria eradication agenda. Para-national institutions such as the African Network for Drugs and Diagnostics Innovation (ANDi) will play a major role in facilitating the development of their natural products patrimony and possibly clinical best practice to bring forward new therapeutics. As in the past, with quinine, lapinone and artemisinin, once the activity of herbal medicinal products in humans is characterised, it can be used to identify new molecular scaffolds which will form the basis of the next generation of anti-malarial therapies.</p
In vitro susceptibility of Plasmodium falciparum Welch field isolates to infusions prepared from Artemisia annua L. cultivated in the Brazilian Amazon
Artemisinin is the active antimalarial compound obtained from the leaves of Artemisia annua L. Artemisinin, and its semi-synthetic derivatives, are the main drugs used to treat multi-drug-resistant Plasmodium falciparum (one of the human malaria parasite species). The in vitro susceptibility of P. falciparum K1 and 3d7 strains and field isolates from the state of Amazonas, Brazil, to A. annua infusions (5 g dry leaves in 1 L of boiling water) and the drug standards chloroquine, quinine and artemisinin were evaluated. The A. annua used was cultivated in three Amazon ecosystems (várzea, terra preta de índio and terra firme) and in the city of Paulínia, state of São Paulo, Brazil. Artemisinin levels in the A. annua leaves used were 0.90-1.13% (m/m). The concentration of artemisinin in the infusions was 40-46 mg/L. Field P. falciparum isolates were resistant to chloroquine and sensitive to quinine and artemisinin. The average 50% inhibition concentration values for A. annua infusions against field isolates were 0.11-0.14 μL/mL (these infusions exhibited artemisinin concentrations of 4.7-5.6 ng/mL) and were active in vitro against P. falciparum due to their artemisinin concentration. No synergistic effect was observed for artemisinin in the infusions
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