198 research outputs found
The Mass Function of Nearby Galaxy Clusters
We present the distribution of virial masses for nearby galaxy clusters, as
obtained from a data-set of 75 clusters, each having at least 20 galaxy members
with measured redshifts within 1 Abell radius. After having accounted for
problems of incompleteness of the data-set, we fitted a power-law to the
cluster mass distribution.Comment: 10 pages (2 figures not included, available upon request), LATEX,
Ref.SISSA 54/93/
Structures in Galaxy Clusters
The analysis of the presence of substructures in 16 well-sampled clusters of
galaxies suggests a stimulating hypothesis: Clusters could be classified as
unimodal or bimodal, on the basis of to the sub-clump distribution in the {\em
3-D} space of positions and velocities. The dynamic study of these clusters
shows that their fundamental characteristics, in particular the virial masses,
are not severely biased by the presence of subclustering if the system
considered is bound.Comment: (16 pages in LATEX, 4 tables in LATEX are at the end of the file, the
figures not included are available upon request), REF SISSA 158/93/
Automation of orbit determination functions for National Aeronautics and Space Administration (NASA)-supported satellite missions
The Flight Dynamics Facility (FDF) at Goddard Space Flight Center (GSFC) provides spacecraft trajectory determination for a wide variety of National Aeronautics and Space Administration (NASA)-supported satellite missions, using the Tracking Data Relay Satellite System (TDRSS) and Ground Spaceflight and Tracking Data Network (GSTDN). To take advantage of computerized decision making processes that can be used in spacecraft navigation, the Orbit Determination Automation System (ODAS) was designed, developed, and implemented as a prototype system to automate orbit determination (OD) and orbit quality assurance (QA) functions performed by orbit operations. Based on a machine-resident generic schedule and predetermined mission-dependent QA criteria, ODAS autonomously activates an interface with the existing trajectory determination system using a batch least-squares differential correction algorithm to perform the basic OD functions. The computational parameters determined during the OD are processed to make computerized decisions regarding QA, and a controlled recovery process isactivated when the criteria are not satisfied. The complete cycle is autonomous and continuous. ODAS was extensively tested for performance under conditions resembling actual operational conditions and found to be effective and reliable for extended autonomous OD. Details of the system structure and function are discussed, and test results are presented
Velocity Dispersions and X-Ray Temperatures of Galaxy Clusters
Using a large and well-controlled sample of clusters of galaxies, we
investigate the relation between cluster velocity dispersions and X-ray
temperatures of intra-cluster gas. In order to obtain a reliable estimate of
the total velocity dispersion of a cluster, independent of the level of
anisotropies in galaxy orbits, we analyze the integrated velocity dispersion
profiles over increasing distances from the cluster centers. Distortions in the
velocity fields, the effect of close clusters, the presence of substructures,
and the presence of a population of (spiral) galaxies not in virial equilibrium
with the cluster potential are taken into account. Using our final sample of 37
clusters, for which a reliable estimate of the velocity dispersion could be
obtained, we derive a relation between the velocity dispersions and the X-ray
temperatures, with a scatter reduced by more than 30 % with respect to previous
works. A chi square fit to the temperature-velocity dispersion relation does
not exclude the hypothesis that the ratio between galaxy and gas energy density
(the so-called spectral beta) is a constant for all clusters. In particular,
the value of beta=1, corresponding to energy equipartition, is acceptable.Comment: 13 pages, uuencoded gzipped postscript file, fig.1 available upon
request, to appear in ApJ on 20th December 1995, corrected misprint in table
Novel algorithms and high-performance cloud computing enable efficient fully quantum mechanical protein-ligand scoring
Ranking the binding of small molecules to protein receptors through
physics-based computation remains challenging. Though inroads have been made
using free energy methods, these fail when the underlying classical mechanical
force fields are insufficient. In principle, a more accurate approach is
provided by quantum mechanical density functional theory (DFT) scoring, but
even with approximations, this has yet to become practical on drug
discovery-relevant timescales and resources. Here, we describe how to overcome
this barrier using algorithms for DFT calculations that scale on widely
available cloud architectures, enabling full density functional theory, without
approximations, to be applied to protein-ligand complexes with approximately
2500 atoms in tens of minutes. Applying this to a realistic example of 22
ligands binding to MCL1 reveals that density functional scoring outperforms
classical free energy perturbation theory for this system. This raises the
possibility of broadly applying fully quantum mechanical scoring to real-world
drug discovery pipelines.Comment: 15 pages, 5 figures, 1 tabl
Novel algorithms and high-performance cloud computing enable efficient fully quantum mechanical protein-ligand scoring
Ranking the binding of small molecules to protein receptors through physics-based computation remains challenging. Though inroads have been made using free energy methods, these fail when the underlying classical mechanical force fields are insufficient. In principle, a more accurate approach is provided by quantum mechanical density functional theory (DFT) scoring, but even with approximations, this has yet to become practical on drug discovery-relevant timescales and resources. Here, we describe how to overcome this barrier using algorithms for DFT calculations that scale on widely available cloud architectures, enabling full density functional theory, without approximations, to be applied to protein-ligand complexes with approximately 2500 atoms in tens of minutes. Applying this to a realistic example of 22 ligands binding to MCL1 reveals that density functional scoring outperforms classical free energy perturbation theory for this system. This raises the possibility of broadly applying fully quantum mechanical scoring to real-world drug discovery pipelines
Proline-Rich Peptides with Improved Antimicrobial Activity against E. coli, K. Pneumoniae, and A. Baumannii.
Proline-rich antimicrobial peptides (PrAMPs) are promising agents to combat multi-drug resistant pathogens due to a high antimicrobial activity, yet low cytotoxicity. A library of derivatives of the PrAMP Bac5(1-17) was synthesized and screened to identify which residues are relevant for its activity. In this way, we discovered that two central motifs -PIRXP- cannot be modified, while residues at N- and C- termini tolerated some variations. We found five Bac5(1-17) derivatives bearing 1-5 substitutions, with an increased number of arginine and/or tryptophan residues, exhibiting improved antimicrobial activity and broader spectrum of activity while retaining low cytotoxicity toward eukaryotic cells. Transcription/translation and bacterial membrane permeabilization assays showed that these new derivatives still retained the ability to strongly inhibit bacterial protein synthesis, but also acquired permeabilizing activity to different degrees. These new Bac5(1-17) derivatives therefore show a dual mode of action which could hinder the selection of bacterial resistance against these molecules
Rifampicin-loaded electrospun polycaprolactone membranes: Characterization of stability, antibacterial effects and urotheliocytes proliferation
Pathological conditions such as infections, cancer, inflammation, or iatrogenic lesions, can hinder the cor-rect functionality of the ureter and its structural integrity. Several strategies for the regeneration of the ureter and the restoration of its functionality are available but the best strategy has not been reached yet. Among the proposed strategies, a promising one is the development of tubular scaffolds, in particular exploiting electrospinning technique. In this work, antibacterial electrospun polycaprolactone/rifampicin (PCL/Rif) membranes were prepared and characterized. The membranes are characterized by randomly oriented nanofibers with a homogeneous diameter, as determined by scanning electron microscopy. The mechanical characterization, performed with uniaxial tensile tests, showed a suitable stability over time and a proper deformability. The rifampicin release, investigated by UV spectrophotometry, showed a burst release in the first part of the experiment and a sustained release over time. The membranes are biocompatible and able to support the adhesion and proliferation of urotheliocytes. Moreover, PCL/Rif membranes showed an antibacterial activity against Escherichia coli and other bacterial strains belonging to the "ESKAPE" group. Considering the possibility to use the electrospinning for the production of tubu-lar scaffolds, the described membranes represent a promising starting point for the preparation of uret-eral scaffolds with antibacterial properties.(c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
New Optical Insights into the Mass Discrepancy of Galaxy Clusters: The Cases of A1689 and A2218
We analyze the internal structures of clusters A1689 and A2218 by applying a
recent development of the method of wavelet analysis, which uses the complete
information obtained from optical data, i.e. galaxy positions and redshifts. We
find that both clusters show the presence of structures superimposed along the
line of sight with different mean redshifts and smaller velocity dispersions
than that of the system as a whole, suggesting that the clusters could be cases
of the on-going merging of clumps. In the case of A2218 we find an acceptable
agreement between our estimate of optical virial mass and X-ray and
gravitational lensing masses. On the contrary, in the case of A1689 we find
that our mass estimates are smaller than X-ray and gravitational lensing ones
at both small and large radii. In any case, at variance with earlier claims,
there is no evidence that X-ray mass estimates are underestimated.Comment: 8 pages, 2 eps figures, Use LaTeX2e, accepted by Astrophysical
Journal, in press November 1997, Vol.49
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