1,037 research outputs found
Water diffusion modulates the cest effect on Tb(III)-mesoporous silica probes
The anchoring of lanthanide(III) chelates on the surface of mesoporous silica nanoparticles (MSNs) allowed their investigation as magnetic resonance imaging (MRI) and chemical exchange saturation transfer (CEST) contrast agents. Since their efficiency is strongly related to the interaction occurring between Ln-chelates and \u201cbulk\u201d water, an estimation of the water diffusion inside MSNs channels is very relevant. Herein, a method based on the exploitation of the CEST properties of TbDO3A-MSNs was applied to evaluate the effect of water diffusion inside MSN channels. Two MSNs, namely MCM-41 and SBA-15, with different pores size distributions were functionalized with TbDO3A-like chelates and polyethylene glycol (PEG) molecules and characterized by HR-TEM microscopy, IR spectroscopy, N2 physisorption, and thermogravimetric analysis (TGA). The different distribution of Tb-complexes in the two systems, mainly on the external surface in case of MCM-41 or inside the internal pores for SBA-15, resulted in variable CEST efficiency. Since water molecules diffuse slowly inside silica channels, the CEST effect of the LnDO3A-SBA-15 system was found to be one order of magnitude lower than in the case of TbDO3A-MCM-41. The latter system reaches an excellent sensitivity of ca. 55 \ub1 5 \ub5M, which is useful for future theranostic or imaging applications
Low-density colloid centrifugation removes bacteria from boar semen doses after spiking with selected species
Single-layer centrifugation (SLC) with a low-density colloid is an efficient method for removing contaminating microorganisms from boar semen while recovering most spermatozoa from the original sample. This study tested the performance of this technique, using 50-ml tubes, by spiking commercial semen doses prepared without antibiotics with selected bacterial species followed by storage at 17 degrees C. The doses were spiked up to 102/ml CFU (colony forming units) of the bacteria Burkholderia ambifaria, Pseudomonas aeruginosa, and Staphylococcus sim-ulans. The semen was processed by SLC (15 ml of sample and 15 ml of colloid) with the colloid Porcicoll at 20% (P20) and 30% (P30), with a spiked control (CTL) and an unspiked control (CTL0), analyzing microbiology and sperm quality on days 0, 3 and 7. SLC completely removed B. ambifaria and S. simulans, considerably reducing P. aeruginosa and overall contamination (especially P30, similar to 104 CFU/ml of total contamination on day 7, median). Sperm viability was lower in P20 and P30 samples at day 0, with higher cytoplasmic ROS. Still, results were similar in all groups on day 3 and reversed on day 7, indicating a protective effect of SLC (possibly directly by removal of damaged sperm and indirectly because of lower bacterial contamination). Sperm chromatin was affected by the treatment (lower DNA fragmentation and chromatin decondensation) and storage (higher overall condensation on day 7 as per chromomycin A3 and monobromobimane staining). In conclusion, SLC with low-density colloids can remove most bacteria in a controlled contamination design while potentially improving sperm quality and long-term storage at practical temperatures
The M4 Core Project with HST --- I. Overview and First-Epoch
We present an overview of the ongoing Hubble Space Telescope large program
GO-12911. The program is focused on the core of M4, the nearest Galactic
globular cluster, and the observations are designed to constrain the number of
binaries with massive companions (black holes, neutron stars, or white dwarfs)
by measuring the ``wobble'' of the luminous (main-sequence) companion around
the center of mass of the pair, with an astrometric precision of ~50
micro-arcseconds. The high spatial resolution and stable medium-band PSFs of
WFC3/UVIS will make these measurements possible. In this work we describe: (i)
the motivation behind this study, (ii) our observing strategy, (iii) the many
other investigations enabled by this unique data set, and which of those our
team is conducting, and (iv) a preliminary reduction of the first-epoch
data-set collected on October 10, 2012.Comment: 25 pages, 14 figures (9 at low resolution), 3 tables. Published in:
Astronomische Nachrichten, Volume 334, Issue 10, pages 1062-1085, December
2013. http://onlinelibrary.wiley.com/doi/10.1002/asna.201311911/abstrac
Star Formation Histories of the LEGUS Dwarf Galaxies (I): recent History of NGC1705, NGC4449 and Holmberg II
We use HST observations from the Legacy Extragalactic UV Survey to
reconstruct the recent star formation histories (SFHs) of three actively
star-forming dwarf galaxies, NGC4449, Holmberg II and NGC1705, from their UV
color-magnitude diagrams (CMDs). We apply a CMD fitting technique using two
independent sets of stellar isochrones, PARSEC-COLIBRI and MIST, to assess the
uncertainties related to stellar evolution modelling. Irrespective of the
adopted stellar models, all the three dwarfs are found to have had almost
constant star formation rates (SFRs) in the last 100-200 Myr, with modest
enhancements (a factor of 2) above the 100 Myr-averaged-SFR. Significant
differences among the three dwarfs are found in the overall SFR, the timing of
the most recent peak and the SFRarea. The Initial Mass Function (IMF) of
NGC1705 and Holmberg II is consistent with a Salpeter slope down to 5
M, whereas it is slightly flatter, s, in NGC4449. The SFHs
derived with the two different sets of stellar models are consistent with each
other, except for some quantitative details, attributable to their input
assumptions. They also share the drawback that all synthetic diagrams predict a
clear separation in color between upper main sequence and helium burning stars,
which is not apparent in the data. Since differential reddening, significant in
NGC4449, or unresolved binaries don't appear to be sufficient to fill the gap,
we suggest this calls for a revision of both sets of stellar evolutionary
tracks.Comment: 22 pages, 17 figures, accepted for publication on Ap
Effect of subinhibitory concentrations of four commonly used biocides on the conjugative transfer of Tn916 in Bacillus subtilis
OBJECTIVES: Large amounts of biocides are used to reduce and control bacterial growth in the healthcare sector, food production and agriculture. This work explores the effect of subinhibitory concentrations of four commonly used biocides (ethanol, hydrogen peroxide, chlorhexidine digluconate and sodium hypochlorite) on the conjugative transposition of the mobile genetic element Tn916. METHODS: Conjugation assays were carried out between Bacillus subtilis strains. The donor containing Tn916 was pre-exposed to subinhibitory concentrations of each biocide for a defined length of time, which was determined by an analysis of the transcriptional response of the promoter upstream of tet(M) using β-glucuronidase reporter assays. RESULTS: Ethanol significantly (P = 0.01) increased the transfer of Tn916 by 5-fold, whereas hydrogen peroxide, chlorhexidine digluconate and sodium hypochlorite did not significantly affect the transfer frequency. CONCLUSIONS: These results suggest that exposure to subinhibitory concentrations of ethanol may induce the transfer of Tn916-like elements and any resistance genes they contain
Opposite-side flavour tagging of B mesons at the LHCb experiment
The calibration and performance of the oppositeside
flavour tagging algorithms used for the measurements
of time-dependent asymmetries at the LHCb experiment
are described. The algorithms have been developed using
simulated events and optimized and calibrated with
B
+ →J/ψK
+, B0 →J/ψK
∗0 and B0 →D
∗−
μ
+
νμ decay
modes with 0.37 fb−1 of data collected in pp collisions
at
√
s = 7 TeV during the 2011 physics run. The oppositeside
tagging power is determined in the B
+ → J/ψK
+
channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty
is statistical and the second is systematic
Differential branching fraction and angular analysis of the decay B0→K∗0μ+μ−
The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Search for CP violation in decays
A model-independent search for direct CP violation in the Cabibbo suppressed
decay in a sample of approximately 370,000 decays is
carried out. The data were collected by the LHCb experiment in 2010 and
correspond to an integrated luminosity of 35 pb. The normalized Dalitz
plot distributions for and are compared using four different
binning schemes that are sensitive to different manifestations of CP violation.
No evidence for CP asymmetry is found.Comment: 13 pages, 8 figures, submitted to Phys. Rev.
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