8,294 research outputs found
Special curves and postcritically-finite polynomials
We study the postcritically-finite (PCF) maps in the moduli space of complex
polynomials . For a certain class of rational curves in
, we characterize the condition that contains infinitely
many PCF maps. In particular, we show that if is parameterized by
polynomials, then there are infinitely many PCF maps in if and only if
there is exactly one active critical point along , up to symmetries; we
provide the critical orbit relation satisfied by any pair of active critical
points. For the curves in the space of cubic
polynomials, introduced by Milnor (1992), we show that
contains infinitely many PCF maps if and only if
. The proofs involve a combination of number-theoretic methods
(specifically, arithmetic equidistribution) and complex-analytic techniques
(specifically, univalent function theory). We provide a conjecture about
Zariski density of PCF maps in subvarieties of the space of rational maps, in
analogy with the Andr\'e-Oort Conjecture from arithmetic geometry.Comment: Final version, appeared in Forum of Math. P
Torsion points and the Lattes family
We give a dynamical proof of a result of Masser and Zannier [MZ2, MZ3] about
torsion points on the Legendre family of elliptic curves. Our methods also
treat points of small height. A key ingredient is the arithmetic
equidistribution theorem on of Baker-Rumely, Chambert-Loir, and
Favre-Rivera-Letelier. Torsion points on the elliptic curve coincide with
preperiodic points for the degree-4 Lattes family of rational functions. Our
main new results concern properties of the bifurcation measures for this Lattes
family associated to marked points.Comment: Theorem 1.3 now states the strongest form of the main theorem, the
result of combining our methods with the conclusions of Masser-Zannier, for
rational points with complex coefficients. To appear, American Journal of
Mat
Effect of Lactobacillus rhamnosus HN001 and Bifidobacterium longum BB536 on the healthy gut microbiota composition at phyla and species level: a preliminary study
AIM:
To evaluate the ability of Lactobacillus rhamnosus HN001 and Bifidobacterium longum BB536 to colonize the intestinal environment of healthy subjects and modify the gut microbiota composition.
METHODS:
Twenty healthy Italian volunteers, eight males and twelve females, participated in the study. Ten subjects took a sachet containing 4 Ă 109 colony-forming units (CFU) of Bifidobacterium longum BB536 and 109 CFU of Lactobacillus rhamnosus HN001, 30 min before breakfast (pre-prandial administration), while ten subjects took a sachet of probiotic product 30 min after breakfast (post-prandial administration). The ability of Lactobacillus rhamnosus HN001 and Bifidobacterium longum BB536 to colonize human gut microbiota was assessed by means of quantitative real-time PCR, while changes in gut microbiota composition were detected by using Ion Torrent Personal Genome Machine.
RESULTS:
Immediately after 1-mo of probiotic administration, B. longum BB536 and L. rhamnosus HN001 load was increased in the majority of subjects in both pre-prandial and post-prandial groups. This increase was found also 1 mo after the end of probiotic oral intake in both groups, if compared to samples collected before probiotic consumption. At phyla level a significant decrease in Firmicutes abundance was detected immediately after 1-mo of B. longum BB536 and L. rhamnosus HN001 oral intake. This reduction persisted up to 1 mo after the end of probiotic oral intake together with a significant decrease of Proteobacteria abundance if compared to samples collected before probiotic administration. Whereas, at species level, a higher abundance of Blautia producta, Blautia wexlerae and Haemophilus ducrey was observed, together with a reduction of Holdemania filiformis, Escherichia vulneris, Gemmiger formicilis and Streptococcus sinensis abundance. In addition, during follow-up period we observed a further reduction in Escherichia vulneris and Gemmiger formicilis, together with a decrease in Roseburia faecis and Ruminococcus gnavus abundance. Conversely, the abundance of Akkermansia muciniphila was increased if compared to samples collected at the beginning of the experimental time course.
CONCLUSION:
B. longum BB536 and L. rhamnosus HN001 showed the ability to modulate the gut microbiota composition, leading to a significant reduction of potentially harmful bacteria and an increase of beneficial ones. Further studies are needed to better understand the specific mechanisms involved in gut microbiota modulation
Identifying conformational changes with site-directed spin labeling reveals that the GTPase domain of HydF is a molecular switch
[FeFe]-hydrogenases catalyse the reduction of protons to hydrogen at a complex 2Fe[4Fe4S] center called H-cluster. The assembly of this active site is a multistep process involving three proteins, HydE, HydF and HydG. According to the current models, HydF has the key double role of scaffold, upon which the final H-cluster precursor is assembled, and carrier to transfer it to the target hydrogenase. The X-ray structure of HydF indicates that the protein is a homodimer with both monomers carrying two functional domains: a C-terminal FeS cluster-binding domain, where the precursor is assembled, and a N-terminal GTPase domain, whose exact contribution to cluster biogenesis and hydrogenase activation is still elusive. We previously obtained several hints suggesting that the binding of GTP to HydF could be involved in the interactions of this scaffold protein with the other maturases and with the hydrogenase itself. In this work, by means of site directed spin labeling coupled to EPR/PELDOR spectroscopy, we explored the conformational changes induced in a recombinant HydF protein by GTP binding, and provide the first clue that the HydF GTPase domain could be involved in the H-cluster assembly working as a molecular switch similarly to other known small GTPases
The mass accretion rate of galaxy clusters: a measurable quantity
We explore the possibility of measuring the mass accretion rate (MAR) of
galaxy clusters from their mass profiles beyond the virial radius . We
derive the accretion rate from the mass of a spherical shell whose inner radius
is , whose thickness changes with redshift, and whose infall velocity
is assumed to be equal to the mean infall velocity of the spherical shells of
dark matter halos extracted from -body simulations. This approximation is
rather crude in hierarchical clustering scenarios where both smooth accretion
and aggregation of smaller dark matter halos contribute to the mass accretion
of clusters.Nevertheless, in the redshift range , our prescription
returns an average MAR within of the average rate derived from the
merger trees of dark matter halos extracted from -body simulations. The MAR
of galaxy clusters has been the topic of numerous detailed numerical and
theoretical investigations, but so far it has remained inaccessible to
measurements in the real universe. Since the measurement of the mass profile of
clusters beyond their virial radius can be performed with the caustic technique
applied to dense redshift surveys of the cluster outer regions, our result
suggests that measuring the mean MAR of a sample of galaxy clusters is actually
feasible. We thus provide a new potential observational test of the
cosmological and structure formation models.Comment: 11 pages, 7 figures, 5 tables, minor text modifications to match the
published version, typos correcte
Service Recommendations with Deep Learning: A Study on Neural Collaborative Engines
Background: The present paper aims to investigate the adoption of Neural Networks for recommendation systems and to propose Deep Learning architectures as advanced frameworks for designing Collaborative Filtering engines. Recommendation systems are data-driven infrastructures which are widely adopted to create effective and cutting-edge smart services, allowing to personalize the value proposition and adapt it to changes and variations in customersâ preferences.
Method: Our research represents an exploratory investigation on the adoption of Neural Networks for Recommendation Systems, inspired by the findings of a recent study on service science that highlighted the suitability of those models for designing cutting-edge recommenders capable of overcoming stable traditional benchmarks like the Singular Value Decomposition and the k-Nearest Neighbors algorithms. Following this study, we designed a more âcomplexâ Feed-Forward Neural Network, trained on the âMovielens 100Kâ dataset using the Mean-Squared Error function to approximate the model loss generated and the Adaptive Moment Estimation algorithm (Adam) for the parameters optimization.
Results: The results of this study demonstrate the primary role of Feed-Forward Neural Networks for designing advanced Collaborative recommenders, consolidating and even improving the outcomes of the work that inspired our research.
Conclusion: Given these assumptions, we confirm the suitability of Feed-Forward Neural Networks as effective recommendation algorithms, laying the foundations for further studies in neural-based recommendation science
Nanoparticle-based receptors mimic protein-ligand recognition
The self-assembly of a monolayer of ligands on the surface of noble metal nanoparticles dictates the fundamental nanoparticle\u2019s behavior and its functionality. In this combined computational\u2013experimental study, we analyze the structure, organization, and dynamics of functionalized coating thiols in monolayer-protected gold nanoparticles (AuNPs). We explain how functionalized coating thiols self-organize through a delicate and somehow counterintuitive balance of interactions within the monolayer itself and with the solvent. We further describe how the nature and plasticity of these interactions modulate nanoparticle-based chemosensing. Importantly, we found that self-organization of coating thiols can induce the formation of binding pockets in AuNPs. These transient cavities can accommodate small molecules, mimicking protein-ligand recognition, which may explain the selectivity and sensitivity observed for different organic analytes in NMR chemosensing experiments. Thus, our findings advocate for the rational design of tailored coating groups to form specific recognition binding sites on monolayer-protected AuNPs
The Global Electroweak and Higgs Fits in the LHC era
We update the global fit to electroweak precision observables, including the
effect of the latest measurements at hadron colliders of the and top-quark
masses and the effective leptonic weak mixing angle. We comment on the impact
of these measurements in terms of constraints on new physics. We also update
the bounds derived from the fit to the Higgs-boson signal strengths, including
the observables measured at the LHC Run 2, and compare the improvements with
respect to the 7 and 8 TeV results.Comment: 5+1 pages, 3 figures, 2 tables. Prepared for the Proceedings of the
5th LHCP Conference -Shanghai, May 2017- and the EPS-HEP 2017 Conference
-Venice, July 2017. (LHCP version.
Epigenetic control of EMT/MET dynamics: HNF4α impacts DNMT3s through miRs-29
Background and aims: Epithelial-to-mesenchymal transition (EMT) and the reverse mesenchymal-to-epithelial
transition (MET) are manifestations of cellular plasticity that imply a dynamic and profound gene expression
reprogramming. While a major epigenetic code controlling the coordinated regulation of a whole transcriptional
profile is guaranteed by DNA methylation, DNA methyltransferase (DNMT) activities in EMT/MET dynamics are
still largely unexplored.
Here, we investigated the molecular mechanisms directly linking HNF4α, the master effector of MET, to the
regulation of both de novo of DNMT 3A and 3B.
Methods: Correlation among EMT/MET markers, microRNA29 and DNMT3s expression was evaluated by
RT-qPCR, Western blotting and immunocytochemical analysis. Functional roles of microRNAs and DNMT3s
were tested by anti-miRs, microRNA precursors and chemical inhibitors. ChIP was utilized for investigating
HNF4α DNA binding activity.
Results: HNF4α silencing was sufficient to induce positive modulation of DNMT3B, in in vitro differentiated
hepatocytes as well as in vivo hepatocyte-specific Hnf4α knockout mice, and DNMT3A, in vitro, but not
DNMT1. In exploring the molecular mechanisms underlying these observations, evidence have been gathered
for (i) the inverse correlation between DNMT3 levels and the expression of their regulators miR-29a and miR-
29b and (ii) the role of HNF4α as a direct regulator of miR-29a-b transcription. Notably, during TGFÎČ-induced
EMT, DNMT3s' pivotal function has been proved, thus suggesting the need for the repression of these DNMTs
in the maintenance of a differentiated phenotype.
Conclusions: HNF4α maintains hepatocyte identity by regulating miR-29a and -29b expression, which in turn
control epigenetic modifications by limiting DNMT3A and DNMT3B levels
Electroweak precision constraints at present and future colliders
We revisit the global fit to electroweak precision observables in the
Standard Model and present model-independent bounds on several general new
physics scenarios. We present a projection of the fit based on the expected
experimental improvements at future colliders, and compare the
constraining power of some of the different experiments that have been
proposed. All results have been obtained with the HEPfit code.Comment: 6 + 1 pages, 4 figures, 6 tables. Minor corrections. Contribution to
the Proceedings of the 38th International Conference on High Energy Physics,
3-10 August 2016, Chicago, U.S.
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