121,258 research outputs found
Porous silica beads produced by nanofluid emulsion freezing
It is shown that porous spherical particles can be obtained via the freezing
of silica nanoparticle aqueous suspensions emulsified in a continuous oil
phase. After two freeze-thaw cycles, nanoparticles turn aggregated into
flocculated objects with microstructure that depends upon emulsion volume
fraction and droplet size. For low volume fractions, regular microspheres are
produced while for large ones, irregular beads with several tens of micrometer
radius are formed. Electronic microscopy, mercury porosimetry and nitrogen
adsorption are used to get insights into these porous particles typical radius,
pore size distribution, surface area and pore network structure. All exhibit
mesopores that result from inter-nanoparticle spacing after flocculation. An
unexpected macroporous domain appears which is not observed when drying
non-emulsified suspensions. This macroporosity is interpreted as the signature
of dendrite formation during the undercooled period, right before freezing
occurs. Beside this additional macroporosity, the protocols presented in this
article constitute also promising emulsion-based routes for porous material
synthesis with original geometry, chemical composition and porosity.Comment: 20 pages, 8 figure
PPH dendrimers grafted on silica nanoparticles: surface chemistry, characterization, silver colloids hosting and antibacterial activity
Polyphosphorhydrazone (PPH) dendrimers have been grafted on silica nanoparticles, and the surface functions of the dendrimers have been derivatized to phosphonates with lateral poly(ethyleneglycol) (PEG) chains. All materials have been thoroughly characterized by MAS NMR, FT-IR, electron microscopy, TGA and elemental analysis. These materials successfully hosted silver and silver oxide nanoparticles. The resulting composites exhibit antibacterial activity
High-resolution spectroscopy of extremely metal-poor stars in the least evolved galaxies: Bootes II
We present high-resolution Magellan/MIKE spectra of the four brightest
confirmed red giant stars in the ultra-faint dwarf galaxy Bootes II (Boo II).
These stars all inhabit the metal-poor tail of the Boo II metallicity
distribution function. The chemical abundance pattern of all detectable
elements in these stars is consistent with that of the Galactic halo. However,
all four stars have undetectable amounts of neutron-capture elements Sr and Ba,
with upper limits comparable to the lowest ever detected in the halo or in
other dwarf galaxies. One star exhibits significant radial velocity variations
over time, suggesting it to be in a binary system. Its variable velocity has
likely increased past determinations of the Boo II velocity dispersion. Our
four stars span a limited metallicity range, but their enhanced
{\alpha}-abundances and low neutron-capture abundances are consistent with the
interpretation that Boo II has been enriched by very few generations of stars.
The chemical abundance pattern in Boo II confirms the emerging trend that the
faintest dwarf galaxies have neutron-capture abundances distinct from the halo,
suggesting the dominant source of neutron-capture elements in halo stars may be
different than in ultra-faint dwarfs.Comment: 10 pages, 5 figures, 4 tables. Updated to match ApJ accepted versio
Recurrent patterns of DNA copy number alterations in tumors reflect metabolic selection pressures.
Copy number alteration (CNA) profiling of human tumors has revealed recurrent patterns of DNA amplifications and deletions across diverse cancer types. These patterns are suggestive of conserved selection pressures during tumor evolution but cannot be fully explained by known oncogenes and tumor suppressor genes. Using a pan-cancer analysis of CNA data from patient tumors and experimental systems, here we show that principal component analysis-defined CNA signatures are predictive of glycolytic phenotypes, including 18F-fluorodeoxy-glucose (FDG) avidity of patient tumors, and increased proliferation. The primary CNA signature is enriched for p53 mutations and is associated with glycolysis through coordinate amplification of glycolytic genes and other cancer-linked metabolic enzymes. A pan-cancer and cross-species comparison of CNAs highlighted 26 consistently altered DNA regions, containing 11 enzymes in the glycolysis pathway in addition to known cancer-driving genes. Furthermore, exogenous expression of hexokinase and enolase enzymes in an experimental immortalization system altered the subsequent copy number status of the corresponding endogenous loci, supporting the hypothesis that these metabolic genes act as drivers within the conserved CNA amplification regions. Taken together, these results demonstrate that metabolic stress acts as a selective pressure underlying the recurrent CNAs observed in human tumors, and further cast genomic instability as an enabling event in tumorigenesis and metabolic evolution
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