693 research outputs found
Intracerebral Implantation of Hydrogel-Coupled Adhesion Peptides: Tissue Reaction
Arg-Gly-Asp peptides (RGD) were synthesized
and chemically coupled to the bulk of N-(2-hydroxypropyl) methacrylamide-based polymer
hydrogels. Fourier Transform Infrared Spectroscopy
(FFIR) and amino acid analysis confirmed
the peptide coupling to the polymer. Activated
and control (unmodified) polymer matrices were
stereotaxically implanted in the striata of rat
brains, and two months later the brains were
processed for immunohistochemistry using antibodies
for glial acidic fibrillary protein (GFAP),
laminin and neurofilaments. RGD-containing
polymer matrices promoted stronger adhesion to
the host tissue than the unmodified polymer
matrices. In addition, the RGD-grafted polymer
implants promoted and supported the growth
and spread of GFAP-positive glial tissue onto
and into the hydrogels. Neurofilament-positive
fibers were also seen running along the surface
of the polymer and, in some instances, penetrating
the matrix. These findings are discussed
in the context of using bioactive polymers as a
new approach for promoting tissue repair and
axonal regeneration of damaged structures of
the central nervous system
Organic matter in termite mounds of an Amazonian rain forest.
This study investigates how termites alter the organic matter in rain forests near Manaus, Brazil. Samples were collected from the outer and inner parts of typical termite nests of Nasutitermes, Termes, Embiratermes, Cornitermes, Anoplotermes, and Constrictotermes genera, as well as from the surrounding topsoil (0cm-10cm) and potential wooden food. The termite nests were signficant sinks for organic matter and its associated nutrients. The organic C contents ranged between 100g kg-1 and 500g kg-1 in the nests, compared to 17g kg-1 to 42g kg-1 in the surrounding topsoils. As lignin contents of the mounds were higher than in wood, lignin may be accumulated in preference to other organic compounds. This findings also sugests that the interior part of the nests is a region of higher organic matter turnover and lignin degradation
Ein neuer Ansatz für die Trockenseparierung von Mikroaggregaten mit unterschiedlicher Textur zur Messung der mechanischen Belastbarkeit und 3D-Porenstruktur
Die Bodenstruktur als Ausdruck der räumlichen Anordnung mineralischer und organischer Bodenbestandteile ist eine zentrale Charakteristik des Bodens. Sie steuert viele wichtige biologische, physikalische und geochemische Prozesse, wie die Rolle des Bodens als Kohlenstoffspeicher oder die Ausbildung bzw. Verteilung von Habitaten für Mikroorganismen. Die Bodenstruktur, deren einfachste Einheit die Aggregate bilden, befindet sich als labile Bodeneigenschaft in einem Zustand ständiger Veränderung. Die Eigenschaften der Aggregate werden durch viele Einflussfaktoren wie Textur, Alter, Quellung und Schrumpfung, sowie die biologische Aktivität gesteuert. Eines der Hauptprobleme bei der Untersuchung der Eigenschaften von Mikroaggregaten im Boden ist deren Separierung. Viele Separierungs-Methoden üben Spannungszustände aus, die die realen Bedingungen im Boden nur sehr bedingt abbilden. So werden z. B. bei Nasssiebungsverfahren hydraulische Spannungen erzeugt, die unter natürlichen Bedingungen nicht auftreten. Hierin liegt ein Risiko, dass Artefakte in den gewonnenen Aggregatfraktionen entstehen (z. B. durch Reaggregierung bei anschließender Trocknung) und die weitere Analyse von Eigenschaften dieser Aggregatfraktionen, bzw. deren Interpretation beeinflussen.
Übergeordnetes Ziel unserer Untersuchungen ist die Erforschung der Genese von Mikroaggregaten und deren (Poren‑)Eigenschaften in Abhängigkeit von Texturunterschieden, sowie des Zusammenhangs von mikroskaligen Deformationsprozessen auf die Entwicklung der Bodenstruktur. Hierfür haben wir mit einem Verfahren der Trockenseparierung in drei Aggregatgrößen-Unterklassen (250-53, 53-20 und <20 µm) eine zuverlässige Methode zur Isolierung einzelner Mikroaggregate entwickelt, welche die Struktur der gewonnenen Aggregate selbst nicht beeinflusst. In einem nächsten Schritt wird die mechanische Belastbarkeit von Mikroaggregaten aus einer Toposequenz (mit unterschiedlichen Tongehalten) an einem Lastrahmen hochauflösend getestet, um die Hypothese zu überprüfen, dass die Stabilität mit abnehmender struktureller Entropie (d. h. zunehmendem Grad an Strukturierung) zunimmt.
Des Weiteren wird die Geometrie des Porennetzwerkes der Mikroaggregate mit unterschiedlichen Tongehalten mittels hochauflösender Computertomographie untersucht, um diese später mit gemessenen Gas- und Wasserflüssen in Verbindung bringen zu können
Long-range Kondo signature of a single magnetic impurity
The Kondo effect, one of the oldest correlation phenomena known in condensed
matter physics, has regained attention due to scanning tunneling spectroscopy
(STS) experiments performed on single magnetic impurities. Despite the
sub-nanometer resolution capability of local probe techniques one of the
fundamental aspects of Kondo physics, its spatial extension, is still subject
to discussion. Up to now all STS studies on single adsorbed atoms have shown
that observable Kondo features rapidly vanish with increasing distance from the
impurity. Here we report on a hitherto unobserved long range Kondo signature
for single magnetic atoms of Fe and Co buried under a Cu(100) surface. We
present a theoretical interpretation of the measured signatures using a
combined approach of band structure and many-body numerical renormalization
group (NRG) calculations. These are in excellent agreement with the rich
spatially and spectroscopically resolved experimental data.Comment: 7 pages, 3 figures + 8 pages supplementary material; Nature Physics
(Jan 2011 - advanced online publication
Avaliação genética em erva-mate pelo procedimento BLUP individual multivariado sob interação genótipo x ambiente.
Geochemistry of the alkaline volcanicsubvolcanic rocks of the Fernando de Noronha Archipelago, southern Atlantic Ocean
A correção do drift instrumental em ICP-AES com espectrômetro seqüencial e a análise de elementos maiores, menores e traços em rochas
Analytical results of major, minor and trace elements are presented, which were obtained on international rock reference materiais during the development of work routines in the ICP-AES Laboratory, Mineralogy and Petrology Department, Instituto de Geociências, São Paulo University. Analyses were performed on an ARL-3410 model with sequential spectrometer using solutions obtained by alkaline fiision of 0.25 g of rock powder with 0.75 g of lithium tetra and metaborate (eutectic mixture), with a 1:1000 sample dilution (method used at the Imperial College, London). In order to minimize the effects of intensity drift, caused mostly by variations in the uptake conditions of the solution, strict procedures of drift controi and off-line correction were adopted. The results show good repeatability and maintain long-term precision, demonstrating that reliable analyses can be obtained by careful correction procedures. However, as it is not possible to controi short-term drift in sequential spectrometers, most of the analyses add up to between 98 and 101%; key major element ratios are nevertheless maintained, ensuring the quality of the analysis. The accuracy is reliable for the analyzed elements, which, besides major and minor elements, also include Zn, Ni, Cr, V, Zr, Sc, Y, La, Ba and Sr, and even for those notoriously difficult to analyze by ICP-AES, such as K, P and La.Apresentam-se resultados de análises quÃmicas de elementos maiores e traços em materiais de referência de rochas, obtidos durante o desenvolvimento de rotina analÃtica no Laboratório de QuÃmica e ICP-AES do Departamento de Mineralogia e Petrologia do Instituto de Geociências da USP. As análises, realizadas em equipamento ARL-3410 dotado de espectrômetro seqüencial, foram efetuadas em soluções obtidas por fusão alcalina, com misturas de 0,75 g de tetra e metaborato de lÃtio e de 0,25 g de pó de rocha, e diluição final dos analitos de 1:1000 (metodologia do Imperial College, Londres). Para mmimizar os efeitos de drift, provenientes especialmente de variações nas condições de introdução da amostra no plasma, adotam-se procedimentos rÃgidos de controle e correção off-line da flutuação do sinal. Os resultados apresentam boa repetibilidade e precisão a longo intervalo, refletindo a eficiência usualmente alcançada pelo procedimento adotado. Em vista da dificuldade de corrigir o drift de pequeno intervalo em plasmas dotados de espectrômetro seqüencial, os fechamentos das análises são variáveis entre 98 e 101%, mas as relações entre os elementos maiores se mantêm constantes, garantindo a qualidade dos resultados. A exatidão é satisfatória para todo o conjunto de elementos por ora estudado (além dos maiores e menores, ainda Zn, Ni, Cr, V, Zr, Sc, Y, La, Sr e Ba), mesmo para aqueles de determinação mais difÃcil no ICP-AES, como K, P e La
Major components of atmospheric organic aerosol in southern California as determined by hourly measurements of source marker compounds
We report the first hourly in-situ measurements of speciated organic aerosol
(OA) composition in an urban environment. Field measurements were made in
southern California at the University of California–Riverside during the
2005 Study of Organic Aerosol at Riverside (SOAR), which included two
separate measurement periods: a summer study (15 July–15 August) and a
fall study (31 October–28 November). Hourly measurements of over 300
semivolatile and nonvolatile organic compounds were made using the thermal
desorption aerosol gas chromatograph (TAG). Positive matrix factorization
(PMF) was performed on a subset of these compounds to identify major
components contributing to submicron (i.e., PM<sub>1</sub>) OA at the site, as
measured by an aerosol mass spectrometer (AMS). PMF analysis was performed
on an 11-day focus period in each season, representing average seasonal
conditions during the summer and a period of urban influence during the
fall. As a result of this analysis, we identify multiple types of primary
and secondary OA (POA and SOA). Secondary sources contribute substantially
to fine OA mass at Riverside, which commonly receives regional air masses
that pass through metropolitan Los Angeles during the summer. Four
individual summertime SOA components are defined, and when combined, they
are estimated to contribute an average 88% of the total fine OA mass
during summer afternoons according to PMF results. These sources appear to
be mostly from the oxidation of anthropogenic precursor gases, with one SOA
component having contributions from oxygenated biogenics. During the fall,
three out of four aerosol components that contain SOA are inseparable from
covarying primary emissions, and therefore we cannot estimate the fraction
of total OA that is secondary in nature during the fall study. Identified
primary OA components are attributed to vehicle emissions, food cooking,
primary biogenics, and biomass burning aerosol. While a distinction between
local and regional vehicle emissions is made, a combination of these two
factors accounted for approximately 11% of observed submicron OA during
both sampling periods. Food cooking operations contributed ~10% of
submicron OA mass during the summer, but was not separable from SOA during
the fall due to high covariance of sources. Biomass burning aerosol
contributed a larger fraction of fine OA mass during the fall (~11%) than compared to summer (~7%). Primary biogenic aerosol
was also identified during the summer, contributing ~1% of the OA,
but not during the fall. While the contribution of both local and regional
primary vehicle OA accounts for only ~11% of total OA during both
seasons, gas-phase vehicle emissions likely create a substantial fraction of
the observed SOA as a result of atmospheric processing
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