3,017 research outputs found
Unusual DNA binding modes for metal anticancer complexes
DNA is believed to be the primary target for many metal-based drugs. For example, platinum-based anticancer drugs can form specific lesions on DNA that induce apoptosis. New platinum drugs can be designed that have novel modes of interaction with DNA, such as the trinuclear platinum complex BBR3464. Also it is possible to design inert platinum(IV) pro-drugs which are non-toxic in the dark, but lethal when irradiated with certain wavelengths of light. This gives rise to novel DNA lesions which are not as readily repaired as those induced by cisplatin, and provides the basis for a new type of photoactivated chemotherapy. Finally, newly emerging ruthenium(II) organometallic complexes not only bind to DNA coordinatively, but also by H-bonding and hydrophobic interactions triggered by the introduction of extended arene rings into their versatile structures. Intriguingly osmium (the heavier congener of ruthenium) reacts differently with DNA but can also give rise to highly cytotoxic organometallic complexes
The nature of correlations in the insulating states of twisted bilayer graphene
The recently observed superconductivity in twisted bilayer graphene emerges
from insulating states believed to arise from electronic correlations. While
there have been many proposals to explain the insulating behaviour, the
commensurability at which these states appear suggests that they are Mott
insulators. Here we focus on the insulating states with electrons or
holes with respect to the charge neutrality point. We show that the theoretical
expectations for the Mott insulating states are not compatible with the
experimentally observed dependence on temperature and magnetic field if, as
frequently assumed, only the correlations between electrons on the same site
are included. We argue that the inclusion of non-local (inter-site)
correlations in the treatment of the Hubbard model can bring the predictions
for the magnetic and temperature dependencies of the Mott transition to an
agreement with experiments and have consequences for the critical interactions,
the size of the gap, and possible pseudogap physics. The importance of the
inter-site correlations to explain the experimental observations indicates that
the observed insulating gap is not the one between the Hubbard bands and that
antiferromagnetic-like correlations play a key role in the Mott transition.Comment: 8 pages (including appendix), 5 figure
Remoción de quistes de giardia duodenalis por filtración rápida
Con el objetivo de evaluar la remoción de quistes de Giardia duodenalis en agua, se construyó un filtro rápido por gravedad, a escala laboratorio, con arena (Tamaño efectivo: 0,95±0,03 mm) como material filtrante. El agua para la prueba de remoción (160 L) se preparó diluyendo una suspensión de quistes con H2Od hasta una turbiedad de 4 UNT. Para recuperar los quistes no removidos, el agua filtrada se pasó a través de membranas de nitrato de celulosa de 0,45 μm. El conteo de quistes se realizó en cámara de Neubauer. Mediante pruebas hidráulicas se estableció el espesor del lecho (0,75 m) y el tiempo de retención (5 min). La concentración de parásitos en el agua de entrada fue de 2,2 104 quistes/L, obteniéndose una remoción de 1,5 log (96,9 %). La turbiedad durante el periodo de filtración fue ≤ 1,22 UNT. Este trabajo confirma que aún en condiciones de filtración apropiadas, los quistes de Giardia
pueden aparecer en el agua tratada cuando ocurre una
elevada contaminación de la fuente.In order to evaluate the removal of cysts of Giardia duodenalis in water, a rapid gravity filter
was constructed on laboratory scale with sand (effective size: 0.95 ± 0.03 mm) as a filter material. Water for the test (160 L) was prepared by diluting a suspension of cysts with H2Od until a turbidity of 4 UNT. To recover the unremoved cysts, the filtered water was passed through 0.45 μm cellulose nitrate membranes. The cysts count was performed in Neubauer chamber. The filter bed thickness (0.75 m) and the retention time (5 min) were established by hydraulic tests. The concentration of parasites in the incoming water was 2.2 104 cysts / L obtaining a removal of 1.5 log (96.9 %). The turbidity during the filtration period was ≤ 1.22 UNT. This investigation confirms that even under appropriate filtration conditions, cysts of Giardia can appear in the treated water when high source contamination occurs.Fil: Pizarro, A..
Universidad Nacional del LitoralFil: Zerbatto, M..
Universidad Nacional del LitoralFil: Pizarro, M..
Universidad Nacional del LitoralFil: Modini, L..
Universidad Nacional del Litora
Internal screening and dielectric engineering in magic-angle twisted bilayer graphene
Magic-angle twisted bilayer graphene (MA-tBLG) has appeared as a tunable
testing ground to investigate the conspiracy of electronic interactions, band
structure, and lattice degrees of freedom to yield exotic quantum many-body
ground states in a two-dimensional Dirac material framework. While the impact
of external parameters such as doping or magnetic field can be conveniently
modified and analyzed, the all-surface nature of the quasi-2D electron gas
combined with its intricate internal properties pose a challenging task to
characterize the quintessential nature of the different insulating and
superconducting states found in experiments. We analyze the interplay of
internal screening and dielectric environment on the intrinsic electronic
interaction profile of MA-tBLG. We find that interlayer coupling generically
enhances the internal screening. The influence of the dielectric environment on
the effective interaction strength depends decisively on the electronic state
of MA-tBLG. Thus, we propose the experimental tailoring of the dielectric
environment, e.g. by varying the capping layer composition and thickness, as a
promising pursuit to provide further evidence for resolving the hidden nature
of the quantum many-body states in MA-tBLG.Comment: 9 pages, 3 figures, supplemental material included (8 figures
Inclusion of [H3PW12O40] and [H4SiW12O40] into a silica gel matrix via "sol-gel" methodology
Indexación: Web of Science; Scopus.Here we report the inclusion of two Keggin Polyoxometalates (POMs), [H3PW12O40] and [H4SiW12O40], into silica gels by integrating them during the preparation of the SiO2 matrix via "sol-gel" methods. Aerogels were produced by supercritical drying of the wet gels impregnated with the POMs, and lyogels were obtained by means of a lyophilization process. These materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared (FT-IR) spectroscopy and thermoanalytical techniques (TGA-DSC). We found that a large fraction of POMs are lost during the aging time, and solvent exchange for lyophilization. However the thermal stability of the bare matrix is modified by the inclusion of POMs. Some aggregates with a high content of POMs were found via SEM-EDX.http://ref.scielo.org/3fg9t
Composition and distribution of the Orthoptera assemblage (Insecta) in an arid basin in North-Central Chile
La cuenca del valle del río Elqui (Región
de Coquimbo, Chile) es un importante foco de
actividad agrofrutícola y turística dentro de la
zona norte-centro de Chile cuyas condiciones
climáticas se caracterizan por el aumento de la
temperatura y la disminución de la precipitación.
En el contexto del calentamiento global es
esperable que la hoya hidrográfica del río
Elqui experimente una tendencia ascendente
en la aridez, alteraciones en la fenología de
plantas y artrópodos y cambios en la riqueza
y biodiversidad local de los ecosistemas. En
este sentido, en el presente trabajo, mediante
colectas manuales en sectores de secano
y cultivo de las localidades de Marquesa,
Diaguitas y Pisco Elqui en el valle de Elqui,
se documentó la composición taxonómica
y abundancia del ensamble de Orthoptera
(Insecta) en la cuenca del valle del Elqui, se
analizó la distribución espacial de las especies
constituyentes del ensamble mediante SIG y
se documentó la importancia de Orthoptera
como potenciales plagas dentro de esta cuenca
árida del norte-centro de Chile. Se capturó
un total de 204 ejemplares, correspondientes
a cuatro familias y seis especies, de las
cuales cinco especies fueron capturadas en
sectores de secano y cultivo. Acrididae fue la
familia más abundante y diversa dentro de los
sitios de estudio (65,2% del total capturado)
y Trimerotropis ochraceipennis la especie
más abundante dentro del sitio de estudio.
Las familias Gryllidae, Ommexechidae y
Tristiridae estuvieron representadas por una
sola especie. La presencia de estas especies
en los sectores de secano puede constituir
un factor de riesgo para la agricultura, al
considerarse potenciales focos irruptivos frente
a determinadas condiciones climáticas, y
además ocasionar daños en cultivos agrícolas,
plantaciones y pastizales. La relación entre la
microdistribución del ensamble de Orthoptera
presente en el valle de Elqui y el índice NDVI
mostró una clara preferencia por la vegetación
densa y poco densa (NDVI = 0,1 - 0,49). El
presente trabajo es una primera aproximación
al estudio de los ortópteros considerados
plagas potenciales para el valle del Elqui.The Elqui river basin (Coquimbo Region,
Chile) is an important fruit-growing and tourist
center in the North and Central area of Chile,
where climate conditions are characterized
by a rise in temperature and decrease in
precipitation. Within the context of global
warming, the hydrographical basin of the
Elqui River is expected to show a rising
trend toward aridity, as well as alterations
in the phenology of plants and arthropods,
and changes in the local biodiversity and
richness of ecosystems. In this respect,
this research analyzes the taxonomic
composition, abundance and distribution
of the assemblage of Orthoptera (Insecta)
through hand-collecting in rangeland and
farmland of the localities of Marquesa,
Diaguitas, and Pisco Elqui in the Elqui
valley. We documented the taxonomic
composition and abundance of the Orthoptera
assemblage (Insecta), and analyzed the
spatial distribution of its component species by
using SIG. We also documented the potential
orthopterans have to become a plague in this
arid watershed of North-Central Chile. A total
of 204 specimens were captured, belonging
to four families and six species, five of which
were common to rangeland and farmland.
Acrididae was the most abundant and
varied family among the study sites (65.2%
of the total captured) and Trimerotropis
ochraceipennis the most abundant species.
The families Gryllidae, Ommexechidae and
Tristiridae were represented by only one
species. The presence of these species
in the rangeland can be a risk factor for
agriculture, considering potential irruptive
outbreaks under certain climate conditions,
and can also cause damage to crops,
plantations and grasslands. The relationship
between microdistribution of the Orthoptera
assemblage present in the Elqui valley and
the NDVI index showed a clear preference
for dense and not so dense vegetation (NDVI
= 0.1 - 0.49). This is a first approach to the
study of orthopterans which are considered
potential plagues to the Elqui valley.Fil: Alfaro, Fermín M..
Universidad de La Serena (Chile)Fil: Pizarro-Araya, Jaime.
Universidad de La Serena (Chile)Fil: Cepeda-Pizarro, Jorge.
Universidad de La Serena (Chile)Fil: Bodini, Andrés.
Centro de Estudios Avanzados en Zonas Áridas (La Serena, Chile
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