2,457 research outputs found
Approaching the Ground State of Frustrated A-site Spinels: A Combined Magnetization and Polarized Neutron Scattering Study
We re-investigate the magnetically frustrated, {\it
diamond-lattice-antiferromagnet} spinels FeAlO and MnAlO using
magnetization measurements and diffuse scattering of polarized neutrons. In
FeAlO, macroscopic measurements evidence a "cusp" in zero field-cooled
susceptibility around 13~K. Dynamic magnetic susceptibility and {\it memory
effect} experiments provide results that do not conform with a canonical
spin-glass scenario in this material. Through polarized neutron scattering
studies, absence of long-range magnetic order down to 4~K is confirmed in
FeAlO. By modeling the powder averaged differential magnetic neutron
scattering cross-section, we estimate that the spin-spin correlations in this
compound extend up to the third nearest-neighbour shell. The estimated value of
the Land\'{e} factor points towards orbital contributions from Fe.
This is also supported by a Curie-Weiss analysis of the magnetic
susceptibility. MnAlO, on the contrary, undergoes a magnetic phase
transition into a long-range ordered state below 40~K, which is
confirmed by macroscopic measurements and polarized neutron diffraction.
However, the polarized neutron studies reveal the existence of prominent
spin-fluctuations co-existing with long-range antiferromagnetic order. The
magnetic diffuse intensity suggests a similar short range order as in
FeAlO. Results of the present work supports the importance of spin-spin
correlations in understanding magnetic response of frustrated magnets like
-site spinels which have predominant short-range spin correlations
reminiscent of the "spin liquid" state.Comment: 10 pages, 10 figures, double-column, accepted in Phys. Rev. B, 201
Superconductivity in Ca-doped graphene
Graphene, a zero-gap semimetal, can be transformed into a metallic,
semiconducting or insulating state by either physical or chemical modification.
Superconductivity is conspicuously missing among these states despite
considerable experimental efforts as well as many theoretical proposals. Here,
we report superconductivity in calcium-decorated graphene achieved by
intercalation of graphene laminates that consist of well separated and
electronically decoupled graphene crystals. In contrast to intercalated
graphite, we find that Ca is the only dopant that induces superconductivity in
graphene laminates above 1.8 K among intercalants used in our experiments such
as potassium, caesium and lithium. Ca-decorated graphene becomes
superconducting at ~ 6 K and the transition temperature is found to be strongly
dependent on the confinement of the Ca layer and the induced charge carrier
concentration. In addition to the first evidence for superconducting graphene,
our work shows a possibility of inducing and studying superconductivity in
other 2D materials using their laminates
Precise and ultrafast molecular sieving through graphene oxide membranes
There has been intense interest in filtration and separation properties of
graphene-based materials that can have well-defined nanometer pores and exhibit
low frictional water flow inside them. Here we investigate molecular permeation
through graphene oxide laminates. They are vacuum-tight in the dry state but,
if immersed in water, act as molecular sieves blocking all solutes with
hydrated radii larger than 4.5A. Smaller ions permeate through the membranes
with little impedance, many orders of magnitude faster than the diffusion
mechanism can account for. We explain this behavior by a network of
nanocapillaries that open up in the hydrated state and accept only species that
fit in. The ultrafast separation of small salts is attributed to an 'ion
sponge' effect that results in highly concentrated salt solutions inside
graphene capillaries
Approaching the Ground State of Frustrated A-site Spinels: A Combined Magnetization and Polarized Neutron Scattering Study
We re-investigate the magnetically frustrated, {\it
diamond-lattice-antiferromagnet} spinels FeAlO and MnAlO using
magnetization measurements and diffuse scattering of polarized neutrons. In
FeAlO, macroscopic measurements evidence a "cusp" in zero field-cooled
susceptibility around 13~K. Dynamic magnetic susceptibility and {\it memory
effect} experiments provide results that do not conform with a canonical
spin-glass scenario in this material. Through polarized neutron scattering
studies, absence of long-range magnetic order down to 4~K is confirmed in
FeAlO. By modeling the powder averaged differential magnetic neutron
scattering cross-section, we estimate that the spin-spin correlations in this
compound extend up to the third nearest-neighbour shell. The estimated value of
the Land\'{e} factor points towards orbital contributions from Fe.
This is also supported by a Curie-Weiss analysis of the magnetic
susceptibility. MnAlO, on the contrary, undergoes a magnetic phase
transition into a long-range ordered state below 40~K, which is
confirmed by macroscopic measurements and polarized neutron diffraction.
However, the polarized neutron studies reveal the existence of prominent
spin-fluctuations co-existing with long-range antiferromagnetic order. The
magnetic diffuse intensity suggests a similar short range order as in
FeAlO. Results of the present work supports the importance of spin-spin
correlations in understanding magnetic response of frustrated magnets like
-site spinels which have predominant short-range spin correlations
reminiscent of the "spin liquid" state.Comment: 10 pages, 10 figures, double-column, accepted in Phys. Rev. B, 201
Impermeable Barrier Films and Protective Coatings Based on Reduced Graphene Oxide
Barrier films preventing permeation of gases and moistures are important for
many industries ranging from food to medical and from chemical to electronic.
From this perspective, graphene has recently attracted particular interest
because its defect free monolayers are impermeable to all gases and liquids.
However, it has proved challenging to develop large-area defectless graphene
films suitable for industrial use. Here we report barrier properties of
multilayer graphitic films made by chemical reduction of easily and cheaply
produced graphene oxide laminates. They are found to provide a practically
perfect barrier that blocks all gases, liquids and aggressive chemicals
including, for example, hydrofluoric acid. In particular, if graphene oxide
laminates are reduced in hydroiodic acid, no permeation of hydrogen and water
could be detected for films as thin as 30 nm, which remain optically
transparent. The films thicker than 100 nm become completely impermeable. The
exceptional barrier properties are attributed to a high degree of
graphitization of the laminates and little structural damage during reduction.
This work indicates a close prospect of thin protective coatings with stability
and inertness similar to that of graphene and bulk graphite, which can be
interesting for numerous applications
Controlling the Decoration of the Reduced Graphene Oxide Surface with Pyrene-Functionalized Gold Nanoparticles
We exploited a non‐covalent approach based on π‐stacking interactions to
address the formation of hybrids between pyrene‐functionalized gold
nanoparticles (PyAuNPs) and reduced graphene oxide (RGO), in which the former
are distributed homogeneously on the surface of the latter with a high degree
of coverage. We used water soluble PyAuNPs of two different average
dimensions, namely 2 and 8 nm, in which the pendant pyrene moieties were
introduced within a mixed monolayer with a choline derivative. The combination
with RGO originates highly insoluble materials, in which microscopy evidences
a complete adhesion of the PyAuNPs onto the carbon nanomaterial layers in a
highly homogeneous fashion, with no traces of free particles, confirming the
high affinity between pyrene‐functionalized species and conjugated carbon
nanostructure surfaces
The capBCA Locus is Required for Intracellular Growth of Francisella tularensis LVS
Francisella tularensis is the causative agent of tularemia and a category A bioterrorism agent. The molecular basis for the extreme virulence of F. tularensis remains unclear. Our recent study found that capBCA, three neighboring genes, are necessary for the infection of F. tularensis live vaccine strain (LVS) in a respiratory infection mouse model. We here show that the capBCA genes are necessary for in vivo growth of F. tularensis LVS in the lungs, spleens, and livers of BALB/c mice. Unmarked deletion of capBCA in type A strain Schu S4 resulted in significant attenuation in virulence although the level of the attenuation in Schu S4 was much less profound than in LVS. We further demonstrated that CapB protein is produced at a low level under the in vitro culture conditions, and capB alone is necessary for in vivo growth of F. tularensis LVS in the lungs of BALB/c mice. Finally, deletional mutations in capB alone or capBCA significantly impaired intracellular growth of F. tularensis LVS in cultured macrophages, thus suggesting that the capBCA genes are necessary for intracellular adaptation of F. tularensis. The requirement of this gene locus in intracellular adaption at least in part explains the significant attenuation of F. tularensis capBCA mutants in virulence
Updated Genes, Lifestyles, and their Interactions for Human Longevity
Healthy aging is the prolonging of optimal wellbeing during the progressive decline in physiological functions that are necessary for survival. Two important components of aging include an individual’s genetic makeup and lifestyle choices such as diet and exercise. Genetic factors are responsible for the functional physiology of the body including cell maintenance, metabolism and apoptosis. The individual effects of genes and lifestyle choices on aging are reported mainly in Caucasian populations, with very limited studies in minority populations. In this review, we included the effects of genes and environment and the interaction between them on aging in Hispanic population in addition to other populations.
Our systematic review focuses on exploring present findings that assess the involvement of genes and lifestyles with healthy aging, as well as the interactions between the two. The purpose of the review is to update current findings of longevity as it pertains to the genetic composition of humans and the lifestyle choices people make. We were specifically looking for research conducted in the US Hispanic population and/or other minority populations. We searched through PubMed to identify reliable and relevant research articles involving ‘genes’, ‘lifestyle’, ‘longevity’, and ‘healthy aging’. We filtered the articles for those that pertain towards humans and are in the English language.
We searched most updated top longevity-associated genes, lifestyles, and their interactions. We found that the biological and environmental factors (e.g., lifestyle) involved in aging are important factors that attribute towards attainment of longevity.
The individual’s genetic composition and lifestyle choices significantly impact the aging process and longevity
- …