605 research outputs found
Stress relief as the driving force for self-assembled Bi nanolines
Stress resulting from mismatch between a substrate and an adsorbed material
has often been thought to be the driving force for the self-assembly of
nanoscale structures. Bi nanolines self-assemble on Si(001), and are remarkable
for their straightness and length -- they are often more than 400 nm long, and
a kink in a nanoline has never been observed. Through electronic structure
calculations, we have found an energetically favourable structure for these
nanolines that agrees with our scanning tunneling microscopy and photoemission
experiments; the structure has an extremely unusual subsurface structure,
comprising a double core of 7-membered rings of silicon. Our proposed structure
explains all the observed features of the nanolines, and shows that surface
stress resulting from the mismatch between the Bi and the Si substrate are
responsible for their self-assembly. This has wider implications for the
controlled growth of nanostructures on semiconductor surfaces.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Dynamical formation and evolution of (2+1)-dimensional charged black holes
In this paper, we investigate the dynamical formation and evolution of 2 +
1-dimensional charged black holes. We numerically study dynamical collapses of
charged matter fields in an anti de Sitter background and note the formation of
black holes using the double-null formalism. Moreover, we include re-normalized
energy-momentum tensors assuming the S-wave approximation to determine
thermodynamical back-reactions to the internal structures. If there is no
semi-classical effects, the amount of charge determines the causal structures.
If the charge is sufficiently small, the causal structure has a space-like
singularity. However, as the charge increases, an inner Cauchy horizon appears.
If we have sufficient charge, we see a space-like outer horizon and a time-like
inner horizon, and if we give excessive charge, black hole horizons disappear.
We have some circumstantial evidences that weak cosmic censorship is still
satisfied, even for such excessive charge cases. Also, we confirm that there is
mass inflation along the inner horizon, although the properties are quite
different from those of four-dimensional cases. Semi-classical back-reactions
will not affect the outer horizon, but they will affect the inner horizon. Near
the center, there is a place where negative energy is concentrated. Thus,
charged black holes in three dimensions have two types of curvature
singularities in general: via mass inflation and via a concentration of
negative energy. Finally, we classify possible causal structures.Comment: 40 pages, 15 figure
Nature of the broken-symmetry phase of the one-dimensional metallic In/Si(111) surface
Can the Horowitz-Maldacena proposal be an alternative to the firewall?
Recently, there have been discussions that black hole complementarity is
inconsistent and that the firewall is required to prohibit the observation of
duplicated information. It is thought that if the Horowitz-Maldacena proposal
works as a selection principle, then this may be an alternative to the
firewall. In this paper, we first point out that the Horowitz-Maldacena
proposal seems to help black hole complementarity for charged black holes.
However, if we consider the Hayden-Preskill argument further, which states that
a black hole can function as an information mirror after the information
retention time, then we can show that the Horowitz-Maldaceana proposal cannot
help black hole complementarity. This can be extended to neutral black hole
cases. Therefore, in conclusion, we find that dynamical black holes do not
respect complementarity, even with the Horowitz-Maldacena proposal.Comment: 11 pages, 3 figure
Nanoscale manipulation of the Mott insulating state coupled to charge order in 1T-TaS2
The controllability over strongly correlated electronic states promises unique electronic devices. A recent example is an optically induced ultrafast switching device based on the transition between the correlated Mott insulating state and a metallic state of a transition metal dichalcogenide 1T-TaS2. However, the electronic switching has been challenging and the nature of the transition has been veiled. Here we demonstrate the nanoscale electronic manipulation of the Mott state of 1T-TaS2. The voltage pulse from a scanning tunnelling microscope switches the insulating phase locally into a metallic phase with irregularly textured domain walls in the charge density wave order inherent to this Mott state. The metallic state is revealed as a correlated phase, which is induced by the moderate reduction of electron correlation due to the charge density wave decoherence.131321sciescopu
Development of an optogenetic toolkit for neural circuit dissection in squirrel monkeys
Optogenetic tools have opened a rich experimental landscape for understanding neural function and disease. Here, we present the first validation of eight optogenetic constructs driven by recombinant adeno-associated virus (AAV) vectors and a WGA-Cre based dual injection strategy for projection targeting in a widely-used New World primate model, the common squirrel monkey Saimiri sciureus. We observed opsin expression around the local injection site and in axonal projections to downstream regions, as well as transduction to thalamic neurons, resembling expression patterns observed in macaques. Optical stimulation drove strong, reliable excitatory responses in local neural populations for two depolarizing opsins in anesthetized monkeys. Finally, we observed continued, healthy opsin expression for at least one year. These data suggest that optogenetic tools can be readily applied in squirrel monkeys, an important first step in enabling precise, targeted manipulation of neural circuits in these highly trainable, cognitively sophisticated animals. In conjunction with similar approaches in macaques and marmosets, optogenetic manipulation of neural circuits in squirrel monkeys will provide functional, comparative insights into neural circuits which subserve dextrous motor control as well as other adaptive behaviors across the primate lineage. Additionally, development of these tools in squirrel monkeys, a well-established model system for several human neurological diseases, can aid in identifying novel treatment strategies
An ES-Like Pluripotent State in FGF-Dependent Murine iPS cells
Recent data demonstrates that stem cells can exist in two morphologically, molecularly and functionally distinct pluripotent states; a naïve LIF-dependent pluripotent state which is represented by murine embryonic stem cells (mESCs) and an FGF-dependent primed pluripotent state represented by murine and rat epiblast stem cells (EpiSCs). We find that derivation of induced pluripotent stem cells (iPSCs) under EpiSC culture conditions yields FGF-dependent iPSCs from hereon called FGF-iPSCs) which, unexpectedly, display naïve ES-like/ICM properties. FGF-iPSCs display X-chromosome activation, multi-lineage differentiation, teratoma competence and chimera contribution in vivo. Our findings suggest that in 129 and Bl6 mouse strains, iPSCs can dominantly adopt a naive pluripotent state regardless of culture growth factor conditions
Determination of the bonding configuration of the metastable molecular oxygen adsorbed on a Si(111)-(7×7) surface
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