1,346 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
The causal structure of dynamical charged black holes
We study the causal structure of dynamical charged black holes, with a
sufficient number of massless fields, using numerical simulations. Neglecting
Hawking radiation, the inner horizon is a null Cauchy horizon and a curvature
singularity due to mass inflation. When we include Hawking radiation, the inner
horizon becomes space-like and is separated from the Cauchy horizon, which is
parallel to the out-going null direction. Since a charged black hole must
eventually transit to a neutral black hole, we studied the neutralization of
the black hole and observed that the inner horizon evolves into a space-like
singularity, generating a Cauchy horizon which is parallel to the in-going null
direction. Since the mass function is finite around the inner horizon, the
inner horizon is regular and penetrable in a general relativistic sense.
However, since the curvature functions become trans-Planckian, we cannot
saymore about the region beyond the inner horizon, and it is natural to say
that there is a 'physical' space-like singularity. However, if we assume an
exponentially large number of massless scalar fields, our results can be
extended beyond the inner horizon. In this case, strong cosmic censorship and
black hole complementarity can be violated.Comment: 23 pages, 23 figure
No-boundary measure and preference for large e-foldings in multi-field inflation
The no-boundary wave function of quantum gravity usually assigns only very
small probability to long periods of inflation. This was a reason to doubt
about the no-boundary wave function to explain the observational universe. We
study the no-boundary proposal in the context of multi-field inflation to see
whether the number of fields changes the situation. For a simple model, we find
that indeed the no-boundary wave function can give higher probability for
sufficient inflation, but the number of fields involved has to be very high.Comment: 16 pages, 2 figure
Journey of water in pine cones
Pine cones fold their scales when it rains to prevent seeds from short-distance dispersal. Given that the scales of pine cones consist of nothing but dead cells, this folding motion is evidently related to structural changes. In this study, the structural characteristics of pine cones are studied on micro-/macro-scale using various imaging instruments. Raindrops fall along the outer scales to the three layers (bract scales, fibers and innermost lignified structure) of inner pine cones. However, not all the layers but only the bract scales get wet and then, most raindrops move to the inner scales. These systems reduce the amount of water used and minimize the time spent on structural changes. The result shows that the pine cones have structural advantages that could influence the efficient motion of pine cones. This study provides new insights to understand the motion of pine cones and would be used to design a novel water transport system.119Ysciescopu
X-ray PIV measurement of blood flow in deep vessels of a rat : An in vivo feasibility study
X-ray PIV measurement is a noninvasive approach to measure opaque blood flows. However, it is not easy to measure real pulsatile blood flows in the blood vessels located at deep position of the body, because the surrounding tissues significantly attenuate the contrast of X-ray images. This study investigated the effect of surrounding tissues on X-ray beam attenuation by measuring the velocity fields of blood flows in deep vessels of a live rat. The decrease in image contrast was minimized by employing biocompatible CO2 microbubbles as tracer particles. The maximum measurable velocity of blood flows in the abdominal aorta of a rat model was found through comparative examination between the PIV measurement accuracy and the level of image contrast according to the input flow rate. Furthermore, the feasibility of using X-ray PIV to accurately measure in vivo blood flows was demonstrated by determining the velocity field of blood flows in the inferior vena cava of a rat. This study may serve as a reference in conducting in vivo X-ray PIV measurements of pulsatile blood flows in animal disease models and investigating hemodynamic characteristics and circulatory vascular diseases.1176Ysciescopu
Nearly Massless Electrons in the Silicon Interface with a Metal Film
We demonstrate the realization of nearly massless electrons in the most
widely used device material, silicon, at the interface with a metal film. Using
angle-resolved photoemission, we found that the surface band of a monolayer
lead film drives a hole band of the Si inversion layer formed at the interface
with the film to have nearly linear dispersion with an effective mass about 20
times lighter than bulk Si and comparable to graphene. The reduction of mass
can be accounted for by repulsive interaction between neighboring bands of the
metal film and Si substrate. Our result suggests a promising way to take
advantage of massless carriers in silicon-based thin-film devices, which can
also be applied for various other semiconductor devices.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Dynamics of false vacuum bubbles in Brans-Dicke theory
We study the dynamics of false vacuum bubbles in the Brans-Dicke theory of
gravity by using the thin shell or thin wall approximation. We consider a false
vacuum bubble that has a different value for the Brans-Dicke field between the
inside false vacuum region and the outside true vacuum region. Within a certain
limit of field values, the difference of field values makes the effective
tension of the shell negative. This allows new expanding false vacuum bubbles
to be seen by the outside observer, which are disallowed in Einstein gravity.Comment: 29 pages, 20 figure
Relationship between temporary emotion of students and performance in learning through comparing facial expression analytics
This paper presents a study on temporary emotion of students and their performance related to learning activities. This paper elucidates different kinds of facial expressions elicited during the activities: quiz and a movie trailer with the help of existing facial expression analyzing applications. The user’s expressions are recorded as video while watching the movie trailer and doing the quiz. The video is processed by different applications which gives the score for different emotions. The results obtained are studied to find which emotion is mostly prevalent among the user in different situations. From this study, it is shown that students experience seemingly different emotions during the activity. The emotions they portrayed were confusion, sadness, anger and neutral. This study explores the use of affective computing for further comprehension of students’ emotion in learning environment
Direct observation of the spin polarization in Au atomic wires on Si(553)
The spin-resolved electronic band structure of Au-induced metallic atomic wires on a vicinal silicon surface, Si(553), was investigated using spin-and angle-resolved photoelectron spectroscopy. We directly measured the spin polarization of three partially filled one-dimensional metallic bands, a one-third-filled band, and the doublet of nearly half-filled bands. For the half-filled doublet, the strong apparent spin polarization was observed near the Fermi energy with a minor out-of-plane spin component. This observation is consistent with the Rashba-type spin-orbit splitting and with a recent experiment on a similar doublet of Si(557)-Au. In contrast, the one-third-filled band does not show a substantial spin polarization within the experimental accuracy, indicating a much smaller spin splitting, if any. These results are discussed for the origin of the partially filled bands and for the intriguing broken-symmetry ground state observed at low temperature.X11116sciescopu
Measurement of real pulsatile blood flow using x-ray PIV technique with CO2 microbubbles
Synchrotron X-ray imaging technique has been used to investigate biofluid flows in a non-destructive manner. This study aims to investigate the feasibility of the X-ray PIV technique with CO2 microbubbles as flow tracer for measurement of pulsatile blood flows under in vivo conditions. The traceability of CO2 microbubbles in a pulsatile flow was demonstrated through in vitro experiment. A rat extracorporeal bypass loop was used by connecting a tube between the abdominal aorta and jugular vein of a rat to obtain hemodynamic information of actual pulsatile blood flows without changing the hemorheological properties. The decrease in image contrast of the surrounding tissue was also investigated for in vivo applications of the proposed technique. This technique could be used to accurately measure whole velocity field information of real pulsatile blood flows and has strong potential for hemodynamic diagnosis of cardiovascular diseases.1155Ysciescopu
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