10,672 research outputs found
Curved Graphene Nanoribbons: Structure and Dynamics of Carbon Nanobelts
Carbon nanoribbons (CNRs) are graphene (planar) structures with large aspect
ratio. Carbon nanobelts (CNBs) are small graphene nanoribbons rolled up into
spiral-like structures, i. e., carbon nanoscrolls (CNSs) with large aspect
ratio. In this work we investigated the energetics and dynamical aspects of
CNBs formed from rolling up CNRs. We have carried out molecular dynamics
simulations using reactive empirical bond-order potentials. Our results show
that similarly to CNSs, CNBs formation is dominated by two major energy
contribution, the increase in the elastic energy due to the bending of the
initial planar configuration (decreasing structural stability) and the
energetic gain due to van der Waals interactions of the overlapping surface of
the rolled layers (increasing structural stability). Beyond a critical diameter
value these scrolled structures can be even more stable (in terms of energy)
than their equivalent planar configurations. In contrast to CNSs that require
energy assisted processes (sonication, chemical reactions, etc.) to be formed,
CNBs can be spontaneously formed from low temperature driven processes. Long
CNBs (length of 30.0 nm) tend to exhibit self-folded racket-like
conformations with formation dynamics very similar to the one observed for long
carbon nanotubes. Shorter CNBs will be more likely to form perfect scrolled
structures. Possible synthetic routes to fabricate CNBs from graphene membranes
are also addressed
Haptic guidance needs to be intuitive not just informative to improve human motor accuracy.
Humans make both random and systematic errors when reproducing learned movements. Intuitive haptic guidance that assists one to make the movements reduces such errors. Our study examined whether any additional haptic information about the location of the target reduces errors in a position reproduction task, or whether the haptic guidance needs to be assistive to do so. Holding a haptic device, subjects made reaches to visible targets without time constraints. They did so in a no-guidance condition, and in guidance conditions in which the direction of the force with respect to the target differed, but the force scaled with the distance to the target in the same way. We examined whether guidance forces directed towards the target would reduce subjects' errors in reproducing a prior position to the same extent as do forces rotated by 90 degrees or 180 degrees, as it might because the forces provide the same information in all three cases. Without vision of the arm, both the accuracy and precision were significantly better with guidance directed towards the target than in all other conditions. The errors with rotated guidance did not differ from those without guidance. Not surprisingly, the movements tended to be faster when guidance forces directed the reaches to the target. This study shows that haptic guidance significantly improved motor performance when using it was intuitive, while non-intuitively presented information did not lead to any improvements and seemed to be ignored even in our simple paradigm with static targets and no time constraints
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Assessment of the tissue distribution of transplanted human endothelial progenitor cells by radioactive labeling
Backgroundâ Transplantation of endothelial progenitor cells (EPCs) improves vascularization and left ventricular function after experimental myocardial ischemia. However, tissue distribution of transplanted EPCs has not yet been monitored in living animals. Therefore, we tested whether radioactive labeling allows us to detect injected EPCs
Using participatory design and visual narrative inquiry to investigate researchersâ data challenges and recommendations for library research data services
Purpose â The purpose of this paper is to report on an information gathering study on usersâ research data-related challenges and proposals for library research data services (RDS). This study probes how early career researchers visually conceptualize the research process in their disciplines, their self-reported research data challenges, and their recommendations for library RDS. Design/methodology/approach â Two focus group sessions were undertaken with a total of eight early career researchers. Adopting the visual narrative inquiry method, the participants were asked to sketch the general research process in their domain. The individualsâ illustrations of the research process were then used as the basis for reflecting on their data-related needs and potential RDS that would assist them during the research process. Findings â Participants presented a research process that was more personal and, in most cases, more imperfect than the research lifecycle models that academic libraries are increasingly using for RDS development and communication. The authors present their data-related challenges, which included data access barriers, low knowledge of best practices for research data management, the need for a deeper understanding of post-publication impact, and inconsistent awareness of existing library and institution RDS. The authors outline RDS recommendations that participants proposed, which included a web-based tools, customized training sessions, and âdistilledâ guides to research data best practices. Practical implications â The study flagged usersâ gaps in understandings of existing library and institutional RDS, suggesting that there may be an opportunity to engage users in the design of communications plans for services. The findings from this user study will inform the development of RDS at the institution. Originality/value â This paper puts forth a methodological approach that academic libraries can adapt for understanding usersâ needs and user-generated design solutions
Transient down-regulation of beta1 integrin subtypes on kidney carcinoma cells is induced by mechanical contact with endothelial cell membranes
Adhesion molecules of the integrin beta1 family are thought to be involved in the malignant progression renal cell carcinoma (RCC). Still, it is not clear how they contribute to this process. Since the hematogenous phase of tumour dissemination is the rate-limiting step in the metastatic process, we explored beta1 integrin alterations on several RCC cell lines (A498, Caki1, KTC26) before and after contacting vascular endothelium in a tumour-endothelium (HUVEC) co-culture assay. Notably, alpha2, alpha3 and alpha5 integrins became down-regulated immediately after the tumour cells attached to HUVEC, followed by re-expression shortly thereafter. Integrin down-regulation on RCC cells was caused by direct contact with endothelial cells, since the isolated endothelial membrane fragments but not the cell culture supernatant contributed to the observed effects. Integrin loss was accompanied by a reduced focal adhesion kinase (FAK) expression, FAK activity and diminished binding of tumour cells to matrix proteins. Furthermore, intracellular signalling proteins RCC cells were altered in the presence of HUVEC membrane fragments, in particular 14-3-3 epsilon, ERK2, PKCdelta, PKCepsilon and RACK1, which are involved in regulating tumour cell motility. We, therefore, speculate that contact of RCC cells with the vascular endothelium converts integrin-dependent adhesion to integrin-independent cell movement. The process of dynamic integrin regulation may be an important part in tumour cell migration strategy, switching the cells from being adhesive to becoming motile and invasive
The Two Fluid Drop Snap-off Problem: Experiments and Theory
We address the dynamics of a drop with viscosity breaking up
inside another fluid of viscosity . For , a scaling theory
predicts the time evolution of the drop shape near the point of snap-off which
is in excellent agreement with experiment and previous simulations of Lister
and Stone. We also investigate the dependence of the shape and
breaking rate.Comment: 4 pages, 3 figure
Chromatic induction and the layout of colours within a complex scene
AbstractA targetâs apparent colour is influenced by the colours in its surrounding. If the surrounding consists of a single coloured surface, the influence is a shift âawayâ from the surfaceâs colour. If the surface is more than 1° from the target area the shift is very small. If there are many surfaces, then not only the average luminance and chromaticity of the surfaces matters, but also the chromatic variability. It is not yet clear whether it makes any difference where the chromatic variability is within the scene, so we constructed stimuli in which the chromatic variability was restricted to certain regions. We found that it made very little difference where the chromatic variability was located. The extent to which the average colour of nearby surfaces influences the apparent colour of the target seems to depend on the average chromatic variability of the whole scene
Correspondence between geometrical and differential definitions of the sine and cosine functions and connection with kinematics
In classical physics, the familiar sine and cosine functions appear in two
forms: (1) geometrical, in the treatment of vectors such as forces and
velocities, and (2) differential, as solutions of oscillation and wave
equations. These two forms correspond to two different definitions of
trigonometric functions, one geometrical using right triangles and unit
circles, and the other employing differential equations. Although the two
definitions must be equivalent, this equivalence is not demonstrated in
textbooks. In this manuscript, the equivalence between the geometrical and the
differential definition is presented assuming no a priori knowledge of the
properties of sine and cosine functions. We start with the usual length
projections on the unit circle and use elementary geometry and elementary
calculus to arrive to harmonic differential equations. This more general and
abstract treatment not only reveals the equivalence of the two definitions but
also provides an instructive perspective on circular and harmonic motion as
studied in kinematics. This exercise can help develop an appreciation of
abstract thinking in physics.Comment: 6 pages including 1 figur
Finite Element Methods for Elliptic Distributed Optimal Control Problems with Pointwise State Constraints
Finite element methods for a model elliptic distributed optimal control
problem with pointwise state constraints are considered from the perspective of
fourth order boundary value problems
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