202 research outputs found
Growth of epitaxially oriented Ag nanoislands on air-oxidized Si(111)-(7x7) surfaces: Influence of short range order on the substrate
Clean Si(111)-(7{x7) surfaces, followed by air-exposure, have been
investigated by reflection high energy electron diffraction (RHEED) and
scanning tunneling microscopy (STM). Fourier transforms (FTs) of STM images
show the presence of short range (7x7) order on the air-oxidized surface.
Comparison with FTs of STM images from a clean Si(111)-(7x7) surface shows that
only the 1/7th order spots are present on the air-oxidized surface. The oxide
layer is ~ 2-3 nm thick, as revealed by cross-sectional transmission electron
microscopy (XTEM). Growth of Ag islands on these air-oxidized Si(111)-(7x7)
surfaces has been investigated by in-situ RHEED and STM and ex-situ XTEM and
scanning electron microscopy. Ag deposition at room temperature leads to the
growth of randomly oriented Ag islands while preferred orientation evolves when
Ag is deposited at higher substrate temperatures. For deposition at 550{\deg}C
face centered cubic Ag nanoislands grow with a predominant epitaxial
orientation [1 -1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si along with its twin
[-1 1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si, as observed for epitaxial growth
of Ag on Si(111) surfaces. The twins are thus rotated by a 180{\deg} rotation
of the Ag unit cell about the Si [111] axis. It is intriguing that Ag
nanoislands follow an epitaxial relationship with the Si(111) substrate in
spite of the presence of a 2-3 nm thick oxide layer between Ag and Si.
Apparently the short range order on the oxide surface influences the
crystallographic orientation of the Ag nanoislands.Comment: 10 figure
Influence of through-flow on linear pattern formation properties in binary mixture convection
We investigate how a horizontal plane Poiseuille shear flow changes linear
convection properties in binary fluid layers heated from below. The full linear
field equations are solved with a shooting method for realistic top and bottom
boundary conditions. Through-flow induced changes of the bifurcation thresholds
(stability boundaries) for different types of convective solutions are deter-
mined in the control parameter space spanned by Rayleigh number, Soret coupling
(positive as well as negative), and through-flow Reynolds number. We elucidate
the through-flow induced lifting of the Hopf symmetry degeneracy of left and
right traveling waves in mixtures with negative Soret coupling. Finally we
determine with a saddle point analysis of the complex dispersion relation of
the field equations over the complex wave number plane the borders between
absolute and convective instabilities for different types of perturbations in
comparison with the appropriate Ginzburg-Landau amplitude equation
approximation. PACS:47.20.-k,47.20.Bp, 47.15.-x,47.54.+rComment: 19 pages, 15 Postscript figure
Capsid and Infectivity in Virus Detection
The spectacular achievements and elegance of viral RNA analyses have somewhat obscured the importance of the capsid in transmission of viruses via food and water. The capsid’s essential roles are protection of the RNA when the virion is outside the host cell and initiation of infection when the virion contacts a receptor on an appropriate host cell. Capsids of environmentally transmitted viruses are phenomenally durable. Fortuitous properties of the capsid include antigenicity, isoelectric point(s), sometimes hemagglutination, and perhaps others. These can potentially be used to characterize capsid changes that cause or accompany loss of viral infectivity and may be valuable in distinguishing native from inactivated virus when molecular detection methods are used
Regulator of G-Protein Signaling 14 (RGS14) Is a Selective H-Ras Effector
Background: Regulator of G-protein signaling (RGS) proteins have been well-described as accelerators of Ga-mediated GTP hydrolysis (‘‘GTPase-accelerating proteins’’ or GAPs). However, RGS proteins with complex domain architectures are now known to regulate much more than Ga GTPase activity. RGS14 contains tandem Ras-binding domains that have been reported to bind to Rap- but not Ras GTPases in vitro, leading to the suggestion that RGS14 is a Rap-specific effector. However, more recent data from mammals and Drosophila imply that, in vivo, RGS14 may instead be an effector of Ras.Methodology/Principal Findings: Full-length and truncated forms of purified RGS14 protein were found to bind indiscriminately in vitro to both Rap- and Ras-family GTPases, consistent with prior literature reports. In stark contrast, however, we found that in a cellular context RGS14 selectively binds to activated H-Ras and not to Rap isoforms. Co- transfection / co-immunoprecipitation experiments demonstrated the ability of full-length RGS14 to assemble a multiprotein complex with components of the ERK MAPK pathway in a manner dependent on activated H-Ras. Small interfering RNA-mediated knockdown of RGS14 inhibited both nerve growth factor- and basic fibrobast growth factor- mediated neuronal differentiation of PC12 cells, a process which is known to be dependent on Ras-ERK signaling.Conclusions/Significance: In cells, RGS14 facilitates the formation of a selective Ras?GTP-Raf-MEK-ERK multiprotein complex to promote sustained ERK activation and regulate H-Ras-dependent neuritogenesis. This cellular function for RGS14 is similar but distinct from that recently described for its closely-related paralogue, RGS12, which shares the tandem Ras- binding domain architecture with RGS14
Disturbance and the resilience of coupled carbon and nitrogen cycling in a north temperate forest
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/96419/1/jgrg864.pd
Evaluation of functional dynamics during osseointegration and regeneration associated with oral implants
The aim of this paper is to review current investigations on functional assessments of osseointegration and assess correlations to the peri-implant structure.The literature was electronically searched for studies of promoting dental implant osseointegration, functional assessments of implant stability, and finite element (FE) analyses in the field of implant dentistry, and any references regarding biological events during osseointegration were also cited as background information.Osseointegration involves a cascade of protein and cell apposition, vascular invasion, de novo bone formation and maturation to achieve the primary and secondary dental implant stability. This process may be accelerated by alteration of the implant surface roughness, developing a biomimetric interface, or local delivery of growth-promoting factors. The current available pre-clinical and clinical biomechanical assessments demonstrated a variety of correlations to the peri-implant structural parameters, and functionally integrated peri-implant structure through FE optimization can offer strong correlation to the interfacial biomechanics.The progression of osseointegration may be accelerated by alteration of the implant interface as well as growth factor applications, and functional integration of peri-implant structure may be feasible to predict the implant function during osseointegration. More research in this field is still needed. To cite this article: Chang P-C, Lang NP, Giannobile WV. Evaluation of functional dynamics during osseointegration and regeneration associated with oral implants. Clin. Oral Impl. Res . 21 , 2010; 1–12.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78668/1/j.1600-0501.2009.01826.x.pd
Materials in particulate form for tissue engineering. 1 Basic concepts
For biomedical applications, materials small in size are growing in importance. In an era where
‘nano’ is the new trend, micro- and nano-materials are in the forefront of developments. Materials in
the particulate form aim to designate systems with a reduced size, such as micro- and nanoparticles.
These systems can be produced starting from a diversity of materials, of which polymers are the
most used. Similarly, a multitude of methods are used to produce particulate systems, and both
materials and methods are critically reviewed here. Among the varied applications that materials
in the particulate form can have, drug delivery systems are probably the most prominent, as these
have been in the forefront of interest for biomedical applications. The basic concepts pertaining
to drug delivery are summarized, and the role of polymers as drug delivery systems conclude this
review
Spectacular horizons: the birth of science fiction film, television, and radio, 1900-1959
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