372 research outputs found
Horizon effects with surface waves on moving water
Surface waves on a stationary flow of water are considered, in a linear model
that includes the surface tension of the fluid. The resulting gravity-capillary
waves experience a rich array of horizon effects when propagating against the
flow. In some cases three horizons (points where the group velocity of the wave
reverses) exist for waves with a single laboratory frequency. Some of these
effects are familiar in fluid mechanics under the name of wave blocking, but
other aspects, in particular waves with negative co-moving frequency and the
Hawking effect, were overlooked until surface waves were investigated as
examples of analogue gravity [Sch\"utzhold R and Unruh W G 2002 Phys. Rev. D 66
044019]. A comprehensive presentation of the various horizon effects for
gravity-capillary waves is given, with emphasis on the deep water/short
wavelength case kh>>1 where many analytical results can be derived. A
similarity of the state space of the waves to that of a thermodynamic system is
pointed out.Comment: 30 pages, 15 figures. Minor change
Radial elasticity of multi-walled carbon nanotubes
We report an experimental and a theoretical study of the radial elasticity of
multi-walled carbon nanotubes as a function of external radius. We use atomic
force microscopy and apply small indentation amplitudes in order to stay in the
linear elasticity regime. The number of layers for a given tube radius is
inferred from transmission electron microscopy, revealing constant ratios of
external to internal radii. This enables a comparison with molecular dynamics
results, which also shed some light onto the applicability of Hertz theory in
this context. Using this theory, we find a radial Young modulus strongly
decreasing with increasing radius and reaching an asymptotic value of 30 +/- 10
GPa.Comment: 5 pages, 3 figure
Mapping of functionalized regions on carbon nanotubes by scanning tunneling microscopy
Scanning tunneling microscopy (STM) gives us the opportunity to map the
surface of functionalized carbon nanotubes in an energy resolved manner and
with atomic precision. But this potential is largely untapped, mainly due to
sample stability issues which inhibit reliable measurements. Here we present a
simple and straightforward solution that makes away with this difficulty, by
incorporating the functionalized multiwalled carbon nanotubes (MWCNT) into a
few layer graphene - nanotube composite. This enabled us to measure energy
resolved tunneling conductance maps on the nanotubes, which shed light on the
level of doping, charge transfer between tube and functional groups and the
dependence of defect creation or functionalization on crystallographic
orientation.Comment: Keywords: functionalization, carbon nanotubes, few layer graphene,
STM, CITS, ST
3D characterization of CdSe nanoparticles attached to carbon nanotubes
The crystallographic structure of CdSe nanoparticles attached to carbon
nanotubes has been elucidated by means of high resolution transmission electron
microscopy and high angle annular dark field scanning transmission electron
microscopy tomography. CdSe rod-like nanoparticles, grown in solution together
with carbon nanotubes, undergo a morphological transformation and become
attached to the carbon surface. Electron tomography reveals that the
nanoparticles are hexagonal-based with the (001) planes epitaxially matched to
the outer graphene layer.Comment: 7 pages, 8 figure
Hindered rolling and friction anisotropy in supported carbon nanotubes
Carbon nanotubes (CNTs) are well known for their exceptional thermal,
mechanical and electrical properties. For many CNT applications it is of the
foremost importance to know their frictional properties. However, very little
is known about the frictional forces between an individual nanotube and a
substrate or tip. Here, we present a combined theoretical and experimental
study of the frictional forces encountered by a nanosize tip sliding on top of
a supported multiwall CNT along a direction parallel or transverse to the CNT
axis. Surprisingly, we find a higher friction coefficient in the transverse
direction compared with the parallel direction. This behaviour is explained by
a simulation showing that transverse friction elicits a soft 'hindered rolling'
of the tube and a frictional dissipation that is absent, or partially absent
for chiral CNTs, when the tip slides parallel to the CNT axis. Our findings can
help in developing better strategies for large-scale CNT assembling and sorting
on a surface.Comment: 8 pages, 5 figure
A multiscale systems perspective on cancer, immunotherapy, and Interleukin-12
Monoclonal antibodies represent some of the most promising molecular targeted immunotherapies. However, understanding mechanisms by which tumors evade elimination by the immune system of the host presents a significant challenge for developing effective cancer immunotherapies. The interaction of cancer cells with the host is a complex process that is distributed across a variety of time and length scales. The time scales range from the dynamics of protein refolding (i.e., microseconds) to the dynamics of disease progression (i.e., years). The length scales span the farthest reaches of the human body (i.e., meters) down to the range of molecular interactions (i.e., nanometers). Limited ranges of time and length scales are used experimentally to observe and quantify changes in physiology due to cancer. Translating knowledge obtained from the limited scales observed experimentally to predict patient response is an essential prerequisite for the rational design of cancer immunotherapies that improve clinical outcomes. In studying multiscale systems, engineers use systems analysis and design to identify important components in a complex system and to test conceptual understanding of the integrated system behavior using simulation. The objective of this review is to summarize interactions between the tumor and cell-mediated immunity from a multiscale perspective. Interleukin-12 and its role in coordinating antibody-dependent cell-mediated cytotoxicity is used illustrate the different time and length scale that underpin cancer immunoediting. An underlying theme in this review is the potential role that simulation can play in translating knowledge across scales
Protein-based identification of quantitative trait loci associated with malignant transformation in two HER2+ cellular models of breast cancer
Background
A contemporary view of the cancer genome reveals extensive rearrangement compared to normal cells. Yet how these genetic alterations translate into specific proteomic changes that underpin acquiring the hallmarks of cancer remains unresolved. The objectives of this study were to quantify alterations in protein expression in two HER2+ cellular models of breast cancer and to infer differentially regulated signaling pathways in these models associated with the hallmarks of cancer. Results
A proteomic workflow was used to identify proteins in two HER2 positive tumorigenic cell lines (BT474 and SKBR3) that were differentially expressed relative to a normal human mammary epithelial cell line (184A1). A total of 64 (BT474-184A1) and 69 (SKBR3-184A1) proteins were uniquely identified that were differentially expressed by at least 1.5-fold. Pathway inference tools were used to interpret these proteins in terms of functionally enriched pathways in the tumor cell lines. We observed protein ubiquitination and apoptosis signaling pathways were both enriched in the two breast cancer models while IGF signaling and cell motility pathways were enriched in BT474 and amino acid metabolism were enriched in the SKBR3 cell line. Conclusion
While protein ubiquitination and apoptosis signaling pathways were common to both the cell lines, the observed patterns of protein expression suggest that the evasion of apoptosis in each tumorigenic cell line occurs via different mechanisms. Evidently, apoptosis is regulated in BT474 via down regulation of Bid and in SKBR3 via up regulation of Calpain-11 as compared to 184A1
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