72 research outputs found
Indentation of a floating elastic sheet: Geometry versus applied tension
The localized loading of an elastic sheet floating on a liquid bath occurs at
scales from a frog sitting on a lily pad to a volcano supported by the Earth's
tectonic plates. The load is supported by a combination of the stresses within
the sheet (which may include applied tensions from, for example, surface
tension) and the hydrostatic pressure in the liquid. At the same time, the
sheet deforms, and may wrinkle, because of the load. We study this problem in
terms of the (relatively weak) applied tension and the indentation depth. For
small indentation depths, we find that the force--indentation curve is linear
with a stiffness that we characterize in terms of the applied tension and
bending stiffness of the sheet. At larger indentations the force--indentation
curve becomes nonlinear and the sheet is subject to a wrinkling instability. We
study this wrinkling instability close to the buckling threshold and calculate
both the number of wrinkles at onset and the indentation depth at onset,
comparing our theoretical results with experiments. Finally, we contrast our
results with those previously reported for very thin, highly bendable
membranes.Comment: 24 pages, revised version submitted to Proc. R. Soc.
Wettability-independent droplet transport by \emph{Bendotaxis}
We demonstrate \textit{bendotaxis}, a novel mechanism for droplet
self-transport at small scales. A combination of bending and capillarity in a
thin channel causes a pressure gradient that, in turn, results in the
spontaneous movement of a liquid droplet. Surprisingly, the direction of this
motion is always the same, regardless of the wettability of the channel. We use
a combination of experiments at a macroscopic scale and a simple mathematical
model to study this motion, focussing in particular on the time scale
associated with the motion. We suggest that \emph{bendotaxis} may be a useful
means of transporting droplets in technological applications, for example in
developing self-cleaning surfaces, and discuss the implications of our results
for such applications.Comment: 5 pages, 4 figures. Supplementary Information available on reques
Dynamics of wrinkling in ultrathin elastic sheets
The wrinkling of thin elastic objects provides a means of generating regular
patterning at small scales in applications ranging from photovoltaics to
microfluidic devices. Static wrinkle patterns are known to be governed by an
energetic balance between the object's bending stiffness and an effective
substrate stiffness, which may originate from a true substrate stiffness or
from tension and curvature along the wrinkles. Here we investigate dynamic
wrinkling, induced by the impact of a solid sphere onto an ultra-thin polymer
sheet floating on water. The vertical deflection of the sheet's centre induced
by impact draws material radially inwards, resulting in an azimuthal
compression that is relieved by the wrinkling of the entire sheet. We show that
this wrinkling is truly dynamic, exhibiting features that are qualitatively
different to those seen in quasi-static wrinkling experiments. Moreover, we
show that the wrinkles coarsen dynamically because of the inhibiting effect of
the fluid inertia. This dynamic coarsening can be understood heuristically as
the result of a dynamic stiffness, which dominates the static stiffnesses
reported thus far, and allows new controls of wrinkle wavelength.Comment: 8 pages, 4 figures. Please see published version for supplementary
movies and SI Appendi
The propagation of air fingers into an elastic branching network
We study experimentally the propagation of an air finger through the
Y-bifurcation of an elastic, liquid-filled Hele-Shaw channel, as a benchtop
model of airway reopening. With channel compliance provided by an elastic upper
boundary, we can impose collapsed channel configurations into which we inject
air with constant volume-flux. We typically observe steady finger propagation
in the main channel, which is lost ahead of the Y-bifurcation but subsequently
recovered in the daughter channels. At low levels of initial collapse, steady
finger shapes and bubble pressure in the daughter channels map onto those in
the main channel, despite small differences in initial collapse in different
parts of the Y-channel. However, at higher levels of initial collapse where the
elastic sheet almost touches the bottom boundary of the channel, experimentally
indistinguishable fingers in the main channel can lead to multiple states of
reopening of the daughter channels. The downstream distance at which steady
propagation is recovered in the daughter channels also varies considerably with
injection flow rate and initial collapse because of a transition in the
mechanics regulating finger propagation. We find that the characteristic time
and length-scales of this recovery are largest in the regime where viscous and
surface tension forces dominate at low flow rate and/or low initial collapse,
and that they decrease towards a constant plateau reached in the limit where
elastic and surface tension forces balance at high flow rate and/or high
initial collapse. Our findings suggest that practical networks are unlikely to
comprise long enough channels for steady state propagation to remain
established.Comment: 36 pages, 13 finger
Impact on floating thin elastic sheets: A mathematical model
We investigate impact of a sphere onto a floating elastic sheet and the
resulting formation and evolution of wrinkles in the sheet. Following impact,
we observe a radially propagating wave, beyond which the sheet remains
approximately planar but is decorated by a series of radial wrinkles whose
wavelength grows in time. We develop a mathematical model to describe these
phenomena by exploiting the asymptotic limit in which the bending stiffness is
small compared to stresses in the sheet. The results of this analysis show
that, at a time after impact, the transverse wave is located at a radial
distance from the impactor, in contrast to the classic scaling observed for capillary--inertia ripples produced by dropping a
stone into a pond. We describe the shape of this wave, starting from the
simplest case of a point impactor, but subsequently addressing a finite-radius
spherical impactor, contrasting this case with the classic Wagner theory of
impact. We show also that the coarsening of wrinkles in the flat portion of the
sheet is controlled by the inertia of the underlying liquid: short-wavelength,
small-amplitude wrinkles form at early times since they accommodate the
geometrically-imposed compression without significantly displacing the
underlying liquid. As time progresses, the liquid accelerates and the wrinkles
grow larger and coarsen. We explain this coarsening quantitatively using
numerical simulations and scaling arguments, and we compare our predictions
with experimental data.Comment: 30 pages, 9 figures. Small edits toaccepted versio
Minimum Requirements for Detecting a Stochastic Gravitational Wave Background Using Pulsars
We assess the detectability of a nanohertz gravitational wave (GW) background
with respect to additive red and white noise in the timing of millisecond
pulsars. We develop detection criteria based on the cross-correlation function
summed over pulsar pairs in a pulsar timing array. The distribution of
correlation amplitudes is found to be non-Gaussian and highly skewed, which
significantly influences detection and false-alarm probabilities. When only
white noise and GWs contribute, our detection results are consistent with those
found by others. Red noise, however, drastically alters the results. We discuss
methods to meet the challenge of GW detection ("climbing mount significance")
by distinguishing between GW-dominated and red or white-noise limited regimes.
We characterize detection regimes by evaluating the number of millisecond
pulsars that must be monitored in a high-cadence, 5-year timing program for a
GW background spectrum with yr.
Unless a sample of 20 super-stable millisecond pulsars can be found --- those
with timing residuals from red-noise contributions ns
--- a much larger timing program on MSPs will be needed. For
other values of , the constraint is . Identification of suitable MSPs itself requires
an aggressive survey campaign followed by characterization of the level of spin
noise in the timing residuals of each object. The search and timing programs
will likely require substantial fractions of time on new array telescopes in
the southern hemisphere as well as on existing ones.Comment: Submitted to the Astrophysical Journa
Granular segregation in a thin drum rotating with periodic modulation
We present the results of an experimental investigation into the effects of a sinusoidal modulation of the rotation rate on the segregation patterns formed in thin drum of granular material. The modulation transforms the base pattern formed under steady conditions by splitting or merging the initial streaks. Specifically, the relation between the frequency of modulation and the rotation rate determines the number of streaks which develop from the base state. The results are in accord with those of Fiedor and Ottino [J. Fluid. Mech. 533, 223 (2005)10.1017/S0022112005003952], and we show that their ideas apply over a wide range of parameter space. Furthermore, we provide evidence that the observed relationship is maintained for filling fractions far from 50% and generalize the result in terms of the geometry of the granular deposit
Is the combination of immunotherapy and radiotherapy in non-small cell lung cancer a feasible and effective approach?
For many years, conventional oncologic treatments such as surgery, chemotherapy, and radiotherapy (RT) have dominated the field of non-small-cell lung cancer (NSCLC). The recent introduction of immunotherapy (IT) in clinical practice, especially strategies targeting negative regulators of the immune system, so-called immune checkpoint inhibitors, has led to a paradigm shift in lung cancer as in many other solid tumors. Although antibodies against programmed death protein-1 (PD-1) and programmed death ligand-1 (PD-L1) are currently on the forefront of the immuno-oncology field, the first efforts to eradicate cancer by exploiting the host's immune system date back to several decades ago. Even then, researchers aimed to explore the addition of RT to IT strategies in NSCLC patients, attributing its potential benefit to local control of target lesions through direct and indirect DNA damage in cancer cells. However, recent pre-clinical and clinical data have shown RT may also modify antitumor immune responses through induction of immunogenic cell death and reprogramming of the tumor microenvironment. This has led many to reexamine RT as a partner therapy to immuno-oncology treatments and investigate their potential synergy in an exponentially growing number of clinical trials. Herein, the authors review the rationale of combining IT and RT across all NSCLC disease stages and summarize both historical and current clinical evidence surrounding these combination strategies. Furthermore, an overview is provided of active clinical trials exploring the IT-RT concept in different settings of NSCLC
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