31 research outputs found
Klein-like tunneling of sound via negative index metamaterials
Klein tunneling is a counterintuitive quantum-mechanical phenomenon,
predicting perfect transmission of relativistic particles through higher energy
barriers. This phenomenon was shown to be supported at normal incidence in
graphene due to pseudospin conservation. Here I show that Klein tunneling
analogue can occur in classical systems, and remarkably, not relying on
mimicking graphene's spinor wavefunction structure. Instead, the mechanism
requires a particular form of constitutive parameters of the penetrated medium,
yielding transmission properties identical to the quantum tunneling in
graphene. I demonstrate this result by simulating tunneling of sound in a
two-dimensional acoustic metamaterial. More strikingly, I show that by
introducing a certain form of anisotropy, the tunneling can be made unimpeded
for any incidence angle, while keeping most of its original Klein dispersion
properties. This phenomenon may be denoted by the omnidirectional Klein-like
tunneling. The new tunneling mechanism and its omnidirectional variant may be
useful for applications requiring lossless and direction-independent
transmission of classical waves
Temporal negative refraction
Negative refraction is a peculiar wave propagation phenomenon that occurs
when a wave crosses a boundary between a regular medium and a medium with both
constitutive parameters negative at the given frequency. The phase and group
velocities of the transmitted wave then turn anti-parallel. Here we propose a
temporal analogue of the negative refraction phenomenon using time-dependent
media. Instead of transmitting the wave through a spatial boundary we transmit
it through an artificial temporal boundary, created by switching both
parameters from constant to dispersive with frequency. We show that the
resulting dynamics is sharply different from the spatial case, featuring both
reflection and refraction in positive and negative regimes simultaneously. We
demonstrate our results analytically and numerically using electromagnetic
medium. In addition, we show that by a targeted dispersion tuning the temporal
boundary can be made nonreflecting, while preserving both positive and negative
refraction
Active Control Approach to Temporal Acoustic Cloaking
We propose a realization of a transformation-based acoustic temporal cloak
using an active closed-loop control approach to an equivalent electromagnetic
problem. Unlike the more common spatial cloaks the goal of which is hiding
fixed objects from detection, the goal of the temporal cloak is hiding the
occurrence of events during a finite period of time. In electromagnetic
systems, in which events represent, for example, leakage of signals from
transmission lines or optical fibers, temporal cloaking solutions usually rely
on nonlinear phenomena related to the fibers properties, or on modulating the
properties of the propagation medium itself. In particular, the
transformation-based solution requires modulating the constitutive parameters
of the medium both in space and time. Our control approach is fully linear,
where the required change in the medium parameters is programmed into the
controllers and created by external actuators in real-time. This cloaking
system keeps the physical medium unchanged, and enables to reprogram the
cloaking parameters upon request. We demonstrate our solution in a simulation
of a one-dimensional water channel
Real-time-controlled artificial quiet channel for acoustic cloaking under varying detection conditions
We consider the problem of hiding non-stationary objects from acoustic
detection in a two-dimensional environment, where both the object's impedance
and the properties of the detection signal may vary during operation. The
detection signal is assumed to be an acoustic beam created by an array of
emitters, which scans the area at different angles and different frequencies.
We propose an active control-based solution that creates an effective moving
dead zone around the object, and results in an artificial quiet channel for the
object to pass through undetected. The control principle is based on mid-domain
generation of near uni-directional beams using only monopole actuators. Based
on real-time response prediction, these beams open and close the dead zone with
a minimal perturbation backwards, which is crucial due to detector observers
being located on both sides of the object's route. The back action wave
determines the cloak efficiency, and is traded-off with the control effort; the
higher is the effort the quieter is the cloaking channel. We validate our
control algorithm via numerical experiments in a two-dimensional acoustic
waveguide, testing variation in frequency and incidence angle of the detection
source. Our cloak successfully intercepts the source by steering the control
beams and adjusting their wavelength accordingly
Coexisting localized and extended in-gap states in non Hermitian system
We study the interplay of two different non-Hermitian constitutive
parameters: directional coupling and onsite gain/loss balancing along with
topology in a coupled one dimensional (1D) lattice chain. This work
demonstrates two distinct localization behaviors for the bulk and discrete
in-gap eigen modes in the system. We numerically show that the bulk and half of
the in-gap modes are strongly confined at the boundaries due to directional
hopping and topological localization, respectively. Whereas, correlation
between the constitutive non-Hermitian parameters can tune the energy and
localization length of the remaining in-gap modes and demonstrates two novel
phenomena: one is when the directional strength and gain/loss match these
states become completely extended. Second, coalescing of these modes into
exceptional point (EP). We present explicit analytical solutions for the eigen
function and energy of in-gap modes, that exactly matches with our numerical
results and uncover the origin of delocalization and emergence of EP
Noncapsulated Klebsiella pneumoniae bearing mannose-containing O antigens is rapidly eradicated from mouse lung and triggers cytokine production by macrophages following opsonization with surfactant protein D
To better understand the relationship between the surface polysaccharides of pulmonary pathogens and components of the lung innate immune system, we employed selected serotypes of Klebsiella pneumoniae expressing distinct capsular polysaccharides and/or O antigen in a murine model of K. pneumoniae infection. In addition, we examined the effect of surfactant protein D (SP-D) on the cytokine response of human monocyte-derived macrophages to these serotypes in vitro. Noncapsulated mannose-containing O3 serotypes (K50/n and K55/n), which react efficiently with SP-D in vitro, triggered high levels of interleukin-1β (IL-1β) and IL-6 production. In vivo, they were more efficiently cleared from the lungs of mice but not from macrophage-depleted mice. They also were more efficiently internalized by alveolar macrophages in vivo. In contrast, galactose-containing O1 serotypes (K2/n and K21a/n), which interact poorly with SP-D, exhibited significantly lower cytokine production and less efficient pulmonary clearance and were ineffectively internalized by alveolar macrophages. These findings are consistent with in vitro results showing that production of IL-1β and IL-6 mRNA and IL-6 protein by human macrophages exposed to mannose-bearing Klebsiella O serotypes is significantly increased by SP-D. Thus, survival of inhaled bacteria in the lung depends partially on the lipopolysaccharide structure of the bacteria and their interactions with innate immunity components. We speculate that an imbalance of host SP-D and therefore cytokine levels may result in high susceptibility of the host to the pathogen
Abdominal wall closure with a silastic patch after repair of congenital diaphragmatic hernia
Hypothesis: Newborns with congenital diaphragmatic hernia (CDH) have a high risk of mortality, ranging from 50% to 70%. Tensioned closure of the narrowed abdominal cavity is detrimental.
Patients and Methods Twelve high-risk newborns underwent operation for CDH. To achieve tension-free closure of the abdominal wall, a Silastic patch was used. The Silastic patch was sutured intermittently to the edges of the abdominal wall fascia with absorbable sutures and left open to the air. The skin was not closed above the Silastic patch, which was lubricated with 1% gentamicin sulfate ointment.
Results: Eleven patients (91.6%) survived. No local or systemic septic complication occurred. The abdominal wall was gradually closed, and total closure was achieved within 4 to 6 weeks (mean, 4.9 weeks).
Conclusion :Because of the high survival rate and the complication-free rapid healing of the abdominal wall, the technique can be used in any case of CHD in which tension-free closure of the abdominal wall cannot be achieved by other methods