Manipulating the quasi-normal modes of radially symmetric resonators.

The frequency response of a resonator is governed by the locations of its quasi-normal modes in the complex frequency plane. The real part of the quasi-normal mode determines the resonance frequency and the imaginary part determines the width of the resonance. For applications such as energy harvesting and sensing, the ability to manipulate the frequency, linewidth and multipolar nature of resonances is key. Here, we derive two methods for simultaneously controlling the resonance frequency, linewidth and multipolar nature of the resonances of radially symmetric structures. Firstly, we formulate an eigenvalue problem for a global shift in the permittivity of the structure to place a resonance at a particular complex frequency. Next, we employ quasi-normal mode perturbation theory to design radially graded structures with resonances at desired frequencies.

Quantum electrodynamics of time-varying gratings.

Gratings which are in apparent motion reveal some startling properties for classical radiation, especially for luminal gratings traveling at or around the speed of light. We show here that their quantum properties are even more remarkable, their effective refractive index modeling the Schwarzschild singularity which as we show generates spontaneous Hawking radiation in correlated photon pairs. Subjected to external radiation, luminal gratings provoke stimulated emission of photon pairs which we propose as a possible means of observing Hawking radiation in the laboratory.

Double-layer geodesic and gradient-index lenses.

A double-layer lens consists of a first gradient-index/geodesic profile in an upper waveguide, partially surrounded by a mirror that reflects the wave into a lower guide where there is a second profile. Here, we derive a new family of rotational-symmetric inhomogeneous index profiles and equivalent geodesic lens shapes by solving an inverse problem of pre-specified focal points. We find an equivalence where single-layer lenses have a different functionality as double-layer lenses with the same profiles. As an example, we propose, manufacture, and experimentally validate a practical implementation of a geodesic double-layer lens that is engineered for a low-profile antenna with a compact footprint in the millimeter wave band. Its unique double-layer configuration allows for two-dimensional beam scanning using the same footprint as an extension of the presented design. These lenses may find applications in future wireless communication systems and sensing instruments in microwave, sub-terahertz, and optical domains.

Memory effect assisted imaging through multimode optical fibres.

When light propagates through opaque material, the spatial information it holds becomes scrambled, but not necessarily lost. Two classes of techniques have emerged to recover this information: methods relying on optical memory effects, and transmission matrix (TM) approaches. Here we develop a general framework describing the nature of memory effects in structures of arbitrary geometry. We show how this framework, when combined with wavefront shaping driven by feedback from a guide-star, enables estimation of the TM of any such system. This highlights that guide-star assisted imaging is possible regardless of the type of memory effect a scatterer exhibits. We apply this concept to multimode fibres (MMFs) and identify a 'quasi-radial' memory effect. This allows the TM of an MMF to be approximated from only one end - an important step for micro-endoscopy. Our work broadens the applications of memory effects to a range of novel imaging and optical communication scenarios.

Coupling and confinement of current in thermoacoustic phased arrays.

When a medium is rapidly heated and cooled, heat transfers to its surroundings as sound. A controllable source of this sound is realized through joule heating of thin, conductive films by an alternating current. Here, we show that arrays of these sources generate sound unique to this mechanism. From the sound alone, we spatially resolve current flow by varying the film geometry and electrical phase. Confinement concentrates heat to such a degree that the film properties become largely irrelevant. Electrical coupling between sources creates its own distinctive sound that depends on the current flow direction, making it unusually sensitive to the interactions of multiple currents sharing the same space. By controlling the flow, a full phased array can be created from just a single film.

Photonic Hall effect and helical Zitterbewegung in a synthetic Weyl system.

Systems supporting Weyl points have gained increasing attention in condensed physics, photonics and acoustics due to their rich physics, such as Fermi arcs and chiral anomalies. Acting as sources or drains of Berry curvature, Weyl points exhibit a singularity of the Berry curvature at their core. It is, therefore, expected that the induced effect of the Berry curvature can be dramatically enhanced in systems supporting Weyl points. In this work, we construct synthetic Weyl points in a photonic crystal that consists of a honeycomb array of coupled rods with slowly varying radii along the direction of propagation. The system possesses photonic Weyl points in the synthetic space of two momenta plus an additional physical parameter with an enhanced Hall effect resulting from the large Berry curvature in the vicinity of the Weyl point. Interestingly, a helical Zitterbewegung (ZB) is observed when the wave packet traverses very close to a Weyl point, which is attributed to the contribution of the non-Abelian Berry connection arising from the near degenerate eigenstates.

Nanoscale Design of the Local Density of Optical States.

We propose a design concept for tailoring the local density of optical states (LDOS) in dielectric nanostructures, based on the phase distribution of the scattered optical fields induced by point-like emitters. First we demonstrate that the LDOS can be expressed in terms of a coherent summation of constructive and destructive contributions. By using an iterative approach, dielectric nanostructures can be designed to effectively remove the destructive terms. In this way, dielectric Mie resonators, featuring low LDOS for electric dipoles, can be reshaped to enable enhancements of 3 orders of magnitude. To demonstrate the generality of the method, we also design nanocavities that enhance the radiated power of a circular dipole, a quadrupole, and an arbitrary collection of coherent dipoles. Our concept provides a powerful tool for high-performance dielectric resonators and affords fundamental insights into light-matter coupling at the nanoscale.

Reversal of orbital angular momentum arising from an extreme Doppler shift.

The linear Doppler shift is familiar as the rise and fall in pitch of a siren as it passes by. Less well known is the rotational Doppler shift, proportional to the rotation rate between source and receiver, multiplied by the angular momentum carried by the beam. In extreme cases the Doppler shift can be larger than the rest-frame frequency and for a red shift, the observed frequency then becomes "negative." In the linear case, this effect is associated with the time reversal of the received signal, but it can be observed only with supersonic relative motion between the source and receiver. However, the rotational case is different; if the radius of rotation is smaller than the wavelength, then the velocities required to observe negative frequencies are subsonic. Using an acoustic source at [Formula: see text]100 Hz we create a rotational Doppler shift larger than the laboratory-frame frequency. We observe that once the red-shifted wave passes into the "negative frequency" regime, the angular momentum associated with the sound is reversed in sign compared with that of the laboratory frame. These low-velocity laboratory realizations of extreme Doppler shifts have relevance to superoscillatory fields and offer unique opportunities to probe interactions with rotating bodies and aspects of pseudorelativistic frame translation.

Combination of ECMO and cytokine adsorption therapy for severe sepsis with cardiogenic shock and ARDS due to Panton-Valentine leukocidin-positive Staphylococcus aureus pneumonia and H1N1.

Sepsis-induced cardiogenic shock in combination with severe acute respiratory failure represents a life-threatening combination that is often refractory to the conventional methods of treatment. We describe the case of a 33-year-old patient who developed acute cardiovascular collapse and ARDS secondary to superinfection of Panton-Valentine leukocidin-positive Staphylococcus aureus and H1N1 pneumonia who underwent successful combination therapy for severe sepsis-related cardiomyopathy and respiratory failure using extracorporeal membrane oxygenation and cytokine adsorption therapy.

Landscape-level movement patterns by lions in western Serengeti: comparing the influence of inter-specific competitors, habitat attributes and prey availability.

BACKGROUND: Where apex predators move on the landscape influences ecosystem structure and function and is therefore key to effective landscape-level management and species-specific conservation. However the factors underlying predator distribution patterns within functional ecosystems are poorly understood. Predator movement should be sensitive to the spatial patterns of inter-specific competitors, spatial variation in prey density, and landscape attributes that increase individual prey vulnerability. We investigated the relative role of these fundamental factors on seasonal resource utilization by a globally endangered apex carnivore, the African lion (Panthera leo) in Tanzania's Serengeti National Park. Lion space use was represented by novel landscape-level, modified utilization distributions (termed "localized density distributions") created from telemetry relocations of individual lions from multiple neighbouring prides. Spatial patterns of inter-specific competitors were similarly determined from telemetry re-locations of spotted hyenas (Crocuta crocuta), this system's primary competitor for lions; prey distribution was derived from 18 months of detailed census data; and remote sensing data was used to represent relevant habitat attributes. RESULTS: Lion space use was consistently influenced by landscape attributes that increase individual prey vulnerability to predation. Wet season activity, when available prey were scarce, was concentrated near embankments, which provide ambush opportunities, and dry season activity, when available prey were abundant, near remaining water sources where prey occurrence is predictable. Lion space use patterns were positively associated with areas of high prey biomass, but only in the prey abundant dry season. Finally, at the broad scale of this analysis, lion and hyena space use was positively correlated in the comparatively prey-rich dry season and unrelated in the wet season, suggesting lion movement was unconstrained by the spatial patterns of their main inter-specific competitors. CONCLUSIONS: The availability of potential prey and vulnerability of that prey to predation both motivate lion movement decisions, with their relative importance apparently mediated by overall prey abundance. With practical and theoretical implications, these results suggest that while top carnivores are consistently cognizant of how landscape features influence individual prey vulnerability, they also adopt a flexible approach to range use by adjusting spatial behaviour according to fluctuations in local prey abundance.

Everolimus Versus Mycophenolate Mofetil De Novo After Lung Transplantation: A Prospective, Randomized, Open-Label Trial.

The role of mammalian target of rapamycin (mTOR) inhibitors in de novo immunosuppression after lung transplantation is not well defined. We compared Everolimus versus mycophenolate mofetil in an investigator-initiated single-center trial in Hannover, Germany. A total of 190 patients were randomly assigned 1:1 on day 28 posttransplantation to mycophenolate mofetil (MMF) or Everolimus combined with cyclosporine A (CsA) and steroids. Patients were followed up for 2 years. The primary endpoint was freedom from bronchiolitis obliterans syndrome (BOS). The secondary endpoints were incidence of acute rejections, infections, treatment failure and kidney function. BOS-free survival in intention-to-treat (ITT) analysis was similar in both groups (p = 0.174). The study protocol was completed by 51% of enrolled patients. The per-protocol analysis shows incidence of bronchiolitis obliterans syndrome (BOS): 1/43 in the Everolimus group and 8/54 in the MMF group (p = 0.041). Less biopsy-proven acute rejection (AR) (p = 0.005), cytomegalovirus (CMV) antigenemia (p = 0.005) and lower respiratory tract infection (p = 0.003) and no leucopenia were seen in the Everolimus group. The glomerular filtration rate (GFR) decreased in both groups about 50% within 6 months. Due to a high withdrawal rate, the study was underpowered to prove a difference in BOS-free survival. The dropout rate was more pronounced in the Everolimus group. Secondary endpoints indicate potential advantages of Everolimus-based protocols but also a potentially higher rate of drug-related serious adverse events.

"Hanging donors": are we still skeptical about the lungs?

BACKGROUND: Suicidal hanging may cause compression of the neck blood vessels and the airway leading, to hypoxic brain damage caused by cerebral ischemia and respiratory distress. Hanging engenders global tissue hypoxia, particularly affecting the lungs as the result of pulmonary edema and barotrauma. There is scant evidence about outcomes of transplantation with the use of lungs from "hanging donors." This study evaluates the outcomes of lung transplantations (LTx) that use organs from this group. METHODS: We retrospectively analyzed lung "organ offers" and LTx at our center between January 2007 and November 2013. The outcomes of LTx with lungs from donors with hanging as the cause of death ("hanging group") were compared with those with donors having other causes of death (control group), with the use of an unadjusted model as well as propensity score matching. RESULTS: LTx (n = 302) were performed during this period and were grouped on the basis of the cause of death in donors: the hanging group (n = 8) and the control group (n = 294). No statistically significant difference was found in the donor characteristics except for the incidence of cardiac arrest, which was significantly higher in hanging donors. Preoperative characteristics in recipients in both groups were comparable. Intra-operative and post-LTx variables including PaO2/FiO2 ratios, duration of mechanical ventilation, and intensive care unit and hospital stays were comparable. One-year and 3-year survival rates were also comparable in both groups. Two recipients in the hanging group required extracorporeal life support after LTx and could not survive. CONCLUSIONS: Suicidal hanging is a relatively rare cause of death for potential organ donors. Because it does not appear to negatively affect outcomes after LTx, it should not be considered per se a contraindication for lung donation. A word of caution is necessary until we gather larger experience with lungs from hanging donors.

Utilization of the organ care system as ex-vivo lung perfusion after cold storage transportation.

The Organ Care System (OCS) allows perfusion and ventilation of the donor lungs under physiological conditions. Ongoing trials to compare preservation with OCS Lung with standard cold storage do not include donor lungs with suboptimal gas exchange and donor lungs treated with OCS following cold storage transportation. We present a case of a 48-yr-old man who received such lungs after cold storage transportation treated with ex-vivo lung perfusion utilizing OCS.

Utilization of the Organ Care System Lung for the assessment of lungs from a donor after cardiac death (DCD) before bilateral transplantation.

In this manuscript, we present the first experience of evaluating donation after circulatory death (DCD) lungs, using the normothermic preservation Organ Care System (OCS) and subsequent successful transplantation. The OCS could be a useful tool for the evaluation of marginal lungs from DCD donors as it allows a proper recruitment and bronchoscopy in such donations in addition to continuous ex-vivo perfusion and assessment and treatment during transport. The OCS could potentially be a standard of care in the evaluation of marginal lungs from DCD.

Evidence of clinical efficacy of counterpulsation therapy methods.

Although heart transplantation remains the ultimate treatment for end-stage heart failure, its epidemiological impact is limited by donor organ availability. Surgical and device-based approaches have been introduced with the aim of increasing systemic perfusion and in some circumstances promoting left ventricular recovery by inducing reverse remodelling. Innovative counterpulsation devices based on the established principle of the intra-aortic balloon pump have been developed, and of these, the CardioVad and the C-Pulse System have been introduced in clinical practice with convincing evidence of haemodynamic efficacy. The evolution from pulsatile to continuous-flow left ventricular assist devices has been associated with improved survival rates during the first 2 years of support with the potential of matching heart transplantation outcomes. However, blood contact with the device remains a significant challenge despite the highly sophisticated technology currently available. Innovative extra-vascular counterpulsation devices have been shown to overcome the limitations of the intra-aortic balloon pump and rend the device suitable for prolonged support. Monitoring of the performance of these novel devices is essential, and carotid Doppler ultrasonography is of utility in assessing the haemodynamic performance of the devices in a clinical setting. Computational modelling has played a role in the simulation of these devices and should continue to assist with their optimisation and implementation in clinical practice.

Oxy-RVAD: rescue in pulmonary complications after LVAD implantation.

Pulmonary complications after left ventricular assist device (LVAD) implantation seldom occur; however, if present, they may prove catastrophic. An Oxy-RVAD (oxygenator in right VAD circuit) is a lifesaving technique in such cases and allows freedom of introducing and removing an oxygenator into the RVAD circuit without opening the chest and competing with LVAD flow.

Outcomes in patients receiving HeartMate II versus HVAD left ventricular assist device as a bridge to transplantation.

OBJECTIVE: Ventricular assist devices have become a standard treatment for patients with advanced heart failure. We present data comparing results after implantation of HeartMate II (HM II) versus HVAD (HW) left ventricular assist devices (LVADs) for the past 7 years at our institution. METHODS: From July 2006 to August 2012, 121 consecutive patients underwent LVAD implantation: 70 (57.9%) received HM II and 51 (42.1%) HW. Patient demographics, perioperative characteristics, and laboratory parameters as well as postoperative outcome were compared retrospectively. RESULTS: Patients in the HM II group were significantly younger (P < .01), with more deranged liver function (higher bilirubin [P = .02] and alanine aminotransferase [P = .01] levels), and had a significantly higher rate of preoperative infections requiring antibiotic treatment (P = .02) and a higher body core temperature (P < .01). Other demographic and preoperative parameters did not show statistical differences. Most postoperative characteristics were also similar between the two groups. HM II patients had a significantly higher transfusion rate, but there were no differences in incidence of resternotomy (P = .156). Recovery and VAD explantation were more likely in the HM II group (P = .02). Although there was no significant difference in survival (log rank test: P = .986; Breslow test: P = .827), HM II patients were more likely to develop a percutaneous site infection (P = .01). CONCLUSIONS: Both HM II and HW provide similar early postoperative outcome and good long-term survival. The differences observed between the groups may be related to demographic and preoperative factors rather than the type of the device used.

Asynchronous food-web pathways could buffer the response of Serengeti predators to El Niño Southern Oscillation.

Understanding how entire ecosystems maintain stability in the face of climatic and human disturbance is one of the most fundamental challenges in ecology. Theory suggests that a crucial factor determining the degree of ecosystem stability is simply the degree of synchrony with which different species in ecological food webs respond to environmental stochasticity. Ecosystems in which all food-web pathways are affected similarly by external disturbance should amplify variability in top carnivore abundance over time due to population interactions, whereas ecosystems in which a large fraction of pathways are nonresponsive or even inversely responsive to external disturbance will have more constant levels of abundance at upper trophic levels. To test the mechanism underlying this hypothesis, we used over half a century of demographic data for multiple species in the Serengeti (Tanzania) ecosystem to measure the degree of synchrony to variation imposed by an external environmental driver, the El Niño Southern Oscillation (ENSO). ENSO effects were mediated largely via changes in dry-season vs. wet-season rainfall and consequent changes in vegetation availability, propagating via bottom-up effects to higher levels of the Serengeti food web to influence herbivores, predators and parasites. Some species in the Serengeti food web responded to the influence of ENSO in opposite ways, whereas other species were insensitive to variation in ENSO. Although far from conclusive, our results suggest that a diffuse mixture of herbivore responses could help buffer top carnivores, such as Serengeti lions, from variability in climate. Future global climate changes that favor some pathways over others, however, could alter the effectiveness of such processes in the future.