Tunable Mie resonance in complex-shaped gadolinium niobate.

Nanoscale particles described by Mie resonance in the UV-vis-NIR region are in high demand for optical applications. Controlling the shape and size of these particles is essential, as it results in the ability to control the wavelength of the Mie resonance peak. In this work, we study the extensive scattering properties of gadolinium niobate particles with complex bar- and cube-like shapes in the UV-vis-NIR region. We perform our experimental analysis by characterizing the morphology and extinction spectra, and our theoretical study by implementing a Mie scattering model for a distribution of spherical particles. We can accurately model the size distribution and extinction spectra of complex shaped particles and isolate the contribution of aggregates to the extinction spectra. We can separate the contributions of dipoles, quadrupoles, and octupoles to the Mie resonances for their respective electric and magnetic parts. Our results show that we can tune the broad Mie resonance peak in the extinction spectra by the nanoscale properties of our system. This behavior can aid in the design of lasing and luminescence-enhanced systems. These dielectric gadolinium niobate submicron particles are excellent candidates for light manipulation on the nanoscale.

Effective Michelson interference observed in fiber-optical analogue of Hawking radiation.

We experimentally observe the stimulated analogue of Hawking radiation produced in a photonic-crystal fiber, with a pulsed pump and a continuous-wave probe. In particular, we propose and demonstrate an innovative method to boost the efficiency and probe the coherence characteristics of the analogue Hawking effect relying on a double pump pulse with a controlled temporal delay. We show that the emitted analogue Hawking radiation corresponds to the coherently-added, interfering Hawking signals resulting from the probe interacting with each pump pulse. We introduce a simple effective Michelson interference model, and demonstrate excellent agreement between our experimental data and the predictions derived from this model. Importantly, while naively increasing the pump power in an attempt to boost the Hawking-radiation generation efficiency results in the distortion of the output signal, we show that at the maxima of the observed Hawking-signal interference pattern, the signal can be increased by a factor of >3 (up to 4 under ideal experimental conditions). This approach could be extended to the use of sequences of m pulses, resulting in a Hawking-signal enhancement of m2.

Frequency and polarization emission properties of a photon-pair source based on a photonic crystal fiber.

In this work, we experimentally demonstrate a photon-pair source with correlations in the frequency and polarization degrees of freedom. We base our source on the spontaneous four-wave mixing (SFWM) process in a photonic crystal fiber. We show theoretically that the two-photon state is the coherent superposition of up to six distinct SFWM processes, each corresponding to a distinct combination of polarizations for the four waves involved and giving rise to an energy-conserving pair of peaks. Our experimental measurements, both in terms of single and coincidence counts, confirm the presence of these pairs of peaks, while we also present related numerical simulations with excellent experiment-theory agreement. We explicitly show how the pump frequency and polarization may be used to effectively control the signal-idler photon-pair properties, defining which of the six processes can participate in the overall two-photon state and at which optical frequencies. We analyze the signal-idler correlations in frequency and polarization, and in terms of fiber characterization, we input the SFWM-peak experimental data into a genetic algorithm which successfully predicts the values of the parameters that characterize the fiber cross section, as well as predict the particular SFWM process associated with a given pair of peaks. We believe our work will help advance the exploitation of photon-pair correlations in the frequency and polarization degrees of freedom.

Hawking radiation in optics and beyond.

Hawking radiation was originally proposed in astrophysics, but it has been generalized and extended to other physical systems receiving the name of analogue Hawking radiation. In the last two decades, several attempts have been made to measure it in a laboratory, and one of the most successful systems is in optics. Light interacting in a dielectric material causes an analogue Hawking effect, in fact, its stimulated version has already been detected and the search for the spontaneous signal is currently ongoing. We briefly review the general derivation of Hawking radiation, then we focus on the optical analogue and present some novel numerical results. Finally, we call for a generalization of the term Hawking radiation. This article is part of a discussion meeting issue 'The next generation of analogue gravity experiments'.

Boosting few-cycle soliton self-frequency shift using negative prechirp.

Soliton self-frequency shifting of light pulses in fibers is used for versatile tunable light sources. Few-cycle pulses of high soliton number offer unique advantages, in particular the rate of Raman frequency shift is extremely fast. However, their dynamics is complicated, which makes the optimization of the frequency shifting difficult and sometimes counter-intuitive. We performed a systematic experimental study of the effects of initial prechirp for different pulse energies (for two different fibers). We found that a negative prechirp around C=-0.75 is the most effective (C being the chirp parameter). With such prechirping we managed to cross the severe OH absorption bands of nonlinear photonic crystal fibers. The mechanism behind the effectiveness of the prechirp appears to be the power distribution between the products of soliton fission.

Observation of Stimulated Hawking Radiation in an Optical Analogue.

The theory of Hawking radiation can be tested in laboratory analogues of black holes. We use light pulses in nonlinear fiber optics to establish artificial event horizons. Each pulse generates a moving perturbation of the refractive index via the Kerr effect. Probe light perceives this as an event horizon when its group velocity, slowed down by the perturbation, matches the speed of the pulse. We have observed in our experiment that the probe stimulates Hawking radiation, which occurs in a regime of extreme nonlinear fiber optics where positive and negative frequencies mix.

Antiplatelet Therapy for Long-Term Management of Patients with Mechanical Aortic Prostheses.

BACKGROUND: A mechanical aortic prosthesis (MAP) may cause platelet activation secondary to shear forces, and the release of adenosine diphosphate (ADP). This platelet-mediated event may lead to arterial embolism. Traditionally, warfarin has been used to treat such cases, although this anticoagulant has no inhibitory effects on platelets. The study aim was to determine if antiplatelet agents could prevent thromboembolic events in patients with a MAP. METHODS: Since 2001, a total of 265 patients (average age 64.5 ± 12.0 years), each of whom received a MAP with or without additional aortic surgery, was followed at the authors' institution. Patients received a loading dose of clopidogrel or prasugrel + asprin 325 mg and tested for platelet inhibition. The maintenance dose was 75 mg clopidogrel or 10 mg prasugrel + 81 mg aspirin. Platelet reactivity was tested, using two different methods, after one month and at six-month intervals thereafter. RESULTS: The average follow up was 47.3 ± 44.3 months; total follow up was 11,688.8 months [974 patient-years (pt-yr)]. Over a 16-year period 51 patients died, primarily from myocardial infarction. Twelve patients had strokes (1.2%/pt-yr); of these patients, 10 had discontinued the antiplatelet medication (and were receiving warfarin). One patient was nonresponsive to clopidrogel and another (a compliant patient) was never tested. Strokes were not observed in compliant patients who responded to antiplatelet agents. Thirteen patients had gastrointestinal bleeding, four required transfusion, and three died due to cerebral aneurysms. CONCLUSIONS: Platelet-mediated thromboembolism following MAP installation can be treated with antiplatelet agents. The 16-year results of the present study suggested that antiplatelet agents can reduce thromboembolic events in patients with MAP. Strokes can be prevented in patients with MAP if treated with the correct antiplatelet agent, if the patient responds to the agent employed and is strictly compliant.

Tumor de Frantz-Gruber, un tumor sólido pseudopapilar del páncreas poco frecuente / Frantz-Gruber tumor, an infrecuent solid pseudopapillary tumor of the pancreas

El tumor de Frantz-Gruber es una masa sólida pseudopapilar de páncreas, poco común y con bajo potencial de malignidad, descrita por primera vez por Franz en 1959. Predomina en mujeres entre la 3era y 4ta década de la vida. La sintomatología está dada principalmente por efecto de masa y se caracteriza por dolor vago y sensación de plenitud. El diagnóstico radiológico incluye estudios como tomografía axial computalizada (TAC) y resonancia magnética, y los estudios histológicos confirman la sospecha clínica. El abordaje es quirúrgico en la mayoría de los casos e incluye una resección completa de tumor. La presencia de metástasis hepática no es infrecuente. La sobrevida a 5 años es por arriba del 90 por ciento. Se reporta el caso de un paciente de 15 años, sin antecedentes patológicos o quirúrgicos, visto en el Servicio de Emergencias por epigastralgia y vómito. Un ultrasonido (US) abdominal demostró una lesión en la cola pancreática, luego por TAC y US endoscópico se logró documentar una masa de aspecto quístico y contenido denso que abarca también el cuerpo del páncreas. Se recomendó abordaje quirúrgico; durante la laparotomía exploratoria se halla tumoración mixta sólidoquística. Se practicó pancreatectomía distal y esplenectomía. La evolución y manejo postoperatorio fue sin complicaciones.

Light-emitting diode spherical packages: an equation for the light transmission efficiency.

Virtually all light-emitting diodes (LEDs) are encapsulated with a transparent epoxy or silicone gel. Here we analyze the optical efficiency of spherical encapsulants. We develop a quasi-radiometric equation for the light transmission efficiency, which incorporates some ideas of Monte Carlo ray tracing into the context of radiometry. The approach includes the extended source nature of the LED chip and the chip radiance distribution. The equation is an explicit function of the size and the refractive index of the package, and also of several chip parameters such as shape, size, radiance, and location inside the package. To illustrate the use of this equation, we analyze several packaging configurations of practical interest, for example, a hemispherical dome with multiple chips, a flat encapsulation as a special case of the spherical package, and approximate calculations of an encapsulant with a photonic crystal LED or a photonic quasi-crystal LED. These calculations are compared with Monte Carlo ray tracing, giving almost identical values.

Sumoylated RGS-Rz proteins act as scaffolds for Mu-opioid receptors and G-protein complexes in mouse brain.

The RGSZ1 and RGSZ2 proteins, members of the RGS-Rz subfamily of GTPase-activating proteins (GAP), are involved in Mu-opioid receptor desensitization. The expression of these proteins, as well as of their main target the Gz protein, is virtually restricted to the nervous tissue. In synaptosomal membranes, these Rz proteins undergo post-translational modifications such as glycosylation and phosphorylation, and they may covalently attach to small ubiquitin-like modifier (SUMO) proteins. While RGSZ1 exists in conjugated and non-conjugated forms, RGSZ2 is mostly conjugated to SUMO-1, SUMO-2 and SUMO-3 proteins. These sumoylated forms of the GAPs readily associated with Mu-opioid receptors but they associated only poorly with Delta receptors. Furthermore, G alpha i2 and G alpha z subunits co-precipitated with the sumoylated forms of RGSZ1/Z2 proteins, but to a lesser extent with the Ser phosphorylated SUMO-free form of RGSZ1. Upon Mu-opioid receptor activation, there is a strong increase in the association of G alpha proteins with RGSZ2 proteins that persists for intervals longer than 24 h. This effect probably accounts for their role in Mu-opioid receptor desensitization. Only a moderate increase was observed with RGSZ1, the non-sumoylated form of which probably acts as an efficient GAP for these G alpha subunits. Therefore, sumoylation regulates the biological activity of RGS-Rz proteins and it is likely that it serves to switch their behavior, from that of a GAP for activated G alpha subunits to that of a scaffold protein for specific signaling proteins.