High forward thrust metasurface beam-riding sail.

The radiation pressure force and torque on a one-dimensional bi-grating composed of a Si-SiO2 high contrast binary metagrating is analyzed for the purpose of stable beam riding whereupon a high power laser having an expanding Gaussian irradiance distribution propels the grating in outer space, free from gravitational forces. The binary metagrating structure has been simultaneously optimized to afford high forward thrust, and corrective restoring forces and torques in the event of small linear and angular disturbances. We demonstrate that stability may be enhanced at the expense of forward thrust. The validity of our metamaterial findings is reinforced owing to good agreements between finite-difference time-domain and finite element numerical methods. To reduce mass and enhance forward acceleration this laser-driven sail was designed to be free of a stabilizing boom.

Optical vortex coronagraphy for high-contrast imaging of femtosecond laser filaments.

A high-contrast imaging technique for phase objects based on the optical vortex coronagraph (OVC) is proposed. This method offers the unique advantage of background-free imaging due to the introduction of azimuthal phase in the Fourier plane. We employed the OVC method to detect femtosecond laser-induced air plasma and compared it with the classic diffractometry and fluorescent imaging methods. We achieved a phase sensitivity of ∼0.035 waves that surpassed the capabilities of the other two methods. The combination of this highly sensitive imaging technique with the pump-probe method holds promise for applications in ultrafast imaging of laser-material interactions.

Broadband radiation pressure on a small period diffractive film.

The p-polarization component of radiation pressure force from an unpolarized blackbody light source is predicted by the use of a Maxwell equation solver for a right triangular prism grating of period 2 µm and refractive index 3.5. The transmitted and reflected angular scattering distributions are found to qualitatively agree with diffraction theory: At relatively short wavelengths the transmitted light is concentrated near the refraction angle, and reflected light is concentrated near the reflection angle. Owing to diffraction and multiple internal reflections, however, the spectral irradiance of transmitted and reflected light was found to significantly vary with wavelength. We found that the high value of the refractive index produced a large fraction of reflected light, thereby reducing the net transverse component of radiation pressure force. These results suggest that low index transmission gratings, anti-reflection coatings, optimized metasurface films, or reflection gratings should be explored for future solar sailing missions.

Parametric control of a diffractive axicon beam rider.

A laser beam rider is a large-scale optical structure designed so that it is attracted toward the optical axis, while also affording forward propulsion via radiation pressure along the beam path. Such structures form the basis of laser-driven light sails. Experimental measurements are described whereby a thin diffractive axicon film is shown to exhibit a natural restoring force when its axis is displaced from the optical axis. This effect is attributed to the optical momentum change of diffracted light. Whereas continuous illumination supports harmonic motion, modulated illumination is shown to support both parametric gain and parametric damping. The 12.7µm period photopolymer axicon grating was suspended in a vacuum torsion oscillator and irradiated with a 1.5 W near-infrared laser modulated at a period of 38 s.

Maslinic acid differentially exploits the MAPK pathway in estrogen-positive and triple-negative breast cancer to induce mitochondrion-mediated, caspase-independent apoptosis.

Breast cancer accounts for 1.4 million new cases every year. Triple-negative breast cancer (TNBC) is one the leading cause of mortality in developing countries and is associated with early age onset (under 40 years old). Chemotherapy has a poor success rate in patients with TNBC as compared to other types of breast cancers. It is due to the lack of expression of three validated molecular markers for breast cancer, the estrogen and progesterone receptors, and the amplification of HER-2/Neu. Therefore, a clear need exists for a greater understanding of TNBC at all levels and for the development of better therapies. We have studied the anti-tumor effects of a potential drug, maslinic acid, which can be extracted from olive oil industry waste. This natural product showed inhibitory effect at concentrations ranging from 30 to 50 µM within 24 h. It exhibited divergent effects in cell cycle progression for the MCF7 (estrogen positive) cell line when compared with TNBCs like MDA-MB-231 and MDA-MB-468. Also, maslinic acid treatment altered the mitochondrial membrane electrochemical potential and the reactive oxygen species (ROS) levels to cause a caspase-independent programmed cell death. In silico approaches and immunoblotting suggested the involvement of the MAPK pathway explaining the variability in cell cycle progression along with the apoptotic cell death caused by maslinic acid.

Optomechanics of a stable diffractive axicon light sail.

Beamed propulsion of a light sail based on radiation pressure benefits from a passively self-stabilizing "beam riding" diffractive film. We describe the optomechanics of a rigid non-spinning light sail that mitigates catastrophic sail walk-off and tumbling by use of a flat axicon diffraction grating. A linear stability analysis and numerical integration of the coupled translational and rotational equations of motion are examined. Stability is traded against longitudinal acceleration. The examined system achieves 90% of the theoretical longitudinal force limit and stability against a relative sail translation up to 30% of the sail radius when the payload is attached to a long boom.

Half-ring point spread functions.

We applied point spread function engineering to design an optimized diffuser producing half-ring irradiance patterns satisfying two objectives: reduced peak irradiance in the focal plane, and high fidelity of the reconstructed image. Applications of these optical elements may include sensor protection or reversible diffusers. Experimental and numerical techniques were used to demonstrate three orders of magnitude of suppression of the peak irradiance. Finally, we found a general power-law trend between the Strehl ratio and the light suppression factor.

Stable diffractive beam rider.

A passively stable laser-driven lightsail is described, which makes use of a spatially variant "bi-grating" sail with a mass (payload) attached to a boom (patent pending). A two-dimensional analytical model of the system, a linear stability analysis, and numerical solutions of the equations of motion are reported. The acceleration of the light sail along the beam path is found to depend on the grating parameters. We identify stability conditions that depend on the grating design, beam parameters, and boom length. The inclusion of damping is found to enhance the dynamic range of stability.

Experimental Verification of a Bigrating Beam Rider.

An optical beam rider making use of a light sail comprising two opposing diffraction gratings is experimentally demonstrated for the first time. We verify that the illuminated space-variant grating structure provides an optical restoring force, exhibiting stable oscillations when the bigrating is displaced from equilibrium. We further demonstrate parametric cooling by illuminating the sail with synchronized light pulses. This experiment enhances the technical feasibility of a laser-driven light sail based on diffractive radiation pressure.

Optimized pupil-plane phase masks for high-contrast imaging.

A differential evolution algorithm (DEA) is shown to improve the design of phase-only pupil plane masks for imaging in the presence of a high-intensity point source. Strehl and suppression ratio metrics for various phase basis functions were experimentally and numerically calculated. Experiments performed with a spatial light modulator demonstrated 100 times suppression of the peak intensity. The Strehl ratio was found to be higher for the DEA masks compared to the individual phase basis function.

Measurements of Radiation Pressure Owing to the Grating Momentum.

The radiation pressure force on a nearly single-order diffraction grating was measured for a transmission grating near the Littrow angles at wavelengths of 808 and 447 nm. The component of force parallel to the grating agreed well with our prediction, being proportional to the product of the grating order and the ratio of the wavelength and grating period. The normal component of force varied with the incident angle, vanishing near the Littrow angle as expected. The measurements verify a correspondence between the Fourier grating momentum and the mechanical momentum. This Letter provides opportunities for in-space fly-by-light sailcraft as well as terrestrial applications.

Experimental observations of a laser suppression imaging system using pupil-plane phase elements.

To help diminish the undesirable effects of laser irradiation on an imaging sensor, a pupil-plane phase element was introduced to broaden the point spread function, thereby reducing the focused laser irradiance. A sharpened image was subsequently restored via Wiener deconvolution. Successful experimental demonstrations employing a spatial light modulator in the pupil plane are reported for the vortex, axicon, and cubic phase. Furthermore, to circumvent information loss owing to zero values in the modulation transfer function, we demonstrate how images with different phase elements, combined with a joint deconvolution operation, provide an improved image.

Randomized apertures: high resolution imaging in far field: erratum.

We note a correction to Eq. (6) for [ Opt. Express25(15), 18296 (2017)].

Randomized apertures: high resolution imaging in far field.

We explore opportunities afforded by an extremely large telescope design comprised of ill-figured randomly varying subapertures. The veracity of this approach is demonstrated with a laboratory scaled system whereby we reconstruct a white light binary point source separated by 2.5 times the diffraction limit. With an inherently unknown varying random point spread function, the measured speckle images require a restoration framework that combine support vector machine based lucky imaging and non-negative matrix factorization based multiframe blind deconvolution. To further validate the approach, we model the experimental system to explore sub-diffraction-limited performance, and an object comprised of multiple point sources.

Negative velocity fluctuations and non-equilibrium fluctuation relation for a driven high critical current vortex state.

Under the influence of a constant drive the moving vortex state in 2H-NbS2 superconductor exhibits a negative differential resistance (NDR) transition from a steady flow to an immobile state. This state possesses a high depinning current threshold ([Formula: see text]) with unconventional depinning characteristics. At currents well above [Formula: see text], the moving vortex state exhibits a multimodal velocity distribution which is characteristic of vortex flow instabilities in the NDR regime. However at lower currents which are just above [Formula: see text], the velocity distribution is non-Gaussian with a tail extending to significant negative velocity values. These unusual negative velocity events correspond to vortices drifting opposite to the driving force direction. We show that this distribution obeys the Gallavotti-Cohen Non-Equilibrium Fluctuation Relation (GC-NEFR). Just above [Formula: see text], we also find a high vortex density fluctuating driven state not obeying the conventional GC-NEFR. The GC-NEFR analysis provides a measure of an effective energy scale (E eff ) associated with the driven vortex state. The E eff corresponds to the average energy dissipated by the fluctuating vortex state above [Formula: see text]. We propose the high E eff value corresponds to the onset of high energy dynamic instabilities in this driven vortex state just above [Formula: see text].

Sodium-Calcium Exchanger in Pig Coronary Artery.

This review focuses on the sodium-calcium exchangers (NCX) in the left anterior descending coronary artery smooth muscle. Bathing tissues in Na+-substituted solutions caused them to contract. In cultured smooth muscle cells, it increased the cytosolic Ca2+ concentration and extracellular entry of 45Ca2+. All three activities were attributed to NCX since they were inhibited by NCX inhibitors. The tissues also expressed the sarco/endoplasmic reticulum (SER) Ca2+ pump SERCA2b whose activity was much greater than that of NCX. Inhibiting SERCA2b with thapsigargin decreased the NCX-mediated 45Ca2+ accumulation by the cells. The decrease was not observed in cells loaded with the Ca2+-chelator BAPTA. The results are consistent with a limited diffusional space model with a proximity between NCX and SERCA2b. NCX molecules appear to be colocalized with the subsarcolemmal SERCA2b based on studies on membrane flotation experiments and microscopic fluorescence imaging of antibody-labeled cells. Thapsigargin inhibition of SERCA2b moved NCX even closer to SER. This provides a model for the NCX-mediated Ca2+ refilling of SER in the arterial smooth muscle. The model for the NCX-mediated refilling of the depleted SER proposed for smooth muscle did not apply to endothelium in which NCX levels were greater and SERCA levels were lower than in smooth muscle. The effect of thapsigargin on the NCX-mediated Ca2+ accumulation which was observed in smooth muscle was absent in the endothelium. We propose that the coupling between NCX and smooth muscle may be tissue dependent.

Intussusception of Small Intestine as a Result of Inflammatory Fibroid Polyp Causing Small Bowel Obstruction in an Adult Patient.

Intussusception is the telescoping of one segment of bowel into the adjacent segment. It is more commonly seen in children,however rarely encountered in adult patients. Proximal segment of bowel is called intussusceptum which is intussuscepted into the lumen of the adjacent distal segment known as intussuscipiens. There is always a lead point causing this disorder especially in adults. We presented a case of a 45 year old man who presented in emergency department of our institute with history and clinical features of acute intestinal obstruction since 10 days. Patient was resuscitated, investigated and taken for exploratory laparotomy under General anaesthesia. Segment of involved small gut was resected and well circumscribed polypoidal mass was found in intussuscepted bowel. Histopathological examination of the specimen revealed the features of inflammatory fibroid polyp.

Study of the sign change of exchange bias across the spin reorientation transition in Co(Cr1-x Fe x )2O4 (x = 0.00-0.125).

We present the evolution of novel phenomena of magnetic compensation effect, exchange bias (EB) effect and the field induced anomalies in '[Formula: see text]' substituted multiferroic compound [Formula: see text]. A few percent of '[Formula: see text]' substitution for '[Formula: see text]' in [Formula: see text] results in the reversal of field cooled magnetization under low applied fields below compensation temperature T comp. Further, increase in the field leads to the spin reorientation transition (T SR). Signature of EB in a narrow temperature window in the vicinity of T SR and its sign change across T SR is observed. Magnitude of EB depends on the amount of compensation and rigidity of the spin reorientation. We also notice the appearance of positive EB below the lock-in transition (T L). Presence of unidirectional anisotropy developed in the commensurate spin-spiral below T L could be responsible for the appearance of EB below T L.