Electrically injected cavity polaritons

We have realised a semiconductor quantum structure that produces electroluminescence while operating in the light-matter strong coupling regime. The mid-infrared light emitting device is composed of a quantum cascade structure embedded in a planar microcavity, based on the GaAs/AlGaAs material system. At zero bias, the structure is characterised using reflectivity measurements which show, up to room temperature, a wide polariton anticrossing between an intersubband transition and the resonant cavity photon mode. Under electrical injection the spectral features of the emitted light change drastically, as electrons are resonantly injected in a reduced part of the polariton branches. Our experiment demonstrates that electrons can be selectively injected into polariton states up to room temperature.Comment: 10 pages, 4 figure

Normal endothelial function in carriers of the apolipoprotein A-IMilano mutant despite low HDL-cholesterol levels

Carriers of the apolipoprotein A-IMilano (apoA-IM) mutant show severe reductions in the plasma concentration of antiatherogenic HDL but do not present with preclinical atherosclerosis and premature CHD. Aim of the present study was to investigate endothelial function in A-IM carriers, since low HDL-C levels have been associated with features of endothelial dysfunction. Plasma concentrations of soluble cell adhesion molecules (sCAMs) and forearm arterial compliance (FAC) during reactive hyperemia were evaluated in 21 A-IM carriers, 21 healthy subjects with low HDL-C, and 42 controls. Low HDL-C subjects had significantly higher plasma sCAM levels than controls (sVCAM-1: 656.3\ub149.3 vs 502.6\ub125.5 ng/ml; sICAM-1: 335.6\ub121.5 vs 267.0\ub18.9 ng/ml; sE-selectin: 62.9\ub14.1 vs 47.9\ub13.0 ng/ml); on the contrary, no differences were detected between A-IM carriers (sVCAM-1: 550.6\ub132.1 ng/ml; sICAM-1: 309.8\ub126.9 ng/ml; sE-selectin: 52.3\ub14.3 ng/ml) and controls. Low HDL-C subjects had lower FAC than controls, while no differences were detected between A-IM carriers and controls. These results suggest that HDL from A-IM carriers may be more efficient than control HDL in modulating endothelial function. To test this hypothesis, plasma HDL were isolated from 6 A-IM carriers and 6 controls, and their ability to inhibit VCAM-1 expression and to induce eNOS was tested in cultured endothelial cells. A-IM HDL were two times more effective than control HDL in reducing TNFalpha-induced VCAM-1 expression; the inhibition occurred at a transcriptional level, as demonstrated by RT-PCR. In addition, cells exposed to A-IM HDL showed higher expression of eNOS than cells treated with control HDL. In conclusion, despite the very low HDL-C levels, A-IM carriers do not display features of endothelial dysfunction, such as the increase of circulating sCAM levels and the impairment of arterial compliance, probably because of a superior ability of A-IM HDL to protect the endothelium

Gain without inversion in a biased superlattice

Intersubband transitions in a superlattice under homogeneous electric field is studied within the tight-binding approximation. Since the levels are equi-populated, the non-zero response appears beyond the Born approximation. Calculations are performed in the resonant approximation with scattering processes exactly taken into account. The absorption coefficient is equal zero for the resonant excitation while a negative absorption (gain without inversion) takes place below the resonance. A detectable gain in the THz spectral region is obtained for the low-doped $GaAs$-based superlattice and spectral dependencies are analyzed taking into account the interplay between homogeneous and inhomogeneous mechanisms of broadening.Comment: 6 pages, 4 figure

Nonequilibrium Green's function theory for transport and gain properties of quantum cascade structures

The transport and gain properties of quantum cascade (QC) structures are investigated using a nonequilibrium Green's function (NGF) theory which includes quantum effects beyond a Boltzmann transport description. In the NGF theory, we include interface roughness, impurity, and electron-phonon scattering processes within a self-consistent Born approximation, and electron-electron scattering in a mean-field approximation. With this theory we obtain a description of the nonequilibrium stationary state of QC structures under an applied bias, and hence we determine transport properties, such as the current-voltage characteristic of these structures. We define two contributions to the current, one contribution driven by the scattering-free part of the Hamiltonian, and the other driven by the scattering Hamiltonian. We find that the dominant part of the current in these structures, in contrast to simple superlattice structures, is governed mainly by the scattering Hamiltonian. In addition, by considering the linear response of the stationary state of the structure to an applied optical field, we determine the linear susceptibility, and hence the gain or absorption spectra of the structure. A comparison of the spectra obtained from the more rigorous NGF theory with simpler models shows that the spectra tend to be offset to higher values in the simpler theories.Comment: 44 pages, 16 figures, appearing in Physical Review B Dec 200

Ultra low threshold current THz quantum cascade lasers based on buried strip-waveguides

THz quantum cascade lasers based on a novel buried cavity geometry are demonstrated by combining double-metal waveguides with proton implantation. Devices are realised with emission at 2.8 THz, displaying ultra low threshold currents of 19 mA at 4K in both pulsed and continuous wave operation. Thanks to the semiconductor material on both sides of the active region and to the narrow width of the top metal strip, the thermal properties of these devices have been greatly improved. A decrease of the thermal resistance by over a factor of two compared to standard ridge double-metal lasers of similar size has been measured.Comment: 10 pages, 3 figures. Submitted for publication to Applied Physiscs Letters (February 2005

Effect of soy on metabolic syndrome and cardiovascular risk factors : a randomized controlled trial

Background: Cardiovascular diseases are currently the commonest cause of death worldwide. Different strategies for their primary prevention have been planned, taking into account the main known risk factors, which include an atherogenic lipid profile and visceral fat excess. Methods: The study was designed as a randomized, parallel, single-center study with a nutritional intervention duration of 12 weeks. Whole soy foods corresponding to 30 g/day soy protein were given in substitution of animal foods containing the same protein amount. Results: Soy nutritional intervention resulted in a reduction in the number of MetS features in 13/26 subjects. Moreover, in the soy group we observed a significant improvement of median percentage changes for body weight ( 121.5 %) and BMI ( 121.5 %), as well as for atherogenic lipid markers, namely TC ( 124.85 %), LDL-C ( 125.25 %), non-HDL-C ( 127.14 %) and apoB ( 1214.8 %). Since the majority of the studied variables were strongly correlated, three factors were identified which explained the majority (52 %) of the total variance in the whole data set. Among them, factor 1, which loaded lipid and adipose variables, explained the 22 % of total variance, showing a statistically significant difference between treatment arms (p = 0.002). Conclusions: The inclusion of whole soy foods (corresponding to 30 g/day protein) in a lipid-lowering diet significantly improved a relevant set of biomarkers associated with cardiovascular risk

Magnetic Resonance Imaging Visualization of Vulnerable Atherosclerotic Plaques at the Brachiocephalic Artery of Apolipoprotein E Knockout Mice by the Blood-pool Contrast Agent B22956/1

The aim of this study was to identify, by magnetic resonance imaging (MRI), the ability of the blood-pool contrast agent B22956/1 to detect atherosclerotic plaques developing at the brachiocephalic artery of apolipoprotein E knockout (apoE-KO) mice and to possibly identify vulnerable atherosclerotic lesions. After high-fat feeding for 8 or 12 weeks, MRIs of brachiocephalic arteries were acquired before and after B22956/1 administration; then vessels were removed and analyzed by histology. B22956/1 injection caused a rapid increase in plaque signal enhancement and plaque to muscle contrast values, which remained stable up to 70 minutes. A linear correlation between signal enhancement and macrophage content was found 10 minutes after B22956/1 injection ( p < .01). Signal enhancement and plaque to muscle contrast values correlated with macrophage content 40 minutes after contrast agent administration ( p < .01). Finally, 70 minutes after B22956/1 infusion, plaque to muscle contrast significantly correlated with the percentage of stenosis ( p < .005). B22956/1 administration to high fat-fed apoE-KO mice resulted in a rapid enhancement of atherosclerotic plaques and in a great ability to rapidly visualize vulnerable plaques, characterized by a high macrophage content. These results suggest that B22956/1 could represent an interesting tool for the identification of atherosclerotic plaques potentially leading to acute cardiovascular events

Quasi-static and propagating modes in three-dimensional THz circuits

We provide an analysis of the electromagnetic modes of three-dimensional metamaterial resonators in the THz frequency range. The fundamental resonance of the structures is fully described by an analytical circuit model, which not only reproduces the resonant frequencies but also the coupling of the metamaterial with an incident THz radiation. We also demonstrate the contribution of the propagation effects, and show how they can be reduced by design. In the optimized design, the electric field energy is lumped into ultra-subwavelength (λ/100) capacitors, where we insert a semiconductor absorber based on the collective electronic excitation in a two dimensional electron gas. The optimized electric field confinement is exhibited by the observation of the ultra-strong light-matter coupling regime, and opens many possible applications for these structures in detectors, modulators and sources of THz radiation