Microwave Dielectric Properties of (1-x)Ba_(3.75)Nd_(9.5)Cr_(0.25)Nb_(0.25)Ti_(17.5)O_(54)-x NdAlO_3 Ceramics

This study presents the microwave dielectric properties calculation of (1-x)Ba_(3.75)Nd_(9.5)Cr_(0.25)Nb_(0.25)Ti_(17.5)O_(54)–xNdAlO_3 ceramics where x denotes the volume molar fraction. From X-ray diffraction results, the solid solution limit is calculated to be about 0.76, where it forms a single BaNd_2Ti_4O_(12) phase in Region I (0≤x<0.76), and both BaNd_2Ti_4O_(12) and NdAlO_3 coexist in Region II (0.76≤x<1). The solid solution limit is confirmed by independently calculating it from the dielectric constant data. There is less than 4% deviation between the measured dielectric constant (εr) and the one calculated from the Maxwell-Wagner formula. The total quality factor (Q) remains almost constant in Region I and increases rapidly with the volume molar fraction of NdAlO_3 in Region II. The measured Q×f, where f is the resonant frequency, is also consistent with the calculated value in both regions. The temperature coefficient at the resonant frequency is −1.4 ppm/°C, which agrees well with the calculated value of 0 ppm/°C. In addition, we observed a close correlation between the bulk density and the phase evolution

Kicking the habit/semiconductor lasers without isolators

In this paper, we propose and demonstrate a solution to the problem of coherence degradation and collapse caused by the back reflection of laser power into the laser resonator. The problem is most onerous in semiconductor lasers (SCLs), which are normally coupled to optical fibers, and results in the fact that practically every commercial SCL has appended to it a Faraday-effect isolator that blocks most of the reflected optical power preventing it from entering the laser resonator. The isolator assembly is many times greater in volume and cost than the SCL itself. This problem has resisted a practical and economic solution despite decades of effort and remains the main obstacle to the emergence of a CMOS-compatible photonic integrated circuit technology. A simple solution to the problem is thus of major economic and technological importance. We propose a strategy aimed at weaning semiconductor lasers from their dependence on external isolators. Lasers with large internal Q-factors can tolerate large reflections, limited only by the achievable Q values, without coherence collapse. A laser design is demonstrated on the heterogeneous Si/III-V platform that can withstand 25 dB higher reflected power compared to commercial DFB lasers. Larger values of internal Qs, achievable by employing resonator material of lower losses and improved optical design, should further increase the isolation margin and thus obviate the need for isolators altogether

Effect of volume ratio on the performance of mid-wave infrared transparent Gd2O3–MgO composite ceramics

Gd2O3–MgO composite ceramics are promising candidates for preparing protective mid-wave infrared (MWIR) windows. However, owing to the different crystal structures of Gd2O3 and MgO after the sintering process, the volume ratio of the two phases must be controlled more precisely to achieve optimum performance. In this study, a nitrate-citrate combustion method was used to prepare Gd2O3–MgO nanopowders with different volume ratios, and composite ceramics were then fabricated via low-temperature pre-sintering and subsequent hot isostatic pressing (HIP). The effect of the Gd2O3:MgO volume ratio on the sintering behaviour, microstructures and optical, thermal and mechanical properties of the composite ceramics was studied in detail. A comprehensive assessment of the above-mentioned properties indicated that the Gd2O3–MgO composite ceramic with a volume ratio of 2:3, which exhibited a transmittance of 80.1–85.8% in the range of 3–5 μm, thermal conductivity of 17.5 W m−1 K−1, Vickers hardness of 9.8 GPa and toughness of 1.84 MPa m1/2, displays the optimum application performance for MWIR windows

The observation and prediction of constant quality factors of LnAlO_3 doped Ba_(6-3x)Ln_(8+2x)Ti_(18)O_(54)(Ln = Nd, Sm, La) ceramics

Usually, the quality factor of a binary-phase ceramic will increase if the volume molar ratio of the high quality factor component increases, and vice versa. However, the quality factor of Ba_(6-3x)Ln_(8+2x)Ti_(18)O_(54) (Ln = Nd, Sm, La) ceramics (~ 2500 at 4 GHz) keeps a constant as the volume molar ratio of LnAlO_3 (~ 9000 at 7 GHz) increases. While previous studies reported the importance of microstructure variation, here by fitting the dielectric constant, via definition we derived a quality factor calculation formula that can precisely determine the quality factor variation versus the volume molar ratio, which is of great significance for guiding the ceramic manufacturing

The Effect of Artichoke on Lipid Profile: a Review of Possible Mechanisms of Action

Cardiovascular disease is a highly prevalent issue worldwide, and one of its main manifestations, dyslipidaemia, needs more attention. Cooked artichoke (Cynara scolymus) hearts or artichoke leaf extract (ALE) are believed to be helpful in the treatment of dyslipidaemia. In this narrative review, we provide a brief overview of the potential impact of artichoke consumption on lipid profile. We appraised the Cochrane, MEDLINE and Web of Science databases, and included articles published between 2000 and June 2018 on intervention in humans only. The main potential of ALE administration observed on lipid profile relates to decreased serum LDL, total cholesterol and triglyceride concentrations, although no strong evidence for increasing HDL appears to exist. Evidence suggests that decreases of 8 to 49 mg/dL for LDL concentration, 12 to 55 mg/dL for total cholesterol, and 11 to 51 mg/dL for triglycerides, can be attributed to 2-3 g/d of ALE, in which its components luteolin and chlorogenic acid may play a key role. On the other hand, the effects of cooked artichoke hearts can be attributed mainly to its soluble fibres, particularly inulin. Despite the convincing evidence on its health benefits, additional long-term clinical trials are pivotal to fully elucidate the potential effects of ALE administration on positive cardiovascular outcome

The observation and prediction of constant quality factors of LnAlO_3 doped Ba_(6-3x)Ln_(8+2x)Ti_(18)O_(54)(Ln = Nd, Sm, La) ceramics

Usually, the quality factor of a binary-phase ceramic will increase if the volume molar ratio of the high quality factor component increases, and vice versa. However, the quality factor of Ba_(6-3x)Ln_(8+2x)Ti_(18)O_(54) (Ln = Nd, Sm, La) ceramics (~ 2500 at 4 GHz) keeps a constant as the volume molar ratio of LnAlO_3 (~ 9000 at 7 GHz) increases. While previous studies reported the importance of microstructure variation, here by fitting the dielectric constant, via definition we derived a quality factor calculation formula that can precisely determine the quality factor variation versus the volume molar ratio, which is of great significance for guiding the ceramic manufacturing

Shrinkage features, microstructure evolution and properties of Gd2O3-MgO optical composite ceramics with Zr as phase stabilizer

A novel composite ceramic, composed of equal-volumetric Zr-stabilized Gd2O3 and MgO phases, was prepared to be transparent in mid-wave infrared range. Zr stabilized Gd2O3 is proved to have a lower lattice parameter (10.7516Å) using XRD refinement. Pressureless sintering behavior of Gd2O3-MgO with/without 2at.% Zr-doping (naming ZGM and GM) was studied via the real-time observation technique. The shrinkage of ZGM green body proceeds steadily up to 1400°C while that of the undoped one shrinks sharply at 1250°C due to Gd2O3 phase transition. The segregation of Zr element along the grain boundaries of Zr-Gd2O3 creates a synergized effect on the grain refinement with pinning effect. Dense ZGM ceramics exhibit superior transmittance of 78.3%‐85.6% at 3-5 μm, which show good consistency with the calculated values. The refractive index of Zr- Gd2O3 varies from 1.87 at 3 μm to 1.80 at 5 μm, which is smaller than those of monoclinic Gd2O3