A topical review of numerical and experimental studies of supercontinuum generation in photonic crystal fiber is presented over the full range of experimentally reported parameters, from the femtosecond to the continuous-wave regime. Results from numerical simulations are used to discuss the temporal and spectral characteristics of the supercontinuum, and to interpret the physics of the underlying spectral broadening processes. Particular attention is given to the case of supercontinuum generation seeded by femtosecond pulses in the anomalous group velocity dispersion regime of photonic crystal fiber, where the processes of soliton fission, stimulated Raman scattering, and dispersive wave generation are reviewed in detail. The corresponding intensity and phase stability properties of the supercontinuum spectra generated under different conditions are also discussed.

Supercontinuum generation, photonic crystal fiber

Ghrelin degradation by serum and tissue homogenates: identification of the cleavage sites

Subsequent to the discovery of ghrelin as the endogenous ligand of growth hormone secretagogue receptor 1a, this unique gut peptide has been found to exert numerous physiological effects, such as appetite stimulation and lipid accumulation via the central regulating mechanisms in the hypothalamus, stimulation of gastric motility, regulation of glucose metabolism and brown fat thermogenesis, and modulation of stress, anxiety, taste sensation, reward-seeking behaviour and the sleep/wake cycle. Prader-Willi syndrome (PWS) has been described as a unique pathological state characterised by severe obesity and high circulating levels of ghrelin. It was hypothesised that hyperghrelinaemia would explain at least a part of the feeding behaviour and body composition of PWS patients, who are characterised by hyperphagia, an obsession with food and food-seeking, and increased adiposity. Initially, the link between hyperghrelinaemia and growth hormone deficiency, which is observed in 90% of the children with PWS, was not fully understood. Over the years, however, the increasing knowledge on ghrelin, PWS features and the natural history of the disease has led to a more comprehensive description of the abnormal ghrelin system and its role in the pathophysiology of this rare and complex neurodevelopmental genetic disease. In the present study, we (a) present the current view of PWS; (b) explain its natural history, including recent data on the ghrelin system in PWS patients; and (c) discuss the therapeutic approach of modulating the ghrelin system in these patients and the first promising results.

Prader-Willi syndrome: A model for understanding the ghrelin system.

Validated determination of losartan and valsartan in human plasma by stir bar sorptive extraction based on acrylate monolithic polymer, liquid chromatographic analysis and experimental design methodology.

The physics and applications of fiber-based supercontinuum (SC) sources have been a subject of intense interest over the last decade, with significant impact on both basic science and industry. New uses for SC sources are also constantly emerging due to their unique properties that combine high brightness, multi-octave frequency bandwidth, fiber delivery, and single-mode output. The last few years have seen significant research efforts focused on extending the wavelength coverage of SC sources towards the 2 to 20µm molecular fingerprint mid-infrared (MIR) region and in the ultraviolet (UV) down to 100 nm, while also improving stability, noise and coherence, output power, and polarization properties. Here we review a selection of recent advances in SC generation in a range of specialty optical fibers, including fluoride, chalcogenide, telluride, and silicon-core fibers for the MIR; UV-grade silica fibers and gas-filled hollow-core fibers for the UV range; and all-normal dispersion fibers for ultralow-noise coherent SC generation.

Recent advances in supercontinuum generation in specialty optical fibers [Invited]

We demonstrate the generation of a low-noise, octave-spanning mid-infrared supercontinuum from 1700 to 4800 nm by injecting femtosecond pulses into the normal dispersion regime of a multimode step-index chalcogenide fiber with 100 µm core diameter. We conduct a systematic study of the intensity noise across the supercontinuum spectrum and show that the initial fluctuations of the pump laser are at most amplified by a factor of three. We also perform a comparison with the noise characteristics of an octave-spanning supercontinuum generated in the anomalous dispersion regime of a multimode fluoride fiber with similar core size and show that the normal dispersion supercontinuum in the multimode chalcogenide fiber has superior noise characteristics. Our results open up novel perspectives for many practical applications such as long-distance remote sensing where high power and low noise are paramount.

Low-noise octave-spanning mid-infrared supercontinuum generation in a multimode chalcogenide fiber

We demonstrate the generation of octave-spanning supercontinuum generation from 1200 nm to over 2500 nm with 600 mW average power in a short length of multimode fluoride fiber with 100 μm core diameter. We perform a detailed study of the supercontinuum generation process as a function of the pump wavelength and for two different fiber lengths. Beam profile characterization at the fiber output in different wavelength bands is also carried out. Our results open up new possibilities for the generation of high-power supercontinuum sources from the near- to mid-infrared.

High-power short-wavelength infrared supercontinuum generation in multimode fluoride fiber

We demonstrate the generation of a low-noise, octave-spanning mid-infrared supercontinuum from 1700 to 4800 nm by injecting femtosecond pulses into the normal dispersion regime of a multimode step-index chalcogenide fiber with 100 $\mu$m core diameter. We conduct a systematic study of the intensity noise across the supercontinuum spectrum and show that the initial fluctuations of the pump laser are at most amplified by a factor of three. We also perform a comparison with the noise characteristics of an octave-spanning supercontinuum generated in the anomalous dispersion regime of a multimode fluoride fiber with similar core size and show that the all-normal dispersion supercontinuum in the multimode chalcogenide fiber has superior noise characteristics. Our results open up novel perspective for many practical applications such as long-distance remote sensing where high power and low noise are paramount.

Background: There is a worldwide concern about the life quality, in this way, one of the most important requirements is safe and nutritious foodconsumption. The administration of antibiotics to cattle in order to treat several infectious diseases has contributed to the contamination of industrialized dairy farms. Objectives: Milk antibiotic contamination is an important problem worldwide, and the quality control of milk samples is essential. Therefore, the aim of this study was to monitor antibiotic contamination in milk samples. Materials and Methods: Samples were collected from six different farms and milk factories in Iran, and were tested by beta-star and cylinder-plate methods. Results: Among 992 raw milk samples, 236 positive samples, 9 suspected and 747 negative samples in respond to beta-star test and among 236 samples, which had positive responses to beta-star test, 28 positive, 0 suspected and 208 negative results of cylinder-plate test were gained. Among 652 pasteurized milk samples, 67 positive, 9 suspected and 576 negative beta-star test results and among 67 samples which had positive responses to beta-star test, 1 positive, 0 suspected and 66 negative results to cylinder-plate test were achieved. Conclusions: The results revealed that cylinder-plate method accompanied with beta-star test can be considered as an appropriate sensitive and selective method for the milk and dairy products quality control. According to the results, it look as if the process of pasteurization reduces the amount of penicillin G in milk samples considerably.

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Comparison Between the Amount of Penicillin G Residue in Raw and Pasteurized Milk in Iran

Profiling and monitoring concentrations of key hormones in body have long been critical aims in clinical therapy. As a crucial hormone, identification and quantification of ghrelin is a fundamental, often key, step in understanding human physiological mechanisms. Through the advances and improvements of different analytical techniques, ghrelin measurement is generally feasible, and the number of successful reports is progressively being increased with new aspects of selectivity, sensitivity and ease of use in various circumstances. Herein we discuss current chromatographic methods for sample collection, separation and a mass spectrometry method for detection and measurement of ghrelin and other proghrelin-derived peptides in biological metrics. We describe the most commonly applied analytical LC–MS procedures for determination of proghrelin-derived peptides and provide illustrative instances representing the state of the art. This review is intended for bioanalytical chemists or clinical researchers who are interested in this field of research.

Zahra Eslami

Papers

Low-noise octave-spanning mid-infrared supercontinuum generation in a multimode chalcogenide fiber

High-power short-wavelength infrared supercontinuum generation in multimode fluoride fiber

Low-noise octave-spanning mid-infrared supercontinuum generation in a multimode chalcogenide fiber

Comparison Between the Amount of Penicillin G Residue in Raw and Pasteurized Milk in Iran

Recent developments in liquid chromatography-mass spectrometry analyses of ghrelin and related peptides.