Wide-bandwidth 25-dB amplitude noise suppression in a pump-and-signal-resonant optical parametric oscillator

We present a pump-and-signal-resonant optical parametric oscillator that provides 25 dB of amplitude noise suppression of the transmitted pump beam from dc to 20 kHz. The upper frequency range of the optical limiter increases as the pump power is increased, up to 1 MHz with 580 mW of input power. The amount of noise suppression is limited by pump-depletion effects. The upper frequency range is limited by the temporal response of the device. We present a numerical analysis that predicts this behavior.     

The development of a quick method for amorphicity determination by isothermal microcalorimetry

This study presents a contribution in the development of a quick and accurate testing method for the determination of amorphous content using isothermal microcalorimetry. Examples demonstrated how the choice of the experimental conditions, especially sample load, temperature and humidity, influences the crystallization of the amorphous material. The suitability of this systematic approach was first tested on well-known lactose and afterwards on nifedipine as model compounds. It was shown that by proper method design and careful selection of experimental conditions, it is possible to achieve quick determination of the amorphous content in samples with a quantification limit of less than 1%, what is considerably better than by classical analytical methods such as DSC and XRPD. Our optimized microcalorimetry method gave also better results compared to previously reported literature data for nifedipine.     

Use of isothermal microcalorimetry for prediction of oxidative stability of several amino acids

Isothermal microcalorimetry has been applied as a method for predicting (in)stability of ascorbic acid and several amino acids that undergo oxidative degradation in aqueous media. The fast and simple method involved the addition of different amounts of hydrogen peroxide. The appearance of the heat flow curves gave a clear general indication of how stability was influenced. The accuracy of the microcalorimetric result was investigated by comparing it with an HPLC assay and a good agreement between the results of both methods was demonstrated. It was also established that susceptibility to oxidative degradation decreases in the following order: cysteine, methionine, ascorbic acid, tyrosine and tryptophan.     

高Tc超导体YBCO磁通钉扎的计算机模拟研究

临界电流密度Jc是影响高温超导体在强电领域应用的一个重要参数,在实际应用中,特别在外加磁场下,临界电流密度与超导材料的磁通钉扎性质密切相关.因此,磁通钉扎一直是高温超导体研究中的一个重要领域.由于高温超导体磁通钉扎力密度Fp的标度律存在,本文根据D.Dew-Hughes总结的钉扎力函数,主要存在两种主要作用类型(正常相和△K).我们将D.Dew-HugBes给出的钉扎力密度Fp标度函数改进为一个简化的具有物理意义的函数表达式.结合文献中已有的实验数据,我们对YBcO进行了计算机模拟,确定了它的磁通钉扎类型,模拟的研究结果与实际情况比较吻合.