多声道耳机真的好吗？——品鉴三款5.1声道耳机

相信大家对5．1声道音箱都比较熟悉,但对耳机产品也许较为陌生。那么市面上的5．1声道耳机能否呈现真实的5．1声道音效呢？与音箱相比,5．1声道耳机的表现到底如何？本文将给大家做详细介绍。     

Optimal control of economic growth with application to Korean economy

This paper is concerned with the application of optimal control theory to the dual growth of the Korean economy. A closed two sector economic growth model is formulated by dividing the economy into agriculture and non-agriculture in order to represent the transitional phenomena between the two sectors. Taking capital and saving as state and control variables, respectively, the model governing the economic growth becomes a non-linear simultaneous differential equations with coupling terms of state and control variables. Assuming the Cobb-Douglas production function and the exponential form of the social welfare function, the necessary and sufficient conditions of the optimal control have been derived for the case of finite planning horizon by using the Pontryagin's maximum principle. Since deriving the optimal trajectories of state and control variables analytically is impossible, a numerical procedure based on the variation of extremals is used to obtain the optimal paths of the aggregate investment and consumption of the Korean economy.     

Green fluorescence of terbium ions in lithium fluoroborate glasses for fibre lasers and display devices

In this paper, for the first time, the visible fluorescence properties, resonance energy transfer mechanism responsible for non-radiative decay rates of ⁵D₄ → ⁷F₅ transition and also quenching of fluorescence intensity of the ⁵D₃ → ⁷F₅ transition of various concentrations of Tb³⁺ ions in LBZLFB glasses are reported. Optical absorption, fluorescence spectra and quantum efficiencies are measured and analysed. Green fluorescence related to ⁵D₄ → ⁷F₅ (548 nm) transition is registered under excitation of 378 nm of Tb³⁺ ions. Based on excitation and fluorescence measurements, several spectroscopic parameters for Tb³⁺ ions are examined as a function of concentration by Judd–Ofelt theory to judge the suitability of studied glasses for display devices and fibre lasers.     

EFFECTS OF DIETARY GLYCINE BETAINE ON BLOOD CHARACTERISTICS AND PORK QUALITY

This study was conducted to determine the effects of dietary glycine betaine on pork quality and blood characteristics. A total of 80 female pigs (Landrace  ×  Yorkshire  ×  Duroc) were randomly allotted into one of four experimental diet groups. Each group of pigs fed with a commercial diet (control) added with 0.2 g glycine betaine (T1), 0.4 g glycine betaine (T2) and 0.6 g glycine betaine (T3)/kg diet during 40 days. Glycine betaine concentrations in plasma and loin muscle were significantly increased by dietary glycine betaine; however, triglyceride concentration in serum was decreased by dietary glycine betaine. Creatine phosphokinase concentrations in plasma had no significant difference among the dietary groups. Redness ( a* ) was significantly higher in T2 and T3; however, at the first and seventh days of storage, redness ( a* ) was not significantly different between dietary groups. Shear force was significantly higher in dietary glycine betaine groups at the first day of storage. Cholesterol content was significantly lower in T2 and T3, whereas T1 was not significantly different compared with the control group. In fatty acid composition, the ratio of saturated fatty acids was increased, whereas unsaturated fatty acids were decreased by dietary glycine betaine.

PRACTICAL APPLICATIONS

Glycine betaine is an amino acid (trimethylglycine) present in most organisms, and is an obligatory intermediate in the catabolism of choline. Glycine betaine has been reported to affect some aspects of pork qualities. As a result of this study, dietary glycine betaine should improve meat redness and reduce cholesterol. However, dietary glycine betaine did not influence creatine phosphokinase levels in plasma. These results will be helpful to the pork industry and meat scientists for improving meat qaulity.     

A new type of ordering in Ba(Zn1/3 Ta2/3)O3 ceramics

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.