存放在計算機中大量信息的安全問題以及敏感信息的防竊取、防篡改問題已經越來越引起人們的關注。為了實現對數據庫管理系統中數據安全的需求，文中對系統的用戶口令、C/S之間的簽名認證、SQL Server 2005數據庫加密、系統分配角色和用戶權限幾方面對數據庫管理系統的安全問題進行研究，使用C#和T-SQL語言進行具體實現。實際應用表明，這些措施能夠準確地實現數據的加密，阻止非法用戶操作系統，保證系統安全，達到了設計要求。
在現代通信系統中，電話語音的頻帶被限制在300 Hz～4 kHz的范圍內，帶來了語音可懂度和自然度的降低。為了在不增加額外成本的前提下提高語音的可懂度和自然度，進行了電話語音頻帶擴展的研究。提出了一種改進的基于碼本映射的語音帶寬擴展算法：在碼本映射的過程中，使用加權系數來得到映射碼本。客觀測試結果表明，用此算法得到的寬帶語音的譜失真度比用一般的碼本映射降低至少2%。主觀測試結果表明，用此算法得到的寬帶語音具有更好的可懂度和自然度。
Abstract:
In modern communication systems， the bandwidth of telephone speech is limited from 300Hz to 4 kHz， which reduces the intelligibility and naturalness of speech. Telephone speech bandwidth extension is researched to get wideband speech and to improve its intelligibility and naturalness， without increasing extra costs. This paper put forward an improved algorithm of speech bandwidth extension based on codebook mapping. In the process of codebook mapping， weighted coefficients were used to get mapping codebook. Objective tests show that spectral distortion of wideband speech obtained by this algorithm reduces at least 2%， comparing to conditional codebook mapping. Subjective tests show that the wideband speech obtained by this algorithm has better intelligibility and naturalness.
