This section will be used to discuss the Unknown Contacts and the Per Account Notifications, as well as, some of the other background features provided by the Advanced System Prefs patches.

这个章节将用来讨论未知联系人和通过账号的信息通知，不仅如此，还会有一些高级系统配置系列补丁后台支持功能。

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Self adaptive predictor is used to extract periodic signals with unknown frequencies from wide band random noise background.

自适应预估器能用来提取宽带随机噪声背景中未知频率的周期性信号。

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Background the comparative efficacy and safety of infliximab and azathioprine therapy alone or in combination for Crohn's disease are unknown.

背景在克罗恩病患者中，英夫利西单抗和硫唑嘌呤单药治疗或联合治疗的相对疗效和安全性尚未被了解。

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The Good Schools Guide noted that 12 out of 41 British gold medal-winners educated in the UK attended private school. (A 42nd medal winner's educational background was unknown and a 43rd was schooled in Germany).

BBC: Magazine

But information about ethnic background can also refine descriptions of an unknown person.

BBC: Painting a suspect's portrait with DNA