0818换库放狗（有数学和越度更新）

amberwangvv08

mdqq 发表于 2018-8-18 19:32
请问构筑第一题 “其他一个点与圆 tangent”是说明了y=0吗

我个人觉得不是这个意思…他的意思是四个小矩形在圆上的点与圆tangent 但是我也没太搞清楚怎么用这个条件?

billyisfragile!

红酒包装 原来厂家用glass包装，后来也有人用便宜的什么carbon方法。

传统观点认为：这样包装密封性不好，容易变质；

第二段讲新观点：这样包装也是有好处的。大概讲了很多葡萄里有breetle影响葡萄酒的口感，这样包装能吧啦吧啦

第三段忘记了…

https://www.economist.com/science-and-technology/2009/06/10/box-clever

The science of ageing wine
Box clever
Some wine can improve if stored in a carton rather than in a bottle
Jun 10th 2009

AMONG snobs and sommeliers, nothing can compete with wine in a glass bottle sealed with a cork stopper. Yet as cheap alternatives to cork have become available and high fuel prices have made transporting glass more expensive, some winemakers have adopted an alternative method of storage: putting wine in cartons, like those used for milk, made from layers of polythene, paper and aluminium foil. Admittedly, serving wine from a carton lacks the aesthetic appeal of a bottle, and cartons have also been criticised for allowing flavour-destroying oxygen to seep in during storage. A new study, however, reveals that although the criticism of wine cartons for allowing oxidation is valid, they have the advantage of soaking up chemicals that can ruin the flavour in other ways.

High levels of chemicals called alkyl-methoxypyrazines can make wines taste as though the fruit from which they were made was under-ripe or low-quality. Originally grapes themselves were thought to be the only source of this class of compounds in wine, but recent research has shown that invasive Asian lady beetles (also known as Harlequin ladybirds) are also involved in the process. These beetles eat grapes and can accidentally get mixed into the winemaking process. They then contribute to the formation of these undesirable chemicals in some North American and French wines.

The wine industry has tried various ways to remove alkyl-methoxypyrazines, but none has been particularly successful. To make matters worse, the Asian lady beetle is becoming more prevalent in Italy, Spain, Argentina and South Africa, which means winemakers from those regions could soon face the problem of dealing with these chemicals, too. But it has long been known that packaging plays a role in controlling wine chemistry and taste by absorbing some volatile compounds in a process known as “flavour scalping”. A team led by Gary Pickering at Brock University in Canada decided to investigate the impact of different forms of packaging on the concentration of alkyl-methoxypyrazines in wines.

The researchers added three types of alkyl-methoxypyrazine to red (cabernet franc) and white (riesling) wines, some of which were stored in cartons, and others in bottles. Natural cork, synthetic cork and screw caps were used to seal the bottles. The researchers then monitored chemical levels in the wines for 18 months.

They report in the Journal of Agricultural and Food Chemistry that at the end of the study the levels of the different types of alkyl-methoxypyrazines, known as IBMP, IPMP and SBMP, had fallen by 45%, 32% and 26% respectively in the wines stored in cartons. In wines stored in bottles, the levels of IBMP (which produces a characteristic “sweet pepper” taste) did not fall as much: by 37% for synthetic cork, 36% for screw cap and 31% for natural cork. When it came to IPMP (associated with “green pea” and “earthy” flavours) the level increased by 2-3% for natural cork, but fell by 7% for screw cap and 19% for synthetic cork. The levels of SBMP (which is thought to help determine aroma) rose in all the bottled wine, but fell in that kept in cartons. The results were similar for both types of grape.

Why the cartons have this effect is not entirely understood, but Dr Pickering speculates that the wine may be seeping through the inner polythene layers and making contact with the aluminium layer beyond. He suggests that the alkyl-methoxypyrazine molecules may be sticking to the aluminium and thus being segregated from the wine. If his theory is correct, fiddling with the composition of box interiors could be a good way for the wine industry to control the concentration of unpleasant chemicals.

Cartons might thus assume an important role in the wine market. They could be ideal for storing wines that are inclined to be high in alkyl-methoxypyrazines but will be drunk relatively soon after purchase, before oxidation can become a significant problem. For grand wines, however, bottles with natural corks are likely to remain the packaging of choice.

是原文吗？