谁能满足我的好奇心？

treesUID: 82785

jorge哥哥，给你提个赚收入的办法吧。把你的程序改改用到十字绣图象上。现在这样的软件普通的使用费也是每人200元以上。非常火暴呢！

angeikimUID: 4857

最初由 auteur 发布
[B]宫老师的? [/B]

宫东风吗？

ballackxjjUID: 134855

最初由 trees 发布
[B]偶正在折腾的东西是关于GIS和GPS的。现在还在程序中，文章没开始呢哪~ [/B]

gps？
军用民用？感兴趣

xqmelissaUID: 140370

最初由 angeikim 发布
[B]宫东风吗？ [/B]

晕！
那个不是搞英语的吗？
我学经济的

我导师是APEC方面的权威
嘿嘿

至于名字嘛~~~~~~~~~~~~~
还是很有名气的呦

nmlyUID: 109487

:D还是兔子的论文最有意思:D哈哈哈哈

imongUID: 140258

SYNTHESIS OF ETHYL 3-HYDROXYBUTYRATE: A BRIEF STUDY ON THE STEREOSELECTIVE REDUCTION OF ETHYL ACETOACETATE

INTRODUCTION
This paper will conduct a brief discussion about the reduction of ethyl acetoacetate to ethyl 3-hydroxybutyrate. We have designed three individual experiments in which the reduction of ethyl acetoacetate is carried out using different reducing agents. In both experiment A and B, the reaction is carried out using sodium borohydride, while (L)-tartaric acid is introduced in B to produce a chiral environment. In experiment C, dried yeast is applied as a reductase for the starting molecule. Based on the experimental results we are looking into the effect of the reducing agent on the reaction and the product as well.

RESULTS AND DISCUSSIONS
In section A, the yield was unexpectedly low with a prolonged boil range (238~257℃ at atmospheric pressure). The major cause might have been the indiscriminate use of ethanol as the solvent. Removal of ethanol is required because it is impossible to extract the product from the aqueous layer by dichloromethane without eliminating this water-miscible organic solvent. In such step, although the temperature of the water bath was strictly controlled not exceeding 50℃, further dehydration of the product to give α,β-unsaturated ester cannot be prevented. Furthermore, as the evaporation of ethanol proceeds, the acidity of the solution becomes too strong to retain the ester group. In this sense, a variety of by-products, such as 3-hydroxybutyric acid, ethyl 2-butenoate, and 2-butenoic acid might have been present, while very little ethyl 3-hydroxybutyrate was preserved. Some water insoluble solvent, such as THF, dichloromethane, might be much promising substitute for ethanol, in that the evaporation before extraction can be avoided. Besides, since no chiral agent had been applied, the product should bear no optical rotation.

In section B, the yield was better than that in A with a satisfactorily constant boiling point under reduced pressure. The increased yield and purity should be attributed to the use of THF instead of ethanol as the solvent. The sample resembled an optical rotation value which indicates that 58.3% R enantiomer and 41.7% S enantiomer was present, given the specific rotation of each pure enantiomer. In the first stage of the reduction in experiment B, sodium borohydride first react with (L)-tartaric acid to form an intermediate which carries both chirality and the hydride group with the evolution of hydrogen gas. This intermediate then served to reduce ethyl acetoacetate preferentially from one side of the ketone group, which gave the above results.

In section C, the yield was the best among all three experiments. The boil range was 215~221℃ (converted to atmospheric pressure). Since an enzyme was applied to be the reducing agent, the reduction had to be carried out only if the orientation of the ketone group fits into the enzyme’s active site. In this sense, the stereoselectivity should be much better than that in section B. Optical rotation value indicates that the sample has a constitution of 83.1% S enantiomer to 16.9% R enantiomer, which corroborates the above reasoning. The IR spectrum has a strong absorption at 1735.8cm-1 and a wide absorption at 3446.1cm-1 with medium intensity which implies the presence of ketone and hydroxyl group. The NMR spectra: 4.19, m, 3H, 3.4, 1H, 2.47, m, 2H, 1.28, t, 3H, 1.23, d, 3H.

EXPERIMENTALS
  Reduction of ethyl acetoacetate via non-chiral reagent: Experiment A
To a 100ml three-necked bottomed flask, containing a magnetic stirrer bar, add 1.5g (40mmol) sodium borohydride and 20ml ethanol, then cool the suspension to 0℃ using an ice bath. Add a solution of 5.0g (38mmol) ethyl acetoacetate in 12ml ethanol dropwise whilst stirring. The temperature should be maintained below 5℃ during the addition. Stir the solution under ice bath for an additional 15 minutes after the addition has been completed and stir the solution for a further 15 minutes at room temperature thereafter. Then cool the solution to 0℃ and neutralize the solution to weakly acidic by 1M hydrochloric acid (no suspension should be present). Stir the mixture for a further 10 minutes. Remove the ethanol on a rotary evaporator at 50℃ or below and dissolve the remaining product in 15ml dichloromethane. Remove the organic layer and extract the aqueous layer with 2×20ml dichloromethane. Dry the combined organic layer over anhydrous magnesium sulphate. Remove the solvent under reduced pressure to produce an oil, and 0.47g transparent liquid (A) is obtained by vacuum distillation at 82~95℃, 7mmHg. The overall yield is 9.3%.

  Reduction of ethyl acetoacetate under chiral environment: Experiment B
To a 100ml three-necked round bottomed flask, containing a magnetic stirrer bar, add 50ml THF, 1.5g (40mmol) sodium borohydride and whilst stirring, 6.0g (40mmol) (L)-tartaric acid. Stir for 15 minutes and then cool the suspension to 0℃ using an ice bath. Add 1.32g (10.2mmol) ethyl acetoacetate dropwise and leave the solution to stir for an hour at room temperature. Then cool the reaction to 0℃ using an ice bath and neutralize the solution to weakly acidic with no presence of suspension. Stir the mixture at room temperature for 10 minutes. Remove the organic layer and extract the aqueous layer with 2×20ml ethyl acetate. Wash the combined organic layer with 40ml saturated sodium hydrocarbonate solution, 40ml brine, then dry over anhydrous magnesium sulphate. Remove the solvent under reduced pressure to produce an oil, and 0.32g transparent liquid (B) is obtained by vacuum distillation at 52℃ (the pressure unidentifiable because of technical problem). The overall yield is 23.8%, [α]D20= -7.63° (c=0.0278 , CHCl3).

  Biocatalyzed reduction of ethyl acetoacetate: Experiment C
To a 500ml round bottomed flask add 1.95g (15mmol) ethyl acetoacetate, 250ml petroleum ether (60~90), 18ml distilled water and 22.5g dried yeast. Fit a mechanical stirrer and stir the reaction vigorously for 12 hours at room temperature. Decant the liquid from the yeast to obtain the organic layer and wash the yeast with 3×30ml ethyl acetate. Dry the combined organic layer over anhydrous magnesium sulphate. Remove the solvent under reduced pressure to produce an oil, and 1.05g transparent liquid (C) is obtained by vacuum distillation at 58~62℃, 5mmHg. The overall yield is 53.0%, [α]D20= +30.45° (c= , CHCl3), with IR spectra obtained.

REFERENCE
1.        Dyson Perrins Lab, University of Oxford 2nd year organic practical course.
2.        Lange's handbook of chemistry(15th ed.). John A. Dean. 1999.

Sample A was combined, and distilled together with Jinjing, Liu; sample C with Peng, Zhao.

Totally e tuo shti, my report...

rainlannyUID: 68597

说实话，前两天我琢磨永动机呢！

想用超导磁体来发电，用在电动汽车上。理论：不同的磁场强度，如果线圈的速度一样，那么磁场越大电流越大。总之就是想到用超导磁体能产生很多电。这样多到永不完－－想到，如果这个理论成立，那么只有有一个初始的力矩，让线圈转动，那么产生的电不仅可以给电池充电，驱动电机，还可以有一部分分出来带动线圈本身旋转－－十足的永动机。自己觉得肯定不对，但是想不出哪里不对。还想，要是这样的，每个人养只松鼠，开车前让松鼠跑两圈，然后……呵呵。

今天突然想到问题出在哪里了，也找了学电机的朋友确认。因为，同样的线圈，在不同的磁场强度环境下要保持速度相同，那么磁场越大，所需要的力矩也就越大。那么，转超导磁体磁场重的线圈，功率就要比普通磁体的那个大很多。因此，多出来的那些电流，其实还是从动能转化过来的。因此，这个计划泡汤了。

我本来还想用这个这么好的想法申请PHD呢:(

princessmiaUID: 121566

最初由 rainlanny 发布
[B]说实话，前两天我琢磨永动机呢！

想用超导磁体来发电，用在电动汽车上。理论：不同的磁场强度，如果线圈的速度一样，那么磁场越大电流越大。总之就是想到用超导磁体能产..

以下省略...... [/B]

友情提示：永动机不能申请专利 ;)

dsnyUID: 22160

Executive Summary

Over the past three years, media reports, both academia and practitioners have been unreservedly reporting the end of the e-business boom. Enthusiasm, in the past, has been replaced entirely with cynicism and gloom.

Thus, we question if the boom is indeed finite? Is the situation returning to conventional “Old Economy” business rules replacing the brief Internet New Order? We would argue that it is non-affirmative.

The convergence of IT, television and telecoms that the Internet has brought about has led to a period of technological change that in many ways is comparable to the Industrial Revolution. This will affect every aspect of our lives and change the rules of economics, just like the original industrial revolution did. The conventional “Old Economy” view of business just will not apply in the future. Business cycles that held reliably throughout the 20th century will break down or become irrelevant as business practices change beyond recognition.  This is where the business model in e-commerce plays its role in defining its success.

Our report evaluates the practices of the e-business model(s) in the real world. We first introduce the conceptual idea of e-business, this comprises of the assessment of the technology involved, to present how e-business can benefit an organization for their growth.  At the core of the report we provide four case studies, which portray both success and failure stories of e-business companies. Finally, we discuss what we can learn from this study, make an assessment and give recommendation in using the appropriate exemplary business model. Eventually, see how they can make a difference between success and failure.

ycljhzUID: 94092

我的...桩性复合地基的

Theory of Reliability and Computation Of Bearing Capacity in Pile Composite Foundation Design

Abstract
Ground improvement is very vivid research field in civil engineering at present. The theory of composite foundation is greatly developed in recent more than ten years. Because the material, strength and effect are not same for the different pile body installed in composite foundation, the work mechanism of all kinds of composite foundation are different. It leads to that the computation methods of bearing capacity of kinds of pile composite foundation are different and difficult. This study was an effort to reform the computation methods of bearing capacity in pile composite foundation by applying the limit state design. Similar to reinforced concrete structure, the concept of limit state design proposes that the composite foundation be designed with reference to several limit states. The most important limit states were strength at ultimate load and settlement at service load. Based on probability, analyzing the probability characteristics of elements (random variability) that affect the bearing capacity and using limit state function to descript the working situation of pile composite foundation will become the predominant approach. I think it is the essence of the reliability theory.