【正文】 s new deal, imposed a five percent excise tax on dividend receipts, imposed a capital stock tax and an excess profits tax, and suspended all deductions for losses (June 16, 1933, ch. 90, 48 Stat. 195). The repeal in 1933 of the eighteenth amendment, which had prohibited the manufacture and sale of alcohol, brought in an estimated $90 million in new liquor taxes in 1934. The social security act of 1935 provided for a wage tax, half to be paid by the employee and half by the employer, to establish a federal retirement fund (Old Age Pension Act, Aug. 14, 1935, ch. 531, 49 Stat. 620). The Wealth Tax Act, also known as the Revenue Act of 1935, increased the maximum tax rate to 79 percent, the Revenue Acts of 1940 and 1941 increased it to 81 percent, the Revenue Act of 1942 raised it to 88 percent, and the Individual Ine Tax Act of 1944 raised the individual maximum rate to 94 percent. The postWorld War II 30 Revenue Act of 1945 reduced the individual maximum tax from 94 percent to 91 percent. The Revenue Act of 1950, during the korean war, reduced it to percent, but it was raised the next year to 92 percent (Revenue Act of 1950, Sept. 23, 1950, ch. 994, Stat. 906). It remained at this level until 1964, when it was reduced to 70 percent. The Revenue Act of 1954 revised the Internal Revenue Code of 1939, making major changes that were beneficial to the taxpayer, including providing for child care deductions (later changed to credits), an increase in the charitable contribution limit, a tax credit against taxable retirement ine, employee deductions for business expenses, and liberalized depreciation deductions. From 1954 to 1962, the Internal Revenue Code was amended by 183 separate acts. In 1974 the employee retirement ine security act (ERISA) created protections for employees whose employers promised specified pensions or other retirement contributions (Pub. L. No. 93406, Sept. 2, 1974, 88 Stat. 829). ERISA required that to be tax deductible, the employer39。 trust, 158 . 601, 15 S. Ct. 912, 39 L. Ed. 1108 [1895]). After many years of debate and promise, the sixteenth amendment to the Constitution was ratified in 1913, providing Congress with the power to lay and collect taxes on ine without apportionment among the states. The objectives of the ine tax were the equitable distribution of the tax burden and the raising of revenue. Since 1913 the . ine tax system has bee very plex. In 1913 the ine tax laws were contained in eighteen pages of legislation。 disdain for this taxation without representation (socalled because the colonies had no voice in the establishment of the taxes) gave rise to revolts such as the Boston Tea Party. However, even after the Revolutionary War and the adoption of the . Constitution, the main source of revenue for the newly created states was money received from customs and excise taxes on items such as carriages, sugar, whiskey, and snuff. Ine tax first appeared in the United States in 1862, during the Civil War. At that time only about one percent of the population was required to pay the tax. A flatrate ine tax was imposed in 1867. The ine tax was repealed in its entirety in 1872. Ine tax was a rallying point for the Populist party in 1892, and had enough support two years later that Congress passed the Ine Tax Act of 1894. The tax at that time was two percent on individual ines in excess of $4,000, which meant that it reached only the wealthiest members of the population. The Supreme Court struck down the tax, holding that it violated the constitutional requirement that direct taxes be apportioned among the states by population (pollock v. farmers39。大學(xué)的每一位同學(xué)、老師都教會(huì)了我很多為人處事的道理，無論將來身處何方，你們都是我不會(huì)也不能忘記的存在。感謝各位評委老師的評價(jià)，由于自己的能力有限，論 文還有很多的不足，希望老師們多多批評指正。在此，向曲建華曲老師表示真誠的謝意。本文能夠順利完成，要特別感謝我的導(dǎo)師曲建華曲老師，論文寫作時(shí)遇到很多困難， 從課題選擇、方案論證到具體設(shè)計(jì)和調(diào)試 ，都離不開曲老師的指導(dǎo)。 通過對 flexsim 軟件的學(xué)習(xí)，配送中心的建模優(yōu)化，我們對仿真軟件和物流配送中心有了更深的了解，同時(shí)增加了我們的學(xué)習(xí)興趣，提高了自己的實(shí)踐能力，同時(shí)也明白：隨著時(shí)代發(fā)展，科學(xué)技術(shù)的不斷發(fā)展，只有不斷學(xué)習(xí)充實(shí)自己，我們才能跟上時(shí)代的步伐。 6 結(jié)論 由此可以得出系統(tǒng)優(yōu)化不僅只追求低成本、高效率，還要考慮所應(yīng)用的商品特性，根據(jù)企業(yè)配送中心工作流程，針對不同類型的商品，選擇不同的設(shè)備配比，同時(shí)兼顧分揀、儲(chǔ)存和加工包裝之間的工作時(shí)間關(guān)系，采用高科技的電子技術(shù)，盡可能的使作業(yè)流程快速高效。 圖 5 臨時(shí)實(shí)體流經(jīng)分揀系統(tǒng)的時(shí)間 圖 6 系統(tǒng)時(shí)間柱狀圖 優(yōu)化后的配送中心，作業(yè)時(shí)在短時(shí)間內(nèi)作業(yè)流暢，系統(tǒng)配置合理，作業(yè)效率高，然而一段時(shí)間后出現(xiàn)操作員忙碌，來不及作業(yè)，導(dǎo)致整個(gè)系統(tǒng)倉儲(chǔ)成本增加，商品堆積，不能及時(shí) 進(jìn)行流通加工、包裝及出庫。下面是優(yōu)化后的操作員和叉車運(yùn)行狀態(tài)圖，粉色代表搬運(yùn)臨時(shí)實(shí)體區(qū)域、紫色代表送完實(shí)體回程時(shí)間、紅色區(qū)域代表空閑時(shí)間、藍(lán)色區(qū)域代表從休息到開始搬運(yùn)臨時(shí)實(shí)體的時(shí)間、綠色代表徒勞無意義行程的時(shí)間，由此可以看出操作員基本沒有空閑時(shí)間 ，而一輛叉車仍然有空閑時(shí)間，可以完成任務(wù)。 圖 9 兩輛叉車運(yùn)行狀態(tài)圖 合成器狀態(tài)分析：合成器是對臨時(shí)實(shí)體進(jìn)行包裝打包的設(shè)備，其運(yùn)行過程的狀態(tài)如圖所示：紅色為空閑時(shí)間，棕色為運(yùn)送臨時(shí)實(shí)體時(shí)間，綠色為加工過程所用時(shí)間，由此可見打包加工過程暢通，且有空閑，所以無需優(yōu)化。 圖 7 操作員 1 狀態(tài)圖 出庫暫存區(qū)的狀態(tài)分析：長柱表示平均暫存的臨時(shí)實(shí)體，短柱表示空閑區(qū)域，暫存區(qū)內(nèi)，暫存臨時(shí)實(shí)體少于容量的一半，實(shí)體流通流暢，無需優(yōu)化。 圖 6 傳送帶 5 的狀態(tài)圖 操作員 1 和操作員 2 的狀態(tài)分析 :圖表中粉色代表搬運(yùn)臨時(shí)實(shí)體區(qū)域、紫色代表送完實(shí)體回程、紅色區(qū)域代表空閑時(shí)間、藍(lán)色區(qū)域代表從休息到開始搬運(yùn)臨時(shí)實(shí)體的時(shí)間、綠色代表徒勞無意義 行程的時(shí)間，由圖看出，兩操作員工作過程中無意義行程和空閑時(shí)間所占比例很大，所以，應(yīng)該對操作員進(jìn)行優(yōu)化，優(yōu)化操作員的配置比，去掉一個(gè)操作員，減少不必要的勞動(dòng)時(shí)間和勞動(dòng)成本。 圖 4 貨架庫存數(shù)量圖 統(tǒng)計(jì)分析堆垛機(jī) 1 和堆垛機(jī) 2 的工作狀態(tài)圖，紅色區(qū)域是堆垛機(jī)閑置時(shí)間，藍(lán)色區(qū)域?yàn)?off set travel loaded 緑色區(qū)域是 off set travel empty，其中紅色區(qū)域只占 10%左右，兩堆垛機(jī)忙碌狀態(tài)和空閑時(shí)間基本相同，切空閑時(shí)間短，所以堆垛機(jī)設(shè)置合理，不需優(yōu)化。 圖 1 暫存區(qū) 1 的狀態(tài)餅狀圖 分揀傳送帶對經(jīng)過的實(shí)體進(jìn)行分揀，在此模型中，它相當(dāng)于現(xiàn)實(shí)的分揀系統(tǒng)，當(dāng)配送中心系統(tǒng)模型運(yùn)行時(shí)，可以得到實(shí)體經(jīng)過分揀傳送帶的時(shí)間柱狀圖： 21 圖 2 實(shí)體經(jīng)過分揀傳送帶的時(shí)間 圖 3 系統(tǒng)運(yùn)行時(shí)間 由圖表 2可知實(shí)體從進(jìn)入配送中心到發(fā)貨經(jīng)過時(shí)間 150，繁忙程度大約 ，而經(jīng)過分揀傳送帶時(shí)間接近 50，有三分之一的時(shí)間在進(jìn)行分揀作業(yè)，分揀時(shí)間太長，降低配送中心的工作效率，所以應(yīng)該縮短分揀流程，盡可能快速準(zhǔn)確的將貨 物分揀完成，所以建模時(shí)，可以縮短分揀傳送帶的長度。其中分揀系統(tǒng)和倉儲(chǔ)系統(tǒng)的入庫都是自動(dòng)化，利用電子技術(shù)，提高了效率，便于管理，自動(dòng)化立體倉庫充分利用了倉庫儲(chǔ)存空間，在現(xiàn)實(shí)物流行業(yè)中，這些技術(shù)已經(jīng)進(jìn)入企業(yè)或公司，得到廣泛應(yīng)用。先按照實(shí)體的輸入輸出流程連接，按住 A 鍵點(diǎn)擊實(shí)體，按住鼠標(biāo)不放，拖到實(shí)體流入的另一實(shí)體，松開鼠標(biāo)，依次連接好實(shí)體的輸入輸出，然后根據(jù)機(jī)械、操作員等的使用，對堆垛機(jī)、操作員、叉車和任務(wù)分派器按照操作要求進(jìn)行中間端口的連接。從模型中拖入一個(gè)發(fā)生器，表示兩類產(chǎn)品的供貨商；兩個(gè)暫存區(qū)、一個(gè)分揀傳送帶、四個(gè)貨架、兩個(gè)堆垛機(jī)、七條傳送帶、兩個(gè)操作員、兩輛叉車、一個(gè)任務(wù)分配器、兩個(gè)多道工序加工器、一個(gè)合成器、一個(gè)吸收器（表示收貨人）。 5 配送中心仿真案例 案例描述及仿真建模 當(dāng)供貨商供應(yīng)兩種商品時(shí)， 典型的配送中心經(jīng)過分揀系統(tǒng)，將貨品分揀入庫，然后按照客戶的要求，進(jìn)行組配、包裝加工，然后運(yùn)送給客戶。 （ 3）、編輯對象參數(shù)，雙擊打開對象的參數(shù)對話框， 可以對模型的參數(shù)根據(jù)需要進(jìn)行設(shè)置，同時(shí)也可以點(diǎn)擊“ properties” 按鈕，可調(diào)出對象屬性對話框，設(shè)置對象的屬性，屬性對話框包括：圖形、常規(guī)、標(biāo)簽、統(tǒng)計(jì)。 建模的基本步驟有： （ 1）、構(gòu)建模型布局，即將仿真需要的對象模型從對象庫中移到仿真試圖窗口中的適當(dāng)位置。