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This article aims to describe the activities of underground economic actors. This article is a literature review of several empirical studies in Indonesia and the world in examining or resolving the impact of the existence of these economic activities. There are several terms used in each country from the underground economy, such as black economy, shadow economy and unofficial economy. Every country, both developed and developing countries, have experienced underground economic activity that continues to increase so that biased measurement often occurs, which is caused by indicators of underground economy that cannot be measured clearly and this economic activity can harm state revenues. The driving force of the underground economy is an increase in the tax burden (directly or indirectly), combined with labor market regulations and the quality of public goods and services, as well as properly measured economic conditions. The need for systematic oversight to reduce the number of corruption by providing convenience to the community through the E-Government program as a direction for the creation of Good Governance..

Perilaku keputusan investasi mulai menarik perhatian akademisi internasional. Penelitian ini dilakukan untuk mengetahui pengaruh behavioral finance dengan menerapkan variabel overconfidence, representativeness, mental accounting, loss aversion dan herding terhadap keputusan investasi. Jumlah sampel yang dikumpulkan dan digunakan dalam penelitian berjumlah 203 responden di Kota Batam dan dianalisis menggunakan metode regresi linier berganda. Hasil penelitian menunjukkan bahwa overconfidence, mental accounting, dan herding berpengaruh positif signifikan terhadap keputusan investasi, sedangkan variabel representativeness dan loss aversion tidak berpengaruh terhadap keputusan investasi.

Steam power plants consist of systems such as Water Treatment Plant (WTP), boiler, turbine-generator, and balance of plant. WTP system consists of sedimentation, desalination, and demineralization. The coagulation mechanism triggered by the mass grave of suspended solids during the sedimentation process, and if it is less than optimal, so will be modified by injecting coagulant-flocculant chemicals. The most common problem is the high dose chemicals used in the rain and tidal sea conditions. However, the output water quality that produced still does not reach the standard requirements. This condition would affect the high costs of water treatment operations. It also would have an impact on the poor feed the next system. The jar-testing technique is research using process and operational variables that theoretically influence the efficiency of the coagulant-flocculant such as doses, setting times, and rotates agitator. Evaluation of experiments using water quality criteria and data results processed by AHP and AHP-TOPSIS. The sensitivities of both methods are analyzed thus compared to select a consistent alternative that obtained sequence the first alternative for D60W30P80 and the second alternative for D40W20P80. The optimal sedimentation process could potentially save 40-60% of the water treatment operational cost while operating conditions achieved.