Exchange Control System Research Articles

Nitrogen precooling heat exchanger replacement and control system upgrade in superfluid cryoplant at CMTF

Liquid nitrogen precooling is used in most cryoplants to achieve cooldown to 80 K temperature range. In one such system at Fermilab’s CMTF superfluid cryoplant, where the helium supply directly exchanges heat with liquid nitrogen, freezing of nitrogen occurred inside the heat exchanger due to heat exchanger flow imbalance during a cryoplant trip. Trapped vapor pockets of nitrogen within the frozen heat exchanger channels were formed while warming up the heat exchanger, creating high localized pressure and subsequent damage/rupture of the heat exchanger. Replacement of the heat exchanger was done, and modifications were made in the system to rectify future occurrences. The control system was updated to bypass the heat exchanger entirely if the incoming helium stream temperature drops below 76 K. This was done by repurposing two control valves as heat exchanger bypass valves that were previously used for a redundant 80 K adsorber in the coldbox. Additional modifications were made to further prevent return of large amount of cold helium gas from cold end during abrupt cryoplant shutdown. This modification has ensured high reliability of heat exchanger with prevention of freezing of nitrogen which can damage the heat exchanger.

МОДЕЛЬ ФУНКЦИОНИРОВАНИЯ ЭРГАТИЧЕСКОЙ СИСТЕМЫ КОНТРОЛЯ ИНФОРМАЦИОННОГО ОБМЕНА

The aim of this article is to create a model that simulates the ergatic system operation for controlling information exchange and evaluates its adequacy to the current system. Since in the modern world there is rapid technology development and the volume of the processed information is increasing, the control over information resources is becoming a key aspect, which determines the article relevance. An analysis of Info Watch’s 2022 information leak statistics is presented to better understand the scale of the problem. The subsystem for monitoring image leaks of the ergatic information exchange control systems is analysed. A model made in the CPN-Tools simulation environment is considered, which will allow examining in detail the presented system operation. This model will give the opportunity to evaluate how effective the information exchange control system is in real conditions. At this stage, it will be possible to gain deeper understanding of how the system works and what measures can be taken to improve its functionality. This article makes an important contribution to the field of information control and data security by proposing a methodology and tools for analysing and improving ergatic information exchange control systems.

Liberalization of the Foreign Exchange Market

There is a pattern in the evolution of exchange control systems. A typical sequence of events is: Phase 1, implementation—in response to a serious balance-of-payments deficit, a free foreign-exchange market is abandoned in favour of price control and rationing of foreign exchange. Initially exchange control applies only to major categories of receipts and payments but is rapidly extended to cover all external transactions. Phase 2, consolidation—a black market appears; regulations are extended and revised to close loopholes, to cope with shortages, and to repair inequities and anomalies. The foreign-exchange market is fragmented and differential treatment is accorded to different types of trade or traders. Taxes, subsidies, or multiple-exchange rates are introduced to offset, in a discriminatory way, iie effect of an overvalued currency on foreign-exchange receipts and the demand >r imports. The system becomes increasingly complex and administratively burdensome. Phase 3, rationalization—the complexity of the system is reduced by consolidation of market fragments. Regulations are simplified and applied to broader categories of transactions. De facto but selective devaluation, through iax, subsidy, and exchange-rate adjustments, becomes a policy instrument. Portions of the market are "liberalized" by returning to a limited free market in which price resumes its functions of evoking supply and limiting demand. Continued disequilibrium, however, sustains the black market which may be "tolerated" as a sort of unofficial free market.

Fabrication, Design, and Performance Investigation of Portable Proton Exchange Membrane Fuel Cell and Control System

Fabrication, Design, and Performance Investigation of Portable Proton Exchange Membrane Fuel Cell and Control System

무인항공기 이동 목표물 추적 비행 및 착륙 성능 개선을 위한 입력 신호 변형 기반의 제어 보조 시스템

In this study, a novel input signal transformer is introduced to remove an overshoot and steady-state error that hinder stable tracking and landing of an unmanned aerial vehicle (UAV) based on image recognition, and the performance is verified. The Input Signal Transformer (IST) is designed in the shape of a sigmoid function to attenuate or amplify the input signal to resolve the aforementioned problems. For the verification of the UAV control system based on the IST, the UAV, target, and sensors were implemented in a virtual environment using the robot operating system (ROS). And data exchange structure and control system were built by the ROS-based message communication. A simulation was performed to confirm the elimination of the overshoot and steady-state error when the UAV to which the above control system was applied tracks and lands a fixed target and a moving target. As a result of the simulation, when the IST was not used, the UAV performed an unstable because of the overshoot and could not land on the target by the steady-state error. Conversely, in the case of using IST, it was confirmed that the flight was stable and landed successfully.

Hybrid Carbon Dioxide Heat Pump for the Multifamily Residential Buildings in the Heat Supply System Based on CHP

The work is devoted to centralized heat supply systems based on CHP plants and the use with them heat pumps (HP) on carbon dioxide as refrigerant. Heat pumps are used in heat supply systems for buildings and use the heat of the outside air and, at the same time, the heat of the return network water (WWR) as a source of low-grade heat (LHP). The aim of the study is to develop a structural diagram of such a heat pump, where the outside air is heated by a heat exchanger installed in the return water line of the heating system, to develop a hydraulic circuit of a heat pump taking into account the law of regulation of the building heating system, to develop an algorithm for controlling the operating modes of the so-called balancing heat exchanger installed after gas cooler and internal heat exchanger of the heat pump. The most significant results were the hydraulic circuit of the heat pump, the aerodynamic circuit of the air supply path to the heat pump evaporator, the balancing heat exchanger control system, taking into account the requirement to ensure the operation of the control valve in a single-phase flow. The significance of the results obtained consisted in obtaining the dependences between the CO temperature graph and the parameters of the thermodynamic cycle of the heat pump, which ensured the operation of the control valve of the heat pump in a single-phase environment.

Cogeneration and heat exchanger control system based on clean energy

Combined cooling, heating, and power systems have received widespread attention for their high efficiency and clean characteristics. The combined cooling, heating, and power system will join the cogeneration system as clean energy and renewable resource of solar energy, further alleviating the energy crisis and environmental pollution problems. To improve the stability of the distributed power grid connection, the article designs a photovoltaic battery system that can smooth the output power and combines it with the traditional combined cooling, heating, and power system to build a comprehensive cogeneration system. Under the two operating modes of thermal follow, and electric follow, considering the impact of electric vehicle charging load, two environmental cost and life cycle cost indicators are evaluated.

Natural circulation experiments in a non-uniform diameter lead bismuth loop and validation of LeBENC code

Experimental studies are carried out on natural circulation in a Lead Bismuth Eutectic (LBE) loop. The loop mainly consists of a heated section, air heat exchanger, valves, various tanks and argon gas control system. All the components and piping are made of SS316L. The dissolved oxygen in the LBE is monitored online by an Yttria Stabilised Zirconia (YSZ) oxygen sensor and controlled during the operation of the loop. In this paper the details of the loop and experimental studies carried out with heater power levels varying from 900 W to 5000 W are described. The temperature range of LBE during the experiments was 200 °C–500 °C. The maximum heat loss in the piping is kept less than 20% of the main heater power. Steady state experimental studies are carried out at different power levels and the LBE flow rate was found to be varying from 0.095 kg/s to 0.135 kg/s. The analysis and results of the performance of the heat exchanger with air and water as the secondary coolants are also discussed in the paper. Transient studies were carried out to simulate various events like heat sink loss, step power change and secondary side coolant flow rate change and reported in the paper. In the start up experiments, where the flow is started from stagnant condition of LBE, the time required for starting of natural circulation is found to be 600 s, 400 s and 240 s with power level of 1200 W, 2400 W and 3000 W respectively. The results are compared with available correlation and prediction of computer code LeBENC.

Experimental and theoretical studies on the natural circulation behavior of molten salt loop

Molten salts are increasingly getting attention as a coolant and storage medium in solar thermal power plants and as a liquid fuel, blanket and coolant in High Temperature Reactors (HTR). A Molten Salt Natural Circulation Loop (MSNCL) has been setup for thermal hydraulics, instrument development and material related studies relevant to HTR and solar power plants. The loop mainly consists of heated section, air heat exchanger, valves, various tanks and argon gas control system. All the components and piping of the loop are made of Inconel 625. Steady state natural circulation experiments at different power level have been performed in the loop. Transient studies for startup of natural circulation, loss of heat sink, heater trip and step change in heater power have also been carried out. A one dimensional code LeBENC, developed in-house to simulate the natural circulation characteristics in closed loops, has been validated with the experimental data obtained from MSNCL. This paper deals with the description of the loop and experimental studies carried out in the loop. Detailed validation of the LeBENC code with the experimental data has also been discussed in the paper.

МОДЕЛИРОВАНИЕ ПОГРЕШНОСТИ ДАТЧИКА ТЕМПЕРАТУРЫ ПРИ РАЗРАБОТКЕ ВЫСОКОТОЧНЫХ ИУС

The resistance thermometer random process error change simulation problem with continuous metering within framework of digital information and control systems is solved. It was shown on the heat exchanger control system example that simulating with errors accounting allows to more accurately evaluate the control quality.

The Public Bond Offering of Petróleos de Venezuela S.A.

In April 2007, Petroleos de Venezuela S.A. (PDVSA) issued debt for USD 7.5 billion, the largest debt offering to date by a Latin American company. The conditions surrounding this issue, which was denominated and tradable in dollars, but payable in bolivars, were quite special, particularly when considering the strict foreign exchange control system put into place by the Venezuelan government in 2003. The fact that the bond issue attempted to fulfill the dual purpose of offering dollars to local companies and investors in the midst of prevailing exchange rate controls, while helping to finance PDVSA as a company, creates a unique dilemma that is ideal for class discussion. This teaching case provides the information necessary for estimating and proposing a price for PDVSA's bond offer.

The public bond offering of Petróleos de Venezuela S.A.

In April 2007, Petróleos de Venezuela S.A. (PDVSA) issued debt for USD 7.5billion, the largest debt offering to date by a Latin American company. The conditions surrounding this issue, which was denominated and tradable in dollars, but payable in bolivars, were quite special, particularly when considering the strict foreign exchange control system put into place by the Venezuelan government in 2003. The fact that the bond issue attempted to fulfill the dual purpose of offering dollars to local companies and investors in the midst of prevailing exchange rate controls, while helping to finance PDVSA as a company, creates a unique dilemma that is ideal for class discussion. This teaching case provides the information necessary for estimating and proposing a price for PDVSA's bond offer.

Smith Predictor Based Fuzzy Estimator for Uncertain Time-Delayed Systems

In this paper, a novel robust control method is proposed for uncertain time-delayed systems. The objective is to guarantee system stability and robustness against modeling errors. A fuzzy estimator is developed to predict the uncertain plant time-delay. Smith predictor is exploited. An adaptive tuning law is developed to further improve the control system performance. The proposed robust control method is successfully applied to a heat exchanger control system. Simulation results show that the approach is indeed effective. System robustness as well as stability is achieved.

Central Banking in Sub-Saharan Africa: Introduction and Overview

African central banks have covered an extraordinary distance since the early 1990s—closing the gap, in the process, between their own policy challenges and those of richer-country central banks. Some striking differences are nonetheless easily missed, amid the many parallels between central banking reforms in Sub-Saharan Africa (SSA) and those in the industrial and emerging-market economies. The abandonment of soft pegs in low-income SSA, for example, had less to do with capital mobility than with the failures of exchange control systems under pressure from fiscal imbalances and external shocks. Fiscal and quasi-fiscal demands, in turn, have almost certainly been more important than conventional stabilisation objectives as potential sources of inflation bias in SSA. Money-based disinflation programmes, to take a final example—often supported by tight fiscal rules under IMF conditionality—do not appear to have involved costly sacrifices of output, outside of South Africa. These observations, and more in the papers collected here, suggest that the distinctive structural and institutional features of low-income countries may have distinctive implications for the design and conduct of monetary policy. Collectively, the papers in this volume issue a compelling call for monetary policy research that focuses squarely on the economic environment of low-income Africa.

Simulation and experimental study of electro-pneumatic valve used in air-powered engine

To evaluate the performance of newly designed electro-pneumatic valves (EPVs) for the air-powered engine (APE) and study laws of parameters affecting them, a simulation model was established based on the thermodynamics and mechanics theories. Experiments were set up to determine the instantaneous effective orifice area of solenoid valve by the constant volume discharge method. The simulation model was also validated by comparing the measured displacement curve with the simulated displacement curve of the valve in the pressure of 0.16 and 0.49 MPa. Simulation and experimental results showed that maximum working frequency of the designed EPV could reach 30 Hz corresponding to 2000 r/min of engine rotating speed. Based on simulation results, impacts of temperature and pressure of control air on delay time, full opening/closing time and seating velocity of EPV were analyzed. The simulation model could also act as EPV simulation prototype in designing the air exchange control system of APE.

The collapse of the rand in 2001 and the effectiveness of exchange controls in South Africa

In an effort to furnish support for the beleaguered rand, which had fallen by roughly 12 per cent against the dollar in 2000 and 19 per cent in 2001, and direct more investments into the local economy, the South African authorities imposed a freeze on new offshore investments undertaken by South African financial institutions, a move which came into effect at the beginning of 2002. Institutional investors transferred R3, 8 billion abroad between February and December 2001. In a further effort to discourage foreign investment, the Minister of Finance in his February 2002 budget statement announced that the exemptions limit of interest and dividend income received from abroad from income tax was set at only R1000 compared with R6000 for interest income received from domestic sources. These steps to block such transfers once again raised questions whether the government's commitment to progressively phase out exchange controls in entirety was still in place at that time and these doubts were further strengthened by the comments of the Reserve Bank governor, Tito Mboweni, in his address at the annual general meeting of the bank in August 2002, when he referred to the desirability of relaxing exchange controls very gradually. The resort to tighter exchange controls had, moreover, occurred at a time when the degree of effectiveness of exchange controls had come to the fore once again. The Myburgh Commission, which had been investigating the fall of the rand in 2001, had been focusing part of its attention upon the exchange control system and whether this system could be effectively administered now that many of the regulations in the exchange control field had been simplified or abolished. The majority report of the commission in 2002 concluded that the administration of exchange controls appeared to work well and was effective, but this was a conclusion which could be seriously challenged. The purpose of this article, therefore, is to review the official moves on the exchange control front in 2001 and 2002, as well as assess the effectiveness of the exchange controls in general in an environment where significant partial relaxations in exchange controls had transpired and the rand had been a structurally weak currency. In the process it will be argued that the exchange control authorities were facing mounting difficulties in effectively administering the remaining exchange control system, which called into question the rationale for exchange controls.

Japan's Restrictive System of Trade and Payments: Operation, Effectiveness, and Liberalization, 1950-1964

The paper summarizes how Japan’s foreign exchange and trade control system operated in the early 1950s, how and how effectively it was used as a tool of external adjustment, and how it was liberalized from the late 1950s into the early 1960s. Although the Japanese government was extensively involved in allocating scarce foreign exchange in the early 1950s, the control system became increasingly flexible over this period. A preliminary analysis based on the behavior of wholesale prices seems to indicate that, along with its liberalization, the restrictive system became less effective as a tool of external adjustment, while the impact of deflationary macroeconomic measures became more dominant.

Japan's Restrictive System of Trade and Payments: Operation, Effectiveness, and Liberalization, 1950-1964

The paper summarizes how Japan`s foreign exchange and trade control system operated in the early 1950s, how and how effectively it was used as a tool of external adjustment, and how it was liberalized from the late 1950s into the early 1960s. Although the Japanese government was extensively involved in allocating scarce foreign exchange in the early 1950s, the control system became increasingly flexible over this period. A preliminary analysis based on the behavior of wholesale prices seems to indicate that, along with its liberalization, the restrictive system became less effective as a tool of external adjustment, while the impact of deflationary macroeconomic measures became more dominant.

The Political Economy of the Won: U.S.-Korean Bilateral Negotiations on Exchange Rates

This paper traces the development of U.S.-Korean negotiations on exchange rates in the second half of the 1980s. Background on Korea's foreign exchange control system is provided, including the evolution of its exchange rate determination mechanisms from 1945 to the current period. The U.S. Congress' rationale for including exchange rates in the Omnibus Trade and Competitiveness Act, the U.S. Treasury's Reports to Congress, and the results of the U.S. Treasury's negotiations with Korea on exchange rate "manipulation" are examined.Korea's current account surpluses emerged at a time when the United States was experiencing record current account deficits, in part due to the rapid appreciation of the dollar in the first half of the 1980s. The fact that the dollar subsequently depreciated against the United. States' industrial-country trading partners but moved little against the currencies of the NIEs prompted the U.S. Congress to examine the exchange rate policies of those economies. Under the Omnibus Trade and Competitiveness Act, Korea and Taiwan were cited in 1988 as "manipulating" their currencies for "unfair" trade gain. With the implementation of the market average-rate system in March 1990, Korea was removed from Treasury's list of exchange rate manipulators. However, the Treasury has complained that even though Korea does not directly manipulate the won within the meaning of the Exchange Rates Act, pervasive capital controls limit potential exchange rate movements and may be used to "manipulate" the value of the won indirectly.

Embedded microprocessor software: case study of an automatic computer exchange

A computer exchange control system has been designed to fulfil the specific requirements of the Brighton Polytechnic Computer Centre. This project raised various software issues that are common to a wide range of embedded applications. Some of these issues are reviewed in the paper, in particular the creation of a multitasking environment, I/O methods, timing and synchronization, debugging and bootstrapping. Before the software aspects are examined, the application and system structure are described in some detail. The role and function of the embedded microprocessor system and its interactions with the rest of the system are discussed.