Estimating the number of errors in a system using a Martingale approach

A new, efficient procedure estimates the number of errors in a system. A known number of seeded errors are inserted into a system. The failure intensities of the seeded and real errors are allowed to be different and time dependent. When an error is detected during the test, it is removed from the system. The testing process is observed for a fixed amount of time τ. Martingale theory is used to derive a class of estimators for the number of seeded errors in a continuous time setting. Some of the estimators and their associated standard deviations have explicit expressions. An optimal estimator among the class of estimators is obtained. A simulation study assesses the performance of the proposed estimators.published_or_final_versio

Impacts of Ageing Population on Monetary and Exchange Rate Managements in Singapore

This paper finds that the ageing of the population in Singapore will cause a reversal of the current net Central Provident Fund (CPF) contribution into a substantial net CPF withdrawal from 2025, with a peak occurring at 2035. The result is qualitatively robust to changes in the underlying assumptions of the projection. The paper then highlights the implications of this change on the exchange rate and monetary managements in Singapore. First, the Monetary Authority of Singapore (MAS)’s ability to influence Singapore’s exchange rate will be greatly hampered. Second, the net CPF withdrawal will mean sustained liquidity injection into (instead of the usual liquidity drain from) the economy. To avoid unnecessary inflation, the MAS has to find a sustainable way to mob up the excess liquidity due to the sustained liquidity injection. As a simple reversal of MAS’s current foreign exchange market operation will result in substantial shrinkage of foreign reserves, the paper proposes the issuance of government bonds to achieve the dual objectives of mobbing up the excess liquidity and avoiding the shrinkage of foreign reserves. This measure will also help the bond market development in Singapore. Finally, the paper proposes two other measures that can help maintain MAS’s influence on Singapore’s exchange rate to a reasonable level in the longer future.Ageing Population, Central Provident Fund, Exchange Rate System, Monetary Policy, Singapore.

On the Maintenance Costs and Exit Costs of the Peg in Hong Kong

This paper attempts to pioneer a discussion on the exit and maintenance costs of the Currency Board System (CBS) in Hong Kong, and hopes to invite more debate on the issue. It suggests that the exit costs will depend on the timing of an exit, whether there are supplementary packages to mitigate the exit costs, and the choice of an alternative exchange rate system. In particular, it suggests that the monitoring band system favored by Williamson (2000) could help to reduce the exit costs. In addition, the paper points out that there are ways to reduce both the exit and maintenance costs. It then proposes a reform that could benefit the economy regardless of whether the policy maker eventually chooses to continue with or abandon the peg. The study is not only crucial to Hong Kong, but also important to other economies with a CBS as well as to the debate on the choice of exchange rate system.currency board, monitoring band, exchange rate policy, Hong Kong, Singapore.

The foxconn suicides and their media prominence: is the werther effect applicable in china?

<p>Abstract</p> <p>Background</p> <p>Media reporting of suicide and its relationship with actual suicide has rarely been investigated in Mainland China. The "Foxconn suicides" is a description referring to a string of suicides/attempts during 2010, all of which were related to a giant electrical manufacturing company, Foxconn. This study aimed to examine the clustering and copycat effects of the Foxconn suicides, and to investigate temporal patterns in how they were reported by the media in Mainland China, Hong Kong (HK), and Taiwan (TW).</p> <p>Methods</p> <p>Relevant articles were collected from representative newspapers published in three big cities in Mainland China (Beijing (BJ), Shenzhen (SZ), and Guangzhou (GZ)), HK, and TW, together with searching intensity data on the topic conducted using the Baidu search engine in Mainland China. The temporal clustering effects of the Foxconn suicides and their media prominence were assessed using the Kolmogorov-Smirnov test. The media reports of the Foxconn suicides' temporal patterns were explored using a nonparametric curve estimation method (that is, the local linear method). The potential mutual interactions between the Foxconn suicides and their media prominence were also examined, using logistic and Poisson regression methods.</p> <p>Results</p> <p>The results support a temporal clustering effect for the Foxconn suicides. The BJ-based newspapers' reporting and the occurrence of a Foxconn suicide/attempt are each found to be associated with an elevated chance of a further Foxconn suicide 3 days later. The occurrence of a Foxconn suicide also immediately influenced the intensity of both Baidu searching and newspaper reporting. Regional diversity in suicide reporting tempo-patterns within Mainland China, and similarities between HK and TW, are also demonstrated.</p> <p>Conclusions</p> <p>The Foxconn suicides were temporally clustered. Their occurrences were influenced by the reporting of BJ-based newspapers, and contagion within the company itself. Further suicide research and prevention work in China should consider its special media environment.</p

Hydrogen Jet Combustion in Engine-relevant Conditions

With the recent advancement in H2 production technology, efforts towards decarbonisation and the ongoing tightening of emission requirements, interest in incorporating H2 as an energy carrier in transportation powertrains have been re-ignited. Direction injection (DI) of H2, ignited by a pilot fuel, to achieve diffusion-like combustion has a high potential to achieve H2 as a main fuel in dual-fuel internal combustion engine (ICE) and thereby significantly reducing carbon-based emissions. The late injection during the compression stroke offers great advantages over H2 port fuel injection (PFI), as it can alleviate issues such as pre-ignition, knocking, backfiring, low volumetric efficiency and compression loss associated with H2 PFI. Nevertheless, the lack of fundamental understanding of H2 diffusion combustion has hindered the development of this dual-fuel mode in ICE. Previous studies on H2 diffusion combustion in engine-relevant conditions focused mainly on the autoignition delay, however, with contradicting findings and no optical information. Therefore, the aims of this thesis study are to: (1) investigate the flame evolution and combustion characteristics of autoigniting H2 jet diffusion flame; (2) examine the effect of various typical engine operating parameters on the combustion characteristics of autoigniting H2 jet diffusion flame; (3) provide insights on H2 jet flame recession and stabilisation in engine-relevant conditions. This work was conducted in an optically-accessible constant-volume combustion chamber under simulated DI compression-ignition engine conditions. Depending on the experiments and aims, the parametric variation could include the injector nozzle orifice diameter (0.31-0.83 mm), injection reservoir pressure (100-200 bar), ambient temperature (600-1140K), density (12.5-24 kg/m3) and O2 concentration (10-21 vol.%). An in-house modified gasoline direct injection injector was used to enable high-pressure H2 injection, and the injection conditions were carefully characterised. High-speed schlieren imaging, OH* chemiluminescence imaging and apparent heat release rate analysis from pressure trace measurements were employed to optically and quantitatively examine the combustion characteristics of the H2 jet flame

Molecular Dynamics Computer Simulation of the Dynamics of Supercooled Silica

We present the results of a large scale computer simulation of supercooled silica. We find that at high temperatures the diffusion constants show a non-Arrhenius temperature dependence whereas at low temperature this dependence is also compatible with an Arrhenius law. We demonstrate that at low temperatures the intermediate scattering function shows a two-step relaxation behavior and that it obeys the time temperature superposition principle. We also discuss the wave-vector dependence of the nonergodicity parameter and the time and temperature dependence of the non-Gaussian parameter.Comment: 5 pages, Latex, 6 postscript figure

A Markov chain model for studying suicide dynamics: an illustration of the Rose theorem

Background: High-risk strategies would only have a modest effect on suicide prevention within a population. It is best to incorporate both high-risk and population-based strategies to prevent suicide. This study aims to compare the effectiveness of suicide prevention between high-risk and population-based strategies. Methods: A Markov chain illness and death model is proposed to determine suicide dynamic in a population and examine its effectiveness for reducing the number of suicides by modifying certain parameters of the model. Assuming a population with replacement, the suicide risk of the population was estimated by determining the final state of the Markov model. Results: The model shows that targeting the whole population for suicide prevention is more effective than reducing risk in the high-risk tail of the distribution of psychological distress (i.e. the mentally ill). Conclusions: The results of this model reinforce the essence of the Rose theorem that lowering the suicidal risk in the population at large may be more effective than reducing the high risk in a small population

Persistent Symptomatic Knee After Total Knee Replacement. Is Knee Arthroscopy Helpful? 全膝關節置換術後的持續性症狀:關節鏡有用嗎?

AbstractPersistent symptoms following total knee replacement (TKR) could be diagnostically challenging. We present three cases of knee arthroscopy following TKR to illustrate the effectiveness of arthroscopy for the diagnosis and treatment of persistent symptomatic knee. It is concluded that arthroscopy after TKR is a relatively safe and effective procedure for well selected cases with persistent symptoms following TKR

Macroeconomic implications of customer-supplier and worker-employer relationships.

This thesis investigates a few examples of customer-supplier and worker-employer relationships which are thought to be important to macroeconomic analysis. Among the literature on sticky price, we suggest that the theory of mark-up pricing and the theory of customer-supplier relationships advocated by Okun (1981), deserve more attention. We also suggest that there are at least three hypotheses implicit in the mark-up equation: (1) a sticky pricing response to demand shocks; (2) a relatively fast pricing response to cost shocks; and (3) 1 % change in average cost will cause an equiproportionate rise in price. In Chapter 2, a reputation cost of changing price is used to summarize Okun's discussion on suppliers' tendency to pledge the constancy of price for some reasonably long period (a type of customer-supplier relationship). A microfoundation model is then built to investigate the three hypothesis in details. With regard to the first hypothesis, it is shown that (a) the reputation cost of changing price; (b) uncertainties about the persistence and generality of an observed demand shock; and (c) their interactions can jointly account for an extensive degree of price stickiness. We also explain that such a modelling of price stickiness could be more convincing than that by the Menu Cost Hypothesis. With regard to the second and third hypotheses, our conclusion is positive in the sense that it is a good approximation, but negative in the sense that it is at most an approximation. We then specify the conditions under which the mark-up equation can be used in macroeconomic analysis. In our discussion of hypothesis 2, we also touched upon the evolution of the practice of cost-oriented, as opposed to demand-oriented, pricing. In Chapter 3, we start with the justification of an implicit, non-binding guarantee of employment for those within the firms (a type of worker-employer relationship). A dynamic programming model is then built to investigate the employment response of the representative employer to demand shocks. It is found that: (a) In the case of mild negative demand shock, the producer will hoard the excessive amount of labour, and production effort will be the variable of adjustment; (b) In the case of adverse negative demand shock, the producer will break the implicit guarantee of employment and make considerable amount of layoffs. From the point of view of maintaining employment, it is always better to stimulate the economy before, rather than after, the layoffs. Mild stimulation policies after the layoffs will have no effect on employment. Chapter 4 attempts to provide an estimate of the cost of changing price. It was found that the cost is much larger than can be explained by the Menu Cost Hypothesis. The estimation also provides some evidence against the Normal Cost Hypothesis. Finally, Chapter 5 is a simulation exercise to check whether Caplin and Spulber's neutrality result, arising from the disappearance of price stickiness on aggregation, can be applied to some more general specifications

An analysis of the Lowest Total Fertility Rate in Hong Kong SAR

Total Fertility Rate (TFR) in Hong Kong has dropped significantly over the past 30 years, from 2.48 births per woman in 1976 to 0.966 in 2005, which is one of the lowest in the world. It is mainly caused by the change of marital distribution which has contributed to about 56% of the decline in the total fertility rate for the period 1976-2001. Delay of marriage and reduction in the marital fertility rate have also been shown to be two major causes for the low TFR. A new measure, called a weighted total marital fertility rate (WTMFR), is introduced such that change of age at marriage and the fertility within marriage can be factored in explaining the decline of the fertility rate. The delay of marriage has contributed to about 52% of the reduction of WTMFR whereas the reduction of the fertility within marriage has accounted for the other 48%. Apparently, the proportion of women remaining single has been stabilized and leveled off recently. However, the preference of having smaller family size has become a norm rather than an exception. It is very unlikely to see a rebound of fertility among the Hong Kong women in the near future if there is no increase in marriages or births outside wedlock. Encouraging more births among married women so as to increase fertility is expected to have limited impact.Age at first marriage, decomposition, Hong Kong, Total fertility rate, Weighted total marital fertility rate