271 research outputs found
The 1961 Kampong Bukit Ho Swee fire and the making of modern Singapore
No full textBy 1970, Singapore’s urban landscape was dominated by high-rise blocks of planned public housing built by the People’s Action Party government, signifying the establishment of a high modernist nation-state. A decade earlier, the margins of the City had been dominated by kampongs, home to semi-autonomous communities of low-income Chinese families which freely built, and rebuilt, unauthorised wooden houses. This change was not merely one of housing but belied a more fundamental realignment of state-society relations in the 1960s. Relocated in Housing and Development Board flats, urban kampong families were progressively integrated into the social fabric of the emergent nation-state. This study examines the pivotal role of an event, the great Kampong Bukit Ho Swee fire of 1961, in bringing about this transformation. The redevelopment of the fire site in the aftermath of the calamity brought to completion the British colonial regime’s ‘emergency’ programmes of resettling urban kampong dwellers in planned accommodation, in particular, of building emergency public housing on the sites of major fires in the 1950s. The PAP’s far greater political resolve, and the timing of and state of emergency occasioned by the scale of the 1961 disaster, enabled the government to rehouse the Bukit Ho Swee fire victims in emergency housing in record time. This in turn provided the HDB with a strategic platform for clearing other kampongs and for transforming their residents into model citizens of the nation-state. The 1961 fire’s symbolic usefulness extended into the 1980s and beyond, in sanctioning the PAP’s new housing redevelopment schemes. The official account of the inferno has also become politically useful for the government of today for disciplining a new generation of Singaporeans against taking the nation’s progress for granted. Against these exalted claims of the fire’s role in the Singapore Story, this study also examines the degree of actual change and continuity in the social and economic lives of the people of Bukit Ho Swee after the inferno. In some crucial ways, the residents continued to occupy a marginal place in society while pondering, too, over the unresolved question of the cause of the fire. These continuities of everyday life reflect the ambivalence with which the citizenry regarded the high modernist state in contemporary Singapore
Enhanced bio-production from CO<sub>2 </sub>by microbial electrosynthesis (MES) with continuous operational mode
No full textTechnologies able to convert CO2 to various feedstocks for fuels and chemicals are emerging due to the urge of reducing greenhouse gas emissions and de-fossilizing chemical production. Microbial electrosynthesis (MES) has been shown a promising technique to synthesize organic products particularly acetate using microorganisms and electrons. However, the efficiency of the system is low. In this study, we demonstrated the simple yet efficient strategy in enhancing the efficiency of MES by applying continuous feeding regime. Compared to the fed-batch system, continuous operational mode provided better control of pH and constant medium refreshment, resulting in higher acetate production rate and more diverse bio-products, when the cathodic potential of -1.0 V Ag/AgCl and dissolved CO2 were provided. It was observed that hydraulic retention time (HRT) had a direct effect on the pattern of production, acetate production rate and coulombic efficiency. At HRT of 3 days, pH was around 5.2 and acetate was the dominant product with the highest production rate of 651.8 ± 214.2 ppm per day and a significant coulombic efficiency of 90%. However at the HRT of 7 days, pH was lower at around 4.5, and lower but stable acetate production rate of 280 ppm per day and a maximum coulombic efficiency of 80% was obtained. In addition, more diverse and longer chain products, such as butyrate, isovalerate and caproate, were detected with low concentrations only at the HRT of 7 days. Although microbial community analysis showed the change in the planktonic cells communities after switching the fed-batch mode to continuous feeding regime, Acetobacterium still remained as the responsible bacteria for CO2 reduction to acetate, dominating the cathodic biofilm
Adaptive caching in a distributed file system
No full textEffective file system caching reduces local disk accesses and remote file server accesses significantly. Traditional file systems use fixed strategies to control caching. This thesis shows that a file system with adaptive caching achieves better performance than traditional file systems.Our file system implements multiple caching strategies and permits performance tuning through customized caching strategies. It adapts to the computing environment by selecting strategies suitable for the environment. It observes file accesses and uses the observed behaviors to anticipate and predict future behaviors. It adapts to different file access behaviors by modifying caching strategies. It does not depend on the application or the user for caching hints but will utilize hints when provided.Experiments with two large workloads having distinct file access characteristics show that adaptive file caching consistently outperforms non-adaptive caching. Adaptive file caching can reduce runtime by 36.6%, cache misses by 20.6%, and network load by 24.2%.In addition, this work also includes innovations in file system architecture. They include continuations for highly-concurrent asynchronous remote accesses, and zombies for efficient memory reclamation.Made available in DSpace on 2011-05-07T12:26:49Z (GMT). No. of bitstreams: 2
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Effects of Applied Potential and Reactants to Hydrogen-Producing Biocathode in a Microbial Electrolysis Cell
No full textUnderstanding the mechanism of electron transfer between the cathode and microorganisms in cathode biofilms in microbial electrolysis cells (MECs) for hydrogen production is important. In this study, biocathodes of MECs were successfully re-enriched and subjected to different operating parameters: applied potential, sulfate use and inorganic carbon consumption. It was hypothesized that biocathode catalytic activity would be affected by the applied potentials that initiate electron transfer. While inorganic carbon, in the form of bicarbonate, could be a main carbon source for biocathode growth, sulfate could be a terminal electron acceptor and thus reduced to elemental sulfurs. It was found that potentials more negative than −0.8 V (vs. standard hydrogen electrode) were required for hydrogen production by the biocathode. In additional, a maximum hydrogen production was observed at sulfate and bicarbonate concentrations of 288 and 610 mg/L respectively. Organic carbons were found in the cathode effluents, suggesting that microbial interactions probably happen between acetogens and sulfate reducing bacteria (SRB). The hydrogen-producing biocathode was sulfate-dependent and hydrogen production could be inhibited by excessive sulfate because more energy was directed to reduce sulfate (E° SO42-/H2S = −0.35 V) than proton (E° H+/H2 = −0.41 V). This resulted in a restriction to the hydrogen production when sulfate concentration was high. Domestic wastewaters contain low amounts of organic compounds and sulfate would be a better medium to enrich and maintain a hydrogen-producing biocathode dominated by SRB. Besides the risks of limited mass transport and precipitation caused by low potential, methane contamination in the hydrogen-rich environment was inevitable in the biocathode after long term operation due to methanogenic activities
Tungsten-oxide modified silica-titania oxidative-acidic bifunctional catalyst for diol synthesis
No full textOxidative-acidic bifunctional catalysts of tungsten oxide modified silica-titania, xW/TiO2-SiO2 (x=1, 5, 10 wt%) were successfully synthesized and characterized. Both XRD and UV-Vis analyses results indicated presence of WO3 phase in samples with higher dopant amount. It also revealed tetrahedral Ti and octahedral coordinated existed as the dominant species in the samples. FTIR analysis suggested formation of Si-O-W in the tungsten oxide modified samples. The catalytic performance of the samples was evaluated via consecutive transformation of 1-octene to 1,2-octanediol through the conversion of 1,2-epoxyoctane using aqueous H2O2 as oxidant. While TiO2-SiO2 and 1W/TiO2-SiO2 showed no catalytic activity in yielding diol, samples 5W/TiO2-SiO2 and 10W/TiO2-SiO2 exhibited bifunctional catalytic activity. It has been demonstrated that sample 10W/TiO2-SiO2 was the best oxidative-acidic bifuntional catalyst which produced 321 ?mol 1,2-epoxyoctane and 51 ?mol 1,2-octanediol after 24 h reaction
Zinc removal and recovery from industrial wastewater with a microbial fuel cell: experimental investigation and theoretical prediction
No full textMicrobial fuel cells (MFCs) that simultaneously remove organic contaminants and recovering metals provide a potential route for industry to adopt clean technologies. In this work, two goals were set: to study the feasibility of zinc removal from industrial effluents using MFCs and to understand the removal process by using reaction rate models. The removal of Zn2+ in MFC was over 96% for synthetic and industrial samples with initial Zn2+ concentrations less than 2.0 mM after 22 h of operation. However, only 83 and 42% of the zinc recovered from synthetic and industrial samples, respectively, was attached on the cathode surface of the MFCs. The results marked the domination of electroprecipitation rather than the electrodeposition process in the industrial samples. Energy dispersive X-ray (EDX) analysis showed that the recovered compound contained not only Zn but also O, evidence that Zn(OH)2 could be formed. The removal of Zn2+ in the MFC followed a mechanism where oxygen was reduced to hydroxide before reacting with Zn2+. Nernst equations and rate law expressions were derived to understand the mechanism and used to estimate the Zn2+ concentration and removal efficiency. The zero-, first- and second-order rate equations successfully fitted the data, predicted the final Zn2+ removal efficiency, and suggested that possible mechanistic reactions occurred in the electrolysis cell (direct reduction), MFC (O2 reduction), and control (chemisorption) modes. The half-life, t1/2, of the Zn2+ removal reaction using synthetic and industrial samples was estimated to be 7.0 and 2.7 h, respectively. The t1/2 values of the controls (without the power input from the MFC bioanode) were much slower and were recorded as 21.5 and 7.3 h for synthetic and industrial samples, respectively. The study suggests that MFCs can act as a sustainable and environmentally friendly technology for heavy metal removal without electrical energy input or the addition of chemicals.</p
A Christian social ethic for Singapore with reference to the works of Ronald H. Preston
No full textThis thesis proposes a contextual Christian social ethic for a plural Singapore where Christianity, as a late arrival in East and Southeast Asia, is still regarded by most Asians as a foreign religion, mainly because of its association with past colonial exploits and present Euro-North American value-systems. Our thesis begins with an historical overview of Singapore from its founding as a British colony to its present position as an independent prosperous republic. Drawing on two failed attempts at Christian social engagement in post- colonial Singapore as examples, we argue against uncritical adoption of any social ethical model which is not culture-sensitive to the peculiar contextual concerns of that city-state. We show that an appropriate and credible Christian social ethic for Singapore can be found, not so much in Liberation Theologies or Ecclesiological Ethics, though they have rightly attracted a lot of attention in recent years, but rather in the social theology of Ronald. Preston and the tradition he represents. Preston's social theology, informed very much by a doctrine of creation, recognises God's grace at work in the life of all people and social structures. It encourages and facilitates constructive Christian social engagement in the political arena and the economic sphere where Christians, as members of overlapping communities, live and work with people of other faiths and those with no religious affiliation. When critically adapted and appropriately supplemented by other theological and philosophical materials in areas where we find deficiencies, Preston's social theology provides the congenial theological resources which can be used to frame a contextual Christian social ethic to meet the multi-faceted challenges of a plural, post-colonial Singapore
Enhancing hydrogen production through anode fed-batch mode and controlled cell voltage in a microbial electrolysis cell fully catalysed by microorganisms
No full textInternational audienceA microbial electrolysis cell (MEC) fully catalysed by microorganisms is an attractive technology because it incorporates the state-of-the-art concept of converting organic waste to hydrogen with less external energy input than conventional electrolysers. In this work, the impact of the anode feed mode on the production of hydrogen by the biocathode was studied. In the first part, three feed modes and MEC performance in terms of hydrogen production were evaluated. The results showed the highest hydrogen production under the continuous mode (14.6 ± 0.4), followed by the fed-batch (12.7 ± 0.4) and batch (0 L m(-2) cathode day(-1)) modes. On one hand, the continuous mode only increased by 15% even though the hydraulic retention time (HRT) (2.78 h) was lower than the fed-batch mode (HRT 5 h). A total replacement (fed-batch) rather than a constant mix of existing anolyte and fresh medium (continuous) was preferable. On the other hand, no hydrogen was produced in batch mode due to the extensive HRT (24 h) and bioanode starvation. In the second part, the fed-batch mode was further evaluated using a chronoamperometry method under a range of applied cell voltages of 0.3-1.6 V. Based on the potential evolution at the electrodes, three main regions were identified depending on the applied cell voltages: the cathode activation (<0.8 V), transition (0.8-1.1 V), and anode limitation (>1.1 V) regions. The maximum hydrogen production recorded was 12.1 ± 2.1 L m(-2) cathode day(-1) at 1.0 V applied voltage when the oxidation and reduction reactions at the anode and cathode were optimal (2.38 ± 0.61 A m(-2)). Microbial community analysis of the biocathode revealed that Alpha-, and Deltaproteobacteria were dominant in the samples with >70% abundance. At the genus level, Desulfovibrio sp. was the most abundant in the samples, showing that these microbes may be responsible for hydrogen evolution
Random walks, the H-space of a random graph, and four miniatures
No full textABSTRACT OF THE DISSERTATION
Random walks, the H-space of a random graph, and four miniatures
By QUENTIN DUBROFF
Dissertation Directors:
Jeff Kahn and Bhargav Narayanan
This thesis is composed of two chapters proving results in discrete probability and
probabilistic combinatorics and a final chapter giving short proofs of four unrelated
results. The introduction gives a brief overview of the two longer results.
Chapter 2 proves the following natural statement that was conjectured by Itai
Benjamini in 2009. Here G is a (simple) graph and τG is the cover time (the time it
takes for a simple random walk on G to visit every vertex).
Theorem 1. For every C, there is an ε > 0 such that for every n-vertex graph G,
P(τG < Cn) < exp[−εn].
A first ingredient in our proof is a similar statement for a general Markov chain with
sufficiently small transition probabilities.
In Chapter 3, we study a version of higher order connectivity in the random graph.
The edge space E(G) of a graph G is the vector space FE(G)
2 with elements naturally
identified with subgraphs of G. For a fixed graph H, the H-space CH (G) is the
subspace of E(G) spanned by copies of H in G. Straightforwardly,
CH (G) ⊆ CH (K) ∩ E(G),
iiwhere K is the complete graph on the vertex set of G. We are interested in under-
standing when (i.e. for which p) equality holds if G = Gn,p. We prove that a simple
necessary condition is w.h.p. sufficient for equality whenever H is strictly 2-balanced.
Such a characterization was only known previously for odd cycles, where in particular
the result for triangles established the first open case of a conjecture of M. Kahle on
the homology of the clique complex of Gn,p.
The final chapter proves four mutually unrelated results. First, we give a proof
that maxi |ai| ≥ n
⌊n/2⌋
if a1, . . . , an are integers with distinct subset sums, which is
the best known lower bound. Second, we prove an identity relating a certain quadratic
form associated to a convex polytope to that of its dual polytope. This identity may
be viewed as a generalization of Minkowski’s identity relating the normal vectors and
facet areas of a polytope. Third, we give a new proof of the van den Berg-Kesten (BK)
inequality on disjoint occurrence which is one line given the Sauer-Shelah lemma and
Harris’s inequality. Finally, we finish with a counterexample to a directed version of
the KKL inequality conjectured by Subhash Khot.Ph.D.Includes bibliographical referencesIncludes vit
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