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Search Results: 1 - 10 of 462586 matches for " Patrick C. K. Li "
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Maternal Malaria and Gravidity Interact to Modify Infant Susceptibility to Malaria
Theonest K Mutabingwa,Melissa C Bolla,Jin-Long Li,Gonzalo J Domingo,Xiaohong Li,Michal Fried,Patrick E Duffy
PLOS Medicine , 2005, DOI: 10.1371/journal.pmed.0020407
Abstract: Background In endemic areas, placental malaria due to Plasmodium falciparum is most frequent and severe in first-time mothers, and increases the risk of infant mortality in their offspring. Placental malaria may increase the susceptibility of infants to malaria parasitemia, but evidence for this effect is inconclusive. Methods and Findings During 2002–2004, we monitored parasitemia in 453 infants, including 69 who were born to mothers with placental malaria, in a region of northeastern Tanzania where malaria transmission is intense. We used a Cox proportional hazards model to evaluate the time from birth to first parasitemia, and a generalized estimating equations logistic regression model to evaluate risk of any parasitemia throughout the first year of life. Compared with infants whose mothers did not have placental malaria at delivery (“PM-negative”), offspring of mothers with placental malaria at delivery (“PM-positive”) were 41% more likely to experience their first parasitemia at a younger age (adjusted hazard ratio [AHR] = 1.41, 95% confidence interval [CI] 1.01–1.99). The odds of parasitemia throughout infancy were strongly modified by the interaction between placental malaria and gravidity (p for interaction = 0.008, Type 3 likelihood ratio test). Offspring of PM-negative primigravidae had lower odds of parasitemia during infancy (adjusted odds ratio [AOR] = 0.67, 95% CI 0.50–0.91) than offspring of PM-negative multigravidae, and offspring of PM-positive primigravidae had the lowest odds (AOR = 0.21, 95% CI 0.09–0.47). In contrast, offspring of PM-positive multigravidae had significantly higher odds of parasitemia (AOR = 1.59, 95% CI 1.16–2.17). Conclusion Although parasitemia is more frequent in primigravid than multigravid women, the converse is true in their offspring, especially in offspring of PM-positive women. While placental malaria is known to increase mortality risk for first-born infants, it surprisingly reduced their risk of parasitemia in this study. Placental malaria of multigravidae, on the other hand, is a strong risk factor for parasitemia during infancy, and therefore preventive antimalarial chemotherapy administered to multigravid women close to term may reduce the frequency of parasitemia in their offspring.
Genotypic Analysis of Klebsiella pneumoniae Isolates in a Beijing Hospital Reveals High Genetic Diversity and Clonal Population Structure of Drug-Resistant Isolates
Qi Wang, Bin Li, Alan K. L. Tsang, Yong Yi, Patrick C. Y. Woo, Cui Hua Liu
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0057091
Abstract: Background The genetic diversity and the clinical relevance of the drug-resistant Klebsiella pneumoniae isolates from hospital settings are largely unknown. We thus conducted this prospective study to analyze the molecular epidemiology of K. pneumoniae isolates from patients being treated in the 306 Hospital in Beijing, China for the period of November 1, 2010–October 31, 2011. Methodology/Principal Findings Antibiotic susceptibility testing, PCR amplification and sequencing of the drug resistance-associated genes, and multilocus sequence typing (MLST) were conducted. A total of 163 isolates were analyzed. The percentage of MDR, XDR and PDR isolates were 63.8% (104), 20.9 (34), and 1.8% (3), respectively. MLST results showed that 60 sequence types (STs) were identified, which were further separated by eBURST into 13 clonal complexes and 18 singletons. The most dominant ST was ST15 (10.4%). Seven new alleles and 24 new STs were first identified in this study. Multiple logistic regression analysis revealed that certain clinical characteristics were associated with those prevalent STs such as: from ICU, from medical ward, from community acquired infection, from patients without heart disease, from patients with treatment success, susceptible to extended spectrum cephalosporin, susceptible to cephamycins, susceptible to fluoroquinolones, and with MDR. Conclusions/Significance Our data indicate that certain drug-resistant K. pneumoniae clones are highly prevalent and are associated with certain clinical characteristics in hospital settings. Our study provides evidence demonstrating that intensive nosocomial infection control measures are urgently needed.
Modelling and Parameters Identification of Through-Hole Type Wind Turbine Contactless Sliprings  [PDF]
Ali Abdolkhani, Aiguo Patrick Hu, Nirmal C.-K. Nair
Engineering (ENG) , 2012, DOI: 10.4236/eng.2012.45036
Abstract: This paper presents a modelling and parameter identification of through-hole type contactless slipring systems for transferring electrical power for wind turbine pitch control. An equivalent circuit model has been developed from the physical structure and dimensions of the contactless slipring using the duality rules, which is very different form traditional transformer. The circuit inductances are determined by the derived expressions from the system reluctances. In particular, the equivalent resistance representing the core loss of the slipring has been determined using phasor diagram of exciting current. FEM (Finite Element Method) models and practical prototypes are developed for testing and verifycations. Both simulation and experimental results have shown that the developed model gives truthful values for numerical calculations in order to obtain the equivalent electric circuit. The effect of fringing flux around the air gap on mutual inductance and the ways of correcting its effects are analysed. The obtained values have shown that the developed models and derived equations are with high accuracy as compared to the FEM simulation and experimental results.
Discovery and Genomic Characterization of a Novel Bat Sapovirus with Unusual Genomic Features and Phylogenetic Position
Herman Tse, Wan-Mui Chan, Kenneth S. M. Li, Susanna K. P. Lau, Patrick C. Y. Woo, Kwok-Yung Yuen
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0034987
Abstract: Sapovirus is a genus of caliciviruses that are known to cause enteric disease in humans and animals. There is considerable genetic diversity among the sapoviruses, which are classified into different genogroups based on phylogenetic analysis of the full-length capsid protein sequence. While several mammalian species, including humans, pigs, minks, and dogs, have been identified as animal hosts for sapoviruses, there were no reports of sapoviruses in bats in spite of their biological diversity. In this report, we present the results of a targeted surveillance study in different bat species in Hong Kong. Five of the 321 specimens from the bat species, Hipposideros pomona, were found to be positive for sapoviruses by RT-PCR. Complete or nearly full-length genome sequences of approximately 7.7 kb in length were obtained for three strains, which showed similar organization of the genome compared to other sapoviruses. Interestingly, they possess many genomic features atypical of most sapoviruses, like high G+C content and minimal CpG suppression. Phylogenetic analysis of the viral proteins suggested that the bat sapovirus descended from an ancestral sapovirus lineage and is most closely related to the porcine sapoviruses. Codon usage analysis showed that the bat sapovirus genome has greater codon usage bias relative to other sapovirus genomes. In summary, we report the discovery and genomic characterization of the first bat calicivirus, which appears to have evolved under different conditions after early divergence from other sapovirus lineages.
Comparisons of Primary HIV-1 Drug Resistance between Recent and Chronic HIV-1 Infection within a Sub-Regional Cohort of Asian Patients
Sasisopin Kiertiburanakul, Romanee Chaiwarith, Sunee Sirivichayakul, Rossana Ditangco, Awachana Jiamsakul, Patrick C. K. Li, Pacharee Kantipong, Christopher Lee, Winai Ratanasuwan, Adeeba Kamarulzaman, Annette H. Sohn, Somnuek Sungkanuparph, for the TREAT Asia Studies to Evaluate Resistance Surveillance and Monitoring Studies
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0062057
Abstract: Background The emergence and transmission of HIV-1 drug resistance (HIVDR) has raised concerns after rapid global antiretroviral therapy (ART) scale-up. There are limited data on the epidemiology of primary HIVDR in resource-limited settings in Asia. We aimed to determine the prevalence and compare the distribution of HIVDR in a cohort of ART-na?ve Asian patients with recent and chronic HIV-1 infection. Methods Multicenter prospective study was conducted in ART-na?ve patients between 2007 and 2010. Resistance-associated mutations (RAMs) were assessed using the World Health Organization 2009 list for surveillance of primary HIVDR. Results A total of 458 patients with recent and 1,340 patients with chronic HIV-1 infection were included in the analysis. The overall prevalence of primary HIVDR was 4.6%. Recently infected patients had a higher prevalence of primary HIVDR (6.1% vs. 4.0%, p = 0.065) and frequencies of RAMs to protease inhibitors (PIs; 3.9% vs. 1.0%, p<0.001). Among those with recent infection, the most common RAMs to nucleoside reverse transcriptase inhibitors (NRTIs) were M184I/V and T215D/E/F/I/S/Y (1.1%), to non-NRTIs was Y181C (1.3%), and to PIs was M46I (1.5%). Of patients with chronic infection, T215D/E/F/I/S/Y (0.8%; NRTI), Y181C (0.5%; non-NRTI), and M46I (0.4%; PI) were the most common RAMs. K70R (p = 0.016) and M46I (p = 0.026) were found more frequently among recently infected patients. In multivariate logistic regression analysis in patients with chronic infection, heterosexual contact as a risk factor for HIV-1 infection was less likely to be associated with primary HIVDR compared to other risk categories (odds ratio 0.34, 95% confidence interval 0.20–0.59, p<0.001). Conclusions The prevalence of primary HIVDR was higher among patients with recent than chronic HIV-1 infection in our cohort, but of borderline statistical significance. Chronically infected patients with non-heterosexual risks for HIV were more likely to have primary HIVDR.
STAIR Codes: A General Family of Erasure Codes for Tolerating Device and Sector Failures
Mingqiang Li,Patrick P. C. Lee
Mathematics , 2014,
Abstract: Practical storage systems often adopt erasure codes to tolerate device failures and sector failures, both of which are prevalent in the field. However, traditional erasure codes employ device-level redundancy to protect against sector failures, and hence incur significant space overhead. Recent sector-disk (SD) codes are available only for limited configurations. By making a relaxed but practical assumption, we construct a general family of erasure codes called \emph{STAIR codes}, which efficiently and provably tolerate both device and sector failures without any restriction on the size of a storage array and the numbers of tolerable device failures and sector failures. We propose the \emph{upstairs encoding} and \emph{downstairs encoding} methods, which provide complementary performance advantages for different configurations. We conduct extensive experiments on STAIR codes in terms of space saving, encoding/decoding speed, and update cost. We demonstrate that STAIR codes not only improve space efficiency over traditional erasure codes, but also provide better computational efficiency than SD codes based on our special code construction. Finally, we present analytical models that characterize the reliability of STAIR codes, and show that the support of a wider range of configurations by STAIR codes is critical for tolerating sector failure bursts discovered in the field.
Loss to Followup in HIV-Infected Patients from Asia-Pacific Region: Results from TAHOD
Jialun Zhou,Junko Tanuma,Romanee Chaiwarith,Christopher K. C. Lee,Matthew G. Law,Nagalingeswaran Kumarasamy,Praphan Phanuphak,Yi-Ming A. Chen,Sasisopin Kiertiburanakul,Fujie Zhang,Saphonn Vonthanak,Rossana Ditangco,Sanjay Pujari,Jun Yong Choi,Tuti Parwati Merati,Evy Yunihastuti,Patrick C. K. Li,Adeeba Kamarulzaman,Van Kinh Nguyen,Thi Thanh Thuy Pham,Poh Lian Lim
AIDS Research and Treatment , 2012, DOI: 10.1155/2012/375217
Abstract: This study examined characteristics of HIV-infected patients in the TREAT Asia HIV Observational Database who were lost to follow-up (LTFU) from treatment and care. Time from last clinic visit to 31 March 2009 was analysed to determine the interval that best classified LTFU. Patients defined as LTFU were then categorised into permanently LTFU (never returned) and temporary LTFU (re-entered later), and these groups compared. A total of 3626 patients were included (71% male). No clinic visits for 180 days was the best-performing LTFU definition (sensitivity 90.6%, specificity 92.3%). During 7697 person-years of follow-up, 1648 episodes of LFTU were recorded (21.4 per 100-person-years). Patients LFTU were younger ( ), had HIV viral load ≥500?copies/mL or missing ( ), had shorter history of HIV infection ( ), and received no, single- or double-antiretroviral therapy, or a triple-drug regimen containing a protease inhibitor ( ). 48% of patients LTFU never returned. These patients were more likely to have low or missing haemoglobin ( ), missing recent HIV viral load ( ), negative hepatitis C test ( ), and previous temporary LTFU episodes ( ). Our analyses suggest that patients not seen at a clinic for 180 days are at high risk of permanent LTFU, and should be aggressively traced. 1. Introduction Loss to followup (LTFU) in patients receiving antiretroviral therapy can cause serious consequences such as discontinuation of treatment and increased risk of death [1–3]. At a program level, LTFU can make it difficult to evaluate outcomes of treatment and care [4, 5]. In resource-limited settings, where treatment has become rapidly available following the rollout of antiretroviral therapy, LTFU presents even more challenging obstacles that require special consideration and approaches [6, 7]. One of the key questions in patient followup is how to define a patient as LTFU. This has varied in studies conducted in different settings [8–10]. Defining LTFU using a very early threshold, for example, a patient with no clinic visit in the last three months, may result in many patients being considered as LTFU who would return to clinic naturally at a later date. Defining LTFU with a long threshold, for example, one year, may mean delaying too long before any effort is made to track patients potentially at risk of LTFU. The majority of research into LTFU in HIV-infected patients receiving antiretroviral treatment in resource-limited settings has been conducted in the sub-Saharan Africa region [3, 10–13]. A few studies have been conducted among Asian, mostly female, patients
Stochastic Modeling of Large-Scale Solid-State Storage Systems: Analysis, Design Tradeoffs and Optimization
Yongkun Li,Patrick P. C. Lee,John C. S. Lui
Computer Science , 2013,
Abstract: Solid state drives (SSDs) have seen wide deployment in mobiles, desktops, and data centers due to their high I/O performance and low energy consumption. As SSDs write data out-of-place, garbage collection (GC) is required to erase and reclaim space with invalid data. However, GC poses additional writes that hinder the I/O performance, while SSD blocks can only endure a finite number of erasures. Thus, there is a performance-durability tradeoff on the design space of GC. To characterize the optimal tradeoff, this paper formulates an analytical model that explores the full optimal design space of any GC algorithm. We first present a stochastic Markov chain model that captures the I/O dynamics of large-scale SSDs, and adapt the mean-field approach to derive the asymptotic steady-state performance. We further prove the model convergence and generalize the model for all types of workload. Inspired by this model, we propose a randomized greedy algorithm (RGA) that can operate along the optimal tradeoff curve with a tunable parameter. Using trace-driven simulation on DiskSim with SSD add-ons, we demonstrate how RGA can be parameterized to realize the performance-durability tradeoff.
Stochastic Analysis on RAID Reliability for Solid-State Drives
Yongkun Li,Patrick P. C. Lee,John C. S. Lui
Computer Science , 2013,
Abstract: Solid-state drives (SSDs) have been widely deployed in desktops and data centers. However, SSDs suffer from bit errors, and the bit error rate is time dependent since it increases as an SSD wears down. Traditional storage systems mainly use parity-based RAID to provide reliability guarantees by striping redundancy across multiple devices, but the effectiveness of RAID in SSDs remains debatable as parity updates aggravate the wearing and bit error rates of SSDs. In particular, an open problem is that how different parity distributions over multiple devices, such as the even distribution suggested by conventional wisdom, or uneven distributions proposed in recent RAID schemes for SSDs, may influence the reliability of an SSD RAID array. To address this fundamental problem, we propose the first analytical model to quantify the reliability dynamics of an SSD RAID array. Specifically, we develop a "non-homogeneous" continuous time Markov chain model, and derive the transient reliability solution. We validate our model via trace-driven simulations and conduct numerical analysis to provide insights into the reliability dynamics of SSD RAID arrays under different parity distributions and subject to different bit error rates and array configurations. Designers can use our model to decide the appropriate parity distribution based on their reliability requirements.
On measuring colloidal volume fractions
Wilson C. K. Poon,Eric R. Weeks,C. Patrick Royall
Physics , 2011,
Abstract: Hard-sphere colloids are popular as models for testing fundamental theories in condensed matter and statistical physics, from crystal nucleation to the glass transition. A single parameter, the volume fraction (phi), characterizes an ideal, monodisperse hard-sphere suspension. In comparing experiments with theories and simulation, researchers to date have paid little attention to likely uncertainties in experimentally-quoted phi values. We critically review the experimental measurement of phi in hard-sphere colloids, and show that while statistical uncertainties in comparing relative values of phi can be as low as 0.0001, systematic errors of 3-6% are probably unavoidable. The consequences of this are illustrated by way of a case study comparing literature data sets on hard-sphere viscosity and diffusion.
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