Energy and System Size Dependence of Charged Hadron Transverse Momentum Spectra from Cu+Cu and Au+Au Collisions at sqrt(s_(NN)) = 62.4 and 200 GeV

The PHOBOS collaboration has measured transverse momentum distributions of charged hadrons produced in Cu+Cu collisions at sqrt(s_(NN)) = 200 and 62.4 GeV. The nuclear modification factor R_(AA)^(Npart) is calculated relative to p+p data at both collision energies as a function of collision centrality. For the same number of participating nucleons, R_(AA)^(Npart) is essentially the same in both systems over the full range of p_(T) that is measured. In addition, we observe that within experimental uncertainties, the ratio of 200 GeV to 62.4 GeV Cu+Cu yields has only a moderate centrality dependence and is consistent with the value previously measured in Au+Au collisions for a broad range of p_(T).Comment: 4 pages, 2 figures, QM2005 Conference poster proceedings published in Acta Physica Hungarica

Mass campaigns with antimalarial drugs: a modelling comparison of artemether-lumefantrine and DHA-piperaquine with and without primaquine as tools for malaria control and elimination

Antimalarial drugs are a powerful tool for malaria control and elimination. Artemisinin-based combination therapies (ACTs) can reduce transmission when widely distributed in a campaign setting. Modelling mass antimalarial campaigns can elucidate how to most effectively deploy drug-based interventions and quantitatively compare the effects of cure, prophylaxis, and transmission-blocking in suppressing parasite prevalence. A previously established agent-based model that includes innate and adaptive immunity was used to simulate malaria infections and transmission. Pharmacokinetics of artemether, lumefantrine, dihydroartemisinin, piperaquine, and primaquine were modelled with a double-exponential distribution-elimination model including weight-dependent parameters and age-dependent dosing. Drug killing of asexual parasites and gametocytes was calibrated to clinical data. Mass distribution of ACTs and primaquine was simulated with seasonal mosquito dynamics at a range of transmission intensities. A single mass campaign with antimalarial drugs is insufficient to permanently reduce malaria prevalence when transmission is high. Current diagnostics are insufficiently sensitive to accurately identify asymptomatic infections, and mass-screen-and-treat campaigns are much less efficacious than mass drug administrations. Improving campaign coverage leads to decreased prevalence one month after the end of the campaign, while increasing compliance lengthens the duration of protection against reinfection. Use of a long-lasting prophylactic as part of a mass drug administration regimen confers the most benefit under conditions of high transmission and moderately high coverage. Addition of primaquine can reduce prevalence but exerts its largest effect when coupled with a long-lasting prophylactic.Comment: 14 pages, 5 figure

Studies of high transverse momentum phenomena in heavy ion collisions using the PHOBOS detector

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 137-149).The use of high-pT particles as calibrated probes has proven to be an effective tool for understanding the properties of the system produced in relativistic heavy ion collisions. In this thesis, two such measurements are presented using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC): 1. The transverse momentum spectra of charged particles produced near mid rapidity in Cu+Cu collisions with center-of-mass energies of 62.4 and 200 GeV per nucleon pair 2. Two-particle correlations with a high transverse momentum trigger particle (pT > 2.5 GeV=c ) in Au+Au collisions at ... 200 GeV over the broad longitudinal acceptance of the PHOBOS detector ... In central Au+Au collisions at 200 GeV, the single-particle yields are suppressed at high-pT by a factor of about five compared to p+p collisions scaled by the number of binary collisions. This is typically understood to be a consequence of energy loss by high-pT partons in the dense QCD medium, as such a suppression is absent in d+Au collisions. In Cu+Cu collisions, the nuclear modification factor, RAA, has been measured relative to p+p data as a function of collision centrality. For the same number of participating nucleons (Npart), RAA is essentially the same for the Cu+Cu and Au+Au systems over the measured range of pT, in spite of the significantly different geometries. At high-pT, the similarity between the two systems can be described by simple, geometric models of parton energy loss. Two-particle angular correlations are a more powerful tool for examining how highpT jets lose energy and how the medium is modified by the deposited energy. In central Au+Au collisions, particle production correlated with a high-pT trigger is strongly modified compared to p+p. Not only is the away-side yield much broader in, the nearside peak of jet fragments now sits atop an unmistakable 'ridge' of correlated partners extending continuously and undiminished all the way to = 4.by Edward Wenger.Ph.D

Optimal population-level infection detection strategies for malaria control and elimination in a spatial model of malaria transmission

Mass campaigns with antimalarial drugs are potentially a powerful tool for local elimination of malaria, yet current diagnostic technologies are insufficiently sensitive to identify all individuals who harbor infections. At the same time, overtreatment of uninfected individuals increases the risk of accelerating emergence of drug resistance and losing community acceptance. Local heterogeneity in transmission intensity may allow campaign strategies that respond to index cases to successfully target subpatent infections while simultaneously limiting overtreatment. While selective targeting of hotspots of transmission has been proposed as a strategy for malaria control, such targeting has not been tested in the context of malaria elimination. Using household locations, demographics, and prevalence data from a survey of four health facility catchment areas in southern Zambia and an agent-based model of malaria transmission and immunity acquisition, a transmission intensity was fit to each household based on neighborhood age-dependent malaria prevalence. A set of individual infection trajectories was constructed for every household in each catchment area, accounting for heterogeneous exposure and immunity. Various campaign strategies (mass drug administration, mass screen and treat, focal mass drug administration, snowball reactive case detection, pooled sampling, and a hypothetical serological diagnostic) were simulated and evaluated for performance at finding infections, minimizing overtreatment, reducing clinical case counts, and interrupting transmission. For malaria control, presumptive treatment leads to substantial overtreatment without additional morbidity reduction under all but the highest transmission conditions. Selective targeting of hotspots with drug campaigns is an ineffective tool for elimination due to limited sensitivity of available field diagnostics

Malaria elimination campaigns in the Lake Kariba region of Zambia: a spatial dynamical model

Background As more regions approach malaria elimination, understanding how different interventions interact to reduce transmission becomes critical. The Lake Kariba area of Southern Province, Zambia, is part of a multi-country elimination effort and presents a particular challenge as it is an interconnected region of variable transmission intensities. Methods In 2012-13, six rounds of mass-screen-and-treat drug campaigns were carried out in the Lake Kariba region. A spatial dynamical model of malaria transmission in the Lake Kariba area, with transmission and climate modeled at the village scale, was calibrated to the 2012-13 prevalence survey data, with case management rates, insecticide-treated net usage, and drug campaign coverage informed by surveillance. The model was used to simulate the effect of various interventions implemented in 2014-22 on reducing regional transmission, achieving elimination by 2022, and maintaining elimination through 2028. Findings The model captured the spatio-temporal trends of decline and rebound in malaria prevalence in 2012-13 at the village scale. Simulations predicted that elimination required repeated mass drug administrations coupled with simultaneous increase in net usage. Drug campaigns targeted only at high-burden areas were as successful as campaigns covering the entire region. Interpretation Elimination in the Lake Kariba region is possible through coordinating mass drug campaigns with high-coverage vector control. Targeting regional hotspots is a viable alternative to global campaigns when human migration within an interconnected area is responsible for maintaining transmission in low-burden areas

High p_T Triggered Delta-eta,Delta-phi Correlations over a Broad Range in Delta-eta

The first measurement of pseudorapidity (Delta-eta) and azimuthal angle (Delta-phi) correlations between high transverse momentum charged hadrons (p_T > 2.5 GeV/c) and all associated particles is presented at both short- (small Delta-eta) and long-range (large Delta-eta) over a continuous pseudorapidity acceptance (-4<Delta-eta<2). In these proceedings, the various near- and away-side features of the correlation structure are discussed as a function of centrality in Au+Au collisions measured by PHOBOS at sqrt(s_NN)=200 GeV. In particular, this measurement allows a much more complete determination of the longitudinal extent of the ridge structure, first observed by the STAR collaboration over a limited eta range. In central collisions the ridge persists to at least Delta-eta=4, diminishing in magnitude as collisions become more peripheral until it disappears around Npart=80.Comment: 5 pages, 2 figures, presented at the 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur, India, February 4-10, 2008. Full author list included and typo corrected in equation

Characterization of the infectious reservoir of malaria with an agent-based model calibrated to age-stratified parasite densities and infectiousness

Background Elimination of malaria can only be achieved through removal of all vectors or complete depletion of the infectious reservoir in humans. Mechanistic models can be built to synthesize diverse observations from the field collected under a variety of conditions and subsequently used to query the infectious reservoir in great detail. Methods The EMOD model of malaria transmission was calibrated to prevalence, incidence, asexual parasite density, gametocyte density, infection duration, and infectiousness data from 9 study sites. The infectious reservoir was characterized by diagnostic detection limit and age group over a range of transmission intensities with and without case management and vector control. Mass screen-and-treat drug campaigns were tested for likelihood of achieving elimination. Results The composition of the infectious reservoir by diagnostic threshold is similar over a range of transmission intensities, and higher intensity settings are biased toward infections in children. Recent ramp-ups in case management and use of insecticide-treated bednets reduce the infectious reservoir and shift the composition toward submicroscopic infections. Mass campaigns with antimalarial drugs are highly effective at interrupting transmission if deployed shortly after ITN campaigns. Conclusions Low density infections comprise a substantial portion of the infectious reservoir. Proper timing of vector control, seasonal variation in transmission intensity, and mass drug campaigns allows lingering population immunity to help drive a region toward elimination.Comment: submitted to Malaria Journal on March 31, 201