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Background: Pneumocystis jirovecii pneumonia is increasingly diagnosed with highly sensitive PCR diagnostics in immunocompromised, HIV-negative individuals. We assessed the performance of our in-house quantitative PCR with the aim to optimise interpretation. Methods: Retrospective audit of all positive P. jirovecii qPCRs on induced sputum or BAL fluid at a single centre from 2012 to 2023. Medical and laboratory records were analysed and people with HIV were excluded. Cases were categorised as colonisation, high-probability PCP or uncertain PCP infection against a clinical gold standard incorporating clinico-radiological data. Quantitative PCR assay targeting the 5s gene was utilised throughout the time period. Results: Of the 82 positive qPCRs, 28 were categorised as high-probability PCP infection, 30 as uncertain PCP and 24 as colonisation. There was a significant difference in qPCR values stratified by clinical category but not respiratory sample type. Current assay performance with a cutoff of 2.5 × 105 copies/mL had a sensitivity of 50% (95% CI, 30.65–69.35%) and specificity of 83.33% (95% CI, 62.62–95.26%). Youden Index calculated at 6.5 × 104 copies/mL had a sensitivity of 75% (56.64–87.32%, 95% CI) and specificity of 66.67% (46.71–82.03%, 95% CI). High and low cutoffs were explored. Significant variables associated with infection were age > 70 years old, the presence of fever, hypoxia or ground glass changes. Conclusions: A single qPCR cutoff cannot reliably determine P. jirovecii infection from colonisation. Low and high cutoffs are useful, however, a large "possible infection" cohort will remain where interpretation of clinic-radiological factors remains essential. Standardisation of assays with prospective validation in specific immunocompromised groups will allow greater generalisability and allow large-scale prospective assay validation to be performed. [ABSTRACT FROM AUTHOR]

Cerebral malaria is the most serious manifestation of severe falciparum malaria. Sequestration of infected red blood cells and microvascular dysfunction are key contributing processes. Whether these processes occur in early stage disease prior to clinical manifestations is unknown. To help localize and understand these processes during the early stages of infection, we performed 18-F fluorodeoxyglucose positron emission tomography/magnetic resonance imaging in volunteers with Plasmodium falciparum induced blood stage malaria (IBSM) infection, and compared results to individuals with P. vivax infection, in whom coma is rare. Seven healthy, malaria-naïve participants underwent imaging at baseline, and at early symptom onset a median 9 days following inoculation (n = 4 P. falciparum, n = 3 P. vivax). Participants with P. falciparum infection demonstrated marked lability in radiotracer uptake across all regions of the brain, exceeding expected normal variation (within subject coefficient of variation (wCV): 14.4%) compared to the relatively stable uptake in participants with P. vivax infection (wCV: 3.5%). No consistent imaging changes suggestive of microvascular dysfunction were observed in either group. Neuroimaging in early IBSM studies is safe and technically feasible, with preliminary results suggesting that differences in brain tropism between P. falciparum and P. vivax may occur very early in infection. [ABSTRACT FROM AUTHOR]

Background The extent of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exposure and transmission in Mali and the surrounding region is not well understood. We aimed to estimate the cumulative incidence of SARS-CoV-2 in 3 communities and understand factors associated with infection. Methods Between July 2020 and January 2021, we collected blood samples and demographic, social, medical, and self-reported symptoms information from residents aged 6 months and older over 2 study visits. SARS-CoV-2 antibodies were measured using a highly specific 2-antigen enzyme-linked immunosorbent assay optimized for use in Mali. We calculated cumulative adjusted seroprevalence for each community and evaluated factors associated with serostatus at each visit by univariate and multivariate analysis. Results Overall, 94.8% (2533/2672) of participants completed both study visits. A total of 31.3% (837/2672) were aged <10 years, 27.6% (737/2672) were aged 10–17 years, and 41.1% (1098/2572) were aged ≥18 years. The cumulative SARS-CoV-2 exposure rate was 58.5% (95% confidence interval, 47.5–69.4). This varied between sites and was 73.4% in the urban community of Sotuba, 53.2% in the rural town of Bancoumana, and 37.1% in the rural village of Donéguébougou. Study site and increased age were associated with serostatus at both study visits. There was minimal difference in reported symptoms based on serostatus. Conclusions The true extent of SARS-CoV-2 exposure in Mali is greater than previously reported and may now approach hypothetical "herd immunity" in urban areas. The epidemiology of the pandemic in the region may be primarily subclinical and within background illness rates. [ABSTRACT FROM AUTHOR]

Background: False positivity may hinder the utility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serological tests in sub-Saharan Africa.Methods: From 312 Malian samples collected before 2020, we measured antibodies to the commonly tested SARS-CoV-2 antigens and 4 other betacoronaviruses by enzyme-linked immunosorbent assay (ELISA). In a subset of samples, we assessed antibodies to a panel of Plasmodium falciparum antigens by suspension bead array and functional antiviral activity by SARS-CoV-2 pseudovirus neutralization assay. We then evaluated the performance of an ELISA using SARS-CoV-2 spike protein and receptor-binding domain developed in the United States using Malian positive and negative control samples. To optimize test performance, we compared single- and 2-antigen approaches using existing assay cutoffs and population-specific cutoffs.Results: Background reactivity to SARS-CoV-2 antigens was common in prepandemic Malian samples. The SARS-CoV-2 reactivity varied between communities, increased with age, and correlated negligibly/weakly with other betacoronavirus and P falciparum antibodies. No prepandemic samples demonstrated functional activity. Regardless of the cutoffs applied, test specificity improved using a 2-antigen approach. Test performance was optimal using a 2-antigen assay with population-specific cutoffs (sensitivity, 73.9% [95% confidence interval {CI}, 51.6-89.8]; specificity, 99.4% [95% CI, 97.7-99.9]).Conclusions: We have addressed the problem of SARS-CoV-2 seroassay performance in Africa by using a 2-antigen assay with cutoffs defined by performance in the target population. [ABSTRACT FROM AUTHOR]

Background: Plasmodium vivax has been proposed to infect and replicate in the human spleen and bone marrow. Compared to Plasmodium falciparum, which is known to undergo microvascular tissue sequestration, little is known about the behavior of P. vivax outside of the circulating compartment. This may be due in part to difficulties in studying parasite location and activity in life.Methods and Findings: To identify organ-specific changes during the early stages of P. vivax infection, we performed 18-F fluorodeoxyglucose (FDG) positron emission tomography/magnetic resonance imaging (PET/MRI) at baseline and just prior to onset of clinical illness in P. vivax experimentally induced blood-stage malaria (IBSM) and compared findings to P. falciparum IBSM. Seven healthy, malaria-naive participants were enrolled from 3 IBSM trials: NCT02867059, ACTRN12616000174482, and ACTRN12619001085167. Imaging took place between 2016 and 2019 at the Herston Imaging Research Facility, Australia. Postinoculation imaging was performed after a median of 9 days in both species (n = 3 P. vivax; n = 4 P. falciparum). All participants were aged between 19 and 23 years, and 6/7 were male. Splenic volume (P. vivax: +28.8% [confidence interval (CI) +10.3% to +57.3%], P. falciparum: +22.9 [CI -15.3% to +61.1%]) and radiotracer uptake (P. vivax: +15.5% [CI -0.7% to +31.7%], P. falciparum: +5.5% [CI +1.4% to +9.6%]) increased following infection with each species, but more so in P. vivax infection (volume: p = 0.72, radiotracer uptake: p = 0.036). There was no change in FDG uptake in the bone marrow (P. vivax: +4.6% [CI -15.9% to +25.0%], P. falciparum: +3.2% [CI -3.2% to +9.6%]) or liver (P. vivax: +6.2% [CI -8.7% to +21.1%], P. falciparum: -1.4% [CI -4.6% to +1.8%]) following infection with either species. In participants with P. vivax, hemoglobin, hematocrit, and platelet count decreased from baseline at the time of postinoculation imaging. Decrements in hemoglobin and hematocrit were significantly greater in participants with P. vivax infection compared to P. falciparum. The main limitations of this study are the small sample size and the inability of this tracer to differentiate between host and parasite metabolic activity.Conclusions: PET/MRI indicated greater splenic tropism and metabolic activity in early P. vivax infection compared to P. falciparum, supporting the hypothesis of splenic accumulation of P. vivax very early in infection. The absence of uptake in the bone marrow and liver suggests that, at least in early infection, these tissues do not harbor a large parasite biomass or do not provoke a prominent metabolic response. PET/MRI is a safe and noninvasive method to evaluate infection-associated organ changes in morphology and glucose metabolism. [ABSTRACT FROM AUTHOR]

Background: Plasmodium malariae is considered a minor malaria parasite, although its global disease burden is underappreciated. The aim of this study was to develop an induced blood-stage malaria (IBSM) model of P. malariae to study parasite biology, diagnostic assays, and treatment.Methods: This clinical trial involved 2 healthy subjects who were intravenously inoculated with cryopreserved P. malariae-infected erythrocytes. Subjects were treated with artemether-lumefantrine after development of clinical symptoms. Prior to antimalarial therapy, mosquito-feeding assays were performed to investigate transmission, and blood samples were collected for rapid diagnostic testing and parasite transcription profiling. Serial blood samples were collected for biomarker analysis.Results: Both subjects experienced symptoms and signs typical of early malaria. Parasitemia was detected 7 days after inoculation, and parasite concentrations increased until antimalarial treatment was initiated 25 and 21 days after inoculation for subjects 1 and 2 respectively (peak parasitemia levels, 174 182 and 50 291 parasites/mL, respectively). The parasite clearance half-life following artemether-lumefantrine treatment was 6.7 hours. Mosquito transmission was observed for 1 subject, while in vivo parasite transcription and biomarkers were successfully profiled.Conclusions: An IBSM model of P. malariae has been successfully developed and may be used to study the biology of, diagnostic testing for, and treatment of this neglected malaria species.Clinical Trials Registration: ACTRN12617000048381. [ABSTRACT FROM AUTHOR]

A form of hydrogenated diamond-like-carbon, “near-frictionless carbon,” developed at Argonne National Laboratory has been studied by several spectroscopic techniques to determine the hydrogen content and carbon bonding within the film. The techniques used include hydrogen forward scattering, ultraviolet Raman spectroscopy, Fourier transform infrared spectroscopy, near-edge x-ray absorption fine structure, and fluctuation microscopy. These complementary techniques reveal the different types of carbon bonding, such as sp2 and sp3, the medium-range order in the film, and its composition. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Focuses on the remarks of entertainment personality Bill Cosby at the 50th anniversary commemoration of the Brown v. Board Education at Howard University in Washington D. C. Description of Cosby on American basketball players; Comment of the celebrity on the quality of black education; Criticism of media people on the speech of Cosby.

Comments on the Black Radical Congress (BRC) on June 18 to 21, 1998 at the University of Illinois. Views on the academic format of the congress; Apparent weaknesses that help explain the proposed petition drive denouncing United States (US) genocide to the United Nations; Agenda needed by the BRC and other progressives; Highlights from the BRC.

Profiles Richard Wright from the perspective of other writers. Includes excerpts from the `New York Herald Tribune' newspaper; `L'Express' newspaper; `La Nef' magazine.

A literary criticism of the book "Malcolm X In Our Own Image" edited by Joe Wood with contributors including Amiri Baraka, Angela Davis, John Edgar Wideman, and Cornel West. It presents essays on African-American Muslim minister and human rights activist Malcolm X. It discusses an understanding of Malcolm X's metamorphosis, his struggle for black liberation, his joining the political religious movement, Nation of Islam, and his autobiography through these essays.

Presents an account of the author's experience at the `Ebony' and `Muhammad Speaks' periodicals. Job responsibilities; Censorship; Servility demonstrations; Column description; Reviews.

Discusses the effect of racism on affirmative action court decisions in the U. S. Details of the emergence of affirmative action cases in the country; Decision of the Supreme court on the Bakke case; Information on a case filed by the Center for Individual Rights against the University of Michigan; Tactics used by nationalists on affirmative action.

Background: Malaria-associated anaemia, arising from symptomatic, asymptomatic and submicroscopic infections, is a significant cause of morbidity worldwide. Induced blood stage malaria volunteer infection studies (IBSM-VIS) provide a unique opportunity to evaluate the haematological response to early Plasmodium falciparum and Plasmodium vivax infection. Methods: This study was an analysis of the haemoglobin, red cell counts, and parasitaemia data from 315 participants enrolled in IBSM-VIS between 2012 and 2019, including 269 participants inoculated with the 3D7 strain of P. falciparum (Pf3D7), 15 with an artemisinin-resistant P. falciparum strain (PfK13) and 46 with P. vivax. Factors associated with the fractional fall in haemoglobin (Hb-FF) were evaluated, and the malaria-attributable erythrocyte loss after accounting for phlebotomy-related losses was estimated. The relative contribution of parasitized erythrocytes to the malaria-attributable erythrocyte loss was also estimated. Results: The median peak parasitaemia prior to treatment was 10,277 parasites/ml (IQR 3566–27,815), 71,427 parasites/ml [IQR 33,236–180,213], and 34,840 parasites/ml (IQR 13,302–77,064) in participants inoculated with Pf3D7, PfK13, and P. vivax, respectively. The median Hb-FF was 10.3% (IQR 7.8–13.3), 14.8% (IQR 11.8–15.9) and 11.7% (IQR 8.9–14.5) in those inoculated with Pf3D7, PfK13 and P. vivax, respectively, with the haemoglobin nadir occurring a median 12 (IQR 5–21), 15 (IQR 7–22), and 8 (IQR 7–15) days following inoculation. In participants inoculated with P. falciparum, recrudescence was associated with a greater Hb-FF, while in those with P. vivax, the Hb-FF was associated with a higher pre-treatment parasitaemia and later day of anti-malarial treatment. After accounting for phlebotomy-related blood losses, the estimated Hb-FF was 4.1% (IQR 3.1–5.3), 7.2% (IQR 5.8–7.8), and 4.9% (IQR 3.7–6.1) in participants inoculated with Pf3D7, PfK13, and P. vivax, respectively. Parasitized erythrocytes were estimated to account for 0.015% (IQR 0.006–0.06), 0.128% (IQR 0.068–0.616) and 0.022% (IQR 0.008–0.082) of the malaria-attributable erythrocyte loss in participants inoculated with Pf3D7, PfK13, and P. vivax, respectively. Conclusion: Early experimental P. falciparum and P. vivax infection resulted in a small but significant fall in haemoglobin despite parasitaemia only just at the level of microscopic detection. Loss of parasitized erythrocytes accounted for < 0.2% of the total malaria-attributable haemoglobin loss. [ABSTRACT FROM AUTHOR]

Background: The spread of SARS-CoV-2 cannot be well monitored and understood in areas without capacity for effective disease surveillance. Countries with a young population will have disproportionately large numbers of asymptomatic or pauci-symptomatic infections, further hindering detection of infection. Sero-surveillance on a country-wide scale by trained medical professionals may be limited in a resource-limited setting such as Mali. Novel ways of broadly sampling the human population in a non-invasive method would allow for large-scale surveillance at a reduced cost. Approach: Here we evaluate the collection of naturally blood-fed mosquitoes to test for human anti-SARS-CoV-2 antibodies in the laboratory and at five field locations in Mali. Results: Immunoglobulin-G antibodies to multiple SARS-CoV-2 antigens were readily detected in mosquito bloodmeals by bead-based immunoassay through at least 10 h after feeding [mean sensitivity of 0.92 (95% CI 0.78-1) and mean specificity of 0.98 (95% CI 0.88-1)], indicating that most blood-fed mosquitoes collected indoors during early morning hours (and likely to have fed the previous night) are viable samples for analysis. We found that reactivity to four SARS-CoV-2 antigens rose during the pandemic from pre-pandemic levels. The crude seropositivity of blood sampled via mosquitoes was 6.3% in October and November 2020 across all sites, and increased to 25.1% overall by February 2021, with the most urban site reaching 46.7%, consistent with independent venous blood-based sero-surveillance estimates. Conclusions: We have demonstrated that using mosquito bloodmeals, countrywide sero-surveillance of human diseases (both vector-borne and non-vectorborne) is possible in areas where human-biting mosquitoes are common, offering an informative, cost-effective, and non-invasive sampling option. [ABSTRACT FROM AUTHOR]

Abstract: A detailed study of the top surface (∼2 nm) of a near frictionless carbon film has revealed new information with respect to the sp3 fraction. Previous work on near frictionless carbon films made at Argonne had shown a large fraction of sp2-hybridized carbon in the bulk of the film. However, in this study of the surface, the majority of the carbon was found to be sp3. In addition we compared and contrasted the behavior of the films after mechanical abrasion and Ar+ etching. The study also revealed that oxygen on untreated samples was rapidly reduced by etching or heating or mechanical abrasion; this finding was corroborated by an angle-resolved study, where different depths of the sample were probed. It was also found that the fraction of sp3 carbon decreased linearly with depth, falling in one film from ∼90% sp3 to ∼80% sp3 in the top 2 nm. [Copyright &y& Elsevier]

The tribological characteristics of a diamondlike carbon (DLC) film deposited on high-speed steel were investigated systematically by using a ball-on-flat reciprocating tribometer over a range of temperatures (from −40° to 20°C). The results indicated that the temperature dependence of the DLC film's tribological behavior was associated with the counterpart material. DLC presented favorable tribological behavior while sliding on itself. However, when a steel ball slides against the DLC film, there is evidence that the heat generated has a significant impact on friction and wear. Microanalysis of wear tracks on the films showed that multiple wear mechanisms took place during testing. At higher temperatures, material transfer dominated the wear behavior, while fatigue-induced microcracking was the predominant wear mechanism at low temperatures. Raman analysis indicated that the DLC film was mechanically worn rather than removed by tribochemical interactions between the friction pairs. [ABSTRACT FROM AUTHOR]

Background MMV390048 is the first Plasmodium phosphatidylinositol 4-kinase inhibitor to reach clinical development as a new antimalarial. We aimed to characterize the safety, pharmacokinetics, and antimalarial activity of a tablet formulation of MMV390048. Methods A 2-part, phase 1 trial was conducted in healthy adults. Part 1 was a double-blind, randomized, placebo-controlled, single ascending dose study consisting of 3 cohorts (40, 80, 120 mg MMV390048). Part 2 was an open-label volunteer infection study using the Plasmodium falciparum induced blood-stage malaria model consisting of 2 cohorts (40 mg and 80 mg MMV390048). Results Twenty four subjects were enrolled in part 1 (n = 8 per cohort, randomized 3:1 MMV390048:placebo) and 15 subjects were enrolled in part 2 (40 mg [n = 7] and 80 mg [n = 8] cohorts). One subject was withdrawn from part 2 (80 mg cohort) before dosing and was not included in analyses. No serious or severe adverse events were attributed to MMV390048. The rate of parasite clearance was greater in subjects administered 80 mg compared to those administered 40 mg (clearance half-life 5.5 hours [95% confidence interval {CI}, 5.2–6.0 hours] vs 6.4 hours [95% CI, 6.0–6.9 hours]; P  = .005). Pharmacokinetic/pharmacodynamic modeling estimated a minimum inhibitory concentration of 83 ng/mL and a minimal parasiticidal concentration that would achieve 90% of the maximum effect of 238 ng/mL, and predicted that a single 120-mg dose would achieve an adequate clinical and parasitological response with 92% certainty. Conclusions The safety, pharmacokinetics, and pharmacodynamics of MMV390048 support its further development as a partner drug of a single-dose combination therapy for malaria. Clinical Trials Registration NCT02783820 (part 1); NCT02783833 (part 2). [ABSTRACT FROM AUTHOR]

Background: (+)-SJ000557733 (SJ733) is a novel, orally bioavailable inhibitor of Plasmodium falciparum ATP4. In this first-in-human and induced blood-stage malaria phase 1a/b trial, we investigated the safety, tolerability, pharmacokinetics, and antimalarial activity of SJ733 in humans.Methods: The phase 1a was a single-centre, dose-escalation, first-in-human study of SJ733 allowing modifications to dose increments and dose-cohort size on the basis of safety and pharmacokinetic results. The phase 1a took place at St Jude Children's Research Hospital and at the University of Tennessee Clinical Research Center (Memphis, TN, USA). Enrolment in more than one non-consecutive dose cohort was allowed with at least 14 days required between doses. Participants were fasted in seven dose cohorts and fed in one 600 mg dose cohort. Single ascending doses of SJ733 (75, 150, 300, 600, 900, or 1200 mg) were administered to participants, who were followed up for 14 days after SJ733 dosing. Phase 1a primary endpoints were safety, tolerability, and pharmacokinetics of SJ733, and identification of an SJ733 dose to test in the induced blood-stage malaria model. The phase 1b was a single-centre, open-label, volunteer infection study using the induced blood-stage malaria model in which fasted participants were intravenously infected with blood-stage P falciparum and subsequently treated with a single dose of SJ733. Phase 1b took place at Q-Pharm (Herston, QLD, Australia) and was initiated only after phase 1a showed that exposure exceeding the threshold minimum exposure could be safely achieved in humans. Participants were inoculated on day 0 with P falciparum-infected human erythrocytes (around 2800 parasites in the 150 mg dose cohort and around 2300 parasites in the 600 mg dose cohort), and parasitaemia was monitored before malaria inoculation, after inoculation, immediately before SJ733 dosing, and then post-dose. Participants were treated with SJ733 within 24 h of reaching 5000 parasites per mL or at a clinical score higher than 6. Phase 1b primary endpoints were calculation of a parasite reduction ratio (PRR48) and parasite clearance half-life, and safety and tolerability of SJ733 (incidence, severity, and drug-relatedness of adverse events). In both phases of the trial, SJ733 hydrochloride salt was formulated as a powder blend in capsules containing 75 mg or 300 mg for oral administration. Healthy men and women (of non-childbearing potential) aged 18-55 years were eligible for both studies. Both studies are registered with ClinicalTrials.gov (NCT02661373 for the phase 1a and NCT02867059 for the phase 1b).Findings: In the phase 1a, 23 healthy participants were enrolled and received one to three non-consecutive doses of SJ733 between March 14 and Dec 7, 2016. SJ733 was safe and well tolerated at all doses and in fasted and fed conditions. 119 adverse events were recorded: 54 (45%) were unrelated, 63 (53%) unlikely to be related, and two (2%) possibly related to SJ733. In the phase 1b, 17 malaria-naive, healthy participants were enrolled. Seven participants in the 150 mg dose cohort were inoculated and dosed with SJ733. Eight participants in the 600 mg dose cohort were inoculated, but two participants could not be dosed with SJ733. Two additional participants were subsequently inoculated and dosed with SJ733. SJ733 exposure increased proportional to the dose through to the 600 mg dose, then was saturable at higher doses. Fasted participants receiving 600 mg exceeded the target area under the concentration curve extrapolated to infinity (AUC0-∞) of 13 000 μg × h/L (median AUC0-∞ 24 283 [IQR 16 135-31 311] μg × h/L, median terminal half-life 17·4 h [IQR 16·1-24·0], and median timepoint at which peak plasma concentration is reached 1·0 h [0·6-1·3]), and this dose was tested in the phase 1b. All 15 participants dosed with SJ733 had at least one adverse event. Of the 172 adverse events recorded, 128 (74%) were mild. The only adverse event attributed to SJ733 was mild bilateral foot paraesthesia that lasted 3·75 h and resolved spontaneously. The most common adverse events were related to malaria. Based on parasite clearance half-life, the derived log10PRR48 and corresponding parasite clearance half-lives were 2·2 (95% CI 2·0-2·5) and 6·47 h (95% CI 5·88-7·18) for 150 mg, and 4·1 (3·7-4·4) and 3·56 h (3·29-3·88) for 600 mg.Interpretation: The favourable pharmacokinetic, tolerability, and safety profile of SJ733, and rapid antiparasitic effect support its development as a fast-acting component of combination antimalarial therapy.Funding: Global Health Innovative Technology Fund, Medicines for Malaria Venture, and the American Lebanese Syrian Associated Charities. [ABSTRACT FROM AUTHOR]

We have studied the effect of oxide impurities on the formation of BaCl2 nanocrystals in Eu-doped fluorochlorozirconate glass-ceramic storage phosphors using x-ray absorption near-edge structure and x-ray diffraction analyses. It is found that annealing the glass with a relatively high level of oxide impurities causes crystallization of BaCl2 and a phase transition from hexagonal to orthorhombic BaCl2. The latter phase is responsible for the storage phosphor effect. In contrast, the glass with a low impurity concentration forms hexagonal BaCl2, but no such phase transition. Our study provides structural clues for understanding the x-ray storage mechanism in fluorozirconate-based glass ceramics. [ABSTRACT FROM AUTHOR]

“Near-frictionless carbon,” a form of amorphous hydrogenated diamondlike carbon developed at Argonne National Laboratory, has been investigated by neutron and x-ray reflectivity under ambient conditions, in vacuum, and at elevated temperature. A series of films was made with different ratios of hydrogen to carbon in the plasma; the deuterated counterparts were also synthesized. The details of scattering length density profiles, thickness, and surface and interfacial roughness of the films were obtained from neutron and x-ray reflectivity profiles. This allowed us to calculate the mass density and hydrogen composition of the bulk carbon film, leading to insight into the frictional properties. From the analysis we found that the magnitude of the scattering length density of the top surface layer was greatly affected by the experimental atmosphere in which the films were contained although the trend with hydrogen in the plasma remained the same. All samples were fitted with a three-layer model in addition to the substrate. [ABSTRACT FROM AUTHOR]

“Near-frictionless carbon,” a form of amorphous hydrogenated diamond-like-carbon developed at Argonne National Laboratory, has been investigated by neutron and x-ray reflectivity under ambient conditions, in vacuum, and at elevated temperature. A series of films was made with different ratios of hydrogen to carbon in the plasma; the deuterated counterparts were also synthesized. The details of scattering length density profiles, thickness, and surface and interfacial roughness of the films were obtained from neutron and x-ray reflectivity profiles. This allowed us to calculate the mass density and hydrogen composition of the bulk carbon film, leading to insight into the frictional properties. From the analysis we found that the magnitude of the scattering length density of the top surface layer was greatly affected by the experimental atmosphere in which the films were contained although the trend with hydrogen in the plasma remained the same. All samples were fitted with a three-layer model in addition to the substrate. [ABSTRACT FROM AUTHOR]

In this work the tribological behavior of hard carbon films on steel substrates has been studied under moderately high contact stress conditions. Diamond-like carbon (DLC) coatings of 1 μm thickness were deposited by a plasma-enhanced chemical vapor deposition (PECVD) process on hardened substrates made from 4140 alloy steel. The coated flat specimens were tested in an oscillatory pin-on-disk configuration in contact with either uncoated or carbon-coated hardened steel balls. Peak Hertzian contact pressures ranged from about 300 to 500 MPa and mean sliding velocity was 50 mm/s. In some tests, the specimens were lubricated with 10W-30 motor oil.It was found that wear of the carbon coatings was approximately linearly proportional to contact force. For unlubricated tests, wear rates of the coated specimens were about 200 times less than rates of wear of uncoated steel specimens for the same contact force. The contacting steel ball (uncoated) showed even greater wear reduction (more than 3 orders of magnitude) when tested against coated substrates. Friction coefficients were four to five times lower for coated specimens. Coating the ball as well as the flat resulted in a further reduction (about 50%) in wear of both ball and flat. Friction and wear reduction brought about by carbon coating in lubricated tests was less than for unlubricated specimens. [Copyright &y& Elsevier]