VL Data Research Articles

The impact of analytical treatment interruptions and trial interventions on time to viral re-suppression in people living with HIV restarting ART in cure-related clinical studies: a systematic review and meta-analysis.

To assess the effectiveness of novel HIV curative strategies, "cure" trials require periods of closely monitored antiretroviral therapy (ART) analytical treatment interruptions (ATIs). We performed a systematic review and meta-analysis to identify the impact of ATI with or without novel therapeutics in cure-related studies on the time to viral re-suppression following ART restart. Medline, Embase and Web of Science databases were searched for human studies involving ATIs from 1 January 2015 till 22 April 2024. The primary outcome was time to first viral re-suppression (plasma HIV viral load [VL] <50 copies/ml) stratified by receipt of interventional drug with ATI (IA) or ATI-only groups. Random-effects proportional meta-analysis and multivariable Cox proportional hazards analysis were performed using R. Of 1073 studies screened, 13 were included that met the inclusion criteria with VL data available after restarting ART (n = 213 participants). There was no difference between time to viral suppression in IA or ATI-only cohorts (p = 0.22). For 87% of participants, viral suppression within 12 weeks of ART restart was achieved, and all eventually had at least one VL <50 copies/ml during follow-up. After adjusting for covariables, while participants in the IA cohort were associated with less rapid suppression (adjusted hazard ratio [aHR] 0.61, 95% CI 0.40-0.94, p = 0.026), other factors include greater log VL at ART restart (aHR 0.56, 95% CI 0.46-0.68, p<0.001), duration since HIV diagnosis (aHR 0.93, 95% CI 0.89-0.96) and longer intervals between HIV VL monitoring (aHR 0.66, 95% CI 0.59-0.74, p<0.001). However, the use of integrase inhibitors was associated with more rapid viral suppression (aHR 1.74, 95% CI 1.16-2.59). When designing studies involving ATIs, information on time to viral re-suppression after restarting ART is important to share with participants, and should be regularly monitored and reported, to assess the impact and safety of specific trial interventions in ATI studies. The majority of participants achieved viral suppression after restarting ART in ATI studies. ART regimens containing integrase inhibitors and frequent VL monitoring should be offered for people restarting ART after ATI studies to ensure rapid re-suppression.

Factors associated with an unsuppressed viral load among HIV-positive individuals attending STI services in South Africa, 2019

BackgroundSexually transmitted infections (STIs), particularly in the absence of viral suppression, increase the risk of HIV transmission to uninfected partners. We determined factors associated with having an unsuppressed VL among HIV-positive individuals attending STI services in South Africa (SA).MethodsWe analysed secondary cross-sectional data collected on HIV-positive individuals presenting with STI symptoms s at sentinel sites in Western Cape and Gauteng provinces between January–December 2019 in SA. We compared demographic characteristics of individuals on ART or not on ART, and a Poisson regression model to identify factors associated with having an unsuppressed VL (≥ 50 copies/ml) was used.ResultsAmong 93 HIV-positive individuals attending STI services with VL data, the median age was 32 years (IQR 27–37). Thirty-two (34.41%) individuals were on ART compared to 61 (65.59%) not on ART. Most of those on ART (56.25%) had an unsuppressed VL, while 86.89% of those not on ART had an unsuppressed VL. ART use was associated with a 33% lower prevalence of having unsuppressed VL. In a model adjusting for age, age at first sex and oral sex, none of the factors were significant. Among those on ART, individuals < 25 years were more likely to have an unsuppressed VL (aPRR = 1.94: 95% CI = 1.27–2.97) compared to those ≥ 25 years.ConclusionART use among HIV-positive individuals was low and VL suppression among those on ART was sub-optimal. Intensified ART initiation and adherence support to HIV-positive individuals seeking STI services could improve VL suppression.

Haematological dynamics following treatment of visceral leishmaniasis: a protocol for systematic review and individual participant data (IPD) meta-analysis

IntroductionVisceral leishmaniasis (VL) is a parasitic disease with an estimated 30 000 new cases occurring annually. Despite anaemia being a common haematological manifestation of VL, the evolution of different haematological...

Host, parasite and drug determinants of clinical outcomes following treatment of visceral leishmaniasis: a protocol for individual participant data meta-analysis

IntroductionVisceral leishmaniasis (VL) is a parasitic disease with an estimated 30 000 new cases occurring annually. There is an observed variation in the efficacy of the current first-line therapies across...

Factors associated with HIV viral suppression among children and adults receiving antiretroviral therapy in Malawi in 2021: Evidence from the Laboratory Management Information System.

To describe the prevalence of HIV viral suppression and assess the factors associated with HIV viral suppression among persons receiving antiretroviral therapy (ART) in Malawi in 2021. Implementation study using routinely collected patient-level HIV RNA-PCR test result data extracted from the national Laboratory Management Information System (LIMS) database managed by the Department of HIV/AIDS in 2021. We calculated frequencies, proportions and odds ratios (OR) of HIV viral suppression with their associated 95% confidence intervals (95%CIs). We performed a random-effects logistic regression to determine the risk factors associated with HIV viral suppression among ART patients, controlling for the spatial autocorrelation between districts and adjusting for other variables. We evaluated 515,797 adults and children receiving ART and having a viral load test in 2021. Of these, 92.8% had HIV viral suppression. ART patients living in urban areas had lower likelihood of HIV viral suppression than those living in rural areas (adjusted OR [aOR]=0.95, 95%CI: 0.92-0.99, p= 0.01). There was an increasing trend in HIV viral suppression with increasing ART duration. Routine VL monitoring samples were 39% more likely to have suppressed VL values than confirmatory HIV VL monitoring samples (aOR=1.39; 95%CI: 1.34-1.43, p< 0.001). This is the first national analysis of Malawi HIV VL data from LIMS. Our findings show the need to particularly consider the urban residents, those below 20 years, males, those on ART for less than a year as well as those on specific ARV regimens in order to persistently suppress HIV VL and consequently achieve the goal of achieving HIV VL suppression by 2030.

Characteristics of adolescents aged 15-19 years living with vertically and horizontally acquired HIV in Nampula, Mozambique.

BackgroundAdolescents living with HIV (ALHIV) 15–19 years of age are a growing proportion of all people living with HIV globally and the population includes adolescents with vertically acquired HIV (AVH) and behaviorally acquired HIV (ABH).MethodsWe conducted a survey to measure sociodemographic characteristics, educational status, health history, and antiretroviral therapy (ART) adherence among a convenience sample of ALHIV at three government health facilities in 2019 in Nampula, Mozambique. ALHIV 15–19 years on ART, including females attending antenatal care, were eligible. Routine HIV care data were extracted from medical charts. Classification of ALHIV by mode of transmission was based on medical charts and survey data. ALHIV who initiated ART <15 years or reported no sex were considered AVH; all others ABH. Frequencies were compared by sex, and within sex, by mode of transmission (AVH vs. ABH) using Chi-square, Fishers exact tests and Wilcoxon rank-sum tests.ResultsAmong 208 ALHIV, 143 (69%) were female and median age was 18 years [interquartile range (IQR) 16–19]. Just over half of ALHIV (53%) were in or had completed secondary or higher levels of education; the most common reason for not being in school reported by 36% of females was pregnancy or having a child. Of all ALHIV, 122 (59%) had VL data, 62% of whom were <1000 copies/mL. Almost half (46%) of ALHIV reported missing ARVs ≥ 1 day in the past month (62% of males vs. 39% of females; p = 0.003). Just over half (58%) of ALHIV in relationships had disclosed their HIV status: 13% of males vs. 69% of females (p<0.001). Among sexually active males, 61% reported using a condom at last sex compared to 26% of females (p<0.001). Among female ALHIV, 50 (35%) were AVH and 93 (65%) were ABH, 67% of whom were not in school compared to 16% of ABH, (p<0.001).DiscussionData from our study underscore the high level of deprivation among ALHIV enrolled in HIV care in Mozambique, as well as important disparities by sex and mode of transmission. These data can inform the development of effective interventions for this complex and important population.

Implementation and operational feasibility of SAMBA I HIV-1 semi-quantitative viral load testing at the point-of-care in rural settings in Malawi and Uganda.

We monitored a large-scale implementation of the Simple Amplification-Based Assay semi-quantitative viral load test for HIV-1 version I (SAMBA I Viral Load=SAMBA I VL) within Médecins Sans Frontières' HIV programmes in Malawi and Uganda, to assess its performance and operational feasibility. Descriptive analysis of routine programme data between August 2013 and December 2016. The dataset included samples collected for VL monitoring and tested using SAMBA I VL in five HIV clinics in Malawi (four peripheral health centres and one district hospital), and one HIV clinic in a regional referral hospital in Uganda. SAMBA I VL was used for VL testing in patients who had been receiving ART for between 6months and ten years, to determine whether plasma VL was above or below 1000 copies/mL of HIV-1, reflecting ART failure or efficacy. Randomly selected samples were quantified with commercial VL assays. SAMBA I instruments and test performance, site throughput, and delays in communicating results to clinicians and patients were monitored. Between August 2013 and December 2016 a total of 60889 patient samples were analysed with SAMBA I VL. Overall, 0.23% of initial SAMBA I VL results were invalid; this was reduced to 0.04% after repeating the test once. Global test failure, including instrument failure, was 1.34%. Concordance with reference quantitative testing of VL was 2620/2727, 96.0% (1338/1382, 96.8% in Malawi; 1282/1345, 95.3% in Uganda). For Chiradzulu peripheral health centres and Arua Hospital HIV clinic, where testing was performed on-site, same-day results were communicated to clinicians for between 91% and 97% of samples. Same-day clinical review was obtained for 84.7% across the whole set of samples tested. SAMBA I VL testing is feasible for monitoring cohorts of 1000 to 5000 ART-experienced patients. Same-day results can be used to inform rapid clinical decision-making at rural and remote health facilities, potentially reducing time available for development of resistance and conceivably helping to reduce morbidity and mortality.

SisLeish: A multi-country standardized information system to monitor the status of Leishmaniasis in the Americas.

BackgroundIn the Americas, leishmaniasis is endemic in 18 countries, and from 2001 through 2015, 17 countries reported 843,931 cases of cutaneous and mucocutaneous leishmaniasis, and 12 countries reported 52,176 cases of visceral leishmaniasis. A Regional Information System (SisLeish) was created in order to provide knowledge of the distribution and tendency of this disease to analyze and monitor the leishmaniasis status. This article analyses the performance and progress of SisLeish from 2012–2015.MethodologyThe performance of SisLeish was evaluated by country adhesion, data completeness and delay in entering the data, and also by the SWOT technique. Furthermore, we outlined the structure and modus operandi of the system and indicators utilized.ResultsIn 2012, only 18% of the countries entered the data in SisLeish before the deadline, where 66.7% and 50% of the countries with autochthonous CL/ML and VL reported their cases to the system, respectively. Whereas in 2015, 59% of the countries reached the deadline, where 94.4% and 58.3% of the countries reported their CL/ML and VL data, respectively. Regarding data completeness, there was great progress for different variables since its launch, such as gender, which had an approximately 100% improvement from 2012 to 2015. The SWOT analysis of SisLeish showed 12 strengths, 11 opportunities, seven weaknesses and six threats.ConclusionsFrom 2012–2015 there has been an improvement in the adhesion, quality and data completeness, showing the effort of the majority of the countries to enhance their national database. The SWOT analysis demonstrated that strengths and opportunities exceed weaknesses and threats; however, it highlighted the system frailties and challenges that need to be addressed. Furthermore, it has stimulated several National Programs to advance their surveillance system. Therefore, SisLeish has become an essential tool to prioritize areas, assist in decision-making processes, and to guide surveillance and control actions.

Low level HIV viremia is more frequent under protease‐inhibitor containing firstline therapy than under NNRTI‐regimens

IntroductionAn association of persistent low level viremia (LLV) below 500 copies/mL and a higher risk of therapy failure is still point of controversial discussion. Furthermore, it seems that LLV occurs more frequently in patients with protease-inhibitor regimens than in NNRTI- / or integrase-inhibitor containing therapies. The focus of this work was to assess the prevalence of LLV (50–200 copies/mL) and weak viremia (201–500 copies/mL) in firstline-treated patients according to their therapy regimen.MethodsA total of 832 and 944 patients from 23 German centres were under firstline therapy in 2012 and 2013, respectively. All patients received their therapy for more than 24 weeks. VL data was related to clinical data retrospectively including ART-composition, subdivided into NNRTIs (Efavirenz, Nevirapine), PIs (Atazanavir, Darunavir, Lopinavir) and INIs (Raltegravir). Low viremic patients were classified into two arms of 50–200 copies/mL (group A) and 201–500 copies/mL (group B).ResultsSuccess of therapy was defined as <50 copies/mL and was observed in 90.0% and 91.1% (2012/2013), respectively. An additional 2.0% and 2.3% had LLV. The amount of viremic patients with VLs <500 copies/mL differed significantly between NNRTI-based firstline regimens 1.7% and 2.5% and PI-based regimens 4.8% and 5.7% (2012/2013), respectively. LLV was clearly less often observed in EFV-based- (1.6% and 1.1% [group A] / 0.4% and 0.4% [group B]) or NVP-based firstline therapies (1.0% and 3.6% [group A] + 0% and 0% [group B]) than in ATV-based- (7.5% and 3.8% [group A] + 1.5% and 2.5% [group B]), DRV-based- (2.9% and 3.0% [group A] + 2.2% and 0% [group B]) or LPV-based firstline therapies (1.6% and 3.3% [group A] + 0.8% and 2.5% [group B]) and also in parts for RAL-based regimens (0% and 3.7% [group A] + 0% and 1.9% [group B]).ConclusionsLLV is more often observed under PI-based firstline than under NNRTI-regimens. Only one NNRTI-patient of group B remained on therapy. A possible explanation for this discrepancy might be the fact that physicians seem to tolerate LLV more often in PI-regimens than in NNRTI-regimens due to a higher genetic barrier against resistance and it remains a point of discussion if constant LLV does affect immune recovery and risk of therapy failure.

Week 48 results of a Phase IV trial of etravirine with antiretrovirals other than darunavir/ritonavir in HIV-1-infected treatment-experienced adults.

IntroductionIn DUET, etravirine (ETR) 200 mg bid had durable efficacy and a favourable safety profile versus placebo, both arms with an optimised background regimen (BR) including darunavir/ritonavir (DRV/r). TMC125IFD3002 (VIOLIN; NCT01422330) investigated ETR plus ARVs other than DRV/r.Materials and MethodsThis was a 48 week, Phase IV, open-label, single-arm, multicentre study. HIV-1-infected treatment-experienced adult patients on=8 weeks ARV therapy prior to screening, switching either for virologic failure (VF) (viral load [VL] =500 c/mL) or regimen simplification/AEs (RS/AE) (VL<50 c/mL), received active ETR 200 mg bid with an investigator-selected BR of =1 active ARVs, but excluding DRV/r or NRTIs only. The primary objective was to evaluate safety, tolerability and pharmacokinetics (PK).ResultsOf 211 treated patients, 55% were female, 61% black/African American. 155 patients (73%) had baseline (BL) VL=50 c/mL versus 56 (27%) with BL VL<50 c/mL. Between these two latter subgroups, median BL VL was 4.42 versus 1.28 log10 c/mL and CD4+ count 238 versus 410.5 cells/mm3. Overall, 96% previously used <2 NNRTIs and 99% used=5 PIs; median number of BL NNRTI RAMs was 2, PI RAMs 5 and NRTI RAMs 1. Overall, most common BR ARVs were PIs (83%), mostly lopinavir/r (62%) and mostly used alone (20%) or with 1 or 2 NRTIs (61%). Raltegravir was used in 9% of patients. Most frequent AEs (any cause/grade) were diarrhoea (17%) and URTI (8%). Incidence of grade 3–4 AEs was 13%, serious AEs 5% (no rashes; none ETR related), AEs leading to discontinuation 4%, AEs possibly related to ETR 23% and AEs of interest: rash (any type) 4%, hepatic 6% and neuropsychiatric 3%. At week 48, VF and RS/AE virologic responses (% patients with VL<50 c/mL; FDA Snapshot) were: 48% (74/155) and 75% (42/56), respectively. VF rates were 42% and 13%; 10% and 13% had no VL data in the week 48 window. The percentage of patients adherent to treatment (assessed based on PK sampling plus ETR pill count) was 47% (69/148) and 57% (30/53), in VF and RS/AE, respectively. Median CD4+ count (NC=F) increases were 0.0 and 24.0 cells/mm3. In 29/49 of VFs with genotypic data at failure, ETR RAMs emerging in =5 patients were Y181C, E138A and M230L. The geometric mean ETR AUC12h was 4877 ng.h/mL and C0h 293 ng/mL (N=199).ConclusionsResults of this study were consistent with those for ETR in other similar populations and support the use of ETR 200 mg bid with a non-DRV/r based BR.

7.0 Obstetric management

7.0 Obstetric management

Long‐Term Variations in Human T Lymphotropic Virus (HTLV)–I and HTLV‐II Proviral Loads and Association with Clinical Data

The human T lymphotropic virus (HTLV)-I or -II proviral load (VL) may be linked to viral pathogenesis, but prospective data on VL and disease outcomes are lacking. Using data from a prospective cohort study of HTLV disease outcomes, we examined baseline VLs with real-time quantitative polymerase chain reaction in 122 HTLV-I- and 319 HTLV-II-infected subjects and serial VLs over the course of 6 visits in a subset of 30 HTLV-I- and 30 HTLV-II-infected subjects. Cox and logistic-regression models were used to test baseline associations, and repeated-measures analysis was used to study variations in VL over time. Over the course of a median of 10.4 years, HTLV-I VLs decreased slightly (slope, -0.017 log(10) copies/10(6) peripheral blood mononuclear cells [PBMCs]/year; P=.042) and HTLV-II VLs did not change (slope, -0.019 log(10) copies/10(6) PBMCs/year; P=.165). Changes in VL over time were associated positively with alcohol use (P=.07) and negatively with black race (P=.03) for HTLV-I and positively with smoking (P=.08) for HTLV-II. In the larger group, there was no association between baseline VL and disease outcomes. In the smaller group with serial VL data, there was an association between increasing VL and bladder or kidney infections for both HTLV-I (P=.005) and HTLV-II (P=.022). HTLV VLs are stable over time, but alcohol and tobacco intake may affect the progression of VLs. The association between increasing VLs and bladder/kidney infection may be explained by early HTLV-related neuropathologic progression.

Extending fuzzy and probabilistic clustering to very large data sets

Approximating clusters in very large (VL=unloadable) data sets has been considered from many angles. The proposed approach has three basic steps: (i) progressive sampling of the VL data, terminated when a sample passes a statistical goodness of fit test; (ii) clustering the sample with a literal (or exact) algorithm; and (iii) non-iterative extension of the literal clusters to the remainder of the data set. Extension accelerates clustering on all (loadable) data sets. More importantly, extension provides feasibility—a way to find (approximate) clusters—for data sets that are too large to be loaded into the primary memory of a single computer. A good generalized sampling and extension scheme should be effective for acceleration and feasibility using any extensible clustering algorithm. A general method for progressive sampling in VL sets of feature vectors is developed, and examples are given that show how to extend the literal fuzzy ( c -means) and probabilistic (expectation-maximization) clustering algorithms onto VL data. The fuzzy extension is called the generalized extensible fast fuzzy c -means (geFFCM) algorithm and is illustrated using several experiments with mixtures of five-dimensional normal distributions.

Approximate clustering in very large relational data

Different extensions of fuzzy c-means (FCM) clustering have been developed to approximate FCM clustering in very large (unloadable) image (eFFCM) and object vector (geFFCM) data. Both extensions share three phases: (1) progressive sampling of the VL data, terminated when a sample passes a statistical goodness of fit test; (2) clustering with (literal or exact) FCM; and (3) noniterative extension of the literal clusters to the remainder of the data set. This article presents a comparable method for the remaining case of interest, namely, clustering in VL relational data. We will propose and discuss each of the four phases of eNERF and our algorithm for this last case: (1) finding distinguished features that monitor progressive sampling, (2) progressively sampling a square N × N relation matrix RN until an n × n sample relation Rn passes a statistical test, (3) clustering Rn with literal non-Euclidean relational fuzzy c-means, and (4) extending the clusters in Rn to the remainder of the relational data. The extension phase in this third case is not as straightforward as it was in the image and object data cases, but our numerical examples suggest that eNERF has the same approximation qualities that eFFCM and geFFCM do. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 817–841, 2006.

Viral load as an independent risk factor for opportunistic infections in HIV-infected adults and adolescents.

We investigated whether HIV plasma RNA (viral load; VL) predicts risk for opportunistic infections (OI) in HIV-infected persons, independent of CD4 lymphocyte count and other factors that might affect disease outcome. Among persons who had initiated antiretroviral therapy (ART), we studied the risk for OI following a VL measurement in the Centers for Disease Control and Prevention Adult and Adolescent Spectrum of HIV Disease (ASD) Project, a medical record review study of HIV-infected persons in 11 US cities. Analysis was limited to persons who had initiated ART and who had VL data, primarily from the period 1996-1999. Persons were considered at risk for OI for 1 to 6 months after a given VL; risk for OI was assessed using a Poisson multiple regression model controlling for CD4 lymphocyte count, ART, and other variables potentially associated with development of OI: history of AIDS OI, age, sex, race, HIV risk category, OI prophylaxis, and calendar year. Although decreasing CD4 count was the strongest predictor of risk for OI [relative risk (RR), 13.3 for persons with CD4 lymphocyte count < 50 x 10(6)/l compared with persons with CD4 lymphocyte count > or = 500 x 10(6)/l], increasing VL was independently associated with increased risk [RR, 1.6, 1.9, 2.7, and 3.5 for VL of 7000-19 999, 20 000-54 999, 55 000-149 999, and > or = 150 000 copies/ml (by reverse transcription-PCR), respectively, compared with VL < 400]. Similar results were obtained when the risk period was reduced to 5, 4, 3, and 2 months after VL measurement. VL is an independent risk factor for OI and should be considered in special situations, such as in decisions to discontinue primary or secondary OI prophylaxis after CD4 lymphocyte counts have increased in response to ART.

Magnetic fields in the distant heliosphere approaching solar minimum: Voyager 1 and 2 observations during 1994

During 1994, Voyager 2 (V2) was at a heliocentric distance 〈R〉 = 43.4 AU and latitude 〈δs/c〉 = 11.9°S, while Voyager 1 (Vl) was at 〈R〉 = 56.3 AU and 〈δs/c〉 = 32.5°N. The mean magnetic field strength observed by Vl during 1994 was 0.05 nT, the weakest and most distant magnetic field ever measured in situ. A bimodal distribution of azimuthal magnetic field directions was observed by V2, and a single‐peaked distribution was observed by Vl. Thus V2 was in the “sector zone” (the range of latitudes that contains the heliospheric current sheet), and Vl was in the unipolar region above it, consistent with the latitudes of the heliospheric current sheet obtained from an extrapolation of the neutral line computed from solar magnetic field observations. A lognormal distribution of the magnetic field strength (hourly averages) was observed for 95% of the Vl data and most of the V2 data. An approximately lognormal distribution of B is a general property of the heliospheric magnetic field, observed out to 58.1 AU and up to 32.6°S latitude. During 1994 an exponential tail in the distribution of the magnetic field strength was observed by both Vl and V2 for fields stronger than average. An exponential tail in the magnetic field strength distribution was observed by Vl and V2 from 1983 to 1994 at latitudes from 11°S to 33°N and at distances from 13 to 58 AU. Thus an exponential tail of the distribution of magnetic field strengths is a basic property pf the heliosphere beyond 13 AU. There was no significant latitudinal gradient in the exponential tail observed by V2 in the sector zone and observed by Vl above the sector zone during 1994. Multifractal structure in the large‐scale fluctuations of the magnetic field strength was observed by Vl for periods from 8 hours to 256 hours equaling 10.7 days for the magnetic fields stronger than average. A multiffactal spectrum is a general property of the large‐scale magnetic field strength fluctuations, from 1983 through 1994 between 13 AU and 58 AU. There remains a need for a statistical theory of the solar wind that can account for these observations and for cosmic ray models that include the effect of multifractal magnetic field strength fluctuations.

Prediction of VL and VLL equilibria of mixtures containing petroleum reservoir fluids and methanol with a cubic EoS

Abstract Avlonitis, D., Danesh, A. and Todd, A.C., 1994. Prediction of VL and VLL equilibria of mixtures containing petroleum reservoir fluids and methanol with cubic EoS. Fluid Phase Equilibria, 94: 181-216. A cubic equation of state, with simple non-density-dependent mixing rules, is used to represent the phase behaviour of multicomponent mixtures containing hydrocarbons up to n -octane, nitrogen, carbon dioxide, hydrogen sulphide, water and methanol. The reliability of the model is tested against diverse experimental VL and VLL equilibrium data of multicomponent systems. The proposed correlation can be applied for efficient design and operation of transfer lines and processing units. The practical value of the theoretically correct concept of density dependence is tested on a density-dependent version of the above mixing rules. It is demonstrated that while both mixing rules produce very similar results when only one polar component is present, the density-dependent mixing rules may be inferior for mixtures containing both water and methanol, owing to an inherent deficiency. It is also demonstrated that an invariant version of the proposed non-density-dependent mixing rule may not lead to indisputably improved predictions for the studied systems.

Balloon observations of X rays in the auroral zone II

Data from a long-duration balloon flight at 35-km height over the auroral zone during August 1959 showed that only very small fluxes of energetic x rays accompany visible auroras at this latitude. The maximum observed photon flux above 25 kev during a bright aurora was 2.5 cm/sup -2/ sec/sup -1/. Much larger fluxes, up to 40 cm/sup -2/ sec/sup -1/, preceded two active visible displays by about 30 min. On August 17 and 18 x-ray influxes were observed for several hours during the daytime. From Explorer Vl data these are believed to be associated with the filling-up of the outer radiation belt after a geomagnetic storm. The scintillation counter employed permitted a determination of the x-ray energy spectrum at 6 g-cm/sup 2/ depth from 25 to 300 kev on this and several other flights. From an analysis the parent electron spectrum is derived and found to be extremely steep. Typically, the ratio of the differertial photon intensity at 30 kev to that at 160 kev is 350 to 1. Other balloon flights during August 1959 show that a large loss of electrons having energy >25 kev is occurring even on magnetically rather quiet days.