High throughput exploration of the oxidation landscape in high entropy alloys.

High entropy alloys (HEAs) have gained interest for structural applications in extreme environments. With a potentially vast chemical and phase space, there are significant opportunities to discover superior performing alloys. Crucial for most high-temperature applications is understanding and mitigating the oxidation behavior of these chemically complex alloys. Most experimental and computational HEA studies have focused on a limited set of compositions and only a fraction of these compositions have been characterized for oxidation. We present a high-throughput framework that utilizes density-functional theory (DFT) in concert with a combined machine-learning model and grand-canonical linear programming for assessing phase stability, phase-fraction, chemical activity and high-temperature survivability of arbitrary HEAs. This framework considers temperature dependent contributions to the Gibbs energy of the competing phases arising from short-range order and vibrational entropy. We demonstrate the effectiveness of the framework by assessing the thermodynamic stability, oxidation behavior, chemical activity, and phase decomposition of body-centered cubic Mo-W-Ta-Ti-Zr refractory HEAs. A total of 51 compositions were analyzed and ranked in order of their survivability based on the Pareto-front analysis. Oxidation was performed at 1373 K on four samples in air showing the difference in oxidation behavior determined experimentally through scale thickness and their mass changes. The insights on oxidation behavior presented in this work will enable the fast assessment of technologically useful HEAs needed for future structural application in extreme conditions.

Martensitic Transformation in Fe_{x}Mn_{80-x}Co_{10}Cr_{10} High-Entropy Alloy.

High-entropy alloys and even medium-entropy alloys are an intriguing class of materials in that structure and property relations can be controlled via alloying and chemical disorder over wide ranges in the composition space. Employing density-functional theory combined with the coherent-potential approximation to average over all chemical configurations, we tune free energies between face-centered-cubic and hexagonal-close-packed phases in Fe_{x}Mn_{80-x}Co_{10}Cr_{10} systems. Within Fe-Mn-based alloys, we show that the martensitic transformation and chemical short-range order directly correlate with the face-centered-cubic and hexagonal-close-packed energy difference and stacking-fault energies, which are in quantitative agreement with recent observation of two phase region (face-centered cubic and hexagonal closed pack) in a polycrystalline high-entropy alloy sample at x=40 at.%. Our predictions are further confirmed by single-crystal measurements on a x=40 at.% using transmission-electron microscopy, selective-area diffraction, and electron-backscattered-diffraction mapping. The results herein offer an understanding of transformation-induced or twinning-induced plasticity in this class of high-entropy alloys and a design guide for controlling the physics at the electronic level.

Glassy Phonon Heralds a Strain Glass State in a Shape Memory Alloy.

Shape memory strain glasses are frustrated ferroelastic materials with glasslike slow relaxation and nanodomains. It is possible to change a NiCoMnIn Heusler alloy from a martensitically transforming alloy to a nontransforming strain glass by annealing, but minimal differences are evident in the short- or long-range order above the transition temperature-although there is a structural relaxation and a 0.18% lattice expansion in the annealed sample. Using neutron scattering we find glasslike phonon damping in the strain glass but not the transforming alloy at temperatures well above the transition. Damping occurs in the mode with displacements matching the martensitic transformation. With support from first-principles calculations, we argue that the strain glass originates not with transformation strain pinning but with a disruption of the underlying electronic instability when disorder resonance states cross the Fermi level.

Enhancement of the selectivity of MXenes (M2C, M = Ti, V, Nb, Mo) via oxygen-functionalization: promising materials for gas-sensing and -separation.

Two-dimensional graphene-like materials, namely MXenes, have been proposed as potential materials for various applications. In this work, the reactivity and selectivity of four MXenes (i.e. M2C (M = Ti, V, Nb, Mo)) and their oxygen-functionalized forms (i.e. O-MXenes or M2CO2) toward gas molecules were investigated by using the plane wave-based Density Functional Theory (DFT) calculations. Small gas molecules, which are commonly found in flue gas streams, are considered herein. Our results demonstrated that MXenes are very reactive. Chemisorption is a predominant process for gas adsorption on MXenes. Simultaneously dissociative adsorption can be observed in most cases. The high reactivity of their non-functionalized surface is attractive for catalytic applications. In contrast, their reactivity is reduced, but the selectivity is improved upon oxygen functionalization. Mo2CO2 and V2CO2 present good selectivity toward NO molecules, while Nb2CO2 and Ti2CO2 show good selectivity toward NH3. The electronic charge properties explain the nature of the substrates and also interactions between them and the adsorbed gases. Our results indicated that O-MXenes are potential materials for gas-separation/capture, -storage, -sensing, etc. Furthermore, their structural stability and SO2-tolerant nature are attractive properties for using them in a wide range of applications. Our finding provides good information to narrow down the choices of materials to be tested in future experimental work.

A Sensory Material Approach for Reducing Variability in Additively Manufactured Metal Parts.

Despite the recent growth in interest for metal additive manufacturing (AM) in the biomedical and aerospace industries, variability in the performance, composition, and microstructure of AM parts remains a major impediment to its widespread adoption. The underlying physical mechanisms, which cause variability, as well as the scale and nature of variability are not well understood, and current methods are ineffective at capturing these details. Here, a Nickel-Titanium alloy is used as a sensory material in order to quantitatively, and rather rapidly, observe compositional and/or microstructural variability in selective laser melting manufactured parts; thereby providing a means to evaluate the role of process parameters on the variability. We perform detailed microstructural investigations using transmission electron microscopy at various locations to reveal the origins of microstructural variability in this sensory material. This approach helped reveal how reducing the distance between adjacent laser scans below a critical value greatly reduces both the in-sample and sample-to-sample variability. Microstructural investigations revealed that when the laser scan distance is wide, there is an inhomogeneity in subgrain size, precipitate distribution, and dislocation density in the microstructure, responsible for the observed variability. These results provide an important first step towards understanding the nature of variability in additively manufactured parts.

A first-principles approach to transition states of diffusion.

We propose a first-principles approach for treating the unstable vibrational mode of transition states in solid-state diffusion. It allows one to determine a number of fundamental quantities associated with the transition state, in particular the enthalpy and entropy of migration and the characteristic vibrational frequency, along with their temperature dependences. Application to pure face centered cubic Al shows good agreement with available experimental measurements and previous theoretical calculations. The procedure is further applied in calculations of the migration properties of Mg, Si and Cu impurities in Al, and the differences among Mg, Si and Cu are discussed.

First-principles calculation of self-diffusion coefficients.

We demonstrate a first-principles method to compute all factors entering the vacancy-mediated self-diffusion coefficient. Using density functional theory calculations of fcc Al as an illustrative case, we determine the energetic and entropic contributions to vacancy formation and atomic migration. These results yield a quantitative description of the migration energy and vibrational prefactor via transition state theory. The calculated diffusion parameters and coefficients show remarkably good agreement with experiments. We provide a simple physical picture for the positive entropic contributions.

Circannual variation in the incidence of uterine cervix cancer.

The impact of uterine cervix cancer (UCC) can be greatly reduced by regular vaginal examination and other preventive measures. With this aim, UCC screening programs had been developed and applied for several years in Mexico and elsewhere. One point still to be considered in such preventive programs is the possible circannual pattern in the morbidity or mortality of UCC. With the aim of identifying a possible circannual pattern of variation in the incidence of UCC, we analyzed the monthly totals of positive detected cases of UCC in the state of Nuevo León (Mexico) between 1978 and 1987. For eliminating bias due to the seasonal variation in the number of preventive check-ups, data were first expressed in percentage of tests done in the same month. The least-squares fit of a 1-year cosine curve to the data reveals a statistically significant circannual pattern (p = 0.013), with a maximum of relative incidence detected in February. Results indicate UCC incidence higher than the yearly average during the winter, with secondary peaks in August and November. This pattern of variation is similar if one considers separately for analysis the relative incidence of type III, IV, or V UCC (relating to cases suggesting, highly suggesting, or concluding a malignant alteration, respectively). For evaluating the cost-effectiveness of the UCC screening campaign providing these data, the monthly totals of screening check-ups done over the same period were also analyzed. Results reveal a statistically significant circannual rhythm (p < 0.001), with a maximum detected in June.(ABSTRACT TRUNCATED AT 250 WORDS)

[Comparison of immunofluorescence, enzyme immunoassay and cell culture for the diagnosis of Chlamydia trachomatis in urogenital infections]. / Comparación de la inmunofluorescencia, ensayo inmunoenzimático y cultivo celular para el diagnóstico de Chlamydia trachomatis en infecciones urogenitales.

We evaluated the usefulness of the direct immunofluorescence test with monoclonal antibodies and the enzyme immunoassay in comparison with isolation in cell cultures for the diagnosis of Chlamydia trachomatis in 55 endocervical specimens from female prostitutes and 21 urethral specimens from men with diagnosis of nongonococcal urethritis. In comparison with culture, the enzyme immunoassay had a sensitivity of 100% and a specificity of 95%. The immunofluorescence test had a sensitivity of 92% and a specificity of 98%. The positive and negative predictive values for the enzyme immunoassay were 81% and 100% and for immunofluorescence 92% and 98% respectively. The immunologic methods appear to be satisfactory alternatives to culture for detecting C trachomatis in genital specimens in the studied populations.

Differences in circannual characteristics of the incidences of amebiasis and giardiasis.

Entamoeba histolytica is the most common pathogenic intestinal parasite in México. Prevalence rates of AM vary widely from place to place, being higher in areas with poor sanitation, households and institutions, and among male homosexuals. Early recognition and treatment may be necessary to prevent its spread in the community. Intervention by preventive health education is indicated. The timing of such educational endeavours may be adjusted to any rhythmic and to that extent predictable changes in the incidence of AM and of any other possibly related gastrointestinal parasitic disease, such as GD. Accordingly, monthly totals of cases of AM and GD detected in Monterrey, (México) between November, 1985, and October, 1987, were fitted by linear least-squares with a 1-year cosine curve. The no-circannual rhythm assumption in the incidence of AM and GD was rejected in both cases (P = .006 and .049, respectively). A comparison of circannual parameters shows differences in M, A and phi between the incidences of AM and GD, the Ps for those comparisons being less than .001, .014 and .041, respectively. A high incidence of GD (above the yearly mean) consistently observed in April could be, however, related to the circannual pattern of AM, showing higher incidences in the spring. The timing of any preventive intervention should take into consideration the circannual variability in the incidence of AM and the differences or correlations with the circannual patterns of other gastrointestinal parasitic diseases.

Circannual incidence of Giardia lamblia in Mexico.

Giardia lamblia, once considered a harmless commensal organism, has become one of the most common pathogenic intestinal parasites. Evidence for various methods of transmission has accumulated and serious physiological and nutritional disturbances as a result of infestation with this parasite have been clinically documented. Giardia lamblia has now been identified as a causative agent of waterborne, foodborne and sexually transmitted infectious diarrhea. Preventive interventions by health education (especially in personal hygiene) are indicated to reduce its spread in the community. The timing of such educational endeavours may be adjusted to the changes in the incidence of giardiasis if such should be predictable insofar as they are rhythmic. Accordingly, monthly totals of positive detected cases of giardiasis reported in Mexico between 1977 and 1985 were first fitted by linear least-squares with a 1-yr cosine curve. Results indicate a predictable circannual variability of Giardia incidence (P less than 0.001), with a crest time situated on the third week of July and monthly means of detected cases above the yearly average incidence between May and September. The validity of this circannual rhythm was further checked by nonlinear least-squares. Results show a presumably 1-yr synchronized estimated period of 8715.1 hr, with a total predictable change (double amplitude of 1788 cases per month) of 43% the average monthly incidence. Moreover, circannual rhythm parameters computed separately for each consecutive year are similar in terms of acrophase (P = 0.771). Awareness of the thus detected circannual predictable variability in the incidence of giardiasis may be important in the prevention, diagnosis and treatment of this infectious disorder. According to the results here found, the timing of prevention interventions by health education should be a readily exploitable factor.

[Markers of HIV infection in prostitutes: analysis of preventive and risk factors]. / Marcadores de infeccion por VIH en prostitutas: analisis de factores preventivos y de riesgo.

We studied 501 prostitutes from the northern and eastern areas of Santiago in november and december, 1987. HIV infection was studied by the HIV antibody and also by HIV antigen. At that time no positive reactors were found. Prostitutes from the northern area were older, of a lower socioeconomic background and less promiscuous, in comparison to prostitutes of the eastern area. However, other disorders of sexual transmission were found in 41% of prostitutes of the northern area and in only 28% of those from the eastern area. This difference may be attributed to the more frequent use of preservative in the latter group.

Evaluación de dos medios de transporte en la recuperación de Neisseria Gonorrhoeae / Evaluation of 2 transportation ways in the neisseria gonorrhoeae recuperation

Se evalúa la recuperación en el tiempo de Neisseria gonorrhoeae en agar Stuart y medio de transporte 2 sacarosa fosfato (2SP), tomando muestra de flujo uretral de 51 pacientes con diagnóstico clínico de gonorrea. Las muestras fueron inoculadas de inmediato en agar Thayer-Martin y en los medios de transporte Stuart y 2SP. Los medios de transporte fueron conservados a 4-C siendo subcultivados a las 2, 6 y 24 hrs. en Thayer-Martin. Paralelamente se inocularon in vitro 4 cepas de gonococo en agar Stuart y 2SP. Una serie de medios fue conservada a 4-C y la otra a temperatura ambiente para ser subcultivadas ambas a las 2, 6 y 24 hrs. en agar Thayer-Martin. De las 51 muestras estudiadas, en el 86,3% se confirmó el diagnóstico de gonorrea (44 muestras). El agar Stuart permitió la recuperación del gonococo en el 100% de las muestras positivas a las 2 y 6 horas y en el 90,9% a las 24 horas de conservación. En el medio de transporte 2SP, la infectividad se mantuvo en el 100% de las muestras a las 2 horas, en el 95,4% a las 6 horas y en el 70,4% a las 24 horas de conservación. Las 4 cepas inoculadas in vitro fueron recuperadas de ambos medios de transporte a 4-C y a temperatura ambiente a las 2 y 6 horas de conservación. A las 24 horas solamente se recuperan 3 cepas a 4-C y 1 a temperatura ambiente

[Seroprevalence of AIDS in Chilean male and female prostitutes. II. Male prostitution]. / Seroprevalencia de SIDA en prostitutas masculinas y femeninas chilenas.1. Prostitución masculina.

ELISA test to detect HIV-1 antibodies was performed to 65 homosexuals and homosexual male prostitutes in a Sexually Transmitted Diseases (STD) Clinic in Santiago de Chile together with a survey about risk factors. It was found that 40 of them (62%) practice prostitution with a rate of 1.5% clients per day. All the studied group presented dissemination of HIV risk factors like low frequency usage of condom, patients hide their homosexual condition, they have donated blood, they do not manifest an attitude towards changing their behaviors and have had intercourse with the opposite sex. We found 1 (1.54%) seropositive confirmed by Western blot in a homosexual who does not practice prostitution.

Seroprevalencia de SIDA en prostitutas masculinas y femeninas chilenas / Seroprevalence of AIDS in Chilean male and female prostitutes. I male prostitution

Se realiza un screening para detectar anticuerpos para VIH-1, a través de la reacción de ELISA a 65 homosexuales y prostitutas homosexuales masculinos en control en un consultorio de enfermedades de transmisión sexual (ETS) en Santiago de Chile, junto a una encuesta sobre factores de riesgo. Encontramos que 40 (62%) practicaban la prostitución con un promedio de 1,5 clientes diarios. Todo el grupo estudiado presentaba factores de riesgo de diseminación del VIH, como ser: baja frecuencia en el uso del condón, ocultan su condición de homosexualidad y/o prostitución, han donado sangre, no manifiestan una actitud de cambio de conducta y mantienen relaciones sexuales con el sexo opuesto. Encontramos sólo uno (1,54%) seropositivo, confirmado por Western blot en un homesexual que no ejercía la prostitución

Estudio de algunos aspectos de la prostitución femenina chilena / II. Some aspects of female prostitution in Chile

Se realiza una encuesta en 100 prostitutas heterosexuales femeninas en un Consultorio de Enfermedades de Transmisión Sexual (ETS) de Santiago con el fin de conocer algunos aspectos epidemiológicos, socios culturales y conocimientos sobre ETS y SIDA en ellas. Comprobamos que la mayoría son solteras, con hijos, de baja escolaridad, un 20% de ellas ejerce en muy diversas comunas de Santiago y un tercio de ellas ha padecido de alguna enfermedad de transmisión sexual. No poseen conocimientos adecuados sobre los mecanismos de transmisión de las ETS, creyendo incluso que se previenen practicando el sexo oral y anal y lógicamente no conocen adecuadamente las medidas preventivas y de higiene. Es un grupo donde las medidas educativas son fáciles de realizar, ya han demostrado su utilidad en Chile y se deberían realizar de rutina, con el objeto de mejorar su calidad de vida y evitar el riesgo de 5-10% de propagación de las ETS que este grupo representa

Identification of penicillinase producing Neisseria gonorrhoeae in Chile during clinical and microbiological study of gonococcal susceptibility to antimicrobial agents.

The first penicillinase producing isolates of Neisseria gonorrhoeae (PPNG) identified in Chile were discovered during a clinical and microbiological study to compare the efficacy of penicillin (4.8 MIU aqueous procaine penicillin G plus 1 g oral probenecid) and tetracycline (1.5 g followed by 500 mg four times daily for four days) treatment regimens for acute uncomplicated gonorrhoea. Penicillin treatment was effective in 93.1% (282) of 303 patients, whereas tetracycline was effective in 98.3% (233) of 237 patients. Six of the penicillin treatment failures were attributable to PPNG strains. In all, 21 PPNG strains were identified during the study. They were genetically identical, having a wild type auxotype, a WII/III serotype (serovar Bajk), and carrying cryptic and transfer plasmids and an Asian type penicillinase producing plasmid. In addition, 674 non-PPNG isolates were tested for their susceptibility to eight antimicrobials. Over 95% were sensitivie to 1 mg/l of penicillin, ampicillin, cefotaxime, cefuroxime, and erythromycin, over 90% were sensitive to 1 mg/l of tetracycline and 2 mg/l of thiamphenicol, and all were sensitive to spectinomycin. Of 226 non-PPNG isolates characterised for plasmid content and auxotype, 90% (205) were either wild type or proline requiring, 67% (153) carried only the cryptic plasmid, and a further 31% (71) carried both cryptic and transfer plasmids. Unusually, three of four isolates lacking the cryptic plasmid carried only the transfer plasmid.