Atomic-Scale Mechanisms of MoS2 Oxidation for Kinetic Control of MoS2/MoO3 Interfaces

Oxidation of transition metal dichalcogenides (TMDs) occurs readily under a variety of conditions. Therefore, understanding the oxidation processes is necessary for successful TMD handling and device fabrication. Here, we investigate atomic-scale oxidation mechanisms of the most widely studied TMD, MoS₂. We find that thermal oxidation results in α-phase crystalline MoO₃ with sharp interfaces, voids, and crystallographic alignment with the underlying MoS₂. Experiments with remote substrates prove that thermal oxidation proceeds via vapor-phase mass transport and redeposition, a challenge to forming thin, conformal films. Oxygen plasma accelerates the kinetics of oxidation relative to the kinetics of mass transport, forming smooth and conformal oxides. The resulting amorphous MoO₃ can be grown with subnanometer to several-nanometer thickness, and we calibrate the oxidation rate for different instruments and process parameters. Our results provide quantitative guidance for managing both the atomic scale structure and thin-film morphology of oxides in the design and processing of TMD devices.

Giant and Controllable Photoplasticity and Photoelasticity in Compound Semiconductors

We show that the wide-band gap compound semiconductors ZnO, ZnS, and CdS feature large photoplastic and photoelastic effects that are mediated by point defects. We measure the mechanical properties of ceramics and single crystals using nanoindentation, and we find that elasticity and plasticity vary strongly with moderate illumination. For instance, the elastic stiffness of ZnO can increase by greater than 40% due to blue illumination of intensity 1.4  mW/cm^{2}. Above-band-gap illumination (e.g., uv light) has the strongest effect, and the relative effect of subband gap illumination varies between samples-a clear sign of defect-mediated processes. We show giant optomechanical effects can be tuned by materials processing, and that processing dependence can be understood within a framework of point defect equilibrium. The photoplastic effect can be understood by a long-established theory of charged dislocation motion. The photoelastic effect requires a new theoretical framework which we present using density functional theory to study the effect of point defect ionization on local lattice structure and elastic tensors. Our results update the longstanding but lesser-studied field of semiconductor optomechanics, and suggest interesting applications.

Time-resolved photoluminescence studies of perovskite chalcogenides

Chalcogenides in the perovskite and related crystal structures ("chalcogenide perovskites" for brevity) may be useful for future optoelectronic and energy-conversion technologies inasmuch as they have good excited-state, ambipolar transport properties. In recent years, several studies have suggested that semiconductors in the Ba-Zr-S system have slow non-radiative recombination rates. Here, we present a time-resolved photoluminescence (TRPL) study of excited-state carrier mobility and recombination rates in the perovskite-structured material BaZrS₃, and the related Ruddlesden-Popper phase Ba₃Zr₂S₇. We measure state-of-the-art single crystal samples, to identify properties free from the influence of secondary phases and random grain boundaries. We model and fit the data using a semiconductor physics simulation, to enable more direct determination of key material parameters than is possible with empirical data modeling. We find that both materials have Shockley-Read-Hall recombination lifetimes on the order of 50 ns and excited-state diffusion lengths on the order of 5 μm at room temperature, which bodes well for ambipolar device performance in optoelectronic technologies including thin-film solar cells.

Interval gastric cancer: A call to attentiveness and action

INTRODUCTION AND AIMS

Endoscopy is the most effective method for identifying gastric adenocarcinoma (GAC). Interval gastric cancer (IGC) is GAC that is diagnosed 2-3 years after a normal endoscopy. Its characteristics are unknown in the Colombian environment. The clinical, histopathologic, and endoscopic characteristics were evaluated, along with the presentation rate, proton pump inhibitor (PPI) use, and IGC survival rate, and compared with other types of GAC.

METHODS

A retrospective, analytic study was conducted on a prospective cohort. It evaluated 513 patients with GAC treated at our institution, within the time frame of January 2012 and June 2018. The patients had endoscopic diagnosis of GAC and endoscopy within the past three years that was negative for tumor.

RESULTS

A total of 513 patients diagnosed with GAC were evaluated. Forty-two of the patients had IGC (8.2%): 9 early lesions and 33 advanced lesions (79%). The IGCs were smaller (31 vs. 41 mm; P < .01), as well as flatter and more depressed (P < .01). There was no association with PPI use, but there was an association with a history of gastrectomy and anastomosis (P = .02), as well as the absence of red flags (P < .003). The most frequent locations were the gastric body (52%) and the antrum (26%). Overall two-year survival was similar between IGC and GAC (37.1 vs. 39.3%, P = .72).

CONCLUSION

A total of 8.2% of recently diagnosed GAC were cases of IGC. The presence of anastomosis and the absence of red flags were related to IGC. Overall survival was poor and there were no differences from the other types of GAC detected.

Impact of intraoperative colonoscopy on anastomotic leakage detection and prevention in colorectal anastomosis for rectal cancer

INTRODUCTION AND AIM

The value of leakage testing during colorectal resections to identify anastomotic leaks or bleeding has not been established. Our aim was to compare the impact of intraoperative colonoscopy (IOC) versus insufflation with a syringe, as leakage testing in lower anterior resection (LAR) for rectal cancer, with respect to the incidence of postoperative leakage (PL).

MATERIALS AND METHODS

A retrospective study utilizing a prospective database of 426 patients with rectal cancer that underwent elective LAR, within the time frame of January 2015 and December 2019, was conducted. The anastomotic leak test was chosen by the surgeon. The incidence of postoperative leakage was compared between patients that underwent IOC and those that had the syringe leak test, utilizing the logistic regression analysis. Propensity score matching was included.

RESULTS

There were no significant differences in the clinical characteristics or morbidity and mortality rates between the two groups. Four patients were excluded, leaving a patient total of 422. Seventy patients with IOC were compared with 352 that had the syringe leak test. The incidence of postoperative leakage was 5.7% in the IOC group and 12.2% in the control group (p = 0.001). After propensity score matching (n = 221), balancing the characteristics between the groups, the incidence of postoperative leakage was 5.7% in the IOC group and 13.9% in the syringe leak test group (p = 0.001).

CONCLUSION

IOC was shown to be a safe method for evaluating the integrity of colorectal anastomosis and was associated with a higher percentage of protective stoma use, appearing to reduce the risk for PL.

Growth Kinetics and Atomistic Mechanisms of Native Oxidation of ZrSxSe2-x and MoS2 Crystals

A thorough understanding of native oxides is essential for designing semiconductor devices. Here, we report a study of the rate and mechanisms of spontaneous oxidation of bulk single crystals of ZrS_xSe_2-x alloys and MoS₂. ZrS_xSe_2-x alloys oxidize rapidly, and the oxidation rate increases with Se content. Oxidation of basal surfaces is initiated by favorable O₂ adsorption and proceeds by a mechanism of Zr-O bond switching, that collapses the van der Waals gaps, and is facilitated by progressive redox transitions of the chalcogen. The rate-limiting process is the formation and out-diffusion of SO₂. In contrast, MoS₂ basal surfaces are stable due to unfavorable oxygen adsorption. Our results provide insight and quantitative guidance for designing and processing semiconductor devices based on ZrS_xSe_2-x and MoS₂ and identify the atomistic-scale mechanisms of bonding and phase transformations in layered materials with competing anions.

Near-infrared photonic phase-change properties of transition metal ditellurides

We use the (Mo,W)Te₂ system to explore the potential of transition metal dichalcogenides (TMDs) as phase-change materials for integrated photonics. We measure the complex optical constant of MoTe₂ in both the 2H and 1T' phases by spectroscopic ellipsometry. We find that both phases have large refractive index, which is good for confined light-matter interaction volume. The change Δn between phases is of ℴ(1), which is large and comparable to established phase-change materials. However, both phases have large optical loss, which limits to figure of merit throughout the measured range. We further measure the NIR reflectivity of MoTe₂ and Mo_0.91W_0.09Te₂, in both the 2H and 1T' phases. The data show that the strong optical contrast between the 2H and 1T' structures persists even as the thermodynamic barrier between them is reduced by alloying. This bodes well for alloy design of phase-change materials.

Opto-Mechanics Driven Fast Martensitic Transition in Two-Dimensional Materials

Diffusional phase-change materials, such as Ge-Sb-Te alloys, are used in rewritable nonvolatile memory devices. But the continuous pursuit of readout/write speed and reduced energy consumption in miniaturized devices calls for an optically driven, diffusionless phase change scheme in ultrathin materials. Inspired by optical tweezers, in this work, we illustrate theoretically and computationally that a linearly polarized laser pulse with selected frequency can drive an ultrafast diffusionless martensitic phase transition of two-dimensional ferroelastic materials such as SnO and SnSe monolayers, where the unit-cell strain is tweezed as a generalized coordinate that affects the anisotropic dielectric function and electromagnetic energy density. At laser power of 2.0 × 10¹⁰ and 7.7 × 10⁹ W/cm², the transition potential energy barrier vanishes between two 90°-orientation variants of ferroelastic SnO and SnSe monolayer, respectively, so displacive domain switching can occur within picoseconds. The estimated adiabatic thermal limit of energy input in such optomechanical martensitic transition (OMT) is at least 2 orders of magnitude lower than that in Ge-Sb-Te alloy.

DNA Advanced Glycation End Products (DNA-AGEs) Are Elevated in Urine and Tissue in an Animal Model of Type 2 Diabetes

More precise identification and treatment monitoring of prediabetic/diabetic individuals will require additional biomarkers to complement existing diagnostic tests. Candidates include hyperglycemia-induced adducts such as advanced glycation end products (AGEs) of proteins, lipids, and DNA. The potential for DNA-AGEs as diabetic biomarkers was examined in a longitudinal study using the Lepr^db/db animal model of metabolic syndrome. The DNA-AGE, N²-(1-carboxyethyl)-2'-deoxyguanosine (CEdG) was quantified by mass spectrometry using isotope dilution from the urine and tissue of hyperglycemic and normoglycemic mice. Hyperglycemic mice (fasting plasma glucose, FPG, ≥ 200 mg/dL) displayed a higher median urinary CEdG value (238.4 ± 112.8 pmol/24 h) than normoglycemic mice (16.1 ± 11.8 pmol/24 h). Logistic regression analysis revealed urinary CEdG to be an independent predictor of hyperglycemia. Urinary CEdG was positively correlated with FPG in hyperglycemic animals and with HbA1c for all mice. Average tissue-derived CEdG was also higher in hyperglycemic mice (18.4 CEdG/10⁶ dG) than normoglycemic mice (4.4 CEdG/10⁶ dG). Urinary CEdG was significantly elevated in Lepr^db/db mice relative to Lepr^wt/wt, and tissue CEdG values increased in the order Lepr^wt/wt < Lepr^wt/db < Lepr^db/db. These data suggest that urinary CEdG measurement may provide a noninvasive quantitative index of glycemic status and augment existing biomarkers for the diagnosis and monitoring of diabetes.

Sub-Kelvin magnetic and electrical measurements in a diamond anvil cell with in situ tunability

We discuss techniques for performing continuous measurements across a wide range of pressure-field-temperature phase space, combining the milli-Kelvin temperatures of a helium dilution refrigerator with the giga-Pascal pressures of a diamond anvil cell and the Tesla magnetic fields of a superconducting magnet. With a view towards minimizing remnant magnetic fields and background magnetic susceptibility, we characterize high-strength superalloy materials for the pressure cell assembly, which allows high fidelity measurements of low-field phenomena such as superconductivity below 100 mK at pressures above 10 GPa. In situ tunability and measurement of the pressure permit experiments over a wide range of pressure, while at the same time making possible precise steps across abrupt phase transitions such as those from insulator to metal.

3.88% efficient tin sulfide solar cells using congruent thermal evaporation

Tin sulfide (SnS), as a promising absorber material in thin-film photovoltaic devices, is described. Here, it is confirmed that SnS evaporates congruently, which provides facile composition control akin to cadmium telluride. A SnS heterojunction solar cell is demons trated, which has a power conversion efficiency of 3.88% (certified), and an empirical loss analysis is presented to guide further performance improvements.

Confirmation of oxidative stress and fatty acid disturbances in two further Papillon-Lefèvre syndrome families with identification of a new mutation

BACKGROUND

We have previously reported oxidative and fatty acids disturbances in one Papillon-Lefèvre syndrome (PLS) family. This Mendelian condition characterized by palmar plantar keratosis and severe aggressive periodontitis, is caused by mutations in the cathepsin C (CTSC) gene. In this study, we have analysed two further unrelated PLS families to confirm this association.

METHODS

Mutations were identified by direct sequencing of CTSC. Biochemical analyses were performed in probands and their relatives in order to determine plasma levels of vitamin E, CoQ10 , lipid hydroperoxides (HP) and fatty acid patterns.

RESULTS

Pathogenic CTSC mutations were identified in both families including a new mutation (c504C>G). Both probands showed low levels of vitamin E and CoQ10 , and high levels of lipid HP, and also very low levels of docohexaenoic acid.

CONCLUSIONS

The previously reported oxidative and fatty acids disturbances were confirmed as a feature of this condition in two further families. There are low levels of antioxidant markers and high levels of oxidative markers, in addition of low levels of some anti-inflammatory fatty acids in persons suffering PLS and some of their relatives.

Four-probe electrical measurements with a liquid pressure medium in a diamond anvil cell

We describe a technique for making electrical transport measurements in a diamond anvil cell using an alcohol pressure medium, permitting acute sensitivity while preserving sample fidelity. The sample is suspended in the liquid medium by four gold leads that are electrically isolated by a composite gasket made of stainless steel and an alumina-loaded epoxy. We demonstrate the technique with four-probe resistivity measurements of chromium single crystals at temperatures down to 4 K and pressures above 10 GPa. Our assembly is optimized for making high precision measurements of the magnetic phase diagram and quantum critical regime of chromium, which require repeated temperature sweeps and fine pressure steps while maintaining high sample quality. The high sample quality enabled by the quasi-hydrostatic pressure medium is evidenced by the residual resistivity below 0.1 μΩ cm and the relative resistivity ratio ρ(120 K)/ρ(5 K) = 15.9 at 11.4 GPa. By studying the quality of Cr's antiferromagnetic transition over a range of pressures, we show that the pressure inhomogeneity experienced by the sample is always below 5%. Finally, we solve for the Debye temperature of Cr up to 11.4 GPa using the Bloch-Gruneisen formula and find it to be independent of pressure.

Impaired NLRP3 inflammasome activity in elderly hosts contributes to the prevalence of primary and secondary Streptococcus pneumoniae infection. (114.4)

Lethal pneumonia has become a serious problem in elderly populations. Although influenza infection alone may lead to pneumonia, secondary bacterial infections, such as Streptococcus pneumoniae, during and shortly after recovery from influenza infections are more common. Previous work has demonstrated that the NLRP3 inflammasome is activated in the lung during influenza viral infection by the M2 ion channel as well as during S. pneumoniae bacterial infection by pneumolysin; however, the impact of aging on inflammasome function during primary or secondary S. pneumoniae infection has not been examined. Here, we show that elderly mice infected with S. pneumoniae alone or shortly after influenza infection produced lower levels of IL-1β and IL-18 during infection when compared to young mice. Further, elderly mice had increased morbidity, decreased cellular infiltration to the lung, and higher bacterial titers in lung during both primary and secondary bacterial infections. Examination of whole lung tissue collected from elderly mice exhibited decreased expression of ASC, NLRP3, TXNIP, and capase-1, but similar expression of pro-IL-1β and pro-IL-18, when compared to young, similarly infected mice during both primary and secondary bacterial infections. Taken together, our study demonstrates that during primary and secondary S. pneumoniae infections, elderly mice have impaired NLRP3 inflammasome activity which may contribute to increased susceptibility for developing pneumonia.

HIV infection, sexual risk behaviour and condom use in the Belize defense force

This study is the first Biological and Behavioral Surveillance Survey to be conducted among personnel in the Belize Defense Force. The purpose of the study was to understand the prevalence of HIV infection and risk behaviours, and to identify key correlates of sexual risk behaviours. A representative sample of personnel underwent serological testing and an Audio Computer-Assisted Self Interview. Of those sampled, 351 completed a blood test and 334 completed a behavioural interview. The prevalence of HIV was 1.14%. Twelve percent had ever reported being diagnosed with a sexually transmitted infection (STI) or screened positive for HIV infection. The odds of ever having an STI/HIV were higher among those who had less education, those who had sex with a commercial sex worker (CSW), those who ever engaged in receptive anal sex and those with post-traumatic stress disorder (PTSD). Alcohol abuse and PTSD were prevalent and associated with HIV risk behaviours. These results are being used to inform current prevention efforts.

Relationship of serum cholesterol levels to atopy in the US population

BACKGROUND

Cholesterol promotes Th2 immunity and allergic inflammation in rodents; whether this occurs in humans is unclear. Reports of both direct and inverse associations between serum cholesterol and atopy in different populations suggest that race and/or other demographic variables may modify these relationships.

AIMS OF THE STUDY

To determine the relationships between levels of three serum cholesterol measures [total cholesterol (TC), high density lipoprotein-cholesterol (HDL-C), and non-HDL-C] and atopy in a sample representative of the US population.

METHODS

Cross-sectional study of 6854 participants aged > or =6 years from the 2005-2006 National Health and Nutrition Examination Survey.

RESULTS

In the overall population, adjusted odds ratios (AORs) per two-standard deviation increase in TC and non-HDL-C for biochemical atopy (defined as > or =1 allergen-specific IgE to 19 allergens) were 1.17 [95% confidence interval (CI), 1.00-1.38] and 1.19 (95% CI, 1.03-1.39), respectively. Interactions by race were noted for the two relationships (interaction P = 0.004 and P = 0.009, respectively) with non-Hispanic Whites (NHWs) having direct relationships [TC: AOR 1.27 (95% CI, 1.03-1.57); non-HDL-C: AOR 1.27 (95% CI, 1.03-1.56)] and non-Hispanic Blacks (NHBs) inverse relationships [TC: AOR 0.77 (95% CI, 0.62-0.95); non-HDL-C: AOR 0.86 (95% CI, 0.69-1.08)]. The adjusted HDL-C-atopy relationship was nonsignificant for NHWs and inverse for NHBs [AOR 0.77 (95% CI, 0.61-0.96)]. Relationships were independent of body mass index and serum C-reactive protein and unmodified by corticosteroid or statin usage. Results were similar using current hay fever/allergy as the atopy outcome.

CONCLUSIONS

There are marked inter-racial differences in the relationship between serum cholesterol and atopy in the US population.

Invited article: High-pressure techniques for condensed matter physics at low temperature

Condensed matter experiments at high pressure accentuate the need for accurate pressure scales over a broad range of temperatures, as well as placing a premium on a homogeneous pressure environment. However, challenges remain in diamond anvil cell technology, including both the quality of various pressure transmitting media and the accuracy of secondary pressure scales at low temperature. We directly calibrate the ruby fluorescence R1 line shift with pressure at T=4.5 K using high-resolution x-ray powder diffraction measurements of the silver lattice constant and its known equation of state up to P=16 GPa. Our results reveal a ruby pressure scale at low temperatures that differs by 6% from the best available ruby scale at room T. We also use ruby fluorescence to characterize the pressure inhomogeneity and anisotropy in two representative and commonly used pressure media, helium and methanol:ethanol 4:1, under the same preparation conditions for pressures up to 20 GPa at T=5 K. Contrary to the accepted wisdom, both media show equal levels of pressure inhomogeneity measured over the same area, with a consistent DeltaP/P per unit area of +/-1.8 %/(10(4) microm(2)) from 0 to 20 GPa. The helium medium shows an essentially constant deviatoric stress of 0.021+/-0.011 GPa up to 16 GPa, while the methanol:ethanol mixture shows a similar level of anisotropy up to 10 GPa, above which the anisotropy increases. The quality of both pressure media is further examined under the more stringent requirements of single crystal x-ray diffraction at cryogenic temperature. For such experiments we conclude that the ratio of sample-to-pressure chamber volume is a critical parameter in maintaining sample quality at high pressure, and may affect the choice of pressure medium.

Sulfur mustard induces immune sensitization in hairless guinea pigs

Sulfur mustard (SM, bis-(2-chloroethyl) sulfide) is a well known chemical warfare agent that may cause long-term debilitating injury. Because of the ease of production and storage, it has a strong potential for chemical terrorism; however, the mechanism by which SM causes chronic tissue damage is essentially unknown. SM is a potent protein alkylating agent, and we tested the possibility that SM modifies cellular antigens, leading to an immunological response to "altered self" and a potential long-term injury. To that end, in this communication, we show that dermal exposure of euthymic hairless guinea pigs induced infiltration of both CD4(+) and CD8(+) T cells into the SM-exposed skin and strong upregulated expression of proinflammatory cytokines and chemokines (TNF-alpha, IFN-gamma, and IL-8) in distal tissues such as the lung and the lymph nodes. Moreover, we present evidence for the first time that SM induces a specific delayed-type hypersensitivity response that is associated with splenomegaly, lymphadenopathy, and proliferation of cells in these tissues. These results clearly suggest that dermal exposure to SM leads to immune activation, infiltration of T cells into the SM-exposed skin, delayed-type hypersensitivity response, and molecular imprints of inflammation in tissues distal from the site of SM exposure. These immunological responses may contribute to the long-term sequelae of SM toxicity.

The succinate:menaquinone reductase of Bacillus cereus: characterization of the membrane-bound and purified enzyme

Utilization of external succinate by Bacillus cereus and the properties of the purified succinate:menaquinone-7 reductase (SQR) were studied. Bacillus cereus cells showed a poor ability for the uptake of and respiratory utilization of exogenous succinate, thus suggesting that B. cereus lacks a specific succinate uptake system. Indeed, the genes coding for a succinate-fumarate transport system were missing from the genome database of B. cereus. Kinetic studies of membranes indicated that the reduction of menaquinone-7 is the rate-limiting step in succinate respiration. In accordance with its molecular characteristics, the purified SQR of B. cereus belongs to the type-B group of SQR enzymes, consisting of a 65-kDa flavoprotein (SdhA), a 29-kDa iron-sulphur protein (SdhB), and a 19-kDa subunit containing 2 b-type cytochromes (SdhC). In agreement with this, we could identify the 4 conserved histidines in the SdhC subunit predicted by the B. cereus genome database. Succinate reduced half of the cytochrome b content. Redox titrations of SQR-cytochrome b-557 detected 2 components with apparent midpoint potential values at pH 7.6 of 79 and -68 mV, respectively; the components were not spectrally distinguishable by their maximal absorption bands as those of Bacillus subtilis. The physiological properties and genome database analyses of B. cereus are consistent with the cereus group ancestor being an opportunistic pathogen.

Pressure-tuned spin and charge ordering in an itinerant antiferromagnet

Elemental chromium orders antiferromagnetically near room temperature, but the ordering temperature can be driven to zero by applying large pressures. We combine diamond anvil cell and synchrotron x-ray diffraction techniques to measure directly the spin and charge order in the pure metal at the approach to its quantum critical point. Both spin and charge order are suppressed exponentially with pressure, well beyond the region where disorder cuts off such a simple evolution, and they maintain a harmonic scaling relationship over decades in scattering intensity. By comparing the development of the order parameter with that of the magnetic wave vector, it is possible to ascribe the destruction of antiferromagnetism to the growth in electron kinetic energy relative to the underlying magnetic exchange interaction.

Direct measurement of antiferromagnetic domain fluctuations

Measurements of magnetic noise emanating from ferromagnets owing to domain motion were first carried out nearly 100 years ago, and have underpinned much science and technology. Antiferromagnets, which carry no net external magnetic dipole moment, yet have a periodic arrangement of the electron spins extending over macroscopic distances, should also display magnetic noise. However, this must be sampled at spatial wavelengths of the order of several interatomic spacings, rather than the macroscopic scales characteristic of ferromagnets. Here we present a direct measurement of the fluctuations in the nanometre-scale superstructure of spin- and charge-density waves associated with antiferromagnetism in elemental chromium. The technique used is X-ray photon correlation spectroscopy, where coherent X-ray diffraction produces a speckle pattern that serves as a 'fingerprint' of a particular magnetic domain configuration. The temporal evolution of the patterns corresponds to domain walls advancing and retreating over micrometre distances. This work demonstrates a useful measurement tool for antiferromagnetic domain wall engineering, but also reveals a fundamental finding about spin dynamics in the simplest antiferromagnet: although the domain wall motion is thermally activated at temperatures above 100 K, it is not so at lower temperatures, and indeed has a rate that saturates at a finite value-consistent with quantum fluctuations-on cooling below 40 K.

Microscopic and macroscopic signatures of antiferromagnetic domain walls

Magnetotransport measurements on small single crystals of Cr, the elemental antiferromagnet, reveal the hysteretic thermodynamics of the domain structure. The temperature dependence of the transport coefficients is directly correlated with the real-space evolution of the domain configuration as recorded by x-ray microprobe imaging, revealing the effect of antiferromagnetic domain walls on electron transport. A single antiferromagnetic domain wall interface resistance is deduced to be of order 5 x 10(-5) mu Omega cm(2) at a temperature of 100 K.

Prevalence of antibody to Trypanosoma cruzi in three populations in Belize

Cross-sectional studies were conducted to determine the prevalence of antibody to Trypanosoma cruzi, the agent of Chagas' disease among three populations in Belize. Specimens were tested using a second-generation enzyme-linked immunoassay (EIA). Confirmatory testing with three single-antigen EIAs and a radioimmunoprecipitation assay (RIPA) were performed. Five (0.5%) of 962 blood donors at the Belize City Hospital were reactive including four (6%) of 65 donors from countries known to be endemic for Chagas' disease and one (0.1%) of 861 from Belize (P < 0.001). Among 467 healthy members of the Belize Defense Force, none were reactive. The third group included workers and families primarily from other Central American countries living on a banana plantation in a rural area of the country. Twenty-seven (6.1%) of 442 sera were reactive. The prevalence was 5.3% of 75 < 15 years of age, 4.2% of 236 15-34 years of age, and 9.7% of 124 > or = 35 years of age (P = 0.11, by chi-square for trend). The prevalence was similar in males (6.7% of 280) and females (5.8% of 154). The prevalence of those born in Belize (4 of 56, 7.1%) was similar with that of those born in El Salvador (9 of 110, 8.2%), Guatemala (6 of 117, 5.1%), and Honduras (8 of 129, 6.2%). Of the four persons with reactive sera who were born in Belize, the immigrant mother of one was also reactive, suggesting possible congenital transmission. Among 31 sera repeatedly reactive by EIA to T. cruzi that were further studied, 22 (71%) were reactive by at least two of three single-antigen confirmatory EIAs and 29 (94%) by RIPA. Additional studies should focus on the epidemiology of T. cruzi and ways to reduce risk of transfusion-related infections in Belize.

Hepatitis B virus, human immunodeficiency virus type-1, and syphilis among women attending prenatal clinics in Belize, Central America

Women and their infants may benefit from therapeutic interventions when hepatitis B, human immunodeficiency virus (HIV), or syphilis are detected during the prenatal period. We initiated hepatitis B and HIV screening of women attending prenatal clinics in Belize. Risk factor assessment information for hepatitis B infection and demographic data were determined by interview. Of 543 evaluable women, 81 (14.9%) were seropositive for hepatitis B core antibody (anti-HBc); one woman had asymptomatic hepatitis B surface antigenemia. Antibodies to HIV-1 were detected in one woman. Reactive syphilis serologies were detected in 15 (2.8%) women. Anti-HBc seroprevalence varied by district (range 3.1-43.5%) and by ethnicity (range 0.0-40.9%). Significant identified risks for anti-HBc seropositivity from univariate analyses included being of the Garifuna ethnic group, residence or birth in the Stann Creek or Toledo districts, a reactive syphilis serology, a household size of eight or greater, and five or more lifetime sexual partners. Multivariate analyses identified ethnicity and a reactive rapid plasma reagin as the best predictors of anti-HBc seropositivity. Highly variable differences in anti-HBc prevalence by district may permit the targeting of limited public health resources for education, screening, and prevention programs.

Randomized comparison of 5 and 10 microgram doses of two recombinant hepatitis B vaccines

The high cost of hepatitis B vaccines remains an obstacle to their use. Since the recommended adult dose of Recombivax HB (MSD) is 10 micrograms and that of Engerix B (SKB) is 20 micrograms, we sought to determine if 10 microgram doses of each vaccine are equally immunogenic. Further, since 5 microgram doses of Recombivax are routinely used in those < or = 29 years of age in the US military, we sought to compare this dose with 5 microgram doses of Engerix B. Lower doses of Engerix would result in vaccine cost savings.

METHODS

members of the Belize Defence Force who were > or = 18 years of age (median 24) without detectable anti-HBc were randomly assigned to receive Recombivax, 5 or 10 micrograms, or ENgerix, 5 or 10 micrograms IM at 0, 1, and 6 months. Randomization was weighted toward Engerix.

RESULTS

after 3 doses, geometric mean concentrations (GMC) of anti-HBs were highest among those receiving Recombivax 10 micrograms (n=22) or 5 micrograms (n=46) with GMC anti-HBs of 744 and 570 mIU ml-1, respectively. Similar proportions in the two groups developed > or = 10 mIU m-1 anti-HBs (100 and 98%). Among the 91 people who received Engerix 10 micrograms, the GMC anti-HBs was 325 mIU ml-1 and 91% developed > or = 10 mIU ml-1. The 87 people who received Engerix 5 micrograms had the lowest GMC, 177 mIU ml-1 (p < 0.05 compared with either Recombivax group). Only 86% attained > or = 10 mIU ml-1 anti-HBs (p > 0.05 compared with other regimens). The proportion attaining > or = 100 mIU ml-1 was lower in the 5 microgram Engerix group (63%) compared with 80% in the 5 microgram or 95% in the 10 microgram Recombivax groups (p < 0.05).

CONCLUSIONS

Engerix administered in 5 microgram doses is less immunogenic than 5 or 10 microgram doses of Recombivax. In healthy populations < 30 years of age, regimens of half the recommended adult dose (5 micrograms of Recombivax or 10 micrograms of Engerix) are highly immunogenic and may result in significant vaccine cost savings.

The prevalence of hepatitis A, B and C infection among different ethnic groups in Belize

Little is known about the prevalence of infection with hepatitis viruses in Belize, Central America. We conducted a serologic survey among members of the Belize Defence Force (BDF), which is composed of the five major ethnic groups in Belize, to estimate prevalence rates of hepatitis A, B, and C among military-aged men and women in Belize. Of approximately 600 men and women in the BDF, 492 (82%) completed a questionnaire and blood collection. Antibody to hepatitis A was found in 94%, with similar rates by age, sex, rank, and ethnicity. Antibody to hepatitis B core antigen (anti-HBc) was found in 31%. Rates of anti-HBc varied significantly among the ethnic groups with the lowest rates in Mestizo (5%) and Mayan Indians (9%), and significantly higher rates among Creoles (30%) and Garifuna (56%). Rates increased with increasing age from 28% in those 18-24 years old to 35% in those > or = 35 years old (P = 0.07, by chi-square test for trend). Hepatitis B surface antigen was found in 21 (4%) overall. Antibody to hepatitis C was found in two (0.4%). In this young healthy population, exposure to hepatitis A before the age of 18 is almost universal, while exposure to hepatitis B is related to age and ethnic origin.

Initial report of a hepatitis investigation in rural Belize

In spring 1991, Belizian health officials expressed concern about a possible hepatitis outbreak in a banana farming district. A study was designed to identify cases and to address the serological prevalence of hepatitis virus markers. Three populations were studied: (i) persons meeting a clinical case definition for hepatitis; (ii) designated banana workers; and (iii) people in a random sample of households in the community. Information was collected using questionnaires and sera were collected for laboratory testing. This report presents the preliminary results of a study conducted in June 1991. Among people who met the clinical case definition, 24% of 42 tested had immunoglobulin M antibody to hepatitis B virus (HBV) core antigen (anti-HBc IgM). In the worker and household survey populations, 284 and 280 people, respectively, were tested for anti-HBc IgM. In each group, 4% were positive. HBV surface antigen was found in 37% of 43 clinical cases, 18% of workers, and 13% of people in the household survey. Among the 3 study populations, the prevalence of HBV core antibody (anti-HBc) ranged from 73% to 81%. Almost all tested persons had evidence of prior hepatitis A virus infection. Evidence of prior infection with hepatitis viruses A and B was widespread, but an aetiology could not be established for most of the clinical cases. However, the prevalence of hepatitis B markers in this population was very high compared to other reports from the Caribbean.

[Urinary oestriol excretion and the lecithin/sphingomyelin ratio in amniotic fluid in Bogota (2600 m) I. Normal pregnancy (author's transl)]

We have studied 22 pregnancies in order to establish normal values for the urinary oestriol excretion in Bogotá, a city 2600 metres above sea level. The study subjects were normal pregnant women attending the prenatal clinic of the Hospital San José de Bogotá, and belong to a racially mixed community of medium to low socio-economic level. In the study, new born weight was found low (mean +/- SEM 2.97 +/-0.06 kg) while placental weight was high (0.6 +/- 0.02 kg) with a high placenta/newborn ratio. Maternal hemoglobin was elevated (12.8 +/- 0.2g/100 ml) reflecting the effect of altitude. In 66 determinations, oestriol excretion was more than 4mg/24 hours from week 31 to 36 and of more than 5 mg/24 hours from week 35 to 40. The decreased excretion of oestriol most likely reflects impaired intrauterine fetal growth, and is probably related to nutrional, racial and socio-economic factors as well as to the altitude. In five normal term pregnancies studied, the lecithin/sphingomyelin ratio was of 2 or more and amniotic fluid creatinine was also elevated, indicating maturity of the pulmonary and renal enzyme systems of the fetus.