Magnetism in cold subducting slabs at mantle transition zone depths.

The Earth's crust-mantle boundary, the Mohorovicic discontinuity, has been traditionally considered to be the interface between the magnetic crust and the non-magnetic mantle1. However, this assumption has been questioned by geophysical observations2,3 and by the identification of magnetic remanence in mantle xenoliths4, which suggest mantle magnetic sources. Owing to their high critical temperatures, iron oxides are the only potential sources of magnetic anomalies at mantle depths5. Haematite (α-Fe2O3) is the dominant iron oxide in subducted lithologies at depths of 300 to 600 kilometres, delineated by the thermal decomposition of magnetite and the crystallization of a high-pressure magnetite phase deeper than about 600 kilometres6. The lack of data on the magnetic properties of haematite at relevant pressure-temperature conditions, however, hinders the identification of magnetic boundaries within the mantle and their contribution to observed magnetic anomalies. Here we apply synchrotron Mössbauer source spectroscopy in laser-heated diamond anvil cells to investigate the magnetic transitions and critical temperatures in Fe2O3 polymorphs7 at pressures and temperatures of up to 90 gigapascals and 1,300 kelvin, respectively. Our results show that haematite remains magnetic at the depth of the transition zone in the Earth's mantle in cold or very cold subduction geotherms, forming a frame of deep magnetized rocks in the West Pacific region. The deep magnetic sources spatially correlate with preferred paths of the Earth's virtual geomagnetic poles during reversals8 that might not reflect the geometry of the transitional field. Rather, the paths might be an artefact caused by magnetized haematite-bearing rocks in cold subducting slabs at mid-transition zone depths. Such deep sources should be taken into account when carrying out inversions of the Earth's geomagnetic data9, and especially in studies of planetary bodies that no longer have a dynamo10, such as Mars.

The Time-resolved and Extreme-conditions XAS (TEXAS) facility at the European Synchrotron Radiation Facility: the energy-dispersive X-ray absorption spectroscopy beamline ID24.

The European Synchrotron Radiation Facility has recently made available to the user community a facility totally dedicated to Time-resolved and Extreme-conditions X-ray Absorption Spectroscopy--TEXAS. Based on an upgrade of the former energy-dispersive XAS beamline ID24, it provides a unique experimental tool combining unprecedented brilliance (up to 10(14) photons s(-1) on a 4 µm × 4 µm FWHM spot) and detection speed for a full EXAFS spectrum (100 ps per spectrum). The science mission includes studies of processes down to the nanosecond timescale, and investigations of matter at extreme pressure (500 GPa), temperature (10000 K) and magnetic field (30 T). The core activities of the beamline are centered on new experiments dedicated to the investigation of extreme states of matter that can be maintained only for very short periods of time. Here the infrastructure, optical scheme, detection systems and sample environments used to enable the mission-critical performance are described, and examples of first results on the investigation of the electronic and local structure in melts at pressure and temperature conditions relevant to the Earth's interior and in laser-shocked matter are given.

Thermal decomposition of ammonium hexachloroosmate.

Structural changes of (NH4)2[OsCl6] occurring during thermal decomposition in a reduction atmosphere have been studied in situ using combined energy-dispersive X-ray absorption spectroscopy (ED-XAFS) and powder X-ray diffraction (PXRD). According to PXRD, (NH4)2[OsCl6] transforms directly to metallic Os without the formation of any crystalline intermediates but through a plateau where no reactions occur. XANES and EXAFS data by means of Multivariate Curve Resolution (MCR) analysis show that thermal decomposition occurs with the formation of an amorphous intermediate {OsCl4}x with a possible polymeric structure. Being revealed for the first time the intermediate was subjected to determine the local atomic structure around osmium. The thermal decomposition of hexachloroosmate is much more complex and occurs within a minimum two-step process, which has never been observed before.

The time-resolved and extreme conditions XAS (TEXAS) facility at the European Synchrotron Radiation Facility: the general-purpose EXAFS bending-magnet beamline BM23.

BM23 is the general-purpose EXAFS bending-magnet beamline at the ESRF, replacing the former BM29 beamline in the framework of the ESRF upgrade. Its mission is to serve the whole XAS user community by providing access to a basic service in addition to the many specialized instruments available at the ESRF. BM23 offers high signal-to-noise ratio EXAFS in a large energy range (5-75 keV), continuous energy scanning for quick-EXAFS on the second timescale and a micro-XAS station delivering a spot size of 4 µm × 4 µm FWHM. It is a user-friendly facility featuring a high degree of automation, online EXAFS data reduction and a flexible sample environment.

Synchrotron radiation Mössbauer spectra of a rotating absorber with implications for testing velocity and acceleration time dilation.

Many Mössbauer spectroscopy (MS) experiments have used a rotating absorber in order to measure the second-order transverse Doppler (TD) shift, and to test the validity of the Einstein time dilation theory. From these experiments, one may also test the clock hypothesis (CH) and the time dilation caused by acceleration. In such experiments the absorption curves must be obtained, since it cannot be assumed that there is no broadening of the curve during the rotation. For technical reasons, it is very complicated to keep the balance of a fast rotating disk if there are moving parts on it. Thus, the Mössbauer source on a transducer should be outside the disk. Friedman and Nowik have already predicted that the X-ray beam finite size dramatically affects the MS absorption line and causes its broadening. We provide here explicit formulas to evaluate this broadening for a synchrotron Mössbauer source (SMS) beam. The broadening is linearly proportional to the rotation frequency and to the SMS beam width at the rotation axis. In addition, it is shown that the TD shift and the MS line broadening are affected by an additional factor assigned as the alignment shift which is proportional to the frequency of rotation and to the distance between the X-ray beam center and the rotation axis. This new shift helps to align the disk's axis of rotation to the X-ray beam's center. To minimize the broadening, one must focus the X-ray on the axis of the rotating disk and/or to add a slit positioned at the center, to block the rays distant from the rotation axis of the disk. Our experiment, using the (57)Fe SMS, currently available at the Nuclear Resonance beamline (ID18) at the ESRF, with a rotating stainless steel foil, confirmed our predictions. With a slit installed at the rotation axis (reducing the effective beam width from 15.6 µm to 5.4 µm), one can measure a statistically meaningful absorption spectrum up to 300 Hz, while, without a slit, such spectra could be obtained up to 100 Hz only. Thus, both the broadening and the alignment shift are very significant and must be taken into consideration in any rotating absorber experiment. Here a method is offered to measure accurately the TD shift and to test the CH.

Local structure of solid Rb at megabar pressures.

We have investigated the local and electronic structure of solid rubidium by means of x-ray absorption spectroscopy up to 101.0 GPa, thus doubling the maximum investigated experimental pressure. This study confirms the predicted stability of phase VI and was completed by the combination of two pivotal instrumental solutions. On one side, we made use of nanocrystalline diamond anvils, which, contrary to the more commonly used single crystal diamond anvils, do not generate sharp Bragg peaks (glitches) at specific energies that spoil the weak fine structure oscillations in the x-ray absorption cross section. Second, we exploited the performance of a state-of-the-art x-ray focussing device yielding a beam spot size of 5 × 5 µm(2), spatially stable over the entire energy scan. An advanced data analysis protocol was implemented to extract the pressure dependence of the structural parameters in phase VI of solid Rb from 51.2 GPa up to the highest pressure. A continuous reduction of the nearest neighbour distances was observed, reaching about 6% over the probed pressure range. We also discuss a phenomenological model based on the Einstein approximation to describe the pressure behaviour of the mean-square relative displacement. Within this simplified scheme, we estimate the Grüneisen parameter for this high pressure Rb phase to be in the 1.3-1.5 interval.

Hyperfine splitting and room-temperature ferromagnetism of Ni at multimegabar pressure.

Magnetic and elastic properties of Ni metal have been studied up to 260 GPa by nuclear forward scattering of synchrotron radiation with the 67.4 keV Mössbauer transition of 61Ni. The observed magnetic hyperfine splitting confirms the ferromagnetic state of Ni up to 260 GPa, the highest pressure where magnetism in any material has been observed so far. Ab initio calculations reveal that the pressure evolution of the hyperfine field, which features a maximum in the range of 100 to 225 GPa, is a relativistic effect. The Debye energy obtained from the Lamb-Mössbauer factor increases from 33 meV at ambient pressure to 60 meV at 100 GPa. The change of this energy over volume compression is well described by a Grüneisen parameter of 2.09.

AIDS pacient's long-term battle with multiply recurrent tuberculosis: reinfection or reactivation?

The advent of Mycobacterium tuberculosis strain genotyping has allowed differentiation between disease relapse and exogenous re-infection. We report here a remarkable case of multiply recurrent tuberculosis in a patient living with HIV. Between 1995 and 2009, a young HIV-infected intravenous drug user, who was reluctant to comply with anti-retroviral treatment, underwent at least five tuberculosis episodes caused by three distinct M. tuberculosis strains sharply differentiated by drug susceptibility profile, genotype and infectious source. Eventually, the patient died during a relapse of tuberculosis due to a notorious multidrug-resistant outbreak-strain, which infected him during a prolonged hospitalization in the epicentre of such outbreak. Whether recurrent tuberculosis is due to a new infection or to reactivation of a previous one is a century-long controversial question. In our patient, both conditions alternated throughout his 15 years of living with HIV. Cases such as this might not be exceptional in certain underprivileged suburban areas of Argentina and should raise concern over three pending issues in tuberculosis control policies, namely secondary preventing therapy, institutional infection control and patient follow-up throughout the health network system.

A laser heating facility for energy-dispersive X-ray absorption spectroscopy.

A double-sided laser heating setup for diamond anvil cells installed on the ID24 beamline of the ESRF is presented here. The setup geometry is specially adopted for the needs of energy-dispersive X-ray absorption spectroscopic (XAS) studies of materials under extreme pressure and temperature conditions. We illustrate the performance of the facility with a study on metallic nickel at 60 GPa. The XAS data provide the temperature of the melting onset and quantitative information on the structural parameters of the first coordination shell in the hot solid up to melting.

Behaviour of niobium during early Earth's differentiation: insights from its local structure and oxidation state in silicate melts at high pressure.

Niobium (Nb) is one of the key trace elements used to understand Earth's formation and differentiation, and is remarkable for its deficiency relative to tantalum in terrestrial rocks compared to the building chondritic blocks. In this context, the local environment of Nb in silica-rich melts and glasses is studied by in situ x-ray absorption spectroscopy (XAS) at high pressure (P) up to 9.3 GPa and 1350 K using resistive-heating diamond-anvil cells. Nb is slightly less oxidized in the melt (intermediate valence between +4 and +5) than in the glass (+5), an effect evidenced from the shift of the Nb-edge towards lower energies. Changes in the pre-edge features are also observed between melt and glass states, consistently with the observed changes in oxidation state although likely enhanced by temperature (T) effects. The oxidation state of Nb is not affected by pressure neither in the molten nor glassy states, and remains constant in the investigated P-range. The Nb-O coordination number is constant and equal to [Formula: see text] below 5 GPa, and only progressively increases up to [Formula: see text] at 9.3 GPa, the maximum P investigated. If these findings were to similarly apply to basaltic melts, that would rule out the hypothesis of Nb/Ta fractionation during early silicate Earth's differentiation, thus reinforcing the alternative hypothesis of fractionation during core formation on reduced pre-planetary bodies.

Nb K-edge x-ray absorption investigation of the pressure induced amorphization in A-site deficient double perovskite La1/3NbO3.

Nb K-edge x-ray absorption spectroscopy is utilized to investigate the changes in the local structure of the A-site deficient double perovskite La1/3NbO3 which undergoes a pressure induced irreversible amorphization. EXAFS results show that with increasing pressure up to 7.5 GPa, the average Nb-O bond distance decreases in agreement with the expected compression and tilting of the NbO6 octahedra. On the contrary, above 7.5 GPa, the average Nb-O bond distance show a tendency to increase. Significant changes in the Nb K-edge XANES spectrum with evident low energy shift of the pre-peak and the absorption edge is found to happen in La1/3NbO3 above 6.3 GPa. These changes evidence a gradual reduction of the Nb cations from Nb(5+) towards Nb(4+) above 6.3 GPa. Such a valence change accompanied by the elongation of the average Nb-O bond distances in the octahedra, introduces repulsion forces between non-bonding adjacent oxygen anions in the unoccupied A-sites. Above a critical pressure, the Nb reduction mechanism can no longer be sustained by the changing local structure and amorphization occurs, apparently due to the build-up of local strain. EXAFS and XANES results indicate two distinct pressure regimes having different local and electronic response in the La1/3NbO3 system before the occurence of the pressure induced amorphization at ∼14.5 GPa.

Evaluation of synthetic pseudo cord-factor-like glycolipids for the serodiagnosis of tuberculosis.

A number of glycolipids were evaluated in an ELISA test for their serodiagnostic usefulness in tuberculosis. One hundred and twelve (112) sera belonging to bacteriologically confirmed TB patients, patients with pathologies other than tuberculosis and healthy individuals were examined against several synthetic "mirror" pseudo cord factors (analogues of trehalose-6,6'-dimycolate or TDM) using natural cord factor and another recently described natural glycolipid (SL-IV) of Mycobacterium tuberculosis as control antigens. Analysis of the results shows that all synthetic "mirror" pseudo cord factors, except one with a short 8-carbon chain, were better recognized by the sera of tuberculosis patients than natural cord factor, with sensitivity and specificity values in the ELISA test similar to those reported for M. tuberculosis species-specific SL-IV. Of all antigens tested in this study, BDA. TDA, a bis(N,N-dioctadecylamide) of "trehalose dicarboxylic acid", [(alpha-D-glucopyranosyluronic acid) (alpha-D-glucopyranosiduranic acid)], showed the highest serodiagnostic discriminating power (93% sensitivity and specificity). We postulate that either these artificial molecules are cross-reactants of similarly structured native glycolipids of M. tuberculosis or that they bear closer resemblance to actual phagosome-lysosome-modified antigens than to native mycobacterial ones.

Evaluation of the effectiveness of BCG vaccination using the case-control method in Buenos Aires, Argentina.

A retrospective case-control study was conducted in Argentina to determine the protection conferred by BCG vaccination against tuberculosis in children under six years of age, in an area where coverage is about 55%. A total of 175 tuberculosis patients were included. Five controls selected from patients treated at the same hospital as those under study for reasons other than tuberculosis were matched to each case on the basis of age, socioeconomic origin, nutritional status and place of residence. Information on BCG vaccination status was collected by an independent examiner. Tuberculosis localizations were as follows: 152 pulmonary, pleural and/or miliary; 18 meningitis; 2 lymphadenitis; 2 osteoarticular; and 1 otic. The diagnosis was based on bacteriological and histopathological tests, computerized tomography, radiology, clinical examination, endoscopy, and proved source of infection. The protective effect of BCG among those who were vaccinated was 73.0% with 95% confidence limits of 82% and 62%. According to these results BCG vaccination given early in life is very effective in preventing tuberculosis.

p53 mutations in basal cell carcinomas arising in routine users of sunscreens.

Sun exposure histories were obtained from a series of patients age 35 or younger following diagnosis and removal of a basal cell carcinoma (BCC). The DNA was extracted from tumor biopsy samples derived from BCC of 10 patients who reported that they did not use sunscreens during youth (age 18 or younger) and 10 patients who routinely employed sunscreens during this age period. Exons 5-9 of the p53 gene were then amplified in three fragments from these samples using a nested polymerase chain reaction (PCR) approach and screened for mutations using an RNA heteroduplex assay. All PCR products displaying evidence of a mutation were sequenced. It was found that 6 of the 10 patients who were not routine sunscreen users displayed mutations in these p53 exons. All of the mutations were located at dipyrimidine sites, five of the six were C-->T transitions and one mutation was a tandem double mutation, consistent with a role for solar UVB in BCC formation. In contrast, only one p53 mutation was detected in the group of 10 patients who routinely employed sunscreens during childhood and adolescence. Hence, a significantly (P = 0.029) lower level of p53 mutations was detected in the BCC obtained from sunscreen users compared with tumors derived from nonusers. These findings suggest that the mechanisms involved in the etiology of skin carcinogenesis differ in sunscreen users compared with people who did not routinely employ sunscreens. These data are also indicative of a protective effect associated with sunscreen use against the formation of p53 mutations. It is possible that the patients who were diagnosed with BCC despite their use of sunscreens possessed a genetic susceptibility for skin cancer formation and developed BCC through a p53-independent pathway. Alternatively, solar UVA wavelengths, that were generally not blocked by the suncare products employed by the sunscreen users, may have played a significant role in BCC development through induction of a mutation(s) in an oncogene and/or a tumor suppressor gene, other than p53, for these patients.

Bovine tuberculosis in Latin America and the Caribbean: current status, control and eradication programs.

Out of the approximately 300 million head which constitute the bovine population in Latin America and the Caribbean, 80 million are found in countries where rates of Mycobacterium bovis infection are very low or nil. The remaining 220 million are found in countries with either a moderate to high prevalence or where no recent information is available. Argentina and Brazil, both have huge cattle populations with estimated prevalences higher than 1%, and together may harbour 3.5 million infected cattle. Information on the impact of M. bovis on human health in the Region is scarce and does not include data on infection of children. In Argentina, human tuberculosis of bovine origin was found to be mainly an occupational disease, transmitted by aerosol. Control or eradication has been achieved in several countries in the Region by use of the tuberculin test followed by sacrifice of reactors. In countries such as Cuba, where the prevalence is already very low, area tuberculin testing is being replaced by slaughter surveillance and epidemiological trace-back. Other countries, where the prevalence is high (e.g. Chile, Paraguay, Peru and Argentina), promote regional campaigns based on the decision and active participation of cattle farmers. Recent diagnostic developments based on the in vitro measurement of humoral and cellular immune responses could be an aid in control and eradication campaigns, provided their usefulness is demonstrated in field trials. In heavily infected areas complementary or alternative strategies should also be proposed, aiming at lowering the prevalence rates prior to the application of the test and slaughter method.

Comparison of different genetic markers for molecular epidemiology of bovine tuberculosis.

In the present study three different genetic markers were used in an RFLP study to differentiate Mycobacterium bovis (M. bovis) isolated in Argentina. The markers were: the insertion sequence IS6110, the direct repeat (DR) sequence flanking IS6110, and a polymorphic GC-rich repetitive sequence (PGRS), called pMBA2. Two restriction enzymes were used, PvuII for IS6110 and DR (DR/PvuII) and AluI for DR (DR/AluI) and pMBA2. DNA from 85 of M. bovis isolates was digested with PvuII and hybridized with IS6110 and Dr. IS6110 was not useful to differentiate M. bovis because most of the isolates contain a single monomorphic copy. The use of DR allowed a limited degree of differentiation. DNA from 44 of these isolates was also digested with AluI and hybridized with DR and pMBA2. In this condition these probes differentiated the isolates in many different RFLP types. By combining the patterns generated with DR/AluI and pMBA2 it was possible to increase the differentiation up to obtain 30 different RFLP types and 54% of the isolates were differentiated because they showed a unique pattern. Six isolates of M. bovis involved in two different outbreaks of bovine tuberculosis were correctly identified. Thus, DR and pMBA2 could be, at the moment, the probes of choice for comparisons of M. bovis isolates in different regions and for epidemiological surveillance of bovine tuberculosis.

Souvenir from the Hamptons - a case of cutaneous larva migrans of six months' duration.

Cutaneous larva migrans is a distinctive serpiginous eruption caused by a reaction to burrowing hookworms. The infection is usually self-limited, normally lasting 2-8 weeks, but may persist for more than a year if misdiagnosed. Biopsies of the creeping eruption rarely reveal an organism. Thus, it is important for the infection to be recognized clinically, so that effective treatment may begin. We found topical thiabendazole to be fast and effective in treating this case of cutaneous larva migrans of six months' duration.

Reciprocal cellular and humoral immune responses in bovine tuberculosis.

A sandwich ELISA for the detection of gamma interferon showed higher sensitivity and specificity than an indirect ELISA for mycobacterial antibodies in the diagnosis of bovine tuberculosis. Circumstantial evidence of an inverse relationship between cellular and humoral immune responses to Mycobacterium bovis was found in cattle with natural infection.

The administration of foot and mouth disease vaccine with oil adjuvant and its influence on the diagnosis of bovine tuberculosis.

The possible influence of vaccination with oil adjuvanted foot and mouth disease vaccines on the tuberculin response was investigated in 32 normal guinea pigs and 190 non-tuberculous bovines. Circulating anti-Mycobacterium bovis IgG antibodies were analysed by an enzyme-linked immunosorbent assay (ELISA), in order to determine the effect of the vaccination on the humoral response against mycobacteria in cattle. Control animals were either nonvaccinated or injected with aluminium hydroxide adjuvanted vaccine. Administration of foot and mouth disease vaccine had no apparent influence on the tuberculin responses of either guinea pigs or cattle, nor did it influence the level of anti-M. bovis antibodies in cattle.

Severely dry skin: clinical evaluation of a highly effective therapeutic lotion.

Four clinical studies are presented on a recently introduced therapeutic lotion for severely dry skin. Two monadic single-blind efficacy studies showed that hands of subjects treated with the product (Lotion V) were significantly improved over untreated hands. Following the completion of a regression study, two subsequent double-blind comparative studies showed Lotion V to be significantly more effective than a well-established therapeutic lotion (Lotion K) for certain major signs and symptoms of dry skin. Results were derived from both objective clinical evaluation by investigating dermatologists and subjective evaluation by participating volunteers.