151 research outputs found
Contaminations contaminate common databases
The polymerase chain reaction (PCR) is a very powerful method to detect and identify pathogens. The high sensitivity of the method, however, comes with a cost; any of the millions of artificial DNA copies generated by PCR can serve as a template in a following experiment. If not identified as contaminations, these may result in erroneous conclusions on the occurrence of the pathogen, thereby inflating estimates of host range and geographic distribution. In the present paper, we evaluate whether several published records of avian haemosporidian parasites, in either unusual host species or geographical regions, might stem from PCR contaminations rather than novel biological findings. The detailed descriptions of these cases are shedding light upon the steps in the work process that might lead to PCR contaminations. By increasing the awareness of this problem, it will aid in developing procedures that keep these to a minimum. The examples in the present paper are from haemosporidians of birds, however the problem of contaminations and suggested actions should apply generally to all kinds of PCR‐based identifications, not just of parasites and pathogens
Electron conductive three-dimensional polymer of cuboidal C60
Single crystals of three-dimensional (3D) C60 polymer were prepared by the topotactic conversion of two-dimensional (2D) C60 polymer single crystals at a pressure of 15 GPa at 600°C. The x-ray single crystal study revealed that the 3D C60 polymer crystallized in a body centered orthorhombic space group Immm, and spherical C60 monomer units were substantially deformed to rectangular parallelepiped (cuboidal) shapes, each unit being bonded to eight cuboidal C60 neighbors via [3+3] cycloaddition. The 3D C60 polymer was electron conductive, in contrast with the nonconductive behavior of 2D polymers
Strongly linked current flow in polycrystalline forms of the new superconductor MgB2
The discovery of superconductivity at 39 K in MgB2[1] raises many issues. One
of the central questions is whether this new superconductor resembles a
high-temperature-cuprate superconductor or a low-temperature metallic
superconductor in terms of its current carrying characteristics in applied
magnetic fields. In spite of the very high transition temperatures of the
cuprate superconductors, their performance in magnetic fields has several
drawbacks[2]. Their large anisotropy restricts high bulk current densities to
much less than the full magnetic field-temperature (H-T) space over which
superconductivity is found. Further, weak coupling across grain boundaries
makes transport current densities in untextured polycrystalline forms low and
strongly magnetic field sensitive[3,4]. These studies of MgB2 address both
issues. In spite of the multi-phase, untextured, nano-scale sub-divided nature
of our samples, supercurrents flow throughout without the strong sensitivity to
weak magnetic fields characteristic of Josephson-coupled grains[3].
Magnetization measurements over nearly all of the superconducting H-T plane
show good temperature scaling of the flux pinning force, suggestive of a
current density determined by flux pinning. At least two length scales are
suggested by the magnetization and magneto optical (MO) analysis but the cause
of this seems to be phase inhomogeneity, porosity, and minority insulating
phase such as MgO rather than by weakly coupled grain boundaries. Our results
suggest that polycrystalline ceramics of this new class of superconductor will
not be compromised by the weak link problems of the high temperature
superconductors, a conclusion with enormous significance for applications if
higher temperature analogs of this compound can be discovered
Giant anharmonicity and non-linear electron-phonon coupling in MgB; A combined first-principles calculations and neutron scattering study
We report first-principles calculations of the electronic band structure and
lattice dynamics for the new superconductor MgB. The excellent agreement
between theory and our inelastic neutron scattering measurements of the phonon
density of states gives confidence that the calculations provide a sound
description of the physical properties of the system. The numerical results
reveal that the in-plane boron phonons (with E symmetry) near the
zone-center are very anharmonic, and are strongly coupled to the partially
occupied planar B bands near the Fermi level. This giant anharmonicity
and non-linear electron-phonon coupling is key to explaining the observed high
T and boron isotope effect in MgBComment: In this revised version (to appear in PRL) we also discuss the boron
isotope effect. Please visit http://www.ncnr.nist.gov/staff/taner/mgb2 for
detail
Superconductivity in the non-oxide Perovskite MgCNi3
The oxide perovskites are a large family of materials with many important
physical properties. Of particular interest has been the fact that this
structure type provides an excellent structural framework for the existence of
superconductivity. The high Tc copper oxides are the most famous examples of
superconducting perovskites, but there are many others [1]. Intermetallic
compounds have been the source of many superconducting materials in the past,
but they have been eclipsed in recent years by the perovskite oxides. The
recent discovery of superconductivity in MgB2 [2] suggests that intermetallic
compounds with simple structure types are worth serious reconsideration as
sources of new superconducting materials. Here we report the observation of
superconductivity at 8 K in the perovskite structure intermetallic compound
MgCNi3, linking what appear at first sight to be mutually exclusive classes of
superconducting materials. The observation of superconductivity in MgCNi3
indicates that MgB2 will not be the only one of its kind within the chemical
paradigm that it suggests for new superconducting materials
Analysis of the BRAF V600E mutation in primary cutaneous melanoma
ABSTRACT. BRAF V600E is the most common mutation in cutaneous melanomas, and has been described in 30-72% of such cases. This mutation results in the substitution of valine for glutamic acid at position 600 of the BRAF protein, which consequently becomes constitutively activated. The present study investigated the BRAF V600E mutation frequency and its clinical implications in a group of 77 primary cutaneous melanoma patients treated in a cancer reference center in Brazil. Mutation analysis 2841 BRAF V600E mutation of primary cutaneous melanomas in Brazil ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 13 (2): 2840-2848 (2014) was accomplished by polymerase chain reaction, restriction fragment length polymorphism, and automated DNA sequencing. The chi-squared and Fischer exact tests were used for comparative analyses. The BRAF V600E mutation was detected in 54/77 (70.1%) melanoma subjects. However, no statistically significant association was found between the presence of the mutation and clinical or prognostic parameters. Our results demonstrated that the BRAF V600E mutation is a common event in melanomas, representing an important molecular target for novel therapeutic approaches in such tumors
Thin Film Magnesium Boride Superconductor with Very High Critical Current Density and Enhanced Irreversibility Field
The discovery of superconductivity at 39 K in magnesium diboride offers the
possibility of a new class of low-cost, high-performance superconducting
materials for magnets and electronic applications. With twice the critical
temperature of Nb_3Sn and four times that of Nb-Ti alloy, MgB_2 has the
potential to reach much higher fields and current densities than either of
these technological superconductors. A vital prerequisite, strongly linked
current flow, has already been demonstrated even at this early stage. One
possible drawback is the observation that the field at which superconductivity
is destroyed is modest. Further, the field which limits the range of practical
applications, the irreversibility field H*(T), is ~7 T at liquid helium
temperature (4.2 K), significantly lower than ~10 T for Nb-Ti and ~20 T for
Nb_3Sn. Here we show that MgB_2 thin films can exhibit a much steeper
temperature dependence of H*(T) than is observed in bulk materials, yielding
H*(4.2 K) above 14 T. In addition, very high critical current densities at 4.2
K, 1 MA/cm_2 at 1 T and 10_5 A/cm_2 at 10 T, are possible. These data
demonstrate that MgB_2 has credible potential for high-field superconducting
applications.Comment: 4 pages pdf, submitted to Nature 3/20/0
Resistance to First-Line Anti-TB Drugs Is Associated with Reduced Nitric Oxide Susceptibility in Mycobacterium tuberculosis
Background and objective: The relative contribution of nitric oxide (NO) to the killing of Mycobacterium tuberculosis in human tuberculosis (TB) is controversial, although this has been firmly established in rodents. Studies have demonstrated that clinical strains of M. tuberculosis differ in susceptibility to NO, but how this correlates to drug resistance and clinical outcome is not known. Methods: In this study, 50 sputum smear- and culture-positive patients with pulmonary TB in Gondar, Ethiopia were included. Clinical parameters were recorded and drug susceptibility profile and spoligotyping patterns were investigated. NO susceptibility was studied by exposing the strains to the NO donor DETA/NO. Results: Clinical isolates of M. tuberculosis showed a dose- and time-dependent response when exposed to NO. The most frequent spoligotypes found were CAS1-Delhi and T3_ETH in a total of nine known spoligotypes and four orphan patterns. There was a significant association between reduced susceptibility to NO (>10% survival after exposure to 1mM DETA/NO) and resistance against first-line anti-TB drugs, in particular isoniazid (INH). Patients infected with strains of M. tuberculosis with reduced susceptibility to NO showed no difference in cure rate or other clinical parameters, but a tendency towards lower rate of weight gain after two months of treatment. Conclusion: There is a correlation between resistance to first-line anti-TB drugs and reduced NO susceptibility in clinical strains of M. tuberculosis. Further studies including the mechanisms of reduced NO susceptibility are warranted and could identify targets for new therapeutic interventions
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