249 research outputs found
Role of interband scattering in neutron irradiated MgB thin films by Scanning Tunneling Spectroscopy measurements
A series of MgB thin films systematically disordered by neutron
irradiation have been studied by Scanning Tunneling Spectroscopy. The c-axis
orientation of the films allowed a reliable determination of local density of
state of the band. With increasing disorder, the conductance peak moves
towards higher voltages and becomes lower and broader, indicating a monotonic
increase of the gap and of the broadening parameter. These results are
discussed in the frame of two-band superconductivity.Comment: The text will be submitted in Latex format, and the corresponding pdf
file should take 6 pages. There are 5 figures (eps files submitted) and 1
tabl
Neutron Irradiation of Mg11B2 : From the Enhancement to the Suppression of Superconducting Properties
In this letter we present the effect of neutron irradiation up to fluences of
3.9 1019 n/cm2 on the superconducting properties of MgB2. In order to obtain a
disorder structure homogeneously distributed, the experiment was carried out on
bulk samples prepared with the 11B isotope. Up to fluences of 1018 n/cm2 the
critical temperature is slightly diminished (36 K) and the superconducting
properties are significantly improved; the upper critical field is increased
from 13.5 T to 20.3 T at 12 K and the irreversibility field is doubled at 5 K.
For larger neutron fluences the critical temperature is suppressed down to 12 K
and the superconducting properties come out strongly degraded.Comment: 13 pages, 4 figures. Submitted to Appl.Phys.Let
Enhanced flux pinning in neutron irradiated MgB2
We study the effect of neutron irradiation on the critical current density Jc
of isotopically pure polycrystalline Mg11B2 samples. For fluences in the range
1017-1018 cm-2, Jc is enhanced and its dependence on magnetic field is
significantly improved: we demonstrate that, in this regime, point-like pinning
centers are effectively introduced in the system proportionally to the neutron
fluence. Instead, for larger fluences, a strong suppression of the critical
temperature accompanied by a decrease of both the upper critical field Bc2 and
Jc is found.Comment: 13 pages, 3 igure
Systematic study of disorder induced by neutron irradiation in MgB2 thin films
The effects of neutron irradiation on normal state and superconducting
properties of epitaxial magnesium diboride thin films are studied up to
fluences of 1020 cm-2. All the properties of the films change systematically
upon irradiation. Critical temperature is suppressed and, at the highest
fluence, no superconducting transition is observed down to 1.8 K. Residual
resistivity progressively increases from 1 to 190 microohmcm; c axis expands
and then saturates at the highest damage level. We discuss the mechanism of
damage through the comparison with other damage procedures. The normal state
magnetoresistivity of selected samples measured up to high fields (28 and 45T)
allows to determine unambiguously the scattering rates in each band; the
crossover between the clean and dirty limit in each sample can be monitored.
This set of samples, with controlled amount of disorder, is suitable to study
the puzzling problem of critical field in magnesium diboride thin films. The
measured critical field values are extremely high (of the order of 50T in the
parallel direction at low fluences) and turns out to be rather independent on
the experimental resistivity, at least at low fluences. A simple model to
explain this phenomenology is presented.Comment: 29 pages, 6 figures, accepted for publication on J. of Applied
Physic
Proteome Profiling of Breast Tumors by Gel Electrophoresis and Nanoscale Electrospray Ionization Mass Spectrometry
We have conducted proteome-wide analysis of fresh surgery specimens derived from breast cancer patients, using an approach that integrates size-based intact protein fractionation, nanoscale liquid separation of peptides, electrospray ion trap mass spectrometry, and bioinformatics. Through this approach, we have acquired a large amount of peptide fragmentation spectra from size-resolved fractions of the proteomes of several breast tumors, tissue peripheral to the tumor, and samples from patients undergoing noncancer surgery. Label-free quantitation was used to generate protein abundance maps for each proteome and perform comparative analyses. The mass spectrometry data revealed distinct qualitative and quantitative patterns distinguishing the tumors from healthy tissue as well as differences between metastatic and non-metastatic human breast cancers including many established and potential novel candidate protein biomarkers. Selected proteins were evaluated by Western blotting using tumors grouped according to histological grade, size, and receptor expression but differing in nodal status. Immunohistochemical analysis of a wide panel of breast tumors was conducted to assess expression in different types of breast cancers and the cellular distribution of the candidate proteins. These experiments provided further insights and an independent validation of the data obtained by mass spectrometry and revealed the potential of this approach for establishing multimodal markers for early metastasis, therapy outcomes, prognosis, and diagnosis in the future. © 2008 American Chemical Society
Excitation Spectrum and Superexchange Pathways in the Spin Dimer VODPO_4 . 1/2 D_2O
Magnetic excitations have been investigated in the spin dimer material
VODPO_4 \cdot 1/2 D_2O using inelastic neutron scattering. A dispersionless
magnetic mode was observed at an energy of 7.81(4) meV. The wavevector
dependence of the scattering intensityfrom this mode is consistent with the
excitation of isolated V^{4+} spin dimers with a V-V separation of 4.43(7) \AA.
This result is unexpected since the V-V pair previously thought to constitute
themagnetic dimer has a separation of 3.09 \AA. We identify an alternative V-V
pair as the likely magnetic dimer, which involves superexchange pathways
through a covalently bonded PO_4 group. This surprising result casts doubt on
the interpretation of (VO)_2P_2O_7 as a spin ladder.Comment: 4 pages, 4 postscript figures - identical to previous paper but
figure 2 and 3 hopefully more compatible .p
Magnetoresistivity in MgB2 as a probe of disorder in p- and s-bands
In this paper we present normal state magnetoresistivity data of magnesium
diboride epitaxial thin films with different levels of disorder, measured at
42K in magnetic fields up to 45 Tesla. Disorder was introduced in a controlled
way either by means of neutron irradiation or by carbon doping. From a
quantitative analysis of the magnetoresistivity curves with the magnetic field
either parallel or perpendicular to the plane of the film, we extract the ratio
of the scattering times in p- and s-bands. We demonstrate that the undoped
unirradiated thin film has p scattering times smaller than s ones; upon
irradiation, both bands become increasingly more disordered; eventually the
highly irradiated sample (neutron fluence 7.7X1017 cm-2) and the C-doped sample
have comparable scattering times in the two types of bands. This description of
the effect of disorder in the two kinds of bands on transport is consistent
with the residual resistivity values and with the temperature dependence of the
resistivity.Comment: 19 pages, 3 tables, 2 figure
Optimal selection of epitopes for TXP-immunoaffinity mass spectrometry
<p>Abstract</p> <p>Background</p> <p>Mass spectrometry (MS) based protein profiling has become one of the key technologies in biomedical research and biomarker discovery. One bottleneck in MS-based protein analysis is sample preparation and an efficient fractionation step to reduce the complexity of the biological samples, which are too complex to be analyzed directly with MS. Sample preparation strategies that reduce the complexity of tryptic digests by using immunoaffinity based methods have shown to lead to a substantial increase in throughput and sensitivity in the proteomic mass spectrometry approach. The limitation of using such immunoaffinity-based approaches is the availability of the appropriate peptide specific capture antibodies. Recent developments in these approaches, where subsets of peptides with short identical terminal sequences can be enriched using antibodies directed against short terminal epitopes, promise a significant gain in efficiency.</p> <p>Results</p> <p>We show that the minimal set of terminal epitopes for the coverage of a target protein list can be found by the formulation as a set cover problem, preceded by a filtering pipeline for the exclusion of peptides and target epitopes with undesirable properties.</p> <p>Conclusions</p> <p>For small datasets (a few hundred proteins) it is possible to solve the problem to optimality with moderate computational effort using commercial or free solvers. Larger datasets, like full proteomes require the use of heuristics.</p
Angiogenic factors: role in esophageal cancer, a brief review
Esophageal cancer has an aggressive behavior with rapid tumor mass growth and frequently poor prognosis; it is known as one of the most fatal types of cancer worldwide. The identification of potential molecular markers that can predict the response to treatment and the prognosis of this cancer has been subject of a vast investigation in the recent years. Among several molecules, various angiogenic factors that are linked to the tumor development, growth, and invasion, such as VEGF, HGF, angiopoietin-2, IL-6, and TGF-B1, were investigated. In this paper, the authors sought to review the role of these angiogenic factors in prognosis and hypothesize how they can be used as a treatment target.info:eu-repo/semantics/publishedVersio
Quantitative proteome landscape of the NCI-60 cancer cell lines
Here we describe a proteomic data resource for the NCI-60 cell lines generated by pressure cycling technology and SWATH mass spectrometry. We developed the DIA-expert software to curate and visualize the SWATH data, leading to reproducible detection of over 3,100 SwissProt proteotypic proteins and systematic quantification of pathway activities. Stoichiometric relationships of interacting proteins for DNA replication, repair, the chromatin remodeling NuRD complex, β-catenin, RNA metabolism, and prefoldins are more evident than that at the mRNA level. The data are available in CellMiner (discover.nci.nih.gov/cellminercdb and discover.nci.nih.gov/cellminer), allowing casual users to test hypotheses and perform integrative, cross-database analyses of multi-omic drug response correlations for over 20,000 drugs. We demonstrate the value of proteome data in predicting drug response for over 240 clinically relevant chemotherapeutic and targeted therapies. In summary, we present a novel proteome resource for the NCI-60, together with relevant software tools, and demonstrate the benefit of proteome analyses
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