355 research outputs found
Magnetic fullerenes inside single-wall carbon nanotubes
C59N magnetic fullerenes were formed inside single-wall carbon nanotubes by
vacuum annealing functionalized C59N molecules encapsulated inside the tubes. A
hindered, anisotropic rotation of C59N was deduced from the temperature
dependence of the electron spin resonance spectra near room temperature.
Shortening of spin-lattice relaxation time, T_1, of C59N indicates a reversible
charge transfer toward the host nanotubes above K. Bound C59N-C60
heterodimers are formed at lower temperatures when C60 is co-encapsulated with
the functionalized C59N. In the 10-300 K range, T_1 of the heterodimer shows a
relaxation dominated by the conduction electrons on the nanotubes
Electronic density of states derived from thermodynamic critical field curves for underdoped La-Sr-Cu-O
Thermodynamic critical field curves have been measured for
over the full range of carrier concentrations
where superconductivity occurs in order to determine changes in the normal
state density of states with carrier concentration. There is a substantial
window in the plane where the measurements are possible because the
samples are both thermodynamically reversible and the temperature is low enough
that vortex fluctuations are not important. In this window, the data fit
Hao-Clem rather well, so this model is used to determine and
for each temperature and carrier concentration. Using N(0) and the ratio of the
energy gap to transition temperature, , as fitting
parameters, the curves give over the
whole range of . Values of N(0) remain rather constant in the optimum-doped
and overdoped regime, but drops quickly toward zero in the underdoped regime.
Dynamics of the Local Moment Induced by Nonmagnetic Defects in Cuprates
We present a study of the spin dynamics of magnetic defects induced by Li
substitution of the plane Cu in the normal state of YBaCuO. The
fluctuations of the coupled Cu magnetic moments in the vicinity of Li are
probed by near-neighbour Y {\it and} Li NMR spin lattice relaxation.
The data indicates that the magnetic perturbation fluctuates as a single entity
with a correlation time which scales with the local static
susceptibility. This behaviour is reminiscent of the low Kondo state of
magnetic impurities in conventional metals. Surprisingly it extends well above
the ``Kondo'' temperature for the underdoped pseudogapped case.Comment: 4 pages, 5 figures (same), major modifications to text, accepted in
PR
Hysteretic behavior of the vortex lattice at the onset of the second peak for HgBaCuO superconductor
By means of local Hall probe ac and dc permeability measurements we
investigated the phase diagram of vortex matter for the HgBaCuO superconductor in the regime near the critical temperature. The second peak
line, , in contrast to what is usually assumed, doesn't terminate
at the critical temperature. Our local ac permeability measurements revealed
pronounced hysteretic behavior and thermomagnetic history effects near the
onset of the second peak, giving evidence for a phase transition of vortex
matter from an ordered qausilattice state to a disordered glass
The GRA Beam-Splitter Experiments and Particle-Wave Duality of Light
Grangier, Roger and Aspect (GRA) performed a beam-splitter experiment to
demonstrate the particle behaviour of light and a Mach-Zehnder interferometer
experiment to demonstrate the wave behaviour of light. The distinguishing
feature of these experiments is the use of a gating system to produce near
ideal single photon states. With the demonstration of both wave and particle
behaviour (in two mutually exclusive experiments) they claim to have
demonstrated the dual particle-wave behaviour of light and hence to have
confirmed Bohr's principle of complementarity. The demonstration of the wave
behaviour of light is not in dispute. But we want to demonstrate, contrary to
the claims of GRA, that their beam-splitter experiment does not conclusively
confirm the particle behaviour of light, and hence does not confirm
particle-wave duality, nor, more generally, does it confirm complementarity.
Our demonstration consists of providing a detailed model based on the Causal
Interpretation of Quantum Fields (CIEM), which does not involve the particle
concept, of GRA's which-path experiment. We will also give a brief outline of a
CIEM model for the second, interference, GRA experiment.Comment: 24 pages, 4 figure
How to detect fluctuating order in the high-temperature superconductors
We discuss fluctuating order in a quantum disordered phase proximate to a
quantum critical point, with particular emphasis on fluctuating stripe order.
Optimal strategies for extracting information concerning such local order from
experiments are derived with emphasis on neutron scattering and scanning
tunneling microscopy. These ideas are tested by application to two model
systems - the exactly solvable one dimensional electron gas with an impurity,
and a weakly-interacting 2D electron gas. We extensively review experiments on
the cuprate high-temperature superconductors which can be analyzed using these
strategies. We adduce evidence that stripe correlations are widespread in the
cuprates. Finally, we compare and contrast the advantages of two limiting
perspectives on the high-temperature superconductor: weak coupling, in which
correlation effects are treated as a perturbation on an underlying metallic
(although renormalized) Fermi liquid state, and strong coupling, in which the
magnetism is associated with well defined localized spins, and stripes are
viewed as a form of micro-phase separation. We present quantitative indicators
that the latter view better accounts for the observed stripe phenomena in the
cuprates.Comment: 43 pages, 11 figures, submitted to RMP; extensively revised and
greatly improved text; one new figure, one new section, two new appendices
and more reference
Affordable flow cytometry for enumeration of absolute CD4(+ )T-lymphocytes to identify subtype C HIV-1 infected adults requiring antiretroviral therapy (ART) and monitoring response to ART in a resource-limited setting
BACKGROUND: The World Health Organization (WHO)'s "3 × 5 program" has spurred efforts to place 3 million people on combination antiretroviral therapy (ART) for treatment of AIDS in resource-limited countries. Paradoxically, the cost of CD4(+ )T-lymphocyte count essential for decision-making to commence HIV positive adults on ART as well as for monitoring responses to ART remains unaffordable in most resource-limited countries. Thus, low-cost methods for enumerating CD4(+ )T-lymphocyte are urgently needed. OBJECTIVE: To evaluate Cyflow cytometry (Cyflow SL, Partec, Munster, Germany) for enumeration of absolute CD4(+ )T-lymphocyte in subtype C HIV-1 seropositive subjects using FACSCount (Becton and Dickinson, Immunocytometry Systems, San Jose, CA, USA) as the "predicate method". METHODS: A total of 150 HIV-1 seropositive subjects were included in the evaluation exercise. Fifty-eight specimens were collected from pregnant HIV-1 seropositive women (subtype C drug resistance study). Twenty-seven specimens were collected from women and their spouses with AIDS followed in a Duke ART study to assess the immunologic and virologic responses to generic ART, comprising Stavudine, Lamivudine and Nevirapine (Stalanev, Varichem Labs, Harare, Zimbabwe). Sixty-five specimens were collected from AIDS patients enrolled in an ongoing Kaposi Sarcoma (KS) study to investigate impact of ART on KS progression. Enumeration of CD4(+ )T-lymphocytes using FACSCount is routinely conducted for all the three studies. The Medical Research Council of Zimbabwe and Medicines Control Authority of Zimbabwe approved the studies. Whole blood was collected in EDTA vacutainer tubes and aliquoted into two tubes (200 μL in each). CD4(+ )T-lymphocyte counts were enumerated using a Cyflow counter, in the Department of Immunology and a FACSCount in the Department of Obstetrics and Gynaecology within 6 hours of phlebotomy following manufacturers' instructions. RESULTS: Using linear regression analysis, there was a very strong correlation (R = 0.991) between the overall CD4(+ )T-lymphocyte counts obtained by FACSCount and those obtained by Cyflow. When data analysis was stratified by study groups, there was a strong correlation between the FACSCount and Cyflow CD4(+ )T-lymphocyte counts from subjects in the three independent studies; Subtype C resistance (R(2 )= 0.987), Duke ART (R(2 )= 0.980) and KS (R(2 )= 0.994), Table 1. Using Bland-Altman plots, the overall, absolute CD4(+ )T lymphocytes obtained by the two methods were in excellent agreement (mean difference 1.21, 95% Confidence Interval {CI): -2.1 to 3.3). For the 0–250 CD4(+ )T-lymphocytes range, the CD4 counts obtained using FACSCount were also in good agreement with those obtained using Cyflow counter (mean difference = 2.6 cells/μL, 95% CI: -1.1 to 6.3). Similarly, in the 251–500 (mean difference 1.0, cells/μL, 95% CI: -3.7 to 5.6) and the 501–1200 (mean difference = 0.29 cells/μL, 95% CI: -8.1 to 8.7) CD4 T-lymphocytes range, good agreement was observed. CONCLUSION: The Cyflow counter is as accurate as the FACSCount in enumerating absolute CD4(+ )T-lymphocytes in the range 1–1200 cells/μL. Cyflow cytometry is relatively affordable, easy to use technology that is useful not only in identifying HIV seropositive individuals who require ART but also for monitoring immunologic responses to ART
Calpain-Catalyzed Proteolysis of Human dUTPase Specifically Removes the Nuclear Localization Signal Peptide
Calpain proteases drive intracellular signal transduction via specific proteolysis of multiple substrates upon Ca(2+)-induced activation. Recently, dUTPase, an enzyme essential to maintain genomic integrity, was identified as a physiological calpain substrate in Drosophila cells. Here we investigate the potential structural/functional significance of calpain-activated proteolysis of human dUTPase.Limited proteolysis of human dUTPase by mammalian m-calpain was investigated in the presence and absence of cognate ligands of either calpain or dUTPase. Significant proteolysis was observed only in the presence of Ca(II) ions, inducing calpain action. The presence or absence of the dUTP-analogue α,β-imido-dUTP did not show any effect on Ca(2+)-calpain-induced cleavage of human dUTPase. The catalytic rate constant of dUTPase was unaffected by calpain cleavage. Gel electrophoretic analysis showed that Ca(2+)-calpain-induced cleavage of human dUTPase resulted in several distinctly observable dUTPase fragments. Mass spectrometric identification of the calpain-cleaved fragments identified three calpain cleavage sites (between residues (4)SE(5); (7)TP(8); and (31)LS(32)). The cleavage between the (31)LS(32) peptide bond specifically removes the flexible N-terminal nuclear localization signal, indispensable for cognate localization.Results argue for a mechanism where Ca(2+)-calpain may regulate nuclear availability and degradation of dUTPase
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