1,138 research outputs found
Evidence for complex order parameter in La_{1.83}Sr_{0.17}CuO_4
The in-plane magnetic field penetration depth (\lambda_{ab}) in
single-crystal La_{1.83}Sr_{0.17}CuO_4 was investigated by means of the
muon-spin rotation (\muSR) technique. The temperature dependence of
\lambda^{-2}_{ab} has an inflection point around 10-15K, suggesting the
presence of two superconducting gaps: a large gap (\Delta_1^d) with d-wave and
a small gap (\Delta_2^s) with s-wave symmetry. The zero-temperature values of
the gaps at \mu_0H=0.02T were found to be \Delta_1^d(0)=8.2(2)meV and
\Delta_2^s(0)=1.57(8)meV.Comment: 5 pages, 3 figure
Mixed order parameter symmetries in cuprate superconductors
The recent observation of an inflection point in the temperature dependence
of the in-plane magnetic field dependence (lambda_ab) is investigated within a
two-band model with coupled order parameters of different symmetries. While the
dominant order parameter has d-wave symmetry, the smaller one is of s-wave
symmetry. Superconductivity is robust in the d-wave channel and induced via
interband interactions in the s-wave subsystem.Comment: 10 pages, 4 figure
Probing helium reionization with kinetic Sunyaev Zel'dovich tomography
Reionization of helium is expected to occur at redshifts and have
important consequences for quasar populations, galaxy formation, and the
morphology of the intergalactic medium, but there is little known empirically
about the process. Here we show that kinetic Sunyaev-Zeldovich (kSZ)
tomography, based on the combination of CMB measurements and galaxy surveys,
can be used to infer the primordial helium abundance as well as the time and
duration of helium reionization. We find a high-significance detection at
can be expected from Vera Rubin Observatory and CMB-S4 in the
near future. A more robust characterization of helium reionization will require
next-generation experiments like MegaMapper (a proposed successor to DESI) and
CMB-HD.Comment: 4+2 pages, 2 figures, comments welcom
Two-band Eliashberg equations and the experimental Tc of the diboride Mg1-xAlxB2
The variation of the superconducting critical temperature Tc as a function of
x in the diboride Mg1-xAlxB2 has been studied in the framework of the two-bands
Eliashberg theory and traditional phonon coupling mechanism. We have solved the
two-bands Eliashberg equations using first-principle calculations or simple
assumptions for the variation of the relevant physical quantities. We have
found that the experimental Tc curve can be explained only if the Coulomb
pseudopotential changes with x by tuning the Fermi level toward the sigma band
edge. In polycrystal samples the x dependence of the sigma and pi-band gap has
been found and is in agreement with experiments.Comment: 6 pages, 7 figure
Three Dimensional Electrical Impedance Tomography
The electrical resistivity of mammalian tissues varies widely and is correlated with physiological
function. Electrical impedance tomography (EIT) can be used to probe such variations in vivo, and offers a
non-invasive means of imaging the internal conductivity distribution of the human body. But the
computational complexity of EIT has severe practical limitations, and previous work has been restricted to
considering image reconstruction as an essentially two-dimensional problem. This simplification can limit
significantly the imaging capabilities of EIT, as the electric currents used to determine the conductivity variations will not in general be confined to a two-dimensional plane. A few studies have attempted three-dimensional EIT image reconstruction, but have not yet succeeded in generating images of a quality suitable for clinical applications. Here we report the development of a three-dimensional EIT system with greatly improved imaging capabilities, which combines our 64-electrode data-collection apparatus with customized matrix inversion techniques. Our results demonstrate the practical potential of EIT for clinical applications, such as lung or brain imaging and diagnostic screening
The evolution of bicontinuous polymeric nanospheres in aqueous solution
Complex polymeric nanospheres in aqueous solution are desirable for their promising potential in encapsulation and templating applications. Understanding how they evolve in solution enables better control of the final structures. By unifying insights from cryoTEM and small angle X-ray scattering (SAXS), we present a mechanism for the development of bicontinuous polymeric nanospheres (BPNs) in aqueous solution from a semi-crystalline comb-like block copolymer that possesses temperature-responsive functionality. During the initial stages of water addition to THF solutions of the copolymer the aggregates are predominantly vesicles; but above a water content of 53% irregular aggregates of phase separated material appear, often microns in diameter and of indeterminate shape. We also observe a cononsolvency regime for the copolymer in THF–water mixtures from 22 to 36%. The structured large aggregates gradually decrease in size throughout dialysis, and the BPNs only appear upon cooling the fully aqueous dispersions from 35 °C to 5 °C. Thus, the final BPNs are ultimately the result of a reversible temperature-induced morphological transition
Antimalarial activity of cupredoxins: the interaction of Plasmodium Merozoite Surface Protein 119 (MSP119) and Rusticyanin
Background: The interaction of MSP119 with the cupredoxin azurin inhibits the growth of Plasmodium falciparum in red blood cells. Results: Rusticyanin forms a well-defined complex with MSP119 upon binding at the same surface area than inhibitory antibodies. Conclusion: Rusticyanin becomes an excellent therapeutic agent for malaria. Significance: Knowing the rusticyanin- MSP119 interface will allow the design of novel anti-malarial drugsJunta de Andalucía P08-CVI-3876, BIO198Ministerio de Economía y Competitividad SAF2011- 26611Fundación Séneca de la Región de Murcia 15354/PI/10Ministerio de Ciencia e Innovación BFU2010-19451Medical Research Council U117574558, U11753206
Multiple Dark Matter as a self-regulating mechanism for dark sector interactions
(Abridged) Present cosmological constraints and the absence of a direct
detection and identification of any dark matter particle candidate leave room
to the possibility that the dark sector of the Universe be actually more
complex than it is normally assumed. In particular, more than one new
fundamental particle could be responsible for the observed dark matter density
in the Universe, and possible new interactions between dark energy and dark
matter might characterize the dark sector. In the present work, we investigate
the possibility that two dark matter particles exist in nature, with identical
physical properties except for the sign of their coupling constant to dark
energy. Extending previous works on similar scenarios, we study the evolution
of the background cosmology as well as the growth of linear density
perturbations for a wide range of parameters of such model. Interestingly, our
results show how the simple assumption that dark matter particles carry a
"charge" with respect to their interaction with the dark energy field allows
for new long-range scalar forces of gravitational strength in the dark sector
without conflicting with present observations both at the background and linear
levels. Our scenario does not introduce new parameters with respect to the case
of a single dark matter species for which such strong dark interactions have
been already ruled out.Comment: 18 pages, 1 table, 9 figures. Invited paper for the special issue of
Annalen der Physik on "Dark Matter" (Ed. Matthias Bartelmann and Volker
Springel
Search for High Energy Gamma Rays from an X-ray Selected Blazar Sample
Our understanding of blazars has been greatly increased in recent years by
extensive multi-wavelength observations, particularly in the radio, X-ray and
gamma-ray regions. Over the past decade the Whipple 10m telescope has
contributed to this with the detection of 5 BL Lacertae objects at very high
gamma-ray energies. The combination of multi-wavelength data has shown that
blazars follow a well-defined sequence in terms of their broadband spectral
properties. Together with providing constraints on emission models, this
information has yielded a means by which potential sources of TeV emission may
be identified and predictions made as to their possible gamma-ray flux. We have
used the Whipple telescope to search for TeV gamma-ray emission from eight
objects selected from a list of such candidates. No evidence has been found for
VHE emission from the objects in our sample, and upper limits have been derived
for the mean gamma-ray flux above 390GeV. These flux upper limits are compared
with the model predictions and the implications of our results for future
observations are discussed.Comment: 15 pages, 2 figures, Accepted for publication in Ap
A Search for Dark Matter Annihilation with the Whipple 10m Telescope
We present observations of the dwarf galaxies Draco and Ursa Minor, the local
group galaxies M32 and M33, and the globular cluster M15 conducted with the
Whipple 10m gamma-ray telescope to search for the gamma-ray signature of
self-annihilating weakly interacting massive particles (WIMPs) which may
constitute astrophysical dark matter (DM). We review the motivations for
selecting these sources based on their unique astrophysical environments and
report the results of the data analysis which produced upper limits on excess
rate of gamma rays for each source. We consider models for the DM distribution
in each source based on the available observational constraints and discuss
possible scenarios for the enhancement of the gamma-ray luminosity. Limits on
the thermally averaged product of the total self-annihilation cross section and
velocity of the WIMP, , are derived using conservative estimates for
the magnitude of the astrophysical contribution to the gamma-ray flux. Although
these limits do not constrain predictions from the currently favored
theoretical models of supersymmetry (SUSY), future observations with VERITAS
will probe a larger region of the WIMP parameter phase space, and
WIMP particle mass (m_\chi).Comment: 33 pages, 12 figures, accepted for publication in the Astrophysical
Journa
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