13,439 research outputs found
Complex Organic Materials in the HR 4796A Disk?
The red spectral shape of the visible to near infrared reflectance spectrum
of the sharply-edged ring-like disk around the young main sequence star HR
4796A was recently interpreted as the presence of tholin-like complex organic
materials which are seen in the atmosphere and surface of Titan and the
surfaces of icy bodies in the solar system. However, we show in this Letter
that porous grains comprised of common cosmic dust species (amorphous silicate,
amorphous carbon, and water ice) also closely reproduce the observed
reflectance spectrum, suggesting that the presence of complex organic materials
in the HR 4796 disk is still not definitive.Comment: 6 pages, 3 figures; To be published in The Astrophysical Journal
Letter
Hydrogenation and Hydro-Carbonation and Etching of Single-Walled Carbon Nanotubes
We present a systematic experimental investigation of the reactions between
hydrogen plasma and single-walled carbon nanotubes (SWNTs) at various
temperatures. Microscopy, infrared (IR) and Raman spectroscopy and electrical
transport measurements are carried out to investigate the properties of SWNTs
after hydrogenation. Structural deformations, drastically reduced electrical
conductance and increased semiconducting nature of SWNTs upon sidewall
hydrogenation are observed. These changes are reversible upon thermal annealing
at 500C via dehydrogenation. Harsh plasma or high temperature reactions lead to
etching of nanotube likely via hydro-carbonation. Smaller SWNTs are markedly
less stable against hydro-carbonation than larger tubes. The results are
fundamental and may have implications to basic and practical applications
including hydrogen storage, sensing, band-gap engineering for novel electronics
and new methods of manipulation, functionalization and etching of nanotubes.Comment: 3 pages, 4 figure
Effective complexity of stationary process realizations
The concept of effective complexity of an object as the minimal description
length of its regularities has been initiated by Gell-Mann and Lloyd. The
regularities are modeled by means of ensembles, that is probability
distributions on finite binary strings. In our previous paper we propose a
definition of effective complexity in precise terms of algorithmic information
theory. Here we investigate the effective complexity of binary strings
generated by stationary, in general not computable, processes. We show that
under not too strong conditions long typical process realizations are
effectively simple. Our results become most transparent in the context of
coarse effective complexity which is a modification of the original notion of
effective complexity that uses less parameters in its definition. A similar
modification of the related concept of sophistication has been suggested by
Antunes and Fortnow.Comment: 14 pages, no figure
Energy scale independence of Koide's relation for quark and lepton masses
Koide's mass relation of charged leptons has been extended to quarks and
neutrinos, and we prove here that this relation is independent of energy scale
in a huge energy range from to . By using the
parameters , and to describe the deviations of quarks and
neutrinos from the exact Koide's relation, we also check the quark-lepton
complementarity of masses such as , and show that it is also independent (or insensitive) of energy scale.Comment: 16 Latex pages, 2 figures, final version to appear in PR
Targeting Metabolic Modulation and Mitochondrial Dysfunction in the Treatment of Heart Failure
Despite significant improvements in morbidity and mortality with current evidence-based pharmaceutical-based treatment of heart failure (HF) over the previous decades, the burden of HF remains high. An alternative approach is currently being developed, which targets myocardial energy efficiency and the dysfunction of the cardiac mitochondria. Emerging evidence suggests that the insufficient availability of ATP to the failing myocardium can be attributed to abnormalities in the myocardial utilisation of its substrates rather than an overall lack of substrate availability. Therefore, the development of potential metabolic therapeutics has commenced including trimetazidine, ranolazine and perhexiline, as well as specific mitochondrial-targeting pharmaceuticals, such as elamipretide. Large randomised controlled trials are required to confirm the role of metabolic-modulating drugs in the treatment of heart failure, but early studies have been promising in their possible efficacy for the management of heart failure in the future
Generalization of Friedberg-Lee Symmetry
We study the possible origin of Friedberg-Lee symmetry. First, we propose the
generalized Friedberg-Lee symmetry in the potential by including the scalar
fields in the field transformations, which can be broken down to the FL
symmetry spontaneously. We show that the generalized Friedberg-Lee symmetry
allows a typical form of Yukawa couplings, and the realistic neutrino masses
and mixings can be generated via see-saw mechanism. If the right-handed
neutrinos transform non-trivially under the generalized Friedberg-Lee symmetry,
we can have the testable TeV scale see-saw mechanism. Second, we present two
models with the global flavour symmetry in the lepton
sector. After the flavour symmetry breaking, we can obtain the charged lepton
masses, and explain the neutrino masses and mixings via see-saw mechanism.
Interestingly, the complete neutrino mass matrices are similar to those of the
above models with generalized Friedberg-Lee symmetry. So the Friedberg-Lee
symmetry is the residual symmetry in the neutrino mass matrix after the
flavour symmetry breaking.Comment: 16 pages, no figure, version published in PR
Fermion Masses and Mixings in GUTs with Non-Canonical U(1)_Y
We discuss fermion masses and mixings in models derived from orbifold GUTs
such that gauge coupling unification is achieved without low energy
supersymmetry by utilizing a non-canonical U(1)_Y. A gauged U(1)_X flavor
symmetry plays an essential role, and the Green-Schwarz mechanism is invoked in
anomaly cancellations. Models containing vector-like particles with masses
close to M_{GUT} are also discussed.Comment: 18 page
- …