13,454 research outputs found
Magnetic field-induced insulating behavior in highly oriented pyrolitic graphite
We propose an explanation for the apparent semimetal-insulator transition
observed in highly oriented pyrolitic graphite in the presence of magnetic
field perpendicular to the layers. We show that the magnetic field opens an
excitonic gap in the linear spectrum of the Coulomb interacting quasiparticles,
in a close analogy with the phenomenon of dynamical chiral symmetry breaking in
the relativistic theories of the 2+1-dimensional Dirac fermions. Our
strong-coupling appoach allows for a non-perturbative description of the
corresponding critical behavior
Behaviour of the Absorptive Part of the W Electromagnetic Vertex
The absorptive part of the vertex induced by massive fermion loops
is considered for different kinematical configurations. We show that the axial
part of this vertex is different from zero not only when massive fermions are
involved but also for massless fermion loops, if one of the W bosons is
space-like and the other is time-like. We also discuss in what sense Low's soft
photon theorem is satisfied.Comment: 17 pages, 1 figure, LaTe
Using Green Fluorescent Protein to Correlate Temperature and Fluorescence Intensity into Bacterial Systems
The unique and stunning spectroscopic properties of Green Fluorescent Protein (GFP) from the jellyfish Aequorea victoria, not to mention of its remarkable structural stability, have made it one of the most widely studied and used molecular tool in medicine, biochemistry, and cell biology. Its high fluorescent quantum yield is due to its chromophore, structure responsible of emitting green visible light when excited at 395 nm. Although it is noteworthy that there is enormous available information of the wonderful luminescent properties of GFP, the fact is that there are features and properties unexplored yet, particulary about its capabilities as molecular reporter in several biological processes. In this work, we used recombinant DNA technology to express the protein in bacteria; prepared the bacterial system both in liquid and solid media, and assembled an experimental set to expose those media to a laser beam; thereby we excited the protein chromophore and used emission spectroscopy in order to observe variations in fluorescence when the bacterial system is exposed to different temperatures
B fields in OB stars (BOB): The discovery of a magnetic field in a multiple system in the Trifid Nebula, one of the youngest star forming regions
Recent magnetic field surveys in O- and B-type stars revealed that about 10%
of the core-hydrogen-burning massive stars host large-scale magnetic fields.
The physical origin of these fields is highly debated. To identify and model
the physical processes responsible for the generation of magnetic fields in
massive stars, it is important to establish whether magnetic massive stars are
found in very young star-forming regions or whether they are formed in close
interacting binary systems.
In the framework of our ESO Large Program, we carried out low-resolution
spectropolarimetric observations with FORS2 in 2013 April of the three most
massive central stars in the Trifid nebula, HD164492A, HD164492C, and
HD164492D. These observations indicated a strong longitudinal magnetic field of
about 500-600G in the poorly studied component HD164492C. To confirm this
detection, we used HARPS in spectropolarimetric mode on two consecutive nights
in 2013 June.
Our HARPS observations confirmed the longitudinal magnetic field in
HD164492C. Furthermore, the HARPS observations revealed that HD164492C cannot
be considered as a single star as it possesses one or two companions. The
spectral appearance indicates that the primary is most likely of spectral type
B1-B1.5V. Since in both observing nights most spectral lines appear blended, it
is currently unclear which components are magnetic. Long-term monitoring using
high-resolution spectropolarimetry is necessary to separate the contribution of
each component to the magnetic signal. Given the location of the system
HD164492C in one of the youngest star formation regions, this system can be
considered as a Rosetta Stone for our understanding of the origin of magnetic
fields in massive stars.Comment: Five pages, six figures, accepted for publication in A&
Precipitation Process in Fe-Ni-Al-based Alloys
This chapter covers first the precipitation and coarsening processes in Fe-Ni-Al alloys aged artificially at high temperatures, as well as their effect on the mechanical properties. These results show the precipitation evolution, morphology of precipitates, coarsening kinetics and mechanical properties such as hardness. Additionally, the effect of alloying elements such as copper and chromium is also studied on the precipitation and coarsening processes. The main results of this section are concerning on the coarsening kinetics and its effect on hardness. Besides, the diffusion couple method is employed to study the precipitation and coarsening process in different Fe-Ni-Al alloy compositions, as well as its effect on the hardness. All the above aspects of precipitation and coarsening are also supported with Thermo-Calc calculations
Transport Properties through Double Barrier Structure in Graphene
The mode-dependent transmission of relativistic ballistic massless Dirac
fermion through a graphene based double barrier structure is being investigated
for various barrier parameters. We compare our results with already published
work and point out the relevance of these findings to a systematic study of the
transport properties in double barrier structures. An interesting situation
arises when we set the potential in the leads to zero, then our 2D problem
reduces effectively to a 1D massive Dirac equation with an effective mass
proportional to the quantized wave number along the transverse direction.
Furthermore we have shown that the minimal conductivity and maximal Fano factor
remain insensitive to the ratio between the two potentials V_2/V_1=\alpha.Comment: 18 pages, 12 figures, clarifications and reference added, misprints
corrected. Version to appear in JLT
Multiplexed vortex beam-based optical tweezers
The design and implementation of a multiplexed spiral phase mask in an
experimental optical tweezer setup are presented. This diffractive optical
element allows the generation of multiple concentric vortex beams with
independent topological charges. The generalization of the phase mask for
multiple concentric vortices is also shown. The design for a phase mask of two
multiplexed vortices with different topological charges is developed. We
experimentally show the transfer of angular momentum to the optically trapped
microparticles by enabling orbiting dynamics around the optical axis
independently within each vortex. The angular velocity of the confined
particles versus the optical power in the focal region is also discussed for
different combinations of topological charges
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