3,835 research outputs found
A very low current scanning tunneling microscope
The applications of the scanning tunneling microscope (STM) in air are usually restricted to good conducting materials as clean metals, doped and passivated semiconductors, or to some molecular adsorbates deposited onto graphite. In order to study poor conducting materials as biological molecules, we have built a very low current STM. This instrument can routinely be operated at 0.1 pA while having a bandwidth of 7 kHz. The advantages of using very low currents are illustrated by imaging 5-nm-thick purple membranes. These membranes can only be imaged at currents smaller than 2 pA. © 1995 American Institute of Physics.DGICYT Nº.PB94-0016 .Peer Reviewe
Generation of a human iPS cell line from a patient with retinitis pigmentosa due to EYS mutation
Retinitis pigmentosa (RP) is an inherited retinal degenerative disease. Mutations in EYS have been associated with autosomal recessive RP. The human iPS cell line, CABi002-A, derived from peripheral blood mononuclear cells from a patient carrying a heterozygous double mutation in EYS gene was generated by non-integrative reprogramming technology, using hOCT3/4, hSOX2, hc-MYC and hKLF4 reprogramming factors. Pluripotency and differentiation capacity were assessed by immunocytochemistry and RT-PCR. This iPSC line can be further differentiated towards the affected cells to understand the pathophysiology of the disease and test new therapeutic strategies.Cellex FoundationFundación Progreso y Salu
Formación en Cinemática y Dinámica de Sistemas Multicuerpo Mediante Coordenadas Naturales
La formación de los futuros ingenieros mecánicos en dinámica de sistemas multicuerpo 3-D rara vez encuentra una materia específica en los planes de estudio, ni siquiera en postgrado. Cuando sólo se dispone de algunas horas (entre 5 y 10 horas de clase y unas 15 de trabajo personal) en el marco de una materia más general, las coordenadas naturales y Matlab son probablemente el único camino para alcanzar ciertos objetivos prácticos. Aquí se aborda cómo se pueden alcanzar estos objetivos, con un aprendizaje basado en .casos reales.
Very often, the curriculum of mechanical engineers doesn't include any specific subject on kinematics and dynamics of multibody systems. In these situations the unique opportunity to introduce MBS is to dedicate from 5 to 10 hours to this subject inside a more general course, plus about 15 hours of personal work. This paper shows how this short time can be enough if natural coordinates are used. Keywords
Multiatom resonant photoemission: Theory and systematics
A first-principles calculation of the recently discovered interatomic multiatom resonant photoemission (MARPE) effect is presented. In this phenomenon, core photoelectron intensities are enhanced when the photon energy is tuned to a core-level absorption edge of nonidentical neighboring atoms, thus enabling direct determination of near-neighbor atomic identities. Both the multiatom character of MARPE and retardation effects in the photon and electron interactions in the resonant channel are shown to be
crucial. Measured peak-intensity enhancements of 40% in MnO and spectral shapes similar to the corresponding x-ray absorption profiles are well reproduced by this theory.This work was supported by the U.S. Department of Energy, under Contract No. DE-AC03-76SF00098, the University of the Basque Country, and the Spanish Ministerio de Educación y Cultura (Fulbright Grant No. FU-98-22726216).Peer reviewe
Energy conditions in modified Gauss-Bonnet gravity
In considering alternative higher-order gravity theories, one is liable to be
motivated in pursuing models consistent and inspired by several candidates of a
fundamental theory of quantum gravity. Indeed, motivations from string/M-theory
predict that scalar field couplings with the Gauss-Bonnet invariant, G, are
important in the appearance of non-singular early time cosmologies. In this
work, we discuss the viability of an interesting alternative gravitational
theory, namely, modified Gauss-Bonnet gravity or f(G) gravity. We consider
specific realistic forms of f(G) analyzed in the literature that account for
the late-time cosmic acceleration and that have been found to cure the
finite-time future singularities present in the dark energy models. We present
the general inequalities imposed by the energy conditions and use the recent
estimated values of the Hubble, deceleration, jerk and snap parameters to
examine the viability of the above-mentioned forms of f(G) imposed by the weak
energy condition.Comment: 9 pages, 8 figures. V2: minor additions and corrections; to appear in
PR
Ultrafast nonlinear optical response of Dirac fermions in graphene
The speed of solid-state electronic devices, determined by the temporal dynamics of charge
carriers, could potentially reach unprecedented petahertz frequencies through direct
manipulation by optical fields, consisting in a million-fold increase from state-of-the-art
technology. In graphene, charge carrier manipulation is facilitated by exceptionally strong
coupling to optical fields, from which stems an important back-action of photoexcited carriers.
Here we investigate the instantaneous response of graphene to ultrafast optical fields,
elucidating the role of hot carriers on sub-100 fs timescales. The measured nonlinear
response and its dependence on interaction time and field polarization reveal the back-action
of hot carriers over timescales commensurate with the optical field. An intuitive picture is
given for the carrier trajectories in response to the optical-field polarization state. We note
that the peculiar interplay between optical fields and charge carriers in graphene may also
apply to surface states in topological insulators with similar Dirac cone dispersion relations.Peer ReviewedPostprint (published version
Enhanced microwave transmission through quasicrystal hole arrays
The authors report on the observation of enhanced microwave transmission through quasiperiodic hole arrays in metal films. The fraction of transmitted light reaches 50% in a self-standing metal film and approaches 90% when the film is sandwiched between thin dielectric slabs, while the holes occupy only 10% of the sample area. The maximum transmission exhibits a Breit-Wigner resonance behavior, accompanied by zero phase change and rendering the film almost invisible over a wide frequency range. The extraordinary transmission phenomenon is interpreted in terms of resonances in the self-consistent interaction between holes, which are represented by effective electric and magnetic dipoles. © 2007 American Institute of Physics.Peer Reviewe
Development of Surface-Coated Polylactic Acid/Polyhydroxyalkanoate (PLA/PHA) Nanocomposites
This work reports on the design and development of nanocomposites based on a polymeric
matrix containing biodegradable Polylactic Acid (PLA) and Polyhydroxyalkanoate (PHA) coated
with either Graphite NanoPlatelets (GNP) or silver nanoparticles (AgNP). Nanocomposites were
obtained by mechanical mixing under mild conditions and low load contents (<0.10 wt %). This
favours physical adhesion of the additives onto the polymer surface, while the polymeric bulk
matrix remains unaffected. Nanocomposite characterisation was performed via optical and focused
ion beam microscopy, proving these nanocomposites are selectively modified only on the surface,
leaving bulk polymer unaffected. Processability of these materials was proven by the fabrication of
samples via injection moulding and mechanical characterisation. Nanocomposites showed enhanced
Young modulus and yield strength, as well as better thermal properties when compared with the
unmodified polymer. In the case of AgNP coated nanocomposites, the surface was found to be
optically active, as observed in the increase of the resolution of Raman spectra, acquired at least
10 times, proving these nanocomposites are promising candidates as surface enhanced Raman
spectroscopy (SERS) substrates
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