53 research outputs found
Femtosecond pulsed laser deposition of nanostructured CdS films
In this work, we report an investigation of the properties of nanostructured deposits obtained from femtosecond pulsed laser deposition of CdS sintered targets. Specifically, we address the effects of laser irradiation wavelength, laser fluence, and substrate temperature (from 25 to 450 °C). The composition of the deposits was characterized using X-ray photoelectron spectroscopy (XPS), their crystallinity by X-ray diffraction (XRD), and the surface morphology was studied by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM). It has been found that the smallest nanoparticles, with an average diameter of 25 nm and a narrow size distribution, together with particulates in the range of 80-120 nm, are obtained at the shortest laser wavelength of 266 nm on room-temperature substrates. Deposits do not contain microscopic droplets in any of the explored conditions. © 2010 American Chemical Society.Peer Reviewe
A detailed experimental and theoretical study of the femtosecond A -band photodissociation of C H3I
The real time photodissociation dynamics of C H3I from the A band has been studied experimentally and theoretically. Femtosecond pump-probe experiments in combination with velocity map imaging have been carried out to measure the reaction times (clocking) of the different (nonadiabatic) channels of this photodissociation reaction yielding ground and spin-orbit excited states of the I fragment and vibrationless and vibrationally excited (symmetric stretch and umbrella modes) C H3 fragments. The measured reaction times have been rationalized by means of a wave packet calculation on the available ab initio potential energy surfaces for the system using a reduced dimensionality model. A 40 fs delay time has been found experimentally between the channels yielding vibrationless CH3(ν=0) and I(2P3/2) and I*(2P1/2) that is well reproduced by the calculations. However, the observed reduction in delay time between the I and I* channels when the C H3 fragment appears with one or two quanta of vibrational excitation in the umbrella mode is not well accounted for by the theoretical model. © 2008 American Institute of Physics.This work has been financed by the Spanish MEC through Grant Nos. CTQ2005-08493-C02-01, FIS-2007- 62002, and Consolider program “Science and Applications of Ultrafast Ultraintense Lasers” No. CSD2007-00013.Peer Reviewe
Biphasic in vitro maturation with C-type natriuretic peptide enhances the developmental competence of juvenile-goat oocytes
In vitro embryo production success in juvenile animals is compromised due to their intrinsic lower oocyte quality. Conventional in vitro maturation (IVM) impairs oocyte competence by inducing spontaneous meiotic resumption. A series of experiments were performed to determine if maintaining meiotic arrest during a pre-maturation culture phase (pre-IVM) prior to conventional IVM improves oocyte competence of juvenile-goat (2 months old) cumulusoocyte complexes (COCs). In experiment 1, COCs were cultured with C-type natriuretic peptide (CNP; 0, 50, 100, 200 nM) for 6 and 8 h. Nuclear stage was assessed, revealing no differences in the incidence of germinal vesicle (GV) breakdown. In experiment 2, the same CNP concentrations were assessed plus 10 nM estradiol, the known upstream agonist activating expression of NPR2, the exclusive receptor of CNP. CNP (200 nM) plus estradiol increased the rate of oocytes at GV stage at 6 h compared to control group (74.7% vs 28.3%; P<0.05) with predominantly condensed chromatin configuration. In experiment 3, relative mRNA quantification revealed NPR2 expression was down-regulated after pre-IVM (6 h). In experiment 4, analysis of transzonal projections indicated that pre-IVM maintained cumulus-oocyte communication after oocyte recovery. For experiments 5 and 6, biphasic IVM (6 h pre-IVM with CNP and estradiol, plus 24 h IVM) and control IVM (24 h) were compared. Biphasic IVM increased intra-oocyte glutathione and decreased ROS, up-regulated DNA-methyltransferase 1 and pentraxin 3 expression and led to an increase in rate of blastocyst development compared to control group (30.2% vs 17.2%; P<0.05). In conclusion, a biphasic IVM, including a pre-IVM with CNP, maintains oocyte meiotic arrest for 6 h and enhances the embryo developmental competence of oocytes from juvenile goats
Generation of femtosecond paraxial beams with arbitrary spatial distribution
We present an approach to generate paraxial laser beams with arbitrary spatial distribution in the femtosecond time regime. The proposed technique is based upon a pair of volume phase holographic gratings working in parallel arrangement. It exploits the spatial coherence properties of the incoming laser beam in a compact and robust setup that mitigates angular and spatial chirp. The gratings were recorded in a photopolymerizable glass with a high optical damage threshold and a large optical throughput. Setup performance is studied and experimentally demonstrated by generating Laguerre-Gaussian femtosecond pulses. © 2010 Optical Society of America.We thank Fransisco del Monte for valuable advice and CAI-UCM facilities. The financial support from the Spanish Ministry of Science and Innovation under projects TEC 2008-04105, CTQ2008-02578/BQU and Consolider SAUUL CSD2007-00013 is acknowledged. M. P. H.-G. and P. V. acknowledge the Spanish Ministry of Foreign Affairs and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (Brazil) for financial support, respectively.Peer Reviewe
Waves, boosted branes and BPS states in M-theory
Certain type II string non-threshold BPS bound states are shown to be related
to non-static backgrounds in 11-dimensional theory. The 11-d counterpart of the
bound state of NS-NS and R-R type IIB strings wound around a circle is a pure
gravitational wave propagating along a generic cycle of 2-torus. The extremal
(q_1,q_2) string with non-vanishing momentum along the circle (or infinitely
boosted black string) corresponds in D=11 to a 2-brane wrapped around 2-torus
with momentum flow along the (q_1,q_2) cycle. Applying duality transformations
to the string-string solution we find type IIA background representing a bound
state of 2-brane and 0-brane. Its lift to 11 dimensions is simply a 2-brane
finitely boosted in transverse direction. This 11-d solution interpolates
between a static 2-brane (zero boost) and a gravitational wave in 11-th
dimension (infinite boost). Similar interpretations are given for various bound
states involving 5-branes. Relations between transversely boosted M-branes and
1/2 supersymmetric non-threshold bound states 2+0 and 5+0 complement relations
between M-branes with momentum in longitudinal direction and 1/4 supersymmetric
threshold bound states 1+0 and 4+0. In the second part of the paper we
establish the correspondence between the BPS states of type IIB strings on a
circle and oscillating states of a fundamental supermembrane wrapped around a
2-torus. We show that the (q_1,q_2) string spectrum is reproduced by the
membrane BPS spectrum, determined using a certain limit. This supports the
picture suggested by Schwarz.Comment: 26 pages, harvmac (minor corrections; T-duality relation between IIB
string-string solution and boosted 0-brane made explicit
New mechanism to cross the phantom divide
Recently, type Ia supernovae data appear to support a dark energy whose
equation of state crosses -1, which is a much more amazing problem than the
acceleration of the universe. We show that it is possible for the equation of
state to cross the phantom divide by a scalar field in the gravity with an
additional inverse power-law term of Ricci scalar in the Lagrangian. The
necessary and sufficient condition for a universe in which the dark energy can
cross the phantom divide is obtained. Some analytical solutions with or
are obtained. A minimal coupled scalar with different potentials,
including quadratic, cubic, quantic, exponential and logarithmic potentials are
investigated via numerical methods, respectively. All these potentials lead to
the crossing behavior. We show that it is a robust result which is hardly
dependent on the concrete form of the potential of the scalar.Comment: 11 pages, 5 figs, v3: several references added, to match the
published versio
Biphasic in vitro maturation with C-type natriuretic peptide enhances the developmental competence of juvenile-goat oocytes
In vitro embryo production success in juvenile animals is compromised due to their intrinsic lower oocyte quality. Conventional in vitro maturation (IVM) impairs oocyte competence by inducing spontaneous meiotic resumption. A series of experiments were performed to determine if maintaining meiotic arrest during a pre-maturation culture phase (pre-IVM) prior to conventional IVM improves oocyte competence of juvenile-goat (2 months old) cumulus-oocyte complexes (COCs). In experiment 1, COCs were cultured with C-type natriuretic peptide (CNP; 0, 50, 100, 200 nM) for 6 and 8 h. Nuclear stage was assessed, revealing no differences in the incidence of germinal vesicle (GV) breakdown. In experiment 2, the same CNP concentrations were assessed plus 10 nM estradiol, the known upstream agonist activating expression of NPR2, the exclusive receptor of CNP. CNP (200 nM) plus estradiol increased the rate of oocytes at GV stage at 6 h compared to control group (74.7% vs 28.3%; P<0.05) with predominantly condensed chromatin configuration. In experiment 3, relative mRNA quantification revealed NPR2 expression was down-regulated after pre-IVM (6 h). In experiment 4, analysis of transzonal projections indicated that pre-IVM maintained cumulus-oocyte communication after oocyte recovery. For experiments 5 and 6, biphasic IVM (6 h pre-IVM with CNP and estradiol, plus 24 h IVM) and control IVM (24 h) were compared. Biphasic IVM increased intra-oocyte glutathione and decreased ROS, up-regulated DNA-methyltransferase 1 and pentraxin 3 expression and led to an increase in rate of blastocyst development compared to control group (30.2% vs 17.2%; P<0.05). In conclusion, a biphasic IVM, including a pre-IVM with CNP, maintains oocyte meiotic arrest for 6 h and enhances the embryo developmental competence of oocytes from juvenile goats.Sandra Soto-Heras, Irene Menéndez-Blanco, Maria-Gracia Catalá, Dolors Izquierdo, Jeremy G. Thompson, Maria-Teresa Parami
Proximity effect and strong coupling superconductivity in nanostructures built with an STM
We present high resolution tunneling spectroscopy data at very low
temperatures on superconducting nanostructures of lead built with an STM. By
applying magnetic fields, superconductivity is restricted to length scales of
the order of the coherence length. We measure the tunneling conductance and
analyze the phonon structure and the low energy DOS. We demonstrate the
influence of the geometry of the system on the magnetic field dependence of the
tunneling density of states, which is gapless in a large range of fields. The
behavior of the features in the tunneling conductance associated to phonon
modes are explained within current models.Comment: 4 figures, 4 page
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