601 research outputs found
Generation of attosecond xuv pulses in strong laser-atom interactions
The generation of radiation pulses that can be as short as 120 attoseconds is demonstrated theoretically. We have employed a two-dimensional exact solution of the Schrodinger equation that allows for arbitrary laser ellipticity. By manipulating the laser ellipticity in time, it is shown that one can control the wave-packet dynamics of the ejected atomic electron. The nonlinear interaction of the electron with the atomic core can thus be restricted to extremely short times. Photon energies up to 160 eV are generated. It is also shown that with a higher laser frequency, even shorter pulses can be produced. [S1050-2947(98)02211-2]
Anatomical variants of the emissary veins: unilateral aplasia of both the sigmoid sinus and the internal jugular vein and development of the petrosquamosal sinus. A rare case report
We report a case of hypoplasia of the right transverse sinus and aplasia of the
ipsilateral sigmoid sinus and the internal jugular vein. In addition, development
of the petrosquamosal sinus and the presence of a large middle meningeal sinus
and sinus communicans were observed. A 53-year-old Caucasian woman was
referred for magnetic resonance imaging (MRI) investigation due to chronic headache.
On the MRI scan a solitary meningioma was observed. Finally MR 2D venography
revealed this extremely rare variant. (Folia Morphol 2011; 70, 4: 305–308
Magnetic versus nonmagnetic doping effects on the magnetic ordering in the Haldane chain compound PbNi2V2O8
A study of an impurity driven phase-transition into a magnetically ordered
state in the spin-liquid Haldane chain compound PbNi2V2O8 is presented. Both,
macroscopic magnetization as well as 51V nuclear magnetic resonance (NMR)
measurements reveal that the spin nature of dopants has a crucial role in
determining the stability of the induced long-range magnetic order. In the case
of nonmagnetic (Mg2+) doping on Ni2+ spin sites (S=1) a metamagnetic transition
is observed in relatively low magnetic fields. On the other hand, the magnetic
order in magnetically (Co2+) doped compounds survives at much higher magnetic
fields and temperatures, which is attributed to a significant anisotropic
impurity-host magnetic interaction. The NMR measurements confirm the predicted
staggered nature of impurity-liberated spin degrees of freedom, which are
responsible for the magnetic ordering. In addition, differences in the
broadening of the NMR spectra and the increase of nuclear spin-lattice
relaxation in doped samples, indicate a diverse nature of electron spin
correlations in magnetically and nonmagnetically doped samples, which begin
developing at rather high temperatures with respect to the antiferromagnetic
phase transition.Comment: 10 pages, 7 figure
Recycling of spent solid CO2 adsorbents via catalytic pyrolysis for the recovery of mesoporous silica and valuable heteroaromatic chemicals
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Semiclassical description of multiphoton processes
We analyze strong field atomic dynamics semiclassically, based on a full
time-dependent description with the Hermann-Kluk propagator. From the
properties of the exact classical trajectories, in particular the accumulation
of action in time, the prominent features of above threshold ionization (ATI)
and higher harmonic generation (HHG) are proven to be interference phenomena.
They are reproduced quantitatively in the semiclassical approximation.
Moreover, the behavior of the action of the classical trajectories supports the
so called strong field approximation which has been devised and postulated for
strong field dynamics.Comment: 10 pages, 11 figure
IL RUOLO DEI PUNTI VENDITA COME STRUMENTO DI IMMAGINE DI MARCA NEL MERCATO CINESE
Preeclampsia (PE) and intrauterine growth restriction (IUGR) are major obstetric health problems. Higher levels of T-helper (Th) 1 (proinflammatory) cytokines have been observed in pregnancies complicated with PE and IUGR; this is in contrast to the predominant Th2 (anti-inflammatory) cytokine environment found in uncomplicated pregnancies. Myostatin is best known as a negative regulator of muscle development and reportedly has a role in fat deposition, glucose metabolism, and cytokine modulation (outside the placenta). Myostatin concentrations in plasma and protein expression in placental tissue are significantly higher in women with PE. Expression of myostatin in IUGR and PE-IUGR and the effect of this protein on the cytokine production from the placenta is unknown. In the current study, significant differences were identified in the expression of myostatin in pregnancies complicated with IUGR, PE, and PE with IUGR. Furthermore, cytokine production by first-trimester placental tissues was altered following myostatin treatment.</p
Nonsequential double ionization of helium
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