635 research outputs found
Multiorbital tunneling ionization of the CO molecule
We coincidently measure the molecular frame photoelectron angular
distribution and the ion sum-momentum distribution of single and double
ionization of CO molecules by using circularly and elliptically polarized
femtosecond laser pulses, respectively. The orientation dependent ionization
rates for various kinetic energy releases allow us to individually identify the
ionizations of multiple orbitals, ranging from the highest occupied to the next
two lower-lying molecular orbitals for various channels observed in our
experiments. Not only the emission of a single electron, but also the
sequential tunneling dynamics of two electrons from multiple orbitals are
traced step by step. Our results confirm that the shape of the ionizing
orbitals determine the strong laser field tunneling ionization in the CO
molecule, whereas the linear Stark effect plays a minor role.Comment: This paper has been accepted for publication by Physical Review
Letter
Role of Endothelial Nitric Oxide Synthase Gene Polymorphisms (Glu298Asp) in Egyptian Patients with Recurrent Spontaneous Abortion
Background: Previous studies indicated an association between endothelial nitric oxide synthase (eNOS) activity and maintenance of pregnancy, but it is rather controversial whether polymorphisms of the gene encoding for eNOS are associated with recurrent spontaneous abortions (RSAs). Aim: The aim was to investigate whether the presence of maternal polymorphism Glu298Asp in exon seven of the eNOS gene increase the risk of RSA in Egyptian women.Subjects and Methods: Hundreds women were randomly selected as the case group. They had at least three RSA before 20th weeks of gestation, same partner and at least one live birth and compared with 100 women, same age range, with no history of abortions or complicated pregnancy as control group. All were investigated for the polymorphism using the polymerase chain reaction‑restriction fragment length polymorphisms method. Data were expressed descriptively as percentages for qualitative values and mean ± standard deviation for quantitative parametric data and comparison of qualitative data was done. Results: Frequency of GG genotype 50/100% in cases and 67/100% in control group. Heterozygous GT frequency was 46/100% in cases and 26/100% in control (P ≤ 0.01, odds ratio [OR] =2.37, and 95% confidence interval [CI] =1.30–4.34). Homozygous TT was 4/100% in the cases and at 7/100% in control (P = 0.68, OR = 0.77, and 95% CI = 0.21–2.76). GG genotype versus GT and GG (P = 0.01, OR = 2.03, and 95% CI = 1.15–3.60). Cases with TT genotype were more susceptible to abortion at an older age with a mean of 29 (4.76) (P = 0.02). Conclusion: In conclusion, (eNOS) Glu298Asp polymorphism was found to be associated with increased risk of RSA in this sample of Egyptian women.KEY WORDS: Endothelial nitric oxide, polymorphism, recurrent spontaneous abortions, synthas
Interatomic Coulombic Decay following Photoionization of the Helium Dimer: Observation of Vibrational Structure
Using synchrotron radiation we simultaneously ionize and excite one helium
atom of a helium dimer (He_2) in a shakeup process. The populated states of the
dimer ion (i.e. He^[*+](n = 2; 3)-He) are found to deexcite via interatomic
coulombic decay. This leads to the emission of a second electron from the
neutral site and a subsequent coulomb explosion. In this letter we present a
measurement of the momenta of fragments that are created during this reaction.
The electron energy distribution and the kinetic energy release of the two He^+
ions show pronounced oscillations which we attribute to the structure of the
vibrational wave function of the dimer ion.Comment: 8 pages, 5 figure
Single photon double ionization of the helium dimer
We show that a single photon can ionize the two helium atoms of the helium
dimer in a distance up to 10 {\deg}A. The energy sharing among the electrons,
the angular distributions of the ions and electrons as well as comparison with
electron impact data for helium atoms suggest a knock-off type double
ionization process. The Coulomb explosion imaging of He_2 provides a direct
view of the nuclear wave function of this by far most extended and most diffuse
of all naturally existing molecules.Comment: 10 pages, 5 figure
A measurement of the evolution of Interatomic Coulombic Decay in the time domain
During the last 15 years a novel decay mechanism of excited atoms has been
discovered and investigated. This so called ''Interatomic Coulombic Decay''
(ICD) involves the chemical environment of the electronically excited atom: the
excitation energy is transferred (in many cases over long distances) to a
neighbor of the initially excited particle usually ionizing that neighbor. It
turned out that ICD is a very common decay route in nature as it occurs across
van-der-Waals and hydrogen bonds. The time evolution of ICD is predicted to be
highly complex, as its efficiency strongly depends on the distance of the atoms
involved and this distance typically changes during the decay. Here we present
the first direct measurement of the temporal evolution of ICD using a novel
experimental approach.Comment: 6 pages, 4 figures, submitted to PR
ATP release from the human ureter on distension and P2X3 receptor expression on suburothelial sensory nerves
It is not clear how the increase in intraluminal pressure behind an obstructing ureteric calculus causes an increase in action potential frequency in ureteric sensory nerves so the pain messages are transmitted to the brain. It has been proposed that ureteric distension causes urothelial release of ATP, which activates purinoceptors on suburothelial nociceptive sensory nerves. The purpose of this study was to determine whether distension of the human ureter results in the release of ATP and whether the nociceptive P2 receptor, P2X3, is expressed on suburothelial sensory nerves in the human ureter. Human ureter segments were perfused with Krebs solution and intermittently distended to a range of pressures. Samples of perfusate were collected throughout and the ATP concentration ([ATP]) was determined using a luciferin-luciferase assay. Sections of ureter were stained using antibodies against P2X3 and capsaicin receptors (TRPV1). [ATP] rose to more than 10 times baseline levels after distension beyond a threshold of 25–30 cmH2O. Immunofluorescence studies on consecutive frozen sections showed that suburothelial nerves stained positively for P2X3 and capsaicin receptors, with no staining in controls. These findings are consistent with the hypothesis that purinergic signalling is involved in human ureteric mechanosensory transduction, leading to nociception
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