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Biomedical subjects

L B Madsen

Publications and source records attributed to L B Madsen.

14 recordsLinked to original sources
PubMed2006

Nondipole ionization dynamics of atoms in superintense high-frequency attosecond pulses.

The ionization of H(1s) in superintense, high-frequency, attosecond pulses is studied beyond the dipole approximation. We identify a unique nondipole 3rd lobe in the angular distribution of the ejected electron and show that this lobe has a well-defined classical counterpart. The ionization is likely to occur in the direction opposite to the laser propagation direction, which is fully understood from an analysis of the classical dynamics.

Journal Article↗
PubMed2005

Strong orientation effects in ionization of H+2 by short, intense, high-frequency light pulses.

We present three-dimensional time-dependent calculations of ionization of arbitrarily spatially oriented H+2 by attosecond, intense, high-frequency laser fields. The ionization probability shows a strong dependence on both the internuclear distance and the relative orientation between the laser field and the internuclear axis. The physical features are explained in terms of two-center interference effects.

Journal Article↗
PubMed2005

Exact nondipole Kramers-Henneberger form of the light-atom hamiltonian: an application to atomic stabilization and photoelectron energy spectra.

The exact nondipole minimal-coupling Hamiltonian for an atom interacting with an explicitly time- and space-dependent laser field is transformed into the rest frame of a classical free electron in the laser field, i.e., into the Kramers-Henneberger frame. The new form of the Hamiltonian is used to study nondipole effects in the high-intensity, high-frequency regime. Fully three-dimensional nondipole ab initio wave packet calculations show that the ionization probability may decrease for increasing field strength. We identify a unique signature for the onset of this dynamical stabilization effect in the photoelectron spectrum.

Journal Article↗
PubMed2005

The determination of absolute anion formation cross sections from electron beam scattering data.

Using recent low energy electron scattering data for CCl4 and SF6, and accompanying theory illustrating the coupling of attachment and elastic scattering, absolute cross sections are derived for electron attachment to CCl4 and SF6 between impact energies, respectively, of 8-52 meV and 7-42 meV. Values of attachment cross sections are compared with those obtained by laser and threshold photoionization techniques, which include normalization to rate coefficient data. Excellent agreement with the latest CCl4 data is obtained, with less precise agreement for SF6, but still lying within experimental uncertainties.

Journal Article↗
PubMed2003

Reaction and scattering in cold electron collisions.

Experimental data are presented for the scattering of electrons by CCl4 between 8 and 200 meV impact energy. These results are used in conjunction with data for the reactive process, yielding Cl-, to study the low energy behavior of a system which simultaneously displays both reactive and elastic scattering channels. Phase shifts are derived and illustrate how channel competition develops as the energy falls. This behavior and the involvement of vibronic effects at impact energies above approximately 30 meV pose a challenge to theory.

Journal Article↗
PubMed2003

Photodetachment of He- in the vicinity of the two-electron escape threshold.

Recording the yield of He(1snl(3)L) Rydberg states for n=11-14, we measure the photodetachment cross sections of metastable He-(1s2s2p(4)P(o)) ions in the vicinity of the two-electron escape threshold. We observe a large number of double Rydberg He- quartet state resonances and report energies and widths of intrashell states in the n=13-15 manifolds. Sharp thresholds are measured at He((3)P(o)) and He((3)D(e)) Rydberg states with preference for population of the former, whereas the He((3)S(e)) states are not populated, in agreement with qualitative theoretical arguments.

Journal Article↗
PubMed2003

Does caffeine and alcohol intake before pregnancy predict the occurrence of spontaneous abortion?

BACKGROUND: Consumption of caffeine and alcohol is suspected to affect pregnancy outcome. Use of both stimulants is widespread and even minor effects on fetal viability are of public health interest. METHODS: We performed a nested case-control study using prospective data from a population-based cohort comprising 11088 women aged 20-29 years. From this cohort, women who experienced either a spontaneous abortion (n = 303) or who gave birth (n = 1381) during follow-up [mean time: 2.1 years (range: 1.6-3.4)] were selected. Associations between self-reported exposures to caffeine and/or alcohol at enrolment and spontaneous abortion were analysed by means of logistic regression. RESULTS: Compared with women with a pre-pregnancy intake of <75 mg caffeine per day, the adjusted odds ratio (95% confidence interval) for spontaneous abortion was 1.26 (0.77-2.06), 1.45 (0.87-2.41), 1.44 (0.87-2.37) and 1.72 (1.00-2.96) for a pre-pregnancy intake on 75-300, 301-500, 501-900 and >900 mg caffeine per day respectively (P = 0.05 for trend). A pre-pregnancy intake of alcohol was not a predictor for spontaneous abortion. CONCLUSIONS: A high intake of caffeine prior to pregnancy seems to be associated with an increased risk of spontaneous abortion, whereas a low-to-moderate alcohol intake does not influence the risk.

Abortion, Spontaneous↗
PubMed2003

Chromosome location, genomic organization of the porcine COL10A1 gene and model structure of the NC1 domain.

The porcine COL10A1 gene, encoding the alpha1(X) chain of type X collagen, has been sequenced. The gene structure is evolutionarily conserved, consisting of three exons and two introns spanning 7100 bp. Linkage mapping localized the gene to chromosome 1, which is in agreement with human-pig homology maps. Furthermore, protein structure comparison of the functionally important carboxyl domain between species revealed that amino acid changes were few and mainly situated in loop regions.

Animals↗
PubMed2002

Blackbody-radiation-assisted laser cooling of molecular ions.

The translational motion of molecular ions can be effectively cooled sympathetically to temperatures below 100 mK in ion traps through Coulomb interactions with laser-cooled atomic ions. The distribution of internal rovibrational states, however, gets in thermal equilibrium with the typically much higher temperature of the environment within tens of seconds. We consider a concept for rotational cooling of such internally hot, but translationally cold, heteronuclear diatomic molecular ions. The scheme relies on a combination of optical pumping from a few specific rotational levels into a "dark state" with redistribution of rotational populations mediated by blackbody radiation.

Journal Article↗
PubMed2002

Excitation in ion-atom collisions inside subfemtosecond laser pulses.

We discuss new excitation mechanisms in energetic ion-atom collisions embedded in short laser pulses. For comparable duration and strength of the pulse and collisional interaction, the laser field will probe and modify the interaction between projectile and target. Coherence effects emerge, insight into reaction dynamics is gained, and new dynamical features are discovered. As an example, we show (i) how a propensity rule for s-p excitation can be dramatically changed, and (ii) how the presence of the laser pulse modifies the ionization process in ion-atom collisions.

Journal Article↗
PubMed2001

Correlated electrons in lithiumlike hollow atoms.

We present a scheme for the explicit construction of highly correlated triply excited hollow states in Coulombic three-electron systems. Our analytical ansatz for the three-electron state is physically well justified and it produces configuration mixing coefficients in good agreement with data obtained from ab initio calculations.

Journal Article↗
PubMed1998

Ethnomedical information and in vitro screening for angiotensin-converting enzyme inhibition of plants utilized as traditional medicines in Gujarat, Rajasthan and Kerala (India).

Plants utilized as traditional medicines in India have been investigated for their ability to inhibit the angiotensin converting enzyme (ACE). In total, 75 species belonging to 42 families have been investigated and new ethnomedical information has been obtained for 41 species. Four species were found to possess a high ACE inhibiting ability and were low in their tannin content.

Angiotensin-Converting Enzyme Inhibitors↗