Energy landscape, two-level systems and entropy barriers in Lennard-Jones clusters

We develop an efficient numerical algorithm for the identification of a large number of saddle points of the potential energy function of Lennard- Jones clusters. Knowledge of the saddle points allows us to find many thousand adjacent minima of clusters containing up to 80 argon atoms and to locate many pairs of minima with the right characteristics to form two-level systems (TLS). The true TLS are singled out by calculating the ground-state tunneling splitting. The entropic contribution to all barriers is evaluated and discussed.Comment: 4 pages, RevTex, 2 PostScript figure

Channel Coupling in A(e⃗,e′N⃗)BA(\vec{e},e' \vec{N})B Reactions

The sensitivity of momentum distributions, recoil polarization observables, and response functions for nucleon knockout by polarized electrons to channel coupling in final-state interactions is investigated using a model in which both the distorting and the coupling potentials are constructed by folding density-dependent effective interactions with nuclear transition densities. Calculations for $^{16}$O are presented for 200 and 433 MeV ejectile energies, corresponding to proposed experiments at MAMI and TJNAF, and for $^{12}$C at 70 and 270 MeV, corresponding to experiments at NIKHEF and MIT-Bates. The relative importance of charge exchange decreases as the ejectile energy increases, but remains significant for 200 MeV. Both proton and neutron knockout cross sections for large recoil momenta, $p_m > 300$ MeV/c, are substantially affected by inelastic couplings even at 433 MeV. Significant effects on the cross section for neutron knockout are also predicted at smaller recoil momenta, especially for low energies. Polarization transfer for proton knockout is insensitive to channel coupling, even for fairly low ejectile energies, but polarization transfer for neutron knockout retains nonnegligible sensitivity to channel coupling for energies up to about 200 MeV. The present results suggest that possible medium modifications of neutron and proton electromagnetic form factors for $Q^2 \gtrsim 0.5 (GeV/c)^2$ can be studied using recoil polarization with relatively little sensitivity due to final state interactions.Comment: Substantially revised version accepted by Phys. Rev. C; shortened to 49 pages including 21 figure

Hepatic iron concentration as a predictor of response to interferon alfa therapy in chronic hepatitis C

Background/Aims: It has been reported that hepatic iron concentration (HIC) may influence response to therapy in chronic viral hepatitis. The aim of this study was to determine the relationship between HIC and response to interferon alfa therapy in patients with chronic hepatitis C. Methods: HIC was measured in liver biopsy specimens from 58 patients with chronic hepatitis C treated at three centers. Three patients had mild chronic hepatitis C, 35 had moderate to severe chronic hepatitis C, and 20 had active cirrhosis. Serum ferritin levels were measured in 51 of these 58 patients. Response to therapy was defined as normalization of alanine aminotransferase levels at the end of treatment. Results: Twenty-four patients (41%) responded to therapy. HICs were generally within the normal range (1100 μg/g and 87% of patients with an elevated serum ferritin concentration did not respond to interferon alfa therapy. Conclusions: HIC seems to influence response to interferon alfa therapy among patients with chronic hepatitis C. A subgroup of patients with chronic hepatitis C has been identified for which an HIC of >1100 μg/g predicted nonresponse in 88% of patients

Ratios of Peroxyacetyl Nitrate to Active Nitrogen Observed During Aircraft Flights Over the Eastern Pacific Ocean and Continental United States

During August and September 1986, 11 aircraft flights were made over the eastern Pacific Ocean and continental United States. The suite of observations included simultaneous measurements of peroxyacetyl nitrate (PAN) and active nitrogen (NOx=NO+NO2). At altitudes of 4.5–6.1 km in the middle free troposphere, PAN was usually 5–6 times NOx in maritime air masses and 2–4 times NOx in continental air masses. In air masses of tropical origin, or in the marine boundary layer, both PAN and NOx were typically less than 20–30 parts per trillion by volume, and the PAN to NOx ratio was less than one. The observations show that PAN can be a major component of the odd nitrogen budget in the middle free troposphere and strongly reinforce earlier views that the abundance is mainly governed by long-range transport processes including formation during transport and continental boundary layer to free tropospheric exchange of PAN and its precursors. Unlike reservoir HNO3, PAN can be transformed to active nitrogen and peroxy radicals by a variety of physical atmospheric processes that lead to air mass warming. Since NOx plays a critical role in determining photochemical O3 production, which in turn determines the oxidative power of the atmosphere, the observed large ratios of reservoir PAN to active NOx imply an important photochemical and dynamical role for PAN in the eastern Pacific remote free troposphere