Study of the

The ^{22}Mg(α,p)^{25}Al reaction rate has been identified as a major source of uncertainty for understanding the nucleosynthesis flow in Type-I x-ray bursts. We report a direct measurement of the energy- and angle-integrated cross sections of this reaction in a 3.3-6.9 MeV center-of-mass energy range using the MUlti-Sampling Ionization Chamber (MUSIC). The new ^{22}Mg(α,p)^{25}Al reaction rate is a factor of ∼4 higher than the previous direct measurement of this reaction within temperatures relevant for x-ray bursts, resulting in the ^{22}Mg waiting point of x-ray burst nucleosynthesis flow to be significantly bypassed via the (α,p) reaction.

Stellar

The ^{36}Ar(n,γ)^{37}Ar (t_{1/2}=35 d) and ^{38}Ar(n,γ)^{39}Ar (269 yr) reactions were studied for the first time with a quasi-Maxwellian (kT∼47 keV) neutron flux for Maxwellian average cross section (MACS) measurements at stellar energies. Gas samples were irradiated at the high-intensity Soreq applied research accelerator facility-liquid-lithium target neutron source and the ^{37}Ar/^{36}Ar and ^{39}Ar/^{38}Ar ratios in the activated samples were determined by accelerator mass spectrometry at the ATLAS facility (Argonne National Laboratory). The ^{37}Ar activity was also measured by low-level counting at the University of Bern. Experimental MACS of ^{36}Ar and ^{38}Ar, corrected to the standard 30 keV thermal energy, are 1.9(3) and 1.3(2) mb, respectively, differing from the theoretical and evaluated values published to date by up to an order of magnitude. The neutron-capture cross sections of ^{36,38}Ar are relevant to the stellar nucleosynthesis of light neutron-rich nuclides; the two experimental values are shown to affect the calculated mass fraction of nuclides in the region A=36-48 during the weak s process. The new production cross sections have implications also for the use of ^{37}Ar and ^{39}Ar as environmental tracers in the atmosphere and hydrosphere.

Study of the

The existence of ^{26}Al (t_{1/2}=7.17×10^{5} yr) in the interstellar medium provides a direct confirmation of ongoing nucleosynthesis in the Galaxy. The presence of a low-lying 0^{+} isomer (^{26}Al^{m}), however, severely complicates the astrophysical calculations. We present for the first time a study of the ^{26}Al^{m}(d,p)^{27}Al reaction using an isomeric ^{26}Al beam. The selectivity of this reaction allowed the study of ℓ=0 transfers to T=1/2, and T=3/2 states in ^{27}Al. Mirror symmetry arguments were then used to constrain the ^{26}Al^{m}(p,γ)^{27}Si reaction rate and provide an experimentally determined upper limit of the rate for the destruction of isomeric ^{26}Al via radiative proton capture reactions, which is expected to dominate the destruction path of ^{26}Al^{m} in asymptotic giant branch stars, classical novae, and core collapse supernovae.

Psychological stress moderates the relationship between running volume and CD4+ T cell subpopulations.

Endurance-based exercise training can lead to alterations in components of the immune system, but it is unknown how psychological stress (another potent immunomodulator) may impact these changes. The purpose of this study was to determine the moderating role of psychological stress on exercise-induced immune changes. Twenty-nine recreational runners were recruited for this study four weeks before completing a marathon. Each subject reported: weekly training volume (miles/wk) for the week prior to the study visit; completed the Perceived Stress Scale (PSS), the state version of the State-Trait Anxiety Inventory (STAI) and the Penn State Worry Questionnaire (PSWQ); and donated blood for assessment of CD4+ T cell subpopulations and mitogen-induced cytokine production. Participants ran an average of 30 (±13.4) miles (1 mile=1.6 km) per week. Average values (SD) for immune biomarkers were: regulatory T cells (Treg), 3.2% (±1.2%); type 1 regulatory cells (Tr1), 27.1% (±8.3%); T helper 3 (Th3), 1.8% (±0.7%); interferon gamma (IFNγ), 3.1 pg/ml (±1.0); interleukin (IL)-4, 1.4 pg/ml (±1.1); IFNγ/IL-4, 8.6 (±1.2); IL-10, 512 pg/ml (±288). There was a significant relationship between running volume and both Treg cell numbers (slope of the regression line (ß)=0.05, p less than 0.001) and IL-10 production ß=-10.6, p=0.002), and there was a trending relationship between running volume and Tr1 cell numbers (ß=-0.2%, p=0.064). Perceived stress was a trending moderator of the running volume-Treg relationship, whereas worry was a significant moderator of the running volume-IFNγ and running volume-IFNγ/IL-4 relationships. These data indicate that various forms of psychological stress can impact endurance exercise-based changes in certain immune biomarkers. These changes may reflect an increased susceptibility to clinical risks in some individuals.

Fusion hindrance for a positive-q-value system (24)Mg+(30)Si.

Measurements of the excitation function for the fusion of (24)Mg+(30)Si (Q=17.89 MeV)have been extended toward lower energies with respect to previous experimental data. The S-factor maximum observed in this large, positive-Q-value system is the most pronounced among such systems studied thus far. The significance and the systematics of an S-factor maximum in systems with positive fusion Q values are discussed. This result would strongly impact the extrapolated cross sections and reaction rates in the carbon and oxygen burnings and, thus, the study of the history of stellar evolution.

Measurements of fusion reactions of low-intensity radioactive carbon beams on 12C and their implications for the understanding of X-ray bursts.

The interaction between neutron-rich nuclei plays an important role for understanding the reaction mechanism of the fusion process as well as for the energy production through pycnonuclear reactions in the crust of neutron stars. We have performed the first measurements of the total fusion cross sections in the systems (10,14,15)C+(12)C using a new active target-detector system. In the energy region accessible with existing radioactive beams, a good agreement between the experimental and theoretical cross sections is observed. This gives confidence in our ability to calculate fusion cross sections for systems which are outside the range of today's radioactive beam facilities.

Direct measurement of the (23)Na(α,p)(26)Mg reaction cross section at energies relevant for the production of galactic (26)Al.

The 1809-keV γ ray from the decay of (26)Al(g) is an important target for γ-ray astronomy. In the convective C/Ne burning shell of massive presupernova stars, the (23)Na(α,p)(26)Mg reaction directly influences the production of (26)Al. We have performed a direct measurement of the (23)Na(α,p)(26)Mg reaction cross section at the appropriate astrophysically important energies. The stellar rate calculated in the present work is larger than the recommended rate by nearly a factor of 40 and could strongly affect the production of (26)Al in massive stars.

Origin and consequences of 12C+12C fusion resonances at deep sub-barrier energies.

Previous explanations for the resonance behavior of (12)C+(12)C fusion at low energies were based on a nonresonant compound-nucleus background and an additional contribution from a series of resonances. This separation into "resonance" and "background" contributions of the cross section is artificial. We propose to explain this phenomenon through the impact on the cross section of the relatively large spacings and the narrow widths of (24)Mg compound levels in the corresponding excitation-energy region.

RETRACTED: A shorter 146Sm half-life measured and implications for 146Sm-142Nd chronology in the solar system.

The extinct p-process nuclide (146)Sm serves as an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its α-decay daughter (142)Nd. Based on analyses of (146)Sm/(147)Sm α-activity and atom ratios, we determined the half-life of (146)Sm to be 68 ± 7 (1σ) million years, which is shorter than the currently used value of 103 ± 5 million years. This half-life value implies a higher initial (146)Sm abundance in the early solar system, ((146)Sm/(144)Sm)(0) = 0.0094 ± 0.0005 (2σ), than previously estimated. Terrestrial, lunar, and martian planetary silicate mantle differentiation events dated with (146)Sm-(142)Nd converge to a shorter time span and in general to earlier times, due to the combined effect of the new (146)Sm half-life and ((146)Sm/(144)Sm)(0) values.

Fusion reactions with the one-neutron halo nucleus (15)C.

The structure of (15)C, with an s(1/2) neutron weakly bound to a closed-neutron shell nucleus (14)C, makes it a prime candidate for a one-neutron halo nucleus. We have for the first time studied the cross section for the fusion-fission reaction (15)C+(232)Th at energies in the vicinity of the Coulomb barrier and compared it to the yield of the neighboring (14)C+(232)Th system measured in the same experiment. At sub-barrier energies, an enhancement of the fusion yield by factors of 2-5 was observed for (15)C, while the cross sections for (14)C match the trends measured for (12,13)C.

First experiment with HELIOS: the structure of 13B.

A first experiment is reported that makes use of a new kind of spectrometer uniquely suited to the study of reactions with radioactive beams in inverse kinematics, the helical orbit spectrometer, HELIOS. The properties of some low-lying states in the neutron-rich N=8 nucleus 13B were studied with good resolution. From the measured angular distributions of the (d,p) reaction and the relative spectroscopic factors, spin and configuration assignments of the first- and third-excited states of this nucleus can be constrained.

¹5C(d,p)¹6C reaction and exotic behavior in ¹6C.

We have studied the ¹5C(d,p)¹6C reaction in inverse kinematics using the Helical Orbit Spectrometer at Argonne National Laboratory. Prior studies of electromagnetic-transition rates in ¹6C suggested an exotic decoupling of the valence neutrons from the core in that nucleus. Neutron-adding spectroscopic factors give a different probe of the wave functions of the relevant states in ¹6C. Shell-model calculations reproduce both the present transfer data and the previously measured transition rates, suggesting that ¹6C may be described without invoking very exotic phenomena.

Nuclear structure relevant to neutrinoless double beta decay: 76Ge and 76Se.

The possibility of observing neutrinoless double beta decay offers the opportunity of determining the effective neutrino mass if the nuclear matrix element were known. Theoretical calculations are uncertain, and measurements of the occupations of valence orbits by nucleons active in the decay can be important. The occupation of valence neutron orbits in the ground states of 76Ge (a candidate for such decay) and 76Se (the daughter nucleus) were determined by precisely measuring cross sections for both neutron-adding and removing transfer reactions. Our results indicate that the Fermi surface is much more diffuse than in theoretical calculations. We find that the populations of at least three orbits change significantly between these two ground states while in the calculations, the changes are confined primarily to one orbit.

[Percutaneous plate osteosynthesis for clavicular fractures. Initial description]. / Die perkutane Plattenosteosynthese der Klavikula. Eine Erstbeschreibung.

Insertion of titanium nails for type A and B clavicular fractures can fail intraoperatively due to the small diameter or irregular nature of the medullary canal. At present, such failures lead to open reduction and fixation (ORIF) with plates. In type C fractures (comminuted fractures), a telescoping effect is observed so that ORIF is the only suitable alternative besides nonoperative therapy. A suitable minimally invasive solution for type C fractures and as a salvage procedure for failed intramedullary nailing of type A and B fractures is presented here for the first time with a percutaneous application of an LC plate to the clavicle.

New determination of the astrophysical S factor SE1 of the 12C(alpha,gamma)16O reaction.

A new measurement of the beta-delayed alpha decay of 16N has been performed using a set of high efficiency ionization chambers. Sources were made by implantation of a 16N beam, yielding very clean alpha spectra down to energies as low as 400 keV. Our data are in good agreement with earlier results. For the S factor S(E1), we obtain a value of 74 +/- 21 keV b. In spite of improvements in the measurement, the error in S(E1) remains relatively large because of the correlations among the fit parameters and the uncertainties inherent to the extrapolation.

[Implantation of matrix-free cartilage transplants in standardized defects in sheep knee joints]. / Die Implantation von matrixfreien dreidimensionalen Knorpeltransplantaten in standardisierte Knorpeldefekte am Schafskniegelenk.

The goal of the current investigation was to make a comparative analysis of regenerative tissue after autologous de novo cartilage transplantation on the femoral condyles of sheep after a chondral defect. One chondral defect measuring 4 mm in diameter was placed in the center of one medial femoral condyle of each of 48 Suffolk sheep. Twelve defects were left to heal spontaneously, 16 defects were covered with periosteal flaps, and 20 defects were filled with autologous de novo cartilage graft. Macroscopic and microscopic assessments were performed at 26 and at 52 weeks. Regeneration was significantly better (p<0.05) in the transplant group than in the control groups at both 26 weeks and 52 weeks. The differences were most evident in the grade of defect filling, cartilage stability, cell distribution, and matrix assessments. Transplantation of immature, autologous de novo cartilage leads to qualitatively better regeneration both macro- and microscopically than does periosteal flap placement alone. The transplanted, immature cartilage tissue undergoes maturation in vivo. The regenerated tissue has hyaline-like features.

[Lecture disasters - and how to prevent them]. / Der grottenschlechte Vortrag - oder wie geht es auch besser.

Presentations at medical conferences can sometimes confuse or compromise understanding of current topics. Although considerable time and financial costs may be taken to be present at such events, all too often one must go through inferior presentations that are poorly structured and do not contribute to one's understanding of the topic at hand. A good presentation is distinguishable by the clear intentions of the speaker to give a good lecture. The presenter has worked extensively with his topic and is familiar with the audience. The presentation has a clear structure and finishes with a take-home message. The speaker takes the listener from his previous level of knowledge to a new understanding. To do so, both voice and body language are used. The supporting slides are simple and direct, and not overloaded with information. The speech conforms exactly with the pre-determined time limit.