A new measurement of the 7Li(d,p)8Li cross section and consequences for 7Be(p,gamma)8B

A novel scheme for measuring the cross section of the 7Be(p,gamma)8B reaction, the major source of high energy neutrinos from t he sun, is presented. The scheme involves a strictly uniform particle beam and overcomes some of the recognized experimental uncertainties of previous measurements. A new measurement of sigma[7Li(d,p)8Li] has been carried out using this setup,and the present value of sigma[7Li(d,p)8Li] = 155(8) mbarn at the top of the E_d(lab.)= 776 keV resonance is compared to previous measurements. A new issue regarding both the (d,p) and (p,gamma) reactions has been examined: reaction-product nuclei which are backscattered out of the target. Measurements and simulations carried out in the course of this investigation are presented and discussed in the context of possible effects on the measured cross sections of these reactions.Comment: 4 figure

Comparative Chromosome Maps of Neotropical Rodents Necromys lasiurus and Thaptomys nigrita (Cricetidae) Established by ZOO-FISH

This work presents chromosome homology maps between Mus musculus (MMU) and 2 South American rodent species from the Cricetidae group: Necromys lasiurus (NLA, 2n = 34) and Thaptomys nigrita (TNI, 2n = 52), established by ZOO-FISH using mouse chromosome-specific painting probes. Extending previous molecular cytogenetic studies in Neotropical rodents, the purpose of this work was to delineate evolutionary chromosomal rearrangements in Cricetidae rodents and to reconstruct the phylogenetic relationships among the Akodontini species. Our phylogenetic reconstruction by maximum parsimony analysis of chromosomal characters confirmed one consistent clade of all Neotropical rodents studied so far. In both species analyzed here, we observed the syntenic association of chromosome segments homologous to MMU 8/13, suggesting that this chromosome form is a synapomorphic trait exclusive to Neotropical rodents. Further, the previously described Akodontini-specific syntenic associations MMU 3/18 and MMU 6/12 were observed in N. lasiurus but not in T. nigrita, although the latter species is considered a member of the Akodontini tribe by some authors. Finally, and in agreement with this finding, N. lasiurus and Akodon serrensis share the derived fission of MMU 13, which places them as basal sister clades within Akodontini. Copyright (C) 2011 S. Karger AG, Base

Low energy measurement of the 7Be(p,gamma)8B cross section

We have measured the cross section of the 7Be(p,gamma)8B reaction for E_cm = 185.8 keV, 134.7 keV and 111.7 keV using a radioactive 7Be target (132 mCi). Single and coincidence spectra of beta^+ and alpha particles from 8B and 8Be^* decay, respectively, were measured using a large acceptance spectrometer. The zero energy S factor inferred from these data is 18.5 +/- 2.4 eV b and a weighted mean value of 18.8 +/- 1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies.Comment: Accepted for publication in Phys. Rev. Let

Management of Immediate Post- Endovascular Aortic Aneurysm Repair Type Ia Endoleaks and Late Outcomes

BACKGROUND—Post-endovascular aortic aneurysm repair (EVAR) endoleaks and the need for reintervention are challenging. Additional endovascular treatment is advised for type Ia endoleaks detected on post-EVAR completion angiogram. This study analyzed management and late outcomes of these endoleaks. STUDY DESIGN—This was a retrospective review of prospectively collected data from EVAR patients during a 10-year period. All post-EVAR type Ia endoleaks on completion angiogram were identified (group A) and their early (30-day) and late outcomes were compared with outcomes of patients without endoleaks (group B). Kaplan-Meier analysis was used for survival analysis, sac expansion, late type Ia endoleak, and reintervention. RESULTS—Seventy-one of 565 (12.6%) patients had immediate post-EVAR type Ia endoleak. Early intervention (proximal aortic cuffs and/or stenting) was used in 56 of 71 (79%) in group A vs 31 of 494 (6%) in group B (p \u3c 0.0001). Late type Ia endoleak was noted in 9 patients (13%) in group A at a mean follow-up of 28 months vs 10 patients (2%) in group B at a mean follow-up of 32 months (p \u3c 0.0001). Late sac expansion and reintervention rates were 9% and 10% for group A vs 5% and 3% for group B (p = 0.2698 and p = 0.0198), respectively. Freedom rates from late type Ia endoleaks at 1, 3, and 5 years for group A were 88%, 85%, and 80% vs 98%, 98%, and 96% for group B (p \u3c 0.001); and for late intervention, were 94%, 92%, and 77% for group A, and 99%, 97%, and 95% for group B (p = 0.007), respectively. Survival rates were similar. CONCLUSIONS—Immediate post-EVAR type Ia endoleaks are associated with higher rates of early interventions, late endoleaks and reintervention, which will necessitate strict post-EVAR surveillance

Andreev Reflection and Spin Injection into s−s- and d−d-wave Superconductors

We study the effect of spin injection into $s-$ and $d-$wave superconductors, with an emphasis on the interplay between boundary and bulk spin transport properties. The quantities of interest include the amount of non-equilibrium magnetization ($m$), as well as the induced spin-dependent current ($I_s$) and boundary voltage ($V_s$). In general, the Andreev reflection makes each of the three quantities depend on a different combination of the boundary and bulk contributions. The situation simplifies either for half-metallic ferromagnets or in the strong barrier limit, where both $V_s$ and $m$ depend solely on the bulk spin transport/relaxation properties. The implications of our results for the on-going spin injection experiments in high $T_c$ cuprates are discussed.Comment: 4 pages, REVTEX, 1 figure included; typos correcte

A New Precision Measurement of the 7Be(p,gamma)8B Cross section with an Implanted 7Be Target

The 7Be(p,gamma)8B reaction plays a central role in the evaluation of solar neutrino fluxes. We report on a new precision measurement of the cross section of this reaction, following our previous experiment with an implanted 7Be target, a raster scanned beam and the elimination of the backscattering loss. The new measurement incorporates a more abundant 7Be target and a number of improvements in design and procedure. The point at Elab=991 keV was measured several times under varying conditions, yielding a value of S17(Ec.m. =850 keV) = 24.0(5) eV b. Measurements were carried out at lower energies as well. Due to the precise knowledge of the implanted 7Be density profile it was possible to reconstitute both the off- and on resonance parts of the cross section and to obtain from the entire set of measurements an extrapolated value of S17(0)=21.2(7) eV b.Comment: 4 Pages, 3 Figure

The Optical Design and Characterization of the Microwave Anisotropy Probe

The primary goal of the MAP satellite, now in orbit, is to make high fidelity polarization sensitive maps of the full sky in five frequency bands between 20 and 100 GHz. From these maps we will characterize the properties of the cosmic microwave background (CMB) anisotropy and Galactic and extragalactic emission on angular scales ranging from the effective beam size, <0.23 degree, to the full sky. MAP is a differential microwave radiometer. Two back-to-back shaped offset Gregorian telescopes feed two mirror symmetric arrays of ten corrugated feeds. We describe the prelaunch design and characterization of the optical system, compare the optical models to the measurements, and consider multiple possible sources of systematic error.Comment: ApJ in press; 22 pages with 11 low resolution figures; paper is available with higher quality figures at http://map.gsfc.nasa.gov/m_mm/tp_links.htm

Local structure study of In_xGa_(1-x)As semiconductor alloys using High Energy Synchrotron X-ray Diffraction

Nearest and higher neighbor distances as well as bond length distributions (static and thermal) of the In_xGa_(1-x)As (0<x<1) semiconductor alloys have been obtained from high real-space resolution atomic pair distribution functions (PDFs). Using this structural information, we modeled the local atomic displacements in In_xGa_(1-x)As alloys. From a supercell model based on the Kirkwood potential, we obtained 3-D As and (In,Ga) ensemble averaged probability distributions. This clearly shows that As atom displacements are highly directional and can be represented as a combination of and displacements. Examination of the Kirkwood model indicates that the standard deviation (sigma) of the static disorder on the (In,Ga) sublattice is around 60% of the value on the As sublattice and the (In,Ga) atomic displacements are much more isotropic than those on the As sublattice. The single crystal diffuse scattering calculated from the Kirkwood model shows that atomic displacements are most strongly correlated along directions.Comment: 10 pages, 12 figure

Experimental evidence of strong phonon scattering in isotopical disordered systems: The case of LiH_xD_{1-x} crystals

The observation of the local - mode vibration, the two - mode behavior of the LO phonons at large isotope concentration, as well as large line broadening in LIH - D mixed crystals directly evidence strong additional phonon scattering due to the isotope - induced disorder.Comment: 9 pages, 4 figure

Localization of Dirac electrons by Moire patterns in graphene bilayers

We study the electronic structure of two Dirac electron gazes coupled by a periodic Hamiltonian such as it appears in rotated graphene bilayers. Ab initio and tight-binding approaches are combined and show that the spatially periodic coupling between the two Dirac electron gazes can renormalize strongly their velocity. We investigate in particular small angles of rotation and show that the velocity tends to zero in this limit. The localization is confirmed by an analysis of the eigenstates which are localized essentially in the AA zones of the Moire patterns.Comment: 4 pages, 5 figure