Difference frequency laser spectroscopy of the nu3 fundamental band of NH⁺₂

The nu3 band of NH + 2 in the X-tilde 3B1 ground electronic state was observed in direct absorption with a tunable difference frequency laser spectrometer in the 3 µ region, using velocity modulation detection. NH + 2 and NH + 3 ions were generated in an ac discharge of He and NH3, or of He, N2, and H2. Fifty-three rovibrational transitions were measured and fit to a triplet A-reduced Hamiltonian to determine rotational, centrifugal distortion, and spin–rotation constants. The band origin was found to be nu0=3359.932 cm^−1, in excellent agreement with a recent calculation of Jensen, Bunker, and McLean. Indirect evidence from the spectrum suggested that NH + 2 is quasilinear, but selection rules prevented a determination of the A rotational constant

s-Process Nucleosynthesis in Carbon Stars

We present the first detailed and homogeneous analysis of the s-element content in Galactic carbon stars of N-type. Abundances of Sr,Y, Zr (low-mass s-elements, or ls) and of Ba, La, Nd, Sm and Ce (high-mass s-elements, hs) are derived using the spectral synthesis technique from high-resolution spectra. The N-stars analyzed are of nearly solar metallicity and show moderate s-element enhancements, similar to those found in S stars, but smaller than those found in the only previous similar study (Utsumi 1985), and also smaller than those found in supergiant post-AGB stars. This is in agreement with the present understanding of the envelope s-element enrichment in giant stars, which is increasing along the spectral sequence M-->MS-->S-->SC-->C during the AGB phase. We compare the observational data with recent $s$-process nucleosynthesis models for different metallicities and stellar masses. Good agreement is obtained between low mass AGB star models (M < 3 M_o) and s-elements observations. In low mass AGB stars, the 13C(alpha, n)16O reaction is the main source of neutrons for the s-process; a moderate spread, however, must exist in the abundance of 13C that is burnt in different stars. By combining information deriving from the detection of Tc, the infrared colours and the theoretical relations between stellar mass, metallicity and the final C/O ratio, we conclude that most (or maybe all) of the N-stars studied in this work are intrinsic, thermally-pulsing AGB stars; their abundances are the consequence of the operation of third dredge-up and are not to be ascribed to mass transfer in binary systems.Comment: 31 pages, 10 figures, 6 tables. Accepted in Ap

When Color meets Gravity; Near-Threshold Exclusive J/ψJ/\psi Photoproduction on the Proton

The proton is one of the main building blocks of all visible matter in the universe. Among its intrinsic properties are its electric charge, mass, and spin. These emerge from the complex dynamics of its fundamental constituents, quarks and gluons, described by the theory of quantum chromodynamics (QCD). Using electron scattering its electric charge and spin, shared among the quark constituents, have been the topic of active investigation until today. An example is the novel precision measurement of the proton's electric charge radius. In contrast, little is known about the proton's inner mass density, dominated by the energy carried by the gluons, which are hard to access through electron scattering since gluons carry no electromagnetic charge. In the present work we chose to probe this gluonic gravitational density using a small color dipole, the $J/\psi$ particle, through its threshold photoproduction. From our data we determined, for the first time, the proton's gluonic gravitational form factors, which encode its mass density. We used a variety of methods and determined in all cases a mass radius that is notably smaller than the electric charge radius. In some cases, the determined radius is in excellent agreement with first-principle predictions from lattice QCD. This work paves the way for a deeper understanding of the salient role of gluons in providing gravitational mass to visible matter.Comment: Under peer revie

Consultocracy and its discontents : A critical typology and a call for a research agenda

Peer reviewe

First Measurement of the EMC Effect in 10^{10}B and 11^{11}B

The nuclear dependence of the inclusive inelastic electron scattering cross section (the EMC effect) has been measured for the first time in $^{10}$B and $^{11}$B. Previous measurements of the EMC effect in $A \leq 12$ nuclei showed an unexpected nuclear dependence; $^{10}$B and $^{11}$B were measured to explore the EMC effect in this region in more detail. Results are presented for $^9$Be, $^{10}$B, $^{11}$B, and $^{12}$C at an incident beam energy of 10.6~GeV. The EMC effect in the boron isotopes was found to be similar to that for $^9$Be and $^{12}$C, yielding almost no nuclear dependence in the EMC effect in the range $A=4-12$. This represents important, new data supporting the hypothesis that the EMC effect depends primarily on the local nuclear environment due to the cluster structure of these nuclei.Comment: Submitted to PR

Molecular Mechanism of the Constitutive Activation of the L250Q Human Melanocortin-4 Receptor Polymorphism †

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65471/1/j.1747-0285.2006.00362.x.pd

Beam-target helicity asymmetry e in K0 Λ and K0 Σ0 photoproduction on the neutron

We report the first measurements of the E beam-target helicity asymmetry for the γ - n - →K0Λ and K0Σ0 channels in the energy range 1.70≤W≤2.34 GeV. The CLAS system at Jefferson Lab uses a circularly polarized photon beam and a target consisting of longitudinally polarized solid molecular hydrogen deuteride with low background contamination for the measurements. The multivariate analysis method boosted decision trees is used to isolate the reactions of interest. Comparisons with predictions from the KaonMAID, SAID, and Bonn-Gatchina models are presented. These results will help separate the isospin I=0 and I=1 photocoupling transition amplitudes in pseudoscalar meson photoproduction

OBSERVATION OF HIGH YLEXCITED STATES OF PROTONATED NITROGEN, N2H4N_{2}H^{4}

$^{1}$ C. S. Gudeman, M. H. Begemann, J. Plaff and R. J. Saykally, J. Chem. Phys. 78, 5837 (1983). $^{2}$ T. J. Sears, J. Opt. Soc. Am. B. 2. 786 (1985). $^{3}$ S. C. Foster and A. R. W. McKellar, J. Chem. Phys, 81, 3424 (1984). $^{4}$ J. C. Owrutsky, C. S. Gudeman, C. C. Martiner, L. M. Tack, N. H. Rosenbaum and R. J. Saykally, J. Chem. Phys. 84, 605 (1986).Author Institution: Department of Chemistry and Astronomy and Astrophysics, University of ChicagoEach of the fundamental vibration bands of $N_{2}H^{+}$ has been previously $observed1-^{4}$ as well as the first hot $band^{4} v_{1}+v_{2}+v_{1}$. In this paper we report the observation of a very dense spectrum in the infrared region between $3240-3120 cm^{-1}$ corresponding to hot bands in each vibrational mode $(2v_{1}+v_{1}, v_{1}+v_{3}, v_{3}$ and $v_{1}+nv_{2}+nv_{2} (n=2,3)$. The spectrum was taken using our difference frequency spectrometer with the velocity modulation technique for detection. N2H was produced in a liquid-nitrogen cooled AC glow discharge with a mixture of 60 torr $N_{2}$. 120 mtorr $H_{2}$ and 7 torr He. The intensity of the lines had only a slight dependence on the amounts of N2 and H2+ whereas the hot bands decrease dramatically with the exclusion of He. Discussion of the vibrational and rotational temperatures will also be presented