The new particles and their significance

In November 1974 a dramatic revolution occurred in high-energy physics when two teams of workers independently discovered a massive subatomic particle named the J or ψmeson (Aubert et al. 1974, Augustin et al. 1974). Within two years the leaders of these two teams (B. Richter and S. C. C. Ting) had been awarded the Nobel Prize for physics. This alone bears testimony to the significance of the discovery. In this article I hope to be able to explain why this discovery was so significant, how it opened up a new conception of the sub-atomic world and describe some of the related discoveries and developments that have been made in the subsequent four years.     

Extended temperature tuning of an external cavity diode laser

We describe the construction and operation of an external cavity diode laser in which the diode is cooled to -45 °C. This technique allows us to pull the wavelength of a nominally 782 nm diode to operate at 766.7 nm, a change of over 15 nm. The important aspects of our design are its ease and low cost as compared to other designs of changing the operating wavelength of laser diodes. We provide background information on thermal design with multiple TECs so the reader can extend this example for use in their own applications. PACS 42.60.By; 42.62.Fi; 32.80.Pj     

A 13C NMR study of mesomorphic solutions of poly(p-phenylene terephthalamide)

Solutions of poly(p-phenylene terephthalamide) in fuming sulfuric acid were characterized by ¹³C NMR spectroscopy and solution viscosity measurements over the 2–28% w/w concentration range. The spectra showed the presence of two distinct amide carbonyl resonances at low concentration, tentatively assigned to cis and trans conformations. As the concentration increased, additional carbonyl lines were observed along with significant broadening. Peak area measurements showed that only the polymer molecules in the isotropic environments contributed to the ¹³C NMR spectra and a considerable amount of the polymer remained in the isotropic phase at concentrations previously considered to consist of polymer in highly anisotropic regions. Spin-lattice relaxation times were measured at six concentrations using the inversion recovery method. The aromatic carbons relaxed at a much faster rate (ca. 0.10 s) than the carbonyls (ca. 0.45 s), but the relaxation rates for both carbons were essentially constant over the concentration range, indicating that the observed isotropic phase is not affected by changes in the macroscopic solution behavior so as to alter spin-lattice relaxation mechanisms.     

Average resonance spectroscopy in 93, 95, 97Tc

The (p, γ) reactions on the ⁹²Mo, ⁹⁴Mo and ⁹⁶Mo isotopes were studied in the energy range E_p = 2.4–3.0 MeV using a Ge(Li) detector incorporated into a three-crystal pair spectrometer and a Ge(Li) detector in coincidence with a NaI(Tl) detector. A three-crystal pair spectrometer was utilized to determine the average yield of γ-rays leading directly to the low-lying states in each of the three residual nuclei. These average yields were examined for a possible correlation between the intensity of high-energy γ-ray transitions and the J^π of the final state. The data indicate that such a correlation exists. A two-dimensional coincidence experiment determined the decay scheme of the low-lying excited states in ⁹³Tc ⁹⁵Tc and ⁹⁷Tc. The J^π assignments inferred from these experiments are consistent with those for the states in ⁹³Tc, ⁹⁵Tc and ⁹⁷Tc which have previously been obtained. For those states which were previously unassigned, the results of this experiment are as follows (all energies are in keV): . The state at 2429 keV in ⁹³Tc has not been reported previously.     

On the role of diquarks in deep inelastic structure functions

Zeitschrift für Physik C Particles and Fields - It has been suggested that almost all theQ 2 dependence of nucleon structure functions can be unberstood in terms of quark (scaling) + diquark...     

Ionization energies of the nucleotides

The vertical ionization energies of the four nucleotides have been computed. Geometries have been chosen to mimic orientations as they appear in B-DNA. The negative charge on the phosphate was neutralized by protonation, and also by the inclusion of counterions. Calculations have been performed with electron propagator methods (P3), M?ller-Plesset second-order perturbation theory, and density functional theory to determine the nature of the orbitals associated with the highest lying ionization energies. Calculations at the MP2/6-311G(d,p)//P3/6-311G(d,p) level of theory yield vertical ionization energies for 5'-dTMP 9.05 eV, for 5'-dCMP 8.40 eV, for 5'-dAMP 8.16 eV and for 5'-dGMP 7.96 eV. In all cases the highest occupied molecular orbital resides on the base moieties.