Analysis of the laser magnetic resonance spectrum of HO2

An analysis of the previously detected laser magnetic resonance spectrum of HO₂ is carried out by (i) assigning M_J quantum numbers to each observed Zeeman line, (ii) determining the quantum numbers (N′_Ka′Kc′-N″_Ka″Kc″) and energies of the zero-field asymmetric rotor transitions involved, and (iii) determining the values of the zero-field spin-rotation doublet splittings in the upper and lower states of each asymmetric rotor transition. The rotational transitions obtained lie in the region 50–150 cm^?1, with quantum numbers 4 ≤ N ≤ 19 and 1 ≤ K_a ≤ 4. They are fit to an asymmetric rotor program to obtain the three rotational constants A, B, C and the three symmetric-top centrifugal distortion constants D_K, D_NK, D_N. The spin splittings are fit to an approximate theoretical expression involving two adjustable linear combinations of components of the spin-rotation interaction tensor ?. Because of the lack of spectra from other isotopic species, a unique molecular geometry cannot be derived.     

Rotational laser magnetic resonance spectroscopy of PH2(X 2B1)

Laser magnetic resonance spectra arising from eight rotational transitions of PH₂ in its vibronic ground state have been measured in the far infrared region. Analysis of the spectra yields more accurate rotational, centrifugal distortion and fine structure parameters than previous spectroscopic results. Determination of the isotropic an anisotropic hyperfine constant from the resolved ³¹P and proton hyperfine structure shows that the unpaired electron is essentially located in a 3p atomic orbital on the phosphorus atom.     

The epistemic,the cognitive,the human: a commentary on the mathematical working space approach

ZDM – Mathematics Education - This article is a commentary on the mathematical working space (MWS) approach and draws on the articles contained in this ZDM issue. The article is divided into...     

Observation of the weakly deformedvi 13 2/2 band in188Hg

High-Spin states in¹⁸⁸Hg have been investigated using the¹⁶⁸Er(²⁴Mg,4n) reaction. The rotation aligned vi ₁₃ ^2/2 band, which intersects the weakly oblate ground state band atI≈10, is observed up toI ^π =20⁺ with an isomeric 12⁺ level with T_1/2=134(15)ns. The coexisting strongly deformed band, built on the 825 keV 0⁺ level, is observed up to the 14⁺ state. The systematics of the vi ₁₃ ^2/2 rotation aligned bands is discussed.     

Superdeformation in144Eu

A ridge has been found in a - coincidence matrix obtained from the reaction¹²²Sn(²⁷Al,5n)¹⁴⁴Euat 142 MeV.The half-width of the valley is 59 keV,which is similar to the energy spacings in the superdeformed bands in ¹⁴³Euand ¹⁴²Sm.This indicates the existence of superdeformed bands in ¹⁴⁴Eu.This work was supported by the Natural Sciences and Engineering Research Council of Canada and AECL Research. We thank the crew and staff at TASCC for supplying the beams, and Dr.R.A.Wyss for use of the CSM and TRS codes.     

pH as a trigger of peptide beta-sheet self-assembly and reversible switching between nematic and isotropic phases

The hierarchical self-assembly of rationally designed synthetic peptides into beta-sheet tapes, ribbons, fibrils, and fibers opens up potentially useful routes to soft-solidlike materials such as hydrogels, organogels, or liquid crystals. Here, it is shown how incorporation of Glu (-CH(2)CH(2)COOH) or Orn (-CH(2)CH(2)CH(2)NH(2)) into the primary structure of an 11 amino acid peptide enables self-assembly to be rapidly (seconds) and reversibly controlled by simply changing pH. Solutions of monomeric peptide, typically at concentrations in excess of 0.003 v/v, can be switched within seconds to, for example, nematic gel states comprised of interconnected orientationally ordered arrays of fibrils or vice versa. This is to be compared with the lyophilized peptide dissolution route to nematic fluids and gels which is impracticably long, taking many hours or even days. An important design principle, that stabilization of fibrillar dispersions requires of the order of one unit of net positive or negative charge per peptide molecule, is first demonstrated and then used to design an 11 amino acid peptide P(11)-3 (CH(3)CO-Gln-Gln-Arg-Phe-Gln-Trp-Gln-Phe-Gln-Gln-Gln-NH(2)) whose self-assembly behavior is independent of pH (1 < pH < 10). pH control is then incorporated by appropriately positioning Glu or Orn side chains so that the peptide-peptide free energy of interaction in the tapelike substructure is strongly influenced by direct electrostatic forces between gamma-COO(-) in Glu(-) or delta-NH(3)(+) in Orn(+), respectively. This design principle is illustrated by the behavior of two peptides: P(11)-4 (CH(3)CO-Gln-Gln-Arg-Phe-Glu-Trp-Glu-Phe-Glu-Gln-Gln-NH(2)) which can be switched from its nematic to its isotropic fluid state by increasing pH and P(11)-5 (CH(3)CO-Gln-Gln-Orn-Phe-Orn-Trp-Orn-Phe-Gln-Gln-Gln-NH(2)) designed to exhibit the converse behavior. Acid-base titrations of fibrillar dispersions reveal deprotonation of the gamma-COOH of Glu or of the delta-NH(3)(+) of Orn(+) occurs over wide bands of up to 5 pH units, a feature of polyelectrolytes. The values of the energy parameters controlling self-assembly can therefore be smoothly and continuously varied by changing pH. This enables isotropic fluid-to-nematic transitions to be triggered by relatively small additions of acid or base, typically 1 part in 10(3) by volume of 1 M HCl or NaOH.     

A note on irreducibility and existence of integer spin zero-rest-mass fields

It is shown that only for spins 1 and 2 (electronmagnetism and gravitation) does the generic integer spin, source-free, zero-rest-mass field generate an irreducible representation of the proper orthochronous Lorentz group,L+. The conclusion is then drawn that as these higher-spin fields can in no sense be considered as elementary we have strong mathematical (and physical) grounds for their (apparent) nonexistence in nature.