The determination of chlorine in organic materials by combustion and microcoulometry

A combustion apparatus capable of burning both solid and liquid samples is described. The samples were vaporized in helium and then burned in humid oxygen. Oxygen was then used to burn non-volatile residues within the vaporization chamber. The use of cheap, disposable vaporization chambers eliminated carryover from one analysis to the next. The application of this instrument to the determination of organochlorine-containing samples is described. The moist effluent hydrogen chloride from the combustion was condensed and the chloride content was determined by microcoulometry. Pure solutions of high-boiling inorganic chlorides did not evolve chloride but the addition of an amino acid resulted in evolution of all of the chloride present.     

Controlling the spontaneous emission rate of single quantum dots in a two-dimensional photonic crystal

We observe large spontaneous emission rate modification of individual InAs quantum dots (QDs) in a 2D photonic crystal with a modified, high-Q single-defect cavity. Compared to QDs in a bulk semiconductor, QDs that are resonant with the cavity show an emission rate increase of up to a factor of 8. In contrast, off-resonant QDs indicate up to fivefold rate quenching as the local density of optical states is diminished in the photonic crystal. In both cases, we demonstrate photon antibunching, showing that the structure represents an on-demand single photon source with a pulse duration from 210 ps to 8 ns. We explain the suppression of QD emission rate using finite difference time domain simulations and find good agreement with experiment.     

Reactive glass and vegetation patterns

The formation of vegetation patterns in the arid and the semiarid climatic zones is studied. Threshold for the biomass of the perennial flora is shown to be a relevant factor, leading to a frozen disordered pattern in the arid zone. In this "glassy" state, vegetation appears as singular plant spots separated by irregular distances, and an indirect repulsive interaction among shrubs is induced by the competition for water. At higher precipitation rates, the diminishing of hydrological losses in the presence of flora becomes important and yields spatial attraction and clustering of biomass. Turing patterns with characteristic length scale emerge from the disordered structure due to this positive-feedback instability.     

L-edge X-ray absorption spectroscopy of non-heme iron sites: experimental determination of differential orbital covalency

X-ray absorption spectroscopy has been utilized to obtain the L-edge multiplet spectra for a series of non-heme ferric and ferrous complexes. Using these data, a methodology for determining the total covalency and the differential orbital covalency (DOC), that is, differences in covalency in the different symmetry sets of the d orbitals, has been developed. The integrated L-edge intensity is proportional to the number of one-electron transition pathways to the unoccupied molecular orbitals as well as to the covalency of the iron site, which reduces the total L-edge intensity and redistributes intensity, producing shake-up satellites. Furthermore, differential orbital covalency leads to differences in intensity for the different symmetry sets of orbitals and, thus, further modifies the experimental spectra. The ligand field multiplet model commonly used to simulate L-edge spectra does not adequately reproduce the spectral features, especially the charge transfer satellites. The inclusion of charge transfer states with differences in covalency gives excellent fits to the data and experimental estimates of the different contributions of charge transfer shake-up pathways to the t(2g) and e(g) symmetry orbitals. The resulting experimentally determined DOC is compared to values calculated from density functional theory and used to understand chemical trends in high- and low-spin ferrous and ferric complexes with different covalent environments. The utility of this method toward problems in bioinorganic chemistry is discussed.     

Induced in-source fragmentation for the selective detection of organic bound iodine by liquid chromatography/electrospray mass spectrometry

The detection of unknown organic compounds, e.g., transformation products of known trace pollutants in environmental samples, is a difficult task which can be simplified if the compounds of interest are characterized by a functional group or a heteroatom which can selectively be detected. For the detection of iodinated benzene derivatives, used as X-ray contrast media, we have studied whether such compounds can be selectively detected by negative ion (NI) electrospray ionization via iodide as a product ion of in-source fragmentation, generated by applying a high cone voltage. It was found that selective detection of iodinated benzene derivatives is possible by liquid chromatography/negative ion electrospray ionization (LC/NI-ESI) if the compounds are destroyed before entering the mass spectrometer. To our knowledge this is the first report of the use of NI in-source fragmentation MS for analyses traditionally performed with inductively coupled plasma (ICP)-MS. The novel application of NI in-source fragmentation MS is a tool for those who do not possess the facilities to perform ICP-MS. Furthermore, NI-ESI at varying cone voltages provides both structural information and elemental detection, whereas ICP-MS can only provide elemental detection.     

Toward a Characterization of Conway's Group Co3

In this paper, Conway's group, Co₃, is characterized among simplegroups of even type with e(G) = 3, by a restriction on the p-localstructure for some odd prime p for which m_2,p(G) = 3. 2000 MathematicsSubject Classification 20D05.     

A Note on Base Change,Identities Involving τ(n), and a Congruence of Ramanujan

We use the theory of quadratic base change to derive some new identities involving the Ramanujan -function, and show how the Ramanujan congruence (n) ₁₁(n) (mod 691) follows.     

Mach's principle and Newtonian mechanics

The union of Mach's principle and Newtonian mechanics gives rise to Relational Mechanics. We find that the characteristics of the revised mechanics are: (1) freedom from any reference to absolute space; (2) the identity of inertial and gravitational mass; (3) the relative acceleration of a body in a gravitational field dependent on the mass of the body. All these results are valid in the context of a Newtonian mechanics which is being developed in the center-of-mass system of all the particles. The conservation of linear momentum, energy, angular momentum are expressed in relational terms, i.e., no reference is made to absolute space. Relational Mechanics is a classical relativistic theory which can be formulated to satisfy Einsteinian relativistic requirements. The Hamiltonian formalism for Relational Mechanics is discussed. Preliminary report Bull. Am. Phys. Soc.14, 15 (1969)     

The q-Zassenhaus formula

A q-deformed analogue of the Zassenhaus formula, expressing the q-exponential of a sum of two noncommuting operators in terms of an infinite product of q-exponentials, is introduced.