Causality in Inflationary Universes with Positive Spatial Curvature

We show that in the case of positively-curved Friedmann-Lemaître universes (k = +1), an inflationary period in the early universe will for most initial conditions not solve the horizon problem, no matter how long inflation lasts. It will only do so for cases where inflation starts in an almost static state, corresponding to an extremely high value of , 1, at the beginning of inflation. For smaller values, it is not possible to solve the horizon problem because the relevant integral asymptotes to a finite value (as happens also in the de Sitter universe in a k = +1 frame). Thus, for these cases, the causal problems associated with the near-isotropy of the Cosmic Background Radiation have to be solved already in the Planck era. Furthermore both compact space sections and event horizons will exist in these universes even if the present cosmological constant dies away in the far future, raising potential problems for M-theory as a theory of gravity.     

Investigations into the interactions between DNA and conformationally constrained pyridylamineplatinum(II) analogues of AMD473

The syntheses of [PtCl(2)(amp)] (amp = 2-pyridylmethylamine) and enantiomerically pure [PtCl(2)(R-pea)] and [PtCl(2)(S-pea)] (pea = 1-(2-pyridyl)ethylamine) and the crystal structure of [PtCl(2)(R-pea)] are reported. The reactions of [PtCl(2)(amp)] and of the enantiomers of [PtCl(2)(pea)] with d(GpG) and with a 52-base-pair oligonucleotide were investigated. Each of the reactions with d(GpG) resulted in the formation of three platinated bifunctional d(GpG) species in a ratio of 1:2:1. These species were shown to be a pair of isomers, one of which exists as a pair of slowly interconverting rotamers that can be separated by HPLC but reequilibrate after 5 days at 37 degrees C. The pyridyl moieties of the pyridylalkylamine ligands are constrained to lie in the coordination plane, and as a consequence, the rotation about the Pt-N7 bond of the adjacent guanine is highly restricted. 2D NMR investigations were carried out on the isomer of [Ptd(GpG)(amp)] that did not form separable rotamers and identified it as the isomer having the pyridine adjacent to the 5'-guanine of the d(GpG). The reaction of each of the three [PtCl(2)(py-R)] complexes (py-R = amp or pea) with a 52-base-pair oligonucleotide resulted in the formation of the same three bifunctional d(GpG) adducts in approximately the same ratios as the reactions with d(GpG), indicating that negligible stereoselectivity results from interactions between the complexes and duplex DNA.     

Experimental demonstration of quantitation errors in MR spectroscopy resulting from saturation corrections under changing conditions

Metabolite concentration measurements in in vivo NMR are generally performed under partially saturated conditions, with correction for partial saturation performed after data collection using a measured saturation factor. Here, we present an experimental test of the hypothesis that quantitation errors can occur due to application of such saturation factor corrections in changing systems. Thus, this extends our previous theoretical work on quantitation errors due to varying saturation factors. We obtained results for two systems frequently studied by 31P NMR, the ischemic rat heart and the electrically stimulated rat gastrocnemius muscle. The results are interpreted in light of previous theoretical work which defined the degree of saturation occurring in a one-pulse experiment for a system with given spin-lattice relaxation times, T(1)s, equilibrium magnetizations, M(0)s, and reaction rates. We found that (i) the assumption of constancy of saturation factors leads to quantitation errors on the order of 40% in inorganic phosphate; (ii) the dominant contributor to the quantitation errors in inorganic phosphate is most likely changes in T(1); (iii) T(1) and M(0) changes between control and intervention periods, and chemical exchange contribute to different extents to quantitation errors in phosphocreatine and gamma-ATP; (iv) relatively small increases in interpulse delay substantially decreased quantitation errors for metabolites in ischemic rat hearts; (v) random error due to finite SNR led to approximately 4% error in quantitation, and hence was a substantially smaller contributor than were changes in saturation factors.     

Estimation of background interference in prompt-gamma neutron activation using MCNP

Prompt-gamma neutron activation (PGNA) is used to measure total-bodynitrogen and hydrogen in humans. Background interference in the gamma spectraarises from both subject and shielding. A Monte Carlo simulation program (MCNP4B2)was used to examine the neutron and gamma signals in the PGNA system ( ²⁴¹AmBe source). N and H peak regions were assessed in the presenceand absence of calibration phantoms. The simulations suggested extracorporealH peak contributions of up to 30%, depending on subject body habitus. MostN background could be attributed to detector pileup events. The MCNP resultsallowed us to improve shielding design and develop background correction algorithmsto improve measurement precision.     

Broad-line NMR studies of molecular motion in cured epoxy resins

The conformation of network chain segments in a rigid glassy DDM-cured bisphenol A epoxy resin has been determined by means of rotational isomeric-state model and confirmed by conformity of experimental NMR second moments with a theoretical estimate based on the model. The glass transition temperatures T_g have been determined from precipitate NMR line narrowing with increase in temperature due to the onset of rapid (>10⁴ Hz) main-chain molecular motion. The temperature dependence of the correlation frequency has been determined and the type and extent of molecular motion that occurs in such epoxy resins is discussed.     

Regge calculus and observations. II. Further applications

The method, developed in an earlier paper, for tracing geodesies of particles and light rays through Regge calculus space-times, is applied to a number of problems in the Schwarzschild geometry. It is possible to obtain accurate predictions of light bending by taking sufficiently small Regge blocks. Calculations of perihelion precession, Thomas precession, and the distortion of a ball of fluid moving on a geodesic can also show good agreement with the analytic solution. However difficulties arise in obtaining accurate predictions for general orbits in these space-times. Applications to other problems in general relativity are discussed briefly.