Positron scattering by the negative hydrogen ion

Results are presented for e(+) scattering by H- in the impact energy range 0less than or equal toE(0)less than or equal to10 eV. These include integrated cross sections for Ps formation in the 1s, 2s, and 2p states, as well as in an aggregate of states with ngreater than or equal to3, and for direct ionization. Differential cross sections for Ps formation in the 1s, 2s, and 2p states are also exhibited. The calculations are based on a coupled pseudostate approach employing 19 Ps pseudostates centered on the e(+). It is found that Ps formation in the 2p state dominates that in the 1s or 2s states below 8 eV, that formation in states with ngreater than or equal to3 exceeds the sum of the n=1 and n=2 cross sections above 2.5 eV, and that direct ionization outstrips total Ps formation above 6.3 eV. The threshold law (E-0-->0) for exothermic Ps formation, which includes the cases Ps(1s), Ps(2s), and Ps(2p), is shown to be 1/E-0.

Escape times for rigid Brownian rotators in a bistable potential from the time evolution of the Green function and the characteristic time of the probability evolution

The greatest relaxation time for an assembly of three- dimensional rigid rotators in an axially symmetric bistable potential is obtained exactly in terms of continued fractions as a sum of the zero frequency decay functions (averages of the Legendre polynomials) of the system. This is accomplished by studying the entire time evolution of the Green function (transition probability) by expanding the time dependent distribution as a Fourier series and proceeding to the zero frequency limit of the Laplace transform of that distribution. The procedure is entirely analogous to the calculation of the characteristic time of the probability evolution (the integral of the configuration space probability density function with respect to the position co-ordinate) for a particle undergoing translational diffusion in a potential; a concept originally used by Malakhov and Pankratov (Physica A 229 (1996) 109). This procedure allowed them to obtain exact solutions of the Kramers one-dimensional translational escape rate problem for piecewise parabolic potentials. The solution was accomplished by posing the problem in terms of the appropriate Sturm-Liouville equation which could be solved in terms of the parabolic cylinder functions. The method (as applied to rotational problems and posed in terms of recurrence relations for the decay functions, i.e., the Brinkman approach c.f. Blomberg, Physica A 86 (1977) 49, as opposed to the Sturm-Liouville one) demonstrates clearly that the greatest relaxation time unlike the integral relaxation time which is governed by a single decay function (albeit coupled to all the others in non-linear fashion via the underlying recurrence relation) is governed by a sum of decay functions. The method is easily generalized to multidimensional state spaces by matrix continued fraction methods allowing one to treat non-axially symmetric potentials, where the distribution function is governed by two state variables. (C) 2001 Elsevier Science B.V. All rights reserved.

Negative photoion spectroscopy of the core-excited bromo- chloro-alkanes, Br(CH2)(n) Cl, n=1-4

Polar photodissociation of a set of bromo-chloro-alkanes in the vicinity of the Br 3d core edge has been observed for the first time. It is shown that negative photoion spectroscopy is a powerful tool for investigating the various decay mechanisms of core-excited molecules. Analysis of these results indicates that the observed polar photodissociation arises from two competing spectator Auger decay processes in which the molecule can dissociate either before or after the core hole relaxation.

Negative photoion spectroscopy of freon molecules in the vicinity of the Cl 2p edge

Polar photodissociation of CFnCl4-n (n=0-2) has been studied using synchrotron radiation within the energy range 195-217 eV. The first observations of negative photoion fragments from these molecules after core excitation are reported. In addition to observing a number of previously known resonances two additional resonant states, just above the Cl 2p ionization limit, are observed and play an important role in the polar photodissociation process. The difficulties in identifying these above threshold spin-split features using negative photoion spectroscopy are discussed.

Evidence for rescattering in intense, femtosecond laser interactions with a negative ion

It is now well established that energetic electron emission, nonsequential ionization, and high harmonic generation, produced during the interaction of intense, femtosecond laser pulses with atoms (and atomic positive ions), can be explained by invoking rescattering of the active electron in the laser field, the so-called rescattering mechanism. In contrast for negative ions, the role of rescattering has not been established experimentally. By irradiating F- ions with ultrashort laser pulses, F+ ion yields as a function of intensity for both linearly and circularly polarized light have been measured. We find that, at intensities well below saturation for F+ production by sequential ionization, there is a small but significant enhancement in the yield for the case of linearly polarized light, providing the first clear experimental evidence for the existence of the rescattering mechanism in negative ions.

The myeloproliferative disorder-associated JAK2 V617F mutant escapes negative regulation by suppressor of cytokine signaling 3

The somatic JAK2 valine-to-phenylalanine (V617F) mutation has been detected in up to 90% of patients with polycythemia and in a sizeable proportion of patients with other myeloproliferative disorders such as essential thrombocythemia and idiopathic myelofibrosis. Suppressor of cytokine signaling 3 (SOCS3) is known to be a strong negative regulator of erythropoietin (EPO) signaling through interaction with both the EPO receptor (EPOR) and JAK2. We report here that JAK2 V617F cannot be regulated and that its activation is actually potentiated in the presence of SOCS3. Instead of acting as a suppressor, SOCS3 enhanced the proliferation of cells expressing both JAK2 V617F and EPOR. Additionally, although SOCS1 and SOCS2 are degraded in the presence of JAK2 V617F, turnover of SOCS3 is inhibited by the JAK2 mutant kinase and this correlated with marked tyrosine phosphorylation of SOCS3 protein. We also observed constitutive tyrosine phosphorylation of SOCS3 in peripheral blood mononuclear cells (PBMCs) derived from patients homozygous for the JAK2 V617F mutant. These findings suggest that the JAK2 V617F has overcome normal SOCS regulation by hyperphosphorylating SOCS3, rendering it unable to inhibit the mutant kinase. Thus, JAK2 V617F may even exploit SOCS3 to potentiate its myeloproliferative capacity.

In vitro activity of tea-tree oil against clinical skin isolates of meticillin-resistant and -sensitive Staphylococcus aureus and coagulase-negative staphylococci growing planktonically and as biofilms

The susceptibility of Staphylococcus aureus [meticillin-resistant (MRSA) and meticillin-sensitive (MSSA)] and coagulase-negative staphylococci (CoNS), which respectively form part of the transient and commensal skin flora, to tea-tree oil (TTO) was compared using broth microdilution and quantitative in vitro time-kill test methods. MRSA and MSSA isolates were significantly less susceptible than CoNS isolates, as measured by both MIC and minimum bactericidal concentration. A significant decrease in the mean viable count of all isolates in comparison with the control was seen at each time interval in time-kill assays. However, the only significant difference in the overall mean log(10) reduction in viable count between the groups of isolates was between CoNS and MSSA at 3 h, with CoNS isolates demonstrating a significantly lower mean reduction. To provide a better simulation of in vivo conditions on the skin, where bacteria are reported to grow as microcolonies encased in glycocalyx, the bactericidal activity of TTO against isolates grown as biofilms was also compared. Biofilms formed by MSSA and MRSA isolates were completely eradicated following exposure to 5 % TTO for 1 h. In contrast, of the biofilms formed by the nine CoNS isolates tested, only five were completely killed, although a reduction in viable count was apparent for the other four isolates. These results suggest that TTO exerts a greater bactericidal activity against biofilm-grown MRSA and MSSA isolates than against some biofilm-grown CoNS isolates.

Testing the possible negative association of type 1 diabetes and atopic disease by analysis of the interleukin 4 receptor gene

Variations in the interleukin 4 receptor A (IL4RA) gene have been reported to be associated with atopy, asthma, and allergy, which may occur less frequently in subjects with type 1 diabetes (T1D). Since atopy shows a humoral immune reactivity pattern, and T1D results from a cellular (T lymphocyte) response, we hypothesised that alleles predisposing to atopy could be protective for T1D and transmitted less often than the expected 50% from heterozygous parents to offspring with T1D. We genotyped seven exonic single nucleotide polymorphisms (SNPs) and the -3223 C>T SNP in the putative promoter region of IL4RA in up to 3475 T1D families, including 1244 Finnish T1D families. Only the -3223 C>T SNP showed evidence of negative association (P=0.014). There was some evidence for an interaction between -3233 C>T and the T1D locus IDDM2 in the insulin gene region (P=0.001 in the combined and P=0.02 in the Finnish data set). We, therefore, cannot rule out a genetic effect of IL4RA in T1D, but it is not a major one.