Experimental investigation of the plasma-wall transition

We report on measurements of the ion velocity distribution as a function of distance to a target immersed in a magnetized argon plasma. Two situations are investigated: (a) practically the whole plasma streams onto a large target, and (b) the size of the target is significantly smaller than the plasma diameter. The Mach number M=u/c_{s} decreases from M=1 at the target surface to values around 0.5 at a typical scale of lambda_{a}=30 mm and lambda_{b}=5 mm, respectively. In order to explain these small decay lengths, the measurements of case (a) are compared with a source-diffusion model and those of (b) to Hutchinson's model. In (a) good agreement between modeling and experiment is obtained assuming a low neutral gas temperature. The data in (b) also agree excellently with modeled profiles, although the large fitting parameter D=20 m;{2}/s indicates that other processes than diffusion contribute significantly to the transport.     

The significance of anti-neuronal antibodies for acute psychiatric disorders: a retrospective case–controlled study

Background

The clinical significance of anti-neuronal antibodies in patients with psychiatric disorders, but without encephalitis, remains unknown. In patients admitted to acute psychiatric inpatient care we aimed to identify clinical features distinguishing anti-neuronal antibody positive patients from matched controls.

Results

Patients who were serum-positive to N-methyl d-aspartate receptor (NMDAR) (n?=?21), contactin-associated protein 2 (CASPR2) (n?=?14) and/or glutamic acid decarboxylase 65 (GAD65) (n?=?9) antibodies (cases) were age and sex matched (1:2) with serum-negative patients from the same cohort (controls). The prevalence and severity of psychiatric symptoms frequently encountered in NMDAR, CASPR2 and GAD65 antibody associated disorders were compared in cases and controls. NMDAR, CASPR2 and GAD65 antibody positive patients did not differ in their clinical presentation from matched serum negative controls.

Conclusion

In this cohort, patients with and without NMDAR, CASPR2 and GAD65 antibodies admitted to acute psychiatric inpatient care had similar psychiatric phenotypes. This does not exclude their clinical relevance in subgroups of patients, and studies further investigating the clinical significance of anti-neuronal antibodies in patients with psychiatric symptomatology are needed.

     

Inhomogeneous Lattice Paths, Generalized Kostka Polynomials and A n −1 Supernomials

Inhomogeneous lattice paths are introduced as ordered sequences of rectangular Young tableaux thereby generalizing recent work on the Kostka polynomials by Nakayashiki and Yamada and by Lascoux, Leclerc and Thibon. Motivated by these works and by Kashiwara's theory of crystal bases we define a statistic on paths yielding two novel classes of polynomials. One of these provides a generalization of the Kostka polynomials, while the other, which we name the A_nу supernomial, is a q-deformation of the expansion coefficients of products of Schur polynomials. Many well-known results for Kostka polynomials are extended leading to representations of our polynomials in terms of a charge statistic on Littlewood-Richardson tableaux and in terms of fermionic configuration sums. Several identities for the generalized Kostka polynomials and the A_nу supernomials are proven or conjectured. Finally, a connection between the supernomials and Bailey's lemma is made.     

The Role of Coherence Transfer Efficiency in Design of TROSY-Type Multidimensional NMR Experiments

An improved method for TROSY-type (Pervushin et al., Proc. Natl. Acad. Sci. USA 94, 12366-12371 (1997)) heteronuclear two-dimensional correlation involving protons of negligible CSA is presented. Rather than applying a simple INEPT sequence for back-transfer to protons (Pervushin et al., J. Am. Chem. Soc. 120, 6394-6400 (1998)), we replace the pi/2 proton pulse in INEPT by a spin-state-selective coherence transfer element (Sorensen et al., J. Biomol. NMR 10, 181-186 (1997)) and maintain broadband decoupling during acquisition. Theoretically that results in a sensitivity enhancement of a factor of 2. The new method is demonstrated using a (13)C,(15)N-labeled protein sample, RAP 18-112 (N-terminal domain of alpha(2)-macroglobulin receptor associated protein), at 750 MHz.     

High-energy collision-induced dissociation mass spectrometry of synthetic mannose-6-phosphate oligosaccharides

The high-energy collision-induced dissociation spectra of a series of linear and branched synthetic mannosyl oligosaccharides that contain 6-phosphate substituents on either or both non-reducing terminal or penultimate residues have been studied. These phosphorylated structures were designed to mimic those of naturally derived N-glycans (Man-6-PO₄) on lysosomal enzymes and to probe the minimally required binding motif for the Man-6-PO₄ receptors. When a phosphate group was present, the spectra were dominated by ions that arise from cleavages at the glycosidic bonds (single and double) with charge retention on the phosphate-containing fragments. The spectra of linear structures that bear the nonreducing terminal Man-6-phosphate residues were devoid of Y-type ions, unlike those with similar phosphorylation at the penultimate residue. The location of the phosphorylated residue was deduced from the presence or absence of unique B and Y ions. In neutral branched structures, the ions were formed by cleavage at the glycosidic bond at either one or both of the branch points and the aglycon, which was attached to the disubstituted mannosyl residue. Branched oligosaccharides that contained one or two terminal Man-6-PO₄ residues also showed double cleavages with charge retention on the phosphate-containing fragment. Our investigation shows that positive mode high energy collision-induced dissociation mass spectrometry can determine the location—terminal or penultimate—of Man-6-PO₄ residues in N-linked type oligosaccharides.     

Absolute rate constants for F + CH3CHO and CH3CO + O2, relative rate study of CH3CO + NO,and the product distribution of the F + CH3CHO reaction

Using a pulse-radiolysis transient UV–VIS absorption system, rate constants for the reactions of F atoms with CH₃CHO (1) and CH₃CO radicals with O₂ (2) and NO (3) at 295 K and 1000 mbar total pressure of SF₆ was determined to be k₁=(1.4±0.2)×10⁻¹⁰, k₂=(4.4±0.7)×10⁻¹², and k₃=(2.4±0.7)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹. By monitoring the formation of CH₃C(O)O₂ radicals (λ>250nm) and NO₂ (λ=400.5nm) following radiolysis of SF₆/CH₃CHO/O₂ and SF₆/CH₃CHO/O₂/NO mixtures, respectively, it was deduced that reaction of F atoms with CH₃CHO gives (65±9)% CH₃CO and (35±9)% HC(O)CH₂ radicals. Finally, the data obtained here suggest that decomposition of HC(O)CH₂O radicals via C C bond scission occurs at a rate of <4.7×10⁵ s⁻¹. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 913–921, 1998     

Oxidation of dimethyl ether: Absolute rate constants for the self reaction of CH3OCH2 radicals,the reaction of CH3OCH2 radicals with O2, and the thermal decomposition of CH3OCH2 radicals

The rate constant for the reaction of CH₃OCH₂ radicals with O₂ (reaction (1)) and the self reaction of CH₃OCH₂ radicals (reaction (5)) were measured using pulse radiolysis coupled with time resolved UV absorption spectroscopy. k₁ was studied at 296K over the pressure range 0.025–1 bar and in the temperature range 296–473K at 18 bar total pressure. Reaction (1) is known to proceed through the following mechanism: CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# → CH₂OCH₂O₂H^# → 2HCHO + OH (k_prod) CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# + M → CH₃OCH₂O₂ + M (k_RO2) k = k_RO2 + k_prod, where k_RO2 is the rate constant for peroxy radical production and k_prod is the rate constant for formaldehyde production. The k₁ values obtained at 296K together with the available literature values for k₁ determined at low pressures were fitted using a modified Lindemann mechanism and the following parameters were obtained: k_RO2,0 = (9.4 ± 4.2) × 10⁻³⁰ cm⁶ molecule⁻² s⁻¹, k_RO2,∞ = (1.14 ± 0.04) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_prod,0 = (6.0 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, where k_RO2,0 and k_RO2,∞ are the overall termolecular and bimolecular rate constants for formation of CH₃OCH₂O₂ radicals and k_prod,0 represents the bimolecular rate constant for the reaction of CH₃OCH₂ radicals with O₂ to yield formaldehyde in the limit of low pressure. k_RO2,∞ = (1.07 ± 0.08) × 10⁻¹¹ exp(−(46 ± 27)/T) cm³ molecule⁻¹ s⁻¹ was determined at 18 bar total pressure over the temperature range 296–473K. At 1 bar total pressure and 296K, k₅ = (4.1 ± 0.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and at 18 bar total pressure over the temperature range 296–523K, k₅ = (4.7 ± 0.6) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. As a part of this study the decay rate of CH₃OCH₂ radicals was used to study the thermal decomposition of CH₃OCH₂ radicals in the temperature range 573–666K at 18 bar total pressure. The observed decay rates of CH₃OCH₂ radicals were consistent with the literature value of k₂ = 1.6 × 10¹³exp(−12800/T)s⁻¹. The results are discussed in the context of dimethyl ether as an alternative diesel fuel. © 1997 John Wiley & Sons, Inc.