Jump conditions for pressure anisotropy and comparison with the Earth's bow shock

International audienceTaking into account the pressure anisotropy in the solar wind, we study the magnetic field and plasma parameters downstream of a fast shock, as functions of upstream parameters and downstream pressure anisotropy. In our theoretical approach, we model two cases: a) the perpendicular shock and b) the oblique shock. We use two threshold conditions of plasma instabilities as additional equations to bound the range of pressure anisotropy. The criterion of the mirror instability is used for pressure anisotropy p \perp /p\parrallel > 1. Analogously, the criterion of the fire-hose instability is taken into account for pressure anisotropy p \perp /p\parrallel < 1. We found that the variations of the parallel pressure, the parallel temperature, and the tangential component of the velocity are most sensitive to the pressure anisotropy downstream of the shock. Finally, we compare our theory with plasma and magnetic field parameters measured by the WIND spacecraft

Comparison of urinary monitoring, faecal monitoring and erythrocyte analysis of stable isotope labels to determine magnesium absorption in human subjects

We have evaluated urinary monitoring and erythrocyte analysis to determine Mg absorption in human subjects as alternatives to the conventional technique of faecal monitoring by stable-isotope techniques. Ten healthy adults received 2·2 mmol 25Mg in water, together with wheat bread, followed 15 min later by intravenous injection of 0·6 mmol 26Mg (day 1). Brilliant blue and Yb (given on day 0 and day 1 respectively) served as qualitative and quantitative faecal markers. Urine was collected for 6 d after test meal intake. Complete collections of faeces were made until excretion of the second brilliant blue marker (given on day 7). Mg isotope ratios were determined by thermal ionisation-MS in urine and faeces and by inductively coupled plasma-MS in erythrocytes. Absorption was determined based on: (1) 6 d urine pools; (2) 24 h urine pools (collected 22-46 h after test meal intake); (3) erythrocytes from a blood sample drawn on day 14; (4) complete 6 d faecal pools; (5) faecal pools based on the first three consecutive stools after excretion of the first brilliant blue marker. Differences in mean Mg absorption (42 44 %) were statistically insignificant between techniques, except when based on 6 d urine pools for which the value was significantly lower (33 (sd 7) %, P=0·0003, ANOVA). The results indicate that Mg absorption can be determined from 24 h urine pools or erythrocytes obtained 14 d after test meal intake, an alternative method to the more time-consuming and labour-intense faecal monitoring. The choice of technique depends on practical and financial consideration

Vibroakustische Sensorik zur aktiven Minimierung der Schallab strahlung schwingender Strukturen

Für die Entwicklung adaptiver Struktursysteme, die u.a. auf die akustische Verbesserung von Bauteilen abzielen, ist die Kenntnis des Zusammenhangs zwischen dem dynamischen Verhalten und dem dadurch induzierten Luftschallfeld notwendig. In den vergangenen Jahren wurden zahlreiche Untersuchungen zur Ermittlung dieses Zusammenhangs durchgeführt. Eine notwendige Bedingung für die Realisierung eines adaptiven vibroakustischen Systems ist die sensorische Erfassung des entstehenden Luftschallfeldes anhand strukturdynamischer Messgrößen. Da die globale Erfassung der abgestrahlten Schallleistung konventionell nur mit externen Messwertaufnehmern möglich ist (z.B. Mikrophone, Schallintensitätssonden) und sich eine solche technische Lösung nur mit sehr hohem Aufwand realisieren lässt, soll hier ein Ansatz vorgestellt werden, der auf strukturapplizierte Sensoren zur Ermittlung der globalen Schallabstrahlung schwingender Strukturen abzielt. Als Sensoren werden piezokeramische Plättchen (PZT-Patches) eingesetzt. Als Maß für die abgestrahlte Schallleistung wird die Volumengeschwindigkeit verwendet, die aus den Sensorsignalen der Patches rekonstruiert wird. Somit entfallen aufwendige akustische Messungen. Ein weiteres Ziel der Arbeit ist die Integration der rekonstruierten Zielfunktion in einen adaptiven Regelkreis

Versuche zur Synthese des Cytisins. Dehydrierung von Tetrahydro-cytisin zu Cytisin

Die Dehydrierung von Tetrahydro-cytisin zu Cytisin mit Palladium verläuft glatt, wenn man die Iminogruppe durch Acetylierung schützt. Durch Erhitzen des N-Acetyl-tetrahydrocytisins mit Pd-Mohr bei 280° erhält man so in guter Ausbeute N-Acetyl-cytisin und daraus durch Abspaltung der Acetyl-gruppe mit Salzsäure das Cytisin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41696/1/706_2004_Article_BF00899864.pd

Charge form factor of π\pi and KK mesons

The charge form factor of $\pi$ and $K$ mesons is evaluated adopting a relativistic constituent quark model based on the light-front formalism. The relevance of the high-momentum components of the meson wave function, for values of the momentum transfer accessible to $CEBAF$ energies, is illustrated. The predictions for the elastic form factor of $\pi$ and $K$ mesons are compared with the results of different relativistic approaches, showing that the measurements of the pion and kaon form factors planned at $CEBAF$ could provide information for discriminating among various models of the meson structure.Comment: 8 pages, latex, 4 figures available as separate .uu fil

A novel magnet-based scratch method for standardisation of wound-healing assays

A novel magnetic scratch method achieves repeatability, reproducibility and geometric control greater than pipette scratch assays and closely approximating the precision of cell exclusion assays while inducing the cell injury inherently necessary for wound healing assays. The magnetic scratch is affordable, easily implemented and standardisable and thus may contribute toward better comparability of data generated in different studies and laboratories

Extended van Royen-Weisskopf formalism for lepton-antilepton meson decay widths within non-relativistic quark models

The classical van Royen-Weisskopf formula for the decay width of a meson into a lepton-antilepton pair is modified in order to include non-zero quark momentum contributions within the meson as well as relativistic effects. Besides, a phenomenological electromagnetic density for quarks is introduced. The meson wave functions are obtained from two different models: a chiral constituent quark model and a quark potential model including instanton effects. The modified van Royen-Weisskopf formula is found to improve systematically the results for the widths, giving an overall good description of all known decays.Comment: 22 pages, 3 figures, RevTex, epsfig. To be published in Nucl. Phys.