Bibliothek

Notizen: [Auszug] Targeting of the replacement vector (pExon8−) led to the deletion of Fac exon 8 and insertion of the neo gene after homologous recombination (Fig. 1a,b). Homozygous mice were produced by breeding offspring of the chimaeras (Fig. 1c). RT-PCR analysis demonstrated that exon 8 was absent from ...

Notizen: Abstract: The contribution of NMDA receptors to regulation of serotonin (5-HT) release was assessed by in vivo microdialysis in freely behaving rats. During infusion of NMDA (30, 100, and 300 µM) into the dorsal raphe nucleus (DRN), 5-HT was increased by ∼25, 100, and 280%, respectively. Competitive and noncompetitive NMDA-receptor antagonists blocked this effect on DRN 5-HT. Infusion of NMDA (300 µM) into the DRN also produced an 80% increase in extracellular 5-HT in the nucleus accumbens. During infusion of NMDA (100 and 300 µM) into the median raphe nucleus (MRN), 5-HT was increased by ∼15 and 80%, respectively. NMDA-receptor antagonists blocked this effect on MRN 5-HT. Infusion of NMDA into the MRN also produced a significant increase in hippocampal 5-HT. In contrast, infusion of NMDA into the nucleus accumbens, frontal cortex, or hippocampus produced small decreases in 5-HT in these forebrain sites. Taken together, these results suggest that NMDA receptors in the midbrain raphe, but not the forebrain, can have an excitatory influence on 5-HT neurons and, thus, produce increased 5-HT release in the forebrain. Furthermore, in comparison with the MRN, DRN 5-HT neurons were more sensitive to the excitatory effect of NMDA.

Notizen: : A study of the timing of first solid foods in the infant diet reveals significant differences, with bottlefeeding mothers more likely to add solid foods prior to the infant's third month than breastfeeding mothers. In addition, the type of food used was related to the timing of its introduction, with bottlefeeding mothers more likely than breastfeeding women to use commercially prepared baby foods rather than home-prepared foods. Although recommendations by established pediatric societies caution against the too-early introduction of solid foods at the expense of the amount of milk received, these recommendations have not yet filtered down to a number of parents, especially those who bottlefeed their infants.

Notizen: We have determined the dependence of the dissociative adsorption probability in the zero coverage limit, S0, for H2 on Cu(111) as a function of translational energy, Ei, and incidence angle, θi, vibrational state, v, and rotational state, J. We have also obtained information on the effect of surface temperature, Ts, on this probability. These results have been obtained by combining the findings of two separate experiments. We have obtained the form of the dependence of S0 on Ei at Ts=925 K for a range of quantum states from desorption experiments via the principle of detailed balance. We have obtained absolute S0 values from direct molecular beam adsorption experiments, which reveal that S0 scales with the so-called "normal energy,'' En=Ei cos2 θi. The desorption experiments provide detailed information for J=0 to 10 of H2(v=0) and for J=0 to 7 of H2(v=1). The beam experiments additionally provide information on the adsorption of H2(v=2), averaged over J. All measurements are consistent with adsorption functions with an s-shaped form, which can be described by S0=A(1+erf(x))/2, where x=(En−E0)/W. Values of W are ∼0.16 and 0.13 eV for v=0 and v=1, respectively, at Ts=925 K, falling by about 0.05 eV for Ts=120 K, and with only a slight dependence on J. Values of A are insensitive to v and J, with a value of ∼0.25. S(En,v,J) curves are thus similar for different v and J, but shifted in En.In contrast, we find that the values of E0, which determine the mid-point of the curves, have a strong dependence on v and J. Specifically, E0 for H2(v=0) molecules is about 0.6 eV, falling to 0.3 and 0.1 eV for H2(v=1) and H2(v=2), respectively. Translational energy is thus about twice as effective as vibrational energy in promoting dissociation. E0 rises with increasing J at low J, before falling at high J, indicating that rotational motion hinders adsorption for low rotational states (J〈4), and enhances adsorption for high rotational states (J(approximately-greater-than)4). Results are compared with similar studies on the D2/Cu(111) system and with recent calculations. Finally, these results are used to predict the dependence of the rate of dissociation on temperature for a "bulb'' experiment with ambient hydrogen gas in contact with a Cu(111) surface. This simulation yields an activation energy of 0.47 eV for temperatures close to 800 K, compared to a literature value of 0.4 eV from experiment. Analysis of the temperature dependence reveals that the dominant reason for the increase in rate at high temperature is the increase in population of the high energy tail of the translational energy distribution. © 1995 American Institute of Physics.

Notizen: Using molecular beam techniques we find that incident D atoms can abstract CD3 from a Cu(111) surface to yield CD4 in a direct (Eley–Rideal) gas–surface reaction with a cross section of ∼10−16 cm2/D atom. Dynamical evidence for a direct reaction includes the observation of an extremely sharp angular distribution that is clearly displaced from the surface normal, and the determination of a very high translational energy of the product, Ef, which is ∼2 eV. For a 0.25 eV D-atom beam incident at 45° on a 95 K surface, this energy varies with the detection angle, θf, as Ef(θf)=(1.8+θf/45) eV, where θf〈0° in the "backscattering'' direction. For these conditions, the angular distribution approximately follows the function cos70(θf−5.5), being peaked 5.5° from the normal with a full width at half maximum of 〈17°. Lowering the beam energy to 0.07 eV gives a broader angular distribution peaked at about 1.5° from the normal, consistent with cos60(θf−1.5). The reaction with 0.25 eV H incident at 45° gives a similar distribution peaked at ∼3.5° from the normal. The shifts in the angular distributions are approximately consistent with parallel momentum conservation. The CD3/Cu(111) surface was prepared by thermal dissociation of CD3I on the surface or by adsorbing CD3 directly from a CD3 beam produced by the pyrolysis of azomethane. © 1996 American Institute of Physics.

Notizen: We have determined the alignment of D2(v,J) desorbed from Cu(111). The measurements reveal a small preference for "helicoptering'' motion that increases with increasing J. At low J, the alignments are much smaller than predicted by recent calculations. We believe that the anisotropic potential may scramble the alignment as the molecules leave the surface. © 1996 American Institute of Physics.

Notizen: We find that CO is displaced from a ∼90 K Cu(111) surface by an incident H atom beam with a cross section of ∼10−16 cm2/H atom. As for a previous study of the ejection of O2 from Pt(111), our results indicate that part of the heat of adsorption of the incident species is carried away by the ejected molecule in a "dynamic displacement'' process. We have determined the internal-state distribution of the ejected CO using quantum-state-specific laser ionization detection. We have also determined its angular and velocity distribution using a rotatable quadrupole mass spectrometer. The rotational distribution of molecules displaced in the v=0 and v=1 vibrational states are close to Boltzmann distributions at 390 K and 940 K, respectively. While the v=1 population is approximately proportional to the CO coverage, that for v=0 has a more complex coverage dependence, approximately following the presence of the CO α state, which gives a distinct temperature-programmed desorption peak for coverages above 1/3 ML. The equivalent vibration temperature ranges from 1500 K at low coverage to 800 K for a saturated surface. The velocity distribution of the ejected molecules is close to a Boltzmann distribution at 1300 K, corresponding to a translational energy of ∼0.22 eV. The angular distribution is symmetric about the normal and is close to a cos5 θf at small angles, desorption angles, θf, approximately following a cosine distribution for θf(approximately-greater-than)40°. We discuss the results in terms of the dynamic displacement model, where desorption of CO(v=0) is driven by a sudden switch from the chemisorption to physisorption wells. In the case of CO(v=1), we suggest that desorption may follow the formation of a temporary HCO intermediate. © 1996 American Institute of Physics.