Measurements of polarization transfer in the inelastic scattering of intermediate energy protons and deuterons have yielded a wealth of data on the spin response of nuclei. This work complements the ...well-known studies of Gamow-Teller strength in charge-exchange reactions. The emphasis here is on a consistent determination of the
S = 1,
T = 0 response, practical only with deuterons, and on the proper separation of
S = 0 and
S = 1 strength in proton spectra for appropriate comparison with sum rules. We concentrate on two nuclei,
40Ca and
12C, at momentum transfers below about 1 fm
−1 and on excitations up to about 50 MeV. The continuum second random phase approximation provides the primary theoretical tool for calculating and interpreting the response in terms of properties of the nucleon-nucleon force inside the nuclear medium. The reaction mechanism is described by the DWIA, applied here to continuum proton scattering almost as rigorously as it is usually applied to low energy excitations. A new DWIA formalism for the description of spin observables in deuteron scattering is used. Comparison of the proton and deuteron data with each other and with RPA/DWIA calculations yields interesting insights into the current state of understanding of collectivity and the nuclear spin response.
Interleukin-7 is widely accepted as a major homeostatic factor involved in T cell development. To assess the IL-7 responsiveness of thymocytes involved in selection processes, we used a new sensitive ...flow cytometry-based assay to detect intracellular phosphorylation of STAT-5 induced by IL-7 in defined mouse thymocyte subsets. Using this method, we found the earliest thymocyte subset (CD4(-)CD8(-)CD25(-)CD44(+)) to contain both IL-7-responsive and nonresponsive cells. Transition through the next stages of development (CD4(-)CD8(-)CD25(+)CD44(+ and -)) was associated with responsiveness of all thymocytes within these populations. Passage of thymocytes through beta-selection resulted in a significant reduction in IL-7 sensitivity. In the next phases of development (TCR(-) and TCR(low)CD69(-)), thymocytes were completely insensitive to the effects of IL-7. STAT-5 phosphorylation in response to IL-7 was again observed, however, in thymocytes involved in the positive selection process (TCR(low)CD69(+) and TCR(intermediate)). As expected, CD4 and CD8 single-positive thymocytes were responsive to IL-7. These findings delineate an IL-7-insensitive population between the beta-selection and positive selection checkpoints encompassing thymocytes predicted to die by neglect due to failure of positive selection. This pattern of sensitivity suggests a two-signal mechanism by which survival of thymocytes at these checkpoints is governed.
Murine fetal thymic organ culture was used to investigate the mechanism by which adenosine deaminase (ADA) deficiency causes T-cell immunodeficiency. C57BL/6 fetal thymuses treated with the specific ...ADA inhibitor 2'-deoxycoformycin exhibited features of the human disease, including accumulation of dATP and inhibition of S-adenosylhomocysteine hydrolase enzyme activity. Although T-cell receptor (TCR) Vbeta gene rearrangements and pre-TCR-alpha expression were normal in ADA-deficient cultures, the production of alphabeta TCR(+) thymocytes was inhibited by 95%, and differentiation was blocked beginning at the time of beta selection. In contrast, the production of gammadelta TCR(+) thymocytes was unaffected. Similar results were obtained using fetal thymuses from ADA gene-targeted mice. Differentiation and proliferation were preserved by the introduction of a bcl-2 transgene or disruption of the gene encoding apoptotic protease activating factor-1. The pan-caspase inhibitor carbobenzoxy-Val-Ala-Asp-fluoromethyl ketone also significantly lessened the effects of ADA deficiency and prevented the accumulation of dATP. Thus, ADA substrates accumulate and disrupt thymocyte development in ADA deficiency. These substrates derive from thymocytes that undergo apoptosis as a consequence of failing to pass developmental checkpoints, such as beta selection.
Virtual Compton scattering, i.e. the exclusive reaction
γ
∗p → γ′p′
with
γ
∗
denoting a virtual photon, provides new insights on the internal structure of the proton. Below
π
0 production threshold, ...this experiment measures the generalized polarizabilities of the proton as defined by Guichon
et al 1, 2 and Drechsel
et al 3. These new electromagnetic observables, functions of
Q
2, enlarge the concept of electric (α0 and magnetic (β) polarizabilities in Real Compton Scattering (
Q
2=0) 4.
The first VCS experiment 5 of this kind was measured at the three spectrometer facility at the Mainz Microtron MAMI for
Q
2=0.33 GeV
2 and we present in this paper the preliminary results.
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