One of the numerous functions of glial cells in Drosophila is the ensheathment of neurons to isolate them from the potassium-rich haemolymph, thereby establishing the blood-brain barrier. Peripheral nerves of flies are surrounded by three distinct glial cell types. Although all embryonic peripheral glia (ePG) have been identified on a single-cell level, their contribution to the three glial sheaths is not known. We used the Flybow system to label and identify each individual ePG in the living embryo and followed them into third instar larva. We demonstrate that all ePG persist until the end of larval development and some even to adulthood. We uncover the origin of all three glial sheaths and describe the larval differentiation of each peripheral glial cell in detail. Interestingly, just one ePG (ePG2) exhibits mitotic activity during larval stages, giving rise to up to 30 glial cells along a single peripheral nerve tract forming the outermost perineurial layer. The unique mitotic ability of ePG2 and the layer affiliation of additional cells were confirmed by in vivo ablation experiments and layer-specific block of cell cycle progression. The number of cells generated by this glial progenitor and hence the control of perineurial hyperplasia correlate with the length of the abdominal nerves. By contrast, the wrapping and subperineurial glia layers show enormous hypertrophy in response to larval growth. This characterisation of the embryonic origin and development of each glial sheath will facilitate functional studies, as they can now be addressed distinctively and genetically manipulated in the embryo.
On theoretical grounds alone, there is no a priori reason why higher taxes should reduce the desired capital stock, since a tax increase reduces marginal returns but also increases depreciation and interest payment allowances. Using a panel of Chilean corporations, this paper estimates a longrun demand for capital valid for a general adjustment-cost structure. Changes in the corporate tax rate are found to have no effect on the long-run demand for capital. Furthermore, when making investment decisions, firms ignore the marginal rates paid by their stockholders, suggesting the presence of a corporate veil. D
In this paper, we deal with reversing and extended symmetries of shifts generated by bijective substitutions. We provide equivalent conditions for a permutation on the alphabet to generate a reversing/extended symmetry, and algorithms how to check them. Moreover, we show that, for any finite group G and any subgroup P of the d-dimensional hyperoctahedral group, there is a bijective substitution which generates an aperiodic hull with symmetry group Z d × G and extended symmetry group (Z d P ) × G.
1. INTRODUCTION 2 2. THEORETICAL FRAMEWORK 8 2.1 Corporations, state of the environment and the standard 8 2.2 Information process 10 2.3 The court 12 2.4 Parties, attempts to reform the standard and the litigation process 12 2.5 Dynamics of the System and Timing of Actions 14 3. THE COURT SETS THE STANDARDS 15 3.1 Litigation strategies 3.2 The Problem faced by the Court 16 4. MAIN RESULTS 18 4.1 Myopic Courts 18 4.2 First Best Solution 19 4.2.1 First Best Standards 19 4.2.2 Frequencies of Litigation 20 4.2.3 First-Best Common Law Legal System 4.3 Second Best Solution (Forward-looking Courts) 4.3.1 Second Best Standards 4.3.2 Frequencies of Litigation 28 4.3.3 Second-Best Common Law Legal System 29 4.4 Too many or too few trials? 4.4.1 Optimal distribution of litigation expenses 4.4.2 The direct effect of litigation expenses 4.4.3 Activists or originalists judges? 5. ROBUSTNESS AND EXTENSIONS 5.1 Robustness of the Results 31 5.2 Law indeterminacy and the possibility of settlement 33 5.3 The Role of Agencies 34 5.4 Rigid or contingent standards? 35
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