Portfolio selection with time constraints and a rational explanation of insufficient diversification and excessive trading

Private investors have limited time available for learning about stocks as they need to divide their time between stock analysis and work. This paper analyzes the influence of learning constraintsin the form of time constraints on portfolio selection and derives both optimal portfolio holdings and time allocation. Under time constraints, rational private investors make portfolio choices similar to those ofi nvestors with bounded rationality, i.e., insufficient diversification and excessive trading. Thus, time constraints offer an alternative, fully rational explanation for these real-world investment phenomena, which have to date been interpreted primarily in the light of behavioral finance. --excessive trading,insufficient diversification,learning,portfolio selection,time constraint

Mechanisms of modulation and adaptation in pheromone-sensitive trichoid sensilla of the hawkmoth Manduca sexta

Most nocturnal moths find their mating partners with the help of pheromones released by the females and attracting the males. The males perceive the pheromone blend with a large number of specialized sensory hairs on their antennae, the sensilla trichoidea. In the sphinx moth Manduca sexta, each trichoid sensillum contains two olfactory receptor neurons, ensheathed by a common set of accessory cells, the innermost thecogen cell, the trichogen and the tormogen cell (Fig. 1; Keil, 1989; Lee and Strausfeld, 1990). The trichogen and the tormogen cell secrete the receptor lymph or sensillum lymph, which fills the receptor lymph cavity and the lumen of the sensory hair. The receptor lymph contains high concentrations of potassium (up to 200 mmol l-1) and pheromonebinding protein (Kaissling et al., 1985; Vogt and Riddiford, 1986). In extracellular tip recordings, the tip of the sensory hair is clipped off, and the recording electrode, containing sensillum lymph ringer, is slipped over the open hair (Kaissling, 1995), while the reference electrode is inserted into the haemolymph space. In this way, the electrical activity of the olfactory receptor neurons and the accessory cells are recorded as a composite signal. In contrast to many other extracellular recording techniques, tip recordings thus give access to a clearly defined set of electrically active cells. The first part of this thesis, comprising Chapters 1–4, presents results obtained in tip recordings. Chapter 1 describes the electrical activity of trichoid sensilla in the absence of pheromone. Oscillations of the transepithelial potential and their negative correlation with flight activity were characterized. The oscillations were influenced by injections of the biogenic amines octopamine and serotonin near the antennal base. In addition, the spontaneous action potential activity of both ORNs was quantitatively investigated. There is obviously no correlation between the time course of the transepithelial potential and the spontaneous action potential activity. Likewise, the action potential activity was not significantly influenced by amine injection. This chapter was published in the Journal of Experimental Biology (Dolzer et al., 2001). Pheromone receptors are made for the detection of pheromone. So Chapters 2 and 3 deal with the responses of trichoid sensilla to stimulation with bombykal, the main component in the conspecific pheromone blend (Tumlinson et al., 1989). In response to pheromone, trichoid sensilla generate a negative deflection of the transepithelial potential, the sensillar potential, and a series of action potentials. These responses were quantitatively investigated, and their dose-dependence was determined in two different states of adaptation. While it has long been known that two different adaptation mechanisms act on the generation of sensillar potentials and action potentials, respectively (Zack, 1979), this study suggests the presence of a third mechanism that presumably acts via stabilization of the resting potential. [...

Pharmacological Investigation of Protein Kinase C- and cGMP-Dependent Ion Channels in Cultured Olfactory Receptor Neurons of the Hawkmoth Manduca sexta

In the hawkmoth Manduca sexta, pheromone stimuli of different strength and duration rise the intracellular Ca2+ concentration in olfactory receptor neurons (ORNs). While second-long pheromone stimuli activate protein kinase C (PKC), which apparently underlies processes of short-term adaptation, minute-long pheromone stimuli elevate cyclic guanosine monophosphate (cGMP) concentrations, which correlates with time courses of long-term adaptation. To identify ion channels involved in the sliding adjustment of olfactory sensitivity, inside-out patch clamp recordings on cultured ORNs of M. sexta were performed to characterize Ca2+-, PKC-, and cGMP-dependent ion channels. Stepping to positive holding potentials in high intracellular Ca2+ elicits different Ca2+-dependent ion channels, namely small-conductance channels (2–20 ps), medium-conductance channels (20–100 ps), and large-conductance channels (>100 ps). Ion channels of 40, 60, and 70 ps opened after PKC activation, whereas 10- and >100-ps channels were observed less frequently. Application of 8-bromo cyclic guanosine monophosphate opened 55- and 70-ps channels and increased the open probability of >100-ps channels, whereas even in the presence of phorbol ester 40-ps channels were inhibited. Thus, cGMP elevations activate a different set of ion channels as compared with PKC and suppress at least one PKC-dependent ion channel

Reimagining the Framework for Resolving Intra-African Commercial Disputes in the Context of the African Continental Free Trade Area Agreement

This article examines the effectiveness of the framework for the resolution of intra-African cross-border commercial disputes, arising from the projected increase in intra-African trade in goods, services, and investments under the African Continental Free Trade Area. It examines the peculiar nature of intra-African trade and of the participating entities to provide the context to discuss the three major processes adopted in commercial dispute resolution (litigation, mediation, and arbitration) in Africa. It then argues for the promotion of arbitration as the dispute resolution process of choice for such disputes. It reimagined the framework for arbitration at the continental level and made two proposals targeted at the greater efficiency of the process: the designation of Regional Arbitration Centres across the African Union's eight recognized Regional Economic Communities, to administer such references; and the establishment of an African Commercial Court as a one-stop court for the enforcement or annulment of the final award