Why Did so Many Poor-Performing Firms Come to Market in the Late 1990s?: Nasdaq Listing Standards and the Bubble

This paper examines the impact of Nasdaq Listing Standards on the composition of new listings in the late 1990s. The Nasdaq has two types of listing standards: one based on profitability and the second based explicitly or implicitly on market capitalization. Specifically, unprofitable firms are allowed to list if either their pro-forma net tangible assets, which include the anticipated proceeds from their IPO, exceeds $18 million or their market capitalization exceeds$75 million. We show that as the market bubble accelerated in the late 1990s, a vast majority of firms entered under a market capitalization based standard, and these firms became a substantial portion of the Nasdaq. Subsequently, these firms performed the poorest both in terms of financial performance, stock return performance as well as involuntary delistings, while firms that listed under the profitability standard performed much better. In addition, firms that entered under market capitalization standards also exhibited the greatest return volatility. These results illustrate the importance of a profitability standard and the danger of a market capitalization based standard (explicit or implicit) in a market that is in, what ex-post turns out to be, a bubble

Stock Option Expense, Forward-Looking Information, and Implied Volatilities of Traded Options

Prior research generally finds that firms underreport option expense by managing assumptions underlying option valuation (e.g. they shorten the expected option lives), but it fails to document management of a key assumption, the one concerning expected stock-price volatility. Using a new methodology, we address two questions: (1) To what extent do companies follow the guidance in FAS 123 and use forward looking information in addition to the readily available historical volatility in estimating expected volatility? (2) What determines the cross-sectional variation in the reliance on forward looking information? We find that firms use both historical and forward-looking information in deriving expected volatility. We also find, however, that the reliance on forward-looking information is limited to situations where this reliance results in reduced expected volatility and thus smaller option expense. We interpret this finding as managers opportunistically use the discretion in estimating expected volatility afforded by FAS 123. In support of this interpretation, we also find that managerial incentives play a key role in this opportunism

Graphene Ambipolar Multiplier Phase Detector

We report the experimental demonstration of a multiplier phase detector implemented with a single top-gated graphene transistor. Ambipolar current conduction in graphene transistors enables simplification of the design of the multiplier phase detector and reduces its complexity in comparison to phase detectors based on conventional unipolar transistors. Fabrication of top-gated graphene transistors is essential to achieve the higher gain necessary to demonstrate phase detection. We report a phase detector gain of −7 mV/rad in this letter. An analysis of key technological parameters of the graphene transistor, including series resistance, top-gate insulator thickness, and output resistance, indicates that the phase detector gain can be improved by as much as two orders of magnitude.NSF CAREER Award CCF-074685

Modeling stochasticity and robustness in gene regulatory networks

Motivation: Understanding gene regulation in biological processes and modeling the robustness of underlying regulatory networks is an important problem that is currently being addressed by computational systems biologists. Lately, there has been a renewed interest in Boolean modeling techniques for gene regulatory networks (GRNs). However, due to their deterministic nature, it is often difficult to identify whether these modeling approaches are robust to the addition of stochastic noise that is widespread in gene regulatory processes. Stochasticity in Boolean models of GRNs has been addressed relatively sparingly in the past, mainly by flipping the expression of genes between different expression levels with a predefined probability. This stochasticity in nodes (SIN) model leads to over representation of noise in GRNs and hence non-correspondence with biological observations. Results: In this article, we introduce the stochasticity in functions (SIF) model for simulating stochasticity in Boolean models of GRNs. By providing biological motivation behind the use of the SIF model and applying it to the T-helper and T-cell activation networks, we show that the SIF model provides more biologically robust results than the existing SIN model of stochasticity in GRNs. Availability: Algorithms are made available under our Boolean modeling toolbox, GenYsis. The software binaries can be downloaded from http://si2.epfl.ch/∼garg/genysis.html. Contact: [email protected]

Investigating the Vascularization of Tissue-Engineered Bone Constructs Using Dental Pulp Cells and 45S5 Bioglass(®) Scaffolds.

Identification of a suitable cell source combined with an appropriate 3D scaffold is an essential prerequisite for successful engineering of skeletal tissues. Both osteogenesis and angiogenesis are key processes for bone regeneration. This study investigated the vascularization potential of a novel combination of human dental pulp stromal cells (HDPSCs) with 45S5 Bioglass(®) scaffolds for tissue-engineered mineral constructs in vivo and in vitro. 45S5 Bioglass scaffolds were produced by the foam replication technique with the standard composition of 45 wt% SiO2, 24.5 wt% Na2O, 24.5 wt% CaO, and 6 wt% P2O5. HDPSCs were cultured in monolayers and on porous 45S5 Bioglass scaffolds under angiogenic and osteogenic conditions for 2-4 weeks. HDPSCs expressed endothelial gene markers (CD34, CD31/PECAM1, and VEGFR2) under both conditions in the monolayer. A combination of HDPSCs with 45S5 Bioglass enhanced the expression of these gene markers. Positive immunostaining for CD31/PECAM1 and VEGFR2 and negative staining for CD34 supported the gene expression data, while histology revealed evidence of endothelial cell-like morphology within the constructs. More organized tubular structures, resembling microvessels, were seen in the constructs after 8 weeks of implantation in vivo. In conclusion, this study suggests that the combination of HDPSCs with 45S5 Bioglass scaffolds offers a promising strategy for regenerating vascularized bone grafts