14,235 research outputs found

    What Drives Venture Capital Fundraising?

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    We examine the determinants of venture capital fundraising in the U.S. over the past twenty-five years. We study industry aggregate, state-level, and firm-specific fundraising to determine if macroeconomic, regulatory, or performance factors affect venture capital activity. We find that shifts in demand for venture capital appear to have a positive and important impact on commitments to new venture capital funds. Commitments by taxable and tax-exempt investors seem equally sensitive to changes in capital gains tax rates that decreases in capital gains tax rates increase the demand for venture capital as more workers are incented to become entrepreneurs. Aggregate and state level venture fundraising are positively affected by easing of pension investment restrictions as well as industrial and academic R&D expenditures. Fund performance and reputation also lead to greater fundraising by venture organizations.

    The Really Long-Run Performance of Initial Public Offerings: The Pre-NASDAQ Evidence

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    Financial economists in recent years have closely examined and intensely debated the performance of initial public offerings using data after the formation of NASDAQ. The paper seeks to shed light on this controversy by undertaking a large, out-of-sample study: we examine the performance for up to five years after listing of nearly 3,661 initial public offerings in the United States from 1935 to 1972. The sample displays some evidence of underperformance when event-time buy-and-hold abnormal returns are used. The underperformance disappears, however, when cumulative abnormal returns are utilized. A calendar-time analysis also shows that over the entire sample period i.e., from 1935 to 1976 IPOs return as much as the market. Finally, the intercepts in CAPM and Fama-French three-factor regressions are insignificantly different from zero suggesting no abnormal performance.

    Superfluidity of "dirty" indirect excitons and magnetoexcitons in two-dimensional trap

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    The superfluid phase transition of bosons in a two-dimensional (2D) system with disorder and an external parabolic potential is studied. The theory is applied to experiments on indirect excitons in coupled quantum wells. The random field is allowed to be large compared to the dipole-dipole repulsion between excitons. The slope of the external parabolic trap is assumed to change slowly enough to apply the local density approximation (LDA) for the superfluid density, which allows us to calculate the Kosterlitz-Thouless temperature Tc(n(r))T_{c}(n(r)) at each local point rr of the trap. The superfluid phase occurs around the center of the trap (r=0\mathbf{r}=0) with the normal phase outside this area. As temperature increases, the superfluid area shrinks and disappears at temperature Tc(n(r=0))T_{c}(n(r=0)). Disorder acts to deplete the condensate; the minimal total number of excitons for which superfluidity exists increases with disorder at fixed temperature. If the disorder is large enough, it can destroy the superfluid entirely. The effect of magnetic field is also calculated for the case of indirect excitons. In a strong magnetic field HH, the superfluid component decreases, primarily due to the change of the exciton effective mass.Comment: 13 pages, 3 figure

    The Level Spacing Distribution Near the Anderson Transition

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    For a disordered system near the Anderson transition we show that the nearest-level-spacing distribution has the asymptotics P(s)exp(As2γ)P(s)\propto \exp(-A s^{2-\gamma }) for s\gg \av{s}\equiv 1 which is universal and intermediate between the Gaussian asymptotics in a metal and the Poisson in an insulator. (Here the critical exponent 0<γ<10<\gamma<1 and the numerical coefficient AA depend only on the dimensionality d>2d>2). It is obtained by mapping the energy level distribution to the Gibbs distribution for a classical one-dimensional gas with a pairwise interaction. The interaction, consistent with the universal asymptotics of the two-level correlation function found previously, is proved to be the power-law repulsion with the exponent γ-\gamma.Comment: REVTeX, 8 pages, no figure

    Athermal Nonlinear Elastic Constants of Amorphous Solids

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    We derive expressions for the lowest nonlinear elastic constants of amorphous solids in athermal conditions (up to third order), in terms of the interaction potential between the constituent particles. The effect of these constants cannot be disregarded when amorphous solids undergo instabilities like plastic flow or fracture in the athermal limit; in such situations the elastic response increases enormously, bringing the system much beyond the linear regime. We demonstrate that the existing theory of thermal nonlinear elastic constants converges to our expressions in the limit of zero temperature. We motivate the calculation by discussing two examples in which these nonlinear elastic constants play a crucial role in the context of elasto-plasticity of amorphous solids. The first example is the plasticity-induced memory that is typical to amorphous solids (giving rise to the Bauschinger effect). The second example is how to predict the next plastic event from knowledge of the nonlinear elastic constants. Using the results of this paper we derive a simple differential equation for the lowest eigenvalue of the Hessian matrix in the external strain near mechanical instabilities; this equation predicts how the eigenvalue vanishes at the mechanical instability and the value of the strain where the mechanical instability takes place.Comment: 17 pages, 2 figures

    A Genetic Locus Regulates the Expression of Tissue-Specific mRNAs from Multiple Transcription Units

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    129 GIX- mice, unlike animals of the congeneic partner strain GIX+, do not express significant amounts of the retroviral antigens gp70 and p30. Evidence is presented indicating that the GIX phenotype is specified by a distinct regulatory gene acting on multiple transcription units to control the levels of accumulation of specific mRNA species. The steady-state levels of retroviral-homologous mRNA from the tissues of GIX+ and GIX- mice were examined by blot hybridization using as probes DNA fragments from cloned murine leukemia viruses. RNA potentially encoding viral antigens was reduced or absent in GIX- mice, even though no differences in integrated viral genomes were detected between these congeneic strains by DNA blotting. Tissue-specific patterns of accumulation of these RNA species were detected in brain, epididymis, liver, spleen, and thymus, and several distinct RNA species were found to be coordinately regulated with the GIX phenotype. Measurements of RNA synthesis suggest a major role for transcriptional control in the regulation of some retroviral messages
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