4,300 research outputs found
The Social Capital of Venture Capitalists and Its Impact on the Funding of Start-Up Firms
How does the social capital of venture capitalists (VCs) affect the funding of start-ups? Extant entrepreneurship literature conceptualizes a substitute effect between the social and financial capital that new firms attain from their investors. On the contrary, by building on the rich social capital literature, we hypothesize a positive effect of VCs’ social capital, derived from past syndication, on the amount of money that start-ups receive. Specifically, we argue that both structural aspects of VCs’ social network, such as the number of connections and the spanning of structural holes, and relational aspects, such as the diversity of network partners’ attributes, provide VCs with superior access to information about current investment objects and opportunities to leverage them in the future, increasing their willingness to invest in these firms. Our empirical results, derived from a novel dataset containing more than 5,000 funding rounds in the Internet and IT sector, strongly confirm our hypotheses. Both structural and relational attributes of VCs’ syndication networks have a significant influence on the funds received by start-up firms, highlighting the importance of a social capital perspective on new venture funding. We discuss the implications of our findings for theories of venture capital and entrepreneurship, showing that the role and effect of VCs’ social capital on start-up firms is much more complex than previously argued in the literature.social networks;social capital;start-ups;venture capital;structural holes
Self-Consistent Response of a Galactic Disk to an Elliptical Perturbation Halo Potential
We calculate the self-consistent response of an axisymmetric galactic disk
perturbed by an elliptical halo potential of harmonic number m = 2, and obtain
the net disk ellipticity. Such a potential is commonly expected to arise due to
a galactic tidal encounter and also during the galaxy formation process. The
self-gravitational potential corresponding to the self-consistent,
non-axisymmetric density response of the disk is obtained by inversion of
Poisson equation for a thin disk. This response potential is shown to oppose
the perturbation potential, because physically the disk self-gravity resists
the imposed potential. This results in a reduction in the net ellipticity of
the perturbation halo potential in the disk plane. The reduction factor
denoting this decrease is independent of the strength of the perturbation
potential, and has a typical minimum value of 0.75 - 0.9 for a wide range of
galaxy parameters. The reduction is negligible at all radii for higher
harmonics (m > or = 3) of the halo potential. (abridged).Comment: 26 pages (LaTex- aastex style), 3 .eps figures. To appear in the
Astrophysical Journal, Vol. 542, Oct. 20, 200
Radial HI Profiles at the Periphery of Galactic Disks: The Role of Ionizing Background Radiation
Observations of neutral hydrogen in spiral galaxies reveal a sharp cutoff in
the radial density profile at some distance from the center. Using 22 galaxies
with known HI distributions as an example, we discuss the question of whether
this effect can be associated exclusively with external ionizing radiation, as
is commonly assumed. We show that before the surface density reaches
(the same for
galaxies of different types), it is hard to expect the gas to be fully ionized
by background radiation. For two of 13 galaxies with a sharp drop in the HI
profile, the "steepening" can actually be caused by ionization. At the same
time, for the remaining galaxies, the observed cutoff in the radial HI profile
is closer to the center than if it was a consequence of ionization by
background radiation and, therefore, it should be caused by other factors.Comment: 15 pages, 6 figure
Nonflammable, antistatic, and heat-sealable film
Antistatic, heat-sealable, nonflammable films prepared from polyvinylidene fluoride and polyvinylidene chloride resin
Labor Standards in the United States and Canada
Block, Roberts, and Clarke offer a method for comparing ten labor standards across political jurisdictions. They then apply this method to the United States and Canada, an exercise that allows them to settle the long-running dispute over whether or not Canada has higher standards than the U.S., and if so, to what degree.https://research.upjohn.org/up_press/1050/thumbnail.jp
The best of both worlds: The benefits of open-specialized and open-diverse syndication networks for new venture success
Open networks give actors non-redundant information that is diverse, while closed networks offer redundant information that is easier to interpret. Integrating arguments about network structure and the similarity of actors’ knowledge, we propose two types of network configurations that combine diversity and ease of interpretation. Closed-diverse networks offer diversity in actors’ knowledge domains and shared third-party ties to help in interpreting that knowledge. In open-specialized networks, structural holes offer diversity, while shared interpretive schema and overlap between received information and actors’ prior knowledge help in interpreting new information without the help of third parties. In contrast, actors in open-diverse networks suffer from information overload due to the lack of shared schema or overlapping prior knowledge for the interpretation of diverse information, and actors in closed-specialized networks suffer from overembeddedness because they cannot access diverse information. Using CrunchBase data on early-stage venture capital investments in the U.S. information technology sector, we test the effect of investors’ social capital on the success of their portfolio ventures. We find that ventures have the highest chances of success if their syndicating investors have either open-specialized or closed-diverse networks. These effects are manifested beyond the direct effects of ventures’ or investors’ quality and are robust to controlling for the possibility that certain investors could have chosen more promising ventures at the time of first funding
High-resolution DCE-MRI of the pituitary gland using radial k-space acquisition with compressed sensing reconstruction
BACKGROUND AND PURPOSE: The pituitary gland is located outside of the blood-brain barrier. Dynamic T1 weighted contrast enhanced sequence is considered to be the gold standard to evaluate this region. However, it does not allow assessment of intrinsic permeability properties of the gland. Our aim was to demonstrate the utility of radial volumetric interpolated brain examination with the golden-angle radial sparse parallel technique to evaluate permeability characteristics of the individual components (anterior and posterior gland and the median eminence) of the pituitary gland and areas of differential enhancement and to optimize the study acquisition time.
MATERIALS AND METHODS: A retrospective study was performed in 52 patients (group 1, 25 patients with normal pituitary glands; and group 2, 27 patients with a known diagnosis of microadenoma). Radial volumetric interpolated brain examination sequences with goldenangle radial sparse parallel technique were evaluated with an ROI-based method to obtain signal-time curves and permeability measures of individual normal structures within the pituitary gland and areas of differential enhancement. Statistical analyses were performed to assess differences in the permeability parameters of these individual regions and optimize the study acquisition time.
RESULTS: Signal-time curves from the posterior pituitary gland and median eminence demonstrated a faster wash-in and time of
maximum enhancement with a lower peak of enhancement compared with the anterior pituitary gland (P .005). Time-optimization
analysis demonstrated that 120 seconds is ideal for dynamic pituitary gland evaluation. In the absence of a clinical history, differences in the signal-time curves allow easy distinction between a simple cyst and a microadenoma.
CONCLUSIONS: This retrospective study confirms the ability of the golden-angle radial sparse parallel technique to evaluate the
permeability characteristics of the pituitary gland and establishes 120 seconds as the ideal acquisition time for dynamic pituitary gland
imaging
Survival Probability of Large Rapidity Gaps in pbar p, pp, gamma p and gamma gamma Collisions
Using an eikonal analysis, we simultaneously fit a QCD-inspired
parameterization of all accelerator data on forward proton-proton and
antiproton-proton scattering amplitudes, together with cosmic ray data (using
Glauber theory), to predict proton-air and proton-proton cross sections at
energies near \sqrt s \approx 30 TeV. The p-air cosmic ray measurements greatly
reduce the errors in the high energy proton-proton and proton-air cross section
predictions--in turn, greatly reducing the errors in the fit parameters. From
this analysis, we can then compute the survival probability of rapidity gaps in
high energy pbar p and pp collisions, with high accuracy in a quasi model-free
environment. Using an additive quark model and vector meson dominance, we note
that that the survival probabilities are identical, at the same energy, for
gamma p and gamma gamma collisions, as well as for nucleon-nucleon collisions.
Significantly, our analysis finds large values for gap survival probabilities,
\approx 30% at \sqrt s = 200 GeV, \approx 21% at \sqrt s = 1.8 TeV and \approx
%%13% at \sqrt s = 14 TeV.Comment: 9 pages, Latex2e, uses epsfig.sty, 4 postscript figure
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