Multifractal Distribution of Dendrite on One-dimensional Support

We apply multifractal analysis to an experimentally obtained quasi-two-dimensional crystal with fourfold symmetry, in order to characterize the sidebranch structure of a dendritic pattern. In our analysis, the stem of the dendritic pattern is regarded as a one-dimensional support on which a measure is defined and the measure is identified with the area, perimeter length, and growth rate distributions. It is found that these distributions have multifractality and the results for the area and perimeter length distributions, in the competitive growth regime of sidebranches, are phenomenologically understood as a simple partitioning process.Comment: 17 pages, 19 figure

Explosive fragmentation of thin ceramic tube using pulsed power

This study experimentally examined the explosive fragmentation of thin ceramic tubes using pulsed power. A thin ceramic tube was threaded on a thin copper wire, and high voltage was applied to the wire using a pulsed power generator. This melted the wire and the resulting vapor put pressure on the ceramic tube, causing it to fragment. We examined the statistical properties of the fragment mass distribution. The cumulative fragment mass distribution obeyed the double exponential or power-law with exponential decay. Both distributions agreed well with the experimental data. We also found that the weighted mean fragment mass was scaled by the multiplicity. This result was similar to impact fragmentation, except for the crossover point. Finally, we obtained universal scaling for fragmentation, which is applicable to both impact and explosive fragmentation.Comment: 5 pages, 6 figure

Binomial multiplicative model of critical fragmentation

We report the binomial multiplicative model for low impact energy fragmentation. Impact fragmentation experiments were performed for low impact energy region, and it was found that the weighted mean mass is scaled by the pseudo control parameter multiplicity. We revealed that the power of this scaling is a non-integer (fractal) value and has a multi-scaling property. This multi-scaling can be interpreted by a binomial multiplicative (simple biased cascade) model. Although the model cannot explain the power-law of fragment-mass cumulative distribution in fully fragmented states, it can produce the multi-scaling exponents that agree with experimental results well.Comment: 10 pages, 6 figures, A typo in Eq.(6b) was improved in Ver.

Dendritic side-branching with anisotropic viscous fingering

We studied dendritic side-branching mechanism in the experiment of anisotropic viscous fingering. We measured the time dependence of growth speed of side-branch and the envelop of side-branches. We found that the speed of side-branch gets to be faster than one of the stem and the growth exponent of the speed changes at a certain time. The envelope of side-branches is represented as Y ~ X^1.47.Comment: 8 pages, 8 figures, to submited in J. Crystal Growt

GaN HEMT DC I-V Device Model for Accurate RF Rectifier Simulation

Recently, various high-efficiency RF rectifiers have been proposed. In this article, to improve the simulation accuracy of RF active rectifier circuits, a new device model for GaN HEMTs is proposed that improves the reproducibility of ID-VDS characteristics in the third-quadrant region (both drain voltage and drain current are negative). Based on measured characteristic data of an actual GaN HEMT, the device parameters for this model have been decided, and the advantage of the new device model has been confirmed

Does Founders’ Human Capital Matter for Innovation? Evidence from Japanese Start-ups

Using a sample from an original questionnaire survey in Japan, this paper explores whether and how founders’ human capital affects innovation outcomes by start-ups. The results provide evidence that founders with greater human capital are more likely to yield innovation outcome. However, because certain types of founders’ human capital may boost R&D investment, which possibly results in innovation outcomes, we estimate the determinants of innovation outcomes by an instrumental variable probit model taking into account the endogeneity of R&D investment. Our findings suggest that specific human capital for innovation, such as founders’ prior innovation experience, is directly associated with innovation outcomes after start-up, while generic human capital, such as founders’ educational background, indirectly affects innovation outcomes through R&D investment.Start-up, Founder, Human capital, Innovations, R&D investment

Determinants of R&D cooperation in Japanese high-tech start-ups

This paper explores the determinants of R&D cooperation in Japanese hightech start-ups. Using a sample from an original survey conducted in 2008, we examine the effects of founder-, firm-, and industry-specific characteristics on R&D cooperation by the type of partners. Our findings indicate that founder-specific characteristics, such as educational background, academic affiliation, and prior innovation output, are fairly important in determining R&D cooperation with universities and public research institutes. We also provide evidence that founders' work experience and prior innovation output have positive and significant effects on R&D cooperation with business partners. With respect to firm-specific characteristics, it is found that firms investing more in R&D tend to engage in R&D cooperation, regardless of the type of partners. Furthermore, it is found that independent firms are less likely to cooperate on R&D with universities and public research institutes, than subsidiaries and affiliated firms.Start-up, R&D cooperation, Founder, University, Business partner