Inversion of GPS measurements for a layer of negative dislocation distribution in north China

Author name used in this publication: Wu, J. C.Author name used in this publication: Tang, H. W.Author name used in this publication: Chen, Y. Q.2003-2004 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Competing Interactions in DNA Assembly on Graphene

We study the patterns that short strands of single-stranded DNA form on the top graphene surface of graphite. We find that the DNA assembles into two distinct patterns, small spherical particles and elongated networks. Known interaction models based on DNA-graphene binding, hydrophobic interactions, or models based on the purine/pyrimidine nature of the bases do not explain our observed crossover in pattern formation. We argue that the observed assembly behavior is caused by a crossover in the competition between base-base pi stacking and base-graphene pi stacking and we infer a critical crossover energy of eV. The experiments therefore provide a projective measurement of the base-base interaction strength

Carbon Nanotube Solar Cells

We present proof-of-concept all-carbon solar cells. They are made of a photoactive side of predominantly semiconducting nanotubes for photoconversion and a counter electrode made of a natural mixture of carbon nanotubes or graphite, connected by a liquid electrolyte through a redox reaction. The cells do not require rare source materials such as In or Pt, nor high-grade semiconductor processing equipment, do not rely on dye for photoconversion and therefore do not bleach, and are easy to fabricate using a spray-paint technique. We observe that cells with a lower concentration of carbon nanotubes on the active semiconducting electrode perform better than cells with a higher concentration of nanotubes. This effect is contrary to the expectation that a larger number of nanotubes would lead to more photoconversion and therefore more power generation. We attribute this to the presence of metallic nanotubes that provide a short for photo-excited electrons, bypassing the load. We demonstrate optimization strategies that improve cell efficiency by orders of magnitude. Once it is possible to make semiconducting-only carbon nanotube films, that may provide the greatest efficiency improvement

Dynamic manipulation of mechanical resonators in the high amplitude regime through optical backaction

Cavity optomechanics enables active manipulation of mechanical resonators through backaction cooling and amplification. This ability to control mechanical motion with retarded optical forces has recently spurred a race towards realizing a mechanical resonator in its quantum ground state. Here, instead of quenching optomechanical motion, we demonstrate high amplitude operation of nanomechanical resonators by utilizing a highly efficient phonon generation process. In this regime, the nanomechanical resonators gain sufficient energy from the optical field to overcome the large energy barrier of a double well potential, leading to nanomechanical slow-down and zero frequency singularity, as predicted by early theories . Besides fundamental studies and interests in parametric amplification of small forces, optomechanical backaction is also projected to open new windows for studying discrete mechanical states, and to foster applications. Here we realize a non-volatile mechanical memory element, in which bits are written and reset via optomechanical backaction by controlling the mechanical damping across the barrier. Our study casts a new perspective on the energy dynamics in coupled mechanical resonator - cavity systems and enables novel functional devices that utilize the principles of cavity optomechanics.Comment: 22 pages, 5 figure

Early international entrepreneurship in China: Extent and determinants

Entrepreneurship, Internationalization, International new ventures, Exports, China,

Transnational entrepreneurship : opportunity identification and venture creation

The present case study focuses on entrepreneurs who have migrated from one developed economy (Sweden or Finland) to another developed economy (Hong Kong Special Administrative Region (HKSAR)). In contrast to the dominating understanding, we find that the transnational entrepreneurial incentives were opportunity driven rather than necessity based. The opportunity types identified varied, but indicate the importance of service opportunities, a type often left out of studies and classifications. A prevalent characteristic of transnational entrepreneurship is opportunity recognition based on introducing processes or products to the country of residence, familiar from the country of origin or based on use of the entrepreneurs’ contacts in the home country. This study showed, however, that although this was the case for two entrepreneurs, some identified opportunities for acting in the opposite direction, or did both import and export. Notably, there was also a fourth category, offering business-facilitating services, bridging differing cultural contexts in relationship-middlemen positions. For these entrepreneurs, there was thus no obvious “domestic market” from the start as assumed in traditional internationalization theories. Furthermore, although their businesses started on a limited scale between two countries, they quickly grew and entered other country markets. These transnational businesses thus represent forms of born globals not included in the high-tech business models often associated with such firms. Our findings finally lend support to arguments that a business-favorable institutional environment facilitates and encourages entrepreneurship.