31,890 research outputs found
University spin-offs, entrepreneurial environment and start-up policy: the cases of Waterloo and Toronto (Ontario) and Columbus (Ohio)
The version of record [Bathelt, H., & Spigel, B. (2011). University spinoffs,
entrepreneurial environment and start-up policy: The cases of
Waterloo and Toronto (Ontario) and Columbus (Ohio). International
Journal of Knowledge-Based Development, 2(2), 202-219.] is available online at:
http://www.inderscienceonline.com/doi/10.1504/IJKBD.2011.041248Universities can be central to a region’s economic growth and development, especially if they support start-up, spin-off and modernisation processes related to the regional core sectors. While many governments and associations have developed programmes to encourage the establishment of university spin-offs, the policies they craft are hampered by two major problems. The first is a narrow understanding of spin-offs that focuses on firms directly based on university research. This approach misses firms that use university-related knowledge and resources, unsponsored through the university. Second, spin-off promotion policies often ignore the role of a larger regional entrepreneurial culture and supporting institutions. This paper argues that a broader view of spin-offs is required; a view that accounts for a larger array of ventures and that looks beyond the firm or university to the broader set of regional structures and relations. The empirical evidence presented draws from start-up and spin-off experiences at universities in the USA and Canada
The Spin Liquid State of the Tb2Ti2O7 Pyrochlore Antiferromagnet: A Puzzling State of Affairs
The pyrochlore antiferromagnet Tb2Ti2O7 has proven to be an enigma to
experimentalists and theorists working on frustrated magnetic systems. The
experimentally determined energy level structure suggests a local Ising
antiferromagnet at low temperatures, T < 10 K. An appropriate model then
predicts a long-range ordered Q = 0 state below approximately 2 K. However,
muon spin resonance experiments reveal a paramagnetic structure down to tens of
milli-Kelvin. The importance of fluctuations out of the ground state effective
Ising doublet has been recently understood, for the measured paramagnetic
correlations can not be described without including the higher crystal field
states. However, these fluctuations treated within the random phase
approximation (RPA) fail to account for the lack of ordering in this system
below 2 K. In this work, we briefly review the experimental evidence for the
collective paramagnetic state of Tb2Ti2O7. The basic theoretical picture for
this system is discussed, where results from classical spin models are used to
motivate the investigation of quantum effects to lowest order via the RPA.
Avenues for future experimental and theoretical work on Tb2Ti2O7 are presented.Comment: Latex2e,6 pages, IOP format, introduction shortened and other minor
corrections, replaced with published version in the Proceedings of the Highly
Frustrated Magnetism 2003 Conference, Grenobl
Heat Transport as a Probe of Electron Scattering by Spin Fluctuations: the Case of Antiferromagnetic CeRhIn5
Heat and charge conduction were measured in the heavy-fermion metal CeRhIn5,
an antiferromagnet with T_N=3.8 K. The thermal resistivity is found to be
proportional to the magnetic entropy, revealing that spin fluctuations are as
effective in scattering electrons as they are in disordering local moments. The
electrical resistivity, governed by a q^2 weighting of fluctuations, increases
monotonically with temperature. In contrast, the difference between thermal and
electrical resistivities, characterized by an omega^2 weighting, peaks sharply
at T_N and eventually goes to zero at a temperature T^* ~ 8 K. T^* thus emerges
as a measure of the characteristic energy of magnetic fluctuations.Comment: 4 pages, 4 figure
Neutron scattering search for static magnetism in oxygen ordered YBa2Cu3O6.5
We present elastic and inelastic neutron scattering results on highly oxygen
ordered YBa2Cu3O6.5 ortho-II. We find no evidence for the presence of ordered
magnetic moments to a sensitivity of 0.003 Bohr magnetons, an order of
magnitude smaller than has been suggested in theories of orbital or
d-density-wave (DDW) currents. The absence of sharp elastic peaks, shows that
the d-density-wave phase is not present, at least for the superconductor with
the doping of 6.5 and the ordered ortho-II structure. We cannot exclude the
possibility that a broad peak may exist with extremely short-range DDW
correlations. For less ordered or more doped crystals it is possible that
disorder may lead to static magnetism. We have also searched for the large
normal state spin gap that is predicted to exist in an ordered DDW phase.
Instead of a gap we find that the Q-correlated spin susceptibility persists to
the lowest energies studied, 6 meV. Our results are compatible with the
coexistence of superconductivity with orbital currents, but only if they are
dynamic, and exclude a sharp phase transition to an ordered d-density-wave
phase.Comment: 6 pages 4 figures RevTex Submitted to Phys Rev B January 23, 200
Exponentially Localized Magnetic Fields for Single-Spin Quantum Logic Gates
An infinite array of parallel current-carrying wires is known, from the field
of neutral particle optics, to produce an exponentially localized magnetic
field when the current direction is antiparallel in adjacent wires. We show
that a finite array of several tens of superconducting Nb nanowires can produce
a peak magnetic field of 10mT that decays by a factor of 10^4 over a length
scale of 500nm. Such an array is readily manufacturable with current
technology, and is compatible with both semiconductor and superconducting
quantum computer architectures. A series of such arrays can be used to
individually address single single-spin or flux qubits spaced as little as
100nm apart, and can lead to quantum logic gate times of 5ns.Comment: 5 pages, incl. 4 figure
Central mode and spin confinement near the boundary of the superconducting phase in YBa2Cu3O6.353 (Tc=18 K)
We have mapped the neutron scattering spin spectrum at low-energies in
YBa2Cu3O6.353 (Tc=18 K) where the doping ~0.06 is near the critical value
(pc=0.055) for superconductivity. No coexistence with long range ordered
antiferromagnetism is found. The spins fluctuate on two energy scales, one a
damped spin response with a ~2 meV relaxation rate and the other a central mode
with a relaxation rate that slows to less than 0.08 meV below Tc. The spectrum
mirrors that of a soft mode driving a central mode. Extremely short correlation
lengths, 42+-5 Angstrom in-plane and 8+-2 Angstrom along the c direction, and
isotropic spin orientations for the central mode indicate that the correlations
are subcritical with respect to any second order transition to Neel order. The
dynamics follows a model where damped spin fluctuations are coupled to the slow
fluctuations of regions with correlations shortened by the hole doping.Comment: 5 pages 4 figures. One figure revised and some text revision.
Accepted PRB Rapids February 14, 200
NMR evidence for Friedel-like oscillations in the CuO chains of ortho-II YBaCuO
Nuclear magnetic resonance (NMR) measurements of CuO chains of detwinned
Ortho-II YBaCuO (YBCO6.5) single crystals reveal unusual and
remarkable properties. The chain Cu resonance broadens significantly, but
gradually, on cooling from room temperature. The lineshape and its temperature
dependence are substantially different from that of a conventional spin/charge
density wave (S/CDW) phase transition. Instead, the line broadening is
attributed to small amplitude static spin and charge density oscillations with
spatially varying amplitudes connected with the ends of the finite length
chains. The influence of this CuO chain phenomenon is also clearly manifested
in the plane Cu NMR.Comment: 4 pages, 3 figures, refereed articl
- …