540 research outputs found
Practical Realization of ZT\u3e1 From the Materials Perspective
For several decades, thermoelectric materials have seen limited use in energy conversion due to their low dimensionless figure-of-merit ZT, which determines the efficiency of thermoelectric devices. Driven by the demand for renewable energy, thermoelectric R&D is actively pursued by physicists, chemists, and engineers. In recent years, some new approaches for controlling the electron and phonon spectra as well as transports have been developed. Today, significant improvements in ZT have been reported. Nanostructuring approach has been shown to be effective in reducing the thermal conductivity, and in some cases, increasing the power factor. Current experiment and theory indicate that there are still plenty of rooms for improving the existing material systems. Aside from the material resource factor, bulk thermoelectric materials need to be designed and fabricated to have long-term, moderate to high temperature operating stability for high-power, high-efficiency thermoelectric energy conversion. Various aspects of TE materials research including those from my collaborative studies will be discussed
Correlation-enhanced Friedel oscillations in amorphous alloys and quasicrystals
We show that quantum correlations induced by electron-electron interactions
in the presence of random impurity scattering can play an important role in the
thermal stabilization of amorphous Hume-Rothery systems: When there is strong
backscattering off local, concentrical ion clusters, the static electron
density response acquires a powerlaw divergence at even
at elevated temperature. This leads to an enhancement as well as to a
systematical phase shift of the Friedel oscillations, both consistent with
experiments. The possible importance of this effect in icosahedral
quasicrystals is discussed.Comment: 3 pages, 2 figures, RevTeX; to be published in proceedings of the
10th int. conference on liquid and amorphous metals LAM10, Physica C (1999
The Economic Contribution of Software: An Alternative Perspective on the Productivity Paradox
The complex relationships between information technology investments and business value have been the focus of intensive research in recent years. There appears to be a discernible trend toward a more nuanced view in which the differential effects of the various categories of IT capital such as hardware, software, and their interactions with organizational factors are systematically investigated. As well, there is emerging evidence of accelerating investments in software and a greater shift toward “softwarization” (Langdon 2003) in which value addition is linked to combining flexible software with increasingly commoditized hardware. In this paper, we focus on the differential contributions of hardware and software capital and their interactions with labor capital. We use industry-level data to extend previous studies in three ways: (1) by using more recent data (1990 to 2002), (2) by focusing on IT-using industries in the private sector, and (3) by treating IT hardware and IT software as two distinct classes of IT capital. We adopt the commonly used log-linear Cobb Douglas production function approach. Our findings indicate that the impacts of software are significantly different in comparison with hardware and that the productivity benefits attributable to IT are largely due to the interactions between software and labor inputs. We conclude that software is the key to productivity growth in the IT-using world, and show that it can be used as the closest surrogate to represent business complementarities to IT in macro-level studies
High Thermoelectric Figure of Merit by Resonant Dopant in Half-Heusler Alloys
Half-Heusler alloys have been one of the benchmark high temperature
thermoelectric materials owing to their thermal stability and promising figure
of merit ZT. Simonson et al. early showed that small amounts of vanadium doped
in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change
with the increased density of states near the Fermi level. We herein report a
systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta)
as prospective resonant dopants in enhancing the ZT of n-type half-Heusler
alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was found to increase
the Seebeck coefficient in the temperature range 300-1000 K, consistent with a
resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as
evident by the systematic decrease in electrical resistivity and Seebeck
coefficient. The combination of enhanced Seebeck coefficient due to the
presence of V resonant states and the reduced thermal conductivity has led to a
state-of-the-art ZT of 1.3 near 850 K in n-type
(Hf0.6Zr0.4)0.99V0.01NiSn0.995Sb0.005 alloys.Comment: Submitted to AIP Advance
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