521 research outputs found
Real Option, Debt Agency Conflicts and Corporate Investment Decisions
This paper studies enterprise investment decisions under debt agency conflicts by the method of real option. It is different from the existed literatures that this paper considers not only the influence of investment goals alienation on investment decisions without bankruptcy agency, but also analyzes the investment decisions distortion under bankruptcy agency conflicts. The study result shows that enterprises with debt usually exist overinvestment; on the one hand, the overinvestment comes from excessive pursuing of the tax benefits under the investment goals alienation, on the other hand, it comes from the protection for shareholders’ investment risk under strategic default bankruptcy. What’s more, under the lower debt level, the former is the dominant mechanism for investment decisions distortion; while under the higher debt level, the influence of the later is prominent
Synthesizing and characterization of hole doped nickel based layer superconductor (LaSr)ONiAs
We report the synthesizing and characterization of the hole doped Ni-based
superconductor (. By substituting La with Sr, the
superconducting transition temperature is increased from 2.75 K of the
parent phase to 3.7 K at the doping levels x= 0.1 - 0.2. The curve
versus hole concentration shows a symmetric behavior as the electron
doped samples . The normal state resistivity in Ni-based
samples shows a good metallic behavior and reveals the absence of an anomaly
which appears in the Fe-based system at about 150 K, suggesting that this
anomaly is not a common feature for all systems. Hall effect measurements
indicate that the electron conduction in the parent phase is
dominated by electron-like charge carriers, while with more Sr doping, a
hole-like band will emerge and finally prevail over the conduction, and
accordingly the superconducting transition temperature increases.Comment: 4 pages, 5 figure
Specific-Heat Measurement of Residual Superconductivity in the Normal State of Underdoped Cuprate Superconductors
We have measured the magnetic field and temperature dependence of specific
heat on single crystals in wide doping and
temperature regions. The superconductivity related specific heat coefficient
and entropy are determined. It is found that
has a hump-like anomaly at and behaves as a long tail which
persists far into the normal state for the underdoped samples, but for the
heavily overdoped samples the anomaly ends sharply just near .
Interestingly, we found that the entropy associated with superconductivity is
roughly conserved when and only the long tail part in the normal state is taken
into account for the underdoped samples, indicating the residual
superconductivity above T.Comment: 4 pages, 4 figures, Accepted for publication in Physical Review
Letter
Hall effect and magnetoresistance in single crystals of NdFeAsOF
Hall effect and magnetoresistance have been measured on single crystals of
with x = 0 ( = 0 K) and x = 0.18 ( = 50 K). For the undoped samples, strong Hall effect and magnetoresistance with
strong temperature dependence were found below about 150 K. The
magnetoresistance was found to be as large as 30% at 15 K at a magnetic field
of 9 T. From the transport data we found that the transition near 155 K was
accomplished in two steps: first one occurs at 155 K which may be associated
with the structural transition, the second one takes place at about 140 K which
may correspond to the spin-density wave like transition. In the superconducting
sample with = 50 K, it is found that the Hall coefficient also reveals
a strong temperature dependence with a negative sign. But the magnetoresistance
becomes very weak and does not satisfy the Kohler's scaling law. These
dilemmatic results (strong Hall effect and very weak magnetoresistance) prevent
to understand the normal state electric conduction by a simple multi-band model
by taking account the electron and hole pockets. Detailed analysis further
indicates that the strong temperature dependence of cannot be easily
understood with the simple multi-band model either. A picture concerning a
suppression to the density of states at the Fermi energy in lowering
temperature is more reasonable. A comparison between the Hall coefficient of
the undoped sample and the superconducting sample suggests that the doping may
remove the nesting condition for the formation of the SDW order, since both
samples have very similar temperature dependence above 175 K.Comment: 8 pages, 9 figure
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