6,600 research outputs found
In-gap bound states and tunneling conductance of multiband superconductors through a normal/superconductor/superconductor junction
The tunneling conductance between a metal and a multiband s-wave
superconductor with a thin layer of single-band s-wave superconductor
sandwiched in between is examined in this paper. We show that an in-gap peak in
conductance curve is found as a result of the formation of in-gap bound state
between the single-band and multiband superconductor junctions if the phases of
the superconducting order parameters of the multiband superconductor are
frustrated. The implication of this result in determining the gap symmetry of
the iron-based superconductors is discussed.Comment: 5 pages, 5 figure
Secure Massive MIMO Transmission in the Presence of an Active Eavesdropper
In this paper, we investigate secure and reliable transmission strategies for
multi-cell multi-user massive multiple-input multiple-output (MIMO) systems in
the presence of an active eavesdropper. We consider a time-division duplex
system where uplink training is required and an active eavesdropper can attack
the training phase to cause pilot contamination at the transmitter. This forces
the precoder used in the subsequent downlink transmission phase to implicitly
beamform towards the eavesdropper, thus increasing its received signal power.
We derive an asymptotic achievable secrecy rate for matched filter precoding
and artificial noise (AN) generation at the transmitter when the number of
transmit antennas goes to infinity. For the achievability scheme at hand, we
obtain the optimal power allocation policy for the transmit signal and the AN
in closed form. For the case of correlated fading channels, we show that the
impact of the active eavesdropper can be completely removed if the transmit
correlation matrices of the users and the eavesdropper are orthogonal. Inspired
by this result, we propose a precoder null space design exploiting the low rank
property of the transmit correlation matrices of massive MIMO channels, which
can significantly degrade the eavesdropping capabilities of the active
eavesdropper.Comment: To appear in ICC 1
The Effect of Timely Loan Loss Recognition in the Banking System on Firmsâ Debt Structure
In this paper, we examine how the system under which banks record loan losses,
specifically, the timeliness of loan loss recognition, affects borrowersâ debt
structure. Using data from 55 countries, we find that more timely loan loss
recognition reduces firmsâ reliance on bank debt relative to public debt. This
result reflects an equilibrium in which firms in an economy rely less on bank
debt when there are greater lending constraints and more borrower monitoring
in a more timely loan loss accounting regime. Consistent with such a regime
resulting in tighter loan conditions, we find an even lower use of bank debt in
countries with stringent bank supervision and among financially constrained
and opaque firms. Overall, our study offers new insight into the real effects of
banksâ accounting on firmsâ debt structure when firms can choose alternative
debt providers
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