13,571 research outputs found
Randomized Rounding for the Largest Simplex Problem
The maximum volume -simplex problem asks to compute the -dimensional
simplex of maximum volume inside the convex hull of a given set of points
in . We give a deterministic approximation algorithm for this
problem which achieves an approximation ratio of . The problem
is known to be -hard to approximate within a factor of for
some constant . Our algorithm also gives a factor
approximation for the problem of finding the principal submatrix of
a rank positive semidefinite matrix with the largest determinant. We
achieve our approximation by rounding solutions to a generalization of the
-optimal design problem, or, equivalently, the dual of an appropriate
smallest enclosing ellipsoid problem. Our arguments give a short and simple
proof of a restricted invertibility principle for determinants
Tunable coupling in circuit quantum electrodynamics with a superconducting V-system
Recent progress in superconducting qubits has demonstrated the potential of
these devices for the future of quantum information processing. One desirable
feature for quantum computing is independent control of qubit interactions as
well as qubit energies. We demonstrate a new type of superconducting charge
qubit that has a V-shaped energy spectrum and uses quantum interference to
provide independent control over the qubit energy and dipole coupling to a
superconducting cavity. We demonstrate dynamic access to the strong coupling
regime by tuning the coupling strength from less than 200 kHz to more than 40
MHz. This tunable coupling can be used to protect the qubit from cavity-induced
relaxation and avoid unwanted qubit-qubit interactions in a multi-qubit system.Comment: 5 pages, 4 figure
Turbojet engine blade damping
The potentials of various sources of nonaerodynamic damping in engine blading are evaluated through a combination of advanced analysis and testing. The sources studied include material hysteresis, dry friction at shroud and root disk interfaces as well as at platform type external dampers. A limited seris of tests was conducted to evaluate damping capacities of composite materials (B/AL, B/AL/Ti) and thermal barrier coatings. Further, basic experiments were performed on titanium specimens to establish the characteristics of sliding friction and to determine material damping constants J and n. All the tests were conducted on single blades. Mathematical models were develthe several mechanisms of damping. Procedures to apply this data to predict damping levels in an assembly of blades are developed and discussed
Offer Price, Target Ownership Structure and IPO Performance
Although the choice of an IPO offer price level would seem to have little economic significance, firms do not decide this arbitrarily. Our findings suggest that firms select their IPO offer prices to target a desired ownership structure, which in turn has implications for underpricing and post-IPO performance. Higher priced IPOs are marketed by more reputed underwriters and attract a relatively larger institutional investment. These IPOs are relatively more underpriced, possibly as compensation for the monitoring and information benefits provided by institutional investors. IPOs whose offer prices are below the median level seem to be targeted towards a retail investor clientele. These IPOs are also relatively more underpriced, possibly as a cost of adverse selection. Our finding that long-run performance increases with offer price confirms that higher priced IPOs are better firms.Initial public offerings; share prices; share allocation
Is Share Price Related to Marketability? Evidence from Mutual Fund Share Splits
We examine the "marketability hypothesis," which states that stock splits enhance the attractiveness of shares to investors by restoring prices to a preferred trading range. We examine splits of mutual fund shares because they provide a clean testing ground for the marketability hypothesis, since the conventional rationales for common stock splits do not apply. We find that splitting funds experience significant increases (relative to non-splitting matched funds) in net assets and shareholders. Stock splits do appear to enhance marketability.
Dispersive Photon Blockade in a Superconducting Circuit
Mediated photon-photon interactions are realized in a superconducting
coplanar waveguide cavity coupled to a superconducting charge qubit. These
non-resonant interactions blockade the transmission of photons through the
cavity. This so-called dispersive photon blockade is characterized by measuring
the total transmitted power while varying the energy spectrum of the photons
incident on the cavity. A staircase with four distinct steps is observed and
can be understood in an analogy with electron transport and the Coulomb
blockade in quantum dots. This work differs from previous efforts in that the
cavity-qubit excitations retain a photonic nature rather than a hybridization
of qubit and photon and provides the needed tolerance to disorder for future
condensed matter experiments.Comment: 4 pages, 3 figure
Linear and nonlinear optical spectroscopy of a strongly-coupled microdisk-quantum dot system
A fiber taper waveguide is used to perform direct optical spectroscopy of a
microdisk-quantum-dot system, exciting the system through the photonic (light)
channel rather than the excitonic (matter) channel. Strong coupling, the regime
of coherent quantum interactions, is demonstrated through observation of vacuum
Rabi splitting in the transmitted and reflected signals from the cavity. The
fiber coupling method also allows the examination of the system's steady-state
nonlinear properties, where saturation of the cavity-QD response is observed
for less than one intracavity photon.Comment: adjusted references, added minor clarification
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