7,824 research outputs found
Parametric instabilities in magnetized multicomponent plasmas
This paper investigates the excitation of various natural modes in a
magnetized bi-ion or dusty plasma. The excitation is provided by parametrically
pumping the magnetic field. Here two ion-like species are allowed to be fully
mobile. This generalizes our previous work where the second heavy species was
taken to be stationary. Their collection of charge from the background neutral
plasma modifies the dispersion properties of the pump and excited waves. The
introduction of an extra mobile species adds extra modes to both these types of
waves. We firstly investigate the pump wave in detail, in the case where the
background magnetic field is perpendicular to the direction of propagation of
the pump wave. Then we derive the dispersion equation relating the pump to the
excited wave for modes propagating parallel to the background magnetic field.
It is found that there are a total of twelve resonant interactions allowed,
whose various growth rates are calculated and discussed.Comment: Published in May 2004; this is a late submission to the archive. 14
pages, 8 figure
Unsteady Crack Motion and Branching in a Phase-Field Model of Brittle Fracture
Crack propagation is studied numerically using a continuum phase-field
approach to mode III brittle fracture. The results shed light on the physics
that controls the speed of accelerating cracks and the characteristic branching
instability at a fraction of the wave speed.Comment: 11 pages, 4 figure
Diagnostic criteria for grading the severity of acute motion sickness
Diagnostic criteria for grading severity of acute motion sicknes
New CP-violation and preferred-frame tests with polarized electrons
We used a torsion pendulum containing polarized
electrons to search for CP-violating interactions between the pendulum's
electrons and unpolarized matter in the laboratory's surroundings or the sun,
and to test for preferred-frame effects that would precess the electrons about
a direction fixed in inertial space. We find and for AU. Our preferred-frame constraints, interpreted in
the Kosteleck\'y framework, set an upper limit on the parameter eV that should be compared to the benchmark
value eV.Comment: 4 figures, accepted for publication in Physical Review Letter
Multi-Objective Gust Load Alleviation Control Designs for an Aeroelastic Wind Tunnel Demonstration Wing
This paper presents several control and gust disturbance estimation techniques applied to a mathematical model of a physical flexible wing wind tunnel model used in ongoing tests at the University of Washington Aeronautical Laboratory's Kirsten Wind Tunnel. Three methods of gust disturbance estimation are presented, followed by three control methods: LQG, Basic Multi-Objective (BMO), and a novel Multi-Objective Prediction Correction (MOPC) controller. The latter of which augments a multi-objective controller, and attempts to correct for errors in the disturbance estimate. A simplified linear simulation of the three controllers is performed and a simple MIMO stability and robustness assessment is performed. Then, the same controllers are simulated in a higher fidelity Simulink environment that captures sampling, saturation and noise effects. This preliminary analysis indicates that the BMO controller provides the best performance and largest stability margins
Parametric instability in dark molecular clouds
The present work investigates the parametric instability of parallel
propagating circularly polarized Alfven(pump) waves in a weakly ionized
molecular cloud. It is shown that the relative drift between the plasma
particles gives rise to the Hall effect resulting in the modified pump wave
characteristics. Although the linearized fluid equations with periodic
coefficients are difficult to solve analytically, it is shown that a linear
transformation can remove the periodic dependence. The resulting linearized
equations with constant coefficients are used to derive an algebraic dispersion
relation. The growth rate of the parametric instability is a sensitive function
of the amplitude of the pump wave as well as to the ratio of the pump and the
modified dust-cyclotron frequencies. The instability is insensitive to the
plasma-beta The results are applied to the molecular clouds.Comment: 27 page, 5 figures, accepted in Ap
Knives and the Second Amendment
This Article is the first scholarly analysis of knives and the Second Amendment. Under the Supreme Court’s standard in District of Columbia v. Heller, knives are Second Amendment “arms” because they are “typically possessed by law-abiding citizens for lawful purposes,” including self-defense. There is no knife that is more dangerous than a modern handgun; to the contrary, knives are much less dangerous. Therefore, restrictions on carrying handguns set the upper limit for restrictions on carrying knives. Prohibitions on carrying knives in general, or of particular knives, are unconstitutional. For example, bans of knives that open in a convenient way (e.g., switchblades, gravity knives, and butterfly knives) are unconstitutional. Likewise unconstitutional are bans on folding knives that, after being opened, have a safety lock to prevent inadvertent closure
Non-malleable encryption: simpler, shorter, stronger
In a seminal paper, Dolev et al. [15] introduced the notion of non-malleable encryption (NM-CPA). This notion is very intriguing since it suffices for many applications of chosen-ciphertext secure encryption (IND-CCA), and, yet, can be generically built from semantically secure (IND-CPA) encryption, as was shown in the seminal works by Pass et al. [29] and by Choi et al. [9], the latter of which provided a black-box construction. In this paper we investigate three questions related to NM-CPA security: 1. Can the rate of the construction by Choi et al. of NM-CPA from IND-CPA be improved? 2. Is it possible to achieve multi-bit NM-CPA security more efficiently from a single-bit NM-CPA scheme than from IND-CPA? 3. Is there a notion stronger than NM-CPA that has natural applications and can be achieved from IND-CPA security? We answer all three questions in the positive. First, we improve the rate in the scheme of Choi et al. by a factor O(λ), where λ is the security parameter. Still, encrypting a message of size O(λ) would require ciphertext and keys of size O(λ2) times that of the IND-CPA scheme, even in our improved scheme. Therefore, we show a more efficient domain extension technique for building a λ-bit NM-CPA scheme from a single-bit NM-CPA scheme with keys and ciphertext of size O(λ) times that of the NM-CPA one-bit scheme. To achieve our goal, we define and construct a novel type of continuous non-malleable code (NMC), called secret-state NMC, as we show that standard continuous NMCs are not enough for the natural “encode-then-encrypt-bit-by-bit” approach to work. Finally, we introduce a new security notion for public-key encryption that we dub non-malleability under (chosen-ciphertext) self-destruct attacks (NM-SDA). After showing that NM-SDA is a strict strengthening of NM-CPA and allows for more applications, we nevertheless show that both of our results—(faster) construction from IND-CPA and domain extension from one-bit scheme—also hold for our stronger NM-SDA security. In particular, the notions of IND-CPA, NM-CPA, and NM-SDA security are all equivalent, lying (plausibly, strictly?) below IND-CCA securit
Using the Uncharged Kerr Black Hole as a Gravitational Mirror
We extend the study of the possibility to use the Schwarzschild black hole as
a gravitational mirror to the more general case of an uncharged Kerr black
hole. We use the null geodesic equation in the equatorial plane to prove a
theorem concerning the conditions the impact parameter has to satisfy if there
shall exist boomerang photons. We derive an equation for these boomerang
photons and an equation for the emission angle. Finally, the radial null
geodesic equation is integrated numerically in order to illustrate boomerang
photons.Comment: 11 pages Latex, 3 Postscript figures, uufiles to compres
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