2,366 research outputs found
Nonmilitary Threats to Soviet National Security
Except, perhaps, in the view of the most brazen martinet, national power is not an end in itself. Rather, it is a means to an end set of ends which usually include such goals as the survival of the nation-state, its culture and its way of life, the improvement in the quality of life of its citizens; and the state\u27s continued ability to increase its infuence with other states in the pursuit of these goals. From this broader perspective, the national security of the Soviet Union is vulnerable to serious structured and systematic industrial and agricultural problems as well as demographic demographic trends which threaten to tear apart from with in the last of the world\u27s great multinational empires
Where Do Riders Park Dockless, Shared Electric Scooters? Findings from San Jose, California
Dockless, shared, electric kick-scooters started popping up on U.S. city streets without warning in 2017. Reaction to the shared scooters came swiftly and strongly. On the one hand, the scooters have proven popular with riders, attracting investment capital and expanding service to additional cities. But others have been less enthusiastic, with a central complaint being how shared scooters are parked. This perspective explores the extent to which parked shared scooters pose a problem to others on streets, sidewalks, and public spaces, using empirical evidence documenting where scooters have been parked in downtown San Jose, California
Degenerate dispersive equations arising in the study of magma dynamics
An outstanding problem in Earth science is understanding the method of
transport of magma in the Earth's mantle. Models for this process, transport in
a viscously deformable porous media, give rise to scalar degenerate,
dispersive, nonlinear wave equations. We establish a general local
well-posedness for a physical class of data (roughly ) via fixed point
methods. The strategy requires positive lower bounds on the solution. This is
extended to global existence for a subset of possible nonlinearities by making
use of certain conservation laws associated with the equations. Furthermore, we
construct a Lyapunov energy functional, which is locally convex about the
uniform state, and prove (global in time) nonlinear dynamic stability of the
uniform state for any choice of nonlinearity. We compare the dynamics to that
of other problems and discuss open questions concerning a larger range of
nonlinearities, for which we conjecture global existence.Comment: 27 Pages, 7 figures are not present in this version. See
http://www.columbia.edu/~grs2103/ for a PDF with figures. Submitted to
Nonlinearit
Photoproduction evidence for and against hidden-strangeness states near 2 GeV
Experimental evidence from coherent diffractive proton scattering has been
reported for two narrow baryonic resonances which decay predominantly to
strange particles. These states, with masses close to 2.0 GeV would, if
confirmed, be candidates for hidden strangeness states with unusual internal
structure. In this paper we examine the literature on strangeness
photoproduction, to seek additional evidence for or against these states. We
find that one state is not confirmed, while for the other state there is some
mild supporting evidence favoring its existence. New experiments are called
for, and the expected photoproduction lineshapes are calculated.Comment: 9 pages, RevTex, five postscript figures, submitted to PR
Suppression of inelastic collisions of polar state molecules in an electrostatic field
Collisions of polar state molecules at ultralow energies are
considered, within a model that accounts for long-range dipole-dipole
interactions, plus rotation of the molecules. We predict a substantial
suppression of dipole-driven inelastic collisions at high values of the applied
electric field, namely, field values of several times . Here is
the rotational constant, and is the electric dipole moment of molecules.
The sudden large drop in the inelastic cross section is attributed to the
onset of degeneracy between molecular rotational levels, which dramatically
alters the scattering Hamiltonian. As a result of the large ratio of elastic to
inelastic collision rates, we predict that evaporative cooling may be feasible
for state molecules in weak-field-seeking states, provided a large
bias electric field is present
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Zeeman spectroscopy of CaH molecules in a magnetic trap
In a recent experiment [Weinstein et al., Nature 395, 148 (1998)] we magnetically trapped 108108ground-statecalcium monohydride molecules, CaH(X2Σ,v″=0,J″=0).CaH(X 2Σ,v″=0, J″=0). The molecules were prepared by laser ablation of a solid sample of CaH2CaH2 and loaded via thermalization with a cold (<1(<1 K) 3He3He buffer gas. The magnetic trap was formed by superconducting coils arranged in the anti-Helmholtz configuration. The detection was done by laser fluorescence spectroscopy excited at 635635 nm (in the B2Σ,v′=0−X2Σ,v″=0B 2Σ,v′=0−X 2Σ,v″=0 band) and detected at 692692 nm (within the B,v′=0−X,v″=1B,v′=0−X,v″=1 band). Both a photomultiplier tube and a CCD camera were used. Due to the thermalization of molecular rotation, only a transition from the lowest rotational state could be detected at zero field, N′=1,J′=3/2←N″=0,J″=1/2.N′=1, J′=3/2←N″=0, J″=1/2. In the magnetic field this rotational transition splits into two features, one shifted towards lower and one towards higher frequencies. The measured shifts are linear in field strength and indicate a small difference (0.02 μB)μB) in the magnetic moments between the ground and excited states. Here we present a theoretical analysis of the observed magnetic shifts. These are identified as arising from a rotational perturbation of the B2Σ,v′=0B 2Σ,v′=0 state by a close-lying A2Π,v′=1A 2Π,v′=1 state that lends the B state some of its A character. We find that the Hamiltonian can be well approximated by a 3×33×3 matrix built out of elements that connect states from within the Σ-doublet and the 2Π3/22Π3/2 manifolds. The interaction parameter describing the Σ−Π coupling in the Zeeman Hamiltonian is determined from the observed shifts and the field-free molecular parameters of CaH given by Berg and Klyning [Phys. Scr. 10, 331 (1974)] and by Martin [J. Mol. Spectrosc 108, 66 (1984)].Physic
Cold and Slow Molecular Beam
Employing a two-stage cryogenic buffer gas cell, we produce a cold,
hydrodynamically extracted beam of calcium monohydride molecules with a near
effusive velocity distribution. Beam dynamics, thermalization and slowing are
studied using laser spectroscopy. The key to this hybrid, effusive-like beam
source is a "slowing cell" placed immediately after a hydrodynamic, cryogenic
source [Patterson et al., J. Chem. Phys., 2007, 126, 154307]. The resulting CaH
beams are created in two regimes. One modestly boosted beam has a forward
velocity of vf = 65 m/s, a narrow velocity spread, and a flux of 10^9 molecules
per pulse. The other has the slowest forward velocity of vf = 40 m/s, a
longitudinal temperature of 3.6 K, and a flux of 5x10^8 molecules per pulse
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