638 research outputs found
Tidal modulation of ice shelf buttressing stresses
Ocean tides influence the flow of marine-terminating glaciers. Observations indicate that the large fortnightly variations in ice flow at Rutford Ice Stream in West Antarctica originate in the floating ice shelf. We show that nonlinear variations in ice shelf buttressing driven by tides can produce such fortnightly variations in ice flow. These nonlinearities in the tidal modulation of buttressing stresses can be caused by asymmetries in the contact stress from migration of the grounding line and bathymetric pinning points beneath the ice shelf. Using a simple viscoelastic model, we demonstrate that a combination of buttressing and hydrostatic stress variations can explain a diverse range of tidal variations in ice shelf flow, including the period, phase and amplitude of flow variations observed at Rutford and Bindschadler Ice Streams
Dean Emeritus Patrick J. Rohan
(Excerpt)
Patrick J. Rohan’s connection to St. John’s reaches back more than half a century. He graduated from St. John’s University in 1954 and from the School of Law in 1956. Two years later, he joined the Law School faculty, where he served for fifty-two years until his retirement in June 2009. He died just a few months later, on November 26, 2009. The School of Law community mourns the passing of this man of St. John’s—Dean Emeritus, Professor of Law, alumnus, supporter, and friend
Good gamers, good managers? A proof-of-concept study with Sid Meier’s Civilization
Human resource professionals increasingly enhance their assessment tools with game elements—a process typically referred to as “gamification”—to make them more interesting and engaging for candidates, and they design and use “serious games” that can support skill assessment and development. However, commercial, off-the-shelf video games are not or are only rarely used to screen or test candidates, even though there is increasing evidence that they are indicative of various skills that are professionally valuable. Using the strategy game Civilization, this proof-of-concept study explores if strategy video games are indicative of managerial skills and, if so, of what managerial skills. Under controlled laboratory conditions, we asked forty business students to play the Civilization game and to participate in a series of assessment exercises. We find that students who had high scores in the game had better skills related to problem-solving and organizing and planning than the students who had low scores. In addition, a preliminary analysis of in-game data, including players’ interactions and chat messages, suggests that strategy games such as Civilization may be used for more precise and holistic “stealth assessments,” including personality assessments
Magnetotunneling spectroscopy of mesoscopic correlations in two-dimensional electron systems
An approach to experimentally exploring electronic correlation functions in
mesoscopic regimes is proposed. The idea is to monitor the mesoscopic
fluctuations of a tunneling current flowing between the two layers of a
semiconductor double-quantum-well structure. From the dependence of these
fluctuations on external parameters, such as in-plane or perpendicular magnetic
fields, external bias voltages, etc., the temporal and spatial dependence of
various prominent correlation functions of mesoscopic physics can be
determined. Due to the absence of spatially localized external probes, the
method provides a way to explore the interplay of interaction and localization
effects in two-dimensional systems within a relatively unperturbed environment.
We describe the theoretical background of the approach and quantitatively
discuss the behavior of the current fluctuations in diffusive and ergodic
regimes. The influence of both various interaction mechanisms and localization
effects on the current is discussed. Finally a proposal is made on how, at
least in principle, the method may be used to experimentally determine the
relevant critical exponents of localization-delocalization transitions.Comment: 15 pages, 3 figures include
Field Theory of the Random Flux Model
The long-range properties of the random flux model (lattice fermions hopping
under the influence of maximally random link disorder) are shown to be
described by a supersymmetric field theory of non-linear sigma model type,
where the group GL(n|n) is the global invariant manifold. An extension to
non-abelian generalizations of this model identifies connections to lattice
QCD, Dirac fermions in a random gauge potential, and stochastic non-Hermitian
operators.Comment: 4 pages, 1 eps figur
Calculation of the Density of States Using Discrete Variable Representation and Toeplitz Matrices
A direct and exact method for calculating the density of states for systems
with localized potentials is presented. The method is based on explicit
inversion of the operator . The operator is written in the discrete
variable representation of the Hamiltonian, and the Toeplitz property of the
asymptotic part of the obtained {\it infinite} matrix is used. Thus, the
problem is reduced to the inversion of a {\it finite} matrix
z~2: An Epoch of Disk Assembly
We explore the evolution of the internal gas kinematics of star-forming
galaxies from the peak of cosmic star-formation at to today.
Measurements of galaxy rotation velocity , which quantify ordered
motions, and gas velocity dispersion , which quantify disordered
motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a
continuous baseline in redshift from to , spanning 10 Gyrs. At
low redshift, nearly all sufficiently massive star-forming galaxies are
rotationally supported (). By , the percentage of
galaxies with rotational support has declined to 50 at low stellar mass
() and 70 at high stellar mass
(). For , the percentage
drops below 35 for all masses. From to now, galaxies exhibit
remarkably smooth kinematic evolution on average. All galaxies tend towards
rotational support with time, and it is reached earlier in higher mass systems.
This is mostly due to an average decline in by a factor of 3 since a
redshift of 2, which is independent of mass. Over the same time period,
increases by a factor of 1.5 for low mass systems, but does not
evolve for high mass systems. These trends in and with
time are at a fixed stellar mass and should not be interpreted as evolutionary
tracks for galaxy populations. When galaxy populations are linked in time with
abundance matching, not only does decline with time as before, but
strongly increases with time for all galaxy masses. This enhances the
evolution in . These results indicate that is a
period of disk assembly, during which the strong rotational support present in
today's massive disk galaxies is only just beginning to emerge.Comment: 12 pages, 8 figures, submitted to Ap
Random Matrix Theory of a Chaotic Andreev Quantum Dot
A new universality class distinct from the standard Wigner-Dyson ones is
identified. This class is realized by putting a metallic quantum dot in contact
with a superconductor, while applying a magnetic field so as to make the
pairing field effectively vanish on average. A random-matrix description of the
spectral and transport properties of such a quantum dot is proposed. The
weak-localization correction to the tunnel conductance is nonzero and results
from the depletion of the density of states due to the coupling with the
superconductor. Semiclassically, the depletion is caused by a a mode of
phase-coherent long-range propagation of electrons and holes.Comment: minor changes, 4 REVTeX page
Random Dirac Fermions and Non-Hermitian Quantum Mechanics
We study the influence of a strong imaginary vector potential on the quantum
mechanics of particles confined to a two-dimensional plane and propagating in a
random impurity potential. We show that the wavefunctions of the non-Hermitian
operator can be obtained as the solution to a two-dimensional Dirac equation in
the presence of a random gauge field. Consequences for the localization
properties and the critical nature of the states are discussed.Comment: 5 pages, Latex, 1 figure, version published in PR
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