19,925 research outputs found
Nanoscale Torsional Optomechanics
Optomechanical transduction is demonstrated for nanoscale torsional
resonators evanescently coupled to optical microdisk whispering gallery mode
resonators. The on-chip, integrated devices are measured using a fully
fiber-based system, including a tapered and dimpled optical fiber probe. With a
thermomechanically calibrated optomechanical noise floor down to 7 fm/sqrt(Hz),
these devices open the door for a wide range of physical measurements involving
extremely small torques, as little as 4x10^-20 N*m.Comment: 4 pages, 4 figures - Accepted to APL Oct 22nd, 2012. To appear in
February 4th issue - as cover articl
Vortex Dynamics in Self-Dual Chern-Simons Higgs Systems
We consider vortex dynamics in self-dual Chern-Simons Higgs systems. We show
that the naive Aharanov-Bohm phase is the inverse of the statistical phase
expected from the vortex spin, and that the self-dual configurations of
vortices are degenerate in energy but not in angular momentum. We also use the
path integral formalism to derive the dual formulation of Chern-Simons Higgs
systems in which vortices appear as charged particles. We argue that besides
the electromagnetic interaction, there is an additional interaction between
vortices, the so-called Magnus force, and that these forces can be put together
into a single `dual electromagnetic' interaction. This dual electromagnetic
interaction leads to the right Aharanov-Bohm phase. We also derive and study
the effective action for slowly moving vortices, which contains terms both
linear and quadratic in the vortex velocity.Comment: 36 pages and three figures (available under request), Columbia and
CERN preprin
Electronic structure of the cuprate superconducting and pseudogap phases from spectroscopic imaging STM
We survey the use of spectroscopic imaging scanning tunneling microscopy (SI-STM) to probe the electronic structure of underdoped cuprates. Two distinct classes of electronic states are observed in both the d-wave superconducting (dSC) and the pseudogap (PG) phases. The first class consists of the dispersive Bogoliubov quasiparticle excitations of a homogeneous d-wave superconductor, existing below a lower energy scale E = Delta(0). We find that the Bogoliubov quasiparticle interference (QPI) signatures of delocalized Cooper pairing are restricted to a k-space arc, which terminates near the lines connecting k = +/-(pi/a(0), 0) to k = +/-(0, pi/a(0)). This arc shrinks continuously with decreasing hole density such that Luttinger's theorem could be satisfied if it represents the front side of a hole-pocket that is bounded behind by the lines between k = +/-(pi/a(0), 0) and k = +/-(0, pi/a(0)). In both phases, the only broken symmetries detected for the vertical bar E vertical bar < Delta(0) states are those of a d-wave superconductor. The second class of states occurs proximate to the PG energy scale E = Delta(1). Here the non-dispersive electronic structure breaks the expected 90 degrees-rotational symmetry of electronic structure within each unit cell, at least down to 180 degrees-rotational symmetry. This electronic symmetry breaking was first detected as an electronic inequivalence at the two oxygen sites within each unit cell by using a measure of nematic (C-2) symmetry. Incommensurate non-dispersive conductance modulations, locally breaking both rotational and translational symmetries, coexist with this intra-unit-cell electronic symmetry breaking at E = Delta(1). Their characteristic wavevector Q is determined by the k-space points where Bogoliubov QPI terminates and therefore changes continuously with doping. The distinct broken electronic symmetry states (intra-unit-cell and finite Q) coexisting at E similar to Delta(1) are found to be indistinguishable in the dSC and PG phases. The next challenge for SI-STM studies is to determine the relationship of the E similar to Delta(1) broken symmetry electronic states with the PG phase, and with the E < Delta(0) states associated with Cooper pairing.Publisher PDFPeer reviewe
Experimental Investigation of Crossing Shock Wave-Turbulent Boundary Layer-Bleed Interaction
Results of an experimental investigation of a symmetric crossing shock wave/turbulent boundary layer/bleed interaction are presented for a freestream unit Reynolds number of 1.68 x 10(exp 7)/m, a Mach number of 2.81, and deflection angles of 8 degrees. The data obtained in this study are bleed mass flow rate using a trace gas technique, qualitative information in the form of oil flow visualization, flow field Pitot pressures, and static pressure measurements using pressure sensitive paint. The main objective of this test is two-fold. First, this study is conducted to explore boundary layer control through mass flow removal near a large region of separated flow caused by the interaction of a double fin-induced shock wave and an incoming turbulent boundary layer. Also, a comprehensive data set is needed for computational fluid dynamics code validation
Integration of E-Learning 2.0 with Web 2.0
A review of studies that have examined the integration of Web 2.0 tools into E-Learning 2.0 within built environment educational programs is undertaken. An analysis of studies undertaken reveals five core themes can be derived: (1) students using Web 2.0 demonstrate the capability for effective learning; (2) Skills learned via Web 2.0 can be transferred to the work and untrained tasks; (3) limited research has compared learning in conventional E-Learning and Web 2.0 environments; (4) E-Learning 2.0 enables social learning process to take place, and (5) the shift from eLearning 1.0 (Web 1.0 based) to E-Learning 2.0 (Web 2.0 based) requires not only a technological shift, but also a fundamental shift in the way knowledge is socially constructed and shared. Future issues and challenges are identified in order to ameliorate the integration of the E-Learning 2.0 experience with Web 2.0 tools
Creativity as a Reflective Learning Exercise: Informing Strategic Marketing Decisions Through Digital Storytelling
As educators we strive to facilitate knowledge and ways of learning that serve students throughout their lives, but we also recognize their sometimes short retention span. The innovation we present in this article consists of the use of digital storytelling as a conduit for students to construct a narrative of their experience in a marketing simulation throughout the semester. We explain the innovation’s implementation as well as the results observed throughout the years in the digital stories developed by students. Finally, we discuss further applications of this innovation in other courses and future research avenues
Global Vortex and Black Cosmic String
We study global vortices coupled to (2+1) dimensional gravity with negative
cosmological constant. We found nonsingular vortex solutions in -theory
with a broken U(1) symmetry, of which the spacetimes do not involve physical
curvature singularity. When the magnitude of negative cosmological constant is
larger than a critical value at a given symmetry breaking scale, the spacetime
structure is a regular hyperbola, however it becomes a charged black hole when
the magnitude of cosmological constant is less than the critical value. We
explain through duality transformation the reason why static global vortex
which is electrically neutral forms black hole with electric charge. Under the
present experimental bound of the cosmological constant, implications on
cosmology as a straight black cosmic string is also discussed in comparison
with global U(1) cosmic string in the spacetime of the zero cosmological
constant.Comment: 35 pages, Late
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