1,781 research outputs found
Two Boats, Three Summers, Five Universities, One Dozen Instructors, and Sixty-Five Teachers: A Collaborative Oceanography Field Program for Earth Science
A three-day ïŹeld workshop was an integral component of the graduate-level course entitled, Oceanography, that was offered by Virginia Earth Science Collaborative Project (VESC) to help Virginia educators earn the earth science teaching endorsement. The VESC partner institutions that offered Oceanographngeorge Mason University, James Madison University, the University of Virginia Southwest Center, and Virginia Commonwealth University-lacked direct access to research and education facilities en the coast. The College of William & Mary, another VESC partner, provided this resource through the Virginia Institute of Marine Scienceâs (VIMS) Eastern Shore Laboratory in Wachapreague, Virginia. The field program agenda and activities were developed and conducted by a team comprised of VESC oceanography faculty, Virginia Sea Grant educators, and a scientist from VIMS. This collaboration resulted in a program design used as the basis for six workshops conducted over three summers. Seventy-nine Virginia middle school and high school science teachers took part in the six workshops, conducted in July of 2005, 2006, and 2007. This article describes the workshop activities and provides perspectives on its design and implementation from the viewpoints of Virginia Sea Grant educators who served as field instructors
Electro-Reflectance Spectra of Blue Bronze
We show that the infrared reflectance of the quasi-one dimensional
charge-density-wave (CDW) conductor K0.3MoO3 (blue bronze) varies with position
when a voltage greater than the CDW depinning threshold is applied. The spatial
dependence and spectra associated with these changes are generally as expected
from the electro-transmission [B.M. Emerling, et al, Eur. Phys. J. B 16, 295
(2000)], but there are some differences which might be associated with changes
in the CDW properties on the surface. We have examined the electro-reflectance
spectrum associated with CDW current investigation for light polarized parallel
to the conducting chains for signs of expected current-induced intragap states,
and conclude that the density of any such states is at least an order of
magnitude lower than expected.Comment: 1)submitted to Eur. Phys. J B 2) revised (July 24) to a) better
emphasize results and b) with new figure insets to make paper more
self-containe
Coupling of the lattice and superlattice deformations and hysteresis in thermal expansion for the quasi one-dimensional conductor TaS
An original interferometer-based setup for measurements of length of
needle-like samples is developed, and thermal expansion of o-TaS crystals
is studied. Below the Peierls transition the temperature hysteresis of length
is observed, the width of the hysteresis loop being up to . The behavior of the loop is anomalous: the length changes so
that it is in front of its equilibrium value. The hysteresis loop couples with
that of conductivity. The sign and the value of the length hysteresis are
consistent with the strain dependence of the charge-density waves (CDW) wave
vector. With lowering temperature down to 100 K the CDW elastic modulus grows
achieving a value comparable with the lattice Young modulus. Our results could
be helpful in consideration of different systems with intrinsic
superstructures.Comment: 4 pages, 3 figures. Phys. Rev. Lett., accepted for publicatio
On the initial value problem for second order scalar fluctuations in Einstein static
We consider fluctuations in a perfect irrotational fluid coupled to gravity
in an Einstein static universe background. We show that the homogeneous linear
perturbations of the scalar and metric fluctuations in the Einstein static
universe must be present if the second order constraint equations are to be
integrable. I.e., the 'linearization stability' constraint forces the presence
of these homogeneous modes. Since these linear homogeneous scalar modes are
well known to be exponentially unstable, the tactic of neglecting these modes
to create a long-lived, almost Einstein universe does not work, even if all
higher order (L 1) modes are dynamically stable.Comment: 8 pages, no figures, changes made to the presentation throughout to
emphasize the linear nature of the analysis and the treatment of the
irrotational perfect fluid. Conclusions unchanged. Submitted to PR
Curvature tensors on distorted Killing horizons and their algebraic classification
We consider generic static spacetimes with Killing horizons and study
properties of curvature tensors in the horizon limit. It is determined that the
Weyl, Ricci, Riemann and Einstein tensors are algebraically special and
mutually aligned on the horizon. It is also pointed out that results obtained
in the tetrad adjusted to a static observer in general differ from those
obtained in a free-falling frame. This is connected to the fact that a static
observer becomes null on the horizon.
It is also shown that finiteness of the Kretschmann scalar on the horizon is
compatible with the divergence of the Weyl component or
in the freely falling frame. Furthermore finiteness of is compatible
with divergence of curvature invariants constructed from second derivatives of
the Riemann tensor.
We call the objects with finite Krestschmann scalar but infinite
``truly naked black holes''. In the (ultra)extremal versions of these objects
the structure of the Einstein tensor on the horizon changes due to extra terms
as compared to the usual horizons, the null energy condition being violated at
some portions of the horizon surface. The demand to rule out such divergencies
leads to the constancy of the factor that governs the leading term in the
asymptotics of the lapse function and in this sense represents a formal analog
of the zeroth law of mechanics of non-extremal black holes. In doing so, all
extra terms in the Einstein tensor automatically vanish.Comment: 21 pages, To appear in Class. Quant. Gra
The metaphysics of Machian frame-dragging
The paper investigates the kind of dependence relation that best portrays Machian frame-dragging in general relativity. The question is tricky because frame-dragging relates local inertial frames to distant distributions of matter in a time-independent way, thus establishing some sort of non-local link between the two. For this reason, a plain causal interpretation of frame-dragging faces huge challenges. The paper will shed light on the issue by using a generalized structural equation model analysis in terms of manipulationist counterfactuals recently applied in the context of metaphysical enquiry by Schaffer (2016) and Wilson (2017). The verdict of the analysis will be that frame-dragging is best understood in terms of a novel type of dependence relation that is half-way between causation and grounding
Viscoelastic response of sonic band-gap materials
A brief report is presented on the effect of viscoelastic losses in a high
density contrast sonic band-gap material of close-packed rubber spheres in air.
The scattering properties of such a material are computed with an on-shell
multiple scattering method, properties which are compared with the lossless
case. The existence of an appreciable omnidirectional gap in the transmission
spectrum, when losses are present, is also reported.Comment: 5 pages, 4 figures, submitted to PR
Vector Theory of Gravity
We proposed a gravitation theory based on an analogy with electrodynamics on
the basis of a vector field. For the first time, to calculate the basic
gravitational effects in the framework of a vector theory of gravity, we use a
Lagrangian written with gravitational radiation neglected and generalized to
the case of ultra-relativistic speeds. This allows us to accurately calculate
the values of all three major gravity experiments: the values of the perihelion
shift of Mercury, the light deflection angle in the gravity field of the Sun
and the value of radar echo delay. The calculated values coincide with the
observed ones. It is shown that, in this theory, there exists a model of an
expanding Universe.Comment: 9 page
Understanding project mobility: the movement of Kingâs Cross to Brussels and Johannesburg
This paper builds on policy mobility research to question how loosely deployed references to specific models or sites reveal how tacit and explicit knowledge are required to effectively replicate urban ideas in new places. Departing from existing analysis of policies and the public sector, we use policy mobility framing to critically engage with the strategies of the private sector. We analyse Kingâs Crossâ arrival in two large-scale redevelopments: Brusselsâ Tour and Taxis and Johannesburgâs Modderfontein, questioning how it was referred to, the success of its deployment and the politics of urban learning. We draw three main conclusions: first, the comparison demonstrates private sector agency in their ability to shape the way expert knowledge arrives. Second, we argue that private sector actors require locally embedded practices and tacit knowledge to leverage international points of reference in their projects. Third, in placing the analytical gaze from the perspective of the project âarrivingâ and adopting a specifically comparative approach, we reveal the myriad of possibilities developers and consultants face and the politics of what they pick from each. Theoretically, these conclusions draw from economic geographyâs politics of learning and mobility research to demonstrate the benefit of analysis that traces a project, rather an idea or a policy, and from âarriving atâ and the subsequent assembling of different project components
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