31 research outputs found
Electromagnetic fluctuation-induced interactions in randomly charged slabs
Randomly charged net-neutral dielectric slabs are shown to interact across a
featureless dielectric continuum with long-range electrostatic forces that
scale with the statistical variance of their quenched random charge
distribution and inversely with the distance between their bounding surfaces.
By accounting for the whole spectrum of electromagnetic field fluctuations, we
show that this long-range disorder-generated interaction extends well into the
retarded regime where higher-order Matsubara frequencies contribute
significantly. This occurs even for highly clean samples with only a trace
amount of charge disorder and shows that disorder effects can be important down
to the nano scale. As a result, the previously predicted non-monotonic behavior
for the total force between dissimilar slabs as a function of their separation
distance is substantially modified by higher-order contributions, and in almost
all cases of interest, we find that the equilibrium inter-surface separation is
shifted to substantially larger values compared to predictions based solely on
the zero-frequency component. This suggests that the ensuing non-monotonic
interaction is more easily amenable to experimental detection. The presence of
charge disorder in the intervening dielectric medium between the two slabs is
shown to lead to an additional force that can be repulsive or attractive
depending on the system parameters and can, for instance, wash out the
non-monotonic behavior of the total force when the intervening slab contains a
sufficiently large amount of disorder charges.Comment: 9 pages, 5 figure
Non-monotoic fluctuation-induced interactions between dielectric slabs carrying charge disorder
We investigate the effect of monopolar charge disorder on the classical
fluctuation-induced interactions between randomly charged net-neutral
dielectric slabs and discuss various generalizations of recent results (A. Naji
et al., Phys. Rev. Lett. 104, 060601 (2010)) to highly inhomogeneous dielectric
systems with and without statistical disorder correlations. We shall focus on
the specific case of two generally dissimilar plane-parallel slabs, which
interact across vacuum or an arbitrary intervening dielectric medium. Monopolar
charge disorder is considered to be present on the bounding surfaces and/or in
the bulk of the slabs, may be in general quenched or annealed and may possess a
finite lateral correlation length reflecting possible `patchiness' of the
random charge distribution. In the case of quenched disorder, the bulk disorder
is shown to give rise to an additive long-range contribution to the total
force, which decays as the inverse distance between the slabs and may be
attractive or repulsive depending on the dielectric constants of the slabs. We
show that in the case of two dissimilar slabs the net effect due to the
interplay between the disorder-induced and the pure van der Waals interactions
can lead to a variety of unusual non-monotonic interaction profiles between the
dielectric slabs. In particular, when the intervening medium has a larger
dielectric constant than the two slabs, we find that the net interaction can
become repulsive and exhibit a potential barrier, while the underlying van der
Waals force is attractive. On the contrary, when the intervening medium has a
dielectric constant in between that of the two slabs, the net interaction can
become attractive and exhibit a free energy minimum, while the pure van der
Waals force is repulsive. Therefore, the charge disorder, if present, can
drastically alter the effective interaction between net-neutral objects.Comment: 13 pages, 8 figure
Data Quality Procedures in Survey Research: An Analysis and Framework for Doctoral Program Curricula
To ensure validity in survey research, it is imperative that we properly educate doctoral students on best practices in data quality procedures. A 14-year analysis of 679 studies in the AIS “Basket of 8” journals noted undercommunication in the most pertinent procedures, consistent across journals and time. Given recent calls for improvements in data transparency, scholars must be educated on the importance and methods for ensuring data quality. Thus, to guide the education of doctoral students, we present a “5-C Framework\u27\u27 of data quality procedures derived from a wide-ranging literature review. Additionally, we describe a set of guidelines regarding enacting and communicating data quality procedures in survey research
Many-body effects in van der Waals-Casimir interaction between graphene layers
Van der Waals-Casimir dispersion interactions between two apposed graphene
layers, a graphene layer and a substrate, and in a multilamellar graphene
system are analyzed within the framework of the Lifshitz theory. This
formulation hinges on a known form of the dielectric response function of an
undoped or doped graphene sheet, assumed to be of a random phase approximation
form. In the geometry of two apposed layers the separation dependence of the
van der Waals-Casimir interaction for both types of graphene sheets is
determined and compared with some well known limiting cases. In a multilamellar
array the many-body effects are quantified and shown to increase the magnitude
of the van der Waals-Casimir interactions.Comment: 13 pages, 13 figure
Sample-to-sample torque fluctuations in a system of coaxial randomly charged surfaces
Polarizable randomly charged dielectric objects have been recently shown to
exhibit long-range lateral and normal interaction forces even when they are
effectively net neutral. These forces stem from an interplay between the
quenched statistics of random charges and the induced dielectric image charges.
This type of interaction has recently been evoked to interpret measurements of
Casimir forces in vacuo, where a precise analysis of such disorder-induced
effects appears to be necessary. Here we consider the torque acting on a
randomly charged dielectric surface (or a sphere) mounted on a central axle
next to another randomly charged surface and show that although the resultant
mean torque is zero, its sample-to-sample fluctuation exhibits a long-range
behavior with the separation distance between the juxtaposed surfaces and that,
in particular, its root-mean-square value scales with the total area of the
surfaces. Therefore, the disorder-induced torque between two randomly charged
surfaces is expected to be much more pronounced than the disorder-induced
lateral force and may provide an effective way to determine possible disorder
effects in experiments, in a manner that is independent of the usual normal
force measurement.Comment: 7 pages, 3 fig
Effects of Spatial Dispersion on the Casimir Force between Graphene Sheets
The Casimir force between graphene sheets is investigated with emphasis on
the effect from spatial dispersion using a combination of factors, such as a
nonzero chemical potential and an induced energy gap. We distinguish between
two regimes for the interaction - T=0 and . It is found that
the quantum mechanical interaction (T=0 ) retains its distance dependence
regardless of the inclusion of dispersion. The spatial dispersion from the
finite temperature Casimir force is found to contribute for the most part from
Matsubara term. These effects become important as graphene is tailored to
become a poor conductor by inducing a band gap.Comment: 6 pages, 9 figures. Submitted to EP
Cardiovascular control and stabilization via inclination and mobilization during bed rest
Cardiovascular deconditioning has long been recognized as a characteristic of the physiological adaptation to long-term bed rest in patients. The process is thought to contribute to orthostatic intolerance and enhance secondary complications in a significant way. Mobilization is a cost-effective and simple method to maintain the cardiovascular parameters (i.e., blood pressure, heart rate) stable, counter orthostatic intolerance and reduce the risk of secondary problems in patients during long-term immobilization. The aim of this project is to control the cardiovascular parameters such as heart rate and blood pressure of bed rest patients via automated leg mobilization and body tilting. In a first step, a nonlinear model predictive control strategy was designed and evaluated on five healthy subjects and 11 bed rest patients. In a next step, a clinically feasible study was conducted on two patients. The mean values differed on average less than 1Â bpm from the predetermined heart rate and less than 2.5Â mmHg from the desired blood pressure values. These results of the feasibility study are promising, although heterogeneous disease etiologies and individual medication strongly influence the mechanically induced reactions. The long-term goal is an automation of the control of physiological signals and the mobilization of bed rest patients in an early phase of the rehabilitation process. Therefore, this new approach could help to strengthen the cardiovascular system and prevent secondary health problems arising from long-term bed rest