323 research outputs found
Effect of Intraduodenal Bile and Taurodeoxycholate on Exocrine Pancreatic Secretion and on Plasma Levels of Vasoactive Intestinal Polypeptide and Somatostatin in Man
Intraduodenal (i.d.) application of bile or Na-taurodeoxycholate (TDC) dose dependently enhances basal exocrine pancreatic secretion. The hydrokinetic effect is mediated at least in part by secretin. This study should show, whether vasoactive intestinal polypeptide (VIP), a partial agonist of secretin, may also be involved in the mediation of the hydrokinetic effect. Furthermore, plasma concentrations of somatostatin-like immunoreactivity (SLI) were measured in order to check whether this counterregulating hormone is also released by bile and TDC. Twenty investigations were carried out on 10 fasting healthy volunteers provided with a double-lumen Dreiling tube. Bile and TDC were intraduodenally applied in doses of 2-6 g and 200-600 mg, respectively, at 65-min intervals. Plasma samples were withdrawn at defined intervals for radioimmunological determination of VIP and SLI. Duodenal juice was collected in 10-min fractions and analyzed for volume, pH, bicarbonate, lipase, trypsin, and amylase. I.d. application of bile or TDC dose dependently stimulated hydrokinetic and ecbolic pancreatic secretion. Bile exerted a slightly stronger effect than TDC. Pancreatic response was simultaneously accompanied by a significant increase of plasma VIP and SLI concentrations. The effect of bile on integrated plasma VIP and SLI concentrations seems to be dose dependent; the effect of TDC on integrated SLI, too. For the increase of integrated plasma VIP concentrations after TDC no dose-response relation could be established. We conclude that VIP may be a further mediator of bile-induced volume and bicarbonate secretion. The release of plasma SLI indicates that inhibitory mechanisms concomitantly are triggered by i.d. bile and TDC, as already shown during digestion for the intestinal phase of pancreatic secretion
Purcell-induced suppression of superradiance for molecular overlayers on noble atom surfaces
We study the impact of an environment on the electromagnetic responses of a
molecule in the presence of a dielectric medium. By applying the dipole-dipole
coupling between the molecule's and the environment's degrees of freedom, we
can reduce the complex system into its components and predict excitation
lifetimes of single and few molecules attached to a dielectric surface by
knowing the entire quantum-mechanical properties of the molecules, such as
transition energies and dipole moments. The derived theory allows for the
description of superradiance between two molecules depending on the geometric
arrangement between both concerning their separation and orientation with
respect to each other. We analyse the possibility of superradiance between two
molecules bound to a dielectric sphere and determine a change of the relevant
length scale where the usually considered wavelength in free space is replaced
with the binding distance, drastically reducing the length scales at which
collective effects can take place
Spectroscopy on nanoparticles without light
One of the most important tools in modern science is the analysis of
electromagnetic properties via spectroscopy. The various types of spectroscopy
can be classified by the underlying type of interactions between energy and
material. In this paper we demonstrate a new class of spectroscopy based on
Casimir interactions between a solid investigated object and a reference
surface embedded in an environmental liquid medium. Our main example is based
on the measurement of Hamaker constants upon changing the concentration of an
intervening two-component liquid, where we demonstrate a possible
reconstruction algorithm to estimate the frequency-dependent dielectric
function of the investigated particle
Probing atom-surface interactions by diffraction of Bose-Einstein condensates
In this article we analyze the Casimir-Polder interaction of atoms with a
solid grating and an additional repulsive interaction between the atoms and the
grating in the presence of an external laser source. The combined potential
landscape above the solid body is probed locally by diffraction of
Bose-Einstein condensates. Measured diffraction efficiencies reveal information
about the shape of the Casimir-Polder interaction and allow us to discern
between models based on a pairwise-summation (Hamaker) approach and Lifshitz
theory.Comment: 5 pages, 4 figure
Orientational dependence of the van der Waals interactions for finite-sized particles
Van der Waals forces as interactions between neutral and polarisable
particles act at small distances between two objects. Their theoretical origin
lies in the electromagnetic interaction between induced dipole moments caused
by the vacuum fluctuations of the ground-state electromagnetic field. The
resulting theory well describes the experimental situation in the limit of the
point dipole assumption. At smaller distances, where the finite size of the
particles has to be taken into account, this description fails and has to be
corrected by higher orders of the multipole expansion, such as quadrupole
moments and so on. With respect to the complexity of the spatial properties of
the particles this task requires a considerable effort. In order to describe
the van der Waals interaction between such particles, we apply the established
method of a spatially spread out polarisability distribution to approximate the
higher orders of the multipole expansion. We hence construct an effective
theory for effects from anisotropy and finite size on the van der Waals
potential
Monolithic atom interferometry
Atom and, more recently, molecule interferometers are used in fundamental
research and industrial applications. Most atom interferometers rely on
gratings made from laser beams, which can provide high precision but cannot
reach very short wavelengths and require complex laser systems to function.
Contrary to this, simple monolithic interferometers cut from single crystals
offer (sub) nano-meter wavelengths with an extreme level of stability and
robustness. Such devices have been conceived and demonstrated several decades
ago for neutrons and electrons. Here, we propose a monolithic design for a
thermal-beam molecule interferometer based on (quantum) reflection. We show, as
an example, how a reflective, monolithic interferometer (Mach-Zehnder type) can
be realised for a helium beam using Si(111)-H(1x1) surfaces, which have
previously been demonstrated to act as very robust and stable diffractive
mirrors for neutral helium atoms
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