Mechanics of cooling liquids by forced evaporation in bubbles

Injecting a non-dissolvable gas into a saturated liquid results in sub-cooling of the liquid due to forced evaporation into the bubble. Previous studies assumed the rate of evaporation of liquid into the bubble to be independent of the degree of sub-cooling. In our study we quantify the bubble growth by direct observation using high speed imaging and prove that this hypothesis is not true. A phenomenological model of the bubble growth as a function of the degree of sub-cooling is developed and we find excellent agreement between the measurements and theory. This bubble cooling process is employed in cooling a liquid. By identification of all heat flows, we can well describe the cool down curve using bubble cooling. Bubble cooling provides an alternative cooling method for liquids without the use of complicated cooling techniques

Collisional effects in the formation of cold guided beams of polar molecules

High fluxes of cold polar molecules are efficiently produced by electric guiding and velocity filtering. Here, we investigate different aspects of the beam formation. Variations of the source parameters such as density and temperature result in characteristic changes in the guided beam. These are observed in the velocity distribution of the guided molecules as well as in the dependence of the signal of guided molecules on the trapping electric field. A model taking into account velocity-dependent collisional losses of cold molecules in the region close to the nozzle accurately reproduces this behavior. This clarifies an open question on the parameter dependence of the detected signal and gives a more detailed understanding of the velocity filtering and guiding process

Internal-state thermometry by depletion spectroscopy in a cold guided beam of formaldehyde

We present measurements of the internal state distribution of electrostatically guided formaldehyde. Upon excitation with continuous tunable ultraviolet laser light the molecules dissociate, leading to a decrease in the molecular flux. The population of individual guided states is measured by addressing transitions originating from them. The measured populations of selected states show good agreement with theoretical calculations for different temperatures of the molecule source. The purity of the guided beam as deduced from the entropy of the guided sample using a source temperature of 150K corresponds to that of a thermal ensemble with a temperature of about 30 K

Trajectories of institutional design in policy networks

This article focuses on the strategies and processes of institutional design. It starts by recognizing that politicians often try to change institutional structures of networks and therefore more theoretical and empirical attention for these strategies is needed. First, t

Kapitein in de Storm? : Een institutionele analyse van de rol van het Productschap Vis in een veranderend zeevisserijnetwerk

De positie van het Productschap Vis is in de afgelopen jaren sterk onder druk komen te staan. Deze positiewijziging is terug te voeren op veranderingen in de institutionele structuur van het netwerk. Deze wijzigt onder invloed van netwerkexterne en –interne ontwikkelingen en dwingt het schap tot een andere rolinvulling

Trajectories of institutional design in policy networks. European interventions in the Dutch fisheries network as an example.

There are important reasons to look at the phenomenon of institutional design more closely both theoretically and empirically. We do that in this paper by first exploring the phenomenon theoretically. We build on network theory to work out a conceptual scheme with which we can analyse interventions in the institutional characteristics of networks. With this conceptual scheme we analyse the institutional design interventions of the European Union in the national fishery networks. In this case we trace the influence of these interventions on the Dutch fishery network between 1990 and 2000. For that we make a detailed analysis of the changes in r

Cold guided beams of water isotopologs

Electrostatic velocity filtering and guiding is an established technique to produce high fluxes of cold polar molecules. In this paper we clarify different aspects of this technique by comparing experiments to detailed calculations. In the experiment, we produce cold guided beams of the three water isotopologs H2O, D2O and HDO. Their different rotational constants and orientations of electric dipole moments lead to remarkably different Stark shift properties, despite the molecules being very similar in a chemical sense. Therefore, the signals of the guided water isotopologs differ on an absolute scale and also exhibit characteristic electrode voltage dependencies. We find excellent agreement between the relative guided fractions and voltage dependencies of the investigated isotopologs and predictions made by our theoretical model of electrostatic velocity filtering.Comment: 14 pages, 13 figures; small changes to the text, updated reference

Managing knowledge in policy networks. Organising joint fact-finding in the Scheldt Estuary.

In this paper we analyse the role of knowledge management in the policy process about the Development Plan 2010 for the Scheldt Estuary (a Dutch-Flemish river basin). The conflicts of interests around this package of measures are sharp. Therefore, knowledge is often strategically used in order to defend stakeholders’ own preferences. The project organisation (ProSes) that prepares the Development Plan organised a joint fact-finding process in order to reach ‘shared knowledge’. In this paper we evaluate this process. Especially the relations between the joint fact-finding process and the traditional democratic decision-making process and the separate organisations, which form part of the policy network, seem to be problematic. We formulate some conclusions about the possibilities and limitations of knowledge management within complex policy processes

Electrostatic extraction of cold molecules from a cryogenic reservoir

We present a method which delivers a continuous, high-density beam of slow and internally cold polar molecules. In our source, warm molecules are first cooled by collisions with a cryogenic helium buffer gas. Cold molecules are then extracted by means of an electrostatic quadrupole guide. For ND$_3$ the source produces fluxes up to $(7 \pm ^{7}_{4}) \times 10^{10}$ molecules/s with peak densities up to $(1.0 \pm ^{1.0}_{0.6}) \times 10^9$ molecules/cm$^3$. For H$_2$CO the population of rovibrational states is monitored by depletion spectroscopy, resulting in single-state populations up to $(82 \pm 10)$.Comment: 4 pages, 4 figures, changes to the text, updated figures and reference

Velocity-selected molecular pulses produced by an electric guide

Electrostatic velocity filtering is a technique for the production of continuous guided beams of slow polar molecules from a thermal gas. We extended this technique to produce pulses of slow molecules with a narrow velocity distribution around a tunable velocity. The pulses are generated by sequentially switching the voltages on adjacent segments of an electric quadrupole guide synchronously with the molecules propagating at the desired velocity. This technique is demonstrated for deuterated ammonia (ND$_{3}$), delivering pulses with a velocity in the range of $20-100\,\rm{m/s}$ and a relative velocity spread of $(16\pm 2)\,$ at FWHM. At velocities around $60\,\rm{m/s}$, the pulses contain up to $10^6$ molecules each. The data are well reproduced by Monte-Carlo simulations, which provide useful insight into the mechanisms of velocity selection.Comment: 8 pages, 6 figure