Search results for "cooling"
showing 10 items of 470 documents
Entangled states of trapped ions allow measuring the magnetic field gradient produced by a single atomic spin
2012
Using trapped ions in an entangled state we propose detecting a magnetic dipole of a single atom at distance of a few $\mu$m. This requires a measurement of the magnetic field gradient at a level of about 10$^{-13}$ Tesla/$\mu$m. We discuss applications e.g. in determining a wide variation of ionic magnetic moments, for investigating the magnetic substructure of ions with a level structure not accessible for optical cooling and detection,and for studying exotic or rare ions, and molecular ions. The scheme may also be used for measureing spin imbalances of neutral atoms or atomic ensembles trapped by optical dipole forces. As the proposed method relies on techniques well established in ion t…
ADIABATIC COOLING OF IONS IN THE PENNING TRAP
1991
An ion cloud in a Penning trap can be cooled by adiabatic expansion by reducing the trap's magnetic and electric fields. We treat the ion cloud as a classical gas and obtain the relations between the temperature and the trapping fields. This cooling method may be useful in trapping and cooling of antiprotons with the aim of measuring the gravitational accleration of anti-protons and other experiments on heavy ions.
Focus on atom optics and its applications
2010
Atom optics employs the modern techniques of quantum optics and laser cooling to enable applications which often outperform current standard technologies. Atomic matter wave interferometers allow for ultra-precise sensors; metrology and clocks are pushed to an extraordinary accuracy of 17 digits using single atoms. Miniaturization and integration are driven forward for both atomic clocks and atom optical circuits. With the miniaturization of information-storage and -processing devices, the scale of single atoms is approached in solid state devices, where the laws of quantum physics lead to novel, advantageous features and functionalities. An upcoming branch of atom optics is the control of …
Interacting Rubidium and Caesium Atoms
2007
Binary mixtures of ultracold atoms are of great interest in the research field of quantum optics and are studied by several groups aiming at different applications. This paper works with rubidium and caesium, which are simultaneously stored in a magnetic trap. Species-selective microwave cooling is used on the rubidium groundstate hyperfine transition. Caesium is sympathetically cooled via elastic collisions with rubidium. When cooling down the mixture to temperatures below 1 muK, below 4 muK we observe strong losses of caesium. Analysing the dynamics of sympathetic cooling, lower limit for the modulus of the rubidium-caesium triplet s-wave scattering length is estimated.
Anisotropic motion of toluene above and below the glass transition studied by 2H NMR
1995
Abstract 2 H nuclear magnetic resonance spin-lattice relaxation experiments on two selectively deuterated toluene molecules have been performed over a wide temperature range, spanning liquid and glassy states, to examine anisotropic molecular dynamics. In the liquid regime, the relaxation data are analyzed by the model of anisotropic rotational diffusion. A more phenomenological ansatz is used for the whole temperature regime to obtain information about anisotropic reorientation and its temperature dependence. We find that the anisotropy is reduced in the supercooled state and the motion becomes approximately isotropic below 140 K which is interpreted as the onset of cooperative reorientati…
Anomalous diffusion of polymers in supercooled melts near the glass transition
2007
Two coarse-grained models for polymer chains in dense melts near the glass transition are investigated: the bond fluctuation lattice model, where long bonds are energetically favored, is studied by dynamic Monte Carlo simulation, and an off-lattice bead-spring model with Lennard-Jones forces between the beads is treated by Molecular Dynamics. We compare the time-dependence of the mean square displacements of both models, and show that they become very similar on mesoscopic scales (i.e., displacements larger than a bond length). The slowing down of motions near the glass transition is discussed in terms of the mode coupling theory and other concepts.
β-process of supercooled o-terphenyl: a comparison of dielectrical and NMR data guided by mode-coupling theory
1990
Abstract According to predictions of mode-coupling theory of the liquid-glass transition, a Cole-Cole dynamical susceptibility is applied to the β-relaxation of supercooled o -terphenyl as studied by 2 H NMR spin-lattice relaxation and by dielectrical relaxation. A temperature-dependent amplitude (1- f ) is assumed for the β-process which yields a description of the NMR data consistent with the dielectrical data. The plateau value f separating the α- and β-processes in the two-step correlation function reveals a similar temperature dependence as compared to the Debye-Waller factor.
Intercomparing different devices for the investigation of ice nucleating particles using Snomax<sup>®</sup> as test subst…
2015
Abstract. Seven different instruments and measurement methods were used to examine the immersion freezing of bacterial ice nuclei from Snomax® (hereafter Snomax), a product containing ice-active protein complexes from non-viable Pseudomonas syringae bacteria. The experimental conditions were kept as similar as possible for the different measurements. Of the participating instruments, some examined droplets which had been made from suspensions directly, and the others examined droplets activated on previously generated Snomax particles, with particle diameters of mostly a few hundred nanometers and up to a few micrometers in some cases. Data were obtained in the temperature range from −2 to …
Real-time simulation and control system for the continuous casting process
2005
In this paper we present a real-time system which is used to simulate the unsteady-state continuous casting process and to control the secondary cooling water sprays. The aim of the control system is to keep the surface temperature of the slab constant with respect to time in spite of casting speed variations, and in this way minimize the formation of cracks in the final product. The simulator calculates the temperature distribution using a mathematical model based on a heat conduction formula with phase changes. The optimal spray water flow rates for each spray cooling zone will be calculated by minimizing the deviation between the target surface temperature and the calculated actual surfa…
Nonsmooth Penalty Techniques in Control of the Continuous Casting Process
1991
We introduce a mathematical model which is used to simulate the continuous casting process and to control the secondary cooling water sprays. The main object is to minimize the defects in the final products. The problem is formulated as an optimal control problem where the cost function is constructed according to certain metallurgical criteria and constraints. The temperature distribution of the strand is calculated by solving a nonlinear heat equation with free boundaries between solid and liquid phases.