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The kinetic energy distribution of ground state muonic hydrogen atoms µp(1S) is determined from time-of-flight spectra measured at 4, 16, and 64 hPa H2 room-temperature gas. A 0.9 keVcomponent is discovered and attributed to radiationless deexcitation of long-lived µp(2S) atoms in collisions with H2 molecules. The analysis reveals a relative population of about 1 %, and a pressuredependent lifetime (e.g. 30.4 +21.4 −9.7 ns at 64 hPa) of the long-lived µp(2S) population, equivalent to a 2S-quench rate in µp(2S)+H2 collisions of 4.4 +2.1 −1.8 × 10 11 s −1 at liquid hydrogen density.PACS numbers: 36.10. Dr, 34.20.Gj A measurement of the Lamb shift in muonic hydrogen, i.e. the energy difference of 0.2 eV between the 2P -and 2S-states of µ − p atoms [1,2,3], is in progress at the Paul Scherrer Institute (PSI), Switzerland [4]. Vacuum polarization shifts the 2S-levels by 0.2 eV below the 2P -levels; fine and hyperfine splittings of the n = 2 levels are much smaller. The finite size effect is 2 % of the Lamb shift.The µp Lamb shift experiment is expected to give a precise value for the root-mean-square charge radius of the proton [5]. Together with recent advances in H-atom spectroscopy [6,7], this leads to a better determination of the Rydberg constant, and to a test of bound-state quantum electrodynamics on a new level of precision [8].The most important prerequisite for such an experiment, the availability of sufficiently long-lived µp(2S) atoms, has so far not been experimentally established. When muons are stopped in H 2 gas, µp atoms are formed at high n-levels and then deexcite predominantly to the ground state ("muonic cascade"). A fraction ε 2S of a few percent reaches the metastable 2S state whose lifetime is, in absence of collisions, essentially given by the muon lifetime of 2.2 µs.In a gas, there is collisional 2S-quenching, with very different rates depending on the µp kinetic energy being above or below the 2S-2P threshold (≈ 0.3 eV in the lab frame) [9]. Most µp(2S) atoms are formed at energies above this threshold [10], where collisional 2S → 2P Stark transitions (followed by 2P → 1S radiative deexcitation) lead to rather fast 2S-depletion. This is the "short-lived" 2S-component with a predicted lifetime [11] τ short 2S∼ 100 ns/p H2 [hPa]. There is, however, a competition between such Stark transitions and deceleration [9]. A fraction of the µp(2S) atoms should therefore survive the process of slowing down below 0.3 eV, where transitions to the 2P state are energetically forbidden. These µp(2S) atoms form the "long-lived" 2S-component, with a lifetime τ long 2S and a population ε long 2S (per µp atom).The 2S-population ε 2S is well determined from the measured µp X-ray yields [12,13,14]. ε long 2S can be derived from the measured 1S kinetic energy distributions [15] by using calculated elastic and inelastic µp(2S) cross sections [9]. At 16 hPa, for example, ε 2S = (4.40 ± 0.17) % and ε long 2S = (1.16 ± 0.12) %. Calculations of the radiative quenching process during collisions [16,17,18] predicted v...

Increasing heat dissipation density is becoming a limiting factor in air-cooled data centers. The main control objective in data center thermal management is to keep the temperature of all the data processing equipment below a certain threshold and at the same time maximize the energy efficiency of the system. Existing work in this field does not take into account unexpected changes in the workload and neglects the cost of control actions taken by the cooling infrastructure. To address this problem, we derive a thermodynamic model of a data center and propose a novel model-based temperature control strategy that combines air flow control and thermal-aware scheduling. The air flow controller is responsible for the long-term decisions by switching between multiple operating points, whereas the scheduler accounts for short-term fluctuations in the workload that are not predictable. Simulations with synthetic and real workload traces show that we can control the temperatures at the racks in an efficient and stable manner with this approach.

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Para-Ortho transitions in solid hydrogen above the 2-point have been measured by inelastic neutron scattering. From the scattered spectra the widths of the rotational lines caused by the quadrupole-quadrupole interaction between the ortho-molecules are determined. The full width at half intensity is found to be 1.22_+ 0.07 and 0.80+ 0.07 meV for 68 and 27 percent ortho-concentration respectively in good agreement with theoretical values. The phononspectrum of solid hydrogen could be extracted from the neutron scattering data. The specific heat and the Debye-temperature which were calculated from the phononspectrum are in fairly good agreement with experimental values. Moreover the double differential scattering cross section of liquid hydrogen (T= 19.8 ~ was measured at 87 and 21.8 meV incident neutron energy. In the case of 87 meV energy there is a relatively good agreement with a simple free rotator model. At 21.8 meV the binding of the molecules in the liquid influence the spectrum. Therefore a description of the measured spectrum by a convolution of the phononspectrum of the solid and a simple diffusion model was tried. This model is superior to the gas model but discrepancies between model and experiment still remain.

Abstract. We consider the problem of real-time sensing and tracking the location of a moving cart in an indoor environment. To this end, we propose to combine position information obtained from an inertial navigation system (INS) and a short-range wireless reference system that can be embedded into a future"network of things". The data produced by the INS lead to accurate short-term position estimates, but due to the drifts inherent to the system, these estimates perform loosely after some time. To solve this problem, we also generate estimates with a wireless reference system. These radio-based estimates can be used as accurate long-term position estimates because their accuracy improves over time as the channel fading can be averaged out. We use a data fusion algorithm based on Kalman filtering with forward/backward smoothing to optimally combine the short-and long-term position estimates. We have implemented this localization system in a real-time testbed. The measurement results, which we obtained using the proposed method, show considerable improvements in accuracy of the location estimates.

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