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Search Results: 1 - 10 of 2592 matches for " Ralf Labouvie "
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Negative differential conductivity in an interacting quantum gas
Ralf Labouvie,Bodhaditya Santra,Simon Heun,Sandro Wimberger,Herwig Ott
Physics , 2014, DOI: 10.1103/PhysRevLett.115.050601
Abstract: Negative differential conductivity (NDC) is a widely exploited effect in modern electronic components. Here, a proof-of-principle is given for the observation of NDC in a quantum transport device for neutral atoms employing a multi-mode tunneling junction. The transport of the many-body quantum system is governed by the interplay between the tunnel coupling, the interaction energy and the thermodynamics of intrinsic collisions, which turn the coherent coupling into a hopping process. The resulting current voltage characteristics exhibit NDC, for which we identify a new microscopic physical mechanism. Our study opens new ways for the future implementation and control of complex neutral atom quantum circuits.
Non-equilibrium steady-states in a driven-dissipative superfluid
Ralf Labouvie,Bodhaditya Santra,Simon Heun,Herwig Ott
Physics , 2015,
Abstract: We experimentally study a driven-dissipative Josephson junction array, realized with a weakly interacting Bose Einstein condensate residing in a one-dimensional optical lattice. Engineered losses on one site act as a local dissipative process, while tunneling from the neighboring sites constitutes the driving force. We characterize the emerging steady-states of this atomtronic device. With increasing dissipation strength $\gamma$ the system crosses from a superfluid state, characterized by a coherent Josephson current into the lossy site to a resistive state, characterized by an incoherent hopping transport. For intermediate values of $\gamma$, the system exhibits bistability, where a superfluid and a resistive branch coexist. We also study the relaxation dynamics towards the steady-state, where we find a critical slowing down, indicating the presence of a non-equilibrium phase transition.
Cross-dimensional phase transition from an array of 1D Luttinger liquids to a 3D Bose-Einstein condensate
Andreas Vogler,Ralf Labouvie,Giovanni Barontini,Sebastian Eggert,Vera Guarrera,Herwig Ott
Physics , 2014, DOI: 10.1103/PhysRevLett.113.215301
Abstract: We study the thermodynamic properties of a 2D array of coupled one-dimensional Bose gases. The system is realized with ultracold bosonic atoms loaded in the potential tubes of a two-dimensional optical lattice. For negligible coupling strength, each tube is an independent weakly interacting 1D Bose gas featuring Tomonaga Luttinger liquid behavior. By decreasing the lattice depth, we increase the coupling strength between the 1D gases and allow for the phase transition into a 3D condensate. We extract the phase diagram for such a system and compare our results with theoretical predictions. Due to the high effective mass across the periodic potential and the increased 1D interaction strength, the phase transition is shifted to large positive values of the chemical potential. Our results are prototypical to a variety of low-dimensional systems, where the coupling between the subsystems is realized in a higher spatial dimension such as coupled spin chains in magnetic insulators.
Thermodynamics of Strongly Correlated One-Dimensional Bose Gases
Andreas Vogler,Ralf Labouvie,Felix Stubenrauch,Giovanni Barontini,Vera Guarrera,Herwig Ott
Physics , 2013, DOI: 10.1103/PhysRevA.88.031603
Abstract: We investigate the thermodynamics of one-dimensional Bose gases in the strongly correlated regime. To this end, we prepare ensembles of independent 1D Bose gases in a two-dimensional optical lattice and perform high-resolution in situ imaging of the column-integrated density distribution. Using an inverse Abel transformation we derive e?ective one-dimensional line-density pro?les and compare them to exact theoretical models. The high resolution allows for a direct thermometry of the trapped ensembles. The knowledge about the temperature enables us to extract thermodynamic equations of state such as the phase-space density, the entropy per particle and the local pair correlation function.
Disposi??o e alternativas ao dirigir alcoolizado entre jovens paulistanos
Pinsky, Ilana;Labouvie, Erich;Laranjeira, Ronaldo;
Revista Brasileira de Psiquiatria , 2004, DOI: 10.1590/S1516-44462004000400006
Abstract: the new brazilian traffic code considers drinking and driving as a traffic crime. a health behavior model suggests that much of the young people's risky behavior is not planned and that questions measuring the willingness to drink and drive are useful. in face of the importance of drinking and driving as a national health problem, the objective of the present study was to analyze the behavior willingness among youngsters about to receive their driver's licenses. methods: the study was carried out at the s?o paulo department of traffic (detran-sp) in 1998. data were obtained from a sample of 2,166 youths, 18 to 25 years old, who took the written drivers' license examination. data about, among other things, alcohol consumption, willingness and alternatives to drinking and driving in the following year was examined. results: in general, individuals displayed willingness to both the risky behavior (drunk driving) and to the safe behavior (alternatives as taking a cab or getting a ride). regression analyzes were done by dividing the sample in three groups. several significant differences were found between the groups, suggesting that the attitudes and behaviors went on a direction from safer to riskier from groups 1 to 3. conclusion: findings suggest that prevention efforts preseting a spectrum of alternatives to drunk driving and the enforcement of drink and driving laws would be two useful addenda to the more severe laws created in the 1998 traffic code.
Trends of Abundance of Salton Sea Fish: A Reversible Collapse or a Permanent Condition?  [PDF]
Ralf Riedel
Natural Resources (NR) , 2016, DOI: 10.4236/nr.2016.710045
Abstract: The Salton Sea is a closed-basin, 980 km2 salt lake in the Sonoran Desert of southern California. Three marine species, bairdiella (Bairdiella icistia), orangemouth corvina (Cynoscion xanthulus), and sargo (Anisotremus davidsoni), established from introductions of over 34 species beginning in 1929. During the late 1960s and early 1970s, a hybrid tilapia (Oreochromis mossambicus × O. urolepis hornorum) invaded the Salton Sea and became dominant by number and weight. Recent surveys show a precipitous decline of all four species above starting sometime between 2001 and 2002. Declines were more evident in nearshore than in estuarine habitats. Corvina has probably declined the soonest, followed by Gulf croaker. Tilapia declines were followed by more recent increases in population numbers. The tilapia rebound observed are probably only sustainable if a curb in Salton Sea salinity levels is realized. The marine species will likely need restocking to reach historic levels, if the salinity of the lake is managed at 40 gL1 or below. Restoration alternatives for the Salton Sea must take into consideration estuarine areas as essential fish habitats and fish refuge against high salinities.
Pathophysiology of Hypertrophic Pyloric Stenosis Revisited: The Use of Isotonic Fluid for Preoperative Infusion Therapy Is Supported  [PDF]
Ralf-Bodo Troebs
Open Journal of Pediatrics (OJPed) , 2014, DOI: 10.4236/ojped.2014.43027
Abstract: Background: The aim of this study was to elucidate the preoperative clinical and biochemical profile of infants with IHPS to optimize infusion therapy. Patients and Method: We retrospectively analyzed data from 56 infants who were operated for IHPS. Our study includes growth and laboratory data prior to the initiation of therapy. Results: Median duration of propulsive vomiting was 4 d; the median age was 37 d (18 - 108), and the median body weight was 3840 g (2760 -5900). Metabolic alkalosis (MAlk) with a pH of 7.45 ± 0.06 and an stHCO3- of 28.7 ± 4.5 mmol/l was found. In a subgroup of the infants, negative base excess (BE) was observed. The sodium concentration was normal or reduced (mean/median of 137 mmol/l). There was a strong negative correlation between stHCO3- and K+. The carbon dioxide partial pressure tended to increase (5.72 ± 0.84 kPa). Calculations of osmolality revealed a normal osmolarity. Hypoglycemia did not occur. The creatinine clearance according to the Schwartz formula remained at a normal level (85.3 ± 24.3 ml/min/1.73 m2). Discussion: The presented case series is characterized by a short duration of preoperative vomiting. MAlk can be classified as a chloride deficiency syndrome. It is accompanied by normo- or hyponatremic dehydration with normal osmolality. Partial respiratory compensation occurred. A normal creatinine clearance indicated good glomerular renal function. Conclusion: The presented study supports the use of an isotonic infusion fluid with a low glucose concentration for preoperative infusion therapy.
Solar versus Non-Solar Urine Diversion Dehydration Toilets—Evaluation of Temperatures inside the Vaults of Different UDDT Systems  [PDF]
Constanze Windberg, Ralf Otterpohl
Journal of Environmental Protection (JEP) , 2016, DOI: 10.4236/jep.2016.79109
Abstract: The Urine Diverting Dehydration Toilet (UDDT) is one of a wide range of technologies Ecological Sanitation (Ecosan) offers. A commonly used type is the so called solar UDDT, constructed with inclined vault doors or panels which are usually made from black iron sheets to increase the temperature inside the vaults and therefore would facilitate dehydration and hygienisation. The study aims to give recommendations on the most appropriate system by comparing solar and non-solar UDDT systems. Existing building standards for UDDTs were reviewed, 133 UDDT sites visited and a comparative temperature study of the temperature inside the vaults of different UDDT systems carried out. The temperature study needed to assess if solar UDDTs would actually succeed in raising the temperature inside the vault. Programmed temperature loggers were placed in the vaults of solar and non-solar UDDTs. The review of building standards showed that the system recommended most is the solar UDDT. The field visits identified a number of problems related to the construction of solar UDDTs. The temperature study showed that solar UDDTs do not necessarily increase the temperature inside the vault significantly and therefore are not speeding up dehydration and pathogen destruction. The study hence concludes that before a solar UDDT system is chosen the climatic conditions have to be assessed carefully. The recommended standard design should be a non-solar UDDT system. It is hoped that the study will facilitate a move towards the construction of non-solar UDDTs.
Adaptive Pitch Transposition: Smart Auditory Spectral Shifts in Cochlear Implants  [PDF]
Kevin Struwe, Ralf Salomon
Engineering (ENG) , 2017, DOI: 10.4236/eng.2017.99045
Abstract: Patients with severe hearing loss have the option to get a cochlear implant device to regain their hearing. Yet, the implantation process is not always optimal, which in some cases results in a shallow insertion depth or an accidental insertion into the wrong cochlear duct. As a consequence, the patients' pitch discrimination ability is suboptimal, leading to an even more decreased vowel identification, which is vital for speech recognition. This paper presents a technical approach to solve this problem: the adaptive pitch transposition module modifies the frequency content in a fashion so that the pitch is fixed to an optimal value. To determine this value, a patient-individual best pitch is determined experimentally by evaluating speech recognition at different pitches. This best pitch is subsequently called the comfort pitch. As a result of the considerations a technical implementation is presented in principle. A system comprised of pitch detection, pitch transposition and an arbitrary chosen comfort pitch is described in depth. It has been implemented prototypically in Matlab/Octave and tested with an example audio file. The system?itself is designed as a preprocessing stage preceding cochlear implant processing.
Controlling the dynamics of an open many-body quantum system with localized dissipation
G. Barontini,R. Labouvie,F. Stubenrauch,A. Vogler,V. Guarrera,H. Ott
Physics , 2012, DOI: 10.1103/PhysRevLett.110.035302
Abstract: We experimentally investigate the action of a localized dissipative potential on a macroscopic matter wave, which we implement by shining an electron beam on an atomic Bose-Einstein condensate (BEC). We measure the losses induced by the dissipative potential as a function of the dissipation strength observing a paradoxical behavior when the strength of the dissipation exceeds a critical limit: for an increase of the dissipation rate the number of atoms lost from the BEC becomes lower. We repeat the experiment for different parameters of the electron beam and we compare our results with a simple theoretical model, finding excellent agreement. By monitoring the dynamics induced by the dissipative defect we identify the mechanisms which are responsible for the observed paradoxical behavior. We finally demonstrate the link between our dissipative dynamics and the measurement of the density distribution of the BEC allowing for a generalized definition of the Zeno effect. Due to the high degree of control on every parameter, our system is a promising candidate for the engineering of fully governable open quantum systems.
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