Detection of spatial correlations in an ultracold gas of fermions

Spatial correlations are observed in an ultracold gas of fermionic atoms close to a Feshbach resonance. The correlations are detected by inducing spin-changing rf transitions between pairs of atoms. We observe the process in the strongly interacting regime for attractive as well as for repulsive atom-atom interactions and both in the regime of high and low quantum degeneracy. The observations are compared with a two-particle model that provides theoretical predictions for the measured rf transition rates.

Lifetime of molecule-atom mixtures near a Feshbach resonance in 40K

We report a dramatic magnetic-field dependence in the lifetime of trapped, ultracold diatomic molecules created through an s-wave Feshbach resonance between fermionic atoms. The molecule lifetime increases from less than 1 ms away from the Feshbach resonance to greater than 100 ms near resonance. We also have measured the trapped atom lifetime as a function of magnetic field near the Feshbach resonance; we find that the atom loss is more pronounced on the side of the resonance containing the molecular bound state.

Observation of resonance condensation of fermionic atom pairs

We have observed condensation of fermionic atom pairs in the BCS-BEC crossover regime. A trapped gas of fermionic 40K atoms is evaporatively cooled to quantum degeneracy and then a magnetic-field Feshbach resonance is used to control the atom-atom interactions. The location of this resonance is precisely determined from low-density measurements of molecule dissociation. In order to search for condensation on either side of the resonance, we introduce a technique that pairwise projects fermionic atoms onto molecules; this enables us to measure the momentum distribution of fermionic atom pairs. The transition to condensation of fermionic atom pairs is mapped out as a function of the initial atom gas temperature T compared to the Fermi temperature T(F) for magnetic-field detunings on both the BCS and BEC sides of the resonance.

The histones H2A/H2B and H3/H4 are imported into the yeast nucleus by different mechanisms

Proteins are imported from the cytoplasm into the nucleus by importin beta-related transport receptors. The yeast Saccharomyces cerevisiae contains ten of these importins, but only two of them are essential. After transfer through the nuclear pore, importins release their cargo upon binding to the Ran GTPase, the key regulator of nuclear transport. We investigated the import of the core histones in yeast and found that four importins are involved. The essential Pse1p and the nonessential importins Kap114p, Kap104p, and Yrb4p/Kap123p specifically bind to histones H2A and H2B. Release of H2 histones from importins requires Ran-GTP and DNA simultaneously suggesting a function of the importins in intranuclear targeting. H3 and H4 associate mainly with Pse1p and the dissociation requires Ran but not DNA, which points to a different import mechanism. Import of green fluorescent protein fusions to H2A and H2B requires primarily Pse1p and Kap114p, whereas Yrb4p plays an auxiliary role. Pse1p is predominantly necessary for nuclear uptake of H3 and H4, while Kap104p and Yrb4p also support import. We conclude from our in vivo and in vitro experiments that import of the essential histones is mediated mainly by the essential importin Pse1p, while the non-essential Kap114p functions in a parallel import pathway for H2A and H2B.

Emergence of a molecular Bose–Einstein condensate from a Fermi gas

The realization of superfluidity in a dilute gas of fermionic atoms, analogous to superconductivity in metals, represents a long-standing goal of ultracold gas research. In such a fermionic superfluid, it should be possible to adjust the interaction strength and tune the system continuously between two limits: a Bardeen-Cooper-Schrieffer (BCS)-type superfluid (involving correlated atom pairs in momentum space) and a Bose-Einstein condensate (BEC), in which spatially local pairs of atoms are bound together. This crossover between BCS-type superfluidity and the BEC limit has long been of theoretical interest, motivated in part by the discovery of high-temperature superconductors. In atomic Fermi gas experiments superfluidity has not yet been demonstrated; however, long-lived molecules consisting of locally paired fermions have been reversibly created. Here we report the direct observation of a molecular Bose-Einstein condensate created solely by adjusting the interaction strength in an ultracold Fermi gas of atoms. This state of matter represents one extreme of the predicted BCS-BEC continuum.

BOLD effects in different areas of the cerebral cortex during painful mechanical stimulation

The contribution of four cortical areas (S1, S2, insular cortex and gyrus cinguli) to pain processing was assessed by functional magnetic resonance imaging (fMRI). Phasic (mechanical impact) and tonic stimuli (squeezing) were applied to the back of a finger, both at two different strengths. Stimuli were adjusted to inflict weak and strong pain sensations. It had been shown before that stronger noxious mechanical stimuli induce a weaker input from myelinated mechanoreceptors, but a more vigorous input from nociceptive primary afferents, and vice versa. Sizes of activation clusters and percent increase of the blood oxygenation level dependent (BOLD) signal during activation were compared in the areas of interest. Phasic stimulus patterns were more closely reflected in the time course of the MR signal in S1, S2 and the cingulate than tonic patterns, since the tonic stimuli tended to induce slow MR signal increase also during the resting periods which is in parallel to the persisting character of the tonic pain sensations. In S1 only the contralateral side was activated in most cases, and the more painful stimuli did not induce greater BOLD responses compared to the less painful stimuli in this area. Paradoxically, more painful stimuli produced smaller activation clusters in S1, both in tonic and phasic stimulus trials. In contralateral S2 more painful phasic stimuli induced significantly stronger BOLD responses than the weaker stimuli. The responses to tonic stimuli did not differentiate painfulness and were significantly smaller than the phasic. Activation clusters in this area were also smaller for tonic stimuli. In the gyrus cinguli more painful phasic stimuli induced stronger BOLD responses, but no difference was seen between tonic stimulation of different strength. Though the insular cortex was often bilaterally activated, no significant differences between stimulus quality or intensity were found. Our results provide evidence for a contribution of the S2 projection area and of the cingulate cortex to the processing of the intensity dimension of phasic mechanical pain. Such evidence was not found for the S1 area, which probably receives dominant input from non-nociceptive mechanoreceptors.

Controlled collisions for multi-particle entanglement of optically trapped atoms

Entanglement lies at the heart of quantum mechanics, and in recent years has been identified as an essential resource for quantum information processing and computation. The experimentally challenging production of highly entangled multi-particle states is therefore important for investigating both fundamental physics and practical applications. Here we report the creation of highly entangled states of neutral atoms trapped in the periodic potential of an optical lattice. Controlled collisions between individual neighbouring atoms are used to realize an array of quantum gates, with massively parallel operation. We observe a coherent entangling-disentangling evolution in the many-body system, depending on the phase shift acquired during the collision between neighbouring atoms. Such dynamics are indicative of highly entangled many-body states; moreover, these are formed in a single operational step, independent of the size of the system.

Coherent cold collisions with neutral atoms in optical lattices

By loading a Bose-Einstein condensate into a three-dimensional optical lattice potential, we have been able to demonstrate several fundamental aspects of coherent cold collisions between neutral atoms. We show experimentally how such collisions lead to a well-defined phase shift in the corresponding many-body wave function. The experimental realization of such interactions can be fundamental for the simulation of complex condensed-matter-physics Hamiltonians, for the creation of large-scale entanglement and for the realization of quantum gates with neutral atoms.

Coherent transport of neutral atoms in spin-dependent optical lattice potentials

We demonstrate the controlled coherent transport and splitting of atomic wave packets in spin-dependent optical lattice potentials. Such experiments open intriguing possibilities for quantum state engineering of many body states. After first preparing localized atomic wave functions in an optical lattice through a Mott insulating phase, we place each atom in a superposition of two internal spin states. Then state selective optical potentials are used to split the wave function of a single atom and transport the corresponding wave packets in two opposite directions. Coherence between the wave packets of an atom delocalized over up to seven lattice sites is demonstrated.

Collapse and revival of the matter wave field of a Bose-Einstein condensate

A Bose-Einstein condensate represents the most 'classical' form of a matter wave, just as an optical laser emits the most classical form of an electromagnetic wave. Nevertheless, the matter wave field has a quantized structure owing to the granularity of the discrete underlying atoms. Although such a field is usually assumed to be intrinsically stable (apart from incoherent loss processes), this is no longer true when the condensate is in a coherent superposition of different atom number states. For example, in a Bose-Einstein condensate confined by a three-dimensional optical lattice, each potential well can be prepared in a coherent superposition of different atom number states, with constant relative phases between neighbouring lattice sites. It is then natural to ask how the individual matter wave fields and their relative phases evolve. Here we use such a set-up to investigate these questions experimentally, observing that the matter wave field of the Bose-Einstein condensate undergoes a periodic series of collapses and revivals; this behaviour is directly demonstrated in the dynamical evolution of the multiple matter wave interference pattern. We attribute the oscillations to the quantized structure of the matter wave field and the collisions between individual atoms.

Quantum phase transition from a superfluid to a Mott insulator in a gas of ultracold atoms

For a system at a temperature of absolute zero, all thermal fluctuations are frozen out, while quantum fluctuations prevail. These microscopic quantum fluctuations can induce a macroscopic phase transition in the ground state of a many-body system when the relative strength of two competing energy terms is varied across a critical value. Here we observe such a quantum phase transition in a Bose-Einstein condensate with repulsive interactions, held in a three-dimensional optical lattice potential. As the potential depth of the lattice is increased, a transition is observed from a superfluid to a Mott insulator phase. In the superfluid phase, each atom is spread out over the entire lattice, with long-range phase coherence. But in the insulating phase, exact numbers of atoms are localized at individual lattice sites, with no phase coherence across the lattice; this phase is characterized by a gap in the excitation spectrum. We can induce reversible changes between the two ground states of the system.

[Quality assurance of data collection and data processing in epidemiologic study data]

Quality assurance of the data generating processes in epidemiologic studies is a prerequisite for the internal validity of study results. This paper presents practical aspects of such a quality assurance system pertaining to the planning, data gathering, data entry and data processing phase of a study. It is concerned with data obtained in the framework of a project rather than with data accumulating continuously in private practices, research institutes or veterinary faculties. During the planning phase of a project, standard operating protocols should be developed that assure a reliable performance of observation, coding and data entry. The data base structure, consisting of tables, input validation rules and queries, should be predefined and well documented. A data safety concept will provide the necessary integrity, physical safety and availability of the data. The paper presents technical solutions to common data processing problems with emphasis on re-coding and relational data base facilities (Microsoft-ACCESS) using a hypothetical study on risk factors for mastitis.

Exploring phase coherence in a 2D lattice of Bose-Einstein condensates

Bose-Einstein condensates of rubidium atoms are stored in a two-dimensional periodic dipole force potential, formed by a pair of standing wave laser fields. The resulting potential consists of a lattice of tightly confining tubes, each filled with a 1D quantum gas. Tunnel coupling between neighboring tubes is controlled by the intensity of the laser fields. By observing the interference pattern of atoms released from more than 3000 individual lattice tubes, the phase coherence of the coupled quantum gases is studied. The lifetime of the condensate in the lattice and the dependence of the interference pattern on the lattice configuration are investigated.

A survival analysis of trypanosomosis diagnostic-test performance under natural infection challenge

Little is known about the time-to-first detection and the time difference (TD) between first parasitological and first serological diagnosis of Trypanosoma spp. infections under natural infection challenge in cattle. The objective of our study was to estimate these measures of "longitudinal aspects" of diagnostic performance and to investigate potential biological factors. Emphasis was on diagnosis at the genus level (Trypanosoma spp.). Twelve N'Dama, 12 Gobra zebu and 12N'DamaxGobra (F1) crossbred cattle (all animals non-infected at the start of the experiment, six male and six female animals in each cohort) were exposed to natural high tsetse challenge in the Niamina East area in The Gambia [Acta Trop. 71 (1998) 57]. The animals were investigated parasitologically (detection of trypanosomes by buffy-coat technique), serologically (detection of T. brucei, T. congolense and T. vivax antigen by enzyme-linked immunosorbent assay (ELISA)) and clinically (packed-cell volume, PCV) over a period of 180 days. The time-to-first detection of trypanosomes, trypanosomal antigen (cut-off as suggested by test supplier) and drop in PCV (subject-based cut-off values) were recorded as outcomes of interest. Thus, incidence was both parasitologically (I(p)), serologically (I(s)) and clinically (I(c)). Recurrent events were not considered. The TD between first parasitological and first serological detection was established as I(s) time minus I(p) time. The effect of breed and sex on the time-to-first detection and on TD was investigated using Cox (proportional hazard) regression and ANOVA, respectively. We found that time-to-first parasitological detection of trypanosomosis in N'Dama animals was significantly longer than in the two other breeds (Cox regression, P=0.002). A similar but less-strong (P=0.063) effect of breed on time-to-first detection of trypanosomal antigen was found, whereas no breed effect was observed for clinical detection (P=0.432). Sex had no effect in all detection systems. The TD varied between -56 and 115 (mean 28). Marked differences among breeds and between sexes were not observed (ANOVA, P=0.8). We suggest that incidence studies are more suitable for detecting risk factors for animal trypanosomosis than prevalence-based (cross-sectional) studies because the latter often result in misinterpretation of factors that increase the survival time with infection as risk factors.

Adrenalectomy regulates apoptotic-associated genes in rat hippocampus

Morphological studies of granular neurons of the hippocampus have shown that adrenalectomy (ADX) induces the cell death of granular neurons, an effect prevented by corticosterone replacement. We addressed the hypothesis that corticosterone regulates the expression of the apoptotic bcl-2 gene family. Five days after adrenalectomy, we observed morphological changes related to hippocampal granule cell apoptosis that was accompanied by terminal dUTP nick and labeling (TUNEL) labeling in nuclei located in the hilus region. Corticosterone replacement prevented the cell death induced by ADX. Using RT-PCR we found a reduction in mRNA levels of the antiapoptotic gene bcl-2 in whole hippocampus, an effect which was prevented by corticosterone administration to ADX rats. However, Bcl-2 protein levels were not altered by this treatment. We did not observe modifications in the level of bcl-X(L) mRNA however, we did find a 40% reduction in Bcl-X(L) protein levels, an effect not reversed by corticosterone. In contrast, we found a reduction in the mRNA of the antiapoptotic gene bax and Bax levels after ADX; both effects were prevented by corticosterone. The reduction in proapoptotic bax and in antiapoptotic bcl-2 mRNA levels in the whole hippocampus, suggests that local variations in these molecules could account for both neuronal viability of the CA1-CA3 and granular cell death detected by morphological means and observed after ADX.

Optics with an atom laser beam

We report on the atom optical manipulation of an atom laser beam. Reflection, focusing, and its storage in a resonator are demonstrated. Precise and versatile mechanical control over an atom laser beam propagating in an inhomogeneous magnetic field is achieved by optically inducing spin flips between atomic ground states with different magnetic moment. The magnetic force acting on the atoms can thereby be effectively switched on and off. The surface of the atom optical element is determined by the resonance condition for the spin flip in the inhomogeneous magnetic field. More than 98% of the incident atom laser beam is reflected specularly.

The nuclear export receptor Xpo1p forms distinct complexes with NES transport substrates and the yeast Ran binding protein 1 (Yrb1p)

Xpo1p (Crm1p) is the nuclear export receptor for proteins containing a leucine-rich nuclear export signal (NES). Xpo1p, the NES-containing protein, and GTP-bound Ran form a complex in the nucleus that translocates across the nuclear pore. We have identified Yrb1p as the major Xpo1p-binding protein in Saccharomyces cerevisiae extracts in the presence of GTP-bound Gsp1p (yeast Ran). Yrb1p is cytoplasmic at steady-state but shuttles continuously between the cytoplasm and the nucleus. Nuclear import of Yrb1p is mediated by two separate nuclear targeting signals. Export from the nucleus requires Xpo1p, but Yrb1p does not contain a leucine-rich NES. Instead, the interaction of Yrb1p with Xpo1p is mediated by Gsp1p-GTP. This novel type of export complex requires the acidic C-terminus of Gsp1p, which is dispensable for the binding to importin beta-like transport receptors. A similar complex with Xpo1p and Gsp1p-GTP can be formed by Yrb2p, a relative of Yrb1p predominantly located in the nucleus. Yrb1p also functions as a disassembly factor for NES/Xpo1p/Gsp1p-GTP complexes by displacing the NES protein from Xpo1p/Gsp1p. This Yrb1p/Xpo1p/Gsp1p complex is then completely dissociated after GTP hydrolysis catalyzed by the cytoplasmic GTPase activating protein Rna1p.

Increased seizures after discontinuing carbamazepine: results from the gabapentin monotherapy trial

Studies in patients with epilepsy undergoing telemetry evaluation for surgery have suggested that discontinuation of carbamazepine (CBZ) is associated with increased seizures. The period of observation in that setting, however, was limited to a few days. The authors reviewed the occurrence of seizures in patients with epilepsy who had all their antiepileptic medications discontinued during an 8-week period, converted to gabapentin monotherapy, and observed for 26 weeks as part of the gabapentin trial #945-082. Two hundred and seventy-five patients were enrolled. Kaplan-Meier estimates of time to exit for all patients showed that 18% of patients previously treated with CBZ completed the study as compared with 30% of the patients receiving other antiepileptic medications. Increase in the frequency of seizures was maximal in the 2 weeks following CBZ discontinuation. Seizures increased both in frequency and severity but no new seizure types were observed. The findings in this study show that removal of CBZ is associated with increased frequency of seizures in patients with a previous history of epilepsy with incompletely controlled seizures. The period of maximal increase was the first 2 weeks after CBZ discontinuation.

Placebo-controlled study of gabapentin treatment of panic disorder

A randomized, double-blind, placebo-controlled, parallel-group study was conducted to evaluate the efficacy and safety of gabapentin in relieving the symptoms of panic disorder. One hundred three patients were randomly assigned to receive double-blind treatment with either gabapentin (dosed flexibly between 600 and 3,600 mg/day) or placebo for 8 weeks. No overall drug/placebo difference was observed in scores on the Panic and Agoraphobia Scale (PAS) (p = 0.606). A post hoc analysis was used to evaluate the more severely ill patients as defined by the primary outcome measure (PAS score > or = 20). In this population, the gabapentin-treated patients showed significant improvement in the PAS change score (p = 0.04). In patients with a PAS score of 20 or greater, women showed a greater response than men regardless of treatment. Adverse events were consistent with the known side effect profile of gabapentin and included somnolence, headache, and dizziness. One patient experienced a serious adverse event during the study. No deaths were reported. The results of this study suggest that gabapentin may have anxiolytic effects in more severely ill patients with panic disorder.

Application of diagnostic tests in veterinary epidemiologic studies

Important applications of diagnostic tests in non-clinical areas of veterinary medicine include surveillance, monitoring or screening for disease, prevalence estimation, and risk-factor studies. In this review, we address the processing and analysis of diagnostic data with special emphasis on serological data from enzyme-linked immunosorbent assays (ELISAs). We describe methods that are used to adjust for misclassification (imperfect sensitivity and specificity) in the different applications of diagnostic tests. These methods often have limitations attributable to the uncertainty of sensitivity and specificity estimates. We review descriptive and analytical statistical methods that allow adequate presentation of non-clinical diagnostic data.

Epidemiologic issues in the validation of veterinary diagnostic tests

In this review, we critically discuss the objectives, methods and limitations of different approaches for the validation of diagnostic tests. We show (based on published data and our own experiences) that estimates for the diagnostic sensitivity and specificity may vary among populations and/or subpopulations of animals, conditional on the distribution of influential covariates. Additional variability in those parameter estimates may be attributable to the sampling strategy. The uncertainty about diagnostic parameters is of concern for the decision-maker in the context of clinical diagnosis or quantitative risk assessment as well as for the epidemiologist who uses test data for prevalence estimation or risk-factor studies. Examples for the calculation of diagnostic parameters are presented together with bias-avoidance strategies. We suggest guidelines for an epidemiologic approach to test validation of veterinary diagnostic tests.

Principles and practical application of the receiver-operating characteristic analysis for diagnostic tests

We review the principles and practical application of receiver-operating characteristic (ROC) analysis for diagnostic tests. ROC analysis can be used for diagnostic tests with outcomes measured on ordinal, interval or ratio scales. The dependence of the diagnostic sensitivity and specificity on the selected cut-off value must be considered for a full test evaluation and for test comparison. All possible combinations of sensitivity and specificity that can be achieved by changing the test's cut-off value can be summarised using a single parameter; the area under the ROC curve. The ROC technique can also be used to optimise cut-off values with regard to a given prevalence in the target population and cost ratio of false-positive and false-negative results. However, plots of optimisation parameters against the selected cut-off value provide a more-direct method for cut-off selection. Candidates for such optimisation parameters are linear combinations of sensitivity and specificity (with weights selected to reflect the decision-making situation), odds ratio, chance-corrected measures of association (e. g. kappa) and likelihood ratios. We discuss some recent developments in ROC analysis, including meta-analysis of diagnostic tests, correlated ROC curves (paired-sample design) and chance- and prevalence-corrected ROC curves.

Helicobacter pylori infection in wild-type and cytokine-deficient C57BL/6 and BALB/c mouse mutants

Helicobacter pylori causes gastroduodenal ulcer disease in humans. T lymphocytes and their cytokines are thought to play a substantial role in the control of H. pylori infection. To determine the importance of T helper (Th) cytokines and background genes we investigated the natural course of H. pylori infection in BALB/c and C57BL/6 wild-type or mutant mice deficient for either interleukin (IL)-4 or interferon (IFN)-gamma. H. pylori SPM 326 persisted for at least six months in C57BL/6 but was cleared by BALB/c wild-type mice nine weeks postinfection. H. pylori was recovered more frequently from IFN-gamma(-/-) BALB/c and IFN-gamma( -/-) C57BL/6 mice than from the respective wild-type animals. In contrast, IL-4 deficiency had no detectable effect on H. pylori recovery rates from either strain of mice. Our data suggest a protective role of IFN-gamma by mediating inflammation in murine H. pylori infection. In addition, our data emphasize that background genes which differ between BALB/c and C57BL/6 mice regulate the clearance of H. pylori.

Impact of tsetse control on the age-specific prevalence of trypanosomosis in village cattle in southeast Uganda

The prevalence of trypanosomosis, mean packed cell volume and anti-trypanosomal antibody levels in village cattle of different age groups (< 0.5 year, 0.5-2 years, > 2-5 years and > 5 years) in the areas with tsetse control were compared with those of corresponding age groups in areas without tsetse control in Tororo, southeast Uganda. The prevalence of trypanosomosis in cattle in the age groups of 0.5-2 years, > 2-5 years and > 5 years in the areas with tsetse control was significantly lower than in cattle in similar age groups in the areas without tsetse control (p < 0.5). Trypanosoma vivax was the most predominant Trypanosoma species in the areas with tsetse control, while T. congolense was the most predominant species in the areas without tsetse control. The mean Trypanosoma antibody levels in cattle in the age groups < 0.5 year, 0.5-2 years and > 2-5 years in the areas with tsetse control were significantly lower than those of the similar age groups in the areas without tsetse control (p < 0.5). The mean PCV values for cattle in the age groups 0.5-2 years, > 2-5 years and > 5 years from the areas with tsetse control were significantly higher than those of the similar age groups in the areas without tsetse control. Tsetse control appeared to have a considerable impact on the prevalence of trypanosomosis, distribution of Trypanosoma species, specific antibody levels and the packed cell volume of cattle in the different age groups.

[Planning of epidemiologic studies using the example of parasitic diseases]

Epidemiology is concerned with the study of diseases and risk factors for diseases in populations. Livestock related studies require that the term disease is extended to cover all conditions that directly or indirectly may affect the economic, social and ecological value of livestock or constitute a public health risk. The objectives of epidemiologic studies range from the quantification of traits, e.g., prevalence of a disease in a population (descriptive approach), to the analysis of correlation between diseases and putative risk factors (analytic approach). The type of epidemiologic study must be selected accordingly. In this paper we present the most important types of epidemiologic studies using example data. Our aim is to give an orientation for the planning of epidemiologic studies.