Topological superfluid defects with discrete point group symmetries.

Discrete symmetries are spatially ubiquitous but are often hidden in internal states of systems where they can have especially profound consequences. In this work we create and verify exotic magnetic phases of atomic spinor Bose-Einstein condensates that, despite their continuous character and intrinsic spatial isotropy, exhibit complex discrete polytope symmetries in their topological defects. Using carefully tailored spinor rotations and microwave transitions, we engineer singular line defects whose quantization conditions, exchange statistics, and dynamics are fundamentally determined by these underlying symmetries. We show how filling the vortex line singularities with atoms in a variety of different phases leads to core structures that possess magnetic interfaces with rich combinations of discrete and continuous symmetries. Such defects, with their non-commutative properties, could provide unconventional realizations of quantum information and interferometry.

Decay of a Quantum Knot.

We experimentally study the dynamics of quantum knots in a uniform magnetic field in spin-1 Bose-Einstein condensates. The knot is created in the polar magnetic phase, which rapidly undergoes a transition toward the ferromagnetic phase in the presence of the knot. The magnetic order becomes scrambled as the system evolves, and the knot disappears. Strikingly, over long evolution times, the knot decays into a polar-core spin vortex, which is a member of a class of singular SO(3) vortices. The polar-core spin vortex is stable with an observed lifetime comparable to that of the condensate itself. The structure is similar to that predicted to appear in the evolution of an isolated monopole defect, suggesting a possible universality in the observed topological transition.

Controlled creation of a singular spinor vortex by circumventing the Dirac belt trick.

Persistent topological defects and textures are particularly dramatic consequences of superfluidity. Among the most fascinating examples are the singular vortices arising from the rotational symmetry group SO(3), with surprising topological properties illustrated by Dirac's famous belt trick. Despite considerable interest, controlled preparation and detailed study of vortex lines with complex internal structure in fully three-dimensional spinor systems remains an outstanding experimental challenge. Here, we propose and implement a reproducible and controllable method for creating and detecting a singular SO(3) line vortex from the decay of a non-singular spin texture in a ferromagnetic spin-1 Bose-Einstein condensate. Our experiment explicitly demonstrates the SO(3) character and the unique spinor properties of the defect. Although the vortex is singular, its core fills with atoms in the topologically distinct polar magnetic phase. The resulting stable, coherent topological interface has analogues in systems ranging from condensed matter to cosmology and string theory.

Quantum gases. Observation of isolated monopoles in a quantum field.

Topological defects play important roles throughout nature, appearing in contexts as diverse as cosmology, particle physics, superfluidity, liquid crystals, and metallurgy. Point defects can arise naturally as magnetic monopoles resulting from symmetry breaking in grand unified theories. We devised an experiment to create and detect quantum mechanical analogs of such monopoles in a spin-1 Bose-Einstein condensate. The defects, which were stable on the time scale of our experiments, were identified from spin-resolved images of the condensate density profile that exhibit a characteristic dependence on the choice of quantization axis. Our observations lay the foundation for experimental studies of the dynamics and stability of topological point defects in quantum systems.

Observation of Dirac monopoles in a synthetic magnetic field.

Magnetic monopoles--particles that behave as isolated north or south magnetic poles--have been the subject of speculation since the first detailed observations of magnetism several hundred years ago. Numerous theoretical investigations and hitherto unsuccessful experimental searches have followed Dirac's 1931 development of a theory of monopoles consistent with both quantum mechanics and the gauge invariance of the electromagnetic field. The existence of even a single Dirac magnetic monopole would have far-reaching physical consequences, most famously explaining the quantization of electric charge. Although analogues of magnetic monopoles have been found in exotic spin ices and other systems, there has been no direct experimental observation of Dirac monopoles within a medium described by a quantum field, such as superfluid helium-3 (refs 10-13). Here we demonstrate the controlled creation of Dirac monopoles in the synthetic magnetic field produced by a spinor Bose-Einstein condensate. Monopoles are identified, in both experiments and matching numerical simulations, at the termini of vortex lines within the condensate. By directly imaging such a vortex line, the presence of a monopole may be discerned from the experimental data alone. These real-space images provide conclusive and long-awaited experimental evidence of the existence of Dirac monopoles. Our result provides an unprecedented opportunity to observe and manipulate these quantum mechanical entities in a controlled environment.

Dynamics of a few corotating vortices in Bose-Einstein condensates.

We study the dynamics of small vortex clusters with a few (2-4) corotating vortices in Bose-Einstein condensates by means of experiments, numerical computations, and theoretical analysis. All of these approaches corroborate the counterintuitive presence of a dynamical instability of symmetric vortex configurations. The instability arises as a pitchfork bifurcation at sufficiently large values of the vortex system angular momentum that induces the emergence and stabilization of asymmetric rotating vortex configurations. The latter are quantified in the theoretical model and observed in the experiments. The dynamics is explored both for the integrable two-vortex particle system, where a reduction of the phase space of the system provides valuable insight, as well as for the nonintegrable three- (or more) vortex case, which additionally admits the possibility of chaotic trajectories.

Real-time dynamics of single vortex lines and vortex dipoles in a Bose-Einstein condensate.

Understanding the behavior of quantized vortices is essential to gaining insight into diverse superfluid phenomena, from critical-current densities in superconductors to quantum turbulence in superfluids. We observe the real-time dynamics of quantized vortices in trapped dilute-gas Bose-Einstein condensates by repeatedly imaging the vortex cores. The precession frequency of a single vortex is measured by explicitly observing its time dependence and is found to be in good agreement with theory. We further characterize the dynamics of vortex dipoles in two distinct configurations: (i) an asymmetric configuration, in which the vortex trajectories are dynamic and nontrivial, and (ii) a stable, symmetric configuration, in which the dipole is stationary.

Nonequilibrium dynamics and superfluid ring excitations in binary Bose-Einstein condensates.

We revisit a classic study [D. S. Hall, Phys. Rev. Lett. 81, 1539 (1998)10.1103/PhysRevLett.81.1539] of interpenetrating Bose-Einstein condensates in the hyperfine states |F=1,m{f}=-1 identical with |1 and |F=2,m{f}=+1 identical with |2 of 87Rb and observe striking new nonequilibrium component separation dynamics in the form of oscillating ringlike structures. The process of component separation is not significantly damped, a finding that also contrasts sharply with earlier experimental work, allowing a clean first look at a collective excitation of a binary superfluid. We further demonstrate extraordinary quantitative agreement between theoretical and experimental results using a multicomponent mean-field model with key additional features: the inclusion of atomic losses and the careful characterization of trap potentials (at the level of a fraction of a percent).

Allograft rejection results from a failed attempt by the immune system to protect foreign tissue.

The focus of our research is to understand the immune response to foreign tissue. We believe that a dichotomy exists within the immune response to an allograft such that part of the response is dedicated to the protection of the graft. Nevertheless, in a dominantly graft-aggressive environment, rejection typically ensues. In this article, we describe models that have been set up to test directly the ability of potentially protective aspects of the immune response to prevent allograft rejection. We discuss our data in the context of a growing body of exciting and often controversial literature.

Pregnancy wantedness in adolescents presenting for pregnancy testing.

PURPOSE: To explore and describe dimensions of pregnancy wantedness in adolescents who present for pregnancy testing. DESIGN: Descriptive survey. METHODS: Adolescents presenting for pregnancy testing at a multiservice teen center were invited to participate by completing the Pregnancy Importance Questionnaire while awaiting the results of their pregnancy test. Eighty-nine adolescents responded to questions concerning their desire for pregnancy, knowledge and access to birth control information and supplies, and expectations of how a pregnancy would change their lives. RESULTS: Approximately 7% wanted the pregnancy test to be positive, 60% wanted it to be negative, and 33% were not sure. There was a moderately low (1.97 out of 5) desire for pregnancy, a moderately high (3.11 out of 5) knowledge of and access to birth control, and moderately low (2.08 out of 5) expected changes with a pregnancy. There were no differences in these dimensions by age group (early, middle, and late adolescence). CLINICAL IMPLICATIONS: All clinicians working with adolescents should explore sexual risk-taking and pregnancy prevention measures among these clients. Appropriate counseling and follow-up is necessary for adolescents who present for pregnancy testing, whether the pregnancy test is positive or negative.

Interactions between nurses and patients on ventilators.

BACKGROUND: Although the effectiveness of communication between nurses and ventilated patients has been identified by the American Association of Critical-Care Nurses as an area of concern, there are few reports of research in this area. OBJECTIVES: To examine the interactions between nurses and patients on ventilators and the relationship between characteristics of these nurses and their communication with patients. METHODS: An analytical, cross-sectional, experimental design was used to examine the work experience of 30 nurses with ventilated patients, the perceived level of consciousness of their ventilated patients, and the actions and reactions of nurses in relation to these patients. RESULTS: Significant correlations were found between the nurse's perception of the patient's degree of responsiveness and the number of positive and negative interactions with the patient, and between the length of time the nurse cared for the patient and the number of positive nurse reactions. Interaction patterns are also apparent from the data collected. CONCLUSIONS: Findings suggest that nurses' perceptions of patients' responsiveness and length of time nurses care for patients will influence nurse-patient interactions. Patterns of interaction suggest that nurses spend more time providing patients with information that the nurses consider important, rather than assessing or responding to patients' needs.

Anury in two Cairn terriers.

Congenital anury (taillessness) was observed in 2 Cairn Terriers. Fecal staining of the hind limbs was evident in both dogs. A mating of the affected dogs produced a litter of 2 apparently normal pups. The small litter size may have been attributable to lethal gene combinations similar to those described in mice. The radiographic appearance of the caudal and sacral vertebrae was atypical in both tailless dogs. Results of myelography and electrodiagnostic testing of anal sphincter function were normal in one of the dogs. One of the tailless dogs was euthanatized and was found to lack specific muscles and muscle parts responsible for normal defecation, which resulted in fecal staining of the hind limbs. Pedigree analysis revealed the tailless dogs to be closely related and slightly inbred, suggesting a hereditary etiologic factor for anury.

Smoking cessation among coal miners as predicted by baseline respiratory function and symptoms: a 5-year prospective study.

A prospective analysis was used to test whether respiratory impairment or the presence of respiratory symptoms predicts 5-year cigarette smoking cessation in a sample of 1,118 U.S. white, male, underground coal miners. Miners were examined in 1977 and re-examined in 1982 by NIOSH, and all miners with test abnormalities were so informed by letter. Respiratory impairment was measured by an index of airways obstruction combining the spirometric measures of Forced Vital Capacity (FVC) and Forced Expiratory Volume in 1 sec (FEV1). Bronchitis symptoms were measured by an index that combined chronic cough (3+ months/year) and chronic phlegm (3 + months/year). Among these coal miners, the presence of chronic respiratory symptoms initially was inversely associated with cigarette smoking cessation. Respiratory impairment, however, was positively associated with cigarette smoking cessation but did not reach statistical significance.

Chronic respiratory effects of exposure to diesel emissions in coal mines.

A 5-yr prospective design was employed to test the hypothesis that exposure to diesel emissions leads to chronic respiratory effects among underground coal miners. Changes in respiratory function and development of chronic respiratory symptoms were measured during a 5-yr study period (i.e., 1977 to 1982) in 280 diesel-exposed and 838 control miners from Eastern and Western United States underground coal mines. Spirometry measures of respiratory function included forced expiratory volume in 1 sec (FEV1.0), forced vital capacity (FVC), and forced expiratory flow rate at 50% of FVC (FEF50). Chronic respiratory symptom measures, which included chronic cough, chronic phlegm, and breathlessness, were obtained by questionnaires, as were smoking status and occupational history. Based upon these data, the pattern of evidence did not support the hypothesis either in an age-adjusted comparison of diesel vs. nondiesel miners or in an internal analysis by cumulative years of diesel exposure.

Behavioral factors and denture status.

The experiences and impressions for most of the 64 patients who entered the project in 1968 reveal that the opportunity to obtain new dentures, prepared according to the best available technology by highly skilled dentists and dental laboratory technicians, has had an identifiable impact on each of the several behavioral variables for which changes were predicted before the study began. There has been general improvement in self-image, confidence, and relaxation, and these changes often were associated with perceived improvement in fit of dentures, ability to eat, ability to talk, and general health. Although some patients experienced serious health problems during the 6 year study period, neither were these attributed to nor did they appear associated in any way with denture status. The patient population, in general, was very cooperative. Fifty-three patients stayed with the study for 6 years. Most kept their appointments and followed the instructions and advice of their dentists on all matters but one--that of removing their dentures at night. In explaining why they did not remove their dentures at night, most of the patients gave evidence of a high degree of sexual symbolism associated with teeth and denture status.