Precision Measurements of the

Measurement of the ^{138}Ba^{+} ^{2}S_{1/2}-^{2}D_{5/2} clock transition frequency and D_{5/2} Landé g_{J} factor are reported. The clock transition frequency ν_{Ba^{+}}=170126432449333.31±(0.39)_{stat}±(0.29)_{sys} Hz, is obtained with accuracy limited by the frequency calibration of the maser used as a reference oscillator. The Landé g_{J} factor for the ^{2}D_{5/2} level is determined to be g_{D}=1.20036739(24), which is a 30-fold improvement on previous measurements. The g-factor measurements are corrected for an ac-magnetic field from trap-drive-induced currents in the electrodes, and data taken over a range of magnetic fields underscores the importance of accounting for this systematic.

Hyperfine Averaging by Dynamic Decoupling in a Multi-Ion Lutetium Clock.

We propose and experimentally demonstrate a scheme that realizes hyperfine averaging during a Ramsey interrogation of a clock transition. The method eliminates the need to average over multiple optical transitions, reduces the sensitivity of the clock to its environment, and reduces inhomogeneous broadening in a multi-ion clock. The method is compatible with autobalanced Ramsey spectroscopy, which facilitates the elimination of residual shifts due to imperfect implementation and ac stark shifts from the optical probe. We demonstrate the scheme using correlation spectroscopy of the ^{1}S_{0}↔^{3}D_{1} clock transition in a three-ion Lu^{+} clock. From the demonstration we are able to provide a measurement of the ^{3}D_{1} quadrupole moment, Θ(^{3}D_{1})=0.634(9)ea_{0}^{2}.

Suppressing Inhomogeneous Broadening in a Lutetium Multi-ion Optical Clock.

We demonstrate precision measurement and control of inhomogeneous broadening in a multi-ion clock consisting of three ^{176}Lu^{+} ions. Microwave spectroscopy between hyperfine states in the ^{3}D_{1} level is used to characterize differential systematic shifts between ions, most notably those associated with the electric quadrupole moment. By appropriate alignment of the magnetic field, we demonstrate suppression of these effects to the ∼10^{-17} level relative to the ^{1}S_{0}↔^{3}D_{1} optical transition frequency. Correlation spectroscopy on the optical transition demonstrates the feasibility of a 10-s Ramsey interrogation in the three ion configuration with a corresponding projection noise limited stability of σ(τ)=8.2×10^{-17}/sqrt[τ].

Blackbody radiation shift assessment for a lutetium ion clock.

The accuracy of state-of-the-art atomic clocks is derived from the insensitivity of narrow optical atomic resonances to environmental perturbations. Two such resonances in singly ionized lutetium have been identified with potentially lower sensitivities compared to other clock candidates. Here we report measurement of the most significant unknown atomic property of both transitions, the static differential scalar polarizability. From this, the fractional blackbody radiation shift for one of the transitions is found to be -1.36(9) × 10-18 at 300 K, the lowest of any established optical atomic clock. In consideration of leading systematic effects common to all ion clocks, both transitions compare favorably to the most accurate ion-based clocks reported to date. This work firmly establishes Lu+ as a promising candidate for a future generation of more accurate optical atomic clocks.

Suppression of Clock Shifts at Magnetic-Field-Insensitive Transitions.

We show that it is possible to significantly reduce rank 2 tensor shifts of a clock transition by operating at a judiciously chosen magnetic-field-insensitive point. In some cases shifts are almost completely eliminated making the transition an effective J=0 to J=0 candidate. This significantly improves the feasibility of a recent proposal for clock operation with large ion crystals. For such multi-ion clocks, geometric constraints and selection rules naturally divide clock operation into two categories based on the orientation of the magnetic field. We discuss the limitations imposed on each type and how calibrations might be carried out for clock operation.

Self-organization threshold scaling for thermal atoms coupled to a cavity.

We make a detailed experimental study of the threshold for the self-organization of thermal 87Rb atoms coupled to a high-finesse cavity over a range of atom numbers and cavity detunings. We investigate the difference between probing with a traveling wave and a retroreflected lattice. These two scenarios lead to qualitatively different behavior in terms of the response of the system as a function of cavity detuning with respect to the probe. In both cases, we confirm a N(-1) scaling of the threshold with atom number.

Detection of strands in native aortic valves by transesophageal echocardiography.

Prevalence and echocardiographic characteristics of strands on the leaflets of native aortic valves were examined. According to our data, the strands we found in 39% of patients are most likely Lambl's excrescences.

Limitations of chest pain follow-up from an urban teaching hospital emergency department.

Close outpatient follow-up of chest pain patients released from the emergency department (ED) has been suggested as an important means of detecting atypical presentations of cardiac ischemia. Urban teaching hospital patient populations often have limited private physician follow-up options and rely upon standard teaching hospital clinic systems. We analyzed the follow-up of 318 patients 30 or more years of age with nontraumatic chest pain released from the ED of a large urban teaching hospital. The planned disposition of the released patients was as follows: a medical clinic (136), another clinic or a private physician (76), or ED "as needed" (98); in addition, some patients left against medical advice (AMA) (8). The medical clinics received only 38% (51/136) of planned referrals. No subsequent record could be found for 13% (17/136) of referred patients. Only 17% (23/136) of referred patients were reevaluated within seven days. Two of the patients referred to medical clinics were admitted to the hospital within 24 hours for unstable angina and another was admitted from a medical clinic 16 days after ED evaluation with an acute myocardial infarction. Of patients with ED follow-up "as needed," one patient required admission for unstable angina 27 days after ED evaluation. Of the patients who left AMA, only two were reevaluated within 30 days. These findings suggest that specific measures to enhance follow-up must be instituted at urban teaching hospitals if chest pain patients are to be closely followed after ED release.

Measurement of "true" glucose production rates in infancy and childhood with 6,6-dideuteroglucose.

"New" glucose production has been measured in 54 infants and children for the first time by continuous three-to-four-hour influsion of the safe, nonradioactive tracer 6,6-dideuteroglucose. The use of combined gas chromatography--mass spectrometry with monitoring of selected ions allowed deuterium enrichment in blood glucose to be measured on microliter samples with an error of less than 2 per cent. In the young child, glucose production increased in a slightly curvilinear manner from 1 kg. to 25 kg. body weight, when it reached 140 mg. per minute, almost the adult value of 173 mg. per minute (2.28 +/- 0.23 mg./kg.-min., mean +/- S.E.). Normalized for weight, glucose production in premature infants was 5.46 +/- 0.31 mg./kg.-min., in term neonates averaged 6.07 +/- 0.27 mg./kg.-min., in children below the age of six years was 7.1 +/- 0.27 mg./kg.-min., and in late childhood averaged 5.4 +/- 0.28 mg./kg.-min. Relative to estimated brain weight, however, glucose production was essentially linear from the 1-kg. premature infant to the 80-kg. adult. These data, the first measurements of "new" glucose production in childhood, suggest that brain size may be a principal determinant of those factors that regulate hepatic glucose output throughout life.

In-vivo measurement of glucose and alanine metabolism with stable isotopic tracers.

This report describes sensitive, precise microtechniques that allow quantification of glucose and alanine metabolism in vivo using stable isotope tracers. By combined gas chromatography--mass spectrometry and selected ion monitoring--deuterium and carbon-13 enrichment in blood glucose and alanine were measured with an error of less than 2 per cent. Estimation of glucose and alanine flux in dogs by stable isotope tracer techniques was compared with simultaneous measurements made in the same animal with conventional radiotracer dilution methods. Application of the described stable isotope methods to determination of glucose and alanine turnover as well as alanine-2,3-13C incorporation into glucose in adult men confirmed the safety and validity of these techniques for human investigation.