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We summarize the nuclear physics interests in the Oklo natural nuclear reactors, focusing particularly on developments over the past two decades. Modeling of the reactors has become increasingly sophisticated, employing Monte Carlo simulations with realistic geometries and materials that can generate both the thermal and epithermal fractions. The water content and the temperatures of the reactors have been uncertain parameters. We discuss recent work pointing to lower temperatures than earlier assumed. Nuclear cross-sections are input to all Oklo modeling and we discuss a parameter, the 175Lu ground state cross-section for thermal neutron capture leading to the isomer 176mLu, that warrants further investigation. Studies of the time dependence of dimensionless fundamental constants have been a driver for much of the recent work on Oklo. We critically review neutron resonance energy shifts and their dependence on the fine structure constant α and the ratio Xq = mq/Λ. (where mq is the average of the u and d current quark masses and Λ is the mass scale of quantum chromodynamics (QCD)). We suggest a formula for the combined sensitivity to a and Xq that exhibits the dependence on proton number Z and mass number A, potentially allowing quantum electrodynamic (QED) and QCD effects to be disentangled if a broader range of isotopic abundance data becomes available. [ABSTRACT FROM AUTHOR]

Background: Uncertainty in the operating temperatures of Oklo reactor zones impacts the precision of bounds derived for time variation of the fine structure constant α. Improved 176Lu/175Lu thermometry has been discussed but its usefulness may be complicated by photoexcitation of the isomeric state l76mLu by 176Lu(γ,γ') fluorescence. Purpose: We calculate prompt, delayed, and equilibrium γ-ray fluxes due to fission of 235U in pulsed mode operation of Oklo zone RZ10. Methods: We use Monte Carlo modeling to calculate the prompt flux. We use improved data libraries to estimate delayed and equilibrium spectra and fluxes. Results: We find γ-ray fluxes as a function of energy and derive values for the coefficients λγγ' that describe burn-up of 176Lu through the isomeric l76mLu state. Conclusion: The contribution of the (γγ') channel to the 176Lu/l75Lu isotopic ratio is negligible in comparison to the neutron burn-up channels. Lutetium thermometry is fully applicable to analyses of Oklo reactor data. [ABSTRACT FROM AUTHOR]

Background: Lutetium thermometry has been used to analyze Oklo natural nuclear reactor zones but leads to widely varying and puzzling predictions for the temperatures T0 which in turn impacts bounds on time variation of the fine structure constant or. Purpose: We revisit results for reactor zone RZ10 in light of new measurements of the isomer branching ratio Bg in l75Lu neutron capture at 5 and 25 keV. Method: We recalculate predictions for T0 as a function of BK using realistic models of the Oklo neutron flux. Results: We find T0 = 100 ± 30 °C using a new value of Bg, in contrast to 350 < T0 < 500 °C using the evaluated value at thermal energy. Conclusions: Lutetium thermometry can be applicable to analyses of Oklo reactor data, but a better measurement of Bs with thermal neutrons is needed to confirm the reliability of temperature predictions. [ABSTRACT FROM AUTHOR]

This paper describes a novel adaptive battery model based on a remapped variant of the well-known Randles' lead-acid model. Remapping of the model is shown to allow improved modeling capabilities and accurate estimates of dynamic circuit parameters when used with subspace parameter-estimation techniques. The performance of the proposed methodology is demonstrated by application to batteries for an all-electric personal rapid transit vehicle from the Urban Light TRAnsport (ULTRA) program, which is designated for use at Heathrow Airport, U.K. The advantages of the proposed model over the Randles' circuit are demonstrated by comparisons with alternative observer/estimator techniques, such as the basic Utkin observer and the Kalman estimator. These techniques correctly identify and converge on voltages associated with the battery state-of-charge (SoC), despite erroneous initial conditions, thereby overcoming problems attributed to SoC drift (incurred by Coulomb-counting methods due to overcharging or ambient temperature fluctuations). Observation of these voltages, as well as online monitoring of the degradation of the estimated dynamic model parameters, allows battery aging (state-of-health) to also be assessed and, thereby, cell failure to be predicted. Due to the adaptive nature of the proposed algorithms, the techniques are suitable for applications over a wide range of operating environments, including large ambient temperature variations. Moreover, alternative battery topologies may also be accommodated by the automatic adjustment of the underlying state-space models used in both the parameter-estimation and observer/estimator stages. [ABSTRACT FROM AUTHOR]

We have analyzed constraints on parity-odd time-reversal noninvariant interactions derived from measurements of the energy dependence of parity-violating polarized neutron capture on unpolarized targets. As previous authors found, a perturbation in energy dependence due to a parity (P)-odd time (T)-odd interaction is present. However, the perturbation competes with T-even terms which can obscure the T-odd signature. We estimate the magnitudes of these competing terms and suggest strategies for a practicable experiment. [ABSTRACT FROM AUTHOR]

Background: Recent years have seen a renewed interest in the Oklo phenomenon, particularly in relation to the study of time variation of the fine structure constant a. The neutron fluence is one of the crucial parameters for Oklo reactors. Several approaches to its determination were elaborated in the past. Purpose: We consider whether it is possible to use the present isotopic 138La--139La data for RZ10 as an additional indicator of neutron fluences in the active cores of the reactors. Results: We calculate the dependence of the Oklo 138La abundance on neutron fluence and elemental lanthanum concentration. Conclusion: The neutron fluence in RZ10 can be deduced from lanthanum isotopic data, but requires reliable data on the primordial elemental abundance. Conversely, if the fluence is known, the isotope ratio provides information on the primordial lanthanum abundance that is not otherwise easily determined. [ABSTRACT FROM AUTHOR]

We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 nu (e) candidate events with energies above 3.4 MeV compared to 365.2+/-23.7 events expected in the absence of neutrino oscillation. Accounting for 17.8+/-7.3 expected background events, the statistical significance for reactor nu (e) disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from nu (e) oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2). A global analysis of data from KamLAND and solar-neutrino experiments yields Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2) and tan((2)theta=0.40(+0.10)(-0.07), the most precise determination to date.

Data corresponding to a KamLAND detector exposure of 0.28 kton yr has been used to search for nu;(e)'s in the energy range 8.3

KamLAND has measured the flux of nu;(e)'s from distant nuclear reactors. We find fewer nu;(e) events than expected from standard assumptions about nu;(e) propagation at the 99.95% C.L. In a 162 ton.yr exposure the ratio of the observed inverse beta-decay events to the expected number without nu;(e) disappearance is 0.611+/-0.085(stat)+/-0.041(syst) for nu;(e) energies >3.4 MeV. In the context of two-flavor neutrino oscillations with CPT invariance, all solutions to the solar neutrino problem except for the "large mixing angle" region are excluded.

Objective: To assess whether crude league tables of mortality and league tables of risk adjusted mortality accurately reflect the performance of hospitals., Design: Longitudinal study of mortality occurring in hospital., Setting: 9 neonatal intensive care units in the United Kingdom., Subjects: 2671 very low birth weight or preterm infants admitted to neonatal intensive care units between 1988 and 1994., Main Outcome Measures: Crude hospital mortality and hospital mortality adjusted using the clinical risk index for babies (CRIB) score., Results: Hospitals had wide and overlapping confidence intervals when ranked by mortality in annual league tables; this made it impossible to discriminate between hospitals reliably. In most years there was no significant difference between hospitals, only random variation. The apparent performance of individual hospitals fluctuated substantially from year to year., Conclusions: Annual league tables are not reliable indicators of performance or best practice; they do not reflect consistent differences between hospitals. Any action prompted by the annual league tables would have been equally likely to have been beneficial, detrimental, or irrelevant. Mortality should be compared between groups of hospitals using specific criteria-such as differences in the volume of patients, staffing policy, training of staff, or aspects of clinical practice-after adjusting for risk. This will produce more reliable estimates with narrower confidence intervals, and more reliable and rapid conclusions.

Objectives: Clinical Risk Index for Babies (CRIB) is a simple instrument used to measure clinical risk and illness severity in very low birth-weight infants. We assessed its reliability, validity beyond the first 12 hrs after birth, and responsiveness to individual change in condition after 7 days., Design: Cohort study., Setting: Three tertiary and three nontertiary UK hospitals., Patients: Three hundred ninety-eight infants whose birth weight was <1501 g or who were born before a 31-wk gestation period., Interventions: Inter- and intrarater reliability of data extraction were assessed by Pearson and intraclass correlation. To validate CRIB, we tested the correlation between clinical risk and illness severity with the risk of: a) death; b) prolonged treatment with supplemental oxygen; and c) disability at 2 yrs. Logistic regression models were fitted to assess validity and responsiveness., Measurements and Main Results: Reliability coefficients ranged from 0.76 (95% confidence interval, 0.71 to 0.81) to 0.97 (0.94 to 1.00). Throughout the first week, CRIB correlated with the risk of death (p < .001), prolonged treatment with oxygen (p < .001), and disability (p < .001 to p = .033). Improved condition, represented by a reduction in CRIB within the first week, was independently associated with lower risks of each adverse outcome, p < .05., Conclusions: During the first week, CRIB was reliable, valid, and responsive. These properties support the use of CRIB in the stratification of infants by risk and illness severity in cohort studies, and they also indicate that CRIB may have the potential to be used in other ways in the future.