The baryon density of the Universe from an improved rate of deuterium burning.

Light elements were produced in the first few minutes of the Universe through a sequence of nuclear reactions known as Big Bang nucleosynthesis (BBN)1,2. Among the light elements produced during BBN1,2, deuterium is an excellent indicator of cosmological parameters because its abundance is highly sensitive to the primordial baryon density and also depends on the number of neutrino species permeating the early Universe. Although astronomical observations of primordial deuterium abundance have reached percent accuracy3, theoretical predictions4-6 based on BBN are hampered by large uncertainties on the cross-section of the deuterium burning D(p,γ)3He reaction. Here we show that our improved cross-sections of this reaction lead to BBN estimates of the baryon density at the 1.6 percent level, in excellent agreement with a recent analysis of the cosmic microwave background7. Improved cross-section data were obtained by exploiting the negligible cosmic-ray background deep underground at the Laboratory for Underground Nuclear Astrophysics (LUNA) of the Laboratori Nazionali del Gran Sasso (Italy)8,9. We bombarded a high-purity deuterium gas target10 with an intense proton beam from the LUNA 400-kilovolt accelerator11 and detected the γ-rays from the nuclear reaction under study with a high-purity germanium detector. Our experimental results settle the most uncertain nuclear physics input to BBN calculations and substantially improve the reliability of using primordial abundances to probe the physics of the early Universe.

Proton-Capture Rates on Carbon Isotopes and Their Impact on the Astrophysical

The ^{12}C/^{13}C ratio is a significant indicator of nucleosynthesis and mixing processes during hydrogen burning in stars. Its value mainly depends on the relative rates of the ^{12}C(p,γ)^{13}N and ^{13}C(p,γ)^{14}N reactions. Both reactions have been studied at the Laboratory for Underground Nuclear Astrophysics (LUNA) in Italy down to the lowest energies to date (E_{c.m.}=60 keV) reaching for the first time the high energy tail of hydrogen burning in the shell of giant stars. Our cross sections, obtained with both prompt γ-ray detection and activation measurements, are the most precise to date with overall systematic uncertainties of 7%-8%. Compared with most of the literature, our results are systematically lower, by 25% for the ^{12}C(p,γ)^{13}N reaction and by 30% for ^{13}C(p,γ)^{14}N. We provide the most precise value up to now of 3.6±0.4 in the 20-140 MK range for the lowest possible ^{12}C/^{13}C ratio that can be produced during H burning in giant stars.

Direct Measurement of the

One of the main neutron sources for the astrophysical s process is the reaction ^{13}C(α,n)^{16}O, taking place in thermally pulsing asymptotic giant branch stars at temperatures around 90 MK. To model the nucleosynthesis during this process the reaction cross section needs to be known in the 150-230 keV energy window (Gamow peak). At these sub-Coulomb energies, cross section direct measurements are severely affected by the low event rate, making us rely on input from indirect methods and extrapolations from higher-energy direct data. This leads to an uncertainty in the cross section at the relevant energies too high to reliably constrain the nuclear physics input to s-process calculations. We present the results from a new deep-underground measurement of ^{13}C(α,n)^{16}O, covering the energy range 230-300 keV, with drastically reduced uncertainties over previous measurements and for the first time providing data directly inside the s-process Gamow peak. Selected stellar models have been computed to estimate the impact of our revised reaction rate. For stars of nearly solar composition, we find sizeable variations of some isotopes, whose production is influenced by the activation of close-by branching points that are sensitive to the neutron density, in particular, the two radioactive nuclei ^{60}Fe and ^{205}Pb, as well as ^{152}Gd.

Erratum: Three New Low-Energy Resonances in the

This corrects the article DOI: 10.1103/PhysRevLett.115.252501.

Direct Capture Cross Section and the E_{p}=71 and 105 keV Resonances in the

The ^{22}Ne(p,γ)^{23}Na reaction, part of the neon-sodium cycle of hydrogen burning, may explain the observed anticorrelation between sodium and oxygen abundances in globular cluster stars. Its rate is controlled by a number of low-energy resonances and a slowly varying nonresonant component. Three new resonances at E_{p}=156.2, 189.5, and 259.7 keV have recently been observed and confirmed. However, significant uncertainty on the reaction rate remains due to the nonresonant process and to two suggested resonances at E_{p}=71 and 105 keV. Here, new ^{22}Ne(p,γ)^{23}Na data with high statistics and low background are reported. Stringent upper limits of 6×10^{-11} and 7×10^{-11} eV (90% confidence level), respectively, are placed on the two suggested resonances. In addition, the off-resonant S factor has been measured at unprecedented low energy, constraining the contributions from a subthreshold resonance and the direct capture process. As a result, at a temperature of 0.1 GK the error bar of the ^{22}Ne(p,γ)^{23}Na rate is now reduced by 3 orders of magnitude.

Improved Direct Measurement of the 64.5 keV Resonance Strength in the

The ^{17}O(p,α)^{14}N reaction plays a key role in various astrophysical scenarios, from asymptotic giant branch stars to classical novae. It affects the synthesis of rare isotopes such as ^{17}O and ^{18}F, which can provide constraints on astrophysical models. A new direct determination of the E_{R}=64.5 keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics (LUNA) accelerator has led to the most accurate value to date ωγ=10.0±1.4_{stat}±0.7_{syst} neV, thanks to a significant background reduction underground and generally improved experimental conditions. The (bare) proton partial width of the corresponding state at E_{x}=5672 keV in ^{18}F is Γ_{p}=35±5_{stat}±3_{syst} neV. This width is about a factor of 2 higher than previously estimated, thus leading to a factor of 2 increase in the ^{17}O(p, α)^{14}N reaction rate at astrophysical temperatures relevant to shell hydrogen burning in red giant and asymptotic giant branch stars. The new rate implies lower ^{17}O/^{16}O ratios, with important implications on the interpretation of astrophysical observables from these stars.

Three New Low-Energy Resonances in the

The ^{22}Ne(p,γ)^{23}Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle affects the synthesis of the elements between ^{20}Ne and ^{27}Al in asymptotic giant branch stars and novae. The ^{22}Ne(p,γ)^{23}Na reaction rate is very uncertain because of a large number of unobserved resonances lying in the Gamow window. At proton energies below 400 keV, only upper limits exist in the literature for the resonance strengths. Previous reaction rate evaluations differ by large factors. In the present work, the first direct observations of the ^{22}Ne(p,γ)^{23}Na resonances at 156.2, 189.5, and 259.7 keV are reported. Their resonance strengths are derived with 2%-7% uncertainty. In addition, upper limits for three other resonances are greatly reduced. Data are taken using a windowless ^{22}Ne gas target and high-purity germanium detectors at the Laboratory for Underground Nuclear Astrophysics in the Gran Sasso laboratory of the National Institute for Nuclear Physics, Italy, taking advantage of the ultralow background observed deep underground. The new reaction rate is a factor of 20 higher than the recent evaluation at a temperature of 0.1 GK, relevant to nucleosynthesis in asymptotic giant branch stars.

First direct measurement of the 2H(α,γ)6Li cross section at big bang energies and the primordial lithium problem.

Recent observations of (6)Li in metal poor stars suggest a large production of this isotope during big bang nucleosynthesis (BBN). In standard BBN calculations, the (2)H(α,γ)(6)Li reaction dominates (6)Li production. This reaction has never been measured inside the BBN energy region because its cross section drops exponentially at low energy and because the electric dipole transition is strongly suppressed for the isoscalar particles (2)H and α at energies below the Coulomb barrier. Indirect measurements using the Coulomb dissociation of (6)Li only give upper limits owing to the dominance of nuclear breakup processes. Here, we report on the results of the first measurement of the (2)H(α,γ)(6)Li cross section at big bang energies. The experiment was performed deep underground at the LUNA 400 kV accelerator in Gran Sasso, Italy. The primordial (6)Li/(7)Li isotopic abundance ratio has been determined to be (1.5 ± 0.3) × 10(-5), from our experimental data and standard BBN theory. The much higher (6)Li/(7)Li values reported for halo stars will likely require a nonstandard physics explanation, as discussed in the literature.

First direct measurement of the 17O(p,γ)18F reaction cross section at Gamow energies for classical novae.

Classical novae are important contributors to the abundances of key isotopes, such as the radioactive (18)F, whose observation by satellite missions could provide constraints on nucleosynthesis models in novae. The (17)O(p,γ)(18)F reaction plays a critical role in the synthesis of both oxygen and fluorine isotopes, but its reaction rate is not well determined because of the lack of experimental data at energies relevant to novae explosions. In this study, the reaction cross section has been measured directly for the first time in a wide energy range E(c.m.)~/= 200-370 keV appropriate to hydrogen burning in classical novae. In addition, the E(c.m.)=183 keV resonance strength, ωγ=1.67±0.12 µeV, has been measured with the highest precision to date. The uncertainty on the (17)O(p,γ)(18)F reaction rate has been reduced by a factor of 4, thus leading to firmer constraints on accurate models of novae nucleosynthesis.

Reliability and validity of four alternative definitions of rapid-cycling bipolar disorder.

OBJECTIVE: This study tested the reliability and validity of four definitions of rapid cycling. METHOD: Two trained psychiatrists, using the Schedule for Affective Disorders and Schizophrenia, independently assessed 210 patients with bipolar disorder. They checked whether each patient met four definitions of rapid cycling: one consistent with DSM-IV criteria, one waiving criteria for duration of affective episodes, one waiving such criteria and requiring at least one switch from mania to depression or vice versa during the reference year, and one waiving duration criteria and requiring at least 8 weeks of fully symptomatic affective illness during the reference year. The interrater reliability was calculated by Cohen's kappa statistic. Patients who met each definition according to both psychiatrists were compared to those who did not meet any definition (nonrapid-cycling group) on demographic and clinical variables. All patients were followed up for 1 year. RESULTS: Kappa values were 0.93, 0.73, 0.75, and 0.80, respectively, for the four definitions of rapid cycling. The groups meeting the second and third definitions included significantly more female and bipolar II patients than did the nonrapid-cycling group. Those two groups also had the lowest proportion of patients with a favorable lithium prophylaxis outcome and the highest stability of the rapid-cycling pattern on follow-up. The four groups of rapid-cycling patients did not differ significantly among themselves on any of the assessed variables. CONCLUSIONS: The expression "rapid cycling" encompasses a spectrum of conditions. The DSM-IV definition, although quite reliable, covers only part of this spectrum, and the conditions that are excluded are very typical in terms of key validators and are relatively stable over time.

Reliability and validity of the DSM-IV diagnostic category of schizoaffective disorder: preliminary data.

BACKGROUND: Concerns have been expressed about the reliability and validity of the DSM-IV criteria for schizoaffective disorder, but no systematic study has been published up to now. METHODS: The Cohen's kappa for the individual items of the DSM-IV definition of schizoaffective disorder, manic episode and major depressive episode was evaluated in 150 patients independently interviewed by two psychiatrists using the Composite International Diagnostic Interview. The two-year outcome of patients with a consensus DSM-IV diagnosis of schizoaffective disorder was compared to that of patients with DSM-IV schizophrenia and schizophreniform disorder, using the Strauss-Carpenter Outcome Scale. RESULTS: The Cohen's kappa was 0.22 for the diagnosis of schizoaffective disorder, 0.71 for that of manic episode, and 0.82 for that of major depressive episode. Schizoaffective patients had a significantly better outcome than those with schizophrenia but a worse outcome than those with schizophreniform disorder. CONCLUSIONS: The inter-rater reliability of the DSM-IV criteria for schizoaffective disorder is not satisfactory. The better outcome of DSM-IV schizoaffective disorder compared with schizophrenia seems to depend more on the inclusion, in the definition of schizophrenia but not in that of schizoaffective disorder, of the six-month duration and functional impairment criteria than on the different symptomatological patterns of the two conditions. LIMITATION: The size of the sample of patients fulfilling DSM-IV criteria for schizoaffective disorder was small. CLINICAL RELEVANCE: The study suggests that the clinical implications of the currently problematic diagnosis of schizoaffective disorder may be modest.

Tooth staining effects of an alexidine mouthwash.

The primary purpose of this study was to determine the amount of tooth staining produced by an alexidine mouthrinse. One hundred and eighty subjects rinsed twice daily for 1 month with either 15 ml of alexidine (0.035%) or a placebo solution. Prior to the study, the subjects were classified according to their smoking, coffee and tea drinking habits and these factors were subsequently considered in the analysis of the stain scores. Additionally, the effects on staining of a prior prophylaxis and the use of a fluoridated toothpaste during the study were determined. Upon termination of the study, subjects utilizing the active mouthrinse manifested a greater degree of staining than placebo users. The amount and intensity of the stain due to alexidine were not influenced (increased) by smoking, tea or coffee drinking habits. A prior prophylaxis did not reduce the staining propensity of alexidine users. The method of scoring developed can be used to assess the degree of tooth staining induced by antiplaque agents.

The effect of an alexidine mouthwash on plaque and gingivitis.

A clinical study was conducted on the effects of an alexidine or placebo oral rinse on plaque and gingivitis. Forty-two male subjects rinsed for 54 days while continuing toothbrushing. This was followed by 4 days of mouthrinsing only. The alexidine mouthrinse significantly reduced the plaque index when used in conjunction with toothbrushing and also when brushing was discontinued. The gingivitis results were inconclusive.

Reflections on the three-year program.

Dental education has twice altered curriculum length from four- to three-year programs. The first switch from four to three years came during World War II to meet the need for additional dentists, but schools rapidly returned to four-year programs after the war. During the early 1970s, 14 dental schools converted to three-year programs; however, by 1976 several of these schools had returned to the four-year programs. At the New Jersey Dental School, one of the first schools to adopt a three-year program in 1970, a return to a four-year program in 1977 was the result of poor acceptance of the program by the faculty, a lack of flexibility in the schedule, and an undiminishing negative attitude by the profession toward the graduates. The experience derived from the three-year curriculum has reenforced the need for designing variable length programs, because a significant number of students can successfully complete the traditional program in three years.

The cost of higher education and its implication for dental education.

In summary, the committee remains convinced that dental education and the dental profession continue to be valuable public resources, greatly respected in the eyes of the public and worthy of the educational investment by students, institutions, federal, and state governments and, ultimately, the public. Among the 54 dental schools, there are 54 different financial situations. It is difficult to generalize about them, but it is not difficult to see, from the information presented, that all are not optimizing their finances and their educational programs. It is the committee's perception that many of the private dental schools and some of the public dental schools are teetering on the verge of extinction. Unless substantial actions are taken, the irretrievable loss of some of these schools is likely to occur. While this committee cannot prescribe actions for all of the schools, it is evident that systematic and sustained effort is needed to prevent these losses. The solution to this complex problem cannot be solely that of dental education. It has to become the concern of all the related constituencies of the profession. Economic factors will continue to increase the cost of education.

Elevating clinical licensing examinations to professional testing standards.

Clinical licensure examinations for graduates have increasingly come under criticism. Studies question whether licensing examinations can discriminate between prepared and unprepared candidates for independent practice. A study at Columbia showed no correlation between student performance on in-school clinical examinations and NERB examinations. The results question whether the NERB clinical examinations meet concurrent validity standards. A recent steep rise in the regional failure rate on the prosthodontics manikin examination questions the reliability of that examination. The authors urge immediate action to bring clinical licensing examinations into line with recent (1992) national guidelines for dental licensing agencies.

PGY1: what is it and why is it important?

The interest in a year of additional training for the practice of dentistry has grown over the past fifteen years. Debates at national conferences and careful study by committees of professional organizations led to the recommendation that over the next five to ten year period the profession should move toward creating a postgraduate experience for each graduate prior to independent practice. While study of this issue will undoubtedly continue, it behooves us to proceed with the process of expanding the number of postgraduate positions, first, to meet the demand by graduating students who are voluntarily selecting a year of additional training, and later, so we are at a position to fully consider such a year as mandatory for independent practice. If we use the next five to ten years productively, we can create an environment where the public and the graduates will benefit from this additional year of training.