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We suggest a candidate for a non-canonical Hermitian operator corresponding to phase angle, based on the Weyl correspondence rule. The matrix elements of this operator, for harmonic oscillator number states, coincide, in the correspondence limit, with those of a phase operator proposed by Barnett and Pegg, when the dimension of their defining space becomes infinite.

The effect of herbivory and nutrient enrichment on the growth of invasive and native macroalgal species was simultaneously studied in two biogeographic regions: the Caribbean and Hawaii. Herbivores suppressed growth of invasive algae in their native (Caribbean) and invaded range (Hawaii), but despite similar levels of herbivore biomass, the intensity of herbivory was lower in Hawaii. Algal species with a circumtropical distribution did not show a similar effect of herbivores on their growth. Nutrient enrichment did not enhance growth of any algal species in either region. The reduction in herbivore intensity experienced by invasive algae in Hawaii rather than an escape from (native) herbivores provided invasive macroalgae with "enemy release" sensu the Enemy Release Hypothesis (ERH). Since native, Hawaiian herbivores still feed and even prefer invasive algae over native species, invasion scenario’s that involve predation (e.g. the ERH) could be falsely dismissed when invasive species are only studied in their invasive range. We therefore argue that escape from herbivores (i.e. enemy release) can only effectively be determined with additional information on the intensity of predation experienced by an invasive species in its native range.

The pine-oak woodlands of the Mexican highlands harbour significant biological diversity, yet little is known about the evolutionary history of organisms inhabiting this region. We assessed genetic and phenotypic differentiation in 482 individuals representing 27 populations of the Mexican jay (Aphelocoma ultramarina) - a widespread bird species of the Mexican highlands - to test whether populations in the central and northern Mexican sierras display discrete breaks between groups, which would be consistent with a role for the different mountain chains in divergence and speciation. We found abrupt breaks in mitochondrial DNA (mtDNA; ND2 and control region) delineating four major genetic groups found in the Sierra Madre Occidental, Sierra Madre Oriental, southern Central Plateau (Bajio), and Transvolcanic Belt. These mtDNA groups were largely corroborated by data from nuclear microsatellites and phenotypic data, except that clades from the Central Plateau and Sierra Madre Oriental showed clinal change in these data sets. Uncertainty about the mutation rate for our mitochondrial markers warrants considerable caution with regard to estimating divergence times, but the major genetic groups appear to have split before the most extreme period of glacial cycling that marked the last 0.7 million years and after Mexico's period of major mountain formation. The fact that some genetic breaks do not coincide with well-known geographic barriers suggests a role for ecology in divergence and speciation, and we discuss implications for taxonomy and conservation.

High precision fundamental neutron physics experiments have been proposed for the intense pulsed spallation neutron beams at JSNS, LANSCE, and SNS to test the standard model and search for new physics. Certain systematic effects in some of these experiments have to be controlled at the few ppb level. The NPD Gamma experiment, a search for the small parity-violating {gamma}-ray asymmetry A{sub Y} in polarized cold neutron capture on parahydrogen, is one example. For the NPD Gamma experiment we developed a radio-frequency resonant spin rotator to reverse the neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high efficiency over a broad cold neutron energy range. The effect of the spin reversal by the rotator on the neutron beam phase space is compared qualitatively to rf neutron spin flippers based on adiabatic fast passage. We discuss the design of the spin rotator and describe two types of transmission-based neutron spin-flip efficiency measurements where the neutron beam was both polarized and analyzed by optically polarized {sup 3}He neutron spin filters. The efficiency of the spin rotator was measured at LANSCE to be 98.8 {+-} 0.5% for neutron energies from 3 to 20 meV over the full phasemore » space of the beam. Systematic effects that the rf spin rotator introduces to the NPD Gamma experiment are considered.« less

Parity-odd asymmetries in the electromagnetic decays of compound nuclei can sometimes be amplified above values expected from simple dimensional estimates by the complexity of compound nuclear states. In this work we use a statistical approach to estimate the root mean square (RMS) of the distribution of expected parity-odd correlations $\vec{s_{n}} \cdot \vec{k_{\gamma}}$, where $\vec {s_{n}}$ is the neutron spin and $\vec{k_{\gamma}}$ is the momentum of the gamma, in the integrated gamma spectrum from the capture of cold polarized neutrons on Al, Cu, and In and we present measurements of the asymmetries in these and other nuclei. Based on our calculations, large enhancements of asymmetries were not predicted for the studied nuclei and the statistical estimates are consistent with our measured upper bounds on the asymmetries., Comment: 22 pages, 6 figures

Song divergence among populations of passerine birds is recognized as a potentially important premating isolation mechanism and may represent the first step in speciation. Because song divergence may be influenced by an array of acoustic, ecological, and genetic factors, the study of its origin requires a multifaceted approach. Here we describe the relationship between acoustic, neutral genetic and ecological variation in five populations of the Swainson's thrush: two from coastal temperate rainforest habitat representing the 'russet-backed' subspecies group, two from inland coniferous forest habitat representing the 'olive-backed' subspecies group, and one mixed locality that resides within a contact zone between the two groups. Song in the five populations is analysed using a multivariate analysis of spectral and temporal measurements, population genetic structure is assessed using an analysis of five microsatellite loci and ecological differences between populations are quantified using an analysis of climatic parameters. Matrix correspondence tests are used to distinguish between the potential for drift and selection in driving song divergence. No significant correlation was found between acoustic and genetic distance suggesting that song divergence cannot be explained by drift alone. A significant correlation between ecological and acoustic distance after accounting for genetic distance, suggests a potential role for ecological selection on divergence in spectral and temporal components of Swainson's thrush song.

Theories of Torres-Vega and Fredrick (1993 J. Chem. Phys. 98 3103), Harriman (1994 J. Chem. Phys. 100 3651) and of Ban (1998 J. Math. Phys. 39 1744), in which phase space points (p, q) are used as configurational variables to formulate quantum mechanics are considered from the standpoint of a class of quantization schemes associating phase space functions with operators. The connection between these schemes and the theories given in Torres-Vega and Fredrick (1993 J. Chem. Phys. 98 3103), Harriman (1994 J. Chem. Phys. 100 3651), Dirac (1930 The Principles of Quantum Mechanics (Oxford: Oxford University Press)), Moller, Jorgensen and Torres-Vega (1997 J. Chem. Phys. 106 7228), Klauder and Skagerstam (1985 Coherent States: Applications in Physics and Mathematical Physics (Singapore: World Scientific)), Li, Wei and Lu (2004 Phys. Rev. A 70 022105), Ban (1998 J. Math. Phys. 39 1744) is made by means of augmented wavefunctions ψ(λ)σ(p, q; t), where λ = 0 corresponds to the ordering of Wigner and Weyl. For that case we use these functions to define a family of positive operator-valued measures for the phase angle of an harmonic oscillator.

The NPDGamma collaboration has constructed and commissioned an apparatus on flight path 12 at LANSCE to measure with a high precision, 5×10−9, the small parity‐violating gamma‐ray asymmetry, Aγ, in polarized neutron capture on protons. This asymmetry can be determined unambiguously the weak pion‐nucleon coupling constant. To study the hadronic weak interaction at low energy, the collaboration has used the NPDGamma apparatus to measure parity‐violating gamma‐ray asymmetries in compound nuclei with cold neutrons. Using the statistical model of compound nuclei and spectroscopic information of the target nuclei, we can set upper limit on the spreading width of the hadronic weak interaction for intermediate‐mass nuclei. We describe the experiment and the preliminary results of measured gamma‐ray asymmetries of Al, Sc, Ti, Mn, and Co.

Models of speciation in African rain forests have stressed either the role of isolation or ecological gradients. Here we contrast patterns of morphological and genetic divergence in parapatric and allopatric populations of the Little Greenbul, Andropadus virens, within different and similar habitats. We sampled 263 individuals from 18 sites and four different habitat types in Upper and Lower Guinea. We show that despite relatively high rates of gene flow among populations, A. virens has undergone significant morphological divergence across the savanna-forest ecotone and mountain-forest boundaries. These data support a central component of the divergence-with-gene-flow model of speciation by suggesting that despite large amounts of gene flow, selection is sufficiently intense to cause morphological divergence. Despite evidence of isolation based on neutral genetic markers, we find little evidence of morphological divergence in fitness-related traits between hypothesized refugial areas. Although genetic evidence suggests populations in Upper and Lower Guinea have been isolated for over 2 million years, morphological divergence appears to be driven more by habitat differences than geographic isolation and suggests that selection in parapatry may be more important than geographic isolation in causing adaptive divergence in morphology.

The NPDGamma experiment will measure with a high precision, 5×10−9, the small parity‐violating gamma‐ray asymmetry, Aγ, in polarized cold neutron capture in a para‐hydrogen target to determine unambiguously the weak pion‐nucleon coupling constant Hπ1. For the experiment the collaboration has built a new high‐flux pulsed cold neutron beam line at LANSCE. In 2004, we first commissioned the beam line and then the apparatus with exception of the hydrogen target. The sensitivity of the apparatus was tested by measuring Aγ on Al, B, Cl, Cu, and In. The Cl has a well‐known large parity‐violating gamma‐ray asymmetry that was used to verify the performance of the apparatus. The other nuclei that were studied during the commissioning run are present in materials used for construction of the experiment and are, therefore, possible sources of the false asymmetries since backgrounds are expected to be about 10% of the signal from the neutron capture on hydrogen. We measured Aγ≈0 for these nuclei except for Cl. We repo...

We have built a CsI(Tl) γ‐ray detector array for the NPDGamma experiment to search for a small parity‐violating directional asymmetry in the angular distribution of 2.2 MeV γ‐rays from the capture of polarized cold neutrons by protons with a sensitivity of several ppb. The weak pion‐nucleon coupling constant can be determined from this asymmetry. The small size of the asymmetry requires control of systematic errors at the ppb level, and the use of current‐mode γ‐ray detection with vacuum photo diodes and low‐noise solid‐state preamplifiers. The detectors were tested for noise performance, sensitivity to magnetic fields, pedestal stability, and cosmic background. False asymmetries due to gain changes and electronic pickup in the detector system were measured to be consistent with zero to an accuracy of 10−9 in a few hours. We show that the detector array operates at counting statistics and present asymmetry results for B4C , CCl4 , 27Al, Cu, and In. B4C , 27Al, Cu, and In are used throughout the experiment...

The NPDGamma experiment will measure the parity-violating directional gamma ray asymmetry A γ in the reaction [Formula: see text]. Ultimately, this will constitute the first measurement in the neutron-proton system that is sensitive enough to challenge modern theories of nuclear parity violation, providing a theoretically clean determination of the weak pion-nucleon coupling. A new beam-line at the Los Alamos Neutron Science Center (LANSCE) delivers pulsed cold neutrons to the apparatus, where they are polarized by transmission through a large volume polarized (3)He spin filter and captured in a liquid para-hydrogen target. The 2.2 MeV gamma rays from the capture reaction are detected in an array of CsI(Tl) scintillators read out by vacuum photodiodes operated in current mode. We will complete commissioning of the apparatus and carry out a first measurement at LANSCE in 2004-05, which would provide a statistics-limited result for A γ accurate to a standard uncertainty of ±5 × 10(-8) level or better, improving on existing measurements in the neutron-proton system by a factor of 4. Plans to move the experiment to a reactor facility, where the greater flux would enable us to make a measurement with a standard uncertainty of ±1 × 10(-8), are actively being pursued for the longer term.

Hypotheses for divergence and speciation in rainforests generally fall into two categories: those emphasizing the role of geographic isolation and those emphasizing the role of divergent selection along gradients. While a majority of studies have attempted to infer mechanisms based on the pattern of species richness and congruence of geographic boundaries, relatively few have tried to simultaneously test alternative hypotheses for diversification. Here we discuss four examples, taken from our work on diversification of tropical rainforest vertebrates, in which we examine patterns of genetic and morphological variation within and between biogeographic regions to address two alternative hypotheses. By estimating morphological divergence between geographically contiguous and isolated populations under similar and different ecological conditions, we attempt to evaluate the relative roles of geographic isolation and natural selection in population divergence. Results suggest that natural selection, even in the presence of appreciable gene flow, can result in morphological divergence that is greater than that found between populations isolated for millions of years and, in some cases, even greater than that found between congeneric, but distinct, species. The relatively small phenotypic divergence that occurs among long-term geographic isolates in similar habitats suggests that morphological divergence via drift may be negligible and/or that selection is acting to produce similar phenotypes in populations occupying similar habitats. Our results demonstrate that significant phenotypic divergence: (1) is not necessarily coupled with divergence in neutral molecular markers; and (2) can occur without geographic isolation in the presence of gene flow.

A number of authors have raised concerns over the external validity of psychological research. This study examined the extent to which empirical articles include human participants from diverse ethnic backgrounds. Articles published over a 5-year period in 14 selected journals representing 3 applied sub-disciplines of psychology were examined. Of the 2,536 articles coded, only 61% indicated the ethnicity of the participants. For those articles, the ethnic compositions approximated U.S. Census estimates, with the exception of an overrepresentation of African Americans and an underrepresentation of Hispanic Americans. The results imply that although the field is apparently adequately recruiting English speakers, representation of non-English speakers should be increased. To further enhance the external validity of psychological research, ethnicity of participants should be not only specified but also analyzed in relation to the results of a study.

This paper presents a wide-ranging theoretical and experimental study of non-adiabatic transient phenomena in a $\Lambda $ EIT system when a strong coupling field is rapidly switched on or off. The theoretical treatment uses a Laplace transform approach to solve the time-dependent density matrix equation. The experiments are carried out in a Rb$^{87}$ MOT. The results show transient probe gain in parameter regions not previously studied, and provide insight into the transition dynamics between bare and dressed states., Comment: 19 Pages, 9 Figures, 1 in colour. RevTex 4.0 Submitted to Physical Review A

The weak pion-nucleon coupling constant Hπ1 remains poorly determined, despite many years of effort. The recent measurement of the 133Cs anapole moment has been interpreted to give a value of Hπ1 almost an order of magnitude larger than the limit established in the 18F parity doublet experiments. A measurement of the gamma ray directional asymmetry Aγ for the capture of polarized neutrons by hydrogen has been proposed at Los Alamos National Laboratory. This experiment will determine Hπ1 independent of nuclear structure effects. However, since the predicted asymmetry is small, Aγ≈5×10−8, systematic effects must be reduced to

We describe the NMR and Rb Zeeman frequency shift polarimeters used for determining the 3He polarization in a recent precision measurement of the neutron spin structure function g1 at SLAC (E-154). We performed a detailed study of the systematic errors associated with the calibration of the NMR polarimeter. A new technique was used for determining the 3He polarization from the frequency shift of the Rb Zeeman resonance.

In the past decade high density polarized 3He fixed targets based on spin-exchange with optically pumped Rb have been used successfully in electron scattering experiments at MIT/Bates and SLAC, as a neutron polarizer, and with proton and pion beams at TRIUMF. In the near future similar targets will be used in physics programs at TJNAF and as neutron polarizers at Los Alamos. Until now, the typical spin exchange target was a sealed design, however there are several advantages to target cells that can be evacuated and filled with a variable pressure of polarized 3He. We have begun development of such an actively filled target, based on technology recently developed for NMR/MRI with hyperpolarized noble gases. The benefits and difficulties of constructing such a “flowing” high density 3He target system are discussed.

The NPDGamma Experiment measures the parity-violating correlation Aγ between neutron spin and photon momentum in the reaction + p → d + γ. Knowledge of Aγ and other parity-violating observables in few-body nuclear systems will provide constraints for a parameterized description of ΔS = 0 parity-violating phenomena free from complications of nuclear structure. The NPDGamma experiment uses a polarized cold pulsed neutron beam, a liquid parahydrogen target, and a cylindrical array of 48 CsI(Tl) scintillation detectors operated in current mode to search for the asymmetry. NPDGamma recently completed the first phase of the program to measure Aγ at the Los Alamos Neutron Science Center with the preliminary result Aγ = (−1.2 ± 2.1(stat.) ± 0.1(sys.)) × 10−7, reproducing the previous upper limit from a measurement at a reactor facility. We discuss the theoretical background and experimental method and report on preliminary analysis of the LANSCE data. The second phase of the program to measure Aγ is in progress at the Spallation Neutron Source at Oak Ridge National Laboratory.

This paper presents the results of a series of model-scale tests of the erosion-reduction capabilities of a partial-span asymmetric preswirl stator on the propeller of a large United States Coast Guard (USCG) patrol boat. The propeller and stator were tested at one-third scale (A - 3 .2) in the DTRC 36-inch Variable Pressure Water Tunnel (VPWT). A single shaft strut upstream of the propeller and a shaft inclination of 9.25° simulated the full-scale propeller flow field. Cavitation erosion tendency was investigated using an erodable coating painted on the propeller blades. Stator performance was evaluated in a series of model tests at 30 knots, both with and without the currently- installed cavitation relief holes, using three different series of stator blade angle of attack settings These high Reynolds number experiments showed that the blade root erosion tendency was almost completely eliminated by the preswirl stator with the cavitation relief holes at the propeller blade root closed. A lesser degree of erosion relief was provided by the preswirl stator with the cavitation relief holes open.

Summary Birds with haemosiderosis absorbed up to 10% of an orally administered test dose of radioactive iron, even when the hepatic iron concentrations were markedly increased. In contrast, rats which were orally loaded with iron to produce a comparable hepatic iron concentration absorbed only ‘ about 1% of administered 59Fe. It is concluded that the absorption of iron at the intestinal mucosa in avian species is not as tightly regulated as that in some mammals.

Renovascular hypertension is potentially curable but of low prevalence. A previous retrospective study has demonstrated the use of a potentiated increase in plasma renin activity after captopril administration as a diagnostic test for renovascular hypertension; this requires two blood samples for plasma renin activity determination and three inclusive criteria for a positive test result. We applied this test prospectively to screen 100 hypertensive patients for renovascular hypertension. We evaluated 29 patients with renovascular hypertension; the remainder were diagnosed as having essential hypertension. In our patient population, a postcaptopril plasma renin activity of 5.7 ng of angiotensin per milliliter per hour (ngAl.mL-1.h-1) or greater had a 100% sensitivity and an 80% specificity for renovascular hypertension. An absolute increase in plasma renin activity with captopril of 4.7 ngAl.mL-1.h-1 or greater had a lower sensitivity of 90% and a specificity of 87%, whereas a fractional increase in plasma renin activity after captopril of 150% or higher had the lowest sensitivity of 69% and a specificity of 86%. A subgroup analysis of 38 patients who were receiving diuretic therapy demonstrated that the test sensitivity was unchanged but the specificity was reduced. In conclusion, a single postcaptopril plasma renin activity value of 5.7 ngAl.mL-1.h-1 or greater is a simplified screening test for renovascular hypertension, with excellent sensitivity and acceptable specificity. This test is well tolerated, inexpensive, and easy to perform.

Purpose To examine self-reported characteristics and risk behaviors of adolescents offered free HIV testing in a community setting in order to increase our understanding of this population and to design effective outreach activities targeting high-risk youth. Methods Adolescents age 14-24 were offered free Orasure HIV tests at community events and given the option of completing a survey to provide demographic information and self-reported risk behaviors including past sexual behavior and drug and alcohol use. Participants who responded positively to the practice of oral, vaginal, or anal intercourse were defined as sexually active. Results Among the 172 participants, 59% reported one or more types of sexual intercourse and 37% reported past drug or alcohol use. Eighty percent of the participants were African American and the mean age was 17.63 years. The mean percentage of sexually active 14-17 year olds was 55%, which was higher than the mean percentage of sexually active 18-21 year olds (52%). In the univariate analysis, age, African American race, lifetime drug use, tobacco use, alcohol use, and marijuana use were found to be significant predictors of sexual activity. In the multivariate models, African American race, lifetime drug use, tobacco use, and alcohol use were each found to be significant predictors of sexual activity. Forty-five percent of sexually active females reported previous drug use. Sexually active drug users were less likely to be African American. Conclusions Our findings indicate that free community HIV testing effectively reaches sexually active teenagers and can increase HIV testing among high-risk youth. The high percentage of sexually active 14-17 year olds indicates that we accessed a high-risk group of adolescents. Although sexual activity was positively correlated with high-risk sexual behaviors and with drug and alcohol use, our study also shows that many sexually active adolescents, especially African American females, are not drug users.

Purpose of Study Our goal was to report preliminary findings regarding the effect of an HIV/sexually transmitted disease (STD) educational intervention on the HIV knowledge, skills, and behavioral intentions of incarcerated adolescents. Compared to their school-based peers, incarcerated adolescents report higher rates of many behaviors correlated with HIV transmission. The self-contained environment of juvenile detention centers provides an opportunity to implement interventions capable of reducing high-risk sexual behaviors. The chosen intervention addressed adolescents who are currently sexually active and accounted for the fact that knowledge and risk perception have little effect on adolescent behavior. Additionally, it presented HIV-risk reduction skills, such as communication between sexual partners and accurate perceptions of peer norms, which have shown to strongly impact sexual decision-making in prior studies. Methods Used Adolescents completed a self-report survey prior to and immediately following an 8-hour HIV/STD educational intervention conducted in two youth detention centers. The pre- and post-intervention group means for each survey item or multi-item scale were compared. Summary of Results Among 53 participants, the mean age was 15.58, and 30% were male. African Americans comprised 60% and whites 34%. Pre-intervention, 83% reported having had sexual intercourse. Significant increases were found in HIV/STD knowledge (14.7%, p

The author gives an expansion for the density matrix subsequent to a single 90 degrees resonant RF pulse for a system of spins with dipole-dipole interactions. The method is analogous to the usual multiple scattering expansion used to approximate the electron density of states in disordered metals but here is applied to certain super operators related to the quantum Liouville operator governing the equation of motion for the density matrix. A simple choice of unperturbed Hamiltonian is discussed giving rise to a systematic expansion. The expansion is not perturbative in the usual sense.

The authors apply the model of molecular motion of Smith (1971-72) to calculate the NMR response from a single (90 degrees ) pulse and from a double (90 degrees - tau -90 degrees 90 degrees ) pulse sequence for a model ensemble of single spin-1 nuclei, with simplified electric quadrupole interactions, flipping randomly and abruptly between just two orientations with respect to a large Zeeman field. The model predicts that the response after the second pulse will be severely attenuated for a range of characteristic flipping times, provided the interpulse time tau is not too short.

Two outbreaks of botulism in central Saskatchewan in which mortality of waterfowl continued into late autumn and then recurred in the same marshes the following spring are described. Small numbers of birds were involved in each instance. Dabbling ducks (predominantly mallards, Anas platyrhynchos and pintails, Anas acuta) and American coots, Fulica americana were affected most commonly in autumn, whereas only diving ducks (predominantly lesser scaup, Aythya affinis) were found to be involved in spring. Live maggots present in carcasses despite sub-freezing temperatures were the probable source of intoxication in the autumn; the source of toxin in the spring was not determined.

Quantum mechanics may be formulated in pseudo-phasespace in the Weyl picture. The semiclassical expression for the Weyl transform of the usual time evolution operator is evaluated by summing over paths a semiclassical approximation for a new propagator in pseudo-phasespace. As an example the Bohr-Sommerfeld quantisation rule is recovered. The new propagator may in principle be used to construct other interesting quantities, such as the propagator governing the time evolution of the Wigner function.

FTMP is a digital computer architecture which has evolved over a ten-year period in connection with several life-critical aerospace applications. Most recently it has been proposed as a fault-tolerant central computer for civil transport aircraft applications. A working emulation has been operating for some time, and the first engineering prototype is scheduled to be completed in late 1979. FTMP is designed to have a failure rate due to random causes of the order of 10-10failures per hour, on ten-hour flights where no air-borne maintenance is available. The prefered maintenance interval is of the order of hundreds of flight hours, and the probability that maintenance will be required earlier than the preferred interval is desired to be at most a few percent. The design is based on independent processor-cache memory modules and common memory modules which communicate via redundant serial buses. All information processing and transmission is conducted in triplicate so that local voters in each module can correct errors. Modules can be retired and/or reassigned in any configuration. Reconfiguration is carried out routinely from second to second to search for latent faults in the voting and reconfiguration elements. Job assignments are all made on a floating basis, so that any processor triad is eligible to execute any job step. The core software in the FFMP will handle all fault detection, diagnosis, and recovery in such a way that applications programs do not need to be involved. Failure-rate models and numerical results are described for both permanent and intermittent faults. A dispatch probability model is also presented. Experience with an experimental emulation is described.