Reproductive value, sensitivity, and nonlinearity: Population-management heuristics derived from classical demography

In classical demographic theory, reproductive value and stable age distribution are proportional to the sensitivities of the asymptotic population size to changes in mortality and maternity, respectively. In this note we point out that analogous relationships hold if the maternity function is allowed to depend on the population density. The relevant formulae can essentially be obtained by replacing the growth rate ("Lotka'sr") with zero. These facts may be used to derive heuristics for population management (pest control)

Dispersion strengthening in vanadium microalloyed steels processed by simulated thin slab casting and direct charging. Part 2 - chemical characterisation of dispersion strengthening precipitates

The composition of the sub-15 nm particles in six related vanadium high strength low alloy steels, made by simulated thin slab direct charged casting, has been determined using electron energy loss spectroscopy (EELS). Such particles are considered to be responsible for dispersion hardening. For the first time, particles down to 4 nm in size have had their composition fully determined. In all the steels, the particles were nitrogen and vanadium rich and possibly slightly sub-stoichiometric carbonitrides. Equilibrium thermodynamics predicted much higher carbon to metal atomic ratios than observed in all cases so that kinetics and mechanical deformation clearly control the precipitation process. Thus it is important to formulate the steel with this in mind

Evolution of precipitates, in particular cruciform and cuboid particles, during simulated direct charging of thin slab cast vanadium microalloyed steels

A study has been undertaken of four vanadium based steels which have been processed by a simulated direct charging route using processing parameters typical of thin slab casting, where the cast product has a thickness of 50 to 80mm ( in this study 50 mm) and is fed directly to a furnace to equalise the microstructure prior to rolling. In the direct charging process, cooling rates are faster, equalisation times shorter and the amount of deformation introduced during rolling less than in conventional practice. Samples in this study were quenched after casting, after equalisation, after 4th rolling pass and after coiling, to follow the evolution of microstructure. The mechanical and toughness properties and the microstructural features might be expected to differ from equivalent steels, which have undergone conventional processing. The four low carbon steels (~0.06wt%) which were studied contained 0.1wt%V (V-N), 0.1wt%V and 0.010wt%Ti (V-Ti), 0.1wt%V and 0.03wt%Nb (V-Nb), and 0.1wt%V, 0.03wt%Nb and 0.007wt%Ti (V-Nb-Ti). Steels V-N and V-Ti contained around 0.02wt% N, while the other two contained about 0.01wt%N. The as-cast steels were heated at three equalising temperatures of 1050C, 1100C or 1200C and held for 30-60 minutes prior to rolling. Optical microscopy and analytical electron microscopy, including parallel electron energy loss spectroscopy (PEELS), were used to characterise the precipitates. In the as-cast condition, dendrites and plates were found. Cuboid particles were seen at this stage in Steel V-Ti, but they appeared only in the other steels after equalization. In addition, in the final product of all the steels, fine particles were seen, but it was only in the two titanium steels that cruciform precipitates were present. PEELS analysis showed that the dendrites, plates, cuboids, cruciforms and fine precipitates were essentially nitrides. The two Ti steels had better toughness than the other steels but inferior lower yield stress values. This was thought to be, in part, due to the formation of cruciform precipitates in austenite, thereby removing nitrogen and the microalloying elements which would have been expected to precipitate in ferrite as dispersion hardening particles

Stimulated Raman adiabatic passage from an atomic to a molecular Bose-Einstein condensate

The process of stimulated Raman adiabatic passage (STIRAP) provides a possible route for the generation of a coherent molecular Bose-Einstein condensate (BEC) from an atomic BEC. We analyze this process in a three-dimensional mean-field theory, including atom-atom interactions and non-resonant intermediate levels. We find that the process is feasible, but at larger Rabi frequencies than anticipated from a crude single-mode lossless analysis, due to two-photon dephasing caused by the atomic interactions. We then identify optimal strategies in STIRAP allowing one to maintain high conversion efficiencies with smaller Rabi frequencies and under experimentally less demanding conditions.Comment: Final published versio

Observation of shock waves in a large Bose-Einstein condensate

We observe the formation of shock waves in a Bose-Einstein condensate containing a large number of sodium atoms. The shock wave is initiated with a repulsive, blue-detuned light barrier, intersecting the BEC, after which two shock fronts appear. We observe breaking of these waves when the size of these waves approaches the healing length of the condensate. At this time, the wave front splits into two parts and clear fringes appear. The experiment is modeled using an effective 1D Gross-Pitaevskii-like equation and gives excellent quantitative agreement with the experiment, even though matter waves with wavelengths two orders of magnitude smaller than the healing length are present. In these experiments, no significant heating or particle loss is observed.Comment: 7 pages, 7 figure

Computerized adaptive testing to screen children for emotional and behavioral problems by preventive child healthcare

BACKGROUND: Questionnaires to detect emotional and behavioral problems (EBP) in Preventive Child Healthcare (PCH) should be short which potentially affects validity and reliability. Simulation studies have shown that Computerized Adaptive Testing (CAT) could overcome these weaknesses. We studied the applicability (using the measures participation rate, satisfaction, and efficiency) and the validity of CAT in routine PCH practice. METHODS: We analyzed data on 461 children aged 10-11 years (response 41%), who were assessed during routine well-child examinations by PCH professionals. Before the visit, parents completed the CAT and the Child Behavior Checklist (CBCL). Satisfaction was measured by parent- and PCH professional-report. Efficiency of the CAT procedure was measured as number of items needed to assess whether a child has serious problems or not. Its validity was assessed using the CBCL as the criterion. RESULTS: Parents and PCH professionals rated the CAT on average as good. The procedure required at average 16 items to assess whether a child has serious problems or not. Agreement of scores on the CAT scales with corresponding CBCL scales was high (range of Spearman correlations 0.59-0.72). Area Under Curves (AUC) were high (range: 0.95-0.97) for the Psycat total, externalizing, and hyperactivity scales using corresponding CBCL scale scores as criterion. For the Psycat internalizing scale the AUC was somewhat lower but still high (0.86). CONCLUSIONS: CAT is a valid procedure for the identification of emotional and behavioral problems in children aged 10-11 years. It may support the efficient and accurate identification of children with overall, and potentially also specific, emotional and behavioral problems in routine PCH

How to observe the Efimov effect

We propose to observe the Efimov effect experimentally by applying an external electric field on atomic three-body systems. We first derive the lowest order effective two-body interaction for two spin zero atoms in the field. Then we solve the three-body problem and search for the extreme spatially extended Efimov states. We use helium trimers as an illustrative numerical example and estimate the necessary field strength to be less than 2.7 V/angstrom.Comment: 4 pages, 2 postscript figures, psfig.sty, revte

Generation of macroscopic pair-correlated atomic beams by four-wave mixing in Bose-Einstein condensates

By colliding two Bose-Einstein condensates we have observed strong bosonic stimulation of the elastic scattering process. When a weak input beam was applied as a seed, it was amplified by a factor of 20. This large gain atomic four-wave mixing resulted in the generation of two macroscopically occupied pair-correlated atomic beams.Comment: Please take eps files for best details in figure

Comparing three short questionnaires to detect psychosocial problems among 3 to 4-year olds

Background: Validated questionnaires help community pediatric services to identify psychosocial problems. Our aim was to assess which of three short questionnaires was most suitable for this identification among pre-school children. Methods: We included 1,650 children (response 64 %) aged 3-4 years undergoing routine well-child health assessments in 18 services across the Netherlands. Child healthcare professionals (CHPs) interviewed and examined children and parents. Parents were randomized regarding filling out the Strengths and Difficulties Questionnaire (SDQ) or the KIPPPI, a Dutch-origin questionnaire. In addition, all filled out the Ages and Stages Questionnaires: Social-Emotional (ASQ:SE) and the Child Behavior Checklist (CBCL). We assessed the internal consistency and validity of each questionnaire, with CBCL and treatment status as criteria, and the degree to which each questionnaire could improve identification based solely on clinical assessment. Results: The internal consistency of the total problems scale of each questionnaire was satisfactory, Cronbach's alphas varied between 0.75 and 0.98. Only the SDQ discriminated sufficiently between children with and without problems as measured by the CBCL (sensitivity = 0.76 at a cut-off point with specificity = 0.90), in contrast to the other two questionnaires (with sensitivity indices varying between 0.51-0.63). Similar results were found for the treatment status criterion, although sensitivity was lower for all questionnaires. The SDQ seemed to add most to the identification of psychosocial problems by CHPs, but the differences between the SDQ and the ASQ: SE were not statistically significant. Conclusions: The SDQ is the best tool for the identification of psychosocial problems in pre-school children by community paediatric services