Population Lifetime Research Articles

Full Open Population Capture–Recapture Models With Individual Covariates

Traditional analyses of capture–recapture data are based on likelihood functions that explicitly integrate out all missing data. We use a complete data likelihood (CDL) to show how a wide range of capture–recapture models can be easily fitted using readily available software JAGS/BUGS even when there are individual-specific time-varying covariates. The models we describe extend those that condition on first capture to include abundance parameters, or parameters related to abundance, such as population size, birth rates or lifetime. The use of a CDL means that any missing data, including uncertain individual covariates, can be included in models without the need for customized likelihood functions. This approach also facilitates modeling processes of demographic interest rather than the complexities caused by non-ignorable missing data. We illustrate using two examples, (i) open population modeling in the presence of a censored time-varying individual covariate in a full robust design, and (ii) full open population multi-state modeling in the presence of a partially observed categorical variable. Supplemental materials for this article are available online.

The Impact of Exposure Metric Choice for Cancers Related to Arsenic in Drinking Water in Central Europe

S-30B2-3 Background/Aims: Past control of water supplies to reduce arsenic intake is good for public health; however, it complicates the task of accurate reconstruction of past exposures in the service of investigating exposure response relationships between arsenic and cancer. Classifying people based on the current drinking water concentrations would be an unsatisfactory option by ignoring individual differences in patterns of concentrations over time. Methods: For the ASHRAM study—-a case-control study investigating arsenic in drinking water and cancer, in counties with arsenic exposure in Hungary, Romania, and Slovakia—-the exposure history of each person was constructed taking into account how much water was consumed (as water, in drinks, and in food), sources of drinking water in their various residences over their lifetime and the concentrations of arsenic in the water supply, in many cases measured in the ASHRAM study, or from routine data based on measurements performed by the authorities in each country. Following 4 indices of exposure were calculated: the current concentration of residential drinking water, the time weighted average concentration of residential drinking water, the highest daily dose of As derived from residential drinking water, and the lifetime cumulative dose. Results: For 1392 participants, the assignment of concentrations to water supplies was very successful with 81% of the population lifetime residential person time being matched to an arsenic concentration. The exposure indices were all log-normally distributed and the median lifetime concentrations were in Hungary 13.3 μg/L, Romania 0.7 μg/L, and Slovakia 0.8 μg/L. Overall, 25% of the population has average concentrations over 10 μg/L and 8% with exposure over 50 μg/L. Conclusion: Classifying exposure by current rather than lifetime measures of arsenic exposure leads to an underestimate of the strength of relationship between arsenic and cancer.

2D IR Spectroscopy of the C–D stretching vibration of the deuterated formic acid dimer

We report transient grating and 2D IR spectra of the C-D stretching vibration of deuterated formic acid dimer. The C-D stretching transition is perturbed by an accidental Fermi resonance interaction that gives rise to a second transition. The transient grating results show that the population lifetime of these states, which are in rapid equilibrium, is 11 ps. 2D IR spectroscopy reveals the energies of the eigenstates in the regions of one quantum and two quanta of C-D stretching excitation. Using these eigenstate energies, we construct a simplified model for the zeroth-order states that we then use to simulate the 2D IR spectrum. The results of this simulation suggest that the model captures the essential features of the vibrational spectroscopy in the region of the C-D stretching transition and compares well with previous gas-phase spectroscopy of the C-D stretch of deuterated formic acid dimer.

Temperature dependence of vibrational relaxation of the OH bending excitation in liquid H 2O

Mid-infrared pump–probe spectroscopy measurements of the OH bending vibration in pure liquid water were performed at different temperatures. The population lifetime increases from 170 ± 15 fs at T = 295 K to 250 ± 15 fs at T = 348 K. This temperature dependence can be explained by the decrease in the spectral overlap between the OH bending and the high-frequency librational modes, supporting the relaxation scenario that the bend vibrational energy is dominantly transferred to librational motions. It was also found that the temperature dependence becomes absent below room temperature, the possible origin for which is discussed.

Cost-effectiveness of interventions to reduce dietary salt intake

ObjectiveTo evaluate population health benefits and cost-effectiveness of interventions for reducing salt in the diet.DesignProportional multistate life-table modelling of cardiovascular disease and health sector cost outcomes over the lifetime of...

Coherent measurements of high-order electronic correlations in quantum wells

Strong, long-range Coulomb interactions can lead to correlated motions of multiple charged particles, which can induce important many-body effects in semiconductors. The exciton states formed from correlated electron-hole pairs have been studied extensively, but basic properties of multiple-exciton correlations-such as coherence times, population lifetimes, binding energies and the number of particles that can be correlated-are largely unknown because they are not spectroscopically accessible from the ground state. Here we present direct observations of high-order coherences in gallium arsenide quantum wells, achieved using two-dimensional multiple-quantum spectroscopy methods in which up to seven successive light fields were used. The measurements were made possible by the combination of a reconfigurable spatial beam-shaper that formed multiple beams in specified geometries and a spatiotemporal pulse-shaper that controlled the relative optical phases and temporal delays among pulses in all the beams. The results reveal triexciton coherences (correlations of three excitons or six particles), whose existence was not obvious because the third exciton spin is unpaired, and the values of their coherence times and binding energies. Rephasing of biexcitons, triexcitons and unbound two-exciton coherences was demonstrated. We also determined that there are no significant unbound correlations of three excitons and no bound or unbound four-exciton (eight-particle) correlations. Thus, the limits, as well as the properties, of many-body correlations in this system were revealed. The measurement methods open a new window into high-order many-body interactions in materials and molecules, and the present results should guide ongoing work on first-principles calculations of electronic interactions in semiconductor nanostructures.

Cost‐effectiveness of Weight Watchers and the Lighten Up to a Healthy Lifestyle program

Intensive weight loss programs that incorporate dietary counselling and exercise advice are popular and are supported by evidence of immediate weight loss benefits. We evaluate the cost-effectiveness of two weight loss programs, Lighten Up to a Healthy Lifestyle and Weight Watchers. Health gains from prevention of chronic disease are modelled over the lifetime of the Australian population. These results are combined with estimates of intervention costs and cost offsets (due to reduced rates of lifestyle-related diseases) to determine the dollars per disability-adjusted life year (DALY) averted by each intervention program, from an Australian health sector perspective. Both weight loss programs produced small improvements in population health compared to current practice. The time and travel associated with attending group-counselling sessions, however, was costly for patients, and overall the cost-effectiveness ratios for Lighten Up ($130,000/DALY) and Weight Watchers ($140,000/DALY) were high. Based on current evidence, these intensive behavioural counselling interventions are not very cost-effective strategies for reducing obesity, and the potential benefits for population health are small. It will be critical to consider other strategies (e.g. changing the 'obesogenic' environment) or explore alternative methods of intervention delivery (e.g. Internet) to see if they offer a more cost-effective approach by effectively reaching a high number of people at a low cost.

The First Millisecond of the Myosin Working Stroke Under Constant Load

Myosin II is the motor protein that drives muscle contraction through cyclical interactions with an actin filament. The working stroke produced by a single myosin head has been previously measured in isolated myosin molecules, but the effects of the high loads acting on the myosin molecule during muscle contraction could not be investigated. In fact, current single molecule techniques apply force with a delay of few milliseconds after actin-myosin binding, when the working stroke of skeletal muscle myosin has already been completed.Here, we developed a novel single molecule technique in which the delay between myosin binding and force application is abolished. This method is capable of resolving the development of the myosin working stroke under different loads with a very high time resolution and detecting events as short as 100 μs.We found that under loads in the range 1 to 10 pN myosin can follow two distinct pathways in its interaction with actin. In the first pathway myosin detaches from actin before producing any movement (weak binding state); these events are very fast (240 ± 23 μs), their duration does not depend on ATP concentration, and is not significantly affected by force. In the second pathway myosin steps and remains bound to actin for a longer time (strong binding state). At low forces (|F| < 2 pN) the lifetime of this second population of events linearly decreases with ATP concentration in the range 5-50 μM. At higher forces this relation becomes non-linear due to premature unbinding of myosin from actin.The working stroke is produced in two steps and its mean amplitude is found to be smaller at increasing loads and vanishes at the isometric force (5.7 ± 0.6 pN).

Cost‐effectiveness of interventions to prevent alcohol‐related disease and injury in Australia

To evaluate cost-effectiveness of eight interventions for reducing alcohol-attributable harm and determine the optimal intervention mix. Interventions include volumetric taxation, advertising bans, an increase in minimum legal drinking age, licensing controls on operating hours, brief intervention (with and without general practitioner telemarketing and support), drink driving campaigns, random breath testing and residential treatment for alcohol dependence (with and without naltrexone). Cost-effectiveness is modelled over the life-time of the Australian population in 2003, with all costs and health outcomes evaluated from an Australian health sector perspective. Each intervention is compared with current practice, and the most cost-effective options are then combined to determine the optimal intervention mix. Cost-effectiveness is measured in 2003 Australian dollars per disability adjusted life year averted. Although current alcohol intervention in Australia (random breath testing) is cost-effective, if the current spending of $71 million could be invested in a more cost-effective combination of interventions, more than 10 times the amount of health gain could be achieved. Taken as a package of interventions, all seven preventive interventions would be a cost-effective investment that could lead to substantial improvement in population health; only residential treatment is not cost-effective. Based on current evidence, interventions to reduce harm from alcohol are highly recommended. The potential reduction in costs of treating alcohol-related diseases and injuries mean that substantial improvements in population health can be achieved at a relatively low cost to the health sector.

Cooling and Trapping 88Sr Atoms with 461 nm Laser

We report the experimental realization of a 88Sr magneto-optical trap (MOT) operating at the wavelength of 461 nm. The MOT is loaded via a 32 cm long spin-flip type Zeeman slower which enhances the MOT population by a factor of 22. The total laser power available in our experiment is about 300 mW. We have trapped 1.6 × 108 88Sr atoms with a 679nm and 707 nm repumping laser. The two repumping lasers enhance the trap population and trap lifetime by factors of 11 and 7, respectively. The 88Sr cloud has a temperature of about 2.3 mK, measured by recording the time evolution of the absorption signal.

Cost-effectiveness of interventions to promote physical activity: a modelling study.

Physical inactivity is a key risk factor for chronic disease, but a growing number of people are not achieving the recommended levels of physical activity necessary for good health. Australians are no exception; despite Australia's image as a sporting nation, with success at the elite level, the majority of Australians do not get enough physical activity. There are many options for intervention, from individually tailored advice, such as counselling from a general practitioner, to population-wide approaches, such as mass media campaigns, but the most cost-effective mix of interventions is unknown. In this study we evaluate the cost-effectiveness of interventions to promote physical activity. From evidence of intervention efficacy in the physical activity literature and evaluation of the health sector costs of intervention and disease treatment, we model the cost impacts and health outcomes of six physical activity interventions, over the lifetime of the Australian population. We then determine cost-effectiveness of each intervention against current practice for physical activity intervention in Australia and derive the optimal pathway for implementation. Based on current evidence of intervention effectiveness, the intervention programs that encourage use of pedometers (Dominant) and mass media-based community campaigns (Dominant) are the most cost-effective strategies to implement and are very likely to be cost-saving. The internet-based intervention program (AUS$3,000/DALY), the GP physical activity prescription program (AUS$12,000/DALY), and the program to encourage more active transport (AUS$20,000/DALY), although less likely to be cost-saving, have a high probability of being under a AUS$50,000 per DALY threshold. GP referral to an exercise physiologist (AUS$79,000/DALY) is the least cost-effective option if high time and travel costs for patients in screening and consulting an exercise physiologist are considered. Intervention to promote physical activity is recommended as a public health measure. Despite substantial variability in the quantity and quality of evidence on intervention effectiveness, and uncertainty about the long-term sustainability of behavioural changes, it is highly likely that as a package, all six interventions could lead to substantial improvement in population health at a cost saving to the health sector. Please see later in the article for Editors' Summary.

Exciton coherence in semiconductor quantum dots

AbstractThe coherent dynamics of excitons in InAs quantum dots (QDs) was investigated in the telecommunication wavelength range using a transient four‐wave mixing technique. The sample was fabricated on an InP(311)B substrate using strain compensation to control the emission wavelength. This technique also enabled us to fabricate a 150‐layer stacked QD structure for obtaining a high S/N in the four‐wave mixing measurements, although no high‐sensitive heterodyne detection was carried out. The dephasing time and transition dipole moment were precisely estimated from the polarization dependence of signals, taking into account their anisotropic properties.The population lifetimes of the excitons were also measured by using a polarization‐dependent pumpprobe technique. A quantitative comparison of these anisotropies demonstrates that in our QDs, non‐radiative population relaxation, polarization relaxation and pure dephasing are considerably smaller than the radiative relaxation. A comparison of the results of the four‐wave mixing and pump‐probe measurements revealed that the pure dephasing could be directly estimated with an accuracy of greater than 0.1 meV by comparing the results of four‐wave mixing and pump‐probe measurements. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Femtosecond time-resolved and two-dimensional vibrational sum frequency spectroscopic instrumentation to study structural dynamics at interfaces

We present a novel setup to elucidate the dynamics of interfacial molecules specifically, using surface-selective femtosecond vibrational spectroscopy. The approach relies on a fourth-order nonlinear optical interaction at the interface. In the experiments, interfacial molecules are vibrationally excited by an intense, tunable femtosecond midinfrared (2500-3800 cm(-1)) pump pulse, resonant with the molecular vibrations. The effect of the excitation and the subsequent relaxation to the equilibrium state are probed using broadband infrared+visible sum frequency generation (SFG) light, which provides the transient vibrational spectrum of interfacial molecules specifically. This IR pump-SFG probe setup has the ability to measure both vibrational population lifetimes as well as the vibrational coupling between different chemical moieties at interfaces. Vibrational lifetimes of interfacial molecules are determined in one-dimensional pump-SFG probe experiments, in which the response is monitored as a function of the delay between the pump and probe pulses. Vibrational coupling between molecular groups is determined in two-dimensional pump-SFG probe experiments, which monitor the response as a function of pump and probe frequencies at a fixed delay time. To allow for one setup to perform these multifaceted experiments, we have implemented several instrumentation techniques described here. The detection of the spectrally resolved differential SFG signal using a combination of a charge-coupled device camera and a piezocontrolled optical scanner, computer-controlled Fabry-Perot etalons to shape and scan the IR pump pulse and the automated sample dispenser and sample trough height corrector are some of the novelties in this setup.

Comparative Studies of Two Araceous Lectins by Steady State and Time-Resolved Fluorescence and CD Spectroscopy

Transitions in the tryptophan microenvironment and secondary structure of two monocot lectins from Sauromatum guttatum and Arisaema tortuosum under different denaturing conditions were studied by steady state and time resolved fluorescence and CD spectroscopy. The lectins exist as tetramers with a single tryptophan residue estimated per monomer, present in a polar environment. Quenching with ionic quenchers showed predominantly electropositive environment for tryptophan residues. Acrylamide had maximum quenching effect. A decrease in KI quenching due to lectin denaturation indicated redistribution of charges as a result of possible conformational change. The two values for lifetimes of tryptophanyl population (1.2-1.4 and 6.3-6.4 ns) reduced substantially on quenching or denaturation. Similarly, both the lectins showed a drastic loss of secondary structure in 5 M Gdn-HCl or 6 M Urea or at pH 2.0 and below. For the first time araceous lectins, like legume lectins are shown to bind adenine. The presence of a compact structure at alkaline pH 10.0-12.0 was observed in CD spectra.

Zeeman-level lifetimes inEr3+:Y2SiO5

We present measurements of Zeeman-level population lifetimes in ${\text{Er}}^{3+}:{\text{Y}}_{2}{\text{SiO}}_{5}$ at low magnetic fields and low temperatures. Using spectral hole burning spectroscopy, we investigate the dynamics and temperature dependence of the hole structure due to the Zeeman interaction. Evidence for population storage in Zeeman levels with lifetimes of up to 130 ms is found in the form of long-lived spectral holes and antiholes. We also observe that a subset of the erbium ions exhibit very long-lived holes with lifetimes as long as 60 s at 2.8 K.

Squint-Free Fourier-Optical RF Beamforming Using a SHB Crystal as an Imaging Detector

We describe and demonstrate a Fourier-optical beamformer that modulates RF energy from an antenna array onto a corresponding array of coherent optical beams and forms RF-frequency-scaled (or beam-squinted), far-field images through a single-lens optical Fourier transform. The squinted image is formed into a cryogenically cooled spectral hole burning (SHB) crystal, where it writes spatially-localized spectral images as holes in the crystal's spatial-spectral absorption profile. The spectral-hole images at each resolvable spectral bin (10 MHz at 4.2 K) integrate during the population lifetime ( 1 ms) for frequencies within the inhomogeneous crystal bandwidth ( 20 GHz). A chirped laser diffracts from the holes, producing a sequence of spectrally resolved RF images. The diffracted light passes through a swept-zoom lens synchronized to the chirped laser readout. This zoom lens compensates for beam squint during readout and forms the squint-free images onto a charge-coupled device (CCD), where they are coherently detected. We demonstrate experimental squinted images from a 5 element array across a 350 MHz bandwidth that are recorded into and read from a Er:Eu:YSiO SHB crystal before a digital zoom compensates for beam squint. This system can be scaled up to form images from 2-D arrays with 1000s of elements across 20 GHz bandwidths.

Vibrational Energy Relaxation of the Bend Fundamental of Dilute Water in Liquid Chloroform and d-Chloroform

The population lifetimes of the bend fundamental of dilute water in liquid chloroform (8.5 ps) and d-chloroform (28.5 ps) display an interesting solvent isotope effect. As the lowest excited vibrational state of the molecule, the water bend fundamental relaxes directly to the ground state with about 1600 cm-1 of energy released to the other degrees of freedom. The strong solvent isotope effect along with the large energy gap indicates the participation of solvent vibrational modes in this vibrational energy relaxation process. We calculate the vibrational energy relaxation rates of the water bend in chloroform and d-chloroform using the Landau-Teller formula with a new potential model developed and parametrized self-consistently to describe the chloroform-water interaction. The computed values are in reasonable agreement with the experimental results, and the trend for the isotope effect is correct. It is found that energy transfer to the solvent vibrations does indeed play an important role. Nevertheless, no single dominant solvent accepting mode can be identified; the relaxation appears to involve both the bend and the C-Cl stretches, and frequency changes of all of these modes upon deuteration contribute to the observed solvent isotope effect.

Radiative and non-radiative relaxation of excitons in strain-compensated quantum dots

We have investigated the population dynamics of excitons in strain-compensated InAs quantum dots (QDs) using a pump–probe technique under resonant excitation. Precise control of polarization directions of incident pulses enabled us to selectively estimate population lifetimes for two orthogonally polarized exciton ground states according to polarization selection rules. Measured decay times of the probe transmissions were highly dependent on the polarization directions of the exciton states. We found that the ratio of the decay times for the orthogonally polarized states is in quantitative agreement with the ratio of square of the transition dipole moments. This indicates that radiative recombination processes have a dominant effect on the population dynamics and that non-radiative and spin relaxations are negligible in our QDs. As a result, we can estimate the radiative lifetimes to be 1.0±0.1 and 1.7±0.2 ns for orthogonally polarized exciton ground states.

A Selective Sparse Coding Model with Embedded Attention Mechanism

Sparse coding theory demonstrates that the neurons in primary visual cortex form a sparse representation of natural scenes in the viewpoint of statistics, but a typical scene contains many different patterns (corresponding to neurons in cortex) competing for neural representation because of the limited processing capacity of the visual system. We propose an attention-guided sparse coding model (AGSC). This model includes two modules: non-uniform sampling module simulating the process of retina and data-driven attention module based on the response saliency (RS). Our experiment results show that the model notably decreases the number of coefficients that may be activated and retains the main vision information at the same time. It provides a way to improve the coding efficiency for sparse coding model and to achieve good performance in both population sparseness and lifetime sparseness.

Life histories of female red squirrels and their contributions to population growth and lifetime fitness

The potential importance of life history traits to population growth rates has been well explored theoretically but has rarely been documented in wild mammals. In this study we used 18 consecutive years of data from a population of North American red squirrels (Tamiasciurus hudsonicus) in the southwest Yukon, Canada, to examine variation in female life history traits and their consequences for population growth rate. Red squirrels in this population experienced severe juvenile mortality, but survivorship beyond age 2 followed a Type I relationship where the annual survival probability decreased with age. Maximum lifespan was 8 y. Some females initiated breeding as yearlings, but most delayed first breeding until 2 y of age or in some cases even later. Annual reproduction generally involved the production of a single litter averaging 3.1 offspring (range: 1 to 7); however, some females attempted a second litter within a single breeding season, either following reproductive failure or, in rare circumstances, after a successful first breeding attempt. Life table characteristics for the 11 cohorts born between 1987 and 1997 indicated a population growth rate close to zero (r = 0.009). Elasticity analysis as well as individual population projection matrices and lifetime reproductive success data indicated that early survival and not age at first reproduction was most strongly associated with a female's contribution to population growth. Lifespan accounted for 83.9% of the variation in population growth rate and was positively correlated with age at first reproduction, such that females who bred as yearlings suffered decreased longevity. Collectively, these results emphasize the importance of female survival and not reproductive output to population growth and lifetime fitness in this system.