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We study a cell growth model with a division function that models cells which divide only after they have reached a certain minimum size. In contrast to the cases studied in the literature, the determination of the steady size distribution entails an eigenvalue that is not known explicitly, but is defined through a continuity condition. We show that there is a steady size distribution solution to this problem.
We have mapped cold atomic gas in 21cm line H i self-absorption (HISA) at arcminute resolution over more than 90% of the Milky Way's disk. To probe the formation of H2 clouds, we have compared our HISA distribution with CO J = 1-0 line emission. Few HISA features in the outer Galaxy have CO at the same position and velocity, while most inner-Galaxy HISA has overlapping CO. But many apparent inner-Galaxy HISA-CO associations can be explained as chance superpositions, so most inner-Galaxy HISA may also be CO-free. Since standard equilibrium cloud models cannot explain the very cold H i in many HISA features without molecules being present, these clouds may instead have significant CO-dark H2.
This paper details the development of a technique to improve the minority carrier lifetime of 4H-SiC thick (≥ 100 μm) n-type epitaxial layers through multiple thermal oxidations. A steady improvement in lifetime is seen with each oxidation step, improving from a starting ambipolar carrier lifetime of 1.09 µs to 11.2 µs after 4 oxidation steps and a high-temperature anneal. This multiple-oxidation lifetime enhancement technique is compared to a single high-temperature oxidation step, and a carbon implantation followed by a high-temperature anneal, which are traditional ways to achieve high ambipolar lifetime in 4H-SiC n-type epilayers. The multiple oxidation treatment resulted in a high minimum carrier lifetime of 6 µs, compared to < 2 µs for other treatments. The implications of lifetime enhancement to high-voltage/high-current 4H-SiC power devices are also discussed.
In this paper we study the probability density function solutions to a second-order pantograph equation with a linear dispersion term. The functional equation comes from a cell growth model based on the Fokker–Planck equation. We show that the equation has a unique solution for constant positive growth and splitting rates and construct the solution using the Mellin transform.
We report a study of the relation between dust and gas over a 100 deg2 area in
the Taurus molecular cloud. We compare the H2 column density derived from dust
extinction with the CO column density derived from the 12CO and 13CO
J = 1 → 0 lines. We derive the visual extinction from reddening
determined from 2MASS data. The comparison is done at an angular size of 200′′,
corresponding to 0.14 pc at a distance of 140 pc. We find that the relation between visual
extinction AV and N(CO) is linear between
AV ≃ 3 and 10 mag in the region associated with the
B213–L1495 filament. In other regions the linear relation flattens for
AV ≳ 4 mag. Accounting for the observed relation between the
column density of CO and CO2 ices and AV, we find a
linear relationship between the column of carbon monoxide and dust for observed visual
extinctions up to the maximum value in our data ≃23 mag.
It is well known that star formation takes place within molecular clouds. However, current observational surveys and investigations usually start by selecting a sample of sites where star formation is ongoing, thus biasing against those clouds and regions with little or no current formation activity. In an attempt to identify samples of clouds both with and without star formation, and to investigate their properties, we present an automated method for associating clouds identified in new 3D CO data with far-IR/sub-mm sources. Given the large number of surveys of the galactic plane currently planned, ongoing or being released, the methods used here may prove instructive in understanding how, where and under what conditions star formation takes place throughout our Galaxy. In addition, this will allow exploration of the properties of star forming regions on a range of spatial scales.
In New Zealand (NZ), Fe deficiency (ID) is present in 14 % of children aged <2 years. Prevalence varies with ethnicity (NZ European 7 %, Pacific 17 %, Maori 20 %). We describe dietary Fe intake, how this varies with ethnicity and whether intake predicts Fe status.
A random sample of children aged 6–23 months. Usual Fe intake and dietary sources were estimated from 2 d weighed food records. Associations were determined between adequacy of Fe intake, as measured by the Estimated Average Requirement (EAR), and ID.
Sampling was stratified by ethnicity. Dietary and blood analysis data were available for 247 children.
The median daily Fe intake was 8·3 mg (age 6–11 months) and 6·3 mg (age 12–23 months). Breast milk and milk formulas (median 58 %; age 6–11 months), and cereals (41 %) and fruit and vegetables (17 %; age 12–23 months), were the predominant dietary sources of Fe. Fe intake was below the EAR for 25 % of the children. Not meeting the EAR increased the risk of ID for children aged 6–11 months (relative risk = 18·45, 95 % CI 3·24, 100·00) and 12–23 months (relative risk = 4·95, 95 % CI 1·59, 15·41). In comparison with NZ European, Pacific children had a greater daily Fe intake (P = 0·04) and obtained a larger proportion of Fe from meat and meat dishes (P = 0·02).
A significant proportion of young NZ children have inadequate dietary Fe intake. This inadequate intake increases the risk of ID. Ethnic differences in Fe intake do not explain the increased risk of ID for Pacific children.
Little is known about the effects of adult attention deficit hyperactivity disorder (ADHD) on work performance or accidents-injuries.
A survey was administered in 2005 and 2006 to employees of a large manufacturing firm to assess the prevalence and correlates of adult ADHD. Respondents (4140 in 2005, 4423 in 2006, including 2656 in both surveys) represented 35–38% of the workforce. ADHD was assessed with the World Health Organization (WHO) Adult ADHD Self-Report Scale (ASRS), a validated screening scale for DSM-IV adult ADHD. Sickness absence, work performance and workplace accidents-injuries were assessed with the WHO Health and Work Performance Questionnaire (HPQ).
The estimated current prevalence (standard error) of DSM-IV ADHD was 1.9% (0.4). ADHD was associated with a 4–5% reduction in work performance (χ12=9.1, p=0.001), a 2.1 relative-odds of sickness absence (χ12=6.2, p=0.013), and a 2.0 relative-odds of workplace accidents-injuries (χ12=5.1, p=0.024). The human capital value (standard error) of the lost work performance associated with ADHD totaled US$4336 (676) per worker with ADHD in the year before interview. No data were available to monetize other workplace costs of accidents-injuries (e.g. destruction of equipment). Only a small minority of workers with ADHD were in treatment.
Adult ADHD is a significantly impairing condition among workers. Given the low rate of treatment and high human capital costs, in conjunction with evidence from controlled trials that treatment can reduce ADHD-related impairments, ADHD would seem to be a good candidate for workplace trials that evaluate treatment cost-effectiveness from the employer's perspective.
The legal rights of parents with mental illness in the United States vary from state to state. This chapter examines the current federal and state laws in the United States regarding termination of parental rights, custody and visitation in cases involving a parent with mental illness. It provides recommendations for attorneys and advocates who are working with mentally ill parents. Recent studies have indicated that parents who are diagnosed with a mental illness too often lose custody of their children, either to another party or to the state. One study found that 70-80% of parents with mental illness lost custody of their children. Practitioners must keep in mind that cases involving children are the most emotional cases, and assisting parents with maintaining contact and a continued relationship with their child is a much-needed service.
In this paper, we study a class of linear functional differential equations of which the pantograph equation is a prominent member. Specifically, we study the existence of solutions holomorphic at a fixed point of the functional argument. The local theory for equations with attracting fixed points is known [17, 13], but little is known about the case where the fixed point is repelling. We formulate an eigenvalue problem for the repelling fixed point case and show that the corresponding spectrum is discrete. Hence, that holomorphic solutions occur only as special cases. The second order pantograph equation is used to illustrate this result. A key step in this process is to reformulate the problem in terms of a compact operator. Aside from exploiting well known results for the spectra of such operators, we use results such as the Fredholm Alternative to derive existence results for the non-homogeneous problem.
Solutions to a boundary-value problem involving a second-order linear functional differential
equation with an advanced argument are investigated in this paper. The boundary conditions
imposed on the differential equation are analogous to conditions defining various singular
Sturm-Liouville problems, and if an eigenvalue parameter is introduced certain properties of
the spectrum can be deduced having analogues with the classical problem. Dirichlet series
solutions are constructed for the problem and it is established that the spectrum contains
an infinite number of real positive eigenvalues. A Laplace transform analysis of the problem
then reveals that the spectrum does not generically consist of isolated points and that there
may be an infinite number of eigenfunctions corresponding to a given eigenvalue. In contrast,
it is also shown that there is a subset of eigenvalues that correspond to the zeros of an entire
function for which the corresponding eigenfunctions are unique.
This talk summarizes recent work that has been done on cataclysmic variables at Oxford and Cambridge. Full details should be sought elsewhere, either from the authors concerned or from the references given below.
In the Cayman Islands a core of Miocene and Oligocene crystalline limestones is overlain unconformably by limestones of the Pleistocene Ironshore Formation. Within this Formation five separate depositional environments are recognized. A reef facies contains corals still in their growth position. This reef facies is succeeded by a back reef facies, followed by a lagoonal facies. The lagoonal facies contains a diverse molluskan fauna of 75 species which differs considerably from that found in the present lagoons around the island. Rocks of these facies are overlain in places by ridges of calcarenite, considered to be shoal deposits. Higher ridges which overlie the Tertiary limestones and reef facies rocks are interpreted as beach ridges. It is thought that the Pleistocene sediments were deposited around a gradually subsiding core of Tertiary rocks.
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