Photon quantum entanglement in the MeV regime and its application in PET imaging.

Positron Emission Tomography (PET) is a widely-used imaging modality for medical research and clinical diagnosis. Imaging of the radiotracer is obtained from the detected hit positions of the two positron annihilation photons in a detector array. The image is degraded by backgrounds from random coincidences and in-patient scatter events which require correction. In addition to the geometric information, the two annihilation photons are predicted to be produced in a quantum-entangled state, resulting in enhanced correlations between their subsequent interaction processes. To explore this, the predicted entanglement in linear polarisation for the two photons was incorporated into a simulation and tested by comparison with experimental data from a cadmium zinc telluride (CZT) PET demonstrator apparatus. Adapted apparati also enabled correlation measurements where one of the photons had undergone a prior scatter process. We show that the entangled simulation describes the measured correlations and, through simulation of a larger preclinical PET scanner, illustrate a simple method to quantify and remove the unwanted backgrounds in PET using the quantum entanglement information alone.

Leptonic and charged kaon decay modes of the phi meson measured in heavy-ion collisions at the CERN super proton synchrotron.

We report on results of a measurement of meson production in central Pb-Au collisions at E(lab) = 158A GeV. For the first time in the history of high energy heavy-ion collisions, phi mesons were reconstructed both in the K+K- and the dilepton decay channels in the same experiment. This measurement yields rapidity densities near midrapidity, from the two decay channels, of 2.05 +/- 0.14(stat) +/- 0.25(syst) and 2.04 +/- 0.49(stat) +/- 0.32(syst), respectively. The shape of the measured transverse momentum spectrum is also in close agreement in both decay channels. The data rule out a possible enhancement of the phi yield in the leptonic over the hadronic decay channel of a factor 1.6 or larger at the 95% C.L. This rules out the discrepancy reported in the literature between measurements of the hadronic and dimuon decay channels by two different experiments.

Semihard scattering unraveled from collective dynamics by two-pion azimuthal correlations in 158A GeV/c Pb+Au collisions.

Elliptic flow and two-particle azimuthal correlations of charged hadrons and high-p(T) pions (p(T)>1 GeV/c) have been measured close to midrapidity in 158A GeV/c Pb+Au collisions by the CERES experiment. Elliptic flow (v(2)) rises linearly with p(T) to a value of about 10% at 2 GeV/c. Beyond p(T) approximately 1.5 GeV/c, the slope decreases considerably, possibly indicating a saturation of v(2) at high p(T). Two-pion azimuthal anisotropies for p(T)>1.2 GeV/c exceed the elliptic flow values by about 60% in midcentral collisions. These nonflow contributions are attributed to nearside and back-to-back jetlike correlations, the latter exhibiting centrality dependent broadening.

Enhanced production of low-mass electron-positron pairs in 40-AGeV Pb-Au collisions at the CERN SPS.

We report on first measurements of low-mass electron-positron pairs in Pb-Au collisions at the CERN SPS beam energy of 40 AGeV. The observed pair yield integrated over the range of invariant masses 0.2e(+)e(-) annihilation with a modified rho propagator. They may be linked to chiral symmetry restoration and support the notion that the in-medium modifications of the rho are more driven by baryon density than by temperature.

Universal pion freeze-out in heavy-ion collisions.

Based on an evaluation of data on pion interferometry and on particle yields at midrapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions lambda(f) reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from the Alternating Gradient Synchrotron to the Relativistic Heavy Ion Collider.

Going to extremes: family structure, children's well-being, and social science.

In this article I argue that public discussions of demographic issues are often conducted in a troubling pattern in which one extreme position is debated in relation to the opposite extreme. This pattern impedes our understanding of social problems and is a poor guide to sound public policies. To illustrate this thesis I use the case of social scientific research examining how children are affected by not living with two biological parents while they are growing up. Over the last decade, I maintain, most of the public, and even many social scientists, have been puzzled and poorly informed by this debate. In particular I consider Judith Wallerstein's clinically based claims of the pervasive, profound harm caused by divorce and, at the other extreme, Judith Rich Harris's reading of behavioral genetics and evolutionary psychology, which leads her to dismiss the direct effects of divorce. Neither extreme gives a clear picture of the consequences of growing up in a single-parent family or a stepfamily.

The long-term effects of parental divorce on the mental health of young adults: a developmental perspective.

The effects of parental divorce during childhood and adolescence on the mental health of young adults (age 23) were examined, using the National Child Development Study (NCDS), a longitudinal, multimethod, nationally representative survey of all children born in Great Britain during 1 week in 1958 (N = 17,414). Children were assessed at birth and subsequently followed up at ages 7, 11, 16, and 23 by means of maternal and child interviews, and by psychological, school, and medical assessments. Parental divorce had a moderate, long-term negative impact on adult mental health, as measured by the Malaise Inventory total score, and controlling for economic status, children's emotional problems, and school performance preceding marital dissolution. The likelihood of scoring above the clinical cutoff of the Malaise Inventory rose from 8% to 11% due to parental divorce. This indicated that the relative risk of serious emotional disorders increased in the aftermath of divorce, but that the large majority of individuals did not exhibit such risks. Path analyses revealed that the negative effects of divorce on adult mental health operated indirectly through higher emotional problems and lower levels of school achievement and family economic status at age 16. Results related to timing of divorce, remarriage, and interactions between age 7 emotional problems and divorce, and between age 7 emotional problems and child gender, are also discussed.

Parental divorce in childhood and demographic outcomes in young adulthood.

We investigated the long-term effects of parental divorce in childhood on demographic outcomes in young adulthood, using a British longitudinal national survey of children. Our analyses control for predisruption characteristics of the child and the family, including emotional problems, cognitive achievement, and socioeconomic status. The results show that by age 23, those whose parents divorced were more likely to leave home because of friction, to cohabit, and to have a child outside marriage than were those whose parents did not divorce. Young adults whose parents divorced, however, were no more or less likely to marry or to have a child in a marriage. Moreover, even in the divorced group, the great majority did not leave home because of friction or have a child outside marriage.

Longitudinal studies of effects of divorce on children in Great Britain and the United States.

National, longitudinal surveys from Great Britain and the United States were used to investigate the effects of divorce on children. In both studies, a subsample of children who were in two-parent families during the initial interview (at age 7 in the British data and at ages 7 to 11 in the U.S. data) were followed through the next interview (at age 11 and ages 11 to 16, respectively). At both time points in the British data, parents and teachers independently rated the children's behavior problems, and the children were given reading and mathematics achievement tests. At both time points in the U.S. data, parents rated the children's behavior problems. Children whose parents divorced or separated between the two time points were compared to children whose families remained intact. For boys, the apparent effect of separation or divorce on behavior problems and achievement at the later time point was sharply reduced by considering behavior problems, achievement levels, and family difficulties that were present at the earlier time point, before any of the families had broken up. For girls, the reduction in the apparent effect of divorce occurred to a lesser but still noticeable extent once preexisting conditions were considered.

The weakening link between marriage and the care of children.

Over the last 20 years, the proportion of births that occur to unmarried women has increased dramatically, children are now much more likely to experience the breakup of their parents' marriage, and a much greater proportion of children live at least part of their childhood with only one parent. These changes have occurred predominantly among nonwhites and low-income women and children, but have occurred among whites and higher income women as well. Since these changes have done well-documented damage to children's socioeconomic conditions and prospects, an important issue is whether we can improve children's well-being by strengthening the link between marriage and child care. For a number of reasons, however--cultural, political and economic--the role of public policy is limited. Nevertheless, stronger public support is possible for people who wish to marry or stay married, but who lack the resources to do so. In a nation like Japan, child care is left almost entirely to the family, while in Sweden, the state assumes much of the responsibility; the United States seems to occupy a sort of middle ground. It is likely that U.S. social policy will continue to rely on both the family and the state to care for dependent children, a strategy that implies a continuing tension between public acceptance of changes in family life and public sentiment for a return to older ways.

PIP: Over the last 20 years, the proportion of births that occur to unmarried women has increased dramatically. Children are now much more likely to experience the breakup of their parents' marriage, and a much greater proportion of children live at least part of their childhood with only 1 parent. These changes have occurred predominantly among nonwhites and low-income women and children, but have occurred among whites and higher income women as well. Since these changes have done well-documented damage to children's socioeconomic conditions and prospects, an important issue is whether their well-being can be improved by strengthening the link between marriage and child care. For a number of reasons, however, the role of public policy is limited. Nevertheless, stronger public support is possible for people who wish to marry or stay married, but who lack the resources to do so. In a nation like Japan, child care is left almost entirely to the family, while in Sweden, the state assumes much of the responsibility. The US occupies a sort of middle ground. It is likely that US social policy will continue to rely on both the family and the state to care for dependent children, a strategy that implies a continuing tension between public acceptance of changes in family life and public sentiment for a return to older ways.

The changing European family: lessons for the American reader.

PIP: The 7 chapters in this journal discuss the European family, including families in Britain, the Federal Republic of Germany, France, the German Democratic Republic, Italy, and Sweden. The authors feel that observers in the US sometimes resort to peculiarly American explanations (the budget deficit, changes in welfare benefits) to account for recent trends in marriage and fertility. The articles in this issue demonstrate that the pattern of post-WWII family change has been generally similar in North America, Western Europe, and even part of Eastern Europe, suggesting that more global rather than particular national explanations need to be sought. The post-WWII years can be divided into 2 periods: 1) the period from 1945 to 1965 that brought the unexpected marriage rush and baby boom, and 2) the period from 1965 to the present that brought a reversal of those trends in the form of later marriage, a great increase in nonmarital cohabitation, a large rise in divorce, and a sharp fall in fertility to below the replacement level. The similarity of these large-scale trends in North America and Western Europe is striking. The US is most like Britain and, beyond Europe, Canada, and Australia, suggesting that influence of the common culture of the English-speaking Western world. Yet the US has, and probably always has had, higher rates of fertility, marriage, and divorce than most Western European nations. The proportion of single-parent families is unusually large, even though some nations such as Sweden and East Germany have higher proportions of births to unmarried but cohabiting women. The level of cohabitation in the US, although greatly increased, is still moderate by European standards. Concern over the burden of government support for the elderly already has prompted changes in the Social Security program. The ability to support programs for children and for poor families is being questioned, even though the level of government support for the family is relatively low by Western standards. Concern about the below-replacement birth rate is just beginning to emerge. For American as well as European readers, the major question left unanswered by the accounts presented in this issue is whether the continuing changes will lead to a greater degree of convergence in the future or to an elaboration of current variations on the Western theme. The former possibility would likely imply a massive erosion of marriage and radical change in the division of labor. The latter would still encompass substantial similarities (generally low fertility, increasing proportions of women in the labor force), but with important differences of historical, cultural, and political origin.^ieng

Variations in marriage patterns in central Thailand.

Data from a survey of marriage patterns in central Thailand illustrate the complexity of change in marriage patterns in a developing society--the diversity of traditional patterns, the different directions of change, and the variations in current patterns. The data were collected in 1978 and 1979 from ever-married women aged 15-44 in three settings:a central plains village, established areas in Bangkok, and a Bangkok squatter settlement. Three forms of entry into marriage were identified:ceremonial marriage with parental involvement in the choice of spouse, ceremonial marriage with self-choice of spouse, and nonceremonial marriage (elopement and living together). All three forms of marriage existed in each setting, and the dominant form differed in each. In general, a family background of higher socioeconomic status led to a greater likelihood of a marriage ceremony and greater parental involvement in spouse choice. Women with more education were also more likely to marry with ceremony, but higher education for daughters was associated with less parental involvement in spouse choice. These findings suggest that marriage patterns may remain diverse in Thailand, even as further development occurs.

A note on maritally-disrupted men's reports of child support in the June 1980 Current Population Survey.

Data from the June 1980 Current Population Survey on fathers' reported provision of financial support to children from previous marriages living elsewhere is compared to previously published tabulations from the April 1979 CPS of women's receipt of child support payments. The comparison indicates that the number of men with children from previous marriages living elsewhere is substantially underreported in the June 1980 CPS. Because of the apparent underreporting, the data on the provision of financial support should be interpreted with caution.

Changing family and household: contemporary lessons from historical research.

"This essay examines the recent historical research on the family with the objective of identifying useful lessons for students of the contemporary family. The following themes in the historical research are discussed: household and family structure, production and reproduction, life course transitions, the emotional content of family life, and the distinctiveness of the 1950s. The essay concludes with a discussion of theoretical and methodological issues in historical research on the family." The primary geographic focus is on the United States and other developed countries.

The effect of children on marital dissolution.

The relationship between the presence of children and divorce and separation is examined using data from the first four years of the National Longitudinal Surveys of Labor Market Experience in Women Aged 30 to 44. The data show that children were a deterrent to separation and divorce only when they were in the preschool ages. Once all the children in a family were in school, they did not seem to influence the probability of separation and divorce. It is suggested that the high costs of child care for preschool children, in terms of time, money, and effort, act as a deterrent to marital dissolution. The associations between several other social demographic variables and marital dissolution also are investigated.