Maintenance of Androdioecy in the Freshwater Shrimp, Eulimnadia Texana: Field Estimates of Inbreeding Depression and Relative Male Survival

Androdioecy is a rare form of reproduction, only found in a few plant and animal species, wherein males co-exist with hermaphrodites. This particular form of mixed mating (mixtures of outcrossing and self-fertilization) is predicted to be evolutionarily unstable, with most androdioecious populations thought to be in a transition from hermaphroditism to dioecy, or vice versa. One well-studied androdioecious species is the freshwater clam shrimp Eulimnadia texana. A model by Otto et al. (1993), exploring the stability of this androdioecious system, predicts that males can co-exist with hermaphrodites when males fertilize an average of over twice the number of offspring that an average hermaphrodite produces in a lifetime. This value proportionally increases if males survive less well than hermaphrodites, and proportionally decreases with increased inbreeding depression. In the present study, we measured relative male longevity and inbreeding depression using laboratory-produced selfed and outcrossed eggs reared in the field. Males had lower survival than hermaphrodites in both mating treatments, but the survival difference was greater in the outcrossed relative to the selfed mating treatments (19 vs 9% difference). Inbreeding depression (6) was estimated at 0.58-0.69, depending on the level of selfing among the parents in the outcrossed treatments. Both estimates of relative male viability and inbreeding depression corresponded well with earlier laboratory estimates of these parameters. Thus the within-pond dynamics outlined in the model of Otto et al. (1993), which are driven by high inbreeding depression and high relative male fertility, may still explain the maintenance of androdioecy in these shrimp. Field estimates of male mating effectiveness are required as a final test of the accuracy of this model

Bostonia: The Boston University Alumni Magazine. Volume 29

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Description of the fluctuating colloid-polymer interface

To describe the full spectrum of surface fluctuations of the interface between phase-separated colloid-polymer mixtures from low scattering vector q (classical capillary wave theory) to high q (bulk-like fluctuations), one must take account of the interface's bending rigidity. We find that the bending rigidity is negative and that on approach to the critical point it vanishes proportionally to the interfacial tension. Both features are in agreement with Monte Carlo simulations.Comment: 5 pages, 3 figures, 1 table. Accepted for publication in Phys. Rev. Let

Measurements in the ionosphere during a solar eclipse Final report

Electron density and temperature, Lyman beta radiation, and X-ray band measurements during solar eclips

Proof of the thermodynamical stability of the E' center in SiO2

The E' center is a paradigmatic radiation-induced defect in SiO2 whose peculiar EPR and hyperfine activity has been known since over 40 years. This center has been traditionally identified with a distorted, positively-charged oxygen vacancy V_O+. However, no direct proof of the stability of this defect has ever been provided, so that its identification is still strongly incomplete. Here we prove directly that distorted V_O+ is metastable and that it satisfies the key requirements for its identification as E', such as thermal and optical response, and activation-deactivation mechanisms.Comment: RevTeX 4 pages, 2 figure

The Physics of the Colloidal Glass Transition

As one increases the concentration of a colloidal suspension, the system exhibits a dramatic increase in viscosity. Structurally, the system resembles a liquid, yet motions within the suspension are slow enough that it can be considered essentially frozen. This kinetic arrest is the colloidal glass transition. For several decades, colloids have served as a valuable model system for understanding the glass transition in molecular systems. The spatial and temporal scales involved allow these systems to be studied by a wide variety of experimental techniques. The focus of this review is the current state of understanding of the colloidal glass transition. A brief introduction is given to important experimental techniques used to study the glass transition in colloids. We describe features of colloidal systems near and in glassy states, including tremendous increases in viscosity and relaxation times, dynamical heterogeneity, and ageing, among others. We also compare and contrast the glass transition in colloids to that in molecular liquids. Other glassy systems are briefly discussed, as well as recently developed synthesis techniques that will keep these systems rich with interesting physics for years to come.Comment: 56 pages, 18 figures, Revie

Associations between palliative chemotherapy and adult cancer patients’ end of life care and place of death: prospective cohort study

Objectives: To determine whether the receipt of chemotherapy among terminally ill cancer patients months before death was associated with patients’ subsequent intensive medical care and place of death. Design: Secondary analysis of a prospective, multi-institution, longitudinal study of patients with advanced cancer. Setting: Eight outpatient oncology clinics in the United States. Participants: 386 adult patients with metastatic cancers refractory to at least one chemotherapy regimen, whom physicians identified as terminally ill at study enrollment and who subsequently died. Main outcome measures Primary outcomes: intensive medical care (cardiopulmonary resuscitation, mechanical ventilation, or both) in the last week of life and patients’ place of death (for example, intensive care unit). Secondary outcomes: survival, late hospice referrals (≤1 week before death), and dying in preferred place of death. Results: 216 (56%) of 386 terminally ill cancer patients were receiving palliative chemotherapy at study enrollment, a median of 4.0 months before death. After propensity score weighted adjustment, use of chemotherapy at enrollment was associated with higher rates of cardiopulmonary resuscitation, mechanical ventilation, or both in the last week of life (14% v 2%; adjusted risk difference 10.5%, 95% confidence interval 5.0% to 15.5%) and late hospice referrals (54% v 37%; 13.6%, 3.6% to 23.6%) but no difference in survival (hazard ratio 1.11, 95% confidence interval 0.90 to 1.38). Patients receiving palliative chemotherapy were more likely to die in an intensive care unit (11% v 2%; adjusted risk difference 6.1%, 1.1% to 11.1%) and less likely to die at home (47% v 66%; −10.8%, −1.0% to −20.6%), compared with those who were not. Patients receiving palliative chemotherapy were also less likely to die in their preferred place, compared with those who were not (65% v 80%; adjusted risk difference −9.4%, −0.8% to −18.1%). Conclusions: The use of chemotherapy in terminally ill cancer patients in the last months of life was associated with an increased risk of undergoing cardiopulmonary resuscitation, mechanical ventilation or both and of dying in an intensive care unit. Future research should determine the mechanisms by which palliative chemotherapy affects end of life outcomes and patients’ attainment of their goals

Fluctuations in glassy systems

We summarize a theoretical framework based on global time-reparametrization invariance that explains the origin of dynamic fluctuations in glassy systems. We introduce the main ideas without getting into much technical details. We describe a number of consequences arising from this scenario that can be tested numerically and experimentally distinguishing those that can also be explained by other mechanisms from the ones that we believe, are special to our proposal. We support our claims by presenting some numerical checks performed on the 3d Edwards-Anderson spin-glass. Finally, we discuss up to which extent these ideas apply to super-cooled liquids that have been studied in much more detail up to present.Comment: 33 pages, 7 figs, contribution to JSTAT special issue `Principles of Dynamical Systems' work-shop at Newton Institute, Univ. of Cambridge, U