Sedimentation of a two-dimensional colloidal mixture exhibiting liquid-liquid and gas-liquid phase separation: a dynamical density functional theory study

We present dynamical density functional theory results for the time evolution of the density distribution of a sedimenting model two-dimensional binary mixture of colloids. The interplay between the bulk phase behaviour of the mixture, its interfacial properties at the confining walls, and the gravitational field gives rise to a rich variety of equilibrium and non-equilibrium morphologies. In the fluid state, the system exhibits both liquid-liquid and gas-liquid phase separation. As the system sediments, the phase separation significantly affects the dynamics and we explore situations where the final state is a coexistence of up to three different phases. Solving the dynamical equations in two-dimensions, we find that in certain situations the final density profiles of the two species have a symmetry that is different from that of the external potentials, which is perhaps surprising, given the statistical mechanics origin of the theory. The paper concludes with a discussion on this

Hotspots for Initiation of Meiotic Recombination.

Homologous chromosomes must pair and recombine to ensure faithful chromosome segregation during meiosis, a specialized type of cell division that occurs in sexually reproducing eukaryotes. Meiotic recombination initiates by programmed induction of DNA double-strand breaks (DSBs) by the conserved type II topoisomerase-like enzyme SPO11. A subset of meiotic DSBs are resolved as crossovers, whereby reciprocal exchange of DNA occurs between homologous chromosomes. Importantly, DSBs are non-randomly distributed along eukaryotic chromosomes, forming preferentially in permissive regions known as hotspots. In many species, including plants, DSB hotspots are located within nucleosome-depleted regions. DSB localization is governed by interconnected factors, including cis-regulatory elements, transcription factor binding, and chromatin accessibility, as well as by higher-order chromosome architecture. The spatiotemporal control of DSB formation occurs within a specialized chromosomal structure characterized by sister chromatids organized into linear arrays of chromatin loops that are anchored to a proteinaceous axis. Although SPO11 and its partner proteins required for DSB formation are bound to the axis, DSBs occur preferentially within the chromatin loops, which supports the "tethered-loop/axis model" for meiotic recombination. In this mini review, we discuss insights gained from recent efforts to define and profile DSB hotspots at high resolution in eukaryotic genomes. These advances are deepening our understanding of how meiotic recombination shapes genetic diversity and genome evolution in diverse species

Rib Truncations and Fusions in the Sp2HMouse Reveal a Role for Pax3 in Specification of the Ventro-lateral and Posterior Parts of the Somite

AbstractThesplotch (Pax3)mouse mutant serves as a model for developmental defects of several types, including defective migration of dermomyotomal cells to form the limb musculature. Here, we describe abnormalities of the ribs, neural arches, and acromion inSp2Hhomozygous embryos, indicating a widespread dependence of lateral somite development onPax3function. Moreover, the intercostal and body wall muscles, derivatives of the ventrolateral myotome, are also abnormal inSp2Hhomozygotes.Pax3is expressed in the dermomyotome, but not in either the sclerotome or the myotome, raising the possibility thatPax3-dependent inductive influences from the dermomyotome are necessary for early specification of lateral sclerotome and myotome. Support for this idea comes from analysis of gene expression markers of lateral sclerotome (tenascin-Candscleraxis) and myotome (myogenin, MyoD,andMyf5). All exhibit ventrally truncated domains of expression inSp2Hhomozygotes, potentially accounting for the rib and intercostal muscle truncations. In contrast, the medial sclerotomal markerPax1is expressed normally in mutant embryos, arguing thatPax3is not required for development of the medial sclerotome. Most of the somitic markers show ectopic expression in anteroposterior and mediolateral dimensions, suggesting a loss of definition of somite boundaries insplotchand explaining the rib and muscle fusions. An exception isMyf5,which is not ectopically expressed inSp2Hhomozygotes, consistent with the previous suggestion thatPax3andMyf5function in different pathways of skeletal myogenesis. PDGFα and its receptor are candidates for mediating signalling between myotome and sclerotome. We find that both genes are misexpressed inSp2Hembryos, suggesting that PDGFα/PDGFRα may function downstream ofPax3,accounting for the close similarities between thesplotchandPatchmutant phenotypes. Our findings point to additional regulatory functions for the Pax3 transcription factor, apart from those already demonstrated for development of the neural tube, neural crest, and dermomyotome

Mechanisms of HIV Transcriptional Regulation and Their Contribution to Latency

Long-lived latent HIV-infected cells lead to the rebound of virus replication following antiretroviral treatment interruption and present a major barrier to eliminating HIV infection. These latent reservoirs, which include quiescent memory T cells and tissue-resident macrophages, represent a subset of cells with decreased or inactive proviral transcription. HIV proviral transcription is regulated at multiple levels including transcription initiation, polymerase recruitment, transcription elongation, and chromatin organization. How these biochemical processes are coordinated and their potential role in repressing HIV transcription along with establishing and maintaining latency are reviewed

An Enquiry into Using Supplementary Bioscience Resources in Health

The learning and teaching of bioscience subjects has been recognised to be problematic for well over 20-30 years. Various reasons have been suggested but it is evident that better support for learning at least is required. Various strategies have been tried and effective online support looks promising, especially as an aid to help those students who struggle with science and for whom English is not their first language. This project sought to introduce an online module designed to support student self-efficacy on the basics of science that are fundamental to gaining an understanding of more advanced bioscience processes. The module went ‘live’ in February 2013 as a voluntary adjunct to curriculum teaching. Though designed with students in mind the subsequent access has been disappointing and raises questions about the willingness of some students to voluntarily access extracurricular material. This might be a focus for further exploration

An evaluation of the implementation of Georgia's Pre-k program: Report of the findings from the Georgia Early Childhood Study (2002-03)

After ten years, Georgia continues to lead the nation in providing full day, publicly subsidized Pre-K to four-year-olds whose parents choose to enroll them. In this report, we assess the extent to which differences in the way Pre-K is implemented affect children's development. Do teachers with higher levels of education have more positive impacts on children's development? Do teaching styles make a difference in terms of children's outcomes by the end of kindergarten? Do children taught using certain curricula fare better than those taught using others? Answers to questions such as these can assist Pre-K administrators in refining Georgia's program and inform those in other states who are developing or expanding their prekindergarten programs

Thermodynamically consistent description of the hydrodynamics of free surfaces covered by insoluble surfactants of high concentration

In this paper we propose several models that describe the dynamics of liquid films which are covered by a high concentration layer of insoluble surfactant. First, we briefly review the 'classical' hydrodynamic form of the coupled evolution equations for the film height and surfactant concentration that are well established for small concentrations. Then we re-formulate the basic model as a gradient dynamics based on an underlying free energy functional that accounts for wettability and capillarity. Based on this re-formulation in the framework of nonequilibrium thermodynamics, we propose extensions of the basic hydrodynamic model that account for (i) nonlinear equations of state, (ii) surfactant-dependent wettability, (iii) surfactant phase transitions, and (iv) substrate-mediated condensation. In passing, we discuss important differences to most of the models found in the literature.Comment: 31 pages, 2 figure

Parent-to-parent support for parents with children who are deaf or hard of hearing: A conceptual framework

Background: Parent-to-parent support for parents with children who are deaf or hard of hearing (D/HH) is identified as an important component of Early Hearing Detection and Intervention (EHDI) programs for children with hearing loss