The Properties of Prestellar Discs in Isolated and Multiple Prestellar Systems

We present high-resolution 3D smoothed particle hydrodynamics simulations of the formation and evolution of protostellar discs in a turbulent molecular cloud. Using a piecewise polytropic equation of state, we perform two sets of simulations. In both cases we find that isolated systems undergo a fundamentally different evolution than members of binary or multiple systems. When formed, isolated systems must accrete mass and increase their specific angular momentum, leading to the formation of massive, extended discs, which undergo strong gravitational instabilities and are susceptible to disc fragmentation. Fragments with initial masses of 5.5 M_jup, 7.4 M_jup and 12 M_jup are produced in our simulations. In binaries and small clusters, we observe that due to competition for material from the parent core, members do not accrete significant amounts of high specific angular momentum gas relative to isolated systems. We find that discs in multiple systems are strongly self-gravitating but that they are stable against fragmentation due to disc truncation and mass profile steeping by tides, accretion of high specific angular momentum gas by other members, and angular momentum being redirected into members' orbits. In general, we expect disc fragmentation to be less likely in clusters and to be more a feature of isolated systems.Comment: 15 pages, 21 figures. Accepted for publication in MNRA

Orthographic facilitation in oral vocabulary acquisition

An experiment investigated whether exposure to orthography facilitates oral vocabulary learning. A total of 58 typically developing children aged 8-9 years were taught 12 nonwords. Children were trained to associate novel phonological forms with pictures of novel objects. Pictures were used as referents to represent novel word meanings. For half of the nonwords children were additionally exposed to orthography, although they were not alerted to its presence, nor were they instructed to use it. After this training phase a nonword-picture matching posttest was used to assess learning of nonword meaning, and a spelling posttest was used to assess learning of nonword orthography. Children showed robust learning for novel spelling patterns after incidental exposure to orthography. Further, we observed stronger learning for nonword-referent pairings trained with orthography. The degree of orthographic facilitation observed in posttests was related to children's reading levels, with more advanced readers showing more benefit from the presence of orthography

CCR5AS lncRNA variation differentially regulates CCR5, influencing HIV disease outcome.

Multiple genome-wide studies have identified associations between outcome of human immunodeficiency virus (HIV) infection and polymorphisms in and around the gene encoding the HIV co-receptor CCR5, but the functional basis for the strongest of these associations, rs1015164A/G, is unknown. We found that rs1015164 marks variation in an activating transcription factor 1 binding site that controls expression of the antisense long noncoding RNA (lncRNA) CCR5AS. Knockdown or enhancement of CCR5AS expression resulted in a corresponding change in CCR5 expression on CD4+ T cells. CCR5AS interfered with interactions between the RNA-binding protein Raly and the CCR5 3' untranslated region, protecting CCR5 messenger RNA from Raly-mediated degradation. Reduction in CCR5 expression through inhibition of CCR5AS diminished infection of CD4+ T cells with CCR5-tropic HIV in vitro. These data represent a rare determination of the functional importance of a genome-wide disease association where expression of a lncRNA affects HIV infection and disease progression

Subharmonic Resonance Stability Prediction for Turbomachinery with Active Magnetic Bearings

Cd. (mm) as the diametrical clearance and a diameter D (m) the equivalent Damping number can be written as, X WniiLoDiL^/Oy CM - (cjoy (2) The usefulness and application of the Damping Number (Cf/) is explained in the following discussion. Consider the plot of growth factor vs. the retainer stiffness for, say, a clearance ratio of 3.25 mm/m, with a damper radius of 177.8 mm (7 in.) and a single land 76.2 mm (3 in.) wide. To obtain the same stability for a different L/D ratio, the new clearance ratio can be calculated using the Damping Number. For example, if the same damper stiffness as the above configuration is desired in a damper with 2 lands, each 38.1 mm (1.5 in.) wide, the new clearance can be calculated as explained below. Let, Li, L2 = land widths of the first and the second damper, respectively, (m) «i, n2 = number of lands on the first and the second damper, respectively Crfi. Cdi = diametrical clearance of the first and the second damper, (mm) Di, D2 = diameter of the first and second the damper, (m) Assuming the same effective viscosity and operating speed, For the above example, Z^ = LJ2 and rix = 1, «2 = 2 and Di = D2. Using these values we obtain the new equivalent clearance ratio to be 2.0 mm/m. This gives an example of the usefulness of the Damping Number. Hence, for a given rotor configuration, if one set of plots of stability vs. retainer stiffness (as in The results generated for the stability of the rotor supported on a squeeze film damper with a single land of 76.2 mm (3 in.) wide, are applicable to other configurations of the damper, and need not be generated again. For the above example, where the new damper had 2 lands each of width 38.1 mm (1.5 in.), the lowest point on the plot in Conclusions 1. For a given rotor, the above design procedure can be adopted to obtain different configurations of the damper, and the stability analysis need be performed only for one configuration. 2. For a given retainer stiffness, the clearance of the damper can be optimized (see 3. Increasing the operating eccentricity ratio decreases the stability of the rotor, for a given centered damper optimum clearance (see 4. For a given rotor configuration, the changes in the parameters of the damper, viz., the land and clearance, can be determined by using the Damping Number (see Eq. 5. In general, the stability of the rotor can be improved by using a squeeze film damper, but care has to be taken in designing the damper, as it is very sensitive to changes in the clearances, operating eccentricity ratio, and nonlinear hardening retainer stiffness characteristics. Introduction Bearing seizure is a form of instability that drives a system to rapidly lose its operating clearance, thus leading to a catastrophic failure. Most susceptible to this type of failure mode are bearings with inadequate lubrication which, particularly during the start-up period, experience an excessive amount of frictional heat generation as a result of (nearly) dry rubbing. Analyses pertaining to this form of seizure have been the subject of a number of research papers. See for example, To gain insight into the seizure phenomenon, a simple model is developed that allows one to establish a relationship between the key parameters that influence the seizure time in a hydrodynamic bearing. For this purpose, the journal bearing system is represented by two concentric cylinders with the inner cylinde

Physics at a Neutrino Factory

In response to the growing interest in building a Neutrino Factory to produce high intensity beams of electron- and muon-neutrinos and antineutrinos, in October 1999 the Fermilab Directorate initiated two six-month studies. The first study, organized by N. Holtkamp and D. Finley, was to investigate the technical feasibility of an intense neutrino source based on a muon storage ring. This design study has produced a report in which the basic conclusion is that a Neutrino Factory is technically feasible, although it requires an aggressive R&D program. The second study, which is the subject of this report, was to explore the physics potential of a Neutrino Factory as a function of the muon beam energy and intensity, and for oscillation physics, the potential as a function of baseline.Comment: 133 pages, 64 figures. Report to the Fermilab Directorate. Available from http://www.fnal.gov/projects/muon_collider/ This version fixes some printing problem

Role of Exonic Variation in Chemokine Receptor Genes on AIDS: CCRL2 F167Y Association with Pneumocystis Pneumonia

Chromosome 3p21–22 harbors two clusters of chemokine receptor genes, several of which serve as major or minor coreceptors of HIV-1. Although the genetic association of CCR5 andCCR2 variants with HIV-1 pathogenesis is well known, the role of variation in other nearby chemokine receptor genes remain unresolved. We genotyped exonic single nucleotide polymorphisms (SNPs) in chemokine receptor genes: CCR3, CCRL2, and CXCR6 (at 3p21) and CCR8 and CX3CR1 (at 3p22), the majority of which were non-synonymous. The individual SNPs were tested for their effects on disease progression and outcomes in five treatment-naïve HIV-1/AIDS natural history cohorts. In addition to the known CCR5 and CCR2associations, significant associations were identified for CCR3, CCR8, and CCRL2 on progression to AIDS. A multivariate survival analysis pointed to a previously undetected association of a non-conservative amino acid change F167Y in CCRL2 with AIDS progression: 167F is associated with accelerated progression to AIDS (RH = 1.90, P = 0.002, corrected). Further analysis indicated that CCRL2-167F was specifically associated with more rapid development of pneumocystis pneumonia (PCP) (RH = 2.84, 95% CI 1.28–6.31) among four major AIDS–defining conditions. Considering the newly defined role of CCRL2 in lung dendritic cell trafficking, this atypical chemokine receptor may affect PCP through immune regulation and inducing inflammation

Regulatory Polymorphisms in the Cyclophilin A Gene, PPIA, Accelerate Progression to AIDS

Human cyclophilin A, or CypA, encoded by the gene peptidyl prolyl isomerase A (PPIA), is incorporated into the HIV type 1 (HIV-1) virion and promotes HIV-1 infectivity by facilitating virus uncoating. We examined the effect of single nucleotide polymorphisms (SNPs) and haplotypes within the PPIA gene on HIV-1 infection and disease progression in five HIV-1 longitudinal history cohorts. Kaplan-Meier survival statistics and Cox proportional hazards model were used to assess time to AIDS outcomes. Among eight SNPs tested, two promoter SNPs (SNP3 and SNP4) in perfect linkage disequilibrium were associated with more rapid CD4+ T-cell loss (relative hazard = 3.7, p = 0.003) in African Americans. Among European Americans, these alleles were also associated with a significant trend to more rapid progression to AIDS in a multi-point categorical analysis (p = 0.005). Both SNPs showed differential nuclear protein-binding efficiencies in a gel shift assay. In addition, one SNP (SNP5) located in the 5′ UTR previously shown to be associated with higher ex vivo HIV-1 replication was found to be more frequent in HIV-1-positive individuals than in those highly exposed uninfected individuals. These results implicate regulatory PPIA polymorphisms as a component of genetic susceptibility to HIV-1 infection or disease progression, affirming the important role of PPIA in HIV-1 pathogenesis

Effects of human TRIM5α polymorphisms on antiretroviral function and susceptibility to human immunodeficiency virus infection

AbstractTRIM5α acts on several retroviruses, including human immunodeficiency virus (HIV-1), to restrict cross-species transmission. Using natural history cohorts and tissue culture systems, we examined the effect of polymorphism in human TRIM5α on HIV-1 infection. In African Americans, the frequencies of two non-coding SNP variant alleles in exon 1 and intron 1 of TRIM5 were elevated in HIV-1-infected persons compared with uninfected subjects. By contrast, the frequency of the variant allele encoding TRIM5α 136Q was relatively elevated in uninfected individuals, suggesting a possible protective effect. TRIM5α 136Q protein exhibited slightly better anti-HIV-1 activity in tissue culture than the TRIM5α R136 protein. The 43Y variant of TRIM5α was less efficient than the H43 variant at restricting HIV-1 and murine leukemia virus infections in cultured cells. The ancestral TRIM5 haplotype specifying no observed variant alleles appeared to be protective against infection, and the corresponding wild-type protein partially restricted HIV-1 replication in vitro. A single logistic regression model with a permutation test indicated the global corrected P value of <0.05 for both SNPs and haplotypes. Thus, polymorphism in human TRIM5 may influence susceptibility to HIV-1 infection, a possibility that merits additional evaluation in independent cohorts

Evolution of reproductive development in the volvocine algae

The evolution of multicellularity, the separation of germline cells from sterile somatic cells, and the generation of a male–female dichotomy are certainly among the greatest innovations of eukaryotes. Remarkably, phylogenetic analysis suggests that the shift from simple to complex, differentiated multicellularity was not a unique progression in the evolution of life, but in fact a quite frequent event. The spheroidal green alga Volvox and its close relatives, the volvocine algae, span the full range of organizational complexity, from unicellular and colonial genera to multicellular genera with a full germ–soma division of labor and male–female dichotomy; thus, these algae are ideal model organisms for addressing fundamental issues related to the transition to multicellularity and for discovering universal rules that characterize this transition. Of all living species, Volvox carteri represents the simplest version of an immortal germline producing specialized somatic cells. This cellular specialization involved the emergence of mortality and the production of the first dead ancestors in the evolution of this lineage. Volvocine algae therefore exemplify the evolution of cellular cooperation from cellular autonomy. They also serve as a prime example of the evolution of complex traits by a few successive, small steps. Thus, we learn from volvocine algae that the evolutionary transition to complex, multicellular life is probably much easier to achieve than is commonly believed