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Sample records for drive neutralization escape

  1. An antibody tag-team: driving neutralization through escape.

    PubMed

    Alter, Galit; Ackerman, Margaret E

    2014-09-01

    HIV rapidly mutates to escape antibody detection, and B cells counter this mutation by continual evolution to restore recognition, serendipitously resulting in the evolution of neutralizing activity in a fraction of infected individuals. A recent Cell paper describes how antibody repertoires stochastically collaborated, shaping the viral swarm and utilizing viral immune evasion to their advantage. Copyright © 2014. Published by Elsevier Ltd.

  2. Viral Escape from HIV-1 Neutralizing Antibodies Drives Increased Plasma Neutralization Breadth through Sequential Recognition of Multiple Epitopes and Immunotypes

    PubMed Central

    Wibmer, Constantinos Kurt; Bhiman, Jinal N.; Gray, Elin S.; Tumba, Nancy; Abdool Karim, Salim S.; Williamson, Carolyn; Morris, Lynn; Moore, Penny L.

    2013-01-01

    Identifying the targets of broadly neutralizing antibodies to HIV-1 and understanding how these antibodies develop remain important goals in the quest to rationally develop an HIV-1 vaccine. We previously identified a participant in the CAPRISA Acute Infection Cohort (CAP257) whose plasma neutralized 84% of heterologous viruses. In this study we showed that breadth in CAP257 was largely due to the sequential, transient appearance of three distinct broadly neutralizing antibody specificities spanning the first 4.5 years of infection. The first specificity targeted an epitope in the V2 region of gp120 that was also recognized by strain-specific antibodies 7 weeks earlier. Specificity for the autologous virus was determined largely by a rare N167 antigenic variant of V2, with viral escape to the more common D167 immunotype coinciding with the development of the first wave of broadly neutralizing antibodies. Escape from these broadly neutralizing V2 antibodies through deletion of the glycan at N160 was associated with exposure of an epitope in the CD4 binding site that became the target for a second wave of broadly neutralizing antibodies. Neutralization by these CD4 binding site antibodies was almost entirely dependent on the glycan at position N276. Early viral escape mutations in the CD4 binding site drove an increase in wave two neutralization breadth, as this second wave of heterologous neutralization matured to recognize multiple immunotypes within this site. The third wave targeted a quaternary epitope that did not overlap any of the four known sites of vulnerability on the HIV-1 envelope and remains undefined. Altogether this study showed that the human immune system is capable of generating multiple broadly neutralizing antibodies in response to a constantly evolving viral population that exposes new targets as a consequence of escape from earlier neutralizing antibodies. PMID:24204277

  3. Complete mapping of viral escape from neutralizing antibodies

    PubMed Central

    Hensley, Scott E.

    2017-01-01

    Identifying viral mutations that confer escape from antibodies is crucial for understanding the interplay between immunity and viral evolution. We describe a high-throughput approach to quantify the selection that monoclonal antibodies exert on all single amino-acid mutations to a viral protein. This approach, mutational antigenic profiling, involves creating all replication-competent protein variants of a virus, selecting with antibody, and using deep sequencing to identify enriched mutations. We use mutational antigenic profiling to comprehensively identify mutations that enable influenza virus to escape four monoclonal antibodies targeting hemagglutinin, and validate key findings with neutralization assays. We find remarkable mutation-level idiosyncrasy in antibody escape: for instance, at a single residue targeted by two antibodies, some mutations escape both antibodies while other mutations escape only one or the other. Because mutational antigenic profiling rapidly maps all mutations selected by an antibody, it is useful for elucidating immune specificities and interpreting the antigenic consequences of viral genetic variation. PMID:28288189

  4. Flexibility in surface-exposed loops in a virus capsid mediates escape from antibody neutralization.

    PubMed

    Kolawole, Abimbola O; Li, Ming; Xia, Chunsheng; Fischer, Audrey E; Giacobbi, Nicholas S; Rippinger, Christine M; Proescher, Jody B G; Wu, Susan K; Bessling, Seneca L; Gamez, Monica; Yu, Chenchen; Zhang, Rebecca; Mehoke, Thomas S; Pipas, James M; Wolfe, Joshua T; Lin, Jeffrey S; Feldman, Andrew B; Smith, Thomas J; Wobus, Christiane E

    2014-04-01

    virion/antibody complex identifies two conformations of the antibody binding domain of the viral capsid: one with a superior fit and the other with an inferior fit to the antibody. These data suggest a unique mode of antibody neutralization. In contrast to other viruses that largely escape antibody neutralization through direct disruption of the antibody-virus interface, we identify mutations that acted indirectly by limiting the conformation of the antibody binding loop in the viral capsid and drive the antibody binding domain into the conformation unable to be bound by the antibody.

  5. Neutral-beam current drive in tokamaks

    SciTech Connect

    Devoto, R.S.

    1986-01-01

    The theory of neutral-beam current drive in tokamaks is reviewed. Experiments are discussed where neutral beams have been used to drive current directly and also indirectly through neoclassical effects. Application of the theory to an experimental test reactor is described. It is shown that neutral beams formed from negative ions accelerated to 500 to 700 keV are needed for this device.

  6. Escape from neutralization by the respiratory syncytial virus-specific neutralizing monoclonal antibody palivizumab is driven by changes in on-rate of binding to the fusion protein.

    PubMed

    Bates, John T; Keefer, Christopher J; Slaughter, James C; Kulp, Daniel W; Schief, William R; Crowe, James E

    2014-04-01

    The role of binding kinetics in determining neutralizing potency for antiviral antibodies is poorly understood. While it is believed that increased steady-state affinity correlates positively with increased virus-neutralizing activity, the relationship between association or dissociation rate and neutralization potency is unclear. We investigated the effect of naturally-occurring antibody resistance mutations in the RSV F protein on the kinetics of binding to palivizumab. Escape from palivizumab-mediated neutralization of RSV occurred with reduced association rate (Kon) for binding to RSV F protein, while alteration of dissociation rate (Koff) did not significantly affect neutralizing activity. Interestingly, linkage of reduced Kon with reduced potency mirrored the effect of increased Kon found in a high-affinity enhanced potency palivizumab variant (motavizumab). These data suggest that association rate is the dominant factor driving neutralization potency for antibodies to RSV F protein antigenic site A and determines the potency of antibody somatic variants or efficiency of escape of viral glycoprotein variants.

  7. Power threshold for neutral beam current drive

    SciTech Connect

    Politzer, P.A. ); Porter, G.D. )

    1989-10-02

    For fully noninductive current drive in tokamaks using neutral beams, there is a power and density threshold condition, setting a minimum value for P{sup 3/2}/n{sup 2}. If this condition is not met, stationary state cannot occur, and a tokamak discharge will collapse. This is a consequence of the coupling between current and electron temperature, or between current drive efficiency and energy confinement time. 4 figs.

  8. Escape from neutralization by the respiratory syncytial virus-specific neutralizing monoclonal antibody palivizumab is driven by changes in on-rate of binding to the fusion protein

    SciTech Connect

    Bates, John T.; Keefer, Christopher J.; Slaughter, James C.; Kulp, Daniel W.; Schief, William R.

    2014-04-15

    The role of binding kinetics in determining neutralizing potency for antiviral antibodies is poorly understood. While it is believed that increased steady-state affinity correlates positively with increased virus-neutralizing activity, the relationship between association or dissociation rate and neutralization potency is unclear. We investigated the effect of naturally-occurring antibody resistance mutations in the RSV F protein on the kinetics of binding to palivizumab. Escape from palivizumab-mediated neutralization of RSV occurred with reduced association rate (K{sub on}) for binding to RSV F protein, while alteration of dissociation rate (K{sub off}) did not significantly affect neutralizing activity. Interestingly, linkage of reduced K{sub on} with reduced potency mirrored the effect of increased K{sub on} found in a high-affinity enhanced potency palivizumab variant (motavizumab). These data suggest that association rate is the dominant factor driving neutralization potency for antibodies to RSV F protein antigenic site A and determines the potency of antibody somatic variants or efficiency of escape of viral glycoprotein variants. - Highlights: • The relationship of affinity to neutralization for virus antibodies is uncertain. • Palivizumab binds to RSV escape mutant fusion proteins, but with reduced affinity. • Association rate (K{sub on}) correlated well with the potency of neutralization.

  9. Escape From Monoclonal Antibody Neutralization Affects Henipavirus Fitness In Vitro and In Vivo

    PubMed Central

    Borisevich, Viktoriya; Lee, Benhur; Hickey, Andrew; DeBuysscher, Blair; Broder, Christopher C.; Feldmann, Heinz; Rockx, Barry

    2016-01-01

    Henipaviruses are zoonotic viruses that can cause severe and acute respiratory diseases and encephalitis in humans. To date, no vaccine or treatments are approved for human use. The presence of neutralizing antibodies is a strong correlate of protection against lethal disease in animals. However, since RNA viruses are prone to high mutation rates, the possibility that these viruses will escape neutralization remains a potential concern. In the present study, we generated neutralization-escape mutants, using 6 different monoclonal antibodies, and studied the effect of these neutralization-escape mutations on in vitro and in vivo fitness. These data provide a mechanism for overcoming neutralization escape by use of cocktails of cross-neutralizing monoclonal antibodies that recognize residues within the glycoprotein that are important for virus replication and virulence. PMID:26357909

  10. Escape From Monoclonal Antibody Neutralization Affects Henipavirus Fitness In Vitro and In Vivo.

    PubMed

    Borisevich, Viktoriya; Lee, Benhur; Hickey, Andrew; DeBuysscher, Blair; Broder, Christopher C; Feldmann, Heinz; Rockx, Barry

    2016-02-01

    Henipaviruses are zoonotic viruses that can cause severe and acute respiratory diseases and encephalitis in humans. To date, no vaccine or treatments are approved for human use. The presence of neutralizing antibodies is a strong correlate of protection against lethal disease in animals. However, since RNA viruses are prone to high mutation rates, the possibility that these viruses will escape neutralization remains a potential concern. In the present study, we generated neutralization-escape mutants, using 6 different monoclonal antibodies, and studied the effect of these neutralization-escape mutations on in vitro and in vivo fitness. These data provide a mechanism for overcoming neutralization escape by use of cocktails of cross-neutralizing monoclonal antibodies that recognize residues within the glycoprotein that are important for virus replication and virulence.

  11. New insights on the collisional escape of light neutrals from Mars

    NASA Astrophysics Data System (ADS)

    Gacesa, Marko; Zahnle, Kevin

    2017-04-01

    Photodissociative recombination (PDR) of atmospheric molecules on Mars is a major mechanism of production of hot (suprathermal) atoms with sufficient kinetic energy to either directly escape to space or to eject other atmospheric species. This collisional ejection mechanism is important for evaluating the escape rates of all light neutrals that are too heavy to escape via Jeans escape. In particular, it plays a role in estimating the total volume of escaped water constituents (i.e., O and H) from Mars, as well as influences evolution of the atmospheric [D]/[H] ratio1. We present revised estimates of total collisional escape rates of neutral light elements including H, He, and H2, based on recent (years 2015-2016) atmospheric density profiles obtained from the NASA Mars Atmosphere and Volatile Evolution (MAVEN) mission. We also estimate the contribution to the collisional escape from Energetic Neutral Atoms (ENAs) produced in charge-exchange of solar wind H+ and He+ ions with atmospheric gases2,3. Scattering of hot oxygen and atmospheric species of interest is modeled using fully-quantum reactive scattering formalism1,3. The escape rates are evaluated using a 1D model of the atmosphere supplemented with MAVEN measurements of the neutrals. Finally, new estimates of contributions of these non-thermal mechanisms to the estimated PDR escape rates from young Mars4 are presented. [1] M. Gacesa and V. Kharchenko, "Non-thermal escape of molecular hydrogen from Mars", Geophys. Res. Lett., 39, L10203 (2012). [2] N. Lewkow and V. Kharchenko, "Precipitation of Energetic Neutral Atoms and Escape Fluxes induced from the Mars Atmosphere", Astroph. J., 790, 98 (2014). [3] M. Gacesa, N. Lewkow, and V. Kharchenko, "Non-thermal production and escape of OH from the upper atmosphere of Mars", Icarus 284, 90 (2017). [4] J. Zhao, F. Tian, Y. Ni, and X. Huang, "DR-induced escape of O and C from early Mars", Icarus 284, 305 (2017).

  12. Generation of Escape Variants of Neutralizing Influenza Virus Monoclonal Antibodies.

    PubMed

    Leon, Paul E; Wohlbold, Teddy John; He, Wenqian; Bailey, Mark J; Henry, Carole J; Wilson, Patrick C; Krammer, Florian; Tan, Gene S

    2017-08-29

    Influenza viruses exhibit a remarkable ability to adapt and evade the host immune response. One way is through antigenic changes that occur on the surface glycoproteins of the virus. The generation of escape variants is a powerful method in elucidating how viruses escape immune detection and in identifying critical residues required for antibody binding. Here, we describe a protocol on how to generate influenza A virus escape variants by utilizing human or murine monoclonal antibodies (mAbs) directed against the viral hemagglutinin (HA). With the use of our technique, we previously characterized critical residues required for the binding of antibodies targeting either the head or stalk of the novel avian H7N9 HA. The protocol can be easily adapted for other virus systems. Analyses of escape variants are important for modeling antigenic drift, determining single nucleotide polymorphisms (SNPs) conferring resistance and virus fitness, and in the designing of vaccines and/or therapeutics.

  13. JC polyomavirus mutants escape antibody-mediated neutralization.

    PubMed

    Ray, Upasana; Cinque, Paola; Gerevini, Simonetta; Longo, Valeria; Lazzarin, Adriano; Schippling, Sven; Martin, Roland; Buck, Christopher B; Pastrana, Diana V

    2015-09-23

    JC polyomavirus (JCV) persistently infects the urinary tract of most adults. Under conditions of immune impairment, JCV causes an opportunistic brain disease, progressive multifocal leukoencephalopathy (PML). JCV strains found in the cerebrospinal fluid of PML patients contain distinctive mutations in surface loops of the major capsid protein, VP1. We hypothesized that VP1 mutations might allow the virus to evade antibody-mediated neutralization. Consistent with this hypothesis, neutralization serology revealed that plasma samples from PML patients neutralized wild-type JCV strains but failed to neutralize patient-cognate PML-mutant JCV strains. This contrasted with serological results for healthy individuals, most of whom robustly cross-neutralized all tested JCV variants. Mice administered a JCV virus-like particle (VLP) vaccine initially showed neutralizing "blind spots" (akin to those observed in PML patients) that closed after booster immunization. A PML patient administered an experimental JCV VLP vaccine likewise showed markedly increased neutralizing titer against her cognate PML-mutant JCV. The results indicate that deficient humoral immunity is a common aspect of PML pathogenesis and that vaccination may overcome this humoral deficiency. Thus, vaccination with JCV VLPs might prevent the development of PML.

  14. Mechanisms of equine infectious anemia virus escape from neutralizing antibody responses define epitope specificity.

    PubMed

    Sponseller, Brett A; Clark, Sandra K; Friedrich, Rachel A

    2012-08-01

    Determining mechanisms of viral escape to particular epitopes recognized by virus-neutralizing antibody can facilitate characterization of host-neutralizing antibody responses as type- versus group-specific, and provides necessary information for vaccine development. Our study reveals that a single N-glycan located in the 5' region of the Wyoming wild-type equine infectious anemia virus (EIAV) principal neutralizing domain (PND) accounts for the differences in neutralization phenotype observed between PND variants, while variations in charged amino acids within the PND do not appear to play a key role in viral escape. Site-directed mutagenesis and peptide mapping of a conserved epitope to neutralizing antibody in the 3' region of the PND showed rapid selective pressure for acquisition of a 5' PND N-glycan responsible for defining the specificity of the neutralizing-antibody response.

  15. CD4 binding site broadly neutralizing antibody selection of HIV-1 escape mutants.

    PubMed

    Dreja, Hanna; Pade, Corinna; Chen, Lei; McKnight, Áine

    2015-07-01

    All human immunodeficiency virus type-1 (HIV-1) viruses use CD4 to enter cells. Consequently, the viral envelope CD4-binding site (CD4bs) is relatively conserved, making it a logical neutralizing antibody target. It is important to understand how CD4-binding site variation allows for escape from neutralizing antibodies. Alanine scanning mutagenesis identifies residues in antigenic sites, whereas escape mutant selection identifies viable mutants. We selected HIV-1 to escape CD4bs neutralizing mAbs b12, A12 and HJ16. Viruses that escape from A12 and b12 remained susceptible to HJ16, VRC01 and J3, whilst six different viruses that escape HJ16 remained sensitive to A12, b12 and J3. In contrast, their sensitivity to VRC01 was variable. Triple HJ16/A12/b12-resistant virus proved that HIV-1 could escape multiple broadly neutralizing monoclonal antibodies, but still retain sensitivity to VRC01 and the llama-derived J3 nanobody. This antigenic variability may reflect that occurring in circulating viruses, so studies like this can predict immunologically relevant antigenic forms of the CD4bs for inclusion in HIV-1 vaccines.

  16. Distribution and escape of the major neutral species from Titan's atmosphere

    NASA Astrophysics Data System (ADS)

    Tenishev, Valeriy; Tucker, Orenthal; Borovikov, Dmitry; Combi, Michael R.

    2016-10-01

    Titan possesses the most significant atmosphere among all satellites in the Solar system, and is an important source of material for the Saturn's magnetosphere. Understanding of the neutral species distribution and escape is important for further understanding of the Titan's atmosphere evolution and loss.The first in situ observations of the Titan's atmosphere were performed by Voyager and continued by Cassini, which measured the atmospheric composition, velocity and temperature, as well as the energy spectra of neutral species, ions and electrons. Analysis and interpretation of the acquired data involves coupled modeling of the Saturn magnetosphere and Titan's atmosphere.Having that in mind we have undertaken numerical modeling of the major neutral species (N2 and CH4) in Titan's upper atmosphere to investigate the effect of the solar EUV and magnetospheric ion energy deposition on the neutral species atmospheric distribution and escape. This modeling combines MHD simulation of the Saturn's magnetosphere plasma interacting with Titan's atmosphere, fluid type simulation of the neutral species in Titan's lower atmosphere, and kinetic modeling of the upper atmosphere and exosphere. Here we present estimations of the neutral species escape rate, and discuss the effect of the magnetospheric ion energy deposition on the atmospheric escape concluded from the results of our modeling.This work was supported by NASA Outer Planet Research grant NNX13AL04G.

  17. Emergent neutrality drives phytoplankton species coexistence

    PubMed Central

    Segura, Angel M.; Calliari, Danilo; Kruk, Carla; Conde, Daniel; Bonilla, Sylvia; Fort, Hugo

    2011-01-01

    The mechanisms that drive species coexistence and community dynamics have long puzzled ecologists. Here, we explain species coexistence, size structure and diversity patterns in a phytoplankton community using a combination of four fundamental factors: organism traits, size-based constraints, hydrology and species competition. Using a ‘microscopic’ Lotka–Volterra competition (MLVC) model (i.e. with explicit recipes to compute its parameters), we provide a mechanistic explanation of species coexistence along a niche axis (i.e. organismic volume). We based our model on empirically measured quantities, minimal ecological assumptions and stochastic processes. In nature, we found aggregated patterns of species biovolume (i.e. clumps) along the volume axis and a peak in species richness. Both patterns were reproduced by the MLVC model. Observed clumps corresponded to niche zones (volumes) where species fitness was highest, or where fitness was equal among competing species. The latter implies the action of equalizing processes, which would suggest emergent neutrality as a plausible mechanism to explain community patterns. PMID:21177680

  18. Two Escape Mechanisms of Influenza A Virus to a Broadly Neutralizing Stalk-Binding Antibody.

    PubMed

    Chai, Ning; Swem, Lee R; Reichelt, Mike; Chen-Harris, Haiyin; Luis, Elizabeth; Park, Summer; Fouts, Ashley; Lupardus, Patrick; Wu, Thomas D; Li, Olga; McBride, Jacqueline; Lawrence, Michael; Xu, Min; Tan, Man-Wah

    2016-06-01

    Broadly neutralizing antibodies targeting the stalk region of influenza A virus (IAV) hemagglutinin (HA) are effective in blocking virus infection both in vitro and in vivo. The highly conserved epitopes recognized by these antibodies are critical for the membrane fusion function of HA and therefore less likely to be permissive for virus mutational escape. Here we report three resistant viruses of the A/Perth/16/2009 strain that were selected in the presence of a broadly neutralizing stalk-binding antibody. The three resistant viruses harbor three different mutations in the HA stalk: (1) Gln387Lys; (2) Asp391Tyr; (3) Asp391Gly. The Gln387Lys mutation completely abolishes binding of the antibody to the HA stalk epitope. The other two mutations, Asp391Tyr and Asp391Gly, do not affect antibody binding at neutral pH and only slightly reduce binding at low pH. Interestingly, they enhance the fusion ability of the HA, representing a novel mechanism that allows productive membrane fusion even in the presence of antibody and hence virus escape from antibody neutralization. Therefore, these mutations illustrate two different resistance mechanisms used by IAV to escape broadly neutralizing stalk-binding antibodies. Compared to the wild type virus, the resistant viruses release fewer progeny viral particles during replication and are more sensitive to Tamiflu, suggesting reduced viral fitness.

  19. Two Escape Mechanisms of Influenza A Virus to a Broadly Neutralizing Stalk-Binding Antibody

    PubMed Central

    Chai, Ning; Swem, Lee R.; Reichelt, Mike; Chen-Harris, Haiyin; Luis, Elizabeth; Park, Summer; Fouts, Ashley; Lupardus, Patrick; Wu, Thomas D.; Li, Olga; McBride, Jacqueline; Lawrence, Michael; Xu, Min; Tan, Man-Wah

    2016-01-01

    Broadly neutralizing antibodies targeting the stalk region of influenza A virus (IAV) hemagglutinin (HA) are effective in blocking virus infection both in vitro and in vivo. The highly conserved epitopes recognized by these antibodies are critical for the membrane fusion function of HA and therefore less likely to be permissive for virus mutational escape. Here we report three resistant viruses of the A/Perth/16/2009 strain that were selected in the presence of a broadly neutralizing stalk-binding antibody. The three resistant viruses harbor three different mutations in the HA stalk: (1) Gln387Lys; (2) Asp391Tyr; (3) Asp391Gly. The Gln387Lys mutation completely abolishes binding of the antibody to the HA stalk epitope. The other two mutations, Asp391Tyr and Asp391Gly, do not affect antibody binding at neutral pH and only slightly reduce binding at low pH. Interestingly, they enhance the fusion ability of the HA, representing a novel mechanism that allows productive membrane fusion even in the presence of antibody and hence virus escape from antibody neutralization. Therefore, these mutations illustrate two different resistance mechanisms used by IAV to escape broadly neutralizing stalk-binding antibodies. Compared to the wild type virus, the resistant viruses release fewer progeny viral particles during replication and are more sensitive to Tamiflu, suggesting reduced viral fitness. PMID:27351973

  20. HIV-1 resistance to neutralizing antibodies: Determination of antibody concentrations leading to escape mutant evolution.

    PubMed

    Magnus, Carsten; Reh, Lucia; Trkola, Alexandra

    2016-06-15

    Broadly neutralizing antibodies against human immunodeficiency virus type 1 (HIV-1) are considered vital components of novel therapeutics and blueprints for vaccine research. Yet escape to even the most potent of these antibodies is imminent in natural infection. Measures to define antibody efficacy and prevent mutant selection are thus urgently needed. Here, we derive a mathematical framework to predict the concentration ranges for which antibody escape variants can outcompete their viral ancestors, referred to as mutant selection window (MSW). When determining the MSW, we focus on the differential efficacy of neutralizing antibodies against HIV-1 in two canonical infection routes, free-virus infection and cell-cell transmission. The latter has proven highly effective in vitro suggesting its importance for both in vivo spread as well as for escaping targeted intervention strategies. We observed a range of MSW patterns that highlight the potential of mutants to arise in both transmission pathways and over wide concentration ranges. Most importantly, we found that only when the arising mutant has both, residual sensitivity to the neutralizing antibody and reduced infectivity compared to the parental virus, antibody dosing outside of the MSW to restrict mutant selection is possible. Emergence of mutants that provide complete escape and have no considerable fitness loss cannot be prevented by adjusting antibody doses. The latter may in part explain the ubiquitous resistance to neutralizing antibodies observed in natural infection and antibody treatment. Based on our findings, combinations of antibodies targeting different epitopes should be favored for antibody-based interventions as this may render complete resistance less likely to occur and also increase chances that multiple escapes result in severe fitness loss of the virus making longer-term antibody treatment more feasible. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

  1. Early Low-Titer Neutralizing Antibodies Impede HIV-1 Replication and Select for Virus Escape

    PubMed Central

    Bar, Katharine J.; Tsao, Chun-yen; Iyer, Shilpa S.; Decker, Julie M.; Yang, Yongping; Bonsignori, Mattia; Chen, Xi; Hwang, Kwan-Ki; Montefiori, David C.; Liao, Hua-Xin; Hraber, Peter; Fischer, William; Li, Hui; Wang, Shuyi; Sterrett, Sarah; Keele, Brandon F.; Ganusov, Vitaly V.; Perelson, Alan S.; Korber, Bette T.; Georgiev, Ivelin; McLellan, Jason S.; Pavlicek, Jeffrey W.; Gao, Feng; Haynes, Barton F.; Hahn, Beatrice H.; Kwong, Peter D.; Shaw, George M.

    2012-01-01

    Single genome sequencing of early HIV-1 genomes provides a sensitive, dynamic assessment of virus evolution and insight into the earliest anti-viral immune responses in vivo. By using this approach, together with deep sequencing, site-directed mutagenesis, antibody adsorptions and virus-entry assays, we found evidence in three subjects of neutralizing antibody (Nab) responses as early as 2 weeks post-seroconversion, with Nab titers as low as 1∶20 to 1∶50 (IC50) selecting for virus escape. In each of the subjects, Nabs targeted different regions of the HIV-1 envelope (Env) in a strain-specific, conformationally sensitive manner. In subject CH40, virus escape was first mediated by mutations in the V1 region of the Env, followed by V3. HIV-1 specific monoclonal antibodies from this subject mapped to an immunodominant region at the base of V3 and exhibited neutralizing patterns indistinguishable from polyclonal antibody responses, indicating V1–V3 interactions within the Env trimer. In subject CH77, escape mutations mapped to the V2 region of Env, several of which selected for alterations of glycosylation. And in subject CH58, escape mutations mapped to the Env outer domain. In all three subjects, initial Nab recognition was followed by sequential rounds of virus escape and Nab elicitation, with Nab escape variants exhibiting variable costs to replication fitness. Although delayed in comparison with autologous CD8 T-cell responses, our findings show that Nabs appear earlier in HIV-1 infection than previously recognized, target diverse sites on HIV-1 Env, and impede virus replication at surprisingly low titers. The unexpected in vivo sensitivity of early transmitted/founder virus to Nabs raises the possibility that similarly low concentrations of vaccine-induced Nabs could impair virus acquisition in natural HIV-1 transmission, where the risk of infection is low and the number of viruses responsible for transmission and productive clinical infection is typically

  2. Neutralization escape mutants define a dominant immunogenic neutralization site on hepatitis A virus

    SciTech Connect

    Stapleton, J.T.; Lemon, S.M.

    1987-02-01

    Hepatitis A virus is an hepatotrophic human picornavirus which demonstrates little antigenic variability. To topologically map immunogenic sites on hepatitis A virus which elicit neutralizing antibodies, eight neutralizing monoclonal antibodies were evaluated in competition immunoassays employing radiolabeled monoclonal antibodies and HM-175 virus. Whereas two antibodies (K3-4C8 and K3-2F2) bound to intimately overlapping epitopes, the epitope bound by a third antibody (B5-B3) was distinctly different as evidenced by a lack of competition between antibodies for binding to the virus. The other five antibodies variably blocked the binding of both K3-4C8-K3-2F2 and B5-B3, suggesting that these epitopes are closely spaced and perhaps part of a single neutralization immunogenic site. Several combinations of monoclonal antibodies blocked the binding of polyclonal human convalescent antibody by greater than 96%, indicating that the neutralization epitopes bound by these antibodies are immunodominant in humans. Spontaneously arising HM-175 mutants were selected for resistance to monoclonal antibody-mediated neutralization. Neutralization resistance was associated with reduced antibody binding. These results suggest that hepatitis A virus may differ from poliovirus in possessing a single, dominant neutralization immunogenic site and therefore may be a better candidate for synthetic peptide or antiidiotype vaccine development.

  3. Estimating Collisionally-Induced Escape Rates of Light Neutrals from Early Mars

    NASA Astrophysics Data System (ADS)

    Gacesa, M.; Zahnle, K. J.

    2016-12-01

    Collisions of atmospheric gases with hot oxygen atoms constitute an important non-thermal mechanism of escape of light atomic and molecular species at Mars. In this study, we present revised theoretical estimates of non-thermal escape rates of neutral O, H, He, and H2 based on recent atmospheric density profiles obtained from the NASA Mars Atmosphere and Volatile Evolution (MAVEN) mission and related theoretical models. As primary sources of hot oxygen, we consider dissociative recombination of O2+ and CO2+ molecular ions. We also consider hot oxygen atoms energized in primary and secondary collisions with energetic neutral atoms (ENAs) produced in charge-exchange of solar wind H+ and He+ ions with atmospheric gases1,2. Scattering of hot oxygen and atmospheric species of interest is modeled using fully-quantum reactive scattering formalism3. This approach allows us to construct distributions of vibrationally and rotationally excited states and predict the products' emission spectra. In addition, we estimate formation rates of excited, translationally hot hydroxyl molecules in the upper atmosphere of Mars. The escape rates are calculated from the kinetic energy distributions of the reaction products using an enhanced 1D model of the atmosphere for a range of orbital and solar parameters. Finally, by considering different scenarios, we estimate the influence of these escape mechanisms on the evolution of Mars's atmosphere throughout previous epochs and their impact on the atmospheric D/H ratio. M.G.'s research was supported by an appointment to the NASA Postdoctoral Program at the NASA Ames Research Center, administered by Universities Space Research Association under contract with NASA. 1N. Lewkow and V. Kharchenko, "Precipitation of Energetic Neutral Atoms and Escape Fluxes induced from the Mars Atmosphere", Astroph. J., 790, 98 (2014) 2M. Gacesa, N. Lewkow, and V. Kharchenko, "Non-thermal production and escape of OH from the upper atmosphere of Mars", arXiv:1607

  4. Mutations That Alter Use of Hepatitis C Virus Cell Entry Factors Mediate Escape From Neutralizing Antibodies

    PubMed Central

    FAUVELLE, CATHERINE; ZAHID, MUHAMMAD NAUMAN; TUREK, MARINE; HEYDMANN, LAURA; CURY, KARINE; HAYER, JULIETTE; COMBET, CHRISTOPHE; COSSET, FRANÇOIS–LOÏC; PIETSCHMANN, THOMAS; HIET, MARIE–SOPHIE; BARTENSCHLAGER, RALF; HABERSETZER, FRANÇOIS; DOFFOËL, MICHEL; KECK, ZHEN–YONG; FOUNG, STEVEN K. H.; ZEISEL, MIRJAM B.; STOLL–KELLER, FRANÇOISE; BAUMERT, THOMAS F.

    2017-01-01

    BACKGROUND & AIMS The development of vaccines and other strategies to prevent hepatitis C virus (HCV) infection is limited by rapid viral evasion. HCV entry is the first step of infection; this process involves several viral and host factors and is targeted by host-neutralizing responses. Although the roles of host factors in HCV entry have been well characterized, their involvement in evasion of immune responses is poorly understood. We used acute infection of liver graft as a model to investigate the molecular mechanisms of viral evasion. METHODS We studied factors that contribute to evasion of host immune responses using patient-derived antibodies, HCV pseudoparticles, and cell culture–derived HCV that express viral envelopes from patients who have undergone liver transplantation. These viruses were used to infect hepatoma cell lines that express different levels of HCV entry factors. RESULTS By using reverse genetic analyses, we identified altered use of host-cell entry factors as a mechanism by which HCV evades host immune responses. Mutations that alter use of the CD81 receptor also allowed the virus to escape neutralizing antibodies. Kinetic studies showed that these mutations affect virus–antibody interactions during postbinding steps of the HCV entry process. Functional studies with a large panel of patient-derived antibodies showed that this mechanism mediates viral escape, leading to persistent infection in general. CONCLUSIONS We identified a mechanism by which HCV evades host immune responses, in which use of cell entry factors evolves with escape from neutralizing antibodies. These findings advance our understanding of the pathogenesis of HCV infection and might be used to develop antiviral strategies and vaccines. PMID:22503792

  5. Mutations that alter use of hepatitis C virus cell entry factors mediate escape from neutralizing antibodies.

    PubMed

    Fofana, Isabel; Fafi-Kremer, Samira; Carolla, Patric; Fauvelle, Catherine; Zahid, Muhammad Nauman; Turek, Marine; Heydmann, Laura; Cury, Karine; Hayer, Juliette; Combet, Christophe; Cosset, François-Loïc; Pietschmann, Thomas; Hiet, Marie-Sophie; Bartenschlager, Ralf; Habersetzer, François; Doffoël, Michel; Keck, Zhen-Yong; Foung, Steven K H; Zeisel, Mirjam B; Stoll-Keller, Françoise; Baumert, Thomas F

    2012-07-01

    The development of vaccines and other strategies to prevent hepatitis C virus (HCV) infection is limited by rapid viral evasion. HCV entry is the first step of infection; this process involves several viral and host factors and is targeted by host-neutralizing responses. Although the roles of host factors in HCV entry have been well characterized, their involvement in evasion of immune responses is poorly understood. We used acute infection of liver graft as a model to investigate the molecular mechanisms of viral evasion. We studied factors that contribute to evasion of host immune responses using patient-derived antibodies, HCV pseudoparticles, and cell culture-derived HCV that express viral envelopes from patients who have undergone liver transplantation. These viruses were used to infect hepatoma cell lines that express different levels of HCV entry factors. By using reverse genetic analyses, we identified altered use of host-cell entry factors as a mechanism by which HCV evades host immune responses. Mutations that alter use of the CD81 receptor also allowed the virus to escape neutralizing antibodies. Kinetic studies showed that these mutations affect virus-antibody interactions during postbinding steps of the HCV entry process. Functional studies with a large panel of patient-derived antibodies showed that this mechanism mediates viral escape, leading to persistent infection in general. We identified a mechanism by which HCV evades host immune responses, in which use of cell entry factors evolves with escape from neutralizing antibodies. These findings advance our understanding of the pathogenesis of HCV infection and might be used to develop antiviral strategies and vaccines. Copyright © 2012 AGA Institute. Published by Elsevier Inc. All rights reserved.

  6. Modeling the near-Earth interaction between ring current ions and exospheric neutrals: escape through energetic neutral atoms (ENAs)

    NASA Astrophysics Data System (ADS)

    LLera, K.; Goldstein, J.; McComas, D. J.; Valek, P. W.

    2016-12-01

    The two major loss processes for ring current decay are precipitation and energetic neutral atoms (ENAs). Since the exospheric neutral density increases with decreasing altitudes, precipitating ring current ions (reaching down to 200 - 800 km in altitude) also produce low-altitude ENA signatures that can be stronger than the ring current emission at equatorial distances ( 2 - 9 Re). The higher density results in multiple collisions between the ring current ions and exospheric oxygen. The affect on hydrogen ions is the focus of this study. Since the H particle sustains energy loss ( 36 eV) at each neutralizing or re-ionizing interaction, the escaped ENAs do not directly reflect the ring current properties. We model the energy loss due to multiple charge exchange and electron stripping interactions of 1 - 100 keV precipitating ring current ions undergo before emerging as low-altitude ENAs. The H particle is either an ion or an ENA throughout the simulation. Their lifetime is analytically determined by the length of one mean free path. We track the ion state with Lorentz motion while the ENA travels ballistically across the geomagnetic field. Our simulations show the energy loss is greater than 20% for hydrogen ring current ions below 30 keV (60 keV for the simulations that wander equatorward). This is the first quantification of the energy loss associated with the creation of low-altitude ENAs. Our model (currently constrained in the meridional plane) has revealed characteristics on how precipitation is affected by the near-Earth neutral exosphere. This ion-neutral interaction removes particles from the loss cone but promotes loss through ENA generation. These findings should be implemented in models predicting the ring current decay and used as an analysis tool to reconstruct the ring current population from observed low-altitude ENAs.

  7. Non-linear diffusion of cosmic rays escaping from supernova remnants - I. The effect of neutrals

    NASA Astrophysics Data System (ADS)

    Nava, L.; Gabici, S.; Marcowith, A.; Morlino, G.; Ptuskin, V. S.

    2016-10-01

    Supernova remnants are believed to be the main sources of galactic cosmic rays (CR). Within this framework, particles are accelerated at supernova remnant shocks and then released in the interstellar medium. The mechanism through which CRs are released and the way in which they propagate still remain open issues. The main difficulty is the high non-linearity of the problem: CRs themselves excite the magnetic turbulence that confines them close to their sources. We solve numerically the coupled differential equations describing the evolution in space and time of the escaping particles and of the waves generated through the CR streaming instability. The warm ionized and warm neutral phases of the interstellar medium are considered. These phases occupy the largest fraction of the disc volume, where most supernovae explode, and are characterized by the significant presence of neutral particles. The friction between those neutrals and ions results in a very effective wave damping mechanism. It is found that streaming instability affects the propagation of CRs even in the presence of ion-neutral friction. The diffusion coefficient can be suppressed by more than a factor of ˜2 over a region of few tens of pc around the remnant. The suppression increases for smaller distances. The propagation of ≈10 GeV particles is affected for several tens of kiloyears after escape, while ≈1 TeV particles are affected for few kiloyears. This might have a great impact on the interpretation of gamma-ray observations of molecular clouds located in the vicinity of supernova remnants.

  8. Precipitation of energetic neutral atoms and induced non-thermal escape fluxes from the Martian atmosphere

    SciTech Connect

    Lewkow, N. R.; Kharchenko, V.

    2014-08-01

    The precipitation of energetic neutral atoms, produced through charge exchange collisions between solar wind ions and thermal atmospheric gases, is investigated for the Martian atmosphere. Connections between parameters of precipitating fast ions and resulting escape fluxes, altitude-dependent energy distributions of fast atoms and their coefficients of reflection from the Mars atmosphere, are established using accurate cross sections in Monte Carlo (MC) simulations. Distributions of secondary hot (SH) atoms and molecules, induced by precipitating particles, have been obtained and applied for computations of the non-thermal escape fluxes. A new collisional database on accurate energy-angular-dependent cross sections, required for description of the energy-momentum transfer in collisions of precipitating particles and production of non-thermal atmospheric atoms and molecules, is reported with analytic fitting equations. Three-dimensional MC simulations with accurate energy-angular-dependent cross sections have been carried out to track large ensembles of energetic atoms in a time-dependent manner as they propagate into the Martian atmosphere and transfer their energy to the ambient atoms and molecules. Results of the MC simulations on the energy-deposition altitude profiles, reflection coefficients, and time-dependent atmospheric heating, obtained for the isotropic hard sphere and anisotropic quantum cross sections, are compared. Atmospheric heating rates, thermalization depths, altitude profiles of production rates, energy distributions of SH atoms and molecules, and induced escape fluxes have been determined.

  9. Envelope-chimeric Entry-targeted Measles Virus Escapes Neutralization and Achieves Oncolysis

    PubMed Central

    Miest, Tanner S; Yaiw, Koon-Chu; Frenzke, Marie; Lampe, Johanna; Hudacek, Andrew W; Springfeld, Christoph; von Messling, Veronika; Ungerechts, Guy; Cattaneo, Roberto

    2011-01-01

    Measles virus (MV) is a promising vector for cancer therapy and multivalent vaccination, but high prevalence of pre-existing neutralizing antibodies may reduce therapeutic efficacy, particularly following systemic administration. MV has only one serotype, but here we show that its envelope glycoproteins can be exchanged with those of the closely related canine distemper virus (CDV), generating a chimeric virus capable of escaping neutralization. To target its entry, we displayed on the CDV attachment protein a single-chain antibody specific for a designated receptor. To enhance oncolytic efficacy we armed the virus with a prodrug convertase gene capable of locally activating chemotherapeutic prodrugs. The new virus achieved high titers, was genetically stable, and was resistant to neutralization by sera from both MV-immunized mice and MV-immune humans. The new virus targeted syngeneic murine tumor cells expressing the designated receptor implanted in immunocompetent mice, and synergized with a chemotherapeutic prodrug in a model of oncolysis. Importantly, the chimeric MV remained oncolytic when administered systemically even in the presence of anti-MV antibodies capable of abrogating the therapeutic efficacy of the parental, nonshielded MV. This work shows that targeting, arming, and shielding can be combined to generate a tumor-specific, neutralization-resistant virus that can synergize with chemotherapeutics. PMID:21610701

  10. Energy escape rate of neutrals from Io and the implications for local magnetospheric interactions

    NASA Astrophysics Data System (ADS)

    Smyth, William H.

    1998-06-01

    The rate at which energy is carried away by atomic oxygen and sulfur escaping from Io because of the interaction of its atmosphere with the corotating magnetospheric plasma is calculated for three different ion-neutral collisional processes: (1) incomplete collisional cascade, (2) slow-velocity charge exchange and direct ejection (centered ~20 km/s), and (3) fast-velocity charge exchange (centered ~60 km/s). The calculations are based on information for the O and S source rates and their velocity distributions at Io as independently determined from the combined results of previous studies for the observed column density and/or brightness morphology of the satellite's neutral corona and extended neutral clouds. The calculated energy escape rates for the three processes are 7.5×109W, 3.3×1010W, and 6.04×1011W and are ~11%, 50%, and 900%, respectively, of the upstream ion kinetic energy flow rate of 6.7×1010W determined for a Voyager corotating plasma flowing through a minimum interaction area of πRIo2, where RIo is Io's radius. A larger more physically appropriate upstream interaction area of 2πRIo2=π(1.414RIo)2 would reduce these percentages by a factors of 2. For incomplete collisional cascade, the calculated energy escape rate is expected to be only ~20% of the total energy deposition rate for this process, indicating a heating rate for the atmosphere of 3.0×1010W (the remaining ~80%). This implies that 56% of the minimum upstream ion kinetic energy flow rate is supplied to the atmosphere through the collisional cascade process, a factor of 2.8 times larger than the previously adopted value, and that the effective deflection of magnetospheric plasma out of the interaction region near Io is less than previously estimated. The total estimated neutral energy rate for all three processes (including heating) is 6.75×1011W and is so large that it can only be supplied by the magnetic field energy, which is partially converted near Io to kinetic energy for the

  11. Cooperation between Strain-Specific and Broadly Neutralizing Responses Limited Viral Escape and Prolonged the Exposure of the Broadly Neutralizing Epitope.

    PubMed

    Anthony, Colin; York, Talita; Bekker, Valerie; Matten, David; Selhorst, Philippe; Ferreria, Roux-Cil; Garrett, Nigel J; Karim, Salim S Abdool; Morris, Lynn; Wood, Natasha T; Moore, Penny L; Williamson, Carolyn

    2017-09-15

    V3-glycan-targeting broadly neutralizing antibodies (bNAbs) are a focus of HIV-1 vaccine development. Understanding the viral dynamics that stimulate the development of these antibodies can provide insights for immunogen design. We used a deep-sequencing approach, together with neutralization phenotyping, to investigate the rate and complexity of escape from V3-glycan-directed bNAbs compared to overlapping early strain-specific neutralizing antibody (ssNAb) responses to the V3/C3 region in donor CAP177. Escape from the ssNAb response occurred rapidly via an N334-to-N332 glycan switch, which took just 7.5 weeks to reach >50% frequency. In contrast, escape from the bNAbs was mediated via multiple pathways and took longer, with escape first occurring through an increase in V1 loop length, which took 46 weeks to reach 50% frequency, followed by an N332-to-N334 reversion, which took 66 weeks. Importantly, bNAb escape was incomplete, with contemporaneous neutralization observed up to 3 years postinfection. Both the ssNAb response and the bNAb response were modulated by the presence/absence of the N332 glycan, indicating an overlap between the two epitopes. Thus, selective pressure by ssNAbs to maintain the N332 glycan may have constrained the bNAb escape pathway. This slower and incomplete viral escape resulted in prolonged exposure of the bNAb epitope, which may in turn have aided the maturation of the bNAb lineage.IMPORTANCE The development of an HIV-1 vaccine is of paramount importance, and broadly neutralizing antibodies are likely to be a key component of a protective vaccine. The V3-glycan-targeting bNAb responses are among the most promising vaccine targets, as they are commonly elicited during infection. Understanding the interplay between viral evolution and the development of these antibodies provides insights that may guide immunogen design. Our work contrasted the dynamics of the early strain-specific antibodies and the later broadly neutralizing responses to

  12. Neutral beam current drive scaling in DIII-D

    SciTech Connect

    Porter, G.D.; Bhadra, D.K.; Burrell, K.H.; Callis, R.W.; Colleraine, A.P.; Ferron, J.R.; James, R.A.; Kellman, A.G.; Kim, J.; Matsuoka, M.

    1989-03-01

    Neutral beam current drive scaling experiments have been carried out on the DIII-D tokamak at General Atomics. These experiments were performed using up to 10 MW of 80 keV hydrogen beams. Previous current drive experiments on DIII-D have demonstrated beam driven currents up to 340 kA. In the experiments reported here we achieved beam driven currents of at least 500 kA, and have obtained operation with record values of poloidal beta (epsilon..beta../sub p/ = 1.4). The beam driven current reported here is obtained from the total plasma current by subtracting an estimate of the residual Ohmic current determined from the measured loop voltage. In this report we discuss the scaling of the current drive efficiency with plasma conditions. Using hydrogen neutral beams, we find the current drive efficiency is similar in Deuterium and Helium target plasmas. Experiments have been performed with plasma electron temperatures up to T/sub e/ = 3 keV, and densities in the range 2 /times/ 10/sup 19/m/sup /minus/3/ < n/sub e/ < 4 /times/ 10/sup 19/m/sup /minus/3/. The current drive efficiency (nIR/P) is observed to scale linearly with the energy confinement time on DIII-D to a maximum of 0.05 /times/ 10/sup 20/m/sup /minus/2/ A/W. The measured efficiency is consistent with a 0-D theoretical model. In addition to comparison with this simple model, detailed analysis of several shots using the time dependent transport code ONETWO is discussed. This analysis indicates that bootstrap current contributes approximately 10--20% of the the total current. Our estimates of this effect are somewhat uncertain due to limited measurements of the radial profile of the density and temperatures. 4 refs., 1 fig., 1 tab.

  13. Characterization of Poliovirus Neutralization Escape Mutants of Single-Domain Antibody Fragments (VHHs)

    PubMed Central

    Schotte, Lise; Thys, Bert; Strauss, Mike; Filman, David J.; Rombaut, Bart

    2015-01-01

    To complete the eradication of poliovirus and to protect unvaccinated people subsequently, the development of one or more antiviral drugs will be necessary. A set of five single-domain antibody fragments (variable parts of the heavy chain of a heavy-chain antibody [VHHs]) with an in vitro neutralizing activity against poliovirus type 1 was developed previously (B. Thys, L. Schotte, S. Muyldermans, U. Wernery, G. Hassanzadeh-Ghassabeh, and B. Rombaut, Antiviral Res 87:257–264, 2010, http://dx.doi.org/10.1016/j.antiviral.2010.05.012), and their mechanisms of action have been studied (L. Schotte, M. Strauss, B. Thys, H. Halewyck, D. J. Filman, M. Bostina, J. M. Hogle, and B. Rombaut, J Virol 88:4403–4413, 2014, http://dx.doi.org/10.1128/JVI.03402-13). In this study, neutralization escape mutants were selected for each VHH. Sequencing of the P1 region of the genome showed that amino acid substitutions are found in the four viral proteins of the capsid and that they are located both in proximity to the binding sites of the VHHs and in regions further away from the canyon and hidden beneath the surface. Characterization of the mutants demonstrated that they have single-cycle replication kinetics that are similar to those of their parental strain and that they are all drug (VHH) independent. Their resistant phenotypes are stable, as they do not regain full susceptibility to the VHH after passage over HeLa cells in the absence of VHH. They are all at least as stable as the parental strain against heat inactivation at 44°C, and three of them are even significantly (P < 0.05) more resistant to heat inactivation. The resistant variants all still can be neutralized by at least two other VHHs and retain full susceptibility to pirodavir and 35-1F4. PMID:26014941

  14. Neutral and Selective Processes Drive Population Differentiation for Iris hexagona

    PubMed Central

    Arnold, Michael L.

    2015-01-01

    Gene flow among widespread populations can be reduced by geographical distance or by divergent selection resulting from local adaptation. In this study, we tested for the divergence of phenotypes and genotypes among 8 populations of Iris hexagona. Using a genotyping-by-sequencing approach, we generated a panel of 750 single nucleotide polymorphisms (SNPs) and used population genetic analyses to determine what may affect patterns of divergence across I. hexagona populations. Specifically, genetic differentiation was compared between populations at neutral and nonneutral SNPs and detected significant differences between the 2 types of markers. We then asked whether loci with the strongest degree of population genetic differentiation were also the loci with the strongest association to morphology or climate differences, allowing us to test if pollinators or climate drive population differentiation or some combination of both. We found 2 markers that were associated with morphology and 1 marker associated with 2 of the environmental variables, which were also identified in the outlier analysis. We then show that the SNPs putatively under selection were positively correlated with both geographic distance and phenotypic distance, albeit weakly to phenotypic distance. Moreover, neutral SNPs were only correlated with geographic distance and thus isolation-by-distance was observed for neutral SNPs. Our data suggest that both deterministic and neutral processes have contributed to the evolutionary trajectory of I. hexagona populations. PMID:26163584

  15. Neutral and Selective Processes Drive Population Differentiation for Iris hexagona.

    PubMed

    Hamlin, Jennafer A P; Arnold, Michael L

    2015-01-01

    Gene flow among widespread populations can be reduced by geographical distance or by divergent selection resulting from local adaptation. In this study, we tested for the divergence of phenotypes and genotypes among 8 populations of Iris hexagona. Using a genotyping-by-sequencing approach, we generated a panel of 750 single nucleotide polymorphisms (SNPs) and used population genetic analyses to determine what may affect patterns of divergence across I. hexagona populations. Specifically, genetic differentiation was compared between populations at neutral and nonneutral SNPs and detected significant differences between the 2 types of markers. We then asked whether loci with the strongest degree of population genetic differentiation were also the loci with the strongest association to morphology or climate differences, allowing us to test if pollinators or climate drive population differentiation or some combination of both. We found 2 markers that were associated with morphology and 1 marker associated with 2 of the environmental variables, which were also identified in the outlier analysis. We then show that the SNPs putatively under selection were positively correlated with both geographic distance and phenotypic distance, albeit weakly to phenotypic distance. Moreover, neutral SNPs were only correlated with geographic distance and thus isolation-by-distance was observed for neutral SNPs. Our data suggest that both deterministic and neutral processes have contributed to the evolutionary trajectory of I. hexagona populations. © The American Genetic Association 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  16. Direct activation of the Mauthner cell by electric field pulses drives ultrarapid escape responses

    PubMed Central

    Tabor, Kathryn M.; Bergeron, Sadie A.; Horstick, Eric J.; Jordan, Diana C.; Aho, Vilma; Porkka-Heiskanen, Tarja; Haspel, Gal

    2014-01-01

    Rapid escape swims in fish are initiated by the Mauthner cells, giant reticulospinal neurons with unique specializations for swift responses. The Mauthner cells directly activate motoneurons and facilitate predator detection by integrating acoustic, mechanosensory, and visual stimuli. In addition, larval fish show well-coordinated escape responses when exposed to electric field pulses (EFPs). Sensitization of the Mauthner cell by genetic overexpression of the voltage-gated sodium channel SCN5 increased EFP responsiveness, whereas Mauthner ablation with an engineered variant of nitroreductase with increased activity (epNTR) eliminated the response. The reaction time to EFPs is extremely short, with many responses initiated within 2 ms of the EFP. Large neurons, such as Mauthner cells, show heightened sensitivity to extracellular voltage gradients. We therefore tested whether the rapid response to EFPs was due to direct activation of the Mauthner cells, bypassing delays imposed by stimulus detection and transmission by sensory cells. Consistent with this, calcium imaging indicated that EFPs robustly activated the Mauthner cell but only rarely fired other reticulospinal neurons. Further supporting this idea, pharmacological blockade of synaptic transmission in zebrafish did not affect Mauthner cell activity in response to EFPs. Moreover, Mauthner cells transgenically expressing a tetrodotoxin (TTX)-resistant voltage-gated sodium channel retained responses to EFPs despite TTX suppression of action potentials in the rest of the brain. We propose that EFPs directly activate Mauthner cells because of their large size, thereby driving ultrarapid escape responses in fish. PMID:24848468

  17. Effects of MHD instabilities on neutral beam current drive

    SciTech Connect

    Podestà, M.; Gorelenkova, M.; Darrow, D. S.; Fredrickson, E. D.; Gerhardt, S. P.; White, R. B.

    2015-04-17

    One of the primary tools foreseen for heating, current drive (CD) and q-profile control in future fusion reactors such as ITER and a Fusion Nuclear Science Facility is the neutral beam injection (NBI). However, fast ions from NBI may also provide the drive for energetic particle-driven instabilities (e.g. Alfvénic modes (AEs)), which in turn redistribute fast ions in both space and energy, thus hampering the control capabilities and overall efficiency of NB-driven current. Based on experiments on the NSTX tokamak (M. Ono et al 2000 Nucl. Fusion 40 557), the effects of AEs and other low-frequency magneto-hydrodynamic instabilities on NB-CD efficiency are investigated. When looking at the new fast ion transport model, which accounts for particle transport in phase space as required for resonant AE perturbations, is utilized to obtain consistent simulations of NB-CD through the tokamak transport code TRANSP. It is found that instabilities do indeed reduce the NB-driven current density over most of the plasma radius by up to ~50%. Moreover, the details of the current profile evolution are sensitive to the specific model used to mimic the interaction between NB ions and instabilities. Finally, implications for fast ion transport modeling in integrated tokamak simulations are briefly discussed.

  18. Effects of MHD instabilities on neutral beam current drive

    DOE PAGES

    Podestà, M.; Gorelenkova, M.; Darrow, D. S.; ...

    2015-04-17

    One of the primary tools foreseen for heating, current drive (CD) and q-profile control in future fusion reactors such as ITER and a Fusion Nuclear Science Facility is the neutral beam injection (NBI). However, fast ions from NBI may also provide the drive for energetic particle-driven instabilities (e.g. Alfvénic modes (AEs)), which in turn redistribute fast ions in both space and energy, thus hampering the control capabilities and overall efficiency of NB-driven current. Based on experiments on the NSTX tokamak (M. Ono et al 2000 Nucl. Fusion 40 557), the effects of AEs and other low-frequency magneto-hydrodynamic instabilities on NB-CDmore » efficiency are investigated. When looking at the new fast ion transport model, which accounts for particle transport in phase space as required for resonant AE perturbations, is utilized to obtain consistent simulations of NB-CD through the tokamak transport code TRANSP. It is found that instabilities do indeed reduce the NB-driven current density over most of the plasma radius by up to ~50%. Moreover, the details of the current profile evolution are sensitive to the specific model used to mimic the interaction between NB ions and instabilities. Finally, implications for fast ion transport modeling in integrated tokamak simulations are briefly discussed.« less

  19. A transmission/escape probabilities model for neutral particle transport in the outer regions of a diverted tokamak

    SciTech Connect

    Stacey, W.M.

    1992-12-01

    A new computational model for neutral particle transport in the outer regions of a diverted tokamak plasma chamber is presented. The model is based on the calculation of transmission and escape probabilities using first-flight integral transport theory and the balancing of fluxes across the surfaces bounding the various regions. The geometrical complexity of the problem is included in precomputed probabilities which depend only on the mean free path of the region.

  20. A transmission/escape probabilities model for neutral particle transport in the outer regions of a diverted tokamak

    SciTech Connect

    Stacey, W.M.

    1992-12-01

    A new computational model for neutral particle transport in the outer regions of a diverted tokamak plasma chamber is presented. The model is based on the calculation of transmission and escape probabilities using first-flight integral transport theory and the balancing of fluxes across the surfaces bounding the various regions. The geometrical complexity of the problem is included in precomputed probabilities which depend only on the mean free path of the region.

  1. Broad CTL Response in Early HIV Infection Drives Multiple Concurrent CTL Escapes.

    PubMed

    Leviyang, Sivan; Ganusov, Vitaly V

    2015-10-01

    Recent studies have highlighted the ability of HIV to escape from cytotoxic T lymphocyte (CTL) responses that concurrently target multiple viral epitopes. Yet, the viral dynamics involved in such escape are incompletely understood. Previous analyses have made several strong assumptions regarding HIV escape from CTL responses such as independent or non-concurrent escape from individual CTL responses. Using experimental data from evolution of HIV half genomes in four patients we observe concurrent viral escape from multiple CTL responses during early infection (first 100 days of infection), providing confirmation of a recent result found in a study of one HIV-infected patient. We show that current methods of estimating CTL escape rates, based on the assumption of independent escapes, are biased and perform poorly when CTL escape proceeds concurrently at multiple epitopes. We propose a new method for analyzing longitudinal sequence data to estimate the rate of CTL escape across multiple epitopes; this method involves few parameters and performs well in simulation studies. By applying our novel method to experimental data, we find that concurrent multiple escapes occur at rates between 0.03 and 0.4 day(-1), a relatively broad range that reflects uncertainty due to sparse sampling and wide ranges of parameter values. However, we show that concurrent escape at rates 0.1-0.2 day(-1) across multiple epitopes is consistent with our patient datasets.

  2. How does the stellar Lyman alpha flux drive the planetary Hydrogen exospheric escape?

    NASA Astrophysics Data System (ADS)

    Beth, Arnaud; Garnier, Philippe; Toublanc, Dominique; Dandouras, Iannis; Mazelle, Christian

    2017-04-01

    Planetary thermal escape, the so-called Jeans escape, occurs in the uppermost layer of the atmosphere, the exosphere. There, the medium is not collisional enough to maintain the velocity distribution function maxwellian and a part of the gas overcomes the escape velocity. However, there is another mechanism which emphasizes the thermal Hydrogen escape: the radiation pressure. The radiation pressure results from the resonant scattering of stellar photons by an atom or molecule. This phenomenon is particularly efficient on hermean Sodium but also on Hydrogen around any planet/exoplanet. In this study, we will quantify the increase of the Jeans escape induced by the radiation pressure on terrestrial planets (up to 30% at Earth) and exoplanets and show the existence of an upper limit for this escape which is none other than the blow-off regime.

  3. GTNEUT: A code for the calculation of neutral particle transport in plasmas based on the Transmission and Escape Probability method

    NASA Astrophysics Data System (ADS)

    Mandrekas, John

    2004-08-01

    GTNEUT is a two-dimensional code for the calculation of the transport of neutral particles in fusion plasmas. It is based on the Transmission and Escape Probabilities (TEP) method and can be considered a computationally efficient alternative to traditional Monte Carlo methods. The code has been benchmarked extensively against Monte Carlo and has been used to model the distribution of neutrals in fusion experiments. Program summaryTitle of program: GTNEUT Catalogue identifier: ADTX Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTX Computer for which the program is designed and others on which it has been tested: The program was developed on a SUN Ultra 10 workstation and has been tested on other Unix workstations and PCs. Operating systems or monitors under which the program has been tested: Solaris 8, 9, HP-UX 11i, Linux Red Hat v8.0, Windows NT/2000/XP. Programming language used: Fortran 77 Memory required to execute with typical data: 6 219 388 bytes No. of bits in a word: 32 No. of processors used: 1 Has the code been vectorized or parallelized?: No No. of bytes in distributed program, including test data, etc.: 300 709 No. of lines in distributed program, including test data, etc.: 17 365 Distribution format: compressed tar gzip file Keywords: Neutral transport in plasmas, Escape probability methods Nature of physical problem: This code calculates the transport of neutral particles in thermonuclear plasmas in two-dimensional geometric configurations. Method of solution: The code is based on the Transmission and Escape Probability (TEP) methodology [1], which is part of the family of integral transport methods for neutral particles and neutrons. The resulting linear system of equations is solved by standard direct linear system solvers (sparse and non-sparse versions are included). Restrictions on the complexity of the problem: The current version of the code can

  4. Temporal analysis of HIV envelope sequence evolution and antibody escape in a subtype A-infected individual with a broad neutralizing antibody response

    PubMed Central

    Bosch, Katherine A.; Rainwater, Stephanie; Jaoko, Walter; Overbaugh, Julie

    2010-01-01

    The origin of broadly neutralizing HIV-specific antibodies and their relation to HIV evolution are not well defined. Here we examined virus evolution and neutralizing antibody escape in a subtype A infected individual with a broad, cross subtype, antibody response. The majority of envelope variants isolated over the first ~ 5 years post-infection were poorly neutralized by contemporaneous plasma that neutralized variants from earlier in infection, consistent with a dynamic process of escape. The majority of variants could be neutralized by later plasma, suggesting these evolving variants may have contributed to the elicitation of new antibody responses. However, some variants from later in infection were recognized by plasma from earlier in infection, including one notably neutralization-sensitive variant that was sensitive due to a proline at position 199 in V2. These studies suggest a complex pattern of virus evolution in this individual with a broad NAb response, including persistence of neutralization-sensitive viruses. PMID:20034648

  5. THE LYMAN ALPHA REFERENCE SAMPLE. V. THE IMPACT OF NEUTRAL ISM KINEMATICS AND GEOMETRY ON Lyα ESCAPE

    SciTech Connect

    Rivera-Thorsen, Thøger E.; Hayes, Matthew; Östlin, Göran; Duval, Florent; Sandberg, Andreas; Guaita, Lucia; Adamo, Angela; Orlitová, Ivana; Verhamme, Anne; Schaerer, Daniel; Mas-Hesse, J. Miguel; Cannon, John M.; Otí-Floranes, Héctor; Atek, Hakim; Herenz, E. Christian; Kunth, Daniel; and others

    2015-05-20

    We present high-resolution far-UV spectroscopy of the 14 galaxies of the Lyα Reference Sample; a sample of strongly star-forming galaxies at low redshifts (0.028 < z < 0.18). We compare the derived properties to global properties derived from multi-band imaging and 21 cm H i interferometry and single-dish observations, as well as archival optical SDSS spectra. Besides the Lyα line, the spectra contain a number of metal absorption features allowing us to probe the kinematics of the neutral ISM and evaluate the optical depth and and covering fraction of the neutral medium as a function of line of sight velocity. Furthermore, we show how this, in combination with the precise determination of systemic velocity and good Lyα spectra, can be used to distinguish a model in which separate clumps together fully cover the background source, from the “picket fence” model named by Heckman et al. We find that no one single effect dominates in governing Lyα radiative transfer and escape. Lyα escape in our sample coincides with a maximum velocity-binned covering fraction of ≲0.9 and bulk outflow velocities of ≳50 km s{sup −1}, although a number of galaxies show these characteristics and yet little or no Lyα escape. We find that Lyα peak velocities, where available, are not consistent with a strong backscattered component, but rather with a simpler model of an intrinsic emission line overlaid by a blueshifted absorption profile from the outflowing wind. Finally, we find a strong anticorrelation between Hα equivalent width and maximum velocity-binned covering factor, and propose a heuristic explanatory model.

  6. HIV-1 clade C escapes broadly neutralizing autologous antibodies with N332 glycan specificity by distinct mechanisms.

    PubMed

    Deshpande, Suprit; Patil, Shilpa; Kumar, Rajesh; Hermanus, Tandile; Murugavel, Kailapuri G; Srikrishnan, Aylur K; Solomon, Suniti; Morris, Lynn; Bhattacharya, Jayanta

    2016-08-30

    The glycan supersite centered on N332 in the V3 base of the HIV-1 envelope (Env) is a target for broadly neutralizing antibodies (bnAbs) such as PGT121 and PGT128. In this study, we examined the basis of resistance of HIV-1 clade C Envs obtained from broadly cross neutralizing (BCN) plasma of an Indian donor with N332 specificity. Pseudotyped viruses expressing autologous envs were found to be resistant to autologous BCN plasma as well as to PGT121 and PGT128 mAbs despite the majority of Envs containing an intact N332 residue. While resistance of one of the Envs to neutralization by autologous plasma antibodies with shorter V1 loop length was found to be correlated with a N332S mutation, resistance to neutralization of rest of the Envs was found to be associated with longer V1 loop length and acquisition of protective N-glycans. In summary, we show evidence of escape of circulating HIV-1 clade C in an individual from autologous BCN antibodies by three distinct mechanisms.

  7. Effects of human anti-spike protein receptor binding domain antibodies on severe acute respiratory syndrome coronavirus neutralization escape and fitness.

    PubMed

    Sui, Jianhua; Deming, Meagan; Rockx, Barry; Liddington, Robert C; Zhu, Quan Karen; Baric, Ralph S; Marasco, Wayne A

    2014-12-01

    The receptor binding domain (RBD) of the spike (S) glycoprotein of severe acute respiratory syndrome coronavirus (SARS-CoV) is a major target of protective immunity in vivo. Although a large number of neutralizing antibodies (nAbs) have been developed, it remains unclear if a single RBD-targeting nAb or two in combination can prevent neutralization escape and, if not, attenuate viral virulence in vivo. In this study, we used a large panel of human nAbs against an epitope that overlaps the interface between the RBD and its receptor, angiotensin-converting enzyme 2 (ACE2), to assess their cross-neutralization activities against a panel of human and zoonotic SARS-CoVs and neutralization escape mutants. We also investigated the neutralization escape profiles of these nAbs and evaluated their effects on receptor binding and virus fitness in vitro and in mice. We found that some nAbs had great potency and breadth in neutralizing multiple viral strains, including neutralization escape viruses derived from other nAbs; however, no single nAb or combination of two blocked neutralization escape. Interestingly, in mice the neutralization escape mutant viruses showed either attenuation (Urbani background) or increased virulence (GD03 background) consistent with the different binding affinities between their RBDs and the mouse ACE2. We conclude that using either single nAbs or dual nAb combinations to target a SARS-CoV RBD epitope that shows plasticity may have limitations for preventing neutralization escape during in vivo immunotherapy. However, RBD-directed nAbs may be useful for providing broad neutralization and prevention of escape variants when combined with other nAbs that target a second conserved epitope with less plasticity and more structural constraint. The emergence of severe acute respiratory syndrome coronavirus (SARS-CoV) in 2002 and Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012 has resulted in severe human respiratory disease with high death

  8. Effects of Human Anti-Spike Protein Receptor Binding Domain Antibodies on Severe Acute Respiratory Syndrome Coronavirus Neutralization Escape and Fitness

    PubMed Central

    Sui, Jianhua; Deming, Meagan; Rockx, Barry; Liddington, Robert C.; Zhu, Quan Karen

    2014-01-01

    ABSTRACT The receptor binding domain (RBD) of the spike (S) glycoprotein of severe acute respiratory syndrome coronavirus (SARS-CoV) is a major target of protective immunity in vivo. Although a large number of neutralizing antibodies (nAbs) have been developed, it remains unclear if a single RBD-targeting nAb or two in combination can prevent neutralization escape and, if not, attenuate viral virulence in vivo. In this study, we used a large panel of human nAbs against an epitope that overlaps the interface between the RBD and its receptor, angiotensin-converting enzyme 2 (ACE2), to assess their cross-neutralization activities against a panel of human and zoonotic SARS-CoVs and neutralization escape mutants. We also investigated the neutralization escape profiles of these nAbs and evaluated their effects on receptor binding and virus fitness in vitro and in mice. We found that some nAbs had great potency and breadth in neutralizing multiple viral strains, including neutralization escape viruses derived from other nAbs; however, no single nAb or combination of two blocked neutralization escape. Interestingly, in mice the neutralization escape mutant viruses showed either attenuation (Urbani background) or increased virulence (GD03 background) consistent with the different binding affinities between their RBDs and the mouse ACE2. We conclude that using either single nAbs or dual nAb combinations to target a SARS-CoV RBD epitope that shows plasticity may have limitations for preventing neutralization escape during in vivo immunotherapy. However, RBD-directed nAbs may be useful for providing broad neutralization and prevention of escape variants when combined with other nAbs that target a second conserved epitope with less plasticity and more structural constraint. IMPORTANCE The emergence of severe acute respiratory syndrome coronavirus (SARS-CoV) in 2002 and Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012 has resulted in severe human respiratory

  9. Glycan shifting on hepatitis C virus (HCV) E2 glycoprotein is a mechanism for escape from broadly neutralizing antibodies.

    PubMed

    Pantua, Homer; Diao, Jingyu; Ultsch, Mark; Hazen, Meredith; Mathieu, Mary; McCutcheon, Krista; Takeda, Kentaro; Date, Shailesh; Cheung, Tommy K; Phung, Qui; Hass, Phil; Arnott, David; Hongo, Jo-Anne; Matthews, David J; Brown, Alex; Patel, Arvind H; Kelley, Robert F; Eigenbrot, Charles; Kapadia, Sharookh B

    2013-06-12

    Hepatitis C virus (HCV) infection is a major cause of liver disease and hepatocellular carcinoma. Glycan shielding has been proposed to be a mechanism by which HCV masks broadly neutralizing epitopes on its viral glycoproteins. However, the role of altered glycosylation in HCV resistance to broadly neutralizing antibodies is not fully understood. Here, we have generated potent HCV neutralizing antibodies hu5B3.v3 and MRCT10.v362 that, similar to the previously described AP33 and HCV1, bind to a highly conserved linear epitope on E2. We utilize a combination of in vitro resistance selections using the cell culture infectious HCV and structural analyses to identify mechanisms of HCV resistance to hu5B3.v3 and MRCT10.v362. Ultra deep sequencing from in vitro HCV resistance selection studies identified resistance mutations at asparagine N417 (N417S, N417T and N417G) as early as 5days post treatment. Comparison of the glycosylation status of soluble versions of the E2 glycoprotein containing the respective resistance mutations revealed a glycosylation shift from N417 to N415 in the N417S and N417T E2 proteins. The N417G E2 variant was glycosylated neither at residue 415 nor at residue 417 and remained sensitive to MRCT10.v362. Structural analyses of the E2 epitope bound to hu5B3.v3 Fab and MRCT10.v362 Fab using X-ray crystallography confirmed that residue N415 is buried within the antibody-peptide interface. Thus, in addition to previously described mutations at N415 that abrogate the β-hairpin structure of this E2 linear epitope, we identify a second escape mechanism, termed glycan shifting, that decreases the efficacy of broadly neutralizing HCV antibodies.

  10. The Lyman Alpha Reference Sample. V. The Impact of Neutral ISM Kinematics and Geometry on Lyα Escape

    NASA Astrophysics Data System (ADS)

    Rivera-Thorsen, Thøger E.; Hayes, Matthew; Östlin, Göran; Duval, Florent; Orlitová, Ivana; Verhamme, Anne; Mas-Hesse, J. Miguel; Schaerer, Daniel; Cannon, John M.; Otí-Floranes, Héctor; Sandberg, Andreas; Guaita, Lucia; Adamo, Angela; Atek, Hakim; Herenz, E. Christian; Kunth, Daniel; Laursen, Peter; Melinder, Jens

    2015-05-01

    We present high-resolution far-UV spectroscopy of the 14 galaxies of the Lyα Reference Sample; a sample of strongly star-forming galaxies at low redshifts (0.028 < z < 0.18). We compare the derived properties to global properties derived from multi-band imaging and 21 cm H i interferometry and single-dish observations, as well as archival optical SDSS spectra. Besides the Lyα line, the spectra contain a number of metal absorption features allowing us to probe the kinematics of the neutral ISM and evaluate the optical depth and and covering fraction of the neutral medium as a function of line of sight velocity. Furthermore, we show how this, in combination with the precise determination of systemic velocity and good Lyα spectra, can be used to distinguish a model in which separate clumps together fully cover the background source, from the “picket fence” model named by Heckman et al. We find that no one single effect dominates in governing Lyα radiative transfer and escape. Lyα escape in our sample coincides with a maximum velocity-binned covering fraction of ≲0.9 and bulk outflow velocities of ≳50 km s-1, although a number of galaxies show these characteristics and yet little or no Lyα escape. We find that Lyα peak velocities, where available, are not consistent with a strong backscattered component, but rather with a simpler model of an intrinsic emission line overlaid by a blueshifted absorption profile from the outflowing wind. Finally, we find a strong anticorrelation between Hα equivalent width and maximum velocity-binned covering factor, and propose a heuristic explanatory model. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO 11522, GO 11727, GO 12027, and GO 12583.

  11. Trivalency of a Nanobody Specific for the Human Respiratory Syncytial Virus Fusion Glycoprotein Drastically Enhances Virus Neutralization and Impacts Escape Mutant Selection.

    PubMed

    Palomo, Concepción; Mas, Vicente; Detalle, Laurent; Depla, Erik; Cano, Olga; Vázquez, Mónica; Stortelers, Catelijne; Melero, José A

    2016-11-01

    ALX-0171 is a trivalent Nanobody derived from monovalent Nb017 that binds to antigenic site II of the human respiratory syncytial virus (hRSV) fusion (F) glycoprotein. ALX-0171 is about 6,000 to 10,000 times more potent than Nb017 in neutralization tests with strains of hRSV antigenic groups A and B. To explore the effect of this enhanced neutralization on escape mutant selection, viruses resistant to either ALX-0171 or Nb017 were isolated after serial passage of the hRSV Long strain in the presence of suboptimal concentrations of the respective Nanobodies. Resistant viruses emerged notably faster with Nb017 than with ALX-0171 and in both cases contained amino acid changes in antigenic site II of hRSV F. Detailed binding and neutralization analyses of these escape mutants as well as previously described mutants resistant to certain monoclonal antibodies (MAbs) offered a comprehensive description of site II mutations which are relevant for neutralization by MAbs and Nanobodies. Notably, ALX-0171 showed a sizeable neutralization potency with most escape mutants, even with some of those selected with the Nanobody, and these findings make ALX-0171 an attractive antiviral for treatment of hRSV infections.

  12. Exploring drive for thinness as a perfectionistic strategy to escape from shame experiences.

    PubMed

    Ferreira, Cláudia; Trindade, Inês A; Ornelas, Luísa

    2015-05-20

    Perfectionistic self-presentation defines the attempt at presenting the self as perfect through the public concealment of personal defects and/or through the display of attributes perceived as capable to gather positive attention of others. Although perfectionism has long been considered a central aspect of eating psychopathology mediational studies between this construct and these conditions are scarce. This study aimed at examining the mediational role of body image-related perfectionistic self-presentation in the effects of external shame and internal shame on drive for thinness, in a sample of young women. Results revealed body image-related perfectionistic self-presentation as a significant mediator (p < .05) of the relationships between external and internal shame, and drive for thinness. Furthermore, 86% and 69% of the effects of external shame and internal shame, respectively, were explained by their indirect effects through body image-related perfectionistic self-presentation on drive for thinness (95% CI). These results highlight that the control over eating may emerge as a maladaptive strategy to deal with shame when mediated by an endorsement in the belief that presenting a perfect body image is crucial to be accepted and valued by others. Study findings suggest that this perfectionistic strategy should be targeted while treating eating psychopathology.

  13. The Bootstrap Current and Neutral Beam Current Drive in DIII-D

    SciTech Connect

    Politzer, P.A.

    2005-10-15

    Noninductive current drive is an essential part of the implementation of the DIII-D Advanced Tokamak program. For an efficient steady-state tokamak reactor, the plasma must provide close to 100% bootstrap fraction (f{sub bs}). For noninductive operation of DIII-D, current drive by injection of energetic neutral beams [neutral beam current drive (NBCD)] is also important. DIII-D experiments have reached {approx}80% bootstrap current in stationary discharges without inductive current drive. The remaining current is {approx}20% NBCD. This is achieved at {beta}{sub N} [approximately equal to] {beta}{sub p} > 3, but at relatively high q{sub 95} ({approx}10). In lower q{sub 95} Advanced Tokamak plasmas, f{sub bs} {approx} 0.6 has been reached in essentially noninductive plasmas. The phenomenology of high {beta}{sub p} and {beta}{sub N} plasmas without current control is being studied. These plasmas display a relaxation oscillation involving repetitive formation and collapse of an internal transport barrier. The frequency and severity of these events increase with increasing {beta}, limiting the achievable average {beta} and causing modulation of the total current as well as the pressure. Modeling of both bootstrap and NBCD currents is based on neoclassical theory. Measurements of the total bootstrap and NBCD current agree with calculations. A recent experiment based on the evolution of the transient voltage profile after an L-H transition shows that the more recent bootstrap current models accurately describe the plasma behavior. The profiles and the parametric dependences of the local neutral beam-driven current density have not yet been compared with theory.

  14. Off-axis Neutral Beam Current Drive for Advanced Scenario Development in DIII-D

    SciTech Connect

    Murakami, M; Park, J; Petty, C; Luce, T; Heidbrink, W; Osborne, T; Wade, M; Austin, M; Brooks, N; Budny, R; Challis, C; DeBoo, J; deGrassie, J; Ferron, J; Gohil, P; Hobirk, J; Holcomb, C; Hollmann, E; Hong, R; Hyatt, A; Lohr, J; Lanctot, M; Makowski, M; McCune, D; Politzer, P; Prater, R; John, H S; Suzuki, T; West, W; Unterberg, E; Van Zeeland, M; Yu, J

    2008-10-13

    Modification of the two existing DIII-D neutral beam lines is proposed to allow vertical steering to provide off-axis neutral beam current drive (NBCD) as far off-axis as half the plasma radius. New calculations indicate very good current drive with good localization off-axis as long as the toroidal magnetic field, B{sub T}, and the plasma current, I{sub p}, are in the same direction (for a beam steered downward). The effects of helicity can be large: e.g., ITER off-axis NBCD can be increased by more than 20% if the B{sub T} direction is reversed. This prediction has been tested by an off-axis NBCD experiment using reduced size plasmas that are vertically shifted with the existing NBI on DIII-D. The existence of off-axis NBCD is evident in sawtooth and internal inductance behavior. By shifting the plasma upward or downward, or by changing the sign of the toroidal field, measured off-axis NBCD profiles, determined from MSE data, are consistent with predicted differences (40%-45%) arising from the NBI orientation with respect to the magnetic field lines. Modification of the DIII-D NB system will strongly support scenario development for ITER and future tokamaks as well as providing flexible scientific tools for understanding transport, energetic particles and heating and current drive.

  15. Limited naturally occurring escape in broadly neutralizing antibody epitopes in hepatitis C glycoprotein E2 and constrained sequence usage in acute infection.

    PubMed

    Rodrigo, Chaturaka; Walker, Melanie R; Leung, Preston; Eltahla, Auda A; Grebely, Jason; Dore, Gregory J; Applegate, Tanya; Page, Kimberly; Dwivedi, Sunita; Bruneau, Julie; Morris, Meghan D; Cox, Andrea L; Osburn, William; Kim, Arthur Y; Schinkel, Janke; Shoukry, Naglaa H; Lauer, Georg M; Maher, Lisa; Hellard, Margaret; Prins, Maria; Luciani, Fabio; Lloyd, Andrew R; Bull, Rowena A

    2017-04-01

    Broadly neutralizing antibodies have been associated with spontaneous clearance of the hepatitis C infection as well as viral persistence by immune escape. Further study of neutralizing antibody epitopes is needed to unravel pathways of resistance to virus neutralization, and to identify conserved regions for vaccine design. All reported broadly neutralizing antibody (BNAb) epitopes in the HCV Envelope (E2) glycoprotein were identified. The critical contact residues of these epitopes were mapped onto the linear E2 sequence. All publicly available E2 sequences were then downloaded and the contact residues within the BNAb epitopes were assessed for the level of conservation, as well as the frequency of occurrence of experimentally-proven resistance mutations. Epitopes were also compared between two sequence datasets obtained from samples collected at well-defined time points from acute (<180days) and chronic (>180days) infections, to identify any significant differences in residue usage. The contact residues for all BNAbs were contained within 3 linear regions of the E2 protein sequence. An analysis of 1749 full length E2 sequences from public databases showed that only 10 out of 29 experimentally-proven resistance mutations were present at a frequency >5%. Comparison of subtype 1a viral sequences obtained from samples collected during acute or chronic infection revealed significant differences at positions 610 and 655 with changes in residue (p<0.05), and at position 422 (p<0.001) with a significant difference in variability (entropy). The majority of experimentally-described escape variants do not occur frequently in nature. The observed differences between acute and chronically isolated sequences suggest constraints on residue usage early in infection.

  16. PAK6 targets to cell–cell adhesions through its N-terminus in a Cdc42-dependent manner to drive epithelial colony escape

    PubMed Central

    Morse, Elizabeth M.; Sun, Xiaowen; Olberding, Jordan R.; Ha, Byung Hak; Boggon, Titus J.; Calderwood, David A.

    2016-01-01

    ABSTRACT The six serine/threonine kinases in the p21-activated kinase (PAK) family are important regulators of cell adhesion, motility and survival. PAK6, which is overexpressed in prostate cancer, was recently reported to localize to cell–cell adhesions and to drive epithelial cell colony escape. Here we report that PAK6 targeting to cell–cell adhesions occurs through its N-terminus, requiring both its Cdc42/Rac interactive binding (CRIB) domain and an adjacent polybasic region for maximal targeting efficiency. We find PAK6 localization to cell–cell adhesions is Cdc42-dependent, as Cdc42 knockdown inhibits PAK6 targeting to cell–cell adhesions. We further find the ability of PAK6 to drive epithelial cell colony escape requires kinase activity and is disrupted by mutations that perturb PAK6 cell–cell adhesion targeting. Finally, we demonstrate that all type II PAKs (PAK4, PAK5 and PAK6) target to cell–cell adhesions, albeit to differing extents, but PAK1 (a type I PAK) does not. Notably, the ability of a PAK isoform to drive epithelial colony escape correlates with its targeting to cell–cell adhesions. We conclude that PAKs have a broader role in the regulation of cell–cell adhesions than previously appreciated. PMID:26598554

  17. Applying antibody-sensitive hypervariable region 1-deleted hepatitis C virus to the study of escape pathways of neutralizing human monoclonal antibody AR5A

    PubMed Central

    Velázquez-Moctezuma, Rodrigo; Bukh, Jens

    2017-01-01

    Hepatitis C virus (HCV) is a major cause of end-stage liver diseases. With 3–4 million new HCV infections yearly, a vaccine is urgently needed. A better understanding of virus escape from neutralizing antibodies and their corresponding epitopes are important for this effort. However, for viral isolates with high antibody resistance, or antibodies with moderate potency, it remains challenging to induce escape mutations in vitro. Here, as proof-of-concept, we used antibody-sensitive HVR1-deleted (ΔHVR1) viruses to generate escape mutants for a human monoclonal antibody, AR5A, targeting a rare cross-genotype conserved epitope. By analyzing the genotype 1a envelope proteins (E1/E2) of recovered Core-NS2 recombinant H77/JFH1ΔHVR1 and performing reverse genetic studies we found that resistance to AR5A was caused by substitution L665W, also conferring resistance to the parental H77/JFH1. The mutation did not induce viral fitness loss, but abrogated AR5A binding to HCV particles and intracellular E1/E2 complexes. Culturing J6/JFH1ΔHVR1 (genotype 2a), for which fitness was decreased by L665W, with AR5A generated AR5A-resistant viruses with the substitutions I345V, L665S, and S680T, which we introduced into J6/JFH1 and J6/JFH1ΔHVR1. I345V increased fitness but had no effect on AR5A resistance. L665S impaired fitness and decreased AR5A sensitivity, while S680T combined with L665S compensated for fitness loss and decreased AR5A sensitivity even further. Interestingly, S680T alone had no fitness effect but sensitized the virus to AR5A. Of note, H77/JFH1L665S was non-viable. The resistance mutations did not affect cell-to-cell spread or E1/E2 interactions. Finally, introducing L665W, identified in genotype 1, into genotypes 2–6 parental and HVR1-deleted variants (not available for genotype 4a) we observed diverse effects on viral fitness and a universally pronounced reduction in AR5A sensitivity. Thus, we were able to take advantage of the neutralization-sensitive HVR1

  18. Substitution at Aspartic Acid 1128 in the SARS Coronavirus Spike Glycoprotein Mediates Escape from a S2 Domain-Targeting Neutralizing Monoclonal Antibody

    PubMed Central

    Ng, Oi-Wing; Keng, Choong-Tat; Leung, Cynthia Sau-Wai; Peiris, J. S. Malik; Poon, Leo Lit Man; Tan, Yee-Joo

    2014-01-01

    The Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) is the etiological agent for the infectious disease, SARS, which first emerged 10 years ago. SARS-CoV is a zoonotic virus that has crossed the species barriers to infect humans. Bats, which harbour a diverse pool of SARS-like CoVs (SL-CoVs), are believed to be the natural reservoir. The SARS-CoV surface Spike (S) protein is a major antigenic determinant in eliciting neutralizing antibody production during SARS-CoV infection. In our previous work, we showed that a panel of murine monoclonal antibodies (mAbs) that target the S2 subunit of the S protein are capable of neutralizing SARS-CoV infection in vitro (Lip KM et al, J Virol. 2006 Jan; 80(2): 941–50). In this study, we report our findings on the characterization of one of these mAbs, known as 1A9, which binds to the S protein at a novel epitope within the S2 subunit at amino acids 1111–1130. MAb 1A9 is a broadly neutralizing mAb that prevents viral entry mediated by the S proteins of human and civet SARS-CoVs as well as bat SL-CoVs. By generating mutant SARS-CoV that escapes the neutralization by mAb 1A9, the residue D1128 in S was found to be crucial for its interaction with mAb 1A9. S protein containing the substitution of D1128 with alanine (D1128A) exhibited a significant decrease in binding capability to mAb 1A9 compared to wild-type S protein. By using a pseudotyped viral entry assay, it was shown that the D1128A substitution in the escape virus allows it to overcome the viral entry blockage by mAb 1A9. In addition, the D1128A mutation was found to exert no effects on the S protein cell surface expression and incorporation into virion particles, suggesting that the escape virus retains the same viral entry property as the wild-type virus. PMID:25019613

  19. Substitution at aspartic acid 1128 in the SARS coronavirus spike glycoprotein mediates escape from a S2 domain-targeting neutralizing monoclonal antibody.

    PubMed

    Ng, Oi-Wing; Keng, Choong-Tat; Leung, Cynthia Sau-Wai; Peiris, J S Malik; Poon, Leo Lit Man; Tan, Yee-Joo

    2014-01-01

    The Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) is the etiological agent for the infectious disease, SARS, which first emerged 10 years ago. SARS-CoV is a zoonotic virus that has crossed the species barriers to infect humans. Bats, which harbour a diverse pool of SARS-like CoVs (SL-CoVs), are believed to be the natural reservoir. The SARS-CoV surface Spike (S) protein is a major antigenic determinant in eliciting neutralizing antibody production during SARS-CoV infection. In our previous work, we showed that a panel of murine monoclonal antibodies (mAbs) that target the S2 subunit of the S protein are capable of neutralizing SARS-CoV infection in vitro (Lip KM et al, J Virol. 2006 Jan; 80(2): 941-50). In this study, we report our findings on the characterization of one of these mAbs, known as 1A9, which binds to the S protein at a novel epitope within the S2 subunit at amino acids 1111-1130. MAb 1A9 is a broadly neutralizing mAb that prevents viral entry mediated by the S proteins of human and civet SARS-CoVs as well as bat SL-CoVs. By generating mutant SARS-CoV that escapes the neutralization by mAb 1A9, the residue D1128 in S was found to be crucial for its interaction with mAb 1A9. S protein containing the substitution of D1128 with alanine (D1128A) exhibited a significant decrease in binding capability to mAb 1A9 compared to wild-type S protein. By using a pseudotyped viral entry assay, it was shown that the D1128A substitution in the escape virus allows it to overcome the viral entry blockage by mAb 1A9. In addition, the D1128A mutation was found to exert no effects on the S protein cell surface expression and incorporation into virion particles, suggesting that the escape virus retains the same viral entry property as the wild-type virus.

  20. Human Monoclonal Antibodies to a Novel Cluster of Conformational Epitopes on HCV E2 with Resistance to Neutralization Escape in a Genotype 2a Isolate

    PubMed Central

    Keck, Zhen-yong; Xia, Jinming; Wang, Yong; Wang, Wenyan; Krey, Thomas; Prentoe, Jannick; Carlsen, Thomas; Li, Angela Ying-Jian; Patel, Arvind H.; Lemon, Stanley M.; Bukh, Jens; Rey, Felix A.; Foung, Steven K. H.

    2012-01-01

    The majority of broadly neutralizing antibodies to hepatitis C virus (HCV) are against conformational epitopes on the E2 glycoprotein. Many of them recognize overlapping epitopes in a cluster, designated as antigenic domain B, that contains residues G530 and D535. To gain information on other regions that will be relevant for vaccine design, we employed yeast surface display of antibodies that bound to genotype 1a H77C E2 mutant proteins containing a substitution either at Y632A (to avoid selecting non-neutralizing antibodies) or D535A. A panel of nine human monoclonal antibodies (HMAbs) was isolated and designated as HC-84-related antibodies. Each HMAb neutralized cell culture infectious HCV (HCVcc) with genotypes 1–6 envelope proteins with varying profiles, and each inhibited E2 binding to the viral receptor CD81. Five of these antibodies neutralized representative genotypes 1–6 HCVcc. Epitope mapping identified a cluster of overlapping epitopes that included nine contact residues in two E2 regions encompassing aa418–446 and aa611–616. Effect on virus entry was measured using H77C HCV retroviral pseudoparticles, HCVpp, bearing an alanine substitution at each of the contact residues. Seven of ten mutant HCVpp showed over 90% reduction compared to wild-type HCVpp and two others showed approximately 80% reduction. Interestingly, four of these antibodies bound to a linear E2 synthetic peptide encompassing aa434–446. This region on E2 has been proposed to elicit non-neutralizing antibodies in humans that interfere with neutralizing antibodies directed at an adjacent E2 region from aa410–425. The isolation of four HC-84 HMAbs binding to the peptide, aa434–446, proves that some antibodies to this region are to highly conserved epitopes mediating broad virus neutralization. Indeed, when HCVcc were passaged in the presence of each of these antibodies, virus escape was not observed. Thus, the cluster of HC-84 epitopes, designated as antigenic domain D, is

  1. Fast wave current drive in neutral beam heated plasmas on DIII-D

    SciTech Connect

    Petty, C.C.; Forest, C.B.; Pinsker, R.I.

    1997-04-01

    The physics of non-inductive current drive and current profile control using the fast magnetosonic wave has been demonstrated on the DIII-D tokamak. In non-sawtoothing discharges formed by neutral beam injection (NBI), the radial profile of the fast wave current drive (FWCD) was determined by the response of the loop voltage profile to co, counter, and symmetric antenna phasings, and was found to be in good agreement with theoretical models. The application of counter FWCD increased the magnetic shear reversal of the plasma and delayed the onset of sawteeth, compared to co FWCD. The partial absorption of fast waves by energetic beam ions at high harmonics of the ion cyclotron frequency was also evident from a build up of fast particle pressure near the magnetic axis and a correlated increase in the neutron rate. The anomalous fast particle pressure and neutron rate increased with increasing NBI power and peaked when a harmonic of the deuterium cyclotron frequency passed through the center of the plasma. The experimental FWCD efficiency was highest at 2 T where the interaction between the fast waves and the beam ions was weakest; as the magnetic field strength was lowered, the FWCD efficiency decreased to approximately half of the maximum theoretical value.

  2. Neutral escape at Mars induced by the precipitation of high-energy protons and hydrogen atoms of the solar wind origin

    NASA Astrophysics Data System (ADS)

    Shematovich, Valery I.

    2017-04-01

    One of the first surprises of the NASA MAVEN mission was the observation by the SWIA instrument of a tenuous population of protons with solar wind energies travelling anti-sunward near periapsis, at altitudes of 150-250 km (Halekas et al., 2015). While the penetration of solar wind protons to low altitude is not completely unexpected given previous Mars Express results, this population maintains exactly the same velocity as the solar wind observed. From previous studies it was known that some fraction of the solar wind can interact with the extended corona of Mars. By charge exchange with the neutral particles in this corona, some fraction of the incoming solar wind protons can gain an electron and become an energetic neutral hydrogen atom. Once neutral, these particles penetrate through the Martian induced magnetosphere with ease, with free access to the collisional atmosphere/ionosphere. The origin, kinetics and transport of the suprathermal O atoms in the transition region (from thermosphere to exosphere) of the Martian upper atmosphere due to the precipitation of the high-energy protons and hydrogen atoms are discussed. Kinetic energy distribution functions of suprathermal and superthermal (ENA) oxygen atoms formed in the Martian upper atmosphere were calculated using the kinetic Monte Carlo model (Shematovich et al., 2011, Shematovich, 2013) of the high-energy proton and hydrogen atom precipitation into the atmosphere. These functions allowed us: (a) to estimate the non-thermal escape rates of neutral oxygen from the Martian upper atmosphere, and (b) to compare with available MAVEN measurements of oxygen corona. Induced by precipitation the escape of hot oxygen atoms may become dominant under conditions of extreme solar events - solar flares and coronal mass ejections, - as it was shown by recent observations of the NASA MAVEN spacecraft (Jakosky et al., 2015). This work is supported by the RFBR project and by the Basic Research Program of the Praesidium of

  3. Viral entry and escape from antibody-mediated neutralization influence hepatitis C virus reinfection in liver transplantation

    PubMed Central

    Fafi-Kremer, Samira; Fofana, Isabel; Soulier, Eric; Carolla, Patric; Meuleman, Philip; Leroux-Roels, Geert; Patel, Arvind H.; Cosset, François-Loïc; Pessaux, Patrick; Doffoël, Michel; Wolf, Philippe

    2010-01-01

    End-stage liver disease caused by chronic hepatitis C virus (HCV) infection is a leading cause for liver transplantation (LT). Due to viral evasion from host immune responses and the absence of preventive antiviral strategies, reinfection of the graft is universal. The mechanisms by which the virus evades host immunity to reinfect the liver graft are unknown. In a longitudinal analysis of six HCV-infected patients undergoing LT, we demonstrate that HCV variants reinfecting the liver graft were characterized by efficient entry and poor neutralization by antibodies present in pretransplant serum compared with variants not detected after transplantation. Monoclonal antibodies directed against HCV envelope glycoproteins or a cellular entry factor efficiently cross-neutralized infection of human hepatocytes by patient-derived viral isolates that were resistant to autologous host-neutralizing responses. These findings provide significant insights into the molecular mechanisms of viral evasion during HCV reinfection and suggest that viral entry is a viable target for prevention of HCV reinfection of the liver graft. PMID:20713596

  4. Neutral stellar winds that drive bipolar outflows in low-mass protostars

    NASA Technical Reports Server (NTRS)

    Lizano, Susana; Heiles, Carl; Koo, Bon-Ghul; Shu, Frank H.; Rodriguez, Luis F.

    1988-01-01

    The Arecibo radio telescope at the 21-cm line of atomic hydrogen has been used to detect a neutral atomic wind in the bipolar flow source HH 7-11. An atomic mass of about 0.015 solar associated with the rapidly flowing gas is deduced. The stellar mass-loss rate is roughly 3 x 10 to the -6th solar mass/yr if the crossing time of the decelerating wind is 5000 yr. The excess emission in the H I line core gives a total duration of the outflow of about 70,000 yr. A detailed analysis of the H I line shape yields a reasonable deceleration rate for the atomic wind if the stellar wind continuously entrains ambient molecular gas as it propagates from the protostar. A stellar wind with the described characteristics and a terminal velocity of 170 km/s would be more than sufficient to drive the known extended CO bipolar outflow in HH 7-11.

  5. Neutral stellar winds that drive bipolar outflows in low-mass protostars

    NASA Technical Reports Server (NTRS)

    Lizano, Susana; Heiles, Carl; Koo, Bon-Ghul; Shu, Frank H.; Rodriguez, Luis F.

    1988-01-01

    The Arecibo radio telescope at the 21-cm line of atomic hydrogen has been used to detect a neutral atomic wind in the bipolar flow source HH 7-11. An atomic mass of about 0.015 solar associated with the rapidly flowing gas is deduced. The stellar mass-loss rate is roughly 3 x 10 to the -6th solar mass/yr if the crossing time of the decelerating wind is 5000 yr. The excess emission in the H I line core gives a total duration of the outflow of about 70,000 yr. A detailed analysis of the H I line shape yields a reasonable deceleration rate for the atomic wind if the stellar wind continuously entrains ambient molecular gas as it propagates from the protostar. A stellar wind with the described characteristics and a terminal velocity of 170 km/s would be more than sufficient to drive the known extended CO bipolar outflow in HH 7-11.

  6. Experimental Investigation and Validation of Neutral Beam Current Drive for ITER Through ITPA Joint Experiments

    SciTech Connect

    Suzuki, T.; Akers, R. J.; Gates, D.A.; Gunter, S.; Heidbrink, W. W.; Hobirk, J.; Luce, T.C.; Murakami, Masanori; Park, Jin Myung; Turnyanskiy, M.

    2011-01-01

    Joint experiments investigating the off-axis neutral beam current drive (NBCD) capability to be utilized for advanced operation scenario development in ITER were conducted in four tokamaks (ASDEX Upgrade (AUG), DIII-D, JT-60U and MAST) through the international tokamak physics activity (ITPA). The following results were obtained in the joint experiments, where the toroidal field, B(t), covered 0.4-3.7 T, the plasma current, I(p), 0.5-1.2 MA, and the beam energy, E(b), 65-350 keV. A current profile broadened by off-axis NBCD was observed in MAST. In DIII-D and JT-60U, the NB driven current profile has been evaluated using motional Stark effect diagnostics and good agreement between the measured and calculated NB driven current profile was observed. In AUG (at low delta similar to 0.2) and DIII-D, introduction of a fast-ion diffusion coefficient of D(b) similar to 0.3-0.5 m(2) s(-1) in the calculation gave better agreement at high heating power (5 MW and 7.2 MW, respectively), suggesting anomalous transport of fast ions by turbulence. It was found through these ITPA joint experiments that NBCD related physics quantities reasonably agree with calculations (with D(b) = 0-0.5 m(2) s(-1)) in all devices when there is no magnetohydrodynamic (MHD) activity except ELMs. Proximity of measured off-axis beam driven current to the corresponding calculation with D(b) = 0 has been discussed for ITER in terms of a theoretically predicted scaling of fast-ion diffusion that depends on E(b)/T(e) for electrostatic turbulence or beta(t) for electromagnetic turbulence.

  7. Dust escape from Io

    NASA Astrophysics Data System (ADS)

    Flandes, Alberto

    2004-08-01

    The Dust ballerina skirt is a set of well defined streams composed of nanometric sized dust particles that escape from the Jovian system and may be accelerated up to >=200 km/s. The source of this dust is Jupiter's moon Io, the most volcanically active body in the Solar system. The escape of dust grains from Jupiter requires first the escape of these grains from Io. This work is basically devoted to explain this escape given that the driving of dust particles to great heights and later injection into the ionosphere of Io may give the particles an equilibrium potential that allow the magnetic field to accelerate them away from Io. The grain sizes obtained through this study match very well to the values required for the particles to escape from the Jovian system.

  8. Atmospheric escape from unmagnetized bodies

    NASA Astrophysics Data System (ADS)

    Brain, D. A.; Bagenal, F.; Ma, Y.-J.; Nilsson, H.; Stenberg Wieser, G.

    2016-12-01

    The upper atmospheres of unmagnetized solar system bodies interact more directly with their local plasma environment than their counterparts on magnetized bodies such as Earth. One consequence of this interaction is that atmospheric particles can gain energy from the flowing plasma, as well as solar photons, and escape to space. Escape proceeds through a number of different mechanisms that can remove neutral particles (Jeans escape, photochemical escape, and sputtering) and mechanisms that can remove ions (ion pickup, magnetic shear and tension-related escape, and pressure gradients). Here we discuss the plasma interactions and escape processes and rates from five solar system objects spanning 3 orders of magnitude in size: comets, Pluto, Titan, Mars, and Venus. We describe similarities and differences in escape for the different objects and provide four open questions that should be addressed in the coming years.

  9. Modeling of neutral beam injection heating and current drive during the ramp-up phase in KSTAR

    NASA Astrophysics Data System (ADS)

    Terzolo, L.

    2014-06-01

    For flexible control of the plasma pressure and the current profiles, which are essential for a high performance plasma with long pulse operation, KSTAR is going to implement several heating and current systems, which include Neutral Beam Injection (NBI), Ion Cyclotron Resonant Heting (ICRH)/Fast Wave Current Drive (FWCD), Lower Hybrid Current Drive (LHCD), and Eclectron Cyclotron Heating (ECH)/Electron Cyclotron Current Drive (ECCD). Here, the NBI system is typically used for the central heating and current drive. For the time being, only one NBI device (composed of 3 sources) is available in KSTAR. The first two sources were successfully commissioned in 2010 and 2013. The last source will be installed in 2014. In this work, we present a simulation study of the heating and current drive of the first NBI system (3 sources) during the ramp-up phase. We consider two different NBI configurations (low and high beam energy). The simulation is performed with NUBEAM, a well-recognized Monte-Carlo code. Several different types of KSTAR target equilibria (scan from lower to higher plasma density) are used for the calculation of the current drive, the heating and the different NB losses (shinethrough, charge exchange and bad orbit). The study shows the dependency of those quantities on the plasma density, the position of the NB source and the beam energy. It also shows that because of the shinethrough loss is too high, each NB source cannot be used when the plasma density is under a certain threshold. This study can be used to determine the starting time of the different NB sources during the KSTAR ramp-up phase.

  10. The Influence of Neutral Beam Injection on the Heating and Current Drive with Electron Cyclotron Wave on EAST

    NASA Astrophysics Data System (ADS)

    Chang, Pengxiang; Wu, Bin; Wang, Jinfang; Li, Yingying; Wang, Xiaoguang; Xu, Handong; Wang, Xiaojie; Liu, Yong; Zhao, Hailin; Hao, Baolong; Yang, Zhen; Zheng, Ting; Hu, Chundong

    2016-11-01

    Both neutral beam injection (NBI) and electron cyclotron resonance heating (ECRH) have been applied on the Experimental Advanced Superconducting Tokamak (EAST) in the 2015 campaign. In order to achieve more effective heating and current drive, the effects of NBI on the heating and current drive with electron cyclotron wave (ECW) are analyzed utilizing the code TORAY and experimental data in the shot #54411 and #54417. According to the experimental and simulated results, for the heating with ECW, NBI can improve the heating efficiency and move the power deposition place towards the inside of the plasma. On the other hand, for the electron cyclotron current drive (ECCD), NBI can also improve the efficiency of ECCD and move the place of ECCD inward. These results will be valuable for the center heating, the achievement of fully non-inductive current drive operation and the suppression of magnetohydrodynamic (MHD) instabilities with ECW on EAST or ITER with many auxiliary heating methods. supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB101001 and 2014DFG61950) and National Natural Science Foundation of China (Nos. 11405212 and 11175211)

  11. Recombinant Receptor-Binding Domains of Multiple Middle East Respiratory Syndrome Coronaviruses (MERS-CoVs) Induce Cross-Neutralizing Antibodies against Divergent Human and Camel MERS-CoVs and Antibody Escape Mutants.

    PubMed

    Tai, Wanbo; Wang, Yufei; Fett, Craig A; Zhao, Guangyu; Li, Fang; Perlman, Stanley; Jiang, Shibo; Zhou, Yusen; Du, Lanying

    2017-01-01

    Middle East respiratory syndrome coronavirus (MERS-CoV) binds to cellular receptor dipeptidyl peptidase 4 (DPP4) via the spike (S) protein receptor-binding domain (RBD). The RBD contains critical neutralizing epitopes and serves as an important vaccine target. Since RBD mutations occur in different MERS-CoV isolates and antibody escape mutants, cross-neutralization of divergent MERS-CoV strains by RBD-induced antibodies remains unknown. Here, we constructed four recombinant RBD (rRBD) proteins with single or multiple mutations detected in representative human MERS-CoV strains from the 2012, 2013, 2014, and 2015 outbreaks, respectively, and one rRBD protein with multiple changes derived from camel MERS-CoV strains. Like the RBD of prototype EMC2012 (EMC-RBD), all five RBDs maintained good antigenicity and functionality, the ability to bind RBD-specific neutralizing monoclonal antibodies (MAbs) and the DPP4 receptor, and high immunogenicity, able to elicit S-specific antibodies. They induced potent neutralizing antibodies cross-neutralizing 17 MERS pseudoviruses expressing S proteins of representative human and camel MERS-CoV strains identified during the 2012-2015 outbreaks, 5 MAb escape MERS-CoV mutants, and 2 live human MERS-CoV strains. We then constructed two RBDs mutated in multiple key residues in the receptor-binding motif (RBM) of RBD and demonstrated their strong cross-reactivity with anti-EMC-RBD antibodies. These RBD mutants with diminished DPP4 binding also led to virus attenuation, suggesting that immunoevasion after RBD immunization is accompanied by loss of viral fitness. Therefore, this study demonstrates that MERS-CoV RBD is an important vaccine target able to induce highly potent and broad-spectrum neutralizing antibodies against infection by divergent circulating human and camel MERS-CoV strains.

  12. Both species sorting and neutral processes drive assembly of bacterial communities in aquatic microcosms.

    PubMed

    Lee, Jack E; Buckley, Hannah L; Etienne, Rampal S; Lear, Gavin

    2013-11-01

    A focus of ecology is to determine drivers of community assembly. Here, we investigate effects of immigration and species sorting (environmental selection) on structuring aquatic bacterial communities in both colonised and previously uncolonised environments. We used nonsterilised and presterilised water from three chemically distinct ponds to establish microcosms, which were opened for 12, 24, 48, 96 or 167 h and then closed again to allow airborne bacterial immigration and subsequent succession. Community similarity, richness, evenness and the parameters of a neutral model were investigated after 167 h. Immigration appeared to govern the assembly of communities in the presterilised water as there were no significant differences in evenness among microcosm communities containing water from each pond. Statistical estimation of neutral model parameters confirmed these findings, because the estimated immigration rate changed significantly with time of exposure to immigration. Species sorting also occurred because significant differences in community similarity (for presterilised and nonsterilised communities) and evenness (only for nonsterilised communities) were detected among microcosms containing different pond water; the magnitude of these differences was greater for communities in nonsterilised microcosms. Our study provides evidence for both processes being important during the colonisation of aquatic environments and presents a novel way to apply the neutral model. © 2013 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

  13. Validation of on- and off-axis neutral beam current drive against experiment in DIII-D

    SciTech Connect

    Park, J. M.; Murakami, M.; Petty, C. C.; Osborne, T. H.; Van Zeeland, M. A.; Prater, R.; Luce, T. C.; Wade, M. R.; Brooks, N. H.; DeBoo, J. C.; DeGrassie, J. S.; Ferron, J. R.; Gohil, P.; Hong, R. M.; Hyatt, A. W.; Lohr, J.; Politzer, P. A.; St John, H. E.; West, W. P.; Heidbrink, W. W.

    2009-09-15

    Neutral beam current drive (NBCD) experiments in DIII-D using vertically shifted plasmas to move the current drive away from the axis have clearly demonstrated robust off-axis NBCD. Time-dependent measurements of magnetic field pitch angles by the motional Stark effect diagnostic are used to obtain the evolution of the poloidal magnetic flux, which indicates a broad off-axis NBCD profile with a peak at about half the plasma minor radius. In most cases, the measured off-axis NBCD profile is consistent with calculations using an orbit-following Monte Carlo code for the beam ion slowing down including finite-orbit effects provided there is no large-scale magnetohydrodynamic activity such as Alfven eigenmodes modes or sawteeth. An alternative analysis method shows good agreement between the measured pitch angles and those from simulations using transport-equilibrium codes. Two-dimensional image of Doppler-shifted fast ion D{sub {alpha}} light emitted by neutralized energetic ions shows clear evidence for a hollow profile of beam ion density, consistent with classical beam ion slowing down. The magnitude of off-axis NBCD is sensitive to the alignment of the beam injection relative to the helical pitch of the magnetic field lines. If the signs of toroidal magnetic field and plasma current yield the proper helicity, both measurement and calculation indicate that the efficiency is as good as on-axis NBCD because the increased fraction of trapped electrons reduces the electron shielding of the injected ion current, in contrast with electron current drive schemes where the trapping of electrons degrades the efficiency. The measured off-axis NBCD increases approximately linearly with the injection power, although a modest amount of fast ion diffusion is needed to explain an observed difference in the NBCD profile between the measurement and the calculation at high injection power.

  14. Validation of on- and off-axis neutral beam current drive against experiment in DIII-D

    SciTech Connect

    Park, Jin Myung; Murakami, Masanori; Unterberg, Ezekial A

    2009-01-01

    Neutral beam current drive (NBCD) experiments in DIII-D using vertically shifted plasmas to move the current drive away from the axis have clearly demonstrated robust off-axis NBCD. Time-dependent measurements of magnetic field pitch angles by the motional Stark effect diagnostic are used to obtain the evolution of the poloidal magnetic flux, which indicates a broad off-axis NBCD profile with a peak at about half the plasma minor radius. In most cases, the measured off-axis NBCD profile is consistent with calculations using an orbit-following Monte Carlo code for the beam ion slowing down including finite-orbit effects provided there is no large-scale magnetohydrodynamic activity such as Alfven eigenmodes modes or sawteeth. An alternative analysis method shows good agreement between the measured pitch angles and those from simulations using transport-equilibrium codes. Two-dimensional image of Doppler-shifted fast ion D-alpha light emitted by neutralized energetic ions shows clear evidence for a hollow profile of beam ion density, consistent with classical beam ion slowing down. The magnitude of off-axis NBCD is sensitive to the alignment of the beam injection relative to the helical pitch of the magnetic field lines. If the signs of toroidal magnetic field and plasma current yield the proper helicity, both measurement and calculation indicate that the efficiency is as good as on-axis NBCD because the increased fraction of trapped electrons reduces the electron shielding of the injected ion current, in contrast with electron current drive schemes where the trapping of electrons degrades the efficiency. The measured off-axis NBCD increases approximately linearly with the injection power, although a modest amount of fast ion diffusion is needed to explain an observed difference in the NBCD profile between the measurement and the calculation at high injection power.

  15. A Single Residue within the V5 Region of HIV-1 Envelope Facilitates Viral Escape from the Broadly Neutralizing Monoclonal Antibody VRC01*

    PubMed Central

    Guo, Dongxing; Shi, Xuanling; Arledge, Kelly C.; Song, Dingka; Jiang, Liwei; Fu, Lili; Gong, Xinqi; Zhang, Senyan; Wang, Xinquan; Zhang, Linqi

    2012-01-01

    VRC01, a broadly neutralizing monoclonal antibody, is capable of neutralizing a diverse array of HIV-1 isolates by mimicking CD4 binding with the envelope glycoprotein gp120. Nonetheless, resistant strains have been identified. Here, we examined two genetically related and two unrelated envelope clones, derived from CRF08_BC-infected patients, with distinct VRC01 neutralization profiles. A total of 22 chimeric envelope clones was generated by interchanging the loop D and/or V5 regions between the original envelopes or by single alanine substitutions within each region. Analysis of pseudoviruses built from these mutant envelopes showed that interchanging the V5 region between the genetically related or unrelated clones completely swapped their VRC01 sensitivity profiles. Mutagenesis analysis revealed that the asparagine residue at position 460 (Asn-460), a potential N-linked glycosylation site in the V5 region, is a key factor for observed resistance in these strains, which is further supported by our structural modeling. Moreover, changes in resistance were found to positively correlate with deviations in VRC01 binding affinity. Overall, our study indicates that Asn-460 in the V5 region is a critical determinant of sensitivity to VRC01 specifically in these viral strains. The long side chain of Asn-460, and potential glycosylation, may create steric hindrance that lowers binding affinity, thereby increasing resistance to VRC01 neutralization. PMID:23100255

  16. A single residue within the V5 region of HIV-1 envelope facilitates viral escape from the broadly neutralizing monoclonal antibody VRC01.

    PubMed

    Guo, Dongxing; Shi, Xuanling; Arledge, Kelly C; Song, Dingka; Jiang, Liwei; Fu, Lili; Gong, Xinqi; Zhang, Senyan; Wang, Xinquan; Zhang, Linqi

    2012-12-14

    VRC01, a broadly neutralizing monoclonal antibody, is capable of neutralizing a diverse array of HIV-1 isolates by mimicking CD4 binding with the envelope glycoprotein gp120. Nonetheless, resistant strains have been identified. Here, we examined two genetically related and two unrelated envelope clones, derived from CRF08_BC-infected patients, with distinct VRC01 neutralization profiles. A total of 22 chimeric envelope clones was generated by interchanging the loop D and/or V5 regions between the original envelopes or by single alanine substitutions within each region. Analysis of pseudoviruses built from these mutant envelopes showed that interchanging the V5 region between the genetically related or unrelated clones completely swapped their VRC01 sensitivity profiles. Mutagenesis analysis revealed that the asparagine residue at position 460 (Asn-460), a potential N-linked glycosylation site in the V5 region, is a key factor for observed resistance in these strains, which is further supported by our structural modeling. Moreover, changes in resistance were found to positively correlate with deviations in VRC01 binding affinity. Overall, our study indicates that Asn-460 in the V5 region is a critical determinant of sensitivity to VRC01 specifically in these viral strains. The long side chain of Asn-460, and potential glycosylation, may create steric hindrance that lowers binding affinity, thereby increasing resistance to VRC01 neutralization.

  17. Chinks in the armor of the HIV-1 Envelope glycan shield: Implications for immune escape from anti-glycan broadly neutralizing antibodies.

    PubMed

    Moyo, Thandeka; Ferreira, Roux-Cil; Davids, Reyaaz; Sonday, Zarinah; Moore, Penny L; Travers, Simon A; Wood, Natasha T; Dorfman, Jeffrey R

    2017-01-15

    Glycans on HIV-1 Envelope serve multiple functions including blocking epitopes from antibodies. We show that removal of glycan 301, a major target of anti-V3/glycan antibodies, has substantially different effects in two viruses. While glycan 301 on Du156.12 blocks epitopes commonly recognized by sera from chronically HIV-1-infected individuals, it does not do so on CAP45.G3, suggesting that removing the 301 glycan has a smaller effect on the integrity of the glycan shield in CAP45.G3. Changes in sensitivity to broadly neutralizing monoclonal antibodies suggest that the interaction between glycan 301 and the CD4 binding site differ substantially between these 2 viruses. Molecular modeling suggests that removal of glycan 301 likely exposes a greater surface area of the V3 and C4 regions in Du156.12. Our data indicate that the contribution of the 301 glycan to resistance to common neutralizing antibodies varies between viruses, allowing for easier selection for its loss in some viruses. Copyright © 2016 Elsevier B.V. All rights reserved.

  18. Human Immunodeficiency Virus Type 1 Escape from Cyclotriazadisulfonamide-Induced CD4-Targeted Entry Inhibition Is Associated with Increased Neutralizing Antibody Susceptibility▿

    PubMed Central

    Vermeire, Kurt; Van Laethem, Kristel; Janssens, Wouter; Bell, Thomas W.; Schols, Dominique

    2009-01-01

    Continuous specific downmodulation of CD4 receptor expression in T lymphocytes by the small molecule cyclotriazadisulfonamide (CADA) selected for the CADA-resistant human immunodeficiency virus type 1 (HIV-1) NL4.3 virus containing unique mutations in the C4 and V5 regions of gp120, likely stabilizing the CD4-binding conformation. The amino acid changes in Env were associated with decreased susceptibility to anti-CD4 monoclonal antibody treatment of the cells and with higher susceptibility of the virus to soluble CD4. In addition, the acquired ability of a CADA-resistant virus to infect cells with low CD4 expression was associated with an increased susceptibility of the virus to neutralizing antibodies from sera of several HIV-1-infected patients. PMID:19570853

  19. Mechanisms of Ionospheric Mass Escape

    NASA Technical Reports Server (NTRS)

    Moore, T. E.; Khazanov, G. V.

    2010-01-01

    The dependence of ionospheric O+ escape flux on electromagnetic energy flux and electron precipitation into the ionosphere is derived for a hypothetical ambipolar pick-up process, powered the relative motion of plasmas and neutral upper atmosphere, and by electron precipitation, at heights where the ions are magnetized but influenced by photo-ionization, collisions with gas atoms, ambipolar and centrifugal acceleration. Ion pick-up by the convection electric field produces "ring-beam" or toroidal velocity distributions, as inferred from direct plasma measurements, from observations of the associated waves, and from the spectra of incoherent radar echoes. Ring-beams are unstable to plasma wave growth, resulting in rapid relaxation via transverse velocity diffusion, into transversely accelerated ion populations. Ion escape is substantially facilitated by the ambipolar potential, but is only weakly affected by centrifugal acceleration. If, as cited simulations suggest, ion ring beams relax into non-thermal velocity distributions with characteristic speed equal to the local ion-neutral flow speed, a generalized "Jeans escape" calculation shows that the escape flux of ionospheric O+ increases with Poynting flux and with precipitating electron density in rough agreement with observations.

  20. Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks

    NASA Astrophysics Data System (ADS)

    Pace, D. C.; Collins, C. S.; Crowley, B.; Grierson, B. A.; Heidbrink, W. W.; Pawley, C.; Rauch, J.; Scoville, J. T.; Van Zeeland, M. A.; Zhu, Y. B.; The DIII-D Team

    2017-01-01

    A first-ever demonstration of controlling power and torque injection through time evolution of neutral beam energy has been achieved in recent experiments at the DIII-D tokamak (Luxon 2002 Nucl. Fusion 42 614). Pre-programmed waveforms for the neutral beam energy produce power and torque inputs that can be separately and continuously controlled. Previously, these inputs were tailored using on/off modulation of neutral beams resulting in large perturbations (e.g. power swings of over 1 MW). The new method includes, importantly for experiments, the ability to maintain a fixed injected power while varying the torque. In another case, different beam energy waveforms (in the same plasma conditions) produce significant changes in the observed spectrum of beam ion-driven instabilities. Measurements of beam ion loss show that one energy waveform results in the complete avoidance of coherent losses due to Alfvénic instabilities. This new method of neutral beam operation is intended for further application in a variety of DIII-D experiments including those concerned with high-performance steady state scenarios, fast particle effects, and transport in the low torque regime. Developing this capability would provide similar benefits and improved plasma control for other magnetic confinement fusion facilities.

  1. Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks

    DOE PAGES

    Pace, D. C.; Collins, C. S.; Crowley, B.; ...

    2016-09-28

    A first-ever demonstration of controlling power and torque injection through time evolution of neutral beam energy has been achieved in recent experiments at the DIII-D tokamak. Pre-programmed waveforms for the neutral beam energy produce power and torque inputs that can be separately and continuously controlled. Previously, these inputs were tailored using on/off modulation of neutral beams resulting in large perturbations (e.g. power swings of over 1 MW). The new method includes, importantly for experiments, the ability to maintain a fixed injected power while varying the torque. In another case, different beam energy waveforms (in the same plasma conditions) produce significantmore » changes in the observed spectrum of beam ion-driven instabilities. Measurements of beam ion loss show that one energy waveform results in the complete avoidance of coherent losses due to Alfvénic instabilities. This new method of neutral beam operation is intended for further application in a variety of DIII-D experiments including those concerned with high-performance steady state scenarios, fast particle effects, and transport in the low torque regime. As a result, developing this capability would provide similar benefits and improved plasma control for other magnetic confinement fusion facilities.« less

  2. Control of power, torque, and instability drive using in-shot variable neutral beam energy in tokamaks

    SciTech Connect

    Pace, D. C.; Collins, C. S.; Crowley, B.; Grierson, B. A.; Heidbrink, W. W.; Pawley, C.; Rauch, J.; Scoville, J. T.; Van Zeeland, M. A.; Zhu, Y. B.

    2016-09-28

    A first-ever demonstration of controlling power and torque injection through time evolution of neutral beam energy has been achieved in recent experiments at the DIII-D tokamak. Pre-programmed waveforms for the neutral beam energy produce power and torque inputs that can be separately and continuously controlled. Previously, these inputs were tailored using on/off modulation of neutral beams resulting in large perturbations (e.g. power swings of over 1 MW). The new method includes, importantly for experiments, the ability to maintain a fixed injected power while varying the torque. In another case, different beam energy waveforms (in the same plasma conditions) produce significant changes in the observed spectrum of beam ion-driven instabilities. Measurements of beam ion loss show that one energy waveform results in the complete avoidance of coherent losses due to Alfvénic instabilities. This new method of neutral beam operation is intended for further application in a variety of DIII-D experiments including those concerned with high-performance steady state scenarios, fast particle effects, and transport in the low torque regime. As a result, developing this capability would provide similar benefits and improved plasma control for other magnetic confinement fusion facilities.

  3. Sputtering at Mars: MAVEN observations of precipitating and escaping oxygen during nominal and extreme conditions

    NASA Astrophysics Data System (ADS)

    Curry, Shannon; Luhmann, Janet; Dong, Chuanfei; Ma, Yingjuan; Leblanc, Francois; Modolo, Ronan; Brain, David; Gruesbeck, Jacob; Hara, Takuya; Halekas, Jasper; Dong, Yaxue; Williamson, Hayley N.; Johnson, Robert E.; McFadden, James; Espley, Jared R.; Mitchell, David; Connerney, Jack; Eparvier, Frank; Lillis, Robert J.; Jakosky, Bruce

    2016-10-01

    Sputtering is believed to be one of the dominant escape mechanisms during the early epochs of our solar system when the solar activity and EUV intensities were much higher than the present day. Mars lacks a global dynamo magnetic field, which creates a scenario where the solar wind directly interacts with the upper atmosphere and newly created ions can be picked up and swept away by the background convection electric field. These pick-up ions can directly escape or precipitate back into the atmosphere and induce atmospheric sputtering of neutrals.The MAVEN spacecraft has observed the Mars upper atmosphere, ionosphere, magnetic topology and interactions with the Sun and solar wind during numerous Interplanetary Coronal Mass Ejection (ICME) impacts spanning from March 2015 to June 2016. ICMEs are associated with enhanced solar wind velocities, densities and magnetic field strength, and often drive heavy ion precipitation at much higher rates than during nominal conditions. Thus, ICMEs provide a unique environment for observing sputtering. We will compare MAVEN observations of heavy ion precipitation during nominal conditions as well as during ICMEs. Additionally, we will present global MHD and test particle simulations of the ICMEs in order to calculate sputtering escape rates for oxygen. Finally, we will use the observed and modeled sputtering escape rates to provide an initial estimate of the total sputtered atmospheric escape from Mars over billions of years.

  4. Observational Constraints on a Pluto Torus of Circumsolar Neutral Gas

    NASA Astrophysics Data System (ADS)

    Hill, M. E.; Kollmann, P.; McNutt, R. L., Jr.; Smith, H. T.; Bagenal, F.; Brown, L. E.; Elliott, H. A.; Haggerty, D. K.; Horanyi, M.; Krimigis, S. M.; Kusterer, M. B.; Lisse, C. M.; McComas, D. J.; Piquette, M. R.; Sidrow, E. J.; Strobel, D. F.; Szalay, J.; Vandegriff, J. D.; Zirnstein, E.; Ennico Smith, K.; Olkin, C.; Weaver, H. A., Jr.; Young, L. A.; Stern, S. A.

    2015-12-01

    We present the concept of a neutral gas torus surrounding the Sun, aligned with Pluto's orbit, and place observational constraints based primarily on comparison of New Horizons (NH) measurements with a 3-D Monte Carlo model adapted from analogous satellite tori surrounding Saturn and Jupiter. Such a torus, or perhaps partial torus, should result from neutral N2 escaping from Pluto's exosphere. Unlike other more massive planets closer to the Sun, neutrals escape Pluto readily owing, e.g., to the high thermal speed relative to the escape velocity. Importantly, escaped neutrals have a long lifetime due to the great distance from the Sun, ~100 years for photoionization of N2 and ~180 years for photoionization of N, which results from disassociated N2. Despite the lengthy 248-year orbit, these long e-folding lifetimes may allow an enhanced neutral population to form an extended gas cloud that modifies the N2 spatial profile near Pluto. These neutrals are not directly observable by NH but once ionized N2+ or N+ are picked up by the solar wind, reaching ~50 keV, making these pickup ions (PUIs) detectable by NH's Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument. PEPSSI observations analyzed to date may constrain the N2 density; the remaining ~95% of the encounter data, scheduled for downlink in August along with similarly anticipated data from the Solar Wind Around Pluto (SWAP) experiment, should help determine the Pluto outgassing rates. Measurements from SWAP include the solar wind speed, a quantity that greatly enhances PUI studies by enabling us to directly account for the PUI distribution's sensitive dependence on plasma speed. Note that anomalous cosmic ray Si observed at Voyager is overabundant by a factor of ~3000 relative to interstellar composition. This might be related to "outer source" PUIs, but the fact that N2 and Si are indistinguishable in many instruments could mean that N2 is actually driving this apparent Si discrepancy.

  5. Antibody Escape Kinetics of Equine Infectious Anemia Virus Infection of Horses

    PubMed Central

    Mealey, Robert H.

    2015-01-01

    Lentivirus escape from neutralizing antibodies (NAbs) is not well understood. In this work, we quantified antibody escape of a lentivirus, using antibody escape data from horses infected with equine infectious anemia virus. We calculated antibody blocking rates of wild-type virus, fitness costs of mutant virus, and growth rates of both viruses. These quantitative kinetic estimates of antibody escape are important for understanding lentiviral control by antibody neutralization and in developing NAb-eliciting vaccine strategies. PMID:25878104

  6. Cooperation of B cell lineages in induction of HIV-1-broadly neutralizing antibodies.

    PubMed

    Gao, Feng; Bonsignori, Mattia; Liao, Hua-Xin; Kumar, Amit; Xia, Shi-Mao; Lu, Xiaozhi; Cai, Fangping; Hwang, Kwan-Ki; Song, Hongshuo; Zhou, Tongqing; Lynch, Rebecca M; Alam, S Munir; Moody, M Anthony; Ferrari, Guido; Berrong, Mark; Kelsoe, Garnett; Shaw, George M; Hahn, Beatrice H; Montefiori, David C; Kamanga, Gift; Cohen, Myron S; Hraber, Peter; Kwong, Peter D; Korber, Bette T; Mascola, John R; Kepler, Thomas B; Haynes, Barton F

    2014-07-31

    Development of strategies for induction of HIV-1 broadly neutralizing antibodies (bnAbs) by vaccines is a priority. Determining the steps of bnAb induction in HIV-1-infected individuals who make bnAbs is a key strategy for immunogen design. Here, we study the B cell response in a bnAb-producing individual and report cooperation between two B cell lineages to drive bnAb development. We isolated a virus-neutralizing antibody lineage that targeted an envelope region (loop D) and selected virus escape mutants that resulted in both enhanced bnAb lineage envelope binding and escape mutant neutralization-traits associated with increased B cell antigen drive. Thus, in this individual, two B cell lineages cooperated to induce the development of bnAbs. Design of vaccine immunogens that simultaneously drive both helper and broadly neutralizing B cell lineages may be important for vaccine-induced recapitulation of events that transpire during the maturation of neutralizing antibodies in HIV-1-infected individuals.

  7. Soil and plant factors driving the community of soil-borne microorganisms across chronosequences of secondary succession of chalk grasslands with a neutral pH.

    PubMed

    Kuramae, Eiko; Gamper, Hannes; van Veen, Johannes; Kowalchuk, George

    2011-08-01

    Although soil pH has been shown to be an important factor driving microbial communities, relatively little is known about the other potentially important factors that shape soil-borne microbial community structure. This study examined plant and microbial communities across a series of neutral pH fields (pH=7.0-7.5) representing a chronosequence of secondary succession after former arable fields were taken out of production. These fields ranged from 17 to >66 years since the time of abandonment, and an adjacent arable field was included as a reference. Hierarchical clustering analysis, nonmetric multidimensional scaling and analysis of similarity of 52 different plant species showed that the plant community composition was significantly different in the different chronosequences, and that plant species richness and diversity increased with time since abandonment. The microbial community structure, as analyzed by phylogenetic microarrays (PhyloChips), was significantly different in arable field and the early succession stage, but no distinct microbial communities were observed for the intermediate and the late succession stages. The most determinant factors in shaping the soil-borne microbial communities were phosphorous and NH(4)(+). Plant community composition and diversity did not have a significant effect on the belowground microbial community structure or diversity.

  8. MAVEN measurements of photochemical escape of oxygen from the Martian atmosphere

    NASA Astrophysics Data System (ADS)

    Lillis, R. J.; Deighan, J.; Fox, J. L.; Bougher, S. W.; Cravens, T. E.; Lee, Y.; Mahaffy, P. R.; Benna, M.; Elrod, M. K.; Andersson, L.; McFadden, J.

    2015-10-01

    One of the primary goals of the Mars Atmosphere and Volatile Evolution Mission (MAVEN) mission is to characterize rates of atmospheric escape at the present epoch and relate those escape rates to solar drivers [1]. One of the major escape processes is known as photochemical escape, which is broadly defined as a process by which a) an exothermic reaction in the atmosphere/ionosphere results in an upward-traveling neutral particle whose velocity exceeds planetary escape velocity and b) the particle is not prevented from escaping through any subsequent collisions[2].At Mars, photochemical escape of oxygen is expected to be a significant channel for atmospheric escape, particularly in the early solar system when extreme ultraviolet (EUV) fluxes were much higher[3]. Thus characterizing this escape process is central to understanding the role escape to space has played in Mars' climate evolution.

  9. Gated escaping of ligand out of protein

    NASA Astrophysics Data System (ADS)

    Sheu, Sheh-Yi; Yang, Dah-Yen

    2000-01-01

    We construct a new gating model and develop a new theory to study the escaping process of a ligand out of a spherical cavity with a puncture (or gate) on the surface. The gate undulation can be regulated by any time-dependent function and the motion of the ligand inside the spherical cavity is mapped into a two-dimensional entropy potential surface. Hence the driving force of our model is entropy only. For a static gate, the escaping process corresponds to climbing a two-dimensional entropy barrier. When the gate open angle is small, the escaping rate is proportional to the square of the opening angle. The prefactor of the escaping rate constant depends on the curvature of the entropy potential surface. For coherent gating, the survival time depends not only on the gate undulation frequency but also on how the initial state is defined. On the escaping from protein, our escaping rate shows it is qualitatively consistent with the experimental result of ligand recombination in myoglobin.

  10. Structured Observations Reveal Slow HIV-1 CTL Escape

    PubMed Central

    Roberts, Hannah E.; Hurst, Jacob; Robinson, Nicola; Brown, Helen; Flanagan, Peter; Vass, Laura; Fidler, Sarah; Weber, Jonathan; Babiker, Abdel; Phillips, Rodney E.; McLean, Angela R.; Frater, John

    2015-01-01

    The existence of viral variants that escape from the selection pressures imposed by cytotoxic T-lymphocytes (CTLs) in HIV-1 infection is well documented, but it is unclear when they arise, with reported measures of the time to escape in individuals ranging from days to years. A study of participants enrolled in the SPARTAC (Short Pulse Anti-Retroviral Therapy at HIV Seroconversion) clinical trial allowed direct observation of the evolution of CTL escape variants in 125 adults with primary HIV-1 infection observed for up to three years. Patient HLA-type, longitudinal CD8+ T-cell responses measured by IFN-γ ELISpot and longitudinal HIV-1 gag, pol, and nef sequence data were used to study the timing and prevalence of CTL escape in the participants whilst untreated. Results showed that sequence variation within CTL epitopes at the first time point (within six months of the estimated date of seroconversion) was consistent with most mutations being transmitted in the infecting viral strain rather than with escape arising within the first few weeks of infection. Escape arose throughout the first three years of infection, but slowly and steadily. Approximately one third of patients did not drive any new escape in an HLA-restricted epitope in just under two years. Patients driving several escape mutations during these two years were rare and the median and modal numbers of new escape events in each patient were one and zero respectively. Survival analysis of time to escape found that possession of a protective HLA type significantly reduced time to first escape in a patient (p = 0.01), and epitopes escaped faster in the face of a measurable CD8+ ELISpot response (p = 0.001). However, even in an HLA matched host who mounted a measurable, specific, CD8+ response the average time before the targeted epitope evolved an escape mutation was longer than two years. PMID:25642847

  11. Natural selection and neutral evolution jointly drive population divergence between alpine and lowland ecotypes of the allopolyploid plant Anemone multifida (Ranunculaceae).

    PubMed

    McEwen, Jamie R; Vamosi, Jana C; Rogers, Sean M

    2013-01-01

    Population differentiation can be driven in large part by natural selection, but selectively neutral evolution can play a prominent role in shaping patters of population divergence. The decomposition of the evolutionary history of populations into the relative effects of natural selection and selectively neutral evolution enables an understanding of the causes of population divergence and adaptation. In this study, we examined heterogeneous genomic divergence between alpine and lowland ecotypes of the allopolyploid plant, Anemone multifida. Using peak height and dominant AFLP data, we quantified population differentiation at non-outlier (neutral) and outlier loci to determine the potential contribution of natural selection and selectively neutral evolution to population divergence. We found 13 candidate loci, corresponding to 2.7% of loci, with signatures of divergent natural selection between alpine and lowland populations and between alpine populations (Fst  = 0.074-0.445 at outlier loci), but neutral population differentiation was also evident between alpine populations (FST  = 0.041-0.095 at neutral loci). By examining population structure at both neutral and outlier loci, we determined that the combined effects of selection and neutral evolution are associated with the divergence of alpine populations, which may be linked to extreme abiotic conditions and isolation between alpine sites. The presence of outlier levels of genetic variation in structured populations underscores the importance of separately analyzing neutral and outlier loci to infer the relative role of divergent natural selection and neutral evolution in population divergence.

  12. Natural Selection and Neutral Evolution Jointly Drive Population Divergence between Alpine and Lowland Ecotypes of the Allopolyploid Plant Anemone multifida (Ranunculaceae)

    PubMed Central

    McEwen, Jamie R.; Vamosi, Jana C.; Rogers, Sean M.

    2013-01-01

    Population differentiation can be driven in large part by natural selection, but selectively neutral evolution can play a prominent role in shaping patters of population divergence. The decomposition of the evolutionary history of populations into the relative effects of natural selection and selectively neutral evolution enables an understanding of the causes of population divergence and adaptation. In this study, we examined heterogeneous genomic divergence between alpine and lowland ecotypes of the allopolyploid plant, Anemone multifida. Using peak height and dominant AFLP data, we quantified population differentiation at non-outlier (neutral) and outlier loci to determine the potential contribution of natural selection and selectively neutral evolution to population divergence. We found 13 candidate loci, corresponding to 2.7% of loci, with signatures of divergent natural selection between alpine and lowland populations and between alpine populations (Fst  = 0.074–0.445 at outlier loci), but neutral population differentiation was also evident between alpine populations (FST  = 0.041–0.095 at neutral loci). By examining population structure at both neutral and outlier loci, we determined that the combined effects of selection and neutral evolution are associated with the divergence of alpine populations, which may be linked to extreme abiotic conditions and isolation between alpine sites. The presence of outlier levels of genetic variation in structured populations underscores the importance of separately analyzing neutral and outlier loci to infer the relative role of divergent natural selection and neutral evolution in population divergence. PMID:23874801

  13. Strong purifying selection at genes escaping X chromosome inactivation.

    PubMed

    Park, Chungoo; Carrel, Laura; Makova, Kateryna D

    2010-11-01

    To achieve dosage balance of X-linked genes between mammalian males and females, one female X chromosome becomes inactivated. However, approximately 15% of genes on this inactivated chromosome escape X chromosome inactivation (XCI). Here, using a chromosome-wide analysis of primate X-linked orthologs, we test a hypothesis that such genes evolve under a unique selective pressure. We find that escape genes are subject to stronger purifying selection than inactivated genes and that positive selection does not significantly affect the evolution of these genes. The strength of selection does not differ between escape genes with similar versus different expression levels in males versus females. Intriguingly, escape genes possessing Y homologs evolve under the strongest purifying selection. We also found evidence of stronger conservation in gene expression levels in escape than inactivated genes. We hypothesize that divergence in function and expression between X and Y gametologs is driving such strong purifying selection for escape genes.

  14. THERMALLY DRIVEN ATMOSPHERIC ESCAPE

    SciTech Connect

    Johnson, Robert E.

    2010-06-20

    Accurately determining the escape rate from a planet's atmosphere is critical for determining its evolution. A large amount of Cassini data is now available for Titan's upper atmosphere and a wealth of data is expected within the next decade on escape from Pluto, Mars, and extra-solar planets. Escape can be driven by upward thermal conduction of energy deposited well below the exobase, as well as by nonthermal processes produced by energy deposited in the exobase region. Recent applications of a model for escape driven by upward thermal conduction, called the slow hydrodynamic escape model, have resulted in surprisingly large loss rates for the atmosphere of Titan, Saturn's largest moon. Based on a molecular kinetic simulation of the exobase region, these rates appear to be orders of magnitude too large. Therefore, the slow hydrodynamic model is evaluated here. It is shown that such a model cannot give a reliable description of the atmospheric temperature profile unless it is coupled to a molecular kinetic description of the exobase region. Therefore, the present escape rates for Titan and Pluto must be re-evaluated using the atmospheric model described here.

  15. The Aeronomy of Mars: Characterization by MAVEN of the Upper Atmosphere Reservoir That Regulates Volatile Escape

    NASA Astrophysics Data System (ADS)

    Bougher, S. W.; Cravens, T. E.; Grebowsky, J.; Luhmann, J.

    2015-12-01

    The Mars thermosphere-ionosphere-exosphere (TIE) system constitutes the atmospheric reservoir (i.e. available cold and hot planetary neutral and thermal ion species) that regulates present day escape processes from the planet. The characterization of this TIE system, including its spatial and temporal (e.g., solar cycle, seasonal, diurnal, episodic) variability is needed to determine present day escape rates. Without knowledge of the physics and chemistry creating this TIE region and driving its variations, it is not possible to constrain either the short term or long term histories of atmosphere escape from Mars. MAVEN (Mars Atmosphere and Volatile Evolution Mission) will make both in-situ and remote measurements of the state variables of the Martian TIE system. A full characterization of the thermosphere (˜100-250 km) and ionosphere (˜100-400 km) structure (and its variability) will be conducted with the collection of spacecraft in-situ measurements that systematically span most local times and latitudes, over a regular sampling of Mars seasons, and throughout the bottom half of the solar cycle. Such sampling will far surpass that available from existing spacecraft and ground-based datasets. In addition, remote measurements will provide a systematic mapping of the composition and structure of Mars neutral upper atmosphere and coronae (e.g. H, C, N, O), as well as probe lower altitudes. Such a detailed characterization is a necessary first step toward answering MAVEN's three main science questions (see Jakosky et al. 2014, this issue). This information will be used to determine present day escape rates from Mars, and provide an estimate of integrated loss to space throughout Mars history.

  16. Neutralizing antibody responses against autologous and heterologous viruses in acute versus chronic human immunodeficiency virus (HIV) infection: evidence for a constraint on the ability of HIV to completely evade neutralizing antibody responses.

    PubMed

    Deeks, Steven G; Schweighardt, Becky; Wrin, Terri; Galovich, Justin; Hoh, Rebecca; Sinclair, Elizabeth; Hunt, Peter; McCune, Joseph M; Martin, Jeffrey N; Petropoulos, Christos J; Hecht, Frederick M

    2006-06-01

    Acute human immunodeficiency virus (HIV) infection is associated with the rapid development of neutralization escape mutations. The degree to which viral evolution persists in chronic infection has not been well characterized, nor is it clear if all patients develop high-level neutralization antibody escape. We therefore measured neutralizing antibody responses against autologous and heterologous viruses in a cohort of acutely and chronically infected subjects (n = 65). Neutralizing antibody responses against both autologous virus and heterologous viruses were lower among individuals with acute infection than among those with chronic infection. Among chronically infected individuals, there was a negative correlation between the level of neutralizing antibodies against autologous virus and the level of viremia. In contrast, there was a positive correlation between the level of neutralizing antibodies against a panel of heterologous viruses and the level of viremia. Viral evolution, as defined by the presence of higher neutralizing titers directed against earlier viruses than against contemporaneous viruses, was evident for subjects with recent infection but absent for those with chronic infection. In summary, neutralizing antibody responses against contemporaneous autologous viruses are absent in early HIV infection but can be detected at low levels in chronic infection, particularly among those controlling HIV in the absence of therapy. HIV replication either directly or indirectly drives the production of increasing levels of antibodies that cross-neutralize heterologous primary isolates. Collectively, these observations indicate that although HIV continuously drives the production of neutralizing antibodies, there may be limits to the capacity of the virus to evolve continuously in response to these antibodies. These observations also suggest that the neutralizing antibody response may contribute to the long-term control of HIV in some patients while protecting

  17. MEMO: Mars Escape and Magnetic Orbiter

    NASA Astrophysics Data System (ADS)

    Chassefiere, E.; Langlais, B.; Leblanc, F.; Sotin, C.; Barabash, S.; Dehant, V.; Dougherty, M.; Lammer, H.; Mandea, M.; Vennerstrom, S.

    There are several reasons to believe that Mars could have become an Earth like planet rather than the present dry and cold planet. In particular, many elements suggest the presence of liquid water at the Martian surface during a relatively short period at an early stage of its history. Since liquid water may have been the birthplace for life on Earth, the fate of Martian water is one of the major key and yet unanswered question to be solved. Mars Escape and Magnetic Orbiter (MEMO) is a low periapsis orbiter of Mars devoted to the measurement of present escape and the characterization of the fossil magnetic field of Mars. The use of a low periapsis altitude orbit (120-150 km) is required to detect and quantify all populations of atoms and molecules involved in escape. It is also required to measure the magnetic field of Mars with an unprecedented spatial resolution that would allow getting a more precise timing of the dynamo and its disappearance. Achieving a full characterization of atmospheric escape, and extrapolating it back to the past requires: (i) to measure escape fluxes of neutral and ion species, and characterize the dynamics and chemistry of the regions of the atmosphere where escape occurs (thermosphere, ionosphere, exosphere), as well as their responses to solar activity, and (ii) to characterize the lateral variations of the magnetic field of lithospheric origin, and by extension, the timing of the Martian dynamo. Of particular interest is the extinction of the dynamo that is thought to have enhanced the atmospheric escape processes still operating today. The proposed low-periapsis orbiter will consist of the following elements: • An "Escape Package" to characterize by both in-situ and remote measurements the thermosphere, ionosphere, exosphere and solar wind interaction regions (from one hundred to several thousand km), including thermal, suprathermal 1 and energetic particles. • A "Magnetic Field Package", to characterize the magnetization of the

  18. Cockroaches keep predators guessing by using preferred escape trajectories

    PubMed Central

    Domenici, P.; Booth, D.; Blagburn, J.M.; Bacon, J. P.

    2009-01-01

    Summary Anti-predator behaviour is vital for most animals, and calls for accurate timing and swift motion. While fast reaction times [1] and predictable, context-dependent, escape initiation distances [2] are common features of most escape systems, previous work has highlighted the need for unpredictability in escape directions, in order to prevent predators from learning a repeated, fixed pattern [3–5]. Ultimate unpredictability would result from random escape trajectories. Although this strategy would deny any predictive power to the predator, it would also result in some escape trajectories towards the threat. Previous work has shown that escape trajectories are in fact generally directed away from the threat, although with a high variability [5–8]. However, the rules governing this variability are largely unknown. Here, we demonstrate tha t individual cockroaches (Periplaneta americana, a much studied model prey species [9–14]) keep each escape unpredictable by running along one of a set of preferred trajectories at fixed angles from the direction of the threatening stimulus. These results provide a new paradigm for understanding the behavio ural strategies for escape responses, underscoring the need to revisit the neural mechanisms controlling escape directions in the cockroach and similar animal models, and the evolutionary forces driving unpredictable, or “protean” [3], anti-predator behaviour. PMID:19013065

  19. Antibody escape kinetics of equine infectious anemia virus infection of horses.

    PubMed

    Schwartz, Elissa J; Nanda, Seema; Mealey, Robert H

    2015-07-01

    Lentivirus escape from neutralizing antibodies (NAbs) is not well understood. In this work, we quantified antibody escape of a lentivirus, using antibody escape data from horses infected with equine infectious anemia virus. We calculated antibody blocking rates of wild-type virus, fitness costs of mutant virus, and growth rates of both viruses. These quantitative kinetic estimates of antibody escape are important for understanding lentiviral control by antibody neutralization and in developing NAb-eliciting vaccine strategies. Copyright © 2015, American Society for Microbiology. All Rights Reserved.

  20. Extended Neutral Cloud around Pluto’s Orbit

    NASA Astrophysics Data System (ADS)

    Sidrow, Evan; Bagenal, F.

    2015-11-01

    Recent studies estimate the approximate escape rate of molecular nitrogen from Pluto as well as its ionization rate. In this study, we focus on the implications of this escaping nitrogen and the resulting extended neutral cloud around Pluto’s orbit by simulating the escaping nitrogen with a numerical model. Several unknown parameters are varied, including the dependence of Pluto’s production rate on orbital distance and the distribution of speeds at which nitrogen is escaping Pluto.

  1. Escape from Mars

    NASA Image and Video Library

    2017-07-10

    This image from NASA's Mars Reconnaissance Orbiter shows one of millions of small (10s of meters in diameter) craters and their ejecta material that dot the Elysium Planitia region of Mars. The small craters were likely formed when high-speed blocks of rock were thrown out by a much larger impact (about 10-kilometers in diameter) and fell back to the ground. Some of these blocks may actually escape Mars, which is how we get samples in the form of meteorites that fall to Earth. Other ejected blocks have insufficient velocity, or the wrong trajectory, to escape the Red Planet. As such, when one of these high-speed blocks impacts the surface, it makes what is called a "secondary" crater. These secondaries can form dense "chains" or "rays," which are radial to the crater that formed them. https://photojournal.jpl.nasa.gov/catalog/PIA21769

  2. The Escaping Upper Atmospheres of Hot Jupiters

    NASA Astrophysics Data System (ADS)

    Davidson, Eric; Jones, Gabrielle; Uribe, Ana; Carson, Joseph

    2017-01-01

    Hot Jupiters are massive gaseous planets which orbit closely to their parent star. The strong stellar irradiation at these small orbital separations causes the temperature of the upper atmosphere of the planet to rise. This can cause the planet's atmosphere to escape into space, creating an exoplanet outflow. We ascertained which factors determine the presence and structure of these outflows by creating one dimensional simulations of the density, pressure, velocity, optical depth, and neutral fraction of hot Jupiter atmospheres. This was done for planets of masses and radii ranging from 0.5-1.5 Mj and 0.5-1.5 Rj. We found the outflow rate to be highest for a planet of 0.5 Mj and 1.5 Rj at 5.3×10-14 Mj/Yr. We also found that the higher the escape velocity, the lower the chance of the planet having an outflow.

  3. Triton: topside ionosphere and nitrogen escape.

    PubMed

    Yung, Y L; Lyons, J R

    1990-09-01

    The principal ion in the ionosphere of Triton is N+. Energetic electrons of magnetospheric origin are the primary source of ionization, with a smaller contribution due to photoionization. To explain the topside plasma scale height, we postulate that N+ ions escape from Triton. The loss rate is 3.4 x 10(7) cm-2 s-1 or 7.9 x 10(24) ions s-1. Dissociative recombination of N2+ produces neutral exothermic fragments that can escape from Triton. The rate is estimated to be 8.6 x 10(6) N cm-2 s-1 or 2.0 x 10(24) atoms s-1. Implications for the magnetosphere of Neptune and Triton's evolution are discussed.

  4. [Escape mutants of hepatitis B virus].

    PubMed

    Jaramillo, Carlos Mario; Navas, María-Cristina

    2015-04-01

    The hepatitis B virus (HBV) infection is a public health problem worldwide. Considering HBV morbidity and mortality and the economic consequences .of this infection, policies and strategies to control it have been implemented, especially in regions where HBV infection is endemic, with high rates of vertical and horizontal infection. One of these strategies is the development of the recombinant vaccine. A 92% of the countries in the world have implemented the vaccine with a global coverage of 69%. The escape variants of HBV correspond to isolates with mutations in the sequence coding for the "a" determinant; these mutations result in changes in the amino acid sequence of the surface antigen (HBsAg) that prevent neutralization of viral particles by antibodies generated in response to vaccination or infection. The escape variants can infect vaccinated individuals and have been identified in the population of countries with different epidemiological patterns.

  5. Spacecraft Escape Capsule

    NASA Technical Reports Server (NTRS)

    Robertson, Edward A.; Charles, Dingell W.; Bufkin, Ann L.; Rodriggs, Liana M.; Peterson, Wayne; Cuthbert, Peter; Lee, David E.; Westhelle, Carlos

    2006-01-01

    A report discusses the Gumdrop capsule a conceptual spacecraft that would enable the crew to escape safely in the event of a major equipment failure at any time from launch through atmospheric re-entry. The scaleable Gumdrop capsule would comprise a command module (CM), a service module (SM), and a crew escape system (CES). The CM would contain a pressurized crew environment that would include avionic, life-support, thermal control, propulsive attitude control, and recovery systems. The SM would provide the primary propulsion and would also supply electrical power, life-support resources, and active thermal control to the CM. The CES would include a solid rocket motor, embedded within the SM, for pushing the CM away from the SM in the event of a critical thermal-protection-system failure or loss of control. The CM and SM would normally remain integrated with each other from launch through recovery, but could be separated using the CES, if necessary, to enable the safe recovery of the crew in the CM. The crew escape motor could be used, alternatively, as a redundant means of de-orbit propulsion for the CM in the event of a major system failure in the SM.

  6. Physical Processes for Driving Ionospheric Outflows in Global Simulations

    NASA Technical Reports Server (NTRS)

    Moore, Thomas Earle; Strangeway, Robert J.

    2009-01-01

    We review and assess the importance of processes thought to drive ionospheric outflows, linking them as appropriate to the solar wind and interplanetary magnetic field, and to the spatial and temporal distribution of their magnetospheric internal responses. These begin with the diffuse effects of photoionization and thermal equilibrium of the ionospheric topside, enhancing Jeans' escape, with ambipolar diffusion and acceleration. Auroral outflows begin with dayside reconnexion and resultant field-aligned currents and driven convection. These produce plasmaspheric plumes, collisional heating and wave-particle interactions, centrifugal acceleration, and auroral acceleration by parallel electric fields, including enhanced ambipolar fields from electron heating by precipitating particles. Observations and simulations show that solar wind energy dissipation into the atmosphere is concentrated by the geomagnetic field into auroral regions with an amplification factor of 10-100, enhancing heavy species plasma and gas escape from gravity, and providing more current carrying capacity. Internal plasmas thus enable electromagnetic driving via coupling to the plasma, neutral gas and by extension, the entire body " We assess the Importance of each of these processes in terms of local escape flux production as well as global outflow, and suggest methods for their implementation within multispecies global simulation codes. We complete 'he survey with an assessment of outstanding obstacles to this objective.

  7. Orbiter escape pole

    NASA Technical Reports Server (NTRS)

    Goodrich, Winston D. (Inventor); Wesselski, Clarence J. (Inventor); Pelischek, Timothy E. (Inventor); Becker, Bruce H. (Inventor); Kahn, Jon B. (Inventor); Grimaldi, Margaret E. (Inventor); McManamen, John P. (Inventor); Castro, Edgar O. (Inventor)

    1989-01-01

    A Shuttle type of aircraft (10) with an escape hatch (12) has an arcuately shaped pole housing (16) attachable to an interior wall and ceiling with its open end adjacent to the escape hatch. The pole housing 16 contains a telescopically arranged and arcuately shaped primary pole member (22) and extension pole member (23) which are guided by roller assemblies (30,35). The extension pole member (23) is slidable and extendable relative to the primary pole member (22). For actuation, a spring actuated system includes a spring (52) in the pole housing. A locking member (90) engages both pole members (22,23) through notch portions (85,86) in the pole members. The locking member selectively releases the extension pole member (23) and the primary pole member (22). An internal one-way clutch or anti-return mechanism prevents retraction of the extension pole member from an extended position. Shock absorbers (54)(150,152) are for absoring the energy of the springs. A manual backup deployment system is provided which includes a canted ring (104) biased by a spring member (108). A lever member (100) with a slot and pin connection (102) permits the mechanical manipulation of the canted ring to move the primary pole member. The ring (104) also prevents retraction of the main pole. The crew escape mechanism includes a magazine (60) and a number of lanyards (62), each lanyard being mounted by a roller loop (68) over the primary pole member (22). The strap on the roller loop has stitching for controlled release, a protection sheath (74) to prevent tangling and a hook member (69) for attachment to a crew harness.

  8. Lyman-Werner UV escape fractions from primordial haloes

    NASA Astrophysics Data System (ADS)

    Schauer, Anna T. P.; Whalen, Daniel J.; Glover, Simon C. O.; Klessen, Ralf S.

    2015-12-01

    Population III (Pop III) stars can regulate star formation in the primordial Universe in several ways. They can ionize nearby haloes, and even if their ionizing photons are trapped by their own haloes, their Lyman-Werner (LW) photons can still escape and destroy H2 in other haloes, preventing them from cooling and forming stars. LW escape fractions are thus a key parameter in cosmological simulations of early reionization and star formation but have not yet been parametrized for realistic haloes by halo or stellar mass. To do so, we perform radiation hydrodynamical simulations of LW UV escape from 9-120 M⊙ Pop III stars in 105-107 M⊙ haloes with ZEUS-MP. We find that photons in the LW lines (i.e. those responsible for destroying H2 in nearby systems) have escape fractions ranging from 0 to 85 per cent. No LW photons escape the most massive halo in our sample, even from the most massive star. Escape fractions for photons elsewhere in the 11.18-13.6 eV energy range, which can be redshifted into the LW lines at cosmological distances, are generally much higher, being above 60 per cent for all but the least massive stars in the most massive haloes. We find that shielding of H2 by neutral hydrogen, which has been neglected in most studies to date, produces escape fractions that are up to a factor of 3 smaller than those predicted by H2 self-shielding alone.

  9. Hypervelocity Technology (HVT) crew escape

    NASA Technical Reports Server (NTRS)

    Jines, Lanny A.

    1987-01-01

    Conceptual designs are being investigated for escape systems applicable to hypervelocity technology class aerospace vehicles. The concepts selected for further development will provide survivable escape and recovery throughout all phases of flight. Sixteen conceptual escape systems were identified, of which two were viable. The study vehicles included a horizontally launched vehicle (HLV) and a vertically launched vehicle (VLV). Computer-aided design models of the candidate escape systems were developed. State-of-the-art or near-term enabling technologies were identified in such areas as propulsion, life support, thermal protection, and deceleration.

  10. Ion Escape Rates from Mars

    NASA Astrophysics Data System (ADS)

    Brain, Dave; McFadden, Jim; Halekas, Jasper; Connerney, Jack; Eparvier, Frank; Mitchell, Dave; Andersson, Laila; Jakosky, Bruce; Dong, Yaxue; Egan, Hilary; Weber, Tristan; Ma, Yingjuan; Dong, Chuanfei; Modolo, Ronan; Bougher, Steve; Luhmann, Janet

    2017-04-01

    The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has been making science measurements of the Martian upper atmosphere and its escape to space since November 2014. A key part of this effort is the measurement of the escape rates of charged particles (ions) at present and over solar system history. The lack of a global dynamo magnetic field at Mars leaves its upper atmosphere more directly exposed to the impinging solar wind than magnetized planets such as Earth. For this reason it is thought that ion escape at Mars may have played a significant role in long term climate change. MAVEN measures escaping planetary ions directly, with high energy, mass, and time resolution. With more than two years of observations in hand, we will report the average ion escape rate and the spatial distribution of escaping ions as measured by MAVEN, including escape as a function of mass and energy. We will then report on the measured variability in ion escape rates with different drivers (e.g. solar EUV, solar wind pressure, etc.). We will use these results to provide an estimate of the total ion escape from Mars over billions of years, and discuss the implications for Mars and unmagnetized planets in general.

  11. Reconstructing the Alcatraz escape

    NASA Astrophysics Data System (ADS)

    Baart, F.; Hoes, O.; Hut, R.; Donchyts, G.; van Leeuwen, E.

    2014-12-01

    In the night of June 12, 1962 three inmates used a raft made of raincoatsto escaped the ultimate maximum security prison island Alcatraz in SanFrancisco, United States. History is unclear about what happened tothe escapees. At what time did they step into the water, did theysurvive, if so, where did they reach land? The fate of the escapees has been the subject of much debate: did theymake landfall on Angel Island, or did the current sweep them out ofthe bay and into the cold pacific ocean? In this presentation, we try to shed light on this historic case using avisualization of a high-resolution hydrodynamic simulation of the San Francisco Bay, combined with historical tidal records. By reconstructing the hydrodynamic conditions and using a particle based simulation of the escapees we show possible scenarios. The interactive model is visualized using both a 3D photorealistic and web based visualization. The "Escape from Alcatraz" scenario demonstrates the capabilities of the 3Di platform. This platform is normally used for overland flooding (1D/2D). The model engine uses a quad tree structure, resulting in an order of magnitude speedup. The subgrid approach takes detailed bathymetry information into account. The inter-model variability is tested by comparing the results with the DFlow Flexible Mesh (DFlowFM) San Francisco Bay model. Interactivity is implemented by converting the models from static programs to interactive libraries, adhering to the Basic ModelInterface (BMI). Interactive models are more suitable for answeringexploratory research questions such as this reconstruction effort. Although these hydrodynamic simulations only provide circumstantialevidence for solving the mystery of what happened during the foggy darknight of June 12, 1962, it can be used as a guidance and provides aninteresting testcase to apply interactive modelling.

  12. Perforin and Fas Cytolytic Pathways Coordinately Shape the Selection and Diversity of CD8+-T-Cell Escape Variants of Influenza Virus

    PubMed Central

    Price, Graeme E.; Huang, Lei; Ou, Rong; Zhang, Menghua; Moskophidis, Demetrius

    2005-01-01

    Antigenic variation is a viral strategy exploited to promote survival in the face of the host immune response and represents a major challenge for efficient vaccine development. Influenza viruses are pathogens with high transmissibility and mutation rates, enabling viral escape from immunity induced by prior infection or vaccination. Intense selection from neutralizing antibody drives antigenic changes in the surface glycoproteins, resulting in emergence of new strains able to reinfect hosts immune to previously circulating viruses. CD8+ cytotoxic T cells (CTLs) also provide protective immunity from influenza virus infection and may contribute to the antigenic evolution of influenza viruses. Utilizing mice transgenic for an influenza virus NP366-374 peptide-specific T-cell receptor, we demonstrated that the respiratory tract is a suitable site for generation of escape variants of influenza virus selected by CTL in vivo. In this report the contributions of the perforin and Fas pathways utilized by influenza virus-specific CTLs in viral clearance and selection of CTL escape variants have been evaluated. While transgenic CTLs deficient in either perforin- or Fas-mediated pathways are efficient in initial pulmonary viral control, variant virus emergence was observed in all the mice studied, although the spectrum of viral CTL escape variants selected varied profoundly. Thus, a less-restricted repertoire of escape variants was observed in mice with an intact perforin cytotoxic pathway compared with a limited variant diversity in perforin pathway-deficient mice, although maximal variant diversity was observed in mice having both Fas and perforin pathways intact. We conclude that selection of viral CTL escape variants reflects coordinate action between the tightly controlled perforin/granzyme pathway and the more promiscuous Fas/FasL pathway. PMID:15956596

  13. Perforin and Fas cytolytic pathways coordinately shape the selection and diversity of CD8+-T-cell escape variants of influenza virus.

    PubMed

    Price, Graeme E; Huang, Lei; Ou, Rong; Zhang, Menghua; Moskophidis, Demetrius

    2005-07-01

    Antigenic variation is a viral strategy exploited to promote survival in the face of the host immune response and represents a major challenge for efficient vaccine development. Influenza viruses are pathogens with high transmissibility and mutation rates, enabling viral escape from immunity induced by prior infection or vaccination. Intense selection from neutralizing antibody drives antigenic changes in the surface glycoproteins, resulting in emergence of new strains able to reinfect hosts immune to previously circulating viruses. CD8+ cytotoxic T cells (CTLs) also provide protective immunity from influenza virus infection and may contribute to the antigenic evolution of influenza viruses. Utilizing mice transgenic for an influenza virus NP366-374 peptide-specific T-cell receptor, we demonstrated that the respiratory tract is a suitable site for generation of escape variants of influenza virus selected by CTL in vivo. In this report the contributions of the perforin and Fas pathways utilized by influenza virus-specific CTLs in viral clearance and selection of CTL escape variants have been evaluated. While transgenic CTLs deficient in either perforin- or Fas-mediated pathways are efficient in initial pulmonary viral control, variant virus emergence was observed in all the mice studied, although the spectrum of viral CTL escape variants selected varied profoundly. Thus, a less-restricted repertoire of escape variants was observed in mice with an intact perforin cytotoxic pathway compared with a limited variant diversity in perforin pathway-deficient mice, although maximal variant diversity was observed in mice having both Fas and perforin pathways intact. We conclude that selection of viral CTL escape variants reflects coordinate action between the tightly controlled perforin/granzyme pathway and the more promiscuous Fas/FasL pathway.

  14. Structural acid-base chemistry in the metallic state: how μ3-neutralization drives interfaces and helices in Ti21Mn25.

    PubMed

    Stacey, Timothy E; Fredrickson, Daniel C

    2013-08-05

    Intermetallic phases remain a large class of compounds whose vast structural diversity is unaccounted for by chemical theory. A recent resurgence of interest in intermetallics, due to their potential in such applications as catalysis and thermoelectricity, has intensified the need for models connecting their compositions to their structures and stability. In this Article, we illustrate how the μ3-acidity model, an extension of the acid/base concept based on the Method of Moments, offers intuitive explanations for puzzling structural progressions occurring in intermetallics formed between transition metals. Simple CsCl-type structures are frequently observed for phases with near 1:1 ratios of transition metals. However, in two compounds, TiCu and Ti21Mn25, structures are adopted which deviate from this norm. μ3-Acidity analysis shows that the formation of CsCl-type phases in these exceptional systems would yield an imbalance in the acid/base strength pairing, resulting in overneutralization of the weaker partner and thus instability. Intriguing geometrical features emerge in response, which serve to improve the neutralization of the constituent elements. In both TiCu and Ti21Mn25, part of the structure shields weaker acids or bases from their stronger partners by enhancing homoatomic bonding in the sublattice of the weaker acid or base. In TiCu, this protection is accomplished by developing doubled layers of Ti atoms to reduce their heteroatomic contacts. In Ti21Mn25 the structural response is more extreme: Ti-poor TiMn2 domains are formed to guard Mn from the Ti atoms, while the remaining Ti segregates to regions between the TiMn2 domains. The geometrical details of this arrangement fine-tune the acid/base interactions for an even greater level of stability. The most striking of these occurs in the Ti-rich region, where a paucity of Mn neighbors leads to difficulty in achieving strong neutralization. The Ti atoms arrange themselves in helical tubes, maximizing

  15. Role of detergents in driving complex structural arrangements in colloidal suspensions of Photosystem I (PS I) via charge stabilization and neutralization

    NASA Astrophysics Data System (ADS)

    Niroomand, Hanieh; Mukherjee, Dibyendu; Khomami, Bamin

    2012-02-01

    Specific concentrations of detergents such as DM (n-Dodecyl-β-D-Maltoside) and Triton X-100 (TX-100) used for Photosystem I (PS I) stabilization in buffer solutions play significant roles in controlling the solution-phase protein-protein interactions. Such control on PS I-PS I interactions facilitates uniform monolayer deposition of PS I on self-assembled monolayer (SAM)/Au substrates, a critical step for their future incorporation into bio-hybrid photovoltaic devices. Moreover, electric-field assisted assembly from PS I solutions with TX-100 as the detergent facilitates the formation of uniform PS I monolayer. But, the same phenomenon is not observed for PS I suspensions with DM as the detergent. To explain the underlying colloidal physics of these systems, in-situ dynamic light scattering experiments under various incubation times and applied voltages reveal the role of DM in charge neutralization and in turn, significant reduction of the PS I dipole moment in solution. Furthermore, small angle X-ray scattering measurements provide the much-needed structural information for a detailed understanding of the protein-detergent complexation process. These detailed investigations point towards the use of random sequential adsorption techniques in creating systematic dense monolayers of PS I.

  16. Xenon Fractionation, Hydrogen Escape, and the Oxidation of the Earth

    NASA Astrophysics Data System (ADS)

    Zahnle, K. J.; Catling, D. C.

    2014-12-01

    Xenon in Earth's atmosphere is severely mass fractionated and depleted compared to any plausible solar system source material, yet Kr is unfractionated. These observations seem to imply that Xe has escaped from Earth. Vigorous hydrodynamic hydrogen escape can produce mass fractionation in heavy gases. The required hydrogen flux is very high but within the range permitted by solar EUV heating when Earth was 100 Myrs old or younger. However this model cannot explain why Xe escapes but Kr does not. Recently, what appears to be ancient atmospheric xenon has been recovered from several very ancient (3-3.5 Ga) terrestrial hydrothermal barites and cherts (Pujol 2011, 2013). What is eye-catching about this ancient Xe is that it is less fractionated that Xe in modern air. In other words, it appears that a process was active on Earth some 3 to 3.5 billion years ago that caused xenon to fractionate. By this time the Sun was no longer the EUV source that it used to be. If xenon was being fractionated by escape — currently the only viable hypothesis — it had to be in Earth's Archean atmosphere and under rather modest levels of EUV forcing. It should be possible for Xe, but not Kr, to escape from Earth as an ion. In a hydrodynamically escaping hydrogen wind the hydrogen is partially ionized. The key concepts are that ions are much more strongly coupled to the escaping flow than are neutrals (so that a relatively modest flow of H and H+ to space could carry Xe+ along with it, the flux can be small enough to be consistent with diffusion-limited flux), and that Xe alone among the noble gases is more easily ionized than hydrogen. This sort of escape is possible along the polar field lines, although a weak or absent magnetic field would likely work as well. The extended history of hydrogen escape implicit in Xe escape in the Archean is consistent with other suggestions that hydrogen escape in the Archean was considerable. Hydrogen escape plausibly played the key role in creating

  17. HIV Evolution and Escape.

    PubMed Central

    Richman, Douglas D.; Little, Susan J.; Smith, Davey M.; Wrin, Terri; Petropoulos, Christos; Wong, Joseph K.

    2004-01-01

    Human immunodeficiency virus (HIV) exemplifies the principles of Darwinian evolution with a telescoped chronology. Because of its high mutation rate and remarkably high rates of replication, evolution can be appreciated over periods of days in contrast to the durations conceived of by Darwin. Certain selective pressures that drive the evolution of HIV include chemotherapy, anatomic compartmentalization and the immune response. Examples of these selective forces on HIV evolution are described. Images Fig. 5 PMID:17060974

  18. THERMALLY DRIVEN ATMOSPHERIC ESCAPE: TRANSITION FROM HYDRODYNAMIC TO JEANS ESCAPE

    SciTech Connect

    Volkov, Alexey N.; Johnson, Robert E.; Tucker, Orenthal J.; Erwin, Justin T.

    2011-03-10

    Thermally driven escape from planetary atmospheres changes in nature from an organized outflow (hydrodynamic escape) to escape on a molecule-by-molecule basis (Jeans escape) with increasing Jeans parameter, {lambda}, the ratio of the gravitational to thermal energy of the atmospheric molecules. This change is described here for the first time using the direct simulation Monte Carlo method. When heating is predominantly below the lower boundary of the simulation region, R{sub 0}, and well below the exobase of a single-component atmosphere, the nature of the escape process changes over a surprisingly narrow range of Jeans parameters, {lambda}{sub 0}, evaluated at R{sub 0}. For an atomic gas, the transition occurs over {lambda}{sub 0} {approx} 2-3, where the lower bound, {lambda}{sub 0} {approx} 2.1, corresponds to the upper limit for isentropic, supersonic outflow. For {lambda}{sub 0} > 3 escape occurs on a molecule-by-molecule basis and we show that, contrary to earlier suggestions, for {lambda}{sub 0} > {approx}6 the escape rate does not deviate significantly from the familiar Jeans rate. In a gas composed of diatomic molecules, the transition shifts to {lambda}{sub 0} {approx} 2.4-3.6 and at {lambda}{sub 0} > {approx}4 the escape rate increases a few tens of percent over that for the monatomic gas. Scaling by the Jeans parameter and the Knudsen number, these results can be applied to thermally induced escape of the major species from solar and extrasolar planets.

  19. Modulation of terrestrial ion escape flux composition /by low-altitude acceleration and charge exchange chemistry/

    NASA Technical Reports Server (NTRS)

    Moore, T. E.

    1980-01-01

    Motivated by recent observations of highly variable hot plasma composition in the magnetosphere, control of the ionospheric escape flux composition by low-altitude particle dynamics and ion chemistry has been investigated for an e(-), H(+), O(+) ionosphere. It is found that the fraction of the steady state escape flux which is O(+) can be controlled very sensitively by the occurrence of parallel or transverse ion acceleration at altitudes below the altitude where the neutral oxygen density falls rapidly below the neutral hydrogen density and the ionospheric source of O(+) tends to be rapidly converted by charge exchange to H(+). The acceleration is required both to overcome the gravitational confinement of O(+) and to violate charge exchange equilibrium so that the neutral hydrogen atmosphere appears 'optically' thin to escaping O(+). Constraints are placed on the acceleration processes, and it is shown that O(+) escape is facilitated by observed ionospheric responses to magnetic activity.

  20. Bursty Escape on Mars

    NASA Astrophysics Data System (ADS)

    Dubinin, E.; Fraenz, M.; Woch, J.; Lundin, R.; Wei, J.; Barabash, S.

    2011-10-01

    Bursty or filamentary structuring of plasma flows is a typical feature of the Martian space. This phenomenon is revealed during time periods when MEX-ASPERA- 3 is operating in the high temporal resolution mode. Frequency of oscillations is about 10-50 mHz. Amplitude of flux variations reaches a factor of 10-30. Bursty origin of fluxes of oxygen ions can be the important process for solar wind induced escape on Mars. There are several mechanisms which can be responsible for the observed periodic bursts. Large-amplitude coherent pressure pulses generated by ion beams upstream the bow shock impact the magnetosphere and produce periodic pulses in forces pushing planetary plasma. Pressure pulses can arise downstream the bow shock - in the magnetosheath, which becomes to be decomposed into a sequence of periodic compressive waves. A wavy dynamics can also appear due to a multi-ion origin of the interacting plasmas since such a medium behaves as a specific rotator. At last, not at least, K-H or other types of large-scale MHD instabilities probably excited in the interface region can generate surface waves which will also modulate the tension forces. We present the different observations which can be interpreted in a favor of all the above mechanisms implying a complex and diverse plasma wave environment at Mars.

  1. Escape from Vela X

    SciTech Connect

    Hinton, J.; Funk, S.; Parsons, R.D.; Ohm, S.; /Leicester U. /Leeds U.

    2012-02-15

    While the Vela pulsar and its associated nebula are often considered as the archetype of a system powered by a {approx} 10{sup 4} year old isolated neutron star, many features of the spectral energy distribution of this pulsar wind nebula are both puzzling and unusual. Here we develop a model that for the first time relates the main structures in the system, the extended radio nebula (ERN) and the X-ray cocoon through continuous injection of particles with a fixed spectral shape. We argue that diffusive escape of particles from the ERN can explain the steep Fermi-LAT spectrum. In this scenario Vela X should produce a distinct feature in the locally-measured cosmic ray electron spectrum at very high energies. This prediction can be tested in the future using the Cherenkov Telescope Array (CTA). If particles are indeed released early in the evolution of PWNe and can avoid severe adiabatic losses, PWN provide a natural explanation for the rising positron fraction in the local CR spectrum.

  2. ESCAPE FROM VELA X

    SciTech Connect

    Hinton, J. A.; Ohm, S.; Funk, S.; Parsons, R. D.

    2011-12-10

    While the Vela pulsar and its associated nebula are often considered as the archetype of a system powered by a {approx}10{sup 4} year old isolated neutron star, many features of the spectral energy distribution of this pulsar wind nebula (PWN) are both puzzling and unusual. Here we develop a model that for the first time relates the main structures in the system, the extended radio nebula (ERN) and the X-ray cocoon through continuous injection of particles with a fixed spectral shape. We argue that diffusive escape of particles from the ERN can explain the steep Fermi-LAT spectrum. In this scenario Vela X should produce a distinct feature in the locally measured cosmic ray (CR) electron spectrum at very high energies. This prediction can be tested in the future using the Cherenkov Telescope Array. If particles are indeed released early in the evolution of PWNe and can avoid severe adiabatic losses, PWN provides a natural explanation for the rising positron fraction in the local CR spectrum.

  3. Photochemical escape of oxygen from the Martian atmosphere: first results from MAVEN

    NASA Astrophysics Data System (ADS)

    Lillis, Rob; Deigan, Justin; Fox, Jane; Bougher, Steve; Lee, Yuni; Cravens, Thomas; Rahmati, Ali; Jakosky, Bruce

    2015-04-01

    One of the primary goals of the MAVEN mission is to characterize rates of atmospheric escape at the present epoch and relate those escape rates to solar drivers. One of the major escape processes is known as photochemical escape, which is broadly defined as a process by which a) an exothermic reaction in the atmosphere results in an upward-traveling neutral particle whose velocity exceeds planetary escape velocity and b) the particle is not prevented from escaping through any subsequent collisions. At Mars, photochemical escape of oxygen is expected to be a significant channel for atmospheric escape, particularly in the early solar system when extreme ultraviolet (EUV) fluxes were much higher. Thus characterizing this escape process is central to understanding the role escape to space has played in Mars' climate evolution. Because escaping hot atoms cannot easily be directly measured, models of production and transport (through the atmosphere) of such atoms must be used to constrain escape rates. These models require altitude profiles of neutral densities and electron and ion densities and temperatures, as well as compositional information. All the relevant quantities upon which photochemical escape depends will be measured by MAVEN at the relevant altitudes (150-250 km). LPW will measure electron density and temperature, NGIMS will measure neutral and ion density and STATIC will measure ion density and temperature. 4 separate calculations must be made for every altitude profile: Profiles of O2+dissociative recombination (DR) rates will be calculated straightforwardly from electron temperature, electron density and O2+density. Profiles of rotational and vibrational distributions of O2+ ions will be calculated from profiles of CO2, O, O2, O+, CO2+ and CO+ via a lookup table from an empirical model. Profiles of energy distributions of hot O atoms will be calculated from the results of step 2 and from profiles of electron and ion temperatures. Profiles of all neutral

  4. Orbital Effects on Mercury's Escaping Sodium Exosphere

    NASA Technical Reports Server (NTRS)

    Schmidt, Carl A.; Wilson, Jody K.; Baumgardner, Jeffrey; Mendillo, Michael

    2009-01-01

    We present results from coronagraphic imaging of Mercury's sodium tail over a 7 deg field of view. Several sets of observations made at the McDonald Observatory since May 2007 show a tail of neutral sodium atoms stretching more than 1000 Mercury radii (R(sub m)) in length, or a full degree of sky. However, no tail was observed extending beyond 120 R(sub m) during the January 2008 MESSENGER Fly-by period, or during a similar orbital phase of Mercury in July 2008. Large changes in Mercury's heliocentric radial velocity cause Doppler shifts about the Fraunhofer absorption features; the resultant change in solar flux and radiation pressure is the primary cause of the observed variation in tail brightness. Smaller fluctuations in brightness may exist due to changing source rates at the surface, but we have no explicit evidence for such changes in this data set. The effects of radiation pressure on Mercury's escaping atmosphere are investigated using seven observations spanning different orbital phases. Total escape rates of atmospheric sodium are estimated to be between 5 and 13 x 10(exp 23) atoms/s and show a correlation to radiation pressure. Candidate sources of Mercury's sodium exosphere include desorption by UV sunlight, thermal desorption, solar wind channeled along Mercury's magnetic field lines, and micro-meteor impacts. Wide-angle observations of the full extent of Mercury's sodium tail offer opportunities to enhance our understanding of the time histories of these source rates.

  5. Orbital Effects on Mercury's Escaping Sodium Exosphere

    NASA Technical Reports Server (NTRS)

    Schmidt, Carl A.; Wilson, Jody K.; Baumgardner, Jeffrey; Mendillo, Michael

    2009-01-01

    We present results from coronagraphic imaging of Mercury's sodium tail over a 7 deg field of view. Several sets of observations made at the McDonald Observatory since May 2007 show a tail of neutral sodium atoms stretching more than 1000 Mercury radii (R(sub m)) in length, or a full degree of sky. However, no tail was observed extending beyond 120 R(sub m) during the January 2008 MESSENGER Fly-by period, or during a similar orbital phase of Mercury in July 2008. Large changes in Mercury's heliocentric radial velocity cause Doppler shifts about the Fraunhofer absorption features; the resultant change in solar flux and radiation pressure is the primary cause of the observed variation in tail brightness. Smaller fluctuations in brightness may exist due to changing source rates at the surface, but we have no explicit evidence for such changes in this data set. The effects of radiation pressure on Mercury's escaping atmosphere are investigated using seven observations spanning different orbital phases. Total escape rates of atmospheric sodium are estimated to be between 5 and 13 x 10(exp 23) atoms/s and show a correlation to radiation pressure. Candidate sources of Mercury's sodium exosphere include desorption by UV sunlight, thermal desorption, solar wind channeled along Mercury's magnetic field lines, and micro-meteor impacts. Wide-angle observations of the full extent of Mercury's sodium tail offer opportunities to enhance our understanding of the time histories of these source rates.

  6. Characterizing Atmospheric Escape from Mars Today and Through Time, with MAVEN

    NASA Astrophysics Data System (ADS)

    Lillis, R. J.; Brain, D. A.; Bougher, S. W.; Leblanc, F.; Luhmann, J. G.; Jakosky, B. M.; Modolo, R.; Fox, J.; Deighan, J.; Fang, X.; Wang, Y. C.; Lee, Y.; Dong, C.; Ma, Y.; Cravens, T.; Andersson, L.; Curry, S. M.; Schneider, N.; Combi, M.; Stewart, I.; Clarke, J.; Grebowsky, J.; Mitchell, D. L.; Yelle, R.; Nagy, A. F.; Baker, D.; Lin, R. P.

    2015-12-01

    Two of the primary goals of the MAVEN mission are to determine how the rate of escape of Martian atmospheric gas to space at the current epoch depends upon solar influences and planetary parameters and to estimate the total mass of atmosphere lost to space over the history of the planet. Along with MAVEN's suite of nine science instruments, a collection of complementary models of the neutral and plasma environments of Mars' upper atmosphere and near-space environment are an indispensable part of the MAVEN toolkit, for three primary reasons. First, escaping neutrals will not be directly measured by MAVEN and so neutral escape rates must be derived, via models, from in situ measurements of plasma temperatures and neutral and plasma densities and by remote measurements of the extended exosphere. Second, although escaping ions will be directly measured, all MAVEN measurements are limited in spatial coverage, so global models are needed for intelligent interpolation over spherical surfaces to calculate global escape rates. Third, MAVEN measurements will lead to multidimensional parameterizations of global escape rates for a range of solar and planetary parameters, but further global models informed by MAVEN data will be required to extend these parameterizations to the more extreme conditions that likely prevailed in the early solar system, which is essential for determining total integrated atmospheric loss. We describe these modeling tools and the strategies for using them in concert with MAVEN measurements to greater constrain the history of atmospheric loss on Mars.

  7. Photochemical escape of oxygen from the Martian atmosphere: new insights from MAVEN

    NASA Astrophysics Data System (ADS)

    Lillis, R. J.; Deighan, J.; Bougher, S. W.; Cravens, T.; Fox, J. L.; Lee, Y.; Rahmati, A.; McFadden, J. P.; Benna, M.; Mahaffy, P. R.; Elrod, M. K.; Andersson, L.; Fowler, C. M.; Curry, S.; Gröller, H.; Jakosky, B. M.

    2015-12-01

    One of the primary goals of the MAVEN mission is to characterize rates of atmospheric escape from Mars at the present epoch and relate those escape rates to solar drivers. One of the known escape processes is photochemical escape, where a) an exothermic chemical reaction in the atmosphere results in an upward-traveling neutral particle whose velocity exceeds planetary escape velocity and b) the particle is not prevented from escaping through any subsequent collisions. Because escaping hot atoms are not directly measured, models of production and transport (through the atmosphere) of such atoms must be used to constrain photochemical escape rates. These models require altitude profiles of neutral densities and electron and ion densities and temperatures, as well as compositional information, all of which are measured by MAVEN instruments at the relevant altitudes (150-300 km). For every altitude profile: Profiles of O2+ dissociative recombination (DR) rates will be calculated from electron temperature, electron density and O2+ density. Profiles of energy distributions of hot O atoms will be calculated from profiles of electron and ion temperatures. Profiles of all neutral densities will be input into models of hot O transport in order to calculate photochemical escape fluxes from DR of O2+. We will present photochemical escape fluxes as a function of several factors, in particular solar zenith angle and EUV flux. This, combined with further simulations with progressively higher EUV fluxes, will eventually enable a total integrated loss estimate over the course of Martian history and hence a determination of the impact of this loss process on the evolution of the Martian climate.

  8. Escape of water molecular from Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Li, Jiaxi; Li, Wenfeng; Zhang, Jianwei

    2014-03-01

    Understanding and controlling the transport of water molecules through nanopores have attracted great interest due to potential applications for designing novel nanofluidic devices, machines and sensors. In this work, we theoretically investigate the effects of an external nonuniform electric field on the escape of water molecules through single-walled carbon nanotubes (SWNTs) by using of molecular dynamics (MD) simulations. When polar water molecules are placed in the gradient electric field, the electric force is experienced that can drive the water molecules. Molecular dynamics simulations show that the escape probability of water obeys the Boltzmann distribution. Our results show that energy barrier delta E is independent of temperature which indicates that it is a single-barrier system. From the MD results statistics, the key parameters could be determined such that the relationship between energy barrier delta E and diameter of SWNTs and nozzle distance of the charge r would be revealed that could deepen our current theoretical understanding on transport of water molecular inside SWNTs with the nonuniform electric field.

  9. MAVEN in situ measurements of photochemical escape of oxygen from Mars

    NASA Astrophysics Data System (ADS)

    Lillis, Robert; Deighan, Justin; Fox, Jane; Bougher, Stephen; Lee, Yuni; Cravens, Thomas; Rahmati, Ali; Mahaffy, Paul; Benna, Mehdi; Groller, Hannes; Jakosky, Bruce

    2016-04-01

    One of the primary goals of the MAVEN mission is to characterize rates of atmospheric escape from Mars at the present epoch and relate those escape rates to solar drivers. One of the known escape processes is photochemical escape, where a) an exothermic chemical reaction in the atmosphere results in an upward-traveling neutral particle whose velocity exceeds planetary escape velocity and b) the particle is not prevented from escaping through subsequent collisions. At Mars, photochemical escape of oxygen is expected to be a significant channel for atmospheric escape, particularly in the early solar system when extreme ultraviolet (EUV) fluxes were much higher. Thus characterizing this escape process and its variability with solar drivers is central to understanding the role escape to space has played in Mars' climate evolution. We use near-periapsis (<400 km altitude) data from three MAVEN instruments: the Langmuir Probe and Waves (LPW) instrument measures electron density and temperature, the Suprathermal And Thermal Ion Composition (STATIC) experiment measures ion temperature and the Neutral Gas and Ion Mass Spectrometer (NGIMS) measures neutral and ion densities. For each profile of in situ measurements, we make several calculations, each as a function of altitude. The first uses electron and temperatures and simulates the dissociative recombination of both O2+ and CO2+ to calculate the probability distribution for the initial energies of the resulting hot oxygen atoms. The second is a Monte Carlo hot atom transport model that takes that distribution of initial O energies and the measured neutral density profiles and calculates the probability that a hot atom born at that altitude will escape. The third takes the measured electron and ion densities and electron temperatures and calculates the production rate of hot O atoms. We then multiply together the profiles of hot atom production and escape probability to get profiles of the production rate of escaping atoms

  10. Escaping from Rejection

    PubMed Central

    Lynch, Raymond J.; Platt, Jeffrey L.

    2009-01-01

    Summary Those engaged in clinical transplantation and transplantation immunology have always taken as a central objective the elucidation of means to prevent graft rejection by the recipient immune system. Conceptually, such mechanisms stem from the concept of Paul Ehrlich that all organisms can selectively avoid autotoxicity; i.e. they exhibit horror autotoxicus. Some mechanisms of horror autotoxicus now understood. T lymphocytes and B lymphocytes recognize foreign antigens but not some auto-antigens. Clonal deletion generates lacunae in what is otherwise a virtually limitless potential to recognize antigens. We call this mechanism structural tolerance. Where imperfections in structural tolerance allow self-recognition, the full activation of lymphocytes and generation of effector activity depends on delivery of accessory signals generated by infection and/or injury. The absence of accessory signals prevents or even suppresses immunological responses. We call this dichotomy of responsiveness conditional tolerance. When, despite structural and conditional tolerance, effector activity perturbs autologous cells, metabolism changes in ways that protect against injury. We use the term accommodation to refer to this acquired protection against injury. Structural and conditional tolerance and accommodation overlap in such a way that potentially toxic products can be generated to control microorganisms and neutralize toxins without overly damaging adjacent cells. The central challenge in transplantation, then, should be the orchestration of structural and conditional tolerance and accommodation in such a way that toxic products can still be generated for defense while preserving graft function and survival. Since the earliest days of transplantation, immunobiologists have sought means by which to prevent recognition and rejection of foreign tissue. The goal of these strategies is the retention of recipient immune function while selectively avoiding graft injury. While

  11. On the hydrodynamic model of thermal escape from planetary atmospheres and its comparison with kinetic simulations

    NASA Astrophysics Data System (ADS)

    Volkov, A. N.

    2016-06-01

    Parkers' model of thermal escape implies the search of solutions of one-dimensional hydrodynamic equations for an inviscid but thermally conducting gas with a critical point and vanishing temperature far from the source. The properties of solutions of this model are studied for neutral mon- and diatomic gases with the viscosity index varying from 1/2 to 1. The domains of existence and uniqueness of solutions in terms of the source Jeans escape parameter and Knudsen number are established. The solutions are found to exist only in a narrow range of the critical point Jeans parameter. The lower and upper limits of this range correspond to solutions that are dominated by either heat conduction or adiabatic expansion. Thermal escape described by Parker's model occurs in two asymptotic regimes: the low-density (LD) regime, when escape is dominated by heat conduction, and the high-density (HD) regime, when escape is dominated by adiabatic expansion. Expressions for the mass and energy escape rates in these regimes are found theoretically. The comparison of results of hydrodynamic and kinetic simulations performed in identical conditions shows that Parker's model is capable of describing thermal escape only in the HD regime, providing decent agreement with the kinetic model in terms of the atmospheric structure below the exobase and the mass and energy escape rates. In the LD regime, Parker's model predicts a much faster drop in atmospheric temperature and less extended atmospheres, and can both over- and underestimate the escape rates in orders of magnitude.

  12. Belt fires and mine escape problems

    SciTech Connect

    Kovac, J.G.; Lazzara, C.P.; Kravitz, J.H.

    1996-12-31

    A conveyor belt fire in an underground coal mine is a serious threat to life and property. About 30% of the reportable underground coal mine fires from 1988 through 1992 occurred in belt entries. In one instance, a fire started in the drive area of a belt line, spread rapidly, and resulted in seating of the entire mine. Large-scale studies conducted by the U.S. Bureau of Mines in an aboveground fire gallery at Lake Lynn Laboratory clearly show the hazards of conveyor belt fires. Mine conveyor belt formulations which passed the current Federal acceptance test for fire-resistant betting were completely consumed by propagating fires or propagated flame, with flame spread rates ranging from 0.3 to 9 m/min. High downstream temperatures and large quantities of smoke and toxic gases, such as carbon monoxide, were generated as the belting burned. The smoke and gases can be spread by the mine`s ventilation system and can create significant problems for miners in the process of evacuation, such as reduction in visibility and incapacitation. In the aftermath of a belt fire, the atmosphere inside of the mine can become smoke filled or unbreathable, forcing miners to evacuate while wearing Self-Contained Self-Rescuers (SCSR`s), Sometimes there is confusion about how to regard the rated duration of an MSHA/NIOSH-approved 60-min. SCSR, especially when an SCSR is used in a way which takes it outside of the test conditions under which it was approved. As examples, for a mine escape that takes a miner from the deepest point of penetration in the mine to the surface: How long will a 60-min. SCSR actually last? and How many SCSR`s will a miner need? To answer these kinds of questions, in-mine data being gathered on escape times, distance and heart rates using miners escaping on foot and under oxygen. A model will be developed and validated which predicts how much oxygen is actually needed for a mine escape, and compares oxygen consumption bare faced versus wearing an SCSR.

  13. Identification of human neutralizing antibodies against MERS-CoV and their role in virus adaptive evolution

    PubMed Central

    Tang, Xian-Chun; Agnihothram, Sudhakar S.; Jiao, Yongjun; Stanhope, Jeremy; Graham, Rachel L.; Peterson, Eric C.; Avnir, Yuval; Tallarico, Aimee St. Clair; Sheehan, Jared; Zhu, Quan; Baric, Ralph S.; Marasco, Wayne A.

    2014-01-01

    The newly emerging Middle East Respiratory Syndrome coronavirus (MERS-CoV) causes a Severe Acute Respiratory Syndrome-like disease with ∼43% mortality. Given the recent detection of virus in dromedary camels, zoonotic transfer of MERS-CoV to humans is suspected. In addition, little is known about the role of human neutralizing Ab (nAb) pressure as a driving force in MERS-CoV adaptive evolution. Here, we used a well-characterized nonimmune human Ab-phage library and a panning strategy with proteoliposomes and cells to identify seven human nAbs against the receptor-binding domain (RBD) of the MERS-CoV Spike protein. These nAbs bind to three different epitopes in the RBD and human dipeptidyl peptidase 4 (hDPP4) interface with subnanomolar/nanomolar binding affinities and block the binding of MERS-CoV Spike protein with its hDPP4 receptor. Escape mutant assays identified five amino acid residues that are critical for neutralization escape. Despite the close proximity of the three epitopes on the RBD interface, escape from one epitope did not have a major impact on neutralization with Abs directed to a different epitope. Importantly, the majority of escape mutations had negative impacts on hDPP4 receptor binding and viral fitness. To our knowledge, these results provide the first report on human nAbs against MERS-CoV that may contribute to MERS-CoV clearance and evolution. Moreover, in the absence of a licensed vaccine or antiviral for MERS, this panel of nAbs offers the possibility of developing human mAb-based immunotherapy, especially for health-care workers. PMID:24778221

  14. The Role of Ionosphere/Thermosphere Coupling Processes in the Escape of Species from Mars

    NASA Astrophysics Data System (ADS)

    Fox, J. L.; Bougher, S. W.

    2004-12-01

    We discuss coupled ionosphere/thermosphere models of Mars and implications for the photochemical escape processes of the atomic species O, C and N. Escape also occurs by ion outflow, and the relative rates of ion loss are determined by ion-neutral chemistry. The escape flux of ions has been computed by a number of investigators, including Ma et al. and S. Brecht, and some measurements are available from the Phobos spacecraft. The relative escape rates of ions depend on the composition of the ionosphere, which is determined by ion-neutral chemistry. Photochemical escape of atoms often occurs by processes that involves ions, such as dissociative recombination of O2+, N2+, CO+, and NO+, which yields fragments of various energies, many of which exceed the escape energy for Mars. Ions other than N2+ are formed mostly or partially by ion-molecule reactions. Except for NO+, the ions may be destroyed by ion-molecule reactions also. The ratio of ion-molecule reactions to dissociative recombination depends on the presence or absence of neutral species with which the ions can react. At high altitudes, the densities of neutral species is smaller than at lower altitudes. Therefore, above the ``exobase", dissociative recombination may be more important. Since many ions react with H2, its density profile is important in determining the photochemical escape of heavy ions. Earlier in the history of Mars, the atmosphere may have been more reducing. A larger abundance of H2 would decrease the densities of O+, N2+, CO+, and CO2+, which react with H2. We model the ionosphere and photochemical escape mechanisms for the higher solar fluxes and more reducing atmosphere of early Mars.

  15. In situ and remote measurements of ions escaping from Venus

    NASA Astrophysics Data System (ADS)

    Kollmann, P.; Brandt, P. C.

    2013-12-01

    Venus is thought to lose a large fraction of its atmosphere in the form ions, mainly via pickup. The relative loss rate of the exosphere as neutrals or ions is not known, nor is the flux of escaping ions well constrained. Knowledge of these processes will shed light on the role an intrinsic magnetic field has in atmospheric erosion. We use the complementary in-situ plasma and energetic neutral atom (ENA) measurements from the Venus Express (VEx) spacecraft in order to constrain the ion escape. VEx completed about 2500 orbits to date and reached altitudes as low as 200km. The ASPERA/IMA instrument measured directional proton and oxygen ion spectra in the 10eV to 40keV range. We bin the data accumulated over the mission in space and bulk flow direction, yielding a direct measure of the local ion escape flux. While such in-situ measurements provide data without ambiguity, they are limited by the orbital coverage. This is why we include remote ENA measurements from the ASPERA/NPD (100eV to 10keV) instrument to our study. ENAs are created when escaping ions charge exchange with the high atmosphere atoms or molecules. We have done an exhaustive analysis of the data, excluding time periods of instrument contamination. Most ENA emission originates from low altitudes above Venus' limb. These measurements will be compared with the in-situ data, which allows constraining the atmospheric density at high altitudes. Interestingly, there are also ENA emissions from other directions, which were not sampled in-situ. This allows us to put a lower limit to the escape from these regions.

  16. Mars H Escape is potentially dominated by a high-altitude water source

    NASA Astrophysics Data System (ADS)

    Chaffin, Michael; Deighan, Justin; Schneider, Nick; Stewart, Ian

    2017-04-01

    H escape from the Mars atmosphere has removed a large part of Mars' initial water inventory. Until recently, this escape was thought to be slow and steady, sourced from long-lived molecular hydrogen whose lightness and volatility in comparison with water allow it to penetrate the upper atmosphere. Contradicting this thinking, observations from the Hubble Space Telescope and Mars Express, as well as more recent MAVEN measurements, indicate that H escape varies by at least a factor of ten over the Mars year and is largest in Southern Summer near perihelion. At the largest rates, H escape exceeds the ability of molecular hydrogen to supply the escape fluxes observed. At the same time in Southern Summer, Mars Express solar occultations have shown unexpectedly large concentrations of water at high altitude, potentially providing a source of escaping H unaccounted for in standard models. Here we show via photochemical modeling that the presence of this high altitude water can partially explain the large escape rates observed in Southern Summer. We further show that this escaping H is not in immediate balance with O escape, and therefore that short-term atmospheric dynamics can drive long-term variations in the oxidation balance and volatile content of planetary atmospheres. Future simultaneous observations by MAVEN, Mars Express, and the Trace Gas Orbiter may provide a direct test of this mechanism.

  17. 42 CFR 84.51 - Entry and escape, or escape only; classification.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... during entry into a hazardous atmosphere, and for escape from a hazardous atmosphere; or (b) Escape only. Respirators designed and approved for use only during escape from a hazardous atmosphere. ...

  18. 42 CFR 84.51 - Entry and escape, or escape only; classification.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... during entry into a hazardous atmosphere, and for escape from a hazardous atmosphere; or (b) Escape only. Respirators designed and approved for use only during escape from a hazardous atmosphere. ...

  19. 42 CFR 84.51 - Entry and escape, or escape only; classification.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... during entry into a hazardous atmosphere, and for escape from a hazardous atmosphere; or (b) Escape only. Respirators designed and approved for use only during escape from a hazardous atmosphere. ...

  20. 42 CFR 84.51 - Entry and escape, or escape only; classification.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... during entry into a hazardous atmosphere, and for escape from a hazardous atmosphere; or (b) Escape only. Respirators designed and approved for use only during escape from a hazardous atmosphere. ...

  1. 42 CFR 84.51 - Entry and escape, or escape only; classification.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... during entry into a hazardous atmosphere, and for escape from a hazardous atmosphere; or (b) Escape only. Respirators designed and approved for use only during escape from a hazardous atmosphere. ...

  2. Lise Meitner's escape from Germany

    NASA Astrophysics Data System (ADS)

    Sime, Ruth Lewin

    1990-03-01

    Lise Meitner (1878-1968) achieved prominence as a nuclear physicist in Germany; although of Jewish origin, her Austrian citizenship exempted her from Nazi racial laws until the annexation of Austria in 1938 precipitated her dismissal. Forbidden to emigrate, she narrowly escaped to the Netherlands with the help of concerned friends in the international physics community.

  3. DYNAMICS OF THE ESCAPE RESPONSE.

    DTIC Science & Technology

    requirements. It has been shown that force is a lawful response measure under positive reinforcement (Notterman and Mintz, 1965). Subjects will adjust...concluded that response force in an escape situation is a lawful response measure, and that it operates in a manner similar to force under positive reinforcement .

  4. Magnetic buoyancy and the escape of magnetic fields from stars

    NASA Astrophysics Data System (ADS)

    Parker, E. N.

    1984-06-01

    Magnetic buoyancy causes the azimuthal magnetic fields of stars to rise rapidly to the surface, from where they are generally assumed to escape freely into space. However, a closer look at the problem reveals the simple fact that disengagement of the field from the gas, and escape into space, require a convoluted field configuration, producing neutral point reconnection of the flux in the tenuous gas above the surface of the star. Only that flux which reconnects can escape. Recent observations of the magnetic fields emerging through the surface of the Sun show that even at sunspot maximum the gaps in longitude between bipolar magnetic regions are so wide as to limit severely the reconnection between regions. We suggest from the observations that no more than perhaps 3% of the flux that is observed to emerge through the surface is able to reconnect and escape. Hence the surface of the Sun approximates to an impenetrable barrier rather than an open surface, with quantitative consequences for theoretical dynamo models. Recent observations of the retraction of bipolar fields at the end of their appearance at the surface suggest active dynamical control by the convection beneath the surface.

  5. Solar forcing and planetary ion escape from Mars

    NASA Astrophysics Data System (ADS)

    Lundin, R.; Barabash, S.; Fedorov, A.; Holmström, M.; Nilsson, H.; Sauvaud, J.-A.; Yamauchi, M.

    2008-05-01

    The variability of planetary ion escape from Mars is studied using data from the Ion Mass Analyzer, IMA, on Mars Express (MEX). 42 orbits were selected during 17 months for different solar wind conditions, focusing on the low energy (~30 - 800 eV) heavy ion (e.g. O+, O2 + and CO2 +) outflow. A strong correlation is found between solar wind forcing of the obstacle, the cross-sectional area enclosing the ion outflow from Mars and the total heavy ion escape flux. The at least one order of magnitude changes of the ion outflow on the short term (hours, days), is directly connected with the variability of solar wind, solar soft x-ray and solar EUV (XEUV). The latter was first inferred from an analysis of how the obstacle size changes with changing solar wind and solar XEUV forcing. The 17-month trend of decreasing ion outflow with EUV during a declining phase of solar cycle 23, the EUV determined from the Neutral Particle Imager (NPI) on MEX, illustrates the influence of solar EUV forcing. On the basis of this we conclude that changes in solar wind- and solar XEUV forcing governs the variable ion escape from Mars. Both forcing terms appear to be equally important for the escape rate. Considering the difference in travel time for XEUV and the solar wind to Mars, the XEUV effect will precede the solar wind effect by several (3-9) days.

  6. Neutral particle beams for space defense

    NASA Astrophysics Data System (ADS)

    Botwin, Robert; Favale, Anthony

    Neutral particle beam (NPB) weapons direct highly focused high energy streams of electrically neutral atomic particles traveling at nearly the speed of light, escaping deflection from the earth's magnetic field and acting on the subatomic structure of a target, destroying it from within. The beam's brief contact with a reentry vehicle produces a nuclear reaction in the latter that yields particle emissions; by detecting and identifying those particles, it becomes possible to effectively distinguish warheads from decoys. Attention is given to the NPB program roles to be played by the Beam Experiment Aboard Rocket and Neutral Particle Beam Integrated Space Experiment projects.

  7. Blue Origin Conducts Pad Escape Test

    NASA Image and Video Library

    Blue Origin conducted a successful pad escape test Oct. 19 at the company's West Texas launch site, firing its pusher escape motor and launching a full-scale suborbital crew capsule from a simulate...

  8. Escape from Tumor Cell Dormancy

    DTIC Science & Technology

    2012-10-01

    3 ESCAPE FROM TUMOR CELL DORMANCY An Organotypic Liver System to Study Tumor Cell Dormancy Alan Wells and Donna Stolz (UPitt), Linda Griffith (MIT...insights into dormancy and the transition that heralds metastatic emergenceis due mainly to the lack of tractable experimental systems with which to... systems are being optimized in others. The main efforts during the first year of this two-year project have been focused on the establishing the

  9. Cold Ion Escape from Mars

    NASA Astrophysics Data System (ADS)

    Fränz, M.; Dubinin, E.; Wei, Y.; Morgan, D.; Andrews, D.; Barabash, S.; Lundin, R.; Fedorov, A.

    2013-09-01

    It has always been challenging to observe the flux of ions with energies of less than 10eV escaping from the planetary ionospheres. We here report on new measurements of the ionospheric ion flows at Mars by the ASPERA-3 experiment on board Mars Express in combination with the MARSIS radar experiment. We first compare calculations of the mean ion flux observed by ASPERA-3 alone with previously published results. We then combine observations of the cold ion velocity by ASPERA-3 with observations of the cold plasma density by MARSIS since ASPERA-3 misses the cold core of the ion distribution. We show that the mean density of the nightside plasma observed by MARSIS is about two orders higher than observed by ASPERA-3 (Fig.1). Combining both datasets we show that the main escape channel is along the shadow boundary on the tailside of Mars (Fig. 2). At a distance of about 0.5 R_M the flux settles at a constant value (Fig. 3) which indicates that about half of the transterminator ionospheric flow escapes from the planet. Possible mechanism to generate this flux can be the ionospheric pressure gradient between dayside and nightside or momentum transfer from the solar wind via the induced magnetic field since the flow velocity is in the Alfvénic regime.

  10. Beyond Viral Neutralization.

    PubMed

    Lewis, George K; Pazgier, Marzena; Evans, David; Ferrari, Guido; Bournazos, Stylianos; Parsons, Matthew S; Bernard, Nicole F; Finzi, Andrés

    2017-01-13

    It has been known for more than 30 years that Human Immunodeficiency Virus 1 (HIV-1) infection drives a very potent B cell response resulting in the production of anti-HIV-1 antibodies targeting several viral proteins, particularly its envelope glycoproteins (Env). Env epitopes are exposed on the surfaces of viral particles and infected cells where they are targets of potentially protective antibodies. These antibodies can interdict infection by neutralization and there is strong evidence suggesting that Fc-mediated effector function can also contribute to protection. Current evidence suggests that Fc-mediated effector function plays a role in protection against infection by broadly neutralizing antibodies (bnAbs) and it might be important for protection by non-neutralizing antibodies. Fc-mediated effector function includes diverse mechanisms that include antibody-dependent cellular cytotoxicity (ADCC), antibody-mediated complement activation (ADC), antibody-dependent cellular phagocytosis (ADCP), antibody-dependent cell-mediated virus inhibition (ADCVI), antibody-mediated trancytosis inhibition, and antibody-mediated virus opsonization. All these functions could be beneficial in fighting viral infections including HIV-1. In this perspective, we discuss the latest developments for ADCC responses discussed at the HIVR4P satellite session on non-neutralizing antibodies, with emphasis on the mechanisms of ADCC resistance employed by HIV-1, the structural basis of epitopes recognized by antibodies that mediate ADCC, NK-cell education and ADCC, and murine models to study ADCC against HIV-1.

  11. Helium escape from the Earth's atmosphere - The charge exchange mechanism revisited

    NASA Technical Reports Server (NTRS)

    Lie-Svendsen, O.; Rees, M. H.; Stamnes, K.

    1992-01-01

    We have studied the escape of neutral helium from the terrestrial atmosphere through exothermic charge exchange reactions between He(+) ions and the major atmospheric constituents N2, O2 and O. Elastic collisions with the neutral background particles were treated quantitatively using a recently developed kinetic theory approach. An interhemispheric plasma transport model was employed to provide a global distribution of He(+) ions as a function of altitude, latitude and local solar time and for different levels of solar ionization. Combining these ion densities with neutral densities from an MSIS model and best estimates for the reaction rate coefficients of the charge exchange reactions, we computed the global distribution of the neutral He escape flux. The escape rates show large diurnal and latitudinal variations, while the global average does not vary by more than a factor of three over a solar cycle. We find that this escape mechanism is potentially important for the overall balance of helium in the Earth's atmosphere. However, more accurate values for the reaction rate coefficients of the charge exchange reactions are required to make a definitive assessment of its importance.

  12. Helium escape from the Earth's atmosphere - The charge exchange mechanism revisited

    NASA Technical Reports Server (NTRS)

    Lie-Svendsen, O.; Rees, M. H.; Stamnes, K.

    1992-01-01

    We have studied the escape of neutral helium from the terrestrial atmosphere through exothermic charge exchange reactions between He(+) ions and the major atmospheric constituents N2, O2 and O. Elastic collisions with the neutral background particles were treated quantitatively using a recently developed kinetic theory approach. An interhemispheric plasma transport model was employed to provide a global distribution of He(+) ions as a function of altitude, latitude and local solar time and for different levels of solar ionization. Combining these ion densities with neutral densities from an MSIS model and best estimates for the reaction rate coefficients of the charge exchange reactions, we computed the global distribution of the neutral He escape flux. The escape rates show large diurnal and latitudinal variations, while the global average does not vary by more than a factor of three over a solar cycle. We find that this escape mechanism is potentially important for the overall balance of helium in the Earth's atmosphere. However, more accurate values for the reaction rate coefficients of the charge exchange reactions are required to make a definitive assessment of its importance.

  13. On ion escape from Venus

    NASA Astrophysics Data System (ADS)

    Jarvinen, R.

    2011-04-01

    This doctoral thesis is about the solar wind influence on the atmosphere of the planet Venus. A numerical plasma simulation model was developed for the interaction between Venus and the solar wind to study the erosion of charged particles from the Venus upper atmosphere. The developed model is a hybrid simulation where ions are treated as particles and electrons are modelled as a fluid. The simulation was used to study the solar wind induced ion escape from Venus as observed by the European Space Agency's Venus Express and NASA's Pioneer Venus Orbiter spacecraft. Especially, observations made by the ASPERA-4 particle instrument onboard Venus Express were studied. The thesis consists of an introductory part and four peer-reviewed articles published in scientific journals. In the introduction Venus is presented as one of the terrestrial planets in the Solar System and the main findings of the work are discussed within the wider context of planetary physics.Venus is the closest neighbouring planet to the Earth and the most earthlike planet in its size and mass orbiting the Sun. Whereas the atmosphere of the Earth consists mainly of nitrogen and oxygen, Venus has a hot carbon dioxide atmosphere, which is dominated by the greenhouse effect. Venus has all of its water in the atmosphere, which is only a fraction of the Earth's total water supply. Since planets developed presumably in similar conditions in the young Solar System, why Venus and Earth became so different in many respects?One important feature of Venus is that the planet does not have an intrinsic magnetic field. This makes it possible for the solar wind, a continuous stream of charged particles from the Sun, to flow close to Venus and to pick up ions from the planet's upper atmosphere. The strong intrinsic magnetic field of the Earth dominates the terrestrial magnetosphere and deflects the solar wind flow far away from the atmosphere. The region around Venus where the planet's atmosphere interacts with the

  14. On ion escape from Venus

    NASA Astrophysics Data System (ADS)

    Jarvinen, Riku

    2011-04-01

    This doctoral thesis is about the solar wind influence on the atmosphere of the planet Venus. A numerical plasma simulation model was developed for the interaction between Venus and the solar wind to study the erosion of charged particles from the Venus upper atmosphere. The developed model is a hybrid simulation where ions are treated as particles and electrons are modelled as a fluid. The simulation was used to study the solar wind induced ion escape from Venus as observed by the European Space Agency's Venus Express and NASA's Pioneer Venus Orbiter spacecraft. Especially, observations made by the ASPERA-4 particle instrument onboard Venus Express were studied. The thesis consists of an introductory part and four peer-reviewed articles published in scientific journals. In the introduction Venus is presented as one of the terrestrial planets in the Solar System and the main findings of the work are discussed within the wider context of planetary physics. Venus is the closest neighbouring planet to the Earth and the most earthlike planet in its size and mass orbiting the Sun. Whereas the atmosphere of the Earth consists mainly of nitrogen and oxygen, Venus has a hot carbon dioxide atmosphere, which is dominated by the greenhouse effect. Venus has all of its water in the atmosphere, which is only a fraction of the Earth's total water supply. Since planets developed presumably in similar conditions in the young Solar System, why Venus and Earth became so different in many respects? One important feature of Venus is that the planet does not have an intrinsic magnetic field. This makes it possible for the solar wind, a continuous stream of charged particles from the Sun, to flow close to Venus and to pick up ions from the planet's upper atmosphere. The strong intrinsic magnetic field of the Earth dominates the terrestrial magnetosphere and deflects the solar wind flow far away from the atmosphere. The region around Venus where the planet's atmosphere interacts with the

  15. Malaria Parasites: The Great Escape

    PubMed Central

    Rénia, Laurent; Goh, Yun Shan

    2016-01-01

    Parasites of the genus Plasmodium have a complex life cycle. They alternate between their final mosquito host and their intermediate hosts. The parasite can be either extra- or intracellular, depending on the stage of development. By modifying their shape, motility, and metabolic requirements, the parasite adapts to the different environments in their different hosts. The parasite has evolved to escape the multiple immune mechanisms in the host that try to block parasite development at the different stages of their development. In this article, we describe the mechanisms reported thus far that allow the Plasmodium parasite to evade innate and adaptive immune responses. PMID:27872623

  16. Wind Enhanced Escape, Ion Pickup and the Evolution of Water on Mars

    NASA Technical Reports Server (NTRS)

    Hartle, Richard

    1999-01-01

    Preferential loss of hydrogen over deuterium from Mars has produced a deuterium rich atmosphere possessing a D/B ratio 5.2 times that of terrestrial water. Rayleigh fractionation is applied, constrained by the deuterium enrichment factor, to determine the magnitudes of ancient and present water reservoirs on the planet. The dominant lose mechanisms of R and D from the current atmosphere are thought to be thermal escape and solar wind ion pickup of the neutral and ion forms of theme constituents, respectively. During an earlier martian epoch, only thermal escape was significant because Mars had a terrestrial sized magnetosphere that protected the atmosphere from solar wind scavenging processes. The magnitudes of present and ancient water reservoirs are estimated when thermal escape is considered alone and subsequently when the effects of ion pickup are added. The escape fluxes of R and D are significantly increased above the respective Jeans fluxes when the effects of thermospheric winds and planetary rotation are accounted for at the exobase. Such wind enhanced escape also increases as the mass of an escaping constituent increases; thus, the increase in the escape flux of D is greater than that of H. When the fractionation process is also constrained by the D/H ratio observed in hydrous minerals of SNC meteorites, an ancient crustal reservoir of Martian water in derived, tens of meters in global-equivalent depth, considerably exceeding that obtained with no winds. The reservoir becomes even larger when ion pickup processes are added.

  17. iDriving (Intelligent Driving)

    SciTech Connect

    Malikopoulos, Andreas

    2012-09-17

    iDriving identifies the driving style factors that have a major impact on fuel economy. An optimization framework is used with the aim of optimizing a driving style with respect to these driving factors. A set of polynomial metamodels is constructed to reflect the responses produced in fuel economy by changing the driving factors. The optimization framework is used to develop a real-time feedback system, including visual instructions, to enable drivers to alter their driving styles in responses to actual driving conditions to improve fuel efficiency.

  18. Wind-Induced Atmospheric Escape: Titan

    NASA Technical Reports Server (NTRS)

    Hartle, Richard; Johnson, Robert; Sittler, Edward, Jr.; Sarantos, Menelaos; Simpson, David

    2012-01-01

    Rapid thermospheric flows can significantly enhance the estimates of the atmospheric loss rate and the structure of the atmospheric corona of a planetary body. In particular, rapid horizontal flow at the exobase can increase the corresponding constituent escape rate. Here we show that such corrections, for both thermal and non-thermal escape, cannot be ignored when calculating the escape of methane from Titan, for which drastically different rates have been proposed. Such enhancements are also relevant to Pluto and exoplanets.

  19. Escape of Hot Oxygen Atoms from the Atmosphere of Mars

    NASA Astrophysics Data System (ADS)

    Rahmati, A.; Croxell, J. A.; Cravens, T.; Pothapragada, S.; Nagy, A. F.; Ledvina, S. A.

    2013-12-01

    The main source of the production of hot oxygen atoms in the Martian atmosphere is the dissociative recombination (DR) reaction of O2+ ions with electrons. In this study, the primary production rate of hot O atoms is found for four energy channels of DR reaction. The one-dimensional energy and altitude dependent up and down flux differential equations are solved using a two-stream transport method, by taking into account the primary, secondary and cascade productions of hot O and also, the interactions with the background atmosphere. The forward and backward scattering probabilities and energy loss coefficients for 12 neutral target species are found using a Monte-Carlo simulation. The neutral target species are H, H2, He, C, N, O, CO, N2, NO, O2, Ar and CO2 for which the density profiles appropriate for Viking landers condition are used. From the up and down fluxes, the energy distribution function of hot O atoms and the escape flux at the exobase of Mars is calculated and by using the Liouville equation, the density profile of hot O is found above the exobase, extending out to several Martian radii. The results are used to study the interaction of escaping hot O atoms with the solar wind and specifically, the fluxes of energetic O+ pickup ions are determined.

  20. Impaired Driving

    MedlinePlus

    Impaired driving is dangerous. It's the cause of more than half of all car crashes. It means operating a ... texting Having a medical condition which affects your driving For your safety and the safety of others, ...

  1. Analysis of variola and vaccinia virus neutralization assays for smallpox vaccines.

    PubMed

    Hughes, Christine M; Newman, Frances K; Davidson, Whitni B; Olson, Victoria A; Smith, Scott K; Holman, Robert C; Yan, Lihan; Frey, Sharon E; Belshe, Robert B; Karem, Kevin L; Damon, Inger K

    2012-07-01

    Possible smallpox reemergence drives research for third-generation vaccines that effectively neutralize variola virus. A comparison of neutralization assays using different substrates, variola and vaccinia (Dryvax and modified vaccinia Ankara [MVA]), showed significantly different 90% neutralization titers; Dryvax underestimated while MVA overestimated variola neutralization. Third-generation vaccines may rely upon neutralization as a correlate of protection.

  2. Electronic Escape Trails for Firefighters

    NASA Technical Reports Server (NTRS)

    Jorgensen, Charles; Schipper, John; Betts, Bradley

    2008-01-01

    A proposed wireless-communication and data-processing system would exploit recent advances in radio-frequency identification devices (RFIDs) and software to establish information lifelines between firefighters in a burning building and a fire chief at a control station near but outside the building. The system would enable identification of trails that firefighters and others could follow to escape from the building, including identification of new trails should previously established trails become blocked. The system would include a transceiver unit and a computer at the control station, portable transceiver units carried by the firefighters in the building, and RFID tags that the firefighters would place at multiple locations as they move into and through the building (see figure). Each RFID tag, having a size of the order of a few centimeters, would include at least standard RFID circuitry and possibly sensors for measuring such other relevant environmental parameters as temperature, levels of light and sound, concentration of oxygen, concentrations of hazardous chemicals in smoke, and/or levels of nuclear radiation. The RFID tags would be activated and interrogated by the firefighters and control-station transceivers. Preferably, RFID tags would be configured to communicate with each other and with the firefighters units and the control station in an ordered sequence, with built-in redundancy. In a typical scenario, as firefighters moved through a building, they would scatter many RFID tags into smoke-obscured areas by use of a compressed-air gun. Alternatively or in addition, they would mark escape trails by dropping RFID tags at such points of interest as mantraps, hot spots, and trail waypoints. The RFID tags could be of different types, operating at different frequencies to identify their functions, and possibly responding by emitting audible beeps when activated by signals transmitted by transceiver units carried by nearby firefighters.

  3. Noninductive current drive in tokamaks

    SciTech Connect

    Uckan, N.A.

    1985-01-01

    Various current drive mechanisms may be grouped into four classes: (1) injection of energetic particle beams; (2) launching of rf waves; (3) hybrid schemes, which are combinations of various rf schemes (rf plus beams, rf and/or beam plus ohmic heating, etc.); and (4) other schemes, some of which are specific to reactor plasma conditions requiring the presence of alpha particle or intense synchrotron radiation. Particle injection schemes include current drive by neutral beams and relativistic electron beams. The rf schemes include current drive by the lower hybrid (LH) waves, the electron waves, the waves in the ion cyclotron range of frequencies, etc. Only a few of these approaches, however, have been tested experimentally, with the broadest data base available for LH waves. Included in this report are (1) efficiency criteria for current drive, (2) current drive by neutral beam injection, (3) LH current drive, (4) electron cyclotron current drive, (5) current drive by ion cyclotron waves - minority species heating, and (6) current drive by other schemes (such as hybrids and low frequency waves).

  4. Inhibition of chaotic escape from a potential well by incommensurate escape-suppressing excitations.

    PubMed

    Chacón, R; Martínez, J A

    2002-03-01

    Theoretical results are presented concerning the reduction of chaotic escape from a potential well by means of a harmonic parametric excitation that satisfies an ultrasubharmonic resonance condition with the escape-inducing excitation. The possibility of incommensurate escape-suppressing excitations is demonstrated by studying rational approximations to the irrational escape-suppressing frequency. The analytical predictions for the suitable amplitudes and initial phases of the escape-suppressing excitation are tested against numerical simulations based on a high-resolution grid of initial conditions. These numerical results indicate that the reduction of escape is reliably achieved for small amplitudes and at, and only at, the predicted initial phases. For the case of irrational escape-suppressing frequencies, the effective escape-reducing initial phases are found to lie close to the accumulation points of the set of suitable initial phases that are associated with the complete series of convergents up to the convergent giving the chosen rational approximation.

  5. Anomalous barrier escape: The roles of noise distribution and correlation

    NASA Astrophysics Data System (ADS)

    Hu, Meng; Zhang, Jia-Ming; Bao, Jing-Dong

    2017-05-01

    We study numerically and analytically the barrier escape dynamics of a particle driven by an underlying correlated Lévy noise for a smooth metastable potential. A "quasi-monochrome-color" Lévy noise, i.e., the first-order derivative variable of a linear second-order differential equation subjected to a symmetric α-stable white Lévy noise, also called the harmonic velocity Lévy noise, is proposed. Note that the time-integral of the noise Green function of this kind is equal to zero. This leads to the existence of underlying negative time correlation and implies that a step in one direction is likely followed by a step in the other direction. By using the noise of this kind as a driving source, we discuss the competition between long flights and underlying negative correlations in the metastable dynamics. The quite rich behaviors in the parameter space including an optimum α for the stationary escape rate have been found. Remarkably, slow diffusion does not decrease the stationary rate while a negative correlation increases net escape. An approximate expression for the Lévy-Kramers rate is obtained to support the numerically observed dependencies.

  6. Escape for the Slow Solar Wind

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-05-01

    that marks the edges of coronal holes and extends outward as the heliospheric current sheet are caused by supergranule-like convective flows. These motions drive magnetic reconnection that funnel plasma from the closed-field region onto enormous arcs that extend far away from the heliospheric current sheet, spanning tens of degrees in latitude and longitude.The simulations by Higginson and collaborators demonstrate that closed-field plasma from coronal-hole boundaries can be successfully channeled into the solar system. Due to the geometry and dynamics of the coronal holes, the plasma can travel far from the heliospheric current sheet, resulting in a slow solar wind of closed-field plasma consistent with our observations. These simulations therefore suggest aprocessthat resolves the long-standing puzzle of the slow solar wind.BonusCheck out the animation below, made from the results of the teams simulations. This video shows the location of a forming heliospheric arc at a distance of 12 solar radii. The arc forms as magnetic field lines at the boundary of a coronal hole change from closed to open, allowing closed-field flux to escape along them.http://aasnova.org/wp-content/uploads/2017/05/apjlaa6d72f4_video.mp4CitationA. K. Higginson et al 2017 ApJL 840 L10. doi:10.3847/2041-8213/aa6d72

  7. Energetic neutral particles from Jupiter and Saturn

    NASA Technical Reports Server (NTRS)

    Cheng, A. F.

    1986-01-01

    The Voyager 1 spacecraft has detected energetic neutral particles escaping from the magnetospheres of Jupiter and Saturn. These energetic neutrals are created in charge exchange reactions between radiation belt ions and ambient atoms or molecules in the magnetosphere. If the Io torus is assumed to be the dominant Jovian source region for energetic neutrals, the Voyager observations can be used to infer upper limits to the average ion intensities there below about 200 keV. No readily interpretable in-situ measurements are available in the Io torus at these energies. The middle and outer Jovian magnetospheres may also be a significant source of energetic neutrals. At Saturn, the observed neutral particle count rates are too high to be explained by charge exchange between fast protons and H atoms of the Titan torus. Most of the energetic neutrals may be produced by charge exchanges between heavy ions and a neutral cloud containing H2O in Saturn's inner magnetosphere. If so, the Voyager measurements of energetic neutral fluxes would be the first detected emissions from this region of Saturn's magnetosphere.

  8. Escape as Reinforcement and Escape Extinction in the Treatment of Feeding Problems

    ERIC Educational Resources Information Center

    LaRue, Robert H.; Stewart, Victoria; Piazza, Cathleen C.; Volkert, Valerie M.; Patel, Meeta R.; Zeleny, Jason

    2011-01-01

    Given the effectiveness of putative escape extinction as treatment for feeding problems, it is surprising that little is known about the effects of escape as reinforcement for appropriate eating during treatment. In the current investigation, we examined the effectiveness of escape as reinforcement for mouth clean (a product measure of…

  9. Generalized Jeans' Escape of Pick-Up Ions in Quasi-Linear Relaxation

    NASA Technical Reports Server (NTRS)

    Moore, T. E.; Khazanov, G. V.

    2011-01-01

    Jeans escape is a well-validated formulation of upper atmospheric escape that we have generalized to estimate plasma escape from ionospheres. It involves the computation of the parts of particle velocity space that are unbound by the gravitational potential at the exobase, followed by a calculation of the flux carried by such unbound particles as they escape from the potential well. To generalize this approach for ions, we superposed an electrostatic ambipolar potential and a centrifugal potential, for motions across and along a divergent magnetic field. We then considered how the presence of superthermal electrons, produced by precipitating auroral primary electrons, controls the ambipolar potential. We also showed that the centrifugal potential plays a small role in controlling the mass escape flux from the terrestrial ionosphere. We then applied the transverse ion velocity distribution produced when ions, picked up by supersonic (i.e., auroral) ionospheric convection, relax via quasi-linear diffusion, as estimated for cometary comas [1]. The results provide a theoretical basis for observed ion escape response to electromagnetic and kinetic energy sources. They also suggest that super-sonic but sub-Alfvenic flow, with ion pick-up, is a unique and important regime of ion-neutral coupling, in which plasma wave-particle interactions are driven by ion-neutral collisions at densities for which the collision frequency falls near or below the gyro-frequency. As another possible illustration of this process, the heliopause ribbon discovered by the IBEX mission involves interactions between the solar wind ions and the interstellar neutral gas, in a regime that may be analogous [2].

  10. Variable Fitness Impact of HIV-1 Escape Mutations to Cytotoxic T Lymphocyte (CTL) Response

    PubMed Central

    Troyer, Ryan M.; McNevin, John; Liu, Yi; Zhang, Shao Chong; Krizan, Randall W.; Abraha, Awet; Tebit, Denis M.; Zhao, Hong; Avila, Santiago; Lobritz, Michael A.; McElrath, M. Juliana; Le Gall, Sylvie; Mullins, James I.; Arts, Eric J.

    2009-01-01

    Human lymphocyte antigen (HLA)-restricted CD8+ cytotoxic T lymphocytes (CTL) target and kill HIV-infected cells expressing cognate viral epitopes. This response selects for escape mutations within CTL epitopes that can diminish viral replication fitness. Here, we assess the fitness impact of escape mutations emerging in seven CTL epitopes in the gp120 Env and p24 Gag coding regions of an individual followed longitudinally from the time of acute HIV-1 infection, as well as some of these same epitopes recognized in other HIV-1-infected individuals. Nine dominant mutations appeared in five gp120 epitopes within the first year of infection, whereas all four mutations found in two p24 epitopes emerged after nearly two years of infection. These mutations were introduced individually into the autologous gene found in acute infection and then placed into a full-length, infectious viral genome. When competed against virus expressing the parental protein, fitness loss was observed with only one of the nine gp120 mutations, whereas four had no effect and three conferred a slight increase in fitness. In contrast, mutations conferring CTL escape in the p24 epitopes significantly decreased viral fitness. One particular escape mutation within a p24 epitope was associated with reduced peptide recognition and high viral fitness costs but was replaced by a fitness-neutral mutation. This mutation appeared to alter epitope processing concomitant with a reduced CTL response. In conclusion, CTL escape mutations in HIV-1 Gag p24 were associated with significant fitness costs, whereas most escape mutations in the Env gene were fitness neutral, suggesting a balance between immunologic escape and replicative fitness costs. PMID:19343217

  11. Submarine 'safe to escape' studies in man.

    PubMed

    Jurd, K M; Seddon, F M; Thacker, J C; Blogg, S L; Stansfield, M R D; White, M G; Loveman, G A M

    2014-01-01

    The Royal Navy requires reliable advice on the safe limits of escape from a distressed submarine (DISSUB). Flooding in a DISSUB may cause a rise in ambient pressure, increasing the risk of decompression sickness (DCS) and decreasing the maximum depth from which it is safe to escape. The aim of this study was to investigate the pressure/depth limits to escape following saturation at raised ambient pressure. Exposure to saturation pressures up to 1.6 bar (a) (160 kPa) (n = 38); escapes from depths down to 120 meters of sea water (msw) (n = 254) and a combination of saturation followed by escape (n = 90) was carried out in the QinetiQ Submarine Escape Simulator, Alverstoke, United Kingdom. Doppler ultrasound monitoring was used to judge the severity of decompression stress. The trials confirmed the previously untested advice, in the Guardbook, that if a DISSUB was lying at a depth of 90 msw, then it was safe to escape when the pressure in the DISSUB was 1.5 bar (a), but also indicated that this advice may be overly conservative. This study demonstrated that the upper DISSUB saturation pressure limit to safe escape from 90 msw was 1.6 bar (a), resulting in two cases of DCS.

  12. Escaping in Literature. Teaching in the Library.

    ERIC Educational Resources Information Center

    Hurst, Carol Otis

    1993-01-01

    Explores the "escape" genre of children's literature, and recommends and describes several books that deal with such topics as escape from prison camps, from slavery, from the Holocaust, from war, and from Utopian societies. These books should provoke meaningful classroom discussions and allow children to view their own world from different…

  13. Learning from escaped prescribed fire reviews [Abstract

    Treesearch

    Anne Black; Dave Thomas; James Saveland

    2011-01-01

    Over the past decade, the wildland fire community has developed a number of innovative methods for conducting a review following escape of a prescribed fire. The stated purpose been to identify methods that not only meet policy requirements, but to reduce future escapes. Implicit is the assumption that a review leads to learning. Yet, as organizational learning expert...

  14. 30 CFR 57.11051 - Escape routes.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Escape routes. 57.11051 Section 57.11051 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE... read direction signs that clearly indicate the ways of escape....

  15. 30 CFR 57.11051 - Escape routes.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Escape routes. 57.11051 Section 57.11051 Mineral Resources MINE SAFETY AND HEALTH ADMINISTRATION, DEPARTMENT OF LABOR METAL AND NONMETAL MINE... read direction signs that clearly indicate the ways of escape....

  16. Broadly neutralizing antibodies developed by an HIV-positive elite neutralizer exact a replication fitness cost on the contemporaneous virus.

    PubMed

    Sather, D Noah; Carbonetti, Sara; Kehayia, Jenny; Kraft, Zane; Mikell, Iliyana; Scheid, Johannes F; Klein, Florian; Stamatatos, Leonidas

    2012-12-01

    Approximately 1% of those infected with HIV-1 develop broad and potent serum cross-neutralizing antibody activities. It is unknown whether or not the development of such immune responses affects the replication of the contemporaneous autologous virus. Here, we defined a pathway of autologous viral escape from contemporaneous potent and broad serum neutralizing antibodies developed by an elite HIV-1-positive (HIV-1(+)) neutralizer. These antibodies potently neutralize diverse isolates from different clades and target primarily the CD4-binding site (CD4-BS) of the viral envelope glycoprotein. Viral escape required mutations in the viral envelope glycoprotein which limited the accessibility of the CD4-binding site to the autologous broadly neutralizing anti-CD4-BS antibodies but which allowed the virus to infect cells by utilizing CD4 receptors on their surface. The acquisition of neutralization resistance, however, resulted in reduced cell entry potential and slower viral replication kinetics. Our results indicate that in vivo escape from autologous broadly neutralizing antibodies exacts fitness costs to HIV-1.

  17. Atmospheric escape, redox evolution, and planetary habitability

    NASA Astrophysics Data System (ADS)

    Catling, D. C.; Zahnle, K. J.

    2011-12-01

    Through the greenhouse effect, the presence and composition of an atmosphere is critical for defining a (conventional) circumstellar habitable zone in terms of planetary surface temperatures suitable for liquid water. Lack of knowledge of planetary atmospheres is likely to frustrate attempts to say with any certainty whether detected terrestrial-sized exoplanets may or may not be habitable. Perhaps an underappreciated role in such considerations is the evolutionary effect of atmospheric escape for determining atmospheric composition or whether an atmosphere exists in the first place. Whether atmospheres exist at all on planets is demonstrably connected to the effect of integrated atmospheric escape. When we observe our own Solar System and transiting exoplanets, the existence of an atmosphere is clearly delineated by a relative vulnerability to thermal escape and impact erosion. The prevalence of thermal escape as a key evolutionary determinant for the presence of planetary atmosphere is shown by a relationship between the relative solar (or stellar) heating and the escape velocity. Those bodies with too much stellar heating and too smaller escape velocity end up devoid of atmospheres. Impact erosion is evident in the relationship between impact velocity and escape velocity. Escape due to impacts is particularly important for understanding the large differences in the atmospheres of giant planet moons, such as Ganymede versus Titan. It is also significant for Mars-sized planets. The oxidation state of atmospheres is important for some theories of the origin of life (where an early reducing atmosphere is helpful for organic synthesis) and the evolution of advanced life (where free molecular oxygen is the best source of high energy metabolism). Surfaces on some relatively small planets and moons are observed to have evolved to an oxidized state, which theory and observation can explain through atmospheric escape. There are several examples in the Solar System where a

  18. Cross Sections for Planetary Escape

    NASA Astrophysics Data System (ADS)

    Tully, C.

    2001-05-01

    Energetic charged-particle bombardment, dissociative recombination and photodissociation processes produce energetic recoil atoms which heat the thermosphere and can lead to escape from a planet affecting the evolution of the atmosphere. In describing these processes by Monte Carlo methods, many of the critical cross sections are not available in the energy range of interest, a few eV to 1 keV. Here we present our recent results for elastic collision and collisional dissociation cross sections relevant to Titan, Triton, Europa and the terrestrial planets [1,2]. Elastic and diffusion cross sections were calculated using both quantum mechanical techniques and the semiclassical JWKB approximation for the collision of ground state oxygen atoms in the energy range 1-10eV [2]. This involved calculation of phase shifts for each of the 18 molecular energy states of O2 which separate to two ground state O atoms. For an O thermosphere the total elastic cross section is close to that typically assumed but the escape depths are shown to be larger than those typically used. Dissociation cross sections of N + N2 were calculated using a semiclassical method, in the energy range 0-30eV. This required treating the vibrational motion quantum mechanically while the rotational and the relative translational motion were treated classically. The evolution of the system was calculated by simultaneous propagation of the classical as well as the quantal degrees of freedom. The solution to the classical part was carried out by solving Hamilton equations of motion using an effective London-Eyring-Polanyi-Sato potential energy surface, calculated by Laganá et al [3]. Propagation of the quantal wavefunction was carried out by solving the time dependent Schrödinger equation using the split operator technique with the help of the fast fourier transform which was used to calculate the second derivatives arising from the kinetic energy operator. This work was supported by NASA's Planetary

  19. Simulations of neutralized final focus

    SciTech Connect

    Welch, D.R.; Rose, D.V.; Genoni, T.C.; Yu, S.S.; Barnard, J.J.

    2005-01-18

    In order to drive an inertial fusion target or study high energy density physics with heavy ion beams, the beam radius must be focused to < 3 mm and the pulse length must be compressed to < 10 ns. The conventional scheme for temporal pulse compression makes use of an increasing ion velocity to compress the beam as it drifts and beam space charge to stagnate the compression before final focus. Beam compression in a neutralizing plasma does not require stagnation of the compression, enabling a more robust method. The final pulse shape at the target can be programmed by an applied velocity tilt. In this paper, neutralized drift compression is investigated. The sensitivity of the compression and focusing to beam momentum spread, plasma, and magnetic field conditions is studied with realistic driver examples. Using the 3D particle-in-cell code, we examine issues associated with self-field generation, stability, and vacuum-neutralized transport transition and focusing.

  20. ESCAP migration study gathers momentum.

    PubMed

    1980-01-01

    A comparative study is being conducted in the ESCAP (Economic and Social Commission for Asia and the Pacific) region on the relationships of migration and urbanization to development. The 1st stage of the study will entail the preparation of country reports on the census analysis of migration, urbanization and development. The 2nd stage will involve preparation of a series of national migration surveys. The 3rd phase will involve assisting member governments to formulate a comprehensive population redistribution policy as part of their national development planning. 1st-phase country reports have been completed in Sri Lanka, South Korea, the Philippines, and Indonesia. Migration in Sri Lanka has largely been rural-to-rural with little urbanization so far. The picture in South Korea has been the opposite, with rapid urbanization in the 1960s and 1970s; the government is hoping to divert some population to smaller cities away from Seoul. The pattern in the Philippines is 1 of urban primacy with the metropolis of Manila accounting for over 1/3 of the country's total population. Indonesia is characterized by a dense heartland in the Java-Bali regions. However, the rate of urbanization here has been slower. Migrants in all the countries studied are preponderantly young. The sex differential varies from country to country. The influence of migration on subsequent fertility is unknown.

  1. Pile Driving

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Machine-oriented structural engineering firm TERA, Inc. is engaged in a project to evaluate the reliability of offshore pile driving prediction methods to eventually predict the best pile driving technique for each new offshore oil platform. Phase I Pile driving records of 48 offshore platforms including such information as blow counts, soil composition and pertinent construction details were digitized. In Phase II, pile driving records were statistically compared with current methods of prediction. Result was development of modular software, the CRIPS80 Software Design Analyzer System, that companies can use to evaluate other prediction procedures or other data bases.

  2. Light weight escape capsule for fighter aircraft

    NASA Technical Reports Server (NTRS)

    Robert, James A.

    1988-01-01

    Emergency crew escape capabilities have been less than adequate for fighter aircraft since before WW II. From the over-the-side bailout of those days through the current ejection seat with a rocket catapult, escaping from a disabled aircraft has been risky at best. Current efforts are underway toward developing a high-tech, smart ejection seat that will give fighter pilots more room to live in the sky, but an escape capsule is needed to meet current and future fighter envelopes. Escape capsules have a bad reputation due to past examples of high weight, poor performance and great complexity. However, the advantages available demand that a capsule be developed. This capsule concept will minimize the inherent disavantages and incorporate the benefits while integrating all aspects of crew station design. The resulting design is appropriate for a crew station of the year 2010 and includes improved combat acceleration protection, chemical or biological combat capability, improved aircraft to escape system interaction, and the highest level of escape performance achievable. The capsule is compact, which can allow a reduced aircraft size and weighs only 1200 lb. The escape system weight penalty is only 120 lb higher than that for the next ejection seat and the capsule has a corresponding increase in performance.

  3. Escape of magnetic toroids from the Sun

    NASA Technical Reports Server (NTRS)

    Bieber, John W.; Rust, David M.

    1995-01-01

    Analysis of heliospheric magnetic fields at 1 AU shows that 10(exp 24) Mx of net azimuthal flux escapes from the Sun per solar cycle. This rate is consistent with rates derived from other indicators of flux escape, including coronal mass ejections and filament eruptions. The toroidal flux escape rate is compared with the apparent rate of flux emergence at the solar surface, and it is concluded that escaping toroids will remove at least 20% of the emerging flux, and may remove as much as 100% of emerging flux if multiple eruptions occur on the toroids. The data imply that flux escapes the Sun with an efficiency far exceeding Parker's upper limit estimate of 3%. Toroidal flux escape is almost certainly the source of the observed overwinding of the interplanetary magnetic field spiral. Two mechanisms to facilitate net flux escape are discussed: helicity charging to push open the fields and flux transport with reconnection to close them off. We estimate the Sun will shed approximately 2 x 10(exp 45) of magnetic helicity per solar cycle, leading to a mean helicity density of 100 Mx(exp 2)cm(exp -3) at 1 AU, which agrees well with observations.

  4. Statin escape phenomenon: Fact or fiction?

    PubMed Central

    Barkas, Fotios; Elisaf, Moses; Klouras, Eleftherios; Dimitriou, Theodora; Tentolouris, Nikolaos; Liberopoulos, Evangelos

    2017-01-01

    AIM To evaluate the presence of the so called “statin escape” phenomenon among hyperlipidemic subjects attending a lipid clinic. METHODS This was a retrospective analysis of 1240 hyperlipidemic individuals followed-up for ≥ 3 years. We excluded those individuals meeting one of the following criteria: Use of statin therapy at baseline visit, discontinuation of statin treatment at most recent visit, change in statin treatment during follow-up and poor compliance to treatment. Statin escape phenomenon was defined as an increase in low-density lipoprotein cholesterol (LDL-C) levels at the most recent visit by > 10% compared with the value at 6 mo following initiation of statin treatment. RESULTS Of 181 eligible subjects, 31% exhibited the statin escape phenomenon. No major differences regarding baseline characteristics were found between statin escapers and non-statin escapers. Both escapers and non-escapers had similar baseline LDL-C levels [174 (152-189) and 177 (152-205) mg/dL, respectively]. In comparison with non-escapers, statin escapers demonstrated lower LDL-C levels at 6 mo after treatment initiation [88 (78-97) mg/dL vs 109 (91-129) mg/dL, P < 0.05], but higher levels at the most recent visit [103 (96-118) mg/dL vs 94 (79-114) mg/dL, P < 0.05]. CONCLUSION These data confirm the existence of an escape phenomenon among statin-treated individuals. The clinical significance of this phenomenon remains uncertain. PMID:28261552

  5. The fast escaping set for quasiregular mappings

    NASA Astrophysics Data System (ADS)

    Bergweiler, Walter; Drasin, David; Fletcher, Alastair

    2014-06-01

    The fast escaping set of a transcendental entire function is the set of all points which tend to infinity under iteration as fast as possible compatible with the growth of the function. We study the analogous set for quasiregular mappings in higher dimensions and show, among other things, that various equivalent definitions of the fast escaping set for transcendental entire functions in the plane also coincide for quasiregular mappings. We also exhibit a class of quasiregular mappings for which the fast escaping set has the structure of a spider's web.

  6. Interspecific evaluation of octopus escape behavior.

    PubMed

    Wood, James B; Anderson, Roland C

    2004-01-01

    The well-known ability of octopuses to escape enclosures is a behavior that can be fatal and, therefore, is an animal welfare issue. This study obtained survey data from 38 participants-primarily scientists and public aquarists who work with octopuses-on 25 described species of octopus. The study demonstrates that the likeliness to escape is species specific (p =.001). The study gives husbandry techniques to keep captive octopuses contained. This first interspecific study of octopus escape behavior allows readers to make informed species-specific husbandry choices.

  7. The Neuroethology of C. elegans Escape

    PubMed Central

    Pirri, Jennifer K.; Alkema, Mark J.

    2012-01-01

    Escape behaviors are crucial to survive predator encounters. Touch to the head of C. elegans induces an escape response where the animal rapidly backs away from the stimulus and suppresses foraging head movements. The coordination of head and body movements facilitates escape from predacious fungi that cohabitate with nematodes in organic debris. An appreciation of the natural habitat of laboratory organisms, like C. elegans, enables a comprehensive neuroethological analysis of behavior. In this review we discuss the neuronal mechanisms and the ecological significance of the C. elegans touch response. PMID:22226513

  8. Antigenic structure of human hepatitis A virus defined by analysis of escape mutants selected against murine monoclonal antibodies.

    PubMed Central

    Ping, L H; Lemon, S M

    1992-01-01

    We examined the antigenic structure of human hepatitis A virus (HAV) by characterizing a series of 21 murine monoclonal-antibody-resistant neutralization escape mutants derived from the HM175 virus strain. The escape phenotype of each mutant was associated with reduced antibody binding in radioimmunofocus assays. Neutralization escape mutations were identified at the Asp-70 and Gln-74 residues of the capsid protein VP3, as well as at Ser-102, Val-171, Ala-176, and Lys-221 of VP1. With the exception of the Lys-221 mutants, substantial cross-resistance was evident among escape mutants tested against a panel of 22 neutralizing monoclonal antibodies, suggesting that the involved residues contribute to epitopes composing a single antigenic site. As mutations at one or more of these residues conferred resistance to 20 of 22 murine antibodies, this site appears to be immunodominant in the mouse. However, multiple mutants selected independently against any one monoclonal antibody had mutations at only one or, at the most, two amino acid residues within the capsid proteins, confirming that there are multiple epitopes within this antigenic site and suggesting that single-amino-acid residues contributing to these epitopes may play key roles in the binding of individual antibodies. A second, potentially independent antigenic site was identified by three escape mutants with different substitutions at Lys-221 of VP1. These mutants were resistant only to antibody H7C27, while H7C27 effectively neutralized all other escape mutants. These data support the existence of an immunodominant neutralization site in the antigenic structure of hepatitis A virus which involves residues of VP3 and VP1 and a second, potentially independent site involving residue 221 of VP1. PMID:1312628

  9. Wind enhanced planetary escape: Collisional modifications

    NASA Technical Reports Server (NTRS)

    Curtis, S. A.; Hartle, R. E.

    1976-01-01

    The problem of thermal escape is considered in which both the effects of thermospheric winds at the exobase and collisions below the exobase are included in a Monte Carlo calculation. The collisions are included by means of a collisional relaxation layer of a background gas which models the transition region between the exosphere and the thermosphere. The wind effects are considered in the limiting cases of vertical and horizontal flows. Two species are considered: terrestrial hydrogen and terrestrial helium. In the cases of terrestrial hydrogen the escape fluxes were found to be strongly filtered or throttled by collisions at high exospheric temperatures. The model is applied to molecular hydrogen diffusing through a methane relaxation layer under conditions possible on Titan. The results are similar to the case of terrestrial hydrogen with wind enhanced escape being strongly suppressed by collisions. It is concluded that wind enhanced escape is not an important process on Titan.

  10. Biogeochemistry: Nocturnal escape route for marsh gas

    NASA Astrophysics Data System (ADS)

    Anthony, Katey Walter; MacIntyre, Sally

    2016-07-01

    A field study of methane emissions from wetlands reveals that more of the gas escapes through diffusive processes than was thought, mostly at night. Because methane is a greenhouse gas, the findings have implications for global warming.

  11. Evolutionary dynamics of escape from biomedical intervention.

    PubMed Central

    Iwasa, Yoh; Michor, Franziska; Nowak, Martin A

    2003-01-01

    Viruses, bacteria, eukaryotic parasites, cancer cells, agricultural pests and other inconvenient animates have an unfortunate tendency to escape from selection pressures that are meant to control them. Chemotherapy, anti-viral drugs or antibiotics fail because their targets do not hold still, but evolve resistance. A major problem in developing vaccines is that microbes evolve and escape from immune responses. The fundamental question is the following: if a genetically diverse population of replicating organisms is challenged with a selection pressure that has the potential to eradicate it, what is the probability that this population will produce escape mutants? Here, we use multi-type branching processes to describe the accumulation of mutants in independent lineages. We calculate escape dynamics for arbitrary mutation networks and fitness landscapes. Our theory shows how to estimate the probability of success or failure of biomedical intervention, such as drug treatment and vaccination, against rapidly evolving organisms. PMID:14728779

  12. Promoter clearance and escape in prokaryotes.

    PubMed

    Hsu, Lilian M

    2002-09-13

    Promoter escape is the last stage of transcription initiation when RNA polymerase, having initiated de novo phosphodiester bond synthesis, must begin to relinquish its hold on promoter DNA and advance to downstream regions (DSRs) of the template. In vitro, this process is marked by the release of high levels of abortive transcripts at most promoters, reflecting the high instability of initial transcribing complexes (ITCs) and indicative of the existence of barriers to the escape process. The high abortive initiation level is the result of the existence of unproductive ITCs that carry out repeated initiation and abortive release without escaping the promoter. The formation of unproductive ITCs is a widespread phenomenon, but it occurs to different extent on different promoters. Quantitative analysis of promoter mutations suggests that the extent and pattern of abortive initiation and promoter escape is determined by the sequence of promoter elements, both in the promoter recognition region (PRR) and the initial transcribed sequence (ITS). A general correlation has been found that the stronger the promoter DNA-polymerase interaction, the poorer the ability of RNA polymerase to escape the promoter. In gene regulation, promoter escape can be the rate-limiting step for transcription initiation. An increasing number of regulatory proteins are known to exert their control at this step. Examples are discussed with an emphasis on the diverse mechanisms involved. At the molecular level, the X-ray crystal structures of RNA polymerase and its various transcription complexes provide the framework for understanding the functional data on abortive initiation and promoter escape. Based on structural and biochemical evidence, a mechanism for abortive initiation and promoter escape is described.

  13. Dynamics of the Pin Pallet Runaway Escapement

    DTIC Science & Technology

    1978-06-01

    pin pallet simulation to a spring- driven timing mechanism. 3. Modification of the present model to accommcdate the simulation of a plate pallet ...NUMULER( Technical Report ARLCD-TFR-77062 4. TITLE (and Sublttle) 5. TYPE OF REPORT & PERIOD COVERED DYNAMICS OF THE PIN PALLET RUNAWAY ESCAPEMENT 6...instantaneous positions of the pallet pin and the escape-wheel form the basis of the controls in the computer program. DO I FJAN 1473AVr1t’I o INOV 6IS

  14. Atomic hydrogen escape rate due to charge exchange with hot plasmaspheric ions

    NASA Technical Reports Server (NTRS)

    Maher, L. J.; Tinsley, B. A.

    1977-01-01

    Data on ion and electron temperatures and concentrations to several thousand kilometers of altitude were obtained from the Atmosphere Explorer C satellite for 1974 and to 850 km from Arecibo incoherent scatter radar measurements. These data were used to normalize diffusive equilibrium profiles. From these profiles and by using the neutral atmospheric model of Jacchia (1971) and a new hydrogen model, the charge-exchange-induced neutral hydrogen escape fluxes for equatorial and middle latitudes were calculated. The data confirm earlier estimates that the charge exchange loss is more important than Jeans escape for the earth. It is also found that inside the plasmapause this charge exchange process with hot plasmapheric ions is the major production and loss process for the satellite population in the hydrogen geocorona.

  15. Submarine tower escape decompression sickness risk estimation.

    PubMed

    Loveman, G A M; Seddon, E M; Thacker, J C; Stansfield, M R; Jurd, K M

    2014-01-01

    Actions to enhance survival in a distressed submarine (DISSUB) scenario may be guided in part by knowledge of the likely risk of decompression sickness (DCS) should the crew attempt tower escape. A mathematical model for DCS risk estimation has been calibrated against DCS outcome data from 3,738 exposures of either men or goats to raised pressure. Body mass was used to scale DCS risk. The calibration data included more than 1,000 actual or simulated submarine escape exposures and no exposures with substantial staged decompression. Cases of pulmonary barotrauma were removed from the calibration data. The calibrated model was used to estimate the likelihood of DCS occurrence following submarine escape from the United Kingdom Royal Navy tower escape system. Where internal DISSUB pressure remains at - 0.1 MPa, escape from DISSUB depths < 200 meters is estimated to have DCS risk < 6%. Saturation at raised DISSUB pressure markedly increases risk, with > 60% DCS risk predicted for a 200-meter escape from saturation at 0.21 MPa. Using the calibrated model to predict DCS for direct ascent from saturation gives similar risk estimates to other published models.

  16. [Escape of transgenes and its ecological risks].

    PubMed

    Lu, Baorong; Zhang, Wenju; Li, Bo

    2003-06-01

    The rapid development of biotechnology, particularly the transgenic technology, has brought us with tremendous opportunities to solve the world's starvation problems that have been caused by the continued expanding of the global population. However, the application of transgenic biotechnology and the environmental release of transgenic organisms have evoked a series of extraordinary debates on biosafety issues related to the prosperity and the future of transgenic technology. The public and scientific communities are desperately interested in knowing whether the transgenic products would pose negative influences on plants and animals, human life and health, as well as on genetic resources and environment. These concerns have become universal hot topics over the last decade. Among the most debated biosafety issues caused potentially by transgenic products, transgene escape to the environment and its consequent ecological risks become one of the appealing focal points. In this review, a series of biosafety issues concerned by public, including the possibility of transgene escape and its various paths, as well as the potential ecological risks caused by such escape were discussed, and various approaches for controlling for transgene escape and the factors to consider when designing safety isolation distance between transgenic varieties and other concerned plants were also examined. The objective of this review is to allow readers to understand the potential biosafety problems caused by environmental release of transgenic crops and by the escape of foreign transgenes in particular, and to use the effective tools to control and avoid transgene escape.

  17. Polymer escape from a confining potential

    SciTech Connect

    Mökkönen, Harri; Ikonen, Timo; Jónsson, Hannes; Ala-Nissila, Tapio

    2014-02-07

    The rate of escape of polymers from a two-dimensionally confining potential well has been evaluated using self-avoiding as well as ideal chain representations of varying length, up to 80 beads. Long timescale Langevin trajectories were calculated using the path integral hyperdynamics method to evaluate the escape rate. A minimum is found in the rate for self-avoiding polymers of intermediate length while the escape rate decreases monotonically with polymer length for ideal polymers. The increase in the rate for long, self-avoiding polymers is ascribed to crowding in the potential well which reduces the free energy escape barrier. An effective potential curve obtained using the centroid as an independent variable was evaluated by thermodynamic averaging and Kramers rate theory then applied to estimate the escape rate. While the qualitative features are well reproduced by this approach, it significantly overestimates the rate, especially for the longer polymers. The reason for this is illustrated by constructing a two-dimensional effective energy surface using the radius of gyration as well as the centroid as controlled variables. This shows that the description of a transition state dividing surface using only the centroid fails to confine the system to the region corresponding to the free energy barrier and this problem becomes more pronounced the longer the polymer is. A proper definition of a transition state for polymer escape needs to take into account the shape as well as the location of the polymer.

  18. Escape of Hydrogen from the Exosphere of Mars

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Dolon; Clarke, John T.; Bertaux, Jean-Loup; Chaufray, Jean-Yves; Mayyasi-Matta, Majd A.

    2016-10-01

    After decades of exploration, the martian neutral hydrogen exosphere has remained largely uncharacterized even today. In my dissertation I have attempted to constrain the characteristics of the martian hydrogen exosphere using Hubble Space Telescope observations obtained during October-November 2007 and 2014. These observations reveal short-term seasonal changes exhibited by the martian hydrogen exosphere that are inconsistent with the diffusion-limited escape scenario. This seasonal behavior adds a new element towards backtracking the history of water loss from Mars. Modeling of the data also indicates the likely presence of a superthermal population of hydrogen created by non-thermal processes at Mars, another key element to understand the present-day escape. Exploration of the latitudinal symmetry of the martian exosphere indicates that it is symmetric above 2.5 martian radii and asymmetric below this altitude, which could be due to temperature differences between the day and night sides. Finally, the large uncertainties in determining the characteristics of the martian exosphere after decades of exploration is due to various assumptions about the intrinsic characteristics of the martian exosphere in the modeling process, degeneracy in the two modeling parameters temperature and density of the hydrogen atoms, unaccounted seasonal effects, and uncertainties introduced from spacecraft instrumentation as well as their viewing geometry.

  19. The ionotail of Venus - Its configuration and evidence for ion escape

    NASA Technical Reports Server (NTRS)

    Brace, L. H.; Kasprzak, W. T.; Taylor, H. A.; Theis, R. F.; Russell, C. T.; Barnes, A.; Mihalov, J. D.

    1987-01-01

    The configuration and morphology of the plasma clouds in the ionotail of Venus (revealed by the Pioneer Venus Orbiter) are studied, and the rate of planetary ion escape, which may be associated with the dissipation and removal of the ionospheric plasma, is estimated. The data supplied by the Orbiter's instruments, the Orbiter electron temperature probe, the ion mass spectrometer, the neutral mass spectrometer, the magnetometer, and the plasma analyzer, are analyzed, and the results of the observations are discussed.

  20. Localized reactive oxygen and nitrogen intermediates inhibit escape of Listeria monocytogenes from vacuoles in activated macrophages.

    PubMed

    Myers, Jesse T; Tsang, Albert W; Swanson, Joel A

    2003-11-15

    Listeria monocytogenes (Lm) evades being killed after phagocytosis by macrophages by escaping from vacuoles into cytoplasm. Activated macrophages are listericidal, in part because they can retain Lm in vacuoles. This study examined the contribution of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates (RNI) to the inhibition of Lm escape from vacuoles. Lm escaped from vacuoles of nonactivated macrophages within 30 min of infection. Macrophages activated with IFN-gamma, LPS, IL-6, and a neutralizing Ab against IL-10 retained Lm within the vacuoles, and inhibitors of ROI and RNI blocked inhibition of vacuolar escape to varying degrees. Measurements of Lm escape in macrophages from gp91(phox-/-) and NO synthase 2(-/-) mice showed that vacuolar retention required ROI and was augmented by RNI. Live cell imaging with the fluorogenic probe dihydro-2',4,5,6,7,7'-hexafluorofluorescein coupled to BSA (DHFF-BSA) indicated that oxidative chemistries were generated rapidly and were localized to Lm vacuoles. Chemistries that oxidized DHFF-BSA were similar to those that retained Lm in phagosomes. Fluorescent conversion of DHFF-BSA occurred more efficiently in smaller vacuoles, indicating that higher concentrations of ROI or RNI were generated in more confining volumes. Thus, activated macrophages retained Lm within phagosomes by the localization of ROI and RNI to vacuoles, and by their combined actions in a small space

  1. Developing a self-consistent description of Titan's upper atmosphere without hydrodynamic escape

    NASA Astrophysics Data System (ADS)

    Bell, Jared M.; Hunter Waite, J.; Westlake, Joseph H.; Bougher, Stephen W.; Ridley, Aaron J.; Perryman, Rebecca; Mandt, Kathleen

    2014-06-01

    In this study, we develop a best fit description of Titan's upper atmosphere between 500 km and 1500 km, using a one-dimensional (1-D) version of the three-dimensional (3-D) Titan Global Ionosphere-Thermosphere Model. For this modeling, we use constraints from several lower atmospheric Cassini-Huygens investigations and validate our simulation results against in situ Cassini Ion-Neutral Mass Spectrometer (INMS) measurements of N2, CH4, H2, 40Ar, HCN, and the major stable isotopic ratios of 14N/15N in N2. We focus our investigation on aspects of Titan's upper atmosphere that determine the amount of atmospheric escape required to match the INMS measurements: the amount of turbulence, the inclusion of chemistry, and the effects of including a self-consistent thermal balance. We systematically examine both hydrodynamic escape scenarios for methane and scenarios with significantly reduced atmospheric escape. Our results show that the optimum configuration of Titan's upper atmosphere is one with a methane homopause near 1000 km and atmospheric escape rates of 1.41-1.47 ×1011 CH4 m-2 s-1 and 1.08 ×1014 H2 m-2 s-1 (scaled relative to the surface). We also demonstrate that simulations consistent with hydrodynamic escape of methane systematically produce inferior fits to the multiple validation points presented here.

  2. Photochemical escape of oxygen from Mars: First results from MAVEN in situ data

    NASA Astrophysics Data System (ADS)

    Lillis, Robert J.; Deighan, Justin; Fox, Jane L.; Bougher, Stephen W.; Lee, Yuni; Combi, Michael R.; Cravens, Thomas E.; Rahmati, Ali; Mahaffy, Paul R.; Benna, Mehdi; Elrod, Meredith K.; McFadden, James P.; Ergun, Robert. E.; Andersson, Laila; Fowler, Christopher M.; Jakosky, Bruce M.; Thiemann, Ed; Eparvier, Frank; Halekas, Jasper S.; Leblanc, François; Chaufray, Jean-Yves

    2017-03-01

    Photochemical escape of atomic oxygen is thought to be one of the dominant channels for Martian atmospheric loss today and played a potentially major role in climate evolution. Mars Atmosphere and Volatile Evolution Mission (MAVEN) is the first mission capable of measuring, in situ, the relevant quantities necessary to calculate photochemical escape fluxes. We utilize 18 months of data from three MAVEN instruments: Langmuir Probe and Waves, Neutral Gas and Ion Mass Spectrometer, and SupraThermal And Thermal Ion Composition. From these data, we calculate altitude profiles of the production rate of hot oxygen atoms from the dissociative recombination of O2+ and the probability that such atoms will escape the Mars atmosphere. From this, we determine escape fluxes for 815 periapsis passes. Derived average dayside hot O escape rates range from 1.2 to 5.5 × 1025 s-1, depending on season and EUV flux, consistent with several pre-MAVEN predictions and in broad agreement with estimates made with other MAVEN measurements. Hot O escape fluxes do not vary significantly with dayside solar zenith angle or crustal magnetic field strength but depend on CO2 photoionization frequency with a power law whose exponent is 2.6 ± 0.6, an unexpectedly high value which may be partially due to seasonal and geographic sampling. From this dependence and historical EUV measurements over 70 years, we estimate a modern-era average escape rate of 4.3 × 1025 s-1. Extrapolating this dependence to early solar system, EUV conditions gives total losses of 13, 49, 189, and 483 mbar of oxygen over 1-3 and 3.5 Gyr, respectively, with uncertainties significantly increasing with time in the past.

  3. Impaired Driving

    MedlinePlus

    ... people were killed in alcohol-impaired driving crashes, accounting for nearly one-third (31%) of all traffic- ... promotion efforts into practice that influence economic, organizational, policy, and school/community action. 13,14 Using community- ...

  4. Distracted Driving

    MedlinePlus

    ... other distractions. 3 At 55 mph, the average text takes your eyes off the road long enough ... risk behaviors among high school students, including sending texts while driving. 6,7 In 2013, more than ...

  5. Pile driving

    SciTech Connect

    Merjan, S.

    1988-02-16

    Process for producing in the ground a driven composite pile is described having (a) a lower pipe stem having an upper part having a top, the lower pipe stem being capable of withstanding pile driving blows applied to the top and (b) an upper corrugated shell stem incapable of withstanding pile driving blows, the corrugated shell stem having a lower end, which process comprises driving the lower pipe stem into the ground fitting to the top of the lower pipe stem a splicer. The splicer comprises a plate having a top face and a bottom face, an integral body portion depending from the plate and surrounding the upper part of the pipe stem and, welded to the top face of the plate, an upwardly extending corrugated shell stub up to about three feet long, screwing the lower end of the upper corrugated shell stem to the shell stub after driving the lower pipe stem into the ground, placing a non-expanding pipe mandrel into the shell stem with the bottom of the mandrel resting on the plate, striking pile-driving blows on the top of the mandrel to drive the composite pile into the ground, and filling the shell stem and pipe stem with concrete from above.

  6. 46 CFR 177.500 - Means of escape.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 7 2011-10-01 2011-10-01 false Means of escape. 177.500 Section 177.500 Shipping COAST...) CONSTRUCTION AND ARRANGEMENT Escape Requirements § 177.500 Means of escape. (a) Except as otherwise provided in... least two means of escape, one of which must not be a watertight door. (b) The two required means of...

  7. Antibody neutralization of retargeted measles viruses.

    PubMed

    Lech, Patrycja J; Pappoe, Roland; Nakamura, Takafumi; Tobin, Gregory J; Nara, Peter L; Russell, Stephen J

    2014-04-01

    The measles virus (MV) vaccine lineage is a promising oncolytic but prior exposure to the measles vaccine or wild-type MV strains limits treatment utility due to the presence of anti-measles antibodies. MV entry can be redirected by displaying a polypeptide ligand on the Hemagglutinin (H) C-terminus. We hypothesized that retargeted MV would escape neutralization by monoclonal antibodies (mAbs) recognizing the H receptor-binding surface and be less susceptible to neutralization by human antisera. Using chimeric H proteins, with and without mutations that ablate MV receptor binding, we show that retargeted MVs escape mAbs that target the H receptor-binding surface by virtue of mutations that ablate infection via SLAM and CD46. However, C-terminally displayed domains do not mediate virus entry in the presence of human antibodies that bind to the underlying H domain. In conclusion, utility of retargeted oncolytic measles viruses does not extend to evasion of human serum neutralization. Copyright © 2014 The Authors. Published by Elsevier Inc. All rights reserved.

  8. Hydrogen Escape from early Earth and Mars

    NASA Astrophysics Data System (ADS)

    Zugger, M. E.; Ramirez, R. M.; Kasting, J. F.

    2012-12-01

    A controversy regarding hydrodynamic escape rates arose when Tian et al. (2005) published transonic escape rates for an atmosphere composed of pure H2. Tian et al. concluded that the hydrogen escape rate from early Earth would have been a factor of 20 or more slower than the diffusion limit, even if the solar EUV (extreme ultraviolet) flux was enhanced by a factor of 5 relative to today. This conclusion was challenged by Catling (2006), who pointed out that solar EUV fluxes could have been much higher than this so that plenty of energy should have been available to power escape. This controversy has remained unresolved to date. Hydrogen escape from early Mars is also of interest. As discussed in this session in a complementary paper by Ramirez et al., collision-induced absorption by molecular hydrogen could have helped to warm early Mars, perhaps explaining the formation of valleys and valley networks. Ramirez et al. have shown that a mixture of 90% CO2 and 10% H2 is capable raising early Mars' surface temperature above the freezing point of water, for surface pressures exceeding ~3 bar. However, we need to understand whether H2 mixing ratios of 10% are physically plausible. The H2 partial pressure in Mars' early atmosphere would have been determined by the balance between volcanic outgassing and escape to space. The 10% mixing ratio is high compared to the value of ~10-3 typically assumed for early Earth. But Mars' early atmosphere may have been more reduced than Earth's (Wadwha, 2001); if the hydrogen escape rate on Mars was also slower than on Earth, then additional increases in atmospheric hydrogen concentration are possible. To answer these questions about the early atmospheres of Earth and Mars, we have modified an existing model of hydrodynamic escape, developed by F. Tian, J. Kasting, and others, to converge for atmospheres with a wide range of hydrogen mixing ratios. The model finds subsonic solutions to the hydrodynamic equations; these can be shown to

  9. Room Escape at Class: Escape Games Activities to Facilitate the Motivation and Learning in Computer Science

    ERIC Educational Resources Information Center

    Borrego, Carlos; Fernández, Cristina; Blanes, Ian; Robles, Sergi

    2017-01-01

    Real-life room-escape games are ludic activities in which participants enter a room in order to get out of it only after solving some riddles. In this paper, we explain a Room Escape teaching experience developed in the Engineering School at Universitat Autònoma de Barcelona. The goal of this activity is to increase student's motivation and to…

  10. Residential smoke alarms and fire escape plans.

    PubMed Central

    Harvey, P A; Sacks, J J; Ryan, G W; Bender, P F

    1998-01-01

    OBJECTIVE: To estimate the proportion of U.S. homes with installed smoke alarms, smoke alarms on the same floor as occupants' bedrooms, and fire escape plans. METHODS: The authors analyzed data on smoke alarm use and fire escape planning from a 1994 stratified random telephone survey of 5238 U.S. households. RESULTS: Respondents from 91% of surveyed households reported the presence of at least one installed smoke alarm, and 94% of respondents reported having an alarm on the same level of the home as their sleeping area. The prevalence of installed smoke alarms varied by highest education level in the household and income level. Sixty percent of all households had designed or discussed a fire escape plan at least once; only 17% of these households had actually practiced one. CONCLUSIONS: Although overall use of smoke alarms was high, certain population subgroups were less likely to have smoke alarms or to have them installed on the same floor as bedrooms. Fire escape planning, another important safety measure, was somewhat less common, and very few respondents reported having practiced a fire escape plan with the members of their household. PMID:9769771

  11. Genes that escape from X inactivation.

    PubMed

    Berletch, Joel B; Yang, Fan; Xu, Jun; Carrel, Laura; Disteche, Christine M

    2011-08-01

    To achieve a balanced gene expression dosage between males (XY) and females (XX), mammals have evolved a compensatory mechanism to randomly inactivate one of the female X chromosomes. Despite this chromosome-wide silencing, a number of genes escape X inactivation: in women about 15% of X-linked genes are bi-allelically expressed and in mice, about 3%. Expression from the inactive X allele varies from a few percent of that from the active allele to near equal expression. While most genes have a stable inactivation pattern, a subset of genes exhibit tissue-specific differences in escape from X inactivation. Escape genes appear to be protected from the repressive chromatin modifications associated with X inactivation. Differences in the identity and distribution of escape genes between species and tissues suggest a role for these genes in the evolution of sex differences in specific phenotypes. The higher expression of escape genes in females than in males implies that they may have female-specific roles and may be responsible for some of the phenotypes observed in X aneuploidy.

  12. Cerebrospinal Fluid HIV Escape from Antiretroviral Therapy.

    PubMed

    Ferretti, Francesca; Gisslen, Magnus; Cinque, Paola; Price, Richard W

    2015-06-01

    CNS infection is a nearly constant facet of systemic CNS infection and is generally well controlled by suppressive systemic antiretroviral therapy (ART). However, there are instances when HIV can be detected in the cerebrospinal fluid (CSF) despite suppression of plasma viruses below the clinical limits of measurement. We review three types of CSF viral escape: asymptomatic, neuro-symptomatic, and secondary. The first, asymptomatic CSF escape, is seemingly benign and characterized by lack of discernable neurological deterioration or subsequent CNS disease progression. Neuro-symptomatic CSF escape is an uncommon, but important, entity characterized by new or progressive CNS disease that is critical to recognize clinically because of its management implications. Finally, secondary CSF escape, which may be even more uncommon, is defined by an increase of CSF HIV replication in association with a concomitant non-HIV infection, as a consequence of the local inflammatory response. Understanding these CSF escape settings not only is important for clinical diagnosis and management but also may provide insight into the CNS HIV reservoir.

  13. Compensatory escape mechanism at low Reynolds number

    PubMed Central

    Gemmell, Brad J.; Sheng, Jian; Buskey, Edward J.

    2013-01-01

    Despite high predation pressure, planktonic copepods remain one of the most abundant groups on the planet. Their escape response provides one of most effective mechanisms to maximize evolutionary fitness. Owing to their small size (100 µm) compared with their predators (>1 mm), increasing viscosity is believed to have detrimental effects on copepods’ fitness at lower temperature. Using high-speed digital holography we acquire 3D kinematics of the nauplius escape including both location and detailed appendage motion. By independently varying temperature and viscosity we demonstrate that at natural thermal extremes, contrary to conventional views, nauplii achieve equivalent escape distance while maintaining optimal velocity. Using experimental results and kinematic simulations from a resistive force theory propulsion model, we demonstrate that a shift in appendage timing creates an increase in power stroke duration relative to recovery stroke duration. This change allows the nauplius to limit losses in velocity and maintain distance during escapes at the lower bound of its natural thermal range. The shift in power stroke duration relative to recovery stroke duration is found to be regulated by the temperature dependence of swimming appendage muscle groups, not a dynamic response to viscosity change. These results show that copepod nauplii have natural adaptive mechanisms to compensate for viscosity variations with temperature but not in situations in which viscosity varies independent of temperature, such as in some phytoplankton blooms. Understanding the robustness of escapes in the wake of environmental changes such as temperature and viscosity has implications in assessing the future health of performance compensation. PMID:23487740

  14. Enhanced Endosomal Escape by Light-Fueled Liquid-Metal Transformer.

    PubMed

    Lu, Yue; Lin, Yiliang; Chen, Zhaowei; Hu, Quanyin; Liu, Yang; Yu, Shuangjiang; Gao, Wei; Dickey, Michael D; Gu, Zhen

    2017-04-12

    Effective endosomal escape remains as the "holy grail" for endocytosis-based intracellular drug delivery. To date, most of the endosomal escape strategies rely on small molecules, cationic polymers, or pore-forming proteins, which are often limited by the systemic toxicity and lack of specificity. We describe here a light-fueled liquid-metal transformer for effective endosomal escape-facilitated cargo delivery via a chemical-mechanical process. The nanoscale transformer can be prepared by a simple approach of sonicating a low-toxicity liquid-metal. When coated with graphene quantum dots (GQDs), the resulting nanospheres demonstrate the ability to absorb and convert photoenergy to drive the simultaneous phase separation and morphological transformation of the inner liquid-metal core. The morphological transformation from nanospheres to hollow nanorods with a remarkable change of aspect ratio can physically disrupt the endosomal membrane to promote endosomal escape of payloads. This metal-based nanotransformer equipped with GQDs provides a new strategy for facilitating effective endosomal escape to achieve spatiotemporally controlled drug delivery with enhanced efficacy.

  15. Wabble gear drive mechanism. [for aerospace environments

    NASA Technical Reports Server (NTRS)

    Winiarski, F. J. (Inventor)

    1967-01-01

    The wabble gear principle was applied in the design of a driving mechanism for controlling spacecraft solar panels. The moving elements, other than the output gear, are contained within a hermetically sealed package to prevent escape of lubricants and ingestion of contaminant particles. The driving gear contains one more tooth than the output gear on a concave, conical pitch surface of slightly larger apex angle. The two gears mesh face to face such that engagement takes place at one point along the circumference. The driving gear is not permitted to rotate by virtue of its attachment through the bellows which permits flexure in the pitch and yaw position, but not in roll. As the bearing carrier rotates, the inclined mounting of the bearing causes the driving gear to perform a wabbling, irrotational motion. This wabbling motion causes the contact point between the output gear and the driving gear to traverse around the circumference of the gears once per revolution of the bearing carrier.

  16. ESCAPE AS REINFORCEMENT AND ESCAPE EXTINCTION IN THE TREATMENT OF FEEDING PROBLEMS

    PubMed Central

    LaRue, Robert H; Stewart, Victoria; Piazza, Cathleen C; Volkert, Valerie M; Patel, Meeta R; Zeleny, Jason

    2011-01-01

    Given the effectiveness of putative escape extinction as treatment for feeding problems, it is surprising that little is known about the effects of escape as reinforcement for appropriate eating during treatment. In the current investigation, we examined the effectiveness of escape as reinforcement for mouth clean (a product measure of swallowing), escape as reinforcement for mouth clean plus escape extinction (EE), and EE alone as treatment for the food refusal of 5 children. Results were similar to those of previous studies, in that reinforcement alone did not result in increases in mouth clean or decreases in inappropriate behavior (e.g., Piazza, Patel, Gulotta, Sevin, & Layer, 2003). Increases in mouth clean and decreases in inappropriate behavior occurred when the therapist implemented EE independent of the presence or absence of reinforcement. Results are discussed in terms of the role of negative reinforcement in the etiology and treatment of feeding problems. PMID:22219525

  17. Escape as reinforcement and escape extinction in the treatment of feeding problems.

    PubMed

    LaRue, Robert H; Stewart, Victoria; Piazza, Cathleen C; Volkert, Valerie M; Patel, Meeta R; Zeleny, Jason

    2011-01-01

    Given the effectiveness of putative escape extinction as treatment for feeding problems, it is surprising that little is known about the effects of escape as reinforcement for appropriate eating during treatment. In the current investigation, we examined the effectiveness of escape as reinforcement for mouth clean (a product measure of swallowing), escape as reinforcement for mouth clean plus escape extinction (EE), and EE alone as treatment for the food refusal of 5 children. Results were similar to those of previous studies, in that reinforcement alone did not result in increases in mouth clean or decreases in inappropriate behavior (e.g., Piazza, Patel, Gulotta, Sevin, & Layer, 2003). Increases in mouth clean and decreases in inappropriate behavior occurred when the therapist implemented EE independent of the presence or absence of reinforcement. Results are discussed in terms of the role of negative reinforcement in the etiology and treatment of feeding problems.

  18. Exploring potential Pluto-generated neutral tori

    NASA Astrophysics Data System (ADS)

    Smith, Howard T.; Hill, Matthew; KollMann, Peter; McHutt, Ralph

    2015-11-01

    The NASA New Horizons mission to Pluto is providing unprecedented insight into this mysterious outer solar system body. Escaping molecular nitrogen is of particular interest and possibly analogous to similar features observed at moons of Saturn and Jupiter. Such escaping N2 has the potential of creating molecular nitrogen and N (as a result of molecular dissociation) tori or partial toroidal extended particle distributions. The presence of these features would present the first confirmation of an extended toroidal neutral feature on a planetary scale in our solar system. While escape velocities are anticipated to be lower than those at Enceladus, Io or even Europa, particle lifetimes are much longer in Pluto’s orbit because as a result of much weaker solar interaction processes along Pluto’s orbit (on the order of tens of years). Thus, with a ~248 year orbit, Pluto may in fact be generating an extended toroidal feature along it orbit.For this work, we modify and apply our 3-D Monte Carlo neutral torus model (previously used at Saturn, Jupiter and Mercury) to study/analyze the theoretical possibility and scope of potential Pluto-generated neutral tori. Our model injects weighted particles and tracks their trajectories under the influence of all gravitational fields with interactions with other particles, solar photons and Pluto collisions. We present anticipated N2 and N tori based on current estimates of source characterization and environmental conditions. We also present an analysis of sensitivity to assumed initial conditions. Such results can provide insight into the Pluto system as well as valuable interpretation of New Horizon’s observational data.

  19. Thermal escape from extrasolar giant planets

    PubMed Central

    Koskinen, Tommi T.; Lavvas, Panayotis; Harris, Matthew J.; Yelle, Roger V.

    2014-01-01

    The detection of hot atomic hydrogen and heavy atoms and ions at high altitudes around close-in extrasolar giant planets (EGPs) such as HD209458b implies that these planets have hot and rapidly escaping atmospheres that extend to several planetary radii. These characteristics, however, cannot be generalized to all close-in EGPs. The thermal escape mechanism and mass loss rate from EGPs depend on a complex interplay between photochemistry and radiative transfer driven by the stellar UV radiation. In this study, we explore how these processes change under different levels of irradiation on giant planets with different characteristics. We confirm that there are two distinct regimes of thermal escape from EGPs, and that the transition between these regimes is relatively sharp. Our results have implications for thermal mass loss rates from different EGPs that we discuss in the context of currently known planets and the detectability of their upper atmospheres. PMID:24664923

  20. Thermal escape from extrasolar giant planets.

    PubMed

    Koskinen, Tommi T; Lavvas, Panayotis; Harris, Matthew J; Yelle, Roger V

    2014-04-28

    The detection of hot atomic hydrogen and heavy atoms and ions at high altitudes around close-in extrasolar giant planets (EGPs) such as HD209458b implies that these planets have hot and rapidly escaping atmospheres that extend to several planetary radii. These characteristics, however, cannot be generalized to all close-in EGPs. The thermal escape mechanism and mass loss rate from EGPs depend on a complex interplay between photochemistry and radiative transfer driven by the stellar UV radiation. In this study, we explore how these processes change under different levels of irradiation on giant planets with different characteristics. We confirm that there are two distinct regimes of thermal escape from EGPs, and that the transition between these regimes is relatively sharp. Our results have implications for thermal mass loss rates from different EGPs that we discuss in the context of currently known planets and the detectability of their upper atmospheres.

  1. Chikungunya viruses that escape monoclonal antibody therapy are clinically attenuated, stable, and not purified in mosquitoes.

    PubMed

    Pal, Pankaj; Fox, Julie M; Hawman, David W; Huang, Yan-Jang S; Messaoudi, Ilhem; Kreklywich, Craig; Denton, Michael; Legasse, Alfred W; Smith, Patricia P; Johnson, Syd; Axthelm, Michael K; Vanlandingham, Dana L; Streblow, Daniel N; Higgs, Stephen; Morrison, Thomas E; Diamond, Michael S

    2014-08-01

    Chikungunya virus (CHIKV) is a reemerging mosquito-transmitted alphavirus that causes epidemics of debilitating polyarthritis in humans. A prior study identified two anti-CHIKV monoclonal antibodies ([MAbs] CHK-152 and CHK-166) against the E2 and E1 structural proteins, which had therapeutic efficacy in immunocompetent and immunocompromised mice. Combination MAb therapy was required as administration of a single MAb resulted in the rapid selection of neutralization escape variants and treatment failure in mice. Here, we initially evaluated the efficacy of combination MAb therapy in a nonhuman primate model of CHIKV infection. Treatment of rhesus macaques with CHK-152 and CHK-166 reduced viral spread and infection in distant tissue sites and also neutralized reservoirs of infectious virus. Escape viruses were not detected in the residual viral RNA present in tissues and organs of rhesus macaques. To evaluate the possible significance of MAb resistance, we engineered neutralization escape variant viruses (E1-K61T, E2-D59N, and the double mutant E1-K61T E2-D59N) that conferred resistance to CHK-152 and CHK-166 and tested them for fitness in mosquito cells, mammalian cells, mice, and Aedes albopictus mosquitoes. In both cell culture and mosquitoes, the mutant viruses grew equivalently and did not revert to wild-type (WT) sequence. All escape variants showed evidence of mild clinical attenuation, with decreased musculoskeletal disease at early times after infection in WT mice and a prolonged survival time in immunocompromised Ifnar1(-/-) mice. Unexpectedly, this was not associated with decreased infectivity, and consensus sequencing from tissues revealed no evidence of reversion or compensatory mutations. Competition studies with CHIKV WT also revealed no fitness compromise of the double mutant (E1-K61T E2-D59N) neutralization escape variant in WT mice. Collectively, our study suggests that neutralization escape viruses selected during combination MAb therapy with CHK

  2. Chikungunya Viruses That Escape Monoclonal Antibody Therapy Are Clinically Attenuated, Stable, and Not Purified in Mosquitoes

    PubMed Central

    Pal, Pankaj; Fox, Julie M.; Hawman, David W.; Huang, Yan-Jang S.; Messaoudi, Ilhem; Kreklywich, Craig; Denton, Michael; Legasse, Alfred W.; Smith, Patricia P.; Johnson, Syd; Axthelm, Michael K.; Vanlandingham, Dana L.; Streblow, Daniel N.; Higgs, Stephen; Morrison, Thomas E.

    2014-01-01

    ABSTRACT Chikungunya virus (CHIKV) is a reemerging mosquito-transmitted alphavirus that causes epidemics of debilitating polyarthritis in humans. A prior study identified two anti-CHIKV monoclonal antibodies ([MAbs] CHK-152 and CHK-166) against the E2 and E1 structural proteins, which had therapeutic efficacy in immunocompetent and immunocompromised mice. Combination MAb therapy was required as administration of a single MAb resulted in the rapid selection of neutralization escape variants and treatment failure in mice. Here, we initially evaluated the efficacy of combination MAb therapy in a nonhuman primate model of CHIKV infection. Treatment of rhesus macaques with CHK-152 and CHK-166 reduced viral spread and infection in distant tissue sites and also neutralized reservoirs of infectious virus. Escape viruses were not detected in the residual viral RNA present in tissues and organs of rhesus macaques. To evaluate the possible significance of MAb resistance, we engineered neutralization escape variant viruses (E1-K61T, E2-D59N, and the double mutant E1-K61T E2-D59N) that conferred resistance to CHK-152 and CHK-166 and tested them for fitness in mosquito cells, mammalian cells, mice, and Aedes albopictus mosquitoes. In both cell culture and mosquitoes, the mutant viruses grew equivalently and did not revert to wild-type (WT) sequence. All escape variants showed evidence of mild clinical attenuation, with decreased musculoskeletal disease at early times after infection in WT mice and a prolonged survival time in immunocompromised Ifnar1−/− mice. Unexpectedly, this was not associated with decreased infectivity, and consensus sequencing from tissues revealed no evidence of reversion or compensatory mutations. Competition studies with CHIKV WT also revealed no fitness compromise of the double mutant (E1-K61T E2-D59N) neutralization escape variant in WT mice. Collectively, our study suggests that neutralization escape viruses selected during combination MAb therapy

  3. Disk Drives

    NASA Technical Reports Server (NTRS)

    1994-01-01

    A new material known as AlBeMet, developed by Brush Wellman for research applications in the National Aero-Space Plane (NASP) program, is now used for high performance disk drives. AlBeMet is a compression of aluminum, beryllium metal matrix composite. It reduces system weight and its high thermal conductivity can effectively remove heat and increase an electrical system's lifetime. The lighter, stiffer AlBeMet (AlBeMet 160) used in the disk drive means heads can be moved faster, improving disk performance.

  4. Bacillus anthracis factors for phagosomal escape.

    PubMed

    Tonello, Fiorella; Zornetta, Irene

    2012-07-01

    The mechanism of phagosome escape by intracellular pathogens is an important step in the infectious cycle. During the establishment of anthrax, Bacillus anthracis undergoes a transient intracellular phase in which spores are engulfed by local phagocytes. Spores germinate inside phagosomes and grow to vegetative bacilli, which emerge from their resident intracellular compartments, replicate and eventually exit from the plasma membrane. During germination, B. anthracis secretes multiple factors that can help its resistance to the phagocytes. Here the possible role of B. anthracis toxins, phospholipases, antioxidant enzymes and capsules in the phagosomal escape and survival, is analyzed and compared with that of factors of other microbial pathogens involved in the same type of process.

  5. Statistical theory of asteroid escape rates.

    PubMed

    Jaffé, Charles; Ross, Shane D; Lo, Martin W; Marsden, Jerrold; Farrelly, David; Uzer, T

    2002-07-01

    Transition states in phase space are identified and shown to regulate the rate of escape of asteroids temporarily captured in circumplanetary orbits. The transition states, similar to those occurring in chemical reaction dynamics, are then used to develop a statistical semianalytical theory for the rate of escape of asteroids temporarily captured by Mars. Theory and numerical simulations are found to agree to better than 1%. These calculations suggest that further development of transition state theory in celestial mechanics, as an alternative to large-scale numerical simulations, will be a fruitful approach to mass transport calculations.

  6. Black holes escaping from domain walls

    SciTech Connect

    Flachi, Antonino; Sasaki, Misao; Pujolas, Oriol; Tanaka, Takahiro

    2006-06-15

    Previous studies concerning the interaction of branes and black holes suggested that a small black hole intersecting a brane may escape via a mechanism of reconnection. Here we consider this problem by studying the interaction of a small black hole and a domain wall composed of a scalar field and simulate the evolution of this system when the black hole acquires an initial recoil velocity. We test and confirm previous results, however, unlike the cases previously studied, in the more general set-up considered here, we are able to follow the evolution of the system also during the separation, and completely illustrate how the escape of the black hole takes place.

  7. Plasma Heating by Neutral Beam Injection

    SciTech Connect

    Koch, R

    2004-03-15

    The additional heating of plasmas by injection of fast neutrals - or Neutral Beam Injection (NBI) - is reviewed. First, the limitations of ohmic heating in tokamaks and the other motivations for using additional heating in fusion machines are discussed. Next, the principle of operation of neutral beam injectors, and state of the art, are outlined. Positive-ion (PNBI) and negative-ion (NNBI) based concepts are discussed. Next, the physical processes by which the beam transfers energy to the plasma, namely ionisation and slowing-down are described. For both, an elementary theory is given and the comparison with experimental results is made. Applications of NBI to heating, current drive and rotation drive are reviewed. The prospects of NBI for ITER are commented.

  8. Martian Atmospheric and Ionospheric plasma Escape

    NASA Astrophysics Data System (ADS)

    Lundin, Rickard

    2016-04-01

    Solar forcing is responsible for the heating, ionization, photochemistry, and erosion processes in the upper atmosphere throughout the lifetime of the terrestrial planets. Of the four terrestrial planets, the Earth is the only one with a fully developed biosphere, while our kin Venus and Mars have evolved into arid inhabitable planets. As for Mars, there are ample evidences for an early Noachian, water rich period on Mars. The question is, what made Mars evolve so differently compared to the Earth? Various hydrosphere and atmospheric evolution scenarios for Mars have been forwarded based on surface morphology, chemical composition, simulations, semi-empiric (in-situ data) models, and the long-term evolution of the Sun. Progress has been made, but the case is still open regarding the changes that led to the present arid surface and tenuous atmosphere at Mars. This presentation addresses the long-term variability of the Sun, the solar forcing impact on the Martian atmosphere, and its interaction with the space environment - an electromagnetic wave and particle interaction with the upper atmosphere that has implications for its photochemistry, composition, and energization that governs thermal and non-thermal escape. Non-thermal escape implies an electromagnetic upward energization of planetary ions and molecules to velocities above escape velocity, a process governed by a combination of solar EUV radiation (ionization), and energy and momentum transfer by the solar wind. The ion escape issue dates back to the early Soviet and US-missions to Mars, but the first more accurate estimates of escape rates came with the Phobos-2 mission in 1989. Better-quality ion composition measurement results of atmospheric/ionospheric ion escape from Mars, obtained from ESA Mars Express (MEX) instruments, have improved our understanding of the ion escape mechanism. With the NASA MAVEN spacecraft orbiting Mars since Sept. 2014, dual in-situ measurement with plasma instruments are now

  9. Extinction Correction Significantly Influences the Estimate of the Lyα Escape Fraction

    NASA Astrophysics Data System (ADS)

    An, Fang Xia; Zheng, Xian Zhong; Hao, Cai-Na; Huang, Jia-Sheng; Xia, Xiao-Yang

    2017-02-01

    The Lyα escape fraction is a key measure to constrain the neutral state of the intergalactic medium and then to understand how the universe was fully reionized. We combine deep narrowband imaging data from the custom-made filter NB393 and the {{{H}}}2S1 filter centered at 2.14 μm to examine the Lyα emitters and Hα emitters at the same redshift z = 2.24. The combination of these two populations allows us to determine the Lyα escape fraction at z = 2.24. Over an area of 383 arcmin2 in the Extended Chandra Deep Field South (ECDFS), 124 Lyα emitters are detected down to NB393 = 26.4 mag at the 5σ level, and 56 Hα emitters come from An et al. Of these, four have both Lyα and Hα emissions (LAHAEs). We also collect the Lyα emitters and Hα emitters at z = 2.24 in the COSMOS field from the literature, and increase the number of LAHAEs to 15 in total. About one-third of them are AGNs. We measure the individual/volumetric Lyα escape fraction by comparing the observed Lyα luminosity/luminosity density to the extinction-corrected Hα luminosity/luminosity density. We revisit the extinction correction for Hα emitters using the Galactic extinction law with color excess for nebular emission. We also adopt the Calzetti extinction law together with an identical color excess for stellar and nebular regions to explore how the uncertainties in extinction correction affect the estimate of individual and global Lyα escape fractions. In both cases, an anti-correlation between the Lyα escape fraction and dust attenuation is found among the LAHAEs, suggesting that dust absorption is responsible for the suppression of the escaping Lyα photons. However, the estimated Lyα escape fraction of individual LAHAEs varies by up to ˜3 percentage points between the two methods of extinction correction. We find the global Lyα escape fraction at z = 2.24 to be (3.7 ± 1.4)% in the ECDFS. The variation in the color excess of the extinction causes a discrepancy of ˜1 percentage point

  10. Constraining the Metallicity and Escape Fraction of Two z≈3.1 Lyman-Alpha Emitting Galaxies

    NASA Astrophysics Data System (ADS)

    Richardson, Mark L. A.; McLinden, E. M.; Malhotra, S.; Rhoads, J. E.; Levesque, E. M.

    2012-05-01

    We observed two z≈3.1 Lyman-α emitting galaxies (LAE) using the Near-infrared Integral Field Spectrometer (NIFS) at Gemini North, specifically looking for [OIII] 4960 & 5008Å, [OII] 3727Å, and H-β 4863Å. We detected the [OIII] doublet in both objects, determined upper limits for [OII] for both objects, and determined upper limits for H-β for one object. With the detections and upper limits we use the [OIII]/[OII] and R23 line diagnostic to attempt to constrain the metallicity and escape fraction of Ly-α. These metallicity constraints are needed to explore the behaviour of the Mass-Metallicty relation in the low-mass regime and also give insight into the star formation histories of LAE which are known to host young stellar populations. The escape fraction, when combined with an extinction correction, gives insight into the presence of neutral gas. This neutral gas is responsible for resonantly scattering any escaped Ly-α photons, increasing its optical depth to dust. For one object we constrain the metallicity to be Z≤ 0.4Z⊙ and constrain the escape fraction of Ly-α to be Fesc ≤ 30%. For the second object we are only able to constrain its escape fraction, finding 6% ≤ Fesc ≤ 40%. We would like to thank the Natural Sciences and Engineering Research Council of Canada for their financial support through a post-graduate fellowship.

  11. Upper limits on carbon group ions near the orbit of Titan: Implications for methane escape from Titan

    NASA Astrophysics Data System (ADS)

    Crary, Frank; Smith, H. Todd; Reisenfeld, Daniel; Young, Dave

    High neutral methane escape rates from Titan (˜3x109 cm-2 s-1 ) have been inferred from Cassini Ion and Neutral Mass Spectrometer observations [Yelle et al., 2008]. This is much higher than past predictions (e.g. due to Jeans loss). To investigate this hypothesis, we have examined Cassini Cassini Plasma Spectrometer (CAPS) data obtained near Titan's orbit. We have used the CAPS linear electric field (LEF) mass spectra, which provide high resolution measurements of atomic ions and the atomic constituents of molecular ions. The expected lifetime of neutral methane is sufficiently long that escaping molecules would not ionize in Titan's immediate vicinity. However, ionospheric methane ions are observed in Titan's atmosphere. To distinguish between these two possible sources of methane ions, we have examined spectra obtained within five Saturn radii of Titan's orbit, but at distances of over one Saturn radius from Titan itself. Between March 2005 and Dec. 2009, 5466 LEF spectra were obtained in this region. These data show a clear oxygen peak, either from atomic O+ or from fragmentation of oxygen-bearing molecular ions. A weaker nitrogen peak, with 5.9% the amplitude of the oxygen peak, is also present. At the instrument's noise level, no carbon peak is present. This non-detection corresponds to an abundance of carbon ions and carbon-bearing molecular ions under 0.28% that of oxygen and oxygen-bearing ions. Estimates of the neutral and ion loss rates, and ion production rates, allow us to convert this upper limit into an upper limit on the escape rate of neutral methane from Titan. Unless there is some currently unknown and efficient loss process for neutral methane (i.e. other than ionization), this upper limit is several orders of magnitude lower than the escape rate determined by Yelle et al., 2008.

  12. On the escape of CH4 from Pluto's atmosphere

    NASA Astrophysics Data System (ADS)

    Koskinen, T. T.; Erwin, J. T.; Yelle, R. V.

    2015-09-01

    We adapted a multispecies escape model, developed for close-in extrasolar planets, to calculate the escape rates of CH4 and N2 from Pluto. In the absence of escape, CH4 should overtake N2 as the dominant species below the exobase. The CH4 profile depends strongly on the escape rate, however, and the typical escape rates predicted for Pluto lead to a nearly constant mixing ratio of less than 1% below the exobase. In this case the CH4 escape rate is only 5-10% of the N2 escape rate. Observations of the CH4 profile by the New Horizons/ALICE spectrograph can constrain the CH4 escape rate and provide a unique test for escape models.

  13. THE EFFECT OF GALACTIC PROPERTIES ON THE ESCAPE FRACTION OF IONIZING PHOTONS

    SciTech Connect

    Fernandez, Elizabeth R.; Shull, J. Michael E-mail: michael.shull@colorado.edu

    2011-04-10

    The escape fraction, f{sub esc}, of ionizing photons from early galaxies is a crucial parameter for determining whether the observed galaxies at z {>=} 6 are able to reionize the high-redshift intergalactic medium. Previous attempts to measure f{sub esc} have found a wide range of values, varying from less than 0.01 to nearly 1. Rather than finding a single value of f{sub esc}, we clarify through modeling how internal properties of galaxies affect f{sub esc} through the density and distribution of neutral hydrogen within the galaxy, along with the rate of ionizing photons' production. We find that the escape fraction depends sensitively on the covering factor of clumps, along with the density of the clumped and interclump medium. One must therefore be cautious when dealing with an inhomogeneous medium. Fewer high-density clumps lead to a greater escape fraction than more numerous low-density clumps. When more ionizing photons are produced in a starburst, f{sub esc} increases, as photons escape more readily from the gas layers. Large variations in the predicted escape fraction, caused by differences in the hydrogen distribution, may explain the large observed differences in f{sub esc} among galaxies. Values of f{sub esc} must also be consistent with the reionization history. High-mass galaxies alone are unable to reionize the universe, because f{sub esc} >1 would be required. Small galaxies are needed to achieve reionization, with greater mean escape fraction in the past.

  14. Analysis of Wave and Particle Signatures Observed in Plasma Escape at Venus

    NASA Technical Reports Server (NTRS)

    Hartle, R. E.; Grebowsky, J. M.; Intriligator, D. S.; Crider, D. H.

    2003-01-01

    Atmospheric gases escape from Venus as neutral and ionized atoms and molecules. Ion escape, considered here, occurs through ion pickup or collective plasma processes. The latter can arise from upward flow of nightside ionospheric plasma into the ionotail, day to night ionospheric flow into the ionotail, and scavenging of ionospheric plasma by ionosphere-magnetosheath instabilities at the ionopause. These plasma processes produce differing signatures in ion velocity and energy distributions and in ULF waves in the magnetic field. Using plasma ion spectra measured by the Pioneer Venus Orbiter (PVO) Orbiter Plasma Analyzer (OPA) and magnetic field fluctuations observed by the PVO Orbiter Magnetometer (OMAG) along with the expected particle and field signatures, various ion escape processes occurring along Pioneer Venus orbits are identified. In particular, OPA ion energy distributions are used in parallel with magnetic field power spectra and wave phase angles derived from OMAG measurements to study the characteristics of escaping ions. The principle ions observed escaping the influence of Venus are H+, He+ and 0'. In the ion energy distributions of the OPA, pickup ions appear hot relative to the much cooler ions flowing away from Venus in the ionotail and in the plasma clouds detached from the ionopause. This energy contrast is particularly evident downstream when PVO crosses the ionotail boundary from the hot solar wind plasma to the much cooler plasma within the tail. Magnetic field signatures accompanying the escaping ions appear as peaks in the power spectra at the corresponding ion cyclotron frequencies. Also, coherent wave trains at the same frequencies are observed in the phase angle plots of magnetic field fluctuations about the mean field.

  15. Developing the E-Scape Software System

    ERIC Educational Resources Information Center

    Derrick, Karim

    2012-01-01

    Most innovations have contextual pre-cursors that prompt new ways of thinking and in their turn help to give form to the new reality. This was the case with the e-scape software development process. The origins of the system existed in software components and ideas that we had developed through previous projects, but the ultimate direction we took…

  16. Animal escapology II: escape trajectory case studies

    PubMed Central

    Domenici, Paolo; Blagburn, Jonathan M.; Bacon, Jonathan P.

    2011-01-01

    Summary Escape trajectories (ETs; measured as the angle relative to the direction of the threat) have been studied in many taxa using a variety of methodologies and definitions. Here, we provide a review of methodological issues followed by a survey of ET studies across animal taxa, including insects, crustaceans, molluscs, lizards, fish, amphibians, birds and mammals. Variability in ETs is examined in terms of ecological significance and morpho-physiological constraints. The survey shows that certain escape strategies (single ETs and highly variable ETs within a limited angular sector) are found in most taxa reviewed here, suggesting that at least some of these ET distributions are the result of convergent evolution. High variability in ETs is found to be associated with multiple preferred trajectories in species from all taxa, and is suggested to provide unpredictability in the escape response. Random ETs are relatively rare and may be related to constraints in the manoeuvrability of the prey. Similarly, reports of the effect of refuges in the immediate environment are relatively uncommon, and mainly confined to lizards and mammals. This may be related to the fact that work on ETs carried out in laboratory settings has rarely provided shelters. Although there are a relatively large number of examples in the literature that suggest trends in the distribution of ETs, our understanding of animal escape strategies would benefit from a standardization of the analytical approach in the study of ETs, using circular statistics and related tests, in addition to the generation of large data sets. PMID:21753040

  17. Developing the E-Scape Software System

    ERIC Educational Resources Information Center

    Derrick, Karim

    2012-01-01

    Most innovations have contextual pre-cursors that prompt new ways of thinking and in their turn help to give form to the new reality. This was the case with the e-scape software development process. The origins of the system existed in software components and ideas that we had developed through previous projects, but the ultimate direction we took…

  18. Centrifugally Stimulated Exospheric Ion Escape at Mercury

    NASA Technical Reports Server (NTRS)

    Delcourt, Dominique; Seki, K.; Terada, N.; Moore, Thomas E.

    2012-01-01

    We investigate the transport of ions in the low-altitude magnetosphere magnetosphere of Mercury. We show that, because of small spatial scales, the centrifugal effect due to curvature of the E B drift paths can lead to significant particle energization in the parallel direction. We demonstrate that because of this effect, ions with initial speed smaller than the escape speed such as those produced via thermal desorption can overcome gravity and escape into the magnetosphere. The escape route of this low-energy exosphere originating material is largely controlled by the magnetospheric convection rate. This escape route spreads over a narrower range of altitudes when the convection rate increases. Bulk transport of low-energy planetary material thus occurs within a limited region of space once moderate magnetospheric convection is established. These results suggest that, via release of material otherwise gravitationally trapped, the E B related centrifugal acceleration is an important mechanism for the net supply of plasma to the magnetosphere of Mercury.

  19. Unconventional Interrogation Yields HIV's Escape Plan.

    PubMed

    Kepler, Thomas B

    2017-06-14

    Chasing HIV-1 across the genotype landscape, unequipped to anticipate its maneuvers, the antibody variable-region genes pursue the virus in futility. In this issue of Cell Host & Microbe, Dingens et al. (2017) exhibit a powerful technology that reveals the escape pathways of HIV-1 and may enable its capture. Copyright © 2017 Elsevier Inc. All rights reserved.

  20. Escape from Albuquerque: An Apache Memorate.

    ERIC Educational Resources Information Center

    Greenfeld, Philip J.

    2001-01-01

    Clarence Hawkins, a White Mountain Apache, escaped from the Albuquerque Indian School around 1920. His 300-mile trip home, made with two other boys, exemplifies the reaction of many Indian youths to the American government's plans for cultural assimilation. The tale is told in the form of traditional Apache narrative. (TD)

  1. Nociception and escape behavior in planarians

    NASA Astrophysics Data System (ADS)

    Schoetz Collins, Eva-Maria

    2015-03-01

    Planarians are famous and widely studied for their regenerative capabilities. When a moving planarian is cut through the middle, the resulting head and tail pieces instantaneously retract and exhibit a characteristic escape response that differs from normal locomotion. In asexual animals, a similar reaction is observed when the planarian undergoes fission, suggesting that reproduction through self-tearing is a rather traumatic event for the animal. Using a multiscale approach, we unravel the dynamics, mechanics, and functional aspects of the planarian escape response. This musculature-driven gait was found to be a dominating response that supersedes the urge to feed or reproduce and quantitatively differs from other modes of planarian locomotion (gliding, peristalsis). We show that this escape gait constitutes the animal's pain response mediated by TRP like receptors and the neurotransmitter histamine, and that it can be induced through adverse thermal, mechanical, electrical or chemical stimuli. Ultimately, we will examine the neuronal subpopulations involved in mediating escape reflexes in planarians and how they are functionally restored during regeneration, thereby gaining mechanistic insight into the neuronal circuits required for specific behaviors. Supported by BWF CASI and Sloan Foundation.

  2. Learning from escaped prescribed fire reviews

    Treesearch

    Anne E. Black; Dave Thomas; James Saveland; Jennifer D. Ziegler

    2011-01-01

    The U.S. wildland fire community has developed a number of innovative methods for conducting a review following escape of a prescribed fire (expanding on the typical regional or local reviews, to include more of a learning focus - expanded After Action Reviews, reviews that incorporate High Reliability Organizing, Facilitated Learning Analyses, etc). The stated purpose...

  3. Life events and escape in conversion disorder.

    PubMed

    Nicholson, T R; Aybek, S; Craig, T; Harris, T; Wojcik, W; David, A S; Kanaan, R A

    2016-09-01

    Psychological models of conversion disorder (CD) traditionally assume that psychosocial stressors are identifiable around symptom onset. In the face of limited supportive evidence such models are being challenged. Forty-three motor CD patients, 28 depression patients and 28 healthy controls were assessed using the Life Events and Difficulties Schedule in the year before symptom onset. A novel 'escape' rating for events was developed to test the Freudian theory that physical symptoms of CD could provide escape from stressors, a form of 'secondary gain'. CD patients had significantly more severe life events and 'escape' events than controls. In the month before symptom onset at least one severe event was identified in 56% of CD patients - significantly more than 21% of depression patients [odds ratio (OR) 4.63, 95% confidence interval (CI) 1.56-13.70] and healthy controls (OR 5.81, 95% CI 1.86-18.2). In the same time period 53% of CD patients had at least one 'high escape' event - again significantly higher than 14% in depression patients (OR 6.90, 95% CI 2.05-23.6) and 0% in healthy controls. Previous sexual abuse was more commonly reported in CD than controls, and in one third of female patients was contextually relevant to life events at symptom onset. The majority (88%) of life events of potential aetiological relevance were not identified by routine clinical assessments. Nine per cent of CD patients had no identifiable severe life events. Evidence was found supporting the psychological model of CD, the Freudian notion of escape and the potential aetiological relevance of childhood traumas in some patients. Uncovering stressors of potential aetiological relevance requires thorough psychosocial evaluation.

  4. Cold Ion Escape from the Martian Ionosphere

    NASA Astrophysics Data System (ADS)

    Fränz, M.; Dubinin, E.; Wei, Y.; Woch, J.; Morgan, D.; Barabash, S.; Fedorov, A.

    2012-09-01

    It has always been challenging to observe the flux of ions with energies of less than 10eV escaping from the planetary ionospheres. We here report on new measurements of the ionospheric ion flows at Mars by the ASPERA-3 experiment on board Mars Express. We first use support from the MARSIS radar experiment for some orbits with fortunate observation geometry. Here we have observed a transterminator flow of O+ and O+ 2 ions with a super-sonic velocity of around 5km/s and fluxes of 0.8 · 109/cm2s. If we assume a symmetric flux around the terminator this corresponds to an ion flow of 3.1 ± 0.5 × 1025/s half of which is expected to escape from Mars (Fraenz et al, 2010). This escape flux is significantly higher than previously observed on the tailside of Mars, we discuss possible reasons for the difference. Since 2008 the MARSIS radar does nightside local plasma density measurement which often coincide with ASPERA-3 measurements. In a new analysis of the combined nightside datasets (Fig. 1) we show that the main escape channel is along the shadow boundary on the tailside of Mars. At a distance of about 0.5 R_M the flux settles at a constant value (Fig. 2) which indicates that about half of the transterminator ionospheric flow escapes from the planet. Possible mechanism to generate this flux can be the ionospheric pressure gradient between dayside and nightside or momentum transfer from the solar wind via the induced magnetic field since the flow velocity is in the Alfvénic regime.

  5. Cold Ion Escape from the Martian Ionosphere

    NASA Astrophysics Data System (ADS)

    Fränz, Markus; Dubinin, Eduard; Wei, Yong; Morgan, David; Barabash, Stas; Lundin, Rickard; Fedorov, Andrei

    2013-04-01

    It has always been challenging to observe the flux of ions with energies of less than 10eV escaping from the planetary ionospheres. We here report on new measurements of the ionospheric ion flows at Mars by the ASPERA-3 experiment on board Mars Express. We first use support from the MARSIS radar experiment for some orbits with fortunate observation geometry. Here we have observed a transterminator flow of O+ and O2+ ions with a super-sonic velocity of around 5km/s and fluxes of 0.8 ? 109/cm2s. If we assume a symmetric flux around the terminator this corresponds to an ion flow of 3.1 ± 0.5 × 1025-s half of which is expected to escape from Mars (Fraenz et al, Plan.Space Sci., 2010). This escape flux is significantly higher than previously observed on the tailside of Mars, we discuss possible reasons for the difference. Since 2008 the MARSIS radar does nightside local plasma density measurements which often coincide with ASPERA-3 measurements. In a new analysis of the combined nightside datasets we show that the main escape channel is along the shadow boundary on the tailside of Mars. At a distance of half a Martian radius the flux settles at a constant value which indicates that about half of the transterminator ionospheric flow escapes from the planet. Possible mechanism to generate this flux can be the ionospheric pressure gradient between dayside and nightside or momentum transfer from the solar wind via the induced magnetic field since the flow velocity is in the Alfvénic regime.

  6. Escape driven by α -stable white noises

    NASA Astrophysics Data System (ADS)

    Dybiec, B.; Gudowska-Nowak, E.; Hänggi, P.

    2007-02-01

    We explore the archetype problem of an escape dynamics occurring in a symmetric double well potential when the Brownian particle is driven by white Lévy noise in a dynamical regime where inertial effects can safely be neglected. The behavior of escaping trajectories from one well to another is investigated by pointing to the special character that underpins the noise-induced discontinuity which is caused by the generalized Brownian paths that jump beyond the barrier location without actually hitting it. This fact implies that the boundary conditions for the mean first passage time (MFPT) are no longer determined by the well-known local boundary conditions that characterize the case with normal diffusion. By numerically implementing properly the set up boundary conditions, we investigate the survival probability and the average escape time as a function of the corresponding Lévy white noise parameters. Depending on the value of the skewness β of the Lévy noise, the escape can either become enhanced or suppressed: a negative asymmetry parameter β typically yields a decrease for the escape rate while the rate itself depicts a non-monotonic behavior as a function of the stability index α that characterizes the jump length distribution of Lévy noise, exhibiting a marked discontinuity at α=1 . We find that the typical factor of 2 that characterizes for normal diffusion the ratio between the MFPT for well-bottom-to-well-bottom and well-bottom-to-barrier-top no longer holds true. For sufficiently high barriers the survival probabilities assume an exponential behavior versus time. Distinct non-exponential deviations occur, however, for low barrier heights.

  7. Biphasic CD8+ T-Cell Defense in Simian Immunodeficiency Virus Control by Acute-Phase Passive Neutralizing Antibody Immunization

    PubMed Central

    Iseda, Sumire; Takahashi, Naofumi; Poplimont, Hugo; Nomura, Takushi; Seki, Sayuri; Nakane, Taku; Nakamura, Midori; Shi, Shoi; Ishii, Hiroshi; Furukawa, Shota; Harada, Shigeyoshi; Naruse, Taeko K.; Kimura, Akinori; Matano, Tetsuro

    2016-01-01

    ABSTRACT Identifying human immunodeficiency virus type 1 (HIV-1) control mechanisms by neutralizing antibodies (NAbs) is critical for anti-HIV-1 strategies. Recent in vivo studies on animals infected with simian immunodeficiency virus (SIV) and related viruses have shown the efficacy of postinfection NAb passive immunization for viremia reduction, and one suggested mechanism is its occurrence through modulation of cellular immune responses. Here, we describe SIV control in macaques showing biphasic CD8+ cytotoxic T lymphocyte (CTL) responses following acute-phase NAb passive immunization. Analysis of four SIVmac239-infected rhesus macaque pairs matched with major histocompatibility complex class I haplotypes found that counterparts receiving day 7 anti-SIV polyclonal NAb infusion all suppressed viremia for up to 2 years without accumulating viral CTL escape mutations. In the first phase of primary viremia control attainment, CD8+ cells had high capacities to suppress SIVs carrying CTL escape mutations. Conversely, in the second, sustained phase of SIV control, CTL responses converged on a pattern of immunodominant CTL preservation. During this sustained phase of viral control, SIV epitope-specific CTLs showed retention of phosphorylated extracellular signal-related kinase (ERK)hi/phosphorylated AMP-activated protein kinase (AMPK)lo subpopulations, implying their correlation with SIV control. The results suggest that virus-specific CTLs functionally boosted by acute-phase NAbs may drive robust AIDS virus control. IMPORTANCE In early HIV infection, NAb responses are lacking and CTL responses are insufficient, which leads to viral persistence. Hence, it is important to identify immune responses that can successfully control such HIV replication. Here, we show that monkeys receiving NAb passive immunization in early SIV infection strictly control viral replication for years. Passive infusion of NAbs with CTL cross-priming capacity resulted in induction of functionally

  8. Escape from viscosity: the kinematics and hydrodynamics of copepod foraging and escape swimming.

    PubMed

    van Duren, Luca A; Videler, John J

    2003-01-01

    Feeding and escape swimming in adult females of the calanoid copepod Temora longicornis Müller were investigated and compared. Swimming velocities were calculated using a 3-D filming setup. Foraging velocities ranged between 2 and 6 mm s(-1), while maximum velocities of up to 80 mm s(-1) were reached during escape responses. Foraging took place at Reynolds numbers between 2 and 6, indicating that viscous forces are considerable during this swimming mode. Inertial forces are much more important during escape responses, when Reynolds numbers of more than 100 are reached. High-speed film recordings at 500 frames s(-1) of the motion pattern of the feeding appendages and the escape movement of the swimming legs revealed that the two swimming modes are essentially very different. While foraging, the first three mouth appendages (antennae, mandibular palps and maxillules) create a backwards motion of water with a metachronal beating pattern. During escape movements the mouth appendages stop moving and the swimming legs beat in a very fast metachronal rhythm, accelerating a jet of water backwards. The large antennules are folded backwards, resulting in a streamlined body shape. Particle image velocimetry analysis of the flow around foraging and escaping copepods revealed that during foraging an asymmetrical vortex system is created on the ventral side of the animal. The feeding motion is steady over a long period of time. The rate of energy dissipation due to viscous friction relates directly to the energetic cost of the feeding current. During escape responses a vortex ring appears behind the animal, which dissipates over time. Several seconds after cessation of swimming leg movements, energy dissipation can still be measured. During escape responses the rate of energy dissipation due to viscous friction increases by up to two orders of magnitude compared to the rate when foraging.

  9. Two Regimes of Interaction of a Hot Jupiter’s Escaping Atmosphere with the Stellar Wind and Generation of Energized Atomic Hydrogen Corona

    NASA Astrophysics Data System (ADS)

    Shaikhislamov, I. F.; Khodachenko, M. L.; Lammer, H.; Kislyakova, K. G.; Fossati, L.; Johnstone, C. P.; Prokopov, P. A.; Berezutsky, A. G.; Zakharov, Yu. P.; Posukh, V. G.

    2016-12-01

    The interaction of escaping the upper atmosphere of a hydrogen-rich non-magnetized analog of HD 209458b with a stellar wind (SW) of its host G-type star at different orbital distances is simulated with a 2D axisymmetric multi-fluid hydrodynamic (HD) model. A realistic Sun-like spectrum of X-ray and ultraviolet radiation, which ionizes and heats the planetary atmosphere, together with hydrogen photochemistry, as well as stellar-planetary tidal interaction are taken into account to generate self-consistently an atmospheric HD outflow. Two different regimes of the planetary and SW interaction have been modeled. These are: (1) the “captured by the star” regime, when the tidal force and pressure gradient drive the planetary material beyond the Roche lobe toward the star, and (2) the “blown by the wind” regime, when sufficiently strong SW confines the escaping planetary atmosphere and channels it into the tail. The model simulates in detail the HD interaction between the planetary atoms, protons and the SW, as well as the production of energetic neutral atoms (ENAs) around the planet due to charge exchange between planetary atoms and stellar protons. The revealed location and shape of the ENA cloud, either as a paraboloid shell between the ionopause and bowshock (for the “blown by the wind” regime), or a turbulent layer at the contact boundary between the planetary stream and SW (for the “captured by the star” regime) are of importance for the interpretation of Lyα absorption features in exoplanetary transit spectra and characterization of the plasma environments.

  10. Escape of asteroids from the main belt

    NASA Astrophysics Data System (ADS)

    Granvik, Mikael; Morbidelli, Alessandro; Vokrouhlický, David; Bottke, William F.; Nesvorný, David; Jedicke, Robert

    2017-02-01

    Aims: We locate escape routes from the main asteroid belt, particularly into the near-Earth-object (NEO) region, and estimate the relative fluxes for different escape routes as a function of object size under the influence of the Yarkovsky semimajor-axis drift. Methods: We integrated the orbits of 78 355 known and 14 094 cloned main-belt objects and Cybele and Hilda asteroids (hereafter collectively called MBOs) for 100 Myr and recorded the characteristics of the escaping objects. The selected sample of MBOs with perihelion distance q > 1.3 au and semimajor axis a < 4.1 au is essentially complete, with an absolute magnitude limit ranging from HV < 15.9 in the inner belt (a < 2.5 au) to HV < 14.4 in the outer belt (2.5 au < a < 4.1 au). We modeled the semimajor-axis drift caused by the Yarkovsky force and assigned four different sizes (diameters of 0.1, 0.3, 1.0, and 3.0 km) and random spin obliquities (either 0 deg or 180 deg) for each test asteroid. Results: We find more than ten obvious escape routes from the asteroid belt to the NEO region, and they typically coincide with low-order mean-motion resonances with Jupiter and secular resonances. The locations of the escape routes are independent of the semimajor-axis drift rate and thus are also independent of the asteroid diameter. The locations of the escape routes are likewise unaffected when we added a model for Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) cycles coupled with secular evolution of the rotation pole as a result of the solar gravitational torque. A Yarkovsky-only model predicts a flux of asteroids entering the NEO region that is too high compared to the observationally constrained flux, and the discrepancy grows larger for smaller asteroids. A combined Yarkovsky and YORP model predicts a flux of small NEOs that is approximately a factor of 5 too low compared to an observationally constrained estimate. This suggests that the characteristic timescale of the YORP cycle is longer than our canonical

  11. Launch Pad Escape System Design (Human Spaceflight)

    NASA Technical Reports Server (NTRS)

    Maloney, Kelli

    2011-01-01

    A launch pad escape system for human spaceflight is one of those things that everyone hopes they will never need but is critical for every manned space program. Since men were first put into space in the early 1960s, the need for such an Emergency Escape System (EES) has become apparent. The National Aeronautics and Space Administration (NASA) has made use of various types of these EESs over the past 50 years. Early programs, like Mercury and Gemini, did not have an official launch pad escape system. Rather, they relied on a Launch Escape System (LES) of a separate solid rocket motor attached to the manned capsule that could pull the astronauts to safety in the event of an emergency. This could only occur after hatch closure at the launch pad or during the first stage of flight. A version of a LES, now called a Launch Abort System (LAS) is still used today for all manned capsule type launch vehicles. However, this system is very limited in that it can only be used after hatch closure and it is for flight crew only. In addition, the forces necessary for the LES/LAS to get the capsule away from a rocket during the first stage of flight are quite high and can cause injury to the crew. These shortcomings led to the development of a ground based EES for the flight crew and ground support personnel as well. This way, a much less dangerous mode of egress is available for any flight or ground personnel up to a few seconds before launch. The early EESs were fairly simple, gravity-powered systems to use when thing's go bad. And things can go bad very quickly and catastrophically when dealing with a flight vehicle fueled with millions of pounds of hazardous propellant. With this in mind, early EES designers saw such a passive/unpowered system as a must for last minute escapes. This and other design requirements had to be derived for an EES, and this section will take a look at the safety design requirements had to be derived for an EES, and this section will take a look at

  12. 34. VIEW OF SUBMARINE ESCAPE TRAINING TANK PRIOR TO ADDITION ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    34. VIEW OF SUBMARINE ESCAPE TRAINING TANK PRIOR TO ADDITION OF BLISTERS IN 1959, LOOKING SOUTHEAST - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  13. 23. VIEW OF ESCAPE TRAINING TANK, LOOKING NORTHWEST, SHOWING TWOLOCK ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    23. VIEW OF ESCAPE TRAINING TANK, LOOKING NORTHWEST, SHOWING TWO-LOCK RECOMPRESSION CHAMBER IN PASSAGEWAY FROM ELEVATOR TO CUPOLA - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  14. 14. DETAIL VIEW OF ESCAPE TRAINING TANK, SHOWING HOLDDOWN RODS, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    14. DETAIL VIEW OF ESCAPE TRAINING TANK, SHOWING HOLD-DOWN RODS, LOOKING SOUTH - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  15. 15. VIEW OF ESCAPE TRAINING TANK, LOOKING EAST ACROSS MEZZANINE, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    15. VIEW OF ESCAPE TRAINING TANK, LOOKING EAST ACROSS MEZZANINE, SHOWING ENTRANCE TO SUBMARINE SECTION AT 110-FOOT LEVEL - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  16. 21. VIEW OF ESCAPE TRAINING TANK, SHOWING INTERIOR OF CUPOLA ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    21. VIEW OF ESCAPE TRAINING TANK, SHOWING INTERIOR OF CUPOLA AND TOP OF THE TANK, LOOKING NORTHEAST - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  17. 18. VIEW OF ESCAPE TRAINING TANK, SHOWING ENCLOSED PASSAGEWAY FROM ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    18. VIEW OF ESCAPE TRAINING TANK, SHOWING ENCLOSED PASSAGEWAY FROM 50-FOOT LOCK TO ELEVATOR, LOOKING WEST - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  18. 17. VIEW OF ESCAPE TRAINING TANK, SHOWING ENCLOSED PASSAGEWAY FROM ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    17. VIEW OF ESCAPE TRAINING TANK, SHOWING ENCLOSED PASSAGEWAY FROM ELEVATOR TO 18-FOOT LOCK, LOOKING EAST - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  19. 46 CFR 127.240 - Means of escape.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... any interior door giving access to either of the two required means of escape, except that a crash... escape that could cause injury, ensnare clothing, or damage lifejackets. (i) No interior stairway, other...

  20. Phenotypic Mismatches Reveal Escape from Arms-Race Coevolution

    PubMed Central

    Hanifin, Charles T; Brodie, Edmund D; Brodie, Edmund D

    2008-01-01

    Because coevolution takes place across a broad scale of time and space, it is virtually impossible to understand its dynamics and trajectories by studying a single pair of interacting populations at one time. Comparing populations across a range of an interaction, especially for long-lived species, can provide insight into these features of coevolution by sampling across a diverse set of conditions and histories. We used measures of prey traits (tetrodotoxin toxicity in newts) and predator traits (tetrodotoxin resistance of snakes) to assess the degree of phenotypic mismatch across the range of their coevolutionary interaction. Geographic patterns of phenotypic exaggeration were similar in prey and predators, with most phenotypically elevated localities occurring along the central Oregon coast and central California. Contrary to expectations, however, these areas of elevated traits did not coincide with the most intense coevolutionary selection. Measures of functional trait mismatch revealed that over one-third of sampled localities were so mismatched that reciprocal selection could not occur given current trait distributions. Estimates of current locality-specific interaction selection gradients confirmed this interpretation. In every case of mismatch, predators were “ahead” of prey in the arms race; the converse escape of prey was never observed. The emergent pattern suggests a dynamic in which interacting species experience reciprocal selection that drives arms-race escalation of both prey and predator phenotypes at a subset of localities across the interaction. This coadaptation proceeds until the evolution of extreme phenotypes by predators, through genes of large effect, allows snakes to, at least temporarily, escape the arms race. PMID:18336073

  1. POLYMORPHISM REGENERATION FOR A NEUTRALIZED SELFISH B CHROMOSOME.

    PubMed

    Zurita, S; Cabrero, J; López-León, M D; Camacho, J P M

    1998-02-01

    Long-run evolution of B chromosomes is mainly made up by an evolutionary arms race between these selfish genetic elements and the standard genome. The suppression of B drive is one of the clearest expressions of genome defense against B chromosomes. After drive neutralization, the B is condemned to extinction unless a new variant showing drive can emerge and replace it. This paper reports the first empirical evidence for the substitution of a neutralized B variant by a new selfish B variant. Such a polymorphism regeneration has recently taken place in a natural population of the grasshopper Eyprepocnemis plorans. © 1998 The Society for the Study of Evolution.

  2. Escape of atmospheres and loss of water

    NASA Technical Reports Server (NTRS)

    Hunten, D. M.; Donahue, T. M.; Walker, J. C. G.; Kasting, J. F.

    1989-01-01

    The properties and limitations of several loss processes for atmospheric gases are presented and discussed. They include thermal loss (Jeans and hydrodynamic); nonthermal loss (all processes involve charged particles); and impact erosion, including thermal escape from a molten body heated by rapid accretion. Hydrodynamic escape, or 'blowoff', is of particular interest because it offers the prospect of processing large quantities of gas and enriching the remainder in heavy elements and isotopes. In a second part, the water budgets and likely evolutionary histories of Venus, Earth and Mars are assessed. Although it is tempting to associate the great D/H enrichment on Venus with loss of a large initial endowment, a steady state with juvenile water (perhaps from comets) is equally probable.

  3. Escape of atmospheres and loss of water

    NASA Technical Reports Server (NTRS)

    Hunten, D. M.; Donahue, T. M.; Walker, J. C. G.; Kasting, J. F.

    1989-01-01

    The properties and limitations of several loss processes for atmospheric gases are presented and discussed. They include thermal loss (Jeans and hydrodynamic); nonthermal loss (all processes involve charged particles); and impact erosion, including thermal escape from a molten body heated by rapid accretion. Hydrodynamic escape, or 'blowoff', is of particular interest because it offers the prospect of processing large quantities of gas and enriching the remainder in heavy elements and isotopes. In a second part, the water budgets and likely evolutionary histories of Venus, Earth and Mars are assessed. Although it is tempting to associate the great D/H enrichment on Venus with loss of a large initial endowment, a steady state with juvenile water (perhaps from comets) is equally probable.

  4. Fixed-ratio escape reinforcement1

    PubMed Central

    Azrin, N. H.; Holz, W. C.; Hake, D. F.; Ayllon, T.

    1963-01-01

    Escape responses of squirrel monkeys were reinforced according to a fixed-ratio schedule. The reinforcement was a period of safety from a stimulus that signalled the delivery of intermittent pain-shocks. When the frequency of shock was gradually reduced, the performance remained at a high level until the shocks were quite infrequent. Similarly, the duration of the period of safety could be reduced to a few seconds with little loss of behavior. Thus, the responses appeared to be reinforced by even a brief period of safety, the actual degree of shock reduction being fairly slight. The changes in responding during this fixed-ratio escape procedure were comparable to the response changes typically obtained during fixed-ratio food procedures. PMID:13965780

  5. Methane in the lunar exosphere: Implications for solar wind carbon escape

    NASA Astrophysics Data System (ADS)

    Hodges, , R. Richard

    2016-07-01

    A positive identification of methane in the lunar exosphere has been made in data from the neutral mass spectrometer on the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft. Like argon-40, methane is adsorbed on the lunar surface during nighttime. However, higher activation energies for methane delay its desorption at sunrise by about an hour local time, creating a postsunrise bulge with peak concentration of approximately 400-450 molecules cm-3 at a reference altitude of 12 km, which is just above the highest topographic feature on the Moon. The rate of escape of carbon as methane derived from the LADEE data is estimated to be in the range 1.5-4.5 × 1021 s-1. A lower bound for solar carbon escape derived separately from Apollo sample analyses is 3.4 × 1021 s-1.

  6. Autonomous Soft Robotic Fish Capable of Escape Maneuvers Using Fluidic Elastomer Actuators.

    PubMed

    Marchese, Andrew D; Onal, Cagdas D; Rus, Daniela

    2014-03-01

    In this work we describe an autonomous soft-bodied robot that is both self-contained and capable of rapid, continuum-body motion. We detail the design, modeling, fabrication, and control of the soft fish, focusing on enabling the robot to perform rapid escape responses. The robot employs a compliant body with embedded actuators emulating the slender anatomical form of a fish. In addition, the robot has a novel fluidic actuation system that drives body motion and has all the subsystems of a traditional robot onboard: power, actuation, processing, and control. At the core of the fish's soft body is an array of fluidic elastomer actuators. We design the fish to emulate escape responses in addition to forward swimming because such maneuvers require rapid body accelerations and continuum-body motion. These maneuvers showcase the performance capabilities of this self-contained robot. The kinematics and controllability of the robot during simulated escape response maneuvers are analyzed and compared with studies on biological fish. We show that during escape responses, the soft-bodied robot has similar input-output relationships to those observed in biological fish. The major implication of this work is that we show soft robots can be both self-contained and capable of rapid body motion.

  7. Autonomous Soft Robotic Fish Capable of Escape Maneuvers Using Fluidic Elastomer Actuators

    PubMed Central

    Onal, Cagdas D.; Rus, Daniela

    2014-01-01

    Abstract In this work we describe an autonomous soft-bodied robot that is both self-contained and capable of rapid, continuum-body motion. We detail the design, modeling, fabrication, and control of the soft fish, focusing on enabling the robot to perform rapid escape responses. The robot employs a compliant body with embedded actuators emulating the slender anatomical form of a fish. In addition, the robot has a novel fluidic actuation system that drives body motion and has all the subsystems of a traditional robot onboard: power, actuation, processing, and control. At the core of the fish's soft body is an array of fluidic elastomer actuators. We design the fish to emulate escape responses in addition to forward swimming because such maneuvers require rapid body accelerations and continuum-body motion. These maneuvers showcase the performance capabilities of this self-contained robot. The kinematics and controllability of the robot during simulated escape response maneuvers are analyzed and compared with studies on biological fish. We show that during escape responses, the soft-bodied robot has similar input–output relationships to those observed in biological fish. The major implication of this work is that we show soft robots can be both self-contained and capable of rapid body motion. PMID:27625912

  8. Avoidance, escape and microstructural adaptations of the tea green leafhopper to water droplets

    PubMed Central

    Lin, Meizhen; Vasseur, Liette; Yang, Guang; Gurr, Geoff M.; You, Minsheng

    2016-01-01

    Rain and dew droplets can dislodge or drown small insects and may be important factors that drive adaptations for avoidance and escape. Studying the microstructure of small insects and insect behaviour can help understand these adaptations. We quantified avoidance behaviour and entrapment of nymphs and adults of the tea green leafhopper (Empoasca onukii) using simulated rainfall onto host plant foliage and made observations of pretarsi and abdomen microstructures. Adults responded rapidly to simulated rainfall and escaped by jumping whilst most young nymphs were washed from water-sprayed leaves though older nymphs tended to remain on leaves and subsequently escaped from water droplets. Adults had denser covering of water-repelling brochosomes on pretarsi and abdomen surface than nymphs, and were able to stand on water film whilst most nymphs had multiple penetrating tarsi. Removal of brochosomes from the abdomen of adults reduced hydrophobicity, demonstrating the hydrophobic significance of brochosomes in the capacity of leafhopper to escape from water droplets. Nymphs exhibited a higher pull-off force than adults. This research is one of the few studies to focus on the wettability and water avoidance of small insect pests and has implications for pest management. PMID:27845388

  9. Dynamic Escape Routes for Naval Ships

    DTIC Science & Technology

    2005-09-01

    3 o Increase the likelihood of successfully salvaging the ship, and o Increase the likelihood that the crew is rescued safely. It will be possible...spans the period before the event that triggers ship abandonment. Escape routes can be configured based on two factors: 6 o “Crew distribution...crewmembers but the guards are resting in cabins and berthing rooms. This is a plausible scenario at night when the ship is in a non-home port. o

  10. Mars Planetary Ion Escape: Assessing Transitional Trajectories

    NASA Astrophysics Data System (ADS)

    Johnson, B. C.

    2016-12-01

    The availability of in situ observations of ions escaping from Mars' atmosphere is vital to descriptions of atmospheric loss, but such point measurements taken by orbiting spacecraft cannot easily differentiate between spatial changes along the spacecraft trajectory and temporal changes, nor can they directly provide information about atmospheric loss rates during Mars' long history. Numerical models are therefore crucial to crystalizing understanding of ion escape processes. One such category are test particle models that release non-interacting ions into background electric and magnetic fields and then calculate ion trajectories and loss rates. To date, such models have focused on the collisionless regime. Another approach is to include collisions between the particles, the Direct Simulation Monte Carlo (DSMC) approach. We present the results of the first fully three dimensional collisional Mars ion DSMC model capable of peering deep into the collionsional atmosphere, beneath the ionospheric peak, i.e., the ion version of the Adaptive Mesh Particle Simulator (AMPS) configured for Mars. Multiple model runs are performed, each with a different cutoff altitude below which collisions are included. Escape rates of O+ are calculated for each run, providing both the asymptotic escape rate as the cutoff altitude extends into the exosphere and also an idea of the altitude range for which collisions must be included for the results to reasonably converge to this value. In other words, how low can a collisionless model go? Furthermore, these results can be used to interpret satellite data of planetary ions, helping to determine if the spacecraft is in the upflow or outflow regime. In other words, how low can observations be used for measuring the loss of planetary ions to deep space? This entire process is repeated a second time, with the first set of runs corresponding to solar minimum input parameters, and the second set of runs corresponding to solar maximum parameters.

  11. Lithium clearance in mineralocorticoid escape in humans

    SciTech Connect

    Boer, W.H.; Koomans, H.A.; Mees, E.J.D.

    1987-03-01

    Lithium clearance (C/sub Li/) has been advanced as an indicator of Na delivery from the proximal tubules. The authors studied C/sub Li/ in eight healthy males before and after mineralocorticoid escape, a maneuver that may induce suppression of fractional proximal Na reabsorption (FPR/sub Na/). FPR/sub Na/ was also estimated from changes in maximal free water clearance (C/sub H/sub 2/O/). Plasma volume was measured as the /sup 131/I-labeled albumin distribution space. Extracellular fluid volume was estimated as the /sup 82/Br vector distribution volume. According to the latter method, FPR/sub Na/ dropped whereas inulin clearance rose. The changes in C/sub Li/ were surprisingly large. If lithium is a valid marker of Na handling in the proximal tubule in humans, this change would imply a fall in FPR/sub Na/, suggesting a much larger shift in tubular Na reabsorption in escape than hitherto suspected. In addition, it would suggest that the inevitable back diffusion of a part of the solute-free water in the distal nephron, and thus overestimation of FPR/sub Na/ by the C/sub H/sub 2/O/ method, increases importantly during escape. Alternately, lithium may not be a good marker of proximal tubular Na handling. For instance, both lithium reabsorption and escape may take place beyond the proximal tubule, or lithium may be excreted in the distal nephron in certain conditions. Present methods do not permit further analysis of these options in the human model.

  12. 46 CFR 177.500 - Means of escape.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... a means of escape must be such as to allow easy movement of persons when wearing life jackets. There must be no protrusions in means of escape that could cause injury, ensnare clothing, or damage life jackets. (f) The minimum clear opening of a door or passageway used as a means of escape must not be less...

  13. 30 CFR 77.1101 - Escape and evacuation; plan.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... event of a fire. (b) All employees shall be instructed on current escape and evacuation plans, fire alarm signals, and applicable procedures to be followed in case of fire. (c) Plans for escape and... Fire Protection § 77.1101 Escape and evacuation; plan. (a) Before September 30, 1971, each operator of...

  14. 30 CFR 77.1101 - Escape and evacuation; plan.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... event of a fire. (b) All employees shall be instructed on current escape and evacuation plans, fire alarm signals, and applicable procedures to be followed in case of fire. (c) Plans for escape and... Fire Protection § 77.1101 Escape and evacuation; plan. (a) Before September 30, 1971, each operator of...

  15. 30 CFR 77.1101 - Escape and evacuation; plan.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... event of a fire. (b) All employees shall be instructed on current escape and evacuation plans, fire alarm signals, and applicable procedures to be followed in case of fire. (c) Plans for escape and... Fire Protection § 77.1101 Escape and evacuation; plan. (a) Before September 30, 1971, each operator of...

  16. 30 CFR 77.1101 - Escape and evacuation; plan.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... event of a fire. (b) All employees shall be instructed on current escape and evacuation plans, fire alarm signals, and applicable procedures to be followed in case of fire. (c) Plans for escape and... Fire Protection § 77.1101 Escape and evacuation; plan. (a) Before September 30, 1971, each operator of...

  17. 30 CFR 77.1101 - Escape and evacuation; plan.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... event of a fire. (b) All employees shall be instructed on current escape and evacuation plans, fire alarm signals, and applicable procedures to be followed in case of fire. (c) Plans for escape and... Fire Protection § 77.1101 Escape and evacuation; plan. (a) Before September 30, 1971, each operator of...

  18. 30 CFR 75.382 - Mechanical escape facilities.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 30 Mineral Resources 1 2013-07-01 2013-07-01 false Mechanical escape facilities. 75.382 Section 75... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Ventilation § 75.382 Mechanical escape facilities. (a) Mechanical escape facilities shall be provided with overspeed, overwind, and automatic stop...

  19. 30 CFR 75.382 - Mechanical escape facilities.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 30 Mineral Resources 1 2014-07-01 2014-07-01 false Mechanical escape facilities. 75.382 Section 75... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Ventilation § 75.382 Mechanical escape facilities. (a) Mechanical escape facilities shall be provided with overspeed, overwind, and automatic stop...

  20. 30 CFR 75.382 - Mechanical escape facilities.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 30 Mineral Resources 1 2012-07-01 2012-07-01 false Mechanical escape facilities. 75.382 Section 75... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Ventilation § 75.382 Mechanical escape facilities. (a) Mechanical escape facilities shall be provided with overspeed, overwind, and automatic stop...

  1. 30 CFR 75.382 - Mechanical escape facilities.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Mechanical escape facilities. 75.382 Section 75... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Ventilation § 75.382 Mechanical escape facilities. (a) Mechanical escape facilities shall be provided with overspeed, overwind, and automatic...

  2. 46 CFR 108.153 - Location of means of escape.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Location of means of escape. 108.153 Section 108.153 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) A-MOBILE OFFSHORE DRILLING UNITS DESIGN AND EQUIPMENT Construction and Arrangement Means of Escape § 108.153 Location of means of escape....

  3. 46 CFR 108.153 - Location of means of escape.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 4 2011-10-01 2011-10-01 false Location of means of escape. 108.153 Section 108.153 Shipping COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) A-MOBILE OFFSHORE DRILLING UNITS DESIGN AND EQUIPMENT Construction and Arrangement Means of Escape § 108.153 Location of means of escape....

  4. 30 CFR 75.382 - Mechanical escape facilities.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... HEALTH MANDATORY SAFETY STANDARDS-UNDERGROUND COAL MINES Ventilation § 75.382 Mechanical escape facilities. (a) Mechanical escape facilities shall be provided with overspeed, overwind, and automatic stop... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Mechanical escape facilities. 75.382 Section...

  5. Xenon Fractionation and Archean Hydrogen Escape

    NASA Technical Reports Server (NTRS)

    Zahnle, K. J.

    2015-01-01

    Xenon is the heaviest gas found in significant quantities in natural planetary atmospheres. It would seem the least likely to escape. Yet there is more evidence for xenon escape from Earth than for any element other than helium and perhaps neon. The most straightforward evidence is that most of the radiogenic Xe from the decay of (129)I (half-life 15.7 Myr) and (244)Pu (half-life 81 Myr) that is Earth's birthright is missing. The missing xenon is often attributed to the impact erosion of early atmospheres of Earth and its ancestors. It is obvious that if most of the radiogenic xenon were driven off by impacts, most of the rest of the atmophiles fared the same fate. The other line of evidence is in the nonradiogenic isotopes of xenon and its silent partner, krypton. Atmospheric xenon is strongly mass fractionated (at about 4% per amu) compared to any known solar system source (Figure 1). This is in stark contrast to krypton, which may not be fractionated at all: atmospheric Kr is slightly heavier than solar Kr (at about 0.5% per amu), but it is the same as in carbonaceous chondrites. Nonradiogenic xenon is also under abundant relative to krypton (the so-called "missing xenon" problem). Together these observations imply that xenon has been subject to fractionating escape and krypton not.

  6. Scrunching: a novel escape gait in planarians.

    PubMed

    Cochet-Escartin, Olivier; Mickolajczyk, Keith J; Collins, Eva-Maria S

    2015-09-10

    The ability to escape a predator or other life-threatening situations is central to animal survival. Different species have evolved unique strategies under anatomical and environmental constraints. In this study, we describe a novel musculature-driven escape gait in planarians, 'scrunching', which is quantitatively different from other planarian gaits, such as gliding and peristalsis. We show that scrunching is a conserved gait among different flatworm species, underlying its importance as an escape mechanism. We further demonstrate that it can be induced by a variety of physical stimuli, including amputation, high temperature, electric shock and low pH. We discuss the functional basis for scrunching as the preferential gait when gliding is impaired due to a disruption of mucus production. Finally, we show that the key mechanical features of scrunching are adequately captured by a simple biomechanical model that is solely based on experimental data from traction force microscopy and tissue rheology without fit parameters. Together, our results form a complete description of this novel form of planarian locomotion. Because scrunching has distinct dynamics, this gait can serve as a robust behavioral readout for studies of motor neuron and muscular functions in planarians and in particular the restoration of these functions during regeneration.

  7. Scrunching: a novel escape gait in planarians

    NASA Astrophysics Data System (ADS)

    Cochet-Escartin, Olivier; Mickolajczyk, Keith J.; Collins, Eva-Maria S.

    2015-10-01

    The ability to escape a predator or other life-threatening situations is central to animal survival. Different species have evolved unique strategies under anatomical and environmental constraints. In this study, we describe a novel musculature-driven escape gait in planarians, ‘scrunching’, which is quantitatively different from other planarian gaits, such as gliding and peristalsis. We show that scrunching is a conserved gait among different flatworm species, underlying its importance as an escape mechanism. We further demonstrate that it can be induced by a variety of physical stimuli, including amputation, high temperature, electric shock and low pH. We discuss the functional basis for scrunching as the preferential gait when gliding is impaired due to a disruption of mucus production. Finally, we show that the key mechanical features of scrunching are adequately captured by a simple biomechanical model that is solely based on experimental data from traction force microscopy and tissue rheology without fit parameters. Together, our results form a complete description of this novel form of planarian locomotion. Because scrunching has distinct dynamics, this gait can serve as a robust behavioral readout for studies of motor neuron and muscular functions in planarians and in particular the restoration of these functions during regeneration.

  8. Escape behavior and escape circuit activation in juvenile crayfish during prey-predator interactions.

    PubMed

    Herberholz, Jens; Sen, Marjorie M; Edwards, Donald H

    2004-05-01

    The neural systems that control escape behavior have been studied intensively in several animals, including mollusks, fish and crayfish. Surprisingly little is known, however, about the activation and the utilization of escape circuits during prey-predator interactions. To complement the physiological and anatomical studies with a necessary behavioral equivalent, we investigated encounters between juvenile crayfish and large dragonfly nymphs in freely behaving animals using a combination of high-speed video-recordings and measurements of electric field potentials. During attacks, dragonfly nymphs rapidly extended their labium, equipped with short, sharp palps, to capture small crayfish. Crayfish responded to the tactile stimulus by activating neural escape circuits to generate tail-flips directed away from the predator. Tail-flips were the sole defense mechanism in response to an attack and every single strike was answered by tail-flip escape behavior. Crayfish used all three known types of escape tail-flips during the interactions with the dragonfly nymphs. Tail-flips generated by activity in the giant neurons were predominantly observed to trigger the initial escape responses to an attack, but non-giant mediated tail-flips were often generated to attempt escape after capture. Attacks to the front of the crayfish triggered tail-flips mediated either by the medial giant neuron or by non-giant circuitry, whereas attacks to the rear always elicited tail-flips mediated by the lateral giant neuron. Overall, tail flipping was found to be a successful behavior in preventing predation, and only a small percentage of crayfish were killed and consumed.

  9. Energy distributions of sputtered copper neutrals and ions

    NASA Technical Reports Server (NTRS)

    Lundquist, T. R.

    1978-01-01

    Direct quantitative analysis of surfaces by secondary ion mass spectrometry will depend on an understanding of the yield ratio of ions to neutrals. This ratio as a function of the energy of the sputtered particles has been obtained for a clean polycrystalline copper surface sputtered by 1000-3000 eV Ar(+). The energy distributions of both neutral and ionized copper were measured with a retarding potential analyzer using potential modulation differentiation and signal averaging. The maximum for both distributions is identical and occurs near 2.5 eV. The energy distributions of neutrals is more sharply peaked than that of the ions, presumably as a consequence of more efficient nutralization of slow escaping ions by the mobile electrons of copper. The ion-neutral ratio is compared with results from various ionization models.

  10. Energy distributions of sputtered copper neutrals and ions

    NASA Technical Reports Server (NTRS)

    Lundquist, T. R.

    1978-01-01

    Direct quantitative analysis of surfaces by secondary ion mass spectrometry will depend on an understanding of the yield ratio of ions to neutrals. This ratio as a function of the energy of the sputtered particles has been obtained for a clean polycrystalline copper surface sputtered by 1000-3000 eV Ar(+). The energy distributions of both neutral and ionized copper were measured with a retarding potential analyzer using potential modulation differentiation and signal averaging. The maximum for both distributions is identical and occurs near 2.5 eV. The energy distributions of neutrals is more sharply peaked than that of the ions, presumably as a consequence of more efficient nutralization of slow escaping ions by the mobile electrons of copper. The ion-neutral ratio is compared with results from various ionization models.

  11. Selection and characterization of human respiratory syncytial virus escape mutants resistant to a polyclonal antiserum raised against the F protein.

    PubMed

    Tomé, Lorena; Frabasile, Sandra; Candia, Claudia; Pittini, Alvaro; Farina, Natalia; Melero, José Antonio; Arbiza, Juan

    2012-06-01

    A human respiratory syncytial virus (HRSV) neutralization escape mutant was obtained after 56 serial passages in the presence of a polyclonal antiserum raised against the F protein. Nucleotide sequence analysis of this escape mutant virus revealed two amino acid substitutions: Asn268Ile and Val533Met. When this virus was allowed to grow in the absence of the anti-F polyclonal serum, only the mutation Asn268Ile was stably maintained. Both the double and single escape mutant viruses lost reactivity with mAbs belonging to antigenic site II of the fusion protein of RSV. Mutation Asn268Ile has already been reported in RS viruses that are resistant to mAbs 47F and 11 and palivizumab (PZ). We have thus identified a novel mutation (Val533Met) in the transmembrane domain of the F protein that was selected under immune pressure.

  12. Cold Ion Escape from the Martian Ionosphere

    NASA Astrophysics Data System (ADS)

    Fraenz, M.; Dubinin, E.; Wei, Y.; Woch, J. G.; Morgan, D. D.; Barabash, S. V.; Lundin, R. N.; Fedorov, A.

    2012-12-01

    It has always been challenging to observe the flux of ions with energies of less than 10eV escaping from the planetary ionospheres. We here report on new measurements of the ionospheric ion flows at Mars by the ASPERA-3 experiment on board Mars Express. We first use support from the MARSIS radar experiment for some orbits with fortunate observation geometry. Here we have observed a transterminator flow of O+ and O2+ ions with a super-sonic velocity of around 5km/s and fluxes of 0.8x10^9/cm^2s. If we assume a symmetric flux around the terminator this corresponds to an ion flow of 3.1x10^25/s half of which is expected to escape from Mars (Fraenz et al, 2010). This escape flux is significantly higher than previously observed on the tailside of Mars, we discuss possible reasons for the difference. Since 2008 the MARSIS radar does nightside local plasma density measurement which often coincide with ASPERA-3 measurements. In a new analysis of the combined nightside datasets (Fig. 1) we show that the main escape channel is along the shadow boundary on the tailside of Mars. At a distance of about 0.5 R_M the flux settles at a constant value (Fig. 2) which indicates that about half of the transterminator ionospheric flow escapes from the planet. Possible mechanism to generate this flux can be the ionospheric pressure gradient between dayside and nightside or momentum transfer from the solar wind via the induced magnetic field since the flow velocity is in the Alfvenic regime.; Median oxygen ion flux reconstructed by combining ion velocity observations of the Mars Express ASPERA-3 IMA sensor and local plasma density observations by the MARSIS radar. Each bin value is the median from observations on about 3000 orbits between May 2007 and July 2011. Horizontal axis is MSO X-axis (Sun towards the left), vertical axis is vertical distance from MSO X-axis. ; Ring median flux of cylindrical ring regions of all bins shown in previous figure. The different colors show median fluxes

  13. Hydrodynamical Modeling of Hydrogen Escape from Rocky Planets

    NASA Astrophysics Data System (ADS)

    Barringer, Daniel; Zugger, M.; Kasting, J.

    2013-01-01

    Hydrogen escape affects both the composition of primitive atmospheres of terrestrial planets and the planet’s state of oxidation. On Mars, hydrogen escape played a critical role in how long the planet remained in a warm wet state amenable to life. For both solar and extrasolar planets, hydrogen-rich atmospheres are better candidates for originating life by way of Miller-Urey-type prebiotic synthesis. However, calculating the rate of atmospheric hydrogen escape is difficult, for a number of reasons. First, the escape can be controlled either by diffusion through the homopause or by conditions in the upper atmosphere, whichever is slower. Second, both thermal and non-thermal escape mechanisms are typically important. Third, thermal escape itself can be subdivided into Jeans escape (thin upper atmosphere), and hydrodynamic escape, and hydrodynamic escape can be further subdivided into transonic escape and slower subsonic escape, depending on whether the exobase occurs above or below the sonic point. Additionally, the rate of escape for real terrestrial planet atmospheres, which are not 100% hydrogen, depends upon the concentration of infrared coolants, and upon heating and photochemistry driven largely by extreme ultraviolet (EUV) radiation. We have modified an existing 1-D model of hydrodynamic escape (F. Tian et al., JGR, 2008) to work in the high- hydrogen regime. Calculations are underway to determine hydrogen escape rates as a function of atmospheric H2 mixing ratio and the solar EUV flux. We will compare these rates with the estimated upper limit on the escape rate based on diffusion. Initial results for early Earth and Mars will later be extended to rocky exoplanets.

  14. Plasma heating with multi-MeV neutral atom beams

    SciTech Connect

    Grisham, L.R.; Post, D.E.; Mikkelsen, D.R.; Eubank, H.P.

    1981-10-01

    We explore the utility and feasibility of neutral beams of greater than or equal to 6 AMU formed from negative ions, and also of D/sup 0/ formed from D/sup -/. The negative ions would be accelerated to approx. 1 to 2 MeV/AMU and neutralized, whereupon the neutral atoms would be used to heat and, perhaps, to drive current in magnetically confined plasmas. Such beams appear feasible and offer the promise of significant advantages relative to conventional neutral beams based on positive deuterium ions at approx. 150 keV.

  15. Risks incurred by hydrogen escaping from containers and conduits

    SciTech Connect

    Swain, M.R.; Grilliot, E.S.; Swain, M.N.

    1998-08-01

    This paper is a discussion of a method for hydrogen leak classification. Leaks are classified as; gas escapes into enclosed spaces, gas escapes into partially enclosed spaces (vented), and gas escapes into unenclosed spaces. Each of the three enclosure classifications is further divided into two subclasses; total volume of hydrogen escaped and flow rate of escaping hydrogen. A method to aid in risk assessment determination in partially enclosed spaces is proposed and verified for several enclosure geometries. Examples are discussed for additional enclosure geometries.

  16. Ion-Ion Neutralization.

    DTIC Science & Technology

    1982-05-31

    Accession No. 3. Recipient’s Catalog Number FGL -TR-82 -0202 b- /- 4. Title (and Subtitle) 5. Type of Report & Period Covered ION-ION NEUTRALIZATION Final...few years under the terms of the grant has been the detailed study of binary ion-ion neutralization reactions involving ions of atmospheric...2TT, England. 1. INTRODUCTION Binary positive-ion negative-ion mutual neutralization viz: A+ + B->C + D (1) can be an important loss process for

  17. ALEX neutral beam probe

    SciTech Connect

    Pourrezaei, K.

    1982-01-01

    A neutral beam probe capable of measuring plasma space potential in a fully 3-dimensional magnetic field geometry has been developed. This neutral beam was successfully used to measure an arc target plasma contained within the ALEX baseball magnetic coil. A computer simulation of the experiment was performed to refine the experimental design and to develop a numerical model for scaling the ALEX neutral beam probe to other cases of fully 3-dimensional magnetic field. Based on this scaling a 30 to 50 keV neutral cesium beam probe capable of measuring space potential in the thermal barrier region of TMX Upgrade was designed.

  18. Geometry of escaping dynamics in nonlinear ship motion

    NASA Astrophysics Data System (ADS)

    Naik, Shibabrat; Ross, Shane D.

    2017-06-01

    Escape from a potential well is a paradigm to understand critical events in chemical physics, celestial mechanics, structural mechanics, and ship dynamics, to name but a few. The consequences of escape could be desirable or undesirable depending on the specific problem at hand, however, the general question is how escape occurs and the effects of environmental noise on the escape. In this article, we answer the first question by discovering the phase space structures that lead to escape and the second question by investigating the effects of random forcing on these structures in the context of ship dynamics and capsize. The phase space structures that lead to escape are the tube manifolds associated to the rank-1 saddles in the conservative system. They are also robust in the sense of predicting high probability regions of escape even in the presence of random forcing.

  19. Radiative lifetimes for 29 N2+ and implications for planetary escape and isotope enrichment

    NASA Astrophysics Data System (ADS)

    Guberman, Steven L.

    2017-07-01

    The Viking missions to Mars found that 15N/14N is enhanced by a factor of 1.62 compared to Earth and it was suggested that the cause was dissociative recombination (DR) of N2+. The high kinetic energy imparted to N in DR drives atmospheric escape. More recent models of the Martian ionosphere show that much of the N2+ is vibrationally excited. If DR of vibrationally excited 29N2+ is important, the energetics are such that the isotope enhancement would be greatly reduced. Here I show that at the Mars exobase electron temperature and density, the excited vibrational levels of 29N2+ radiate before they can recombine. The isotope enhancement arising from DR is due entirely to DR of 28N2+ with a small contribution to 14N escape arising from DR of the ground vibrational level of 29N2+.

  20. Escape process in systems characterized by stable noises and position-dependent resting times

    NASA Astrophysics Data System (ADS)

    Srokowski, Tomasz

    2016-06-01

    Stochastic systems characterized by a random driving in a form of the general stable noise are considered. The particle experiences long rests due to the traps the density of which is position dependent and obeys a power-law form attributed to the underlying self-similar structure. Both the one- and two-dimensional cases are analyzed. The random walk description involves a position-dependent waiting time distribution. On the other hand, the stochastic dynamics is formulated in terms of the subordination technique where the random time generator is position dependent. The first passage time problem is addressed by evaluating a first passage time density distribution and an escape rate. The influence of the medium nonhomogeneity on those quantities is demonstrated; moreover, the dependence of the escape rate on the stability index and the memory parameter is evaluated. Results indicate essential differences between the Gaussian case and the case involving Lévy flights.

  1. Global analysis of fungal morphology exposes mechanisms of host cell escape.

    PubMed

    O'Meara, Teresa R; Veri, Amanda O; Ketela, Troy; Jiang, Bo; Roemer, Terry; Cowen, Leah E

    2015-03-31

    Developmental transitions between single-cell yeast and multicellular filaments underpin virulence of diverse fungal pathogens. For the leading human fungal pathogen Candida albicans, filamentation is thought to be required for immune cell escape via induction of an inflammatory programmed cell death. Here we perform a genome-scale analysis of C. albicans morphogenesis and identify 102 negative morphogenetic regulators and 872 positive regulators, highlighting key roles for ergosterol biosynthesis and N-linked glycosylation. We demonstrate that C. albicans filamentation is not required for escape from host immune cells; instead, macrophage pyroptosis is driven by fungal cell-wall remodelling and exposure of glycosylated proteins in response to the macrophage phagosome. The capacity of killed, previously phagocytized cells to drive macrophage lysis is also observed with the distantly related fungal pathogen Cryptococcus neoformans. This study provides a global view of morphogenetic circuitry governing a key virulence trait, and illuminates a new mechanism by which fungi trigger host cell death.

  2. A single amino acid deletion in the matrix protein of porcine reproductive and respiratory syndrome virus confers resistance to a polyclonal swine antibody with broadly neutralizing activity.

    PubMed

    Trible, Benjamin R; Popescu, Luca N; Monday, Nicholas; Calvert, Jay G; Rowland, Raymond R R

    2015-06-01

    Assessment of virus neutralization (VN) activity in 176 pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV) identified one pig with broadly neutralizing activity. A Tyr-10 deletion in the matrix protein provided escape from broad neutralization without affecting homologous neutralizing activity. The role of the Tyr-10 deletion was confirmed through an infectious clone with a Tyr-10 deletion. The results demonstrate differences in the properties and specificities of VN responses elicited during PRRSV infection.

  3. Cold Ion Escape from the Martian Ionosphere

    NASA Astrophysics Data System (ADS)

    Fränz, Markus; Dubinin, Eduard; Andrews, David; Nilsson, Hans; Fedorov, Andrei

    2014-05-01

    It has always been challenging to observe the flux of ions with energies of less than 10eV escaping from the planetary ionospheres. We here report on new measurements of the ionospheric ion flows at Mars by the ASPERA-3 experiment on board Mars Express. The ion sensor IMA of this experiment has in principle a low-energy cut-off at 10eV but in negative spacecraft charging cold ions are lifted into the range of measurement but the field of view is restricted to about 4x360 deg. In a recent paper Nilsson et al. (Earth Planets Space, 64, 135, 2012) tried to use the method of long-time averaged distribution functions to overcome these constraints. In this paper we first use the same method to show that we get results consistent with this when using ASPERA-3 observations only. But then we can show that these results are inconsistent with observations of the local plasma density by the MARSIS radar instrument on board Mars Express. We demonstrate that the method of averaged distribution function can deliver the mean flow speed of the plasma but the low-energy cut-off does usually not allow to reconstruct the density. We then combine measurements of the cold ion flow speed with the plasma density observations of MARSIS to derive the cold ion flux. In an analysis of the combined nightside datasets we show that the main escape channel is along the shadow boundary on the tailside of Mars. At a distance of about 0.5 Martian radii the flux settles at a constant value which indicates that about half of the transterminator ionospheric flow escapes from the planet. Possible mechanism to generate this flux can be the ionospheric pressure gradient between dayside and nightside or momentum transfer from the solar wind via the induced magnetic field since the flow velocity is in the Alfvénic regime.

  4. Heating and acceleration of escaping planetary ions

    NASA Astrophysics Data System (ADS)

    Nilsson, Hans

    2010-05-01

    The magnetic field of the Earth acts like a shield against the solar wind, leading to a magnetopause position many planetary radii away from the planet, in contrast to the situation at non- or weakly magnetized planets such as Mars and Venus. Despite this there is significant ion outflow due to solar wind interaction from the cusp and polar cap regions of the Earth's ionosphere. Effective interaction regions form, in particular in the ionospheric projection of the cusp, where ionospheric plasma flows up along the field-lines in response to magnetospheric energy input. Strong wave-particle interaction at altitudes above the ionosphere further accelerates the particles so that gravity is overcome. For the particles to enter a direct escape path they must be accelerated along open magnetic field lines so that they cross the magnetopause or reach a distance beyond the region of return flow in the tail. This return flow may also be either lost to space or returned to the atmosphere. Throughout this transport chain the heating and acceleration experienced by the particles will have an influence on the final fate of the particles. We will present quantitative estimates of centrifugal acceleration and perpendicular heating along the escape path from the cusp, through the high altitude polar cap/mantle, based on Cluster spacecraft data. We will open up for a discussion on the benefits of a ponderomotive force description of the acceleration affecting the ion circulation and escape. Finally we will compare with the situation at the unmagnetized planets Mars and Venus and discuss to what extent a magnetic field protects an atmosphere from loss through solar wind interaction.

  5. X-chromosome inactivation and escape

    PubMed Central

    DISTECHE, CHRISTINE M.; BERLETCH, JOEL B.

    2016-01-01

    X-chromosome inactivation, which was discovered by Mary Lyon in 1961 results in random silencing of one X chromosome in female mammals. This review is dedicated to Mary Lyon, who passed away last year. She predicted many of the features of X inactivation, for e.g., the existence of an X inactivation center, the role of L1 elements in spreading of silencing and the existence of genes that escape X inactivation. Starting from her published work here we summarize advances in the field. PMID:26690513

  6. Suicide as escape from psychotic panic.

    PubMed

    Goldblatt, Mark J; Ronningstam, Elsa; Schechter, Mark; Herbstman, Benjamin; Maltsberger, John T

    2016-01-01

    Suicides of patients in states of acute persecutory panic may be provoked by a subjective experience of helpless terror threatening imminent annihilation or dismemberment. These patients are literally scared to death and try to run away. They imagine suicide is survivable and desperately attempt to escape from imaginary enemies. These states of terror occur in a wide range of psychotic illnesses and are often associated with command hallucinations and delusions. In this article, the authors consider the subjective experience of persecutory panic and the suicide response as an attempt to flee from danger.

  7. Evolutionary escape from the prisoner's dilemma.

    PubMed

    Worden, Lee; Levin, Simon A

    2007-04-07

    The classic prisoner's dilemma model of game theory is modified by introducing occasional variations on the options available to players. Mutation and selection of game options reliably change the game matrix, gradually, from a prisoner's dilemma game into a byproduct mutualism one, in which cooperation is stable, and "temptation to defect" is replaced by temptation to cooperate. This result suggests that when there are many different potential ways of interacting, exploring those possibilities may make escape from prisoner's dilemmas a common outcome in the world. A consequence is that persistent prisoner's dilemma structures may be less common than one might otherwise expect.

  8. Modeling Fluorescence Escape from Tissue Phantoms

    NASA Astrophysics Data System (ADS)

    Gardner, Craig Morris

    1995-01-01

    This dissertation represents a contribution to the field of quantitative fluorescence spectroscopy of biological tissue. The absorption and scattering properties of a turbid medium affect the propagation of fluorescence to the medium surface. Optical properties also affect the amount of light reaching a detector placed to monitor fluorescence non-invasively. These facts have in part limited fluorescence spectroscopy of turbid media to a qualitative science. To study the general characteristics of turbid medium fluorescence, a Monte Carlo algorithm of fluorescence light propagation was developed. Modifications to the general algorithm were made to study several specific light distribution quantities associated with optical fiber fluorescent measurement devices. The Monte Carlo-based studies were also used to develop simple, accurate expressions describing the one -dimensional distribution of excitation light within a turbid medium and the escape of fluorescence from the medium. The expressions have accuracy comparable to solutions of the radiative transport equation. The two expressions were combined to derive a simple expression relating the fluorescence power escaping a turbid medium due to surface excitation, to the medium intrinsic fluorescence coefficient, as a function of the medium optical properties. Based on this expression and a description of the fluorescence escape power intercepted by a distant detector, a method was developed to recover the intrinsic fluorescence coefficient from surface measurements of fluorescence and optical properties. Experiments with water-based, turbid media verified the recovery method. The method used to recover the intrinsic fluorescence coefficient was modified for use with a clinical measurement geometry, specifically a small diameter optical fiber probe. Modification required a calibration method to estimate two optical property variables from two unique surface measurements of diffuse reflectance made with the optical

  9. Neutral Beam Injection in the Electric Tokamak

    NASA Astrophysics Data System (ADS)

    Gourdain, P.-A.; Carter, T. A.; Gauvreau, J.-L.; Grossman, A.; Lafonteese, D. J.; Pace, D. C.; Schmitz, L. W.; Taylor, R. J.; White, A. E.; Yates, T. F.

    2004-11-01

    The Electric Tokamak (ET) at UCLA (Bt=0.25T, R=5m, a=1m, Te(0)=300eV, tau(0)=1s) is now running long shots (5s). A new development program was started last year to include a neutral beam in the daily operations of the machine. As a result, a 10kV neutral beam injector was built to deal with plasma and measurement issues. The design and parameters of the beam are discussed. The source is based on an RF generated plasma, with a single extraction grid providing an accel-decel configuration. Plasma neutralization efficiency is also presented. Co- or counter injection is now possible using a single beam. The construction of a second beam is planned for simultaneous co- and counter injections for toroidal momentum input control. Plasma toroidal and poloidal rotation, particle diffusion and current drive effects will be presented.

  10. Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: implications for atmospheric escape on evolutionary timescales

    NASA Astrophysics Data System (ADS)

    Slapak, Rikard; Schillings, Audrey; Nilsson, Hans; Yamauchi, Masatoshi; Westerberg, Lars-Göran; Dandouras, Iannis

    2017-06-01

    We have investigated the total O+ escape rate from the dayside open polar region and its dependence on geomagnetic activity, specifically Kp. Two different escape routes of magnetospheric plasma into the solar wind, the plasma mantle, and the high-latitude dayside magnetosheath have been investigated separately. The flux of O+ in the plasma mantle is sufficiently fast to subsequently escape further down the magnetotail passing the neutral point, and it is nearly 3 times larger than that in the dayside magnetosheath. The contribution from the plasma mantle route is estimated as ˜ 3. 9 × 1024exp(0. 45 Kp) [s-1] with a 1 to 2 order of magnitude range for a given geomagnetic activity condition. The extrapolation of this result, including escape via the dayside magnetosheath, indicates an average O+ escape of 3 × 1026 s-1 for the most extreme geomagnetic storms. Assuming that the range is mainly caused by the solar EUV level, which was also larger in the past, the average O+ escape could have reached 1027-28 s-1 a few billion years ago. Integration over time suggests a total oxygen escape from ancient times until the present roughly equal to the atmospheric oxygen content today.

  11. Strong Constraint on Human Genes Escaping X-Inactivation Is Modulated by their Expression Level and Breadth in Both Sexes.

    PubMed

    Slavney, Andrea; Arbiza, Leonardo; Clark, Andrew G; Keinan, Alon

    2016-02-01

    In eutherian mammals, X-linked gene expression is normalized between XX females and XY males through the process of X chromosome inactivation (XCI). XCI results in silencing of transcription from one ChrX homolog per female cell. However, approximately 25% of human ChrX genes escape XCI to some extent and exhibit biallelic expression in females. The evolutionary basis of this phenomenon is not entirely clear, but high sequence conservation of XCI escapers suggests that purifying selection may directly or indirectly drive XCI escape at these loci. One hypothesis is that this signal results from contributions to developmental and physiological sex differences, but presently there is limited evidence supporting this model in humans. Another potential driver of this signal is selection for high and/or broad gene expression in both sexes, which are strong predictors of reduced nucleotide substitution rates in mammalian genes. Here, we compared purifying selection and gene expression patterns of human XCI escapers with those of X-inactivated genes in both sexes. When we accounted for the functional status of each ChrX gene's Y-linked homolog (or "gametolog"), we observed that XCI escapers exhibit greater degrees of purifying selection in the human lineage than X-inactivated genes, as well as higher and broader gene expression than X-inactivated genes across tissues in both sexes. These results highlight a significant role for gene expression in both sexes in driving purifying selection on XCI escapers, and emphasize these genes' potential importance in human disease. © The Author 2015. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

  12. Immunogenetic Mechanisms Driving Norovirus GII.4 Antigenic Variation

    PubMed Central

    Donaldson, Eric F.; Corti, Davide; Swanstrom, Jesica; Debbink, Kari; Lanzavecchia, Antonio; Baric, Ralph S.

    2012-01-01

    Noroviruses are the principal cause of epidemic gastroenteritis worldwide with GII.4 strains accounting for 80% of infections. The major capsid protein of GII.4 strains is evolving rapidly, resulting in new epidemic strains with altered antigenic potentials. To test if antigenic drift may contribute to GII.4 persistence, human memory B cells were immortalized and the resulting human monoclonal antibodies (mAbs) characterized for reactivity to a panel of time-ordered GII.4 virus-like particles (VLPs). Reflecting the complex exposure history of the volunteer, human anti-GII.4 mAbs grouped into three VLP reactivity patterns; ancestral (1987–1997), contemporary (2004–2009), and broad (1987–2009). NVB 114 reacted exclusively to the earliest GII.4 VLPs by EIA and blockade. NVB 97 specifically bound and blocked only contemporary GII.4 VLPs, while NBV 111 and 43.9 exclusively reacted with and blocked variants of the GII.4.2006 Minerva strain. Three mAbs had broad GII.4 reactivity. Two, NVB 37.10 and 61.3, also detected other genogroup II VLPs by EIA but did not block any VLP interactions with carbohydrate ligands. NVB 71.4 cross-neutralized the panel of time-ordered GII.4 VLPs, as measured by VLP-carbohydrate blockade assays. Using mutant VLPs designed to alter predicted antigenic epitopes, two evolving, GII.4-specific, blockade epitopes were mapped. Amino acids 294–298 and 368–372 were required for binding NVB 114, 111 and 43.9 mAbs. Amino acids 393–395 were essential for binding NVB 97, supporting earlier correlations between antibody blockade escape and carbohydrate binding variation. These data inform VLP vaccine design, provide a strategy for expanding the cross-blockade potential of chimeric VLP vaccines, and identify an antibody with broadly neutralizing therapeutic potential for the treatment of human disease. Moreover, these data support the hypothesis that GII.4 norovirus evolution is heavily influenced by antigenic variation of neutralizing epitopes

  13. Investigating the Consequences of Interference between Multiple CD8+ T Cell Escape Mutations in Early HIV Infection

    PubMed Central

    Garcia, Victor; Feldman, Marcus W.; Regoes, Roland R.

    2016-01-01

    During early human immunodeficiency virus (HIV) infection multiple CD8+ T cell responses are elicited almost simultaneously. These responses exert strong selective pressures on different parts of HIV’s genome, and select for mutations that escape recognition and are thus beneficial to the virus. Some studies reveal that the later these escape mutations emerge, the more slowly they go to fixation. This pattern of escape rate decrease(ERD) can arise by distinct mechanisms. In particular, in large populations with high beneficial mutation rates interference among different escape strains –an effect that can emerge in evolution with asexual reproduction and results in delayed fixation times of beneficial mutations compared to sexual reproduction– could significantly impact the escape rates of mutations. In this paper, we investigated how interference between these concurrent escape mutations affects their escape rates in systems with multiple epitopes, and whether it could be a source of the ERD pattern. To address these issues, we developed a multilocus Wright-Fisher model of HIV dynamics with selection, mutation and recombination, serving as a null-model for interference. We also derived an interference-free null model assuming initial neutral evolution before immune response elicitation. We found that interference between several equally selectively advantageous mutations can generate the observed ERD pattern. We also found that the number of loci, as well as recombination rates substantially affect ERD. These effects can be explained by the underexponential decline of escape rates over time. Lastly, we found that the observed ERD pattern in HIV infected individuals is consistent with both independent, interference-free mutations as well as interference effects. Our results confirm that interference effects should be considered when analyzing HIV escape mutations. The challenge in estimating escape rates and mutation-associated selective coefficients posed by

  14. The effects of steady swimming on fish escape performance.

    PubMed

    Anwar, Sanam B; Cathcart, Kelsey; Darakananda, Karin; Gaing, Ashley N; Shin, Seo Yim; Vronay, Xena; Wright, Dania N; Ellerby, David J

    2016-06-01

    Escape maneuvers are essential to the survival and fitness of many animals. Escapes are frequently initiated when an animal is already in motion. This may introduce constraints that alter the escape performance. In fish, escape maneuvers and steady, body caudal fin (BCF) swimming are driven by distinct patterns of curvature of the body axis. Pre-existing muscle activity may therefore delay or diminish a response. To quantify the performance consequences of escaping in flow, escape behavior was examined in bluegill sunfish (Lepomis macrochirus) in both still-water and during steady swimming. Escapes executed during swimming were kinematically less variable than those made in still-water. Swimming escapes also had increased response latencies and lower peak velocities and accelerations than those made in still-water. Performance was also lower for escapes made up rather than down-stream, and a preference for down-stream escapes may be associated with maximizing performance. The constraints imposed by pre-existing motion and flow, therefore, have the potential to shape predator-prey interactions under field conditions by shifting the optimal strategies for both predators and prey.

  15. Synthesizing within-host and population-level selective pressures on viral populations: the impact of adaptive immunity on viral immune escape

    PubMed Central

    Volkov, Igor; Pepin, Kim M.; Lloyd-Smith, James O.; Banavar, Jayanth R.; Grenfell, Bryan T.

    2010-01-01

    The evolution of viruses to escape prevailing host immunity involves selection at multiple integrative scales, from within-host viral and immune kinetics to the host population level. In order to understand how viral immune escape occurs, we develop an analytical framework that links the dynamical nature of immunity and viral variation across these scales. Our epidemiological model incorporates within-host viral evolutionary dynamics for a virus that causes acute infections (e.g. influenza and norovirus) with changes in host immunity in response to genetic changes in the virus population. We use a deterministic description of the within-host replication dynamics of the virus, the pool of susceptible host cells and the host adaptive immune response. We find that viral immune escape is most effective at intermediate values of immune strength. At very low levels of immunity, selection is too weak to drive immune escape in recovered hosts, while very high levels of immunity impose such strong selection that viral subpopulations go extinct before acquiring enough genetic diversity to escape host immunity. This result echoes the predictions of simpler models, but our formulation allows us to dissect the combination of within-host and transmission-level processes that drive immune escape. PMID:20335194

  16. A New Maneuver for Escape Trajectories

    NASA Technical Reports Server (NTRS)

    Adams, Robert B.

    2008-01-01

    This presentation put forth a new maneuver for escape trajectories and specifically sought to find an analytical approximation for medium thrust trajectories. In most low thrust derivations the idea is that escape velocity is best achieved by accelerating along the velocity vector. The reason for this is that change in specific orbital energy is a function of velocity and acceleration. However, Levin (1952) suggested that while this is a locally optimal solution it might not be a globally optimal one. Turning acceleration inward would drop periapse giving a higher velocity later in the trajectory. Acceleration at that point would be dotted against a higher magnitude V giving a greater rate of change of mechanical energy. The author then hypothesized that decelerating from the initial orbit and then accelerating at periapse would not lead to a gain in greater specific orbital energy--however, the hypothesis was incorrect. After considerable derivation it was determined that this new maneuver outperforms a direct burn when the overall DeltaV budget exceeds the initial orbital velocity (the author has termed this the Heinlein maneuver). The author provides a physical explanation for this maneuver and presents optimization analyses.

  17. Escape mechanisms of dust in Io

    NASA Astrophysics Data System (ADS)

    Flandes, A.

    The injection of material into the jovian magnetosphere through Io's volcanic activity makes possible the formation of structures such as the plasma torus and the dust ballerina skirt. Io's high temperature volcanism produces spectacular plumes, but even the tallest plumes, as those of Pelen Patera, will not produce enough energy to defeat the gravitational attraction of Io. The fact is that dust escapes from Io, which implies that a second mechanism is acting on the grains. Grains brought to the top of the highest plumes by the volcanic forces are still under Io's gravitational pull, but need only a minimum charge (~10-1 4 C) so that the Lorentz force due to the Jovian magnetic field equilibrates this attraction. In the volcanic vents, the escape velocity of the ejected material and its own density produces enough collisions to create charges. On top of the highest plumes (~500km) charged grains are exposed to the plasma torus that co-rotates rigidly with Jupiter and, due to the relative velocity among Io and the torus, the grains will be dragged away from Io. As it is well known, these dust grains will also be dragged away from Jupiter.

  18. The escape problem for mortal walkers

    NASA Astrophysics Data System (ADS)

    Grebenkov, D. S.; Rupprecht, J.-F.

    2017-02-01

    We introduce and investigate the escape problem for random walkers that may eventually die, decay, bleach, or lose activity during their diffusion towards an escape or reactive region on the boundary of a confining domain. In the case of a first-order kinetics (i.e., exponentially distributed lifetimes), we study the effect of the associated death rate onto the survival probability, the exit probability, and the mean first passage time. We derive the upper and lower bounds and some approximations for these quantities. We reveal three asymptotic regimes of small, intermediate, and large death rates. General estimates and asymptotics are compared to several explicit solutions for simple domains and to numerical simulations. These results allow one to account for stochastic photobleaching of fluorescent tracers in bio-imaging, degradation of mRNA molecules in genetic translation mechanisms, or high mortality rates of spermatozoa in the fertilization process. Our findings provide a mathematical ground for optimizing storage containers and materials to reduce the risk of leakage of dangerous chemicals or nuclear wastes.

  19. F111 Crew Escape Module pilot parachute

    SciTech Connect

    Tadios, E.L.

    1991-01-01

    A successfully deployment of a parachute system highly depends on the efficiency of the deployment device and/or method. There are several existing methods and devices that may be considered for a deployment system. For the F111 Crew Escape Module (CEM), the recovery parachute system deployment is initiated by the firing of a catapult that ejects the complete system from the CEM. At first motion of the pack, a drogue gun is fired, which deploys the pilot parachute system. The pilot parachute system then deploys the main parachute system, which consists of a cluster of three 49-ft diameter parachutes. The pilot parachute system which extracts the F111 Crew Escape Module recovery parachute system must provide reasonable bag strip velocities throughout the flight envelope (10 psf to 300 psf). The pilot parachute system must, therefore, have sufficient drag area at the lower dynamic pressures and a reduced drag area at the high end of the flight envelope. The final design that was developed was a dual parachute system which consists of a 5-ft diameter guide surface parachute tethered inside a 10-ft diameter flat circular parachute. The high drag area is sustained at the low dynamic pressures by keeping both parachutes intact. The drag area is reduced at the higher extreme by allowing the 10-ft parachute attachment to fail. The discussions to follow describe in detail how the system was developed. 4 refs., 10 figs., 2 tabs.

  20. Effects of escape to alone versus escape to enriched environments on adaptive and aberrant behavior.

    PubMed Central

    Golonka, Z; Wacker, D; Berg, W; Derby, K M; Harding, J; Peck, S

    2000-01-01

    Escape-maintained aberrant behavior may be influenced by two outcomes: (a) a break from the activity and (b) subsequent access to preferred activities. To assess this hypothesis, a treatment was developed that analyzed response allocation across two break options: break alone and break with access to preferred social activities. The break with preferred activities decreased aberrant behavior and increased appropriate behavior. PMID:10885532

  1. Spatial calibration of a tokamak neutral beam diagnostic using in situ neutral beam emission

    SciTech Connect

    Chrystal, C.; Burrell, K. H.; Pace, D. C.; Grierson, B. A.

    2015-10-15

    Neutral beam injection is used in tokamaks to heat, apply torque, drive non-inductive current, and diagnose plasmas. Neutral beam diagnostics need accurate spatial calibrations to benefit from the measurement localization provided by the neutral beam. A new technique has been developed that uses in situ measurements of neutral beam emission to determine the spatial location of the beam and the associated diagnostic views. This technique was developed to improve the charge exchange recombination (CER) diagnostic at the DIII-D tokamak and uses measurements of the Doppler shift and Stark splitting of neutral beam emission made by that diagnostic. These measurements contain information about the geometric relation between the diagnostic views and the neutral beams when they are injecting power. This information is combined with standard spatial calibration measurements to create an integrated spatial calibration that provides a more complete description of the neutral beam-CER system. The integrated spatial calibration results are very similar to the standard calibration results and derived quantities from CER measurements are unchanged within their measurement errors. The methods developed to perform the integrated spatial calibration could be useful for tokamaks with limited physical access.

  2. Spatial calibration of a tokamak neutral beam diagnostic using in situ neutral beam emission

    DOE PAGES

    Chrystal, Colin; Burrell, Keith H.; Grierson, Brian A.; ...

    2015-10-20

    Neutral beam injection is used in tokamaks to heat, apply torque, drive non-inductive current, and diagnose plasmas. Neutral beam diagnostics need accurate spatial calibrations to benefit from the measurement localization provided by the neutral beam. A new technique has been developed that uses in-situ measurements of neutral beam emission to determine the spatial location of the beam and the associated diagnostic views. This technique was developed to improve the charge exchange recombination diagnostic (CER) at the DIII-D tokamak and uses measurements of the Doppler shift and Stark splitting of neutral beam emission made by that diagnostic. These measurements contain informationmore » about the geometric relation between the diagnostic views and the neutral beams when they are injecting power. This information is combined with standard spatial calibration measurements to create an integrated spatial calibration that provides a more complete description of the neutral beam-CER system. The integrated spatial calibration results are very similar to the standard calibration results and derived quantities from CER measurements are unchanged within their measurement errors. Lastly, the methods developed to perform the integrated spatial calibration could be useful for tokamaks with limited physical access.« less

  3. Spatial calibration of a tokamak neutral beam diagnostic using in situ neutral beam emission.

    PubMed

    Chrystal, C; Burrell, K H; Grierson, B A; Pace, D C

    2015-10-01

    Neutral beam injection is used in tokamaks to heat, apply torque, drive non-inductive current, and diagnose plasmas. Neutral beam diagnostics need accurate spatial calibrations to benefit from the measurement localization provided by the neutral beam. A new technique has been developed that uses in situ measurements of neutral beam emission to determine the spatial location of the beam and the associated diagnostic views. This technique was developed to improve the charge exchange recombination (CER) diagnostic at the DIII-D tokamak and uses measurements of the Doppler shift and Stark splitting of neutral beam emission made by that diagnostic. These measurements contain information about the geometric relation between the diagnostic views and the neutral beams when they are injecting power. This information is combined with standard spatial calibration measurements to create an integrated spatial calibration that provides a more complete description of the neutral beam-CER system. The integrated spatial calibration results are very similar to the standard calibration results and derived quantities from CER measurements are unchanged within their measurement errors. The methods developed to perform the integrated spatial calibration could be useful for tokamaks with limited physical access.

  4. Impact of Clade, Geography, and Age of the Epidemic on HIV-1 Neutralization by Antibodies

    PubMed Central

    Hraber, Peter; Korber, Bette T.; Lapedes, Alan S.; Bailer, Robert T.; Seaman, Michael S.; Gao, Hongmei; Greene, Kelli M.; McCutchan, Francine; Williamson, Carolyn; Kim, Jerome H.; Tovanabutra, Sodsai; Hahn, Beatrice H.; Swanstrom, Ronald; Thomson, Michael M.; Gao, Feng; Harris, Linda; Giorgi, Elena; Hengartner, Nicholas; Bhattacharya, Tanmoy; Mascola, John R.

    2014-01-01

    ABSTRACT Neutralizing antibodies (nAbs) are a high priority for vaccines that aim to prevent the acquisition of HIV-1 infection. Vaccine effectiveness will depend on the extent to which induced antibodies neutralize the global diversity of circulating HIV-1 variants. Using large panels of genetically and geographically diverse HIV-1 Env-pseudotyped viruses and chronic infection plasma samples, we unambiguously show that cross-clade nAb responses are commonly induced in response to infection by any virus clade. Nonetheless, neutralization was significantly greater when the plasma clade matched the clade of the virus being tested. This within-clade advantage was diminished in older, more-diverse epidemics in southern Africa, the United States, and Europe compared to more recent epidemics in Asia. It was most pronounced for circulating recombinant form (CRF) 07_BC, which is common in China and is the least-divergent lineage studied; this was followed by the slightly more diverse Asian CRF01_AE. We found no evidence that transmitted/founder viruses are generally more susceptible to neutralization and are therefore easier targets for vaccination than chronic viruses. Features of the gp120 V1V2 loop, in particular, length, net charge, and number of N-linked glycans, were associated with Env susceptibility and plasma neutralization potency in a manner consistent with neutralization escape being a force that drives viral diversification and plasma neutralization breadth. The overall susceptibility of Envs and potencies of plasma samples were highly predictive of the neutralization outcome of any single virus-plasma combination. These findings highlight important considerations for the design and testing of candidate HIV-1 vaccines that aim to elicit effective nAbs. IMPORTANCE An effective HIV-1 vaccine will need to overcome the extraordinary variability of the virus, which is most pronounced in the envelope glycoproteins (Env), which are the sole targets for neutralizing

  5. Impact of clade, geography, and age of the epidemic on HIV-1 neutralization by antibodies.

    PubMed

    Hraber, Peter; Korber, Bette T; Lapedes, Alan S; Bailer, Robert T; Seaman, Michael S; Gao, Hongmei; Greene, Kelli M; McCutchan, Francine; Williamson, Carolyn; Kim, Jerome H; Tovanabutra, Sodsai; Hahn, Beatrice H; Swanstrom, Ronald; Thomson, Michael M; Gao, Feng; Harris, Linda; Giorgi, Elena; Hengartner, Nicholas; Bhattacharya, Tanmoy; Mascola, John R; Montefiori, David C

    2014-11-01

    Neutralizing antibodies (nAbs) are a high priority for vaccines that aim to prevent the acquisition of HIV-1 infection. Vaccine effectiveness will depend on the extent to which induced antibodies neutralize the global diversity of circulating HIV-1 variants. Using large panels of genetically and geographically diverse HIV-1 Env-pseudotyped viruses and chronic infection plasma samples, we unambiguously show that cross-clade nAb responses are commonly induced in response to infection by any virus clade. Nonetheless, neutralization was significantly greater when the plasma clade matched the clade of the virus being tested. This within-clade advantage was diminished in older, more-diverse epidemics in southern Africa, the United States, and Europe compared to more recent epidemics in Asia. It was most pronounced for circulating recombinant form (CRF) 07_BC, which is common in China and is the least-divergent lineage studied; this was followed by the slightly more diverse Asian CRF01_AE. We found no evidence that transmitted/founder viruses are generally more susceptible to neutralization and are therefore easier targets for vaccination than chronic viruses. Features of the gp120 V1V2 loop, in particular, length, net charge, and number of N-linked glycans, were associated with Env susceptibility and plasma neutralization potency in a manner consistent with neutralization escape being a force that drives viral diversification and plasma neutralization breadth. The overall susceptibility of Envs and potencies of plasma samples were highly predictive of the neutralization outcome of any single virus-plasma combination. These findings highlight important considerations for the design and testing of candidate HIV-1 vaccines that aim to elicit effective nAbs. An effective HIV-1 vaccine will need to overcome the extraordinary variability of the virus, which is most pronounced in the envelope glycoproteins (Env), which are the sole targets for neutralizing antibodies (n

  6. Crystal engineering of a zwitterionic drug to neutral cocrystals: a general solution for floxacins.

    PubMed

    Gunnam, Anilkumar; Suresh, Kuthuru; Ganduri, Ramesh; Nangia, Ashwini

    2016-10-18

    The transformation of zwitterionic Sparfloxacin (SPX) to the neutral form is achieved by cocrystallization. Neutral forms of drugs are important for higher membrane permeability, while zwitterions are more soluble in water. The twin advantages of higher solubility/dissolution rate and good stability of neutral SPX are achieved in a molecular cocrystal compared to its zwitterionic SPX hydrate. The amine-phenol supramolecular synthon drives cocrystal formation, with the paraben ester acting as a "proton migrator" for the ionic to neutral transformation.

  7. Characterization of epitopes on the rabies virus glycoprotein by selection and analysis of escape mutants.

    PubMed

    Fallahi, Firouzeh; Wandeler, Alexander I; Nadin-Davis, Susan A

    2016-07-15

    The glycoprotein (G) is the only surface protein of the lyssavirus particle and the only viral product known to be capable of eliciting the production of neutralizing antibodies. In this study, the isolation of escape mutants resistant to monoclonal antibody (Mab) neutralization was attempted by a selection strategy employing four distinct rabies virus strains: the extensively passaged Evelyn Rokitnicki Abelseth (ERA) strain and three field isolates representing two bat-associated variants and the Western Canada skunk variant (WSKV). No escape mutants were generated from either of the bat-associated viral variants but two neutralization mutants were derived from the WSKV isolate. Seven independent ERA mutants were recovered using Mabs directed against antigenic sites I (four mutants) and IIIa (three mutants) of the glycoprotein. The cross-neutralization patterns of these viral mutants were used to determine the precise location and nature of the G protein epitopes recognized by these Mabs. Nucleotide sequencing of the G gene indicated that those mutants derived using Mabs directed to antigenic site (AS) III all contained amino acid substitutions in this site. However, of the four mutants selected with AS I Mabs, two bore mutations within AS I as expected while the remaining two carried mutations in AS II. WSKV mutants exhibited mutations at the sites appropriate for the Mabs used in their selection. All ERA mutant preparations were more cytopathogenic than the parental virus when propagated in cell culture; when in vivo pathogenicity in mice was examined, three of these mutants exhibited reduced pathogenicity while the remaining four mutants exhibited comparable pathogenic properties to those of the parent virus.

  8. Structural basis of hepatitis C virus neutralization by broadly neutralizing antibody HCV1

    SciTech Connect

    Kong, Leopold; Giang, Erick; Robbins, Justin B.; Stanfield, Robyn L.; Burton, Dennis R.; Wilson, Ian A.; Law, Mansun

    2012-10-29

    Hepatitis C virus (HCV) infects more than 2% of the global population and is a leading cause of liver cirrhosis, hepatocellular carcinoma, and end-stage liver diseases. Circulating HCV is genetically diverse, and therefore a broadly effective vaccine must target conserved T- and B-cell epitopes of the virus. Human mAb HCV1 has broad neutralizing activity against HCV isolates from at least four major genotypes and protects in the chimpanzee model from primary HCV challenge. The antibody targets a conserved antigenic site (residues 412-423) on the virus E2 envelope glycoprotein. Two crystal structures of HCV1 Fab in complex with an epitope peptide at 1.8-{angstrom} resolution reveal that the epitope is a {beta}-hairpin displaying a hydrophilic face and a hydrophobic face on opposing sides of the hairpin. The antibody predominantly interacts with E2 residues Leu{sup 413} and Trp{sup 420} on the hydrophobic face of the epitope, thus providing an explanation for how HCV isolates bearing mutations at Asn{sup 415} on the same binding face escape neutralization by this antibody. The results provide structural information for a neutralizing epitope on the HCV E2 glycoprotein and should help guide rational design of HCV immunogens to elicit similar broadly neutralizing antibodies through vaccination.

  9. Distinct germinal center selection at local sites shapes memory B cell response to viral escape

    PubMed Central

    Adachi, Yu; Onodera, Taishi; Yamada, Yuki; Daio, Rina; Tsuiji, Makoto; Inoue, Takeshi; Kobayashi, Kazuo; Kurosaki, Tomohiro; Ato, Manabu

    2015-01-01

    Respiratory influenza virus infection induces cross-reactive memory B cells targeting invariant regions of viral escape mutants. However, cellular events dictating the cross-reactive memory B cell responses remain to be fully defined. Here, we demonstrated that lung-resident memory compartments at the site of infection, rather than those in secondary lymphoid organs, harbor elevated frequencies of cross-reactive B cells that mediate neutralizing antibody responses to viral escape. The elevated cross-reactivity in the lung memory compartments was correlated with high numbers of VH mutations and was dependent on a developmental pathway involving persistent germinal center (GC) responses. The persistent GC responses were focused in the infected lungs in association with prolonged persistence of the viral antigens. Moreover, the persistent lung GCs supported the exaggerated B cell proliferation and clonal selection for cross-reactive repertoires, which served as the predominant sites for the generation of cross-reactive memory progenitors. Thus, we identified the distinct GC selection at local sites as a key cellular event for cross-reactive memory B cell response to viral escape, a finding with important implications for developing broadly protective influenza vaccines. PMID:26324444

  10. Initial Concepts for a Mars Upper Atmosphere Orbiter Mission to Study Atmospheric Escape

    NASA Astrophysics Data System (ADS)

    Retherford, K. D.; Gladstone, G. R.; Stern, S. A.; Miller, G. P.; Slater, D. C.; Young, D. T.; Waite, J. H.; Bougher, S. W.; Nagy, A. F.

    2003-05-01

    According to the recent decadal survey "New Frontiers in the Solar System: An Integrated Exploration Strategy" report by the National Academy of Sciences, a Mars Upper Atmosphere Orbiter (MUAO) mission is required to "provide quantitative information on the various atmospheric escape fluxes, thus quantifying current escape rates and providing a basis for backwards extrapolation in our attempt to understand the evolution of Mars' atmosphere." Mars' atmosphere may once have been thick, warm, and wet, but how did it evolve into the thin, dry atmosphere of today? Specifically, how much water was lost by escape to space versus sequestration in the surface? We are investigating several candidate MUAO missions and instrument suites that address these questions of Martian climate change. SwRI held a workshop last spring (and a general Mars Aeronomy Workshop is planned for this meeting) to discuss the science goals and measurement needs for this mission with members of the Mars upper atmosphere community. We report a preliminary list of science goals and needed measurements for a MUAO mission. Initial results from a design study of neutral mass spectrometer, plasma analyzer, and far-ultraviolet spectrometer instruments conducted by SwRI will be discussed, along with future prospects for a NASA Mars Scout size MUAO mission. We gratefully acknowledge internal support from SwRI, through Southwest Initiative for Mars (SwIM) grant 15-R9366.

  11. Non-thermal production and escape of OH from the upper atmosphere of Mars

    NASA Astrophysics Data System (ADS)

    Gacesa, M.; Lewkow, N.; Kharchenko, V.

    2017-03-01

    We present a theoretical analysis of formation and kinetics of hot OH molecules in the upper atmosphere of Mars produced in reactions of thermal molecular hydrogen and energetic oxygen atoms. Two major sources of energetic O considered are the photochemical production, via dissociative recombination of O2+ ions, and energizing collisions with fast atoms produced by the precipitating Solar Wind (SW) ions, mostly H+ and He2+ , and energetic neutral atoms (ENAs) originating in the charge-exchange collisions between the SW ions and atmospheric gases. Energizing collisions of O with atmospheric secondary hot atoms, induced by precipitating SW ions and ENAs, are also included in our consideration. The non-thermal reaction O + H2(v, j) → H + OH(v‧, j‧) is described using recent quantum-mechanical state-to-state cross sections, which allow us to predict non-equilibrium distributions of excited rotational and vibrational states (v‧, j‧) of OH and expected emission spectra. A fraction of produced translationally hot OH is sufficiently energetic to overcome Mars' gravitational potential and escape into space, contributing to the hot corona. We estimate its total escape flux from the dayside of Mars for low solar activity conditions at about 1.1 × 1023 s-1 , or about 0.1% of the total escape rate of atomic O and H. The described non-thermal OH production mechanism is general and expected to contribute to the evolution of atmospheres of the planets, satellites, and exoplanets with similar atmospheric compositions.

  12. Some Possible Cases of Escape Mimicry in Neotropical Butterflies.

    PubMed

    Pinheiro, C E G; Freitas, A V L

    2014-10-01

    The possibility that escape or evasive mimicry evolved in butterflies and other prey insects in a similar fashion to classical Batesian and Müllerian mimicry has long been advanced in the literature. However, there is a general disagreement among lepidopterists and evolutionary biologists on whether or not escape mimicry exists, as well as in which mimicry rings this form of mimicry has evolved. Here, we review some purported cases of escape mimicry in Neotropical butterflies and suggest new mimicry rings involving several species of Archaeoprepona, Prepona, and Doxocopa (the "bright blue bands" ring) and species of Colobura and Hypna (the "creamy bands" ring) where the palatability of butterflies, their ability to escape predator attacks, geographic distribution, relative abundance, and co-occurrence in the same habitats strongly suggest that escape mimicry is involved. In addition, we also indicate other butterfly taxa whose similarities of coloration patterns could be due to escape mimicry and would constitute important case studies for future investigation.

  13. Strain-Specific V3 and CD4 Binding Site Autologous HIV-1 Neutralizing Antibodies Select Neutralization-Resistant Viruses.

    PubMed

    Moody, M Anthony; Gao, Feng; Gurley, Thaddeus C; Amos, Joshua D; Kumar, Amit; Hora, Bhavna; Marshall, Dawn J; Whitesides, John F; Xia, Shi-Mao; Parks, Robert; Lloyd, Krissey E; Hwang, Kwan-Ki; Lu, Xiaozhi; Bonsignori, Mattia; Finzi, Andrés; Vandergrift, Nathan A; Alam, S Munir; Ferrari, Guido; Shen, Xiaoying; Tomaras, Georgia D; Kamanga, Gift; Cohen, Myron S; Sam, Noel E; Kapiga, Saidi; Gray, Elin S; Tumba, Nancy L; Morris, Lynn; Zolla-Pazner, Susan; Gorny, Miroslaw K; Mascola, John R; Hahn, Beatrice H; Shaw, George M; Sodroski, Joseph G; Liao, Hua-Xin; Montefiori, David C; Hraber, Peter T; Korber, Bette T; Haynes, Barton F

    2015-09-09

    The third variable (V3) loop and the CD4 binding site (CD4bs) of the HIV-1 envelope are frequently targeted by neutralizing antibodies (nAbs) in infected individuals. In chronic infection, HIV-1 escape mutants repopulate the plasma, and V3 and CD4bs nAbs emerge that can neutralize heterologous tier 1 easy-to-neutralize but not tier 2 difficult-to-neutralize HIV-1 isolates. However, neutralization sensitivity of autologous plasma viruses to this type of nAb response has not been studied. We describe the development and evolution in vivo of antibodies distinguished by their target specificity for V3 and CD4bs epitopes on autologous tier 2 viruses but not on heterologous tier 2 viruses. A surprisingly high fraction of autologous circulating viruses was sensitive to these antibodies. These findings demonstrate a role for V3 and CD4bs antibodies in constraining the native envelope trimer in vivo to a neutralization-resistant phenotype, explaining why HIV-1 transmission generally occurs by tier 2 neutralization-resistant viruses.

  14. Strain-Specific V3 and CD4 Binding Site Autologous HIV-1 Neutralizing Antibodies Select Neutralization-Resistant Viruses

    DOE PAGES

    Moody, M.  Anthony; Gao, Feng; Gurley, Thaddeus  C.; ...

    2015-09-09

    The third variable (V3) loop and the CD4 binding site (CD4bs) of the viral envelope are frequently targeted by neutralizing antibodies (nAbs) in HIV-1-infected individuals. In chronic infection, virus escape mutants repopulate the plasma and V3 and CD4bs nAbs emerge that can neutralize heterologous tier 1 easy-to-neutralize, but not tier 2 difficult-to-neutralize HIV-1 isolates. However, neutralization sensitivity of autologous plasma viruses to this type of nAb response has not been studied. We describe the development and evolution in vivo of antibodies distinguished by their target specificity for V3and CD4bs epitopes on autologous tier 2 viruses but not on heterologous tiermore » 2 viruses. A surprisingly high fraction of autologous circulating viruses was sensitive to these antibodies. These findings demonstrate a role for V3 and CD4bs antibodies in constraining the native envelope trimer in vivo to a neutralization-resistant phenotype, explaining why HIV-1 transmission generally occurs by tier 2 neutralization-resistant viruses.« less

  15. Strain-Specific V3 and CD4 Binding Site Autologous HIV-1 Neutralizing Antibodies Select Neutralization-Resistant Viruses

    SciTech Connect

    Moody, M.  Anthony; Gao, Feng; Gurley, Thaddeus  C.; Amos, Joshua  D.; Kumar, Amit; Hora, Bhavna; Marshall, Dawn  J.; Whitesides, John  F.; Xia, Shi-Mao; Parks, Robert; Lloyd, Krissey  E.; Hwang, Kwan-Ki; Lu, Xiaozhi; Bonsignori, Mattia; Finzi, Andrés; Vandergrift, Nathan  A.; Alam, S.  Munir; Ferrari, Guido; Shen, Xiaoying; Tomaras, Georgia  D.; Kamanga, Gift; Cohen, Myron  S.; Sam, Noel  E.; Kapiga, Saidi; Gray, Elin S.; Tumba, Nancy  L.; Morris, Lynn; Zolla-Pazner, Susan; Gorny, Miroslaw  K.; Mascola, John  R.; Hahn, Beatrice H.; Shaw, George  M.; Sodroski, Joseph  G.; Liao, Hua-Xin; Montefiori, David C.; Hraber, Peter T.; Korber, Bette T.; Haynes, Barton F.

    2015-09-09

    The third variable (V3) loop and the CD4 binding site (CD4bs) of the viral envelope are frequently targeted by neutralizing antibodies (nAbs) in HIV-1-infected individuals. In chronic infection, virus escape mutants repopulate the plasma and V3 and CD4bs nAbs emerge that can neutralize heterologous tier 1 easy-to-neutralize, but not tier 2 difficult-to-neutralize HIV-1 isolates. However, neutralization sensitivity of autologous plasma viruses to this type of nAb response has not been studied. We describe the development and evolution in vivo of antibodies distinguished by their target specificity for V3and CD4bs epitopes on autologous tier 2 viruses but not on heterologous tier 2 viruses. A surprisingly high fraction of autologous circulating viruses was sensitive to these antibodies. These findings demonstrate a role for V3 and CD4bs antibodies in constraining the native envelope trimer in vivo to a neutralization-resistant phenotype, explaining why HIV-1 transmission generally occurs by tier 2 neutralization-resistant viruses.

  16. INDIRECT EVIDENCE FOR ESCAPING IONIZING PHOTONS IN LOCAL LYMAN BREAK GALAXY ANALOGS

    SciTech Connect

    Alexandroff, Rachael M.; Heckman, Timothy M.; Borthakur, Sanchayeeta; Overzier, Roderik; Leitherer, Claus

    2015-09-10

    A population of early star-forming galaxies is the leading candidate for the re-ionization of the universe. It is still unclear, however, what conditions and physical processes would enable a significant fraction of the ionizing (Lyman continuum) photons to escape from these gas-rich galaxies. In this paper we present the results of the analysis of Hubble Space Telescope Cosmic Origins Spectrograph far-UV (FUV) spectroscopy plus ancillary multi-waveband data of a sample of 22 low-redshift galaxies that are good analogs to typical star-forming galaxies at high redshift. We measure three parameters that provide indirect evidence of the escape of ionizing radiation (leakiness): (1) the residual intensity in the cores of saturated interstellar low-ionization absorption lines, which indicates incomplete covering by that gas in the galaxy; (2) the relative amount of blueshifted Lyα line emission, which can indicate the existence of holes in the neutral hydrogen on the front-side of the galaxy outflow, and (3) the relative weakness of the [S ii] optical emission lines that trace matter-bounded H ii regions. We show that our residual intensity measures are only negligibly affected by infilling from resonance emission lines. We find all three diagnostics agree well with one another. We use these diagnostics to rank-order our sample in terms of likely leakiness, noting that a direct measure of escaping Lyman continuum has recently been made for one of the leakiest members of our sample. We then examine the correlations between our ranking and other proposed diagnostics of leakiness. We find a good correlation with the equivalent width of the Lyα emission line, but no significant correlations with either the flux ratio of the [O iii]/[O ii] emission lines or the ratio of star-formation rates derived from the (dust-corrected) FUV and Hα luminosities. Turning to galaxy properties, we find the strongest correlations with leakiness are with the compactness of the star

  17. Equivalent Neutral Wind

    NASA Technical Reports Server (NTRS)

    Liu, W. Timothy; Tang, Wenqing

    1996-01-01

    The definition of equivalent neutral wind and the rationale for using it as the geophysical product of a spaceborne scatterometer are reviewed. The differences between equivalent neutral wind and actual wind, which are caused by atmospheric density stratification, are demonstrated with measurements at selected locations. A method of computing this parameter from ship and buoy measurements is described and some common fallacies in accounting for the effects of atmospheric stratification on wind shear are discussed. The computer code for the model to derive equivalent neutral wind is provided.

  18. A high energy neutral beam system for reactors

    SciTech Connect

    Anderson, O.A.; Chan, C.F.; Cooper, W.S.; Leung, K.N.; Lietzke, A.F.; Kim, C.H.; Kunkel, W.B.; Kwan, J.W.; Purgalis, P.; Schlachter, A.S.

    1988-09-01

    High energy neutral beams provide a promising method of heating and driving current in steady-state tokamak fusion reactors. As an example, we have made a conceptual design of a neutral beam system for current drive on the International Thermonuclear Experimental Reactor (ITER). The system, based on electrostatic acceleration of D/sup /minus// ions, can deliver up to 100 MW of 1.6 MeV D/sup 0/ neutrals through three ports. Radiation protection is provided by locating sensitive beamline components 35 to 50 m from the reactor. In an application to a 3300 MW power reactor, a system delivering 120 MW of 2-2.4 MeV deuterium beams assisted by 21 MW of lower hybrid wave power drives 25 MA and provides an adequate plasma power gain (Q = 24) for a commercial fusion power plant. 8 refs., 1 fig., 2 tabs.

  19. The atmospheric escape at Mars: complementing the scenario

    NASA Astrophysics Data System (ADS)

    Lilensten, Jean; Simon, Cyril; Barthélémy, Mathieu; Thissen, Roland; Ehrenreich, David; Gronoff, Guillaume; Witasse, Olivier

    2013-04-01

    In the recent years, the presence of dications in the atmospheres of Mars, Venus, Earth and Titan has been modeled and assessed. These studies also suggested that these ions could participate to the escape of the planetary atmospheres because a large fraction of them is unstable and highly ener- getic. When they dissociate, their internal energy is transformed into kinetic energy which may be larger than the escape energy. This study assesses the impact of the doubly-charged ions in the escape of CO2-dominated planetary atmospheres and to compare it to the escape of thermal photo-ions.We solve a Boltzmann transport equation at daytime taking into account the dissociative states of CO++ for a simplified single constituent atmosphere of a 2 case-study planet. We compute the escape of fast ions using a Beer-Lambert approach. We study three test-cases. On a Mars-analog planet in today's conditions, we retrieve the measured electron escape flux. When comparing the two mechanisms (i.e. excluding solar wind effects, sputtering ...), the escape due to the fast ions issuing from the dissociation of dications may account for up to 6% of the total and the escape of thermal ions for the remaining. We show that these two mechanisms cannot explain the escape of the atmosphere since the magnetic field vanished but complement the other processes and allow writing the scenario of the Mars escape. We show that the atmosphere of a Mars analog planet would empty in another giga years and a half. At Venus orbit, the contribution of the dications in the escape rate is negligible.When simulating the hot Jupiter HD209458b, the two processes cannot explain the measured escape flux of C+.

  20. Escaping hydrogen from HD209458b

    NASA Astrophysics Data System (ADS)

    Erwin, Justin; Yelle, Roger V.; Koskinen, Tommi T.

    2014-11-01

    Recent modeling of the atmosphere of HD209458b has been used to interpret the Lyman-α line and other observations during transits. In this presentation, we model the hydrogen exosphere of the short period, Hot Jupiter planet to investigate the dynamics of the extended hydrogen cloud and to determine the observability of the solar ionization and acceleration on the escaping hydrogen.Koskinen et al (2010) used a hydrostatic density profile in the thermosphere combined with the Voigt profile to estimate the Lyman-α transit depths for an array of model parameters. A detailed photochemical-dynamical model of the thermosphere was developed by Koskinen et al (2013a) and used to again estimate model parameters to fit not only the Lyman-α transits, but also the transits in the O I, C II and Si III lines (Koskinen et al, 2013b).Recently, Bourrier et al (2013) modeled the escape of hydrogen from the extended atmospheres of HD209458b and HD189733b and used the results to interpret Lyman-α observations. They included acceleration of hydrogen by stellar radiation pressure to obtain the high velocity tails in the escaping velocity distribution, arguing that the observations are explained by high velocity gas in the system, while Voigt broadening is negligible.In this work we connect a free molecular flow (FMF) model, similar to Bourrier et al (2013), to the results of Koskinen et al (2013b) to simulate the extended atmosphere of HD209458b. We include ionization and radiation pressure in the extended atmosphere along with self-shielding due to the extended atmosphere and thermosphere. The extended atmosphere and absorption rates are iteratively computed to obtain a consistent solution. In this manner, we can interpret the importance of the various physical processes by comparing the simulated line profiles, consisting of velocity and natural broadening, to observations (Koskinen et al, 2010). Furthermore, the transit depths of this model can be used to re-evaluate the

  1. Managing Pacific salmon escapements: The gaps between theory and reality

    USGS Publications Warehouse

    Knudsen, E. Eric; Knudsen, E. Eric; Steward, Cleveland R.; MacDonald, Donald D.; Williams, Jack E.; Reiser, Dudley W.

    1999-01-01

    There are myriad challenges to estimating intrinsic production capacity for Pacific salmon populations that are heavily exploited and/or suffering from habitat alteration. Likewise, it is difficult to determine whether perceived decreases in production are due to harvest, habitat, or hatchery influences, natural variation, or some combination of all four. There are dramatic gaps between the true nature of the salmon spawner/recruit relationship and the theoretical basis for describing and understanding the relationship. Importantly, there are also extensive practical difficulties associated with gathering and interpreting accurate escapement and run-size information and applying it to population management. Paradoxically, certain aspects of salmon management may well be contributing to losses in abundance and biodiversity, including harvesting salmon in mixed population fisheries, grouping populations into management units subject to a common harvest rate, and fully exploiting all available hatchery fish at the expense of wild fish escapements. Information on U.S. Pacific salmon escapement goal-setting methods, escapement data collection methods and estimation types, and the degree to which stocks are subjected to mixed stock fisheries was summarized and categorized for 1,025 known management units consisting of 9,430 known populations. Using criteria developed in this study, only 1% of U.S. escapement goals are by methods rated as excellent. Escapement goals for 16% of management units were rated as good. Over 60% of escapement goals have been set by methods rated as either fair or poor and 22% of management units have no escapement goals at all. Of the 9,430 populations for which any information was available, 6,614 (70%) had sufficient information to categorize the method by which escapement data are collected. Of those, data collection methods were rated as excellent for 1%, good for 1%, fair for 2%, and poor for 52%. Escapement estimates are not made for 44

  2. Feedback regulated escape of ionising radiation from high redshift galaxies

    NASA Astrophysics Data System (ADS)

    Trebitsch, M.; Blaizot, J.

    2016-12-01

    Small galaxies are thought to provide the bulk of the radiation necessary to reionise the Universe by z ˜ 6. Their ionising efficiency is usually quantified by their escape fraction f_{esc}, but it is extremely hard to constrain from observations. With the goal of studying the physical processes that determine the values of the escape fraction, we have run a series of high resolution, cosmological, radiative hydrodynamics simulations centred on three galaxies. We find that the variability of the escape fraction follows that of the star formation rate, and that local feedback is necessary for radiation to escape.

  3. Experimental self-punishment and superstitious escape behavior.

    PubMed

    MIGLER, B

    1963-07-01

    Rats were trained to escape from shock by pressing a bar. Bar holding was subsequently punished with very brief shocks. This treatment failed to depress bar-holding behavior. In some cases, although the escape shocks were delivered very infrequently, bar holding was maintained and resulted in the delivery of several thousand punishments per session. These and other effects of the punishment treatment were investigated. Finally, some of the possibilities of superstitious escape responding were explored by presenting inescapable shocks to rats that had been trained to escape shock by lever pressing. Although responding during these shocks had no programmed consequences, responding was sustained.

  4. Experimental self-punishment and superstitious escape behavior

    PubMed Central

    Migler, Bernard

    1963-01-01

    Rats were trained to escape from shock by pressing a bar. Bar holding was subsequently punished with very brief shocks. This treatment failed to depress bar-holding behavior. In some cases, although the escape shocks were delivered very infrequently, bar holding was maintained and resulted in the delivery of several thousand punishments per session. These and other effects of the punishment treatment were investigated. Finally, some of the possibilities of superstitious escape responding were explored by presenting inescapable shocks to rats that had been trained to escape shock by lever pressing. Although responding during these shocks had no programmed consequences, responding was sustained. PMID:13935675

  5. Species ages in neutral biodiversity models.

    PubMed

    Chisholm, Ryan A; O'Dwyer, James P

    2014-05-01

    Biogeography seeks to understand the mechanisms that drive biodiversity across long temporal and large spatial scales. Theoretical models of biogeography can be tested by comparing their predictions of quantities such as species ages against empirical estimates. It has previously been claimed that the neutral theory of biodiversity and biogeography predicts species ages that are unrealistically long. Any improved theory of biodiversity must rectify this problem, but first it is necessary to quantify the problem precisely. Here we provide analytical expressions for species ages in neutral biodiversity communities. We analyse a spatially implicit metacommunity model and solve for both the zero-sum and non-zero-sum cases. We explain why our new expressions are, in the context of biodiversity, usually more appropriate than those previously imported from neutral molecular evolution. Because of the time symmetry of the spatially implicit neutral model, our expressions also lead directly to formulas for species persistence times and species lifetimes. We use our new expressions to estimate species ages of forest trees under a neutral model and find that they are about an order of magnitude shorter than those predicted previously but still unrealistically long. In light of our results, we discuss different models of biogeography that may solve the problem of species ages.

  6. Neutralization Assay for Chikungunya Virus Infection: Plaque Reduction Neutralization Test.

    PubMed

    Azami, Nor Azila Muhammad; Moi, Meng Ling; Takasaki, Tomohiko

    2016-01-01

    Neutralization assay is a technique that detects and quantifies neutralizing antibody in serum samples by calculating the percentage of reduction of virus activity, as the concentration of virus used is usually constant. Neutralizing antibody titer is conventionally determined by calculating the percentage reduction in total virus infectivity by counting and comparing number of plaques (localized area of infection due to cytopathic effect) with a standard amount of virus. Conventional neutralizing test uses plaque-reduction neutralization test (PRNT) to determine neutralizing antibody titers against Chikungunya virus (CHIKV). Here we describe the plaque reduction neutralization assay (PRNT) using Vero cell lines to obtain neutralizing antibody titers.

  7. Solar Neutral Particles

    NASA Image and Video Library

    This animation shows a neutral solar particle's path leaving the sun, following the magnetic field lines out to the heliosheath. The solar particle hits a hydrogen atom, stealing its electron, and ...

  8. Gated Narrow Escape Time for Molecular Signaling

    NASA Astrophysics Data System (ADS)

    Reingruber, Jürgen; Holcman, David

    2009-10-01

    The mean time for a diffusing ligand to activate a target protein located on the surface of a microdomain can regulate cellular signaling. When the ligand switches between various states induced by chemical interactions or conformational changes, while target activation occurs in only one state, this activation time is affected. We investigate this dynamics using new equations for the sojourn times spent in each state. For two states, we obtain exact solutions in dimension one, and asymptotic ones confirmed by Brownian simulations in dimension 3. We find that the activation time is quite sensitive to changes of the switching rates, which can be used to modulate signaling. Interestingly, our analysis reveals that activation can be fast although the ligand spends most of the time “hidden” in the nonactivating state. Finally, we obtain a new formula for the narrow escape time in the presence of switching.

  9. Escape dynamics through a continuously growing leak

    NASA Astrophysics Data System (ADS)

    Kovács, Tamás; Vanyó, József

    2017-06-01

    We formulate a model that describes the escape dynamics in a leaky chaotic system in which the size of the leak depends on the number of the in-falling particles. The basic motivation of this work is the astrophysical process, which describes the planetary accretion. In order to study the dynamics generally, the standard map is investigated in two cases when the dynamics is fully hyperbolic and in the presence of Kolmogorov-Arnold-Moser islands. In addition to the numerical calculations, an analytic solution to the temporal behavior of the model is also derived. We show that in the early phase of the leak expansion, as long as there are enough particles in the system, the number of survivors deviates from the well-known exponential decay. Furthermore, the analytic solution returns the classical result in the limiting case when the number of particles does not affect the leak size.

  10. Simulating dynamical features of escape panic

    NASA Astrophysics Data System (ADS)

    Helbing, Dirk; Farkas, Illés; Vicsek, Tamás

    2000-09-01

    One of the most disastrous forms of collective human behaviour is the kind of crowd stampede induced by panic, often leading to fatalities as people are crushed or trampled. Sometimes this behaviour is triggered in life-threatening situations such as fires in crowded buildings; at other times, stampedes can arise during the rush for seats or seemingly without cause. Although engineers are finding ways to alleviate the scale of such disasters, their frequency seems to be increasing with the number and size of mass events. But systematic studies of panic behaviour and quantitative theories capable of predicting such crowd dynamics are rare. Here we use a model of pedestrian behaviour to investigate the mechanisms of (and preconditions for) panic and jamming by uncoordinated motion in crowds. Our simulations suggest practical ways to prevent dangerous crowd pressures. Moreover, we find an optimal strategy for escape from a smoke-filled room, involving a mixture of individualistic behaviour and collective `herding' instinct.

  11. Escape of Black Holes from the Brane

    NASA Astrophysics Data System (ADS)

    Flachi, Antonino; Tanaka, Takahiro

    2005-10-01

    TeV-scale gravity theories allow the possibility of producing small black holes at energies that soon will be explored at the CERN LHC or at the Auger observatory. One of the expected signatures is the detection of Hawking radiation that might eventually terminate if the black hole, once perturbed, leaves the brane. Here, we study how the “black hole plus brane” system evolves once the black hole is given an initial velocity that mimics, for instance, the recoil due to the emission of a graviton. The results of our dynamical analysis show that the brane bends around the black hole, suggesting that the black hole eventually escapes into the extra dimensions once two portions of the brane come in contact and reconnect. This gives a dynamical mechanism for the creation of baby branes.

  12. Ions and neutralization

    NASA Astrophysics Data System (ADS)

    Poncet, A.

    After a short presentation of intensity limitations examples due to trapped ions, the processes of ionization and neutralization build up in particle accelerators and storage rings are briefly reviewed. The tolerable limits in neutralization are then assessed at the light of current theories of incoherent and coherent effects driven by ions. Finally the usual antidotes such as clearing electrodes, missing bunch schemes and beam shaking are presented.

  13. The escape of Lyman photons from a young starburst: the case of Haro11†

    NASA Astrophysics Data System (ADS)

    Hayes, Matthew; Östlin, Göran; Atek, Hakim; Kunth, Daniel; Mas-Hesse, J. Miguel; Leitherer, Claus; Jiménez-Bailón, Elena; Adamo, Angela

    2007-12-01

    Lyman α (Lyα) is one of the dominant tools used to probe the star-forming galaxy population at high redshift (z). However, astrophysical interpretations of data drawn from Lyα alone hinge on the Lyα escape fraction which, due to the complex radiative transport, may vary greatly. Here, we map the Lyα emission from the local luminous blue compact galaxy Haro11, a known emitter of Lyα and the only known candidate for low-z Lyman continuum emission. To aid in the interpretation, we perform a detailed ultraviolet and optical multiwavelength analysis and model the stellar population, dust distribution, ionizing photon budget, and star-cluster population. We use archival X-ray observations to further constrain properties of the starburst and estimate the neutral hydrogen column density. The Lyα morphology is found to be largely symmetric around a single young star-forming knot and is strongly decoupled from other wavelengths. From general surface photometry, only very slight correlation is found between Lyα and Hα, E(B - V), and the age of the stellar population. Only around the central Lyα bright cluster do we find the Lyα/Hα ratio at values predicted by the recombination theory. The total Lyα escape fraction is found to be just 3 per cent. We compute that ~90 per cent of the Lyα photons that escape do so after undergoing multiple resonance scattering events, masking their point of origin. This leads to a largely symmetric distribution and, by increasing the distance that photons must travel to escape, decreases the escape probability significantly. While dust must ultimately be responsible for the destruction of Lyα, it plays a little role in governing the observed morphology, which is regulated more by interstellar medium kinematics and geometry. We find tentative evidence for local Lyα equivalent width in the immediate vicinity of star clusters being a function of cluster age, consistent with hydrodynamic studies. We estimate the intrinsic production

  14. Non-thermal escape of H2 and OH from the upper atmosphere of Mars

    NASA Astrophysics Data System (ADS)

    Gacesa, Marko; Kharchenko, Vasili

    2016-10-01

    Two major sources of energetic O atoms in the upper atmosphere of Mars are photochemical production, via dissociative recombination (DR) of O2+ and CO2+ molecular ions, and energizing collisions with fast energetic neutral atoms (ENA) produced by the precipitating solar wind ions. The non-thermal O atoms can either directly escape to space, forming a hot oxygen corona, or participate in collisions with background thermal atmospheric gases, such as H2. In this study we present a theoretical analysis of formation and kinetics of hot OH molecules in the upper atmosphere of Mars, produced in reactions of thermal molecular hydrogen and suprathermal oxygen atoms energized by both DR and ENAs. The non-thermal chemical reaction O + H2(v',j') → H + OH(v',j') is described using recent quantum-mechanical state-to-state cross sections[1], which allow us to predict non-equilibrium distributions of excited rotational and vibrational states (v',j') of OH and expected emission spectra for different geometry and solar activity conditions. A potential consequence is appearance or enhancement of faint Meinel bands in the upper atmosphere of Mars. Moreover, a fraction of produced translationally hot H2 and OH are sufficiently energetic to overcome Mars' gravitational potential and escape into space, contributing to the hot corona. The described non-thermal mechanisms produce estimated total escape fluxes of OH and H2 from dayside of Mars, for low solar activity conditions, equal to about 5×1022 s-1 for OH, or about 0.1% of the total escape rate of atomic O and H, and 1023 s-1 for H2 [2]. If HD molecules are considered instead of H2, the non-thermal mechanisms are about 30 times more efficient than Jeans escape, contribute about 5-10% of the total D escape rate, potentially of interest in atmospheric models of water evolution on Mars.[1] M. Gacesa and V. Kharchenko, J. Chem. Phys. 141, 4324 (2014)[2] M. Gacesa, P. Zhang, V. Kharchenko, Geophys. Res. Lett. 39, L10203 (2012).

  15. Studies on Neutral Beam Injection into the SSPX Spheromak Plasma

    SciTech Connect

    Jayakumar, R; Pearlstein, L D; Casper, T A; Fowler, T K; Hill, D N; Hudson, B; McLean, H; Moller, J

    2007-10-19

    In the Sustained Spheromak Physics Experiment, (SSPX) ['Improved operation of the SSPX spheromak', R.D. Wood, D.N. Hill, E.B. Hooper, S. Woodruff1, H.S. McLean and B.W. Stallard, Nucl. Fusion 45 1582-1588 (2005)], plasmas with core electron temperatures reaching up to 500 eV at densities of 10{sup 20}/m{sup 3} have been sustained for several milliseconds, making them suitable as targets for neutral beam injection. High performance and further progress in understanding Spheromak plasma physics are expected if neutral beams are injected into the plasma. This paper presents the results of numerical 1.5 D modeling of the plasma to calculate neutral beam current drive and ion and electron heating. The results are presented for varying initial conditions of density, temperatures and profiles and beam energy, injection angle and power. Current drive efficiency (Ampere/Watt of absorbed power) of up to 0.08 can be achieved with best performance SSPX shots as target. Analyses of neutral beam heating indicate that ion temperatures of up to 1.5 keV and electron temperatures of up to 750 eV can be obtained with injection of about 1 MW of neutral beam for 5-10 ms and with diffusivities typically observed in SSPX. Injection targeting near the magnetic axis appears to be the best for heating and current drive. Effect of the current drive and evolution of SSPX equilibrium are discussed.

  16. Energy-limited escape revised. The transition from strong planetary winds to stable thermospheres

    NASA Astrophysics Data System (ADS)

    Salz, M.; Schneider, P. C.; Czesla, S.; Schmitt, J. H. M. M.

    2016-01-01

    Gas planets in close proximity to their host stars experience photoevaporative mass loss. The energy-limited escape concept is generally used to derive estimates for the planetary mass-loss rates. Our photoionization hydrodynamics simulations of the thermospheres of hot gas planets show that the energy-limited escape concept is valid only for planets with a gravitational potential lower than log 10(-ΦG)< 13.11 erg g-1 because in these planets the radiative energy input is efficiently used to drive the planetary wind. Massive and compact planets with log 10(-ΦG) ≳ 13.6 erg g-1 exhibit more tightly bound atmospheres in which the complete radiative energy input is re-emitted through hydrogen Lyα and free-free emission. These planets therefore host hydrodynamically stable thermospheres. Between these two extremes the strength of the planetary winds rapidly declines as a result of a decreasing heating efficiency. Small planets undergo enhanced evaporation because they host expanded atmospheres that expose a larger surface to the stellar irradiation. We present scaling laws for the heating efficiency and the expansion radius that depend on the gravitational potential and irradiation level of the planet. The resulting revised energy-limited escape concept can be used to derive estimates for the mass-loss rates of super-Earth-sized planets as well as massive hot Jupiters with hydrogen-dominated atmospheres.

  17. Influenza virus resistance to human neutralizing antibodies.

    PubMed

    Crowe, James E

    2012-01-01

    The human antibody repertoire has an exceptionally large capacity to recognize new or changing antigens through combinatorial and junctional diversity established at the time of V(D)J recombination and through somatic hypermutation. Influenza viruses exhibit a relentless capacity to escape the human antibody response by altering the amino acids of their surface proteins in hypervariable domains that exhibit a high level of structural plasticity. Both parties in this high-stakes game of shape shifting drive structural evolution of their functional proteins (the B cell receptor/antibody on one side and the viral hemagglutinin and neuraminidase proteins on the other) using error-prone polymerase systems. It is likely that most of the genetic mutations that occur in these systems are deleterious, resulting in the failure of the B cell or virus with mutations to propagate in the immune repertoire or viral quasispecies. A subset of mutations is tolerated in functional surface proteins that enter the B cell or virus progeny pool. In both cases, selection occurs in the population of mutated and unmutated species. In cases where the functional avidity of the B cell receptor is increased significantly, that clone may be selected for preferential expansion. In contrast, an influenza virus that "escapes" the inhibitory effect of secreted antibodies may represent a high proportion of the progeny virus in that host. The recent paper by O'Donnell et al. [C. D. O'Donnell et al., mBio 3(3):e00120-12, 2012] identifies a mechanism for antibody resistance that does not require escape from binding but rather achieves a greater efficiency in replication.

  18. Energy Release, Acceleration, and Escape of Solar Energetic Ions

    NASA Astrophysics Data System (ADS)

    de Nolfo, G. A.; Ireland, J.; Ryan, J. M.; Young, C. A.

    2013-12-01

    Solar flares are prodigious producers of energetic particles, and thus a rich laboratory for studying particle acceleration. The acceleration occurs through the release of magnetic energy, a significant fraction of which can go into the acceleration of particles. Coronal mass ejections (CMEs) certainly produce shocks that both accelerate particles and provide a mechanism for escape into the interplanetary medium (IP). What is less well understood is whether accelerated particles produced from the flare reconnection process escape, and if so, how these same particles are related to solar energetic particles (SEPs) detected in-situ. Energetic electron SEPs have been shown to be correlated with Type III radio bursts, hard X-ray emission, and EUV jets, making a very strong case for the connection between acceleration at the flare and escape along open magnetic field lines. Because there has not been a clear signature of ion escape, as is the case with the Type III radio emission for electrons, sorting out the avenues of escape for accelerated flare ions and the possible origin of the impulsive SEPs continues to be a major challenge. The key to building a clear picture of particle escape relies on the ability to map signatures of escape such as EUV jets at the Sun and to follow the progression of these escape signatures as they evolve in time. Furthermore, nuclear γ-ray emissions provide critical context relating ion acceleration to that of escape. With the advent observations from Fermi as well as RHESSI and the Solar Dynamics Observatory (SDO), the challenge of ion escape from the Sun can now be addressed. We present a preliminary study of the relationship of EUV jets with nuclear γ-ray emission and Type III radio observations and discuss the implications for possible magnetic topologies that allow for ion escape from deep inside the corona to the interplanetary medium.

  19. Escape behaviour in the stomatopod crustacean Squilla mantis, and the evolution of the caridoid escape reaction.

    PubMed

    Heitler, W J; Fraser, K; Ferrero, E A

    2000-01-01

    The mantis shrimp Squilla mantis shows a graded series of avoidance/escape responses to visual and mechanical (vibration and touch) rostral stimuli. A low-threshold response is mediated by the simultaneous protraction of the thoracic walking legs and abdominal swimmerets and telson, producing a backwards 'lurch' or jump that can displace the animal by up to one-third of its body length, but leaves it facing in the same direction. A stronger response starts with similar limb protraction, but is followed by partial abdominal flexion. The maximal response also consists of limb protraction followed by abdominal flexion, but in this case the abdominal flexion is sufficiently vigorous to pull the animal into a tight vertical loop, which leaves it inverted and facing away from the stimulus. The animal then swims forward (away from the stimulus) and rights itself by executing a half-roll. A bilaterally paired, large-diameter, rapidly conducting axon in the dorsal region of the ventral nerve excites swimmeret protractor motoneurons in several ganglia and is likely to be the driver neuron for the limb-protraction response. The same neuron also excites unidentified abdominal trunk motoneurons, but less reliably. The escape response is a key feature of the malacostracan caridoid facies, and we provide the first detailed description of this response in a group that diverged early in malacostracan evolution. We show that the components of the escape response contrast strongly with those of the full caridoid reaction, and we provide physiological and behavioural evidence for the biological plausibility of a limb-before-tail thesis for the evolution of the escape response.

  20. 7. VIEW OF ESCAPE TRAINING TANK, LOOKING UP SOUTH SIDE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. VIEW OF ESCAPE TRAINING TANK, LOOKING UP SOUTH SIDE FROM 50-FOOT PASSAGEWAY, SHOWING 25-FOOT BLISTER AT LEFT, 18-FOOT PASSAGEWAY AND PLATFORM AT RIGHT - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  1. 22. VIEW OF ESCAPE TRAINING TANK, LOOKING WEST FROM EAST ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    22. VIEW OF ESCAPE TRAINING TANK, LOOKING WEST FROM EAST SIDE OF CUPOLA TOWARD ELEVATOR. TWO-LOCK RECOMPRESSION CHAMBER AT REAR - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  2. 29. VIEW OF SUBMARINE ESCAPE TRAINING TANK DURING CONSTRUCTION AT ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    29. VIEW OF SUBMARINE ESCAPE TRAINING TANK DURING CONSTRUCTION AT POINT JUST ABOVE THE SUBMARINE SECTION AT THE 110-FOOT LEVEL 1929-1930 - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  3. 36. VIEW OF CUPOLA, SUBMARINE ESCAPE TRAINING TANK, SHOWING ROVING ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    36. VIEW OF CUPOLA, SUBMARINE ESCAPE TRAINING TANK, SHOWING ROVING RESCUE BELL SUSPENDED ABOVE TANK, WITH TWO-LOCK RECOMPRESSION CHAMBER AT REAR, LOOKING WEST. Photo taken after installation of recompression chamber in 1956. - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  4. 35. INTERIOR VIEW OF EQUIPMENT HOUSE, SUBMARINE ESCAPE TRAINING TANK, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    35. INTERIOR VIEW OF EQUIPMENT HOUSE, SUBMARINE ESCAPE TRAINING TANK, PRIOR TO ENLARGEMENT OF ROOM AND INSTALLATION OF TRIPLE-LOCK RECOMPRESSION CHAMBER IN 1957 - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  5. 31. VIEW OF SUBMARINE ESCAPE TRAINING TANK DURING CONSTRUCTION OF ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    31. VIEW OF SUBMARINE ESCAPE TRAINING TANK DURING CONSTRUCTION OF THE ELEVATOR AND PASSAGEWAYS TO THE 18- AND 50-FOOT LOCKS AND CUPOLA 1932 - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  6. 46 CFR 116.500 - Means of escape.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... this section, each space accessible to passengers or used by the crew on a regular basis, must have at... escape must be widely separated and, if possible, at opposite ends or sides of the space to minimize the... windows. (d) The number and dimensions of the means of escape from each space must be sufficient for rapid...

  7. 46 CFR 177.500 - Means of escape.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... this section, each space accessible to passengers or used by the crew on a regular basis, must have at... escape must be widely separated and, if possible, at opposite ends or sides of the space to minimize the... windows. (d) The number and dimensions of the means of escape from each space must be sufficient for rapid...

  8. 46 CFR 116.500 - Means of escape.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... this section, each space accessible to passengers or used by the crew on a regular basis, must have at... escape must be widely separated and, if possible, at opposite ends or sides of the space to minimize the... windows. (d) The number and dimensions of the means of escape from each space must be sufficient for rapid...

  9. 46 CFR 177.500 - Means of escape.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... this section, each space accessible to passengers or used by the crew on a regular basis, must have at... escape must be widely separated and, if possible, at opposite ends or sides of the space to minimize the... windows. (d) The number and dimensions of the means of escape from each space must be sufficient for rapid...

  10. 46 CFR 177.500 - Means of escape.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... this section, each space accessible to passengers or used by the crew on a regular basis, must have at... escape must be widely separated and, if possible, at opposite ends or sides of the space to minimize the... windows. (d) The number and dimensions of the means of escape from each space must be sufficient for rapid...

  11. 46 CFR 116.500 - Means of escape.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... this section, each space accessible to passengers or used by the crew on a regular basis, must have at... escape must be widely separated and, if possible, at opposite ends or sides of the space to minimize the... windows. (d) The number and dimensions of the means of escape from each space must be sufficient for rapid...

  12. The Origins and Underpinning Principles of E-Scape

    ERIC Educational Resources Information Center

    Kimbell, Richard

    2012-01-01

    In this article I describe the context within which we developed project e-scape and the early work that laid the foundations of the project. E-scape (e-solutions for creative assessment in portfolio environments) is centred on two innovations. The first concerns a web-based approach to portfolio building; allowing learners to build their…

  13. 33 CFR 143.101 - Means of escape.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Means of escape. 143.101 Section 143.101 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) OUTER CONTINENTAL SHELF ACTIVITIES DESIGN AND EQUIPMENT OCS Facilities § 143.101 Means of escape. (a) “Primary...

  14. Teachers Offering Healthy Escape Options for Teenagers in Pain

    ERIC Educational Resources Information Center

    Kaywell, Joan F.

    2005-01-01

    "[T]wenty-five percent of today's teenagers have inordinate emotional baggage beyond the normal angst of adolescence." This burden can lead to unhealthy escapes, including substance abuse, sexual activity, violence, eating disorders, and suicide. One healthy escape, however, lies in books, where students can read about teenagers living in painful…

  15. Green Pea Galaxies Reveal Secrets of Lyα Escape

    NASA Astrophysics Data System (ADS)

    Yang, Huan; Malhotra, Sangeeta; Gronke, Max; Rhoads, James E.; Dijkstra, Mark; Jaskot, Anne; Zheng, Zhenya; Wang, Junxian

    2016-04-01

    We analyze archival Lyα spectra of 12 “Green Pea” galaxies observed with the Hubble Space Telescope, model their Lyα profiles with radiative transfer models, and explore the dependence of the Lyα escape fraction on various properties. Green Pea galaxies are nearby compact starburst galaxies with [O iii] λ5007 equivalent widths (EWs) of hundreds of Å. All 12 Green Pea galaxies in our sample show Lyα lines in emission, with an Lyα EW distribution similar to high-redshift Lyα emitters. Combining the optical and UV spectra of Green Pea galaxies, we estimate their Lyα escape fractions and find correlations between Lyα escape fraction and kinematic features of Lyα profiles. The escape fraction of Lyα in these galaxies ranges from 1.4% to 67%. We also find that the Lyα escape fraction depends strongly on metallicity and moderately on dust extinction. We compare their high-quality Lyα profiles with single H i shell radiative transfer models and find that the Lyα escape fraction anticorrelates with the derived H i column densities. Single-shell models fit most Lyα profiles well, but not the ones with the highest escape fractions of Lyα. Our results suggest that low H i column density and low metallicity are essential for Lyα escape and make a galaxy an Lyα emitter.

  16. How many ions have escaped the Martian atmosphere?

    NASA Astrophysics Data System (ADS)

    Brain, David; McFadden, James; Halekas, Jasper; Connerney, J. E. P.; Eparvier, Frank; Mitchell, David; Bougher, Stephen W.; Bowers, Charlie; Curry, Shannon; Dong, Chuanfei; Dong, Yaxue; Egan, Hilary; Fang, Xiaohua; Harada, Yuki; Jakosky, Bruce; Lillis, Robert; Luhmann, Janet; Ma, Yingjuan; Modolo, Ronan; Weber, Tristan

    2016-10-01

    The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission has been making science measurements of the Martian upper atmosphere and its escape to space since November 2014. A key part of this effort is the measurement of the escape rates of charged particles (ions) at present and over solar system history. The lack of a global dynamo magnetic field at Mars leaves its upper atmosphere more directly exposed to the impinging solar wind than magnetized planets such as Earth. For this reason it is thought that ion escape at Mars may have played a significant role in long term climate change. MAVEN measures escaping planetary ions directly, with high energy, mass, and time resolution.With nearly two years of observations in hand, we will report the average ion escape rate and the spatial distribution of escaping ions as measured by MAVEN and place them in context with previous measurements of ion loss by other spacecraft (e.g. Phobos 2 and Mars Express). We will then report on the measured variability in ion escape rates with different drivers (e.g. solar EUV, solar wind pressure, etc.). Finally, we will use these results to provide an initial estimate of the total ion escape from Mars over billions of years.

  17. The Origins and Underpinning Principles of E-Scape

    ERIC Educational Resources Information Center

    Kimbell, Richard

    2012-01-01

    In this article I describe the context within which we developed project e-scape and the early work that laid the foundations of the project. E-scape (e-solutions for creative assessment in portfolio environments) is centred on two innovations. The first concerns a web-based approach to portfolio building; allowing learners to build their…

  18. 46 CFR 169.313 - Means of escape.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... a hold-back to hold the scuttle in an open position. (e) The required means of escape must not have... escape is acceptable provided that— (1) There is no source of fire in the space, such as a galley stove... back of the ladder; and (4) Except when unavoidable obstructions are encountered, there must be...

  19. Nonlinear response of a linear chain to weak driving

    NASA Astrophysics Data System (ADS)

    Hennig, D.; Mulhern, C.; Burbanks, A. D.; Schimansky-Geier, L.

    2014-01-01

    We study the escape of a chain of coupled units over the barrier of a metastable potential. It is demonstrated that a very weak external driving field with a suitably chosen frequency suffices to accomplish speedy escape. The latter requires passage through a transition state, the formation of which is triggered by permanent feeding of energy from a phonon background into humps of localized energy and elastic interaction of the arising breather solutions. In fact, cooperativity between the units of the chain entailing coordinated energy transfer is shown to be crucial for enhancing the rate of escape in an extremely effective and low-energy cost way where the effects of entropic localization and breather coalescence conspire.

  20. Split-second escape decisions in blue tits (Parus caeruleus)

    NASA Astrophysics Data System (ADS)

    Lind, Johan; Kaby, Ulrika; Jakobsson, Sven

    2002-07-01

    Bird mortality is heavily affected by birds of prey. Under attack, take-off is crucial for survival and even minor mistakes in initial escape response can have devastating consequences. Birds may respond differently depending on the character of the predator's attack and these split-second decisions were studied using a model merlin (Falco columbarius) that attacked feeding blue tits (Parus caeruleus) from two different attack angles in two different speeds. When attacked from a low attack angle they took off more steeply than when attacked from a high angle. This is the first study to show that escape behaviour also depends on predator attack speed. The blue tits responded to a high-speed attack by dodging sideways more often than when attacked at a low speed. Escape speed was not significantly affected by the different treatments. Although they have only a split-second before escaping an attack, blue tits do adjust their escape strategy to the prevailing attack conditions.

  1. Escape rate scaling in infinite measure preserving systems

    NASA Astrophysics Data System (ADS)

    Munday, Sara; Knight, Georgie

    2016-02-01

    We investigate the scaling of the escape rate from piecewise linear dynamical systems displaying intermittency due to the presence of an indifferent fixed point. Strong intermittent behaviour in the dynamics can result in the system preserving an infinite measure. We define a neighbourhood of the indifferent fixed point to be a hole through which points escape and investigate the scaling of the rate of this escape as the length of the hole decreases, both in the finite measure preserving case and infinite measure preserving case. In the infinite measure preserving systems we observe logarithmic corrections to and polynomial scaling of the escape rate with hole length. Finally we conjecture a relationship between the wandering rate and the observed scaling of the escape rate.

  2. Split-second escape decisions in blue tits (Parus caeruleus).

    PubMed

    Lind, Johan; Kaby, Ulrika; Jakobsson, Sven

    2002-09-01

    Bird mortality is heavily affected by birds of prey. Under attack, take-off is crucial for survival and even minor mistakes in initial escape response can have devastating consequences. Birds may respond differently depending on the character of the predator's attack and these split-second decisions were studied using a model merlin (Falco columbarius) that attacked feeding blue tits (Parus caeruleus) from two different attack angles in two different speeds. When attacked from a low attack angle they took off more steeply than when attacked from a high angle. This is the first study to show that escape behaviour also depends on predator attack speed. The blue tits responded to a high-speed attack by dodging sideways more often than when attacked at a low speed. Escape speed was not significantly affected by the different treatments. Although they have only a split-second before escaping an attack, blue tits do adjust their escape strategy to the prevailing attack conditions.

  3. Neutral particle lithography

    NASA Astrophysics Data System (ADS)

    Craver, Barry Paul

    Neutral particle lithography (NPL) is a high resolution, proximity exposure technique where a broad beam of energetic neutral particles floods a stencil mask and transmitted beamlets transfer the mask pattern to resist on a substrate, such that each feature is printed in parallel, rather than in the serial manner of electron beam lithography. It preserves the advantages of ion beam lithography (IBL), including extremely large depth-of-field, sub-5 nm resist scattering, and the near absence of diffraction, yet is intrinsically immune to charge-related artifacts including line-edge roughness and pattern placement errors due to charge accumulation on the mask and substrate. In our experiments, a neutral particle beam is formed by passing an ion beam (e.g., 30 keV He+) through a high pressure helium gas cell (e.g., 100 mTorr) to convert the ions to energetic neutrals through charge transfer scattering. The resolution of NPL is generally superior to that of IBL for applications involving insulating substrates, large proximity gaps, and ultra-small features. High accuracy stepped exposures with energetic neutral particles, where magnetic or electrostatic deflection is impossible, have been obtained by clamping the mask to the wafer, setting the proximity gap with a suitable spacer, and mechanically inclining the mask/wafer stack relative to the beam. This approach is remarkably insensitive to vibration and thermal drift; nanometer scale image offsets have been obtained with +/-2 nm placement accuracy for experiments lasting over one hour. Using this nanostepping technique, linewidth versus dose curves were obtained, from which the NPL lithographic blur was determined as 4.4+/-1.4 nm (1sigma), which is 2-3 times smaller than the blur of electron beam lithography. Neutral particle lithography has the potential to form high density, periodic patterns with sub-10 nm resolution.

  4. Tautomerism in neutral histidine.

    PubMed

    Bermúdez, Celina; Mata, Santiago; Cabezas, Carlos; Alonso, José L

    2014-10-06

    Histidine is an important natural amino acid, involved in many relevant biological processes, which, because of its physical properties, proved difficult to characterize experimentally in its neutral form. In this work, neutral histidine has been generated in the gas phase by laser ablation of solid samples and its N(ε)H tautomeric form unraveled through its rotational spectrum. The quadrupole hyperfine structure, arising from the existing three (14)N nuclei, constituted a site-specifically probe for revealing the tautomeric form as well as the side chain configuration of this proteogenic amino acid.

  5. On geometric factors for neutral particle analyzers.

    PubMed

    Stagner, L; Heidbrink, W W

    2014-11-01

    Neutral particle analyzers (NPA) detect neutralized energetic particles that escape from plasmas. Geometric factors relate the counting rate of the detectors to the intensity of the particle source. Accurate geometric factors enable quick simulation of geometric effects without the need to resort to slower Monte Carlo methods. Previously derived expressions [G. R. Thomas and D. M. Willis, "Analytical derivation of the geometric factor of a particle detector having circular or rectangular geometry," J. Phys. E: Sci. Instrum. 5(3), 260 (1972); J. D. Sullivan, "Geometric factor and directional response of single and multi-element particle telescopes," Nucl. Instrum. Methods 95(1), 5-11 (1971)] for the geometric factor implicitly assume that the particle source is very far away from the detector (far-field); this excludes applications close to the detector (near-field). The far-field assumption does not hold in most fusion applications of NPA detectors. We derive, from probability theory, a generalized framework for deriving geometric factors that are valid for both near and far-field applications as well as for non-isotropic sources and nonlinear particle trajectories.

  6. Ion Neutral Mass Spectrometer Measurements from Titan

    NASA Technical Reports Server (NTRS)

    Waite, J. H., Jr.; Niemann, H.; Yelle, R. V.; Kasprzak, W.; Cravens, T.; Luhmann, J.; McNutt, R.; Ip, W.-H.; Gell, D.; Muller-Wordag, I. C. F.

    2005-01-01

    Introduction: The Ion Neutral Mass Spectrometer (INMS) aboard the Cassini orbiter has obtained the first in situ composition measurements of the neutral densities of molecular nitrogen, methane, argon, and a host of stable carbon-nitrile compounds in its first flyby of Titan. The bulk composition and thermal structure of the moon s upper atmosphere do not appear to be changed since the Voyager flyby in 1979. However, the more sensitive techniques provided by modern in-situ mass spectrometry also give evidence for large-spatial-scale large-amplitude atmospheric waves in the upper atmosphere and for a plethora of stable carbon-nitrile compounds above 1174 km. Furthermore, they allow the first direct measurements of isotopes of nitrogen, carbon, and argon, which provide interesting clues about the evolution of the atmosphere. The atmosphere was first accreted as ammonia and ammonia ices from the Saturn sub-nebula. Subsequent photochemistry likely converted the atmosphere into molecular nitrogen. The early atmosphere was 1.5 to 5 times more substantial and was lost via escape over the intervening 4.5 billion years due to the reduced gravity associated with the relatively small mass of Titan. Carbon in the form of methane has continued to outgas over time from the interior with much of it being deposited in the form of complex hydrocarbons on the surface and some of it also being lost to space.

  7. On geometric factors for neutral particle analyzers

    NASA Astrophysics Data System (ADS)

    Stagner, L.; Heidbrink, W. W.

    2014-11-01

    Neutral particle analyzers (NPA) detect neutralized energetic particles that escape from plasmas. Geometric factors relate the counting rate of the detectors to the intensity of the particle source. Accurate geometric factors enable quick simulation of geometric effects without the need to resort to slower Monte Carlo methods. Previously derived expressions [G. R. Thomas and D. M. Willis, "Analytical derivation of the geometric factor of a particle detector having circular or rectangular geometry," J. Phys. E: Sci. Instrum. 5(3), 260 (1972); J. D. Sullivan, "Geometric factor and directional response of single and multi-element particle telescopes," Nucl. Instrum. Methods 95(1), 5-11 (1971)] for the geometric factor implicitly assume that the particle source is very far away from the detector (far-field); this excludes applications close to the detector (near-field). The far-field assumption does not hold in most fusion applications of NPA detectors. We derive, from probability theory, a generalized framework for deriving geometric factors that are valid for both near and far-field applications as well as for non-isotropic sources and nonlinear particle trajectories.

  8. On geometric factors for neutral particle analyzers

    SciTech Connect

    Stagner, L.; Heidbrink, W. W.

    2014-11-15

    Neutral particle analyzers (NPA) detect neutralized energetic particles that escape from plasmas. Geometric factors relate the counting rate of the detectors to the intensity of the particle source. Accurate geometric factors enable quick simulation of geometric effects without the need to resort to slower Monte Carlo methods. Previously derived expressions [G. R. Thomas and D. M. Willis, “Analytical derivation of the geometric factor of a particle detector having circular or rectangular geometry,” J. Phys. E: Sci. Instrum. 5(3), 260 (1972); J. D. Sullivan, “Geometric factor and directional response of single and multi-element particle telescopes,” Nucl. Instrum. Methods 95(1), 5–11 (1971)] for the geometric factor implicitly assume that the particle source is very far away from the detector (far-field); this excludes applications close to the detector (near-field). The far-field assumption does not hold in most fusion applications of NPA detectors. We derive, from probability theory, a generalized framework for deriving geometric factors that are valid for both near and far-field applications as well as for non-isotropic sources and nonlinear particle trajectories.

  9. Coaxial Redundant Drives

    NASA Technical Reports Server (NTRS)

    Brissette, R.

    1983-01-01

    Harmonic drives allow redundancy and high out put torque in small package. If main drive fails, standby drive takes over and produces torque along same axis as main drive. Uses include power units in robot for internal pipeline inspection, manipulators in deep submersible probes or other applications in which redundancy protects against costly failures.

  10. Sensitization of the Tritonia escape swim.

    PubMed

    Frost, W N; Brandon, C L; Mongeluzi, D L

    1998-03-01

    When repeatedly elicited, the oscillatory escape swim of the marine mollusc Tritonia diomedea undergoes habituation of the number of cycles per swim. Previous work has shown that this habituation is accompanied by sensitization of another feature of the behavior: latency to swim onset. Here we focused on the behavioral features of sensitization itself. Test swims elicited 5 min after a strong sensitizing head stimulus differed in several ways from control swims: sensitized animals had shorter latencies for gill and rhinophore withdrawal, a shorter latency for swim onset, a lower threshold for swim initiation, and an increased number of cycles per swim. Sensitized animals did not, however, swim any faster (no change in cycle period). A separate experiment found that swim onset latency also sensitized when Tritonia came into contact with one of their natural predators, the seastar Pycnopodia helianthoides, demonstrating the ecological relevance of this form of nonassociative learning. These results define the set of behavioral changes to be explained by cellular studies of sensitization in Tritonia.

  11. WANDERING STARS: AN ORIGIN OF ESCAPED POPULATIONS

    SciTech Connect

    Teyssier, Maureen; Johnston, Kathryn V.; Shara, Michael M.

    2009-12-10

    We demonstrate that stars beyond the virial radii of galaxies may be generated by the gravitational impulse received by a satellite as it passes through the pericenter of its orbit around its parent. These stars may become energetically unbound (escaped stars), or may travel to further than a few virial radii for longer than a few Gyr, but still remain energetically bound to the system (wandering stars). Larger satellites (10%-100% the mass of the parent), and satellites on more radial orbits are responsible for the majority of this ejected population. Wandering stars could be observable on Mpc scales via classical novae, and on 100 Mpc scales via Type Ia supernova. The existence of such stars would imply a corresponding population of barely bound, old, high-velocity stars orbiting the Milky Way, generated by the same physical mechanism during the Galaxy's formation epoch. Sizes and properties of these combined populations should place some constraints on the orbits and masses of the progenitor objects from which they came, providing insight into the merging histories of galaxies in general and the Milky Way in particular.

  12. Escaping the resource curse in China.

    PubMed

    Cao, Shixiong; Li, Shurong; Ma, Hua; Sun, Yutong

    2015-02-01

    Many societies face an income gap between rich regions with access to advanced technology and regions that are rich in natural resources but poorer in technology. This "resource curse" can lead to a Kuznets trap, in which economic inequalities between the rich and the poor increase during the process of socioeconomic development. This can also lead to depletion of natural resources, environmental degradation, social instability, and declining socioeconomic development. These problems will jeopardize China's achievements if the current path continues to be pursued without intervention by the government to solve the problems. To mitigate the socioeconomic development gap between western and eastern China, the government implemented its Western Development Program in 2000. However, recent data suggest that this program has instead worsened the resource curse. Because each region has its own unique strengths and weaknesses, China must escape the resource curse by accounting for this difference; in western China, this can be done by improving education, promoting high-tech industry, adjusting its economic strategy to balance regional development, and seeking more sustainable approaches to socioeconomic development.

  13. Immune Escape Strategies of Malaria Parasites

    PubMed Central

    Gomes, Pollyanna S.; Bhardwaj, Jyoti; Rivera-Correa, Juan; Freire-De-Lima, Celio G.; Morrot, Alexandre

    2016-01-01

    Malaria is one of the most life-threatening infectious diseases worldwide. Immunity to malaria is slow and short-lived despite the repeated parasite exposure in endemic areas. Malaria parasites have evolved refined machinery to evade the immune system based on a range of genetic changes that include allelic variation, biomolecular exposure of proteins, and intracellular replication. All of these features increase the probability of survival in both mosquitoes and the vertebrate host. Plasmodium species escape from the first immunological trap in its invertebrate vector host, the Anopheles mosquitoes. The parasites have to pass through various immunological barriers within the mosquito such as anti-microbial molecules and the mosquito microbiota in order to achieve successful transmission to the vertebrate host. Within these hosts, Plasmodium species employ various immune evasion strategies during different life cycle stages. Parasite persistence against the vertebrate immune response depends on the balance among virulence factors, pathology, metabolic cost of the host immune response, and the parasites ability to evade the immune response. In this review we discuss the strategies that Plasmodium parasites use to avoid the vertebrate host immune system and how they promote successful infection and transmission. PMID:27799922

  14. Immune Escape Strategies of Malaria Parasites.

    PubMed

    Gomes, Pollyanna S; Bhardwaj, Jyoti; Rivera-Correa, Juan; Freire-De-Lima, Celio G; Morrot, Alexandre

    2016-01-01

    Malaria is one of the most life-threatening infectious diseases worldwide. Immunity to malaria is slow and short-lived despite the repeated parasite exposure in endemic areas. Malaria parasites have evolved refined machinery to evade the immune system based on a range of genetic changes that include allelic variation, biomolecular exposure of proteins, and intracellular replication. All of these features increase the probability of survival in both mosquitoes and the vertebrate host. Plasmodium species escape from the first immunological trap in its invertebrate vector host, the Anopheles mosquitoes. The parasites have to pass through various immunological barriers within the mosquito such as anti-microbial molecules and the mosquito microbiota in order to achieve successful transmission to the vertebrate host. Within these hosts, Plasmodium species employ various immune evasion strategies during different life cycle stages. Parasite persistence against the vertebrate immune response depends on the balance among virulence factors, pathology, metabolic cost of the host immune response, and the parasites ability to evade the immune response. In this review we discuss the strategies that Plasmodium parasites use to avoid the vertebrate host immune system and how they promote successful infection and transmission.

  15. Dications and thermal ions in planetary atmospheric escape

    NASA Astrophysics Data System (ADS)

    Lilensten, J.; Simon Wedlund, C.; Barthélémy, M.; Thissen, R.; Ehrenreich, D.; Gronoff, G.; Witasse, O.

    2013-01-01

    In the recent years, the presence of dications in the atmospheres of Mars, Venus, Earth and Titan has been modeled and assessed. These studies also suggested that these ions could participate to the escape of the planetary atmospheres because a large fraction of them is unstable and highly energetic. When they dissociate, their internal energy is transformed into kinetic energy which may be larger than the escape energy. The goal of this study is to assess the impact of the doubly-charged ions in the escape of CO2-dominated planetary atmospheres and to compare it to the escape of thermal photo-ions. We solve a Boltzmann transport equation at daytime taking into account the dissociative states of CO2++ for a simplified single constituent atmosphere of a case-study planet. We compute the escape of fast ions using a Beer-Lambert approach. We study three test-cases. On a Mars-analog planet in today's conditions, we retrieve the measured electron escape flux. When comparing the two mechanisms (i.e. excluding solar wind effects, sputtering, etc.), the escape due to the fast ions issuing from the dissociation of dications may account for up to 6% of the total and the escape of thermal ions for the remaining. We show that these two mechanisms cannot explain the escape of the atmosphere since the magnetic field vanished and even contribute only marginally to this loss. We show that with these two mechanisms, the atmosphere of a Mars analog planet would empty in another giga years and a half. At Venus orbit, the contribution of the dications in the escape rate is negligible. When simulating the hot Jupiter HD 209458 b, the two processes cannot explain the measured escape flux of C+. This study shows that the dications may constitute a source of the escape of planetary atmospheres which had not been taken into account until now. This source, although marginal, is not negligible. The influence of the photoionization is of course large, but cannot explain alone the loss of Mars

  16. Bleach Neutralizes Mold Allergens

    ERIC Educational Resources Information Center

    Science Teacher, 2005

    2005-01-01

    Researchers at National Jewish Medical and Research Center have demonstrated that dilute bleach not only kills common household mold, but may also neutralize the mold allergens that cause most mold-related health complaints. The study, published in the Journal of Allergy and Clinical Immunology, is the first to test the effect on allergic…

  17. CO2-Neutral Fuels

    NASA Astrophysics Data System (ADS)

    Goede, Adelbert; van de Sanden, Richard

    2016-06-01

    Mimicking the biogeochemical cycle of System Earth, synthetic hydrocarbon fuels are produced from recycled CO2 and H2O powered by renewable energy. Recapturing CO2 after use closes the carbon cycle, rendering the fuel cycle CO2 neutral. Non-equilibrium molecular CO2 vibrations are key to high energy efficiency.

  18. Bleach Neutralizes Mold Allergens

    ERIC Educational Resources Information Center

    Science Teacher, 2005

    2005-01-01

    Researchers at National Jewish Medical and Research Center have demonstrated that dilute bleach not only kills common household mold, but may also neutralize the mold allergens that cause most mold-related health complaints. The study, published in the Journal of Allergy and Clinical Immunology, is the first to test the effect on allergic…

  19. Modelling the evolution and spread of HIV immune escape mutants.

    PubMed

    Fryer, Helen R; Frater, John; Duda, Anna; Roberts, Mick G; Phillips, Rodney E; McLean, Angela R

    2010-11-18

    During infection with human immunodeficiency virus (HIV), immune pressure from cytotoxic T-lymphocytes (CTLs) selects for viral mutants that confer escape from CTL recognition. These escape variants can be transmitted between individuals where, depending upon their cost to viral fitness and the CTL responses made by the recipient, they may revert. The rates of within-host evolution and their concordant impact upon the rate of spread of escape mutants at the population level are uncertain. Here we present a mathematical model of within-host evolution of escape mutants, transmission of these variants between hosts and subsequent reversion in new hosts. The model is an extension of the well-known SI model of disease transmission and includes three further parameters that describe host immunogenetic heterogeneity and rates of within host viral evolution. We use the model to explain why some escape mutants appear to have stable prevalence whilst others are spreading through the population. Further, we use it to compare diverse datasets on CTL escape, highlighting where different sources agree or disagree on within-host evolutionary rates. The several dozen CTL epitopes we survey from HIV-1 gag, RT and nef reveal a relatively sedate rate of evolution with average rates of escape measured in years and reversion in decades. For many epitopes in HIV, occasional rapid within-host evolution is not reflected in fast evolution at the population level.

  20. The Impacts of Orbital Distance on Exoplanetary Atmospheric Escape

    NASA Astrophysics Data System (ADS)

    Yang, M.; Guo, J. H.

    2016-11-01

    Driven by the high energy radiation of host stars, atmospheric escape is very important for planet evolution. While the flux drops dramatically with the increase of orbital distance, it is essential to study the impacts of orbital distance on atmospheric escape. We consider the hydrodynamic escape of exoplanets driven by the XUV (X-ray and extreme-ultraviolet) radiation of their host stars. We aim to study the mass-loss rate, the transition of escape mechanism, the structures of temperature and velocity, based on a one-dimensional hydrodynamic model which includes radiative transfer processes and photochemical reactions. As the stellar XUV emission varies with the stellar evolution, we use XSPEC (X-Ray Spectral Fitting Package) to construct the XUV spectra of solar-type stars at different ages. We find that with the increase of orbital distance, the mass-loss rates drop significantly, and when the stellar XUV flux is too small to preserve the hydrodynamic escape, it will turn to Jeans escape. This transition occurs in larger distance for younger and smaller planets. For young planets, hydrodynamic escape can occur in 1-2 au. For very young and close-in planets, the relation between mass-loss rate and stellar flux is not as significant as planets that are not close to their host stars, and the energy-limited equation can lead to large overestimate.

  1. A new paradigm for evaluating avoidance/escape motivation.

    PubMed

    Tsutsui-Kimura, Iku; Bouchekioua, Youcef; Mimura, Masaru; Tanaka, Kenji F

    2017-05-06

    Organisms have evolved to approach pleasurable opportunities and to avoid or escape from aversive experiences. These two distinct motivations are referred to as approach and avoidance/escape motivations and are both considered vital for survival. Despite several recent advances in understanding the neurobiology of motivation, most studies addressed approach but not avoidance/escape motivation. Here we develop a new experimental paradigm to quantify avoidance/escape motivation and examine the pharmacological validity. We set up an avoidance variable ratio 5 (VR-5) task in which mice were required to press a lever for variable times to avoid an upcoming aversive stimulus (foot shock) or to escape the ongoing aversive event if mice failed to avoid it. We intraperitoneally injected ketamine (0, 1, or 5 mg/kg) or buspirone (0, 5, or 10 mg/kg) 20 or 30 minutes before the behavioral task in order to see if ketamine enhanced avoidance/escape behavior and buspirone diminished it as previously reported. We found that the performance on the avoidance VR-5 task was sensitive to the intensity of the aversive stimulus. Treatment with ketamine increased, while that with buspirone decreased, the probability of avoidance from an aversive stimulus in the VR-5 task, being consistent with previous reports. Our new paradigm will prove usefulness for quantifying avoidance/escape motivation and will contribute to a more comprehensive understanding of motivation.

  2. Evolutionary escape on complex genotype-phenotype networks.

    PubMed

    Ibáñez-Marcelo, Esther; Alarcón, Tomás

    2016-04-07

    We study the problem of evolutionary escape that is the process whereby a population under sudden changes in the selective pressures acting upon it try to evade extinction by evolving from previously well-adapted phenotypes to those that are favoured by the new selective pressure. We perform a comparative analysis between results obtained by modelling genotype space as a regular hypercube (H-graphs), which is the scenario considered in previous work on the subject, to those corresponding to a complex genotype-phenotype network (B-graphs). In order to analyse the properties of the escape process on both these graphs, we apply a general theory based on multi-type branching processes to compute the evolutionary dynamics and probability of escape. We show that the distribution of distances between phenotypes in B-graphs exhibits a much larger degree of heterogeneity than in H-graphs. This property, one of the main structural differences between both types of graphs, causes heterogeneous behaviour in all results associated to the escape problem. We further show that, due to the heterogeneity characterising escape on B-graphs, escape probability can be underestimated by assuming a regular hypercube genotype network, even if we compare phenotypes at the same distance in H-graphs. Similarly, it appears that the complex structure of B-graphs slows down the rate of escape. Copyright © 2016 Elsevier Ltd. All rights reserved.

  3. Efficiently estimating salmon escapement uncertainty using systematically sampled data

    USGS Publications Warehouse

    Reynolds, Joel H.; Woody, Carol Ann; Gove, Nancy E.; Fair, Lowell F.

    2007-01-01

    Fish escapement is generally monitored using nonreplicated systematic sampling designs (e.g., via visual counts from towers or hydroacoustic counts). These sampling designs support a variety of methods for estimating the variance of the total escapement. Unfortunately, all the methods give biased results, with the magnitude of the bias being determined by the underlying process patterns. Fish escapement commonly exhibits positive autocorrelation and nonlinear patterns, such as diurnal and seasonal patterns. For these patterns, poor choice of variance estimator can needlessly increase the uncertainty managers have to deal with in sustaining fish populations. We illustrate the effect of sampling design and variance estimator choice on variance estimates of total escapement for anadromous salmonids from systematic samples of fish passage. Using simulated tower counts of sockeye salmon Oncorhynchus nerka escapement on the Kvichak River, Alaska, five variance estimators for nonreplicated systematic samples were compared to determine the least biased. Using the least biased variance estimator, four confidence interval estimators were compared for expected coverage and mean interval width. Finally, five systematic sampling designs were compared to determine the design giving the smallest average variance estimate for total annual escapement. For nonreplicated systematic samples of fish escapement, all variance estimators were positively biased. Compared to the other estimators, the least biased estimator reduced bias by, on average, from 12% to 98%. All confidence intervals gave effectively identical results. Replicated systematic sampling designs consistently provided the smallest average estimated variance among those compared.

  4. High Resolution Observations of Escaping Ions in the Martian Magnetotail

    NASA Astrophysics Data System (ADS)

    Halekas, J. S.; Raman, C.; Brain, D.; DiBraccio, G. A.; Harada, Y.; McFadden, J. P.; Mitchell, D. L.; Connerney, J. E. P.; Jakosky, B. M.

    2016-12-01

    Ions escape from the Martian upper atmosphere via a number of channels, including the central plasmasheet of the magnetotail. Mars Express observations show that the heavy ions O+ and O2+ escaping through the central tail often have approximately the same energy, suggesting acceleration in a quasi-static electric field, which has been interpreted as a Hall electric field. The Solar Wind Ion Analyzer (SWIA) on MAVEN was designed to measure the upstream solar wind. However, during orbit segments with appropriate spacecraft attitude, SWIA can also make high resolution measurements of escaping ions in the tail. During the prime mission, these observations were only returned sporadically, during periods of intense escaping fluxes that fortuitously triggered a mode switch. Now, in the extended mission, we return high resolution observations from SWIA routinely. Some of these high resolution measurements reveal slight differences in both the direction and energy of escaping O+ and O2+ ions, which may help determine the acceleration process(es). We investigate the location and solar wind conditions for which the escaping ions separate in energy and angle and the systematics of their energies and flow vectors, and discuss the implications for ion acceleration and the overall picture of Martian atmospheric escape.

  5. Predictions for the escape of CH4 from Pluto

    NASA Astrophysics Data System (ADS)

    Koskinen, Tommi; Erwin, Justin T.; Yelle, Roger V.

    2015-11-01

    Observations of Pluto’s extended atmosphere by the New Horizons/ALICE instrument have the potential to constrain models of energy-limited escape from planetary atmospheres. Such models have wide applicability, ranging from dwarf planets in the solar system to giant extrasolar planets, but the opportunities to test them in actual atmospheres are limited. We adapted a multi-species escape model from close-in extrasolar planets to calculate the escape rates of CH4 and N2 from Pluto. In the absence of escape, CH4 should overtake N2 as the dominant species below the exobase. Theory suggests, however, that Pluto’s atmosphere undergoes rapid escape that leads to a nearly constant CH4 mixing ratio of about 1 % below the exobase, with CH4 escaping at a rate that is only 5-10 % of the N2 escape rate. Simultaneous observations of the N2 and CH4 profiles in the upper atmosphere, together with our model, can be used to test if this is the case and infer an estimate of the mass loss rate.

  6. Modelling the Evolution and Spread of HIV Immune Escape Mutants

    PubMed Central

    Fryer, Helen R.; Frater, John; Duda, Anna; Roberts, Mick G.; Phillips, Rodney E.; McLean, Angela R.

    2010-01-01

    During infection with human immunodeficiency virus (HIV), immune pressure from cytotoxic T-lymphocytes (CTLs) selects for viral mutants that confer escape from CTL recognition. These escape variants can be transmitted between individuals where, depending upon their cost to viral fitness and the CTL responses made by the recipient, they may revert. The rates of within-host evolution and their concordant impact upon the rate of spread of escape mutants at the population level are uncertain. Here we present a mathematical model of within-host evolution of escape mutants, transmission of these variants between hosts and subsequent reversion in new hosts. The model is an extension of the well-known SI model of disease transmission and includes three further parameters that describe host immunogenetic heterogeneity and rates of within host viral evolution. We use the model to explain why some escape mutants appear to have stable prevalence whilst others are spreading through the population. Further, we use it to compare diverse datasets on CTL escape, highlighting where different sources agree or disagree on within-host evolutionary rates. The several dozen CTL epitopes we survey from HIV-1 gag, RT and nef reveal a relatively sedate rate of evolution with average rates of escape measured in years and reversion in decades. For many epitopes in HIV, occasional rapid within-host evolution is not reflected in fast evolution at the population level. PMID:21124991

  7. Neutral particle dynamics in the Alcator C-Mod tokamak

    SciTech Connect

    Niemczewski, Artur P.

    1995-08-01

    This thesis presents an experimental study of neutral particle dynamics in the Alcator C-Mod tokamak. The primary diagnostic used is a set of six neutral pressure gauges, including special-purpose gauges built for in situ tokamak operation. While a low main chamber neutral pressure coincides with high plasma confinement regimes, high divertor pressure is required for heat and particle flux dispersion in future devices such as ITER. Thus we examine conditions that optimize divertor compression, defined here as a divertor-to-midplane pressure ratio. We find both pressures depend primarily on the edge plasma regimes defined by the scrape-off-layer heat transport. While the maximum divertor pressure is achieved at high core plasma densities corresponding to the detached divertor state, the maximum compression is achieved in the high-recycling regime. Variations in the divertor geometry have a weaker effect on the neutral pressures. For otherwise similar plasmas the divertor pressure and compression are maximum when the strike point is at the bottom of the vertical target plate. We introduce a simple flux balance model, which allows us to explain the divertor neutral pressure across a wide range of plasma densities. In particular, high pressure sustained in the detached divertor (despite a considerable drop in the recycling source) can be explained by scattering of neutrals off the cold plasma plugging the divertor throat. Because neutrals are confined in the divertor through scattering and ionization processes (provided the mean-free-paths are much shorter than a typical escape distance) tight mechanical baffling is unnecessary. The analysis suggests that two simple structural modifications may increase the divertor compression in Alcator C-Mod by a factor of about 5. Widening the divertor throat would increase the divertor recycling source, while closing leaks in the divertor structure would eliminate a significant neutral loss mechanism.

  8. The Connection Between Reddening, Gas Covering Fraction, and the Escape of Ionizing Radiation at High Redshift

    NASA Astrophysics Data System (ADS)

    Reddy, Naveen A.; Steidel, Charles C.; Pettini, Max; Bogosavljević, Milan; Shapley, Alice E.

    2016-09-01

    Using a large sample of spectroscopically confirmed z∼ 3 galaxies, we establish an empirical relationship between reddening (E(B-V)), neutral gas covering fraction ({f}{{cov}}({{H}} {{I}})), and the escape of ionizing (Lyman continuum, LyC) photons. Our sample includes 933 galaxies at z∼ 3,121 of which have deep spectroscopic observations (≳ 7 hr) at 850≲ {λ }{{rest}}≲ 1300 Å with the Low Resolution Imaging Spectrograph on Keck. The high covering fraction of outflowing optically thick {{H}} {{I}} indicated by the composite spectra of these galaxies implies that photoelectric absorption, rather than dust attenuation, dominates the depletion of LyC photons. By modeling the composite spectra as the combination of an unattenuated stellar spectrum including nebular continuum emission with one that is absorbed by {{H}} {{I}} and reddened by a line-of-sight extinction, we derive an empirical relationship between E(B-V) and {f}{{cov}}({{H}} {{I}}). Galaxies with redder UV continua have larger covering fractions of {{H}} {{I}} characterized by higher line-of-sight extinctions. We develop a model which connects the ionizing escape fraction with E(B-V), and which may be used to estimate the ionizing escape fraction for an ensemble of galaxies. Alternatively, direct measurements of the escape fraction for our sample allow us to constrain the intrinsic LyC-to-UV flux density ratio to be < S(900 \\mathring{{A}} )/S(1500 \\mathring{{A}} ){> }{{int}}≳ 0.20, a value that favors stellar population models that include weaker stellar winds, a flatter initial mass function, and/or binary evolution. Last, we demonstrate how the framework discussed here may be used to assess the pathways by which ionizing radiation escapes from high-redshift galaxies. Based on data obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous

  9. Oxygen ion escape from Venus: The acceleration mechanisms and the escape rate under different IMF configurations

    NASA Astrophysics Data System (ADS)

    Masunaga, K.; Futaana, Y.; Yamauchi, M.; Barabash, S.; Zhang, T.; Fedorov, A.; Okano, S.; Terada, N.

    2012-12-01

    Using data obtained from ASPERA-4 (Analyser of Space Plasma and Energetic Atoms) and MAG (magnetometer) experiments onboard Venus Express, we investigate the acceleration mechanisms, the escape rate of the oxygen ions from the Venus upper atmosphere, and the contribution of the upstream condition to them. We first produce spatial distribution maps of O+ fluxes (>100 eV) around Venus for two different convection electric fields, namely the solar wind electric field (SWEF; Esw = -Vsw x Bsw) and the local convection electric field (LCEF; EL = -VL x BL where VL and BL are the local proton velocity and the local magnetic field that obtained over one-scan (192 s)). Comparison between the two distributions, we find that the O+ fluxes are frequently observed in the hemisphere where LCEF orients. Moreover, such structure can be identified regardless of the upstream interplanetary magnetic field (IMF) direction. Thus we conclude that the O+ ions are accelerated more effectively by LCEF rather than SWEF in the Venusian upper atmosphere. In the induced magnetosphere, O+ fluxes are frequently associated with Bx reversals where the IMF curvature is strong. It indicates that a magnetic tension force also contributes to O+ acceleration. We also investigate the dependency of the O+ escape rates on the upstream IMF directions. Here, the IMF condition is classified into two cases: the perpendicular IMF case and the parallel IMF case, where IMF directs nearly perpendicular to the Venus-Sun line (60° < θ < 120°) and nearly parallel to it (0° < θ < 30° or 150° < θ < 180°). During the data period between 20 Jun 2006 and 20 Dec 2009 we have obtained 141 perpendicular IMF cases and 71 parallel IMF cases. Using these data, total O+ escape rates are estimated by integrating the anti-sunward fluxes in the nightside region. We find that the total escape rates between the two IMF cases are of the same order, and thus we conclude that the upstream IMF direction does not significantly

  10. Emergence of Ebola Virus Escape Variants in Infected Nonhuman Primates Treated with the MB-003 Antibody Cocktail.

    PubMed

    Kugelman, Jeffrey R; Kugelman-Tonos, Johanny; Ladner, Jason T; Pettit, James; Keeton, Carolyn M; Nagle, Elyse R; Garcia, Karla Y; Froude, Jeffrey W; Kuehne, Ana I; Kuhn, Jens H; Bavari, Sina; Zeitlin, Larry; Dye, John M; Olinger, Gene G; Sanchez-Lockhart, Mariano; Palacios, Gustavo F

    2015-09-29

    MB-003, a plant-derived monoclonal antibody cocktail used effectively in treatment of Ebola virus infection in non-human primates, was unable to protect two of six animals when initiated 1 or 2 days post-infection. We characterized a mechanism of viral escape in one of the animals, after observation of two clusters of genomic mutations that resulted in five nonsynonymous mutations in the monoclonal antibody target sites. These mutations were linked to a reduction in antibody binding and later confirmed to be present in a viral isolate that was not neutralized in vitro. Retrospective evaluation of a second independent study allowed the identification of a similar case. Four SNPs in previously identified positions were found in this second fatality, suggesting that genetic drift could be a potential cause for treatment failure. These findings highlight the importance selecting different target domains for each component of the cocktail to minimize the potential for viral escape.

  11. Modeling thermospheric neutral density

    NASA Astrophysics Data System (ADS)

    Qian, Liying

    Satellite drag prediction requires determination of thermospheric neutral density. The NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) and the global-mean Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIMEGCM) were used to quantify thermospheric neutral density and its variations, focusing on annual/semiannual variation, the effect of using measured solar irradiance on model calculations of solar-cycle variation, and global change in the thermosphere. Satellite drag data and the MSIS00 empirical model were utilized to compare to the TIEGCM simulations. The TIEGCM simulations indicated that eddy diffusion and its annual/semiannual variation is a mechanism for annual/semiannual density variation in the thermosphere. It was found that eddy diffusion near the turbopause can effectively influence thermospheric neutral density. Eddy diffusion, together with annual insolation variation and large-scale circulation, generated global annual/semiannual density variation observed by satellite drag. Using measured solar irradiance as solar input for the TIEGCM improved the solar-cycle dependency of the density calculation shown in F10.7 -based thermospheric empirical models. It has been found that the empirical models overestimate density at low solar activity. The TIEGCM simulations did not show such solar-cycle dependency. Using historic measurements of CO2 and F 10.7, simulations of the global-mean TIMEGCM showed that thermospheric neutral density at 400 km had an average long-term decrease of 1.7% per decade from 1970 to 2000. A forecast of density decrease for solar cycle 24 suggested that thermospheric density will decrease at 400 km from present to the end of solar cycle 24 at a rate of 2.7% per decade. Reduction in thermospheric density causes less atmospheric drag on earth-orbiting space objects. The implication of this long-term decrease of thermospheric neutral density is that it will increase the

  12. 16. INTERIOR VIEW OF SUBMARINE SECTION AT 110FOOT LEVEL, ESCAPE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    16. INTERIOR VIEW OF SUBMARINE SECTION AT 110-FOOT LEVEL, ESCAPE TRAINING TANK, SHOWING LADDER TO ESCAPE TANK, LOOKING SOUTH - U.S. Naval Submarine Base, New London Submarine Escape Training Tank, Albacore & Darter Roads, Groton, New London County, CT

  13. Cervical spine rotation and range of motion: pilot measurements during driving.

    PubMed

    Shugg, Jarrod A J; Jackson, Christopher D; Dickey, James P

    2011-02-01

    Previous studies have evaluated the cervical range of axial rotation during simulated driving conditions. The goals of this pilot study were to describe cervical spine rotation during in-car driving and determine the percentage of time outside neutral neck rotation and peak cervical axial rotation angles that the subjects adopted during various driving conditions. Subjects drove around a specified route through the city of Guelph, Ontario, which included residential, thruway, and highway driving; additional minor driving tasks, such as lane changes, were also included. The cervical range of motion was measured continuously throughout the drive using an electromagnetic sensor; we also used videotape to document the specific driving tasks. The subjects spent 87.0 percent (SD=8.8) of time with their cervical spine in the neutral axial rotation position (±15 degrees). The percentage of time that the subjects spent outside of the neutral range of cervical axial rotation depended upon the driving section (including residential, thruway, and highway), and driving task being performed (starts, stops, and lane changes). The subjects spent a significantly greater proportion of time with their necks rotated beyond neutral during residential driving compared to thruway and highway driving (19.1% SD=8.3 vs. 10.7% SD=9.5 and 9.3% SD=8.7, respectively; p<.001). During driving, the peak angles of cervical axial rotation were an average of 35.7 degrees (SD=14.2) left and 42.5 degrees (SD=18.0) right. We observed a large degree of variability in cervical axial rotation during driving. We observed that most of the driving tasks related to stopping had increased proportion of time out of neutral rotation. Also, right-hand lane changes increased time out of neutral rotation more than left-hand lane changes. Drivers routinely adopt nonneutral head positions (on average 13% of the time); this is likely not enough to lead to injury.

  14. Escape of Pluto's Atmosphere: In Situ Measurements from New Horizons and Remote Observations from Chandra

    NASA Astrophysics Data System (ADS)

    McNutt, R. L., Jr.; Hill, M. E.; Kollmann, P.; Krimigis, S. M.; Brown, L. E.; Kusterer, M. B.; Lisse, C. M.; Mitchell, D. G.; Vandegriff, J. D.; McComas, D. J.; Bagenal, F.; Elliott, H. A.; Ennico Smith, K.; Horanyi, M.; Olkin, C.; Piquette, M. R.; Stern, A.; Strobel, D. F.; Szalay, J.; Valek, P. W.; Weaver, H. A., Jr.; Weidner, S.; Young, L. A.; Zirnstein, E.; Wolk, S. J.

    2015-12-01

    The escape rate of Pluto's atmosphere is of significant scientific interest. It is a Group 1 science goal of the New Horizons mission. In addition, a Group 3 science goal of the mission has been to characterize the energetic particle environment of the Pluto system. The Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) is a compact, energy by time-of-flight (TOF) instrument developed to address both of these science goals. Pluto is known to have an atmosphere, and current models postulate a majority N2 composition with free escape of up to ~1028 molecules/sec. This is very similar to the physical situation of a variety comets observed in the inner heliosphere. However, the gravitational field of Pluto exerts a significant effect on the escaping neutrals, unlike at a comet. The ionization of neutrals emitted from comets results in heavy ions, which are accelerated by the convective solar-wind electric field. The expected major ionization product near Pluto is singly ionized N2 molecules with pickup energies sufficient to be measured with PEPSSI. In the process of measuring the local energetic particle environment, such measurements will also provide constraints on the local density of Pluto's extended atmosphere, which, along with plasma measurements from the Solar Wind Around Pluto (SWAP) instrument also on New Horizons should allow the inference of the strengh and extent of mass-loading of the solar wind due to Pluto's atmosphere. Pluto's neutral atmosphere also provides a source population for charge exchange of highly ionized, minor ions in the solar wind, such as O, C, and N. This process allows these ions to capture one electron and be left in an excited state. That state, in turn decays with the emission of a low-energy (100 eV to 1 keV) X-ray, which can be detected at Earth. Such observations have been made of comets since the X-ray emission discovery in 1996 and used to infer cometary outgassing rates. Similar observatins have been made

  15. Mass fractionation in hydrodynamic escape. [of gases from planetary atmospheres

    NASA Technical Reports Server (NTRS)

    Hunten, Donald M.; Pepin, Robert O.; Walker, James C. G.

    1987-01-01

    In mass fractionation during the hydrodynamic escape of gases from an inner planet's atmosphere, the readier escape of light gases generates a linear or concave downward line in a plotting of the log of remaining inventory against atomic mass. Just as such an episode of hydrodynamic escape during Mars' early history could have led to the mass-dependent depletion of the noble gases that has been noted in the Martian atmosphere, in the event that the Martian atmosphere was initially hydrogen-rich, an early earth-history episode may have resulted in a mass-dependent fractionation of the xenon isotopes.

  16. Delayed escape from light by the albino rat1

    PubMed Central

    Keller, John V.

    1966-01-01

    Two albino rats were trained to terminate an aversive light for 1 min by pressing a bar. After 19 hr of conditioning they were exposed to successive delays of 1, 2, 5, and 10 sec imposed between occurrence of the escape response and light termination. No stimulus change accompanied the delay interval, and any additional responses made at this time reset the delay timer. For both rats the relative frequency of escape responses with very long latencies increased as the delay interval increased. The modal escape latency, however, remained essentially unchanged for all delay values of greater than 1 sec. “Superstitious” responding was observed during the delay interval. PMID:5970387

  17. Proposed magnetoelectrostatic ring trap for neutral atoms

    SciTech Connect

    Hopkins, Asa; Lev, Benjamin; Mabuchi, Hideo

    2004-11-01

    We propose a trap for confining cold neutral atoms in a microscopic ring using a magnetoelectrostatic potential. The trapping potential is derived from a combination of a repulsive magnetic field from a hard drive atom mirror and the attractive potential produced by a charged disk patterned on the hard drive surface. We calculate a trap frequency of [29.7,42.6,62.8] kHz and a depth of [16.1,21.8,21.8] MHz for [{sup 133}Cs, {sup 87}Rb, {sup 40}K], and discuss a simple loading scheme and a method for fabrication. This device provides a one-dimensional potential in a ring geometry that may be of interest to the study of trapped quantum degenerate one-dimensional gases.

  18. Escape of Hydrogen from HD209458b

    NASA Astrophysics Data System (ADS)

    Erwin, Justin; Yelle, Roger; Koskinen, Tommi

    2017-04-01

    Recent modeling of the atmosphere of HD209458b has been used to interpret the Lyman-α line and other observations during transits. Koskinen et al. (2010) used a hydrostatic density profile in the thermosphere combined with the Voigt profile to estimate the Lyman-alpha transit depths for an array of model parameters. A detailed photochemical-dynamical model of the thermosphere was developed by Koskinen et al. (2013a) and used to again estimate model parameters to fit not only the Lyman-alpha transits, but also the transits in the O I, C II and Si III lines (Koskinen et al., 2013b). Recently, Bourrier and Lecavelier (2013) modeled the escape of hydrogen from the extended atmospheres of HD209458b and HD189733b and used the results to interpret Lyman-alpha observations. They included acceleration of hydrogen by radiation pressure and stellar wind protons to simulate the high velocity tails of the velocity distribution, arguing that the observations are explained by high velocity gas in the system while Voigt broadening is negligible. In this work we connect a free molecular flow (FMF) model similar to Bourrier and Lecavelier (2013) to the results of Koskinen et al. (2013b) and properly include absorption by the extended thermosphere in the transit model. In this manner, we can interpret the necessity of the various physical processes in matching the observed line profiles. Furthermore, the transit depths of this model can be used to re-evaluate the atmospheric model parameters to determine if they need to be adjusted due

  19. Structure of Rotavirus Outer-Layer Protein VP7 Bound with a Neutralizing Fab

    SciTech Connect

    Aoki, Scott T.; Settembre, Ethan C.; Trask, Shane D.; Greenberg, Harry B.; Harrison, Stephen C.; Dormitzer, Philip R.

    2009-06-17

    Rotavirus outer-layer protein VP7 is a principal target of protective antibodies. Removal of free calcium ions (Ca{sup 2+}) dissociates VP7 trimers into monomers, releasing VP7 from the virion, and initiates penetration-inducing conformational changes in the other outer-layer protein, VP4. We report the crystal structure at 3.4 angstrom resolution of VP7 bound with the Fab fragment of a neutralizing monoclonal antibody. The Fab binds across the outer surface of the intersubunit contact, which contains two Ca{sup 2+} sites. Mutations that escape neutralization by other antibodies suggest that the same region bears the epitopes of most neutralizing antibodies. The monovalent Fab is sufficient to neutralize infectivity. We propose that neutralizing antibodies against VP7 act by stabilizing the trimer, thereby inhibiting the uncoating trigger for VP4 rearrangement. A disulfide-linked trimer is a potential subunit immunogen.

  20. Calculation of the resonance escape factor of magnesium spectral line shapes in the case of a MgCl{sub 2}--water plasma

    SciTech Connect

    Hannachi, R.; Cressault, Y.; Teulet, Ph.; Gleizes, A.; Ben Lakhdar, Z.; Taieeb, G.

    2007-09-19

    The resonance escape factors for the lines emitted by a neutral magnesium atom MgI at 285.2127 nm (3 {sup 1}S-3 {sup 1}P) and of ionic magnesium MgII at 279.5528 nm (3 {sup 2}S-3 {sup 2}P) are calculated assuming a Voigt profile and in the case of MgCl{sub 2}-water plasma. The dependence of the escape factor on the optical thickness {tau}{sub 0} from the line center which itself depends on the two main spectral line shape broadening mechanisms (pressure and Doppler effects) are considered. The variation of the resonance escape factors with the temperature and the MgCl{sub 2} molar proportion are also investigated. This calculation is useful for the application of laser induced breakdown spectroscopy in the quantitative analysis of elemental composition.

  1. Dynamics of ion beam charge neutralization by ferroelectric plasma sources

    DOE PAGES

    Stepanov, Anton D.; Gilson, Erik P.; Grisham, Larry R.; ...

    2016-04-27

    Ferroelectric Plasma Sources (FEPSs) can generate plasma that provides effective space-charge neutralization of intense high-perveance ion beams, as has been demonstrated on the Neutralized Drift Compression Experiment NDCX-I and NDCX-II. This article presents experimental results on charge neutralization of a high-perveance 38 keV Ar+ beam by a plasma produced in a FEPS discharge. By comparing the measured beam radius with the envelope model for space-charge expansion, it is shown that a charge neutralization fraction of 98% is attainable with sufficiently dense FEPS plasma. The transverse electrostatic potential of the ion beam is reduced from 15V before neutralization to 0.3 V,more » implying that the energy of the neutralizing electrons is below 0.3 eV. Measurements of the time-evolution of beam radius show that near-complete charge neutralization is established similar to –5 μs after the driving pulse is applied to the FEPS and can last for 35 μs. It is argued that the duration of neutralization is much longer than a reasonable lifetime of the plasma produced in the sub-mu s surface discharge. Measurements of current flow in the driving circuit of the FEPS show the existence of electron emission into vacuum, which lasts for tens of mu s after the high voltage pulse is applied. Lastly, it is argued that the beam is neutralized by the plasma produced by this process and not by a surface discharge plasma that is produced at the instant the high-voltage pulse is applied.« less

  2. Dynamics of ion beam charge neutralization by ferroelectric plasma sources

    SciTech Connect

    Stepanov, Anton D.; Gilson, Erik P.; Grisham, Larry R.; Kaganovich, Igor D.; Davidson, Ronald C.

    2016-04-27

    Ferroelectric Plasma Sources (FEPSs) can generate plasma that provides effective space-charge neutralization of intense high-perveance ion beams, as has been demonstrated on the Neutralized Drift Compression Experiment NDCX-I and NDCX-II. This article presents experimental results on charge neutralization of a high-perveance 38 keV Ar+ beam by a plasma produced in a FEPS discharge. By comparing the measured beam radius with the envelope model for space-charge expansion, it is shown that a charge neutralization fraction of 98% is attainable with sufficiently dense FEPS plasma. The transverse electrostatic potential of the ion beam is reduced from 15V before neutralization to 0.3 V, implying that the energy of the neutralizing electrons is below 0.3 eV. Measurements of the time-evolution of beam radius show that near-complete charge neutralization is established similar to –5 μs after the driving pulse is applied to the FEPS and can last for 35 μs. It is argued that the duration of neutralization is much longer than a reasonable lifetime of the plasma produced in the sub-mu s surface discharge. Measurements of current flow in the driving circuit of the FEPS show the existence of electron emission into vacuum, which lasts for tens of mu s after the high voltage pulse is applied. Lastly, it is argued that the beam is neutralized by the plasma produced by this process and not by a surface discharge plasma that is produced at the instant the high-voltage pulse is applied.

  3. Dynamics of ion beam charge neutralization by ferroelectric plasma sources

    SciTech Connect

    Stepanov, Anton D.; Gilson, Erik P.; Grisham, Larry R.; Kaganovich, Igor D.; Davidson, Ronald C.

    2016-04-15

    Ferroelectric Plasma Sources (FEPSs) can generate plasma that provides effective space-charge neutralization of intense high-perveance ion beams, as has been demonstrated on the Neutralized Drift Compression Experiment NDCX-I and NDCX-II. This article presents experimental results on charge neutralization of a high-perveance 38 keV Ar{sup +} beam by a plasma produced in a FEPS discharge. By comparing the measured beam radius with the envelope model for space-charge expansion, it is shown that a charge neutralization fraction of 98% is attainable with sufficiently dense FEPS plasma. The transverse electrostatic potential of the ion beam is reduced from 15 V before neutralization to 0.3 V, implying that the energy of the neutralizing electrons is below 0.3 eV. Measurements of the time-evolution of beam radius show that near-complete charge neutralization is established ∼5 μs after the driving pulse is applied to the FEPS and can last for 35 μs. It is argued that the duration of neutralization is much longer than a reasonable lifetime of the plasma produced in the sub-μs surface discharge. Measurements of current flow in the driving circuit of the FEPS show the existence of electron emission into vacuum, which lasts for tens of μs after the high voltage pulse is applied. It is argued that the beam is neutralized by the plasma produced by this process and not by a surface discharge plasma that is produced at the instant the high-voltage pulse is applied.

  4. Dynamics of ion beam charge neutralization by ferroelectric plasma sources

    SciTech Connect

    Stepanov, Anton D.; Gilson, Erik P.; Grisham, Larry R.; Kaganovich, Igor D.; Davidson, Ronald C.

    2016-04-27

    Ferroelectric Plasma Sources (FEPSs) can generate plasma that provides effective space-charge neutralization of intense high-perveance ion beams, as has been demonstrated on the Neutralized Drift Compression Experiment NDCX-I and NDCX-II. This article presents experimental results on charge neutralization of a high-perveance 38 keV Ar+ beam by a plasma produced in a FEPS discharge. By comparing the measured beam radius with the envelope model for space-charge expansion, it is shown that a charge neutralization fraction of 98% is attainable with sufficiently dense FEPS plasma. The transverse electrostatic potential of the ion beam is reduced from 15V before neutralization to 0.3 V, implying that the energy of the neutralizing electrons is below 0.3 eV. Measurements of the time-evolution of beam radius show that near-complete charge neutralization is established similar to –5 μs after the driving pulse is applied to the FEPS and can last for 35 μs. It is argued that the duration of neutralization is much longer than a reasonable lifetime of the plasma produced in the sub-mu s surface discharge. Measurements of current flow in the driving circuit of the FEPS show the existence of electron emission into vacuum, which lasts for tens of mu s after the high voltage pulse is applied. Lastly, it is argued that the beam is neutralized by the plasma produced by this process and not by a surface discharge plasma that is produced at the instant the high-voltage pulse is applied.

  5. Dynamics of ion beam charge neutralization by ferroelectric plasma sources

    NASA Astrophysics Data System (ADS)

    Stepanov, Anton D.; Gilson, Erik P.; Grisham, Larry R.; Kaganovich, Igor D.; Davidson, Ronald C.

    2016-04-01

    Ferroelectric Plasma Sources (FEPSs) can generate plasma that provides effective space-charge neutralization of intense high-perveance ion beams, as has been demonstrated on the Neutralized Drift Compression Experiment NDCX-I and NDCX-II. This article presents experimental results on charge neutralization of a high-perveance 38 keV Ar+ beam by a plasma produced in a FEPS discharge. By comparing the measured beam radius with the envelope model for space-charge expansion, it is shown that a charge neutralization fraction of 98% is attainable with sufficiently dense FEPS plasma. The transverse electrostatic potential of the ion beam is reduced from 15 V before neutralization to 0.3 V, implying that the energy of the neutralizing electrons is below 0.3 eV. Measurements of the time-evolution of beam radius show that near-complete charge neutralization is established ˜5 μs after the driving pulse is applied to the FEPS and can last for 35 μs. It is argued that the duration of neutralization is much longer than a reasonable lifetime of the plasma produced in the sub-μs surface discharge. Measurements of current flow in the driving circuit of the FEPS show the existence of electron emission into vacuum, which lasts for tens of μs after the high voltage pulse is applied. It is argued that the beam is neutralized by the plasma produced by this process and not by a surface discharge plasma that is produced at the instant the high-voltage pulse is applied.

  6. Monitoring the Escape of DNA from a Nanopore Using an Alternating Current Signal

    PubMed Central

    Lathrop, Daniel K.; Ervin, Eric N.; Barrall, Geoffrey A.; Keehan, Michael G.; Kawano, Ryuji; Krupka, Michael A.; White, Henry S.; Hibbs, Andrew H.

    2010-01-01

    We present the use of an alternating current (AC) signal as a means to monitor the conductance of an α-hemolysin (αHL) pore as a DNA hairpin with a polydeoxyadenosine tail is driven into and released from the pore. Specifically, a 12 base pair DNA hairpin attached to a 50-nucleotide poly-A tail (HP-A50) is threaded into an αHL channel using a DC driving voltage. Once the HP-A50 molecule is trapped within the αHL channel, the DC driving voltage is turned off and the conductance of the channel is monitored using an AC voltage. The escape time, defined as the time it takes the HP-A50 molecule to transport out of the αHL channel, is then measured. This escape time has been monitored as a function of AC amplitude (20 to 250 mVac), AC frequency (60–200 kHz), DC drive voltage (0 to 100 mVdc), and temperature (−10 to 20 °C), in order to determine their effect on the predominantly diffusive motion of the DNA through the nanopore. The applied AC voltage used to monitor the conductance of the nanopore has been found to play a significant role in the DNA/nanopore interaction. The experimental results are described by a one-dimensional asymmetric periodic potential model that includes the influence of the AC voltage. An activation enthalpy barrier of 1.74 × 10−19 J and a periodic potential asymmetry parameter of 0.575 are obtained for the diffusion at zero electrical bias of a single nucleotide through αHL. PMID:20099878

  7. Neutral gas outflows in nearby [U]LIRGs via optical NaD feature

    NASA Astrophysics Data System (ADS)

    Cazzoli, S.; Arribas, S.; Maiolino, R.; Colina, L.

    2016-05-01

    We studied the properties of the neutral gas in a sample of 38 local luminous and ultra luminous infrared galaxies ([U]LIRGs, 51 individual galaxies at z ≤ 0.09), which mainly covers the less explored LIRG luminosity range. This study is based on the analysis of the spatially integrated and spatially resolved spectra of the NaDλλ 5890, 5896 Å feature obtained with the integral field unit (IFU) of VIMOS at the Very Large Telescope. Analyzing spatially integrated spectra, we find that the contribution of the stars to the observed NaD equivalent width is small (<35%) for about half of the sample, and therefore this feature is dominated by inter stellar medium (ISM) absorption. After subtracting the stellar contribution, we find that the pure-ISM integrated spectra generally show blueshifted NaD profiles, indicating neutral gas outflow velocities, V, in the range 65-260 km s-1. Excluding the galaxies with powerful AGNs, V shows a dependency with the star formation rate (SFR) of the type V ∝ SFR0.15, which is in rather good agreement with previous results. The spatially resolved analysis could be performed for 40 galaxies, 22 of which have neutral gas velocity fields dominated by noncircular motions with signatures of cone-like winds. However, a large number of targets (11/40) show disk rotation signatures. Based on a simple model, we found that the wind masses are in the range 0.4-7.5 × 108 M⊙, reaching up to ~3% of the dynamical mass of the host. The mass rates are typically only ~0.2-0.4 times the corresponding global SFR indicating that, in general, the mass loss is too small to slow down the star formation significantly. In the majority of cases, the velocity of the outflowing gas is not sufficient to escape the host potential well and, therefore, most of the gas rains back into the galaxy disk. On average V/vesc is higher in less massive galaxies, confirming that the galaxy mass has a primary role in shaping the recycling of gas and metals. The

  8. Power semiconductor controlled drives

    NASA Astrophysics Data System (ADS)

    Dubey, Gopal K.

    This book presents power semiconductor controlled drives employing dc motors, induction motors, and synchronous motors. The dynamics of motor and load systems are covered. Open-loop and closed-loop drives are considered, and thyristor, power transistor, and GTO converters are discussed. In-depth coverage is given to ac drives, particularly those fed by voltage and current source inverters and cycloconverters. Full coverage is given to brushless and commutatorless dc drives, including load-commuted synchronous motor drives. Rectifier-controlled dc drives are presented in detail.

  9. Heating and current drive systems for TPX

    SciTech Connect

    Swain, D.; Goranson, P.; Halle, A. von; Bernabei, S.; Greenough, N.

    1994-05-24

    The heating and current drive (H and CD) system proposed for the TPX tokamak will consist of ion cyclotron, neutral beam, and lower hybrid systems. It will have 17.5 MW of installed H and CD power initially, and can be upgraded to 45 MW. It will be used to explore advanced confinement and fully current-driven plasma regimes with pulse lengths of up to 1,000 s.

  10. Heating and current drive systems for TPX

    SciTech Connect

    Swain, D.; Goranson, P.; Halle, A. von; Bernabei, S.; Greenough, N.

    1994-11-01

    The heating and current drive (H&CD) system proposed for the TPX tokamak will consist of ion cyclotron, neutral beam, and lower hybrid systems. It will have 17.5 MW of installed H&CD power initially, and can be upgraded to 45 MW. It will be used to explore advanced confinement and fully current-driven plasma regimes with pulse lengths of up to 1000 s.

  11. Oxygen Escape from Venus During High Dynamic Pressure ICMEs

    NASA Astrophysics Data System (ADS)

    McEnulty, Tess; Luhmann, J. G.; Brain, D. A.; Fedorov, A.; Jian, L. K.; Russell, C. T.; Zhang, T.; Möstl, C.; Futaana, Y.; de Pater, I.

    2013-10-01

    Previous studies using data from Pioneer Venus suggested that oxygen ion escape flux may be enhanced by orders of magnitude during Interplanetary Coronal Mass Ejections. However, this large enhancement has been ambiguous in Venus Express ion data - with some analyses showing no flux enhancement or a small enhancement (within 2 times undisturbed cases). One possible explanation is that high escape flux may be due to high dynamic pressure in the solar wind, and the dynamic pressure has been lower during the VEX time period. So, we focus on ICMEs with the largest dynamic pressure and with VEX sampling of the escaping ions during the sheath of the ICMEs (during which the highest dynamic pressures in the solar wind occur). We will show the characteristics of these large events measured by VEX, and compare them to the largest ICMEs measured by PVO. We will then discuss estimates of the oxygen ion escape flux during these events.

  12. Pilot Fullerton dons ejection escape suit (EES) on middeck

    NASA Technical Reports Server (NTRS)

    1982-01-01

    Pilot Fullerton dons ejection escape suit (EES) (high altitude pressure garment) life preserver unit (LPU) on forward port side of middeck above potable water tank. Fullerton also adjusts lapbelt fitting and helmet holddown strap.

  13. Prey escaping wolves, Canis lupus, despite close proximity

    USGS Publications Warehouse

    Nelson, M.E.; Mech, L.D.

    1993-01-01

    We describe attacks by wolf (Canis lupus) packs in Minnesota on a white-tailed deer (Odocoileus virginianus) and a moose (Alces alces) in which wolves were within contact distance of the prey but in which the prey escaped.

  14. Dissociated neural effects of cortisol depending on threat escapability.

    PubMed

    Montoya, Estrella R; van Honk, Jack; Bos, Peter A; Terburg, David

    2015-11-01

    Evolution has provided us with a highly flexible neuroendocrine threat system which, depending on threat imminence, switches between active escape and passive freezing. Cortisol, the "stress-hormone", is thought to play an important role in both fear behaviors, but the exact mechanisms are not understood. Using pharmacological functional magnetic resonance imaging we investigated how cortisol modulates the brain's fear systems when humans are under virtual-predator attack. We show dissociated neural effects of cortisol depending on whether escape from threat is possible. During inescapable threat cortisol reduces fear-related midbrain activity, whereas in anticipation of active escape cortisol boosts activity in the frontal salience network (insula and anterior cingulate cortex), which is involved in autonomic control, visceral perception and motivated action. Our findings suggest that cortisol adjusts the human neural threat system from passive fear to active escape, which illuminates the hormone's crucial role in the adaptive flexibility of fear behaviors.

  15. Experimental Analysis and Extinction of Self-Injurious Escape Behavior.

    ERIC Educational Resources Information Center

    Iwata, Brian A.; And Others

    1990-01-01

    Three studies investigated environmental correlates of self-injurious behavior in seven developmentally disabled children and adolescents which were then later used for treatment. Correlates investigated included positive reinforcement, negative reinforcement, automatic reinforcement, and control. "Escape extinction" was successfully…

  16. 39. VIEW OF HORSE AND ESCAPE STEPS ON ARIZONA CANAL, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    39. VIEW OF HORSE AND ESCAPE STEPS ON ARIZONA CANAL, LOOKING NORTH ON THE SALT RIVER INDIAN RESERVATION Photographer: James Eastwood, June 1990 - Arizona Canal, North of Salt River, Phoenix, Maricopa County, AZ

  17. 14. View inside Building 802, the "Escape Hatch" at the ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    14. View inside Building 802, the "Escape Hatch" at the rear of the "Sleeping Quarters", facing south. - Naval Air Station Fallon, 100-man Fallout Shelter, 800 Complex, off Carson Road near intersection of Pasture & Berney Roads, Fallon, Churchill County, NV

  18. Electron yields and escape depths from spacecraft materials

    SciTech Connect

    Yang, K.Y.

    1986-01-01

    Secondary electron emission (SEE) characteristics and photoelectron yields were determined for several insulating materials used onboard a space shuttle. These materials are: kapton, teflon, spaceshuttle tiles, and space suit cloth. Secondary electron escape depth and photoelectron escape depth from kapton were calculated from the experimental data. Sternglass' theory and Dionne's method were used in the calculation. Some semi-empirical theories of SEE and three-step theory of photoemission were reviewed. Pulsed beam techniques were used to reduce surface charging problems. Three ..mu..sec pulses of electrons were used in SEE experiments, and 100 msec to 1 sec pulses were used in photoemission experiments. The maximum SEE yields of the materials studied range from 1.75 ro 2.70. The secondary electron escape depth in kapton was calculated to be 55 +/- 5 A. All samples have photoyields lower than 1.0%. The photoelectrons excited by 21-eV photons have 87 +/- 30 A escape depth in kapton.

  19. 46 CFR 116.500 - Means of escape.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... wearing life jackets. There must be no protrusions in means of escape that could cause injury, ensnare clothing, or damage life jackets. (f) The minimum clear opening of a door or passageway used as a means of...

  20. Survey of space escape/rescue/survivability capabilities.

    NASA Technical Reports Server (NTRS)

    Fleisig, R.; Bolger, P. H.; Heath, G. W.

    1971-01-01

    Discussion of preventive or remedial systems to achieve safer space flight operations. Escape, rescue, and survival systems are defined by categories: on board, prepositioned aid, and earth-launched concepts. The survey considers separable escape or survival capsules; standby escape or rescue systems; and earth-launched manned and unmanned rescue systems. Reports covering such systems are listed, and the contents are classified as to scope of investigation, space mission, and design approach. Mission classes considered are earth orbit, lunar, and interplanetary. Results of the space escape, rescue, and survivability investigations are summarized in terms of system features and performance, including apparent voids or limitations in rescue capability. Recovery requirements and resources for space rescue are discussed.

  1. Critical escape velocity of black holes from branes

    SciTech Connect

    Flachi, Antonino; Sasaki, Misao; Pujolas, Oriol; Tanaka, Takahiro

    2006-08-15

    In recent work we have shown that a black hole stacked on a brane escapes once it acquires a recoil velocity. This result was obtained in the probe-brane approximation, i.e., when the tension of the brane is negligibly small. Therefore, it is not clear whether the effect of the brane tension may prevent the black hole from escaping for small recoil velocities. The question is whether a critical escape velocity exists. Here, we analyze this problem by studying the interaction between a Dirac-Nambu-Goto brane and a black hole assuming adiabatic (quasistatic) evolution. By describing the brane in a fixed black hole spacetime, which restricts our conclusions to lowest order effects in the tension, we find that the critical escape velocity does not exist for codimension one branes, while it does for higher codimension branes.

  2. Carbon neutral hydrocarbons.

    PubMed

    Zeman, Frank S; Keith, David W

    2008-11-13

    Reducing greenhouse gas emissions from the transportation sector may be the most difficult aspect of climate change mitigation. We suggest that carbon neutral hydrocarbons (CNHCs) offer an alternative pathway for deep emission cuts that complement the use of decarbonized energy carriers. Such fuels are synthesized from atmospheric carbon dioxide (CO2) and carbon neutral hydrogen. The result is a liquid fuel compatible with the existing transportation infrastructure and therefore capable of a gradual deployment with minimum supply disruption. Capturing the atmospheric CO2 can be accomplished using biomass or industrial methods referred to as air capture. The viability of biomass fuels is strongly dependent on the environmental impacts of biomass production. Strong constraints on land use may favour the use of air capture. We conclude that CNHCs may be a viable alternative to hydrogen or conventional biofuels and warrant a comparable level of research effort and support.

  3. Heterosis or Neutrality?

    PubMed Central

    Watterson, G. A.

    1977-01-01

    Various statistics have been proposed on an ad hoc basis to test whether alleles at a locus are selectively neutral. By considering population models in which selection operates, this paper shows that the population homozygosity is a powerful test statistic for testing departures from neutrality, in the direction of heterozygote advantage or disadvantage. The sample homozygosity plays a similar role when only sample data are available. Some numerical examples are included, showing the application of the test.—An analysis is made of the effect of heterosis on such quantities as the expected number of alleles in the population or sample, the effective number of alleles, the expected homozygosity, and on the population and sample allele frequency distributions generally. PMID:863245

  4. Pioneer Venus Orbiter (PVO) Ionosphere Evidence for Atmospheric Escape

    NASA Astrophysics Data System (ADS)

    Grebowsky, J. M.; Hoegy, W. R.

    2009-12-01

    An early estimate of escape of H2O from Venus [McElroy et al., 1982] using observed hot oxygen densities inferred by Nagy et al. [1981] from PVO OUVS 1304 Å dayglow and using ionization rates from photoionization and electron impact. This resulted in an estimated oxygen ionization rate planet-wide above the plasmapause of 3x1025 atoms/s. Based on the energetic O+ being swept up and removed by solar wind, McElroy et al. [1982] gave an estimate of a loss rate for O of 6x106 atoms/cm2/s. Using a different method of estimating escape based data in the ionotail of Venus, Brace et al. [1987] estimated a total planetary O+ escape rate of 5x1025 ions/s. Their estimate was based on PVO measurements of superthermal O+ (energy range 9-16 eV) in the tail ray plasma between 2000 and 3000 km. Their estimated global mean flux was 107 atoms/cm2/s. The two escape rates are remarkably close considering all the errors involved in such estimates of escape. A study of escape by Luhmann et al. [2008] using VEX observations at low solar activity finds modest escape rates, prompting the authors to reconsider the evidence from both PVO and VEX of the possibility of enhanced escape during extreme interplanetary conditions. We reexamine the variation of escape under different solar wind conditions using ion densities and plasma content in the dayside and nightside of Venus using PVO ionosphere density during times of high solar activity. Citations: Brace, L.H., W. T. Kasprzak, H.A. Taylor, R. F. Theis, C. T. Russess, A. Barnes, J. D. Mihalov, and D. M. Hunten, "The Ionotail of Venus: Its Configuration and Evidence for Ion Escape", J. Geophys. Res. 92, 15-26, 1987. Luhmann, J.G., A. Fedorov, S. Barabash, E. Carlsson, Y. Futaana, T.L. Zhang, C.T. Russell, J.G. Lyon, S.A. Ledvina, and D.A. Brain, “Venus Express observations of atmospheric oxygen escape during the passage of several coronal mass ejections”, J. Geophys. Res., 113, 2008. McElroy, M. B., M. J. Prather, J. M. Rodiquez, " Loss

  5. Neutral atom traps.

    SciTech Connect

    Pack, Michael Vern

    2008-12-01

    This report describes progress in designing a neutral atom trap capable of trapping sub millikelvin atom in a magnetic trap and shuttling the atoms across the atom chip from a collection area to an optical cavity. The numerical simulation and atom chip design are discussed. Also, discussed are preliminary calculations of quantum noise sources in Kerr nonlinear optics measurements based on electromagnetically induced transparency. These types of measurements may be important for quantum nondemolition measurements at the few photon limit.

  6. Antihypertensive neutral lipid

    DOEpatents

    Snyder, Fred L.; Blank, Merle L.

    1986-01-01

    The invention relates to the discovery of a class of neutral acetylated ether-linked glycerolipids having the capacity to lower blood pressure in warm-blooded animals. This physiological effect is structure sensitive requiring a long chain alkyl group at the sn-1 position and a short carbon chain acyl group (acetyl or propionyl) at the sn-2 position, and a hydroxyl group at the sn-3 position.

  7. Antihypertensive neutral lipid

    DOEpatents

    Snyder, F.L.; Blank, M.L.

    1984-10-26

    The invention relates to the discovery of a class of neutral acetylated either-linked glycerolipids having the capacity to lower blood presure in warm-blooded animals. This physiological effect is structure sensitive requiring a long chain alkyl group at the sn-1 position and a short carbon chain acyl group (acetyl or propionyl) at the sn-2 position, and a hydroxyl group at the sn-3 position.

  8. Exercise Equipment: Neutral Buoyancy

    NASA Technical Reports Server (NTRS)

    Shackelford, Linda; Valle, Paul

    2016-01-01

    Load Bearing Equipment for Neutral Buoyancy (LBE-NB) is an exercise frame that holds two exercising subjects in position as they apply counter forces to each other for lower extremity and spine loading resistance exercises. Resistance exercise prevents bone loss on ISS, but the ISS equipment is too massive for use in exploration craft. Integrating the human into the load directing, load generating, and motion control functions of the exercise equipment generates safe exercise loads with less equipment mass and volume.

  9. Neutral Buoyancy Simulator Test

    NASA Technical Reports Server (NTRS)

    1995-01-01

    A diver tests a secondary camera and maneuvering platform in Marshall's Neutral Buoyancy Simulator (NBS).The secondary camera will be beneficial for recording repairs and other extra vehicular activities (EVA) the astronuats will perform while making repairs on the Hubble Space Telescope (HST). The maneuvering platform was developed to give the astronauts something to stand on while performing maintenance tasks. These platforms were developed to be mobile so that the astronauts could move them to accommadate different sites.

  10. Neutral particle beam intensity controller

    DOEpatents

    Dagenhart, William K.

    1986-01-01

    A neutral beam intensity controller is provided for a neutral beam generator in which a neutral beam is established by accelerating ions from an ion source into a gas neutralizer. An amplitude modulated, rotating magnetic field is applied to the accelerated ion beam in the gas neutralizer to defocus the resultant neutral beam in a controlled manner to achieve intensity control of the neutral beam along the beam axis at constant beam energy. The rotating magnetic field alters the orbits of ions in the gas neutralizer before they are neutralized, thereby controlling the fraction of neutral particles transmitted out of the neutralizer along the central beam axis to a fusion device or the like. The altered path or defocused neutral particles are sprayed onto an actively cooled beam dump disposed perpendicular to the neutral beam axis and having a central open for passage of the focused beam at the central axis of the beamline. Virtually zero therough 100% intensity control is achieved by varying the magnetic field strength without altering the ion source beam intensity or its species yield.

  11. Photoelectron escape fluxes over the equatorial and midlatitude regions

    NASA Technical Reports Server (NTRS)

    Narasingarao, B. C.; Singh, R. N.; Maier, E. J.

    1972-01-01

    Satellite measurements of photoelectron escape flux around noontime made by Explorer 31 in 600-800 km altitude range are reported for the equatorial and midlatitude regions. The pitch angle distributions and the spectral distributions are derived from the data. Analyzed data show that the flux for equatorial regions is lower by a factor 2 to 3 in comparison to that of midlatitude regions. Theoretical calculations are also made to compare with observed escape fluxes.

  12. GREEN PEA GALAXIES REVEAL SECRETS OF Lyα ESCAPE

    SciTech Connect

    Yang, Huan; Wang, Junxian; Malhotra, Sangeeta; Rhoads, James E.; Gronke, Max; Dijkstra, Mark; Jaskot, Anne; Zheng, Zhenya E-mail: huan.y@asu.edu E-mail: James.Rhoads@asu.edu

    2016-04-01

    We analyze archival Lyα spectra of 12 “Green Pea” galaxies observed with the Hubble Space Telescope, model their Lyα profiles with radiative transfer models, and explore the dependence of the Lyα escape fraction on various properties. Green Pea galaxies are nearby compact starburst galaxies with [O iii] λ5007 equivalent widths (EWs) of hundreds of Å. All 12 Green Pea galaxies in our sample show Lyα lines in emission, with an Lyα EW distribution similar to high-redshift Lyα emitters. Combining the optical and UV spectra of Green Pea galaxies, we estimate their Lyα escape fractions and find correlations between Lyα escape fraction and kinematic features of Lyα profiles. The escape fraction of Lyα in these galaxies ranges from 1.4% to 67%. We also find that the Lyα escape fraction depends strongly on metallicity and moderately on dust extinction. We compare their high-quality Lyα profiles with single H i shell radiative transfer models and find that the Lyα escape fraction anticorrelates with the derived H i column densities. Single-shell models fit most Lyα profiles well, but not the ones with the highest escape fractions of Lyα. Our results suggest that low H i column density and low metallicity are essential for Lyα escape and make a galaxy an Lyα emitter.

  13. Ion escape from Venus using statistical distribution functions

    NASA Astrophysics Data System (ADS)

    Nordstrom, T.; Stenberg, G.; Nilsson, H.; Barabash, S.; Futaana, Y.

    2012-04-01

    We use more than three years of data from the ASPERA-4 instrument onboard Venus Express to compile statistical distribution functions of ion flux in and around induced magnetosphere of Venus. We present samples of statistical distribution functions, as well average flux patterns in the near Venus space based on the statistical distribution functions. The statistical distribution functions allows for a compensation of biased sampling regarding both position and angular coverage of the instrument. Protons and heavy ions (mass/charge > 16) are the major ion species escaping from Venus. The escape is due to acceleration of planetary ions by energy transfer from the solar wind. The ion escape appears to exclusively take place in the induced magnetotail region and no heavy ions are present in the magnetosheath. Protons of solar wind origin are travelling around the planet and penetrating the tail, resulting in a mix of planetary and solar wind protons inside the induced magnetosphere boundary. The escape rates of ions inside the tail agree with results from recent published studies, where other analysis methods have been used. We also compare our results for Venus with a recent study of ion escape from Mars, where the same analysis method has been applied to data from the ASPERA-3 instrument on Mars Express. Both Mars and Venus are unmagnetized planets and are expected to interact similarly with the solar wind. On Mars the heavy ions are seen escaping in both the magnetosheath and tail regions as opposed to Venus where escape only takes place inside the tail. A possible explanation is that the magnetosphere of Mars is smaller compared to the ion gyroradius, making it easier for the ions to pass through the induced magnetosphere boundary. On both planets the escape rates of heavy ions in the tail are constant with increasing tail distance, verifying that the ions are leaving the planet in this region.

  14. Link between intraphagosomal biotin and rapid phagosomal escape in Francisella

    PubMed Central

    Napier, Brooke A.; Meyer, Lena; Bina, James E.; Miller, Mark A.; Sjöstedt, Anders; Weiss, David S.

    2012-01-01

    Cytosolic bacterial pathogens require extensive metabolic adaptations within the host to replicate intracellularly and cause disease. In phagocytic cells such as macrophages, these pathogens must respond rapidly to nutrient limitation within the harsh environment of the phagosome. Many cytosolic pathogens escape the phagosome quickly (15–60 min) and thereby subvert this host defense, reaching the cytosol where they can replicate. Although a great deal of research has focused on strategies used by bacteria to resist antimicrobial phagosomal defenses and transiently pass through this compartment, the metabolic requirements of bacteria in the phagosome are largely uncharacterized. We previously identified a Francisella protein, FTN_0818, as being essential for intracellular replication and involved in virulence in vivo. We now show that FTN_0818 is involved in biotin biosynthesis and required for rapid escape from the Francisella-containing phagosome (FCP). Addition of biotin complemented the phagosomal escape defect of the FTN_0818 mutant, demonstrating that biotin is critical for promoting rapid escape during the short time that the bacteria are in the phagosome. Biotin also rescued the attenuation of the FTN_0818 mutant during infection in vitro and in vivo, highlighting the importance of this process. The key role of biotin in phagosomal escape implies biotin may be a limiting factor during infection. We demonstrate that a bacterial metabolite is required for phagosomal escape of an intracellular pathogen, providing insight into the link between bacterial metabolism and virulence, likely serving as a paradigm for other cytosolic pathogens. PMID:23071317

  15. Optimal escapement in stage-structured fisheries with environmental stochasticity.

    PubMed

    Holden, Matthew H; Conrad, Jon M

    2015-11-01

    Stage-structured population models are commonly used to understand fish population dynamics and additionally for stock assessment. Unfortunately, there is little theory on the optimal harvest of stage-structured populations, especially in the presence of stochastic fluctuations. In this paper, we find closed form optimal equilibrium escapement policies for a three-dimensional, discrete-time, stage-structured population model with linear growth, post-harvest nonlinear recruitment, and stage-specific pricing and extend the analytic results to structured populations with environmental stochasticity. When only fishing reproductive adults, stochasticity does not affect optimal escapement policies. However, when harvesting immature fish, the addition of stochasticity can increase or decrease optimal escapement depending on the second and third derivative of the recruitment function. For logistic recruitment, stochasticity reduces optimal immature escapement by a multiplicative factor of one over one plus the variance of the environmental noise. Using hard clam, Mercenaria mercenaria, as an example and assuming Beverton-Holt recruitment, we show that optimal fishing of hard clam targets the immature stage class exclusively and that environmental stochasticity increases optimal escapement for low discount rates and decreases optimal escapement for high discount rates. Copyright © 2015 Elsevier Inc. All rights reserved.

  16. Extreme hydrodynamic atmospheric loss near the critical thermal escape regime

    NASA Astrophysics Data System (ADS)

    Erkaev, N. V.; Lammer, H.; Odert, P.; Kulikov, Yu. N.; Kislyakova, K. G.

    2015-04-01

    By considering martian-like planetary embryos inside the habitable zone of solar-like stars we study the behaviour of the hydrodynamic atmospheric escape of hydrogen for small values of the Jeans escape parameter β < 3, near the base of the thermosphere, that is defined as a ratio of the gravitational and thermal energy. Our study is based on a 1D hydrodynamic upper atmosphere model that calculates the volume heating rate in a hydrogen-dominated thermosphere due to the absorption of the stellar soft X-ray and extreme ultraviolet (XUV) flux. In case of a monatomic gas, we find that when the β value near the mesopause/homopause level exceeds a critical value of ˜2.5, there exists a steady hydrodynamic solution with a smooth transition from subsonic to supersonic flow. For a fixed XUV flux, the escape rate of the upper atmosphere is an increasing function of the temperature at the lower boundary. Our model results indicate a crucial enhancement of the atmospheric escape rate, when the Jeans escape parameter β decreases to this critical value. When β becomes ≤2.5, there is no stationary hydrodynamic transition from subsonic to supersonic flow. This is the case of a fast non-stationary atmospheric expansion that results in extreme thermal atmospheric escape rates.

  17. Foraging behavior delays mechanically-stimulated escape responses in fish.

    PubMed

    Bohórquez-Herrera, Jimena; Kawano, Sandy M; Domenici, Paolo

    2013-11-01

    Foraging and the evasion of predators are fundamental for the survival of organisms, but they impose contrasting demands that can influence performance in each behavior. Previous studies suggested that foraging organisms may experience decreased vigilance to attacks by predators; however, little is known about the effect of foraging on escape performance with respect to the kinematics and the timing of the response. This study tested the hypothesis that engaging in foraging activities affected escape performance by comparing fast-start escape responses of silver-spotted sculpins Blepsias cirrhosus under three conditions: (1) control (no foraging involved), (2) while targeting prey, and (3) immediately after capture of prey. Escape response variables (non-locomotor and locomotor) were analyzed from high-speed videos. Responsiveness was lower immediately after capturing a prey item compared with the other two treatments, and latency of performance was higher in the control treatment than in the other two. Locomotor variables such as maximum speed, maximum acceleration, and turning rates did not show statistical differences among the three groups. Our results demonstrate that foraging can negatively affect two fundamental components of the escape response: (1) responsiveness and (2) latency of escape, suggesting that engaging in foraging may decrease an individual's ability to successfully evade predators.

  18. Group chase and escape with sight-limited chasers

    NASA Astrophysics Data System (ADS)

    Wang, Huodong; Han, Wenchen; Yang, Junzhong

    2017-01-01

    We study group chase and escape with sight-limited chasers. Two search strategies, random-walk-strategy and relocation-strategy, are introduced for chasers when escapers are out of their fields of vision. There exist two regimes for the group lifetime of escapers. In the narrow sight regime, the group lifetime is a decreasing function of chasers' sight range. In the wide sight regime, the group lifetime stays at a constant when chasers adopting random-walk-strategy while increases with the sight range when chasers adopting relocation-strategy. The impacts of the two search strategies on group chase and escape are studied by investigating the lifetime distribution of all escapers and the dependence of the minimum lifetime on the number of chasers. We also find that, to reach the most efficient and the lowest energy cost chase for chasers, the ratio between the number of chasers and escapers stays at around 6 under random-walk-strategy. However, the optimal number of chasers vanishes and the energy cost monotonically increases with increasing the number of chasers under relocation-strategy.

  19. Dementia and driving

    MedlinePlus

    ... medlineplus.gov/ency/patientinstructions/000028.htm Dementia and driving To use the sharing features on this page, ... their independence is being taken away. Signs That Driving May No Longer be Safe People with signs ...

  20. Ocular disease and driving.

    PubMed

    Wood, Joanne M; Black, Alex A

    2016-09-01

    As the driving population ages, the number of drivers with visual impairment resulting from ocular disease will increase given the age-related prevalence of ocular disease. The increase in visual impairment in the driving population has a number of implications for driving outcomes. This review summarises current research regarding the impact of common ocular diseases on driving ability and safety, with particular focus on cataract, glaucoma, age-related macular degeneration, hemianopia and diabetic retinopathy. The evidence considered includes self-reported driving outcomes, driving performance (on-road and simulator-based) and various motor vehicle crash indices. Collectively, this review demonstrates that driving ability and safety are negatively affected by ocular disease; however, further research is needed in this area. Older drivers with ocular disease need to be aware of the negative consequences of their ocular condition and in the case where treatment options are available, encouraged to seek these earlier for optimum driving safety and quality of life benefits.

  1. Impaired Driving - Multiple Languages

    MedlinePlus

    ... Are Here: Home → Multiple Languages → All Health Topics → Impaired Driving URL of this page: https://medlineplus.gov/languages/ ... V W XYZ List of All Topics All Impaired Driving - Multiple Languages To use the sharing features on ...

  2. Glutamate Utilization Couples Oxidative Stress Defense and the Tricarboxylic Acid Cycle in Francisella Phagosomal Escape

    PubMed Central

    Ramond, Elodie; Gesbert, Gael; Rigard, Mélanie; Dairou, Julien; Dupuis, Marion; Dubail, Iharilalao; Meibom, Karin; Henry, Thomas; Barel, Monique; Charbit, Alain

    2014-01-01

    Intracellular bacterial pathogens have developed a variety of strategies to avoid degradation by the host innate immune defense mechanisms triggered upon phagocytocis. Upon infection of mammalian host cells, the intracellular pathogen Francisella replicates exclusively in the cytosolic compartment. Hence, its ability to escape rapidly from the phagosomal compartment is critical for its pathogenicity. Here, we show for the first time that a glutamate transporter of Francisella (here designated GadC) is critical for oxidative stress defense in the phagosome, thus impairing intra-macrophage multiplication and virulence in the mouse model. The gadC mutant failed to efficiently neutralize the production of reactive oxygen species. Remarkably, virulence of the gadC mutant was partially restored in mice defective in NADPH oxidase activity. The data presented highlight links between glutamate uptake, oxidative stress defense, the tricarboxylic acid cycle and phagosomal escape. This is the first report establishing the role of an amino acid transporter in the early stage of the Francisella intracellular lifecycle. PMID:24453979

  3. Neutral particle beam intensity controller

    DOEpatents

    Dagenhart, W.K.

    1984-05-29

    The neutral beam intensity controller is based on selected magnetic defocusing of the ion beam prior to neutralization. The defocused portion of the beam is dumped onto a beam dump disposed perpendicular to the beam axis. Selective defocusing is accomplished by means of a magnetic field generator disposed about the neutralizer so that the field is transverse to the beam axis. The magnetic field intensity is varied to provide the selected partial beam defocusing of the ions prior to neutralization. The desired focused neutral beam portion passes along the beam path through a defining aperture in the beam dump, thereby controlling the desired fraction of neutral particles transmitted to a utilization device without altering the kinetic energy level of the desired neutral particle fraction. By proper selection of the magnetic field intensity, virtually zero through 100% intensity control of the neutral beam is achieved.

  4. Gear bearing drive

    NASA Technical Reports Server (NTRS)

    Weinberg, Brian (Inventor); Mavroidis, Constantinos (Inventor); Vranish, John M. (Inventor)

    2011-01-01

    A gear bearing drive provides a compact mechanism that operates as an actuator providing torque and as a joint providing support. The drive includes a gear arrangement integrating an external rotor DC motor within a sun gear. Locking surfaces maintain the components of the drive in alignment and provide support for axial loads and moments. The gear bearing drive has a variety of applications, including as a joint in robotic arms and prosthetic limbs.

  5. Does a threat appeal moderate reckless driving? A terror management theory perspective.

    PubMed

    Ben-Ari, O T; Florian, V; Mikulincer, M

    2000-01-01

    A series of two studies examined the effects of threat appeals on reckless driving from a terror management theory perspective. In both studies, all the participants (N = 109) reported on the relevance of driving to their self-esteem, and, then, half of them were exposed to a road trauma film and the remaining to a neutral film. In Study 1, the dependent variable was the self-report of intentions to drive recklessly in hypothetical scenarios. In Study 2, the dependent variable was actual behavior (driving speed) in a driving simulator. Findings indicated that a road trauma film led to less reported intentions of reckless driving, but to higher driving speed than a neutral film. These effects were only found among participants who perceived driving as relevant to their self-esteem. The discussion emphasized the self-enhancing mechanisms proposed by the terror management theory.

  6. Trade-offs between performance and variability in the escape responses of bluegill sunfish (Lepomis macrochirus)

    PubMed Central

    Hitchcock, Amanda C.; Chen, Tiffany; Connolly, Erin; Darakananda, Karin; Jeong, Janet; Quist, Arbor; Robbins, Allison; Ellerby, David J.

    2015-01-01

    Successful predator evasion is essential to the fitness of many animals. Variation in escape behaviour may be adaptive as it reduces predictability, enhancing escape success. High escape velocities and accelerations also increase escape success, but biomechanical factors likely constrain the behavioural range over which performance can be maximized. There may therefore be a trade-off between variation and performance during escape responses. We have used bluegill sunfish (Lepomis macrochirus) escape responses to examine this potential trade-off, determining the full repertoire of escape behaviour for individual bluegill sunfish and linking this to performance as indicated by escape velocity and acceleration. Fish escapes involve an initial C-bend of the body axis, followed by variable steering movements. These generate thrust and establish the escape direction. Directional changes during the initial C-bend were less variable than the final escape angle, and the most frequent directions were associated with high escape velocity. Significant inter-individual differences in escape angles magnified the overall variation, maintaining unpredictability from a predator perspective. Steering in the latter stages of the escape to establish the final escape trajectory also affected performance, with turns away from the stimulus associated with reduced velocity. This suggests that modulation of escape behaviour by steering may also have an associated performance cost. This has important implications for understanding the scope and control of intra- and inter-individual variation in escape behaviour and the associated costs and benefits. PMID:25910940

  7. Effects of convincing power and neutrality on minority opinion spreading

    NASA Astrophysics Data System (ADS)

    Wu, Yue; Xiong, Xi; Zhang, Yi

    2017-02-01

    The dynamics evolution of the minority opinion in public debates is studied using a convincing power (CP) model with neutrality. In a given group, an agent with a definite standpoint (yes or no) can be persuaded to be a neutral agent, if its capacity of persuasion is lower than the average CP of its opponents. Besides that a neutral agent will change its state and follow a more persuasive opinion. Starting from two opposite opinions with different rates, repeated local discussions are found to drive the minority reversal. It reveals that in addition to the initial minority, the number of neutral agents is also an important factor to the eventual winners. During the process of consensus, there exists a threshold of initial fraction to guarantee one side win. The results have a guiding significance for designing strategies to win a public debate.

  8. Imaging of magnetospheric dynamics using low energy neutral atom detection

    SciTech Connect

    Funsten, H.O.; McComas, D.J.; Moore, K.R.; Scime, E.E.

    1993-05-01

    Recent advances in low energy neutral atom (LENA) detection technology show that magnetospheric imaging is achievable with 4{sub o}{times}4{sub o} resolution and can distinguish numerous features of the magnetosphere. A critical factor in detecting low energy neutrals is their removal from the ambient UV background. One technique to accomplish this is by ionizing the neutrals by their transmission through an untrathin charge modification foil and subsequent electrostatic deflection. In this type of instrument, the driving factor for resolution and sensitivity is scattering in the foil and the ionization probability of transiting neutrals. We describe results of a prototype LENA imager using a collimated beam of 10 key H. Additionally, we illustrate model results of anticipated LENA images of the magnetosphere based on the Rice Convection Model and show that plasma variations resulting from geomagnetic storm disturbances can be observed using a LENA imager.

  9. Imaging of magnetospheric dynamics using low energy neutral atom detection

    SciTech Connect

    Funsten, H.O.; McComas, D.J.; Moore, K.R.; Scime, E.E.

    1993-01-01

    Recent advances in low energy neutral atom (LENA) detection technology show that magnetospheric imaging is achievable with 4[sub o][times]4[sub o] resolution and can distinguish numerous features of the magnetosphere. A critical factor in detecting low energy neutrals is their removal from the ambient UV background. One technique to accomplish this is by ionizing the neutrals by their transmission through an untrathin charge modification foil and subsequent electrostatic deflection. In this type of instrument, the driving factor for resolution and sensitivity is scattering in the foil and the ionization probability of transiting neutrals. We describe results of a prototype LENA imager using a collimated beam of 10 key H. Additionally, we illustrate model results of anticipated LENA images of the magnetosphere based on the Rice Convection Model and show that plasma variations resulting from geomagnetic storm disturbances can be observed using a LENA imager.

  10. Grieving while Driving

    ERIC Educational Resources Information Center

    Rosenblatt, Paul C.

    2004-01-01

    Secondary analysis of data from 84 people in 2 interview studies shows that some bereaved people grieve actively while driving. The grief can be intense, even years after a death. Grief while driving may erupt spontaneously or be set off by a wide range of reminders. Some bereaved people seem to save their grieving for times when they drive,…

  11. Sequential Dependencies in Driving

    ERIC Educational Resources Information Center

    Doshi, Anup; Tran, Cuong; Wilder, Matthew H.; Mozer, Michael C.; Trivedi, Mohan M.

    2012-01-01

    The effect of recent experience on current behavior has been studied extensively in simple laboratory tasks. We explore the nature of sequential effects in the more naturalistic setting of automobile driving. Driving is a safety-critical task in which delayed response times may have severe consequences. Using a realistic driving simulator, we find…

  12. Sequential Dependencies in Driving

    ERIC Educational Resources Information Center

    Doshi, Anup; Tran, Cuong; Wilder, Matthew H.; Mozer, Michael C.; Trivedi, Mohan M.

    2012-01-01

    The effect of recent experience on current behavior has been studied extensively in simple laboratory tasks. We explore the nature of sequential effects in the more naturalistic setting of automobile driving. Driving is a safety-critical task in which delayed response times may have severe consequences. Using a realistic driving simulator, we find…

  13. Magnetic drive coupling

    NASA Technical Reports Server (NTRS)

    Carter, Edward L. (Inventor)

    1987-01-01

    The driving and driven members of a magnetic drive are separated by en enlarged gap to provide clearance for a conduit or other member. Flux pins in the gap maintain the torque transmitting capability of the drive. The spacing between two of the flux pins is increased to provide space for the conduit.

  14. Atmospheric Escape and Climate Evolution of Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Tian, F.; Chassefière, E.; Leblanc, F.; Brain, D.

    The climate of a planet is primarily determined by its orbital distance from its star, the luminosity of the star, the existence of oceans, the pressure of its atmosphere, and the composition of its atmosphere. The last two components are what could be impacted by atmosphere escape. The Sun, as the dominant energy source driving the climate of terrestrial planets, was not always as bright as it is today. Stellar evolution theory predicts that the luminosity of the young Sun was 75% of its present luminosity, at approximately 4 b.y. ago (4 Ga) (Gough, 1981). Although the Sun could have lost some of its mass, thus making the very young Sun somewhat more massive than it is now and therefore could have emitted more energy, most of this mass loss was completed prior to 4 Ga (Wood et al., 2005). Thus the Sun has provided increasingly more energy to solar system planets during the past 4 b.y. Contrary to the evolutionary trend of the total luminosity increasing with time, the young Sun should have emitted much stronger EUV, soft X-ray, and far-UV photons than at present. These photons are from the upper atmosphere of the Sun and are linked to solar magnetic activity. Generally speaking, a young star rotates much faster and thus has stronger magnetic activity. Observations of solar-type stars with different ages show that the EUV energy flux from a 0.5-b.y.-old solar-type star could be as much as 20 times that of the present Sun (Ribas et al., 2005). Accompanying this much-enhanced solar extreme ultraviolet (XUV) radiation is a much stronger solar wind, with mass flux up to 1000 times more intense than the present solar wind flux (Wood et al., 2005). It can be expected that many more energetic-particle events were caused by the young Sun. The fate of the atmospheres of terrestrial planets in such an environment and the consequences for their climates are the focus of this chapter.

  15. Neutrality between Government and Religion.

    ERIC Educational Resources Information Center

    Mawdsley, Ralph D.

    1996-01-01

    The overall guiding principle of neutrality between government and religion masks a tension that exists between free exercise of religion and establishment of religion. Reviews the development and current status of "Lemon" as a test for neutrality; proposes a new test for neutrality, evenhandedness, that is common to both the Free…

  16. Neutrality between Government and Religion.

    ERIC Educational Resources Information Center

    Mawdsley, Ralph D.

    1996-01-01

    The overall guiding principle of neutrality between government and religion masks a tension that exists between free exercise of religion and establishment of religion. Reviews the development and current status of "Lemon" as a test for neutrality; proposes a new test for neutrality, evenhandedness, that is common to both the Free…

  17. Selectionism and Neutralism in Molecular Evolution

    PubMed Central

    Nei, Masatoshi

    2006-01-01

    Charles Darwin proposed that evolution occurs primarily by natural selection, but this view has been controversial from the beginning. Two of the major opposing views have been mutationism and neutralism. Early molecular studies suggested that most amino acid substitutions in proteins are neutral or nearly neutral and the functional change of proteins occurs by a few key amino acid substitutions. This suggestion generated an intense controversy over selectionism and neutralism. This controversy is partially caused by Kimura's definition of neutrality, which was too strict (|2Ns| ≤ 1). If we define neutral mutations as the mutations that do not change the function of gene products appreciably, many controversies disappear because slightly deleterious and slightly advantageous mutations are engulfed by neutral mutations. The ratio of the rate of nonsynonymous nucleotide substitution to that of synonymous substitution is a useful quantity to study positive Darwinian selection operating at highly variable genetic loci, but it does not necessarily detect adaptively important codons. Previously, multigene families were thought to evolve following the model of concerted evolution, but new evidence indicates that most of them evolve by a birth-and-death process of duplicate genes. It is now clear that most phenotypic characters or genetic systems such as the adaptive immune system in vertebrates are controlled by the interaction of a number of multigene families, which are often evolutionarily related and are subject to birth-and-death evolution. Therefore, it is important to study the mechanisms of gene family interaction for understanding phenotypic evolution. Because gene duplication occurs more or less at random, phenotypic evolution contains some fortuitous elements, though the environmental factors also play an important role. The randomness of phenotypic evolution is qualitatively different from allele frequency changes by random genetic drift. However, there is

  18. Nitrogen and Oxygen Budget ExpLoration (NOBEL) for ESA M5-call: Measurement requirements to understand the atmospheric escape/budget

    NASA Astrophysics Data System (ADS)

    Yamauchi, Masatoshi; Dandouras, Iannis; Rème, Henri; Marghitu, Octav

    2016-04-01

    The NOBEL mission aims to study the thermal and non-thermal escape of major atmospheric components (nitrogen, oxygen, and their isotopes) from the Earth, a magnetized planet. This requires the first-time exploration of the Earth's entire exosphere as well as the first-time examination of isotope ratios in an extended altitude range from the upper ionosphere (800 km high) up to the magnetosphere. The measurement quality should allow connecting the various types of escape from the Earth to the different gravity mass-filtering and chemical reactions on a geological time scale, such that the result will be used as a good reference to understand the atmospheric/ionospheric evolution of magnetized planets based on their 17,18O/16O isotope ratio and N/O ratio. Since the solar EUV and solar wind conditions during solar maximum at present are comparable to the solar minimum conditions 1-2 billion years ago, the escaping amount and the isotope and N/O ratios should be obtained as a function of external forcing (solar and geomagnetic conditions) to allow a scaling to the past. To achieve these goals, the ion measurements in this mission should be able to separate nitrogen species (N, N2, N+ and N2+) from oxygen (O, O+), near the exobase, in the exosphere (for modelling thermal escape, hydrodynamics escape, and the pre-acceleration amount of non-thermal escape) and up in the magnetosphere (for modelling non-thermal escape and circulation of all ions). Furthermore, these aims require the capability to measure isotope ratios of cold oxygen ions and neutrals. We briefly discuss why we focus on the exosphere, on isotope ratios, and nitrogen measurements, and finally describe the current idea of a mission profile using a spinning satellite in a 500 km × 33000 km altitude high-inclination orbit.

  19. Dynamics of Ion Beam Charge Neutralization by Ferroelectric Plasma Sources

    NASA Astrophysics Data System (ADS)

    Stepanov, Anton D.; Gilson, Erik P.; Grisham, Larry R.; Kaganovich, Igor D.; Davidson, Ronald C.; Ji, Qing; Persaud, Arun; Seidl, Peter A.; Schenkel, Thomas

    2016-10-01

    Ferroelectric Plasma Sources (FEPSs) can generate plasma that provides effective space-charge neutralization of intense high-perveance ion beams. Here we present experimental results on charge neutralization of a high-perveance 38 keV Ar+ beam by a FEPS plasma. By comparing the measured beam radius with the envelope model for space-charge expansion, it is shown that a charge neutralization fraction of 98% is attainable. The transverse electrostatic potential of the ion beam is reduced from 15 V before neutralization to 0.3 V, implying that the energy of the neutralizing electrons is below 0.3 eV. Near-complete charge neutralization is established 5 μs after the driving pulse is applied to the FEPS, and can last for 35 μs. It is argued that the duration of neutralization is much longer than a reasonable lifetime of the plasma produced in the sub- μs surface discharge. Measurements of current flow in the driving circuit of the FEPS suggest that plasma can be generated for tens of μs after the high voltage pulse is applied. This is confirmed by fast photography of the plasma in the 1-meter long FEPS on NDCX-II, where effective charge neutralization of the beam was achieved with the optimized FEPS timing. This work was supported by the Office of Science of the US Department of Energy under contracts DE-AC0209CH11466 (PPPL) and DE-AC0205CH11231 (LBNL).

  20. A mechanism of hypoxia-mediated escape from adaptive immunity in cancer cells.

    PubMed

    Barsoum, Ivraym B; Smallwood, Chelsea A; Siemens, D Robert; Graham, Charles H

    2014-02-01

    Immune escape is a fundamental trait of cancer in which mechanistic knowledge is incomplete. Here, we describe a novel mechanism by which hypoxia contributes to tumoral immune escape from cytotoxic T lymphocytes (CTL). Exposure of human or murine cancer cells to hypoxia for 24 hours led to upregulation of the immune inhibitory molecule programmed cell death ligand-1 (PD-L1; also known as B7-H1), in a manner dependent on the transcription factor hypoxia-inducible factor-1α (HIF-1α). In vivo studies also demonstrated cellular colocalization of HIF-1α and PD-L1 in tumors. Hypoxia-induced expression of PD-L1 in cancer cells increased their resistance to CTL-mediated lysis. Using glyceryl trinitrate (GTN), an agonist of nitric oxide (NO) signaling known to block HIF-1α accumulation in hypoxic cells, we prevented hypoxia-induced PD-L1 expression and diminished resistance to CTL-mediated lysis. Moreover, transdermal administration of GTN attenuated tumor growth in mice. We found that higher expression of PD-L1 induced in tumor cells by exposure to hypoxia led to increased apoptosis of cocultured CTLs and Jurkat leukemia T cells. This increase in apoptosis was prevented by blocking the interaction of PD-L1 with PD-1, the PD-L1 receptor on T cells, or by addition of GTN. Our findings point to a role for hypoxia/HIF-1 in driving immune escape from CTL, and they suggest a novel cancer immunotherapy to block PD-L1 expression in hypoxic-tumor cells by administering NO mimetics.

  1. Syncope and Driving.

    PubMed

    Guzman, Juan C; Morillo, Carlos A

    2015-08-01

    The occurrence of syncope while driving has obvious implications for personal and public safety. Neurally mediated syncope is the most common type of syncope in general and, thereby, also while driving. The presence of structural heart disease (reduced ejection fraction, previous myocardial infarction, significant congenital heart disease) potentially leads to high risk and should determine driving restrictions pending clarification of underlying heart disease and etiology of syncope. The clinical approach to syncope evaluation and recommendations for driving should not differ, whether or not the syncopal spell occurred while driving.

  2. Ultracold neutral plasmas

    NASA Astrophysics Data System (ADS)

    Lyon, M.; Rolston, S. L.

    2017-01-01

    By photoionizing samples of laser-cooled atoms with laser light tuned just above the ionization limit, plasmas can be created with electron and ion temperatures below 10 K. These ultracold neutral plasmas have extended the temperature bounds of plasma physics by two orders of magnitude. Table-top experiments, using many of the tools from atomic physics, allow for the study of plasma phenomena in this new regime with independent control over the density and temperature of the plasma through the excitation process. Characteristic of these systems is an inhomogeneous density profile, inherited from the density distribution of the laser-cooled neutral atom sample. Most work has dealt with unconfined plasmas in vacuum, which expand outward at velocities of order 100 m/s, governed by electron pressure, and with lifetimes of order 100 μs, limited by stray electric fields. Using detection of charged particles and optical detection techniques, a wide variety of properties and phenomena have been observed, including expansion dynamics, collective excitations in both the electrons and ions, and collisional properties. Through three-body recombination collisions, the plasmas rapidly form Rydberg atoms, and clouds of cold Rydberg atoms have been observed to spontaneously avalanche ionize to form plasmas. Of particular interest is the possibility of the formation of strongly coupled plasmas, where Coulomb forces dominate thermal motion and correlations become important. The strongest impediment to strong coupling is disorder-induced heating, a process in which Coulomb energy from an initially disordered sample is converted into thermal energy. This restricts electrons to a weakly coupled regime and leaves the ions barely within the strongly coupled regime. This review will give an overview of the field of ultracold neutral plasmas, from its inception in 1999 to current work, including efforts to increase strong coupling and effects on plasma properties due to strong coupling.

  3. Neutralization of acid waters

    SciTech Connect

    Simonin, H.A.

    1988-10-01

    In this article, the author reviews the positive and the negative aspects of liming and its practical application of the problem of acidic deposition. One primary concern is that liming does not mitigate many of the problems that result from acidic deposition. Although lake neutralization is a useful practice, it is not presented as a solution to the acid rain problem. Liming is a means of restoring or protecting a few systems affected by acidic deposition while legislators pass a fair and equitable program to control the source of the problem - excessive emission of sulfur dioxide and nitrogen oxides.

  4. Pulsed field sample neutralization

    DOEpatents

    Appelhans, Anthony D.; Dahl, David A.; Delmore, James E.

    1990-01-01

    An apparatus and method for alternating voltage and for varying the rate of extraction during the extraction of secondary particles, resulting in periods when either positive ions, or negative ions and electrons are extracted at varying rates. Using voltage with alternating charge during successive periods to extract particles from materials which accumulate charge opposite that being extracted causes accumulation of surface charge of opposite sign. Charge accumulation can then be adjusted to a ratio which maintains a balance of positive and negative charge emission, thus maintaining the charge neutrality of the sample.

  5. Neutral beam injection system

    SciTech Connect

    Duesing, G.; Altmann, H.; Falter, H.; Goede, A.; Haange, R.; Hemsworth, R.S.; Kupschus, P.; Stork, D.; Thompson, E.

    1987-01-01

    The development of the neutral injection (NI) system for the Joint European Torus and its status in 1985 are reported. First the system parameters are discussed and the layout is described, followed by a summary of the physics design calculations, the development, production, and testing of the components and the subsystem assembly. The system commissioning is presented, including a description of the function and the realization of the NI test bed. A summary of performance predictions for 80-keV beam heating experiments, and of the experimental evidence on balanced versus coinjection, is presented. The operational experience with the first injector and the plasma physics results obtained so far are summarized.

  6. Oxygen or carbogen breathing before simulated submarine escape.

    PubMed

    Gennser, M; Blogg, S L

    2008-01-01

    Raised internal pressure in a distressed submarine increases the risk of bubble formation and decompression illness after submarine escape. The hypothesis that short periods of oxygen breathing before submarine escape would reduce decompression stress was tested, using Doppler-detectable venous gas emboli as a measure. Twelve goats breathed oxygen for 15 min at 0.1 MPa before exposure to a simulated submarine escape profile to and from 2.5 MPa (240 m/seawater), whereas 28 control animals underwent the same dive without oxygen prebreathe. No decompression sickness (DCS) occurred in either of these two groups. Time with high bubble scores (Kisman-Masurel >or=3) was significantly (P < 0.001) shorter in the prebreathe group. In a second series, 30 goats breathed air at 0.2 MPa for 6 h. Fifteen minutes before escape from 2.5 MPa, animals were provided with either air (n = 10), oxygen (n = 12), or carbogen (97.5% O(2) and 2.5% CO(2)) gas (n = 8) as breathing gas. Animals breathed a hyperoxic gas (60% O(2)-40% N(2)) during the escape. Two animals (carbogen group) suffered oxygen convulsions during the escape but recovered on surfacing. Only one case of DCS occurred (carbogen group). The initial bubble score was reduced in the oxygen group (P < 0.001). The period with bubble score of Kisman-Masurel >or=3 was also significantly reduced in the oxygen group (P < 0.001). Oxygen breathing before submarine escape reduces initial bubble scores, although its significance in reducing central nervous system DCS needs to be investigated further.

  7. Green Pea Galaxies Reveal Secrets of Lyα Escape

    NASA Astrophysics Data System (ADS)

    Yang, Huan; Malhotra, Sangeeta; Gronke, Max; Rhoads, James E.; Jaskot, Anne; Zheng, Zhenya; Dijkstra, Mark; Wang, JunXian

    2016-01-01

    In star-forming galaxies, a lot of Lyα photons were generated in HII regions surrounding massive stars. The escape of Lyα photons from galaxies is a key issue in studying high redshift galaxies and probing cosmic reionization with Lyα. To understand Lyα escape, it is valuable to study high quality Lyα profiles in Lyα emitters. However, such studies are rare due to the faintness of high-z Lyα emitters and the lack of local analogs with high Lyα equivalent width. Here we show that "Green Pea" galaxies are the best local analogs of high-z Lyα emitters and their high quality Lyα profiles demonstrate low HI column density is the key to Lyα escape. The Lyα escape fraction shows correlations with the ratio of Lyα blue peak velocity to Hα line width, the normalized flux density at valley of Lyα profile, and a few other features of Lyα profiles. We compared the Lyα profiles with outflowing HI shell radiative transfer model and found that the best-fit HI column density is anti-correlated with the Lyα escape fraction. We also found an anti-correlation between Lyα escape fraction and galactic metallicity. Our results support that LAEs with high Lyα escape fraction have low metallicity, low HI column density, and mild HI gas outflow.

  8. Reconfigurable Drive Current System

    NASA Technical Reports Server (NTRS)

    Alhorn, Dean C. (Inventor); Dutton, Kenneth R. (Inventor); Howard, David E. (Inventor); Smith, Dennis A. (Inventor)

    2017-01-01

    A reconfigurable drive current system includes drive stages, each of which includes a high-side transistor and a low-side transistor in a totem pole configuration. A current monitor is coupled to an output of each drive stage. Input channels are provided to receive input signals. A processor is coupled to the input channels and to each current monitor for generating at least one drive signal using at least one of the input signals and current measured by at least one of the current monitors. A pulse width modulation generator is coupled to the processor and each drive stage for varying the drive signals as a function of time prior to being supplied to at least one of the drive stages.

  9. Fin-tail coordination during escape and predatory behavior in larval zebrafish.

    PubMed

    McClenahan, Phil; Troup, Michael; Scott, Ethan K

    2012-01-01

    Larval zebrafish innately perform a suite of behaviors that are tightly linked to their evolutionary past, notably escape from threatening stimuli and pursuit and capture of prey. These behaviors have been carefully examined in the past, but mostly with regard to the movements of the trunk and tail of the larvae. Here, we employ kinematics analyses to describe the movements of the pectoral fins during escape and predatory behavior. In accord with previous studies, we find roles for the pectoral fins in slow swimming and immediately after striking prey. We find novel roles for the pectoral fins in long-latency, but not in short-latency C-bends. We also observe fin movements that occur during orienting J-turns and S-starts that drive high-velocity predatory strikes. Finally, we find that the use of pectoral fins following a predatory strike is scaled to the velocity of the strike, supporting a role for the fins in braking. The implications of these results for central control of coordinated movements are discussed, and we hope that these results will provide baselines for future analyses of cross-body coordination using mutants, morphants, and transgenic approaches.

  10. Fin-Tail Coordination during Escape and Predatory Behavior in Larval Zebrafish

    PubMed Central

    McClenahan, Phil; Troup, Michael; Scott, Ethan K.

    2012-01-01

    Larval zebrafish innately perform a suite of behaviors that are tightly linked to their evolutionary past, notably escape from threatening stimuli and pursuit and capture of prey. These behaviors have been carefully examined in the past, but mostly with regard to the movements of the trunk and tail of the larvae. Here, we employ kinematics analyses to describe the movements of the pectoral fins during escape and predatory behavior. In accord with previous studies, we find roles for the pectoral fins in slow swimming and immediately after striking prey. We find novel roles for the pectoral fins in long-latency, but not in short-latency C-bends. We also observe fin movements that occur during orienting J-turns and S-starts that drive high-velocity predatory strikes. Finally, we find that the use of pectoral fins following a predatory strike is scaled to the velocity of the strike, supporting a role for the fins in braking. The implications of these results for central control of coordinated movements are discussed, and we hope that these results will provide baselines for future analyses of cross-body coordination using mutants, morphants, and transgenic approaches. PMID:22359680

  11. Drill drive mechanism

    DOEpatents

    Dressel, Michael O.

    1979-01-01

    A drill drive mechanism is especially adapted to provide both rotational drive and axial feed for a drill of substantial diameter such as may be used for drilling holes for roof bolts in mine shafts. The drill shaft is made with a helical pattern of scroll-like projections on its surface for removal of cuttings. The drill drive mechanism includes a plurality of sprockets carrying two chains of drive links which are arranged to interlock around the drill shaft with each drive link having depressions which mate with the scroll-like projections. As the chain links move upwardly or downwardly the surfaces of the depressions in the links mate with the scroll projections to move the shaft axially. Tangs on the drive links mate with notch surfaces between scroll projections to provide a means for rotating the shaft. Projections on the drive links mate together at the center to hold the drive links tightly around the drill shaft. The entire chain drive mechanism is rotated around the drill shaft axis by means of a hydraulic motor and gear drive to cause rotation of the drill shaft. This gear drive also connects with a differential gearset which is interconnected with a second gear. A second motor is connected to the spider shaft of the differential gearset to produce differential movement (speeds) at the output gears of the differential gearset. This differential in speed is utilized to drive said second gear at a speed different from the speed of said gear drive, this speed differential being utilized to drive said sprockets for axial movement of said drill shaft.

  12. Oscillating field current drive for reversed field pinch discharges

    SciTech Connect

    Schoenberg, K.F.; Gribble, R.F.; Baker, D.A.

    1984-06-01

    Oscillating Field Current Drive (OFCD), also known as F-THETA pumping, is a steady-state current-drive technique proposed for the Reversed Field Pinch (RFP). Unlike other current-drive techniques, which employ high-technology, invasive, and power intensive schemes using radio frequency or neutral particle injection, F-THETA pumping entails driving the toroidal and poloidal magnetic field circuits with low-frequency (audio) oscillating voltage sources. Current drive by this technique is a consequence of the strong nonlinear plasma coupling in the RFP. Because of its low frequency and efficient plasma coupling, F-THETA pumping shows excellent promise as a reactor-relevant current-drive technique. A conceptual and computational study of this concept, including its experimental and reactor relevance, is explored in this paper.

  13. 42 CFR 84.300 - Closed-circuit escape respirator; description.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 42 Public Health 1 2014-10-01 2014-10-01 false Closed-circuit escape respirator; description. 84... Closed-Circuit Escape Respirators § 84.300 Closed-circuit escape respirator; description. The closed-circuit escape respirator (CCER), technically a subset of self-contained breathing apparatus (SCBAs) which...

  14. 42 CFR 84.300 - Closed-circuit escape respirator; description.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 42 Public Health 1 2013-10-01 2013-10-01 false Closed-circuit escape respirator; description. 84... Closed-Circuit Escape Respirators § 84.300 Closed-circuit escape respirator; description. The closed-circuit escape respirator (CCER), technically a subset of self-contained breathing apparatus (SCBAs) which...

  15. Recombination Drives Vertebrate Genome Contraction

    PubMed Central

    Nam, Kiwoong; Ellegren, Hans

    2012-01-01

    Selective and/or neutral processes may govern variation in DNA content and, ultimately, genome size. The observation in several organisms of a negative correlation between recombination rate and intron size could be compatible with a neutral model in which recombination is mutagenic for length changes. We used whole-genome data on small insertions and deletions within transposable elements from chicken and zebra finch to demonstrate clear links between recombination rate and a number of attributes of reduced DNA content. Recombination rate was negatively correlated with the length of introns, transposable elements, and intergenic spacer and with the rate of short insertions. Importantly, it was positively correlated with gene density, the rate of short deletions, the deletion bias, and the net change in sequence length. All these observations point at a pattern of more condensed genome structure in regions of high recombination. Based on the observed rates of small insertions and deletions and assuming that these rates are representative for the whole genome, we estimate that the genome of the most recent common ancestor of birds and lizards has lost nearly 20% of its DNA content up until the present. Expansion of transposable elements can counteract the effect of deletions in an equilibrium mutation model; however, since the activity of transposable elements has been low in the avian lineage, the deletion bias is likely to have had a significant effect on genome size evolution in dinosaurs and birds, contributing to the maintenance of a small genome. We also demonstrate that most of the observed correlations between recombination rate and genome contraction parameters are seen in the human genome, including for segregating indel polymorphisms. Our data are compatible with a neutral model in which recombination drives vertebrate genome size evolution and gives no direct support for a role of natural selection in this process. PMID:22570634

  16. Random perturbations of a periodically driven nonlinear oscillator: escape from a resonance zone

    NASA Astrophysics Data System (ADS)

    Lingala, Nishanth; Sri Namachchivaya, N.; Pavlyukevich, Ilya

    2017-04-01

    For nonlinear oscillators, frequency of oscillations depends on the oscillation amplitude. When a nonlinear oscillator is periodically driven, the phase space consists of many resonance zones where the oscillator frequency and the driving frequency are commensurable. It is well known that, a small subset of initial conditions can lead to capture in one of the resonance zones. In this paper we study the effect of weak noise on the escape from a resonance zone. Using averaging techniques we obtain the mean exit time from a resonance zone and study the dependence of the exit rate on the parameters of the oscillator. Paper dedicated to Professor Peter W Sauer of University of Illinois on the occasion of his 70th birthday.

  17. Is /h/ phonetically neutral?

    PubMed

    Robb, Michael P; Chen, Yang

    2009-11-01

    Use of /h/ in the phrase, 'Say /hVC/ again' has been tacitly assumed to provide a neutral phonetic context in which to study the articulatory characteristics of speech either preceding or following /h/ articulation. Yet, assessment of the stability or neutrality of /h/ has gone untested. The current study sought to determine whether articulation of /h/ differs according to sex and language accent, as well as to examine its influence on subsequent vowel articulation. Selected acoustic features of /hVC/ were measured in 40 speakers of American English (AE) and 40 speakers of Mandarin-accented English (MAE). Results of an analysis of /h/ duration revealed no sex differences within each language group, however considerable variation was found according to accented vs unaccented English. Clear sex differences were found for the production of /h/, occurring more often among male speakers regardless of language variety. Considerable variation in production of /h/ was found between language groups. Analysis of vowel formant frequencies immediately following /h/ articulation indicated minimal coarticulatory effects for both AE and MAE speakers. The present results appear to support the suggestion that /h/ is not exclusively sex-linked and may indeed vary according to non-biological factors. In spite of these variations, /h/ articulation appears to have a negligible influence on neighbouring vowel articulation.

  18. Neutralization of HIV-1: a paradox of humoral proportions.

    PubMed

    Nara, P L; Garrity, R R; Goudsmit, J

    1991-07-01

    . Thus a relatively restricted clonal-dominance of the neutralization response results. The V3 domain, apparently in concert with the rest of the molecule, provides an epitope that can tolerate and utilize its conformational flexibility to allow immune escape while maintaining its functional role in infectivity. Sixteen other putative epitopes have been described as being involved in the induction of neutralizing Ig. Currently the biologically functional role of neutralizing Ig to these other epitopes are complicated by a prior lack of knowledge and appreciation of the in vitro variables affecting their measurements.(ABSTRACT TRUNCATED AT 400 WORDS)

  19. Spatial calibration of a tokamak neutral beam diagnostic using in situ neutral beam emission

    SciTech Connect

    Chrystal, Colin; Burrell, Keith H.; Grierson, Brian A.; Pace, David C.

    2015-10-20

    Neutral beam injection is used in tokamaks to heat, apply torque, drive non-inductive current, and diagnose plasmas. Neutral beam diagnostics need accurate spatial calibrations to benefit from the measurement localization provided by the neutral beam. A new technique has been developed that uses in-situ measurements of neutral beam emission to determine the spatial location of the beam and the associated diagnostic views. This technique was developed to improve the charge exchange recombination diagnostic (CER) at the DIII-D tokamak and uses measurements of the Doppler shift and Stark splitting of neutral beam emission made by that diagnostic. These measurements contain information about the geometric relation between the diagnostic views and the neutral beams when they are injecting power. This information is combined with standard spatial calibration measurements to create an integrated spatial calibration that provides a more complete description of the neutral beam-CER system. The integrated spatial calibration results are very similar to the standard calibration results and derived quantities from CER measurements are unchanged within their measurement errors. Lastly, the methods developed to perform the integrated spatial calibration could be useful for tokamaks with limited physical access.

  20. Structural controls on fluid escape from the subduction interface

    NASA Astrophysics Data System (ADS)

    Reynard, Bruno; Tauzin, Benoit; Bodin, Thomas; Perrillat, Jean-Philippe; Debayle, Eric

    2017-04-01

    Seismic activity and non-volcanic tremors are often associated with fluid circulation resulting from the dehydration of subducting plates. Tremors in the overriding continental crust of several subduction zones suggest fluid circulation at shallower depths, but potential fluid pathways are still poorly documented. Fluids are also released at different depths in hot and cold subduction zones, which may result in different schemes of fluid escape. We document potential fluid pathways in Cascadia, one of the hottest subduction zone, using receiver function analysis. We provide evidence for a seismic discontinuity near 15 km depth in the crust of the overriding North American plate. This interface is segmented, and its interruptions are spatially correlated with conductive regions of the forearc and shallow swarms of seismicity and non-volcanic tremors. The comparison of seismological and electrical conductivity profiles suggests that fluid escape is controlled by fault zones between blocks of accreted terranes in the overriding plate. These zones constitute fluid escape routes that may influence the seismic cycle by releasing fluid pressure from the megathrust. Results on Cascadia are compared to fluid escape routes suggested by former geophysical observations in NE Japan, one of the coldest subduction zones. Links between fluid escape, permeability and fluid-rock reactions at or above the plate interface are discussed.