3,282 research outputs found
The Abundance of Molecular Hydrogen and its Correlation with Midplane Pressure in Galaxies: Non-Equilibrium, Turbulent, Chemical Models
Observations of spiral galaxies show a strong linear correlation between the
ratio of molecular to atomic hydrogen surface density R_mol and midplane
pressure. To explain this, we simulate three-dimensional, magnetized
turbulence, including simplified treatments of non-equilibrium chemistry and
the propagation of dissociating radiation, to follow the formation of H_2 from
cold atomic gas. The formation time scale for H_2 is sufficiently long that
equilibrium is not reached within the 20-30 Myr lifetimes of molecular clouds.
The equilibrium balance between radiative dissociation and H_2 formation on
dust grains fails to predict the time-dependent molecular fractions we find. A
simple, time-dependent model of H_2 formation can reproduce the gross behavior,
although turbulent density perturbations increase molecular fractions by a
factor of few above it. In contradiction to equilibrium models, radiative
dissociation of molecules plays little role in our model for diffuse radiation
fields with strengths less than ten times that of the solar neighborhood,
because of the effective self-shielding of H_2. The observed correlation of
R_mol with pressure corresponds to a correlation with local gas density if the
effective temperature in the cold neutral medium of galactic disks is roughly
constant. We indeed find such a correlation of R_mol with density. If we
examine the value of R_mol in our local models after a free-fall time at their
average density, as expected for models of molecular cloud formation by
large-scale gravitational instability, our models reproduce the observed
correlation over more than an order of magnitude range in density.Comment: 24 pages, 4 figures, accepted for publication in Astrophys. J,
changes include addition of models with higher radiation fields and
substantial clarification of the narrativ
The geometry of reaction norms yields insights on classical fitness functions for Great Lakes salmon.
Life history theory examines how characteristics of organisms, such as age and size at maturity, may vary through natural selection as evolutionary responses that optimize fitness. Here we ask how predictions of age and size at maturity differ for the three classical fitness functions-intrinsic rate of natural increase r, net reproductive rate R0, and reproductive value Vx-for semelparous species. We show that different choices of fitness functions can lead to very different predictions of species behavior. In one's efforts to understand an organism's behavior and to develop effective conservation and management policies, the choice of fitness function matters. The central ingredient of our approach is the maturation reaction norm (MRN), which describes how optimal age and size at maturation vary with growth rate or mortality rate. We develop a practical geometric construction of MRNs that allows us to include different growth functions (linear growth and nonlinear von Bertalanffy growth in length) and develop two-dimensional MRNs useful for quantifying growth-mortality trade-offs. We relate our approach to Beverton-Holt life history invariants and to the Stearns-Koella categorization of MRNs. We conclude with a detailed discussion of life history parameters for Great Lakes Chinook Salmon and demonstrate that age and size at maturity are consistent with predictions using R0 (but not r or Vx) as the underlying fitness function
Nihilation of femininity in the battle of looks: a Sartrean reading of Jhumpa Lahiri’s “A temporary matter”
The panoptic gaze is vested in with a constitutive impact upon the subjectivity of individuals.
Feminist scholars like Luce Irigaray have charged that the metaphor of vision is intimately
connected with the construction of gender and sexual difference. By pointing to the
masculine logic of Western thought, Irigaray confirms that a woman’s entry into a dominant
scopic economy signifies her inevitable confinement to passivity. This essay aims to examine
the sexual politics of metaphors of vision in a literary text that is controversially argued to be
a voice for the subordinated Indian immigrant women in the US. As one of the most
influential schools of thought in Western philosophy, the Sartrean paradigm of sexual
difference is employed to investigate this allegation by identifying the latent binary system at
work in the fiction of Jhumpa Lahiri, who has garnered substantial yet controversial critical
attention over her representations of gender. Specifically, this essay focuses on Lahiri’s
prefatory story to her Pulitzer Prize-winning short story collection, Interpreter of Maladies
(2000), to unravel the manner her exercise of vision in this narrative perpetuates the
dichotomies of a male subject and a female object pre-established in the traditional
hierarchies of gender in the West. In this story, Lahiri (un)wittingly privileges masculinity
over femininity and reduces the latter to a typically disgusting Sartrean female body of holes
and slime. Hence, notwithstanding infrequent emasculated images of the male subject, it is
ultimately the masculine that, in the battle of looks between male and female, nihilates the
Other to the state of “being-in-itself” and enjoys supremacy over the feminine
Nihilation of Femininity in the Battle of Looks: A Sartrean Reading of Jhumpa Lahiri’s “A Temporary Matter”
The panoptic gaze is vested in with a constitutive impact upon the subjectivity of individuals.
Feminist scholars like Luce Irigaray have charged that the metaphor of vision is intimately
connected with the construction of gender and sexual difference. By pointing to the
masculine logic of Western thought, Irigaray confirms that a woman’s entry into a dominant
scopic economy signifies her inevitable confinement to passivity. This essay aims to examine
the sexual politics of metaphors of vision in a literary text that is controversially argued to be
a voice for the subordinated Indian immigrant women in the US. As one of the most
influential schools of thought in Western philosophy, the Sartrean paradigm of sexual
difference is employed to investigate this allegation by identifying the latent binary system at
work in the fiction of Jhumpa Lahiri, who has garnered substantial yet controversial critical
attention over her representations of gender. Specifically, this essay focuses on Lahiri’s
prefatory story to her Pulitzer Prize-winning short story collection, Interpreter of Maladies
(2000), to unravel the manner her exercise of vision in this narrative perpetuates the
dichotomies of a male subject and a female object pre-established in the traditional
hierarchies of gender in the West. In this story, Lahiri (un)wittingly privileges masculinity
over femininity and reduces the latter to a typically disgusting Sartrean female body of holes
and slime. Hence, notwithstanding infrequent emasculated images of the male subject, it is
ultimately the masculine that, in the battle of looks between male and female, nihilates the
Other to the state of “being-in-itself” and enjoys supremacy over the feminine
Efficient targeted transgenesis of large donor DNA into multiple mouse genetic backgrounds using bacteriophage Bxb1 integrase.
The development of mouse models of human disease and synthetic biology research by targeted transgenesis of large DNA constructs represent a significant genetic engineering hurdle. We developed an efficient, precise, single-copy integration of large transgenes directly into zygotes using multiple mouse genetic backgrounds. We used in vivo Bxb1 mediated recombinase-mediated cassette exchange (RMCE) with a transgene landing pad composed of dual heterologous Bxb1 attachment (att) sites in cis, within the Gt(ROSA)26Sor safe harbor locus. RMCE of donor was achieved by microinjection of vector DNA carrying cognate attachment sites flanking the donor transgene with Bxb1-integrase mRNA. This approach achieves perfect vector-free integration of donor constructs at efficiencies \u3e 40% with up to ~ 43 kb transgenes. Coupled with a nanopore-based Cas9-targeted sequencing (nCATS), complete verification of precise insertion sequence was achieved. As a proof-of-concept we describe the development of C57BL/6J and NSG Krt18-ACE2 models for SARS-CoV2 research with verified heterozygous N1 animals within ~ 4 months. Additionally, we created a series of mice with diverse backgrounds carrying a single att site including FVB/NJ, PWK/PhJ, NOD/ShiLtJ, CAST/EiJ and DBA/2J allowing for rapid transgene insertion. Combined, this system enables predictable, rapid development with simplified characterization of precisely targeted transgenic animals across multiple genetic backgrounds
Ovarian cancer symptom awareness and anticipated time to help-seeking for symptoms among UK women.
OBJECTIVES: To determine levels of awareness of ovarian cancer symptoms and to identify barriers to help-seeking and predictors of a longer time to help-seeking in a UK female population-based sample. METHODS: A UK population-based sample of women [n=1000, including a subsample of women at higher risk due to their age (≥45 years, n=510)] completed the Ovarian Cancer Awareness Measure by telephone interview. Questions measured symptom awareness (using recall and recognition), barriers to medical help-seeking and anticipated time to help-seeking. Regression analyses identified predictors of a higher score on a scale of anticipated time to help-seeking. RESULTS: Most women (58% overall sample; 54% subgroup) were unable to recall any symptoms but 99% recognised at least one. Recognition was lowest for difficulty eating and persistently feeling full. In the sample overall, higher socio-economic status and higher endorsement of practical and service barriers independently predicted a longer anticipated time to help-seeking for more symptoms. White ethnicity was an additional predictor in the older subgroup. CONCLUSIONS: This study suggests awareness of ovarian cancer symptoms is low in the UK, and varies widely between symptoms. It identifies variables that may be involved in a longer time to help-seeking for possible ovarian cancer symptoms and highlights the need for more in-depth research into the factors related to time to help-seeking in real-world situations
Modeling H2 formation in the turbulent ISM: Solenoidal versus compressive turbulent forcing
We present results from high-resolution three-dimensional simulations of the
turbulent interstellar medium that study the influence of the nature of the
turbulence on the formation of molecular hydrogen. We have examined both
solenoidal (divergence-free) and compressive (curl-free) turbulent driving, and
show that compressive driving leads to faster H2 formation, owing to the higher
peak densities produced in the gas. The difference in the H2 formation rate can
be as much as an order of magnitude at early times, but declines at later times
as the highest density regions become fully molecular and stop contributing to
the total H2 formation rate. We have also used our results to test a simple
prescription suggested by Gnedin et al. (2009) for modeling the influence of
unresolved density fluctuations on the H2 formation rate in large-scale
simulations of the ISM. We find that this approach works well when the H2
fraction is small, but breaks down once the highest density gas becomes fully
molecular.Comment: 13 pages, 8 figures, accepted for publication in MNRA
Magnetorotational turbulence transports angular momentum in stratified disks with low magnetic Prandtl number but magnetic Reynolds number above a critical value
The magnetorotational instability (MRI) may dominate outward transport of
angular momentum in accretion disks, allowing material to fall onto the central
object. Previous work has established that the MRI can drive a mean-field
dynamo, possibly leading to a self-sustaining accretion system. Recently,
however, simulations of the scaling of the angular momentum transport parameter
\alphaSS with the magnetic Prandtl number \Prandtl have cast doubt on the
ability of the MRI to transport astrophysically relevant amounts of angular
momentum in real disk systems. Here, we use simulations including explicit
physical viscosity and resistivity to show that when vertical stratification is
included, mean field dynamo action operates, driving the system to a
configuration in which the magnetic field is not fully helical. This relaxes
the constraints on the generated field provided by magnetic helicity
conservation, allowing the generation of a mean field on timescales independent
of the resistivity. Our models demonstrate the existence of a critical magnetic
Reynolds number \Rmagc, below which transport becomes strongly
\Prandtl-dependent and chaotic, but above which the transport is steady and
\Prandtl-independent. Prior simulations showing \Prandtl-dependence had
\Rmag < \Rmagc. We conjecture that this steady regime is possible because the
mean field dynamo is not helicity-limited and thus does not depend on the
details of the helicity ejection process. Scaling to realistic astrophysical
parameters suggests that disks around both protostars and stellar mass black
holes have \Rmag >> \Rmagc. Thus, we suggest that the strong \Prandtl
dependence seen in recent simulations does not occur in real systems.Comment: 17 pages, 9 figures. as accepted to Ap
Characterizing star formation activity in infrared dark cloud MSXDC G048.65-00.29
Infrared Dark Clouds (IRDCs), condensed regions of the ISM with high column
densities, low temperatures and high masses, are suspected sites of star
formation. Thousands of IRDCs have already been identified. To date, it has not
been resolved whether IRDCs always show star formation activity and, if so, if
massive star formation (> 8 solar masses) is the rule or the exception in
IRDCs. Previous analysis of sub-millimeter cores in the cloud MSXDC
G048.65-00.29 (G48.65) indicates embedded star formation activity. To
characterize this activity in detail, mid-infrared photometry (3-30 micron) has
been obtained with the Spitzer Space Telescope. This paper analyzes the point
sources seen in the 24 micron band, combined with counterparts or upper limits
at shorter and longer wavelengths. Data points in wavelength bands ranging from
1 up to 850 micron are used to compare each 24 micron source to a set of
Spectral Energy Distributions of Young Stellar Object (YSO) models. By
assessing the models that fit the data, an attempt is made to identify YSOs as
such and determine their evolutionary stages and stellar masses. A total of 17
sources are investigated, 13 of which are classified as YSOs, primarily - but
not exclusively - in an early embedded phase of star formation. The modeled
masses of the central stellar objects range from sub-solar to ~8 solar masses.
Every YSO is at less than 1 pc projected distance from its nearest YSO
neighbor. We conclude that IRDC G48.65 is a region of active star formation. We
find YSOs in various evolutionary phases, indicating that the star formation in
this cloud is not an instantaneous process. The inferred masses of the central
objects suggest that this IRDC hosts only low to intermediate mass YSOs and
none with masses exceeding ~8 solar masses.Comment: 10 pages, 6 figures; v2: minor editorial changes to match published
versio
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Women's interpretation of and responses to potential gynaecological cancer symptoms: a qualitative interview study
OBJECTIVE: To explore women's experiences of symptoms potentially indicative of gynaecological cancer in a community-based sample without imposing a cancer perspective.
DESIGN: A qualitative interview study with thematic analysis of transcripts.
PARTICIPANTS: 26 women aged ≥30 years, who had experienced a symptom that might indicate gynaecological cancer in the past 3 months, were recruited using a screening questionnaire distributed online and in community settings.
SETTING: London, UK.
RESULTS: Women attributed gynaecological symptoms to existing illnesses/conditions or considered themselves to be predisposed to them, either through their 'genes' or previous personal experience. Normalising symptoms by attributing them to demographic characteristics (e.g., age, sex) was common, as was considering them a side effect of hormonal contraception. When women raised cancer as a possible cause, they often dismissed it as unlikely. Responses to symptoms included self-management (e.g., self-medicating, making lifestyle changes), adopting a 'lay system of care', or consulting a healthcare professional. Triggers to help-seeking included persistent, painful or debilitating symptoms, concern about symptom seriousness, and feeling that help-seeking was legitimised. Barriers to help-seeking included lack of concern, vague symptoms, unusual symptom location, competing time demands, previous negative experiences with the healthcare system, and not wanting to be perceived as a time-waster.
CONCLUSIONS: Attributions of symptoms potentially indicative of a gynaecological cancer were varied, but most often involved women fitting symptoms into their expectations of what was 'normal'. Normalising acted as a barrier to seeking help from a healthcare professional, alongside competing time demands and negative attitudes towards help-seeking. These barriers may lead to later diagnosis and poorer cancer survival. Our findings could be used to inform the development of interventions to encourage appropriate help-seeking
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