971 research outputs found
Distant red galaxies in the Hubble Ultra Deep Field
We take advantage of the Hubble Ultra Deep Field (UDF) data to study the
restframe optical and ultra violet (UV) morphologies of the novel population of
Distant Red Galaxies (DRGs). Six galaxies with J-Ks > 2.3 are found to Ks=21.5,
five of which have photometric redshifts z_phot > 2, corresponding to a surface
density of 0.9/arcmin^2. The surface brightness distributions of the z_phot > 2
galaxies are better represented by exponential disks than R^{1/4}-laws. Two of
the z_phot > 2 galaxies are extended, while three have compact morphologies.
The restframe optical morphology of the z_phot > 2 galaxies is quite different
from the restframe UV morphology: all the galaxies have red central components
which dominate in the NICMOS H_{160}-band images, and distinct off-center blue
features which show up in (and often dominate) the ACS images. The mean
measured effective radius of the z_phot > 2 galaxies is =1.9+/-1.4 kpc,
similar (within the errors) to the mean size of LBGs at similar redshifts. All
the DRGs are resolved in the ACS images, while four are resolved in the NICMOS
images. Two of the z_phot > 2 galaxies are bright X-ray sources and hence host
AGN. The diverse restframe optical and UV morphological properties of DRGs
derived here suggest that they have complex stellar populations, consisting of
both evolved populations that dominate the mass and the restframe optical
light, and younger populations, which show up as patches of star formation in
the restframe UV light; in many ways resembling the properties of normal local
galaxies. This interpretation is supported by fits to the broadband SEDs, which
for all five z_phot > 2 are best represented by models with extended star
formation histories and substantial amounts of dust.Comment: Accepted for publication in APJ
The human genome; you gain some, you lose some
Copy number variations (CNVs) in the human genome are inherent in both evolutionary progression as well as the etiology of disease. The introduction of this thesis will review CNVs that appear to be neutral as well as CNVs that appear to be related to a phenotypic trait. This will be followed by a review of the many different technical approaches that can be used for detecting genomic rearrangements. The articles (chapter II & III) describe several studies that have applied the rapidly evolving techniques for CNV detection to the clinical problem of unexplained mental retardation and congenital malformation(s). The availability of the new diagnostic tools will greatly increase our understanding of the genetic causes of mental retardation and congenital malformation(s), and might one day lead to therapeutic interventions in some cases.LUMC, afd. Klinische Genetica en Humane GeneticaThe Netherland Organisation for Health Research and Development (ZonMW). Registration number 940-37-032.Genoomkartering en moleculaire cytogenetic
Alternative Conceptions about Simple Electric Circuits amongst High School FET Band Learners
Institute for Science and Technology Education (ISTE
Recommended from our members
Cobimetinib and trametinib inhibit platelet MEK but do not cause platelet dysfunction
The MEK inhibitors cobimetinib and trametinib are used in combination with BRAF inhibitors to treat metastatic melanoma but increase rates of hemorrhage relative to BRAF inhibitors alone. Platelets express several members of the MAPK signalling cascade including MEK1 and MEK2 and ERK1 and ERK2 but their role in platelet function and haemostasis is ambiguous as previous reports have been contradictory. It is therefore unclear if MEK inhibitors might be causing platelet dysfunction and contributing to increased hemorrhage. In the present study we performed pharmacological characterisation of cobimetinib and trametinib in vitro to investigate potential for MEK inhibitors to cause platelet dysfunction.
We report that whilst both cobimetinib and trametinib are potent inhibitors of platelet MEK activity, treatment with trametinib did not alter platelet function. Treatment with cobimetinib results in inhibition of platelet aggregation, integrin activation, alpha-granule secretion and adhesion but only at suprapharmacological concentrations. We identified that the inhibitory effects of high concentrations of cobimetinib are associated with off-target inhibition on Akt and PKC. Neither inhibitor caused any alteration in thrombus formation on collagen under flow conditions in vitro.
Our findings demonstrate that platelets are able to function normally when MEK activity is fully inhibited, indicating MEK activity is dispensable for normal platelet function. We conclude that the MEK inhibitors cobimetinib and trametinib do not induce platelet dysfunction and are therefore unlikely to contribute to increased incidence of bleeding reported during MEK inhibitor therapy
Boards and governance in African national cricket organisations: An exploratory study
Sport organisations face escalating performance pressures from various stakeholders, which places increasing demands on the governance structures of such organisations. However, little research has been undertaken to understand sport governance of national sports organisations within the African context. This paper will focus on the roles and structures of the boards of African national cricket organisations to enhance the understanding of board involvement in strategic planning and implementation. This study used a sequential mixed method design to gather empirical data from 23 cricket associations affiliated to the International Cricket Council’s (ICC) African Cricket Association (ACA). The research reports on the composition of the boards of African cricket organisations as well as the perceived roles and responsibilities of boards in the strategic planning process and implementation thereof. It explores the perceived influence of the ICC on the governance compliance of African National Cricket organisations, and lastly indicates the strategic management activities performed by such boards.Key words: governance, national sport organisations, boards, strategic managemen
X-ray properties of K-selected galaxies at 0.5<z<2.0: Investigating trends with stellar mass, redshift and spectral type
We examine how the total X-ray luminosity correlates with stellar mass,
stellar population, and redshift for a K-band limited sample of ~3500 galaxies
at 0.5<z<2.0 from the NEWFIRM Medium Band Survey in the COSMOS field. The
galaxy sample is divided into 32 different galaxy types, based on similarities
between the spectral energy distributions. For each galaxy type, we further
divide the sample into bins of redshift and stellar mass, and perform an X-ray
stacking analysis using the Chandra COSMOS (C-COSMOS) data. We find that full
band X-ray luminosity is primarily increasing with stellar mass, and at similar
mass and spectral type is higher at larger redshifts. When comparing at the
same stellar mass, we find that the X-ray luminosity is slightly higher for
younger galaxies (i.e., weaker 4000\AA breaks), but the scatter in this
relation is large. We compare the observed X-ray luminosities to those expected
from low and high mass X-ray binaries (XRBs). For blue galaxies, XRBs can
almost fully account for the observed emission, while for older galaxies with
larger 4000\AA breaks, active galactic nuclei (AGN) or hot gas dominate the
measured X-ray flux. After correcting for XRBs, the X-ray luminosity is still
slightly higher in younger galaxies, although this correlation is not
significant. AGN appear to be a larger component of galaxy X-ray luminosity at
earlier times, as the hardness ratio increases with redshift. Together with the
slight increase in X-ray luminosity this may indicate more obscured AGNs or
higher accretion rates at earlier times.Comment: 9 pages, 9 figures, ApJ accepte
Ultradeep Infrared Array Camera Observations of sub-L* z~7 and z~8 Galaxies in the Hubble Ultra Deep Field: the Contribution of Low-Luminosity Galaxies to the Stellar Mass Density and Reionization
We study the Spitzer Infrared Array Camera (IRAC) mid-infrared (rest-frame
optical) fluxes of 14 newly WFC3/IR-detected z=7 z_{850}-dropout galaxies and 5
z=8 Y_{105}-dropout galaxies. The WFC3/IR depth and spatial resolution allow
accurate removal of contaminating foreground light, enabling reliable flux
measurements at 3.6 micron and 4.5 micron. None of the galaxies are detected to
[3.6]=26.9 (AB, 2 sigma), but a stacking analysis reveals a robust detection
for the z_{850}-dropouts and an upper limit for the Y_{105}-dropouts. We
construct average broadband SEDs using the stacked ACS, WFC3, and IRAC fluxes
and fit stellar population synthesis models to derive mean redshifts, stellar
masses, and ages. For the z_{850}-dropouts, we find z=6.9^{+0.1}_{-0.1},
(U-V)_{rest}=0.4, reddening A_V=0, stellar mass M*=1.2^{+0.3}_{-0.6} x 10^9
M_sun (Salpeter IMF). The best-fit ages ~300Myr, M/L_V=0.2, and
SSFR=1.7Gyr^{-1} are similar to values reported for luminous z=7 galaxies,
indicating the galaxies are smaller but not younger. The sub-L* galaxies
observed here contribute significantly to the stellar mass density and under
favorable conditions may have provided enough photons for sustained
reionization at 7<z<11. In contrast, the z=8.3^{+0.1}_{-0.2} Y_{105}-dropouts
have stellar masses that are uncertain by 1.5 dex due to the near-complete
reliance on far-UV data. Adopting the 2 sigma upper limit on the M/L(z=8), the
stellar mass density to M_{UV,AB} < -18 declines from
rho*(z=7)=3.7^{+1.0}_{-1.8} x 10^6 M_sun Mpc^{-3} to rho*(z=8) < 8 x 10^5 M_sun
Mpc^{-3}, following (1+z)^{-6} over 3<z<8. Lower masses at z=8 would signify
more dramatic evolution, which can be established with deeper IRAC
observations, long before the arrival of the James Webb Space Telescope.Comment: 6 pages, 3 figures, 2 tables, emulateapj, accepted for publication in
ApJ
Can dry merging explain the size evolution of early-type galaxies?
The characteristic size of early-type galaxies (ETGs) of given stellar mass
is observed to increase significantly with cosmic time, from redshift z>2 to
the present. A popular explanation for this size evolution is that ETGs grow
through dissipationless ("dry") mergers, thus becoming less compact. Combining
N-body simulations with up-to-date scaling relations of local ETGs, we show
that such an explanation is problematic, because dry mergers do not decrease
the galaxy stellar-mass surface-density enough to explain the observed size
evolution, and also introduce substantial scatter in the scaling relations.
Based on our set of simulations, we estimate that major and minor dry mergers
increase half-light radius and projected velocity dispersion with stellar mass
(M) as M^(1.09+/-0.29) and M^(0.07+/-0.11), respectively. This implies that: 1)
if the high-z ETGs are indeed as dense as estimated, they cannot evolve into
present-day ETGs via dry mergers; 2) present-day ETGs cannot have assembled
more than ~45% of their stellar mass via dry mergers. Alternatively, dry
mergers could be reconciled with the observations if there was extreme fine
tuning between merger history and galaxy properties, at variance with our
assumptions. Full cosmological simulations will be needed to evaluate whether
this fine-tuned solution is acceptable.Comment: 5 pages, 2 figures. Accepted for publication in ApJ Letter
The Relation between Dynamical Mass-to-light Ratio and Color for Massive Quiescent Galaxies out to z ~ 2 and Comparison with Stellar Population Synthesis Models
Article / Letter to editorSterrewach
Spatially resolved kinematics in the central 1 kpc of a compact star-forming galaxy at z=2.3 from ALMA CO observations
We present high spatial resolution (FWHM0.14'') observations of the
CO() line in GDS-14876, a compact star-forming galaxy at with
total stellar mass of . The spatially resolved
velocity map of the inner ~kpc reveals a continous velocity
gradient consistent with the kinematics of a rotating disk with km s and . The
gas-to-stellar ratios estimated from CO() and the dust continuum emission
span a broad range, and
, but are nonetheless consistent given the
uncertainties in the conversion factors. The dynamical modeling yields a
dynamical mass of which is
lower, but still consistent with the baryonic mass, (M=
M + M/M), if the smallest
CO-based gas fraction is assumed. Despite a low, overall gas fraction, the
small physical extent of the dense, star-forming gas probed by CO(),
smaller than the stellar size, implies a strong concentration
that increases the gas fraction up to
in the central 1 kpc. Such a gas-rich center, coupled with a high
star-formation rate, SFR 500 M yr, suggests that
GDS-14876 is quickly assembling a dense stellar component (bulge) in a strong
nuclear starburst. Assuming its gas reservoir is depleted without
replenishment, GDS-14876 will quickly ( Myr) become a
compact quiescent galaxy that could retain some fraction of the observed
rotational support.Comment: Accepted for Publication in ApJL. Kinematic maps are shown in Figures
2 and
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