The divergence of distinct cell populations from multipotent progenitors is poorly understood, particularly in vivo. The gonad is an ideal place to study this process, because it originates as a ...bipotential primordium where multiple distinct lineages acquire sex-specific fates as the organ differentiates as a testis or an ovary. To gain a more detailed understanding of the process of gonadal differentiation at the level of the individual cell populations, we conducted microarrays on sorted cells from XX and XY mouse gonads at three time points spanning the period when the gonadal cells transition from sexually undifferentiated progenitors to their respective sex-specific fates. We analyzed supporting cells, interstitial/stromal cells, germ cells, and endothelial cells. This work identified genes specifically depleted and enriched in each lineage as it underwent sex-specific differentiation. We determined that the sexually undifferentiated germ cell and supporting cell progenitors showed lineage priming. We found that germ cell progenitors were primed with a bias toward the male fate. In contrast, supporting cells were primed with a female bias, indicative of the robust repression program involved in the commitment to XY supporting cell fate. This study provides a molecular explanation reconciling the female default and balanced models of sex determination and represents a rich resource for the field. More importantly, it yields new insights into the mechanisms by which different cell types in a single organ adopt their respective fates.
We report the real-time discovery of a fast radio burst (FRB 131104) with the Parkes radio telescope in a targeted observation of the Carina dwarf spheroidal galaxy. The dispersion measure of the ...burst is 779 cm super(-3) pc, exceeding predictions for the maximum line-of-sight Galactic contribution by a factor of 11. The temporal structure of the burst is characterized by an exponential scattering tail with a timescale of (ProQuest: Formulae and/or non-USASCII text omitted) ms at 1582 MHz that scales as frequency to the power (ProQuest: Formulae and/or non-USASCII text omitted) (all uncertainties represent 95% confidence intervals). We bound the intrinsic pulse width to be <0.64 ms due to dispersion smearing across a single spectrometer channel. Searches in 78 hr of follow-up observations with the Parkes telescope reveal no additional sporadic emission and no evidence for associated periodic radio emission. We hypothesize that the burst is associated with the Carina dwarf galaxy. Follow-up observations at other wavelengths are necessary to test this hypothesis.
Abstract Plant virus-based nanoparticles (VNPs) are a novel class of nanocarriers with unique potential for biomedical applications. VNPs have many advantageous properties such as ease of manufacture ...and high degree of quality control. Their biocompatibility and biodegradability make them an attractive alternative to synthetic nanoparticles (NPs). Nevertheless, as with synthetic NPs, to be successful in drug delivery or imaging, the carriers need to overcome several biological barriers including innate immune recognition. Plasma opsonization can tag (V)NPs for clearance by the mononuclear phagocyte system (MPS), resulting in shortened circulation half lives and non-specific sequestration in non-targeted organs. PEG coatings have been traditionally used to ‘shield’ nanocarriers from immune surveillance. However, due to broad use of PEG in cosmetics and other industries, the prevalence of anti-PEG antibodies has been reported, which may limit the utility of PEGylation in nanomedicine. Alternative strategies are needed to tailor the in vivo properties of (plant virus-based) nanocarriers. We demonstrate the use of serum albumin (SA) as a viable alternative. SA conjugation to tobacco mosaic virus (TMV)-based nanocarriers results in a ‘camouflage’ effect more effective than PEG coatings. SA-‘camouflaged’ TMV particles exhibit decreased antibody recognition, as well as enhanced pharmacokinetics in a Balb/C mouse model. Therefore, SA-coatings may provide an alternative and improved coating technique to yield (plant virus-based) NPs with improved in vivo properties enhancing drug delivery and molecular imaging.
Fast radio bursts (FRBs) are millisecond-duration events thought to originate beyond the Milky Way galaxy. Uncertainty surrounding the burst sources, and their propagation through intervening plasma, ...has limited their use as cosmological probes. We report on a mildly dispersed (dispersion measure 266.5 ± 0.1 parsecs per cubic centimeter), exceptionally intense (120 ± 30 janskys), linearly polarized, scintillating burst (FRB 150807) that we directly localize to 9 square arc minutes. On the basis of a low Faraday rotation (12.0 ± 0.7 radians per square meter), we infer negligible magnetization in the circum-burst plasma and constrain the net magnetization of the cosmic web along this sightline to <21 nanogauss, parallel to the line-of-sight. The burst scintillation suggests weak turbulence in the ionized intergalactic medium.
Searches for transient astrophysical sources often reveal unexpected classes of objects that are useful physical laboratories. In a recent survey for pulsars and fast transients, we have uncovered ...four millisecond-duration radio transients all more than 40° from the Galactic plane. The bursts' properties indicate that they are of celestial rather than terrestrial origin. Host galaxy and intergalactic medium models suggest that they have cosmological redshifts of 0.5 to 1 and distances of up to 3 gigaparsecs. No temporally coincident x-or gamma-ray signature was identified in association with the bursts. Characterization of the source population and identification of host galaxies offers an opportunity to determine the baryonic content of the universe.
The flux reconstruction approach to high-order methods is robust, efficient, simple to implement, and allows various high-order schemes, such as the nodal discontinuous Galerkin method and the ...spectral difference method, to be cast within a single unifying framework. Utilizing a flux reconstruction formulation, it has been proved (for one-dimensional linear advection) that the spectral difference method is stable for all orders of accuracy in a norm of Sobolev type, provided that the interior flux collocation points are located at zeros of the corresponding Legendre polynomials. In this article the aforementioned result is extended in order to develop a new class of one-dimensional energy stable flux reconstruction schemes. The energy stable schemes are parameterized by a single scalar quantity, which if chosen judiciously leads to the recovery of various well known high-order methods (including a particular nodal discontinuous Galerkin method and a particular spectral difference method). The analysis offers significant insight into why certain flux reconstruction schemes are stable, whereas others are not. Also, from a practical standpoint, the analysis provides a simple prescription for implementing an infinite range of energy stable high-order methods via the intuitive flux reconstruction approach.
The flux reconstruction (FR) approach unifies various high-order schemes, including collocation based nodal discontinuous Galerkin methods, and all spectral difference methods (at least for a linear ...flux function), within a single framework. Recently, an infinite number of linearly stable FR schemes were identified, henceforth referred to as Vincent–Castonguay–Jameson–Huynh (VCJH) schemes. Identification of VCJH schemes offers significant insight into why certain FR schemes are stable (whereas others are not), and provides a simple prescription for implementing an infinite range of linearly stable high-order methods. However, various properties of VCJH schemes have yet to be analyzed in detail. In the present study one-dimensional (1D) von Neumann analysis is employed to elucidate how various important properties vary across the full range of VCJH schemes. In particular, dispersion and dissipation properties are studied, as are the magnitudes of explicit time-step limits (based on stability considerations). 1D linear numerical experiments are undertaken in order to verify results of the 1D von Neumann analysis. Additionally, two-dimensional non-linear numerical experiments are undertaken in order to assess whether results of the 1D von Neumann analysis (which is inherently linear) extend to real world problems of practical interest.
The detection of five new fast radio bursts (FRBs) found in the 1.4-GHz High Time Resolution Universe high-latitude survey at Parkes, is presented. The rate implied is 7
$^{+5}_{-3}\times 10^3$
...(95 per cent) FRBs sky−1 d−1 above a fluence of 0.13 Jy ms for an FRB of 0.128 ms duration to 1.5 Jy ms for 16 ms duration. One of these FRBs has a two-component profile, in which each component is similar to the known population of single component FRBs and the two components are separated by 2.4 ± 0.4 ms. All the FRB components appear to be unresolved following deconvolution with a scattering tail and accounting for intrachannel smearing. The two-component burst, FRB 121002, also has the highest dispersion measure (1629 pc cm−3) of any FRB to-date. Many of the proposed models to explain FRBs use a single high-energy event involving compact objects (such as neutron-star mergers) and therefore cannot easily explain a two-component FRB. Models that are based on extreme versions of flaring, pulsing, or orbital events, however, could produce multiple component profiles. The compatibility of these models and the FRB rate implied by these detections is discussed.
Abstract
We present the first interferometric detections of fast radio bursts (FRBs), an enigmatic new class of astrophysical transient. In a 180-d survey of the Southern sky, we discovered three ...FRBs at 843 MHz with the UTMOST array, as a part of commissioning science during a major ongoing upgrade. The wide field of view of UTMOST (≈9 deg2) is well suited to FRB searches. The primary beam is covered by 352 partially overlapping fan-beams, each of which is searched for FRBs in real time with pulse widths in the range 0.655–42 ms, and dispersion measures ≤2000 pc cm−3. Detections of FRBs with the UTMOST array place a lower limit on their distances of ≈104 km (limit of the telescope near-field) supporting the case for an astronomical origin. Repeating FRBs at UTMOST or an FRB detected simultaneously with the Parkes radio telescope and UTMOST would allow a few arcsec localization, thereby providing an excellent means of identifying FRB host galaxies, if present. Up to 100 h of followup for each FRB has been carried out with the UTMOST, with no repeating bursts seen. From the detected position, we present 3σ error ellipses of 15 arcsec × 8
${^{\circ}_{.}}$
4 on the sky for the point of origin for the FRBs. We estimate an all-sky FRB rate at 843 MHz above a fluence
$\cal F_\mathrm{lim}$
of 11 Jy ms of ∼78 events sky−1 d−1 at the 95 per cent confidence level. The measured rate of FRBs at 843 MHz is two times higher than we had expected, scaling from the FRB rate at the Parkes radio telescope, assuming that FRBs have a flat spectral index and a uniform distribution in Euclidean space. We examine how this can be explained by FRBs having a steeper spectral index and/or a flatter logN–log
$\mathcal {F}$
distribution than expected for a Euclidean Universe.
PDF
