M-CSF instructs myeloid lineage fate in single haematopoietic stem cells

Under stress conditions such as infection or inflammation the body rapidly needs to generate new blood cells that are adapted to the challenge. Haematopoietic cytokines are known to increase output of specific mature cells by affecting survival, expansion and differentiation of lineage-committed progenitors, but it has been debated whether long-term haematopoietic stem cells (HSCs) are susceptible to direct lineage-specifying effects of cytokines. Although genetic changes in transcription factor balance can sensitize HSCs to cytokine instruction, the initiation of HSC commitment is generally thought to be triggered by stochastic fluctuation in cell-intrinsic regulators such as lineage-specific transcription factors, leaving cytokines to ensure survival and proliferation of the progeny cells. Here we show that macrophage colony-stimulating factor (M-CSF, also called CSF1), a myeloid cytokine released during infection and inflammation, can directly induce the myeloid master regulator PU.1 and instruct myeloid cell-fate change in mouse HSCs, independently of selective survival or proliferation. Video imaging and single-cell gene expression analysis revealed that stimulation of highly purified HSCs with M-CSF in culture resulted in activation of the PU.1 promoter and an increased number of PU.1(+) cells with myeloid gene signature and differentiation potential. In vivo, high systemic levels of M-CSF directly stimulated M-CSF-receptor-dependent activation of endogenous PU.1 protein in single HSCs and induced a PU.1-dependent myeloid differentiation preference. Our data demonstrate that lineage-specific cytokines can act directly on HSCs in vitro and in vivo to instruct a change of cell identity. This fundamentally changes the current view of how HSCs respond to environmental challenge and implicates stress-induced cytokines as direct instructors of HSC fate

Mode structure and ray dynamics of a parabolic dome microcavity

We consider the wave and ray dynamics of the electromagnetic field in a parabolic dome microcavity. The structure of the fundamental s-wave involves a main lobe in which the electromagnetic field is confined around the focal point in an effective volume of the order of a cubic wavelength, while the modes with finite angular momentum have a structure that avoids the focal area and have correspondingly larger effective volume. The ray dynamics indicates that the fundamental s-wave is robust with respect to small geometrical deformations of the cavity, while the higher order modes are associated with ray chaos and short-lived. We discuss the incidence of these results on the modification of the spontaneous emission dynamics of an emitter placed in such a parabolic dome microcavity.Comment: 50 pages, 17 figure

An assessment of the strength of knots and splices used as eye terminations in a sailing environment

Research into knots, splices and other methods of forming an eye termination has been limited, despite the fact that they are essential and strongly affect the performance of a rope. The aim of this study was to carry out a comprehensive initial assessment of the breaking strength of eye terminations commonly used in a sailing environment, thereby providing direction for further work in the field. Supports for use in a regular tensile testing machine were specially developed to allow individual testing of each sample and a realistic spread of statistical data to be obtained. Over 180 break tests were carried out on four knots (the bowline, double bowline, figure-of-eight loop and perfection loop) and two splices (three-strand eye splice and braid-on-braid splice). The factors affecting their strength were investigated. A statistical approach to the analysis of the results was adopted. The type of knot was found to have a significant effect on the strength. This same effect was seen in both types of rope construction (three-strand and braid-on-braid). Conclusions were also drawn as to the effect of splice length, eye size, manufacturer and rope diameter on the breaking strength of splices. Areas of development and further investigation were identified

Muon-Spin Rotation Spectra in the Mixed Phase of High-T_c Superconductors : Thermal Fluctuations and Disorder Effects

We study muon-spin rotation (muSR) spectra in the mixed phase of highly anisotropic layered superconductors, specifically Bi_2+xSr_2-xCaCu_2O_8+delta (BSCCO), by modeling the fluid and solid phases of pancake vortices using liquid-state and density functional methods. The role of thermal fluctuations in causing motional narrowing of muSR lineshapes is quantified in terms of a first-principles theory of the flux-lattice melting transition. The effects of random point pinning are investigated using a replica treatment of liquid state correlations and a replicated density functional theory. Our results indicate that motional narrowing in the pure system, although substantial, cannot account for the remarkably small linewidths obtained experimentally at relatively high fields and low temperatures. We find that satisfactory agreement with the muSR data for BSCCO in this regime can be obtained through the ansatz that this ``phase'' is characterized by frozen short-range positional correlations reflecting the structure of the liquid just above the melting transition. This proposal is consistent with recent suggestions of a ``pinned liquid'' or ``glassy'' state of pancake vortices in the presence of pinning disorder. Our results for the high-temperature liquid phase indicate that measurable linewidths may be obtained in this phase as a consequence of density inhomogeneities induced by the pinning disorder. The results presented here comprise a unified, first-principles theoretical treatment of muSR spectra in highly anisotropic layered superconductors in terms of a controlled set of approximations.Comment: 50 pages Latex file, including 10 postscript figure

Oscillations of a solid sphere falling through a wormlike micellar fluid

We present an experimental study of the motion of a solid sphere falling through a wormlike micellar fluid. While smaller or lighter spheres quickly reach a terminal velocity, larger or heavier spheres are found to oscillate in the direction of their falling motion. The onset of this instability correlates with a critical value of the velocity gradient scale $\Gamma_{c}\sim 1$ s$^{-1}$. We relate this condition to the known complex rheology of wormlike micellar fluids, and suggest that the unsteady motion of the sphere is caused by the formation and breaking of flow-induced structures.Comment: 4 pages, 4 figure

Reliability of the beamsplitter based Bell-state measurement

A linear 50/50 beamsplitter, together with a coincidence measurement, has been widely used in quantum optical experiments, such as teleportation, dense coding, etc., for interferometrically distinguishing, measuring, or projecting onto one of the four two-photon polarization Bell-states $|\psi^{(-)}>$. In this paper, we demonstrate that the coincidence measurement at the output of a beamsplitter cannot be used as an absolute identifier of the input state $|\psi^{(-)}>$ nor as an indication that the input photons have projected to the $|\psi^{(-)}>$ state.Comment: 4 pages, two-colum

Improvements in the determination of ISS Ca II K parameters

Measurements of the ionized Ca II K line are one of the major resources for long-term studies of solar and stellar activity. They also play a critical role in many studies related to solar irradiance variability, particularly as a ground-based proxy to model the solar ultraviolet flux variation that may influence the Earth's climate. Full disk images of the Sun in Ca II K have been available from various observatories for more than 100 years and latter synoptic Sun-as-a-star observations in Ca II K began in the early 1970s. One of these instruments, the Integrated Sunlight Spectrometer (ISS) has been in operation at Kitt Peak (Arizona) since late 2006. The ISS takes daily observations of solar spectra in nine spectra bands, including the Ca II K and H line s. We describe recent improvements in data reduction of Ca II K observations, and present time variations of nine parameters derived from the profile of this spectral line

Phase Separation of Rigid-Rod Suspensions in Shear Flow

We analyze the behavior of a suspension of rigid rod-like particles in shear flow using a modified version of the Doi model, and construct diagrams for phase coexistence under conditions of constant imposed stress and constant imposed strain rate, among paranematic, flow-aligning nematic, and log-rolling nematic states. We calculate the effective constitutive relations that would be measured through the regime of phase separation into shear bands. We calculate phase coexistence by examining the stability of interfacial steady states and find a wide range of possible ``phase'' behaviors.Comment: 23 pages 19 figures, revised version to be published in Physical Review

Ultrathin Solar Cells Based on Atomic Layer Deposition of Cubic versus Orthorhombic Tin Monosulfide

Tin monosulfide can be grown in cubic (π-SnS) and orthorhombic (α-SnS) polymorphs by low-temperature atomic layer deposition (ALD). The optical properties of these polymorphs make them attractive for the realization of plasmonic solar cells with ultrathin absorber layers down to 10 nm in thickness. SnS is also an earth-abundant and nontoxic compound semiconductor of high interest for regular thin-film photovoltaics. To better understand the behavior of the two SnS polymorphs in ultrathin solar cell configurations, we here fabricate, characterize, and analyze a range of such devices. ALD is used to grow SnS and form heterojunctions with zinc oxysulfide [Zn(O,S)], acting as a buffer layer with a composition-tunable bandgap. Apart from the roles of the SnS polymorph and Zn(O,S) composition, the effects of the back contact material and thicknesses of buffer and absorber layers are investigated. Devices using π-SnS and pure ZnO buffers yield the highest photocurrents (3.1 mA/cm2) and higher open circuit voltage (159 mV) than similar α-SnS-based devices. Analysis of the equivalent-circuit parameters suggests that interface recombination limits the voltage for these devices. While Zn(O,S) with a higher sulfur content provides chemical passivation of the SnS interface and excessive open circuit voltages above 600 mV, it also exhibits a too high conduction band offset, which hampers current collection. A growth delay during the ALD of Zn(O,S) on SnS initially amplifies the known sulfur–oxygen exchange reaction, such that a sulfur-rich Zn(O,S) region forms next to the SnS interface. This causes a thin ZnS-like barrier to form already for low cycle fractions of the H2S precursor in the ALD super-cycle. Voltage and fill factor trends suggest an optimal SnS absorber layer thickness in the range of 15–35 nm, presenting an opportunity for plasmonic absorption enhancement. Devices with π-SnS show most promise, but interface recombination versus current-blocking is a dilemma for the SnS/Zn(O,S) heterojunction

Quenching of chlorophyll fluorescence induced by silver nanoparticles

The interaction between chlorophyll (Chl) and silver nanoparticles (AgNPs) was evaluated by analyzing the optical behavior of Chl molecules surrounded by different concentrations of AgNPs (10, 60, and 100 nm of diameter). UV–Vis absorption, steady state and time-resolved fluorescence measurements were performed for Chl in the presence and absence of these nanoparticles. AgNPs strongly suppressed the Chl fluorescence intensity at 678 nm. The Stern-Volmer constant (KSV) showed that fluorescence suppression is driven by the dynamic quenching process. In particular, KSV was nanoparticle size-dependent with an exponential decrease as a function of the nanoparticle diameter. Finally, changes in the Chl fluorescence lifetime in the presence of nanoparticles demonstrated that the fluorescence quenching may be induced by the excited electron transfer from the Chl molecules to the metal nanoparticles