The spectral resolution of a dispersive spectrograph is dependent on the width of the entrance slit. This means that astronomical spectrographs trade-off throughput with spectral resolving power. ...Recently, optical guided-wave transitions known as photonic lanterns have been proposed to circumvent this trade-off, by enabling the efficient reformatting of multimode light into a pseudo-slit which is highly multimode in one axis, but diffraction-limited in the other. Here, we demonstrate the successful reformatting of a telescope point spread function into such a slit using a three-dimensional integrated optical waveguide device, which we name the photonic dicer. Using the CANARY adaptive optics (AO) demonstrator on the William Herschel Telescope, and light centred at 1530 nm with a 160 nm full width at half-maximum, the device shows a transmission of between 10 and 20 per cent depending upon the type of AO correction applied. Most of the loss is due to the overfilling of the input aperture in poor and moderate seeing. Taking this into account, the photonic device itself has a transmission of 57 ± 4 per cent. We show how a fully-optimized device can be used with AO to provide efficient spectroscopy at high spectral resolution.
The spectral resolution of a dispersive astronomical spectrograph is limited by the trade-off between throughput and the width of the entrance slit. Photonic guided wave transitions have been ...proposed as a route to bypass this trade-off, by enabling the efficient reformatting of incoherent seeing-limited light collected by the telescope into a linear array of single modes: a pseudo-slit which is highly multimode in one axis but diffraction-limited in the dispersion axis of the spectrograph. It is anticipated that the size of a single-object spectrograph fed with light in this manner would be essentially independent of the telescope aperture size. A further anticipated benefit is that such spectrographs would be free of 'modal noise', a phenomenon that occurs in high-resolution multimode fibre-fed spectrographs due to the coherent nature of the telescope point spread function (PSF). We seek to address these aspects by integrating a multicore fibre photonic lantern with an ultrafast laser inscribed three-dimensional waveguide interconnect to spatially reformat the modes within the PSF into a diffraction-limited pseudo-slit. Using the CANARY adaptive optics (AO) demonstrator on the William Herschel Telescope, and 1530 plus or minus 80 nm stellar light, the device exhibits a transmission of 47-53 per cent depending upon the mode of AO correction applied. We also show the advantage of using AO to couple light into such a device by sampling only the core of the CANARY PSF. This result underscores the possibility that a fully optimized guided-wave device can be used with AO to provide efficient spectroscopy at high spectral resolution.
We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < or =Q2 < or =1.0 GeV2. These asymmetries, arising from interference of ...the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, Q2 dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments.
Surfactant-mediated synthesis methods have attracted much interest for the production of inorganic mesoporous materials, which can, on removal of the surfactant template, incorporate polymeric, ...organic, inorganic and organometallic ‘guests’ in their pores. These materials—initially made of silica, but now also available in the form of other oxides, sulphides, phosphates and metals—could find application in fields ranging from catalysis, adsorption and sensing technology to nanoelectronics. The extension of surfactant-mediated synthesis to produce inorganic–organic hybrid material (that is, materials that contain organic groups as an integral part of their framework structure) promises access to an even wider range of application possibilities. Such hybrid materials have been produced in the form of amorphous silicates (xerogels) that indeed display unique properties different to those of the individual components, but their random networks with broad pore-size distributions severely limit the shape and size selectivity of these materials. Mesoporous hybrid materials with periodic frameworks have been synthesized, but the organic groups are all terminally bonded to the pore surface, rather than incorporated into the pore walls. Here we describe a periodic mesoporous organosilica containing bridge-bonded ethene groups directly integrated into the silica framework. We are able to solvent-extract and ion-exchange the surfactant templates to create a stable and periodic mesoporous ethenesilica with high surface area and ethene groups that are readily accessible for chemical reaction. Recent syntheses of similar periodic mesoporous organosilicas and the ability to incorporate a variety of bridging organic and organometallic species raise the prospect of being able to fuse organic synthesis and inorganic materials chemistry to generate new materials with interesting chemical, mechanical electronic, optical and magnetic properties.
Understanding and prediction of Indian monsoon onset is of paramount importance for agricultural planning, which affects food production and the gross domestic product of the country. A recent ...observational study suggests that the progression of the Indian monsoon onset in a northwestward direction, which is perpendicular to the mean flow, is reinforced by the moistening of the free troposphere by pre‐monsoon showers and wetting of the land surface. As the onset progresses, the mid‐tropospheric dry layer is thought to be constantly moistened from below by detrainment from shallow cumulus and congestus clouds from the southeast. The dry layer becomes much shallower towards southeast India, making the profile closer to moist adiabatic, providing favourable conditions for deep cumulus convection. Increased moistening of the free troposphere thereby pushes the northern limit of moist convection northwestwards. Here, we examine the representation of this process in hindcast simulations from the fully coupled atmosphere–ocean seasonal forecast system of the UK Met Office, GloSea5. The model effectively captures the mid‐level dry‐air intrusion from the northwest that suppresses convection over the northwestern parts of India. We also show that detrainment from shallow convection, measured by moisture tendencies around the freezing level, acts to saturate the free troposphere ahead of the monsoon onset, eroding the dry layer from the southeast. This work suggests that initialized coupled models are capable of simulating dynamic and thermodynamic processes inherent in monsoon progression during the onset.
Northwest‐to‐southeast vertical section of ISCCP cloud fraction on pressure levels for cloud optical thickness, tau > 0.3 (shaded) and change in specific humidity (contoured) around (a) May 15 (averaged from May 13–17), (b) June 1 (averaged from May 30–June 3), (c) June 15 (averaged from June 13–17), (d) July 1 (averaged from June 29–July 3) and (e) July 15 (averaged from July 13–17). The orange dashed line represents the freezing level (T=0°C).A recent observational study suggests that the Indian monsoon progression in a north‐westward direction perpendicular to the mean flow occurs due to a moistening of the free troposphere and wetting of land surface. Using an initialized fully‐coupled model, we show that detrainment from shallow convection, measured by moisture tendencies around the freezing level, acts to saturate the free troposphere ahead of monsoon onset, eroding the dry‐layer from the southeast; thereby pushing the northern limit of moist convection to move north‐westwards.
A new class of bifunctional periodic mesoporous organosilicas (BPMOs) containing two differently bonded organic moieties in a mesoporous host has been synthesized and characterized. By incorporating ...bridge-bonded ethylene groups into the walls and terminally bonded vinyl groups protruding into the channel space, both the chemistry and physical properties of the resulting BPMO could be modified. The materials have periodic mesoporous structures in which the bridging ethylene plays a structural and mechanical role and the vinyl groups are readily accessible for chemical transformations. The vinyl groups in the material underwent hydroboration with BH3·THF and the resulting organoborane in the BPMO was quantitatively transformed into an alcohol using either H2O2/NaOH or NaBO3·4H2O. The materials retained ordered structures after subsequent in situ reactions with largely unchanged pore volumes, specific surface areas and pore size distributions. Other organic functionalized BPMO materials may be synthesized in a similar manner or by further functionalizing the resulting borylated or alcohol functionalized BPMO materials. The thermal properties of the BPMO materials have also been investigated and are compared to those of the periodic mesoporous organosilica (PMO) materials. Noteworthy thermal events concern intrachannel reactions between residual silanols or atmospheric oxygen and organics in BPMOs. They begin around 300 °C and smoothly interconvert bridging ethylene to terminal vinyl groups and terminal vinyl to gaseous ethene and ethane, ultimately producing periodic mesoporous silica at 900 °C that exhibits good structural order and a unit-cell size decreased relative to that of the parent BPMO.
We have investigated the time variations in the light curves from a sample of long and short Fermi/GBM gamma-ray bursts (GRBs) using an impartial wavelet analysis. The results indicate that in the ...source frame, the variability time-scales for long bursts differ from that for short bursts, variabilities of the order of a few milliseconds are not uncommon and an intriguing relationship exists between the minimum variability time and the burst duration.
ABSTRACT For a sample of Swift and Fermi gamma-ray bursts, we show that the minimum variability timescale and the spectral lag of the prompt emission is related to the bulk Lorentz factor in a ...complex manner. For small Γ's, the variability timescale exhibits a shallow (plateau) region. For large Γ's, the variability timescale declines steeply as a function of Γ ( ). Evidence is also presented for an intriguing correlation between the peak times, tp, of the afterglow emission and the prompt emission variability timescale.
ABSTRACT
We present a direct link between the minimum variability time‐scales extracted through a wavelet decomposition and the rise times of the shortest pulses extracted via fits of 34 Fermi ...Gamma‐ray Burst Monitor (GBM) Gamma‐Ray Burst (GRB) light curves comprised of 379 pulses. Pulses used in this study were fitted with lognormal functions, whereas the wavelet technique used employs a multiresolution analysis that does not rely on identifying distinct pulses. By applying a corrective filter to published data fitted with pulses, we demonstrate agreement between these two independent techniques and offer a method for distinguishing signal from noise.
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