Wide Solid Angle Research Articles

Energy flows in thick accretion discs and their consequences for black hole feedback

We study energy flows in geometrically thick accretion discs, both optically thick and thin, using general relativistic, three-dimensional simulations of black hole accretion flows. We find that for non-rotating black holes the efficiency of the total feedback from thick accretion discs is $3\%$ - roughly half of the thin disc efficiency. This amount of energy is ultimately distributed between outflow and radiation, the latter scaling weakly with the accretion rate for super-critical accretion rates, and returned to the interstellar medium. Accretion on to rotating black holes is more efficient because of the additional extraction of rotational energy. However, the jet component is collimated and likely to interact only weakly with the environment, whereas the outflow and radiation components cover a wide solid angle.

Narrowband thermal radiation from closed-end microcavities

High spectral selectivity of thermal radiation is important for achieving high-efficiency energy systems. In this study, intense, narrowband, and low directional absorption/radiation were observed in closed-end microcavity which is a conventional open-end microcavity covered by a semi-transparent thin metal film. The quality factor (Q factor) of optical absorption band strongly depended on the film electrical conductivity. Asymmetric and narrow absorption band with a Q factor of 25 at 1.28 μm was obtained for a 6-nm-thick Au film. Numerical simulations suggest that the formation of a fixed-end mode at the cavity aperture contributes to the narrowband optical absorption. The closed-end microcavity filled with SiO2 exhibits intense and isotropic thermal radiation over a wide solid angle according to numerical simulation. The narrow and asymmetric absorption spectrum was experimentally confirmed in a model of closed-end microcavity.

Recent polarizing supermirror projects at the ILL

We present a status of recent projects involving the in-house production of neutron multilayer optics, mainly polarizing supermirrors, at the ILL. Our main "mass production" project is for the wide-solid angle analyzing benders for the future instrument WASP (Wide Angle Spin Echo). The current status of this project based on Co/Ti supermirrors, which spans several years, will be presented. Some parameters of polarizing supermirrors for cavity polarizers, mainly based on Fe/Si supermirrors and produced in the past few years for various ILL instruments, are also reported. Some supermirror samples produced in order to study depolarization effects are also mentioned.

A multipurpose ultra-high vacuum-compatible chamber for in situ X-ray surface scattering studies over a wide range of temperature and pressure environment conditions

A low/high temperature (60-1000K) and pressure (10−10−3x103 mbar) "baby chamber", specially adapted to the grazing-incidence X-ray scattering station, has been designed, developed and installed at the Spanish CRG BM25 SpLine beamline at European Synchrotron Radiation Facility. The chamber has a cylindrical form with 100 mm of diameter, built on a 360° beryllium nipple of 150 mm height. The UHV equipment and a turbo pump are located on the upper part of the chamber to leave a wide solid angle for exploring reciprocal space. The chamber features 4 CF16 and 5 CF40 ports for electrical feed through and leak valves, ion gun, etc. The heat exchanger is a customized compact LN2 (or LHe) continuous flow cryostat. The sample is mounted on a Mo support on the heat exchanger, which has in the back side a BORALECTRIC® Heater Elements. Experiments of surfaces/interfaces/ multilayer materials, thin films or single crystals in a huge variety of environments can be performed, also in situ studies of growth or evolution of the samples. Data measurement can be collected with a punctual and a bi-dimensional detector, being possible to simultaneously use them.

Neutron Devices at J-PARC/MLF

The IBARAKI biological crystal diffractometer, iBIX at BL03 [1] was constructed to meet demands on the structure analysis of biological macromolecules and organic compounds with unit cell dimensions up to 135 Å. It is strenuous requirement that a detector covers a wide solid angle around a sample with less gap and has a spatial resolution of 1mm and a pulse pair resolution of 1 μsec.

Formation of the radio profile components of the Crab pulsar

The induced Compton scattering of radio emission off the particles of the ultrarelativistic electron-positron plasma in the open field line tube of a pulsar is considered. We examine the scattering of a bright narrow radio beam into the background over a wide solid angle and specifically study the scattering in the transverse regime, which holds in a moderately strong magnetic field. Making use of the angular distribution of the scattered intensity and taking into account the effect of rotational aberration in the scattering region, we simulate the profiles of the backscattered components as applied to the Crab pulsar. It is suggested that the interpulse (IP), the high-frequency interpulse (IP') and the pair of the so-called high-frequency components (HFC1 and HFC2) result from the backward scattering of the main pulse (MP), precursor (PR) and the low-frequency component (LFC), respectively. The components of the high-frequency profiles, the IP' and HFCs, are interpreted for the first time. The HFC1 and HFC2 are argued to be a single component split by the rotational aberration close to the light cylinder. It is demonstrated that the observed spectral and polarization properties of the profile components of the Crab pulsar as well as the giant pulse phenomenon outside of the MP can be explained in terms of our model.

The role of plasma ejections in the development of large solar flares of various durations

Recent observations indicate that relatively strong plasma ejections are accompanied by the formation of systems of coronal loops with two glowing ribbons near their footpoints. However, while two-ribbon flares can sometimes last for many hours, for example, soft X rays, they sometimes decay within tens of minutes. We study here factors affecting the durations of flares using four major flares occurring in July 15–18, 2002, as examples. Various ground-based and satellite observations are used to show that short-duration events involved collimated (narrow) plasma ejections directed to the north and the subsequent formation of compact loops in the leading part of the active region. During one event, a powerful eastward ejection in a wide solid angle was followed by the formation of an extended arch system in the trailing part, which determined the long duration of the flare. It is proposed that in events involving collimated jets and corresponding narrow features in coronal mass ejections (CMEs), systems of coronal loops do form, but post-eruptive energy release either does not occur or is expressed very faintly. So the energy does not go downward from this region, and the plasma is emitted free in the coronal loops. In contrast to such rapid flares, wide ejections and bright, large-scale CMEs are accompanied by the formation and prolonged existence of an extended arch system. Thus, powerful nonstationary solar processes involve a large-scale CME and the flare itself, with the pattern of a particular event determined by the reconnection scenario and the evolution of the ejected plasma.

Construction of an electron analyzer with a wide acceptance solid angle

We have developed a new electron energy analyzer with a large solid angle of 0.14 π, which is comparable to that of cylindrical mirror analyzer. Typical energy resolution was Δ E/ E 0 ∼ 0.016 for the aperture of 1 mm and central radius of 100 mm, and typical angular resolution was less than 0.5°.

Sources of mass bias and isotope ratio variation in multi-collector ICP-MS: optimization of instrumental parameters based on experimental observations

In this work, several contributing factors to the observed mass bias in inductively coupled plasma mass spectrometry (ICP-MS) have been identified. Analyses of the isotopic compositions of B deposited on sampler and skimmer cones demonstrate enrichment of 10B on the former and 11B on the latter. Grounding the capacitive discharge system to enhance sensitivity also magnified the level of 11B enrichment on the skimmer cone more than four-fold. This supersonic expansion of the ion beam behind the sampler is confirmed to be an important source of mass bias. Isotopic analyses of the Fe, Zn and Tl leached from used extraction lenses yielded a linear relationship between the levels of lighter isotope depletion and mass ratio. Although consistent with the space-charge effect, the fact that isotopically-heavy deposits were found demonstrates that the ion beam diverges into a relatively wide solid angle in the field-free region behind the skimmer. This severely impairs transmission of, in particular, the lighter isotopes. For a wide range of elements (Li, B, Fe, Ni, Cu, Sb, Ce, Hf and Re), the magnitude of the mass bias was found to be affected by the sample gas flow rate, as well as the distance between the sampler and the end of the torch, i.e., the sampling depth, employed in the Neptune multi-collector ICP-MS instrument. Mathematical analysis of the profiles of intensity variations as a function of these instrumental parameters revealed that the response peaks closer to the torch for the heavier isotopes of all studied elements. Owing to this spatial non-coincidence, tuning for maximum intensity on either isotope will result in sampling from a region where even slight plasma instabilities will be translated into substantial variations in mass bias. Therefore, in-plasma processes also contribute to the degree and temporal stability of mass bias. In light of these findings, recommendations for optimizing multi-collector ICP-MS with respect to obtaining the highest possible precision are presented.

Experimental evidence of differences in properties of fast ion fluxes from short-pulse and long-pulse laser-plasma interactions

Essential differences in properties of fast ion fluxes from the interaction of 1 ps and 0.5 ns laser pulses with Au target have been observed. In the short-pulse case, only a single fast ion group with a small angular divergence is generated and ions are likely to be accelerated by an axial ponderomotive force from the skin-layer interaction. In the long-pulse case, at least two groups of fast ions are emitted into a wide solid angle and the ion flux properties seem to be determined by self-focussing of the laser beam in plasma.

Imaging Large-Scale Structure in the X-Ray Sky

We present the first results from a wide solid angle, moderately deep {\it Chandra} survey of the Lockman Hole North-West region. Our 9 ACIS-I fields cover an effective solid angle of 0.4 deg$^{2}$ and reach a depth of $3 \times 10^{-16}$ \ergpcmsqps in the 0.4--2 keV band and $3 \times 10^{-15}$ \ergpcmsqps in the 2--8 keV band. The best fit logN-logS for the entire field, the largest contiguous {\it Chandra} field yet observed, matches well onto that of the {\it Chandra} Deep Field North. We show that the full range of the `cosmic variance' previously seen in different {\it Chandra} fields is reproduced in this small region of the sky. Counts-in-cells analysis shows that the hard band sources are more strongly correlated than the soft band sources.

Fibre remote optoelectronic gamma dosimetry based on optically stimulated luminescence of Al2O3:C.

Optically stimulated luminescence dosimetry (OSL-D) used in conjunction with fibre optics enables a remote measurement of dose, for the purpose of radioprotection in the nuclear industry and in medicine (radiology, radiotherapy). Alumina OSL crystals are used because of their low Z, low fading and optical transparency, which improves the sensitivity. An optoelectronic portable dosemeter has been designed and tested that shows a dose detection of 50 microGy with a 20 metre-long fibre. Following irradiation, all trapped electrons are released under light stimulation while the OSL is integrated to provide dose-equivalent measurements. A compensation technique is designed with the help of the MCNP4b code, so that both angular and photon energy characteristics comply with international standards (CEI 61066) for photon dose equivalent Hp(10). Two sensors are described that allow measurements over a wide solid angle (95% of 4piSr), for photon energies ranging from 15 keV to 3 MeV.

21.1: Electro‐optical Characterization of Reflective LCDs

AbstractThe concept of the BRDF (Bidirectional Reflectance Distribution Function) is applied to analyze, characterize and understand the reflective properties of LCDs and their components in more detail. BRDFs are measured in the plane of light incidence with a goniometric apparatus (“in‐plane BRDF”) while the full 2‐dimensional BRDF is measured with a conoscopic device. BRDF‐curves of typical reflective LCDs clearly show the individual contributions of the first surface (unwanted reflections) and the component from the reflector, which is modulated by the LC‐cell and is thus carrying the information to be displayed. The effect of anti‐glare coatings on the front polarizer surface is analyzed via BRDF measurements.Based on the acquired BRDF data we explain the function of a device for diffuse reflective illumination that can be considered as the correspondence to the “dark‐room condition” in the case of transmissive LCDs since it is designed to effectively avoid disturbing unwanted reflections from the first display to air interface and, at the same time assuring illumination over a wide solid angle (up to 70°).

Novel techniques of neutron powder diffraction and their applications to superconducting oxides

The time-of-flight (TOF) neutron powder diffractometer Vega, whose wide solid angle enables us to collect intensity data very efficiently, was utilized for the structure refinement of (K 0.87Bi 0.13)BiO 3 prepared at high pressure. Partial profile relaxation improved R factors more or less in Rietveld refinements of superconductors and related materials. An integrated software, REMEDY, for whole-pattern fitting combined with a maximum-entropy method was successfully applied to the determination of nuclear densities in HgBa 2CuO 4+ δ .

Type Ia Supernova Explosions in Binary Systems: The Impact on the Secondary Star and Its Consequences

One method of discriminating between the many Type Ia progenitor scenarios is by searching for contaminating hydrogen and helium stripped from the companion star. However, this requires an understanding of the effect of the impact of the supernova shell on different companion stars to predict the amount of mass stripped and its distribution in velocity and solid angle for the types of binary scenarios that have been proposed as Type Ia progenitor models. We present several high-resolution two-dimensional numerical simulations of the impact of a Type Ia supernova explosion with hydrogen-rich main-sequence, subgiant, and red giant companions. The binary parameters were chosen to represent several classes of single-degenerate Type Ia progenitor models that have been suggested in the literature. We use realistic stellar models and supernova debris profiles to represent each binary system. For each scenario, we explore the hydrodynamics of the supernova-secondary interaction, calculate the amount of stellar material stripped from the secondary and the kick delivered by the impact, and construct the velocity and solid angle distributions of the stripped material. We find that the main-sequence and subgiant companions lose 0.15-0.17 M? as a result of the impact of the supernova shell, 15% of their mass. The red giant companions lose 0.53-0.54 M?, 96%-98% of their envelopes. The characteristic velocity of the stripped hydrogen is less than 103 km s-1 for all the scenarios: 420-590 km s-1 for the red giant companions, 820 km s-1 for the main-sequence companion, and 890 km s-1 for the subgiant companion. The stripped hydrogen and helium contaminate a wide solid angle behind the companion: 115? from the downstream axis for the red giant, 66? for the main-sequence star, and 72? for the subgiant. With such low velocities, the bulk of the stripped hydrogen and helium is embedded within the low-velocity iron of the supernova ejecta. The hydrogen and helium may be visible in the late-time spectra as narrow emission lines.?????Although most of the stripped material is ejected at low velocities, all the numerical simulations yield a small high-velocity tail. The main-sequence, subgiant, and red giant companions are just under the upper limit determined by Della Valle et al. in 1996 from observations of SN 1990M taken near maximum light. The main-sequence companion receives a kick of 86 km s-1, and the subgiant receives a kick of 49 km s-1. In all cases, the kick to the remnant is smaller than the original orbital velocity. Because it is too small to intercept more than a negligible amount of momentum, the red giant core will not receive an appreciable kick.?????The impact of the supernova ejecta with the secondary star creates a hole in the supernova debris with an angular size of ~30? in the high-velocity ejecta and with an angular size of ~40? in the low-velocity ejecta. This corresponds to 7%-12% of the ejecta's surface. Because we explore binary scenarios that are close enough, or almost close enough, to be in Roche lobe overflow, the degree of asymmetry is similar for all the models. The asymmetry in the supernova debris could have observational consequences beyond the change in morphology of the supernova remnant. The asymmetry in the supernova atmosphere will result in distorted P Cygni profiles that might indicate the presence of the companion star, but it will be difficult to use the degree of asymmetry alone to discriminate between a main-sequence, subgiant, or red giant companion.?????The impact of the supernova shell will have consequences for the future evolution of the secondary star. After the impact, the main-sequence star is puffed up, much like a pre-main-sequence star. The luminosity will rise dramatically, to as high as ~5000 L?, as the extended envelope relaxes back into thermal equilibrium. The subgiant companion will follow a similar sequence of events. The star will not be contaminated by much supernova debris from the initial impact, but it may accrete low-velocity iron-group elements (or oxygen and silicon if the ejecta is radially mixed) at late times.?????A He pre-white dwarf will be left behind after a supernova explosion with a red giant companion. Almost all of the envelope will be ejected by the impact, but a residual amount of material (~0.02 M?) will form an extended, hydrogen-rich envelope around the degenerate core. The star will evolve away from the red giant branch on a timescale of 105-106 yr. On its post-red giant track, it may appear as an underluminous O or B star before passing through an sdO or sdB phase on its way to a standard He white dwarf cooling track. This binary scenario could be a possible pathway for the formation of a subset of single, low-mass He white dwarfs.

Fully resolved kinematics of grazing-incidence (e,2e) experiments

The capability of grazing-incidence (e,2e) spetroscopy to map the spectral momentum density ρ( ε, q ) of the valence electronic states in surfaces was demonstrated by a pioneering experiment in which both the band structure (binding energy, ε, versus momentum, q ) and the momentum density, ρ, were obtained [S. Rioual et al., Phys. Rev. B 57 (1998) 2545]. (e,2e) experiments reveal, in coincidence, after energy and angle selection, the two final electrons generated by the impact of a primary electron on the surface. The momentum resolution achieved by the first experiment was limited because of the integration over the wide solid angle accepted by the ejected-electrons analyzer. This limitation has been overcome in the present work by upgrading the ejected-electrons analyzer with a position-sensitive detector (PSD). The PSD allows us to measure the azimuth angle of the ejected electrons, and hence to collect in a parallel mode (e,2e) spectra that are fully differential in momentum. Preliminary data relative to the ionization of the π-band of highly oriented pyrolitic graphite (HOPG) show that a momentum resolution better than 0.2 Å −1 has been achieved without degrading the overall spectrometer luminosity.

Semitransparent metal or distributed Bragg reflector for wide-viewing-angle organic light-emitting-diode microcavities

Microcavities for organic light-emitting devices (OLED’s) with a metal mirror on one side and a distributed Bragg reflector (DBR) on the other side have been extensively studied in the literature. Usually the DBR is highly reflective, and the resulting emission of the microcavity depends strongly on angle and wavelength. With a thick metal mirror on one side and a semi-transparent metal mirror on the other side of the OLED, a microcavity can be obtained with an optical thickness of 1 half-wavelength. Because the emission is enhanced over a wide solid angle, with a small spectral dependence, this structure is very promising for display applications. For a TPD/ALq3 structure with a typical intrinsic emission spectrum, embedded in a microcavity with a thick and a semitransparent silver mirror, the integrated emission in air, the color variation with angle, and the change in the decay time are compared with those in a DBR-based microcavity.

Analysis of InGaN High-Brightness Light-Emitting Diodes

InGaN high-brightness light-emitting diodes (LEDs) have been analyzed. The analysis, based on non-absorbing ohmic electrode model, shows that InGaN LEDs have an extremely wide escape cone solid angle which is about 2.8 times that in conventional high-brightness LEDs. As a result, the external quantum efficiency in InGaN LEDs is as high as 9% despite the presumably very low internal quantum efficiency.

High-resolution photon detection system for inverse-photoemission spectroscopy

A new type of photon detection system has been developed for inverse-photoemission spectrometry. The photon detection system is made up of MgF 2 prisms, two parabolic mirrors and a photon detector, and has a wide solid acceptance angle of 0.35 sr. The energy resolution has been determined to be as high as 94 meV by measuring a line spectrum (Xe i; 9.569 eV) using this detection system. The overall energy resolution of the inverse-photoemission spectrometer consisting of the present photon detection system and of an electron gun with a BaO cathode has been estimated to be 0.30 eV using data collected from polycrystalline Au.

A method for reaching detection efficiencies necessary for optical loophole-free Bell experiments

A method for preparing loophole-free four-photon Bell experiments which requires a detection efficiency of 67% is proposed. It enables realistic detection efficiencies of 75% at a visibility of 85%. Each of the two type-II crystals down converts one correlated photon pair and we entangle one photon from one pair with one photon from the other pair on a highly transparent beam splitter. The entanglement selects two other conjugate photons into a Bell state. Wide solid angles for the conjugate photons then enable us to collect close to 100% of them. The cases when both photon pairs come from only one of the two crystals are successfully taken into account. Hardy's equalities are discussed.