Greater Radius Research Articles

The Parker–Levy reversal mechanism

Parker and Levy proposed that geomagnetic reversals result from fluctuations in the location of cyclonic convection cells that reverse the toroidal flux in mid-latitudes, as exhibited by a mean field dynamo model with differential rotation concentrated at the outer boundary, and α at a moveable interior point. Roberts studied a more realistic model with α and ω spread over a volume, but found that it produced oscillatory rather than stationary fields without sufficient meridian circulation. This difference in behaviour is explored with a dynamo model where the concentrated quantities used by Levy have been replaced with broader functions. Stationary solutions are obtained when ω is concentrated at a greater radius than α, provided α is at sufficiently low latitudes. Toroidal flux is reversed when α is in high latitudes, as required by the Parker–Levy reversal mechanism. At very high latitudes, the dynamo oscillates, the transition between stationary and oscillatory modes suggesting a different mechanism for reversal. When ω is at a smaller radius than α, toroidal flux does not reverse, and the solutions are always steady, so in this case the reversal mechanism will not work. When α and ω overlap, stationary solutions are only possible with α at very low latitudes; otherwise, solutions are oscillatory. Sufficient meridian circulation leads to stationary solutions for all locations of α with reversed toroidal flux when α is at high latitudes. I conclude that the Parker–Levy reversal mechanism can apply provided the cyclonic convection is inside the differential rotation, or sufficient meridian circulation exists to stabilise the geodynamo when α and ω overlap. Reversal behaviour also occurs in many instances where the preferred dynamo mode becomes oscillatory.

Flames structure measurement of single, isolated aluminum particles burning in air

Spatially resolved measurements of the flame structure about single, isolated aluminum particles burning in air were made using planar laser-induced fluorescence (PLIF) and electron probe microanalysis (EPMA). Spherical aluminum particles of 210 μ m diameter were generated continuously by mechanical chopping of wire strands and laser heating, which also ignited the particles. After ignition, combustion was found to occur in two stages consisting of an initial steady burning phase, characterized by a spherical flame positioned off the surface, and a second violent, unsteady burning phase, during which gaseous ejections occurred from the particle surface. PLIF was used to measure the radial profiles of gaseous AlO and AlO vibrational temperature during the steady burning stage of particle free fall. The radial distribution of condensed-phase Al 2 O 3 was measured by impaction and rapid quenching of individual particles and their associated oxide clouds on silicon plates. Analysis of the impacted cloud distribution was performed off-line with EPMA and Abel transform techniques. Results indicated a flame structure of finite thickness, wherein AlO is a gas-phase intermediate. Relative peak concentrations of AlO and Al 2 O 3 were measured at r/r s =2.8 and r/r s =3.5, respectively. The temperature rose from ∼2350 K at the particle surface to a nearly constant value of ∼3800 K between 5< r/r s <6. The surface temperature agrees well with previously reported ignition temperatures, while the plateau temperature is ∼300 K higher than the theoretically predicted adiabatic flame temperature for a stoichiometric Al-air mixture. The species and temperature measurements support previously proposed models where gasification can occur by both vaporization and heterogeneous surface reactions. Transport of Al outward and reaction with inward-diffusing molecular oxygen yields AlO. Subsequent heterogeneous reactions involving AlO yield condensed-phase Al 2 O 3 at even greater radii.

Abell 2163: Temperature, Mass, and Hydrostatic Equilibrium

Using ASCA data, we have measured the electron temperature in Abell 2163 out to 1.5 h<SUP>-1</SUP> Mpc (¾ of the virial radius, or 10a<SUB>x</SUB>, where a<SUB>x</SUB> is the X-ray core-radius) from the center, in three radial bins. The obtained temperatures are 12.2<SUP>+1.9</SUP><SUB>-1.2</SUB> keV, 11.5<SUP>+2.7</SUP><SUB>-2.9</SUB> keV, and 3.8<SUP>+1.1</SUP><SUB>-0.9</SUB> keV in the 0-3a<SUB>x</SUB> (0-3'.5), 3-6a<SUB>x</SUB> and 6-13a<SUB>x</SUB> spherical shells, respectively. [Errors are 90% throughout the paper unless otherwise stated and h = H<SUB>0</SUB>(100 km s<SUP>-1</SUP> Mpc<SUP>-1</SUP>)<SUP>-1</SUP>.] Formally applying the hydrostatic equilibrium and spherical symmetry assumptions and using these data together with the Ginga spectral and the ROSAT imaging data, we were able to severely limit the possible binding mass distribution of the generic form ρ = ρ<SUB>0</SUB>(1 + r<SUP>2</SUP>/a<SUP>2</SUP><SUB>b</SUB>)<SUP>-n/2</SUP>. All the allowed binding mass profiles are steeper than the gas density profiles, and mass profiles with the same slope as gas are excluded at a greater than 99% confidence. The total mass inside 0.5 h<SUP>-1</SUP> Mpc is 4.3±0.5 × 10<SUP>14</SUP> h<SUP>-1</SUP> M<SUB>sun</SUB>, of which 0.074h<SUP>-3/2</SUP> is gas, while inside 1.5h<SUP>-1</SUP> Mpc, the mass is 1.07±0.13 × 10<SUP>15</SUP> h<SUP>-1</SUP> M<SUB>sun</SUB>. <P />The strongest constraint on the mass profile is the observed quick drop of the temperature at large radii, which can be reconciled only marginally with the ROSAT detection of gas at an even greater radius. We note that in the outer part of this cluster, which is likely to be a recent merger, the timescale for reaching electron- ion temperature equality via collisions is comparable to the merger timescale, so the measured electron temperature may give an underestimate of the gas pressure there. Otherwise, if our low value is indeed representative of the gas temperature in the outer shell, the cluster atmosphere should be convectionally unstable, and gas turbulence should exist. Bulk motions of the gas are also expected during the merger. Their existence would increase the total gas pressure above that indicated by the observed temperature. Thus, failure of the model in which dark matter and gas have the same distribution at the radii of interest, which is favored by hydrodynamic simulations, may be due to the neglect of these phenomena, which leads to an underestimate of the total density and an overestimate of the baryonic fraction at large radii. The mass estimate at the smaller radius, where there is no evidence of departing from equilibrium, is likely to be correct. <P />Our measured electron temperatures, combined with the previously reported Sunyaev-Zeldovich decrement toward this cluster and the ROSAT gas density profile, under the assumption of spherical symmetry, are consistent with a Hubble constant between 42 and 110 km s<SUP>-1</SUP> Mpc<SUP>-1</SUP> (68% interval), where the uncertainty is dominated by that of the available SZ measurement.

The radii inversion problem associated with the Hg capillary pressure experiment

Today's practice of interpreting Hg capillary pressure curves — a widespread method in porosimetry — is generally unsatisfactory. This has already been demonstrated by Fatt. First, the saturation branch of such a curve is interpreted using the concept of a pore space model in which essential features of a network structure are disregarded. Second, the data provided by the desaturation branch are not used. Distributions of radii of capillaries within porous materials derived by this technique are usually incorrect in that the frequencies of occurrence of the greater radii turn out too small, those of the smaller radii too large. We present a more reliable approach which constrains radii frequency ranges for the Hg saturated pore space and for both the part of the pore space that desaturates and the part that traps mercury when Hg pressure is released. The pore space may be of an arbitrary geometrical structure, the radii distribution may be continuous. Also, the Hg desaturation may enable one to distinguish experimentally between structural and contact angle hysteresis.

Alterations of heart development in Xenopus laevis by galactoside-binding lectin or its sugar hapten inhibitor.

The early heart anlagen of Xenopus laevis embryos were exposed to purified embryonic galactoside-binding lectin or its potent hapten inhibitor thiodigalactoside (TDG). Heart development was then studied using a variety of microscopical techniques. Conotruncal morphology and positioning with respect to the ventricle are altered in treated animals. In 34% of animals treated with lectin and 35% treated with TDG, the conotruncus leaves the ventricle from an abnormal location. Lectin or TDG treatments are also correlated with altered conotruncal shape, with the conotruncal regions showing greater radii of curvature compared to controls. Conotruncal myocyte differentiation is altered by the test treatments, with lack of development of organized myofibrillar arrays. Conotruncal cushion development is also affected. Changes occur in the shape and size of the primary conotruncal cushion, and alterations of outflow tract septation develop. Less maturation of ventricular myocytes is also observed in test animals. The results suggest that galactose-lectin interactions are important in heart development.

Geminate recombination after binary photoionization

A kinetic law is derived for geminate recombination which results from binary encounters of photoexcited donor with electron acceptors in liquid solution. The initial distribution over ion pair separation is found for both slow and fast ionization. When ionization is controlled by diffusion, the spherical reaction layer, where ions are mainly born, is shown to have a greater radius than the closest-approach distance.

Rotation measures of low-latitude extragalactic sources and the magnetoionic structure of the Galaxy

view Abstract Citations (99) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Rotation Measures of Low-Latitude Extragalactic Sources and the Magnetoionic Structure of the Galaxy Clegg, Andrew W. ; Cordes, James M. ; Simonetti, John M. ; Kulkarni, Shrinivas R. Abstract We have obtained Faraday rotation measurements of 56 extragalactic sources predominantly in the range 45^deg^ < l < 93^deg^, |b| < 5^deg^. The data complement the few rotation measures (RMs) that have been published for low-latitude extragalactic sources, and are used to probe the Galactic magnetic field and electron density to great distances. Within the longitude range sampled here, we find RM(l) = 1600 sin (l_0_ - l) rad m^2^, with a null in RM occurring at l_0_ = 62^deg^. Under the assumption of a uniform circular geometry for the magnetic field lines, the magnetoionic medium must exist to a Galactocentric radius R_m_ ~ 25 kpc to produce the observed magnitudes of the RMs, where we have assumed that n_e_ and |B| equal their local values of 0.03 cm^-3^ and 2.1 microG out to R_m_. The medium must exist to an even greater radius if n_e_ and/or |B| decrease with R, as is likely. The null in RM at l_0_ confirms that a field reversal occurs interior to R_0_ (the radius of the solar orbit about the Galactic center) and requires that the product quantity n_e_|B| be greater inside the field-reversed region than in the local ISM. Comparison of extragalactic and pulsar RMs along nearly coincident lines of sight is consistent with at least one field reversal exterior to R_0_. An anomalous RM contribution of >~1000 rad m^2^ is found at l = 92^deg^, b = 0^deg^, with an angular size of ~1^deg^-8^deg^. The phenomenon is akin to enhanced RMs observed behind the Cygnus region. The majority of our sources are components of double- lobed objects with lobe separations of 30"-200". This allows us to study variations in Galactic Faraday rotation over small angular scales. The differences exceed those expected from a large-scale ordered field by more than two orders of magnitude. The implied linear scales for fluctuations in the magnetoionic medium are ~0.1-10 pc. We are able to explain the small-scale variations in RM solely in terms of previously observed electron density turbulence in the interstellar medium. Publication: The Astrophysical Journal Pub Date: February 1992 DOI: 10.1086/171000 Bibcode: 1992ApJ...386..143C Keywords: Extragalactic Radio Sources; Faraday Effect; Interstellar Magnetic Fields; Magnetoionics; Pulsars; Astronomical Models; Galactic Rotation; Milky Way Galaxy; Astrophysics; GALAXY: GENERAL; ISM: MAGNETIC FIELDS; POLARIZATION; RADIO CONTINUUM: GALAXIES full text sources ADS | data products NED (76) SIMBAD (75)

Human-plant relationships during the Copper and Bronze Ages in the Baza and Guadix basins (Granada, Spain)

SummaryThe anthracological study of six sites in the north of province of Granada (Spain) has uncovered vegetation for the Copper Age formed by a dense oak grove belonging to the association Rhamno-Quercetum cocciferae. In the Bronze Age, the intensification of agriculture caused changes in the vegetation, reflected in the anthracological diagrams by the increase in Pinus halepensis and the decrease of Quercus ilex-coccifera, as well a decline in the woodlands and an expansion of the legumes.The different species present in the vicinity of the site (or in a greater radius), servings such specific functions as the making of tools and utensils, house construction, and firewood for the hearth or for fours, give us preliminary insights into the ways in which these populations used space and their vegetal environment.

Neural network architecture for circular features extraction in binary patterns

A new neural network architecture developed for circular features recognition in binary images is introduced. The methodology involves a so called ‘growing the field of vision’ technique, and employs a new transfer function based on the classical sigmoid function. At any instant the method processes only cells within a circular cluster, and as time progresses the network searches for circular features of greater radii. The method is immune to translation, scaling, rotation, and, depending on the training schedule, distortion of patterns. Training procedures are presented together with the results of the recognition of some example patterns.

Dynamic mechanism of polaron pairing in a two-layer model for high- Tc oxides

Based on a polaron concept the Hubbard-type model with correlated hoppings τ is analyzed for two adjacent layers. It is shown that the presence of the second layer can stabilize the two-fermion bound state of great radius. For a finite particle concentration c⪡1 the corresponding BCS Hamiltonian leads to a finite gap in the fermion spectrum even for the strong Hubbard repulsion Uå ¦τ¦.

Experimental intracerebral haematoma: The role of blood constituents in early ischaemia

In patients with intracerebral haematoma, ischaemic damage and final outcome are often more serious than the size of the lesion would suggest. The aetiology of the ischaemia in relation to space-occupying effects or specific factors present in blood is unclear. In a rat model of an intracerebral space-occupying lesion, the pathophysiological effects of a haematoma were compared with those of an equal volume of inert fluid (mock cerebrospinal fluid [CSF] or silicone oil). Cerebral blood flow was measured at 1 min by 14C iodoantipyrine autoradiography, and ischaemic cell damage was assessed by light microscopy at 4 h. In all animals, cerebral blood flow was reduced immediately adjacent to the lesion. In the group with a haematoma, blood flow was reduced (p less than 0.001) over a greater radius and also in the ipsilateral frontal and parietal cortex. Ischaemic damage was seen in animals lesioned with blood or oil of blood viscosity, but not in animals with CSF lesions. These data suggest that both tissue pressure and vasoactive substances are components of the immediate reduction in blood flow following intracranial haemorrhage. Tissue pressure may be the more important factor in later ischaemic neuronal damage.

Selection of Intestinal Segments for Bladder Substitution: Physical and Physiological Characteristics

Detubularized bowel segments provide greater capacity at lower pressure and require a shorter length of intestine than do intact segments. Four factors account for their superiority: 1) their configuration takes advantage of the geometric fact that volume increases by the square of the radius so that a patch or pouch has a larger diameter than a tube, 2) they accommodate to filling more readily because, as LaPlace’s law states, the container with the greater radius and, thus, the greater mural tension will hold larger volumes at lower pressure, 3) compliance is superior to that of the tubular bowel and 4) contractile ability is blunted by the failure of contractions to encompass the entire circumference. For these reasons detubularized segments store more urine at lower pressures.

C/He abundances in WC stars

The C/He abundances in 17 southern WC stars have been derived from spectra in the H and K bands using, for the most part, recombination theory with allowance for collision redistribution. As appropriate calculations for C III are not available, two extremes are considered; LTE treatment of C III gives C/He values that range from 0.04 to 0.3, by number. Maximum allowance for possible non-LTE effects gives values from 0.1 to 0.7, by number. C/He decreases from WC4 to WC7. C/He in WC8 and 9 stars is uncertain because of contributions from C2+ and possibly neutral helium, but may be as high as for WC5−7 stars. The ionization balance is lower than found in previous studies. He+/He2+ is approximately constant, 2.6−3.0, for WC5−8 stars, increasing to 7 for WC9 stars. C3+/C4+ increases from WC4 to WC9, the values are 0.6−3 for LTE treatment and 5–10 times higher if non-LTE effects are important. C2+ becomes important only for WC8 and 9 stars. Comparison with Torres indicates that in the IR region (observed by us) the photosphere is at a greater radius than in the optical range (observed by Torres), and that the ionization decreases outwards. Continuum slopes and corrections for the emission line contribution to the H and K magnitudes are derived.

Expansion of various types of ileal reservoirs in situ. An experimental study in rats.

In experiments on rats four types of ileal reservoirs were constructed and left to expand in situ. After 3 months the volumes and tissue weights of the various reservoirs were compared. The reservoir types were: two loops, isoperistaltic (type I), two loops, antiperistaltic (type II), three loops, S-shaped (type III) and "four loops', double-folded U loop (Kock pouch) (type IV). There was a considerable volume increase in all types of reservoir as well as a marked increase in their tissue weight. The expansion of the reservoirs in groups III and IV was significantly greater than that in groups I and II. The difference in expansion could possibly be explained by the greater radius in three- and four-loop reservoirs compared with two-loop reservoirs if Laplace's law is applied to this process. According to this law the tension in the wall of a tube increases with increasing radius.

Impact on the earth, ocean and atmosphere

On the basis of finite-difference techniques, cratering flow calculations are used to obtain the spatial attenuation of shock pressure with radius along the impact axis for the impact of silicate rock and iron impactors on a silicate half-space at speeds of 5 to 45 km/sec. Upon impact of a 10 to 30 km diameter silicate or water object onto a 5 km deep ocean overlying a silicate half-space planet at 30 km/sec, it is found that from 12 to 15 percent of the incident energy is coupled into the water. The mass of atmosphere lost due to impacts of 1 to 5 km radius projectiles is calculated.

Determination of coordination sites in polyether phosphoryl ligands using model compounds

1. The oxide of the macrocyclic phosphine and its acyclic analog have been synthesized, as well as complexing agents of the monopodand type. 2. By using model compounds it has been shown that when the phosphoryl-containing macrocycle complexes with the lithium ion, the phosphoryl group oxygen and, apparently, the central ethereal oxygen, participate in the coordination. For ions of greater radius, the ether oxygens only are involved. 3. In the phosphoryl-containing podands, coordination with the lithium ion via the phosphoryl groups is preferred. In complex formation with ions of larger radii, the ether oxygens participate in the coordination.

Improvement in the separation of liquids of heterogenous systems

In liquid separators the separation surface is formed by a stack of conical plates~ The natural way to increase I is to increase both the dimensions (diameter and height) and also the number of the plates. However, this leads ultimately to an unacceptable increase in the rotor height, impairing the dynamic characteristics of the separators, and increasing the feed nonuniformity over the height of the stack. It is known that the current ratios between diameters and heights of the rotors have been dictated by experience over many years and have been supported by theoretical considerations in the details of the optimum dynamic characteristics of the separators. Increasing the number of plates is possible both due to a certain increase in the rotor height and also due to a decrease of the clearance between the plates for the individual liquids being separated. The volume bounded by a single plate of the separating stack, having a constant shape, may be expressed by the product aR~, where a is a constant of proportionality and R T is the greatest radius of the plate.

Magnetic properties and structure of some ternary chromium chalcogenides with thallium and silver

The structure and magnetic properties of TlCr X 2 ( X= S, Se, Te), Tl 3CrS 3, Tl 3Cr 3S 5, TlCr 3S 5, TlCl 5S 8 and AgCrO 2 have been investigated. TlCrS 2, TlCrSe 2 and Tl 3CrS 3 order ferromagnetically with Curie temperatures in the range 60–140 K. The other compounds are antiferromagnetics with negative paramagnetic Curie temperatures, whereas TlCrTe 2 is antiferromagnetic with a positive paramagnetic Curie temperature. In the case of the layered hexagonal TlCrS 2 and TlCrSe 2 owing to the great radius of the Tl-ion and the large Cr-Cr-distance the intralayer exchange interaction is positive giving rise to the ferromagnetic order. For AgCrO 2 the smaller intralayer Cr-Cr-distance gives rise to negative exchange interaction and antiferromagnetism.

Alluvial Fans and Their Deposits in Devonian Hornelen Basin, Norway: ABSTRACT

Conglomerate alluvial-fan bodies are well exposed around the fault margins of Hornelen basin. Detailed mapping of the bodies and of their internal facies variation together with logging of laterally equivalent profiles allows reconstruction of fan processes, geometry, internal cyclicity, and relation to contemporaneous flood-basin deposits. Of particular interest is fan-to-fan variation through Hornelen basin's 25 km succession, as illustrated by six examples from the northern and southern margins. Some fan bodies, particularly with small radius ( 30 cm/km) are entirely dominated by debris flows. The latter are commonly poorly sorted and massive or inversely graded. The ratio of bed thickness to maximum particle size in debris flows is usually less than 3. Other fans, usually thinner bodies, with greater radius (<6 km) and less abrupt downfan grain-size gradients, contain a significant amount of fluvial (braided stream) or sheet-flood deposits, which are usually concentrated in the middle or lower fan reaches. End_of_Article - Last_Page 828------------

Bose‐Einstein condensation of free excitons in AgBr‐type crystals at high excitation

AbstractThe shape of the excitonic luminescence band is studied for degenerate excitons of great radius at T ≠ 0 K in crystals with indirect bandgap. A calculation is made of the transition probability from a macroscopically occupied exciton state with wave vector k correeponding to the boundary of the Brillouin zone, under photon and phonon emission. The luminescence band consists of a δ‐type peak and a broader, and less intense, short‐wavelength satellite. The theory is compared with experiments for AgBr crystals.