Saddle dolomite: a new view of its nature and origin

1989 ◽  
Vol 53 (373) ◽  
pp. 547-555 ◽  
Author(s):  
Alison Searl
Keyword(s):  
Boundary Layer ◽  
Hydrothermal Activity ◽  
Lattice Expansion ◽  
Continuous Growth ◽  
Saddle Dolomite ◽  
The Face ◽  
Rapid Transport ◽  
Backscatter Scanning Electron Microscopy ◽  
Layer Solution ◽  
Scanning Electron

AbstractSaddle dolomite is a common product of late-stage diagenesis and hydrothermal activity. It has been suggested that during growth Ca enrichment occurs towards crystal edges leading to a lattice expansion relative to face centres. However, backscatter scanning electron microscopy of eight samples has revealed that, instead of edge associated Ca enrichment, saddle dolomites have a series of edge associated Mg enriched wedges, between 5 and 20 µm thick and 300 µm long. Wedge geometry implies development of extra lattice layers at edges relative to face centres. It is suggested that the wedges develop during rapid, transport-controlled, crystal growth. The wedges possibly reflect a switching from continuous growth across the face to edge-nucleated growth as the boundary layer solution becomes progressively depleted. Continuous growth might be reinstigated through convective turnover of the boundary layer presenting fresh solution to the growing crystal.

Convective diffusion to a slowly rotating spherical electrode; Basic model for Re → O, Pe → ∞

1983 ◽  
Vol 48 (6) ◽  
pp. 1571-1578 ◽  
Author(s):  
Ondřej Wein
Keyword(s):  
Boundary Layer ◽  
Flow Regime ◽  
Peclet Number ◽  
Convective Diffusion ◽  
Creeping Flow ◽  
Péclet Number ◽  
Spherical Electrode ◽  
Basic Model ◽  
Boundary Layer Solution ◽  
Layer Solution

Theory has been formulated of a convective rotating spherical electrode in the creeping flow regime (Re → 0). The currently available boundary layer solution for Pe → ∞ has been confronted with an improved similarity description applicable in the whole range of the Peclet number.

A histological examination of the holding sacs and glandular scent organs of some bat species (Emballonuridae, Hipposideridae, Phyllostomidae, Vespertilionidae, and Molossidae)

2000 ◽  
Vol 78 (4) ◽  
pp. 613-623 ◽  
Author(s):  
William MR Scully ◽  
M B Fenton ◽  
A SM Saleuddin
Keyword(s):  
Electron Microscope ◽  
Sexual Dimorphism ◽  
Sebaceous Glands ◽  
Microscope Examination ◽  
Scent Gland ◽  
Light Microscope Level ◽  
Histological Techniques ◽  
Saccopteryx Bilineata ◽  
The Face ◽  
Scanning Electron

Using histological techniques at the light-microscope level, we examined and compared structure and sexual dimorphism of the wing sacs and integumentary glandular scent organs of 11 species of microchiropteran bats. The antebrachial wing sacs of the Neotropical emballonurids Peropteryx macrotis, Saccopteryx bilineata, and Saccopteryx leptura differed in size and location but lacked sudoriferous and sebaceous glands, confirming that they were holding sacs rather than glandular scent organs. Glandular scent organs from 11 species consisted of sebaceous and (or) sudoriferous glands in emballonurids (P. macrotis, S. bilineata, S. leptura, Taphozous melanopogon, Taphozous nudiventris), hipposiderids (Hipposiderous fulvus, Hipposiderous ater), the phyllostomid Sturnira lilium, the vespertilionid Rhogeessa anaeus, and molossids (Molossus ater and Molossus sinaloe). Glandular scent organs were located on the face (H. fulvus, H. ater), gular region (S. bilineata, P. macrotis, T. melanopogon, M. ater, M. sinaloe), chest (T. nudiventris), shoulder (S. lilium), or ears (R. anaeus). Glandular scent organs showed greater similarities within than between families, and typically were rudimentary or lacking in females. Scanning electron microscope examination revealed that the hairs associated with glandular areas of male T. melanopogon were larger and had a different cuticular-scale pattern than body hairs. These were osmetrichia, hairs specialized for holding and dispersing glandular products. In S. lilium, hairs associated with the shoulder scent-gland area were larger than body hairs but similar in cuticular-scale pattern.

The solution of heat-transfer problems by the Wiener—Hopf technique II. Trailing edge of a hot film

1974 ◽  
Vol 337 (1610) ◽  
pp. 395-412 ◽  
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Half Plane ◽  
Dimensionless Temperature ◽  
Fluid Temperature ◽  
Trailing Edge ◽  
Boundary Layer Solution ◽  
Leading Term ◽  
Hot Film ◽  
Layer Solution

An incompressible fluid of constant thermal diffusivity k , flows with velocity u = Sy in the x -direction, where S is a scaling factor for the velocity gradient at the wall y = 0. The region — L ≤ x ≤ 0 is occupied by a heated film of temperature T 1 , the rest of the wall being insulated. Far from the film the fluid temperature is T 0 < T 1 . The finite heated film is approximated by a semi-infinite half-plane x < 0 by assuming that the boundary-layer solution is valid somewhere on the finite region upstream of the trailing edge. Exact solutions in terms of Fourier inverse integrals are obtained by using the Wiener-Hopf technique for the dimensionless temperature distribution on the half-plane x > 0 and the heat transfer from the heated film. An asymptotic expansion is made in inverse powers of x and the coefficient of the leading term is used to calculate the exact value of the total heat-transfer as a function of the length L . It is shown that the boundary layer solution differs from the exact solution by a term of order L -1/3 for large L . An expansion in powers of x for the heat transfer upstream of the trailing edge is also found. Application of the theory, together with that of Springer & Pedley (1973), to hot films used in experiments are discussed for the range of values of L(S/K) ½ , up to 20.

scholarly journals Occurrence and growth of sub-50 nm aerosol particles in the Amazonian boundary layer

2021 ◽  
Author(s):  
Marco A. Franco ◽  
Florian Ditas ◽  
Leslie Ann Kremper ◽  
Luiz A. T. Machado ◽  
Meinrat O. Andreae ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Meteorological Data ◽  
Cloud Condensation Nuclei ◽  
Deep Convection ◽  
Potential Temperature ◽  
Meteorological Conditions ◽  
Subsequent Growth ◽  
Wet Season ◽  
Particle Injection ◽  
Continuous Growth

Abstract. New particle formation (NPF), referring to the nucleation of molecular clusters and their subsequent growth into the cloud condensation nuclei (CCN) size range, is a globally significant and climate-relevant source of atmospheric aerosols. Classical NPF exhibiting continuous growth from a few nanometers to the Aitken mode around 60–70 nm is widely observed in the planetary boundary layer (PBL) around the world, but not in central Amazonia. Here, classical NPF events are rarely observed in the PBL, but instead, NPF begins in the upper troposphere (UT), followed by downdraft injection of sub-50 nm (CN< 50) particles into the PBL and their subsequent growth. Central aspects of our understanding of these processes in the Amazon have remained enigmatic, however. Based on more than six years of aerosol and meteorological data from the Amazon Tall Tower Observatory (ATTO, Feb 2014 to Sep 2020), we analyzed the diurnal and seasonal patterns as well as meteorological conditions during 254 of such Amazonian growth events on 217 event days, which show a sudden occurrence of particles between 10 and 50 nm in the PBL, followed by their growth to CCN sizes. The occurrence of events was significantly higher during the wet season, with 88 % of all events from January to June, than during the dry season, with 12 % from July to December, probably due to differences in the condensation sink (CS), atmospheric aerosol load, and meteorological conditions. Across all events, a median growth rate (GR) of 5.2 nm h−1 and a median CS of 0.0011 s−1 were observed. The growth events were more frequent during the daytime (74 %) and showed higher GR (5.9 nm h−1) compared to nighttime events (4.0 nm h−1), emphasizing the role of photochemistry and PBL evolution in particle growth. About 70 % of the events showed a negative anomaly of the equivalent potential temperature (∆θ'e) – as a marker for downdrafts – and a low satellite brightness temperature (Tir) – as a marker for deep convective clouds – in good agreement with particle injection from the UT in the course of strong convective activity. About 30 % of the events, however, occurred in the absence of deep convection, partly under clear sky conditions, and with a positive ∆θ'e anomaly. Therefore, these events do not appear to be related to downdraft injection and suggest the existence of other currently unknown sources of the sub-50 nm particles.

scholarly journals A numerical process study on the rapid transport of stratospheric air down to the surface over western North America and the Tibetan Plateau

2019 ◽  
Vol 19 (9) ◽  
pp. 6535-6549 ◽  
Author(s):  
Bojan Škerlak ◽  
Stephan Pfahl ◽  
Michael Sprenger ◽  
Heini Wernli
Keyword(s):  
Boundary Layer ◽  
Tibetan Plateau ◽  
Surface Ozone ◽  
Vertical Transport ◽  
The Tibetan Plateau ◽  
Near Surface ◽  
Air Mass ◽  
Ozone Concentrations ◽  
Rapid Transport ◽  
Upper Level

Abstract. Upper-level fronts are often associated with the rapid transport of stratospheric air along tilted isentropes to the middle or lower troposphere, where this air leads to significantly enhanced ozone concentrations. These plumes of originally stratospheric air can only occasionally be observed at the surface because (i) stable boundary layers prevent an efficient vertical transport down to the surface, and (ii) even if boundary layer turbulence were strong enough to enable this transport, the originally stratospheric air mass can be diluted by mixing, such that only a weak stratospheric signal can be recorded at the surface. Most documented examples of stratospheric air reaching the surface occurred in mountainous regions. This study investigates two such events, using a passive stratospheric air mass tracer in a mesoscale model to explore the processes that enable the transport down to the surface. The events occurred in early May 2006 in the Rocky Mountains and in mid-June 2006 on the Tibetan Plateau. In both cases, a tropopause fold associated with an upper-level front enabled stratospheric air to enter the troposphere. In our model simulation of the North American case, the strong frontal zone reaches down to 700 hPa and leads to a fairly direct vertical transport of the stratospheric tracer along the tilted isentropes to the surface. In the Tibetan Plateau case, however, no near-surface front exists and a reservoir of high stratospheric tracer concentrations initially forms at 300–400 hPa, without further isentropic descent. However, entrainment at the top of the very deep boundary layer (reaching to 300 hPa over the Tibetan Plateau) and turbulence within the boundary layer allows for downward transport of stratospheric air to the surface. Despite the strongly differing dynamical processes, stratospheric tracer concentrations at the surface reach peak values of 10 %–20 % of the imposed stratospheric value in both cases, corroborating the potential of deep stratosphere-to-troposphere transport events to significantly influence surface ozone concentrations in these regions.

The Determination of Fabric Loop Length

1977 ◽  
Vol 47 (12) ◽  
pp. 795-801 ◽  
Author(s):  
T. J. Little ◽  
A. Hepworth
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Loop Length ◽  
Research Association ◽  
Alternative Approach ◽  
The Face ◽  
Course Length ◽  
Recorded Image ◽  
Scanning Electron

An alternative approach towards the measurement of loop length while in fabric form is proposed employing techniques of scanning electron microscopy and aerogrammetry. Distortions inherent in the recorded image have been taken into account by obtaining coordinates at intervals as determined by a micrograph of a cross-ruled grid. The lengths of all the resultant elements have been summed to obtain an estimate of the loop length, which was found to be 4–5% different from that obtained using the HATRA (Hosiery and Allied Trades Research Association, Nottingham, England) Course Length Tester. Some suggestions are offered for improving the estimated loop length by obtaining coordinates for both the face and back views of the same knitted loop. It is proposed that a similar approach would be beneficial towards an understanding of parameters governing the geometry of the knitted loop.

scholarly journals Deformation induced martensite characterization in Fe-30%Ni-5%Cu alloy

2012 ◽  
Vol 48 (2) ◽  
pp. 259-264 ◽  
Author(s):  
E. Güler ◽  
M. Güler
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Dsc Measurements ◽  
Cu Alloy ◽  
The Face ◽  
Xrd Techniques ◽  
Scanning Electron

Deformation induced martensite properties were examined according to existing martensite morphology, crystallography and formation temperatures for different prior austenite homogenization conditions in Fe-30%Ni-5%Cu alloy. Scanning electron microscope (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques were employed to investigation. Scanning electron microscope observations showed elongated deformation induced martensite morphology in the austenite phase of alloy. As well, after deformation martensite start temperatures (Ms) were determined as -101?C and -105?C from DSC measurements for different homogenization conditions. In addition, X-ray diffraction analysis revealed the face centred cubic (fcc) of austenite phases and body centred cubic (bcc) deformation induced martensite phases for all studied samples.

A Step Toward the Elucidation of Quantitative Laws of Nature

2020 ◽  
Vol 13 ◽  
pp. 72-82
Author(s):  
Stephen Perry ◽  
Keyword(s):  
Boundary Layer ◽  
Stokes Equations ◽  
Applied Mathematics ◽  
Laws Of Nature ◽  
Navier Stokes ◽  
Natural Phenomena ◽  
Navier Stokes Equations ◽  
Fine Grain ◽  
The World ◽  
Layer Solution

When we mathematically model natural phenomena, there is an assumption concerning how the mathematics relates to the actual phenomenon in question. This assumption is that mathematics represents the world by “mapping on” to it. I argue that this assumption of mapping, or correspondence between mathematics and natural phenomena, breaks down when we ignore the fine grain of our physical concepts. I show that this is a source of trouble for the mapping account of applied mathematics, using the case of Prandtl’s Boundary Layer solution to the Navier-Stokes equations.

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