Circular Pits Research Articles

Surface topography of oxidized HOPG by scanning tunneling microscopy

Scanning tunneling microscopy (STM) has been used to image the surface structure of gasified highly oriented pyrolytic graphite (HOPG). Surfaces of HOPG were oxidized in air at 650 °C by TGA to 5 and 30 wt% burnoffs. The pits that were formed following this oxidation were examined by STM. Removal of carbon atoms adjacent to the vacancy in the same plane as well as removal of carbon atoms in planes below the surface were observed. The initial oxidation resulted in the formation of circular nm-sized pits. After oxidation to a depth of a few basal planes the nm-sized pits elongated into channels. Upon further oxidation, these elongated pits and channels collapsed to form hexagonal μm-sized pits (of the order of several μm). Steep μm-sized pit walls that are nearly vertical were observed in some images. The cross-sectional analyses of these μm-sized pits showed deeper intrusion at the sides of the pit rather than at the center of the pit floor (a few hundred basal planes), giving the pit floor a dome-like appearance. Because oxidation in the z-direction was expected to be much slower than in the x- y-direction the steepness of the pits was unexpected. One possible explanation is that the pit is formed from oxidation on a very deep screw dislocation or at the micro-crystallite grain boundaries. A second explanation is that naturally occurring vacancies in the basal planes allow oxygen to react with many layers relatively quickly. A third explanation could be the association with small sized impurities (catalysts) on the surface. However, scans were made of the unoxidized HOPG prior to oxidation and no defects were imaged. A cross-sectional analysis of the initial circular nm-sized pits showed the presence of these surface-oxide complexes.

On Peter Riley's Lyric Excavations

Opening to the first page of Peter Riley's Distant Points (1995), the first volume in an ongoing series of what the book's jacket describes well enough as prose-poems in which any singular voice is constantly interrupted by itself in another guise, and a whole theatre of masks jostles for position around the central condition of meditation, we find two poems or passages which look like this: 1. the body in final commerce: love and despair for a completed memory or spoken heart enclosed in a small inner dome of grey/drab-coloured [river-bed] clay, brought from some distance (from the valley bottoms) and in, So my journey ended in the substance of I depart and afire over the dome and a final tumulus of local topsoil / benign memorial where the heart is brought to the exchange: death for life, relict for pain / double-sealed, signed and delivered - under all that press released to articulate long silence, long descended * tensed wing / spread fan / drumming over the hill. C39. in river clay, the boat on the hilltop lying East-West facing upwards Right hand on Right shoulder Left arm across the body gradients of sleep, to die, to dream, or mean/beyond his feet to the East a row of three circular pits or stake-holes dawn trap as the compass arc closes southwards and the heart is secured by azimuth, all terrors past: She only drave me to dispaire/dead child, cancelled future in a satellite cloak hovering to SE. Yet the loss, into sails adroit in the clay ship over and habit, bound for (to) this frozen screen where [cursive] we don't live, but do (love) say, and fail.(1) How might the reader negotiate such a text? A first sentence fragment juxtaposes two phrases on opposite sides of a colon, perhaps to offer an initial articulation of the poem's concerns - the body in its final commerce (what could that mean?), the emotions attendant upon the desire to speak and in some sense complete memory and emotion. Clearly, we know at least that we are on some of the most traditional grounds of lyric, seeking a language adequate for our mortality, remembering the anguish of the word that would redeem while memorializing. But that's to get ahead of myself, reading the last lines of the second passage, where loss, folded into history, is taken as the ground not only enabling but in some sense requiring a writing that cannot fail. Our first reading of the poem must take account of the disjuncture between that first sentence-fragment and a next set in italics, that strangely affect-less description of what (at first reading) we do not know. With brackets and parentheses, this phrase itself is interrupted, as if by qualifying or clarifying commentary. Then a third, bold typeface makes first appearance, together with the first-person. A journey's end is declared, to be followed after the return of the normative typeface which describes arrival as moulded (like clay?) by another bold-face fragment declaring the beginning of a journey. An ending before a beginning. Reading down below in the second passage we note that this bold-face font there presents antiquated spellings, indicating perhaps that such language has been imported from another source. It reads like lyric poetry, like renaissance song. But of course I am being willfully naive here. We think we know from The Waste Land, from Pound's Cantos, and from many another modernist poem, how to negotiate the poetics of collage and juxtaposition - we have experienced these texts and read the commentaries over the course of time. Moreover, in the book's notes, Riley provides more help in explaining that his meditative texts are concerned with the human burial deposits of the so-called Neolithic/Bronze Age culture of what is now the Yorkshire Wolds, and are based upon late nineteenth century tumulus excavation accounts by J. R. Mortimer (1905) and Canon William Greenwell (1877) - though the volume we are reading here uses only the Mortimer text (60). …

Oldest Living Confederate Chaplain Tells All?: Or, James B. Avirett and the Rise and Fall of the Rich Lands

ESSAY Oldest living Confederate ChaplainTells All? Or,James B. Avirett and the Rise and Fall ofthe Rich Lands by David S. Cecelski I ^^^h ecently I toured the former site of the Rich Lands in the old r ^^Ê M piney woods of Onslow County, North Carolina. The Rich _ ^^^^H Lands had been one ofthe great plantations in the naval stores '^^L ^^| industry of the Old South. John Avirett and more than 1 25 _^^^^_^^ slaves built a kingdom out of the long-leafpine's resinous gum, producing rivers of turpentine, tar, pitch, and rosin whose swelling tides literally carried sailing vessels to every continent on earth. Succeeded long ago by corporate timberlands and loblolly thickets, the Rich Lands once sprawled across more than 22,000 acres just southeast ofwhat is now the small farm town ofRichlands, fourteen miles from the Adantic coast. With the help ofDennisJones, a local historian and educator, I went in search of the Rich Lands' former glory. Poking around pine woods, we found circular imprints ofold tar pits still scarring the earth. Dennis showed me a sticky layer of rosin residue by the banks of Catherine's Lake, the former site of Avirett's turpentine distilleries. He also pointed out an old rice-field dam and, along the banks ofthe New River, a weary sun-baked marl bed, once a source oflime for the plantation 's fields. A half-chiseled grindstone protruded from the marl, the labor of extricating it from the rock interrupted at least 140 years ago. Toward dusk Dennis led me to where Alum Spring rises out ofa gaping limestone rift. Now in deep forest, the spring used to be a popular picnic spot for some of the wealthiest planters in North Carolina. Finally, out by the Jacksonville highway, Dennis revealed an old brick cistern that is the last trace of the Rich Lands manor house. Nearby we found the Avirett family cemetery: a few graves within a crumbling brick wall tangled in trumpet vine. Across the road I could barely make out the low spot where the Rich Lands slaves are said to have buried their dead. Dennis and I only recognized most of these landmarks because James Batde Avirett, John Avirett's son, wrote an extraordinary memoir of growing up at the Rich Lands. Published in 1901, The OldPlantation: How WeLivedin GreatHouse and Cabin Before the Warlong ago faded into obscurity, but it is an unparalleled account ofNorth Carolina's turpentine boom days—the days that gave the state's citizens the name "Tar Heels."1 Indeed, there is no better account ofplantation life in the piney woods of the antebellum South. After reading Avirett's memoir, you can practically see the Rich Lands as it was 1 5o years ago: the fine manor house, the slave quarters, the distilleries, the picnics at Alum Spring, and the great piney woods itself. No aspect ofRich Lands life or turpentining seems to have escaped him. YetJames Avirett did not tell all. When I explored the Rich Lands not so long ago, I discovered that behind The Old Plantation is an untold saga, a mystery far more intriguing than the book itself. In reality, Avirett's flattering portrait of the Rich Lands conceals a forgotten tale ofecological ruin and personal tragedy. His memoir provides a wealth of raw material for the study of turpentine plantation life and piney woods culture in the antebellum South. It is a portrait of the Rich Lands so detailed, so elaborated with specific names, places, and incidents, and as insightful about slaves as their masters, that it cannot help but raise a host of intriguing issues about plantation life, material culture, daily work routines, the annual rhythms of labor, slave culture, and the society and oudook of the planter class. But it is, ultimately, something even far more interesting: a story of nostalgia and deceit that goes to the heart of plantation slavery's impact on the southern landscape and how we remember the Old South today. PINEY WOODS WEALTH AND THE FAMILY THAT CLAIMED IT The long-leaf pine, Pinuspalustris, once defined the American South as distinctively as the tall-grass prairie set apart the Great...

Implementation of Electrochemically Synthesized Silver Nanocrystallites for the Preferential SERS Enhancement of Defect Modes on Thermally Etched Graphite Surfaces

Highly oriented pyrolytic graphite (HOPG) surfaces, on which atomically well-defined roughness has been introduced via high-temperature gasification reactions, are investigated by noncontact mode atomic force microscopy (NC-AFM) and Raman spectroscopy both before and after the electrochemical deposition of silver nanocrystallites on these surfaces. Exposure of freshly cleaved HOPG surfaces to an O(2)-rich ambient at 650 °C for a few minutes caused the formation of 1-monolayer-deep, circular etch pits on the HOPG basal plane surface. Silver nanocrystallites were electrochemically deposited onto these etched surfaces at two coverages: 0.5 mC cm(-)(2) (or 5 nmol of Ag(0) cm(-)(2)) and 2.4 mC cm(-)(2) (25 nmol of Ag(0) cm(-)(2)). At the lower coverage, NC-AFM images revealed that silver decorated only the circumference of the circular etch pits, forming a uniform annular ring with an apparent diameter of 200-250 Å and a height of ∼15 Å. At the higher silver coverage, an increase in the height but not the diameter of this annulus was observed, and additional silver nanostructures [Formula: see text] having dimensions of 300-350 Å diameter and 15 Å height [Formula: see text] were observed on atomically smooth regions of the graphite basal plane. The Raman spectroscopy of these surfaces was investigated and compared with spectra for nanocrystallite-modified but unetched HOPG basal plane surfaces and thermally etched surfaces on which no silver was deposited. For for thermally etched HOPG surfaces at either silver coverage, SERS-augmented Raman spectra were obtained in which defect modes of the graphite surface [Formula: see text] derived from "finite" graphite domains at the surface [Formula: see text] were strongly and preferentially enhanced. In addition, an enhanced band near 2900 cm(-)(1) was assigned to ν(OH) from carboxylate moieties present at step edges based on the basis of the observed pH dependence of the enhancement.

Mechanism of Molecular Ordering in Monolayer Liquid Crystal Films

Scanning tunneling microscopy and “molecule corrals” were used to measure the temperature dependence of the rate of molecular ordering in monolayer liquid crystal films. Molecule corrals are circular etch pits, 3.35 A deep on the basal surface of graphite formed by high-temperature oxidation. A strong negative relationship between temperature and nucleation rate was observed, consistent with a nucleation growth mechanism of molecular self-assembly. From a fit of classical nucleation theory the melting temperature of the film was found to be Tmelt = 318 ± 6 K, the thermodynamic driving force for nucleation ΔFn(Tmelt − T)/Tmelt = 1.1 ± 0.3 kcal mol-1, and the preexeponential factor A = (1.8 ± 0.8) × 108 A-2 s-1.

The excavation of a late 15th- to 17th-century tanning complex at The Green, Northampton

Excavations at The Green, Northampton, in 1983 revealed up to three tanneries. These are described and discussed. Earlier excavations immediately to the north at St Peter’s Street had uncovered evidence of two further tanneries. These are reassessed in the light of the evidence from The Green. The phase of tanning activity can be divided into two: sub-phase 1 (c. 1470-1550) comprises the Western, Northern (Phase 1) and North-Western Tanneries and sub-phase 2 (c. 1550-1700) is composed of the Northern (Phase 2), Eastern and Central Tanneries, although it is possible that all three formed a single tanning complex. Evidence of earlier activity in the area, principally of late Saxon - medieval date, was uncovered, but the main phase of tanning activity coincided with a period of dereliction.The tanneries were composed of circular and rectangular pits. The animal bone evidence would suggest that cattle and horse hides and sheep skins were all being processed, despite contemporary prohibitions of this practice. All of the tanneries were small, the largest, the Western Tannery, comprising 36-37 pits. Many of the pits contained deposits of lime and ash which were used in the de-hairing process. Chemical analyses of soil samples from the pits suggest that they were used both for pre-tanning operations and for tanning itself. A primitive form of tanning is suggested.The archaeological findings are amplified by documentary evidence that a number of tanners were working in the area from the 16th century onwards; it is likely that the Northern and Western Tanneries were in the tenure of one man, John Buckby, who was of some importance in the town. Two streets with names linked to tanning (Tanner Street and Barker Street) were located nearby.

Characteristics of polarization splitters constructed from a circular hollow pit outside the cores

AbstractIn this paper, a polarization splitter is proposed in which a single‐core fiber (Fiber 1) and a fiber with a circular hollow pit outside the core (Fiber 2) are coupled. Corresponding to the extraction of the two linear polarizations (x and y polarizations) from the HE11 mode excited in to Fiber 1, the polarization splitting method can be clasified into the x‐polarization type or the y polarization type. In the x‐polarization type, the x‐polarization is extracted from Fiber 1 and the y‐polarization from Fiber 2. In the y‐polarization type, the y‐polarization is extracted from Fiber 1 and the x polarization from Fiber 2. This paper discussed the structural parameters (core radius, relative refractive index difference, and core spacing), which reduce the device length of the x polarization and y polarization types and at the same time make the extinction ratio small. The main results are as follows: (1) When the relative refractive index difference of Fiber 2 was made constant, the minimum values of the device length and the extinction ratio of the x polarization type can be made smaller than those of the y polarization type. (2) When the relative refractive index difference of Fiber 2 is increased from 0.4 percent to 1.0 percent, 1 the device lengths of both the x‐ and y‐polarization types can be reduced by 0.26 times, and 2 the minimum value of the extinction ratio of the x polarization type increases +4.1 dB from ‐38.2 dB and that of the y polarization increases +4.3 dB from ‐34.1 dB.

Ice-melt collapse pits and associated features in the 1991 lahar deposits of Volcán Hudson, Chile: criteria to distinguish eruption-induced glacier melt

In subaerial volcaniclastic sequences structures formed by ice blocks can provide information about a volcano's history of lahar generation by glacier melt. At Volcan Hudson in Chile, catastrophic lahars were initiated by eruption-induced melting of glacier ice in August and October 1991. They transported large ice blocks 50 km down the Rio de los Huemules valley to the sea. Large current crescents with lee-side lenses were formed where ice blocks were deposited during waning stages of the flood. When stranded blocks of ice melted, they left cone-shaped and ring-shaped heaps of ice-rafted debris on the sediment surface. Several hundred ice blocks were completely buried within the aggrading lahar sediment, and when these melted circular collapse pits formed in the sediment. Collapse types included subsided coherent blocks of sediment bounded by an outward-dipping ring-fracture, trapdoor structures with horseshoe-shaped fractures, downsag pits with centroclinal dips locally up to 60°, pits with peripheral graben and crevasses, piecemeal (highly fragmented) collapse structures and funnel-shaped pits containing disaggregated sediment. A sequence of progressive collapse is inferred in which initial downsag and subsidence on an outward-dipping ring fracture produces a small diameter pit. This is followed by widening of the pit by progressive development of concentric ring fractures and downsag outside the early formed pit, and by collapse of overhanging pit walls to produce vertical to inward-dipping walls and aprons of collapse debris on the pit floor. The various structures have potential for preservation even in regions prone to high rainfall and flooding, and they can be used to indicate that former lahars contained abundant blocks of ice.

KeV-polyatomic-ion-impact-nucleated oxidative etch pitting in highly oriented pyrolytic graphite

The tendency of freshly cleaved highly oriented pyrolytic graphite (HOPG) to form nanometer-sized circular pits during high temperature oxidative etching is an example of a controllable, nanoscale tailoring of a surface with a number of potential applications. Here we explore the possibility of modulating the number density, shapes, and dimensions of such etch pits by deliberately nucleating defects at or near the surface by bombardment with kiloelectronvolt polyatomic projectiles. We observed that bombardment of HOPG by 176 keV apomyoglobin ions resulted in the nucleation of a large population of deep hexagonal etch pits upon baking. The depths of the pits also give new information on the depth to which a material is damaged by impinging energetic polyatomic projectiles.

Acoustic scattering from a circular aperture in a thick hard screen

Acoustic plane-wave scattering from a circular aperture in a thick hard screen is reexamined. The Hankel transform is applied to express the scattered field in the spectral domain and the boundary conditions are enforced to obtain simultaneous equations for the transmitted field inside the thick hard screen. The simultaneous equations are solved to represent the transmitted and scattered fields in series forms. Numerical computations are performed to illustrate the behavior of scattering and transmission in terms of the aperture size, frequency, and incident angle. It is found that scattering from a circular pit exhibits the resonance versus the pit depth when the pit radius is larger than a wavelength. The numerical comparisons to other available data show excellent agreement. The presented series solution is numerically efficient and general in that it includes scattering from a circular aperture, pit, and semi-infinite pipe altogether.

Progress of high-resolution photon scanning tunneling microscopy due to a nanometric fiber probe

The present status of a photon scanning tunneling microscope (PSTM) and its application are reviewed. In order to realize a nanometric apertured fiber probe, a highly reproducible chemical etching process was developed to realize a sharpened fiber with the cone angle and tip diameter as small as 14/spl deg/ and 3 nm, respectively. The possibility of tailoring the shapes of the sharpened fibers was presented. Chemical etching and nanometric photolithography were developed to fabricate a metallic aperture with a diameter of 30 nm (or even smaller) on the sharpened fiber tip. Imaging experiments with biological specimens were carried out by operating the PSTM in the collection mode and illumination mode geometries. Dependencies of these images on the polarization state of the incident light were found, and a resolution of 10 nm or even smaller was achieved. Nondestructive inspection of dielectric optical waveguides with subwavelength resolution was proposed by presenting the diagnosed results of a proton-exchanged LiTaO/sub 3/ waveguide. Possibilities of diagnosing nanometric active photonic devices were also demonstrated through imaging experiments of semiconductor quantum dots. Experiments on fluorescence detection from dye-doped nanometric polystyrene spheres confirmed the enhanced efficiency of coupling of the fluorescence to the fiber tip, and this was attributed to the spatially inhomogeneous spontaneous emission due to the short-range electromagnetic interaction between the sphere and probe tip. To demonstrate the possibilities of nanometric fabrication, high density optical storage, especially the photon-mode storage, was demonstrated to realize a stored circular pit of 100 nm diameter on an organic thin film. As an ultimate goal of fabrication to explore the future technology of atomic-level material processing, an atom guide using a hollow fiber and atom trapping by the illumination mode PSTM were proposed to control the thermal motion of freely dying atoms in vacuum. The concept of a virtual photon based on an intuitive modeling of the localized evanescent light was introduced to provide a semiclassical theory of the PSTM. Transfer functions of the PSTM were calculated by using this model, which agreed qualitatively with the experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

"Molecule Corrals" for Studies of Monolayer Organic Films

Scanning tunneling microscopy (STM) studies have demonstrated that monolayer-deep, flat-bottomed, circular etch pits can be grown on highly ordered pyrolytic graphite by high-temperature etching in the presence of oxygen. In this work, these graphite etch pits are used as "molecule corrals" to isolate ensembles of molecules for study by STM. The nucleation of self-assembled molecular films in the corrals took place by nucleation events separate from those leading to self-assembly on the surrounding terrace and allowed the measurement of the nucleation rate constant in the corrals. The dependence of the nucleation rate for self-assembly on pit size shows that nucleation occurs at open terrace sites and that step edges (that is, the corral's perimeter) and confinement inhibit film growth.

Atomic force microscopy of ultraviolet-induced surface erosion on potassium iodide

Abstract Ultraviolet laser radiation (Ti: sapphire 4th harmonic) tuneable in the exciton absorption region of KI was used to produce near-surface excitation of potassium iodide samples on the stage of an atomic force microscope. Surface images with lateral resolution of ∼50 nm and vertical resolution of ∼3 nm have been recorded versus exposure to 5.9-eV light. Ultraviolet exposures in air were made both during AFM scanning and with the tip disengaged. Circular pits of a size dependent on uv intensity are formed quickly, followed by appearance of islands ascribed to potassium (oxidized), and finally formation of a rough eroded surface, which continues to develop after termination of the uv irradiation. Thallium doping slows the rate of erosion.

Morphology and development of flow-pattern defect with extended nonagitated Secco etching

The D defect, which causes the degradation of gate oxide integrities (GOI), can be revealed by Secco etching as flow pattern defect (FPD) in both float zone (FZ) and Czochralski (Cz) silicon crystal or as crystal originated particles (COP) by a multiple-step SC-1 cleaning process. By decreasing the crystal growth rate or high temperature annealing, the FPD density can be reduced, while the D defectsize increased. During the etching, the FPD surface density and etch pit size (FPD #1) increased withthe etch depth, while the wedge shaped contours do not change their positions and curvatures (FIG.l).In this paper, with atomic force microscopy (AFM), a simple model for FPD morphology by non-crystallographic preferential etching, such as Secco etching, was established.One sample wafer (FPD #2) was Secco etched with surface removed by 4 μm (FIG.2). The cross section view shows the FPD has a circular saucer pit and the wedge contours are actually the side surfaces of a terrace structure with very small slopes. Note that the scale in z direction is purposely enhanced in the AFM images. The pit dimensions are listed in TABLE 1.

Observation by scanning tunneling microscopy of the morphology change of Pt/HOPG after NO-CO reaction

We performed STM experiments to investigate the effects of NO-CO reaction the morphology change of Pt deposited on a HOPG surface. The gasification reaction on the Pt/HOPG resulted in straight channels, multidirection channels, and circular monoatomic step pits on the basal plane. We have observed more channel formation than pit formation in the presence of platinum particles, suggesting that catalyzed gasification is much faster than noncatalyzed gasification reaction. The observed channeling structure was found to be 3 to 8 monolayers deep and is due to NO-CO reaction at higher temperature at which Pt particles attack the edges and steps of the basal plane of graphite. The unique ability of STM technique was used to resolve atomic structure of 3 to 8 monolayers deep inside channel. The corrugation width of adjacent hexagons was found to be 2.5 Å, which is in good agreement with the C-C interatomic distance in the literature.

A single-polarization optical fiber of hollow pit type with zero total dispersion at wavelength of 1.55 μm

This paper gives a design method for the single-polarization optical fiber which satisfies simultaneously the wide single-polarization bandwidth, the large modal birefringence, and the zero total dispersion at the wavelength of 1.55 /spl mu/m. As a type of single-polarization fiber, the optical fiber with two hollow circular pits across the core-clad interface is proposed and designed. The normalized power (=/spl Delta/ the power in the core/the total power) in the core is also evaluated for the designed fibers. It was found from the numerical analysis that when the zero total dispersion is satisfied at the wavelength of 1.55 /spl mu/m, the maximum modal birefringence of 1.133/spl times/10/sup -3/ and the maximum single-polarization bandwidth of 100.6 nm are attained for the relative index difference of 1.6%. Then the normalized power in the core is 0.859. >

Conifer wood from the Upper Jurassic of Utah, USA-Part II: Araucarioxylon hoodii sp. nov.

The new species, Araucarioxylon hoodii, collected from the Brushy Basin member of the Upper Jurassic Morrison Formation in South central Utah, USA is compared to other species of Araucarioxylon and Dadoxylon, Dadoxylon (Araucarimylon) japonicum Shimakura from Japan being the closest. They differ by the round to elliptical crossfield pits in A. hoodia having round apertures, lacking oppositely arranged tracheary pitting and having larger tangential pits of A. hoodia whereas Dadoxylon (A.) japonicum has circular pits with obliquely elongated lenticular, included apertures. Opposite tracheary pits are often present in the latter species, and its tangential pits are smaller than A. hoodia. Araucarioxylon hoodia is the first member of the genus to be described with assurance from the Jurassic of the Colorado Plateau, USA. Associated fossil plants and the anatomical structure of A. hoodia suggest that it grew under a fairly equable damp climate in which its growth rings were not well developed.

An evaluation of pollutant induced changes in the gills of rainbow trout using scanning electron microscopy

Abstract The effects of phenol, copper and ammonia on the surface ultrastructure of the gills of rainbow trout were determined by scanning electron microscopy (SEM). Although the gills exhibited some common pollutant‐induced changes, certain types of pathological response were pollutant‐specific. Phenol caused destruction of epithelial layers down to supporting cartilage. Copper damage was characterized by lamellar fusion, swelling in the tips of the filaments and formation of epithelial swellings and ridges. Ammonia caused the development of distinctive circular depressions and pits in the epithelium. These results suggest that SEM of fish gills should be evaluated further as a diagnostic tool in water pollution investigations.

Reactions of NO, O 2, H 2O, and CO 2 with the basal plane of graphite

The reactions of NO, O 2, H 2O, and CO 2 with graphite between 400 and 900°C have been studied by STM to obtain quantitative kinetics by measuring the number and size of monolayer pits on the basal plane versus temperature and time. At low temperature, reactions initiate exclusively from point defect sites on the basal plane of graphite, forming circular or hexagonal pits one monolayer deep of uniform radius which varies linearly with time and can be used to obtain quantitative kinetics. The activation energies of the monolayer reactions on graphite vary from 89 kJ/mol with NO to 205 kJ/mol with H 2O. At higher temperature, these gases also react with carbon atoms in the basal plane, creating new defect sites which nucleate monolayer pit formation. This was examined quantitatively by counting the number of pits versus time and temperature. Activation energies of basal plane attack vary from 164 kJ/mol with NO to 370 kJ/mol with H 2O.

Tetracentron Wood from the Miocene of Noto Peninsula, Central Japan, with a short revision of homoxylic fossil woods

A vesselless fossil wood was discovered in the Miocene Yanagida Formation in the Noto Peninsula, central Japan. This fossil has distinct growth rings with gradual transition from the early- to the latewood ; tracheids, which are called 'usual traeheids' here, constitute the ground mass of the wood and have typical scalariform bordered pits on radial walls in the earlywood and circular sparse pits on those in the latewood ; rays are 1\2-4 cells wide and heterogeneous with low to high uniseriate wings; axial parenchyma strands are scattered in the latewood. This wood has a peculiar feature; sporadic radial files of broad tracheids whose tangential walls have crowded alternate bordered pits. The radial walls have crowded half-bordered pits to ray cells, but no pits to the usual tracheids. Among all of the extant and extinct angiosperms and gymnosperms, these unusual tracheids occur only in Tetracentron. From these features, we refer the fossil to the extant genus Tetracentron, and name it T. japonoxylum. A revision of homoxylic woods is made for comparision with the present fossil. Tetracentron japonoxylum is the only fossil wood of Tetracentron.