Flat Inclination Research Articles

Theoretical study of a new forging technology with additional macroshift using fem simulation in deform

In this paper the finite element method is used to simulate the process of forging round-section blanks in strikers of a new design. It is shown that the use of a radial joint of the faces has a positive influence on the hydrostatic pressure distribution along the entire length of the metal-tool contact. The comparative research of models with various values of flat zones inclination angles showed that the best variant is the tool with an angle value 30°. In this case a deep strain distribution over the cross section occurs in the billet with a significantly lower deformation force than when using tool with an angle value 0°. The simulation of the sequence of technological forging operations was also carried out. Two first compressions were performed with the workpiece turning at 90° to close possible internal defects. Then the angle of the turning is lowered to 45° and 30° in order to bring the cross-section shape closer to the round one.

A review of the frictional contact in rock cutting with a PDC bit

Drilling is one of the most expensive processes in the oil and gas exploration and exploitation processes which is commonly performed with polycrystalline diamond compact (PDC) fixed-cutter bits (or PDC bits as they are often referred to) due to their good stability and high flexibility in design. The PDC bit longevity strongly depends on the wear flat surface that changes during progression through rock materials. The wear flat size increases with time and can greatly influences the bit performance and efficiency. The increase in wear causes increasing weight-on-bit (WOB) on the PDC bit to keep the rate of penetration (ROP) constant. Over the past decades, contrary to the pure cutting process, not many investigations have been devoted to studying the friction mechanism at the wear flat–rock interface, resulting in poor understanding of the friction mechanism. The objective of this paper is to provide a detailed review of the state-of-the-art in rock cutting with particular focus on the frictional mechanism of the blunt PDC cutters and issues associated with the contact stress and the friction coefficient at the wear flat–rock interface. Moreover, the contact forces at the wear flat are governed by the wear flat inclination angle. Gaining a better understanding of the frictional contact process can eventually play a significant role in addressing practical issues such as drilling efficiency, optimization, and susceptibility to vibrations. Further, in spite of some obvious differences between the indentation and rock cutting processes, the main similarities between these two processes are also discussed which can provide new insights for the further studies. • A brief review of the cutting forces acting on the sharp PDC cutters. • An extensive review of the contact forces acting on the wear flat of the PDC bits. • Analysis of the factors affecting the contact stress and friction coefficient at the wear flat–rock interface. • A new comparison between the indention test and the rock cutting process. • Review of the factors affecting the development of the wear in the PDC bit/cutters.

Methodology investigation: Impact of crown geometry, crown, abutment and antagonist material and thermal loading on the two-body wear of dental materials

To investigate the impact of crown geometry, crown/abutment/antagonist material and thermal loading on the two-body wear of dental materials caused by chewing simulation. For the crown geometry, crowns (polymethylmethacrylate (PMMA), polyetheretherketone (PEEK) and silicate ceramic (SiO2)) were milled with a flat, steep, or medium cusp inclination (CINC). For the crown/abutment material, crowns (PMMA, PEEK and SiO2) were combined with PMMA, polymer-infiltrated-ceramic-network (PICN), cobalt-chrome alloy (CoCr) and natural teeth (ENAM) abutments. For the antagonist material, antagonists were fabricated from PICN, CAD/CAM resin composite (RECO), steatite (STEA), steel (STL) and ENAM and tested against flat specimens (substrates) made of veneering ceramic (VC). For thermal loading, the duration (30s, 60s, 120s) and presence of temperature changes (37°C versus 5°C/55°C) was varied. Material losses were determined by matching scanned specimens before and after aging (400,000 chewing cycles, 50N, 1.3Hz). Martens parameters were determined for the antagonists/substrates. Data were analyzed using Kolmogorov-Smirnov-test, Kruskal-Wallis H, Scheffé-Post-Hoc-tests, pairwise comparisons, Bonferroni correction, one-way ANOVA, Mann-Whitney-U and Spearman rho. PMMA crowns presented the highest and PEEK the lowest material losses. Flat CINC showed the lowest material losses for PEEK and SiO2 crowns. CoCr and ENAM abutments presented material losses in the same range. Antagonist and cumulative material losses for RECO and ENAM were similar. Thermal loading did not influence material losses. Crown geometry influences the crown and antagonists wear, with an increased cusp inclination entailing increased wear. For in vitro set-ups, CoCr abutments and RECO antagonists present valid alternatives to natural teeth. For polymers, in vitro chewing simulations may be performed at a constant temperature (37°C).

A Comparison of the Antioxidant Effects Between Hydrogen Gas Inhalation and Vitamin C Supplementation in Response to a 60-Min Treadmill Exercise in Rat Gastrocnemius Muscle.

The reactive oxygen species (ROS) produced during exercise act as a double-edged sword because they may cause oxidative damage but also play a role in the signaling pathways. A supplementation of exogenous antioxidants can reduce the total amount of ROS during exercise while it may also affect the ROS’ role in the signaling pathways of mitochondrial biogenesis. It has been suggested that hydrogen gas, as an antioxidant, can selectively scavenge hydroxyl radicals but does not affect superoxide anion’s signal transduction. The aim of this study was to compare the effects of 1-h hydrogen gas inhalation 30min prior to a treadmill exercise on the key biomarkers of mitochondrial biogenesis and related signaling pathways, and the activities of endogenous antioxidant enzymes, with those of vitamin C, in the rat skeletal muscle. Eighty-one 8-week-old male Sprague–Dawley (SD) rats were randomly assigned to three interventions (exercise-only, exercise+4%H2, and exercise+vitamin C at 500mg/kg weight, with 27 rats under each intervention), and sampled at pre-, immediately post and 4h post a 60-min treadmill exercise at speed of 27m/min and flat inclination, with nine rats in each sub-group. Expression of mitochondrial biogenetic markers and related signaling molecules in gastrocnemius muscle, and concentrations of oxidative stress markers in serum were measured. Two-way ANOVA or Kruskal–Wallis analyses showed that both hydrogen inhalation and vitamin C supplementation significantly reduced serum levels of MDA immediately after exercise and AGEs 4h after exercise. The pre-exercise supplement of vitamin C significantly reduced mitochondrial complex IV concentrations and PGC-1α, NRF-1, TFAM gene expression levels compared to the pre-exercise group, but the hydrogen gas intervention did not result in a reduction in these measurements. Unlike vitamin C, hydrogen inhalation did not blunt post-exercise mitochondrial biogenetic signals, but resulted in an increase in complex IV concentration, activation of PGC-1α, and TFAM and NRF-2 gene transcription, and up-regulation of PGC-1α protein expression. The findings indicated that hydrogen gas inhalation could play the role as an effective antioxidant in response to the exercise, whilst it did not significantly affect mitochondrial biogenesis. The dose–response relationship and antioxidant effects in different types of exercise for hydrogen inhalation require further investigation.

Thermohydraulic Performance of a Fin and Inclined Flat Tube Heat Exchanger: A Numerical Analysis

Proper determination of inclination angle of a flat tube may increase the overall heat transfer performance without extending heat transfer surface. In this paper, the inclined flat tube heat exchanger with plain fins is numerically investigated. The influence of flat tube inclination angle and Reynolds number on the thermo-hydraulic performance index was evaluated. Tube pitch, fin spacing and flat tube size are fixed. Solving 3D computational domain with the symmetric boundary condition is used to reduce computation time. The results show that when increasing the inclination angle of the flat tube from 0 to 45°, both heat transfer and pressure loss increase because the free area of air flow decreases leading to an increase in air velocity and impingement heat transfer. The variation of inclination angle from 0 to 15°, the increase in heat transfer is stronger than the increase in the pressure loss penalty, so the performance index reaches a maximum of 0.405 at the angle of 15°. Contours of temperature, pressure and velocity at different inclination angles are presented to clarify the thermo-hydraulic characteristics of finned-tube heat exchangers using inclined flat tubes. The current work yields heat transfer enhancement ability by adjusting inclination angle of a heat transfer flat tube.

Specular-reflection photonic hook generation under oblique illumination of a super-contrast dielectric microparticle

The possibility of overcoming the critical condition for localized photonic nanojet (PNJ) upon plane optical wave diffraction at mesoscale dielectric particle, which is commonly known as ‘the refractive index contrast is less than two’, was recently reported in our works. To this end, the novel geometrical scheme of PNJ generation in ‘reflection mode’ was proposed recently based on a super-contrast microparticle placed near a flat mirror. In this paper, through the numerical FDTD calculations of optical near-field structure of 2D and 3D dielectric microparticles (cylinder, sphere) we extend our considerations to the case of oblique particle-at-mirror illumination and present new physical phenomena arising in the considered photonic geometry. Specifically, we report on the generation of a quasi-retrograde PNJ which follows the inclined particle illumination and propose a new principle for obtaining a curvilinear photonic flux in the form of a ‘specular-reflection photonic hook’ (s-Hook) in the opposite to the illuminated wavevector direction. Two different regimes of s-Hook formation are analyzed by changing the direction of light incidence on a dielectric particle and by flat mirror inclination. Self-bending property of PNJ at oblique illumination is investigated.

Analysis of Radiographic Relationship between Distal Radius, Ulna, and Lunate.

Background Wrist anatomy variability is associated with differing susceptibility to pathology. For example, a flat radial inclination is associated with Kienbock's disease. Lunate facet inclination (LFI) also exhibits variability. Its relationship with other wrist features is poorly documented. Purposes We tested the hypothesis that high LFI is associated with increased uncovering of the lunate, negative ulnar variance (UV), and type 2 lunates to balance forces across wrists. Methods In total, 50 bilateral and 100 unilateral wrist posteroanterior radiographs were reviewed. Lunate type, lunate uncovering index (LUI), lunate tilting angle (LTA), UV, and sigmoid notch angle (SNA) were measured, and correlation with LFI was assessed on 150 right wrist radiographs followed by an assessment of differences based on lunate morphology. Symmetry of 50 bilateral wrists was assessed. Results There was no correlation of LFI with lunate morphology, LUI, and LTA. There was a low correlation of LFI with SNA and UV. There was an inverse relationship between UV and SNA. Wrists with type 2 lunates had more oblique sigmoid notches and higher LTA in comparison to wrists with type 1 lunates. Side-to-side comparison revealed strong correlation except for LUI, which exhibited moderate correlation. Conclusions There is no correlation between LFI, LUI, and lunate morphology. Type 2 lunates are associated with higher LTA and more oblique SNA. Wrists were symmetrical. Clinical Relevance Factors other than lunate morphology are essential in balancing forces across wrists. A better understanding of soft tissue and other factors will improve the understanding of wrist biomechanics and pathology. Contralateral wrist radiographs can guide reconstructive surgery.

Analysis of rock cutting process with a blunt PDC cutter under different wear flat inclination angles

Abstract It is generally accepted that drilling with drag bits (Polycrystalline Diamond Compact bits) simultaneously consists of “pure cutting” and “frictional contact” processes. To date, the mechanics of rock cutting have been mostly based on the assumption that these two processes are fully independent as the influence of wear flat inclination angle (β) with respect to the cutter velocity vector ( v ) on the frictional contact force is often not accounted for. The specific aim of this study is to determine the effect of wear flat inclination angle on the frictional force acting on the wear flat surface of a single blunt cutter over a wide range of depths of cut (d). For this purpose, an extensive and comprehensive set of cutting experiments was performed on two sedimentary rock samples (a limestone and a sandstone) using a state-of-the-art rock cutting equipment and a unique cutter holder. The results show that the normal contact stress (σ) at the wear flat-rock interface (and therefore the normal frictional force acting on the wear flat) is dependent on the depth of cut within the elastoplastic and particularly plastic regimes of frictional contact; however, the contact stress is invariant with depth of cut within the elastic regime. Further investigations indicate that the assumption that the force acting on the wear flat surface of a blunt cutter is independent of the cutting process taking place ahead of the cutter is not valid in particular, for the large values of inclination angles.

Experimental investigation on the effect of wear flat inclination on the cutting response of a blunt tool in rock cutting

A vast majority of experimental researches focuses on the cutting action of a sharp cutter, while there has been limited experimental work devoted to the study of the contact process at the wear flat-rock interface. The specific objective of this study is to determine the effect of the wear flat inclination angle ( $$\beta$$ ) with respect to the cutter velocity vector ( $$\varvec{v}$$ ) on both the contact stress ( $$\sigma$$ ) and friction coefficient ( $$\mu$$ ) mobilized at the wear flat-rock interface. An extensive and comprehensive set of cutting experiments was carried out on thirteen different sedimentary quarry rock samples using a state-of-the-art rock cutting equipment. A unique cutter holder was purposely designed and manufactured along with a precise experimental protocol implemented in order to change the back rake angle and therefore the inclination $$\beta$$ by steps of $$0.10^{\circ }$$ . The experimental observations confirm the existence of three regimes of frictional contact (identified as elastic, elasto-plastic and plastic) for all rock samples. Further, the results suggest that the scaled contact stress is predominantly controlled by a dimensionless number $$\eta =\frac{E^{*}\tan \beta }{q}$$ with $$E^{*}$$ the plane strain elastic modulus and q the rock strength.

Effect of Cutting Tool Properties and Depth of Cut in Rock Cutting: An Experimental Study

The current paper is designed to investigate the effect of worn (blunt) polycrystalline diamond compact cutter properties on both the contact stress ( $$\sigma$$ ) and friction coefficient (μ) mobilized at the wear flat–rock interface at different inclination angles of the wear flat surface and at a wide range of depths of cut. An extensive and comprehensive set of cutting experiments is carried out on two sedimentary rocks (one limestone and one sandstone) using a state-of-the-art rock cutting equipment (Wombat) and various blunt cutters. Experiments with blunt cutters are characterized by different wear flat inclination angles ( $$\beta$$ ), different wear flat surface roughness ( $$R_{a}$$ ), different wear flat material, and different cutting tool velocities ( $${\varvec{v}}$$ ) were conducted. The experimental results show that both the contact stress and friction coefficient are predominantly affected by the wear flat roughness at all inclination angles of the wear flat; however, the cutting tool velocity has a negligible influence on both the contact stress and friction coefficient. Further investigations suggest that the contact stress is greatly affected by the depth of cut within the plastic regime of frictional contact while the contact stress is insensitive to the depth of cut within the elastic regime.

Investigation of thermal-hydraulic performance in flat tube heat exchangers at various tube inclination angles

The performance of compact fin-and-flat tube heat exchangers (HE) can be affected by many geometrical and processing factors and one of them is tube inclination angle. However, the effect of flat tube inclination angle on the thermal-hydraulic performance of the HE is not fully examined. This paper investigates the effects of flat tube inclination angles on heat transfer and pressure drop characteristics of fined flat tube HE when the tubes are deployed in in-line and staggered arrangements. A symmetric numerical method based on FLUENT software was carried out with six different tube inclination angles (0°, 30°, 60°, 90°, 120°, and 150°) in moderately high Reynolds number. From the results, it was observed that heat transfer coefficient increased with the augmentation of the tube inclination angle from 0o to 90o and decreased for 120o and 150o . With the increase of tube inclination angle, the average Nusselt number rose by 36.3%. This might be due to the reason that the tube surface area increases with the inclination angle, which also results in the largest increment of the pressure drop by 42.0%. Overall, the 90o tube inclination angle showed the highest enhancement in heat transfer for both inline and staggered configurations with a maximum enhancement of 41.2% for in-line and 32.2% for staggered arrangements. However, the heat transfer enhancements were accompanied by high-pressure drop penalties of up to 44.2% and 42.6% for in-line and staggered arrangements, respectively. Therefore, inclining the tubes at 90o is recommended where high heat transfer is required. On the other hand, 0o tube inclination angle is recommended where pumping power is a crucial issue.

PIV Measurements of a Turbulent Boundary Layer Perturbed by a Wall-Mounted Transverse Circular Cylinder Element

The perturbation induced by a wall-mounted transverse circular cylinder element (TCCE) to a turbulent boundary layer (TBL) is studied using particle image velocimetry (PIV). Measurements are also performed on a smooth wall, which is used as baseline for comparison. The modification of the TBL caused by the sudden perturbation, in a statistical sense, is quantified by comparing the distributions of mean velocity, Reynolds stresses and shape factor in the two geometrical configurations. The impact of the TCCE on the TBL is found to extend more than 9 boundary-layer thickness downstream. Combining the side- and top-view PIV data indicates that the packet-like structures are stretched along the streamwise direction within a flat inclination angle when climbing over the TCCE, and retain their large spatial scales. The separated vortices induced downstream of the TCCE, are quickly lifted up to form the hairpin vortices within strong swirling strength. Then, the robust hairpin packets are generated downstream through the auto-generation scenario, which occupies the low-speed regions beneath the residual hairpin packet’s heads and impairs the process that the low-momentum fluids feed the concentrated vorticity into the residual hairpin heads. Meanwhile, the streamwise-stretched low-momentum regions (LMRs) are redeveloped in the inner layer underneath the new-generated hairpin packets. Further downstream, even though the residual hairpin packets’ heads are merged by the robust hairpin packets, they are not completely dissipated, and still interact with the new-generated hairpin packets in the outer layer to the end of the field of view.

Palatal Morphology Can Influence Speaker-Specific Realizations of Phonemic Contrasts

The purpose of this study was to further explore the understanding of speaker-specific realizations of the /s/-/ʃ/ contrast in German in relation to individual differences in palate shape. Two articulatory experiments were carried out with German native speakers. In the first experiment, 4 monozygotic and 2 dizygotic twin pairs were recorded by means of electromagnetic articulography. In the second experiment, 12 unrelated speakers were recorded by means of electropalatography. Interspeaker variability in the articulatory distance between the sibilants was measured and was correlated with several parameters of the palate shape. The results were twofold: (a) Similar palatal morphologies as found in monozygotic twins yield similar articulatory realizations of the /s/-/ʃ/ contrast regarding vertical and horizontal distance of the target tongue tip positions, and (b) the realization of the contrast was influenced by palatal steepness, especially the inclination angle of the alveolo-palatal region. Speakers with flat inclination angles mainly retracted their tongue to realize the contrast, whereas speakers with steep inclination angles also elevated their tongue. The articulatory realization of the sibilant contrast is influenced not only by speaker-specific auditory acuity, as previously observed, but also by palatal shape morphology, which affects the somatosensory feedback speakers receive.

Magnetostratigraphy and mid-palaeolatitude VGP dispersion during the Permo-Carboniferous Superchron: results from Paraná Basin (Southern Brazil) rhythmites

SUMMARY A detailed magnetostratigraphic and rock-magnetism study of two Late Palaeozoic rhythmite exposures (Itu and Rio do Sul) from the Itarare Group (Parana Basin, Brazil) is presented in this paper. After stepwise alterning-field procedures and thermal cleaning were performed, samples from both collections show reversed characteristic magnetization components, which is expected for Late Palaeozoic rocks. However, the Itu rocks presented an odd, flat inclination pattern that could not be corrected with mathematical methods based on the virtual geomagnetic pole (VGP) distributions. Correlation tests between the maximum anisotropy of the magnetic susceptibility axis (K1) and the magnetic declination indicated a possible mechanical influence on the remanence acquisition. The Rio do Sul sequence displayed medium to high inclinations and provided a high-quality palaeomagnetic pole (after shallowing corrections of f = 0.8) of 347.5°E 63.2°S (N = 119; A95 = 3.3; K = 31), which is in accordance with the Palaeozoic apparent wander pole path of South America. The angular dispersion (Sb) for the distribution of the VGPs calculated on the basis of both the 45° cut-off angle and Vandamme method was compared to the best-fit Model G for mid-latitudes. Both of the Sb results are in reasonable agreement with the predicted (palaeo) latitudinal S-λ relationship during the Cretaceous Normal Superchron (CNS), although the Sb value after the Vandamme cut-off has been applied is a little lower than expected. This result, in addition to those for low palaeolatitudes during the Permo-Carboniferous Reversed Superchron (PCRS) previously reported, indicates that the low secular variation regime for the geodynamo that has already been discovered in the CNS might have also been predominant during the PCRS.

REE geochemical characteristics and depositional environment of the black shale-hosted Baiguoyuan Ag-V deposit in Xingshan, Hubei Province, China

By means of techniques such as inductively coupled plasma-mass spectrometry (ICP-MS) and X-ray fluorescence spectrometry (XRF), REE geochemical characteristics and depositional environment of the black shales in Baiguoyuan Ag-V deposit, Xingshan, Hubei Province, were studied in this work. The black shales in a typical TC5 profile of Doushantuo Formation of upper Sinian period were obviously enriched in REE, especially in LREE. The REE patterns of the investigated samples normalized by Post Archean Australian Shale (PAAS) showed a flat or slight rightward inclination. The characteristic elements, their ratio and correlation diagrams showed that it should be hot-water deposit and the black shale in the study area was of a sedimentary origin. Redox sensitive metal elements pattern, trace elements index measurement in anoxic environment, Ce anomaly and δEu negative anomaly showed that the deposit environment of the black shales was a reducing and anoxic one and a slight change of the sea level could be identified. The samples relatively focused on the superimposed area of sedimentary rock and basalt in the diagram of La/Yb-ΣREE and La/Yb-Ce/La. So there might be accession of hot-water sedimentation during the period of the formation of the black rock series, mostly in normal terrigenous sedimentation with the participation of deep hot-water deposit.

Optimization of solar flat collector inclination

Solar collectors need to be inclined at the optimum angle to maximize the receiving energy. In spite of many theoretical and experimental investigations on optimization of solar collector inclination, there is an inconsistency in presented results. In this paper, solar global radiation on a horizontal surface was estimated using a mathematical model and the results were compared with the recorded data from the Zahedan city meteorological station. Total received solar energy by a flat inclined collector was determined in a certain day, and searching for the angle which has the maximum incident energy was the general procedure in determination of daily optimum tilt angle. In case of operational limitation for daily tilt adjustment, this procedure is repeated for other specific period of time and monthly, seasonal, semi-annual and annual optimum tilt angles were determined. A MATLAB-based code is used to calculate the daily optimum tilt angle. The results were in good agreement with the obtained data of a new constructed device. Finally, in the case of stationary devices, some recommendations were presented with respect to their typical application.

Numerical Study of Airflow around Vehicle A-pillar Region and Windnoise Generation Prediction

Flow separation and reattachment around the vehicle A-pillar region dictates strong pressure fluctuations on the side window surfaces and can also lead to generate aerodynamic noise. The objective of this work is to investigate qualitative flow visualization of airflow behaviour around vehicle A-pillar and its potential to generate windnoise in this region. By means of Computational Fluid Dynamic (CFD) under laboratory operating conditions, a series of three-dimensional Navier-Stokes simulations for the vortical flow around two simplified basic car models with different A-pillar/windshield geometry were carried out at different cruising speed. Both models were made with 60° flat inclination angles but with deferent A-pillar/windshield curvature, a small semi-ellipsoidal shape, a slanted sharp-edged shape. Investigations were carried out at velocities 60,100 and 140 for 0 and 15 degrees yaw angles. Results of mean pressure coefficient obtaining using CFD modeling were also compared against available experimental data. Furthermore, using Boundary Layer Noise Source Model, an approximate measure of the local contribution to total acoustic power per unit surface area was carried out in a given turbulence field. The studies provided reasonable agreement against available experimental data. The studies show that the surface mean pressure coefficients magnitudes are independent of Reynolds numbers and dependent largely to A-pillar and windshield effective corner radii. In addition, surface acoustic power level analyses show that A-pillar and windshield local corner radii effects significantly to potential of noise generation around A-pillar region.

Classification and interpretation of piezometer well hydrographs in parts of southeastern peninsular India

Well hydrographs from 275 piezometers between 1998 and 2001 in the southeastern parts of peninsular India were used in this study. The area has a monsoon-type climate. Hard rocks cover 85% of the area. The form (shape) of the hydrograph depends upon (1) climatic and hydrogeologic parameters and (2) the scale of the graph. Therefore, hydrographs are drawn to a defined and standardised scale, which allows comparison of hydrographs and helps in bringing out reasons for different forms of the hydrographs. Hydrographs can be divided into seasonal segments and the slope of each segment then used as the basic element of a classification scheme. Slopes are classed as flat (inclination <20°), obtuse (between 20 and 45°), acute (45 and 80°), right angled (80 and 90°) and homoclinal (segments of hydrographs are either rising or falling during one complete water year). Hydrographs are assigned names that are a combination of these classes and begin with the rising segment, such as acute-obtuse. Seventy-six percent of segments were homoclinal-falling in 1999, which had a poor monsoon. Flat segments constitute 27% of all segments in confined Mesozoic aquifer systems. Water table fluctuations suggest an approximate recharge of 120 to 180 mm per annum constituting 18% of the annual precipitation. Cumulative rainfall required to affect a rise in water table is between 45 to 200 mm and lag time varies from 30 minutes to 200 rainy days, which suggests that moisture in the vadose zone holds a part of the annual replenishment for these aquifers.

The Long-Term Dynamical Behavior of Short-Period Comets

We have developed and carefully tested a new computer code to follow the long-term dynamical evolution of a swarm of test particles in the solar system. This new integrator is approximately an order of magnitude faster than previously existing codes. The technique efficiently and accurately handles close approaches between test particles and planets while retaining the powerful features of recently developed mixed variable symplectic integrators. We use the new code to numerically integrate the orbits of the known short-period comets (those with periods P < 200 years) under the influence of the Sun and all the planets except Mercury and Pluto, for times up to 10 7 years. It is found under a classification based on period that most comets move between Jupiter-family ( P < 20 yr) and Halley-family ( P > 20 yr) orbits many times in their dynamical lifetimes. However, it is found that the Tisserand parameter, T , does not vary substantially for most comets. Therefore, we adopt a classification originally suggested by Carusi et al. (1987) that defines Jupiter-family comets (JFCs) as comets with T > 2 and Halley-family comets (HFCs) as those with T < 2. In this scheme, less than 8% of comets change families during the integration and most of those that change tend to remain near the Tisserand dividing line throughout. Thus, the JFCs (as defined by the Tisserand parameter) are dynamically distinct from the HFCs. We find that in our forward integration, 92% of comets are ejected from the solar system, and that ≈6% are destroyed by becoming sun-grazers. The number of sun-grazers is far more than would be expected from the existing analytic theories. The median lifetime of all known short-period comets from the current time to ultimate destruction or ejection is approximately 4.5 × 10 5 years. The very flat inclination distribution of Jupiter-family comets is found to become more distended as it ages. Since JFCs are dynamically distinct from HFCs, they must have an inclination distribution, when they first become visible, that is even flatter than that currently observed. For reasonable values of the physical lifetime before fading, we calculate that there should be roughly 5-20 times as many extinct JFCs as currently known JFCs. Our prediction for the mean cos ( i ) of the extinct JFCs is consistent with the existing data on these objects.

Message from the IFIP President

By means of techniques such as inductively coupled plasma-mass spectrometry (ICP-MS) and X-ray fluorescence spectrometry (XRF), REE geochemical characteristics and depositional environment of the black shales in Baiguoyuan Ag-V deposit, Xingshan, Hubei Province, were studied in this work. The black shales in a typical TC5 profile of Doushantuo Formation of upper Sinian period were obviously enriched in REE, especially in LREE. The REE patterns of the investigated samples normalized by Post Archean Australian Shale (PAAS) showed a flat or slight rightward inclination. The characteristic elements, their ratio and correlation diagrams showed that it should be hot-water deposit and the black shale in the study area was of a sedimentary origin. Redox sensitive metal elements pattern, trace elements index measurement in anoxic environment, Ce anomaly and δEu negative anomaly showed that the deposit environment of the black shales was a reducing and anoxic one and a slight change of the sea level could be identified. The samples relatively focused on the superimposed area of sedimentary rock and basalt in the diagram of La/Yb-ΣREE and La/Yb-Ce/La. So there might be accession of hot-water sedimentation during the period of the formation of the black rock series, mostly in normal terrigenous sedimentation with the participation of deep hot-water deposit.