Influência dos parâmetros operacionais no comportamento dinâmico de chumaceiras axiais de esmagamento de película compressível

No presente trabalho são estudadas chumaceiras axiais de esmagamento de película compressível. A lubrificação deste componente mecânico, é conseguida por meio de um fluido gasoso justificando a obtenção de soluções por via de experimentação numérica, uma vez que atualmente ainda não é possível recorrer-se a métodos analíticos. Através da simulação numérica, analisa-se a influência de alguns parâmetros operacionais na resposta deste tipo de chumaceira. Na análise dos resultados verifica-se que a posição média final do elemento suportado é independente da espessura de película inicial utilizada, desde que esta não ultrapasse o valor limite em que a pressão gerada não consiga fazer face à aceleração da massa durante a fase descendente, resultando no contacto entre as superfícies dos elementos da chumaceira. A utilização de frequências elevadas é recomendável uma vez que promove uma maior separação de superfícies, menor dissipação de energia por parte da película lubrificante e menor amplitude de oscilação do elemento suportado, embora com as desvantagens do período transiente ser superior e do ganho do afastamento do elemento suportado se reduzir significativamente, seguindo um modelo assimptótico. Em condições de pressão constante e frequência elevada, o sistema, com o aumento da massa, reage de forma a permitir uma melhor lubrificação da chumaceira e a reduzir a oscilação do elemento suportado. Por outro lado, a rigidez do sistema aumenta fazendo face a uma possível sobrecarga.

Simulation of the cake formation and growth in cake filtration

A computer model was developed to simulate the cake formation and growth in cake filtration at an individual particle level. The model was shown to be able to generate structural information and quantify the cake thickness, average cake solidosity, filtrate volume, filtrate flowrate for constant pressure filtration or pressure drop across the filter unit for constant rate filtration as a function of filtration time. The effects of particle size distribution and key operational variables such as initial filtration flowrate, maximum pressure drop and initial solidosity were examined based on the simulated results. They are qualitatively comparable to those observed in physical experiments. The need for further development in simulation was also discussed. (c) 2006 Elsevier Ltd. All rights reserved.

Diversity in the sunflower: Puccinia helianthi pathosystem in Australia

Sunflower rust caused by Puccinia helianthi is the most important disease of sunflower in Australia with the potential to cause significant yield losses in susceptible hybrids. Rapid and frequent virulence changes in the rust fungus population limit the effective lifespan of commercial cultivars and impose constant pressure on breeding programs to identify and deploy new sources of resistance. This paper contains a synopsis of virulence data accumulated over 25 years, and more recent studies of genotypic diversity and sexual recombination. We have used this synopsis, generated from both published and unpublished data, to propose the origin, evolution and distribution of new pathotypes of P. helianthi. Virulence surveys revealed that diverse pathotypes of P. helianthi evolve in wild sunflower populations, most likely because sexual recombination and subsequent selection of recombinant pathotypes occurs there. Wild sunflower populations provide a continuum of genetically heterogeneous hosts on which P. helianthi can potentially complete its sexual cycle under suitable environmental conditions. Population genetics analysis of a worldwide collection of P. helianthi indicated that Australian isolates of the pathogen are more diverse than non-Australian isolates. Additionally, the presence of the same pathotype in different genotypic backgrounds supported evidence from virulence data that sexual recombination has occurred in the Australian population of P. helianthi at some time. A primary aim of the work described was to apply our knowledge of pathotype evolution to improve resistance in sunflower to sunflower rust. Molecular markers were identified for a number of previously uncharacterised sunflower rust R-genes. These markers have been used to detect resistance genes in breeding lines and wild sunflower germplasm. A number of virulence loci that do not recombine were identified in P. helianthi. The resistance gene combinations corresponding to these virulence loci are currently being introgressed with breeding lines to generate hybrids with durable resistance to sunflower rust.

Experimental and analytical study of the effect of contact angle on liquid convective heat transfer in microchannels

In this paper we examine the effect of contact angle (or surface wettability) on the convective heat transfer coefficient in microchannels. Slip flow, where the fluid velocity at the wall is non-zero, is most likely to occur in microchannels due to its dependence on shear rate or wall shear stress. We show analytically that for a constant pressure drop, the presence of slip increases the Nusselt number. In a microchannel heat exchanger we modified the surface wettability from a contact angle of 20 degrees-120 degrees using thin film coating technology. Apparent slip flow is implied from pressure and flow rate measurements with a departure from classical laminar friction coefficients above a critical shear rate of approximately 10,000 s(-1). The magnitude of this departure is dependant on the contact angle with higher contact angles surfaces exhibiting larger pressure drop decreases. Similarly, the non-dimensional heat flux is found to decrease relative to laminar non-slip theory, and this decrease is also a function of the contact angle. Depending on the contact angle and the wall shear rate, variations in the heat transfer rate exceeding 10% can be expected. Thus the contact angle is an important consideration in the design of micro, and even more so, nano heat exchangers. (c) 2006 Elsevier Ltd. All rights reserved.

Transition in inclined internally heated fluid layers

Non-linear solutions and studies of their stability are presented for flows in a homogeneously heated fluid layer under the influence of a constant pressure gradient or when the mass flux across any lateral cross-section of the channel is required to vanish. The critical Grashof number is determined by a linear stability analysis of the basic state which depends only on the z-coordinate perpendicular to the boundary. Bifurcating longitudinal rolls as well as secondary solutions depending on the streamwise x-coordinate are investigated and their amplitudes are determined as functions of the supercritical Grashof number for various Prandtl numbers and angles of inclination of the layer. Solutions that emerge from a Hopf bifurcation assume the form of propagating waves and can thus be considered as steady flows relative to an appropriately moving frame of reference. The stability of these solutions with respect to three-dimensional disturbances is also analyzed in order to identify possible bifurcation points for evolving tertiary flows.

A micro gas turbines for UK domestic combined heat and power

Various micro-radial compressor configurations were investigated using one-dimensional meanline and computational fluid dynamics (CFD) techniques for use in a micro gas turbine (MGT) domestic combined heat and power (DCHP) application. Blade backsweep, shaft speed, and blade height were varied at a constant pressure ratio. Shaft speeds were limited to 220 000 r/min, to enable the use of a turbocharger bearing platform. Off-design compressor performance was established and used to determine the MGT performance envelope; this in turn was used to assess potential cost and environmental savings in a heat-led DCHP operating scenario within the target market of a detached family home. A low target-stage pressure ratio provided an opportunity to reduce diffusion within the impeller. Critically for DCHP, this produced very regular flow, which improved impeller performance for a wider operating envelope. The best performing impeller was a low-speed, 170 000 r/min, low-backsweep, 15° configuration producing 71.76 per cent stage efficiency at a pressure ratio of 2.20. This produced an MGT design point system efficiency of 14.85 per cent at 993 W, matching prime movers in the latest commercial DCHP units. Cost and CO2 savings were 10.7 per cent and 6.3 per cent, respectively, for annual power demands of 17.4 MWht and 6.1 MWhe compared to a standard condensing boiler (with grid) installation. The maximum cost saving (on design point) was 14.2 per cent for annual power demands of 22.62 MWht and 6.1 MWhe corresponding to an 8.1 per cent CO2 saving. When sizing, maximum savings were found with larger heat demands. When sized, maximum savings could be made by encouraging more electricity export either by reducing household electricity consumption or by increasing machine efficiency.

Bifurcation contrasts between plane Poiseuille flow and plane Magnetohydrodynamic flow

The stability characteristics of an incompressible viscous pressure-driven flow of an electrically conducting fluid between two parallel boundaries in the presence of a transverse magnetic field are compared and contrasted with those of Plane Poiseuille flow (PPF). Assuming that the outer regions adjacent to the fluid layer are perfectly electrically insulating, the appropriate boundary conditions are applied. The eigenvalue problems are then solved numerically to obtain the critical Reynolds number Rec and the critical wave number ac in the limit of small Hartmann number (M) range to produce the curves of marginal stability. The non-linear two-dimensional travelling waves that bifurcate by way of a Hopf bifurcation from the neutral curves are approximated by a truncated Fourier series in the streamwise direction. Two and three dimensional secondary disturbances are applied to both the constant pressure and constant flux equilibrium solutions using Floquet theory as this is believed to be the generic mechanism of instability in shear flows. The change in shape of the undisturbed velocity profile caused by the magnetic field is found to be the dominant factor. Consequently the critical Reynolds number is found to increase rapidly with increasing M so the transverse magnetic field has a powerful stabilising effect on this type of flow.

The mediating effect of innovation on the relationship between corporate reputation and performance in U.S. firms

In recent years, corporate reputation has gained the attention of many scholars in the strategic management and related fields. There is a general consensus that higher corporate reputation is positively related to firm success or performance. However, the link is not always straightforward; as a result, it calls for researchers to dedicate their efforts to investigate the causes and effects of firm reputation and how it is related to performance. In this doctoral dissertation, innovation is suggested as a mediating variable in this relationship. Innovation is a critical factor for firm success and survival. Highly reputed firms are in a more advantageous position to attract critical resources for innovation such as human and financial capital. These firms face constant pressure from external stakeholders, e.g. the general public, or customers, to achieve and remain at high levels of innovativeness. As a result, firms are in constant search, internally or externally, for new technologies expanding their knowledge base. Consequently, these firms engage in firms acquisitions. In the dissertation, the author assesses the effects of domestic versus international acquisitions as well as related versus unrelated acquisitions on the level of innovativeness and performance. Building upon an established measure of firm-level degree of internationalization (DOI), the dissertation proposes a more detailed and enhanced measure for the firm's DOI. It is modeled as an interaction effect between corporate reputation and resources for innovation. More specifically, firms with higher levels of internationalization will have access to resources for innovation, i.e. human and financial capital, at a global scale. Additionally, the distance between firms and higher education institutions, i.e. universities, is considered as another interaction effect for the human capital attraction. The dissertation is built on two theoretical frameworks, the resource-based view of the firm and institutional theory. It studies 211 U.S. firms using a longitudinal panel data structure from 2006 to 2012. It utilizes a linear dynamic panel data estimation methodology for its hypotheses analyses. Results confirm the hypotheses proposed in the study.

Monitoring of down-hole parameters for early kick detection

The sudden hydrocarbon influx from the formation into the wellbore poses a serious risk to the safety of the well. This sudden influx is termed a kick, which, if not controlled, may lead to a blowout. Therefore, early detection of the kick is crucial to minimize the possibility of a blowout occurrence. There is a high probability of delay in kick detection, apart from other issues when using a kick detection system that is exclusively based on surface monitoring. Down-hole monitoring techniques have a potential to detect a kick at its early stage. Down-hole monitoring could be particularly beneficial when the influx occurs as a result of a lost circulation scenario. In a lost circulation scenario, when the down-hole pressure becomes lower than the formation pore pressure, the formation fluid may starts to enter the wellbore. The lost volume of the drilling fluid is compensated by the formation fluid flowing into the well bore, making it difficult to identify the kick based on pit (mud tank) volume observations at the surface. This experimental study investigates the occurrence of a kick based on relative changes in the mass flow rate, pressure, density, and the conductivity of the fluid in the down-hole. Moreover, the parameters that are most sensitive to formation fluid are identified and a methodology to detect a kick without false alarms is reported. Pressure transmitter, the Coriolis flow and density meter, and the conductivity sensor are employed to observe the deteriorating well conditions in the down-hole. These observations are used to assess the occurrence of a kick and associated blowout risk. Monitoring of multiple down-hole parameters has a potential to improve the accuracy of interpretation related to kick occurrence, reduces the number of false alarms, and provides a broad picture of down-hole conditions. The down-hole monitoring techniques have a potential to reduce the kick detection period. A down-hole assembly of the laboratory scale drilling rig model and kick injection setup were designed, measuring instruments were acquired, a frame was fabricated, and the experimental set-up was assembled and tested. This set-up has the necessary features to evaluate kick events while implementing down-hole monitoring techniques. Various kick events are simulated on the drilling rig model. During the first set of experiments compressed air (which represents the formation fluid) is injected with constant pressure margin. In the second set of experiments the compressed air is injected with another pressure margin. The experiments are repeated with another pump (flow) rate as well. This thesis consists of three main parts. The first part gives the general introduction, motivation, outline of the thesis, and a brief description of influx: its causes, various leading and lagging indicators, and description of the several kick detection systems that are in practice in the industry. The second part describes the design and construction of the laboratory scale down-hole assembly of the drilling rig and kick injection setup, which is used to implement the proposed methodology for early kick detection. The third part discusses the experimental work, describes the methodology for early kick detection, and presents experimental results that show how different influx events affect the mass flow rate, pressure, conductivity, and density of the fluid in the down-hole, and the discussion of the results. The last chapter contains summary of the study and future research.

Pitit se rìches malere [Children are the wealth of the poor]: The Influence of Gender and Power on Choice and Uptake of Long Acting Contraceptives

Background: Haiti has the highest maternal mortality rate in the Latin American and Caribbean region. Despite the fact that Haiti has received twice as much family planning assistance as any other country in the western hemisphere, the unmet need for contraception remains particularly high. Our hypothesis is that unsuccessful efforts of family planning programs may be related to a misconstrued understanding of the complex role of gender in relationships and community in Haiti. This manuscript is one of four parts of a study that intends to examine some of these issues with a particular focus on the influence of uptake and adherence to long acting contraceptive (LAC) methods.

Methods: We conducted a three-month community-based qualitative assessment through 20 in-depth interviews in Fondwa, Haiti. Participants were divided into 4 groups of five: female users, female non-users, men and key community stakeholders.

Results: Based on the qualitative interviews, we found that main barriers included lack of access to family planning education and services and concerns regarding side effects and health risks, especially related to menstrual disruption and fears of infertility. Women have a constant pressure to remain fertile and bear children, due not only to social but also economic needs. As relationships are conceived as means for economic provision, the likelihood of uptake of irreversible methods (vasectomy and tubal ligation) was restricted by loss of fertility. Consequently, the discourse of family planning, though self-recognized in their favor, assumes women can afford not to bear children. This assumption should be questioned given the complexities of the other social determinants at play, all which affect the reproductive decisions made by Haitians.

Conclusions: Overall, our study indicated awareness surrounding contraception in the Haitian Fondwa community. Combining the substantial impact of birth spacing with the elevated yet unmet need for contraceptives in the area, it is necessary to address the intricacies of gender issues in order to implement successful programing. In Haiti not being able to bear a child poses a threat to economic and social survival, possibly explaining a dimension of the low uptake of LACs in the region, even when made available. For this reason, we believe IUDs (Intrauterine Devices) provide a suitable alternative, allowing the couple to comprehend all of the factors involved in decision making, thus decreasing the imbalances of power and knowledge prior to considering an irreversible alternative.

Entre o cartão-postal e a cidade real: um estudo sobre paisagem e produção imobiliária em Natal/RN

Recent studies concerning the landscape have investigated the most important activities that contribute for its modification and have tried to better understand the society through the marks left by its quotidian. It is understood that singular landscapes constitute the cultural patrimonies of the cities, once they are part of the daily life of the citizens and are present in their social representations. Some contemporary authors defend the preservation of the natural and urban landscape trying, specially, to keep its importance for the local population. Natal is a city where the ambient qualities are well defined and known by the beauty of the area where it is located. Situated just between a river and the sea, the city grew following its geographic characteristics. The Potengi River, the Atlantic Ocean and the vast dunes ecosystem represented natural limits to the urban expansion; at the same time they have favored the development of a landscape pattern marked by the dialectic between the natural elements and the human interventions. However, this relationship changed after the intensification of the high rising development process that took place since the 1960s. The urban legislation tried to preserve the features of the local landscape delimiting Areas for Controlling Building High , destined to protect the scenic value of some parts of the city. On the other hand, the civil construction sector has made constant pressure in sense to abolish or to modify this legal instrument, aiming profits that have increased, in the 1990s, because of the consumption and the qualification of the urban space for tourist activities. It is necessary the raising of new elements to stimulate the quarrel about the landscape preservation, the process of the urban space production and the best way for the legislation implementation. This work tries to raise elements about the subject at local level, in sense to use Natal City experience to contribute for the formulation of indicators to raise the question about the lack of measure for subjective values, for example the cultural and affective value of the landscape. The natural elements inserted in the urban profile, represent strong visual references and supply identity to the town; they are part of the collective imaginary and are detached in the social context of the city. Then, why the preservation of the landscape, that estimates the improvement in the quality of life, is not enough to justify the controlling building high already previewed as part of Natal City Legislation? These questions send us to the approach of the landscape, as a community patrimony, alerting that some of its significant esthetics attributes must be preserved as a legacy for the future generations

Distribution of neutral prilocaine in a phospholipid bilayer: Insights from molecular dynamics simulations

In this work, we report a 20-ns constant pressure molecular dynamics simulation of prilocaine (PLC), in amine-amide local anesthetic, in a hydrated liquid crystal bilayer of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine. The partition of PLC induces the lateral expansion of the bilayer and a concomitant contraction in its thickness. PLC molecules are preferentially found in the hydrophobic acyl chains region, with a maximum probability at similar to 12 angstrom from the center of the bilayer (between the C(4) and C(5) methylene groups). A decrease in the acyl chain segmental order parameter, vertical bar S-CD vertical bar, compared to neat bilayers, is found, in good agreement with experimental H-2-NMR studies. The decrease in vertical bar S-CD vertical bar induced by PLC is attributed to a larger accessible volume per lipid in the acyl chain region. (C) 2008 Wiley Periodicals, Inc.

Preferential location of prilocaine and etidocaine in phospholipid bilayers: A molecular dynamics study

In this work, we report a 20-ns constant pressure molecular dynamics simulation of the uncharged form of two amino-amide local anesthetics (LA). etidocaine and prilocaine, present at 1:3 LA:lipid, molar ratio inside the membrane, in the hydrated liquid crystal bilayer phase of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC). Both LAs induced lateral expansion and a concomitant contraction in the bilayer thickness. A decrease in the acyl chain segment order parameter, -S(CD), compared to neat bilayers, was also observed. Besides, both LA molecules got preferentially located in the hydrophobic acyl chains region, with a maximum probability at similar to 12 and similar to 10 angstrom from the center of the bilayer for prilocaine and etidocaine, respectively. (C) 2009 Elsevier B.V. All rights reserved.

Construção, caracterização e aplicação de eletrodos para descarga por arco de cátodo oco

The system built to characterize electrodes and, consequently, deposited fine films are constituted by a hollow cathode that works to discharges and low pressures (approximately 10-3 to 5 mbar), a source DC (0 to 1200 V), a cylindrical camera of closed borossilicato for flanges of stainless steel with an association of vacuum bombs mechanical and spread. In the upper flange it is connected the system of hollow cathode, which possesses an entrance of gas and two entrances for its refrigeration, the same is electrically isolated of the rest of the equipment and it is polarized negatively. In front of the system of hollow cathode there is a movable sample in stainless steel with possibility of moving in the horizontal and vertical. In the vertical, the sample can vary its distance between 0 and 70 mm and, in the horizontal, can leave completely from the front of the hollow cathode. The sample and also the cathode hollow are equipped with cromel-alumel termopares with simultaneous reading of the temperatures during the time of treatment. In this work copper electrodes, bronze, titanium, iron, stainless steel, powder of titanium, powder of titanium and silício, glass and ceramic were used. The electrodes were investigated relating their geometry change and behavior of the plasma of the cavity of hollow cathode and channel of the gas. As the cavity of hollow cathode, the analyzed aspects were the diameter and depth. With the channel of the gas, we verified the diameter. In the two situations, we investigated parameters as flow of the gas, pressure, current and applied tension in the electrode, temperature, loss of mass of the electrode with relationship at the time of use. The flow of gas investigated in the electrodes it was fastened in a work strip from 15 to 6 sccm, the constant pressure of work was among 2.7 to 8 x 10-2 mbar. The applied current was among a strip of work from 0,8 to 0,4 A, and their respective tensions were in a strip from 400 to 220 V. Fixing the value of the current, it was possible to lift the curve of the behavior of the tension with the time of use. That curves esteem in that time of use of the electrode to its efficiency is maximum. The temperatures of the electrodes were in the dependence of that curves showing a maximum temperature when the tension was maximum, yet the measured temperatures in the samples showed to be sensitive the variation of the temperature in the electrodes. An accompaniment of the loss of mass of the electrode relating to its time of use showed that the electrodes that appeared the spherical cavities lost more mass in comparison with the electrodes in that didn't appear. That phenomenon is only seen for pressures of 10-2 mbar, in these conditions a plasma column is formed inside of the channel of the gas and in certain points it is concentrated in form of spheres. Those spherical cavities develop inside of the channel of the gas spreading during the whole extension of the channel of the gas. The used electrodes were cut after they could not be more used, however among those electrodes, films that were deposited in alternate times and the electrodes that were used to deposit films in same times, those films were deposited in the glass substrata, alumina, stainless steel 420, stainless steel 316, silício and steel M2. As the eletros used to deposit films in alternate time as the ones that they were used to deposit in same times, the behavior of the thickness of the film obeyed the curve of the tension with relationship the time of use of the electrode, that is, when the tension was maximum, the thickness of the film was also maximum and when the tension was minimum, the thickness was minimum and in the case where the value of the tension was constant, the thickness of the film tends to be constant. The fine films that were produced they had applications with nano stick, bio-compatibility, cellular growth, inhibition of bacterias, cut tool, metallic leagues, brasagem, pineapple fiber and ornamental. In those films it was investigated the thickness, the adherence and the uniformity characterized by sweeping electronic microscopy. Another technique developed to assist the production and characterization of the films produced in that work was the caloteste. It uses a sphere and abrasive to mark the sample with a cap impression, with that cap form it is possible to calculate the thickness of the film. Through the time of life of the cathode, it was possible to evaluate the rate of waste of its material for the different work conditions. Values of waste rate up to 3,2 x 10-6 g/s were verified. For a distance of the substratum of 11 mm, the deposited film was limited to a circular area of 22 mm diameter mm for high pressures and a circular area of 75 mm for pressure strip. The obtained films presented thickness around 2,1 µm, showing that the discharge of arch of hollow cathode in argon obeys a curve characteristic of the tension with the time of life of the eletrodo. The deposition rate obtained in this system it is of approximately 0,18 µm/min

Electron microprobe investigations of metamorphic reactions and mineral growth histories, Kwoiek area, British Columbia

The Kwoiek Area of British Columbia contains a pendant or screen of metamorphosed sedimentary and volcanic rocks almost entirely surrounded by a portion of the Coast Range Batholith, and intruded by several dozen stocks. The major metamorphic effects were produced by the quartz diorite batholithic rocks, with minor and later effects by the quartz diorite stocks. The sequence of important metamorphic reactions in the metasedimentary and metavolcanic rocks, ranging in grade from chlorite to sillimanite, is:

1. chlorite + carbonate + muscovite → epidote + biotite

2. chlorite + carbonate → actinolite + epidote

3. chlorite + muscovite → garnet + biotite

4. chlorite + epidote → garnet + hornblende

5. chlorite + muscovite → garnet + staurolite + biotite

6. chlorite + muscovite → aluminum silicate + biotite

7. muscovite + staurolite → garnet + aluminum silicate + biotite

8. staurolite → garnet + aluminum silicate

Continuous reactions, occurring between reactions 5 and 7, are:

A. chlorite + (high Ti) biotite + Al₂O₃ (from plagioclase?)→ garnet + staurolite + (low Ti) biotite + O₂

B. muscovite (phengitic) → garnet + staurolite +muscovite (less phengitic) + O₂ (?)

Detailed electron microprobe work on garnet, staurolite, biotite, and chlorite shows that:

(1) The garnet porphyroblasts are zoned according to a depletion model, called the Rayleigh depletion model, which assumes equilibrium between the edge of a growing garnet and the minerals which are unzoned, notably biotite, chlorite, and muscovite, but which assumes disequilibrium within the garnet.

(2) The staurolite porphyroblasts are also zoned, and from their zoning patterns reactions A, B, and 5 are documented. Progressive reduction of iron with increasing grade of metamorphism is also inferred from the staurolite zoning patterns.

(3) During a late period of falling temperature garnet continued to grow and the biotite and chlorite reequilibrated. The biotite, chlorite, and garnet edge compositions can vary from point to point in a given thin section, indicating that the volume of equilibrium at the final stage of metamorphism was only a few cubic microns.

(4) The horizon within the garnet that grew at maximum temperature can be identified. The Mg/Fe ratio of this horizon, if the garnet composition is a limiting composition in the Al₂O₃ - K₂O - FeO - MgO tetrahedron, increases systematically with increasing metamorphic grade. Biotite and chlorite compositions also show a general increase in Mg/Fe ratio with increasing metamorphic grade, but staurolite appears to show the reverse effect.

(5) The Mg/Fe ratio at the maximum temperature horizon of the garnet porphyroblasts is a function of its Mn content as evidenced from the study of five garnet-bearing rocks, collected from one outcrop area, with the same assemblage but with differing proportions of minerals.

An important implication of zoned minerals is that the effective composition of a system in a phase lies on the join between the homogeneous minerals (if there are two) and not within three-or- four-phase fields when a zoned mineral, such as garnet or staurolite, is present in the assemblage.

Study of the three aluminum silicates found in the Kwoiek Area showed that a constant pressure change in polymorphs from andalusite to kyanite to sillimanite took place with increasing temperature. This transition series is best explained by the metastable formation of andalusite.

Photographic materials on pages 15, 121, 160, 162, and 164 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.