Understanding Of Mass Research Articles

Basin-scale 3D modelling of the northern Upper Rhine Graben: insights into basement fault-related geothermal flow pathways

A regional assessment of the potential for geothermal heat production, power generation and also heat storage requires an evaluation of the heat in place and its recharge. Both are controlled by the flow properties and natural fluid flow through the reservoir at the present day, which must be thoroughly analysed based on the understanding and modelling of the architecture of deep reservoirs. In the Upper Rhine Graben, well known for its vast geothermal potential, a characterization of the structural organization at the basin scale and an understanding of mass and heat transfer are, therefore, useful for correctly estimating the technical and economic potential for geothermal energy. The distribution of the resources can be quantified based on the basin analysis approach. This is classically used for hydrocarbon resources and is applied in this study to predict the geothermal fluid-flow paths. The role of faults and their hydraulic regime on temperature field heterogeneities is investigated. Several scenarios with or without rift basin internal faults and various transmissivity ranges along these faults are analysed and compared. The measured temperature field is used for the calibration of the different model scenarios results. The scenario with the most significant role for internal faults as fluid-flow pathways in the western Upper Rhine Graben is the one that provides the most accurate reproduction of the temperature field. Such output highlights the importance of quantifying the hydraulic behaviour of faults and associated fracture networks in space and time. Supplementary material: dataset containing geometry, facies distribution and main results of scenario 4 is available at https://doi.org/10.6084/m9.figshare.c.6628506

Theoretical modeling of the drag reduction influenced by film boiling heat transfer on a spherical body

Drag reduction is a common phenomenon in various fields, such as enhanced heat transfer process of micro-channels, or fuel-coolant interaction (FCI) during severe accidents in nuclear power plants. It significantly affects the solidification process of hot particles and the likelihood of occurrence of vapor explosion, as well. In this work, theoretical modeling of the drag reduction influenced by film boiling heat transfer on a spherical body is conducted, and a fitting method is adopted to obtain a semi-empirical model of drag coefficient (CD), which can be described as a function of particle Froude number (Frp), entrainment Reynolds number (Reα), and the ratio of steam density to coolant density (ρ0). There seems to be a positive relationship between Reα and CD, however, negative relationships occur between Frp and CD, and between ρ0 and CD. Verifications against single effect experiments and an integral experiment under different initial conditions for a hot solid/melts moving downward in the coolant, and several classical correlations of convective heat transfer and drag coefficient under non-isothermal conditions strongly ensure the accuracy of the present physical model. It can be evaluated from the present model that a negative relationship between the drag coefficient and Reynolds number still occurs in turbulent regime, and there is a significant difference of CD under different sphere diameters in turbulent regime, which haven't been recognized and presented by various classical models yet. The present work can guide to solve the issue of drag reduction during FCI or thermal management and provide a new understanding of mass, momentum, and heat transfer under multi-phase flow conditions which may take place in different kinds of chemical reactions, as well.

A Remote Sensing Perspective on Mass Wasting in Contrasting Planetary Environments: Cases of the Moon and Ceres

Mass wasting, as one of the most significant geomorphological processes, contributes immensely to planetary landscape evolution. The frequency and diversity of mass wasting features on any planetary body also put engineering constraints on its robotic exploration. Mass wasting on other Solar System bodies shares similar, although not identical, morphological characteristics with its terrestrial counterpart, indicating a possible common nature for their formation. Thus, planetary bodies with contrasting environmental conditions might help reveal the effects of the atmosphere, subsurface fluids, mass accumulation/precipitation, and seismicity on mass wasting, and vice versa. Their relative positions within our Solar System and the environmental and geophysical conditions on the Moon and the dwarf planet Ceres are not only extremely different from Earth’s but from each other too. Their smaller sizes coupled with the availability of global-scale remote sensing datasets make them ideal candidates to understand mass wasting processes in widely contrasting planetary environments. Through this concept article, we highlight several recent advances in and prospects of using remote sensing datasets to reveal unprecedented details on lunar and Cerean mass wasting processes. We start with briefly discussing several recent studies on mass wasting using Lunar Reconnaissance Orbiter Camera (LROC) data for the Moon and Dawn spacecraft data for Ceres. We further identify the prospects of available remote sensing data in advancing our understanding of mass wasting processes under reduced gravity and in a scant (or absent) atmosphere, and we conclude the article by suggesting future research directions.

COMMON KAZAKHSTAN CONSCIOUSNESS: CONCEPT AND DEFINITION

The article discusses actual issues of common Kazakhstan consciousness, which have not yet been studied in socio-political science. The article elaborates on the nature, concept, definition of self-awareness and the relationship between national and common Kazakh consciousness. The article states that common Kazakh self-awareness is the mass understanding of Kazakh people (for example, the people of Kazakhstan) of the unity of a particular ethno-political and civil community and of its difference from other multinational and mono-national communities (social systems). Common Kazakh consciousness is being formed as a result of the natural historical development of equal and united relations among the peoples of Kazakhstan. In addition, the article also focuses on discussion issues.

PENGARUH KOMUNIKASI POLITIC ENTERTAINMENT MELALUI IKLAN TERHADAP TINGKAT KETERPILIHAN PARTAI POLITIK PADA PEMILIHAN UMUM 2019

Globalization demands the development of communication media, which is TV advertisment. Indonesian political dynamics is one of the most unique and fresh studies discussed in various perspectives. It concerns ondecision making and ethical political differentiation that empirically influences the political legitimacy in political representation. Digital politics is very popular within the society it could be categorized as swing voters. Digital politic is growing close to the 2019 general election as the effort of low politics tendencies that can be analyzed using the cultural value. Political parties have a polarization to use TV advertisement to be a media for socialization their political goals. The implementation of this style is usually called politics entertainment. This research explains the influence of digital political style and entertainment politics with TV advertisement on the level of electability of political parties in the general election 2019 through data interpretation method. The research is conducted as a means to explain the understanding ofmass polarization in online setting. Additionally, it is also purposed to know the effectiveness of digital politics and entertainment politics in its use in the 2019 general election.

Parametrizing nonbonded interactions between silica and water from first principles

Silica has been used in a vast number of micro/nano-fluidic technologies where interactions of water with silica at the molecular level play a key role. In such small systems, an understanding of mass and heat transport or surface wetting relies on accurate calculations of the water-silica interface coupling through atomic interactions. Molecular dynamics (MD) is a convenient tool for such use, but force field parameters for nonbonded interactions are required as an input, which are very limited in literature. These interaction parameters can be predicted by density functional theory, but dispersion forces are not calculated in standard models for electron correlations that additional correction models have been proposed at different levels of sophistications, and still under development. Accordingly, this work employs state of the art quantum chemistry to compute the binding energies. Force field parameters for silica/water van der Waals interactions were calculated, and later tested in MD simulations of water droplet on silica surface. While the standard dispersion corrections overestimated the binding energy, Becke-Johnson model yielded interactions parameters recovering experimentally measured wetting behavior of silica with a water contact angle of approximately 12.4° on the flat and clean silica surface. Results will be useful for the current molecular modelling attempts by providing transferable parameters for simple silica/water van der Waals interactions as an alternative to existing complex surface interaction models.

Using drawings and discussion to gain insights into young learners’ understanding of mass

In this paper, we explore the possible value of an open-ended assessment task, Impress Me, and followup interview as ways to gain insights into children’s learning of mathematics,. Ten children in their first or second year of school recorded their understanding using drawing and/or writing after the period in which they were taught lessons on the measurement of mass. Later they met individually with an interviewer/researcher to discuss their drawing/writing and their learning. The Impress Me recording was found to be a useful prompt for the children to stimulate discussion about their learning.

A Simple Pressurized SOFC Test Rig for Measurements of Cell Performance, Impedance, and Various Overvoltages

Nowadays, our modern society is facing many serious environmental and energy shortage problems. Delay of action will jeopardize the ability of future generations to meet their needs. Thus, how to develop highly efficient power generation systems with very low emissions is an urgent need for our modern society. Probably, a pressurized solid oxide fuel cells (PSOFC) integrating with a gas turbine (GT) or micro gas turbine (MGT), the hybrid PSOFC-GT or -MGT power system, which has the highest efficiency up to 70%, is the best candidate. The development of such hybrid power system helps to the consolidation of the fuel cell industry, the expansion of the gas turbine industry, and the improvement of the environment. As such, the hybrid PSOFC-MGT power system has become an emerging topic in the 21th century with wide interest, as evidenced by a large volume of literature and several demonstration projects. For examples, Siemens demonstrated a 220 kW PSOFC-MGT hybrid system in 2002, the Korea Institute of Energy Research displayed a 30 kW (5 kW PSOFC integrated with 25 kW MGT) hybrid system in 2006, and Mitsubishi Heavy Industries run a 200 kW hybrid PSOFC-MGT combined-cycle power plant in 2011. Indeed, considerable progresses have been made over the past two decades in optimization of geometry and development of new materials and in understanding of mass and heat transports together with electrochemical reactions in porous microstructures. However, there are still technical challenges remaining to be solved step by step with limited but controllable parameters before a stable operation among different components of the hybrid PSOFC-MGT system can be assured and the status of the development can be then elevated from a module level. One of the challenges is the detail electrochemical impedance spectra (EIS) of PSOFC, which is still rare in literatures. This motivates us to design a simple efficient high-pressure full/half button cell testing platform for measurements of the effect of pressurization and increasing temperature on EIS and various overvoltages of PSOFC. The testing platform has several parts, from inside out including a specially thread-designed housing carrier for the full/half button cell, a serpentine heating pipe system for uniform heating of the supplied fuel and air gases, a temperature-controlled furnace, and a large high-pressure vessel together with measuring devices and their associates. Hence, current-voltage curves and AC impedance spectra of any full/half button cells can be measured. In this study, we present power-generating characteristics and EIS data of an anode-supported full button cell over wide ranges of pressure (p = 1~5 atm) and temperature (T = 700~850 oC). We apply constant gas flow rates, 200ml min-1 H2 in anode and 200ml min-1 air in cathode, for all experimental events. Results show that, for any given values of T or p, power densities increase with increasing p or T at any fixed current densities. Such enhancement on power densities is more sensitive to the increase of T than to the increase of p. These results are explained by the corresponding EIS data. The latter shows that both high and low frequency arcs of impedance spectra decrease with increasing p, resulting in a reduction of the total polarization resistance. Specifically, the high frequency arcs decrease rather weakly with increasing p as compared to that of the low frequency arcs. Further, we found that the characteristic frequencies of high and low frequency arcs occur around 100 ~ 1000 Hz and at about 10 Hz, respectively. The former may be attributed to the cathode activation polarization and the latter may be due to the diffusion processes in the anode electrode. Hence, pressurization can simultaneously decrease the cathode activation polarization and the anodic diffusion concentration polarization. In addition to the aforesaid power-generating characteristics and EIS results, this study reports analyses of activation and concentration overvoltages using the Butler-Volmer equation and the related concentration overvoltage equation based on a 1D diffusion model. We found that both activation and concentration overvoltages decrease with increasing p. Two important parameters, the exchange current density and the anodic effective diffusion coefficient, are also calculated by applying the present measured data. Results show that pressurization enhances the exchange current density leading to an increase of the electrochemical reaction rate. Though pressurization reduces slightly the anodic effective diffusion coefficient, it can increase the molar concentration and thus the overall gas-phase diffusion rate in porous electrode. These overvoltage results will be compared with previous numerical and experimental data to enhance our understanding of the effect of pressurization on the polarization mechanisms in SOFCs. Figure 1

Seventh Grade Students’ Qualitative Understanding of the Concept of Mass Influenced By Real Experiments and Virtual Experiments

This research is conducted among 65 seventh graders (12-14 years old) who attend introductory course on physics. Tests and interviews are used to trace the roots of the students’ misconceptions about mass. Results from the research reveal serious weaknesses in students’ understanding of concept of mass, and its confusion with concepts of density and weight. Pre-conceptions about dependence of volume and mass of physical body and concept of heavy materials have deep impact on students understanding of mass and its measurement. Also, poor understanding of inertia signals that it might be more natural way for students to present mass as property of matter that comprises the body. Sources of misconceptions are found in the prior students’ experience in informal, as well as in formal education. Later include students’ vocabulary development, physics curriculum structure, and physics textbook. Weaknesses are detected in the non-physics teachers’ competences who teach physics concepts. All of the research findings are supported by similar findings in other researches which confirm that detected misconceptions are generic. In order to minimize the existence of detected misconceptions, directions for revision of the curriculum and textbook are proposed. Also, directions for methodological approach are given.

Mass Transfer in Infrared Drying of Gel-Coated Seeds

In order to contribute for a better understanding of mass transfer in drying of shrinking particles, in this study shrinkage and drying characteristics of sorghum seeds encapsulated into gel-based polymeric matrix were experimentally determined by using infrared (IR) radiation. IR drying of gel coated seeds was carried out at three different temperatures (65℃, 80℃ and 93℃). The shrinkage of the individual particles during drying was quantified by means of the volume and surface area changes evaluated from geometric measurements. The product quality was evaluated in terms of the changes of particle density and percent of cracks in gel coating incurred during drying. Surface area and volume of the gel-seed system decreased about 65% and 80% until the end of the process, respectively, stressing the need to take into account the surface area changes to calculate water flux density as function of moisture content and obtain an accurate interpretation of the drying mechanisms well as to include the volume shrinkage in mass transfer models to determine reliable values of moisture diffusivity. The IR drying behavior of gel-coated seeds was then characterized by the presence of three drying periods: heating up, constant moisture flux and falling moisture flux. Accelerated drying of gel coated seeds was obtained by applying higher IR radiation intensities. The effect of IR source temperature on the particle shrinkage was more pronounced at the constant moisture flux period and practically negligible at the decreasing moisture flux period. Neglecting shrinkage of individual coated-seeds during IR drying led to an erroneous absence of constant flux period and overestimation of the mass transfer by diffusion. Apparent density of the particles was greater at low-temperature IR drying than at high-temperature IR drying. Coated particles keep their original geometry, but a significant cracking of gel coating was observed at rapid drying rate conditions.

Weyl geometric gravity and electroweak symmetry “breaking”

AbstractA Weyl geometric scale covariant approach to gravity due to Omote, Dirac, and Utiyama (1971ff) is reconsidered. It can be extended to the electroweak sector of elementary particle fields, taking into account their basic scaling freedom. Already Cheng (1988) indicated that electroweak symmetry breaking, usually attributed to the Higgs field with a boson expected at 0.1–0.3 TeV, may be due to a coupling between Weyl geometric gravity and electroweak interactions. Weyl geometry seems to be well suited for treating questions of elementary particle physics, which relate to scale invariance and its “breaking”. This setting suggests the existence of a scalar field boson at the surprisingly low energy of ∼ 1 eV. That may appear unlikely; but, as a payoff, the acquirement of mass arises as a result of coupling to gravity in agreement with the understanding of mass as the gravitational charge of fields.

Feeling ‘Protected’ In Mass Organized Group Tours

This study provides further understanding of mass organized tourists byidentifying the push factors for mass tourism in a Korean context. It is proposed that ‘protection seeking’ tendency and perceived travel risks are two push factors thatencourage Korean tourists to choose mass tourism products. This study employed amixed method approach in which qualitative and quantitative approaches weresequentially conducted across two stages. This study successfully identified thedimension of ‘protection seeking’ and found it has a significant role in a Koreantourist context. The ‘protection seeking’ tendency increases the likelihood of potential tourists to choose the mass organized tours. However, perceived risks were not foundto be directly related to choosing the mass organized tours; perceived risks weresignificantly related to ‘protection seeking’. This study reveals that a critical reasonwhy Korean tourists choose mass tourism products is because they want apsychological ‘shelter’ and the ability to call for help in case of emergency. Thisimplies that various types of mass organize tours are needed to be designed for thefuture. This result is particularly of significance for those who desire to make theirholiday products more attractive to Korean outbound tourists.

Analysis to current situation of TCM science popularization based on internet

By analyzing the current situation of TCM science popularization, We found that internet is serving as the most influential and rapid developing media at present. Therefore, a through excavation and utilization of internet as a tool for TCM science popularization will not only expand TCM science popularization platform, enhance mass foundation, promote mass understanding and recognition of TCM, but also meet the need of TCM self-development. Key words: Mainland China and Taiwan; Traditional Chinese medicine; Resource sharing

Einstein on mass and energy

This paper explores the evolution of Einstein’s understanding of mass and energy. Early on, Einstein embraced the idea of a speed-dependent mass but changed his mind in 1906 and thereafter carefully avoided that notion entirely. He shunned, and explicitly rejected, what later came to be known as “relativistic mass.” Nonetheless many textbooks and articles credit him with the relation E=mc2, where E is the total energy, m is the relativistic mass, and c is the vacuum speed of light. Einstein never derived this relation, at least not with that understanding of the meaning of its terms. He consistently related the “rest energy” of a system to its invariant inertial mass.

Fluid Flow, Heat Transfer, and Solute Transport at Nuclear Waste Storage Tanks in the Hanford Vadose Zone

At the Hanford Site, highly radioactive and chemically aggressive waste fluids have leaked from underground storage tanks into the vadose zone. This paper addresses hydrogeological issues at the 241‐SX tank farm, especially focusing on Tank SX‐108, which is one of the highest heat load, supernate density and ionic strength tanks at Hanford and a known leaker. The behavior of contaminants in the unsaturated zone near SX‐108 is determined by an interplay of multiphase fluid flow and heat transfer processes with reactive chemical transport in a complex geological setting. Numerical simulation studies were performed to obtain a better understanding of mass and energy transport in the unique hydrogeologic system created by the SX tank farm. Problem parameters are patterned after conditions at Tank SX‐108, and measured data were used whenever possible. Borrowing from techniques developed in geothermal and petroleum reservoir engineering, our simulations feature a comprehensive description of multiphase processes, including boiling and condensation phenomena, and precipitation and dissolution of solids. We find that the thermal perturbation from the tank causes large‐scale redistribution of moisture and alters water seepage patterns. During periods of high heat load, fluid and heat flow near the tank are dominated by vapor–liquid counterflow (heat pipe), which provides a much more efficient mechanism than heat conduction for dissipating tank heat. The heat pipe mechanism is also very effective in concentrating dissolved solids near the heat source, where salts may precipitate even if they were only present in small concentrations in ambient fluids. Tank leaks that released aqueous fluids of high ionic strength into the vadose zone were also modeled. The heat load causes formation dry‐out beneath the tank, which is accompanied by precipitation of solutes. These may become remobilized at a later time when tank temperatures decline and previously dried out regions are rewetted. Simulated temperature and moisture distributions compare well with borehole measurements performed in 2000. The temperature maximum observed beneath Tank SX‐108 can be explained from past thermal history of the tank; it is not necessary to invoke heat generation from leaked radioactive contaminants. A novel composite medium model is used to explore effects of moisture tension–dependent anisotropy, which is shown to have important impacts on fluid flow and solute transport in the Hanford sediments.

Fluid Flow, Heat Transfer, and Solute Transport at Nuclear Waste Storage Tanks in the Hanford Vadose Zone

At the Hanford Site, highly radioactive and chemically aggressive waste fluids have leaked from underground storage tanks into the vadose zone. This paper addresses hydrogeological issues at the 241-SX tank farm, especially focusing on Tank SX-108, which is one of the highest heat load, supernate density and ionic strength tanks at Hanford and a known leaker. The behavior of contaminants in the unsaturated zone near SX-108 is determined by an interplay of multiphase fluid flow and heat transfer processes with reactive chemical transport in a complex geological setting. Numerical simulation studies were performed to obtain a better understanding of mass and energy transport in the unique hydrogeologic system created by the SX tank farm. Problem parameters are patterned after conditions at Tank SX-108, and measured data were used whenever possible. Borrowing from techniques developed in geothermal and petroleum reservoir engineering, our simulations feature a comprehensive description of multiphase processes, including boiling and condensation phenomena, and precipitation and dissolution of solids. We find that the thermal perturbation from the tank causes large-scale redistribution of moisture and alters water seepage patterns. During periods of high heat load, fluid and heat flow near the tank are dominated by vapor–liquid counterflow (heat pipe), which provides a much more efficient mechanism than heat conduction for dissipating tank heat. The heat pipe mechanism is also very effective in concentrating dissolved solids near the heat source, where salts may precipitate even if they were only present in small concentrations in ambient fluids. Tank leaks that released aqueous fluids of high ionic strength into the vadose zone were also modeled. The heat load causes formation dry-out beneath the tank, which is accompanied by precipitation of solutes. These may become remobilized at a later time when tank temperatures decline and previously dried out regions are rewetted. Simulated temperature and moisture distributions compare well with borehole measurements performed in 2000. The temperature maximum observed beneath Tank SX-108 can be explained from past thermal history of the tank; it is not necessary to invoke heat generation from leaked radioactive contaminants. A novel composite medium model is used to explore effects of moisture tension–dependent anisotropy, which is shown to have important impacts on fluid flow and solute transport in the Hanford sediments.

Fluid Flow, Heat Transfer, and Solute Transport at Nuclear Waste Storage Tanks in the Hanford Vadose Zone

At the Hanford Site, highly radioactive and chemically aggressive waste fluids have leaked from underground storage tanks into the vadose zone. This paper addresses hydrogeological issues at the 241-SX tank farm, especially focusing on Tank SX-108, which is one of the highest heat load, supernate density and ionic strength tanks at Hanford and a known leaker. The behavior of contaminants in the unsaturated zone near SX-108 is determined by an interplay of multiphase fluid flow and heat transfer processes with reactive chemical transport in a complex geological setting. Numerical simulation studies were performed to obtain a better understanding of mass and energy transport in the unique hydrogeologic system created by the SX tank farm. Problem parameters are patterned after conditions at Tank SX-108, and measured data were used whenever possible. Borrowing from techniques developed in geothermal and petroleum reservoir engineering, our simulations feature a comprehensive description of multiphase processes, including boiling and condensation phenomena, and precipitation and dissolution of solids. We find that the thermal perturbation from the tank causes large-scale redistribution of moisture and alters water seepage patterns. During periods of high heat load, fluid and heat flow near the tank are dominated by vapor–liquid counterflow (heat pipe), which provides a much more efficient mechanism than heat conduction for dissipating tank heat. The heat pipe mechanism is also very effective in concentrating dissolved solids near the heat source, where salts may precipitate even if they were only present in small concentrations in ambient fluids. Tank leaks that released aqueous fluids of high ionic strength into the vadose zone were also modeled. The heat load causes formation dry-out beneath the tank, which is accompanied by precipitation of solutes. These may become remobilized at a later time when tank temperatures decline and previously dried out regions are rewetted. Simulated temperature and moisture distributions compare well with borehole measurements performed in 2000. The temperature maximum observed beneath Tank SX-108 can be explained from past thermal history of the tank; it is not necessary to invoke heat generation from leaked radioactive contaminants. A novel composite medium model is used to explore effects of moisture tension–dependent anisotropy, which is shown to have important impacts on fluid flow and solute transport in the Hanford sediments.

A Model of Heat and Mass Transfer in a Porous Cometary Nucleus Based on a Kinetic Treatment of Mass Flow

The main aspect of this paper is to provide a synthesis between two major lines of development in the understanding of mass and heat transfer in a volatile porous medium. The first one is a macroscopic approach, where the medium is considered as a continuum, and heat and mass transfer equations are solved under appropriate boundary conditions for temperature and gas pressure (G. Steiner and N. I. Kömle 1991, Planet. Space Sci. 39, 507–513; Y. Mekler et al. 1990, Astrophys. J. 356, 682–686; S. J. Espinasse et al. 1991, Icarus 92, 350–365), while the second one is a kinetic model, calculating gas flow in tubes under the assumption of a known temperature distribution (N. I. Kömle and G. Dettleff 1991, Icarus 89, 73–84; Yu. V. Skorov et al. 1999, Icarus 140, 173–188). We review briefly the main aspects of this previous work, and subsequently present a combined consistent model, which uses a macroscopic heat transfer equation, but kinetic solutions for the gas flow. This new model was implemented as a numerical code and its performance is demonstrated by a couple of example calculations. The main advantage of the new model in comparison to the macroscopic approach is the fact that it avoids specifying a boundary condition for gas pressure at the surface, because the emitted gas flux is found at any time with the aid of the kinetic calculation. The local balance of sublimation and condensation in the interior of the porous ice can be calculated more consistently than is possible by macroscopic models only, because surface pressure and density develop in a “natural” way and no external boundary condition for the pressure must be imposed. We consider the development of temperature distribution and gas flux in ice samples in response to surface irradiation. Both pure ice and ice covered by a dust mantle are studied. The results are compared with corresponding solutions obtained on the basis of a macroscopic model, and differences are discussed in detail. Finally, experimental data obtained from previous comet simulation experiments (KOSI and related laboratory experiments) are reconsidered. In particular, temperature profiles and gas fluxes from the KOSI-9 experiment (E. Grün et al., 1993, J. Geophys. Res. 98, 15,091–15,104) are interpreted in terms of the kinetic approach.

Oxygen in Unevolved Metal-Poor Stars from Keck Ultraviolet HIRES Spectra

The determination of the abundance of oxygen (O) is important in our understanding of mass¨ spectrum of previous generations of stars, the evolution of the Galaxy, stellar evolution, and the age- metallicity relation. We have measured O in 24 unevolved stars with Keck HIRES observations of the OH lines in the ultraviolet spectral region at a spectral resolution of D45,000. The spectra have high signal-to-noise ratios, typically 60¨110, and high dispersion, 0.022 per pixel. Very special care has been Ae taken in determining the stellar parameters in a consistent way and we have done this for two diUerent, plausible temperature scales. The O abundance from OH has been computed by spectrum synthesis tech- niques for all 24 stars plus the Sun for which we have a Keck spectrum of the daytime sky. In addition, we determined O abundances from the O I triplet with our stellar parameters and the published equiva- lent widths of the three O I lines from six sources. The comparison of data analyzed with the same, consistently determined, parameter sets show generally excellent agreement in the O abundances; diUer- ences in the origin of the models (not the parameters) may result in abundance diUerences of 0.07 to 0.11 dex. We show that the O abundances from OH and from O I are reliable and independent and average the two for the adopted O. This averaging has the great bene—t of neutralizing uncertainties in the parameters since OH and O I strengths depend on eUective temperature and gravity in opposite direc- tions. For these cool, unevolved stars we —nd that O is enhanced relative to Fe with a completely linear relation between (O/H) and (Fe/H) over 3 orders of magnitude with very little scatter; taking the errors into account in determining the —ts, we —nd (O/H) \) 0.66 (^0.02) (Fe/H) ) 0.05 (^0.04). The O abundances from 76 disk stars of Edvardsson et al. have a measured slope of 0.66 (identical to our halo dwarf stars) and —t this relationship smoothly. The relation between (O/Fe) and (Fe/H) is robustly linear and shows no sign of a break at metallicities between (1.0 and (2.0, as has been discussed by others. At low metallicities, (Fe/H) (3.0, (O/Fe) ( )1.0. The —t to this relationship (taking the errors into account) is (O/Fe) \( 0.35 (^0.03) (Fe/H) ) 0.03 (^0.05). The enrichment of O is prob- ably still from massive stars and Type II supernovae; however, the absence of a break in (O/Fe) versus (Fe/H) runs counter to traditional galactic evolution models, and the interplay of Type II and Type Ia supernovae in the production of O and Fe should be reexamined. It appears that either Fe or O can be used as a chronometer in studies of galactic evolution.

Teaching for Understanding: A Study of Students' Preinstruction Theories of Matter and a Comparison of the Effectiveness of Two Approaches to Teaching About Matter and Density

Thirty 8th-grade students were given an interview and a written test before and after a 10-week curriculum unit concerning matter, mass, volume, and density. The instruments probed qualitative understandings of matter; ability to differentiate weight and density using qualitative reasoning; formal, quantitative understandings of mass, weight, volume, and density; and ability to integrate both qualitative and quantitative reasoning about density. In Part 1 of the study, we examined the organization of student ideas prior to instruction. We found evidence to support our idea that students' qualitative conceptions of matter and density were organized in commonsense theories of matter that constrained their understanding of density: Students who believed that all material objects have weight, no matter how small or light the object, were much more likely to have made a beginning differentiation between weight and density than those who did not. We also showed that a qualitative understanding of density emerged prior to a formal, quantitative understanding of density, although most students were able to engage in explicit proportional reasoning about another, more familiar quantity (i.e., sweetness). In Part 2, we compared the effectiveness of two teaching approaches. One approach to teaching about matter and density-the standard Introductory Physical Science (IPS) curriculum-emphasized formal definitions, measurement, and explicit quantitative reasoning. Because it asked students to work formally with complex concepts before assuring that relevant qualitative understanding was in place, we designed a modified IPS curriculum that addressed this problem by encouraging students to make their initial assumptions about matter explicit and open to debate. The modified curriculum also used visual models and qualitative reasoning to help students bridge the gap between their starting conceptions and formal, quantitative definitions. We found that both curricula were effective in promoting a good quantitative understanding of mass, volume, and density. The modified cumculum, however, was more effective at restructuring students' qualitative conceptions and at promoting an integrated understanding of density. Thus, we conclude that science curricula should integrate both qualitative and quantitative reasoning to be effective at promoting conceptual change.