Temporary Plateau Research Articles

Direct numerical simulations of incompressible Rayleigh–Taylor instabilities at low and medium Atwood numbers

Direct numerical simulations of two-dimensional (2D) and three-dimensional (3D), single-mode and multi-mode, incompressible immiscible Rayleigh–Taylor (RT) instabilities are performed using a phase-field approach and high-order finite-difference schemes. Various combinations of Atwood number, Reynolds number, surface tension, and initial perturbation amplitude are investigated. It is found that at high Reynolds numbers, the surface tension, if significant, could prevent the formation of Kelvin–Helmholtz type instabilities within the bubble region. A relationship is proposed for the vertical distance of the bubble and spike vs the Atwood number. The spike and bubble reaccelerate after reaching a temporary plateau due to the reduction of the friction drag as a result of the formation of the spike vortices and also the formation of a momentum jet traveling upward within the bubble region. The interface for a 3D single-mode instability grows exponentially; however, a higher Reynolds number and/or a lower Atwood number could result in a noticeably larger surface area after the initial growth. It is also shown that a 3D multi-mode RT instability initially displays an exponential interface growth rate similar to single-mode RT instabilities. Due to the collapse and merging of individual single-mode instabilities, the interface area for a multi-mode RT instability is strongly dependent to the mesh resolution after the exponential growth rate. However, the ratio of kinetic energy over released potential energy exhibits an almost steady state after the initial exponential growth, with values around 0.4, independently of the mesh resolution.

PEMFOSILAN DALAM BAHASA ANTARA GENERASI MUDA SUKU DUSUN TINDAL

The majority of Dusun Tindal tribe learners in Sabah failed to achieve competency as native Malay speakers due to the fossilization mechanism which is performance-related. Hence, this research aims to examine the fossilization mechanism in the interlanguage of the young generation from the Dusun Tindal tribe. The case study was conducted at Tenghilan Secondary School, Tuaran, Sabah which involved 69 students. Besides the students, 12 language teachers were interviewed to get detailed information on target language learning strategies that allowed students to cross the interlanguage. Two informants from the Dusun Tindal community have provided a missing link to the Dusun Tindal tribe in Sabah. The first important finding involved trends in existing native language domains within Dusun Tindal communities that show multilingual equivalence. Secondly, most essay writing scores in the Malay language itself was still having interlanguage. Thirdly, the highest factor of fossilization causation was cognitive. The mapping of lexical and syntax elements into the target language domain was affecting students' thoughts. It was obvious sentences accommodate the overgeneralization form in the student interlanguage depicts a temporary plateau and they most often use message omission strategy. Fifthly, the continuum of interlanguage was based on the knowledge of native and the Malay language of the students most at acrolect level, namely one level lower than the native speaker competency. Language teachers suggested a number of strategies to dissolve the fossilization in interlanguage, specifically taking the right attitude towards student language errors.

Anomalous packing and dynamics of a polymer chain confined in a static porous environment.

Polymers in confined porous environments are ubiquitous throughout biology, physics, materials science, and engineering. Several experiments have suggested that in some porous environments, chain dynamics can become extremely slow. While phenomenological explanations exist, the exact mechanisms for these slow dynamics have not been fully characterized. In this work, we initiate a joint simulation-theory study to investigate chain packing and dynamics in a static porous environment. The main theoretical concept is the free energy of the chain partitioning into several chambers of the porous environment. Both the theoretical results and Langevin dynamics simulations show that chain packing in each of the chambers is predominantly independent of chain length; it is determined by the maximal packing of segments in each chamber. Dynamically, short chains (compared to the chamber size) become trapped in a single chamber and dynamics become extremely slow, characteristic of an Ogston sieving-like behavior. For longer chains, on the other hand, a hierarchy of slow dynamics is observed due to entropic trapping, characterized by sub-diffusive behavior and a temporary plateau in the mean square displacement. Due to the slow nature of the dynamics, the inevitable long-time diffusive behavior of the chains is not captured by our simulations. Theoretically, the slow dynamics are understood in terms of a free energy barrier required to thread the chain from one chamber to the next. There is overall qualitative and quantitative agreement between simulations and theory. This work provides foundations for a better understanding of how chain dynamics are affected by porous environments.

Explaining “peak car” with economic variables

Many western countries have seen a plateau and subsequent decrease of car travel during the 21st century. What has generated particular interest and debate is the statement that the development cannot be explained by changes in traditional explanatory factors such as GDP and fuel prices. Instead, it has been argued, the observed trends are indications of substantial changes in lifestyles, preferences and attitudes to car travel; what we are experiencing is not just a temporary plateau, but a true “peak car”. However, this study shows that the traditional variables GDP and fuel price are in fact sufficient to explain the observed trends in car traffic in all the countries included in our study: the United States, France, the United Kingdom, Sweden and (to a large extent) Australia and Germany. We argue that the importance of the fuel price increases in the early 2000s has been underappreciated in the studies that shaped the later debate. Results also indicate that GDP elasticities tend to decrease with rising GDP, and that fuel price elasticities tend to increase at high price levels and during periods of rapid price increases.

Larry Cohen, indomitable pioneer.

Larry Cohen, indomitable pioneer.

Silicon solar cells: Past, present and the future

There has been a great demand for renewable energy for the last few years. However, the solar cell industry is currently experiencing a temporary plateau due to a sluggish economy and an oversupply of low-quality cells. The current situation can be overcome by reducing the production cost and by improving the cell is conversion efficiency. New materials such as compound semiconductor thin films have been explored to reduce the fabrication cost, and structural changes have been explored to improve the cell’s efficiency. Although a record efficiency of 24.7% is held by a PERL — structured silicon solar cell and 13.44% has been realized using a thin silicon film, the mass production of these cells is still too expensive. Crystalline and amorphous silicon — based solar cells have led the solar industry and have occupied more than half of the market so far. They will remain so in the future photovoltaic (PV) market by playing a pivotal role in the solar industry. In this paper, we discuss two primary approaches that may boost the silicon — based solar cell market; one is a high efficiency approach and the other is a low cost approach. We also discuss the future prospects of various solar cells.

Time-dependent transport in graphene nanoribbons

We theoretically investigate the time-dependent ballistic transport in metallic graphene nanoribbons after the sudden switch-on of a bias voltage $V$. The ribbon is divided in three different regions, namely two semi-infinite graphenic leads and a central part of length $L$, across which the bias drops linearly and where the current is calculated. We show that during the early transient time the system behaves like a graphene bulk under the influence of a uniform electric field $E=V/L$. In the undoped system the current does not grow linearly in time but remarkably reaches a temporary plateau with dc conductivity $\sigma_{1}=\pi e^{2}/2h$, which coincides with the minimal conductivity of two-dimensional graphene. After a time of order $L/v_{F}$ ($v_{F}$ being the Fermi velocity) the current departs from the first plateau and saturates at its final steady state value with conductivity $\sigma_{2}=2e^{2}/h$ typical of metallic nanoribbons of finite width.

Software appropriation over time: from adoption to stabilization and beyond

Technologies are introduced into an organization with the aim of improving productivity. However, persistent use of an information system is required to enhance productivity and user satisfaction. In this paper, we examine the process of technology appropriation and the factors that encourage and discourage use of an information system over time. In a longitudinal field study in an educational setting, we identify changing expectations and influences that encourage persistent use of a technology above and beyond adoption. Our work indicates that stabilization of a technology may only be a temporary plateau. Further appropriation may occur beyond initial stabilization as expectations and influences encourage persistent use of a technology. We have found that the driving forces in encouraging productive use of a technology are the ability for users to experience the technology as useful and to have easy access to ongoing training.

Accumulation pattern and biotransformation enzyme induction in rainbow trout embryos exposed to sublethal aqueous concentrations of 3,3 ′,4,4 ′-tetrachlorobiphenyl

Accumulation pattern of 3,3 ′,4,4 ′-tetrachlorobiphenyl (PCB 77) and the exposure time needed to activate the monooxygenase (EROD) and conjugation (GST) enzyme systems of fish at the advanced embryonic stage were studied. Eyed stage embryos of rainbow trout ( Oncorhynchus mykiss) were exposed to sublethal doses (0, 1, 10, and 100 μg/l) of PCB 77. Results indicated direct accumulation of the chemical into the eggs, but the exposure time was not long enough for PCB 77 to reach constant steady state. However, at the two lowest test concentrations (1 μg/l and 10 μg/l) a temporary plateau at chemical accumulation was reached at the third exposure day (185 and 1221 ng PCB/g egg w.w). At the highest concentration (100 μg/l) the decrease in the accumulation rate was already evident after the first day (2182 ng PCB/g egg w.w). The chemical uptake increased again at day 7 in all the exposure groups. That event could have been caused by the increased metabolic rate of the embryos in preparation for the upcoming hatching event. The microsomal CYP1A monooxygenase system (EROD) was shown to be a sensitive indicator of embryonic exposure, being induced at the low (1 μg/l, 182 ng/g egg) PCB concentration and after a short (3 day) exposure time. The conjugation enzyme system (GST) was shown to be functioning already at the advanced embryonic stage, although no response to the studied chemical stress was detected.

Kinetics of long and short range order: Comparison of simulations with theory

Abstract Computer simulations of ordering processes in a 1-to-1 binary system have been performed yielding the long- and short-range order parameters versus time. These results have been employed to check predictions of a theory of kinetics of ordering and clustering published previously by one of the authors. The quantitative agreement is satisfactory. One special feature of the simulations, a temporary plateau in the short-range order parameter, can be readily explained although quantitative agreement is less obvious here. This minor disagreement is ascribed to the imperfection of the quasi-chemical approximation which could be avoided in the theoretical model if a better alternative were available.

Human temporary threshold shift (TTS) and damage risk

Information regarding the relation of human temporary threshold shift (TTS) to properties of steady-state and intermittent noise published since the 1966 appearance of the CHABA damage risk contours is reviewed. The review focuses on results from four investigative areas relevant to potential revision of the CHABA contours including effects of long-duration exposure and asymptotic threshold shifts (ATS); equivalent quiet and/or safe noise levels; effects of intermittency; and use of noise-induced temporary threshold shift (NITTS) to predict susceptibility to noise-induced permanent threshold shift (NIPTS). These data indicate that two of three major postulates on which the original contours were based are not valid. First, recovery from TTS is not independent of the conditions that produced the TTS as was assumed. Second, the assumption that all exposures that produce equal TTS2 are equally hazardous is not substantiated. The third postulate was that NIPTS produced by 10 years of daily exposure is approximately equal to the TTS2 produced by the same noise after an 8-h exposure. Based upon several TTS experiments showing that TTS reaches an asymptote after about 8 h of exposure, the third CHABA postulate can be reworded to state the hypothesis that ATS produced by sound of fixed level and spectrum represents an upper bound on PTS produced by that sound regardless of the exposure duration or the number of times exposed. This hypothesis has a strong, logical foundation if ATS represents a true asymptote for TTS, not a temporary plateau, and if threshold shifts do not increase after the noise exposure ceases.

The cytochrome system of sea urchin eggs and embryos

The cytochrome system in eggs and embryos of the sea urchin, Hemicentrotus pulcherrimus, was investigated. Difference spectra of the mitochondrial fraction demonstrated the presence of a complete cytochrome system in unfertilized eggs. Cytochrome levels and the activities of respiratory enzymes were measured in crude extracts of eggs both before and after fertilization. Unfertilized eggs contained cytochromes aa 3, b, and c + c 1 in a ratio of 1.0:1.8:0.7. Gastrulae contained almost the same amount of cytochromes aa 3and b as unfertilized eggs. However, the amount of cytochrome c + c 1 in gastrulae was 1.5 times greater than that in unfertilized eggs. The activity of cytochrome oxidase remained unchanged during development. No cytochrome oxidase inhibitor was found in unfertilized eggs. Both antimycin A-sensitive and insensitive NADH-cytochrome c reductase activities increased during development. The activity of succinate-cytochrome c reductase increased during early development, reached a temporary plateau, and then declined at the pluteus stage. These results are discussed in relation to the increase of respiration during early development.

Wellbore Effects in the Analysis of Two-Phase Geothermal Well Tests

Abstract A method of designing and analyzing pressure transient well tests of two-phase (steam/water) reservoirs is given. Wellbore storage is taken into account, and the duration of it is estimated. It is shown that the wellbore flow can dominate the downhole pressure signal completely such that large changes in the downhole pressure that might be expected because of changes in kinematic mobility are not seen. Changes in the flowing enthalpy from the reservoir can interact with the wellbore flow so that a temporary plateau in the downhole transient curve is measured. Application of graphical and nongraphical methods to determine reservoir parameters from drawdown tests is demonstrated.

A quantitative investigation of some presynaptic terminal parameters during synaptogenesis

The molecular layer of rat cerebral cortex (midcoronal section) was studied by electron microscopy at 7 to 75 postnatal days. The following parameters were analyzed: total surface area and volume of the presynaptic terminals per unit volume of tissue, total surface area and volume of the synaptic vesicles per terminal, number of terminals and number of synaptic vesicles per terminal, surface area and volume of individual terminals, surface area and volume of individual synaptic vesicles, and length of the postsynaptic thickening. Steady increases were evident during development in the total surface area and volume of the presynaptic terminals and the number of terminals per unit volume of tissue. By contrast, there were decreases in the surface areas and volumes of individual terminals, more particularly during the latter part of development. Increases in the total surface area and volume of synaptic vesicles were prominent from 7 to 15 days and from 21 to 75 days with a temporary plateau between 15 and 21 days. Vesicle numbers per terminal increased consistently throughout development, whereas the surface areas of individual vesicles increased initially, decreased between 15 and 21 days, and changed little thereafter. The volumes of individual vesicles did not change significantly with development. The length of the postsynaptic thickening decreased between 10 and 21 days. Other features of presynaptic profiles were also quantified to provide further information about the distribution of membrane within the presynaptic terminal. These results, coupled with the quantitative analysis of terminal and vesicle parameters, help elucidate possible interrelationships between membrane compartments during synaptogenesis.

Uterine Involution, Ovarian Activity, and Fertility after Melengestrol Acetate and Estradiol in Early Postpartum Cows

Twenty-seven Holstein cows were assigned to control, melengestrol acetate,22Melengestrol acetate was generously supplied by Dr. J. W. Lauderdale, The Upjohn Company, Kalamazoo, Michigan. or melengestrol acetate plus estradiol groups. Melengestrol acetate was fed 1 mg/cow per day for 14 days beginning 21 ±1 days after calving. Estradiol benzoate33Sigma Chemical Co. (500μg) was injected intramuscularly 48h after the last melengestrol acetate feeding. Cows were inseminated at first and any subsequent estrus after 50 days postpartum. Weekly palpation per rectum revealed diameter of the largest uterine horn decreased until 7 wk postpartum, but there was no significant difference among treatment groups. A temporary plateau in diameter of the largest uterine horn in cows treated with melengestrol acetate occurred the week after treatment. Cows receiving melengestrol acetate had more follicles>1.0cm diameter but only during treatment. There was no significant difference in interval to first ovulation or corpus luteum formation among the three groups. Control, melengestrol acetate, and melengestrol acetate plus estradiol group means for interval from calving to first estrus, days open for cows conceiving, and services per conception were 63±11, 37±9, and 41±7; 153±15, 83±6, and 101± 15; and 3.3±.8, 1.7±.3, and 2.1 ±.4. Values for the control group were higher than values for the other two groups. There was no difference in milk yield among the groups during the lactation in which melengestrol acetate was administered.

Development of the Research Department

In planning for a new major mental health facility, the need for building in a potential for self-description and evaluation seemed selfevident. Consequently, almost a year before the first patients arrived, plans were made to develop such a potential in the form of an extensive semiautomated information retrieval system. A plan submitted to the National Institute of Mental Health (NIMH) was approved, and the system receives a great deal of its support under grants from that agency.' In addition, budgetary requests approved by the state after the first year of operation made possible the development of research positions independent of grant support. The combined state and NIMH support provided seven professional and 10 supporting and technical research positions. The department reached what is, hopefully, a temporary plateau in the fall of 1964, when the director, Dr. Paul Polak, and the research psychiatrist, Dr. Bernardo Gaviria, left for two years' leave, Dr. Polak to work with Maxwell Jones in Scotland and Dr. Gaviria to study at the Menninger Foundation. The evolution of the two components of the research department, the project staff and the state-supported staff, has given the department its unique character, each component contributing special strengths to the over-all effort. We will briefly trace this evolution to give the necessary background for the studies reported in the next section.