Showing papers by "David W. Johnson published in 1998"
Book•
11 Oct 1998TL;DR: Cooperative, competitive, and individualistic learning as discussed by the authors ) are three types of cooperative learning: cooperative base groups, competitive learning, and competitive individualistic (CIL) learning.
Abstract: Preface. 1.Cooperative, Competitive, and Individualistic Learning. 2.Cooperative Learning. 3.Informal Cooperative Learning. 4.Cooperative Base Groups. 5.Basic Elements of Cooperative Learning. 6.Integrated Use of All Types of Cooperative Learning. 7.Assessment and Evaluation. 8.Structuring Competitive Learning. 9.Structuring Individualistic Learning. 10.Integrated Use of Cooperative, Competitive, and Individualistic Learning. 11.Reflections. Glossary. References. Index.
1,754 citations
TL;DR: Cooperative Learning Returns To College What Evidence Is There that It Works? Change: The Magazine of Higher Learning: Vol. 30, No. 4, pp. 26-35.
Abstract: (1998). Cooperative Learning Returns To College What Evidence Is There That It Works? Change: The Magazine of Higher Learning: Vol. 30, No. 4, pp. 26-35.
1,003 citations
TL;DR: The current discussions of partner notification may be informed by recognizing that it is a subset of a broader and potentially more powerful approach, which calls some basic tenets of syphilis epidemiology into question.
Abstract: Background and objectives Partner notification has been the cornerstone for the prevention and control of syphilis in the United States. This technique may not make full use of contextual data that an ethnographic and social network approach can offer. Goals of the study The occasion of a syphilis outbreak among young people was used to investigate the applicability of a social network approach and to test the validity of several traditional approaches to syphilis epidemiology. Study design An outbreak of syphilis was investigated by interviewing both infected and noninfected people, by directing resources based on network association, by creating and evaluating network diagrams as an aid to the epidemiologic process, and by including ethnographic observations as part of outbreak management. Results Diagrammatic display of network growth provided a useful alternative to the traditional epidemic curve. Case prevention was demonstrated by identifying uninfected people with multiple concurrent exposures. Concurrent, overlapping exposure in infected people rendered traditional "source" and "spread" criteria moot. Conclusions The current discussions of partner notification may be informed by recognizing that it is a subset of a broader and potentially more powerful approach. This approach calls some basic tenets of syphilis epidemiology into question.
177 citations
TL;DR: It is demonstrated that long-term chronic inputs of pollutant N can significantly increase microbial biomass and activity in N-limited heathland ecosystems, but may reduce microbes biomass and microbial activity in P-limited grasslands.
151 citations
TL;DR: In children with moderately severe croup, treatment with intramuscular dexamethasone or nebulized budesonide resulted in more rapid clinical improvement than did the administration of placebo, with dexamETHasone offering the greatest improvement.
Abstract: Background In children with croup, treatment with nebulized budesonide decreases symptoms, but it is uncertain how budesonide compares with dexamethasone, the conventional therapy for croup, and whether either reduces the rate of hospitalization. Methods We performed a double-blind, randomized trial involving 144 children with moderately severe croup. The children were treated with racepinephrine and a single dose of 4 mg of nebulized budesonide (48 children), 0.6 mg of intramuscular dexamethasone per kilogram of body weight (47 children), or placebo (49 children). The children were assessed before treatment and then hourly for five hours after treatment. Physicians who were unaware of the treatment assignments determined the children's need for further treatment and hospitalization. Results The characteristics of the groups were similar at base line, including the types of viruses identified, the types of croup, and the clinical severity of the illness. The overall rates of hospitalization were 71 percen...
141 citations
TL;DR: PTC modulate the biological behavior of neighboring cortical fibroblasts in the human kidney through paracrine mechanisms, which include the production and release of PDGF-AB and TGF-beta1 and T GF- beta1, which culminates in excessive fibroblast proliferation and interstitial fibrosis.
122 citations
TL;DR: Findings support the hypothesis that biologically active TGF- β plays a pathogenetic role in diabetic kidney disease and suggest that β ig-h3 may be a useful index of T GF- β 1 bioactivity in the kidney.
83 citations
TL;DR: Small intestine submucosa provides a collagen framework that becomes remodeled, grows, and acquires a nonthrombogenic endothelial lining, which makes it potentially well suited as a cardiovascular substitute in children.
82 citations
TL;DR: In this simplified paradigm of a homoplasmic mitochondrial mutation in a single kindred who all live in the similar environment of a small village, the penetrance of the mitochondrial mutation appears to depend on the interaction of multiple nuclear genes.
Abstract: The relationship between mitochondrial genotype and clinical phenotype is complicated in most instances by the heteroplasmic nature of pathogenic mitochondrial mutations. We have previously shown that maternally inherited hearing loss in a large Arab-Israeli kindred is due to the homoplasmic A1555G mutation in the mitochondrial 12S ribosomal RNA gene [Prezant et al., 1993: Nat Genet 4:289-294]. Family members with this mutation have phenotypes ranging from profound hearing loss to completely normal hearing, and we have shown that there is genetic and biochemical evidence for nuclear gene involvement in this family [Bu et al., 1993: Genet Epidemiol 9 :27-44 ; Guan et al., 1996: Hum Mol Genet 5 :963-971]. To identify such a nuclear locus, two candidate genes were excluded through linkage analysis and sequencing, and a genome-wide linkage search in family members who all have the identical homoplasmic mitochondrial mutation, but differ in their hearing status, was performed. In two stages a total of 560 polymorphic genetic markers was genotyped, and the data were analyzed under model-dependent and model-free assumptions. No chromosomal region was identified as a major contributor to the phenotypic expression of the mitochondrial mutation. Thus, in this simplified paradigm of a homoplasmic mitochondrial mutation in a single kindred who all live in the similar environment of a small village, the penetrance of the mitochondrial mutation appears to depend on the interaction of multiple nuclear genes.
78 citations
TL;DR: The ability to control composition as a function of distance in one direction in these reactants permits the synthesis of crystalline superlattices has also been used to control synthesis of new binary and ternary compounds which are thermodynamically unstable relative to disproportionation as discussed by the authors.
Abstract: The design of modulated elemental reactants permits synthetic solid state chemists to control reaction intermediates. This has resulted in the synthesis of new binary and ternary compounds which are thermodynamically unstable relative to disproportionation into known compounds. The ability to control composition as a function of distance in one direction in these reactants permits the synthesis of crystalline superlattices.
TL;DR: A hydride cold-trapping technique was developed and optimised for the measurement of urinary arsenic metabolites and up to two fold increases of urinary ASi excretion in rats compared with control rats were also observed in animals dosed with various forms of arsenicals.
Abstract: A hydride cold-trapping technique was developed and optimised for the measurement of urinary arsenic metabolites. The analytical precision of the method was found to be 6.1, 4.0 and 4.8% (n = 5) for inorganic arsenic (Asi), monomethylarsonate (MMA) and dimethylarsinate (DMA), respectively, with recoveries close to 100%. The detection limits were 1.0, 1.3 and 3 ng for Asi, MMA and DMA, respectively. The method was then used to analyse urine samples obtained from three groups of workers for occupational exposure in three companies where copper chrome arsenate was used for timber treatment. The results were compared with those for a normal control group of laboratory workers. Arsenic and its metabolites were also measured in experimental rats given 5 mg As kg–1 body mass by oral gavage in the form of sodium arsenite, calcium arsenite or sodium arsenate. Occupational workers showed a significantly higher excretion of Asi. Up to two fold increases of urinary Asi excretion in rats compared with control rats were also observed in animals dosed with various forms of arsenicals. The method is suitable for the measurement of arsenic metabolites in urine of both humans and experimental animals.
TL;DR: One hundred-fiftyeight educators who participated in the first statewide cooperative learning staff development training program in South Carolina were surveyed three years later to determine the level of their use of cooperative learning and the factors influencing the effectiveness of the training as discussed by the authors.
TL;DR: This article found that the author's claims and credibility, style and tone, and terminology and coverage seriously affected their ability to find his story convincing, and they also discovered that this book, which they expected to be a narrative of hegemony, was instead an illustration of the use of narrative as a hegemonic tool.
Abstract: Reading Robert Phillipson's Linguistic Imperialism in a graduate seminar in World Englishes at Purdue University prompted intense discussion and debate not only of the issues of language dominance and spread that the author raised, but also of the rhetorical style and strategies that he chose to present a story of linguistic oppression. This article documents the reactions of seminar participants to how Phillipson presented his argument and their conclusion that the rhetorical choices he made seriously affected their ability to find his story convincing. In particular, participants – representing English language speakers in Brazil, Greece, Hong Kong, Japan, Singapore, and the USA – identified problems with the author's claims and credibility, style and tone, and terminology and coverage. They also discovered that this book, which they expected to be a narrative of hegemony, was instead an illustration of the use of narrative as a hegemonic tool.
TL;DR: In this paper, the feasibility of negative income tax was investigated using NATSEM's microsimulation model STINMOD and it was found that to ensure that no current social security beneficiaries become worse off under such a system would either be very expensive to introduce or require a tax rate that is likely to be unacceptably high.
Abstract: The undue complexity of the Australian tax-transfer system is outlined as are the associated high effective marginal tax rates for many individuals and families. A negative income tax system is a possible solution to these problems.
The most radical version of negative income tax is a ‘basic income/flat tax’ system which combines universal tax credits (that vary according to presence of children, disability etc.) and a flat tax rate on private income. Using NATSEM’s microsimulation model STINMOD it is found that to ensure that no current social security beneficiaries become worse off under such a system would either be very expensive to introduce or require a tax rate that is likely to be unacceptably high. Less radical versions of negative income tax are also costed, incorporating the possibility of varying tax rates, the tapering out of tax credits, and placing some restrictions on the granting of tax credits. This makes negative income tax look more feasible.
The analysis does not incorporate behavioural responses. Since the motivation for a negative income tax system is largely to achieve such responses (for example, labour supply responses), this feasibility analysis might have been unduly harsh. Research is required to incorporate behavioural responses into the analysis.
TL;DR: In this paper, the activation energy of the nucleation event was found to be 1.9 eV and activation energy was obtained for molybdenum disilicide at 400 °C.
Abstract: Modulated elemental reactants containing alternating elemental layers of molybdenum and silicon with overall thicknesses less than 50 A were found to crystallize various molybdenum silicides depending on their compositions. Modulated reactants with compositions near 1:2 Mo:Si formed β-molybdenum disilicide at 400 °C, even though β-molybdenum disilicide is metastable with respect to α-molybdenum disilicide below 1900 °C. The activation energy of the nucleation event was found to be 1.9 eV. Modulated reactants with compositions near 5:3 Mo:Si formed Mo5Si3 at 650 °C with an activation energy of 3.0 eV. Modulated reactants with compositions near 3:1 crystallize Mo3Si at 750 °C with an activation energy of 2.2 eV. Low-angle X-ray diffraction indicates that significant interdiffusion occurs during annealing below the formation temperatures of the compounds. Transmission electron microscopy data collected on samples annealed below the formation temperatures indicate that the samples were amorphous. The nucleati...
TL;DR: Despite recent dramatic ED and ward treatment changes, ICU admission rates for pediatric asthma remain relatively constant, however, intensive treatment may have contributed to the decrease in ICU admissions via the ED to ward route in slightly less critical cases.
Abstract: OBJECTIVE Significant changes have occurred in the intensity of treatment of children with severe asthma in the last decade. The objectives of this study are 1) to describe the changes in treatment of asthmatic children needing care in the intensive care unit (ICU) initially treated in our emergency department (ED) in 1983 to 1985 (I) and in 1990 to 1992 (II), and 2) to examine if these changes correspond to changes in clinical outcomes. DESIGN Retrospective descriptive study. PATIENTS All asthmatic children less than 18 years old treated in the ED and admitted to the ICU directly or via the ward with a primary diagnosis of asthma. SETTING Pediatric tertiary care hospital. RESULTS A total of 89 ICU admissions were required for patients initially treated in our ED, 54 in 1983 to 1985 and 35 in 1990 to 1992. In 1985, 29.7% of asthma patients required hospital admission and 0.5% needed ICU admission, while 30.7 and 0.7% required hospital and ICU admission, respectively, in 1992. Admissions to the ICU directly via the ED were similar in both time periods (I, 27; II, 30), while those admitted to the ICU via the ward decreased significantly (I, 27; II, 5; P < 0.01). Recently, while in the ED, these ICU patients, on average, were treated with < or =q1h albuterol inhalations longer (I, 1.7 hours; II, 3.4 hours; P < 0.001), more frequently (I, 1.8 inhalations/h; II, 3.3 inhalations/h; P < 0.001), and with greater dosages (I, 0.20 mg/kg/h; II, 0.55 mg/kg/h; P < 0.001), than previously. Only 72% of patients in 1983 to 1985 received i.v. steroids in the ED versus 100% in 1990 to 1992. Ward patients in 1990 to 1992 received < or =q1h inhalations for a greater proportion of their ward stay (I, 6.9/14.7 hours = 47%; II, 9.2/9.2 hours = 100%). There was a recent trend toward longer ICU treatment with < or =q1h albuterol inhalations (I, 8.7 hours; II, 12.3 hours; P = 0.24) and with i.v. albuterol (I, 29.4 hours; II, 37.4 hours; P = 0.26). Ventilation rates were low (I, 5/54 = 9.3%; II, 2/35 = 5.7%; P = NS) and the average duration of ICU stay remained unchanged (I, 40.6 hours; II, 42.1 hours; P = NS). CONCLUSIONS Despite recent dramatic ED and ward treatment changes, ICU admission rates for pediatric asthma remain relatively constant. However, intensive treatment may have contributed to the decrease in ICU admissions via the ED to ward route in slightly less critical cases.
TL;DR: In this article, a collaborative study was performed to assess accuracy, repeatability, and reproducibility of a near-infrared (near-IR) method for determining crude protein content (PC) of whole-grain wheat.
Abstract: A collaborative study was performed to assess accuracy, repeatability, and reproducibility of a near-infrared (near-IR) method for determining crude protein content (PC) of whole-grain wheat. Four types of commercially available near-IR instruments, representing various combinations of wavelength region, mode of energy capture, method of energy dispersion, and treatment of spectral data, were used. Eight, 9, 10, and 11 collaborators were involved, the exact number depending on instrument type. All collaborators received 22 samples of whole-grain hard red winter (HRW) wheat. They were furnished reference PCs (i.e., protein concentrations, w/w) corrected to a 12% moisture basis for instrument standardization. AOAC Method 990.03-combustion analysis-was the reference procedure. Standardization consisted of performing one of the following treatments to the instrument manufacturer's (or federal agency's) PC equation: (1) bias correction, (2) slope and intercept correction, or (3) recalibration with inclusion of standardization sample spectra. Standardized equations were then applied to a test set of 12 unknown HRW wheat sample spectra, with 2 samples blindly duplicated. The PCs of test samples ranged from 9 to 16%. Near-IR predictions were compared with reference measurements. Averaged within instrument type, root mean square of differences were 0.22, 0.24, 0.25, and 0.26% PC, depending on instrument. Corrected for bias within the test set, standard errors became 0.22, 0.18, 0.21, and 0.24% PC, respectively. These values were approximately twice the estimated lower limit for error (representing sample inhomogeneity). Overall repeatability relative standard deviation (RSDr) values were 0.92, 0.36, 0.42, and 0.74%, respectively. Overall reproducibility relative standard deviation (RSD Ρ ) values were 1.15, 0.61, 1.53, and 1.38%. Such values for within-laboratory and between-laboratory variations of the near-IR methods were equivalent to values reported for the combustion method (990.03) for wheat. An inhouse study that examined all 6 U.S. wheat classes with one of the 4 instrument types produced repeatability and reproducibility values similar to those of the collaborative study, suggesting that the near-IR technique may be applied to red, white, hard, soft, and durum wheats. The near-IR method for determination of PC of whole-grain wheat has been adopted First Action (997.06) by AOAC INTERNATIONAL.
TL;DR: Although hyperleptinemia correlates poorly with dialysis adequacy and protein intake, a strong and significant relationship was maintained between serum leptin and fat mass and Serum leptin could therefore serve as a useful clinical marker of body fat content in PD patients.
Abstract: .Objectives: In view of previous studies demonstrating hyperleptinemia in uremic and hemodialysis patients, the aims of the present study were to determine whether serum leptin levels are elevated in peritoneal dialysis (PD) patients, to establish whether leptin is significantly removed by PD, and to elucidate the relationship of plasma leptin to body composition, dietary intake, nutritional indices, and dialysis adequacy. .Design: Cross-sectional analysis of PD patients and matched healthy controls. .Setting:Tertiary-care institutional dialysis center. .Participants: The study included 49 PD patients [35 women and 14 men; median age 63 years, interquartile range (IQR) 49.5 -68.5 yr; body mass index (BMI) 25.5 :I: 0.8] and 27 controls (11 men and 16 women; median age 42 years, IQR 34.8 51; BMI 27.2 :I: 0.9). For evaluation of leptin clearance, 8 patients receiving nocturnal intermittent PD were also evaluated. .Main Outcome Measures: The primary outcome measure was plasma leptin concentration. Dialysate leptin concentration was also measured in 7 patients. .Results: Serum leptin levels were significantly higher (p < 0.01) in patients (males: median 11 nglmL, IQR 9 19 ng/mL; females: 53 ng/mL, 19.5 -128 ng/mL) compared with controls (males: 5.5 nglmL, 4 9.5 nglmL; females: 12 ng/mL, 9.8 17.3 ng/mL). Leptin levels in both groups correlated positively with BMI (r = 0.64 and 0.60, respectively; p < 0.0001) and with percentage body fat determined by dual -energy x-ray absorptiometry (r = 0.86 and 0.82, respectively; p < 0.01 ). Dialysis patients exhibited a greater increase in serum leptin for any given increase in BMI. No significant correlation was observed between leptin con
Patent•
24 Mar 1998TL;DR: In this article, thermodynamically metastable skutterudite crystalline-structured compounds are disclosed having preselected stoichiometric compositions and superior optimizable thermoelectric properties.
Abstract: Thermodynamically metastable skutterudite crystalline-structured compounds are disclosed having preselected stoichiometric compositions and superior optimizable thermoelectric properties. The compouds are formed at low nucleation temperatures and satisfy the formula: M1-x M'4-y Coy M''12 wherein: M = any metal, metalloid, or mixture thereof, except for La, Ce, Pr, Nd, and Eu when x = 0 and M' = Fe, Ru, or Os and M'' = Sb, P or As; M' = Fe, Ru, Os, Rh, or mixtures thereof; M'' = Sb, As, P, Bi, Ge 0.5-wSe0.5+w, wherein w = 0 to 0.5, or mixtures thereof; x = 0 to 1; y = 0 to 4; and wherein M' and/or M'' are doped or undoped.
TL;DR: It is shown that TGF-β 1 elicits distinct PTC growth responses in the presence and absence of IGF-I, without modification of NHE activity, and the combination of predominant PTC hypertrophy and enhanced proximal tubule Na + reabsorption found in many conditions that are associated with renal growth is likely to require the integrated actions of both TGF -β 1 and IGF- I.
01 Jan 1998
TL;DR: A good example of the potential latent problem is the increase in total tissue nitrogen concentration in ombrotrophic bryophytes as discussed by the authors, which is an inevitable and widespread response to enhanced atmospheric nitrogen deposition.
Abstract: The changing nature of the pollution climate in the second half of the 20th Century has resulted in the increased importance of ozone and nitrogen pollutants and a decreased importance of sulphur dioxide. However, there have been few studies of the effects of any dry deposited gas on individual bryophyte species or on bryophyterich plant communities. In those studies which have been made, there is evidence that well hydrated bryophytes may not be particularly sensitive to ozone or NOx at realistic atmospheric concentrations. Ombrotrophic bryophytes are largely dependent on wet deposition as a source of nitrogen. A good example of the potential latent problem is the increase in total tissue nitrogen concentration in ombrotrophic bryophytes. There is ample evidence to suggest that this is an inevitable and widespread response to enhanced atmospheric nitrogen deposition. The responses of bryophytes to wet atmospheric nitrogen deposition can be examined most readily through studies of nitrate assimilation in near pristine environments.
TL;DR: In this article, the conductance and superconducting transition temperature of a set of Mo/Si multilayers, as a function of the metal layer thickness (from 7\char21{}85 \AA{}) for a constant semiconductor layer thickness of 22
Abstract: We report new measurements of the conductance and superconducting transition temperature of a set of Mo/Si multilayers, as a function of the metal layer thickness (from 7\char21{}85 \AA{}) for a constant semiconductor layer thickness of 22 \AA{}. Unlike previously reported measurements, we do not observe oscillations in either the resistivity, resistivity ratio, or the superconducting transition temperature with the metal layer thickness. Rather, we observe monotonic variations in the transport properties as the metal layer thickness increases. The sheet conductance and its change between 10 and 300 K both vary approximately linearly with the metal layer thickness, above a threshold thickness. The conductance starts to grow with metal layer thickness at approximately 10 \AA{}, whereas the temperature coefficient of resistance changes sign at approximately 25 \AA{}, exhibiting a Mooij correlation with a crossover resistivity of 125 \ensuremath{\mu}\ensuremath{\Omega} cm. The observed temperature dependence of the conductance rules out localization as the origin of the negative temperature coefficient of resistance. The conductance data are analyzed using a simple phenomenological model involving transport in interfacial and metallic layers, whose relative contribution to the conductance depends on the metal layer thickness and the temperature. The model is applied to separate two competing contributions that determine the overall temperature dependence of the conductance. We attribute the differences between our measurements and previous measurements to differences in bulk metallic conductivities and interface morphologies, due to differences in thermal evaporation versus sputtering fabrication processes. Our results show that the level and nature of disorder is an important ingredient in any theory that explains the cause of the observed oscillations.
TL;DR: In this paper, the authors focus on the inspection of primary mathematics and provide evidence of the potential tensions between "experience and expertise" and "baggage" at different levels of the inspection process, and suggest that some primary inspectors are less aware of problems arising from lack of expertise than of those arising from preferences for particular teaching styles or methods.
Abstract: There is an assumption that, under the Office for Standards in Education system, inspectors will, through training, learn to put aside their preferred ways of working and come to look at school practice unencumbered by ‘baggage’. Yet primary team inspectors are allocated certain subjects for inspection, based on their previous experience and, to a certain extent, their chosen preferences. The research reported here focuses on the inspection of primary mathematics and provides evidence of the potential tensions between ‘experience and expertise’, and ‘baggage’, at different levels of the inspection process. It seems that some primary inspectors are less aware of problems arising from lack of expertise than of those arising from preferences for particular teaching styles or methods. It may be the case that the greater the expertise, the more likely it is that judgements will be related to mathematical criteria, rather than merely to general teaching criteria—is this then still baggage?
TL;DR: The Policy Forum as mentioned in this paper identifies the need for reform of the interaction of the tax and social security systems and foreshadowing approaches to such reform, and proposes a tax reform framework.
Abstract: this paper introduces the Policy Forum, identifying the need for reform of the interaction of the tax and social security systems and foreshadowing approaches to such reform.
03 Sep 1998
TL;DR: This paper defined the colonial and post-colonization of Shakespeare as follows: the colonial Shakespeare is the Shakespeare of the period of colonial rule, and the post-colonial Shakespeare the Shakespeare from the postcolonial period.
Abstract: My definitions here of the colonial and post-colonial are historical, rather than in terms of changing fashions in literary criticism. In other words, the colonial Shakespeare I explore is the Shakespeare of the period of colonial rule, and the post-colonial Shakespeare the Shakespeare of the post-colonial period. More precisely, I have chosen the 1930s, the twilight decade of the British Empire, to represent the colonial, and the 1980s, the decade of late capital and globalization, to represent the post-colonial. For both periods, I focus on Shakespeare's journeys to Africa. My versions of the colonial and post-colonial Shakespeares are assembled from representative metropolitan Shakespeare critics, and educational policy-makers for Africa. For the colonial Shakespeare, I accordingly focus on G. Wilson Knight's criticism of The Tempest, and British education policy-maker for Africa, A. Victor Murray. My picture of the post-colonial Shakespeare is based on Stephen Greenblatt's criticism of The Tempest, and World Bank plans for education in Africa.
In focusing thus on the metropolitan mind, I inevitably present an incomplete picture. A more comprehensive study would provide detailed examination of distinct African contexts and their histories, analysis of English school syllabuses, and Shakespeare performances in the different African settings, and instances of African resistance to and appropriations of Shakespeare. In confining my attention in this way, however, my hope is to convey some sense of the wider contexts in which metropolitan productions of the colonial and the post-colonial Shakespeare resonate.
TL;DR: In this article, the synthesis of skutterudite superlattices by controlled crystallization of elementally modulated reactants of a series of kinetically stable, crystalline Skutterudites (M′ 1−x M 4 Sb 12) is discussed.
Abstract: The synthesis by controlled crystallization of elementally modulated reactants of a series of kinetically stable, crystalline skutterudites (M′ 1−x M 4 Sb 12 where M′ = vacancy, RE, Hf, Al, Sn, Pb, Bi, In, Ga, Al and Y; M = Fe, Co) is discussed. Low angle diffraction data demonstrates that the elemental layers interdiffuse at temperatures below 150°C. Nucleation of the skutterudite structure occurs exothermically on annealing at temperatures near 200°C regardless of the ternary metal. The metastable ternary compounds and the new binary compound were found to decompose exothermically on higher temperature annealing. The decomposition temperature ranged from 300°C for the binary compound FeSb 3 to 550°C for Eu′ 1−x; Fe 4 Sb 12 to higher temperatures for the filled cobalt end members. The occupation of the lattice site for the ternary cation was found to depend on the composition of the initial reactant. Samples up to a half gram in size have been synthesized and hot-pressed into pellets for measurement of both electrical properties and thermal conductivity. Preliminary evidence is presented for the formation of skutterudite superlattices, again synthesized by the controlled crystallization of elementally modulated reactants.
TL;DR: There is an association between bile resistant Helicobacter species and gallbladder disease, and the authors hypothesize that the ammonia generated by the urease of the Helicobacteria damages the hepatocytes adjacent to the bacteria, or that the antibodies to Helicob bacteria react with bile canaliculi and/or hepatocytes causing autoimmune mediated damage.
TL;DR: In this article, the formation of stable molybdenum selenide was investigated using elementally modulated reactants to control overall composition and diffusion length, and a new compound, Mo3Se, was observed to form.
Abstract: The kinetics of compound formation in the molybdenum−selenium system has been investigated using elementally modulated reactants to control overall composition and diffusion length. We observed the facile formation of MoSe2 at low temperatures when the composition was above 50 atom % selenium. No evidence was found for the low-temperature formation of the other known stable molybdenum selenide, the cluster compound Mo6Se8. When the composition of the initially modulated reactant was close to 25% selenium, a previously unreported compound was observed to form. This new compound, Mo3Se, has the A-15 crystal structure. The superconducting transition temperature appears to be very sensitive to composition, with a sharp resistive transition at 7 K in one sample and a sharp diamagnetic transition observed in a second sample at 2.2 K. The kinetics of phase formation in this system is analyzed in terms of nucleation kinetics.
TL;DR: In this article, the authors used a university cost function to examine the costs and revenues of overseas students in Australia and to estimate the unobservable cost of providing education for only domestic students.