886 resultados para Difference-in-Difference


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The Japanese inchoative-lexical causative pair poses an interesting problem for the Minimalist Program – how should the lexical causative and the syntactic causative be structurally represented and theoretically accounted for? The lexical causative verb and the syntactic causative verb formed by suffixing the syntactic causative morpheme sase onto the inchoative counterpart are both single causative constructions that are semantically similar. Yet, they differ in some ways, most significantly in their clausality – the lexical causative is monoclausal in nature while the syntactic causative is biclausal, comparable to English biclausal constructions formed with let or force. This paper investigates how this difference can be represented by investigating the possible VP shell structures of different Japanese sentences, and the analysis from the discussion suggests a different structure where a CP is embedded into a higher VP shell as the sister of Agro head.

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The artificial dissipation effects in some solutions obtained with a Navier-Stokes flow solver are demonstrated. The solvers were used to calculate the flow of an artificially dissipative fluid, which is a fluid having dissipative properties which arise entirely from the solution method itself. This was done by setting the viscosity and heat conduction coefficients in the Navier-Stokes solvers to zero everywhere inside the flow, while at the same time applying the usual no-slip and thermal conducting boundary conditions at solid boundaries. An artificially dissipative flow solution is found where the dissipation depends entirely on the solver itself. If the difference between the solutions obtained with the viscosity and thermal conductivity set to zero and their correct values is small, it is clear that the artificial dissipation is dominating and the solutions are unreliable.

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Although plant growth is often limited at high pH, little is known about root-induced changes in the rhizospheres of plants growing in alkaline soils. The effect of Mn deficiency in Rhodes grass (Chloris gayana cv. Pioneer) and of legume inoculation in lucerne (Medicago sativa L. cv. Hunter River), on the rhizosphere pH of plants grown in highly alkaline bauxite residue was investigated. Rhizosphere pH was measured quantitatively, with a micro pH electrode, and qualitatively, with an agar/pH indicator solution. Manganese deficiency in Rhodes grass increased root-induced acidification of the rhizosphere in a soil profile in which N was supplied entirely as NO3-. Rhizosphere pH in the Mn deficient plants was up to 1.22 pH units lower than that of the bulk soil, while only 0.90 to 0.62 pH units lower in plants supplied with adequate Mn. When soil N was supplied entirely as NO3-, rhizosphere acidification was more efficient in inoculated lucerne (1.75 pH unit decrease) than in non-inoculated lucerne (1.16 pH unit decrease). This difference in capacity to lower rhizosphere pH is attributable to the ability of the inoculated lucerne to fix atmospheric N2 rather than relying on the soil N (NO3 ) reserves as the non-inoculated plants. Rhizosphere acidification in both Rhodes grass and lucerne was greatest in the meristematic root zone and least in the maturation root zone.

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Despite the increasing prevalence of salinity world-wide, the measurement of exchangeable cation concentrations in saline soils remains problematic. Two soil types (Mollisol and Vertisol) were equilibrated with a range of sodium adsorption ratio (SAR) solutions at various ionic strengths. The concentrations of exchangeable cations were then determined using several different types of methods, and the measured exchangeable cation concentrations compared to reference values. At low ionic strength (low salinity), the concentration of exchangeable cations can be accurately estimated from the total soil extractable cations. In saline soils, however, the presence of soluble salts in the soil solution precludes the use of this method. Leaching of the soil with a pre-wash solution (such as alcohol) was found to effectively remove the soluble salts from the soil, thus allowing the accurate measurement of the effective cation exchange capacity (ECEC). However, the dilution associated with this pre-washing increased the exchangeable Ca concentrations while simultaneously decreasing exchangeable Na. In contrast, when calculated as the difference between the total extractable cations and the soil solution cations, good correlations were found between the calculated exchangeable cation concentrations and the reference values for both Na (Mollisol: y=0.873x and Vertisol: y=0.960x) and Ca (Mollisol: y=0.901x and Vertisol: y=1.05x). Therefore, for soils with a soil solution ionic strength greater than 50 mM (electrical conductivity of 4 dS/m) (in which exchangeable cation concentrations are overestimated by the assumption they can be estimated as the total extractable cations), concentrations can be calculated as the difference between total extractable cations and soluble cations.

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Large-scale patterns of species diversity in the gastrointestinal helminth faunas of the coral reef fish Epinephelus merra (Serranidae) were investigated in French Polynesia and the South Pacific Ocean. The richer barrier reef community in French Polynesia supported richer parasite communities in E. merra than that on the fringing reef. While parasite communities among fish from the same archipelago were similar, differences in potential host species and the distance between archipelagos may have contributed to a qualitative difference in parasite communities between archipelagos. Digenean community diversity in coral reef fishes was greater in the western South Pacific, following similar patterns in free-living species. However, overall species diversity of camallanid nematodes of coral reef fishes does not appear to have been similarly affected.

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Brain electrical activity related to working memory was recorded at 15 scalp electrodes during a visuospatial delayed response task. Participants (N = 18) touched the remembered position of a target on a computer screen after either a 1 or 8 sec delay. These memory trials were compared to sensory trials in which the target remained present throughout the delay and response periods. Distracter stimuli identical to the target were briefly presented during the delay on 30% of trials. Responses were less accurate in memory than sensory trials, especially after the long delay. During the delay slow potentials developed that were significantly more negative in memory than sensory trials. The difference between memory and sensory trials was greater at anterior than posterior electrodes. On trials with distracters, the slow potentials generated by memory trials showed further enhancement of negativity whereas there were minimal effects on accuracy of performance. The results provide evidence that engagement of visuospatial working memory generates slow wave negativity with a timing and distribution consistent with frontal activation. Enhanced brain activity associated with working memory is required to maintain performance in the presence of distraction. © 1997 by the Massachusetts Institute of Technology

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This paper reports the application of linearly increasing stress testing (LIST) to the study of stress corrosion cracking (SCC) of carbon steel in 4 N NaNO3 and in Bayer liquor. LIST is similar to the constant extension-rate testing (CERT) methodology with the essential difference that the LIST is load controlled whereas the CERT is displacement controlled. The main conclusion is that LIST is suitable for the study of the SCC of carbon steels in 4 N NaNO3 and in Bayer liquor. The low crack velocity in Bayer liquor and a measured maximum stress close to that of the reference specimen in air both indicate that a low applied stress rate is required to study SCC in this system. (C) 1998 Chapman & Hall.

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The electrochemical behaviour of magnesium was studied in representative chloride and sulphate solutions including NaCl, Na2SO4, NaOH and their mixed solutions, HCl, and H2SO4: (1) by measuring electrochemical polarisation curves, (2) by using electrochemical impedance spectroscopy (EIS), and (3) by simultaneous measurement of hydrogen gas evolution and measurement of magnesium dissolution rates using inductively coupled plasma atomic emission spectrophotometry (ICPEAS). These experiments showed that a partially protective surface film played an important role in the dissolution of magnesium in chloride and sulphate solutions. Furthermore, the experimental data were consistent with the involvement of the intermediate species Mg+ in magnesium dissolution at film imperfections or on a film-free surface. At such sites, magnesium first oxidised electrochemically to the intermediate species Mg+, and then the intermediate species chemically reacted with water to produce hydrogen and Mg2+. The presence of Cl- ions increased the film free area, and accelerated the electrochemical reaction rate from magnesium metal to Mg+. (C) 1997 Elsevier Science Ltd.

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Multifrequency bioimpedance analysis has the potential to provide a non-invasive technique for determining body composition in live cattle. A bioimpedance meter developed for use in clinical medicine was adapted and evaluated in 2 experiments using a total of 31 cattle. Prediction equations were obtained for total body water, extracellular body water, intracellular body water, carcass water and carcass protein. There were strong correlations between the results obtained through chemical markers and bioimpedance analysis when determined in cattle that had a wide range of liveweights and conditions. The r(2) values obtained were 0.87 and 0.91 for total body water and extracellular body water respectively. Bioimpedance also correlated with carcass water, measured by chemical analysis (r(2) = 0.72), but less well with carcass protein (r(2) = 0.46). These correlations were improved by inclusion of liveweight and sex as variables in multiple regression analysis. However, the resultant equations were poor predictors of protein and water content in the carcasses of a group of small underfed beef cattle, that had a narrow range of liveweights. In this case, although there was no statistical difference between the predicted and measured values overall, bioimpedance analysis did not detect the differences in carcass protein between the 2 groups that were apparent following chemical analysis. Further work is required to determine the sensitivity of the technique in small underfed cattle, and its potential use in heavier well fed cattle close to slaughter weight.

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Baekground: Patients with schizophrenia tend to have impaired performance on tests of working memory (WM). Neurocognitive models have linked WM to certain symptoms of schizophrenia. This study aimed to assess WM in schizophrenia and mania in the acute and subacute phases of the illness and explore correlations between WM and symptom clusters. Methods: A visuo-spatial delayed response task was used to assess WM in schizophrenia (n=20), mania (n= 14) and well controls (n=20). Patients were tested during the first week of an acute admission, and subjects were retested after four weeks. WM, symptoms (PANSS, TLC) and executive ability (COWAT, Stroop, Trail Making) were assessed at both time points. Results: When assessed for overall WM errors (both sensory and memory), there was a significant group difference (F- 11.53, df 2, 40; p

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To simulate cropping systems, crop models must not only give reliable predictions of yield across a wide range of environmental conditions, they must also quantify water and nutrient use well, so that the status of the soil at maturity is a good representation of the starting conditions for the next cropping sequence. To assess the suitability for this task a range of crop models, currently used in Australia, were tested. The models differed in their design objectives, complexity and structure and were (i) tested on diverse, independent data sets from a wide range of environments and (ii) model components were further evaluated with one detailed data set from a semi-arid environment. All models were coded into the cropping systems shell APSIM, which provides a common soil water and nitrogen balance. Crop development was input, thus differences between simulations were caused entirely by difference in simulating crop growth. Under nitrogen non-limiting conditions between 73 and 85% of the observed kernel yield variation across environments was explained by the models. This ranged from 51 to 77% under varying nitrogen supply. Water and nitrogen effects on leaf area index were predicted poorly by all models resulting in erroneous predictions of dry matter accumulation and water use. When measured light interception was used as input, most models improved in their prediction of dry matter and yield. This test highlighted a range of compensating errors in all modelling approaches. Time course and final amount of water extraction was simulated well by two models, while others left up to 25% of potentially available soil water in the profile. Kernel nitrogen percentage was predicted poorly by all models due to its sensitivity to small dry matter changes. Yield and dry matter could be estimated adequately for a range of environmental conditions using the general concepts of radiation use efficiency and transpiration efficiency. However, leaf area and kernel nitrogen dynamics need to be improved to achieve better estimates of water and nitrogen use if such models are to be use to evaluate cropping systems. (C) 1998 Elsevier Science B.V.

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Kidney function and the role of the cloacal complex in osmoregulation was investigated in estuarine crocodile (Crocodylus porosus) exposed to three environmental salinities: hypo-, iso- and hyperosmotic to the plasma. Plasma homeostasis was maintained over the range of salinities. Antidiuresis occurred with increased salinity. Although urine from the kidneys retained an osmotic pressure between 77% and 82% of the plasma, over 93% and 98% of plasma chloride filtered at the glomeruli was reabsorbed during passage through the kidneys under hypo and hyperosmotic conditions, respectively, and only 64% in iso-osmotic water. The kidneys were the primary site of sodium reabsorption under hypo-and hyperosmotic conditions. Secondary processing of urine during storage in the cloaca varied with salinity. During post renal storage of urine, the difference in urine osmotic pressure increased from -26.1 +/- 15.5 to 35.66 +/- 9.29 mOsM with increased salinity, and potassium concentration of urine increased over 3-fold in C. porosus from freshwater. The almost complete reabsorption of both sodium and chloride under hyperosmotic conditions indicates the necessity for secretory activity by the lingual salt glands. The osmoregulatory response of the kidneys and cloacal complex to environmental salinity is both plastic and complementary. (C) 1998 Elsevier Science Inc.

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Algorithms for explicit integration of structural dynamics problems with multiple time steps (subcycling) are investigated. Only one such algorithm, due to Smolinski and Sleith has proved to be stable in a classical sense. A simplified version of this algorithm that retains its stability is presented. However, as with the original version, it can be shown to sacrifice accuracy to achieve stability. Another algorithm in use is shown to be only statistically stable, in that a probability of stability can be assigned if appropriate time step limits are observed. This probability improves rapidly with the number of degrees of freedom in a finite element model. The stability problems are shown to be a property of the central difference method itself, which is modified to give the subcycling algorithm. A related problem is shown to arise when a constraint equation in time is introduced into a time-continuous space-time finite element model. (C) 1998 Elsevier Science S.A.

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Parkinson's disease (PD) is a neurodegenerative movement disorder primarily due to basal ganglia dysfunction. While much research has been conducted on Parkinsonian deficits in the traditional arena of musculoskeletal limb movement, research in other functional motor tasks is lacking. The present study examined articulation in PD with increasingly complex sequences of articulatory movement. Of interest was whether dysfunction would affect articulation in the same manner as in limb-movement impairment. In particular, since very Similar (homogeneous) articulatory sequences (the tongue twister effect) are more difficult for healthy individuals to achieve than dissimilar (heterogeneous) gestures, while the reverse may apply for skeletal movements in PD, we asked which factor would dominate when PD patients articulated various grades of artificial tongue twisters: the influence of disease or a possible difference between the two motor systems. Execution was especially impaired when articulation involved a sequence of motor program heterogeneous in terms of place of articulation. The results are suggestive of a hypokinesic tendency in complex sequential articulatory movement as in limb movement. It appears that PD patients do show abnormalities in articulatory movement which are similar to those of the musculoskeletal system. The present study suggests that an underlying disease effect modulates movement impairment across different functional motor systems. (C) 1998 Academic Press.