50,308 research outputs found
Value Network Dynamics in 3G-4G Wireless Communications: a System Thinking approach to the Strategic Value Assessment Model
No full textThis article develops a map to analyze the dynamic forces that influence the structure and development of 3G (third generation) wireless communications value networks. The analysis builds on the Strategic Value Assessment Model (Fine, et al. 2002) and
utilizes a qualitative System Dynamics mapping approach. The map focuses on the driving forces affecting user adoption of 3G services, focusing on customer dynamics, competitive dynamics, and technology dynamics. To analyze adoption of 3G services by customers, the articles maps the dynamics of (1) network investment and user population, (2) entry of service innovators as well as price competitors, (3) the effects of positive network externalities arising from a larger user population, (4) price compression as lower willingness-to-pay users adopt 3G services, (5) scale economies in terminal costs and prices, and (6) new content development as a draw to new users. Applying inductive systems diagrams hypotheses are integrated into a causal loop map and tested with data collected at 15 communications-industry workshops attended by 190 participants in Europe. The map aims to deepen the understanding of the possible evolutionary paths of the 3G wireless value network. The article seeks also to assess which future scenarios are plausible and what dynamic triggers might make them likely
Designing a manufacturing strategy
No full text"September 1984."Bibliography: p. 34-35.Charles H. Fine, Arnoldo C. Hax
In situ water absorption by tree fine roots measured in real time using miniature sap-flow gauges
No full text1. Root water uptake is a key process in the circulation of water in forest ecosystems. Until recently, water absorption by tree fine roots could not be measured in situ in undisturbed soil. 2. We present a new technique that allows continuous recording of the water absorption of fine root endings in mature stands without altering soil structure, hydrology or mycorrhizal infection. 3. The approach combines miniature sap-flow gauges mounted on small-diameter tree roots (3-4 mm) with a complete extraction and visual surface analysis of the adjacent absorbing fine root endings. This technique yields continuous data on water absorption per fine root surface area, and allows analysis of the spatial heterogeneity of root water uptake in the rhizosphere of forests. 4. We present the results of laboratory and field calibration experiments with Fagus sylvatica L. roots (3-4 mm), which show a good agreement between gauge flow data and synchronous gravimetric flow measurements for flows between 2 and >50 g h(-1) . Gauge readings were unreliable during low flows (<2 g h(-1) ) at night. In these periods, which cover approximate to10% of daily flow, we used an empirically derived linear relationship between root temperature difference and flow. 5. Measurements on F. sylvatica root endings during 10 summer days showed daily water absorption maxima ranging between 0.20 (rainy days) and 0.58 mmol m(-2) root surface area s(-1) (bright or overcast days). The corresponding daily maxima of leaf transpiration rate were approximate to10 times higher (2-4 mmol m(-2) leaf area s(-1) ). 6. The combination of miniature sap-flow gauges and determination of fine root surface area provides a promising tool for analysing water absorption by tree root systems in situ
The nanostructure and degradation of C-S-H in Portland and blended cements
No full textThe microstructure and composition of water and KOH activated hardened pastes of commercial neat white Portland cement (WPC) and blends with 30% fly ash (PFA) have been characterised using a multi-technique approach, With particular emphasis on the nature of the C-S-H phase. The neat and fly ash blended pastes were activated with water or a 5M KOH solution and cured for one year at 25'C, one month at 55'C and one month at 85'C. The mean length of the aluminosilicate anion structure of C-S-H (29 Si MAS NMR) increased with age and it was higher in the fly ash blended systems. Formulae were presented for the average structural units in the C-S-H present in the systems analysed by TEM-EDX. SEM micrographs showed that as hydration occurred,
the microstructure became denser because outer product C-S-H was formed in the water filled spaces and additional C-S-H resulted from the pozzolanic reaction. The chemical
composition of C-S-H could not be determined by SEM-EDX because of intermixing with other phases; TEM-EDX was necessary. Inner product C-S-H morphology was fine and homogeneous and that of outer product C-S-H was fibrillar in the water activated systems and foil-like with alkali activation. Fly ash replacement did not change the morphology of lp and Op C-S-H. Small fully hydrated cement and PFA particles were filled with a less dense lp C-S-H with morphology very similar to the foil-like one. TEM-EDX showed that, in general, the mean Ca/(AI+Si) atomic ratio was lower in the water activated blends than that in the neat cement pastes due to the fly ash reaction. The composition- structure data were discussed in terms of models for the nanostructure of C-S-H.
Higher curing temperature accelerated the rate of the cement hydration. The mean length of the aluminosilicate of the C-S-H anions was much higher than that of C-S-H formed at lower temperatures, and it was also higher in the blended pastes than with neat cement. Backscattered electron images showed that the grey level of C-S-H in the
systems cured at 55T and 85T was in places quite similar to that of the calcium hydroxide: that is, it was brighter than in pastes cured at lower temperature. SEM also showed that the microstructure of the systems cured at higher temperature exhibited non uniform porosity. Inner product C-S-H with a fine scale, homogeneous morphology,
was abundant in all systems cured at 55'C and 85'C. Op C-S-H was generally fibrillar with Nvater, and foil-like with alkali. However, the higher temperature curing did result
in coarser fibrillar morphology (water activated systems) than that formed at lower temperatures.
The C-S-H gel formed in the commercial WPC-30% PFA blended paste hydrated for one year at 25'C and water leached for twelve weeks was also characterised in this work. A matrix effect was clearly observed by 29 Si MAS NMR. Cross-linking of the aluminosilicate anion structure of C-S-H occurred after leaching the sample for four weeks. Formulae were also presented for the average structural units in the C-S-H
present in the unleached and four weeks water leached systems analysed by TEM-EDX. lp C-S-H morphology was fine and homogeneous and Op C-S-H had fibrillar morphology. There were many areas in the microstructure of the leached sample where Op C-S-H with foil-like morphology coexisted with fibrillar Op C-S-H
Measurement of spatial and temporal fine sediment dynamics in a small river
No full textEmpirical measurements on fine sediment dynamics and fine sediment infiltration and accumulation have been conducted worldwide, but it is difficult to compare the results because the applied methods differ widely. We compared common methods to capture temporal and spatial dynamics of suspended sediment (SS), fine sediment infiltration and accumulation and tested them for their suitability in a small, canalized river of the Swiss Plateau. Measurement suitability was assessed by data comparison, relation to hydrological data and in the context of previously published data. SS concentration and load were assessed by optical backscatter (OBS) sensors and SS samplers. The former exhibit a better temporal resolution, but were associated with calibration problems. Due to the relatively low cost and easy mounting of SS samplers, they can provide a higher spatial distribution in the river’s cross section. The latter resulted in a better correlation between sediment infiltration and SS load assessed by SS samplers than SS concentrations measured with OBS sensors. Sediment infiltration baskets and bed loadtraps capture the temporal and spatial distribution of fine sediment infiltration. Data obtained by both methods were positively correlated with water level and SS. In contrast, accumulation baskets do not assess the temporal behaviour offine sediment, but the net accumulation over a certain time period. Less fine sediment accumulated in upwelling zonesand within areas of higher mean water level due to scouring of fine sediments. Even though SS and sediment infiltration assessed with the bedload traps increased from up- to downstream, less fine sediment accumulated downstream. This is probably also attributable to more scouring downstream
Site-selective enzymatic C‒H amidation for synthesis of diverse lactams
No full textPlease note that this work has been retracted by the authors.After publication of the Report “Site-selective enzymatic C‒H amidation for synthesis of diverse lactams” in Science (1, also linked in metadata), efforts to reproduce the work showed that the enzymes do not catalyze the reactions with the activities and selectivities claimed. Careful examination of the first author’s lab notebook then revealed missing contemporaneous entries and raw data for key experiments. The authors therefore have retracted the article from Science and are now retracting the preprint from ChemRxiv. The original paper can be accessed by selecting “Version 1” of the preprint below, or by accessing https://doi.org/10.26434/chemrxiv.7711418.v1. Inha Cho, Zhi-Jun Jia, Frances H. Arnold*Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.*Corresponding author. Email: [email protected]. I. Cho, Z.-J. Jia, F. H. Arnold, Science 364, 575 (2019). DOI: 10.1126/science.aaw9068*******************************************************************************************Directed evolution of cytochrome P450 enzymes fine-tunes site selectivity of new-to-nature C‒H amidation for modular, sustainable and scalable preparation of enantio-enriched β-, γ- and δ-lactams.</p
In situ measurement of fine root water absorption in three temperate tree species - Temporal variability and control by soil and atmospheric factors
No full textMiniature heat balance-sap flow gauges were used to measure water flows in small-diameter roots (3-4 mm) in the undisturbed soil of a mature beech-oak-spruce mixed stand. By relating sap flow to the surface area of all branch fine roots distal to the gauge, we were able to calculate real time water uptake rates per root surface area (J(S)) for individual fine root systems of 0.5-1.0m in length. Study aims were (i) to quantify root water uptake of mature trees under field conditions with respect to average rates, and diurnal and seasonal changes of J(S), and (ii) to investigate the relationship between uptake and soil moisture theta, atmospheric saturation deficit D, and radiation 1. On most days, water uptake followed the diurnal course of D with a midday peak and low night flow. Neighbouring roots of the same species differed up to 10-fold in their daily totals of J(S) ( < 100-2000 g m(-2) d(-1)) indicating a large spatial heterogeneity in uptake. Beech, oak and spruce roots revealed different seasonal patterns of water uptake although they were extracting water from the same soil volume. Multiple regression analyses on the influence of D, I and theta on root water uptake showed that D was the single most influential environmental factor in beech and oak (variable selection in 77% and 79% of the investigated roots), whereas D was less important in spruce roots (50% variable selection). A comparison of root water uptake with synchronous leaf transpiration (porometer data) indicated that average water fluxes per surface area in the beech and oak trees were about 2.5 and 5.5 times smaller on the uptake side (roots) than on the loss side (leaves) given that all branch roots < 2 mm were equally participating in uptake. Beech fine roots showed maximal uptake rates on mid-summer days in the range of 48-205 g m-2 h(-1) (i.e. 0.7-3.2 mmol m(-2) s(-1)), oak of 12-160 g m(-2) h(-1) (0.2-2.5 mmol m(-2) s(-1)). transpiration rates ranged from 3 to 5 and from 5 to 6 mmol m(-2) s(-1) for sun canopy leaves of beech and oak, respectively. We conclude that instantaneous rates of root water uptake in beech, oak and spruce trees are above all controlled by atmospheric factors. The effects of different root conductivities, soil moisture, and soil hydraulic properties become increasingly important if time spans longer than a week are considered. (c) 2005 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved
Population differences in immune responses to Bacille Calmette-Guérin vaccination in infancy.
No full textBacille Calmette-Guérin (BCG) vaccination induces a marked increase in the interferon (IFN)-gamma response to Mycobacterium tuberculosis purified protein derivative (Mtb PPD) in UK adolescents, but not in Malawian adolescents. We hypothesized that Mtb PPD-induced IFN-gamma after BCG vaccination would be similar in infants from these 2 countries. Infants were vaccinated with BCG during the first 3-13 weeks of life. Three months after BCG vaccination, 51 (100%) of 51 UK infants had an IFN-gamma response to Mtb PPD, compared to 41 (53%) of 78 of Malawian infants, in whom responses varied according to their season of birth. We conclude that population differences in immune responses after BCG vaccination are observed among infants, as well as among young adults
Rapid growth of Coalescing Droplets and Observation of Fine Structures in Turbulent Flow
No full textI will present our results on size-growth dynamics of coalescing droplets in simulation of isotropic turbulent flow. In the short time limit, we observe very fast growth due to correlations of these droplets which can be related to the interaction between their inertia to turbulent advection (this work is done with colleagues at affiliations 1 \& 2). In a later part, I will describe our attempt to experimentally observe the intermittent fine structures of turbulence flow using high resolution Particle Image Velocimetry (PIV) technique (this work is done with colleagues at affiliation 3)
An Introduction to the Kent C++CSP Library
No full textThis paper reports on a CSP library for C++, developed over the past year at the University of Kent. It is based on the OO-design and API of JCSP and the lightweight algorithms of KRoC occam, with extensions to exploit specific C++ capabilities (such as templates). Both user-level and operating system threads are used to provide a range of oimplementation options and semantics (e.g. for managing blocking system calls intelligently) that run efficiently under either Windows or Linux. The library is presented from the user's point of view, mainly by way of a tutorial. Implementation details are also outlines and some benchmark results given. The performance of C++CSP is between that of KRoC occam and JCSP -- fairly close to KRoC
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