Linear Transfer Model Research Articles

Mass transfer behavior of methane in porous carbon materials

AbstractThe low mass transfer rate in porous materials hinders the use of adsorbed natural gas as vehicle fuel. Fundamentally, the mass transfer rate depends on the structures of the adsorbents and the operating conditions. Therefore, in this study, the effects of adsorbent (activated carbons) structure and operating conditions on the mass transfer rate of methane (main component of natural gas) were investigated quantitatively, providing a theoretical basis for the synthesis of efficient adsorbent materials. By performing Monte Carlo and molecular dynamics simulations and utilizing a nonequilibrium thermodynamic linearization transfer model, the mass transfer behavior of methane in porous carbon materials was quantitatively evaluated, specifically focusing on the material structure, operating conditions, and feasibility of using natural gas as vehicle fuel. The proposed linear nonequilibrium thermodynamic mass transfer model is applicable to interfacial gas species and provides a valuable tool for gas separation.

Utilization of Vector Autoregressive and Linear Transfer Models to Follow Up the Antibiotic Resistance Spiral in Gram-negative Bacteria From Cephalosporin Consumption to Colistin Resistance.

Increasing antibiotic resistance may reciprocally affect consumption and lead to use of broader-spectrum alternatives; a vicious cycle that may gradually limit therapeutic options. Our aim in this study was to demonstrate this vicious cycle in gram-negative bacteria and show the utility of vector autoregressive (VAR) models for time-series analysis in explanatory and dependent roles simultaneously. Monthly drug consumption data in defined daily doses per 100 bed-days and incidence densities of gram-negative bacteria (Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa, and Acinetobacter baumannii) resistant to cephalosporins or to carbapenems were analyzed using VAR models. These were compared to linear transfer models used earlier. In case of all gram-negative bacteria, cephalosporin consumption led to increasing cephalosporin resistance, which provoked carbapenem use and consequent carbapenem resistance and finally increased colistin consumption, exemplifying the vicious cycle. Different species were involved in different ways. For example, cephalosporin-resistant Klebsiella spp. provoked carbapenem use less than E. coli, and the association between carbapenem resistance of P. aeruginosa and colistin use was weaker than that of A. baumannii. Colistin use led to decreased carbapenem use and decreased carbapenem resistance of P. aeruginosa but not of A. baumannii. VAR models allow analysis of consumption and resistance series in a bidirectional manner. The reconstructed resistance spiral involved cephalosporin use augmenting cephalosporin resistance primarily in E. coli. This led to increased carbapenem use, provoking spread of carbapenem-resistant A. baumannii and consequent colistin use. Emergence of panresistance is fueled by such antibiotic-resistance spirals.

Variability of summer humidity during the past 800 years on the eastern Tibetan Plateau inferred from δ<sup>18</sup>O of tree-ring cellulose

Abstract. We present an 800-year δ18O chronology from the eastern part of the Tibetan Plateau (TP). The chronology dates back to AD 1193 and was sampled in AD 1996 from living Juniperus tibetica trees. This first long-term tree-ring-based δ18O chronology for eastern Tibet provides a reliable archive for hydroclimatic reconstructions. Highly significant correlations were obtained with hydroclimatic variables (relative humidity, vapour pressure, and precipitation) during the summer season. We applied a linear transfer model to reconstruct summer season relative humidity variations over the past 800 years. More moist conditions prevailed during the termination of the Medieval Warm Period while a systematic shift during the Little Ice Age is not detectable. A distinct trend towards more dry conditions since the 1870s is apparent. The moisture decline weakened around the 1950s but still shows a negative trend. The mid-19th century humidity decrease is in good accordance with several multiproxy hydroclimate reconstructions for south Tibet. However, the pronounced summer relative humidity decline is stronger on the central and eastern TP. Furthermore, the relative humidity at our study site is significantly linked to the relative humidity at large parts of the TP. Therefore, we deduce that the reconstructed relative humidity is mostly controlled by local and mesoscale climatic drivers, although significant connections to the higher troposphere of west-central Asia were observed.

A comparative study between linear transfer models of low order and ARX model of high order depending on spatial series

A comparative study between linear transfer models of low order and ARX model of high order depends on spatial series. The research includes a comparison between efficiency of the different linear transfer function f stationary time – spatial series with low order models ( ARX11k , ARMAX2221 ,O.E221 , B.J22221 , pss1 ) and high order ARX model according to the percentage rate of coincidence of the model to the data . The comparison is made on a spatial – time series which shows the effect resulted on the biological factors of the soil as a consequence of changes in the chemical factors on one hand and physical factors on the other, and the two factors all are together as an input–output model ( multiple–uni ) in one time and (multiple–multiple) on another time . It appears that ARX models of high order has a high percentage fit compared with the transfer models of low order .

A comparative study between linear transfer models of low order and ARX model of high order depending on spatial series

A comparative study between linear transfer models of low order and ARX model of high order depending on spatial series

When more means less: a paradox BOLD response in human visual cortex

The predictions of the 'Linear Transfer Model' (LTM) have been tested only by modulating the frequency of the action potentials while keeping the size of the activated neuronal population constant. The LTM states that the blood oxygenation level-dependent contrast (BOLD) signal is directly proportional to the neuronal activity averaged over milliseconds or seconds. We examined the influence on the BOLD response, of manipulating the size of the activated neuronal population while maintaining the electrical discharge activity constant. We performed functional MR measurements on 30 awake, healthy adult volunteers (15 male and 15 female) using a flashed and reversing checkerboard. These stimuli induced the same vascular response and the same increase in the electrical discharge activity but varied in the size of the neuronal population being activated. The BOLD response measured by the extent of activation and the BOLD signal amplitude, was larger for the flashed than to the reversing checkerboard. An assessment of the local deoxyhemoglobin (HbR) concentration indicated that the neuronal activity was lower during the flashed checkerboard than the reversing checkerboard. Because the checkerboard associated with the lower neuronal activity yielded the larger number of activated voxels and the larger BOLD signal, our results run contrary to the predictions of the 'Linear Transfer Model' and for this reason we refer to them as paradoxical. Stimuli defined by luminance contrast or a chromatic contrast yielded identical results. We conclude that the 'LTM' may apply to stimuli that modulate the electrical discharge activity but not to stimuli that modulate the size of the activated neuronal population.

Mechanisms affecting the dissolution of nonaqueous phase liquids into the aqueous phase in slow‐stirring batch systems

Understanding the kinetics of the exchange processes between nonaqueous phase liquids (NAPLs) and water is important in predicting the fate of anthropogenic compounds such as petroleum hydrocarbons, i.e., benzene, toluene, ethylbenzene, and xylene (BTEX) as well as polynuclear aromatic hydrocarbons (PAHs). Exchange processes occurring in the environment resemble the experimental setup of the slow-stirring method (SSM) designed to determine solubilities and octanol-water partition coefficients. Data obtained from SSM experiments for diesel fuel compounds are interpreted by a linear transfer model that is characterized by an aqueous molecular boundary layer and the water/NAPL equilibrium partition coefficient. For the chosen experimental setup, the boundary layer thickness is 2.42 x 10(-2) cm. Typical equilibration times lie between 1 and 2 d. Due to the temperature dependence of the aqueous diffusivity, this time increases with decreasing temperature. Transport within the NAPL phase can slow down the exchange process for the more water-soluble compounds (e.g., benzene) provided that the stirring rate exceeds a critical value.

MECHANISMS AFFECTING THE DISSOLUTION OF NONAQUEOUS PHASE LIQUIDS INTO THE AQUEOUS PHASE IN SLOW-STIRRING BATCH SYSTEMS

Understanding the kinetics of the exchange processes between nonaqueous phase liquids (NALs) and water is important in predicting the fate of anthropogenic compounds such as petroleum hydrocarbons, i.e., benzene, toluene, ethylbenzene, and xylene (BTEX) as well as polynuclear aromatic hydrocarbons (PAHs). Exchange processes occurring in the environment resemble the experimental setup of the slow-stirring method (SSM) designed to determine solubilities and octanol-water partition coefficients. Data obtained from SSM experiments for diesel fuel compounds are interpreted by a linear transfer model that is characterized by an aqueous molecular boundary layer and the water/NAPL equilibrium partition coefficient. For the chosen experimental setup, the boundary layer thickness is 2.42 × 10−2 cm. Typical equilibration times lie between 1 and 2 d. Due to the temperature dependence of the aqueous diffusivity, this time increases with decreasing temperature. Transport within the NAPL phase can slow down the exchange process for the more water-soluble compounds (e.g., benzene) provided that the stirring rate exceeds a critical value.

On the reconstruction of temperature records from proxy data in mid Europe

The problem of the reconstruction of mean summer temperatures from proxy data on a rigorous statistical basis is addressed: Cross spectral analysis is used for evaluating the suitability of linear transfer models between proxy data and temperature, the linear model is estimated from the data of a calibration period and it is verified using the data of a different period. Strict statistical tests are applied at every step of the analysis. Three examples using the proposed method are given: the reconstruction of mean April–July temperatures at Basel from grape harvest data in NE France (1484–1768), mean April–September temperatures at Basel from late wood density of trees from the Swiss Prealps (1270‐1768), and mean April–September temperatures at Great St. Bernhard from the late wood proxy too (1270–1850). The grape harvest data give a very good reconstruction, the resulting temperatures from 1500–1768 are documented. The late wood data fails to give a good reconstruction.

An event‐based model of recharge from an ephemeral stream

Estimating annual recharge is an important input to the management of groundwater resources. Available hydrologic information is used to derive a model‐based prior distribution function of annual recharge from an ephemeral stream. To illustrate the methodology, a linear transfer model defining groundwater recharge as a function of streamflow is postulated from stream characteristics in arid lands. Parameters of the groundwater model are identified by using streamflow data as input and recharge data as output. The parameters are then used in an event‐based approach to determine the distribution function for annual recharge. The model is applied to the Rillito Creek, a part of the Tucson alluvial basin, Arizona. The method, however, is applicable to other areas, can incorporate more sophisticated transfer functions, and may be extended to include larger watersheds consisting of multiple reaches.