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In order to enhance the selectivity of metal oxide gas sensors, we use a flow modulation method to exploit transient sensor information. The method is based on modulating the flow of the carrier gas that brings the species to be measured into the sensor chamber. We present an active perception strategy by using a DQN which can optimize the flow modulation online. The advantage of DQN is not only that the classification accuracy is higher than traditional methods such as PCA, but also that it has a good adaptability under small samples and labeled data. From observed values of the sensors array and its past experiences, the DQN learns an action policy to change the flow speed dynamically that maximizes the total rewards (or minimizes the classification error). Meanwhile, a CNN is trained to predict sample class and reward according to current actions and observation of sensors. We demonstrate our proposed methods on a gases classification problem in a real time environment. The results show that the DQN learns to modulate flow to classify different gas and the correct rates of gases are: sesame oil 100%, lactic acid 80%, acetaldehyde 80%, acetic acid 80%, and ethyl acetate 100%, the average correct rate is 88%. Compared with the traditional method, the results of PCA are: sesame oil 100%, acetic acid 24%, acetaldehyde 100%, lactic acid 56%, ethyl acetate 68%, the average accuracy rate is 69.6%. DQN uses fewer steps to achieve higher recognition accuracy and improve the recognition speed, and to reduce the training and testing costs.

Traditional therapeutic options for complex thoracoabdominal aneurysm include open repair, hybrid repair or endovascular repair (involving fenestrated or branched endografts). The Streamliner Multilayer Flow Modulator has been available for treatment of thoracoabdominal aneurysms since 2010. Its design permits blood flow to perfuse through the mesh in a modus that preserves collateral branch patency, while modulating turbulent to laminar flow within the device. The flow then stagnates over time within the surrounding aneurysm sac. Significant complications, including paraplegia, renal failure and cerebrovascular accident, are much lower with Streamliner Multilayer Flow Modulator treatment. Application of the Streamliner Multilayer Flow Modulator to complex aortic pathologies presents a novel solution to an, as of yet, unmet clinical need, and has resulted in promising clinical outcomes when compared to existing solutions. The Streamliner Multilayer Flow Modulator offers potential for treatment of thoracoabdominal aortic pathologies in patients and is not just confined to those with complexity that dictates no other management options. While current literature illustrates that there is a decreased risk of mortality and associated complications when this new disruptive technology is utilised, there is still a need for prospective, long-term clinical trials, as well as comparative trials to accurately assess outcomes of Streamliner Multilayer Flow Modulator treatment that are both precise and reproducible. This article is a review of current clinical literature regarding contemporary flow modulating technology compared with open, branched and fenestrated managements, presenting early outcomes.

The present research is based on the development of an effective, environmentally-friendly and low-cost method for investigation of minor components in vegetable oils, exploiting the advantages of a miniaturized solid-phase extraction (SPE) and the potential of flow modulation (FM) comprehensive two-dimensional gas chromatography (GC×GC), coupled to a mass spectrometer (MS) and a flame ionization detector (FID). The initial sample preparation step was carried out using a miniaturized approach characterized by a SPE process in a Pasteur pipette. Then, the isolated fraction was injected into an FM GC×GC system. Tentative identification was carried out by means of MS spectral information, while quantification was carried out by using the FID data. Four different vegetable oil samples were analyzed using the proposed method, namely an extra virgin olive oil (EVO), a hazelnut oil (HO), a borage oil, and an EVO/HO mixture.

Experimental study of mechanical treatment effect of rotary flow modulation device on coal-water fuel rheological properties were conducted. The slurry was prepared on the basis of low-grade 3B coal from Balakhtinskoe deposit.

Das Popliteaaneurysma ist das haufigste periphere Aneurysma und imponiert klinisch meist mit Symptomen einer peripheren Verschlusskrankheit, einer akuten Embolisation oder Thrombose. Die Ruptur ist ein extrem seltenes Ereignis. Aufgrund des hohen Risikos des Extremitatenverlusts sollte die Behandlung fruhzeitig erfolgen. Neben den gangigen Bypassverfahren haben sich die endovaskularen Optionen in den vergangenen Jahren weiterentwickelt, die Entscheidung fur den Einsatz gecoverter Stents basiert jedoch auf wenigen, teils widerspruchlichen Daten und die Systeme unterliegen erheblichen Limitierungen bei gleichzeitig hohen Kosten. Eine Alternative zum gecoverten Stent ist der Flowdiverter, hier in Form eines 2-lagig implantierten Bare Metal Stents mit fur die A. poplitea optimalen Materialeigenschaften. Die vorliegenden Ergebnisse dieser Pilotstudie mit 13 Aneurysmen zeigen im Follow-up von 2 bis 23 Monaten vielversprechende Ergebnisse ohne perioperative Komplikationen, Stentfrakturen, Migration oder Separation von Stentanteilen bei 100 % technischem Erfolg mit kompletter Thrombosierung der Aneurysmen und deutlich geringeren Kosten als gecoverte Stents. Die Reverschlussrate lag, wie zu erwarten, bei den elektiv operierten Patienten deutlich niedriger als bei einer Primarintervention im akuten Verschlussstadium mit Aspirationsthrombektomie und adjuvanter Thrombolyse. Die erreichten Ergebnisse erlauben es, das Prinzip der kompletten Aneurysmaausschaltung durch Bypass oder gecoverte Stents infrage zu stellen.

This paper presents the results of pulsed-GaCl flow modulation epitaxy (FME) on hydride vapor phase epitaxy (HVPE) at various interval times, supply times, and V/III ratios under a constant NH 3 flow. The best performance was observed at an interval time of 30 s, GaCl gas supply time of 10 s in one cycle and V/III ratio of 10. As compared to the conventional HVPE growth, the utilization efficiency of the GaCl gas improved by 2.5 times in the present method and the root-mean-square (RMS) values reduced to one-fifth of the original, without degradation of crystalline quality. We concluded that the dynamic change in the V/III ratio in one cycle of an FME sequence contributed to a change in the growth mode, resulting in an improved utilization efficiency of the GaCl gas.

Familiarized with the steady state behavior and advantages of the trickle bed reactors (TBR), for the past two decades, researchers and process engineers are continuously exploring the unsteady state hydrodynamics of periodically (or cyclic) operated trickle bed reactors to extract even more from its efficiency and performance. Despite its complicated nonlinear behavior that attributes to the process control safety at the commercial scale, cyclic operation of TBR is a promising process intensification technology that has immense potential for implementation on industrial TBR. In this paper, we have summarized and reviewed the research and progresses made in recent years on cyclic operation of TBR and potential applications of various mode of its operation. Several issues associated with its hydrodynamics scale-up and designs have been discussed with an emphasis on shock wave attenuation that arises during flow modulation.

Experiments on hydrolysis of tetraethoxysilane in a rotor device with a stirrer were described and discussed.

The present contribution is focused on the measurement of the analytical sensitivity attained in untargeted/targeted MS/MS experiments, performed using flow-modulator comprehensive 2D and 1D GC. The comprehensive 2D experiment was performed by diverting part of the high flow (circa 80%) to flush the accumulation loop (about 28 mL/min) to waste, to reduce the gas flow entering the ion source. 1D analyses were performed through: (i) unmodulated and (ii) single column applications. An equivalent temperature program was applied in the modulated and unmodulated analyses, while a faster one was employed in the single column one. In all application types, the (same) triple quadrupole instrument was operated in the full-scan and multiple reaction monitoring modes. A genuine sweet orange oil and the same sample spiked with 20 phytosanitary compounds were employed to reach the research objective. The results highlight the problems related to the flow modulation-MS combination. Specifically, it was found that sensitivity was on average three to four times higher in unmodulated and optimized single-column applications.

Gas analyzers based on gas sensors are the devices which enable recognition of various kinds of volatile compounds. They have continuously been developed and investigated for over three decades, however there are still limitations which slow down the implementation of those devices in many applications. For example, the main drawbacks are the lack of selectivity, sensitivity and long term stability of those devices caused by the drift of utilized sensors. This implies the necessity of investigations not only in the field of development of gas sensors construction, but also the development of measurement procedures or methods of analysis of sensor responses which compensate the limitations of sensors devices. One of the fields of investigations covers the dynamic measurements of sensors or sensor-arrays response with the utilization of flow modulation techniques. Different gas delivery patterns enable the possibility of extraction of unique features which improves the stability and selectivity of gas detecting systems. In this article three utilized flow modulation techniques are presented, together with the proposition of the evaluation method of their usefulness and robustness in environmental pollutants detecting systems. The results of dynamic measurements of an commercially available TGS sensor array in the presence of nitrogen dioxide and ammonia are shown.

The performances of forward flow fill and flush (FFF) and of reverse flow fill and flush (RFF) in flow modulated comprehensive two-dimensional gas chromatography (GC×GC) using the same volume of the sampling channel have been studied and compared. Sample models include a reference mixture of hydrocarbons at low concentration, a petroleum reformate product and the essential oil of Rosa damascena Miller. The latter samples contain solutes in different concentrations but some up to 30% allowing to study overloading phenomena in detail. For solutes injected at low quantity, the performance of FFF and RFF is similar. For solutes present in a sample at high quantity, RFF guarantees less broadening and spreading resulting in better quantitation.

The present research is based on the development and use of a flow-modulation (FM) comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC×GC-qMS) method for the determination of recently-highlighted (by the Scientific Committee on Consumer Safety) fragrance allergens (54) in cosmetics. FM GC×GC-qMS conditions were finely tuned to generate flow conditions (≈7 mL min(-1)) compatible with the qMS system used. Six-point calibration curves, over the range 1, 5, 10, 20, 50, 100 mg L(-1), were constructed for the 54 target allergens, with satisfactory linearity observed in all cases. Absolute quantification was performed by using extracted ions; target analyte identification was performed through measurement of ion ratios (qualifier/quantifier), full-scan MS database matching and the use of linear retention indices. Additional analytical figures of merit subjected to measurement were intra-day repeatability, accuracy at the 25 and 5 mg L(-1) levels, and limits of detection and quantification. The number of data points per peak, along with mass spectral skewing, was also subjected to evaluation. Finally, the FM GC×GC-qMS method was used not only for the quantification of target allergens in five commercial perfumes, but also for general qualitative profiling.

The present investigation is focused on a simple flow modulator (FM), for comprehensive two-dimensional gas chromatography (GC×GC). The interface is stable at high temperatures, and consists of a metallic disc (located inside the GC oven) with seven ports, which are connected to an auxiliary pressure source via two branches, to the first and second dimension, to a waste branch (linked to a needle valve) and to an exchangeable modulation loop (2 ports). The ports are connected via micro-channels, etched on one of the inner surfaces of the disc. Modulation is achieved using a two-way electrovalve, connected on one side to the additional pressure source, and to the two metal branches, on the other. An FM enantio-GC×polar-GC method (using a flame ionization detector) was optimized (a 40-μL loop was employed), for the analysis of essential oils. As an example, an application on spearmint oil is shown; the method herein proposed was subjected to validation. Finally, an FM GC×GC diesel experiment was carried out, using an apolar-polar column combination, to demonstrate the effectiveness of the modulator in the analysis of a totally different sample-type.

The influence of periodic operation on trickle-bed reactor (TBR) hydrodynamics and gas–liquid mass transfer was investigated. Two-phase pressure drop, dynamic liquid hold-up and gas–liquid mass transfer coefficient (kLa) were determined at various liquid flow rates and for different modes of liquid flow variation (increasing and decreasing liquid flow rate). The results reveal the considerable influence of type of liquid flow rate modulation on kLa values (deviations of up to 80% in kLa). Simulation studies on gas-limited reaction in a periodically operated TBR indicate that an enhancement in conversion of about 14% can be expected from an appropriate selection of the operating mode, thus clearly demonstrating the quantitative process intensification feasible through increased gas–liquid mass transfer.

In this paper, the use of a new technique to obtain transient sensor information is introduced and its usefulness to improve the selectivity of metal oxide gas sensors is discussed. The method is based on modulating the flow of the carrier gas that brings the species to be measured into the sensor chamber. In such a way, the analytes’ concentration at the surface of the sensors is altered. As a result, reproducible patterns in the sensor response develop, which carry important information for helping the sensor system, not only to discriminate among the volatiles considered but also to semi-quantify them. This has been proved by extracting features from sensor dynamics using the discrete wavelet transform (DWT) and by building and validating support vector machine (SVM) classification models. The good results obtained (100% correct identification among 5 volatile compounds and nearly a 89% correct simultaneous identification and quantification of these volatiles), which clearly outperform those obtained when the steady-state response is used, prove the concept behind flow modulation.

Aim To measure the impact of French national consensus guidelines on the clinical practices of primary care paediatricians and general practitioners. Design Non-randomized intervention study, with a first survey 1 year before the consensus development conference and a second survey 1 year after. Intervention Implementation of bronchiolitis management guidelines through the medical press and the Internet. Subjects Paediatricians and general practitioners treating infants 1 year of age and under consulting for a first-time episode of bronchiolitis. Results Ninety-three doctors and 510 infants were included during the first phase of the study and 96 doctors and 394 infants during the second phase. This study showed a slight increase in adherence to the guidelines for non-validated drugs (6.6% adherence before and 14.3% after), general advice (29.0% adherence before and 57.1% after) and flow modulation respiratory physical therapy (91.9% adherence before and 98.8% after). Increase in adherence to guidelines for other practices, that is, hospitalization, prescribing antibiotics and complementary examinations, was not statistically significant. Adherence to the guidelines on providing general advice increased the most between the two studies. Conclusion The guidelines helped practitioners evolve slightly in their approach to the treatment of bronchiolitis. Non-validated drugs remain frequently used. Additional resources for implementing the guidelines should be provided to improve primary care doctors’ practices.

The design of bioinspired systems for chemical sensing is an engaging line of research in machine olfaction. Developments in this line could increase the lifetime and sensitivity of artificial chemo-sensory systems. Such approach is based on the sensory systems known in live organisms, and the resulting developed artificial systems are targeted to reproduce the biological mechanisms to some extent. Sniffing behaviour, sampling odours actively, has been studied recently in neuroscience, and it has been suggested that the respiration frequency is an important parameter of the olfactory system, since the odour perception, especially in complex scenarios such as novel odourants exploration, depends on both the stimulus identity and the sampling method. In this work we propose a chemical sensing system based on an array of 16 metal-oxide gas sensors that we combined with an external mechanical ventilator to simulate the biological respiration cycle. The tested gas classes formed a relatively broad combination of two analytes, acetone and ethanol, in binary mixtures. Two sets of low-frequency and high-frequency features were extracted from the acquired signals to show that the high-frequency features contain information related to the gas class. In addition, such information is available at early stages of the measurement, which could make the technique suitable in early detection scenarios. The full data set is made publicly available to the community. (C) 2014 Elsevier B.V. All rights reserved.

High-speed gas chromatographic (GC) separation of residual solvents in pharmaceutical preparations, using a flow-modulation technique, is described. These volatile compounds are separated on a series-coupled (tandem) column ensemble consisting of a polyethylene glycol column and a trifluoropropylmethyl/dimethylpolysiloxane column. This column ensemble is operated in stop-flow mode to enhance, or "tune", the separation. A valve between the junction point of the tandem column ensemble and a source of carrier gas at a pressure above the GC inlet pressure is opened for intervals of 2-8 s. This stops or slightly reverses the flow of carrier gas in the first column. Stop-flow pulses are used to increase the separation of target analytes that overlap in the total ensemble chromatogram, compared to non-stop-flow, or conventional, operation. All 36 target compounds, based on ICH Classes I and II residual solvent lists, are resolved in 12 min using the stop-flow technique and a single chromatographic analysis.

Monkey data suggest that of all perceptual abilities, motion perception is the most likely to survive striate damage. The results of studies on motion blindsight in humans, though, are mixed. We used an indirect strategy to examine how responses to visible stimuli were modulated by blind-field stimuli. In a 26-year-old man with focal striate lesions, discrimination of visible optic flow was enhanced about 7% by blind-field flow, even though discrimination of optic flow in the blind field alone (the direct strategy) was at chance. Pursuit of an imagined target using peripheral cues showed reduced variance but not increased gain with blind-field cues. Preceding blind-field prompts shortened reaction times to visible targets by about 10 msec, but there was no attentional crowding of visible stimuli by blind-field distractors. A similar efficacy of indirect blind-field optic flow modulation was found in a second patient with residual vision after focal striate damage, but not in a third with more extensive medial occipito-temporal damage. We conclude that indirect modulatory strategies are more effective than direct forced-choice methods at revealing residual motion perception after focal striate lesions.

Low temperature (LT) flow modulation epitaxy (FME) or “pulsed” growth was successfully used to prevent magnesium from Metalorganic Chemical Vapor Deposition (MOCVD) grown p-GaN:Mg layers riding into subsequently deposited n-type layers. Mg concentration in the subsequent layers was lowered from ∼1 × 1018 cm−3 for a medium temperature growth at 950 °C to ∼1 × 1016 cm−3 for a low temperature growth at 700 °C via FME. The slope of the Mg concentration drop in the 700 °C FME sample was 20 nm/dec—the lowest ever demonstrated by MOCVD. For growth on Mg implanted GaN layers, the drop for a medium temperature regrowth at 950 °C was ∼10 nm/dec compared to >120 nm/dec for a high temperature regrowth at 1150 °C. This drop-rate obtained at 950 °C or lower was maintained even when the growth temperature in the following layers was raised to 1150 °C. A controlled silicon doping series using LT FME was also demonstrated with the lowest and highest achieved doping levels being 5 × 1016 cm−3 and 6 × 1019 cm−3, respectively.

Recent studies in neuroscience suggest that sniffing, namely sampling odors actively, plays an important role in olfactory system, especially in certain scenarios such as novel odorant detection. While the computational advantages of high frequency sampling have not been yet elucidated, here, in order to motivate further investigation in active sampling strategies, we share the data from an artificial olfactory system made of 16 MOX gas sensors under gas flow modulation. The data were acquired on a custom set up featured by an external mechanical ventilator that emulates the biological respiration cycle. 58 samples were recorded in response to a relatively broad set of 12 gas classes, defined from different binary mixtures of acetone and ethanol in air. The acquired time series show two dominant frequency bands: the low-frequency signal corresponds to a conventional response curve of a sensor in response to a gas pulse, and the high-frequency signal has a clear principal harmonic at the respiration frequency. The data are related to the study in [1], and the data analysis results reported there should be considered as a reference point.The data presented here have been deposited to the web site of The University of California at Irvine (UCI) Machine Learning Repository (https://archive.ics.uci.edu/ml/datasets/Gas+sensor+array+under+flow+modulation). The code repository for reproducible analysis applied to the data is hosted at the GutHub web site (https://github.com/variani/pulmon).The data and code can be used upon citation of [1].

The present paper contains research data relative to an approach herein defined as flow-modulation (FM) low-pressure comprehensive two-dimensional gas chromatography, abbreviated as "GC×LP GC". The abbreviation LP is positioned before the second GC abbreviation because LP conditions were generated across a mega-bore second-dimension column (10m×0.53mm ID), it being connected to a quadrupole mass spectrometer (qMS). Flow modulation was performed with MS-compatible gas flows (7-8mL/min), following recent research work [7]; using such an approach, the main disadvantage of flow modulation, specifically the generation of excessively high second-dimension flows, is avoided. A further noteworthy aspect of the investigation was the use of a long accumulation loop (e.g., 51cm), a modification that greatly improved the general post-modulation peak shape quality. FM GC×LP GC-qMS applications on pure standard compounds, as well as on milk and fish oil fatty acid methyl esters, are shown and discussed.

The goal of this study was to examine whether the lower limit of the graft-to-recipient weight ratio (GRWR) can be safely reduced to make better use of the left lobe graft in adult-to-adult living donor liver transplantation in combination with portal pressure control. Beginning December 2007, the acceptable limit for GRWR was lowered to ≥0.7% and by April 2009, it was further lowered to ≥0.6%. A portal pressure control program targeting a final portal pressure

The present research is specifically based on the use of greatly-reduced gas flows, in flow-modulator (FM) comprehensive two-dimensional gas chromatography systems. In particular, focus of the present research is directed to FM devices characterized by an accumulation stage, and a much briefer re-injection step. It has been widely accepted that the operation of such FM systems requires high gas flows (≥20 mL/min), to re-inject the gas-phase contents of sample (or accumulation) loops, onto the second column. On the contrary, it will be herein demonstrated that much lower gas flows (≈ 6–8 mL/min) can efficiently perform the modulation step of re-injection. The possibility of using such improved operational conditions is given simply by a fine optimization of the processes of accumulation and re-injection. The application of lower gas flows not only means that second-dimension separations are carried out under better analytical conditions, but, even more importantly, greatly reduces problems which arise when using mass spectrometry (i.e., sensitivity and instrumental pumping capacity).

A new method to form compositionally graded multilayer films by using a single deposition source has been developed. In this method, the reactive gas flow rate has been changed periodically to form multilayers. As a result, the composition of the multilayer films obtained by this technique changes periodically without any interrupted interfaces. To form multilayers using this technique, a non-linear relationship between the reactive gas flow rate and the deposition parameters such as deposition rate and reactive gas consumption should be considered because they cause a non-linear relationship between the reactive gas flow rate and the composition distribution towards the film depth of deposited films. Without considering this, the film with a sinusoidal component distribution that is assumed to originate novel properties cannot be obtained. By comparing the oxygen distribution towards the film depth obtained by Auger electron spectroscopy with that calculated from O 2 consumption during film deposition, it was found that oxygen diffused towards the metal-rich underlayers during deposition of oxygen-rich layers. This diffusion makes it difficult to estimate and control film layer composition distribution from deposition parameters. By optimizing the gas flow rate change a TiO x multilayer film with a 5-layered sinusoidal component distribution has been obtained.

The relationship between portal pressure and small-for-size syndrome (SFSS) is unsettled. The purpose of this study was to evaluate the role of portal pressure in predicting SFSS.Thirty-four patients with end-stage liver disease who received adult-to-adult living-donor liver transplantation (ALDLT) were included. Recipients were grouped based on whether they received portal flow modulation or not. The intraoperative portal vein flow volume (PVFV) and portal venous pressure (PVP) between the 2 groups were compared. The relationship of PVP to PVFV, graft weight-to-recipient weight ratio (GRWR), and graft weight-to-recipient spleen size ratio (GRSSR) were analyzed.Persistent portal hypertension was found after ALDLT. The PVP was linearly correlated with PVFV but not with GRWR or GRSSR. With the use of the following criteria, (1) PVFV250 mL/min/100 g graft weight, (2) GRWR 0.8%, and (3) GRSSR 0.6, modulation of the portal flow was performed in 3 cases. The receiver operating characteristic analysis showed that 23 mm Hg was the cutoff point for PVP, with a sensitivity of 83% and specificity of 43%.PVP is a weak parameter to use for portal flow modulation after ALDLT. It is sensitive but not specific to predict SFSS.

Comprehensive two-dimensional gas chromatography (GC×GC) offers an interesting tool for profiling bacterial fatty acids. Flow modulated GC×GC using a commercially available system was evaluated, and different parameters such as column flows and modulation time were optimized. The method was tested on bacterial fatty acid methyl esters (BAMEs) from Stenotrophomonas maltophilia by using parallel flame ionization detector (FID)/mass spectrometry (MS). The GC×GC plots obtained for a reference sample of bacterial fatty acid esters and a bacteria sample (S. maltophilia) were very similar to those obtained by using thermal modulated GC×GC. The parallel FID/MS set-up is useful since the MS allows identification and confirmation, while the FID allows comparison of the relative fatty acid composition with existing databases. The data show that flow modulated GC×GC-FID/MS method can be applied in a routine environment and offers interesting perspectives for chemotaxonomy of bacteria.

Flow modulation of methane-doped carrier gas is used to visualize the second dimension hold-up time in GC x GC continuously throughout the run. This provides an internal reference of hold-up time and presents a straightforward means of examining retention in each dimension of GC x GC. Retention factors on similar and dissimilar column pairs are examined. Stationary phase bleed is shown to be retained by the second dimension column.

The main purpose of this paper is to describe a new experimental setup for testing static and dynamic behav-iour of the AQUAI-MOD® hydraulic controller coupled with a standard PRV, as well as to develop mathe-matical models which represent static and dynamic properties of such a system. The controller has been ex-perimentally tested to assess its performance in different conditions and operating ranges. The device in all cases has showed good performance by modulating the outlet pressure as expected between two points corre-sponding to the minimum and the maximum flow. The mathematical models of the controller have been im-plemented and solved using the Mathematical software package to represent both steady state and dynamics conditions. The results of the steady state model have been compared with experimental data and showed a good agreement in the magnitude and trends. The steady state model can be used to simulate the behaviour of a PRV and the AQUAI-MOD® hydraulic controller in typical network applications. It can be also used at the design stage and to compute the required adjustments for the minimum and maximum head set points before installing the controller in the field. Subsequently, a dynamic model of the PRV and the AQUAI-MOD® hy-draulic controller system has been developed and solved. Again the dynamic model showed a good agreement with the experimental data. The main time constant in the system model corresponds to the movement of the main element of the PRV. The research presented here has been carried out within the Neptune project (www.neptune.ac.uk) which is a Strategic Partnership between EPSRC, ABB, Yorkshire Water and United Utilities.

One of the predicaments of traditional well testing is the requirement of shutting-in a well to conduct a pressure buildup test for the purpose of obtaining well and reservoir properties. This deterrent factor is more prominent in prolific wells due to loss of revenue and problems associated with crossflow or when bringing a well back on production. Moreover, in case of commingled reservoirs, conventional buildup provides only average values of permeability, skin, and pressure. An innovative periodic well testing technique named WTPL (Well Testing by Production Logging) has been developed in which a cyclic wave function is imposed in the wellbore by modulating the flowrate. The analysis of the acquired rate function and the resulting pressure wave then provides formation characteristics such as permeability and skin in the vicinity of the well. This technique eliminates the disadvantage of shutting-in a well and maintains the production with a modulating periodic pattern. In addition, the WTPL can be easily applied to commingled reservoirs to estimate the individual permeability and skin for each layer. This effort has also resulted in the development of a downhole flow modulation tool capable of creating the cyclic flow patterns needed for the new testing method.

The sections in this article are Introduction Dynamic Kinetic Model General Approaches to Reactor Modeling Analysis and Optimization of Cyclic Processes Inlet Composition and Temperature Modulation Partial Oxidation in Fluidized-Bed and Riser Reactors Dynamic Phenomena in a Fixed-Bed Reactor Forced Unsteady-State Processes in Fixed-Bed Reactors Reverse-Flow Operation Migration of a Reaction Zone through a Reactor Network Inlet Temperature Modulation Flow Modulation in Three-Phase Reactors Periodically Operated Adsorptive Reactors Chromatographic Reactors Flow-Reversal Adsorptive Reactors Pressure-Swing Reactors NOx Storage Reduction Systems Stabilization of Unstable Steady States Keywords: unsteady-state reactors; reactor modeling; inlet compositions; temperature modulation; flow modulation; reverse flow reactors; periodic flow reversal; chromatographic reactors; pressure-swing reactors