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• Pulse-width modulation (PWM) is proposed to control subcritical R744 ejectors. • PWM is also proposed to control subcritical R744 ejector motive nozzles. • Subcritical PWM motive nozzle is as effective as a high-pressure expansion valve. • PWM ejector controls the high pressure effectively in transition regime. • PWM ejector increase COP by up to 7.9 % compared to a high-pressure expansion valve. The target of this study is to experimentally compare the performance of three different expansion devices for small-capacity subcritical R744 vapour-compression refrigeration units. The first considered expansion device was the conventional high-pressure expansion valve, which was selected as the baseline. The second assessed expansion device was a two-phase ejector for expansion work recovery whose refrigerant flow was modulated via the pulse-width modulation (PWM) strategy. Finally, the PWM approach was employed for controlling the refrigerant flow of the ejector motive nozzle while the refrigerant was not permitted to be drawn by the ejector suction nozzle. The results showed that the motive nozzle controlled via PWM effect offers similar effectiveness to a conventional high-pressure expansion valve in the subcritical regime. Furthermore, it was observed that the PWM ejector is able to control the high pressure effectively while increasing the coefficient of performance (COP) by up to 5.3 % without and by up to 7.9 % with overfed evaporator compared to the baseline in the transition regime. The results also showed that the installation of the conventional high-pressure expansion valve is not necessary. Finally, the yearly performance of the aforementioned expansion devices was assessed in five different locations, i.e., Athens (Greece), Phoenix (USA), New Delhi (India), Riyadh (Saudi Arabia) and Bangkok (Thailand). The outcomes revealed that the PWM ejector allows for a higher in yearly average COP (COP yearly avg) from 4.9 % (in Athens) to 11.8 % (in Bangkok) over the baseline. [ABSTRACT FROM AUTHOR]

• Influence of heat sink temperature on PWM ejector and system performance is studied. • Influence of compressor speed and evaporator overfeeding is also studied. • PWM ejector with overfed evaporator shows COP increases up to 15.1% over basic unit. • PWM ejector shows COP enhancements up to 10.2% compared to passive ejector. • PWM ejector offers higher COP improvements than its currently available competitors. Ejector-equipped transcritical R744 condensing units are believed to lead to a low-to-zero commercial refrigeration sector. In order to overcome the persisting barrier to their wider adoption represented by the lack of an affordable ejector control technique, the novel pulse-width modulation (PWM) ejector, being low cost, simple and invulnerable to clogging was recently implemented. However, additional experimental evaluations are needed. Therefore, in this experimental work the performance of two PWM ejector-equipped transcritical R744 condensing units, i.e. with and without overfed evaporator, was carried out. The experimental assessment was implemented at the medium temperature (MT) of about -5 °C, heat sink temperatures from 30 °C to 40 °C and compressor speeds from 40 Hz to 60 Hz. The outcomes obtained revealed that the PWM ejector can effectively control the high pressure in transcritical operating conditions, regardless of the selected heat sink temperature and compressor speed. In addition, at the same cooling capacity, the PWM ejector-equipped R744 system was found to permit energy savings between 7.0% and 11.1% without overfed evaporator and between 11.5% and 16.3% with overfed evaporator compared to the standard R744 unit (i.e. with vapour by-pass valve and without ejector), respectively. Finally, higher values of coefficient of performance (COP) were found to be offered by the PWM ejector compared with its today's available competitors. [ABSTRACT FROM AUTHOR]

The conventional reverse fill/flush flow modulation for comprehensive two‐dimensional gas chromatography requires a bleed capillary column to be connected to the outlet of the modulator channel. The purpose of this capillary, which does not contain the stationary phase, is to provide pressure resistance to the modulator channel flow. In this way, the desired modulator volumetric flow can be achieved, and channel over‐filling can be avoided. Normally, the length and the internal diameter of the bleed capillary are chosen so as to obtain the modulator flow that is close to the flow of the first separation column. Thus, for any chosen set of chromatographic conditions, the required dimensions of the bleed capillary can be completely different, making the two‐dimensional gas chromatography method development tedious and generating additional costs in consumables and analyst time. In this work, a tuneable pressure source generating a suitable backpressure was used instead of the fixed bleed capillary which has the advantage of the possibility to freely adapt the pressure resistance and generate the required modulator channel flow for any conditions. This set‐up has been evaluated and compared in terms of the impact on the modulation performance to the set‐up involving a fixed bleed capillary demonstrating comparable performance. [ABSTRACT FROM AUTHOR]

Spatially resolved fluid-flow modulation and its corresponding integration becomes a crucial aspect to consider when designing high-performing paper-based analytical devices. As such, high demand exists for cost-effective techniques able to selectively control flow in patternable regions of the device. In this regard, a solution composed of potassium alum and animal glue; sizing materials used in the fabrication of calligraphy Xuan paper, is successfully adapted for the first time in a revolutionary approach to efficiently modulate the capillary flow in paper microfluidic channels. Flow delays are achieved by coating the substrate systematically through the variation of parameters such as the ratio of alum to glue, the concentration of alum-glue in the solution, and the number of subsequent coating layers of alum-glue. Moreover, digitized patterning with alum-glue is developed to achieve programmable wicking profiles of accelerating, decelerating, and quasi-linear flow displacement by alternating coated and uncoated zones in the channel. Additionally, the influence of alum-glue when performing biometric assays is investigated by performing a horseradish peroxidase activity colorimetric assay and found to have negligible effects on reading, where a negligible difference of 5.2% was observed in an assay performed in a coated paper substrate, compared to an uncoated one.

This study examines how the height and width of peaks exiting the secondary column of a comprehensive two-dimensional gas chromatography (GC × GC) separation are affected by the width of the pulse introduced to the secondary column. A flow-modulated GC × GC apparatus was assembled that allowed input pulse widths to be controlled precisely over a range of 10 to 70 ms. GC × GC chromatograms were obtained using secondary columns containing a polyethylene glycol stationary phase with internal diameters of 0.25 and 0.32 mm. The area, height, and width of peaks emerging from the secondary column were found to be accurately modeled by the convolution of a rectangular function with a Gaussian distribution. The rectangular function represents the input pulse, and the Gaussian distribution represents the broadening that occurs in the secondary column. The minimum peak width that could be produced by the secondary column was determined for a wide range of compounds. Injection pulse widths that matched a compound's minimum peak width produced peaks that were 25% wider than the minimum width and had heights that were 76% of the maximum possible peak height. Increasing the injection width significantly above the minimum width yielded substantially broader peaks with only a modest increase (< 25%) in peak height. [ABSTRACT FROM AUTHOR]

The present research is focused on the development of a green and sustainable analytical method, based on the use of headspace solid-phase microextraction (HS SPME), and hydrogen as carrier gas, within the context of fast flow-modulation comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (FM GC × GC-ToFMS), for the investigation of the volatile composition of Capsicum peppers. In such a respect, three different species were analysed: Annuum, Baccatum, and Chinense. Following HS SPME FM GC × GC-ToFMS analysis, a tile-based Fisher-ratio software was used to easily determine compounds that varied the most within the same variety of Capsicum samples. Particular emphasis was also devoted to the aroma profile of the thirty most sample-distinguishing compounds.

Introduction: Post hepatectomy liver failure is the most common cause of death following major hepatic resections with a perioperative mortality rate between 40% to 60%. Various strategies have been devised to increase the volume and function of future liver remnant (FLR). This study aims to review the strategies used for volume and flow modulation to reduce the incidence of post hepatectomy liver failure. Method: An electronic search was performed of the MEDLINE, EMBASE and PubMed databases from 2000 to 2022 using the following search strategy "Post hepatectomy liver failure", "flow modulation", "small for size flow syndrome", "portal vein embolization", "dual vein embolization", "ALPPS" and "staged hepatectomy" to identify all articles published relating to this topic. Results: Volume and flow modulation strategies have evolved over time to maximize the volume and function of FLR to mitigate the risk of PHLF. Portal vein with or without hepatic vein embolization/ligation, ALPPS, and staged hepatectomy have resulted in significant hypertrophy and kinetic growth of FLR. Similarly, techniques including portal flow diversion, splenic artery ligation, splenectomy and pharmacological agents like somatostatin and terlipressin are employed to reduce the risk of small for size flow syndrome SFSF syndrome by decreasing portal venous flow and increasing hepatic artery flow at the same time. Conclusion: The current review outlines the various strategies of volume and flow modulation that can be used in isolation or combination in the management of patients at risk of PHLF. [ABSTRACT FROM AUTHOR]

The present research is focused on the use and evaluation of hydrogen, as a more sustainable alternative to helium, within the context of fast flow modulation comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry. In such a respect, a comparison was made between the two mobile phases in terms of speed and overall chromatography performance. All experiments were carried out by using the following column set: low polarity with dimensions 10 m × 0.25 mm ID × 0.25 µm df and medium polarity with dimensions 2 m × 0.10 mm ID × 0.10 µm df. Fundamental gas chromatography parameters (efficiency, resolution) were measured under different experimental conditions, using the two carrier gases. Efficiency was measured in both the first and second dimensions, using a probe compound under isothermal conditions; after defining the optimum carrier gas conditions, a mixture containing 20 pesticides was analyzed to measure resolution, again in the first and second dimensions, using a temperature program. It was found (as expected) that a similar chromatography performance could be attained when using hydrogen, albeit with a circa 25% reduction in analysis time. Signal-to-noise ratios of the pesticides were calculated, using both carrier gases, with such values generally reduced (on average by 14%) when using hydrogen. Finally, a comparison was made between mass spectral profiles obtained analyzing the pesticides and fatty acid methyl esters using the two mobile phases. Even though mass spectral differences were observed, the ion profiles could be considered generally similar. [ABSTRACT FROM AUTHOR]

Spatially resolved fluid-flow modulation and its corresponding integration becomes a crucial aspect to consider when designing high-performing paper-based analytical devices. As such, high demand exists for cost-effective techniques able to selectively control flow in patternable regions of the device. In this regard, a solution composed of potassium alum and animal glue; sizing materials used in the fabrication of calligraphy Xuan paper, is successfully adapted for the first time in a revolutionary approach to efficiently modulate the capillary flow in paper microfluidic channels. Flow delays are achieved by coating the substrate systematically through the variation of parameters such as the ratio of alum to glue, the concentration of alum-glue in the solution, and the number of subsequent coating layers of alum-glue. Moreover, digitized patterning with alum-glue is developed to achieve programmable wicking profiles of accelerating, decelerating, and quasi-linear flow displacement by alternating coated and uncoated zones in the channel. Additionally, the influence of alum-glue when performing biometric assays is investigated by performing a horseradish peroxidase activity colorimetric assay and found to have negligible effects on reading, where a negligible difference of 5.2% was observed in an assay performed in a coated paper substrate, compared to an uncoated one. [ABSTRACT FROM AUTHOR]

IntroductionPost hepatectomy liver failure is the most common cause of death following major hepatic resections with a perioperative mortality rate between 40% to 60%. Various strategies have been devised to increase the volume and function of future liver remnant (FLR). This study aims to review the strategies used for volume and flow modulation to reduce the incidence of post hepatectomy liver failure.MethodAn electronic search was performed of the MEDLINE, EMBASE and PubMed databases from 2000 to 2022 using the following search strategy “Post hepatectomy liver failure”, “flow modulation”, “small for size flow syndrome”, “portal vein embolization”, “dual vein embolization”, “ALPPS” and “staged hepatectomy” to identify all articles published relating to this topic.ResultsVolume and flow modulation strategies have evolved over time to maximize the volume and function of FLR to mitigate the risk of PHLF. Portal vein with or without hepatic vein embolization/ligation, ALPPS, and staged hepatectomy have resulted in significant hypertrophy and kinetic growth of FLR. Similarly, techniques including portal flow diversion, splenic artery ligation, splenectomy and pharmacological agents like somatostatin and terlipressin are employed to reduce the risk of small for size flow syndrome SFSF syndrome by decreasing portal venous flow and increasing hepatic artery flow at the same time.ConclusionThe current review outlines the various strategies of volume and flow modulation that can be used in isolation or combination in the management of patients at risk of PHLF.

The present research is focused on the proposal of use of flow-modulation comprehensive two-dimensional enantio-gas chromatography (FM eGC × GC) as a valid, flexible, and possibly superior alternative to heart-cutting multidimensional enantio-GC (eMDGC). The latter, a technique of demonstrated utility, is used specifically for the targeted separation of chiral compounds, whereas FM eGC × GC can produce both targeted and high-resolution untargeted information in a single run. It is clearly possible to use eMDGC for untargeted analysis, often with a flame ionization detector (stand-by analysis), to monitor a first-dimension (1D) separation, of much lower peak capacity compared to FM eGC × GC. If eMDGC is used with mass spectrometry (MS), it is normally exploited to monitor the second-dimension (2D) separation. The analytical instrument consisted of automated solid-phase microextraction (SPME), and a low duty-cycle FM eGC × GC system (with time-of-flight MS), equipped with an enantioselective 1D column (2,3-di- O -methyl-6- t -butyl silyl β-cyclodextrin derivative) and a 2D polyethylene glycol one. Ten Marsala wines were subjected to analysis, for the determination of chiral lactones (many at the low ppb level, due to the high concentration capacity of SPME) and for general analyte profiling. In many instances, highly complex chromatograms were attained, with statistical analysis (ANOVA-simultaneous component analysis and partial least squares discriminant analysis) used for sample differentiation. [Display omitted] • A valid alternative to heart-cutting multidimensional GC is proposed. • Enantiomeric and untargeted information was obtained in a single analysis. • Statistical analysis was used for sample differentiation. • About three hundred and thirty volatiles were tentatively identified. [ABSTRACT FROM AUTHOR]

Background: Patients with continuous flow ventricular assist devices (CF‐VADs) are at high risk for non‐surgical bleeding, speculated to associate with the loss of pulsatility following CF‐VAD placement. It has been hypothesized that continuous shear stress causes elongation and increased enzymatic degradation of von Willebrand Factor (vWF), a key player in thrombus formation at sites of vascular damage. However, the role of loss of pulsatility on the unravelling behavior of vWF has not been widely explored. Methods: vWF molecules were immobilized on the surface of microfluidic devices and subjected to various pulsatile flow profiles, including continuous flow and pulsatile flow of different magnitudes, dQ/dt (i.e., first derivative of flow rate) of pulsatility and pulse frequencies to mimic in vivo shear flow environments with and without CF‐VAD support. VWF elongation was observed using total internal reflection fluorescence (TIRF) microscopy. Besides, the vWF level is measured from the patients' blood sample before and after CF‐VAD implantation from a clinical perspective. To our knowledge, this work is the first in providing direct, visual observation of single vWF molecule extension under controlled‐pulsatile shear flow. Results: Unravelling of vWF (total sample size n ~ 200 molecules) is significantly reduced under pulsatile flow (p < 0.01) compared to continuous flow. An increase in the magnitude of pulsatility further reduces unravelling lengths, while lower frequency of pulsatility (20 vs. 60 pulses per min) does not have a major effect on the maximum or minimum unravelling lengths. Evaluation of CF‐VAD patient blood samples (n = 13) demonstrates that vWF levels decreased by ~40% following CF‐VAD placement (p < 0.01), which correlates to single‐molecule observations from a clinical point of view. Conclusions: Pulsatile flow reduces unfolding of vWF compared to continuous flow and a lower pulse frequency of 20 pulses/minute yielded comparable vWF unfolding to 60 pulses/minute. These findings could shed light on non‐surgical bleeding associated with the loss of pulsatility following CF‐VAD placement. [ABSTRACT FROM AUTHOR]

Dynamic reactor operations will gain interest with the increase of intermittent electricity from renewable sources. Periodic operation of catalytic reactors can also be used for kinetic studies with better parameter estimation than steady‐state operation. This methodology is exemplified for the case of acetylene hydrogenation over Pd/α‐Al2O3 using small amplitude flow oscillations. It allows the evaluation of several elementary kinetic parameters from one set of dynamic data for a reaction mechanism based on a single catalytic site. The optimized transient model is able to reproduce the time‐evolution of the reactant and product molar fractions at the outlet of a fixed bed operated with modulations of different amplitudes and frequencies. It further shows that the acetylene conversion is controlled by two steps, the hydrogen adsorption step and the hydrogenation of the surface vinyl intermediate into adsorbed ethylene. [ABSTRACT FROM AUTHOR]

In free-field operation, many aerodynamic systems are confronted with changing turbulent inflow conditions. Wind turbines are a prominent example. Here, the rotation of the rotor blades causes incoming wind gusts to result in a local change in the angle of incidence for the blade segments, which changes the effective angle of attack and can lead to dynamic non-linear effects like dynamic stall. Dynamic stall is known to produce a significant overshoot in the acting forces and thus an increase in loads acting on the wind turbine, leading to long-term fatigue. To gain a better understanding, it is necessary to perform wind tunnel experiments under realistic and reproducible inflow with defined conditions. In this study, a so-called 2D active grid is presented, which allows the generation of defined two-dimensional inflow conditions for wind tunnel experiments. The focus is on generating sinusoidal transversal and longitudinal gusts with high amplitudes and frequencies. Different grid configurations and sizes are tested to investigate differences in the generated flow fields. Transversal gusts imposed in this way can be used to study dynamic phenomena without having to move the object under investigation itself. Inertial effects during force measurements and a changing shadow casting due to moving airfoils in particle image velocimetry measurements are thus avoided. The additional possibility to generate defined longitudinal gusts allows to generate a broad range of reproducible inflow situations like yaw or tower shadow effects during experimental investigations. [ABSTRACT FROM AUTHOR]

The ejector rocket is one of the core components of the rocket based combined cycle propulsion system, and must be capable of variable working conditions. In order to meet technical requirements for RBCC application, the variable duty operating ejector rocket using the gas Oxygen/Kerosene was designed based on the gas pressurized propellant feed systems. Hot firing tests of four different working conditions had been completed. Experimental results show that the designed ejector rocket engine was stable and reliable, and the working parameters met the design requirements, and the working conditions were adjusted quickly. It lays a foundation for the study of the RBCC engine test and the engine technology of large adjustment ratio.

This preliminary research is focused on the task of defining an equivalent standard column set between cryogenic and flow-modulation comprehensive two-dimensional gas chromatography (GC × GC) combined with mass spectrometry (MS). Cryogenic modulation (CM) was carried out by using a loop-type device, while the flow modulator used was a seven-port wafer chip, equipped with an external accumulation loop. Initially, a common low-polarity + mid-polarity CM GC × GC column set was selected (30 m × 0.25 mm ID × 0.25 μm d f + 1.5 m × 0.25 mm ID × 0.25 μm d f), a method was developed, and a GC × GC-MS fingerprint was attained (on a sample of bio-oil derived from coconut fibers). After, a column set with the same stationary phases was selected for the flow modulation GC × GC-MS method (20 m × 0.18 mm ID × 0.18 μm d f + 5 m × 0.32 mm ID × 0.25 μm d f), with the capability to provide a-similar-as-possible separation. A side-by-side measurement of several chromatography parameters (efficiency, peak capacity, resolution, peak widths, retention factors, elution temperatures) was made. Image 1 • A standard column set for flow-modulation GC × GC has been proposed. • A standard column set for cryogenic-modulation GC × GC was also used. • A comparison was made between the flow- and cryogenic-modulation results. • An altogether very similar separation performance was attained. [ABSTRACT FROM AUTHOR]

High pressure in water distribution networks leads to various problems such as increased leakage, bursts and unexpected consumptions. Hence, pressure management plans are implemented using pressure reducing valves (PRVs), tanks and pump stations. In this study, PRVs are applied for pressure management in three different approaches; fixed outlet, time modulation and flow modulation. In fixed outlet PRVs, a steady set pressure is considered for each PRV during the day. A simulation-optimization model is developed to find the optimal set pressures for all PRVs. In time modulation approach, PRVs are able to apply different pressure settings at different hours of the day which results the better control of the hourly pressure fluctuations in the water network. In this approach, optimization of set pressures is carried out. In flow modulation PRVs, the set pressure is regulated according to the average pressure in the network. In addition, in this study a new reliability index is introduced considering the average pressure and hourly pressure fluctuations and their effects on consumer’s satisfaction. This index is considered as an optimization objective function. Finally, comparing the performance of the above approaches shows that flow modulation, time modulation and fixed outlet approach are the most reliable, respectively.

Highlights • New method for the analysis of exhaled breath VOCs by TD-GC × GC-FID/qMS. • Optimisation of flow modulation and dual detection alongside clinical requirements. • Addresses key challenges of using GC × GC for large-scale breath metabolomics. Abstract Precision medicine has spurred new innovations in molecular pathology leading to recent advances in the analysis of exhaled breath as a non-invasive diagnostic tool. Volatile organic compounds (VOCs) detected in exhaled breath have the potential to reveal a wealth of chemical and metabolomic information. This study describes the development of a method for the analysis of breath, based on automated thermal desorption (TD) combined with flow modulated comprehensive two-dimensional gas chromatography (GC×GC) with dual flame ionisation and quadrupole mass spectrometric detection (FID and qMS). The constrained optimisation and analytical protocol was designed to meet the practical demands of a large-scale multi-site clinical study, while maintaining analytical rigour to produce high fidelity data. The results demonstrate a comprehensive method optimisation for the collection and analysis of breath VOCs by GC×GC, integral to the standardisation and integration of breath analysis within large clinical studies. [ABSTRACT FROM AUTHOR]

Abstract One of the greatest advancements in the field of gas chromatography (GC) has been the development of comprehensive two-dimensional gas chromatography (GC × GC). As the field of GC evolved from one-dimensional gas chromatography (1D-GC) to heart cutting (GC–GC), followed by the advent of GC × GC, the critical component at the center of this evolution has been the interface between the separation columns. The interface, referred to as the modulator for GC × GC, links the primary and secondary columns. This review covers the evolution of modulator systems from the founding of GC × GC in 1991 by Liu and Phillips, while focusing on the last six years. Since its inception, modulators have evolved into two distinct categories: thermal, and valve-based. The advantages and shortcomings of each category will be covered. Recent developments in the research, development, and commercialization of these various modulators is provided, with a glimpse into future modulator designs. Highlights • The past six years of GC × GC modulator advances are highlighted. • Two classes of modulators are discussed and compared: thermal and valve-based. • Valve-based modulation includes differential flow and flow diversion modulation. • Cryogen free thermal modulation is reviewed, contrasted with cryogen based systems. • Recent advances have allowed valve-based modulation periods as fast as 50 ms. [ABSTRACT FROM AUTHOR]

Graphical Abstract Image, graphical abstract BACKGROUND Continuous-flow ventricular assist devices (CF-VADs) produce non-physiologic flow with diminished pulsatility, which is a major risk factor for development of adverse events, including gastrointestinal (GI) bleeding and arteriovenous malformations (AVMs). Introduction of artificial pulsatility by modulating CF-VAD flow has been suggested as a potential solution. However, the levels of pulsatility and frequency of CF-VAD modulation necessary to prevent adverse events are currently unknown and need to be evaluated. METHODS The purpose of this study was to use human aortic endothelial cells (HAECs) cultured within an endothelial cell culture model (ECCM) to: (i) identify and validate biomarkers to determine the effects of pulsatility; and (ii) conclude whether introduction of artificial pulsatility using flow-modulation approaches can mitigate changes in endothelial cells seen with diminished pulsatile flow. Nuclear factor erythroid 2–related factor 2 (Nrf-2)–regulated anti-oxidant genes and proteins and the endothelial nitric oxide synthase/endothelin-1 (eNOS/ET-1) signaling pathway are known to be differentially regulated in response to changes in pulsatility. RESULTS Comparison of HAECs cultured within the ECCM (normal pulsatile vs CF-VAD) with aortic wall samples from patients (normal pulsatile [ n = 5] vs CF-VADs [ n = 5]) confirmed that both the Nrf-2–activated anti-oxidant response and eNOS/ET-1 signaling pathways were differentially regulated in response to diminished pulsatility. Evaluation of 2 specific CF-VAD flow-modulation protocols to introduce artificial pulsatility, synchronous (SYN, 80 cycles/min, pulse pressure 20 mm Hg) and asynchronous (ASYN, 40 cycles/min, pulse pressure 45 mm Hg), suggested that both increased expression of Nrf-2–regulated anti-oxidant genes and proteins along with changes in levels of eNOS and ET-1 can potentially be minimized with ASYN and, to a lesser extent, with SYN. CONCLUSIONS HAECs cultured within the ECCM can be used as an accurate model of large vessels in patients to identify biomarkers and select appropriate flow-modulation protocols. Pressure amplitude may have a greater effect in normalizing anti-oxidant response compared with frequency of modulation. [ABSTRACT FROM AUTHOR]

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 research is focused on the use of a triple quadrupole mass spectrometer (QqQ MS) coupled with flow modulated comprehensive two-dimensional gas chromatography (FM GC × GC) for a multilevel elucidation of biodegradation potentiality of natural marine microbial populations during a bioremediation (biostimulation) treatment. The crude oil used for the evaluation of the bioremediation process, namely Dansk Blend Pier E1, represents a very complex sample. Hence, in order to understand the metabolic activity of microbial populations during the bioremediation process, a GC × GC system was used. The high separation power has allowed a detailed characterization of the different chemical families; moreover, thanks to the high acquisition frequency of the QqQ MS spectrometer, both full scan and multiple reaction monitoring (MRM) data were acquired in the same run. By using this system, both qualitative analysis of untargeted hydrocarbons mixture (crude oil) and qualitative analysis of biomarker compounds, present in low amount and often hindered under the bulk of the sample (i.e. adamantanes, diamantanes, steranes and hopanes), were performed simultaneously. The bioremediation capability of biostimulated bacteria was evaluated at four (T 4 ), eight (T 8 ) and fourteen (T 14 ) days. Progressive degradation of linear, branched, and aromatic hydrocarbons, adamantanes, and diamantanes has been showed, whereas, results underline the lack of any kind of activity against steranes, and hopanes. [ABSTRACT FROM AUTHOR]

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. Fromobserved 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. [ABSTRACT FROM AUTHOR]

The present paper is focused on the use of a vacuum ultraviolet absorption spectrometer (VUV) for gas chromatography (GC), within the context of flow modulated comprehensive two-dimensional gas chromatography (FM GC × GC). The features of the VUV detector were evaluated through the analysis of petrochemical and fatty acids samples. Besides responding in a predictable fashion via Beer’s law principles, the detector provides additional spectroscopic information for qualitative analysis. Virtually all chemical species absorb and have unique gas phase absorption features in the 120–240 nm wavelength range monitored. The VUV detector can acquire up to 90 full range absorption spectra per second, allowing its coupling with comprehensive two-dimensional gas chromatography. This recent form of detection can address specific limitations related to mass spectrometry ( e.g., identification of isobaric and isomeric species with very similar mass spectra or labile chemical compounds), and it is also able to deconvolute co-eluting peaks. Moreover, it is possible to exploit a pseudo-absolute quantitation of analytes based on pre-recorded absorption cross-sections for target analytes, without the need for traditional calibration. Using this and the other features of the detector, particular attention was devoted to the suitability of the FM GC × GC-VUV system toward qualitative and quantitative analysis of bio-diesel fuel and different kinds of fatty acids. Satisfactory results were obtained in terms of tailing factor (1.1), asymmetry factor (1.1), and similarity (average value 97%), for the FAMEs mixtures analysis. [ABSTRACT FROM AUTHOR]

Unsteady flows of granular media are ubiquitous yet remain largely unexplored. In this research, we apply unsteady flows to strongly segregating granular materials to control the segregation pattern and enhance overall mixing. Size-bidisperse granular mixtures with large size ratios flowing onto a quasi-2D bounded heap form stratified layers of large and small particles when the flow rate is modulated. These layers exhibit better average mixing than the segregated patterns generated by steady feed rates. The mechanisms of layer formation under modulated flow differ from those for spontaneous stratification and are related to changes in the composition of the flowing layer at different stages in each feed cycle. The thickness and length of the stratified layers can be controlled by changing the feed rates and feed cycle durations, which is potentially useful for reducing segregation in industrial processes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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.

Recently, a novel intrasaccular device (contour neurovascular system, contour) was introduced to treat intracranial aneurysms. Contour is placed at thе aneurysm neck and reduces the intraaneurysmal blood inflow. Contour comes in a range of sizes to target different aneurysms. The efficiency of altering flow with contour and the effect of device size have not yet been investigated. Therefore, we studied the effect of the device size with patient-based aneurysm models using 2D digital subtraction angiography (DSA).Three patient-based aneurysm models with necks ranging from 2.7 to 9.7 mm were produced, providing standardized testing conditions. Contours with diameters of 5, 11, and 14 mm were implanted into the models, four of each size. 2D DSA images were acquired before and after implanting contour (15 frames/s, manual contrast injection). After injecting angiographic contrast agent, the DSA signal was recorded over time to calculate the contrast washout time (WOT), which is a measure of flow diversion efficiency.All contour devices caused contrast agent stasis and increased WOT in aneurysm sac (p-value = 0.0005). The median relative WOT was largest for 5-mm contour (6.6 ± 3.2) and similar for 11-mm contour (3.4 ± 2.6) and 14-mm contour (3.2 ± 3.8). The implantation procedure might affect WOT values even for contours of the same size; the overall relative WOT ranged between 1.5 and 10.89.The 5-mm contour showed the longest WOT value in our study, while no apparent difference between 11-mm contour and 14-mm contour was found. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Comprehensive two-dimensional gas chromatography is a technique that is becoming more widespread within the analytical community, especially in the separation of complex mixtures. Modulation in comprehensive two-dimensional gas chromatography can be achieved by manipulating temperature or flow and offers many advantages such as increased separation power, but one underutilized advantage is increased detectability due to the reduction of peak width from the use of a modulator. A flow modulator was used to selectively target analytes for increased detectability with a standard flame ionization detector operated at 100 Hz, without the need for cryogens or advanced modulation software. By the collection of the entire peak volume followed by peak transfer rather than further separation, an increase of 12 times in peak height and detectability was realized for the analytes tested using an internal loop modulator configuration. An external loop flow modulator configuration allowed for more volatile analytes (with k < 5), and demonstrated an analyte detectability enhancement factor of at least 6. The collection loop size can be readily increased with an external loop configuration to accommodate for these naturally broader peaks. This novel flow modulated targeted signal enhancement approach was applied to industrially significant analyses like the analysis of methanol in a hydrocarbon streams. Methanol was detected at 7 ppb with a conventional flame ionization detector and without the need for pre-concentration. [ABSTRACT FROM AUTHOR]

Purpose: To examine the safety and short-term efficacy of the Streamliner Multilayer Flow Modulator (SMFM) in the management of patients with complex thoracoabdominal aortic pathology who are unfit for alternative interventions.Methods: Biomedical databases were systematically searched for articles published between 2008 and 2015 on the SMFM. A patient-level meta-analysis was used to evaluate aneurysm-related survival. Secondary outcomes were all-cause survival, stroke, spinal cord ischemia, renal impairment, and branch vessel patency. Other considerations were the impact of compliance with the instructions for use (IFU) on clinical outcome. Mean values and Kaplan-Meier estimates are presented with the 95% confidence interval (CI).Results: Fifteen articles (3 multicenter cohort studies, 3 observational cohort studies, and 9 case reports) were included, presenting 171 patients (mean age 68.8±12.3 years; 139 men). The mean aneurysm diameter was 6.7±1.6 cm (95% CI 6.4 to 6.9 cm). Technical success reported in 15 studies was 77.2%. Aneurysm-related survival at 1 year was 78.7% (95% CI 71.7% to 84.4%). One-year all-cause survival was 53.7% (95% CI 46.0% to 61.3%). There were no reported cases of spinal cord ischemia, renal insult, or stroke.Conclusion: The SMFM can be safely utilized in some patients with complex thoracoabdominal pathologies provided operators adhere to the IFU. The SMFM is a novel technology with no long-term published data on its sustained effectiveness and a lack of comparative studies. Randomized clinical trials, registries, and continued assessment are essential before this flow-modulating technology can be widely disseminated. [ABSTRACT FROM AUTHOR]

The main objective of the herein described research was focused on performing satisfactory flow modulation (FM), in comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC–MS), using an MS-compatible second-dimension gas flow of approx. 4 mL min −1 . The FM model used was based on that initially proposed by Seeley et al. [3] . The use of limited gas flows was enabled through fine tuning of the FM parameters, in particular the duration of the re-injection (or flushing) process. Specifically, the application of a long re-injection period (i.e., 700 ms) enabled efficient accumulation-loop flushing with gas flows of about 4 mL min −1 . It was possible to apply such extended re-injection periods by using different restrictor lengths in the connections linking the modulator to the auxiliary pressure source. FM GC × GC–MS applications were performed on a mixture containing C 9–10 alkanes, and on a sample of essential oil. GC × GC–MS sensitivity was compared with that attained by using conventional GC–MS analysis, in essential oil applications. It was observed that signal intensities were, in general, considerably higher in the FM GC × GC–MS experiments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The operation of water distribution networks (WDN) with a dynamic topology is a recently pioneered approach for the advanced management of District Metered Areas (DMAs) that integrates novel developments in hydraulic modeling, monitoring, optimization, and control. A common practice for leakage management is the sectorization of WDNs into small zones, called DMAs, by permanently closing isolation valves. This facilitates water companies to identify bursts and estimate leakage levels by measuring the inlet flow for each DMA. However, by permanently closing valves, a number of problems have been created including reduced resilience to failure and suboptimal pressure management. By introducing a dynamic topology to these zones, these disadvantages can be eliminated while still retaining the DMA structure for leakage monitoring. In this paper, a novel optimization method based on sequential convex programming (SCP) is outlined for the control of a dynamic topology with the objective of reducing average zone pressure (AZP). A key attribute for control optimization is reliable convergence. To achieve this, the SCP method we propose guarantees that each optimization step is strictly feasible, resulting in improved convergence properties. By using a null space algorithm for hydraulic analyses, the computations required are also significantly reduced. The optimized control is actuated on a real WDN operated with a dynamic topology. This unique experimental program incorporates a number of technologies set up with the objective of investigating pioneering developments in WDN management. Preliminary results indicate AZP reductions for a dynamic topology of up to 6.5% over optimally controlled fixed topology DMAs. [ABSTRACT FROM AUTHOR]

Comprehensive two-dimensional gas chromatography (GC×GC) modulators normally transfer primary column effluent to the head of the secondary column as a series of sharp pulses. Such pulses are produced with time-varying temperature gradients in thermal modulation or with time-varying flow patterns in flow modulation. Thermal modulators produce narrow peaks at optimal flow rates, but require large amounts of consumables or a highly engineered heating/cooling system. Flow modulators involve simpler hardware and no additional consumables. However, flow modulators require a large increase in secondary column flow or transfer only a small portion of the primary effluent to the secondary column. This study examines a new method of producing GC×GC separations with a flow modulator. Instead of injecting narrow pulses, the modulator transfers primary effluent to the secondary column in the form of an intricate injection pattern. The detector signal is deconvoluted and converted to a two-dimensional chromatogram. The high duty cycle of the technique (>50%) leads to deconvoluted peaks with twenty times greater intensity than those produced by conventional modulation with a Deans switch modulator. Pattern modulation can be produced without requiring elevated carrier flows. This study evaluates the efficacy of pattern modulation GC×GC by analyzing a standard mixture of 43 oxygenated organic compounds and an E85 fuel sample. [ABSTRACT FROM AUTHOR]

The present research is focused on the use and evaluation of a novel helium ionization detector, defined as barrier discharge ionization detector (BID), within the context of (low-)flow modulation comprehensive two-dimensional gas chromatography (FM GC × GC). The performance of the BID device was compared to that of a flame ionization detector (FID), under similar FM GC × GC conditions. Following development and optimization of the FM GC × GC method, the BID was subjected to fine tuning in relation to acquisition frequency and discharge flow. Moreover, the BID performance was measured and compared to that of the FID, in terms of extra-column band broadening, sensitivity and dynamic range. The comparative study was carried out by using standard compounds belonging to different chemical classes, along with a sample of diesel fuel. Advantages and disadvantages of the BID system, also within the context of FM GC × GC, are critically discussed. In general, the BID system was characterized by a more limited dynamic range and increased sensitivity, compared to the FID. Additionally, BID and FID contribution to band broadening was found to be similar under the operational conditions applied. Particular attention was devoted to the behaviour of the FM GC × GC-BID system toward saturated and aromatic hydrocarbons, for a possible future use in the field of mineral-oil food contamination research. [ABSTRACT FROM AUTHOR]

The present research is focused on the development of a flow-modulated comprehensive two-dimensional gas chromatography–triple quadrupole mass spectrometry (FM GC × GC–MS/MS) method for the determination of classes of aromatic organic sulphur compounds (benzothiophenes, dibenzothiophenes, and benzonaphthothiophene) in heavy gas oil (HGO). The MS/MS instrument was used to provide both full-scan and multiple-reaction-monitoring (MRM) data. Linear retention index (LRI) ranges were used to define the MRM windows for each chemical class. Calibration solutions (internal standard: 1-fluoronaphthalene) were prepared by using an HGO sample, depleted of S compounds. Calibration information was also derived for the thiophene class (along with MRM and LRI data), even though such constituents were not present in the HGO. Linearity was satisfactory over the analyzed concentration range (1–100 mg/L); intra-day precision for the lowest calibration point was always below 17%. Accuracy was also satisfactory, with a maximum percentage error of 3.5% (absolute value) found among the S classes subjected to (semi-)quantification. The highest limit of quantification was calculated to be 299 μg/L (for the C1-benzothiophene class), while the lowest was 21 μg/L (for the C4-benzothiophene class). [ABSTRACT FROM AUTHOR]