Pulsed Valve Research Articles

Cluster Catalysis with Lattice Oxygen: Tracing Oxygen Transport from a Magnetite (001) Support onto Small Pt Clusters

Oxidation catalysis on reducible oxide-supported small metal clusters often involves lattice oxygen. In the present work, we trace the path of lattice oxygen from Fe3O4(001) onto small Pt clusters during the CO oxidation, aiming at differentiating whether the reaction takes place at the cluster/support interface or on the cluster. While oxygen vacancies form on many other supports, magnetite maintains its surface stoichiometry upon reduction thanks to a high cation mobility. In order to investigate whether size-dependent oxygen affinities play a role, we study two specific cluster sizes, Pt5 and Pt19. By separating different reaction steps in our experiment, lattice oxygen can be accumulated on the clusters. Temperature programmed desorption (TPD) and sophisticated pulsed valve experiments indicate that the CO oxidation takes place on the Pt clusters rather than at the interface. Scanning tunneling microscopy (STM) shows a decrease in apparent height of the clusters, which density functional theory (DFT) explains as a restructuring following lattice oxygen reverse spillover.

Bimodal velocity and size distributions of pulsed superfluid helium droplet beams.

We report detailed measurements of velocities and sizes of superfluid helium droplets produced from an Even-Lavie pulse valve at stagnation pressures of 20-60 atm and temperatures between 5.7 and 18.0 K. By doping neutral droplets with Rhodamine 6G cations produced from an electrospray ionization source and detecting the positively charged droplets at two different locations along the beam path, we determine the velocities of the different groups of droplets. By subjecting the doped droplet beam to a retardation field, size distributions can then be analyzed. We discover that at stagnation temperatures above 8.0 K, a single group of droplets is observed at both locations, but at 8.0 K and below, two different groups of droplets with different velocities are detectable. The slower group, considered from fragmentation of liquid helium, cannot be deterred by the retardation voltage at 9 kV, implying an exceedingly large size. The faster group, considered from condensation of gaseous helium, has a bimodal distribution when the stagnation temperatures are below 12.3 K at 20 and 40 atm, or 16.1 K at 60 atm. We also report similar size measurements using low energy electrons for impact ionization, and this latter method can be used for facile in situ characterization of pulsed droplet beams. The mechanism of the bimodal size distribution of the condensation group and the reason for the coexistence of both the condensation and fragmentation groups remain elusive.

Verification of Microwave Effects on Molecular Clusters by Using Supersonic Molecular Jets.

The origin of the specific effect of microwaves on chemical reactions (the microwave effect) was investigated by examining the effect of microwaves on small groups of molecules such as clusters. The origin of the effect was verified by introducing 2.45 GHz microwaves into a system equipped with a supersonic molecular jet and a special microwave feedthrough to record the fluorescence excitation spectrum of molecules. The carrier gas was bubbled through water and introduced into a phenol-filled sample holder to generate phenol-water clusters. Subsequently, it was confirmed that exposure of the phenol-water clusters contained in the molecular jet ejected from the pulse valve to microwave radiation increased the fluorescence derived from the phenol monomer. This is considered to occur because the phenol-water clusters in the molecular jet absorb microwaves and collapse, thereby increasing the abundance of phenol monomers. This result suggests that microwaves affect not only bulk systems but also small groups of molecules, and that local selective heating, which is one of the causes of the microwave effect, may occur.

Properties of toroidal magnetic fields in axial plasma flow on the PF-1000U plasma focus facility

This paper presents the results of studies of plasma flow parameters on the PF-1000U facility. A distinctive feature of this facility is the ability to create profiled initial gas distributions using gas puffs. In the experiments described, a combined system for filling the vacuum chamber with a working gas was used, in which an additional injection of various gases (deuterium, helium, neon and their mixtures) into the axial region of the chamber prefilled with deuterium was performed using a pulse valve. Thus, both the pinching processes and, accordingly, the generation of axial plasma flows and the conditions of their propagation in the background gas of the facility chamber were affected. Regimes with the generation of compact stable plasma formations propagating over long distances were found. The results obtained can be used in laboratory modelling of astrophysical jets from young stellar objects.

Endothelial Dysfunction-related Neurological Bleeds with Continuous Flow-Left Ventricular Assist Devices Measured by Digital Thermal Monitor.

Endothelial dysfunction has been demonstrated in patients with Continuous Flow-Left Ventricular Assist Devices (CF-LVADs) but association with adverse events has not been shown. We used a noninvasive, operator-independent device called VENDYS® to assess vasodilatory function based on digital thermal measurements postrelease of a brachial artery occlusion in ambulatory patients with CF-LVAD (n = 56). Aortic valve opening and pulse perception were also documented before the test. Median duration of CF-LVAD support was 438 days. The VENDYS® test generates a vascular reactivity index (VRI). Outcomes for the CF-LVAD patients were compared between VRI < 1 and VRI ≥ 1. The bleeding events were driven primarily by a difference in neurologic bleeds. Multivariate analysis showed that VRI < 1 correlated with future bleeding events (HR: 5.56; P = 0.01). The C-statistic with the VRI dichotomized as above was 0.82. There was a trend toward a worse survival in patients with poor endothelial function. Endothelial vasodilatory dysfunction measured by a simple test utilizing digital thermal monitoring can predict adverse bleeding events in patients with CF-LVADs.

CVD-diamond nanoparticle synthesis for DLC film application

Diamond-like carbon (DLC) films have been extensively applied as a solid lubricant and as a protective coating due to their attractive chemical, mechanical, and tribological properties. Furthermore, these properties of DLC coatings can be improved with the incorporation of nanoparticles of different materials, especially diamond nanoparticles (DNPs). Herein, the incorporation of chemical vapor deposition (CVD) DNPs was done from a deionized aqueous colloidal solution by using a controlled pulsed valve, which is an innovative aspect of this work. The CVD DNPs were pulverized into the plasma region and incorporated in the DLC films bulk with controllable size particle distribution and density. In addition, an enhanced process to obtain DNPs with suitable size distribution was established by using a high energy ball milling technique, centrifugation, and a special chemical cleaning process. The DLC films were deposited on a metallic substrate via a modified, pulsed DC plasma-enhanced chemical vapor deposition (PECVD) technique, with an additional cathode. X-ray diffractometry (XRD) and scanning electronic microscopy (SEM) techniques showed that an aqueous colloidal solution of high-purity DNPs with a mean diameter of 32 nm was obtained. Dynamic light scattering (DLS) results showed that it is possible to control particle size distribution by varying the milling and centrifugation time lengths. Therefore, a valuable result was that DLC films could be deposited with DNPs by using clean water without affecting deposition rate, the adhesion between the DLC films and substrates, the structural quality of the film, and keeping lower coefficient of friction.

A systematic investigation of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry with dynamic pressure gradient modulation for high peak capacity separations

Dynamic pressure gradient modulation (DPGM) in full modulation mode is optimized for comprehensive two-dimensional (2D) gas chromatography (GC × GC) with time-of-fight mass spectrometry (TOFMS) detection to obtain high peak capacity separations and demonstrate broad applicability for complex samples. A pulse valve introduces an auxiliary carrier gas flow at a T-union connecting the first dimension (1D) column to the second dimension (2D) column. At a sufficiently high auxiliary pressure (Paux) the 1D flow is temporarily stopped. Then, during each modulation period (PM) the valve is turned off briefly, a period termed the pulse width (pw), allowing the 1D effluent to essentially be reinjected onto the 2D column for the modulated separations. Modifications to the modulator assembly are provided to improve performance. Method optimization is demonstrated for a 116-component test mixture by tuning the Paux and the pw. For a PM = 2 s and 1F of 0.10 ml/min, the optimal pw and initial Paux selected were 200 ms and 330.9 kPa (33 psig), respectively. The 30 min separation of the test mixture provided a 1D peak capacity of 1nc = 330 and a 2D peak capacity of 2nc = 15, hence an ideal 2D peak capacity nc,2D = 1nc × 2nc = 4950. Likewise, the 2D peak capacity corrected for undersampling of the 1D separation was 4500 and corrected for both undersampling and sampling variation via statistical overlap theory was 4090. These results provide a 2-fold improvement in peak capacity relative to the previous DPGM study in full modulation mode for GC × GC-TOFMS. The optimized conditions were applied for a variety of applications: diesel fuel, derivatized cow serum, solid phase microextraction (SPME) of coffee headspace, and SPME of river water headspace. Additionally, the fraction of 2D separation space utilized (fcoverage), as defined by the minimum convex hull method, ranged from 0.60 to 0.85. We observed that any fcoverage correction to 2D peak capacity is highly sample dependent, since all samples, except for the diesel sample, were run with the same separation conditions, and yet the fcoverage ranged from 0.60 to 0.80.

Фазоуправляемый вентильно-конденсаторный источник импульсного тока для электротехнологий

Фазоуправляемый вентильно-конденсаторный источник импульсного тока для электротехнологий

Pulse assessment is important with blood pressure measurement in individuals with continuous flow left ventricular assist devices.

While Doppler and cuff blood pressure techniques are prevalent methods of assessing blood pressure in patients with continuous flow left ventricular assist devices, the impact of pulsatility on measurement is not well established. Retrospective chart analysis of clinical variables including pulse perception, blood pressure (Doppler and standard cuff), and aortic valve opening on echo at clinic visit were abstracted. Stable outpatients on continuous flow left ventricular assist devices support with concomitant portable echo assessment were included. Mean average difference was calculated and Pearson's correlation performed for all those patients who had both Doppler and cuff pressure obtained. In all, 74 Heartmate-II patients with a median time from implant of 380 days were analyzed. A pulse was perceived in 82% of patients with persistent aortic valve opening on portable echo and also in 30% of those who had a persistently closed aortic valve. The mean average difference between the Doppler and systolic cuff pressure was ~13 mmHg (r = 0.5, p = 0.004) when a pulse was present and ~11 mmHg when aortic valve was open (r = 0.68, p < 0.0001). Pulse presence seems to reflect aortic valve opening a majority of the time but not always. In the presence of a prominent pulse or persistent aortic valve opening, the Doppler pressure seems to be more reflective of a systolic pressure than mean perfusion pressure. Hence, assessment of pulsatility needs to be incorporated into blood pressure measurement methods for patients with continuous flow left ventricular assist devices.

Identification of the Jahn-Teller active trichlorosiloxy (SiCl3O) free radical in the gas phase.

The Ã2A1-X̃2E electronic transition of the jet-cooled trichlorosiloxy (SiCl3O) free radical has been observed for the first time in the 650-590 nm region by laser induced fluorescence (LIF) detection. The radical was produced by a pulsed electric discharge through a mixture of silicon tetrachloride and oxygen in high pressure argon at the exit of a pulsed molecular beam valve. The LIF spectrum shows low frequency intervals, which we assign as activity in the normally forbidden degenerate v5 ' and v6 ' modes, indicative of a significant Jahn-Teller effect in the ground state. Single vibronic level emission spectra show level dependent spin-orbit splittings in the ground state and Jahn-Teller predictable variations depending on which upper state level is pumped. The measured lower state energy levels have been fitted to a Jahn-Teller model that simultaneously includes spin-orbit coupling and linear and quadratic multimode coupling. In SiCl3O, the Jahn-Teller interaction predominates over spin-orbit effects.

Study on the Effect of Diaphragm Booster on the Pulsed Heat Transfer of Cooling System

This paper has developed a diesel engine cylinder liner and cooling water heat exchange enhancement device, including diesel engine cylinder liner, cylinder liner water cooler, hydraulic accumulator, check valve, diaphragm booster, centrifugal water pump, pulse valve and Conical tube. As well as the pulsating circulation system and booster system composed of equipment. The device heats the heat generated by the diesel engine cylinder liner in a pulsating circulation system through a cylinder circulator in a pulsating circulation system to exchange heat with the external low-temperature seawater. By controlling the opening and closing of the pulsating valve in the pulsating circulation system, fluid is generated in the pipe. Pulsing and hydraulically impacting the diaphragm booster connected near the pulsation valve pipeline, the fluid at the outlet of the diaphragm booster is subjected to hydraulic shock and circulates in a closed booster circuit connected to the diaphragm booster and passes through the cone during the flow. The shaped tube accelerates the fluid to return to the diaphragm supercharger, and the kinetic energy of the fluid is converted into the pressure in the pulsating heat exchange system by impacting the elastic diaphragm of the diaphragm supercharger, so that the pulsating speed is increased. The present invention is to increase the pulsating velocity of the diaphragm. Based on the design of the compressor drive, it improves energy efficiency, avoids the use of high-power water pumps, and saves equipment construction and daily operation.

Pulse safety device with adaptive controller for technical systems with high reliability requirements

To ensure the protection of technical systems against excessive pressure, pulse-safety devices (pilot-operated relief values, or PORV) are used, which differ from spring-loaded safety valves in their increased throughput and high accuracy of operation at set pressures. At the same time, PORVs are less reliable due to the complexity of the design. Their reliability depends on the operability of two valves - pulse and main ones. The pulse valve that controls the entire safety system is still the weakest PORV element. This is especially true for systems that have high safety and reliability requirements, for example, for aerospace technology and the nuclear industry, because the resource of sensitive elements decreases sharply when working in extreme operating conditions. The article proposes a PORV design with redundancy of the valve sensing element by a system in the form of a metal bellows and a slide valve. The reliability values of the standard and proposed PORV designs are analyzed.

Characterisation and modeling of a pulsed molecular beam

Standard techniques used in real-time reaction dynamics experiments, namely photoionization by a pulsed laser and velocity imaging are applied to document the time dependent velocity distribution of 2-hydroxypyridine (2-HP) molecules in a pulsed beam where 2-HP is seeded in either helium or argon. The purpose is to identify features which cannot be assigned to a pure free molecular (effusive in the present case) or a pure continuum (supersonic here) flow regime. The beam is generated in a two stage expansion, where the first stage is driven by a pulsed valve. The experimental work is complemented by simulations. Two phenomena retain the attention: (i) a slow return to the effusive flow regime after the valve opening has generated an intense supersonic flow; (ii) development of a shock wave a short time after the valve opening.

The electronic spectrum of the jet-cooled stibino (SbH2) free radical.

The Ã2A1-X̃2B1 electronic transition of the jet-cooled stibino (SbH2 and SbD2) free radical has been observed for the first time using laser induced fluorescence (LIF) detection. The radicals were produced by a pulsed electric discharge through a mixture of stibine (SbH3 or SbD3) in high pressure argon at the exit of a pulsed molecular beam valve. SbH2 exhibits only three LIF bands, assigned as 21 0, 00 0, and 20 1, with a fluorescence lifetime (τ), which decreases from ∼50 ns for 00 to <10 ns for 21. LIF transitions to the 00 (τ ∼ 2 µs), 21 (τ ∼ 400 ns), and 22 (τ ∼ 75 ns) upper vibronic states of SbD2 were also observed. High-resolution spectra exhibited large spin-rotation splittings and small resolved antimony hyperfine splittings due to a substantial Fermi contact interaction in the excited state. The experimentally determined rotational constants gave effective molecular structures of r0 ″ = 1.724(2) Å, θ0 ″ = 90.38(7)° and r0 ' = 1.693(6) Å, θ0 ' = 120.6(3)°. The ground state bending vibrational levels up to eight quanta (6404 cm-1) in SbH2 and 12 quanta (6853 cm-1) in SbD2 were measured from dispersed fluorescence spectra. All indications are that SbH2 undergoes a dissociative process at low vibrational energies in the excited electronic state.

Rapid desorption of low-volatility compounds in liquid droplets accompanied by the flash evaporation of solvent below the Leidenfrost temperature.

The objective of this work is to study the interaction of methanol droplets with the heated surface for the improved detection of low-volatility and thermally labile compounds by the flash evaporation that occurs below the Leidenfrost temperature. 5 μL solutions of low-volatility compounds in methanol were introduced into the heated tube. Desorbed analytes were ionized in the sealed atmospheric pressure chemical ionization (APCI) source by direct current (DC) corona discharge using air as the reagent gas. The rapid desorption of low-volatility compounds accompanied by the flash evaporation of methanol solvent was observed in the temperature range of 60-100°C. Linear relationships between the signal intensities and the solute concentrations in the range of 0.01-5 ppm for morphine, cocaine, methamphetamine, and amphetamine were obtained at 95°C. The observed rapid desorption of low-volatility compounds below the Leidenfrost temperature would provide useful information in many fields, e.g., the interaction of liquid droplets with heated matter, liquid sample introduction into the injection port of a gas chromatograph, coupling of the flash evaporation with pulse valve operated miniaturized mass spectrometer, etc.

Chemometric decomposition of comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry data employing partial modulation in the negative pulse mode

Partial modulation in the negative pulse mode was optimized for comprehensive two-dimensional gas chromatography (GC × GC) coupled to time-of-flight mass spectrometry (TOFMS). With partial modulation in the negative pulse mode, a flow of auxiliary carrier gas is applied through a pulse valve to a T-junction joining the first (1D) and second (2D) dimension columns for nearly all of the modulation period (PM). This results in dilution of the 1D eluate, followed by briefly turning off the pulse valve for a specified pulse width (pw), effectively “injecting” undiluted 1D eluate onto the 2D column. The raw data has the appearance of 2D separations superimposed on top of the 1D separation. While high peak capacity GC × GC data are produced, there are challenges that needed to be addressed regarding the use of chemometrics for analyte decomposition, identification, and quantification. Herein, these data analysis challenges are addressed using multivariate curve resolution - alternating least squares (MCR-ALS). An isothermal separation of a 15-component mixture of similar compounds is obtained in 20 s using a PM = 250 ms and a pw = 6 ms. Various peak overlap situations were purposely produced to facilitate the chemometric method demonstration. The MCR-ALS chromatographic loadings (peak profiles) were used to determine retention times (tR) and width-at-base (Wb) in both separation dimensions. MCR-ALS readily decomposed 1D × 2D regions for analytes with severe 1D overlap if they were fully resolved on 2D. Decomposition was more challenging for analytes severely overlapped on both GC × GC dimensions when their spectra were similar, though ultimately all 15 compounds were successfully decomposed. Additionally, the 2D concentration peak profiles obtained via MCR-ALS are demonstrated to be reliable for identification and quantifiable. The predicted versus prepared concentration values are in good agreement for two representative analytes, with percent deviation values of −5.6% (±2.2%) for 1-hexene, and 1.8% (±3.4%) for 2-pentanone.

Formation of Al + (C 6 H 6 ) 13 : The Origin of Magic Number in Metal–Benzene Clusters Determined by the Nature of the Core

The identification of highly abundant, “magic” species in the mass spectra of clusters have proven to be valuable in nanoscience, leading to the discovery of new stable species such as fullerenes a...

Multicenter Randomized Controlled Trial of Vitamin K Antagonist Replacement by Rivaroxaban with or without Vitamin K2 in Hemodialysis Patients with Atrial Fibrillation: the Valkyrie Study.

Vitamin K antagonists (VKAs), although commonly used to reduce thromboembolic risk in atrial fibrillation, have been incriminated as probable cause of accelerated vascular calcification (VC) in patients on hemodialysis. Functional vitamin K deficiency may further contribute to their susceptibility for VC. We investigated the effect of vitamin K status on VC progression in 132 patients on hemodialysis with atrial fibrillation treated with VKAs or qualifying for anticoagulation. Patients were randomized to VKAs with target INR 2-3, rivaroxaban 10 mg daily, or rivaroxaban 10 mg daily plus vitamin K2 2000 µg thrice weekly during 18 months. Systemic dp-ucMGP levels were quantified to assess vascular vitamin K status. Cardiac and thoracic aorta calcium scores and pulse wave velocity were measured to evaluate VC progression. Baseline dp-ucMGP was severely elevated in all groups. Initiation or continuation of VKAs further increased dp-ucMGP, whereas levels decreased in the rivaroxaban group and to a larger extent in the rivaroxaban+vitamin K2 group, but remained nevertheless elevated. Changes in coronary artery, thoracic aorta, and cardiac valve calcium scores and pulse wave velocity were not significantly different among the treatment arms. All cause death, stroke, and cardiovascular event rates were similar between the groups. Bleeding outcomes were not significantly different, except for a lower number of life-threatening and major bleeding episodes in the rivaroxaban arms versus the VKA arm. Withdrawal of VKAs and high-dose vitamin K2 improve vitamin K status in patients on hemodialysis, but have no significant favorable effect on VC progression. Severe bleeding complications may be lower with rivaroxaban than with VKAs.

Integration of a Multichannel Pulsed-Valve Inlet System to a Linear Quadrupole Ion Trap Mass Spectrometer for the Rapid Consecutive Introduction of Nine Reagents for Diagnostic Ion/Molecule Reactions.

Gas-phase ion/molecule reactions have been used extensively for the structural elucidation of organic compounds in tandem mass spectrometry. Reagents for ion/molecule reactions can be introduced into a mass spectrometer via a continuous flow apparatus or through a pulsed inlet system. However, most of these approaches enable the use of only a single reagent at a time. In this work, a multichannel pulsed-valve inlet system was developed for the rapid consecutive introduction of up to nine different reagents or reagent systems into a linear quadrupole ion trap mass spectrometer for diagnostic gas-phase ion/molecule reactions. Automated triggering of the pulsed valves enabled these experiments to be performed on the high-performance liquid chromatography (HPLC) time scale. This enables high-throughput screening of several functionalities in analytes as they elute from an HPLC column.

Trapping of C2− in a digital ion trap

In this article we present the production of a pulsed molecular C2− beam and the subsequent trapping of C2− in a digital ion trap (DIT). The anionic molecules were produced in a pulsed discharge valve from acetylene and carbon dioxide gas in a helium carrier. The mass spectrum of the pulsed anion beam is initially recorded using a Wien filter. Subsequently, we measured the mass spectrum using the DIT and its stability diagram. The results are compared to a theoretical description of the trap’s stability conditions. The research is relevant for future laser cooling experiments of trapped C2− and for sympathetic cooling experiments of other anionic species (antiprotons, electrons, anionic atoms and molecules) and are of interest for precision experiments on antihydrogen as performed at the antiproton decelerator facility at CERN.