Instantaneous Reaction Research Articles

In-situ synthesis of ZrC in Cu melts using the graphite as the source of C

In this work, ZrC particles have been successfully synthesized in the Cu melts using graphite as the source of C. It is considered that the instantaneous reaction between Zr and C which can realize the reactive wetting of Cu and graphite is attributed to the effective introduction of graphite into the melts. However, because it is impossible that all the graphite can contact with Zr in the mixture by the present method, only a fraction of graphite can be reactive wetted and the others will be burned out. As a result, when the Zr/C atomic ratio is 1:1 in the raw Zr-G mixture, Zr will ultimately be excessive for the formation of ZrC. Increasing the Zr/C ratio in the mixture is one of the effective methods to introducing more graphite into the melts. It is found that, besides the synthesis of more ZrC particles, the morphology, size and distribution of ZrC can also be remarkably improved with the Zr/C ratio increasing.

Chemical oxidation methods for treatment of real industrial olive oil mill wastewater

Abstract High organic load (up to 36.7 g O2/L) and the presence of phenolic compounds (up to 0.460 g/L) characterize olive oil mill wastewaters (OMW). The oxidative degradation of the OMW was investigated by means of three methods (ultraviolet light ‘UV’, UV/H2O2 and UV/H2O2/TiO2 using different catalyst concentration). Instantaneous reactions were registered and the degradation occurs on one-step during a few minutes (1–2 min). Phenolic compounds degradation by photocatalytic reaction has occurred in two-step reaction, the first was instantaneous, whereas the second was slower fitting to a second order reaction. For all oxidation systems used, the conversion degree on total organic carbon during the photoreaction time was fitted to pseudo-first order model, registering a reaction constant value equal to 3.72 and 37.9 1/h for UV and UV/H2O2 systems, respectively. In the photocatalytic system the reaction constant values varied along with the catalyst concentration studied (TiO2 concentrations = 0.12, 0.25, 0.50, 1.00, 1.50, 2.00 and 3.00 g/L) among 2.70 and 10.5 1/h.

Lead Chalcogenide Nanoparticles and Their Size-Controlled Self-Assemblies for Thermoelectric and Photovoltaic Applications

We report a facile, room temperature synthesis of PbS, PbSe, PbSxSe1–x, and PbTe nanoparticles and their microscale assemblies by combining a chalcogen solution and a lead halide solution in select thiol–amine mixtures. Selection of an appropriate thiol–amine pair and/or the use of appropriate amine to thiol ratio has demonstrated a size control on nanoparticle self-assemblies ranging from nano- to microscale. Proper washing of these particles has yielded phase-pure and compositionally uniform material with minimal or no presence of any carbonaceous ligands on the particle surface, making it attractive for electronic device fabrication. The resulting PbS material exhibits bandgaps in the range 0.6 eV to as high as 1.2 eV for various assembly sizes. These optical bandgaps confirm the retention of quantum confinement of PbS material even in self-assembled nano/microstructures, which could be an interesting phenomenon for future photovoltaic development. Along with carbon-free, quantum-confined self-assemblies, this chemistry also provides a room temperature and instantaneous reaction route to synthesize individually dispersed PbS and PbSe particles with long chain ligand capping similar to traditional synthesis routes. The PbSe material synthesized from this route shows the ability to alloy with PbS at room temperature in the entire composition range and also demonstrates thermoelectric performance comparable to results in existing undoped PbSe literature.

A novel method of ultraviolet/NaClO2-NH4OH for NO removal: Mechanism and kinetics.

The key step for nitric oxide (NO) removal using oxidation method is to efficiently oxidize NO. This study developed a novel advanced oxidation process (AOP) of ultraviolet light (UV) catalysis of chlorite (NaClO2) to oxidize NO. The production of nitric dioxide (NO2) and photo-production of chlorine dioxide (ClO2) were suppressed by adding ammonium hydroxide (NH4OH). The NO conversion efficiency was 98.1% using UV/NaClO2-NH4OH. Electron spin resonance (ESR) tests confirmed the roles of hydroxyl radical (HO) and oxychloride radical (ClO/Cl2O2) in the oxidation of NO. Kinetics analyses showed that NO flux was significantly enhanced by radical-induced (HO/ClO) oxidation of NO. In the presence of UV, the overall reaction rates (kov1*) were 3-8 times higher than those without UV. The Hatta number, namely the enhanced factor, was calculated in the range of 229-403 and 730-780 corresponding to without and with UV light, suggesting that NO oxidation belonged to fast and/or instantaneous reaction. Thus, the gas-film mass transfer resistance was the rate-determining step. N-containing product was determined as NH4+ and NO3- according to X-ray photoelectron spectroscopy (XPS).

Mixing Time Scale Determination in Microchannels Using Reaction Calorimetry

AbstractMixing time scales are derived from heat flux profiles for an instantaneous and exothermic reaction in a commercially available microreactor. A continuous reaction calorimeter, based on numerous heat flux sensors, is used to record spatially resolved heat flux profiles in steady state. Total volumetric flow rate is varied at constant flow rate ratio and the region of main reaction progress is shifted within the microreactor according to the advancement of the mixing process. Secondary flow patterns, induced by Dean mixing elements within the microchannel at higher flow rates, enhance the mixing. Results display a decrease in mixing time at increased flow rates and energy dissipation rate. Additionally, the passive micromixer is evaluated regarding its efficiency.

Do stock markets witness instantaneous reactions to changes in dividend tax laws: Evidence from India

In this paper, we examine whether the dividend tax law changes in India in 2002 cause any instantaneous stock price reactions. Using high frequency data, we devise a novel method to segregate the impact of a particular stimulus from a series of stimuli. We show that investors did not react instantaneously to the dividend tax law changes. We examine four alternative explanations for this result: first, the demand for dividend paying stocks by tax-advantaged investors is matched by the supply from tax-disadvantaged investors. Second, markets are not efficient to depict any instantaneous reaction. Third, our methodology cannot isolate the effect of a single announcement made as part of a series of announcements. Lastly, there is a time lag before we witness investor reactions. Our results rule out all four alternative explanations. We conclude that dividend taxes are not an important criterion for investors to effect instantaneous stock price reactions.

DO STOCK MARKETS WITNESS INSTANTANEOUS REACTIONS TO CHANGES IN DIVIDEND TAX LAWS : EVIDENCE FROM INDIA

In this paper, we examine whether the dividend tax law changes in India in 2002 cause any instantaneous stock price reactions. Using high frequency data, we devise a novel method to segregate the impact of a particular stimulus from a series of stimuli. We show that investors did not react instantaneously to the dividend tax law changes. We examine four alternative explanations for this result: first, the demand for dividend paying stocks by tax-advantaged investors is matched by the supply from tax-disadvantaged investors. Second, markets are not efficient to depict any instantaneous reaction. Third, our methodology cannot isolate the effect of a single announcement made as part of a series of announcements. Lastly, there is a time lag before we witness investor reactions. Our results rule out all four alternative explanations. We conclude that dividend taxes are not an important criterion for investors to effect instantaneous stock price reactions.

An allosteric switch-based hairpin for label-free chemiluminescence detection of ribonuclease H activity and inhibitors.

To assay enzyme activities and screen its inhibitors, we demonstrated a novel label-free chemiluminescent (CL) aptasensor for the sensitive detection of RNase H activity based on hairpin technology. The specific hairpin structure was a DNA-RNA chimeric strand, which contained a streptavidin aptamer sequence and a blocked RNA sequence. RNase H could specifically recognize and cleave the RNA sequence of the DNA-RNA hybrid stem, liberating the streptavidin aptamer which could be accumulated by streptavidin-coated magnetic microspheres (SA-MP). Then the CL signal was generated due to an instantaneous derivatization reaction between the specific CL reagent 3,4,5-trimethoxyphenyl-glyoxal (TMPG) and the guanine (G) nucleotides in the SA aptamer. This novel assay method exhibited a good linear relationship in the range of 0.1-10 U mL-1 under the optimized conditions. Our results suggested that the developed system was a promising platform for monitoring the RNase H activity and showed great potential in biomedical studies and drug screening.

Detection of hydrogen sulfide in water samples with 2-(4-hydroxyphenyl)-4,5-di(2-pyridyl)imidazole-copper(II) complex using environmentally green microplate fluorescence assay method

Hydrogen sulfide (H2S) is a colorless toxic gas which can be found as HS− in rivers and waste waters especially in the occupational susceptible environment. Herein we synthesized a lophine analogue, 2-(4-hydroxyphenyl)-4,5-di(2-pyridyl)imidazole (HPI), which fluoresces at 410 nm after excitation at 280 nm. HPI has an imidazole ring and a pyridine ring which are capable of forming coordinate bonds with copper (Cu(II)) that cause quenching of HPI fluorescence. We found that HS− can selectively liberate HPI from the complex via formation of CuS, thus, HPI regains its fluorescence properties. Interestingly, the probe was proved to be regenerable. This reaction was used for the development of a fluorescence microplate assay for the determination of HS− in environmental samples. The method was applied to river water samples and was able to detect HS− in concentrations down to 5 ppb with acceptable accuracy (90.3–103.0%) and good precision (%RSD ≤ 4.1). The method showed many advantages over the previously reported ones including instantaneous reaction, simple probe synthesis, high-throughput, high selectivity toward hydrogen sulfide over other ions and sulfur or thiol containing compounds and at last, it complies with the green chemistry rules through using a regenerable probe, aqueous solvents, and miniaturized measurement system.

Mixing and reaction in turbulent plumes: the limits of slow and instantaneous chemical kinetics

We investigate the behaviour of a reactive plume in the two limiting cases of slow and instantaneous chemical reactions. New laboratory measurements show that, whereas the slow reaction between the source and entrained chemical species takes place within the whole volume of each eddy in the plume, the fast reaction develops preferentially at the periphery of the eddies. We develop a new model that quantifies the mixing of the reactive buoyant fluids at the Batchelor scale and thereby the progress of the fast reaction. We present a series of new experimental results that suggest that a critical distance from the source, $z_{crit}$, exists at which the volume of fluid that is entrained from the ambient is equal to that which is mixed within the plume at the Batchelor scale. For $z>z_{crit}$, only a fraction of the entrained fluid is rapidly mixed and reacts with the plume fluid. The results of the new experiments enable us to quantify the distance from the source at which an instantaneous reaction reaches completion, and show that it can be significantly larger than the distance $L_{s}$ at which the stoichiometric dilution of the plume fluid is achieved. In the limit of an instantaneous reaction, the longitudinal profiles of source chemical concentration in the plume depend on $(z_{crit}/L_{s})^{5/6}$. The predictions of the model are validated against the experimental results, and the profiles of source chemical concentration in the plume for slow and fast reactions are compared.

Effects of diffusional constraints on lifetime and selectivity in methanol-to-olefins catalysis on HSAPO-34

Reaction-transport formalisms show that the effects of crystallite size, H+ density, and Si speciation of HSAPO-34 on catalyst lifetime and selectivity in methanol-to-olefins catalysis are all manifestations of diffusional constraints. Both structural catalyst properties—i.e., crystallite size and H+ density—and intrinsic kinetic constants (per H+)—regulated, in silicoaluminophosphates, by Si speciation—affect the severity of these diffusional restrictions. Methanol-to-olefins catalysis on HSAPO-34 occurs by a complex network of autocatalytic reactions in which temporal gradients persist along with spatial gradients inherent to continuous-flow, fixed-bed reactors. Invocation of reaction rates in the interpretation of lifetime and selectivity trends in such systems requires defined quantities averaged in both time and space because measured observables conflate instantaneous reaction rates with spatial and temporal gradients. Quantities defined herein, i.e., total turnovers and cumulative selectivity, provide such rigorous assessments of lifetime and selectivity that permit causative correlation between rates of reactions within the complex network of autocatalytic reactions and material properties of HSAPO-34. Total turnovers decreases with increasing diffusional constraints because dehydrocyclization reactions experience stronger diffusional constraints than olefins methylation, aromatics dealkylation, and methanol transfer hydrogenation. Cumulative selectivity to paraffins increases with increasing diffusional constraints because transfer hydrogenation reactions of methanol, ethylene, and propylene experience stronger diffusional constraints than all other reactions within the complex reaction network. The approaches detailed herein codify the chemical and physical origins of trends in process outcomes with system variables for reaction systems characterized by complex reaction networks and prevailing spatial and temporal concentration gradients.

Stochastic cost-optimization and risk assessment of in situ chemical oxidation for dense non-aqueous phase liquid (DNAPL) source remediation

This study involved development of a computer program to determine optimal design variables for in situ chemical oxidation (ISCO) of dense nonaqueous phase liquid (DNAPL) sites to meet site-wide remediation objectives with minimum life-cycle remediation cost while taking uncertainty in site characterization data and model predictions into consideration. A physically-based ISCO performance model computes field-scale DNAPL dissolution, instantaneous reaction of oxidant with contaminant and with readily oxidizable natural oxidant demand (NOD), second-order kinetic reactions for slowly oxidizable NOD, and time to reach ISCO termination criteria. Remediation cost is computed by coupling the performance model with a cost module. ISCO termination protocols are implemented that allow different treatment subregions (e.g., zones with different estimated contaminant concentrations) to be terminated independently based on statistical criteria related to confidence limits of contaminant concentrations estimated from soil and/or groundwater sampling data. The ISCO model was implemented in the program called Stochastic Cost Optimization Toolkit, which includes modules for additional remediation technologies that can be implemented serially or in parallel coupled with a dissolved plume model to enable design optimization to meet plume-scale cleanup objectives. This study focuses on optimization of ISCO design to meet specified source zone remediation objectives. ISCO design parameters considered for optimization include oxidant concentration and injection rate, frequency and number of soil or groundwater samples, and cleanup criteria for termination of subregion injection. Sensitivity studies and example applications are presented to demonstrate the benefits of proposed stochastic optimization methodology.

Navigating conflict and difference in medical education: insights from moral psychology

Medical students and educators face a myriad of complex moral disagreements and conflicts both in preclinical and clinical training environments. Inability to deal with these conflicts effectively and compassionately can lead to undesirable consequences and threaten important relationships in high-stakes healthcare environments. We suggest that the integration of moral psychology into medical education can help trainees and faculty constructively respond to behavior they may find immoral or misguided. Here we focus on the application of Moral Foundations Theory (MFT), which demonstrates how the instantaneous gut reactions which guide reactionary behavior can be categorized into six foundational categories. These categories offer psychological explanations for human behavior which can help medical trainees and professionals navigate challenging moral conflicts.

Confronting Subconscious Bias: Ethics in the Pediatric Emergency Department.

Physicians are only human. Upon graduating from medical school, physicians take an oath declaring veracity and fidelity toward our patients. We are told to lay aside negative feelings toward patients in exchange for integrity, truth, honor, and compassion. The idea is simple, but following through on it is quite a challenge. Pediatric emergency medicine physicians generally have rapid focused patient interactions, yet even in these brief encounters, instantaneous and subconscious reactions to difficult patients occur. Difficult patients are those who raise negative feelings within the clinician such as anxiety, frustration, guilt, and dislike. Recognition of these reactions and emotions will help physicians understand more about themselves, and assist in interacting more favorably with challenging patients. It is common for doctors to attempt to suppress their human reactions to maintain clinical objectivity, yet these reactions facilitate a better doctor-patient relationship. Allowing ourselves to yield to our emotions help the patient realize that the physician is a human being.

Brown coal char CO2‐gasification kinetics with respect to the char structure part II: Kinetics and correlations

AbstractCoal's physical structure is known to affect high‐temperature coal conversion processes such as gasification or combustion. This paper is Part II of the study of brown coal char structural changes during gasification. Firstly, German Lusatian brown coal was gasified in a laboratory‐scale fluidized bed reactor in CO2 within a temperature range of 800–950 °C at atmospheric pressure. Then, physical structure properties were extensively evaluated by means of various techniques. Char specific surface area and its changes during gasification reaction were evaluated using N2 and CO2 physical adsorption techniques. Adsorption isotherms were also interpreted employing unconventional methods in order to obtain the specific surface areas of pores of different sizes. Gasification kinetics were evaluated employing three widely applied kinetic models: the random pore model (RPM), the volume reaction model (VM), and the shrinking core model (SCM). Finally, the instantaneous gasification reaction rate was correlated with the char structural properties at the corresponding conversion degrees. The closest linear correlation appeared between the gasification reaction rate and the specific surface area of mesopores (as determined by N2 adsorption). Furthermore, correlations of the other structural properties with char conversion are provided. Observed structural changes were compared with the assumptions of the kinetic models.

Car Following Prediction Based on Support Vector Regression and Multi-adaptive Regression Spline by Considering Instantaneous Reaction Time

Car following modeling is one of the major issues in microscopic traffic simulation, and the accuracy and reliability of microscopic simulation models highly depend on the models. This research used a highly efficient method of regression for car following modeling such as support vector regression and compared it with multi-adaptive regression spline method as a nonparametric method. Meanwhile, the factors of “speed” and “distance to the following car” were used as the model’s inputs and it was proved that the accuracy of support vector regression model exceeded that of multi-adaptive regression spline. Driver’s reaction time is another unavoidable factor in car following modeling, which varies based on driver–vehicle features and traffic conditions. The research determines this value with respect to the time lag between the diagrams of the following and leading cars distance, the speed of the following car, and the execution of support vector regression model. The model was then implemented using the microdata of a highway traffic flow in the USA for 3 lanes. The research shows that the proposed model has a proper validity after entering driver’s instantaneous reaction time, which is based on the proximity of the results to the real condition of car following in simulation. A comparison was made between the simulations carried out using traditional models and the models proposed in this research. The results can be considered as a basis for other studies on car following modeling and microscopic traffic simulation in highway field.

Lesser lower extremity mechanical loading associates with a greater increase in serum cartilage oligomeric matrix protein following walking in individuals with anterior cruciate ligament reconstruction

BackgroundAberrant mechanical loading during gait is hypothesized to contribute to the development of posttraumatic osteoarthritis following anterior cruciate ligament reconstruction. Our purpose was to determine if peak vertical ground reaction force and instantaneous vertical ground reaction force loading rate associate with the acute change in serum cartilage oligomeric matrix protein following a 20-minute bout of walking. MethodsWe enrolled thirty individuals with a unilateral anterior cruciate ligament reconstruction. Peak vertical ground reaction force and instantaneous vertical ground reaction force loading rate were extracted from the first 50% of the stance phase of gait during a 60-second trial. Blood samples were collected immediately before and after 20 min of treadmill walking at self-selected speed. The change in serum cartilage oligomeric matrix protein from pre- to post-walking was calculated. Stepwise linear regression models were used to determine the association between each outcome of loading and the change in serum cartilage oligomeric matrix protein after accounting for sex, gait speed, time since anterior cruciate ligament reconstruction, graft type, and history of concomitant meniscal procedure (ΔR2). FindingsLesser peak vertical ground reaction force (ΔR2 = 0.208; β = −0.561; P = 0.019) and instantaneous vertical ground reaction force loading rate (ΔR2 = 0.168; β = −0.519; P = 0.037) on the anterior cruciate ligament reconstructed limb associated with a greater increase in serum cartilage oligomeric matrix protein following 20 min of walking. InterpretationMechanical loading may be a future therapeutic target for altering the acute biochemical response to walking in individuals with an anterior cruciate ligament reconstruction.

Role of chemical reaction and drag force during drop impact gelation process

An instantaneous chemical reaction and solidification have been experimentally explored during sodium alginate drop impact on calcium chloride liquid pool through a high-speed imaging system. Here, different concentrations of sodium alginate are used to study the effect on gelation process. As soon as the alginate drop touches the calcium chloride pool, a crosslinking polymerization reaction starts under the liquid pool surface. The consequence of crosslinking is rapid formation of calcium alginate gel which denotes instantaneous freezing of liquid drop. The drop impact solidification immediately results in the formation of a strong gel layer in front of it which is having significant role in spherical shape recovery. This layer formation is favoured by increasing sodium alginate concentration in the drop and thus crater growth is hindered also. The initial reaction time which is determined as soon as the drop touches the surface, is found to be dependent on the drop kinetic energy. However, the drop gelation time reduces with drop concentration and it controls the final shape and morphology of gel. Such reduction in gelation time is inferred from the enhanced rate of crosslinking reaction. The motion of liquid drop through liquid pool while interacting with the surroundings influences the drag around the spherical drop. The shape evolution in the solidifying gel is governed by the dynamics between the fluid drag and chemical reaction. The morphology of the gel surface has also been studied and its roughness variation has been measured from fractal box counting method.

Diffusivity ratio effect on the onset of the buoyancy-driven instability of an A + B → C chemical reaction system in a Hele-Shaw cell: Asymptotic and linear stability analyses

The effects of an A + B → C chemical reaction and different diffusivity on the onset of the buoyancy-driven instability in a Hele-Shaw cell are analyzed theoretically. For an instantaneous chemical reaction system, new concentration and density fields are derived, and based on the density profiles, asymptotic stability characteristics are analyzed. Also, using the linear stability theory, we derive new stability equations and obtain the onset time of instabilities by solving the linear stability equations theoretically and numerically. As expected, the onset instabilities are dependent on the various parameters, such as the diffusivity ratio, reactant concentration ratio, and densification coefficient ratio. Through the asymptotic analysis, we propose that the system can be gravitationally unstable without an adverse density gradient due to the double diffusive effects. In addition, a newly proposed stability condition is tested through systematic linear stability analysis. The linear stability analysis shows that the effects of different diffusivities accelerate and retard the onset of instabilities and induce them without an adverse density gradient. The present asymptotic and linear stability analyses are in good agreement.

Normal variants of ductus venosus spectral Doppler flow patterns in normal pregnancies

Objectives: Ductus venosus (DV) Doppler examinations in pregnancy have a widespread use for several important indications and play a crucial role in order to determine the fetal well-being. DV is usually visualized by the color Doppler mapping. We observed the instantaneous spectral flow type changes in pulsed Doppler examinations in spite of performing with the correct technique published by several authors. The variability of the pattern makes the sonographer/physician to be unsure for the correct placements of the sample gate despite fulfilling the all the criteria required for the vessel sampling. It is aimed in the study to define variations of the normal DV spectral flow types in the duration of the pulsed Doppler examinations instead of in a single cardiac cycle in normal pregnancies.Methods: This prospective study was conducted between January 2016 and February 2017. Wide-band Doppler technique was used for color mapping of the DV. Normal spectral Doppler waveforms in pregnancies are classified as types. When DV spectral flow pattern was not in the standard type, the spectral flow patterns were obtained from not only the umbilical artery and/or middle cerebral artery. Maximum and minimum blood flow velocities in the umbilical vein are measured. All Doppler examinations are performed by a single experienced specialist (CG), who had been certificated for DV flow and Doppler examinations by the Fetal Medicine Foundation.Results: A total of seven types of flow patterns were recorded during the study period and DV flow patterns were divided into two main categories as classic flow pattern and the other patterns. The classic pattern was observed in 160 (99.4%) cases in the first trimester, 495 (94.1%) cases in the second trimester and 206 (60.8%) cases in the third trimester.Conclusions: We think that the fetal circulation is complicated more than estimated. There might be some endocrine agents released in the instantaneous physiologic reactions and changing the venous return abruptly or due to decreasing of the cardiac output directed to the placenta after 34 weeks influence the volume of the circulating blood in the fetus and so thereby the flow velocities instantaneously. The spectral waveform recognition approach is not reliable to identify if the DV spectral Doppler pattern is not the classic (standard) type and the DV should be visualized by wide-band color Doppler techniques particularly in the third trimester for the pulsed Doppler examinations. Studies are needed to evaluate the normal spectral variants of the flows correlated with the physiological compensatory mechanisms.