Effect Of Different Solutions Research Articles

Rooftop pools - a problem from an acoustic point of view: how to identify and solve it

There is no standard with specific methods for acoustic testing of rooftop swimming pools in Brazil. On the other hand, although the compatible requirement for impact noise from rooftop leisure environments is not the type of noise generated by swimming pools, it is a current requirement in the Brazilian performance standard. To study the subject, evaluate possible solutions and improve the state of the art, this article brings measurement results for impact noise in the same situation without and with the application of an acoustic solution. The study also presents sound pressure level and vibration measurements in an environment below a swimming pool after the application of the acoustic solution. Vibrations were measured as well in the pool structure and in the slab below, making it possible to identify the vibrational behavior of the pool. Measurements of impact noise took place in a situation where the pool is three floors above the last residential unit to verify the influence of technical slabs. With the measured values in the three situations, it was possible to identify the frequency range for which acoustic solutions should be designed for this type of source and to monitor the effectiveness of different solutions.

Enhancement of power density and hydrogen productivity of the reverse electrodialysis process by optimizing the temperature gradient between the working solutions

Reverse electrodialysis (RED) is an emerging technology that converts the salinity gradient energy (SGE) embedded in two solutions of different concentrations into electricity or hydrogen productivity. Given that two solutions containing SGE in nature are often at different temperatures, this study experimentally investigated the effects of the temperature and salinity ratio of the working solutions on the performance of RED systems. The results show that the power density and hydrogen productivity of RED systems could be markedly improved by adjusting the imposed temperature difference on the basis of the salinity gradient. The degree of improvement mainly depends on the magnitude and direction of the temperature difference between the high- and low-concentration solutions. The enhancement effect was more pronounced under a negative temperature difference (NTD) than under a positive temperature difference (PTD). Additionally, the improvement in system performance owing to the temperature difference was not affected by the endothermic or exothermic effects of different solutes in the water. At a NTD of 25℃ and a concentration of 0.1 M aqueous NaOH as the electrode solution a RED system based on LiBr solution with a salinity ratio of 4.5 M/0.02 M as the working solution achieved a maximum power density of 0.754 ± 0.006 W∙m−2 and the highest hydrogen productivity of 1.128 ± 0.019 mol∙m−2∙h−1, which was 15.1 % and 5.5 % higher than the hydrogen productivity under LiCl and NaCl solution conditions, respectively. These results show the great potential of LiBr solution in the field of RED hydrogen productivity.

Experimental study on mechanical aging properties of self‑swelling anchorage bolt under chemical corrosion

ABSTRACT Chemical corrosion is found to influence the strength of grouted rockbolt reinforcement in underground excavations leading to catastrophic. As such, in this paper, we investigated the impact of the chemical corrosion on the new self-swelling anchorage rockbolt, designed by us, during long-term corrosion processes and accelerated corrosion tests with different chemical solutions. The self-swelling anchorage rockbolt uses a self-swelling anchoring agent that hydrates and expands, providing high anchoring force. The impact of pure water, acidic, and salt solutions on the load-bearing capacity and deformability of self‑swelling anchorage bolts was analysed. Additionally, a microscopic XRD component analysis method was used to reveal the changes in microscopic composition of self‑swelling anchoring agents. It was found that after 180 days of accelerated corrosion, pure water and salt solutions had a small effect on the anchorage force of self‑swelling anchorage bolts, whereas the anchorage force of self‑swelling anchorage bolts decreased by 73.4% in an acidic solution with a PH of four. In addition, the deformation capacity of the bolt deteriorates with the time regardless of the chemical solutions. Combined with XRD micro-composition analysis, the effects of different solutions on the mechanical properties of self‑swelling anchorage bolts were as follows in descending order: PH = 4>6% NaSO4>6% NaCl>3% NaSO4 + 3% NaCl>water.

The Study of Remazolam Combined With Propofol on Painless Gastroscopy: A Randomized Controlled Trial

PurposeGastroscopy is one of the most commonly used diagnostic modalities for upper gastrointestinal disorders. Remazolam besylate, a new type of ultrashort-acting benzodiazepine drug, has been less studied in gastroscopy. In this study, we studied the efficacy and safety of remazolam combined with propofol for painless gastroscopy. DesignThis was a single-center, placebo-controlled randomized trial. MethodsOne hundred patients undergoing painless gastroscopy were included in this study and randomly divided into 2 groups (n = 50 per group): the control group (Con group) and the remazolam group (Rem group). Sufentanil, remazolam, and propofol were used to anesthetize the patients, and then, the effects of different solutions on these patients were compared and analyzed. The patient's general condition, vital signs at different times, the dosage of propofol (mg) and additional times, complications, duration of gastroscopy (minutes), recovery time (minutes), length of stay in the recovery room (minutes), and adverse reactions were recorded. FindingsRem group systolic blood pressure was more stable (P < .05). The amount of additional propofol in Rem group was less (P < .05). The incidence of hypotension, bradycardia, and dizziness was lower in Rem group, as well as the time of awakening and stay in the recovery room were shorter (P < .05). ConclusionsRemazolam combined with sufentanil and propofol has less effect on hemodynamics in painless gastroscopy, and the patients have shorter awakening times.

Removal efficiency of a fast setting pozzalan-based bioactive cement: a micro CT study

AimThe aim of this study was to evaluate the removal efficiency of PRMTA and ECMPremixed applied to the coronal third according to the RET by UI and to examine the effect of different solutions on material removal.Materials and methods40 permanent upper central teeth were used to simulate immature teeth. The samples were irrigated with 1.5% NaOCl and calcium hydroxide was placed. Samples were incubated in PBS. Then irrigation was done with 17% EDTA, the samples were randomly divided into 2 groups (n = 20):Group 1: PRMTA, Group 2: ECM Premixed. The materials were placed in the samples. Then the samples were scanned with micro-CT. Materials were removed by UI. Micro-CT scan of the samples was performed. Each material group was divided into 2 subgroups (n = 10): Group1 was MTAD, group2 was irrigated with 10% CA; then micro-CT was performed. Obtained images were positioned in DataViewer and analyzed with CTAn. The obtained data were statistically analyzed in IBM SPSS 25. The significance level was determined as 5%.ResultsThere was no significant difference between the initial volumes of the materials (p > 0.05). The amount of the remaining material after UI was significantly higher in the PRMTA (0.7471%) group compared to the ECM Premixed (0.0093%). There was no significant difference in terms of remaining material after irrigation with MTAD and CA in both groups (p > 0.05).ConclusionA great deal of the materials were removed by UI under the operation microscope. ECM Premixed was removed more effectively compared to the PRMTA. And, acidic solutions did not provide any additional benefit in material removal.

Evaluating the Effect of Different Mouthrinses on Properties of the Enamel and Dental Composite Surfaces

This study investigated the effects of different solutions (artificial saliva, Listerine Cool Mint-alcohol containing and Colgate Plax-alcohol free) on the nanohardness, elastic modulus and surface roughness of enamel surface and composite materials (Admira Fusion, Clearfil Majesty Esthetic and Mosaic Universal). Specimens of 2 mm depth and 5 mm diameter were stored in solutions for 12 h at 37�C. Baseline and final measurements were obtained using a HYSITRON TI 950 TriboIndenter testing machine. The applied force to each specimen increased from 0 to 1000 �N. For SEM images, one sample in each group was covered with a thin layer of mix of gold and palladium using a sputter coater (Quorum Q150R ES, UK). Scanning electron microscopy (SEM) images were taken at 5000� magnifications to evaluate the surface morphology. Statistical analysis for hardness, elastic modulus and roughness was performed by Two-way ANOVA, Benferroni and Tukey HSD at a significance level 0.05. The results of this study showed that the highest value of surface roughness and lowest hardness and elastic modulus were presented by Admira (p[0.001). Listerine caused significantly increased surface roughness (p[0.001) and decreased hardness and elastic modulus parameters (p[0.001). The mouthrinse containing alcohol caused more significant changes in the nanohardness, elastic modulus, surface roughness values of enamel and composite surfaces.

Experimental characterization of energy consumption in 5-axis milling machine and developing optimization strategy

The optimization of machining processes is of paramount significance because of its pivotal role in modern manufacturing. Efficient machining techniques not only enhance product quality but also reduce costs and environmental impacts. This study focuses on the experimental characterization of energy consumption in a 5-axis milling machine and the simulation of possible solutions to reduce it. The first step is to understand the key drivers of energy consumption which is crucial for enhancing energy management and optimization. This was achieved by developing a mathematical model that uses the most common machining parameters as input using a Response Surface Methodology experimental test plan and an analysis of the contributions of the auxiliary systems to the overall energy consumption. As a second step, the effectiveness of different solutions was simulated considering different application scenario, like the type of operations. Such solutions include the introduction of duty cycle strategies for some auxiliary systems and the optimization of process parameters.

Evaluating the color stability of 3D-printed resins against various solutions.

The purpose of this study was to investigate the effect of different solutions on the optical behavior of two types of 3D-printed resin (Detax and Asiga). The samples were randomly divided into 4 groups of cola, orange juice, tea and artificial saliva (control group) in the form of 14 x 10 mm blocks with a thickness of 1.5 ± 0.3 mm (10 samples in each group). By spectrophotometric device, the color of the examined samples was recorded in the CIE system and in three parameters *L (brightness), a* (red-green) and b* (blue-yellow) as the initial record. The color difference of the samples was recorded on 7 and 30 days after immersion as a secondary record. After that, using the formula, the color difference (ΔE) were calculated. T-test also was used to analyze the data. There was no significant difference between the amount of ΔE on 7th and 30th days after exposure to artificial saliva and cola and on 7th days after exposure to orange juice and tea. But on the 30th day, a significant difference was found in orange juice and tea drinks (p<0.05), so that the value of ΔE in Asiga printer was lower than Detax. ΔE changes in orange juice solution were more than other drinks. On the 30th day of immersion in tea drinks and orange juice, Asiga printer had significantly less color difference than Detax printer.

An educational game for teaching osmolarity and tonicity: opinions of dental and medical students.

In health courses, the students must be familiar with the effects of intravenous solutions on cell volume and function, a topic where there can be learning difficulties and misunderstandings. Since educational games can assist in understanding complex concepts, we created a game relating solution osmolarity and tonicity to red blood cell volume that was used in undergraduate Dentistry and Medicine courses. The students, working in groups, completed the game board by indicating the effect of the solutions on the red blood cell volume, classifying the solutions in terms of tonicity and osmolarity. The student indicated that use of the educational game contributed to their understanding of osmolarity and tonicity.

The effect of intraoperative immersion solutions on acellular dermal matrix: Biofilm formation and mechanical property

Acellular dermal matrix (ADM) is generally used on implant-based breast operations; However, it can increase surgical site infection. Many immersion solutions are applied to ADM, however, the most effective solution is unknown. The purpose of this study is to determine the effect of different solutions on the biofilm formation and mechanical properties of ADM. Aseptic porcine-derived ADMs were immersed in 5 different solutions for 30min; sterile normal saline, 10% povidone-iodine, 0.5% chlorhexidine, antibiotics (cefazolin, gentamicin, and vancomycin), and taurolidine. They are transferred to 10ml suspension of methicillin-sensitive/resistant Staphylococcus aureus (MSSA/MRSA) or Staphylococcus epidermidis and an overnight culture was performed. After rinsing and sonication to obtain the biofilm on ADM, colony forming unit (CFU) was measured. In addition, the maximum load before ADM deformation and the elongation length of ADM at the start of the maximum load was determined. Regardless of strains, povidone-iodine, chlorhexidine, and taurolidine group had lower CFUs than the saline group with statistical significance. Meanwhile, the antibiotics group did not show statistical difference from the saline group. Moreover, only taurolidine group showed higher tensile strength (MRSA, p=0.0003; S. epidermidis, p=0.0023) and elongation length (MSSA, p=0.0015) than the saline group. The antibiotics and chlorhexidine group yielded lower tensile strength and elongation length than the povidone-iodine and taurolidine groups. It was suggested that the 10% povidone-iodine or taurolidine solution is effective. In contrast, the antibiotics solution could be considered as an effective intraoperative solution.

Exploring expert perceptions about microplastics: from sources to potential solutions

Concern about plastic pollution, including microplastics, is high amongst European citizens, and effective actions are needed to reduce microplastic pollution. However, there is still uncertainty and debate about the major sources, impacts, and in particular the solutions. The aim of the current study was to gather expert perceptions about the risks of different microplastic sources to the natural environment and human health (measured as the likelihood and severity of negative impacts resulting from exposure), as well as the feasibility and effectiveness of different solutions. Experts were identified as scientists working on plastic. Usable responses were received from 73 experts with an average of 5 years’ experience in plastic research. Experts thought that there was currently stronger evidence for microplastic impacts on the natural environment than on human health, that, accordingly, the risks were higher, and they were more worried about impacts on the natural environment than on human health. Experts perceived tyre particles and textile fibres to be the main sources of microplastics presenting risk for both natural environment and human health. Various solutions were rated as relatively effective and feasible overall. Solutions that were rated as above-average in terms of effectiveness and feasibility included education and awareness programmes, washing machine filters, bans of plastic items, simplified design of products, and circular economy approaches. However, experts were uncertain about the effectiveness and feasibility of recovery and clean-up solutions, with overall ratings for these being below-average in comparison to other solutions earlier in the plastic life cycle. An improved understanding of expert views on these matters could inform the distribution of limited research resources and help prioritise research questions, especially with regard to potential solutions and interventions which will be critical for the success of the UN Plastics Treaty.

Determination of the effective component on hatching media of Echinococcus granulosus eggs

The present study deals with the determination of effective component in the hatching media . it reaveled that there is a large variability in the effects of different solutions on the percentage ofhatching . The hatching index of the different solutions showed that bile was most effective component and respond for 55.3% of hatching . The second factor was sodium bicarbonate ( NaHCO3 ) solution 42.83%, trypsin gave 14.0% of hatching and then the pancreatin which gave10.2% . Each of hydrochloric acid and pepsin solution doesn’t affect the percentage of hatching. The component of Artificial Intestinal Solution ( AIS ) is very important for the completion of hatching process , where the absence of each component resulted in a change of the hatching rate . There were significant differences between the percentage of hatching.

Evaluation of new solution for cardiac graft preservation on cellular model

Evaluation of new solution for cardiac graft preservation on cellular model. Organ transplantation faces a growing shortage of grafts. To deal with this, surgeons have to consider organs from so-called “extended criteria” donors (elderly donors, smokers, donors with co-morbidities…) with increased sensitivity to ischemia-reperfusion injury. To improve preservation of these grafts, two approaches are possible: static preservation or dynamic preservation. Our laboratory has developed and patented a new solution, called LYPS (LYon Preservative Solution), intended for these two situations. The objective of the present study is to demonstrate the superiority of the LYPS compare to the other solutions currently used in clinical practice. In order to simultaneously study the effect of different solutions on cell conservation at different temperatures, we used a “Hypothermal Bioreactor”, specially developed for this work. We determined the impact of 6 different preservative solutions (LYPS, Celsior, UW, custodiol, Plegisol and IGL1) on H9C2 cells. We performed a 20 hours cold (5 °C) or mild hypothermic (20 °C) static preservation and 2 h of warm so-called “reoxygenation” (37 °C). Cell viability was assessed by MTT assay; and PI and Dilc1 staining determined cell necrosis and mitochondrial membrane potential by flow cytometry. We used a new automated cell imaging system (ImageXpress Pico) and metabolic biosensors to evaluate cytosolic NAD+ levels with SoNar and mitochondrial ATP levels modifications with ATeam-mito. It appears that, at the two temperatures studied (5 and 20 °C), the LYPS solution provides better viability at 5 and 20 °C (viability increased by 5.75 and 11.57 times compare to Plegisol). Necrosis after 20 h of preservation reached 17.3% and 13.54% at 5 and 20 °C with LYPS that is statically lower compared to the others solutions used. We also observed a smaller decrease of DYm with the use of LYPS solution. The levels of NAD and ATP were monitored and seem to be less impacted by the 20 hours of preservation in the presence of LYPS compared to the other solutions. All of these data show that the LYPS solution seems superior to the other solutions tested for the preservation of H9C2 cardiac cells, whether at 5 or at 20 °C. The following step is now to evaluate LYPS on heart preservation on porcine preclinical model.

Effect of Different Solutions on Seed Germination and Physiological Changes in Seeds of Lepidium sativum and Miscanthus sinensis

Effect of Different Solutions on Seed Germination and Physiological Changes in Seeds of Lepidium sativum and Miscanthus sinensis

Effect of Different Solutions on the Colour Stability of Nanoparticles or Fibre Reinforced PMMA.

This study aimed to evaluate the colour stability of polymethyl methacrylate (PMMA) denture base reinforced with ZrO2 nanoparticles, E-glass fibres, and TiO2 nanoparticles at various concentrations over 180-day storage in Steradent™ (STD) denture cleaner or coffee (CF). A total of 130 disc-shaped specimens were fabricated at various filler concentrations and divided into four main groups to measure the colour changes. Groups Z, T, and E consisted of PMMA reinforced with ZrO2 nanoparticles, TiO2 nanoparticles, or E-glass fibre, respectively, while Group C consisted of PMMA specimens without filler served as the control group (n = 10). The three reinforced groups were further subdivided according to the filler content (n = 10) added to the PMMA (1.5%, 3.0%, 5.0%, and 7.0% wt.%). Half of the specimens were stored in STD, while the other half was stored in CF for 180 days. A Minolta Chroma Meter was used to measure the colour changes (ΔE) at 7, 30, 90 and then 180 days. The results were assessed using two-way repeated-measures analysis of variance (RM-ANOVA) along with Bonferroni post hoc tests at a p ≤ 0.05 significance level. Significant different colour changes (ΔΕ) were observed between all tested groups and across different time points. TiO2-reinforced PMMA in STD/CF showed the lowest colour stability, while the E-glass fibre-reinforced PMMA in STD/CF showed the highest colour stability. Furthermore, coffee appeared to have the greatest impact on the colour change in comparison to the SteradentTM. The results indicated that the filler type and concentration, type of solution, and length of storage all affected the colour stability of the tested specimens.

The effect of different solutions in tracheal suctioning on the incidence of pneumonia in patients on the ventilator.

Ventilator-associated pneumonia (VAP) is a common nosocomial infection in patients admitted to intensive care units (ICU), leading to prolonged stay in the ICU, increased hospital costs, and mortality. This study aimed to compare the effect of using normal saline with eucalyptus in endotracheal suctioning on the rate of ventilator-dependent pneumonia. For this purpose, a randomized clinical trial study was performed on 120 patients under a ventilator in the hospital ICU. Patients were randomly divided into control and intervention groups. The control group consisted of 60 patients who used 0.9% normal saline to dilute endotracheal secretions. The intervention group also included 60 patients treated with 0.9% normal saline with 5% eucalyptus to dilute endotracheal secretions. The sensitivity of isolated microbes was determined by the diffusion susceptibility test Kirby-Bauer disk protocol. The CDC protocol was used to diagnose VAP. 100 CFU/ml of endotracheal aspiration was considered the differentiation number between the microbe responsible for VAP and colonization. Whenever a VAP guess was made, a blood culture was done. Finally, the incidence of ventilator-associated pneumonia in the two groups was compared. The results showed that the incidence of VAP during using normal saline and normal saline with eucalyptus as a diluent for pulmonary secretions was different between the two groups (P = 0.042). Also, among infected patients with VAP, there was a difference between the types of microorganisms in the two groups (P = 0.019). Seven cases of Klebsiella pneumonia were observed in the control group, while no case of this bacterium was observed in the intervention group. In terms of the prevalence of Pseudomonas (two cases), both groups had a similar situation. These findings can reassure nurses and the treatment team that they can use normal saline solution with 5% eucalyptus during suction to dilute pulmonary secretions.

Multi-Analytical Approach to Study Fresh-Cut Apples Vacuum Impregnated with Different Solutions.

The aim of this study was to evaluate the effect of different solutions for vacuum impregnation (VI) of fresh-cut (FC) apples through an innovative multi-analytical approach. In particular, the individual and synergistic effects of ascorbic acid and calcium lactate on the preservation of freshness of FC apples was assessed through color, texture, microscopy, isothermal calorimetry, and time-domain nuclear magnetic resonance (TD-NMR) evaluations. The analysis was performed immediately after VI and after 24 h of refrigerated storage. The obtained results showed a good preservation of color and higher firmness in the impregnated samples. Concerning the metabolic heat production, a decrease following the VI treatment was observed, especially when the combined solution was used for the impregnation. The TD-NMR studies showed higher changes in terms of signal intensity and transversal relaxation time T2 after 24 h of storage, evidencing the meta-stability of the plant material for its dynamic tissue nature, and the dewatering/impregnation processes evolution until the achievement of dynamic equilibrium.

Analysis of Stress Response and Analgesic Effect of Remazolam Combined with Etomidate in Painless Gastroenteroscopy.

In order to explore more ideal intravenous anesthesia drug in clinical practice, the analgesic effect of remazolam combined with etomidate in painless gastroenteroscopy and its effect on stress response is investigated. A total of 100 patients are selected for the gastric disease screening, and they are randomly divided into the single-drug group and composite group, with 50 cases in each group. Etomidate, mazzolone, and etomidate are used to anesthetize the patients, and then, the effects of different solutions on analgesia, sedation, and stress response are compared and analyzed, and the adverse reactions are improved. The etomidate and red horse azole shimron composite etomidate anesthesia were applied, and the comparative analysis of different solutions of analgesic, sedative effect, and response to stress is conducted. Then, the improvement of adverse reactions is analyzed. The experimental results demonstrate that remazolam combined with etomidate anesthesia can reduce the level of pain mediators and enhance the analgesia and sedation effect. Meanwhile, combined anesthesia can reduce the stress response and adverse reactions of patients and shorten the examination period effectively.

Mapping of consumptive water use by winter wheat in the right-bank part of Сherkasy region

The article considers the issues of mapping and providing users with data on consumptive water use of winter wheat with a probability of 5%, 10%, 25%, 50%, 75%, 90%, 95% for administrative subject. The problem, which is the need to provide farmers with relevant data on consumptive water use of winter wheat and tools for its analysis, is formulated. The study of consumptive water use of winter wheat was carried out by the method of water balance. Statistical processing of data of consumptive water use of winter wheat was carried out by the method of ordinal statistics on the basis of which empirical curves of security of various probability were constructed. On the basis of equally probable values of water consumption, maps of consumptive water use (mm) of winter wheat with probability of 5%, 10%, 25%, 50%, 75%, 90%, 95% for the right-bank part of Cherkasy region were compiled and generalized. Cartograms of consumptive water use of winter wheat were complied by the method of isolines, which were obtained by interpolation at test points. As a result, information on individual meteorological stations was approximated to the entire study area. High complexity of measurement and the need to study the variability of consumptive water use over time and area have led to creation of a number of methods for determining consumptive water use. However, in our opinion, it is more convenient to use directly water consumption data provided by us for the growing seasons with a probability of 5%, 10%, 25%, 50%, 75%, 90%, 95% and presented in the form of cartograms winter wheat water consumption. The information obtained during the study of cartograms can be used to identify factors that affect consumptive water use of winter wheat or to carry out appropriate differentiated agronomic and reclamation measures necessary to achieve the planned yield. Farmers should be interested in precision farming, as they will always be able to evaluate the effectiveness of different solutions to determine the most effective one in specific conditions.

Effects of different solutes on the physical chemical properties of aqueous solutions via rearrangement of hydrogen bonds in water

The Attenuated Total Reflection – Fourier Transform Infrared (ATR-FTIR) spectra of the OH-stretch band in aqueous solutions of inorganic salts and organic materials; Na2SO4, NaCl, NaClO4, NaSCN, trimethylamine N-oxide, urea, poly(ethylene glycol), polyvinylpyrrolidone, and copolymer of ethylene glycol and propylene glycol (Ucon) were studied at various concentrations. The decomposition of the band into four Gaussian components peaking at 3080, 3230, 3400, and 3550 cm−1 fits every compound examined here with essentially flat residuals. These components were viewed as representing four different subpopulations of water with different H-bond arrangements. The experimentally estimated relative contributions of these components depend on solute type and concentration, and correlate strongly with previously reported experimentally measured solvent features of water such as solvent dipolarity/polarizability, π*, solvent H-bond donor acidity, α, and solvent H-bond acceptor basicity, β. We suggest that water includes an ensemble of four different subpopulations of molecules with various hydrogen bond strengths, geometry, and bond defects depending on the solute. This assumption is obviously oversimplified, but for the wide range of solutes examined here we find that a given solute changes the relative amounts of these subpopulations and hence the above solvent features of water. The solvent features, π* and α, in particular, describe a variety of physicochemical properties, such as water activity, osmotic coefficient, relative viscosity, permittivity, and surface tension, of aqueous solutions of various compounds. It follows therefore that all these physicochemical properties of aqueous solutions are determined by the relative amounts of the above subpopulations of water molecules.