Partition System Research Articles

Seguridade social e déficit orçamentário: a reforma estrutural e seus reflexos no trabalho

Social Security is a fundamental right in Brazil, characterized as a public regime in which prevails “partition system”, which may suffer substantial changes in a context of probable structural reform of Brazilian Social Security and in a context of flexibilization of Labour Law. The main justification to those reforms, as the inclusion of capitalization system, is the change of Brazilian demographic shape. The article makes a correlation between Social Security system and the Brazil’s Federal fiscal deficit; however, the General Regime of Social Security (GRSS) from INSS (National Institute of Health and Safety and Social Security) and the whole social security system are not the major expenses of Brazilian Federal Government. There are other matters, as refinancing of public debt and tax exemptions, which prejudice the Federal Government fund raising in Brazil. Concerning labor interests, the alterations on Social Security Law and Labour Law make direct impacts on worker’s life, that they have as perspectives the diminution of legal guarantees, lower access to pension benefits and decrease of quality of life. In the end, the conclusion is that it’s necessary to end up with Federal Government fiscal deficit, to come back to budget surplus, without affecting worker’s quality of life, in a way that it’s possible to equilibrate expenses in affairs that create more costs than Social Security, as far as possible.

A stochastic model for protein localization in Caulobacter crescentus bacterium

Caulobacter crescentus bacterial cells use a minimal three component Par partition system to segregate DNA during asymmetric division. Precise division plane placement is tightly controlled by MipZ protein gradients that are thought to interact with Par proteins. How these complex protein interactions generate precise measurements in the face of stochastic fluctuations is of significant interest. Here, we first developed a detailed computational model used to study key interactions between Par and MipZ proteins that control chromosome segregation. In addition, we developed a minimal intermittent-search model that captured key ParB/ParA interactions in support of chromosome copy movement. Lastly, we found the competition between ParA and MipZ proteins for ParB complex binding sites to be sufficient in order to generate experimentally observed MipZ bipolar gradients. Our models provide a framework to study how the movement of the DNA copy could communicate with the division site placement proteins in Caulobacter crescentus cells.

Performance validation and manufacture feasibility for an advanced constructive system considering facilities integration

The growing demand to save material and energy resources, and increasing concern over environmental issues, are forcing solutions that entail a lower environmental impact of the materials and products used. This is particularly relevant for internal wall partitions which, due to their volume, greatly contribute to the environmental repercussion of buildings. A significant percentage of this impact is waste derived from the integration of plumbing and electricity installations. The present research deals with the development of a new ceramic system for partitions and internal facade sheets that enable the integration of facilities with minimum waste generation.The proposed ceramic system ensures an appropriate thermal, acoustic and mechanical performance. In addition to the design description and manufacturing process, acoustic performance is measured by empirical validation, while thermal performance by numerical simulations via the finite element method (FEM). Mechanical performance is assessed by a set of experimental tests carried out on masonry walls subject to different load types, and by FEM simulation.From the results obtained, it is possible to conclude that the innovative masonry unit fulfills all the thermal, acoustic and mechanical requirements prescribed for partition systems, even improving on the results for conventional solutions.

Determination and Optimisation of Descriptor Values of Safrole by Gas-Liquid Chromatographic Methods and Liquid-Liquid Partition Systems

In recent years, accumulation of harmful organic chemicals in various environmental and biological compartments causes regrettable harmful effects to humans and ecosystems. Therefore, determining their distribution levels and controlling their risks in these compartments is important for environmental risk assessment procedures. However, experimental determination of their distribution for dose-response and exposure assessments needs a large amount of economical, technical, and human resources. Moreover, such requirements are difficult to afford by developing countries like Sri Lanka. As a solution to this problem, Quantitative-Structure Property Relationship (QSPR) method can be used to establish a quantitative relationship between the structures of the compounds and their chemical and physical properties. In this study, Abraham’s solvation parameter model, was used as the QSPR together with experimental values to determine descriptor values for safrole. Safrole is a harmful organic chemical which is used as a flavouring agent, a fragrance agent, and a raw material in many industries including the drug and perfumery. Because sufficient levels of safrole were identified as a carcinogen, the use of safrole was prohibited by United States Food and Drug Administration (US FDA) since 1970. According to the food additive regulations, safrole in soft drinks, beverages, and food must be lower than 1 μg ml-1 .Safrole is a constituent compound of some spices which are being used for commercial beverage productions and is also used widely in the perfumery industry. Here, descriptor values for safrole were determined using gas-liquid chromatographic retention factors combined with liquid-liquid partition coefficients. Isothermal retention factors were determined at 20o C intervals over the temperature range of 60o C to 160o C for poly (cyanopropylphenyldimethylsiloxane) stationary phase with 14% cyanopropylphenyl monomer. Previously measured retention factors for poly (dimethyldiphenylsiloxane) stationary phase with 5% diphenylsiloxane monomer were optimized in this research study, over the temperature range of 80o C to 280o C. Partition coefficients of safrole were determined using eight different totally organic partition systems (n-heptane-formamide, n-heptane-methanol, n-heptane-n,n-dimethyl formamide, n-heptanetrifluoroethanol, n-heptane-dimethyl sulfoxide, isopentyl ether-ethylene glycol, isopentyl ether-dimethylsulfoxide, and n-hexane-acetonitrile). Then the descriptor values were determined using Solver Algorithm in excel using the measured retention factors and partition coefficients. Solver is an algorithm which assigns the values for the descriptors such that the standard deviation between the experimental solute property and the calculated solute property would be minimum. Determined descriptor values for safrole using these stationary phases and solvent systems are E=1.108, S=1.123, A=0.000, L=5.340, B=0.174, B (0)=0.365 and V=1.246. Validity of the descriptors were tested with theoretical models. The determined descriptor values have a small standard deviation (0.068). Therefore, the determined descriptor values will be useful in determining the distribution level of safrole in environmental compartments. Keywords: QSPR, Solvation parameter model, Safrole, Gas-liquid chromatography, Liquid-liquid partition systems

One-step recovery of latex papain from Carica papaya using three phase partitioning and its use as milk-clotting and meat-tenderizing agent

Three Phase Partitioning (TPP) system as an elegant non-chromatographic and bulk separation method was successfully applied for the extraction and recovery of papain from the latex of Carica papaya. The optimized parameters of TPP allowed achieving a purification fold of 11.45 and activity recovery of 134% with 40% (NH4)2SO4, 1.0:0.75 ratio of crude extract: t-BuOH at pH and temperature of 6.0 and 25 °C, respectively. The recovered papain had a molecular weight of 23.2 kDa and revealed maximum activity at pH 6.0 and temperature of 50 °C. The maximum values of Km and Vmax parameters were 10.83 mg mL−1 and 33.33 U mL−1, respectively. The protease with 4 isoforms was stable at 40–80 °C and a pH range of 6.0–7.5 against numerous metal ions and none of them inactivated the recovered protease. Moreover, 10 mM Ca2+ improved 2-folds the activity and half-life of the protease at temperatures from 30 to 50 °C. The milk-clotting activity tests revealed high stability of latex papain at storage, namely at −20 °C compared to 4 °C and 25 °C for up than 5 weeks. As a meat tenderizing agent, it showed promising role under different treatments by improving the texture of tough meat. The findings indicated that one-step TPP system is a simple, quick, economical and very attractive process for fast recovery of latex papain compared to other proposed protocols.

New insights on Pseudoalteromonas haloplanktis TAC125 genome organization and benchmarks of genome assembly applications using next and third generation sequencing technologies

Pseudoalteromonas haloplanktis TAC125 is among the most commonly studied bacteria adapted to cold environments. Aside from its ecological relevance, P. haloplanktis has a potential use for biotechnological applications. Due to its importance, we decided to take advantage of next generation sequencing (Illumina) and third generation sequencing (PacBio and Oxford Nanopore) technologies to resequence its genome. The availability of a reference genome, obtained using whole genome shotgun sequencing, allowed us to study and compare the results obtained by the different technologies and draw useful conclusions for future de novo genome assembly projects. We found that assembly polishing using Illumina reads is needed to achieve a consensus accuracy over 99.9% when using Oxford Nanopore sequencing, but not in PacBio sequencing. However, the dependency of consensus accuracy on coverage is lower in Oxford Nanopore than in PacBio, suggesting that a cost-effective solution might be the use of low coverage Oxford Nanopore sequencing together with Illumina reads. Despite the differences in consensus accuracy, all sequencing technologies revealed the presence of a large plasmid, pMEGA, which was undiscovered until now. Among the most interesting features of pMEGA is the presence of a putative error-prone polymerase regulated through the SOS response. Aside from the characterization of the newly discovered plasmid, we confirmed the sequence of the small plasmid pMtBL and uncovered the presence of a potential partitioning system. Crucially, this study shows that the combination of next and third generation sequencing technologies give us an unprecedented opportunity to characterize our bacterial model organisms at a very detailed level.

The Tcp plasmids of Clostridium perfringens require the resP gene to ensure stable inheritance

Many of the disease-causing toxins of the pathogenic bacterium Clostridium perfringens are harboured on large, highly stable, conjugative plasmids. Previous work has established the requirement of a ParMRC-like partitioning system for plasmid maintenance, but little is known about other mechanisms used to ensure stable plasmid inheritance. The archetypal 47 kb Tcp plasmid, pCW3, encodes a gene, resP, whose putative product has sequence similarity to members of the serine recombinase family of site-specific recombinases. ResP is therefore likely to function to resolve plasmid multimers. Sequence analysis identified that resP genes are present on all C. perfringens plasmid families, suggesting a conserved function in these plasmids. To assess the requirement of resP for the stability of pCW3, deletion mutants were constructed. Deletion of resP from pCW3 resulted in a marked instability phenotype that was rescued upon complementation with the wild-type resP gene. Complementation with resP genes from two different C. perfringens plasmids demonstrated that only closely related resP genes can complement the mutation on pCW3. The function of ResP in vivo was examined using an Escherichia coli model system, which determined that two directly repeated res sites were required for the resolution of DNA and that ResP could resolve multimeric plasmid forms into monomeric units. Based on these findings we concluded that ResP could catalyse the resolution of plasmid multimers and was required for the maintenance of Tcp plasmids within C. perfringens. Overall, the results of this study have significant implications for our understanding of the maintenance of toxin-encoding plasmids within C. perfringens.

Plasmid Localization and Partition in Enterobacteriaceae.

Plasmids are ubiquitous in the microbial world and have been identified in almost all species of bacteria that have been examined. Their localization inside the bacterial cell has been examined for about two decades; typically, they are not randomly distributed, and their positioning depends on copy number and their mode of segregation. Low-copy-number plasmids promote their own stable inheritance in their bacterial hosts by encoding active partition systems, which ensure that copies are positioned in both halves of a dividing cell. High-copy plasmids rely on passive diffusion of some copies, but many remain clustered together in the nucleoid-free regions of the cell. Here we review plasmid localization and partition (Par) systems, with particular emphasis on plasmids from Enterobacteriaceae and on recent results describing the in vivo localization properties and molecular mechanisms of each system. Partition systems also cause plasmid incompatibility such that distinct plasmids (with different replicons) with the same Par system cannot be stably maintained in the same cells. We discuss how partition-mediated incompatibility is a consequence of the partition mechanism.

A Feasible Way to Enhance CBIR using Histogram of Oriented Gradients Method

Content Based Image Retrieval (CBIR) is a creating pattern in Digital Image Processing (DIP) for seeking and recovering the inquiry picture from extensive variety of databases. CBIR structure contain distinctive stages to think and match the highlights and discover the photos from the extensive scale picture databases dependent on visual substance, for example, Color, Shape and Texture as indicated by the client's advantage. To supply the sensible response to the customer inquiry, CBIR gives some keep running of work. Another strategy is arranged in this paper for shading picture ordering by building up the simplicity of SVM framework. A New strategy is proposed on this paper for hue photo ordering by means of misusing the effortlessness of the HOG technique. In this calculation, presently we have proposed a blend of shading, shape and surface highlights. In this methodology, the past work is improved to accomplish better accuracy. In this paper we propose HOG to upgrade picture quality and associated partition system to enhance result than base work.

Lecithin liposomes and microemulsions as new chromatographic phases

Lecithins are phospholipidic mixtures that can be part of microemulsions and liposomes. In this work, ready-to-use preparations of lecithin have been tested as pseudostationary and mobile phases in EKC and LC, respectively. The selectivity of two EKC systems, one based on lecithin microemulsions (LMEEKC) and another on liposomes (LLEKC), and of a LC system based on lecithin microemulsions (MELC) has been evaluated through the solvation parameter model. In all cases, solute volume and hydrogen-bond basicity are the main descriptors that drive the partition process. While solute volume favors the retention of solutes, hydrogen-bond basicity has the contrary effect. In lecithin-based EKC systems the hydrogen-bond acidity of the solute leads to a higher retention while in the lecithin-based LC system a minor retention is produced. The three lecithin systems have been compared through the solvation parameter model to other chromatographic systems, most of them containing phospholipids. Principal component analysis reveals that lecithin systems cluster together with the other EKC systems based on phospholipids, with an immobilized artificial membrane (IAM) LC system, with the octanol/water reference partition system, and with a SDS-based microemulsion. Thus, they all show similar selectivity. However, the great advantage of using the ready-to use lecithin systems is that the laborious liposome preparation is avoided, and that their commercial availability makes them more affordable than IAM LC columns. Finally, taking into account that lecithin has a high semblance to the mammalian cell membranes composition, the ability of the three lecithin systems to mimic the pass of the solutes through the membranes has been evaluated. Experimental determinations have demonstrated that the skin partition of neutral solutes can be easily emulated, especially using the lecithin-microemulsion EKC method. The model is robust and shows good prediction ability.

Abraham model correlation for direct water-to-2,2,5,5-tetramethyloxolane solute transfer partitioning process revisited

ABSTRACT Questions are raised concerning a previously published Abraham model correlation for describing the direct partitioning behaviour of solutes between water and 2,2,5,5-tetramethyloxolane. Numerous errors were found in the numerical values of the solute descriptors used in deriving the published correlation. The Abraham model correlation has been re-determined using the corrected solute descriptors. Principal Component Analysis of our derived water-to-2,2,5,5-tetramethyloxolane correlation with Abraham model correlations for other water-to-organic solvent partition systems confirms the suggestion of Byrne and co-workers that the green solvent 2,2,5,5-tetramethyloxolane can replace the solvent toluene, certainly as far as partition-related processes are concerned.

Application of artificial intelligence to estimate phycocyanin pigment concentration using water quality data: a comparative study

In the present investigation, the usefulness and capabilities of four artificial intelligence (AI) models, namely feedforward neural networks (FFNNs), gene expression programming (GEP), adaptive neuro-fuzzy inference system with grid partition (ANFIS-GP) and adaptive neuro-fuzzy inference system with subtractive clustering (ANFIS-SC), were investigated in an attempt to evaluate their predictive ability of the phycocyanin pigment concentration (PC) using data from two stations operated by the United States Geological Survey (USGS). Four water quality parameters, namely temperature, pH, specific conductance and dissolved oxygen, were utilized for PC concentration estimation. The four models were evaluated using root mean square errors (RMSEs), mean absolute errors (MAEs) and correlation coefficient (R). The results showed that the ANFIS-SC provided more accurate predictions in comparison with ANFIS-GP, GEP and FFNN for both stations. For USGS 06892350 station, the R, RMSE and MAE values in the test phase for ANFIS-SC were 0.955, 0.205 μg/L and 0.148 μg/L, respectively. Similarly, for USGS 14211720 station, the R, RMSE and MAE values in the test phase for ANFIS-SC, respectively, were 0.950, 0.050 μg/L and 0.031 μg/L. Also, using several combinations of the input variables, the results showed that the ANFIS-SC having only temperature and pH as inputs provided good accuracy, with R, RMSE and MAE values in the test phase, respectively, equal to 0.917, 0.275 μg/L and 0.200 μg/L for USGS 06892350 station. This study proved that artificial intelligence models are good and powerful tools for predicting PC concentration using only water quality variables as predictors.

Flexible 3D Model Partitioning System for nD-Based BIM Implementation of Alignment-Based Civil Infrastructure

AbstractThree-dimensional (3D) building information modeling (BIM) models of alignment-based civil infrastructures such as roads, railways, and tunnels are built as an integrated surface model for ...

An efficient and rapid method to extract and purify protein – Liquid Triphasic Flotation system

Microalgae are rich in valuable biomolecules and grow on non-arable land with rapid growth rate, which has a host of new possibility as alternative protein sources. In the present study, extraction of proteins from Chlorella vulgaris via an efficient technique, Liquid Triphasic Flotation (LTF) system, was studied. The optimized conditions in LTF system were 70% v/v of t-butanol, 40% w/v of salt solution, 0.5% w/v of biomass, pH 5.54, 1:1 of salt to t-butanol solution, and 10 min of air flotation time to attain 87.23% of protein recovery and 56.72% of separation efficiency. Besides, the study on recycling t-butanol has demonstrated that only one run was sufficient to maintain the performance of system. The efficiency of LTF in extracting protein has performed better than just Three Phase Partitioning (TPP) system. LTF system is hence an effective protein extraction and purification method with minimum operation unit and processing time.

Optimization of aqueous two-phase partitioning of Aureobasidium pullulans α-amylase via response surface methodology and investigation of its thermodynamic and kinetic properties

Industrial enzymes such as α-amylase must be thermostable and also easily purified/concentrated. Hence, aqueous two-phase partitioning systems (ATPS) was exploited for the partitioning of α-amylase from Aureobasidium pullulans due to its numerous advantages over conventional purification strategy. A. pullulans α-amylase was partially purified using ATPS via response surface methodology (RSM). The potentials of the ATPS-purified enzyme for possible industrial application such as resistance to thermal inactivation was investigated in comparison with the crude enzyme. PEG-6000 was the polymer of choice for ATPS as it resulted in higher purification factor (PF), %yield (Y), and partition coefficient (PC). At optimum levels (% w/v) of 20, 12 and 7.5 for PEG-6000, sodium citrate and sodium chloride respectively, maximum PF, Y and PC of 4.2, 88%, and 9.9 respectively were obtained. The response model validation and reliability were established based on the closeness between the experimented and predicted values. The kinetic and thermodynamic parameters such as Q10, t1/2, kd, D − value, Ed, ΔHd∗,ΔGd∗andΔSd∗ of the ATPS-purified α-amylase indicated that it was thermostable at 50 to 60 °C compared to the crude α-amylase. A thermodynamically stable and ATPS-purified α-amylase from A. pullulans has properties easily applicable for most industrial processes.

A Medium-Term Conflict Detection and Resolution Method for Open Low-Altitude City Airspace Based on Temporally and Spatially Integrated Strategies

The balancing of civil airspace capacities with customer demands is achieved through air traffic management (ATM), which uses decision support tools in ATM systems that are ensured by advanced communications and contemporary navigation technologies. However, uncertainties and perturbations can emerge during low-altitude airspace traffic management when considering plans to gradually open up low-altitude airspace in China. Domino effects of time and space deviations to one trajectory may lead to the generation of other 4-D trajectories (4-D trajectories defined based on a series of sequential waypoints recording three dimensions of spatial information and their relevant time information) due to strong levels of spatiotemporal connectivity between trajectories, rendering management challenging. This paper introduces background information and a literature review about conflict detection and resolution (CD&R) for open low-altitude airspace. From our analysis, a CD algorithm for a spatial grid partition system (SGPS) is presented. A conflict resolution (CR) framework of temporally and spatially integrated strategies including the time scheduling-based technique and vertical change-based technique (VCBT) was applied to the CR process. The CD&R algorithm was tested based on a practical maneuver scenario to check its validity, and an analysis of computational performance levels was conducted through several experiments. Airspace capacities can be enhanced to alleviate local airspace network perturbations through the use of the proposed CD&R algorithm.

Two-step chromosome segregation in the stalked budding bacterium Hyphomonas neptunium

Chromosome segregation typically occurs after replication has finished in eukaryotes but during replication in bacteria. Here, we show that the alphaproteobacterium Hyphomonas neptunium, which proliferates by bud formation at the tip of a stalk-like cellular extension, segregates its chromosomes in a unique two-step process. First, the two sister origin regions are targeted to opposite poles of the mother cell, driven by the ParABS partitioning system. Subsequently, once the bulk of chromosomal DNA has been replicated and the bud exceeds a certain threshold size, the cell initiates a second segregation step during which it transfers the stalk-proximal origin region through the stalk into the nascent bud compartment. Thus, while chromosome replication and segregation usually proceed concurrently in bacteria, the two processes are largely uncoupled in H. neptunium, reminiscent of eukaryotic mitosis. These results indicate that stalked budding bacteria have evolved specific mechanisms to adjust chromosome segregation to their unusual life cycle.

Aqueous two-phase systems for cephalexin monohydrate partitioning using poly ethylene glycol and sodium tartrate dihydrate: Experimental and thermodynamic modeling

The partitioning of cephalexin monohydrate in aqueous two-phase system (ATPS) of polyethylene glycol (PEG) with different molecular weights (1000, 2000, 6000, and 8000) and sodium tartrate dihydrate salt was investigated. Equilibrium compositions of two liquid phases were obtained in each system. The experimental data were correlated using the extended NRTL and a modified UNIQUAC (UNIQUAC+DH) models by adding a Debye-Huckel term (DH) to original models for taking into account the long range forces term of activity coefficient of components. The results show that the molecular weight of the polymer has a considerable effect on the partition coefficient of cephalexin monohydrate. The comparison of results for presented models with the experimental data demonstrates that the investigated thermodynamic models can correlate the equilibrium composition very well. The extended NRTL model with AARD of 0.099 is superior to UNIQUAC+DH.

Use of Aqueous Two-Phase and Three-Phase Partitioning Systems for Purification of Lipase Obtained in Solid-State Fermentation by Rhizopus arrhizus

Background: Purification of enzymes by conventional methods such as precipitation and chromatographic techniques is a costly and time-consuming procedure and may lead to low yields of enzyme activity. Alternative liquid-liquid extraction methods such as Aqueous Two-Phase Systems (ATPS) and Three Phase Partitioning (TPP) are characterized by the high enzyme yields and purification degree. Objective: The objective of this study was the application of partitioning systems ATPS and TPP for purification of lipase produced in solid-state fermentation by Rhizopus arrhizus. Methods: ATPS and TPP were used for purification of lipase, obtained by solid state cultivation of Rhizopus arrhizus. Results: Lipase was isolated with PEG4000/potassium sodium tartrate ATPS and the effect of the system composition, including PEG 4000 and potassium sodium tartrate concentrations on lipase partitioning was studied. When using 30% PEG4000/21% potassium sodium tartrate, lipase was distributed in the top phase, and the highest recovery yield of 217% and purification fold of 6.1 were achieved. It was found that at PEG4000 concentration of or higher than 15%, the enzyme was present in the top polymer-rich phase with a partitioning yield of over 90%. Upon application of TPP for lipase isolation, the effect of t-butanol concentration, ammonium sulfate concentration and pH on enzyme partitioning was investigated. The highest lipase recovery yield of 71% and 19.1-fold purification were achieved in the interfacial phase in the presence of 30% ammonium sulfate saturation with 1.0:0.5 crude extract/t-butanol ratio at pH 7 in a single step. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis and zymographic analysis showed significant purification of lipase by TPP and the presence of two multiple forms of the enzyme. Conclusion: ATPS (PEG4000/ Potassium sodium tartrate) and TPP (1.0:0.5 crude extract/t-butanol ratio, 30% ammonium sulfate saturation, pH 7) proved to be rapid methods for the isolation and purification of lipase and they can be used in downstream processing for industrial preparation of the enzyme.

QSAR characterization of new synthesized hydantoins with antiproliferative activity.

Hydantois have been identified as constituents of a number of pharmacologically active molecules. In the present study, we have examined in vitro antiproliferative activity against human colon cancer cell lines HCT-116 of three series of 3-(4-substituted benzyl)-hydantoins with various substituent attached in position 5 of the hydantoin ring. Since the investigated compounds have recently been synthesized and show antiproliferative activity, a good understanding of the properties of the potential drug responsible for their pharmacokinetics is an important goal for their further development. One of the important properties is lipophilicity. Lipophilicity has been assessed by reversed-phase liquid chromatography (high-performance thin-layer chromatography and high-pressure liquid chromatography) by means of direct and indirect (using calibration curve) methods. Chromatographic lipophilicity indices in addition to calculated logP values were compared by hierarchical cluster analysis. The linear solvation energy relationship approach was used to understand and compare the types and relative strength of the molecular interactions that occur in the chromatographic as well as in the n-octanol-water partitioning systems. Finally, correlation between in silico pharmacokinetic predictors and antiproliferative activity was examined. Preliminary quantitative structure-activity relationship modeling indicates that pharmacokinetic predictors capture only one-quarter of all chemical features that are important for antiproliferative activity itself. Among selected descriptors are chromatographic lipophilicity indices.