Positron scattering from structurally related biomolecules.

We report the integral elastic, momentum transfer, and inelastic (positronium formation and ionisation) cross sections for positron scattering from structurally related molecules. The molecules chosen for the current investigation are formamide, formylphosphine, formic acid, N-methylformamide, acetone, acetic acid, and formaldehyde. The cross sections were calculated using the optical potential approach and the complex scattering potential-ionisation contribution method for impact energies between 1 and 5 keV. A sizable repository of data is now available for positron scattering from various atoms and molecules; however, data on the impact of positrons on current targets is still scarce and fragmented. While most cross sections are the first of their kind, we analyze our total cross sections (TCSs) with the previous literature available, which has become attractive to researchers trying to model the tracks of charged particles in matter. TCSs have recently seen a resurgence in popularity thanks to their utility in specifying the mean-free path between the collisions of such simulations. We find good qualitative convergence between experimental and theoretical results below and above the positronium formation threshold. However, around the threshold region, a significant discrepancy is encountered, which can be accounted for due to the experiment's lack of forward angle scattering effect discrimination. This level of agreement evolves to become quantitative at intermediate and higher energies.

Low-Energy Electron Scattering from Pyrrole and Its Isomers.

Low-energy electron scattering from pyrrole and its isomers, such as 2-H pyrrole, cyclopropanecarbonitrile, and Z-2 butenenitrile, is explored in detail in this article. The electron interaction with the target molecules was studied through R-matrix theory. We have used minimal STO-3G and advanced DZP basis sets on a fine energy grid from 0.1 to 12 eV electron energy in the calculation. The properties of the STO-3G and DZP-based targets, such as their ionization energy, polarizability, dipole moment, rotational constant, principal moment of inertia, ground-state energy, and orbital energies, were investigated and compared to previously reported data. The elastic and inelastic channels showed the appearance of shape and Feshbach resonances for pyrrole and its isomers. The ultralow-energy region resonance was observed for Z-2 butenenitrile at 0.47 eV. With STO-3G and DZP basis sets, we estimated elastic, excitation, and momentum-transfer cross sections. The differential cross section for the present polar molecules was studied at 5 eV. The dissociative electron attachment channel for pyrrole and its isomers was studied for the pyrrolide anion. The data presented here will be helpful in astrophysical, astrochemical, atmospheric, and low-energy plasma modeling due to the presence of pyrrole and its isomers and the pyrrolide anion in the celestial bodies. The estimated data are also helpful in the biomedical field, radiation therapy, and pharmaceuticals.

Study of Electron Collisions with Isoprene, 1,2-Butadiene, and Their Isomers.

Isoprene, 1,2-butadiene, and their isomers play an important role in aerosols in the atmosphere, interstellar media, and extraterrestrial life. Since electrons are everywhere, studying how electrons interact with these molecules is an important part of studying such environments. To date, however, little investigation has been conducted in this area. Bearing this in mind, we conducted a thorough investigation to report the various electron scattering cross sections of isoprene, 1,2-butadiene, and their isomers. The methods used for this purpose are reliable within the limits of adopted model potentials. The optical potential method was used to get the total elastic and inelastic cross sections, while the complex scattering potential ionization contribution method was used to get the total ionization cross section from the inelastic contribution. The results from these approximations are pretty close to the results from earlier experiments and theories. Furthermore, most of these isomers are being explored for the first time. Besides, their isomeric effect is also discussed. A correlation between the cross sections of molecules is demonstrated, which can be used to predict cross sections of those molecules where previous data are not available.

Mean Free Paths and Cross Sections for Electron Scattering from Liquid Water.

Electron collision with liquid water is theoretically investigated and reported in this article. The range of projectile energy considered is 10-5000 eV, covering all major channels, viz., ionization, inelastic, elastic, and total scattering. The liquid phase electron charge density and static potential are generated and used in the calculation under a spherical complex optical potential formalism to achieve the goals. For the ionization channel, the complex scattering potential-ionization contribution method is used. The agreement with available theoretical data is satisfactory. The study on the total electron scattering from liquid water, using a common method for elastic and inelastic cross sections, is new and requires further attempts to support the reported data.

Electron Scattering Cross Sections for Anthracene and Pyrene.

UK molecular R-matrix calculations have been carried out for electron scattering from anthracene and pyrene. These molecules belong to the family of polycyclic hydrocarbons (PAHs) and are found in a nebula known as the Red Rectangle. Static exchange (SE), static exchange plus polarization (SEP), and close coupling (CC) approximations are used for scattering calculations. Different elastic and inelastic cross sections are computed in the present work in the energy range of 0.1-15 eV. Dissociative electron attachment cross sections are also calculated for both the molecules. Various shape, Feshbach/core-excited, and mixed resonances are detected for these molecules below 10 eV. All of the resonances detected in the present study are in agreement with the existing experimental and theoretical results. Due to the complexity of the present targets, electron collision cross sections are essentially unknown and hence most of the results are presented for the first time.

Positron Scattering from Pyridine and Pyrimidine.

Positron impact scattering cross-sections for pyridine and pyrimidine are reported here. Spherical complex optical potential formalism is used to calculate the positronium formation, elastic, total, and differential cross-sections. The ionization cross-sections calculated here are obtained employing the complex scattering potential-ionization contribution method. To account for the complex molecular structure of the target, an effective potential method is employed in our formalism for the first time. The contribution from rotational excitation is also included, which shows a reasonable comparison with the experimental data. The results obtained using the modified approach are encouraging and show very good agreement with the measurements. The differential cross-section for pyridine is reported for the first time.

Low-Energy Electron Scattering from Dimethyl Ether.

Low-energy (0.1 to 15 eV) R-matrix calculation is performed for dimethyl ether molecule. Electronic excitation and momentum transfer cross section for low energies are reported for the first time. Present differential cross sections show good agreement with previous data in terms of shape but are significantly higher in magnitude. Apart from low energies, we have also performed high-energy calculation (11-5000 eV) using spherical complex optical potential formalism. To deal with the molecular nature of the present target, we have applied an effective potential method in our computation for the first time. Good consistency can be seen at the overlapping energies of the two calculations.

Effects of amine fluoride and probiotic mouthwash on levels of Porphyromonas gingivalis in orthodontic patients: A randomized controlled trial.

INTRODUCTION: Porphyromonas gingivalis is one among the major etiological agent in periodontal diseases and has been proved to cause gingival inflammation under orthodontic appliances. AIM: To assess the effect of amine fluoride and probiotic mouthwashes on levels of P. gingivalis during orthodontic treatment, using real time-polymerase chain reaction (RT-PCR). MATERIALS AND METHODS: A randomised controlled trial was performed including 45 patients. There were three groups: Group A (control group), Group B (patients using Amflor mouthwash) and Group C (patients using probiotic mouthwash). During the treatment, all the 3 groups were advised to brush twice a day using Colgate tooth paste and Group B patients were advised to swish 15 ml fluoridated mouthwash (Amflor) and Group C advised to swish probiotic for 60 s before swallowing, once in the morning and once before sleep. After gently removing supragingival plaque, subgingival plaque samples were collected by inserting a sterile dental curette into the bottom of the gingival crevice around 31, 32, 41, and 42 at two different intervals: T1 at start and T2 after 6 months of fixed orthodontic treatment. Sub-gingival plaque samples collected were transferred to laboratory within 48 h for RT-PCR analysis in Tris-buffer solution, to maintain the integrity of bacterial DNA. RESULTS: The levels of P. gingivalis were significantly decreased with probiotic mouth wash. CONCLUSIONS: Probiotic mouth wash can be used as an adjunctive measure along with regular brushing to improve periodontal status during fixed orthodontic treatment.

Total ionization cross section of cyclic organic molecules.

Two independent methods, namely, Binary-encounter Bethe (BEB) and complex scattering potential-ionization contribution (CSP-ic) methods, are employed to calculate the total ionization cross section (Qion) for cyclic organic molecules from ionization threshold to 5 keV for which there is a paucity of data in the literature. The Qion calculated with the (BEB/ωB97X) combination is found to give good agreement with the experimental results, the CSP-ic method, and the Qion calculated from Irikura orbital energies. The Qion for most of the targets are calculated for the first time over such a wide energy range. Hence, to check the consistency and reliability of the present data, we have also computed the static polarizability for all the targets and the variation of maximum ionization cross section (Qion,max) with polarizability is studied. A linear relationship is observed between these quantities indicating the consistency and reliability of the present Qion data. The targets studied are important for industrial applications, radiation biology, and astrophysics.

Association of Undernutrition and Early Childhood Dental Caries.

OBJECTIVE: To determine the association between early childhood caries and nutritional status in preschool children. METHODS: Cross-sectional study among preschool children (N=550, age 8-60 mo) were selected in tribal, rural and urban health care units of Kerala. An oral examination for early childhood caries status was done using Deft index. The anthropometric measurements were recorded. Multiple logistic regression with other covariates was used to determine the association between the early childhood caries and nutritional status. RESULTS: The mean (SD) Deft scores were 0.93 (1.73), 2.22 (2.92) and 3.40 (3.23) for children with normal nutritional status, borderline undernutrition and undernutrition, respectively. Children with borderline undernutrition (adjusted OR 2.05, 95% CI 1.20, 3.49) or undernutrition (adjusted OR 3.46, 95% CI 1.93, 6.29) had higher odds of dental caries in comparison to those with normal nutritional status. CONCLUSION: Undernutrition is associated with early childhood caries among preschool children.

Positron Scattering from Methyl Halides.

The well-known spherical complex optical potential (SCOP) and complex scattering potential-ionization contribution (CSP-ic) methods with appropriate modifications are applied to the CH3X (X = F, Cl, Br, and I) molecules to compute positron scattering cross sections, which rather is the first theoretical attempt to report the same. Besides, various inelastic cross sections are also predicted for the first time in this Article. We have utilized the multiscattering spherical complex optical potential (MSCOP) approach to derive these cross sections. In general, a reasonable accordance has been found between the present total cross sections and the experimental measurements. Apart from the inconsistency between the present theoretical and previous experimental cross sections in the low energy region, the present theory is found to produce consistent and reliable results at all other energies.

Career Satisfaction Among Dental Public Health Specialists in India - A Cross-sectional Survey.

INTRODUCTION: The satisfaction in career is an important indicator for the growth of the discipline and the profession. An empirical investigation of satisfaction in career and amendments needed in course and profession may help in growth of discipline. AIM: To assess career satisfaction among Dental Public Health (DPH) specialists working in India and analyze their perspective on changes required in the profession. MATERIALS AND METHODS: Questionnaire for this cross-sectional survey was adapted from Minnesota Job Satisfaction Survey which included 40 enquiries to understand the reasons for choosing public health dentistry as career, competencies of public health dentists, satisfaction as a public health dentist and changes required in the profession. The questions were both open and closed end type. Updated electronic mail details of all registered public health dentists were collected from the head office of Indian Association of Public Health Dentistry. Each participant was contacted by electronic mail and consent to participate were sought. Reminders were e-mailed thrice during three months. A total of 580 participants were contacted. A total of 183 responses were received, among which 179 consented. RESULTS: Nearly half of the respondents felt they are yet to achieve the accomplishment from the present career as public health dentist. Only 46.9% felt that there is advancement in the profession as career. Nearly three-fourth of respondents could not attain recognition as a public health dentist. A 45.8% of respondents were of the opinion that career in public health dentistry would provide them a steady employment and 53.1% of public health dentists would envision as satisfied in their career in next 10 years. Nearly 85% felt public health dentistry training needs a major course correction. CONCLUSION: There has been some reservation or skepticism about the future of the specialty as the jobs are in declining stage. This information provides insight about success and failures of public health dentistry as profession which would be needed for planning the dental manpower.

Calculation of total and ionization cross sections for electron scattering by primary benzene compounds.

The total and ionization cross sections for electron scattering by benzene, halobenzenes, toluene, aniline, and phenol are reported over a wide energy domain. The multi-scattering centre spherical complex optical potential method has been employed to find the total elastic and inelastic cross sections. The total ionization cross section is estimated from total inelastic cross section using the complex scattering potential-ionization contribution method. In the present article, the first theoretical calculations for electron impact total and ionization cross section have been performed for most of the targets having numerous practical applications. A reasonable agreement is obtained compared to existing experimental observations for all the targets reported here, especially for the total cross section.

Theoretical Formalism To Estimate the Positron Scattering Cross Section.

A theoretical formalism is introduced in this article to calculate the total cross sections for positron scattering. This method incorporates positron-target interaction in the spherical complex optical potential formalism. The study of positron collision has been quite subtle until now. However, recently, it has emerged as an interesting area due to its role in atomic and molecular structure physics, astrophysics, and medicine. With the present method, the total cross sections for simple atoms C, N, and O and their diatomic molecules C2, N2, and O2 are obtained and compared with existing data. The total cross section obtained in the present work gives a more consistent shape and magnitude than existing theories. The characteristic dip below 10 eV is identified due to the positronium formation. The deviation of the present cross section with measurements at energies below 10 eV is attributed to the neglect of forward angle-discrimination effects in experiments, the inefficiency of additivity rule for molecules, empirical treatment of positronium formation, and the neglect of annihilation reactions. In spite of these deficiencies, the present results show consistent behavior and reasonable agreement with previous data, wherever available. Besides, this is the first computational model to report positron scattering cross sections over the energy range from 1 to 5000 eV.

Electron impact ionization of cycloalkanes, aldehydes, and ketones.

The theoretical calculations of electron impact total ionization cross section for cycloalkane, aldehyde, and ketone group molecules are undertaken from ionization threshold to 2 keV. The present calculations are based on the spherical complex optical potential formalism and complex scattering potential ionization contribution method. The results of most of the targets studied compare fairly well with the recent measurements, wherever available and the cross sections for many targets are predicted for the first time. The correlation between the peak of ionization cross sections with number of target electrons and target parameters is also reported. It was found that the cross sections at their maximum depend linearly with the number of target electrons and with other target parameters, confirming the consistency of the values reported here.

Electron impact total cross section for acetylene over an extensive range of impact energies (1 eV-5000 eV).

Comprehensive study on electron impact for acetylene molecule is performed in terms of eigenphase diagram, electronic excitation cross sections as well as total cross section calculations from 1 eV to 5000 eV in this article. Computation of cross section over such a wide range of energy is reported for the first time. We have employed two distinct formalisms to derive cross sections in these impact energies. From 1 eV to ionization threshold of the target we have used the ab initio R-matrix method and then spherical complex optical potential method beyond that. At the crossing point of energy, both theories matched quite well and hence prove that they are consistent with each other. The results presented here expectedly give excellent agreement with other experimental values and theories available. The techniques employed here are well established and can be used to predict cross sections for other targets where data are scarce or not available. Also, this methodology may be integrated to online database such as Virtual Atomic and Molecular Data Centre to provide cross section data required by any user.