Noncovalent Interactions in Mechanical Response of Thermoset Epoxy Resin.

Free volume in polymers is known to influence the mechanical response of the polymers. Noncovalent interactions such as hydrogen bonds, Coulombic electrostatic interactions, and van der Waals interactions are present within these free volume regions. The manuscript presents a comprehensive identification, characterization, and evolution of noncovalent interactions as a thermoset epoxy resin (typically used as an interfacial adhesive material) is subjected to uniaxial tension, shear, and shock loading. Even though noncovalent interactions dominate uniaxial tension and shear response (up to strain levels of 50% wherein covalent bond dissociation is not observed), both covalent and noncovalent interactions define response for shock loading. Van der Waals interactions dominate the response as the samples are subjected to strain levels of 50% in tension and shear. In contrast, hydrogen bonds influence shock response.

Stereomutations in silicate oligomerization: the role of steric hindrance and intramolecular hydrogen bonding.

Stereomutation has previously been explored in the literature with regard to the different mechanisms and activation energy barriers between different forms. However, the forces which govern stereomutations within the intermediate steps in chemical reactions have not been explored previously, a topic addressed in this article. The process of silicate oligomerization has been chosen in this study and it is demonstrated that steric hindrance of molecules and intramolecular hydrogen bonding govern the stereomutation of intermediate pentacoordinate silicon compounds in the silicate oligomerization process. It could be observed that the combined effect of intramolecular hydrogen bonding and steric hindrance in the silicate oligomerization process facilitates the conventional berry pseudorotation mechanism rather than other pseudorotation mechanisms reported in the literature.

Catalytic Behavior of Hydrogen Bonded Water in Oligomerization of Silicates.

Even though much research has been done to demonstrate the oligomerization of zeolites and silicates, there has been almost no study that investigates the role of hydrogen bonds in these reaction pathways. This study demonstrates the catalytic activity of hydrogen bonds in the silicate oligomerization reaction pathway. The presence of hydrogen bonding has been shown to enhance the energetic favorability of the anionic-I mechanism. Catalysis is prevalent in the Si-OH rupture process of the reaction pathway. Simultaneously, the dependence of the activation barrier on the equatorial or apical nature of the cleaving hydroxyl group has also been shown. The preceding steps such as condensation and fluxional influence the strength of hydrogen bonds. An increase in hydrogen bond strength enhances its catalytic effect, leading to a higher extent of reduction in the activation barrier of the particular reaction step. Even though the quantum study focuses on the oligomerization of calcium silicate as a test case, it can be anticipated that such similar effects can be perceived in general for the oligomerization of silicates containing metallic ions in sol-gel chemistry and zeolite synthesis.

Silica dimerization in the presence of divalent cations.

The presence of monovalent cations and organic tetraalkylammonium ions is known to affect the reaction pathway and chemical kinetics of the silica oligomerization reaction which is important for sol-gel chemistry studies. A detailed theoretical study focusing on the chemical reaction pathway for the dimerisation process in the presence of a divalent cation is presented in this study. Different condensation pathways such as neutral, anionic-I and anionic-II along with their relative possibilities in dimerization have been explored. It has been demonstrated that with an increase in the pH of solution, manifested through the presence of deprotonated ions (as in the anionic cases with or without the presence of divalent cations), the activation activation barrier of the dimerization reaction is lowered. It has also been demonstrated that the addition of divalent cations raises the activation barriers for the reaction and delays the overall dimerisation reaction. The stability and bond characteristics of the bridging Si-OH bond of the resulting dimer products have also been determined. Activation energy barriers for the anionic case have also been observed to vary based upon the dihedral arrangement of the hydroxyl group bonded with the silicon and the orientation of the nucleophilic attack.

Seroprevalence of SARS-CoV-2 antibodies in the general population of Oman: results from four successive nationwide sero-epidemiological surveys.

OBJECTIVE: To assess the seroprevalence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) in Oman and longitudinal changes in antibody levels over time within the first 11 months of the coronavirus disease 2019 (COVID-19) pandemic. METHODS: This nationwide cross-sectional study was conducted as a four-cycle serosurvey using a multi-stage stratified sampling method from July to November 2020. A questionnaire was used and included demographics, history of acute respiratory infection and list of symptoms, COVID-19 contact, previous diagnosis or admission, travel history and risk factors. RESULTS: In total, 17,457 participants were surveyed. Thirty percent were female and 66.3% were Omani. There was a significant increase in seroprevalence throughout the study cycles, from 5.5% (4.8-6.2%) in Cycle 1 to 22% (19.6-24.6%) in Cycle 4. There was no difference in seroprevalence between genders, but significant differences were found between age groups. There was a transition of seroprevalence from being higher in non-Omanis than Omanis in Cycle 1 [9.1% (7.6-10.9%) vs 3.2% (2.6-3.9%)] to being higher in Omanis than non-Omanis in Cycle 4 [24.3% (21.0-27.9%) vs 16.8% (14.9-18.9%)]. There was remarkable variation in the seroprevalence of SARS-CoV-2 according to governorate. Close contacts of people with COVID-19 had a 96% higher risk of having the disease [adjusted odds ratio (AOR) 1.96, 95% confidence intervals (CI) 1.64-2.34]. Labourers had 58% higher risk of infection compared with office workers (AOR 1.58, 95% CI 1.04-2.35). CONCLUSION: This study showed a wide variation in the spread of SARS-CoV-2 across governorates in Oman, with higher estimated seroprevalence in migrants in the first two cycles. Prevalence estimates remain low and are insufficient to provide herd immunity.

Knowledge, Attitudes and Practices Related to HIV Stigma and Discrimination Among Healthcare Workers in Oman.

OBJECTIVES: Stigma and discrimination undermine the quality of life of people with HIV and their access to health services. This study aimed to assess HIV-related knowledge, attitudes and practices among healthcare workers (HCWs) in Oman. METHODS: This cross-sectional study took place between July and November 2016. A questionnaire was distributed to 1,400 government HCWs to determine HIV-related knowledge, attitudes and practices. RESULTS: A total of 1,281 HCWs participated (response rate = 92%). Routine tasks, such as dressing wounds, drawing blood and touching clothes, were a cause of concern for 24-52% of HCWs. Only 69% correctly answered questions regarding the transmission of HIV via eating/drinking and mosquito bites. Compared to other HCWs, doctors had significantly higher knowledge (mean = 0.46, 95% confidence interval [CI]: 0.19 to 0.73; P <0.001), attitude (mean = 0.77, 95% CI: 0.31 to 1.24; P = 0.001) and practice (mean = 2.07, 95% CI: 1.59 to 2.55; P <0.001) scores. Expatriates also scored significantly higher in knowledge (mean = 1.08, 95% CI: 0.93 to 1.23; P <0.001), attitude (mean = 1.23, 95% CI: 0.98 to 1.48; P <0.001) and practice (mean = 1.08, 95% CI: 0.82 to 1.34; P <0.001) compared to Omani nationals. Finally, those with >15 years' work experience scored significantly higher on knowledge (mean = -0.60, 95% CI: -1.12 to -0.08; P = 0.025) and attitude (mean = -0.99, 95% CI: -1.87 to -0.10; P = 0.029) compared to those with less experience. CONCLUSION: The high rate of HIV-related stigma among HCWs in Oman should be rectified in order to achieve the 90-90-90 target set by the Joint United Nations Programme on HIV/AIDS.

Intermolecular Dynamics of Water: Suitability of Reactive Interatomic Potential.

Reactive interatomic potentials for water have been developed by researchers based on their ability of bond breaking and formation, which have numerous advantages and applications in different fields. The question that is being addressed in this work is whether these reactive interatomic potentials properly account for the intermolecular dynamics of water that includes both hydrogen bonding as well as librational motions. It should be noted that breaking and reformation of hydrogen bonds occur prior to covalent bond breaking of water molecules (which requires a significant amount of energy), which has numerous applications in absorption as well as solvation problems. Based on correlations with experimental observations, it has been demonstrated that the current forms of the reactive potentials perform poorly in comparison to other well-established empirical interatomic potential models of water, such as TIP4P/2005f, with regard to the intermolecular dynamics of water. Translational and rotational diffusivities, power spectra, and hydrogen-bond lifetime analyses are carried out and compared to available experimental data as well as those obtained from TIP4P/2005f models to arrive at such conclusions.

Intermolecular dynamics of ultraconfined interlayer water in tobermorite: influence on mechanical performance.

Ultraconfined interlayer water within the tobermorite molecular structure is responsible for changes in the uniaxial tensile and compressive response of the family of tobermorites: 9, 11 and 14 Å. These confined interlayer water molecules are engaged in solvation of cations and anions within the tobermorite structure, which has been demonstrated through the intermolecular vibrational spectra and hydrogen bond lifetime of the water molecules. This study demonstrates that instead of ionization of water molecules (as proposed in an earlier study), breaking of hydrogen bonds of water is more plausible leading to solvation of ions within the molecular structure of tobermorite. A schematic of the coordinate covalent bonds between the water molecules and the cations and anions of the tobermorite structure has been proposed in this study.

A metastable phase of shocked bulk single crystal copper: an atomistic simulation study.

Structural phase transformation in bulk single crystal Cu in different orientation under shock loading of different intensities has been investigated in this article. Atomistic simulations, such as, classical molecular dynamics using embedded atom method (EAM) interatomic potential and ab-initio based molecular dynamics simulations, have been carried out to demonstrate FCC-to-BCT phase transformation under shock loading of 〈100〉 oriented bulk single crystal copper. Simulated x-ray diffraction patterns have been utilized to confirm the structural phase transformation before shock-induced melting in Cu(100).

Evaluation of stone-free rate using Guy's Stone Score and assessment of complications using modified Clavien grading system for percutaneous nephro-lithotomy.

To prospectively evaluate the ability of Guy's Stone Score (GSS) in predicting stone clearance rate and complication rate (by modified Clavien grade) for renal stones treated by percutaneous nephrolithotomy (PNL). From January 2013 to June 2014, a total of 142 patients undergoing PNL were evaluated prospectively. Patients with co-morbidities like hypertension, diabetes, renal failure were excluded from the study. All patients were classified according to GSS based on the findings of pre-operative intravenous urography (IVU) and per-operative retrograde pyelography (RGP). All PNL procedures were done by standard technique in prone position and success was defined as no residual stone visible on X-ray KUB done on the third postoperative day. Complications were classified according to modified Clavien grading system. The initial stone clearance rate was 71.1% and overall final stone clearance rate was 90.14%. The complication rate according to Clavien grading system was 40.1%. The final stone clearance rates were 93.9, 85.71, 90.47, and 77.77% in GSS I, II, III, and IV, respectively (p<0.001, <0.05, <0.05 and >0.05, respectively). The Clavien complication rates were 23, 61, 52, and 77.7% in GSS I, II, III, and IV, respectively (p<0.001). The GSS is a simple and easily reproducible system to preoperatively predict stone-free rate and perioperative complication rate. It helps in better patient counseling preoperatively.

Transrectal ultrasonography (TRUS)-guided pelvic plexus block to reduce pain during prostate biopsy: a randomised controlled trial.

OBJECTIVE: To assess the role of pelvic plexus block (PPB) in reducing pain during transrectal ultrasonography(TRUS)-guided prostate biopsy, compared with the conventional periprostatic nerve block (PNB). PATIENTS AND METHODS: A prospective, double-blind observational study was conducted with patients being randomised into three groups. Group-1 (47 patients) received intrarectal local anaesthesia (IRLA) with 10 mL 2% lignocaine jelly along with pelvic plexus block (PPB) with 2.5 mL 2% lignocaine injection bilaterally. Group-2 (46 patients) received IRLA with periprostatic nerve block (PNB). Group-3 (46 patients) received only IRLA without any type of nerve block. The patients were requested to rate the level of pain from 0 to 10 on a visual analogue scale (VAS) at two time points: VAS-1: during biopsy procedure and VAS-2: 30 min after the procedure. RESULTS: The mean age of the patients, mean volume of the prostates and mean serum PSA values were comparable among the three groups. The mean pain score during biopsy was significantly less in the PPB group [mean (range) sore of 2.91 (2-4)] compared with the PNB group [mean (range) score of 4 (3-5)], and both these groups were superior to the no nerve block group [mean score of 5.4 (3-7)]. There was no significant difference between the mean pain scores, 30 min after the procedure among the three groups with the mean (range) scores being 2.75 (2-4), 2.83 (2-4) and 2.85 (2-4), respectively. CONCLUSION: PPB is superior to conventional periprostatic nerve block (PNB) for pain control during TRUS-guided biopsy and both are in turn superior to no nerve block.

Parameatal Cyst : A report of Two Cases and Review of Literature.

Cyst formation in the parameatal area is a relatively rare entity and not many cases have been reported in the literature. Two such cases are reported here. First patient was a 46 year old sexually active male who developed a spherical, cystic swelling of 1 cm in size on right lip of external urethral meatus. The second case was a 4 year old boy who presented with asymptomatic recurrent left parameatal swelling. In both the cases, cysts were completely excised and defects were sutured. Histologically, the cyst walls were lined by tall squamous and columnar epithelium. Good cosmetic results were obtained in these two cases without any recurrence at 2 two months follow up.

Reinforced tension line suture closure after midline laparotomy in emergency surgery.

Midline laparotomy is an emergency surgical operation frequently performed in cases of intra-abdominal pathology. Closure of the incision is usually done by continuous suturing by mass closure. In an emergency operation the intra-abdominal milieu is usually contaminated leading to gut oedema and, hence, an increase in postoperative intra-abdominal pressure. It is complicated by wound dehiscence, burst abdomen, etc. The cause of this complication is an increase in horizontal tensile forces on the site of the insertion of sutures which cuts the sheath. In this technique of reinforced tension line suture peak tensile forces are distributed from the suture base to the surrounding tissue through a horizontal suture, thereby preventing the suture from cutting through the tissue. From July 2007 to June 2009 patients requiring laparotomy were randomly divided into test and control groups by a 'closed envelope' technique. Their postoperative intra-abdominal pressure was recorded by urinary bladder catheter manometry. The result of this technique was compared with the incidence of burst abdomen in cases where it was closed by continuous suture. A total of 190 patients underwent laparotomy. In 90 the abdomen was closed by reinforced tension line (RTL) and in 100 patients by continuous suturing. None of the RTL group had a burst abdomen. Thirteen who had closure by continuous suture had a burst abdomen. The analysis of the results was done using the chi-square test. On comparing the incidence of burst abdomen in cases operated by continuous suture technique and by RTL, the P value was found to be 0.0026 which is highly significant. On analysis of the incidence of burst abdomen in cases having a grade II intra-abdominal pressure the P value was found to be 0.0009 which is highly significant. Closure of midline incision by RTL reduces the incidence of burst abdomen. Registration No. PROVCTRI/2008/091/000269 (http://www.ctri.in).

Heteropagus twins-a tale of two cases.

Heteropagus twinning is a rare occurrence. Parasitic and asymmetric conjoined twins are rarer anomalies of monochorionic monoamniotic twins; which consist of an incomplete twin attached to the fully developed body of the co-twin. We present here two such cases of Heteropagus twinning.

Congenital intra-mesosigmoid hernia- a case report of a rare sigmoid mesocolon hernia.

Internal hernia is the protrusion of the viscera through normal or abnormal peritoneal or mesenteric apertures within the confines of peritoneal cavities.

Etiology and outcome of acute intestinal obstruction: a review of 367 patients in Eastern India.

BACKGROUND/AIM: The etiology of acute intestinal obstruction, which is one of the commonest surgical emergencies, varies between countries and has also changed over the decades. We aimed to provide a complete epidemiological description of acute intestinal obstruction in a tertiary care hospital in Eastern India. MATERIALS AND METHODS: This was a retrospective study of patients admitted in our unit with a diagnosis of acute intestinal obstruction between the years 2005 and 2008 at Medical College, Calcutta. The study comprised of 367 patients. RESULTS: Acute intestinal obstruction was the diagnosis in 9.87% of all patients admitted with males (75.20%) grossly outnumbering females. The commonest age group affected was 20-60 years. In our patients, the main cause of obstruction was obstructed hernia followed by malignancy with adhesions coming third. Intestinal tuberculosis was an important cause for obstruction in our patients comprising 14.17% of patients. Conservative management was advocated in 79 patients while the rest underwent surgery. Postoperative complications occurred in 95 patients and of these, 38 patients had a single complication and the rest, more than 1. The main complications were wound infection, basal atelectasis, burst abdomen and prolonged ileus. The mortality rate was 7.35% (27 patients). The highest mortality occurred in those with intestinal tuberculosis. CONCLUSION: This study demonstrates that the pattern of intestinal obstruction differs from the Western world with obstructed hernias being the most important cause and also emphasizes the fact that intestinal tuberculosis assumes a prominent role. It also highlights the necessity of using universal precautions because of the ever increasing number of HIV patients in those with intestinal obstruction.

Is ligation of hernial sac during orchiopexy mandatory?

AIM: Traditionally, ligation of hernial sac during orchiopexy is considered mandatory to prevent postoperative development of hernia. A prospective study was carried out to see if it is actually required based on the fact that any peritoneal defect closes within 24 hours by metamorphosis of the in situ mesodermal cells. METHODS: Fifty cases of undescended testis, age ranging from eight months to 12 years were enrolled. All of them underwent standard orchiopexy without ligation of the hernial sac. RESULTS: Follow up of all cases ranged between 1.5 years to three years. Not a single case was reported with evidence of hernia. CONCLUSIONS: It is unnecessary to ligate the hernial sac during orchiopexy.