Vibrational Sum Frequency Generation (VSFG) Spectroscopy Measurement of the Rotational Barrier of Methyl Groups on Methyl-Terminated Silicon(111) Surfaces

The methyl-terminated Si(111) surface possesses a 3-fold in-plane symmetry, with the methyl groups oriented perpendicular to the substrate. The propeller-like rotation of the methyl groups is hindered at room temperature and proceeds via 120° jumps between three isoenergetic minima in registry with the crystalline Si substrate. We have used line-shape analysis of polarization-selected vibrational sum frequency generation spectroscopy to determine the rotational relaxation rate of the surface methyl groups and have measured the temperature dependence of the relaxation rate between 20 and 120 °C. By fitting the measured rate to an Arrhenius dependence, we extracted an activation energy (the rotational barrier) of 830 ± 360 cm^(–1) and an attempt frequency of (2.9 ± 4.2) × 10^(13) s^(–1) for the methyl rotation process. Comparison with the harmonic frequency of a methyl group in a 3-fold cosine potential suggests that the hindered rotation occurs via uncorrelated jumps of single methyl groups rather than concerted gear-like rotation

KPC-2-producing Klebsiella pneumoniae ST147 in a neonatal unit: Clonal isolates with differences in colistin susceptibility attributed to AcrAB-TolC pump

This study characterizes four KPC-2-producing Klebsiella pneumoniae isolates from neonates belonging to a single sequence type 147 (ST147) in relation to carbapenem resistance and explores probable mechanisms of differential colistin resistance among the clonal cluster. Whole genome sequencing (WGS) revealed that the isolates were nearly 100% identical and harbored resistance genes (blaKPC-2,OXA-9,CTX-M-15,SHV-11,OXA-1,TEM-1B, oqxA, oqxB, qnrB1, fosA, arr-2, sul1, aacA4, aac(6′)Ib-cr, aac(6′)Ib), and several virulence genes. blaKPC-2 was the only carbapenem-resistant gene found, bracketed between ISKpn7 and ISKpn6 of Tn4401b on a non-conjugative IncFII plasmid. Remarkably, one of the clonal isolates was resistant to colistin, the mechanistic basis of which was not apparent from comparative genomics. The transmissible colistin resistance gene, mcr, was absent. Efflux pump inhibitor, carbonyl cyanide 3-chlorophenylhydrazone (CCCP) rendered a 32-fold decrease in the minimum inhibitory concentration (MIC) of colistin in the resistant isolate only. acrB, tolC, ramA, and soxS genes of the AcrAB-TolC pump system overexpressed exclusively in the colistin-resistant isolate, although the corresponding homologs of the AcrAB-TolC pump, regulators and promoters were mutually identical. No change was observed in the expression of other efflux genes (kpnE/F and kpnG/H) or two-component system (TCS) genes (phoP/phoQ, pmrA/pmrB). Colistin resistance in one of the clonal KPC-2-producing isolates is postulated to be due to overexpression of the AcrAB-TolC pump. This study is probably the first to report clinical clonal K. pneumoniae isolates with differences in colistin susceptibility. The presence of carbapenem-resistant isolates with differential behavior in the expression of a genomically identical pump system indicates the nuances of the resistance mechanisms and the difficulty of treatment thereof

Performance analysis of the limited bandwidth allocation scheme with excess distribution

\ua9 2009-2012 OSA. The limited scheme with excess distribution (LS-ED), being a superior grant-sizing protocol in terms of average delay minimization while providing fairness and quality of service (QoS) satisfaction in Ethernet passive optical networks (EPONs), has already been deployed in diverse technologies. An analysis of the protocol is of paramount importance for obtaining deeper insight into several network design and deployment aspects. Thus, the primary objective of this paper is to perform a rigorous mathematical analysis of LS-ED, for the first time to the best of our knowledge, with the help of a discrete time Markov chain (DTMC). Owing to the dependency of the grant size of a particular optical network unit (ONU) on the queue length of other ONUs, the exact queuing analysis of this scheme necessitates solving a Markov model of the same dimension as the number of ONUs, which makes the analysis complicated and mathematically intractable. A lower-dimensional valid approximation model may allow us to perform such an analysis. In this paper, for the first time to the best of our knowledge, we present an analysis of the scheme, wherein the system dynamics are captured from the perspective of the scheduler leading to an approximate model. The model aids in obtaining a closed-form expression for the average cycle time and throughput along with closed-form expressions for average buffer occupancy and average delay at low load. Finally, we provide useful design insights for EPONs employing LS-ED

On the Assignment of the Vibrational Spectrum of the Water Bend at the Air/Water Interface

We previously reported the spectrum of the water bend vibrational mode (ν₂) at the air/water interface measured using sum-frequency generation (SFG). Here, we present experimental evidence to aid the assignment of the ν₂ spectral features to H-bonded classes of interfacial water, which is in general agreement with two recent independently published theoretical studies. The dispersive line shape shows an apparent frequency shift between SSP and PPP polarization combinations (SFG–​visible–​infrared). This is naturally explained as an interference effect between the negative (1630 cm^–1) and positive (1662 cm^–1) peaks corresponding to “free–OH” and “H-bonded” species, respectively, which have different orientations and thus different amplitudes in SSP and PPP spectra. A surfactant monolayer of sodium dodecyl sulfate (SDS) was used to suppress the free OH species at the surface, and the corresponding SFG spectral changes indicate that these water molecules with one of the hydrogens pointing up into the air phase contribute to the negative peak at 1630 cm^–1

Clinical studies on the effect of Neem (Azadirachta indica) bark extract on gastric secretion and gastroduodenal ulcer

We have shown earlier that Neem (Azadirachta indica) bark aqueous extract has potent antisecretory and antiulcer effects in animal models and has no significant adverse effect (Bandyopadhyay et al., Life Sciences, 71, 2845–2865, 2002). The objective of the present study was to investigate whether Neem bark extract had similar antisecretory and antiulcer effects in human subjects. For this purpose, a group of patients suffering from acidrelated problems and gastroduodenal ulcers were orally treated with the aqueous extract of Neem bark. The lyophilised powder of the extract when administered for 10 days at the dose of 30 mg twice daily caused a significant (p b 0.002) decrease (77%) in gastric acid secretion. The volume of gastric secretion and its pepsin activity were also inhibited by 63% and 50%, respectively. Some important blood parameters for organ toxicity such as sugar, urea, creatinine, serum glutamate oxaloacetate transaminase, serum glutamate pyruvate transaminase, albumin, globulin, hemoglobin levels and erythrocyte sedimentation rate remained close to the control values. The bark extract when taken at the dose of 30–60 mg twice daily for 10 weeks almost completely healed the duodenal ulcers monitored by barium meal X-ray or by endoscopy. One case of esophageal ulcer (gastroesophageal reflux disease) and one case of gastric ulcer also healed completely when treated at the dose of 30 mg twice daily for 6 weeks. The levels of various blood parameters for organ toxicity after Neem treatment a