Statistical modeling of daily extreme rainfall in Colombo

The occurrence of heavy rainfalls in Sri Lanka results in significant damage to agriculture, ecology, infrastructure systems, disruption of human activities, injuries and the loss of life. The modelling of extreme rainfall has to be developed to manage the natural resources and the built environment to face the impacts of climate change. The main goal of this study is to find the best fitting distribution to the extreme daily rainfalls measured over the Colombo region for the years 1900-2009 by using the maximum likelihood approach. The study also predicts the extreme rainfalls for return periods and their confidence bands. In this study extreme rainfall events are defined by two different methods based on (1) the annual maximums of the daily rainfalls and (2) the daily rainfalls exceeds some specific threshold value. The Generalized Extreme Value distribution and the Generalized Pareto distribution are fitted to data corresponding to the methods 1 and 2 to describe the extremes of rainfall and to predict its future behaviour. Finally we find the evidence to suggest that the Gumbel distribution provides the most appropriate model for the annual maximums of daily rainfall and the Exponential distribution gives the reasonable model for the daily rainfall data over the threshold value of 100mm for the Colombo location. We derive estimates of 5, 10, 20, 50 and 100 years return levels and its corresponding confidence intervals for extreme daily rainfalls

Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.

Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability

Photophysical and electroluminescence properties of bis(2′,6′-difluoro-2,3′-bipyridinato-N,C4′)iridium(picolinate) complexes: effect of electron-withdrawing and electron-donating group substituents at the 4′ position of the pyridyl moiety of the cyclometalated ligand

Herein, we have synthesized a series of 2′,6′-difluoro-2,3′-bipyridine cyclometalating ligands by substituting electron-withdrawing (–CHO, –CF3, and –CN) and electron-donating (–OMe and –NMe2) groups at the 4′ position of the pyridyl moiety and utilized them for the construction of five new iridium(III) complexes (Ir1–Ir5) in the presence of picolinate as an ancillary ligand. The photophysical properties of the developed iridium(III) compounds were investigated with a view to understand the substituent effects. The strong electron-withdrawing (–CN) group containing the iridium(III) compound (Ir3) exhibits highly efficient genuine green phosphorescence (λmax = 508 nm) at room temperature in solution and in thin film, with an excellent quantum efficiency (ΦPL) of 0.90 and 0.98, respectively. On the other hand, the –CF3 group substituted iridium(III) compound (Ir2) displays a sky-blue emission (λmax = 468 nm) with a promising quantum efficiency (ΦPL = 0.88 and 0.84 in solution and in thin film, respectively). The –CHO substituted iridium(III) complex (Ir1) showed greenish-yellow emission (λmax = 542 nm). Most importantly, the strong electron-donating –NMe2 substituted iridium(III) complex (Ir5) gives a structureless and a broad emission profile in the wavelength region 450 to 700 nm (λmax = 520 nm) with a poor quantum efficiency. An intense blue phosphorescence with impressive quantum efficiency, especially in thin-film noted in the case of the –OMe substituted iridium(III) complex (Ir4). Comprehensive density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches have been performed on the ground and excited states of the synthesized iridium(III) complexes, in order to obtain information about the absorption and emission processes and to gain deeper insights into the photophysical properties. The combinations of a smaller ΔES1–T1 and higher contribution of 3MLCT in the emission process result in the higher quantum yields and lifetime values for complexes Ir1–Ir3. Multi-layered Phosphorescent Organic Light Emitting Diodes (PhOLEDs) were designed using the phosphorescent dopants Ir2, Ir3 and Ir4 and their elecroluminescence properties were evaluated. Compound Ir4 at a doping level of 5 wt% shows the best performance with an external quantum efficiency of 4.7%, in the nonoptimized device, and a power efficiency of 5.8 lm W-1, together with a true-blue chromacity CIEx,y = 0.15, 0.17 recorded at the maximum brightness of 33 180 cd m-2

Influence of Thiophenes on Molecular Order, Mesophase, and Optical Properties of π‑Conjugated Mesogens

Increasing interest in π-conjugated aromatic cores built essentially with thiophene rings is recognized owing to their applications in optoelectronics. In this investigation, an attempt is made to understand the influence of terminal thiophene rings on the molecular order, mesophase, and optical properties of mesogens in which phenyl benzoate is part of the core. Accordingly, mono-, di-, and terthiophene units are linked to two phenyl ring core by Suzuki cross coupling reaction. The synthesized thiophene-based π-conjugated mesogens exhibit enantiotropic nematic and smectic phases with excellent mesophase range. The tendency for smectic phases and the mesophase range enhanced with increased thiophene rings. The layer ordering in smectic A and smectic C phase is established by powder X-ray diffraction, while the orientational order of all the rings of core unit is accomplished by ¹³C NMR spectroscopy. Thus the ¹³C–¹H dipolar couplings determined from 2D separated local field NMR experiments show a very high value for terminal C–H of thiophene ring (∼9–11 kHz) irrespective of number of thiophenes in the mesogenic core. The density functional theory and time-dependent density functional theory calculations indicate the intramolecular charge-transfer transition between the phenyl-thiophene to phenyl benzoate unit. The solution absorption and fluorescence spectral studies reveal interesting features. The monothiophene-based mesogen is nonfluorescent, while those based on bithiophene and terthiophene show intense fluorescence. The well-resolved vibronic peaks observed in fluorescence spectra of mesogens are characteristic of oligothiophenes. Furthermore, the fluorescence excitation anisotropy measured by monitoring the vibronic features of the mesogens is found to be similar, signifying that the emission originates from the identical electronic energy level. Therefore, the investigation encompassing wide-ranging techniques manifests that the insertion of more thiophenes in the mesogenic core favors polymesomorphism and intense emission, enabling them for application in polarized emission

Proton affinities of pertechnetate (TcO4-) and perrhenate (ReO4-).

The anions pertechnetate, TcO4-, and perrhenate, ReO4-, exhibit very similar chemical and physical properties. Revealing and understanding disparities between them enhances fundamental understanding of both. Electrospray ionization generated the gas-phase proton bound dimer (TcO4-)(H+)(ReO4-). Collision induced dissociation of the dimer yielded predominantly HTcO4 and ReO4-, which according to Cooks' kinetic method indicates that the proton affinity (PA) of TcO4- is greater than that of ReO4-. Density functional theory computations agree with the experimental observation, providing PA[TcO4-] = 300.1 kcal mol-1 and PA[ReO4-] = 297.2 kcal mol-1. Attempts to rationalize these relative PAs based on elementary molecular parameters such as atomic charges indicate that the entirety of bond formation and concomitant bond disruption needs to be considered to understand the energies associated with such protonation processes. Although in both the gas and solution phases, TcO4- is a stronger base than ReO4-, it is noted that the significance of even such qualitative accordance is tempered by the very different natures of the underlying phenomena

High-Resolution Solid State ¹³C NMR Studies of Bent-Core Mesogens of Benzene and Thiophene

Bent-core mesogens are an important class of thermotropic liquid crystals as they exhibit unusual properties as well as morphologies distinctly different from rodlike mesogens. Two bent-core mesogens with differing center rings namely benzene and thiophene are considered and investigated using high-resolution oriented solid state ¹³C NMR method in their liquid crystalline phases. The mesogens exhibit different phase sequences with the benzene-based mesogen showing a B₁ phase, while the one based on thiophene showing nematic and smectic C phases. The 2-dimensional separated local field (2D-SLF) NMR method was used to obtain the ¹³C–¹H dipolar couplings of carbons in the center ring as well as in the side-wing phenyl rings. Couplings, characteristic of the type of the center ring, that also provide orientational information on the molecule in the magnetic field were observed. Together with the dipolar couplings of the side-wing phenyl ring carbons from which the local order parameters of the different subunits of the core could be extracted, the bent angle of the mesogenic molecule could be obtained. Accordingly, for the benzene mesogen in its B₁ phase at 145 °C, the center ring methine ¹³C–¹H dipolar couplings were found to be significantly larger (9.5–10.2 kHz) compared to those of the side-wing rings (1.6–2.1 kHz). From the local order parameter values of the center (0.68) as well as the side-wing rings (0.50), a bent-angle of 130.3° for this mesogen was obtained. Interestingly, for the thiophene mesogen in its smectic C phase at 210 °C, the ¹³C–¹H dipolar coupling of the center ring methine carbon (2.11 kHz) is smaller than those of the side-wing phenyl ring carbons (2.75–3.00 kHz) which is a consequence of the different structures of the thiophene and the benzene rings. These values correspond to local order parameters of 0.85 for the center thiophene ring and 0.76 for the first side-wing phenyl ring and a bent-angle of 149.2°. Thus, the significant differences in the dipolar couplings and the order parameter values between different parts in the rigid core of the mesogens are a direct consequence of the nature of the center ring and the bent structure of the molecule. The present investigation thus highlights the ability of the ¹³C 2D-SLF technique to provide the geometry of the bent-core mesogens in a straightforward manner through the measurement of the ¹³C–¹H dipolar couplings

Monolayer to Interdigitated Partial Bilayer Smectic C Transition in Thiophene-Based Spacer Mesogens: X‑ray Diffraction and ¹³C Nuclear Magnetic Resonance Studies

Mesophase organization of molecules built with thiophene at the center and linked via flexible spacers to rigid side arm core units and terminal alkoxy chains has been investigated. Thirty homologues realized by varying the span of the spacers as well as the length of the terminal chains have been studied. In addition to the enantiotropic nematic phase observed for all the mesogens, the increase of the spacer as well as the terminal chain lengths resulted in the smectic C phase. The molecular organization in the smectic phase as investigated by temperature dependent X-ray diffraction measurements revealed an interesting behavior that depended on the length of the spacer <i>vis-a-vis</i> the length of the terminal chain. Thus, a tilted interdigitated partial bilayer organization was observed for molecules with a shorter spacer length, while a tilted monolayer arrangement was observed for those with a longer spacer length. High-resolution solid state ¹³C NMR studies carried out for representative mesogens indicated a U-shape for all the molecules, indicating that intermolecular interactions and molecular dynamics rather than molecular shape are responsible for the observed behavior. Models for the mesophase organization have been considered and the results understood in terms of segregation of incompatible parts of the mesogens combined with steric frustration leading to the observed lamellar order

A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

A new phosphorescent iridium­(III) complex, bis­[2′,6′-difluorophenyl-4-formylpyridinato-<i>N</i>,<i>C</i>4′]­iridium­(III) (picolinate) (<b>IrC</b>), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN^– on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed <b>IrC</b> was authenticated by single-crystal X-ray diffraction. Notably, the iridium­(III) complex exhibits intense red phosphorescence in the solid state at 298 K (Φ_PL = 0.16) and faint emission in acetonitrile solution (Φ_PL = 0.02). The cyanide anion binding properties with <b>IrC</b> in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV–vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium­(III) complex in acetonitrile (<i>c</i> = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of <b>IrC</b> at 480 nm was dramatically enhanced ∼5.36 × 10²-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10^–8 M. The cyanohydrin formation mechanism is further supported by results of a ¹H NMR titration of <b>IrC</b> with CN^–. As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with <b>IrC</b> for the trace detection of CN^– in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium­(III) complex probe and its cyanide adduct

A Highly Selective Chemosensor for Cyanide Derived from a Formyl-Functionalized Phosphorescent Iridium(III) Complex

A new phosphorescent iridium­(III) complex, bis­[2′,6′-difluorophenyl-4-formylpyridinato-<i>N</i>,<i>C</i>4′]­iridium­(III) (picolinate) (<b>IrC</b>), was synthesized, fully characterized by various spectroscopic techniques, and utilized for the detection of CN^– on the basis of the widely known hypothesis of the formation of cyanohydrins. The solid-state structure of the developed <b>IrC</b> was authenticated by single-crystal X-ray diffraction. Notably, the iridium­(III) complex exhibits intense red phosphorescence in the solid state at 298 K (Φ_PL = 0.16) and faint emission in acetonitrile solution (Φ_PL = 0.02). The cyanide anion binding properties with <b>IrC</b> in pure and aqueous acetonitrile solutions were systematically investigated using two different channels: i.e., by means of UV–vis absorption and photoluminescence. The addition of 2.0 equiv of cyanide to a solution of the iridium­(III) complex in acetonitrile (<i>c</i> = 20 μM) visibly changes the color from orange to yellow. On the other hand, the PL intensity of <b>IrC</b> at 480 nm was dramatically enhanced ∼5.36 × 10²-fold within 100 s along with a strong signature of a blue shift of the emission by ∼155 nm with a detection limit of 2.16 × 10^–8 M. The cyanohydrin formation mechanism is further supported by results of a ¹H NMR titration of <b>IrC</b> with CN^–. As an integral part of this work, phosphorescent test strips have been constructed by impregnating Whatman filter paper with <b>IrC</b> for the trace detection of CN^– in the contact mode, exhibiting a detection limit at the nanogram level (∼265 ng/mL). Finally, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to understand the electronic structure and the corresponding transitions involved in the designed phosphorescent iridium­(III) complex probe and its cyanide adduct