Building Water Models, A Different Approach

Simplified, classical models of water are an integral part of atomistic molecular simulations, especially in biology and chemistry where hydration effects are critical. Yet, despite several decades of effort, these models are still far from perfect. Presented here is an alternative approach to constructing point charge water models - currently, the most commonly used type. In contrast to the conventional approach, we do not impose any geometry constraints on the model other than symmetry. Instead, we optimize the distribution of point charges to best describe the "electrostatics" of the water molecule, which is key to many unusual properties of liquid water. The search for the optimal charge distribution is performed in 2D parameter space of key lowest multipole moments of the model, to find best fit to a small set of bulk water properties at room temperature. A virtually exhaustive search is enabled via analytical equations that relate the charge distribution to the multipole moments. The resulting "optimal" 3-charge, 4-point rigid water model (OPC) reproduces a comprehensive set of bulk water properties significantly more accurately than commonly used rigid models: average error relative to experiment is 0.76%. Close agreement with experiment holds over a wide range of temperatures, well outside the ambient conditions at which the fit to experiment was performed. The improvements in the proposed water model extend beyond bulk properties: compared to the common rigid models, predicted hydration free energies of small molecules in OPC water are uniformly closer to experiment, root-mean-square error < 1kcal/mol

Physical Informal Learning Environment on Campus Ground: A Review

Past few decades, there has been a raft amplifying interest in higher education institutions, nationally and internationally, in the creation of new types of learning environment supporting learner-centered or constructivist pedagogy. This paper reviews the effectiveness of the physical informal learning environment initiated by learners outside their formal lecture hours in higher education. The aim of this paper is to present a synthesis of 40 studies from 1979 to 2016 on pyhsical informal learning setting on campus. Learning is the essential activity of colleges and universities. Commonly learning occurs in classrooms which identified as formal learning and sometimes its results from serendipitous interactions among individuals at transitional spaces which classified as informal learning. Space whether physical or virtual can have an impact on learning. Thus, it can bring people together, encourage exploration, collaboration, and discussion. Space can carry an unspoken message of silence which mentioned as the power of built pedagogy in colleges and universities. Nevertheless, the subject remains topical due to the dynamism of the variables, particularly the pedagogy, learning media, spaces, learners themselves and the study location. However, exploring the intermediate space as physical informal learning environment that affect students’ performance and satisfaction in higher education remain crucial and decisive among educators and researchers. Therefore, there is a growing interest in higher education institutions, nationally and internationally, in the creating of new types of learning environment supporting learnercentered or constructivist pedagogy. Hence, The Next Generation Learning Spaces project team (NGLS) under Australian Learning & Teaching Council ( The University Of Queensland) , explored the interdependence of pedagogy, space, and technology to develop the Pedagogy-Space-Technology (PST) framework which permits institutions to develop new teaching and learning setting that will strengthen student engagement and enhance learning outcomes. This paper contributes to the paramount significance of the quality informal learning environment in order to accomplish functional obligation and cater for learner’s emotional urgency for enthusiasm and touch of identity

Point Charges Optimally Placed to Represent the Multipole Expansion of Charge Distributions

We propose an approach for approximating electrostatic charge distributions with a small number of point charges to optimally represent the original charge distribution. By construction, the proposed optimal point charge approximation (OPCA) retains many of the useful properties of point multipole expansion, including the same far-field asymptotic behavior of the approximate potential. A general framework for numerically computing OPCA, for any given number of approximating charges, is described. We then derive a 2-charge practical point charge approximation, PPCA, which approximates the 2-charge OPCA via closed form analytical expressions, and test the PPCA on a set of charge distributions relevant to biomolecular modeling. We measure the accuracy of the new approximations as the RMS error in the electrostatic potential relative to that produced by the original charge distribution, at a distance the extent of the charge distribution–the mid-field. The error for the 2-charge PPCA is found to be on average 23% smaller than that of optimally placed point dipole approximation, and comparable to that of the point quadrupole approximation. The standard deviation in RMS error for the 2-charge PPCA is 53% lower than that of the optimal point dipole approximation, and comparable to that of the point quadrupole approximation. We also calculate the 3-charge OPCA for representing the gas phase quantum mechanical charge distribution of a water molecule. The electrostatic potential calculated by the 3-charge OPCA for water, in the mid-field (2.8 Å from the oxygen atom), is on average 33.3% more accurate than the potential due to the point multipole expansion up to the octupole order. Compared to a 3 point charge approximation in which the charges are placed on the atom centers, the 3-charge OPCA is seven times more accurate, by RMS error. The maximum error at the oxygen-Na distance (2.23 Å ) is half that of the point multipole expansion up to the octupole order

Ultrasonic Machining as an Aid to Ceramic Etching

Ceramics are difficult to etch. Their chemical inertness makes them very stable and often hot etching techniques are required to obtain their microstructures. This communication reports a technique developed to ease the process of ceramic etching

MW-​enhanced high-​speed deprotection of Boc group using p-​TsOH and concomitant formation of N-​Me-​amino acid benzyl ester p-​TsOH salts

A high-​speed, complete deprotection of Boc group from Boc (Boc = tert-​butoxycarbonyl) amino acids and protected peptide esters employing p-​TsOH in toluene under microwave irradn. is found to be complete in 30 s. The deprotection can be carried out in methanol and acetonitrile also. Under the present conditions, C-​peptide benzyl esters and O-​benzyl ethers have been found to be stable. This has permitted us to carry out the synthesis of [Leu]​enkephalin employing the Boc​/Bzl-​group strategy. Further more, it has been found that both Nα-​Fmoc (Fmoc = 9-​fluorenylmethyloxycarbonyl) and Nα-​Z (Z = benzyloxycarbonyl) groups are completely stable. The present conditions can be extended for the concomitant removal of the Boc group and the formation of C-​benzyl amino acid esters as well. This has been utilized for the synthesis of N-​Me amino acid benzyl esters starting from Boc-​N-​Me amino acids in a single step

Synthesis of peptidyl ureas using p-​nitrophenyl (9-​fluorenylmethoxycarbonylamino)​methylcarbamate derivatives

Carbamates Fmoc-​NHCHRNHCO2C6H4NO2-​p (Fmoc is 9-​fluorenylmethoxycarbonyl, R is an amino acid side chain) were prepd. using isocyanates derived from Fmoc-​amino acid azides and p-​nitrophenol in the presence of an equimolar quantity of N-​ethyldiisopropylamine. The carbamates were coupled with amino acid ester hydrochlorides to afford dipeptidyl ureas

Effect of Curing On the Strength Behaviour of Lime-Fly Ashexpansive Soil Mixes

Expansive soils occupying almost 3 lakh km2 in the Indian subcontinent found to be highly problematic due to their extensive swelling and shrinkage nature. This rapid volume change leads to upliftment of foundations, differential settlements, heaving, rutting, etc. on the overlying structures. Concerning with the above problems an effective, economical and long-term method lime stabilisation was selected. In this work it is attempted to study the effect of curing period on the strength behaviour expansive soil treated with lime and fly ash by conducting triaxial shear (UU) test for 0, 3, 7, 14, 28 days with some twenty different proportions

Under water Image preprocessing by Average filter and a comparison study

Underwater image pre-processing is extremely essential because, under water images suffer from quality degradation due to low transmission of light.  When an underwater image is captured, pre-processing is necessary to correct and adjust the image for further  processing. Different filtering techniques are discussed in the literature for pre-processing of underwater images. The filters used normally improve the image quality, suppress the noise, preserves the edges in an image, enhance and smoothen the image. Therefore an effort has been made to evaluate the performance of three filters namely, homomorphic filter, anisotropic diffusion and wavelet denoising by average filter used for under water image pre-processing. Further  studied to identify the suitable filters that process the image to preserve the image quality